Positive electrode slurry, positive electrode sheet, electrochemical device comprising positive electrode sheet, and electronic device

Abstract

A positive electrode slurry, a positive electrode sheet, an electrochemical device comprising the positive electrode sheet, and an electronic device. The positive electrode slurry comprises an active material, a conductive agent, and a dispersant, and the positive electrode slurry satisfies (I), wherein S is the specific surface area of the active material, and has a unit m2 / g, D1 is the volume percentage of particles having a particle size less than 300 nm in the active material, A% is the percentage of the mass of the dispersant accounting for the solid mass of the positive electrode slurry, Y% is the percentage of the mass of the conductive agent accounting for the solid mass of the positive electrode slurry, and D2 is the mass percentage of a granular conductive agent in the conductive agent.

Description

Positive electrode slurry, positive electrode sheet, electrochemical device and electronic device comprising the same

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on December 18, 2023, with application number 202311748635.5 and application name “Positive electrode slurry, positive electrode sheet, electrochemical device and electronic device comprising the same”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the field of energy storage, and in particular to a positive electrode slurry, a positive electrode sheet, an electrochemical device comprising the same, and an electronic device. Background Art

[0003] As the new energy electric vehicle market continues to grow rapidly, demand for power batteries is also rapidly expanding. Lithium iron phosphate (LFP) has surpassed traditional ternary materials to become a mainstream material for lithium-ion power batteries due to its relatively low price and improved safety. However, LFP still faces unresolved technical challenges, such as low electronic conductivity, poor low-temperature performance, and low energy density.

[0004] Specifically, the particle size of nano-scale LFP particles is usually between 50nm and 500nm, and the distribution of large and small particles is uneven. Due to the large specific surface area of ​​nano-scale LFP particles, the intermolecular force and adsorption effect are enhanced, which makes the particles attract each other, resulting in particle agglomeration. In addition, the conductive agent added to the slurry has a small particle size and a large specific surface area, and contains a variety of polar functional groups on the surface. Due to the interaction force between the particles, the conductive agent is also difficult to stably disperse in the slurry, which makes the conductive agent prone to agglomeration. These agglomeration phenomena lead to poor processing performance of the slurry. Slurry gel may appear in the front slurry process, and the viscosity increases rapidly, affecting the consistency of the coating, which in turn has an adverse effect on the performance of the battery cell. To address these problems, solutions need to be found to ensure that the nano-scale LFP material and the conductive agent are evenly dispersed in the slurry, improve the viscosity stability of the slurry, and the energy density and cycle performance of the battery cell.

[0005] Summary of the Invention

[0006] In view of the above-mentioned problems existing in the prior art, the present application proposes a positive electrode slurry, a positive electrode sheet, an electrochemical device and an electronic device including the same. By matching the specific surface area of ​​the active material in the positive electrode slurry, the volume percentage of particles with a diameter less than 300 nm in the active material, the mass percentages of the dispersant and conductive agent, and the mass percentage of the particulate conductive agent in the conductive agent, the present application increases the solid content of the slurry while effectively maintaining the viscosity stability of the slurry, thereby improving the energy density and cycle performance of lithium-ion batteries and reducing impedance.

[0007] A first aspect of the present application provides a positive electrode slurry, the positive electrode slurry comprising an active material, a conductive agent, and a dispersant, wherein the positive electrode slurry satisfies:

[0008] Where S is the specific surface area of ​​the active material, unit is m 2 / g; D1 is the volume percentage of particles with a particle size of less than 300nm in the active material; A% is the percentage of the mass of the dispersant to the mass of the positive electrode slurry solid; Y% is the percentage of the mass of the conductive agent to the mass of the positive electrode slurry solid; D2 is the mass percentage of the granular conductive agent in the conductive agent.

[0009] A second aspect of the present application provides a positive electrode sheet formed by solidifying the above-mentioned positive electrode slurry.

[0010] A third aspect of the present application provides an electrochemical device comprising the aforementioned positive electrode sheet.

[0011] A fourth aspect of the present application provides an electronic device comprising the aforementioned electrochemical device.

[0012] The technical solution of this application can achieve the following beneficial effects:

[0013] The present invention adjusts the relationship between the specific surface area S of the active material in the positive electrode slurry, the volume percentage D1 of particles with a diameter less than 300 nm in the active material, the mass percentage A% of the dispersant, the mass percentage Y% of the conductive agent, and the mass percentage D2 of the granular conductive agent in the conductive agent to meet the following conditions: The positive electrode slurry that meets the above-mentioned limiting conditions can form a good dispersion system between the components in the positive electrode slurry, reduce the lithium ion transmission impedance, increase the solid content of the positive electrode slurry, and effectively maintain the viscosity stability of the positive electrode slurry, thereby improving the energy density and cycle performance of the lithium-ion battery and reducing the impedance. DETAILED DESCRIPTION

[0014] To make the purpose, technical solutions, and advantages of this application more clear, the technical solutions of this application will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are part of the embodiments of this application, rather than all the embodiments. The relevant embodiments described herein are illustrative and are used to provide a basic understanding of this application. The embodiments of this application should not be interpreted as limiting this application.

[0015] For the sake of clarity, only some numerical ranges are specifically disclosed herein. However, any lower limit may be combined with any upper limit to form an unspecified range; and any lower limit may be combined with other lower limits to form an unspecified range, and similarly, any upper limit may be combined with any other upper limit to form an unspecified range. In addition, each individually disclosed point or single value may itself serve as a lower limit or upper limit and be combined with any other point or single value, or with other lower limits or upper limits, to form an unspecified range.

