Two-component negative electrode binder and use method thereof

Abstract

The invention relates to the technical field of lithium battery negative electrode binders, in particular to a two-component negative electrode binder and a using method thereof.The two-component negative electrode binder comprises a component A and a component B. The component A is formed by copolymerization of acrylamide substances, fluorinated acrylate substances and acrylic acid, and the component B is formed by copolymerization of fluorinated acrylate substances and acrylic acid. The component B is formed by copolymerizing acrylic acid, acrylate, a fluorinated acrylate substance, an acrylamide substance and sulfydryl acrylate, and the component A accounts for 30wt%-70wt% of a mixture of the component A and the component B during use; when the adhesive is used for preparing the negative electrode slurry, a glue solution A and a glue solution B are prepared respectively, the glue solution A is added after the solid raw materials are subjected to dry mixing, the glue solution B is added after the solid raw materials are fully stirred, and finally the leveling aid is added. The two-component negative electrode binder provided by the invention has both rigidity and softness, strong binding power with a main material, strong self-adaptive expansion capability, high release force retention rate after long circulation, and good interface stability.

Description

Technical Field

[0001] This invention relates to the field of lithium battery negative electrode binder technology, and in particular to a two-component negative electrode binder and its application method. Background Technology

[0002] Silicon-based anodes are considered next-generation lithium-ion battery materials due to their ultra-high theoretical specific capacity (4200 mAh / g, 10 times that of graphite anodes). However, silicon undergoes a volume expansion of up to 300% during charging and discharging, leading to electrode material pulverization, SEI film rupture, detachment of active material from current collector, cracking and peeling forces, and ultimately damage to the conductive network. As a key component for maintaining electrode integrity, the binder must possess high adhesion, flexibility, and interfacial stability.

[0003] Traditional negative electrode binders, such as PVDF, have low elastic modulus and rely solely on van der Waals forces for bonding. They cannot withstand the expansion stress of silicon, leading to easy cracking and detachment of the electrode after cycling. Newer elastic binders, such as PAA, SBR, and CMC, offer some improvement, but struggle to balance bond strength with ionic and electronic conductivity. Existing technologies also employ two-component negative electrode binders, where component A is a polymeric adhesive and component B is a crosslinking agent. During use, components A and B are mixed in a specific ratio, and heating or light exposure forms a more stable network structure to meet the requirements of highly expandable negative electrodes such as silicon-based anodes. While two-component negative electrode binders exhibit good bonding performance, the amount of crosslinking agent added is strictly limited. Even slight deviations result in unstable crosslinking effects, weakening interfacial adhesion and causing peel strength to drop faster than with single-component binders.

[0004] Therefore, this application is submitted. Summary of the Invention

[0005] Based on the background technology, the present invention provides a two-component negative electrode binder and its application method, aiming to solve the problems of unstable crosslinking effect and low peel force retention rate after long cycle of existing two-component negative electrode binders.

[0006] To achieve the above objectives, the main technical solutions adopted by the present invention include:

[0007] On the one hand, the present invention proposes a two-component negative electrode binder, comprising component A and component B;

[0008] Component A is copolymerized from the following components in the following proportions: 75wt%-80wt% acrylamide, 5wt%-15wt% fluoroacrylate and 5wt%-15wt% acrylic acid;

[0009] Component B is copolymerized from the following components in the following proportions: 30wt%-50wt% acrylic acid, 30wt%-50wt% acrylate, 5wt%-10wt% fluoroacrylate, 5wt%-10wt% acrylamide, and 0.1wt%-5wt% mercaptoacrylate.

[0010] When used, component A accounts for 30wt%-70wt% of the mixture of component A and component B.

[0011] Component A, primarily composed of acrylamide, is the flexible component in the negative electrode binder. Its main function is to bind the active particles of the negative electrode. It can form strong coordination bonds with the hydroxyl groups on the surface of the silicon-based negative electrode, resulting in a tight bond. While accommodating the volume expansion of the silicon-based negative electrode, it can also dynamically repair microcracks and interface debonding problems generated during charging and discharging. Component B, primarily composed of acrylic acid and acrylates, is the rigid component in the negative electrode binder. Its main function is to inhibit the expansion of the silicon-based negative electrode. It forms the skeleton structure of the negative electrode binder, providing appropriate mechanical strength and reducing the breakage of the active particles. Figure 1 As shown: Component A is tightly bonded to the negative electrode active particles, while component B is combined with component A through intermolecular interactions. Its rigidity is used to suppress silicon-based expansion. This combination of rigidity and flexibility in the molecular design achieves a dynamic balance between the flexibility and mechanical strength of the negative electrode binder, ensuring both a tight connection with the negative electrode material and adapting to and limiting the expansion of the silicon-based negative electrode. Furthermore, the addition of a certain amount of hydrophobic fluorinated acrylates to components A and B reduces the affinity of acrylamide-based substances for water molecules, making the moisture content of the negative electrode sheet easier to control.

