Effect Of Mixed Carbon Materials In Negative Plates On Performance Of Lead Acid Batteries

Due to the braking and starting,the lead acid batteries used to hybrid electric vehicle(HEV)will sustain the high current charge and discharge rates,which will result in the formation of fine sulfate on negative plates.It is noted that it is difficult for sulfate to transform into Pb and PbO2,which will influence the discharge capacity and life of the lead acid battery.The addition of different carbon materials into negative plates can effectively inhibit the sulfation.Effects of different carbon materials on charge acceptance of batteries,capacity at different discharge rates at room and low temperature as well as the cyclic life of batteries in high-rate partial-state-of-charge(HRPSoC)were studied in this paper.The conclusions are drawn as follows:Four types of carbon materials were chosen in this paper,including carbon black,acetylene black,expanded graphite and flake graphite.Effects of different carbon materials on battery performances were studied by assembling the flood lead acid cells with the negative plate containing different carbons.The fully charged cells were discharged at 2h and 2C rates at 25? as well as at 1C and 2C rates at 0?,respectively.The results show that negative plates of the cells containing 0.5%carbon black,1%acetylene black,1.5%expanded graphite or 2%flake graphite can improve charge acceptance performance at most.The results present that the capacity of the cells at 2h rates rised by 14.4%,13.1%,21.3%and 10.6%at room temperature,and the capacity at 2C rate increased by 59.3%,58%,58%and 43.2%at room temperature,respectively.For the capacity at 1C rate,it increased by 45.4%,57%,46.5%and 37.2%,whereas the capacity at 2C rate was rised by 87.5%,66.1%,75%and 73.2%,respectively,when a certain amount of carbon black,acetylene black,expanded graphite or flake graphite were added into negative plates.Based on the above results,negative plates of the cells containing 0.5%carbon black and 1.5%expanded graphite can improve charge acceptance performance and discharge capacity at most.Mixing carbon black and expanded graphite in appropriate proportions is conducive to exerting their advantages,which will improve the battery performance.Negative plates of the cells containing 1%CB1EG1,1%CB1EG2,1.5%CB1EG3 or 1.5%CB1EG4 can improve charge acceptance performance at most.The times arriving the highest voltage(2.45V)are 304.3 min,335.08 min,306.53 min and 293.75 min.At room temperature,the capacity of the cells containing 1%CB1EG1,1%CB1EG2,1.5%CB1EG3 or 1.5%CB1EG4 at 2h rate rised by 12.5%,26.3%,16.3%and 14.4%,and the capacity at 2C rate increased by 56.8%,72.8%,60.5%and 60.5%,respectively.At low temperature,the negative plates of the cells containing 1%mixed carbon materials can improve discharge capacity.For capacity at 1C rate,it increased by 30.2%,50%,44.4%and 41.9%,whereas the capacity at 2C rate was rised by 50%,67.9%,64.3%and 55.4%,respectively.Compared to the cyclic life of the cell without carbon in HRPSoC(1214 cycles),the cyclic lifes of the cells,which contain 1%CB1EG1 1%CB1EG2,1.5%CB1EG3 or 1.5%CB1EG4,were 2979,3795,3318,3137 cycles,respectively.The results exhibit that the battery possessed the best performances when the ratio of carbon black and expanded graphite is 1:2 and the mixed carbon materials content is 1%.