On the Optimization of Core-Shell Hybrid Cathode Materials for Extreme Fast-Charging: First Principles Computational Insights

Abstract

Core-shell and core-gradient hybrid cathode materials for lithium-ion batteries display enhanced rate capability over their homogeneous counterparts. The apparent enhancement of transport is shown to arise from advective flow of Li+ from the higher free-energy core towards the lower free-energy shell compositions. First-principles analysis of a planar model of these hybrid structures concludes that the inbuilt free-energy gradient enhances the Li+ de-intercalation process by reducing the average overpotential during extreme fast-charging. Analysis of representative LiNi0.8Co0.1Mn0.1O2||LiNi0.4Co0.2Mn0.4O2 core/shell reveals: (i) an optimal components ratio exists that maximizes storage capacity during fast-charging and (ii) components should be selected with appreciably large chemical potential difference between the core and shell to further exploit the free-energy gradient effects provided volume ratios are optimized against the potential gradient. In the case of NCM811||NCM424 studied herein, a balanced (ca. 40/60 vol.%) structure appears optimal. This finding indicates that the shell must not necessarily be confined to a thin chemically-protective coating; higher relative volumes of the lower free-energy shell may provide performance benefits at high-rates. The presented insights will serve towards optimizing and developing high capacity, more rate capable core-shell particles for extreme fast charging batteries. Figure 1