[0012] It should be noted that the preparation methods of components A and B are not limited. For example, this invention employs a micro-suspension polymerization method, specifically as follows: Each polymerization raw material is added to an aqueous ethanol solvent (water to ethanol volume ratio 7:3) in proportion, followed by the addition of an emulsifier and dispersant, and stirring to obtain a suspension; the suspension is heated and an initiator is added dropwise while stirring, and polymerization is carried out under a nitrogen atmosphere; the mixture is then filtered, washed, dried, pulverized, and sieved; wherein: the emulsifier is at least one of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, Span 80, and Tween 20; the dispersant is at least one of polyvinylpyrrolidone, polyvinyl alcohol, hydroxypropyl cellulose, gelatin, and polyacrylate; the initiator is one of potassium persulfate, sodium persulfate, azobisisobutyronitrile, azobisisoheptanenitrile, and dimethyl azobisisobutyrate; the initiator is added at a mass of 0.3%-1% of the total monomer mass; the polymerization temperature is 60-80℃, and the polymerization time is 8-12 hours.

[0013] Furthermore, before use, component A and component B are respectively modified with end groups to introduce carbon-carbon double bonds; preferably, the carbon-carbon double bonds are selected from allyl or fumarate groups.

[0014] In addition to intermolecular interactions, components A and B can also undergo secondary processing of the negative electrode binder by introducing carbon-carbon double bonds into their end groups and subsequently adding an initiator to activate their activity through a cross-linking reaction: (1) Secondary processing enables the flexible component A and the rigid component B to form a "soft-hard" interpenetrating network. The rigid component maintains the skeleton structure, limits excessive deformation, and prevents electrode pulverization, while the flexible component absorbs the stress caused by the volume expansion of the silicon-based negative electrode. The synergistic effect further enhances the interfacial stability; (2) Secondary processing forms a porous structure, which can promote electrolyte wetting and facilitate more uniform distribution of conductive materials, reduce interfacial impedance, and ultimately optimize ion / electron conduction. Therefore, secondary processing can further improve the overall performance of the two-component negative electrode binder.

[0015] It should be noted that since the negative electrode binder needs to be dissolved in a solvent to form an adhesive solution, the crosslinking density involved in secondary processing should not be too high. Excessive crosslinking density may sacrifice the density of polar groups, weakening interfacial adhesion. Allyl and fumarate groups are relatively mild, with moderate crosslinking densities. Through repeated experiments, this invention has found that when components A and B are end-modified with allyl or fumarate groups, the crosslinking modification effect is good, helping to balance the elasticity and strength of the crosslinked product, further improving interfacial adhesion and enhancing interfacial stability after long-term cycling.

[0016] Furthermore, before use, allyl bromide reagent is used to modify the end groups of component A and component B to introduce allyl groups. There are many methods for introducing allyl groups through end group modification, all of which are existing technologies. Exemplarily, in this technical solution, allyl bromide reagent is used for end group modification.

[0017] Furthermore, the molecular weight of component A is 10w-15w, and the molecular weight of component B is 15w-25w.

[0018] The raw materials and their contents specified in the above technical solution are copolymerized to obtain component A with a molecular weight of 10w-15w and component B with a molecular weight of 15w-25w. The combination of the two is more suitable for silicon-based anodes. The low molecular weight component A can fully penetrate into the electrode pores, ensuring full coverage of the active material and reducing the viscosity of the slurry, resulting in more uniform coating. The high molecular weight component B forms the framework, firmly locking in the anode active particles and ensuring that they do not crack during cycling. The combination of components A and B within the above molecular weight range is easy to process, has good wettability, and exhibits good anti-swelling effect after drying.

[0019] Furthermore, the glass transition temperature of the two-component negative electrode binder is 80-110℃.

