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

Abstract

A positive electrode slurry, a positive electrode sheet, an electrochemical device comprising same, and an electronic device. The positive electrode slurry comprises an active material and a conductive agent. The positive electrode slurry satisfies: (I), wherein θ represents the percentage by volume of particles having a particle size less than 300 nm in the active material; X1 represents the percentage of the mass of the active material in the solid mass of the positive electrode slurry; X2 represents the percentage of the mass of the conductive agent in the solid mass of the positive electrode slurry; S1 represents the specific surface area of the active material, with the unit of m2 / g; S2 represents the specific surface area of the conductive agent, with the unit of m2 / g; D1 represents the particle size distribution coefficient of the active material; and D2 represents the particle size distribution coefficient of the conductive agent. According to the positive electrode slurry satisfying the limiting condition, various components in the slurry can form a good dispersion system, thereby effectively keeping the dispersity and stability of the positive electrode slurry while increasing the solid content of the positive electrode slurry, thus improving the rate and cycle performance of a battery cell and reducing impedance.

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 202311748616.2 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, the demand for power batteries is also expanding rapidly. Lithium iron phosphate (LFP) has surpassed traditional ternary materials to become one of the mainstream materials for lithium-ion power batteries due to its relatively low price and higher safety.

[0004] However, the particle size distribution of lithium iron phosphate material particles is relatively wide, and the distribution of large and small particles is uneven. Nano-scale small particles have a large specific surface area, and the intermolecular force and adsorption effect are enhanced, which makes the particles attract each other and easily aggregate. 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, so that the conductive agent is also 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 electrical performance and cycle performance of the battery cell. To address these problems, solutions need to be found to ensure that the lithium iron phosphate material and the conductive agent are evenly dispersed in the slurry, improve the stability of the slurry, and improve the rate performance 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 mass percentage of active material and conductive agent in the positive electrode slurry, the particle size distribution coefficient, the specific surface area, and the volume percentage of active material particles with a size less than 300 nm, the present application effectively improves the dispersibility and stability of the positive electrode slurry, thereby improving the electrochemical performance and cycling performance of the electrochemical device.

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

[0008] Where θ represents the volume percentage of particles with a diameter of less than 300 nm in the active material; X1 represents the percentage of the mass of the active material to the mass of the positive electrode slurry solids; X2 represents the percentage of the mass of the conductive agent to the mass of the positive electrode slurry solids; S1 represents the specific surface area of ​​the active material, in m 2 / g; S2 represents the specific surface area of ​​the conductive agent, unit is m 2 / g; D1 represents the particle size distribution coefficient of the active material; D1 = (D901-D101) / D501, D101 represents the particle size distribution of the active material on a volume basis, the volume cumulative 10% particle size, D501 represents the particle size distribution of the active material on a volume basis, the volume cumulative 50% particle size, D901 represents the particle size distribution of the active material on a volume basis, the volume cumulative 90% particle size, the units of D101, D501 and D901 are is μm; D2 represents the particle size distribution coefficient of the conductive agent; D2 = (D902-D102) / D502, D102 represents the particle size of the conductive agent with 10% cumulative volume in the volume-based particle size distribution, D502 represents the particle size of the conductive agent with 50% cumulative volume in the volume-based particle size distribution, D902 represents the particle size of the conductive agent with 90% cumulative volume in the volume-based particle size distribution, and the units of D102, D502 and D902 are all μm.

[0009] A second aspect of the present application provides a method for preparing a positive electrode slurry, which is used to prepare the aforementioned positive electrode slurry.

[0010] A third aspect of the present application provides a positive electrode sheet, which is formed by solidifying the positive electrode slurry or the positive electrode slurry prepared according to the above-mentioned preparation method.

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

[0012] A fifth aspect of the present application provides an electronic device comprising the aforementioned electrochemical device.

[0013] The technical solution of this application can achieve the following beneficial effects:

[0014] The present application regulates the distribution relationship between the mass percentage, specific surface area, particle size distribution coefficient of the active material and the conductive agent in the positive electrode slurry, and the volume percentage of particles with a particle size of less than 300 nm in the active material to meet specific limiting conditions. The positive electrode slurry that meets the limiting conditions can form a good dispersion system between the components in the slurry, increase the solid content of the positive electrode slurry, and effectively maintain the dispersibility and stability of the positive electrode slurry, thereby improving the electrochemical performance and cycle performance of the electrochemical device and reducing the impedance. DETAILED DESCRIPTION

[0015] 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.

[0016] 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.

[0017] In the description herein, unless otherwise specified, “above” and “below” include the number itself.

[0018] 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).

[0019] 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.

