Modified positive electrode material and preparation method thereof, positive electrode sheet and lithium ion battery

Abstract

The present invention provides a modified positive electrode material, a preparation method thereof, a positive electrode plate, and a lithium-ion battery. The preparation method of the modified positive electrode material comprises the following steps: S1: uniformly mixing an inorganic conductive carbon material, a stabilizer, and a first organic solvent to obtain a conductive slurry; S2: simultaneously applying the glue solution and the conductive slurry to the positive electrode active material powder located on a conductive plate through electrostatic weaving, allowing the mixture to stand, then microwave drying to form a two-dimensional nano-network structure, and finally mechanically grinding to obtain the modified positive electrode material. The present invention achieves directional arrangement of the conductive material on the active material through a combination of electrostatic weaving, microwave drying, and mechanical grinding, thereby achieving uniform dispersion and sufficient contact, and then gradually improving the stability between the two, ultimately producing a modified positive electrode material in which the conductive material is more evenly distributed on the surface of the active material, in closer contact, and more stable.

Description

Technical Field

[0001] The present invention belongs to the technical field of cathode material preparation, and in particular relates to a modified cathode material and a preparation method thereof, a cathode pole piece and a lithium ion battery. Background Art

[0002] With the increasing depletion of global oil resources and the growing severity of automobile exhaust pollution, the development of high-performance, low-cost, and environmentally friendly electric vehicles has gradually become a key development direction in the automotive industry. High-performance, low-cost, and environmentally friendly lithium-ion batteries are a key development focus and hot topic. As one of the key factors affecting the overall performance of lithium-ion batteries, lithium-ion battery cathode materials have received significant attention.

[0003] Currently, the most widely used positive electrode materials for lithium-ion batteries are lithium iron phosphate-based positive electrode active materials and ternary-based positive electrode active materials.

[0004] Batteries made of lithium iron phosphate are not resistant to low temperature conditions. One of the reasons is that the intrinsic properties of lithium iron phosphate - the electronic conductivity and ion diffusion rate in the bulk phase are as low as 10 at room temperature. -8 ~10 -10 S / cm and 10 -12 ~10 -14 cm 2 / s. If used at low temperatures, severe polarization will occur, resulting in low battery capacity and rate capability. To address this shortcoming, one current approach to improving lithium iron phosphate cathode materials is to use small-sized lithium iron phosphate particles, minimizing the diffusion distance of lithium ions within the particles. However, particles that are too small suffer from poor fluidity due to their high specific surface area, making efficient production impossible. Furthermore, their low compaction density leads to low energy density, so the improvement effect of small-sized lithium iron phosphate solutions is very limited. Another approach to improving lithium iron phosphate cathode materials is to thermally decompose organic carbon-based materials to form amorphous carbon, which is then coated on the surface of lithium iron phosphate particles in an adsorbed state. However, the electrical conductivity of amorphous carbon is lower than that of morphous carbon, leaving room for further improvement. Coating the surface of lithium iron phosphate particles with inorganic conductive carbon materials to improve their conductivity is attempted, but the materials obtained by existing methods suffer from problems such as easy particle agglomeration, loose contact between the carbon and lithium iron phosphate particles, and gaps in the contact surface. This means that uniform coating of amorphous carbon is difficult to achieve.

[0005] However, the particles of nickel-cobalt-manganese ternary cathode materials are slightly larger than those of lithium iron phosphate materials, resulting in a longer lithium ion transmission path. Furthermore, as the nickel content in ternary cathode materials increases, they also suffer from the following shortcomings: 1) surface side reactions, which produce a variety of side reaction products; and 2) poor thermal stability, with electrochemical performance significantly degrading under high temperature conditions. To improve their performance, existing technologies also use surface coatings with conductive carbon materials.

[0006] For example, patent application CN 115172725 A discloses a carbon-coated positive electrode material and its preparation method, which first puts the positive electrode material and the conductive carbon material into a mixing device and mixes them to obtain a mixed powder; then the mixed powder is sintered under the protection of an inert gas, and after sintering, the temperature is cooled to room temperature to obtain a carbon-coated positive electrode material. This method coats inorganic carbon on the surface of lithium iron phosphate particles or nickel-cobalt-manganese ternary materials through mixing and sintering. In the positive electrode material obtained, the contact between the coated carbon layer and the positive electrode active material is not tight, and there is a gap on the contact surface, resulting in limited improvement in the battery's low temperature, rate and cycle performance. Therefore, it is very necessary to find a method that can effectively improve the contact tightness between the carbon material in the carbon coating layer and the surface of the positive electrode active material. Summary of the Invention

[0007] In view of the above technical defects, the purpose of the present invention is to provide a modified positive electrode material and its preparation method, a positive electrode plate and a lithium-ion battery, which can solve the problem in the prior art that the conductive material of the coating layer and the coated active material are not in sufficient contact and the coating is uneven, thereby affecting the performance of the lithium-ion battery.

[0008] In order to achieve the above object, the present invention adopts the following technical solutions:

[0009] In a first aspect, the present invention further provides a method for preparing a modified positive electrode material, comprising the following steps:

[0010] S1: uniformly mixing an inorganic conductive carbon material, a stabilizer and a first organic solvent to obtain a conductive slurry;

[0011] S2: The glue and the conductive slurry are simultaneously spread onto the positive electrode active material powder on the conductive plate through electrostatic weaving, left to stand, and then microwave dried to form a two-dimensional nano-network structure, and finally mechanically ground to obtain the modified positive electrode material.

