Binder as well as preparation method and application thereof

Abstract

The invention discloses a binder as well as a preparation method and application thereof. The binder is prepared from a raw material consisting of a main material and an auxiliary material, the auxiliary material comprises an initiator, and the main material comprises a component A (unsaturated hydrophilic sodium salt and / or unsaturated hydrophilic lithium salt), a component B (cytosine monomer grafted with double bonds) and a component C (guanine monomer grafted with double bonds); the content of the component A in the main material is 30wt%-50wt%, and the ratio of the content of the component B to the content of the component C is 0.8-1.2. The binder can be applied to preparation of a battery negative electrode plate, the solubility of the binder in water can be ensured by adopting the component A with a specific dosage, and the binding performance and the dynamic performance of the binder are improved; the component B and the component C which are in a specific ratio and both contain double bonds are adopted, triple hydrogen-bond interaction can be formed between the component B and the component C, the mechanical strength of the binder can be effectively improved, the binder has a certain self-healing effect, and the component B and the component C cooperate to improve cyclic expansion of a negative plate, reduce the expansion rate of a battery cell and improve the capacity retention rate of the battery.

Description

Technical Field

[0001] The present invention relates to the field of battery technology, in particular to a binder and a preparation method and application thereof, and further to a negative electrode binder and a preparation method and application thereof. Background Art

[0002] Currently, silicon anodes are becoming the future development direction of lithium-ion battery anode materials due to their high theoretical capacity (approximately 4200mAh / g). However, silicon anodes undergo significant volume expansion and contraction during the charge and discharge process, which in turn leads to instability of the electrode-electrolyte interface and failure of the bonding network and conductive network, seriously affecting the battery's cycle life and charge and discharge efficiency. Currently, the lithium battery industry mostly uses polyacrylic acid (PAA) / polyacrylamide (PAM) binders to improve the expansion problem of silicon anodes, but the mechanical strength of PAA / PAM binders is low, making it difficult to improve the cyclic expansion problem of silicon anode materials in high silicon content (≥10%) systems. Summary of the Invention

[0003] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, the present invention provides a binder and a preparation method and application thereof.

[0004] In a first aspect of the present invention, a binder is provided, which is prepared from the following raw materials: a main material and an auxiliary material; the auxiliary material includes an initiator; the main material includes an unsaturated hydrophilic metal salt, a modified cytosine monomer and a modified guanine monomer; wherein the unsaturated hydrophilic metal salt is selected from at least one of an unsaturated hydrophilic sodium salt and an unsaturated hydrophilic lithium salt, and the content of the unsaturated hydrophilic metal salt in the main material (i.e., the percentage of the mass of the unsaturated hydrophilic metal salt to the total mass of the main material) A1 is 30wt% to 50wt%; the modified cytosine monomer is a cytosine monomer connected to a double bond, and the modified guanine monomer is a guanine monomer connected to a double bond; and the content A2 of the modified cytosine monomer and the content A3 of the modified guanine monomer in the main material satisfy: 0.8≤A2 / A3≤1.2.

[0005] According to the binder of the embodiment of the present invention, there are at least the following beneficial effects: the raw materials for preparing the binder include an unsaturated hydrophilic metal salt, a cytosine monomer connected to a double bond, and a guanine monomer connected to a double bond; the binder can be used for the preparation of a negative electrode sheet, wherein the unsaturated hydrophilic metal salt contains an unsaturated group and a hydrophilic group, and the unsaturated group can be used for polymerization reaction to effectively introduce the component on the binder, and because the hydrophilic group in the unsaturated hydrophilic metal salt carries a negative charge and has a large steric hindrance, when it is applied to the preparation of a negative electrode sheet, it can promote the dispersion of the negative electrode main material particles, and can increase the solubility of the binder in water, promote the dissolution of the binder, reduce the viscosity of the adhesive glue, and at the same time help to improve the ion conductivity of the binder and improve the kinetic performance of the battery cell. In addition, the hydrophilic group can form a hydrogen bond with the polar functional group on the surface of the negative electrode current collector or the negative electrode main material, which is beneficial to improve the bonding force and cohesion of the negative electrode sheet and improve the structural stability of the negative electrode sheet. The modified cytosine monomer and the modified guanine monomer both contain double bonds, and triple hydrogen bonds can be formed between the two to generate a cross-linked network structure, which can improve the mechanical strength of the binder. At the same time, the triple hydrogen bond effect can make the binder have a certain self-healing effect. The two can work together to effectively reduce the cyclic expansion of the negative electrode system (especially the silicon-based negative electrode system). The binder can be used in the preparation of battery negative electrode sheets, especially the preparation of silicon-based negative electrode sheets, which can improve the mechanical strength of the sheets, effectively improve the cyclic expansion of the negative electrode material, reduce the expansion rate of the battery cell, and improve the capacity retention rate of the battery.

[0006] Since modified cytosine and modified guanine monomers have low solubility in water, the introduction of an unsaturated hydrophilic metal salt can increase the solubility of the binder in water, thereby enhancing the binder's application value. However, if the amount of unsaturated hydrophilic metal salt added (A1) is too low (less than 30 wt%), the resulting binder has low solubility in water, which is not conducive to practical application. Furthermore, since the introduction of the unsaturated hydrophilic metal salt does not significantly contribute to the mechanical strength of the binder, if its content (A1) is too high (greater than 50 wt%), while the binder can achieve excellent solubility, the content of the modified cytosine and modified guanine monomers will be too low, resulting in reduced mechanical strength of the binder. Furthermore, considering the practical application and mechanical properties, the content A1 of the unsaturated hydrophilic metal salt in the main material of the binder is controlled within 30wt% to 50wt%, which can ensure the solubility and mechanical properties of the binder and its practical applicability, so as to give full play to the coordinated effect of the modified cytosine monomer and the modified uracil monomer, effectively improve the mechanical strength of the binder, and thus maintain the structural integrity of the negative electrode during the cycle, improve the cycle expansion of the battery cell, and improve the cycle stability of the battery.

[0007] Moreover, in the main ingredients of the above binders, the metal ions in the unsaturated hydrophilic metal salts will affect the kinetic performance of the bonding. Since lithium-ion batteries mainly rely on the transmission of lithium ions between the positive and negative electrodes, the lithium ions are embedded in the negative electrode to complete the charging process. If the ionic radius of the metal ions in the unsaturated hydrophilic metal salts is too large, the larger ionic radius will cause the interlayer spacing of the negative electrode active material to increase excessively, which can easily cause the interlayer structure to be destroyed, and the number of lithium insertion sites on the active material to be reduced. As a result, the lithium released from the positive electrode during the cycle cannot be timely embedded in the interlayer of the negative electrode active material, causing lithium precipitation, and thus causing the capacity retention rate and cycle expansion rate of the battery cell to deteriorate. The unsaturated hydrophilic metal salts in the raw materials of the binder of the present invention use unsaturated hydrophilic lithium salts and / or unsaturated hydrophilic sodium salts, which can be beneficial to improving the kinetic performance of the binder. The ionic radius of the lithium ions and sodium ions is suitable, and when embedded in the interlayer of the negative electrode active material, it will not cause the interlayer structure to be destroyed and affect the number of lithium insertion sites, thereby avoiding the occurrence of lithium precipitation and improving the cycle stability of the battery cell.

