At the 2012 IEEE Symposium on Product Compliance Engineering (IEEE PSES) on Nov. 5th 2012 in Portland, Oregon, TÜV SÜD America's Erik J Spek, presented on "Lithium Ion Abuse Test Methods Improvement."

1. Lithium Ion Abuse Test Methods
Lithium Ion Abuse Test Methods
Improvement
Erik J Spek,
Dr. Mehdi Hosseinifar, TÜV SÜD
Portland
5 – 7 November 2012
Oregon
http://www.psessymposium.org/
1

2. Abuse Testing of Lithium Ion Cells
• Summary y
• Introduction Abuse Testing
• Role of Standards
Role of Standards
• Standardization of Test Methods
• Response to Abuse Tests
Response to Abuse Tests
• Survey of TÜV SÜD Nail Penetration Tests since 2009
2

3. Summary
y
The increasing use of high energy, high power lithium ion batteries for electric
and hybrid vehicles has progressed to the point of commercial introduction
introduction.
Nevertheless, these cells are yet to show strong resistance to thermal,
mechanical and electrical abuse.
Despite the availability of test recommended procedures and standards for
characterizing the cell response to abuse stimuli, b
h ii h ll b i li better engineered and
i d d
robust test methods need to be developed within the context of these
standards.
Attempts to improve the nail penetration abuse test procedure are described
p p p p
in this presentation.
The effects of various parameters on the hazard response level of Li‐ion cells
have been evaluated.
It is concluded that Li ion technologies are generally becoming less sensitive
Li‐ion
to abuse conditions.
3

4. Introduction‐1
• Expectation: survivability in accidents and benign response
under abuse conditions.
• Standards help support the expectation that electrified vehicles
are subject to at least the same expectations.
• Standards for ICE based vehicles developed over 100 years
– are effective in ensuring vehicles are robust & hazards are managed
– occupants can survive accident scenarios that are survivable.
• These standards have been augmented to account for the
electrification component that comes with elevated voltage and
significant amounts of stored electrical energy.
• New risks in these electrified vehicles need to be considered in
the design and development
• The task of writing and then proving out these standards
– slow and laborious process with stakeholders coming together,
putting aside individual interests
putting aside individual interests
– publish a tool that is effective but flexible enough to consider
different technologies
4

5. Introduction‐2
• Standards documents for batteries and other vehicle
electrification components.
electrification components
• Issues to improve standards robustness, consistency and
universality.
• American National Standards Institute (ANSI) through the Electric
Vehicles Standards Panel (EVSP) has identified gaps
( )
• Standards only effective if test methods satisfy intent consistently.
• Some of the first organizations to encounter this issue while
implementing new test methods are third party test agencies.
p g p y g
– build or acquire the specialized equipment
– develop the skills and methods that minimize test risk, and develop
consistent and effective testing.
– test method shortcomings and opportunities for improvement are
g pp p
discovered
• Issues TÜV SÜD has resolved to make nail penetration abuse
testing effective.
• Large format cells of many descriptions analyzed for the effects of
Large format cells of many descriptions analyzed for the effects of
parameters on the reaction to abuse test conditions.
5

6. Abuse Testing of Lithium‐Ion Cells
g
Role of TÜV SÜD
• Third party, ISO 17025 certified, global testing company.
Third party, ISO 17025 certified, global testing company.
• Abuse tests establish reaction of cells, modules or complete batteries to
conditions exceeding those expected to be encountered in normal use.
• Data used by battery manufacturers and OEMs for design decision making
• Lithium‐ion energy storage devices need to prove compliance,
– little operational track record over many years of service, under abuse
conditions.
• TÜV SÜD, is privy to an overview of cell technology trends that cell, battery
and OEM organizations may not see due to their focused efforts.
• Individual companies are often immersed in one technology family
Individual companies are often immersed in one technology family.
• Would be loath to change direction based only on reports of more progress
with competing technologies.
• Reports from independent testing agencies from a general point of view.
– the technology is improving
the technology is improving,
– boost overall confidence for the electric vehicle market and customers.
6

