Positive electrode conductive paste, preparation method thereof and application of positive electrode conductive paste in positive plate and lithium ion battery

Abstract

The invention belongs to the technical field of lithium ion batteries, and particularly relates to positive conductive paste, a preparation method thereof and application of the positive conductive paste in a positive plate and a lithium ion battery. The preparation method of the positive electrode conductive paste comprises the following steps: performing first mixing treatment on a linear high-molecular compound, a first organic solvent and a dispersing agent to obtain a mixture A, and performing second mixing treatment on hard carbon particles, graphene and a coupling agent in the presence of a solvent to obtain a graphene-hard carbon compound B, and carrying out third mixing treatment on the mixture A, the graphene and hard carbon compound B and a stabilizer to obtain the positive electrode conductive paste containing the composite conductive agent. When the positive electrode conductive paste provided by the invention is used for preparing a positive plate and a lithium ion battery, the resistivity can be reduced, and the liquid retention capacity is improved, so that the first coulombic efficiency and the cycle performance of the battery are improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium ion batteries, and in particular relates to a positive electrode conductive slurry and a preparation method thereof, and applications in positive electrode sheets and lithium ion batteries. Background Art

[0002] Conductive slurry is an indispensable auxiliary material in lithium-ion batteries, and is closely related to the conductivity of the pole piece, the service life and energy density of the lithium battery. Conductive slurry is a viscous solid-liquid two-phase suspension mixture, usually a mixture of organic solvents, conductive agents, dispersants, etc. stirred in a certain proportion. The core component of conductive slurry is conductive agent, and its main types include: one-dimensional or two-dimensional structural carbon materials such as carbon black, conductive graphite, carbon fiber, carbon nanotubes and graphene.

[0003] The conductive agent in the traditional conductive paste is usually uniform in structure, and the structure is granular, fibrous or flaky, but this uniform structure is difficult to greatly improve the conductivity of the lithium battery pole piece. The current research hotspot is to use two or more conductive agents for compounding to form a conductive network in the pole piece. For example, the Chinese patent document with publication number CN109830685A discloses a composite conductive paste, which includes a composite material composed of multi-walled carbon nanotubes and few-layer graphene, which overcomes the problem of difficult dispersion of carbon nanotubes and graphene, and reduces the resistivity of the electrode pole piece prepared by the composite conductive paste. In addition, the commonly used conductive agents are mainly carbon nanotubes and graphene. Although the performance of the two is excellent, the cost is high and it is difficult to meet the actual needs. At the same time, the composite conductive agent materials disclosed in the prior art have limited improvement on the conductivity of the pole piece, and the improvement effect on the performance of the pole piece and the performance of the lithium-ion battery under high-voltage conditions is even more limited. Therefore, it is urgent to develop a new conductive paste to meet the performance requirements of high-performance lithium-ion batteries. Summary of the invention

[0004] The purpose of the present invention is to provide a positive electrode conductive paste and its preparation method and application in positive electrode sheets and lithium-ion batteries in view of the shortcomings of the conductive paste disclosed in the prior art in improving the conductive properties of the electrode sheet and the first coulombic efficiency and cycle performance of the lithium battery to a limited extent.

[0005] In a first aspect, the present invention provides a positive electrode conductive paste. The preparation method of the positive electrode conductive paste comprises the following steps: a linear polymer compound, a first organic solvent and a dispersant are subjected to a first mixing treatment to obtain a mixture A, hard carbon particles, graphene, and a coupling agent are subjected to a second mixing treatment in the presence of a solvent to obtain a graphene@hard carbon composite B in which graphene is coated on the surface of the hard carbon particles, and the mixture A, the graphene@hard carbon composite B and a stabilizer are subjected to a third mixing treatment to obtain a positive electrode conductive paste containing a composite conductive agent.

[0006] In a preferred embodiment, the solid content of the mixture A is 3-9 wt %.

[0007] In a preferred embodiment, in the mixture A, the mass ratio of the linear polymer compound to the dispersant is 1:(0.1-0.3).

[0008] In a preferred embodiment, the mass ratio of the hard carbon particles, graphene and coupling agent is (8-16):1:(0.2-0.5).

[0009] In a preferred embodiment, the mass ratio of the mixture A, the graphene@hard carbon composite B, and the stabilizer is (0.8-3):1:(0.005-0.02).

[0010] In a preferred embodiment, the solid content of the positive electrode conductive slurry is 14-18 wt %.

[0011] In a preferred embodiment, the first mixing treatment is mechanical stirring treatment I.

[0012] In a preferred embodiment, the time of the mechanical stirring treatment I is 2 to 6 hours.

[0013] In a preferred embodiment, the second mixing treatment is a mechanical stirring treatment II.

[0014] In a preferred embodiment, the conditions of the mechanical stirring treatment II include: a temperature of 50 to 70° C. and a time of 3 to 4 hours.

[0015] In a preferred embodiment, the third mixing process is a ball milling process.

