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abstract
The influence of adding the room-temperature ionic liquid 1-ethyl-3-methyllimidazolium
bis(trifluoromethylsulfonyl)imide (EMImTFSI) to poly(ethylene oxide) (PEO)elithium
difluoro(oxalato)borate (LiDFOB) solid polymer electrolyte and the use of these electrolytes
in solid-state Li/LiFePO4 batteries has been investigated. Different structural, thermal,
electrical and electrochemical studies exhibit promising characteristics of these polymer
electrolyte membranes, suitable as electrolytes in rechargeable lithium-ion batteries. The
crystallinity decreased significantly due to the incorporation of ionic liquid, investigated by
X-ray diffraction (XRD) and differential scanning calorimetry (DSC). The ionepolymer
interaction, particularly the interaction of cations in LiDFOB and ionic liquid with ether
oxygen atom of PEO chains, has been evidenced by FT-IR studies. The polymer electrolyte
with ~40 wt% of ionic liquid offers a maximum ionic conductivity of ~1.85 104 S/cm at
30 C with improved electrochemical stabilities. The Li/PEO-LiDFOB-40 wt% EMImTFSI/
LiFePO4 coin-typed cell cycled at 0.1 C shows the 1st discharge capacity about 155 mAh g1
,
and remains 134.2 mAh g1 on the 50th cycle. The addition of the ionic liquid to PEO20-
LiDFOB polymer electrolyte has resulted in a very promising improvement in performance
of the lithium polymer batterie
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