WO2024239692A1 - 一种复合正极片及其制备方法以及包括其的锂离子电池 - Google Patents

一种复合正极片及其制备方法以及包括其的锂离子电池 Download PDF

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WO2024239692A1
WO2024239692A1 PCT/CN2024/073479 CN2024073479W WO2024239692A1 WO 2024239692 A1 WO2024239692 A1 WO 2024239692A1 CN 2024073479 W CN2024073479 W CN 2024073479W WO 2024239692 A1 WO2024239692 A1 WO 2024239692A1
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coating layer
positive electrode
slurry
particle size
electrode sheet
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French (fr)
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WO2024239692A9 (zh
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谢炎崇
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Xiamen Hithium Energy Storage Technology Co Ltd
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Xiamen Hithium Energy Storage Technology Co Ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/136—Electrodes based on inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/04—Processes of manufacture in general
    • H01M4/0402—Methods of deposition of the material
    • H01M4/0404—Methods of deposition of the material by coating on electrode collectors
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/139—Processes of manufacture
    • H01M4/1397—Processes of manufacture of electrodes based on inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/5825—Oxygenated metallic salts or polyanionic structures, e.g. borates, phosphates, silicates, olivines
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/028—Positive electrodes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present application belongs to the field of energy storage technology, and specifically relates to a composite positive electrode sheet and a preparation method thereof, and a lithium-ion battery including the composite positive electrode sheet.
  • Lithium-ion batteries have a high safety factor, a long service life, and a wide range of application prospects.
  • the performance and structure of the positive electrode of lithium-ion batteries have an important impact on the overall performance of lithium-ion batteries.
  • the specific preparation method is as follows: 1 Premixing: Add the main material of the slurry into the mixer for stirring and premixing to obtain a mixture; 2 Wetting: Under vacuum conditions, according to 65% to 70% solid content, stir and disperse the mixture with an organic solvent; 3 High-speed dispersion: Add an organic solvent and stir and disperse at high speed under vacuum conditions to obtain a mixed slurry; 4 Sieving: Sieve the mixed slurry obtained in the high-speed dispersion step to remove large particles to obtain a positive electrode slurry.
  • the present application provides a composite positive electrode sheet with excellent electrochemical performance and capacity performance and a preparation method thereof.
  • the present application provides a positive electrode sheet, characterized in that the positive electrode sheet comprises a current collector and an active material layer; the active material layer comprises a coating layer A, a coating layer B and a coating layer C; the coating layer A is arranged on the surface of the current collector, the coating layer B is arranged on the surface of the coating layer A, and the coating layer C is arranged on the surface of the coating layer B;
  • the median particle size Dv50 of the positive electrode active material of the coating layer A is ⁇ the median particle size Dv50 of the positive electrode active material of the coating layer C ⁇ the median particle size Dv50 of the positive electrode active material of the coating layer B, wherein the active material is a common positive electrode active material in the art, such as lithium manganese iron phosphate, lithium iron phosphate, lithium vanadium phosphate, lithium cobalt phosphate, etc.
  • the present application adopts a positive electrode sheet with a three-layer structure, and controls the size relationship of the median particle sizes of the coating layer A, the coating layer B and the coating layer C, that is, the particle sizes of the coating layer A and the coating layer C are smaller than the particle size of the middle coating layer B;
  • the coating layer A and the coating layer C use small particles, so that the material properties can be fully utilized, such as shortening the lithium ion migration path, reducing electrochemical polarization, and improving the capacity performance of the lithium battery;
  • the coating layer B uses large particles to increase the compaction density of the electrode sheet, and the gaps between large particles are larger than those between small particles, which is beneficial to the infiltration of the electrolyte into the interior of the electrode sheet and is beneficial to the electrochemical performance of the lithium battery.
  • Another object of the present application is to provide a method for preparing the positive electrode sheet of the present application, which specifically comprises the following steps:
  • step (2) coating the positive electrode slurry 2 on the surface of the coating layer A of the coating layer A/current collector composite structure obtained in step (1), vacuum drying, and rolling to obtain a coating layer B/coating layer A/current collector composite structure;
  • step (3) coating the positive electrode slurry 3 on the surface of the coating layer B of the coating layer B/coating layer A/current collector composite structure obtained in step (2), vacuum drying, and rolling to obtain the positive electrode sheet;
  • the median particle size Dv50 of the positive electrode slurry 1 is less than or equal to the median particle size Dv50 of the positive electrode slurry 3 and less than the median particle size Dv50 of the positive electrode slurry 2.
  • the present application adopts a positive electrode sheet with a three-layer active material layer structure and adjusts the size and relationship of its active material particles to prepare a positive electrode sheet with excellent electrochemical performance and capacity performance. And by optimizing the pulping process of the positive electrode material, the problems of raw material waste and high economic cost in the pulping process of the prior art are solved.
  • FIG1 is a schematic diagram of the pulping process of lithium iron manganese phosphate of the present application.
  • FIG2 is a schematic diagram of the structure of the composite positive electrode sheet of the present application.
  • FIG3 is a SEM image of the particle morphology of the lithium iron manganese phosphate powder in Example 1, wherein a) shows a normal-sized particle powder, and b) shows an unbroken large particle powder;
  • FIG4 is a physical picture of a portion of the large-particle powder slurry sieved in step 3 of Example 1;
  • FIG5 is a particle size distribution diagram of positive electrode slurries C and D prepared in Example 1;
  • FIG6 is a diagram showing the particle morphology and distribution of the cross section of the positive electrode sheet prepared in Example 1, wherein FIGa) shows the cross section of coating layer A; and FIGb) shows the cross section of coating layer B.
  • any matters or items not mentioned are directly applicable to matters known in the art without any changes.
  • any embodiment described herein can be freely combined with one or more other embodiments described herein, and the technical solutions or technical ideas formed thereby are regarded as part of the original disclosure or original record of this application, and should not be regarded as new contents not disclosed or anticipated herein, unless a person skilled in the art considers that the combination is obviously unreasonable.
  • the present application provides a positive electrode sheet, characterized in that the positive electrode sheet comprises a current collector and an active material layer; the active material layer comprises a coating layer A, a coating layer B and a coating layer C; the coating layer A is arranged on the surface of the current collector, the coating layer B is arranged on the surface of the coating layer A, and the coating layer C is arranged on the surface of the coating layer B;
  • the median particle size Dv50 of the positive electrode active material of the coating layer A is ⁇ the median particle size Dv50 of the positive electrode active material of the coating layer C ⁇ the median particle size Dv50 of the positive electrode active material of the coating layer B, wherein the active material is a common positive electrode active material in the art, such as lithium manganese iron phosphate, lithium iron phosphate, lithium vanadium phosphate, lithium cobalt phosphate, etc.
  • the present application adopts a positive electrode sheet with a three-layer structure, and controls the size relationship of the median particle sizes of the coating layer A, the coating layer B and the coating layer C, that is, the particle sizes of the coating layer A and the coating layer C are smaller than the particle size of the middle coating layer B;
  • the coating layer A and the coating layer C use small particles, so that the material properties can be fully utilized, such as shortening the lithium ion migration path, reducing electrochemical polarization, and improving the capacity performance of the lithium battery;
  • the coating layer B uses large particles to increase the compaction density of the electrode sheet, and the gaps between large particles are larger than those between small particles, which is beneficial to the infiltration of the electrolyte into the interior of the electrode sheet and is beneficial to the electrochemical performance of the lithium battery.
  • the median particle size Dv50 of the positive electrode active material of the coating layer A is equal to the median particle size Dv50 of the positive electrode active material of the coating layer C.
  • the median particle size of the positive electrode active material of the coating layer A is The median particle size Dv50 of the positive electrode active material of the coating layer C is 0.4 ⁇ m-0.6 ⁇ m, and the median particle size Dv50 of the positive electrode active material of the coating layer B is 0.8 ⁇ m-1 ⁇ m.
  • the three-layer structure of the positive electrode sheet adopts a smaller particle size, that is, all within 1 ⁇ m, which can significantly improve the capacity performance of the battery compared to a large-size structure.
  • the ratio of the compaction density of the coating layer A to the coating layer B is 1:(1-1.5); the ratio of the compaction density of the coating layer C to the coating layer B is 1:(1-1.5).
  • the ratio of the compaction density of the coating layer B to the coating layer A is 1.3:1.
  • the ratio of the compaction density of the coating layer C to the coating layer A is 1:1.
  • the thickness of the coating layer B is 20 ⁇ m-60 ⁇ m.
  • the thickness of the coating layer B is 50 ⁇ m.
  • the capacity performance of the positive electrode sheet can be further improved by adjusting the thickness of the coating layer B.