[0020] Furthermore, the acrylamides in both component A and component B are arbitrarily selected from one or more of acrylamide, N-methylacrylamide, N-ethylacrylamide, and N-phenylacrylamide; the fluorinated acrylates in both component A and component B are arbitrarily selected from one or more of trifluoroethyl methacrylate, trifluoroethyl acrylate, propyl tetrafluoroacrylate, propyl tetrafluoromethacrylate, butyl hexafluoroacrylate, butyl hexafluoromethacrylate, octafluoropentyl acrylate, octafluoropentyl methacrylate, isobutyl octafluoroacrylate, n-heptyl dodecyl acrylate, heptyl dodecyl methacrylate, perfluorooctyl ethyl acrylate, perfluorooctyl ethyl methacrylate, perfluorohexyl ethyl acrylate, perfluorohexyl ethyl methacrylate, p-trifluoromethylphenyl acrylate, p-trifluoromethylphenyl methacrylate, perfluoropolyether acrylate, and fluorocyclohexyl acrylate.

[0021] The mercaptoacrylate is selected from mercaptopolyethylene glycol acrylate and / or mercaptomethacrylate.

[0022] On the other hand, the present invention also proposes a method for using a two-component negative electrode binder, wherein component A and component B are dissolved in an aqueous solvent to prepare adhesive solution A and adhesive solution B respectively; when preparing the negative electrode slurry, after the solid raw materials are dry mixed, adhesive solution A is added first, and after thorough stirring, adhesive solution B is added, and finally a leveling agent is added.

[0023] In use, the solid raw materials in the negative electrode main material, such as the negative electrode active material and conductive agent, are dry-mixed in proportion. Then, adhesive solution A is added first, and the mixture is stirred thoroughly to allow component A to interact with the silicon-based negative electrode surface. Next, adhesive solution B is added, and component B then interacts with component A. This order of addition prevents excessive interaction between component B and component A, which would occupy more active sites in component A, and weakens the interaction between component A and the silicon-based negative electrode surface.

[0024] It should be noted that the aqueous solvents mentioned here include, but are not limited to, water, alcohol, water-alcohol mixtures, N-methylpyrrolidone, and dimethyl sulfoxide.

[0025] Furthermore, secondary processing can employ either heat treatment crosslinking or photo-initiated crosslinking.

[0026] When using heat treatment crosslinking, a crosslinking agent and triethylamine are also added to the negative electrode slurry. After the negative electrode slurry is coated onto the negative electrode current collector, it undergoes high-temperature treatment under nitrogen protection. For example, PETMP (pentaerythritol tetrakis(3-mercaptopropionic acid) ester) is used as the crosslinking agent, with an addition amount of 2wt%-3.5wt% of the negative electrode binder. The high-temperature treatment conditions are 80-100℃ for 5-15 minutes. Another example is PEGDA (polyethylene glycol diacrylate) as the crosslinking agent, with an addition amount of 0.5wt%-1.5wt% of the two-component negative electrode binder. The high-temperature treatment conditions are 105-110℃ for 8-12 minutes. The above heat treatment crosslinking is only illustrative; other types of crosslinking agents can also be used.

[0027] When photo-initiated crosslinking is used, for example: a photoinitiator is also added to the negative electrode slurry. After the negative electrode slurry is coated onto the negative electrode current collector, it is subjected to photo-irradiation under nitrogen protection. For example, Irgacure 2959 (full name 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylphenylacetone) is used as the photoinitiator, and its addition amount is 0.1wt%-1wt% of the two-component negative electrode binder. It is irradiated with ultraviolet light with a wavelength of 365nm or 405nm and a light intensity of 50-200mW / cm². 2 Irradiate for 5 seconds to 10 minutes. The above photoinitiated crosslinking is only an example; other types of photoinitiators can also be used.

[0028] Furthermore, the leveling agent is selected from one of polyether-modified polysiloxane, polyester-modified polysiloxane, and reactive organosilicon, such as polyether-modified polydimethylsiloxane, to improve the overall performance of the negative electrode slurry and enhance its smoothness after coating; the leveling aid accounts for 0.1wt%-1wt% of the negative electrode slurry.

