Positive electrode material, method for producing the same, positive electrode composite material, and battery

Abstract

Provided is a positive electrode material comprising a plurality of composite secondary particles, each of which comprises a plurality of positive electrode material primary particles, wherein the composite secondary particles satisfy the relationship 0.9≦0.1d / a+b×c≦20, where a represents the particle size D50 value of the positive electrode material primary particles in μm, b represents the particle size D50 value of the composite secondary particles in μm, and c represents the specific surface area value of the composite secondary particles in m 2 / g, and d represents the number of positive electrode material primary particles in the composite secondary particles.

Description

Technical Field

[0001] (Cross - reference to related applications) This application claims priority to Chinese Patent Application No. “202010681792.9” with the application title “Positive Electrode Material and Its Manufacturing Method, Positive Electrode Composite Material and Battery” filed by VIEWD Technology Company Limited on July 15, 2020.

[0002] This application relates to the field of batteries, and specifically to positive electrode materials and their manufacturing methods, positive electrode composite materials and batteries.

Background Art

[0003] Currently, there are two general designs of positive electrode materials in the market. One of them is composed of one or a small number (less than 5) of primary particles. This material has advantages such as high structural stability, high cycle performance, and less gas generated during storage. At the same time, with the same metal ratio, it has disadvantages such as low capacity, high battery impedance, and low power. The other is a secondary particle material composed of multiple primary particles, which also has many problems. For example, in secondary particle materials of the same particle size, if there are too many primary particles, the primary particles will become smaller, the specific surface area will become larger, the side reactions with the electrolyte and gas generation will be serious. This secondary particle material has disadvantages such as being easily crushed in the compression process, low cycle performance, low thermal stability, and low safety.

Summary of the Invention

Problems to be Solved by the Invention

[0004] The purpose of this application is to solve at least one of the technical problems in the prior art. For this purpose, this application provides a positive electrode material that improves the stability of the battery.

Means for Solving the Problems

[0005] The positive electrode material includes a plurality of composite secondary particles each containing a plurality of positive electrode material primary particles, and the composite secondary particles satisfy the following relational expression 1. 0.9 ≦ 0.1d / a + b×c ≦ 20 (Relational expression 1) (In the formula, a represents the value of the particle size D50 of the positive electrode material primary particles, the unit is μm, b represents the value of the particle size D50 of the composite secondary particles, the unit is μm, c represents the value of the specific surface area of the composite secondary particles, the unit is m 2 / g, and d represents the number of the positive electrode material primary particles in the composite secondary particles)

[0006] Thereby, in the composite secondary particles of the positive electrode material according to the present application, when the particle size D50 of the positive electrode material primary particles, the particle size D50 of the composite secondary particles, the specific surface area of the composite secondary particles, and the number of the positive electrode material primary particles in the composite secondary particles are set to satisfy the above relational expression 1, the battery manufactured with the positive electrode material has a low battery impedance, a high cycle capacity retention rate, and a low thickness change rate of the battery, which indicates that there is less gas generated in the battery, less side reaction between the positive electrode plate and the electrolyte, and higher battery stability.

[0007] The manufacturing method of the positive electrode material is mixing a first precursor and a second precursor, and pre-sintering and obtain a pre-sintered mixture step, and said performing a first sintering on the pre-sintered mixture, and performing a first crushing after the first sintering to obtain a positive electrode material including a plurality of composite secondary particles each containing a plurality of positive electrode material primary particles.

[0008] The positive electrode composite material includes the above-mentioned positive electrode material and a coating layer coated on the surface of the positive electrode material.

[0009] The battery includes a positive electrode plate, the positive electrode plate includes a current collector and a positive electrode active material layer provided on the current collector, and the positive electrode active material layer includes the above-mentioned positive electrode composite material.

Advantages of the Invention

[0010] Additional aspects and advantages of the present application will be shown in part in the following description, and in part will become apparent in the following description or be understood by the implementation of the present application.

Embodiments for Carrying Out the Invention

[0011] Hereinafter, embodiments of the present application will be described in detail. Examples of the above embodiments are shown in the drawings, and the same or similar reference numerals throughout indicate the same or similar components, or components having the same or similar functions. Hereinafter, the embodiments described with reference to the drawings are exemplary and should be understood as merely interpreting the present application and not limiting the present application.

[0012] It should be noted that the terms "first" and "second" are merely for the purpose of explanation and should not be understood as indicating or suggesting relative importance or implicitly indicating the number of the indicated technical features. Thus, the features limited by "first" and "second" may explicitly or implicitly include one or more of such features. Further, in the description of the present application, unless otherwise specifically explained, "a plurality" means two or more.

[0013] The positive electrode material according to the embodiment of the present application includes a plurality of composite secondary particles each including a plurality of positive electrode material primary particles, and the composite secondary particles satisfy the following relational expression 1. 0.9 ≦ 0.1d / a + b × c ≦ 20 (Relational Expression 1) (In the formula, a represents the value of the particle size D50 of the positive electrode material primary particles, the unit is μm, b represents the value of the particle size D50 of the composite secondary particles, the unit is μm, c represents the value of the specific surface area of the composite secondary particles, the unit is m 2 / g, and d represents the number of positive electrode material primary particles in the composite secondary particles)

[0014] In the charge and discharge process of a battery, lithium ions desorb / insert into the cathode material and the anode material, and the desorption / insertion rate of lithium ions affects the electrical performance of the battery. In the present application, the size of the D50 particle diameter of the primary particles of the cathode material is directly related to the length of the diffusion path of lithium ions in the cathode material. If the D50 particle diameter of the primary particles of the cathode material is too large, the diffusion path of lithium ions becomes longer, so that the capacity of the material is poorly exerted, and the impedance of the battery increases. If the D50 particle diameter of the primary particles of the cathode material is too small, the number of primary particles of the cathode material in the composite secondary particles with the same D50 particle diameter increases, and further the specific surface area of the composite secondary particles increases. Therefore, the side reaction between the composite secondary particles and the electrolyte increases, gas generation becomes serious, and the cycle performance of the battery is affected.

