A method for preparing a lead-acid battery membrane electrode

Abstract

The present application relates to the technical field of lead-acid battery electrode, aiming at the problem of thick lead paste on the existing lead-acid battery plate, large resistance during charging and poor rate discharge performance of the battery, a preparation method of lead-acid battery membrane electrode is disclosed, comprising the following steps: adding a binder to the prepared lead paste, rolling the lead paste containing the binder on the lead skin to form a lead paste film layer, immersing the lead skin and the attached lead paste film layer in a sulfuric acid solution, and solidifying and drying after taking out; the binder is polytetrafluoroethylene emulsion or a binder containing polytetrafluoroethylene emulsion. Unlike the high molecular film attached to the surface of the lead-acid battery plate in the prior art, the present application obtains a thin film electrode with thin thickness, uniform active material dispersion, large active material and current collector contact area and good conductivity, and has the advantages of large rate charge and discharge cycle.

Description

A method for preparing a membrane electrode for a lead-acid battery Technical Field

[0001] This invention relates to the field of lead-acid battery electrode technology, and specifically to a method for preparing a lead-acid battery membrane electrode. Background Technology

[0002] The plates of a lead-acid battery are a key component that determines the battery's discharge capacity and discharge capability. Plates are made by pressing lead paste active material into a grid made of materials such as lead-calcium alloy and then curing it. The grid ribs support and hold the active material, resulting in a thicker layer of lead paste on the grid, higher plate resistance, poorer rate charge / discharge performance, and the tendency for the active material to detach from the grid after a certain number of charge / discharge cycles.

[0003] To prevent the shedding of active materials and improve the cycle life of the electrode, Chinese patent application CN101989654A proposed a membrane electrode for lead-acid batteries. By depositing a layer of polymer material film on the surface of existing plates, the problem of active material shedding during cycling can be solved to some extent. However, this membrane electrode not only does not reduce the charging and discharging resistance of the plates, but also increases the resistance, which reduces the rate discharge performance of the battery. Summary of the Invention

[0004] To address the problems of thick lead paste on the plates of existing lead-acid batteries, resulting in high resistance during charging and poor rate discharge performance, the present invention aims to provide a method for preparing a thin-film electrode for lead-acid batteries. By thinning the lead-acid battery electrode, the electrode resistance is reduced, and it has advantages such as high-rate charge-discharge cycle performance.

[0005] This invention provides the following technical solution:

[0006] A method for preparing a lead-acid battery membrane electrode includes the following steps:

[0007] A binder is added to the lead paste to be prepared. The lead paste containing the binder is rolled onto the lead sheet to form a lead paste film. The lead sheet and the attached lead paste film are then immersed in a sulfuric acid solution, removed, cured, and dried.

[0008] The adhesive is a polytetrafluoroethylene emulsion or an adhesive containing a polytetrafluoroethylene emulsion.

[0009] This invention provides a method for preparing a thin-film lead-acid battery electrode. Lead sheet is used as the current collector, and a binder is added to lead paste. The active material of the lead paste is rolled and spread onto the surface of the lead sheet to form a film. The lead sheet thickness is 0.01–5 mm. The smooth surface of the lead sheet allows the active material of the lead paste to be rolled into a film. The binder is a key factor in achieving effective adhesion and film formation of the lead paste film; therefore, the selection of the binder is very important. By optimizing the selection of polytetrafluoroethylene (PTFE) emulsion as the binder, the network formed by the fibrous formation of PTFE emulsion can maintain good adhesion between the active materials of the lead paste and between the lead paste and the lead sheet, thus obtaining a thin-film lead-acid battery electrode. Although the insulation properties of PTFE partially offset the low resistance advantage brought by the thin-film method, the resulting film electrode has lower resistance and higher rate charge / discharge performance compared to ordinary lead-acid battery electrodes.

[0010] As a preferred embodiment of the method of the present invention,

[0011] The binder containing polytetrafluoroethylene emulsion includes: polytetrafluoroethylene emulsion, epoxy resin, epoxy-modified carbon nanotubes, and curing agent;

[0012] The mass ratio of epoxy resin to polytetrafluoroethylene emulsion is 1:2 to 3.5;

[0013] The mass ratio of epoxy resin to epoxy-modified carbon nanotubes is 1:0.2 to 0.3.