[0029] Compared with existing technologies, this invention uses a flexible-rigid molecular design to divide the negative electrode binder into flexible and rigid components. These two components are combined in a specific ratio and bonded together through intermolecular interactions, achieving both strong adhesion to the negative electrode substrate and adapting to and rigidly restricting the expansion of the silicon-based negative electrode. Furthermore, carbon-carbon double bond modification of the end groups of both components, through crosslinking modification, dynamically adjusts the flexibility and mechanical strength of the negative electrode binder, further enhancing its overall performance. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 This is a schematic diagram of the bonding between the two-component negative electrode binder and the negative electrode active material proposed in this invention, wherein: 1, negative electrode active material; 2, component A; 3, component B. Detailed Implementation

[0032] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0033] All chemical raw materials used in the following examples and comparative examples were commercially available, and all apparatuses and operations involved were conventional in the art. All testing methods involved were conventional in the art.

[0034] In the following embodiments and comparative examples:

[0035] The specific preparation method of component A is as follows: fluorinated acrylates, acrylamides and acrylic acid are added to a mixed solvent of water and ethanol in a volume ratio of 7:3 in proportion, followed by the addition of Tween 20 and polyacrylate and stirring to obtain a suspension; the suspension is heated to 75°C and potassium persulfate initiator of 0.5% of the total mass of monomers is added dropwise, and polymerization is carried out under a nitrogen atmosphere for 12 hours while stirring; the mixture is then filtered, washed, dried, pulverized and sieved.

[0036] The specific preparation method of component B is as follows: Fluoroacrylate, mercaptoacrylate, acrylamide, acrylic acid and acrylate are added to a mixed solvent of water and ethanol in a volume ratio of 7:3 in proportion. Then sodium dodecylbenzenesulfonate and polyvinyl alcohol are added and stirred to obtain a suspension. The suspension is heated to 80°C and 0.8% of the total mass of monomers of initiator azobisisobutyronitrile is added dropwise. Polymerization is carried out under a nitrogen atmosphere for 12 hours while stirring. The mixture is then filtered, washed, dried, pulverized and sieved.

[0037] The specific procedure for introducing an allyl group at the end of component A is as follows: Dissolve component A in a DMF / THF (volume ratio 9:1) mixed solvent and stir at 60°C until completely dissolved. Then, under nitrogen protection, add triethylamine and allyl bromide dropwise, with 1.3 ml of allyl bromide and 3.6 ml of triethylamine added for every 1 g of component A. After the addition is complete, the reaction is carried out at 60°C under nitrogen protection, with magnetic stirring and in the dark for 12 h. After the reaction is completed, the mixture is cooled in an ice bath and a small amount of methanol is added to quench any unreacted allyl bromide. Then, the product with a molecular weight cutoff of 3.5 kDa is retained by dialysis with deionized water and washed multiple times with ethanol and dried under vacuum.

[0038] The specific operation method for introducing allyl groups at the end of component B is the same as above, but the amount of raw materials added is adjusted. 0.6 ml of allyl bromide and 1.7 ml of triethylamine are added for every 1 g of component B.

[0039] Example 1

[0040] A two-component negative electrode binder comprises 45% by mass of component A and 55% by mass of component B. Component A is copolymerized from the following components in the following amounts: 80 wt% acrylamide, 10 wt% trifluoroethyl methacrylate and 10 wt% acrylic acid. Component B is copolymerized from the following components in the following amounts: 40 wt% acrylic acid, 40 wt% acrylate, 8 wt% trifluoroethyl methacrylate, 8 wt% acrylamide and 4 wt% mercaptopolyethylene glycol acrylate.

[0041] After allyl modification of the end groups of components A and B, they are used to prepare negative electrode slurry and negative electrode sheet. The specific operation is as follows: (1) Allyl-modified component A and allyl-modified component B are dissolved in deionized water to prepare adhesive solution A with a solid content of 10% and adhesive solution B with a solid content of 8%; (2) Silicon carbon and graphite are mixed at a mass ratio of 3:7 to obtain negative electrode active material and dry-mixed with conductive carbon. Then adhesive solution A is added first, and adhesive solution B is added after thorough stirring. After thorough stirring again, leveling agent polyether-modified polydimethylsiloxane is added. After stirring evenly again, negative electrode slurry is obtained. The mass ratio of negative electrode active material, conductive agent graphite, and two-component negative electrode binder is 96:1:3. The mass percentage of polyether-modified polydimethylsiloxane in the negative electrode slurry is 0.8%; (3) 0.5wt% of Irgacure negative electrode binder is added to the negative electrode slurry. 2959 and stir evenly; (4) Use NMP solvent to adjust the solid content of the product from the previous step to 45% and coat it on the copper current collector and use a wavelength of 365nm and a light intensity of 150mW / cm. 2 The sample was irradiated with ultraviolet light for 6 minutes, followed by multi-stage drying (including five temperature zones: zone 1 at 82℃, zone 2 at 95℃, zone 3 at 98℃, zone 4 at 100℃, and zone 5 at 85℃), and then rolled to obtain a compacted density of 1.65 g / cm³. 3 The negative electrode sheet.

