An electrolyte for lead-acid batteries

Abstract

This invention discloses an electrolyte for lead-acid batteries, belonging to the field of lead-acid battery technology. This invention uses potassium sulfate, aluminum sulfate, sodium tetraborate, and perfluorooctyl sulfonate as additives in the electrolyte for lead-acid batteries. Through the eutectic effect of potassium sulfate and aluminum sulfate, the buffering effect of sodium tetraborate, and the adsorption effect of perfluorooctyl sulfonate, these additives synergistically inhibit phenomena such as positive electrode grid corrosion and negative electrode sulfation, thereby extending the lifespan of the lead-acid battery.

Description

Technical Field

[0001] This invention belongs to the field of lead-acid battery technology, and specifically relates to an electrolyte for lead-acid batteries. Background Technology

[0002] Since its invention, lead-acid batteries have dominated the secondary battery field for over a century and a half due to their stable performance, low price, and high resource recyclability, with a wide range of applications covering starting, power, and energy storage. However, lead-acid batteries also have many drawbacks, such as low energy density and relatively poor lifespan. Currently, with the rapid rise of high-performance new energy sources like lithium batteries, some applications of lead-acid batteries are gradually being replaced. Nevertheless, lead-acid batteries will inevitably continue to play an important role for a considerable period of time, especially in the power sectors of low-speed electric vehicles and electric bicycles. Traditional power lead-acid batteries suffer from a series of problems, including early capacity decay and short cycle life. Their failure modes mainly manifest as positive plate grid corrosion, softening and shedding of positive electrode active material, and negative electrode sulfation. Positive plate grid corrosion occurs throughout the entire process of plate solidification, battery formation, and cycling, involving both solid-phase and liquid-phase reactions. After repeated use, a thicker corrosion layer forms, existing in the form of lead sulfate and non-stoichiometric lead oxide. This corrosion layer contains various defects and produces multidirectional cracks. The growth of this corrosion layer leads to a rapid increase in interfacial or internal resistance, which is a major factor affecting the cycle life of lead-acid batteries. The softening and shedding of the positive electrode active material is caused by interfacial passivation, α-PbO2 consumption, etc., and its evolution is influenced by many factors such as sulfuric acid concentration, electrolyte stratification, and operating temperature. Strictly speaking, negative electrode sulfation should be called irreversible negative electrode sulfation. Under normal conditions, lead-acid batteries form lead sulfate crystals during discharge, which can be easily reduced to lead during charging. However, if the battery is frequently undercharged or over-discharged due to improper use and maintenance, a coarse and hard lead sulfate will gradually form on the negative electrode. This lead sulfate is almost insoluble and difficult to reconstitute into active material using conventional charging methods. This directly leads to a reduction in battery capacity, eventually causing premature battery life.

[0003] The invention patent report with patent authorization number CN103268966B discloses an electrolyte additive for extending the life of lead-calcium batteries. The electrolyte is composed of organosilane, phosphoric acid, mannitol, polyoxyethylene ether, organosilicon oil, and polyacrylamide, which can effectively improve the cycle life of lead-acid batteries by more than 50%.

[0004] Patent CN1170396C discloses an electrolyte for lead-acid batteries, comprising carbon, sodium sulfate, magnesium sulfate, sodium silicate, sodium acetate, cobalt acetate, phosphoric acid, 2,6-di-tert-butyl-p-cresol, and pyridoxal 2,5-phosphate. This additive can effectively reduce the battery's internal resistance, improve the battery's ability to accept high current, and extend the battery's cycle life, making it suitable for fast-charging batteries.

[0005] However, the cycle life of lead-acid batteries with electrolyte formulations in the aforementioned prior art is still relatively short. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide an electrolyte for lead-acid batteries, which uses potassium sulfate, aluminum sulfate, sodium tetraborate and perfluorooctyl sulfonate added to the electrolyte in a certain mass percentage. Through the eutectic effect of potassium sulfate and aluminum sulfate, the buffering effect of sodium tetraborate and the adsorption effect of perfluorooctyl sulfonate, the corrosion of positive electrode grid and sulfation of negative electrode are suppressed, thereby extending the cycle life of lead-acid batteries, especially lead-acid batteries for electric bicycles.