[0012] The present invention realizes the directional arrangement of the conductive carbon material on the positive electrode active material by electrostatic weaving, basically achieving uniform dispersion and sufficient good contact between the conductive carbon material and the positive electrode active material. In order to fix this state, the present invention further fixes it by adding glue at the same time as adding the conductive slurry and a subsequent microwave drying process, thereby improving the stability of the state between the conductive material and the active material.

[0013] By simultaneously adding a conductive slurry and a glue, the present invention allows the conductive carbon material to be fixed to the surface of the positive electrode active material in a directional arrangement. If the conductive slurry is added first and then the glue, the glue will not have a bonding effect; if the glue is added first and then the conductive slurry, the glue will be severely blocked between the conductive material and the active material, preventing the conductive material and the active material from mixing. Compared with other directional arrangement methods, the present invention uses a directional arrangement method of electrostatic weaving. On the one hand, it can control the addition rate of the conductive material to control the relative content of the conductive material and the adhesive material, achieving a balance between conductive performance and adhesive performance. On the other hand, it can use the impact force and dilution effect of the electrostatic weaving to remove any possible glue agglomerations.

[0014] The stabilizer in the conductive paste can prevent the agglomeration of the various material components in the conductive paste.

[0015] In the above preparation method, the standing time in step S2 is to allow the glue to solidify properly so as to keep the conductive carbon material in a directional arrangement on the surface of the active material and facilitate the subsequent drying. The specific standing time can be determined according to the type of glue binder used.

[0016] The present invention adopts microwave drying. Compared with common drying methods, such as air drying and rotary drying, the microwave drying method does not introduce mechanical force, vibration, etc. to destroy the metastable state of the conductive material and the active material. The solvent can be fully evaporated to achieve drying while maintaining the uniform dispersion and sufficient good contact state caused by the electrostatic weaving network. At the same time, during the solvent volatilization process, the contact between the conductive material, the active material and the binder will be more sufficient and close, forming a more stable contact between the three.

[0017] In the above preparation method, the mechanical grinding process is set up after microwave drying, which can further improve the contact stability between the conductive material, the active material and the binder by squeezing the conductive carbon material and the positive electrode active material. At the same time, mechanical grinding can also break up the micro-agglomerates in the material to form a powder material with uniform particle size.

[0018] In the above preparation method, as a preferred embodiment, the electrostatic weaving is performed by spraying the conductive slurry and glue onto the positive electrode active material powder using high voltage static electricity.

[0019] In the above preparation method, as a preferred embodiment, the specific surface area of the two-dimensional nano-network structure is 1-100m 2 / g (for example: 10m 2 / g, 20m 2 / g、30m 2 / g, 40m 2 / g, 50m 2 / g, 60m2 / g、70m 2 / g、80m 2 / g、90m 2 / g).

[0020] Furthermore, simultaneously spreading the glue and the conductive slurry onto the positive electrode active material powder through the electrostatic mesh specifically includes: simultaneously spraying the glue and the conductive slurry onto the surface of the dispersed positive electrode active material powder through adjacent parallel nozzles at a specific voltage.

[0021] Furthermore, the equipment used to complete the electrostatic weaving includes an electrostatic sprayer, a high-voltage power supply and a conductive plate, the nozzle of the electrostatic sprayer and the conductive plate are respectively connected to the two poles of the power supply, the nozzle of the electrostatic sprayer is a pair of adjacent nozzles in parallel, one nozzle is used to spray the glue, and the other nozzle is used to spray the conductive slurry, and the nozzle of the electrostatic sprayer is aligned with the center of the conductive plate;

[0022] Preferably, the process conditions of the electrostatic weaving are as follows:

[0023] The positive electrode active material powder is laid on the conductive plate with a thickness of 0.1-10 mm (for example, 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm);

[0024] The injection flow rates of the glue and the conductive paste are 1-20 μL / min (for example, 2 μL / min, 4 μL / min, 6 μL / min, 8 μL / min, 10 μL / min, 12 μL / min, 14 μL / min, 16 μL / min, and 18 μL / min) and 1-20 μL / min (for example, 2 μL / min, 4 μL / min, 6 μL / min, 8 μL / min, 10 μL / min, 12 μL / min, 14 μL / min, 16 μL / min, and 18 μL / min), respectively;

[0025] The operating voltage of the equipment is 10-30kV;

[0026] The distance between the tip of the electrostatic nozzle and the conductive plate is 10-20 cm (for example, 12 cm, 14 cm, 16 cm, 18 cm);

[0027] The ambient humidity is controlled at 5-15% RH (for example: 6% RH, 8% RH, 12% RH, 14% RH), the temperature is 20-30° C., and the spraying time is 0.5-6 h (for example: 1 h, 2 h, 3 h, 4 h).

[0028] In the above preparation method, as a preferred embodiment, the power of the microwave drying is 100-500W (for example: 200W, 400W);

[0029] And / or, the microwave drying time is 2-20 min (for example: 3 min, 5 min, 8 min, 12 min, 15 min, 18 min);

[0030] And / or, the microwave drying temperature is 50-200°C (for example: 60°C, 120°C, 140°C, 160°C, 180°C).

[0031] In the above preparation method, as a preferred embodiment, the rotation speed of the mechanical grinding is 100-800 r / min (for example: 300 r / min, 400 r / min, 600 r / min), and the time of the mechanical grinding is 1-10 h (for example: 2 h, 4 h, 6 h, 8 h).