[0008] In addition, the excellent mechanical properties and self-healing properties of the above adhesives mainly rely on the triple hydrogen bonding between modified cytosine monomers and modified guanine monomers on different molecular chains. However, the modified cytosine monomers and the modified guanine monomers cannot form triple hydrogen bonding well. If the A2 / A3 is too high or too low, the excess modified cytosine monomers or modified guanine monomers will not be able to participate in the formation of the triple hydrogen bonding network, thereby causing the mechanical properties and self-healing properties of the obtained adhesive to decrease. Therefore, controlling A2 / A3 within 0.8-1.2 can ensure that the modified cytosine monomers and modified guanine monomers are fully and efficiently formed with triple hydrogen bonding, thereby fully improving the adhesion, mechanical properties and self-healing properties of the adhesive.

[0009] In the main ingredients of the above binder, the content A1 of the unsaturated hydrophilic metal salt can be any value among 30wt%, 32wt%, 33.5wt%, 35wt%, 37wt%, 38.5wt%, 40wt%, 42wt%, 44wt%, 45wt%, 46.5wt%, 48wt%, 50wt%, or a range of any two of them; the ratio (A2 / A3) of the content A2 of the modified cytosine monomer and the content A3 of the modified guanine monomer can be any value among 0.8, 0.82, 0.85, 0.86, 0.9, 0.92, 0.95, 0.96, 0.98, 1.0, 1.05, 1.1, 1.12, 1.15, 1.2, or a range of any two of them.

[0010] In some embodiments of the present invention, the binder is prepared by polymerization of raw materials consisting of a main ingredient and auxiliary ingredients. The initiator in the auxiliary ingredients is used to initiate and promote the polymerization reaction between the main ingredients. After the polymerization reaction, triple hydrogen bonds are formed between the modified cytosine monomers and the modified guanine monomers, i.e., triple hydrogen bonds are formed between the modified cytosine monomers and the modified guanine monomers in the binder.

[0011] In some embodiments of the present invention, the main ingredient satisfies at least one of the following conditions:

[0012] A2 satisfies: 25wt%≤A2≤35wt%;

[0013] A3 satisfies: 25wt%≤A3≤35wt%;

[0014] A1, A2 and A3 satisfy: 0.3≤A1 / (A1+A2+A3)≤0.5.

[0015] For example, A2 may be any value among 25wt%, 26.5wt%, 27wt%, 27.5wt%, 28wt%, 29wt%, 30wt%, 30.5wt%, 31.5wt%, 32wt%, 33wt%, 34wt%, 35wt%, or any two ranges thereof; A3 may be 25wt%, 25.5wt%, 26wt%, 27.5wt%, 28wt%, 29wt%, 30 wt%, 31wt%, 31.5wt%, 32wt%, 33.5wt%, 34wt%, 35wt% or any two of the values; A1 / (A1+A2+A3) can be any value among 0.3, 0.32, 0.325, 0.33, 0.35, 0.375, 0.38, 0.4, 0.415, 0.42, 0.45, 0.475, 0.5 or any two of the values.

[0016] The above is to effectively improve the mechanical strength of the binder by controlling the amount of modified cytosine monomer and modified guanine monomer. Since the role of the unsaturated hydrophilic metal salt is mainly to increase the solubility of the binder in water, and mainly to increase the solubility of the modified cytosine monomer and modified guanine monomer in water, and compared with the modified cytosine monomer and modified guanine monomer, the unsaturated hydrophilic metal salts of different binder molecules cannot form hydrogen bonds, that is, the introduction of unsaturated hydrophilic metal salts does not contribute much to the mechanical strength of the binder. Therefore, if the content of unsaturated hydrophilic metal salts in the main material is too high, although the solubility of the binder in water can be effectively improved, the relative proportion of modified cytosine monomer and modified guanine monomer will be too low, resulting in a decrease in the mechanical strength of the binder, and cannot effectively solve the problem of large cycle expansion of the negative electrode system (especially the silicon-based negative electrode system). Therefore, by controlling the A1 / (A1+A2+A3) in the raw materials within the above range, the solubility of the binder can be ensured while the mechanical strength of the binder can be effectively improved, thereby maintaining the structural integrity of the negative electrode sheet during the cycle, improving the cycle expansion of the battery cell, and improving the cycle stability of the battery.

[0017] In some embodiments of the present invention, in the main ingredients, A1, A2, and A3 simultaneously satisfy the following conditions: 0.8 ≤ A2 / A3 ≤ 1.2, and A1 / (A1+A2+A3) = 0.3-0.5. By controlling the content ratio of the main binder raw materials within the above range, the unsaturated hydrophilic metal salt can effectively cooperate with the modified cytosine monomer and the modified guanine monomer, fully leveraging their respective and mutual effects, thereby enabling the binder to possess excellent solubility, mechanical properties, self-healing properties, bonding properties, and dynamic properties.

[0018] In some embodiments of the present invention, the main material consists of an unsaturated hydrophilic metal salt, a modified cytosine monomer and a modified guanine monomer.

[0019] In some embodiments of the present invention, the unsaturated hydrophilic metal salt contains an unsaturated group, and the unsaturated group includes an ethylenically unsaturated group.

[0020] In some embodiments of the present invention, the unsaturated group is an ethylenically unsaturated group.

[0021] In some embodiments of the present invention, the ethylenically unsaturated group is selected from at least one of vinyl and propenyl.

[0022] In some embodiments of the present invention, the unsaturated hydrophilic metal salt contains a hydrophilic group, wherein the hydrophilic group includes an anionic acid group. Because the hydrophilic group is an anionic acid group, it has a large atomic group radius and high polarizability, resulting in a strong polarity, which is conducive to the occurrence of polymerization reactions. At the same time, it can form hydrogen bonds with modified guanine and modified cytosine to exert a synergistic effect, further enhancing the mechanical and kinetic properties of the resulting binder.

[0023] In some embodiments of the present invention, the hydrophilic group in the unsaturated hydrophilic metal salt is an anionic acid group.

[0024] In some embodiments of the present invention, the hydrophilic group in the unsaturated hydrophilic metal salt is selected from at least one of a sulfonic acid group, a boric acid group, and a phosphoric acid group; or, the anionic acid group is selected from at least one of a sulfonic acid group, a boric acid group, and a phosphoric acid group.

