Crash Course on Batteries

8/3/2019 Crash Course on Batteries

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Crash Course on Batteries

When was the Battery Invented?One of the most remarkable and novel discoveries in the last 400 years was electricity. Wemight ask, Has electricity been around that long? The answer is yes, and perhaps muchlonger, but its practical use has only been at our disposal since the mid to late 1800s, and in alimited way at first. One of the earliest public works gaining attention was enlightening the 1893Chicagos World Columbia Exposition with 250,000 light bulbs, and illuminating a bridge overthe river Seine during the 1900 World Fair in Paris.

The use of electricity may go back further. While constructing a railway in 1936 near Baghdad,workers uncovered what appeared to be a prehistoric battery, also known as the ParthianBattery. The object dates back to the Parthianperiod and is believed to be 2,000 years old. Thebattery consisted of a clay jar that was filled with a vinegar solution into which an iron rod

surrounded by a copper cylinder was inserted. This device produced 1.1 to 2.0 volts ofelectricity. Figure 1 illustrates the Parthian Battery.

.

Figure 1: Parthian Battery. A clay jar of a prehistoric battery holds an iron rod surrounded by acopper cylinder. When filled with vinegar or electrolytic solution, the jar produces 1.1 to 2 volts.

Not all scientists accept the Parthian Battery as a source of energy. It is possible that the devicewas used for electroplating, such as adding a layer of gold or other precious metals to a

surface. The Egyptians are said to have electroplated antimony onto copper over 4,300 yearsago. Archeological evidence suggests the Babylonians were the first to discover and employ agalvanic technique in the manufacturing of jewelry by using an electrolyte based on grape juiceto gold plate stoneware. The Parthians, who ruled Baghdad (ca. 250 BC), may have usedbatteries to electroplate silver.

One of the earliest methods to generate electricity in modern times was through creating a staticcharge. In 1660, Otto von Guericke constructed an electrical machine using a large sulfur globewhich, when rubbed and turned, attracted feathers and small pieces of paper. Guericke wasable to prove that the sparks generated were electrical in nature.

The first practical use of static electricity was the electric pistol, which Alessandro Volta (17451827) invented. He thought of providing long-distance communications, albeit only one Booleanbit. An iron wire supported by wooden poles was to be strung from Como to Milan, Italy. At thereceiving end, the wire would terminate in a jar filled with methane gas. To signal a coded


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event, an electrical spark would be sent by wire for the purpose of detonating the electric pistol.This communications link was never built. Figure 1-2 shows a pencil rendering of AlessandroVolta.

Figure 2: Alessandro

Volta, inventor of the

electric battery

Voltas discovery of thedecomposition of water by

an electrical current laidthe foundation ofelectrochemistry.

Courtesy of Cadex

In 1791, while working at Bologna University, Luigi Galvani discovered that the muscle of a frog

would contract when touched by a metallic object. This phenomenon became known as animalelectricity. Prompted by these experiments, Volta initiated a series of experiments using zinc,lead, tin and iron as positive plates (cathode); and copper, silver, gold and graphite as negativeplates (anode). The interest in galvanic electricity soon became widespread.

Early Batteries

Volta discovered in 1800 that certain fluids would generate a continuous flow of electrical powerwhen used as a conductor. This discovery led to the invention of the first voltaic cell, morecommonly known as the battery. Volta discovered further that the voltage would increase whenvoltaic cells were stacked on top of each other. Figure 3 illustrates such a serial connection.

Figure 1-3: Four variations

of Voltas electric battery

Metals in a battery have different electricaleffects. Volta noticed that the voltagepotential with dissimilar substances gotstronger the farther apart they were fromone another.

The first number in the metals listed below

is the affinity to attract electrons; the secondis the standard potential from the first


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oxidation state.

Zinc = 1.6 / -0.76 V

Lead = 1.9 / -0.13 V

Tin = 1.8 / -1.07 V

Iron = 1.8 / -0.04 V

Copper = 1.9 / 0.159 V

Silver = 1.9 / 1.98 V

Gold = 2.4 / 1.83 V

Carbon = 2.5 / 0.13 V

The metals determine the battery voltage;they were separated with moist papersoaked in salt water.

Courtesy of Cadex

In the same year, Volta released his discovery of a continuous source of electricity to the RoyalSociety of London. No longer were experiments limited to a brief display of sparks that lasted afraction of a second. An endless stream of electric current now seemed possible.

France was one of the first nations to officially recognize Voltas discoveries. This was during atime when France was approaching the height of scientific advancements and new ideas werewelcomed with open arms, helping to support of the countrys political agenda. By invitation,Volta addressed the Institute of France in a series of lectures at which Napoleon Bonaparte waspresent as a member of the institute (see Figure 4).


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Figure 4: Voltas experimentations at the Institute of FranceVoltas discoveries so impressed the world that in November 1800 the French National Instituteinvited him to lectures at events in which Napoleon Bonaparte participated. Napoleon helpedwith the experiments, drawing sparks from the battery, melting a steel wire, discharging anelectric pistol and decomposing water into its elements.

Courtesy of Cadex

In 1800, Sir Humphry Davy, inventor of the miners safety lamp, began testing the chemicaleffects of electricity and found out that decomposition occurred when passing electrical currentthrough substances. This process was later called electrolysis. He made new discoveries byinstalling the worlds largest and most powerful electric battery in the vaults of the RoyalInstitution of London. Connecting the battery to charcoal electrodes produced the first electriclight. Witnesses reported that his voltaic arc lamp produced the most brilliant ascending arch oflight ever seen.

In 1802, William Cruickshank designed the first electric battery for mass production.Cruickshank arranged square sheets of copper with equal-sized sheets sizes of zinc. Thesesheets were placed into a long rectangular wooden box and soldered together. Grooves in thebox held the metal plates in position, and the sealed box was then filled with an electrolyte ofbrine, or a watered-down acid. This resembled the flooded battery that is still with us today.Figure 5 illustrates the battery workshop of Cruickshank.


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Figure 5: Cruickshank and the first flooded battery. William Cruickshank, an Englishchemist, built a battery of electric cells by joining zinc and copper plates in a wooden box filledwith an electrolyte solution. This flooded design had the advantage of not drying out with useand provided more energy than Voltas disc arrangement.

Courtesy of Cadex

Invention of the Rechargeable Battery

In 1836, John F. Daniell, an English chemist, developed an improved battery that produced asteadier current than earlier devices. Until this time, all batteries were primary, meaning theycould not be recharged. In 1859, the French physicist Gaston Plant invented the first

rechargeable battery. It was based on lead acid, a system that is still used today.

In 1899, Waldmar Jungner from Sweden invented the nickel-cadmium battery (NiCd), whichused nickel for the positive electrode (cathode) and cadmium for the negative (anode). Highmaterial costs compared to lead acid limited its use and two years later, Thomas Edisonproduced an alternative design by replacing cadmium with iron. Low specific energy, poorperformance at low temperature and high self-discharge limited the success of the nickel-ironbattery. It was not until 1932 that Shlecht and Ackermann achieved higher load currents andimproved the longevity of NiCd by inventing the sintered pole plate. In 1947, Georg Neumannsucceeded in sealing the cell.

For many years, NiCd was the only rechargeable battery for portable applications. In the 1990s,environmentalists in Europe became concerned about environmental contamination if NiCd

were carelessly disposed; they began to restrict this chemistry and asked the consumer industryto switch to Nickel-metal-hydride (NiMH), an environmentally friendlier battery. NiMH is similar


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to NiCd, and many predict that NiMH will be the stepping-stone to the more enduring lithium-ion(Li-ion).

Most research activities today revolve around improving lithium-based systems. Besidespowering cellular phones, laptops, digital cameras, power tools and medical devices, Li-ion isalso used for electric vehicles. The battery has a number of benefits, most notably its high

specific energy, simple charging, low maintenance and being environmentally benign.

Electricity Through Magnetism

The discovery of how to generate electricity through magnetism came relatively late. In 1820,Andr-Marie Ampre (17751836) noticed that wires carrying an electric current were at timesattracted to and at other times repelled from one another. In 1831, Michael Faraday (17911867) demonstrated how a copper disc provided a constant flow of electricity while revolving ina strong magnetic field. Faraday, assisting Davy and his research team, succeeded ingenerating an endless electrical force as long as the movement between a coil and magnetcontinued. This led to the invention of the electric generator, and reversing the process enabledthe electric motor. Shortly thereafter, transformers were developed that converted alternating

current (AC) to any desired voltage. In 1833, Faraday established the foundation ofelectrochemistry on which Faradays law is based. Faradays law of induction relates toelectromagnetism linked to transformers, inductors, and many types of electrical motors andgenerators.

Once the relationship with magnetism was understood, large generators began producing asteady flow of electricity. Motors followed that enabled mechanical movement, and the Edisonlight bulb appeared to conquer darkness. After George Westinghouse lit up Chicago's WorldColumbian Exposition in 1893, Westinghouse built three large generators to transform energyfrom the Niagara Falls to electricity. The three-phase AC technology developed by Nikola Teslaenabled transmission lines to carry electric power over great distances. Electricity was thusmade widely available to humanity to improve the quality of life.

