Process for the preparation and use of a crosslinking polymeric binder

Abstract

The application discloses a preparation method of a crosslinking polymerization type adhesive, wherein n-octyl (meth) acrylate, N-hydroxymethyl methacrylamide, lithium p-styrenesulfonate and KH570 are added into DMF to obtain a monomer mixture liquid, N2 is continuously introduced, dibenzoyl peroxide is added, and temperature is increased to stir and react, so as to obtain a polymer; lithium hydroxide ethanol solution is added to adjust the pH of the system, then succinic acid dihydrazide is added, and stirring reaction is conducted, so as to obtain the crosslinking polymerization type adhesive; the crosslinking polymerization type adhesive is used for a secondary battery; the application can effectively adapt to the volume change of a negative active material in the lithium ion embedding / extraction process, significantly inhibit the expansion of a lithium ion battery, effectively reduce the loss of active substances and the attenuation of battery capacity, and improve the cycle stability and cycle life of the battery.

Description

Technical Field

[0001] This invention relates to the field of secondary battery technology, specifically to a method for preparing a cross-linked polymeric binder and its application in secondary batteries. Background Technology

[0002] Since its commercialization in 1991, lithium-ion batteries have made tremendous progress and are widely used in various portable electronic devices and new energy vehicles, making them the most widely used chemical power source. As lithium-ion batteries are applied from portable electronic devices to large-scale energy storage systems, further improving their energy density is crucial. Traditional lithium-ion batteries use graphite as the anode, with a theoretical specific capacity of only 372 mAh / g, making it difficult to significantly increase the energy density. Silicon, with its ultra-high theoretical specific capacity (up to 4200 mAh / g at high temperatures), high volumetric specific capacity (9786 mAh / cm³), low lithium insertion / extraction potential (<0.5V vs. Li / Li+), high storage capacity, and low pollution, has become one of the most promising next-generation anode materials. However, silicon-based anode materials also have some defects. For example, a huge volume change occurs during the lithium insertion / extraction process, and the resulting stress can easily cause silicon particles to break and pulverize and lose activity. In addition, the large volume change will also cause the solid electrolyte interphase (SEI) film to break and recombine continuously, resulting in the consumption of active lithium. All of these factors combined lead to a sharp decline in the capacity of silicon-based anodes during cycling and severely limit the practical application of silicon-based anodes.

[0003] Binders are crucial inactive components of lithium-ion batteries, adhering the electrode active materials and conductive agents to the current collector. Their performance directly impacts the battery's electrochemical performance. Water-based binders used in lithium-ion batteries primarily include: styrene-butadiene rubber (SBR) / sodium carboxymethyl cellulose (CMC), polyacrylic acid (PAA), sodium alginate (NaAlg), and polyvinyl alcohol (PVA). When using SBR as a binder, CMC must be added simultaneously as a thickener. However, CMC generally has low viscosity, is brittle, and lacks flexibility, making the electrode prone to cracking during charging and discharging. Using PAA as a binder presents challenges due to its high glass transition temperature and hardness at room temperature. Electrodes prepared with this type of binder may experience binder breakage during lithium insertion / extraction due to volume changes in the active material, leading to the active material detaching from the electrode.

[0004] Polyhydroxy polymers have good thermal stability and film-forming properties, and can form hydrogen bonds with hydroxyl functional groups on the silicon surface, which can buffer the volume expansion of silicon anodes to a certain extent.

[0005] Chinese patent document CN202310814397.7 discloses a modified polyvinyl alcohol binder and its preparation method, as well as a modified composite current collector. The preparation method includes the following steps: alternatingly freezing and thawing an aqueous solution of polyvinyl alcohol to obtain pre-crosslinked polyvinyl alcohol; treating the pre-crosslinked polyvinyl alcohol in a lithium salt solution to obtain the modified polyvinyl alcohol binder, which has a double crosslinked network and rich branched structure, and exhibits high elongation, excellent adhesion performance, and lithium replenishment effect.

[0006] However, using a single polyhydroxy polymer binder has drawbacks such as low viscosity, poor functionality, and poor dispersion of electrode materials, leaving significant room for improvement in the electrochemical performance of silicon anodes. Therefore, there is an urgent need to develop polymer binders with high adhesion, high flexibility, and high electron transport efficiency to maintain electrode structural stability and improve battery cycle life. Summary of the Invention

[0007] To address the shortcomings of existing technologies, one objective of this invention is to provide a method for preparing a cross-linked polymeric binder. The prepared cross-linked polymeric binder can effectively adapt to the volume changes of the negative electrode active material during the lithium-ion insertion / extraction process, significantly suppress the expansion of the lithium-ion battery, effectively reduce the loss of active material and the decay of battery capacity, and improve the cycle stability and cycle life of the battery.

