Positive electrode material and modification method therefor, method for preparing positive electrode film of lithium battery by means of dry method, positive electrode film and lithium-ion battery

Abstract

The present application relates to a positive electrode material and a modification method therefor, a method for preparing a positive electrode film of a lithium battery by means of a dry method, a positive electrode film and a lithium-ion battery. The positive electrode material is subjected to surface modification by using a composite modifier comprising a titanate coupling agent and an orthosilicate, the surface-modified positive electrode material is used for preparing a positive electrode film, the modification layer is further polymerized during the process of preparing the positive electrode film, and the polymerized modification layer forms a three-dimensional reticular structure among a binder, a conductive substance and a positive electrode.

Description

Positive electrode material and modification method thereof, dry method for preparing positive electrode film of lithium battery, positive electrode film and lithium ion battery

[0001] This application claims priority to the Chinese patent application filed with the Patent Office of China on October 30, 2023, with application number 202311436546.7 and invention name “Positive electrode material and modification method thereof, method for dry preparation of positive electrode membrane of lithium battery and positive electrode membrane and lithium-ion battery”. The entire contents of the above application are incorporated into this application by reference. Technical Field

[0002] The present application relates to the technical field of lithium-ion batteries, and in particular to a positive electrode material and a modification method thereof, a method for dry-process preparation of a positive electrode film for a lithium battery, a positive electrode film, and a lithium-ion battery. Background Art

[0003] Lithium-ion batteries are currently widely used in portable electronic devices such as mobile phones and laptops, as well as electric vehicles. The active energy storage medium of lithium-ion batteries is the positive and negative electrode materials that have the ability to reversibly embed and de-intercalate lithium ions.

[0004] In recent years, dry electrode preparation has garnered significant attention. Dry electrode preparation generally involves uniformly mixing powders of active material, conductive agent, and binder, then coating the mixture on the current collector surface using methods such as magnetron sputtering, electrostatic spraying, or spray drying, or by rolling / hot pressing the mixed materials to form a self-supporting electrode sheet. However, dry electrode preparation currently faces several challenges. For example, the bounding agent, present in a constrained state, only makes point contact with the surface of the active material particles, resulting in poor contact uniformity and tightness between the active material particles and between the active material particles and the conductive agent, as well as poor electrode flexibility and durability. To improve the contact uniformity and adhesion of the active material, as well as the flexibility, durability, and specific capacity of the electrode, strategies such as increasing the binder dosage, introducing organic polymers, developing alternative binders, and improving preparation equipment are commonly employed. While these strategies can address some of the challenges associated with dry electrode preparation, they are limited in effectiveness and are costly. Furthermore, increasing the amount of inactive materials such as binders and organic polymers can affect the electrode surface density and the energy density of the corresponding battery system.

[0005] Therefore, it is necessary to seek a dry electrode preparation strategy with simple process and low cost, which can reduce the amount of binder while ensuring uniform dispersion and good contact between materials, reduce the amount of inactive substances, and increase the electrode surface density and the energy density of the corresponding battery system. SUMMARY OF THE INVENTION

[0006] The present application provides a positive electrode material and a method for modifying the same, a method for dry-process preparation of a positive electrode film for a lithium battery, a positive electrode film, and a lithium-ion battery, so as to improve the uniformity and adhesion between materials in dry-process electrode preparation through simple processes and lower costs, and reduce the amount of inactive substances on the basis of improving the uniformity and adhesion between materials.

[0007] The technical solution of this application is as follows:

[0008] In a first aspect, an embodiment of the present application provides a method for modifying a cathode material, comprising:

[0009] S1.1: Prepare cathode material dispersion;

[0010] S1.2: Adding a composite modifier to the positive electrode material dispersion to form a mixed solution to modify the positive electrode material, wherein the composite modifier includes a titanate coupling agent and an orthosilicate.

[0011] In one embodiment of the present application, the mass ratio of the positive electrode material to the composite modifier is (99.5:0.5)-(90:10).

[0012] In one embodiment of the present application, the mass ratio of the titanate coupling agent to the orthosilicate is (1:9)-(9:1).

[0013] In one embodiment of the present application, the titanate coupling agent includes one or more of tetrabutyl titanate, diisostearyl ethyl titanate, triisostearyl isopropyl titanate, tetraisopropyl di(dioctyl phosphite) titanate, isopropoxy tri(dodecylbenzenesulfonyloxy) titanate, isopropyl trioleyl titanate, and isopropyl dioleyl (dioctyl phosphate) titanate.

[0014] In one embodiment of the present application, the orthosilicate includes one or more of methyl orthosilicate, ethyl orthosilicate, butyl orthosilicate, and isopropyl orthosilicate.

[0015] In one embodiment of the present application, in S1.2, after adding the composite modifier to the positive electrode material dispersion, an ultrasonic frequency of 30-50 kHz is applied for 5-20 minutes, or magnetic stirring is performed at a speed of 300-1000 r / min for 10-30 minutes to fully mix the positive electrode material and the composite modifier.

[0016] In one embodiment of the present application, it further includes:

[0017] S1.3: adding a pH regulating solution to adjust the pH value of the mixed solution to 4-5, drying the mixed solution with a pH value of 4-5, and obtaining a positive electrode material modified with a composite modifier.

[0018] In one embodiment of the present application, before S1.3, a pH regulator is added to an alcohol aqueous solution and fully dispersed to prepare the pH regulating solution with a concentration of 1-3 mol / L.

[0019] In one embodiment of the present application, the pH regulator includes at least one of formic acid, glacial acetic acid and oxalic acid, and the alcohol aqueous solution includes an alcohol solvent and deionized water in a mass ratio of (90:10) to (70:30), and the alcohol solvent includes at least one of methanol, ethanol, ethylene glycol and isopropanol.

