Binder, positive pole piece and secondary battery

Abstract

The invention provides a binder, a positive pole piece and a secondary battery. The adhesive provided by the invention comprises a first polymer, in the first polymer, R1 is any one of-H,-CH3,-Cl,-COOH and-COOCH3, and R2 is any one of-H and-CH3; the number average molecular weight of the first polymer is Mn, and 1 * 104 < = Mn < = 1 * 106. In the first polymer, the cyano group can play roles in conducting Li < + > and protecting the positive electrode material; the trihydroxy benzene ring enables the binder to have good dispersibility and cohesiveness. Besides, the cyano group and the hydroxyl group have good polarity, and the first polymer is easily dissolved in NMP, so that when the binder is used in the positive pole piece, along with volatilization of NMP, the first polymer in the binder shrinks and generates channels, thereby increasing lithium ion transmission channels of the positive pole piece, and well improving the rate capability and the cycle performance of the secondary battery.

Description

Technical Field

[0001] The present application relates to the field of secondary batteries, and more specifically, to a binder, a positive electrode sheet, and a secondary battery. Background Art

[0002] The rapid evolution of apps for mobile phones, tablets, and computers, coupled with increasing RAM requirements, places higher demands on batteries, necessitating an urgent need to improve battery energy density to enhance competitiveness. Increasing the thickness of the electrode coating can increase the amount of active material per unit volume without changing the battery's chemical system, thereby boosting the battery's energy density. However, increasing the coating weight and thickness of the electrode leads to uneven distribution of material within the electrode, obstructing lithium-ion transport pathways and resulting in poor rate and cycle performance. Summary of the Invention

[0003] The present application can provide a binder, a positive electrode plate and a secondary battery. The binder of the present application is used in the electrode plate to provide a lithium ion transmission channel for the electrode plate, thereby improving the rate performance and cycle performance of the secondary battery.

[0004] In a first aspect, the present application provides a binder comprising a first polymer, wherein the first polymer comprises a structure as shown in the following formula I:

[0005]

[0006] Wherein R1 is any one of -H, -CH3, -Cl, -COOH, -COOCH3, R2 is any one of -H, -CH3; the number average molecular weight of the first polymer is M n , 1ⅹ10 4 ≤M n ≤1ⅹ10 6 .

[0007] In the above technical solution, the cyano group is a strong polar group with a short bond length, which has good high voltage stability and can conduct Li +and protect the positive electrode material; the trihydroxybenzene ring can form strong hydrogen bonds with functional groups such as H atoms or amino groups, and has excellent bonding properties, which can make the binder have good dispersibility and bonding properties; Cl atoms, as halogen atoms with high polarity, can greatly improve the conductivity of the material, increase the electron transmission speed during the charge and discharge process, and reduce the polarization problem caused by the poor conductivity of the material, thereby improving the rate discharge performance of the secondary battery and reducing the internal resistance of the secondary battery. In addition, since cyano and hydroxyl groups have good polarity, the first polymer has a high affinity for polar solvents such as NMP (N-methylpyrrolidone) and is easily soluble in polar solvents such as NMP. Therefore, when the binder is used in the positive electrode sheet, as the NMP evaporates, the first polymer in the binder will shrink and form channels, thereby increasing the lithium ion transmission channels of the positive electrode sheet, which can greatly improve the rate performance and cycle performance of the secondary battery.

[0008] In one possible implementation, the binder satisfies the following conditions: wherein R1 is either H or -COOCH3. When R1 is further any of the above functional groups, the first polymer in the binder can be further caused to shrink and generate more channels, thereby further increasing the lithium ion transmission channels of the positive electrode sheet and further optimizing the rate performance and cycle performance of the secondary battery.

[0009] In a possible implementation, the adhesive satisfies at least one of the following conditions: (1) 80≤m≤500; (2) 75≤n≤3200; (3) 2.5×10 4 ≤M n ≤8.5ⅹ10 5 .

[0010] In one possible implementation, in the infrared spectrum of the binder, at 600 cm -1 ~800cm -1 Has characteristic peaks.

[0011] In the above technical solution, it is explained that there is a C-Cl bond in the binder, which means that the first polymer can be stably present in the binder.

[0012] In a possible implementation, the X-ray diffraction spectrum of the binder has a characteristic peak when the diffraction angle is 33° to 40°, and the characteristic peak is a quadruple peak.

[0013] In the above technical solution, the trihydroxybenzene ring in the adhesive can form strong hydrogen bonds with functional groups such as H atoms or amino groups, providing excellent hydrogen bonding force. Moreover, the diffraction angle of the strong hydrogen bond in the XRD spectrum is in the range of 33° to 40°. Therefore, in the X-ray diffraction pattern of the adhesive, a quadruple characteristic peak appears when the diffraction angle is 33° to 40°.

[0014] In a second aspect, the present application provides a positive electrode plate, which includes a positive electrode current collector, at least one surface of which is provided with a positive electrode active layer, and the positive electrode active layer includes the above-mentioned binder.

[0015] In the above technical solution, the positive electrode plate contains the above binder, so the positive electrode plate not only has good cohesion, but also can enhance the rate performance and cycle performance of the secondary battery when used in the secondary battery.

[0016] In a possible implementation, based on the mass of the positive electrode active layer, the mass content of the binder is a%, and 0.5≤a≤2.

[0017] In the above technical solution, when the binder mass content meets the above conditions, the positive electrode sheet can not only have good cohesion, but also further improve the lithium ion transport performance of the positive electrode active layer. Therefore, when the positive electrode sheet is used in a secondary battery, the rate performance and cycle performance of the secondary battery can be further improved.

[0018] In one possible implementation, the positive electrode sheet satisfies at least one of the following conditions: (1) the thickness of the positive electrode current collector is d μm, 8 ≤ d ≤ 30; (2) the dyne value of the positive electrode current collector is x, 20 ≤ x ≤ 100; (3) the single-layer surface density of the positive electrode sheet is cw mg / 1540.25 mm 2 , 100≤cw≤1000; (4) The compaction density of the positive electrode sheet is PD g / cc, 3.8≤PD≤4.23.

[0019] In one possible implementation, 300≤cw≤700.