[0014] While the rate charge-discharge performance of the membrane electrode has been improved, its cycle charge-discharge capability still lags behind that of a conventional lead-acid battery. This may be because polytetrafluoroethylene (PTFE) has weak toughness; prolonged contact with lead-acid battery electrolyte and absorption of water reduces its molecular weight and viscosity, making it prone to swelling. Furthermore, PTFE emulsion is a point-type binder, bonding with the active material at points, lacking long-distance connections, resulting in poor electrode mechanical properties and easy detachment of the active material. Therefore, the inventors, through research, selected epoxy resin with high adhesion, acid and alkali resistance, good dimensional stability, and low internal stress for use in conjunction with the PTFE emulsion, and introduced epoxy-modified carbon nanotubes for reinforcement. The carbon nanotubes participate in the cross-linking and curing of the epoxy resin, improving the toughness and impact resistance of the resin system. Moreover, the conductivity of the carbon nanotubes can compensate to some extent for the increased resistance caused by the insulation properties of the epoxy resin and PTFE. This results in a membrane electrode that, compared to ordinary grid electrodes, not only has higher rate charge-discharge performance but also maintains its cycle charge-discharge capability.

[0015] As a preferred embodiment of the method of the present invention,

[0016] Epoxy-based surface-modified carbon nanotubes are obtained through the following process:

[0017] Carbon nanotubes were dispersed in an alkaline alcohol-water solution and ball-milled. After removal, the carbon nanotubes were rinsed until neutral and then dried to obtain hydroxyl-modified carbon nanotubes. These were then dispersed in an alcohol-water solution with an epoxy-based silane coupling agent for modification. After removal, the carbon nanotubes were rinsed and dried to obtain epoxy-based modified carbon nanotubes.

[0018] Carbon nanotubes are hydroxylated on the surface through ball milling in alkaline and alcoholic water, and then reacted with a silane coupling agent containing epoxy groups. After the silane coupling agent is hydrolyzed, carbon nanotubes are grafted onto the surface, so that the carbon nanotubes have epoxy groups on the surface. This allows the carbon nanotubes to participate in the curing and cross-linking of epoxy resin, and as a component of the cross-linking network, it effectively improves the toughness and impact resistance of the resin layer.

[0019] As a preferred embodiment of the method of the present invention,

[0020] The alkali used is sodium hydroxide or potassium hydroxide, and the mass ratio of carbon nanotubes to alkali is 1:15 to 30.

[0021] The ratio of carbon nanotubes to alcohol aqueous solution is 1g:100-200mL;

[0022] The mass ratio of carbon nanotubes to epoxy silane coupling agent is 1:0.06 to 0.1.

[0023] As a preferred embodiment of the method of the present invention,

[0024] The binder containing polytetrafluoroethylene emulsion also includes epoxy-modified nano-fumed silica;

[0025] The mass ratio of epoxy resin to epoxy-modified nano-fumed silica is 1:0.1 to 0.15.

[0026] Using epoxy resin, polytetrafluoroethylene emulsion, and carbon nanotubes as a binder can improve the cycle charge-discharge capability of thin-film electrodes, but the cycle charge-discharge performance varies between different batches. Analysis suggests this may be due to the fact that carbon nanotubes are one-dimensional materials, while lead powder and other materials are particulate. Furthermore, the one-dimensional dimension (length) of carbon nanotubes can reach tens to hundreds of micrometers, while the particle size of lead powder is mostly around 5 μm. Although the flexibility of carbon nanotubes allows them to be added to lead paste, the mismatch in shape and size between carbon nanotubes and lead powder increases the randomness of carbon nanotubes' inability to effectively participate in the cross-linking of epoxy resin. What works well one time may not work well the next, resulting in variations in the cycle charge-discharge capability between different batches of electrodes within a certain range. Therefore, epoxy-modified nano-fumed silica is further introduced into the binder. The particle size of nano-fumed silica is generally 5-10 nm, which is much smaller than that of lead powder and carbon nanotubes (the diameter of carbon nanotubes is generally 2-100 nm). It fills the places where carbon nanotubes cannot be dispersed and participates in cross-linking and curing, thus supplementing the carbon nanotubes and further improving the stability of electrode cycling capability.

