Structure and Conductivity of Li3/8Sr7/16−xAxZr1/4Nb3/4O3 (A = Ca, Ba) Li-ion Solid Electrolytes

Li 3/8 Sr 7/16− x A x Zr 1/4 Nb 3/4 O 3 (A = Ca, Ba) ceramics were prepared by the conventional solid-state reaction method. The structures of prepared ceramic materials changed from cubic perovskite to tetragonal tungsten bronze with increasing barium (Ba) content as indicated by the x-ray diffraction (XRD) patterns. Li 3/8 Sr 7/16− x Ba x Zr 1/4 Nb 3/4 O 3 ( x = 0.05, 0.10) samples are mixtures of perovskite and tetragonal tungsten bronze phases. Calcium ions (Ca 2+ ) can partially occupy the Sr sites, and thus the cubic perovskite structure remains intact. However, an unknown phase could form because of a complete substitution of Ca for Sr; the ionic conductivity measured by the alternating-current impedance spectra of samples decreases with increasing Ba and Ca content. Parent Li 3/8 Sr 7/16 Zr 1/4 Nb 3/4 O 3 exhibits the highest ionic conductivity of 1.23 × 10 −5 S cm −1 at 25°C. Additionally, a half cell of LiFePO 4 /Li performed well in charge–discharge experiments, retaining a discharge capacity of 87.9 mAhg −1 after 300 cycles when Li 3/8 Sr 7/16 Zr 1/4 Nb 3/4 O 3 was selected as the solid electrolyte separator.