7. Available Standards & Practices‐1
• Many tests covering electrical, mechanical and thermal/environmental abuse that are used to gauge
product robustness.
• Mechanical abuse tests cover mechanisms as nail penetration, crush, drop, impact or shock and vibration.
Mechanical abuse tests cover mechanisms as nail penetration, crush, drop, impact or shock and vibration.
• Simulate the actual use and abuse conditions that may be beyond the normal safe operating limits [2].
• Nail penetration is typically the most reactive of all the mechanical abuse tests
• Frequently used to assess cell robustness with short test turnaround time.
• Three principle nail penetration test standards:
Three principle nail penetration test standards:
– United States Advanced Battery Consortium (USABC),
– Society of Automotive Engineers (SAE),
– Automotive Industry Standard of the People’s Republic of China.
• Most commonly requested nail penetration tests for automotive batteries:
os co o y eques ed a pe e a o es s o au o o e ba e es
– SAE J2464 section 4.3.3 [3] and FreedomCAR through SAND 2005‐3123 section 3.2 [2].
• Nail penetration testing is also described in QC/T 743‐2006, Lithium‐ion Batteries for Electric Vehicles,
Automotive Industry Standard of the People’s Republic of China [4].
• The Japan Storage Battery Association (JSBA) has a Guideline for Safety Evaluation on Secondary Lithium
Cells [5].
– primarily for small size portable electrical appliances which use cells smaller than 5 Ah.
– In contrast, most cells for automotive PHEV and EV applications are greater than 5 Ah and reach as high as 75 Ah.
– Nail diameter in JSBA is specified as between 2.5 to 5 mm with no nail material nor nail speed specified.
– In contrast, both SAE J2464 section 4.3.3 and SAND 2005‐3123 section 3.2 specify one nail diameter and mild steel
I t t b th SAE J2464 ti 4 3 3 d SAND 2005 3123 ti 3 2 if il di t d ild t l
with nail speed greater than 8 cm/s for single cells.
7

8. Available Standards & Practices‐2
• SAE and SAND tests do not present pass and fail criteria,
• SBA requires that no explosion and no fire result from the test.
q p
• QC/T 743‐2006 section 6.2.12.7 provides for two nail diameters of 10 and 40 mm and no nail speed
but it also requires no explosion and no fire.
• Test specifications are open to interpretation in methodology due to:
– the short history of lithium ion battery development,
– large ampere‐hour and pouch prismatic cells
large ampere‐hour and pouch prismatic cells
• Test methods were standardized at TUV SUD driven by significant uncontrolled variations
• Since 2009, TÜV SÜD, has pursued a path of continuous test methodology improvement for the cell
penetration testing.
• Accredited TÜV SÜD test procedure used to test hundreds of large format lithium ion cells.
• Scope does not begin to cover all cells from all manufacturers ‐ it is a snapshot of a population of
nail penetration tests conducted at TÜV SÜD.
• This work is different from what is typically found in literature [6‐15] in that it covers commercial
large format cells rather than experimental low capacity cells.
• The equipment and safe practices used have been developed specifically and exclusively for these
q p p p p y y
tests.
• A large number of tests are carried out on a variety of cells as opposed to a few tests.
8

9. Drive to Standardize
• Failed cell or battery tests in 3rd party testing ‐> subsequent ripple effect.
– Ripple effect for phone call or email that implies that ‘The product failed the
test so the test method must be wrong’ or ‘another test organization did the
h h d b ’ ‘ h dd h
same test and the product passed there so you must be wrong’.
– Resolution consumes significant resources to explain test results
– Most test organizations work hard to ensure test equipment, methods and
facilities are robust and consistent.
– The benefit is that proving competence when called upon is easily and
The benefit is that proving competence when called upon is easily and
confidently carried out.
• The SAE/FreedomCAR cell penetration test was selected as an ideal early
candidate for this kind of improvement effort.
• TÜV SÜD performs tests to customer requirements.
• The tests conducted have been selected by the customer as being
The tests conducted have been selected by the customer as being
application relevant.
• When standard tests are not deemed application relevant, TÜV SÜD
works with customers to develop tests that are suited to the
requirements.
• It is not the role of TÜV SÜD to pass judgment on cell or battery designs.
I i h l f TÜV SÜD j d ll b d i
9

