A binder, a positive electrode sheet, a battery

Abstract

The application provides a kind of binder, positive plate, battery, including copolymer, the copolymer includes polyurethane chain segment, imide structural unit and phosphate structural unit;The polyurethane chain segment includes flexible chain segment, and the swelling rate of the binder is 28-160%.The binder has high adhesion, high mechanical strength and good flexibility, which is beneficial to promote the migration of active ions in the battery, is beneficial to reduce the battery impedance, improves the first charge-discharge efficiency, cycle stability and other performances of the battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of batteries, in particular to a binder, a positive electrode sheet and a battery. BACKGROUND

[0002] Batteries are currently common electrochemical energy storage devices. For example, lithium batteries have been widely used in portable electronic devices, electric vehicles and energy storage systems due to their high energy density, long cycle life and environmental friendliness. As an important component of the electrode sheet of the battery, the binder plays a key role in the performance of the electrode sheet.

[0003] The commonly used binder is mainly polyvinylidene fluoride (PVDF), however, PVDF belongs to fluorinated chemical materials and causes serious environmental pollution. Due to the defects of low mechanical strength and poor adhesion of the existing PVDF binder, the battery generally has problems such as high impedance, low first charge-discharge efficiency, poor cycle stability and poor overcharge safety, which need to be solved. SUMMARY

[0004] The present application provides a binder, a positive electrode sheet and a battery. The binder has high adhesion, high mechanical strength and good flexibility, which is beneficial to promote the migration of active ions in the battery, reduce the impedance of the battery, and improve the performance of the battery such as the first charge-discharge efficiency, cycle stability and overcharge safety, thereby solving the defects of the prior art.

[0005] In one aspect of the present application, a binder is provided, which comprises a copolymer, the copolymer comprising a polyurethane segment, an imide structural unit and a phosphate structural unit; the polyurethane segment comprises a flexible segment, and the binder has a swelling rate of 28-160%.

[0006] According to an embodiment of the present application, the binder has a weight average molecular weight of 100000-300000 g / mol.

[0007] According to an embodiment of the present application, the binder has an elastic modulus of 700-2600 MPa.

[0008] According to an embodiment of the present application, the binder has an elongation at break of 15-100%.

[0009] According to an embodiment of the present application, the binder is obtained by reaction of raw materials of a diisocyanate monomer, a dihydric alcohol polymer, an acid anhydride monomer and a phosphate structural unit monomer; the phosphate structural unit monomer is obtained by reaction of a raw material composition of a thiol-containing polyol monomer and a double bond-containing phosphate monomer.

[0010] The molar ratio of the double bond-containing phosphate ester monomer, the dihydric alcohol-based polymer, and the acid anhydride-based monomer according to an embodiment of the present application is (0.04-1.00):(0.20-1.00):(0.80-1.00), and the molar amount of the phosphate ester structural unit monomer accounts for 1-25% of the total mass of the raw materials.

[0011] According to an embodiment of the present application, the molar ratio of the diisocyanate-based monomer to the sum of the dihydric alcohol-based polymer, the acid anhydride-based monomer, and the double bond-containing phosphate ester monomer is (1.97-2.03):2.

[0012] According to an embodiment of the present application, the mass of the dihydric alcohol-based polymer accounts for 10-50% of the total mass of the raw materials, and the number average molecular weight of the dihydric alcohol-based polymer is 100-10000 g / mol.

[0013] Another aspect of the present application provides a positive electrode sheet including an electrode current collector and an electrode active material layer located on at least one side surface of the electrode current collector, the electrode active material layer including the above-described binder or the binder prepared according to the above-described binder preparation method.

[0014] Another aspect of the present application provides a battery including the above-described electrode sheet.

[0015] The present application uses a copolymer having a phosphate ester group as a binder, which has high adhesion, high mechanical strength, and good flexibility, is beneficial to promote the migration of active ions in a battery, is beneficial to reduce the impedance of the battery, and improves the first charge-discharge efficiency, cycle stability, overcharge safety, and other performances of the battery. DETAILED DESCRIPTION

[0016] To make the objectives, technical solutions, and advantages of the present application clearer, the technical solutions in the embodiments of the present application will be described below in conjunction with the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the scope of protection of the present application.

