Battery binder for energy storage, preparation method, silicon-based negative plate, battery and power utilization device

Abstract

The invention discloses a battery binder for energy storage, a preparation method, a silicon-based negative plate, a battery and a power utilization device.The battery binder comprises a copolymer, the copolymer comprises a first component, a second component and a third component, the first component comprises an acrylic monomer and / or an acrylic derivative monomer, the second component comprises a second component and a third component, and the third component comprises a second component and a third component. The second component comprises an alkylene sulfonate monomer, and the third component comprises a lipoic acid ester monomer; the molar ratio of the first component to the second component to the third component is (7-9.5): (0.25-2): (0.25-1). The water-based polymer binder has high bonding strength and excellent dynamic performance, and is suitable for being used as a binder of a silicon-based system battery negative electrode.

Description

Technical Field

[0001] This application belongs to the field of batteries, and specifically relates to battery binders, preparation methods, silicon-based negative electrode sheets, batteries, and electrical devices. Background Art

[0002] As an advanced energy storage technology, lithium-ion batteries have been widely used in portable electronic devices, new energy vehicles, and large-scale energy storage systems due to their advantages such as high cycle life, wide operating temperature range, large energy density, and power density. With the continuous growth of technological progress and market demand, higher requirements are put forward for battery performance, including higher energy density, longer cycle life, and better safety. However, traditional graphite negative electrode materials have approached their theoretical capacity limit and are difficult to meet the increasing energy density requirements. Therefore, silicon-based negative electrode materials, with a theoretical specific capacity of up to about 4200 mAh / g (372 mAh / g for graphite), are regarded as an ideal choice to replace graphite. However, silicon-based materials will experience significant volume changes during charge and discharge processes, resulting in the destruction of the electrode structure and the decline of cycle performance; among them, the quality of the binder directly affects the stability and service life during the battery cycle and becomes one of the key factors to improve the performance of silicon-based batteries.

[0003] The main function of the binder in the silicon-based negative electrode is to tightly bind silicon particles with the conductive agent and the current collector to form a stable electrode structure. If the binder has poor performance, it will not only cause the electrode material to peel off during charge and discharge, but also seriously affect the cycle performance and service life of the battery. Currently, the commonly used binders in lithium-ion batteries include sodium carboxymethyl cellulose / styrene-butadiene rubber (CMC / SBR) composite systems and polyvinylidene fluoride (PVDF). CMC / SBR is favored due to its low cost, wide application range, and environmental friendliness, but its low conductivity and poor mechanical strength limit its application in high-performance silicon-based batteries. In contrast, PVDF has excellent chemical stability, but its preparation process relies on N-methylpyrrolidone (NMP) as a solvent, which not only increases the manufacturing cost but also brings potential environmental problems. To overcome the limitations of existing binders and further improve the performance of silicon-based negative electrodes, researchers have begun to explore new binder materials. Polyacrylic acid (PAA) and its derivatives contain a high density of polar carboxyl functional groups, which can form covalent bonds or hydrogen bonds with the hydroxyl groups on the surface of silicon particles, effectively alleviating the volume change of silicon particles during charge and discharge and maintaining the integrity of the electrode structure. At the same time, PAA improves the lithium-ion transport efficiency, reduces the polarization phenomenon of the electrode, and enhances the stability of the solid electrolyte interface (SEI) film. Therefore, PAA is regarded as one of the ideal binders for silicon-based negative electrodes of lithium-ion batteries.

[0004] In recent years, researchers at home and abroad have conducted extensive explorations on the modification of PAA binders. Among them, Magasinski et al. (ACS Appl. Mater. Interfaces, 2010, 2(11): 3004 - 3010) first confirmed that pure PAA containing a high concentration of carboxyl functional groups can be used as a binder for silicon anodes, and it exhibits superior electrochemical performance compared to sodium carboxymethyl cellulose binder.

[0005] In related technologies, Chinese Patent CN 112142988A discloses a polyacrylic acid - polyethylene glycol copolymer, its preparation method and application. This binder is composed of polyacrylic acid (PAA), polyethylene glycol (PEG), 4 - dimethylaminopyridine (DMAP), and 1 - (3 - dimethylaminopropyl) - 3 - ethylcarbodiimide (EDC), where the molar ratio of PAA to PEG is (3 - 4):1, the molar ratio of PEG to DMAP is 1:1, and the molar ratio of DMAP to EDC is 1:2. This binder forms a three - dimensional network structure and has excellent mechanical properties, which can effectively prevent irreversible displacement of electrode active substances, thereby contributing to improving the stability of the electrode.

[0006] Chinese Patent CN 110137498A discloses a binder for new energy vehicle lithium batteries and its preparation method. This binder is composed of a polymer A containing carboxyl functional groups, a polymer B containing hydroxyl functional groups, and a polymer C containing double - amino functional groups. The polymer A containing carboxyl functional groups can be selected from polymaleic acid, polymethacrylic acid, polyacrylic acid, polylactic acid, or sodium carboxymethyl cellulose, and its number - average molecular weight is greater than 30000. The polymer B containing hydroxyl functional groups can be selected from polyethylene glycol, chitin, or polyvinyl alcohol, and the number - average molecular weight of this polymer B should be less than 5000. The polymer C containing double - amino functional groups is polyetheramine with bifunctionality, and its number - average molecular weight ranges from 2000 to 5000. This binder can effectively reduce the swelling rate of the electrode sheet and improve the peeling strength of the electrode sheet.

[0007] The polyacrylic acid polymer chain is relatively fragile and is prone to breakage during charge - discharge processes. Its main limitation lies in its inherent brittleness. Therefore, it is necessary to enhance its structural stability through modification or compounding with other materials to effectively relieve the stress generated by the volume change of silicon, better inhibit the volume expansion of silicon, and improve the binding performance. In addition, the PAA binder forms a film on the surface of the negative electrode active material, which, although improving the initial efficiency of the battery to a certain extent, also causes difficulties in the transport of lithium ions during the cycling process and ultimately affects the rate performance and cycling stability of the battery. Therefore, developing a PAA binder with both excellent flexibility and high kinetics is of great significance for promoting the application of such binders in lithium - ion batteries with silicon - based anodes. Summary of the Invention

[0008] To solve at least one of the problems of insufficient flexibility of polyacrylic acid binders in existing silicon-based systems, the inability to inhibit the large volume expansion of silicon and the resulting pulverization of electrode sheets in the later stage of cycling, and the fact that existing PAA binders still cannot meet the battery kinetics requirements and have poor rate performance, the present invention provides a battery binder, a preparation method, a silicon-based negative electrode sheet, a battery, and an electrical device.

[0009] The present invention adopts the following technical solutions:

[0010] The present invention provides a battery binder, comprising a copolymer, the raw materials of the copolymer including a first component, a second component, and a third component, the first component including acrylic acid monomers and / or acrylic acid derivative monomers, the second component including olefin sulfonate monomers, and the third component including thioester monomers; the molar ratio of the first component, the second component, and the third component is (7-9.5):(0.25-2):(0.25-1).

[0011] The present invention takes acrylic acid monomers and / or acrylic acid derivative monomers as the main body, hydrophilic olefin sulfonate monomers and lipophilic thioester monomers as modifiers. The three enhance the bonding strength of the PAA binder through hydrogen bonds and ion-complex interaction forces. At the same time, sulfonates, ester groups, and polar carbon-sulfur bonds further improve the ion conduction performance. That is, the present invention provides an aqueous PAA binder with high bonding strength, high toughness, and improved kinetics. This binder can be applied to high-content silicon-based systems, effectively preventing problems such as electrode sheet demoulding and material loss in the later stage of cycling, and significantly improving the high-rate performance of the battery.

