Enhanced Electrochemical Storage Properties of Na- and Mg- Intercalated B-Doped-Graphene Based Heterostructures and Bilayers

Modern technology requires novel materials to develop efficient storage systems, which offer high storage capacities and charging/discharging rates while maintaining good mechanical stability and cyclic lifetime. The extended surface areas in the lightweight two-dimensional (2D) materials are useful to achieve a high gravimetric capacity. Among various 2D materials, Ti2CO2 and B-doped graphene (approximate to 8%) were selected because of their low molecular weight and good electrical conductivity. Highly abundant Na and Mg are convenient to lower the production cost of ion storage. In this study, we performed first-principles calculations to examine the suitability of Na and Mg intercalation in Ti2CO2/B-doped-graphene (B-Gr) heterostructures and B-Gr bilayers. Even though Na- and Mg-intercalated bare graphene bilayers are not energetically stable, our studies reveal that (B-Gr) bilayers facilitate the storing of those ions. As a consequence of smaller atomic size, Mg-intercalated systems show low structural deformations and interlayer distance change (<= 0.5 angstrom) and low in-plane lattice constant change (<= 0.1%), indicating good mechanical stability during the charging/discharging process. The considered bilayers provide higher capacities than MXene-based heterostructures. Na- and Mg-intercalated Ti2CO2/B-Gr systems allow 240.4 and 295.1 mA h/g storage capacities, respectively. In comparison, the calculated gravimetric storage capacities for Na- and Mg-intercalated B-Gr bilayers are 283.8 and 320.6 mA h/g, respectively. All ion-intercalated systems provide average voltages greater than 0.75 V. Our diffusion barrier calculations revealed that very low diffusion barriers, as small as 0.18 eV, are expected for the Na-intercalated systems, offering fast charging/discharging rates for battery applications.