  • the coating layer A has a thickness of 10 ⁇ m-30 ⁇ m, preferably 30 ⁇ m.
  • the thickness of the coating layer C is 10 ⁇ m-30 ⁇ m, preferably 30 ⁇ m.
  • the current collector is an aluminum foil having a thickness of 10-20 ⁇ m, preferably 16 ⁇ m.
  • Another object of the present application is to provide a method for preparing the positive electrode sheet of the present application, which specifically comprises the following steps:
  • step (2) coating the positive electrode slurry 2 on the surface of the coating layer A of the coating layer A/current collector composite structure obtained in step (1), vacuum drying, and rolling to obtain a coating layer B/coating layer A/current collector composite structure;
  • the median particle size Dv50 of the positive electrode slurry 1 is less than or equal to the median particle size Dv50 of the positive electrode slurry 3 and less than the median particle size Dv50 of the positive electrode slurry 2.
  • the vacuum drying temperature in each of the above steps is independently 120° C. to 180° C., preferably 150° C.; the vacuum drying time is independently 8 h to 12 h, preferably 10 h.
  • the rolling equipment is a roller press.
  • the positive electrode slurry of the present application is prepared by a method comprising the following steps:
  • Ball milling premixing The positive electrode active material, the conductive agent and the binder are loaded into a ball mill for ball milling premixing to obtain a mixed material, wherein the positive electrode active material accounts for 90-97wt%, the conductive agent accounts for 1-5wt%, and the binder accounts for 2-5wt%;
  • step S2 wetting and ball milling: adding an organic solvent to the mixed material obtained in step S1, and performing ball milling dispersion treatment to obtain a dispersed mixed material, wherein the organic solvent is N-methylpyrrolidone (NMP);
  • NMP N-methylpyrrolidone
  • step S3 sieving: filtering the dispersed mixed material obtained in step S2 through a 180-mesh sieve to remove the large-particle powder slurry, which is mixed slurry A; the rest is mixed slurry B;
  • high-speed dispersion the treated mixed slurry A and 20% mixed slurry B are combined in a stirring tank, and the slurry is fully dispersed by high-speed stirring and dispersion; 80% mixed slurry B is also treated in the same high-speed stirring manner, wherein the conditions of the high-speed stirring are: revolution speed 50 rpm, dispersion speed 25 m/s;
  • the particle size of the obtained positive electrode slurry can be adjusted by adjusting the rotation speed and time of ball milling and the rotation speed and time of dispersion.
  • step S1 the ball milling step is performed in a ball mill.
  • the process is carried out, wherein the ball mill of the ball mill is one or more of a ceramic ball mill, an agate ball mill, and a polyurethane ball mill; and the ball mill beads are made of one or more of a zirconia ball and a polyurethane ball.
  • the conductive agent is any one or more of conductive carbon black, graphene, carbon nanotubes, and Ketjen black; and the binder is polyvinylidene fluoride (PVDF).
  • PVDF polyvinylidene fluoride
  • Another object of the present application is to provide an energy storage device, which includes the above-mentioned positive electrode sheet or the positive electrode sheet prepared by the above-mentioned preparation method.
  • the energy storage device is a secondary battery.
  • FIG1 A specific preparation process of the positive electrode slurry of the present application is shown in FIG1 , and includes the following steps:
  • Ball milling premixing The positive electrode active material such as lithium manganese iron phosphate accounting for about 90-97%, the conductive agent accounting for about 1-5%, and the binder accounting for about 2-5% are sequentially loaded into a ball mill for ball milling premixing to obtain a mixed material, wherein the ball milling jar of the ball mill is one or more of a ceramic ball milling jar, an agate ball milling jar, and a polyurethane ball milling jar; the ball milling beads are made of one or more of zirconia balls and polyurethane balls; the conductive agent is any one or more of conductive carbon black, graphene, carbon nanotubes, and Ketjen black; and the binder is polyvinylidene fluoride (PVDF).
  • PVDF polyvinylidene fluoride
  • NMP N-methylpyrrolidone
  • step 2) The dispersed mixed material obtained in step 2) is filtered through a 180-mesh screen to remove the large-particle powder slurry, i.e., mixed slurry A, and the remaining uniformly mixed slurry is mixed slurry B.
  • Treatment of mixed slurry A crush large particles of powder into smaller ones through low/high speed ball milling to obtain treated mixed slurry A, wherein the rotation speed of the low speed ball mill is 200 rpm to 400 rpm, and the rotation speed of the high speed ball mill is 1200 rpm to 1800 rpm; divide the mixed slurry B into two parts, namely 20% mixed slurry B and 80% mixed slurry B.
  • High-speed dispersion The treated mixed slurry A and 20% mixed slurry B are combined in a double planetary stirring tank, and the slurry is fully dispersed by high-speed stirring and dispersion; 80% mixed slurry B is also treated in the same high-speed stirring manner, wherein the conditions of the high-speed stirring are: revolution speed 50 rpm, dispersion speed 25 m/s.
  • Post-treatment The mixed slurry after high-speed stirring and dispersion is subjected to vacuum degassing, sieving and viscosity testing to obtain positive electrode slurry.
  • the obtained positive electrode can be adjusted. Particle size of the slurry.
  • a specific process flow of the composite positive electrode sheet of the present application includes the following steps:
  • coating layer A First, the positive electrode slurry 1 was coated on a 16 ⁇ m aluminum foil, placed in a vacuum oven, dried at 150° C. for 10 h, and then rolled on a roller press.
  • the coating layer A had a thickness of about 30 ⁇ m and a compaction density of about 1.8 g/cm 3 , thereby obtaining a coating layer A/current collector composite structure;
  • coating layer B Preparation of coating layer B: first, the positive electrode slurry 2 is coated on the coating layer A of the coating layer A/current collector composite structure prepared in step 1, and placed in a vacuum oven, dried at 150°C for 10 hours, and then rolled on a roller press.
  • the thickness of the coating layer B is about 20 ⁇ m, and the compaction density is 1:1 with the coating layer A, i.e., 1.8 g/cm 3 , to obtain a coating layer B/coating layer A/current collector composite structure;
  • Preparation of coating layer C First, the positive electrode slurry 3 is coated on the coating layer B of the coating layer B/coating layer A/current collector composite structure prepared in step 2, and placed in a vacuum oven, dried at 150°C for 10 hours, and then rolled on a roller press.
  • the thickness of the coating layer C is about 30 ⁇ m, and the compaction density is 1:1 with the coating layer A, i.e., 1.8g/ cm3 , to obtain a positive electrode sheet having coating layers A, B, and C.
  • the median particle size Dv50 of the positive electrode slurry 1 is less than or equal to the median particle size Dv50 of the positive electrode slurry 3 and less than the median particle size Dv50 of the positive electrode slurry 2.
  • the positive electrode slurries 1, 2, and 3 can all be prepared by the preparation method described above, wherein the parameters in the preparation process can be adjusted according to the desired particle size, such as the rotation speed and time of ball milling, and the rotation speed and time of dispersion.
  • the particle size of the positive electrode slurry changes little after vacuum drying, the difference between the particle size of the particles in the positive electrode slurry and the particle size of the particles in the corresponding coating layer can be ignored.
  • the slurry of coating layer A and coating layer C can be the same or different, as long as the following conditions are met: the median particle size Dv50 of the positive electrode active material of coating layer A ⁇ the median particle size Dv50 of the positive electrode active material of coating layer C ⁇ the median particle size Dv50 of the positive electrode active material of coating layer B.
  • the specific preparation process of the lithium-ion battery of the present application may include the following steps:
  • the positive and negative electrode discs are placed in a glove box filled with argon protective atmosphere for battery assembly, wherein a solution obtained by dissolving 1 mol/L lithium hexafluorophosphate in a mixed solvent of ethylene carbonate and diethyl carbonate with a molar ratio of 1:1 is used as an electrolyte; the positive electrode disc, the negative electrode disc, the polyethylene diaphragm and other components are assembled together, and then the electrolyte is injected to finally obtain a lithium-ion battery.
  • Ball milling premixing lithium manganese iron phosphate, a conductive agent, and a binder are weighed in a mass ratio of 95%, 2%, and 3%, respectively, and are sequentially loaded into a ball mill for ball milling premixing.
  • the ball milling method is as follows: a rotation speed of 350 rpm, a ball-to-material ratio of 3:1, and a ball milling time of 1 h to obtain a mixed material, wherein the ball milling jar of the ball mill is a ceramic ball milling jar, and the ball milling beads are made of zirconia balls; the conductive agent is conductive carbon black, and the binder is polyvinylidene fluoride (PVDF).