10. Table 1: EUCAR Hazard Severity Levels (HSL)
TABLE I
EUCAR HAZARD SEVERITY LEVELS (HSL)
HAZARD SEVERITY
DESCRIPTION CLASSIFICATION CRITERIA AND EFFECT
LEVEL
0 No Effect No effect. No loss of functionality
No damage or hazard; reversible loss of function. Replacement or re-
1 Passive Protection Activated setting of protection device is sufficient to restore normal
functionality
No hazard but damage to RESS*; irreversible loss of function.
2 g
Defect/Damage
Replacement or repair needed.
R l t i d d
Evidence of cell leakage or venting with RESS weight loss < 50% of
3 Minor Leakage/Venting
electrolyte weight.
Evidence of cell leakage or venting with RESS weight loss > 50% of
4 Major Leakage/Venting
electrolyte weight.
Loss of mechanical integrity of the RESS container, resulting in
5 Rupture release of contents. The kinetic energy of released material is not
contents
sufficient to cause physical damage external to the RESS.
Ignition and sustained combustion of flammable gas or liquid
6 Fire or Flame
(approximately more than one second). Sparks are not flames.
Very fast release of energy sufficient to cause pressure waves and/or
projectiles that may cause considerable structural and/or bodily
7 Explosion
p damage, depending on the size of the RESS. The kinetic energy of
g , p g gy
flying debris from the RESS may be sufficient to cause damage as
well.
10

11. Testing Response ‐ 1
g p
• Cells that are abused may react in a number of ways from
no reaction to total and violent destruction.
no reaction to total and violent destruction
• Both Sandia National Labs [2] and SAE J2464 [3] use the
EUCAR Hazard Severity Levels [16] to describe to what
extent a cell can react to a specific abuse.
extent a cell can react to a specific abuse
• Table I depicts the Hazard Severity Levels as in SAE J2464.
Levels 5 and 6 are reversed in the Sandia table.
• A cell undergoing a level 7 reaction is more than a designer
A cell undergoing a level 7 reaction is more than a designer
would want to cope with in any battery pack.
• Most OEM and battery companies look for level 2 as a
worst case response with level 3 as acceptable in some
worst case response with level 3 as acceptable in some
circumstances.
• There is no ‘pass’ or ‘fail’ criteria yet for this test.
11

12. Testing Response ‐ 2
g p
• The risk of personal injury
with this level of testing is
ith thi l l f t ti i
high and is therefore
conducted in purpose‐
designed chambers.
designed chambers
• 3 chambers used at TÜV SÜD
in Newmarket, Ontario,
Canada for cell abuse testing.
C d f ll b t ti
• Pressure vessel style for single
cell tests up to hazard severity
level (HSL) 7.
• ISO Style chambers used in
Auburn Hills, MI for pack tests
, p
12

13. Testing Response ‐ 3
g p
• one of 3 concrete
bunkers at TÜV
b k TÜV
SÜD in Garching,
Germany designed
to withstand HSL
ih d
up to 7 for up to
full packs.
• fully equipped
with gas cleaning,
p p
multiple pressure
relief features and
blast proof
p
viewports.
13

14. Test Methodology‐Development History
gy p y
Table 2: SAE J2464 Cell Penetration Test Variables
Parameter
P t Measured value
M d l Value
V l
Nail material mild steel
diameter 3 mm (no tolerance)
Point taper
Point taper No values for length, included
No values for length included
angle or surface finish
Surface finish No value specified
Straightness No value specified
orientation Perpendicular to electrodes
Penetration Rate ≥8 cm/s
depth Through cell
Constraints Preload None specified
Supporting scheme None specified
Electrical Resistance of path from DUT to ground
Resistance of path from DUT to ground None specified
None specified
14

