Computational screening and first-principles investigations of NASICON-type LixM2(PO4)3 as solid electrolytes for Li batteries

Abstract

Li-containing NASICONs (Na super ionic conductors) usually have high ionic conductivity and can serve as solid electrolytes for Li batteries. In this work, we screened the Materials Project database and found seven kinds of Li_xM₂(PO₄)₃ (M = Bi, Ge, In, Mo, Sb, Sc, and Zr) which could be applied as solid electrolytes for Li batteries. The most thermodynamically stable phases of each series of Li_xM₂(PO₄)₃ were investigated through density functional theory computations. The results indicate that all these materials are wide-band-gap semiconductors with the band gap ranging from 3.55 to 4.88 eV. Meanwhile, the width of their electrochemical window is not directly related to the band gap; instead, it is mainly determined by the chemical potential of Li ions in these materials. Ab initio molecular dynamics simulations indicate that NASICONs with more Li ions or monoclinic symmetry possess higher Li ion conductivity at room temperature, among which Li₃Bi₂(PO₄)₃ has the highest conductivity of ∼10⁻³ S cm⁻¹. Comprehensively considering the stability, the width of the electrochemical window, the band gap and the ionic conductivity, we propose that Li₃Sc₂(PO₄)₃ could be a very promising solid electrolyte for Li batteries.