High-temperature-resistant and low-moisture water-based resin and preparation method thereof

Abstract

The present application relates to the technical field of lithium battery separator, in particular to a high-temperature-resistant and low-moisture water-based resin and a preparation method thereof. The present application can significantly improve the heat resistance (above 150 DEG C) of the coated separator, effectively reduce the hydrophilicity of the coating by reducing the content of hydrophilic monomers and increasing the content of hydrophobic monomers under the condition of ensuring Tg, thereby reducing the moisture content of the coated separator, greatly improving the safety of lithium battery, and also avoiding the attenuation of lithium battery capacity and cycle performance.

Description

Technical Field

[0001] This invention relates to the field of lithium battery separator technology, and more specifically, to a high-temperature resistant, low-moisture aqueous resin and its preparation method. Background Technology

[0002] Currently, lithium-ion and lithium-ion polymer batteries use polyolefin-based separators to prevent short circuits between the positive and negative electrodes. However, because polyolefin-based separators have a melting point of 130°C or lower, they can shrink or melt when the battery temperature rises due to internal or external factors, causing volume changes. This makes short circuits between the positive and negative electrodes caused by separator shrinkage or melting highly likely, potentially leading to accidents such as battery explosions caused by discharge. Therefore, it is necessary to provide a separator that does not cause thermal shrinkage at high temperatures.

[0003] In related technologies, the commonly used adhesives for lithium-ion battery separators on the market are polyacrylate emulsions (ordinary adhesives) and polyacrylic acid solutions (heat-resistant). Two-component adhesives, containing a combination of polyacrylate polymer and a curing agent, are used for higher heat resistance. Currently, polyacrylate emulsions have relatively poor temperature resistance, generally only maintaining around 130℃. Polyacrylic acid solutions can withstand temperatures up to 180℃, but have drawbacks such as strong hydrophilicity, high moisture content, and high permeability. However, most adhesives improve heat resistance by using hydrophilic high-Tg monomers (high glass transition temperature monomers). This approach results in a certain amount of moisture remaining in the lithium-ion battery separator after coating and drying. Excessive moisture content significantly deteriorates the battery's cycle performance, presenting a new application challenge.

[0004] Therefore, in the field of ceramic diaphragm coating, there is a strong demand for a suitable water-based binder that can improve the heat resistance of the diaphragm (above 150°C) while avoiding excessive moisture content, thereby solving the core safety issues of current lithium batteries. Summary of the Invention

[0005] The purpose of this invention is to provide a high-temperature resistant, low-moisture water-based resin and its preparation method, which solves the technical problem of excessive moisture content in existing lithium battery separator adhesives after heat shrinkage at temperatures above 150°C.

[0006] To achieve the above objectives, the present invention is implemented through the following solutions; A method for preparing a high-temperature resistant, low-moisture waterborne resin includes the following steps: (1) Disperse 100-150 parts of acrylic (ester) monomer, 100-130 parts of high Tg monomer, 20-30 parts of crosslinking agent in 300-450 parts of deionized water under the action of 8-15 parts of emulsifier to obtain a pre-emulsified monomer mixture; (2) Add 400-600 parts of deionized water and 8-15 parts of emulsifier to the reaction vessel, disperse evenly, raise the temperature, add 5-10 parts of sodium hydroxide solution, and stir evenly; (3) Add part of the pre-emulsified monomer mixture obtained in step (1) to the reactor, heat to 75-85℃, add 0.2-0.5 parts of initiator, maintain the stirring speed at 100-300 rpm, and continue stirring for 0.5-1 hour until the emulsion turns blue to obtain the seed emulsion. (4) Then add the remaining pre-emulsified monomer mixture and 1.5-2.5 parts of initiator to the reactor dropwise. The dropwise addition time is between 2-5 hours. After the dropwise addition is completed, keep the temperature at 75-85℃ for 1-4 hours. (5) After the heat preservation is completed, the temperature is lowered to 65-70℃. First, add 0.1-0.5 parts of oxidant, then add 0.1-0.5 parts of reducing agent, and keep warm for 0.5-2 hours. (6) Cool down to below 45°C, add pH adjuster, bactericide and preservative, stir, filter, and discharge to obtain a high temperature resistant and low moisture water-based resin.

[0007] Preferably, the acrylic (ester) monomer is composed of methyl methacrylate, butyl acrylate, and methacrylic acid.

