Basics of LIB Armand!

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H O R I Z O N S

Batteries are currentlybeing developed to poweran increasingly diverserange of applications, fromcars to microchips. Howcan scientists achieve theperformance that eachapplication demands?How will batteries be able

to power the many other portable devices thatwill no doubt be developed in the comingyears? And how can batteries become a sus-tainable technology for the future?

The technological revolution of the past fewcenturies has been fuelled mainly by varia-tions of the combustion reaction, the fire thatmarked the dawn of humanity. But this hascome at a price: the resulting emissions of car-bon dioxide have driven global climate change.For the sake of future generations, we urgentlyneed to reconsider how we use energy in every-thing from barbecues to jet aeroplanes andpower stations.

If a new energy economy is to emerge, itmust be based on a cheap and sustainableenergy supply. One of the most flagrantlywasteful activities is travel, and here batterydevices can potentially provide a solution,especially as they can be used to store energyfrom sustainable sources such as the wind andsolar power.

Because batteries are inherently simple inconcept, it is surprising that their developmenthas progressed much more slowly than otherareas of electronics. As a result, they are oftenseen as being the heaviest, costliest and least-green components of any electronic device. It

was the lack of good batteries that slowed downthe deployment of electric cars and wirelesscommunication, which date from at least 1899and 1920, respectively (Fig. 1). The slow prog-ress is due to the lack of suitable electrode mat-erials and electrolytes, together with difficultiesin mastering the interfaces between them.

All batteries are composed of two electrodesconnected by an ionically conductive materialcalled an electrolyte. The two electrodes havedifferent chemical potentials, dictated by thechemistry that occurs at each. When these elec-trodes are connected by means of an externaldevice, electrons spontaneously flow from the

more negative to the more positive potential.Ions are transported through the electrolyte,

maintaining the charge balance, and electricalenergy can be tapped by the external circuit. Insecondary, or rechargeable, batteries, a largervoltage applied in the opposite direction cancause the battery to recharge.

The amount of electrical energy per massor volume that a battery can deliver is a func-tion of the cells voltage and capacity, whichare dependent on the chemistry of the sys-

tem. Another important parameter is power,which depends partly on the batterys engi-

neering but crucially on the chemicals the bat-tery contains. Hundreds of electrochemicalcouples were proposed during the nineteenthand early twentieth centuries, the most nota-ble primary battery being ZnMnO2, withleadacid and NiCd being the most commonsecondaries1.

The stored energy content of a battery canbe maximized in three ways: (1) by having

a large chemical potential difference betweenthe two electrodes; (2) by making the mass (or

Building better batteriesM. Armand and J.-M. Tarascon

Researchers must find a sustainable way of providing the power our modern lifestyles demand.

Figure 1 | Revisiting the past. In 1899 a Belgian car, La jamais contente (top left), equipped with leadacid batteries, reached a speed of 30 metres per second (ref. 26). In the same year, at a car competitionin Paris, the only petrol-driven car was disqualified for having unpractically high consumption. Insidethe United States, between 1900 and 1920, the proportion of electrical cars produced fell from 60%to 4% of the total. One century later, fully electrical cars, such as the Tesla roadster (bottom left), arecoming back into the picture. Meanwhile, the first wireless communication took place in Pennsylvaniain 1920 (top right, after ref. 27). Nearly 100 years later, the latest mobile phones (bottom right) canperform a wide range of functions.

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PbO2

H2O

H2SO4/H2O

H+

PbSO4

SO42

+

e

2.0 V

Pb

PbSO4

Leadacid

Li1-xCoO2

LiPF6EC-DMC

LiPF6EC-DMC

Li+

Li+

LiCoO2

+

e

3.8 V

LiC6

C6

Lithium ion

Future batteries?

