All-organic non-aqueous redox flow batteries with advanced composite polymer-ceramic Li-conductive membrane

• Composite PVdF+45 wt.% LAGTP membrane was fabricated, characterized and tested. • Membrane shows high ionic conductivity 2.7•10 −4 s cm −1 and moderate permeability 3.6•10 −6 cm 2 min −1 . • Promising battery characteristics were obtained: CE = 97%, VE = 53%, EE = 51%. • Capacity of 37 mA h L − 1 (70% of theoretical value) was stable during 50 cycles. Composite membranes based on polyvinylidene fluoride (PVdF) binder and Li 1.4 Al 0.4 Ge 0.2 Ti 1.4 (PO 4 ) 3 (LAGTP) ceramic filler as prospective solid electrolytes for non-aqueous redox flow batteries were investigated. Membrane fabrication details and thorough material characterization is provided to show improved performance. Studied membranes possess high Li-ion conductivity of (2.7 ± 0.6)•10 −4 S cm −1 , uniform microstructure, and excellent stability towards acetonitrile. Moreover, a new redox flow battery configuration is demonstrated with designed composite membranes in all-organic non-aqueous redox flow batteries. For the comparison, commercial Neosepta AHA anion-exchange membranes were evaluated. Triarylamine-based catholyte and viologen-based anolyte materials, which were recently designed in our laboratory, were used as redox couples. The comparison revealed lower resistance, but faster crossover of composite PVdF + LAGTP membrane (permeability rates < 10 -5 cm 2 min -1 ); still, this is considered as acceptable for application in flow batteries. H-cells assembled with novel composite membrane exhibit Coulombic efficiency of over 97% and high charge-discharge cycling stability: after the initial 15 cycles, the capacity stabilized at 37 mA h L − 1 corresponding to 70% utilization of active materials. The membrane proposed exhibits a beneficial combination of functional characteristics that allows considering it as a credible alternative to the contemporary available polymeric commercial membranes for all-organic redox flow batteries.