[0008] The technical solution adopted by this invention to solve its technical problem is: a method for preparing a cross-linked polymeric adhesive, comprising the following steps: (1) Add (meth) octyl acrylate, N-hydroxymethyl methacrylamide, lithium p-styrene sulfonate and KH570 to DMF, stir evenly to obtain monomer mixture, continuously introduce N2, preheat the monomer mixture, add benzoyl peroxide, heat up and stir to react to obtain polymer; (2) Add lithium hydroxide ethanol solution to the reaction system of step (1), adjust the pH of the system, add succinic acid dihydrazide, stir the reaction, and remove unreacted substances by dialysis after the reaction is completed to obtain cross-linked polymerized adhesive.

[0009] In the preparation method of the crosslinking polymerized adhesive, the weight ratio of (meth)acrylate n-octyl acrylate, N-hydroxymethyl methacrylamide, lithium p-styrene sulfonate, and KH570 in step (1) is 6-12:5-8:2.1-4.21:0.9-1.7.

[0010] Furthermore, in step (1), the amount of DMF used is 20 to 30 times the total amount of monomers, and the amount of benzoyl peroxide added is 0.5 to 2% of the total amount of monomers.

[0011] Furthermore, in step (1), the temperature is preheated to 30-45°C, then raised to 60-80°C, and the reaction is carried out under stirring conditions of 600-800 r / min for 8-12 hours.

[0012] In the preparation method of the cross-linked polymeric adhesive, the concentration of lithium hydroxide ethanol solution in step (2) is 10 wt%, and the pH of the system is adjusted to 8-10.

[0013] Furthermore, in step (2), the amount of succinic dihydrazide added is 2 to 15% of the total amount of monomer.

[0014] Furthermore, in step (2), the stirring reaction conditions are 40-60℃ and 420-500r / min for 2-6 hours.

[0015] The second objective of this invention is to provide a cross-linked polymeric adhesive prepared by the above-described preparation method.

[0016] A second objective of this invention is to provide a secondary battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein at least one of the positive electrode, the negative electrode, and the separator contains the aforementioned cross-linked polymeric binder.

[0017] Furthermore, the secondary battery is a lithium-ion battery, and the negative electrode sheet includes a negative electrode current collector and a negative electrode slurry. The negative electrode slurry includes a conductive agent, a negative electrode active material, and the aforementioned cross-linked polymeric binder.

[0018] Compared with the prior art, the present invention has the following beneficial effects: 1. The cross-linked polymeric binder of this invention can improve the lithium-ion conductivity of the binder and enhance the ion transport capability of the electrode. On the other hand, it also has good mechanical properties, film-forming properties, and adhesion. It is suitable for silicon-based anode active materials and can form hydrogen bonds and chemical bonds with the hydroxyl functional groups on the silicon surface. This allows the binder to effectively adapt to the volume changes of the anode active material during the lithium-ion insertion / extraction process, significantly suppress the expansion of the anode material, effectively reduce the loss of active material and the decay of battery capacity, and improve the cycle stability and cycle life of the battery.

[0019] 2. The crosslinking polymeric adhesive of this invention uses (meth)acrylate n-octyl acrylate, N-hydroxymethylmethacrylamide, lithium p-styrene sulfonate, and KH570 as monomers. Under the initiation of benzoyl peroxide, a polymer is obtained. The resulting polymer is mainly composed of acrylate and hydroxyl-containing acrylamide. The chain segments also contain two types of functional segments: styrene structural units with sulfonic acid groups in the side chains and structural units with siloxane groups in the side chains. The polymer segments contain abundant polar functional groups such as ester bonds, hydroxyl groups, and amide groups, which can form hydrogen bonds with the surface of silicon particles, improving the adhesion to silicon-based active materials. The introduction of rigid benzene rings in lithium p-styrene sulfonate increases the glass transition temperature of the adhesive, improves the Young's modulus and mechanical properties of the adhesive, thereby better suppressing the volume expansion of silicon and alleviating electrode cracking. The sulfonic acid groups have a strong affinity for lithium ions. This process significantly improves the ion conductivity of the battery, enhances the ion transport capability of the binder, and increases the battery's specific capacity and cycle life. Furthermore, KH570 is used to introduce siloxane segments into the binder. These siloxane segments, after hydrolysis, can undergo a condensation reaction with the hydroxyl groups on the surface of the active material and current collector. During charge and discharge, this tightly bonds the silicon-based active material and conductive agent to the current collector, further improving the binder's bonding strength. This significantly suppresses the volume expansion of the negative electrode active material during lithium intercalation / deintercalation, preventing pulverization and detachment, thereby further extending the cycle performance of the lithium-ion battery. Finally, succinic dihydrazide is used as a crosslinking agent to prepare a crosslinked polymeric binder. After crosslinking, the binder's toughness is further improved, allowing it to fully encapsulate the active material, thus suppressing battery expansion and extending the battery's capacity and retention rate. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. Of course, the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0021] Unless otherwise specified, all chemical reagents and materials in this invention are purchased from the market or synthesized from raw materials purchased from the market.