[0042] The above negative electrode sheets are baked and then assembled into a soft-pack battery: active material lithium cobalt oxide, binder PVDF, and conductive graphite are mixed evenly in a ratio of 97wt%:1wt%:2wt% to form a positive electrode slurry, which is then coated on an aluminum current collector and dried, rolled, and slit to obtain a positive electrode sheet; the electrolyte is a 1M LiPF6 solution (the solvent is EC, DMC, and EMC in a volume ratio of 1:1:1, and 1.5v% FEC is added as a film-forming aid); the separator is a high-strength PP-based ceramic-coated separator, and the ceramic coating is specifically alumina with a thickness of 1μm; the positive electrode sheet, separator, and negative electrode sheet are stacked in sequence to form a cell, which is then placed in an aluminum-plastic film, injected with electrolyte, and sealed to obtain a soft-pack battery.

[0043] Example 2

[0044] Compared with Example 1, the ratio of component A to component B has been adjusted. Specifically, the mass percentage of component A is 30% and the mass percentage of component B is 70%, while the rest remains the same as in Example 1.

[0045] Example 3

[0046] Compared with Example 1, the ratio of component A to component B has been adjusted, specifically: the mass percentage of component A is 35% and the mass percentage of component B is 65%, while the rest remains the same as in Example 1.

[0047] Example 4

[0048] Compared with Example 1, the ratio of component A to component B has been adjusted. Specifically, the mass percentage of component A is 50% and the mass percentage of component B is 50%, while the rest remains the same as in Example 1.

[0049] Example 5

[0050] Compared with Example 1, the ratio of component A to component B has been adjusted. Specifically, the mass percentage of component A is 60% and the mass percentage of component B is 40%, while the rest remains the same as in Example 1.

[0051] Example 6

[0052] Compared with Example 1, the ratio of component A to component B has been adjusted. Specifically, the mass percentage of component A is 70% and the mass percentage of component B is 30%, while the rest remains the same as in Example 1.

[0053] Example 7

[0054] Compared with Example 1, the copolymer raw materials and their proportions of component A have been adjusted. Component A is copolymerized by the following components in the following amounts: N-methacrylamide 75wt%, trifluoroethyl acrylate 10wt%, and acrylic acid 15wt%, while the rest remain the same as in Example 1.

[0055] Example 8

[0056] Compared with Example 1, the copolymer raw materials and their proportions of component A have been adjusted. Component A is copolymerized by the following components in the following amounts: 85 wt% N-ethylacrylamide, 5 wt% trifluoroethyl methacrylate and 10 wt% acrylic acid, with the rest remaining the same as in Example 1.

[0057] Example 9

[0058] Compared with Example 1, the copolymer raw materials and their proportions of component A have been adjusted. Component A is copolymerized by the following components in the following amounts: 80 wt% N-phenylacrylamide, 15 wt% perfluorooctyl ethyl acrylate and 5 wt% acrylic acid, with the remainder being consistent with Example 1.

[0059] Example 10

[0060] Compared with Example 1, the copolymer raw materials and their proportions of component B have been adjusted. Component B is copolymerized by the following components in the following amounts: 30 wt% acrylic acid, 50 wt% acrylate, 9.9 wt% perfluorooctyl ethyl acrylate, 10 wt% N-phenylacrylamide and 0.1 wt% mercaptomethacrylate, with the remainder being consistent with Example 1.

[0061] Example 11

[0062] Compared with Example 1, the copolymer raw materials and their proportions of component B have been adjusted. Component B is copolymerized by the following components in the following amounts: 50 wt% acrylic acid, 39.9 wt% acrylate, 5 wt% trifluoroethyl acrylate, 5 wt% N-ethylacrylamide, and 0.1 wt% mercaptopolyethylene glycol acrylate. The rest are consistent with Example 1.

