Water-soluble adhesive for lithium battery, preparation method of water-soluble adhesive, positive pole piece of lithium battery and lithium battery

Abstract

The invention discloses a lithium battery water-soluble adhesive and a preparation method thereof, a lithium battery positive pole piece and a lithium battery, and the preparation method comprises the following steps: under the protection of nitrogen, 60-80 parts by weight of pure water is used as a solvent and is put into a reaction kettle; the preparation method comprises the following steps: mixing 0.1-0.3 part by weight of an initiator and 5-15 parts by weight of pure water to prepare a solution A; mixing polyol or polyoxyethylene ether with double bonds with an acrylic monomer to prepare a solution B; the temperature in the reaction kettle is controlled to be 65-95 DEG C, and the solution A and the solution B are slowly dropped into the reaction kettle within 1-4 h; and adjusting the temperature in the reaction kettle to 35-65 DEG C after reacting for 1-3 hours, adding 0.1-0.3 part by weight of a neutralizing agent, neutralizing for 0.5-1 hour, and cooling to obtain the water-soluble adhesive for the lithium battery. The water-soluble adhesive for the lithium battery can form a uniform and stable priming coat on the surface of an aluminum foil, so that the stability of an electrode structure is improved, the stripping of a pole piece is reduced, and the long-term cycle performance is improved.

Description

Technical Field

[0001] The present invention relates to the field of lithium batteries, and particularly to a water-soluble binder for lithium batteries, a preparation method thereof, a positive electrode sheet of a lithium battery, and a lithium battery. Background Art

[0002] In recent years, due to the rapid development of electric vehicles, the demand for lithium batteries has been strong. During the manufacturing process of lithium batteries, the bonding performance of the positive electrode sheet has an important impact on the cycle stability, mechanical strength, and overall performance of the lithium battery. The positive electrode sheet usually uses aluminum foil as the current collector, and its surface needs to be firmly combined with the positive electrode active material (such as ternary positive electrode material LiNiMnCoO2, lithium iron phosphate LiFePO4, etc.) and the binder (the most commonly used is polyvinylidene fluoride PVDF). However, since the surface of the aluminum foil is relatively smooth and chemically inert, its direct adhesion force with the binder is weak. During long-term use, peeling and pulverization of the active material layer may occur, thereby affecting the reliability and life of the battery.

[0003] To solve this problem, researchers have introduced polyacrylic acid (PAA) as a primer for the aluminum foil to enhance the bonding performance. PAA is a water-soluble polymer containing abundant carboxyl groups (-COOH), which can form a strong chemical bond with the aluminum oxide layer (Al2O3) on the surface of the aluminum foil, improving the bonding strength. In addition, the PAA primer can also form a uniform buffer layer at the interface, which helps to reduce the stress between the binder and the aluminum foil and improve the overall mechanical stability.

[0004] Currently, the PAA primer is used in the manufacture of some high-energy density batteries. However, the traditional PAA primer still has some problems. For example, it is easy to absorb water and expand in a high-humidity environment, resulting in a decrease in bonding performance; it is prone to thermal degradation under high-temperature process conditions, affecting long-term reliability. In addition, the compatibility between the PAA primer and the PVDF binder is insufficient, which may affect the interface bonding effect.

[0005] With the continuous development of lithium battery technology, especially the increasing demand for high energy density, high safety, and long life, the optimization and modification of the PAA primer will play a key role in improving the overall performance of lithium batteries. Therefore, exploring new PAA primer materials and their application processes will bring more competitive solutions to the lithium battery industry. Therefore, there is an urgent need to develop a binder for lithium batteries with high adhesiveness and flexibility to maintain the stability of the electrode structure and improve the battery cycle life. Summary of the Invention

[0006] In order to achieve the above technical objectives, the present invention first proposes a water-soluble binder for lithium batteries, and its detailed technical solution is as follows:

[0007] A preparation method of a water-soluble adhesive for lithium batteries, which comprises:

[0008] Under nitrogen protection, 60-80 parts by weight of pure water as a solvent is put into a reaction kettle;

[0009] 0.1-0.3 parts by weight of an initiator and 5-15 parts by weight of pure water are mixed to form solution A;

[0010] 1-3 parts by weight of a polyol or polyoxyethylene ether with double bonds and 20-22 parts by weight of an acrylic monomer are mixed to form solution B;

[0011] The temperature in the reaction kettle is controlled to 65-95 °C, and solution A and solution B are slowly dropped into the reaction kettle respectively within 1-4 h;

[0012] After reacting for 1-3 h, the temperature in the reaction kettle is adjusted to 35-65 °C, 0.1-0.3 parts by weight of a neutralizing agent is added, and after neutralizing for 0.5-1 h, it is cooled to obtain the water-soluble adhesive for lithium batteries.

