Optimization And Performance Evaluation On The Moulded Electrodes For Capacitive Deionization

Capacitive deionization is a new desalination technology which accomplishesdesalination using the Flow-Through Capacitor (FTC) structure and thecharge/discharge principle. Electrode as a core component of the CDI, its performancewill directly determine the desalting effect of good or bad, therefore, it is necessary tostudy the Electrode forming process. In this paper, with poly (vinylidene fluoride) asbinder, graphite as conductive material and activated carbon powder and carbonnanotubes as active material respectively, electrodes for CDI process were preparedthrough compression modeling method. The effects of binder content, moldingpressure and thickness of the electrode on the conductivity of the electrode, thespecific capacitance, AC impedance and desalination performance was studied. Theresults show that: for activated carbon powder, as PVDF content increased from8%to18%, the conductivity is decreased, the specific capacitance and the specificadsorption volume first increases and then decreases; As the pressure increases from5MPa to25MPa, the conductivity increased, the specific capacitance and specificadsorption volume first increases and then decreases; With the thickness increase to0.16mm from0.08mm, the electrical conductivity of the electrode graduallydecreased, the specific capacitance and the specific adsorption capacity showed adownward trend, but does not reflect the continuous changes, Performance wassignificantly attenuated only in a thickness exceeding0.14mm. The best productionconditions of the activated carbon powder electrode as follows:15%of PVDF content,molding pressure of15MPa, thickness less than0.14mm, in this condition, thespecific capacitance51.68F/g, than the adsorption capacity of11.04mg/g. When theactive material is carbon nanotubes, the performance variation is same to the variationof the activated carbon electrode, but the best production conditions are different, theoptimum production conditions are:10%PVDF content, molding pressure of10MPa,thickness less than0.14mm, in this condition, the specific capacitance80.44F/g, thanthe adsorption capacity of14.14mg/g.The paper also did some exploratory study on coating molding process conditions.Special mold was designed for the coating method to produce electrode. Affect ofdrying temperature and the wet thickness to the electrode molding were studied, and investigated the influence of the binder content on the electrode performance. Withthe wet layer thickness from0.2mm to0.5mm, electrodes gradually appear dryphenomenon, the phenomenon get more obvious with the thickness of the electrodeget greater. As the drying temperature increased from50°C to80°C, the electrode dryseverity. And the influence wet layer thickness of more than the drying temperature.Produced a series of electrodes of different PVDF content in the wet layer thicknessof0.2mm and the drying temperature at50℃,studied the performance of theelectrode capacitance qualitatively, the results show that: with the PVDF contentincreased from5%to25%, the electrode of the capacitor performance declining.