[0063] Example 12

[0064] Compared with Example 1, the copolymer raw materials and their proportions of component B have been adjusted. Component B is copolymerized by the following components in the following proportions: 45 wt% acrylic acid, 30 wt% acrylate, 10 wt% trifluoroethyl methacrylate, 10 wt% N-methacrylamide, and 5 wt% mercaptoacrylate (a mixture of mercaptomethacrylate and mercaptopolyethylene glycol acrylate in a mass ratio of 2:1), while the rest remains the same as in Example 1.

[0065] Example 13

[0066] Compared with Example 1, the end groups of components A and B were not modified with allyl groups, and the rest remained the same as in Example 1.

[0067] Example 14

[0068] Compared with Example 1, the terminal groups of components A and B were not modified with allyl groups, but with fumarate groups. During the modification, the carboxyl groups of components A and B were first activated, and then monoethyl fumarate and triethylamine were added to modify the fumarate groups through an esterification reaction; the rest was the same as in Example 1.

[0069] Comparative Example 1

[0070] The negative electrode sheet was prepared by replacing the two-component negative electrode binder in Example 1 with PVDF and a soft-pack battery was assembled. All other aspects were the same as in Example 1.

[0071] Comparative Example 2

[0072] The negative electrode sheet was prepared and the soft-pack battery was assembled using PMMA instead of the two-component negative electrode binder in Example 1, and all other aspects remained the same as in Example 1.

[0073] Comparative Example 3

[0074] The negative electrode sheet was prepared and the soft-pack battery was assembled using PAA-CMC-SBR instead of the two-component negative electrode binder in Example 1. All other aspects remained the same as in Example 1.

[0075] Comparative Example 4

[0076] The negative electrode sheet was prepared and the soft-pack battery was assembled by replacing the two-component negative electrode binder of Example 1 with PAN, and all other aspects were the same as in Example 1.

[0077] Comparative Example 5

[0078] Compared with Example 1, the ratio of component A to component B has been adjusted, specifically: the mass percentage of component A is 25% and the mass percentage of component B is 75%, while the rest remains the same as in Example 1.

[0079] Comparative Example 6

[0080] Compared with Example 1, the ratio of component A to component B has been adjusted. Specifically, the mass percentage of component A is 75% and the mass percentage of component B is 25%, while the rest remains the same as in Example 1.

[0081] Comparative Example 7

[0082] Compared with Example 1, the copolymer raw materials of component A do not include trifluoroethyl methacrylate, and the remaining raw materials of component A are of the same mass as those in Example 1, and all other aspects are consistent with those in Example 1.

[0083] Comparative Example 8

[0084] Compared with Example 1, the copolymer raw materials of component B do not include trifluoroethyl methacrylate, and the remaining raw materials of component B are of the same mass as those in Example 1, and all other aspects are consistent with those in Example 1.

[0085] Comparative Example 9

[0086] Compared with Example 1, neither component A nor component B contains trifluoroethyl methacrylate in their copolymer raw materials. The remaining raw materials of components A and B are of the same mass as those in Example 1, and everything else is consistent with Example 1.

[0087] Comparative Example 10

[0088] Compared with Example 1, the end groups of components A and B were not modified with allyl groups, but were modified with acrylates. During the modification, the carboxyl groups of components A and B were first activated, and then hydroxyethyl acrylate and triethylamine were added to modify the acrylate groups through esterification. All other aspects were the same as in Example 1.

[0089] Comparative Example 11

[0090] Compared with Example 1, the end groups of components A and B were not modified with allyl groups, but were modified with maleimide groups. During the modification, the carboxyl groups of components A and B were first activated, and then 3-maleimide propylamine and triethylamine were added to carry out a grafting reaction to introduce maleimide groups; the rest was the same as in Example 1.