[0020] In one possible implementation, a channel is provided in the electrode sheet, the length of the channel is h mm, 0.01≤h≤0.2, at least part of the channel extends toward the surface of the positive electrode sheet and forms a through hole on the surface of the positive electrode sheet, the aperture of the through hole is d mm, 0.01≤d≤0.1; in any area on the surface of the positive electrode sheet, the total projected area of the through holes in the area has a coverage of S%, 15≤S≤30, and the length of the area is 5 cm and the width is 5 cm.

[0021] In the above technical solution, since the first polymer in the binder is easily soluble in N-methylpyrrolidone (NMP), when NMP is sprayed, the first polymer in the binder absorbs NMP, causing the binder to expand. When the NMP in the positive electrode plate dries, the first polymer contracts, and channels are formed in the positive active layer of the positive electrode plate. The channels are conducive to improving the lithium ion transport performance of the positive electrode plate. Moreover, when the channels meet the above conditions, the lithium ion transport performance of the positive electrode plate can be further improved. When used in a secondary battery, the rate performance and cycle performance of the secondary battery can be further improved.

[0022] In one possible implementation, 0.04≤d≤0.08, and 0.05≤h≤0.15.

[0023] In one possible implementation, after the positive electrode is fully charged, the cohesive force of the positive electrode is FN / m and the resistance is RΩ; 20≤F≤35, 0.05≤R≤0.8, 6≤F×R≤15.

[0024] In a third aspect, the present application provides a secondary battery comprising the above-mentioned positive electrode sheet. Therefore, the secondary battery of the present application has good performance.

[0025] Beneficial effects of this application:

[0026] The present application provides a binder, a positive electrode sheet, and a secondary battery. The binder of the present application includes a first polymer, in which R1 is any one of -H, -CH3, -Cl, -COOH, and -COOCH3, and R2 is any one of -H and -CH3; the number average molecular weight of the first polymer is M n , 1ⅹ10 4 ≤M n ≤1ⅹ10 6 The cyano group in the first polymer of the present application is a strong polar group with a short bond length, which has good high voltage stability and can conduct Li +The trihydroxybenzene ring has excellent bonding properties, which can make the binder have good dispersibility and bonding properties. Cl atoms, as halogen atoms with high polarity, can significantly improve the conductivity of the material, increase the electron transfer rate during the charge and discharge process, and reduce the polarization problem caused by the poor conductivity of the material, thereby improving the rate discharge performance of the secondary battery and reducing the internal resistance of the secondary battery. In addition, due to the good polarity of cyano and hydroxyl groups, the first polymer has a high affinity for polar solvents such as NMP (N-methylpyrrolidone) and is easily soluble in polar solvents such as NMP. Therefore, when the binder is used in the positive electrode sheet, as the NMP evaporates, the first polymer in the binder will shrink and form channels, thereby increasing the lithium ion transmission channels of the positive electrode sheet, which can greatly improve the rate performance and cycle performance of the secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments of the present application. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without creative work.

[0028] Figure 1 This is a picture showing the effect of the positive electrode sheet in Example 1-2 of the present application being sprayed with NMP and then dried;

[0029] Figure 2 This is the infrared spectrum of the binder in Examples 1-2 of the present application;

[0030] Figure 3 This is the X-ray diffraction spectrum of the binder in Examples 1-2 of the present application. DETAILED DESCRIPTION

[0031] To make the purpose, technical solutions and advantages of the examples of the present application clearer, the technical solutions in the examples of the present application will be described clearly and completely below. Where specific conditions are not specified in the examples, conventional conditions or conditions recommended by the manufacturer are used. Where the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be purchased commercially.

[0032] In order to improve the energy density of secondary batteries, the coating thickness and weight of the electrode are usually increased. However, this will cause the coating material in the electrode to be unevenly distributed, resulting in obstruction of the lithium ion transmission path. Currently, the following methods are mainly used to improve the problem of obstructed lithium ion transmission path: 1. Reduce the compaction density. Lowering the compaction density can increase the pores between the electrode particles and increase the lithium ion transmission channel. However, this will affect the volume energy density of the secondary battery. 2. Add a pore-forming agent to the coating slurry, and use the high temperature during coating to vaporize the pore-forming agent. After the electrode is dried, pores are generated in the coated layer structure. At the same time, the cold pressing process controls the compaction density, filling some pores while leaving some pores for lithium ion transmission. However, pore-forming agents usually contain acidic or alkaline groups, which have a certain impact on the stability of the slurry. They will also corrode the current collector, affecting the strength of the current collector and causing the current collector to break after hot pressing. This not only fails to increase the lithium ion transmission channel, but also leads to a decrease in energy density.

[0033] Based on the above technical problems, the present application provides a binder, a positive electrode sheet and a secondary battery. The binder of the present application has a high affinity for polar solvents such as NMP and is easily soluble in polar solvents such as NMP. Therefore, when the binder is used in the positive electrode sheet, the positive electrode sheet is sprayed with NMP and then dried. The NMP evaporates and channels are generated in the positive electrode sheet, which can greatly improve the problem of obstructed lithium ion transmission, thereby improving the rate performance and cycle performance of the secondary battery.

[0034] In a first aspect, the binder provided by the present application includes a first polymer, and the first polymer includes a structure shown in the following formula I:

[0035]

[0036] Wherein R1 is any one of -H, -CH3, -Cl, -COOH, -COOCH3, R2 is any one of -H, -CH3; the number average molecular weight of the first polymer is M n , 1ⅹ10 4 ≤M n ≤1ⅹ10 6 , preferably 2.5 x 10 4 ~8.5ⅹ10 5 , preferably R1 is any one of -H and -COOCH3.

[0037] The cyano group in the first polymer is a strong polar group with a short bond length, which has good high voltage stability and can conduct Li +and protect the positive electrode material; the trihydroxybenzene ring has excellent bonding properties, which can make the binder have good dispersibility and bonding properties. In addition, since the cyano group and the hydroxyl group have good polarity, the first polymer has a high affinity for polar solvents such as NMP (N-methylpyrrolidone) and is easily soluble in polar solvents such as NMP. Therefore, when the binder is used in the positive electrode sheet, as NMP is added and volatilized, the first polymer in the binder will first expand and then contract, thereby generating lithium ion transmission channels, improving the lithium ion transmission capacity of the positive electrode sheet, and can greatly improve the rate performance and cycle performance of the secondary battery. Furthermore, when R1 is any one of -H and -COOCH3, the lithium ion transmission channels of the positive electrode sheet can be increased, which can better improve the rate performance and cycle performance of the secondary battery.

