Releasing Free Radicals in Precursor Triggers the Formation of Closed Pores in Hard Carbon for Sodium‐Ion Batteries

Abstract

Increasing closed pore volume in hard carbon is considered to be the most effective way to enhance the electrochemical performance in sodium‐ion batteries. However, there lack of systematic insights into the formation mechanisms of closed pores at molecular level. In this study, a regulation strategy of closed pores via adjustment of the content of free radicals is reported. Sufficient free radicals are exposed by part delignification of bamboo, which is related to the formation of well‐developed carbon layers and rich closed pores. In addition, excessive free radicals from nearly total delignification lead to more reactive sites during pyrolysis, which competes for limited precursor debris to form smaller microcrystals and therefore compact the material. The optimal sample delivers large closed pore volume of 0.203 cm3 g−1, which leads to high reversible capacity of 350 mAh g−1 at 20 mA g−1 and enhanced Na+ transfer kinetics. This work provides insights into the formation mechanisms of closed pores at molecular level, enabling rational design of hard carbon pore structures.This article is protected by copyright. All rights reserved

Simultaneously enabling superior ICE and high rate/cycling stability with a hollow carbon nanosphere anode for sodium-ion storage

“…The strategies for developing low defects and closed pores in HCs include tightening of pore width via selective chemical vapor deposition (CVD), 19,20 templating with metal species, 21–23 chemical etching of precursors, 24,25 chemical activation, 26,27 and regulation of pyrolysis temperatures. 28,29 Some approaches involve complicated and time-consuming procedures such as template removal, chemical activation or the CVD process, and there is still plenty of room to further increase ICE to over 80%. 19,27 More importantly, it is speculated that the low-potential plateau region demonstrates sluggish kinetics and large volume variation owing to diffusion-limited intercalation and pore filling, giving rise to inferior rate and cycling performance.…”

“…83.6 mA h g −1 at 1 A g −1 and 79.5 at 0.5 A g −1 ). 28,32 Consequently, the trade-off between ICE and rate/cycling stability remains challenging and becomes an impediment to the practical applications of HCs. We envisage that rational engineering of microstructures, by combining the manipulation of low defects, enriched closed pores and nanoarchitecture in a simple approach, could overcome the current intractable paradox.…”

Heteroatom doping-induced formation of closed pores for high-performance sodium storage hard carbon anodes

“…The rough morphology provides a large specific surface area, which can provide more reactive sites. 20,21 Similarly, RF resin spheres are very homogeneous and well dispersed with smooth surfaces (Fig. S2a and b, ESI†), and the morphology of CDRF without heteroatom doping is also unchanged after carbonization (Fig.…”