A Complex Investigation of LATP Ceramic Stability and LATP+PVDF Composite Membrane Performance: The Effect of Solvent in Tape-Casting Fabrication

Redox flow batteries (RFBs) are a prospective energy storage platform to mitigate the discrepancy between barely adjustable energy production and fluctuating demand. The energy density and affordability of RFBs can be improved significantly through the transition from aqueous systems to non-aqueous (NAq) due to their wider electrochemical stability window and better solubility of active species. However, the NAqRFBs suffer from a lack of effective membranes with high ionic conductivity (IC), selectivity (low permeability), and stability. Here, we for the first time thoroughly analyse the impact of tape-casting solvents (dimethylformamide—DMF; dimethylsulfoxide—DMSO; N-methyl-2-pyrrolidone—NMP) on the properties of the composite Li-conductive membrane (Li1.3Al0.3Ti1.7(PO4)3 filler within poly(vinylidene fluoride) binder—LATP+PVDF). We show that the prolonged exposure of LATP to the studied solvents causes slight morphological, elemental, and intrastructural changes, dropping ceramic’s IC from 3.1 to 1.6–1.9 ∙ 10−4 S cm−1. Depending on the solvent, the final composite membranes exhibit IC of 1.1–1.7 ∙ 10−4 S cm−1 (comparable with solvent-treated ceramics) along with correlating permeability coefficients of 2.7–3.1 ∙ 10−7 cm2 min−1. We expect this study to complement the understanding of how the processes underlying the membrane fabrication impact its functional features and to stimulate further in-depth research of NAqRFB membranes.