Hollow Co0.85Se 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 potassiumresources. However, the lack of high-capacity electrode materials still inhibits the further development of KIBs. Here, we report a unique hollow metallic Co0.85Se cubes encapsulated in graphene (Co0.85Se/G) for KIBs anode. The unique hollow structure features high surface area that guarantees Co0.85Se enough contact with electrolyte. The graphene wrapping blocks the agglomeration and relieves the volume changes of Co0.85Se. The metallic property of Co0.85Se and high conductivity of graphene can boost the rate performance. As a consequence, Co0.85Se/G delivers a high capacity of 324 mAh g(-1) at 50 mAg(-1) over 200 cycles, and the capacity can be kept at 213mAh g(-1) even at of 1000 mA g(-1) over 1000 cycles.