cost and performance penalty of mitigation measures · aluminum foam aluminum air gap with central...

Dr. Bernhard Brunnsteiner, Dr. Wenzel Prochazka

AVL List GmbH (Headquarters)

Confidential

Cost and performance

penalty of mitigation

measuresSession 5 – Thermal Propagation Workshop @JRC

Dr. Bernhard Brunnsteiner, Dr. Wenzel Prochazka | Global Battery Competence Team | 09 März 2018 | 2Confidential

• Introduction

• Mitigation measures for different cell types

• Performance Penalties?

• Comparison on energy density (efficiency) of various measures

• Cost?

• Are safe cells available?

• Summary

Content


Serviceability

Production Capability

Efficiency

Performance

Driver Experience

Cost

EngineeringRequirements

Safety

8 attributes of traction batteries as key factor for success.


Chevrolet BOLT Mitsubishi Outlander PHEVTesla Model X

Mitigation measures for different cell types

2,3mm

PC isolation 0,3mm

Cooling pipe1mm

Compressionpad 2,1 mm

Cartridge cover0,5 mm

Picture source: SAE Matthe 2016


Venting Strategies compared

Chevrolet BOLT Mitsubishi Outlander PHEVTesla Model X

Front sideLeft side

4 pressure equalization & ventingmembranes

Venting plugs assembly

3 pressure equalization & venting membranes Nitto Denko

15 fluorosilicone venting plugs


Safety CRITERIA RATING Cell Level – EUCAR Hazard Levels

Parameter TESLA Model X BOLTMitsubishi

OUTLANDER PHEV

Overcharge 1CEUCAR Hazard Level

2 3 6

Nail (GB/T)EUCAR Hazard Level

6 3 4

Max Temp. @ Nail 767 °C 56 °C 369 °C

Thermal stabilityEUCAR Hazard Level

4 4 4

Thermal stabilitycell temperature @event

130°C 120°C 145°C

Short circuitEUCAR Hazard Level

3 3 3

Overcharge protection is easily handled on pack level

G/NCA vulnerable to damage

--- 1--- 1--- 1


Safety Parameters: Venting strategy and fire protection measures

Parameter TESLA Model X Chevrolet BOLTMitsubishi

OUTLANDER PHEV

Distances cell to cell0.3 mm isolation

1 mm cooling pipe2.1 mm foam

0.5 mm Aluminum2.3 mm air

Materials between cells

PC (Polycarbonat)Aluminum

FoamAluminum

Air gap with centralfoam pad

Containment measures between modules

MICA plates - -

Cross section venting elements

15 times 530 mm² 4 times 289 mm² 3 times 72 mm²

Battery cover materialSheet metal

(DX51D)PP GP3156F PP GF40

Battery to vehicle isolation

Insulating Blanket 9,3mm

Air gap Air gap

Widely varying venting cross sections


What is a performance penalty for cell integration into module or pack?

▪ Increased cost (€/kWh)

▪ Loss of energy density (Wh/L)

▪ Increased weight (Wh/kg)

▪ Increase in assembly complexity (€/kWh)

▪ durability/reliability

▪ Lifetime

▪ Field failures

▪ …

Performance Penalty?

Joining of cooling

elements

BMS Unit

Tab cooling on opposite ended tabs

Cell frames, one form only, forces pouches in

position


▪ Insulation foils between cells

▪ For prismatic & pouch the foils are also used to position and glue the cells together

▪ In cylindrical modules weaved in foils are possible usually collides with cooling

interface

Cell2Cell conductionceramic insulators

adhesive isolation layer

EXAMPLE: AVL MODULE FOR PRISMATIC CELLS

Penalty:▪ Cost▪ Assembly complexity


▪ Intumescent foils between cells

▪ For prismatic & pouch the foils are also used to position and glue the cells together

Cell2Cell conductionintumescent material

cells

intumescentmaterial

compressionpads

housing

Pouch cells movePrismatic cells material expands into

surrounding

Penalty:▪ Cost▪ Weight▪ Assembly complexity▪ Reliabiltiy


▪ Fire insulation foils and channel over directed vents

▪ For pouch the venting is not directed / no so energy dense not needed

Directed venting conductionprotective measures

Penalty:▪ Energy Density▪ Assembly complexity▪ Cost!!


Safety Critical Cell BehaviorInternal short circuit & thermal runaway simulation

Simulation of internal short circuits with electrochemical and electro-thermal battery model

• Implemented FIRE (AVL software)release 2016

Necessary input

• Cell abuse tests

• Cell deformation simulation in crash/crush case

SOC @ 500sec. Temp @ 500sec.

Simulating internal short circuits in AVL FIRE

Test Simulation


Safety Critical Cell BehaviorDirected venting conduction pack level simulation

Optimized venting flow

guidance

No venting flow guidance

Cell in thermal runaway and venting

Additional heat input to the cell above by venting leads to fast temperature rise

animation

Neighboring cells are heated via radiation & venting gas input

Design strategy:Guiding and separating of the venting flow to distribute the heat source of all cells

Cell in thermal runaway

Neighboring cells

Optimized venting gas flow distribution by design controlled guiding allows avoiding of propagation

Propagation safe


Cost of introduced measures

Cell 2 cell insulation:

▪ Ceramic material

~10% of module cost excl. cells

▪ Intumescent material

~15% of module cost excl. cells


Cost Summary on module level in benchmark vehicle Tesla Model X

Additional cost on battery housing=15% of housing frame cost


Just a recap of yesterdays presentations:

▪ LFP might be safer or not?

▪ Fire good or not?

▪ Directed venting preferable or not? In Sim yes in reality no? ☺

My experience:

▪ Cells with more than EUCAR Hazard Level 4 in GB/T 31487-2015 are not used in automotive

▪ Cells with higher hazard levels are sold by cell manufactures to small scale applications!

▪ Triggering external induced thermal runaway in real application is very different for prismatic, cylindrical and pouch!

Safe Cells? – many influences!


C

Comparison: conventional Lithium-Ion Cell vs. All-Solid-State Cell

All-solid-state cell with conventional C/Si anode

Liquid electrolyte in porous electrodes replaced by solid (orange cycles)

Electrolyte soaked separator is completelyreplaced by solid (orange cycles)

Possible increase in volumetric energy density by using silicon anodes

No significant change in energy density

No flammable liquids, reduced ageing

Conventional Li-ion cell

Liquid electrolyte in pores of electrodes and separator

porous anode (graphite grey circles)

porous cathode (metal oxide, e.g. NMC violet circles)

separator

2023?

Good for

BEV!

No base material

for thermal runaway

PHEV?


▪ Current automotive packs have a host of mitigation measures included

▪ Mitigation measure development needs to be done in view of cell & module & pack & application!

▪ Defining measures on cell level, module level or pack level – independent of each other may lead to high cost, but maybe not to an increase in safety (weakest link principle!)

▪ Future cells (solid state) might decrease the risks

reduced risk BEV

but small PHEV stay in need of low resistance cells with liquid electrolyte for the time horizon foreseeable

Summary

www.avl.com

Thank You

cost and performance penalty of mitigation measures · aluminum foam aluminum air gap with central...

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