Research On Gelled Electrolyte Lead-acid Battery For Electric Vehicle

The battery is the key to affect the performance of electric vehicle andconstrainment of electric vehicle industrial development. Lead-acid batteryhas been used and studied extensively because of its rich resource, lowprice, mature technology, safety and reliability, high recovery of lead forwaste battery cycling. However, there are some disadvantages for lead-acidbattery. In order to improve the performance of battery, gelled electrolytehas been used for the manufacture of the battery. Much research work hadbeen done in the present paper such as the preparation of gelled electrolyte,comment of the effect of gelled electrolyte on the reaction process ofnegative plate during charge-discharge process and the performance of thebattery and the failure modes of gel batteries.A certain percentage of fumed silica was dispersed in water and mixedwith sulfuric acid solution which had been treated by low temperature forthe preparation of gelled electrolyte. Appropriate additives were added tothe gel electrolyte and dispersed efficiently mechanically. The viscosity, geltime, gel strength and other properties of gelled electrolyte were measuredand analyzed theoretically. It was found that the electrolyte could formstable gel when the amount of SiO₂reached4%, It would be easy to arisehydration and stratification of the electrolyte when the SiO₂content wasless than4%. It would be difficult to dilute the gelled electrolyte and thethixotropy of gelled electrolyte would be poor when the SiO₂content washigher than6%. The kinetics of electrochemical reaction process of negative electrodehad been studied by cyclic voltammetry, chronoamperometry, chro-nopotentiometry, electro-chemical impedance spectroscopy and otherelectrochemical test methods. It was found that the internal resistancebecame larger and the current of the oxidation process became smaller withthe increase of silica content in the gelled electrolyte. However at the samecathodic polarization conditions, the hydrogen evolution current ofnegative electrode reduced. It was also found that the differentialcapacitance and the exchange current density of negative electrodedecreased to a certain extent with the increase of fumed silica content in thegelled electrolyte.The preparation and performance of the gelled batteries had beeninvestigated systematically in the paper. It was found that the gelledelectrolyte could be filled into the battery when the SiO₂content was lowerthan6%. It would be much more difficult to fill when the SiO₂content washigher than6%.It would be good to improve the uniform distribution of thegelled electrolyte in the separators if the traditional technology of batteryassembling was varied and the assembling pressure made lower.Simulated batteries were made with the plate of electric vehiclebattery and gelled electrolyte. It was found that the initial capacity,low-temperature capacity, capacity retention capacity, the adaptabilityunder the PSOC condition and deep discharge cycle life of the simulatedbatteries were associated with the SiO₂content in gelled electrolyte basedon the results of charge-discharge performance test of simulated battery.The ideal result was obtained when the SiO₂content was4%.It was found that gelled electrolyte could inhibit acid stratification andimprove battery cycle life based on the results of failure analysis and thepractical performance test of the gel batteries. The transformation process of α-PbO₂to β-PbO₂for the positive active material of gel batteries wouldoccur easily during the process of charge-discharge, which would affect thecycle life of the battery. The irreversible sulfate, short circuit and otherfailure modes of gel batteries can be reduced whereas failure mode becauseof softening and shedding of positive active material would occur easily. Itwas believed that softening and shedding of positive active material wouldbe inhibited with the adoption of tubular positive electrode and gelledelectrolyte.