[0027] As a preferred embodiment of the method of the present invention,

[0028] Epoxy-modified nano-fumed silica is obtained by dispersing nano-fumed silica and epoxy-based silane coupling agents in an alcohol-water solution for modification reaction, followed by rinsing and drying.

[0029] The density of silanol groups on the surface of nano-vaporized silica is 1.5–2.5 per nm. 2 ;

[0030] The mass ratio of nano-fumed silica to epoxy silane coupling agent is 1:0.05–0.1;

[0031] The ratio of nano-fumed silica to alcohol-water solution is 1g:100-200mL.

[0032] The surface of nano-fumed silica should maintain an appropriate density of silanol groups. Excessive silanol group density will cause excessive cross-linking centered on fumed silica, resulting in increased stress in the cross-linking network, which is not conducive to enhancing cycle capacity.

[0033] As a preferred embodiment of the method of the present invention,

[0034] The epoxy silane coupling agent used is selected from 2-(3,4-epoxycyclohexyl)ethyltriethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane and 3-(2,3-epoxypropoxy)propyltrimethoxysilane;

[0035] The alcohol-water solution used is an aqueous solution of ethanol, ethylene glycol, or propanol, with a volume ratio of alcohol to water of 5 to 10:1.

[0036] As a preferred embodiment of the method of the present invention, the epoxy resin is selected from one or more of bisphenol A epoxy resin, bisphenol F epoxy resin, bisphenol AD ​​epoxy resin, bisphenol S epoxy resin, resorcinol-type epoxy resin, hydroxymethyl bisphenol A epoxy resin, hydrogenated bisphenol A epoxy resin, and organosilicon-modified bisphenol A epoxy resin.

[0037] As a preferred embodiment of the method of the present invention, the mass of the adhesive is 1 to 10% of the mass of the lead paste.

[0038] As a preferred embodiment of the method of the present invention, the thickness of the lead paste film after curing and drying is 70-100 μm.

[0039] The beneficial effects of this invention are as follows:

[0040] This invention provides a method for preparing a thin-film electrode for lead-acid batteries. Unlike the prior art of attaching a polymer film to the surface of a lead-acid battery plate, this invention yields a thin-film electrode with thin thickness, uniform dispersion of active material, large contact area between active material and current collector, and good conductivity. It has the advantages of high-rate charge-discharge cycle performance, and the battery active material is not easily detached, resulting in good cycle charge-discharge performance. Detailed Implementation

[0041] The specific embodiments of the present invention will be further described below.

[0042] Unless otherwise specified, all raw materials used in this invention are commercially available or commonly used in the field. Unless otherwise specified, the methods in the following embodiments are conventional methods in the field.

[0043] This invention provides a method for preparing a membrane electrode for a lead-acid battery, comprising the following steps:

[0044] A binder is added to the lead paste to be prepared. The lead paste containing the binder is rolled onto the lead sheet to form a lead paste film. The lead sheet and the attached lead paste film are then immersed in a sulfuric acid solution, removed, cured, and dried.

[0045] The adhesive is a polytetrafluoroethylene emulsion or an adhesive containing a polytetrafluoroethylene emulsion;

[0046] The mass of the adhesive is 1 to 10% of the mass of the lead paste.

[0047] In some preferred embodiments, the mass of the adhesive is 5-10% of the mass of the lead paste.

[0048] In some embodiments provided by the present invention, the thickness of the current collector lead sheet is 0.01 to 5 mm.

[0049] In some embodiments provided by this invention, the concentration of the sulfuric acid solution used is 1.05–1.15 g / cm³. 3 .

[0050] In some embodiments provided by the present invention, the solid content of the polytetrafluoroethylene emulsion used is 60±2%.

