Yolk-shell structured CoSe2/C nanospheres as multifunctional anode materials for both full/half sodium-ion and full/half potassium-ion batteries

Transition metal selenides (TMSs) are suitable for SIBs and PIBs owing to their satisfactory theoretical capacity and superior electrical conductivity. However, the large radius of Na+/K+ easily leads to sluggish kinetics and poor conductivity, which hinder the development of SIBs and PIBs. Structure design is an effective method to solve these obstacles. In this study, Co2+ ions combined with glycerol molecules to form self-assembled nanospheres at first, and then they were in situ converted into CoSe2 nanoparticles embedded in a carbon matrix during the selenization process. This structure has three-dimensional ion diffusion channels that can effectively hamper the aggregation of metal compound nanoparticles. Meanwhile, the CoSe2/C of the yolk-shell structure and a large number of pores help alleviate volume expansion and facilitate electrolyte wettability. These structural advantages of CoSe2/C endow it with remarkable electrochemical performances for full/half SIBs and full/half PIBs. The obtained CoSe2/C exhibits superior stability and excellent performance (312.1 mA h g(-1) at 4 A g(-1) after 1600 cycles) for SIBs. When it is used as an anode material for PIBs, 369.2 mA h g(-1) can be retained after 200 cycles at 50 mA g(-1) and 248.1 mA h g(-1) can be retained after 200 cycles at 500 mA g(-1); in addition, CoSe2/C also shows superior rate capacity (186.4 mA h g(-1) at 1000 mA g(-1)). A series of ex situ XRD measurements were adapted to explore the possible conversion mechanism of CoSe2/C as the anode for PIBs. It is worth noting that the full-cell of CoSe2/C//Na3V2(PO4)(3)@rGO for SIBs and the full-cell of CoSe2/C//PTCDA-450 for PIBs were successfully assembled. The relationship between the structure and performance of CoSe2/C was investigated through density functional theory (DFT).

Automated summary

Transition metal selenides show potential for sodium and potassium ion batteries due to their theoretical capacity and electrical conductivity. Through structural design, CoSe2/C materials were successfully synthesized, demonstrating remarkable electrochemical performances in both SIBs and PIBs with high stability and superior capacity retention.