3D Micro‐Flower Structured BiFeO 3 Constructing High Energy Efficiency/Stability Potassium Ion Batteries Over Wide Temperature Range

Abstract The fatty K + ion calls for suitable host materials to meet the requirement for high safety and long‐term stability of potassium‐ion batteries (PIBs) to rival lithium‐ion batteries, thus anode materials possessing high capacity, high stability, and well‐defined plateaus involving favorable working voltage (≈0.5 V) have always been desired. Here, a 3D BiFeO 3 with micro‐flower structure (BFO‐MF) constructed by nanosheets is proposed as an anode for PIBs. Density functional theory calculations evidence that the intrinsically favorable affinity and diffusion for K + ion render fast electrochemical kinetics and attenuated voltage‐hysteresis, and electrochemical measurements indicate that the stable 3D structure of BFO‐MF enables to achieve impressive performances including a high capacity of 606 mAh g −1 , flat plateaus at ≈0.5 V, stable performances for 5000 cycles at 500 mA g −1 , and 500 cycles at 100 mA g −1 upon −20 °C. In situ and ex situ characterizations definitely elucidate the conversion and alloy/dealloy mechanism. The satisfying features of BFO‐MF anode ensure full‐cells to achieve excellent cyclic performances, and a high energy efficiency retention rate of ≈98.2% for the cathode, with energy density/power density output up to 177.1 Wh kg −1 /2152.8 W kg −1 , respectively. This work can provide new insights for developing advanced anodes for PIBs.