[0020] 1. Cathode slurry

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

[0022] Where θ represents the volume percentage of particles with a diameter of less than 300 nm in the active material; X1 represents the percentage of the mass of the active material to the mass of the positive electrode slurry solids; X2 represents the percentage of the mass of the conductive agent to the mass of the positive electrode slurry solids; S1 represents the specific surface area of ​​the active material, in m 2 / g; S2 represents the specific surface area of ​​the conductive agent, unit is m 2 / g; D1 represents the particle size distribution coefficient of the active material; D1 = (D901-D101) / D501, D101 represents the particle size distribution of the active material on a volume basis, the volume cumulative 10% particle size, D501 represents the particle size distribution of the active material on a volume basis, the volume cumulative 50% particle size, D901 represents the particle size distribution of the active material on a volume basis, the volume cumulative 90% particle size, the units of D101, D501 and D901 are is μm; D2 represents the particle size distribution coefficient of the conductive agent; D2 = (D902-D102) / D502, D102 represents the particle size of the conductive agent with 10% cumulative volume in the volume-based particle size distribution, D502 represents the particle size of the conductive agent with 50% cumulative volume in the volume-based particle size distribution, D902 represents the particle size of the conductive agent with 90% cumulative volume in the volume-based particle size distribution, and the units of D102, D502 and D902 are all μm.

[0023] The present application regulates the distribution relationship between the mass percentage of the active material and the conductive agent in the positive electrode slurry, the specific surface area, the particle size distribution coefficient, and the volume percentage of particles with a particle size of less than 300 nm in the active material to meet the above-mentioned specific limiting conditions. The positive electrode slurry that meets the limiting conditions can form a good dispersion system between the components in the slurry, increase the solid content of the positive electrode slurry, and effectively maintain the dispersibility and stability of the positive electrode slurry, thereby improving the electrochemical performance and cycle performance of the electrochemical device and reducing the impedance.

[0024] In some embodiments, 0.15, 0.2, 0.4, 0.6, 0.8, 1.0, 1.2, 1.4, 1.6, 1.8, 2.0, 2.2, 2.4, 2.6, 2.8, 3.0, 3.2, 3.4, 3.6, 3.8, 4.0, 4.2, 4.6, 4.8, 5.0, 5.2, 5.4, 5.58 or a range consisting of any two of the above values.

[0025] In some embodiments, Within this limited range, the components in the slurry are evenly dispersed, which is beneficial to improving the stability of the slurry and reducing the diaphragm resistance of the electrode, thereby facilitating the performance of the lithium-ion battery's electrical properties and improving its cycle performance.

[0026] In some embodiments, the volume percentage θ of particles with a particle size of less than 300 nm in the active material satisfies: 0<θ≤10%. If the volume percentage of particles with a particle size of less than 300 nm in the active material is too high, the agglomeration of the active material will be more serious, resulting in poor dispersion and stability of the slurry, increased diaphragm resistance of the corresponding electrode, and thus affecting electrochemical performance and cycle performance. In some embodiments, the volume percentage θ of particles with a particle size of less than 300 nm in the active material satisfies: 5%≤θ≤10%. In some embodiments, the volume percentage θ of particles with a particle size of less than 300 nm in the active material is 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, or a range consisting of any two of the above values.

[0027] In some embodiments, the percentage of active material mass to the solid mass of the positive electrode slurry, X1, satisfies the following conditions: 92% ≤ X1 ≤ 97%. If the percentage of active material mass to the solid mass of the positive electrode slurry, X1, is too high, the corresponding conductive agent or binder ratio is too low, resulting in excessive electrode sheet resistance or low bonding strength, further leading to poor battery cell performance or membrane peeling; if the percentage of active material mass to the solid mass of the positive electrode slurry, X1, is too low, it will seriously reduce the energy density of the battery cell; controlling the percentage of active material mass to the solid mass of the positive electrode slurry, X1, within this range is conducive to the electrical performance and energy density of the battery cell. In some embodiments, the percentage of active material mass to the solid mass of the positive electrode slurry, X1, is 92%, 92.5%, 93%, 93.5%, 94%, 94.5%, 95%, 95.5%, 96%, 96.50%, 97%, or a range consisting of any two of the above values. In some embodiments, the percentage of active material mass to the solid mass of the positive electrode slurry, X1, satisfies the following conditions: 95% ≤ X1 ≤ 97%.