[0051] In some embodiments provided by the present invention, the binder containing polytetrafluoroethylene emulsion includes: polytetrafluoroethylene emulsion, epoxy resin, epoxy-modified carbon nanotubes, and curing agent;

[0052] The mass ratio of epoxy resin to polytetrafluoroethylene emulsion is 1:2 to 3.5;

[0053] The mass ratio of epoxy resin to epoxy-modified carbon nanotubes is 1:0.2–0.3.

[0054] The epoxy resin is selected from one or more of the following: bisphenol A epoxy resin, bisphenol F epoxy resin, bisphenol AD ​​epoxy resin, bisphenol S epoxy resin, resorcinol-type epoxy resin, hydroxymethyl bisphenol A epoxy resin, hydrogenated bisphenol A epoxy resin, and organosilicon-modified bisphenol A epoxy resin.

[0055] The curing agent used is selected from commonly used acid anhydride curing agents for epoxy resin curing, such as maleic anhydride, pyromellitic anhydride, phthalic anhydride, etc., or boron trinitride ethylamine complex; the mass ratio of epoxy resin to curing agent is 1:0.03 to 0.05.

[0056] In some embodiments provided by the present invention,

[0057] Epoxy-based surface-modified carbon nanotubes are obtained through the following process:

[0058] Carbon nanotubes were dispersed in an alkaline alcohol-water solution and ball-milled. After removal, the carbon nanotubes were rinsed until neutral and then dried to obtain hydroxyl-modified carbon nanotubes. Then, they were dispersed in an alcohol-water solution with an epoxy-silane coupling agent for modification reaction. After removal, they were rinsed and dried to obtain epoxy-modified carbon nanotubes.

[0059] The alkali used is sodium hydroxide or potassium hydroxide, and the mass ratio of carbon nanotubes to alkali is 1:15 to 30.

[0060] The ratio of carbon nanotubes to alcohol aqueous solution is 1g:100-200mL;

[0061] The mass ratio of carbon nanotubes to epoxy silane coupling agent is 1:0.06–0.1;

[0062] The length of carbon nanotubes ranges from 5 to 30 μm;

[0063] The epoxy silane coupling agent used is selected from 2-(3,4-epoxycyclohexyl)ethyltriethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane or 3-(2,3-epoxypropoxy)propyltrimethoxysilane;

[0064] The alcohol-water solution used is an aqueous solution of ethanol, ethylene glycol, or propanol, with a volume ratio of alcohol to water of 5 to 10:1.

[0065] In some embodiments provided by the present invention,

[0066] The binder containing polytetrafluoroethylene emulsion also includes epoxy-modified nano-fumed silica;

[0067] The mass ratio of epoxy resin to epoxy-modified nano-fumed silica is 1:0.1 to 0.15.

[0068] In some embodiments provided by the present invention,

[0069] Epoxy-modified nano-fumed silica is obtained by dispersing nano-fumed silica and epoxy-based silane coupling agents in an alcohol-water solution for modification reaction, followed by rinsing and drying.

[0070] The density of silanol groups on the surface of nano-vaporized silica is 1.5–2.5 per nm. 2 ;

[0071] The particle size of nano-fumed silica is 5–10 nm;

[0072] The mass ratio of nano-fumed silica to epoxy silane coupling agent is 1:0.05–0.1;

[0073] The ratio of nano-fumed silica to alcohol-water solution is 1g:100-200mL;

[0074] The epoxy silane coupling agent used is selected from 2-(3,4-epoxycyclohexyl)ethyltriethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane or 3-(2;3-epoxypropoxy)propyltrimethoxysilane;

[0075] The alcohol-water solution used is an aqueous solution of ethanol, ethylene glycol, or propanol, with a volume ratio of alcohol to water of 5 to 10:1.

[0076] In some embodiments provided by the present invention, the thickness of the lead paste film after curing and drying is 70-100 μm.

[0077] Based on the above, we will now provide a more detailed explanation through more specific implementation cases.