[0016] In a preferred embodiment, the ball milling treatment conditions include: a rotation speed of 200 to 300 rpm and a time of 6 to 8 hours.

[0017] In a preferred embodiment, the third mixing treatment further includes a fourth mixing treatment, and the steps of the fourth mixing treatment are as follows: the mixture containing the composite conductive agent obtained by the third mixing treatment is subjected to a fourth mixing treatment with the second organic solvent to obtain a positive electrode conductive slurry containing the composite conductive agent.

[0018] In a preferred embodiment, the solid content of the positive electrode conductive slurry is 14-18 wt %.

[0019] In a preferred embodiment, the fourth mixing treatment is a mechanical stirring treatment III.

[0020] In a preferred embodiment, the time of the mechanical stirring treatment III is 1 to 3 hours.

[0021] In a preferred embodiment, the linear polymer compound is selected from at least one of polyacrylamide compounds, polyolefin compounds and polyester compounds.

[0022] In a preferred embodiment, the linear polymer compound has a diameter of 0.05 to 0.1 μm and a length of 4 to 8 μm.

[0023] In a preferred embodiment, the polyacrylamide compound is selected from at least one of polyacrylamine hydrochloride, polyacrylic acid-acrylamide copolymer, and styrene-acrylamide copolymer.

[0024] In a preferred embodiment, the dispersant is selected from at least one of polyethylene wax, polyvinyl pyrrolidone, hydrogenated petroleum resin, and fatty alcohol polyoxyethylene ether.

[0025] In a preferred embodiment, the first organic solvent is selected from at least one of N-methylpyrrolidone, N-cyclohexanepyrrolidone, N,N-dimethylformamide and dimethylacetamide.

[0026] In a preferred embodiment, the hard carbon particles are spherical and / or spheroidal.

[0027] In a preferred embodiment, the Dv50 particle size of the hard carbon particles is 0.3-0.5 μm.

[0028] In a preferred embodiment, the specific surface area of ​​the hard carbon particles is 600 to 800 m 2 / g.

[0029] In a preferred embodiment, the coupling agent is selected from titanate and / or silane coupling agent.

[0030] In a preferred embodiment, the stabilizer is selected from at least one of diethyl sulfoxide, sodium salicylate, and aqueous sodium alginate.

[0031] In a second aspect, the present invention provides a positive electrode conductive slurry prepared by the above method.

[0032] In a third aspect, the present invention provides a positive electrode sheet, wherein the raw materials for preparing the positive electrode sheet include the positive electrode conductive slurry mentioned above.

[0033] In a fourth aspect, the present invention further provides a lithium-ion battery comprising the above-mentioned positive electrode sheet.

[0034] Beneficial effect: In the preparation method provided by the present invention, a graphene@hard carbon composite with hard carbon particles as a core and graphene as a coating layer is synthesized in the presence of a coupling agent, and then the graphene@hard carbon composite is mixed with a linear polymer compound to obtain a composite conductive agent. The coupling agent added during the preparation process can strengthen the interaction between the hard carbon particles, the graphene layer and the linear polymer compound to form a whole with a three-dimensional structure, and the added dispersant and stabilizer can improve the stability of the composite conductive agent in the slurry. On this basis, it is compounded with an organic solvent to obtain a positive electrode conductive slurry. The positive electrode conductive slurry is used to prepare a positive electrode sheet and a lithium-ion battery, which can reduce the resistivity and increase the liquid retention, thereby improving the first coulomb efficiency (first efficiency) and cycle performance of the battery. The reason may be that: the composite conductive agent has a stable structure and is not easy to deform and break during the rolling process of the positive electrode sheet, which is beneficial to increase the battery's liquid retention, reduce resistivity, and promote the transmission of ions and electrons during battery charging and discharging, thereby improving the battery's charging and discharging performance. At the same time, the positive electrode slurry has good fluidity and dispersibility, which enables the composite conductive agent to be evenly dispersed in the positive electrode sheet. The characteristics of its three-dimensional structure can effectively connect the active material particles and enhance the conductivity of the positive electrode material, thereby improving the battery's initial efficiency and cycle performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a schematic structural diagram of the composite conductive agent provided by the present invention. DETAILED DESCRIPTION

[0036] The preparation method of the positive electrode conductive paste provided by the present invention comprises the following steps: a linear polymer compound, a first organic solvent and a dispersant are subjected to a first mixing treatment to obtain a mixture A; hard carbon particles, graphene and a coupling agent are subjected to a second mixing treatment in the presence of a solvent to obtain a graphene@hard carbon composite B in which graphene is coated on the surface of the hard carbon particles; and the mixture A, the graphene@hard carbon composite B and a stabilizer are subjected to a third mixing treatment to obtain a positive electrode conductive paste containing a composite conductive agent.

[0037] In the present invention, the solid content of the mixture A is preferably 3-9wt%, such as 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt% or any value therebetween.

