A Testing Method for the Thin Film Resistance of the Positive Electrode Additive of Lead-Acid Batteries

Abstract

The present invention relates to the technical field of positive electrode additives for lead-acid batteries, and particularly relates to a method for testing the thin film resistance of positive electrode additives for lead-acid batteries, which includes: (1) taking two lead plates with clean surfaces, and uniformly coating the positive electrode additive to be tested on one side surface of the lead plates in the form of an emulsion; (2) vacuum-drying the coated two lead plates, and keeping the coated surfaces of the lead plates facing upward; (3) after drying, closely fitting the coated surfaces of the two lead plates, distributing and attaching the two test electrodes of the resistance meter to the outer side surfaces of the two lead plates, and reading the resistance after stabilization. The testing method of the present invention simulates the state of the coated lead particles under the use state of the positive electrode additive, can accurately and stably test the conductive performance of different positive electrode additives, provides a basis for comparing the enhancement effects of different positive electrode additives on the electron conduction ability between particles, and selecting suitable positive electrode additives, and has the possibility of being transformed into an enterprise or industry testing specification.

Description

Technical Field

[0001] The present invention relates to the technical field of positive electrode additives for lead-acid batteries, and specifically relates to a method for testing the thin film resistance of positive electrode additives for lead-acid batteries. Background Art

[0002] At present, the power density and energy density of lead-acid batteries are relatively low. In addition to the relatively large density of lead and lead compounds, since the positive electrode reaction requires hydrogen ions to participate, the positive electrode potential is more sensitive to the change of acid density. At the same time, the resistance of lead dioxide is greater than that of spongy lead, resulting in a lower utilization rate of the positive electrode active material than that of the negative electrode. Therefore, improving the utilization rate of the positive electrode active material is an important indicator for improving the energy density of lead-acid batteries, leading to a low utilization rate of the active material.

[0003] To improve the utilization rate of the active material, a relatively common practice is to add additives to the positive electrode active material, including non-conductive additives and conductive additives. Among them, the purpose of non-conductive additives such as zeolite is to increase the porosity of the electrode plate and the specific surface area of the active material, while the purpose of conductive agents such as graphite is to improve the conductivity of the electrode plate. At present, adding polymer emulsion as an additive to the positive electrode active material has become a research direction. The polymer mainly plays the role of improving the conductivity between the particles of the positive electrode active material and maintaining the skeleton of the active material. However, the performance differences of different polymers are relatively large, especially the conductivity. Moreover, the conductivity of the polymer after being added to the positive electrode active material is very different from the conductivity when it is in the form of an emulsion. How to appropriately characterize the conductivity of the polymer after being added to the positive electrode active material and provide a reference for selecting a suitable polymer as an additive has become an urgent technical problem to be solved.

[0004] The conductivity of polymer materials can generally be measured by an insulation resistance tester. Specifically, for example, measurement electrodes and high-voltage electrodes of the insulation resistance tester are connected to both sides of polymer thin films such as PMMA, PTFE or PVC, and protection electrodes are applied. The resistance of the thin film between the high-voltage electrode and the measurement electrode is measured in the volume resistance mode, and the resistivity can be calculated. However, this test method mainly targets finished polymer film materials, where the conductivity is consistent everywhere, and the resistance itself is relatively large, generally reaching an order of magnitude above 10 13 Moreover, after the polymer emulsion is added to the positive electrode active material and dried into a film, on the one hand, due to the small addition amount and the relatively thin covering film thickness, usually less than a few micrometers, and due to the presence of conductive substances, the overall resistance is usually very small; on the other hand, its resistance performance is not only related to the polymer itself, but also related to the uniformity of film formation, etc. Therefore, the existing insulation resistance tester has poor applicability to the test method for the conductivity of polymer emulsion. Summary of the Invention

[0005] To test the electrical conductivity of polymer and provide reference for selecting appropriate additives, the purpose of the method of the present invention is to provide a method for testing the thin film resistance of the positive electrode additive of lead-acid battery, simulate the film-forming use state of additives such as polymer, and measure its electrical conductivity.

