Engineering of the Crystalline Lattice of Hard Carbon Anodes Toward Practical Potassium‐Ion Batteries

Abstract Hard carbons have attracted increased interest as an alternative of graphite for the anodes of potassium‐ion batteries (PIBs). However, the practical applications of hard carbon anodes are hampered by their low capacities, high potential platforms, and large potential hysteresis. Hard carbons coupled with graphitic nanodomains can achieve stable potassium‐ion storage behaviors with low potential platforms and low potential hysteresis. Herein, the crystalline lattice in hard carbon anodes is tuned by incorporating graphene oxide in renewable lignin precursors. The modified hard carbon (i.e., QLGC) anodes show graphitized nanodomains in the carbon matrix with an expanded interlayer spacing (0.42 nm) in the amorphous regions, which results in a stable potassium‐ion (de)intercalation behavior. Thus, the QLGC anodes exhibit a high capacity of 164 mAh g −1 with low potential hysteresis in the low potential platform region. Moreover, the QLGC anode delivered a highly stabilized capacity of 283 mAh g −1 at 50 mA g −1 , a high‐rate capability, and stable cycling performance. Furthermore, the charge storage mechanisms of QLGC anode are elucidated by electro‐kinetic analysis and ex/in situ physicochemical characterizations. This study opens a new avenue for designing hard carbon anodes with engineered crystalline lattices toward practical PIBs.