[0017] According to the research of the inventor, polyimide is a high-performance polymer material with excellent thermal stability, chemical stability and mechanical strength. However, the solubility of polyimide is poor, which limits its use as an adhesive; the molecular chain of polyurethane contains polar groups such as urethane groups, which has good adhesion to electrode active materials, and can firmly bond electrode active materials, electrode conductive agents and other materials together to form a stable electrode sheet structure. At the same time, polyurethane has excellent flexibility and can adapt to the volume change of electrode active materials during battery charging and discharging, reducing the cracking and peeling of the electrode sheet and improving the cycle stability of the electrode. However, the thermal stability of polyurethane is insufficient, and its adhesion and other properties will decrease in high temperature environment. In the case of overcharging, overdischarging or high-power charging and discharging, high temperature may occur inside the battery, which may cause the performance of the polyurethane adhesive to deteriorate, affecting the stability of the electrode and the safety of the battery.

[0018] Based on this, the embodiment of the present application provides an adhesive, which comprises a copolymer, the copolymer comprises urethane structural units, imide structural units and phosphate structural units; the swelling rate of the adhesive is 28-160%.

[0019] In the above system, the copolymer comprises polyurethane segments, imide structural units and phosphate structural units; the polyurethane segments comprise flexible segments, which are beneficial to improve the adhesion, mechanical strength and flexibility of the adhesive, promote the migration of active ions in the battery, reduce the battery impedance and improve the first charge-discharge efficiency, cycle stability and overcharge safety of the battery. Specifically, the flexible segments are beneficial to improve the flexibility and adhesion of the adhesive, the imide structural units are beneficial to improve the heat resistance and mechanical strength of the adhesive, and the synergistic effect of the two is beneficial to improve the adhesion of the adhesive (specifically reflected in the adhesion between the adhesive and the electrode active material and the electrode conductive agent), and to enhance the stability of the electrode sheet structure. In the process of battery charging and discharging cycle, the adhesive in the embodiment of the present application can maintain good adhesion performance, effectively inhibit the shedding of electrode active material and the destruction of electrode sheet structure, thereby improving the cycle stability of the battery. In addition, the phosphate structural units can dynamically coordinate with the active ions in the battery, which is beneficial to promote the migration of active ions, improve the ion conductivity of the battery, reduce the internal resistance of the battery, and improve the cycle stability and overcharge safety of the battery. In addition, the copolymer also has good thermal stability and chemical stability.

[0020] The side chain of the copolymer comprises phosphate structural units, which is beneficial to further improve the adhesion of the adhesive and the migration speed of the active ions, improve the ion conductivity of the battery, reduce the internal resistance of the battery, and improve the cycle stability and overcharge safety of the battery.

[0021] In some embodiments, the adhesive has a swelling rate of 28-160%, for example, 28%, 50%, 75%, 100%, 125%, 150%, 160%, or a range defined by any two of them.

[0022] In some preferred embodiments, the adhesive has a swelling rate of 28-150%, for example, 28%, 50%, 75%, 100%, 125%, 150%, or a range defined by any two of them.

[0023] In some embodiments, the adhesive has a weight average molecular weight of 100000-300000 g / mol, for example, 100000 g / mol, 130000 g / mol, 150000 g / mol, 170000 g / mol, 200000 g / mol, 230000 g / mol, 250000 g / mol, 270000 g / mol, 300000 g / mol, or a range defined by any two of them.

[0024] In some embodiments, the adhesive has an elastic modulus of 700-2600 MPa, for example, 700 MPa, 1200 MPa, 1700 MPa, 2200 MPa, 2600 MPa, or a range defined by any two of them. The adhesive has an elongation at break of 15-100%, for example, 15%, 30%, 45%, 60%, 75%, 90%, 100%, or a range defined by any two of them.

[0025] In some embodiments, the adhesive is obtained by reacting raw materials of a diisocyanate monomer, a dihydric alcohol polymer, an acid anhydride monomer, and a phosphate structural unit monomer; the phosphate structural unit monomer is obtained by reacting a raw material composition of a thiol-containing polyol monomer and a double bond-containing phosphate monomer.