[0020] In one embodiment of the present application, in S1.3, the pH regulating liquid is added to the mixed liquid while stirring, and then stirring is continued, and the pH value is measured once every set time interval. After the pH value stabilizes between 4-5, the mixed liquid is dried to obtain a positive electrode material modified with a composite modifier.

[0021] In one embodiment of the present application, in S1.3, stirring is performed at a rotation speed of 200-1200 r / min, and the set time is 0.5-1 h.

[0022] In a second aspect, an embodiment of the present application provides a method for dry-processing a positive electrode film for a lithium battery, comprising:

[0023] S2.1, mixing the cathode material modified with the composite modifier obtained by the cathode material modification method according to any one of the first aspects with a conductive agent and a binder to prepare a premixed modified cathode mixture;

[0024] S2.2, crushing, dispersing and fiberizing the premixed modified cathode mixture to obtain a fiberized modified cathode mixture;

[0025] S2.3, heating and calendering the fiberized modified cathode mixture to obtain a dry-process modified cathode film;

[0026] S2.4, compounding the dry-process modified positive electrode film with a current collector to obtain a positive electrode film.

[0027] In one embodiment of the present application, in S2.1, the conductive agent includes at least one of conductive carbon black, Ketjen black, acetylene black, carbon fiber, and carbon nanotubes; the binder includes at least one of ethylene-tetrafluoroethylene copolymer, polytetrafluoroethylene, and tetrafluoroethylene-hexafluoropropylene copolymer;

[0028] The mass ratio of the positive electrode material modified by the composite modifier, the conductive agent and the binder is (90-96): (2-5): (2-5).

[0029] In one embodiment of the present application, in S2.1, the positive electrode material modified by the composite modifier, the conductive agent and the binder are ball-milled and mixed at a rate of 100-350 rpm for 0.5-3 h, or stirred and mixed at a rate of 500-2500 rpm for 0.5-3 h to prepare a premixed modified positive electrode mixture.

[0030] In one embodiment of the present application, in S2.2, the premixed modified positive electrode mixture is subjected to high-speed dispersion and airflow crushing to achieve the purpose of crushing, dispersion and fiberization treatment, wherein the high-speed dispersion rate is 10000rpm-20000rpm, the dispersion time is 5-120min, the airflow crushing speed is 20m / s-100m / s, the airflow pressure is 0.3-1.2MPa, the feeding pressure is 0.3-1.0MPa, and the temperature is 20℃-60℃.

[0031] In one embodiment of the present application, in S2.3, the fiberized modified cathode mixture is subjected to a heating and calendering treatment at a pressure of 80-800 kPa and a temperature of 40-300° C. to prepare the dry-process modified cathode film having a thickness of 100-500 μm.

[0032] In one embodiment of the present application, in S2.4, the dry-modified positive electrode film and the current collector are composited by heating calendering or high-temperature rolling to form a positive electrode film with a thickness of 50-100 μm, wherein the pressure of heating calendering is 200-600 kPa and the temperature is 40-300°C, and the temperature of high-temperature rolling is 200-300°C.

[0033] In a third aspect, an embodiment of the present application provides a positive electrode material, the surface of which is coated with a titanate coupling agent and an orthosilicate; or the positive electrode material is processed and formed using the positive electrode material modification method described in any one of the first aspects.

[0034] In a fourth aspect, an embodiment of the present application provides a positive electrode film:

[0035] The positive electrode film comprises a positive electrode film and a current collector, wherein the positive electrode film is made of the positive electrode material described in the third aspect;

[0036] Alternatively, the positive electrode film is formed by the dry method for preparing a positive electrode film for a lithium battery as described in any one of the second aspects.

[0037] In a fifth aspect, an embodiment of the present application provides a lithium-ion battery, comprising:

[0038] The positive electrode material according to the third aspect;

[0039] Alternatively, the positive electrode film described in the fourth aspect. Beneficial effects of the present invention

[0040] (1) The surface of the positive electrode material is modified in advance using a composite modifier including a titanate coupling agent and an orthosilicate. The orthosilicate material has good chemical stability and can optimize the surface properties of the positive electrode material after being coated with it. The addition of the titanate coupling agent also improves the high temperature resistance of the dry-process electrode and promotes the safety of the battery cell. The chemical bond formed between the modified layer formed by the composite modifier and the positive electrode is more stable than the physical adsorption effect. Therefore, when the materials are mixed at a low speed, the agglomeration of the positive electrode particles can be effectively suppressed. The modified positive electrode material not only has a smaller charge and discharge polarization, but also has a higher first charge and discharge efficiency, a higher capacity retention rate, and better cycle performance.

[0041] (2) After the conductive agent and binder are mixed at a low speed with the positive electrode material modified by the composite modifier, the binder and conductive material are evenly distributed around the positive electrode particles. During the further high-speed stirring, shearing or grinding process, the modified layer polymerizes. After polymerization, a coating network is formed between the binder, the conductive material and the positive electrode, which can achieve uniform mixing of the various components and avoid the decrease in the adhesion between the materials. Therefore, when the amount of binder is reduced, the material contact and mixing uniformity will not be affected.

[0042] (3) The dry method is used for electrode preparation. No solvent is used in the mixing process of the components, which avoids the problem of electrode stratification caused by solvent evaporation. Compared with special equipment, this strategy is simple to operate, reduces equipment cost and energy consumption, and is simple to optimize the strategy and preparation process, saves material cost, and is beneficial to environmental safety. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without creative work.