[0025] In some embodiments of the present invention, the unsaturated hydrophilic metal salt contains an unsaturated group and a hydrophilic group; the unsaturated group is an ethylenically unsaturated group, and the hydrophilic group is an anionic acid group. The ethylenically unsaturated group may be at least one of a vinyl group and a propenyl group; and the anionic acid group may be at least one of a sulfonic acid group, a boric acid group, and a phosphoric acid group.

[0026] In some embodiments of the present invention, the unsaturated hydrophilic metal salt is selected from at least one of lithium vinyl sulfonate, sodium vinyl sulfonate, lithium propylene sulfonate, sodium propylene sulfonate, lithium vinyl borate, sodium vinyl borate, lithium propylene borate, sodium propylene borate, lithium vinyl phosphate, sodium vinyl phosphate, lithium propylene phosphate, and sodium propylene phosphate.

[0027] In some embodiments of the present invention, the mass ratio of the main ingredient to the auxiliary material is 5 to 10: 1. For example, the mass ratio of the main ingredient to the auxiliary material can be any value of 5: 1, 5.5: 1, 6: 1, 6.2: 1, 6.5: 1, 6.8: 1, 7: 1, 7.5: 1, 8: 1, 8.6: 1, 8.8: 1, 9: 1, 9.2: 1, 9.5: 1, 9.8: 1, 10: 1, or any range of two values.

[0028] In some embodiments of the present invention, the modified cytosine monomer is prepared by a preparation method comprising the following steps: dissolving the cytosine monomer in dimethylformamide, then adding an organic base to adjust the pH to 8-9, and stirring in an ice-water bath for 20-30 minutes; adding an olefinic acid halide, and stirring and reacting under vacuum at room temperature; and then settling with an ether solvent.

[0029] In the above-mentioned preparation method of the modified cytosine monomer, since the alkenyl acyl halide is relatively active, the system is stirred in an ice-water bath before adding the alkenyl acyl halide to reduce the system temperature and thus its reactivity. After adding the alkenyl acyl halide, vacuum is applied to prevent the reaction of oxygen, water, and the alkenyl acyl halide. The reaction is carried out at room temperature to prevent the acyl halide from being unstable due to excessively high temperature, while also preventing the temperature from being too low, which would result in a slow reaction rate.

[0030] In some embodiments of the present invention, the method for preparing the modified cytosine monomer satisfies at least one of the following conditions:

[0031] The structural formula of the alkenyl acyl halide is CH2=CH-(CH2) n -COX, wherein n is a natural number, and X is at least one of fluorine, chlorine, and bromine;

[0032] The organic base is selected from at least one of pyridine, piperidine, ethanolamine, diisopropylethylamine, dimethylisopropylamine, diisopropylamine, methylamine, ethylamine, diethylamine, and triethylamine;

[0033] The ether solvent is selected from at least one of diethyl ether, dimethyl ether, and methyl ethyl ether;

[0034] The stirring speed of the stirring reaction is 500 rpm to 800 rpm.

[0035] In some embodiments of the present invention, the preparation of the modified cytosine monomer further includes solid-liquid separation after sedimentation; further, the solid-liquid separation may be a filtration treatment; further, after the solid-liquid separation is completed, the solid phase obtained by the solid-liquid separation may be further washed and dried.

[0036] In some embodiments of the present invention, the modified guanine monomer can be prepared by a preparation method similar to that of the modified cytosine monomer. Specifically, the modified guanine monomer can be prepared by a preparation method comprising the following steps: dissolving the guanine monomer in dimethylformamide, then adding an organic base to adjust the pH to 8-9, and stirring in an ice-water bath for 20-30 minutes; adding an olefinic acid halide, and stirring and reacting under vacuum at room temperature; and then settling with an ether solvent.

[0037] The organic base, alkenyl acyl halide and ether solvent used in the preparation of the modified guanine monomer and the preparation of the modified cytosine may be the same or different.

[0038] In some embodiments of the present invention, the initiator is selected from at least one of potassium persulfate, ammonium persulfate, sodium persulfate, tert-butyl peroxide, and benzoyl peroxide.

[0039] In some embodiments of the present invention, the carbonization temperature of the binder is 340°C to 400°C.

[0040] In a second aspect of the present invention, a method for preparing any of the aforementioned binders of the present invention is proposed, comprising: dissolving a main material comprising an unsaturated hydrophilic metal salt, a modified cytosine monomer, and a modified guanine monomer in an organic solvent, and then adding an auxiliary material comprising an initiator to carry out a polymerization reaction to obtain the binder.

[0041] In some embodiments of the present invention, the polymerization reaction is carried out with stirring at room temperature.

[0042] In some embodiments of the present invention, the polymerization reaction time is 3 h to 4 h. For example, the polymerization reaction time can be any one of 3 h, 3.2 h, 3.5 h, 3.6 h, 3.8 h, and 4 h, or a range of any two of them.

[0043] In some embodiments of the present invention, after the polymerization reaction is completed, a solid-liquid separation process is further included.

[0044] In some embodiments of the present invention, the solid-liquid separation process is a rotary evaporation process.

[0045] In some embodiments of the present invention, after the solid-liquid separation process is completed, the solid phase material is collected and then washed and dried. The solid phase material can be collected by scraping.

[0046] In some embodiments of the present invention, before dissolving the main material in the organic solvent, the preparation of the modified cytosine monomer and the modified guanine monomer is included;

[0047] The preparation of the modified cytosine monomer and the modified guanine monomer comprises: dissolving the cytosine monomer and the guanine monomer in dimethylformamide, respectively, then adding an organic base to adjust the pH to 8-9, and stirring in an ice-water bath for 20-30 minutes; adding an olefinic acid halide, and reacting by stirring under vacuum at room temperature; and then precipitating with an ether solvent to obtain the modified cytosine monomer and the modified uracil monomer, respectively. The organic base, olefinic acid halide, and ether solvent used in the preparation process of the modified cytosine monomer and the preparation process of the modified guanine monomer can be the same or different.

[0048] In some embodiments of the present invention, the structural formula of the alkenyl acyl halide is CH2=CH-(CH2) n -COX, wherein n is a natural number, and X is at least one of fluorine, chlorine, and bromine.

[0049] In some embodiments of the present invention, the organic base is selected from at least one of pyridine, piperidine, ethanolamine, diisopropylethylamine, dimethylisopropylamine, diisopropylamine, methylamine, ethylamine, diethylamine, and triethylamine.

[0050] In some embodiments of the present invention, the ether solvent is selected from at least one of diethyl ether, dimethyl ether, and methyl ethyl ether.

[0051] In some embodiments of the present invention, the stirring speed of the stirring reaction process is 500rpm~800rpm.For example, the stirring speed of the stirring reaction process can be any value among 500rpm, 520rpm, 550rpm, 560rpm, 570rpm, 580rpm, 600rpm, 620rpm, 650rpm, 690rpm, 700rpm, 730rpm, 750rpm, 760rpm, 800rpm or the range value of any two.

