Transition Metal Dissolution in Lithium-Ion Cells: A Piece of the Puzzle

Static leaching tests were performed using the chemically delithiated positive electrode materials, LiFePO4, LiCoO2, LiMn2O4, LiNiO2, and LiNi0.8Mn0.1Co0.1O2. Instead of the common electrolyte, which contains LiPF6, the solvent consisted of only ethylene carbonate (EC) and ethyl methyl carbonate (EMC), limiting the possible reactions to only those that depend on the solvent. The product liquids from these experiments showed that there were lithium-bearing species in common, such as Li(EC)+ and Li(EMC)+. Interestingly, we found evidence of electrolyte degradation products in both the positive-and negative -ion mass spectral results. The positive-ion results showed that the products tended to coordinate to lithium. The negative-ion results showed that most of the products tended to complex with transition metals. It was difficult to discern which positive ion was associated with which negative ion.