[0008] Preferably, the weight ratio of methyl methacrylate, butyl acrylate, and methacrylic acid is (4-10):(3-6):(1-3).

[0009] Preferably, the emulsifier is composed of anionic emulsifier and nonionic emulsifier mixed in a weight ratio of (1-3):1.

[0010] Preferably, the anionic emulsifier is selected from at least one of alkyl sulfonates, alkyl sulfates, alkylbenzene sulfonates, and alkyl succinates; the nonionic emulsifier is selected from at least one of alkylphenol polyoxyethylene ethers and fatty alcohol polyoxyethylene ethers.

[0011] Preferably, the high-T monomer is selected from at least one of acrylamide, methacrylamide, methylstyrene, and maleimide.

[0012] Preferably, the initiator is selected from at least one of sodium persulfate, ammonium persulfate, and potassium persulfate.

[0013] Preferably, the oxidant is selected from at least one of ammonium persulfate, tert-butyl hydroperoxide, and hydrogen peroxide; the reducing agent is at least one of sodium metabisulfite, sodium formaldehyde sulfoxylate, and sodium bisulfite.

[0014] Preferably, a pH adjuster is added to neutralize the pH to 7-8.

[0015] Another object of the present invention is to provide a high-temperature resistant, low-moisture waterborne resin, which is prepared by the aforementioned preparation method.

[0016] The present application has the following beneficial effects: The high temperature and low moisture waterborne resin of the present application can significantly improve the heat resistance (above 150℃) of the coated separator. Under the condition of ensuring Tg, by reducing the content of hydrophilic monomers and increasing the content of hydrophobic monomers, the hydrophilicity of the coating is effectively weakened, thereby reducing the moisture content of the coated separator. This greatly improves the safety of lithium battery and avoids the degradation of lithium battery capacity and cycle performance. Detailed Implementation

[0017] The present invention will be further described below with reference to embodiments, but the scope of protection of the present invention is not limited to the scope described in the embodiments. Example 1

[0018] A method for preparing a high-temperature resistant, low-moisture waterborne resin includes the following steps: (1) 135 parts of acrylic (ester) monomer, 120 parts of high Tg monomer, 25 parts of crosslinking agent, and 10 parts of emulsifier are uniformly dispersed in 300 parts of deionized water to obtain a pre-emulsified monomer mixture; (2) Add 450 parts of deionized water and 10 parts of emulsifier to the reaction vessel, disperse evenly, heat to 60°C, add 7 parts of 10wt% sodium hydroxide solution, and stir evenly; (3) Add 1 / 5 of the weight of the pre-emulsified monomer mixture obtained in step (1) to the reactor, heat to 80±3℃, add 0.3 parts of initiator, maintain the stirring speed at 200±50 rpm, and continue stirring for 0.5-1 hour until the emulsion turns blue to obtain the seed emulsion. (4) Next, add the remaining 4 / 5 of the weight of the pre-emulsified monomer mixture obtained in step (1) and 2.3 parts of initiator to the reactor. The addition time is between 3-4 hours. After the addition is completed, keep the temperature at 80±3℃ for 2 hours. (5) After the heat preservation is completed, the temperature is lowered to 65°C. First, add 0.2 parts of oxidant, then add 0.2 parts of reducing agent, and keep warm for 1.5 hours. (6) Cool down to below 45°C, add an appropriate amount of pH adjuster to neutralize the pH to 7-8, 0.5 parts of bactericide and preservative, stir, filter, and discharge to obtain a high temperature resistant and low moisture water-based resin.

[0019] In this embodiment, the acrylic (ester) monomer is obtained by uniformly mixing methyl methacrylate, butyl acrylate, and methacrylic acid in a weight ratio of 5.1:4.4:1.5. The high Tg monomer is obtained by uniformly mixing maleimide, methylstyrene, and acrylamide in a weight ratio of 0.8:2.5:8. The crosslinking agent is β-carboxyethyl acrylate. The emulsifier is obtained by uniformly mixing alkyl sulfonate, alkylbenzene sulfonate, alkyl succinate, and alkylphenol polyoxyethylene ether in a weight ratio of 1:1:1:2. The initiator is obtained by uniformly mixing potassium persulfate and ammonium persulfate in a weight ratio of 1:1. The oxidizing agent is a mixture of tert-butyl hydroperoxide and hydrogen peroxide. The reducing agent is a mixture of sodium bisulfite and sodium metabisulfite. Example 2