[0078] To facilitate the explanation of the method of the present invention, the following examples and comparative examples use lead paste, a common material in the field of lead-acid batteries, to prepare the negative electrode plate. The composition of the negative electrode paste is as follows: 10 kg lead powder, 6 g chemical short fibers, 30 g sodium lignosulfonate, 65 g barium sulfate, 20 g carbon black, 1.5 kg pure water, and 1 kg sulfuric acid (density 1.4 g / cm³ at 25°C). 3 ).

[0079] The inventors should note that the above-mentioned lead paste composition was chosen for the purpose of illustrative purposes, and not to limit the invention. The invention is applicable to conventional / common lead pastes in the art.

[0080] Example 1

[0081] A method for preparing a lead-acid battery membrane electrode includes the following steps:

[0082] (1) Add 7wt% binder to the negative electrode lead paste to be prepared. The binder used is polytetrafluoroethylene emulsion with a solid content of 60%, and stir evenly.

[0083] (2) Roll out and spread the lead paste containing binder onto a lead sheet with a thickness of 0.2 mm to form a lead paste film layer;

[0084] (3) Place the lead sheet and the attached lead paste film together in a container with a density of 1.15 g / cm³. 3 The lead paste is immersed in a sulfuric acid solution, then removed and placed in a conventional lead-acid battery curing chamber for curing and drying to obtain a lead-acid battery membrane electrode, i.e., a negative electrode plate. The thickness of the cured lead paste film layer is 80 μm.

[0085] Example 2

[0086] A method for preparing a lead-acid battery membrane electrode differs from Example 1 in that:

[0087] The adhesive used has the following composition:

[0088] The mixture comprises polytetrafluoroethylene emulsion, bisphenol A type epoxy resin, epoxy-modified carbon nanotubes, and boron trinitride ethylamine complex; wherein the mass ratio of bisphenol A type epoxy resin to polytetrafluoroethylene emulsion is 1:3, the mass ratio of bisphenol A type epoxy resin to epoxy-modified carbon nanotubes is 1:0.3, and the mass ratio of bisphenol A type epoxy resin to boron trinitride ethylamine complex is 1:0.05.

[0089] Epoxy-based surface-modified carbon nanotubes are obtained through the following process:

[0090] Carbon nanotubes were dispersed in an ethanol-water solution containing potassium hydroxide (volume ratio 10:1) and ball-milled. The mass ratio of carbon nanotubes to potassium hydroxide was 1:20. The volume ratio of carbon nanotubes to the ethanol-water solution was 1 g:150 mL. After removal, the carbon nanotubes were rinsed until neutral. Then, they were dispersed with silane coupling agent KH560 in an ethanol-water solution (volume ratio 10:1) and stirred (1000 rpm, 60 min). The mass ratio of carbon nanotubes to KH560 was 1:0.08. After removal, the mixture was rinsed and dried to obtain epoxy-modified carbon nanotubes.

[0091] The adhesive preparation process is as follows: Bisphenol A type epoxy resin is dissolved in acetone, epoxy-modified carbon nanotubes and boron trinitride ethylamine complex are added, and then mixed with polytetrafluoroethylene emulsion with a solid content of 60% to prepare the adhesive.

[0092] Example 3

[0093] A method for preparing a lead-acid battery membrane electrode differs from Example 1 in that:

[0094] The adhesive used has the following composition:

[0095] The mixture comprises polytetrafluoroethylene emulsion, bisphenol A type epoxy resin, epoxy-modified carbon nanotubes, and boron trinitride ethylamine complex; wherein the mass ratio of bisphenol A type epoxy resin to polytetrafluoroethylene emulsion is 1:2, the mass ratio of bisphenol A type epoxy resin to epoxy-modified carbon nanotubes is 1:0.2, and the mass ratio of bisphenol A type epoxy resin to boron trinitride ethylamine complex is 1:0.03.

