Trace high-valence ions induced surface coherent phase stabilized high voltage LiCoO2

Abstract

Employing higher voltage (≥4.6 V) is an effective strategy to achieve higher energy densities in LiCoO₂ based lithium-ion batteries. However, higher-voltage operation was generally followed by more severely surface to bulk structure deterioration, leading to rapid battery performance decay. Herein, a co-doping strategy involving in trace high-valence tantalum and niobium doping in LiCoO₂ material was proposed. Owing to the charge neutralization effect, the incorporated Ta and Nb ions induced the Co to lower valence state, which could further migrate to the Li layer for the similar ionic radius, and thus a nanoscale disordered layer on LiCoO₂ surface was successfully constructed. The stable disordered layer with tiny lattice mismatch to inner layered structure (coherent phase) could serve as an “armor” to restrain surface side reactions with electrolyte. Furthermore, the strong Ta-O and Nb-O bonding could act as an “oxygen anchor” to inhibit excessive oxygen oxidation under high-voltage operation. This helped the modified cathode showed 82.1% capacity retention after 100 cycles (4.6 V). Furthermore, the full cell composed of modified cathode and graphite anode revealed a remarkable capacity retention of 98% after 400 cycles. This study provides deep insights into the different phenomena associated with interfacial and structural parameters that need to be tuned to enhance the electrochemical performance at elevated voltages.