Enhancing long-cycle stability of CuFeS2/EG anode for sodium-ion batteries by mitigating crosstalk effect

The practical deployment of transition metal sulfide anodes for sodium-ion batteries (SIBs) is hindered by critical challenges, including rapid voltage decay and poor cycling stability, primarily attributed to polysulfide shuttle effects and structural degradation. Herein, CuFeS2/expanded graphite (CFS/EG) composite is synthesized using a molten-state solid-phase sulfidation strategy, leveraging EG's high conductivity and two-dimensional layered structure to enhance electronic transport and mitigate polysulfide dissolution. Electrochemical evaluations reveal the CFS/EG composite's excellent rate capability and cycling stability, retaining 422.7 mAh g−1 (89.9% retention) after 1500 cycles at 5 A g−1. Mechanistic insights from in situ XRD and Raman spectroscopy demonstrate reversible phase transitions during Na+ insertion/extraction. Notably, the composite exhibits remarkable low-temperature performance, delivering 382 mAh g−1 after 400 cycles at 1 A g−1 at −10 °C. This study highlights the synergistic role of CuFeS2 and EG in suppressing polysulfide crosstalk and maintaining structural reversibility, positioning the CFS/EG composite as a promising anode material for next-generation high performance SIBs.