Suppressing fluorine loss of KVPO4F by surface chromium substitution for high-efficiency potassium-ion batteries

Abstract

Potassium-ion batteries (PIBs) have developed with great rapidity and are currently regarded as promising candidates for next-generation energy storage systems. KVPO₄F (KVPF) is a widely studied cathode material for PIBs due to its high working voltage and three-dimensional potassium ion shuttle channels. However, the electrochemical performance of KVPF is greatly constrained by the loss of fluorine during the synthesis process and cycling. It is therefore crucial to exploit KVPF cathodes that can stabilize fluorine and enhance structural stability. Herein, a new material KV_0.95Cr_0.05PO₄F (designated KVCPF-5) is synthesized through in-situ implantation of Cr³⁺. The combined results of experimental studies and theoretical calculations indicate that the incorporation of chromium into KVPF can strengthen the surface V–F bonds, thereby reducing the loss of fluorine. In addition, the KVCPF-5 cathode exhibits a low migration barrier, leading to faster K⁺ migration kinetics. When evaluated as a PIB cathode material, KVCPF-5 demonstrates an excellent reversible capacity (104.9 mAh g⁻¹ at 0.2C), outstanding rate capability (82.7 mAh g⁻¹ at 50C) and stable cycling performance (91.8 mAh g⁻¹ at 10C, with a retention rate of 82.1 % after 1000 cycles). Moreover, the K storage mechanism of KVCPF-5 is plainly unraveled through in-situ X-ray diffraction.