[0012] In some preferred embodiments, the molar ratio of the first component, the second component, and the third component is (7.5-8.5):(1-1.5):(0.5-1); more preferably, the molar ratio of the first component, the second component, and the third component is 8.5:1:0.5. Under this optimized ratio, it is more conducive to achieving the balance of the flexibility, bonding force, and kinetic performance of the binder, and at the same time obtaining a more uniform three-dimensional cross-linked network; not only having a more suitable swelling rate to improve the battery cycle stability, but also having a more direct and rapid ion transport path to promote ion conduction and improve the rate performance of the battery.

[0013] In some embodiments, the acrylic acid monomers are selected from at least one of acrylic acid, acrylate salts, methacrylic acid, and methacrylate salts, and the acrylate salts and the methacrylate salts are respectively at least one of lithium salts, sodium salts, and potassium salts;

[0014] The acrylic acid derivative monomers are selected from at least one of acrylamide monomers and acrylonitrile monomers;

[0015] The acrylamide monomers are selected from at least one of acrylamide, methacrylamide, N-methylacrylamide, N-ethylacrylamide, N-hydroxymethylacrylamide, N-hydroxyethylacrylamide, N-hydroxypropylacrylamide, N,N-dimethylacrylamide, and N,N-diethylacrylamide;

[0016] The acrylonitrile monomers are selected from at least one of acrylonitrile, α-methylacrylonitrile, and α-ethylacrylonitrile.

[0017] In some embodiments, the first component includes acrylic acid monomers, acrylamide monomers, and acrylonitrile monomers, and the molar ratio is: (4-8):(1-4):(7-14).

[0018] In some embodiments, the molar ratio of the second component to the third component is (1-3):1. By adjusting the ratio of the olefin-based sulfonate monomers (as hydrophilic monomers) and the thioester monomers (as hydrophobic monomers), the swelling property of the binder can be effectively controlled. When the molar ratio of the second component to the third component is (1-3):1, it can not only ensure that the electrolyte fully infiltrates the electrode sheet, thus guaranteeing the effective migration of lithium ions, but also maintain the excellent adhesiveness of the binder. Otherwise, if the swelling degree is too high, it may cause stress concentration at the interface between the binder and the current collector, increasing the risk of active material shedding; if the swelling degree is insufficient, it may lead to difficulty in the electrolyte fully penetrating into the negative electrode sheet, thereby hindering the migration of lithium ions. Therefore, precisely regulating the ratio of these two monomers is crucial for achieving the best battery performance.

[0019] In some embodiments, the olefin-based sulfonate monomers are selected from at least one of the structures shown in Formula I below:

[0020]

[0021] M is lithium ion, sodium ion, or potassium ion;

[0022] R1 is a bond or a C1-C3 straight-chain alkyl group, a C6-C8 aryl group;

[0023] R2 is hydrogen or methyl;

[0024] R3 is hydrogen or methyl;

[0025] R4 is hydrogen or a C1-C 14 straight-chain or branched-chain alkyl group, a C6-C 14 straight-chain or branched-chain aryl group, a C1-C 14 straight-chain or branched-chain alkyl group containing a hydroxyl group, a C1-C 14 straight-chain or branched-chain alkyl group containing an amino group and / or an imino group, a C1-C 14 straight-chain or branched-chain alkyl group.

[0026] In some embodiments, in the olefin-based sulfonate monomers, R4 is selected from one of the following groups:

[0027]

[0028] In some embodiments, the olefin-based sulfonate monomers are selected from at least one of the following structures:

[0029]

[0030] In some embodiments, the lipoate monomers are selected from at least one of the structures shown in Formula II below:

[0031]

[0032]

[0033] R5 is hydrogen or a C1-C4 straight-chain or branched-chain alkyl group;

[0034] R6 is hydrogen or a C1-C4 straight-chain or branched-chain alkyl group;

[0035] R7 is hydrogen or a C1-C4 straight-chain or branched-chain alkyl group;

[0036] R8 is hydrogen or a C1-C4 straight-chain or branched-chain alkyl group;

[0037] R9 contains a C1-C 14 straight-chain or branched-chain alkyl group, a C6-C 14 straight-chain or branched-chain aryl group, a C1-C containing a hydroxyl group 14 straight-chain or branched-chain alkyl group, a C1-C containing an amino group and / or an imino group 14 straight-chain or branched-chain alkyl group, a C1-C containing a carboxyl group 14 straight-chain or branched-chain alkyl group.

[0038] In some embodiments, in the lipoate monomers, R9 is selected from one of the following groups:

[0039]

[0040] In some embodiments, the lipoate monomers are selected from at least one of the following structures:

[0041]

[0042] In some embodiments, in Formula I, R3 is hydrogen and R4 is hydrogen; in Formula II, R9 is a C1-C3 straight-chain alkyl group. Thus, the olefin sulfonate monomer has high free radical polymerization activity and can regulate the degree of branching and crosslinking density of the copolymer. The short-chain alkyl group linked by the ester group of the lipoic acid ester monomer can, compared with long-chain alkyl groups or aryl groups, more moderately isolate the segments in terms of steric hindrance effect, balance flexibility and strength, and improve the cycle stability of the battery.

[0043] In some embodiments, the weight-average molecular weight of the copolymer is 350,000-750,000. More preferably, the weight-average molecular weight is 480,000-620,000. Within this preferred range, the binder has a suitable balance range of binding performance and flexibility, can effectively cope with the volume expansion of the silicon-based negative electrode during charge and discharge, improve the cycle stability and capacity retention rate of the battery. Moreover, the binder within this molecular weight range has good processing performance during the preparation of the electrode sheet, can uniformly cover the surface of the silicon-based negative electrode material, form a stable protective film, and further extend the service life of the battery.

[0044] The present invention also provides a preparation method of the above battery binder, including the following steps:

[0045] S1: Add part of the acrylic monomers, NaOH aqueous solution and part of the acrylamide monomers to water, keep the temperature at 50-80 °C and hold the reaction for 15-35 min, then add part of the acrylonitrile monomers and initiator, and keep the temperature at 65-90 °C and hold the reaction for 2-5 h;

[0046] S2: Take the remaining acrylic monomers, the remaining acrylamide monomers, the remaining acrylonitrile monomers, the olefin sulfonate monomer and the lipoic acid ester monomer, mix them evenly, and then dropwise add them to the solution in S1; keep the temperature for 7-13 h to complete the reaction;

[0047] S3: Neutralize the reactant obtained in step S2 and dilute it to prepare the battery binder.

[0048] In some embodiments, the amount of acrylic monomers added in step S1 is 60-75% of the total amount of acrylic monomers; the amount of acrylamide monomers added in step S1 is 50-65% of the total amount of acrylamide monomers; the amount of acrylonitrile monomers added in step S1 is 45-60% of the total amount of acrylonitrile monomers.

[0049] In some embodiments, the amount of the initiator is 0.05-0.1% of the total mass of the monomers for preparing the battery binder.

[0050] In some embodiments, the initiator is selected from at least one of ammonium persulfate, sodium persulfate or potassium persulfate. Preferably, the initiator is ammonium persulfate.