[0044] FIG1 is a first-cycle charge and discharge curve diagram of the battery of Example 1 of the present application and the battery of Comparative Example 1;

[0045] FIG2 is a graph showing the capacity retention of the battery of Example 1 of the present application and the battery of Comparative Example 1 after 100 charge and discharge cycles;

[0046] FIG3 is a cross-sectional electron microscope test image (1 μm) of the dry-process modified NCM811 positive electrode membrane provided in Example 1 of the present application;

[0047] FIG4 is a cross-sectional electron microscope test image (10 μm) of the dry-modified NCM811 positive electrode membrane provided in Example 1 of the present application. Modes for Carrying Out the Invention

[0048] Among electrochemical energy storage devices, lithium-ion batteries have become the mainstream in today's battery field due to their advantages such as high operating voltage, high specific capacity, wide operating temperature range, good cycle performance and long life. They have been widely used in portable electronic devices such as mobile phones and laptops, as well as electric vehicles, and are gradually expanding into the fields of energy storage and cordless power tools. The active energy storage medium of lithium-ion batteries is a positive and negative electrode material that has the ability to reversibly embed and deintercalate lithium ions. The traditional method for preparing lithium-ion battery electrodes mainly adopts a wet coating process, that is, the active material, conductive agent, binder and solvent are mixed to form a slurry, and the slurry is then coated on a foil to evaporate the solvent. The entire process not only has energy waste caused by drying and environmental pollution caused by high-cost organic solvents, but also electrode stratification caused by the sedimentation of active materials during solvent evaporation, the limited thickness of the electrode obtained by the process, and the impact of solvent residue on battery performance. These problems cannot be ignored.

[0049] To address the issues encountered in wet electrode preparation, researchers have begun to focus on dry electrode preparation. Dry electrode preparation involves uniformly mixing the powders of active material, conductive agent, and binder, and then coating them on the surface of the current collector using methods such as magnetron sputtering, electrostatic spraying, or spray drying, or by rolling / hot pressing the mixed material to form a self-supporting electrode. Dry electrode technology avoids the use of any solvents when preparing electrodes. This simplified process not only reduces the cost of solvent materials and the cost of solvent drying, recovery, and drying equipment, but also helps control the microstructure of the electrode, inhibit electrode stratification, and achieve controllable electrode thickness and surface density.

[0050] The technical core of the dry electrode lies in the fiberization of the binder during the powder mixing process to form a self-supporting dry electrode film. However, there are still some problems to be solved in the dry electrode technology, which has led to the fact that some mainstream lithium-ion batteries have not yet promoted the use of dry electrode preparation processes. On the one hand, the dry electrode does not use solvents in the production process, and the binder exists in a fibrous state, with only point contact with the surface of the active material particles, resulting in poor contact uniformity and tightness between the active material particles inside the electrode and between the active material particles and the conductive agent, as well as poor electrode flexibility and durability. On the other hand, in order to improve the uniformity and adhesion of the mixed powder, the amount of binder used in the dry electrode preparation process is increased, such as increasing the amount of polytetrafluoroethylene (PTFE) used as a binder, which leads to a significant reduction in the electrode specific capacity.

[0051] To balance the issues of uniformity and tightness of contact between active material particles and between them and the conductive agent, as well as electrode flexibility, durability, and specific capacity, improvement plans from multiple different directions are currently being considered. For example, introducing organic polymers into the formula to improve the adhesion between the mixed materials, developing alternative binders to reduce their usage to increase the specific energy of the electrode, or developing special equipment based on the preparation equipment to improve binder fiberization. Although these improvement plans can improve the problems in dry electrode preparation to a certain extent, they are limited in effectiveness, are costly, and the increased amount of inactive material will affect the electrode surface density and the energy density of the corresponding battery system.

[0052] Based on this, the inventors proposed a technical solution, which is to pre-modify the surface of the positive electrode material using a composite modifier including a titanate coupling agent and an orthosilicate. During the preparation of the positive electrode film, the modified layer is further polymerized. The polymerized modified layer is used to form a three-dimensional network structure between the binder, the conductive material and the positive electrode, so as to significantly improve the adhesion between the materials. Therefore, while reducing the amount of binder used, close contact and uniform mixing between the materials are guaranteed, thereby reducing costs and increasing battery energy density.

[0053] The technical solution of this application is as follows:

[0054] In a first aspect, a method for modifying a positive electrode material is provided, comprising:

[0055] S1.1: Prepare cathode material dispersion;

[0056] S1.2: Add a composite modifier to the positive electrode material dispersion and mix thoroughly to form a mixed solution. The composite modifier includes a titanate coupling agent and an orthosilicate.

[0057] In S1.1, a certain amount of positive electrode material is weighed and dispersed in a solvent using ultrasonic, mechanical stirring, or ball milling to prepare a uniform positive electrode dispersion. The positive electrode material includes at least one of lithium cobalt oxide (LiCoO2), lithium manganese oxide (LiMn2O4), lithium nickel manganese oxide (LiNi0.5Mn1.5O4), lithium iron phosphate (LiFePO4), lithium manganese phosphate (LiMnPO4), lithium nickel cobalt manganese oxide (LiNixCoyMnzO2, where x+y+z=1), and a lithium-rich compound. The solvent is at least one of methanol, ethanol, ethylene glycol, and isopropanol. The concentration of the positive electrode material is 0.1-2 g / ml. The ultrasonic dispersion frequency is 50-80 kHz and the duration is 10-30 minutes. The mechanical stirring conditions include a stirring rate of 1500-3000 rpm and a duration of 10-30 minutes. The ball milling conditions include a ball milling rate of 200-300 rpm and a duration of 5-20 minutes.

[0058] In some embodiments, in S1.2, the mass ratio of the positive electrode material to the composite modifier is (99.5:0.5) to (90:10). Alternatively, the mass ratio of the positive electrode material to the composite modifier is (98:2) to (95:5). Alternatively, the mass ratio of the positive electrode material to the composite modifier is (97:3) to (96:4).

[0059] In some embodiments, in S1.2, the mass ratio of the titanate coupling agent to the orthosilicate is (1:9) to (9:1). Alternatively, the mass ratio of the titanate coupling agent to the orthosilicate is (1:3) to (3:1). Alternatively, the mass ratio of the titanate coupling agent to the orthosilicate is (2:3) to (3:2).

