Binder, positive plate and battery

Abstract

The invention provides a binder, a positive plate and a battery, the binder comprises a copolymer, the copolymer comprises a polyurethane chain segment, an imide structural unit and a phosphate structural unit; the polyurethane chain segment comprises a flexible chain segment, and the swelling ratio of the binder is 28-160%. The binder has high binding power, high mechanical strength and good flexibility, is beneficial to promoting migration of active ions in the battery, is beneficial to reducing the impedance of the battery, and improves the first charge-discharge efficiency, cycle stability and other performances of the battery.

Description

Technical Field

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

[0002] Batteries are currently common electrochemical energy storage devices. Lithium-ion batteries, for example, are widely used in portable electronic devices, electric vehicles, and energy storage systems due to their high energy density, long cycle life, and environmental friendliness. Binders, as a crucial component of battery electrodes, play a key role in their performance.

[0003] Currently, the most commonly used binder is polyvinylidene fluoride (PVDF). However, PVDF is a fluorine-based chemical material that poses a serious environmental risk. Limited by the low mechanical strength and poor adhesion of existing binders like PVDF, batteries generally suffer from high impedance, low initial charge and discharge efficiency, poor cycle stability, and poor overcharge safety, all of which urgently need to be addressed. Summary of the Invention

[0004] The present application provides a binder, a positive electrode sheet, and a battery. The binder has high bonding force, high mechanical strength, and good flexibility, which is beneficial to promoting the migration of active ions in the battery, reducing battery impedance, and improving the battery's initial charge and discharge efficiency, cycle stability, and overcharge safety, thereby solving the defects of the prior art.

[0005] One aspect of the present invention provides an adhesive, comprising a copolymer, wherein the copolymer comprises a polyurethane segment, an imide structural unit, and a phosphate structural unit; the polyurethane segment comprises a flexible segment, and the swelling rate of the adhesive is 28-160%.

[0006] According to one embodiment of the present invention, the weight average molecular weight of the binder is 100,000-300,000 g / mol.

[0007] According to one embodiment of the present invention, the elastic modulus of the adhesive is 700-2600 MPa.

[0008] According to one embodiment of the present invention, the elongation at break of the adhesive is 15-100%.

[0009] According to one embodiment of the present invention, the binder is obtained by reacting diisocyanate monomers, diol polymers, anhydride monomers and phosphate structural unit monomers; the phosphate structural unit monomers are obtained by reacting a raw material composition of a mercapto-containing polyol monomer and a double-bond-containing phosphate monomer.

[0010] According to one embodiment of the present invention, the molar ratio of the double-bond phosphate monomer, the diol polymer and the acid anhydride monomer is (0.04-1.00): (0.20-1.00): (0.80-1.00), and the molar amount of the phosphate structural unit monomer accounts for 1-25% of the total mass of the raw materials.

[0011] According to one embodiment of the present invention, the molar ratio of the diisocyanate monomer to the sum of the diol polymer, the acid anhydride monomer, and the double-bond-containing phosphate monomer is (1.97-2.03):2.

[0012] According to one embodiment of the present invention, the mass ratio of the diol polymer to the total mass of the raw materials is 10-50%, and the number average molecular weight of the diol polymer is 100-10000 g / mol.

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

[0014] Another aspect of the present invention provides a battery comprising the above-mentioned electrode sheet.

[0015] The present invention uses a copolymer having a phosphate group as a binder. The binder has high bonding force, high mechanical strength and good flexibility, which is beneficial to promoting the migration of active ions in the battery, reducing battery impedance, and improving the battery's initial charge and discharge efficiency, cycle stability, overcharge safety and other performance. DETAILED DESCRIPTION

[0016] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0017] According to the inventors' research, polyimide is a high-performance polymer material with excellent thermal stability, chemical stability, and mechanical strength. However, the poor solubility of polyimide limits its use as a binder. Polyurethane contains polar groups such as carbamate groups in its molecular chain, which give it excellent adhesion to electrode active materials. It can firmly bond the electrode active materials and electrode conductive agents together to form a stable electrode sheet structure. Polyurethane also has excellent flexibility, which can adapt to the volume changes of electrode active materials during battery charging and discharging, reduce cracking and shedding of electrode sheets, and improve the cycling stability of the electrode. However, polyurethane has insufficient thermal stability, and its adhesion and other properties will deteriorate in high-temperature environments. In cases such as overcharging, over-discharging, or high-power charging and discharging, high temperatures may be generated inside the battery, which may cause the performance of the polyurethane binder to deteriorate, affecting the stability of the electrode and the safety of the battery.

