Polymer, binder including the polymer, and negative electrode, method for producing negative electrode

Abstract

The application provides a polymer, which comprises a main chain and a side chain. The main chain mainly comprises a water-soluble acrylonitrile copolymer, and the polymerized monomers of the acrylonitrile copolymer comprise acrylic monomers and acrylonitrile monomers. One end of the side chain is connected to the main chain, and the other end is connected to an organic silicon group X1, X2 and X3, which are independently selected from one of C1-C4 alkyl, hydroxyl, halogen atom and C1-C4 alkoxy, and X1, X2 and X3 are not alkyl at the same time. The number of chain atoms of the side chain is greater than or equal to 3. The application also provides a binder, a negative electrode and a secondary battery comprising the polymer, an application of the polymer and a preparation method of the negative electrode. The main chain of the polymer has high mechanical strength, can maintain the stability of the micro-skeleton structure of the electrode, and the side chain can be stretched and contracted while achieving multi-dimensional bonding of the silicon particles, and can buffer the volume and stress changes of the silicon particles in the charging and discharging process.

Description

Technical Field

[0001] This application relates to a polymer, a binder comprising the polymer, a negative electrode comprising the polymer, a secondary battery comprising the polymer, the application of the polymer as a binder, and a method for preparing the negative electrode. Background Technology

[0002] Currently, rechargeable batteries are widely used in mobile phones, laptops, portable electronic mobile devices, drones, electric vehicles, and other mobile terminals. Rechargeable batteries include lithium-ion batteries, sodium-ion batteries, potassium-ion batteries, magnesium-ion batteries, and lithium-sulfur batteries. As a type of rechargeable battery, lithium-ion batteries typically use lithium cobalt oxide / ternary / lithium iron phosphate as the positive electrode material and graphite as the negative electrode material. However, with the increasing market demand for the energy density of lithium-ion batteries, the research and development of high-capacity lithium-ion battery materials is becoming increasingly urgent. For lithium-ion battery negative electrode materials, silicon, with its extremely high theoretical lithium storage capacity (up to 4200 mAh / g), abundant reserves, and low cost, has become one of the most researched and promising high-capacity negative electrode materials. However, as a typical alloy-type negative electrode material, silicon undergoes a volume expansion of over 300% when forming an alloy with lithium. The mechanical stress generated by this huge volume change easily causes silicon to pulverize, leading to the deactivation of the electrochemical activity of the silicon particles. Simultaneously, the volume change of silicon also leads to the destruction of the electrode structure, resulting in rapid capacity decay and a sharp deterioration in cycle performance. Current strategies for addressing silicon anode expansion can be implemented through binder design, thus binder design has gradually gained attention and research. As a key component of the electrode structure, the binder provides the interconnected structure and mechanical strength for the electrodes, maintaining electron / ion transfer during battery cycling and playing a crucial role in overall electrochemical performance. Simultaneously, binders are one solution to address electrode expansion. By employing binders with single or combined properties such as high elastic modulus, high adhesion, self-healing properties, and soft-hard block copolymers, the volume expansion of silicon during cycling can be restrained. Summary of the Invention

[0003] The first aspect of this application provides a polymer, comprising:

[0004] The main chain mainly comprises a water-soluble acrylonitrile copolymer, wherein the polymerizable monomers of the acrylonitrile copolymer include acrylic monomers and acrylonitrile monomers;

[0005] The side chain has one end connected to the main chain and the other end connected to an organosilicon group. X1, X2 and X3 are each independently selected from C1-C4 alkyl, hydroxyl, halogen, and C1-C4 alkoxy, and X1, X2 and X3 are not all alkyl at the same time;

[0006] The side chain has ≥3 chain atoms, where the number of chain atoms is the total number of non-hydrogen atoms in the unbranched side chain.

[0007] The polymer of this application introduces side chains into the main chain structure of a water-soluble acrylonitrile copolymer, and the organosilicon groups attached to these side chains can form strong interactions with silicon particles with silanol groups on their surface, thereby achieving multidimensional adhesion to the silicon particles. In addition, the main chain of the acrylonitrile copolymer has high mechanical strength, which can maintain the stability of the electrode microstructure, while the side chains are stretchable, effectively buffering the huge volume changes and stress changes of the silicon particles during charging and discharging.

[0008] In this embodiment of the application, the polymer contains 4% to 30% nitrile groups by weight, and silicon by weight is 0.01% to 5%.

[0009] In this embodiment of the application, the polymer contains 20% to 29% nitrile groups by weight.

[0010] In this embodiment of the application, the weight percentage of silicon in the polymer is 0.1% to 1%.

[0011] In this embodiment of the application, the acrylic monomer includes at least one of acrylic acid, acrylate, methacrylic acid and methacrylate, wherein the acrylate and the methacrylate are at least one of sodium salt, potassium salt, lithium salt, rubidium salt and cesium salt, respectively.

[0012] In this embodiment of the application, the acrylonitrile monomer includes at least one of acrylonitrile and methacrylonitrile.

[0013] In this embodiment of the application, the polymer monomers of the acrylonitrile copolymer also include acrylamide monomers or epoxy-containing olefin monomers.

[0014] Introducing acrylamide monomers or epoxy-containing olefin monomers can not only endow the copolymer with other functions, but also introduce amide groups or epoxy groups, which facilitates the grafting of the side chains.

[0015] In the embodiments of this application, the acrylamide monomer is at least one selected from acrylamide, N-methylacrylamide, N-ethylacrylamide, N,N-dimethylacrylamide, N,N-diethylacrylamide, 2-methylacrylamide, N-hydroxymethylacrylamide, N-hydroxyethylacrylamide, and N-hydroxypropylacrylamide; the epoxy-containing olefin monomer is at least one selected from glycidyl acrylate, glycidyl methacrylate, and allyl glycidyl ether.