[0013] The water-soluble adhesive for lithium batteries prepared by the present invention has acrylic monomers and a polyol or polyoxyethylene ether with double bonds as the main materials. Among them, after the acrylic monomers form a copolymer structure with the polyol or polyoxyethylene ether with double bonds, they can form a strong chemical bond with the alumina layer on the surface of the aluminum foil, thereby ensuring the bonding strength of the adhesive. The polyol or polyoxyethylene ether with double bonds can improve the flexibility and interfacial compatibility of the adhesive, and the introduction of hydroxyl groups can further increase the density of intermolecular hydrogen bonds, thereby enhancing the binding force between the adhesive and the PVDF binder.

[0014] The water-soluble adhesive for lithium batteries of the present invention can form a uniform and stable bottom coating on the surface of the aluminum foil, improve the stability of the electrode structure, reduce the peeling of the electrode sheet, and improve the long-term cycling performance.

[0015] In some embodiments, the initiator is at least one of ammonium persulfate, potassium persulfate, sodium bisulfite, sodium hypophosphite, 2,2'-azobis(2-methylpropionamidine) dihydrochloride, and 2,2'-azobis(2-methylpropionitrile) dihydrochloride.

[0016] Several initiators with better initiation effects are provided, and they can all generate free radicals, cations or anions in the polymerization reaction, thereby initiating a chain reaction, initiating the polymerization of acrylic monomers, forming a copolymer structure, and ensuring the bonding strength of the adhesive.

[0017] In some embodiments, the acrylic monomer is at least one of acrylic acid, methacrylic acid, itaconic acid, acrylonitrile, methacrylonitrile, acrylamide, methacrylamide, and hydroxybutyl acrylate.

[0018] Several acrylic monomers are provided, all of which can form a copolymer structure with a polyol or a polyethylene oxide ether having a double bond, thereby significantly improving the bonding strength of the adhesive.

[0019] In some embodiments, the acrylic monomer is a mixture of acrylic acid, acrylonitrile, and acrylamide.

[0020] Among them, acrylic acid provides abundant carboxyl groups, enabling the adhesive to form strong chemical bonds with the oxide layer on the surface of the aluminum foil. Acrylamide introduces polar amide groups, enhancing water solubility and interfacial wettability. The rigid molecular structure of acrylonitrile, on the other hand, improves the heat resistance and mechanical stability of the adhesive.

[0021] In some embodiments, the polyol or polyethylene oxide ether having a double bond is at least one of allyl polyethylene oxide ether, methallyl polyethylene oxide ether, allyl polypropylene oxide ether, 2-((allyloxy)methyl)-2-(hydroxymethyl)propane-1,3-diol, and allyl glycerol.

[0022] Several polyols or polyethylene oxide ethers having a double bond are provided, all of which can form a copolymer structure with the acrylic monomer.

[0023] In some embodiments, the molecular weight of allyl polyethylene oxide ether is 300 - 4000, the number average molecular weight of methallyl polyethylene oxide ether is 300 - 4000, and that of allyl polypropylene oxide ether is 300 - 4000.

[0024] In some embodiments, the neutralizing agent is at least one of lithium hydroxide, sodium hydroxide, potassium hydroxide, calcium hydroxide, lithium carbonate, sodium carbonate, potassium carbonate, triethylamine, ammonia water, N,N-dialkyl ethanolamine, and N,N-dialkyl hydroxylamine.

[0025] Several neutralizing agents with better neutralizing effects are provided, all of which can neutralize the acidic substances generated during the polymerization reaction, ensuring the stability and purity of the finally formed adhesive.

[0026] In the second aspect of the present invention, a water-soluble adhesive for lithium batteries is provided, which is prepared by the preparation method of the water-soluble adhesive for lithium batteries described in any one of the above.

[0027] The water-soluble adhesive for lithium batteries provided by the present invention has acrylic monomers and a polyol or a polyethylene oxide ether having a double bond as its main materials. Among them, after the acrylic monomer forms a copolymer structure with the polyol or the polyethylene oxide ether having a double bond, it can form a strong chemical bond with the alumina layer on the surface of the aluminum foil, thereby ensuring the bonding strength of the adhesive. The polyol or the polyethylene oxide ether having a double bond can improve the flexibility and interfacial compatibility of the adhesive, thereby enhancing the bonding force between the adhesive and the PVDF binder.

