Dry-method electrode binder and preparation method thereof

Abstract

The invention discloses a dry-method electrode binder and a preparation method thereof. The dry-method electrode binder comprises polyethylene glycol-methacrylate. According to the invention, the limitation of the existing polytetrafluoroethylene as a dry-method electrode binder is overcome, so that the preparation process of the battery electrode and the performance of the battery are improved. According to the invention, the structure is optimized through copolymerization modification. Through copolymerization with a monomer with a functional group, the molecular structure of polyethylene glycol-methacrylate can be further adjusted, so that higher bonding strength, good thermal stability and better conductivity are realized. The copolymerization modification can also effectively improve the temperature resistance and corrosion resistance of the polyethylene glycol-methacrylate, so that the polyethylene glycol-methacrylate keeps better performance under different environmental conditions, thereby effectively improving the performance of the battery, reducing the production cost and promoting the innovation and optimization of the lithium battery manufacturing process.

Description

Technical Field

[0001] The present invention relates to the technical field of new energy batteries, and particularly to a dry electrode binder and a preparation method thereof. Background Art

[0002] In the manufacturing process of lithium-ion batteries, the traditional wet electrode preparation process has always been dominant. This method involves dissolving active materials, conductive agents, and binders in a solvent to form a uniform slurry, which is then coated on a metal current collector and undergoes steps such as drying and compaction to finally obtain the electrode. However, the limitations of the wet process are becoming increasingly apparent, especially in terms of environmental protection and production costs. Commonly used solvents such as NMP (N-methylpyrrolidone), although having good solubility, have problems of volatility and toxicity, posing potential hazards to workers' health and the environment. In addition, the wet process has cumbersome steps. In particular, the drying process not only consumes a large amount of energy but also prolongs the production cycle, increases the complexity of the process, and the maintenance cost of the equipment. Therefore, an environmentally friendly and low-cost production method has become the research direction, and the dry electrode preparation technology has thus emerged.

[0003] The core of the dry electrode preparation technology lies in eliminating the use of organic solvents, avoiding the solvent pollution and complex solvent recovery problems in the wet process. In the early exploration of this technology, researchers tried to use solid binders such as polytetrafluoroethylene (PTFE), which became an ideal choice due to its excellent chemical stability and mechanical properties. By directly mixing PTFE powder with active materials and applying high temperature and pressure, these materials can be effectively bonded tightly into an electrode film. Compared with the wet process, a significant advantage of the dry process is that it greatly simplifies the production process, reduces energy consumption and waste gas emissions. At the same time, the dry process has also gradually explored other binder materials, such as hot-melt binders. These binders become fluid when heated and can be mixed with active materials, forming a stable electrode structure after cooling. Although the use of such binders requires considering their heat resistance and chemical stability, they provide an effective solution, further promoting the application of the dry process in lithium battery production.

[0004] Polytetrafluoroethylene (PTFE) has certain advantages in the preparation of lithium battery electrodes, but its fluorine element characteristics also pose challenges to its application. Due to its fluorinated structure, PTFE, although having excellent chemical stability and high-temperature resistance, also has some disadvantages.

[0005] First of all, the fluorine-containing characteristics of PTFE pose certain problems in terms of environmental friendliness. The strong chemical inertness of fluorine makes it difficult to undergo effective chemical reactions with many materials, restricting its synergistic effects with other functional materials or binders. This characteristic results in a weak adhesion force between PTFE and electrode materials. Especially during multiple charge and discharge processes, the active materials are prone to falling off or separating, reducing the cycle performance and capacity retention of the battery. In addition, the high fluorine content in PTFE may release harmful gases in some environments. At high temperatures or under specific conditions, fluorides may volatilize or react with other substances, causing environmental pollution or having a corrosive effect on equipment. Especially during the production process, higher requirements are imposed on the process environment and waste gas treatment. This increases the complexity and cost of production, especially in terms of emission control and solvent recovery.

[0006] The fluorination characteristics of PTFE also endow it with high electrical insulation, restricting its application in electrodes, especially in areas where conductivity is required. In addition, since PTFE itself does not possess electronic conductivity, a large amount of conductive agents (such as carbon black or carbon nanotubes) need to be added, further increasing the material cost and potentially affecting the conductive efficiency of the electrodes. In summary, although PTFE exhibits excellent performance in chemical stability, high temperature resistance, and corrosion resistance, its low adhesion, environmental protection issues, and high processing requirements caused by its fluorine-containing nature limit its wide application in the field of lithium batteries.

[0007] In view of this, overcoming the technical defects existing in the above-mentioned prior art is an urgent problem to be solved in this technical field. Summary of the Invention

[0008] In view of the above defects or improvement requirements of the prior art, the present invention provides a dry electrode binder and a preparation method thereof, aiming to improve the overall performance and processability of electrode materials.

[0009] To achieve the above object, according to one aspect of the present invention, a dry electrode binder is provided, comprising: polyethylene glycol - methacrylate.

