An aqueous binder, its preparation method and uses

Abstract

The present invention belongs to the technical field of lithium-ion batteries, and particularly relates to an aqueous binder, a preparation method and a use thereof. The aqueous binder comprises a polymer containing at least two monomer units. The polymer comprises a first monomer unit and a second monomer unit. The first monomer unit has a structure shown in Formula I, and the second monomer unit has a structure shown in Formula II, wherein R1, R2 and R3 are the same or different and each independently represents hydrogen, a straight-chain alkyl group or a branched-chain alkyl group; R5 is a group with a hydroxyl group at the end. The aqueous binder provided by the present invention has excellent binding properties, can significantly inhibit the swelling of the silicon negative electrode, and at the same time enables the prepared electrode sheet to have excellent flexibility, improving the cycle performance of the battery.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries, and particularly relates to an aqueous binder, a preparation method thereof, and uses thereof. Background Art

[0002] Secondary batteries, especially lithium-ion batteries, have properties such as high capacity, long cycle life, no memory effect, low self-discharge, wide operating temperature range, and high rate performance, and have been widely applied to fields such as mobile phones, computers, electric bicycles, and electric vehicles. In the negative electrode film, there are graphite, silicon materials as negative electrode active materials, and a binder. Silicon-based materials have advantages such as high capacity, good cycle performance, and good rate performance, and are attracting more and more attention. However, during the charge and discharge process, the volume expands greatly, affecting the cycle performance of the battery and restricting its application.

[0003] Commonly used silicon negative electrode binders in the prior art are SBR (styrene-butadiene rubber) and PAA (polyacrylic acid) binders. The SBR binder is usually used in combination with CMC. The SBR itself has low strength and poor adhesion, and has a poor inhibitory effect on the expansion of the electrode sheet. Therefore, when applied to the silicon negative electrode, its cycle performance is often very poor; the flexibility and processability of the electrode sheet prepared with the PAA binder in the prior art are poor, and it is difficult to recover after the structure of the electrode sheet is damaged, and the cycle performance is poor.

[0004] Therefore, developing a binder with excellent adhesion performance, flexibility performance, and cycle performance to meet the application requirements of high-performance electrode sheets and lithium-ion batteries is an urgent problem to be solved in this field. Summary of the Invention

[0005] Aiming at the above deficiencies in the prior art, the purpose of the present invention is to provide an aqueous binder, a preparation method thereof, and uses thereof. The aqueous binder provided by the present invention has excellent adhesion performance, can significantly inhibit the expansion of the silicon negative electrode, and at the same time enables the prepared electrode sheet to have excellent flexibility performance, improving the cycle performance of the battery.

[0006] To achieve the above purpose, the present invention adopts the following technical solutions:

[0007] In a first aspect, the present invention provides an aqueous binder, the aqueous binder comprising a polymer containing at least two monomer units, the polymer comprising a first monomer unit and a second monomer unit, the first monomer unit having the structure shown in Formula I, and the second monomer unit having the structure shown in Formula II,

[0008]

[0009] Among them, R1, R2 and R3 are the same or different and each independently represents hydrogen, a straight-chain alkyl group or a branched-chain alkyl group; R5 is a group with a hydroxyl group at the end.

[0010] Here, the selection of R1, R2, and R3 is based on the principle of maintaining the water solubility of the monomer, and the selection of R5 is based on the principle of maintaining the water solubility of the monomer.

[0011] The aqueous binder provided by the present invention has excellent binding properties, can significantly inhibit the swelling of the silicon negative electrode, and at the same time enables the prepared electrode sheet to have excellent flexibility, improving the cycle performance of the battery.

[0012] In the above aqueous binder, as a preferred embodiment, R5 represents a straight-chain alkyl group with 1-6 carbon atoms substituted by a hydroxyl group, a branched-chain alkyl group with 1-6 carbon atoms substituted by a hydroxyl group, -CH2CH2OCH2CH2OH or -(CH2CH2O) n H, n≥3 (for example, n can be 3, 5, 7 or 10, etc.).

[0013] In the above aqueous binder, as a preferred embodiment, R1, R2 and R3 are the same or different and each independently represents hydrogen, a straight-chain alkyl group with 1-6 carbon atoms or a branched-chain alkyl group with 1-6 carbon atoms.

[0014] In the above aqueous binder, as a preferred embodiment, R5 represents -CH2CH2OH, -CH2CH2CH2OH, -CH2CH2OCH2CH2OH or -(CH2CH2O) n H, n≥3 (for example, n can be 3, 5, 7 or 10, etc.).

[0015] In the above aqueous binder, as a preferred embodiment, R1 represents hydrogen, methyl, ethyl, propyl, -CH(CH3)2, -CH2CH2CH2CH3 or -CH2CH(CH3)2; R2 represents hydrogen, methyl, ethyl, propyl, -CH(CH3)2, -CH2CH2CH2CH3 or -CH2CH(CH3)2; R3 represents hydrogen, methyl, ethyl, propyl, -CH(CH3)2, -CH2CH2CH2CH3 or -CH2CH(CH3)2.

[0016] In the above aqueous binder, as a preferred embodiment, the polymer further includes a third monomer unit, and the third monomer unit has the structure shown in Formula III:

[0017] Among them, R4 represents hydrogen, a straight-chain alkyl group or a branched-chain alkyl group; M represents H, Li, Na or K.

[0018] In the above-mentioned aqueous binder, as a preferred embodiment, R4 represents hydrogen, a straight-chain alkyl group with 1-6 carbon atoms, or a branched-chain alkyl group with 1-6 carbon atoms. For example, R4 represents hydrogen, methyl, ethyl, or -CH(CH3)2.

[0019] In the above-mentioned aqueous binder, as a preferred embodiment, the aqueous binder further includes water. The solid content of the aqueous binder is 9.5-11%, and the viscosity is 8000-30000 cps (for example, the viscosity can be 8000 cps, 10000 cps, 15000 cps, 20000 cps, 25000 cps, or 30000 cps, etc.).

