Battery Technology for EVs

IntroductionTypes of EV BatteriesThe future of EV Batteries

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IntroductionThere is a need for awareness ofthe greenhouse effect and thenecessity to conserve theenvironment. There is now a greenalternative in the automobilemarket to combat increasing fuelprices of diesel and petrol –electrically-powered cars.Electric vehicles will be a game-changer in the transportationsector. With this comes the needto make electric vehicles morecost-effective and fuel powerefficient.

An electric-vehicle battery (EVB)is a battery used to power theelectric motors of a batteryelectric vehicle (BEV) also knownas a hybrid electric vehicle(HEV). These batteries areusually rechargeable and aretypically lithium-ion batteries.These batteries are specificallydesigned for a high ampere-hour(or kilowatt-hour) capacity,which is the battery's unit ofpower generation capacity.

Electric-vehicle batteriesdiffer from starting, lighting,and ignition (SLI) batteries asthey are designed to give powerover sustained periods of timeand are deep-cycle batteries.

Batteries for electric vehiclesare characterized by theirrelatively high power-to-weightratio, specific energy, andenergy density; smaller,lighter batteries are desirablebecause they reduce the weightof the vehicle and thereforeimprove its performance.

Compared to liquid fuels, mostcurrent battery technologieshave much lower specificenergy, and this often impactsthe maximum all-electric rangeof the vehicles.

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Note: An SLI battery is a lead-acid andrechargeable type of battery that is mainly used inautomobiles. SLI means starting, lighting, andignition; these processes are all consuming energythat is supplied by the vehicle's battery.

Source: UPS Battery Center; Omega Institute forResearch

An Illustration of SLI

Flooded lead-acid batteries arethe cheapest and, in the past,most common vehicle batteriesavailable. There are two maintypes of lead-acid batteries:automobile engine starterbatteries, and deep cyclebatteries.

Automobile engine starterbatteries are designed to use asmall percentage of theircapacity to provide high chargerates to start the engine.Automobile engine starterbatteries are designed to use asmall percentage of theircapacity to provide high chargerates to start the engine, whiledeep cycle batteries are used toprovide continuous electricity torun electric vehicles likeforklifts or golf carts. Deepcycle batteries are also used asauxiliary batteries inrecreational vehicles, but theyrequire different, multi-stagecharging. No lead-acid batteryshould be discharged below 50% ofits capacity, as it shortens thebattery's life. Flooded batteriesrequire inspection of electrolytelevels and occasional replacementof water, which gases away duringthe normal charging cycle.

The Types

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Nickel-metal hydride These are now consideredrelatively mature technology.While less efficient (60–70%)in charging and dischargingthan even lead-acid, they havea specific energy of 30–80Wh/kg, far higher than lead-acid. When used properly,nickel-metal hydride batteriescan have exceptionally longlives, as has been demonstratedin their use in hybrid cars andin the surviving first-generation NiMH Toyota RAV4 EVs that still operate wellafter 100,000 miles (160,000km) and over a decade ofservice. Downsides include poorefficiency, high self-discharge, very finicky chargecycles, and poor performance incold weather.

Sodium Nickel ChlorideAnother type is the SodiumNickel Chloride or "Zebra"battery, it uses a moltensodium chloroaluminate(NaAlCl4) salt as theelectrolyte. A relativelymature technology, the Zebrabattery has a specific energyof 120 Wh/kg. Since the batterymust be heated for use, coldweather does not stronglyaffect its operation except forincreasing heating costs. Theyhave been used in several EVssuch as the Modec commercial

vehicle. Zebra batteries can lastfor a few thousand charge cyclesand are nontoxic. The downsidesto the Zebra battery include poorspecific power (<300 W/kg) andthe requirement of having to heatthe electrolyte to about 270 °C(518 °F), which wastes someenergy, presents difficulties inlong-term storage of charge, andis potentially a hazard.

Lithium-IonThe most used type of batterynowadays is the Lithium-Ionbattery. Lithium-ion (and themechanically similar lithiumpolymer) batteries, wereinitially developed andcommercialized for use in laptopsand consumer electronics. Withtheir high energy density andlong cycle life they have becomethe leading battery type for usein EVs. The first commercializedlithium-ion chemistry was alithium cobalt oxide cathode anda graphite anode firstdemonstrated by N. Godshall in1979, and by John Goodenough, andAkira Yoshino shortly thereafter.The downside of traditionallithium-ion batteries includessensitivity to temperature, low-temperature power performance,and performance degradation withage. Due to the volatility oforganic electrolytes, thepresence of highly oxidized metaloxides, and the thermalinstability of the

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anode SEI layer, traditionallithium-ion batteries pose afire safety risk ifpunctured or chargedimproperly. These earlycells did not accept orsupply charge when extremelycold, and so heaters can benecessary in some climatesto warm them. The maturityof this technology ismoderate. The Tesla Roadster(2008) and other carsproduced by the company useda modified form oftraditional lithium-ion"laptop battery" cells.