[0016] In the description herein, unless otherwise specified, “above” and “below” include the number itself.

[0017] Unless otherwise specified, the terms used in this application have the commonly understood meanings commonly understood by those skilled in the art. Unless otherwise specified, the numerical values ​​of the various parameters mentioned in this application can be measured using various measurement methods commonly used in the art (for example, they can be tested according to the methods given in the examples of this application).

[0018] A list of items connected by the terms "at least one of," "at least one of," "at least one of," or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may contain a single component or multiple components. Item B may contain a single component or multiple components. Item C may contain a single component or multiple components.

[0019] In order to improve the energy density of lithium-ion batteries using LFP as the main material, increasing the compaction density of LFP is a feasible and effective technical means. By designing the particle size of the active material LFP, that is, by using a method of mixing large and small particle size LFP particles, the compaction density of LFP can be improved. Therefore, the introduction of nano-scale LFP (particle size <300nm) can improve the size matching of LFP particles. Due to its large specific surface area and high surface energy, nano-scale LFP small particles easily agglomerate during the slurry preparation process, resulting in high slurry viscosity and low solid content, which makes subsequent coating difficult and affects battery cell performance. The positive electrode slurry proposed in the present invention is used to solve the above problems.

[0020] 1. Cathode slurry

[0021] One or more embodiments of the present application provide a positive electrode slurry, comprising an active material, a conductive agent, and a dispersant, wherein the positive electrode slurry satisfies:

[0022] Where S is the specific surface area of ​​the active material, unit is m 2 / g; D1 is the volume percentage of particles with a particle size of less than 300nm in the active material; A% is the percentage of the mass of the dispersant to the mass of the positive electrode slurry solid; Y% is the percentage of the mass of the conductive agent to the mass of the positive electrode slurry solid; D2 is the mass percentage of the granular conductive agent in the conductive agent.

[0023] The present application adjusts the relationship between the specific surface area S of the active material in the positive electrode slurry, the volume percentage D1 of particles with a diameter less than 300 nm in the active material, the mass percentage A% of the dispersant, the mass percentage Y% of the conductive agent, and the mass percentage D2 of the granular conductive agent in the conductive agent to meet the following conditions: The positive electrode slurry that meets the above-mentioned limiting conditions can form a good dispersion system between the various components of the slurry, increase the solid content of the positive electrode slurry while effectively maintaining the viscosity stability of the positive electrode slurry, thereby improving the energy density and cycle performance of the lithium-ion battery and reducing the impedance.

[0024] In some embodiments, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1.0, 1.05, 1.1, 1.15, 1.2, 1.25, 1.3, 1.35, 1.4, 1.45, 1.5, 1.55, 1.6, 1.65, 1.7, 1.75, 1.8, 1.85, 1.9, 1.95, 2.0, 2.05, 2.1, 2.15, 2.2, 2.25, or a range consisting of any two of the above values. In some embodiments, Also meets:

[0025] In some embodiments, the specific surface area S of the active material satisfies the following: 10 ≤ S ≤ 15. A larger specific surface area of ​​the active material allows for more electrolyte adsorption, providing more particle transport channels for lithium ion transmission. However, an excessively large specific surface area of ​​the active material means that the active material particles are prone to agglomeration, forming aggregates that are not conducive to uniform dispersion and result in poor slurry stability. An excessively small specific surface area of ​​the active material results in a lower compaction density of the positive electrode sheet, which in turn affects the energy density of the battery cell. Controlling the specific surface area of ​​the active material within the aforementioned range can both ensure slurry stability and improve the energy density of the battery cell. In some embodiments, the specific surface area S of the active material is 10.0, 10.2, 10.4, 10.6, 10.8, 11.0, 11.2, 11.4, 11.6, 11.8, 12.0, 12.2, 12.4, 12.6, 12.8, 13.0, 13.2, 13.4, 13.6, 13.8, 14.0, 14.2, 14.4, 14.6, 14.8, 15.0, or a range consisting of any two of the foregoing values. In some embodiments, the specific surface area S of the active material satisfies: 11≤S≤14.

[0026] In some embodiments, the volume percentage D1 of the active material with a particle size less than 300 nm satisfies the following: 0 < D1 ≤ 10%. Nanosized active materials can reduce the diffusion path of lithium ions and increase the diffusion rate of lithium ions. In addition, the gaps between nanoparticles can relieve the stress of lithium ion intercalation and deintercalation, thereby improving the cycle life of the battery. However, nanosized particles mean that the active material agglomerates more severely, which leads to poor slurry stability and affects coating consistency. Research has found that active material particles with a particle size less than 300 nm have a more serious impact on agglomeration. Therefore, this application controls the volume percentage of active material particles with a particle size less than 300 nm within the above range to ensure the energy density of the lithium-ion battery and achieve good cycle performance. In some embodiments, the volume percentage D1 of active material particles with a particle size less than 300 nm satisfies the following: 5% ≤ D1 ≤ 10%. In some embodiments, the mass percentage D1 of the active material particles with a particle size less than 300 nm is 5%, 6%, 7%, 8%, 9%, 10%, or a range consisting of any two of the above values.

[0027] In some embodiments, the particle size distribution of particles in the active material with a particle size less than 300 nm is between 50 nm and 300 nm. In some embodiments, the particle size of the active material is 50 nm, 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, or a range consisting of any two of the foregoing values.