[0060] In some embodiments, in S1.2, the titanate coupling agent includes one or more of tetrabutyl titanate, diisostearyl ethyl titanate, triisostearyl isopropyl titanate, tetraisopropyl di(dioctyl phosphite) titanate, isopropoxy tri(dodecylbenzenesulfonyloxy) titanate, isopropyl trioleyl titanate, and isopropyl dioleyl (dioctyl phosphate) titanate.

[0061] In some embodiments, in S1.2, the orthosilicate includes one or more of methyl orthosilicate, ethyl orthosilicate, butyl orthosilicate, and isopropyl orthosilicate.

[0062] In some embodiments, in S1.2, after the composite modifier is added to the positive electrode material dispersion, an ultrasonic frequency of 30-50 kHz is applied for 5-20 min, or magnetic stirring is performed at a speed of 300-1000 r / min for 10-30 min to fully mix the positive electrode material and the composite modifier.

[0063] To facilitate the storage and application of positive electrode materials, in some embodiments, after the positive electrode material is modified with a composite modifier, the liquid obtained after S1.2 is also dried. For example, the positive electrode material modification method provided in the embodiment of the present application also includes step S1.3: adding a pH adjusting liquid to adjust the pH value of the mixed liquid to 4-5, drying the mixed liquid with a pH value of 4-5, and obtaining a positive electrode material modified with a composite modifier.

[0064] In some embodiments, a pH adjusting solution is prepared before step S1.3. For example, a pH adjusting agent is added to an alcohol-water solution and fully dispersed to prepare a pH adjusting solution with a concentration of 1-3 mol / L.

[0065] The pH regulator includes at least one of formic acid, glacial acetic acid and oxalic acid, the alcohol aqueous solution includes an alcohol solvent and deionized water in a mass ratio of (90:10)-(70:30), and the alcohol solvent includes at least one of methanol, ethanol, ethylene glycol and isopropanol.

[0066] In some embodiments, in S1.3, a pH regulating liquid is added to the mixed liquid while stirring, and then stirring is continued. The pH value is measured once every set time interval. After the pH value stabilizes between 4-5, the mixed liquid is dried to obtain a positive electrode material modified with a composite modifier.

[0067] In some embodiments, in S1.3, stirring is performed at a speed of 200-1200 r / min, and the set time is 0.5-1 h.

[0068] In a second aspect, an embodiment of the present application provides a method for dry-processing a positive electrode film for a lithium battery, comprising:

[0069] S2.1, mixing the positive electrode material modified with the composite modifier obtained by the positive electrode material modification method with a conductive agent and a binder to prepare a premixed modified positive electrode mixture;

[0070] S2.2, crushing, dispersing and fiberizing the premixed modified cathode mixture to obtain a fiberized modified cathode mixture;

[0071] S2.3, heating and calendering the fiberized modified cathode mixture to obtain a dry-process modified cathode film;

[0072] S2.4, compounding the dry-process modified positive electrode film with a current collector to obtain a positive electrode film.

[0073] In some embodiments, in S2.1, the conductive agent includes at least one of conductive carbon black, Ketjen black, acetylene black, carbon fiber, and carbon nanotubes; the binder includes at least one of ethylene-tetrafluoroethylene copolymer polyacrylonitrile, polytetrafluoroethylene, and tetrafluoroethylene-hexafluoropropylene copolymer.

[0074] Among them, the mass ratio of the positive electrode material modified by the composite modifier, the conductive agent and the binder is (90-96): (2-5): (2-5).

[0075] In some embodiments, in S2.1, the cathode material modified with the composite modifier, the conductive agent, and the binder are ball-milled and mixed at a rate of 100-350 rpm for 0.5-3 h, or stirred and mixed at a rate of 500-2500 rpm for 0.5-3 h to prepare a premixed modified cathode mixture.

[0076] In some embodiments, in S2.2, the premixed modified positive electrode mixture is subjected to high-speed dispersion and air flow milling to achieve the purpose of crushing, dispersion and fiberization treatment, wherein the high-speed dispersion rate is 10000rpm-20000rpm, the dispersion time is 5-120min, the air flow milling speed is 20m / s-100m / s, the air flow pressure is 0.3-1.2MPa, the feeding pressure is 0.3-1.0MPa, and the temperature is 20℃-60℃.

[0077] In S2.1, after the conductive agent and the binder are mixed at a low speed with the positive electrode material modified by the composite modifier, the binder and the conductive material are evenly distributed around the positive electrode material particles. Further through S2.2, the modified layer is polymerized during high-speed stirring, shearing or grinding. After polymerization, a coating network is formed between the binder, the conductive material and the positive electrode material. Thus, uniform mixing of the various components can be achieved and a decrease in the adhesion between the materials can be avoided. Therefore, when the amount of binder is reduced, the material contact and mixing uniformity will not be affected.

[0078] In addition, the modification layer including titanate coupling agent and orthosilicate also plays a certain hydrophobic role, which is conducive to the implementation of subsequent steps of dry preparation and avoids moisture interference caused by factors such as equipment, environment, and reaction during the preparation process.

[0079] In some embodiments, in S2.3, the fiberized modified cathode mixture is subjected to a heat calendering treatment at a pressure of 80-800 kPa and a temperature of 40-300° C. to prepare a dry-process modified cathode film with a thickness of 100-500 μm.

[0080] Fiberization can transform cathode materials into fibrous structures, where conductive agents such as carbon black or conductive nanomaterials are coated with the fibers and form a conductive network with the cathode material. Binders are used to firmly bind these fibers and the conductive agent to the cathode material.

[0081] Hot calendering involves heating the mixture to an appropriate temperature and applying pressure, causing it to bond and densify under the combined action of thermal and mechanical forces. After the cathode material, conductive agent, and binder are uniformly mixed to form a fibrous, three-dimensional network structure, hot pressing is applied to reduce the gaps between the structures, further enhancing the binder's function, strengthening the material's bonding strength and integrity, and forming a denser cathode film.