[0028] The third aspect of the present invention provides a positive electrode sheet for a lithium battery, which contains the above-mentioned water-soluble binder for a lithium battery.

[0029] The fourth aspect of the present invention provides a lithium battery provided with an electrode, and the electrode contains the above-mentioned water-soluble binder for a lithium battery. Detailed implementation manners

[0030] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0031] Example 1

[0032] Step 1: Under nitrogen protection, 70 parts by weight of pure water is put into the reaction kettle as a solvent.

[0033] Step 2: 0.15 part by weight of ammonium persulfate and 10 parts by weight of pure water are mixed to form solution A.

[0034] Step 3: 12 parts by weight of acrylic acid, 4 parts by weight of acrylonitrile, 4 parts by weight of acrylamide, and 3 parts by weight of allyl polyoxyethylene ether (number average molecular weight 300) are mixed to form solution B.

[0035] Step 4: After reaching 90 °C, solution A is uniformly added dropwise to the reaction kettle within 3 h, and solution B is uniformly added dropwise to the reaction kettle within 2 h.

[0036] Step 6: After reacting for 1 - 3 h, it is adjusted to 60 °C, 0.2 part by weight of sodium hydroxide is added, and after neutralizing for 0.5 h, it is cooled to obtain the water-based binder.

[0037] The viscosity of the water-based binder is tested according to GB / T2794-2022, and the measured viscosity of the water-based binder is 2272 mPa·s. The non-volatile content of the water-based binder is set according to GB / T2793-1995, and the measured non-volatile content is 23.58%.

[0038] Example 2

[0039] The water-based binder is prepared in the same manner as in Example 1, except that:

[0040] In step 3, solution B is adjusted to be a mixture of 12 parts by weight of acrylic acid, 4 parts by weight of acrylonitrile, 4 parts by weight of acrylamide, and 3 parts by weight of allyl polyoxyethylene ether (number average molecular weight 500) to form solution B.

[0041] The viscosity of the aqueous adhesive was tested according to GB / T 2794-2022, and the viscosity of the aqueous adhesive was measured to be 2630 mPa·s. The non-volatile content of the aqueous adhesive was set according to GB / T 2793-1995, and its non-volatile content was measured to be 23.5%.

[0042] Example 3

[0043] The aqueous binder was prepared in the same manner as in Example 1, except that:

[0044] In step 3, solution B was adjusted to be a mixture of 12 parts by weight of acrylic acid, 5 parts by weight of acrylonitrile, 5 parts by weight of acrylamide, and 1 part by weight of allyl polyoxyethylene ether (number average molecular weight 500) to form solution B.

[0045] The viscosity of the aqueous adhesive was tested according to GB / T 2794-2022, and the viscosity of the aqueous adhesive was measured to be 2354 mPa·s. The non-volatile content of the aqueous adhesive was set according to GB / T 2793-1995, and its non-volatile content was measured to be 23.42%.

[0046] Example 4

[0047] The aqueous binder was prepared in the same manner as in Example 1, except that:

[0048] In step 3, solution B was adjusted to be a mixture of 11 parts by weight of acrylic acid, 6 parts by weight of acrylonitrile, 3 parts by weight of acrylamide, and 3 parts by weight of methyl allyl polyoxyethylene ether (number average molecular weight 500) to form solution B.

[0049] The viscosity of the aqueous adhesive was tested according to GB / T 2794-2022, and the viscosity of the aqueous adhesive was measured to be 2775 mPa·s. The non-volatile content of the aqueous adhesive was set according to GB / T 2793-1995, and its non-volatile content was measured to be 23.53%.

[0050] Example 5

[0051] The aqueous binder was prepared in the same manner as in Example 1, except that:

[0052] In step 3, solution B was adjusted to be a mixture of 12 parts by weight of acrylic acid, 4 parts by weight of acrylonitrile, 4 parts by weight of acrylamide, and 3 parts by weight of allyl polyoxyethylene ether (number average molecular weight 2000) to form solution B.

[0053] The viscosity of the water-based adhesive was tested according to GB / T 2794-2022, and the viscosity of the water-based adhesive was measured to be 3240 mPa·s. The non-volatile content of the water-based adhesive was set according to GB / T 2793-1995, and its non-volatile content was measured to be 23.52%.

