Tailoring Submicron Cobblestone-Like Carbon-Free CoSe2 with High Energy Density for Sodium-Ion Batteries

CoSe2 with high theoretical capacity has drawn massive attention as an ideal anode material for sodium-ion batteries (SIBs). However, developing a CoSe2 anode with high energy density to satisfy the practical application remains a very intractable challenge. Here, a carbon-free and compact submicron cobblestone-like CoSe2 anode material was designed and synthesized, which can promote tap density via eliminating the introduction of carbon species, nanostructure, and hollow construction. Benefiting from the contribution of partial pseudocapacitive contributes, CoSe2 displays high reversible capacity, outstanding rate property, and durable cycling stability (414.6 mAh g–1 after 700 loops at 0.2 A g–1 and 416.5 mAh g–1 after 1350 loops even at 2 A g–1). The enhanced tap density and remarkable sodium storage capability greatly improved volumetric energy density and gravimetric energy density and, subsequently, energy density. Meanwhile, ex situ XRD and Raman measurements were utilized to further understand the sodium storage mechanism of as-prepared CoSe2. This work opens up a new opportunity regarding the practical application of the CoSe2 anode with high energy density in SIBs.