Cathode material, preparation method thereof, cathode composite material, preparation method thereof, secondary battery, and electric device

Abstract

A positive electrode material includes positive electrode material particles and a coating layer on a surface of the positive electrode material particles, a material of the coating layer includes an antioxidant, and the antioxidant includes one or more of a hindered phenol antioxidant and an amine antioxidant.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of secondary batteries, and more particularly to a positive electrode material and a preparation method thereof, a positive electrode composite material and a preparation method thereof, a secondary battery, and an electric device. BACKGROUND

[0002] The statements herein are provided only to enhance understanding of the present application and are not necessarily intended to constitute the prior art.

[0003] Due to the shortage of petroleum chemical energy and the deterioration of the natural environment, new energy vehicles gradually increase the market share of automobiles, and have the possibility of replacing oil vehicles in the future. Since an automobile is a large power consumption electric device, the rate performance and cycle performance of a battery directly affect the user experience, and therefore, how to improve the rate performance and cycle performance of a secondary battery is a research hotspot in the field. SUMMARY

[0004] According to various embodiments of the present application, a positive electrode material and a preparation method thereof, a positive electrode composite material and a preparation method thereof, a secondary battery, and an electric device are provided.

[0005] In a first aspect of the present application, a positive electrode material is provided, comprising positive electrode material particles and a coating layer located on the surface of the positive electrode material particles, the material of the coating layer comprising an antioxidant, the antioxidant comprising one or more of a hindered phenolic antioxidant and an amine antioxidant.

[0006] During long-term cycling, the positive electrode active material is prone to breakage, forming positive electrode material particles. The fresh surface exposed by the positive electrode material particles has strong oxidizing properties, which continuously consumes electrolyte and reduces the rate performance and cycle performance of the battery. By selecting an appropriate type of antioxidant to form a coating layer on the surface of the positive electrode material particles, the consumption of electrolyte caused by the oxidizing properties of the positive electrode material particles can be effectively improved, without causing significant negative effects on other performance of the battery, and the rate performance and cycle performance of the battery can be effectively improved.

[0007] In some embodiments, the hindered phenolic antioxidant comprises one or more of 2,6-di-tert-butyl-4-methylphenol, 2,6-di-tert-butyl-4-aminophenol, 2,6-di-tert-butyl-4-(dimethylaminomethyl)phenol, tert-butyl hydroquinone, and 2,5-di-tert-butyl hydroquinone. The aforementioned hindered phenolic antioxidant not only has good antioxidant properties, but also does not cause negative effects on other performance of the battery, and can form a good coating on the positive electrode material particles.

[0008] In some embodiments, the amine antioxidant includes one or more of N,N'-di-sec-butyl-p-phenylenediamine, (3,5-di-tert-butyl-4-hydroxybenzyl) aniline, 2,2,6,6-tetramethylpiperidine, bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate, bis(1-octyloxy-2,2,6,6-tetramethyl-4-piperidyl) sebacate, stearyl(2,2,6,6-tetramethyl-4-piperidyl) sebacate, and N,N'-bis(2,2,6,6-tetramethyl-4-piperidyl)-1,3-benzenedicarboxamide. The aforementioned amine antioxidants not only have good antioxidant properties, but also do not negatively affect other properties of the battery, and can form a good coating on the positive electrode material particles.

[0009] In some embodiments, the mass percentage of the antioxidant in the positive electrode material is 0.1% to 3%. A suitable amount of antioxidant provides antioxidant properties and forms a coating layer with a suitable coating density, avoids adversely affecting the transport of lithium ions, and does not excessively occupy the mass of the positive electrode material, thereby reducing the energy density of the battery.

[0010] In some embodiments, the material of the coating layer further includes a conductive agent.

[0011] Optionally, the conductive agent includes one or more of a polypyrrole conductive agent, a polyaniline conductive agent, and a functional conductive carbon.

[0012] Further optionally, the functional conductive carbon includes one or more of carbon nanotubes, carbon black, and graphite, and the functional conductive carbon has one or more of carboxyl groups, hydroxyl groups, and amino groups grafted on the surface thereof.

[0013] The introduction of the conductive agent having groups such as carboxyl groups, hydroxyl groups, or amino groups into the coating layer can form hydrogen bonds with the antioxidant, thereby improving the binding force between the antioxidant and the positive electrode material particles. On the other hand, the conductive agent can form a conductive network between the positive electrode particles, thereby avoiding the deactivation of the positive electrode material particles due to the loss of electrical contact after the particles are broken during cycling, and affecting the electrical performance of the battery. In particular, the conductive agent having amino groups can adsorb metal ions dissolved from the positive electrode material due to the strong electronegativity of the lone pair of electrons on the nitrogen atom of the amino group, thereby improving the cycle performance of the battery.

[0014] In some embodiments, the mass percentage of the conductive agent in the positive electrode material is 0.5% to 10%. A suitable amount of conductive agent provides conductive properties and improves the binding force between the antioxidant and the positive electrode material particles, while forming a coating layer with a suitable coating density, avoiding adversely affecting the transport of lithium ions, and not excessively occupying the mass of the positive electrode material, thereby reducing the energy density of the battery.

[0015] In some embodiments, the positive electrode material is a primary particle, and the Dv50 particle size of the positive electrode material ranges from 100 nm to 1 μm. A suitable particle size allows the primary particle to be more easily prepared into a secondary particle with a uniform particle size distribution.

[0016] In some embodiments, the thickness of the coating layer ranges from 2 nm to 100 nm; alternatively, the thickness of the coating layer ranges from 2 nm to 50 nm; further alternatively, the thickness of the coating layer ranges from 5 nm to 30 nm. A suitable thickness of the coating layer provides sufficient oxidation resistance and electrical conductivity, while not hindering the transport of lithium ions, affecting the performance of the battery.

[0017] In some embodiments, the positive electrode material particle comprises one or more of LiCoO2, LiNi a Co b Mn (1-a-b) O2, LiNi c Co d Al (1-c-d) O2, eLi2MnO3.(1-e)LiMO2.

[0018] wherein a to e are independently selected from 0 to 1.

[0019] M comprises one or more of Ni, Co, and Mn.

[0020] A suitable type of positive electrode material particle is more suitable for the thickness of the coating layer and other parameters in the present application, thereby further improving the oxidation resistance and electrical conductivity of the positive electrode material particle.

