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Cu9S5 nanoparticles encapsulated in N, S co-doped carbon nanofibers as anodes for high-performance lithium-ion and sodium-ion batteries

Copper sulfides (Cu x S) have gained increasing attention for using as anodes of rechargeable batteries owing to their high theoretical capacity and good electron conductivity. However, the structure instability and sluggish reaction kinetics seriously deteriorate their electrochemical performance. To tackle with these inherent drawbacks, an elaborate hierarchical architecture composed of N, S co-doped carbon nanofibers and well-dispersed Cu9S5 nanocrystallines (Cu9S5/CNFs) was fabricated. After sulfurization, the Cu9S5 nanoparticles that uniformly distributed on the CNFs surface are well-encapsulated inside the graphitic carbon shell. For the hierarchical Cu9S5/CNFs, the ion diffusion pathways can be shortened by the nano-sized Cu9S5 while the graphitized carbon shell can provide rapid electron transfer as well as accommodate the volume variation of Cu9S5 upon cycling. Additionally, the heteroatom within CNFs can provide abundant edges and defects for adsorbing lithium/sodium ions, thus boosting the reaction kinetics of batteries. Benefiting from all of these merits, the Cu9S5/CNFs composite obtained under 600 °C (Cu9S5/CNFs-600) used as anode for lithium-ion batteries (LIBs) demonstrates high specific capacity (709.2 mAh g−1 at 0.1 A g−1 after 100 cycles), good rate performance (509.1 mAh g−1 at 2 A g−1) and excellent durability (540.2 mAh g−1 at 1 A g−1 after 800 cycles with a ultrahigh capacity retention of 92.5%). And it also exhibits stable cycling performance (with a capacity retention of 90.5% after 1500 cycles at 1 A g−1) and excellent rate performance in sodium-ion batteries (SIBs). This work provides a promising strategy to prepare high-performance copper sulfides-based anode materials for LIBs and SIBs.