CoSe2 nanoparticles anchored on porous carbon network structure for efficient Na-ion storage

Cobalt selenide, as a star material in battery industry, has attracted much attention. However, when it is applied solely in sodium ion batteries, it will cause large volume expansion and material agglomeration, which will seriously affect the overall performance of batteries. In this work, we use ice bath impregnation to combine CoSe2 nanoparticles with porous nitrogen-doped carbon networks (NC) as advanced anodes for ultra-long cycle life sodium ion batteries (SIBs). CoSe2 nanoparticles are evenly attached to NC with strong interfacial contacts in CoSe2@NC. The strong contact of CoSe2 on the porous carbon network, along with the carbon network's unique network cross-linking structure, results in rapid electron transfer and Na ion diffusion kinetics of CoSe2@NC, resulting in superior electrochemical performance. Besides, we have synthesized CoSe2@NC with different loading by changing Co2+ concentration. The results show that CoSe2@NC anode thus provides a high reversible capacity of 406 mAh/g. In addition, at high current 5 A/g, it can keep a reversible capacity of 300 mAh/g after 4500 cycles with an average capacity loss of less than 0.01 % per cycle. The excellent anchoring structure enables it to form stable solid electrolyte film (SEI) and reduce the amount of dead sodium in the first charge-discharge process, showing high Initial Coulombic Efficiency (ICE) (89.2 %). Finally, CoSe2@NC and Na3V2(PO4)3 (NVP) are assembled into a full cell and the results shows an ultra-long cycle stability at 0.1 A/g. This strategy will facilitate the application of transition metal selenides in next-generation energy storage systems.