[0028] In some embodiments, the percentage A% of the mass of the dispersant in the mass of the positive electrode slurry solids satisfies: 0.05% ≤ A% ≤ 0.5%. If the mass of the dispersant in the mass of the positive electrode slurry solids is too high, although the slurry has good dispersibility, the slurry leveling will be poor due to the low viscosity of the slurry, affecting normal coating and even causing cracking of the electrode during the coating and drying process; if the mass of the dispersant in the mass of the positive electrode slurry solids is too low, the dispersion effect on the slurry is limited, resulting in a low solid content of the slurry and affecting the processing performance; controlling the mass of the dispersant in the mass of the positive electrode slurry solids within the above range is conducive to increasing the solid content of the slurry and ensuring the stability of the slurry viscosity. In some embodiments, the mass of the dispersant in the mass of the positive electrode slurry solids A% is 0.05%, 0.10%, 0.15%, 0.20%, 0.25%, 0.30%, 0.35%, 0.40%, 0.45%, 0.50%, or a range consisting of any two of the above values. In some embodiments, the percentage A% of the mass of the dispersant to the mass of the positive electrode slurry solids satisfies: 0.1%≤A%≤0.4%.

[0029] In some embodiments, the dispersant includes at least one of polyesters, polyacrylates, amine alcohols, polyolefins, and polyethers.

[0030] In some embodiments, the polyesters include polyphosphates.

[0031] In some embodiments, the phosphate compound includes at least one of the compounds shown in Formula I,

[0032] In Formula I, R 1 、R 2 、R 3 Each is independently selected from H, C1-C8 alkyl, fluorine-substituted C1-C8 alkyl, C1-C8 alkenyl, fluorine-substituted C1-C8 alkenyl, C1-C8 alkoxy, fluorine-substituted C1-C8 alkoxy, SO3 - 、COO - , NT2 or NT 3+ ; wherein T is selected from H, C1-C8 alkyl, fluorine-substituted C1-C8 alkyl, C1-C8 alkenyl, fluorine-substituted C1-C8 alkenyl, C1-C8 alkoxy or fluorine-substituted C1-C8 alkoxy.

[0033] Exemplarily, the phosphate esters include at least one of phosphate esters or polyphosphates. Exemplarily, the polyphosphates include at least one of sodium hexametaphosphate, sodium polyphosphate (Calgon N), potassium tripolyphosphate (KTPP) and tetrapotassium pyrophosphate (TKPP).

[0034] In some embodiments, the polyester may be a polyester compound generated by the reaction of a carboxyl-terminated polyester and a polyamine or an alcoholamine, with -C-NH- or -CO- as a bridge group and an amine as an anchoring group.

[0035] In some embodiments, the polyacrylate compound includes at least one compound of Formula II,

[0036] In formula II, R is selected from H, C1-C8 alkyl, fluorine-substituted C1-C8 alkyl, C1-C6 alkenyl, fluorine-substituted C1-C8 alkenyl, C1-C8 alkoxy, fluorine-substituted C1-C8 alkoxy, SO3 - 、COO - , NT2 or NT 3+ ; wherein T is selected from H, C1-C8 alkyl, fluorine-substituted C1-C8 alkyl, C1-C8 alkenyl, fluorine-substituted C1-C8 alkenyl, C1-C8 alkoxy or fluorine-substituted C1-C8 alkoxy;

[0037] R' is selected from H, C1-C8 alkyl, fluorine-substituted C1-C8 alkyl, C1-C6 alkenyl, fluorine-substituted C1-C8 alkenyl, C1-C8 alkoxy, fluorine-substituted C1-C8 alkoxy;

[0038] n is a natural number greater than 1.

[0039] Illustratively, the polyacrylates include at least one of carboxyl-terminated polyacrylate, hydroxyl-terminated polyacrylate, polyacrylic acid, and polyurethane-modified acrylic acid.

[0040] Illustratively, the polyolefin includes terminal polyisobutylene.

[0041] Exemplarily, the amino alcohol compound includes at least one of a polymer polyol compound and an amino alcohol compound. Exemplarily, the amino alcohol compound is preferably ethanolamine or 2-amino-2-methyl-1-propanol.

[0042] For example, the polyether compounds include but are not limited to perfluoropolyether compounds and polyetherimide compounds.

[0043] The common feature of the above-mentioned dispersants is that the main chain is a saturated hydrocarbon polymer with high oxidation resistance, and the main chain is linked to at least one anchoring group of ester, carboxyl, phosphate, amino or hydroxyl, and the anchoring group has a good affinity for the active material particles and the conductive agent nanoparticles; in addition, a side chain is introduced into the main chain, and the side chain is a flexible solvated chain that can extend into the dispersion medium, and the agglomeration between the carbon-coated lithium iron phosphate nanoparticles and the conductive agent nanoparticles is suppressed through the steric hindrance effect, thereby effectively solving the dispersion problem of the active material and the conductive agent in the slurry and maintaining the stability of the slurry viscosity.

[0044] In some embodiments, the active material includes a lithium iron phosphate material; the lithium iron phosphate material includes LiFe y A (1-y) At least one of PO4 materials, wherein A comprises at least one of Mn, Co, Ti, Mg, Ca, Cr, Cu, Ni, V, Mo, Zn, Al, B, and Nb, and 0 < y ≤ 1. In some embodiments, the lithium iron phosphate material is preferably LiFePO4.