[0052] In some embodiments of the present invention, the preparation process of the modified cytosine monomer and the modified guanine monomer further includes solid-liquid separation treatment after sedimentation; further, the solid-liquid separation treatment can be a filtration treatment; further, after the solid-liquid separation treatment is completed, the solid phase obtained by the solid-liquid separation treatment is further washed and dried.

[0053] The third aspect of the present invention provides the use of any of the aforementioned binders of the present invention or a binder prepared by any of the aforementioned binder preparation methods of the present invention in preparing a negative electrode sheet.

[0054] In some embodiments of the present invention, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer provided on at least one side of the negative electrode current collector, and the negative electrode active material layer contains the binder.

[0055] In some embodiments of the present invention, the negative electrode active material layer comprises a negative electrode active material and the binder, and the negative electrode active material comprises a silicon-based negative electrode active material.

[0056] In some embodiments of the present invention, the silicon-based negative electrode active material is at least one of a silicon-carbon negative electrode active material and a silicon-oxygen negative electrode active material.

[0057] In some embodiments of the present invention, the negative electrode active material layer comprises a negative electrode active material and the binder, and the negative electrode active material includes a graphite active material and a pure silicon negative electrode active material.

[0058] In some embodiments of the present invention, the silicon content of the negative electrode active material layer is greater than or equal to 10%, that is, the negative electrode sheet is a negative electrode sheet with a high silicon content.

[0059] In a fourth aspect of the present invention, a negative electrode sheet is proposed, comprising a negative electrode current collector and a negative electrode active material layer disposed on at least one side of the negative electrode current collector; the negative electrode active material layer comprises any one of the aforementioned binders of the present invention, or a binder prepared by the preparation method of any one of the aforementioned binders of the present invention.

[0060] In some embodiments of the present invention, the negative electrode active material layer further comprises a negative electrode active material, and the negative electrode active material comprises a silicon-based negative electrode active material.

[0061] In some embodiments of the present invention, the silicon-based negative electrode active material is at least one of a silicon-carbon negative electrode active material and a silicon-oxygen negative electrode active material.

[0062] In some embodiments of the present invention, the negative electrode active material layer further comprises a negative electrode active material, and the negative electrode active material comprises a graphite negative electrode active material and a pure silicon negative electrode active material.

[0063] In some embodiments of the present invention, the silicon content of the negative electrode active material layer is greater than or equal to 10%, that is, the negative electrode sheet is a negative electrode sheet with a high silicon content.

[0064] In some embodiments of the present invention, the negative electrode active material layer further contains a conductive agent.

[0065] In some embodiments of the present invention, the conductive agent includes one or more of conductive graphite, conductive carbon black, carbon nanotubes, VGCF, and graphene.

[0066] In some embodiments of the present invention, the negative electrode active material layer further contains a dispersant.

[0067] In some embodiments of the present invention, the dispersant is selected from at least one of sodium carboxymethyl cellulose and lithium carboxymethyl cellulose.

[0068] In some embodiments of the present invention, the negative electrode active material layer is prepared from an aqueous negative electrode slurry.

[0069] In some embodiments of the present invention, the negative electrode active material layer is prepared by a method comprising the following steps: mixing the components of the negative electrode active material layer with a solvent to form a negative electrode slurry, and then coating the negative electrode slurry on at least one side of the negative electrode current collector; wherein the solvent is water.

[0070] In a fifth aspect of the present invention, a lithium-ion battery is provided, comprising any one of the aforementioned negative electrode sheets of the present invention.

[0071] In some embodiments of the present invention, the lithium-ion battery further includes a positive electrode sheet and a separator, wherein the separator is sandwiched between the positive electrode sheet and the negative electrode sheet.

[0072] In some embodiments of the present invention, the positive electrode sheet, the separator, and the negative electrode sheet are wound to form a core structure.

[0073] In some embodiments of the present invention, the lithium-ion battery further includes a packaging shell and an electrolyte, and the core structure and the electrolyte are accommodated in the packaging shell. DETAILED DESCRIPTION

[0074] The following will clearly and completely describe the concept and technical effects of the present invention in conjunction with the embodiments to fully understand the purpose, features and effects of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative work are all within the scope of protection of the present invention.

[0075] Example 1

[0076] This embodiment provides a binder prepared by polymerization reaction of raw materials consisting of a main ingredient and an auxiliary ingredient. The main ingredient and the auxiliary ingredient have a mass ratio of 6:1; the main ingredient comprises lithium vinyl sulfonate, a modified cytosine monomer, and a modified guanine monomer in a mass ratio of 4:3:3, i.e., the main ingredient comprises 40% by weight of lithium vinyl sulfonate, 30% by weight of the modified cytosine monomer, and 30% by weight of the modified guanine monomer. The modified cytosine monomer is a cytosine monomer with a double bond, and the modified guanine monomer is a guanine monomer with a double bond. The auxiliary ingredient is an initiator.

[0077] The binder is prepared from raw materials comprising the following steps:

[0078] S1. Preparation of modified cytosine monomer and modified guanine monomer, comprising: dissolving cytosine monomer and guanine monomer in dimethylformamide (DMF), respectively, adding triethylamine to adjust the pH of the solution to 8-9, and then stirring in an ice bath for 20 min to 30 min, adding acryloyl chloride, vacuuming at room temperature and stirring at a speed of 500 rpm to 800 rpm for 6 h to 8 h, and then precipitating with ether, filtering, washing, and drying to respectively obtain modified cytosine monomer (i.e., cytosine monomer connected to a double bond) and modified guanine monomer (i.e., guanine monomer connected to a double bond).

[0079] S2. Dissolve lithium vinyl sulfonate, modified cytosine monomer and modified guanine monomer in a solvent DMF at a mass ratio of 4:3:3, add an initiator, and slowly stir at room temperature for 3 to 4 hours to carry out a polymerization reaction. Then, rotary evaporate the solution until there is no obvious solvent, scrape, wash, and dry to obtain the product adhesive.

[0080] Example 2

[0081] This embodiment provides a binder, which differs from Example 1 in that the mass ratio of lithium vinyl sulfonate, modified cytosine monomer, and modified guanine monomer in the main material of this embodiment is 3:3.5:3.5, that is, the content A1 of lithium vinyl sulfonate in the main material is 30wt%, the content A2 of modified cytosine monomer is 35wt%, and the content A3 of modified guanine monomer is 35wt%; other aspects are the same as Example 1.

[0082] Example 3

[0083] This embodiment provides a binder, which differs from Example 1 in that: the mass ratio of lithium vinyl sulfonate, modified cytosine monomer and modified guanine monomer in the main material of this embodiment is 5:2.5:2.5 (i.e., 2:1:1), that is, the content A1 of lithium vinyl sulfonate in the main material is 50wt%, the content A2 of modified cytosine monomer is 25wt%, and the content A3 of modified guanine monomer is 25wt%; otherwise, it is the same as Example 1.