[0016] In this embodiment of the application, the side chain has ≥5 chain atoms.

[0017] Side chains with ≥3 atoms can stretch and contract better to accommodate the periodic, large volume changes of silicon particles during charging and discharging.

[0018] In this embodiment of the application, the structural formula of the side chain is as follows: At least one of the following; wherein the two ends of the main chain of the side chain structure are respectively connected to the main chain of the polymer and the Si of the organosilicon group.

[0019] A second aspect of this application provides an adhesive comprising the polymer described in the first aspect of this application.

[0020] The polymer used in this application serves as a binder, particularly as a binder for the silicon-based negative electrode of a battery. Because the organosilicon groups connected to the side chains of the polymer can form a strong interaction with the silicon particles with silanol groups on the surface of the negative electrode, multidimensional bonding of the silicon particles is achieved, thus the binder has good adhesion. In addition, because the side chains of the polymer are stretchable, they can suppress the huge volume change of the silicon particles to a certain extent during battery cycling, effectively suppressing electrode expansion.

[0021] In this embodiment of the application, the adhesive is the adhesive for the negative electrode of the battery.

[0022] The third aspect of this application provides an application of the polymer described in the first aspect of this application as an adhesive.

[0023] A fourth aspect of this application provides a negative electrode for a battery, comprising a negative electrode active material and a binder, wherein the binder comprises the polymer described in the first aspect of this application.

[0024] The aqueous polymer of this application, as a binder for silicon-based anodes, exhibits good adhesion and can suppress the large volume change of silicon particles to a certain extent during cycling, effectively inhibiting electrode expansion.

[0025] In this embodiment of the application, the negative electrode active material includes silicon-based materials.

[0026] In this embodiment of the application, the negative electrode includes a current collector and a layer of negative electrode active material attached to the current collector, wherein the layer of negative electrode active material includes the negative electrode active material and the binder.

[0027] A fifth aspect of this application provides a secondary battery, including a negative electrode, a positive electrode, an electrolyte, and a separator located between the negative electrode and the positive electrode. The negative electrode includes a negative electrode active material and a binder, and the binder includes the polymer described in the first aspect of this application.

[0028] The aqueous polymer binder of this application, as the binder for silicon-based negative electrodes, exhibits excellent adhesion and can suppress the large volume change of silicon particles to a certain extent during cycling, effectively maintaining the adhesion between the active material and the current collector. This can effectively reduce the internal resistance of the negative electrode sheet, suppress electrode expansion, and effectively extend the battery's lifespan.

[0029] In this embodiment of the application, the negative electrode active material includes silicon-based materials.

[0030] In this embodiment of the application, the negative electrode includes a current collector and a layer of negative electrode active material attached to the current collector, wherein the layer of negative electrode active material includes the negative electrode active material and the binder.

[0031] The sixth aspect of this application provides a method for preparing a negative electrode of a battery, comprising:

[0032] A negative electrode active material, a binder, and a solvent are mixed to form a slurry, wherein the binder includes the polymer described in the first aspect of the embodiments of this application;

[0033] The slurry is coated onto the negative electrode current collector and then dried.

[0034] In this embodiment of the application, the solvent is water.

[0035] In this embodiment of the application, the negative electrode active material includes silicon-based materials.

[0036] In this embodiment of the application, the negative electrode active material further includes graphite. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the structure of a lithium-ion battery.

[0038] Figure 2 This is a schematic diagram of the polymer in an embodiment of this application.

[0039] Explanation of main component symbols

[0040] 100 Lithium-ion batteries

[0041] Positive electrode 10

[0042] Negative electrode 30

[0043] Diaphragm 50 Detailed Implementation

[0044] The embodiments of this application are described below with reference to the accompanying drawings.

[0045] Figure 1The secondary battery shown can be a lithium-ion battery, sodium-ion battery, potassium-ion battery, magnesium-ion battery, lithium-sulfur battery, etc. This application uses a lithium-ion battery as an example for illustration. The lithium-ion battery 100 mainly includes a positive electrode 10 containing positive electrode material, a negative electrode 30 containing negative electrode material, a separator 50, and an electrolyte (not shown, usually filling the pores of the positive electrode, negative electrode, and separator). During charging, lithium ions are extracted from the crystal lattice of the positive electrode material, pass through the electrolyte, and insert into the crystal lattice of the negative electrode material, making the negative electrode lithium-rich and the positive electrode lithium-poor. During discharging, lithium ions are extracted from the crystal lattice of the negative electrode material, pass through the electrolyte, and insert into the crystal lattice of the positive electrode material, making the positive electrode lithium-rich and the negative electrode lithium-poor. The difference in potential between the positive and negative electrode materials and metallic lithium during lithium ion insertion and extraction is the operating voltage of the battery.

[0046] When silicon-based materials are used for the negative electrode, the volume expansion and contraction that occurs during lithium insertion and extraction can easily lead to bonding failure as the cycle progresses, causing the negative electrode sheet and the cell to expand. In severe cases, this may even lead to safety hazards.

[0047] Existing aqueous binders with acrylonitrile copolymers as the main chain structure possess high adhesive strength and excellent chemical and electrochemical properties, exhibiting superior overall performance as binders for graphite anode materials. However, when used in silicon-based anodes, as the number of cycles increases, their rigid polymer chains cannot adapt to the periodic and significant volume changes of silicon particles. This leads to a gradual deterioration in the adhesion and constraint of the silicon particles, resulting in cracking of the anode sheet or peeling of the active material coating, ultimately causing battery failure.