[0015] The D50 particle diameter of the primary particles of the cathode material and the number of primary particles of the cathode material constituting the composite secondary particles directly affect the D50 particle diameter and the specific surface area of the composite secondary particles. In the design of composite secondary particles with the same particle diameter, if the D50 particle diameter of the primary particles of the cathode material is too small, the number of primary particles of the cathode material increases, so that the specific surface area of the composite secondary particles increases, and the area where side reactions occur increases. Also, if the number of primary particles of the cathode material in the composite secondary particles is too large, crushing occurs between the primary particles of the cathode material during the compression and cycling of the electrode plate, and further a new interface is formed, resulting in a decrease in battery performance. If the D50 particle diameter of the primary particles of the cathode material is too large, accordingly, the number of primary particles of the cathode material constituting the composite secondary particles decreases, but since the diffusion path of lithium ions is directly lengthened by the primary particles of the cathode material with a large particle diameter, the capacity of the material is poorly exerted, the battery impedance increases, and the power performance decreases.

[0016] In the present application, as can be seen from a large amount of experimental data, when the particle size D50 of the primary particles of the positive electrode material in the composite secondary particles, the particle size D50 of the composite secondary particles, the specific surface area of the composite secondary particles, and the number of primary particles of the positive electrode material in the composite secondary particles satisfy the above relational expression 1, the battery manufactured with the positive electrode material has a low battery impedance, a high cycle capacity retention rate, and a low thickness change rate of the battery, which indicates that there is less gas generated in the battery, less side reactions between the positive electrode plate and the electrolyte, and higher battery stability.

[0017] In some embodiments, the composite secondary particles satisfy 2.5 ≦ 0.1d / a + b × c ≦ 9. As can be seen from the experimental data, the composite secondary particles within the above value range have excellent performance effects.

[0018] The value range of a may be 0.5 ≦ a ≦ 3.5. Further, the value range of a is preferably 1.5 ≦ a ≦ 2.5.

[0019] In some embodiments, the value range of b may be 3 ≦ b ≦ 12. Further, the value range of b is preferably 4.5 ≦ b ≦ 7.

[0020] The value range of c may be 0.3 ≦ c ≦ 1.2. Further, the value range of c is preferably 0.5 ≦ c ≦ 1.0.

[0021] In some embodiments, the value range of d may be 1 ≦ d ≦ 50. Further, the value range of d is preferably 3 ≦ d ≦ 20.

[0022] In some embodiments, the primary particles of the positive electrode material are a positive electrode material having a layered structure.

[0023] The primary particles of the positive electrode material are LiNi x Co y M zwhere the range of the value of x is 0.33 ≦ x ≦ 0.98, the range of the value of y is 0.01 ≦ y ≦ 0.33, the range of the value of z is 0.01 ≦ z ≦ 0.33, and x + y + z = 1, and M is at least one of Mn, Al, Zr, Ti, Y, Sr, and W.

[0024] The method for manufacturing a positive electrode material according to an embodiment of the present application may include step S100 and step S200. The detailed steps are as follows.

[0025] In step S100, a first precursor and a second precursor are mixed and pre-sintered and obtain a pre-sintered mixture .

[0026] The first precursor includes Ni e Co f Q g (OH)2, Ni e Co f Q g O, or at least one of hydroxides or oxides of Ni, Co, and Q, where the ranges of the values of e, f, and g in Ni e Co f Q g (OH)2 and Ni e Co f Q g O are 0.33 ≦ e ≦ 0.98, 0.01 ≦ f ≦ 0.33, 0.01 ≦ g ≦ 0.33, and e + f + g = 1, and Q is at least one of Mn, Al, Zr, Ti, Y, Sr, and W. The second precursor includes at least one of lithium hydroxide, lithium carbonate, lithium nitrate, and lithium acetate. The molar ratio of the first precursor to the second precursor is 1:(1 - 1.05).

[0027] In some embodiments, the temperature of pre-sintering may be 200°C to 500°C, and the time of pre-sintering may be 4 h to 6 h. Stirring may not be required in the pre-sintering process, and pre-sintering is carried out in a roller hearth kiln. The purpose of pre-sintering is to volatilize the moisture in the first precursor and the second precursor, which is beneficial for the first precursor and the second precursor to fully react in the first sintering process, and is beneficial for the formation of the cathode material.

[0028] In step S200, the pre-sintered mixture is subjected to first sintering, and after the first sintering, first crushing is carried out to obtain a cathode material including a plurality of composite secondary particles each including a plurality of cathode material primary particles. After the first sintering and the first crushing, the particle size D50 of the cathode material primary particles, the particle size D50 of the composite secondary particles, the specific surface area of the composite secondary particles, and the number of cathode material primary particles in the composite secondary particles can be determined.