[0010] According to the second aspect of the present invention, a preparation method of the dry electrode binder as described in the first aspect is provided, and the method includes:

[0011] Dissolution step: Take appropriate amounts of polyethylene glycol and methacrylic acid according to the molar ratio, add a reaction solvent to completely dissolve the polyethylene glycol and methacrylic acid, and form a uniform solution;

[0012] Esterification reaction step: Add an appropriate amount of catalyst and stir evenly, carry out the esterification reaction, and add an appropriate amount of dehydrating agent to adsorb the water generated by the esterification reaction;

[0013] Neutralization treatment step: After the reaction is completed, an appropriate amount of dilute sodium hydroxide solution is added to the solution to neutralize the residual acidic catalyst, and the reaction by-products and residual acid are removed by washing to obtain a polyethylene glycol-methacrylate solution;

[0014] Solvent evaporation and concentration step: The reaction solvent is removed to obtain a concentrated product;

[0015] Purification step: The concentrated product is subjected to solvent recrystallization to obtain pure polyethylene glycol-methacrylate, and then separated by filtration and dried. The obtained pure polyethylene glycol-methacrylate is used as a dry electrode binder.

[0016] Preferably, in the dissolution step, the reaction solvent is anhydrous xylene or dichloromethane.

[0017] Preferably, in the esterification reaction step, during the esterification reaction, the temperature is maintained at 100 - 130 °C.

[0018] Preferably, in the dissolution step, the molar ratio of polyethylene glycol to methacrylic acid is 1:2 or 1:3.

[0019] In a third aspect, a dry electrode binder is provided, comprising: a polyethylene glycol-methacrylate-polythiophene copolymer, and the copolymerization chemical formula of the polyethylene glycol-methacrylate-polythiophene copolymer is:

[0020] HO-(CH 2 CH 2 O) m -COO-CH=CH-(-C 4 H 3 S-) n ;

[0021] wherein both m and n are positive integers.

[0022] According to the fourth aspect of the present invention, a preparation method of the dry electrode binder as described in the third aspect is provided, and the method includes:

[0023] Dissolution step: Appropriate amounts of polyethylene glycol and methacrylic acid are taken according to the molar ratio, and then a solvent is added to completely dissolve the polyethylene glycol and methacrylic acid to obtain a uniform solution;

[0024] Esterification reaction step: An appropriate amount of catalyst is added and stirred evenly, an esterification reaction is carried out, and an appropriate amount of dehydrating agent is added to adsorb the water generated in the esterification reaction; Solvent evaporation and concentration step:

[0025] The reaction solvent is removed to obtain a concentrated product;

[0026] Purification step: The concentrated product is subjected to solvent recrystallization to obtain polyethylene glycol-methacrylate;

[0027] Polymerization reaction step: Mix polyethylene glycol - methacrylate and thiophene to obtain a mixed solution;

[0028] Dropwise add ammonium persulfate solution, and gradually carry out a polymerization reaction between ammonium persulfate and thiophene, and collect the generated polythiophene precipitate;

[0029] Wash to remove unreacted thiophene monomers and residual ammonium persulfate, and dry to obtain a polyethylene glycol - methacrylate - polythiophene copolymer as a dry - process electrode binder.

[0030] Preferably, in the polymerization reaction step, first wash with deionized water until the filtrate is neutral; then wash with absolute ethanol.

[0031] Preferably, in the polymerization reaction step, during the mixing and polymerization reaction processes, maintain the temperature at 0 - 5 °C.

[0032] Preferably, in the esterification reaction step, the catalyst added is p - toluenesulfonic acid.

[0033] Generally speaking, compared with the prior art by the above - mentioned technical solution conceived by the present invention, the following beneficial effects are obtained:

[0034] First, polyethylene glycol - methacrylate significantly enhances the adhesion with the electrode active material through copolymer modification. Especially in combination with high - specific - surface - area materials (such as silicon, lithium cobaltate, etc.), it can effectively reduce the shedding and peeling of the active material during charge and discharge, thereby improving the cycle stability and capacity retention of the battery.

[0035] Second, polyethylene glycol - methacrylate has good flexibility. Especially after copolymer modification, the modification of its molecular chain enhances the crack resistance of the electrode, can effectively relieve the volume expansion and contraction during charge and discharge, avoid the generation of cracks and peeling of the electrode film, and extend the cycle life of the battery.

[0036] Third, polyethylene glycol - methacrylate significantly improves its conductivity after copolymer modification by introducing conductive monomers. In this way, it can reduce the dependence on external conductive agents (such as carbon black, carbon nanotubes, etc.), reduce the material cost and improve the charge - discharge efficiency of the battery.

[0037] Fourth, polyethylene glycol - methacrylate also has a low processing temperature and good processing adaptability, and can directly prepare the electrode through a dry - process, which simplifies the production process, reduces energy consumption, reduces the demand for high - temperature and high - pressure equipment, and further reduces the production cost and equipment maintenance cost.