[0038] In the present invention, in the mixture A, the mass ratio of the linear polymer compound to the dispersant is preferably 1:(0.1-0.3), such as 1:0.1, 1:0.15, 1:0.2, 1:0.25, 1:0.3 or any value therebetween. This is more conducive to the stable dispersion of the linear polymer compound in the mixture A.

[0039] In the present invention, the mass ratio of the hard carbon particles, graphene, and coupling agent is preferably (8-16):1:(0.2-0.5). Taking the mass of the graphene as 1 part by weight, the amount of the hard carbon particles is preferably 8-16 parts by weight, such as 8, 9, 10, 12, 14, 15, 16 parts by weight or any value therebetween; the amount of the coupling agent is preferably 0.2-0.5 parts by weight, such as 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5 parts by weight or any value therebetween.

[0040] In the present invention, the mass ratio of the mixture A, the graphene @ hard carbon composite B, and the stabilizer is preferably (0.8-3):1:(0.005-0.02). Taking the mass of the graphene @ hard carbon composite B as 1 part by weight, the amount of the mixture A is preferably 0.8-3 parts by weight, such as 0.8, 1, 1.5, 2, 2.5, 3 parts by weight or any value therebetween; the amount of the stabilizer is preferably 0.005-0.2 parts by weight, such as 0.005, 0.008, 0.01, 0.012, 0.015, 0.018, 0.02 parts by weight or any value therebetween. At this time, it is more conducive to forming a three-dimensional composite conductive agent with a stable structure.

[0041] In the present invention, the first mixing treatment can be any one of the existing mixing methods, such as ultrasonic mixing, mechanical mixing, oscillation mixing, etc., preferably mechanical stirring treatment I. The time of the mechanical stirring treatment I is based on the full mixing of the linear polymer compound and the first organic solvent, preferably 2 to 6 hours, such as 2 hours, 3 hours, 4 hours, 5 hours, 6 hours or any value therebetween. The mechanical stirring treatment I can be carried out at room temperature, and the temperature can also be adjusted according to the actual experimental situation.

[0042] In the present invention, the second mixing treatment can be any one of the existing mixing methods, such as ultrasonic mixing, mechanical mixing, oscillation mixing, etc., preferably mechanical stirring treatment II. The conditions of the mechanical stirring treatment II preferably include: a temperature of 50 to 70°C, such as 50°C, 55°C, 60°C, 65°C, 70°C or any value therebetween; a time of 3 to 4h, such as 3h, 3.2h, 3.5h, 3.8h, 4h or any value therebetween.

[0043] In the present invention, the third mixing treatment can be any one of the existing mixing methods, such as ultrasonic mixing, mechanical mixing, oscillation mixing, etc., preferably ball milling. The conditions of the ball milling treatment may include: the rotation speed is preferably 200-300 rpm, such as 200 rpm, 220 rpm, 250 rpm, 280 rpm, 300 rpm or any value therebetween; the time is preferably 6-8 h, such as 6 h, 6.5 h, 7 h, 7.5 h, 8 h or any value therebetween.

[0044] In the present invention, the third mixing treatment preferably includes a fourth mixing treatment, and the solid content of the positive electrode conductive paste can be further adjusted by this step. The fourth mixing treatment is as follows: the mixture containing the composite conductive agent obtained by the third mixing treatment is subjected to a fourth mixing treatment with the second organic solvent to obtain a positive electrode conductive paste containing the composite conductive agent.

[0045] In the present invention, the fourth mixing treatment can be any one of the existing mixing methods, such as ultrasonic mixing, mechanical mixing, oscillation mixing, etc., preferably mechanical stirring treatment III. The time of the mechanical stirring treatment III is preferably 1 to 3 hours, such as 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours or any value therebetween. The mechanical stirring treatment III can be carried out at room temperature, and the temperature can also be adjusted according to the actual experimental situation.

[0046] In the present invention, the solid content of the positive electrode conductive paste is preferably 14-18wt%, such as 14wt%, 15wt%, 16wt%, 17wt%, 18wt% or any value therebetween.

[0047] In the present invention, the linear polymer compound is preferably selected from at least one of polyacrylamide compounds, polyolefin compounds, and polyester compounds, and is more preferably a polyacrylamide compound. In this case, the nitrogen-containing groups on the polyacrylamide compound can be combined with the groups on the graphene, which is more conducive to improving the three-dimensional structural stability of the composite conductive agent, improving the liquid retention and the conductivity between the positive electrode materials. Specific examples of the polyacrylamide compound include, but are not limited to, at least one of polyacrylamine hydrochloride, polyacrylic acid-acrylamide copolymer, and styrene-acrylamide copolymer.

[0048] In the present invention, the linear polymer compound preferably has a linear morphology, and its diameter is preferably 0.05 to 0.1 μm, such as 0.05 μm, 0.06 μm, 0.07 μm, 0.08 μm, 0.09 μm, 0.1 μm or any value therebetween; the length is preferably 4 to 8 μm, such as 4 μm, 5 μm, 6 μm, 7 μm, 8 μm or any value therebetween.