[0029] The cathode material primary particles refer to particles with different orientations in the cathode material measured by using EBSD (electron backscatter diffraction technology). The orientation refers to the orientation of the particles on the coordinate axes with an arbitrary point on the indicated interface as the origin. That is, when the cathode material is measured by EBSD, particles with a plurality of different orientations can be observed, and the particles with different orientations are the cathode material primary particles.

[0030] The composite secondary particles refer to material particles in which a plurality of cathode material primary particles are combined. That is, the composite secondary particles have a plurality of cathode material primary particles with different orientations.

[0031] In some embodiments, the first sintering includes a first temperature rising stage, a first constant temperature stage, a second temperature rising stage, a second constant temperature stage, and a cooling stage in sequence.

[0032] The temperature in the first heating stage is set to 200°C to 800°C, the time in the first heating stage is set to 1.5 h to 3.5 h, the temperature in the first constant temperature stage is set to 700°C to 800°C, the time in the first constant temperature stage is set to 5.0 h to 8.0 h, the temperature in the second heating stage is set to 800°C to 1100°C, the time in the second heating stage is set to 2.0 h to 3.5 h, the temperature in the second constant temperature stage is set to 1000°C to 1100°C, and the time in the second constant temperature stage is set to 8.0 h to 10.0 h.

[0033] In the first heating stage and the second heating stage, continuous heating may be performed, or heating may be continued after a short stop in heating in each heating stage. Preferably, continuous heating is performed.

[0034] The first precursor and the second precursor perform a thermal decomposition reaction in the first heating stage and the second heating stage. The by-products generated by decomposition contain water and / or carbon dioxide. When the first precursor contains a hydroxide, the first precursor decomposes to generate water and a metal oxide, the second precursor decomposes to generate water and lithium oxide. When the second precursor contains lithium carbonate, lithium carbonate decomposes to generate carbon dioxide and lithium oxide. Preferably, the first heating stage and the second heating stage are performed in a heating furnace having an exhaust pipe. The exhaust pipe can remove gases such as water vapor and carbon dioxide generated by the thermal decomposition of the first precursor and / or the lithium source, and promote the decomposition reaction of the first precursor and the second precursor. If the heating rate in the first heating stage and the second heating stage is too fast, the decomposition reaction will be insufficient, the discharge of by-products will be incomplete, which will have side effects on the subsequent solid-phase reaction. On the one hand, it will corrode the subsequent reaction device, and on the other hand, it will cause the content of free lithium on the surface of the cathode material to be too high, resulting in an increase in the impedance of the cathode material. The solid-phase reaction refers to a reaction in which lithium oxide reacts with a metal oxide to generate primary particles of the cathode material.

[0035] In the first constant temperature stage and the second constant temperature stage, solid-phase reactions occur, lithium oxide and metal oxide undergo ion diffusion, the reaction temperature and reaction time in the constant temperature stage affect the size of the primary particles of the cathode material and the quality of crystallinity, and directly affect the final performance of the cathode material. Exhaust pipes may not be necessary in the first constant temperature stage and the second constant temperature stage. Note that the temperature in the constant temperature stage may vary within a certain predetermined range. For example, the temperature in the first constant temperature stage may vary within the range of 750°C to 780°C.

[0036] When sintering is carried out in a manner of alternately performing a heating stage and a constant temperature stage in the first sintering, the first precursor and the second precursor can react more sufficiently.

[0037] The cooling stage includes a first cooling sub-stage and a second cooling sub-stage. The temperature of the first cooling sub-stage is set to 1100°C to 600°C, the time is set to 2.5 to 4.0 h, the temperature of the second cooling sub-stage is set to 600°C to 200°C, and the time is set to 0.5 to 2.0 h. The first cooling sub-stage and the second cooling sub-stage may be continuously cooled, or the cooling may be continued after a short stop in each cooling stage. Preferably, continuous cooling is performed.

[0038] In the cooling stage, if the material is discharged from the furnace at a high temperature, the subsequent equipment will be corroded. If the cooling is too fast, large stress will remain inside the composite secondary particles, resulting in cracks in the material during subsequent use processes and cycle processes, affecting the performance of the material.

[0039] In this application, as can be seen from experiments, when the temperatures and times of the first heating stage, the first constant temperature stage, the second heating stage, the second constant temperature stage, and the cooling stage in the first sintering are within the above ranges, it has high performance, the size of the primary particles of the cathode material can be determined after the first sintering, and the primary particles of the cathode material after the first sintering aggregate to form aggregates.

[0040] The first crushing includes the steps of ball-milling the sintered aggregate after the first sintering to obtain primary crushed material, and then air-flow pulverizing the primary crushed material. The rotation speed of the ball-milling is 4000 r / min to 8000 r / min, the time of the ball-milling is 1.5 h to 2.5 h, the pressure of the air-flow pulverizing is 5 MPa to 10 MPa, and the time of the air-flow pulverizing is 0.5 h to 1.5 h. In this step, the particle size D50 of the composite secondary particles, the specific surface area of the composite secondary particles, and the number of primary particles of the cathode material in the composite secondary particles can be determined.

[0041] The cathode composite material according to the embodiment of the present application includes the cathode material described in any one of the above items and a coating layer coated on the surface of the cathode material.

