Dynamic behavior on multi-stage sodium storage in disordered carbon

Abstract

The structural complexity and heterogeneity of disordered carbons give rise to significant challenges in elucidating the sodiation mechanism in them. Herein, by means of a precisely controlled gaseous corrosion strategy, disordered carbon samples with tailored local structures are prepared elaborately so that we are able to unravel the sodium storage explicitly in such materials. In terms of results, a multi-stage sodium storage model comprising “physical adsorption - chemical interaction –(solid phase diffusion) - sodium cluster filling” is proposed. This work is the first to highlight the critical role of “solid phase diffusion” as an essential kinetic bridge, which is activated upon the saturation of defect sites and functional groups and governs the initial stage of sodium cluster formation within closed pores. Furthermore, our study reveals that sodium storage mechanisms are related to structures of disorder carbon materials, dictated by their defect concentrations, types and spatial distributions. It is demonstrated that a superior disordered carbon anode for a sodium ion battery necessitates an elaborate balance between abundant closed pores and moderate monovacancy-type defects so as to possess good capacity, rate performance and initial coulombic efficiency. With balanced features, the disordered carbon sample delivers a high reversible capacity of 367.1 mA h g^-1, and the full cell achieves an energy density of 307.7 Wh kg⁻¹ while maintains 95.1 % capacity retention after 160 cycles. This research advances the understanding of sodium storage and provides new insights for engineering next-generation high-performance carbon anodes for sodium ion batteries.