[0020] In the above-mentioned aqueous binder, as a preferred embodiment, the polymer has the structure shown in Formula IV:

[0021]

[0022] Among them, M represents H, Li, Na, or K;

[0023] R1 represents hydrogen, a straight-chain alkyl group, or a branched-chain alkyl group. Preferably, R1 represents hydrogen, a straight-chain alkyl group with 1-6 carbon atoms, or a branched-chain alkyl group with 1-6 carbon atoms. More preferably, R1 represents hydrogen, methyl, ethyl, propyl, -CH(CH3)2, -CH2CH2CH2CH3, or -CH2CH(CH3)2;

[0024] R2 represents hydrogen, a straight-chain alkyl group, or a branched-chain alkyl group. Preferably, R2 represents hydrogen, a straight-chain alkyl group with 1-6 carbon atoms, or a branched-chain alkyl group with 1-6 carbon atoms. More preferably, R2 represents hydrogen, methyl, ethyl, propyl, -CH(CH3)2, -CH2CH2CH2CH3, or -CH2CH(CH3)2;

[0025] R3 represents hydrogen, a straight-chain alkyl group, or a branched-chain alkyl group. Preferably, R3 represents hydrogen, a straight-chain alkyl group with 1-6 carbon atoms, or a branched-chain alkyl group with 1-6 carbon atoms. More preferably, R3 represents hydrogen, methyl, ethyl, propyl, -CH(CH3)2, -CH2CH2CH2CH3, or -CH2CH(CH3)2;

[0026] R4 represents hydrogen, a straight-chain alkyl group, or a branched-chain alkyl group. Preferably, R4 represents hydrogen, a straight-chain alkyl group with 1-6 carbon atoms, or a branched-chain alkyl group with 1-6 carbon atoms. For example, R4 represents hydrogen, methyl, ethyl, or -CH(CH3)2;

[0027] R5 represents a group with a hydroxyl group at the end group. Preferably, R5 represents a straight-chain alkyl group with 1-6 carbon atoms substituted by a hydroxyl group, a branched-chain alkyl group with 1-6 carbon atoms substituted by a hydroxyl group, -CH2CH2OCH2CH2OH or -(CH2CH2O) n H, n≥3 (for example, n can be 3, 5, 7, 10, etc.). More preferably, R5 represents -CH2CH2OH, -CH2CH2CH2OH, -CH2CH2OCH2CH2OH or -(CH2CH2O) n H, n≥3 (for example, n can be 3, 5, 7, 10, etc.);

[0028] a:b:c = (30-80):(0-50):(5-50). For example, a:b:c can be 60:10:30, 30:50:20, 80:0:20, 40:20:40 or 50:20:30, etc. a:b:c is the molar ratio of each monomer unit.

[0029] In the above aqueous binder, as a preferred embodiment, based on the total molar number of the first monomer unit, the second monomer unit and the third monomer unit being 100%, the molar percentage of the first monomer unit is 30%-80% (for example, it can be 30%, 50%, 70% or 80%, etc.), the molar percentage of the second monomer unit is 5%-50% (for example, it can be 5%, 10%, 20%, 30%, 40% or 50%, etc.), and the molar percentage of the third monomer unit is 0-50% (for example, it can be 0%, 10%, 20%, 30%, 40% or 50%, etc.).

[0030] In a second aspect, the present invention provides a preparation method of the aqueous binder as described in the first aspect, including the following steps:

[0031] Under the action of an initiator, the polymer monomers are subjected to a polymerization reaction in a reaction solvent to obtain the aqueous binder, wherein the polymer monomers include acrylamide monomers and vinyl ether monomers.

[0032] The aqueous binder prepared by using the preparation method provided by the present invention has a high adhesive force, can significantly inhibit the expansion of the silicon negative electrode, and improve the cycle performance of the battery.

[0033] In the above preparation method of the aqueous binder, as a preferred embodiment, the polymer monomers further include the acrylic acid monomers.

[0034] In the preparation method of the above-mentioned aqueous binder, as a preferred embodiment, the molar ratio of the acrylamide monomer, the acrylic acid monomer and the vinyl ether monomer is (30-80):(0-50):(5-50), for example, it can be 60:10:30, 30:50:20, 80:0:20, 40:20:40 or 50:20:30, etc.

[0035] In the preparation method of the above-mentioned aqueous binder, as a preferred embodiment, based on the total molar number of the acrylamide monomer, the acrylic acid monomer and the vinyl ether monomer being 100%, the molar percentage of the acrylamide monomer is 30%-80%, the molar percentage of the acrylic acid monomer is 0%-50%, and the molar percentage of the vinyl ether monomer is 5%-50%.

[0036] If the molar percentage of the vinyl ether monomer is too large, the water solubility of the aqueous binder is poor and the mechanical strength is low. If the molar percentage of the vinyl ether monomer is too small, the flexibility of the aqueous binder is poor.

[0037] In the preparation method of the above-mentioned aqueous binder, as a preferred embodiment, the acrylamide monomer has the structure shown in Formula V, the vinyl ether monomer has the structure shown in Formula VI, and the acrylic acid monomer has the structure shown in Formula VII,

[0038]

[0039] wherein, the definitions of M, R1, R2, R3, R4 and R5 are the same as those of M, R1, R2, R3, R4 and R5 in the aqueous binder described in the first aspect.

[0040] In the preparation method of the above-mentioned aqueous binder, as a preferred embodiment, based on the total molar number of the polymer monomers being 100%, the molar number of the initiator is 0.02%-1.0%, for example, it can be 0.02%, 0.1%, 0.3%, 0.6% or 1%, etc.

[0041] In the preparation method of the above-mentioned aqueous binder, as a preferred embodiment, under the action of the initiator, the polymer monomers are subjected to a polymerization reaction in a reaction solvent to obtain the aqueous binder, including the following steps:

[0042] S1. Add the polymer monomers into the reaction solvent, stir and disperse to obtain a mixed solution;

[0043] S2. Add the initiator to the mixed solution to carry out a polymerization reaction. After the reaction is completed, carry out vacuum pumping, alkali neutralization, sieving and demagnetization to obtain the aqueous binder.

[0044] Here, the aqueous binder can be a water-soluble binder for silicon anodes.

[0045] In the preparation method of the above aqueous binder, as a preferred embodiment, the reaction solvent is water, preferably deionized water.

[0046] In the preparation method of the above aqueous binder, as a preferred embodiment, in step S1, the stirring speed is 100 - 800 rpm, for example, it can be 100 rpm, 300 rpm, 500 rpm or 800 rpm, etc.