15. Test Methodology‐Development History
gy p y
• For both cylindrical and prismatic cells.
• However, most have been soft prismatic (pouch) cells for
nail penetration.
nail penetration
• First TÜV SÜD test device was an air driven pneumatic
cylinder (see Figure 3) set at 100 cm/sec.
• High value for speed used to ensure that the minimum
nail velocity occurring during the ‘through the thickness’
il l i i d i h ‘h h h hi k ’
penetra on of cells as thick as 12 mm would be ˃
specified 8 cm/sec.
• This value pales in comparison to the 2,780 cm/sec that a
nail might be launched at when a vehicle travelling at 100
km/h impacts a nail.
• It is not the purpose of this presentation to comment on the relevancy of this test velocity but
it is helpful to consider that a single cell, similar to a vehicle occupant, is not expected to be
it is helpful to consider that a single cell, similar to a vehicle occupant, is not expected to be
subjected to a projectile hurled at that velocity.
• Battery and vehicle as a system designed to protect an individual cell from this event.
• May be achieved by crumple zones, energy absorbing layers or shielding materials or as part of
the vehicle.
15

16. Test Methodology‐Development History
gy p y
• Since pneumatic cylinder force was considered substantial at 1.7 kN, there was little
concern for a slowing down of the nail through the cell thickness to ˂8 cm/sec.
• An initial group of cells were tested in this manner but results could not be
An initial group of cells were tested in this manner but results could not be
correlated to the cell suppliers’ similar penetration test data.
• Parameters in Table 2 were compared: between the TUV SUD values and cell
supplier’s values.
• The comparison showed that, like the SAE Recommended Practice, most of the
Th i h d h lik h SAE R d dP i f h
parameters including the actual nail penetration speed were not measured at the
cell supplier.
• Several such as nail diameter and material were not in line with the SAE
requirements.:
– Specifically, nail diameter was 5 mm where SAE J2464 specified 3mm
– Material was stainless steel where SAE J2464 specified mild steel.
• To establish a starting point for those parameters lacking values, a review of the
To establish a starting point for those parameters lacking values a review of the
tests conducted to date that for those with HSL response values of <5
16

17. Test Methodology‐Development History
gy p y
• Note that the HSL <5 was chosen since the test population size was small
with high HSL variability.
• The starting values listed in Table 3 were assigned.
Th t ti l li t d i T bl 3 i d
• With these starting values adopted, more cells were tested of selected
anode and cathode chemistries, % state of charge (SOC) and capacities.
• Mild steel nails had a high incidence of buckling in thicker cells. This was
Mild steel nails had a high incidence of buckling in thicker cells This was
resolved by using high carbon steel nails made from commercial drill rod.
The resistivity of the high carbon steel is similar to the specified mild steel.
17

18. Test Methodology‐Development History
gy p y
Table 3: TUV SUD Values for SAE J2464 Cell Penetration Test Variables
Parameter
P t Measured value
M d l Value
V l
Nail material Tool steel (C1090)
diameter 3 mm (no tolerance)
Point taper
Point taper 28o included angle
included angle
Surface finish Ra<1.6
Straightness Within 0.5mm within 100mm length
orientation Perpendicular to test bed within
Perpendicular to test bed within
0.5mm
Penetration Rate ≥8 cm/s, ˂8.5 c/s measured in free
space
depth
d th Through cell
Th h ll
Constraints Preload Customer selected
Supporting scheme None specified
Electrical Resistance of path from DUT to Nail electrically isolated from DUT
ground
18