[0007] The specific technical solution of the present invention is as follows:

[0008] An electrolyte for lead-acid batteries includes a sulfuric acid solution and additives, wherein the additives, by mass percentage of the total electrolyte, comprise the following components: 0.2%–2% potassium sulfate, 0.2%–2% aluminum sulfate, 0.2%–2% sodium tetraborate, and 0.001%–0.01% perfluorooctyl sulfonate.

[0009] The electrolyte involved in this invention contains an aqueous sulfuric acid solution, and sodium tetraborate is used instead of sodium sulfate. In addition to acting as a buffer for sodium sulfate, it can also alleviate the grid corrosion caused by sodium sulfate. Furthermore, potassium sulfate, aluminum sulfate and perfluorooctyl sulfonate are added.

[0010] The potassium sulfate used is a colorless and transparent crystalline powder, and the aluminum sulfate used is aluminum sulfate octadechydrate, which is a white powder.

[0011] During battery charging, potassium sulfate and aluminum sulfate co-deposit with Pb on the negative electrode plate, forming mixed crystals embedded in the lead lattice. During discharge, potassium and aluminum are oxidized and ionized, entering the solution and leaving vacancies in the lattice. This prevents the formation of continuous, coarse crystals on the electrode surface, thus avoiding sulfation, reducing battery internal resistance, and significantly improving electrochemical performance. It also prevents the formation of fine, dense lead sulfate, thereby preventing negative electrode plate shrinkage failure. Furthermore, potassium sulfate increases the oxygen evolution overpotential at the positive electrode, promoting the charging reaction and improving charging efficiency. Aluminum sulfate increases the water content in the gel region of the active material, which is beneficial for the formation of amorphous and hydrated PbO2. It also refines particle size, increasing the bonding area and strength between active materials.

[0012] The sodium tetraborate used is sodium tetraborate decahydrate, which is a colorless and transparent crystalline powder.

[0013] Sodium tetraborate decomposes in sulfuric acid into sodium ions and borate ions. The sodium ions, like traditional sodium sulfate additives, prevent dendrite formation and short circuits, while the borate ions, due to their weak acid properties, mitigate corrosion of the positive electrode grid. They also refine the grain size and reduce self-discharge.

[0014] The perfluorooctyl sulfonate used is a colorless powder with a content of ≥95%.

[0015] Perfluorooctyl sulfonate is an anionic surfactant that can react with Pb during discharge through adsorption. 2+ The ions form a "lead-sulfonate" complex intermediate, which prevents the formation of a dense lead sulfate layer on the substrate metal surface. During charging, the morphology of PbO2 crystals is changed, making them smaller in size and more porous, which increases the surface area of ​​the electrode, thereby improving the utilization rate of the positive electrode active material and thus increasing the battery capacity.

[0016] Preferably, the additive comprises the following components by mass percentage of the total electrolyte: potassium sulfate 0.5%–1.5%, aluminum sulfate 0.5%–1.5%, sodium tetraborate 0.8%–1.2%, and perfluorooctyl sulfonate 0.002%–0.008%.

[0017] More preferably, the additive comprises the following components by mass percentage of the total electrolyte: 0.5% potassium sulfate, 1.5% aluminum sulfate, 0.8% sodium tetraborate, and 0.008% perfluorooctyl sulfonate.

[0018] Alternatively, the additive may comprise the following components by mass percentage of the total electrolyte: 1.5% potassium sulfate, 0.5% aluminum sulfate, 1.2% sodium tetraborate, and 0.002% perfluorooctyl sulfonate.

[0019] The sulfuric acid solution has a density of 1.245 g / cm³. 3 .

[0020] The present invention also provides a method for preparing the electrolyte for the lead-acid battery, wherein sodium tetraborate, aluminum sulfate, potassium sulfate, and perfluorooctyl sulfonate are added sequentially to a sulfuric acid solution with continuous stirring during the addition process. Preferably, sodium tetraborate, aluminum sulfate, potassium sulfate, and perfluorooctyl sulfonate are added sequentially to the sulfuric acid solution, with the next substance added only after the previous one has completely dissolved.

