Hierarchical Flower-Like Porous Carbon Nanosheets with Richly Exposed (002) Planes for High-Performance Sodium–Ion Batteries
Zhenqian Wu, Xianwei Li, Xudong Ma, Ling Xin, Zhijian Huang, Xiao Yu, Yong Liu
Abstract
Hard carbon is the most promising anode material for sodium–ion batteries (SIBs). However, its electrochemical performance is still unsatisfactory, especially at high-current densities. Herein, we propose a self-assembly strategy to synthesize hierarchical flower-like hard carbon nanosheets with richly exposed (002) planes (HFHCN) and combined micro- and mesopores, which provide more storage sites and faster reaction kinetics than the commercial hard carbon microspheres without pores (CHCM), resulting in better electrochemical performance, especially at high-current densities. The HFHCN electrode achieved a higher charge capacity (390.8 mA h g –1 at 0.02 A g –1 ) and better rate capability (104.8 mA h g –1 at 2.0 A g –1 ). With increasing current densities, the HFHCN electrodes maintain an almost unchanged initial Coulomb efficiency and electrochemical polarization and a slowly decreasing charge capacity at the low-voltage plateau, whereas the CHCM electrode shows a drastically deteriorated performance in these aspects. A turning point for their significant difference in electrochemical performance occurs at 0.5 A g –1, where the charging capacity at the low-voltage plateau is 72 mA h g –1 for the HFHCN electrode, but 0 for the CHCM electrode. When matched with the NVP (Na 3 V 2 (PO 4 ) 3 ) cathode, HFHCN∥NVP full-cells show a higher initial discharge capacity (273.5 mA h g –1 at 0.1 A g –1 ) and better rate performance (63.2 mA h g –1 at 5 A g –1 ) than those of the CHCM∥NVP full-cell (180.2 mA h g –1 at 0.1 A g –1 and 2.8 mA h g –1 at 5 A g –1 ). In addition, HFHCN∥NVP full-cells also have a longer operating plateau and lower electrochemical polarization than the CHCM∥NVP full-cell, which are also the main factors contributing to the higher energy density.