A compact Bi2WO6 microflowers anode for potassium-ion storage: Taming a sequential phase evolution toward stable electrochemical cycling

Abstract Potassium-ion batteries (KIBs) are considered an important alternative for lithium-ion batteries owing to the abundant potassium (K) resources and low-cost. To date, most reported anode materials for KIBs have been limited to carbonaceous materials which can well accommodate the large potassium ions (K+) but show humble capacity performance. As compared, metal oxide-based anodes can potentially provide higher capacity yet cyclability is poor, which has been rarely researched. Herein, we report a sequential phase evolution mechanism for bimetallic oxide anode. Upon potassiation, the microflower-like Bi2WO6 undergoes a multistep evolution process, which first combines with K+ then converts into a highly reversible phase of Bi, then via a solid-solution reaction eventually it forms the K3Bi alloy. After repeated cycling process, such unique hierarchical and mesoporous morphology of Bi2WO6 can be well maintained, leading to superior cyclability with a high specific potassium storage capacity (652 mAh g−1 at 100 mA g−1). Even at a large current density of 1 A g−1, a reversible specific capacity of 216 mAh g−1 can still be delivered over 300 cycles. Such a novel working mechanism of bimetallic oxide anodes will promote the practical use of KIBs in diverse energy storage applications.