Synergistic N-doped carbon encapsulation in porous CoSe2 nanospheres for enhancing the anode performance of sodium-ion batteries

Abstract

Transition metal selenides (TMSes) are considered one of the most promising anode materials for advancing sodium-ion batteries (SIBs) due to their high specific capacity and energy density. However, they suffer from significant volume expansion and poor conductivity, which lead to unsatisfactory electrochemical performance. In this work, CoSe₂@NC composites with an N-doped carbon (NC) coating were fabricated via a self-assembly strategy combined with chemical vapor deposition. The obtained sample exhibits a uniform porous spherical architecture with an ultrathin N-doped carbon shell, thereby effectively buffering the volumetric strain of CoSe₂ and accelerating the electron/ion transport kinetics. Specifically, the CoSe₂@NC anode delivers a high initial discharge specific capacity of 513.7 mAh g⁻¹ and retains 431.3 mAh g⁻¹ after 100 cycles, demonstrating excellent capacity retention. CV and EIS analyses confirm that the N-doped carbon coating significantly enhances pseudocapacitive contributions (82.5% at 1 mV s⁻¹) and facilitates the Na⁺ insertion/extraction kinetics. This work presents a practical methodology for the rational design and fabrication of advanced metal selenide anodes for sodium-ion batteries.