INFORMATIONAL PAPER – presented at Informal Working Group Meeting, Washington, DC,
September 30, 2014.
Testing of large format lithium batteries and battery assemblies
Transmitted by the experts in the United States
Background
1. The UN Working Group (WG) meeting hosted by PRBA on Large Format Lithium Batteries held
on October 2 through October 5, 2013 in Washington, DC and the 2nd UN WG meeting on Large
Format Lithium Batteries held on February 11 through February 12, 2014 in Brussels, Belgium
have recognized the need to examine the UN Manual of Tests and Criteria as it relates to the
testing of large format lithium batteries.
2. The WG noted the four areas of regulations for large format batteries which are expected to
continue through the biennium. These are 1. Testing requirements applicable large format
lithium batteries; 2. Need to review the definitions of large batteries; 3. Harmonize other
existing tests recognizing test equivalents; and 4. Develop proposals for regulatory text for
inclusion in Section 38.3 of the Manual, if needed.
3. The WG recognized the need to revisit the existing difference of definitions between small and
large lithium batteries.
4. The UN presently defined large format batteries in excess of 12 kg in weight which was noted to
have a nominal energy in terms of Watt-hours for lithium ion batteries and grams of lithium
metal for lithium metal batteries.
5. The WG also recognized that the g force requirement in the shock test (T.4) could be related to
the mass and the energy in the system and that and a need for sliding scale in this respect exists
after reviewing several papers submitted by COSTHA.
6. The WG at the 2nd UN WG meeting suggested reviewing the conditions of the shock, including
whether a half-sine wave was appropriate and was questioning the start of 12 kg to be a large
format battery.
7. The WG at the 2nd UN WG meeting indicated that the UN38.3 tests were designed to determine
what happens when a battery is exposed to abuse conditions.
8. The WG noted an option of investigating a relationship between mass and acceleration as a
follow up to the PRBA’s comment that the 50 gn acceleration is very large compared to other
standards.
9. The WG indicated that they felt the tests are not designed to reproduce exactly conditions
encountered in transport but to ensure that the cells and batteries are safe to transport.
Introduction
10. The UN test requirement for Test T.4 (Shock) test for large cells and large batteries is that these
cells and batteries shall be subjected to a half-sine shock of peak acceleration of 50 gn and pulse
duration of 11 milliseconds for a total of 18 shocks with three repetitive shocks and at different
shock directions.
11. A battery assembly with a lithium content of 500 grams in the case of lithium metal batteries
and with a Watt-hour rating of more than 6,200 Wh in the case of a lithium ion battery does not
need to be tested if it is equipped with a system capable of monitoring the battery assembly
during transport and preventing short circuits, or over discharge between the batteries in the
assembly and any overheat or overcharge of the battery assembly.
12. The purpose of this paper to examine whether or not the current requirement of peak
acceleration of 50 gn and pulse duration of 11 milliseconds represents reasonable dynamic
acceleration conditions experienced during normal transportation and handling scenarios.
Review of Published Information on Shock Test
13. Large format batteries during transportation (road, rail, air and sea) experience a variety of
dynamic forces. These forces can be divided into two categories. The first category covers
shocks and vibration due to such conditions as those encountered on the road surface
imperfections and load bouncing, switching operations, take-off and landing, and transitory
motions from waves slamming the ship’s hulls, during road, rail, air, and sea transportation
respectively. The second category includes relatively infrequent, non-repetitive shock
encountered in handling. These forces provide velocity and acceleration to batteries which may
contribute to structural fatigue, mechanical wear of battery components, and eventual failures
of cells and batteries.
