A binder, its preparation and use

Abstract

The application discloses a kind of binder and its preparation method and application, belong to battery material technical field.The structure unit shown in general formula I is included: M is at least one in H, Na, Li, K;R1, R2 each independently include at least one in H, substituted or unsubstituted C1-10 straight chain or branched alkyl;R3 is conductive polymer;R4, R5 each independently include at least one in H, C1-10 straight chain or branched alkyl, C1-10 alkanoyloxy;n1 is the integer of 10~100, n2 is the integer of 2~20, n3 is the integer of 10~35;m1 is the integer of 10~50;m3 is the integer of 2~30;m4 is the integer of 10~100, m5 is the integer of 10~100;m7 is the integer of 5~20;m2+m6 is the integer of 300~3000.The application solves the problem of battery bonding failure, improves overall performance and production efficiency.

Description

Technical Field

[0001] This invention relates to the field of battery materials technology, and in particular to a binder, its preparation method, and its application. Background Technology

[0002] Among lithium-ion battery anode materials, silicon-carbon composites have attracted much attention due to their high capacity. However, silicon-carbon particles undergo significant volume expansion and contraction during charge and discharge, leading to adhesion failure between particles and current collectors, and between particles themselves. This results in increased battery thickness and internal resistance, severely impacting cycle life and electrical performance stability. On the other hand, pure silicon materials have low conductivity, requiring the addition of conductive agents such as SP to enhance their conductivity. However, the poor dispersibility of these conductive agents can lead to a decrease in the proportion of active materials, further affecting the battery's energy density and low-temperature performance.

[0003] Therefore, there is an urgent need to find an adhesive to solve the problems of adhesion failure and low conductivity in the existing technologies. Summary of the Invention

[0004] This invention aims to solve at least one of the technical problems existing in the prior art. To this end, this invention proposes a binder that effectively solves the problem of bonding failure and improves the kinetic and electrical performance of the battery.

[0005] The present invention also provides a method for preparing the adhesive.

[0006] The present invention also provides a negative electrode sheet comprising the binder.

[0007] The present invention also provides a battery including the negative electrode.

[0008] According to an embodiment of a first aspect of the present invention, an adhesive is provided, wherein the electrode comprises:

[0009] The adhesive is a polymer containing structural units comprising the following:

[0010] The adhesive comprises structural units represented by general formula I:

[0011] Formula I;

[0012] Wherein, M is at least one of H, Na, Li, and K;

[0013] R1 and R2 each independently contain at least one of H, substituted or unsubstituted C1-10 straight-chain or branched alkyl groups; R3 is a conductive polymer; R4 and R5 each independently contain at least one of H, C1-10 straight-chain or branched alkyl groups, and C1-10 alkoxy groups.

[0014] n1 is an integer from 10 to 100, n2 is an integer from 2 to 20, and n3 is an integer from 10 to 35;

[0015] m1 is an integer from 10 to 50; m3 is an integer from 2 to 30; m4 is an integer from 10 to 100; m5 is an integer from 10 to 100; m7 is an integer from 5 to 20; and m2+m6 is an integer from 300 to 3000.

[0016] The adhesive according to embodiments of the present invention has at least the following beneficial effects:

[0017] The binder of this invention contains conductive segments that can directly conduct electrons, thereby reducing the resistance of the electrode. Compared with traditional methods, it does not require the addition of conductive agents such as SP and CNT in the silicon system. This not only simplifies the material formulation but also increases the content ratio of active materials, thereby improving the energy density of the electrode and the overall performance of the battery.

[0018] The binder described in this invention can directly coat the surface of active materials, efficiently disperse and stabilize particles such as silicon and carbon materials, and prevent their aggregation and sedimentation. Compared with traditional CMC dispersants, due to the incomplete coating of the chain structure, it can effectively increase the contact area between the active material and the electrolyte, thereby improving the kinetic performance and cycle stability of the battery.

[0019] According to some embodiments of the present invention, the main-chain polymer monomer includes polyacrylic acid monomer, polyacrylate monomer, and straight-chain or branched alkyl polymer monomers having 1 to 4 carbon atoms.