Figure 6: 250,000 light bulbs illuminate Chicago's World Columbian Exposition in 1896.

The success of the electric light led to building three large hydro generators at Niagara Falls.

Courtesy of the Brooklyn Museum Archives. Goodyear Archival Collection

The invention of the electronic vacuum tube in the early 1900s formed the significant next steptowards high technology, enabling frequency oscillators, signal amplifications and digital


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switching. This led to radio broadcasting in the 1920s and the first digital computer, calledENIAC, in 1946. The discovery of the transistor in 1947 paved the way for the arrival of theintegrated circuit 10 years later, and the microprocessor ushered in the Information Age, foreverchanging the way we live and work.

Humanity depends on electricity, and with increased mobility people have gravitated more and

more towards portable power first for wheeled applications, then portability and finallywearable use. As awkward and unreliable as the early batteries may have been, futuregenerations may look at todays technologies as nothing more than clumsy experiments.

Battery Developments

Inventions in the 1700s and 1800s are well documented and credit goes to the dignifiedinventors. Benjamin Franklin invented the Franklin stove, bifocal eyeglasses and the lightningrod. He was unequaled in American history as an inventor until Thomas Edison emerged.Edison was a good businessman who may have taken credit for inventions others had made.Contrary to popular belief, Edison did not invent the light bulb; he improved upon a 50-year-oldidea by using a small, carbonized filament lit up in a better vacuum. Although a number of

people had worked on this idea before, Edison gained the financial reward by making theconcept commercially viable to the public. The phonograph is another success story for whichEdison received due credit.

Countries often credit their own citizens for having made important inventions, whether or notthey deserve it. When visiting museums in Europe, the USA and Japan one sees suchbestowment. The work to develop the car, x-ray machines, telephones, broadcast radio,televisions and computers might have been done in parallel, not knowing of othersadvancements at that time, and the rightful inventor is often not clearly identified. Similaruncertainties exist with the invention of new battery systems, and we give respect to researchteams and organizations rather than individuals. Table 1 summarizes battery advancementsand lists inventors when available.

Year Inventor Activity

1600 William Gilbert (UK) Establishment of electrochemistry study

1791 Luigi Galvani (Italy) Discovery of animal electricity

1800

1802

1820

1833

1836

1839

1859

1868

1899

Alessandro Volta (Italy)

William Cruickshank (UK)

Andr-Marie Ampre (France)

Michael Faraday (UK)

John F. Daniell (UK)

William Robert Grove (UK)

Gaston Plant (France)

Georges Leclanch (France)

Waldmar Jungner (Sweden)

Invention of the voltaic cell (zinc, copper disks)

First electric battery capable of mass production

Electricity through magnetism

Announcement of Faradays law

Invention of the Daniell cell

Invention of the fuel cell (H2/O2)

Invention of the lead acid battery

Invention of the Leclanch cell (carbon-zinc)

Invention of the nickel-cadmium battery

19011932

Thomas A. Edison (USA)Shlecht & Ackermann (D)

Invention of the nickel-iron batteryInvention of the sintered pole plate


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1947

1949

1970s

1990

1991

1994

1996

1996

Georg Neumann (Germany)

Lew Urry, Eveready Battery

Group effort

Group effort

Sony (Japan)

Bellcore (USA)

Moli Energy (Canada)

University of Texas (USA)

Successfully sealing the nickel-cadmium battery

Invention of the alkaline-manganese battery

Development of valve-regulated lead acid battery

Commercialization of nickel-metal-hydride battery

Commercialization of lithium-ion battery

Commercialization of lithium-ion polymer

Introduction of Li-ion with manganese cathode

Identification of Li-phosphate (LiFePO4)

2002 University of Montreal, QuebecHydro, MIT, others

Improvement of Li-phosphate, nanotechnology,

commercialization

Table 1: History of modern battery development. No new major battery system has entered

the commercial market since the invention of Li-phosphate in 1996.

Battery Developments

Inventions in the 1700s and 1800s are well documented and credit goes to the dignifiedinventors. Benjamin Franklin invented the Franklin stove, bifocal eyeglasses and thelightning rod. He was unequaled in American history as an inventor until ThomasEdison emerged. Edison was a good businessman who may have taken credit forinventions others had made. Contrary to popular belief, Edison did not invent the lightbulb; he improved upon a 50-year-old idea by using a small, carbonized filament lit up

in a better vacuum. Although a number of people had worked on this idea before,Edison gained the financial reward by making the concept commercially viable to thepublic. The phonograph is another success story for which Edison received due credit.

Countries often credit their own citizens for having made important inventions, whetheror not they deserve it. When visiting museums in Europe, the USA and Japan one seessuch bestowment. The work to develop the car, x-ray machines, telephones, broadcastradio, televisions and computers might have been done in parallel, not knowing ofothers advancements at that time, and the rightful inventor is often not clearlyidentified. Similar uncertainties exist with the invention of new battery systems, and wegive respect to research teams and organizations rather than individuals. Table 1

summarizes battery advancements and lists inventors when available.

Year Inventor Activity

1600 William Gilbert (UK) Establishment of electrochemistry study

1791 Luigi Galvani (Italy) Discovery of animal electricity

1800 Alessandro Volta (Italy) Invention of the voltaic cell (zinc, copper


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1802

1820

1833

1836

1839

1859

1868

1899

William Cruickshank (UK)

Andr-Marie Ampre(France)

Michael Faraday (UK)

John F. Daniell (UK)

William Robert Grove (UK)

Gaston Plant (France)

Georges Leclanch (France)

Waldmar Jungner(Sweden)

disks)

First electric battery capable of massproduction

Electricity through magnetism

Announcement of Faradays law

Invention of the Daniell cell

Invention of the fuel cell (H2/O2)

Invention of the lead acid battery

Invention of the Leclanch cell (carbon-zinc)

Invention of the nickel-cadmium battery

1901

1932

1947

1949

1970s

1990

1991

1994

1996

1996

Thomas A. Edison (USA)

Shlecht & Ackermann (D)

Georg Neumann (Germany)

Lew Urry, Eveready Battery

Group effort

Group effort

Sony (Japan)

Bellcore (USA)

Moli Energy (Canada)

University of Texas (USA)

Invention of the nickel-iron battery

Invention of the sintered pole plate

Successfully sealing the nickel-cadmiumbattery

Invention of the alkaline-manganese battery

Development of valve-regulated lead acidbattery

Commercialization of nickel-metal-hydridebattery

Commercialization of lithium-ion battery

Commercialization of lithium-ion polymer

Introduction of Li-ion with manganesecathode

Identification of Li-phosphate (LiFePO4)

2002University of Montreal,Quebec Hydro, MIT, others

Improvement of Li-phosphate,nanotechnology, commercialization


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Table 1: History of modern battery development. No new major battery system hasentered the commercial market since the invention of Li-phosphate in 1996.

Global Battery Markets

The battery market is expanding, and the global revenue in 2009 was a whopping $47.5billion.* With the growing demand for portable electronics and the desire to connectand work outside the confines of four walls, experts predict that this figure will reach$74 billion in 2015. These numbers are speculative and include batteries for the electricpowertrain of cars.

An Overview of Battery Types

Batteries are divided into two categories:primary and secondary. In 2009, primarybatteries made up 23.6 percent of the global market. Frost & Sullivan (2009) predict a7.4 percent decline of the primary battery in revenue distribution by 2015. Primarybatteries are used in watches, electronic keys, remote controls, childrens toys, lightbeacons and military devices.

The real growth lies in secondary batteries. Frost & Sullivansay that rechargeablebatteriesaccount for 76.4 percent of the global market, a number that is expected toincrease to 82.6 percent in 2015. Batteries are also classified by chemistry and the mostcommon are lithium-, lead-, and nickel-based systems. Figure 1 illustrates thedistribution of these chemistries.

Figure 1: Revenue contributions by different battery chemistries

Courtesy of Frost & Sullivan (2009)

Lithium-ion is the battery of choice for consumer products, and no other systemsthreaten to interfere with its dominance at this time. The lead acid market is similar in


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power delivery on demand. Figure 2 illustrates the energy and power densities of leadacid, nickel-cadmium (NiCd), nickel-metal-hydride (NiMH) and the Li-ion family (Li-ion).

Figure 1-8: Specific energy and specific power of rechargeable batteries.

Specific energy is the capacity a battery can hold in watt-hours per kilogram (Wh/kg);specific power is the batterys ability to deliver power in watts per kilogram (W/kg).

Rechargeable lithium-metal batteries (Li-metal) were introduced in the 1980s, butinstability with metallic lithium on the anode prompted a recall in 1991. Its high specificenergy and good power density are challenging manufacturers revisit into this powerfulchemistry again. Enhanced safety may be possible by mixing metallic lithium with tinand silicon. Experimental Li-metal batteries achieve 300Wh/kg, a specific energy that isof special interest to the electric vehicle. Read more about Experimental RechargeableBatteries.

* All references to dollar ($) pricing are in US dollars at the time of writing.

Getting to Know the Battery

The battery dictates the speed with which mobility advances. So important is thisportable energy source that any incremental improvement opens new doors for manyproducts. The better the battery, the greater our liberty will become.