  • PVDF polyvinylidene fluoride
  • the particle morphology of the lithium iron manganese phosphate powder is shown in FIG3 . It can be seen from FIG3 that in addition to the particles of normal size, there are also some large particles that have not been crushed in the lithium iron manganese phosphate powder raw material.
  • NMP N-methylpyrrolidone
  • Treatment of mixed slurry A first use low-speed ball milling (speed 300 rpm, time for 1 h) to disperse the particles, and then use high-speed ball milling (speed 1500 rpm, time for 1 h) to break up the large particles into smaller particles to form a slurry with smaller particle size;
  • Treatment of mixed slurry B divide the mixed slurry into two parts, namely 20% mixed slurry B and 80% mixed slurry B.
  • High-speed dispersion The treated mixed slurry A and 20% mixed slurry B are combined in a double planetary stirring tank, and the slurry is fully dispersed and has a suitable viscosity by high-speed stirring and dispersion (revolution speed of 50 rpm, dispersion speed of 25 m/s, time of 2 h); 80% mixed slurry B is also dispersed in the same manner. High-speed stirring method.
  • Positive electrode slurries C and D were sampled for particle size distribution testing. The results are shown in FIG5 .
  • the particle size Dv50 of positive electrode slurry C is approximately 0.8 ⁇ m-1 ⁇ m, and the particle size Dv50 of positive electrode slurry D is approximately 0.4 ⁇ m-0.6 ⁇ m.
  • Coating layer A and rolling First, the positive electrode slurry D was coated on a 16 ⁇ m aluminum foil and placed in a vacuum oven and dried at 150° C. for 10 h. Then, it was rolled on a roller press. The thickness of the coating layer A was about 30 ⁇ m and the compaction density was about 1.8 g/cm 3 , thereby obtaining a coating layer A/current collector composite structure.
  • Coating layer B and rolling first, the positive electrode slurry C is coated on the coating layer A of the coating layer A/current collector composite structure prepared in step 1, and placed in a vacuum oven, dried at 150°C for 10 hours, and then rolled on a roller press.
  • the thickness of the coating layer B is about 20 ⁇ m, and the compaction density is 1:1 with the coating layer A, i.e., 1.8g/ cm3 , to obtain a coating layer B/coating layer A/current collector composite structure.
  • Coating layer C and rolling First, the positive electrode slurry D is coated on the coating layer B of the coating layer B/coating layer A/current collector composite structure prepared in step 2, and placed in a vacuum oven, dried at 150°C for 10 hours, and then rolled on a roller press.
  • the thickness of the coating layer C is about 30 ⁇ m, and the compaction density is 1:1 with the coating layer A, i.e., 1.8g/ cm3 , to obtain a positive electrode sheet with coating layers A, B, and C.
  • the particle size distributions of the coating layers A, B, and C in the composite positive electrode sheet prepared in this embodiment are 0.4 ⁇ m-0.6 ⁇ m, 0.8 ⁇ m-1 ⁇ m, and 0.4 ⁇ m-0.6 ⁇ m, respectively.
  • the particles of coating layer A are fine and evenly distributed, while the particles of coating layer B are large in size, which is beneficial to improving the compaction density and electrolyte infiltration effect.
  • the compaction density of coating layer B in step 2 of preparing the composite positive electrode sheet is adjusted, and the ratio of the compaction density of coating layer B to coating layer A is changed from 1:1 to 1.1:1, that is, 1.98 g/cm 3 , and the compaction density of coating layer A and coating layer C remain unchanged.
  • the compaction density of coating layer B in step 2 of the preparation of the composite positive electrode sheet was adjusted, and the ratio of the compaction density of coating layer B to coating layer A was changed from 1:1 to 1.2:1, that is, 2.16 g/cm 3 , and the compaction density of coating layer A and coating layer C remained unchanged.
  • the compaction density of coating layer B in step 2 of the preparation of the composite positive electrode sheet was adjusted, and the ratio of the compaction density of coating layer B to coating layer A was changed from 1:1 to 1.3:1, that is, 2.34 g/cm 3 , and the compaction density of coating layer A and coating layer C remained unchanged.
  • the compaction density of coating layer B in step 2 of the preparation of the composite positive electrode sheet was adjusted, and the ratio of the compaction density of coating layer B to coating layer A was changed from 1:1 to 1.4:1, that is, 2.52 g/cm 3 , and the compaction density of coating layer A and coating layer C remained unchanged.
  • the compaction density of coating layer B in step 2 of the preparation of the composite positive electrode sheet was adjusted, and the ratio of the compaction density of coating layer B to coating layer A was changed from 1:1 to 1.5:1, that is, 2.70 g/cm 3 , and the compaction density of coating layer A and coating layer C remained unchanged.
  • the thickness of the coating layer B in step 2 of the preparation of the composite positive electrode sheet is adjusted, and the thickness of the coating layer B is increased from 20 ⁇ m to 30 ⁇ m.
  • the thickness of the coating layer B in step 2 of the preparation of the composite positive electrode sheet is adjusted, and the thickness of the coating layer B is increased from 20 ⁇ m to 40 ⁇ m.
  • the thickness of the coating layer B in step 2 of the preparation of the composite positive electrode sheet is adjusted, and the thickness of the coating layer B is increased from 20 ⁇ m to 50 ⁇ m.
  • the thickness of the coating layer B in step 2 of the preparation of the composite positive electrode sheet is adjusted, and the thickness of the coating layer B is increased from 20 ⁇ m to 60 ⁇ m.
  • Ball milling premixing lithium manganese iron phosphate, a conductive agent, and a binder are weighed in a mass ratio of 95%, 2%, and 3%, respectively, and are sequentially loaded into a ball mill for ball milling premixing.
  • the ball milling method is as follows: a rotation speed of 350 rpm, a ball-to-material ratio of 3:1, and a ball milling time of 1 h to obtain a mixed material, wherein the ball milling jar of the ball mill is a ceramic ball milling jar, and the ball milling beads are made of zirconia balls; the conductive agent is conductive carbon black, and the binder is polyvinylidene fluoride (PVDF).
  • PVDF polyvinylidene fluoride
  • NMP N-methylpyrrolidone
  • High-speed dispersion Add about 0.1% of the dispersant (polyacrylic acid) to the double planetary stirring tank according to the mass ratio of the main material of the slurry, and then add a certain amount of NMP. Through high-speed stirring and dispersion (revolution speed of 50rpm, dispersion speed of 25m/s, time of 2h), the slurry is fully dispersed and the viscosity is appropriate.
  • the dispersant polyacrylic acid
  • the particle size Dv50 of the positive electrode slurry in Comparative Example 1 is 0.7-0.9 ⁇ m.
  • Coating layer A and rolling First, the positive electrode slurry was coated on a 16 ⁇ m aluminum foil and placed in a vacuum oven and dried at 150° C. for 10 h. Then, the foil was rolled on a roller press. The thickness of the coating layer A was about 30 ⁇ m and the compaction density was about 1.8 g/cm 3 , thereby obtaining a coating layer A/current collector composite structure.
  • Coating layer B and rolling First, the positive electrode slurry is coated on the coating layer A/ The coating layer B is placed on the coating layer A of the current collector composite structure and placed in a vacuum oven, dried at 150°C for 10 hours, and then rolled on a roller press.
  • the thickness of the coating layer B is about 20 ⁇ m, and the ratio of the compaction density to the coating layer A is 1:1, that is, 1.8 g/cm 3 , to obtain a coating layer B/coating layer A/current collector composite structure.
  • Coating layer C and rolling First, the positive electrode slurry is coated on the coating layer B of the coating layer B/coating layer A/current collector composite structure prepared in step 2, and placed in a vacuum oven, dried at 150°C for 10 hours, and then rolled on a roller press.
  • the thickness of the coating layer B is about 30 ⁇ m, and the compaction density is 1:1 with the coating layer A, i.e., 1.8g/ cm3 , to obtain a positive electrode sheet with coating layers A, B, and C.
  • Gluing lithium manganese iron phosphate (the number of particles with a particle size >10 ⁇ m accounts for about 0.5%), a conductive agent, and a binder are weighed in a mass ratio of 95%, 2%, and 3%, respectively.
  • the conductive agent and the binder are first loaded into a double planetary stirring tank, and then a certain amount of NMP is added. The speed is set to 800 rpm and the stirring time is 2 hours to obtain a PVDF glue solution, wherein the conductive agent is conductive carbon black and the binder is polyvinylidene fluoride (PVDF).
  • PVDF polyvinylidene fluoride
  • High-speed dispersion The weighed lithium iron phosphate powder and a dispersant (polyacrylic acid) accounting for about 0.1% of the mass ratio of the main material of the slurry are added into a double planetary stirring tank, and then a certain amount of NMP is added. The slurry is fully dispersed by high-speed stirring and dispersion (revolution speed of 50 rpm, dispersion speed of 25 m/s, time of 2 h).
