Achieving High-Rate and Durable Sodium Storage through Confined Construction of NiSe2 Particles Embedded in Porous N-Doped Carbon Spheres

As one type of promising anode material, transition-metal selenides have aroused great attention in the research field of sodium-ion batteries (SIBs) on account of their high theoretical capacity. Nevertheless, the intrinsically inferior conductivity, huge volume changes, as well as severe aggregation of transition-metal selenides that take place upon cycling lead to fast degradation of sodium storage performance. In this work, we report the confined construction of NiSe2 particles embedded in porous N-doped carbon spheres (NiSe2/NC) with polydopamine spheres as the functional template involving successive solvothermal, carbonization, and selenization processes. As expected, the porous N-doped carbon spheres could improve the conductivity, facilitate the migration of Na+, and also serve as a stable mechanical support to NiSe2 particles by effectively avoiding the aggregation of NiSe2 and mitigating the volume changes. Consequently, the NiSe2/NC hybrid spheres exhibit a high reversible capacity (489 mA h g–1 at 0.1 A g–1), superior rate capability (212 mA h g–1 at 5 A g–1), and outstanding cycling stability (351 mA h g–1 after 1600 cycles at 1 A g–1). The delicate design of NiSe2/NC hybrid spheres fundamentally offers a valuable guidance for the development of transition-metal selenides, as well as other high capacity anodes with decent electrochemical performance.