A binder, a negative electrode sheet, a battery

Abstract

In view of the problem that the peeling strength between the existing active material layer and the current collector is weak, the present application provides a kind of binder, negative electrode sheet, battery.The binder includes core and shell, the core includes first polymer, the shell includes second polymer, the first polymer and the second polymer each independently includes aromatic vinyl structure unit, acrylate structure unit and crosslinking structure unit;The second polymer also includes phosphate structure unit, amide structure unit and olefinic acid structure unit, the mass ratio of phosphate structure unit, amide structure unit and olefinic acid structure unit is (1~8):(1~5):(1~8).The binder provided by the present application controls the mass ratio of phosphate structure unit, amide structure unit and olefinic acid structure unit in the shell, so that the stability of the binder in electrolyte is better, and has better liquid retaining capacity while having stronger adhesive force.

Description

Technical Field

[0001] This invention belongs to the field of secondary battery technology, specifically relating to an adhesive, a negative electrode sheet, and a battery. Background Technology

[0002] Lithium-ion batteries, with their advantages of high energy density, long cycle life, and environmental friendliness, have been widely used in new energy vehicles, portable electronic devices, and energy storage systems. Their performance is closely related to the stability and reliability of the manufacturing process. As a key component of lithium-ion batteries, the structural stability of the negative electrode directly determines the overall performance of the battery. The interfacial bonding strength between the copper foil, the current collector of the negative electrode, and the active material layer is one of the core factors affecting the structural stability of the negative electrode.

[0003] With the continuous increase in the demand for high energy density in power batteries, silicon-based anodes, due to their ultra-high theoretical specific capacity of 4200 mAh / g, are gradually being developed and applied as anode materials. However, silicon-based materials experience a volume expansion of 300% to 400% during charging and discharging, resulting in huge interfacial stress between the active material layer and the copper foil current collector. This easily leads to problems such as active material layer peeling and electrode pulverization, causing rapid capacity decay and shortened cycle life.

[0004] Therefore, there is an urgent need for a new type of binder to improve the peel strength between the active material layer and the current collector, maintain the integrity of the electrode structure, achieve excellent electrochemical performance, and improve the cycle stability of the battery. Summary of the Invention

[0005] This invention addresses the problem of weak peel strength between the existing active material layer and the current collector by providing an adhesive, a negative electrode sheet, and a battery.

[0006] To solve the above-mentioned technical problems, in a first aspect, the present invention provides an adhesive comprising a core and a shell, wherein the shell is disposed on the surface of the core and at least partially covers the core, the core comprising a first polymer and the shell comprising a second polymer; The first polymer and the second polymer each independently comprise aromatic vinyl structural units, acrylate structural units, and crosslinking structural units; The second polymer also includes phosphate ester structural units, amide structural units and olefinic acid structural units, wherein the mass ratio of the phosphate ester structural units, amide structural units and olefinic acid structural units is (1~8):(1~5):(1~8).

[0007] Preferably, the surface of the shell layer has an uneven structure, and the roughness Sa of the shell layer is 0.2μm≤Sa≤0.5μm.

[0008] Preferably, in the first polymer, the mass ratio of the aromatic vinyl structural unit, the acrylate structural unit, and the crosslinking structural unit is (37~44):(1~15):(2~8). Preferably, in the second polymer, the mass ratio of the aromatic vinyl structural unit, acrylate structural unit, crosslinking structural unit, phosphate ester structural unit, amide structural unit and olefinic acid structural unit is (6~30):(6~15):(3~15):(1~8):(1~5):(1~8).

[0009] Preferably, the second polymer further includes vinylsilane structural units; in the second polymer, the mass ratio of the aromatic vinyl structural units, acrylate structural units, crosslinking structural units, phosphate ester structural units, amide structural units, olefinic acid structural units, and vinylsilane structural units is (6~30):(6~15):(3~15):(1~8):(1~5):(1~8):(1~5).

[0010] Preferably, the vinyl silane structural unit includes at least one of vinyltrimethoxysilane structural unit, vinyltriethoxysilane structural unit, vinyltri(2-methoxyethoxy)silane structural unit, vinyltriisopropoxysilane structural unit, and 3-methacryloyloxypropyltrimethoxysilane structural unit.

[0011] Preferably, the glass transition temperature of the first polymer is 50°C to 80°C, and the glass transition temperature of the second polymer is 0°C to 20°C.

[0012] Preferably, the adhesive is an emulsion, and the contact angle between the emulsion and the copper foil is <60°.

[0013] Preferably, the mass swelling rate of the adhesive is 30% to 50%.

[0014] Secondly, this application provides a negative electrode sheet, including a negative electrode current collector, a base coating layer, and a negative electrode active material layer. The base coating layer is disposed on at least one side surface of the negative electrode current collector, and the negative electrode active material layer is disposed on the side of the base coating layer facing away from the negative electrode current collector. The base coating includes an adhesive as described in any of the preceding claims.

[0015] Thirdly, this application provides a battery including the negative electrode sheet as described above.

[0016] In this application, the first polymer in the core, by controlling the types of structural units, gives the core excellent mechanical strength and rigidity, providing support for the adhesive and resisting the stress generated by the volume expansion of the silicon-based material. The second polymer in the shell contains phosphate ester structural units, amide structural units, and olefinic acid structural units, and its polar groups can form high adhesion to the copper foil surface. In addition, by controlling the mass ratio of phosphate ester structural units, amide structural units, and olefinic acid structural units in the shell, the adhesive has strong bonding force.

