Effect Of Positive-electrode Additives On Electrochemical Performance Of Valve Regulated Lead-acid Battery

Lead-acid battery is considered to be one of the most promising vehicle power supply, but low capacity and softening of positive-electrode plate limits its development. In order to improve the capacity and cycle life of valve regulated lead-acid(VRLA), this paper start with positive-electrode grid and positive-electrode additives. In this paper, electrochemical performance of positive-electrode grid with different preparation technologies, electrochemical behavior of positive-electrode grid with different scaning rates or temperatures and the effect of three kinds of positive-electrode additives as well as carbon fiber, titanium oxide and silicon dioxide on the performance of VRLA battery is investigated by discharge test, cycle life test, cycling voltammetry(CV), electrochemical impedance spectroscopy(EIS), Tafel curves, x-ray diffraction test(XRD) and scanning electron micrographs test(SEM).The results show that the technologies with 520 °C furnace temperature, 540 °C spoon temperature and 90 °C aging technology are more suitable for lead-acid battery plate grid. In this case, the amount of oxygen evolution and dissolved Pb is little, deep cycle performance is good, early capacity attenuation is relatively less. Also, the grid corrosion resistance and electric conductivity is balanced. There are constraints in furnace temperature, spoon temperature and aging temperature which affects lead-acid battery performance together. Contradictory properties make multiple factors need to be considered in positive grid technology. High temperature accelerates corrosion rate of positive grid and increases the amount of oxygen and hydrogen precipitation and capacity of lead-acid battery.Carbon fiber positive additive is beneficial to improve discharge performance and cycling life of VRLA battery. The specific surface area is bigger, the effect is greater. The optimal amount of carbon fiber additive in positive active material(PAM) is 0.5‰. A small amount of carbon fiber makes particles of positive plates tinier and more uniform. A small amount of carbon fiber in PAM can constitute conductive grid. It is in favour of the formation of plates, the distribution of electric current and the stiffness of positive plates which is good for the discharge performance and cycle life of lead-acid battery and makes the amount of oxygen and hydrogen precipitation less.Ti4O7 positive additive can improve capacity of VRLA battery. High rate discharge makes the effort mort evident. There is a 13% improvement of capacity of the battery in 3C discharge rate when used 5‰ of Ti4O7 in PAM. Ti4O7 can improve the amount of PbO of positive plates and make the size of particles of positive plates more equal and smaller.SiO2 can aslo improve capacity of VRLA as positive additive. At room temperature, it makes a 7.5% growth of capacity of the battery in 3C discharge when used 3‰ of SiO2 in PAM. At low temperature, adding 5‰ of SiO2 in PAM makes the maximum capacity which is 12% more than the battery without SiO2. The mechanism of high rate discharge and low temperature discharge is not completely the same. The amount of PbO is about as high as 40% with adding 3‰ or 5‰ SiO2 in positive plate, respectively. Adding SiO2 makes the tightness of particles of positive plates appropriate which is good for electrode reaction and the bonding force between the particles.