[0049] In the present invention, the weight average molecular weight Mw of the linear polymer compound is preferably 9000-5000000 g / mol, such as 9000 g / mol, 10000 g / mol, 15000 g / mol, 20000 g / mol, 30000 g / mol, 50000 g / mol, 100000 g / mol, 500000 g / mol, 1000000 g / mol, 5000000 g / mol or any value therebetween.

[0050] In the present invention, specific examples of the dispersant include, but are not limited to, at least one of polyethylene wax, polyvinyl pyrrolidone, hydrogenated petroleum resin, and fatty alcohol polyoxyethylene ether.

[0051] In the present invention, the first organic solvent and the second organic solvent can be organic solvents commonly used in the art, and are each independently preferably at least one selected from N-methylpyrrolidone (NMP), N-cyclohexanepyrrolidone (CHP), N,N-dimethylformamide (DMF), and dimethylacetamide (DMAC).

[0052] In the present invention, the hard carbon particles may have a spherical, quasi-spherical or other conventional morphological structures, preferably a spherical and / or quasi-spherical shape. The Dv50 particle size of the hard carbon particles is preferably 0.3 to 0.5 μm, such as 0.3 μm, 0.35 μm, 0.4 μm, 0.45 μm, 0.5 μm or any value therebetween. The hard carbon particles preferably have a porous structure, and their specific surface area is preferably 600 to 800 m 2 / g, such as 600m 2 / g, 650m 2 / g、700m 2 / g, 750m 2 / g、800m 2 / g or any value therebetween, which is more conducive to increasing the liquid retention of the electrode during the charge and discharge process and further improving the cycle performance of the battery. The hard carbon particles can be purchased or prepared according to existing methods or improved methods. The term "Dv50" refers to the particle size corresponding to the cumulative volume distribution reaching 50% in the particle size distribution.

[0053] In the present invention, the coupling agent is preferably selected from titanate coupling agents and / or silane coupling agents. Specific examples of the titanate coupling agent include, but are not limited to, at least one of isopropyl trioleyl titanate, bis(acetylacetonato) diisopropyl titanate, bis(dioctyl pyrophosphate) ethylene titanate, isopropyl tri(dioctyl pyrophosphate) titanate, isopropyl tri(dioctyl phosphate) titanate, isopropyl dioleyl (dioctyl phosphate) titanate, and tetraisopropyl di(dioctyl phosphite) titanate. The silane coupling agent is preferably selected from alkenyl silane and / or aminosilane, and specific examples thereof include but are not limited to: at least one of vinyl triethoxy silane, vinyl trimethoxy silane, N-aminoethyl-3-aminopropyl triethoxy silane, ethylenediamine propyl trimethoxy silane, 3-(methyl)acryloxypropyl trimethoxy silane, 3-(methyl)acryloxypropyl triethoxy silane, 3-(methyl)acryloxypropyl methyl dimethoxy silane, 3-(methyl)acryloxypropyl methyl diethoxy silane, N-aminoethyl-3-aminopropyl trimethoxy silane, 3-aminopropyl trimethoxy silane, and 3-aminopropyl triethoxy silane.

[0054] In the present invention, specific examples of the stabilizer include, but are not limited to, at least one of diethyl sulfoxide, sodium salicylate, and aqueous sodium alginate. This is more conducive to uniform dispersion of the components in the third mixing process to form a composite conductive agent with uniform structure and stability, while giving the positive electrode conductive slurry better fluidity and stability.

[0055] The positive electrode conductive paste prepared by the above method includes a composite conductive agent, a dispersant, a stabilizer and a first organic solvent. The composite conductive agent has a three-dimensional structure, including a hard carbon particle core, a graphene layer coated on the surface of the hard carbon particle core, and a linear polymer compound composited on the surface of the graphene layer through a coupling agent. The specific structure can be as follows Figure 1 shown.

[0056] In addition, the terms "first", "second", "third", "fourth" and "Ⅰ, Ⅱ, Ⅲ" are only for the purpose of convenience of description and should not be understood as special limitations on the type and quantity of the defined technical features.

[0057] The present invention will be described in detail below through specific embodiments.

[0058] Preparation Example 1

[0059] Graphene oxide was prepared by Hummers method. The specific steps were as follows: Zou Zhengguang, Yu Huijiang, Long Fei, et al. Ultrasonic assisted Hummers method for preparing graphene oxide [J]. Journal of Inorganic Chemistry, 2011, 27(9), 1753-1757:5. DOI: CNKI: SUN: WJHX.0.2011-09-016, thereby preparing an aqueous solution of few-layer graphene with a graphene content of 50 wt%.

[0060] Preparation Example 2

[0061] Corn starch and sodium trimetaphosphate crosslinking agent were mechanically mixed in a mass ratio of 1:0.3, and reacted at 80°C for 3 hours to obtain esterified starch; the esterified starch was pre-carbonized at 700°C for 2 hours in a nitrogen atmosphere to obtain a pre-carbonized material; the pre-carbonized material was mixed with potassium hydroxide in a mass ratio of 1:0.35, and pre-carbonized at 1200°C for 2 hours in a nitrogen atmosphere, washed with deionized water until neutral and then dried, and after crushing, screening and demagnetization, hard carbon particles Y1 were obtained, with a Dv50 particle size of 0.3μm and a specific surface area of ​​725m 2 / g.