[0082] In the dense positive electrode film, the fibrous structure provides a larger specific surface area, and the conductive agent forms a conductive network, which is conducive to the full and rapid progress of the electrochemical reaction.

[0083] In some embodiments, in S2.4, the dry-modified positive electrode film and the current collector are compounded by heating calendering or high-temperature rolling to form a positive electrode film with a thickness of 50-100 μm, wherein the pressure of heating calendering is 200-600 kPa and the temperature is 40-300°C, and the temperature of high-temperature rolling is 200-300°C.

[0084] The current collector includes one of aluminum foil and carbon-coated aluminum foil.

[0085] The positive electrode material and positive electrode film are prepared by the method provided in the embodiments of the present application. No solvent is used in the mixing process of the components, which avoids the electrode stratification problem caused by solvent evaporation. Compared with special equipment, this strategy is simple to operate, reduces equipment cost and energy consumption, and the optimization strategy and preparation process are simple, saving material costs and being beneficial to environmental safety.

[0086] In a third aspect, the present application provides a positive electrode material, the surface of which is coated with a titanate coupling agent and an orthosilicate, or the positive electrode material is processed and formed using the positive electrode material modification method provided in any of the aforementioned embodiments.

[0087] Orthosilicate materials possess excellent chemical stability, and after coating, they optimize the surface properties of the cathode material. The addition of a titanate coupling agent also enhances the high-temperature resistance of the dry-process electrode, contributing to the safety of the battery cell. The chemical bond formed between the modified layer and the cathode is more stable than physical adsorption, effectively suppressing agglomeration of cathode particles during low-speed mixing of the materials.

[0088] In a fourth aspect, the present application provides a positive electrode film, comprising a positive electrode film and a current collector, wherein the positive electrode film is stacked on the current collector and compositely formed, wherein the positive electrode film is formed by heating and calendering after fiberization modification of a positive electrode material, a conductive agent and a binder, and the surface of the positive electrode material is coated with a titanate coupling agent and an orthosilicate; or the positive electrode film is formed by the dry method for preparing a positive electrode film for a lithium battery provided in any of the aforementioned embodiments.

[0089] As mentioned above, the current collector includes one of aluminum foil and carbon-coated aluminum foil.

[0090] The positive electrode film has a dense fibrous structure. The positive electrode material and the conductive agent are evenly mixed and tightly adhered under the action of the binder. The electrode is not stratified and the amount of inactive substances used is relatively small.

[0091] In a fifth aspect, the present application provides a lithium-ion battery comprising the aforementioned positive electrode membrane, negative electrode membrane and electrolyte.

[0092] The positive electrode film not only has a dense structure, a large specific surface area, and good conductivity, but the addition of its titanate coupling agent also improves the high-temperature resistance of the dry-process electrode and improves the safety of the lithium-ion battery cell.

[0093] The present application will be described in detail below through specific examples. The following examples are only some examples of the present application and are not limitations of the present application.

[0094] Example 1

[0095] An embodiment of the present application provides a lithium battery, wherein the positive electrode film is formed by combining a positive electrode film and a current collector, and the positive electrode material used in the positive electrode film is modified by a composite modifier, and the preparation method is as follows.

[0096] First, the surface of the cathode material is modified:

[0097] S1.1 Cathode Material Pretreatment: Weigh 100g of lithium nickel cobalt manganese oxide (LiNi0.8Co0.1Mn0.1O2, hereinafter referred to as NCM811) and disperse it in 500ml of ethanol solvent by ball milling to obtain a uniform NCM811 cathode material dispersion. The NCM811 concentration is 0.2g / ml. The ball milling process is performed at a rate of 300 rpm for 15 minutes.

[0098] S1.2 Prepare pH adjusting solution: Weigh 120 g of glacial acetic acid pH adjusting agent into an alcohol-water solution and thoroughly disperse it by ultrasonication to obtain a glacial acetic acid-alcohol-water solution. The mass ratio of alcohol solvent to deionized water in the alcohol-water solution is 90:10, and the concentration of glacial acetic acid is 2 mol / L. Ultrasonication conditions include a frequency of 30 kHz and a duration of 10 min.

[0099] S1.3 Mix the positive electrode material and the composite modifier: Add 2.08g of tetrabutyl titanate and 2.08g of ethyl orthosilicate as a composite modifier to the NCM811 positive electrode material dispersion obtained in S1.1, that is, the mass ratio of tetrabutyl titanate and ethyl orthosilicate in the composite modifier is 1:1, and the mass ratio of NCM811 positive electrode material to composite modifier is about 96:4, and then use magnetic stirring to form a uniform mixed liquid, the stirring speed is 1000r / min, and the time is 30min.

[0100] S1.4 Adjust the pH value and dry: Use the glacial acetic acid alcohol aqueous solution in S1.2 to adjust the pH of the mixed solution in S1.3 to 4.5, continue stirring during the adjustment process, and then continue stirring for 1 hour and repeat the pH test to ensure that the pH of the mixed solution is 4.5, wherein the stirring speed is 1000r / min; after the pH of the mixed solution stabilizes, place it in an oven and dry it until the solvent is completely removed. The drying temperature is 60℃ and the drying time is 24h. Finally, the NCM811 positive electrode material modified with the composite modifier is obtained.

[0101] The order of S1.2 is not limited. It only needs to be performed before S1.4 to complete the preparation of the pH regulating solution.

[0102] Then, the positive electrode material modified by the composite modifier is used to prepare the positive electrode film by dry method:

[0103] S2.1 Prepare a premixed modified cathode mixture: Weigh 94 g of composite modifier-modified NCM811 cathode material, 3 g of acetylene black, and 3 g of polytetrafluoroethylene (PTFE) and stir to obtain a premixed modified cathode mixture. The mass ratio of composite modifier-modified NCM811 cathode material, conductive agent acetylene black, and binder polytetrafluoroethylene is 94:3:3. Stir at a rate of 1500 rpm for 2 hours.