[0048] Therefore, this application provides an adhesive that can be used in silicon-based anodes to meet the requirements of low cycle expansion and long cycle life of silicon-based anodes.

[0049] The adhesive includes polymers, such as... Figure 2 As shown, the polymer comprises a main chain and at least one side chain connecting the main chain. Each side chain has one end connected to the main chain and the other end connected to an organosilicon group. X1, X2, and X3 may be the same or different from each other, and are each independently selected from one of C1-C4 alkyl, hydroxyl, halogen atom, and C1-C4 alkoxy; and X1, X2, and X3 are not all alkyl, that is, at least one of X1, X2, and X3 is one of hydroxyl, halogen atom, and C1-C4 alkoxy.

[0050] The organosilicon groups connected to the side chains can form strong interactions with silicon particles (with silanol groups on their surface), thereby achieving multidimensional adhesion of the silicon particles. These strong interactions refer to the formation of strong physical or chemical bonds such as hydrogen bonds, ionic bonds, or covalent bonds between the organosilicon groups and the active silicon particles.

[0051] The main chain primarily comprises a water-soluble acrylonitrile copolymer. The acrylonitrile copolymer is an aqueous copolymer that can be uniformly dispersed in water and is polymerized from several monomers. The monomers of the acrylonitrile copolymer include acrylic acid monomers and acrylonitrile monomers. The acrylic acid monomers include at least one selected from acrylic acid, acrylates, methacrylic acid, and methacrylates, and the acrylonitrile monomers include at least one selected from acrylonitrile and methacrylonitrile. The acrylates and methacrylates are at least one selected from sodium salts, potassium salts, lithium salts, rubidium salts, and cesium salts, respectively.

[0052] The polymerizable monomers of the acrylonitrile copolymer may further include acrylamide monomers or epoxy-containing olefin monomers. That is, the acrylonitrile copolymer includes at least the following types: First, two types of polymerizable monomers, namely acrylic monomers and acrylonitrile monomers; second, three types of polymerizable monomers, namely at least one of acrylamide monomers and epoxy-containing olefin monomers, an acrylic monomer, and an acrylonitrile monomer. The acrylamide monomer is at least one of acrylamide, N-methylacrylamide, N-ethylacrylamide, N,N-dimethylacrylamide, N,N-diethylacrylamide, 2-methylacrylamide, N-hydroxymethylacrylamide, N-hydroxyethylacrylamide, and N-hydroxypropylacrylamide. The epoxy-containing olefin monomer may be at least one of glycidyl acrylate, glycidyl methacrylate, and allyl glycidyl ether. Introducing acrylamide monomers or epoxy-containing olefin monomers not only imparts other functions to the copolymer but also introduces amide groups or epoxy groups, facilitating the grafting of the side chains.

[0053] In this application, the side chain may contain alkane groups, alkoxy groups, or other chain segment structural units with stretchable characteristics. The side chain is grafted onto the main chain via chemical bonds. The side chain can stretch or compress, acting like a spring to buffer the large volume and stress changes of the silicon particles during charging and discharging.

[0054] The side chain can be a straight chain or contain branches. The side chain has ≥3 chain atoms, where the number of chain atoms refers to the total number of non-hydrogen atoms in the main chain of the side chain, excluding the number of non-hydrogen atoms in the branches, i.e., the total number of non-hydrogen atoms in the unbranched side chain, and excluding the number of atoms of the organosilicon groups attached to the ends. Studies have found that chain segments with ≥3 chain atoms can stretch and contract well to accommodate the periodic large volume changes of silicon particles during charging and discharging. The side chain does not contain silicon, but the ends of the side chain are connected to organosilicon groups containing silicon.

[0055] When the side chain is a straight chain, the number of chain atoms is the total number of C, O, N, S, etc. atoms in the side chain. When the side chain contains branches, the number of chain atoms is the total number of C, O, N, S, etc. atoms in the main chain of the side chain. For example, when the structural formula of the side chain is... When the chain has 6 atoms, the two ends of the main chain of the structure are respectively connected to the main chain of the polymer and the Si of the organosilicon group.

[0056] In some embodiments, the side chain has ≥5 chain atoms. In some embodiments, the side chain has 5 to 50 chain atoms. In other embodiments, the side chain has 5 to 20 chain atoms. In still other embodiments, the side chain has 5 to 15 chain atoms.

[0057] The polymer contains nitrile groups (-CN), and the weight percentage of the nitrile groups in the polymer is 4% to 30%. Preferably, the weight percentage of the nitrile groups in the polymer is 20% to 29%. The nitrile groups mainly originate from the main chain. When the side chain does not contain nitrile groups, all the nitrile groups originate from the main chain; when the side chain contains nitrile groups, the nitrile groups mainly originate from the main chain, with a small portion originating from the side chain.

[0058] The silicon element originates from the organosilicon groups attached to the side chains, and the weight percentage of silicon element in the polymer is 0.01% to 5%. In some embodiments, the weight percentage of silicon element in the polymer is 0.1% to 1%.

[0059] The structural formula of the side chain can be: At least one of the following; wherein, the two ends of the main chain of the side chain structure listed above are respectively connected to the main chain of the polymer and the Si of the organosilicon group. In this application, there is no specific limitation on which end is connected to the main chain of the polymer and which end is connected to the Si of the organosilicon group. For example, the left end of the main chain of the side chain structure is connected to the main chain of the polymer, and the right end is connected to the Si of the organosilicon group; or the right end of the main chain of the side chain structure is connected to the main chain of the polymer, and the left end is connected to the Si of the organosilicon group.

