On the stability of LiFePO4 olivine cathodes under various conditions (electrolyte solutions, temperatures)

Formula is one of the most important cathode materials for Li-ion batteries studied over the past few years. Impressive work has revealed important structural aspects and the correlations between structure and composition and electrochemical properties. Fewer efforts have been devoted to the surface chemical aspects of this material. We report herein on a study of the stability aspects of Formula at two temperatures, 30 and Formula . Three types of solutions were used based on EC-DMC 1:1 solvent mixtures those involving no acidic contamination (using Formula as the electrolyte), those contaminated by HF(using Formula as the Li salt), and Formula solutions deliberately contaminated with Formula . Iron dissolution from Formula in these electrolytes, as well as the electrochemical response as a function of solution composition and aging, were studied at the two temperatures. The effect of additives that neutralize acidic species in solution was also studied. In general, Formula develops a unique surface chemistry. Highly stable behavior of Formula cathodes, without any substantial iron dissolution at elevated temperatures, was observed and measured when the solution contains no acidic or protic contaminants.