[0028] In some embodiments, the percentage of the mass of the conductive agent in the mass of the positive electrode slurry solids X2 satisfies: 0.25% ≤ X2 ≤ 3%. If the mass of the conductive agent in the mass of the positive electrode slurry solids is too high, the proportion of active material will be reduced, thereby affecting the energy density of the battery cell and not conducive to the improvement of the dispersion and stability of the slurry; if the mass of the conductive agent in the mass of the positive electrode slurry solids is too low, the diaphragm resistance of the electrode sheet will be too high, thereby reducing the electrical performance of the battery cell; controlling the mass of the conductive agent in the mass of the positive electrode slurry solids within this range is beneficial to the performance of the battery cell and the improvement of the energy density of the battery cell and the dispersion stability of the slurry. In some embodiments, the mass percentage of the conductive agent in the positive electrode slurry X2 is 0.25%, 0.4%, 0.6%, 0.8%, 1.0%, 1.2%, 1.4%, 1.6%, 1.8%, 2.0%, 2.2%, 2.4%, 2.6%, 2.8%, 3.0% or a range consisting of any two of the above values. In some embodiments, the percentage X2 of the mass of the conductive agent to the solid mass of the positive electrode slurry satisfies: 0.8%≤X2≤2%.

[0029] In some embodiments, the specific surface area S1 of the active material satisfies: 10≤S1≤15. If the specific surface area of ​​the active material is too large, the agglomeration of the active material will be more serious, resulting in poor dispersion and stability of the slurry, affecting the electrochemical performance and cycle performance. If the specific surface area of ​​the active material is too small, it will be unfavorable to increase the compaction density of the electrode, thereby affecting the improvement of the volume energy density of the battery cell. Therefore, it is necessary to limit the specific surface area of ​​the active material to the above range. In some embodiments, the specific surface area S1 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 above values. In some embodiments, the specific surface area S1 of the active material satisfies: 11≤S1≤14.

[0030] In some embodiments, the specific surface area S2 of the conductive agent satisfies: 120≤S2≤200. If the specific surface area of ​​the conductive agent is too large, the agglomeration of the conductive agent will be more serious, resulting in poor dispersion and stability of the slurry, affecting the electrochemical performance and cycle performance. If the specific surface area of ​​the conductive agent is too small, it will not be conducive to the improvement of the electrode compaction density, thereby affecting the improvement of the volume energy density of the battery cell. Therefore, it is necessary to limit the specific surface area of ​​the conductive agent to the above range. In some embodiments, the specific surface area S2 of the conductive agent is 120, 125, 130, 135, 140, 145, 150, 155, 160, 165, 170, 175, 180, 185, 190, 195, 200 or a range consisting of any two of the above values. In some embodiments, the specific surface area S2 of the conductive agent satisfies: 150≤S2≤200.

[0031] In some embodiments, the particle size distribution coefficient D1 of the active material satisfies: 2.5≤D1≤18. The larger the particle size distribution coefficient of the active material, the more difficult it is to disperse evenly, affecting the electrochemical performance and cycle performance; the smaller the particle size distribution coefficient of the active material, the less conducive it is to improving the compaction density of the electrode, which in turn affects the improvement of the volume energy density of the battery cell; controlling the particle size distribution coefficient of the active material within this range is beneficial to the performance of the battery cell's electrical performance and the improvement of its volume energy density. In some embodiments, the particle size distribution coefficient D1 of the active material is 2.5, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18 or a range consisting of any two of the above values. In some embodiments, the particle size distribution coefficient D1 of the active material satisfies: 5≤D1≤15.

[0032] In some embodiments, the particle size distribution coefficient D2 of the conductive agent satisfies: 1.2≤D2≤2.0. The larger the particle size distribution coefficient of the conductive agent, the more difficult it is to disperse evenly, affecting the electrochemical performance and cycle performance; the smaller the particle size distribution coefficient of the conductive agent, the less conducive it is to improving the compaction density of the electrode; controlling the particle size distribution coefficient of the conductive agent within this range is beneficial to the performance of the battery cell's electrical performance and the improvement of its volume energy density. In some embodiments, the particle size distribution coefficient D2 of the conductive agent is 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0 or a range consisting of any two of the above values. In some embodiments, the particle size distribution coefficient D2 of the conductive agent satisfies: 1.5≤D2≤2.0.

[0033] In some embodiments, the D501 of the active material satisfies: 0.8≤D501≤1.8. In some embodiments, the D501 of the active material is 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, or a range consisting of any two of the foregoing values.

[0034] In some embodiments, D901 of the active material satisfies: 10≤D901≤14.5. In some embodiments, D901 of the active material is 10.0, 10.5, 11.0, 11.5, 12.0, 12.5, 13.0, 13.5, 14.0, 14.5, or a range consisting of any two of the foregoing values.

[0035] In some embodiments, D101 of the active material satisfies: 0.3≤D101≤0.6. In some embodiments, D101 of the active material is 0.3, 0.4, 0.5, 0.6, or a range consisting of any two of the above values.