[0042] The coating layer may be a protective layer formed on the surface of the cathode material, which can reduce the side reaction between the cathode material and the electrolyte, contribute to the stability of the surface layer structure of the material, improve the cycle performance of the material, or the coating layer is a heat insulation layer formed on the surface of the cathode material, which can reduce the heat diffusion rate of the material and improve the safety of the material.

[0043] In some embodiments, the mass ratio of the coating layer in the cathode composite material is 300 ppm to 900 ppm. Within this mass ratio range, the coating layer can effectively reduce the side reaction between the composite secondary particles and the electrolyte, reduce the gas generated in the material to a certain extent, play a role in heat insulation, reduce the heat diffusion rate, and improve the safety performance of the material. Also, if the usage amount of the coating layer is too large, there will be a layer different from the main body structure on the surface of the composite secondary particles, which is disadvantageous for the desorption of lithium ions, reduces the content of the active component in the composite secondary particles, and is disadvantageous for the improvement of the specific capacity, rate, and low-temperature performance of the cathode material. If the usage amount of the coating layer is too small, the coating layer is too thin or the surface area of the composite secondary particles that can be coated is insufficient, and there is a phenomenon that the exposed composite secondary particles contact the electrolyte and side reactions occur, which is disadvantageous for the performance of the material. In the present application, as can be seen from experiments, when the mass ratio of the coating layer in the cathode composite material is within the above range and satisfies the above relational expression 1, the cathode composite material and the manufactured battery have excellent performance effects.

[0044] In some embodiments, the material of the coating layer is a hydroxide and / or an oxide of at least one element among Zr, Mn, Y, Ti, W, Al, Co, B, and Mg. More preferably, the material of the coating layer is at least one of Ti3O4, Mg(OH)2, W2O3, Al2O3, Co(OH)2, and B(OH)3.

[0045] The coating layer can be formed on the surface of the positive electrode material by the following method to obtain a positive electrode composite material.

[0046] Mix the positive electrode material and the coating material, then perform a second sintering, and perform a second crushing on the mixture after the second sintering to obtain a positive electrode composite material.

[0047] In some embodiments of the present application, the temperature of the second sintering is 500°C to 800°C, the time of the second sintering is 5.0 h to 8.0 h, the second crushing is performed using mechanical polishing, the rotation speed during mechanical polishing is 2000 r / min to 4000 r / min, and the time of the second crushing is 0.5 to 1 h. The purpose of the second sintering is to sinter the coating material on the surface of the composite secondary particles to form a coating layer to obtain a positive electrode composite material. In the second sintering process, some composite secondary particles are bonded by the coating material. The purpose of the second crushing is to separate the composite secondary particles bonded in the second sintering process, and to separate the coating material between the composite secondary particles. When the parameters within the above range are used for the second crushing, it does not affect the particle size of the composite secondary particles.

[0048] The battery according to the present application includes a positive electrode plate. The positive electrode plate includes a current collector and a positive electrode active material layer provided on the current collector. The positive electrode active material layer includes the positive electrode composite material according to any one of the above. The positive electrode active material layer is a film formed by applying a positive electrode slurry to the current collector.

[0049] Since the positive electrode plate in the present application includes the above positive electrode composite material, the compression density of the positive electrode plate is 3.5 g / mm 3The above is the case. Regarding the orientation of the electrode plate after compression, the intensity ratio of the 003 peak to the 110 peak is low, which indicates that the lower the orientation, the less likely it is to expand during charge and discharge.

[0050] The battery includes a positive electrode plate as described above, can reduce the battery impedance and the thickness change rate during high-temperature storage of the battery, improve the capacity retention rate after 500 cycles of the battery, and improve the electrical performance of the battery.

[0051] In some embodiments, the positive electrode slurry further includes a conductive agent and a binder, and the mass ratio of the positive electrode composite material, the conductive agent, and the binder is 100:(0.5 - 2):(0.5 - 2). Alternatively, the positive electrode active material layer includes a positive electrode composite material, a conductive agent, and a binder, and the mass ratio of the positive electrode composite material, the conductive agent, and the binder is 100:(0.5 - 2):(0.5 - 2).

[0052] The conductive agent includes at least one of carbon nanotubes, carbon black, and graphene. Preferably, the conductive agent includes carbon nanotubes, carbon black, and graphene.

[0053] The binder includes a first copolymer obtained by copolymerizing vinylidene fluoride and an ethylene hydrocarbon compound containing an active group, and a second copolymer obtained by copolymerizing vinylidene fluoride and chlorotrifluoroethylene. In the first copolymer, the mass ratio of vinylidene fluoride to the ethylene hydrocarbon compound containing an active group is (85.00 - 99.99):(0.01 - 15.00), and the active group includes at least one of a carboxyl group, an epoxy group, a hydroxy group, and a sulfonic acid group. In the second copolymer, the mass ratio of vinylidene fluoride to chlorotrifluoroethylene is (85.00 - 99.05):(0.05 - 15.00).

[0054] To better explain the technical means of the present application, the following will be described with reference to a plurality of specific embodiments.

Example

[0055] Manufacture of the positive electrode material: In step S100, a nickel cobalt manganese precursor and a second precursor are mixed and pre-sintered in a roller hearth kiln. In this embodiment, Ni 0.7 Co 0.1 Mn 0.2 (OH)2 is selected as the nickel cobalt manganese precursor, lithium hydroxide is selected as the second precursor, the temperature of the pre-sintering is 200°C to 500°C, and the time of the pre-sintering is 4 h to 6 h.

