Hollow Co_0.85Se cubes encapsulated in graphene for enhanced potassium storage

Potassium-ion batteries (KIBs) have been regarded as prospective energy storage system due to the rich reserves and affordable price of potassium resources. However, the lack of high-capacity electrode materials still inhibits the further development of KIBs. Here, we report a unique hollow metallic Co_0.85Se cubes encapsulated in graphene (Co_0.85Se/G) for KIBs anode. The unique hollow structure features high surface area that guarantees Co_0.85Se enough contact with electrolyte. The graphene wrapping blocks the agglomeration and relieves the volume changes of Co_0.85Se. The metallic property of Co_0.85Se and high conductivity of graphene can boost the rate performance. As a consequence, Co_0.85Se/G delivers a high capacity of 324 mAh g⁻¹ at 50 mA g⁻¹ over 200 cycles, and the capacity can be kept at 213 mAh g⁻¹ even at of 1000 mA g⁻¹ over 1000 cycles.