We demonstrate that liquid-feed flame spray pyrolysis (LF-FSP) processing provides non-aggregated nanopowders that can be used immediately to tape cast, producing thin films (<100 μm) of Li⁺ ion conducting membranes when sintered. Glass-ceramic or sol–gel processing methods are commonly used for such but require additional high-energy milling and/or calcining to obtain powder feedstock. Li_1+x+yAl_xTi_2−xSi_yP_3−yO₁₂ (x = 0.1, 0.3/y = 0.2, 0.4) nanopowders were prepared by LF-FSP with a primary focus on the effects of Al_0.3/Si_0.4 doping on conductivities. Furthermore, the effects of excess Li₂O on Al_0.3/Si_0.4 doped materials were studied. Li_1.7Al_0.3Ti_1.7Si_0.4P_2.6O₁₂ pellets sintered to 93–94% of theoretical density and samples with varying excess Li₂O contents all show superionic conductivities of 2–3 × 10⁻³ S cm⁻¹ at room temperature. Li₂O lowers both the crystallization temperatures and temperatures required to sinter. Total conductivities range from 2 × 10⁻³ to 5 × 10⁻² S cm⁻¹ in the temperature span of 25°–125 °C. Small grain sizes of 600 ± 200 nm were produced. Initial attempts to make thin films gave films with thicknesses of 52 ± 1 μm on sintering just to 1000 °C. Measured conductivities were 3–5 × 10⁻⁴ S cm⁻¹; attributed to final densities of only ≈88%.