  • the particle size Dv50 of the positive electrode slurry in Comparative Example 2 is 1-1.2 ⁇ m.
  • Coating layer A and rolling First, the positive electrode slurry was coated on a 16 ⁇ m aluminum foil and placed in a vacuum oven and dried at 150° C. for 10 h. Then, the foil was rolled on a roller press. The thickness of the coating layer A was about 30 ⁇ m and the compaction density was about 1.8 g/cm 3 , thereby obtaining a coating layer A/current collector composite structure.
  • Coating layer B and rolling First, the positive electrode slurry is coated on the coating layer A of the coating layer A/current collector composite structure prepared in step 1, and placed in a vacuum oven, dried at 150°C for 10 hours, and then rolled on a roller press.
  • the thickness of the coating layer B is about 20 ⁇ m, and the compaction density is similar to that of the coating layer B.
  • the ratio of A is 1:1, that is, 1.8 g/cm 3 , to obtain a coating layer B/coating layer A/current collector composite structure.
  • Coating layer C and rolling First, the positive electrode slurry is coated on the coating layer B of the coating layer B/coating layer A/current collector composite structure prepared in step 2, and placed in a vacuum oven, dried at 150°C for 10 hours, and then rolled on a roller press.
  • the thickness of the coating layer C is about 30 ⁇ m, and the compaction density is 1:1 with the coating layer A, i.e., 1.8g/ cm3 , to obtain a positive electrode sheet with coating layers A, B, and C.
  • Premixing lithium manganese iron phosphate (the number of particles with a particle size >10 ⁇ m accounts for about 0.5%), a conductive agent, and a binder are weighed in a mass ratio of 95%, 2%, and 3%, respectively, and are sequentially loaded into a double planetary stirring tank for premixing. The speed is set to 350 rpm and the ball milling time is 1 h to obtain a mixed material, wherein the conductive agent is conductive carbon black and the binder is polyvinylidene fluoride (PVDF).
  • PVDF polyvinylidene fluoride
  • High-speed dispersion Add about 0.1% of the dispersant (polyacrylic acid) to the double planetary stirring tank according to the mass ratio of the main material of the slurry, and then add a certain amount of NMP.
  • Use high-speed stirring and dispersion method (revolution speed is 50rpm, dispersion speed is 25m/s, time is 2h) to fully disperse the slurry.
  • the particle size of the positive electrode slurry in Comparative Example 3 is 1.5-2 ⁇ m.
  • Coating layer A and rolling First, the positive electrode slurry was coated on a 16 ⁇ m aluminum foil and placed in a vacuum oven and dried at 150° C. for 10 h. Then, the foil was rolled on a roller press. The thickness of the coating layer A was about 30 ⁇ m and the compaction density was about 1.8 g/cm 3 , thereby obtaining a coating layer A/current collector composite structure.
  • Coating layer B and rolling First, the positive electrode slurry is coated on the coating layer A of the coating layer A/current collector composite structure prepared in step 1, and placed in a vacuum oven, dried at 150°C for 10 hours, and then rolled on a roller press.
  • the thickness of the coating layer B is about 20 ⁇ m, and the ratio of compaction density to the coating layer A is 1:1, that is, 1.8g/ cm3 , to obtain a coating layer B/coating layer A/current collector composite structure.
  • Coating layer C and rolling First, the positive electrode slurry is coated on the coating layer B of the coating layer B/coating layer A/current collector composite structure prepared in step 1, and then placed in a vacuum oven at 150°C. After drying for 10 hours, the coating was rolled on a roller press.
  • the thickness of the coating layer C was about 30 ⁇ m, and the ratio of compaction density to the coating layer A was 1:1, that is, 1.8 g/cm 3 , and a positive electrode sheet with coating layers A, B, and C was obtained.