[0062] Preparation Example 3

[0063] Corn starch and phosphorus oxychloride crosslinking agent were mechanically mixed in a mass ratio of 1:0.35, and reacted at 110°C for 4 hours to obtain esterified starch; the esterified starch was pre-carbonized at 700°C for 2 hours in a nitrogen atmosphere to obtain a pre-carbonized material; the pre-carbonized material was mixed with potassium hydroxide in a mass ratio of 1:0.25, and pre-carbonized at 1200°C for 2 hours in a nitrogen atmosphere, washed with deionized water until neutral and then dried, and after crushing, screening and demagnetization, hard carbon particles Y2 were obtained, with a Dv50 particle size of 0.4μm and a specific surface area of ​​789m 2 / g.

[0064] Preparation Example 4

[0065] Corn starch and sodium tripolyphosphate crosslinking agent were mechanically mixed in a mass ratio of 1:0.2, and reacted at 90°C for 8 hours to obtain esterified starch; the esterified starch was pre-carbonized at 700°C for 2 hours in a nitrogen atmosphere to obtain a pre-carbonized material; the pre-carbonized material was mixed with potassium hydroxide in a mass ratio of 1:0.3, and pre-carbonized at 1200°C for 2 hours in a nitrogen atmosphere, washed with deionized water until neutral and then dried, and after crushing, screening and demagnetization, hard carbon particles Y3 were obtained, with a Dv50 particle size of 0.5μm and a specific surface area of ​​654m 2 / g.

[0066] Preparation Example 5

[0067] Corn starch and sodium hexametaphosphate crosslinking agent were mechanically mixed in a mass ratio of 1:0.15, and reacted at 80°C for 6 hours to obtain esterified starch; the esterified starch was pre-carbonized at 700°C for 2 hours in a nitrogen atmosphere to obtain a pre-carbonized material; the pre-carbonized material was mixed with potassium hydroxide in a mass ratio of 1:0.1, and pre-carbonized at 1200°C for 2 hours in a nitrogen atmosphere, washed with deionized water until neutral and then dried, and after crushing, screening and demagnetization, hard carbon particles Y4 were obtained, with a Dv50 particle size of 0.3μm and a specific surface area of ​​267m 2 / g.

[0068] Example 1

[0069] 600 g of polyacrylamine hydrochloride (purchased from Aladdin, brand P194734, Mw = 15000 g / mol, which has a linear morphology, a diameter of about 0.08 μm, and a length of about 4 μm, as shown by scanning electron microscopy), 180 g of polyethylene wax dispersant and 14.1 kg of N-methylpyrrolidone were mechanically stirred for 4 hours to obtain a mixed slurry A with a solid content of 5.2 wt%; 1.2 kg of the aqueous solution containing few-layer graphene obtained in Preparation Example 1 (the content of graphene is 50 wt%), 5 kg of hard carbon particles Y1 (Dv50 particle size is 0.3 μm, the specific surface area is 725 m 2 / g) and 200g of isopropyl trioleyl titanate, mechanically stirred at 60°C for 3h, then washed by centrifugation to pH=7, and then freeze-dried to obtain graphene@hard carbon composite B; the obtained graphene@hard carbon composite B was added to the mixed slurry A, and then 60g of diethyl sulfoxide stabilizer was added and wet ball milled, the dispersion speed of the wet ball milling was set to 200rpm, and the running time was 8h to obtain a composite conductive agent;

[0070] The composite conductive agent was mixed with 26.69 kg of N-methylpyrrolidone, and after mechanical stirring for 2 hours, a positive electrode conductive slurry with a solid content of 14 wt % was obtained.

[0071] Example 2

[0072] 450g of polyacrylic acid-acrylamide copolymer (purchased from Shanghai Yuanye Biotechnology Co., Ltd., brand T24543, Mw=5000000g / mol, which has a linear morphology, a diameter of about 0.09μm, and a length of about 6μm as shown by scanning electron microscopy), 90g of polyvinyl pyrrolidone dispersant and 7.2kg of N-methylpyrrolidone were mechanically stirred for 4h to obtain a mixed slurry A with a solid content of 7wt%; 1.44kg of the aqueous solution containing few-layer graphene obtained in Preparation Example 1 (the content of graphene is 50wt%), 7kg of hard carbon particles Y2 (Dv50 particle size is 0.4μm, specific surface area is 789m 2 / g) and 150g of vinyl triethoxysilane coupling agent, mechanically stirred at 70°C for 3h, then dispersed by centrifugation, washed to pH=7, and freeze-dried to obtain graphene@hard carbon composite B; added the obtained graphene@hard carbon composite B to the mixed slurry A, and then added 100g of sodium salicylate stabilizer and wet ball milled, the dispersion speed of the wet ball mill was set to 280rpm, and the running time was 7h to obtain a composite conductive agent;

[0073] The composite conductive agent was mixed with 37.33 kg of N-methylpyrrolidone, and after mechanical stirring for 2 hours, a positive electrode conductive slurry with a solid content of 16 wt % was obtained.