14. There are several published information proposing criteria and methods for meeting shock test
performance standards tailored to application needs on large format batteries. The UN
proposals, ST/SG/AC.10/C.3/2010/72 and ST/SG/AC.10/C.3/2012/94, presented a review of
criteria and standards considered similar to the T.4 test. This information and additional
information collected are presented in a tabular form:
REFERENCE
UN38.3 T.4
SAE J2464
RTCA DO160F
Airborne
Equipment
USAF ASDTR-76-30
December
1977 FAA
14CFR
25.561
Pulse
Number of
Acceleration Duration
Shocks
Pulse Form
gn
milliseconds
50
11
18 Half sine
25
15
18 Half sine
20
9
11
6 Saw tooth
Crash data
ISO/DIS
12405-1
Annex 8 to
Regulation
No. 100, 02
Series of
amendments 17-28
UL2580
UL 2271
50
10
25
80
15
>12≤100 kg
>100 kg
Axle Mounted
Single step
18
11
15
20
IEC61373
Class A & B
Body Mounted
Bogie
Mounted
6
Half sine
50
25
10
≤ 12 kg
6
18
3.1-5.1
30
30.6
102
18
6
15. The above tabulation indicates that the standards provided in each application vary However,
no data supporting the standards was provided and no information as to how the standards
were derived was provided.
16. The Naval Surface Warfare Center (NSWC) under contract to the PHMSA collected additional
published data on batteries experiencing a variety of dynamic forces similar to shock forces
during transportation:
Shock Scenario
Typical wooden
packages
impacting a
wood load
platform during
carriage over
rough roads
Landing-fixed
wing propeller
aircraft
Rail-Switching
operations
Pulse
Acceleration Duration
gn milliseconds
40
Not provided
2
Not provided
15
Not provided
Number of
Shocks
Pulse Form
Not
Provided
Not
provided
Not
provided
Not
provided
Not
provided
Not
provided
MIL-STD-810G,
Method 516.6
Drop
heights
range from
18"-48"
depending
on weight.
The number
of drops
ranges from
5 to 26
depending
on weight.
Not
provided
17. The dynamic forces during transportation shown above were provided in terms of acceleration
without the pulse duration. The military standards (MIL-STD-810G) were given in terms of the
drop heights and the number of drops for testing depending on weight categories. Based on
experiments conducted by the NSWC, it was estimated that the 24 inch drop on a 2 inch thick
plywood backed by concrete could provide a peak acceleration of about 358 gn with pulse
duration of in the range of 0.95 milliseconds with an equivalent energy dropped from the same
height on a 1” thick foam with a gn force of 77 and a pulse duration of 11 milliseconds. The gn
force and the pulse duration are dependent upon the type of surface on which a battery is
dropped, the weight of the battery, and the height from which the battery is dropped.
Experimental Research Results
18. The UN Manual prescribes a peak acceleration of 50 gn and pulse duration of 11 milliseconds
determined from a half sine force application. The pulse duration is determined at 10 % of the
peak acceleration. A total of 18 shocks are required in different directions.
19. In response to concerns over performing the shock test on large format lithium batteries and in
view of several proposals that were reviewed by the UN experts to modify the exiting
acceleration requirements in the UN T.4 shock test, the NSWC under contract with the PHMSA
conducted shock test experiments using an electrodynamic shaker which was available at a
university laboratory and a drop tower assembled by the NSWC.
20. A lithium ion battery having cobalt oxide chemistry and weighting 16 kg (35 Lbs.) with a capacity
of 50-60 Ah and a nominal voltage of 13 V was subjected to the acceleration forces and pulse
duration using these equipment.
21. Parameters measured before and after subjecting the battery to acceleration forces and pulse
durations include forensic analysis on battery internals using x-ray examinations, temperature,
voltage, and visual examinations of the battery integrity.
22. The electrodynamic shaker was used to replicate an acceleration of 50 gn and a pulse duration of
11 millisecond and to determine if the battery survives the requirements indicated in the UN
Manual. No change in the battery performance in terms of the parameters monitored was
noticed. The x-ray data noticed no change in the battery internal configurations. No
temperature and voltage variations were noticed.
