The safety of lithium ion battery is one obstacle to
limit its large-scale application in automobile. Some researches show that decomposition
of electrolyte on cathode under high potential is one reason leading to the
thermal runaway or even the combustion of electrolyte. In order to solve the
above problem, one way is to form a thin film on cathode surface to prevent the
decomposition of electrolyte on it. Researchers have found that 3, 4-ethylene
dioxythiophene (EDOT) can be used as electrolyte additive to improve the safety
of the battery. And the addition of EDOT has no effect on electrochemical
performance of lithium ion battery. Some details of the experiment are
described as follows.
In the experiment, LiCoO2 was used as
cathode and EDOT was added into the standard electrolyte. Oxidation potential
of EDOT was measured by cyclic voltammetry which oxidation peak occurred at 3.95V,
which is situated at the range of charge voltage of LiCoO2. So EDOT
can be oxidized to form polymerization film (PEDOT) on cathode surface in the
first charge-discharge cycle. And TEM experiment also verifies this. The
polymerization film on cathode surface suppresses the decomposition of
electrolyte to improve the lithium ion battery safety.
The thermal stability of LiCoO2 cathode
after delithiation in the electrolyte with EDOT or without is detected by DSC. The
experiment results show that PEDOT-modified cathode has a 26% exothermic
reduction. And this demonstrates the heat generation due to electrolyte decomposition
is reduced to a certain extent. The cyclic performance of the full cell shows
that the capacity retention is improved for the electrolyte with addition of
EDOT.
In a word, EDOT polymer as electrolyte additive can improve
the safety of lithium ion battery. And it has no effect on electrochemical performance
of lithium ion battery.
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