[0074] Example 3

[0075] 750g of styrene-acrylonitrile copolymer (purchased from Shanghai Myrel Biochemical Technology Co., Ltd., brand M69223, Mw = 165000g / mol, which has a linear morphology with a diameter of about 0.1μm and a length of about 8μm as shown by scanning electron microscopy), 220g of hydrogenated petroleum resin dispersant and 12.88kg of N-methylpyrrolidone were mechanically stirred for 4h to obtain a mixed slurry A with a solid content of 7wt%; 0.99kg of an aqueous solution containing few-layer graphene (the content of graphene is 50wt%), 6kg of hard carbon particles Y3 (Dv50 particle size is 0.5μm, specific surface area is 654m 2 / g) and 240g of ethylenediaminepropyltriethoxysilane coupling agent, mechanically stirred at 50°C for 4h, then dispersed by centrifugation, washed to pH=7, and freeze-dried to obtain graphene@hard carbon composite B; the obtained graphene@hard carbon composite B was added to the mixed slurry A, and then 100g of aqueous sodium alginate stabilizer was added and wet ball milled, the dispersion speed of the wet ball milling was set to 300rpm, and the running time was 8h to obtain a composite conductive agent;

[0076] The complex conductive agent was mixed with 22.7 kg of N-methylpyrrolidone, and mechanically stirred for 2 hours to obtain a positive electrode conductive slurry with a solid content of 18 wt%.

[0077] Example 4

[0078] The positive electrode conductive paste was prepared according to the method of Example 1, except that the hard carbon particles Y4 used had a Dv50 particle size of 0.3 μm and a specific surface area of ​​267 m 2 / g, and the other conditions are the same as those in Example 1, thereby preparing a positive electrode conductive slurry.

[0079] Example 5

[0080] A positive electrode conductive slurry was prepared according to the method of Example 1, except that the same mass of polycarbonate resin (purchased from Shanghai Mairui Chemical Technology Co., Ltd., brand M60481, Mw = 45000 g / mol) was used instead of polyacrylamine hydrochloride (purchased from Aladdin, brand P194734, Mw = 15000 g / mol), and the other conditions were the same as in Example 1, thereby preparing a positive electrode conductive slurry.

[0081] Comparative Example 1

[0082] A reference positive electrode conductive slurry was prepared according to the method of Example 1, except that the same mass of N-methylpyrrolidone was used instead of the polyethylene wax dispersant, and the other conditions were the same as those of Example 1, thereby preparing a reference positive electrode conductive slurry.

[0083] Comparative Example 2

[0084] A reference positive electrode conductive paste was prepared according to the method of Example 1, except that the same mass of N-methylpyrrolidone was used instead of isopropyl trioleate acyloxy titanate, and the other conditions were the same as those of Example 1, thereby preparing a reference positive electrode conductive paste.

[0085] Comparative Example 3

[0086] A reference positive electrode conductive slurry was prepared according to the method of Example 1, except that the same mass of N-methylpyrrolidone was used instead of the diethyl sulfoxide stabilizer, and the other conditions were the same as those of Example 1, thereby preparing a reference positive electrode conductive slurry.

[0087] Comparative Example 4

[0088] A reference positive electrode conductive slurry was prepared according to the method of Example 1, except that polyacrylamine hydrochloride (purchased from Aladdin, brand P194734, Mw=15000 g / mol) was not used. The other conditions were the same as those in Example 1, thereby preparing a reference positive electrode conductive slurry.

[0089] Comparative Example 5

[0090] A reference positive electrode conductive slurry was prepared according to the method of Example 1, except that an aqueous solution containing 600 g of few-layer graphene was not used. The other conditions were the same as those of Example 1, thereby preparing a reference positive electrode conductive slurry.

[0091] Comparative Example 6

[0092] A reference positive electrode conductive slurry was prepared according to the method of Example 1, except that the same mass of graphene carbon material was used instead of hard carbon particles (Dv50 particle size of 0.3 μm, specific surface area of ​​725 m 2 / g), and the other conditions were the same as those in Example 1, thereby preparing a reference positive electrode conductive slurry.

[0093] Test Case

[0094] The positive electrode conductive slurry obtained in the above embodiments and comparative examples was used to prepare positive electrode sheets according to the following method and assembled into soft-pack batteries. The positive electrode sheet membrane resistance, soft-pack battery electrolyte retention, first coulomb efficiency and cycle performance tests were performed, and the results are shown in Table 1.