[0051] In some embodiments, in step S1, the concentration of the NaOH aqueous solution is 1-10%.

[0052] In some embodiments, the entire reaction process of step S1 is carried out under an inert atmosphere;

[0053] In some embodiments, the inert atmosphere is selected from any one of nitrogen and argon.

[0054] In some embodiments, the flow rate of the inert atmosphere is 500-1500 mL / min.

[0055] In some embodiments, step S1 is carried out under oil bath heating.

[0056] In some embodiments, the dropping time of step S2 is greater than or equal to 2 h.

[0057] In some embodiments, the neutralization in step S3 means that one or more strong base aqueous solutions of LiOH, NaOH, and KOH are gradually added dropwise to the reactants to adjust the pH to 7-8.

[0058] In some embodiments, the concentration of the strong base aqueous solution is 10-20%.

[0059] In some embodiments, in step S3, water dilution is used, and further, deionized water is used for dilution.

[0060] In a third aspect,

[0061] The present invention also provides a silicon-based negative electrode sheet, which is made of a current collector and a negative electrode paste loaded on the current collector; the negative electrode paste is mixed by a silicon-based active material, a conductive agent, and the above binder.

[0062] In some embodiments, the silicon-based active material includes silicon particulate materials, silicon-oxygen composite materials, or silicon-carbon composite materials; as some specific examples: the silicon-oxygen composite materials include one or more of silicon monoxide and silicon dioxide; the silicon-carbon composite materials include one or more of silicon / graphite composite materials, silicon / carbon nanotube composite materials, and silicon / graphene composite materials.

[0063] In some embodiments, the silicon content of the silicon-based active material is 5-30%.

[0064] The suitable binder selected in this application has excellent binding properties and flexibility, can tightly bind silicon-based active material particles together, and at the same time adapt to the volume change of the silicon-based negative electrode during charge and discharge, effectively relieve the stress caused by cyclic swelling, and improve the cycle stability of the battery. Secondly, the binder can form a stable protective film in a high-content silicon-based system (silicon content ≥ 10%), prevent the direct contact between the silicon-based active material and the electrolyte, reduce the occurrence of side reactions, and thus improve the initial efficiency and capacity retention rate of the battery.

[0065] In some embodiments, the conductive agent includes at least one of carbon nanotubes, carbon black, carbon fiber, and graphene.

[0066] In the fourth aspect,

[0067] The present invention also provides a battery, which includes a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte, and the negative electrode sheet is the above-mentioned silicon-based negative electrode sheet.

[0068] The embodiment of the present invention also provides an electrochemical device, which includes the above-mentioned battery.

[0069] The embodiment of the present application also provides an electrical device, which includes the above-mentioned battery or the above-mentioned electrochemical device to provide electrical energy for the electrical device.

[0070] In some embodiments, the electrical device can be a terminal consumer product, such as common 3C products, and non-limiting examples include computers, tablet computers, mice, mobile phones, digital cameras, walkmans, electronic dictionaries, digital audio players, smart watches, MP3s, MP4s, radios, and Bluetooth headsets.

[0071] In some embodiments, the electrical device can also be a large electrical device, such as a transportation electrical device, and the transportation electrical device includes but is not limited to automobiles (private cars, buses), motorcycles, motorized bicycles, subways, high-speed rails, airplanes, ships, etc.

[0072] The present invention has the following advantages and beneficial effects:

[0073] The present invention provides a preparation method of an olefin-based sulfonate and thioester-modified PAA polymer aqueous binder. In the present invention, acrylic monomers and / or acrylic derivative monomers are used as the main body, and hydrophilic olefin sulfonate monomers and lipophilic thioester monomers are used as modifiers. The three enhance the bonding strength of the PAA binder through hydrogen bonding and ion-complex interaction forces. The thioester can significantly improve the flexibility of the PAA chain segment and solve the problem of excessive brittleness. The highly polarized sulfur atom in the thioester can provide appropriate coordination, and the C-S bond can generate appropriate sites near the lithium ion transmission to achieve rapid transmission. At the same time, the oxygen element in the groups of the thioester and sulfonate radical has lone electron pairs, which continuously complex and decomplex with lithium ions under the action of an electric field, thereby promoting the diffusion of lithium ions. This aqueous polymer binder has high bonding strength and excellent kinetic performance, and is suitable for use as a binder for the negative electrode of a silicon-based system battery.

[0074] Furthermore, in the present invention, by adjusting the ratio of olefin-based sulfonate monomers and thioester monomers, the swelling property of the binder can be controlled, and accurately regulating the ratio of these two monomers is crucial for achieving the best battery performance. Detailed implementation mode

[0075] The embodiments of the present invention are described in detail below. The following described embodiments are exemplary and are intended to explain the present invention and should not be construed as a limitation of the present invention.

[0076] The experimental methods used in the following examples are all conventional methods unless otherwise specified.

[0077] The materials, reagents, devices, etc. used in the following examples can be obtained from commercial sources or prepared according to the methods in the published literature unless otherwise specified.

[0078] In this article, when a value is described as a range, it should be understood that this disclosure includes the disclosure of all possible sub-ranges within this range, as well as specific numerical values falling within this range, regardless of whether the specific numerical values or specific sub-ranges are explicitly indicated.

[0079] The following are term or word explanations, and unless otherwise defined, all technical and scientific terms used in this article have the meanings commonly understood by those skilled in the art to which the present invention belongs.

[0080] In this article, the words "comprising" and "including" and their various variants mean that other elements or wholes that may be included are allowed but not specifically described.

[0081] In this article, the phrase "and / or" is merely a description of the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B may represent: A exists alone, A and B exist simultaneously, and B exists alone.

[0082] In this text, any expression of a numerical range related to the number of carbon atoms, such as "C1-C4", refers to the enumeration of all positive integers within its upper and lower limits. For example, "C1-C4" represents "C1, C2, C3, C4".

[0083] In this text, the terms "linear alkyl" and "branched alkyl" refer to groups formed by removing one hydrogen from an alkane in which all carbon atoms are connected by carbon-carbon single bonds and do not form a ring, and the remaining valence bonds are all combined with hydrogen.

[0084] In this text, "aryl" refers to a hydrocarbon group containing at least one aromatic ring, including non-fused aromatic groups and fused aromatic groups. A fused aromatic group is a group formed by connecting two or more aromatic rings through two adjacent ring atoms shared, that is, a fused ring. An aromatic ring refers to an aromatic cyclic hydrocarbon compound: that is, a hydrocarbon compound with a cyclic closed-loop conjugated system.

[0085] The term "C1-C 14 linear or branched alkyl containing a hydroxyl group" refers to C1-C 14 linear or branched alkyl in which at least one hydrogen is replaced by a hydroxyl group.

[0086] The term "C1-C 14 linear or branched alkyl containing an amino group and / or an imino group" refers to C1-C 14 linear or branched alkyl in which at least one hydrogen is replaced by an amino group or an imino group.

[0087] The term "C1-C 14 linear or branched alkyl containing a carboxyl group" refers to C1-C 14 linear or branched alkyl in which at least one hydrogen is replaced by a carboxyl group.

[0088] The present invention provides a battery binder, including a copolymer, the raw materials of the copolymer include a first component, a second component and a third component, the first component includes acrylic acid monomers and / or acrylic acid derivative monomers, the second component includes olefin sulfonate monomers, and the third component includes thioester monomers; the molar ratio of the first component, the second component and the third component is (7-9.5):(0.25-2):(0.25-1).