[0036] In some embodiments, the active material includes a lithium iron phosphate material; the lithium iron phosphate material includes Li x Fe y A (1-y) At least one of the PO4 materials, wherein A includes at least one of the elements Mn, Co, Ti, Mg, Ca, Cr, Cu, Ni, V, Mo, Zn, Al, B and Nb, 0.05≤x≤1.2, 0<y≤1.

[0037] In some embodiments, the dispersant includes at least one of polyesters, polyacrylates, amine alcohols, polyolefins, and polyethers.

[0038] In some embodiments, the polyesters include polyphosphates.

[0039] In some embodiments, the phosphate esters include at least one compound of Formula I,

[0040] 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.

[0041] 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).

[0042] 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.

[0043] In some embodiments, the polyacrylate compound includes at least one compound of Formula II,

[0044] 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;

[0045] 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;

[0046] n is a natural number greater than 1.

[0047] Illustratively, the polyacrylates include at least one of carboxyl-terminated polyacrylate, hydroxyl-terminated polyacrylate, polyacrylic acid, and polyurethane-modified acrylic acid.

[0048] Illustratively, the polyolefin includes terminal polyisobutylene.

[0049] 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.

[0050] For example, the polyether compounds include but are not limited to perfluoropolyether compounds and polyetherimide compounds.

[0051] 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 selected from ester, carboxyl, phosphate, amino and hydroxyl groups, and the anchoring group has a good affinity for carbon-coated lithium iron phosphate nanoparticles and 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, thereby inhibiting the agglomeration between the carbon-coated lithium iron phosphate nanoparticles and the conductive agent nanoparticles through the steric hindrance effect, effectively solving the dispersion problem of lithium iron phosphate and the conductive agent in the slurry, and maintaining the stability of the slurry viscosity.

[0052] In some embodiments, the mass percentage of the dispersant, expressed as F, based on the solid mass of the positive electrode slurry satisfies the following: 0.2% ≤ F ≤ 1.0%. In some embodiments, the mass percentage of the dispersant, F, is 0.2%, 0.4%, 0.6%, 0.8%, 1.0%, or a range consisting of any two of the foregoing values.

[0053] In some embodiments, the conductive agent includes at least one of carbon black, carbon nanotubes, carbon nanofibers, Ketjen black, acetylene black, and graphene.

[0054] In some embodiments, the conductive agent includes carbon black and carbon nanotubes, and the mass ratio of carbon black to carbon nanotubes is 1: 1 to 5: 1. The ratio of carbon black to carbon nanotubes can be adjusted, and the embodiments of the present application do not impose any specific limitation thereto.

[0055] In some embodiments, the solid content of the positive electrode slurry is 50% to 68%. In some embodiments, the solid content of the positive electrode slurry is 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, or a range consisting of any two of the above values. In some embodiments, the solid content of the positive electrode slurry is 52% to 64%.

[0056] 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 4000 mPa·s to 10000 mPa·s.

[0057] 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).

[0058] In some embodiments, the weight percentage of the binder, expressed as E, based on the solid mass of the positive electrode slurry satisfies the following: 1.5% ≤ E ≤ 5%. In some embodiments, the weight percentage of the binder, E, is 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5.0%, or a range consisting of any two of the above values.

[0059] One or more embodiments of the present application further provide a method for preparing the above-mentioned positive electrode slurry, comprising the following steps:

[0060] S1, dispersing and stirring a dispersant, a conductive agent, and a solvent to obtain a first mixed slurry;

[0061] S2, stirring the active material, binder, solvent and the first mixed slurry at high viscosity to obtain a second mixed slurry;

[0062] S3. Dispersing and stirring the solvent and the second mixed slurry at a high speed to obtain a positive electrode slurry.

[0063] In some embodiments, the stirring revolution speed of S1 is 5 rpm to 30 rpm. In some embodiments, the stirring revolution speed is 5 rpm, 10 rpm, 15 rpm, 20 rpm, 25 rpm, 30 rpm, or a range consisting of any two of the above values.

[0064] In some embodiments, the dispersion speed of S1 is 300 rpm to 3000 rpm. In some embodiments, the dispersion speed is 300 rpm, 500 rpm, 1000 rpm, 1500 rpm, 2000 rpm, 2500 rpm, 3000 rpm, or a range consisting of any two of the above values.

[0065] In some embodiments, the stirring time of S1 is 30 min to 60 min. In some embodiments, the stirring time is 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, 60 min, or a range consisting of any two of the above values.