[0032] In the above preparation method, as a preferred embodiment, the adhesive solution is formed by dissolving a first binder in a second organic solvent. Further preferably, the first binder is a polymeric organic substance, and the polymeric organic substance includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, polytetrafluoroethylene-ethylene copolymer, styrene-butadiene rubber, polyacrylamide, polyacrylonitrile, polyimide, polystyrene, and polystyrene-butadiene copolymer. Further preferably, the polymeric organic substance is polyvinylidene fluoride.

[0033] In the above preparation method, as a preferred embodiment, the viscosity of the glue is 1000-20000 mPa·s (for example: 6000 mPa·s, 10000 mPa·s, 14000 mPa·s, 18000 mPa·s); the solid content of the glue is 3%-8% (for example: 5%, 6%, 7%).

[0034] In the above preparation method, as a preferred embodiment, the mass ratio of the inorganic conductive carbon material, the positive electrode active material powder and the first binder is (0.1-4.0):100:(0.1-3.0).

[0035] In the above preparation method, as a preferred embodiment, the inorganic conductive carbon material is graphene and / or carbon nanotubes.

[0036] Furthermore, the graphene includes one or more of graphene obtained by mechanical exfoliation, graphene obtained by reduction-oxidation, and graphene obtained by vapor deposition;

[0037] The carbon nanotubes include single-walled carbon nanotubes and / or multi-walled carbon nanotubes.

[0038] In the above preparation method, as a preferred embodiment, in step S1, the mass ratio of the inorganic conductive carbon material, the stabilizer and the first organic solvent is (0.2-12):(0.01-5):100; further preferably, when the inorganic conductive carbon material is graphene and carbon nanotubes, the mass ratio of the graphene, carbon nanotubes, the stabilizer and the first organic solvent is (0.1-6):(0.1-6):(0.01-5):100.

[0039] In the above preparation method, as a preferred embodiment, the solid content of the conductive paste is 1-10%.

[0040] In the above preparation method, as a preferred embodiment, the first organic solvent and the second organic solvent respectively include one or more of hexane, benzene, toluene, xylene, methylnaphthalene, acetone, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethylenetriamine, N,N-dimethylaminopropylamine, diethyl ether, propylene oxide, tetrahydrofuran, N-methylpyrrolidone, dimethylformamide, dimethylacetamide, hexamethylphosphoramide, and dimethyl sulfoxide. The first organic solvent and the second organic solvent are the same or different.

[0041] In the above preparation method, as a preferred embodiment, the stabilizer includes one or more of triethylhexyl phosphate, sodium hexametaphosphate, sodium tripolyphosphate, sodium pyrophosphate, aniline oligomer, sodium polyacrylate, polyethylene glycol octylphenyl ether, polyvinyl pyrrolidone and lignin sulfite.

[0042] In the above preparation method, as a preferred embodiment, the positive electrode active material is a nickel-cobalt-manganese ternary material or a lithium iron phosphate material.

[0043] As an embodiment, the general formula of the nickel-cobalt-manganese ternary material is Li x (Ni y Co z Mn 1-y-z )O2, 1.0≤x≤1.1, 0.3<y<0.99, 0<z<1; the general formula of the lithium iron phosphate material is Li a Fe b M c PO4, 1.0≤a≤1.1, 0<b≤1, 0≤c<1, b+c=1, M is one or more of Mn, Co, Ni, Mg, and V.

[0044] In a second aspect, the present invention provides a modified positive electrode material obtained by the above-mentioned preparation method, wherein the modified positive electrode material comprises: a positive electrode active material and a conductive carbon material coating layer attached to the surface of the positive electrode active material.

[0045] In a third aspect, the present invention further provides a positive electrode sheet comprising a current collector and an active material layer, wherein the active material layer comprises the modified positive electrode material, a conductive agent, and a second binder. The positive electrode sheet of the present invention can be prepared by either a dry process or a wet process.

[0046] In a fourth aspect, the present invention further provides a lithium-ion battery, wherein the positive electrode sheet thereof is a positive electrode sheet made of the above-mentioned modified positive electrode material.

[0047] The above lithium-ion battery can be prepared by the following method:

[0048] The modified positive electrode material, the second binder, the conductive agent and the third solvent are uniformly mixed to form a slurry, which is then coated to form a positive electrode sheet. The positive electrode sheet, the negative electrode sheet, the electrolyte, the separator and the shell are then assembled into the lithium-ion battery.

[0049] In the present invention, the third solvent is not particularly limited and is a commonly used solvent in the art for preparing positive electrode sheets, such as N-methylpyrrolidone.

[0050] In the present invention, the second binder is not particularly limited and is a solvent commonly used in the art for preparing positive electrode plates, such as polyvinylidene fluoride, polytetrafluoroethylene, polytetrafluoroethylene-ethylene copolymer, styrene-butadiene rubber, polyacrylamide, polyacrylonitrile, polyimide, polystyrene and polystyrene-butadiene copolymer.

[0051] The negative electrode sheet, electrolyte, separator and shell of the lithium-ion battery in the present invention are all conventional technologies.

[0052] Compared with the prior art, the present invention has at least one of the following beneficial effects:

[0053] 1. The modified positive electrode material provided by the present invention has a conductive carbon material that is uniform on the surface of the active material and has close and stable contact, further enhancing the lithium-ion battery's ability to withstand low-temperature conditions and its ability to exert its low-temperature capacity, and improving the lithium-ion battery's rate, low-temperature, and cycle performance.

[0054] 2. The present invention achieves directional alignment of the conductive material on the active material through electrostatic weaving, particularly through controlled electrostatic weaving process conditions. This essentially achieves uniform dispersion and sufficient contact between the conductive and active materials. However, electrostatic weaving alone still maintains a semi-stable state between the conductive and active materials. Therefore, the addition of a binder improves the stability of this state between the conductive and active materials. By simultaneously and slowly injecting the conductive paste and adhesive through the electrostatic weaving process, it is possible to prevent significant aggregation of polymeric organic matter.

