Influence of Temperature on the Interface Chemistry of Li x Mn2O4 Electrodes

The temperature dependence of surface layer formation on Li x Mn2O4 electrodes in carbonate-based electrolytes has been studied. No significant differences were observed in the elemental composition of the surface film for cycled and stored samples. This argues against an electrochemical contribution to the surface film formation at elevated temperature. A surface film is formed at higher temperatures containing poly(oxyethylene)/polycarbonate, LiF, Li x PO y F z , and phosphorus oxides (or Li x BO y F z and boron oxides, depending on the electrolyte salt). The thickness and coverage increase at higher temperatures. No onset temperature could be found for the formation process, suggesting a general increase in reaction kinetics with temperature. A model is presented for the surface layer formed on Li x Mn2O4 (0 ≤ x ≤ 1) electrodes in contact with carbonate-based electrolytes. Polymeric compounds were found to precipitate closest to the electrode surface, with an intermediate layer of LiF and a phosphorus-rich layer outermost.