[0022] The present invention will be further described below through specific embodiments. Example 1

[0023] The preparation method of the crosslinked polymeric adhesive in this embodiment includes the following steps: (1) 1.2g of (meth)acrylate n-octyl ester, 0.8g of N-hydroxymethyl methacrylamide, 0.42g of lithium p-styrene sulfonate and 0.17g of KH570 were added to 55g of DMF and stirred evenly to obtain a monomer mixture. N2 was continuously introduced and the monomer mixture was preheated to 45°C. 0.05g of benzoyl peroxide was added and the temperature was raised to 80°C. The mixture was stirred at 800r / min for 12h to obtain a polymer.

[0024] (2) Add 10wt% lithium hydroxide ethanol solution to the reaction system of step (1), adjust the pH of the system to 8, and then add 0.38g of succinic acid dihydrazide. Stir the reaction at 60℃ and 500r / min for 6h. After the reaction is completed, remove the unreacted material by dialysis to obtain the cross-linked polymerized adhesive.

[0025] The method for preparing a lithium-ion battery using the cross-linked polymeric binder of this embodiment includes the following steps: Preparation of negative electrode sheet: The negative electrode active material SiOx / graphite composite negative electrode material (SiOx content 10wt%, specific capacity of composite negative electrode is 450mAh / g), the cross-linked polymeric binder prepared above, and conductive carbon black are dispersed in deionized water. After stirring, a uniformly dispersed negative electrode slurry is obtained, which contains 80wt% SiOx / graphite composite negative electrode material, 10wt% cross-linked polymeric binder, and 10wt% conductive carbon black. The solid content of the negative electrode slurry is 45wt%. The negative electrode slurry was passed through a 150-mesh screen and then evenly coated on both sides of a copper foil. After drying at 120°C for 4 hours, it was compacted using a roller press to obtain a silicon-based negative electrode sheet. Preparation of the positive electrode sheet: The positive electrode active material lithium cobalt oxide, binder PVDF and conductive carbon black were dispersed in N-methylpyrrolidone. After stirring, a uniformly dispersed positive electrode slurry was obtained, in which the solid components included 80wt% lithium cobalt oxide, 10wt% PVDF and 10wt% conductive carbon black. The positive electrode slurry was uniformly coated on both sides of the aluminum foil, dried at 120℃ for 4 hours, and then compacted using a roller press to obtain the positive electrode sheet. The preparation of the lithium-ion battery: the positive electrode sheet, negative electrode sheet and separator (PP / PE / PP composite film, 9μm thick, 41% porosity) were wound into a cell, then baked, injected with electrolyte (a binary solvent of dimethyl carbonate and ethylene carbonate in a volume ratio of 1:1 containing 1mol / L lithium hexafluorophosphate, and 10wt% fluoroethylene carbonate as an additive), formed, and then sealed to obtain the lithium-ion battery. Example 2

[0026] The preparation method of the crosslinked polymeric adhesive in this embodiment includes the following steps: (1) Add 1g of (meth)acrylate n-octyl ester, 0.7g of N-hydroxymethylmethacrylamide, 0.38g of lithium p-styrenesulfonate and 0.15g of KH570 to 45g of DMF, stir evenly to obtain a monomer mixture, continuously introduce N2, preheat the monomer mixture to 40℃, add 0.04 benzoyl peroxide, raise the temperature to 70℃ and stir at 750r / min for 10h to obtain the polymer.