[0026] In some embodiments, the molar ratio of the double bond-containing phosphate monomer, the dihydric alcohol polymer, and the acid anhydride monomer is (0.04-1.00):(0.20-1.00):(0.80-1.00), for example, 0.04:0.2:0.80, 0.24:0.4:0.84, 0.44:0.6:0.88, 0.74:0.8:0.94, 1.00:1.00:1.00, or a range defined by any two of them. The molar percentage (molar content) of the molar amount of the phosphate structural unit monomer in the total molar amount of the raw materials is 1-25%, for example, 1%, 6%, 11%, 16%, 21%, 25%, or a range defined by any two of them, wherein the molar amount is the amount of substance (unit: mol), i.e., the amount of substance percentage of the amount of substance of the phosphate structural unit monomer in the total amount of substance of the raw materials is 1-25%.

[0027] In some embodiments, the mole percentage (mole content) of the phosphate structural unit monomer is substantially equal to the mole percentage of the mole amount of the phosphate structural unit monomer in the total mole amount of the raw materials, i.e., the mole percentage of the phosphate structural unit monomer = the mole amount of the phosphate structural unit monomer / (the mole amount of the diisocyanate monomer + the mole amount of the dihydric alcohol polymer + the mole amount of the anhydride monomer + the mole amount of the phosphate structural unit monomer).

[0028] In some embodiments, the mole ratio of the sum of the diisocyanate monomer, the dihydric alcohol polymer, the anhydride monomer, the mercapto polyol monomer, and the double bond-containing phosphate monomer is (1.97~2.03):2, for example, can be 1.97:2, 2:2, 2.03:2, or a range consisting of any two of them.

[0029] In some embodiments, the anhydride monomer includes one or more of pyromellitic dianhydride (PMDA), 4,4'-oxybisphthalic anhydride (OPDA), 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 4,4'-diphenyl ether dianhydride, 3,3',4,4'-diphenyltetracarboxylic dianhydride, 4,4'-(4,4'-isopropylidene diphenyloxy) dipthalic anhydride, butane tetracarboxylic dianhydride, 3,3',4,4'-diphenyl sulfone tetracarboxylic dianhydride, p-phenyl bis(trimellitate) dianhydride, trimellitic anhydride.

[0030] In some embodiments, the diisocyanate monomer includes one or more of toluene diisocyanate (TDI), isophorone diisocyanate (IPDI), diphenylmethane diisocyanate (MDI), dicyclohexylmethane diisocyanate, hexamethylene diisocyanate, lysine diisocyanate.

[0031] In some embodiments, the number average molecular weight of the dihydric alcohol polymer is 100-10000 g / mol, for example, 100 g / mol, 500 g / mol, 1000 g / mol, 2000 g / mol, 5000 g / mol, 10000 g / mol, or a range consisting of any two of them,

[0032] In some embodiments, the mass percentage (proportion) of the dihydric alcohol polymer in the total mass of the raw materials is 10%~50%, for example, 10%, 20%, 30%, 40%, 50%, or a range consisting of any two of them, which is conducive to further improving the solubility and mechanical strength of the adhesive, reducing electrolyte swelling, and improving the adhesion of the adhesive, the stability of the pole piece, the cycle stability of the battery, and the overcharge safety performance.

[0033] Specifically, the mass percentage of the dihydric alcohol polymer in the total mass of the raw materials = mass of the dihydric alcohol polymer / (mass of the diisocyanate monomer + mass of the dihydric alcohol polymer + mass of the acid anhydride monomer + mass of the mercapto polyol monomer + mass of the double bond-containing phosphate ester monomer).

[0034] In some embodiments, the dihydric alcohol polymer includes one or more of a polyether dihydric alcohol polymer, a polysiloxane dihydric alcohol polymer, and a polyolefin dihydric alcohol polymer, the polyether dihydric alcohol polymer including polyethylene glycol (PEG) or polytetramethylene ether glycol (PTMEG); the dihydric alcohol polymer is conducive to further improving the flexibility and solubility of the binder, and is conducive to improving the adhesion of the binder, the stability of the electrode, the cycle stability of the battery, and the overcharge safety, etc.

