AUTOMOTIVE BATTERIES 101 - Warwick

1 JULY 2018 WMG, University of WarwickProfessor David Greenwood, Advanced Propulsion SystemsAUTOMOTIVE BATTERIES 1012 2018 The battery is the defining component of an electrified vehicleRangePackageRide and HandlingLifePowerCost3 2018 Primary functions of the battery across vehicle typesENGINEMOTOR battery battery FUNCTIONCONVENTIONAL (ICE)100kW Full transientStarter motor Stop/start12V3kW, 1kWhEngine starting (3kW, 2-5Wh) Ancillary loads (400W average, 4kW peak, ~1kWh)MILD HYBRID (MHEV)90-100kW Full transient3-13kW Torque boost/re-gen12-48V 5-15kW, 1kWhAbsorb regenerated braking energyFULL HYBRID (HEV)60-80kWLess transient20-40kWLimited EV mode100-300V20-40kW, 2kWhSupport accelerationPLUG-IN HYBRID (PHEV)40-60kWLess transient40-60kW Stronger EV mode300-600V 40-60kW, 5-20kWhProvide primary power and energyRANGE-EXTENDED (REEV)30-50kWNo transient100kWFull EV mode300-600V100kW, 10-30kWhProvide primary power and energyELECTRIC VEHICLE (EV)

2 No Engine100kWFull EV mode300-600V100kW, 30-80kWhProvide sole power and energy sourceIncreasing power to energy ratio4 2018 Biggest challenge for mass market uptake is costCOMPONENT COSTS FOR ELECTRIFICATION OF POWERTRAIN Engine/Transmission battery Power Electronics Motor Charger E-ancillariesConventional MHEVHEVPHEVEV0200040006000 Bill-of-Materials Component Cost 80001000012000 battery COST IS THE SINGLE BIGGEST FACTOR5 2018 Lithium-ion BATTERIES are improving rapidly Costs have fallen dramatically due to technology, production volume and market dynamics Pack cost fallen from $1,000/kWh to <$250/kWh in less than 8 years Volumetric energy density is increasing due to better materials and cell structure Doubled in 15 years Requires continuous chemistry and materials innovation to continue01002003004005006007008009001,00 01,1001,2001,3001,4001,5001,6001,7001,80 01,9002,0002005201020152020 Year202520302014 US$ per kWh95% conf interval whole industry95% conf interval market leadersPublications, reports and journalsNews items with expert statementsLog fit of news, reports, and journals: 12 6% declineAdditional cost estimates without clear methodMarket leader, Nissan Motors, LeafMarket leader, Tesla Motors, Model SOther battery electric vehiclesLog fit of market leaders only: 8 8% declineLog fit of all estimates.

3 14 6% declineFuture costs estimated in publications<US$150 per kWh goal for commercializationLithium-ion BATTERIES are improving rapidly18650 CELL CAPACITY (MAH)40003000200010001995200020052010201 50 Graph credit: Nkyvist et al 20146 2018 What makes up an AUTOMOTIVE battery ?As a single unit, a cell performs the primary functions of a rechargeable battery . Cells come in varied formats: Cylindrical Cells Pouch Cells Prismatic CellsA module is formed by connecting multiple cells , providing them with a mechanical support structure and thermal interface and attaching terminals. Modules are designed according to cell format, target pack voltage and vehicle pack is formed by connecting multiple modules with sensors and a controller and then housing the unit in a case. Electric vehicles are equipped with BATTERIES in a pack state which are connected to the pouch or cylindrical module for pouch cells (Nissan Leaf) pack for pouch cells (Nissan Leaf)7 2018 How a Lithium-ion cell works Lithium-ion (Li-ion) is a general term for a variety of BATTERIES whose properties rely on lithium as the charge carrier.

4 Li-ion offers advantages over other chemistries such as weight and voltage. For AUTOMOTIVE purposes, rechargeable cells are used There are many types of Li-ion battery depending on the exact combination of materials used for the anode and cathode During charging, the positively charged lithium-ions flow from the cathode, through the electrolyte/separator, to the anode where they are stored. Electrons flow from the negative electrode to the positive through the outer circuit (the power supply). When no more lithium-ions will flow, the battery is fully charged During discharge, the lithium-ions flow back through the electrolyte/separator to the cathode. Electrons flow back to the anode through the outer circuit. When all ions have moved back, the battery is fully discharged and needs recharging A motor converts the electrical energy from the battery into mechanical energy to turn the wheels Electricity from the grid is used to charge the batteryAnode/cathode materials: specific capacities and operating voltages vs pure lithiumDifferent chemistries suit specific requirementsENERGY CarbonsMetal NitridesM vs Li(V)Specific Capacity (mAh/g) V x 141 Ah/kg = 512 Wh/kgNiO6 LiCathodeAnodeChargingLi+Li+Li+Li+e-e-e- e-ChargeAnode graphiteCathode LiCoO2 Discharge8 2018 Current lithium-ion battery chemistries.

