On the Stability of LiFePO4 Olivine Cathodes under Various Conditions (Electrolyte Solutions, Temperatures)

LiFePO 4 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 LiFePO 4 at two temperatures, 30 and 60°C. Three types of solutions were used based on EC-DMC 1:1 solvent mixtures those involving no acidic contamination (using LiClO 4 as the electrolyte), those contaminated by HF(using LiPF 6 as the Li salt), and LiPF 6 solutions deliberately contaminated with H 2 O. Iron dissolution from LiFePO 4 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, LiFePO 4 develops a unique surface chemistry. Highly stable behavior of LiFePO 4 cathodes, without any substantial iron dissolution at elevated temperatures, was observed and measured when the solution contains no acidic or protic contaminants.

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