[0047] In the preparation method of the above aqueous binder, as a preferred embodiment, in step S1, after adding the polymer monomer to the reaction solvent, an inert gas is introduced to remove the oxygen in the mixed solution.

[0048] In the preparation method of the above aqueous binder, as a preferred embodiment, the inert gas is nitrogen or argon.

[0049] In the preparation method of the above aqueous binder, as a preferred embodiment, the initiator is a water-soluble initiator.

[0050] In the preparation method of the above aqueous binder, as a preferred embodiment, the initiator includes at least one of sodium persulfate, potassium persulfate, ammonium persulfate, ammonium persulfate / sodium sulfite, ammonium persulfate / sodium bisulfite, hydrogen peroxide / ferrous ion.

[0051] In the preparation method of the above aqueous binder, as a preferred embodiment, adding the initiator to the mixed solution for polymerization reaction includes: adding a first initiator to the mixed solution for a first polymerization reaction, and then adding a second initiator for a second polymerization reaction.

[0052] In the preparation method of the above aqueous binder, as a preferred embodiment, the molar ratio of the first initiator to the second initiator is (0.5 - 3):1, for example, it can be 0.5:1, 1:1, 1.5:1, 2:1 or 3:1, etc.

[0053] In the preparation method of the above aqueous binder, as a preferred embodiment, the first initiator includes at least one of sodium persulfate, potassium persulfate, ammonium persulfate.

[0054] In the preparation method of the above aqueous binder, as a preferred embodiment, the second initiator is a redox initiator, including at least one of ammonium persulfate / sodium sulfite, ammonium persulfate / sodium bisulfite, hydrogen peroxide / ferrous ion.

[0055] Here, the ferrous ion can be a ferrous salt, such as ferrous sulfate, ferrous chloride, etc.

[0056] In the preparation method provided by the present invention, by adding a second initiator and restricting the second initiator to a redox initiator, the residual monomers can be further made to react and the reaction rate can be increased, making the polymerization reaction more complete.

[0057] In the above preparation method of the aqueous binder, as a preferred embodiment, the temperature of the first polymerization reaction is 40°C to 80°C (for example, it can be 40°C, 45°C, 50°C, 55°C, 60°C, 70°C or 80°C, etc.), and the time is 3 to 10 h (for example, it can be 3 h, 5 h, 7 h or 10 h, etc.); the temperature of the second polymerization reaction is 70°C to 90°C (for example, it can be 70°C, 80°C or 90°C, etc.), and the time is 1 - 3 h (for example, it can be 1 h, 2 h or 3 h, etc.).

[0058] In the above preparation method of the aqueous binder, as a preferred embodiment, in step S2, vacuum is pumped for 1 to 2 h, and the absolute vacuum degree is 5 to 50 KPa (for example, it can be 5 KPa, 10 KPa, 15 KPa, 20 KPa, 40 KPa or 50 KPa, etc.), preferably 10 to 20 KPa.

[0059] In the above preparation method of the aqueous binder, as a preferred embodiment, in step S2, the alkali neutralization includes neutralizing with lithium hydroxide, sodium hydroxide or potassium hydroxide until the pH value is 6.0 to 9.0 (for example, it can be 6.0, 7.0, 8.0 or 9.0, etc.).

[0060] In the above preparation method of the aqueous binder, as a preferred embodiment, in step S2, the mesh number of the sieve used for sieving is 150 to 400 meshes, for example, it can be 150 meshes, 200 meshes, 300 meshes or 400 meshes, etc.

[0061] In the above preparation method of the aqueous binder, as a preferred embodiment, in step S2, in the demagnetization process, a super-strong magnetic bar demagnetizer is used for demagnetization. Since the prepared aqueous binder will be applied to secondary batteries, demagnetization treatment is carried out according to the requirements of its application field.

[0062] In the above preparation method of the aqueous binder, as a preferred embodiment, in step S2, after the alkali neutralization and before the sieving, the solid content is adjusted to 10 ± 1%.

[0063] In the third aspect, the present invention provides a use of the aqueous binder according to the first aspect or the aqueous binder prepared by the preparation method of the aqueous binder according to the second aspect, and the aqueous binder is used for the preparation of lithium-ion batteries.

[0064] In the above use of the aqueous binder, as a preferred embodiment, the aqueous binder is used for the preparation of the negative electrode sheet in a lithium-ion battery.

[0065] The method of using a binder to prepare a battery negative electrode is well-known to those skilled in the art. Preferably, one method of preparing a negative electrode sheet with the binder of the present invention is as follows:

[0066] The binder, conductive agent and active material of the present invention are slurried in deionized water, and the obtained slurry is coated on a current collector to form a negative electrode sheet.

[0067] In the above use of the aqueous binder, as a preferred embodiment, the negative electrode active material in the negative electrode sheet includes a silicon-based material.

[0068] Compared with the prior art, the beneficial effects of the present invention at least include one of the following:

[0069] (1) The aqueous binder provided by the present invention has excellent binding performance, can significantly inhibit the expansion of the silicon negative electrode, and at the same time enables the prepared electrode sheet to have excellent flexibility, improving the cycle performance of the battery.

[0070] (2) The present invention uses acrylamide and its derivatives, acrylic acid and its derivatives, and vinyl ether monomers to carry out free radical polymerization in an aqueous solution to obtain a water-soluble polymer with a certain flexibility. Through the polar groups -OH, -CONR2R3, etc. in the polymer, hydrogen bonds or chemical bonds are formed with silicon particles in the silicon negative electrode, increasing the interaction force between the silicon material and graphite, and between the binder and the active material, forming a three-dimensional network three-dimensional structure. Therefore, while improving the binding force, the expansion of the silicon negative electrode is reduced and its cycle life is greatly improved. Specific Embodiments

[0071] To make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Those skilled in the art should understand that the embodiments are only for helping to understand the present invention and should not be regarded as specific limitations on the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts fall within the scope of protection of the present invention.

[0072] The embodiments of the present invention are implemented on the premise of the technical solutions of the present invention, and detailed implementation manners and processes are given. However, the protection scope of the present invention is not limited to the following embodiments. For the process parameters without specific conditions noted in the following embodiments, they are usually in accordance with conventional conditions.