[0055] 3. The present invention uses microwave drying. Compared with common drying methods, such as air drying and rotary drying, microwave drying does not introduce mechanical force, vibration, etc. that may destroy the metastable state of the conductive material and the active material. Only this special drying method is sufficient to maintain the uniform dispersion and sufficient good contact state caused by the electrostatic weaving network, and fully evaporate the solvent to achieve drying. At the same time, during the solvent evaporation process, the contact between the conductive material, the active material and the binder will be more complete and close, forming a more stable contact between the three.

[0056] 4. The present invention adopts mechanical grinding to further improve the contact stability between the conductive material, the active material and the binder by squeezing the conductive material and the active material. At the same time, micro-agglomerates in the material can also be broken by mechanical grinding.

[0057] 5. Under preferred process conditions, the present invention combines the main technical treatment method of electrostatic weaving with the auxiliary treatment methods of microwave drying and mechanical grinding to first achieve the directional arrangement of the conductive material on the active material to achieve uniform dispersion and sufficient good contact, and then gradually improve the stability between the two, and finally prepare a modified positive electrode material in which the conductive material is more evenly distributed on the surface of the active material, in closer contact, and more stable. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Figure 1 This is the SEM image of the modified positive electrode material prepared in Example 1;

[0059] Figure 2 for Figure 1 A partial enlarged view of

[0060] Figure 3 This is the SEM image of the positive electrode material prepared in Comparative Example 1;

[0061] Figure 4 This is the SEM image of the positive electrode material prepared in Comparative Example 2;

[0062] Figure 5 This is the SEM image of the positive electrode material prepared in Comparative Example 3. DETAILED DESCRIPTION

[0063] In order to make the purpose, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of the present invention.

[0064] The embodiments of the present invention are implemented on the premise of the technical solution of the present invention, and detailed implementation methods and processes are given. However, the protection scope of the present invention is not limited to the following embodiments. The process parameters in the following embodiments that do not specify specific conditions are generally based on conventional conditions.

[0065] The endpoints of the ranges and any values disclosed herein are not limited to the precise ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values can be combined with each other to form one or more new numerical ranges, and these numerical ranges should be considered to be specifically disclosed in the present invention.

[0066] In the present invention, unless otherwise specified and / or explained, all numerical values involving the amounts of components are "parts by weight". The process parameters in the following examples that are not specified in specific conditions are generally based on conventional conditions.

[0067] The following examples further describe a method for preparing a modified positive electrode material of the present invention. The examples are provided for the purpose of illustrating the present invention only and are not intended to limit the scope of the present invention. The following examples may serve as a basis for further improvement or application by persons of ordinary skill in the art and do not in any way constitute specific limitations on the present invention.

[0068] In embodiments of the present invention, the apparatus for electrostatically weaving a web comprises an electrostatic ejector, a power supply, and a conductive plate. The ejector head and the conductive plate are connected to the two poles of the power supply, respectively. The ejector head comprises two adjacent ejectors, one for spraying glue and the other for spraying conductive slurry. The ejector heads are aligned with the center of the conductive plate. The operating principle of this apparatus is similar to that of an electrospinning apparatus and, in the following embodiments, this apparatus is referred to as an electrospinning apparatus having two adjacent ejectors.

[0069] Example 1

[0070] This embodiment provides a method for preparing a modified positive electrode material, comprising the following steps:

[0071] Prepare a conductive paste: Mix 3.6 g of graphene, 1.44 g of polyvinyl pyrrolidone, and 720 g of acetone in a ratio of 0.5:0.2:100 to obtain a conductive paste. Remove 1 / 100 of the weight of the paste to prepare the modified positive electrode material.

[0072] Preparation of the slurry: To prepare a 4% solids slurry, mix 2.4g of polyvinylidene fluoride with 57.6g of N-methylpyrrolidone. The viscosity of the slurry is approximately 4000 mPa·s ± 1000 mPa·s. Remove 1 / 100 of the weight of the slurry to prepare the modified positive electrode material.

[0073] Preparation of modified cathode material: Using an electrospinning device with adjacent double nozzles, the conductive slurry and glue were sprayed onto 6g of a thin layer of nickel-cobalt-manganese ternary material (Li(Ni 0.6 Co 0.2 Mn 0.2 )O2) powder, wherein the ternary material powder is laid on the conductive plate with a laying thickness of 0.33 mm, the operating voltage of the equipment is 20 kV, the distance between the nozzle tip of the electrostatic nozzle and the conductive plate is 15 cm, the ambient humidity is controlled at 10% RH, the temperature is 25°C, the injection flow rate of the glue is 1.8 μL / min, the injection time of the glue is 5.1 h, the injection flow rate of the conductive slurry is 20 μL / min, the injection time of the conductive slurry is 5 h, and it is allowed to stand, and then microwave drying is performed (the microwave drying power is 400 w, the time is 10 min, and the temperature is 100°C), thereby forming a two-dimensional nano-network structure (specific surface area of about 16.4 m 2 / g), and finally mechanically ground (the mechanical grinding speed is 500r / min, and the time is 5h) to obtain the modified positive electrode material.

[0074] The microstructure of the modified cathode material prepared in this example is shown in Figure 1 and Figure 2 ,pass Figure 1 and Figure 2 It can be seen that there is no agglomeration in the prepared modified positive electrode material, and the conductive material and the active material are in good contact.