  • the positive and negative electrode discs are placed in a glove box filled with argon protective atmosphere for battery assembly, wherein a solution obtained by dissolving 1 mol/L lithium hexafluorophosphate in a mixed solvent of ethylene carbonate and diethyl carbonate with a molar ratio of 1:1 is used as an electrolyte; the positive electrode disc, the negative electrode disc, the polyethylene diaphragm and other components are assembled together, and then the electrolyte is injected to finally obtain a lithium-ion battery.
  • Capacity retention rate calculation method In the 1C charge and discharge cycle test, the capacity of the first cycle is taken as the initial capacity, and the capacity of the 150th cycle is divided by the initial capacity to obtain the retention rate value.
  • Example 1 and Comparative Example 1 (conventional method), Comparative Example 2 (wet slurry mixing process), and Comparative Example 3 (dry slurry mixing process), the slurry of the present application method has good fluidity, appropriate viscosity, and the size of large particles becomes smaller, and the overall particle size distribution is more appropriate, showing higher discharge capacity and cycle performance.
  • the thickness of the coating layer A of the composite positive electrode sheet of the present application is about 30 ⁇ m, and the compaction density is about 1.8 g/cm 3 .
  • the compaction density ratio of the coating layer A to the coating layer B gradually increases from 1:1 to 1:1.5.
  • the electrochemical performance of the lithium battery first increases and then decreases. The reason is that if the compaction density of the coating layer B is too high, the electrolyte infiltration effect will be deteriorated and it is difficult to exert the material properties. Therefore, the optimal compaction density ratio of the coating layers A and B of the composite positive electrode sheet is 1:1.3.
  • the thickness of the coating layer A of the composite positive electrode sheet of the present application is about 30 ⁇ m, and the thickness of the coating layer B increases from 20 ⁇ m to 60 ⁇ m.
  • the electrochemical performance of the lithium battery first increases and then decreases. The reason is that when the thickness of the coating layer B is too thick, it will make it difficult for the electrolyte to infiltrate into the interior and the material properties cannot be exerted. Therefore, the optimal thickness of the coating layer B of the composite positive electrode sheet is 50 ⁇ m.

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Abstract

一种复合正极片及其制备方法以及包括该复合正极片的锂离子电池，所述正极片包括集流体和活性物质层；所述活性物质层包括涂覆层A、涂覆层B和涂覆层C；所述涂覆层A设置于所述集流体的表面，所述涂覆层B设置于所述涂覆层A的表面，所述涂覆层C设置于所述涂覆层B的表面；所述涂覆层A的正极活性物质的中值粒径Dv50≤所述涂覆层C的正极活性物质的中值粒径Dv50<所述涂覆层B的正极活性物质的中值粒径Dv50；其中，所述活性物质选自磷酸锰铁锂、磷酸铁锂、磷酸钒锂、磷酸钴锂中的一种或其组合。通过采用具有三层活性物质层结构的正极片且调控其活性物质颗粒的尺寸大小及关系，制备得到了具有优异电化学性能和容量性能的正极片。并通过优化正极材料的制浆工艺，解决了现有技术的制浆工艺中原料浪费、经济成本高的问题。

Description

一种复合正极片及其制备方法以及包括其的锂离子电池 技术领域
本申请属于储能技术领域，具体涉及一种复合正极片及其制备方法以及包括该复合正极片的锂离子电池。
背景技术
锂离子电池安全系数高、使用周期长、具有广泛的应用前景。而且锂离子电池正极片的性能与结构对锂离子电池的整体性能有着重要的影响。
在锂离子电池正极浆料的制备过程中，制浆工艺的优化也有着十分重要的地位。锂电池正极材料的制浆工艺与其电化学性能发挥紧密相关，锂电池的常用制浆工艺只是简单的混合、搅拌分散，具体制备方法：①预混：将浆料主材加入到搅拌机中进行搅拌预混，得到混合物；②润湿：在真空条件下，按照65％～70％固含量，将所述混合物与有机溶剂进行搅拌分散；③高速分散：再加入有机溶剂，在真空条件下进行高速搅拌分散，得到混合浆料；④过筛：对所述高速分散步骤制得的混合浆料进行过筛去除大颗粒，得到正极浆料。由于常用制浆工艺很难处理正极浆料中未破碎的大颗粒粉末，只能经过筛处理后去除，这会造成原料浪费，而且可能造成极片涂布细微区域出现成分不均匀现象，导致材料电化学性能下降。
发明内容
针对现有技术的不足，本申请提供一种具有优异电化学性能与容量性能的复合正极片及其制备方法。
本申请提供了一种正极片，其特征在于，所述正极片包括集流体和活性物质层；所述活性物质层包括涂覆层A、涂覆层B和涂覆层C；所述涂覆层A设置于所述集流体的表面，所述涂覆层B设置于所述涂覆层A的表面，所述涂覆层C设置于所述涂覆层B的表面；
所述涂覆层A的正极活性物质的中值粒径Dv50≤所述涂覆层C的正极活性物质的中值粒径Dv50<所述涂覆层B的正极活性物质的中值粒径Dv50，其中，所述活性物质为本领域中常见的正极活性物质，如磷酸锰铁锂、磷酸铁锂、磷酸钒锂、磷酸钴锂等。
本申请通过采用具有三层结构的正极片，且通过控制涂覆层A、涂覆层B和涂覆层C的中值粒径的大小关系，即涂覆层A和涂覆层C的粒径尺寸小于中间涂覆层B的粒径尺寸；涂覆层A和涂覆层C采用小颗粒，可以使材料特性充分发挥，比如缩短锂离子迁移路径，降低电化学极化，提高锂电池的容量性能；涂覆层B采用大颗粒可以提高极片压实密度，而且大颗粒间隙比小颗粒的大，有利于电解液的浸润到极片内部，有利于锂电池的电化学性能。
本申请的另一目的是提供本申请的正极片的制备方法，具体包括以下步骤：
(1)将正极浆料1涂覆于集流体上，真空干燥，辊压，得到涂覆层A/集流体复合结构；
(2)将正极浆料2涂覆于经过步骤(1)得到的涂覆层A/集流体复合结构的涂覆层A表面，真空干燥，辊压，得到涂覆层B/涂覆层A/集流体复合结构；
(3)将正极浆料3涂覆于经过步骤(2)得到的涂覆层B/涂覆层A/集流体复合结构的涂覆层B表面，真空干燥，辊压，得到所述正极片；
