detektion kritischer batteriezustände und erhöhung der

© ams AG 2015

Detektion kritischer Batteriezustände

und Erhöhung der Betriebssicherheit

durch Gassensoren

Detection of failure modes and

protection solutions for Li-Ion energy

packs by means of gas sensors

Dr. Martin Herold

Presented by: Bryan Snider

2015 NASA Aerospace Battery Workshop

© ams AG 2015

ams´ Smart Battery Mgmt. 2 main fields of activity today

Smart Battery Mgmt. system solutions

1. Current and Voltage Measurement. 2. Cell Supervision Circuit (CSC).

Cell Monitoring

and Cell Balancing

for 7 Cells. Only 1

discharge Resistor

for Passive or 1

transformer for

Active Balancing

simultaneous capture of

current and voltage in

(shunt based) battery

sensor applications

AS8801

© ams AG 2015

Existing techniques for detecting unsafe conditions Most BMS’s today only monitors and reacts to electronic signals and temperature

• Voltage

• Cells- AS8506 for autonomously equalizing voltages & monitoring temperature “CSC” (Active or Passive)

• Pack – AS8510 for charge/discharge control

• Current (mA – kA)

• AS8510 +/- 0.5% accuracy for coulomb counting and power & Impedance calculation measures both V&I simultaneously

• Temperature

• Monitoring ambient, cells, pack, & shunt

• Redundant Measurement points

• Multiple communication paths to report faults

• Improves safety

Confidential © ams AG 2015

AS8510 + AS8506 + AS8801 Tool

48V BMS reference design

• High side current sense on copper shunt

• 14 cell monitoring and balancing

• Solid state high side battery disconnect

• AS8801 precision attenuator

• AS8524 high side current sense companion IC for up to

70V nominal supply as a test chip

© ams AG 2015

Motivation for using a gas sensor Added safety for small costs

gas sensors are used for monitoring

of battery charging stations

yet not used with Li-batteries

new application offers new market

venting detection

leakage detection

added safety for minor costs

small design can fit into existing packs

easy interfacing with BMS

Detects: Alcohols, aldehydes, ketones,

organic amines, and aliphatic &

aromatic hydrocarbons

PolyGUard EX-Sensor

MSR ElectronicGmbH

thermal runaway

© ams AG 2015

VOC sensor commercialized www.elgato.com

Blue Tooth core module need to be

a Mfi licensee for development

http://www.elgato.com/

© ams AG 2015

Metal Oxide Gas Sensors Sensitive to volatile organic compounds, CO and H2

chip size: 2 mm2

0.078in2

power: 30-40mW small hot spot

© ams AG 2015

Operation principle Resistance will change with exposure to gases

metal oxide

CO2

H2O

VOCs

heated membrane

MEMS substrate

electrodes

DG

O2- O2- O2- O2-

0 5 10 155

10

15

20

25ethanol, 10ppm

time [min]

G [µ

S]

air, 50% r.h.

combustion of volatile organic compounds at metal

oxide surface

change of resistance of heated oxide layer

reversible process

sensor reacts to all combustible gases

© ams AG 2015

Air Classification Module Automotive sensor platform for gas detection

rugged design

IP67

withstands minor

explosions

2 sensors

- VOC/CO/H2

- NO2

PWM or UART

© ams AG 2015

Battery Pack Battery management system with gas sensor

• 15 Cells (LiFePO4) at 40Ah

• < 60V technology

• gas sensor for emergency shutdown

• portable demonstrator pack

• includes new BMS µC

• active balancing

• no destructive tests with

battery pack performed

gas sensor

© ams AG 2015

Tests performed Most test were destructive

nail penetration

overcharging

short circuit

charging cycles

temperature cycling

leakage

© ams AG 2015

5 10 15

500

1000

1500

2000

2500

time [min]

Sig

nal [a

.u.]

Battery charging Small signals during battery cycling experiments

0 24 48 72 96

10

15

20

25

30

35

40

0

500

1000

1500

2000

Time [h]

T [

°C]

VO

C [

au]

2 ppm

1.5 ppm

• max. signal equal to 1-2ppm of H2

• LOD < 1 ppm

• data measured in lab air

• temperature variations < 10c

• small periodic signals

• source of VOC or H2 unknown

© ams AG 2015

Sensitivity to hydrogen

0 10 20 30 40 50 60

0

2,000

4,000

6,000

8,000

10,000

12,000

14,000

16,000

time [min]

Sig

na

l [a

.u.]

5000

5500

6000

0 5 10 15 20 25 30 35 40

0

2,000

4,000

6,000

8,000

10,000

12,000

14,000

H2 [ppm]

Sig

nal [a

.u.]