[0017] In particular, when the binder is used in the base coating, it can enhance the peel strength between the negative electrode current collector and the negative electrode active material layer, thereby improving the battery's electrical performance. Attached Figure Description

[0018] Figure 1 This is an electron microscope image of the adhesive provided in Example 1. Detailed Implementation

[0019] To make the technical problems solved, the technical solutions, and the beneficial effects of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0020] One embodiment of this application provides an adhesive comprising a core and a shell, wherein the shell is disposed on the surface of the core and at least partially covers the core, the core comprising a first polymer and the shell comprising a second polymer; The first polymer and the second polymer each independently include aromatic vinyl structural units, acrylate structural units and crosslinking structural units; the second polymer also includes phosphate structural units, amide structural units and olefin structural units, and the mass ratio of the phosphate structural units, amide structural units and olefin structural units is (1~8):(1~5):(1~8).

[0021] In this embodiment, the first polymer of the core, by controlling the types of structural units, gives the core excellent mechanical strength and rigidity, providing support for the adhesive and resisting the stress generated by the volume expansion of the silicon-based material. The second polymer of the shell contains phosphate ester structural units, amide structural units, olefinic acid structural units, and vinyl silane structural units. The phosphate ester and amide groups it contains can form high adhesion to the copper foil surface. The carboxylic acid groups can improve the stability of the adhesive itself while improving the wetting ability for peeling. The phosphate ester, amide, and carboxylic acid groups are introduced independently in the shell, which can form a concave-convex structure, and the functions of different components can achieve a synergistic effect. This concave-convex structure will generate a higher specific surface area during the subsequent electrode rolling process, increasing the contact sites with the copper foil, thereby improving peeling. On the other hand, the gaps generated in the contact sites with the active material after rolling are also conducive to ion transport, solving the contradiction between improving the peeling of the carbon-coated foil and balancing electrical performance.

[0022] In addition, by controlling the mass ratio of phosphate ester structural units, amide structural units, and olefinic acid structural units in the shell within the above range, the binder has good affinity with the electrolyte, resulting in good stability in the electrolyte, good liquid retention capacity, and strong adhesion.

[0023] In particular, when the binder is used in the base coating, it can enhance the peel strength between the negative electrode current collector and the negative electrode active material layer, thereby improving the peel strength of the carbon foil and balancing the electrical performance, thus improving the battery's electrical performance.

[0024] Specifically, the mass ratio of phosphate ester structural units, amide structural units, and olefinic acid structural units in the second polymer includes, but is not limited to, 1:1:1, 4:3:4, 8:5:8, 4:1:1, 8:1:1, 1:3:1, 1:5:1, 1:1:4, and 1:1:8.

[0025] like Figure 1 As shown, in some embodiments, the surface of the shell layer has an uneven structure, and the roughness Sa of the shell layer is 0.2μm≤Sa≤0.5μm.

[0026] The uneven structure formed on the shell surface defines the roughness range of the shell, further enhancing adhesion to the copper foil surface. Additionally, the uneven structure of the adhesive, after being coated on the foil and rolled, generates a larger contact area, further improving the peel strength of the negative electrode sheet. Simultaneously, the uneven structure on the shell surface can form a porous structure at the interface with the negative electrode active material layer, improving the physical channels for ion transport, reducing the internal resistance of the adhesive itself, and further enhancing the electrochemical performance and rate performance of the battery.

[0027] Specifically, the roughness of the shell includes, but is not limited to, 0.2 μm, 0.25 μm, 0.3 μm, 0.35 μm, 0.4 μm, 0.45 μm or 0.5 μm.

[0028] In one embodiment, the mass ratio of the aromatic vinyl structural unit, the acrylate structural unit, and the crosslinking structural unit in the first polymer is (37~44):(1~15):(2~8). In one embodiment, the second polymer comprises phosphate ester structural units, amide structural units, and olefinic acid structural units; preferably, in the second polymer, the mass ratio of the aromatic vinyl structural units, acrylate structural units, crosslinking structural units, phosphate ester structural units, amide structural units, and olefinic acid structural units is (6~30):(6~15):(3~15):(1~8):(1~5):(1~8).

[0029] It should be noted that the aromatic vinyl structural units, acrylate structural units, and crosslinking structural units in the first polymer and the second polymer may be the same or different. In the second polymer, the phosphate ester groups originate from phosphate ester structural units, the amide groups originate from amide structural units, and the carboxylic acid groups originate from olefinic acid structural units.

[0030] Specifically, the mass ratio of aromatic vinyl structural units, acrylate structural units and crosslinked structural units in the first polymer includes, but is not limited to, 37:1:2, 44:15:8, 40:8:5, 40:1:2, 44:1:2, 37:8:2, 37:15:2, 37:1:5 or 37:1:8.