NiOOH

KOH/H2O

H+

Ni(OH)2

Cd(OH)2

OH

+

e

1.2 V

Cd

NiCd

NiOOH

KOH/H2O

H+

Ni(OH)2

MHx

OH

+

e

1.2 V

M

NiMH

MPO4

Li+

Li+

LiMPO4

Si, Sn, M, X

+

e

3 V

Lix (Si/Sn)LiX + M

Lithium ion basedon nanomaterials

Ionic liquids

O2

Li+

Li+

Li2O2

+

e

3.3 V

Lithium

metal

Lithiumair

Lithium-basedelectrolytes

Li+

Li+

+

e

32 V

Lithiumorganic

1859 1909 1975 1990 2010 2050

volume) of the reactants per exchanged electron assmall as possible; and (3) by ensuring that theelectrolyte is not consumed in the chemistry ofthe battery. This final condition was not true ofthe three principal battery technologies devel-oped in the twentieth century, but holds for themore recent NiMH and lithium-ion batteries.

One of the key elements of these two batteriesis that the same ion (H+ for NiMH and Li+ forlithium-ion batteries) participates at both elec-trodes, being reversibly inserted and extractedfrom the electrode material, with the concomi-tant addition or removal of electrons. NiMHbatteries are used to power hybrid vehiclesand cheaper electronics, whereas lithium-ionbatteries have conquered high-end electronicsand are now being used in power tools. Lith-ium-ion batteries are also entering the hybridelectric-vehicle market and are a serious con-tender to power the electric cars of the future.

The lithium-ion battery, first commercial-

ized by Sony in 1991, owes its name to theexchange of the Li+ ion between the graphite(LixC6) anode and a layered-oxide (Li1xT

MO2)cathode2, with TM being a transition metal(usually cobalt but sometimes nickel or man-ganese). The energy it stores (180 Wh kg1)at an average voltage of 3.8 V is only a factorof 5 higher than that stored by the much olderleadacid batteries. This may seem poor in thelight of Moores law in electronics (accordingto which memory capacity doubles every 18months), but it still took a revolution in materi-als science to achieve it.

Billions of lithium-ion cells are produced

for portable electronics, but this is not sustain-able as cobalt must be obtained from natural

resources (it makes up 20 parts per million ofEarths crust3,4). In addition, there are safetyconcerns, as the presence of both combus-tible material and an oxidizing agent carriesa risk of runaway reactions resulting in firesor explosions. Improvements in the electro-lyte composition could make the chemistry

safer, but accidents are mainly a result of fiercecost-cutting and attempts to cram more activematerial in the same volume, causing internalshort-circuits. As a result, improvements inmonitoring and management are essential iflithium-ion batteries are to fulfil their potentialin the automotive market.

Lithium-ion batteries would also need toreduce their carbon footprint, which is cur-rently about 70 kg CO2 per kWh (ref. 5). Thecarbon-related benefits of electric vehicles orplug-in hybrids become apparent only afteraround 120 recharges with respect to electric-ity from coal, assuming a power-plant effi-

ciency of 35% and that the batteries replace apetrol engine in which 20% of the heat fromcombustion is converted into useable energy.However, these break-even numbers need tobe reduced.

Replacing each of the worlds 800 millioncars and lorries with electric vehicles or plug-in hybrids powered by 15-kWh lithium-ionbatteries would use up to 30% of the worldsknown reserves of lithium. But lithium is alsofound in unlimited quantities in sea water3,4,and concentrating it from brines is muchgreener (requiring just solar energy) thanconventional mining. The demand for lith-

ium could also be eased by recycling, whichhas already proved its value with leadacid

batteries. All these problems must be overcomeif lithium batteries are to take their place as thebatteries of the future (Fig. 2).

The nanotechnology revolutionMost attempts to improve the design of lithium-ion batteries have tackled the problem at the

macroscopic scale, but work is now focusingon the nanoscale. Nanomaterials were slow toenter the field of energy storage because theeffective increase in the electrodes surface arearaised the risk of secondary reactions involvingelectrolyte decomposition. Only as recently as2000 was it realized that such reactions couldbe controlled by coating the electrodes to pro-tect the electrolyte from unwanted oxidationor reduction by the electrode materials. Thearrival of nanomaterials gave lithium-ion bat-teries a new lease of life6 and provided benefitsin terms of capacity, power, cost and materialssustainability that are still far from being fully

exploited.Electrode kinetic issues can be circumventedby switching to nanomaterials combined withcarbon nano-painting7, in which the grainsare coated with a thin layer of carbon to bringthe required conductivity to individual grains,whose small size shortens the diffusion pathfor ions and electrons. Moreover, by accom-modating the strains associated with lithiuminsertion/removal reactions, as the volumecan expand or contract several-fold, this hasalso made it possible to use materials with largevolume changes on reaction with lithium, suchas alloys. But there are pitfalls, the most impor-

tant being the poor packing density of elec-trodes based on nanomaterials, which limits

Figure 2 | Battery

chemistry over the

years. Present-daybattery technologiesare being outpacedby the ever-increasing powerdemands from newapplications. As wellas being inherently

safe, batteries of thefuture will have tointegrate the conceptof environmentalsustainability.