[0038] Fifth, almost no organic solvents or only a small amount of solvents are required in the production process of polyethylene glycol - methacrylate. Detailed implementation manners

[0039] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below in conjunction with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0040] The dry electrode binder of the embodiment of the present invention includes polyethylene glycol-methacrylate. Its preparation method includes: Dissolution step: Take appropriate amounts of polyethylene glycol and methacrylic acid according to the molar ratio, add a reaction solvent to completely dissolve the polyethylene glycol and methacrylic acid, and form a uniform solution;

[0041] Esterification reaction step: Add an appropriate amount of catalyst and stir evenly, carry out the esterification reaction, and add an appropriate amount of dehydrating agent to adsorb the water generated by the esterification reaction;

[0042] Neutralization treatment step: After the reaction is completed, add an appropriate amount of dilute sodium hydroxide solution to the solution to neutralize the residual acidic catalyst, and wash to remove the reaction by-products and residual acid to obtain a polyethylene glycol-methacrylate solution;

[0043] Solvent evaporation and concentration step: Remove the reaction solvent to obtain a concentrated product;

[0044] Purification step: Recrystallize the concentrated product with a solvent to obtain pure polyethylene glycol-methacrylate, and then separate and dry by filtration, and use the obtained pure polyethylene glycol-methacrylate as the dry electrode binder.

[0045] The adhesion between polyethylene glycol-methacrylate and the electrode active material is significantly enhanced through copolymer modification. Especially in combination with high specific surface area materials (such as silicon, lithium cobaltate, etc.), it can effectively reduce the shedding and peeling of the active material during charge and discharge, thereby improving the cycle stability and capacity retention of the battery.

[0046] Polyethylene glycol-methacrylate has good flexibility. Especially after copolymer modification, the modification of its molecular chain enhances the crack resistance of the electrode, can effectively relieve the volume expansion and contraction during charge and discharge, avoid the generation of cracks and peeling of the electrode film, and extend the cycle life of the battery.

[0047] By introducing conductive monomers, the conductivity of polyethylene glycol-methacrylate is significantly improved after copolymer modification. This can reduce the dependence on external conductive agents (such as carbon black, carbon nanotubes, etc.), reduce the material cost and improve the charge and discharge efficiency of the battery.

[0048] Polyethylene glycol - methacrylate also has a relatively low processing temperature and good processing adaptability, and can directly prepare electrodes through a dry process, which simplifies the production process, reduces energy consumption, reduces the demand for high - temperature and high - pressure equipment, and thus reduces production costs and equipment maintenance costs.

[0049] Almost no organic solvents or only a small amount of solvents are required in the production process of polyethylene glycol - methacrylate.

[0050] The novel dry - process electrode binder of the embodiments of the present invention includes a polyethylene glycol - methacrylate - polythiophene copolymer. The embodiments of the present invention further optimize its performance through copolymerization modification to overcome the limitations of existing polytetrafluoroethylene (PTFE) as a dry - process electrode binder, thereby improving the preparation process of battery electrodes and the performance of batteries. Its preparation method includes:

[0051] Dissolution step: Take appropriate amounts of polyethylene glycol and methacrylic acid according to the molar ratio, and then add a solvent to completely dissolve the polyethylene glycol and methacrylic acid to obtain a uniform solution;

[0052] Esterification reaction step: Add an appropriate amount of catalyst and stir evenly, carry out the esterification reaction, and add an appropriate amount of dehydrating agent to adsorb the water generated by the esterification reaction; Solvent evaporation and concentration step:

[0053] Remove the reaction solvent to obtain the concentrated product;

[0054] Purification step: Recrystallize the concentrated product with a solvent to obtain polyethylene glycol - methacrylate;

[0055] Polymerization reaction step: Mix polyethylene glycol - methacrylate with thiophene to obtain a mixed solution;

[0056] Dropwise add an ammonium persulfate solution to gradually carry out a polymerization reaction between ammonium persulfate and thiophene, and collect the generated polythiophene precipitate;

[0057] Wash to remove unreacted thiophene monomers and residual ammonium persulfate, and dry to obtain a polyethylene glycol - methacrylate - polythiophene copolymer as a dry - process electrode binder.

[0058] Traditional PTFE, as a dry electrode binder, requires high temperature and high pressure during the processing, resulting in a complex production process and high energy consumption. At the same time, due to the low flexibility and poor adhesion performance of PTFE, it is easy to cause cracks or shedding of active materials in the electrode during use, affecting the cycle life and capacity retention of the battery. In addition, due to the electrical insulation of PTFE, a large amount of additional conductive agent is required, which further increases the cost and complexity of battery production. The present invention optimizes its structure through copolymerization modification. By copolymerizing with monomers having functional groups, the molecular structure of polyethylene glycol-methacrylate can be further adjusted to achieve higher adhesion strength, good thermal stability, and better electrical conductivity. Copolymerization modification can also effectively improve the temperature resistance and corrosion resistance of polyethylene glycol-methacrylate, enabling it to maintain good performance under different environmental conditions, thereby effectively improving the performance of the battery, reducing production costs, and promoting the innovation and optimization of lithium battery manufacturing processes.