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Besides packing more energy into the battery, engineers have also made strides inreducing power consumption of portable equipment. These advancements go hand-in-hand with longer runtimes but are often counteracted by the demand for additionalfeatures and more power.The end result is similar runtimes but enhanced performance.

The battery has not advanced at the same speed as microelectronics, and the industryhas only gained 8 to 10 percent in capacity per year during the last two decades. This isa far cry from Moores Law* that specifies a doubling of the number of transistors in anintegrated circuit every two years. Instead of two years, the capacity of lithium-ion took10 years to double.

In parallel with achieving capacity gain, battery makers must also focus on improvingmanufacturing methods to ensure better safety. The recent recall of millions of lithium-cobaltpacks caused by thermal runaway is a reminder of the inherent risk in condensingtoo much energy into a small package. Better manufacturing practices should make such

recalls a thing of the past. A generation of Li-ion batteries is emerging that are built forlongevity. These batteries have a lower specific energy (capacity) than those forportable electronics and are increasingly being considered for the electric powertrain ofvehicles.

People want an inexhaustible pool of energy in a package that is small, cheap, safe andclean, and the battery industry can only fulfill this desire partially. As long as the batteryis an electrochemical process, there will be limitations on capacity and life span. Only arevolutionary new storage system could satisfy the unquenchable thirst for mobilepower, and its anyones guess whether this will be lithium-air, the fuel cell, or someother ground-breaking new power generator, such as atomic fusion. For most of us, thebig break might not come in our lifetime.

Meeting Expectations

Many battery novices argue, wrongly, that all advanced battery systems offer highenergy densities, deliver thousands of charge/discharge cycles and come in a small size.While some of these attributes are possible, this is not attainable in one and the samebattery in a given chemistry.

A battery may be designed for high specific energy and small size, but the cycle life is

short. Another battery may be built for high load capabilities and durability, and thecells are bulky and heavy. A third pack may have high capacity and long service life,but the manufacturing cost is out of reach for the average consumer. Batterymanufacturers are well aware of customer needs and respond by offering products thatbest suit the application intended. The mobile phone industry is an example of thisclever adaptation. The emphasis is on small size, high energy density and low price.Longevity is less important here.

The terms nickel-metal-hydride (NiMH) and lithium-ion (Li-ion) do not automaticallymean high specific energy. For example, NiMH for the electric powertrain in vehicleshas a specific energy of only 45Wh/kg, a value that is not much higher than lead acid.

The consumer NiMH, in comparison, has about 90Wh/kg. The Li-ion battery for hybridand electric vehicles can have a specific energy as low as 60Wh/kg, a value that is


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comparable with nickel-cadmium. Li-ion for cell phones and laptops, on the other hand,has two to three times this specific energy.

The Cadex-sponsored website www.BatteryUniversity.com generates many interestingquestions. Those that stand out are, Whats the best battery for a remote-controlled car,

a portable solar station, an electric bicycle or electric car? There is no universal batterythat fits all needs and each application is unique. Although lithium-ion would in mostinstances be the preferred choice, high price and the need for an approved protectioncircuit exclude this system from use by many hobbyists and small manufacturers.Removing Li-ion leads back to the nickel- and lead-based options. Consumer productsmay have benefited the most from battery advancements. High volume made Li-ionrelatively inexpensive.

Will the battery replace the internal combustion engine of cars? It may come as asurprise to many that we dont yet have an economical battery that allows long-distancedriving and lasts as long as the car. Batteries work reasonably well for portable

applications such as cell phones, laptops and digital cameras. Low power enables aneconomical price; the relative short battery life is acceptable in consumer products; andwe can live with a decreasing runtime. While the fading capacity can be annoying, itdoes not endanger safety.

As we examine the characteristics of battery systems and compare alternative powersources, such as the fuel cell and the internal combustion (IC) engine, we realize that thebattery is best suited for portable and stationary systems. For motive applications suchas trains, ocean going ships and aircraft, the battery lacks capacity, endurance andreliability. The dividing line, in my opinion, lies with the electric vehicle.

* In 1965, Gordon Moore said that the number of transistors in an integrated circuitwould double every two years. The prediction became true and is being carried intothe 21st century. Applied to a battery, Moores Law would shrink a starter battery ina car to the size of a coin.

Comparing the Battery with other Power

Sources

This article begins with the positive traits of the battery, and then moves into thelimitations when compared with other power sources.

Energy storage

Batteries store energy well and for a considerable length of time. Primary batteries (non-rechargeable) hold more energy than secondary (rechargeable), and the self-discharge islower. Alkaline cells are good for 10 years with minimal losses. Lead-, nickel- andlithium-based batteries need periodic recharges to compensate for lost power.


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Specific energy (Capacity)

A battery may hold adequate energy for portable use, but this does not transfer equallywell for large mobile and stationary systems. For example, a 100kg (220lb) batteryproduces about 10kWh of energy an IC engine of the same weight generates 100kW.

Responsiveness

Batteries have a huge advantage over other power sources in being ready to deliver onshort notice think of the quick action of the camera flash! There is no warm-up, as isthe case with the internal combustion (IC) engine; the power from the battery flowswithin a fraction of a second. In comparison, a jet engine takes several seconds to gainpower, a fuel cell requires a few minutes, and the cold steam engine of a locomotiveneeds hours to build up steam.

Power bandwidth

Rechargeable batteries have a wide power bandwidth, a quality that is shared with thediesel engine. In comparison, the bandwidth of the fuel cell is narrow and works bestwithin a specific load. Jet engines also have a limited power bandwidth. They have poorlow-end torque and operate most efficiently at a defined revolution-per-minute (RPM).

Environment

The battery runs clean and stays reasonably cool. Sealed cells have no exhaust, are quietand do not vibrate. This is in sharp contrast with the IC engine and larger fuel cells thatrequire noisy compressors and cooling fans. The IC engine also needs air and exhauststoxic gases.

Efficiency

The battery is highly efficient. Below 70 percent charge, the charge efficiency is closeto 100 percent and the discharge losses are only a few percent. In comparison, theenergy efficiency of the fuel cell is 20 to 60 percent, and the thermal engines is 25 to 30percent. (At optimal air intake speed and temperature, the GE90-115 on the Boeing 777

jetliner is 37 percent efficient.)

Installation

The sealed battery operates in any position and offers good shock and vibrationtolerance. This benefit does not transfer to the flooded batteries that must be installed inthe upright position. Most IC engines must also be positioned in the upright position andmounted on shock- absorbing dampers to reduce vibration. Thermal engines also needair and an exhaust.


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Operating cost

Lithium- and nickel-based batteries are best suited for portable devices; lead acidbatteries are economical for wheeled mobility and stationary applications. Cost andweight make batteries impractical for electric powertrains in larger vehicles. The price

of a 1,000-watt battery (1kW) is roughly $1,000 and it has a life span of about 2,500hours. Adding the replacement cost of $0.40/h and an average of $0.10/kWh forcharging, the cost per kWh comes to about $0.50. The IC engine costs less to build perwatt and lasts for about 4,000 hours. This brings the cost per 1kWh to about $0.34.Read more about the Battery Against Fossil Fuel.

Maintenance

With the exception of watering of flooded lead batteries and discharging NiCds toprevent memory, rechargeable batteries require low maintenance. Service includes

cleaning of corrosion buildup on the outside terminals and applying periodicperformance checks.

Service life

The rechargeable battery has a relatively short service life and ages even if not in use. Inconsumer products, the 3- to 5-year lifespan is satisfactory. This is not acceptable forlarger batteries in industry, and makers of the hybrid and electric vehicles guaranteetheir batteries for 8 to 10 years. The fuel cell delivers 2,000 to 5,000 hours of serviceand, depending on temperature, large stationary batteries are good for 5 to 20 years.

Temperature extremes

Like molasses, cold temperatures slow the electrochemical reaction and batteries do notperform well below freezing. The fuel cell shares the same problem, but the internalcombustion engine does well once warmed up. Charging must always be done abovefreezing. Operating at a high temperature provides a performance boost but this causesrapid aging due to added stress. Read about Discharging at High and LowTemperatures.

Charge time

Here, the battery has an undisputed disadvantage. Lithium- and nickel-based systemstake 1 to 3 hours to charge; lead acid typically takes 14 hours. In comparison, filling upa vehicle only takes a few minutes. Although some electric vehicles can be charged to80 percent in less than one hour on a high-power outlet, users of electric vehicles willneed to make adjustments.

Disposal

Nickel-cadmium and lead acid batteries contain hazardous material and cannot be

disposed of in landfills. Nickel-metal-hydrate and lithium systems are environmentally


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friendly and can be disposed of with regular household items in small quantities.Authorities recommend that all batteries be recycled.

Battery Definitions

Batteries come in all shapes and sizes and there could be as many types as there arespecies of dog. Rather than giving batteries unique names as we do with pets, wedistinguish batteries by chemistry, voltage, size, specific energy (capacity), specificpower, (delivery of power) and more. A battery can operate as a single cell to power acellular phone, or be connected in series to deliver several hundred volts to serve a UPS(uninterruptible power supply system) and the electric powertrain of a vehicle. Somebatteries have high capacity but cannot deliver much power, while a starter battery has arelatively low capacity but can crank the engine with 300A.