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Insertion

Conversion 3050 3050

MX2 MX2

MX MX

LiMX2

e e

e

e

Li2X + M

Discharge Charge

Discharge Charge

M

M

Li XLi+ Li+

Li+ Li+

the energy that can be stored per unit volumeor mass because there is a larger proportion ofinert components such as current collectorsor electrolyte.

Another advantage of nanomaterials is that

they can change the reaction pathway, afford-ing high capacities, rechargeability and gener-ality to a range of battery systems8. One suchreaction pathway is referred to as a conversionfrom transition-metal oxides:

TMxOy + 2ye + 2yLi+ x[T

M]0 +yLi2O;

the final product consists of a homogeneousdistribution of metal nanoparticles ([TM]0,where the superscript 0 indicates the metal-lic form) embedded in a Li2O matrix (Fig. 3).The drawback with this mechanism, however,is that the large voltage difference between

charge and discharge results in poor energyefficiency. This problem is being addressedby studies of both the material chemistry andmorphology and the electrode configuration.The hunt is also under way for materials thatcan undergo conversion reactions involvingmultiple electrons at high potential, for use ascathode materials. However, the full impactof nanomaterials on living cells has yet to beappraised, although the risk is minimal whenthey are produced in situ, as they are for theconversion reaction.

Solid electrolytes were quicker to benefitfrom the use of nanomaterials9. The addition

of nano-fillers (nano-grains dispersed ina polymer, such as Al2O3 or TiO2) to simple

polyether-based electrolytes increases the con-ductivity several-fold at 6080 C, but there isno advantage at room temperature. Organ-izing the polymer strands in such a way as toincrease the order locally (using crystalline

whorls, stretching or even chirality) can alsoprovide benefits, by increasing conductivity atlow temperatures, and further work is neededto assess the merits of using block co-polymers(AB or ABA)10. The phase separation inherentto these systems results in good mechanicalproperties, but also offers a way of increasingdissociation by partitioning anions and cationsin the two sub-phases. Giving the two phasesdifferent wetting or adhesion properties canhelp by avoiding grain growth as the polymersnano-domains will determine the partitioningof space.

True polymer batteries may still be some

way off, but in the meantime we will see moreattempts to use ionic liquids as either solventsfor lithium salts or plasticizers for polyether-based electrolytes. Ionic liquids have exceed-ingly low vapour pressures, are non-flammableand have high conductivities, making themserious contenders for safer batteries. But itremains to be seen whether they can be pro-duced cheaply enough, at the desired purity, withsufficient conductivity at low temperature.

Beyond nanomaterialsThe components of todays lithium-ionbatteries, such as LiCoO2 and LiMn2O4, are not

produced from renewable energy resourcesbut from ores, and extracting the raw materials

and manufacturing the electrodes will requireincreasing amounts of energy as they becomescarcer. Will the lithium-ion battery, which isso energetically expensive to fabricate, remainattractive and viable in the long term? In 50years, if all cars become electric and rely onthese scarce materials, might we face stag-gering price increases like those recentlyseen with fossil fuels? Not if we find a way

of making lithium-ion batteries sustainablewhile maintaining or exceeding the perform-ance of todays batteries. One option is touse renewable electrodes made from naturalresources, just as fuel cells can use hydrogenor (m)ethanol made from biomass. But whatwould these electrodes be like?

Inspired by natureWhen scientists need new approaches, theyoften turn to the chemistry of life, with itsvirtually unlimited and incredible reactionmechanisms. The batterys insertion reac-tion may have no real equivalent in the living

world, but the materials themselves could befabricated in living cells. Phosphate species aremanipulated to make DNA and ATP, so it isnot so hard to envisage an enzyme-mediatedsynthesis of LiFePO4, especially as the pH forthe precipitation is close to the physiologicalvalue of 7. The same outlook applies to con-version reactions, as preliminary work11 hasdemonstrated the synthesis of hydrated Co3O4and MnO2 with the help of a virus and a bac-terium, respectively.