[0066] In some embodiments, the stirring temperature of S1 is 15° C. to 45° C. In some embodiments, the stirring and mixing temperature is 15° C., 20° C., 25° C., 30° C., 35° C., 40° C., 45° C., or a range consisting of any two of the above values.

[0067] In S1, the dispersant and the conductive agent are first mixed with a portion of the solvent to prepare a first mixed slurry, so that the conductive agent that is difficult to disperse can be pre-dispersed into a uniform and stable slurry.

[0068] In some embodiments, the stirring revolution speed of S2 is 10 rpm to 25 rpm. In some embodiments, the stirring revolution speed is 10 rpm, 15 rpm, 20 rpm, 25 rpm, or a range consisting of any two of the above values.

[0069] In some embodiments, the dispersion speed of S2 is 0 to 100 rpm. In some embodiments, the dispersion speed is 0, 20 rpm, 40 rpm, 60 rpm, 80 rpm, 100 rpm, or a range consisting of any two of the above values.

[0070] In some embodiments, the stirring time of S2 is 30 min to 75 min. In some embodiments, the stirring time is 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, 60 min, 65 min, 70 min, 75 min or a range consisting of any two of the above values.

[0071] In some embodiments, the stirring temperature of S2 is 25° C. to 70° C. In some embodiments, the stirring and mixing temperature is 25° C., 30° C., 35° C., 40° C., 45° C., 50° C., 55° C., 60° C., 65° C., 70° C., or a range consisting of any two of the above values.

[0072] The high-viscosity kneading and stirring in S2 is beneficial to the shear dispersion of the nano-agglomerated particles and also to the coating and deagglomeration of the agglomerated particles by the dispersant.

[0073] In some embodiments, the stirring revolution speed of S3 is 10 rpm to 30 rpm. In some embodiments, the stirring revolution speed is 10 rpm, 15 rpm, 20 rpm, 25 rpm, 30 rpm, or a range consisting of any two of the above values.

[0074] In some embodiments, the dispersion speed of S3 is 500 rpm to 3000 rpm. In some embodiments, the dispersion speed is 500 rpm, 1000 rpm, 1500 rpm, 2000 rpm, 2500 rpm, 3000 rpm, or a range consisting of any two of the above values.

[0075] In some embodiments, the stirring time of S3 is 60 min to 180 min. In some embodiments, the stirring time is 60 min, 70 min, 80 min, 90 min, 100 min, 110 min, 120 min, 130 min, 140 min, 150 min, 160 min, 170 min, 180 min or a range consisting of any two of the above values.

[0076] In some embodiments, the stirring temperature of S3 is 15° C. to 45° C. In some embodiments, the stirring and mixing temperature is 15° C., 20° C., 25° C., 30° C., 35° C., 40° C., 45° C., or a range consisting of any two of the above values.

[0077] 2. Positive electrode

[0078] One or more embodiments of the present application also provide a positive electrode plate, which includes a positive electrode current collector and a positive electrode active material layer arranged on at least one side of the positive electrode current collector, and the positive electrode active material layer is solidified by the above-mentioned positive electrode slurry or the positive electrode slurry prepared by the above-mentioned preparation method.

[0079] 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.

[0080] 3. Electrochemical Device

[0081] One or more embodiments of the present application further provide an electrochemical device comprising the aforementioned positive electrode sheet.

[0082] The electrochemical device of the present application further includes a negative electrode sheet, an electrolyte and a separator.

[0083] 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.

[0084] 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.

[0085] The electrochemical device of the present application further includes an electrolyte, which includes a lithium salt and a non-aqueous solvent.

[0086] 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. Exemplarily, the lithium salt may be LiPF6.

[0087] The non-aqueous solvent includes, but is not limited to, one or more of a carbonate compound, a carboxylate compound, or an ether compound.

[0088] 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).

[0089] 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.

[0090] 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.

[0091] In some embodiments, a separator is provided between the positive and negative electrode plates 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.

[0092] 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.

[0093] 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.

[0094] 4. Electronic Devices

[0095] One or more embodiments of the present application further provide an electronic device, which includes the aforementioned electrochemical device.

[0096] 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.

[0097] Hereinafter, the electrochemical device of the present application will be further described in conjunction with specific embodiments and comparative examples.

[0098] Examples and Comparative Examples

[0099] Hereinafter, the present application will be described in more detail with reference to Examples and Comparative Examples. However, the present application is not limited to these Examples unless departing from the gist of the present application.

[0100] The active materials, dispersants, conductive agents, binders and solvents used in the following examples are all commercially available.