[0089] As an example, the molar ratio of the first component, the second component and the third component can be: 7:0.25:0.5, 7:2:1, 7.5:1.5:1, 8:1:1, 8.5:1:0.5, 8:1.5:0.5, 9.5:2:1, etc.

[0090] In some preferred embodiments, the molar ratio of the first component, the second component and the third component is (7.5 to 8.5):(1 to 1.5):(0.5 to 1); more preferably, the molar ratio of the first component, the second component and the third component is 8.5:1:0.5.

[0091] In some embodiments, the acrylic monomer is selected from at least one of acrylic acid, acrylate, methacrylic acid, and methacrylate, and the acrylate and the methacrylate are each at least one of a lithium salt, a sodium salt, and a potassium salt;

[0092] The acrylic derivative monomer is selected from at least one of acrylamide monomers and acrylonitrile monomers;

[0093] The acrylamide monomers are selected from at least one of acrylamide, methacrylamide, N-methylacrylamide, N-ethylacrylamide, N-hydroxymethylacrylamide, N-hydroxyethylacrylamide, N-hydroxypropylacrylamide, N,N-dimethylacrylamide, and N,N-diethylacrylamide;

[0094] The acrylonitrile monomers are selected from at least one of acrylonitrile, α-methylacrylonitrile, and α-ethylacrylonitrile.

[0095] In some embodiments, the first component includes acrylic monomers, acrylamide monomers and acrylonitrile monomers, and the molar ratio is (4 to 8):(1 to 4):(7 to 14). As an example, the molar ratio can be 4:2:9, 5:3:10, 5.5:3.5:12, 7:2:10, 7.5:3:11, 8:4:13, etc.

[0096] In some embodiments, the molar ratio of the second component to the third component is (1 to 3):1. As an example, the molar ratio can be 1:1, 1.5:1, 2:1, 2.5:1, 3:1, etc.

[0097] In some embodiments, the olefin sulfonate monomer is selected from at least one of the structures shown in Formula I below:

[0098]

[0099] M is a lithium ion, a sodium ion, or a potassium ion;

[0100] R1 is a bond or a C1-C3 straight-chain alkyl group or a C6-C8 aryl group;

[0101] R2 is hydrogen or methyl;

[0102] R3 is hydrogen or methyl;

[0103] R4 is hydrogen or C1-C 14Linear or branched alkyl, C6-C 14 Linear or branched aryl, C1-C containing a hydroxyl group 14 Linear or branched alkyl, C1-C containing an amino group and / or an imino group 14 Linear or branched alkyl, C1-C containing a carboxyl group 14 Linear or branched alkyl.

[0104] In some embodiments, in the olefin sulfonate monomers, R4 is selected from one of the following groups:

[0105]

[0106] In some embodiments, the olefin sulfonate monomers are selected from at least one of the following structures:

[0107]

[0108] In some embodiments, the lipoate monomers are selected from at least one of the structures shown in Formula II below:

[0109]

[0110] R5 is hydrogen or a C1-C4 linear or branched alkyl;

[0111] R6 is hydrogen or a C1-C4 linear or branched alkyl;

[0112] R7 is hydrogen or a C1-C4 linear or branched alkyl;

[0113] R8 is hydrogen or a C1-C4 linear or branched alkyl;

[0114] R9 contains C1-C 14 Linear or branched alkyl, C6-C 14 Linear or branched aryl, C1-C containing a hydroxyl group 14 Linear or branched alkyl, C1-C containing an amino group and / or an imino group 14 Linear or branched alkyl, C1-C containing a carboxyl group 14 Linear or branched alkyl.

[0115] In some embodiments, in the lipoate monomers, R9 is selected from one of the following groups:

[0116]

[0117] In some embodiments, the lipoate monomers are selected from at least one of the following structures:

[0118]

[0119] In some embodiments, in Formula I, R3 is hydrogen and R4 is hydrogen; in Formula II, R9 is a C1-C3 linear alkyl group (for example, R9 is methyl, ethyl, or propyl).

[0120] In some embodiments, the weight-average molecular weight of the copolymer is 350,000-750,000. More preferably, the weight-average molecular weight is 480,000-620,000. By way of example, the weight-average molecular weight of the copolymer can be 350,000, 380,000, 420,000, 480,000, 520,000, 550,000, 620,000, 750,000, etc.

[0121] The present invention also provides a method for preparing the above battery binder, which comprises the following steps:

[0122] S1: Add part of the acrylic monomers, NaOH aqueous solution, and part of the acrylamide monomers into water, and carry out a heat preservation reaction at 50-80°C (such as 50°C, 55°C, 60°C, 70°C, 80°C, etc.) for 15-35 min (15 min, 20 min, 25 min, 30 min, 35 min, etc.). Then add part of the acrylonitrile monomers and initiator, and carry out a heat preservation reaction at 65-90°C (such as 65°C, 70°C, 75°C, 80°C, 90°C, etc.) for 2-5 h (such as 2 h, 2.5 h, 3 h, 4 h, 5 h, etc.);

[0123] S2: Take the remaining acrylic monomers, the remaining acrylamide monomers, the remaining acrylonitrile monomers, the olefin sulfonate monomers, and the thioester monomers, mix them evenly, and then dropwise add them to the solution obtained in S1; carry out a heat preservation reaction for 7-13 h (such as 7 h, 8 h, 9 h, 10 h, 13 h, etc.), and the reaction is completed;

[0124] S3: Neutralize the reactant obtained in step S2 and dilute it to prepare the battery binder.

[0125] In some embodiments, the amount of acrylic monomers added in step S1 is 60-75% of the total amount of acrylic monomers (by way of example, such as 60%, 65%, 70%, 75%, etc.); the amount of acrylamide monomers added in step S1 is 50-65% of the total amount of acrylamide monomers (by way of example, such as 50%, 55%, 60%, 65%, etc.); the amount of acrylonitrile monomers added in step S1 is 45-60% of the total amount of acrylonitrile monomers (by way of example, such as 45%, 50%, 55%, 60%, etc.).

[0126] In some embodiments, the amount of the initiator used is 0.05-0.1% of the total mass of the monomers for preparing the battery binder. By way of example, such as 0.05%, 0.06%, 0.07%, 0.08%, 0.1%, etc.

[0127] In some embodiments, the initiator is selected from at least one of ammonium persulfate, sodium persulfate, or potassium persulfate. Preferably, the initiator is ammonium persulfate.

[0128] In some embodiments, in step S1, the concentration of the NaOH aqueous solution is 1-10%. As an example, the concentration can be 1%, 2%, 5%, 10%, etc.

[0129] In some embodiments, the entire reaction process of step S1 is carried out under an inert atmosphere;

[0130] In some embodiments, the inert atmosphere is selected from any one of nitrogen and argon.

[0131] In some embodiments, the flow rate of the inert atmosphere is 500-1500 mL / min. As an example, it can be 500 mL / min, 1000 mL / min, 1500 mL / min, etc.

[0132] In some embodiments, step S1 is carried out under oil bath heating.

[0133] In some embodiments, the dropping time of step S2 is greater than or equal to 2 h. As an example, it can be 2 h, 2.5 h, 3 h, 3.5 h, 4 h, etc.