[0038] It should be noted that in the binder of the present application, the first polymer is usually obtained by homopolymerizing two different monomers to obtain two homopolymers, and then connecting the two homopolymers. The two monomers are monomers corresponding to the structural units of the first polymer, that is, one of the monomers is The monomer corresponding to the structural unit, the other monomer is The monomer corresponding to the structural unit, and the types of R1 and R2 do not have to be exactly the same during the homopolymerization process of the monomer, as long as they meet the scope of the general formula. This application does not limit the homopolymer and the specific reaction steps for connecting the two homopolymers, as long as the purpose of this application can be achieved. In addition, in order to make the number average molecular weight of the first polymer between 1×10 4 ~1ⅹ10 6 In the range of m≤6900, 30≤n≤2500; as an example, in some embodiments of the present application, 80≤m≤500, and / or 75≤n≤3200, so that the number average molecular weight of the compound of formula I is more likely to fall within 2.5x10 4 ~8.5ⅹ10 5 In addition, in some embodiments of the present application, preferably R1 is -COOCH3 and R2 is -H.

[0039] In some embodiments of the present application, the stability of the first polymer in the binder can be detected by infrared spectroscopy and X-ray diffraction spectra. Specifically, in some embodiments of the present application, since the first polymer in the binder contains C-Cl bonds, the first polymer in the binder has a C-Cl bond at 600 cm-1 in the infrared spectrum of the binder. -1 ~800cm -1In addition, in some embodiments of the present application, based on XRD (X-Ray Diffractometer) characterization, the binder has a characteristic peak in the diffraction angle range of 2θ=(33, 40), and the characteristic peak is a quadruple peak, which indicates that the binder.

[0040] In a second aspect, the present application further provides a positive electrode plate, which includes a positive electrode current collector, at least one surface of which is provided with a positive electrode active layer, and the positive electrode active layer includes the above-mentioned binder.

[0041] The positive electrode plate of the present application contains the above-mentioned binder, so when NMP is used to spray the positive electrode plate, the first polymer in the binder will absorb NMP and expand; when the NMP is dried, the binder will shrink, thereby generating a channel in the positive electrode active layer, which can serve as a transmission path for lithium ions, thereby making the positive electrode plate have good lithium ion transmission capacity; therefore, in the present application, when the positive electrode plate is used in a secondary battery, the positive electrode plate is generally first sprayed with NMP and then dried. In addition, in some embodiments of the present application, the parameters of the generated channel meet the following conditions: the length of the channel is h mm, 0.01≤h≤0.2, and at least part of the channel extends to the surface of the positive electrode sheet (that is, the surface of the positive electrode active layer) and forms a through hole on the surface of the positive electrode sheet, the aperture of the through hole is d mm, 0.01≤d≤0.1; in any area on the surface of the positive electrode sheet, the total projected area of the through holes in the area is S, 15≤S≤30, and the length of the area is 5 cm and the width is 5 cm. When the generated channel meets the above conditions, the lithium ion transmission capacity of the positive electrode sheet will be better, and when used in a secondary battery, the rate performance and cycle performance of the secondary battery can be further improved. In addition, the inventors have found that when 0.04≤d≤0.08 and 0.05≤h≤0.15, the lithium ion transmission performance of the positive electrode sheet is better, and the rate performance and transmission performance of the secondary battery can be further improved.

[0042] In some embodiments of the present application, the binder content by mass is a%, based on the mass of the positive electrode active layer, with 0.5 ≤ a ≤ 2. This not only ensures good cohesion in the positive electrode sheet, but also further enhances the lithium ion transport performance of the positive electrode active layer. Therefore, when the positive electrode sheet is used in a secondary battery, the rate capability and cycle performance of the secondary battery can be further improved.

[0043] Although the binder of the present application does not contain fluorine-containing components such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene, fluorinated polyvinylidene fluoride, polytetrafluoroethylene-ethylene copolymer, or other fluorine-based polymers, it still has good bonding properties, can greatly improve the bonding strength of the positive electrode sheet, and reduce the resistance of the positive electrode sheet. Specifically, in some embodiments of the present application, the positive electrode sheet, after full discharge, has a cohesive force of FN / m and a resistance of RΩ; 20≤F≤35, 0.05≤R≤0.8, 6≤F×R≤15.

[0044] It should be noted that, in this application, "a positive electrode active layer is provided on at least one surface of the positive electrode current collector" means that the positive electrode active material layer can be provided on one surface of the positive electrode current collector in the thickness direction, or on both surfaces of the positive electrode current collector in the thickness direction. Moreover, in this application, "the surface of the positive electrode current collector" can be the entire area of the positive electrode current collector or a portion of the positive electrode current collector. This is not particularly limited in this application, as long as the purpose of this application can be achieved.

[0045] In the positive electrode sheet, the type of positive electrode current collector is not particularly limited and can be any known material suitable for use as a positive electrode current collector. Materials for the positive electrode current collector include, but are not limited to, metal materials such as aluminum, stainless steel, nickel plating, titanium, and tantalum; and materials such as carbon cloth and carbon paper. Furthermore, in some embodiments of the present application, to further enhance the lithium ion transport capability of the positive electrode sheet, the thickness of the positive electrode current collector is dμm, with 8≤d≤30; and / or the dyne value of the positive electrode current collector is x, with 20≤x≤100.

[0046] In addition, the positive electrode active layer contains not only a binder but also a positive electrode active material, a positive electrode conductive agent, etc. The present application does not particularly limit the types of the positive electrode active material and the positive electrode conductive agent, as long as they can meet the purpose of the present application. Specifically, the positive electrode active material can be any material that can reversibly embed and de-embed Li + 、Na + For example, the positive electrode active material includes but is not limited to at least one of lithium iron phosphate (LiFePO4), lithium cobalt oxide (LiCoO2), lithium manganese oxide, lithium nickel oxide, and ternary materials, and the ternary materials include but are not limited to LiNi x Co y Mn z O2、LiNi x Co y Al z At least one of O2, etc., and the content of Ni, Co, Mn, Al, etc. can be adjusted to ensure that x+y+z=1. For example, the ternary material can be LiNi0.6 Co 0.2 Mn 0.2 O2、LiNi 0.88 Co 0.08 Mn 0.04 O2、LiNi 0.8 Co 0.15 Mn 0.05 O2、LiNi 0.8 Co 0.1 Mn 0.1 O2、LiNi 0.88 Co 0.1 Mn 0.02 O2、LiNi 0.8 Co 0.15 Al 0.05 O2、LiNi 0.88 Co 0.1 Al 0.02 O2, etc. The positive electrode conductive agent includes, but is not limited to, at least one of carbon black such as acetylene black and Super-P, amorphous carbon such as needle coke, carbon nanotubes, and graphene.