The largest battery systems are used for grid storage to store and delivery energy

derived from renewable power sources such as wind turbines and solar systems. A 30-megawatt (MW) wind farm uses a storage battery of about 15MW. This is theequivalent of 20,000 starter batteries and costs about $10 million. One mega-watt feeds50 houses or a super Walmart store. Lets now examine each of the batterycharacteristics further.

Chemistry

The most common chemistries are lead, nickel and lithium. Each system requires itsown charging algorithm. Unless provisions are made to change the charge setting,

different battery chemistries cannot be interchanged in the same charger. Also observethe chemistry when shipping and disposing of batteries; each type has a differentregulatory requirement.

Voltage

Voltage describes the nominal open circuit voltage (OCV), which varies with chemistryand number of cells connected in series. Always observe the correct voltage whenconnecting to a load or a charger. Do not proceed if the voltage does not agree.

Capacity

Capacity represents the specific energy in ampere-hours (Ah). Manufacturers oftenoverrate a battery by giving a higher Ah rating than it can provide. You can use abattery with different Ah (but correct voltage), provided the rating is high enough.Chargers have some tolerance to batteries with different Ah ratings. A larger batterywill take longer to charge than a small one.

Cold cranking amps (CCA)

CCA specifies the ability to draw high load current at 18C (0F) on starter batteries.

Different norms specify dissimilar load durations and end voltages.


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Specific energy and energy density

Specific energy or gravimetric energy density defines the battery capacity in weight(Wh/kg); energy density or volumetric energy density is given in size (Wh/l). A batterycan have a high specific energy but poor specific power (load capability), as is the case

in an alkaline battery. Alternatively, a battery may have a low specific energy but candeliver high specific power, as is possible with the supercapacitor. Specific energy issynonymous with battery capacity and runtime.

Specific power

Specific power or gravimetric power density indicates the loading capability, or theamount of current the battery can provide. Batteries for power tools exhibit high specificpower but have reduced specific energy (capacity). Specific power is synonymous withlow internal resistance and the delivery of power.

C-rates

C-rates specify charge and discharge currents. At 1C, the battery charges and dischargesat a current that is par with the marked Ah rating; at 0.5C the current is half, and at 0.1Cit is one tenth. On charge, 1C charges a good battery in about one hour; 0.5C takes 2hours and 0.1C 10 to 14 hours. Read more about What is the C-rate?

Load

Also known as electromotive force (EMF), the load draws energy from the battery.Internal battery resistance and depleting state-of-charge cause the voltage to drop.

Watts and Volt-amps (VA)

Power drawn from a battery is expressed in watts (W) or volt-amps (VA). Watt is thereal powerthat is being metered; VA is the apparent powerthat determines the wiringsizing and the circuit breakers. On a purely resistive load, watt and VA readings arealike; a reactive load such as an inductive motor or florescent light causes a drop in thepower factor (pf) from the ideal one (1) to 0.7 or lower. For example, a pf of 0.7 has apower efficiency of 70.

Primary Batteries

The growth has been in secondary batteries (rechargeable) but non-rechargeable orprimary batteries are equally important. They continue to fill an important niche marketin applications such as wristwatches, remote controls, electric keys and childrens toys.Primary batteries also assist when charging is impractical or impossible, such asmilitary combat, rescue missions and forest-fire services. Other applications of primarybatteries are tire pressure gauges in cars and trucks, transmitters for bird tracking,

pacemakers for heart patients, intelligent drill bits for mining,as well as light beaconsand remote repeater stations. High specific energy, long storage times and operational


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readiness make this battery well suited for such applications. The battery can be carriedto remote locations and used instantly, even after long storage. Most primary batteriesare inexpensive, readily available and environmentally friendly.

Carbon-zinc, also known as theLeclanch battery, is the least expensive battery and

comes with consumer devices when batteries are included. These general purposebatteries are used for applications with low power drain, such as remote controls,flashlights, childrens toys and wall clocks. One of the most common primary batteriesfor consumers is the alkaline-manganese, or alkaline for short. Lewis Urry invented it in1949 while working with the Eveready Battery Company Laboratory in Parma, Ohio.Alkaline delivers more energy at higher load currents than carbon-zinc. Best of all,alkaline does not leak when depleted, as carbon-zinc does. On the negative side,alkaline is more expensive than carbon-zinc.

Primary batteries have one of the highest energy densities. Although secondary batterieshave improved, a regular household alkaline provides 50 percent more energy than

lithium-ion. The most energy-dense primary is the lithium battery made for filmcameras and military combat. It holds more than three times the energy of lithium-ionand comes in various blends, such as lithium-metal, lithium manganese dioxide,lithium-sulfur dioxide, lithium-thionyl chloride, lithium oxygen and others. Figure 1compares the typical gravimetric energy densities of lead acid, NiMH, Li-ion, alkalineand lithium primary batteries.

Figure 1: Specific energy comparison of secondary and primary batteriesSecondary batteries are typically rated at 1C; alkaline uses much lower dischargecurrents.

Courtesy of Cadex

Specific energy indicates the energy a battery can hold. This, however, does notguarantee delivery. Primary batteries tend to have high internal resistance, which limits


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the discharge to light loads such as remote controls, flashlights and portableentertainment devices. Digital cameras are borderline a power drill on alkaline wouldbe unthinkable.

Manufacturers of primary batteries only specify specificenergy; the specific power

(ability to deliver power) is not published. While most secondary batteries are rated at adischarge current of 1C, the capacity of primary batteries is measured by dischargingthem at a very low current of 25mA, or a fraction of a C. In addition, the batteries areallowed to go down to a very low voltage of 0.8 volts per cell. This evaluation methodprovides impressive readings on paper, but the results are poor under a more demandingload.

To compare primary and secondary batteries side by side, we discharge both types witha current of 1C and plot the results as Actual beside the already plotted Rated,which the manufacturer provides (Figure 2). While the primary batteries do well on theratedcapacity with load currents similar to a portable entertainment device, secondary

batteries have lower capacities but are more resilient at a load of 1C.

Figure 2: Energy comparison under load. Rated refers to a mild discharge;Actual is a load at 1C. High internal resistance limits alkaline battery to light loads.

Courtesy of Cadex

The reason for the sharp performance drop on primary batteries is the high internalresistance, which causes the voltage to drop under load. The already high resistanceincreases further as the battery depletes on discharge. When the battery goes flat on adigital camera, for example, precious capacity is often left behind. A spent alkaline canoften power a kitchen clock for two years. Figure 1-10 shows the largest discrepancybetween Rated and Actual on alkaline. A long-life alkaline (not shown on chart)

will deliver better results.


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Table 3 illustrates the capacity of standard alkaline batteries with loads that are typicalof personal entertainment devices or small flashlights. Discharging at fractional C-ratesproduces high capacities; increasing the discharge rate would drastically reduce it.

Table 3: Alkaline specifications. The discharge resembles entertainment devices with

low loads.

Courtesy of Panasonic

The use of primary batteries can be expensive, and the inability to recharge increasesthe cost of power by about thirty fold over secondary batteries. The pricing issuebecomes even more acute if the packs are being replaced after each mission, regardlessof length of service. Discarding partially used batteries is common, especially in fleetapplications and critical missions. It is more convenient and safer to simply issue thetroops fresh packs with each call rather than estimating the remaining state-of-charge. AUS Army general once said that half of the batteries discarded still have 50 percent

energy left.

Estimating the battery state-of-charge would help, but such instruments areexpensive and inaccurate. The most basic method is measuring the open circuit voltageand reading the internal resistance by applying a brief load and checking the voltagedrop. A large voltage differential would relate to rising resistance, a hint to the end oflife. A more accurate way is to count the out-flowing energy, a measurement that is alsoknown as coulomb counting, but this requires expensive circuitry. See How to MeasureState-of-charge. Due to high cost and inherent inaccuracies, fuel gauges are seldom usedon primary batteries.

Secondary Batteries

Rechargeable batteries play an important role in our life and many daily chores wouldbe unthinkable without the ability to recharge an empty battery. Points of interest arespecific energy, years of service life, load characteristics, safety, price, self-discharge,environmental issues, maintenance requirements, and disposal.

Lead Acid One of the oldest rechargeable battery systems; is rugged, forgiving ifabused and economical in price; has a low specific energy and limited cycle life. Lead

acid is used for wheelchairs, golf cars, personnel carriers, emergency lighting anduninterruptible power supply (UPS).


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Nickel-cadmium (NiCd) Mature and well understood; is used where long servicelife, high discharge current, extreme temperatures and economical price are ofimportance. Due to environmental concerns, NiCd is being replaced with otherchemistries. Main applications are power tools, two-way radios, aircraft and UPS.

Nickel-metal-hydride (NiMH) A practical replacement for NiCd; has higherspecific energy with fewer toxic metals. NiMH is used for medical instruments, hybridcars and industrial applications. NiMH is available in AA and AAA cells for consumeruse.

