Investigation Of The Effect Of Positive Additives And Separators In Valve-regulated Lead-acid Batteries

Lead-acid batteries are safe,reliable,and inexpensive,and they are widely used in all walks of life.At present,the main factor that restricts the electrical performance of lead-acid batteries is the positive plate,so how to improve its performance has important significance in the investigation of lead-acid batteries.It is an easy and available method to use the positive plate additives in lead-acid batteries.This thesis focus on the effects of white carbon black,fumed silica,rare earth lanthanum oxide,carbon fiber and hollow glass microsphere additives on performance of valve-regulated lead-acid(VRLA)batteries,when they are added into positive lead paste respectively.And the inhibitory effect of the absorptive glass mat(AGM)-+-polyethylene(PE)composite separators on short circuit of lead dendrite was studied under the overdischarge condition of valve-regulated lead-acid batteries.The conclusions are drawn as follow:1.In this thesis,the effects of five kinds of positive additives,such as white carbon black,fumed silica,rare earth lanthanum oxide,carbon fiber and hollow glass microsphere on the performance of valve-regulated lead-acid batteries were studied.The optimum addition amount in the positive active material(PAM)is 0.3%of white carbon black,0.15%of fumed silica,0.05%of rare earth lanthanum oxide,0.05%of carbon fiber,and 0.1%of hollow glass microsphere.Carbon fiber needs to be dispersed in 2%sodium carboxymethyl cellulose(CMC)before the additive is mixed with lead powder.Hollow glass microsphere should be immersed in 1%HF solution for 10 minutes for surface hole making.Compared with control batteries in the test of cycle life,the battery stable capacities with these additives at the 0.5 C rate increase by 34.8%,27.3%,19.7%,15%and 38.5%,respectively,and their cycle life at the 0.5 C rate increases by 60.2%,77.8%,66.7%,90.7 and 163%,respectively.2.The electrochemical performance of the batteries with five positive additives has been studied.The results are as follows:The addition of carbon fiber and fumed silica shortens the formation time of positive plate.The former is due to its good conductivity and forms a conductive network in the plate.The latter is due to the small particle size and increases the specific surface area of the active material.But the rare earth lanthanum oxide is relatively large and non-conductive,which weakens the conductivity of the plate and prolongs the formation time of positive plate.The 0.05%carbon fiber content increases the initial capacity of the battery by 9.8%.When 0.1%hollow glass microsphere content is added to the positive plate,the capacity of the battery at the 1 C and 2 C rates are increased by 5%and 13.3%,respectively.3.By investigating the cycles of alternating normal and deep discharge for the batteries with ordinary AGM separator and AGM+PE composite separators,and using the scanning electron microscope(SEM),the back scattered electron microscope(BSE)as well as the energy dispersive spectrometer(EDS)etc,the causes of battery failure and the influences of separators on the short circuit of lead dendrites were investigated.The results show that in the VRLA battery with ordinary AGM separator,due to its larger pore size,the lead dendrites grow continuously in the pores of AGM separator,causing the battery to fail due to short circuit.In the VRLA battery with the AGM+PE composite separators,since the pore size of the PE separator is very small,the lead dendrites do not penetrate the PE separator from the negative plate into the AGM separator.Therefore,the AGM+PE composite separators can well solve the problem of short circuit of the lead dendrites in the VRLA battery under the overdischarge condition.