[0031] Specifically, the mass ratio of aromatic vinyl structural units, acrylate structural units, crosslinking structural units, phosphate ester structural units, amide structural units, and olefinic acid structural units in the second polymer includes, but is not limited to, 6:6:3:1:1:1, 30:15:15:8:5:8, 18:10:9:4:3:4, 9:15:3:2:2:2, 6:12:3:2:2:2, 6:12:12:2:2:2, 6:12:3:7:2:2, 6:12:3:2:5:2, 6:12:3:2:2:6, 6:12:3:7:2:6, or 6:12:3:7:5:6.

[0032] Furthermore, the aromatic vinyl structural unit is a structural unit obtained by polymerizing aromatic vinyl monomers, including but not limited to at least one of styrene, methylstyrene, isopropylstyrene, 4-methoxystyrene, and 2,5-dimethylstyrene. The selection of aromatic vinyl monomers improves the stability and mechanical strength of the binder.

[0033] Acrylic ester structural units are structural units obtained by polymerization of acrylate monomers. These monomers include, but are not limited to, at least one of methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, glycidyl acrylate, glycidyl methacrylate, butyl acrylate, butyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, hydroxyethyl acrylate, hydroxyethyl methacrylate, isooctyl acrylate, isooctyl methacrylate, lauryl acrylate, and lauryl methacrylate. By selecting the above-mentioned acrylate monomers, the affinity between the binder and the electrolyte, as well as the adhesion between the binder and the negative electrode active material, can be further improved.

[0034] The cross-linked structural unit is a structural unit obtained by polymerization of cross-linking monomers. These cross-linking monomers include, but are not limited to, at least one of the following: trimethicone, pentaerythritol triacrylate, triallyl isocyanurate, trimethylolpropane triacrylate, ethylene glycol diacrylate, diethylene glycol diacrylate, 1,6-hexanediol diacrylate, divinylbenzene, ethylene glycol dimethacrylate, and allyl methacrylate. By adding cross-linking monomers, polymerization can be promoted to form a cross-linked structure, increasing the degree of cross-linking in the binder, controlling the swelling and dissolution of the binder in the electrolyte, and improving the stability of the binder in the electrolyte.

[0035] Phosphate ester structural units are structural units obtained by polymerization of phosphate ester monomers, including but not limited to at least one of vinyl dimethyl phosphate, vinyl diethyl phosphate, vinyl diphenyl phosphate, and phenyl divinyl phosphate. The phosphate ester groups are highly polar and undergo multiple chemical interactions with the copper foil surface, which can further improve the adhesion strength between the negative electrode active material layer and the copper foil, and improve the peel strength of the negative electrode sheet.

[0036] Acrylamide structural units are structural units obtained by polymerization of acrylamide monomers, including but not limited to at least one of acrylamide, methacrylamide, N-isopropylacrylamide, N-hydroxymethylacrylamide, and N,N-dimethylacrylamide. The amide groups can form hydrogen bonds and coordinate with the surface groups of the copper foil, and synergistically with phosphate ester monomers, can further improve the adhesion strength between the negative electrode active material layer and the copper foil, and increase the peel strength of the negative electrode sheet.

[0037] The olefinic structural unit is a structural unit obtained by polymerization of unsaturated carboxylic acid monomers, including but not limited to at least one of methacrylic acid, acrylic acid, ethylacrylic acid, maleic anhydride, and itaconic acid. The carboxyl group can coordinate with the hydroxyl groups and cuprous oxide on the copper foil surface to form a stable Cu-O chemical bond. Simultaneously, the strong polarity of the carboxyl group can improve the wetting properties between the binder and the copper foil. In synergy with phosphate ester monomers and acrylamide monomers, it can further improve the adhesion strength between the negative electrode active material layer and the copper foil, and increase the peel strength of the negative electrode sheet. Specifically, the structural unit formed by the maleic anhydride monomer can hydrolyze in an aqueous environment to generate a carboxyl group, yielding the corresponding olefinic structural unit.

[0038] In some embodiments, the glass transition temperature of the first polymer is higher than that of the second polymer. By adjusting the glass transition temperatures of the first and second polymers, the synergistic effect of the core-shell structure is further optimized, enabling the adhesive to possess both excellent rigidity and flexibility, thereby improving the adhesion between the adhesive and the foil.

[0039] In some embodiments, the glass transition temperature of the first polymer is 50°C to 80°C, and the glass transition temperature of the second polymer is 0°C to 20°C. The glass transition temperature of the second polymer in the shell layer is between 0°C and 20°C, which improves the adhesion and toughness of the adhesive itself.

[0040] In some embodiments, the second polymer further includes vinylsilane structural units. In the second polymer, the mass ratio of the aromatic vinyl structural units, acrylate structural units, crosslinking structural units, phosphate ester structural units, amide structural units, olefinic acid structural units, and vinylsilane structural units is (6~30):(6~15):(3~15):(1~8):(1~5):(1~8):(1~5). By introducing vinylsilane structural units into the second polymer, the surface tension of the adhesive emulsion is reduced, resulting in better wetting ability of the adhesive and improved adhesion between the adhesive and the foil.

[0041] Specifically, the mass ratio of aromatic vinyl structural units, acrylate structural units, crosslinking structural units, phosphate ester structural units, amide structural units, olefinic acid structural units, and vinylsilane structural units in the second polymer includes, but is not limited to, 6:6:3:1:1:1:1, 30:15:15:8:5:8:5, 18:10:9:4:3:4:3, 9:15:3:2:2:2:3, 6:12:3:2:2:2:3, 6:12:12:2:2:2:1, 6:12:3:7:2:2:5, 6:12:3:2:5:2:3, 6:12:3:2:2:6:5, 6:12:3:7:2:6:3, or 6:12:3:7:5:6:5.