[0047] In addition, to reduce the electronic contact resistance between the positive electrode current collector and the positive electrode active material layer, a conductive additive or conductive coating may be provided on the surface of the positive electrode current collector. Conductive additives include, but are not limited to, carbon and precious metals such as gold, platinum, and silver. The conductive coating may be a mixture of an inorganic oxide, a conductive agent, and a positive electrode binder.

[0048] When preparing the positive electrode sheet, the components in the above-mentioned positive electrode active material layer can be dissolved or dispersed in a liquid solvent to prepare a positive electrode slurry, and then the positive electrode slurry is coated on the positive electrode collector and dried to form a positive electrode active material layer on the positive electrode collector, thereby obtaining a positive electrode sheet. When using this method to prepare the positive electrode sheet, there is no special restriction on the solvent in the positive electrode slurry, as long as it can dissolve or disperse the above-mentioned components. Specifically, the solvent in the positive electrode slurry includes but is not limited to NMP, ethylene carbonate (EC), etc. In addition, when preparing the positive electrode sheet, the various components in the positive electrode active material layer can also be dry-mixed to form a sheet, and then the obtained sheet can be pressed onto the positive electrode collector.

[0049] In some embodiments of the present application, the single-layer density of the prepared positive electrode sheet is cw mg / 1540.25 mm 2, 100 ≤ cw ≤ 1000, preferably 300 ≤ cw ≤ 700; this facilitates subsequent expansion and contraction of the first polymer in the binder, thereby creating more channels for lithium ion transmission in the positive electrode. Similarly, in some embodiments of the present application, to enable the binder to create more channels for lithium ion transmission in the positive electrode, the compacted density of the positive electrode is PDg / cc, 3.8 ≤ PD ≤ 4.23.

[0050] In a third aspect, the present application further provides a secondary battery comprising the above-mentioned positive electrode sheet. Due to the presence of the above-mentioned positive electrode sheet, the secondary battery of the present application has good performance. Specifically, after the secondary battery of the present application is cycled 600 times at 45°C, the remaining capacity (State Of Charge, SOC) of the secondary battery is still not less than 80%; and / or, the internal resistance of the secondary battery is R cc mΩ, 13≤R cc ≤25.

[0051] In addition to the above-mentioned positive electrode sheet, the secondary battery of the present application also includes a positive electrode sheet, a separator and an electrolyte. The specific structure of each component is as follows:

[0052] electrolyte

[0053] The electrolyte can transport lithium ions and electrons, ensuring the formation of a pathway inside the secondary battery. The electrolyte usually contains lithium salt and a non-aqueous solvent.

[0054] The present application has no particular restrictions on the type of lithium salt, as long as the purpose of the present application can be achieved. For example, the lithium salt may include but is not limited to at least one of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3 or Li2SiF6. The present application has no particular restrictions on the content of lithium salt in the electrolyte, as long as the purpose of the present application can be achieved. For example, based on the mass of the electrolyte, the mass percentage of lithium salt is 8% to 15%. The present application has no particular restrictions on the non-aqueous solvent, as long as the purpose of the present application can be achieved. For example, the non-aqueous solvent may include but is not limited to at least one of carbonate compounds, carboxylate compounds, ether compounds or other organic solvents. The above-mentioned carbonate compounds may include but are not limited to at least one of chain carbonate compounds, cyclic carbonate compounds or fluorocarbonate compounds. Above-mentioned linear carbonate compound can include but is not limited to at least one of dimethyl carbonate (DMC), dipropyl carbonate (DPC), diethyl carbonate (DEC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC) or ethyl methyl carbonate (EMC). Above-mentioned cyclic carbonate can include but is not limited to at least one of ethylene carbonate, propylene carbonate, butylene carbonate (BC) or vinyl ethylene carbonate (VEC). Fluorinated carbonate compound can include but is not limited to at least one of fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate or trifluoromethylethylene carbonate. The carboxylate compound may include but is not limited to at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanoic acid, valerolactone or caprolactone. The ether compound may include but is not limited to at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran or tetrahydrofuran. The other organic solvents may include but are not limited to at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate or trioctyl phosphate.

[0055] The present application has no particular limitation on the content of the non-aqueous solvent in the electrolyte, as long as the purpose of the present application can be achieved.

[0056] Negative electrode

[0057] The negative electrode comprises a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector. The components of the negative electrode active material layer include a negative electrode active substance. That is, in this application, the negative electrode active material layer can be disposed on one surface of the negative electrode current collector in the thickness direction, or on both surfaces in the thickness direction of the negative electrode current collector. Furthermore, in this application, the "surface of the negative electrode current collector" can refer to the entire area of the negative electrode current collector or a portion of the negative electrode current collector. This is not particularly limited in this application, as long as the objectives of this application can be achieved.

[0058] The negative electrode active material layer generally contains a negative electrode active material. This application does not specifically limit the negative electrode active material. Specifically, the negative electrode active material may include at least one of a carbon material or a silicon-based material. More specifically, the carbon material includes, but is not limited to, at least one of natural graphite, artificial graphite, mesophase microcarbon beads, hard carbon, or soft carbon; the silicon-based material includes, but is not limited to, at least one of silicon, a silicon-oxygen composite material, or a silicon-carbon composite material.

[0059] In some embodiments, the negative electrode active material layer typically further comprises a negative electrode conductive agent. The present application does not particularly limit the type of negative electrode conductive agent, as long as it can achieve the objectives of the present application. For example, the negative electrode conductive agent includes, but is not limited to, at least one of acetylene black, Ketjen black, carbon nanotubes, carbon fibers, carbon dots, or graphene.