[0101] Example 1

[0102] Preparation of positive electrode slurry:

[0103] S1. 15 kg of solvent N-methylpyrrolidone (NMP), 0.406 kg of dispersant (terminated polyisobutylene), 0.649 kg of super conductive carbon, and 8.114 kg of multi-walled carbon nanotubes (solid content 4%) were sequentially added into a 100 L double planetary mixer. The mixer was mixed and dispersed at a revolution of 20 rpm, a dispersion speed of 1800 rpm, a stirring time of 60 min, and a temperature of 30° C. to obtain a first mixed slurry.

[0104] S2, 78.142 kg of active material LiFePO4, 1.623 kg of binder polyvinylidene fluoride (PVDF) and 4.258 kg of solvent N-methylpyrrolidone (NMP) were added to the double planetary mixer containing the first mixture in sequence, and the solid content of the mixture was controlled to be 75%; the mixer was stirred at high viscosity according to the parameters of revolution 10 rpm, dispersion 50 rpm, stirring time 45 min, and temperature 45° C. to obtain a second mixed slurry;

[0105] S3. Add 36.578 kg of solvent N-methylpyrrolidone (NMP) to the second mixed slurry, and perform high-speed dispersion and stirring with the stirrer according to the parameters of revolution 20 rpm, dispersion 2000 rpm, stirring time 170 min, and temperature 30°C to obtain a positive electrode slurry with a solid content of 56% and a viscosity value of 8000 mPa·s.

[0106] In the positive electrode active material, the volume percentage θ of particles with a particle size of less than 300 nm is 8%; the specific surface area S1 of the active material is 12.5 m 2 / g; the particle size distribution coefficient D1 of the active material is 7.5. In the positive electrode slurry, the solid mass of the positive electrode slurry is 81.144kg; the mass percentage of the active material is X1 is 96.3%; the mass percentage of the conductive agent is X2 is 1.2%; the mass percentage of the dispersant is 0.5%; the mass percentage of the binder is 2.0%; the specific surface area S2 of the conductive agent is 180m 2 / g; the particle size distribution coefficient D2 of the conductive agent is 1.6.

[0107] Preparation of positive electrode sheet: The positive electrode slurry prepared by the above method is evenly coated on both surfaces of a positive electrode current collector aluminum foil with a thickness of 12 μm, dried and rolled to obtain a positive electrode sheet.

[0108] Preparation of negative electrode sheets: Artificial 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.

[0109] 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 volume of the solvent, and 5% vinylene carbonate (VC) was added as an additive based on the mass of the solvent to obtain an electrolyte.

[0110] Diaphragm: 11μm thick PE porous polymer membrane is used.

[0111] 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.

[0112] Examples 2 to 11

[0113] Examples 2 to 11 were obtained based on Example 1 by adjusting the mass percentages X1 and X2 of the active material and the conductive agent in the positive electrode slurry, the specific surface areas S1 and S2, the particle size distribution coefficients D1 and D2, the volume percentage θ of particles with a diameter less than 300 nm in the active material, and the type and percentage of the dispersant. Specific data are shown in Table 1. The other preparation methods of Examples 2 to 11 are the same as those of Example 1.

[0114] Comparative Example 1

[0115] Preparation of positive electrode slurry:

[0116] 78.953 kg of active material LiFePO4, 1.996 kg of binder polyvinylidene fluoride (PVDF), 62.977 kg of solvent N-methylpyrrolidone (NMP), 0.162 kg of super conductive carbon and 0.8114 kg of multi-walled carbon nanotubes (solid content 4%) were added in sequence to a 100 L double planetary mixer. The mixer was mixed and dispersed according to the parameters of revolution 20 rpm, dispersion 2000 rpm, stirring time 180 min and temperature 30 ° C to obtain a positive electrode slurry with a solid content of 56% and a viscosity value of 8500 mPa·s.

[0117] In the positive electrode active material, the volume percentage θ of particles with a particle size less than 300 nm is 0.2%; the specific surface area S1 of the active material is 9.5 m 2 / g; the particle size distribution coefficient D1 of the active material is 2.4. In the positive electrode slurry, the solid mass of the positive electrode slurry is 81.14kg; the mass percentage of the active material is X1 is 97.3%; the mass percentage of the conductive agent is X2 is 0.24%; the mass percentage of the binder is 2.46%; the specific surface area S2 of the conductive agent is 115m 2 / g; the particle size distribution coefficient D2 of the conductive agent is 2.5.

[0118] Preparation of positive electrode sheet: The positive electrode slurry prepared by the above method is evenly coated on both surfaces of a positive electrode current collector aluminum foil with a thickness of 12 μm, dried and rolled to obtain a positive electrode sheet.

[0119] Preparation of negative electrode sheets: Artificial 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.