[0018] Based on this, an embodiment of the present invention provides a binder including a copolymer, wherein the copolymer includes a carbamate structural unit, an imide structural unit, and a phosphate structural unit; the swelling rate of the binder is 28-160%.

[0019] In the above system, the copolymer comprises polyurethane segments, imide structural units, and phosphate structural units. The polyurethane segments include flexible segments, which improve the adhesive strength, mechanical strength, and flexibility of the binder, facilitate the migration of active ions in the battery, reduce battery impedance, and enhance the battery's initial charge and discharge efficiency, cycle stability, and overcharge safety. Specifically, the flexible segments enhance the binder's flexibility and adhesion, while the imide structural units enhance the binder's heat resistance and mechanical strength. The synergistic effect of the two enhances the binder's adhesion (specifically, its adhesion to the electrode active material and the electrode conductive agent), and strengthens the stability of the electrode sheet structure. During the battery's charge and discharge cycles, the binder in the embodiments of the present invention maintains good adhesion, effectively inhibiting the shedding of the electrode active material and damage to the electrode sheet structure, thereby improving the battery's cycle stability. Furthermore, the phosphate structural units dynamically coordinate with the active ions in the battery, promoting the migration of active ions, improving the battery's ion conductivity, reducing the battery's internal resistance, and improving the battery's cycle stability and overcharge safety. Furthermore, the copolymer exhibits excellent thermal and chemical stability.

[0020] The copolymer side chain includes a phosphate structural unit, which is beneficial to further improve the adhesive properties such as the adhesive and the migration speed of the active ions, enhance the battery's ion conductivity, reduce the battery's internal resistance, and improve the battery's cycle stability and overcharge safety.

[0021] In an embodiment of the present invention, the swelling rate of the binder is 28-160%, for example, it can be 28%, 50%, 75%, 100%, 125%, 150%, 160% or a range consisting of any two thereof.

[0022] In some preferred embodiments, the swelling ratio of the binder is 28%-150%, for example, it can be 28%, 50%, 75%, 100%, 125%, 150% or a range consisting of any two thereof.

[0023] In some embodiments, the binder has a weight average molecular weight of 100,000 to 300,000 g / mol, for example, 100,000 g / mol, 130,000 g / mol, 150,000 g / mol, 170,000 g / mol, 200,000 g / mol, 230,000 g / mol, 250,000 g / mol, 270,000 g / mol, 300,000 g / mol, or a range consisting of any two thereof.

[0024] In some embodiments, the elastic modulus of the binder is 700-2600 MPa, for example, 700 MPa, 1200 MPa, 1700 MPa, 2200 MPa, 2600 MPa, or any combination thereof. The elongation at break of the binder is 15-100%, for example, 15%, 30%, 45%, 60%, 75%, 90%, 100%, or any combination thereof.

[0025] In some embodiments, the binder is obtained by reacting diisocyanate monomers, diol polymers, anhydride monomers and phosphate structural unit monomers; the phosphate structural unit monomers are obtained by reacting a raw material composition of a mercapto-containing polyol monomer and a double-bond-containing phosphate monomer.

[0026] In some embodiments, the molar ratio of the double-bond phosphate monomer, the diol polymer, and the 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 consisting of any two thereof; the molar amount of the phosphate structural unit monomer accounts for a molar percentage (molar content) of the total molar amount of the raw material of 1-25%, for example, 1%, 6%, 11%, 16%, 21%, 25%, or a range consisting of any two thereof, wherein the molar amount is the amount of substance (in mol), that is, the amount of the phosphate structural unit monomer accounts for an amount of 1-25% of the total amount of the raw material.

[0027] In some embodiments, the molar percentage (molar content) of the phosphate structural unit monomer is substantially equal to the molar percentage of the molar amount of the phosphate structural unit monomer to the total molar amount of the raw materials, that is, the molar percentage of the phosphate structural unit monomer = the molar amount of the phosphate structural unit monomer / (the molar amount of the diisocyanate monomer + the molar amount of the diol polymer + the molar amount of the anhydride monomer + the molar amount of the phosphate structural unit monomer).

