The Reaction of Lithium-Manganese Oxides for the Cathode Materials of Rechargeable Lithium Batteries with Nonaqueous Electrolyte

Abstract

Instability of the lithium-manganese oxide, which has the spinel structure, in nonaqueous electrolyte solution was investigated. The lithium-manganese oxide powder samples were soaked in various kinds of nonaqueous electrolyte solutions at 85°C for 4 days. The amount of manganese ions which were dissolved in the electrolyte solutions were analyzed by ICP-AES. The chemical state of the manganese ions in the solutions were identified by ESR. From the results of ESR, it had been shown that the manganese ions formed at least three different formes of Mn2+ complexes in the nonaqueous electrolyte solution. The hydrolysis of the lithium hexafluorophosphate electrolyte in the nonaqueous electrolyte solutions were followed by 31P-NMR. We suppose that the hydrofluoric acid, which was caused from the hydrolysis reaction of the lithium hexafluorophosphate electrolyte with trace amounts of water in the electrolyte solution or in lithium-manganese oxide powder, induced the solubility of manganese ions from lithium-manganese oxides.