[0075] Example 2

[0076] This embodiment provides a method for preparing a modified positive electrode material, comprising the following steps:

[0077] Prepare a conductive slurry: Mix a conductive carbon material (5.5g graphene + 5.5g carbon nanotubes), 0.55g polyvinyl pyrrolidone, and 5500g acetone in a ratio of 0.2:0.01:100 to obtain a conductive slurry. Remove 1 / 10000 of the weight of the slurry to prepare the modified positive electrode material.

[0078] Preparation of the slurry: To prepare a 3% solids slurry, mix 11g of polyvinylidene fluoride with 355.67g of N-methylpyrrolidone until uniformly mixed. The viscosity of the slurry is approximately 3000 mPa·s ± 1000 mPa·s. A 10,000th of this weight is used to prepare the modified positive electrode material.

[0079] Preparation of modified cathode material: Using an electrospinning device with two adjacent nozzles, the conductive slurry and glue were sprayed onto 1.1 g of lithium iron phosphate material (LiFe 0.5 Mn 0.5 PO4) powder, wherein the lithium iron phosphate material powder is laid on the conductive plate with a laying thickness of 0.1 mm, the working voltage of the equipment is 20 kV, the distance between the nozzle tip of the electrostatic nozzle and the conductive plate is 15 cm, the ambient humidity is controlled at 10% RH, the temperature is 25 ° C, the injection flow rate of the glue is 1 μL / min, the injection flow rate of the conductive slurry is 13.7 μL / min, the injection time of the glue and the conductive slurry is 0.6 h, and then it is allowed to stand and then microwave dried (the power of the microwave drying is 300 w, the time is 15 min, and the temperature is 150 ° C), thereby forming a two-dimensional nano-network structure on its surface (specific surface area is about 1.4 m 2 / g), and finally mechanically ground (the mechanical grinding speed is 700r / min, and the time is 4h) to obtain the modified positive electrode material.

[0080] From the microscopic pictures, it can be seen that the modified positive electrode material prepared in this embodiment has no agglomeration phenomenon, and the conductive material and the active material are in good contact.

[0081] Example 3

[0082] This embodiment provides a method for preparing a modified positive electrode material, comprising the following steps:

[0083] Prepare a conductive slurry: Mix the conductive carbon material (3.5g graphene + 3.5g carbon nanotubes), 2.92g polyvinyl pyrrolidone, and 58.33g acetone in a ratio of 12:5:100 to obtain a conductive slurry. Remove 1 / 10 of the weight from the mixture to prepare the modified positive electrode material.

[0084] Preparation of the adhesive: To prepare an 8% solids adhesive, mix 5.25g of polyvinylidene fluoride with 60.38g of N-methylpyrrolidone and stir until uniform. The adhesive viscosity is approximately 8000 mPa·s ± 1000 mPa·s. Remove 1 / 10 of the weight from the mixture to prepare the modified positive electrode material.

[0085] Preparation of modified cathode material: Using an electrospinning device with two adjacent nozzles, the conductive slurry and glue were sprayed onto 17.5 g of lithium iron phosphate material (LiFe0.5 Mn 0.5 PO4) powder, wherein the lithium iron phosphate material powder is laid on the conductive plate with a laying thickness of 1.59 mm, the working voltage of the equipment is 20 kV, the distance between the nozzle tip of the electrostatic nozzle and the conductive plate is 15 cm, the ambient humidity is controlled at 10% RH, the temperature is 25 ° C, the injection flow rate of the glue is 20 μ L / min, the injection flow rate of the conductive slurry is 19.1 μ L / min, the injection time of the glue and the conductive slurry is 5 h, and then it is allowed to stand and then microwave dried (the microwave drying power is 300 w, the time is 20 min, and the temperature is 80 ° C), thereby forming a two-dimensional nano network structure (specific surface area is about 52.9 m 2 / g), and finally mechanically ground (the mechanical grinding speed is 200r / min, and the time is 8h) to obtain the modified positive electrode material.

[0086] From the microscopic pictures, it can be seen that the modified positive electrode material prepared in this embodiment has no agglomeration phenomenon, and the conductive material and the active material are in good contact.

[0087] Example 4

[0088] This embodiment provides a method for preparing a modified positive electrode material, comprising the following steps:

[0089] Prepare a conductive paste: Mix 18g of graphene, 0.9g of polyvinyl pyrrolidone, and 9000g of acetone in a ratio of 0.2:0.01:100 to obtain a conductive paste. 1 / 10000 of the paste was used to prepare the modified positive electrode material.

[0090] Preparation of the adhesive: To prepare a 3% solids adhesive, mix 18g of polyvinylidene fluoride with 582g of N-methylpyrrolidone until uniformly mixed. The adhesive has a viscosity of approximately 3000 mPa·s ± 1000 mPa·s. Remove 1 / 10000 of this by weight for the modified positive electrode material.

[0091] Preparation of modified cathode material: Using an electrospinning device with adjacent double nozzles, the conductive slurry and glue were sprayed onto 1.8g of a thin layer of nickel-cobalt-manganese ternary material (Li(Ni 0.6 Co 0.2 Mn 0.2)O2) powder, wherein the ternary material powder is laid on the conductive plate with a laying thickness of 0.1mm, the working voltage of the equipment is 20kV, the distance between the nozzle tip of the electrostatic nozzle and the conductive plate is 15cm, the ambient humidity is controlled at 10%RH, the temperature is 25℃, the injection flow rate of the glue is 1μL / min, the injection flow rate of the conductive slurry is 13.8μL / min, the injection time of the glue and the conductive slurry is 0.9h, and then it is allowed to stand and then microwave dried (the microwave drying power is 400w, the time is 10min, and the temperature is 100℃), thereby forming a two-dimensional nano-network structure (specific surface area is about 3.4m 2 / g), and finally mechanically ground (the mechanical grinding speed is 500r / min, and the time is 5h) to obtain the modified positive electrode material.

