Wide Range Temperature Sensitivity Of Charge/discharge Efficiency Of Lead Flow Battery And Its Attenuation Mechanism

Turning the unsteady wind and solar power generation into a steady-state electric energy output will affect the transformation of my country’s energy consumption structure and realize the goal of "carbon peak and carbon neutrality".Among them,the indispensable and important link is the energy storage system that has the characteristics of large capacity,low cost,long life,and deep cold/high temperature service around wind and solar power plants.Due to the fact that the reversible reaction kinetics of the positive electrode PbO2/Pb2+ of lead flow battery is more sensitive to high and low temperature than those of the negative electrode Pb2+/Pb,and the slowing escape kinetics of the gas produced by the side reaction below 0℃ cause the defects on deposits,the lead flow battery still cannot satisfy the requirements of energy storage for my country’s wind and solar power plants due to the fluctuation of temperature between day and night of-40～50℃ in the four seasons.If its sensitivity to ambient temperature can be clarified and further develop an energy storage technology whose cycling efficiency little affected by the fluctuation of wide range temperature,the lead flow battery is expected to meet the requirements of high-temperature/cryogenic service of the energy storage systems.In view of above scientific and engineering problems,the high/low temperature charge/discharge performance,sensitivity mechanism and desensitization methods of lead flow batteries are systematically investigated from the physicochemical properties of electrolyte,electrode reaction process and positive/negative electrode deposition layers.The results are obtained as followed:(1)The charge/discharge efficiency of battery with Pb(CH3SO3)2/CH3SO3H electrolyte is examined in the temperature range of-20～50℃.Its coulombic efficiency rises continuously from-20℃ to 30℃.Contrarily it continuously decreases from 30℃ to 50℃.The highest coulombic efficiency,96.6%,is achieved at 30℃.The sensitivity law is clarified that the appearance of inflection point is due to the reversibility of positive and negative redox reaction weakened at high temperature(≥40℃),and pore defects in the positive/negative electrode deposition layers and the slowing ion diffusion rate at low temperature(≤0℃).The voltage efficiency continuously increases from 67.2%at-20℃ to 91.0%at 50℃ since the polarization overpotential decreases with the increase of temperature.It is laid the foundation for the following study on sensitivity mechanism and desensitization technology.(2)From the perspective of the electrode reaction process and the properties of the positive/negative electrode deposition layers,the high/low temperature sensitivity mechanism of charge/discharge efficiency is studied.It has been found that the redox reversibility,polarization overpotential,charge transfer resistance and deposition layer composition of the positive electrode couple of PbO2/Pb2+are more sensitive to temperature than those of the negative electrode couple of Pb2+/Pb over the temperature range of-20～50℃.The weatherability of battery is mainly affected by the positive electrode reaction of PbO2/Pb2+.Further research reveals that the electrochemical polarization overpotential is the key factor for the positive PbO2/Pb2+,whose reversibility is more sensitive to temperature.The ratio ofα-PbO2 in the positive electrode PbO2 and the content of lattice O,etc.increases with decreasing temperature,and the redox activity of positive deposition layers are improved,but the diffusion of Pb2+ during electrode reaction significantly slow down with decreasing temperature,and the continuous increase of the electrochemical reaction impedance results in a rapid increase of electrode potential,and the limit current density and the exchange current density are significantly reduced,the electrode reaction kinetics weakened significantly.It is found that the slowing of electrode reaction kinetic process has a greater impact on the charge/discharge performance of battery at wide range temperature than the improvement of the activity of deposition layers.The battery’s weatherability are also mainly affected by the electrode reaction kinetics.(3)Based on the sensitive mechanism,the desensitization technology of the battery’s charge/discharge efficiency at high and low temperature are studied.It has been found that hydrogen evolution reaction can be inhibited by increasing the concentration of Pb2+ at high temperature,and the polarization can be reduced by increasing the concentration of H+at low temperature.The high and low temperature sensitivity of the electrode reaction can be weakened by optimizing the contents of Pb2+ and H+.the electrochemical polarization overpotential can be increased by constant voltage charging mode at high temperature and constant current charging mode at low temperature.Thus the high and low temperature sensitivity of the PbO2 deposit activity can be attenuated using the different charging mode.In order to break through the limit of-20℃,HBF4,HClO4 and CF3SO3H with high electronegativity ions F-and Cl-are selected as high phase transition entropy electrolytes in the next work.It has been found that the impedance of the electrode reaction in Pb(BF4)2/HBF4 electrolyte can be decreased over the low temperature range of-40～0℃.The degree of polarization is reduced.Coulombic efficiency of 94.6 ± 1.3%is achieved due to the low hydrogen evolution potential and the high oxygen evolution potential.However,the graphite electrode is seriously corroded due to the high corrosion current density over the high temperature range of 30～50℃.Corrosion failure of the electrode leads to degradation of the battery’s charge/discharge performance.It exhibits the lower efficiency in Pb(BF4)2/HBF4 electrolyte than in Pb(CH3SO3)2/CH3SO3H electrolyte.(4)A mixed-acid electrolyte with synergistic adsorption of CH3SO3H and HBF4 is utilized to investigate the desensitized ability and mechanism to the high and low temperature(-40～50℃).It has been found that the charge transfer resistance can be lowered due to the strong hydrolysis of HBF4,and the reaction activation energy can be lowered due to the surface adsorption of HBF4 at low temperature.The reduction of side reaction of hydrogen evolution and oxygen evolution is beneficial for the electrodeposition of high-quality PbO2.At high temperature,the high stability of CH3SO3H inhibits the ionization of HBF4 and CH3SO3H and maintains a stable content of free H+in the electrolyte,avoiding excessive corrosion current density that causes the corrosion and failure of the graphite electrode.In the mixed acid electrolyte of 1 M Pb(CH3SO3)2+0.4 M CH3SO3H+1.6 M HBF4,coulombic efficiency of the battery is maintained at 87.3%～95.1%over the temperature range of-40～50℃.The energy efficiency is higher than 74%.The lead flow battery exhibits an excellent weatherability.