[0028] In some embodiments, the molar ratio of the diisocyanate monomer to the sum of the diol polymer, the acid anhydride monomer, the mercapto polyol monomer, and the double-bond-containing phosphate monomer is (1.97-2.03):2, for example, it can be 1.97:2, 2:2, 2.03:2, or a range consisting of any two thereof.

[0029] In some embodiments, the anhydride monomer includes one or more of pyromellitic dianhydride (PMDA), 4,4'-oxydiphthalic anhydride (OPDA), 3,3',4,4'-diphenyl ether dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 4,4'-(4,4'-isopropyldiphenyldiphenoxy)diphthalic anhydride, butanetetracarboxylic dianhydride, 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride, p-phenylenedi(trimellitic acid ester) dianhydride, and 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, and lysine diisocyanate.

[0031] In some embodiments, the number average molecular weight of the diol polymer is 100-10,000 g / mol, such as 100 g / mol, 500 g / mol, 1,000 g / mol, 2,000 g / mol, 5,000 g / mol, 10,000 g / mol, or any two thereof.

[0032] In some embodiments, the mass percentage (proportion) of the mass of the diol polymer to the total mass of the raw materials is 10% to 50%, for example, 10%, 20%, 30%, 40%, 50% or a range composed of any two thereof, which is beneficial to further improve the solubility and mechanical strength of the binder, reduce electrolyte swelling, and improve the adhesiveness of the binder, the stability of the electrode, the cycle stability of the battery, and the overcharge safety.

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

[0034] In some embodiments, the diol polymer includes one or more of a polyether diol polymer, a polysiloxane diol polymer, and a polyolefin diol polymer, and the polyether diol polymer includes polyethylene glycol (PEG) or polytetramethylene ether glycol (PTMEG); the diol polymer is beneficial for further improving the flexibility and solubility of the binder, while taking into account the improvement of the adhesiveness of the binder, the stability of the electrode, the cycle stability of the battery, and the overcharge safety.

[0035] An embodiment of the present invention also provides a method for preparing the above-mentioned adhesive, comprising the following steps: reacting a diisocyanate monomer with a diol polymer and a phosphate structural unit monomer to generate an isocyanate-terminated intermediate product, and copolymerizing the intermediate product with an anhydride monomer to obtain the adhesive.

[0036] Specifically, the flexible chain segments in the binder are obtained by reacting diol polymers; the imide structural units are obtained by reacting the isocyanate structure contained in the isocyanate-terminated intermediate product with the anhydride structure in the anhydride monomer; and the phosphate structural units are obtained by reacting the phosphate structural unit monomers.

[0037] In the embodiments of the present invention, the molecular structure and properties of the binder can be regulated by controlling the types of raw materials, the proportion of the added amounts, and the reaction conditions (such as temperature, time, etc.), further improving the flexibility and adhesion of the binder while improving the battery's impedance, initial charge and discharge efficiency, cycle stability, and overcharge safety.

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

[0039] In some embodiments, the process of copolymerizing the intermediate product with the anhydride monomer includes: reacting the intermediate product with the anhydride monomer at 40-80°C (recorded as the first temperature) for 1-6 hours (recorded as the first time), then heating to 70-150°C (recorded as the second temperature) and reacting (recorded as the second time) for 1-4 hours to obtain a binder. Generally, 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 phosphate structural unit monomer is obtained by reacting a thiol-containing polyol monomer and a double-bond-containing phosphate monomer.

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

[0043] In addition, the molar ratio of the mercapto groups in the mercapto polyol to the double bond groups of the double bond phosphate ester is 1 to 2:1, for example, 1:1, 1.2:1, 1.5:1, 1.8:1, 2:1 or a range consisting of any two thereof.

[0044] In a specific implementation, a mercapto polyol, a double-bond phosphate, a photosensitizer, and a solvent can be added to a reaction vessel under inert gas protection. The reaction is stirred and irradiated with a 365 nm ultraviolet lamp for 0.25 to 2 hours, for example, 0.25 hours, 0.75 hours, 1.25 hours, 1 hour, 75 hours, 2 hours, or a range consisting of any two thereof, followed by column chromatography to obtain a monomer containing a phosphate group (phosphate structural unit monomer). The inert gas can be nitrogen.