[0096] Epoxy-based surface-modified carbon nanotubes are obtained through the following process:

[0097] Carbon nanotubes were dispersed in an ethanol-water solution containing potassium hydroxide (volume ratio 5:1) and ball-milled. The mass ratio of carbon nanotubes to potassium hydroxide was 1:15. The volume ratio of carbon nanotubes to the ethanol-water solution was 1 g:200 mL. After removal, the carbon nanotubes were rinsed until neutral. Then, they were dispersed with silane coupling agent KH560 in an ethanol-water solution (volume ratio 5:1) and stirred (1000 rpm, 60 min). The mass ratio of carbon nanotubes to KH560 was 1:0.06. After removal, the mixture was rinsed and dried to obtain epoxy-modified carbon nanotubes.

[0098] The adhesive preparation process is as follows: Bisphenol A type epoxy resin is dissolved in acetone, epoxy-modified carbon nanotubes and boron trinitride ethylamine complex are added, and then mixed with polytetrafluoroethylene emulsion with a solid content of 60% to prepare the adhesive.

[0099] Example 4

[0100] A method for preparing a lead-acid battery membrane electrode differs from Example 1 in that:

[0101] The adhesive used has the following composition:

[0102] The mixture comprises polytetrafluoroethylene emulsion, bisphenol A type epoxy resin, epoxy-modified carbon nanotubes, and boron trinitride ethylamine complex; wherein the mass ratio of bisphenol A type epoxy resin to polytetrafluoroethylene emulsion is 1:3.5, the mass ratio of bisphenol A type epoxy resin to epoxy-modified carbon nanotubes is 1:0.3, and the mass ratio of bisphenol A type epoxy resin to boron trinitride ethylamine complex is 1:0.04.

[0103] Epoxy-based surface-modified carbon nanotubes are obtained through the following process:

[0104] Carbon nanotubes were dispersed in an ethanol-water solution containing potassium hydroxide (volume ratio 8:1) and ball-milled. The mass ratio of carbon nanotubes to potassium hydroxide was 1:30. The volume ratio of carbon nanotubes to the ethanol-water solution was 1 g:100 mL. After removal, the carbon nanotubes were rinsed until neutral. Then, they were dispersed with silane coupling agent KH560 in an ethanol-water solution (volume ratio 8:1) and stirred (1000 rpm, 60 min). The mass ratio of carbon nanotubes to KH560 was 1:0.1. After removal, the mixture was rinsed and dried to obtain epoxy-modified carbon nanotubes.

[0105] The adhesive preparation process is as follows: Bisphenol A type epoxy resin is dissolved in acetone, epoxy-modified carbon nanotubes and boron trinitride ethylamine complex are added, and then mixed with polytetrafluoroethylene emulsion with a solid content of 60% to prepare the adhesive.

[0106] Example 5

[0107] A method for preparing a lead-acid battery membrane electrode differs from Example 2 in that:

[0108] The adhesive also contains epoxy-modified nano-fumed silica. The mass ratio of bisphenol A type epoxy resin to epoxy-modified nano-fumed silica is 1:0.1. The preparation process of the epoxy-modified nano-fumed silica is as follows:

[0109] Nano-sized fumed silica (with a silanol density of 2.5 hydroxyl groups / nm) 2 The nano-fumed silica and KH560 were dispersed in an ethanol aqueous solution (volume ratio of 10:1) and stirred (1000 rpm for 60 min). After being removed, the mixture was rinsed and dried. The mass ratio of nano-fumed silica to epoxy silane coupling agent was 1:0.1, and the volume ratio of nano-fumed silica to ethanol aqueous solution was 1 g:200 mL.

[0110] Example 6

[0111] A method for preparing a lead-acid battery membrane electrode differs from Example 2 in that:

[0112] The adhesive also contains epoxy-modified nano-fumed silica. The mass ratio of bisphenol A type epoxy resin to epoxy-modified nano-fumed silica is 1:0.15. The preparation process of the epoxy-modified nano-fumed silica is as follows:

[0113] Nano-sized fumed silica (with a silanol density of 1.5 hydroxyl groups / nm) 2The nano-fumed silica and KH560 were dispersed in an ethanol aqueous solution (volume ratio of 5:1) and stirred (1000 rpm for 60 min). After stirring, the mixture was rinsed and dried. The mass ratio of nano-fumed silica to epoxy silane coupling agent was 1:0.05, and the volume ratio of nano-fumed silica to ethanol aqueous solution was 1 g:100 mL.