[0092] From the microscopic pictures, it can be seen that the modified positive electrode material prepared in this embodiment has no agglomeration phenomenon, and the conductive material and the active material are in good contact.

[0093] Example 5

[0094] This embodiment provides a method for preparing a modified positive electrode material, comprising the following steps:

[0095] Prepare a conductive slurry: Mix 7g of graphene, 2.92g of polyvinyl pyrrolidone, and 58.33g of acetone in a ratio of 12:5:100 to obtain a conductive slurry. Remove 1 / 10 of the weight of the slurry to prepare the modified positive electrode material.

[0096] Preparation of the adhesive: To prepare an 8% solids adhesive, mix 5.25g of polyvinylidene fluoride with 60.38g of N-methylpyrrolidone and stir until uniform. The adhesive viscosity is approximately 8000 mPa·s ± 1000 mPa·s. Remove 1 / 10 of the weight from the mixture to prepare the modified positive electrode material.

[0097] Preparation of modified cathode material: Using an electrospinning device with adjacent double nozzles, the conductive slurry and glue were sprayed onto 17.5 g of a thin layer of nickel-cobalt-manganese ternary material (Li(Ni 0.6 Co 0.2 Mn 0.2)O2) powder, wherein the ternary material powder is laid on the conductive plate with a laying thickness of 0.97 mm, the working voltage of the equipment is 20 kV, the distance between the nozzle tip of the electrostatic nozzle and the conductive plate is 15 cm, the ambient humidity is controlled at 10% RH, the temperature is 25 ° C, the injection flow rate of the glue is 20 μ L / min, the injection flow rate of the conductive slurry is 19.1 μ L / min, the injection time of the glue and the conductive slurry is 5 hours, and then it is allowed to stand and then microwave dried (the microwave drying power is 400 w, the time is 10 minutes, and the temperature is 100 ° C), thereby forming a two-dimensional nano network structure (specific surface area is about 99.1 m 2 / g), and finally mechanically ground (the mechanical grinding speed is 500r / min, and the time is 5h) to obtain the modified positive electrode material.

[0098] From the microscopic pictures, it can be seen that the modified positive electrode material prepared in this embodiment has no agglomeration phenomenon, and the conductive material and the active material are in good contact.

[0099] Comparative Example 1

[0100] This comparative example provides a method for preparing a modified positive electrode material, comprising the following steps:

[0101] Prepare a conductive paste: Mix 3.6 g of graphene, 1.44 g of polyvinyl pyrrolidone, and 720 g of acetone in a ratio of 0.5:0.2:100 to obtain a conductive paste. Remove 1 / 100 of the weight of the paste to prepare the modified positive electrode material.

[0102] Preparation of the slurry: To prepare a 4% solids slurry, mix 2.4g of polyvinylidene fluoride with 57.6g of N-methylpyrrolidone. The viscosity of the slurry is approximately 4000 mPa·s ± 1000 mPa·s. Remove 1 / 100 of the weight of the slurry to prepare the modified positive electrode material.

[0103] Preparation of modified positive electrode material: the conductive paste and glue were mixed with 6g nickel-cobalt-manganese ternary material (Li(Ni 0.6 Co 0.2 Mn 0.2 )O2) powder was mixed and stirred for 5 hours, then allowed to stand, and then microwave dried (the power of microwave drying was 400w, the time was 10min, and the temperature was 100°C), and finally mechanically ground (the speed of mechanical grinding was 500r / min, and the time was 5h) to obtain a modified positive electrode material.

[0104] The microstructure of the modified cathode material prepared in this comparative example is shown in Figure 3 ,pass Figure 3It can be seen that the prepared positive electrode material has serious agglomeration phenomenon. The part circled with a dotted circle in the figure shows that the graphene itself is seriously agglomerated, which makes it impossible to achieve uniform and tight coverage of graphene on the surface of the active material.

[0105] Comparative Example 2

[0106] This comparative example provides a method for preparing a modified positive electrode material, comprising the following steps:

[0107] Prepare a conductive paste: Mix 3.6 g of graphene, 1.44 g of polyvinyl pyrrolidone, and 720 g of acetone in a ratio of 0.5:0.2:100 to obtain a conductive paste. Remove 1 / 100 of the weight of the paste to prepare the modified positive electrode material.

[0108] Preparation of the slurry: To prepare a 4% solids slurry, mix 2.4g of polyvinylidene fluoride with 57.6g of N-methylpyrrolidone. The viscosity of the slurry is approximately 4000 mPa·s ± 1000 mPa·s. Remove 1 / 100 of the weight of the slurry to prepare the modified positive electrode material.

[0109] Preparation of modified cathode material: Using an electrospinning device with adjacent double nozzles, the conductive slurry and glue were sprayed onto 6g of a thin layer of nickel-cobalt-manganese ternary material (Li(Ni 0.6 Co 0.2 Mn 0.2 )O2) powder, wherein the ternary material powder is laid on the conductive plate with a laying thickness of 0.33mm, the working voltage of the equipment is 20kV, the distance between the nozzle tip of the electrostatic nozzle and the conductive plate is 15cm, the ambient humidity is controlled at 10%RH, the temperature is 25℃, the injection flow rate of the glue is 1.8μL / min, the injection time of the glue is 5.1h, the injection flow rate of the conductive slurry is 20μL / min, the injection time of the conductive slurry is 5h, let it stand, and then carry out blower drying (time is 10min, temperature is 100℃), and finally mechanically grind (the mechanical grinding speed is 500r / min, time is 5h) to obtain the modified positive electrode material.