[0060] In some embodiments, the negative electrode active material layer may also contain a negative electrode binder and a thickener. The present application does not particularly limit the types of the negative electrode binder and thickener, as long as they can achieve the purpose of the present application. For example, the negative electrode binder may include, but is not limited to, at least one of polyvinyl alcohol, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, styrene-butadiene rubber, or acrylated styrene-butadiene rubber; the thickener in the negative electrode slurry may include, but is not limited to, at least one of sodium carboxymethyl cellulose and lithium carboxymethyl cellulose.

[0061] In the negative electrode sheet, the negative electrode current collector may be made of, but is not limited to, copper foil, aluminum foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or a polymer substrate coated with a conductive metal, and is not particularly limited in this application. The conductive metal may include, but is not limited to, copper, nickel, or titanium, and the polymer substrate may include, but is not limited to, at least one of polyethylene, polypropylene, ethylene-propylene copolymer, polyethylene terephthalate, polyethylene naphthalate, or poly(p-phenylene terephthalamide).

[0062] In addition, in this application, there is no particular limitation on the thickness of the negative electrode current collector and the negative electrode active material layer, as long as the purpose of this application can be achieved. For example, the thickness of the negative electrode current collector is 4 μm to 12 μm, and the thickness of the single-sided negative electrode active material layer is 30 μm to 160 μm.

[0063] In addition, similar to the preparation of positive electrode sheets, when preparing negative electrode sheets, the negative electrode slurry can be prepared and then coated onto the negative electrode current collector and dried to form a negative electrode active material layer on the negative electrode current collector to obtain a negative electrode sheet. Alternatively, the components of the negative electrode active material layer can be dry-mixed to form a sheet, and the resulting sheet can be press-bonded onto the negative electrode current collector to form a negative electrode active material layer to obtain a negative electrode sheet. The solvent in the negative electrode slurry includes any of an aqueous solvent and an organic solvent. Aqueous solvents include, but are not limited to, a mixed solvent of alcohol and water or water. Organic solvents include, but are not limited to, aliphatic hydrocarbons such as hexane; aromatic hydrocarbons such as benzene, toluene, xylene, and methylnaphthalene; heterocyclic compounds such as quinoline and pyridine; ketones such as acetone, methyl ethyl ketone, and cyclohexanone; esters such as methyl acetate and methyl acrylate; amines such as diethylenetriamine and N,N-dimethylaminopropylamine; ethers such as diethyl ether, propylene oxide, and tetrahydrofuran (THF); amides such as N-methylpyrrolidone (NMP), dimethylformamide, and dimethylacetamide; aprotic polar solvents such as hexamethylphosphoramide and dimethyl sulfoxide. In addition, in some other embodiments, when using an aqueous solvent, the components of the negative electrode slurry will also include a thickener and styrene-butadiene rubber (SBR) emulsion to slurry the negative electrode slurry, thereby adjusting the viscosity of the negative electrode slurry. The types of thickeners in the positive electrode slurry include, but are not limited to, at least one of carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, casein, and their salts.

[0064] Isolation film

[0065] To prevent short circuits, a separator is usually provided between the positive electrode and the negative electrode. In this case, the electrolyte of the present application is usually used by permeating the separator.

[0066] There is no particular restriction on the material and shape of the isolation membrane, as long as the effect of the present application is not significantly impaired. The material of the isolation membrane may be a resin, glass fiber, inorganic substance, etc. formed from a material that is stable to the electrolyte of the present application. In some embodiments, the isolation membrane includes a porous sheet or a non-woven fabric-like material with excellent liquid retention. Examples of materials for resin or glass fiber isolation membranes include but are not limited to polyolefins, aromatic polyamides, polytetrafluoroethylene, polyethersulfone, etc. In some embodiments, the polyolefin is polyethylene or polypropylene. In some embodiments, the polyolefin is polypropylene. The materials of the above-mentioned isolation membranes can be used alone or in any combination.

[0067] The separator may also be a material formed by laminating the above materials. Examples thereof include, but are not limited to, a three-layer separator formed by laminating polypropylene, polyethylene, and polypropylene in this order.

[0068] Inorganic materials include, but are not limited to, oxides such as aluminum oxide and silicon dioxide, nitrides such as aluminum nitride and silicon nitride, and sulfates (eg, barium sulfate, calcium sulfate, etc.). The form of the inorganic material includes, but is not limited to, granular or fibrous forms.

[0069] The separator may be in the form of a thin film, including but not limited to non-woven fabrics, woven fabrics, microporous films, etc. In the thin film form, the separator has a pore size of 0.01 μm to 1 μm and a thickness of 5 μm to 50 μm. In addition to the above-mentioned independent thin film separators, the following separators can also be used: a separator formed by forming a composite porous layer containing the above-mentioned inorganic particles on the surface of the positive electrode and / or negative electrode using a resin-based adhesive. For example, a separator formed by using fluororesin as an adhesive to form a porous layer of aluminum oxide particles with a particle size of 90% less than 1 μm on both sides of the positive electrode.

[0070] The thickness of the separator is arbitrary. In some embodiments, the separator has a thickness greater than 1 μm, greater than 5 μm, or greater than 8 μm. In some embodiments, the separator has a thickness less than 50 μm, less than 40 μm, or less than 30 μm. When the separator has a thickness within the above range, insulation and mechanical strength are ensured, and the rate characteristics and energy density of the electrochemical device can be maintained.

[0071] In the present application, the diaphragm may include a substrate and a surface treatment layer. The substrate may be a non-woven fabric or a composite film having a porous structure, and the material of the substrate may include at least one of polyethylene, polypropylene, polyethylene terephthalate or polyimide. Optionally, a polypropylene porous film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven fabric or a polypropylene-polyethylene-polypropylene porous composite film may be used. Optionally, a surface treatment layer is provided on at least one surface of the substrate, and the surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by a mixed polymer and an inorganic material. For example, the inorganic layer includes inorganic particles and a binder. The present application has no particular restrictions on the above-mentioned inorganic particles, and for example, it may include at least one of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide or barium sulfate. The present application has no particular restrictions on the above-mentioned binder, and for example, it may be at least one of the aforementioned binders. The polymer layer includes a polymer, and the material of the polymer includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyvinyl pyrrolidone, polyvinyl ether, polyvinylidene fluoride or poly(vinylidene fluoride-hexafluoropropylene).

[0072] The secondary battery of this application also includes a packaging bag for containing the positive electrode sheet, separator, negative electrode sheet, and electrolyte, as well as other components of the secondary battery known in the art. This application does not limit these other components. This application does not specifically limit the packaging bag and can be any packaging bag known in the art, as long as it can achieve the purpose of this application.