[0134] In some embodiments, the neutralization in step S3 means using an aqueous solution of one or more strong bases such as LiOH, NaOH, and KOH, gradually dropping it into the reactants, and adjusting the pH to 7-8. As an example, adjusting the pH to 7, 7.2, 7.5, 8, etc.

[0135] In some embodiments, the concentration of the strong base aqueous solution is 10-20%. As an example, it can be 10%, 12%, 15%, 20%, etc.

[0136] In some embodiments, in step S3, water dilution is used. Further, deionized water is used for dilution.

[0137] In some embodiments, a method for preparing a battery binder includes the following steps:

[0138] Add 10-25 g of acrylic monomers, 3-10 g of a 1-10% NaOH aqueous solution, and 3-9 g of acrylamide monomers into a three-necked flask containing 200-350 mL of water;

[0139] The entire reaction process is protected by passing an inert atmosphere, and the atmosphere flow rate is controlled at 500-1500 mL / min;

[0140] Raise the temperature until the temperature of the reaction system is maintained at 50-80 °C, keep it warm for 15-35 min, and the entire system is carried out under oil bath heating;

[0141] After the reaction temperature stabilizes, add 10 - 25 g of acrylonitrile monomers and 0.01 - 0.1 g of initiator. Ammonium persulfate is used as the initiator.

[0142] Raise the temperature to keep the reaction system temperature at 65 - 90 °C and keep it warm for 2 - 5 h.

[0143] Take 5 - 15 g of acrylic acid, 3 - 9 g of acrylamide monomers, 10 - 25 g of acrylonitrile monomers, 15 - 25 g of olefin sulfonate monomers, and 10 - 20 g of thioester monomers, mix them evenly, and drip them into the flask. The dripping time is ≥ 2 h. After the dripping is completed, keep it warm for 7 - 13 h to complete the reaction.

[0144] Neutralize the obtained reactants above: Use an aqueous solution of one or more strong bases such as LiOH, NaOH, and KOH, and gradually drip it into the flask until the pH is 7 - 8. The alkali concentration should be controlled at 10 - 20%.

[0145] Dilute with deionized water to the required solid content.

[0146] In a third aspect,

[0147] The present invention also provides a silicon-based negative electrode sheet, which is made of a current collector and a negative electrode paste loaded on the current collector; the negative electrode paste is mixed by a silicon-based active material, a conductive agent, and the above binder.

[0148] In some embodiments, the silicon-based active material includes silicon particle materials, silicon-oxygen composite materials, or silicon-carbon composite materials; as some specific examples: the silicon-oxygen composite materials include one or more of silicon monoxide and silicon dioxide; the silicon-carbon composite materials include one or more of silicon / graphite composite materials, silicon / carbon nanotube composite materials, and silicon / graphene composite materials.

[0149] In some embodiments, the silicon content of the silicon-based active material is 5 - 30%.

[0150] For the selection of a suitable binder in this application, it has excellent binding properties and flexibility, can tightly bond the silicon-based active material particles together, and at the same time adapt to the volume change of the silicon-based negative electrode during charge and discharge, effectively relieve the stress caused by cyclic swelling, and improve the cycle stability of the battery. Secondly, this binder can form a stable protective film in a high-silicon-based system (silicon content ≥ 10%), prevent the direct contact between the silicon-based active material and the electrolyte, reduce the occurrence of side reactions, and thus improve the initial efficiency and capacity retention rate of the battery.

[0151] In some embodiments, the conductive agent includes at least one of carbon nanotubes, carbon black, carbon fibers, and graphene.

[0152] Fourth aspect,

[0153] The present invention also provides a battery, which includes a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte. The negative electrode sheet is the above-mentioned silicon-based negative electrode sheet.

[0154] An embodiment of the present invention also provides an electrochemical device, which includes the above battery.

[0155] An embodiment of the present application also provides an electrical device, which includes the above battery or the above electrochemical device to provide electrical energy for the electrical device.

[0156] In some embodiments, the electrical device can be a terminal consumer product, such as common 3C products. Non-limiting examples include computers, tablet computers, mice, mobile phones, digital cameras, walkmans, electronic dictionaries, digital audio players, smart watches, MP3s, MP4s, radios, and Bluetooth headsets.

[0157] In some embodiments, the electrical device can also be a large electrical device. For example, it can be a transportation electrical device, and the transportation electrical device includes but is not limited to automobiles (private cars, buses), motorcycles, motorized bicycles, subways, high-speed rails, airplanes, ships, etc.

[0158] Example 1

[0159] A preparation method of a battery binder includes the following steps:

[0160] Add 23.6 g of acrylic acid, 5.5 g of 1% NaOH aqueous solution, and 7.6 g of acrylamide into a three-necked flask containing 250 mL of water;

[0161] The entire reaction process needs to be protected by an inert atmosphere (nitrogen), and the atmosphere flow rate is controlled at 1000 mL / min;

[0162] Raise the temperature until the reaction system temperature is maintained at 55 °C and keep it warm for 30 min. The whole system is carried out under oil bath heating;

[0163] After the reaction temperature is stable, add 20.8 g of acrylonitrile and 0.09 g of ammonium persulfate initiator;

[0164] Raise the temperature to keep the reaction system temperature at 65 °C and keep it warm for 3 h;

[0165] Take 10.1 g of acrylic acid, 5.0 g of acrylamide, 17.1 g of acrylonitrile, 20.8 g of sodium vinyl sulfonate, and 18.7 g of ethyl thioacetate, mix them evenly, and drop them into the flask within 3.5 h; keep it warm for 9 h, and the reaction is completed;

[0166] Neutralize the obtained reactants above: Use a strong alkaline aqueous solution of 10% NaOH, and gradually add it dropwise into the flask until the pH = 7.

[0167] Dilute with deionized water to a solid content of 6% to obtain Example 1.

[0168] Examples 2 - 12

[0169] Change the preparation conditions of Example 1, and the binder is prepared in the same manner as Example 1 for the rest, as recorded in Table 1.

[0170] Table 1

[0171]

[0172]

[0173] Comparative Example 1

[0174] Add 22.1 g of acrylic acid, 5.2 g of 1% NaOH aqueous solution, and 7.1 g of acrylamide to a three-necked flask containing 250 mL of water;

[0175] The entire reaction process needs to be protected by an inert atmosphere (nitrogen), and the atmosphere flow rate is controlled at 1000 mL / min;

[0176] Raise the temperature until the reaction system temperature is maintained at 55 °C, and keep it warm for 30 min. The entire system is carried out under oil bath heating;

[0177] After the reaction temperature is stable, add 19.5 g of acrylonitrile and 0.06 g of ammonium persulfate initiator;

[0178] Raise the temperature to 65 °C and keep it warm for 3 h;

[0179] Take 9.5 g of acrylic acid, 4.7 g of acrylamide, and 16.0 g of acrylonitrile, mix them evenly, and add them dropwise to the flask within 3.5 h; keep it warm for 9 h, and the reaction is completed;

[0180] Neutralize the obtained reactants above: Use a strong alkaline aqueous solution of 10% NaOH, and gradually add it dropwise into the flask until the pH is 7. Dilute with deionized water to the required solid content of 6% to obtain Comparative Example 1.