Lithium-ion (Li-ion) Most promising battery systems; is used for portable consumerproducts as well as electric powertrains for vehicles; is more expensive than nickel- andlead acid systems and needs protection circuit for safety.

The lithium-ion family is divided into three major battery types, so named by theircathode oxides, which are cobalt, manganese and phosphate. The characteristics of these

Li-ion systems are as follows.

Lithium-ion-cobalt or lithium-cobalt(LiCoO2): Has high specific energy withmoderate load capabilities and modest service life. Applications include cell phones,laptops, digital cameras and wearable products.

Lithium-ion-manganese or lithium-manganese(LiMn2O4): Is capable of high chargeand discharge currents but has low specific energy and modest service life; used forpower tools, medical instruments and electric powertrains.

Lithium-ion-phosphate or lithium-phosphate (LiFePO4): Is similar to lithium-manganese; nominal voltage is 3.3V/cell; offers long cycle life, has a good safe recordbut exhibits higher self-discharge than other Li-ion systems.

There are many other lithium-ion based batteries, some of which are described furtheron this website. Missing in the list is also the popular lithium-ion-polymer, orLi-

polymer. While Li-ion systems get their name from their unique cathode materials, Li-polymer differs by having a distinct architecture. Nor is the rechargeable lithium-metalmentioned. This battery requires further development to control dendrite growth, whichcan compromise safety. Once solved, Li-metal will become an alternative battery choicewith extraordinary high specific energy and good specific power.

Table 1 compares the characteristics of four commonly used rechargeable batterysystems showing average performance ratings at time of publication.


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Table 1: Characteristics of commonly used rechargeable batteries

The figures are based on average ratings of commercial batteries at time of publication;

experimental batteries with above-average ratings are excluded.

1 Internal resistance of a battery pack varies with milliampere-hour (mAh) rating,wiring and number of cells. Protection circuit of lithium-ion adds about 100mW.2 Based on 18650 cell size. Cell size and design determines internal resistance.3 Cycle life is based on battery receiving regular maintenance.4 Cycle life is based on the depth of discharge (DoD). Shallow DoD improves cyclelife.5 Self-discharge is highest immediately after charge. NiCd loses 10% in the first 24hours, then declines to 10% every 30 days. High temperature increases self-discharge.6 Internal protection circuits typically consume 3% of the stored energy per month.7 The traditional voltage is 1.25V; 1.2V is more commonly used.8 Low internal resistance reduces the voltage drop under load and Li-ion is often


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the same amount in one year. Lead acid work well at cold temperatures and is superiorto lithium-ion when operating in subzero conditions.

Sealed Lead Acid

The first sealed, or maintenance-free, lead acid emerge in the mid-1970s. The engineersargued that the term sealed lead acid is a misnomer because no lead acid battery canbe totally sealed. This is true and battery designers added a valve to control venting ofgases during stressful charge and rapid discharge. Rather than submerging the plates ina liquid, the electrolyte is impregnated into a moistened separator, a design thatresembles nickel- and lithium-bases system. This enables to operate the battery in anyphysical orientation without leakage.

The sealed battery contains less electrolyte than the flooded type, hence the term acid-starved. Perhaps the most significant advantage of the sealed lead acid is the ability tocombine oxygen and hydrogen to create water and prevent water loss. Therecombination occurs at a moderate pressure of 0.14 bar (2psi). The valve serves assafety vent if gases buildup during over-overcharge or stressful discharge. Repeatedventing would lead to an eventual dry out.

Driven by these advantages, several types of sealed lead acid have emerged and themost common are gel, also known as valve-regulated lead acid(VRLA), and absorbentglass mat(AGM). The gel cell contains a silica type gel that suspends the electrolyte ina paste. Smaller packs with capacities of up to 30A are called SLA (sealed lead acid).Packaged in a plastic container, these batteries are used for small UPS, emergencylighting, ventilators for healthcare and wheelchairs. Because of economical price,

dependable service and low maintenance, the SLA remains the preferred choice forbiomedical and healthcare in hospitals and retirement homes. The VRLA is the largergel variant used as power backup for cellular repeater towers, Internet hubs, banks,hospitals, airports and other sites.

The AGM is a newer design and suspends the electrolytein aspecially designed glassmat. This offers several advantages to lead acid systems, including faster charging andinstant high load currents on demand. AGM works best as a mid-range battery withcapacities of 30 to 100Ah and is less suited for large systems, such as UPS. Typical usesare starter batter for motorcycles, start-stop function for micro-hybrid cars, as well asmarine and RV that need some cycling.

With cycling and age, the capacity of AGM fades gradually; gel, on the other hand, hasa dome shaped performance curve and stays in the high performance range longer butthen drops suddenly towards the end of life. AGM is more expensive than flooded, butis cheaper than gel.(Gel would be too expensive for start/stop use in cars.) SeeAbsorbent Glass Mat (AGM).

Unlike the flooded, the sealed lead acid battery is designed with a low over-voltagepotential to prohibit the battery from reaching its gas-generating potential during charge.Excess charging causes gassing, venting and subsequent water depletion and dry out.Consequently, gel, and in part also AGM, cannot be charged to their full potential and

the charge voltage limit must be set lower than that of a flooded. The float charge onfull charge must also be lowered. In respect to charging, the gel and AGM are no direct


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replacements to the flooded type. If no designated charger is available with lowervoltage settings, disconnect the charger after 24 hours of charge. This prevents gassingdue to a float voltage that is set too high. See Charging Lead Acid.

The optimum operating temperature for a VRLA battery is 25C (77F); every 8C

(15F) rise above this temperature threshold cuts battery life in half. See Heat, Loadingand Battery Life. Lead acid batteries are rated at a 5-hour (0.2C) and 20-hour (0.05C)discharge. The battery performs best when discharged slowly and the capacity readingsare notably higher at a slow discharge rate. Lead acid can, however, deliver high pulsecurrents of several C if done for only a few seconds. This makes the lead acid wellsuited as a starter battery, also known as starter-light-ignition (SLI). The high leadcontent and the sulfuric acid make lead acid environmentally unfriendly.

The following paragraphs look at the different architectures within the lead acid familyand explain why one battery type does not fit all.

Starter and Deep-cycle Batteries

The starter battery is designed to crank an engine with a momentary high power burst;the deep-cycle battery, on the other hand, is built to provide continuous power for awheelchair or golf car. From the outside, both batteries look alike; however, there arefundamental differences in design. While the starter battery is made for high peak powerand does not like deep cycling, the deep-cycle battery has a moderate power output butpermits cycling. Lets examine the architectural difference between these batteriesfurther.

Starter batteries have a CCA rating imprinted in amperes; CCA refers to cold crankingamps, which represents the amount of current a battery can deliver at cold temperature.SAE J537 specifies 30 seconds of discharge at 18C (0F) at the rated CCA amperewithout dropping below 7.2 volts. (SAE stands for Society of Automotive Engineers.)

Starter batteries have a very low internal resistance, and the manufacturer achieves thisby adding extra plates for maximum surface area (Figure 1). The plates are thin and thelead is applied in a sponge-like form that has the appearance of fine foam. This methodextends the surface area of the plates to achieve low resistance and maximum power.Plate thickness isless important here because the discharge is short and the battery isrecharged while driving;the emphasis is on power rather than capacity.

Figure 1: Starter battery

The starter battery has many thin plates inparallel to achieve low resistance with highsurface area. The starter battery does notallow deep cycling.

Courtesy of Cadex

Deep-cycle lead acid batteries for golf cars, scooters and wheelchairs are built formaximum capacity and high cycle count. The manufacturer achieves this by making the


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lead plates thick (Figure 2). Although the battery is designed for cycling, full dischargesstill induce stress, and the cycle count depends on the depth-of-discharge (DoD). Deep-cycle batteries are marked in Ah or minute of runtime.

Figure 2: Deep-cycle battery

The deep-cycle battery has thick plates forimproved cycling abilities. The deep-cyclebattery generally allows about 300 cycles.

Courtesy of Cadex

A starter battery cannot be swapped with a deep-cycle battery and vice versa. While aninventive senior may be tempted to install a starter battery instead of the more expensive

deep-cycle on his wheelchair to save money, the starter battery wont last because thethin sponge-like plates would quickly dissolve with repeated deep cycling. There arecombination starter/deep-cycle batteries available for trucks, buses, public safety andmilitary vehicles, but these units are big and heavy. As a simple guideline, the heavierthe battery is, the more lead it contains, and the longer it will last. Table 3 compares thetypical life of starter and deep-cycle batteries when deep-cycled.

Depth of Discharge Starter Battery Deep-cycle Battery

100%

50%

30%

1215 cycles

100120 cycles

130150 cycles

150200 cycles

400500 cycles

1,000 and more cycles

Table 3: Cycle performance of starter and deep-cycle batteries. A discharge of100% refers to a full discharge; 50% is half and 30% is a moderate discharge with 70%remaining.

Lead is toxic and environmentalists would like to replace the lead acid battery withanother chemistry. Europe succeeded to keep nickel-cadmium batteries out of consumerproducts, and authorities try to do it with the starter battery. The choices are NiMH andlithium-ion, but at a price tag of $3,000 for Li-ion, this will not fly. In addition, Li-ionhas poor performance at sub-freezing temperature. Regulators hope that advancementsin the electric powertrain will lower the cost, but such a large price reduction to matchthe low-cost lead acid may not be possible. Lead acid will continue to be the battery ofchoice to crank the engines.