其中，所述正极浆料1的中值粒径Dv50≤所述正极浆料3的中值粒径Dv50<所述正极浆料2的中值粒径Dv50。
有益效果：
本申请通过采用具有三层活性物质层结构的正极片且调控其活性物质颗粒的尺寸大小及关系，制备得到了具有优异电化学性能和容量性能的正极片。并通过优化正极材料的制浆工艺，解决了现有技术的制浆工艺中原料浪费、经济成本高的问题。
附图说明
图1是本申请磷酸锰铁锂的制浆工艺流程示意图；
图2是本申请的复合正极片结构示意图；
图3是实施例1中磷酸锰铁锂粉末的颗粒形貌SEM图，其中a)图显示的是正常尺寸的颗粒粉末，b)图显示的是未破碎的大颗粒粉末；
图4是实施例1中步骤3过筛的部分大颗粒粉末浆料实物图；
图5是实施例1中制备的正极浆料C、D的粒径分布图；
图6是实施例1中制备的正极片的横截面的颗粒形貌及分布情况图，其中a)图显示的是涂覆层A的横截面；b)图显示的是涂覆层B的横截面。
具体实施方式
下面参考具体实施例对本申请的技术方案做进一步说明。本申请的保护范围不限于以下实施例，列举这些实施例仅出于示例性目的而不以任何方式限制本申请。
在本说明书的上下文中，除了明确说明的内容之外，未提到的任何事宜或事项均直接适用本领域已知而无需进行任何改变的事宜。而且，本文描述的任何实施方式均可以与本文描述的一种或多种其他实施方式自由结合，由此而形成的技术方案或技术思想均视为本申请原始公开或原始记载的一部分，而不应被视为是本文未曾披露或预期过的新内容，除非本领域技术人员认为该结合是明显不合理的。
本申请提供了一种正极片，其特征在于，所述正极片包括集流体和活性物质层；所述活性物质层包括涂覆层A、涂覆层B和涂覆层C；所述涂覆层A设置于所述集流体的表面，所述涂覆层B设置于所述涂覆层A的表面，所述涂覆层C设置于所述涂覆层B的表面；
所述涂覆层A的正极活性物质的中值粒径Dv50≤所述涂覆层C的正极活性物质的中值粒径Dv50<所述涂覆层B的正极活性物质的中值粒径Dv50，其中，所述活性物质为本领域中常见的正极活性物质，如磷酸锰铁锂、磷酸铁锂、磷酸钒锂、磷酸钴锂等。
本申请通过采用具有三层结构的正极片，且通过控制涂覆层A、涂覆层B和涂覆层C的中值粒径的大小关系，即涂覆层A和涂覆层C的粒径尺寸小于中间涂覆层B的粒径尺寸；涂覆层A和涂覆层C采用小颗粒，可以使材料特性充分发挥，比如缩短锂离子迁移路径，降低电化学极化，提高锂电池的容量性能；涂覆层B采用大颗粒可以提高极片压实密度，而且大颗粒间隙比小颗粒的大，有利于电解液的浸润到极片内部，有利于锂电池的电化学性能。
根据本申请一具体实施方式，所述涂覆层A的正极活性物质的中值粒径Dv50等于所述涂覆层C的正极活性物质的中值粒径Dv50。
根据本申请一具体实施方式，所述涂覆层A的正极活性物质的中值粒 径Dv50为0.4μm-0.6μm，所述涂覆层C的正极活性物质的中值粒径Dv50为0.4μm-0.6μm，所述涂覆层B的正极活性物质的中值粒径Dv50为0.8μm-1μm。
在本申请的技术方案中，正极片的三层结构均采用较小的粒径尺寸，即均在1μm以内，相较于大尺寸的结构，可以显著提高电池的容量性能。
根据本申请一具体实施方式，所述涂覆层A与所述涂覆层B的压实密度的比值为1：(1-1.5)；所述涂覆层C与所述涂覆层B的压实密度的比值为1：(1-1.5)。
根据本申请一具体实施方式，所述涂覆层B与所述涂覆层A的压实密度的比值为1.3:1。
根据本申请一具体实施方式，所述涂覆层C与所述涂覆层A的压实密度的比值为1:1。
根据本申请一具体实施方式，所述涂覆层B的厚度为20μm-60μm。
根据本申请一具体实施方式，所述涂覆层B的厚度为50μm。
在本申请的技术方案中，通过调控涂覆层B的厚度，可以进一步提高正极片的容量性能。
根据本申请一具体实施方式，所述涂覆层A的厚度为10μm-30μm，优选为30μm。
根据本申请一具体实施方式，所述涂覆层C的厚度为10μm-30μm，优选为30μm。
根据本申请一具体实施方式，所述集流体为铝箔。铝箔厚度为10-20μm，优选为16μm。
本申请的另一目的是提供本申请的正极片的制备方法，具体包括以下步骤：
(1)将正极浆料1涂覆于集流体上，真空干燥，辊压，得到涂覆层A/集流体复合结构；
(2)将正极浆料2涂覆于经过步骤(1)得到的涂覆层A/集流体复合结构的涂覆层A表面，真空干燥，辊压，得到涂覆层B/涂覆层A/集流体复合结构；
(3)将正极浆料3涂覆于经过步骤(2)得到的涂覆层B/涂覆层A/ 集流体复合结构的涂覆层B表面，真空干燥，辊压，得到所述正极片；
其中，所述正极浆料1的中值粒径Dv50≤所述正极浆料3的中值粒径Dv50<所述正极浆料2的中值粒径Dv50。
根据本申请一具体实施方式，上述各步骤中真空干燥的温度独立地为120℃至180℃，优选为150℃；真空干燥的时间独立地为8h至12h，优选为10h。
根据本申请一具体实施方式，辊压的设备为辊压机。
根据本申请一具体实施方式，通过包括以下步骤的方法制备本申请的正极浆料：
S1、球磨预混：将正极活性物质、导电剂、粘结剂装入球磨机中进行球磨预混合，制得混合物料，其中正极活性物质占90-97wt％、导电剂占1-5wt％、粘结剂占2-5wt％；
S2、润湿与球磨：在经过步骤S1得到的所述混合物料中加入有机溶剂，球磨分散处理，得到分散混合物料，其中有机溶剂是N-甲基吡咯烷酮(NMP)；
S3、过筛：将步骤S2所得分散混合物料通过180目的筛网过滤出大颗粒粉末浆料，即为混合浆料A；剩下的为混合浆料B；
S4、通过低/高速球磨处理混合浆料A，使浆料中颗粒的粒度进一步降低，得到处理后混合浆料A，其中低速球磨的转速为200rpm至400rpm，高速球磨的转速为1200rpm至1800rpm；将混合浆料B分成两部分，即20％混合浆料B、80％混合浆料B；
S5、高速分散：将处理后混合浆料A、20％混合浆料B汇合于搅拌罐中，通过高速搅拌分散方式，使浆料得到充分分散；80％混合浆料B也按相同高速搅拌方式处理，其中所述高速搅拌的条件为：公转速度50rpm，分散速度25m/s；
S6、后处理：将高速搅拌分散后的混合浆料进行真空脱泡处理、过筛及粘度测试，制得所述正极浆料。
在本申请的方法中，通过调整球磨的转速和时间、分散的转速和时间，可以调整所得正极浆料的颗粒尺寸。
根据本申请一具体实施方式，在步骤S1中，所述球磨步骤在球磨机中 进行，其中所述球磨机的球磨罐为陶瓷球磨罐、玛瑙球磨罐、聚氨酯球磨罐中的一种或多种；球磨珠材质为氧化锆球、聚氨酯球中的一种或多种。
根据本申请一具体实施方式，在步骤S1中，导电剂为导电炭黑、石墨烯、碳纳米管、科琴黑的任意一种或几种；粘结剂为聚偏氟乙烯(PVDF)。
本申请的另一目的是提供一种储能装置，其包括上述正极片或上述制备方法制备得到的正极片。
根据本申请一具体实施方式，所述储能装置是二次电池。
本申请的正极浆料的一个具体的制备工艺流程如图1所示，包括以下步骤：
1)球磨预混：将正极活性材料如磷酸锰铁锂占约90～97％、导电剂占约1～5％、粘结剂占约2～5％依次装入球磨机中进行球磨预混合，制得混合物料，其中所述球磨机的球磨罐为陶瓷球磨罐、玛瑙球磨罐、聚氨酯球磨罐中的一种或多种；球磨珠材质为氧化锆球、聚氨酯球中的一种或多种；导电剂为导电炭黑、石墨烯、碳纳米管、科琴黑的任意一种或几种；粘结剂为聚偏氟乙烯(PVDF)。
2)润湿与球磨：在通过步骤1)制备得到的混合物料中，加入一定量的N-甲基吡咯烷酮(NMP)，先低速球磨(例如150rpm至300rpm)使NMP充分分散开及润湿粉料，再通过高速球磨(例如800rpm至1200rpm)使浆料主材磨为一体，充分分散，降低材料颗粒团聚程度，得到分散混合物料。
3)过筛：将步骤2)所得分散混合物料通过180目的筛网过滤出大颗粒粉末浆料，即混合浆料A，剩下混合均匀的浆料为混合浆料B。
4)混合浆料A处理：通过低/高速球磨将大颗粒粉末破碎变小，得到处理后混合浆料A，其中低速球磨的转速为200rpm至400rpm，高速球磨的转速为1200rpm至1800rpm；将混合浆料B分成两部分，即20％混合浆料B、80％混合浆料B。
5)高速分散：将处理后混合浆料A、20％混合浆料B汇合于双行星式搅拌罐中，通过高速搅拌分散方式，使浆料得到充分分散；80％混合浆料B也按相同高速搅拌方式处理，其中所述高速搅拌的条件为：公转速度50rpm，分散速度25m/s。
6)后处理：将高速搅拌分散后的混合浆料进行真空脱泡处理、过筛及粘度测试，制得正极浆料。
通过调整球磨的转速和时间、分散的转速和时间，可以调整所得正极 浆料的颗粒尺寸。
本申请的复合正极片的一个具体的工艺流程包括以下步骤：
1)涂覆层A的制备：首先将正极浆料1涂覆在16μm铝箔上，并放入真空烘箱中，在150℃下烘干10h，然后在辊压机上进行辊压，涂覆层A的厚度约为30μm，压实密度约为1.8g/cm3，制得涂覆层A/集流体复合结构；
2)涂覆层B的制备：首先将正极浆料2涂覆在步骤1制得的涂覆层A/集流体复合结构的涂覆层A上，并放入真空烘箱中，在150℃下烘干10h，然后在辊压机上进行辊压，涂覆层B的厚度约为20μm，压实密度与涂覆层A的比例为1：1，即为1.8g/cm3，制得涂覆层B/涂覆层A/集流体复合结构；
3)涂覆层C的制备：首先将正极浆料3涂覆在步骤2制得的涂覆层B/涂覆层A/集流体复合结构的涂覆层B上，并放入真空烘箱中，在150℃下烘干10h，然后在辊压机上进行辊压，涂覆层C的厚度约为30μm，压实密度与涂覆层A的比例为1：1，即为1.8g/cm3，制得具有涂覆层A、B、C的正极片，