[0045] In some embodiments, the percentage Y% of the mass of the conductive agent in the mass of the positive electrode slurry solids satisfies the following: 0.25% ≤ Y% ≤ 3%. If the mass of the conductive agent in the mass of the positive electrode slurry solids is too high, it will improve the electronic conductivity of the positive electrode sheet to a certain extent, but it will also cause serious agglomeration of the conductive agent, which is not conducive to uniform dispersion and leads to poor slurry stability. If the mass of the conductive agent in the mass of the positive electrode slurry solids is too low, the resistivity of the positive electrode sheet is large, resulting in an increase in the internal resistance of the battery cell, which is not conducive to electron conduction and affects the cycle performance of the battery. Controlling the mass of the conductive agent in the mass of the positive electrode slurry solids within the above range is conducive to electron conduction, thereby reducing the internal resistance of the battery cell, improving the cycle performance of the battery cell, and ensuring the stability of the slurry. Exemplarily, the percentage Y% of the mass of the conductive agent to the mass of the positive electrode slurry solids is 0.25%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 1.0%, 1.2%, 1.4%, 1.6%, 1.8%, 2.0%, 2.2%, 2.4%, 2.6%, 2.8%, 3%, or a range consisting of any two of the above values. In some embodiments, the percentage of the mass of the conductive agent to the mass of the positive electrode slurry solids satisfies: 0.8%≤Y%≤2%.

[0046] In some embodiments, the conductive agent includes at least one of a granular conductive agent, a linear tubular conductive agent, a fibrous conductive agent, and graphene.

[0047] In some embodiments, the particle size of the granular conductive agent is 20 nm to 300 nm. If the particle size of the granular conductive agent is too small, the agglomeration of the conductive agent will be more serious, resulting in poor stability of the slurry and affecting the consistency of the coating. In some embodiments, the particle size of the granular conductive agent is 20 nm, 50 nm, 80 nm, 100 nm, 120 nm, 150 nm, 180 nm, 200 nm, 220 nm, 250 nm, 280 nm, 300 nm, or a range consisting of any two of the above values. In some embodiments, the particle size of the granular conductive agent is 100 nm to 300 nm.

[0048] In some embodiments, the particle-type conductive agent comprises at least one of carbon black, Ketjen black, and acetylene black. In some embodiments, the particle-type conductive agent is preferably carbon black particles.

[0049] In some embodiments, the length of the linear tubular conductive agent is 1 μm to 10 μm. In some embodiments, the length of the linear tubular conductive agent is 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, or a range consisting of any two of the above values.

[0050] In some embodiments, the diameter of the linear tubular conductive agent is 1 nm to 10 nm. In some embodiments, the diameter of the linear tubular conductive agent is 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, or a range consisting of any two of the above values.

[0051] In some embodiments, the linear tubular conductive agent has an aspect ratio of 100 to 10,000. In some embodiments, the linear carbon nanotubes have an aspect ratio of 100, 200, 300, 400, 500, 600, 700, 800, 900, 1,000, 2,000, 3,000, 4,000, 5,000, 6,000, 7,000, 8,000, 9,000, 10,000, or a range consisting of any two of the foregoing values.

[0052] In some embodiments, the linear tubular conductive agent is preferably a linear carbon nanotube.

[0053] In some embodiments, the conductive agent includes carbon black and carbon nanotubes, and the weight percentage of carbon black is 10% to 100% based on the total weight of the carbon black and carbon nanotubes. In some embodiments, the conductive agent includes carbon black and carbon nanotubes, and the weight percentage of carbon black is 30% to 100% based on the total weight of the carbon black and carbon nanotubes. The weight percentage of carbon black can be adjusted and is not specifically limited in the embodiments of this application.

[0054] In some embodiments, the solid content of the positive electrode slurry is 54% to 68%. In some embodiments, the solid content of the positive electrode slurry is 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, or a range consisting of any two of the foregoing values. In some embodiments, the solid content of the positive electrode slurry is 58% to 65%.

[0055] In some embodiments, the viscosity of the positive electrode slurry is 3000 mPa·s to 15000 mPa·s. In some embodiments, the viscosity of the positive electrode slurry is 3000 mPa·s, 4000 mPa·s, 5000 mPa·s, 6000 mPa·s, 7000 mPa·s, 8000 mPa·s, 9000 mPa·s, 10000 mPa·s, 11000 mPa·s, 12000 mPa·s, 13000 mPa·s, 14000 mPa·s, 15000 mPa·s, or a range consisting of any two of the foregoing values. In some embodiments, the viscosity of the positive electrode slurry is 3500 mPa·s to 10000 mPa·s.

[0056] In some embodiments, the positive electrode slurry further includes a binder, which includes, but is not limited to, at least one of polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, or nylon. In some embodiments, the binder is preferably polyvinylidene fluoride (PVDF).

[0057] In some embodiments, in the positive electrode slurry solid, the mass ratio of the active material, binder, conductive agent and dispersant satisfies: (94~98):(1~3):(0.25~3):(0.05~0.5). The ratio of the active material, binder and conductive agent can be adjusted, and the embodiments of the present application do not impose specific restrictions on this.

[0058] One or more embodiments of the present application further provide a method for preparing a positive electrode slurry, comprising:

[0059] S1, mixing a dispersant and a solvent to obtain a dispersant solution;

[0060] S2. dry-mixing the active material, the granular conductive agent, and the binder to obtain a dry-mixed powder;

[0061] S3, mixing the dispersant solution with the dry mixed powder to obtain a kneaded slurry;

[0062] S4, dispersing the solvent and the adhesive slurry at a high speed to obtain a first slurry;

[0063] S5. Dispersing the linear tubular conductive agent and the first slurry at a high speed to obtain a second slurry; mixing the solvent with the second slurry to obtain a positive electrode slurry.