Perhaps the ultimate in conversion reactionsalso comes from living systems. The proteinapoferritin, which encloses a small crystal of

iron oxide (Fe2O3.nH2O), can either grow ordissolve the particle according to the organismscurrent need for iron12. So could polymers withproperties rather similar to proteins, adsorbedon the surface of a conversion electrode, con-trol the growth or dissolution of the TMxOy andLi2O crystals, the reversible formation of whichis key to increasing the energy efficiency?

Regarding the feasibility of using electro-chemically active organic molecules as cathodematerials, the use of polyaniline13 and otherredox polymers14 has been much hyped overthe years, but development has been disap-pointing. However, because lithium-exchang-

ing materials do not involve the electrolyte intheir redox processes, substituting the cath-ode for an organic material might boost thecapacity. The feasibility of using active LixC6O6organic molecules that can be prepared fromnatural sugars common in living systems(Fig. 4) is currently under investigation15. Inthe light of such findings, we can speculate onthe use of hypericine (a polyquinone-basedactive ingredient of St Johns wort) or the con-densation polymers of malic acid as potentialhigh-capacity cathode materials.

The close relationship between carbo-hydrates and their oxidized polyketone forms

makes the former the logical starting pointfor the design of new electrode materials.

Figure 3 | Reaction mechanisms. Schematic representation showing the contrasting reactionmechanisms occurring during discharge for insertion (top) and conversion reactions (bottom).The insertion reaction demonstrates a maximum of 1 electron transfer per transition metal (heredesignated M), whereas the conversion reaction can transfer 2 to 6 electrons (derived from ref. 28).

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Lithium Electrolyte Compositeelectrode

Li+

O2

O2

Li+

Discharge

+

e e

OH

Li+

Recycling

C

OH

Extraction

Elaboration viagreen chemistry

Batteryassembly

CO2

+ 2pLi+ + 2pe

Li+

xLi+

x

OH

OHHO

HO

HO

p p

Polyketones can be obtained from naturalsources and are unlimited because sugars canbe made by living species or artificially in greenchemistry16. Nor have sugars been overlookedfor use in bio fuel-cells, a much improved ver-sion of which has recently been unveiled17.

Although complex and unlikely to yieldinstant results, the search for electroactiveorganic molecules synthesized from biomasscould pave the way for the next generationof lithium-based batteries. Organic materials

have already made considerable inroads intothe semiconducting industry, in light-emittingdiodes, solar cells and transistors, and they areexpected to penetrate the energy field in thecoming decades. However, it would be foolishto ignore the fact that organic materials haveseveral disadvantages in terms of their lim-ited thermal stability, low specific gravity andappreciable solubility in electrolytes.

Lithiumoxygen batteriesAir electrodes and metalair battery tech-nologies have already been used in primarysystems such as fuel cells, but the use of lithium

instead of zinc as the metal will increase theenergy output eightfold. An oxygen electrodeproceeding in tandem with lithium accordingto the reaction 2Li + O2 Li2O2 can deliver acapacity of 1,200 mAh g1. The first lithiumaircell was successfully assembled and dischargedin 1996 (ref. 18), but attractive rechargeabilitywas demonstrated only recently19.

It could be argued that such a system uniteswithin the same device the two most promi-nent failures of battery and fuel-cell technolo-gies, namely the inability to master lithiumand oxygen electrodes. These perceived issueshave prevented the practical use of lithiumair

batteries. However, one advantage of such a sys-tem is the formation of Li2O2 without cleaving

the OO bond, which has limited both kineticsand rechargeability in aqueous systems becausethere is a large activation energy and platinumcatalysts are often required.

Improving energy storage and preventingLi2O2 from clogging the electrode require abetter understanding of the reaction mecha-nism of the oxygen electrode. Engineering andchemical advances are also required to pre-vent the ingress of either CO2 or H2O, whichcould react with either Li2O2 or lithium metal.

