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Distributed Battery Thermal Management Using ThermoelectricsAuthor(s): Todd Barnhart1, Madhav Karri1, Dmitri Kossakovski1, Alfred Piggott1, Kandler Smith2

Organization: Gentherm Inc.

1 , NREL2

Paper Number: 13TMSS-0006

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Overview

Concept Description

Proposed Packaging

Experiment Summary

Thermal Impact Simulations

Battery Life Calculations

Future Development Testing

BTMS Value

Summary

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Battery Thermal Management via Thermoelectrics

Approach: localized, individually controlled, distributed thermal management of individual cells via direct conductor cooling using thermoelectric devices

* Patent pending

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Thermal Gradients in Working Cells

Cell level thermal gradients:Simulated thermal gradient of discharging cell (Tata Motors, UK)S. Chacko, Y.M. Chung / Journal of Power Sources 213 (2012) 296-303

Pack level thermal gradients:Also: .. a 5 K difference across the pack would result in an approximate 25 % acceleration of the aging kinetics (JCI, EVS24 2009).

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Thermoelectrics Can Compensate for Thermal Gradients

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Advantages of Thermoelectrics

Provide low power active cooling solutions for start/stop or mild/micro-hybrid battery applications.

Air cooled TE solutions can provide a “stand-alone” active cooling system.• “Stand-alone” = No liquid or refrigerant loops required.

Potential enabler to allow under-hood packaging of Li-ion batteries.

Precision independent cell cooling, reducing pack gradient and improving life.

Light weight and compact packaging.

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30 Watt TE Cooling System

• 12 V Li-ion Battery for hybrid electrical system.

• 4 cells - per DIN SPEC 91252 dimensions for prismatic cells.

• 10 Watt TED’s integrated into bus bars.

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Thermoelectric Battery Thermal Management

• BTMS fully integrated with existing BMS (Battery Management System).

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Assembly details

Integrated Battery Management System (BMS) and Thermoelectric Management System (TMS)

Integrated TED and bus bar.

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Modeling of Benefits of Distributed Thermal Management – Gentherm/NREL

StudyApproach:

- Simulate a pack of 50 power cells- Use existing thermal network models- Apply TEDs either to all or selected cells- Use typical drive cycles- Analyze thermal conditions and predict life Lump thermal

network model, excludes 3D FEA of cells/pack

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Simulation Definition

Application: HEVBattery warranty: 10 years, 150k miles Cell: 5 Ah (power cell) Pack: 50 cells Driving:

US06 cycle (48A RMS current, 8.01 miles/cycle,48.4 mph average speed)

41.1 miles/day (150k miles, 10 years) 2 driving trips/day (20.5 min ea.), 8 am and 5 pm

Ambient temperature 28°C (e.g. Phoenix average) Chilled fluid @ 23°C (e.g. via secondary HVAC loop) Or, conditioned air from cabin

Heat transfer: •Cooled surface area: 0.0208 m2/cell •Air ~ 9 W/m2 K •Liquid ~ 85 W/m2 K

Thermal Management Objectives used in Simulation:

• Lumped cooling:  Maintain pack average temperature at 25oC

• Distributed cooling: Maintain individual cell temperatures at 25oC

Thermal Management Modes of Operation:

• Nominal cooling:  Key-on

• Standby cooling:  Key-off, drawing power from either HEV battery (50 Wh limit) or external source such as solar panel

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Lumped cooling: Cell-to-cell T difference

Temperature of cell

vs. cell location

Temperature of cell

vs. cell location

High ambient T

Low ambient T

DT across pack vs. Ambient temp

Distributed cooling is preferred over

lumped

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Battery Life vs. Control Strategy @ Various Cooling Power Levels

Notes: The results are specific to pack model, control algorithm and environmental conditions.

>10 yr life with TE-only (no chilled air or liquid) cooling becomes feasible with ~5 W/cell

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Future Development Testing

Modeling & Test Plan: Evaluate 2 TE based cooling

concepts. Evaluate 2 air cooled solutions for

baseline comparison. Testing to be conducted by NREL. Use simplified 48V micro-hybrid

cycle. Averages 3.5 – 5.0W of heat

generation per cell.

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Development Test Configuration

Electrode Tab TE Cooling

Power Cell

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Charge/Discharge Cycle

Simplified 48V Drive Cycle

Cell Based Cycle

Cycle generates 3.5 – 5.0 Watts of heat per cell, depending on cell temperature.

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Value of Thermal Management

The value equation for BTM systems is still TBD for small pack formats: Life targets are still being established; 4, 6, 8 or

10years?

Replacement cost vs. customer expectations

Life targets will set thresholds for peak operating temperatures.

The BMS will limit battery function to avoid exceeding peak operating temperatures.

BTM systems value will be in enabling wider operating ranges, which allows OEM’s more output (FEI) and life from their battery. TE based BTMS is first being targeted for applications requiring

“Stand-alone” solutions requiring 50-200W of cooling.

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Summary

TE cooling may be well aligned with start/stop or micro-hybrid battery applications. Affordable & flexibility of design options.

TE’s provide light weight, solid-state, scalable & “Stand alone” cooling systems.

Optimized BTM systems add value by allowing OEMs to drive batteries harder and still meeting life targets. (Delivers more FEI)