[0021] In a second aspect, the present application provides a method for preparing the positive electrode material according to one or more of the preceding embodiments, comprising the following steps:

[0022] According to the positive electrode material according to one or more of the preceding embodiments, raw materials are prepared, and each raw material is ball milled.

[0023] In some embodiments, the ball milling satisfies one or more of the following (1) to (7):

[0024] (1) the ball milling medium comprises one or more of zirconium balls, stainless steel balls, and polyurethane balls;

[0025] (2) the diameter of the ball milling medium ranges from 5 mm to 20 mm;

[0026] (3) the ball milling medium comprises large balls and small balls, the diameter of the large balls ranges from 10 mm to 20 mm, and the diameter of the small balls ranges from 5 mm to 10 mm; alternatively, the mass percentage content of the small balls in the ball milling medium ranges from 10% to 30%, and the mass percentage content of the large balls in the ball milling medium ranges from 70% to 90%.

[0027] (4) The mass ratio of raw material to ball milling media is (10-20):1;

[0028] (5) The ball milling is a wet ball milling process, and the solvent used includes one of chloroform, acetone, toluene and benzene; optionally, the mass ratio of the raw material to the solvent is 1:(1 to 10);

[0029] (6) The rotation speed of the ball mill is 400 rpm to 600 rpm;

[0030] (7) The ball milling time is 0.5h to 2h.

[0031] Appropriate ball milling process parameters are more conducive to forming a uniform coating layer with suitable thickness and good adhesion to the cathode material particles, thereby improving the rate performance and cycle performance of the battery.

[0032] A third aspect of this application provides a positive electrode composite material, comprising the positive electrode material described in one or more of the foregoing embodiments and a lithium-containing binder;

[0033] Optionally, the lithium-containing binder includes one or more of lithium carboxymethyl cellulose, lithium polyacrylate, and lithium alginate.

[0034] Preparing the aforementioned cathode material with a lithium-containing binder to form a cathode composite material can improve dispersibility during slurry preparation, preventing agglomeration due to small particle size, and avoiding coating detachment caused by mechanical friction during slurry preparation. Furthermore, it can increase the compaction density of the electrode sheet. Since the binder contains lithium, it can further enhance the lithium-ion conductivity, thereby further improving the rate performance of the battery.

[0035] In some embodiments, the lithium-containing binder in the cathode composite material has a mass percentage of 1% to 10%. Appropriate amounts of lithium-containing binder can provide sufficient adhesion while avoiding excessive amounts that could reduce the battery's energy density.

[0036] In some embodiments, the positive electrode composite material contains 90% to 99% by mass of the positive electrode material.

[0037] In some embodiments, the cathode composite material is a secondary particle with a Dv50 particle size ranging from 5 μm to 20 μm. A suitable particle size allows for better dispersion of the cathode composite material during slurry preparation, resulting in a more uniform active material layer, which is beneficial for improving the battery's electrical performance and reducing resistance.

[0038] A fourth aspect of this application provides a method for preparing the positive electrode composite material described in one or more of the foregoing embodiments, comprising the following steps:

[0039] The cathode material, the lithium-containing binder, and the solvent are mixed and then spray-granulated.

[0040] In some embodiments, the spray granulation temperature is 120°C to 140°C, and the spray granulation discharge rate is 5 mL / min to 20 mL / min. Suitable spray granulation process parameters contribute to the formation of a cathode composite material with uniform particle size distribution and uniform cathode material distribution.

[0041] A fifth aspect of this application provides a secondary battery, including a positive electrode, a negative electrode, and a separator, wherein the separator is disposed between the positive electrode and the negative electrode.

[0042] The positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector. The positive active material layer includes one or more of the positive electrode materials described in one or more of the foregoing embodiments and the positive electrode composite materials described in one or more of the foregoing embodiments.

[0043] In some embodiments, the positive electrode active material layer further includes an auxiliary antioxidant, which includes one or more of phosphites and thioesters;

[0044] Optionally, the auxiliary antioxidant in the positive electrode active material layer has a mass percentage content of 0.01% to 2%.

[0045] The introduction of auxiliary antioxidants can further enhance antioxidant performance, and the appropriate amount of auxiliary antioxidants balances the contradiction between antioxidant properties and energy density.

[0046] A sixth aspect of this application provides a battery module comprising the aforementioned secondary battery.

[0047] A seventh aspect of this application provides a battery pack that includes the aforementioned battery module.

[0048] An eighth aspect of this application provides an electrical device that includes one or more of the aforementioned secondary battery, battery module, and battery pack.

[0049] Details of one or more embodiments of this application are set forth in the following drawings and description. Other features, objects, and advantages of this application will become apparent from the specification, drawings, and claims. Attached Figure Description

[0050] To better describe and illustrate embodiments or examples of the inventions disclosed herein, reference may be made to one or more accompanying drawings. Additional details or examples used to describe the drawings should not be considered as limiting the scope of any of the disclosed inventions, the embodiments or examples currently described, or the best mode of these inventions as currently understood.

[0051] Figure 1 This is a schematic diagram of a secondary battery according to one embodiment of this application.

[0052] Figure 2 yes Figure 1 An exploded view of a secondary battery according to one embodiment of this application is shown.

[0053] Figure 3 This is a schematic diagram of a battery module according to one embodiment of this application.

[0054] Figure 4 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0055] Figure 5 yes Figure 4 An exploded view of a battery pack according to one embodiment of this application is shown.

[0056] Figure 6 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application.

[0057] Explanation of reference numerals in the attached figures:

[0058] 1: Battery pack; 2: Upper casing; 3: Lower casing; 4: Battery module; 5: Secondary battery; 51: Housing; 52: Electrode assembly; 53: Cover plate; 6: Electrical device. Detailed Implementation

[0059] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0060] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0061] Improving the rate performance and cycle performance of rechargeable batteries has always been a research hotspot in the battery field. Many factors influence rate and cycle performance. For example, extensive research has shown that positive electrode active materials are prone to breakage during long-term cycling, forming positive electrode material particles. The exposed fresh surfaces of these particles have strong oxidizing properties, continuously consuming electrolyte and adversely affecting the battery's rate and cycle performance.

[0062] Based on the above background, in a first aspect, this application provides a positive electrode material, including positive electrode material particles and a coating layer located on the surface of the positive electrode material particles. The coating layer is made of an antioxidant, which includes one or more of hindered phenolic antioxidants and amine antioxidants.