[0020] A method for preparing a high-temperature resistant, low-moisture waterborne resin includes the following steps: (1) 100 parts of acrylic (ester) monomer, 105 parts of high Tg monomer, 20 parts of crosslinking agent, and 8 parts of emulsifier are uniformly dispersed in 350 parts of deionized water to obtain a pre-emulsified monomer mixture; (2) Add 550 parts of deionized water and 12 parts of emulsifier to the reaction vessel, disperse evenly, heat to 60°C, add 8 parts of 10wt% sodium hydroxide solution, and stir evenly; (3) Add 1 / 5 of the weight of the pre-emulsified monomer mixture obtained in step (1) to the reactor, heat to 80±3℃, add 0.2 parts of initiator, maintain the stirring speed at 200±50 rpm, and continue stirring for 0.5-1 hour until the emulsion turns blue to obtain the seed emulsion. (4) Next, add the remaining 4 / 5 of the weight of the pre-emulsified monomer mixture obtained in step (1) and 2.0 parts of initiator to the reactor. The addition time is between 3-4 hours. After the addition is completed, keep the temperature at 80±3℃ for 2 hours. (5) After the heat preservation is completed, the temperature is lowered to 65°C. First, add 0.2 parts of oxidant, then add 0.2 parts of reducing agent, and keep warm for 1.5 hours. (6) Cool down to below 45°C, add an appropriate amount of pH adjuster to neutralize the pH to 7-8, 0.5 parts of bactericide and preservative, stir, filter, and discharge to obtain a high temperature resistant and low moisture water-based resin.

[0021] In this embodiment, the acrylate monomers, high Tg monomers, crosslinking agents, emulsifiers, initiators, oxidants, and reducing agents are the same as in Example 1. The difference lies in the weight proportions of each component in the preparation of the core-layer preemulsion and the shell-layer preemulsion. Example 3

[0022] A method for preparing a high-temperature resistant, low-moisture waterborne resin includes the following steps: (1) 150 parts of acrylic (ester) monomer, 130 parts of high Tg monomer, 30 parts of crosslinking agent, and 12 parts of emulsifier are uniformly dispersed in 450 parts of deionized water to obtain a pre-emulsified monomer mixture. (2) Add 600 parts of deionized water and 15 parts of emulsifier to the reaction vessel, disperse evenly, heat to 60°C, add 10 parts of 10wt% sodium hydroxide solution, and stir evenly; (3) Add 1 / 5 of the weight of the pre-emulsified monomer mixture obtained in step (1) to the reactor, heat to 80±3℃, add 0.5 parts of initiator, maintain the stirring speed at 200±50 rpm, and continue stirring for 0.5-1 hour until the emulsion turns blue to obtain the seed emulsion. (4) Next, add the remaining 4 / 5 of the weight of the pre-emulsified monomer mixture obtained in step (1) and 2.5 parts of initiator to the reactor. The addition time is between 3-4 hours. After the addition is completed, keep the temperature at 80±3℃ for 2 hours. (5) After the heat preservation is completed, the temperature is lowered to 65°C. First, add 0.2 parts of oxidant, then add 0.2 parts of reducing agent, and keep warm for 1.5 hours. (6) Cool down to below 45°C, add an appropriate amount of pH adjuster to neutralize the pH to 7-8, 0.5 parts of bactericide and preservative, stir, filter, and discharge to obtain a high temperature resistant and low moisture water-based resin.

[0023] In this embodiment, the acrylate monomers, high Tg monomers, crosslinking agents, emulsifiers, initiators, oxidants, and reducing agents are the same as in Example 1. The difference lies in the weight proportions of each component in the preparation of the core-layer preemulsion and the shell-layer preemulsion.

[0024] Comparative Example 1 Commercially available adhesives.

[0025] To test the performance of the binders prepared in Examples 1-3 and commercially available binders, they were each applied to the lithium battery separator preparation process to prepare corresponding lithium battery separators. The lithium battery separator preparation process is as follows: calcined alumina with a D50 of 0.8±0.1μm was mixed with pure water and CMC at a weight ratio of 4:6:0.051 and dispersed in a disperser at 1500r / min-2000r / min to prepare a dispersion; 4.5% by weight of binder and 0.05% by weight of wetting agent were added to the dispersion; the mixture was dispersed in a disperser at 300-500r / min to prepare a coating slurry, which was then coated onto the surface of a PE separator to a thickness of 2μm and cured at 60-80℃ to obtain the lithium battery separator.