[0059] Materials required for preparing the novel dry electrode binder of the present invention:

[0060] Polyethylene glycol: The molecular weight can be selected from 1000 to 20000, ensuring a high-purity product;

[0061] Methacrylic acid: High-purity product;

[0062] Catalyst: p-Toluenesulfonic acid;

[0063] Solvent: Anhydrous xylene or dichloromethane;

[0064] Others: Nitrogen.

[0065] The preparation process is as follows:

[0066] 1. Raw material preparation

[0067] Polyethylene glycol: Take the polyethylene glycol with the required molecular weight, weigh it, and dry it in a vacuum oven at 60 °C for several hours to remove adsorbed moisture.

[0068] Methacrylic acid: Dry it to ensure it is pure and free of moisture, and dry it in a vacuum dryer for several hours.

[0069] 2. Dissolution step

[0070] Add an appropriate amount of polyethylene glycol and methacrylic acid to the reaction flask according to the molar ratio. Add the solvent anhydrous xylene, and place the reaction flask in a water bath or oil bath, heat it to 100 - 130 °C, and dissolve the polyethylene glycol and methacrylic acid completely to form a homogeneous solution.

[0071] 3. Esterification reaction step

[0072] Add an appropriate amount of p-toluenesulfonic acid as a catalyst and stir evenly. The dosage of the catalyst is generally 0.5–1% of the total mass of the reactants. Keep the temperature at 100-130 °C and continuously stir the reaction for 4-6 hours. During the esterification reaction, a small amount of water is generated. Add an appropriate amount of anhydrous sodium sulfate or anhydrous calcium chloride as a dehydrating agent to adsorb the water generated by the reaction and prevent the water from affecting the efficiency of the esterification reaction.

[0073] 4. Neutralization treatment step

[0074] After the reaction is completed, add an appropriate amount of dilute sodium hydroxide solution to the solution to neutralize the residual acidic catalyst, and wash to remove the reaction by-products and residual acid to obtain a polyethylene glycol-methacrylate solution.

[0075] 5. Solvent evaporation and concentration step

[0076] Use a rotary evaporator to remove the reaction solvent at a temperature of 40-50 °C to obtain a semi-solid crude product. To remove the residual solvent, dry the product in a vacuum oven at a low temperature to ensure no thermal decomposition, and obtain the concentrated product.

[0077] 6. Purification step

[0078] Recrystallize the concentrated product with a solvent (such as using ethanol or a dichloromethane / ethanol mixed solvent) to obtain pure polyethylene glycol-methacrylate. Separate the crystal product by filtration and place it in a vacuum drying oven to dry to obtain pure polyethylene glycol-methacrylate powder.

[0079] The purified polyethylene glycol-methacrylate product can be obtained through the above operations.

[0080] Chemically modify the purified polyethylene glycol-methacrylate. Use ammonium persulfate as an oxidant through a chemical oxidation polymerization method to prepare a copolymer of polyethylene glycol-methacrylate and thiophene. The preparation of the copolymer involves generating conductive polythiophene chains while combining with the active groups in polyethylene glycol-methacrylate.

[0081] 1. Raw material preparation

[0082] Raw material preparation: Select polyethylene glycol-methacrylate with an appropriate molecular weight, high-purity thiophene reagent (C 4 H 5 S), and select ammonium persulfate ((NH 4 ) 2 S 2 O 8 ) as the oxidant.

[0083] Polymerization reaction: Pour the mixed solution of polyethylene glycol - methacrylate and thiophene into a three - necked flask, and connect a condenser and a dropping funnel. Place the three - necked flask in an ice bath to keep the reaction temperature at 0 - 5 °C. This inhibits the excessive polymerization of thiophene and the occurrence of side reactions. Connect a magnetic stirrer and keep stirring at a medium speed to ensure the uniformity of the mixture.

[0084] Slowly add the prepared ammonium persulfate solution to the mixed solution in the three - necked flask through the dropping funnel. Control the dropping time within 10 - 20 minutes to ensure that ammonium persulfate reacts with thiophene gradually and avoid overly violent local reactions. As the dropping progresses, the color of the solution gradually changes from colorless to dark green or black, and thiophene is oxidized, and radical - initiated polymerization occurs.

[0085] After the dropping is completed, continue to stir for 1 - 2 hours at the ice - bath temperature (0 - 5 °C) to inhibit the occurrence of side reactions and allow the polymerization reaction to proceed fully. Then remove the ice bath and let the reaction system gradually rise to room temperature and continue stirring for 3 - 4 hours. At this time, the dark suspension gradually becomes thick, and the formed polythiophene precipitate begins to form.

