Composite A2M6O13 anodes (A = Li, Na; M = Ti, Zr) for Li–Na dual cation batteries: a theoretical investigation

Abstract

The development of advanced anode materials is critical for improving the efficiency and durability of alkali-ion batteries. In this study, large-scale molecular dynamics simulations are employed to investigate the transport properties of A₂M₆O₁₃ (A = Li, Na; M = Ti, Zr) compounds in mono-, bi-crystalline and composite forms. Grain boundaries exert a decisive influence on ion migration in enhancing Na⁺ mobility in bi-Na₂Zr₆O₁₃ but slightly restrict transport in bi-Na₂Ti₆O₁₃. Composite architectures integrating both Li- and Na-based phases (Li₂Zr₆O₁₃@Na₂Ti₆O₁₃, LZNTO; Li₂Ti₆O₁₃@Na₂Zr₆O₁₃, LTNZO) exhibit superior conductivity compared to Na-only counterparts, underscoring the higher intrinsic mobility of Li⁺ ions. Population-weighted mean square displacement analysis confirms that effective diffusivity and conductivity in dual-cation composites are mathematically equivalent to the sum of species-resolved contributions, thereby capturing simultaneous transport effects. Of the studied systems, Na₂Ti₆O₁₃ demonstrates excellent Na⁺ transport with the lowest activation energy, while Li-containing composites achieve moderate conductivity through synergistic Li⁺/Na⁺ migration. These findings provide evidence of synchronized transport in dual-cation titanate/zirconate composites, establishing LZNTO and LTNZO as promising anode candidates for next generation Li–Na dual-cation battery systems.