Bismuth Embedded in Holey Expanded Graphite as a Sodium Ion Battery Anode with Superior Rate Capability

As a promising anode for sodium-ion batteries (SIBs), bismuth (Bi) with a high theoretical volumetric capacity of 3750 mAh cm–3 and optimal operation voltage plateau suffers from severe volume expansion and the formation of an unstable solid–electrolyte interphase. Although expanded graphite (EG) mitigates volume changes of Bi in the Bi@EG composite, the sluggish transportation kinetics of Na+ between graphitic structures remains a bottleneck. Herein, we report a series of Bix@EG1–x (x = 0.2, 0.4, 0.6, and 0.8) and Bix@hEG1–x (x = 0.6 and 0.8) composites as anodes for SIBs. Benefiting from the synergistic effect between the high capacity of Bi nanoparticles and the layered/holey structures of holey expanded graphite (hEG), Bi0.6@hEG0.4 exhibited exceptional sodium storage properties including excellent rate capabilities (e.g., 232.0 and 206.3 mAh g–1 at 10 and 20 A g–1, respectively) and long cycling stability (e.g., a high reversible capacity of 234.9 mAh g–1 after 4000 cycles at 5 A g–1 with an initial capacity retention of 93.5%). When it was paired with Na3V2(PO4)3 as the cathode (NVP//Bi0.6@hEG0.4), NVP//Bi0.6@hEG0.4 achieved a high initial capacity of 102.1 mAh g–1 at 1 C (1 C = 117 mA g–1) and maintained a high reversible capacity of 86.7 mAh g–1 after 900 cycles at 10 C with an 84.9% initial capacity retention.