[0060] When X1, X2, and X3 are methoxy groups (CH3O-), then the organosilicon groups... Group is

[0061] When X1 and X2 are methoxy groups and X3 is a methyl (-CH3) group, then the organosilicon group... Group is

[0062] When X1, X2, and X3 are ethoxy groups (C2H5O-), then the organosilicon groups... Group is

[0063] When X1 and X2 are ethoxy groups and X3 is a methyl (-CH3) group, then the organosilicon group... Group is

[0064] The organosilicon group The group can be At least one of them.

[0065] The binder of this application introduces side chains into the main chain structure of a water-soluble acrylonitrile copolymer, and these side chains are connected to organosilicon groups. These organosilicon groups can form a strong anchoring interaction with silicon particles bearing silanol groups on their surface, thereby achieving multidimensional adhesion of the silicon particles. The rigid main chain of the polyacrylonitrile copolymer possesses high mechanical strength, maintaining the stability of the electrode's microstructure, while the stretchable side chains buffer the significant volume and stress changes of the silicon particles during charging and discharging. Simultaneously, the acrylonitrile copolymer in the main chain of this polymer, as a solid electrolyte component, exhibits excellent lithium-ion conductivity. Therefore, using the aqueous binder of this application as a binder for silicon-based anodes provides excellent adhesion and, to a certain extent, suppresses the significant volume changes of silicon particles during cycling, effectively maintaining the adhesion between the active material and the current collector. This effectively reduces the internal resistance of the electrode, inhibits electrode expansion, and extends the battery's lifespan.

[0066] The water-soluble binder of this application has less steric hindrance compared to the styrene-butadiene rubber (SBR) system. Furthermore, when the polymerizable monomer of the acrylonitrile copolymer includes acrylate monomers, and the acrylate monomers are lithium salts, the acrylonitrile copolymer contains lithium acrylate fragments, which can help lithium-ion conduction and improve the fast-charging performance and low-temperature performance of the system.

[0067] In the preparation of the polymer, the ratio of acrylic monomers to acrylonitrile monomers can be conventional in the art, as long as their water solubility is guaranteed. The binder composed of the polymer is water-soluble, so that the binder can be mixed more uniformly when added to the aqueous negative electrode slurry. In some embodiments, the weight ratio of acrylic monomers to acrylonitrile monomers is 1:(0.1-2.5). Preferably, the weight ratio of acrylic monomers to acrylonitrile monomers is 1:(0.8-2.0). In some embodiments, when the polymerizing monomers of the acrylonitrile copolymer also include acrylamide monomers or epoxy-containing olefin monomers, the weight ratio of acrylamide monomers or epoxy-containing olefin monomers, acrylic monomers, and acrylonitrile monomers is (0.1-2.5):1:(0.1-2.5), preferably (0.8-2.0):1:(0.8-2.0).

[0068] The polymer of this application can be prepared by conventional methods. For example, it can be formed by copolymerizing or grafting monomer raw materials.

[0069] This application also provides a negative electrode for a battery, comprising a negative electrode active material and the aforementioned binder. The negative electrode active material comprises a silicon-based material. In some embodiments, the negative electrode active material may further comprise graphite. The silicon-based material is an element or compound containing silicon, for example, selected from one or more of silicon-carbon, silicon suboxide, silicon oxide, ferrosilicon alloy, silicon nanowires, micron-sized silicon, nano-sized silicon, porous silicon, and silicon-germanium alloy. It is understood that the polymer described in this application is not limited to use as a binder for the negative electrode of a battery, but may also be used as a binder in other possible fields or products.

[0070] In some embodiments, the negative electrode includes a current collector and a layer of negative electrode active material attached to the current collector. The negative electrode active material layer includes a negative electrode active material, a conductive agent, and the aforementioned binder. The negative electrode active material includes silicon-based materials and graphite. The negative electrode can be manufactured using methods conventional in the art.

[0071] This application also provides a method for preparing a negative electrode, comprising: mixing the binder, negative electrode active material, and solvent described in this application to form a slurry; coating the slurry onto a negative electrode current collector and performing drying and compaction steps. The solvent is water. The negative electrode active material includes a silicon-based material, or contains both a silicon-based material and graphite. The negative electrode current collector may be copper foil. An appropriate amount of conductive agent is also added to the slurry.

[0072] This application also provides a lithium-ion battery, including a negative electrode, a positive electrode, and an electrolyte. The positive electrode and the electrolyte can be commonly used in the art. Preferably, the lithium-ion battery further includes a separator located between the negative electrode and the positive electrode. The separator can effectively prevent the positive and negative electrodes from contacting each other, thus preventing internal short circuits. It can also prevent larger molecules from passing through while allowing only small charged ions to pass, increasing the concentration difference near the positive and negative electrodes, which is beneficial for ion diffusion and thus improving the battery's storage efficiency. The separator uses a commonly used battery separator in the art. The negative electrode is the aforementioned negative electrode sheet. It is understood that the binder is not limited to lithium-ion battery systems but can also be used in other secondary battery systems, such as sodium-ion batteries, potassium-ion batteries, magnesium-ion batteries, lithium-sulfur batteries, etc.

[0073] This application also provides a battery pack including a plurality of the aforementioned lithium-ion batteries. The battery pack may comprise a battery module composed of multiple lithium-ion batteries. The plurality of lithium-ion batteries may be connected in series or in parallel.

[0074] The technical solutions of the embodiments of this application will be further described below through specific examples.

[0075] In Examples 1-14 and Comparative Examples 1-4 below, the parts of each raw material are by weight.

[0076] Example 1

[0077] Example 1 describes the preparation of a silicon-based anode binder by copolymerizing sodium acrylate, acrylonitrile, and 3-(acryloyloxy)propyltrimethoxysilane in an aqueous phase.