[0020] According to some embodiments of the present invention, m2 and m6 are the degrees of polymerization of polyacrylic acid monomers.

[0021] According to some embodiments of the present invention, m4 is the degree of polymerization of the polyacrylate monomer.

[0022] According to some embodiments of the present invention, m1 is the number of branches of the polyacrylic acid monomer.

[0023] According to some embodiments of the present invention, m3 is the number of branches of the polyacrylamide monomer.

[0024] According to some embodiments of the present invention, m5 is the number of branches of a straight-chain or branched alkyl polymer monomer with 1 to 4 carbon atoms.

[0025] According to some embodiments of the present invention, m7 is the number of branches of the conductive polymer.

[0026] According to some embodiments of the present invention, the conductive polymer monomer comprises thiophene or aniline.

[0027] According to some embodiments of the present invention, the solid content of the adhesive is 1%-15%.

[0028] Preferably, the solid content of the adhesive is 5%-10%.

[0029] According to some embodiments of the present invention, the viscosity of the adhesive is 1000-100000 mPa·s.

[0030] Preferably, the viscosity of the adhesive is 8000-25000 mPa·s.

[0031] According to an embodiment of a second aspect of the present invention, a method for preparing the adhesive is provided, the method comprising the steps of:

[0032] S1. Acrylic acid, a first initiator, and a solvent are mixed in an inert atmosphere to carry out a first reaction to obtain a first product. Then, a crosslinking agent, polyacrylamide, paraffin, and acrylate are added to continue the reaction. The pH is adjusted and the product is dried to obtain a second product.

[0033] S2. Dissolve the second product, add conductive polymer monomer, crosslinking agent and second initiator to carry out the second reaction, and filter to obtain the adhesive.

[0034] The structural formula I of the first product and the structural formula II of the second product are as follows:

[0035] .

[0036] The preparation method according to embodiments of the present invention has at least the following beneficial effects:

[0037] The preparation method of this invention generates polyacrylic acid through free radical polymerization. The double bonds of acrylic acid open under the action of free radicals, forming active centers for continuous polymerization to form a long-chain polymer. During the polymerization process, the double bonds of the crosslinking agent react with the active centers on the polyacrylic acid chains to form a crosslinked structure, improving the mechanical strength and stability of the polymer. Monomers such as polyacrylamide, paraffin wax, and acrylates copolymerize with the polyacrylic acid chains in the continued polymerization reaction, forming a polymer with multiple functional groups, thus improving the multifunctionality of the adhesive. Through the copolymerization reaction of conductive polymer monomers with the second product, the adhesive becomes conductive, and a more stable adhesive network structure is formed, ensuring the physical and chemical stability of the adhesive during use.

[0038] The adhesive provided by this invention is a solution design that can be directly added to a mixing tank to make slurry, eliminating the need for pre-prepared adhesive solution like traditional CMC adhesives. This saves on adhesive equipment, improves production efficiency, and reduces manufacturing costs.

[0039] According to some embodiments of the present invention, in step S1, the first initiator is azobisisobutyronitrile (AIBN, CAS No.: 78-67-1).

[0040] According to some embodiments of the present invention, in steps S1 and S2, the crosslinking agent is N,N'-methylenebisacrylamide (MBAA, CAS No.: 110-26-9).

[0041] According to some embodiments of the present invention, in step S2, the conductive polymer monomer includes thiophene or aniline (ANI, CAS No.: 62-53-3).

[0042] Preferably, in step S2, the thiophene class includes 3,4-ethylenedioxythiophene (EDOT).

[0043] According to some embodiments of the present invention, in step S2, the second initiator comprises ammonium persulfate (APS, CAS No.: 7727-54-0).

[0044] According to some embodiments of the present invention, in step S1, relative to 500 parts by weight of acrylic acid, the amount of the raw materials includes: 1-3 parts by weight of the first initiator, 0.1-0.3 parts by weight of the crosslinking agent, 2-7 parts by weight of polyacrylamide, 20-60 parts by weight of paraffin, and 100-200 parts by weight of acrylate.

