Impact of Shell Composition, Thickness and Heating Temperature on the Performance of Nickel-Rich Cobalt-Free Core-Shell Materials

Abstract

Ni-rich lithium transition metal oxides have high specific capacity but generally have inferior cycling performance compared to their lower Ni content counterparts. core–shell structures with a Ni-rich core and a Mn-containing shell have been reported to improve the cycling performance of Ni-rich materials, but the impact of the shell on the performance of core–shell materials needs to be elaborated more. In this work, three core–shell precursors having a Ni(OH)2 core, but different shell compositions and thicknesses, were lithiated at various temperatures and the resulting materials were examined physically and electrochemically. They were compared to the corresponding uniform “shell” materials lithiated at the same temperatures. The selection of heating temperature is crucial and must be made with care to limit the interdiffusion between core and shell compositions while still heating to sufficient temperature to prepare crystalline materials with little lithium in the transition metal layer. Once these factors are understood, core–shell structures with an optimized shell thickness and Mn content can be made to simultaneously achieve high specific capacity and long cycle life.