[0056] In step S200, the pre-sintered mixture is subjected to a first sintering, and after the first sintering, a first crushing is performed to obtain a positive electrode material. The first sintering includes, in sequence, a first temperature-rising stage, a first constant-temperature stage, a second temperature-rising stage, a second constant-temperature stage, and a cooling stage. The temperature of the first temperature-rising stage is 200°C to 800°C, the time of the first temperature-rising stage is 1.5 h to 3.5 h, the temperature of the first constant-temperature stage is 700°C to 800°C, the time of the first constant-temperature stage is 5.0 h to 8.0 h, the temperature of the second temperature-rising stage is 800°C to 1100°C, the time of the second temperature-rising stage is 2.0 h to 3.5 h, the temperature of the second constant-temperature stage is 1000°C to 1100°C, the time of the second constant-temperature stage is 8.0 h to 10.0 h. The cooling stage includes a first cooling sub-stage and a second cooling sub-stage. The temperature of the first cooling sub-stage is 1100°C to 600°C, the time is 2.5 to 4.0 h, the temperature of the second cooling sub-stage is 600°C to 200°C, the time is 0.5 to 2.0 h. The first crushing includes the steps of ball-milling the sintered agglomerates after the first sintering to obtain primary crushed products, and then jet-milling the primary crushed products. The rotation speed of the ball-milling is 4000 r / min to 8000 r / min, the time of the ball-milling is 1.5 h to 2.5 h, the pressure of the jet-milling is 5 MPa to 10 MPa, and the time of the jet-milling is 0.5 h to 1.5 h.

[0057] The obtained positive electrode material includes a plurality of composite secondary particles each including a plurality of positive electrode material primary particles. The positive electrode material primary particles are positive electrode materials having a layered structure, and the chemical formula is LiNi 0.7 Co 0.1 Mn 0.2 .

[0058] According to the method of the above embodiment, the manufacturing parameters are adjusted to obtain different cathode materials, and the particle size D50 of the cathode material, the specific surface area of the composite secondary particles, the number of primary cathode material particles in the composite secondary particles, and their particle size D50 are measured. The results are summarized in Table 1. a represents the value of the particle size D50 of the primary cathode material particles, with the unit of μm; b represents the value of the particle size D50 of the composite secondary particles, with the unit of μm; c represents the value of the specific surface area of the composite secondary particles, with the unit of m 2 / g; and d represents the number of primary cathode material particles in the composite secondary particles. The measurement methods for each item are as follows.

[0059] The measurement method for the particle size D50 of the primary cathode material particles is to use a CP-SEM image at 5000 times magnification to statistically analyze the long-side dimensions of about 300 primary cathode material particles, perform statistical distribution of the data, and obtain the particle size D50 of the primary cathode material particles.

[0060] Regarding the measurement method for the particle size D50 of the composite secondary particles, a laser particle size analyzer is used as the measurement device, and the reference model is Malvern 2000 / 3000. The measurement method is to disperse it in deionized water, perform ultrasonic treatment for more than 10 minutes, and then measure to obtain the particle size D50 of the composite secondary particles.

[0061] The measurement method for the specific surface area of the composite secondary particles is to use the gas adsorption method for multi-point measurement and use ISO-9277 / GB / T19587-2004 as the measurement standard.

[0062] The measurement method for the number of primary cathode material particles in the composite secondary particles is to use EBSD (electron backscatter diffraction) to measure various orientations of the primary cathode material particles inside the composite secondary particles. Different orientations of the primary cathode material particles are different and are shown in different colors by EBSD. In the EBSD image at 10K, calculate the average number of primary cathode material particles in the composite secondary particles within a unit area of 10 μm × 10 μm, and then obtain the average number of primary cathode material particles in one composite secondary particle based on the area of one composite secondary particle.

[0063] Manufacture of the positive electrode material composite: Mix the manufactured positive electrode material and the coating material, then perform a second sintering, and perform a second crushing on the mixture after the second sintering to obtain the positive electrode composite material. In this example, Ti3O4 is selected as the coating material, and the content of the coating material in the formed positive electrode composite material is 300 to 900 ppm. The temperature of the second sintering is 500°C to 800°C, the time of the second sintering is 5.0 h to 8.0 h, the second crushing is performed using mechanical polishing, the rotation speed during mechanical polishing is 2000 r / min to 4000 r / min, and the time of the second crushing is 0.5 to 1 h.

[0064] Manufacture of the positive electrode slurry: Mix the manufactured positive electrode composite material, the conductive agent, and the binder in a mass ratio of 100:1.2:1.2 to obtain the positive electrode slurry. The conductive agent includes carbon nanotubes, carbon black, and graphene, and the mass ratio of carbon nanotubes, carbon black, and graphene is 0.6:0.5:0.3. The binder consists of a first copolymer obtained by copolymerizing vinylidene fluoride and an ethylene hydrocarbon compound containing an active group, and a second copolymer obtained by copolymerizing vinylidene fluoride and chlorotrifluoroethylene. The molar ratio of the first copolymer to the second copolymer is 1:1. In the first copolymer, the mass ratio of vinylidene fluoride to the ethylene hydrocarbon compound containing an active group is 95.00:5.00, the active group contains a carboxyl group, and in the second copolymer, the mass ratio of vinylidene fluoride to chlorotrifluoroethylene is 96.00:4.00.