Recent EVs are using newvariations on lithium-ionchemistry that sacrificespecific energy and specificpower to provide fireresistance, environmentalfriendliness, rapid charging(as quickly as a fewminutes), and longerlifespans. These variants(phosphates, titanates,spinels) have been shown tohave a much longer lifetime,with A123 types usinglithium iron phosphatelasting at least more than10 years and more than 7000charge/discharge cycles, and

LG Chem expecting their lithium-manganese spinel batteries tolast up to 40 years.

Much work is being done onlithium-ion batteries in the lab.Lithium vanadium oxide hasalready made its way into theSubaru prototype G4e, doublingenergy density. Siliconnanowires, silicon nanoparticles,and tin nanoparticles promiseseveral times the energy densityin the anode, while composite andsuperlattice cathodes alsopromise significant densityimprovements.

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New data has shown thatexposure to heat and the useof fast charging promote thedegradation of Lithium-ionbatteries more than age andactual use, and that theaverage electric vehiclebattery will retain 90% of itsinitial capacity after 6 yearsand 6 months of service. Forexample, the battery in aNissan LEAF, will degradetwice as fast as the batteryin a Tesla, because the LEAFdoes not have an activecooling system for itsbattery.

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Reference: Bloomberg New Energy Finance (NEF) 2019 Battery Price Survey; OmegaInstitute for Research

Note: Industry-weighted average battery pack prices have already fallen to $156per kWh. This is over 13% lower than the 2018 average ($180/kWh, when adjustedfor inflation), and BNEF foresees cost reductions continuing, with $100/kWhpotentially being reached by 2023.

2019 BNEF Battery PriceSurvey（with Cell and Pack split）

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The above graph shows the cost ofbatteries over the years past. Itcan be seen that over the years,the prices have fallencontinuously for all batterytypes, except the Li-ionbatteries which had a spike in2013, followed by a downfall.This can be due to the rise anddemand and the price inelasticnature.

With being the latest to getintroduced in the market, Li-ionseems to be best in terms ofefficiency too. Li-ion has bettermiles to life ratio than thelead-acid battery. In 2016, theLi-Ion battery is estimated tolast over 10 years of batterylife, while being able to run forover 1,000,000 miles,outperforming all other batterytypes.

The Future of EVBWhile the Li-ion battery willcontinue to progress, it will besolid-state and lithium-silicontechnologies that will be thereal EVB game changer. Ongoingand significant improvements inbattery technology will pave theway for an installed EV base of100 million by 2028, according tothe global tech market advisoryfirm, ABI Research. Between 2023 and 2025,continually increasing silicon inbatteries to the point where

www.industryweek.com/technology-and-iiot/article/22028055/next-gen-batteries-to-powerup-electric-vehicle-installed-base-to-100-million-by-2028https://about.bnef.com/blog/battery-pack-prices-fall-as-market-ramps-up-with-market-average-at-156-kwh-in-2019/

developments will enablesilicon-dominant anodes.

Given the research takingplace in lithium-siliconbatteries and the increasingpercentage of silicon in EVbatteries, ABI Researchbelieves this is the nextlogical step. Silicon-dominantbatteries would likely enableenergy densities of up to 400Wh/kg by 2025. Most vehiclesusing this technology willlikely have to charge powersof 300 kilowatts.

Silicon dominant anodes willbe the primary solution until2026 – at the earliest - whensolid-state batteryarchitectures will start to bedeployed and reachcommercialization. Solid-statebatteries will enable energydensities of at least 500Wh/kg, offer 500 kW+ chargingpower.

References

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https://www.abiresearch.com/press/next-gen-batteries-will-power-electric-vehicle-installed-base-100-million-2028/https://link.springer.com/referenceworkentry/10.1007%2F978-1-4419-0851-3_663https://www.greencarcongress.com/solid-state/https://www.aftermarketnews.com/next-gen-batteries-will-power-up-electric-vehicle-installed-base-to-100m-by-2028/

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Battery Technology for EVs