[0110] The microstructure of the modified cathode material prepared in this comparative example is shown in Figure 4 ,pass Figure 4 It can be seen that the prepared modified cathode material exhibits agglomeration, resulting in poor contact between the conductive and active materials. In the area encircled by the dotted circle on the left side of the figure, graphene aggregates and has poor contact with the active material.

[0111] Comparative Example 3

[0112] This comparative example provides a method for preparing a modified positive electrode material, comprising the following steps:

[0113] Preparation of the slurry: To prepare a 4% solids slurry, mix 2.4g of polyvinylidene fluoride with 57.6g of N-methylpyrrolidone. The viscosity of the slurry is approximately 4000 mPa·s ± 1000 mPa·s. Remove 1 / 100 of the weight of the slurry to prepare the modified positive electrode material.

[0114] Preparation of modified positive electrode material: the above glue solution was mixed with 6g nickel-cobalt-manganese ternary material (Li(Ni 0.6 Co 0.2 Mn 0.2 )O2) powder was stirred and dispersed, and then air dried (time was 10 min, temperature was 100°C), and finally crushed by air flow mill to obtain modified positive electrode material.

[0115] The microstructure of the modified cathode material prepared in this comparative example is shown in Figure 5 ,pass Figure 5 It can be seen that there is no conductive substance on the surface of the active material in the prepared modified positive electrode material.

[0116] Test Case

[0117] The modified positive electrode active material prepared in Examples 1-3 and Comparative Examples 1-3, the binder polyvinylidene fluoride, and the conductive agent carbon black were dispersed in an organic solvent N-methylpyrrolidone in a mass ratio of 97.0:1.5:1.5, and then evenly coated on a current collector aluminum foil. After drying, the material was rolled to the required compaction density, cut into strips, and the tabs were welded to obtain a positive electrode sheet for a lithium-ion battery.

[0118] Artificial graphite, binder styrene-butadiene rubber, thickener sodium carboxymethyl cellulose, and conductive agent carbon black are dispersed in an organic solvent N-methylpyrrolidone in a mass ratio of 96.6:1.2:1.6:0.6, and then evenly coated on a current collector copper foil. After drying, the mixture is rolled to the required compaction density, cut into strips, and then the tabs are welded to obtain the negative electrode sheet used in lithium-ion batteries.

[0119] The positive electrode sheet, PP separator, and negative electrode sheet are wound into a core, and after adding lithium-ion battery electrolyte, they are chemically converted into a lithium-ion battery that can be charged and discharged. The theoretical capacity of the lithium-ion battery is about 2.0Ah.

[0120] The assembled lithium-ion batteries are subjected to performance tests. The performance test indicators include the lithium-ion battery's rate capability, low-temperature operating capability, low-temperature capacity utilization capability and cycle performance.

[0121] Lithium-ion battery rate dischargeThe test method is as follows: the battery is subjected to charge and discharge cycles under a constant temperature environment of 25°C. In Example 1, Example 4, Example 5, Comparative Example 1, Comparative Example 2, and Comparative Example 3, due to the material properties, the voltage range is 2.50V to 4.30V. In Example 2 and Example 3, due to the material properties, the voltage range is 2.50V to 4.40V. The charge and discharge cycles are carried out for multiple weeks. The charging rate of this test is always 0.2C rate charging, and the discharge rates of each week are 0.2C rate discharge, 0.5C rate discharge, 1.0C rate discharge, 2.0C rate discharge, and 3.0C rate discharge. The 3C / 0.2C rate discharge capacity retention rate is the ratio of the capacity at 3.0C rate discharge to the capacity at 0.2C rate discharge. The closer the ratio is to 100%, the better the rate discharge capability.

[0122] The test method for the low-temperature operating capability (low-temperature capacity performance) of lithium-ion batteries is as follows: the battery is charged at a rate of 0.2C at 25℃ and discharged at a rate of 0.2C at a specified temperature under different ambient temperatures. The voltage range is the same as the voltage range of the above-mentioned rate discharge test. The charge and discharge cycles are repeated for multiple weeks, and the specified temperatures for each week are 25℃, 0℃, -10℃, and -20℃ respectively. The -20℃ / 25℃ capacity retention rate is the ratio of the capacity at the -20℃ rate discharge to the capacity at the 25℃ rate discharge. The closer the ratio is to 100%, the better the low-temperature discharge capability.

[0123] The test method for the cycle performance of lithium-ion batteries is as follows: the battery is placed in a constant temperature environment of 25°C and the voltage range is the same as the voltage range of the above-mentioned rate discharge test, and the charge and discharge cycle is carried out for multiple cycles, with a charge rate of 0.5C and a discharge rate of 1.0C; the capacity retention rate of the cycle at 25°C after multiple cycles is the ratio of the discharge capacity in the last week to the discharge capacity in the first week. The higher the ratio, the better the battery cycle performance.

[0124] The test method for the AC internal resistance (ACIR) of a lithium-ion battery is as follows: Place the battery on an AC impedance tester at a constant temperature of 25°C, contact the positive and negative electrodes of the battery with the test fixtures of the tester respectively, and adjust the test parameters to a frequency of 1kHz and a voltage of 300V.