[0063] This application forms a coating layer on the surface of cathode material particles by selecting appropriate types of antioxidants. During cycling, hydrogen atoms in these antioxidants can be released from the antioxidant molecules and combine with peroxide free radicals formed by oxidation reactions in the battery, thereby eliminating free radicals and inhibiting further oxidation reactions caused by peroxide free radicals. This effectively improves electrolyte consumption caused by the oxidation of cathode material particles and does not have a significant negative impact on other battery performance, thus effectively improving the rate performance and cycle performance of the battery.

[0064] In some embodiments, the hindered phenolic antioxidants include one or more of 2,6-di-tert-butyl-4-methylphenol, 2,6-di-tert-butyl-4-aminophenol, 2,6-di-tert-butyl-4-(dimethylaminomethyl)phenol, tert-butylhydroquinone, and 2,5-di-tert-butylhydroquinone. These hindered phenolic antioxidants not only possess excellent antioxidant properties but also do not negatively impact other battery performance characteristics and can effectively coat the cathode material particles.

[0065] In some embodiments, the amine antioxidants include one or more of N,N'-di-sec-butyl-p-phenylenediamine, (3,5-di-tert-butyl-4-hydroxybenzyl)aniline, 2,2,6,6-tetramethylpiperidine, bis(2,2,6,6-tetramethyl-4-piperidinyl) sebacate, bis(1-octoxy-2,2,6,6-tetramethyl-4-piperidinyl) sebacate, stearate (2,2,6,6-tetramethyl-4-piperidinol) ester, and N,N'-bis(2,2,6,6-tetramethyl-4-piperidinyl)-1,3-phenylenediamide. These amine antioxidants not only possess excellent antioxidant properties but also do not negatively impact other battery performance characteristics and can effectively coat the cathode material particles.

[0066] In some embodiments, the antioxidant content in the cathode material is 0.1% to 3% by mass. Appropriate antioxidant dosage provides antioxidant performance while forming a coating layer with suitable density, avoiding adverse effects on lithium-ion transport, and does not excessively occupy the mass of the cathode material, thus preventing a decrease in battery energy density.

[0067] In some embodiments, the coating layer may also include a conductive agent;

[0068] Optionally, the conductive agent includes one or more of polypyrrole conductive agents, polyaniline conductive agents, and functional conductive carbon;

[0069] Further optionally, the functional conductive carbon includes one or more of carbon nanotubes, carbon black, and graphite, and the surface of the functional conductive carbon is grafted with one or more of carboxyl groups, hydroxyl groups, and amino groups.

[0070] Introducing conductive agents containing carboxyl, hydroxyl, or amino groups into the coating layer can, on the one hand, form hydrogen bonds with antioxidants, enhancing the binding force between antioxidants and cathode material particles; on the other hand, it can form a conductive network between cathode particles, preventing the cathode material particles from detaching from electrical contacts and becoming inactive after cycle breakage, thus affecting the battery's rate performance. In particular, conductive agents containing amino groups, due to the lone pair electrons in the amino nitrogen atoms, possess strong electronegativity and can adsorb metal ions dissolved from the cathode material, which is beneficial for improving the battery's cycle performance.

[0071] Preferably, the conductive agent includes one or more of polypyrrole-based conductive agents, polyaniline-based conductive agents, and carbon nanotubes; more preferably, the conductive agent includes one or more of polypyrrole-based conductive agents and polyaniline-based conductive agents. Linear conductive agents such as polypyrrole, polyaniline, and carbon nanotubes are beneficial for forming a more comprehensive coating on the surface of the cathode material particles, especially polypyrrole and polyaniline, which are more conducive to the formation of the coating layer due to their better flexibility.

[0072] In some embodiments, the weight-average molecular weight range of the polypyrrole-based conductive agent and the polyaniline-based conductive agent is independently from 100,000 Da to 1,000,000 Da. Optionally, the weight-average molecular weight range of the polypyrrole-based conductive agent and the polyaniline-based conductive agent may also be independently from 200,000 Da, 300,000 Da, 400,000 Da, 500,000 Da, 600,000 Da, 700,000 Da, 800,000 Da, or 900,000 Da. A suitable weight-average molecular weight allows the conductive agent to have a suitable size, which is more conducive to the formation of the coating layer and makes it easier to form a coating layer with a suitable coating density.

[0073] In some embodiments, the carbon nanotubes have a diameter of 5 nm to 100 nm and a length of 20 μm to 80 μm. Optionally, the diameter of the carbon nanotubes can also be, for example, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, 75 nm, 80 nm, 85 nm, 90 nm, or 95 nm; and the length of the carbon nanotubes can also be, for example, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, 60 μm, 65 μm, 70 μm, or 75 μm. Carbon nanotubes of suitable size are more conducive to the formation of the coating layer and make it easier to form a coating layer with a suitable coating density.

[0074] In some embodiments, the Dv50 particle size range of carbon black and graphite is independently 30 nm to 150 nm. Optionally, the Dv50 particle size range of carbon black and graphite can also be independently 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 110 nm, 120 nm, 130 nm, or 40 nm, for example. Carbon black or graphite with suitable particle size is more conducive to the formation of the coating layer and makes it easier to form a coating layer with a suitable coating density.

[0075] In some embodiments, the mass percentage of the conductive agent in the cathode material is 0.5% to 10%. Optionally, the mass percentage of the conductive agent may also be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, or 9%. A suitable amount of conductive agent provides conductivity, enhances the bonding force between the antioxidant and the cathode material particles, and forms a coating layer with a suitable coating density, avoiding adverse effects on lithium-ion transport, and without excessively occupying the mass of the cathode material, thus preventing a decrease in battery energy density.

[0076] In some embodiments, the cathode material is a primary particle, and the Dv50 particle size range of the cathode material is 100 nm to 1 μm. Optionally, the Dv50 particle size of the cathode material can be, for example, 150 nm to 550 nm, or even 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, or 900 nm. A suitable particle size makes it easier to prepare secondary particles with a uniform particle size distribution from the primary particles.

[0077] In this application, Dv50 refers to the particle size at which the cumulative volume distribution number of particles reaches 50% in the particle size cumulative distribution curve. Physically, it means that the volume percentage of particles smaller than (or larger than) this particle size value is 50%. As an example, Dv50 can be conveniently determined using a laser particle size analyzer, such as the Mastersizer 2000E laser particle size analyzer from Malvern Instruments Ltd., UK, according to GB / T 19077-2016 Particle Size Distribution Laser Diffraction Method.