[0054] Example 6

[0055] The water-based binder was prepared in the same manner as in Example 1, except that:

[0056] Solution B in Step 3 was adjusted to be a solution B prepared by mixing 12 parts by weight of acrylic acid, 4 parts by weight of acrylonitrile, 4 parts by weight of acrylamide, and 3 parts by weight of methyl allyl polyoxyethylene ether (number average molecular weight 500).

[0057] The viscosity of the water-based adhesive was tested according to GB / T 2794-2022, and the viscosity of the water-based adhesive was measured to be 2535 mPa·s. The non-volatile content of the water-based adhesive was set according to GB / T 2793-1995, and its non-volatile content was measured to be 23.43%.

[0058] Example 7

[0059] The water-based binder was prepared in the same manner as in Example 1, except that:

[0060] Solution B in Step 3 was adjusted to be a solution B prepared by mixing 12 parts by weight of acrylic acid, 4 parts by weight of acrylonitrile, 4 parts by weight of acrylamide, and 3 parts by weight of allyl polyoxypropylene ether (number average molecular weight 500).

[0061] The viscosity of the water-based adhesive was tested according to GB / T 2794-2022, and the viscosity of the water-based adhesive was measured to be 2487 mPa·s. The non-volatile content of the water-based adhesive was set according to GB / T 2793-1995, and its non-volatile content was measured to be 23.22%.

[0062] Example 8

[0063] The water-based binder was prepared in the same manner as in Example 1, except that:

[0064] Solution B in Step 3 was adjusted to be a solution B prepared by mixing 12 parts by weight of acrylic acid, 4 parts by weight of acrylonitrile, 5 parts by weight of acrylamide, and 2 parts by weight of 2-((allyloxy)methyl)-2-(hydroxymethyl)propane-1,3-diol.

[0065] The viscosity of the water-based adhesive was tested according to GB / T 2794-2022, and the viscosity of the water-based adhesive was measured to be 2721 mPa·s. The non-volatile content of the water-based adhesive was set according to GB / T 2793-1995, and its non-volatile content was measured to be 23.37%.

[0066] Example 9

[0067] The water-based binder was prepared in the same manner as in Example 1, except that:

[0068] In step 3, solution B was adjusted to be made of 12 parts by weight of acrylic acid, 4 parts by weight of acrylonitrile, 4 parts by weight of acrylamide, and 3 parts by weight of allyl glycerol.

[0069] The viscosity of the water-based adhesive was tested according to GB / T 2794-2022, and the viscosity of the water-based adhesive was measured to be 2915 mPa·s. The non-volatile content of the water-based adhesive was set according to GB / T 2793-1995, and its non-volatile content was measured to be 23.44%.

[0070] Example 10

[0071] The water-based binder was prepared in the same manner as in Example 1, except that:

[0072] In step 3, solution B was adjusted to be made of 10 parts by weight of acrylic acid, 4 parts by weight of acrylonitrile, 4 parts by weight of acrylamide, 2 parts by weight of itaconic acid, and 3 parts by weight of allyl polyoxyethylene ether (number average molecular weight 500).

[0073] The viscosity of the water-based adhesive was tested according to GB / T 2794-2022, and the viscosity of the water-based adhesive was measured to be 2928 mPa·s. The non-volatile content of the water-based adhesive was set according to GB / T 2793-1995, and its non-volatile content was measured to be 23.38%.

[0074] Example 11

[0075] The water-based binder was prepared in the same manner as in Example 1, except that:

[0076] In step 3, solution B was adjusted to be made of 10 parts by weight of acrylic acid, 4 parts by weight of acrylonitrile, 4 parts by weight of acrylamide, 2 parts by weight of hydroxybutyl acrylate, and 3 parts by weight of allyl polyoxyethylene ether (number average molecular weight 500).

[0077] The viscosity of the water-based adhesive was tested according to GB / T 2794-2022, and the viscosity of the water-based adhesive was measured to be 3061 mPa·s. The non-volatile content of the water-based adhesive was set according to GB / T 2793-1995, and its non-volatile content was measured to be 23.36%.

[0078] Comparative Example 1

[0079] The water-based binder was prepared in the same manner as in Example 1, except that:

[0080] Solution B in Step 3 was adjusted to 23 parts by weight of acrylic acid as Solution B.