Table 4 spells out the advantages and limitations of common lead acid batteries in usetoday.

Advantages

Inexpensive and simple to manufacture; low cost per watt-hour

Low self-discharge; lowest among rechargeable batteries


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High specific power, capable of high discharge currents

Good low and high temperature performance

Limitations

Low specific energy; poor weight-to-energy ratio

Slow charge; fully saturated charge takes 14 hours

Must be stored in charged condition to prevent sulfation

Limited cycle life; repeated deep-cycling reduces battery life

Flooded version requires watering

Transportation restrictions on the flooded type

Not environmentally friendly

Table 4: Advantages and limitations of lead acid batteries. Dry systems haveadvantages over flooded but are less rugged.

Absorbent Glass Mat (AGM)

AGM technology was developed in 1985 for military aircraft to reduce weight, increase

power handling and improve reliability. The acid is absorbed by a very fine fiberglassmat, making the battery spill-proof. This enables shipment without hazardous materialrestrictions. The plates can be made flat to resemble a standard flooded lead acid pack ina rectangular case; they can also be wound into a cylindrical cell.

AGM has very low internal resistance, is capable to deliver high currents on demandand offers a relatively long service life, even when deep-cycled. AGM is maintenancefree, provides good electrical reliability and is lighter than the flooded lead acid type. Itstands up well to low temperatures and has a low self-discharge. The leading advantagesare a charge that is up to five times faster than the flooded version, and the ability todeep cycle. AGM offers a depth-of-discharge of 80 percent; the flooded, on the other

hand, is specified at 50 percent DoD to attain the same cycle life. The negatives areslightly lower specific energy and higher manufacturing costs that the flooded. AGMhas a sweet spot in midsize packs from 30 to 100Ah and is less suitable for large UPSsystem.

AGM batteries are commonly built to size and are found in high-end vehicles to runpower-hungry accessories such as heated seats, steering wheels, mirrors andwindshields. NASCAR and other auto racing leagues choose AGM products becausethey are vibration resistant. AGM is the preferred battery for upscale motorcycles.Being sealed, AGM reduces acid spilling in an accident, lowers the weight for the sameperformance and allows installation at odd angles. Because of good performance at coldtemperatures, AGM batteries are also used for marine, motor home and roboticapplications.


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Ever since Cadillac introduced the electric starter motor in 1912, lead acid became thenatural choice to crank the engine. The classic flooded type is, however, not robustenough for the start-stop function and most batteries in a micro-hybrid car are AGM.Repeated cycling of a regular flooded type causes a sharp capacity fade after two yearsof use. See Heat, Loading and Battery Life.

As with all gelled and sealed units, AGM batteries are sensitive to overcharging. Thesebatteries can be charged to 2.40V/cell (and higher) without problem; however, the floatcharge should be reduced to between 2.25 and 2.30V/cell (summer temperatures mayrequire lower voltages). Automotive charging systems for flooded lead acid often have afixed float voltage setting of 14.40V (2.40V/cell), and a direct replacement with a sealedunit could spell trouble by exposing the battery to undue overcharge on a long drive.See Charging Lead Acid.

AGM and other sealed batteries do not like heat and should be installed away from theengine compartment. Manufacturers recommend halting charge if the battery core

reaches 49C (120F). While regular lead acid batteries need a topping charge every sixmonths to prevent the buildup of sulfation, AGM batteries are less prone to this and cansit in storage for longer before a charge becomes necessary. Table 1 spells out theadvantages and limitations of AGM.

Advantages

Spill-proof through acid encapsulation in matting technology

High specific power, low internal resistance, responsive to load

Up to 5 times faster charge than with flooded technology

Better cycle life than with flooded systems

Water retention (oxygen and hydrogen combine to produce water)

Vibration resistance due to sandwich construction

Stands up well to cold temperature

Limitations

Higher manufacturing cost than flooded (but cheaper than gel)

Sensitive to overcharging (gel has tighter tolerances than AGM)

Capacity has gradual decline (gel has a performance dome)

Low specific energy

Must be stored in charged condition (less critical than flooded)

Not environmentally friendly (has less electrolyte, lead that flooded)

Table 4: Advantages and limitations AGM. The gel system shares many of thecharacteristics.


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New Lead Acid Systems

Lead acid batteries continue to hold a leading position, especially in wheeled mobilityand stationary applications. This strong market appeal entices manufacturers to explore

ways to make the batteries better. Improvements have been made and some claims areso promising that one questions the trustworthiness. It is no secret that researchersprefer publishing the positive attributes while keeping the negatives under wraps. Thefollowing information on lead acid developments was obtained from available printedresources at the time of writing.

Firefly Energy

The composite plate material of the Firefly Energy battery is based on a lead acidvariant that is lighter, longer living and has higher active material utilization thancurrent lead acid systems. The battery includes foam electrodes for the negative plates,which gives it a performance that is comparable to NiMH but at lower manufacturingcosts. Design concerns include microtubule blockage through crystal growth during lowcharge conditions. In addition, crystal expansion causes a reduction of the surface area,which will result in lower capacity with aging. Pricing is also a concern. It currentlycosts about $450 to manufacture a Firefly battery as opposed to $150 for a regular leadacid version. Firefly Energy is a spin-off of Caterpillar and went into bankruptcy in2010.

Altraverda Bipolar

Similar to the Firefly Energy battery, the Altraverda battery is based on lead. It uses aproprietary titanium sub-oxide ceramic structure, called Ebonex, for the grid and anAGM separator. The un-pasted plate contains Ebonex particles in a polymer matrixthat holds a thin lead alloy foil on the external surfaces. With 5060Wh/kg, the specificenergy is about one-third larger than regular lead acid and is comparable with NiCd.Based in the UK, Altraverda works with East Penn in the USA, and the battery is wellsuited for higher voltage applications.

Axion Power

The Axion Power e3 Supercell is a hybrid battery/ultracapacitor in which the positiveelectrode consists of standard lead dioxide and the negative electrode is activatedcarbon, while maintaining an assembly process that is similar to lead acid. The AxionPower battery offers faster recharge times and longer cycle life on repeated deepdischarges than what is possible with regular lead acid systems. This opens the door forthe start-stop application in micro-hybrid cars. The lead-carbon combination of theAxion Power battery lowers the lead content on the negative plate, which results in aweight reduction of 30 percent compared to a regular lead acid. This, however, alsolowers the specific energy to 1525Wh/kg instead of 3050Wh/kg, which a regular leadacid battery normally provides.


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CSIRO Ultrabattery

The CSIRO Ultrabattery combines an asymmetric ultracapacitor and a lead acid batteryin each cell. The capacitor enhances the power and lifetime of the battery by acting as abuffer during charging and discharging, prolonging the lifetime by a factor of four over

customary lead acid systems and producing 50 percent more power. The manufactureralso claims that the battery is 70 percent cheaper to produce than current hybrid electricvehicle (HEV) batteries. CSIRO batteries are undergoing road trials in a Honda InsightHEV and show good results. Furukawa Battery in Japan licensed the technology. TheCSIRO battery is also being tested for start-stop applications in micro-hybrid cars toreplace the lead acid starter battery. This battery promises extended life when exposedto frequent start-stop conditions and is able to take a fast charge.

EEStor

This is the mystery battery/ultracapacitor combination that receives much mediaattention. The battery is based on a modified barium titanate ceramic powder and claimsa specific energy of up to 280Wh/kg, higher than lithium-ion. The company is verysecretive about their invention and releases only limited information. Some of theirastonishing claims are: One-tenth of the weight of a NiMH battery in a hybridapplication, no deep-cycle wear-down, three- to six-minute charge time, no hazardousmaterial, similar manufacturing costs to lead acid, and a self-discharge that is only 0.02percent per month, a fraction of that of lead acid and Li-ion.

Nickel-based Batteries

The following section describes nickel-based batteries, and we begin withnickel-cadmium (NiCd), an older chemistry for which extensive data is available.Much of these characteristics also apply to nickel-metal-hydride (NiMH), asthese two systems are close cousins. The toxicity of NiCd is limiting this solidand robust battery to specialty applications.

Nickel-cadmium (NiCd)

The nickel-cadmium battery, invented by Waldmar Jungner in 1899, offered several advantagesover lead acid, but the materials were expensive and the early use was restricted.

Developments lagged until 1932 when attempts were made to deposit the active materialsinside a porous nickel-plated electrode. Further improvements occurred in 1947 by trying toabsorb the gases generated during charge. This led to the modern sealed NiCd battery in usetoday.

For many years, NiCd was the preferred battery choice for two-way radios, emergency medicalequipment, professional video cameras and power tools. In the late 1980s, the ultra-high-capacity NiCd rocked the world with capacities that were up to 60 percent higher than thestandard NiCd. This was done by packing more active material into the cell, but the gain wasmet with the side effects of higher internal resistance and shorter cycle.