[0073] In the ranges disclosed in the present invention, the endpoints and any values are not limited to the exact ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed in the present invention.

[0074] For the process parameters without specific conditions noted in the following examples, they are generally in accordance with conventional conditions. The experimental reagents used in the following examples are all conventional biochemical reagents without special instructions; the amounts of the experimental reagents used are all the amounts of reagents in conventional experimental operations without special instructions.

[0075] In a first aspect, an embodiment of the present invention provides an aqueous binder, and the aqueous binder includes a polymer containing at least two monomer units. The polymer includes a first monomer unit and a second monomer unit. The first monomer unit has a structure shown in Formula I, and the second monomer unit has a structure shown in Formula II.

[0076]

[0077] Wherein, R1 represents hydrogen, methyl, ethyl, propyl, -CH(CH3)2, -CH2CH2CH2CH3 or -CH2CH(CH3)2; R2 represents hydrogen, methyl, ethyl, propyl, -CH(CH3)2, -CH2CH2CH2CH3 or -CH2CH(CH3)2; R3 represents hydrogen, methyl, ethyl, propyl, -CH(CH3)2, -CH2CH2CH2CH3 or -CH2CH(CH3)2, and R5 represents -CH2CH2OH, -CH2CH2CH2OH, -CH2CH2OCH2CH2OH or -(CH2CH2O) n H, n≥3;

[0078] The polymer further includes a third monomer unit, and the third monomer unit has a structure shown in Formula III:

[0079]

[0080] Wherein, R4 represents hydrogen, methyl, ethyl or -CH(CH3)2; M represents H, Li, Na or K.

[0081] The polymer has a structure shown in Formula IV:

[0082]

[0083]

[0084] Among them, the definitions of M, R1, R2, R3, R4, and R5 are the same as those in the embodiments of the present invention for M, R1, R2, R3, R4, and R5, and a:b:c = (30-80):(0-50):(5-50);

[0085] When the solid content of the aqueous binder is 9.5-11%, the viscosity is 8000-30000 cps.

[0086] The present invention discloses a water-soluble binder for a silicon negative electrode of a lithium-ion battery and a preparation method thereof. The technical problem to be solved is the problems of low adhesion, excessive swelling, and poor cycle performance existing in the application of traditional binders to high-silicon negative electrodes (specific capacity ≥ 500 mAh / g).

[0087] Based on the commonly used PAA-based binder, the present invention introduces a hydroxyl-containing monomer. The obtained binder has high strength and certain flexibility while being applied to a high-silicon negative electrode, which is beneficial to the dispersion of the conductive agent and the negative electrode material. The polar groups on the polymer can form strong hydrogen bond and chemical bond interactions with the polar groups on the surface of the silicon material, thereby forming a three-dimensional cross-linked network structure as a whole, improving the adhesion while reducing the swelling of the silicon negative electrode and greatly improving its cycle life.

[0088] In a second aspect, an embodiment of the present invention provides a preparation method of the aqueous binder as described in the first aspect, including the following steps:

[0089] S1. Add polymer monomers to deionized water, stir and disperse to obtain a mixed solution, and introduce an inert gas to remove oxygen in the mixed solution. Among them, the stirring speed is 100-800 rpm, the inert gas is nitrogen or argon, the polymer monomers include acrylamide monomers, vinyl ether monomers, and the polymer monomers also include the acrylic acid monomers. The molar ratio of the acrylamide monomers, acrylic acid monomers, and vinyl ether monomers is (30-80):(0-50):(5-50). The acrylamide monomers have the structure shown in formula V, the vinyl ether monomers have the structure shown in formula VI, and the acrylic acid monomers have the structure shown in formula VII.

[0090]

[0091] Among them, the definitions of M, R1, R2, R3, R4, and R5 are the same as those in the aqueous binder described in the first aspect for M, R1, R2, R3, R4, and R5.

[0092] S2. Add a first initiator to the mixed solution to carry out a first polymerization reaction, and then add a second initiator to carry out a second polymerization reaction. After the reaction is completed, evacuate for 1 - 2 h until the absolute vacuum degree is 5 - 50 KPa, and then carry out alkali neutralization, sieving, and demagnetization to obtain the aqueous binder. Wherein, based on the total molar amount of the polymer monomers being 100%, the sum of the molar amounts of the first initiator and the second initiator is 0.02% - 1.0%, the molar ratio of the first initiator to the second initiator is (0.5 - 3):1, the first initiator includes at least one of sodium persulfate, potassium persulfate, and ammonium persulfate, the second initiator is a redox initiator, including at least one of ammonium persulfate / sodium sulfite, ammonium persulfate / sodium bisulfite, and hydrogen peroxide / ferrous ion. The temperature of the first polymerization reaction is 40°C - 80°C, and the time is 3 - 10 h; the temperature of the second polymerization reaction is 70°C - 90°C, and the time is 1 - 3 h. The alkali neutralization includes neutralizing with lithium hydroxide, sodium hydroxide, or potassium hydroxide until the pH value is 6.0 - 9.0. The mesh number of the sieve for sieving is 150 - 400 meshes. In the demagnetization, a super-strong magnetic bar demagnetizer is used for demagnetization. After the alkali neutralization and before the sieving, adjust the solid content to 10 ± 1%.

[0093] In a third aspect, an embodiment of the present invention provides a use of the aqueous binder according to the first aspect or the aqueous binder prepared by the preparation method of the aqueous binder according to the second aspect. The aqueous binder is used for the preparation of the negative electrode sheet in a lithium-ion battery, wherein the negative electrode active material in the negative electrode sheet includes a silicon-based material.

[0094] To further understand the present invention, the following examples are used to illustrate in detail the aqueous binder provided by the present invention, its preparation method, and its use. The protection scope of the present invention is not limited by the following examples.

[0095] Example 1

[0096] The aqueous binder provided in this example includes a polymer with the following structure:

[0097]

[0098] Wherein, a:b:c = 60:10:30.