[0086] After the reaction is completed, cool the reaction system to room temperature. Filter using filter paper to collect the formed dark precipitate. Put the collected precipitate into a beaker and wash it repeatedly with a large amount of deionized water until the filtrate is neutral. Then further wash it with anhydrous ethanol to remove unreacted thiophene monomers and residual ammonium persulfate.

[0087] After washing, place the precipitate in a vacuum dryer and dry it at 40 - 60 °C for 12 - 24 hours until the product is completely dry and the mass is constant. Finally, a black powdery polyethylene glycol - methacrylate - polythiophene copolymer is obtained.

[0088] During the polymerization process, thiophene is oxidized to a radical cation:

[0089] C 4 H 5 S+(NH 4 ) 2 S 2 O 8 →C 4 H 4 S + +H + +SO 4 2- 。

[0090] The thiophene radical cation forms long - chain polythiophene PTh through radical addition:

[0091] n·C 4 H 4 S + →(-C 4H 3 S -) n + n·H + 。

[0092] Copolymerization reaction of polyethylene glycol - methacrylate and thiophene:

[0093] HO-(CH 2 CH 2 O) m -COO-CH=CH 2 + n·C 4 H 5 S+(NH 4 ) 2 S 2 O 8 →

[0094] {PEG - PTh}+(NH 4 ) 2 SO 4 + by - products.

[0095] The double - bond part in polyethylene glycol - methacrylate reacts with the free radicals in the polythiophene chain to form a copolymer structure and finally generate a copolymer. Polyethylene glycol is bound to polythiophene through the double - bond at its end. The copolymerization chemical formula of polyethylene glycol - methacrylate and polythiophene is:

[0096] HO-(CH 2 CH 2 O) m -COO-CH=CH-(-C 4 H 3 S -) n ;

[0097] where m and n are both positive integers.

[0098] Example 1

[0099] First, weigh polyethylene glycol with a molecular weight of 1000 and dry it in a vacuum oven at 60 °C for 3 hours to remove adsorbed moisture. Take an appropriate amount of methacrylic acid and dry it in a vacuum desiccator for 1 hour. Add the dried polyethylene glycol and methacrylic acid to a reaction flask in a molar ratio of 1:2, add dichloromethane as a solvent, and place the reaction flask in a water bath or oil bath and heat it to 100 °C to completely dissolve the polyethylene glycol and methacrylic acid to form a homogeneous solution. Then, add an appropriate amount of p-toluenesulfonic acid (PTSA) as a catalyst, and the amount of the catalyst is 0.5% of the total mass of the reactants. Keep the temperature at 100 °C and stir for 4 hours for the esterification reaction, and add an appropriate amount of anhydrous sodium sulfate as a dehydrating agent to adsorb the water generated by the reaction and prevent the water from affecting the efficiency of the esterification reaction. Monitor the progress of the reaction by thin-layer chromatography (TLC) to observe the formation of maleate and determine the completion of the reaction.

[0100] After the reaction is completed, add a small amount of dilute sodium hydroxide solution to neutralize the residual acidic catalyst in the system. Wash the reaction system with distilled water multiple times to remove reaction by-products and residual acid. Then use a rotary evaporator to remove the reaction solvent (dichloromethane) at 40 °C to obtain a semi-solid crude product. To remove the residual solvent, dry the product in a vacuum oven at a low temperature to ensure no thermal decomposition, and obtain a crude product of polyethylene glycol-methacrylate. Dissolve the crude product in an appropriate amount of dichloromethane, and then add an appropriate amount of thiophene monomer so that the molar ratio of polyethylene glycol-methacrylate to thiophene is 1:1. Add ammonium persulfate as an oxidant to initiate the polymerization of thiophene. Place the reaction system in an ice bath and cool it to 0 °C to prevent the reaction from being too violent. Slowly add the ammonium persulfate solution to ensure uniform progress of the reaction. After stirring at a low temperature for 1 hour, remove the ice bath and continue to stir at room temperature for 3 hours to ensure sufficient copolymerization of polyethylene glycol-methacrylate and thiophene.

[0101] Collect the copolymer precipitate by filtration and wash it repeatedly with deionized water and anhydrous ethanol to remove unreacted thiophene monomers and by-products. After washing, use a rotary evaporator to remove the solvent to obtain a crude polyethylene glycol-methacrylate-polythiophene copolymer. For further purification, dissolve the crude product in a mixed solvent of dichloromethane and ethanol for solvent recrystallization to obtain pure polyethylene glycol-methacrylate-polythiophene copolymer crystals. Separate the crystals by filtration and place them in a vacuum drying oven to dry to obtain the final polyethylene glycol-methacrylate-polythiophene copolymer powder.

[0102] The purified poly(ethylene glycol)-methyl methacrylate-polythiophene copolymer powder was used for the preparation of a dry electrode for the positive electrode of a lithium-ion battery. 90 wt% of lithium iron phosphate (LiFePO4) was weighed as the active material, 5 wt% of the poly(ethylene glycol)-methyl methacrylate-polythiophene copolymer powder was used as the binder, and 5 wt% of conductive carbon black was used as the conductive agent. These materials were added to a high-speed mixer and mixed thoroughly to ensure that the binder and the conductive carbon black were evenly distributed among the active material particles. The mixed dry powder material was uniformly pressed into an electrode film with a thickness of 100 microns.