[0073] The use of the secondary battery of the present application is not particularly limited, and it can be used in any electronic device known in the prior art. In some embodiments, the secondary battery of the present application can be used for, but not limited to, laptop computers, pen-input computers, mobile computers, e-book players, portable phones, portable fax machines, portable copiers, portable printers, head-mounted stereo headphones, video recorders, LCD televisions, portable cleaners, portable CD players, mini-discs, transceivers, electronic notepads, calculators, memory cards, portable recorders, radios, backup power supplies, motors, cars, motorcycles, power-assisted bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries and lithium-ion capacitors, etc.

[0074] Example

[0075] The following uses lithium-ion batteries as an example to illustrate the present invention in more detail with reference to Examples and Comparative Examples. Those skilled in the art will appreciate that the preparation methods described in the present invention are merely examples, and any other suitable preparation methods are within the scope of the present invention.

[0076] Test methods and equipment:

[0077] Rate performance test

[0078] At room temperature (25°C), fully charge the secondary battery at a rate of 0.2C to 4.51V, then discharge it at a rate of 0.2C to 3V, and record the discharge capacity. Then, fully charge the secondary battery at 0.2C to 4.51V, then fully discharge it at a rate of 2C to 3V, and record the capacity. The final rate test result is calculated as 2C rate discharge capacity / full charge capacity*100%. A higher value indicates better rate performance.

[0079] Cycle performance, secondary battery internal resistance and SOC testing

[0080] Cycle performance:

[0081] At 25°C, use a 2C rate to charge the secondary battery to 4.2V at a constant current, then charge it to 0.8C at a constant voltage, then charge it to 4.5V at a 0.8C rate, then charge it to 0.05C at a constant voltage, and let it rest for 10 minutes. Use a 1C rate to discharge the secondary battery to 3.75V, then use a 0.5C rate to discharge it to 3V, and let it rest for 10 minutes. The above charge and discharge process is cycled 1000 times, and then the capacity retention rate is calculated according to the following formula:

[0082] Capacity retention rate = full charge capacity of the secondary battery after 1000 cycles / initial full charge capacity of the secondary battery * 100%. A higher value indicates better cycle performance.

[0083] Secondary battery internal resistance test:

[0084] Rcc = real-time voltage value / real-time current value, calculated and recorded every 10ms.

[0085] SOC test after 600 cycles at 45°C:

[0086] The SOC is calculated by integrating the current. The cycling operation can be referred to the cycling process in "Cycling Performance", except that the ambient temperature is 45°C when testing the SOC. The initial SOC is known to be 0, and the cumulative change in charge is calculated by measuring the battery's charge and discharge current.

[0087] Cohesion test

[0088] (1) The secondary battery was fully charged at room temperature (25°C) and a low current (0.2C) from 3V to 4.51V. After the full charge process, the voltage was discharged from 4.51V to 3V at 0.2C. The positive electrode was then removed from the fully discharged secondary battery at 3V at 25°C. The residual electrolyte on the surface of the positive electrode was wiped off with a dust-free paper, and the electrode was immersed in dichloromethane (DMC) solvent for 2 hours and air-dried.

[0089] (2) Bake the positive electrode in a muffle furnace at 131°C for 0.25 h.

[0090] (3) Under the universal tensile testing machine, the cohesive force of the baked positive electrode sheet and the fully loaded positive electrode sheet is tested respectively, as follows: first, use a blade to cut a sample with a width of 30mm and a length of 100mm to 160mm. Then, stick the double-sided tape on the steel plate, with the tape width of 20mm and length of 90mm to 150mm. Stick the cut positive electrode sheet sample on the double-sided tape with the test surface facing down, and then stick the green tape (width of 20mm and length of 90mm to 150mm) tightly to the surface of the positive electrode sheet. Then, insert a paper tape with a width equal to that of the positive electrode sheet and a length greater than the sample length of 80mm to 200mm under the green tape and fix it with wrinkle glue. Finally, turn on the tensile testing machine and adjust the limit block to the appropriate position.

[0091] Positive electrode internal resistance test after full discharge

[0092] After fully discharging the secondary battery, disassemble the secondary battery to obtain the positive electrode, then soak it in DMC for 2 hours and air-dry it in a fume hood. Then, use a resistance meter to measure the resistance of the positive electrode after full discharge (RΩ).

[0093] Infrared spectrum measurement

[0094] Sample preparation: Fully discharge the secondary battery, disassemble it, remove the positive electrode, and then soak it in DMC to clean the surface electrolyte and air-dry it. Then soak the positive electrode in NMP solution and stir it to dissolve the positive electrode active layer in the NMP. Then filter it, collect the filtered solution, dry it, and grind it to obtain the binder powder.

[0095] Take 2 mg of the above powder and test it on a Fourier transform infrared spectrometer using the potassium bromide tablet method to obtain an infrared spectrum. The infrared spectrum is compared with the peak wavenumber of the group to determine the group.

[0096] X-ray diffraction pattern measurement

[0097] Sample preparation: refer to the sample preparation method in "Infrared spectroscopy measurement".

[0098] The prepared sample powder was ground in an agate mortar until the powder was fine and without obvious particles, put into a sample bag, and sent to an X-ray diffraction analysis institution for testing.

[0099] Binder quality content test

[0100] Fully discharge the charged secondary battery, disassemble it, remove the positive electrode, and then soak it in DMC to clean the surface electrolyte and air-dry it. Then soak the positive electrode in NMP solution and stir it to dissolve the positive electrode active layer in the NMP. Then filter it and collect the resulting solution and solid. Dry and weigh them separately. The weight of the solid after drying and weighing is recorded as m1, and the weight of the solution after drying and weighing is recorded as m2. The binder mass content is calculated as: m2 / (m1+m2)×100%.

[0101] Single-layer density measurement

[0102] Use a ruler to measure the length and width of the empty aluminum foil to get the area. Divide the m2 value in the "Binder Mass Content Test" by the area to get the surface density, which is mg / 1540.25mm 2 .

[0103] Compaction density measurement of positive electrode sheets

[0104] First measure the single-layer surface density of the positive electrode sheet, and then use a thickness gauge to measure the thickness of the single-layer positive active layer in the positive electrode sheet. The compacted density of the positive electrode sheet PD = surface density / thickness of the positive electrode active layer, the unit is g / cc.