[0078] In some embodiments, the thickness of the coating layer is 2 nm to 100 nm; optionally, the thickness of the coating layer is 2 nm to 50 nm; more preferably, the thickness of the coating layer is 5 nm to 30 nm. The thickness of the coating layer can also be, for example, 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, 75 nm, 80 nm, 85 nm, 90 nm, or 95 nm. A suitable coating layer thickness provides sufficient oxidation resistance and conductivity without hindering lithium-ion transport and affecting battery performance.

[0079] In some embodiments, the cathode material particles include LiCoO2 and LiNi. a Co b Mn (1-a-b) O2, LiNi c Co d Al (1-c-d) One or more of O2, eLi2MnO3·(1-e)LiMO2;

[0080] Where a to e are independently selected from 0 to 1;

[0081] M includes one or more of Ni, Co, and Mn.

[0082] a to e can also be independently selected from 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, or 0.9.

[0083] Suitable types of cathode material particles are more suitable for various parameters such as coating thickness in this application, thereby further improving the oxidation resistance and conductivity of cathode material particles.

[0084] A second aspect of this application provides a method for preparing a positive electrode material according to one or more of the foregoing embodiments, comprising the following steps:

[0085] The raw materials involved in the cathode material according to one or more of the aforementioned embodiments are prepared, and each raw material is ball-milled.

[0086] In some implementations, the ball mill satisfies one or more of the following conditions (1) to (7):

[0087] (1) The milling media include one or more of zirconium balls, stainless steel balls and polyurethane balls;

[0088] (2) The diameter of the ball milling media is 5 mm to 20 mm; the diameter of the ball milling media can also be, for example, 10 nm or 15 nm;

[0089] (3) The milling media includes large balls and small balls, the diameter of the large balls is 10 mm to 20 mm, and the diameter of the small balls is 5 mm to 10 mm; optionally, the mass percentage of small balls in the milling media is 10% to 30%, and the mass percentage of large balls in the milling media is 70% to 90%; the mass percentage of small balls in the milling media can also be, for example, 15%, 20%, or 25%; the mass percentage of large balls in the milling media can also be, for example, 75%, 80%, or 85%;

[0090] (4) The mass ratio of raw material to ball milling media is (10-20):1; the mass ratio of raw material to ball milling media can also be, for example, 12:1, 14:1, 16:1 or 18:1;

[0091] (5) The ball milling is a wet ball milling process, and the solvent used includes one of chloroform, acetone, toluene and benzene; optionally, the mass ratio of raw material to solvent is 1:(1 to 10); the mass ratio of raw material to solvent can also be 1:2, 1:4, 1:6 or 1:8.

[0092] (6) The rotation speed of the ball mill is 400 rpm to 600 rpm; the rotation speed of the ball mill can also be, for example, 450 rpm, 500 rpm or 550 rpm;

[0093] (7) The ball milling time is 0.5h to 2h; the ball milling time can also be 1h or 1.5h.

[0094] Appropriate ball milling process parameters are more conducive to forming a uniform coating layer with suitable thickness and good adhesion to the cathode material particles, thereby improving the rate performance and cycle performance of the battery.

[0095] A third aspect of this application provides a positive electrode composite material, comprising a positive electrode material of one or more of the foregoing embodiments and a lithium-containing binder;

[0096] Optionally, the lithium-containing binder includes one or more of lithium carboxymethyl cellulose, lithium polyacrylate, and lithium alginate.

[0097] Preparing the aforementioned cathode material with a lithium-containing binder to form a cathode composite material can improve dispersibility during slurry preparation, preventing agglomeration due to small particle size, and avoiding coating detachment caused by mechanical friction during slurry preparation. Furthermore, it can increase the compaction density of the electrode sheet. Since the binder contains lithium, it can further enhance the lithium-ion conductivity, thereby further improving the rate performance of the battery.

[0098] In some embodiments, the lithium-containing binder in the cathode composite material has a mass percentage of 1% to 10%. Optionally, the mass percentage of the lithium-containing binder may be, for example, 1.5% to 5%, or even 2%, 4%, 6%, or 8%. A suitable amount of lithium-containing binder can provide sufficient adhesion while avoiding excessive use that would reduce the battery's energy density.

[0099] In some embodiments, the mass percentage of the cathode material in the cathode composite material is 90% to 99%. The mass percentage of the cathode material can also be, for example, 92%, 94%, 96%, or 98%.

[0100] In some embodiments, the cathode composite material is a secondary particle, and the Dv50 particle size range of the cathode composite material is 5 μm to 20 μm. The Dv50 particle size of the cathode composite material can also be, for example, 6 μm, 8 μm, 10 μm, 12 μm, 14 μm, 16 μm, or 18 μm. A suitable particle size allows for better dispersion of the cathode composite material during slurry preparation, resulting in a more uniform active material layer, which is beneficial for improving the electrical performance of the battery and reducing resistance.

[0101] A fourth aspect of this application provides a method for preparing the positive electrode composite material according to one or more of the foregoing embodiments, comprising the following steps:

[0102] The cathode material, lithium-containing binder, and solvent are mixed and then spray-granulated.

[0103] In some embodiments, the spray granulation temperature is 120°C to 140°C, and the spray granulation discharge rate is 5 mL / min to 20 mL / min. Optionally, the spray granulation temperature may also be 125°C, 130°C, or 135°C; and the spray granulation discharge rate may also be 10 mL / min or 15 mL / min. Suitable spray granulation process parameters help to form a cathode composite material with uniform particle size distribution and uniform cathode material distribution.

[0104] A fifth aspect of this application provides a secondary battery, including a positive electrode, a negative electrode, and a separator, wherein the separator is disposed between the positive electrode and the negative electrode.

[0105] The positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector. The positive active material layer includes one or more of the positive electrode materials of the aforementioned one or more embodiments and the positive electrode composite materials of the aforementioned one or more embodiments.

[0106] In some embodiments, the positive electrode active material layer also includes an auxiliary antioxidant, which includes one or more of phosphites and thioesters;

[0107] Optionally, the mass percentage of the auxiliary antioxidant in the positive electrode active material layer is 0.01% to 2%. Optionally, the amount of auxiliary antioxidant may also be, for example, 0.5%, 1%, or 1.5%.