[0103] After the preparation of the electrode film, its volume resistance and adhesion strength were tested to evaluate the performance of the poly(ethylene glycol)-methyl methacrylate-polythiophene copolymer as a binder.

[0104] Example 2:

[0105] First, polyethylene glycol with a molecular weight of 5000 was weighed and dried in a vacuum oven at 60 °C for 3 hours to remove the adsorbed moisture. An appropriate amount of methacrylic acid was taken and dried in a vacuum desiccator for 1 hour. The dried polyethylene glycol and methacrylic acid were added to a reaction flask in a molar ratio of 2:3, and dichloromethane was added as a solvent. The reaction flask was placed in a water bath or an oil bath and heated to 100 °C to completely dissolve the polyethylene glycol and methacrylic acid to form a homogeneous solution. Then, an appropriate amount of p-toluenesulfonic acid was added as a catalyst, and the amount of the catalyst was 0.5% of the total mass of the reactants. The temperature was maintained at 100 °C, and the mixture was stirred for 4 hours for the esterification reaction. An appropriate amount of anhydrous sodium sulfate was added as a dehydrating agent to adsorb the water generated by the reaction and prevent the water from affecting the efficiency of the esterification reaction.

[0106] After the reaction was completed, a small amount of dilute sodium hydroxide solution was added to neutralize the residual acidic catalyst in the system. Then, the reaction solvent (dichloromethane) was removed at 40 °C using a rotary evaporator. To remove the residual solvent, the product was dried at a low temperature in a vacuum oven to ensure no thermal decomposition, and the crude product of poly(ethylene glycol)-methyl methacrylate was obtained. The crude product was dissolved in an appropriate amount of dichloromethane, and then an appropriate amount of thiophene monomer was added so that the molar ratio of poly(ethylene glycol)-methyl methacrylate to thiophene was 1:2. Ammonium persulfate was added as an oxidant to initiate the polymerization of thiophene. The reaction system was cooled to 0 °C in an ice bath to prevent the reaction from being too violent. The ammonium persulfate solution was slowly added to ensure the uniform progress of the reaction. After stirring at a low temperature for 2 hours, the ice bath was removed, and stirring was continued at room temperature for 3 hours to ensure the full copolymerization of polyethylene glycol and thiophene.

[0107] The purified polyethylene glycol-methacrylate-polythiophene powder was used in the preparation of a dry electrode for the positive electrode of a lithium-ion battery. Weigh 90 wt% of lithium iron phosphate (LiFePO4) as the active material, 5 wt% of polyethylene glycol-methacrylate-polythiophene powder as the binder, and 5 wt% of conductive carbon black as the conductive agent. The mixed dry powder material was uniformly pressed into an electrode film with a thickness of 100 microns. After the preparation of the electrode film, its volume resistance and bond strength were tested to evaluate the performance of polyethylene glycol-methacrylate-polythiophene as a binder.

[0108] Example 3:

[0109] First, weigh polyethylene glycol with a molecular weight of 10,000 and dry it in a vacuum oven at 60 °C for 3 hours to remove adsorbed moisture. Take an appropriate amount of methacrylic acid and dry it in a vacuum desiccator for 1 hour. Add the dried polyethylene glycol and methacrylic acid to the reaction flask in a molar ratio of 2:3, add dichloromethane as the solvent, and place the reaction flask in a water bath or oil bath and heat it to 110 °C to completely dissolve the polyethylene glycol and methacrylic acid to form a homogeneous solution. Then, add an appropriate amount of p-toluenesulfonic acid as a catalyst, and the amount of the catalyst is 0.5% of the total mass of the reactants. Keep the temperature at 110 °C and stir for 4 hours for the esterification reaction, and add an appropriate amount of anhydrous sodium sulfate as a dehydrating agent to adsorb the water generated by the reaction and prevent the water from affecting the efficiency of the esterification reaction.

[0110] After the reaction is completed, add a small amount of dilute sodium hydroxide solution to neutralize the residual acidic catalyst in the system. Then use a rotary evaporator to remove the reaction solvent (dichloromethane) at 40 °C. To remove the residual solvent, the product was dried at low temperature in a vacuum oven to ensure no thermal decomposition, and the crude product of polyethylene glycol and methacrylic acid was obtained. Dissolve the crude product in an appropriate amount of dichloromethane, and then add an appropriate amount of thiophene monomer so that the molar ratio of polyethylene glycol, methacrylic acid, and thiophene is 1:1. Add ammonium persulfate (ammonium persulfate) as an oxidant to initiate the polymerization of thiophene. Cool the reaction system to 0 °C in an ice bath to prevent the reaction from being too violent. Slowly add the ammonium persulfate solution to ensure the uniform progress of the reaction. After stirring at low temperature for 3 hours, remove the ice bath and continue to stir at room temperature for 3 hours to ensure the full copolymerization of polyethylene glycol and thiophene.