[0105] Determine the channel length, through-hole diameter, and through-hole coverage of the positive electrode sheet

[0106] Preparation of the sample to be tested: After the secondary battery is fully discharged, it is disassembled to obtain the positive electrode sheet, which is soaked in DMC for 2 hours and then dried to obtain the sample to be tested.

[0107] Channel length and through-hole diameter test: Use ion polishing to cut a uniform electrode section from the sample to be tested, and use SEM observation and measurement software to measure the height h mm of the channel appearing in the cross section and the aperture d mm of the through-hole on the surface.

[0108] Coverage test: Take eight 5cm×5cm areas at equal distances on the sample to be tested, use the SEM area measurement tool to measure the total area of the through holes, and then divide the total area of the through holes by the area of the area (25cm). 2 , and calculate the average value to get the through-hole coverage S%.

[0109] Dyne value test

[0110] Use a dyne pen to determine the dyne value of the positive electrode current collector as follows:

[0111] Use an arcotest dyne pen and first use a dyne pen with a dyne value of 10, 20, 30... to draw a line on the aluminum foil. If the drawn line does not shrink within 5 seconds, the dyne value of the aluminum foil is higher than the dyne value marked on the dyne pen. You can choose a dyne pen with a higher dyne value to test until the line drawn by the dyne pen shrinks.

[0112] Number average molecular weight test:

[0113] Tetrahydrofuran (THF) was used as the solvent, and the column temperature (25°C to 40°C) and flow rate (0.5 mL / min) were set.

[0114] Configure the detector: differential refractive index detector (RI), inject the polymer sample into the system, record the sample chromatogram, obtain the retention time and detector response, and convert the sample retention time into molecular weight based on the calibration curve.

[0115] Example 1-1

[0116] <Preparation of Electrolyte>

[0117] In a dry argon atmosphere glove box, EC, DEC and EMC in a volume ratio of 3:5:2 were mixed to form a mixed solution, and then lithium hexafluorophosphate (LiPF6), fluoroethylene carbonate (FEC) and 1,3-propane sultone (PS) were added to the mixed solution to form an electrolyte; based on the total volume of the electrolyte, the concentration of LiPF6 was 1 mol / L; based on the total mass of the electrolyte, the mass contents of FEC and PS were 5% and 3%, respectively, and the remainder was the mixed solution.

[0118] <Preparation of positive electrode sheet>

[0119] The positive electrode active material lithium cobalt oxide, the conductive agent SP, and the binder first polymer are mixed, N-methylpyrrolidone (NMP) is added, and the mixture is stirred evenly under the action of a vacuum mixer to obtain a positive electrode slurry with a solid content of 70wt%. The positive electrode slurry is evenly coated on the upper and lower surfaces of the positive electrode current collector aluminum foil with a thickness of 9μm, dried, pressurized, and cut into a specified size to obtain a positive electrode sheet. The positive electrode sheet is then sprayed with NMP and dried to form a channel in the positive electrode sheet. Based on the total mass of the positive electrode sheet, the mass content of the binder is a%, and the value of a and the specific parameters of the first polymer are shown in the table.

[0120] The single layer density in the positive electrode sheet is cw mg / 1540.25mm 2 , the compaction density is PD g / cc, the thickness of the positive electrode current collector is dμm, and the dyne value is m. The specific values are shown in the table.

[0121] <Preparation of negative electrode sheet>

[0122] Artificial graphite, styrene-butadiene rubber (SBR), polyacrylic acid (PAA), carbon nanotubes (CNTs), and carboxymethyl cellulose (CMC) were mixed in a mass ratio of 95.8:2.4:0.5:0.5:0.8. Deionized water was then added as a solvent and stirred thoroughly to prepare a negative electrode slurry with a solid content of 45 wt%. The negative electrode slurry was evenly coated on the upper and lower surfaces of a 6 μm thick negative electrode current collector copper foil, dried, pressurized, and then cut into the specified size to produce the negative electrode sheet.

[0123] <Isolation Film>

[0124] A ceramic coated diaphragm with a thickness of 5μm is used.

[0125] <Preparation of Secondary Battery>

[0126] The positive and negative electrode sheets fabricated as described above are connected to their respective tabs. These are then stacked together via a separator to form a laminate. The laminate, along with the electrolyte, is then housed in an aluminum laminate casing. The casing's opening is heat-sealed, and the secondary battery is manufactured through formation and degassing steps.

[0127] Example 1-2 to Example 1-17

[0128] Except for adjusting the parameters of the first polymer according to Table 1, the rest is basically the same as Example 1-1.

[0129] Comparative Examples 1 to 4

[0130] Except for adjusting the parameters of the first polymer according to Table 1, the rest is basically the same as Example 1-2.

[0131] Comparative Example 5

[0132] Compared with Examples 1-5, the use replace

[0133] Comparative Example 6

[0134] Compared to Examples 1-3, PVDF was used instead of the fluorine-free first polymer.

[0135] Table 1

[0136]

[0137]

[0138] As shown in Table 1, the results of the Examples and Comparative Examples show that when the binder of the present application is used in the positive electrode sheet, as NMP evaporates, the first polymer in the binder shrinks and forms through-holes, thereby increasing the lithium ion transmission channels of the positive electrode sheet, which can significantly improve the rate performance and cycle performance of the secondary battery. As shown in Comparative Examples 1 and 2, if the number average molecular weight of the first polymer in the binder is too small or too large, the first polymer will not be able to effectively improve the rate performance and cycle performance of the secondary battery. This is because if the number average molecular weight is too small, even if NMP evaporates, it is difficult for the first polymer to shrink and form channels in the positive electrode sheet, so the rate performance and cycle performance of the secondary battery cannot be improved. If the number average molecular weight is too large, the solubility of the first polymer in NMP decreases, and after NMP evaporates, it is difficult to form channels in the positive electrode sheet, and the rate performance and cycle performance of the secondary battery cannot be improved. Comparative Examples 3-4 show that when R1 and R2 in the first polymer are outside the scope of this application, the rate performance and cycle performance of the secondary battery are also poor. This is because the trihydroxybenzene in the binder has difficulty forming strong hydrogen bonds, resulting in relatively poor dispersibility and bonding properties of the binder, which in turn affects the cycle performance and rate performance of the secondary battery. Comparative Example 5 shows that when the first polymer does not contain units containing chlorine atoms, the rate performance and cycle performance of the secondary battery are also poor. This is because the lack of chlorine atoms reduces the conductivity of the binder. The large difference in conductivity between different materials in the positive electrode sheet leads to reduced rate performance and cycle performance of the secondary battery. Comparing Comparative Example 6 with Examples 1-3, it can be seen that the fluorine-containing binder cannot form channels in the active layer of the positive electrode sheet, thereby not being conducive to improving the lithium ion transport performance of the positive electrode sheet. The first polymer in the fluorine-free binder absorbs NMP, causing the binder to expand. When the NMP in the positive electrode sheet dries, the first polymer shrinks, and channels are formed in the positive active layer of the positive electrode sheet. The channels are conducive to improving the lithium ion transport performance of the positive electrode sheet. Moreover, when the channels meet the above conditions, the lithium ion transport performance of the positive electrode sheet can be further improved. When used in a secondary battery, the rate performance and cycle performance of the secondary battery can be further improved.