The standard NiCd remains one of the most rugged and forgiving batteries but needs proper

care to attain longevity. It is perhaps for this reason that NiCd is the favorite battery of manyengineers. Table 1 lists the advantages and limitations of the standard NiCd.


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Advantages

Fast and simple charging even after prolonged storage

High number of charge/discharge cycles; provides over1,000 charge/discharge cycles with proper maintenance

Good load performance; rugged and forgiving if abused

Long shelf life; can be stored in a discharged state

Simple storage and transportation; not subject to regulatory control

Good low-temperature performance

Economically priced; NiCd is the lowest in terms of cost per cycle

Available in a wide range of sizes and performance options

Limitations

Relatively low specific energy compared with newer systems

Memory effect; needs periodic full discharges

Environmentally unfriendly; cadmium is a toxic metal and cannot bedisposed of in landfills

High self-discharge; needs recharging after storage

Table 1: Advantages and limitations of NiCd batteries

Nickel-metal-hydride (NiMH)

Research of nickel-metal-hydride started in 1967; however, instabilities with the metal-hydrideled scientists to develop the nickel-hydrogen battery (NiH) instead. Today, NiH is mainly used insatellites.

New hydride alloys discovered in the 1980s offered better stability and the development ofNiMH advanced in earnest. Today, NiMH provides 40 percent higher specific energy than astandard NiCd, but the decisive advantage is the absence of toxic metals.

The advancements of NiMH are impressive. Since 1991, the specific energy has doubled andthe life span extended. The hype of lithium-ion may have dampened the enthusiasm for NiMH a

bit but not to the point to turn HEV makers away from this proven technology. Batteries for theelectric powertrain in vehicles must meet some of the most demanding challenges, and NiMHhas two major advantages over Li-ion here. These are price and safety. Makers of hybridvehicles claim that NiMH costs one-third of an equivalent Li-ion system, and the relaxation onsafety provisions contribute in part to this price reduction.

Nickel-metal-hydride is not without drawbacks. For one, it has a lower specific energy than Li-ion, and this is especially true with NiMH for the electric powertrain. The reader should bereminded that NiMH and Li-ion with high energy densities are reserved for consumer products;they would not be robust enough for the hybrid and electric vehicles. NiMH and Li-ion for theelectric powertrain have roughly one-third less capacity than consumer batteries.

NiMH also has high self-discharge and loses about 20 percent of its capacity within the first 24hours, and 10 percent per month thereafter. Modifying the hydride materials lowers the self-discharge and reduces corrosion of the alloy, but this decreases the specific energy. Batteries


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for the electric powertrain make use of this modification to achieve the needed robustness andlife span.

There are strong opinions and preferences between battery chemistries, and some experts saythat NiMH will serve as an interim solution to the more promising lithium systems. There aremany hurdles surrounding Li-ion also and these are cost and safety. Li-ion cells are not offered

to the public in AA, AAA and other popular sizes in part because of safety. Even if they weremade available, Li-ion has a higher voltage compared to nickel-based batteries.

Consumer Application

NiMH has become one of the most readily available and low-cost rechargeable batteries forportable devices. NiMH is non-toxic and offers a higher specific energy than NiCd. Batterymanufacturers, such as Sanyo, Energizer, Duracell and GP, have recognized the need for adurable and low-cost rechargeable battery for consumers and offer NiMH in AA and AAA sizes.The battery manufacturers hope to persuade buyers to switch to rechargeable batteries andreduce the environmental impact of throwaway primary cells.

The NiMH battery for the consumer market can be viewed as an alternative to the failedreusable alkalinethat appeared in the 1990s. Limited cycle life and poor loading characteristicshindered its success.

What is of ongoing concern to the consumer using rechargeable batteries is the high self-discharge, and NiMH behaves like a leaky basketball or bicycle tire. A flashlight or portableentertainment device with a NiMH battery gets flat when put away for only a few weeks.Having to recharge the device before each use does not sit well. The Eneloop NiMH by Sanyohas reduced the self-discharge by a factor of six. This means that you can store the chargedbattery six times longer than a regular NiMH before a recharge becomes necessary. Thedrawback is a slightly lower specific energy compared to a regular NiMH. Other NiMHmanufacturers such as ReCyko by GP claim similar results.

Table 2 summarizes the advantages and limitations of industrial-grade NiMH. The table doesnot include the Eneloop and equivalent consumer brands.

Advantages

3040 percent higher capacity than a standard NiCd

Less prone to memory than NiCd

Simple storage and transportation; not subject to regulatory control

Environmentally friendly; contains only mild toxins

Nickel content makes recycling profitable

Limitations

Limited service life; deep discharge reduces service life

Requires complex charge algorithm

Does not absorb overcharge well; trickle charge must be kept low

Generates heat during fast-charge and high-load discharge

High self-discharge; chemical additives reduce self-discharge at the


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expense of capacity

Performance degrades if stored at elevated temperatures; should bestored in a cool place at about 40 percent state-of-charge

Table 2: Advantages and limitations of NiMH batteries

Lithium-based Batteries

Pioneer work with the lithium battery began in 1912 under G.N. Lewis, but it was notuntil the early 1970s that the first non-rechargeable lithium batteries becamecommercially available. Attempts to develop rechargeable lithium batteries followed inthe 1980s but the endeavor failed because of instabilities in the metallic lithium used asanode material.

Lithium is the lightest of all metals, has the greatest electrochemical potential andprovides the largest specific energy per weight. Rechargeable batteries with lithiummetal on the anode (negative electrodes)* could provide extraordinarily high energydensities; however, it was discovered in the mid 1980s that cycling produced unwanteddendrites on the anode. These growth particles penetrate the separator and cause anelectrical short. When this occurs, the cell temperature rises quickly and approaches themelting point of lithium, causing thermal runaway, also known as venting with flame.A large number of rechargeable metallic lithium batteries sent to Japan were recalled in1991 after a battery in a mobile phone released flaming gases and inflicted burns to amans face.

The inherent instability of lithium metal, especially during charging, shifted research toa non-metallic solution using lithium ions. Although lower in specific energy thanlithium-metal, Li-ion is safe, provided cell manufacturers and battery packers followsafety measures in keeping voltage and currents to secure levels. Read more aboutProtection Circuits. In 1991, Sony commercialized the first Li-ion battery, and todaythis chemistry has become the most promising and fastest growing on the market.Meanwhile, research continues to develop a safe metallic lithium battery.

The specific energy of Li-ion is twice that of NiCd, and the high nominal cell voltage of3.60V as compared to 1.20V for nickel systems contributes to this gain. Improvements

in the active materials of the electrode have the potential of further increases in energydensity. The load characteristics are good, and the flat discharge curve offers effectiveutilization of the stored energy in a desirable voltage spectrum of 3.70 to 2.80V/cell.Nickel-based batteries also have a flat discharge curve that ranges from 1.25 to1.0V/cell.

In 1994, the cost to manufacture Li-ion in the 18650** cylindrical cell with a capacityof 1,100mAh was more than $10. In 2001, the price dropped to $2 and the capacity roseto 1,900mAh. Today, high energy-dense 18650 cells deliver over 3,000mAh and thecosts have dropped further. Cost reduction, increase in specific energy and the absenceof toxic material paved the road to make Li-ion the universally accepted battery for

portable application, first in the consumer industry and now increasingly also in heavyindustry, including electric powertrains for vehicles.


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In 2009, roughly 38 percent of all batteries by revenue were Li-ion. Li-ion is a low-maintenance battery, an advantage many other chemistries cannot claim. The batteryhas no memory and does not need exercising (deliberate full discharge) to keep inshape. Self-discharge is less than half that of nickel-based systems. This makes Li-ionwell suited for fuel gauge applications. The nominal cell voltage of 3.60V can directly

power cell phones and digital cameras, offering simplifications and cost reductions overmulti-cell designs. The drawbacks are the need for protection circuits to prevent abuse,as well as high price.

Types of Lithium-ion Batteries

Similar to the lead- and nickel-based architecture, lithium-ion uses a cathode (positiveelectrode), an anode (negative electrode) and electrolyte as conductor. The cathode is ametal oxide and the anode consists of porous carbon. During discharge, the ions flowfrom the anode to the cathode through the electrolyte and separator; charge reverses thedirection and the ions flow from the cathode to the anode. Figure 1 illustrates theprocess.

Figure 1: Ion flow

in lithium-ion

battery.When the cell chargesand discharges,ions shuttle betweencathode (positiveelectrode) and anode

(negative electrode).On discharge, theanode undergoesoxidation,or loss of electrons,and the cathode seesa reduction, or a gainof electrons. Chargereverses themovement.

Li-ion batteries come in many varieties but all have one thing in common thecatchword lithium-ion. Although strikingly similar at first glance, these batteries varyin performance, and the choice of cathode materials gives them their unique personality.

Common cathode materials areLithium Cobalt Oxide (or Lithium Cobaltate),LithiumManganese Oxide (also known as spinel or Lithium Manganate),Lithium IronPhosphate, as well asLithiumNickel Manganese Cobalt(or NMC)*** andLithium

Nickel Cobalt Aluminum Oxide (or NCA). All these materials possess a theoreticalspecific energy with given limits. (Lithium-ion has a theoretically capacity of about2,000kWh. This is more than 10 times the specific energy of a commercial Li-ionbattery.)