[0042] In some embodiments, the vinyl silane structural unit includes at least one of vinyltrimethoxysilane structural unit, vinyltriethoxysilane structural unit, vinyltri(2-methoxyethoxy)silane structural unit, vinyltriisopropoxysilane structural unit, and 3-methacryloyloxypropyltrimethoxysilane structural unit.

[0043] Specifically, the vinyl silane structural unit is a structural unit formed by the polymerization of vinyl silane monomers, and the vinyl silane monomers include at least one of vinyltrimethoxysilane (A-171), vinyltriethoxysilane (A-151), vinyltri(2-methoxyethoxy)silane (A-172), vinyltriisopropoxysilane (A-173), and 3-methacryloyloxypropyltrimethoxysilane (KH570).

[0044] The vinylsilane structural unit contains siloxane groups, which can undergo condensation reactions with hydroxyl groups on the surface of silicon-based active materials or foils to form a stable chemical bond. This significantly enhances the compatibility and adhesion between the binder and the silicon-based active material layer and foil, and improves the peel strength of the negative electrode sheet.

[0045] In some embodiments, the volume average particle size D of the adhesive 50 The particle size is 400~1000nm. This particle size range ensures both suitable bonding performance and that the gaps created by the binder facilitate ion transport, thus improving both kinetics and exfoliation.

[0046] Specifically, the volume average particle size D of the binder 50 This includes, but is not limited to, any single value or a range between any two values ​​from 400nm, 450nm, 500nm, 550nm, 600nm, 650nm, 700nm, 750nm, 800nm, 900nm, or 1000nm. Specifically, the particle size of the binder is controlled by adjusting the content of the emulsifier and the concentration of the monomer.

[0047] In some embodiments, the adhesive is an emulsion, and the contact angle between the emulsion and the copper foil is <60°. A contact angle of <60° indicates that the adhesive emulsion has good wettability and can spread rapidly on the copper foil surface to form a uniform film. If the contact angle is ≥60°, the spreadability of the adhesive emulsion on the copper foil surface is poor, easily forming local accumulations or voids, resulting in a weak bond between the adhesive and the copper foil, affecting the interfacial bonding strength. This embodiment improves the wettability and coating performance of the adhesive on the copper foil surface by controlling the contact angle between the adhesive emulsion and the copper foil, ensuring that the adhesive can bond tightly to the copper foil and improving the interfacial bonding strength between the adhesive and the copper foil.

[0048] In some embodiments, the swelling rate of the adhesive is 30% to 50%. By controlling the swelling rate of the adhesive within a reasonable range, it is ensured that the adhesive can maintain good mechanical strength and bonding performance in the electrolyte.

[0049] Specifically, the swelling rate of the adhesive in DMC (dimethyl carbonate) solvent is 30% to 50%.

[0050] In some embodiments, the mass ratio of the core to the shell is (15~37):(15~45).

[0051] Furthermore, one embodiment of this application provides a method for preparing an adhesive, comprising the following steps: Nucleus: 1) Mix 0.5-5 parts emulsifier, 0.5-2 parts buffer and 20-30 parts water evenly and stir thoroughly. This mixture is labeled A1. 2) Mix 37-44 parts of aromatic vinyl monomers, 1-15 parts of acrylate monomers, 2-8 parts of crosslinking monomers, and 0.5-2 parts of regulator in a pre-emulsification tank until homogeneous. Then, add 2 / 3 of A1 to the pre-emulsification tank and stir at 1000-1500 rpm for 1-2 hours until a milky white emulsion is formed and there is no separation. This is called A2. 3) In another pre-emulsification vessel, mix 1-5 parts of initiator and 5-20 parts of water, stir well and record as A3; 4) Add 1 / 3 of A1 into the reactor, turn on the heater, set the temperature to 75~77℃, and the rotation speed to 100 rpm; 5) After the temperature of the reactor has stabilized, slowly add A2 and A3.

[0052] 6) After the reaction is complete, cool down to 60~62℃, and maintain the reactor under a negative pressure of -1.0~-1.3MPa for 2~4 hours; 7) After the reaction is complete, the emulsion is collected, filtered through a filter screen, and the filtrate is collected to finally obtain the M1 emulsion of the nucleus.