[0181] Comparative Example 2

[0182] Add 22.9 g of acrylic acid, 5.3 g of 1% NaOH aqueous solution, and 7.3 g of acrylamide to a three-necked flask containing 250 mL of water;

[0183] The entire reaction process needs to be protected by an inert atmosphere (nitrogen), and the atmosphere flow rate is controlled at 1000 mL / min;

[0184] Raise the temperature until the temperature of the reaction system remains at 55 °C, and keep it warm for 30 min. The whole system is carried out under oil bath heating;

[0185] After the reaction temperature is stable, add 20.2 g of acrylonitrile and 0.06 g of ammonium persulfate initiator;

[0186] Raise the temperature until the temperature of the reaction system remains at 65 °C, and keep it warm for 3 h;

[0187] Take 9.8 g of acrylic acid, 4.9 g of acrylamide, 16.5 g of acrylonitrile, and 19.5 g of sodium vinyl sulfonate, mix them evenly, and drop them into the flask within 3.5 h; keep it warm for 9 h, and the reaction is completed;

[0188] Neutralize the obtained reactants above: Use a 10% NaOH strong alkaline aqueous solution and gradually drop it into the flask until pH = 7.

[0189] Dilute with deionized water to a solid content of 6% to obtain Comparative Example 2.

[0190] Comparative Example 3

[0191] Add 23.1 g of acrylic acid, 5.4 g of 1% NaOH aqueous solution, and 7.4 g of acrylamide to a three-necked flask containing 250 mL of water;

[0192] The whole reaction process needs to be protected by an inert atmosphere (nitrogen), and the atmosphere flow rate is controlled at 1000 mL / min;

[0193] Raise the temperature until the temperature of the reaction system remains at 55 °C, and keep it warm for 30 min. The whole system is carried out under oil bath heating;

[0194] After the reaction temperature is stable, add 20.5 g of acrylonitrile and 0.06 g of ammonium persulfate initiator;

[0195] Raise the temperature until the temperature of the reaction system remains at 65 °C, and keep it warm for 3 h;

[0196] Take 9.9 g of acrylic acid, 5.0 g of acrylamide, 16.7 g of acrylonitrile, and 18.4 g of ethyl thioacetate, mix them evenly, and drop them into the flask within 3.5 h; keep it warm for 9 h, and the reaction is completed;

[0197] Neutralize the obtained reactants above: Use a 10% NaOH strong alkaline aqueous solution and gradually drop it into the flask until pH = 7.

[0198] Dilute with deionized water to a solid content of 6% to obtain Comparative Example 3.

[0199] Comparative Example 4

[0200] Add 19.2 g of acrylic acid, 4.9 g of 1% NaOH aqueous solution, and 6.2 g of acrylamide to a three-necked flask containing 250 mL of water;

[0201] The entire reaction process needs to be protected by an inert atmosphere (nitrogen), and the atmosphere flow rate is controlled at 1000 mL / min;

[0202] Raise the temperature until the reaction system temperature is maintained at 55 °C and keep warm for 30 min. The entire system is carried out under oil bath heating;

[0203] After the reaction temperature is stable, add 16.9 g of acrylonitrile and 0.06 g of ammonium persulfate initiator;

[0204] Raise the temperature until the reaction system temperature is maintained at 65 °C and keep warm for 3 h;

[0205] Take 8.2 g of acrylic acid, 4.1 g of acrylamide, 13.9 g of acrylonitrile, 43.4 g of sodium vinyl sulfonate, and 15.2 g of ethyl thioacetate, mix them evenly, and add them dropwise to the flask within 3.5 h; keep warm for 9 h, and the reaction is completed;

[0206] Neutralize the obtained reactants above: Use a 10% NaOH strong base aqueous solution and gradually add it dropwise into the flask until pH = 7.

[0207] Dilute with deionized water to a solid content of 6% to obtain Comparative Example 4.

[0208] Comparative Example 5

[0209] Add 18.4 g of acrylic acid, 4.8 g of 1% NaOH aqueous solution, and 5.9 g of acrylamide to a three-necked flask containing 250 mL of water;

[0210] The entire reaction process needs to be protected by an inert atmosphere (nitrogen), and the atmosphere flow rate is controlled at 1000 mL / min;

[0211] Raise the temperature until the reaction system temperature is maintained at 55 °C and keep warm for 30 min. The entire system is carried out under oil bath heating;

[0212] After the reaction temperature is stable, add 16.3 g of acrylonitrile and 0.06 g of ammonium persulfate initiator;

[0213] Raise the temperature until the reaction system temperature is maintained at 65 °C and keep warm for 3 h;

[0214] Take 7.9 g of acrylic acid, 3.9 g of acrylamide, 13.3 g of acrylonitrile, 16.3 g of sodium vinyl sulfonate, and 37.7 g of ethyl thioacetate, mix them evenly, and add them dropwise to the flask within 3.5 h; keep warm for 9 h, and the reaction is completed;

[0215] Neutralize the above-obtained reactants: Use a strong alkaline aqueous solution of 10% NaOH and gradually add it dropwise into the flask until the pH = 7.

[0216] Dilute with deionized water to a solid content of 6% to obtain Comparative Example 5.

[0217] Comparative Example 6

[0218] Add 22.9 g of acrylic acid, 5.4 g of 1% NaOH aqueous solution, and 7.3 g of acrylamide into a three-necked flask containing 250 mL of water;

[0219] The entire reaction process needs to be protected by an inert atmosphere (nitrogen), and the atmosphere flow rate is controlled at 1000 mL / min;

[0220] Raise the temperature until the reaction system temperature is maintained at 55 °C and keep it warm for 30 min. The entire system is carried out under oil bath heating;

[0221] After the reaction temperature stabilizes, add 20.2 g of acrylonitrile and 0.08 g of ammonium persulfate initiator;

[0222] Raise the temperature to 65 °C and keep it warm for 3 h;

[0223] Take 9.8 g of acrylic acid, 4.9 g of acrylamide, 16.5 g of acrylonitrile, 20.2 g of sodium vinyl sulfonate, and 11.0 g of ethyl cyclopentanecarboxylate, mix them evenly, and add them dropwise into the flask within 3.5 h; keep it warm for 9 h, and the reaction is completed;

[0224] Neutralize the above-obtained reactants: Use a strong alkaline aqueous solution of 10% NaOH and gradually add it dropwise into the flask until the pH = 7.

[0225] Dilute with deionized water to a solid content of 6% to obtain Comparative Example 6.

[0226] Specific test methods and conditions:

[0227] (1) Battery preparation: Graphite + Super P (SP) + nano-silicon + the products of each example or comparative example were mixed at a mass ratio of 70:5:15:10 and then coated on the current collector copper foil. After drying, cold pressing, and slitting, the negative electrode sheet was obtained; Lithium nickel cobalt manganese oxide (NCM811) + Super P (SP) + polyvinylidene fluoride (PVDF) were mixed at a mass ratio of 8:1:1 and then coated on the current collector aluminum foil. After drying, cold pressing, and slitting, the positive electrode sheet was obtained; A 12-μm-thick PP was used as the separator; Ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) were mixed at a volume ratio of 1:1:1, and LiPF6 was added to the mixed solution to obtain a solution with a concentration of 1 mol / L as the electrolyte. The positive electrode sheet, separator, and negative electrode sheet were stacked in sequence, wrapped with an aluminum-plastic film, transferred to a vacuum oven for drying at 120 °C, injected with electrolyte and then sealed, and a soft-pack battery was obtained after formation and formation and capacity testing.

