Positive electrode slurry and preparation method thereof, positive electrode plate and battery

Abstract

The invention relates to the field of battery materials, in particular to positive electrode slurry and a preparation method thereof, a positive plate and a battery, and the preparation method of the positive electrode slurry comprises the following steps: S1, mixing a first positive electrode active material, 10-90wt% of a second positive electrode active material, a conductive agent and a binder to obtain a first mixture; s2, dispersing the first mixture obtained in the step S1 into a solvent to obtain a second mixture; s3, mixing the second mixture obtained in the step S2 with the remaining second positive electrode active material to obtain a third mixture; and S4, adding or not adding a solvent into the third mixture to obtain the positive electrode slurry. According to the method, the complete coating effect on the surfaces of the first positive electrode active material particles is achieved, so that the homogenizing effect of the positive electrode slurry is greatly improved, the process flow is simple, and the process time is effectively controlled.

Description

Technical Field

[0001] The present application relates to the field of battery materials, and in particular to a positive electrode slurry and a preparation method thereof, a positive electrode sheet and a battery. Background Art

[0002] The current research and development trend of lithium-ion batteries in the field of new energy storage is mainly to improve their energy density and safety at the same time. In the preparation of lithium batteries, the preparation of battery pole pieces is crucial. In the process of preparing positive pole pieces, the preparation of positive pole slurry is usually involved. The preparation of positive pole slurry usually involves the preparation of active materials, conductive agents, binders, solvents, etc. through conventional processing procedures, including pre-mixing, kneading, rapid dispersion procedures and other steps to achieve full mixing of these ingredients. The slurry with good preparation effect is usually characterized by low slurry viscosity, high solid content, excellent slurry viscosity stability, and small scraping particle size.

[0003] In order to meet the needs of lithium-ion batteries in terms of energy density, rate performance, low-temperature performance, and cost reduction, the use of large-particle and small-particle positive electrode active materials to form a mixed positive electrode material system is an important branch of the current development of the lithium-ion battery field. However, due to their large particle size, large-particle positive electrode active materials can be completely wetted by the solvent and coated with PVDF in a short time, while small-particle positive electrode active materials require a longer solvent wetting time. It becomes more difficult to fit large-particle positive electrode active materials and small-particle positive electrode active materials after solvent wetting and PVDF coating. Small-particle positive electrode active materials tend to spontaneously agglomerate, which is manifested in the large particles of the mixed positive electrode in the homogenization process stage and very poor slurry dispersion performance. Therefore, this type of mixed positive electrode material system is difficult to homogenize due to the differences in solvent infiltration speed and dispersion ability of large and small particles when making the positive electrode, resulting in coating cracking, uneven pole piece structure, and partial loss of the internal electronic conductive network of the pole piece, which is manifested as higher battery impedance and degraded electrical performance. Summary of the invention

[0004] The mixed positive electrode material system formed by large and small particles of positive electrode active materials leads to increased battery impedance and deteriorated electrical performance due to the difference in solvent infiltration speed and dispersion ability of large and small particles. The present application provides a positive electrode slurry and a preparation method thereof, a positive electrode sheet and a battery to improve the homogenization effect.

[0005] In a first aspect, the present application provides a method for preparing a positive electrode slurry, wherein the positive electrode slurry comprises a positive electrode active material, a conductive agent, a binder and a solvent; the positive electrode active material comprises a first positive electrode active material and a second positive electrode active material; the particle size of the first positive electrode active material is greater than the particle size of the second positive electrode active material;

[0006] The method for preparing the positive electrode slurry comprises the following steps:

[0007] Step S1: Dry-mix the first positive electrode active material, 10 wt% - 90 wt% of the second positive electrode active material, a conductive agent, and a binder to obtain a first mixture;

[0008] Step S2: Disperse the first mixture obtained in Step S1 in a solvent to obtain a second mixture;

[0009] Step S3: Mix the second mixture obtained in Step S2 with the remaining second positive electrode active material to obtain a third mixture;

[0010] Step S4: Add a solvent to the third mixture to obtain a positive electrode paste.

[0011] In an optional embodiment, based on the total mass of the positive electrode active material being 100 wt%, the mass ratio of the first positive electrode active material is 5 wt% - 95 wt%; preferably 40 wt% - 60 wt%, and the mass ratio of the second positive electrode active material is 5 wt% - 95 wt%; preferably 40 wt% - 60 wt%.

[0012] In an optional embodiment, the D50 particle size of the first positive electrode active material is 2 - 8 μm, and the D50 particle size of the second positive electrode active material is 0.5 - 2 μm; preferably, the D50 particle size of the first positive electrode active material is 3 - 4 μm, and the D50 particle size of the second positive electrode active material is 0.8 - 1.2 μm.

[0013] In an optional embodiment, the ratio of the D50 particle size of the first positive electrode active material to the D50 particle size of the second positive electrode active material is 3:1 - 4:1.

[0014] In an optional embodiment, the first positive electrode active material or the second positive electrode active material includes one or more of a ternary positive electrode material, lithium manganate material (LiMn2O4), lithium nickel manganate material (LiNiO2), lithium iron phosphate material (LFP), and lithium manganese iron phosphate material;

[0015] Preferably, the ternary positive electrode material includes a nickel-containing ternary positive electrode material; more preferably, the molecular formula of the nickel-containing ternary positive electrode material is LiNi x M 1-x O2, 0 < x < 1, and M is selected from at least two elements of Co, Mn, and Al;

[0016] Preferably, the molecular formula of the lithium manganese iron phosphate is LiMn a Fe 1-a PO4, 0 < a < 1;

[0017] Preferably, the lithium nickel manganate material has the following molecular formula: LiMn 2-xNi x O4, where 0≤x≤0.3.

[0018] In an optional embodiment, the conductive agent includes one or more of conductive graphite, graphene, acetylene black, carbon black, and carbon nanotubes; and / or the binder includes one or more of oil-based polyvinylidene fluoride, water-based polytetrafluoroethylene, sodium carboxymethyl cellulose, chitosan, sodium lignocellulose, styrene-butadiene rubber, styrene-acrylic rubber, sodium polymethacrylate, lithium polymethacrylate, and polymethacrylate.

