Enhanced Na storage performance through in situ depolymerization–repolymerization in bamboo-derived hard carbon anodes

Abstract

Producing hard carbons from lignocellulosic precursors has been acknowledged as a development direction for sodium-ion battery anodes. However, the recalcitrant nature of lignocellulosic precursors, due to their tightly crosslinked structure, hinders the formation of sufficient closed pores, which inherently limits the performance capability of hard carbons. Herein, we demonstrate that diammonium hydrogen phosphate-assisted in situ depolymerization of bamboo, followed by repolymerization, enables the formation of abundant closed pores in hard carbons. The presence of diammonium hydrogen phosphate not only accelerates the depolymerization of three major fractions within bamboo to release a wealth of free-radical fragments but also triggers the formation of curved carbon layers during the carbonization process. The folding of such layers and the coalescence of nanopores inclined to form a uniform gradient microporous structure ranging from 0.42–0.70 nm to 0.70–1.10 nm, which enhances active surface accessibility and improves sodium ion diffusion kinetics in the plateau region. The optimized HC-20 sample, as an anode material, delivers a high reversible capacity of 352.4 mA h g⁻¹ at 30 mA g⁻¹ and excellent rate capability by retaining 205.8 mA h g⁻¹ at 1000 mA g⁻¹. This work presents a versatile approach to utilize low-cost lignocellulosic precursors to produce high-capacity and high-rate anodes for sodium ion batteries.