[0084] Example 4

[0085] This embodiment provides a binder, which differs from Example 1 in that the mass ratio of lithium vinyl sulfonate, modified cytosine monomer, and modified guanine monomer in the main material of this embodiment is 1.2:0.8:1, that is, the content A1 of lithium vinyl sulfonate in the main material is 40wt%, the content A2 of modified cytosine monomer is 26.7wt%, and the content A3 of modified guanine monomer is 33.3wt%; other aspects are the same as Example 1.

[0086] Example 5

[0087] This embodiment provides a binder, which differs from Example 1 in that the mass ratio of lithium vinyl sulfonate, modified cytosine monomer, and modified guanine monomer in the main material of this embodiment is 1.5:1.2:1, that is, the content A1 of lithium vinyl sulfonate in the main material is 40wt%, the content A2 of modified cytosine monomer is 32.7wt%, and the content A3 of modified guanine monomer is 27.3wt%; other aspects are the same as Example 1.

[0088] Example 6

[0089] This embodiment proposes a binder. The difference between this embodiment and embodiment 1 is that the lithium vinyl sulfonate in the main material of embodiment 1 is replaced by sodium vinyl sulfonate. The rest is the same as embodiment 1.

[0090] Comparative Example 1

[0091] In this comparative example, commercially available PAA-Na material (sodium polyacrylate, molecular weight Mw=1,200,000-1,400,000, a mass-produced material of Meishan Yindile) is used as the binder.

[0092] Comparative Example 2

[0093] This comparative example proposes a binder, which differs from Example 1 in that: lithium vinyl sulfonate is not added to the main ingredient of this comparative example, and the mass ratio of the modified cytosine monomer to the modified guanine monomer is 1:1, that is, the content A1 of lithium vinyl sulfonate in the main ingredient is 0, the content A2 of the modified cytosine monomer is 50wt%, and the content A3 of the modified guanine monomer is 50wt%; otherwise, it is the same as Example 1.

[0094] Comparative Example 3

[0095] This comparative example proposes a binder, which differs from Example 1 in that: no modified cytosine monomer is added to the main material of this comparative example, and the mass ratio of lithium vinyl sulfonate to modified guanine monomer is 1:1, that is, the content A1 of lithium vinyl sulfonate in the main material is 50wt%, the content A2 of modified cytosine monomer is 0, and the content A3 of modified guanine monomer is 50wt%; otherwise, it is the same as Example 1.

[0096] Comparative Example 4

[0097] This comparative example proposes a binder, which differs from Example 1 in that: no modified guanine monomer is added to the main ingredient of this comparative example, and the mass ratio of lithium vinyl sulfonate to modified cytosine monomer is 1:1, that is, the content A1 of lithium vinyl sulfonate in the main ingredient is 50wt%, the content A2 of the modified cytosine monomer is 50wt%; and the content A3 of the modified guanine monomer is 0; otherwise, the same as in Example 1.

[0098] Comparative Example 5

[0099] This comparative example proposes a binder, which differs from Example 1 in that: the mass ratio of lithium vinyl sulfonate, modified cytosine monomer and modified guanine monomer in the main material of this comparative example is 2:4:4 (i.e., 1:2:2), that is, the content A1 of lithium vinyl sulfonate in the main material is 20wt%, the content A2 of modified cytosine monomer is 40wt%, and the content A3 of modified guanine monomer is 40wt%; otherwise, it is the same as Example 1.

[0100] Comparative Example 6

[0101] This comparative example proposes a binder, which differs from Example 1 in that: the mass ratio of lithium vinyl sulfonate, modified cytosine monomer and modified guanine monomer in the main ingredients of this comparative example is 8:1:1, that is, the content A1 of lithium vinyl sulfonate in the main ingredient is 80wt%, the content A2 of modified cytosine monomer is 10wt%, and the content A3 of modified guanine monomer is 10wt%; otherwise, it is the same as Example 1.

[0102] Comparative Example 7

[0103] This comparative example proposes a binder, which differs from Example 1 in that: the mass ratio of lithium vinyl sulfonate, modified cytosine monomer and modified guanine monomer in the main material of this comparative example is 4:4:2 (i.e., 2:2:1), that is, the content A1 of lithium vinyl sulfonate in the main material is 40wt%, the content A2 of modified cytosine monomer is 40wt%, and the content A3 of modified guanine monomer is 20wt%; otherwise, it is the same as Example 1.

[0104] Comparative Example 8

[0105] This comparative example proposes a binder, which differs from Example 1 in that: the mass ratio of lithium vinyl sulfonate, modified cytosine monomer and modified guanine monomer in the main material of this comparative example is 4:2:4 (i.e., 2:1:2), that is, the content A1 of lithium vinyl sulfonate in the main material is 40wt%, the content A2 of modified cytosine monomer is 20wt%, and the content A3 of modified guanine monomer is 40wt%; otherwise, it is the same as Example 1.

[0106] Comparative Example 9

[0107] This comparative example proposes a binder, which differs from Example 1 in that: in this comparative example, lithium vinyl sulfonate in the main ingredient of Example 1 is replaced by potassium vinyl sulfonate; the rest is the same as Example 1.

[0108] Comparative Example 10

[0109] This comparative example proposes a binder, which differs from Example 1 in that: in this comparative example, the modified cytosine monomer in the main material of Example 1 is replaced with a modified thymine monomer; the rest is the same as Example 1.

[0110] The preparation of the modified thymine monomer is similar to the preparation of the modified cytosine monomer in Example 1, comprising: dissolving the thymine monomer in DMF, adding triethylamine to adjust the pH of the solution to 8-9, and then stirring in an ice bath for 20 min to 30 min, adding acryloyl chloride, vacuuming at room temperature and stirring at a speed of 500 rpm to 800 rpm for 6 h to 8 h, and then settling with ether, filtering, washing, and drying to obtain a modified thymine monomer (i.e., a thymine monomer with a double bond).

[0111] Comparative Example 11

[0112] This comparative example proposes a binder, which differs from Example 1 in that: in this comparative example, the modified guanine monomer in the main material of Example 1 is replaced with a modified adenine monomer; the rest is the same as Example 1.

[0113] The preparation of the modified adenine monomer is similar to the preparation of the modified guanine monomer in Example 1, comprising: dissolving the adenine monomer in DMF, adding triethylamine to adjust the pH of the solution to 8-9, and then stirring in an ice bath for 20 min to 30 min, adding acryloyl chloride, vacuuming at room temperature and stirring at a speed of 500 rpm to 800 rpm for 6 h to 8 h, and then settling with ether, filtering, washing, and drying to obtain a modified adenine monomer (i.e., an adenine monomer with a double bond).

[0114] Comparative Example 12

[0115] This comparative example proposes a binder, which differs from Example 1 in that: in this comparative example, the modified guanine monomer in the main material of Example 1 is replaced by a modified adenine monomer, and the modified cytosine monomer is replaced by a modified thymine monomer; the rest is the same as Example 1.

