Understanding the Role of Solution Equilibrium and Precipitation Rate on Precursor Composition for Lithium-ion Battery Active Materials

Transition metal oxides are among the most successful lithium-ion battery cathode materials. Much prior work has been completed in the literature describing the sensitivity of final electrochemical performance of the active materials to the detailed composition and processing of the transition metal oxides. Co-precipitation is a popular, scalable route to synthesize these transition metal oxide cathode materials. First, a precursor is synthesized through co-precipitation using solution chemistry, followed by mixing the precursor particles with a lithium salt and calcining the mixture at elevated temperature to produce the final desired material. The particle morphology of the precursor can be well-retained even after high temperature firing, which makes this synthesis approach an attractive method to achieve control over particle size and shape; however, the deviation of the precursor composition from feed conditions is a challenge that has generally been ignored in previous studies. Using a target final material of the high voltage spinel LiMn1.5Ni0.5O4 as an example, we show in this study that the compositional deviation caused by the co-precipitation reaction to form the precursor particles can play an important role in determining the electrochemical properties of the final active materials. A series of studies were conducted to understand the role of solution equilibrium and rate of precipitation of the transition metals during precursor formation. This knowledge was then used to provide rational control of the precursor composition and finally to synthesize, with high precision, the target stoichiometry necessary to produce LiMn1.5Ni0.5O4.