[0064] In some embodiments, the solid content of the bonding slurry in S3 is preferably 72% to 74%.

[0065] In some embodiments, in S4 and S5, the linear speed of the high-speed dispersion is preferably 15 m / s.

[0066] 2. Positive electrode

[0067] One or more embodiments of the present application further provide a positive electrode sheet, which includes a positive electrode current collector and a positive electrode active material layer disposed on at least one side of the positive electrode current collector, wherein the positive electrode active material layer is formed by solidifying the aforementioned positive electrode slurry.

[0068] In some embodiments, the positive electrode current collector includes, but is not limited to, a metal foil or a composite current collector. For example, aluminum foil can be used. The composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer substrate.

[0069] 3. Electrochemical Device

[0070] One or more embodiments of the present application further provide an electrochemical device comprising the aforementioned positive electrode sheet.

[0071] The electrochemical device of the present application further includes a negative electrode sheet and an electrolyte.

[0072] In some embodiments, the negative electrode plate includes a negative electrode current collector and a negative electrode active material. The negative electrode active material includes at least one of a silicon-based material, a carbon-based material, a tin-based material, a phosphorus-based material, and metallic lithium. The silicon-based material includes at least one of silicon, a silicon alloy, a silicon oxide, and a silicon-carbon compound. The carbon-based material includes at least one of graphite, soft carbon, hard carbon, carbon nanotubes, and graphene. The tin-based material includes at least one of tin, tin oxide, and a tin alloy. The negative electrode current collector includes at least one of copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, or any combination thereof.

[0073] In some embodiments, the negative electrode plate further includes a binder and a conductive agent. The binder includes, but is not limited to: at least one of polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene 1,1-difluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylic (ester) styrene-butadiene rubber, epoxy resin or nylon. The conductive agent includes, but is not limited to: at least one of carbon-based materials, metal-based materials, conductive polymers and mixtures thereof. In some embodiments, the carbon-based material includes natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber or any combination thereof. In some embodiments, the metal-based material includes metal powder, metal fiber, copper, nickel, aluminum or silver. In some embodiments, the conductive polymer includes a polyphenylene derivative.

[0074] The electrochemical device of the present application further includes an electrolyte, which includes a lithium salt and a non-aqueous solvent.

[0075] In some embodiments of the present application, the lithium salt includes but is not limited to one or more of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, LiSiF6, LiBOB or lithium difluoroborate.

[0076] Exemplarily, the lithium salt may be LiPF6.

[0077] The non-aqueous solvent includes, but is not limited to, one or more of a carbonate compound, a carboxylate compound, or an ether compound.

[0078] Exemplary, carbonate compounds include, but are not limited to, one or more of linear carbonate compounds or cyclic carbonate compounds. Specifically, linear carbonate compounds include, but are not limited to, one or more of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), or methylethyl carbonate (MEC); cyclic carbonate compounds include, but are not limited to, one or more of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), or vinylethylene carbonate (VEC).

[0079] Exemplary carboxylic acid ester compounds include, but are not limited to, one or more of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanoic acid lactone, valerolactone, or caprolactone.

[0080] Exemplarily, the ether compound includes, but is not limited to, one or more of dibutyl ether, tetraglyme, diglyme, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, or tetrahydrofuran.

[0081] In some embodiments, a separator is provided between the positive and negative electrode sheets to prevent short circuits. The material and shape of the separator used in the embodiments of the present application are not particularly limited and may be any known prior art material. In some embodiments, the separator comprises a polymer or inorganic material, for example, formed from a material that is stable to the electrolyte of the present application.

[0082] The electrochemical devices of the present application include, but are not limited to, all types of primary batteries, secondary batteries, fuel cells, solar cells, or capacitors. In some embodiments, the electrochemical device is a lithium secondary battery. In some embodiments, the lithium secondary battery includes, but is not limited to, a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

[0083] In a specific example of the present invention, the electrochemical device is a lithium-ion battery. The present application does not impose any specific restrictions on the type of lithium-ion battery, and it can be any type of lithium-ion battery, such as button-type, cylindrical, soft-pack lithium-ion battery, etc.

[0084] 4. Electronic Devices

[0085] One or more embodiments of the present application further provide an electronic device, which includes the aforementioned electrochemical device.

[0086] In some embodiments, the electronic devices of the present application include but are not limited to: laptop computers, pen-type computers, mobile computers, e-book players, portable phones, portable fax machines, portable copiers, portable printers, head-mounted stereo headphones, video recorders, LCD TVs, 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 or lithium-ion capacitors, etc.

[0087] Hereinafter, the electrochemical device of the present application will be further described in conjunction with specific embodiments and comparative examples.

[0088] Examples and Comparative Examples

[0089] The materials and reagents used in the following examples and comparative examples were all commercially available.