[0108] The introduction of auxiliary antioxidants can further enhance antioxidant performance, and the appropriate amount of auxiliary antioxidants balances the contradiction between antioxidant properties and energy density.

[0109] A sixth aspect of this application provides a battery module comprising the aforementioned secondary battery.

[0110] A seventh aspect of this application provides a battery pack that includes the aforementioned battery module.

[0111] An eighth aspect of this application provides an electrical device that includes one or more of the aforementioned secondary battery, battery module, and battery pack.

[0112] Details of one or more embodiments of this application are set forth in the following drawings and description. Other features, objects, and advantages of this application will become apparent from the specification, drawings, and claims.

[0113] In addition, the secondary battery, battery module, battery pack and power device of this application will be described below with appropriate reference to the accompanying drawings.

[0114] In one embodiment of this application, a secondary battery is provided.

[0115] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0116] Positive electrode sheet

[0117] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector. The positive electrode film layer includes one or more of the conventional positive electrode active material, the positive electrode material of the first aspect of this application, and the positive electrode composite material of the third aspect of this application.

[0118] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0119] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0120] In some embodiments, conventional positive electrode active materials may be those known in the art for use in batteries. As an example, conventional positive electrode active materials may include at least one of the following: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co o.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05 At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0121] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0122] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0123] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0124] Negative electrode sheet

[0125] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0126] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0127] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0128] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0129] In some embodiments, the negative electrode film layer may optionally include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0130] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0131] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0132] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0133] electrolytes

[0134] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0135] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0136] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0137] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0138] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0139] Separating membrane

[0140] In some embodiments, the secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0141] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0142] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0143] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0144] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0145] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 This is an example of a square-structured secondary battery 5.

[0146] In some implementations, refer to Figure 2 The outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed over the opening to close the receiving cavity. A positive electrode, a negative electrode, and a separator can be formed into an electrode assembly 52 using a winding or stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0147] In some implementations, the secondary batteries can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0148] Figure 3 This is battery module 4, used as an example. (See reference...) Figure 3 In battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary batteries 5 can be fixed in place using fasteners.

[0149] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0150] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0151] Figure 4 and Figure 5 This is battery pack 1 as an example. (See reference...) Figure 4 and Figure 5The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0152] In addition, this application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided in this application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices, electric vehicles, electric trains, ships and satellites, energy storage systems, etc. Among them, mobile devices may be, for example, mobile phones, laptops, etc.; electric vehicles may be, for example, pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc., but are not limited to these.

[0153] As the electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0154] Figure 6 Here is an example of an electrical device 6. This electrical device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of the secondary battery for this electrical device, a battery pack or battery module can be used.

[0155] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0156] The present application will be further described in detail below with reference to specific embodiments and comparative examples. Experimental parameters not specified in the following specific embodiments should first be referred to the guidelines given in this application, and may also be referred to experimental manuals or other experimental methods known in the art, or the experimental conditions recommended by the manufacturer. It is understood that the instruments and raw materials used in the following embodiments are relatively specific, and may not be limited to these in other specific embodiments; the weight of the relevant components mentioned in the embodiments of this application may not only refer to the specific content of each component, but also to the proportional relationship between the weights of the components. Therefore, as long as the content of the relevant components is scaled up or down proportionally according to the embodiments of this application, it is within the scope disclosed in the embodiments of this application. Specifically, the weights mentioned in the embodiments of this application may be well-known units of mass in the chemical industry, such as μg, mg, g, and kg.

[0157] Example 1

[0158] (1) Preparation of positive electrode sheet

[0159] a. Prepare 0.4Li2MnO3, 0.6LiNi0.5Mn0.5O2 (denoted as lithium-rich material), 2,6-di-tert-butyl-4-methylphenol (BHT), and polypyrrole (weight average molecular weight 300,000 Da) in a ratio of 97.5:0.5:2. Use zirconium beads as the ball milling medium (80% of the large balls are 15 mm in diameter and 20% of the small balls are 5 mm in diameter). Control the mass ratio of raw materials to ball milling medium to be 15:1. Dry ball mill at 500 rpm for 1 h to obtain a cathode material with a Dv50 particle size of 300 nm. The thickness of the coating layer in the cathode material is 20 nm.

[0160] b. Dissolve the cathode material obtained in step a in a 2% (w / w) aqueous solution of lithium carboxymethyl cellulose (CMC-Li) and stir at 800 rpm for 3 h to obtain a premix (in the premix, the mass ratio of cathode material to lithium carboxymethyl cellulose is 100:3). Then, using nitrogen as the carrier gas and controlling the discharge rate at 10 mL / min, spray granulation is performed at 120 °C to obtain a cathode composite material with a Dv50 particle size of 8 μm.

[0161] c. The positive electrode composite material, conductive agent acetylene black, and binder PVDF (polyvinylidene fluoride) obtained in step b are mixed in a weight ratio of 94:4:2. N-methylpyrrolidone solvent is added and the mixture is stirred and mixed thoroughly to obtain a positive electrode slurry. The slurry is then coated on both surfaces of the positive electrode current collector aluminum foil, dried, and cold-pressed to obtain the positive electrode sheet.

[0162] (2) Preparation of negative electrode sheet

[0163] Artificial graphite, conductive agent acetylene black, binder SBR (styrene-butadiene rubber latex), and binder CMC (sodium carboxymethyl cellulose) are mixed in a weight ratio of 95:1.5:3.1:0.4. Deionized water is added as a solvent, and the mixture is stirred thoroughly to obtain a negative electrode slurry. This slurry is then coated onto both surfaces of the negative electrode current collector copper foil. After drying and cold pressing, the negative electrode sheet is obtained.

[0164] (3) Preparation of electrolyte

[0165] In an argon-atmosphere glove box with a water content of <10ppm, EC (ethylene carbonate), PC (polycarbonate), and DMC (dimethyl carbonate) were mixed in a weight ratio of EC:PC:DMC = 3:3:3. Then, LiPF6, VC, DTD, and PS were added and stirred until homogeneous to obtain the electrolyte. The concentration of LiPF6 in the lithium-ion battery electrolyte was 1 mol / L, and the mass percentages of VC, DTD, and PS were 3%, 1%, and 1%, respectively.