[0116] The preparation of the modified adenine monomer is the same as that of the modified adenine monomer in Comparative Example 11, and the preparation of the modified thymine monomer is the same as that of the modified thymine monomer in Comparative Example 10.

[0117] Comparative Example 13

[0118] This comparative example proposes a binder, which differs from Example 1 in that: in this comparative example, the modified guanine monomer in the main material of Example 1 is replaced with an unmodified guanine monomer; the rest is the same as Example 1.

[0119] Comparative Example 14

[0120] This comparative example proposes a binder, which differs from Example 1 in that the lithium vinyl sulfonate in the main ingredient of Example 1 is replaced with styrene; the rest of the ingredients are the same as Example 1.

[0121] The raw material configurations of the adhesives in Examples 1 to 6 and Comparative Examples 1 to 14 are shown in Table 1 below:

[0122] Table 1

[0123]

[0124] Example 7

[0125] This embodiment proposes a negative electrode sheet, which includes a negative electrode current collector and a negative electrode active material layer arranged on both side surfaces of the negative electrode current collector, the negative electrode active material layer containing a graphite negative electrode active material (D50 = 13 μm) with a mass ratio of 76.0:20:0.3:0.6:2.5:0.6, a pure silicon negative electrode active material (D50 = 7-8 μm), a conductive agent single-walled carbon nanotubes, a binder styrene-butadiene rubber, the binder of Example 1 and a dispersant sodium carboxymethyl cellulose (CMC).

[0126] The negative electrode sheet is prepared by a preparation method comprising the following steps: fully stirring and mixing a graphite negative electrode active material (D50=13 μm), a pure silicon negative electrode active material (D50=7-8 μm), a conductive agent single-walled carbon nanotubes, a binder styrene-butadiene rubber, a binder of Example 1, and a dispersant CMC in a solvent water in a mass ratio of 76.0:20:0.3:0.6:2.5:0.6 to obtain a negative electrode slurry with a solid content of 30wt%-35wt% and a viscosity of 3000mPa·s-9000mPa·s; then coating the negative electrode slurry on both sides of a negative electrode current collector Cu foil with a single-side coating thickness of 60 μm, drying, cold pressing, and slitting to obtain a negative electrode sheet.

[0127] Examples 8 to 12

[0128] Examples 8 to 12 respectively propose a negative electrode sheet. The difference between them and Example 7 is that Examples 8 to 12 respectively use the binders obtained in Examples 2 to 6 instead of the binder in Example 1 used in Example 7. Other aspects are the same as Example 7.

[0129] Comparative Examples 15 to 28

[0130] Comparative Examples 12 to 22 respectively propose a negative electrode sheet, which differs from Example 7 in that Comparative Examples 15 to 28 respectively use the binders obtained in Comparative Examples 1 to 14 instead of the binder of Example 1 used in Example 7, and the rest are the same as Example 7.

[0131] Example 13

[0132] This embodiment proposes a lithium-ion battery, which includes a positive electrode sheet, a negative electrode sheet of Example 7, and a separator. The separator is sandwiched between the positive electrode sheet and the negative electrode sheet and wound to form a core structure; the lithium-ion battery also includes a packaging shell and an electrolyte, and the core structure and the electrolyte are accommodated in the packaging shell.

[0133] Among them, the diaphragm adopts polyethylene (PE) porous polymer film; the positive electrode sheet includes a positive electrode collector aluminum foil and a positive electrode active material layer arranged on the two side surfaces of the positive electrode collector, and the positive electrode active material layer includes a positive electrode active material lithium cobalt oxide, a conductive agent carbon black, and a binder polyvinylidene fluoride (PVDF) in a mass ratio of 98:0.8:1.2; the electrolyte adopts lithium salt LiPF6 and a non-aqueous organic solvent in a mass ratio of 8:92, and the non-aqueous organic solvent adopts ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), propyl propionate (PP) and vinylene carbonate (VC) in a mass ratio of 20:30:20:28:2.

[0134] The lithium-ion battery is prepared by a preparation method comprising the following steps:

[0135] S1. The positive electrode active material lithium cobalt oxide, the conductive agent carbon black, and the binder polyvinylidene fluoride (PVDF) are thoroughly stirred and mixed in a solvent N-methylpyrrolidone (NMP) in a mass ratio of 98:0.8:1.2 to obtain a positive electrode slurry with a solid content of 76 wt% to 78 wt% and a viscosity of 3000 mPa·s to 9000 mPa·s. The positive electrode slurry is then coated on both sides of the positive electrode current collector aluminum foil, dried, cold pressed, and slit to obtain a positive electrode sheet;

[0136] S2, using a polyethylene (PE) porous polymer film as a separator;

[0137] S3, lithium salt LiPF6 and non-aqueous organic solvent (i.e., EC, DEC, PC, PP and VC with a mass ratio of 20:30:20:28:2) are mixed in a mass ratio of 8:92 to prepare an electrolyte;

[0138] S4. Stack the positive electrode sheet prepared in step S1, the separator in step S2, and the negative electrode sheet of Example 7 in order, so that the separator is placed between the positive electrode sheet and the negative electrode sheet to play a safe isolation role, and wind them into a roll core structure; place the roll structure in a packaging shell, inject the electrolyte in step S3 and encapsulate it to obtain a lithium-ion battery.

[0139] Examples 14 to 18

[0140] Examples 14 to 18 respectively propose a lithium-ion battery. The difference between them and Example 13 is that Examples 14 to 18 respectively use the negative electrode sheets of Examples 8 to 12 instead of the negative electrode sheet of Example 7 used in Example 13, and the rest is the same as Example 13.

[0141] Comparative Examples 29 to 42

[0142] Comparative Examples 29 to 42 respectively propose a lithium-ion battery, which differs from Example 13 in that Comparative Examples 29 to 42 respectively use the binders obtained in Comparative Examples 15 to 28 instead of the negative electrode sheet of Example 7 used in Example 13, and the rest are the same as Example 13.

[0143] Performance Testing

[0144] (1) Binder carbonization temperature test

[0145] The binders of Examples 1 to 6 and Comparative Examples 1 to 14 were subjected to TG (thermogravimetric analysis) tests, respectively, under the following test conditions: 25°C to 800°C, Al2O3 crucible, heating rate of 10°C / min, and N2 atmosphere.

[0146] (2) Binder solubility test

[0147] The binders of Examples 1 to 6 and Comparative Examples 1 to 14 were dissolved in water starting from 0.1 wt % and in a gradient of 0.1 wt %, respectively, and stirred at 3000 rpm for 2 h. If there was still obvious powder solid after stirring for 2 h, the experiment was repeated twice with the current mass ratio; if the results of the three experiments were similar, this mass ratio was regarded as the upper limit of the solubility of the binder and recorded.