[0019] In an optional embodiment, in the positive electrode slurry, the mass ratio of the positive electrode active material, the conductive agent and the binder is 95-98.4:0.5-2:1.0-2.5.

[0020] In an optional embodiment, the theoretical solid content of the second mixture is 70-85%.

[0021] In an optional embodiment, the step S2 or step S3 further comprises the step of mixing other additives into the first mixture obtained in step S1 or the second mixture obtained in step S2;

[0022] Preferably, the other additives include a dispersant; more preferably, the dispersant includes one or more of polyacrylate polymers, polymethacrylate grafted polyacrylonitrile, polyester polymers, and polyphosphate polymers;

[0023] Preferably, the dispersant accounts for 0.1-0.5% of the total mass of dry matter in the positive electrode slurry.

[0024] In an optional embodiment, the step S2 further comprises kneading the first mixture with a solvent to obtain a kneaded product having a theoretical solid content of 79-90% before dispersing, and then dispersing the kneaded product in a solvent to obtain a second mixture;

[0025] Preferably, the kneading process is carried out under stirring at a speed of 100-300 r / min for 30-60 min;

[0026] Preferably, the dispersion process is carried out under stirring at a rotation speed of 500-4000 r / min for a time of 30-90 min.

[0027] In an optional embodiment, in the step S3, the mixing is carried out under stirring at 500-4000 r / min for 30-90 min; and / or, in the step S1, the mixing is carried out under stirring at 500-4000 r / min for 10-60 min.

[0028] In an optional embodiment, in step S1, the second positive electrode active material used is 20 wt%-40 wt% of the second positive electrode active material used in the entire positive electrode slurry.

[0029] In a second aspect, the present application provides a positive electrode slurry, wherein the positive electrode slurry comprises at least one of the positive electrode slurries prepared by the preparation method described in the first aspect of the present application;

[0030] Preferably, the theoretical solid content of the positive electrode slurry is 60-75%.

[0031] In a third aspect, the present application provides a positive electrode sheet, which is formed by coating the positive electrode slurry described in the second aspect of the present application on a positive electrode current collector and then drying it.

[0032] In a fourth aspect, the present application provides a battery, comprising the positive electrode sheet described in the third aspect of the present application.

[0033] In a fifth aspect, the present application provides an electrical device, comprising the battery described in the fourth aspect of the present application.

[0034] The technical solution of this application has the following advantages:

[0035] The present application provides a method for preparing a positive electrode slurry, the positive electrode slurry comprising a positive electrode active material, a conductive agent, a binder and a solvent; the positive electrode active material comprises a first positive electrode active material and a second positive electrode active material; the particle size of the first positive electrode active material is larger than the particle size of the second positive electrode active material; the method for preparing the positive electrode slurry comprises the following steps: step S1: dry-mixing the first positive electrode active material, 10wt%-90wt% of the second positive electrode active material, the conductive agent and the binder to obtain a first mixture; step S2: dispersing the first mixture obtained in step S1 in a solvent to obtain a second mixture; step S3: mixing the second mixture obtained in step S2 with the remaining second positive electrode active material to obtain a third mixture; step S4, adding a solvent to the third mixture to obtain a positive electrode slurry. In the present application, by adding a first positive electrode active material with a larger particle size and a portion of a second positive electrode active material with a smaller particle size, a conductive agent, and a binder in step S1, the surface energy of the materials can be utilized after dry mixing, so that the binder dry powder and the second positive electrode active material pre-coat the first positive electrode active material, which is beneficial to the direct physical contact between the second positive electrode active material and the first positive electrode active material, and is also beneficial to the dispersion of the second positive electrode active material, effectively reducing the self-agglomeration of the second positive electrode active material. By adding the solvent in step S2, the solvent molecules interact with the binder to effectively wet the surface of the first positive electrode active material, which is manifested as the binder dissolving, and the second positive electrode active material coating the first positive electrode active material to form a better dispersed state; then in step S3, the remaining part of the second positive electrode active material is added, and the second positive electrode active material interacts with the surface part of the first positive electrode active material that is not coated by the second positive electrode active material during the premixing and dispersion process, so as to achieve a complete coating effect on the surface of the first positive electrode active material particles, so that the homogenization effect of the positive electrode slurry is greatly improved, the process flow is simple, and the process time is effectively controlled, thereby significantly reducing the impedance of the battery including the positive electrode active material and significantly improving the electrical performance of the battery.

[0036] Additional aspects and advantages of the embodiments of the present application will be described and shown in part in the subsequent description, or explained through the implementation of the embodiments of the present application. DETAILED DESCRIPTION

[0037] The following examples are provided for a better understanding of the present application, but are not limited to the best implementation mode described, and do not limit the content and protection scope of the present application. Any product identical or similar to the present application obtained by anyone under the inspiration of the present application or by combining the features of the present application with other prior arts shall fall within the protection scope of the present application.

[0038] In the description of the present application, it should be noted that the terms "inside", "outside", etc. indicating the orientation or positional relationship are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present application. In addition, the terms "first", "second", and "third" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0039] If no specific experimental steps or conditions are specified in the examples, the conventional experimental steps or conditions described in the literature in the field can be used. If no manufacturer is specified for the reagents or instruments used, they are all conventional reagent products that can be obtained commercially.

[0040] In addition, the technical features involved in the different embodiments of the present application described below can be combined with each other as long as they do not conflict with each other.

[0041] The present application provides a method for preparing a positive electrode slurry, wherein the positive electrode slurry comprises a positive electrode active material, a conductive agent, a binder and a solvent; the positive electrode active material comprises a first positive electrode active material and a second positive electrode active material; wherein the particle size of the first positive electrode active material is greater than the particle size of the second positive electrode active material;

[0042] The method for preparing the positive electrode slurry comprises the following steps:

[0043] Step S1: mixing a first positive electrode active material, 10 wt% to 90 wt% of a second positive electrode active material, a conductive agent and a binder to obtain a first mixture;

[0044] Step S2: dispersing the first mixture obtained in step S1 in a solvent to obtain a second mixture;

[0045] Step S3: mixing the second mixture obtained in step S2 with the remaining second positive electrode active material to obtain a third mixture;

[0046] Step S4, adding or not adding a solvent to the third mixture to obtain a positive electrode slurry.