[0166] (4) Preparation of the separating membrane

[0167] Polyethylene porous membrane is used as the separation membrane.

[0168] (5) Preparation of lithium-ion secondary batteries

[0169] The positive electrode sheet obtained in step (1), the separator in step (4), and the negative electrode sheet obtained in step (2) are stacked in sequence, so that the separator is in the middle of the positive and negative electrodes to play a role in isolation, and a bare cell is obtained; the bare cell is placed in an outer packaging, injected with the electrolyte prepared in step (3), and sealed for formation to obtain a lithium-ion secondary battery.

[0170] Example 2

[0171] The results are basically the same as in Example 1, except that in step (1)a, the mass ratio of lithium-rich material, 2,6-di-tert-butyl-4-methylphenol and polypyrrole is 94.5:3.5:2, the Dv50 particle size of the resulting cathode material is 390 nm, and the thickness of the coating layer is 60 nm.

[0172] Example 3

[0173] The results are basically the same as in Example 1, except that in step (1)a, the mass ratio of lithium-rich material, 2,6-di-tert-butyl-4-methylphenol and polypyrrole is 95:3:2, the Dv50 particle size of the obtained cathode material is 360 nm, and the thickness of the coating layer is 40 nm.

[0174] Example 4

[0175] The results are basically the same as in Example 1, except that in step (1)a, the mass ratio of lithium-rich material, 2,6-di-tert-butyl-4-methylphenol and polypyrrole is 97.9:0.1:2, the Dv50 particle size of the resulting cathode material is 280 nm, and the thickness of the coating layer is 7 nm.

[0176] Example 5

[0177] The results are basically the same as in Example 1, except that in step (1)a, the mass ratio of lithium-rich material, 2,6-di-tert-butyl-4-methylphenol and polypyrrole is 97.5:0.5:2, the Dv50 particle size of the resulting cathode material is 100 nm, and the thickness of the coating layer is 15 nm.

[0178] Example 6

[0179] The results are basically the same as in Example 1, except that in step (1)a, the mass ratio of lithium-rich material, 2,6-di-tert-butyl-4-methylphenol and polypyrrole is 97.5:0.5:2, the Dv50 particle size of the resulting cathode material is 1000 nm, and the thickness of the coating layer is 25 nm.

[0180] Example 7

[0181] The results are basically the same as in Example 1, except that in step (1)a, the mass ratio of lithium-rich material, 2,6-di-tert-butyl-4-methylphenol and polypyrrole is 97.95:0.05:2, the Dv50 particle size of the resulting cathode material is 270 nm, and the thickness of the coating layer is 4 nm.

[0182] Example 8

[0183] The results are basically the same as in Example 1, except that in step (1)a, the mass ratio of lithium-rich material, 2,6-di-tert-butyl-4-methylphenol and polypyrrole is 87.5:0.5:12, the Dv50 particle size of the resulting cathode material is 450 nm, and the thickness of the coating layer is 110 nm.

[0184] Example 9

[0185] The results are basically the same as in Example 1, except that in step (1)a, the mass ratio of lithium-rich material, 2,6-di-tert-butyl-4-methylphenol and polypyrrole is 89.5:0.5:10, the Dv50 particle size of the resulting cathode material is 430 nm, and the thickness of the coating layer is 100 nm.

[0186] Example 10

[0187] The results are basically the same as in Example 1, except that in step (1)a, the mass ratio of lithium-rich material, 2,6-di-tert-butyl-4-methylphenol and polypyrrole is 99.4:0.5:0.1, the DvSO particle size of the resulting cathode material is 260 nm, and the thickness of the coating layer is 2 nm.

[0188] Example 11

[0189] It is basically the same as Example 1, except that in step (1)a, polypyrrole is replaced with an equal amount of carbon nanotubes (50 nm in diameter and 30 μm in length), and amino groups are grafted onto the surface of the carbon nanotubes.

[0190] Example 12

[0191] It is basically the same as Example 1, except that in step (1)a, polypyrrole is replaced with an equal amount of carbon black (Dv50 particle size 80nm), and amino groups are grafted onto the surface of the carbon black.

[0192] Example 13

[0193] It is basically the same as Example 1, except that in step (1)a, there is no polypyrrole, and the mass ratio of lithium-rich material and 2,6-di-tert-butyl-4-methylphenol is 99.5:0.5.

[0194] Example 14

[0195] It is basically the same as Example 1, except that in step (1)b, the mass ratio of the positive electrode material to lithium carboxymethyl cellulose in the premixed solution is 85:15.

[0196] Example 15

[0197] It is basically the same as Example 1, except that in step (1)b, the mass ratio of the positive electrode material to lithium carboxymethyl cellulose in the premixed solution is 90:10.

[0198] Example 16

[0199] It is basically the same as Example 1, except that in step (1)b, the mass ratio of the positive electrode material to lithium carboxymethyl cellulose in the premixed solution is 99:1.

[0200] Example 17

[0201] It is basically the same as Example 1, except that in step (1)b, the spray granulation temperature is 100°C and the Dv50 particle size of the resulting positive electrode composite material is 22μm.

[0202] Example 18

[0203] It is basically the same as Example 1, except that in step (1)b, the spray granulation temperature is 160°C.

[0204] Example 19

[0205] The results are basically the same as in Example 1, except that in step (1)b, the discharge rate of spray granulation is 2 mL / min, and the Dv50 particle size of the resulting positive electrode composite material is 3 μm.

[0206] Example 20

[0207] The results are basically the same as in Example 1, except that in step (1)b, the discharge rate of spray granulation is 25 mL / min, and the Dv50 particle size of the resulting positive electrode composite material is 23 μm.

[0208] Example 21

[0209] It is basically the same as Example 1, except that LiNi is used. 0.8 Co 0.1 Mn 0.1 Using O2 (referred to as high-nickel material) instead of lithium-rich material, the resulting cathode material has a Dv50 particle size of 190 nm and a coating thickness of 20 nm.

[0210] Example 22

[0211] It is basically the same as Example 1, except that step (1)a is as follows:

[0212] LiNi 0.8Co 0.1 Mn 0.1 O2 (referred to as high-nickel material), N,N'-di-sec-butyl-p-phenylenediamine (antioxidant 44PD), and polyaniline (weight average molecular weight 500,000 Da) were prepared in a ratio of 97.5:0.5:2. Zirconium beads with a diameter of 15 mm were used as the ball milling medium, and the mass ratio of raw materials to ball milling medium was controlled at 10:1. Acetone (the amount of acetone was 5 times the mass of the raw materials) was used as the solvent. The mixture was wet-milled at 400 rpm for 2 hours to obtain a cathode material with a Dv50 particle size of 200 nm. The thickness of the coating layer in the cathode material was 25 nm.