[0148] (3) Film tensile strength and electrode adhesion test

[0149] The binders of Examples 1 to 6 and Comparative Examples 1 to 14 were dissolved in deionized water to prepare a 5% solid content solution, which was then poured into a 5 mm deep mold, dried in the shade at room temperature for 10 days, and then baked at 80°C for 2 hours. The molds were trimmed into 10 mm * 100 mm strips and subjected to elastic modulus testing using a universal tensile testing machine at a tensile speed of 5 mm / min.

[0150] In addition, a universal tensile testing machine was used to test the adhesion of the negative electrode sheets of Examples 7 to 12 and Comparative Examples 15 to 28 at a tensile speed of 250 mm / min.

[0151] (4) Battery cycle performance test

[0152] Five lithium-ion batteries from Examples 13 to 18 and Comparative Examples 29 to 42 were taken as a group, and the lithium-ion batteries were fully charged and discharged by the following steps. The cycle capacity retention rates of the lithium-ion batteries were calculated, and then the average value of each group was taken:

[0153] First, the first charge and discharge were carried out in an environment of 25°C. Constant current and constant voltage charging was performed at a charging current of 0.5C (i.e., the current value at which the theoretical capacity is fully charged within 2 hours) until the upper limit voltage was 4.53V. Then, constant current discharge was performed at a discharge current of 0.2C until the final voltage was 3V, and the discharge capacity of the first cycle was recorded. Then, constant current and constant voltage charging was performed at a charging current of 0.5C for 1 hour, and the thickness of the battery cell in the half-charged state was measured with a PPG thickness gauge. Then, 800 charge and discharge cycles were performed at 1C / 1C, and the discharge capacity of the 800th cycle and the thickness of the battery cell in the fully charged state were recorded.

[0154] Wherein, cycle capacity retention rate = (discharge capacity at the 800th cycle / discharge capacity at the first cycle) × 100%;

[0155] Cell cycle expansion rate = (full-charge thickness at the 800th cycle / initial half-charge thickness) × 100%.

[0156] The above methods were used to test the binders, negative electrodes and lithium-ion batteries of the examples and comparative examples, respectively. The results are shown in Tables 2 and 3.

[0157] Table 2 Test results of adhesive carbonization temperature, solubility, film tensile strength and electrode bonding strength

[0158]

[0159] Table 3 Lithium-ion battery cycle performance test results

[0160]

[0161]

[0162] By comparing the test results shown in Tables 2 to 3, it can be seen that compared with the binders of Comparative Examples 1 to 14, the binders of Examples 1 to 6 have higher mechanical strength, bonding performance and electrochemical performance.

[0163] Among them, comparing the test results of the binders of Examples 1 to 6 and their corresponding negative electrodes and lithium ion batteries, and the test results of the binder of Comparative Example 1 and its corresponding negative electrode sheet and lithium ion battery, the molecular structures of lithium vinyl sulfonate / sodium vinyl sulfonate, modified cytosine monomer (i.e., cytosine monomer connected with a double bond) and modified guanine monomer (i.e., guanine monomer connected with a double bond) in the raw materials of the binders of Examples 1 to 6 contain a large number of N, O heteroatoms and polar functional groups, which are beneficial to the conduction of lithium ions. At the same time, these N, O heteroatoms and polar functional groups can provide abundant hydrogen bonding sites, which can strengthen the bonding between the binder and the silicon negative electrode main material particles and between the binder and the foil, thereby strengthening the contact between the silicon negative electrode main material particles and the foil. The two are synergistic and beneficial to improving the cycle performance of the silicon negative electrode system and reducing the cycle expansion rate.

[0164] Comparing the test results of the binder of Example 1 and its corresponding negative electrode sheet and lithium-ion battery, and the test results of the binders of Comparative Examples 3, 4, and 6 and their corresponding negative electrode sheets and lithium-ion batteries, the cytosine monomers with double bonds and the guanine monomers with double bonds in the raw materials of the binder of Example 1 can pair with each other to produce triple hydrogen bonds, thereby forming a network cross-linked structure, which can improve the mechanical strength of the binder. At the same time, the abundant hydrogen bonding sites on the cytosine monomers with double bonds and the guanine monomers with double bonds give the binder a certain self-healing effect, which can self-repair the damaged bonding network during the cycle. The two can work together to effectively alleviate the huge volume expansion effect of the silicon negative electrode material during the lithium insertion and extraction process, thereby improving the structural stability of the negative electrode sheet and reducing the cycle expansion rate of the battery cell. Further combined with the test results of the binders of Comparative Examples 7 and 8 and their corresponding negative electrodes and lithium-ion batteries, it can be seen that in the raw materials of the binder of Example 1, only the cytosine monomer with a double bond and the guanine monomer with a double bond can be paired with each other, and the ratio of the addition amount of the two is between 0.8 and 1.2:1. The cytosine monomer with a double bond and the guanine monomer with a double bond can be fully utilized for pairing, and the effect between the two can be effectively exerted to form a triple hydrogen bond, thereby fully improving the mechanical properties and self-healing properties of the binder. If the above range is exceeded, the binder cannot fully form a network cross-linked structure, the mechanical strength of the binder will decrease, and the battery cell cycle expansion rate will increase. Combined with the test results of the binder of Comparative Example 13 and its corresponding negative electrode and lithium-ion battery, it can be seen that the cytosine monomer and the guanine monomer must be modified with an olefinic acid halide to effectively synthesize a binder with high mechanical properties and certain self-healing properties. Unmodified monomers are easily washed away during the synthesis process. At the same time, these monomers cannot play a bonding and self-healing role in the negative electrode sheet. Therefore, the performance of the resulting binder is equivalent to that of the binder obtained by adding only a single monomer (Comparative Examples 3 to 4 and Comparative Example 13).

[0165] Comparing the test results of the binder of Example 1 and its corresponding negative electrode sheet and lithium-ion battery with the test results of the binder of Comparative Examples 2 and 14 and its corresponding negative electrode sheet and lithium-ion battery, it is found that since the solubility of double-bonded cytosine monomers and double-bonded guanine monomers in water is relatively low, the addition of unsaturated hydrophilic metal salt lithium vinyl sulfonate is crucial and can improve the solubility of the binder in water. However, as in Comparative Example 14, when the water-soluble unsaturated hydrophilic metal salt lithium vinyl sulfonate is replaced with water-insoluble styrene, the solubility of the resulting binder is less than 3%, and its practical application value is relatively low. In addition, comparing the test results of the binder of Example 1 and its corresponding negative electrode sheet and lithium-ion battery with the test results of the binder of Comparative Examples 2, 5, and 6 and their corresponding negative electrode sheets and lithium-ion batteries, it can be seen that if the content of the unsaturated hydrophilic metal salt in the main material is controlled to 30wt% to 50wt%, the resulting binder can take into account solubility, mechanical strength, bonding properties, and dynamic properties. As in Comparative Examples 2 and 5, when the content of the unsaturated hydrophilic metal salt lithium vinyl sulfonate in the main material is less than 30wt%, the solubility of the resulting binder in water is below 3%, and the practical application value is relatively low; as in Comparative Example 6, if the content of lithium vinyl sulfonate in the main material is greater than 50wt%, the content of modified cytosine monomer and modified guanine monomer in the binder will be too low, resulting in a decrease in the mechanical strength of the binder and a deterioration in the bonding performance, and thus, compared with the lithium ion battery of Example 1, its cycle performance deteriorates. It should be noted that the binder mentioned in this patent is mainly used in the field of negative electrode binders. Because the negative electrode slurry in the field of lithium ion batteries is currently mainly water-based, the practical application value of the binder with lower solubility (Comparative Examples 2, 5, and 14) is relatively low, and this patent does not use organic solvents to dissolve to make the adhesive film.