[0035] The present application also provides a preparation method of the binder, including the following steps: reacting the diisocyanate monomer with the dihydric alcohol polymer and the phosphate ester structural unit monomer to generate an isocyanate-terminated intermediate product, and copolymerizing the intermediate product with the acid anhydride monomer to obtain the binder.

[0036] Specifically, the flexible chain segment in the binder is obtained by reaction of the dihydric alcohol polymer; the imide structural unit is obtained by reaction of the isocyanate structure contained in the isocyanate-terminated intermediate product with the acid anhydride structure in the acid anhydride monomer; and the phosphate ester structural unit is obtained by reaction of the phosphate ester structural unit monomer.

[0037] In the present application, the molecular structure and performance of the binder can be regulated by controlling the types, proportions of the added amounts, and reaction conditions (such as temperature and time) of the raw materials, which is conducive to further improving the flexibility and adhesion of the binder, and is conducive to improving the impedance, the first charge-discharge efficiency, the cycle stability, and the overcharge safety of the battery, etc.

[0038] In specific implementation, the product after the copolymerization reaction of the intermediate product and the acid anhydride monomer is a glue solution of the binder, and the binder can be separated by using a conventional method in the art, wherein the solid content (i.e. the mass percentage of the binder in the glue solution) of the glue solution is 5% to 40%, for example, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, or a range formed by any two of them.

[0039] In some embodiments, the process of copolymerizing the intermediate product with the acid anhydride monomer includes: reacting the intermediate product with the acid anhydride monomer at 40-80℃ (denoted as the first temperature) for 1-6h (denoted as the first time), then increasing the temperature to 70-150℃ (denoted as the second temperature) for 1-4h (denoted as the second time) to obtain the binder, and in general, the second temperature is greater than the first temperature.

[0040] Specifically, the first temperature can be 40℃, 50℃, 60℃, 70℃, 80℃, or a range consisting of any two of them, the first time can be 1h, 2h, 3h, 4h, 5h, 6h, or a range consisting of any two of them, the second temperature can be 70℃, 80℃, 90℃, 100℃, 110℃, 120℃, 130℃, 140℃, 150℃, or a range consisting of any two of them, and the second time can be 1h, 2h, 3h, 4h, or a range consisting of any two of them.

[0041] In some embodiments, the phosphonate structural unit monomer is obtained by reacting raw materials including a thiol-containing polyol monomer and a double-bond-containing phosphonate monomer.

[0042] Specifically, the thiol-containing polyol monomer includes 3-mercapto-1,2-propanediol. The double-bond-containing phosphonate monomer (phosphonate monomer) includes one or more of methacrylic acid ethylene glycol phosphate, acrylate phosphate, methacrylate phosphate, vinyl phosphate, and diethyl vinyl phosphate.

[0043] In addition, the molar ratio of the thiol group in the thiol-containing polyol to the double-bond group of the double-bond-containing phosphonate is 1-2:1, such as 1:1, 1.2:1, 1.5:1, 1.8:1, 2:1, or a range consisting of any two of them.

[0044] In specific implementation, the thiol-containing polyol, the double-bond-containing phosphonate, the photosensitizer, and the solvent can be put into a reaction kettle under the protection of an inert gas, and then the reaction kettle is placed under the irradiation of a 365nm ultraviolet lamp in a stirring state for 0.25-2h, such as 0.25h, 0.75h, 1.25h, 1h, 75h, 2h, or a range consisting of any two of them, to perform column chromatography to obtain the phosphonate group-containing monomer (phosphonate structural unit monomer). The inert gas can be nitrogen.

[0045] Specifically, the mass ratio of the photosensitizer to the double-bond-containing phosphonate monomer is 0.5-3%, such as 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, or a range consisting of any two of them, and the photosensitizer includes benzoin dimethyl ether.