[0021] The present invention also provides a lead-acid battery, including an electrolyte, and using the electrolyte for lead-acid batteries. The lead-acid battery is used in electric bicycles.

[0022] The beneficial effects of this invention are:

[0023] This invention uses potassium sulfate, aluminum sulfate, sodium tetraborate, and perfluorooctyl sulfonate as additives in the electrolyte for lead-acid batteries. Through the eutectic effect of potassium sulfate and aluminum sulfate, the buffering effect of sodium tetraborate, and the adsorption effect of perfluorooctyl sulfonate, the positive electrode grid corrosion and negative electrode sulfation are inhibited in a synergistic manner, thereby extending the life of lead-acid batteries. Attached Figure Description

[0024] Figure 1 The cycling performance of the battery prepared with the electrolyte of Comparative Example 1 is shown in the figure.

[0025] Figure 2 The cycling performance of the battery prepared with the electrolyte of Comparative Example 2 is shown in the figure.

[0026] Figure 3 The cycling performance of the battery prepared with the electrolyte of Comparative Example 3 is shown in the figure.

[0027] Figure 4 The graph shows a comparison of the cycle performance of the batteries prepared with the electrolytes of Examples 1 and 2 with conventional batteries (in this invention patent, conventional batteries refer to batteries with an electrolyte containing 0.8% anhydrous sodium sulfate by mass, the same below). Detailed Implementation

[0028] Example 1

[0029] At 25℃, the density is taken as 1.4 g / cm³. 3 64.1 kg of sulfuric acid was added to 33.1 kg of pure water. The sulfuric acid was placed in a container and stirred thoroughly with a stirrer until the sulfuric acid was evenly distributed, resulting in a solid content of 33.5% (density approximately 1.245 g / cm³). 3 A sulfuric acid solution was prepared. Then, 800g of sodium tetraborate was added while stirring until it was completely dissolved. Then, 1500g of aluminum sulfate was added while stirring until it was completely dissolved. Then, 500g of potassium sulfate was added while stirring until it was completely dissolved. Then, 8g of perfluorooctyl sulfonate was added while stirring until it was completely dissolved. The electrolyte for the lead-acid battery was obtained.

[0030] Example 2

[0031] At 25℃, the density is taken as 1.4 g / cm³. 3 63.9 kg of sulfuric acid was added to 32.9 kg of pure water. The sulfuric acid was poured into the water and stirred thoroughly with a stirrer until the sulfuric acid was evenly distributed, resulting in a solid content of 33.5% (density approximately 1.245 g / cm³). 3A sulfuric acid solution was prepared. Then, 1200g of sodium tetraborate was added while stirring until it was completely dissolved. Then, 500g of aluminum sulfate was added while stirring until it was completely dissolved. Then, 1500g of potassium sulfate was added while stirring until it was completely dissolved. Then, 2g of perfluorooctyl sulfonate was added while stirring until it was completely dissolved. The electrolyte for the lead-acid battery was obtained.

[0032] Example 3

[0033] At 25℃, the density is taken as 1.4 g / cm³. 3 58.7 kg of sulfuric acid was added to 40.7 kg of pure water. The sulfuric acid was poured into the water and stirred thoroughly with a stirrer until the sulfuric acid was evenly distributed, resulting in a solid content of 30.0% (density approximately 1.215 g / cm³). 3 A sulfuric acid solution was prepared. Then, 200g of sodium tetraborate was added while stirring until it was completely dissolved. Then, 200g of aluminum sulfate was added while stirring until it was completely dissolved. Then, 200g of potassium sulfate was added while stirring until it was completely dissolved. Then, 1g of perfluorooctyl sulfonate was added while stirring until it was completely dissolved. The electrolyte for the lead-acid battery was obtained.