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Sonys original lithium-ion battery used coke as the anode (coal product). Since 1997,most Li-ion manufacturers, including Sony, have shifted to graphite to attain a flatterdischarge curve. Graphite is a form of carbon that is also used in the lead pencil. Itstores lithium-ion well when the battery is charged and has long-term cycle stability.Among the carbon materials, graphite is the most commonly used, followed by hard and

soft carbons. Other carbons, such as carbon nanotubes, have not yet found commercialuse. Figure 2-8 illustrates the voltage discharge curve of a modern Li-ion with graphiteanode and the early coke version.

Figure 2: Voltage

discharge curve of

lithium-ion

A battery should have

a flat voltage curve inthe usable dischargerange. The moderngraphite anode doesthis better than theearly coke version.

Courtesy of Cadex

Developments also occur on the anode and several additives are being tried, includingsilicon-based alloys. Silicon achieves a 20 to 30 percent increase in specific energy atthe cost of lower load currents and reduced cycle life. Nano-structured lithium-titanateas an anode additive shows promising cycle life, good load capabilities, excellent low-temperature performance and superior safety, but the specific energy is low.

Mixing cathode and anode material allows manufacturers to strengthen intrinsicqualities; however, enhancing one attribute may compromise another. Battery makerscan, for example, optimize the specific energy (capacity) to achieve extended runtime,increase the specific power for improved current loading, extend service life for better

longevity, and enhance safety to endure environmental stresses. But there aredrawbacks. A higher capacity reduces the current loading; optimizing current loadinglowers the specific energy; and ruggedizing a cell for long life and improved safetyincreases battery size and adds to cost due to a thicker separator. The separator is said tobe the most expensive part of a battery.

Manufacturers can attain a high specific energy and low cost relatively easily by addingnickel in lieu of cobalt, but this makes the cell less stable. While a start-up companymay focus on high specific energy to gain quick market acceptance, safety anddurability cannot be compromised. Reputable manufacturers place high integrity onsafety and longevity.


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Table 3 summarizes the characteristics of Li-ion with different cathode material. Thetable limits the chemistries to the four most commonly used lithium-ion systems andapplies the short form to describe them. The batteries areLi-cobalt, Li-manganese,Li-

phosphate andNMC. NMC stands for nickel-manganese-cobalt, a chemistry that isrelatively new and can be tailored for applications needing either high capacity or high

loading capabilities. Lithium-ion-polymer is not mentioned as this is not a uniquechemistry and only differs in construction. Li-polymer can be made in variouschemistries and the most widely used format is Li-cobalt.

SpecificationsLi-cobalt

LiCoO2 (LCO)Li-manganese

LiMn2O4 (LMO)Li-phosphate

LiFePO4 (LFP)NMC

1LiNiMnCoO2

Voltage 3.60V 3.80V 3.30V 3.60/3.70V

Charge limit 4.20V 4.20V 3.60V 4.20V

Cycle life2 5001,000 5001,000 1,0002,000 1,0002,000

Operating

temperatureAverage Average Good Good

Specific energy 150190Wh/kg 100135Wh/kg 90120Wh/kg 140-180Wh/kg

Specific power 1C 10C, 40C pulse 35C continuous 10C

Safety

Average. Requires protectioncircuit and cell balancing of multicell pack. Requirements for smallformats with 1 or 2 cells can berelaxed

Very safe,needs cellbalancing and

V protection.

Safer than Li-cobalt. Needscell balancing

and protection.

Thermal.

runaway3

150C(302F)

250C(482F)

270C(518F)

210C(410F)

CostRaw materialhigh

Moli Energy,NEC Hitachi,Samsung

High High

In use since 1994 1996 1999 2003

Researchers,

manufacturers

Sony, Sanyo,GS Yuasa, LGChem SamsungHitachi,Toshiba

Hitachi,

Samsung, Sanyo,GS Yuasa, LGChem, ToshibaMoli Energy,NEC

A123, Valence,GS Yuasa,BYD, JCI/Saft,Lishen

Sony, Sanyo, LGChem, GS Yuasa,

Hitachi Samsung

Notes

Very highspecific energy,limited power;cell phones,laptops

High power,good to highspecific energy;power tools,medical, EVs

High power,averagespecific energy,elevated self-discharge

Very highspecific energy,high power;tools, medical,EVs


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Table 3: Characteristics of the four most commonly used lithium-ion batteries Specific energy refers to capacity (energy storage); specific power denotes loadcapability.

1 NMC, NCM, CMN, CNM, MNC and MCN are basically the same. The

stoichiometry is usually Li[Ni(1/3)Co(1/3)Mn(1/3)]O2. The order of Ni, Mn and Codoes not matter much.

2 Application and environment govern cycle life; the numbers do not always applycorrectly.

3 A fully charged battery raises the thermal runaway temperature, a partial chargelowers it.

Never was the competition to find an ideal battery more intense than today.Manufacturers see new applications for automotive propulsion systems, as well as

stationary and grid storage, also knows as load leveling. At time of writing, the batteryindustry speculates that the Li-manganese and/or NMC might be the winners for theelectric powertrain.

Industrys experience has mostly been in portable applications, and the long-termsuitability of batteries for automotive use is still unknown. A clear assessment of thecycle life, performance and long-term operating cost will only be known after havinggone through a few generations of batteries for vehicles with electric powertrains, andmore is known about the customers behavior and climate conditions under which thebatteries are exposed. Table 4 summarizes the advantages and limitations of Li-ion.

Advantages

High energy density

Relatively low self-discharge; less than half that of NiCd and NiMH

Low maintenance. No periodic discharge is needed; no memory.

Limitations

Requires protection circuit to limit voltage and current

Subject to aging, even if not in use (aging occurs with all batteries

and modern Li-ion systems have a similar life span to otherchemistries)

Transportation regulations when shipping in larger quantities

Table 4: Advantages and limitations of Li-ion batteries

* When consuming power, as in a diode, vacuum tube or a battery on charge,the anode is positive; when withdrawing power, as in a battery on discharge, theanode becomes negative.


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** Standard of a cylindrical Li-ion cell developed in the mid 1990s; measures18mm in diameter and 65mm in length; commonly used for laptops. Read moreabout Battery Formats.

*** Some Lithium Nickel Manganese Cobalt Oxide systems go by designation

of NCM, CMN, CNM, MNC and MCN. The systems are basically the same.

Types of Lithium-ion

The casual battery user may think there is only one lithium-ion battery. As there aremany species of apple trees, so do also lithium-ion batteries vary and the difference liesmainly in the cathode materials. Innovative materials are also appearing in the anode tomodify or replace graphite.

Scientists prefer to name batteries by their chemical name and the material used, and

unless you are a chemist, these terms might get confusing. Table 1 offers clarity bylisting these batteries by their full name, chemical definition, abbreviations and shortform. (When appropriate, this essay will use the short form.) To complete the list ofpopular Li-ion batteries, the table also includes NCA and Li-titanate, two lesser-knownmembers of the Li-ion family.

Chemical

nameMaterial Abbreviation Short form

Notes

Lithium

Cobalt Oxide1Also LithiumCobalate orlithium-ion-cobalt)

LiCoO2(60% Co)

LCOLi-cobalt

High capacity;for cell phonelaptop, camera

Lithium

Manganese

Oxide1

Also LithiumManganateor lithium-ion-manganese

LiMn2O4 LMOLi-manganese,

or spinel Most safe;lower capacitythan Li-cobaltbut highspecific powerand long life.

Power tools,e-bikes, EV,medical,hobbyist.

Lithium

Iron

Phosphate1

LiFePO4 LFP Li-phosphate

Lithium

Nickel

Manganese

Cobalt

Oxide1

, alsolithium-

LiNiMnCoO2(1020% Co)

NMCNMC


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manganese-cobalt-oxide

Lithium

Nickel Cobalt

AluminumOxide

1

LiNiCoAlO2

9% Co)NCA NCA

Gaining

importancein electricpowertrain andgrid storageLithium

Titanate2

Li4Ti5O12 LTO Li-titanate

Table 1: Reference names for Li-ion batteries.We willuse the short form whenappropriate.

1 Cathode material 2 Anode material

To learn more about the unique characters and limitations of the six most commonlithium-ion batteries, we use spider charts and look at the overall performance. Webegin with Li-cobalt, the most commonly used battery for high-end consumer products,and then move to Li-manganese and Li- phosphate, batteries deployed in power tools,and finally address the newer players such as NME, NCA and Li-titanate.

Lithium Cobalt Oxide(LiCoO2)

Its high specific energy make Li-cobalt the popular choice for cell phones, laptops anddigital cameras. The battery consists of a cobalt oxide cathode and a graphite carbon

anode. The cathode has a layered structure and during discharge lithium ions move fromthe anode to the cathode. The flow reverses on charge. The drawback of Li-cobalt is arelatively short life span and limited load capabilities (specific power). Figure 2illustrates the structure.

Figure 2: Li-cobalt structure

The cathode

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Crash Course on Batteries