[0099] The preparation method of the aqueous binder provided in this example includes the following steps:

[0100] At room temperature, 400 g of deionized water was added to the reaction kettle, and then 0.6 mol of acrylamide, 0.1 mol of acrylic acid, and 0.3 mol of vinyl ethylene glycol ether were added in sequence. Stir and disperse at a stirring speed of 200 rpm. Nitrogen was introduced (nitrogen flow rate was 2 L / h) for 1 h to remove the oxygen in the solution system (mixed solution). Then the temperature was raised to 50 °C. After the temperature was stabilized, 0.001 mol of initiator potassium persulfate was added to carry out the polymerization reaction for 7 h. The temperature was adjusted to 80 °C, and then 0.001 mol of redox initiator ammonium persulfate and 0.001 mol of sodium bisulfite were added to carry out the polymerization reaction for 2 h to remove the residual monomers. After the reaction was completed, vacuum was pumped for 1 h until the absolute vacuum degree reached 10 KPa to further remove the residual monomers. Then lithium hydroxide monohydrate was added for neutralization until the pH value reached 7.5, and deionized water was added for dilution to obtain a light yellow colloidal solution. The colloidal solution was sieved through a 150-mesh sieve and demagnetized using a super-strong magnetic bar demagnetizer to obtain the target product (aqueous binder). The solid content of this aqueous binder was 10.6%, and the viscosity was 25000 cps.

[0101] Example 2

[0102] The aqueous binder provided in this example includes a polymer with the following structure:

[0103]

[0104] Among them, a:b:c = 30:50:20.

[0105] The preparation method of the aqueous binder provided in this example includes the following steps:

[0106] At room temperature, 500 g of deionized water was added to the reaction kettle, and then 0.3 mol of acrylamide, 0.5 mol of acrylic acid, and 0.2 mol of vinyl ethylene glycol ether were added in sequence. Stir and disperse at a stirring speed of 200 rpm. Nitrogen was introduced (nitrogen flow rate 2 L / h) for 1 h to remove the oxygen in the solution system (mixed solution). Then the temperature was raised to 60 °C. After the temperature was stabilized, 0.0015 mol of initiator ammonium persulfate was added to carry out the polymerization reaction for 5 h. The temperature was adjusted to 80 °C, and then 0.001 mol of redox initiator ammonium persulfate and 0.001 mol of sodium bisulfite were added to carry out the polymerization reaction for 2 h to remove the residual monomers. After the reaction was completed, vacuum was pumped for 1 h until the absolute vacuum degree reached 9 KPa to further remove the residual monomers. Then lithium hydroxide monohydrate was added for neutralization until the pH value reached 7.6, and deionized water was added for dilution to obtain a light yellow colloidal solution. The colloidal solution was sieved through a 150-mesh sieve and demagnetized using a super-strong magnetic bar demagnetizer to obtain the target product (aqueous binder). The solid content of this aqueous binder was 10.5%, and the viscosity was 16500 cps.

[0107] Example 3

[0108] The aqueous binder provided in this example includes a polymer having the structure shown below:

[0109]

[0110] Among them, a:c = 80:20.

[0111] The preparation method of the aqueous binder provided in this example includes the following steps:

[0112] At room temperature, 400 g of deionized water is added to the reaction kettle, and then 0.8 mol of acrylamide and 0.2 mol of vinyl glycol ether are added in sequence, stirred and dispersed, the stirring speed is 200 rpm, nitrogen is introduced (nitrogen flow rate 2 L / h), and the nitrogen introduction time is 1 h to remove oxygen in the solution system (mixed solution). Then the temperature is raised to 50 °C. After the temperature is stabilized, 0.001 mol of initiator potassium persulfate is added, and polymerization reaction is carried out for 7 h; the temperature is adjusted to 80 °C, and then 0.001 mol of redox initiator ammonium persulfate and 0.001 mol of sodium bisulfite are added, and polymerization reaction is carried out for 2 h to remove residual monomers. After the reaction is completed, vacuum is pumped for 1 h until the absolute vacuum degree is 8 KPa to further remove residual monomers. Then lithium hydroxide monohydrate is added for neutralization until the pH value is 7.7, and diluted with deionized water to obtain a light yellow colloidal solution. The colloidal solution is sieved through a 150-mesh sieve and demagnetized using a super-strong magnetic bar demagnetizer to obtain the target product (aqueous binder). The solid content of this aqueous binder is 9.8%, and the viscosity is 22000 cps.

[0113] Example 4

[0114] The aqueous binder provided in this example includes a polymer having the structure shown below:

[0115]

[0116] Among them, a:b:c = 40:20:40.

[0117] The preparation method of the aqueous binder provided in this example includes the following steps:

[0118] At room temperature, 400 g of deionized water was added to a reaction kettle, and then 0.4 mol of acrylamide, 0.2 mol of methacrylic acid, and 0.4 mol of vinyl glycol ether were added in sequence. After stirring and dispersing at a stirring speed of 200 rpm, nitrogen gas (nitrogen gas flow rate 2 L / h) was introduced for 1 h to remove the oxygen in the solution system (mixed solution). Then the temperature was raised to 50 °C. After the temperature was stabilized, 0.001 mol of potassium persulfate as an initiator was added, and a polymerization reaction was carried out for 7 h. The temperature was adjusted to 80 °C, and then 0.001 mol of ammonium persulfate and 0.001 mol of sodium bisulfite as a redox initiator were added, and a polymerization reaction was carried out for 2 h to remove the residual monomers. After the reaction was completed, vacuum was pumped for 1 h until the absolute vacuum degree reached 11 KPa to further remove the residual monomers. Then lithium hydroxide monohydrate was added for neutralization until the pH value reached 7.7. Deionized water was added for dilution to obtain a light yellow colloidal solution. The colloidal solution was passed through a 150-mesh sieve and demagnetized using a super-strong magnetic rod demagnetizer to obtain the target product (aqueous binder). The solid content of this aqueous binder was 10.0% and the viscosity was 17,500 cps.

[0119] Example 5

[0120] The aqueous binder provided in this example includes a polymer having the following structure:

[0121]

[0122] Among them, a:b:c = 50:20:30.

