Development of P3-type K0.70[Cr0.86Sb0.14]O2 cathode for high-performance K-ion batteries

Abstract

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 K0.70 [Cr0.86Sb0.14]O2 as a potential cathode material for high-performance KIBs. The P3-type K0.70 [Cr0.86Sb0.14]O2 was successfully fabricated via electrochemical ion-exchange of Na+/K+. At a current density of 15 mA/g, P3–K0.70 [Cr0.86Sb0.14]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 K0.70 [Cr0.86Sb0.14]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-KxCrO2 demonstrates inferior electrochemical properties; this comparison implies that substitution of 0.14 mol Sb into Cr sites significantly improves structural stability with reversible Cr3+/4+ redox reaction during charge-discharge process.