Bulk Bismuth as a High-Capacity and Ultralong Cycle-Life Anode for Sodium-Ion Batteries by Coupling with Glyme-Based Electrolytes

Sodium-ion batteries (SIBs) have attracted great interest for large-scale electric energy storage in recent years. However, anodes with long cycle life and large reversible capacities are still lacking and therefore limiting the development of SIBs. Here, a bulk Bi anode with surprisingly high Na storage performance in combination with glyme-based electrolytes is reported. This study shows that the bulk Bi electrode is gradually developed into a porous integrity during initial cycling, which is totally different from that in carbonate-based electrolytes and ensures facile Na⁺ transport and structural stability. The achievable capacity of bulk Bi in the NaPF₆-diglyme electrolyte is high up to 400 mAh g⁻¹, and the capacity retention is 94.4% after 2000 cycles, corresponding to a capacity loss of 0.0028% per cycle. It exhibits two flat discharge/charge plateaus at 0.67/0.77 and 0.46/0.64 V, ascribed to the typical two-phase reactions of Bi NaBi and NaBi Na₃Bi, respectively. The excellent performance is attributed to the unique porous integrity, stable solid electrolyte interface, and good electrode wettability of glymes. This interplay between electrolyte and electrode to boost Na storage performance will pave a new pathway for high-performance SIBs.

The bulk Bi anode coupled with glyme-based electrolytes presents a high reversible capacity of 400 mAh g⁻¹ and capacity retention of 94.4% after 2000 cycles, corresponding to a capacity loss of 0.0028% per cycle. This is attributed to the unique porous integrity evolved during initial cycles, stable solid electrolyte interface, and good electrode wettability of glymes.

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