In Situ Revealing the Electroactivity of PO and PC Bonds in Hard Carbon for High‐Capacity and Long‐Life Li/K‐Ion Batteries

Abstract The low capacity and unsatisfactory rate capability of hard carbon still restricts its practical application for Li/K‐ion batteries. Herein, a low‐cost and large‐scale method is developed to fabricate phosphorus‐doped hard carbon (PHC‐700) by crosslinking phosphoric acid and epoxy resin and followed by annealing at 700 °C. H 3 PO 4 acts not only as a crosslinker to solidify epoxy resin for promoting the degree of graphitization and lowering the specific surface area, but also as phosphorus source for forming PC and PO bonds, thus providing more active sites for Li/K storage. As a result, the PHC‐700 electrode delivers a highly reversible capacity of 1294.8 mA h g −1 at 0.1 A g −1 and a capacity of 214 mA h g −1 after 10 000 cycles at 10 A g −1 . As for potassium‐ion batteries, PHC‐700 exhibits a reversible capacity of 381.9 mA h g −1 at 0.1 A g −1 and a capacity of 260 mA h g −1 after 1000 cycles at 0.2 A g −1 . In situ Raman and in situ NMR measurements reveal that the P‐containing bonds can enhance the adsorption to alkali metal ions, and the PC bond can participate in electrochemical redox reaction by forming Li x PC y . Additionally, P‐doped hard carbon shows better structural/interfacial stability for improved long‐term cycling stability.