Mixed phase Mo-doped CoSe2 nanosheets encapsulated in N-doped carbon shell with boosted sodium storage performance

Transition metal selenides have aroused considerable interests as promising anodes for sodium ion batteries (SIBs). However, they still face big challenges toward practical application such as huge volume changes and slow electrochemical reaction kinetics, giving rise to the insufficient sodium conversion reactions and poor stability during the cycling process. In this work, self-supporting nanosheet arrays of Mo-doped CoSe 2 encapsulated in N-doped carbon shell (labeled as Mo-CoSe 2 @NC) are fabricated by an ion-exchange reaction of cobalt metal-organic frameworks (Co-MOF) as the template, combined with a successive electrodeposition and one-step carbonization/selenization approach. Regarding the ingeniously designed Mo-CoSe 2 @NC nanosheets, the external N-doped carbon shell is able to promote the electron transfer and mitigate volume variation of the composite, while the introduction of Mo ions can not only activate the conversion reaction of CoSe 2 , but also induce the generation of mixed phases of CoSe 2 with more sodium storage active sites and enhanced electrical conductivity. Benefiting from these merits, the Mo-CoSe 2 @NC anode applied in half-cell of SIBs exhibits a high reversible capacity (672 mAh g −1 after 200 cycles at 0.5 A g −1 ) and reasonably good rate property (313 mAh g −1 at 5.0 A g −1 ). • Mo 6+ doping can induce the generation of mixed phases o -CoSe 2 and c -CoSe 2 . • More defects caused by Mo 6+ doping provide a large number of active sites. • The reasonable design of the N-doped carbon shell enhances structural integrity. • The binder- and additive-free electrodes facilitate rapid electrolyte infiltration.