[0065] Perform a performance test on the manufactured positive electrode slurry, including measurement of the compression density of the electrode plate, measurement of the orientation after compression of the electrode plate, measurement of the battery impedance, cycle performance test, and storage performance test.

[0066] The method for measuring the compression density of the electrode plate is to apply the positive electrode slurry manufactured in each example to the electrode plate to form an uncompressed positive electrode plate, make the uncompressed positive electrode plate have a size of 40×100 mm, compress it with a Ohno compressor, and calculate the compression density of the electrode plate based on the areal density of the electrode plate and the thickness of the electrode plate after compression.

[0067] The method for measuring the orientation after compression of the electrode plate is to measure according to the general rules of the polycrystalline X-ray diffraction method of JY / T 009-1996, and characterize it by the peak intensity ratio of (003) and (110) respectively.

[0068] The method for measuring the battery impedance is to manufacture each of the produced cathode materials into a corresponding battery, adjust the battery to 60% SOC, and use a measurement method with a current of 3C and a charge-discharge time of 10s to measure the DCIR of the battery, and characterize the battery impedance by the product of the numerical value of the DCIR of the battery and the discharge capacity of 1 / 3C of the battery.

[0069] The cycle performance test method is to manufacture each of the produced cathode materials into a corresponding battery, and use a test method of charging to 4.2V at a constant current of 1C and discharging to 2.5V at a constant current of 1C under a temperature condition of 45±5°C. After 500 cycles, with the discharge capacity C1 of the first cycle as a reference, calculate the capacity retention rate, which is represented as cycle 45°C - C500 in Table 2.

[0070] The storage performance test method is to manufacture each of the produced cathode materials into a corresponding battery, charge the battery to 4.2V at a constant current of 0.2C, leave it standing at room temperature for 2h, record the initial thickness of the battery, store the battery in a constant temperature cabinet at 60°C for 28D, record the thickness after storage, and calculate the thickness change, which is represented as the 60°C - 28D thickness change rate in Table 2.

Table 1

[0071] Comparative Examples 1 to 3 are composite secondary particles manufactured by methods different from the above examples, and the values of a, b, c, and d of the composite secondary particles are shown in Table 1.

[0072] For the present application, Comparative Examples 4 to 14 are further added.

[0073] In Comparative Example 4, the manufacturing method of Comparative Example 4 is almost the same as that of Example 1. In the first sintering, it is different in that it does not use the method of alternately performing the heating stage and the constant temperature stage, but directly raises the temperature to 1000 °C to 1100 °C for sintering, and the sintering time is the same as that of Example 1.

[0074] In Comparative Example 5, the manufacturing method of Comparative Example 5 is almost the same as that of Example 1. In the first sintering, it is different in that it does not use the method of alternately performing the heating stage and the constant temperature stage, but uses a method including three sintering stages: a first sintering stage at a temperature of 400 to 600 °C for 4 h, a second sintering stage at a temperature of 600 to 700 °C for 4 h, and a third sintering stage at a temperature of 700 to 900 °C for 13 h.

[0075] In Comparative Example 6, the manufacturing method of Comparative Example 6 is almost the same as that of Example 1. It is different in that it uses a heating stage with a temperature of 200 °C to 1100 °C and a time equal to the total time of the first heating stage and the second heating stage of Example 1, and a constant temperature stage with a temperature of 1000 °C to 1100 °C and a time equal to the total time of the first constant temperature stage and the second constant temperature stage of Example 1 for sintering.

[0076] In Comparative Example 7, the manufacturing method of Comparative Example 7 is almost the same as that of Example 1. It is different in that the cooling time in the cooling stage is 1 h, that is, the cooling time of Comparative Example 7 is much smaller than that of Example 1.

[0077] In Comparative Example 8, the manufacturing method of Comparative Example 8 is almost the same as that of Example 1. It is different in that the rotation speed of the ball milling in the first crushing process is 2000 r / min, which is smaller than the rotation speed of the ball milling in Example 1.

[0078] In Comparative Example 9, the manufacturing method of Comparative Example 9 is substantially the same as that of Example 1, except that the rotational speed of ball milling in the first crushing process is 10,000 r / min, which is higher than the rotational speed of ball milling in Example 1.

[0079] In Comparative Example 10, the manufacturing method of Comparative Example 10 is substantially the same as that of Example 1, except that the pressure of jet milling is 3 MPa, which is lower than the pressure of jet milling in Example 1.

[0080] In Comparative Example 11, the manufacturing method of Comparative Example 11 is substantially the same as that of Example 1, except that the pressure of jet milling is 20 MPa, which is higher than the pressure of jet milling in Example 1.

[0081] In Comparative Example 12, the manufacturing method of Comparative Example 12 is substantially the same as that of Example 1, except that the usage amount of the coating material added in Step S300 is 2,000 ppm.

[0082] In Comparative Example 13, a small particle material is manufactured, the small particle material is composed of 1 to 3 primary particles of the positive electrode material, and the primary particles of the positive electrode material are LiNi 0.7 Co 0.1 Mn 0.2 and.

[0083] In Comparative Example 14, a secondary particle material is manufactured, the secondary particle material is composed of a plurality of primary particles of the positive electrode material, the particle size D50 of the secondary particle material is 50 μm, that is, the secondary particle material has a very large number of primary particles of the positive electrode material, and the primary particles of the positive electrode material are LiNi 0.7 Co 0.1 Mn 0.2 and.

