Rational Design of Biaxial Tensile Strain for Boosting Electronic and Ionic Conductivities of Na2MnSiO4 for Rechargeable Sodium-Ion Batteries

Using first-principles calculations, biaxial tensile (epsilon=2 and 4 %) and compressive (epsilon=-2 and -4 %) straining of Na2MnSiO4 lattices resulted into radial distance cut offs of 1.65 and 2 angstrom, respectively, in the first and second nearest neighbors shell from the center. The Si-O and Mn-O bonds with prominent probability density peaks validated structural stability. Wide-band gap of 2.35 (epsilon=0 %) and 2.54 eV (epsilon=-4 %), and narrow bandgap of 2.24 eV (epsilon=+4 %) estimated with stronger coupling of p-d sigma bond than that of the p-d pi bond, mainly contributed from the oxygen p-state and manganese d-state. Na+-ion diffusivity was found to be enhanced by three orders of magnitude as the applied biaxial strain changed from compressive to tensile. According to the findings, the rational design of biaxial strain would improve the ionic and electronic conductivity of Na2MnSiO4 cathode materials for advanced rechargeable sodium-ion batteries.