[0047] In the present application, by adding a first positive electrode active material with a larger particle size and a portion of a second positive electrode active material with a smaller particle size, a conductive agent, and a binder in step S1, the surface energy of the materials can be utilized after dry mixing, so that the binder dry powder and the second positive electrode active material pre-coat the first positive electrode active material, which is beneficial to the direct physical contact between the second positive electrode active material and the first positive electrode active material, and is also beneficial to the dispersion of the second positive electrode active material, effectively reducing the self-agglomeration of the second positive electrode active material. By adding the solvent in step S2, the solvent molecules interact with the binder to effectively wet the surface of the first positive electrode active material, which is manifested as the binder dissolving, and the second positive electrode active material coating the first positive electrode active material to form a better dispersed state; then in step S3, the remaining part of the second positive electrode active material is added, and the second positive electrode active material interacts with the surface part of the first positive electrode active material that is not coated by the second positive electrode active material during the premixing and dispersion process, so as to achieve a complete coating effect on the surface of the first positive electrode active material particles, so that the homogenization effect of the positive electrode slurry is greatly improved, the process flow is simple, and the process time is effectively controlled, thereby significantly reducing the impedance of the battery including the positive electrode active material and significantly improving the electrical performance of the battery.

[0048] "10wt%-90wt% of the second positive electrode active material" means that the second positive electrode active material added in step S1 is the mass proportion of the second positive electrode active material used in the entire positive electrode slurry, which affects the coating of the second positive electrode active material to the first positive electrode active material, and is manifested as the solid content and fineness of the slurry obtained in the final stage of homogenization. Controlling within this range can achieve better coating of the first positive electrode active material by the second positive electrode active material, and at the same time reserve a bonding site for the binder on the surface of the first positive electrode active material. Adding more than 90wt% of the second positive electrode active material in step S1 is likely to cause the second positive electrode active material added in step S1 to self-agglomerate, and adding less than 10wt% of the second positive electrode active material in step S1 is likely to cause the second positive electrode active material added in step S3 to self-agglomerate, which is not conducive to the uniform coating of the first material by the second positive electrode active material and the uniform dispersion of the second positive electrode active material. For example, the mass proportion of the second positive electrode active material added in step S1 is 10wt%, 20wt%, 30wt%, 50wt%, 70wt%, 90wt%, etc.

[0049] In an optional embodiment, based on the total mass of the positive electrode active material being 100wt%, the mass proportion of the first positive electrode active material is 5wt%-95wt%; preferably 40wt%-60wt%, and the mass proportion of the second positive electrode active material is 5wt%-95wt%; preferably 40wt%-60wt%. The higher the proportion of the first positive electrode active material, the lower the proportion of the second positive electrode active material, which will cause a large amount of space to remain in the pole piece structure after the second positive electrode active material is laminated to the first positive electrode active material, affecting the compaction and improvement effect of the pole piece, which is not conducive to the battery energy improvement goal. Excessive second positive electrode active material will cause the remaining second positive electrode active material to self-agglomerate after the second positive electrode active material is coated and laminated to the first positive electrode active material, which is manifested as poor homogenization, poor coating effect and reduced electrical performance. Therefore, in order to improve the energy density, cost control, and rate / low temperature performance of lithium batteries, a relatively complete conductive network should be formed in the pole piece structure to achieve uniform dispersion of the first and second positive electrode active materials and close fit between the first and second positive electrode active materials. The mass proportion of the first positive electrode active material should be controlled to be 5wt%-95wt%; preferably 40wt%-60wt%, and the mass proportion of the second positive electrode active material should be controlled to be 5wt%-95wt%; preferably 40wt%-60wt%. For example, the mass proportions of the first positive electrode active material and the second positive electrode active material are 5% and 95%; 25% and 75%; 40% and 60%; 50% and 50%; 60% and 40%; 75% and 25%, etc.; 95% and 5%.

[0050] In an alternative embodiment, the D50 particle size of the first positive electrode active material is 2 - 8 μm, and the D50 particle size of the second positive electrode active material is 0.5 - 2 μm; preferably, the D50 particle size of the first positive electrode active material is 3 - 4 μm, and the D50 particle size of the second positive electrode active material is 0.8 - 1.2 μm. This application is applicable to the case where the particle size of the first positive electrode active material is larger than that of the second positive electrode active material. When the particle size of the first positive electrode active material is too small (D50 < 2 μm) or the particle size of the second positive electrode active material is too large (D50 > 2 μm), the improvement in the material dispersion effect by using the method of this application is reduced, and instead, it will cause an extension of the homogenization process time and an increase in energy consumption. When the first particle size is too large (D50 > 8 μm) or the particle size of the second positive electrode active material is too small (D50 < 0.5 μm), the improvement in the dispersion effect of the second positive electrode active material by using the method of this application is reduced. Due to the too large difference in particle size between the second positive electrode active material and the first positive electrode active material, the fitting area between the first positive electrode active material and the second positive electrode active material is too small, and the self-aggregation of the second positive electrode active material is extremely difficult to avoid. By controlling the particle sizes of the first positive electrode active material and the second positive electrode active material within the above ranges, good fitting between the first and second positive electrode active materials can be achieved, and the fitting area is relatively large, realizing good dispersion of the first and second positive electrode active materials.

[0051] In an alternative embodiment, the first positive electrode active material or the second positive electrode active material includes one or more of a ternary positive electrode material, a lithium manganate material, a lithium nickel manganate material, a lithium iron phosphate material, and a lithium manganese iron phosphate material;

[0052] Preferably, the ternary positive electrode material includes a nickel-containing ternary positive electrode material; more preferably, the nickel-containing ternary positive electrode material has the following molecular formula: LiNi x M 1-x O2, 0 < x < 1, and M is selected from at least two elements of Co, Mn, and Al;

[0053] Preferably, the lithium manganese iron phosphate material has the following molecular formula: LiMn a Fe 1-a PO4, 0 < a < 1;

[0054] Preferably, the lithium nickel manganate material has the following molecular formula: LiMn 2-x Ni x O4, where 0 ≤ x ≤ 0.3.