[0104] S2.2 Preparation of a Fiberized Modified Cathode Mixture: The premixed modified cathode mixture obtained in step S2.1 was crushed, dispersed, and fiberized using airflow milling to produce a fiberized modified NCM811 cathode mixture. The airflow milling speed was 50 m / s, the airflow pressure was 0.5 MPa, the feed pressure was 0.5 MPa, and the temperature was 30°C.

[0105] S2.3 Preparation of dry-modified positive electrode membrane: Under the conditions of pressure of 500 kPa and temperature of 250°C, the fiberized modified NCM811 positive electrode mixture was heated and calendered to obtain a dry-modified NCM811 positive electrode membrane with a thickness of 300 μm.

[0106] S2.4 Preparation of positive electrode film: At a temperature of 300°C, the dry-modified NCM811 positive electrode film obtained in S2.3 and the aluminum foil current collector are rolled to make the dry-modified NCM811 positive electrode film and the aluminum foil current collector composite to obtain a dry-modified NCM811 positive electrode film with a thickness of 50 μm.

[0107] Then, the above-mentioned positive electrode film is used to prepare a button-type lithium-ion battery:

[0108] S3.1 Select the negative electrode material (silicon-graphite composite material) and cut it into 16 mm diameter discs to serve as the negative electrode sheets.

[0109] S3.2 Cut the positive electrode film obtained in S2.4 into round pieces with a diameter of 14 mm to serve as positive electrode sheets;

[0110] S3.3 Cut the polyethylene homopolymer film into 19 mm diameter discs to serve as separators;

[0111] S3.4 In an argon-filled glove box, the positive electrode sheet, negative electrode sheet, and separator are stacked, electrolyte is added, and the battery is sealed to form a button-type lithium-ion battery. The electrolyte is 1M LiPF6 in FEC-DMC (volume ratio 1:4).

[0112] Example 2

[0113] An embodiment of the present application provides a lithium battery, wherein the positive electrode film is formed by combining a positive electrode film and a current collector, and the positive electrode material used in the positive electrode film is modified by a composite modifier, and the preparation method is as follows.

[0114] First, the surface of the cathode material is modified:

[0115] S1.1 Cathode Material Pretreatment: Weigh 100g of lithium iron phosphate (LiFePO4) cathode material and disperse it in 500ml of ethanol solvent by ball milling to obtain a uniform lithium iron phosphate cathode material dispersion. The lithium iron phosphate concentration is 0.2g / ml. The ball milling speed is 300rpm and the time is 15min.

[0116] S1.2 Prepare pH adjusting solution: Weigh 120 g of glacial acetic acid pH adjusting agent into an alcohol-water solution and thoroughly disperse it by ultrasonication to obtain a glacial acetic acid-alcohol-water solution. The mass ratio of alcohol solvent to deionized water in the alcohol-water solution is 90:10, and the concentration of glacial acetic acid is 2 mol / L. Ultrasonication conditions include a frequency of 30 kHz and a duration of 10 min.

[0117] S1.3 Mix the positive electrode material and the composite modifier: add 2.63g of tetrabutyl titanate and 2.63g of ethyl orthosilicate as a composite modifier to the lithium iron phosphate positive electrode material dispersion obtained in S1.1, that is, the mass ratio of tetrabutyl titanate and ethyl orthosilicate in the composite modifier is 1:1, and the mass ratio of the lithium iron phosphate positive electrode material to the composite modifier is about 95:5, and then use magnetic stirring to form a uniform mixed liquid, the stirring speed is 1000r / min, and the time is 30min.

[0118] S1.4 Adjust the pH value and dry: Use the glacial acetic acid alcohol aqueous solution in S1.2 to adjust the pH of the mixed solution in S1.3 to 4.5, continue stirring during the adjustment process, and then continue stirring for 1 hour and repeat the pH test to ensure that the pH of the mixed solution is 4.5, wherein the stirring speed is 1000r / min; after the pH of the mixed solution stabilizes, place it in an oven and dry it until the solvent is completely removed. The drying temperature is 60°C and the drying time is 24 hours. Finally, a lithium iron phosphate positive electrode material modified with a composite modifier is obtained.

[0119] The order of S1.2 is not limited. It only needs to be performed before S1.4 to complete the preparation of the pH regulating solution.

[0120] Then, the positive electrode material modified by the composite modifier is used to prepare the positive electrode film by dry method:

[0121] S2.1 Prepare a premixed modified cathode mixture: Weigh 94 g of composite modifier-modified lithium iron phosphate cathode material, 3 g of acetylene black, and 3 g of polytetrafluoroethylene (PTFE) and stir to obtain a premixed modified cathode mixture. The mass ratio of composite modifier-modified lithium iron phosphate cathode material, conductive agent acetylene black, and binder polytetrafluoroethylene is 94:3:3. Stir at a rate of 1500 rpm for 2 hours.

[0122] S2.2 Preparation of a Fiberized Modified Cathode Mixture: The premixed modified cathode mixture obtained in step S2.1 was crushed, dispersed, and fiberized using a jet milling process to produce a Fiberized Modified LiFePO4 Cathode Mixture. The jet milling process was performed at a speed of 50 m / s, a pressure of 0.5 MPa, a feed pressure of 0.5 MPa, and a temperature of 30°C.

[0123] S2.3 Preparation of dry-process modified positive electrode membrane: Under the conditions of a pressure of 500 kPa and a temperature of 250°C, the fiberized modified lithium iron phosphate positive electrode mixture is subjected to a heating and rolling treatment to obtain a dry-process modified lithium iron phosphate positive electrode membrane with a thickness of 300 μm.