[0045] Preferably, in step S1, the amount of the raw materials to be prepared relative to 500 parts by weight of acrylic acid includes: 2 parts by weight of the first initiator, 0.2 parts by weight of the crosslinking agent, 15 parts by weight of polyacrylamide, 50 parts by weight of paraffin, and 170 parts by weight of acrylate.

[0046] According to some embodiments of the present invention, in step S2, relative to 400 parts by weight of the second product, the amount of the raw materials includes: 60-100 parts by weight of conductive polymer monomer, 0.3-0.5 parts by weight of second initiator, and 0.5-0.7 parts by weight of crosslinking agent.

[0047] Preferably, in step S2, the amount of the raw materials for preparation, relative to 400 parts by weight of the second product, includes: 80 parts by weight of conductive polymer monomer, 0.4 parts by weight of the second initiator, and 0.6 parts by weight of crosslinking agent.

[0048] According to some embodiments of the present invention, in step S1, the solvent is methanol.

[0049] According to some embodiments of the present invention, in step S1, the reaction temperature is 50~70°C, for example, it can be 50°C, 55°C, 60°C, 65°C, or 70°C.

[0050] According to some embodiments of the present invention, in step S1, the time for the first reaction is 20 to 40 minutes, for example, 20 minutes, 25 minutes, 30 minutes, 35 minutes, or 40 minutes.

[0051] According to some embodiments of the present invention, in step S1, the time for the second reaction is 3 to 4 hours, for example, 3 hours, 3.5 hours, or 4 hours.

[0052] According to some embodiments of the present invention, in step S1, the pH adjustment step includes adjusting the pH value to 6~6.5 using sodium hydroxide.

[0053] According to some embodiments of the present invention, in step S1, the inert atmosphere includes at least one of nitrogen, argon, and helium.

[0054] According to some embodiments of the present invention, in step S1, the paraffin is a mixture of alkanes with 14 to 30 carbon atoms and a melting point of 5.5 to 65.5°C;

[0055] Preferably, in step S1, the paraffin is a mixture of alkanes with 14 to 22 carbon atoms and a melting point of 5.5 to 44.4°C.

[0056] According to some embodiments of the present invention, in step S2, the solvent in which the second product is dissolved is a mixture of dimethyl sulfoxide and water.

[0057] According to some embodiments of the present invention, the ratio of dimethyl sulfoxide to water is 1:5 to 1:10.

[0058] According to some embodiments of the present invention, in step S2, the reaction temperature is 60~70°C, for example, it can be 60°C, 62°C, 65°C, 68°C, or 70°C.

[0059] According to some embodiments of the present invention, in step S2, the reaction time is 1 to 3 hours, for example, 1 hour, 1.5 hours, 2 hours, 2.5 hours, or 3 hours.

[0060] According to an embodiment of a third aspect of the present invention, a negative electrode sheet is provided, comprising a negative electrode active material and the above-described binder;

[0061] According to some embodiments of the present invention, the negative electrode active material includes carbon materials and / or silicon materials.

[0062] According to some embodiments of the present invention, the mass ratio of the carbon material, the silicon material and the binder is (91~93):(4~6):(2~4).

[0063] According to some embodiments of the present invention, the mass ratio of the carbon material, the silicon material and the binder is 92:5:3.

[0064] According to an embodiment of a third aspect of the present invention, a lithium battery is provided, comprising the above-described negative electrode, as well as a positive electrode, a separator, and an electrolyte.

[0065] Unless otherwise specified, the term "about" in this invention actually means that the error is allowed to be within ±2%, for example, about 100 is actually 100 ± 2% × 100.

[0066] Unless otherwise specified, "between" in this invention includes the number itself, for example, "between 2 and 3" includes the endpoint values ​​2 and 3.

[0067] The structural formula in this invention appears as " "" indicates the junction position between the main chain polymer and the branched polymer.

[0068] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. Detailed Implementation

[0069] The following will describe the concept and technical effects of the present invention clearly and completely with reference to embodiments, so as to fully understand the purpose, features and effects of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention.

[0070] In the description of this invention, unless otherwise explicitly defined, terms such as "set up," "install," and "connect" should be interpreted broadly, and those skilled in the art can reasonably determine the specific meaning of the above terms in this invention in conjunction with the specific content of the technical solution.

