A surface-to-bulk tuning deep delithiation strategy for 5C fast-charging 4.6 V LiCoO2

Abstract

Achieving highly reversible anionic redox reactions (ARR) in high-voltage LiCoO₂ (LCO) is critical for increasing its power/energy density but still lacks a reliable tuning strategy. Herein, we report a comprehensive surface-to-bulk tuning deep delithiation strategy by coupling trace Mg–Nb–Al Li-layer co-doping with ultrathin interfacial hierarchical fluorination, featured by a unique ultra-thin double-layer cathode electrolyte interphase structure consisting of an inner1 nm-thick LiF-rich layer and an outer 2 nm-thick Li_xPO_yF_z layer, to extremely stabilize fast charging of 4.6 V-LCO. The slight cation disorder induced by Li-layer co-doping and synergistically confined interfacial hierarchical fluorination enhances the bulk-to-surface anion/cation redox process of LCO and suppresses interfacial side reactions during fast-charging cycles, and the Mg–Nb–Al pillars strengthen the layered lithium diffusion channels. Consequently, our LCO achieves a record reversible capacity of 198 mA h g⁻¹ and a 77.8% capacity retention at 5C fast-charging after 500 cycles. The assembled graphite‖LCO pouch cell demonstrates the state-of-the-art cyclability with virtually no capacity decay after 1400 cycles at 5C charge and 10C discharge. It is theoretically unraveled that suppressing oxygen electronic hole generation through an Nb⁵⁺-induced high spin-polarized weak Co–O octahedral crystal field is the key to highly reversible ARR in 4.6 V-LCO. This work provides a design guidance for achieving reversible deep delithiation of high-voltage LCO.