[0006] The present invention provides the following technical solutions:

[0007] A method for testing the thin film resistance of the positive electrode additive of lead-acid battery, comprising the following steps:

[0008] (1) Take two lead plates with clean surfaces, and evenly coat the positive electrode additive to be tested on one side surface of the lead plates in the form of emulsion.

[0009] (2) Vacuum-dry the two coated lead plates, and keep the coated surfaces of the lead plates facing upward.

[0010] (3) After drying, closely attach the coated surfaces of the two lead plates, distribute and attach the two test electrodes of the resistance meter to the outer side surfaces of the two lead plates, and read the resistance after stabilization.

[0011] The testing method of the present invention simulates the situation when the additive is coated on lead particles for use. The additive is coated on the lead plates. At the same time, the resistivity of the lead plates is low and their own resistance is small, and the obtained results can more truly reflect the resistance or electrical conductivity of the positive electrode additive. When testing, the positive electrode additive is formed into a film on the surfaces of the two lead plates, and the measurement is carried out after being joined together. This greatly improves the testing accuracy compared with only using one lead plate, or using two lead plates but only coating the positive electrode additive on the surface of one lead plate. The reasons are as follows: When only using one lead plate and coating the positive electrode additive on its surface, due to the microporous structure of the coating film itself, even a slight movement when the electrode end contacts the coating film directly may cause a change in the reading, resulting in unstable test results; when using two lead plates and only coating the positive electrode additive on one lead plate, although the other lead plate is closely attached to the coating film, there is a large space hindrance at the contact surface between the coating film and this lead plate because they do not adhere to each other, so the measurement error will be increased. When coating and distributing on two lead plates and closely attaching them, the contact effect between the two coating films is much better than the contact effect between the coating film and the lead plate. Therefore, the overall measurement result is more accurate and stable.

[0012] As a preference of the method of the present invention, the thickness of the lead plates is 0.6 - 1 mm, and the size of the lead plates is 40×40 mm - 60×60 mm. Select small and thin lead plates to reduce the influence of the resistance of the lead plates.

[0013] As a preference of the method of the present invention, the coating thickness of the emulsion is 1 - 2 μm. The coating thickness should not be too large, which is likely to cause the tendency of the outer film to detach.

[0014] Preferably, in step (2) of the method of the present invention, the vacuum drying temperature ≤ 60°C.

[0015] Preferably, in step (2) of the method of the present invention, after the lead plate is vacuum dried to a water content of 10 - 15 wt%, it is converted to freeze drying, the freeze drying temperature is -30 to -20°C, and the drying pressure is 20 - 30 Pa.

[0016] Although the actual coating film is used in a water-containing environment, in the test state, the water contained in the coating film will affect the test accuracy. Removing the water as much as possible and presenting it in the form of pure additives will result in more comparable results. Dehydration by methods such as vacuum drying or hot air drying is actually still a kind of heat drying (even vacuum drying requires a suitable heating temperature). Excessive dehydration easily leads to micropores or surface cracking of the coated film, and can further cause cracking and material loss when the two lead plates are closely attached, thus deviating from the true state of the coated film and affecting the test results. Therefore, in the present invention, on the basis of vacuum drying for film forming and shaping, further freeze drying treatment is carried out to remove water without damaging the film structure. If only freeze drying is used, the large amount of sublimation of water can cause changes in the structure of the emulsion. After all, the emulsion gradually forms a film during the drying process, which is different from directly freeze drying to remove water in a solid.

[0017] Preferably, in step (2) of the method of the present invention, the lead plate is placed at a temperature of 25 - 30°C and a pressure of 3 - 5 atm for 2 - 4 hours and then vacuum dried to a water content of 10 - 15 wt%. The water contained in the coated film after vacuum drying is made fully uniform by standing still.

[0018] Preferably, in step (3) of the method of the present invention, the two test electrodes of the resistance meter test the centers of the outer sides of the two lead plates.

[0019] Preferably, the dried lead plate is allowed to stand at 20 ± 2°C for 12 - 24 hours before measurement to eliminate the influence of temperature on the resistance test.

[0020] Preferably, the positive electrode additive is a polymer additive.

