K_0.54[Co_0.5Mn_0.5]O₂: New cathode with high power capability for potassium-ion batteries

We propose P3-K_0.54[Co_0.5Mn_0.5]O₂, which is rationally designed as a promising cathode material for high-performance potassium-ion batteries (KIBs). Its composition adopts the use of the valence state of Mn above 3.5 + to minimize the disruptive effect of Jahn–Teller distortion in the MnO₆ octahedra during the electrochemical reaction. Unlike other types of layered materials that suffer from the sluggish diffusion of large potassium ions accompanying multi-step voltage profiles, P3-K_0.54[Co_0.5Mn_0.5]O₂ delivers a high specific discharge capacity of 120.4 mAh (g-oxide)⁻¹ with smooth charge and discharge curves. First-principles calculations predict an activation barrier energy of ∼260 meV for a large K⁺ diffusion, which is comparable to those observed in conventional layered cathode materials for lithium-ion batteries. As a result, even at 500 mA g⁻¹, P3-K_0.54[Co_0.5Mn_0.5]O₂ is able to deliver a high discharge capacity of 78 mAh g⁻¹, which is a retention of 65% versus the capacity obtained at 20 mA g⁻¹. Combination studies using operando X-ray diffraction, the ex-situ X-ray absorption near-edge structure, and first-principles calculations elucidate the nature of the excellent potassium storage mechanism of K_0.54[Co_0.5Mn_0.5]O₂. This work provides a new insight for the development of efficient cathode materials for KIBs.