[0078] The preparation method is as follows: 40 parts of acrylic acid and 566 parts of distilled water are added to a reaction vessel and stirred to dissolve. The stirring speed is 300 r / min. Sodium hydroxide is added to adjust the pH value to 7-8. Acrylic acid will react with sodium hydroxide to generate sodium acrylate. Then, 58 parts of acrylonitrile and 2 parts of 3-(acryloyloxy)propyltrimethoxysilane are added. Nitrogen gas is introduced to remove oxygen for 30 min. The mixture is heated to 70℃, and then 0.05 parts of ammonium persulfate is added to initiate the reaction. After reacting for 9 h, a transparent silicon-based negative electrode binder is obtained.

[0079] Example 2

[0080] Example 2 describes the preparation of a silicon-based negative electrode binder by copolymerizing sodium methacrylate, acrylonitrile, and 3-(methacryloyloxy)propyltrimethoxysilane in an aqueous phase.

[0081] The preparation method is as follows: 45 parts of methacrylic acid and 566 parts of distilled water are added to a reaction vessel and stirred to dissolve. The stirring speed is 300 r / min. Sodium hydroxide is added to adjust the pH value to 7-8. Then, 53 parts of acrylonitrile and 2 parts of 3-(methacryloyloxy)propyltrimethoxysilane are added. Nitrogen gas is introduced to remove oxygen for 30 min. The mixture is heated to 70℃, and then 0.05 parts of ammonium persulfate is added to initiate the reaction. After reacting for 9 h, a transparent silicon-based negative electrode binder is obtained.

[0082] Example 3

[0083] Example 3 describes the preparation of a silicon-based negative electrode binder by copolymerizing sodium methacrylate, acrylonitrile, and 3-(methacryloyloxy)propylmethyldimethoxysilane in an aqueous phase.

[0084] The preparation method is as follows: 40 parts of methacrylic acid and 566 parts of distilled water are added to a reaction vessel and stirred to dissolve. The stirring speed is 300 r / min. Sodium hydroxide is added to adjust the pH value to 7-8. Then, 57 parts of acrylonitrile and 3 parts of 3-(methacryloyloxy)propylmethyldimethoxysilane are added. Nitrogen gas is introduced to remove oxygen for 30 min. The mixture is heated to 70℃, and then 0.05 parts of ammonium persulfate are added to initiate the reaction. After reacting for 9 h, a transparent silicon-based negative electrode binder is obtained.

[0085] Example 4

[0086] Example 4: Sodium methacrylate, acrylamide and acrylonitrile were first copolymerized in an aqueous phase, and then 3-glycidyl etheroxypropyltriethoxysilane was added to prepare a silicon-based negative electrode binder.

[0087] The preparation method is as follows: 35 parts of methacrylic acid and 566 parts of distilled water are added to a reaction vessel and stirred to dissolve. The stirring speed is 300 r / min. Sodium hydroxide is added to adjust the pH value to 7-8. Then, 52 parts of acrylonitrile and 10 parts of acrylamide are added. Nitrogen gas is introduced to remove oxygen for 30 min. The mixture is heated to 70℃. Then, 0.05 parts of ammonium persulfate are added to initiate the reaction. After the polymerization reaction has been going on for 9 h, 3 parts of 3-glycidyl etheroxypropyltriethoxysilane are added. The reaction is stirred for another 2 h to obtain the silicon-based negative electrode binder.

[0088] Example 5

[0089] Example 5: Sodium acrylate, acrylamide and acrylonitrile were first copolymerized in an aqueous phase, and then 3-glycidyl etheroxypropylmethyldimethoxysilane was added to prepare a silicon-based negative electrode binder.

[0090] The preparation method is as follows: 30 parts of acrylic acid and 566 parts of distilled water are added to a reaction vessel and stirred to dissolve. The stirring speed is 300 r / min. Sodium hydroxide is added to adjust the pH value to 7-8. Then, 55 parts of acrylonitrile and 10 parts of acrylamide are added. Nitrogen gas is introduced to remove oxygen for 30 min. The mixture is heated to 70℃. Then, 0.05 parts of ammonium persulfate are added to initiate the reaction. After the polymerization reaction has been going on for 9 h, 5 parts of 3-glycidyl etheroxypropylmethyldimethoxysilane are added. The reaction is continued to be stirred for 2 h to obtain the silicon-based negative electrode binder.

[0091] Example 6

[0092] Example 6: Sodium methacrylate, acrylamide and acrylonitrile were first copolymerized in an aqueous phase, and then 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane was added to prepare a silicon-based negative electrode binder.

[0093] The preparation method is as follows: 35 parts of methacrylic acid and 566 parts of distilled water are added to a reaction vessel and stirred to dissolve. The stirring speed is 300 r / min. Sodium hydroxide is added to adjust the pH value to 7-8. Then, 52 parts of acrylonitrile and 10 parts of acrylamide are added. Nitrogen gas is introduced to remove oxygen for 30 min. The mixture is heated to 70℃. Then, 0.05 parts of ammonium persulfate are added to initiate the reaction. After the polymerization reaction has been going on for 9 h, 3 parts of 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane are added. The reaction is stirred for another 2 h to obtain the silicon-based negative electrode binder.

[0094] Example 7

[0095] Example 7: Sodium acrylate, acrylonitrile and glycidyl methacrylate were first copolymerized in an aqueous phase, and then 3-aminopropyltriethoxysilane was added to prepare a silicon-based negative electrode binder.