But there are reasons for optimism. The useof nanomaterials makes it possible to designporous, catalysed, three-dimensional elec-trodes20 (Fig. 5) with improved kinetics and

energy efficiency. The use of ionic liquids,which can be made hydrophobic, will put anend to problems caused by the entry of water.However, if ionic liquids are to be used as elec-trolytes, they must be combined with a highlyhygroscopic Li salt, so preparing them remainsa serious challenge.

Lithium has been the anode of choice foryears, but much more work is still needed.

When used with liquid electrolytes and gels,the metal is redeposited unevenly in the formof dendrites, leading to inherently unsafe cellswith a short lifetime. It has been suggestedthat the cause lies in current inhomogenei-ties induced by the passivation layer presenton the surface of lithium metal21. Using drypolymer electrolytes instead keeps the prob-lem at bay for the first 600 cycles, but doesnot solve it. The classic strategy22 to get uni-form microcrystalline metal deposition inan aqueous solution from anionic complexes(for example, silver metal from Ag(CN)2

)has not been applied to the lithium elec-

trode. In this strategy, the surges in localcurrent result in a drift of the negative ionsfrom the interface, leading to a depletion ofthe plating species and hindering the forma-tion of metal dendrites. The same principlecould be applied to lithium systems by usingcharged chelating complexes of the LiX2

type,formed, for instance, using bidentate ligandsof the 1,3-dione family (acetylacetone) andhaving K+ as a counter-cation (see Fig. 6).

Another approach would be to use unipolarelectrolytes, in which only the cations carrycharge, but these have never been seriouslystudied in the context of plating lithium metal.

This is surprising because polyelectrolytes withfixed negative charges attached to a macromole-cule are the only way to avoid the depletion orover-concentration of salt arising from the

Figure 5 | Lithiumair batteries. Left, the mechanism used in lithiumair batteries (courtesy ofA. Debard et al., Univ. St Andrews). Right, three-dimensional nanoarchitectured electrodes madefrom depositing 10- to 20-nm-thick layers of MnO2 onto a carbon foam using a low-temperature

process (according to ref. 20) that could be used to enhance the kinetics of the lithiumair electrode(three-dimensional schematic courtesy of J. W. Long and D. R. Rolison, US Naval Research Lab.).

Figure 4 | An organic future. Proposed sustainable organic-based batteries based on electrodematerials made from biomass.Myo-inositol extracted from corn can be used to prepare

electrochemically active Li2C6O6, whereas malic acid from apples can undergo polycondensationto a polyquinone that is electrochemically active to lithium (centre). (Derived from ref. 15.)

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C

N

H

C

O

H

Li

+2H+ +2e

mobility of the anions. These two strategies(anionic lithium salts and unipolar conductivity)

should be further explored to ensure that allavenues towards making the lithium-metalelectrode viable have been exhausted.

Alternatives to lithiumAlthough we have focused on lithium, thereare several alternatives for use as electrodes(Table 1). The metals worth considering aremagnesium (ref. 23) and aluminium (ref. 24)because of their light weight, but they deliverless voltage, undermining their use as anodes,and repetitive plating of these metals is dif-ficult using most electrolytes. Similarly, onlyhigh-capacity cathode materials can be consid-

ered, which narrows it down to oxygen or sul-phur for magnesium, or graphite fluoride foraluminium, to harness the metals high affinityfor fluorine. However, little is known about thekinetics of electrode reactions involving themotion of multivalent species, and addressingthese challenges would need extensive collabo-ration between organometal researchers andelectrochemists.

Proton-based battery technologies havebeen well studied, but do they still have any-thing to offer? Even with the best air electrode,to be competitive with lithium-ion batteries, ahydrogen system, with a voltage of 1.01.5 V,

requires the anode to have an extremely lowequivalent mass, far below that of conventional

hydrogen-storing alloys. The only candidatesare light elements, given that CH bonds are

too covalent and cannot (yet) be activated forreversible room-temperature systems. Anotheralternative for the negative electrode would beto exploit the reversibility of the NH bond insemiconjugated polymers (see Fig. 6). Theselow-potential (Vversus H2/H

+) materials couldbe used as high-capacity electrodes, althoughtheir low electronic conductivity could proveproblematic.