[0071] In the description of this invention, the terms "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0072] Example 1

[0073] This embodiment provides an adhesive, the specific preparation method of which includes:

[0074] Step 1: Add 500 parts acrylic acid, 90 parts butyl acrylate, 2 parts AIBN as initiator, and an appropriate amount of methanol as solvent according to the weight. Pass N2 in, react at 60℃ for 30 min, keep warm at 45℃ for 20 min, and dry to remove solvent to obtain the first product.

[0075] The structural formula of the first product is as follows:

[0076] .

[0077] Step 2: Add 600 parts of the first product, 5 parts of AIBN initiator, and 0.2 parts of crosslinking agent N,N'-methylenebisacrylamide (MBAA), using toluene as solvent. Keep the mixture at 60°C for 30 minutes. Add 70 parts of acrylic acid, 15 parts of acrylamide, and 50 parts of molten paraffin dropwise. Pour in N2 and react at 60°C for 3 hours. Add NaOH to adjust the pH to 6.5. Remove the solvent and dry to obtain the second product.

[0078] The structural formula of the second product is as follows:

[0079] .

[0080] Step 3: Dissolve 80 parts of 3,4-ethylenedioxythiophene (EDOT) in a mixed solvent of dimethyl sulfoxide and water, add 0.4 parts of initiator ammonium persulfate (APS), 0.6 parts of crosslinking agent N,N'-methylenebisacrylamide (MBAA), and 400 parts of the second product, and react at 45°C with stirring for 10 hours. Remove dimethyl sulfoxide by vacuum distillation at 60°C, adjust the pH to 7, and obtain the final product binder with the following structural formula:

[0081] .

[0082] This embodiment also provides a negative electrode sheet, the specific preparation method of which includes:

[0083] Graphite, silicon, and the aforementioned binder are mixed in a mass ratio of 92:5:3 and thoroughly stirred to disperse, resulting in a negative electrode slurry. This slurry is then processed into a negative electrode sheet through baking, rolling, slitting, and welding of tabs.

[0084] This embodiment also provides a lithium-ion battery, the specific preparation method of which includes:

[0085] Preparation of positive electrode sheet: The active material lithium cobalt oxide, conductive carbon black, and binder PVDF (CAS No.: 24937-79-9) are mixed in a mass ratio of 96:2:2. N-methylpyrrolidone (NMP, CAS No.: 872-50-4) is added and stirred thoroughly to obtain a positive electrode slurry. The slurry is then uniformly coated on the positive electrode current collector aluminum foil and prepared into a positive electrode sheet through processes such as baking, rolling, slitting, and welding of electrode tabs.

[0086] Preparation of lithium-ion batteries: Assemble the above-mentioned positive electrode, negative electrode, separator, and aluminum-plastic film, bake them, inject electrolyte, and then proceed with processes such as settling, formation, secondary sealing, and testing to obtain lithium-ion batteries.

[0087] Example 2

[0088] The difference between this embodiment and Embodiment 1 lies in the preparation method of the adhesive, specifically including:

[0089] Step 3: Add 2.2 parts of initiator APS ammonium persulfate, 8000 parts of water, 400 parts of the second product, and 34 parts of dodecylbenzenesulfonic acid (DBSA). Under N2 protection, add 80 parts of aniline (ANI) dropwise. React at 55°C with stirring for 13 hours. Adjust the pH to 7 using ammonia water to obtain the binder, with the following structural formula. The rest is the same as in Example 1.

[0090] .

[0091] Where X: the reducing unit of polyaniline; 1-X: the oxidizing unit of polyaniline; n4: the degree of polymerization of the polyaniline branched chain.

[0092] Examples 3-9

[0093] The number of each monomer is shown in Table 1, and the rest is the same as in Example 1.

[0094] Table 1. Number of monomer components in Examples 1-9 of the present invention

[0095]

[0096] Table 2 shows the corresponding values ​​of n1~n4 and m1~m7 in embodiments 1~9 of the present invention.