[0095] (1) Preparation of positive electrode sheet: lithium iron phosphate, a positive electrode active material of a lithium-ion battery, the positive electrode conductive slurry obtained in the above-mentioned embodiments and comparative examples (calculated by solid content), positive electrode conductive agent carbon black (Super-P), and positive electrode binder (polyvinylidene fluoride, PVDF) were mixed in a mass ratio of 96:2:1:2, and solvent N-methylpyrrolidone (NMP) was added to a planetary vacuum mixer and mixed by a dry process to obtain a positive electrode slurry. The positive electrode slurry was coated on both sides of an aluminum foil, and a positive electrode sheet with a length × width × thickness of 80 mm × 60 mm × 150 μm (±2 μm) was obtained by drying, rolling, cutting, and die-cutting.

[0096] Preparation of negative electrode sheet: The negative electrode active material graphite of lithium-ion battery, conductive agent carbon black (Super-P), negative electrode binder 1 (sodium carboxymethyl cellulose, CMC), and binder 2 (styrene-butadiene rubber, SBR) are mixed in a mass ratio of 94:2:2:2, deionized water is added to a planetary vacuum mixer, and mixed using a dry process to obtain a negative electrode slurry. The negative electrode slurry is evenly coated on both sides of an aluminum foil, and a negative electrode sheet with a length × width × thickness of 85 mm × 63 mm × 110 μm (± 2 μm) is obtained by drying, rolling, cutting, and die-cutting.

[0097] Preparation of electrolyte: In a glove box filled with argon, diethyl carbonate (DEC), propylene carbonate (PC), and dimethyl carbonate (DMC) were mixed in a volume ratio of 1:1:1, lithium salt lithium hexafluorophosphate LiPF6 and vinylene carbonate (VC) were added, and after magnetic stirring, an electrolyte was prepared (LiPF6 concentration was 1 mol / L, VC concentration was 2 wt%).

[0098] Diaphragm selection: Select a diaphragm with good porosity, permeability and thermal stability, use a PP / PE two-layer composite diaphragm, and use alumina as the coating layer.

[0099] Soft-pack battery assembly: The positive electrode sheet, negative electrode sheet and composite separator prepared above are dried, assembled into bare cells through a lamination process, and then the positive and negative electrode tabs are welded and loaded into a battery shell of aluminum-plastic film, and the prepared electrolyte is injected. The finished soft-pack battery is obtained through the steps of sealing, high-temperature standing, formation, and secondary sealing. The capacity of the soft-pack battery is about 10Ah.

[0100] (2) Positive electrode diaphragm resistance test: The diaphragm resistance test of the positive electrode in (1) is performed using a four-probe method. The positive electrode is cut into circular electrodes with a diameter of 15 mm using a sampler. The cut positive electrode diaphragm is placed between the two electrodes of the test instrument to ensure that the diaphragm is in full contact with the electrodes. The test pressure of the positive electrode is set to 20 MPa and the pressure holding time is selected to be 15 s. After the test is completed, the resistivity data of the diaphragm is read from the instrument.

[0101] (3) Soft-pack battery electrolyte retention test: The soft-pack battery assembled in (1) is subjected to an electrolyte retention test according to the following steps: Before injection, the soft-pack battery is weighed using a ten-thousandth precision electronic balance, and the mass of the battery at this time is recorded as M1. The electrolyte is injected into the soft-pack battery according to the standard of 5g / Ah, and the soft-pack battery after injection is weighed again using the same electronic balance, and the mass of the battery at this time is recorded as M2, and the injection volume is M2-M1; the soft-pack battery is formed with a current of 0.1C and charged to a capacity of 100% SOC, and the charging capacity C1 is recorded. Then, the soft-pack battery is left to stand at 50°C for 24 hours and weighed for the third time, and the mass is recorded as M3. The retention amount is calculated by the formula (M3-M1) / C1.

[0102] (4) Soft-pack battery electrical performance test: The test system is the Nebula test system, which tests the soft-pack battery assembled in (1).

[0103] The first coulomb efficiency test at room temperature 25℃±2℃: charge to 3.7V at 0.1C constant current, cut-off current 0.05C, and stand for 10min; then discharge to 2.5V at 0.1C constant current, cut-off current 0.05C, record the first charge capacity and first discharge capacity during the charge and discharge process, and calculate the first coulomb efficiency (first coulomb efficiency = first discharge capacity / first charge capacity*100*) and the first discharge specific capacity;

[0104] Cyclic test at room temperature 25℃±2℃: charge to 3.7V at 1C constant current, cut off current 0.05C, let stand for 10min, then discharge to 2.5V at 1C constant current, cut off current 0.05C, let stand for 10min. Take the above cycle as one cycle, record the discharge capacity after 500 cycles, and calculate the discharge capacity specific capacity and capacity retention rate after 500 cycles.