[0027] (2) Add 10wt% lithium hydroxide ethanol solution to the reaction system of step (1), adjust the pH of the system to 9, and then add 0.22g of succinic acid dihydrazide. Stir the reaction at 55℃ and 480r / min for 4h. After the reaction is completed, remove the unreacted material by dialysis to obtain the cross-linked polymerized adhesive.

[0028] The method for preparing a lithium-ion battery using the cross-linked polymeric binder of this embodiment includes the following steps: Preparation of negative electrode sheet: The negative electrode active material SiOx / graphite composite negative electrode material (SiOx content 10wt%, specific capacity of composite negative electrode is 450mAh / g), the cross-linked polymeric binder prepared above, and conductive carbon black are dispersed in deionized water. After stirring, a uniformly dispersed negative electrode slurry is obtained, which contains 80wt% SiOx / graphite composite negative electrode material, 10wt% cross-linked polymeric binder, and 10wt% conductive carbon black. The solid content of the negative electrode slurry is 45wt%. The negative electrode slurry was passed through a 150-mesh screen and then evenly coated on both sides of a copper foil. After drying at 120°C for 4 hours, it was compacted using a roller press to obtain a silicon-based negative electrode sheet. Preparation of the positive electrode sheet: The positive electrode active material lithium cobalt oxide, binder PVDF and conductive carbon black were dispersed in N-methylpyrrolidone. After stirring, a uniformly dispersed positive electrode slurry was obtained, in which the solid components included 80wt% lithium cobalt oxide, 10wt% PVDF and 10wt% conductive carbon black. The positive electrode slurry was uniformly coated on both sides of the aluminum foil, dried at 120℃ for 4 hours, and then compacted using a roller press to obtain the positive electrode sheet. The preparation of the lithium-ion battery: the positive electrode sheet, negative electrode sheet and separator (PP / PE / PP composite film, 9μm thick, 41% porosity) were wound into a cell, then baked, injected with electrolyte (a binary solvent of dimethyl carbonate and ethylene carbonate in a volume ratio of 1:1 containing 1mol / L lithium hexafluorophosphate, and 10wt% fluoroethylene carbonate as an additive), formed, and then sealed to obtain the lithium-ion battery. Example 3

[0029] The preparation method of the crosslinked polymeric adhesive in this embodiment includes the following steps: (1) Add 0.8g of (meth)acrylate n-octyl ester, 0.6g of N-hydroxymethylmethacrylamide, 0.31g of lithium p-styrenesulfonate, and 0.12g of KH570 to 36g of DMF, stir evenly to obtain a monomer mixture, continuously introduce N2, preheat the monomer mixture to 35°C, add 0.03g of benzoyl peroxide, raise the temperature to 65°C and stir at 700r / min for 9h to obtain the polymer.

[0030] (2) Add 10wt% lithium hydroxide ethanol solution to the reaction system of step (1), adjust the pH of the system to 9, add 0.18g succinic acid dihydrazide, stir the reaction at 50℃ and 450r / min for 3h, and remove unreacted substances by dialysis after the reaction to obtain cross-linked polymerized adhesive.

[0031] The method for preparing a lithium-ion battery using the cross-linked polymeric binder of this embodiment includes the following steps: Preparation of negative electrode sheet: The negative electrode active material SiOx / graphite composite negative electrode material (SiOx content 10wt%, specific capacity of composite negative electrode is 450mAh / g), the cross-linked polymeric binder prepared above, and conductive carbon black are dispersed in deionized water. After stirring, a uniformly dispersed negative electrode slurry is obtained, which contains 80wt% SiOx / graphite composite negative electrode material, 10wt% cross-linked polymeric binder, and 10wt% conductive carbon black. The solid content of the negative electrode slurry is 45wt%. The negative electrode slurry was passed through a 150-mesh screen and then evenly coated on both sides of a copper foil. After drying at 120°C for 4 hours, it was compacted using a roller press to obtain a silicon-based negative electrode sheet. Preparation of the positive electrode sheet: The positive electrode active material lithium cobalt oxide, binder PVDF and conductive carbon black were dispersed in N-methylpyrrolidone. After stirring, a uniformly dispersed positive electrode slurry was obtained, in which the solid components included 80wt% lithium cobalt oxide, 10wt% PVDF and 10wt% conductive carbon black. The positive electrode slurry was uniformly coated on both sides of the aluminum foil, dried at 120℃ for 4 hours, and then compacted using a roller press to obtain the positive electrode sheet. The preparation of the lithium-ion battery: the positive electrode sheet, negative electrode sheet and separator (PP / PE / PP composite film, 9μm thick, 41% porosity) were wound into a cell, then baked, injected with electrolyte (a binary solvent of dimethyl carbonate and ethylene carbonate in a volume ratio of 1:1 containing 1mol / L lithium hexafluorophosphate, and 10wt% fluoroethylene carbonate as an additive), formed, and then sealed to obtain the lithium-ion battery. Example 4

