JULY 2018

WMG, University of WarwickProfessor David Greenwood, Advanced Propulsion Systems

AUTOMOTIVE BATTERIES 101

2© 2018

The battery is the defining component of an electrified vehicle

Range

Package

Ride and Handling

Life

PowerCost

3© 2018

Primary functions of the battery across vehicle types

ENGINE MOTOR ‘BATTERY’ BATTERY FUNCTION

CONVENTIONAL (ICE)

100kW Full transient

Starter motor Stop/start

12V3kW, 1kWh

Engine starting (3kW, 2-5Wh) Ancillary loads (400W average, 4kW peak, ~1kWh)

MILD HYBRID (MHEV)

90-100kW Full transient

3-13kW Torque boost/re-gen

12-48V 5-15kW, 1kWh

Absorb regenerated braking energy

FULL HYBRID (HEV)

60-80kWLess transient

20-40kWLimited EV mode

100-300V20-40kW, 2kWh

Support acceleration

PLUG-IN HYBRID (PHEV)

40-60kWLess transient

40-60kW Stronger EV mode

300-600V 40-60kW, 5-20kWh

Provide primary power and energy

RANGE-EXTENDED (REEV)

30-50kWNo transient

100kWFull EV mode

300-600V100kW, 10-30kWh

Provide primary power and energy

ELECTRIC VEHICLE (EV)

No Engine 100kWFull EV mode

300-600V100kW, 30-80kWh

Provide sole power and energy source

Incr

easin

g po

wer

to e

nerg

y ra

tio

4© 2018

Biggest challenge for mass market uptake is cost

COMPONENT COSTS FOR ELECTRIFICATION OF POWERTRAIN

Engine/Transmission Battery Power Electronics Motor Charger E-ancillaries

Conventional

MHEV

HEV

PHEV

EV

0 2000 4000 6000

Bill-of-Materials Component Cost €

8000 10000 12000

BATTERY COST IS THE SINGLE BIGGEST FACTOR

5© 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 continue

0

100

200

300

400

500

600

700

800

900

1,000

1,100

1,200

1,300

1,400

1,500

1,600

1,700

1,800

1,900

2,000

2005 2010 2015 2020

Year

2025 2030

20

14 U

S$ p

er

kWh

95% conf interval whole industry

95% conf interval market leaders

Publications, reports and journals

News items with expert statements

Log fit of news, reports, and journals: 12 ± 6% decline

Additional cost estimates without clear method

Market leader, Nissan Motors, Leaf

Market leader, Tesla Motors, Model S

Other battery electric vehicles

Log fit of market leaders only: 8 ± 8% decline

Log fit of all estimates: 14 ± 6% decline

Future costs estimated in publications

<US$150 per kWh goal for commercialization

Lithium-ion batteries are improving rapidly

18650 CELL CAPACITY (MAH)

4000

3000

2000

1000

1995 2000 2005 2010 20150

Graph credit: Nkyvist et al 2014

6© 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 Cells

A ‘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 requirements.

A ‘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 powertrain.

Lithium-ion cell Module Pack

e.g. pouch or cylindrical cell e.g. module for pouch cells (Nissan Leaf) e.g. 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. 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 battery

Anode/cathode materials: specific capacities and operating voltages vs pure lithiumDifferent chemistries suit specific requirements

ENERGY DENSITYCathode

Anode

LiMn1.5Ni0.5O4

LiMn1/3Co1/3Ni1/3O2LiMn2O4

LiNiO2LiCoO2

LiFePO4

Li2FeS2

TiO2-B

LTO

Graphite

Hard CarbonsMetal Nitrides

M alloysSilicon Lithium

00 200 400 600 3500 4200

1

1.52

2.53

3.5

44.5

5

Volta

ge v

s Li(V

)

Specific Capacity (mAh/g)

3.7V

3.2V

2.8V

3.5V

2.0V

3.8V

141 mAh/g

3.7 V x 141 Ah/kg = 512 Wh/kg

NiO6

Li

Cathode

AnodeCharging

Li+

Li+

Li+

Li+

e-

e-

e-

e-

Charge

Anode Materiale.g. graphite

Cathode Materiale.g. LiCoO2

Discharge

8© 2018

Current lithium-ion battery chemistries: CATHODE/ANODE MATERIAL STRENGTHS WEAKNESSES