[0081] The viscosity of the water-based adhesive was tested according to GB / T 2794-2022, and the viscosity of the water-based adhesive was measured to be 982 mPa·s. The non-volatile content of the water-based adhesive was set according to GB / T 2793-1995, and its non-volatile content was measured to be 23.55%.

[0082] Comparative Example 2

[0083] The water-based binder was prepared in the same manner as in Example 1, except that:

[0084] Solution B in Step 3 was adjusted to a mixture of 13 parts by weight of acrylic acid, 5 parts by weight of acrylonitrile, and 5 parts by weight of acrylamide to form Solution B.

[0085] The viscosity of the water-based adhesive was tested according to GB / T 2794-2022, and the viscosity of the water-based adhesive was measured to be 1979 mPa·s. The non-volatile content of the water-based adhesive was set according to GB / T 2793-1995, and its non-volatile content was measured to be 23.46%.

[0086] Table 1. Test results of examples and comparative examples

[0087]

[0088]

[0089] By comparing the examples and the comparative examples, it is found that the water-based PAA-modified adhesive obtained by the preparation method provided by the present invention has the following beneficial effects: 1. It is more environmentally friendly as there are no other solvents and emulsifiers except pure water; 2. By introducing polyols or ethers containing double bonds, both the flexibility and the bonding strength are improved.

[0090] The above are only the embodiments of the present invention, and thus do not limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made by using the content of the specification of the present invention, or directly or indirectly applied in other related technical fields, shall be similarly included in the patent protection scope of the present invention.

Claims

1. A method for preparing a water-soluble adhesive for lithium batteries, characterized in that: It includes: Under nitrogen protection, 60 to 80 parts by weight of pure water as a solvent are added into the reaction kettle; 0.1 to 0.3 parts by weight of an initiator and 5 to 15 parts by weight of pure water are mixed to prepare a solution A; 1 to 3 parts by weight of a polyol or polyoxyethylene ether having a double bond and 20 to 22 parts by weight of an acrylic monomer are mixed to prepare a solution B; The temperature in the reactor is controlled to 65-95°C, and solution A and solution B are slowly dripped into the reactor within 1-4 hours; After reacting for 1 to 3 hours, the temperature in the reaction kettle is adjusted to 35 to 65° C., 0.1 to 0.3 parts by weight of a neutralizer is added, and the reaction is neutralized for 0.5 to 1 hour and then cooled to obtain the water-soluble adhesive for lithium batteries.

2. The preparation method according to claim 1, characterized in that The initiator is at least one of ammonium persulfate, potassium persulfate, sodium bisulfite, sodium hypophosphite, azobisisobutylimidazoline hydrochloride, and azobisisobutylamidine hydrochloride.

3. The preparation method according to claim 1, characterized in that: The acrylic monomer is at least one of acrylic acid, methacrylic acid, itaconic acid, acrylonitrile, methacrylonitrile, acrylamide, methacrylamide, and hydroxybutyl acrylate.

4. The preparation method according to claim 1, characterized in that: The acrylic monomer is a mixture of acrylic acid, acrylamide and acrylonitrile.

5. The preparation method according to claim 1, characterized in that: The polyol with double bonds is at least one of allyl polyoxyethylene ether, methyl allyl polyoxyethylene ether, allyl polyoxypropylene ether, 2-((allyloxy)methyl)-2-(hydroxymethyl)propane-1,3-diol and allyl glycerol.

6. The preparation method according to claim 5, characterized in that: The molecular weight of allyl polyoxyethylene ether is 300-4000, the number average molecular weight of methyl allyl polyoxyethylene ether is 300-4000, and the number average molecular weight of allyl polyoxypropylene ether is 300-4000.

7. The preparation method according to claim 1, characterized in that: The neutralizing agent is at least one of lithium hydroxide, sodium hydroxide, potassium hydroxide, calcium hydroxide, lithium carbonate, sodium carbonate, potassium carbonate, triethylamine, ammonia water, N,N-dialkylethanolamine and N,N-dialkylhydroxylamine.

8. A water-soluble adhesive for lithium batteries, characterized in that: The water-soluble adhesive for lithium batteries is prepared by the preparation method according to any one of claims 1 to 7.

9. A positive electrode plate for a lithium battery, characterized in that: The lithium battery positive electrode sheet is coated with the lithium battery water-soluble adhesive as claimed in claim 8.

10. A lithium battery having electrodes, characterized in that: The electrode contains the water-soluble binder for lithium batteries as claimed in claim 8.

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