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-1 at 10 A g-1) and excellent cycle stability with a capacity of 208 mAh g-1 after 5000 cycles at 2 A g-1. Impressively, the as-assembled potassium-ion hybrid capacitor based on BHSC anode delivers a great energy/power density (116 Wh kg-1/12980 W kg-1) 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. A facile in situ SiO2-template strategy is proposed and realized to synthesize a series of hollow porous bowl-like hard-soft carbon hybrid materials (BHSC-800/900/1000), where the outer and inner walls of the hard carbon bowls are uniformly wrapped by soft carbon. Due to the unique structural advantages, the prepared BHSC-900 anode presents excellent potassium-ion storage performance.image

Automated summary

Hollow porous bowl-like hard-soft carbon hybrid materials (BHSCs) were synthesized using an in situ hard-template strategy. The outer and inner walls of the hard carbon bowls were wrapped by graphene-like soft carbon, resulting in improved electron transport and potassium-ion insertion. The BHSC anode showed excellent rate capability and cycle stability, and was used to assemble a potassium-ion hybrid capacitor with high energy/power density and outstanding capacity retention.