Miniature powerhousesAs well as large-scale applications, such as elec-tric vehicles, batteries must also be developed

to satisfy recent advances in microelectronics.These require miniature power sources, suchas solid-state, lithium-based, thin-film bat-teries. Much of the work has focused on flat,two-dimensional configurations, but theseare limited in terms of energy output, and theneed for greater performance has recently ledmicrobattery researchers to explore the thirddimension25. This might seem relatively easy,

given the spectacular three-dimensional cir-cuitry that the silicon microelectronic industrynow has to offer. However, microlithographyprocesses have proved both awkward andcostly to transfer to batteries.

A combined chemicalelectrochemicalapproach has much to offer as a way of man-ipulating materials at the atomic scale, andcould be used to develop skyscraper batteries(Fig. 7). Similarly, adding a third dimensionopens the way to a larger variety of configura-tions (such as the assembly of positivenegativeelectrodes and electrolyte) while maintaininga short diffusion length for electrodes and

ions, which is essential if a battery is to havethe required power.

ConclusionsIt is not yet clear whether the next generationof batteries could be successfully integratedinto an energy market that is currently linkedto global warming. Fame and fortune certainlyawait anyone who can come up with a viablealternative to fossil fuels. Furthermore, it is dif-ficult to see how the performance gap betweenthe internal-combustion engine and lithium-ion batteries will be filled using only new bat-tery technology; other approaches, such as

fuel cells, will be needed, but here a completeoverhaul of present systems will probably berequired.

In our journey into the future we havereinvestigated existing systems and suggestednew trends and ideas that require much workto become a reality. Designing green and sus-tainable battery systems is essential, so criteriasuch as life cycle, abundance of raw materialsand electrode recycling are becoming cru-cial. For these reasons, much is expected ofthe lithiumair system, which offers a greatimprovement in energy density, and lithium-

Figure 6 | Wild cards. Lithium-bearing anionic complexes that could be explored for efficient lithiumplating (left) and a contender for a high-capacity proton-exchanging polymer (right).

Table 1 | Battery chemistries

Battery type Features Environmental impact

NiMH(established)

Low voltage, moderate energy density,high power densityApplications: portable, large-scale

Nickel not green (difficult extraction/unsustainable), toxic. Not rare but limitedRecyclable

Leadacid(established)

Poor energy density, moderate power rate,low costApplications: large-scale, start-up power,stationary

High-temperature cyclability limitedLead is toxic but recycling is efficient to 95%

Lithium ion(established)

High energy density, power rate, cycle life,costlyApplications: portable, possibly large-scale

Depletable elements (cobalt) in mostapplications; replacements manganese andiron are green (abundant and sustainable)Lithium chemistry relatively green (abundantbut the chemistry needs to be improved)Recycling feasible but at an extra energy cost

Zincair(established)

Medium energy density, high power densityApplications: large-scale

Mostly primary or mechanicallyrechargeableZinc smelting not green, especially if primaryEasily recyclable

Lithiumorganic(future)

High capacity and energy density but limitedpower rate. Technology amenable to a lowcostApplications: medium- and large-scale, withthe exception of power tools

RechargeableExcellent carbon footprintRenewable electrodesEasy recycling

Lithiumair

(future)

High energy density but poor energy

efficiency and rate capabilityTechnology amenable to a low costApplications: large-scale, preferablystationary

Rechargeability to be proven

Excellent carbon footprintRenewable electrodesEasy recycling

Magnesiumsulphur(future)

Predicted: high energy density, power densityunknown, cycle life unknown

Magnesium and sulphur are greenRecyclableSmall carbon footprint

AlCFx

(future) Predicted: moderate energy density, powerdensity unknown

Aluminium and fluorine are green butindustries are notRecyclable

Proton battery(future)

Predicted: all organic, low voltage, moderateenergy density, power density unknown

Green, biodegradable

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Currentcollector

Currentcollector

Solid electrolyteSi Si substrate

Barrier layer

LiCoO2

+

based systems that use electroactive organicmolecules, which could be obtained frombiomass using green chemistry. Yet it seemsincongruous to insist that batteries are sus-tainable while the car or appliance they driveis not.

