Spontaneous passivation on high-voltage manganese-based layered oxide cathodes via Selective surface doping for potassium-ion batteries

Abstract

The resourceful manganese-based layered oxide cathodes, benefitting from a high redox activity in Mn^4+/3+ couple and a superior reaction kinetics in prismatic configuration, presented desirable energy densities and rate capabilities in low-cost potassium-ion batteries (PIBs). Unfortunately, their harsh depotassiation/potassiation processes at high voltages still confronted notorious lattice distortions and irreversible phase transformations with interfacial side reactions, resulting in rapid capacity degradations. Herein, a novel surface-doping strategy, involving an atomic layer deposition and a subsequent annealing treatment, was adopted to address the structural/interfacial instabilities of P3-type K_0.5MnO₂ cathode. Theoretically, the Zn²⁺ derived from ZnO with a lowest diffusion barrier among different cations in K_0.5MnO₂ was primarily selected to reconstruct thermodynamically stable passivation surfaces on unstable cathode materials. Interestingly, the gradient integrations of highly electronegative Zn²⁺ into cathodes without changing phases/morphologies could enrich labile surfaces with intrinsically stable Mn⁴⁺ through charge balance and ameliorate structural/interfacial stabilities upon cycling. Between 4.2 ∼ 1.5 V, the discharging capacity retentions at 50 mA g⁻¹ over 50 cycles and 100 mA g⁻¹ over 100 cycles can be significantly enhanced from 37.5 % and 26.7 % for pristine K_0.5MnO₂ to 70.2 % and 51.3 % for K_0.5MnO₂-Zn-30C, respectively. Simultaneously, the optimized K_0.5MnO₂-Zn-30C cathode could still retain an outstanding rate capability of 69 mAh g⁻¹ at 500 mA g⁻¹, outperforming a corresponding parameter of 50 mAh g⁻¹ for pristine K_0.5MnO₂ cathode. Importantly, the conductive and robust passivation layers on K_0.5MnO₂ could boost the solid-state reaction kinetics upon K⁺ uptakes/removals, suppress the irreversible phase formations during cycling, and stabilize the deformable layered structures in the whole voltages. This innovative research on interfacial reconstructions of unstable layered oxides could enlighten the surface modifications on high-voltage cathodes for cost-effective and high-energy PIBs.