[0055] In an optional embodiment, the conductive agent includes one or more of conductive graphite, graphene, acetylene black, carbon black, and carbon nanotubes; and / or the binder includes one or more of oil-based polyvinylidene fluoride, water-based polytetrafluoroethylene, sodium carboxymethyl cellulose, chitosan, sodium lignocellulose, styrene-butadiene rubber, styrene-acrylic rubber, sodium polymethacrylate, lithium polymethacrylate, and polymethacrylate.

[0056] In an optional embodiment, in the positive electrode slurry, the mass ratio of the positive electrode active material, the conductive agent and the binder is 95-98.4:0.5-2:1.0-2.5. For example, the mass ratio of the positive electrode active material, the conductive agent and the binder can be 95:2:2.5; 98.4:0.5:1.0; 97:1:2, etc.

[0057] In an optional embodiment, the theoretical solid content of the second mixture is 70-85%. For example, the theoretical solid content of the second mixture is 70%, 75%, 80%, 85%, etc.

[0058] In an optional embodiment, step S2 or step S3 further includes the step of mixing other additives into the first mixture obtained in step S1 or the second mixture obtained in step S2.

[0059] In an optional embodiment, the other additives include a dispersant; more preferably, the dispersant includes one or more of polymethacrylate grafted polyacrylonitrile and polyester polymers. In order to reduce the viscosity of the slurry, increase the solid content, improve the liquid retention capacity, and improve the dispersion performance, a dispersant is used as an additive. For example, polyester polymers include polyacrylates (such as polyethyl acrylate, polypropyl acrylate, etc.), polyphosphates (PPE), etc. Polymethacrylate grafted polyacrylonitrile, such as polymethyl methacrylate grafted polyacrylonitrile and polyethyl methacrylate grafted polyacrylonitrile.

[0060] In an optional embodiment, the dispersant accounts for 0.1-0.5% of the total mass of dry matter in the positive electrode slurry. For example, the dispersant accounts for 0.1%, 0.2%, 0.3%, 0.5%, etc. of the total mass of dry matter in the positive electrode slurry.

[0061] In an optional embodiment, the step S2 further includes kneading the first mixture with a solvent before dispersing to obtain a kneaded product with a theoretical solid content of 79-90%, and then dispersing the kneaded product in a solvent to obtain a second mixture. The kneaded product first formed with the solvent in step S2 is not a necessary step. The kneaded product is dispersed to obtain the second mixture after reaching the kneaded state, which can further increase the dispersion state of the positive electrode slurry and improve the homogenization effect. For example, the theoretical solid content of the kneaded product is 79%, 82%, 85%, 90%, etc.

[0062] In an optional embodiment, the kneading process is carried out under stirring at a speed of 100-300 r / min for 30-60 min. For example, the speed of the kneading process can be 100 r / min, 150 r / min, 200 r / min, 300 r / min, etc.; the time can be 30 min, 40 min, 50 min, 60 min, etc. The kneading at a lower speed and for a longer time can make the wettability of the dry powder reach an excellent state. Controlling within this range can comprehensively achieve the purpose of controllable energy consumption and process time.

[0063] In an optional embodiment, the dispersion process is carried out under stirring at a speed of 500-4000 r / min for 30-90 min. The speed of the dispersion process can be 500 r / min, 1000 r / min, 2000 r / min, 3000 r / min, 400 r / min, etc.; the time can be 30 min, 40 min, 50 min, 60 min, 90 min, etc. The above-mentioned dispersion at a higher speed and a longer dispersion time are conducive to maintaining good fluidity and uniformity of the slurry. Controlling within this range can achieve controllable energy consumption and process duration.

[0064] In an optional embodiment, in step S3, mixing is performed under stirring at 500-4000 r / min for 30-90 min. The mixing speed can be 500 r / min, 1000 r / min, 2000 r / min, 3000 r / min, 4000 r / min, etc.; the time can be 30 min, 40 min, 50 min, 60 min, 90 min, etc. The above-mentioned dispersion at a higher speed and a longer dispersion time are conducive to maintaining good fluidity and uniformity of the slurry. Controlling within this range can achieve controllable energy consumption and process duration.

[0065] In an optional embodiment, in step S1, mixing is performed under stirring at 500-4000 r / min for 10-60 min. The mixing speed can be 500 r / min, 1000 r / min, 2000 r / min, 3000 r / min, 4000 r / min, etc.; the time can be 10 min, 20 min, 30 min, 50 min, 60 min, etc. The above-mentioned dispersion at a higher speed and a longer dispersion time are conducive to maintaining good fluidity and uniformity of the slurry. Controlling within this range can achieve controllable energy consumption and process duration.

[0066] In an optional embodiment, in step S1, the second positive electrode active material used is 20 wt%-40 wt% of the second positive electrode active material used in the entire positive electrode slurry.

[0067] In a second aspect, the present application provides a positive electrode slurry, wherein the positive electrode slurry comprises at least one of the positive electrode slurries prepared by the preparation method described in the first aspect of the present application;

[0068] Preferably, the theoretical solid content of the positive electrode slurry is 60-75%. For example, the theoretical solid content of the positive electrode slurry is 60%, 70%, 75%, etc.

[0069] The first positive electrode active material and the second positive electrode active material of the present application can be purchased from the market, or can be prepared by conventional techniques in the art, such as solid phase sintering, sol-gel method or coprecipitation method.

[0070] In a third aspect, the present application provides a positive electrode sheet, which is formed by coating the positive electrode slurry described in the second aspect of the present application on a positive electrode current collector and then drying it.

[0071] The positive electrode sheet can be prepared by conventional operations in the art. For example, the positive electrode slurry can be coated on the positive electrode current collector, and the positive electrode sheet can be obtained after drying, rolling, cold isostatic pressing or hot isostatic pressing.

[0072] In a fourth aspect, the present application provides a battery, comprising the positive electrode sheet described in the third aspect of the present application.

[0073] In some embodiments, the battery further includes a negative electrode sheet, the negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, the negative electrode film layer including a negative electrode active material.