[0046] In some embodiments, the preparation process of the isocyanate-terminated intermediate product includes: reacting raw materials including a diisocyanate monomer, a diol polymer, and a phosphonate structural unit monomer to generate the isocyanate-terminated intermediate product.

[0047] In some embodiments, the temperature of the reaction in the preparation of the isocyanate-terminated intermediate product is 40-100℃, for example, it can be 40℃, 50℃, 60℃, 70℃, 80℃, 90℃, 100℃, or a range defined by any two of them; the reaction time is 2-8h, for example, it can be 2h, 3h, 4h, 5h, 6h, 7h, 8h, or a range defined by any two of them.

[0048] The present application also provides a positive electrode sheet, which comprises an electrode current collector and an electrode active material layer on at least one side surface of the electrode current collector, and the electrode active material layer comprises the above-mentioned binder or the binder prepared according to the above-mentioned preparation method of the binder, and has properties corresponding to the above-mentioned binder, which will not be repeated here.

[0049] Specifically, the electrode active material layer comprises an electrode active material, a conductive agent and the above-mentioned binder.

[0050] The positive electrode active material, the conductive agent and the positive electrode current collector of the positive electrode sheet in the present application can all be conventional materials in the art, for example, the positive electrode active material can comprise one or more of lithium iron phosphate, lithium cobaltate, lithium manganate and positive electrode ternary materials, the positive electrode ternary material can comprise nickel-cobalt-manganese ternary material and / or nickel-cobalt-aluminum ternary material, the conductive agent can comprise one or more of conductive carbon black (Super. P), conductive graphite, carbon nanotube (CNT), acetylene black, graphene, ketjen black and carbon fiber, and the positive electrode current collector can comprise carbon-coated aluminum foil.

[0051] The positive electrode active material layer in the present application can further comprise a dispersant, and the dispersant comprises polyvinylpyrrolidone and hydrogenated butyronitrile polymer.

[0052] In the present application, the positive electrode sheet can be prepared by conventional methods in the art, for example, by a coating method, specifically, the positive electrode active material, the conductive agent, the above-mentioned binder and the like can be dispersed in a positive electrode solvent, for example, the positive electrode solvent comprises N-methylpyrrolidone (NMP), to prepare a positive electrode slurry, which is then coated on the surface of the positive electrode current collector, and after drying, rolling, cutting and the like, the positive electrode sheet is prepared. The coating, drying, rolling and cutting and the like are conventional operations for preparing the positive electrode sheet by the coating method, and are not particularly limited.

[0053] Exemplarily, the positive electrode slurry can be coated on the carbon-coated aluminum foil, dried at 80℃, and then rolled and cut to form a strip of 20mm×100mm, thereby obtaining the positive electrode sheet.

[0054] The present application also provides a battery comprising the above-mentioned positive electrode sheet, which has properties corresponding to the above-mentioned positive electrode sheet, which will not be repeated here.

[0055] In some embodiments, the above-mentioned battery can be a lithium ion battery.

[0056] Generally, the battery comprises a cell, an electrolyte, and a shell encapsulating the cell, the electrolyte is injected into the cell in the shell, and the cell comprises a positive plate, a negative plate, and a separator between the positive plate and the negative plate. The cell can be a laminated cell, i.e., the cell is formed by interleaving and stacking the positive plate, the separator, and the negative plate.

[0057] The battery can be prepared by a conventional method in the art, for example, the positive plate, the separator, and the negative plate can be interleaved and stacked to form a laminated cell; then the cell is placed in the shell, and the battery is prepared after conventional processes such as liquid injection (i.e., injection of electrolyte), encapsulation, standing, formation, and capacity distribution.

[0058] In the embodiments of the present application, the separator is used to separate the positive plate and the negative plate to avoid short circuit caused by contact between the positive plate and the negative plate. The separator used in the embodiments of the present application can be a conventional separator in the art, for example, the separator comprises a polypropylene film (PP film) and polyethylene (PE), but is not limited thereto.

[0059] The present application will be further described below through specific embodiments.

