Transition metal dichalcogenides are regarded as promising anode materials for potassium-ion batteries (PIBs) because of their high theoretical capacities. However, due to the large atomic radius of K+, the structural damage caused by the huge volume expansion upon potassiation is much more severe than that of their lithium counterparts. In this research, a stress-dispersed structure with Co3Se4 nanocrystallites orderly anchored on graphene sheets is achieved through a two-step hydrothermal treatment to alleviate the structural deterioration. The ability to reduce the contact stress by the well-dispersed Co3Se4 nanocrystallites during K+ intercalation, together with the highly conductive graphene matrix, provides a more reliable and efficient anode architecture than its two agminated counterparts. Given these advantages, the optimized electrode delivers excellent cycling stability (301.8 mA h g-1 after 500 cycles at 1 A g-1), as well as an outstanding rate capacity (203.8 mA h g-1 at 5 A g-1). Further in situ and ex situ characterizations and density functional theory calculations elucidate the potassium storage mechanism of Co3Se4 during the conversion reaction and reveal the fast electrochemical kinetics of the rationally designed electrode. This work provides a practical approach for constructing stable metal-selenide anodes with long cycle life and high-rate performance for PIBs.
Keywords: cobalt selenide; conversion-type anode; nanocrystallites; potassium-ion batteries; stress dispersion.