[0091] The porosity, peeling force, and half-electric rebound of the negative electrode sheets obtained from each embodiment and comparative example were tested, as well as the cycle life and rate performance of each pouch cell. The porosity test employed the BET method. For the peel force test, a universal testing machine was used to peel the active material layer from the current collector at a 180° peel angle and a rate of 50 mm / min, recording the peel force curve and obtaining the peel force value. The half-cell rebound rate specifically refers to charging the pouch battery to 50% SOC, allowing it to stand for 1 hour, measuring the negative electrode thickness T1, and comparing it with the initial negative electrode thickness T0 to calculate the rebound rate: Half-cell rebound rate = (T1-T0) / T0*100%. The ambient temperature was kept stable at 25±1℃ during thickness measurement, and three tests were performed each time, with the average value taken. The cycle life test conditions were: charging and discharging at 25℃ at a rate of 0.5C / 0.7C; the cycle life is the number of cycles when the remaining capacity is less than 80% of the initial capacity. For the rate performance test, the ratio of the discharge capacity at 0.2C / 3C to the discharge capacity at 0.2C / 0.2C was measured. Test conditions not described in detail all used conventional test conditions in this field.

[0092] For ease of listing, Examples 1, 2, ... are respectively referred to as S1, S2, ...; Comparative Examples 1, 2, ... are respectively referred to as D1, D2, ...

[0093] Table 1. Product performance parameters of negative electrode and pouch cell in each embodiment and comparative example.

[0094]

[0095]

[0096] like Figure 1 As shown in Table 1:

[0097] (1) The test results of Examples 1-14 and Comparative Examples 1-4 show that compared with existing binders such as PVDF, PMMA, PAA-CMC-SBR and PAN, the two-component negative electrode binder proposed in this invention can effectively buffer expansion and maintain electrode integrity through the synergistic effect of component A and component B. It significantly improves the peeling force and long-cycle peeling force retention rate of the negative electrode sheet and reduces the half-cycle rebound rate. The resulting negative electrode sheet can significantly improve the cycle life and rate performance of lithium batteries after being used in lithium batteries.

[0098] (2) Comparison of the test results of Examples 1-6 with Comparative Examples 5 and 6 shows that the ratio of component A to component B has a certain influence on the performance of the two-component negative electrode binder. When the mass percentage of component A is 30%-70%, the overall performance of the two-component binder is good. If the content of component A is too low, such as 25% as shown in Comparative Example 5, the adhesion is weak, the peeling force is small, the peeling force retention rate is poor, and the interface is unstable after long cycle (500cls), resulting in poor cycle life of the lithium battery. If the content of component A is too high, such as 75% as shown in Comparative Example 6, the adhesion is strong but the rigidity is poor. Although the peeling performance is good, the cycle life and rate performance of the lithium battery deteriorate, especially the cycle life drops significantly. Obviously, excessive pursuit of adhesion is not conducive to the electrochemical performance of lithium batteries.

[0099] (3) The test results of Example 1 and Comparative Examples 7, 8 and 9 show that although the addition of fluorinated acrylates in Component A and Component B has no significant effect on the peel force and half-electric rebound rate of the electrode, it will improve the long-cycle peel force retention rate to a certain extent. The hydrophobicity of fluorinated acrylates helps to improve the hydrophilicity of the electrode, avoid strong water absorption leading to binder swelling failure, resulting in poor interface stability, increased internal resistance of the electrode, and deterioration of the cycle life and rate performance of the lithium battery.

[0100] (4) The test results of Examples 1, 13, 14, 10 and 11 show that: specific carbon-carbon double bond modification of the end groups of components A and B, and secondary processing of the two-component negative electrode binder through cross-linking reaction during slurry preparation can further significantly improve its performance. For example, allyl modification or fumarate modification can significantly improve the peeling force and long-cycle peeling force retention rate of the negative electrode sheet and significantly reduce the half-cycle rebound rate. When used in lithium batteries, it can significantly improve the cycle life of lithium batteries.

[0101] Further experiments revealed that, although the product obtained after secondary processing exhibited excellent bonding properties and improved negative electrode peeling performance when modified with acrylate or maleimide groups with high crosslinking density, the cycle life and rate performance of the lithium battery actually deteriorated. The reason for this is likely that the high-viscosity negative electrode binder easily coats the conductive agent and hinders the wetting of the electrolyte on the negative electrode, leading to the disconnection of the electronic pathway and slower lithium-ion transport.

[0102] In summary, through repeated verification and cross-comparison of the above experimental data, it can be confirmed that the two-component negative electrode binder proposed in this invention not only achieves strong adhesion to the negative electrode main material, but also adapts to the expansion of the silicon-based negative electrode and rigidly restricts its expansion, significantly improving the peeling force of the negative electrode sheet and the long-cycle peeling force retention rate, which helps to improve the cycle life and rate performance of lithium batteries.