[0090] Example 1

[0091] Preparation of positive electrode slurry: (1) Dissolve or dilute 0.002 kg of dispersant (phosphate) in 1.855 kg of N-methylpyrrolidone (NMP) solvent. High-speed dispersing equipment or mechanical stirrer can be used for dispersion or stirring to prepare a dispersant solution; (2) Dry mix 3.5 kg of LiFePO4 nanoparticles, 0.038 kg of conductive agent carbon black (Super P) and 0.067 kg of binder (PVDF) in a double planetary mixer, and mix the materials evenly to obtain a dry mixed powder; (3) Add 1.678 kg of dispersant solution to the dry mixed powder and perform slurry bonding for 1 hour to obtain a bonded slurry. The solid content of the kneaded slurry in this step is controlled to 72%; (4) Add 0.946 kg of (5) 0.408 kg of conductive carbon nanotube (CNT) slurry with a solid content of 4% was added to the first slurry and the mixture was dispersed at high speed for 2 hours at a linear velocity of 15 m / s. (6) 0.05 kg of NMP was added to the second slurry to adjust the viscosity and obtain a positive electrode slurry. The fluidity of the positive electrode slurry was tested. The discharge viscosity was controlled at 4000 ± 1000 mPa·s, the fineness was 5 μm, and the solid content of the slurry was 64%.

[0092] In the positive electrode active material, the specific surface area S of the active material is 13.3m 2 / g; the volume percentage D1 of particles with a particle size of less than 300nm in the active material is 10%; in the positive electrode slurry solid, the mass percentage of the positive electrode active material is 96.6%, the mass percentage A% of the dispersant is 0.05%; the mass percentage Y% of the conductive agent is 1.5%, of which the mass percentage D2 of the carbon black in the conductive agent is 70%, and the particle size of the carbon black particles is 40nm; the length of the carbon nanotubes is 5μm, the diameter is 10nm, and the aspect ratio is 500.

[0093] Preparation of positive electrode sheet: The positive electrode slurry prepared above was evenly coated on both surfaces of a positive electrode current collector aluminum foil with a thickness of 12 μm, dried, and roll-pressed to obtain a positive electrode sheet.

[0094] Preparation of negative electrode sheets: Graphite is used as the negative electrode active material, and the negative electrode active material, binder SBR, CMC, PAA, conductive carbon black, and carbon nanotubes are mixed in a mass ratio of negative electrode active material: SBR: CMC: PAA: conductive carbon black: carbon nanotubes = 96:1:0.5:1:1:0.5. Ultrapure water is added, and a negative electrode slurry is obtained by a high-speed mixer. The negative electrode slurry is evenly coated on the surface of a negative electrode current collector copper foil with a thickness of 8 μm, dried, and roll-pressed to obtain a negative electrode sheet.

[0095] Preparation of electrolyte: Dimethyl carbonate (DMC), ethylene carbonate (EC), and ethyl methyl carbonate (EMC) were mixed in a mass ratio of 1:1:1 as a solvent, 1 mol / L LiPF6 was added as a lithium salt based on the solvent, and 5% vinylene carbonate (VC) was added as an additive to obtain an electrolyte.

[0096] Diaphragm: 11μm thick PE porous polymer membrane is used.

[0097] Preparation of lithium-ion batteries: After the negative and positive electrode sheets are cut into a size of 46mm by 54mm, they are stacked together with the separator, assembled into a bare battery cell, and then the tabs are welded and assembled into an aluminum-plastic film. The battery is then filled with liquid, allowed to stand, formed, and divided into different capacities to produce a lithium-ion battery.

[0098] Examples 2 to 10

[0099] Examples 2 to 10 were prepared based on Example 1 by adjusting the specific surface area S of the active material in the positive electrode slurry, the volume percentage D1 of particles with a particle size less than 300 nm in the active material, the mass percentage A% of the dispersant, the mass percentage Y% of the conductive agent, and the mass percentage D2 of the particulate conductive agent in the conductive agent. Specific data are shown in Table 1. The remaining preparation methods of Examples 2 to 10 are the same as those of Example 1.

[0100] Comparative Examples 1 to 2

[0101] Comparative Examples 1 and 2 were prepared based on Example 1 without the addition of a dispersant. The specific surface area S of the active material in the positive electrode slurry, the volume percentage D1 of particles with a particle size less than 300 nm in the active material, the mass percentage Y% of the conductive agent, and the mass percentage D2 of the particulate conductive agent in the conductive agent were adjusted. Specific data are shown in Table 1. The remaining preparation methods for Comparative Examples 1 and 2 were the same as those for Example 1.

[0102] Comparative Examples 3 to 8

[0103] Comparative Examples 3 to 8 were prepared based on Example 1 by adjusting the specific surface area S of the active material in the positive electrode slurry, the volume percentage D1 of particles with a particle size less than 300 nm in the active material, the mass percentage A% of the dispersant, the mass percentage Y% of the conductive agent, and the mass percentage D2 of the particulate conductive agent in the conductive agent. Specific data are shown in Table 1. The remaining preparation methods for Comparative Examples 3 to 8 are the same as those for Example 1.

[0104] Test Method

[0105] 1. Particle size test:

[0106] 1) Place the selected powder sample into the sample cup in the instrument and place the sample cup at the measuring position of the laser particle size analyzer.

[0107] 2) Turn on the power of the laser particle size analyzer and start the measurement program. In the program interface, you can select different measurement modes as needed, such as single measurement, continuous measurement, etc.

[0108] 3) During the measurement process, the sample cup must be kept stable and free from vibration or shaking. The measurement program parameters must be set, including the measurement range, measurement time, and volume distribution.

[0109] 4) After starting the measurement, the laser particle size analyzer will begin to measure the powder sample. By analyzing the scattered light intensity of the powder sample, the particle size and volume distribution data of the powder sample can be obtained.