[0074] In some embodiments, the negative electrode active material may be a negative electrode active material for a battery known in the art. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, silicon-based materials, tin-based materials, lithium titanate, and the like.

[0075] In some embodiments, the battery further includes an electrolyte, which acts as a conductor of ions between the positive electrode and the negative electrode. The present application does not specifically limit the type of electrolyte, and it can be selected according to needs. For example, the electrolyte can be liquid, gel, or all-solid.

[0076] In some embodiments, the battery further includes a separator. The present application has no particular restrictions on the type of separator, and any known porous separator with good chemical stability and mechanical stability can be selected. The material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride.

[0077] In a fifth aspect, the present application provides an electrical device, including the battery described in the fourth aspect of the present application. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0078] The present application is further described in detail below in conjunction with specific examples, which should not be construed as limiting the scope of protection claimed in the present application. In all examples and comparative examples of the present application, the unit wt% represents the mass percentage content.

[0079] Example 1

[0080] The present embodiment provides a positive electrode slurry and a preparation method thereof. Based on the dry matter weight of the positive electrode slurry being 100 wt%, the positive electrode slurry comprises 48.3 wt% of a first positive electrode active material (type: lithium nickel cobalt manganese oxide, molecular formula: LiNi 0.6 Co 0.1 Mn 0.3 O2), 48.3wt% of the second positive electrode active material (type: lithium manganese iron phosphate, molecular formula: LiMn 0.6 Fe 0.4 PO4), 1.5wt% conductive agent (specific type: conductive carbon black), 1.8wt% binder (specific type: PVDF) and 0.1wt% dispersant (specific type: polyethyl acrylate). The particle size D50 of the first positive electrode active material is 5.1μm; the particle size D50 of the second positive electrode active material is 1.2μm.

[0081] Its preparation method is as follows:

[0082] Step S1: All the first positive electrode active material (actual amount 5kg, that is, the weight of the first positive electrode active material used in this step accounts for 48.3% of the dry matter weight of the positive electrode slurry) and 70% of the second positive electrode active material (actual amount 3.5kg, that is, the weight of the second positive electrode active material used in this step accounts for 33.8% of the dry matter weight of the positive electrode slurry) are rapidly stirred with a conductive agent (0.1553kg) and a binder powder (0.186kg) at a speed of 500r / min for 30min, pre-mixed evenly, and a first mixture is obtained.

[0083] Step S2: adding a solvent (NMP, 2.224 kg) and a suspension containing a dispersant (0.069 kg, the solid content of the suspension is 15%, and the solvent is NMP) to the first mixture, slowly stirring at a speed of 150 r / min for 60 min to form a kneading state, and the theoretical solid content is 79.5%, adding a solvent (NMP, 1.745 kg), and quickly dispersing at a speed of 3000 r / min for 90 min to form a second mixture with a theoretical solid content of 68.7%;

[0084] Step S3: adding 30% of the second positive electrode active material (i.e., the weight of the second positive electrode active material used in this step accounts for 14.5% of the dry matter weight of the positive electrode slurry, 1.5 kg), and rapidly dispersing at a rotation speed of 3000 r / min for 90 min;

[0085] Step S4: by adding solvent (NMP, 1.54 kg), adjusting the viscosity of the slurry, detecting the dispersion state of the slurry, reaching the discharge standard, filtering, and discharging, a positive electrode slurry with a theoretical solid content of 65% is obtained.

[0086] Example 2

[0087] The present embodiment provides a positive electrode slurry and a preparation method thereof, which are basically the same as those of Embodiment 1, except that in steps S1 and S3, the amounts of the second positive electrode active material added are different. In step S1 of the present embodiment, 50% of the second positive electrode active material is added (i.e., the weight of the second positive electrode active material used in this step accounts for 24.15% of the dry matter weight of the positive electrode slurry), and in step S3, 50% of the second positive electrode active material is added (i.e., the weight of the second positive electrode active material used in this step accounts for 24.15% of the dry matter weight of the positive electrode slurry).

[0088] Example 3

[0089] The present embodiment provides a positive electrode slurry and a preparation method thereof, which are basically the same as those of Embodiment 1, except that in steps S1 and S3, different amounts of the second positive electrode active material are added. In step S1 of the present embodiment, 30% of the second positive electrode active material is added (i.e., the weight of the second positive electrode active material used in this step accounts for 14.49% of the dry matter weight of the positive electrode slurry), and in step S3, 70% of the second positive electrode active material is added (i.e., the weight of the second positive electrode active material used in this step accounts for 33.81% of the dry matter weight of the positive electrode slurry).

[0090] Example 4

[0091] This embodiment provides a positive electrode slurry and a preparation method thereof, which are basically the same as those of Embodiment 3, except that the stirring time of step S1 is different. The stirring time of this embodiment is 15 minutes.

[0092] Example 5

[0093] This embodiment provides a positive electrode slurry and a preparation method thereof, which are basically the same as those of Embodiment 3, except that the rapid dispersion time of step S3 is different. The rapid dispersion time of this embodiment is 60 minutes.

[0094] Example 6

[0095] The present embodiment provides a positive electrode slurry and a preparation method thereof, which are basically the same as Example 3, except that the mass proportions of the first positive electrode active material and the second positive electrode active material are different. In the present embodiment, taking the dry matter weight of the positive electrode slurry as 100wt%, the mass proportion of the first positive electrode active material is 72.45%, and the mass proportion of the second positive electrode active material is 24.15%.

[0096] Example 7

[0097] The present embodiment provides a positive electrode slurry and a preparation method thereof, which are basically the same as Example 3, except that the mass proportions of the first positive electrode active material and the second positive electrode active material are different. In the present embodiment, taking the dry matter weight of the positive electrode slurry as 100wt%, the mass proportion of the first positive electrode active material is 57.96%, and the mass proportion of the second positive electrode active material is 38.64%.

[0098] Example 8

[0099] The present embodiment provides a positive electrode slurry and a preparation method thereof, which are basically the same as Example 6, except that the mass proportions of the first positive electrode active material and the second positive electrode active material are different. In the present embodiment, taking the dry matter weight of the positive electrode slurry as 100wt%, the mass proportion of the first positive electrode active material is 38.64%, and the mass proportion of the second positive electrode active material is 57.96%.