[0123] The preparation method of the aqueous binder provided in this example includes the following steps:

[0124] At room temperature, 450 g of deionized water was added to the reaction kettle, and then 0.5 mol of acrylamide, 0.2 mol of methacrylic acid, and 0.3 mol of vinyl diglycol ether were added in sequence. Stir and disperse at a stirring speed of 300 rpm. Nitrogen was introduced (nitrogen flow rate 2 L / h) for 1 h to remove oxygen in the solution system (mixed solution). Then the temperature was raised to 50 °C. After the temperature was stabilized, 0.005 mol of potassium persulfate as the initiator was added, and a polymerization reaction was carried out for 7 h. The temperature was adjusted to 80 °C, and then 0.001 mol of ammonium persulfate and 0.001 mol of sodium bisulfite as redox initiators were added, and a polymerization reaction was carried out for 2 h to remove residual monomers. After the reaction was completed, vacuum was pumped for 1 h until the absolute vacuum degree reached 15 KPa to further remove residual monomers. Then lithium hydroxide monohydrate was added for neutralization until the pH value reached 7.5. Deionized water was added for dilution to obtain a light yellow colloidal solution. The colloidal solution was sieved through a 150-mesh sieve and demagnetized using a super-strong magnetic bar demagnetizer to obtain the target product (aqueous binder). The solid content of this aqueous binder was 10.0%, and the viscosity was 10000 cps.

[0125] Example 6

[0126] The aqueous binder provided in this example includes a polymer having the following structure:

[0127]

[0128] Among them, a:b:c = 60:10:30.

[0129] The preparation method provided in this example is basically the same as that in Example 1, except that acrylamide was replaced with methacrylamide. The solid content of the obtained aqueous binder was 10.1%, and the viscosity was 19200 cps.

[0130] Example 7

[0131] The aqueous binder provided in this example includes a polymer having the following structure:

[0132]

[0133] Among them, a:b:c = 60:10:30.

[0134] The preparation method of the aqueous binder provided in this example includes the following steps:

[0135] At room temperature, 300 g of deionized water was added to a reaction kettle, and then 0.6 mol of N-isopropylacrylamide, 0.1 mol of isopropylacrylic acid, and 0.3 mol of vinyl ethylene glycol ether were added in sequence. After stirring and dispersing at a stirring speed of 400 rpm, nitrogen gas (nitrogen gas flow rate was 2 L / h) was introduced for 1 h to remove oxygen in the solution system (mixed solution). Then the temperature was raised to 70 °C. After the temperature was stabilized, 0.001 mol of initiator potassium persulfate was added, and a polymerization reaction was carried out for 6 h. The temperature was adjusted to 90 °C, and then 0.001 mol of redox initiator ammonium persulfate and 0.001 mol of sodium sulfite were added, and a polymerization reaction was carried out for 1.5 h to remove residual monomers. After the reaction was completed, vacuum was pumped for 1 h until the absolute vacuum degree reached 30 KPa to further remove residual monomers. Then sodium hydroxide was added for neutralization until the pH value reached 7.5, and deionized water was added for dilution to obtain a light yellow colloidal solution. The colloidal solution was passed through a 250-mesh sieve and demagnetized using a super-strong magnetic bar demagnetizer to obtain the target product (aqueous binder). The solid content of this aqueous binder was 9.5%, and the viscosity was 18300 cps.

[0136] Example 8

[0137] The aqueous binder provided in this example includes a polymer having the following structure:

[0138]

[0139] Among them, a:b:c = 60:10:30.

[0140] The preparation method provided in this example is basically the same as that in Example 1, except that acrylamide was replaced with the monomer corresponding to monomer unit a, acrylic acid was replaced with ethylacrylic acid, and vinyl ethylene glycol ether was replaced with vinyl propylene glycol ether. The solid content of the obtained aqueous binder was 10.8%, and the viscosity was 27000 cps.

[0141] Example 9

[0142] The aqueous binder provided in this example includes a polymer having the following structure:

[0143]

[0144] Among them, a:b:c = 40:40:20.

[0145] The preparation method provided in this example is basically the same as that in Example 1, except that 0.6 mol of acrylamide is replaced by 0.4 mol of N,N-dimethylacrylamide, 0.1 mol of acrylic acid is replaced by 0.4 mol of acrylic acid, and 0.3 mol of vinyl ethylene glycol ether is replaced by 0.2 mol of vinyl triethylene glycol ether. The solid content of the prepared aqueous binder is 10.4%, and the viscosity is 24000 cps.

[0146] Comparative Example 1

[0147] A commercially available styrene-butadiene rubber SBR from a certain company was used as the binder and used in combination with sodium carboxymethyl cellulose (CMC) at a mass ratio of 1:1.

[0148] Comparative Example 2

[0149] A commercially available acrylic resin PAA from a certain company was used as the binder.

[0150] Comparative Example 3

[0151] The aqueous binder provided in this comparative example has the following structure:

[0152]

[0153] Among them, a:b = 86:14.

[0154] The preparation method provided in this comparative example is basically the same as that in Example 1, except that vinyl ethylene glycol ether, 0.86 mol of acrylamide, and 0.14 mol of acrylic acid are not added.

[0155] Performance Test

[0156] The binders prepared in Examples 1-9 and Comparative Examples 1-3 were used as binders for silicon negative electrode materials to fabricate negative electrode sheets. The method is as follows:

[0157] The silicon-carbon composite material (using a silicon-based / graphite composite negative electrode material with a specific capacity of 600 mAh / g), conductive carbon black, single-walled carbon nanotubes, and the binder prepared in the example or comparative example (taking the aqueous binder prepared in the example or comparative example, wherein the mass ratio of the solid in the aqueous binder to the mass of the silicon-carbon composite material is 6.25:93.0) were mixed. The mass ratio of the silicon-carbon composite material, conductive carbon black, single-walled carbon nanotubes, and the binder prepared in the example or comparative example (calculated based on the mass of the solid in the binder) is 93.0:0.5:0.25:6.25. An appropriate amount of deionized water was added according to the proportion of the total solid component being 35% to make a battery electrode sheet slurry. After the uniformly dispersed slurry was passed through a 100-mesh sieve, it was coated on a 10-μm-thick copper foil serving as a current collector, dried at 120°C for 5 minutes, and then at room temperature at 10×10 4The negative electrode sheet is obtained by calendering the load per unit length of N / m.

[0158] Using lithium nickel cobalt manganese oxide NCM622 as the positive electrode, a mixed solvent of ethylene carbonate EC: ethyl methyl carbonate EMC: diethyl carbonate DEC in a mass ratio of 3:2:5, containing 1 M LiPF6, as the electrolyte, and using a PP material of the prior art as the separator to fabricate a 425060P lithium-ion battery.

