Theoretical prediction of two-dimensional metallic AM2B8 (AM = K, Rb, Cs) as anode materials for Na-ion batteries

The development of two-dimensional anode materials with superior performance is becoming a critical undertaking for the advancement of Na-ion battery technology. Using isoelectronic substitution strategies, we predicted three alkali metal borides AMB (AM = K, Rb, Cs) based on the SrB monolayer. Ab initio molecular dynamics simulations and phonon dispersion relationship calculations demonstrated their stability. Using density functional theory, we predict the feasibility of these three new metal nanosheets as anodes for Na-ion batteries. The AMB monolayer retains its metallicity after the insertion of Na ions, ensuring that the anode has good electrical conductivity. In addition, AMB has a low diffusion barrier and open circuit voltage (KB is 0.08 eV and 0.26 V) during charge/discharge. In the voltage range that inhibits dendrite growth, KB can reach the maximum theoretical specific capacity (326 mAh/g). These results indicate that AMB, especially KB, is a promising anode material for Na-ion batteries.