Designing a binary sulfides/carbon polyhedron for secondary batteries with high electrochemical and thermal performances

Abstract

Sodium-ion (Na-ion) batteries are attractive for large-scale storage owing to the abundance of Na, its ionization energy comparable to Li, and the low Na+/Na redox potential. However, currently available anode materials remain suboptimal, limited by sluggish ion/electron transport and large volume changes during cycling. Here, we report a heterostructured binary sulfides/carbon (Cu7S4/Co9S8/C) polyhedron for Na-ion battery anode, which exhibits high performance across diverse cycling rates and temperatures. In situ X-ray diffraction and Raman spectroscopy demonstrate reversible structural evolution during cycling. Cu7S4/Co9S8/C anode achieves a high capacity of 556 mAh g-1 after 300 cycles at 0.5 A g-1 with a Coulombic efficiency > 99%, and maintains 508 mAh g-1 after 1300 cycles at 3.0 A g-1. It also exhibits strong thermal tolerance, retaining 486 mAh g-1 after 500 cycles at 50 °C. Moreover, pairing Cu7S4/Co9S8/C anode with a NaVPO4 cathode yields excellent full-cell performance, underscoring practical potential. To further evaluate the thermal properties, 3ω method is employed to quantify the effective thermal conductivity of the composite. The Cu7S4/Co9S8/C architecture delivers a thermal conductivity of 0.30 W m-1 K-1, improving by ~25% and ~20% over Cu7S4/C and Co9S8/C, respectively. These findings highlight a generalizable heterostructure design strategy for high-performance anodes and provide guidance for engineering energy-storage materials and safe secondary batteries.