[0213] Step (1)c is as follows:

[0214] The positive electrode composite material, phosphite, conductive agent acetylene black, and binder PVDF (polyvinylidene fluoride) obtained in step b are mixed in a weight ratio of 94:2:2:2. N-methylpyrrolidone solvent is added and the mixture is stirred and mixed thoroughly to obtain a positive electrode slurry. The slurry is then coated on both surfaces of the positive electrode current collector aluminum foil, dried, and cold-pressed to obtain the positive electrode sheet.

[0215] Comparative Example 1

[0216] It is basically the same as Example 1, except that in step (1)a, 2,6-di-tert-butyl-4-methylphenol (BHT) is replaced with an equal mass of FeS.

[0217] Comparative Example 2

[0218] This is basically the same as Example 1, except that step (1)a does not contain 2,6-di-tert-butyl-4-methylphenol (BHT) and 0.4Li2MnO3.0.6LiNi 0.5 Mn 0.5 The mass ratio of O2 (referred to as lithium-rich material) to polypyrrole is 98:2.

[0219] Comparative Example 3

[0220] This is basically the same as Example 1, except that step (1)a is omitted and the positive electrode material in step (1)b is replaced with 0.4Li2MnO3.0.6LiNi with a Dv50 particle size of 280nm. 0.5 Mn 0.5 O2 (referred to as lithium-rich material).

[0221] Characterization tests:

[0222] The secondary batteries prepared in the above embodiments and comparative examples were tested as follows, and the test results are listed in Table 1.

[0223] (1) Capacity test

[0224] At 25℃, the secondary battery is charged at a constant current rate of 0.33C to 4.55V, then charged at a constant voltage rate to a current of 0.05C, left to stand for 5 minutes, and then discharged at a constant current rate of 0.33C to 2V. The discharge capacity at this time is recorded as the 0.33C discharge capacity.

[0225] (2) Ratio Performance Test

[0226] At 25°C, the secondary batteries of each embodiment and comparative example were charged at a constant current rate of 0.1C to 4.55V, then charged at a constant voltage rate to a current of 0.05C, left to stand for 5 minutes, and then discharged at a constant current rate of 0.1C to 2V. The discharge capacity at this time was recorded, which is the 0.1C discharge capacity. After standing for 30 minutes, the secondary batteries were charged at a constant current rate of 0.1C to 4.55V, then charged at a constant voltage rate to a current of 0.05C, left to stand for 5 minutes, and then discharged at a constant current rate of 1C to 2V. The discharge capacity at this time was recorded, which is the 1C discharge capacity.

[0227] The rate performance of a battery is calculated as 1C / 0.1C (%) = 1C discharge capacity / 0.1C discharge capacity × 100%.

[0228] (3) Cyclic performance test

[0229] At 25°C, the capacitor is charged to 4.55V with a constant current of 1C, then charged to 0.05C with a constant voltage of 4.55V, and then discharged to 2.5V with a constant current of 1C. The discharge specific capacity of the first cycle (Cd1) is obtained. This charging and discharging process is repeated until the 500th cycle, and the discharge specific capacity after 500 cycles is denoted as Cdn.

[0230] Capacity retention rate = discharge specific capacity after 500 cycles (Cdn) / discharge specific capacity in the first cycle (Cd1).

[0231] In the above battery performance testing process, the upper limit of charging voltage for lithium-rich materials is 4.55V, and the upper limit of charging voltage for high-nickel materials is 4.25V.

[0232] Table 1

[0233]

[0234]

[0235] Analyzing the data in Table 1, compared to Example 1, Comparative Example 1 replaced the hindered phenolic antioxidant with FeS, which can also be used as an antioxidant in everyday life. However, since the antioxidant performance of FeS is based on its reducing properties, when used as a positive electrode material, charging causes most of the ferrous ions to be oxidized to ferric ions, thus losing its antioxidant properties. The performance is comparable to Comparative Example 2, which does not contain an antioxidant. Therefore, not all antioxidants are suitable for the scheme of this application. In Comparative Example 3, the polypyrrole conductive agent was removed, and the rate performance was significantly lower than that of Comparative Example 2.

[0236] Compared to Example 1, Examples 2 and 3 used a larger amount of BHT, which hindered lithium-ion transport and resulted in a certain degree of decrease in rate performance. Examples 4 and 7 used a smaller amount of BHT, which could not provide sufficient antioxidant effect, thus reducing cycle performance. Examples 5 and 6 show that Dv50 particle size also has a certain impact on battery performance; a suitable particle size can further balance various battery performance aspects. In Examples 8 and 9, the higher amount of polypyrrole, the lower proportion of active material, reduced specific capacity, and hindered lithium-ion transport, resulting in a decrease in rate performance. In Example 10, the insufficient amount of polypyrrole led to a decrease in rate performance, and the inability of BHT to be fixed on the primary particles also reduced cycle performance. In Example 11, carbon nanotubes were used instead of polypyrrole. Although carbon nanotubes are also linear, their flexibility is worse than that of polypyrrole, resulting in poorer coating ability and uneven distribution of antioxidants on the surface of the primary particles, thus reducing cycle performance. The following examples show a decrease in performance: In Example 12, carbon black was used instead of polypyrrole. Since carbon black is not linear, its performance further decreased compared to Example 11, which was coated with carbon nanotubes. In Example 13, the absence of polypyrrole conductive agent meant that BHT could not effectively adhere to the surface of the primary particles during cycling, further reducing rate and cycle performance. In Examples 14 and 15, the higher proportion of CMC-Li in the active material reduced the specific capacity, and the thicker coating hindered lithium-ion transport, resulting in a decrease in rate performance. In Example 16, the lower amount of CMC-Li led to a slight decrease in rate performance. In Example 17, the excessively low temperature and in Example 20, the excessively high discharge rate caused the secondary particles to agglomerate into large particles, resulting in a decrease in rate performance. In Example 18, the excessively high temperature damaged the structure of the antioxidant to some extent, leading to a decrease in cycle performance. In Example 19, the excessively low discharge rate resulted in small secondary particles with a large retained active area, leading to a decrease in cycle performance. Examples 21 and 22 demonstrate that the technical solutions of this application can also be applied to high-nickel cathode materials.