[0100] Example 9

[0101] The present embodiment provides a positive electrode slurry and a preparation method thereof, which are basically the same as Example 6, except that the mass proportions of the first positive electrode active material and the second positive electrode active material are different. In the present embodiment, taking the dry matter weight of the positive electrode slurry as 100wt%, the mass proportion of the first positive electrode active material is 24.15%, and the mass proportion of the second positive electrode active material is 72.45%.

[0102] Example 10

[0103] The present embodiment provides a positive electrode slurry and a preparation method thereof, which are basically the same as Example 6, except that the mass proportions of the first positive electrode active material and the second positive electrode active material are different. In the present embodiment, taking the dry matter weight of the positive electrode slurry as 100wt%, the mass proportion of the first positive electrode active material is 4.83%, and the mass proportion of the second positive electrode active material is 91.77%.

[0104] Embodiment 11

[0105] This embodiment provides a positive electrode slurry and a preparation method thereof, which are basically the same as Example 7, except that the particle sizes of the first positive electrode active material and the second positive electrode active material are different. In this embodiment, the particle size D50 of the first positive electrode active material is 2.21 μm, and the particle size D50 of the second positive electrode active material is 0.52 μm.

[0106] Example 12

[0107] This embodiment provides a positive electrode slurry and a preparation method thereof, which are basically the same as Example 7, except that the particle size of the first positive electrode active material is different. In this embodiment, the particle size D50 of the first positive electrode active material is 7.4 μm, and the particle size D50 of the second positive electrode active material is 1.74 μm.

[0108] Example 13

[0109] This embodiment provides a positive electrode slurry and a preparation method thereof, which are basically the same as Embodiment 7, except that the particle size of the first positive electrode active material is different from that of the second positive electrode active material. The particle size of the first positive electrode active material: D50 is 3.4 μm. The particle size of the second positive electrode active material: D50 is 1.0 μm.

[0110] Compared with Example 7, the difference is that the particle size D50 of the first positive electrode active material: the particle size D50 of the second positive electrode active material=3.4:1, while in Example 7, the ratio of the particle sizes D50 of the two positive electrode materials is 4.25:1.

[0111] Embodiment 14

[0112] This embodiment provides a positive electrode slurry and a preparation method thereof. Taking the dry matter weight of the positive electrode slurry as 100wt%, the positive electrode slurry includes 57.72wt% of a first positive electrode active material (lithium manganate, molecular formula: LiMn2O4), 38.48wt% of a second positive electrode active material (lithium iron phosphate, molecular formula: LiFePO4), 1.7wt% of a conductive agent (Ketjen black, 0.176kg), 2.0wt% of a binder (PVDF, 0.207kg) and 0.1wt% of a dispersant (specific type: commercially available polyacrylate dispersant). The particle size D50 of the first positive electrode active material is 6.8μm; the particle size D50 of the second positive electrode active material is 1.1μm.

[0113] The preparation method is the same as that of Example 7.

[0114] Embodiment 15

[0115] The present embodiment provides a positive electrode slurry and a preparation method thereof, which are basically the same as Example 7, except that step S2 is different. Step S2 of the present embodiment is to add a solvent (NMP, 3.969 kg) and a suspension containing a dispersant (0.069 kg, the solid content of the suspension is 15%) to the first mixture, and quickly disperse it at a rotation speed of 3000 r / min for 90 minutes to form a second mixture with a theoretical solid content of 68.7%.

[0116] Comparative Example 1

[0117] This comparative example provides a positive electrode slurry and a preparation method thereof, which are basically the same as those of Example 7, except that all the second positive electrode active material is added in step S1, and step S3 is omitted.

[0118] Comparative Example 2

[0119] This comparative example provides a positive electrode slurry and a preparation method thereof, which are basically the same as those in Example 7, except that step S1 is omitted. In step S2, all of the first positive electrode active material (i.e., the weight of the first positive electrode active material used in this step accounts for 57.96% of the dry matter weight of the positive electrode slurry), 70% of the second positive electrode active material (i.e., the weight of the second positive electrode active material used in this step accounts for 27.05% of the dry matter weight of the positive electrode slurry), a conductive agent (0.1553 kg), a binder powder (0.186 kg) and a solvent (NMP, 2.224 kg) are slowly stirred at a speed of 150 r / min for 60 min to form a kneading state, and the theoretical solid content is 79.5%. A solvent (NMP, 1.745 kg) is added, and the mixture is rapidly dispersed at a speed of 3000 r / min for 90 min to form a second mixture with a theoretical solid content of 68.7%. The remaining operations and processes are the same as those in Example 1.

[0120] Test Case

[0121] 1. The viscosity, solid content and scraper fineness of the positive electrode slurries prepared in various embodiments and comparative examples were characterized. The specific results are shown in Table 1.

[0122] Viscosity test: Use a rotational viscometer, use a No. 4 needle, and test at 30r / min.

[0123] Solid content test: Adopt drying method, use fast moisture test instrument, heat to 160℃ at 10℃ / min, and keep until constant weight.

[0124] Test of scraper fineness: Use a scraper fineness meter to measure and record the fineness at the position where particles begin to appear.

[0125] The electrode resistance test: adopt the four-probe method, use the four-probe tester, after the positive electrode is vacuum dried, it is measured at room temperature in a dry environment, the electrode diameter is: 4mm.

[0126] 2. Preparation of batteries and testing of battery internal resistance:

[0127] The positive electrode slurries of the embodiments and comparative examples were used to prepare batteries according to the following methods.