[0097]

[0098] Comparative Example 1

[0099] This comparative example provides an electrode sheet that differs from Example 1 in that it comprises graphite, silicon, dispersant CMC, and commercially available binder PAA in a mass ratio of 92:5:1:2.

[0100] This comparative example also provides a lithium-ion battery, the specific preparation method of which is the same as in Example 1.

[0101] The CMC (sodium carboxymethyl cellulose) provided in this comparative example is CMC2200 from Daicel Corporation; the PAA (polyacrylic acid) is LA133 from Indira Gandhi.

[0102] Comparative Example 2

[0103] This comparative example provides an electrode sheet that differs from Example 1 in that it comprises graphite, silicon, dispersant CMC, commercially available binder PAA, and conductive agent CNT in a mass ratio of 91.5:5:1:2:0.5.

[0104] Test Example 1

[0105] Viscosity tests were conducted on the negative electrode slurries prepared in Examples 1-9 and Comparative Examples 1-2, and electrode resistance and adhesion tests were conducted on the electrodes. The results are shown in Table 2.

[0106] Viscosity: The above raw materials were thoroughly mixed directly in a mixing tank until a slurry was formed. The mixing conditions were 60 minutes at 700 rpm, followed by standing for 24 hours, and then slow mixing at 200 rpm for 30 minutes before testing the viscosity.

[0107] Solid content: Take a slurry sample and dry it in an oven at 150℃ until constant weight, for 2 hours. Weigh the sample after drying and calculate the solid content. The formula is as follows:

[0108]

[0109] Table 2 Test results of Examples 1-9 and Comparative Examples 1-2

[0110]

[0111] According to the results in Table 2, the viscosity of the slurries prepared in Examples 1-9 increased slightly after standing for 24 hours, while the solid content of the lower layer remained basically unchanged, indicating that no sedimentation occurred. The viscosity of the slurries prepared in Comparative Examples 1-2 increased significantly after standing, and obvious stratification and sedimentation occurred. Meanwhile, because the binders provided in Examples 1-9 effectively dispersed the silicon-carbon-graphite mixed particles, the electrode adhesion was significantly higher than that in Comparative Examples 1-2. From the electrode resistance data, it can be seen that, at the same addition amount, the conductivity of Example 2 (aniline monomer) was slightly worse than that of Example 1 (3,4-ethylenedioxythiophene monomer), and increased with decreasing monomer addition (Examples 8 and 9). Furthermore, the conductive groups of polythiophene and polyaniline conduct electrons, and the electrode resistance was significantly lower than that of Comparative Example 1.

[0112] Test Example 2

[0113] Low-temperature discharge tests were conducted on the batteries prepared in Examples 1-9 and Comparative Examples 1-2, and the results are shown in Table 3:

[0114] The assembled 4600mAh battery was charged to 4.45V at room temperature using a 0.2C current. It was then left to stand for 1 hour to ensure full charging. After charging, the battery was placed in a 25℃ environment and discharged at a 0.2C current until the discharge termination voltage reached 3V. The discharge capacity at 25℃ was recorded as the baseline capacity. The battery was then placed in environments at 0℃, -10℃, and -20℃ for 12 hours each to allow it to reach a stable low-temperature state.

[0115] Table 3 Battery capacity retention rates of Examples 1-9 and Comparative Examples 1-2

[0116]

[0117] The data in Table 3 show that the batteries prepared in Examples 1-9 have significantly better low-temperature performance than those in Comparative Examples 1-2. This is because the binder provided by this invention can be dispersed and coated on the surface of active materials such as graphite and silicon carbon, and also contains electrolyte-affinity groups such as acrylates, which enhance the lithium-ion exchange rate between the active materials and the electrolyte, thereby improving the charge-discharge efficiency and stability of the battery. Furthermore, different acrylate monomers exhibit different low-temperature performances; Example 1 (butyl acrylate) performs better than Example 3 (isooctyl acrylate).

[0118] This invention achieves high-efficiency production, excellent active material dispersibility, improved battery performance, stable electrode performance, and superior low-temperature performance through a unique binder structure design and optimized preparation process.