[0124] S2.4 Preparation of positive electrode film: At a temperature of 300°C, the dry-modified lithium iron phosphate positive electrode film obtained in S2.3 is rolled with the aluminum foil current collector to composite the dry-modified lithium iron phosphate positive electrode film and the aluminum foil current collector to obtain a dry-modified lithium iron phosphate positive electrode film with a thickness of 50 μm.

[0125] Then, the above-mentioned positive electrode film is used to prepare a button-type lithium-ion battery:

[0126] S3.1 Select the negative electrode material (silicon-graphite composite material) and cut it into 16 mm diameter discs to serve as the negative electrode sheets.

[0127] S3.2 Cut the positive electrode film obtained in S2.4 into round pieces with a diameter of 14 mm to serve as positive electrode sheets;

[0128] S3.3 Cut the polyethylene homopolymer film into 19 mm diameter discs to serve as separators;

[0129] S3.4 In an argon-filled glove box, the positive electrode sheet, negative electrode sheet, and separator are stacked, electrolyte is added, and the battery is sealed to form a button-type lithium-ion battery. The electrolyte is 1M LiPF6 in FEC-DMC (volume ratio 1:4).

[0130] Example 3

[0131] An embodiment of the present application provides a lithium battery, wherein the positive electrode film is formed by combining a positive electrode film and a current collector, and the positive electrode material used in the positive electrode film is modified by a composite modifier, and the preparation method is as follows.

[0132] First, the surface of the cathode material is modified:

[0133] S1.1 Cathode Material Pretreatment: Weigh 100g of lithium manganese phosphate (LiMnPO4) cathode material and disperse it in 500ml of ethanol solvent by ball milling to obtain a uniform lithium manganese phosphate cathode material dispersion. The concentration of lithium manganese phosphate is 0.2g / ml. The ball milling speed is 300rpm and the time is 15min.

[0134] S1.2 Prepare pH adjusting solution: Weigh 120 g of glacial acetic acid pH adjusting agent into an alcohol-water solution and thoroughly disperse it by ultrasonication to obtain a glacial acetic acid-alcohol-water solution. The mass ratio of alcohol solvent to deionized water in the alcohol-water solution is 90:10, and the concentration of glacial acetic acid is 2 mol / L. Ultrasonication conditions include a frequency of 30 kHz and a duration of 10 min.

[0135] S1.3 Mix the positive electrode material and the composite modifier: add a composite modifier of 1.02g of tetrabutyl titanate and 1.02g of ethyl orthosilicate to the lithium manganese phosphate positive electrode material dispersion obtained in S1.1, that is, the mass ratio of tetrabutyl titanate and ethyl orthosilicate in the composite modifier is 1:1, and the mass ratio of the lithium manganese phosphate positive electrode material to the composite modifier is about 98:2, and then use ultrasonic dispersion to form a uniform mixed liquid, and the ultrasonic dispersion conditions are 45kHz and 20min.

[0136] S1.4 Adjust the pH value and dry: Use the glacial acetic acid alcohol aqueous solution in S1.2 to adjust the pH of the mixed solution in S1.3 to 4.5, stir continuously during the adjustment process, and then continue stirring for 1 hour and repeat the pH test to ensure that the pH of the mixed solution is 4.5, wherein the stirring speed is 1000r / min; after the pH of the mixed solution stabilizes, place it in an oven and dry it until the solvent is completely removed, the drying temperature is 60°C, and the drying time is 24 hours, and finally a lithium manganese phosphate positive electrode material modified with a composite modifier is obtained.

[0137] The order of S1.2 is not limited. It only needs to be performed before S1.4 to complete the preparation of the pH regulating solution.

[0138] Then, the positive electrode material modified by the composite modifier is used to prepare the positive electrode film by dry method:

[0139] S2.1 Prepare a premixed modified cathode mixture: Weigh 94 g of composite modifier-modified lithium manganese phosphate cathode material, 3 g of acetylene black, and 3 g of polytetrafluoroethylene (PTFE) and stir to obtain a premixed modified cathode mixture. The mass ratio of composite modifier-modified lithium manganese phosphate cathode material, acetylene black, and binder polytetrafluoroethylene is 94:3:3. Stir at a rate of 1500 rpm for 2 hours.

[0140] S2.2 Preparation of a Fiberized Modified Cathode Mixture: The premixed modified cathode mixture obtained in step S2.1 was crushed, dispersed, and fiberized using a jet milling process to produce a Fiberized Modified Lithium Manganese Phosphate Cathode Mixture. The jet milling process was performed at a speed of 50 m / s, an airflow pressure of 0.5 MPa, a feed pressure of 0.5 MPa, and a temperature of 30°C.

[0141] S2.3 Preparation of dry-process modified positive electrode membrane: Under the conditions of pressure of 500 kPa and temperature of 250°C, the fiberized modified lithium manganese phosphate positive electrode mixture is heated and rolled to obtain a dry-process modified lithium manganese phosphate positive electrode membrane with a thickness of 300 μm.

[0142] S2.4 Preparation of positive electrode film: At a temperature of 300°C, the dry-modified lithium manganese phosphate positive electrode film obtained in S2.3 is rolled with the aluminum foil current collector to composite the dry-modified lithium manganese phosphate positive electrode film with the aluminum foil current collector to obtain a dry-modified lithium manganese phosphate positive electrode film with a thickness of 50 μm.

[0143] Then, the above-mentioned positive electrode film is used to prepare a button-type lithium-ion battery:

[0144] S3.1 Select the negative electrode material (silicon-graphite composite material) and cut it into 16 mm diameter discs to serve as the negative electrode sheets.

[0145] S3.2 Cut the positive electrode film obtained in S2.4 into round pieces with a diameter of 14 mm to serve as positive electrode sheets;

[0146] S3.3 Cut the polyethylene homopolymer film into 19 mm diameter discs to serve as separators;

[0147] S3.4 In an argon-filled glove box, the positive electrode sheet, negative electrode sheet, and separator are stacked, electrolyte is added, and the battery is sealed to form a button-type lithium-ion battery. The electrolyte is 1M LiPF6 in FEC-DMC (volume ratio 1:4).