19. Test Methodology‐Development History
gy p y
• Pneumatic nail driving system was capable for thin pouch type cells,
but questionable for thicker cells
• Pneumatic system replaced with a hydraulically driven system
• Capable of delivering 45 kN with more precise and accurate control
of velocity, acceleration and depth of penetration.
• This set of measurements was then used on a further set of cells to
determine if the HSL was the same for pneumatic and hydraulic
p y
systems.
• Discrepancies were found under otherwise apparently identical
parameters.
• Key differences in methodologies studied
• In spite of all these test improvement efforts, the hydraulic system
In spite of all these test improvement efforts the hydraulic system
HSLs were markedly different from that of the pneumatic system.
• Further analysis was carried out to verify the velocities of the air
system and the hydraulic system using independent test methods.
• High force of the hydraulic system was sufficient to overcome the
resistance of cells in up to 1 cm of cell thickness without loss of
resistance of cells in up to 1 cm of cell thickness without loss of
velocity while pneumatic slowed down by up to 3cm/sec
• Hydraulic system is the most robust and consistent for nail
penetration tests on pouch cells.
19

20. Penetration Test to Date
• A total of over 250 cells have been subjected to the TUV SUD standard cell
p
penetration test to date.
• This paper examines the results of the tests as conducted.
• In recognition of the proprietary nature of some of the data, no information about
cell manufacturer, specific size or electrochemistry is referenced.
• The sample cells in these tests had the following attributes:
The sample cells in these tests had the following attributes:
– Soft and hard pouch prismatic
– Cylindrical
– Nameplate capacity from 8 Ah to 60 Ah
– %SOC from 60 to 100
%SOC from 60 to 100
– Undisclosed cathode, anode, separator and electrolyte formulations
• The test method and equipment include:
– Both pneumatic (earlier method) and hydraulic
– Standard nail configuration (material, diameter, point angle & finish, alignment)
g ( , ,p g , g )
– Standard apparatus to support the DUT
– Both restrained and unrestrained cell fixturing
– 10,000 liter abuse chamber
– Multi channel data acquisition system for DUT parameters (voltage, temperatures, internal
pressure) and abuse apparatus parameters such as nail velocity.
) d b t t h il l it
20

21. Penetration Test to Date
• The data from all of these tests have been analyzed to search for trends and influencing factors on
HSL.
• Reporting of HSL in each test is not an exact takeoff of the 0‐7 rating EUCAR system.
– For example, the range 0‐2 is used to report any HSL in that range.
• In order to distinguish between the individual values in the range, a post abuse test functional test
would be required and this rarely requested. Objectively, the reasoning may be that whether a cell
is a 0, 1 or 2 HSL has little influence on the criteria for the pack engineer regarding safety when
, p g g g y
compared to HSL > 3.
• Similarly, the range 3‐5 represents any of the three individual HSLs in that range.
– Since 3 and 4 are a function of the electrolyte weight loss and electrolyte weight is seldom disclosed,
distinguishing between them is not definitively possible.
– Similarly HSL 5 calls for rupture which can be argued to have happened for both 3 and 4.
y p g pp
– HSLs 6 and 7 also present judgment quandaries since explosions have occurred with no flames and large
vapor clouds have ignited and burned out in fractions of a second.
• Independent spark source was not used in any of these tests.
• All tests in this population were conducted at room temperature.
• It is known from other TUV SUD abuse tests conducted at 55oC that HSLs can be significantly higher
It is known from other TUV SUD abuse tests conducted at 55 C, that HSLs can be significantly higher
than at room temperature. Accordingly, running these tests at the recommended maximum cell
operating temperature may be instructive.
21

22. Results
• As a first indicator of confidence in the test method and cell quality,
data was sorted to search for the time dependent trend in HSL.
data was sorted to search for the time dependent trend in HSL
• Acceptable HSL was selected as HSL≤3.
• Rationale for HSL≤3 => a largely favorable result while HSL>3
indicates more cell development work required if cell behavior at
indicates more cell development work required if cell behavior at
HSL>3 cannot be managed by pack design or pack management.
• Note HSL≤3 is a convenient decision level but does not take into
account that HSL=3 may in fact in some tests be an actual HSL=4
due to the possible interpretation latitude of the test result.
• The penetration tests database makes possible analysis for more
questions such as: i) what effect does %SOC have on HSL, ii) what
effect does restraining the sample have versus unrestrained, iii) is
effect does restraining the sample have versus unrestrained iii) is
there a difference between pneumatic and hydraulic methods, and
iv) how does nail velocity affect HSL.
22

