// 2 Common additives //

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2.1 Short fibers

2.1.1 Types and properties

Short fiber according to the use of different materials, generally divided into polyester fiber (polyester material), PP fiber (polypropylene material) and polyacrylonitrile fiber (acrylic material), different materials have different properties, the short fiber used in the polar plate additives in addition to the fiber diameter, length, in 70 ℃ acid in the acid acid resistance as well as dispersion in acid (whether or not to settle) have an impact on the performance of the polar plate.

2.1.2 Role

Positive and negative lead paste are used, its main role: to increase the mechanical strength of the active material, to prevent shedding, thereby improving the cycle performance, some literature reports that a small amount of addition is conducive to the diffusion of H2SO4 to the inside of the electrode, which can improve the porosity of the positive plate and improve the initial capacity; but the initial capacity will not be beneficial when adding a large amount.

2.2 Carbon material

2.2.1 Species and characteristics

Carbon materials are: acetylene black (carbon black), superconducting carbon black, carbon fiber, graphite. Acetylene black is a nano-material with high dispersion, graphite has a layered structure, and carbon fiber has a diameter of 0.1-1.0 μm, and its resistance is basically the same as that of PbO2. The most important characteristic of carbon fiber is that the fiber is long and thin, adding lead paste does not reduce its performance density, easy to be oxidized, and half of the loss in the chemical formation.

2.2.2 Role

These substances can improve the utilization rate of the active substance and the performance of low-temperature high-current discharge, but each has its own characteristics: the addition of anisotropic graphite, which is subjected to anodic oxidation at the time of anodization of the positive electrode, sulfuric acid immersed in the graphite between the layers of the layer and the layer of the active substance after the formation of the active substance has been increased in the capillary pores of the active substance, and the role of this large-diameter micropore to the inside of the polar plate to supply electrolyte, thus increasing the utilization rate of the active substance. Yang Chengying et al [2] found that: the addition of high-purity graphite has the following effects: ① improve the porosity and wettability of the electrode, can improve the utilization rate of the active substance of the positive electrode and capacity; ② reduce the internal resistance, improve the electrical conductivity; ③ add graphite so that the positive electrode of the self-discharge increases, must pay attention to the content of impurities in graphite to different origins of the comparison of the choice. Zhang Yufeng et al [1] found that the addition of -quantity of carbon fibers in the cathode plate increased the utilization of active substance by 9 % and the low temperature discharge performance by 50 %, and that the use of graphite may lead to excessive expansion, which dislodges the active substance. Zhu Songran [3] et al. found that increasing the carbon content in the negative electrode can increase the battery capacity and charge acceptance, but it will reduce the overpotential of hydrogen precipitation by 10-20 mV.D.P. Poden [4] found that: the role of carbon black is to increase the electrical conductivity of the active substance during deep discharge, because of deep discharge, the impedance of the higher concentration of lead sulfate are high. But Vind is of the opinion that carbon black has almost no effect on the capacity, only slightly at low temperatures, but when chemically formed, it has a flushing effect on the plates and also slows down the phenomenon of high final charging voltage due to other components in the additives, and acts as a conductor when chemically formed or discharged, and its use is about the same as that of lignin, and no one is prepared to use an excessive amount of carbon black.

Now lead-acid battery manufacturers use more carbon black, some in positive and negative plates are used.

2.3 Barium sulfate

2.3.1 Species and properties

There are two kinds of barium sulfate used as additives: one is barite powder, which is precipitated from solution, and its particle diameter is 1 μm, and the other is barite, a rounded fine ore, and its particle diameter is 3-5 μm, and barite is much worse than barite powder. Mr. Wu Shousong [5] also proposed the use of BaSO4 produced by precipitation method, some domestic manufacturers in the production of ultrafine BaSO4 is said to be able to pass 1 250 mesh molecular sieve.

Barium sulfate has a similar structure to PbSO4, barium sulfate is insoluble in sulfuric acid and has low electrochemical activity, these properties ensure that it remains chemically stable in the negative plate.

 2.4.2 Role

The biggest role of lignin is that it can improve the low temperature high rate discharge capacity of the battery, which is recognized, but it has a corresponding disadvantage, Yang Jun [8] and Wu Shousong [5] found that lignin has an effect on the charging acceptance ability of the negative electrode. Zhang Yongjian [1] and Guo Zhigang [9] et al. found that lignin was diluted in and paste, and there was an early capacity decay and skinning after chemical formation. The negative electrode plate has the problem of adhesion, which is directly proportional to the solubility of lignin in acid, and the higher the temperature, the more serious the adhesion.

2.5 Humic acid

2.5.1 Characteristics and types

Humic acid is a natural organic polymer compounds, exist in the soil humus and low-grade coal material, with aromatic nuclei, hydroxyl, carboxyl, quinone, methoxy and other active groups, humic acid is a black-brown or black amorphous powder, dispersion and emulsification. According to the different production methods, there are mainly acid humic acid and alkali humic acid, with the different regions, the content of impurities in humic acid is also different, and the performance of the battery is also different.

2.5.2 Role

Humic acid is used as an additive for the negative electrode active substance, which can be adsorbed on the surface of the lead crystals of the negative electrode plate. So that the lead can maintain its high dispersion, in the discharge process, the formation of PbSO4 can not directly surround the lead particles, to prevent the negative plate contraction, so humic acid to improve the discharge capacity of the battery, especially the battery's low-temperature discharge capacity effect is obvious, humic acid at the same time has to improve the hydrogen over-potential, reduce the role of self-discharge, which the carboxyl group of the humic acid on the depolarization of the lead battery to play an important role. The low temperature high rate discharge performance of humic acid is worse than lignin.

2.6 Stearic acid

2.6.1 Species and properties

As negative electrode additives, barium stearate and sodium stearate are mainly used, which react with sulfuric acid to form stearic acid (with two carboxyl groups) and BaSO4 (or Na2SO4).

2.6.2 Role

Because of the reaction to generate stearic acid and BaSO4 (or Na2SO4), stearic acid for the surface and active agent, to prevent the lead electrode surface shrinkage, the role of BaSO4 with the death of the use of barium stearate can reduce the amount of barium sulfate added.

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// 3 Other additives //

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Organic additives and cowhide lignin class, naphthalene sulfonate, azo anthracene blue, tannic acid and other organic synthetics.

Inorganic additives in the synthesis of SrSO4, SiO2, TiO2, Al2 (SO4), and so on.

These additives battery manufacturers are now rarely used, its performance on the battery is not clear.

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// 4 Selection and application //

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For additives, can't use too much or too little, the wrong additives have serious damage to the battery performance. For the selection of additives, the following factors are mainly considered:

① The content of metal impurities.

② The main components or basic groups.

③ Application of the battery (SLI, power, VRLA standby, remote area energy supply).

④Type of separator (PE, PVC, AGM).

⑤ Usage environment (tropical, cold zone, subtropical); ⑥ Required service life (PE, PVC, AGM).

⑥Required service life (more than 1 a, 3