Surface Chemistry, Passivation, and Electrode Performance in Core–Shell Architectures of LiCoO2 Nanoplates

Abstract

Core–shell structures offer opportunities to overcome challenges to the durability of Li-ion batteries with high energy density due to instability at the cathode/electrolyte interface. Achieving complete stability requires fundamental understanding of the role of the shell in providing passivation without compromising carrier transport, by tuning surface chemistry and structural features in a highly conformal barrier layer. Here, individual LiCoO2 nanoplates were employed as the core, and passivating shells were grown at a tailored thickness and composition, through different Al loadings and annealing temperatures. Depending on the annealing conditions, the sub-5 nm shells were shown to vary from amorphous aluminum oxide layers to LiAlxCo1–xO2 gradients, resulting in an Al-rich outer layer on a Co-rich core. This control revealed the differing balance between effective minimization of redox-active Co3+ at the surface and transport properties of the two types of shell. Based on correlations with electrode performance, the requirements in thickness of the layers were proposed to critically depend on their chemical composition, with epitaxial shells based on surface substitution being favored. The outcomes of the study simultaneously advance the ability to assemble complex oxides into heterostructures and refine the rules of design for tunable passivation through a barrier layer, so as to maximize electrode properties in practical batteries.