23. Fig 5: HSL Trend over Time
g
• population of 182
p p 100
penetration test cells 90
selected for HSL less than 80
% of samples showing HSL ≤ 3
30-40 Ah,
or equal to 3. 70 restrained,
std test spec.
60
• Except for the last data
Except for the last data
50
point, trend of HSL for
40 HSL ≤ 3
HSL< 3 is favorable 30
direction over last 12 20
%
quarters. 10
• This trend is encouraging 0
10-1
10-2
10-3
10-4
11-1
11-2
11-3
11-4
12-1
12-2
and supports the Year‐Quarter
improvements made in the
improvements made in the
test method.
23

24. Fig 6a: Effect of SOC on HSL _ restrained
g _
• %SOC at a selected cell
range of 30‐40 Ah on HSL
for restrained cells for a
population of 173
samples.
samples.
• At 100% SOC in this cell
capacity range, from this
data, it is more likely that
the cell, when penetrated
h ll h d
will have a >3 HSL
reaction than HSL<3. This
likelihood declines as SOC
declines and for this
population, all cells at
70% SOC had an HSL<3.
24

25. Fig 6b: Effect of SOC on HSL _ unrestrained
g _
• SOC on HSL for 44
unrestrained cells over
unrestrained cells over
range of 8‐60 Ah.
• For SOC of 100%, the
likelihood of HSL>3 is
almost the same as for
the larger population
in figure 6a while an
SOC of 60% had all 8
SOC of 60% had all 8
samples react with an
HSL<3.
• Note 8 samples from a
population of 2 mfgrs,
4 Ah capacities and
similar chemistries.
25

26. Fig 7: Effect of Nail Speed on HSL
g p
• population of 258 samples.
• 30‐40 Ah in the restrained
state and at >80% SOC.
• All samples tested at 100
cm/s had an HSL >3.
• Two thirds of the samples
Two thirds of the samples
tested at 8 cm/s had an HSL
<3.
• All the samples at 5.5 cm/s
had an HSL ≤ 3
• However, the small lot of 4
samples tested at the very
slow 1.1 cm/s showed
slow 1 1 cm/s showed
unexpected behavior in
that the lot had HSL>3.
26

27. Conclusion
• The shortcomings of the standardized nail penetration abuse test are addressed
and a robust procedure has been developed.
p p
• This method is utilized for abuse testing of hundreds of Li‐ion cells and the
following results are obtained:
– In general, cells are exhibiting a trend of increasing robustness to abuse as measured by HSL
values over the last two and one half years in the TÜV SÜD population of nail penetration
tests.
– Cells tested at lower SOCs of 60‐70% in this population are strongly showing HSLs < 3.
– Nail velocity at 100 cm/s shows a strong tendency to produce HSLs > 3.
• As a guideline for battery pack design it can be concluded that until cells are robust
enough to withstand high velocity projectiles, packs need to be designed to
enough to withstand high velocity projectiles packs need to be designed to
protect the cells from these events.
• From the population in these tests, there appears to be an opportunity for risk
reduction in the area of penetration abuse at high SOCs (90‐100%).
• As a third party, ISO 17025 testing agency, TÜV SÜD is committed to help develop
As a third party ISO 17025 testing agency TÜV SÜD is committed to help develop
robust and reliable testing processes for the advanced battery industry.
27

28. Acknowledgement
g
• The Authors would like to thank the personnel of
p
TÜV SÜD Canada, Newmarket, ON, for their role in
conducting the tests.
• The invaluable comments of Mr. Malcolm Shemmans
are also greatly appreciated.
• The work was supported in part by the Natural
Sciences and Engineering Research Council of Canada
(NSERC)
28

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