DEVELOPMENT OF COBALT-FREE HIGH ENERGY DENSITY POSITIVE ELECTRODE MATERIALS FOR LI-ION BATTERIES

Abstract

The positive electrode constitutes a key component of the Li-ion cell and helps determine the energy density and cost of the cell. Co-rich positive electrode active materials have been widely commercialized, with proven success, and maintain a reliable performance record across markets. And yet, due to economic reasons and ethical concerns, Li-ion manufacturers are turning to Co- free, Ni-rich materials. But eliminating Co is not without its drawbacks. Co-free, Ni-rich materials can deliver high capacity; they can also deliver long lifetime. However, it has been challenging to design materials that can deliver both simultaneously. Besides the fact that electrode materials with both high capacity and long lifetime are more attractive to consumers, they also provide an environmentally sustainable solution. Using higher energy density materials reduces the size of the cell or the number of cells needed to make battery systems. Increasing the lifetime of the cell extends the period until the cell needs to be disposed of or recycled and reduces the rate at which critical metals need to be mined and treated to make new cells. This work extensively examines the effects of Al and W in LiNi1-xMnxO2 (NM) systems and optimizes the material to increase both the gravimetric capacity and cycle life of the cell. Since Ni- rich materials are susceptible to reactions with water, the materials are characterized thoroughly with a focus on the surface’s sensitivity to moisture and washing. Furthermore, this work demonstrates that greater attention needs to be paid to the mechanical properties of the material particles to identify, in a time-efficient manner, the propensity of the material to crack and, in turn, better understand the degradation mechanisms of the electrode. When studying Ni-rich materials, the safety of the material is also of interest; the thermal stability of the materials at a high state of charge were characterized and reported in this work. Through these methods, Co-free, Ni-rich materials were designed with high energy density and impressive charge-discharge capacity retention.