Development of P3-type K_0.70[Cr_0.86Sb_0.14]O₂ cathode for high-performance K-ion batteries

Potassium-ion batteries (KIBs) are one of the most promising alternatives to lithium-ion batteries because of the high standard hydrogen electrode of K⁺/K, which is the second lowest after lithium. However, the large ionic size of K⁺ generally hinders the reversible intercalation and results in the undesirable structural changes during charge-discharge process. Thus, it is very important to develop stable cathode materials that accommodate K⁺ into their crystal structure with minimal structural changes. Here we propose P3-type K_0.70 [Cr_0.86Sb_0.14]O₂ as a potential cathode material for high-performance KIBs. The P3-type K_0.70 [Cr_0.86Sb_0.14]O₂ was successfully fabricated via electrochemical ion-exchange of Na⁺/K⁺. At a current density of 15 mA/g, P3–K_0.70 [Cr_0.86Sb_0.14]O₂ delivered a reversible capacity of 126.1 mAh/g with a high coulombic efficiency of 98.7%, corresponding to the de/intercalation of 0.57 mol of K⁺ ions from/into the structure. In addition, P3-type K_0.70 [Cr_0.86Sb_0.14]O₂ showed excellent cycling stability over 200 cycles at a current density of 150 mA/g and power capability even at high current rate of 750 mA/g. In contrast, P3-K_xCrO₂ demonstrates inferior electrochemical properties; this comparison implies that substitution of 0.14 mol Sb into Cr sites significantly improves structural stability with reversible Cr^3+/4+ redox reaction during charge-discharge process.