[0034] Example 4

[0035] At 25℃, the density is taken as 1.4 g / cm³. 3 64.8 kg of sulfuric acid was added to 29.2 kg of pure water. The sulfuric acid was poured into the water and stirred thoroughly with a stirrer until the sulfuric acid was evenly distributed, resulting in a solid content of 35.0% (density approximately 1.256 g / cm³). 3 A sulfuric acid solution was prepared. Then, 2000g of sodium tetraborate was added while stirring until it was completely dissolved. Then, 2000g of aluminum sulfate was added while stirring until it was completely dissolved. Then, 2000g of potassium sulfate was added while stirring until it was completely dissolved. Then, 10g of perfluorooctyl sulfonate was added while stirring until it was completely dissolved. The electrolyte for the lead-acid battery was obtained.

[0036] Comparative Example 1

[0037] Single-factor validation of aluminum sulfate: Aluminum sulfate with different addition amounts (1.0, 2.0, 2.5, 3.75, 5.0, 6.25 wt.%). Preparation method of electrolyte with added aluminum sulfate: At 25℃, samples with a density of 1.4 g / cm³ were taken... 3Sulfuric acid was prepared in quantities of 65.3 kg, 64.7 kg, 64.3 kg, 63.5 kg, 62.7 kg, and 61.9 kg. Pure water was then added to each container in quantities of 33.7 kg, 33.3 kg, 33.2 kg, 32.7 kg, 32.3 kg, and 31.9 kg. The sulfuric acid was added to the water, and the mixture was stirred thoroughly with a stirrer until the sulfuric acid was evenly distributed. Six groups of solutions were obtained, each with a solid content of 33.5% (density approximately 1.245 g / cm³). 3 A sulfuric acid solution was prepared. Then, 1000g, 2000g, 2500g, 3750g, 5000g, and 6250g of aluminum sulfate were added to each of the six sulfuric acid solutions while stirring until they were completely dissolved. The electrolyte for the lead-acid battery was obtained.

[0038] Comparative Example 2

[0039] Single-factor validation of sodium tetraborate: Sodium tetraborate with different addition amounts (0.8, 1.2, 1.6, 2.0 wt.%). Preparation method of electrolyte with added sodium tetraborate: At 25℃, samples with a density of 1.4 g / cm³ were taken... 3 Sulfuric acid was prepared in quantities of 65.5 kg, 65.2 kg, 64.9 kg, and 64.7 kg. Pure water was then added in quantities of 33.7 kg, 33.6 kg, 33.5 kg, and 33.3 kg, respectively. The sulfuric acid was added to the water in separate containers, and the mixture was stirred thoroughly with a stirrer until the sulfuric acid was evenly distributed. Four groups of solutions were obtained, each with a solid content of 33.5% (density approximately 1.245 g / cm³). 3 A sulfuric acid solution was prepared. Then, 800g, 1200g, 1600g, and 2000g of sodium tetraborate were added to each of the four sulfuric acid solutions while stirring until they were completely dissolved. The electrolyte for the lead-acid battery was obtained.

[0040] Comparative Example 3

[0041] Single-factor validation of perfluorooctyl sulfonate: Perfluorooctyl sulfonate with different addition amounts (0.002, 0.004, 0.008, 0.016 wt.%). Preparation method of electrolyte with added perfluorooctyl sulfonate: At 25℃, samples with a density of 1.4 g / cm³ were taken... 3 Four groups of sulfuric acid, each weighing 66 kg, were prepared, and four groups of pure water, each weighing 34 kg, were also prepared. Sulfuric acid was added to the water in separate containers, and the mixture was stirred thoroughly with a stirrer until the sulfuric acid was evenly distributed. The resulting four groups had a solid content of 33.5% (density approximately 1.245 g / cm³). 3 A sulfuric acid solution was prepared. Then, 2g, 4g, 8g, and 16g of perfluorooctyl sulfonate were added to each of the four sulfuric acid solutions while stirring until they were completely dissolved. The electrolyte for the lead-acid battery was obtained.