[0045] Specifically, the mass ratio of the photosensitizer to the double-bond-containing phosphate monomer is 0.5-3%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3% or a range consisting of any two thereof, 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 diisocyanate monomers, diol polymers, and phosphate structural unit monomers to generate the isocyanate-terminated intermediate product.

[0047] In some embodiments, during the preparation of the isocyanate-terminated intermediate, the reaction temperature is 40-100°C, for example, 40°C, 50°C, 60°C, 70°C, 80°C, 90, 100°C, or a range consisting of any two thereof; the reaction time is 2-8h, for example, 2h, 3h, 4h, 5h, 6h, 7h, 8h, or a range consisting of any two thereof.

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

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

[0050] The positive electrode active material, conductive agent, and positive electrode current collector of the positive electrode sheet in the embodiment of the present invention can all be conventional materials in the field. For example, the positive electrode active material may include one or more of lithium iron phosphate, lithium cobalt oxide, lithium manganese oxide, and positive electrode ternary materials. The positive electrode ternary material may include nickel-cobalt-manganese ternary material and / or nickel-cobalt-aluminum ternary material. The conductive agent may include one or more of conductive carbon black (Super. P), conductive graphite, carbon nanotubes (CNT), acetylene black, graphene, Ketjen black, and carbon fiber. The positive electrode current collector may include carbon-coated aluminum foil.

[0051] The positive electrode active material layer in the embodiment of the present invention may further include a dispersant, and the dispersant includes polyvinyl pyrrolidone and hydrogenated butyronitrile polymer.

[0052] In the embodiments of the present invention, the positive electrode sheet can be prepared by conventional methods in the art, such as by a coating method. Specifically, the components used to form the positive electrode active material layer, such as the positive electrode active material, the conductive agent, and the above-mentioned binder, can be dispersed in a positive electrode solvent, such as N-methylpyrrolidone (NMP), to prepare a positive electrode slurry, which is then coated on the surface of the positive electrode current collector. After drying, rolling, cutting, and other processes, the positive electrode sheet is prepared. The coating, drying, rolling, cutting, and other processes involved are conventional operations for preparing positive electrode sheets using a coating method and are not particularly limited thereto.

[0053] For example, the positive electrode slurry can be coated on a carbon-coated aluminum foil, dried at 80° C., rolled, and cut into strips of 20 mm×100 mm to obtain a positive electrode sheet.

[0054] An embodiment of the present invention further provides a battery, including the above-mentioned positive electrode sheet, which has properties corresponding to the above-mentioned positive electrode sheet and will not be described in detail here.

[0055] In some embodiments, the battery may be a lithium-ion battery.

[0056] Generally, a battery consists of a cell, an electrolyte, and a casing that encapsulates the cell. The electrolyte is injected into the cell within the casing. The cell includes a positive electrode sheet, a negative electrode sheet, and a separator located between the positive and negative electrodes. The cell can be a laminated cell, meaning that the cell is composed of alternating positive electrode sheets, separators, and negative electrode sheets.

[0057] The embodiments of the present invention can prepare batteries by conventional methods in the art. For example, the positive electrode sheets, separators, and negative electrode sheets can be stacked alternately to produce a laminated battery cell. The battery cell is then placed in a casing and subjected to conventional processes such as liquid injection (i.e., injecting electrolyte), packaging, standing, formation, and capacity separation to produce a battery.

[0058] In the embodiment of the present invention, the separator is used to separate the positive electrode sheet and the negative electrode sheet to prevent the positive electrode sheet and the negative electrode sheet from short-circuiting. The embodiment of the present invention can adopt conventional separators in the field, for example, the separator includes polypropylene film (PP film) and polyethylene (PE), but is not limited thereto.

[0059] The present invention is further described below through specific examples.