[0159] The performance measurement method is as follows:

[0160] Measuring the peel strength: Cut the negative electrode sheet made of the binder prepared in the examples and comparative examples into strips of 10 cm × 2.5 cm. Bond a 1 mm thick steel plate on the current collector side with double-sided tape, and paste a transparent tape on the coating layer side. Use a tensile testing machine to peel in the 180° direction at a speed of 100 mm / min, and measure the peel stress.

[0161] Measuring the flexibility of the electrode sheet: Place a mandrel with a diameter Φ = 3 mm on the current collector side of the rolled electrode sheet made of the binder prepared in the examples and comparative examples, and conduct a bending experiment. Observe the state of the electrode sheet at this time through an optical microscope. If the electrode sheet is intact, it is recorded as ○, and if peeling or cracking occurs, it is recorded as ×.

[0162] Measuring the initial efficiency of the battery: At 25 °C, in the voltage range of 2.5 - 4.2 V, perform charge and discharge cycles at 0.33 C, and use the constant current method to test the first Coulomb efficiency of its charge and discharge cycles;

[0163] Measuring the full charge expansion: At 25 °C, in the voltage range of 2.5 - 4.2 V, after performing charge and discharge cycles twice at 0.33 C, then fully charge the battery, disassemble the battery, and test the thickness d2 of the negative electrode sheet. Assuming the original thickness of the electrode sheet is d1, the full charge expansion rate is: (d2 - d1) / d1 × 100%.

[0164] Measuring the capacity retention rate after 300 cycles: At 25 °C, in the voltage range of 2.5 - 4.2 V, charge at 0.5 C and discharge at 1.0 C for charge and discharge cycles, and use the constant current method to test the capacity retention rate after 300 cycles. The capacity retention rate = the discharge gram capacity in the 300th cycle / the discharge gram capacity in the first cycle.

[0165] The test results are shown in Table 1 and Table 2.

[0166] Table 1

[0167]

[0168] Table 2

[0169] Project Example 7 Example 8 Example 9 Peeling strength (N / m) 68.23 68.79 69.81 Flexibility of the electrode sheet ○ ○ ○ Initial efficiency (%) 85.06 85.32 85.24 Swelling at full charge (%) 36.29 37.04 36.58 Capacity retention rate after 300 cycles (%) 81.15 80.67 80.94

[0170] As can be seen from Table 1 and Table 2, compared with the commercially available SBR (Comparative Example 1), the binders provided in Examples 1-9 have very obvious improvements in terms of peel strength, initial efficiency, full charge swelling, and cycle capacity retention rate; compared with the commercially available PAA-based binder (Comparative Example 2), the binders provided in Examples 1-9 also have obvious improvements in terms of peel strength, flexibility of the electrode sheet, initial efficiency, full charge swelling, and cycle capacity retention rate. This shows that the aqueous binder provided by the present invention has excellent binding performance, can significantly inhibit the swelling of the silicon negative electrode, and at the same time enables the prepared electrode sheet to have excellent flexibility, improving the cycle performance of the battery.

[0171] Compared with Example 1, in Comparative Example 3, vinyl glycol ether was not added during the preparation of the binder, resulting in poor flexibility of the electrode sheet and a significant decrease in cycle performance.

[0172] Obviously, the above examples are merely examples given for clear illustration and are not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to enumerate all the implementation manners here. And the obvious changes or modifications derived therefrom are still within the protection scope of the present invention.

Claims

1. An aqueous binder, characterized in that, The aqueous binder includes a polymer containing at least two monomer units. The polymer includes a first monomer unit and a second monomer unit. The first monomer unit has the structure shown in Formula I, and the second monomer unit has the structure shown in Formula II. Wherein, R1, R2, and R3 are the same or different and each independently represents hydrogen, a straight-chain alkyl group, or a branched-chain alkyl group; R5 is a group with a hydroxyl group at the end. The preparation method of the aqueous binder is as follows: Under the action of an initiator, polymer monomers are subjected to a polymerization reaction in a reaction solvent to obtain the aqueous binder. The polymer monomers include acrylamide monomers and vinyl ether monomers, and the method includes the following steps: S1. Add the polymer monomers to the reaction solvent, stir and disperse to obtain a mixed solution; the acrylamide monomers have the structure shown in Formula V, and the vinyl ether monomers have the structure shown in Formula VI. S2. Add a first initiator to the mixed solution to carry out a first polymerization reaction, and then add a second initiator to carry out a second polymerization reaction. After the reaction is completed, perform vacuum pumping, alkali neutralization, sieving, and demagnetization to obtain the aqueous binder. Among them, the molar ratio of the first initiator to the second initiator is (0.5-3):

1. The first initiator includes at least one of sodium persulfate, potassium persulfate, and ammonium persulfate. The second initiator is a redox initiator, including at least one of ammonium persulfate / sodium sulfite, ammonium persulfate / sodium bisulfite, and hydrogen peroxide / ferrous ion.

2. The aqueous binder according to claim 1, characterized in that, The R5 represents a straight-chain alkyl group with 1-6 carbon atoms substituted by a hydroxyl group, a branched-chain alkyl group with 1-6 carbon atoms substituted by a hydroxyl group, -CH2CH2OCH2CH2OH or -(CH2CH2O) n H, n≥3; And / or, R1, R2, and R3 are the same or different and each independently represents hydrogen, a straight-chain alkyl group with 1-6 carbon atoms, or a branched-chain alkyl group with 1-6 carbon atoms.

3. The aqueous binder according to claim 1, characterized in that, R5 represents -CH2CH2OH, -CH2CH2CH2OH, -CH2CH2OCH2CH2OH or -(CH2CH2O) n H, n≥3; R1 represents hydrogen, methyl, ethyl, propyl, -CH(CH3)2, -CH2CH2CH2CH3 or -CH2CH(CH3)2; R2 represents hydrogen, methyl, ethyl, propyl, -CH(CH3)2, -CH2CH2CH2CH3 or -CH2CH(CH3)2; R3 represents hydrogen, methyl, ethyl, propyl, -CH(CH3)2, -CH2CH2CH2CH3 or -CH2CH(CH3)2.

