Developing cathode materials for high energy density Li ion batteries

Abstract

Rechargeable Li-ion batteries have become a key enabler for transformational changes in our society by powering advanced portable electronics and deploying electric vehicles and grid-scale applications. To meet this demands of rechargeable Li-ion batteries, developing novel cathode materials, which is strongly determined overall energy density of Li-ion batteries, urgent required for low-cost, resource-friendly, high-energy-density to satisfy the rapidly increasing need for electrical energy storage. Conventional cathode material (e.g. layered LiCoO2) are mainly composed with cobalt, which are limited resources and are associated with safety problems. Given the limits of energy density that can be achieved with the layered NMCs and the potential resource constraints on cobalt, it is of interest to develop high-capacity cathode materials based on 3d-transition metal but minimized those elements. In this regards, next generation cathode materials should be developed to high energy density based on low cost and high abundance of the metal than cobalt, such as nickel and manganese. In the chapter 2, the researches have focused on the understanding the structural properties of high redox potential LiNi0.5Mn1.5O4 spinel and the relationship with electrochemical properties, especially phase transition during electrochemical reaction. The fundamental understanding gained from this work could be applied to the development of other phase-separating compounds to improve their electrochemical performance. In the chapter 3, the researches have proposed the strategy of achieving both high energy density and power density in Mn-rich materials by controlling the atoms solubility between the spinel phase and layered phase in a composite. Based on this research, limited atomic solubility in the spinel phase can induce the reaction between these two phases resulting in the defective spinel structure and partially increased cation-disordered layered structure, which can be achieved high energy density in Mn-rich materials. In the chapter 4, the researches firstly proposed a way of control the parameter of oxygen redox contribution in Li-rich materials. The new controlling parameter can provide a way of fully increasing the oxygen redox reaction via Li-TMs inter-diffusion between the phases in Li-rich materials that are the composite of the two phases. From these researches, the induced chemical/structural features in Li-rich materials caused by the Li-TMs inter diffusion can fully activate the oxygen redox reaction, enabling full extraction of Li with high reversible capacity.