[0084] For the positive electrode materials manufactured in the above Examples 1 to Example 8 and Comparative Examples 1 to Comparative Example 15 performance tests were carried out, and the performance effect data are shown in Table 2.

Table 2

[0085] As can be seen from the experimental data in Table 2, the cathode materials manufactured in Examples 1 to 8 have excellent performance effects. The compression density of the electrode plate is the highest, reaching 3.70 g / cm 3 . The higher the value of the compression density of the electrode plate, the higher the energy density of the cathode material. Regarding the orientation of the electrode plate after compression, the 003 peak / 110 peak intensity ratio can reach the lowest value of 25. The smaller the peak intensity ratio, the lower the orientation of the cathode material, which is beneficial for reducing the expansion degree during charge and discharge of the electrode plate. The battery impedance can reach the lowest value of 50 mΩ. The smaller the value of the battery impedance, the higher the conductivity of the battery. Regarding the cycle performance, the value of cycle 45°C - C500 (capacity retention rate) is the highest at 95% and can reach the lowest at 85%. This indicates that it has excellent cycle performance. Regarding the storage performance, the 60°C - 28D thickness change rate can reach the lowest value of 6%. The lower the value of the thickness change rate, the higher and more stable the storage performance of the battery.

[0086] As can be seen from Comparative Example 1, when the value of Relational Expression 1 is not within the scope of the present application and the number of primary particles of the cathode material in the composite secondary particles is too large, crushing occurs between the primary particles of the cathode material during the processes of compression and cycling of the electrode plate, and furthermore, new interfaces are formed, resulting in a decrease in battery performance. The orientation, cycle performance, and storage performance of the electrode plate in Comparative Example 1 are all low.

[0087] As can be seen from Comparative Example 2, when the value of Relational Expression 1 is not within the scope of the present application and the particle size D50 of the primary particles of the cathode material is too large, it directly affects the length of the diffusion path of lithium ions, so the capacity of the material is poorly exerted, the battery impedance increases, and the cycle performance and storage performance decrease. The cycle performance and storage performance of Comparative Example 2 are both low.

[0088] As can be seen from Comparative Example 3, when the value of Relational Expression 1 is not within the scope of the present application, the specific surface area of the composite secondary particles is too large, and the number of primary particles of the positive electrode material in the composite secondary particles is too large, the specific surface area of the composite secondary particles is too large, the side reaction between the composite secondary particles and the electrolytic solution increases, gas generation becomes serious, which affects the cycle performance of the battery. When the number of primary particles of the positive electrode material in the composite secondary particles is too large, during the compression of the electrode plate and the process of cycling, crushing occurs between the primary particles of the positive electrode material, and furthermore, a new interface is formed, resulting in a decrease in battery performance. The compression density of the electrode plate, the orientation after compression of the electrode plate, the battery impedance, the cycle performance, and the storage performance of Comparative Example 3 are all low.

[0089] As can be seen from Comparative Example 4, each performance data of the composite secondary particles manufactured without using the method of sintering in a stepwise temperature-dividing manner and the method of sintering by alternately performing a temperature-rising stage and a constant-temperature stage is slightly inferior to the data of Examples 1 to 8 Examples, but is superior to the data of Comparative Examples 1 to 3, which indicates that using the first sintering method of the present application is advantageous for forming a positive electrode material that satisfies Relational Expression 1 of the present application.

[0090] As can be seen from Comparative Example 5, when using the method of sintering in a stepwise temperature-dividing manner but without using the method of sintering by alternately performing a temperature-rising stage and a constant-temperature stage, each performance data of the composite secondary particles is slightly inferior to the data of Examples 1 to 8 Examples, but is superior to the data of Comparative Examples 1 to 3, which indicates that using the first sintering method of the present application is advantageous for forming a positive electrode material that satisfies Relational Expression 1 of the present application.

[0091] As can be seen from Comparative Example 6 and Comparative Example 7, when the first sintering is within the scope of the present application, it is advantageous for the formation of the positive electrode material that satisfies the relational expression 1 of the present application. In Comparative Example 6, since only one temperature increase and one constant temperature are used, the thermal decomposition process of the lithium source and the precursor material in the early stage is insufficient, the removal of their moisture or CO2 is insufficient, and the positive electrode material in the sintering process cannot be sufficiently crystallized. In Comparative Example 7, when the cooling rate is too fast, a large stress remains inside the composite secondary particles. Therefore, after the material is rapidly cooled, the internal stress of the material particles is large, and different degrees of crushing occur in both the primary particles and the composite secondary particles of the positive electrode material, and cracks occur in the subsequent use process and the cycle process, affecting the performance of the material.

[0092] As can be seen from Comparative Example 8 and Comparative Example 9, when the speed of ball milling is within the scope of the present application, it is advantageous for the formation of the positive electrode material that satisfies the relational expression 1 of the present application. When the speed of ball milling is too fast, the composite secondary particles are too small, and when the speed of ball milling is too slow, the composite secondary particles are too large, affecting the performance of the material.