[0166] From the comparison of Example 13 (the negative electrode sheet adopts the binder of Example 1), Example 18 (the negative electrode sheet adopts the binder of Example 6) and Comparative Example 37 (the negative electrode sheet adopts the binder of Comparative Example 9), it can be seen that the different metal ions contained in the unsaturated hydrophilic metal salt will have a certain impact on the kinetic properties of the resulting binder. Since the lithium-ion battery mainly relies on the transmission of lithium ions between the positive and negative electrodes, the lithium ions are embedded in the anode to complete the charging process. The ionic radius of lithium ions, sodium ions and potassium ions gradually increases. When potassium ions are embedded in the graphite interlayer, their larger ionic radius will cause the interlayer spacing of the negative electrode active material (especially the interlayer spacing of the graphite) to increase excessively, the interlayer structure will be destroyed, and the number of lithium insertion sites of the graphite will be reduced, resulting in the lithium released from the positive electrode during the cycle being unable to be embedded in the negative electrode active material interlayer (or graphite interlayer) in time, triggering the lithium precipitation phenomenon and thus causing the capacity retention rate and cycle expansion rate of the battery cell to deteriorate, as shown in Comparative Example 37.

[0167] Comparing the test results of the binder of Example 1 and its corresponding negative electrode sheet and lithium-ion battery, and the test results of the binders of Comparative Examples 10, 11, and 12 and their corresponding negative electrode sheets and lithium-ion batteries, it can be seen that cytosine and guanine in Example 1 can form a triple hydrogen bond, and the binder synthesized from these two monomers has excellent mechanical properties and self-healing properties, thereby making the battery cell using the binder have better cycle performance. However, it should be noted that only double hydrogen bonds can be formed between cytosine and adenine in Comparative Example 11, between guanine and thymine in Comparative Example 10, and between thymine and adenine in Comparative Example 12. The mechanical properties of the resulting binder are worse than those of the binder synthesized from cytosine and guanine monomers. The cycle performance of the resulting battery cell is also deteriorated because the resulting binder material cannot suppress the large expansion stress generated by the silicon negative electrode material during the cycle.

[0168] The above-described embodiments merely illustrate several implementations of the present invention. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, and all such variations and improvements fall within the scope of protection of the present invention.

Claims

1. A binder, characterized in that: The invention is prepared from the following raw materials: a main material and an auxiliary material; the auxiliary material includes an initiator; the main material includes an unsaturated hydrophilic metal salt, a modified cytosine monomer and a modified guanine monomer; wherein the unsaturated hydrophilic metal salt is selected from at least one of an unsaturated hydrophilic sodium salt and an unsaturated hydrophilic lithium salt, and the content A1 of the unsaturated hydrophilic metal salt in the main material is 30wt% to 50wt%; the modified cytosine monomer is a cytosine monomer connected to a double bond, and the modified guanine monomer is a guanine monomer connected to a double bond, and the content A2 of the modified cytosine monomer and the content A3 of the modified guanine monomer in the main material satisfy the following relationship: 0.8≤A2 / A3≤1.

2.

2. The adhesive according to claim 1, characterized in that The main ingredient meets at least one of the following conditions: A2 satisfies: 25wt%≤A2≤35wt%; The A3 satisfies: 25wt%≤A3≤35wt%.

3. The adhesive according to claim 1, characterized in that The unsaturated hydrophilic metal salt contains an unsaturated group and a hydrophilic group; The unsaturated group is an ethylenically unsaturated group, and / or the hydrophilic group is an anionic acid group.

4. The adhesive according to claim 3, characterized in that The ethylenically unsaturated group is selected from at least one of vinyl and propenyl groups; the anionic acid group is selected from at least one of sulfonic acid groups, boric acid groups, and phosphoric acid groups.

5. The adhesive according to claim 1, characterized in that The mass ratio of the main material to the auxiliary material is 5 to 10:

1.

6. The adhesive according to claim 5, characterized in that The initiator is selected from at least one of potassium persulfate, ammonium persulfate, sodium persulfate, tert-butyl peroxide, and benzoyl peroxide.

7. The adhesive according to any one of claims 1 to 6, characterized in that The carbonization temperature of the binder is 340°C to 400°C.

8. The method for preparing the binder according to any one of claims 1 to 7, characterized in that: include: The main material is dissolved in an organic solvent, the auxiliary material is added, and the mixture is polymerized to obtain the product.

9. The method for preparing the adhesive according to claim 8, characterized in that: After the polymerization reaction is completed, solid-liquid separation treatment is also included.

10. The method for preparing the adhesive according to claim 9, characterized in that: Before dissolving the main material in an organic solvent, the process also includes preparing a modified cytosine monomer and a modified guanine monomer; The preparation of the modified cytosine monomer and the modified guanine monomer comprises: dissolving the cytosine monomer and the guanine monomer in dimethylformamide respectively, then adding an organic base to adjust the pH to 8-9, and stirring in an ice-water bath for 20-30 minutes; adding an olefinic acid halide, and stirring and reacting under vacuum at room temperature; and then using an ether solvent for precipitation to obtain the modified cytosine monomer and the modified uracil monomer respectively.

11. The method for preparing the adhesive according to claim 10, characterized in that: The preparation of the modified cytosine monomer and the modified guanine monomer satisfies at least one of the following conditions: The structural formula of the alkenyl acyl halide is CH2=CH-(CH2) n -COX, wherein n is a natural number, and X is at least one of fluorine, chlorine, and bromine; The organic base is selected from at least one of pyridine, piperidine, ethanolamine, diisopropylethylamine, dimethylisopropylamine, diisopropylamine, methylamine, ethylamine, diethylamine, and triethylamine; The ether solvent is selected from at least one of diethyl ether, dimethyl ether and methyl ethyl ether.

12. Use of the binder according to any one of claims 1 to 7 or the binder prepared by the method for preparing the binder according to any one of claims 8 to 11 in preparing a negative electrode sheet.

13. A negative electrode sheet, characterized in that: It comprises a negative electrode current collector and a negative electrode material layer provided on at least one side of the negative electrode current collector; the negative electrode material layer contains the binder according to any one of claims 1 to 7, or the binder prepared by the preparation method of the binder according to any one of claims 8 to 11.

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