[0111] The purified polyethylene glycol-methacrylate-polythiophene powder was used for the preparation of the dry electrode of the lithium-ion battery cathode. Weigh 90 wt% of lithium iron phosphate (LiFePO4) as the active material, 5 wt% of polyethylene glycol-methacrylate-polythiophene powder as the binder, and 5 wt% of conductive carbon black as the conductive agent. The mixed dry powder material was uniformly pressed into an electrode film with a thickness of 100 microns. After the preparation of the electrode film, its volume resistance and adhesion strength were tested to evaluate the performance of polyethylene glycol-methacrylate-polythiophene as a binder.

[0112] Example 4:

[0113] First, weigh polyethylene glycol with a molecular weight of 20,000 and dry it in a vacuum oven at 60 °C for 3 hours to remove the adsorbed moisture. Take an appropriate amount of methacrylic acid and dry it in a vacuum desiccator for 1 hour. Add the dried polyethylene glycol and methacrylic acid to the reaction flask in a molar ratio of 1:2, add dichloromethane as the solvent, and place the reaction flask in a water bath or oil bath and heat it to 105 °C to completely dissolve the polyethylene glycol and methacrylic acid to form a homogeneous solution. Then, add an appropriate amount of p-toluenesulfonic acid as a catalyst, and the dosage of the catalyst is 0.5% of the total mass of the reactants. Keep the temperature at 105 °C and stir for 4 hours for the esterification reaction, and add an appropriate amount of anhydrous sodium sulfate as a dehydrating agent to adsorb the water generated by the reaction and prevent the water from affecting the efficiency of the esterification reaction.

[0114] After the reaction is completed, add a small amount of dilute sodium hydroxide solution to neutralize the residual acidic catalyst in the system. Then use a rotary evaporator to remove the reaction solvent (dichloromethane) at 40 °C. In order to remove the residual solvent, the product was dried at low temperature in a vacuum oven to ensure no thermal decomposition, and the crude product of polyethylene glycol and methacrylic acid was obtained. Dissolve the crude product in an appropriate amount of dichloromethane, and then add an appropriate amount of thiophene monomer so that the molar ratio of polyethylene glycol, methacrylic acid and thiophene is 1:2. Add ammonium persulfate as an oxidant to initiate the polymerization of thiophene. Cool the reaction system to 0 °C in an ice bath to prevent the reaction from being too violent. Slowly add the ammonium persulfate solution to ensure the uniform progress of the reaction. After stirring at low temperature for 3 hours, remove the ice bath and continue to stir at room temperature for 3 hours to ensure the full copolymerization of polyethylene glycol and thiophene.

[0115] The purified polyethylene glycol-methacrylate-polythiophene powder was used for the preparation of the dry electrode of the lithium-ion battery cathode. 90 wt% of lithium iron phosphate (LiFePO4) was weighed as the active material, 5 wt% of the polyethylene glycol-methacrylate-polythiophene powder as the binder, and 5 wt% of conductive carbon black as the conductive agent. The mixed dry powder material was uniformly pressed into an electrode film with a thickness of 100 microns. After the preparation of the electrode film, volume resistance testing and bond strength testing were carried out to evaluate the performance of the polyethylene glycol-methacrylate-polythiophene as a binder.

[0116] Comparative Example 1:

[0117] Polyethylene glycol with a molecular weight of 5000 and methacrylic acid were weighed and added to a reaction flask in a molar ratio of 1:2. Dichloromethane was used as the solvent and heated to complete dissolution in a water bath at 100 °C. 0.5% p-toluenesulfonic acid was added as a catalyst, and the reaction was stirred for 4 hours. Anhydrous sodium sulfate was added to remove water, and after neutralization with dilute sodium hydroxide, it was washed several times with water. The solvent was removed by rotary evaporation to obtain polyethylene glycol-methacrylate powder without thiophene copolymerization. 90 wt% of lithium iron phosphate, 5 wt% of the un-copolymerized polyethylene glycol-methacrylate, and 5 wt% of conductive carbon black were mixed and pressed into an electrode film with a thickness of 100 microns. Volume resistance testing and bond strength testing were carried out.

[0118] Comparative Example 2:

[0119] PTFE powder with a molecular weight of 5000000 was selected. 90 wt% of lithium iron phosphate, 5 wt% of the PTFE powder, and 5 wt% of conductive carbon black were mixed and pressed into an electrode film with a thickness of 100 microns. Volume resistance testing and bond strength testing were carried out.

[0120] The results of the resistance testing are shown in Table 1, and the results of the bond strength testing are shown in Table 2.

