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

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, LiPF6 and LiN(SO2CF3)2 (LiTFSI). While standard electrolyte solutions for Li ion batteries based on EC-DMC-LiPF6 have poor specific conductivity at low temperatures, diglyme/LiTFSI, VC (2%)-EC-DMC, FEC-DMC and 2FEC-DMC with LiPF6 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/LiPF6 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.