[0114] Comparative Example 1 (Conventional Negative Plate)

[0115] The negative electrode lead paste was pressed into a lead-calcium alloy grid with a thickness of 1.7 mm, and then... 3 The plates are soaked in sulfuric acid solution, removed and placed in a conventional lead-acid battery curing chamber for curing and drying to obtain conventional lead-acid battery plates.

[0116] Comparative Example 2 (without carbon nanotubes)

[0117] Compared to Example 2, the addition of carbon nanotubes was omitted from the binder.

[0118] Comparative Example 3 (unmodified carbon nanotubes)

[0119] Compared to Example 2, the carbon nanotubes used in the binder do not have epoxy-based surface modification.

[0120] Comparative Example 4 (Unmodified Fumed Silica)

[0121] Compared to Example 5, the fumed silica used in the adhesive is not epoxy-modified.

[0122] Comparative Example 5 (High hydroxyl density in fumed silica)

[0123] Compared to Example 5, the density of silanol groups in the binder before modification with fumed silica reached 4.5 per nm. 2 .

[0124] The negative electrode plates prepared in the above embodiments and comparative examples were combined with the positive electrode plate and electrolyte of a lead-acid battery to form a lead-acid battery, and the charge-discharge capacity was tested.

[0125] The positive electrode paste uses the standard positive electrode paste composition found in lead-acid batteries: 10kg lead powder, 6g chemical short fibers, 1.5kg pure water, and 1kg sulfuric acid (density 1.4g / cm³ at 25℃). 3 );

[0126] The electrolyte is a sulfuric acid solution with a relative density of 1.28 g / cm³. 3 .

[0127] The rate charge / discharge test process is as follows:

[0128] 1) Experimental ambient temperature: 25±1℃;

[0129] 2) Discharge: Discharge at a constant current of 1C until the single-cell voltage reaches 1.75V;

[0130] 3) Charging: First stage, constant current 1C charging to 2.40V; second stage, constant current 0.35C charging to 2.45V; third stage, constant voltage 2.45V current-limited 0.35C charging for 3 hours to complete.

[0131] 4) Let stand: 10 minutes;

[0132] 5) Repeat the above steps to complete the rate charge / discharge test.

[0133] The cyclic charge-discharge test procedure is as follows:

[0134] 1) Experimental ambient temperature: 25±1℃;

[0135] 2) Discharge: Discharge at a constant current of 0.5C until the single-cell voltage reaches 1.75V;

[0136] 3) Charging: The first stage is constant voltage 2.46V and current limited 0.175C charging until the current is less than 0.02C; the second stage is constant voltage 2.3V charging for 3 hours to complete the process.

[0137] 4) Let stand: 10 minutes;

[0138] 5) Repeat the above steps to complete the cyclic charge-discharge test.

[0139] Charge and discharge tests of the assembled lead-acid batteries.

[0140]

[0141] As can be seen from Example 1 in the table above, the lead-acid battery assembled with the thin-film electrode prepared by the method of this application has a higher rate performance, which is about 5.2% higher than that of the lead-acid battery with conventional negative plate in Comparative Example 1. However, the coulombic efficiency after multiple cycles is lower than that of Comparative Example 1. This may be because polytetrafluoroethylene is a point-type binder and its long-distance bonding ability is not strong, thus resulting in poor long-term cycle performance. As shown in Example 2, compared with Comparative Examples 2 and 3, the addition of epoxy-modified carbon nanotubes to the binder can improve the cycle performance and rate performance of the cross-linked carbon nanotubes. Further addition of modified fumed silica to the binder, as shown in Example 5, compared with the addition of unmodified fumed silica in Comparative Example 4, can improve the stability of battery cycle performance while maintaining a rate performance comparable to that of Example 2. The coulombic efficiency of parallel battery tests is closer, and the cycle performance is also improved to a certain extent, comparable to Comparative Example 1. However, this requires the silanol density on the surface of fumed silica to be within a suitable range. As described in Comparative Example 5, when fumed silica with a high silanol density is used, it may be due to excessive participation of fumed silica in network crosslinking and the small particle size of fumed silica, which causes an increase in internal stress in the film layer, resulting in a greater difference in coulombic efficiency in parallel cell tests compared to Example 2.

