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The lithium-ion charge is on

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Even though the internal-combustionengine will for the foreseeable fu-ture remain the principal powerplantfor car and truck propulsion, in the longterm electric-drive technology is the keyto environmentally sustainable roadtransportation. Electric power meansbatteries, of course, and as anyone whouses a mobile phone or laptop computerknows, current electrochemical energy-storage systems often leave much to bedesired in terms of energy density and

capacity. The limitations of large-format,high-power batteries for vehicles areeven more severe.

Such is the case because functionalbatteries are boxes of technical trade-offs and compromises, as one notedbattery expert puts it. Maximization ofnearly any important performance char-acteristic or feature nearly always re-sults in the diminution of another. Rightnow, scientists and engineers are wres-tling with the many interrelated techni-cal factors that determine battery per-formance to produce Goldilocks sys-tems with properties optimized to be

just right for powering the hybrid-electric (HEV), plug-in hybrid electric

(PHEV) and, eventually, pure-electric(EV) vehicles. The quest for truly effec-tive energy storage for electric-drivetechnology, though promising, will haveto continue for many years to come.

Still, that there has been progress inrechargeable battery technology is un-deniable. Nickel metal-hydride (NiMH)batteries, which only became well-es-tablished during the past few years, willhelp power about a million newly builthybrid vehicles in 2010 globally, accord-ing to market forecasts. And recent de-velopments in lithium-ion cell technol-ogy, which offers superior performance

and cycle life, have in large part ad-dressed earlier concerns with calendar

life at elevated storage temperaturesand tolerance to abuse. Along with theexpectations of significantly lower costsas production volumes rise, this con-tinuing evolution should lead to the riseof PHEVs in the coming decade. In themeantime, provisions in the recentCongressional stimulus bill for billionsof dollars of support for advanced-bat-tery development and manufacturingfacilities and the installation of electric-grid storage capabilities to enable wideruse of renewable energy could helpjump-start a new, multibillion-dollarbusiness in the U.S. On the other hand,

The lithium-ioncharge is on

Multiple engineering trade-offs define thecapabilities and limitations of the latest lithium-ion batteries for next-generation hybrid, plug-in,and pure-electric vehicles.

bySteven Ashley


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The lithium-ion charge is on

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suitable Li-ion batteries is about $1000per kWh. By 2012, say DOE cost mod-els, the cost should drop to $500 perkWh and, ultimately, to $300 per kWh.

To accomplish their even more dif-ficult functions, EV batteries need to

produce about 40 kWh of continuous-discharge energy and be capable of onecharge each week, Howell said. Butno current battery can do that now be-cause of significant technical challenges.DOE cost goals for future EV batteries is$150 per kWh. By comparison, todaysconsumer-electronics batteries go forabout $250 per kWh.

Li-ion chemistryNext-generation HEVs and the newPHEVs will use Li-ion technology, thebattery chemistry that today providesenergy for a majority of consumer-elec-tronics applications following Sonyscommercial introduction of the technol-ogy in 1991. Li-ion cells are typicallybased on an anode made of graphiticcarbon and a cathode of layered (a two-dimensional structure) metal oxide, saidM. Stanley Whittingham, who manyexperts consider to be the father of Li-ion batteries. Li-ion technology, said theProfessor of chemistry and materialsscience at Binghamton University inNew York, relies on the relative ease

with which lithium ions can move inand out of the electrodes withoutchanging their molecular structure (andthus volume)a process known as in-tercalation. An organic carbonate sol-vent serves as the liquid electrolytethemedium that carries internal charge be-tween the electrodesfor these cells, hesaid.

Whittingham pointed out that fear ofa growing scarcity of lithium metal fromproducing countries such as Bolivia,China, and Russia is a red herring. The

DOE, he reported, says that there willbe no problem with lithium supply untilat least 2050, and by then widespreadbattery recycling will be in force. Infact, market shortfalls of nickel and co-balt supplies may turn out to have agreat impact on price and productionlevels of various battery types.

Li-ion battery technology variants,generally distinguished by the materialused for the cathode, are being studied,said Gary Henricksen, Manager ofElectrochemical Energy Storage atArgonne National Laboratory. Severalmanufacturers, such as Johnson

Controls, Saft, and Panasonic, today

believe that a formulation of nickel(80%), cobalt (15%), and aluminum (5%)is the best compromise, but that couldeasily change over the next few years,he said. This NCA chemistry is ther-mally most difficult to control because itis exothermically reactive at a high stateof charge, which can lead to combus-tion, Henricksen explained. If over-charged, an NCA cell can generate heatand start releasing oxygen at the elec-trode. The combination of high volt-age, heat, a flammable electrolyte, and

oxygen constitutes a potential fire haz-ard. But with sufficient thermal controls,NCA systems avoid so-called thermalrunaway. NCA systems will be used inthe new Mercedes-Benz S-Class mildhybrid, the BMW 7 Series hybrid,Toyota and Fords PHEV prototypes,and a hybrid delivery vehicle fromAzure Dynamics.

