Mixed ionic-electronic conduit of Ca2+ confined by two-dimensional multicomponent boron-carbon layers

Abstract

Mixed ionic-electronic conductor (MIEC) materials have widespread applications in fuel cells, all-solid-state battery electrode interface modification materials, and memory devices. Here, we reveal the two-dimensional superionic conduction between graphene-like B–C layers in the Ca–B–C (Ca₂BC₁₁, CaBC₅, CaB₂C₄, and CaB₃C₃) compounds. Through molecular dynamics simulations driven by high-precision machine learning potentials, which can be tuned within the range of 900–2100 K with defect concentrations as high as 4.8 %. We discovered that the vacancy mechanism between the hexagonal prism drives its superionic diffusion. The ratio of B and C within the framework can modify the covalent (ICOHP) and ionic (Bader) interactions between the compound and Ca²⁺, along with the interlayer spacing, thereby significantly influencing the superionic transition temperature. Furthermore, the superionic behavior across multiple phases obviates the need for synthesizing pure-phase materials. With excellent thermal and mechanical stability, these compounds of varying compositions are prospective candidates for high-temperature-resistant electrodes and interface enhancement materials and possess potential applications in many extreme conditions.