Layer Shape LiFePO4 Obtained by Powder Extrusion Molding as Solid Boosters for Ferro/Ferricyanide Catholyte in Semisolid Redox Flow Battery: Effect of Porosity and Shape

Powder extrusion molding is proposed to fabricate ceramic LiFePO4 layers (0.5-1.0 mm thickness) as solid booster for ferricyanide electrolyte in semisolid redox flow battery. In some extruded layers, the binder is partially decomposed, while in others it is completely removed and, afterwards, the material is sintered, so materials with different porosity and dimensions are obtained. After characterizing the materials, the kinetics for the reaction with ferricyanide is evaluated, being the binderless materials the ones which react faster and reach larger degrees of oxidation. For the material with 1.0 mm thick comparable results to the ones already published are obtained (69% capacity for LiFePO4 compared to the theoretical value). In the case of the 0.5 mm thick sintered solid, an outstanding performance is achieved, reaching almost the theoretical capacity (94%) with a very high coulombic efficiency (> 99%) at 1 mA cm(-2), results that were only obtained at much lower current densities in previous works.