Study On The Independent Preparation Of The ?/?-PbO₂ From Positive Electrode Of Lead-acid Flow Battery And Its Electrochemical Performance

The development of the stable, reliable and low-cost equipment of energy storage is the main technical approach to establish the micro grid system so as to realize local consumption of renewable energy. Lead-acid flow battery is highly concerned due to the reversible oxidation-reduction characteristics of Pb²⁺ and the structural design of proton exchange membranes. However,the incomplete reduction of PbO₂ of the battery and the loose of its crystal particles in the discharge process lead to the loss of the battery, which greatly reduces the efficiency and life of the battery. Thus, this paper first studied the influence law of H+concentration, temperature and sedimentary current density on the crystal form of PbO₂ of the positive sediment in the methanesulfonic acid solution system, and by controlling the deposition conditions, the ?-PbO₂, ?-PbO₂ and mixed sediments with specific crystal proportion were prepared to investigate the discharge capacity, conductivity as well as intergranular stress of different sediments as positive active materials. Meanwhile the effect of these properties on the discharge capacity and intergranular bonding force of the active sedimentary layer were compared, and optimizing the best crystal ratio of PbO₂ as the active material of positive electrode in order to improve the coulombic efficiency and energy efficiency of the lead methanesulfonic flow battery.The results showed that: ?1? By controlling the concentration of H+, temperature and current density of the solution in the electrodeposition conditions, ?-PbO₂, ?-PbO₂ and different ratios of two-phase mixed sediments can be obtained. The increase of H+ concentration and current density all improve the overpotential of the electrodeposition, which lead a transition of the sediments from the single phase of ?-PbO₂ to the mixed phase of ?-PbO₂ and ?-PbO₂, and the increase of temperature accelerates the mass transfer process and promotes the formation of?-PbO₂. ?2? With the increase of the current density, it promotes the growth of PbO₂ crystal and the increase of its grain size. ? 3 ? The discharge capacity of ?-PbO₂ is two times that of ?-PbO₂,whose coulombic and energy efficiency are 20% higher than that of ?-PbO₂. While during thirty times of cyclic charge and discharge process, the stability of coulombic efficiency of?-PbO₂ is higher than that of ?-PbO₂. Compared to the other three kinds of positive active material of PbO₂, the discharge capacity reaches the highest when the mass ratio of ?-PbO₂ and?-PbO₂ in the mixture is 2:8, and at this time, the coulombic efficiency of cyclic charge and discharge as well as energy efficiency also reach the highest of 95% and 76% respectively with a good cyclic stability as well. ?4? The charge-transfer resistance of ?-PbO₂ is the minimum which is easier to be dissolved electrochemically, the mixture of ?-PbO₂ and ?-PbO₂ with a mass ratio of 2:8 takes the second place and that of ?-PbO₂ is the maximum.However, the oxygen exchange current density of the mixture is the least which is hard for oxygen evolution,?-PbO₂ takes the second place and that of ?-PbO₂ reaches the highest. ?5?The mixed deposition layer with a mass ratio of 2:8 of ?-PbO₂ and ?-PbO₂ is no crack, small internal stress and tight bonding between grains, and the loss of active substances in the discharge process is the least.Therefore.the mixed deposition layer of ?-PbO, and ?-PbO₂ with a mass ratio of 2:8 has the best comprehensive performance.