[0105] Table 1

[0106]

[0107] It can be seen from the results of Table 1 that, compared with Comparative Examples 1 to 6, the positive electrode sheet prepared by the positive electrode conductive slurry provided in Examples 1 to 5 has a lower resistivity, and the lithium battery containing the positive electrode sheet has a higher liquid retention, a higher first coulomb efficiency and an excellent cycle capacity retention rate. From the comparison results of Example 1 and Comparative Examples 1 to 3, it can be seen that the lack of any one of the dispersant (polyethylene wax), coupling agent (isopropyl trioleate acyloxy titanate), and stabilizer (diethyl sulfoxide) will lead to an increase in the resistivity of the electrode sheet, a decrease in the liquid retention of the battery, and a decrease in both the first-effect performance and the cycle performance. From the comparison results of Example 1 and Comparative Examples 4 to 6, it can be seen that if no linear polymer compound is added, or if no graphene is added, or if other carbon materials are used to replace the hard carbon particles, the resistivity of the electrode sheet will increase and the liquid retention, first-effect performance and cycle performance of the battery will all be significantly reduced.

[0108] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention without departing from the principles and purpose of the present invention.

Claims

1. A method for preparing a positive electrode conductive slurry, characterized in that: The preparation method of the positive electrode conductive paste comprises the following steps: a linear polymer compound, a first organic solvent and a dispersant are subjected to a first mixing treatment to obtain a mixture A; hard carbon particles, graphene and a coupling agent are subjected to a second mixing treatment in the presence of a solvent to obtain a graphene@hard carbon composite B in which graphene is coated on the surface of the hard carbon particles; and the mixture A, the graphene@hard carbon composite B and a stabilizer are subjected to a third mixing treatment to obtain a positive electrode conductive paste containing a composite conductive agent.

2. The method for preparing a positive electrode conductive paste according to claim 1, characterized in that: The solid content of the mixture A is 3 to 9 wt %; Preferably, in the mixture A, the mass ratio of the linear polymer compound to the dispersant is 1:(0.1-0.3); Preferably, the mass ratio of the hard carbon particles, graphene, and coupling agent is (8-16):1:(0.2-0.5); Preferably, the mass ratio of the mixture A, the graphene@hard carbon composite B, and the stabilizer is (0.8-3):1:(0.005-0.02).

3. The method for preparing a positive electrode conductive paste according to claim 1, characterized in that: The first mixing treatment is mechanical stirring treatment I; Preferably, the mechanical stirring treatment I lasts for 2 to 6 hours; Preferably, the second mixing treatment is mechanical stirring treatment II; Preferably, the conditions of the mechanical stirring treatment II include: a temperature of 50 to 70° C. and a time of 3 to 4 hours.

4. The method for preparing a positive electrode conductive paste according to claim 1, characterized in that: The third mixing process is ball milling; Preferably, the conditions of the ball milling treatment include: a rotation speed of 200 to 300 rpm and a time of 6 to 8 hours; Preferably, the third mixing treatment further includes a fourth mixing treatment, and the steps of the fourth mixing treatment are as follows: the mixture containing the composite conductive agent obtained by the third mixing treatment is subjected to a fourth mixing treatment with the second organic solvent to obtain a positive electrode conductive slurry containing the composite conductive agent; Preferably, the solid content of the positive electrode conductive slurry is 14-18wt%; Preferably, the fourth mixing treatment is mechanical stirring treatment III; Preferably, the time of the mechanical stirring treatment III is 1 to 3 hours.

5. The method for preparing a positive electrode conductive paste according to claim 1, characterized in that: The linear polymer compound is selected from at least one of polyacrylamide compounds, polyolefin compounds, and polyester compounds; Preferably, the linear polymer compound has a diameter of 0.05 to 0.1 μm and a length of 4 to 8 μm; Preferably, the polyacrylamide compound is selected from at least one of polyacrylamine hydrochloride, polyacrylic acid-acrylamide copolymer, and styrene-acrylamide copolymer.

6. The method for preparing a positive electrode conductive paste according to claim 1, characterized in that: The dispersant is selected from at least one of polyethylene wax, polyvinyl pyrrolidone, hydrogenated petroleum resin, and fatty alcohol polyoxyethylene ether; Preferably, the first organic solvent is selected from at least one of N-methylpyrrolidone, N-cyclohexanepyrrolidone, N,N-dimethylformamide, and dimethylacetamide; Preferably, the hard carbon particles are spherical and / or spherical-like; Preferably, the Dv50 particle size of the hard carbon particles is 0.3 to 0.5 μm; Preferably, the specific surface area of ​​the hard carbon particles is 600 to 800 m 2 / g.

7. The method for preparing a positive electrode conductive paste according to claim 1, characterized in that: The coupling agent is selected from titanate coupling agent and / or silane coupling agent; Preferably, the stabilizer is selected from at least one of diethyl sulfoxide, sodium salicylate and aqueous sodium alginate.

8. A positive electrode conductive slurry prepared by the method according to any one of claims 1 to 7.

9. A positive electrode sheet, characterized in that: The raw materials for preparing the positive electrode sheet include the positive electrode conductive paste according to claim 8.

10. A lithium ion battery, characterized in that: The lithium-ion battery comprises the positive electrode sheet according to claim 9.

Images