[0139] In particular, it can be seen from Examples 1-3 and 1-4, and 1-14 to 1-17 that when 80≤m≤500 or 75≤n≤3200, the number average molecular weight of the first polymer can fall within the range of 2.5x10 4 ~8.5ⅹ10 5 range, the rate performance and cycle performance of the secondary battery can be further improved at this time. This is because the channels generated by the first polymer in the positive electrode sheet can better improve the lithium ion transmission performance in the positive electrode sheet, thereby improving the rate performance and cycle performance of the secondary battery.

[0140] Example 2-1 to Example 2-18

[0141] Except for adjusting the parameters related to the positive electrode according to Table 2, the rest is basically the same as Example 1-2.

[0142] Table 2

[0143]

[0144]

[0145] In particular, in Table 2, it can be seen from Examples 2-1 to 2-4 that when the binder content is in the range of 0.5% to 2%, the positive electrode sheet has good cohesion, and the channels generated are more conducive to improving the lithium ion transmission performance of the positive electrode active layer, so the rate performance and cycle performance of the secondary battery are better.

[0146] Example 3-1 to Example 3-24

[0147] Except for adjusting the relevant parameters according to Table 3, the rest is basically the same as Example 1-2.

[0148] Table 3

[0149]

[0150]

[0151] It can be seen from Table 3 that when the channel length h is 0.01-0.2, the length d is 0.01-0.1, and the coverage S% is 15%-30%, the positive electrode active layer has good lithium ion transport performance, which is beneficial to improving the rate performance and cycle performance of the secondary battery; in particular, when 0.05≤h≤0.15, 0.04≤d≤0.08, the lithium ion transport performance of the positive electrode active layer can be further improved, and at this time the rate performance and cycle performance of the secondary battery can also be further improved.

[0152] The above are merely examples of the present application and are not intended to limit the scope of protection of the present application. Those skilled in the art will appreciate that various modifications and variations are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present application shall be included within the scope of protection of the present application.

Claims

1. A binder, characterized in that: It includes a first polymer, which includes a structure shown in the following formula I: Wherein R1 is any one of -H, -CH3, -Cl, -COOH, -COOCH3, R2 is any one of -H, -CH3; the number average molecular weight of the first polymer is M n , 1ⅹ10 4 ≤M n ≤1ⅹ10 6 .

2. The adhesive according to claim 1, characterized in that Wherein R1 is any one of -H or -COOCH3.

3. The adhesive according to claim 1, characterized in that It satisfies at least one of the following conditions: (1)80≤m≤500； (2)75≤n≤3200； (3)2.5ⅹ10 4 ≤M n ≤8.5ⅹ10 5 。 4. The adhesive according to claim 1, characterized in that In the infrared spectrum of the binder, at 600 cm -1 ~800cm -1 Has characteristic peaks.

5. The adhesive according to claim 1, characterized in that The X-ray diffraction spectrum of the binder has a characteristic peak when the diffraction angle is 33° to 40°, and the characteristic peak is a quadruple peak.

6. A positive electrode plate, characterized in that: The invention comprises a positive electrode current collector, at least one surface of which is provided with a positive electrode active layer, and the positive electrode active layer comprises the binder according to any one of claims 1 to 5.

7. The positive electrode sheet according to claim 6, characterized in that: Based on the mass of the positive electrode active layer, the mass content of the binder is a%, and 0.5≤a≤2.

8. The positive electrode sheet according to claim 6, characterized in that: It satisfies at least one of the following conditions: (1) The thickness of the positive electrode current collector is d μm, 8≤d≤30; (2) The dyne value of the positive electrode current collector is x, 20≤x≤100; (3) The single-layer density of the positive electrode sheet is cw mg / 1540.25 mm 2 , 100≤cw≤1000; (4) The compacted density of the positive electrode sheet is PD g / cc, 3.8≤PD≤4.

23.

9. The positive electrode sheet according to claim 8, characterized in that: 300≤cw≤700.

10. The positive electrode sheet according to claim 6, characterized in that: The positive electrode sheet is provided with a channel, the length of the channel is h mm, 0.01≤h≤0.2, at least part of the channel extends toward the surface of the positive electrode sheet and forms a through hole on the surface of the positive electrode sheet, the aperture of the through hole is d mm, 0.01≤d≤0.1; in any area on the surface of the positive electrode sheet, the total projected area of the through holes in the area has a coverage of S% in the area, 15≤S≤30, and the length of the area is 5 cm and the width is 5 cm.

11. The positive electrode sheet according to claim 10, characterized in that: 0.05≤h≤0.15, 0.04≤d≤0.

08.

12. The positive electrode sheet according to claim 6, characterized in that: After the positive electrode sheet is fully placed, the cohesive force of the positive electrode sheet is FN / m and the resistance is RΩ; 20≤F≤35, 0.05≤R≤0.8, 6≤F×R≤15.

13. A secondary battery, characterized in that: It comprises the positive electrode sheet according to any one of claims 6 to 12.

14. The secondary battery according to claim 13, wherein: After the secondary battery is cycled 600 times at 45° C., at least one of the following conditions is met: (1) The remaining capacity of the secondary battery is not less than 80%; (2) The internal resistance of the secondary battery is R cc mΩ, 13≤R cc ≤25.

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