Battery & Electrification Technology - May/June 2024 - 10

Sponsored Content
INSIDE STORY
The continuous increase in energy demand and for improved performance are stimulating the rapid
maturation of lithium-ion batteries in large, energy-intensive applications such as electric vehicles (EVs)
and various renewable energy storage systems (ESS). However, the rapid increase in battery usage, energy
density and high-speed charging and discharging comes with a rise in fire and explosion incidents.
In this interview, Anthony Lu, Product Manager at Chroma ATE Inc., discusses the typical causes of EV
battery fires and how the enhanced capabilities of the company's Battery Cell Insulation Tester can help
to reduce the potential for battery cell insulation-related fires.
Battery & Electrification Technology: Why is it difficult to
analyze the cause of most lithium-ion battery fires?
Anthony Lu: Most fire-involved accidents
with lithium-ion batteries are
initiated by severe inflammation and
it is difficult to analyze the actual
cause. Common reports cite electrical
control system errors or the lithium
metal deposition compiling over a long
time and growing into lithium dendrite,
which causes internal short-circuits in
the battery. Although these certainly
are possible factors, detailed analysis shows that they are difficult
to establish in the bulk of battery accidents due to acute
cluster chemical combustion.
B&ET: What is the usual root cause of lithium-ion battery fires?
Lu: Most fire accidents in various products using lithium-ion
batteries, including EVs, occur while charging. The main reason
for this is that the negative electrode material (graphite
or mixed silicon) continues to inflate after repeated charging
cycles, reducing the distance between the positive and negative
electrodes. This results in the effective distance between these
electrodes becoming shorter than the original design due to
electrode burrs or metallic particles, increasing the risk of an
internal short-circuit.
B&ET: Why is it difficult to detect defects in the general
production process - such as the separator being partially
punctured by electrode burrs or metal particles?
Lu: The most prevalent problems in production inspection of
battery cells are too-low dry cell (jelly roll) insulation test voltage
(<350V) and failure to detect the electrical flashover caused by
electrode burrs or metallic particles during insulation testing.
From a fire-protection perspective, insulation tests of lithium-ion
battery cells should check the distance between electrodes,
rather than measure the insulation resistance. From the air
breakdown voltage versus distance data, even if the gap distance
is as short as several μm, the breakdown voltage is higher than
350V, so the insulation voltage test should be conducted at
higher than 350V. Also, testing for the occurrence of breakdown
or flashover enables effective assessment of whether the insulation
distance is sufficient.
B&ET: How should test voltage be set to detect poor withstand
voltage (WV)?
Lu: According to Chroma's recent test results of withstand voltage
(WV) in commercial separators, the normal product has WV
distribution of about 800V - 1200V; the short-circuited product
can be easily detected by low voltage (< 250V).
As for the abnormal product of separator break-through,
the WV distribution is 400V ~ 600V, which seems to be in
keeping with the relationship between the air breakdown
voltage and the gap. Partial-puncture high-risk product has
a WV distribution of about 450V ~ 700V, which is between
the normal product and the abnormal product of separator
break-through. From this result, we know that usually the
test voltage setting ≤ 250V can only identify the short-circuited
abnormal products, while abnormal products of
separator break-through and high-risk products with partial
punctures cannot be detected. The electrical characteristics
of air breakdown mean this potential must be greater than
350V. And if you want to detect high-risk products more effectively,
you can set about 750V, according to our research
case (for reference only, different separators may have
different WV distributions; it is recommended to use the WV
distribution of a small number of trial-produced good products
as a reference).
B&ET: Can you detail Chroma ATE Inc.'s solution, the 11210
Battery Cell Insulation Tester?
Lu: To improve the insulation-quality test for lithium-ion
batteries, Chroma specially designed the built-in +Flash Test
function, which can be set to test whether the electrode
distance is sufficient by first using a short-term high voltage,
then applying a higher voltage in the second stage. There
also is a long-duration, low-voltage test to detect abnormal
leakage current that may be caused by other extremely fine
particles or defects in the separator. The +Flash Test function
allows two test conditions to meet two test requirements at
one time during the entire test process, achieving a quick and
complete lithium-ion battery insulation-quality inspection
solution, reducing the risk of lithium-ion battery fire. This
enhances EVs and contributes to improving the safety of the
energy storage system.
For more information on the Chroma 11210 Battery Cell Insulation
Tester, visit www.chromaate.com.
10
Battery & Electrification Technology, May/June 2024
http://info.hotims.com/86255-708
Battery & Electrification Technology - May/June 2024

Table of Contents for the Digital Edition of Battery & Electrification Technology - May/June 2024