[0119] The embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention. Furthermore, the embodiments of the present invention and the features thereof can be combined with each other unless otherwise specified.

Claims

1. An adhesive, characterized in that, The adhesive comprises a structural unit of type I: Formula I; Wherein, M is at least one of H, Na, Li, and K; R1 and R2 each independently contain at least one of H, substituted or unsubstituted C1-10 straight-chain or branched alkyl groups; R3 is a conductive polymer; R4 and R5 each independently contain at least one of H, C1-10 straight-chain or branched alkyl groups, and C1-10 alkoxy groups. n1 is an integer from 10 to 100, n2 is an integer from 2 to 20, and n3 is an integer from 10 to 35; The m1 is the number of branches in the polyacrylic acid monomer; the m3 is the number of branches in the polyacrylamide monomer; the m5 is the number of branches in the alkyl polymer monomer with 1 to 4 carbon atoms (straight-chain or branched); the m7 is the number of branches in the conductive polymer; the m2 and m6 are the degrees of polymerization of the polyacrylic acid monomer; the m4 is the degree of polymerization of the polyacrylate monomer; m1 is an integer from 10 to 50; m3 is an integer from 2 to 30; m4 is an integer from 10 to 100; m5 is an integer from 10 to 100; m7 is an integer from 5 to 20; wherein, m2 + m6 is an integer from 300 to 3000.

2. The adhesive according to claim 1, characterized in that, The conductive polymer monomer contains thiophene or aniline.

3. The adhesive according to claim 1, characterized in that, The solid content of the adhesive is 1%-15%.

4. The adhesive according to claim 1, characterized in that, The viscosity of the adhesive is 1000-100000 mPa·s.

5. A method for preparing an adhesive as described in any one of claims 1 to 4, characterized in that, The preparation method includes the following steps: S1. Acrylic acid, the first initiator and the solvent are mixed in an inert atmosphere to carry out the first reaction to obtain the first product. Then, the crosslinking agent, polyacrylamide, paraffin and acrylate are added to carry out the second reaction. The pH is adjusted and the product is dried to obtain the second product. S2. Dissolve the second product, add conductive polymer monomer, crosslinking agent and second initiator to carry out the third reaction, and filter to obtain the adhesive. The structural formula I of the first product and the structural formula II of the second product are as follows: 。 6. The preparation method according to claim 5, characterized in that, It also includes at least one of the following (1) to (8): (1) In step S1, the first initiator is azobisisobutyronitrile; (2) In steps S1 and S2, the crosslinking agent is N,N'-methylenebisacrylamide; (3) In step S2, the conductive polymer monomer includes at least one of ethylenedioxythiophene and aniline; (4) In step S2, the second initiator includes ammonium persulfate; (5) The pH value in step S1 is 6~7; (6) The reaction temperature in step S1 is 50~70℃; (7) The reaction temperature in step S2 is 60~70℃; (8) In step S1, the paraffin is a mixture of alkanes with 14 to 30 carbon atoms and a melting point of 5.5 to 65.5°C; and / or, in step S1, the paraffin is a mixture of alkanes with 14 to 22 carbon atoms and a melting point of 5.5 to 44.4°C.

7. The preparation method according to claim 5, characterized in that, In step S1, relative to 500 parts by weight of acrylic acid, the amount of the raw materials includes: 1-3 parts by weight of the first initiator, 0.1-0.3 parts by weight of the crosslinking agent, 2-7 parts by weight of polyacrylamide, 20-60 parts by weight of paraffin, and 100-200 parts by weight of acrylate.

8. The preparation method according to claim 5, characterized in that, In step S2, relative to 400 parts by weight of the second product, the amount of the raw materials includes: 60-100 parts by weight of conductive polymer monomer, 0.3-0.5 parts by weight of second initiator, and 0.5-0.7 parts by weight of crosslinking agent.

9. A negative electrode sheet, characterized in that, It includes a negative electrode active material and a binder as described in any one of claims 1 to 4 and / or a binder prepared by any one of claims 5 to 8.

10. A lithium battery, characterized in that, It includes the negative electrode as described in claim 9, as well as the positive electrode, the separator, and the electrolyte.

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