Research On Synthesis, Characterization And Electrochemical Properties Of Na₂FeO₄ Thin Film Electrode

Ferrate is a new general of electrodes materials with advantages of environmental advantage, low cost and high capacity. When using in Li-ion battery(LIB), ferrate electrodes show high initial capacity, however the cyclic performance is problematic. By electrodepositing a thin film electrode, the electrochemical properties are improved.In this paper, Nas2FeO4 solution was synthesized by electrolysis method, then thin film electrode was electrodeposited on the Pt base in such a solution system. XPS and SEM were given to characterize the film electrodes. The SEM result showed morphology of thin film was different when the electrodeposited potential changed. The XPS result indicated the film was mainly FeOOH. Cycle voltammetry and galvanostatic charge/discharge cycles were tested to describe the electrochemistry properties. The CV result indicated the film is electrochemical active in LIB system. The effect of electrodeposited potential, electrolyte system, charge/discharge rate was studied. When electrodeposited potential of -0.6V (vs. Ag/AgCl), electrolyte system of 1mol/L LiClO4/PC+DME(1:1), after 20 cycles capacity fade, the galvanostatic charge/discharge capacity keeped 300mAh/g in the following 150 cycles.The mechanism of thin film electrode in LIB system was explored though the EQCM technology. The thin film was electrodeposited on the quartz Au electrode by the similar method as on Pt base, and the calculated result with mass change and charge indicated the product is FeOOH, but the efficient of electrodeposited was not 100%. By a sim-LIB system with the thin film electrodes based on quartz Au electrode, the CV coupled with EQCM was tested to describe the electrochemical properties. The result showed there were both lithiation/delithiation of Li-ion and deposit/dissolve of SEI actions in the full potential area. In 3.0V to 4.0V of cathodic and anodic progress, the action current was nearly 0. And in 2.2V to 2.6V of cathodic progress and 2.0V to 2.3V of anodic progress, the measured mass change per mole electron (mpe)value indicated the lithiation/delithiation of Li-ion was the only action, while in other area, both actions were happened. In continuous several cycles, the mass change after a full cycle was minus, showed that the rate of SEI founding is low. The effect of SEI is minus after several cycles. When scan rate was 10mV/s, the measured mpe increased in some potential area, meaned that the proportion of current use for the deposit/dissolve of SEI is higher in slow scan rate. The existence of non- lithiation/delithiation of Li-ion is the main reason of the phenomenon that discharge capacity is more than the charge capacity.