[0103] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make modifications, alterations, substitutions, and variations to the above embodiments within the scope of the present invention. Furthermore, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of the different embodiments or examples.

Claims

1. A two-component negative electrode binder, characterized by: comprising component A and component B; said component A is copolymerized from acrylamide 75wt%-80wt%, fluoroacrylate 5wt%-15wt% and acrylic acid 5wt%-15wt% by weight; said component B is copolymerized from acrylic acid 30wt%-50wt%, acrylate 30wt%-50wt%, fluoroacrylate 5wt%-10wt%, acrylamide 5wt%-10wt% and mercaptoacrylate 0.1wt%-5wt% by weight; when used, the proportion of component A in the mixture of component A and component B is 30wt%-70wt%.

2. The dual-component anode binder of claim 1, wherein: before use, the end groups of component A and component B are modified to introduce carbon-carbon double bond respectively; preferably, the carbon-carbon double bond is selected from allyl or fumarate.

3. The dual-component anode binder of claim 2, wherein: before use, the end groups of component A and component B are modified to introduce allyl by using allyl bromide reagent.

4. The dual-component anode binder of claim 1, wherein: the molecular weight of component A is 10w-15w, and the molecular weight of component B is 15w-25w.

5. The dual-component anode binder of claim 1, wherein: its glass transition temperature is 80-110℃.

6. The two-component negative electrode binder according to any one of claims 1-5, characterized in that: the acrylamide in component A and component B is arbitrarily selected from one or more of acrylamide, N-methyl acrylamide, N-ethyl acrylamide, N-phenyl acrylamide; the fluoroacrylate in component A and component B is arbitrarily selected from one or more of trifluoroethyl methacrylate, trifluoroethyl acrylate, propyl tetrafluoroacrylate, propyl tetrafluoromethacrylate, butyl hexafluoroacrylate, butyl hexafluoromethacrylate, octafluoropentyl acrylate, octafluoropentyl methacrylate, isobutyl octafluoroacrylate, n-heptyl dodecafluoroacrylate, heptyl dodecafluoromethacrylate, perfluoro octyl ethyl acrylate, perfluoro octyl ethyl methacrylate, perfluoro hexyl ethyl acrylate, perfluoro hexyl ethyl methacrylate, p-trifluoromethyl phenyl acrylate, p-trifluoromethyl phenyl methacrylate, perfluoro polyether acrylate, fluorocyclohexyl acrylate; the mercaptoacrylate is mercapto polyethylene glycol acrylate or / and mercapto methacrylate.

7. A method of using the dual-component negative electrode binder of any one of claims 1-6, characterized by: component A and component B are dissolved in aqueous solvent respectively to prepare glue solution A and glue solution B; when preparing negative electrode slurry, the solid raw materials are dry mixed, then the glue solution A is added, after sufficient stirring, the glue solution B is added, and finally the leveling aid is added.

8. The method of using a two-component negative electrode binder of claim 7, wherein: crosslinking agent and triethylamine are also added in the negative electrode slurry, and the negative electrode slurry is coated on the negative electrode current collector and then subjected to high temperature treatment under nitrogen protection; preferably, the crosslinking agent is PETMP, the addition amount is 2wt%-3.5wt% of the two-component negative electrode binder, and the high temperature treatment condition is 80-100℃ for 5-15min. Preferably, the cross-linking agent is a mixture of BPO and TAIC with a mass ratio of 1:2, the addition amount is 0.5wt%-1.5wt% of the two-component adhesive, and the high-temperature treatment condition is 105-110℃ for 8-12min.

9. The method of using a dual-component anode binder of claim 7, wherein: A photoinitiator is further added in the negative electrode slurry, and the negative electrode slurry is subjected to light irradiation treatment under nitrogen protection after being coated on the negative electrode current collector. Preferably, the photo-initiator is Irgacure 2959, and the amount of addition is 0.1wt%-1wt% of the two-component adhesive, and the UV light with wavelength of 365nm or 405nm is used, and the light intensity is 50-200mW / cm 2 , and the irradiation time is 5s-10min.

10. The method of using a dual-component negative electrode binder of claim 7, wherein: The leveling agent is selected from one of polyether-modified polysiloxane, polyester-modified polysiloxane and reactive silicone. Preferably, the proportion of the leveling aid in the negative electrode slurry is 0.1wt%-1wt%.

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