[0125] The specific test results are shown in the following table:

[0126]

[0127]

[0128] It can be seen from the above table that the use of the main technical treatment method of electrostatic weaving combined with the auxiliary treatment methods of microwave drying and mechanical grinding further enhances the lithium-ion battery's ability to withstand low-temperature conditions and its ability to exert its low-temperature capacity, improves the lithium-ion battery's rate, low-temperature, and cycle performance, and reduces the battery's internal resistance.

[0129] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention are within the scope of protection of the pending claims of the present invention.

Claims

1. A method for preparing a modified positive electrode material, characterized in that: The following steps are involved: S1: uniformly mixing an inorganic conductive carbon material, a stabilizer and a first organic solvent to obtain a conductive slurry; S2: Spreading the glue and the conductive slurry onto the positive electrode active material powder on the conductive plate through electrostatic weaving, letting it stand, then performing microwave drying to form a two-dimensional nano-network structure, and finally mechanically grinding to obtain the modified positive electrode material; The glue and the conductive slurry are simultaneously spread onto the positive electrode active material powder located on the conductive plate through the electrostatic mesh, specifically comprising: the glue and the conductive slurry are simultaneously sprayed onto the surface of the dispersed positive electrode active material powder through adjacent parallel nozzles at a specific voltage.

2. The method for preparing a modified positive electrode material according to claim 1, wherein: The specific surface area of the two-dimensional nano-network structure is 1-100m 2 / g.

3. The method for preparing the modified positive electrode material according to claim 1, wherein: The equipment used to complete the electrostatic weaving includes an electrostatic sprayer, a high-voltage power supply, and a conductive plate. The spray head of the electrostatic sprayer and the conductive plate are respectively connected to the two poles of the power supply. The spray heads of the electrostatic sprayer are parallel and adjacent to each other, one of which is used to spray the glue and the other is used to spray the conductive slurry. The spray head of the electrostatic sprayer is aligned with the center of the conductive plate. And / or, the process conditions of the electrostatic weaving are as follows: The positive electrode active material powder is laid on the conductive plate with a thickness of 0.1-10 mm; The injection flow rates of the glue and conductive paste are 1-20 μL / min and 1-20 μL / min respectively; The working voltage of the electrostatic mesh is 10-30kV; The ambient humidity is controlled at 5-15% RH, the temperature is 20-30°C, and the spraying time is 0.5-6h.

4. The method for preparing the modified positive electrode material according to claim 3, wherein: The distance between the nozzle tip of the electrostatic sprayer and the conductive plate is 10-20 cm.

5. The method for preparing the modified positive electrode material according to claim 1, wherein: The power of the microwave drying is 100-500W; And / or, the microwave drying time is 2-20 min; And / or, the microwave drying temperature is 50-200°C; And / or, the rotation speed of the mechanical grinding is 100-800 r / min, and the time of the mechanical grinding is 1-10 h.

6. The method for preparing a modified positive electrode material according to claim 1, wherein: The adhesive is formed by dissolving a first binder in a second organic solvent; the first binder is a polymer organic substance, and the polymer organic substance includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, polytetrafluoroethylene-ethylene copolymer, styrene-butadiene rubber, polyacrylamide, polyacrylonitrile, polyimide, polystyrene and polystyrene-butadiene copolymer; and / or, the first organic solvent comprises one or more of hexane, benzene, toluene, xylene, methylnaphthalene, acetone, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethylenetriamine, N,N-dimethylaminopropylamine, diethyl ether, propylene oxide, tetrahydrofuran, N-methylpyrrolidone, dimethylformamide, dimethylacetamide, hexamethylphosphoramide, and dimethyl sulfoxide; And / or, the inorganic conductive carbon material is graphene and / or carbon nanotubes; and / or, the stabilizer comprises one or more of triethylhexyl phosphate, sodium hexametaphosphate, sodium tripolyphosphate, sodium pyrophosphate, aniline oligomer, sodium polyacrylate, polyethylene glycol octylphenyl ether, polyvinyl pyrrolidone and lignin sulfite; And / or, the positive electrode active material is a nickel-cobalt-manganese ternary material or a lithium iron phosphate material.

7. The method for preparing the modified positive electrode material according to claim 6, wherein: The second organic solvent includes one or more of hexane, benzene, toluene, xylene, methylnaphthalene, acetone, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethylenetriamine, N,N-dimethylaminopropylamine, ethyl ether, propylene oxide, tetrahydrofuran, N-methylpyrrolidone, dimethylformamide, dimethylacetamide, hexamethylphosphoramide and dimethyl sulfoxide.

8. The method for preparing the modified positive electrode material according to claim 6, wherein: The mass ratio of the inorganic conductive carbon material, the positive electrode active material powder and the first binder is (0.1-4.0):100:(0.1-3.0); And / or, the viscosity of the glue is 1000-20000 mPa·s; the solid content of the glue is 3%-8%; And / or, in step S1, the mass ratio of the inorganic conductive carbon material, the stabilizer and the first organic solvent is (0.2-12):(0.01-5):

100.

9. A modified positive electrode material obtained by the preparation method according to any one of claims 1 to 8, characterized in that: The modified positive electrode material comprises: a positive electrode active material and a conductive carbon material coating layer attached to the surface of the positive electrode active material.

10. A positive electrode plate, characterized in that: The positive electrode sheet includes a current collector and an active material layer, wherein the active material layer includes the modified positive electrode material according to claim 9, a conductive agent, and a second binder.

11. A lithium-ion battery, characterized in that: Including the positive electrode sheet according to claim 10.

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