Design technology of high rate discharge 18650 battery 2600mah

　　In 1971, the American Gates Company used its patented technology of liquid-absorbing cylindrical VRLA batteries to realize the application of oxygen recombination principle in commercial batteries for the first time, making the manufacturing technology of lead-acid batteries achieve significant progress in more than 100 years. breakthrough. After 30 years of development and improvement, the application scope of VRLA batteries has expanded from traditional backup float charging to motor vehicle starting, power traction, solar and wind energy storage, etc. As my country's economy continues to develop rapidly, China will likely become the world's largest communications market in the next 20 years. The communications industry is the main user of lead-acid batteries, and VRLA batteries currently account for 2/3 of the total market demand [1]. Faced with the continuous updating and upgrading of electronic technology, stringent requirements will be placed on the performance of supporting batteries. Obviously, competition in the performance-price ratio of VRLA batteries is unavoidable in the future, especially after China joins the WTO. How to effectively shorten the life of domestic batteries? The gap with well-known foreign brands has become an urgent problem before us to be solved.

　　2 Factors affecting the performance of high-rate discharge VRLA batteries

　　VRLA batteries using pb?Ca alloy as grid material and using AGM separator and oxygen composite technology have better high-rate discharge performance than open lead-acid batteries. This is because the conductivity of pb?Ca alloy is better than that of pb? Sb alloy, this property is more obvious at low temperatures. Table 1 lists the performance comparison of ordinary open-type and valve-regulated sealed 12V7Ah batteries for motorcycles with the same lead paste formula and structural design (3 positive/4 negative per cell), but different grid alloy conditions. Normally, high-rate discharge VRLA batteries are used in shallow discharge cycles or backup float charging methods, and the early capacity loss (pCL) caused by pb?Ca alloy is not the main influencing factor here. However, from the economic point of view of low-cost use, grid corrosion, one of the main factors limiting battery life, needs to be considered. Since pb?Ca?Sn?Al alloy has good properties such as corrosion resistance, creep resistance and prevention of passivation layer formation, comprehensive evaluation shows that it is necessary to use this alloy for the positive grid. The grid is not only the supporting skeleton of the active material, but also the channel for the conversion and output of chemical energy and electrical energy inside the battery. Reasonable design of grid thickness, current collector grid and pole tab position is necessary to ensure lower internal resistance and higher active material utilization during large current output, as well as to slow down electrode polarization. Since the high-current discharge performance of lead-acid batteries is often controlled by the negative electrode, and the performance of the negative electrode depends on the function of the expansion agent, for many years, lead-acid battery researchers around the world have used the optimization of negative electrode additives as a way to improve and improve The most important measure for negative electrode performance. Most domestic battery manufacturers generally use dry-charged electrode plates to assemble VRLA batteries. In order to prevent the negative plate from being oxidized, a certain amount of antioxidants need to be added to the lead paste. Most of the antioxidants are organic compounds, together with organic expansion agents. , often have a negative impact on the battery's charge acceptance ability. For secondary batteries, charge acceptance is a very important performance indicator, which characterizes the degree of reversible transformation of active materials in the battery. Experience tells us that insufficient charging will lead to a reduction in the high current discharge performance of lead-acid batteries, especially the starting discharge capability at low temperatures. In VRLA batteries, due to the presence of oxygen recombination, the negative electrode is always in an incompletely charged state. At the same time, the oxidative decomposition of the organic expansion agent is more serious than in open batteries, which ultimately leads to the decline of negative electrode performance. In addition, a large number of research results show that the increase in the polarization potential of the positive electrode is the main factor that causes the closed-circuit voltage to decrease and the duration to shorten during high-rate discharge of lead-acid batteries. Therefore, in the design of high-rate discharge VRLA batteries, the role of the positive electrode cannot be ignored. This also shows that improving the positive electrode manufacturing process is one of the reliable methods to improve the battery's high-current discharge performance. VRLA batteries using AGM separators are liquid-limited designs. As the main carrier of sulfuric acid electrolyte, AGM separators not only provide the sulfuric acid required for the electrode reaction, but also provide the necessary gas channels for oxygen recombination. The AGM separator has a great influence on the pressure of the electrode group. When the saturation of the AGM separator is reduced to a certain level, peeling will occur between the AGM separator and the electrode plate, and the internal resistance will continue to increase, making the high rate Discharge performance drops sharply. Therefore, on the premise of ensuring the amount of electrolyte required for the electrode reaction, increasing the tight assembly of the electrode groups is conducive to improving high-rate discharge performance and extending battery life.

