Hioki DM7275 Series - Appx. 2 Measuring The Enclosure; Lithium-Ion Batteries; X84; Internal Insulation Defects in Lithium-Ion Batteries

Appx.2
Measuring the Enclosure Potential of Laminated Lithium-ion Batteries
Appx.2 Measuring the Enclosure Potential of
LaminatedLithium-ionBatteries
This appendix addresses measurement of the enclosure potential of laminated lithium-ion batteries,
including a description of causes of such potentials and precautions that should be observed during
measurement.
Internal insulation defects in lithium-ion batteries
Internal insulation defects in lithium-ion batteries cause degraded characteristics and may lead to
serious accidents under certain conditions. Lithium-ion batteries are prone to a variety of insulation
defects, as described in the following table:
Internal insulation defects in laminated lithium-ion batteries
Defect location Cause Phenomenon
Between positive
electrode and negative
electrode
Penetration of separator due to
metal deposition, contamination with
metallic particles, fold misalignment,
etc.
Increased self-discharging, abnormal
heating
Between positive
electrode and enclosure
aluminum
Contamination with metallic
particles, defective seal on aluminum
laminated foil
The positive electrode’s current collector is
usually made from aluminum, making this
an unlikely issue.
Between negative
electrode and enclosure
aluminum
Contamination with metallic
particles, defective seal on aluminum
laminated foil
The lithium-ion battery’s performance may
be degraded if cracks form in the enclosure
aluminum’s insulating lm.
Between the electrolyte
and the enclosure
aluminum
Cracks in the aluminum laminated
foil
The lithium-ion battery’s performance may
be degraded if there is a defect in the
insulation between the negative electrode
and the enclosure aluminum.
Insulation defects between the positive electrode and the negative electrode lead to increased self-
discharging and abnormal heating of the battery. In general, they can be identied by a voltage
drop after aging the battery for a period ranging from several days to several weeks.
Insulation defects between the enclosure aluminum and the positive electrode, negative electrode,
or electrolyte are not immediately problematic since they do not form a closed loop through the
enclosure aluminum.
When a lithium-ion battery is subject to repeated expansion and contraction due to charging and
discharging, cracks more readily form in the insulating lm that coats the surface of the aluminum
laminated foil. Such cracks can lead to defective insulation between the electrolyte and enclosure
aluminum. When an insulation defect occurs between the positive electrode or negative electrode
and the enclosure aluminum, the likelihood of a closed loop being formed through the enclosure
aluminum and the electrolyte increases.
In general, the standard electrode potentials of lithium-ion batteries are as shown in the following
table:
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