其中，所述正极浆料1的中值粒径Dv50≤所述正极浆料3的中值粒径Dv50<所述正极浆料2的中值粒径Dv50。
正极浆料1、2、3均可以采用上文所述的制备方法制备得到，其中可以根据所需的粒径来调整制备过程中的参数，例如球磨的转速和时间、分散的转速和时间。
由于正极浆料经真空干燥后其粒径变化很小，所以正极浆料中颗粒的粒径与相应的涂覆层中颗粒的粒径之间的差异可以忽略不计。
在本申请的技术方案中，涂覆层A与涂覆层C的浆料可以相同也可以不同，只要满足：所述涂覆层A的正极活性物质的中值粒径Dv50≤所述涂覆层C的正极活性物质的中值粒径Dv50<所述涂覆层B的正极活性物质的中值粒径Dv50即可。
本申请的锂离子电池的具体制备工艺流程可以包括以下步骤：
1)按质量比95％：2.5％：2.5％称取对应量的人造石墨、导电炭黑、羧甲基纤维素钠于搅拌罐中，加入适量去离子水搅拌5h后得到粘度合适的均匀浆料；再将浆料涂布于厚度10μm的铜箔上，并放入真空烘箱中，在150℃下烘干15h后得到负极片。
2)将正、负极片放入压力机中进行压制，然后采用打孔器分别截取 Φ15mm的正极圆片、Φ18mm的负极圆片。
3)将正、负极圆片放入充满氩气保护气氛的手套箱中进行电池组装，其中使用1mol/L六氟磷酸锂溶于摩尔比为1：1的碳酸亚乙酯与碳酸二乙酯中的混合溶剂中所得的溶液作为电解液；将正极圆片、负极圆片、聚乙烯隔膜及其它组件一起组装，然后注入电解液，最后制得锂离子电池。
实施例
正极浆料以及正极片的制备
实施例1
(1)正极浆料的制备：
1)球磨预混：按照质量比95％、2％、3％分别称取磷酸锰铁锂、导电剂、粘结剂，依次装入球磨机中进行球磨预混合，球磨方式：转速350rpm，球料比为3:1，球磨时间为1h，制得混合物料，其中所述球磨机的球磨罐为陶瓷球磨罐，球磨珠材质为氧化锆球；导电剂为导电炭黑，粘结剂为聚偏氟乙烯(PVDF)。
磷酸锰铁锂粉末的颗粒形貌如图3所示，由图3可以看出，磷酸锰铁锂粉末原料中，除了正常尺寸的颗粒粉末，还有部分未破碎的大颗粒粉末。
2)润湿与球磨：加入一定量的N-甲基吡咯烷酮(NMP)，先低速球磨(转速200rpm，时间为1h)使NMP充分分散开及润湿粉料，再通过高速球磨(转速1000rpm，时间为2h)使浆料主材磨为一体，充分分散，降低材料颗粒团聚程度。
3)过筛：通过180目的筛网过滤出大颗粒粉末浆料如图4所示，即混合浆料A，剩下混合均匀的浆料为混合浆料B。
4)混合浆料A处理：先低速球磨(转速300rpm，时间为1h)使颗粒分散开，再通过高速球磨(转速1500rpm，时间为1h)，使大颗粒粉末破碎变小，形成粒度更小的浆料；混合浆料B处理：将混合浆料分成两部分，即20％混合浆料B、80％混合浆料B。
5)高速分散：将处理后混合浆料A、20％混合浆料B汇合于双行星式搅拌罐中，通过高速搅拌分散方式(公转速度为50rpm，分散速度为25m/s，时间为2h)，使浆料得到充分分散，粘度合适；80％混合浆料B也按相同 高速搅拌方式处理。
6)后处理：将高速搅拌分散后的混合浆料进行真空脱泡处理、过筛及粘度测试，制得正极浆料C、D。
对正极浆料C、D取样进行粒径分布测试，结果如图5所示，正极浆料C的粒径Dv50约为0.8μm-1μm，正极浆料D的粒径Dv50约为0.4μm-0.6μm。
(2)复合正极片的制备：
1)涂覆层A及辊压：首先将正极浆料D涂覆在16μm铝箔上，并放入真空烘箱中，在150℃下烘干10h，然后在辊压机上进行辊压，涂覆层A的厚度约为30μm，压实密度约为1.8g/cm3，制得涂覆层A/集流体复合结构。
2)涂覆层B及辊压：首先将正极浆料C涂覆在步骤1制得的涂覆层A/集流体复合结构的涂覆层A上，并放入真空烘箱中，在150℃下烘干10h，然后在辊压机上进行辊压，涂覆层B的厚度约为20μm，压实密度与涂覆层A的比例为1：1，即为1.8g/cm3，制得涂覆层B/涂覆层A/集流体复合结构。
3)涂覆层C及辊压：首先将正极浆料D涂覆在步骤2制得的涂覆层B/涂覆层A/集流体复合结构的涂覆层B上，并放入真空烘箱中，在150℃下烘干10h，然后在辊压机上进行辊压，涂覆层C的厚度约为30μm，压实密度与涂覆层A的比例为1：1，即为1.8g/cm3，制得具有涂覆层A、B、C的正极片。
由于正极浆料经真空干燥后其粒径变化很小，所以正极浆料中颗粒的粒径与相应的涂覆层中颗粒的粒径之间的差异可以忽略不计。因此，本实施例中制备得到的复合正极片中涂覆层A、B、C的粒径分布分别为0.4μm-0.6μm、0.8μm-1μm、0.4μm-0.6μm。
再观察复合正极片横截面形貌，如图6所示，涂覆层A的颗粒粒度细小且分布均匀，涂覆层B的颗粒粒度大，有利于提高压实密度及电解液浸润效果。
实施例2
其他条件不变，调变复合正极片的制备中步骤2中涂覆层B的压实密度，将涂覆层B的压实密度与涂覆层A的比例由1：1改为1.1:1，即为1.98g/cm3，涂覆层A和涂覆层C的压实密度不变。
实施例3
其他条件不变，调变复合正极片的制备中步骤2中涂覆层B的压实密度，将涂覆层B的压实密度与涂覆层A的比例由1：1改为1.2:1，即为2.16g/cm3，涂覆层A和涂覆层C的压实密度不变。
实施例4
其他条件不变，调变复合正极片的制备中步骤2中涂覆层B的压实密度，将涂覆层B的压实密度与涂覆层A的比例由1：1改为1.3:1，即为2.34g/cm3，涂覆层A和涂覆层C的压实密度不变。
实施例5
其他条件不变，调变复合正极片的制备中步骤2中涂覆层B的压实密度，将涂覆层B的压实密度与涂覆层A的比例由1：1改为1.4:1，即为2.52g/cm3，涂覆层A和涂覆层C的压实密度不变。
实施例6
其他条件不变，调变复合正极片的制备中步骤2中涂覆层B的压实密度，将涂覆层B的压实密度与涂覆层A的比例由1：1改为1.5:1，即为2.70g/cm3，涂覆层A和涂覆层C的压实密度不变。
实施例7
其他条件不变，调变复合正极片的制备中步骤2中涂覆层B的厚度，涂覆层B的厚度由20μm增加到30μm。
实施例8
其他条件不变，调变复合正极片的制备中步骤2中涂覆层B的厚度，涂覆层B的厚度由20μm增加到40μm。
实施例9
其他条件不变，调变复合正极片的制备中步骤2中涂覆层B的厚度，涂覆层B的厚度由20μm增加到50μm。
实施例10
其他条件不变，调变复合正极片的制备中步骤2中涂覆层B的厚度，涂覆层B的厚度由20μm增加到60μm。
对比例1
(1)正极浆料的制备(物料与实施例1完全相同)：
1)球磨预混：按照质量比95％、2％、3％分别称取磷酸锰铁锂、导电剂、粘结剂，依次装入球磨机中进行球磨预混合，球磨方式：转速350rpm，球料比为3:1，球磨时间为1h，制得混合物料，其中所述球磨机的球磨罐为陶瓷球磨罐，球磨珠材质为氧化锆球；导电剂为导电炭黑，粘结剂为聚偏氟乙烯(PVDF)。
2)润湿与球磨：加入一定量的N-甲基吡咯烷酮(NMP)，先低速球磨(转速200rpm，时间为1h)使NMP充分分散开及润湿粉料，再通过高速球磨(转速1000rpm，时间为2h)使浆料主材磨为一体，充分分散，降低材料颗粒团聚程度。
3)高速分散：按浆料主材质量比占约0.1％的分散剂(聚丙烯酸)加入于双行星式搅拌罐中，再加入一定量的NMP，通过高速搅拌分散方式(公转速度为50rpm，分散速度为25m/s，时间为2h)，使浆料得到充分分散，粘度合适。
4)后处理：将高速搅拌分散后的混合浆料进行真空脱泡处理(真空度为-100kPa)、过筛及粘度测试，最终制得的正极浆料。
对比例1中正极浆料的粒径Dv50为0.7-0.9μm。
(2)复合正极片的制备：
1)涂覆层A及辊压：首先将正极浆料涂覆在16μm铝箔上，并放入真空烘箱中，在150℃下烘干10h，然后在辊压机上进行辊压，涂覆层A的厚度约为30μm，压实密度约为1.8g/cm3，制得涂覆层A/集流体复合结构。
2)涂覆层B及辊压：首先将正极浆料涂覆在步骤1制得的涂覆层A/ 集流体复合结构的涂覆层A上，并放入真空烘箱中，在150℃下烘干10h，然后在辊压机上进行辊压，涂覆层B的厚度约为20μm，压实密度与涂覆层A的比例为1：1，即为1.8g/cm3，制得涂覆层B/涂覆层A/集流体复合结构。
3)涂覆层C及辊压：首先将正极浆料涂覆在步骤2制得的涂覆层B/涂覆层A/集流体复合结构的涂覆层B上，并放入真空烘箱中，在150℃下烘干10h，然后在辊压机上进行辊压，涂覆层B的厚度约为30μm，压实密度与涂覆层A的比例为1：1，即为1.8g/cm3，制得具有涂覆层A、B、C的正极片。
对比例2
(1)正极浆料的制备(物料与实施例1完全相同)(湿法合浆工艺)：
1)打胶：按照质量比95％、2％、3％分别称取磷酸锰铁锂(粒径>10μm的颗粒数占比约为0.5％)、导电剂、粘结剂，首先将导电剂、粘结剂装入双行星式搅拌罐中，再加入一定量的NMP，设置转速800rpm，搅拌时间为2h，制得PVDF胶液，其中导电剂为导电炭黑，粘结剂为聚偏氟乙烯(PVDF)。
2)高速分散：将称取后磷酸铁锂粉末、按浆料主材质量比占约0.1％的分散剂(聚丙烯酸)继续加入于双行星式搅拌罐中，再加入一定量的NMP，通过高速搅拌分散方式(公转速度为50rpm，分散速度为25m/s，时间为2h)，使浆料得到充分分散。
3)后处理：将高速搅拌分散后的混合浆料进行真空脱泡处理(真空度为-100kPa)、过筛及粘度测试，最终制得正极浆料。
对比例2中正极浆料的粒径Dv50为1-1.2μm。
(2)复合正极片的制备
