Surface study of electrodes after long-term cycling in Li_(1.2)Ni_(0.15)Mn_(0.55)Co_(0.1)O_2-graphite lithium-ion cells

摘要

Lithium- and manganese-rich layered-oxides (LMR-NMC) have potential application for electric vehicles due to the high energy density. Electrochemical measurements and ex-situ surface analysis of cells containing Li_(1.2)Ni_(0.15)Mn_(0.55)Co_(0.1)O_2-based positive electrodes and graphite-based negative electrodes has been conducted. Electrochemical cycling reveals significant capacity fade and voltage decrease after 1500 cycles. Ex-situ surface analysis including scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIR) were conducted for cells with long term cycling at 30 ℃. The surface analysis supports the formation of surface film on both cathodes and anodes after formation cycling. Upon long term cycling, both the cathode and anode surface films become thicker although more significant changes appear to be occurring to the anode. Fresh LMR-NMC powder has been stored in the presence of electrolyte, 1.2 M LiPF_6 in EC/EMC 3:7, at 85 ℃ for 7 days. The surface film on the LMR-NMC powder after storage is similar to the surface film after cycling. The presence of the LMR-NMC powder inhibits the thermal decomposition of the electrolyte.