• non-linear calibration curve

• alarm level equals 30ppm H2

• data measured in lab air

• very high sensitivity to hydrogen

• good repeatability

• small sensor to sensor variation

© ams AG 2015

Abuse tests Results from abuse tests at beginning of the ESTRELIA project

cell

actuator

gas sensors

nail

Setup not optimal

• dead volume of chamber

• position of sensors

Tests performed

• nail penetration

• overcharging

• short circuit

• charging cycles

Cells tested

• LiFePO4,10Ah

• LiMnO2, 20Ah

• LiCoO2, 5Ah

© ams AG 2015

Nail penetration test Immediate and massive outgassing LiFePO4,10Ah

© ams AG 2015

Nail penetration test Puncture of a LiFePO4 pouch cell

punctured cell emits

smoke and catches fire

after 15s

position of gas sensors

too far away

air flow inside box keeps

smoke and fumes away

from sensor

0 50 100 150 200 250 300 350 400 450 500

0

20

40

60

80

100

1300

1400

1500

1600

0.0

20.0k

40.0k

60.0k

80.0k

0

1

2

3

4

time [s]

Tcell [°

C]

H2 [m

V]

VO

C [au]

Ucell [V

]

cell voltage

VOC

hydrogen

cell temp.

cell punctured

© ams AG 2015

Nail penetration test Multiple punctures into a LiMnO2 pouch cell

LiMnO2 pouch cell

0 200 400 600 800 1000 1200 1400 1600

15

20

25

1400

1500

1600

0.0

20.0k

40.0k

60.0k

3.0

3.5

4.0

time [s]

Tcell [°

C]

H2 [m

V]

VO

C [au]

Ucell [V

]

cell voltage

VOC

hydrogen

cell temp.

cell punctured 4 times

temp. stays low

sensors repositioned

closer to cell

nail punctured cell

several times without

any effect

4th puncture led to

venting and gas detection

fast sensor recovery

caused by ventilation of

measurement chamber

© ams AG 2015

Overcharging 5Ah LiCoO2 pouch cell in 12C overcharging experiment

© ams AG 2015

Overcharging 5Ah LiCoO2 pouch cell in 12C overcharging experiment

200 250 300 350 400 450 500 550 600 650 700

0

20

40

60

80

100

1400

1500

1600

0

10k

20k

30k

40k

05

1015202530

time [s]

Tce

ll [°C

]

H2 [m

V]

VO

C [a

u]

Uce

ll [V]

cell voltage

VOC

hydrogen

cell temp. 310⁰C max

42 sec.

suggested signal for shutdown

© ams AG 2015

Abuse test setup Setup at Fraunhofer IISB

Test setup:

NMC Li-Ion cell

max. 12C overcharge

manual shutdown after gas

detection

measurement of:

• gas (VOC/CO/H2)

• cell voltage

• cell temperature

• gas pressure

camera documentation

if necessary, the whole setup

can be immersed in water

© ams AG 2015

Overcharging at 1C 5Ah pouch cell in 1C overcharging experiment

noisy signal caused by wind

fast sensor response at venting

high gas sensor signal at low

cell temperature

• no thermal runaway

• cell did not catch fire

© ams AG 2015


0.0

2.0x104

4.0x104

6.0x104

8.0x104

0.0

5.0x104

1.0x105

1.5x105

2.0x105

0

200

400

600

800

300 400 500 600 700 800

0

2

4

6

8

10

VO

C [

pp

m]

Se

nso

r O

ut

99.2057.70

Te

mp

ert

ure

[°C

]

601.5

7.06

498.1

5.16

Vo

lta

ge

[V

]

Time [s]

noisy signal caused by wind

fast sensor response at venting

gas sensor signal at low

cell temperature

• gas sensor signal 100s

prior to thermal runaway

• cell exploded

© ams AG 2015

Overcharging at 12C 5Ah pouch cell in 12C overcharging experiment with manual shutdown

gas sensor signal 3s ahead

of voltage drop

very short flash at cell venting

© ams AG 2015

Hardware Evolution Size optimization and power reduction

iAQ-core (2013)

3.3VDC

67mW

I2C

BEM-100 (2011)

12VDC

550mW

PWM

iAQ-engine (2011)

5VDC

240mW

I2C, 0-5V

56mm

2.2in

17mm

0.67in

© ams AG 2015

Summary Extra level of safety

gas sensors are capable of increasing safety in large lithium-ion battery systems

costs are relatively small

gas venting from a cell under abuse is detected

electrolyte leaks are easily detected

user can be warned and an emergency shutdown performed to prevent further damage

gas sensors might detect a rise in VOC concentration even before a bloated cell fully opens

automated shutdown may prevent cell venting

the absolute value of the sensor resistance is not always indicative and change in the resistance value should be taken into account.

Not calibrated signal. Measures delta; changes in resistance.

© ams AG 2015

Acknowledgement

The research leading to these results has received funding from the European

Union as part of the Seventh Framework Program under grant agreement

n° 285739 (“ESTRELIA - Energy Storage with lowered cost and improved Safety

and Reliability for electrical vehicles”).

M.M. Wenger, V.R.H. Lorentz, R. Waller, M. März

Fraunhofer IISB

Department of Power Electronics

Erlangen

detektion kritischer batteriezustände und erhöhung der

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