An article titled “NASICON-type La³⁺substituted LiZr₂(PO₄)₃ with improved ionic conductivity as solid electrolyte” authored by V. Ramar, S. Kumar, S.R. Sivakkumar and P. Balaya, has been accepted for publication in Electrochimica Acta.  [DOI: 10.1016/j.electacta.2018.03.115]

Abstract

NASICON-structured Li_1+xZr_2-xLa_x(PO₄)₃ (x = 0–0.2) solid electrolytes are prepared by sol-gel method. The influence of substitution of La³⁺ for Zr⁴⁺ on the ionic conductivity, morphology, and structure of the parent compound LiZr₂(PO₄)₃ (LZP) is investigated. Rietveld refinement of powder x-ray diffraction data reveals that the La³⁺ substitution stabilizes the LZP in the highly conducting rhombohedral Rc phase at room temperature. La³⁺ substituted LZP display enhanced ionic conductivity, showing the highest ionic conductivity of 0.72 × 10⁻⁴ S/cm at room temperature for the composition Li_1.1Zr_1.9La_0.1(PO₄)₃. The improvement in conductivity of LZP with another aliovalent substituent, Mg²⁺, whose ionic radii is similar to Zr⁴⁺ (0.72 Å) is also investigated. Further, the activation energy decreases from 0.53 eV for the parent LZP to 0.42 eV for x = 0.1 La³⁺ substituted LZP. Lithium-ion transference number obtained by direct current polarization for Li_1.1Zr_1.9La_0.1(PO₄)₃ is 0.99, confirming the high ionic conducting nature of the solid electrolyte. Cyclic voltammetry recorded for Li_1.1Zr_1.9La_0.1(PO₄)₃ shows electrochemical stability window up to ∼4.0 V vs. Li. In particular, La³⁺ substituted NASICON-type LZP (x = 0.1) exhibits good chemical and structural stability after exposing to air, water, Li metal, acidic and basic solutions.