[0042] Test Example 1

[0043] The electrolytes prepared in Examples 1-2 and Comparative Examples 1-3 were assembled into 6-EVF-20 (12V 20Ah) batteries and then subjected to cycle performance testing. The test conditions were as follows:

[0044] 1) Discharge at 10A until the battery terminal voltage drops to 10.5V;

[0045] 2) Charge at a constant current until the battery terminal voltage reaches 14.8V;

[0046] 3) Switch to constant voltage charging. When the total time for constant current charging and constant voltage charging reaches 4.25 hours, charging will terminate.

[0047] 4) Let stand for 0.5 hours.

[0048] Steps 1) through 4) above constitute one cycle. Repeat this cycle until the capacity drops below 80% of the initial capacity, at which point the battery life ends. Battery life is characterized by the number of cycles completed. Test results are as follows: Figures 1-4 As shown.

[0049] like Figure 1 As shown, single-factor validation of aluminum sulfate on a 6-EVF-20 (12V 20Ah) electric bicycle battery did not achieve the expected results, with 9-98 fewer cycle times than conventional batteries. Furthermore, when the addition amount exceeded 2.0 wt.%, the cycle life decreased further with increasing aluminum sulfate content.

[0050] like Figure 2 As shown, the single-factor test results for sodium tetraborate also did not yield a positive effect, with 3-8 fewer cycle times compared to conventional batteries. Furthermore, when the content exceeds 2.0 wt.%, it significantly increases grid corrosion.

[0051] like Figure 3 As shown, verification of perfluorooctyl sulfonate revealed that while it does not improve battery cycle performance, resulting in 5–21 fewer cycles compared to conventional batteries, it can increase the initial capacity of the battery to some extent.

[0052] like Figure 4 As shown, the conventional battery with 0.8% anhydrous sodium sulfate added by mass had a cycle life of 253 cycles. The battery in Example 1, with the addition of potassium sulfate, aluminum sulfate, sodium tetraborate, and perfluorooctyl sulfonate to the electrolyte, had a cycle life of 293 cycles, representing a 15.8% increase. The battery in Example 2 had a cycle life of 299 cycles, representing an 18.2% increase. Overall, the electrolyte additives described in this invention can significantly improve battery cycle life by more than 15%, demonstrating remarkable effectiveness and having significant implications for extending the lifespan and enhancing the competitiveness of lead-acid batteries.

Claims

1. An electrolyte for lead-acid batteries, comprising a sulfuric acid solution and additives, characterized in that, The additive, by mass percentage of the total electrolyte, consists of the following components: potassium sulfate 0.5%–1.5%, aluminum sulfate 0.5%–1.5%, sodium tetraborate 0.8%–1.2%, and perfluorooctyl sulfonate 0.002%–0.008%.

2. The electrolyte for a lead-acid battery according to claim 1, characterized in that, The additive, by mass percentage of the total electrolyte, consists of the following components: 0.5% potassium sulfate, 1.5% aluminum sulfate, 0.8% sodium tetraborate, and 0.008% perfluorooctyl sulfonate. Alternatively, the additive may consist of the following components by mass percentage of the total electrolyte: 1.5% potassium sulfate, 0.5% aluminum sulfate, 1.2% sodium tetraborate, and 0.002% perfluorooctyl sulfonate.

3. The electrolyte for a lead-acid battery according to claim 1, characterized in that, The sulfuric acid solution has a density of 1.215–1.256 g / cm³. 3 .

4. A method for preparing the electrolyte for a lead-acid battery according to any one of claims 1 to 3, characterized in that, Sodium tetraborate, aluminum sulfate, potassium sulfate, and perfluorooctyl sulfonate were added to the sulfuric acid solution in sequence, with continuous stirring during the addition process.

5. The preparation method according to claim 4, characterized in that, Sodium tetraborate, aluminum sulfate, potassium sulfate, and perfluorooctyl sulfonate were added to a sulfuric acid solution in sequence, with each addition added only after the previous one had completely dissolved.

6. A lead-acid battery, comprising an electrolyte, characterized in that, Use the electrolyte for lead-acid batteries according to any one of claims 1 to 3.

7. The lead-acid battery as described in claim 6, characterized in that, The lead-acid battery is used in electric bicycles.

Images