[0021] The beneficial effects of the present invention are as follows:

[0022] The test method of the present invention simulates the state of the coated lead particles under the use state of the positive electrode additive, can accurately and stably test the conductive performance of different positive electrode additives, provides a basis for comparing the enhancement effects of different positive electrode additives on the inter-particle electron conduction ability, and selecting suitable positive electrode additives, and has the possibility of being transformed into an enterprise or industry test standard. Specific Embodiments

[0023] The following further describes the specific embodiments of the present invention.

[0024] Unless otherwise specified, the raw materials used in the present invention can be obtained from the market or are commonly used in the art. Unless otherwise specified, the methods in the following examples are all conventional methods in the art.

[0025] In the following examples and comparative examples, polytetrafluoroethylene emulsion (solid content 60%) is used as the positive electrode additive for illustration.

[0026] Example 1

[0027] A method for testing the film resistance of a positive electrode additive for a lead-acid battery is as follows:

[0028] (1) Clean and dry the surfaces of two pure lead plates with a thickness of 0.8 mm and a size of 52×52 mm, and then evenly coat the surfaces of one side of the two pure lead plates with polytetrafluoroethylene emulsion, with a coating thickness of 1 μm;

[0029] (2) Place the coated surfaces of the two pure lead plates upward in a vacuum drying oven and dry at 60°C until the water content is 1±0.1 wt% (which can be calculated by weighing before and after drying);

[0030] (3) Take out the two pure lead plates, closely attach the coated surfaces of the two lead plates, and clamp them with a plastic clip. Let them stand at 20±2°C for 24 hours, and then place the two test electrodes of the resistance meter at the center positions of the outer sides of the two lead plates for measurement. Record when the reading is stable. Measure three times in total and take the average result.

[0031] Example 2

[0032] A method for testing the film resistance of a positive electrode additive for a lead-acid battery is as follows:

[0033] (1) Clean and dry the surfaces of two pure lead plates with a thickness of 0.8 mm and a size of 52×52 mm, and then evenly coat the surfaces of one side of the two pure lead plates with polytetrafluoroethylene emulsion, with a coating thickness of 1 μm;

[0034] (2) Place the coated surfaces of the two pure lead plates upward in a vacuum drying oven and dry at 60°C until the water content is 15±0.1 wt%;

[0035] (3) Freeze-dry the two lead plates at a temperature of -20°C and a pressure of 30 Pa until the water content is 1±0.1 wt%;

[0036] (4) Take out the two pure lead plates, closely attach the coated surfaces of the two lead plates, and clamp them with a plastic clip. Let them stand at 20±2°C for 24 hours, and then place the two test electrodes of the resistance meter at the center positions of the outer sides of the two lead plates for measurement. Record when the reading is stable. Measure three times in total and take the average result.

[0037] Example 3

[0038] A test method for the thin film resistance of a positive electrode additive of a lead-acid battery is as follows:

[0039] (1) Clean and dry the surfaces of two pure lead plates with a thickness of 0.8 mm and a size of 52×52 mm, and then evenly coat the surfaces of one side of the two pure lead plates with polytetrafluoroethylene emulsion, with a coating thickness of 1 μm;

[0040] (2) Place the coated surfaces of the two lead plates upward, let them stand still for 2 hours at 25°C and 3 atm, transfer them to a vacuum drying oven, and dry at 60°C until the water content is 15±0.1 wt%;

[0041] (3) Freeze-dry the two lead plates at a temperature of -20°C and a pressure of 30 Pa until the water content is 1±0.1 wt%;

[0042] (4) Take out the two pure lead plates, closely fit the coated surfaces of the two lead plates together, clamp them with a plastic clip, and then let them stand still for 24 hours at 20±2°C. Then, place the two test electrodes of the resistance meter at the center positions of the outer sides of the two lead plates for measurement. After the reading is stable, record it. Measure three times in total and take the average result.