[0096] The preparation method is as follows: 30 parts of acrylic acid and 566 parts of distilled water are added to a reaction vessel and stirred to dissolve. The stirring speed is 300 r / min. Sodium hydroxide is added to adjust the pH value to 7-8. Then, 55 parts of acrylonitrile and 10 parts of glycidyl methacrylate are added. Nitrogen gas is introduced to remove oxygen for 30 min. The mixture is heated to 70℃. Then, 0.05 parts of potassium persulfate are added to initiate the reaction. After the polymerization reaction has been going on for 9 h, 5 parts of 3-aminopropyltriethoxysilane are added. The reaction is continued to be stirred for 2 h to obtain the silicon-based negative electrode binder.

[0097] Example 8

[0098] Example 8: Sodium acrylate, acrylonitrile and glycidyl methacrylate were first copolymerized in an aqueous phase, and then 3-aminopropylmethyldiethoxysilane was added to prepare a silicon-based negative electrode binder.

[0099] The preparation method is as follows: 35 parts of acrylic acid and 566 parts of distilled water are added to a reaction vessel and stirred to dissolve. The stirring speed is 300 r / min. Sodium hydroxide is added to adjust the pH value to 7-8. Then, 52 parts of acrylonitrile and 8 parts of glycidyl methacrylate are added. Nitrogen gas is introduced to remove oxygen for 30 min. The mixture is heated to 70℃. Then, 0.05 parts of potassium persulfate are added to initiate the reaction. After the polymerization reaction has been going on for 9 h, 5 parts of 3-aminopropylmethyldiethoxysilane are added. The reaction is stirred for another 2 h to obtain the silicon-based negative electrode binder.

[0100] Example 9

[0101] Example 9: Sodium methacrylate, acrylonitrile and allyl glycidyl ether were first copolymerized in an aqueous phase, and then 3-diethylenetriaminopropylmethyldimethoxysilane was added to prepare a silicon-based negative electrode binder.

[0102] The preparation method is as follows: 40 parts of methacrylic acid and 566 parts of distilled water are added to a reaction vessel and stirred to dissolve. The stirring speed is 300 r / min. Sodium hydroxide is added to adjust the pH value to 7-8. Then, 48 parts of acrylonitrile and 8 parts of allyl glycidyl ether are added. Nitrogen gas is introduced to remove oxygen for 30 min. The mixture is heated to 70℃. Then, 0.05 parts of potassium persulfate are added to initiate the reaction. After the polymerization reaction has been going on for 9 h, 4 parts of 3-diethylenetriaminopropylmethyldimethoxysilane are added. The reaction is continued to be stirred for 2 h to obtain the silicon-based negative electrode binder.

[0103] Example 10

[0104] Example 10 describes the preparation of a silicon-based anode binder by copolymerizing lithium acrylate, acrylonitrile, and 3-(acryloyloxy)propyltrimethoxysilane in an aqueous phase.

[0105] The preparation method is as follows: 40 parts of acrylic acid and 566 parts of distilled water are added to a reaction vessel and stirred to dissolve. The stirring speed is 300 r / min. Lithium hydroxide is added to adjust the pH value to 7-8. Acrylic acid will react with lithium hydroxide to generate lithium acrylate. Then, 58 parts of acrylonitrile and 2 parts of 3-(acryloyloxy)propyltrimethoxysilane are added. Nitrogen gas is introduced to remove oxygen for 30 min. The mixture is heated to 70℃, and then 0.05 parts of ammonium persulfate is added to initiate the reaction. After reacting for 9 h, a transparent silicon-based negative electrode binder is obtained.

[0106] Example 11

[0107] Example 11: Lithium acrylate, acrylamide, and acrylonitrile were first copolymerized in an aqueous phase, and then 3-glycidyl etheroxypropylmethyldimethoxysilane was added to prepare a silicon-based negative electrode binder.

[0108] The preparation method is as follows: 30 parts of acrylic acid and 566 parts of distilled water are added to a reaction vessel and stirred to dissolve. The stirring speed is 300 r / min. Lithium hydroxide is added to adjust the pH value to 7-8. Then, 55 parts of acrylonitrile and 10 parts of acrylamide are added. Nitrogen gas is introduced to remove oxygen for 30 min. The mixture is heated to 70℃. Then, 0.05 parts of ammonium persulfate are added to initiate the reaction. After the polymerization reaction has been going on for 9 h, 5 parts of 3-glycidyl etheroxypropylmethyldimethoxysilane are added. The reaction is continued to be stirred for 2 h to obtain the silicon-based negative electrode binder.

[0109] Example 12

[0110] Example 12: First, lithium acrylate, acrylonitrile, and glycidyl methacrylate were copolymerized in an aqueous phase, and then 3-aminopropyltriethoxysilane was added to prepare a silicon-based negative electrode binder.

[0111] The preparation method is as follows: 30 parts of acrylic acid and 566 parts of distilled water are added to a reaction vessel and stirred to dissolve. The stirring speed is 300 r / min. Lithium hydroxide is added to adjust the pH value to 7-8. Then, 55 parts of acrylonitrile and 10 parts of glycidyl methacrylate are added. Nitrogen gas is introduced to remove oxygen for 30 min. The mixture is heated to 70℃. Then, 0.05 parts of potassium persulfate are added to initiate the reaction. After the polymerization reaction has been going on for 9 h, 5 parts of 3-aminopropyltriethoxysilane are added. The reaction is continued to be stirred for 2 h to obtain the silicon-based negative electrode binder.

[0112] Example 13

[0113] Example 13 describes the preparation of a silicon-based anode binder by copolymerizing lithium methacrylate, acrylonitrile, and 3-(methacryloyloxy)propyltrimethoxysilane in an aqueous phase.