The next generation of lithium-ion batter-ies fully based on nanomaterials will soon behere, followed by lithiumair batteries andothers using organic materials. And there isplenty to inspire us in the living world, as longas we can capture the function of each moleculein a cumulative sequential process, which is not

an easy task. Both biofuel cells and high-volt-age liquid-electrolyte microbatteries inspiredby electric eels have already been demon-strated. We all live on organic-based energy,so why shouldnt our appliances and vehiclesuse it too?

One thing is clear, however. Solving theremaining challenges will require researchersfrom a range of disciplines, and their successwill depend on the efficiency of their cross-fertilization.

M. Armand and J.-M. Tarascon* are at the LRCS,

CNRS UMR-6007, Universit de Picardie Jules

Verne, Amiens, France.

*Corresponding author:

e-mail: [email protected]

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3. Lutgens, F. K. & Tarbuck, E. J.Essentials of Geology 7th edn(Prentice Hall, New York, 2000).

4. Ward, R. D. & Brownlee, D. Rare Earth (Copernicus, NewYork, 2000).

5. Ishihara, K. 5th Int. Conf. Ecobalance, Tsukuba (2002).6. Arico, A. S., Bruce, P., Scrosati, B., Tarascon, J.-M. &

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(1999).8. Poizot, P., Laruelle, S., Grugeon, S., Dupont, L. & Tarascon,

J.-M. Nature407,496499 (2000).9. Croce, F., Appetecchi, G. B., Persi, L. & Scrosati, B. Nature

394,456458 (1998).10. Sadoway, D. R. et al.J. Power Sources 9798,621623 (2001).11. Nam, K. T.et al. Science312,885888 (2006).12. Hoare, R. J., Harrison, P. M. & Hoy, T. G.Nature255,

653654 (1975).13. MacDiarmid, A. G., Yang, L. S., Huang, W. S. & Humphrey,

B. D. Synth. Metals18,393398 (1987).14. Novak, P., Mller, K., Santhanam, K. S. V. & Haas, O. Chem.

Rev.97,207282 (1997).

15. Chen, H. et al.ChemSusChem (in the press).16. Anastas, P. & Warner, J. C.Green Chemistry (Oxford Univ.

Press, New York, 1998).17. http://www.sony.net/SonyInfo/News/Press/200708/

07-074E/index.html18. Abraham, K. M. & Jiang, Z.J. Electrochem. Soc.143,N01

(1996).19. Ogasawara, T., Debart, A., Holzapfel, M., Novak, P. &

Bruce, P.J. Am. Chem. Soc.128, 13901393 (2006).20. Fischer, A. E., Pettigrew, K. A., Rolison, D. R., Stroud, R. M.

& Long, J. W. Nano Lett.7,281286 (2007).21. Rosso, M. et al. Electrochim. Acta51,53345340 (2006).22. Glasstone, S. The Fundamentals of Electrochemistry and

Electrodeposition (American Electroplaters Society, NewYork, 1943).

23. Aurbach, D. et al.J. Electrochem. Soc.149,A115A121 (2002).24. Kamavaram, V. & Reddy, R. G. Electrochemical Studies

of Aluminum Deposition in Ionic Liquids at Ambient

Temperatures: Light Metals (Warrendale, 2002).25. Long, J. W., Dunn, B., Rolison, D. R. & White, H. S. Chem.

Rev.104,44634492 (2004).26.A travers le monde (ed. Hachette) 213214 (1899).27. La Science et la Vie N50, (May 1920).28. Amatucci, G. G. & Pereira, N.J. Fluorine Chem.128,

243262 (2007).

AcknowledgementsThe authors wish to thank thescientific community in the field of energy storage and

conversion for laying the foundations for these views.They are also grateful to G. Amatucci, D. Murphy andP. Poizot for valuable comments.

Figure 7 | Entering the third dimension. Schematic representation of athree-dimensional, integrated, solid-state lithium-ion battery. The surfacearea of the battery has increased 25-fold compared with a two-dimensionalthin-film battery with the same footprint surface area, and will therefore be

able to provide enough energy to power smart autonomous network devicesrelated to sensing applications. (Courtesy of P. H. L. Notten, R. A. H. Niessenand L. Baggetto, Philips Research Laboratories, and Technical University ofEindhoven, the Netherlands.)

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Basics of LIB Armand!