Challenges toward higher temperature operation of LiFePO4

Large-scale lithium-ion batteries operating at higher temperature may provide additional advantageous aspects such as higher power and use of new materials which are inactive at ambient temperatures. As a first step for this direction, we applied LiFePO4 cathode to middle-temperature region of 60 degrees C-115 degrees C and investigated temperature-dependent charge-discharge properties. By selecting suitable electrolyte and battery components tolerant to the elevated temperature, stable operation was attained for no less than 50 cycles below 115 degrees C. High-rate performance was significantly improved as operating temperature increased up to 100 degrees C, but suffered from abrupt increase in polarization above 100 degrees C, where the corresponding impedance signal emerged, which might be assigned to some side reactions occurring at the surface of LiFePO4 particles. At 100 degrees C, the discharge capacity over 100 mAh g(-1), was achieved at 200C rate, even with 10wt% of carbon in the electrode composite of LiFePO4. Shrinkage of miscibility gap was not confirmed for samples larger than 40 nm at < 115 degrees C. (C) 2012 Elsevier B.V. All rights reserved.