Anions induced evolution of Co3X4 (X = O, S, Se) as sodium-ion anodes: The influences of electronic structure, morphology, electrochemical property

Abstract

Sodium-ion batteries (SIBs) are regarded as a promising candidate for large-scale energy storage applications, however, its sluggish sodiation kinetics limit high power capabilities. First-principles density functional theory (DFT) calculations demonstrates that the replacement of large anions, within a Co3X4 (X = O, S, Se) complex, can facilitate electron transfer through the reduction of the energy band gap (Eg) and the regulation of structural, electronic and bonding properties of Co-X, suggesting that the substituted Co3X4 in the following order O < S < Se can provide enhanced Na-storage capability. Accordingly, Co3X4 have been successfully designed, in which the selection of anions induces the evolution of microstructure, creating an enhancement of specific surface area with the effective introduction of defects. Note that the similar phys/chemical properties of anions within the Co3X4 possess analogous conversion mechanisms, further confirmed by in-situ XRD. Quantitative kinetics analysis reveals that the levels of the surface-dominated redox behaviors are greatly promoted by the decreased binding energy of Na2X (Na2O > Na2S > Na2Se) with the increased active sites, which are paramount for electrochemical properties. The work in this article sheds light on the in-depth understanding of the improved sodium-storage behavior with the advancing VI group anions and provides an effective strategy for the design of high-rate electrode materials for SIBs.