Preparation Of Carbon-based Composites For The Negative Plate Of Lead-acid Batteries And Study On Their Mechanisms

In electric vehicles and hybrid electric vehicles,lead-acid batteries are operated continuously in high-rate partial-state-of-charge(HRPSoC)modes,resulting in progressive accumulation of irreversible PbS04 on the negative active mass(NAM),and therefore,the cycle life of batteries is reduced.Adding carbon materials into the negative plate can restrain its irreversible sulfation,however,the carbon materials will produce severe hydrogen evolution within the working potential range of the negative plate,which has not been well solved until now.In order to find suitable additives for the negative plate to inhibit its hydrogen evolution and prolong the HRPSoC cycle life of lead-acid batteries,various carbon-based composites were prepared and their effects on the hydrogen evolution performance of the negative plate and the HRPSoC cycle life of batteries were studied in this thesis.Based on the investigations of the involved mechanisms for different kinds of carbon-based composites,the key factors for the composites and their influence on the battery performance were determined so as to provide theoretical support to the further development of the composites for the negative plate.The main conclusions are as follows:1.Lead oxide(PbO)/carbon black(CB)composites prepared with a new pyrolysis-pickling method and their effects on the performance of lead-acid batteries.A new pyrolysis-pickling method was developed to prepare various PbO/CB composites.Compared with CB,the PbO/CB composites prepared by the pyrolysis-pickling method have higher content of alkaline surface functional groups(Calkaline)and less content of carboxyl surface functional groups(CCOOH)on CB particles which are still covered with small amount of PbO,meanwhile they have smaller BET surface area,but larger pore volume and average pore width.The hydrogen evolution process in the negative plates containing the PbO/CB composites(1%)is inhibited effectively due to the increased Calkaline on CB,while the redox processes(Pb?PbSO4)in these negative plates are accelerated obviously owing to the changes in their micro structure.The PbO/CB composites can impede the growth of PbSO4 crystals and significantly increase the HRPSoC cycle life of the simulated test cells.Among the prepared PbO/CB composites,the Pb-C-N500-50℃prepared by the 500℃ pyrolysis-50℃ pickling method has the best performance.With an increase in the content of the Pb-C-N500-50℃ in the negative plate(0.5%,1%and 2%),the BET surface area and the pore volume of the negative plate increase,but the average pore width decreases.The hydrogen evolution process in the negative plate can be effectively inhibited,while the redox processes(Pb?PbS04)are gradually accelerated.More additive particles are adsorbed on the NAM,which can inhibit the growth of PbSO4 crystals and increase the HRPSoC cycle life of these cells.2.The preparation of PbO/graphene oxide(GO)composites and their effects on the performance of lead-acid batteries.GO with super capacitor performance was introduced in the composites to prepare various PbO/GO composites using the same pyrolysis-pickling method.Compared with GO,the Pb-GO-N500-UP composite prepared by the 500℃ pyrolysis-25 ℃ ultrasonic pickling method has less content of CCOOH and nitrogen(N)atoms doped into GO layers,on which some undissolved PbO was distributed.There exist stable absorption bands between GO layers and undissolved PbO.Compared with the NAM+GO(1%)plate,the negative plate containing 1%Pb-GO-N500-UP has larger pore volume,smaller total impedance and accelerated redox processes(Pb?PbSO4),and prolongs the HRPSoC cycle life of the simulated test cell obviously.The hydrogen evolution process in the negative plate containing the Pb-GO-N500-UP can be inhibited effectively due to the doped nitrogen atoms and decreased CCOOH on GO layers.In general,the content of the undissolved PbO in the PbO/GO composites,stable absorption bands between GO layers and PbO as well as the effect of ultrasonic pickling on the composite micro structure have important influence on the HRPSoC performance of the battery.Adding different content of the Pb-GO-N500-UP composite(0.5%,1%and 2%)can improve those performance of the negative plates and the simulated test cells.Under the studied conditions,the negative plate containing 1%Pb-GO-N500-UP composite has the best performance.3.The preparation of polypyrrole(PPy)/GO composites and their effects on the performance of lead-acid batteries.In-situ polymerization synthesis method was employed to prepare PPy/GO composites with different weight ratio of pyrrole to GO(mpy/mGO),in which high content of pyrrolic N in PPy was distributed on GO layers.In different PPy/GO composites,PPy covers on the surface of GO sheets and their micro structure changed with the mpy/mGO ratio,among which the PG1(mpy/mGO=1:1)composite has the largest BET surface area and pore volume.Compared with the NAM+GO(1%)plate,the incorporation of the proper content of PPy with GO can effectively inhibit the H2 evolution of the negative plate.Moreover,adding 1%different PPy/GO composite in the negative plate also decreases its total impedance,accelerates the redox processes between Pb and PbSO4 on it and increases its specific capacitance.The negative plates containing 1%GO and PG1 can significantly increase the HRPSoC cycle life of the simulated test cells.Considering the H2 evolution performance and the HRPSoC cycle performance,the PG1 composite is the appropriate additive for the negative plate of lead-acid batteries.Adding different content of PG1(0.5%,1%and 2%)can improve those performance of the negative plates and the simulated test cells.Under the studied conditions,the negative plate containing 1%PG1 composite has the best performance.4.Effects of different composites on the electrochemical behavior of the negative plate during the HRPSoC cycles.Electrochemical impedance spectrum(EIS)at open circuit potential(EOCP)and on-line EIS of the blank negative plate and those containing 1%different composites in the discharge process were also detected in different HRPSoC cycle states to differentiate the effects of the different composites on the electrochemical processes of the negative plates.The microstructure of the negative plates containing different additives in the middle and the last HRPSoC cycle state were analysed using SEM.The results indicate that compared with the blank plate,the transient hydrogen evolution behavior has been inhibited significantly by these additives.The transient hydrogen evolution behavior of the negative plate is determined by the real reaction area(Sreal)of the negative plate,while the steady hydrogen evolution behavior of the negative plate is determined by the real reaction area of the additives in the negative plate(Saddtive)and the content of the surface functional groups(or some components)of additives with the ability to inhibit hydrogen evolution.In different HRPSoC cycle states,the EIS characteristic parameters obtained from the open circuit state or the on-line discharge state can reflect the performance attenuation of the negative plates with an increase in cycles.Compared with the blank plate,those containing different composites have larger surface capacitance and smaller reaction resistance,resulting in the lower polarization degree of the negative plate and slow increase in the polarization degree with an increase in cycles.In addition,the PbSO4 layers on their surface are looser and in smaller crystal size.The affinity between different composites and NAM has an important influence on the pore volume,average pore width and pore number of the negative plate,which will determine the Sreal,Sadditive and capacitance of the negative plate,which can largely increase the Sreal,Sadditive and capacitance of the negative plate so as to prolong the HRPSoC cycle life of batteries significantly.Among the studied three composites,Pb-GO-N500-UP has the best performance.