[0043] Comparative Example 1

[0044] A test method for the thin film resistance of a positive electrode additive of a lead-acid battery is as follows:

[0045] (1) Clean and dry the surface of a pure lead plate with a thickness of 0.8 mm and a size of 52×52 mm, and then evenly coat the surface of one side of the pure lead plate with polytetrafluoroethylene emulsion, with a coating thickness of 1 μm;

[0046] (2) Place the coated surface of the pure lead plate upward in a vacuum drying oven and dry at 60°C until the water content is nearly 1±0.1 wt%;

[0047] (3) Take out the pure lead plate and let it stand still for 24 hours at 20±2°C. Then, place the two test electrodes of the resistance meter at the center positions of the two sides of the lead plate for measurement. After the reading is stable, record it. Measure three times in total and take the average result.

[0048] Comparative Example 2

[0049] A test method for the thin film resistance of a positive electrode additive of a lead-acid battery is as follows:

[0050] (1) Clean and dry the surfaces of two pure lead plates with a thickness of 0.8 mm and a size of 52×52 mm, and then evenly coat the surface of one side of one of the pure lead plates with polytetrafluoroethylene emulsion, with a coating thickness of 1 μm;

[0051] (2) Place the coated surface of the pure lead plate upward in a vacuum drying oven and dry at 60 °C until the water content is nearly 1 ± 0.1 wt%.

[0052] (3) Take out the pure lead plate, closely attach the coated surface of another lead plate to the coated surface of the lead plate coated with polytetrafluoroethylene, clamp it with a plastic clip, let it stand at 20 ± 2 °C for 24 hours, then place the two test electrodes of the resistance meter at the center positions of the outer sides of the two lead plates respectively for measurement. Record when the reading is stable. Measure three times in total and take the average result.

[0053] Comparative Example 3

[0054] A test method for the thin-film resistance of a lead-acid battery positive electrode additive is as follows:

[0055] (1) Clean and dry the surfaces of two pure lead plates with a thickness of 0.8 mm and a size of 52 × 52 mm, and then evenly coat the surfaces of one side of the two pure lead plates with polytetrafluoroethylene emulsion, with a coating thickness of 1 μm.

[0056] (2) Place the coated surfaces of the two pure lead plates upward and freeze-dry at a temperature of -20 °C and a pressure of 30 Pa until the water content is 1 ± 0.1 wt%.

[0057] (3) Take out the two pure lead plates, closely attach the coated surfaces of the two lead plates, clamp them with a plastic clip, then let them stand at 20 ± 2 °C for 24 hours, and then place the two test electrodes of the resistance meter at the center positions of the outer sides of the two lead plates respectively for measurement. Record when the reading is stable. Measure three times in total and take the average result.

[0058] Comparative Example 4

[0059] A test method for the thin-film resistance of a lead-acid battery positive electrode additive is as follows:

[0060] (1) Clean and dry the surfaces of two pure lead plates with a thickness of 0.8 mm and a size of 52 × 52 mm, and then evenly coat the surfaces of one side of the two pure lead plates with polytetrafluoroethylene emulsion, with a coating thickness of 1 μm.

[0061] (2) Place the coated surfaces of the two lead plates upward, let them stand at 25 °C and 3 atm for 2 hours, then transfer them to a vacuum drying oven and dry at 60 °C until the water content is 1 ± 0.1 wt%.

[0062] (3) Take out the two pure lead plates, closely attach the coated surfaces of the two lead plates, clamp them with a plastic clip, then let them stand at 20 ± 2 °C for 24 hours, and then place the two test electrodes of the resistance meter at the center positions of the outer sides of the two lead plates respectively for measurement. Record when the reading is stable. Measure three times in total and take the average result.

[0063] Comparative Example 5

[0064] A test method for the thin film resistance of a positive electrode additive of a lead-acid battery is as follows:

[0065] (1) Clean and dry the surfaces of two pure lead plates with a thickness of 0.8 mm and a size of 52×52 mm, and then evenly coat the surface of each side of the two pure lead plates with polytetrafluoroethylene emulsion, with a coating thickness of 1 μm;

[0066] (2) Place the coated surfaces of the two lead plates upward, let them stand still in an environment of 25°C and normal pressure for 2 hours, transfer them to a vacuum drying oven, and dry at 60°C until the water content is 15±0.1 wt%;

[0067] (3) Freeze-dry the two lead plates at a temperature of -20°C and a pressure of 30 Pa until the water content is 1±0.1 wt%;

[0068] (4) Take out the two pure lead plates, closely fit the coated surfaces of the two lead plates together, clamp them with a plastic clip, and then place the two test electrodes of a resistance meter at the center positions of the outer sides of the two lead plates respectively for measurement after standing still at 20±2°C for 24 hours. Record when the reading is stable, measure three times in total, and take the average result.