[0060] Example 1

[0061] 1. Preparation of binder

[0062] Step 1: Under inert gas protection, 3-mercapto-1,2-propanediol (1.20 mol), ethylene glycol methacrylate (1.00 mol), dimethyl benzoate (0.02 mol), and 319 g of N-methylpyrrolidone (NMP) were added to a reactor and stirred under 365 nm ultraviolet light for 1 hour. Column precipitation was performed to obtain a dihydroxy monomer containing a phosphate group side group, i.e., a phosphate structural unit monomer;

[0063] Step 2: PEG (number average molecular weight of 600 g / mol, 1.0 mol) and the dihydroxy monomer containing a phosphate group side group obtained in the first step (0.4 mol) were vacuum-dehydrated at 110°C for 2 hours, cooled to 75°C under a nitrogen atmosphere, and toluene diisocyanate (2.0 mol) was added and reacted for 2 hours; then, the mixture was cooled to 50°C, NMP was added to dissolve and dilute to a solid content of 15%, and pyromellitic dianhydride (0.6 mol) was added and reacted for 4 hours. The mixture was then heated to 120°C and reacted for 4 hours to obtain a uniform and stable brown adhesive solution.

[0064] 2. Preparation of positive electrode

[0065] The positive electrode active particles NCM622, conductive carbon black Super P, carbon nanotubes, and the aforementioned binder are dispersed in NMP to form a positive electrode slurry. The positive electrode slurry is evenly coated on aluminum foil by a coating method. After baking and rolling, a positive electrode including a positive electrode active layer is obtained.

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

[0067] 3. Preparation of negative electrode sheet

[0068] Deionized water is used to disperse negative electrode active particles of artificial graphite, conductive carbon black Super P, and a binder of sodium carboxymethyl cellulose and styrene butadiene latex to form a negative electrode slurry; then a negative electrode active layer is formed on the surface of the negative electrode current collector through coating, baking, and roller pressing processes to obtain a negative electrode; wherein the mass ratio of the negative electrode active particles, the conductive agent, and the binder (the mass ratio of sodium carboxymethyl cellulose to styrene butadiene latex is 1:1.5) is 96.5:1.0:2.5.

[0069] 4. Preparation of batteries

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

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

[0072] Examples 2 to 11

[0073] Most of the steps of Examples 2 to 11 are the same as those of Example 1, except that the formulations in Tables 1 and 2 are used.

[0074] Comparative Example 1

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

[0076] The molar content of the dihydroxy monomer (phosphate structural unit monomer) containing a phosphate group side group and the mass proportion of the diol polymer in each example were tested by the following process. The results are shown in Table 2.

[0077] 1. Test for the molar content of dihydroxy monomers containing phosphate ester side groups (phosphate structural unit monomers): Molar content of dihydroxy monomers containing phosphate ester side groups = molar amount of dihydroxy monomers containing phosphate ester side groups / (molar amount of diisocyanate monomers + molar amount of diol polymers + molar amount of anhydride monomers + molar amount of phosphate structural unit monomers).

[0078] 2. Test of the mass proportion of diol polymers: Mass proportion of diol polymers = mass of diol polymers / (mass of diisocyanate monomers + mass of diol polymers + mass of anhydride monomers + mass of mercapto polyol monomers + mass of phosphate monomers containing double bonds).

[0079] The binders, positive electrodes, and batteries in the examples and comparative examples were tested using the following procedures. The results are shown in Table 3.

[0080] 1. Film electrolyte swelling test method (i.e., test method for adhesive swelling rate): After the adhesive is made into a film, cut it into pieces and weigh and record m1. Then soak it in electrolyte (EC:EMC:DEC=3:5:2, 1mol / L LiPF6) and test it at 60℃ for 72h. After removing the film, wipe the residual electrolyte on the surface of the film with a cloth and weigh and record m2. Calculate the test swelling rate change rate: adhesive swelling rate = (m2-m1) / m1*100%.

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

[0082] Sample Preparation: The adhesive solution was spread flat in a mold and dried at 80°C for 12 hours. The temperature was then raised to 120°C and baked for another 12 hours. The temperature was then raised to 150°C and baked for 2 hours to produce a bubble-free, 0.03mm thick film. The dried film was cut into 150mm x 10mm x 0.03mm strips and tested using a universal tensile tester. The elastic modulus and elongation at break of the adhesive were measured and are shown in Table 3. Test conditions: Test speed: 200mm / min, gauge length: 25.00mm, test temperature: 25°C, test humidity: 45-55%.

