Feasibility of Phase Immersion Precipitation for the Application of Electrode Production: A Literature & Parameter study.
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To attain high accessible amounts of active material in electrodes of aqueous batteries, this thesis investigates the possibility to create porous structures by introducing a simple low-cost production method for polymeric supports solidifying active material, without applying heat nor pressure. This technique is based on phase inversion activated by liq- uid/liquid or gas/liquid demixing. The polymerbinder used for this technique has to be resistant to chemicals, temperature- and volume changes occurring on and in the anode and yet be highly miscible in solutes to be used for phase inversion techniques as well. As a case study common used polymers, Polyvinylidene Fluoride and Polyethersulfone, and common used enhancement techniques for the production of synthetic membrane filters have been applied to create Iron Sulphide anodes. SEM and porosity analysis show that films produced by phase immersion precipitation do solidify Iron Sulphide and an open homogeneous microporous structure can be obtained with cross-section pore sizes rang- ing from 0,1-10 μm and surface pores ranging from 0,5-6 μm with a pore volume of 60 %. In comparison pore sizes ranging from 0,1-0,5 μm with a pore volume of 50 % results by using conventional pressed electrodes. Caution needs to be taken for to highly porous structures and to high amounts of insulating polymer binder as well, as both could negatively affect electronic conductivity. As a proof of principal cycling experiments of anodes produced by this novel production method for a Nickel-Iron Sulphide battery show capacities of 180 mAh/g for more than 55 cycles with an average Charge/discharge efficiency of 82 % can be obtained, by cycling between Fe(II)/Fe(III) only, to prevent the hydrogen evolution. The achievement of interesting porous structures and increase in porosity compared to conventional production techniques combined with promising cycling results suggest PI by liquid/liquid and gas/liquid demixing techniques could be an interesting production technique.