High voltage stable LiCoO2 enabled by surface strengthening and bulk doping

Enhancing the operating voltage of LiCoO₂ (LCO) beyond 4.45 V significantly enhances the energy density of rechargeable Li-ion batteries; however, it also intensifies interfacial reactions, induces phase transitions, and promotes surface oxygen loss, leading to fast capacity decay. Here, we present a robust strategy to achieve stable cycling of LCO cathode above 4.6 V by integrating surface and bulk modifications through a wet chemical approach, which forms a conformal Ni₃(PO₄)₂ nanoshell around LCO particles; the subsequent heat treatment induces Ni²⁺ doping into the bulk and PO₄^3- modification on the surface, resulting in a thin rock-salt-like phase and a protective Li₃PO₄ layer. These modifications mitigate irreversible phase transitions and parasitic reactions, resulting in significantly improved stability; the modified LCO demonstrates 98.2 % capacity retention at 4.6 V (88.1 % at 4.7 V) after 100 cycles at 1C in half-cells and achieves 80 % retention over 346 cycles in 4.6 V LCO/graphite full cell. This work highlights the critical role of integrated lattice and surface engineering in advancing layered oxide cathodes and provides valuable insights for developing high-energy–density Li-ion batteries.