　　Table 1 Effect of grid alloy on high rate discharge performance of lead-acid battery (open type) pb? Sb alloy (sealed type) pb? Ca alloy 1# battery 2# battery 3# battery 1# battery 2# battery 3# battery-10 ℃/8C10 starting discharge 12.67/9.7210012.68/9.649812.68/9.7110013.20/10.3314913.20/10.3214913.19/10.33145

　　Project Note: The data recorded at low temperature starting is: open circuit voltage (V)/5s voltage (V), discharge time (s).

　　Table 2 Effect of positive electrode additives on the high-rate discharge performance of VRLA batteries Adding scrapped active materials Adding graphite 1# Battery 2# Battery 1# Battery 2# Battery - 10℃/8C10 starting discharge 13.18/10.3213513.17/10.3313513.17/10.1312713. 18/10.21125

　　category

　　Project Note: The data recorded at low temperature starting is: open circuit voltage (V)/5s voltage (V), discharge time (s)

　　From a design perspective, in addition to the above influencing factors, the optimized design of the battery structure to meet high-rate discharge is also necessary, such as busbar and pole design, which is especially important for small VRLA batteries with high-rate discharge. Since this aspect is not the focus of this article, it will not be discussed again.

　　3 Discussion on high-rate discharge 18650 battery 2600mah design technology

　　There is such a relationship between the discharge rate of lead-acid batteries and the utilization rate of active materials: the greater the discharge rate, the more limited the utilization rate of active materials. Generally speaking, whether it is an open battery or a 18650 battery 2600mah, it is necessary to adopt a thin plate design to meet high-rate discharge performance. The thin plate increases the electrode reaction area, improves the utilization rate of active materials, and reduces the internal resistance of the battery, thus achieving good high-current discharge performance. Although the "stretch mesh" and "lead cloth" technologies that make flat plate grids very thin have become commercialized, their large-scale application is far less than that of "gravity casting" technology. In addition, it is difficult to use "gravity casting" to make the grid very thin. In particular, thin grids have to go through multiple processes such as subsequent coating, solidification, formation, splitting, and welding, and will face plate waste. Quality problems such as large damage and frequent battery failures. It is worth mentioning that a 18650 battery 2600mah with a thin plate design consumes more lead than a thick plate design with the same active material weight, and the grid's ability to withstand chemical and electrochemical corrosion is also reduced. . Therefore, the design of thin plates suitable for high-rate discharge requires mastering certain principles. The charge and discharge performance of the battery is ultimately reflected by the interaction between the positive and negative active materials and the electrolyte. D.Simonsson theoretically studied the dependence of the mass transfer process, discharge state and pbSO4 formation conditions, and summarized the incomplete utilization of active materials as: pbSO4 blockage at the orifice and the limited pore size caused diffusion obstacles, resulting in Poverty of electrolyte in the pores [2]. A certain active material structure determines a certain utilization rate. Changing the structure of the active material can be affected by controlling some process parameters such as paste mixing and curing, or by adding additives to the lead paste [3]. Relatively speaking, the latter is more conducive to process and process control, and has practical promotion value. Below we illustrate this effectiveness with some examples of actual formulation design.

　　3.1 Effect of positive electrode paste formula on the discharge performance of high-rate VRLA batteries

　　Table 4 Effects of different electrolyte formulas on the high-rate discharge performance of VRLA batteries 3C2012 Electrolyte formula A1 #7.107.052 #7.857.953 #7.787.85 Electrolyte formula B1 #7.707.702 #8.008.063 #7.908.03 Electrolyte Formula C1#8.678.502#8.888.633#8.378.18 Electrolyte formula D1#9.509.452#9.239.023#9.759.45

　　From the previous analysis, it can be concluded that slowing down and reducing the increase of the positive electrode polarization potential is an important measure to ensure the improvement of high-rate discharge performance. The selection of positive electrode additives in the 18650 battery 2600mah formula should focus on the ability to form a good microporous structure and conductive network of the positive active material, or to slow down and eliminate the impact of the passivation layer at the interface between the active material and the pb?Ca grid. Due to the high potential of the positive electrode, general additives will be oxidized and decomposed, making it difficult to function throughout their lifetime. This is a "bottleneck" problem when selecting positive electrode additives. Table 2 lists the performance comparison of the scrapped cathode active material added to the cathode lead paste in a certain proportion and the performance of the cathode lead paste added with graphite. The results show that the former is beneficial to improving the low-temperature and high-rate discharge performance of VRLA batteries. From a production point of view, scrapped positive plates always exist, and reusing their active materials has practical significance for saving material consumption and reducing costs [4].