1)涂覆层A及辊压：首先将正极浆料涂覆在16μm铝箔上，并放入真空烘箱中，在150℃下烘干10h，然后在辊压机上进行辊压，涂覆层A的厚度约为30μm，压实密度约为1.8g/cm3，制得涂覆层A/集流体复合结构。
2)涂覆层B及辊压：首先将正极浆料涂覆在步骤1制得的涂覆层A/集流体复合结构的涂覆层A上，并放入真空烘箱中，在150℃下烘干10h，然后在辊压机上进行辊压，涂覆层B的厚度约为20μm，压实密度与涂覆层 A的比例为1：1，即为1.8g/cm3，制得涂覆层B/涂覆层A/集流体复合结构。
3)涂覆层C及辊压：首先将正极浆料涂覆在步骤2制得的涂覆层B/涂覆层A/集流体复合结构的涂覆层B上，并放入真空烘箱中，在150℃下烘干10h，然后在辊压机上进行辊压，涂覆层C的厚度约为30μm，压实密度与涂覆层A的比例为1：1，即为1.8g/cm3，制得具有涂覆层A、B、C的正极片。
对比例3
(1)正极浆料的制备(物料与实施例1完全相同)(干法合浆工艺)：
1)预混：按照质量比95％、2％、3％分别称取磷酸锰铁锂(粒径>10μm的颗粒数占比约为0.5％)、导电剂、粘结剂，依次装入双行星式搅拌罐中进行预混合，设置转速350rpm，球磨时间为1h，制得混合物料，其中导电剂为导电炭黑，粘结剂为聚偏氟乙烯(PVDF)。
2)高速分散：按浆料主材质量比占约0.1％的分散剂(聚丙烯酸)加入于双行星式搅拌罐中，再加入一定量的NMP，通过高速搅拌分散方式(公转速度为50rpm，分散速度为25m/s，时间为2h)，使浆料得到充分分散。
3)后处理：将高速搅拌分散后的混合浆料进行真空脱泡处理(真空度为-100kPa)、过筛及粘度测试，最终制得正极浆料。
对比例3中正极浆料的粒径为1.5-2μm。
(2)复合正极片的制备
1)涂覆层A及辊压：首先将正极浆料涂覆在16μm铝箔上，并放入真空烘箱中，在150℃下烘干10h，然后在辊压机上进行辊压，涂覆层A的厚度约为30μm，压实密度约为1.8g/cm3，制得涂覆层A/集流体复合结构。
2)涂覆层B及辊压：首先将正极浆料涂覆在步骤1制得的涂覆层A/集流体复合结构的涂覆层A上，并放入真空烘箱中，在150℃下烘干10h，然后在辊压机上进行辊压，涂覆层B的厚度约为20μm，压实密度与涂覆层A的比例为1：1，即为1.8g/cm3，制得具有涂覆层B/涂覆层A/集流体复合结构。
3)涂覆层C及辊压：首先将正极浆料涂覆在步骤1制得的涂覆层B/涂覆层A/集流体复合结构的涂覆层B上，并放入真空烘箱中，在150℃下 烘干10h，然后在辊压机上进行辊压，涂覆层C的厚度约为30μm，压实密度与涂覆层A的比例为1：1，即为1.8g/cm3，制得具有涂覆层A、B、C的正极片。
电池的制备及测试
1)按质量比95％：2.5％：2.5％称取对应量的人造石墨、导电炭黑、羧甲基纤维素钠于搅拌罐中，加入适量去离子水搅拌5h后得到粘度合适的均匀浆料；再将浆料涂布于厚度10μm的铜箔上，并放入真空烘箱中，在150℃下烘干15h后得到负极片；
2)将实施例1至10、对比例1至3中制备的正极片以及步骤1)中得到的负极片放入压力机中进行压制，然后采用打孔器分别截取Φ15mm的正极圆片、Φ18mm的负极圆片；
3)将正、负极圆片放入充满氩气保护气氛的手套箱中进行电池组装，其中使用1mol/L六氟磷酸锂溶于摩尔比为1：1的碳酸亚乙酯与碳酸二乙酯中的混合溶剂中所得的溶液作为电解液；将正极圆片、负极圆片、聚乙烯隔膜及其它组件一起组装，然后注入电解液，最后制得锂离子电池。
将如上所得的锂离子扣式半电池使用电池测试仪(Neware CT4000新威尔电子有限公司)进行电化学性能测试，其测试结果如表1所示。容量保持率计算方式：1C充放电循环测试中，以第1圈的容量为初始容量，第150圈的容量除以初始容量得到保持率数值。
表1锂离子扣式半电池的电化学性能测试结果

由实施例1与对比例1(常规方法)、对比例2(湿法合浆工艺)、对比例3(干法合浆工艺)，本申请方法的浆料流动性好，粘度合适，而且大颗粒尺寸变小，整体粒径分布更加合适，表现出更高的放电容量、循环性能。
由表1中实施例1、2、3、4、5、6、7，本申请的复合正极片涂覆层A的厚度约为30μm，压实密度约为1.8g/cm3,与涂覆层B的压实密度比例由1:1逐渐增加到1:1.5，锂电池的电化学性能先增加后下降，原因是涂覆层B的压实密度太高会恶化电解液浸润效果而难以发挥材料特性，所以该复合正极片的涂覆层A、B的最佳压实密度比例为1:1.3。
由表1中实施例1、7、8、9、10，本申请的复合正极片涂覆层A的厚度约为30μm，涂覆层B的厚度由20μm增加到60μm，锂电池的电化学性能先增加后下降，原因是涂覆层B的厚度太厚时会导致电解液难以浸润到内部而无法发挥材料特性，所以该复合正极片的涂覆层B的最佳厚度为50μm。

Claims (14)

  1. 一种正极片，其特征在于，所述正极片包括集流体和活性物质层；所述活性物质层包括涂覆层A、涂覆层B和涂覆层C；所述涂覆层A设置于所述集流体的表面，所述涂覆层B设置于所述涂覆层A的表面，所述涂覆层C设置于所述涂覆层B的表面；
    所述涂覆层A的正极活性物质的中值粒径Dv50≤所述涂覆层C的正极活性物质的中值粒径Dv50<所述涂覆层B的正极活性物质的中值粒径Dv50。
    其中，所述活性物质选自磷酸锰铁锂、磷酸铁锂、磷酸钒锂、磷酸钴锂中的一种或其组合。
  2. 根据权利要求1所述的正极片，其特征在于，所述涂覆层A的正极活性物质的中值粒径Dv50为0.4μm-0.6μm，所述涂覆层C的正极活性物质的中值粒径Dv50为0.4μm-0.6μm，所述涂覆层B的正极活性物质的中值粒径Dv50为0.8μm-1μm。
  3. 根据权利要求1所述的正极片，其特征在于，所述涂覆层A与所述涂覆层B的压实密度的比值为1：(1-1.5)，优选为1:1.3；所述涂覆层C与所述涂覆层B的压实密度的比值为1：(1-1.5)。
  4. 根据权利要求1所述的正极片，其特征在于，所述涂覆层A与所述涂覆层B的压实密度的比值为1:1.3。
  5. 根据权利要求1所述的正极片，其特征在于，所述涂覆层C与所述涂覆层A的压实密度的比值为1:1。
  6. 根据权利要求1所述的正极片，其特征在于，所述涂覆层B的厚度为20μm-60μm。
  7. 根据权利要求1所述的正极片，其特征在于，所述涂覆层B的厚度为50μm。
  8. 权利要求1至7中任一项所述正极片的制备方法，其特征在于，具体包括以下步骤：
    (1)将正极浆料1涂覆于集流体上，真空干燥，辊压，得到涂覆层A/集流体复合结构；
    (2)将正极浆料2涂覆于经过步骤(1)得到的涂覆层A/集流体复合 结构的涂覆层A表面，真空干燥，辊压，得到涂覆层B/涂覆层A/集流体复合结构；
    (3)将正极浆料3涂覆于经过步骤(2)得到的涂覆层B/涂覆层A/集流体复合结构的涂覆层B表面，真空干燥，辊压，得到所述正极片；
    其中，所述正极浆料1的中值粒径Dv50≤所述正极浆料3的中值粒径Dv50<所述正极浆料2的中值粒径Dv50。
  9. 根据权利要求8所述的方法，其特征在于，各步骤中真空干燥的温度独立地为120℃至180℃，优选为150℃；真空干燥的时间独立地为8h至12h，优选为10h。
  10. 根据权利要求8所述的方法，其特征在于，通过包括以下步骤的方法制备正极浆料：
    S1、球磨预混：将正极活性物质、导电剂、粘结剂装入球磨机中进行球磨预混合，制得混合物料，其中正极活性物质占90-97wt％、导电剂占1-5wt％、粘结剂占2-5wt％；
    S2、润湿与球磨：在经过步骤S1得到的所述混合物料中加入有机溶剂，球磨分散处理，得到分散混合物料，其中有机溶剂是N-甲基吡咯烷酮(NMP)；
    S3、过筛：将步骤S2所得分散混合物料通过180目的筛网过滤出大颗粒粉末浆料，即为混合浆料A；剩下的为混合浆料B；
    S4、通过低/高速球磨处理混合浆料A，使浆料中颗粒的粒度进一步降低，得到处理后混合浆料A，其中低速球磨的转速为200rpm至400rpm，高速球磨的转速为1200rpm至1800rpm；将混合浆料B分成两部分，即20％混合浆料B、80％混合浆料B；
    S5、高速分散：将处理后混合浆料A、20％混合浆料B汇合于搅拌罐中，通过高速搅拌分散方式，使浆料得到充分分散；80％混合浆料B也按相同高速搅拌方式处理，其中所述高速搅拌的条件为：公转速度50rpm，分散速度25m/s；
    S6、后处理：将高速搅拌分散后的混合浆料进行真空脱泡处理、过筛及粘度测试，制得所述正极浆料。
  11. 根据权利要求10所述的方法，其特征在于，在步骤S1中，导电 剂为导电炭黑、石墨烯、碳纳米管、科琴黑的任意一种或几种；粘结剂为聚偏氟乙烯(PVDF)。
  12. 根据权利要求10所述的方法，其特征在于，在步骤S2中，如下进行球磨：先通过转速为150rpm至300rpm的低速球磨使NMP充分分散开及润湿粉料，再通过转速为800rpm至1200rpm的高速球磨使浆料主材磨为一体。
  13. 一种储能装置，其特征在于，包括权利要求1至7中任一项所述正极片。
  14. 根据权利要求13所述的储能装置，其特征在于，所述储能装置是二次电池。
PCT/CN2024/073479 2023-05-19 2024-01-22 一种复合正极片及其制备方法以及包括其的锂离子电池 Ceased WO2024239692A1 (zh)

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