[0228] (2) Swelling rate test of the adhesive film: The binder synthesized in each example or comparative example was poured into a polytetrafluoroethylene mold with a length of 50 mm, a width of 50 mm, and a depth of 5 mm, and placed in an oven for constant-temperature drying at 45 °C for 48 h to obtain an adhesive film without moisture and with a thickness of 1.25 mm. A 20-mm-long and 20-mm-wide adhesive film was taken and soaked in a lithium salt electrolyte without additives (note that the electrolyte needs to be kept in an environment with humidity control. The environment for soaking the adhesive film in this invention is in a glove box). After sealing, it was placed in an oven at a constant temperature of 75 °C for storage, and the mass change of the adhesive film after 9 days was recorded. The increase value relative to the initial mass of the adhesive film divided by the initial mass of the adhesive film is the swelling rate.

[0229] (3) Peel force and cohesion test: The peel force test is used to evaluate the bonding strength between the active material coating on the battery electrode sheet and the current collector (copper foil). During the test, a specimen with a length of 100 mm and a width of 20 mm was cut from the electrode sheet, one end was fixed on the fixture, and the other end was peeled off from the current collector at a constant speed of 90° (usually 300 mm / min), and the maximum peel force was recorded. The cohesion test checks the bonding strength of the active material coating itself to prevent the coating from delaminating or falling off during use. The test method is to fix both ends of the specimen on the fixture and stretch it at a speed of 300 mm / min until the coating ruptures, and record the required pulling force to evaluate the stability of the coating.

[0230] (4) Impedance test: It is carried out when the battery is in a stable state, that is, the battery has been fully charged or discharged and reaches the specified state of charge (50% SOC). The test should be completed in a constant-temperature environment of 25 °C to avoid the influence of temperature fluctuations on the results. In addition, to ensure the accuracy of the test results, a suitable frequency range and AC signal amplitude need to be selected. Therefore, the frequency range is set to 0.001 - 100000 Hz, the AC amplitude is 5 mV, and at the same time, ensure that the battery remains stationary throughout the test process.

[0231] (5) Cycling performance test: The battery is cycled in a thermostat maintained at a temperature of 25 °C. Set the voltage range to 2.5 - 4.2 V and the current magnitude to 0.5 C, and record the number of cycles when the battery capacity retention rate drops to 80%.

[0232] (6) Rate performance test: The battery is subjected to a rate discharge test in a thermostat maintained at a temperature of 25 °C. Set the voltage range to 2.5 - 4.2 V, the charging current uniformly to 0.5 C, and the discharge currents successively to 0.5 C, 1.0 C, 1.5 C, 2.0 C, 2.5 C, and 3.0 C. Based on the discharge capacity at 0.5 C (100%), calculate the discharge capacity retention rates at different current densities.

[0233] (7) Battery swelling rate: Under room temperature conditions of 25 °C, use a thickness gauge to measure the initial thickness of the fabricated battery. After the battery cycling is completed, use a thickness gauge to measure the final thickness of the battery. The battery swelling rate is calculated as (final thickness - initial thickness) / initial thickness.

[0234] Table 2

[0235]

[0236]

[0237] From the data of Examples 1 - 12 and Comparative Examples 1 - 6, it can be seen that the binders prepared in Examples 1 - 12 have relatively high viscosity, appropriate molecular weight, and moderate swelling property in the electrolyte. At the same time, the binder of the present invention has high adhesive force and cohesive force, low electrochemical impedance value, excellent rate performance, and long cycle stability in the application of silicon-based anode batteries. This is because the three components enhance the bonding strength of the polymer binder through hydrogen bonds and ion - complex interaction forces. At the same time, sulfonate, ester group, and polar carbon - sulfur bonds further enhance the ion conduction performance, ultimately improving the electrochemical performance of the battery.

[0238] From the comparative analysis of Examples 1 - 3, it can be seen that after changing the ratios of the three components, the viscosity and molecular weight of the prepared binder will also change to a certain extent. Compared with Example 1, in Example 2, increasing the dosage of thioester monomers will increase the swelling property of the binder in the electrolyte, reduce the impedance value and improve the rate performance. However, the adhesion and cohesion of the binder will decrease, and the cycle life will also become slightly worse. In Example 3, after simultaneously increasing the dosages of olefin sulfonate monomers and thioester monomers, both the adhesion and cohesion have recovered, and the electrochemical performance of the battery has also been improved accordingly. However, overall, the effect of Example 3 is not as good as that of Example 1. This is because although the ester group in the thioester monomer can effectively alleviate the excessive rigidity caused by the strong hydrogen bond in the acrylic acid system, which may lead to the fracture of the cross - linked network of the binder and improve its flexibility and kinetic performance, it cannot effectively inhibit the volume expansion of the silicon - based anode. After the active material particles are broken, new interfaces are exposed and will continuously react with the electrolyte, consuming lithium ions, resulting in the cycle stability of the battery in the later stage being inferior to that of Example 1.

[0239] From the comparative analysis of Examples 1, 4 - 12, it can be seen that the selection of olefin sulfonate monomers and thioester monomers will affect the performance of the binder. The structural type of the monomer will affect its segment distribution in the polymer and the ease of polymerization, which is directly manifested as changes in the viscosity, molecular weight and swelling rate of the binder. The rigidity of the monomer will affect the peel strength and cohesion of the binder.

[0240] From the comparative analysis of Example 1 and Comparative Example 1, it can be seen that when neither olefin sulfonate monomers nor thioester monomers are added, the peel strength and cohesion of the binder prepared in Comparative Example 1 in the electrode are relatively low, the impedance value of the battery is large, and the poor kinetics leads to poor rate performance. At the same time, the cycle stability is also poor. This is because the strong hydrogen bond in the binder prepared by the acrylic acid system causes excessive rigidity and too poor flexibility, resulting in brittle electrodes that are easy to crack, unable to effectively inhibit the volume expansion of the silicon - based anode, and the active material is easy to fall off during the cycle, leading to poor electrochemical performance.

[0241] From the comparative analysis of Example 1 and Comparative Examples 1 and 2, it can be seen that compared with Comparative Example 1, although Comparative Example 2 can reduce the electrochemical impedance value and improve the ionic conductivity to a certain extent after introducing olefin sulfonate monomers, the effect is limited, and its swelling also decreases accordingly.

[0242] From the comparative analysis of Example 1 and Comparative Examples 1 and 3, it can be seen that compared with Comparative Example 1, although Comparative Example 3 improves the kinetics to some extent after adding thioester monomers, the adhesion and cohesion of the prepared binder decrease, which is not conducive to maintaining the integrity of the silicon - based anode, and the cycle life of the battery has not been significantly improved.

[0243] Through the comparative analysis of the examples and Comparative Examples 4 and 5, it can be seen that when the olefin sulfonate monomers (Comparative Example 4) or thioester monomers (Comparative Example 5) are added in excess, the molecular weight of the prepared binder decreases significantly. Neither the adhesion nor the cohesion is as good as those of the examples, and the cycle life of the battery is also relatively short. Among them, too high a content of olefin sulfonate monomers will lead to too low a swelling rate of the binder, while too high a content of thioester monomers will lead to too high a swelling rate of the binder and obvious swelling of the cycle-terminated battery cells. It shows that the binder components and types within the optimized range are more conducive to achieving the balance of the flexibility, adhesion and kinetic performance of the binder, and obtaining a more uniform three-dimensional cross-linked network at the same time; not only having a more appropriate swelling rate to improve the cycle stability of the battery, but also having a more direct and rapid ion transport path to promote ion conduction and improve the rate performance of the battery.

