LEAK TESTING OF COMPONENTS

Lithium-Ion Battery Cells
TECHNICAL CHALLENGE
The production of lithium-ion battery cells has recently ramped up significantly,
driven by increasing numbers of mobile devices, as well as the growing market
of New Energy Vehicles with electric cars, hybrid cars and fuel cell vehicles.
The functional safety of a lithium-ion battery is very important, but sufficient
lifetime and performance of the battery is also needed. This is especially true
with the new drive train technology application where high quality batteries areindispensable to create a positive reputation for the new technology.
There are four different mechanical designs of a battery cell: cylindrical cells,
coin cells, prismatic cells and pouch type cells. Cylindrical cells, coin cells andprismatic cells have a sturdy housing, whereas pouch-type cells have a flexiblehousing (they are also referred to as flexible battery cells).
Battery cells need to be tested for physical leakage because:
Humidity must not get into the battery, as humidity will also negatively
impact the battery’s performance and even destroy the battery
completely over timeFor pouch cells any air intake will also increase the internal pressure sothat the pouch cell will lose its mechanical integrity which leads to a lossof capacity

No electrolyte must leak out of the battery cell, as missing electrolyte
will have a negative impact on the battery’s performance

Different designs of battery cells are used tocreate power batteries for electrical andhybrid vehicles. Cylindrical cells are used in
the Tesla Model S for example, but morecommonly prismatic and pouch-type cells areused. Pouch cells as well as coin cells arealso widely used in mobile devices.

To guarantee these requirements, modern battery cells must be leak tested toleaks in the range of a few micrometers in diameter equaling leak rates in therange of 10-6 mbar*l/s. These small leaks cannot be detected with older
technologies like water bath or soap spray testing, nor with pressure decay
testing.
THE INFICON SOLUTION
Production testing of prismatic cells is performed in several steps:
Pretesting of prismatic battery cells
Sometimes the battery cell housings of prismatic battery cells are pretested
before filling with electrolyte to ensure e.g. electric feedthroughs do not leak.
This pretesting is usually performed in vacuum chamber leak testing with highthroughput. The housing of the battery cell is filled with helium and then placedin a testing chamber connected to a vacuum system. Once the chamber lid isclosed, large vacuum pumps pull a vacuum on the testing chamber. Helium
then has the opportunity to migrate outwards and if a leak is present, anLDS3000 Helium Leak Detector (connected to the vacuum chamber) detects
the helium as it emerges from the battery cell.

Battery cells prefilled with helium are
typically tested via vacuum chamber leakdetection. This process is very common forprismatic battery cells.

LEAK TESTING OF COMPONENTS
Lithium-Ion Battery Cells

Only if the housing of the battery cell tests okay, can it be filled with electrolyte
and finally be sealed. This type of pretesting cannot be applied to pouch cells.
Even if the housing of the battery cell has been pretested as described above,
the filled and sealed battery cell must be retested to ensure the integrity of thefinal seal. Pouch-type batteries are typically only tested once after final sealing.
End-of-line testing of fully assembled hard case battery cells
For integrity testing of filled hard case cells (prismatic, round, coin) the processof direct electrolyte detection is used. For this process, the battery cells to betested are placed in a test chamber which is evacuated to a pressure level below
the vapor pressure of the electrolyte solvent. Electrolyte will leak from any leakchannels into the test chamber where the solvent of the electrolyte will
evaporate. The solvent will then be detected by the sensor, in this case aquadrupole mass spectrometer in the ELT3000 battery cell leak detector.
End-of-line testing of filled and sealed pouch cells
For integrity testing of hermetically sealed pouch cells, the same process of
direct electrolyte detection can be used. However, a different type of chamber isneeded as pouch cells inflate in a vacuum chamber damaging the sealing of thepouch cell. This challenge is overcome by the use of a flexible chamberconsisting of two layers of a flexible material. The pouch cells to be tested areplaced in-between the two flexible layers and a vacuum is created in this“customized” test chamber. The flexible material supports the pouch cell during
the vacuum test and allow for a true non-destructive leak test. The solvent
escaping from any potential leaks are also detected by an ELT3000 battery cellleak detector.

BENEFITS OF LEAK TESTING WITH TRACER GAS
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Accurate and repeatable measurements for reliable leak testing
Highly sensitive testing method for detecting smallest leaks of a few
micrometres diameter (~10-6 mbar l/s range)
Highly automated process with high throughput
Test result independent of operator intervention
Dry, non-destructive process

For more information, please visit us atwww.inficonautomotive.com
or call your nearest sales representative.

www.inficon.com

reachus@inficon.com

Due to our continuing program of product improvements, specifications are subject to change without notice.
mial00en-04 (2011)©2020 INFICON

The ELT3000 battery cell leak detector candetect smallest leaks down to the µm level bydirect electrolyte detection. Different chamber
designs are employed for different cell
designs.