[0060] Embodiment 1

[0061] 1. Preparation of the binder

[0062] Step 1: Under the protection of inert gas, 3-mercapto-1,2-propanediol (1.20 mol), methyl methacrylate phosphoglycol ester (1.00 mol), benzoin dimethyl ether (0.02 mol), and 319 g of N-methyl pyrrolidone (NMP) were stirred and placed under the irradiation of a 365 nm ultraviolet lamp for 1 h, column sedimentation was performed, and a double-hydroxyl monomer containing a phosphonate group side group, i.e., a phosphonate structural unit monomer, was obtained;

[0063] Step 2: PEG (number average molecular weight 600 g / mol, 1.0 mol) and the double-hydroxyl monomer containing a phosphonate group side group obtained in step 1 (0.4 mol) were vacuumed to remove water at 110°C for 2 h, cooled to 75°C under nitrogen atmosphere, and toluene diisocyanate (2.0 mol) was added and reacted for 2 h; then, NMP was added to dissolve and dilute to 15% solid content, pyromellitic dianhydride (0.6 mol) was added, reacted for 4 h, and then the temperature was increased to 120°C and reacted for 4 h, to obtain a uniform and stable tea-colored binder glue.

[0064] 2. Preparation of the positive plate

[0065] The positive electrode active particles NCM622, conductive carbon black Super P, carbon nanotubes and the above binder are dispersed by NMP to form a positive electrode slurry; the positive electrode slurry is uniformly coated on the aluminum foil by coating, and after the baking and rolling processes, a positive electrode including a positive electrode active layer is obtained.

[0066] The mass ratio of the positive electrode active particles, the conductive carbon black, the carbon nanotubes and the binder is 97.8:0.5:0.5:1.2.

[0067] 3. Preparation of the negative electrode sheet

[0068] The negative electrode active particles artificial graphite, conductive carbon black Super P, and the binder carboxymethyl cellulose sodium and butyl rubber latex are dispersed by deionized water to form a negative electrode slurry; then the negative electrode active layer is formed on the surface of the negative electrode current collector by coating, baking and rolling processes to obtain a negative electrode; the mass ratio of the negative electrode active particles, the conductive agent and the binder (the mass ratio of carboxymethyl cellulose sodium and butyl rubber latex is 1:1.5) is 96.5:1.0:2.5.

[0069] 4. Preparation of the battery

[0070] The prepared positive electrode, the separator and the negative electrode are sequentially stacked and then wound to obtain an electric core, the electric core is placed in an aluminum plastic film, an electrolyte is injected into the bare electric core, and after the vacuum packaging, standing, formation, shaping and capacity testing processes, a battery is obtained.

[0071] The electrolyte includes lithium hexafluorophosphate, ethylene carbonate, methyl ethyl carbonate and diethyl carbonate, wherein the mass ratio of ethylene carbonate to methyl ethyl carbonate to diethyl carbonate is 3:2:5, and the concentration of lithium hexafluorophosphate is 1 mol / L.

[0072] Examples 2-11

[0073] Examples 2-11 and most of the steps of Example 1 are the same, except that the formulations in Tables 1 and 2 are used.

[0074] Comparative Example 1

[0075] Compared with Example 1, Comparative Example 1 uses a commercially available PVdF (Solef ® 5130) as the positive electrode binder, and the other conditions are the same as those of Example 1.

[0076] The molar content of the phosphonate group side group-containing dihydroxy monomer (phosphonate structure unit monomer) and the mass ratio of the dihydric alcohol polymer in each example are tested by the following processes, and the results are shown in Table 2.

[0077] 1. Test of the molar content of the phosphonate group side group-containing dihydroxy monomer (phosphonate structural unit monomer): molar content of the phosphonate group side group-containing dihydroxy monomer = molar amount of the phosphonate group side group-containing dihydroxy monomer / (molar amount of the diisocyanate monomer + molar amount of the dihydric alcohol polymer + molar amount of the anhydride monomer + molar amount of the phosphonate structural unit monomer).

[0078] 2. Test of the mass proportion of the dihydric alcohol polymer: mass proportion of the dihydric alcohol polymer = mass of the dihydric alcohol polymer / (mass of the diisocyanate monomer + mass of the dihydric alcohol polymer + mass of the anhydride monomer + mass of the mercapto polyol monomer + mass of the phosphonate monomer containing double bond).