[0120] 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 volume of the solvent, and 5% vinylene carbonate (VC) was added as an additive based on the mass of the solvent to obtain an electrolyte.

[0121] Diaphragm: 11μm thick PE porous polymer membrane is used.

[0122] 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.

[0123] Comparative Example 2

[0124] Comparative Example 2 was prepared based on Comparative Example 1 by adjusting the mass percentages X1 and X2 of the active material and the conductive agent in the positive electrode slurry, the specific surface areas S1 and S2, the particle size distribution coefficients D1 and D2, and the volume percentage θ of particles with a particle size less than 300 nm in the active material. Specific data are shown in Table 1. The remaining preparation methods of Comparative Example 2 were the same as those of Comparative Example 1.

[0125] Comparative Examples 3-4

[0126] Comparative Examples 3-4 were prepared based on Example 1 by adjusting the mass percentages X1 and X2 of the active material and the conductive agent in the positive electrode slurry, the specific surface areas S1 and S2, the particle size distribution coefficients D1 and D2, the volume percentage θ of particles with a diameter less than 300 nm in the active material, and the type and percentage of the dispersant. Specific data are shown in Table 1. The other preparation methods of Comparative Examples 3-4 are the same as those of Example 1.

[0127] Test Method

[0128] 1. Particle size test:

[0129] 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.

[0130] 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.

[0131] 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.

[0132] 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.

[0133] 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.

[0134] The particle size data are used to read D10, D50, D90 and the volume percentage of particles with a particle size less than 300 nm.

[0135] 2. Particle specific surface area test:

[0136] 1) Place the sample to be tested (30-500 mg, depending on the specific surface area of ​​the sample) into the sample tube.

[0137] 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.

[0138] 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.

[0139] 4) After the test is completed, remove the sample from the sample tube, wash the sample tube, and dry it for later use.

[0140] 3. Slurry solid content test:

[0141] 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.

[0142] 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℃

[0143] 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.

[0144] 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.

[0145] 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.

[0146] 4. Slurry viscosity test:

[0147] 1) Using a rotational viscometer, screw the rotor into the connecting screw (turn left to install, turn right to remove).

[0148] 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.

[0149] 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.

[0150] 5. Impedance test:

[0151] 1) Fully charge, adjust the temperature to 25℃, a. rest for 10 minutes; b. 0.5℃ DC 2.5V; c. rest for 5 minutes;

[0152] 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.

[0153] 6. Cycle performance test:

[0154] 1) Adjust the temperature to 25°C and let it rest for 10 minutes;

[0155] 2) 0.5C DC 2.5V;

[0156] 3) rest 5 minutes;

[0157] 4) 1C CC to 3.65V, 3.65V CV throw 0.05C;

[0158] 5) rest 5 minutes;

[0159] 6) 1C DC to 2.5V (the capacity in this step is recorded as C);

[0160] 7) Repeat steps 4-7 for 3 cycles (take the average of the 3 steps 6 as the initial capacity C0);

[0161] 8) rest 5 minutes;

[0162] 9)1C CC to 3.65V, 3.65V CV to 0.05C;

[0163] 10) rest 5 minutes;

[0164] 11) 1C DC to 2.5V;

[0165] 12) Repeat steps 8-11 for 200 cycles (take the capacity C of step 11 at the 200th cycle 200 );

[0166] 13) Calculate the capacity retention rate, C 200 / C0.

[0167] The test results are shown in Table 1 below.

[0168] Table 1

[0169] By comparing the data of Examples 1-11 with Comparative Examples 1-4, it can be seen that by adjusting the distribution relationship between the mass percentage of active material and conductive agent in the positive electrode slurry, specific surface area, particle size distribution coefficient and the volume percentage of particles with a diameter of less than 300 nm in the active material, the following conditions are met: The viscosity and solid content of the slurry are relatively stable, thereby ensuring that the cycle capacity retention rate of the electrochemical device reaches more than 96% and the impedance is as low as 0.3 ohm or less, which is significantly improved compared to Comparative Examples 1-4. This is because, under these limited conditions, a good dispersion system can be formed between the components in the slurry, while increasing the solid content of the positive electrode slurry while effectively maintaining the dispersion and stability of the positive electrode slurry, thereby improving the electrochemical performance and cycle performance of the electrochemical device and reducing the impedance.

[0170] By comparing the data of Examples 1-9 with those of Examples 10-11, it can be seen that by adjusting the distribution relationship between the mass percentage of active material and conductive agent in the positive electrode slurry, specific surface area, particle size distribution coefficient and the volume percentage of particles with a diameter of less than 300 nm in the active material, it can be further satisfied. Under this limited condition, the components in the slurry are dispersed more evenly, the viscosity and stability of the slurry are further improved, and the cycle capacity retention rate of the electrochemical device reaches 98% or above and the impedance is lower than 0.28ohm.