23. The same experiments were performed using the drop tower at the same gn force acceleration
and the pulse duration. No change in the battery integrity was noticed. The battery met the
requirements in the UN Manual.
24. The Naval Research Laboratory used a drop tower to measure the acceleration (gn) encountered
and the corresponding pulse duration. In addition, other parameters were monitored and
examined including the voltage, temperature, and x-ray examinations for internal components.
The heights from which the battery was dropped are 12.7 cm (5 inches), 28 cm (11 inches), 61
cm (24 inches), 91.4 cm (36 inches), and 121.9 cm (48 inches). The surfaces on which the battery
was dropped from the drop tower include rubber padding, wood, concrete, and steel (only from
28 cm (11 inches) because of the limitation of accelerometer reading (up to 2,500 gn)).
25. A computerized system recorded values for the desired parameters.
Experimental Observations
26. The first phase of experiments involved the use of the drop tower subjecting the battery to
accelerations and pulse durations by dropping it three times from each of various heights (12.7
cm, 28 cm, 61 cm, 91.4 cm, and 121.9 cm) over the surface of 1.9 cm (¾ inch) rubber padding.
The acceleration recorded on the three accelerometers used were on average 27 gn, 50 gn, 77
gn, 97 gn, and, and 127 gn for the corresponding heights. The pulse duration remained the same
11 milliseconds at all heights used.
27. The next phase was to drop the battery on 5.08 cm (two (2) inches) plywood from the heights of
28 cm, 61 cm, 91.4 cm and 121.9 cm. The gn forces averaged from the three drops were 149 gn,
360 gn, 789 gn, and 993 gn from the corresponding heights. The pulse durations varied from 0.53
milliseconds to 0.95 milliseconds with an average value of about 0.6 milliseconds.
28. The next experiment pertained to dropping the battery on the surface of a steel plate (1/2’’ inch
thickness). A drop was made from a height of 28 cm with the acceleration of 666 gn and the
pulse duration of 0.6 milliseconds. When the battery was dropped from a height of 61 cm, the
acceleration registered was above the peak measurable level for the accelerometer of 2,500 gn.
However, no abnormalities in the parameters measured noticed. No external damage on the
battery can be observed. After this trial, the experiment on the steel plate was interrupted.
29. In the last experiment, the battery was dropped on concrete floor from the heights of 28 cm,
61cm and 91 cm. The gn value and pulse duration were 548 gn and 0.5 milliseconds when
dropped from the height of 28 cm. When dropped from the height of 61 cm, the gn value and
the pulse duration were 1,335 gn and 0.35 milliseconds. When dropped from the height of 91
cm, the gn value was above the peak measurable value for the accelerometer. Hence, the
experiment was stopped.
30. These test data can be summarized in a tabular form as follows:
SUMMARY OF DATA (16 kg battery weight)
SURFACE
TYPE(see
below)
Foam
Plywood
gn
50
149
28
Pulse
duration
(ms)
11
0.6
Drop Height (cm)
61
gn
Pulse
duration
(ms)
77
11
358
0.95
91
gn
93
789
122
Pulse
duration
(ms)
11
0.53
gn
127
993
Pulse
duration
(ms)
10
0.55
Concrete
548
0.5
1335
Steel
666
0.16
Foam = 2” plywood+2”rubber mattes+1”foam
Plywood = 2” plywood backed by concrete
Concrete = concrete floor
Steel = ½” steel plate
0.35
31. As can be seen from the data, the types of surface on which the battery was dropped related to
the pulse duration. The stiffer the surface the shorter the pulse duration. As the drop heights
were raised, the higher accelerations on the surface were observed.
32. In separate experiments, the dependence of acceleration on weights was measured by dropping
different weights on the same surface at a fixed height. The results were approximately an
inverse relationship between the square-rooted weight and the acceleration as predicted by the
engineering principles; as the battery weights were increased, the gn forces decreased
approximately in the inverse relationship of the square-rooted weight when dropped from the
same height and on the same surface.