[0079] The adhesives, the positive electrode sheets, and the batteries in the examples and the comparative examples were respectively tested by the following processes, and the results are shown in Table 3:

[0080] 1. Test method of the swelling of the gel film electrolyte (i.e. test method of the swelling rate of the adhesive): after the adhesive was made into a gel film, the gel film was cut into pieces, weighed, and recorded as m1, then the gel film was soaked in an electrolyte (EC: EMC: DEC = 3: 5: 2, 1 mol / L LiPF6), and the test was performed at 60°C for 72 hours. After the gel film was taken out, the electrolyte remaining on the surface of the gel film was wiped off with a wiping cloth, and then the gel film was weighed and recorded as m2. The swelling degree change rate was calculated, and the swelling rate of the adhesive = (m2-m1) / m1*100%.

[0081] 2. Test method of the mechanical strength of the gel film (i.e. test method of the elastic modulus and the elongation at break of the adhesive):

[0082] Sample preparation method: the adhesive gel was spread in a mold, and was dried at 80°C for 12 hours, then was heated to 120°C and was baked for another 12 hours, and then was heated to 150°C and was baked for 2 hours, so as to prepare a gel film with a thickness of 0.03 mm and without air bubble defects. The dried gel film was cut into a sample with a size of 150 mm*10 mm*0.03 mm, and the sample was tested by a universal tensile testing machine. The elastic modulus and the elongation at break of the adhesive were measured and are shown in Table 3. Test conditions: test speed: 200 mm / min, gauge length: 25.00 mm, test temperature: 25°C, test humidity: 45-55%.

[0083] 3. Combustion performance (i.e. combustion performance of the gel film, or combustion performance of the adhesive): the gel film was tested by the vertical combustion method according to GB / T 8333-2008 Test Method for Combustion Performance of Rigid Foam Plastics, and was rated. The rating results are shown in Table 3. V-0: the vertical sample stopped burning within 10 seconds; no liquid drops were allowed; V-1: the vertical sample stopped burning within 30 seconds; no liquid drops were allowed; V-2: the vertical sample stopped burning within 30 seconds; liquid drops were allowed.

[0084] 4. Positive electrode sheet adhesion force test (sheet peeling strength test): Referring to GB / T 2792-2014 Test method of adhesive tape peeling strength, the adhesion force test of the positive electrode sheet was carried out by 180° adhesive tape peeling method through GBH-1 type tension testing machine, the test sample (i.e. positive electrode sheet) size was 20mm x 100mm, the tensile rate was 50mm / min, and the sheet peeling strength was measured and seen in Table 3.

[0085] 5. Flexibility test (sheet flexibility test): The flexibility of the positive electrode sheet in each example and the comparative example was tested according to the method of GB / T 1731-2020, and seen in Table 3.

[0086] 6. Battery internal resistance test (i.e. internal resistance test): The battery in each example and the comparative example was charged at 0.03C to 3.4V for 240min, then charged at 0.1C to 3.75V for 420min, then charged at 0.5C to 4.2V with a cutoff current of 0.02C, then discharged at 0.5C to 3.0V, and the discharge capacity was recorded; charged at 0.5C to 4.2V with a cutoff current of 0.02C, then discharged at 0.5C to 3.0V, and the discharge capacity was recorded; charged at 0.5C to 50% SOC, and the battery internal resistance was tested, and seen in Table 3.

[0087] 7. First charge-discharge efficiency test: The battery in each example and the comparative example was charged at 0.5C to 4.2V, then charged at a constant voltage to a cutoff current of 0.05C, and the charge capacity at this time was recorded as the first charge capacity; then discharged at 0.5C to 3V, and the discharge capacity at this time was recorded as the first discharge capacity, and the first charge-discharge efficiency = first discharge capacity / first charge capacity.

[0088] 8. Normal temperature cycle stability (capacity retention rate) test: Under the condition of 25±2℃, the battery was left for 1h, then charged at 1C constant current and constant voltage to 4.2V with a cutoff current of 0.05C; discharged at 1C current to 3V, and the discharge capacity was recorded; the above steps were repeated for 500 times, and the normal temperature capacity retention rate was calculated and seen in Table 3.

