Structural and electrochemical stabilization enabling high‐energy P3‐type Cr‐based layered oxide cathode for K‐ion batteries

Abstract Layered‐type transition metal (TM) oxides are considered as one of the most promising cathodes for K‐ion batteries because of the large theoretical gravimetric capacity by low molar mass. However, they suffer from severe structural change by de/intercalation and diffusion of K⁺ ions with large ionic size, which results in not only much lower reversible capacity than the theoretical capacity but also poor power capability. Thus, it is important to enhance the structural stability of the layered‐type TM oxides for outstanding electrochemical behaviors under the K‐ion battery system. Herein, it is investigated that the substitution of the appropriate Ti⁴⁺ contents enables a highly enlarged reversible capacity of P3‐type K_xCrO₂ using combined studies of first‐principles calculation and various experiments. Whereas the pristine P3‐type K_xCrO₂ just exhibits the reversible capacity of ∼120 mAh g⁻¹ in the voltage range of 1.5–4.0 V (vs. K⁺/K), the ∼0.61 mol K⁺ corresponding to ∼150 mAh g⁻¹ can be reversible de/intercalated at the structure of P3‐type K_0.71[Cr_0.75Ti_0.25]O₂ under the same conditions. Furthermore, even at the high current density of 788 mA g⁻¹, the specific capacity of P3‐type K_0.71[Cr_0.75Ti_0.25]O₂ is ∼120 mAh g⁻¹, which is ∼81 times larger than that of the pristine P3‐type K_xCrO₂. It is believed that this research can provide an effective strategy to improve the electrochemical performances of the cathode materials suffered by severe structural change that occurred during charge/discharge under not only K‐ion battery system but also other rechargeable battery systems.