[0032] The preparation method of the crosslinked polymeric adhesive in this embodiment includes the following steps: (1) Add 0.6g of (meth)acrylate n-octyl ester, 0.5g of N-hydroxymethylmethacrylamide, 0.21g of lithium p-styrenesulfonate, and 0.09g of KH570 to 30g of DMF, stir evenly to obtain a monomer mixture, continuously introduce N2, preheat the monomer mixture to 30℃, add 0.015g of benzoyl peroxide, raise the temperature to 60℃ and stir at 600r / min for 8h to obtain the polymer.

[0033] (2) Add 10wt% lithium hydroxide ethanol solution to the reaction system of step (1), adjust the pH of the system to 10, add 0.14g succinic acid dihydrazide, stir the reaction at 40℃ and 420r / min for 2h, and remove unreacted substances by dialysis after the reaction to obtain cross-linked polymerized adhesive.

[0034] The method for preparing a lithium-ion battery using the cross-linked polymeric binder of this embodiment includes the following steps: Preparation of negative electrode sheet: The negative electrode active material SiOx / graphite composite negative electrode material (SiOx content 10wt%, specific capacity of composite negative electrode is 450mAh / g), the cross-linked polymeric binder prepared above, and conductive carbon black are dispersed in deionized water. After stirring, a uniformly dispersed negative electrode slurry is obtained, which contains 80wt% SiOx / graphite composite negative electrode material, 10wt% cross-linked polymeric binder, and 10wt% conductive carbon black. The solid content of the negative electrode slurry is 45wt%. The negative electrode slurry was passed through a 150-mesh screen and then evenly coated on both sides of a copper foil. After drying at 120°C for 4 hours, it was compacted using a roller press to obtain a silicon-based negative electrode sheet. Preparation of the positive electrode sheet: The positive electrode active material lithium cobalt oxide, binder PVDF and conductive carbon black were dispersed in N-methylpyrrolidone. After stirring, a uniformly dispersed positive electrode slurry was obtained, in which the solid components included 80wt% lithium cobalt oxide, 10wt% PVDF and 10wt% conductive carbon black. The positive electrode slurry was uniformly coated on both sides of the aluminum foil, dried at 120℃ for 4 hours, and then compacted using a roller press to obtain the positive electrode sheet. The preparation of the lithium-ion battery: the positive electrode sheet, negative electrode sheet and separator (PP / PE / PP composite film, 9μm thick, 41% porosity) were wound into a cell, then baked, injected with electrolyte (a binary solvent of dimethyl carbonate and ethylene carbonate in a volume ratio of 1:1 containing 1mol / L lithium hexafluorophosphate, and 10wt% fluoroethylene carbonate as an additive), formed, and then sealed to obtain the lithium-ion battery.

[0035] Comparative Example 1. A method for preparing an adhesive, comprising the following steps: adding 1.2 g of (meth)acrylate n-octyl ester, 0.8 g of N-hydroxymethylmethacrylamide, 0.42 g of lithium p-styrene sulfonate, and 0.17 g of KH570 to 55 g of DMF, stirring until homogeneous to obtain a monomer mixture, continuously introducing N2, preheating the monomer mixture to 45 °C, adding 0.05 g of benzoyl peroxide, raising the temperature to 80 °C, and stirring at 800 r / min for 12 h to obtain the adhesive.

