Hierarchical porous Co0.85Se@reduced graphene oxide ultrathin nanosheets with vacancy-enhanced kinetics as superior anodes for sodium-ion batteries

The vertically oriented Co0.85Se ultrathin nanosheets loaded on rGO with hierarchical porous structure exhibited superior electrochemical performances, which can be ascribed to three reasons: (I) abundant pores is conducive to the fast Na+ transport and relieve volume expansion during sodiation/desodiation; (II) special morphology provides strong pseudo-capacitance effect; (III) vacancies with gradient concentration in Co0.85Se enhance sodium storage kinetics.405