Lithium Cobalt Oxide(LCO) Cathode

• High energy• High power

• Thermally unstable• Relatively short life span• Limited load capabilities

Lithium 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 management

Lithium Nickel Cobalt Aluminium Oxide (NCA) Cathode

• High specific energy• Good specific power• Long life cycle

• Safety issues• Cost

Lithium 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 energy

Lithium Iron Phosphate (LFP) Cathode

• Inherently safe; tolerant to abuse• Acceptable thermal stability• High current rating• Long cycle life

• Lower energy density due to low operating voltage and capacity

Graphite/Carbon-basedAnode

• Good mechanical stability• Good conductivity and Li-ion transport• Good gravimetric capacity

• Low volumetric capacity

Lithium Titanate (LTO) Anode

• Withstands fast charge/discharge rates• Inherently safe• Long cycle life

• Lower energy density compared to graphitic anodes

• Cost

Silicon Alloy (Si) Anode

• High gravimetric/volumetric capacity• Low cost• Chemical stability

• High degree of mechanical expansion on charging

Cath

ode

Anod

e

9© 2018

Promising battery chemistries: early stage research

CHEMISTRY* PROPERTIES/BENEFITS RESEARCH CHALLENGES

Solid 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; less need for cooling

• Improving poor conductivity• High volume manufacturing at

acceptable cost

Metal Air Batteriese.g. 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 power

Lithium 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 stability

Sodium-ion (Na-ion)

• Sodium is a low cost, abundant material• Improved safety for battery transportation

• Issues of volumetric/gravimetric energy density compared to Li-ion

Silicon-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 scale.

10© 2018

Automotive battery: cell components

Active electrodes: Thinly wound or stacked into alternating sheets of material following a pattern: cathode – separator – anode.

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, e.g. conductive additives

• Current Interrupt Device: A pressure valve disables the cell in case of over-charge/over-heating

+ve/-ve Terminals

CathodeSeparator

Electrolyte

Anode

Metallised foil pouch

+ve/-ve Terminals

CathodeSeparatorAnode

Metal case

Electrolyte

11© 2018

Cell assembly/electrical formation

Powder

Cell stacking

Electrode manufacturing

Coating Calendering SlittingDrying

Electrolyte Filling

Mixing

Tab welding Formation/ageing EoL TestingPackaging

Production steps for electrode/ cell manufacturing

12© 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 space

Cylindrical cells Pouch cells Prismatic cells

Challenges: • Relatively heavy• Shape reduces packaging

density

Challenges: • 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: • 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 requirements

Image credit: Panasonic

13© 2018

Cell supply chain: materials content

Separator 2%

Electrolyte 12%Cathode Material e.g. NCA 42%

Separator 14%

Electrolyte 9%

Cathode Material e.g. 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

e.g. graphite 29%

Anode Current Collector (Cu) 9%

Anode Binders 1%

Cathode Material e.g. NCA Cathode Conductors

Cathode Current Collector (Al) Anode Material e.g. Graphite

Anode Binders Anode Current Collector (Cu)

Separator Electrolyte

TYPICAL MATERIAL VOLUME (CYLINDRICAL CELL) MATERIAL COMPONENT COST BREAKDOWN (CYLINDRICAL CELL)

Anode Material e.g. graphite 29%

Anode Binders 1%

Breakdown by relative weight and cost of cell materials shows the value is spread across components, not just from the primary electrochemical materials.

Figures source: ITRI, Taiwan

Anode Current Collector (Cu) 5%

14© 2018

Cell supply chain: materials sourcing

Image credit: Institut francais des relations internationales (ifri)

15© 2018

Automotive battery: module components

Casing: Metal casing provides mechanical support to the cells and holds them under slight compression for best performance

Clamping frame: Steel clamping frames secure the modules to the battery case

Temperature sensors: Sensors in the modules monitor the cell temperatures to allow the battery management system to control cooling and power delivery within safe limits

Cells: Each module in a pack contains the same number of cells. The number of cells varies by format and usage requirements

Terminals: Two terminals on the module allow it to be electrically connected to other modules via the bus bars