[0053] Adhesive: (1) Add 15-37 parts of the core and 20-30 parts of water to the reactor, stir for 3-5 hours at a speed of 100-300 rpm, and turn on the nitrogen protection. (2) In another container, stir and mix 1-5 parts of initiator and 10-20 parts of water until homogeneous to obtain a mixed solution. Take 3 / 4 of the mixed solution and record it as A4, and the remaining solution as A5. (3) Add 0.5-1.5 parts of emulsifier and 1-10 parts of water to a pre-emulsification vessel and stir at 300-500 rpm for 1-2 hours. Add 2-10 parts of aromatic vinyl monomer, 2-5 parts of acrylate monomer, 1-8 parts of phosphate monomer, 1-5 parts of crosslinking monomer, and 0.1-2 parts of regulator to the pre-emulsification vessel, mix and stir evenly, and stir at 1000-1500 rpm for 1-2 hours until a white emulsion is formed and there is no separation, which is recorded as A6; (4) Add 0.5-1.5 parts of emulsifier, 1-10 parts of water, 2-10 parts of aromatic ethylene monomer, 2-5 parts of acrylate monomer, 1-8 parts of unsaturated carboxylic acid monomer, 1-5 parts of crosslinking monomer, and 0.1-2 parts of regulator to another pre-emulsification kettle, mix and stir evenly, stir at 1000-1500 rpm for 1-2 hours until a white emulsion is formed and no layering occurs, and record it as A7; (5) Add 0.5-1.5 parts of emulsifier, 1-10 parts of water, 2-10 parts of aromatic ethylene monomer, 2-5 parts of acrylate monomer, 1-5 parts of acrylamide monomer, 1-5 parts of crosslinking monomer, and 0.1-2 parts of regulator to another pre-emulsification vessel, mix and stir evenly, and stir at 1000-1500 rpm for 1-2 hours until a white emulsion is formed and no layering occurs, which is recorded as A8; (6) Add 1 to 5 parts of vinylsilane monomer to another pre-emulsification vessel, designated as A9; (7) Set the temperature of the reactor to 75~77℃. After the temperature is constant, add A6, A7, A8 and A9 dropwise at a rate of 1~25mL / min. After 0.5~1h, start adding A4 dropwise. The reaction lasts for 6~12h. (8) Then raise the temperature to 80~82℃, add A5 and continue the reaction for 2~4h; (9) After the reaction is complete, the temperature is lowered to 60~62℃, and the reactor is kept under negative pressure of -1.0~-1.5MPa for 2~5 hours; (10) After the reaction is complete, the emulsion is collected, filtered with a filter screen, and the filtrate is collected to obtain the binder.

[0054] A6, A7, A8, and A9 are added separately. Due to their different degrees of polymerization and poor compatibility, the shell layers are in a state of heterogeneous separation, resulting in an uneven structure on the shell surface. The purpose of separately emulsifying and adding the phosphate ester monomers, acrylamide monomers, and acrylic monomers in A6, A7, and A8 is to ensure that the polar groups in the monomers are independent units, and that the polar groups do not affect each other. This further promotes the interaction between the polar groups and the foil, improving the adhesion of the adhesive.

[0055] Furthermore, in some embodiments, the emulsifier includes at least one selected from sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, sodium vinyl sulfonate, sodium allyl sulfonate, sodium 3-allyloxy-2-hydroxy-1-propanesulfonate, octylphenol polyoxyethylene ether, polyethylene glycol monooctyl ether, and polyethylene glycol dioctyl ether. By adding the emulsifier, the surface tension of the emulsion is reduced, allowing the monomers and water to form a stable emulsion, preventing the aggregation of oily monomers, thereby improving the emulsion stability.

[0056] The initiator includes at least one of persulfate compounds and peroxide compounds, and in some embodiments, is selected from at least one of ammonium persulfate (APS), potassium persulfate (KPS), and sodium persulfate.

[0057] Buffers include sodium bicarbonate or disodium hydrogen phosphate, which help maintain the pH stability of the reaction system and prevent the emulsifier from becoming ineffective due to excessively low pH.

[0058] The regulator includes at least one of tert-dodecyl mercaptan and n-dodecyl mercaptan. The polymerization rate is controlled by the regulator, thereby controlling the molecular weight of the binder emulsion to be within a narrow distribution.

[0059] In this invention, each of the aforementioned structural units represents the structural portion of the corresponding monomer present in the resulting polymer after the monomer participates in the polymerization reaction. The mass ratio of each structural unit is based on the mass content of the corresponding monomer in the total amount of monomers participating in the polymerization.

[0060] As those skilled in the art will know, the reactions described above are conventional free radical polymerization reactions, and the specific methods and reaction conditions are common free radical polymerization methods in the prior art, which will not be elaborated upon in this invention.

[0061] An embodiment of the present invention also provides a negative electrode sheet, including a negative electrode current collector, a base coating layer and a negative electrode active material layer, wherein the base coating layer is disposed on at least one side surface of the negative electrode current collector, and the negative electrode active material layer is disposed on the side of the base coating layer opposite to the negative electrode current collector; The base coating includes an adhesive as described in any of the preceding claims.

[0062] Through the transition effect of the base coating, the interfacial bonding strength between the negative electrode current collector and the negative electrode active material layer is significantly improved, the pulverization of the electrode sheet and the peeling of the active material layer caused by the volume expansion of the silicon-based active material are suppressed, and the structural stability of the negative electrode sheet is improved.

[0063] The underground coating further includes a conductive agent, which includes at least one of carbon nanotubes, graphene, spherical carbon, and conductive carbon black.

[0064] Furthermore, the mass ratio of conductive agent, binder and CMC is (5~7):(3~5):(0.1~1).

[0065] An embodiment of the present invention also provides a battery, including the negative electrode sheet as described above. Applying the above-described high-performance negative electrode sheet to battery assembly improves the overall performance of the battery by enhancing the performance of the negative electrode sheet, thus solving the problems of poor cycle stability and short lifespan in existing batteries.

[0066] The present invention will be further illustrated by the following examples.

