Unveiling nanoplates-assembled Bi₂MoO₆ microsphere as a novel anode material for high performance potassium-ion batteries

Bismuth (Bi)-based electrode has aroused tremendous interest in potassium-ion batteries (PIBs) on account of its low cost, high electronic conductivity, low charge voltage and high theoretical capacity. However, the rapid capacity fading and poor lifespan induced by the normalized volume expansion (up to ~ 406%) and serious aggregation of Bi during cycling process hinder its application. Herein, bismuth molybdate (Bi₂MoO₆) microsphere assembled by 2D nanoplate units is successfully prepared by a facile solvothermal method and demonstrated as a promising anode for PIBs. The unique microsphere structure and the self-generated potassium molybdate (K-Mo-O species) during the electrochemical reactions can effectively suppress mechanical fracture of Bi-based anode originated from the volume variation during charge/discharge of the battery. As a result, the Bi₂MoO₆ microsphere without hybridizing with any other conductive carbon matrix shows superior electrochemical performance, which delivers a high reversible capacity of 121.7 mAh·g^-1 at 100 mA·g^-1 over 600 cycles. In addition, the assembled perylenetetracarboxylic dianhydride (PTCDA)//Bi₂MoO₆ full-cell coupled with PTCDA cathode demonstrates the potential application of Bi₂MoO₆ microsphere. Most importantly, the phase evolution of Bi₂MoO₆ microsphere during potassiation/depotassiation process is successfully deciphered by ex situ X-ray diffraction (XRD), X-ray photoemission spectroscopy (XPS), and transmission electron microscopy (TEM) technologies, which reveals a combination mechanism of conversion reaction and alloying/dealloying reaction for Bi₂MoO₆ anode. Our findings not only open a new way to enhance the performance of Bi-based anode in PIBs, but also provide useful implications to other alloy-type anodes for secondary alkali-metal ion batteries.