Cell interconnects: Each cell has two tabs – one positive and one negative. These are welded together in series then connected to the terminals

Cooling channels: Liquid coolant runs between rows of cells to withdraw heat and avoid thermal runaway. Other packs, such as Nissan Leaf, instead use air cooling

1

2

3

4

5

6

7

34 56

Image credit:Nissan UK

Pouch cell module (Nissan Leaf)

Cylindrical cell module (Tesla)

1 26

5

3 4 6 71

16© 2018

Module assembly - manufacturing process

• Assembling the cells into a carrier• Joining the conductors in

architecture (typically welded)

• Installing the module control unit with voltage and temperature sensors

• Inserting cooling system components if required

• Testing the system functionality

Lower cost achieved through increased automation.

Module BoL Test

Cell Insertion

Module Welder

Welding Verification

Contact Welder

Welding Verification

Module EoLTest

Storage

ModuleDelivery

Storage

HandlingAssembly

Test

CellDelivery

MODULE ASSEMBLY LINE

Primary tasks:

17© 2018

Upper case: Provides fire protection and watertight casing for the battery components and protects it from dirt ingress. Also shields service personnel from high voltage components

Battery modules: A ‘module’ is formed by connecting multiple ‘cells’, supporting those cells in a structural frame and then attaching terminals. Modules are designed according to cell format and vehicle requirements

Bus bars: Electrically connect the battery modules together, and connect the modules to the contactors

Contactors: Electrically isolate the battery pack from the vehicle. Closed upon completion of safety tests and opened in the event of a crash or battery fault

Fusing: Fuses protect expensive components from damage due to power surges and faults

Disconnect: Used to electrically isolate the battery from the vehicle during servicing or maintenance

Cooling: Modules require cooling. Packs may be cooled using air, water or vehicle air conditioning system

Battery management system (BMS): The BMS ensures the cells remain within their safe operating temperatures and voltages. It measures the remaining charge in the battery and reports on state of health. It also ensures the battery is correctly connected and isolated before closing the contactors

Lower case: Structural casing supports the mass of the battery pack and protects it from damage

Automotive battery: pack components

8

9

Image credits: Nissan UK

1

2

3

4

5

6

7

569 8 7

1

2

3 4

18© 2018

Battery management system (BMS) Cells need to be monitored and controlled, e.g. temperature, voltage. The BMS is an electronic system that manages cells in a battery pack.

• The BMS monitors and controls:

- State of charge (SOC) - State of health (SOH) - State of function (SOF) - Safety and critical safeguards - Load balancing/individual

cell efficiency

• Advances in BMS can provide improved cell usage and efficiency and reduce the amount of battery content required

• Requires highly skilled electronics and software engineering talent

Balance cells

Estimate state of health

(SOH)Compute

power limitsEstimate state

of charge (SOC)

Meas. voltagecurrent

temperature

Loop each measurement interval while pack is active

key on: initialize

key off: store data

Interface Module

BMM Core Module BMM Core Module

Battery Pack

BMM Core Module

CAN

CAN

CAN

8 Cell Stack

Cell

Cell

Cell

Cell

Cell

Cell

Cell

Cell

8 Cell Stack

Cell

Cell

Cell

Cell

Cell

Cell

Cell

Cell

8 Cell Stack

Cell

Cell

Cell

Cell

Cell

Cell

Cell

BATTERY MANAGEMENT SYSTEM

CAN CurrentSensor

BatteryCharger

VehicleController

TractionInverter

CAN

CAN

Cell

19© 2018

Electrical Distribution System (EDS)The primary function of the EDS is to provide the electrical conduction path through the battery pack.