[0036] A method for preparing a lithium-ion battery includes the following steps: Preparation of the negative electrode sheet: The negative electrode active material SiOx / graphite composite negative electrode material (SiOx content 10wt%, specific capacity of composite negative electrode is 450mAh / g), the binder prepared above, and conductive carbon black are dispersed in deionized water, and after stirring, a uniformly dispersed negative electrode slurry is obtained, which contains 80wt% SiOx / graphite composite negative electrode material, 10wt% binder, and 10wt% conductive carbon black, and the solid content of the negative electrode slurry is 45wt%. The negative electrode slurry was passed through a 150-mesh screen and then evenly coated on both sides of a copper foil. After drying at 120°C for 4 hours, it was compacted using a roller press to obtain a silicon-based negative electrode sheet. Preparation of the positive electrode sheet: The positive electrode active material lithium cobalt oxide, binder PVDF and conductive carbon black were dispersed in N-methylpyrrolidone. After stirring, a uniformly dispersed positive electrode slurry was obtained, in which the solid components included 80wt% lithium cobalt oxide, 10wt% PVDF and 10wt% conductive carbon black. The positive electrode slurry was uniformly coated on both sides of the aluminum foil, dried at 120℃ for 4 hours, and then compacted using a roller press to obtain the positive electrode sheet. The preparation of the lithium-ion battery: the positive electrode sheet, negative electrode sheet and separator (PP / PE / PP composite film, 9μm thick, 41% porosity) were wound into a cell, then baked, injected with electrolyte (a binary solvent of dimethyl carbonate and ethylene carbonate in a volume ratio of 1:1 containing 1mol / L lithium hexafluorophosphate, and 10wt% fluoroethylene carbonate as an additive), formed, and then sealed to obtain the lithium-ion battery.

[0037] Comparative Example 2. A method for preparing an adhesive, comprising the following steps: (1) 1.2g of (meth)acrylate n-octyl ester, 0.8g of N-hydroxymethylmethacrylamide and 0.42g of lithium p-styrene sulfonate are added to 55g of DMF and stirred evenly to obtain a monomer mixture. N2 is continuously introduced and the monomer mixture is preheated to 45°C. 0.05g of benzoyl peroxide is added and the temperature is raised to 80°C. The mixture is stirred at 800r / min for 12h to obtain a polymer. (2) 10wt% lithium hydroxide ethanol solution is added to the reaction system of step (1), the pH of the system is adjusted to 8, and 0.38g of succinic acid dihydrazide is added. The mixture is stirred at 60°C and 500r / min for 6h. After the reaction is completed, unreacted substances are removed by dialysis to obtain the adhesive.

[0038] A method for preparing a lithium-ion battery includes the following steps: Preparation of the negative electrode sheet: The negative electrode active material SiOx / graphite composite negative electrode material (SiOx content 10wt%, specific capacity of composite negative electrode is 450mAh / g), the binder prepared above, and conductive carbon black are dispersed in deionized water, and after stirring, a uniformly dispersed negative electrode slurry is obtained, which contains 80wt% SiOx / graphite composite negative electrode material, 10wt% binder, and 10wt% conductive carbon black, and the solid content of the negative electrode slurry is 45wt%. The negative electrode slurry was passed through a 150-mesh screen and then evenly coated on both sides of a copper foil. After drying at 120°C for 4 hours, it was compacted using a roller press to obtain a silicon-based negative electrode sheet. Preparation of the positive electrode sheet: The positive electrode active material lithium cobalt oxide, binder PVDF and conductive carbon black were dispersed in N-methylpyrrolidone. After stirring, a uniformly dispersed positive electrode slurry was obtained, in which the solid components included 80wt% lithium cobalt oxide, 10wt% PVDF and 10wt% conductive carbon black. The positive electrode slurry was uniformly coated on both sides of the aluminum foil, dried at 120℃ for 4 hours, and then compacted using a roller press to obtain the positive electrode sheet. The preparation of the lithium-ion battery: the positive electrode sheet, negative electrode sheet and separator (PP / PE / PP composite film, 9μm thick, 41% porosity) were wound into a cell, then baked, injected with electrolyte (a binary solvent of dimethyl carbonate and ethylene carbonate in a volume ratio of 1:1 containing 1mol / L lithium hexafluorophosphate, and 10wt% fluoroethylene carbonate as an additive), formed, and then sealed to obtain the lithium-ion battery.

[0039] Comparative Example 3. A method for preparing an adhesive, comprising the following steps: (1) 1.2g of (meth)acrylate n-octyl ester, 0.8g of N-hydroxymethyl methacrylamide and 0.17g of KH570 are added to 55g of DMF and stirred evenly to obtain a monomer mixture. N2 is continuously introduced and the monomer mixture is preheated to 45°C. 0.05g of benzoyl peroxide is added and the temperature is raised to 80°C. The mixture is stirred at 800r / min for 12h to obtain a polymer. (2) 10wt% lithium hydroxide ethanol solution is added to the reaction system of step (1), the pH of the system is adjusted to 8, and 0.38g of succinic acid dihydrazide is added. The mixture is stirred at 60°C and 500r / min for 6h. After the reaction is completed, unreacted substances are removed by dialysis to obtain the adhesive.