[0128] (1) Preparation of positive electrode sheet: The positive electrode slurry is coated by an extrusion coater (coating speed: 7 m / min), and then prepared into positive electrode sheets through conventional drying (drying temperature: 90°C), cutting, and die-cutting processes;

[0129] (2) Preparation of negative electrode sheet: Graphite, conductive carbon black, negative electrode binder sodium carboxymethyl cellulose and negative electrode binder styrene butadiene rubber are mixed uniformly in a mass ratio of 96.0:1.0:1.2:1.8, and water is added to prepare a negative electrode slurry. The negative electrode sheet is prepared through conventional coating (coating speed: 5 m / min), drying (drying temperature: 70° C.), cutting and die-cutting processes;

[0130] (3) Battery preparation: The positive electrode sheet and the negative electrode sheet as well as the polyethylene organic separator are stacked and subjected to conventional drying (temperature: 100°C, time: 16 h), liquid injection (using commercially available lithium hexafluorophosphate electrolyte), formation, and capacity division processes to prepare a soft-pack lithium-ion battery with a rated capacity of 5 Ah.

[0131] Battery internal resistance test conditions: adjust the capacity to 50% SOC, let it stand for 60 minutes, then discharge at 2C for 10 seconds.

[0132] Table 1 Electrical properties of lithium-ion secondary batteries

[0133]

[0134] In a series of embodiments and comparative examples, in order to ensure the comparability of data, the final designed solid content of all slurries remains consistent, which is 65% theoretical solid content. Due to differences in homogenization processes and different proportions of the first positive electrode active material and the second positive electrode active material, the viscosity, solid content, and fineness of the slurries obtained during the implementation of different embodiments and comparative examples vary.

[0135] It can be seen from Table 1 that compared with Comparative Examples 1 and 2, each embodiment mixes the small-particle second positive electrode active material with the first positive electrode active material in steps, and utilizes the dry mixing process in step S1 to pre-coat the large-particle first positive electrode active material with the small-particle second positive electrode active material and the binder PVDF dry powder, and then adds a solvent for kneading. After the binder PVDF is dissolved, the surface of the large-particle first positive electrode active material still retains sites that can be bonded with the second positive electrode active material. The second positive electrode active material added later can be uniformly coated and surface-bonded with the first positive electrode active material, thereby achieving good dispersibility of the first and second positive electrode active materials.

[0136] The mass proportion of the first positive electrode active material in the positive electrode active material is recorded as C1, and the mass proportion of the second positive electrode active material in the positive electrode active material is recorded as C2. By comparing Examples 1-3, it can be seen that under the condition of C1 / C2=5 / 5, Example 3 in which 30% of the second positive electrode active material is added for the first time in step S1 and 70% of the second positive electrode active material is added in the later batch in step S3 has the best homogenization effect. Compared with Example 1, the viscosity of the slurry obtained in Example 3 can be reduced by 18.6%, the solid content is increased by 1.3%, the fineness is reduced from 65μm to 45μm, the electrode sheet resistance is reduced by 26.9%, and the battery internal resistance is reduced by 18.7%.

[0137] By comparing Example 3 with Examples 4-5, it can be seen that reducing the dry mixing time or the dispersion time after the addition of the later batch C2 will cause the slurry viscosity to increase in a small range (about 6%-8%), but it is still within the conventional positive electrode slurry viscosity range of 5000-8000mPa.s. Therefore, the homogenization process advocated by this patent has the beneficial effects of shortening the process time and reducing energy consumption.

[0138] Comparing Example 3 with Examples 6-10, it can be seen that the homogenization effect is better when 30% of the second positive electrode active material is added for the first time and 70% of the second positive electrode active material is added in the later batches. The total proportion of the first positive electrode active material and the second positive electrode active material has a greater influence on the slurry dispersion effect. It can be seen from Examples 3, 6-10 that Examples 3, 7-8 have the best homogenization effect by adding the second positive electrode active material in a distribution between 40%:60%-60%:40% of the first positive electrode active material / the second positive electrode active material. This is mainly attributed to the fact that in the process of dry mixing of small-particle second positive electrode active materials, more PVDF contact sites can be reserved on the surface of large-particle first positive electrode active materials, while avoiding the self-agglomeration of small-particle second positive electrode active materials in the subsequent kneading process, so that the second positive electrode active material particles can form a more complete coating on the first positive electrode active material particles, and the improvement effect on the slurry is better. Compared with Example 3, the best Example 7 has a 2.3% decrease in the pole sheet resistance.

[0139] Comparing Example 7 with Examples 11-13, it can be seen that too small a particle size of the second positive electrode active material D50 or too large a particle size of the first positive electrode active material D50 will result in limited improvement in slurry and improvement in electrode sheet resistance and battery resistance. However, Example 13 controls the particle size D50 of the first positive electrode active material and the particle size D50 of the second positive electrode active material and the particle size ratio within the preferred range, showing significantly lower electrode sheet resistance and battery internal resistance than Example 7 (the particle size ratio of the first positive electrode active material D50 to the second positive electrode active material D50 is 4.25:1).

[0140] By comparing Example 7 with Example 14, it can be seen that when the type of positive electrode material and the proportion of each substance in the positive electrode (the proportion of PVDF binder and conductive agent is different) are changed, the slurry still exhibits the characteristics of high solid content and low fineness, and the electrode sheet resistance is low.

[0141] Comparing Example 7 with Example 15, it can be seen that in the slurry preparation process of the present application, the first mixture is kneaded with the solvent before dispersion to obtain a kneaded product with a theoretical solid content of 70-85%, and the positive electrode slurry obtained has lower electrode sheet resistance and battery internal resistance. A large amount of solvent can also be added in step S2, and the dispersion is directly performed without the kneading process. In this process, the electrode sheet resistance and battery internal resistance are increased to a certain extent.

[0142] Comparing Example 7 with Comparative Example 1, it can be seen that the preparation method of the positive electrode slurry provided by the present application has obvious advantages over the conventional method of directly mixing all the first and second positive electrode active materials. The significantly lower solid content in Comparative Example 1 should be attributed to the uneven dispersion of the materials, which caused a certain degree of slurry agglomeration, thereby causing slurry sedimentation, and the slurry fineness prepared in Comparative Example 1 reached 70μm, with obvious agglomeration; the pole sheet resistance of Comparative Example 1 increased by nearly 60% compared with Example 7, causing the battery internal resistance to increase by 42%.

