Batteries for Small VehiclesPhilosophy, Design and Development

Prabhjot Kaur, PhD

CEO, Centre for Battery Engineering and Electrical Vehicles (C-BEEV)

IIT Maras

Batteries dominate the cost of an EV

• Larger the battery, more the cost• Bigger batteries impact energy efficiency

• Smaller battery will create range anxiety

• We are generally thrilled with longer RangeBut, who can afford?

• Batteries can be swapped when they run out

September 1, 2018 2

Dilemma

Category Percentage

Buses and Trucks 3%

Economy Cars 12%

Premium Cars 2%

2 Wheelers 79%

3 Wheelers 4%

We clearly need affordable vehicles

Batteries have to be small, LAST LONGER

Small Batteries: Swap in addition to Charge

• Answer : Separate vehicle business & energy business

• Energy Operator to procure bulk batteries and lease charged batteries

• For business viability, design• Lowest cost battery

• Long Life with temperature Compensation / control

• Charge at 0.5 C and at 25deg C, discharge at ambient (Indian temperatures)

• Safety against Theft

September 1, 2018 3

ReliabilityInvestment

“Fear of Dead Investment”

DemandRight balance of stock

Ownership of batteries

Swapping Concerns

Designing Batteries

September 1, 2018 4

Right Cells

BMS

Thermal Mgmt

Mech.Design

Accurate SOC / SOH

Protection

Charge, Discharge

Control

✓ Chemistry✓ Lifecycles✓ charge/dis rates✓ power, range✓ operating conditions

✓ Stability: vibration, shock / impacts, drops

✓ Determination / Managementalgorithms, Cell balancing,Optimization

✓ Over Current✓ Over/Under Voltage✓ Over/Under Temperature✓ Short-Circuit✓ Reverse battery/charger

Connection✓ Pre-Charge

✓ Cooling requirement of pack

✓ Optimal charging✓ limiting the discharge✓ Life cycle control and tradeoffs

To Handle Indian Temperatures (45 – 55 degrees)

September 1, 2018 5

Battery Thermal Management Various Methods Modes

Active

Air LiquidRefriger

antHybrid

Passive

PCMMicro

Channel

Technically and Commercially ViableApt for Swappable Batteries

Unaffordable and too complex for a small battery

What did we Do?

• Mix of Internal and External Cooling• Phase Change material (PCM) internally for limited hours duration

• Cool before operation (start at 25 deg C)

• Discharge at ambient temperature – make sure that internal battery is retained at 35deg C mostly during four-five hours operation (PCM + battery starts at 25)

• Refrigerant based Cooling while Charging• Thermal Plates for heat exchange while charging batteries at 0.5C

• Ensure that charging is done at below 25 deg C

September 1, 2018 6

So Batteries Have

September 1, 2018 7

Featured Packed BMSWell Engineered

Battery Pack

Certifications compliance

Safety and Protection:

AIS-048 and UN-38.3 IEC62133

Heading towards Functional Safety

compliance

ISO 26262

Safety against theft

Locked Smart Batteries (LS Batteries)

• Can not be charged except through authorised Chargers

• Can not feed power except to authorised vehicle• Encrypted Key exchange between Charger / vehicle

and LS-batt

• Relay turns on only after authentication (each LS-batt has unique ID)

8September 1, 2018

Relay

MonitorBatteries while charging

while In-useto maximise life,

performance and value

September 1, 2018 9

Accurate battery health calculation and easier sorting

of batteries

Battery sends multiple data points during

operation

Regular monitoring of

each parameter

LS VBCC Protocol Suite(Locked Smart- Vehicle Battery Charger Cloud)

September 1, 2018 10

Demo

UI

UIDB

Swapping & Charging Station

EV Driver

EV

Some Early Trials and Learnings

September 1, 2018 11

5 OEMsLohia, Goenka, Kinetic,

Electrotherm, Mahindra

3 Battery ManufacturersAmaraja, Exide, Exicom

EO: Essel

Bulk Charger: Exicom

Software and Management PlatformsEsmito

Vehicles on DrivePilot of LS Battery swapping at IITM Campus

Test vehicle with school kids, residents and staff in IITM campus

September 1, 2018 12

Battery pack energy, voltage and current during driving

Discharging current

Gradually decreasing voltage during drive

Gradually decreasing energy during drive

13September 1, 2018

Individual Cell Voltage and Temperature while charging

Gradual increase

of voltage while

charging

Gradual increase of

temperature while

charging

14September 1, 2018

Cell voltage and temperature monitoring during driving

Gradual decrease

of cell voltages

while driving

Gradual increase of

cell temperatures while driving

15September 1, 2018

Performance Comparison

September 1, 2018 16

S.No Make and Model Wh/Km

Distance

travelled

(Kms)

1 Make 1, Model A 44 36

3 Make 1, Model C 38 27

4 Make 2, Model A 42 43

5 Make 2, Model B 37 51

6 Make 3 39 46

7 Make 4 58 31

8 Make 5 41 46

Sample Dated: 14th June, 2018

S.NoVehicle Make Total Rides Avg. Wh/Km

1 Make 1/C 164 40.36

2 Make 2 331 44.15

3 Make 3 324 44.28

4 Make 4 419 46.29

5 Make 5 82 52.18

All 1320 45.45

Cumulative of 4 Months

Driving – All Cell temperatures for all sessions (34 Million data points)

17

Incorrect range – To be analyzed. 11,815 points above 100 deg.C

September 1, 2018

Charging – All Cell temperatures for all sessions (~ 6 Million data points)

18

Normal operating range –25 to 50 deg.C

Wrong values - to be analyzedSeptember 1, 2018

How is this data helpful?

September 1, 2018 19

• All use cases: Driving (Discharge and driving pattern) and charging impact batteries

• Battery Performance evaluation and optimization• Redesigning • Cycles assurance• Redo Mechanical Design, Redo Thermal: all required corrections • Better cut offs and control

• Aiding in Driving Patterns• Reduced / Increased discharge rates (current drawn)• Warnings and alarms • Go back to drawing board (learnings from problematic batteries)

• Business cases