[0110] 5) After the measurement is completed, the experimental data needs to be recorded and analyzed. The particle size distribution of the powder sample can be displayed by drawing a particle size distribution curve to obtain the volume particle size data.

[0111] 2. Particle specific surface area test:

[0112] 1) Place the sample to be tested (30-500 mg, depending on the specific surface area of ​​the sample) into the sample tube.

[0113] 2) Install the sample tube into the degassing station. When installing the sample tube, be sure to align the sample tube with the port and tighten the screws to ensure a secure seal. Then put the heating pack on the sample tube and set the parameters such as file information and degassing temperature. Turn on the vacuum pump and start heating and vacuum degassing the sample to remove the gas adsorbed on the surface of the material. After degassing, turn off the heating power supply, wait for the sample to cool to room temperature, and then backfill with helium. After filling with helium to atmospheric pressure, remove the sample tube and immediately cover it with a rubber stopper. Weigh to 0.1 mg and record the weight of the helium-filled sample tube, stopper, and filler rod. This is the gross weight of the sample tube. Use the same sample tube, stopper, and filler rod to perform the following work. The sample is weighed using the reduction method: a. Place the stand on the balance and tar it to zero; b. Plug the sample tube with a sealed filter plug or place the plug on the stand and record the reading m1; c. Load the sample into the sample tube through the funnel, plug it with a sealed plug or stopper, weigh it, and record the reading m2; d. Place the sample tube in the degassing station for degassing; e. Place the degassed and cooled sample tube on the stand after the zeroing operation, weigh it, and record the reading m3; f. Subtract the count m1 from the reading m3 to obtain the sample mass.

[0114] 3) Load the weighed sample tube into the analysis station, add liquid nitrogen to the Dewar flask, and enter the sample mass into the analysis file. Set the test parameters and start the adsorption and desorption test process.

[0115] 4) After the test is completed, remove the sample from the sample tube, wash the sample tube, and dry it for later use.

[0116] 3. Slurry solid content test:

[0117] 1) To test using an infrared drying solids meter, connect the instrument to the main power supply and turn the two level adjustment feet of the balance until the bubble is in the center of the level indicator.

[0118] 2) When the solid content meter is in a stable state, place the standard weight on the tray, wait for the reading to stabilize, record the data, and set the defined drying temperature to 140℃

[0119] 3) Place copper foil or aluminum foil of the same size as the tray on the tray and weigh it. After the reading stabilizes, press the zero key to return to zero.

[0120] 4) Test the solid content of the slurry. Use a spoon to spread 0.8-1.2g of sample thinly and evenly on the copper foil or aluminum foil, close the top cover, and press the "Start" button to start the test.

[0121] 5) The screen shows that the test reaction is completed, the solid content percentage of the sample is read and the test results are recorded.

[0122] 4. Slurry viscosity test:

[0123] 1) Using a rotational viscometer, screw the rotor into the connecting screw (turn left to install, turn right to remove).

[0124] 2) Place 450-500 mL of the sample to be tested directly under the meter head. Lower the meter head so that the rotor notch is level with the sample level and the rotor is in the center of the beaker. Place the thermometer in the slurry and the rotor notch is flush with the sample level.

[0125] 3) Click the "Start" button to start the test; you can monitor the progress of the test by clicking "View Data"; after the measurement timer ends, read the viscosity and temperature values ​​of the sample to be tested from the display and record the test results.

[0126] 5. Impedance test:

[0127] 1) Fully charge, adjust the temperature to 25℃, a. rest for 10 minutes; b. 0.5℃ DC 2.5V; c. rest for 5 minutes;

[0128] 2) 5°C 2C DCR test 10%-100% SOC: a. 1C CC for 6 minutes; b. rest for 3 hours, ensuring that the deviation between the cell temperature and the ambient temperature is less than 2°C, and recording the terminal voltage V0; c. 2C DC for 30 seconds (0.1s step-by-step), record the discharge voltage for 1s / 5s / 10s / 30s, and calculate the DCR (voltage sampling frequency 0.1s, lower cut-off voltage 2.0V); d. rest for 40 seconds, record the terminal voltage V1; e. 1.5C CC for 30 seconds (0.1s step-by-step), record the discharge voltage for 1s / 5s / 10s / 30s, and calculate the DCR (voltage sampling frequency 0.1s, upper cut-off voltage 3.75V); f. Repeat steps a and e 9 times; g. rest for 5 minutes.

[0129] 6. Cycle performance test:

[0130] 1) Adjust the temperature to 25°C and let it rest for 10 minutes;

[0131] 2) 0.5C DC 2.5V;

[0132] 3) rest 5 minutes;

[0133] 4) 1C CC to 3.65V, 3.65V CV throw 0.05C;

[0134] 5) rest 5 minutes;

[0135] 6) 1C DC to 2.5V (the capacity in this step is recorded as C);

[0136] 7) Repeat steps 4-7 for 3 cycles (take the average of the 3 steps 6 as the initial capacity C0);

[0137] 8) rest 5 minutes;

[0138] 9)1C CC to 3.65V, 3.65V CV to 0.05C;

[0139] 10) rest 5 minutes;

[0140] 11) 1C DC to 2.5V;

[0141] 12) Repeat steps 8-11 for 200 cycles (take the capacity C of step 11 at the 200th cycle 200 );

[0142] 13) Calculate the capacity retention rate, C 200 / C0.

[0143] The test results are shown in Table 1 below.

