Structural and interface design of hierarchical porous carbon derived from soybeans as anode materials for potassium-ion batteries

Potassium-ion batteries (KIBs) are an attractive energy storage system for large-scale applications, due to the high abundance of potassium (K) and low redox potential of K/K+. However, the development of KIBs has been hindered by the absence of a suitable carbon anode. Herein, we developed a high-performance hard carbon anode for KIBs by using low-cost and abundant soybeans as the starting material. The hard carbon obtained at 500 °C exhibited the highest discharge capacity of 225 mA h g−1, good rate capability, and long lifetime of 900 cycles. Low activation temperature yielded hard carbon with medium surface area, large interplanar spacing of graphene layers, and low degree of graphitization, which favored adsorption-dominated K-ion storage mechanism and were considered as the key merits for the soybeans-derived carbon anode for KIBs. Moreover, a thin Al2O3 coating (~2 nm) by atomic layer deposition was used as an artificial solid electrolyte interphase on hard carbon, and improved the average Coulombic efficiency from 99.0% to 99.6%. Clarification on the correlation among electrochemical performance, structural and physical properties, and K-ion storage mechanism of hard carbon provides new insights critical for knowledge-based design and synthesis of carbonaceous materials with improved K-ion storage capacity and efficiency for practical KIBs.