Claims

1. A method for preparing a membrane electrode for a lead-acid battery, characterized in that, Includes the following steps: A binder is added to the lead paste to be prepared, and the lead paste containing the binder is rolled onto a lead sheet to form a lead paste film. The lead sheet and the attached lead paste film are then immersed in a sulfuric acid solution, removed, cured, and dried. The binder includes: polytetrafluoroethylene emulsion, epoxy resin, epoxy-modified carbon nanotubes, and a curing agent. The mass ratio of epoxy resin to polytetrafluoroethylene emulsion is 1:2 to 3.5; the mass ratio of epoxy resin to epoxy-modified carbon nanotubes is 1:0.2 to 0.

3.

2. The method for preparing the lead-acid battery membrane electrode according to claim 1, characterized in that, Epoxy-modified carbon nanotubes are obtained through the following process: carbon nanotubes are dispersed in an alkaline alcohol-water solution and ball-milled. After removal, the carbon nanotubes are rinsed until neutral and then dried to obtain hydroxyl-modified carbon nanotubes. Then, they are dispersed in an alcohol-water solution with an epoxy-silane coupling agent for modification reaction. After removal, they are rinsed and dried to obtain epoxy-modified carbon nanotubes.

3. The method for preparing the lead-acid battery membrane electrode according to claim 2, characterized in that, The alkali used is sodium hydroxide or potassium hydroxide, and the mass ratio of carbon nanotubes to alkali is 1:15-30; the volume ratio of carbon nanotubes to alcohol aqueous solution is 1g:100-200mL; and the mass ratio of carbon nanotubes to epoxy silane coupling agent is 1:0.06-0.

1.

4. The method for preparing the lead-acid battery membrane electrode according to claim 1, characterized in that, The adhesive also includes epoxy-modified nano-fumed silica; the mass ratio of epoxy resin to epoxy-modified nano-fumed silica is 1:0.1 to 0.

15.

5. The method for preparing the lead-acid battery membrane electrode according to claim 4, characterized in that, Epoxy-modified nano-fumed silica was obtained by dispersing nano-fumed silica with an epoxy-based silane coupling agent in an alcohol-water solution, followed by rinsing and drying. The density of silanol groups on the surface of the nano-fumed silica was 1.5–2.5 per nm. 2 The mass ratio of nano-fumed silica to epoxy silane coupling agent is 1:0.05-0.1; the volume ratio of nano-fumed silica to alcohol-water solution is 1g:100-200mL.

6. The method for preparing a lead-acid battery membrane electrode according to claim 2, 3, or 5, characterized in that, The epoxy silane coupling agent used is 2-(3,4-epoxycyclohexyl)ethyltriethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, or 3-(2,3-epoxypropoxy)propyltrimethoxysilane; the alcohol-water solution used is an aqueous solution of ethanol, ethylene glycol, or propanol, with a volume ratio of alcohol to water of 5 to 10:

1.

7. The method for preparing a lead-acid battery membrane electrode according to claim 1, characterized in that, The epoxy resin is selected from one or more of the following: bisphenol A epoxy resin, bisphenol F epoxy resin, bisphenol AD ​​epoxy resin, bisphenol S epoxy resin, resorcinol-type epoxy resin, hydroxymethyl bisphenol A epoxy resin, hydrogenated bisphenol A epoxy resin, and organosilicon-modified bisphenol A epoxy resin.

8. The method for preparing the lead-acid battery membrane electrode according to claim 1, characterized in that, The mass of the adhesive is 1 to 10% of the mass of the lead paste.

9. The method for preparing a lead-acid battery membrane electrode according to claim 1, characterized in that, The thickness of the lead paste film after curing and drying is 70–100 µm.

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