Advanced Potassium Ion Batteries Anode Enhanced by Fe-Doping Strategy

Abstract

KVPO4F (KVPF) is a novel insertion-type anode for potassium ion batteries. For improving its electrochemical performance, the doping strategy was selected and a series of Fe-doped KVPF materials were synthesized by a facile solid-state sintering method to find out the suitable ratio. After comparation, KVPF sample with 5% Fe-doped ratio (KVPF/Fe-5) delivers the best performance, e.g. rate capacity (94.3 mA h g−1 at 500 mA g−1) and long-term discharge capacity (74.1 mA h g−1 after 1000 cycles at 200 mA g−1, 0.03% capacity decay ratio per cycle), which is mainly attributed to its higher K+ diffusion rate. The in-situ XRD analysis clarify the two-step K+ storage mechanism of KVPF/Fe-5 anode, and the DFT calculations verify that Fe-doping can reduce diffusion energy barrier of K+ and increase electronic conductivity of KVPF. When used as cathode, KVPF/Fe-5 delivers 51.8 mA h g−1 at 100 mA g−1 after cycling 200 cycles. In addition, the symmetric cell of employing KVPF/Fe-5 as anode and cathode simultaneously was also assembled successfully, pointing out a new research direction for potassium-ion batteries.

Keywords: Potassium ion batteries, KVPO4F, Fe-doping strategy, In-situ XRD, Symmetric cell