Hioki DM7275 Series, Инструкция по эксплуатации

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Appx.
3
Measuring the Enclosure Potential of Laminated Lithium-ion Batteries
Standard electrode potential of materials used in lithium-ion batteries
Area Material
Standard electrode
potential
Positive electrode Li
(1-n)
CoO
2
+1 V
Enclosure Al -1.7 V
Negative electrode Li
(1-n)
C
6
-2.9 V
Because the enclosure aluminum has a high potential relative to the negative electrode, the
occurrence of an insulation defect between the negative electrode and the enclosure aluminum
while another insulation defect is occurring between the electrolyte and the enclosure aluminum
can trigger a reduction reaction of the aluminum enclosure, generating an Li-Al alloy. This alloy is
extremely fragile, leading to the formation of pinholes in the enclosure aluminum. If moisture gets
into the battery through these pinholes, it will react with the electrolyte to form a gas, causing a
dramatic reduction in the service life of the lithium-ion battery.
On the other hand, if an insulation defect between the positive electrode and the enclosure
aluminum occurs at the same time as another insulation defect between the electrolyte and the
enclosure aluminum, the enclosure aluminum will undergo an oxidation reaction, and no unstable
Li-Al alloy will be formed. In short, insulation defects between the positive electrode and the
enclosure aluminum do not adversely affect the service life of lithium-ion batteries.
For the above reasons, the enclosure potential of laminated lithium-ion batteries is assessed by
measuring the potential difference between the positive electrode and the enclosure aluminum in
order to detect insulation defects between the negative electrode and the enclosure aluminum.
Enclosure potential measurement
When the potential difference between the positive electrode and the enclosure aluminum is
measured, the voltage will vary depending on whether there are any internal insulation defects in
the lithium-ion battery (see table below).
Insulation defect locations and observed potentials
Insulation defect location
Voltage observed between
the positive electrode and the
enclosure aluminum
Between positive electrode and enclosure
aluminum
0 V
Between negative electrode and enclosure
aluminum
Up to 4 V
Between electrolyte and enclosure aluminum Up to 2.7 V
No insulation defect
Indeterminate
Observe the following precautions when measuring the enclosure potential.
Input resistance
The observed voltage will be indeterminate when you measure a non-defective lithium-ion battery
with no insulation defects. Consequently, it is necessary to connect a resistor with a high resistance
between the voltmeter’s HIGH and LOW terminals so as to determine the electrical potential.
For this instrument, it is recommended to set the input resistance to AUTO and connect a resistor
externally with a resistance of 10 M
Ω
to 1 G
Ω
between the voltmeter’s HIGH and LOW terminals.
(p. 76)
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Appx.
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