[0143] Comparing Example 7 with Comparative Example 2, it can be seen that the present application is based on the dry-mixed pre-coating strategy of the first positive electrode active material with the conductive agent, the binder powder and part of the second positive electrode active material, which has significant advantages in improving the slurry dispersion effect compared with the wet premixing of the first positive electrode active material and part of the second positive electrode active material in Comparative Example 2. This is mainly due to the wet premixing of the first and second positive electrode active materials in Comparative Example 2, and the lack of clear binding force between the first and second positive electrode active materials, which improves the slurry dispersion effect much less than Example 7. Compared with Comparative Example 2, the electrode sheet resistance prepared in Example 7 is reduced by 32%, and the battery internal resistance is reduced by 25.5%.

[0144] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the scope of protection created by this application.

Claims

1. A method for preparing a positive electrode slurry, characterized in that: The positive electrode slurry comprises a positive electrode active material, a conductive agent, a binder and a solvent; the positive electrode active material comprises a first positive electrode active material and a second positive electrode active material; the particle size of the first positive electrode active material is larger than the particle size of the second positive electrode active material; The method for preparing the positive electrode slurry comprises the following steps: Step S1: dry-mixing a first positive electrode active material, 10 wt% to 90 wt% of a second positive electrode active material, a conductive agent and a binder to obtain a first mixture; Step S2: dispersing the first mixture obtained in step S1 in a solvent to obtain a second mixture; Step S3: mixing the second mixture obtained in step S2 with the remaining second positive electrode active material to obtain a third mixture; Step S4, adding a solvent to the third mixture to obtain a positive electrode slurry.

2. The method for preparing the positive electrode slurry according to claim 1, characterized in that: Based on the total mass of the positive electrode active material being 100wt%, the mass proportion of the first positive electrode active material is 5wt%-95wt%; preferably 40wt%-60wt%, and the mass proportion of the second positive electrode active material is 5wt%-95wt%; preferably 40wt%-60wt%.

3. The method for preparing the positive electrode slurry according to claim 1 or 2, characterized in that: The particle size D50 of the first positive electrode active material is 2-8 μm, and the particle size D50 of the second positive electrode active material is 0.5-2 μm; preferably, the particle size D50 of the first positive electrode active material is 3-4 μm, and the particle size D50 of the second positive electrode active material is 0.8-1.2 μm.

4. The method for preparing the positive electrode slurry according to any one of claims 1 to 3, characterized in that: The ratio of the particle size D50 of the first positive electrode active material to the particle size D50 of the second positive electrode active material is 3-10:1, preferably 3-4:

1.

5. The method for preparing the positive electrode slurry according to any one of claims 1 to 4, characterized in that: The first positive electrode active material or the second positive electrode active material comprises one or more of a ternary positive electrode material, a lithium manganese oxide material, a lithium nickel manganese oxide material, a lithium iron phosphate material, and a lithium manganese iron phosphate material; Preferably, the ternary cathode material includes a nickel-containing ternary cathode material; more preferably, the nickel-containing ternary cathode material has the following molecular formula: LiNi x M 1-x O2, where 0 < x < 1, and M is selected from at least two elements of Co, Mn, and Al; Preferably, the lithium iron manganese phosphate material has the following molecular formula: LiMn a Fe 1-a PO4,0 <a<1; Preferably, the lithium nickel manganese oxide material has the following molecular formula: LiMn 2-x Ni x O4, where 0≤x≤0.

3.

6. The method for preparing the positive electrode slurry according to any one of claims 1 to 5, characterized in that: The conductive agent includes one or more of conductive graphite, graphene, acetylene black, carbon black, and carbon nanotubes; and / or the binder includes one or more of oil-based polyvinylidene fluoride, water-based polytetrafluoroethylene, sodium carboxymethyl cellulose, chitosan, sodium lignocellulose, styrene-butadiene rubber, styrene-acrylic rubber, sodium polymethacrylate, lithium polymethacrylate, and polymethacrylate.

7. The method for preparing the positive electrode slurry according to any one of claims 1 to 6, characterized in that: In the positive electrode slurry, the mass ratio of the positive electrode active material, the conductive agent and the binder is 95-98.4:0.5-2:1.0-2.

5.

8. The method for preparing the positive electrode slurry according to any one of claims 1 to 7, characterized in that: The theoretical solid content of the second mixture is 70-85%.

9. The method for preparing the positive electrode slurry according to any one of claims 1 to 8, characterized in that: The step S2 or step S3 further includes the step of mixing other additives into the first mixture obtained in step S1 or the second mixture obtained in step S2; Preferably, the other additives include a dispersant; more preferably, the dispersant includes one or more of polymethacrylate grafted polyacrylonitrile and polyester polymers; Preferably, the dispersant accounts for 0.1-0.5% of the total mass of dry matter in the positive electrode slurry.

10. The method for preparing the positive electrode slurry according to any one of claims 1 to 9, characterized in that: In the step S2, before dispersing, the first mixture is kneaded with a solvent to obtain a kneaded product with a theoretical solid content of 79-90%, and then the kneaded product is dispersed in a solvent to obtain a second mixture; Preferably, the kneading process is carried out under stirring at a speed of 100-300 r / min for 30-60 min; Preferably, the dispersion process is carried out under stirring at a rotation speed of 500-4000 r / min for a time of 30-90 min.

11. The method for preparing the positive electrode slurry according to any one of claims 1 to 10, characterized in that: In the step S3, the mixing is carried out under stirring at 500-4000 r / min for 30-90 min; and / or, in the step S1, the mixing is carried out under stirring at 500-4000 r / min for 10-60 min.

12. The method for preparing the positive electrode slurry according to any one of claims 1 to 11, characterized in that: In step S1, the second positive electrode active material used is 20 wt%-40 wt% of the second positive electrode active material used in the entire positive electrode slurry.

13. A positive electrode slurry, characterized in that: The positive electrode slurry comprises at least one of the positive electrode slurries prepared by the preparation method according to any one of claims 1 to 12; Preferably, the theoretical solid content of the positive electrode slurry is 60-75%.

14. A positive electrode sheet, characterized in that: The positive electrode slurry according to claim 13 is coated on the positive electrode current collector and then dried.

15. A battery, characterized in that: Including the positive electrode sheet as described in claim 14.

16. An electrical device, characterized in that: Comprising the battery of claim 15.

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