[0144] Table 1

[0145] By comparing the data of Example 1-10 and Comparative Example 1-8 in Table 1, it can be seen that the solid content of the positive electrode slurry of Example 1-10 is higher than that of Comparative Example 1-8 as a whole, the viscosity change rate of the positive electrode slurry in Example 1-10 after being placed for 72 hours is controlled within 300%, the lithium ion battery cycle capacity retention rate of Example 1-10 is significantly higher than that of Comparative Example 1-8, and the lithium ion battery impedance of Example 1-10 is significantly lower than that of Comparative Example 1-8. Experimental data show that the present application satisfies the relationship between the specific surface area S of the active material in the positive electrode slurry, the volume percentage D1 of particles with a particle size less than 300nm in the active material, the mass percentage A% of the dispersant, the mass percentage Y% of the conductive agent, and the mass percentage D2 of the granular conductive agent in the conductive agent by regulating the active material. The positive electrode slurry that meets the specified conditions can form a good dispersion system between the components in the positive electrode slurry, which can ensure that the positive electrode slurry has appropriate dispersibility and viscosity. While increasing the solid content of the positive electrode slurry, it can effectively maintain the viscosity stability of the positive electrode slurry, thereby improving the energy density and cycle performance of the battery cell and reducing impedance.

[0146] By comparing the data of Examples 1-8 and Examples 9-10 in Table 1, it can be seen that the present application further satisfies the following conditions by regulating the relationship between the specific surface area S of the active material in the positive electrode slurry, the volume percentage D1 of particles with a particle size of less than 300 nm in the active material, the mass percentage A% of the dispersant, the mass percentage Y% of the conductive agent, and the mass percentage D2 of the granular conductive agent in the conductive agent: The positive electrode slurry that meets the limiting conditions further forms a more uniform dispersion system between the components in the positive electrode slurry, which can ensure that the positive electrode slurry has better dispersibility and viscosity, further increase the solid content of the positive electrode slurry, and ensure that the viscosity change rate of the positive electrode slurry after 72 hours is controlled within 200%, further improve the cycle capacity retention rate of the battery cell to more than 86%, and further reduce the impedance to below 1.8ohm.

[0147] Although some exemplary embodiments of the present application have been illustrated and described, the present application is not limited to the disclosed embodiments. On the contrary, those skilled in the art will recognize that some modifications and changes may be made to the described embodiments without departing from the spirit and scope of the present application as described in the appended claims.

Claims

1. A positive electrode slurry, characterized in that: The positive electrode slurry comprises an active material, a conductive agent and a dispersant, and the positive electrode slurry satisfies: Where S is the specific surface area of ​​the active material, in m 2 / g; D1 is the volume percentage of particles in the active material with a particle size less than 300 nm; A% is the percentage of the mass of the dispersant to the mass of the positive electrode slurry solids; Y% is the percentage of the conductive agent mass to the solid mass of the positive electrode slurry; D2 is the mass percentage of the particle-type conductive agent in the conductive agent.

2. The positive electrode slurry according to claim 1, characterized in that Also meets:

3. The positive electrode slurry according to claim 1 or 2, characterized in that: At least one of the following conditions is also met: (1)10≤S≤15； (2)0＜D1≤10％； (3)0.05％≤A％≤0.5％； (4)0.25％≤Y％≤3％； (5)10％≤D2≤100％。 4. The positive electrode slurry according to claim 3, characterized in that: At least one of the following conditions is also met: (1)11≤S≤14； (2)5％≤D1≤10％； (3)0.1％≤A％≤0.4％； (4)0.8％≤Y％≤2％； (5)30％≤D2≤100％。 5. The positive electrode slurry according to any one of claims 1 to 4, characterized in that: The dispersant includes at least one of polyesters, polyacrylates, amine alcohols, polyolefins and polyethers.

6. The positive electrode slurry according to any one of claims 1 to 5, characterized in that: The active material includes lithium iron phosphate material; The lithium iron phosphate material includes LiFe y A (1-y) At least one of PO4 materials, wherein A includes Mn, Co, At least one of the elements Ti, Mg, Ca, Cr, Cu, Ni, V, Mo, Zn, Al, B and Nb, 0<y≤1.

7. The positive electrode slurry according to any one of claims 1 to 6, characterized in that: The conductive agent includes at least one of a particle-type conductive agent, a linear tubular conductive agent, a fibrous conductive agent, and graphene.

8. The positive electrode slurry according to claim 7, characterized in that: At least one of the following conditions is also met: (1) The particle-type conductive agent includes at least one of carbon black, Ketjen black and acetylene black; (2) The particle size of the granular conductive agent is 20 nm to 300 nm; (3) The linear tubular conductive agent comprises linear carbon nanotubes; (4) The linear tubular conductive agent has a length of 1 μm to 10 μm, a diameter of 1 nm to 10 nm, and an aspect ratio of 100 to 10000; (5) The conductive agent includes a granular conductive agent and a linear tubular conductive agent.

9. A positive electrode sheet, characterized in that: The invention comprises a positive electrode current collector and a positive electrode active material layer arranged on the positive electrode current collector, wherein the positive electrode active material layer is prepared according to the positive electrode slurry according to any one of claims 1 to 8.

10. An electrochemical device, characterized in that: It comprises a negative electrode plate, a separator, an electrolyte and a positive electrode plate according to claim 9.

11. An electronic device, characterized in that: Comprising the electrochemical device according to claim 10.

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