[0040] A method for preparing a lithium-ion battery includes the following steps: Preparation of the negative electrode sheet: The negative electrode active material SiOx / graphite composite negative electrode material (SiOx content 10wt%, specific capacity of composite negative electrode is 450mAh / g), the binder prepared above, and conductive carbon black are dispersed in deionized water, and after stirring, a uniformly dispersed negative electrode slurry is obtained, which contains 80wt% SiOx / graphite composite negative electrode material, 10wt% binder, and 10wt% conductive carbon black, and the solid content of the negative electrode slurry is 45wt%. The negative electrode slurry was passed through a 150-mesh screen and then evenly coated on both sides of a copper foil. After drying at 120°C for 4 hours, it was compacted using a roller press to obtain a silicon-based negative electrode sheet. Preparation of the positive electrode sheet: The positive electrode active material lithium cobalt oxide, binder PVDF and conductive carbon black were dispersed in N-methylpyrrolidone. After stirring, a uniformly dispersed positive electrode slurry was obtained, in which the solid components included 80wt% lithium cobalt oxide, 10wt% PVDF and 10wt% conductive carbon black. The positive electrode slurry was uniformly coated on both sides of the aluminum foil, dried at 120℃ for 4 hours, and then compacted using a roller press to obtain the positive electrode sheet. The preparation of the lithium-ion battery: the positive electrode sheet, negative electrode sheet and separator (PP / PE / PP composite film, 9μm thick, 41% porosity) were wound into a cell, then baked, injected with electrolyte (a binary solvent of dimethyl carbonate and ethylene carbonate in a volume ratio of 1:1 containing 1mol / L lithium hexafluorophosphate, and 10wt% fluoroethylene carbonate as an additive), formed, and then sealed to obtain the lithium-ion battery.

[0041] Comparative Example 4. A method for preparing an adhesive, comprising the following steps: adding 1.2 g of (meth)acrylate n-octyl ester and 0.8 g of N-hydroxymethyl methacrylamide to 55 g of DMF, stirring evenly to obtain a monomer mixture, continuously introducing N2, preheating the monomer mixture to 45 °C, adding 0.05 g of benzoyl peroxide, raising the temperature to 80 °C, and stirring at 800 r / min for 12 h to obtain the adhesive.

[0042] A method for preparing a lithium-ion battery includes the following steps: Preparation of the negative electrode sheet: The negative electrode active material SiOx / graphite composite negative electrode material (SiOx content 10wt%, specific capacity of composite negative electrode is 450mAh / g), the binder prepared above, and conductive carbon black are dispersed in deionized water, and after stirring, a uniformly dispersed negative electrode slurry is obtained, which contains 80wt% SiOx / graphite composite negative electrode material, 10wt% binder, and 10wt% conductive carbon black, and the solid content of the negative electrode slurry is 45wt%. The negative electrode slurry was passed through a 150-mesh screen and then evenly coated on both sides of a copper foil. After drying at 120°C for 4 hours, it was compacted using a roller press to obtain a silicon-based negative electrode sheet. Preparation of the positive electrode sheet: The positive electrode active material lithium cobalt oxide, binder PVDF and conductive carbon black were dispersed in N-methylpyrrolidone. After stirring, a uniformly dispersed positive electrode slurry was obtained, in which the solid components included 80wt% lithium cobalt oxide, 10wt% PVDF and 10wt% conductive carbon black. The positive electrode slurry was uniformly coated on both sides of the aluminum foil, dried at 120℃ for 4 hours, and then compacted using a roller press to obtain the positive electrode sheet. The preparation of the lithium-ion battery: the positive electrode sheet, negative electrode sheet and separator (PP / PE / PP composite film, 9μm thick, 41% porosity) were wound into a cell, then baked, injected with electrolyte (a binary solvent of dimethyl carbonate and ethylene carbonate in a volume ratio of 1:1 containing 1mol / L lithium hexafluorophosphate, and 10wt% fluoroethylene carbonate as an additive), formed, and then sealed to obtain the lithium-ion battery.

