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. Li1+x+y Al x Ti2−x Si y P3−y O12 (x = 0.1, 0.3/y = 0.2, 0.4) nanopowders were prepared by LF-FSP with a primary focus on the effects of Al0.3/Si0.4 doping on conductivities. Furthermore, the effects of excess Li2O on Al0.3/Si0.4 doped materials were studied. Li1.7Al0.3Ti1.7Si0.4P2.6O12 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%.