nan 董全峰

Impedance studies of spinel LiMn2O4 electrode/electrolyte interfaces

The formation process of solid electrolyte interphase(SEI) film on spinel LiMn2O4 electrode surface was studied by electrochemical impedance spectroscopy(EIS) during the initial storage in 1 mol/L LiPF6-EC:DMC:DEC electrolyte and in the subsequent first charge-discharge cycle. It has been demonstrated that the SEI film thickness increased with the increase of storage time,and spontaneous reactions occurring between spinel LiMn2O4 electrode and electrolyte can be prevented by the SEI film. In the first charge-discharge cycle succeeding the storage, the electrolyte oxidation coupled with Li-ion insertion is evidenced as the main origin to increase the resistance of SEI film. The results also confirm that the variations of the charge transfer resistance(Rct) with the electrode potential(E) can be well described using a classical equation. Keywords Li-ion batteries; SEI film; Electrochemical impedance spectroscopy; Spinel LiMn2O4

Influence of Temperature on the Performance of a Graphite Electrode

The first lithiation of a graphite electrode in 1 mol.L-1 LiPF6-EC(ethylene carbonate)∶DEC(diethyl carbonate)∶DMC(dimethyl carbonate) electrolyte at 25 and 60 ℃,and in 1 mol.L-1 LiPF6-EC∶DEC:DMC+5%VC(vinylene carbonate) electrolyte at 60 ℃ were investigated by electrochemical impedance spectroscopy(EIS) combined with cyclic voltammetry(CV).It was found that deterioration of the graphite electrode′s electrochemical performance was mainly caused by the unstable solid electrolyte interphase(SEI) film on the electrode′s surface in 1 mol.L-1 LiPF6-EC:DEC:DMC electrolyte at 60 ℃.However,the use of VC as an additive to the above electrolyte significantly improved the electrochemical performance of the graphite electrode,which was attributed to an improvement in the stability of the SEI film that formed on the graphite electrode′s surface.