5 CATHODE/ANODE MATERIALSTRENGTHSWEAKNESSESL ithium Cobalt Oxide(LCO) Cathode High energy High power Thermally unstable Relatively short life span Limited load capabilitiesLithium Manganese Oxide Spinel (LMO) Cathode High power and thermal stability Enhanced safety Low cost Low capacity compared to other cathode materials Limited life cycle Need advanced thermal managementLithium Nickel Cobalt Aluminium Oxide (NCA) Cathode High specific energy Good specific power Long life cycle Safety issues CostLithium Nickel Manganese Cobalt Oxide (NMC) Cathode Ni has high specific energy; Mn adds low internal resistance Can be tailored to offer high specific energy or power Nickel has low stability Manganese offers low specific energyLithium Iron Phosphate (LFP) Cathode Inherently safe.

6 Tolerant to abuse Acceptable thermal stability High current rating Long cycle life Lower energy density due to low operating voltage and capacityGraphite/Carbon-basedAnode Good mechanical stability Good conductivity and Li-ion transport Good gravimetric capacity Low volumetric capacityLithium Titanate (LTO) Anode Withstands fast charge/discharge rates Inherently safe Long cycle life Lower energy density compared to graphitic anodes CostSilicon Alloy (Si) Anode High gravimetric/volumetric capacity Low cost Chemical stability High degree of mechanical expansion on chargingCathodeAnode9 2018 Promising battery chemistries: early stage researchCHEMISTRY*PROPERTIES/BENEFITSRES EARCH CHALLENGESS olid State BATTERIES Solid electrolyte and separator components; no concerns over leakage Improved safety due to lack of liquid electrolyte High operating voltages increase potential energy density Lighter and more space efficient.

7 Less need for cooling Improving poor conductivity High volume manufacturing at acceptable costMetal Air Li, Al, Zn, Na Pure metal anode and ambient air/O2 cathode Very high theoretical capacity Increased safety vs Li-ion No use of heavy metals Short life cycle Issues with practical rechargeability Air handling Energy density reduces at high powerLithium Sulphur (Li-S) High theoretical gravimetric energy density Sulphur is a low cost, abundant material Improved safety Poor volumetric energy density Issues with power density and discharge rate Issues with cycle life stabilitySodium-ion (Na-ion) Sodium is a low cost, abundant material Improved safety for battery transportation Issues of volumetric/gravimetric energy density compared to Li-ionSilicon-based Electrodes (Si) Si has ~x10 gravimetric capacity compared to graphite Could be lighter and/or store more energy Does not offer long cycle life Practical application constraints* Promising chemistries included are those demonstrating suitable application potential for AUTOMOTIVE requirements at lab 2018 AUTOMOTIVE battery : cell componentsActive electrodes: Thinly wound or stacked into alternating sheets of material following a pattern: cathode separator anode.

8 quality and purity of material has an impact on charge efficiency and battery life. Cathode: Positively charged electrode in the battery cell, often made of a lithium metal oxide and coated on to a current collecting aluminium (Al) foil. Anode: Negatively charged electrode in the battery cell, often made of graphite and coated on to a current collecting copper (Cu) foil. Terminals: positive and negative contacts to connect the cells and module. Separator: Thin layer of polymer electrically isolates the cathode and anode from one another to prevent short circuit. Its structure allows lithium ions to pass through, allowing current to flow through the cell (microporosity) Electrolyte: A liquid transport medium which surrounds the electrodes and soaks into the separator, allowing lithium ions to flow freely Additives: Electrode and electrolyte properties can be improved by adding small amounts of other components, conductive additives Current Interrupt Device.

9 A pressure valve disables the cell in case of over-charge/over-heating+ve/-ve TerminalsCathodeSeparatorElectrolyteAnod eMetallised foil pouch+ve/-ve TerminalsCathodeSeparatorAnodeMetal caseElectrolyte11 2018 Cell assembly/electrical formationPowderCell stackingElectrode manufacturingCoatingCalenderingSlittingD ryingElectrolyte FillingMixingTab weldingFormation/ageingEoL TestingPackagingProduction steps for electrode/ cell manufacturing12 2018 Cell formats Highly developed Standard sizes Used widely in consumer goods (well standardised) Mechanically self-supporting High volumes and price competitive market Highest power and energy density at cell level Needs volume for commercialisation Relatively lightweight and easy to package for effective use of spaceCylindrical cellsPouch cellsPrismatic cellsChallenges: Relatively heavy Shape reduces packaging densityChallenges: Little standardisation of format (VDA) Requires supporting structure within a module Some cooling constraints Large format cells contain high energy (safety issues if damaged)Challenges.

10 Little standardisation of format (VDA) Can be expensive to manufacture Large format cells contain high energy (safety issues if damaged) Benefits lie part-way between cylindrical and pouch cells Layered approach improves space utilisation Allows highly flexible module design for differing requirementsImage credit: Panasonic13 2018 Cell supply chain: materials contentSeparator 2%Electrolyte 12%Cathode Material NCA 42%Separator 14%Electrolyte 9%Cathode Material NCA 53%Cathode Conductors 1%Cathode Binder 0%Cathode Binder 0%Cathode Conductors 0%Cathode Current Collector (Al) 4%Cathode Current Collector (Al) 1%Anode Material graphite 29%Anode Current Collector (Cu) 9%Anode Binders 1% Cathode Material NCA Cathode Conductors Cathode Current Collector (Al) Anode Material Graphite Anode Binders Anode Current Collector (Cu) Separator ElectrolyteTYPICAL MATERIAL VOLUME (CYLINDRICAL CELL)MATERIAL COMPONENT COST BREAKDOWN (CYLINDRICAL CELL)