Structural Engineering of Hard-Soft Carbon Hybrid Anodes for Ultrafast and Ultradurable Potassium-Ion Storage.

Hard-soft carbon hybrid materials, harvesting the expanded interlayer spacing of hard carbon and the high conductivity of soft carbon, hold great promise as anode materials for potassium-ion batteries, but efficient and precise structural control remains a major challenge. Herein, hollow porous bowl-like hard-soft carbon hybrid materials (BHSCs) are facilely synthesized by an in situ hard-template strategy. It is found that the outer and inner walls of the hard carbon bowls are uniformly wrapped by graphene-like soft carbon, which accelerates electron transport and promotes the insertion of potassium ions. Finite element simulation further reveals that the soft-hard-soft carbon shell structure releases stress during the insertion of potassium ions. As a result, BHSC anode exhibits an extraordinary rate capability (209 mAh g at 10 A g) and excellent cycle stability with a capacity of 208 mAh g after 5000 cycles at 2 A g. Impressively, the as-assembled potassium-ion hybrid capacitor based on BHSC anode delivers a great energy/power density (116 Wh kg/12980 W kg) and outstanding capacity retention of 83% after 8000 cycles. This work provides guidance for rational structural design of hard-soft carbon hybrid materials to improve their potassium-ion storage performance.