Batteries for electric commercial

vehicles and mobile machinery

Tekes EVE annual seminar, Dipoli 6.11.2012

Dr. Mikko Pihlatie

VTT Technical Research Centre of Finland

2 07/11/2012

Outline

1. Battery technology for electric vehicles and mobile machinery

Current state-of-the-art

Challenges and limitations

Beyond state-of-the-art

2. From battery cells to applications

Application-specific requirements

Battery use and operation window

Cost analysis factors

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What is a battery?

A battery contains one or more electrochemical cells

for storage of electric energy; these may be

connected in series or parallel to provide the desired

voltage and power

The anode is the negative electrode from which

electrons are generated to do external work

The cathode is the positive electrode to which positive

ions migrate inside the cell and electrons migrate

through the external electrical circuit

The electrolyte allows the flow of positive ions from

one electrode to another. The electrolyte is commonly

a liquid solution containing a salt dissolved in a

solvent. The electrolyte must be stable in the

presence of both electrodes. Typically lithium salt

(LiPF6) + mixed organic solvent (ethylene carbonate-

dimethyl carbonate EC-DMC).

The current collectors allow the transport of electrons

to and from the electrodes.

B. Scrosati, Journal of Power Sources 195 (2010) 2419–2430

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Basic principle of Li-ion battery charging - discharging

Source: auto.howstaffworks.com

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Operation principle of SEI formation in a C/LiCoO2 battery

The C/LiMO2 system with current

electrolytes is thermodynamically

unstable (low kinetics!)

Reaction with the electrolyte

creates a passive Solid

Electrolyte Interface (SEI) on the

anode side

Normally the SEI stabilises the

cell (normal operation limits)

Abnormal conditions can lead to

oxidative processes on the

cathode cell failure risk

B. Scrosati, Journal of Power Sources 195 (2010) 2419–2430

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Li-ion batteries – a large range of possible materials combinations

Positive electrodes

Electrode material Average potential

difference Specific capacity Specific energy

LiCoO2 3.7 V 140 mA·h/g 0.518 kW·h/kg

LiMn2O4 4.0 V 100 mA·h/g 0.400 kW·h/kg

LiNiO2 3.5 V 180 mA·h/g 0.630 kW·h/kg

LiFePO4 3.3 V 150 mA·h/g 0.495 kW·h/kg

Li2FePO4F 3.6 V 115 mA·h/g 0.414 kW·h/kg

LiCo1/3Ni1/3Mn1/3O2 3.6 V 160 mA·h/g 0.576 kW·h/kg

Li(LiaNixMnyCoz)O2 4.2 V 220 mA·h/g 0.920 kW·h/kg

Negative electrodes

Electrode material Average potential

difference Specific capacity Specific energy

Graphite (LiC6) 0.1-0.2 V 372 mA·h/g 0.0372-0.0744 kW·h/kg

Hard Carbon (LiC6) ? V 450 mA·h/g ? kW·h/kg

Titanate (Li4Ti5O12) 1-2 V 160 mA·h/g 0.16-0.32 kW·h/kg

Si (Li4.4Si)[38] 0.5-1 V 4212 mA·h/g 2.106-4.212 kW·h/kg

Ge (Li4.4Ge)[39] 0.7-1.2 V 1624 mA·h/g 1.137-1.949 kW·h/kg

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Li-ion battery materials roadmap – expected innovations

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Tradeoffs among state-of-the-art Li-ion battery technologies

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The safe operability window for Lithium-ion battery

The battery should

be strictly kept in the

proper operating

window

Safety concerns

from improper use

or conditions

Durability and

performance suffer

greatly when

misoperated

Requirements for pack

design and battery

management

FTA, US Department of Transportation, Report No. FTA-MA-26-7125-2011.1

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Li-ion and beyond – status and outlook

Energy density insufficient for full EV operation

New electrode materials for higher capacity / lower cost

Lithium-metal alloys for anode, e.g. Li-Si (4000 mAh/g) and Li-Sn (990 mAh/g) anodes

instead of graphite (370 mAh/g)

Higher voltage cathodes, such as LMO ( stability of electrolytes!)

Challenges with safety of operation

Replacement of the organic carbonate lquid electrolyte solutions with more reliable and

safer electrolytes

E.g., solid polymer or ionic liquid electrolytes

Inherently safe electrode materials, such as LTO anodes ( improved cycle life)

Power capability – when quick charging becomes imprative, both

electrodes have to be optimised for this

Completely new systems will take several years to come to

demonstrations, but clear performance improvements are expected

Metal-air (Li-air) batteries bring potentially high electrode capacity (1200 mAh/g)

Li-S Lithium-suphur batteries offer potentially great capacity (2500 Wh/kg)

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Battery pack engineering towards application – case by case

Nissan Leaf battery

pack

Exact designs highly

dependent on vehicle /

application

Geometries and the

available space vary

drastically depending

on vehicle / application

Source: Wikipedia

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Relative performance of electrochemical storage devices

Different types of

power sources

have each their

optimal

application areas

Li-ion batteries

are struggling to

fulfil

requirements for

all-electric

vehicles

Venkat Srinivasan, Almaden Conf. 2009: “The Batteries for

Advanced Transportation Technologies (BATT) Program.”)

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Battery management system vs. vehicle energy balance

The tasks of the BMS

Protect the cells or the

battery from damage

Prolong the life of the

battery

Maintain the battery in a

state in which it can fulfil

the functional requirements

of the application for which

it was specified

Communication interfaces

BMS – vehicle control

BMS – charger

Charger – power/energy

grid

Source: Electropaedia, http://www.mpoweruk.com/bms.htm

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15 07/11/2012

Comparison of different current Li-ion battery types

(power/energy)

Work cycle analysis

and end-user view

are central in

designing the

driveline and energy

storages

Right choice of

battery type and

battery design are

the key to succesful

EV design

Source: Al-Hallaj, EV Li-ion Battery forum, Barcelona 2012

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Batteries cost OEM’s about 1100 $/kWh at low volumes (2010)

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Battery cost will decline drastically by 2020

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Battery lifetime has a crucial impact on the total system cost

Calendar life or cycle life

may be limiting

Different fading modes

Capacity loss

Impedance rise

Increase in self

discharge

Strong effect from how

the battery is used

Load cycles (C-rate)

Temperature

Depth of discharge

20 07/11/2012

Thank you!

www.ecv.fi