4. The aqueous binder according to any one of claims 1-3, characterized in that, The polymer further includes a third monomer unit, and the third monomer unit has the structure shown in Formula III: Wherein, R4 represents hydrogen, a straight-chain alkyl group, or a branched-chain alkyl group; M represents H, Li, Na, or K.

5. The aqueous binder according to claim 4, characterized in that, R4 represents hydrogen, a straight-chain alkyl group with 1-6 carbon atoms, or a branched-chain alkyl group with 1-6 carbon atoms; And / or, the solid content of the aqueous binder is 9.5-11%, and the viscosity is 8000-30000 cps.

6. The aqueous binder according to claim 4, characterized in that, The polymer has the structure shown in Formula IV: Wherein, the definitions of M, R1, R2, R3, R4, and R5 are the same as the definitions of M, R1, R2, R3, R4, and R5 in Claim 4, and a:b:c = (30-80):(0-50):(5-50).

7. The aqueous binder according to claim 4, characterized in that, The temperature of the first polymerization reaction is 40°C to 80°C, and the time is 3 to 10 h; the temperature of the second polymerization reaction is 70°C to 90°C, and the time is 1-3 h.

8. A method for preparing an aqueous binder, characterized in that, Under the action of an initiator, polymer monomers are subjected to a polymerization reaction in a reaction solvent to obtain the aqueous binder. The polymer monomers include acrylamide monomers and vinyl ether monomers, and the method includes the following steps: S1. Add the polymer monomers to the reaction solvent, stir and disperse to obtain a mixed solution; the acrylamide monomers have the structure shown in Formula V, and the vinyl ether monomers have the structure shown in Formula VI. Wherein, R1, R2, and R3 are the same or different and each independently represents hydrogen, a straight-chain alkyl group, or a branched-chain alkyl group; R5 is a group with a hydroxyl group at the end; S2. Add a first initiator to the mixed solution to carry out a first polymerization reaction, and then add a second initiator to carry out a second polymerization reaction. After the reaction is completed, perform vacuum pumping, alkali neutralization, sieving, and demagnetization to obtain the aqueous binder. Among them, the molar ratio of the first initiator to the second initiator is (0.5 - 3):

1. The first initiator includes at least one of sodium persulfate, potassium persulfate, and ammonium persulfate. The second initiator is a redox initiator, including at least one of ammonium persulfate / sodium sulfite, ammonium persulfate / sodium bisulfite, and hydrogen peroxide / ferrous ion.

9. The method for preparing an aqueous binder according to claim 8, characterized in that, The polymer monomer further includes an acrylic monomer, and the molar ratio of the acrylamide monomer, acrylic monomer, and vinyl ether monomer is (30 - 80):(0 - 50):(5 - 50); The acrylic monomer has the structure shown in Formula VII: Wherein, R4 represents hydrogen, a straight-chain alkyl group, or a branched-chain alkyl group; M represents H, Li, Na, or K.

10. The method for preparing an aqueous binder according to claim 8, characterized in that, The temperature of the first polymerization reaction is 40°C to 80°C, and the time is 3 to 10 h; the temperature of the second polymerization reaction is 70°C to 90°C, and the time is 1 - 3 h.

11. The preparation method of the aqueous binder according to claim 8, characterized in that, The aqueous binder includes a polymer containing at least two monomer units. The polymer includes a first monomer unit and a second monomer unit. The first monomer unit has the structure shown in Formula I, and the second monomer unit has the structure shown in Formula II. Wherein, R1, R2, and R3 are the same or different and each independently represents hydrogen, a straight-chain alkyl group, or a branched-chain alkyl group; R5 is a group with a hydroxyl group at the end.

12. The preparation method of the aqueous binder according to claim 8, characterized in that, The R5 represents a straight-chain alkyl group with 1-6 carbon atoms substituted by hydroxyl groups, a branched-chain alkyl group with 1-6 carbon atoms substituted by hydroxyl groups, -CH2CH2OCH2CH2OH or -(CH2CH2O) n H, where n ≥ 3; And / or, R1, R2, and R3 are the same or different and each independently represents hydrogen, a straight-chain alkyl group with 1 - 6 carbon atoms, or a branched-chain alkyl group with 1 - 6 carbon atoms.

13. The preparation method of the aqueous binder according to claim 8, characterized in that, R5 represents -CH2CH2OH, -CH2CH2CH2OH, -CH2CH2OCH2CH2OH or -(CH2CH2O) n H, where n ≥ 3; R1 represents hydrogen, methyl, ethyl, propyl, -CH(CH3)2, -CH2CH2CH2CH3 or -CH2CH(CH3)2; R2 represents hydrogen, methyl, ethyl, propyl, -CH(CH3)2, -CH2CH2CH2CH3 or -CH2CH(CH3)2; R3 represents hydrogen, methyl, ethyl, propyl, -CH(CH3)2, -CH2CH2CH2CH3 or -CH2CH(CH3)2.

14. The preparation method of the aqueous binder according to claim 11, characterized in that, The polymer further includes a third monomer unit, and the third monomer unit has the structure shown in Formula III: Wherein, R4 represents hydrogen, a straight-chain alkyl group, or a branched-chain alkyl group; M represents H, Li, Na, or K.

15. The preparation method of the aqueous binder according to claim 9 or 14, characterized in that, R4 represents hydrogen, a straight-chain alkyl group with 1 - 6 carbon atoms, or a branched-chain alkyl group with 1 - 6 carbon atoms.

16. The preparation method of the aqueous binder according to claim 8, characterized in that, The solid content of the aqueous binder is 9.5 - 11%, and the viscosity is 8000 - 30000 cps.

17. The preparation method of the aqueous binder according to claim 8, characterized in that, The polymer has the structure shown in Formula IV: Wherein, M represents H, Li, Na, or K; R4 represents hydrogen, a straight-chain alkyl group, or a branched-chain alkyl group; a:b:c = (30 - 80):(0 - 50):(5 - 50).

18. The use of an aqueous binder according to any one of claims 1-7 or an aqueous binder prepared by the preparation method of an aqueous binder according to any one of claims 8-17, characterized in that, The aqueous binder is used for the preparation of lithium-ion batteries.

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