[0114] The preparation method is as follows: 45 parts of methacrylic acid and 566 parts of distilled water are added to a reaction vessel and stirred to dissolve. The stirring speed is 300 r / min. Lithium hydroxide is added to adjust the pH value to 7-8. Then, 53 parts of acrylonitrile and 2 parts of 3-(methacryloyloxy)propyltrimethoxysilane are added. Nitrogen gas is introduced to remove oxygen for 30 min. The mixture is heated to 70℃, and then 0.05 parts of ammonium persulfate are added to initiate the reaction. After reacting for 9 h, a transparent silicon-based negative electrode binder is obtained.

[0115] Example 14

[0116] Example 14: First, lithium methacrylate, acrylonitrile, and allyl glycidyl ether were copolymerized in an aqueous phase, and then 3-diethylenetriaminopropylmethyldimethoxysilane was added to prepare a silicon-based negative electrode binder.

[0117] The preparation method is as follows: 40 parts of methacrylic acid and 566 parts of distilled water are added to a reaction vessel and stirred to dissolve. The stirring speed is 300 r / min. Lithium hydroxide is added to adjust the pH value to 7-8. Then, 48 parts of acrylonitrile and 8 parts of allyl glycidyl ether are added. Nitrogen gas is introduced to remove oxygen for 30 min. The mixture is heated to 70℃. Then, 0.05 parts of potassium persulfate are added to initiate the reaction. After the polymerization reaction has been going on for 9 h, 4 parts of 3-diethylenetriaminopropylmethyldimethoxysilane are added. The reaction is stirred for another 2 h to obtain the silicon-based negative electrode binder.

[0118] Comparative Example 1

[0119] Comparative Example 1 prepared a silicon-based negative electrode binder by copolymerizing sodium acrylate, acrylonitrile, and vinyltrimethoxysilane in an aqueous phase.

[0120] The preparation method is as follows: 40 parts of acrylic acid and 566 parts of distilled water are added to a reaction vessel and stirred to dissolve. The stirring speed is 300 r / min. Sodium hydroxide is added to adjust the pH value to 7-8. Then, 58 parts of acrylonitrile and 2 parts of vinyltrimethoxysilane are added. Nitrogen gas is introduced to remove oxygen for 30 min. The mixture is heated to 70℃, and then 0.05 parts of ammonium persulfate are added to initiate the reaction. After reacting for 9 h, a silicon-based negative electrode binder is obtained.

[0121] Comparative Example 2

[0122] Comparative Example 2: Sodium acrylate and acrylonitrile were first copolymerized in an aqueous phase, and then 3-(acryloyloxy)propyltrimethoxysilane was added for blending to prepare a silicon-based negative electrode binder.

[0123] The preparation method is as follows: 40 parts of acrylic acid and 566 parts of distilled water are added to a reaction vessel and stirred to dissolve. The stirring speed is 300 r / min. Sodium hydroxide is added to adjust the pH value to 7-8. Then 58 parts of acrylonitrile are added, nitrogen gas is introduced to remove oxygen for 30 min, and the mixture is heated to 70℃. Then 0.05 parts of ammonium persulfate are added to initiate the reaction. After the polymerization reaction is stopped for 9 h, 2 parts of 3-(acryloyloxy)propyltrimethoxysilane are added, and the mixture is stirred evenly to obtain the silicon-based negative electrode binder.

[0124] Comparative Example 3

[0125] Comparative Example 3 prepared a silicon-based anode binder by copolymerizing lithium acrylate, acrylonitrile and vinyltrimethoxysilane in an aqueous phase.

[0126] The preparation method is as follows: 40 parts of acrylic acid and 566 parts of distilled water are added to a reaction vessel and stirred to dissolve. The stirring speed is 300 r / min. Lithium hydroxide is added to adjust the pH value to 7-8. Then, 58 parts of acrylonitrile and 2 parts of vinyltrimethoxysilane are added. Nitrogen gas is introduced to remove oxygen for 30 min. The mixture is heated to 70℃, and then 0.05 parts of ammonium persulfate are added to initiate the reaction. After reacting for 9 h, a silicon-based negative electrode binder is obtained.

[0127] Comparative Example 4

[0128] Comparative Example 4 first copolymerized lithium acrylate and acrylonitrile in an aqueous phase, and then added 3-(acryloyloxy)propyltrimethoxysilane for blending to prepare a silicon-based negative electrode binder.

[0129] The preparation method is as follows: 40 parts of acrylic acid and 566 parts of distilled water are added to a reaction vessel and stirred to dissolve. The stirring speed is 300 r / min. Lithium hydroxide is added to adjust the pH value to 7-8. Then 58 parts of acrylonitrile are added, nitrogen gas is introduced to remove oxygen for 30 min, and the mixture is heated to 70℃. Then 0.05 parts of ammonium persulfate are added to initiate the reaction. After the polymerization reaction is stopped for 9 h, 2 parts of 3-(acryloyloxy)propyltrimethoxysilane are added and stirred evenly to obtain the silicon-based negative electrode binder.

[0130] The silicon anode lithium-ion battery is prepared using the following method:

[0131] Using water as a solvent, 0.95 parts by weight of a composite anode active material of silicon suboxide and graphite, 0.02 parts by weight of a conductive agent (carbon black, SP), and 0.03 parts by weight of the silicon-based anode binder prepared in the above examples and comparative examples (mass parts are based on the solid content after complete drying) were mixed, stirred, and ground to prepare a cathode slurry. After adjusting the solid content of the slurry to 50%, it was uniformly coated on copper foil, and then dried, compacted, and stamped to obtain a cathode sheet. The obtained cathode sheet was vacuum dried at 100±5℃ for 24 hours, and then placed in a glove box under a dry argon atmosphere. A coin cell was assembled using a lithium metal sheet as the counter electrode. The separator was a polyolefin microporous membrane, and the electrolyte was a commercially available silicon-based anode lithium-ion battery electrolyte.

