The lead-acid battery is composed of lead dioxide positive plate, lead negative plate, microfiber diaphragm, sulfuric acid electrolyte, battery shell, and pole. When discharging, lead dioxide on the positive plate and sulfuric acid electrolyte undergo a reduction reaction to obtain electrons to generate sulfuric acid. Lead, the spongy lead on the negative plate and the sulfuric acid electrolyte undergo an oxidation reaction to generate lead sulfate, that is, bipolar sulfation. When charging, it returns to its original state, the positive electrode generates lead dioxide, and the negative electrode generates spongy lead.
When lead-acid batteries are used in automobiles, according to the operating environment requirements of different states of charge, conventional automobile start-stop and micro-hybrid electric vehicles, since the batteries are generally used at 90% charge, conventional lead-acid batteries can be used normally. For moderate hybrid vehicles, when the battery is used at 70-90% of the charge, the negative plate is easily sulfated; for full hybrid vehicles, the battery is used at 30-80% of the charge, and the negative plate will be quickly and irreversibly sulfated, making the battery expire prematurely.
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In response to this problem, L.T.Lam prepared a super battery for the first time in 2006. It improved the ordinary negative plate into half of the normal lead negative plate and half of the carbon negative plate. under sulfation. However, due to the potential difference between the two negative electrodes, the capacitor potential is more negative, and the hydrogen evolution at the negative electrode is severe. In order to solve the problems of hydrogen evolution and cumbersome assembly of two negative electrodes. The carbon material is directly mixed with the spongy lead to make the negative plate. The manufacturing method is close to that of the traditional lead-acid battery, and it has better battery performance and operability, that is, the lead-carbon battery.
Lead-carbon batteries can prolong the cycle life of hybrid electric vehicles under high-rate partial charge (HR-PSOC) working conditions. Lead-carbon batteries and related technological innovations are as follows:
1.The grid, the grid is used to conduct current and support the active material, usually the grid is lead-calcium-tin-aluminum alloy, in order to slow down the corrosion of the positive grid and cause the battery to fail. Firstly, the surface of the grid can be treated by soaking in aniline to reduce the physical resistance. Secondly, graphene can be added. Both graphene and metal lead have fine and uniform grains and dense arrangement, which can effectively reduce the corrosion of the grid. At the same time, during the oxidation-reduction reaction, the grain resistance formed by metallic lead and graphene is much smaller than that of pure metallic lead grains, so the current density is also greatly increased. In addition, graphene can increase the hardness of the grid, shorten the hardening time of the grid, reduce the inventory cycle, improve the capital turnover rate, and effectively reduce the production cost;
2. Positive plate, the positive active material is Barton lead powder and ball-milled lead powder with an oxidation degree of 70-88%. Hu et al. synthesized a nanostructured lead oxide containing a porous carbon skeleton, which was mixed with ball-milled lead powder and used to increase the utilization rate of the positive active material to 72.5%. Due to the complex structural transformation of lead dioxide, additives are likely to have negative effects on it. Graphene-like porous carbon can be added to accelerate the formation of the positive plate, while reducing the interface impedance, increasing the gap between the lead sulfate crystals of the reaction product, improving the charge transfer efficiency, and controlling lead sulfate. crystal size, thereby avoiding negative sulfation and prolonging battery life. Lang et al. added 4% 4BS (nano 4 basic sulfate) to the positive electrode to significantly improve the battery cycle life, and the application effect is obvious.
3.The negative plate, the negative plate is the key to the lead-carbon battery, and it must have both the characteristics of a battery and a capacitor. Therefore, a certain proportion of electrochemically active carbon materials should be added to the negative electrode to achieve capacitive buffering and depolarization. Common additives for negative plate lead paste active materials include: sulfonated lignin and humic acid organic expansion agents, conductive carbon, barium sulfate and short fibers, etc. It mainly plays the role of increasing the capacity of the active material of the negative plate, slowing down the sulfation, improving the structural stability, and enhancing the charging rate of the negative plate. The lead-carbon battery negative plate is to add a higher proportion of capacitive carbon materials such as carbon nanotubes and graphene oxide materials to the conventional lead paste, and at the same time add a dispersant that helps to disperse the carbon materials with high specific surface area, and inhibit the carbon Additives such as indium oxide, which cause hydrogen evolution problems, and PTFE, the binder that causes low strength of the negative plate after carbon addition, can prolong the curing time and adopt internalization process to prevent the oxidation of the negative plate.
4.Electrolyte, the electrolyte is a dilute sulfuric acid aqueous solution, which participates in the battery reaction, the concentration increases during charging, and decreases during discharging, and the charging process is accompanied by hydrogen evolution reaction. As the water decreases, the concentration will increase, affecting battery performance. The additives in the electrolyte mainly include sodium salts and potassium salts to improve conductivity, and phosphoric acid slows down the shedding of positive active materials. And metals and their compounds or ionic liquids with high hydrogen evolution overpotential are used to suppress hydrogen evolution. Zhao et al. used 240 mg/L cetyltrimethylammonium bromide and 20 mg/L benzylidene acetone as electrolyte additives, which significantly improved cycle life and concluded that they could inhibit hydrogen evolution.
5.Compared with lead-acid batteries, lead-carbon batteries increase charging speed by 8 times, discharge power by 3 times, and cycle life by 6 times. Compared with the energy density of lead-acid batteries of 20-40Wh/kg, lead-carbon batteries can be increased to 40-60Wh/kg, and the cost performance has been greatly improved.
Lead-carbon battery, as an innovative technology of lead-acid battery, not only expands its application in the field of medium-hybrid and full-hybrid vehicles, but also further reflects its value in the field of large-scale and ultra-large-scale energy storage.