Stepwise delithiation and interfacial electric field engineering enabling stable cycling of LiNi0.8Co0.1Mn0.1O2/LiFePO4 hybrid cathode under harsh conditions

Abstract

The severe structural and surficial instability of Ni-rich layered oxide cathodes during deep delithiation at high voltages limits their high-capacity advantage, especially under harsh conditions. Blending with highly stable olivine cathodes can be a useful technique to complement stability, however how to exploiting the heterointerface to facilitate the homogenous deep delithiation kinetics of layered oxide is a challenge. Here, we propose an interfacial electric field engineering strategy to integrate LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811)/ LiFePO₄ (LFP) through a simple grinding-calcination process, enabling rational regulation of lithium extraction in hybrid cathodes and enhancing battery stability. Revealed by theoretical calculation and simulation, the preferential delithiation of LFP into FePO₄ at low voltage induces a built-in electric field across the NCM811/FePO₄ heterointerface, which reconstructs the interfacial charge distribution and facilitates Li⁺ migration. The resulting homogenous deep delithiation of NCM811 at high voltage effectively suppresses phase transition, strain accumulation and microcrack generation in the bulk, while alleviating the surface deterioration by preventing parasitic side reactions and oxygen release, where the mitigated structural evolution and accelerated electrochemical kinetic processes are monitored and verified by in-situ characterizations and analysis. The optimized NP-30 cathode (30 wt% LFP) with engineered heterointerface remarkably delivers a capacity of 167.3 mAh g⁻¹ with 80.94% capacity retention after 140 cycles at 65 °C and 1 C, and maintains 81.12% capacity retention after 200 cycles at 5 C. This work not only establishes a scalable interfacial engineering strategy for stabilizing Ni-rich cathodes under harsh conditions, but also provides fundamental design principles for next generation high-energy-density batteries.