[0067] Specifically, the adhesive, negative electrode sheet, and battery disclosed in this invention are described.

[0068] Example 1 1. Adhesive Nucleosome synthesis: (1) Mix 0.5 parts sodium dodecyl sulfate, 0.5 parts sodium bicarbonate and 30 parts water evenly and stir thoroughly. This mixture is recorded as A1. (2) Mix 40 parts styrene, 8 parts isooctyl acrylate, 2 parts allyl methacrylate and 0.5 parts n-dodecyl mercaptan evenly in a pre-emulsification tank. Then take 2 / 3 of A1 and add it to the pre-emulsification tank. Stir at 1500 rpm for 2 hours until a milky white emulsion is formed and there is no separation. This is recorded as A2. (3) In another pre-emulsification vessel, mix 2 parts of potassium persulfate and 7.5 parts of water, stir well and record as A3; (4) Add 1 / 3 of A1 into the reactor, turn on the heating, set the temperature to 75℃ and the rotation speed to 100 rpm; (5) After the temperature of the reactor is constant, slowly add A2 and A3, with a dropping time of 3h and 3.5h respectively; (6) After the reaction is complete, the temperature is lowered to 60°C, and the reactor is kept under negative pressure of -1.0MPa for 2 hours; (7) After the reaction is complete, the emulsion is collected, filtered through a 200-mesh filter, and the filtrate is collected to finally obtain the M1 emulsion of the nucleus; Synthesis of adhesives: (1) Add 18 parts of the core and 30 parts of water to the reactor, stir at 100 rpm for 3 hours, and turn on the nitrogen protection. (2) In another container, stir and mix 1 part potassium persulfate and 10 parts water until they are evenly mixed to obtain a mixed solution. Take 3 / 4 of the mixed solution and record it as A4, and the remaining solution as A5. (3) Add 0.5 parts sodium dodecyl sulfate and 10 parts water to the pre-emulsification vessel and stir at 300 rpm for 1 hour until the emulsifier is completely dissolved. Add 3 parts styrene, 4 parts butyl acrylate, 2 parts dimethyl vinyl phosphate, 1 part ethylene glycol dimethacrylate, and 0.2 parts n-dodecyl mercaptan as a modifier to the pre-emulsification vessel and stir at 1500 rpm for 2 hours until a white emulsion is formed and does not separate into layers, and record this as A6; (4) Add 0.5 parts sodium dodecyl sulfate and 10 parts water to a pre-emulsification vessel and stir at 300 rpm for 1 h until the emulsifier is completely dissolved. Add 3 parts styrene, 4 parts isooctyl acrylate, 2 parts methacrylic acid, 1 part ethylene glycol dimethacrylate and 0.2 parts n-dodecyl mercaptan as a regulator to the pre-emulsification vessel and mix and stir evenly. Stir at 1500 rpm for 2 h until a white emulsion is formed and there is no separation. Record this as A7. (5) Add 0.5 parts sodium dodecyl sulfate and 10 parts water to another pre-emulsification vessel and stir at 300 rpm for 1 h. Add 3 parts styrene, 4 parts butyl acrylate, 2 parts acrylamide, 1 part ethylene glycol dimethacrylate, and 0.2 parts n-dodecyl mercaptan as a modifier to the pre-emulsification vessel, mix and stir evenly, and stir at 1500 rpm for 2 h until a white emulsion is formed and no separation occurs, which is recorded as A8; (6) Add 2 parts of vinyltrimethoxysilane to the pre-emulsification vessel, denoted as A9; (7) Set the temperature of the reactor to 75℃. After the temperature is constant, add A6, A7, A8 and A9 dropwise at a rate of 5 mL / min. After 0.5 h, start adding A4 dropwise. The dropwise addition time of A6, A7, A8 and A9 is 4 h, and the dropwise addition time of A4 is 4.5 h. (8) Then raise the temperature to 80°C, add A5 and continue the reaction for 2 hours; (9) After the reaction is complete, the temperature is lowered to 60°C, and the reactor is kept under negative pressure of -1.0MPa for 2 hours; (10) After the reaction is complete, the emulsion is collected and filtered through a 200-mesh filter to obtain the binder.

[0069] 2. Negative electrode plate Conductive agent Super P, binder, and CMC were mixed in a mass ratio of 7:4:1, and an appropriate amount of deionized water was added to control the solid content of the primer slurry at 15%. The mixture was stirred at 500 rpm for 1 hour to obtain the primer slurry. The primer slurry was then screen-printed onto copper foil, with a coating thickness controlled at 1 μm. The baking temperature was 70℃, and the baking time was 20 minutes. After drying, carbon-coated copper foil was obtained.

[0070] A mixture of 3 wt% negative electrode binder (Shenzhen Haodian Technology Co., Ltd., model HD3201), 74.5 wt% graphite (model PQ1-X3), 20% silicon (Lanxi Zhide New Energy Materials Co., Ltd., model: S0332), 1 wt% conductive carbon black (Ruiyat Tianjin Chemical Co., Ltd., model: SP conductive carbon black), and 1.5 wt% thickener sodium carboxymethyl cellulose (Changshu Weiyi Technology Co., Ltd., model: 2300) was mixed with deionized water and stirred to control the slurry solid content at 50% and the slurry viscosity at 3500 cP, thus preparing the negative electrode slurry. The negative electrode slurry was then coated onto the aforementioned carbon-coated copper foil, and after drying, cold pressing, and slitting, the final negative electrode sheet was obtained.

