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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
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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
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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
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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
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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
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VOC sensor commercialized www.elgato.com
Blue Tooth core module need to be
a Mfi licensee for development
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Metal Oxide Gas Sensors Sensitive to volatile organic compounds, CO and H2
chip size: 2 mm2
0.078in2
power: 30-40mW small hot spot
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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
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Air Classification Module Automotive sensor platform for gas detection
rugged design
IP67
withstands minor
explosions
2 sensors
- VOC/CO/H2
- NO2
PWM or UART
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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
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Tests performed Most test were destructive
nail penetration
overcharging
short circuit
charging cycles
temperature cycling
leakage
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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
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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
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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
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Nail penetration test Immediate and massive outgassing LiFePO4,10Ah
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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
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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
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Overcharging 5Ah LiCoO2 pouch cell in 12C overcharging experiment
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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
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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
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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
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Overcharging at 6C 5Ah pouch cell in 6C overcharging experiment
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
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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
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Overcharging at 12C 5Ah pouch cell in 12C overcharging experiment
gas sensor signal 40s ahead
of thermal runaway
cell caught fire
complete destruction of cell
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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
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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.
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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
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Thank you
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