[0026] The binders from Examples 1-3 and Comparative Example 1 were used as binders in the above-described lithium battery separator preparation process, and then coated separators were prepared according to the above-described lithium battery separator preparation process. The prepared coated separators were compared in terms of air permeability, peel strength, thermal shrinkage rate, and moisture content using conventional methods, and the results are shown in Table 1.

[0027] Table 1. Lithium-ion battery separator test data

[0028] In summary, the adhesive provided by this invention has a membrane heat shrinkage rate of less than 5% after heat treatment at 150°C for 1 hour, a moisture content of ≤1000 PPM, an air permeability increase of ≥25 S / 100mL, a peel strength of ≥65 N / m, and can be cured at low temperatures of 60-80°C. This solves the technical problem that traditional adhesives have a moisture content of more than 1000 PPM after heat shrinkage at temperatures above 150°C.

[0029] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a high-temperature resistant, low-moisture waterborne resin, characterized in that, Includes the following steps: (1) Disperse 100-150 parts of acrylic (ester) monomer, 100-130 parts of high Tg monomer, 20-30 parts of crosslinking agent in 300-450 parts of deionized water under the action of 8-15 parts of emulsifier to obtain a pre-emulsified monomer mixture; (2) Add 400-600 parts of deionized water and 8-15 parts of emulsifier to the reaction vessel, disperse evenly, raise the temperature, add 5-10 parts of sodium hydroxide solution, and stir evenly; (3) Add part of the pre-emulsified monomer mixture obtained in step (1) to the reactor, heat to 75-85℃, add 0.2-0.5 parts of initiator, maintain the stirring speed at 100-300 rpm, and continue stirring for 0.5-1 hour until the emulsion turns blue to obtain the seed emulsion. (4) Then add the remaining pre-emulsified monomer mixture and 1.5-2.5 parts of initiator to the reactor dropwise. The dropwise addition time is between 2-5 hours. After the dropwise addition is completed, keep the temperature at 75-85℃ for 1-4 hours. (5) After the heat preservation is completed, the temperature is lowered to 65-70℃. First, add 0.1-0.5 parts of oxidant, then add 0.1-0.5 parts of reducing agent, and keep warm for 0.5-2 hours. (6) Cool down to below 45°C, add pH adjuster, bactericide and preservative, stir, filter, and discharge to obtain a high temperature resistant and low moisture water-based resin.

2. The preparation method according to claim 1, characterized in that, The acrylic (ester) monomer is composed of methyl methacrylate, butyl acrylate, and methacrylic acid.

3. The preparation method according to claim 2, characterized in that, The weight ratio of methyl methacrylate, butyl acrylate, and methacrylic acid is (4-10):(3-6):(1-3).

4. The preparation method according to claim 1, characterized in that, The emulsifier is composed of anionic emulsifier and nonionic emulsifier mixed in a weight ratio of (1-3):

1.

5. The preparation method according to claim 4, characterized in that, The anionic emulsifier is selected from at least one of alkyl sulfonates, alkyl sulfates, alkylbenzene sulfonates, and alkyl succinates; the nonionic emulsifier is selected from at least one of alkylphenol polyoxyethylene ethers and fatty alcohol polyoxyethylene ethers.

6. The preparation method according to claim 1, characterized in that, The high-T monomer is selected from at least one of acrylamide, methacrylamide, methylstyrene, and maleimide.

7. The preparation method according to claim 1, characterized in that, The initiator is selected from at least one of sodium persulfate, ammonium persulfate, and potassium persulfate.

8. The preparation method according to claim 1, characterized in that, The oxidizing agent is selected from at least one of ammonium persulfate, tert-butyl hydroperoxide, and hydrogen peroxide; the reducing agent is at least one of sodium metabisulfite, sodium formaldehyde sulfoxylate, and sodium bisulfite.

9. The preparation method according to claim 1, characterized in that, Add a pH adjuster to neutralize the pH to 7-8.

10. A high-temperature resistant, low-moisture waterborne resin, characterized in that, It is prepared by any one of claims 1-9.

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