[0237] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0238] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this application should be determined by the appended claims.

Claims

1. A positive electrode material, characterized in that, It includes positive electrode material particles and a coating layer located on the surface of the positive electrode material particles. The coating layer is made of an antioxidant, which includes one or more of hindered phenolic antioxidants and amine antioxidants.

2. The cathode material according to claim 1, characterized in that, The hindered phenolic antioxidants include one or more of 2,6-di-tert-butyl-4-methylphenol, 2,6-di-tert-butyl-4-aminophenol, 2,6-di-tert-butyl-4-(dimethylaminomethyl)phenol, tert-butylhydroquinone, and 2,5-di-tert-butylhydroquinone.

3. The cathode material according to claim 1, characterized in that, The amine antioxidants include one or more of N,N'-di-sec-butyl-p-phenylenediamine, (3,5-di-tert-butyl-4-hydroxybenzyl)aniline, 2,2,6,6-tetramethylpiperidine, bis(2,2,6,6-tetramethyl-4-piperidinyl) sebacate, bis(1-octoxy-2,2,6,6-tetramethyl-4-piperidinyl) sebacate, stearate (2,2,6,6-tetramethyl-4-piperidinol) ester, and N,N'-bis(2,2,6,6-tetramethyl-4-piperidinyl)-1,3-phenylenediamide.

4. The cathode material according to any one of claims 1 to 3, characterized in that, In the cathode material, the antioxidant has a mass percentage content of 0.1% to 3%.

5. The cathode material according to any one of claims 1 to 3, characterized in that, The coating layer also includes a conductive agent.

6. The cathode material according to claim 5, characterized in that, The conductive agent includes one or more of polypyrrole conductive agents, polyaniline conductive agents, and functional conductive carbon.

7. The cathode material according to claim 6, characterized in that, The functional conductive carbon includes one or more of carbon nanotubes, carbon black, and graphite, and the surface of the functional conductive carbon is grafted with one or more of carboxyl groups, hydroxyl groups, and amino groups.

8. The positive electrode material according to claim 5, characterized in that, In the positive electrode material, the mass percentage of the conductive agent is 0.5% to 10%.

9. The cathode material according to any one of claims 1 to 3, characterized in that, The cathode material is a primary particle, and the Dv50 particle size range of the cathode material is 100 nm ~ 1 μm.

10. The cathode material according to any one of claims 1 to 3, characterized in that, The thickness of the coating layer is 2 nm to 100 nm.

11. The cathode material according to claim 10, characterized in that, The thickness of the coating layer is 2 nm to 60 nm.

12. The cathode material according to any one of claims 1 to 3, characterized in that, The cathode material particles include LiCoO2 and LiNi. a Co b Mn (1-a-b) O2, LiNi c Co d Al (1-c-d) One or more of O2, eLi2MnO3·(1-e)LiMO2; Where a~e are independently selected from 0~1; M includes one or more of Ni, Co, and Mn.

13. A method for preparing a positive electrode material, characterized in that, Includes the following steps: The raw materials involved in the cathode material according to any one of claims 1 to 12 are prepared by ball milling each raw material.

14. The preparation method according to claim 13, characterized in that, The ball mill satisfies one or more of the following conditions (1) to (7): (1) The milling media include one or more of zirconium balls, stainless steel balls, and polyurethane balls; (2) The diameter of the ball milling media is 5 mm ~ 20 mm; (3) The grinding media includes large balls and small balls, wherein the diameter of the large balls is 10 mm to 20 mm and the diameter of the small balls is 5 mm to 10 mm; (4) The mass ratio of raw material to ball milling media is (10~20):1; (5) The ball milling is a wet ball milling process, and the solvent used includes one of chloroform, acetone, toluene and benzene; (6) The rotation speed of the ball mill is 400 rpm ~ 600 rpm; (7) The ball milling time is 0.5 h ~ 2 h.

15. The preparation method according to claim 14, characterized in that, The small balls have a mass percentage of 10% to 30% in the ball milling media, and the large balls have a mass percentage of 70% to 90% in the ball milling media.

16. The preparation method according to claim 14 or 15, characterized in that, The mass ratio of the raw material to the solvent is 1:(1~10).

17. A positive electrode composite material, characterized in that, It includes the cathode material and lithium-containing binder as described in any one of claims 1 to 12.

18. The positive electrode composite material according to claim 17, characterized in that, The lithium-containing binder includes one or more of lithium carboxymethyl cellulose, lithium polyacrylate, and lithium alginate.

19. The positive electrode composite material according to claim 17, characterized in that, In the positive electrode composite material, the mass percentage of the lithium-containing binder is 1% to 10%.

20. The positive electrode composite material according to any one of claims 17 to 19, characterized in that, In the positive electrode composite material, the mass percentage of the positive electrode material is 90%~99%.

21. The positive electrode composite material according to any one of claims 17 to 19, characterized in that, The cathode composite material consists of secondary particles, and the Dv50 particle size range of the cathode composite material is 5 μm ~ 20 μm.

22. The method for preparing the positive electrode composite material according to any one of claims 17 to 21, characterized in that, Includes the following steps: The cathode material, the lithium-containing binder, and the solvent are mixed and then spray-granulated.

23. The preparation method according to claim 22, characterized in that, The spray granulation temperature is 120℃~140℃, and the spray granulation discharge rate is 5 mL / min~20 mL / min.

24. A secondary battery, characterized in that, It includes a positive electrode, a negative electrode, and a separator, wherein the separator is disposed between the positive electrode and the negative electrode; The positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector. The positive active material layer includes one or more of the positive electrode material according to any one of claims 1 to 12 and the positive electrode composite material according to any one of claims 17 to 21.

25. The secondary battery according to claim 24, characterized in that, The positive electrode active material layer also includes an auxiliary antioxidant, which includes one or more of phosphites and thioesters.

26. The secondary battery according to claim 25, characterized in that, In the positive electrode active material layer, the mass percentage of the auxiliary antioxidant is 0.01% to 2%.

27. An electrical appliance, characterized in that, Includes the secondary battery as described in any one of claims 24 to 26.

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