[0071] 3. Battery After assembling the negative electrode, separator (Shenzhen Xingyuan Material Technology Co., Ltd., model: SW16), and positive electrode (Ningbo Ronbay New Energy Technology Co., Ltd., model: NCM 523 series S701C) into a dry cell, the electrolyte is injected to obtain a lithium battery. The electrolyte model is LBC435E53. After encapsulation, the lithium-ion battery is obtained through processes such as formation and degassing.

[0072] Examples 2-27, Comparative Examples 1-6 Examples 2-27, Comparative Examples 1-6, and Example 1 follow most of the same steps, except that the first polymer uses the formulation in Table 1, and the second polymer uses the formulation in Table 2. In these examples, aromatic vinyl monomers are distributed in A6, A7, and A8 in a 1:1:1 mass ratio; acrylate monomers are distributed in A6, A7, and A8 in a 1:1:1 mass ratio; and crosslinking monomers are distributed in A6, A7, and A8 in a 1:1:1 mass ratio.

[0073] Comparative Example 7 Comparative Example 7 and Example 1 follow most of the same steps, except that in the preparation of the adhesive, A6, A7 and A8 are mixed and emulsified to obtain a mixed solution, which is then directly added to the reaction vessel with a roughness Sa of 0.12 μm.

[0074] Table 1 Table 2 Table 3 The binders, negative electrode sheets, and batteries prepared in the above embodiments and comparative examples were tested as follows.

[0075] 1. Volume average particle size test of binder: The test was conducted using a Malvern 3000 laser particle size analyzer with water as the medium, a refractive index of 1.33, a sample absorptivity of 0.01, and a refractive index of 1.596.

[0076] 2. Electrolyte swelling rate test: Take 10g of the solids portion of the above adhesive (emulsion) and place it in a 40℃ oven for 24 hours. After the emulsion forms a film, take a certain weight (m1) of the film and place it in 100mL of dimethyl carbonate (DMC). Store it at 80℃ for 72 hours. After wiping the surface dry, weigh it. The weight at this time is m2. The swelling rate of the film is calculated according to the following method: The swelling ratio is calculated as follows: M = [(m2-m1) / m1] × 100%.

[0077] 3. Contact angle test: The test was conducted in accordance with GB / T30447-2013. The substrate was copper foil and the liquid was an adhesive emulsion. The contact angle 10 seconds after the liquid came into contact with the foil was recorded as the final result.

[0078] 4. Peel strength test: After the base-coated electrode is prepared according to the above method, a tensile testing machine is used to measure it. The test method refers to GB2792—2014.

[0079] 5. Glass transition temperature test: The glass transition temperature of the first polymer is tested according to the test standard of GB / T19466.2-2004. The glass transition temperature of the second polymer is tested under the above standard after being synthesized separately according to the method of the second polymer.

[0080] 6. Cyclic performance test: At 25℃, charge at a constant current of 1C to 3.65V, then charge at a constant voltage with a cutoff current of 0.15A, rest for 10 minutes, discharge at a constant current of 1C to 2.5V, rest for 10 minutes, and take the discharge capacity at this point as the initial discharge capacity Qt; repeat this cycle for 500 cycles, then discharge at a constant current of 1C to 2.5V, record the discharge capacity Qret, and use this as the holding capacity to calculate the capacity retention rate; Cyclic capacity retention = (Qret / Qt) × 100% 7. Rate Performance Test: After the battery has been left to stand until its temperature reaches 25℃±2℃, charge it at 1C constant current and constant voltage to 4.35V, with a cutoff current of 0.05C; discharge it at 1C constant current to 2.75V and record the discharge capacity; repeat this cycle for 10 cycles, using the discharge capacity of the 10th cycle as the 1C discharge baseline capacity Q0; then charge it again at 1C constant current and constant voltage to 4.35V, with a cutoff current of 0.05C; discharge it at 2C current to 2.75V and record the 2C discharge capacity Q1. Calculate the 2C discharge capacity retention rate Q = (Q1 / Q0). 100%.

[0081] 8. Adhesive shell roughness Sa test: The test is conducted using Keyence VK-X1000 according to the method of ISO 25178 and Appendix X1 of ASTM D7127. The surface roughness is judged by the magnitude of Sa (arithmetic mean deviation). The larger the value, the rougher the surface.

[0082] The test results are shown in Table 4.