[0244] Through the comparative analysis of the examples and Comparative Example 6, it can be seen that when the ester monomers added in Comparative Example 6 do not contain polar C-S bonds, their impedance values and rate discharge performance are not as good as those of the example groups. It shows that the highly polarized sulfur atoms in the thioester can provide appropriate coordination, and the C-S bond can generate appropriate sites near the lithium ion transport to achieve rapid transport.

[0245] In the present invention, the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples", etc. mean that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic descriptions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples.

[0246] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A battery binder, characterized in that, It includes a copolymer. The raw materials of the copolymer include a first component, a second component, and a third component. The first component includes acrylic acid monomers and / or acrylic acid derivative monomers. The second component includes olefin sulfonate monomers. The third component includes thioester monomers. The molar ratio of the first component, the second component, and the third component is (7 to 9.5):(0.25 to 2):(0.25 to 1).

2. The battery binder according to claim 1, wherein the molar ratio of the first component, the second component, and the third component is (7.5 to 8.5):(1 to 1.5):(0.5 to 1); more preferably, the molar ratio of the first component, the second component, and the third component is 8.5:1:0.

5.

3. The battery binder according to claim 1, wherein the acrylic acid monomers are selected from at least one of acrylic acid, acrylate salts, methacrylic acid, and methacrylate salts. The acrylate salts and the methacrylate salts are respectively at least one of lithium salts, sodium salts, and potassium salts; the acrylic acid derivative monomers are selected from at least one of acrylamide monomers and acrylonitrile monomers; the acrylamide monomers are selected from at least one of acrylamide, methacrylamide, N-methylmethacrylamide, N-ethylmethacrylamide, N-hydroxymethylmethacrylamide, N-hydroxyethylmethacrylamide, N-hydroxypropylmethacrylamide, N,N-dimethylmethacrylamide, and N,N-diethylmethacrylamide; the acrylonitrile monomers are selected from at least one of acrylonitrile, α-methylacrylonitrile, and α-ethylacrylonitrile. And / or, the first component includes acrylic acid monomers, acrylamide monomers, and acrylonitrile monomers, and the molar ratio is: (4 to 8):(1 to 4):(7 to 14); And / or, the molar ratio of the second component to the third component is (1 to 3):

1.

4. The battery binder according to claim 1, wherein, The olefin sulfonate monomers are selected from at least one of the structures shown in Formula I below: M is lithium ion, sodium ion, or potassium ion; R1 is a bond or a C1-C3 straight-chain alkyl group or a C6-C8 aryl group; R2 is hydrogen or methyl; R3 is hydrogen or methyl; R4 is hydrogen or C1-C 14 a straight-chain or branched-chain alkyl group, C6-C 14 a straight-chain or branched-chain aryl group, C1-C containing a hydroxyl group 14 a straight-chain or branched-chain alkyl group, C1-C containing an amino group and / or an imino group 14 a straight-chain or branched-chain alkyl group, C1-C containing a carboxyl group 14 a straight-chain or branched-chain alkyl group; Optionally, in the olefin sulfonate monomers, R4 is selected from one of the following groups: Optionally, the olefin sulfonate monomers are selected from at least one of the following structures:

5. A battery binder according to claim 4, characterized in that, The thioester monomers are selected from at least one of the structures shown in Formula II below: R5 is hydrogen or a C1-C4 straight-chain or branched-chain alkyl group; R6 is hydrogen or a C1-C4 straight-chain or branched-chain alkyl group; R7 is hydrogen or a C1-C4 straight-chain or branched-chain alkyl group; R8 is hydrogen or a C1-C4 straight-chain or branched-chain alkyl group; R9 is a group containing C1-C 14 linear or branched alkyl, C6-C 14 linear or branched aryl, C1-C containing a hydroxyl group 14 linear or branched alkyl, C1-C containing an amino group and / or an imino group 14 linear or branched alkyl, C1-C containing a carboxyl group 14 linear or branched alkyl; Optionally, in the thioester monomers, R9 is selected from one of the following groups: Optionally, the thioester monomers are selected from at least one of the following structures:

6. The battery binder according to claim 5, characterized in that, ​ 7. A battery binder according to any one of claims 1-6, characterized in that, ​ 8. The preparation method of the battery binder according to any one of claims 1-7, characterized in that, ​ S1: Add partial acrylic monomers, NaOH aqueous solution and partial acrylamide monomers into water, keep the temperature at 50 - 80 °C and hold for reaction for 15 - 35 min. Then add partial acrylonitrile monomers and initiator, keep the temperature at 65 - 90 °C and hold for 2 - 5 h; S2: Take the remaining acrylic monomers, the remaining acrylamide monomers, the remaining acrylonitrile monomers, olefin sulfonate monomers and thioester monomers, mix them evenly, and then dropwise add them into the solution of S1; keep the temperature for 7 - 13 h until the reaction is completed; S3: Neutralize the reactant obtained in step S2, and dilute it to prepare the battery binder; Further, the dosage of acrylic monomers added in step S1 is 60 - 75% of the total dosage of acrylic monomers; the dosage of acrylamide monomers added in step S1 is 50 - 65% of the total dosage of acrylamide monomers; the dosage of acrylonitrile monomers added in step S1 is 45 - 60% of the total dosage of acrylonitrile monomers; Further, the dosage of the initiator is 0.05 - 0.1% of the total mass of the monomers for preparing the battery binder; Further, the initiator is selected from at least one of ammonium persulfate, sodium persulfate or potassium persulfate. More preferably, the initiator is ammonium persulfate; Further, in step S1, the concentration of the NaOH aqueous solution is 1 - 10%. Further, the whole reaction process of step S1 is carried out under an inert atmosphere; more preferably, the inert atmosphere is selected from any one of nitrogen and argon; Further, the flow rate of the inert atmosphere is 500 - 1500 mL / min; Further, step S1 is carried out under oil bath heating; Further, the dropping time of step S2 is greater than or equal to 2 h; Further, the neutralization in step S3 means gradually dropping one or more strong base aqueous solutions of LiOH, NaOH, KOH into the reactant to adjust the pH to 7 - 8; Further, the concentration of the strong base aqueous solution is 10 - 20%; Further, in step S3, water dilution is adopted. Further, deionized water is used for dilution.

9. A silicon-based negative electrode sheet, characterized in that, The silicon-based negative electrode sheet is made of a current collector and a negative electrode paste loaded on the current collector; the negative electrode paste is mixed by a silicon-based active material, a conductive agent and the binder according to any one of claims 1 - 7 or the binder prepared by the method of claim 8. Optionally, the silicon-based active material includes silicon particle materials, silicon-oxygen composite materials or silicon-carbon composite materials; Optionally, the silicon content of the silicon-based active material is 5 - 30%.

10. A battery, an electrochemical device, and an electrical equipment containing the silicon-based negative electrode sheet according to claim 9, characterized in that The battery includes a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, and the negative electrode sheet is the silicon-based negative electrode sheet according to claim 9; The electrochemical device includes a battery containing the silicon-based negative electrode sheet according to claim 9; The electrical equipment includes a battery containing the silicon-based negative electrode sheet according to claim 9, or an electrochemical device containing the battery containing the silicon-based negative electrode sheet according to claim 9.

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