　　3.2 Negative lead paste formula for high-rate 18650 battery 2600mah discharge

　　Performance impact

　　Unlike the positive electrode, the microporous structure of the negative electrode active material has no obvious impact on high-rate discharge. For VRLA batteries used at low temperatures, if the porosity of the negative electrode increases, it will hinder the diffusion of electrolyte, ultimately leading to a reduction in battery discharge performance. Therefore, the performance of the negative electrode depends more on the type of expansion agent. Lignin has a good promoting effect on high current discharge, but the high solubility of domestic lignin acid reduces the expansion effect of the negative electrode during its life. There are few manufacturers using this kind of lignin. Imported lignin has good performance but is expensive. No matter what kind of lignin is used, the charge acceptance ability of the negative electrode will be affected to a certain extent, which is even more serious for the negative electrode of VRLA batteries. Through reasonable matching with other negative electrode additives, humic acid also has a good effect in improving high-current discharge. Because it is cheap, has stable performance, and the filling properties of lead paste after addition are very suitable for mechanized coating, it is commonly used in China. use. In recent years, some humic acid manufacturers have successively developed high-purity humic acid with lower impurity content and suitable for VRLA batteries. In order to further improve the performance of the negative electrode, currently, the process formula of synthesizing lignin and humic acid or mixing the two in a certain proportion is also attracting attention. To this end, we have conducted optimization research on the mixing ratio of the two. The relevant data are shown in Table 3. The improved formula is beneficial to improving battery charge and discharge performance and reducing battery costs, and has practical promotion value.

　　Table 3 Effect of improvement of organic expander ratio on 18650 battery 2600mah performance Before improvement After improvement 1# battery 2# battery 3# battery 1# battery 2# battery 3# battery C5 (Ah) 4.024.184.274.434.374.43C20 (min )7.478.128.358.738.758.60

　　category

　　Project 3.3 Electrolyte formula for high-rate 18650 battery 2600mah discharge

　　Performance impact

　　For a long time, a lot of research has been conducted at home and abroad on the impact of adding certain additives to the sulfuric acid electrolyte on the performance of VRLA batteries. Since the use of electrolyte additives has the advantages of not changing the battery industrial production process, low additional costs, good effects, and easy promotion, selecting appropriate electrolyte additives has become one of the main ways to improve the performance of lead-acid batteries [5] . We believe that the role of 18650 battery 2600mah electrolyte additives can be attributed to the following points:

　　(1) Enhance the conductivity of the electrolyte and improve the capacity recovery performance and recharge acceptance of the battery after over-discharge;

　　(2) Inhibit the occurrence of dendrite short circuit;

　　(3) Increase battery capacity and suppress early capacity loss;

　　(4) Prevent the softening and shedding of active substances and slow down the corrosion of the grid. In our experiments, we found that some additives only have one of the above effects, while other additives have several effects at the same time. Table 4 compares the effects of four electrolyte formulas on high-rate discharge performance. It can be seen that just changing the electrolyte composition will cause a big difference in the discharge performance of the battery.

　　4 Conclusion

　　(1) The design and improvement of lead paste and electrolyte formulas are achieved by focusing on optimizing various additives and their ratios. It is an important technical route for VRLA batteries to meet high-performance requirements. Compared with the usual improvement measures to optimize battery structure, excellent formulas are more conducive to improving battery performance and stabilizing quality.

　　(2) The application of certain additives not only improves the discharge performance of VRLA batteries, but also helps reduce battery costs, thus ensuring further improvement in performance-price ratio.

　　There are many kinds of additives suitable for improving the performance of VRLA batteries, but not many are actually promoted and applied. In this regard, there is still a big gap between my country and developed countries. This shows that although most domestic battery manufacturing companies regard battery formula as their core technology, the process of practical research and development of formulas is very slow. Since there is a broad R&D space for improving the battery formula process, we believe that with the continuous strengthening of R&D efforts in the future, it will have a profound impact on the overall performance and product quality of VRLA batteries in my country.

Read recommendations:

801738 450MAH 3.7V

The difference between lithium battery and polymer lithium battery.connector for energy storage batt

Solid state batteries leading the next wave of lithium batteries, starting from soft packs!

lithium battery 18650 3.7v

AG4 battery