It also:• Isolates the conduction path

• Measures current and voltage in the high voltage (HV) line

• Provides pre-charge function when energising HV line

• Fuses the HV line in case of over-current

• Provides manual disconnect of the HV line for vehicle servicing

• Monitors effectiveness of the electrical insulation

• The Low Voltage (LV) wiring also provides power for the battery control functions and allows communication between the battery and vehicle (CAN protocol). The LV wiring also carries a signal (HVIL) to confirm all external connectors are correctly in place and to ensure that HV conductors can not be contacted externally

• The BMS receives inputs from voltage and temperature sensors in the modules. In some packs, the BMS may also provide outputs to drive other components such as fans, pumps or valves for the battery cooling system

• External connectors enable robust and safe connection between the battery pack and other vehicle systems. These are typically split into HV and LV connectors and potentially other auxiliary connectors (to chargers or HV accessories)

MCB

MCB

MCB

Manual Service Disconnect

MCB

MCB

MCB

Current sensor

Main Fuse

Pre-CH Fuse

Pre-CH registor

HV -VE

HV +VE

+VE Contactor

+VE sensor

LVConnector

HVConnector

Pre-CHARGE Contactor

Battery Management

System(BMS)

20© 2018

Battery pack assembly - manufacturing process

• Assembling the modules into the pack

• Joining the modules in pack architecture

• Connecting and testing power electronics

• Inserting cooling system components if required

• Testing pack quality and system functionality

Lower cost achieved through increased automation.

Module Delivery

Battery Shipping

ModuleBoL Test

EoL AcceptanceTesting

ModuleAcceptance

CoolingSystem Test

Lower CasePre-assembly

Case Pressure Test

ModuleInsertion

Bus bar Assembly

Electrical Integrity Test

Cooling SystemAssembly

BMS/EDS Connection

Top CoverAssembly

PACK ASSEMBLY LINE

HandlingAssembly

Test

Primary tasks:

21© 2018

OEM DEVELOPMENTCYCLE

PRODUCT VALIDATION

INDUSTRIAL PLANTDEVELOPMENT

3 Years

MATERIALSCALE UP

2 Years

PROOF OF CONCEPT RESEARCH

Min. 3 Years decades

Typical R&D timeline for potential chemistries/technologiesNew chemistries at proof of concept stage in the lab will take typically 10 years to emerge as market products.

MATERIALDEVELOPMENT

? ? ?

• Investigating new chemistries

• Understanding properties and characterisation

• Chemical lab-based/university -led activity

• No limit to potential timescale for breakthrough to occur

• Developing promising materials at gram scale

• Testing and analysing properties for application

• Lab-based/university-led activity

• Timescale dependent upon chemistry maturity

• Scale up of promising materials from lab to commercially viable cell

• Testing and analysis of impact of scale up on chemistry

• Validation of manufacturing processes

• University and/or industry led activity

• Proving out at-volume cell manufacturing application

• Supply chain validation of R&D

• Optimisation of industrial scale manufacturing

• Industry and university led activity

• Validation of R&D at the cell stage

• At-volume testing of cells to industrial standards

• OEM validation of required quality, reliability and safety levels

• Industry-led activity/OEM

• OEM ready to bring technology into 3-year development cycle

• OEM led activity

1-1.5 Years 2-3 Years

22© 2018

Where should batteries be in 20 years?

23© 2018

The UK Battery Industrialisation Centre (UKBIC)

UKBIC is part of the UK Government’s Faraday Battery Challenge.

The establishment of this new facility is being led by Coventry City Council, Coventry and Warwickshire Local Enterprise Partnership, and WMG, at the University of Warwick. The consortium were awarded £80 million, through a competition led by the Advanced Propulsion Centre and supported by Innovate UK.

UKBIC will be an open access facility, opening early 2020 in the Coventry/Warwickshire area.

The UK Battery Industrialisation Centre will:• Be a ‘Learning factory’ for high speed,

high quality manufacturing of cells, modules and packs at GWh/year scale

• Enable users to develop and prove manufacturing processes, and train staff

• Be capable of bespoke cell development /prototype/low volume manufacture

Powdersin

Electrodemixing D

ryin

g Cylinder cell assembly

Pouch cell assembly

Pack assembly Module assembly

Formation

Cell EoL testing

Module BoLtesting

Anode coating lines

Cathode coating lines

ModulesoutModules in

ElectrodesinElectrodes

out

Cellsout

Cellsin

Packsout

UK BIC: SCHEMATIC VISION

EdinburghGlasgow

Newcastle

LiverpoolManchester

Nottingham

Leamington Spa

London

Cardiff

Coventry

Birmingham

Dublin

Belfast

APC Electric Energy Storage Spoke WMG, International Manufacturing Centre, University of Warwick, Coventry, CV4 7AL www.wmg.warwick.ac.uk

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