An alternative to a Li-ion cell isbased on a manganese-oxide (or spinel)cathode, which Henricksen said releasesless oxygen at higher charge states.Manganese oxide based batteries suffer,however, when the manganese metal

Machine operators at Safts lithium-ionautomotive battery manufacturing facility inNersac, France, complete a quality check atthe end of the coating line, where positiveand negative electrode films are applied toconductive metal foils on rollers.

dissolves into the organic electrolyte,

reducing battery capacity. The leadingproponent of this battery chemistry isKoreas LG Chem; another is EnerDel, asubsidiary of Indiana-based Ener1.According to Mohamed Alamgir,Director of Research at Compact Power,LG Chems U.S. supplier of vehicularbatteries, the manganese-based cathodechemistry contains additives to improvecalendar life under high-temperatureconditions. The cells also feature specialtemperature-resistant separators (themembranes between the electrodes) that

are mechanically reinforced to betterwithstand internal electrical shorts andovercharges.

Even better safety is offered by a bat-tery chemistry founded on iron-phos-phate cathodes, which produce no oxy-gen at high states of charge, ArgonnesHenricksen said. Unfortunately, ironphosphate isnt very conductive, whichcuts the resulting cells voltage and lim-its battery capacity. Researchers atA123Systems of Cambridge, MA, fabri-cate cathodes from a powder-like pre-cursor of iron-phosphate particles thatare smaller than 100 nm (3.94 m) in

Saft,DidierCocatrix


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LG Chem/Compact Power uses highlyautomated fabrication lines to mass-produce manganese oxide-basedlithium-ion cells, which helps keepmanufacturing costs down.

size, explained Yet-Ming Chang,

Materials Science Professor at theMassachusetts Institute of Technologyand A123 co-founder. Beyond applica-tions in hybrid buses from Daimler AGand EVs from Think, he said, the iron-phosphate chemistry is being employedin a special cell optimized for ultra-highpower output. The cell, which was in-troduced this year in the kinetic-energyrecovery system (KERS) in the McLarenFormula One car driven by LewisHamilton, is charged by regenerativebraking energy and provides 6 or 7 s of

boost when engaged.Yet another variation on the Li-ion

theme is a battery with an anode madeof lithium-titanium oxide (LTO), whichwas developed by Ener1 in collabora-tion with Argonne Lab, saidHenricksen. Use of LTO in the anoderather than graphite reduces the possi-bility of runaway thermal events de-rived from anode reactions (as opposedto the more severe ones at the cathode)and extends battery life. Whereasgraphite may experience up to a 9%change in volume caused by microstruc-tural alterations as electrical charges

enter and exit the material over the lifeof a battery, LTO hardly changes at all.The company produces Li-ion batteriesfor Think.

Mass productionIt is generally agreed that manufacturingis the key to cutting battery costs. In thisarea, Japanese firms hold a clear advan-tage, having for years produced Li-ionbatteries for consumer electronics appli-cations in volumes constituting billionsof cells. Standard cell design involveslong, thin electrodes that are woundtogether and placed in metal enclosures

filled with electrolyte. Japanese makersare working on their fourth or fifth gen-erations of automated manufacturingprocesses, said battery consultantAnderman.

Although prior practice had been tofabricate larger, high-power cells in thefamiliar metal cans (both cylindrical andprismatic in shape), companies such asLG Chem, NEC, and EnerDel more re-cently begun to fabricate cells usinglaminated metal-polymer film packag-ing. Manufacture of the earlier can for-

mat involves laborious winding oflong strips of cathode, anode, and sepa-rator materials, said Compact PowersAlamgir, who went on to describe hisfirms proprietary stack-and-fold de-sign, an adaptation of our consumerelectronics process that is considerablyeasier to scale up. The laminatedpackaging is especially suitable forplate-type electrodes and involves farfewer parts than its metal counterpart, sothat it has advantages both with respectto manufacturing and cost, he added.

Fabrication of the plate-type cath-odes and anodes involves coating cop-

per foil with the precursor electrodematerialsgraphite, metal oxide, bind-ersin powder form, Alamgir ex-plained. The electrodes enter a slittingmachine, which calenders and sizesthem to the desired dimensions.

Automated equipment next stacks thethin electrode plates with the polymerseparators in between. The stacks areplaced in individual laminated polymerand metal film packages, which are thenfilled with electrolyte and sealed. Thenthe cells are subjected to a so-called for-mation step in which they are chargedfor the first time and tested. Assemblyinto a battery packs follows.

Although recent U.S. governmentfunding for the development of a do-mestic battery manufacturing infra-structure will support the engineeringof competitive mass-production pro-cesses, many observers worry that suchsupport may be putting the cart beforethe horse, since Li-ion battery chemis-tries are not yet fully optimized. Othersquestion the governments ability tospend these vast sums of money effi-ciently and effectively in the short term.

Meanwhile, researchers worldwidecontinue to pursue other, potentiallymore powerful chemistries for vehicularbatteries. Were currently looking atLi-metal), sodium-metal-chloride, and

Li-air, all of which have safety issues,said the DOEs Howell. The last systemon the listLi-air batteriesis in factconsidered by experts to be the HolyGrail of lithium cell technology becausethe cathode would obtain its electroniccharges for free from atmosphericoxygen molecules that are stripped ofelectrons by a catalyst, he noted.Current catalysts are, however, too costlyand operate at low efficiencies. In addi-tion, said Howell, lithium is a terrificanode material, but the very difficult

challenge is controlling the formation oflithium metal dendrites, tree-like struc-tures that short out the system.

It is unclear whether this exploratoryresearch on novel battery chemistrieswill bear fruit, but as sales of electric-drive vehicles rise, greater effort to de-velop better ways to power them willsurely come as well. aei

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