Enhanced aqueous stability of Sc4N3O2 over Sc4C3O2 MXene Cathodes: Aqueous Zn ion batteries

초록

Sc-based MXenes have emerged as promising candidates for next-generation aqueous Zn ion battery (AZIB) cathodes; however, their synthesizability, aqueous stability, and electrochemical suitability remain insufficiently explored. Here, we comparatively evaluate Sc4N3O2 and Sc4C3O2, using ab initio calculations and ab initio molecular dynamics simulations. The thermodynamic stability of the corresponding MAX precursors, Sc4AlN3 and Sc4AlC3, confirms the synthesizability, while Al binding energy calculations support the feasibility of MAXto-MXene transformation. Binding energy analysis indicates that O termination is energetically preferred over F. Electronic structure analysis reveals excellent conductivity in both MXenes, with Sc4N3O2 demonstrating stronger Sc-N covalent bonding than Sc4C3O2. Both materials deliver high theoretical Zn-ion storage capacities of 844.62 and 879.15 mAh/g, respectively, exceeding those of conventional cathodes (e.g., beta-MnO2: 375 mAh/g and V2O5: 224 mAh/g). The aqueous stability is then investigated in H2O and various Zn-based electrolytes, including ZnCl2, ZnSO4, Zn(TFSI), and Zn(CF3SO3). Analysis of Sc(MXene)-O(H2O) and Sc(MXene)-Zn (electrolyte) distance evolution reveals that Sc4N3O2 maintains structural integrity across all electrolyte conditions, whereas Sc4C3O2 undergoes structural degradation in Zn(CF3SO3) and ZnSO4 electrolytes. This behavior is consistent with the stronger Sc-N bonding identified in the electronic-structure analysis, which suppresses destabilizing metal-ion interactions at the interface.

키워드