In Situ Revealing the Electroactivity of PO and PC Bonds in Hard Carbon for High‐Capacity and Long‐Life Li/K‐Ion Batteries

• Published in: Advanced energy materials 2019-09, Vol.9 (34), p.n/a
• Main Authors: Qian, Yong, Jiang, Song, Li, Yang, Yi, Zheng, Zhou, Jie, Li, Tieqiang, Han, Ying, Wang, Yusong, Tian, Jie, Lin, Ning, Qian, Yitai
• Format: Article
• Language: English
• Subjects: Alkali metals; Carbon; Crosslinking; Electroactivity; Epoxy resins; Graphitization; hard carbon; in situ measurement; Interface stability; Lithium; LixPCy; NMR; Nuclear magnetic resonance; Phosphoric acid; Phosphorus; phosphorus‐containing bonds; Rechargeable batteries; Structural stability
• ISSN: 1614-6832; 1614-6840
• DOI: 10.1002/aenm.201901676

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. H3PO4 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 Lix PCy . Additionally, P‐doped hard carbon shows better structural/interfacial stability for improved long‐term cycling stability. According to in situ Raman, in situ NMR measurements, and electrochemical analysis, PC and PO bonds can enhance the adsorption of alkali metal ions, and the PC bond can participate in the electrochemical redox reaction by forming Lix PCy , accompanyied by a (de)intercalation reaction of lithium ions, which all contributes to a high capacity and an excellent rate capability.