N-Doped Carbon Nanosheet-Confined CoSe2 Enabling High-Rate and Durable Sodium Storage

Abstract Transition-metal selenides (TMSes) show considerable potential as anodes of sodium-ion batteries, benefiting from their diverse redox reactions and large theoretical capacities. Despite these merits, TMSes suffer from drastic volumetric changes and sluggish electron transport, leading to a degraded cycling stability and poor rate performance. Herein, an integrated CoSe2@NC nanoarchitecture was developed through a Co-hexamethylenetetramine precursor-mediated selenization strategy, yielding ultrafine CoSe2 nanoparticles encapsulated within interconnected nitrogen-doped carbon nanosheets. The two-dimensional nanosheet morphology maximizes the accessible electrochemical interface and facilitates rapid Na+ migration, while the nitrogen-doped carbon nanosheet serves as a conductive network for efficient electron transport and a structural scaffold that accommodates the volumetric variation. Benefiting from this synergy, CoSe2@NC delivers a considerable reversible capacity, superior rate capability, and robust cycling capability. Quantitative kinetic analyses reveal that the superior performance originates from dominant pseudocapacitive charge storage, lowered interfacial impedance, and accelerated Na+ diffusion. Additionally, CoSe2@NC exhibits a competent performance when assembled into sodium-ion capacitors, further demonstrating its potential for practical sodium-based energy storage.