Regulating the Multiscale Stability of Li-Rich Cathode through Lewis Acid Gas Treatment

Lattice oxygen redox reactions dedicate the extra retrievable capacities from the lithium-rich layered oxides (LLOs) cathodes, however, the widespread adoption of which in the energy-dense batteries faces a series of obstacles, such as oxygen loss during the initial activation, cycling-induced structural degradation as well as the retard Li⁺ diffusivity impeded by the interfacial impurities. Here, a Lewis acid gas treatment of LLOs is proposed, namely the PF₅ etching to enhance the cycling endurance and high-temperature tolerance of the electrode. The multiscale modifications involve the F⁻ doping in the bulk lattice, the phosphate coating to kinetically suppress the O₂ release as well as the removal of surface impurities in a single step. The gas-phase treatment constructs a continuous pathway across the densely-packed LLO electrode, enhancing Li⁺ diffusivity by fivefold compared to the untreated electrode. Notably, the transmission-mode operando X-ray diffraction of the modified LLOs cathode confirms a 71.4% reduction of self-discharge rate during the idle charged state at 55 °C, as well as the 16% mitigation of lattice contraction (Δc/a) during the dynamic galvanostatic cycling. By pairing the lithium foil (50 µm) with the modified LLO cathode (12.75 mg cm⁻²) in a pouch-format cell model, the 0.2 Ah prototype achieves the gravimetric energy/power densities as well as cycling endurance across a wide temperature range. This scalable, Lewis-acid gas modification strategy presents a practical approach for deploying LLOs in energy-dense cell prototyping.