[0121] Table 1

[0122] Example Volume Resistivity 1 Volume Resistivity 2 Volume Resistivity 3 Volume Resistivity 4 Example 1 97 102 93 99 Example 2 87 83 92 91 Example 3 65 68 62 61 Example 4 58 59 61 54 Comparative Example 1 127 121 134 138 Comparative Example 2 324 341 332 329

[0123] Table 2

[0124] Example Adhesive Strength 1 Adhesive Strength 2 Adhesive Strength 3 Adhesive Strength 4 Example 1 3.9 3.2 3.1 3.5 Example 2 4.2 3.8 3.5 3.6 Example 3 5.1 5.2 5.8 5.5 Example 4 6.2 6.8 6.1 5.4 Comparative Example 1 2.2 2.4 1.9 1.7 Comparative Example 2 1.5 1.0 1.2 0.9

[0125] The dry electrode sheet of the present invention comprises poly(ethylene glycol) methacrylate and / or poly(ethylene glycol) methacrylate-polythiophene copolymer, that is, poly(ethylene glycol) methacrylate and / or poly(ethylene glycol) methacrylate-polythiophene copolymer is used to replace polytetrafluoroethylene (PTFE) as the binder during the preparation of the dry electrode sheet. Thiophene is oxidized to a radical cation under the action of ammonium persulfate, and then radical polymerization occurs to form a conductive polythiophene chain, which is covalently bonded to poly(ethylene glycol) methacrylate. After modification, it has excellent electrical conductivity when used as a dry electrode binder.

[0126] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A dry electrode binder, characterized in that: include: Polyethylene glycol methacrylate.

2. A method for preparing a dry electrode binder as claimed in claim 1, characterized in that the method include: Dissolution step: taking appropriate amounts of polyethylene glycol and methacrylic acid in molar ratio, adding a reaction solvent to completely dissolve the polyethylene glycol and methacrylic acid to form a uniform solution; Esterification reaction steps: adding an appropriate amount of catalyst and stirring evenly to carry out esterification reaction, and adding an appropriate amount of dehydrating agent to absorb the water generated by the esterification reaction; Neutralization treatment step: after the reaction is completed, add an appropriate amount of dilute sodium hydroxide solution to the solution to neutralize the residual acid catalyst, and wash to remove the reaction by-products and residual acid to obtain a polyethylene glycol-methacrylate solution; Solvent evaporation and concentration step: removing the reaction solvent to obtain a concentrated product; Purification step: The concentrated product is subjected to solvent recrystallization to obtain pure polyethylene glycol-methacrylate, which is then separated by filtration and dried to obtain pure polyethylene glycol-methacrylate as a dry electrode binder.

3. The method for preparing a dry electrode binder according to claim 2, characterized in that: The reaction solvent in the dissolving step is anhydrous xylene or dichloromethane.

4. The method for preparing a dry electrode binder according to claim 2, characterized in that: In the esterification step, the temperature is maintained at 100-130°C during the esterification reaction.

5. The method for preparing a dry electrode binder according to claim 2, characterized in that: In the dissolving step, the molar ratio of polyethylene glycol to methacrylic acid is 1:2 or 2:

3.

6. A dry electrode binder, characterized in that: The invention comprises polyethylene glycol-methacrylate-polythiophene copolymer, and the copolymerization chemical formula of the polyethylene glycol-methacrylate-polythiophene copolymer is: HO-(CH2CH2O) m -COO-CH=CH2-(-C4H3S-) n ; Wherein, m and n are both positive integers.

7. The method for preparing a dry electrode binder according to claim 6, characterized in that the method include: Dissolution step: taking appropriate amounts of polyethylene glycol and methacrylic acid in molar ratio, and then adding a solvent to completely dissolve the polyethylene glycol and methacrylic acid to obtain a uniform solution; Esterification reaction step: add an appropriate amount of catalyst and stir evenly to carry out esterification reaction, and add an appropriate amount of dehydrating agent to absorb the water generated by the esterification reaction; solvent evaporation and concentration step: removing the reaction solvent to obtain a concentrated product; Purification step: the concentrated product is subjected to solvent recrystallization to obtain polyethylene glycol-methacrylate; A polymerization reaction step: mixing polyethylene glycol-methacrylate and thiophene to obtain a mixed solution; Adding ammonium persulfate solution dropwise to allow ammonium persulfate to gradually polymerize with thiophene, and collecting the generated polythiophene precipitate; The unreacted thiophene monomer and residual ammonium persulfate are removed by washing, and the polyethylene glycol-methacrylate-polythiophene copolymer is obtained by drying to serve as a dry electrode binder.

8. The method for preparing a dry electrode binder according to claim 7, characterized in that: In the polymerization step, deionized water is first used for washing until the filtrate is neutral; then anhydrous ethanol is used for washing.

9. The method for preparing a dry electrode binder according to claim 7, characterized in that: In the polymerization step, the molar ratio of polyethylene glycol-methacrylate to thiophene is 1:1 or 1:

2.

10. The method for preparing a dry electrode binder according to claim 7, characterized in that: In the esterification step, the added catalyst is p-toluenesulfonic acid.