[0083] 3. Combustion performance (i.e., film combustion performance, or binder combustion performance): The film is tested and rated using the vertical combustion method according to GB / T 8333-2008, Test Method for Combustion Performance of Rigid Foam Plastics. The rating results are shown in Table 3; V-0: The vertical specimen stops burning within 10 seconds; no dripping is allowed; V-1: The vertical specimen stops burning within 30 seconds; no dripping is allowed; V-2: The vertical specimen stops burning within 30 seconds; dripping of burning materials is allowed.

[0084] 4. Positive electrode sheet adhesion test (electrode sheet peel strength test): Referring to the test method for adhesive tape peel strength in GB / T 2792-2014, the positive electrode sheet adhesion test was performed using a GBH-1 tensile testing machine with a 180° tape peeling method. The test specimen (i.e., positive electrode sheet) had a size of 20 mm × 100 mm and a tensile rate of 50 mm / min. The measured electrode sheet peel strength is shown in Table 3.

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

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

[0087] 7. Initial charge and discharge efficiency test: After charging the batteries in each embodiment and comparative example at a constant current of 0.5C to 4.2V, they were charged at a constant voltage to a cutoff current of 0.05C, and the charge capacity at this time was recorded, which was recorded as the initial charge capacity; then they were discharged at a constant current of 0.5C to 3V, and the discharge capacity at this time was recorded, which was recorded as the initial discharge capacity. Initial charge and discharge efficiency = initial discharge capacity / initial charge capacity.

[0088] 8. Room-temperature cycle stability (capacity retention) test: After the battery is left at 25±2°C for 1 hour, charge it at 1C constant current and constant voltage to 4.2V, with a cut-off current of 0.05C. Discharge it at 1C constant current to 3V, and record the discharge capacity. Repeat the above steps 500 times. Calculate the room-temperature capacity retention rate (see Table 3).

[0089] 9. High-temperature cycling stability (capacity retention) test: After standing at 45°C for 1 hour, charge the battery at 1C constant current and constant voltage to 4.2V, with a cut-off current of 0.05C. Discharge the battery at 1C constant current to 3V, and record the discharge capacity. Repeat these steps 500 times. Calculate the high-temperature capacity retention (see 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] It can be seen from the experimental data that the binder in this application has excellent mechanical strength, flame retardancy, bonding properties and flexibility. When applied to batteries, the batteries have good internal resistance, initial charge and discharge efficiency, and 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 invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A binder, characterized in that: The invention comprises a copolymer, wherein the copolymer comprises a polyurethane segment, an imide structural unit and a phosphate structural unit; the polyurethane segment comprises a flexible segment, and the swelling rate of the adhesive is 28-160%.

2. The adhesive according to claim 1, characterized in that The weight average molecular weight of the binder is 100,000-300,000 g / mol.

3. The adhesive according to claim 1, characterized in that The elastic modulus of the binder is 700-2600 MPa.

4. The adhesive according to claim 1, characterized in that The elongation at break of the adhesive is 15-100%.

5. The adhesive according to any one of claims 1 to 4, characterized in that: The binder is obtained by reacting diisocyanate monomers, diol polymers, acid anhydride monomers and phosphate structural unit monomers; the phosphate structural unit monomers are obtained by reacting a raw material composition of mercapto-containing polyol monomers and double-bond-containing phosphate monomers.

6. The adhesive according to claim 5, characterized in that The molar ratio of the double-bond phosphate monomer, the diol polymer, and the anhydride monomer is (0.04-1.00):(0.20-1.00):(0.80-1.00); the molar percentage of the molar amount of the phosphate structural unit monomer to the total molar amount of the raw materials is 1-25%.

7. The adhesive according to claim 6, characterized in that The molar ratio of the diisocyanate monomer to the sum of the diol polymer, the acid anhydride monomer, and the double-bond-containing phosphate monomer is (1.97-2.03):

2.

8. The adhesive according to claim 5, characterized in that The mass ratio of the diol polymer to the total mass of the raw materials is 10-50%, and the number average molecular weight of the diol polymer is 100-10000 g / mol.

9. A positive electrode sheet, characterized in that: The invention comprises an electrode current collector and an electrode active material layer located on at least one side surface of the electrode current collector, wherein the electrode active material layer comprises the binder according to any one of claims 1 to 8.

10. A battery, characterized in that: Including the positive electrode sheet according to claim 9.

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