Interpretation of Experimental Data
33. Meeting the current 50 gn 11 ms shock tests requirements for large batteries requires a trial and
error to find a drop height and a surface which will provide pulse duration of 11 milliseconds
which can be provided by using a relatively soft drop surface such as foam or spring.
34. As the weight of battery increases, the height of drop should be increased to match 50 gn which
may be difficult or impracticable to do for large batteries.
35. The 50 gn, 11 ms shock test is not universally representative of transportation environment for
every battery design and economically impracticable for large format batteries.
36. The drop test encompasses all the dynamic forces experienced during transportation and
requires a simple test apparatus.
37. Repeatability can be an issue depending upon the surfaces used for the 50 gn, 11 ms shock test
and the drop test.
38. A comparison of the “drop test” and the “50 gn 11ms shock test” can be summarized as:
Drop Test
Encompasses all the dynamic forces
experienced during transportation.
50 gn 11 ms shock
Not universally representative of
transportation environment for every battery
design
Simpler test apparatus
Economically impractical for large format
batteries.
39. When a large battery is dropped, the energy retained by the battery is dependent upon its mass
and the drop height, not the type of the surfaces used.
40. When a battery is dropped on a hard surface, its energy can be partially dissipated by external
damage to the battery. On the other hand, when a battery is dropped on a soft surface such as
foam or spring, its energy can be absorbed by the cushioning effect of the foam or the spring
(the external energy absorption).
41. It would be optimal to let the drop energy be absorbed by the internal make-up of the battery
so that it can experience all the dynamic forces possible during transportation. The external
damage to the battery or the external absorption of the drop energy should be avoided.
42. The plywood backed by concrete is proposed for the test because the surface of steel or
concrete can be prone to the external damage to the battery and because the use of foam pad
or spring as used in the current 50 gn 11 ms test can easily absorb the energy the battery
possesses from dropping.
43. Testing indicated that the fixed acceleration and pulse duration parameters defined in the
current T.4 shock test could induce responses in test items that are not representative of abuse
conditions during transportation.
44. Data suggests that drop testing is more representative of worst case transportation conditions.
45. The energy absorbed by the battery from the shock test is proportional to the weight of the
battery dropped and the square of the acceleration and pulse duration. From this relationship
one can derive that the acceleration is inversely proportional to the square root of the battery
weight at the same energy level that the battery absorbed.
Proposal
46. Based on the experimental data obtained from the research efforts and the information
publically available, the shock test requirement should be modified to accommodate large
format batteries because they could be susceptible to damage when test from a very high
height and because the energy absorbed by the battery should be a determining factor for the
shock test.
47. The energy impacting the drop surface when dropping a 16 kg battery from a height of 61 cm
(24”) is the same whether it is dropped on the 5cm (2”) Plywood or 5 cm (2”) foam pad. The
energy absorption on the plywood is less likely than on the cushioning foam pad.
48. There was no leakage, no venting, no disassembly, no rupture, no fire and no change in voltage
registering an acceleration of 358 gn and a pulse duration of 0.95 ms and 77 gn and a pulse
duration of 11 ms on the average in the cases of plywood and foam, respectively.
49. The foams have tendency of absorbing the drop energy more readily than the harder plywood,
not to consider the foam surface in the drop or shock test.
50. Providing the same energy as done in the experiments to different sizes of batteries is the intent
of this proposal. To do that, the following simplified table can be prepared.
Kg
Height(cm)
12
81
15
65
51. The table can be plotted as follows:
20
49
25
39
30
33
35
28
40
24
45
22
Greater than 45
22
52. The proposal is that large cells and large batteries shall be subjected to a shock from dropping it
on 5 cm (2”) plywood backed by concrete from a height in accordance with the mass vs. height
table. Each cell or battery is subjected to three shocks in the positive direction followed by
three shocks in the negative direction of each of three mutually perpendicular mounting
position of the cell for a total of 18 shocks.