[0093] As can be seen from Comparative Example 10 and Comparative Example 11, when the pressure of air flow pulverization is within the scope of the present application, it is advantageous for the formation of the positive electrode material that satisfies the relational expression 1 of the present application. When the pressure of air flow pulverization is too small, the composite secondary particles are too large and the particle size distribution of the composite secondary particles becomes wide. When the pressure of air flow pulverization is too large, the composite secondary particles are too small and the particle size distribution of the composite secondary particles becomes wide, and there are many fine powders, affecting the performance of the material.

[0094] As can be seen from Comparative Example 12, when a large amount of coating material is coated on the surface of the positive electrode material, it becomes difficult for lithium to desorb and insert during the charge and discharge process of the material, and the battery impedance of Comparative Example 12 increases, but the cycle performance and storage performance are still higher than those of Comparative Examples 1 to 5.

[0095] As can be seen from Comparative Example 13 and Comparative Example 14, currently, when the performance of the conventional small particle materials and secondary particle materials does not satisfy the relational expression 1 of the present application, the performance effect is low.

[0096] Although the embodiments of the present application have been shown and described, those skilled in the art can make various changes, modifications, substitutions, and variations to these embodiments without departing from the principle and spirit of the present application, and it can be understood that the scope of the present application is limited by the claims and their equivalents.

Claims

1. A positive electrode composite material comprising a positive electrode material and a coating layer coated on the surface of the positive electrode material, wherein the mass ratio of the coating layer in the positive electrode composite material is 300 ppm to 900 ppm; the positive electrode material includes a plurality of composite secondary particles, each of the composite secondary particles includes a plurality of positive electrode material primary particles, and the composite secondary particles satisfy the following relational expression 1: 0.9 ≤ 0.1d / a + b × c ≤ 20 (Relational Expression 1) (In the formula, a represents the value of the D50 particle size of the primary particles of the positive electrode material, the unit is μm, b represents the value of the D50 particle size of the composite secondary particles, the unit is μm, c represents the value of the specific surface area of the composite secondary particles, and the unit is m ２ / g, and d represents the number of the primary particles of the positive electrode material in each composite secondary particle). the range of the value of a is 0.5 ≤ a ≤ 3.5, the range of the value of b is 3 ≤ b ≤ 12, the range of the value of c is 0.3 ≤ c ≤ 1.2, and the range of the value of d is 3 ≤ d ≤ 20; The primary particles of the positive electrode material are LiNi ｘ Co ｙ M ｚ wherein the value range of x is 0.33 ≦ x ≦ 0.98, the value range of y is 0.01 ≦ y ≦ 0.33, the value range of z is 0.01 ≦ z ≦ 0.33, and x + y + z = 1, and M is at least one of Mn, Al, Zr, Ti, Y, Sr, and W. A positive electrode composite material characterized by this.

2. mixing a first precursor and a second precursor, and performing preliminary sintering to obtain a preliminarily sintered mixture; performing first sintering on the preliminarily sintered mixture, and performing first crushing after the first sintering to obtain a positive electrode material including a plurality of composite secondary particles, wherein each of the plurality of composite secondary particles includes a plurality of positive electrode material primary particles, the method for manufacturing the positive electrode composite material according to claim 1, characterized by comprising the steps.

3. the composite secondary particles satisfy the following relational expression 2, the method for manufacturing the positive electrode composite material according to claim 2, characterized by this. 2.5 ≤ 0.1d / a + b × c ≤ 9 (Relational Expression 2) (In the formula, a represents the value of the D50 particle size of the primary particles of the positive electrode material, the unit is μm, b represents the value of the D50 particle size of the composite secondary particles, the unit is μm, c represents the value of the specific surface area of the composite secondary particles, the unit is m ２ / g, and d represents the number of the primary particles of the positive electrode material in the composite secondary particles.)

4. the first sintering sequentially includes a first temperature rising stage, a first constant temperature stage, a second temperature rising stage, a second constant temperature stage and a cooling stage; the temperature of the first temperature rising stage is 200°C to 800°C, the time of the first temperature rising stage is 1.5 h to 3.5 h, the temperature of the first constant temperature stage is 700°C to 800°C, the time of the first constant temperature stage is 5.0 h to 8.0 h, the temperature of the second temperature rising stage is 800°C to 1100°C, the time of the second temperature rising stage is 2.0 h to 3.5 h, the temperature of the second constant temperature stage is 1000°C to 1100°C, and the time of the second constant temperature stage is 8.0 h to 10.0 h; the cooling stage includes a first cooling sub-stage and a second cooling sub-stage, the temperature of the first cooling sub-stage is 1100°C to 600°C, the time is 2.5 to 4.0 h, the temperature of the second cooling sub-stage is 600°C to 200°C, and the time is 0.5 to 2.0 h, the method for manufacturing the positive electrode composite material according to claim 2 or 3, characterized by this.

5. The first crushing includes the steps of ball-milling the sintered aggregate after the first sintering to obtain primary crushed material, and then jet-milling the primary crushed material. The rotational speed of the ball-milling is 4000 r / min to 8000 r / min, the time of the ball-milling is 1.5 h to 2.5 h, the pressure of the jet-milling is 5 MPa to 10 MPa, and the time of the jet-milling is 0.5 h to 1.5 h. The method for manufacturing the positive electrode composite material according to any one of claims 2 to 4 is characterized by the above.

6. A battery comprising a positive electrode plate, the positive electrode plate including a current collector and a positive electrode active material layer provided on the current collector, the positive electrode active material layer including the positive electrode composite material according to claim 1.

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