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

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 KxCrO2 using combined studies of first-principles calculation and various experiments. Whereas the pristine P3-type KxCrO2 just exhibits the reversible capacity of similar to 120 mAh g-1 in the voltage range of 1.5-4.0 V (vs. K+/K), the similar to 0.61 mol K+ corresponding to similar to 150 mAh g-1 can be reversible de/intercalated at the structure of P3-type K0.71[Cr0.75Ti0.25]O2 under the same conditions. Furthermore, even at the high current density of 788 mA g-1, the specific capacity of P3-type K0.71[Cr0.75Ti0.25]O2 is similar to 120 mAh g-1, which is similar to 81 times larger than that of the pristine P3-type KxCrO2. 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. This study investigates Ti4+ substitution to significantly enhance the reversible capacity of P3-type KxCrO2. Using first-principles calculations and experiments, it is confirmed that substituting 0.25 mol of Ti on the Cr site lowers K+ diffusion barrier, enhancing structural stability during charge/discharge, leading to improved electrochemical properties. Compared to P3-type K0.69CrO2, P3-type K0.71[Cr0.75Ti0.25]O2 offers superior K+ storage properties with enhanced structural reversibility. Herein, we demonstrated the enhancement for reversible capacity and structural change of P3-type KxCrO2 via the substitution of Ti4+. Using first-principles calculations and various experiments, we verified that substituting 0.25 mol of Ti on the Cr site enhances structural stability during charge/discharge, leading to improved electrochemical properties. image