[0043] Performance tests were conducted on the adhesives prepared in Examples 1-4 and Comparative Examples 1-4. The peel strength was tested using a universal tensile testing machine, referring to GB / T 2790-1995 "Adhesives - 180° Peel Strength Test Method - Flexible Materials vs. Rigid Materials". The test method was as follows: Two copper foil sheets with dimensions of 40mm × 100mm were taken out and cleaned with alcohol before use. During the test, sufficient electrode paste was coated on one end of the two copper foil sheets, with a coating area of ​​5.5cm × 1.3cm. After coating, the sheets were placed in a 120℃ oven for 4 hours to dry. Finally, one end of the sample was fixed to a tensile probe, and a 180° peel was performed at a constant speed of 10mm / min. The magnitude of the peel force during the peeling process was used to characterize the adhesive strength.

[0044] Performance tests were conducted on the batteries prepared in Examples 1-4 and Comparative Examples 1-4. A LAND-CT2001A tester was used to perform constant current charge-discharge cycle tests at 25°C. The discharge cutoff voltage was 0.005V, and the charge cutoff voltage was 1.5V. First, the batteries were charged and discharged three times at a current density of 100mA / g, and then charged and discharged three times at a current density of 500mA / g. The battery capacity retention rate after 300 cycles was calculated, and the percentage increase in battery thickness relative to the original thickness (denoted as the expansion rate) was recorded. Specific data are shown in the table below.

[0045] .

[0046] To address the modifications proposed in this invention, the inventors specifically prepared four comparative examples. Comparative Example 1 lacked the crosslinking treatment of the copolymer using succinic dihydrazide in step (2) compared to the scheme provided by this invention. Comparative Example 2 lacked the treatment of embedding siloxane functional segments using KH570 in step (1). Comparative Example 3 lacked the treatment of embedding sulfonic acid functional segments using lithium styrene sulfonate in step (1). Comparative Example 4 lacked the modification of lithium styrene sulfonate and KH570 in step (1) and the crosslinking treatment in step (2). According to the data in the table, the adhesive obtained in Comparative Example 4 is significantly worse than the example in terms of peel strength, expansion rate, and battery electrochemical performance. The adhesives obtained in Comparative Examples 1 and 2 are significantly worse than the example in terms of peel strength, expansion rate, and cycle performance. The adhesive obtained in Comparative Example 3 has a significantly worse first discharge specific capacity than the example.

[0047] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a cross-linked polymeric adhesive, characterized in that: Includes the following steps (1) Add (meth)acrylate n-octyl acrylate, N-hydroxymethylmethacrylamide, lithium p-styrenesulfonate and KH570 in a weight ratio of 6~12:5~8:2.1~4.21:0.9~1.7 to DMF, stir evenly to obtain monomer mixture, continuously introduce N2, preheat the monomer mixture, add benzoyl peroxide, heat up and stir to react to obtain polymer; (2) Add lithium hydroxide ethanol solution to the reaction system of step (1), adjust the pH of the system, and then add succinic acid dihydrazide, wherein the amount of succinic acid dihydrazide added is 2 to 15% of the total amount of monomer. Stir the reaction, and remove the unreacted material by dialysis after the reaction is completed to obtain the cross-linked polymerized adhesive.

2. The method for preparing a cross-linked polymeric adhesive according to claim 1, characterized in that, In step (1), the amount of DMF used is 20 to 30 times the total amount of monomers, and the amount of benzoyl peroxide added is 0.5 to 2% of the total amount of monomers.

3. The method for preparing a cross-linked polymeric adhesive according to claim 1, characterized in that, In step (1), the temperature is preheated to 30-45°C, then raised to 60-80°C, and the reaction is carried out under stirring conditions of 600-800 r / min for 8-12 hours.

4. The method for preparing a cross-linked polymeric adhesive according to claim 1, characterized in that, In step (2), the concentration of the lithium hydroxide ethanol solution is 10 wt%, and the pH of the system is adjusted to 8-10.

5. The method for preparing a cross-linked polymeric adhesive according to claim 1, characterized in that, In step (2), the stirring reaction conditions are 40-60℃ and 420-500r / min for 2-6 hours.

6. A crosslinked polymeric adhesive prepared by the preparation method according to any one of claims 1 to 5.

7. A secondary battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, characterized in that, At least one of the positive electrode, negative electrode, and separator contains the cross-linked polymeric binder as described in claim 6.

8. A secondary battery according to claim 7, characterized in that, The secondary battery is a lithium-ion battery, and the negative electrode sheet includes a negative electrode current collector and a negative electrode slurry. The negative electrode slurry includes a conductive agent, a negative electrode active material, and the cross-linked polymeric binder as described in claim 6.