Flame made nanoparticles permit processing of dense, flexible, Li+ conducting ceramic electrolyte thin films of cubic-Li7La3Zr2O12 (c-LLZO)

Abstract

Ceramic electrolytes are proposed as key components in resolving challenges extant in developing next generation, high energy density Li batteries by replacing liquid electrolytes to improve safety and performance. Among numerous candidates, c-LLZO offers multiple desirable properties: high ionic conductivities (0.1–1 mS cm⁻¹), Li stability, a wide electrochemical operating window (∼6 V) and pH stability (7–11.5). However, incorporation into prototype cells has yet to be demonstrated as c-LLZO membranes at thicknesses <50 μm have not been achieved. Processing dense, thin films matching bulk counterpart properties remains a very difficult target arising from energy and/or equipment intensive sintering, Li volatilization, and contamination from substrates. We show that using metalloorganic derived flame made nanoparticles can overcome these processing challenges resulting in a significantly reduced energy input required for densification, 10–40 fold shorter dwell times at sintering temperatures, compared to common solid state reaction derived c-LLZO. Furthermore, surface/volume ratios of the films are determined to be a critical factor affecting final microstructures and phase compositions of the sintered films. Through careful control of the processing variables, 10–15 grains thick, dense (94 ± 1%) c-LLZO thin (<30 μm), flexible films with high ambient ionic conductivities (0.2 ± 0.03 mS cm⁻¹) are achieved using conventional casting–sintering of flame made nanoparticles. These c-LLZO membranes greatly increase the selection of complementary cell components and simplify battery configurations broadening opportunities for cell designs.