[0083] Table 4 As shown in Tables 1-4 of the examples and Table 4 of the test results, in Comparative Example 1, the second polymer of the shell lacks phosphate ester structural units, which prevents the formation of strong interfacial adhesion with the copper foil. Simultaneously, the roughness decreases, reducing ion conduction channels and leading to a significant decrease in adhesive peel strength, resulting in a significant reduction in battery cycle and rate performance. In Comparative Example 2, the content of phosphate ester structural units in the second polymer of the shell exceeds the upper limit, resulting in poor shell wetting ability, increased swelling, and decreased interfacial bonding, leading to a decrease in adhesive peel strength and a decline in battery cycle performance. In Comparative Example 3, the second polymer of the shell lacks amide structural units, which prevents the formation of strong hydrogen bonds with the active material, significantly reducing shell cohesion, roughness, and effective bonding surface area. The reduced area leads to a significant decrease in adhesive peel strength, resulting in a significant deterioration in battery cycle and rate performance. In Comparative Example 4, the content of amide structural units in the second polymer of the shell exceeds the upper limit, resulting in excessive shell rigidity, decreased adhesion, and decreased bonding interface stability, leading to a decrease in adhesive peel strength and battery cycle performance. In Comparative Example 5, the second polymer of the shell lacks olefin structural units, resulting in a decrease in polar bonding force with the copper foil, leading to a significant decrease in adhesive peel strength and battery cycle and rate performance. In Comparative Example 6, the content of olefin structural units in the second polymer of the shell exceeds the upper limit, the glass transition temperature of the shell exceeds the upper limit, the shell becomes hard and brittle, leading to a decrease in adhesive peel strength and battery cycle performance.

[0084] As can be seen from the test results of Examples 1 and 11 and 12, when the structural unit mass ratio and glass transition temperature of the first polymer core deviate from the preferred range, the mechanical support performance of the core decreases, the resistance to volume expansion stress of the silicon-based anode material weakens, the peel strength of the binder decreases slightly, and the cycle retention rate of the battery decreases slightly.

[0085] The test results of Examples 1 and 20, 23-25 ​​show that when the structural unit mass ratio, glass transition temperature and roughness of the second polymer in the shell deviate from the preferred range, the bonding toughness and interfacial bonding force of the shell decrease slightly, the peel strength of the adhesive decreases slightly, and the cycle and rate performance of the battery decreases slightly.

[0086] The test results from Examples 1, 6-19, 21-22, and 26-27 show that when the mass ratio of aromatic vinyl, acrylate, and crosslinking structural units of the first polymer in the core is in the range of (37~44):(1~15):(2~8), and the glass transition temperature is in the range of 50℃~80℃, while the mass ratio of aromatic vinyl, acrylate, crosslinking, phosphate, amide, olefin, and vinylsilane structural units of the second polymer in the shell is in the range of (6~30):(6~15):(3~15):(1~8):(1~5):(1~8):(1~5), the glass transition temperature is in the range of 0℃~20℃, and the surface roughness Sa is in the range of 0.2μm≤Sa≤0.5μm, the peel strength of the binder can be significantly improved, the contact angle and swelling rate can be optimized, and the cycle and rate performance of the battery can be greatly improved.

[0087] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An adhesive, characterized in that, The adhesive includes a core and a shell, the shell being disposed on the surface of the core and at least partially covering the core, the core comprising a first polymer, and the shell comprising a second polymer; The first polymer and the second polymer each independently comprise aromatic vinyl structural units, acrylate structural units, and crosslinking structural units; The second polymer also includes phosphate ester structural units, amide structural units and olefinic acid structural units, wherein the mass ratio of the phosphate ester structural units, amide structural units and olefinic acid structural units is (1~8):(1~5):(1~8).

2. The adhesive according to claim 1, characterized in that, The surface of the shell has an uneven structure, and the roughness Sa of the shell is 0.2μm≤Sa≤0.5μm.

3. The adhesive according to claim 1 or 2, characterized in that, In the first polymer, the mass ratio of the aromatic vinyl structural unit, the acrylate structural unit and the crosslinked structural unit is (37~44):(1~15):(2~8). And / or, in the second polymer, the mass ratio of the aromatic vinyl structural unit, acrylate structural unit, crosslinking structural unit, phosphate structural unit, amide structural unit and olefinic structural unit is (6~30):(6~15):(3~15):(1~8):(1~5):(1~8).

4. The adhesive according to claim 3, characterized in that, The second polymer further includes vinylsilane structural units; in the second polymer, the mass ratio of the aromatic vinyl structural units, acrylate structural units, crosslinking structural units, phosphate structural units, amide structural units, olefinic structural units, and vinylsilane structural units is (6~30):(6~15):(3~15):(1~8):(1~5):(1~8):(1~5).

5. The adhesive according to claim 4, characterized in that, The vinyl silane structural units include at least one of vinyltrimethoxysilane structural units, vinyltriethoxysilane structural units, vinyltri(2-methoxyethoxy)silane structural units, vinyltriisopropoxysilane structural units, and 3-methacryloyloxypropyltrimethoxysilane structural units.

6. The adhesive according to claim 1, characterized in that, The glass transition temperature of the first polymer is 50℃~80℃, and the glass transition temperature of the second polymer is 0℃~20℃.

7. The adhesive according to claim 1, characterized in that, The adhesive is an emulsion, and the contact angle between the emulsion and the copper foil is <60°.

8. The adhesive according to claim 1, characterized in that, The mass swelling rate of the adhesive is 30% to 50%.

9. A negative electrode sheet, characterized in that, It includes a negative electrode current collector, a base coating, and a negative electrode active material layer. The base coating is disposed on at least one side surface of the negative electrode current collector, and the negative electrode active material layer is disposed on the side of the base coating opposite to the negative electrode current collector. The base coating comprises the adhesive as described in any one of claims 1-8.

10. A battery, characterized in that, Includes the negative electrode sheet as described in claim 9.

Images