[0171] 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 includes an active material and a conductive agent, and the positive electrode slurry satisfies: Wherein, θ represents the volume percentage of particles in the active material having a particle size less than 300 nm; X1 represents the percentage of the mass of the active material to the solid mass of the positive electrode slurry; X2 represents the percentage of the conductive agent mass to the solid mass of the positive electrode slurry; S1 represents the specific surface area of ​​the active material, in m 2 / g; S2 represents the specific surface area of ​​the conductive agent, in m 2 / g; D1 represents the particle size distribution coefficient of the active material; D1=(D901-D101) / D501, D101 represents the particle size of the active material with a volume accumulation of 10%, D501 represents the particle size of the active material with a volume accumulation of 50%, and D901 represents the particle size of the active material with a volume accumulation of 90%, and the units of D101, D501 and D901 are all μm; D2 represents the particle size distribution coefficient of the conductive agent; D2 = (D902-D102) / D502, D102 represents the particle size of 10% cumulative volume in the volume-based particle size distribution of the conductive agent, D502 represents the particle size of 50% cumulative volume in the volume-based particle size distribution of the conductive agent, D902 represents the particle size of 90% cumulative volume in the volume-based particle size distribution of the conductive agent, and the units of D102, D502 and D902 are all μm.

2. The positive electrode slurry according to claim 1, characterized in that The positive electrode slurry also meets the following requirements:

3. The positive electrode slurry according to claim 1 or 2, characterized in that: The positive electrode slurry also satisfies at least one of the following conditions: (1) 0%<θ≤10%; (2)92％≤X1≤97％； (3)0.25％≤X2≤3％； (4)10≤S1≤15； (5)120≤S2≤200； (6)2.5≤D1≤18； (7)1.2≤D2≤2.0。 4. The positive electrode slurry according to claim 1 or 2, characterized in that: The positive electrode slurry also satisfies at least one of the following conditions: (1) 5% ≤ θ ≤ 10%; (2)95％≤X1≤97％； (3)0.8％≤X2≤2％； (4)11≤S1≤14； (5)150≤S2≤200； (6)5≤D1≤15； (7)1.5≤D2≤2.0。 5. The positive electrode slurry according to any one of claims 1 to 4, characterized in that: The positive electrode slurry also satisfies at least one of the following conditions: (1) The active material includes a lithium iron phosphate material; the lithium iron phosphate material includes Li x Fe y A (1-y) At least one of PO4 materials, wherein A includes at least one of Mn, Co, Ti, Mg, Ca, Cr, Cu, Ni, V, Mo, Zn, Al, B and Nb elements, 0.05≤x≤1.2, 0<y≤1; (2)0.8≤D501≤1.8； (3)10≤D901≤14.5； (4)0.3≤D101≤0.6。 6. The positive electrode slurry according to any one of claims 1 to 5, characterized in that: The positive electrode slurry also satisfies at least one of the following conditions: (1) The positive electrode material further includes a dispersant, and the dispersant includes at least one of polyesters, polyacrylates, amine alcohols, polyolefins and polyethers; (2) The positive electrode material further includes a dispersant. Based on the solid mass of the positive electrode slurry, the mass percentage of the dispersant is expressed as F, and satisfies: 0.2%≤F≤1.0%; (3) The conductive agent includes at least one of carbon black, carbon nanotubes, carbon nanofibers, Ketjen black, acetylene black and graphene; (4) The conductive agent comprises carbon black and carbon nanotubes, and the mass ratio of the carbon black to the carbon nanotubes is 1:1 to 5:1; (5) The positive electrode slurry further includes a binder. The mass percentage of the binder, expressed as E, based on the solid mass of the positive electrode slurry, satisfies: 1.5%≤E≤5%.

7. A method for preparing a positive electrode slurry according to any one of claims 1 to 6, characterized in that: The following steps are involved: S1, mixing the dispersant, the conductive agent and the solvent to obtain a first mixed slurry; S2, mixing the active material, the binder, the solvent and the first mixed slurry to obtain a second mixed slurry; S3. Mixing the solvent with the second mixed slurry to obtain the positive electrode slurry.

8. 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 formed by solidifying the positive electrode slurry according to any one of claims 1 to 6 or the positive electrode slurry prepared by the preparation method according to claim 7.

9. An electrochemical device, characterized in that: It comprises a negative electrode plate, a separator, an electrolyte and a positive electrode plate according to claim 8.

10. An electronic device, characterized in that: Comprising the electrochemical device according to claim 9.

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