[0069] Repeat each of the examples and comparative examples 5 times, record the results of each time, calculate the average value, standard deviation and coefficient of variation, and the results are shown in Table 1.

[0070] Table 1 Repeated test results of each example and comparative example

[0071]

[0072] As can be seen from the above table, more stable and accurate test results can be obtained by using the test method of the present application:

[0073] Compared with the direct testing of the single-board coating in Comparative Example 1 and the double-board lamination of the single-board coating in Comparative Example 2, as shown in Example 1, the coefficient of variation of the measurement results using double-board coating and double-board lamination is small and the stability is higher. At the same time, the average test value of the double-board lamination of the single-board coating in Comparative Example 2 is larger compared with other groups of Examples and Comparative Examples, indicating that the measured value is on the high side. As shown in Example 2, after vacuum drying the coated film to a water content of 10-15 wt%, followed by freeze drying, the stability of the measurement results can be further improved compared with Example 1, and the coefficient of variation is smaller. However, directly using freeze drying to replace vacuum drying, as shown in Comparative Example 3, the overall test results are comparable to those of Example 1, but the energy consumption is higher and the operation time is longer. And as shown in Example 3, first applying water leveling under a certain pressure, and then performing vacuum drying and freeze drying will help to further improve the stability of the measurement results. However, combining pressure water leveling and vacuum drying, as shown in Comparative Example 4, the overall test results are comparable to those of Example 1. This may be because although water leveling helps to homogenize the film structure, the high degree of dehydration during vacuum drying causes cracks and even slight material loss in the coating layer, weakening the effect brought by water leveling. Or water leveling under normal pressure, and then vacuum drying and freeze drying, as shown in Comparative Example 5, the overall test results are comparable to those of Example 2, that is, water leveling requires a certain pressure and can only play its corresponding role when combined with vacuum drying and freeze drying.

Claims

1. A test method for the thin film resistance of a positive electrode additive of a lead-acid battery, comprising the following steps: (1) Take two lead plates with clean surfaces, and evenly coat the positive electrode additive to be tested on one side surface of the lead plates in the form of an emulsion, and the coating thickness of the emulsion is 1-2 µm; (2) Vacuum dry the two coated lead plates and keep the coated surfaces of the lead plates facing upward; (3) After drying, closely attach the coated surfaces of the two lead plates, distribute and attach the two test electrodes of the resistance meter to the outer side surfaces of the two lead plates, and read the resistance after stabilization.

2. The test method according to claim 1, characterized in that The thickness of the lead plates is 0.6-1 mm, and the size of the lead plates is 40×40 mm to 60×60 mm.

3. The test method according to claim 1, wherein In step (2), the vacuum drying temperature ≤ 60°C.

4. The test method according to claim 1 or 3, characterized in that Step (2) also includes vacuum drying the lead plates until the water content is 10-15 wt%, then converting to freeze drying, the freeze drying temperature is -30 to -20°C, and the drying pressure is 20-30 Pa.

5. The testing method according to claim 1, wherein In step (1), the lead plates are placed at a temperature of 25-30°C and a pressure of 3-5 atm for 2-4 hours and then vacuum dried until the water content is 10-15 wt%.

6. The test method according to claim 1, wherein In step (3), the two test electrodes of the resistance meter test the centers of the outer side surfaces of the two lead plates.

7. The test method according to claim 1, characterized in that, The dried lead plates are left standing at 20 ± 2°C for 12-24 hours and then the resistance is measured.

8. The test method according to claim 1, characterized in that, The positive electrode additive is a polymer additive.

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