[0132] The silicon anode lithium-ion batteries prepared using the binders in Examples 1-14 above are numbered A1-A14, and the silicon anode lithium-ion batteries prepared using the binders in Comparative Examples 1-4 are numbered C1-C4. The silicon anode lithium-ion batteries prepared above were subjected to charge-discharge tests at 25°C, and their performance is shown in the table.

[0133]

[0134]

[0135] As shown in the table above, the silicon anode lithium-ion batteries prepared using the binders described in Examples 1 to 14 exhibit excellent cycle performance, with a capacity retention rate of 90% or higher after 50 charge-discharge cycles, significantly outperforming the lithium-ion batteries prepared using the silicon anodes in Comparative Examples 1 to 4. In Comparative Examples 2 and 4, the silane coupling agents added did not chemically graft onto the binder backbone to form side chains, while the silane coupling agents used in Comparative Examples 1 and 3, after copolymerization with the backbone monomers, did not contain side chains, resulting in insufficient side chain extensibility. Therefore, the binders in the comparative examples could not effectively stabilize the electrode structure during the charge-discharge process of the silicon anode lithium-ion batteries, thus causing differences in cycle performance.

[0136] It should be noted that the above are merely specific embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Where there is no conflict, the embodiments and features described in the embodiments of this application can be combined with each other. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A polymer for use as a binder for a negative electrode of a battery, characterized in that, Comprising: a main chain mainly comprising a water-soluble acrylonitrile copolymer, polymerized monomers of the acrylonitrile copolymer comprising at least one of an acrylic monomer and an acrylonitrile monomer; side chain, one end of which is connected to the main chain and the other end of which is connected to an organosilicon group X1, X2, and X3 are each independently selected from one of C1-C4 alkyl, hydroxyl, halogen atom, C1-C4 alkoxy, and X1, X2, and X3 are not simultaneously alkyl, the side chain does not contain a silicon element, and the end of the side chain is connected to the organosilicon group; the number of chain atoms of the side chain is ≥ 5, the number of chain atoms being the total number of non-hydrogen atoms in the non-branched chain of the side chain, and excluding the number of atoms of the organosilicon group connected at the end.

2. The polymer of claim 1, wherein The weight percentage of nitrile groups contained in the polymer in the polymer is 4% to 30%; the weight percentage of silicon element in the polymer is 0.01% to 5%.

3. The polymer according to claim 1 or 2, characterized in that, The weight percentage of nitrile groups contained in the polymer in the polymer is 20% to 29%.

4. The polymer of claim 1, wherein The weight percentage of silicon element in the polymer is 0.1% to 1%.

5. The polymer of claim 1, wherein The acrylic monomer comprises at least one of acrylic acid, acrylic acid salt, methacrylic acid and methacrylic acid salt, and the acrylic acid salt and the methacrylic acid salt are at least one of sodium salt, potassium salt, lithium salt, rubidium salt and cesium salt.

6. The polymer of claim 1, wherein The acrylonitrile monomer comprises at least one of acrylonitrile and methacrylonitrile.

7. The polymer of claim 1, wherein The polymerized monomers of the acrylonitrile copolymer further comprise acrylamide monomers or epoxy-containing olefin monomers.

8. The polymer of claim 7, wherein, The acrylamide monomer is at least one of acrylamide, N-methyl acrylamide, N-ethyl acrylamide, N,N-dimethyl acrylamide, N,N-diethyl acrylamide, 2-methyl acrylamide, N-hydroxymethyl acrylamide, N-hydroxyethyl acrylamide and N-hydroxypropyl acrylamide; and the epoxy-containing olefin monomer is at least one of glycidyl acrylate, glycidyl methacrylate and allyl glycidyl ether.

9. The polymer of claim 1, wherein a structure formula of the side chain is , , , , , , , , and ; wherein, two ends of the main chain of the structure formula of the side chain are connected with the main chain of the polymer and Si of the organosilicon group respectively.

10. A binder comprising the polymer of any one of claims 1 to 9.

11. The binder of claim 10, wherein, The binder is a binder for a negative electrode of a battery.

12. Use of the polymer of any one of claims 1 to 9 as a binder.

13. A negative electrode of a battery comprising a negative electrode active material and a binder, characterized by, The binder comprises the polymer of any one of claims 1 to 9.

14. The negative electrode of claim 13, wherein The negative electrode active material comprises a silicon-based material.

15. The negative electrode of claim 13, wherein The negative electrode comprises a current collector and a negative electrode active material layer attached to the current collector, and the negative electrode active material layer comprises the negative electrode active material and the binder.

16. A secondary battery comprising a negative electrode, a positive electrode, and an electrolyte, characterized by The negative electrode comprises a negative electrode active material and a binder, wherein the binder comprises the polymer of any one of claims 1 to 9.

17. The secondary battery according to claim 16, characterized by The negative electrode active material comprises a silicon-based material.

18. The secondary battery according to claim 16, characterized by The negative electrode comprises a current collector and a negative electrode active material layer attached to the current collector, and the negative electrode active material layer comprises the negative electrode active material and the binder.

19. A method of producing a negative electrode of a battery, characterized by, Comprising: mixing a negative electrode active material, a binder, and a solvent to form a slurry, the binder comprising the polymer of any one of claims 1 to 9; coating the slurry on a negative electrode current collector and drying.

20. The method of producing a negative electrode of a battery according to claim 19, wherein The solvent is water.

21. The method of producing a negative electrode of a battery according to claim 19, wherein The negative electrode active material comprises a silicon-based material.

22. The method of producing a negative electrode of a battery according to claim 21, wherein The negative electrode active material further comprises graphite.

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