[0089] 9. High temperature cycle stability (capacity retention rate) test: Under the condition of 45℃, the battery was left for 1h, then charged at 1C constant current and constant voltage to 4.2V with a cutoff current of 0.05C; discharged at 1C current to 3V, and the discharge capacity was recorded; the above steps were repeated for 500 times, and the high temperature capacity retention rate was calculated and seen in Table 3.

[0090] Table 1 Example feeding data

[0091]

[0092] Table 2 Example feeding and synthesis data

[0093]

[0094] Table 3 Performance test

[0095]

[0096] From the experimental data, the binder in the application has excellent mechanical strength, flame retardant property, bonding property and flexibility. When applied to the battery, the battery has good internal resistance, first charge and discharge efficiency, good room temperature cycle stability and high temperature cycle stability.

[0097] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, but not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A positive electrode binder, characterized by, The copolymer comprises polyurethane segments, imide structural units and phosphate structural units; the polyurethane segments comprise flexible segments; the phosphate structural units are obtained by reacting phosphate structural unit monomers, which are obtained by reacting a raw material composition of a thiol-containing polyol monomer and a double bond-containing phosphate monomer; the thiol-containing polyol monomer is 3-mercapto-1,2-propanediol; and the double bond-containing phosphate monomer is one or more of phosphoglycol methacrylate, acrylate phosphate, methacrylate phosphate, vinyl phosphate and diethyl vinyl phosphate. The swelling rate of the positive electrode binder in a solvent is 50-100%, and the test method of the swelling rate of the positive electrode binder is as follows: after the positive electrode binder is made into a glue film, the weight is recorded as m1 after cutting, and then the glue film is soaked in an electrolyte, the solvent in the electrolyte is composed of ethylene carbonate, methyl ethyl carbonate and diethyl carbonate according to a mass ratio of 3:5:2, the concentration of LiPF6 in the electrolyte is 1 mol / L, the glue film is soaked at 60°C for 72 hours, the electrolyte remaining on the surface of the glue film is wiped off with a wiping cloth, then the weight is recorded as m2, and the swelling rate of the positive electrode binder is (m2-m1) / m1. 100%; The preparation method of the positive electrode binder comprises the following steps: reacting a diisocyanate monomer with a dihydric alcohol polymer and phosphate structural unit monomers to obtain an isocyanate-terminated intermediate product, and copolymerizing the intermediate product with an acid anhydride monomer to obtain the binder. The molar ratio of the double bond-containing phosphate monomer, the dihydric alcohol polymer and the acid anhydride monomer is (0.24-0.74):(0.40-0.8):(0.80-1.00); the molar percentage of the molar amount of the phosphate structural unit monomers in the total molar amount of the diisocyanate monomer, the dihydric alcohol polymer, the acid anhydride monomer and the phosphate structural unit monomers is 6-11%; the molar ratio of the diisocyanate monomer to the sum of the dihydric alcohol polymer, the acid anhydride monomer and the double bond-containing phosphate monomer is (1.97-2.03):2; and the mass ratio of the mass of the dihydric alcohol polymer to the total mass of the diisocyanate monomer, the dihydric alcohol polymer, the acid anhydride monomer and the phosphate structural unit monomers is 30-50%, and the dihydric alcohol polymer is a polyethylene glycol or a polysiloxane dihydric alcohol with a number average molecular weight of 600-1000 g / mol. The weight average molecular weight of the positive electrode binder is 100000-300000 g / mol. The elastic modulus of the positive electrode binder is 700-1849 MPa.

2. The positive electrode binder according to claim 1, characterized by, The electrode comprises an electrode current collector and an electrode active material layer located on at least one side surface of the electrode current collector, and the electrode active material layer comprises the positive electrode binder according to any one of claims 1-3.

3. The positive electrode binder according to claim 1, characterized by, The positive electrode sheet comprises the positive electrode according to claim 4.

4. A positive electrode sheet characterized by comprising: ​ 5. A battery, characterized by ​

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