Carbon Negative Electrodes for Li-Ion Batteries: The Effect of Solutions and Temperatures

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In this paper we report on the behavior of some carbonaceous materials as anodes for Li ion batteries in several selected electrolyte solutions and over a wide range of temperatures, from −30°C to 45°C. The solution components studied include alkyl carbonates (ethylene carbonate (EC), dimethyl carbonate (DMC)) mono-fluorinated and bi-fluorinated ethylene carbonates (FEC, 2FEC), vinylene carbonate (VC), diglyme, LiPF 6 and LiN(SO 2 CF 3 ) 2 (LiTFSI). While standard electrolyte solutions for Li ion batteries based on EC-DMC-LiPF 6 have poor specific conductivity at low temperatures, diglyme/LiTFSI, VC (2%)-EC-DMC, FEC-DMC and 2FEC-DMC with LiPF 6 exhibit reasonable conductivities (>2 mS/cm) at −30°C. Graphitic materials exhibit poor low temperature performance, while soft carbons behave better at low temperatures. It was found that FEC-DMC/LiPF 6 solutions are very suitable for carbon electrodes over a wide temperature domain. In fact, using these solutions enables soft carbon electrodes to demonstrate higher specific capacity than graphite electrodes below 0°C, although the room temperature specific capacity of graphite is 1.5 times higher than that of soft carbon.