Research On Mechanism And Effect Of Carbon Additives In Negative Plates On Performance Of Lead Acid Batteries

The negative plates of lead acid battery are easy to be sulfated on the surface in a hybrid electric vehicle operating. As a result, the electrolyte can’t diffuse into interior of the negative plate and it leads the battery to failure. Adding carbon additives into the negative plates can effectively inhibit the sulfation. Effect of different carbons on charge acceptance of batteries, capacity at different discharge rates at room and low temperature and the cyclic life of batteries in HRPSoC was studied in this paper. The conclusions are drawn as follow:Four types of carbon are chosen in this paper. They are carbon black, expanded graphite, flake graphite and colloid graphite. Effect of different carbons on conductivity was studied by measuring conductivity of Pb power containing different carbons. The results show that the ability of improving conductivity of plates containing carbons is carbon black> flake graphite> expanded graphite> colloid graphite. Effect of different carbons on charge acceptance of cells was studied by adding different types and different amounts of carbons into plates and taking charge performance test. The results show that it is most helpful to improve charge acceptance performance when cells contain only a little carbon black in negative plates and it possess the best charge acceptance performance when cells contain a relatively large amount of graphitic carbon in negative plates.The fully charged cells were discharged at 2h and 2C rates at 25 ℃ as well as at 1C and 2C rates at 0℃, respectively. Effect of different carbons on the performance of cells at different discharge rates at room and low temperatures was studied. The results show that certain amounts of carbon black, expanded graphite, flake graphite or colloid graphite were added into negative plates of cells. Capacities of these cells rise by 18.2%,22.5%,11.1% and 6.85% at most at 2h rate and increase by 28.4%, 29.0%,30.9% and 19.5% to the max at 2C rate at room temperature. At low temperature, excessive carbons minish pore size of the active material and it is not helpful for electrolyte to diffuse. The results show that carbon black, expanded graphite, flake graphite or colloid graphite was added into the negative plates of cells. Capacities of these cells rise by 23.6%,21.3%,33.0% and 23.5%at most at 1C rate as well as increase by 26.1%,25.9%,20.7% and 21.5% to the max at 2C rate respectively at low temperature.Cells with different carbons were tested in HRPSoC and effect of different carbon additives on cyclic life of cells in HRPSoC was studied. The results show that it is helpful to improve cycle life in HRPSoC of cells when carbon black or expanded graphite was added into the negative plates. The cells contain carbon black and expanded graphite in negative plates possess a largest cycle number of 12508 cycles and 11434 cycles, respectively, which is 3 times longer than that of the cell without carbon. The cyclic life of the cells containing flake graphite in negative plates only improves a little. Its cycle life is just 2000 cycles more than that of the cell without carbon. It does not improve the cyclic performance of cells in HRPSoC but it reduces the cycle life when a small amount of colloid graphite is added into negative plates.