Unraveling structure–performance relationships: tailored d-band centers in monolayer MSi2N4 and MoSi2Z4 by atomic substitution

Abstract

This work presents the construction of a family of isostructural MSi₂N₄ (M = Cr, W, Ta, Ti, Zr and Hf) and MoSi₂Z₄ (Z = P and As) materials for establishing a d-band center optimization framework to tailor alkali metal ion battery (AMIB) anode activity through substitution strategies. We explore the influence of substituent atomic size on the structural characteristics, surface activity, mechanical properties, and electrochemical performance using first principles calculations. The results demonstrate that substituents with larger atomic volumes induce pronounced steric hindrance effects and significantly weaken the mechanical performance. Quantitative analysis of the steric hindrance effects via system energy evolution reveals the substantial impact on the applicability of the d-band center model. Notably, monolayer MSi₂N₄ exhibits superior performance compared to monolayer MoSi₂Z₄ as a promising anode. Specifically, theoretical capacities for TiSi₂N₄, ZrSi₂N₄, HfSi₂N₄, and TaSi₂N₄ are 1004.40, 790.56, 552.96, and 548.64 mA h g⁻¹, respectively, for Li storage and 632.40, 527.04, 358.40, and 365.76 mA h g⁻¹, respectively, for Na storage. This work provides valuable insights and design strategies for future anode development and identifies promising candidates for high-performance anodes in AMIBs.