Enhancing the Charge Transportation Ability of Yolk–Shell Structure for High-Rate Sodium and Potassium Storage
Yi Zhao, Xiuling Shi, Samuel Jun Hoong Ong, Qianqian Yao, Bingbing Chen, Kun Hou, Chuntai Liu, Zhichuan J. Xu, Lunhui Guan
Abstract
The microstructure of large-capacity anodes is of great importance in determining the performance of sodium- and potassium-ion batteries. Yolk–shell nanostructures promise excellent structural stability but suffer from insufficient charge transfer rate during cycles. Herein, we tackle this challenge by constructing a single-walled carbon nanotube (SWNT) internally bridged yolk–shell structure, inside which SWNTs cover the surface of the yolk and connect the yolk and shell, for better electron/ion transportation. Combining the merits of both yolk–shell structure and conductive SWNT channels, the as-prepared Fe1–xS/SWNT@C composite manifests high reversible capacity and ultralong cycling stability up to 8700 cycles. Moreover, it displays the best rate capability (317 mA h g–1 at 20 A g–1 for Na+ and 236 mA h g–1 at 10 A g–1 for K+) among the reported yolk–shell structures and iron-sulfide-based anodes thus far. The kinetic analysis and density functional theory calculations further reveal that the Fe1–xS/SWNT heterointerface can effectively enhance the reversibility of K+ storage and decrease the K+ diffusion energy barrier, leading to excellent pseudocapacitive behavior and fast ion transportation for outstanding rate capability.