Novel Structural Design and Adsorption/Insertion Coordinating Quasi‐Metallic Na Storage Mechanism toward High‐performance Hard Carbon Anode Derived from Carboxymethyl Cellulose

Abstract

AbstractHard Carbon have become the most promising anode candidates for sodium‐ion batteries, but the poor rate performance and cycle life remain key issues. In this work, N‐doped hard carbon with abundant defects and expanded interlayer spacing is constructed by using carboxymethyl cellulose sodium as precursor with the assistance of graphitic carbon nitride. The formation of N‐doped nanosheet structure is realized by the CN• or CC• radicals generated through the conversion of nitrile intermediates in the pyrolysis process. This greatly enhances the rate capability (192.8 mAh g−1 at 5.0 A g−1) and ultra‐long cycle stability (233.3 mAh g−1 after 2000 cycles at 0.5 A g−1). In situ Raman spectroscopy, ex situ X‐ray diffraction and X‐ray photoelectron spectroscopy analysis in combination with comprehensive electrochemical characterizations, reveal that the interlayer insertion coordinated quasi‐metallic sodium storage in the low potential plateau region and adsorption storage in the high potential sloping region. The first‐principles density functional theory calculations further demonstrate strong coordination effect on nitrogen defect sites to capture sodium, especially with pyrrolic N, uncovering the formation mechanism of quasi‐metallic bond in the sodium storage. This work provides new insights into the sodium storage mechanism of high‐performance carbonaceous materials, and offers new opportunities for better design of hard carbon anode.