[0148] Example 4

[0149] An embodiment of the present application provides a lithium battery, wherein the positive electrode film is formed by combining a positive electrode film and a current collector, and the positive electrode material used in the positive electrode film is modified by a composite modifier, and the preparation method is as follows.

[0150] First, the surface of the cathode material is modified:

[0151] S1.1 Cathode Material Pretreatment: Weigh 100g of lithium nickel cobalt manganese oxide (LiNi0.8Co0.1Mn0.1O2, hereinafter referred to as NCM811) and disperse it in 500ml of ethanol solvent by ball milling to obtain a uniform NCM811 cathode material dispersion. The NCM811 concentration is 0.2g / ml. The ball milling process is performed at a rate of 300 rpm for 15 minutes.

[0152] S1.2 Prepare pH adjusting solution: Weigh 120 g of glacial acetic acid pH adjusting agent into an alcohol-water solution and thoroughly disperse it by ultrasonication to obtain a glacial acetic acid-alcohol-water solution. The mass ratio of alcohol solvent to deionized water in the alcohol-water solution is 90:10, and the concentration of glacial acetic acid is 2 mol / L. Ultrasonication conditions include a frequency of 30 kHz and a duration of 10 min.

[0153] S1.3 Mix the positive electrode material and the composite modifier: Add a composite modifier of 2.10g of diisostearyl ethyl titanate and 3.15g of ethyl orthosilicate to the NCM811 positive electrode material dispersion obtained in S1.1, that is, the mass ratio of diisostearyl ethyl titanate and ethyl orthosilicate in the composite modifier is 4:6, and the mass ratio of NCM811 positive electrode material to the composite modifier is about 95:5. Then use magnetic stirring to form a uniform mixed liquid, the stirring speed is 1000r / min, and the time is 30min.

[0154] S1.4 Adjust the pH value and dry: Use the glacial acetic acid alcohol aqueous solution in S1.2 to adjust the pH of the mixed solution in S1.3 to 4.5, continue stirring during the adjustment process, and then continue stirring for 1 hour and repeat the pH test to ensure that the pH of the mixed solution is 4.5, wherein the stirring speed is 1000r / min; after the pH of the mixed solution stabilizes, place it in an oven and dry it until the solvent is completely removed. The drying temperature is 60℃ and the drying time is 24h. Finally, the NCM811 positive electrode material modified with the composite modifier is obtained.

[0155] The order of S1.2 is not limited. It only needs to be performed before S1.4 to complete the preparation of the pH regulating solution.

[0156] Then, the positive electrode material modified by the composite modifier is used to prepare the positive electrode film by dry method:

[0157] S2.1 Prepare a premixed modified cathode mixture: Weigh 95g of composite modifier-modified NCM811 cathode material, 3g of acetylene black, and 2g of polytetrafluoroethylene (PTFE) and stir to obtain a premixed modified cathode mixture. The mass ratio of composite modifier-modified NCM811 cathode material, conductive agent acetylene black, and binder polytetrafluoroethylene is 95:3:2. Stir at a rate of 1500 rpm for 2 hours.

[0158] S2.2 Preparation of a Fiberized Modified Cathode Mixture: The premixed modified cathode mixture obtained in step S2.1 was crushed, dispersed, and fiberized using airflow milling to produce a fiberized modified NCM811 cathode mixture. The airflow milling speed was 50 m / s, the airflow pressure was 0.5 MPa, the feed pressure was 0.5 MPa, and the temperature was 30°C.

[0159] S2.3 Preparation of dry-modified positive electrode membrane: Under the conditions of pressure of 500 kPa and temperature of 250°C, the fiberized modified NCM811 positive electrode mixture was heated and calendered to obtain a dry-modified NCM811 positive electrode membrane with a thickness of 300 μm.

[0160] S2.4 Preparation of positive electrode film: At a temperature of 300°C, the dry-modified NCM811 positive electrode film obtained in S2.3 and the aluminum foil current collector are rolled to make the dry-modified NCM811 positive electrode film and the aluminum foil current collector composite to obtain a dry-modified NCM811 positive electrode film with a thickness of 50 μm.

[0161] Then, the above-mentioned positive electrode film is used to prepare a button-type lithium-ion battery:

[0162] S3.1 Select the negative electrode material (silicon-graphite composite material) and cut it into 16 mm diameter discs to serve as the negative electrode sheets.

[0163] S3.2 Cut the positive electrode film obtained in S2.4 into round pieces with a diameter of 14 mm to serve as positive electrode sheets;

[0164] S3.3 Cut the polyethylene homopolymer film into 19 mm diameter discs to serve as separators;

[0165] S3.4 In an argon-filled glove box, the positive electrode sheet, negative electrode sheet, and separator are stacked, electrolyte is added, and the battery is sealed to form a button-type lithium-ion battery. The electrolyte is 1M LiPF6 in FEC-DMC (volume ratio 1:4).

[0166] Example 5

[0167] An embodiment of the present application provides a lithium battery, wherein the positive electrode film is formed by combining a positive electrode film and a current collector, and the positive electrode material used in the positive electrode film is modified by a composite modifier, and the preparation method is as follows.

[0168] First, the surface of the cathode material is modified:

[0169] S1.1 Cathode Material Pretreatment: Weigh 100g of lithium nickel cobalt manganese oxide (LiNi0.8Co0.1Mn0.1O2, hereinafter referred to as NCM811) and disperse it in 500ml of ethanol solvent by ball milling to obtain a uniform NCM811 cathode material dispersion. The NCM811 concentration is 0.2g / ml. The ball milling process is performed at a rate of 300 rpm for 15 minutes.

[0170] S1.2 Prepare pH adjusting solution: Weigh 120 g of glacial acetic acid pH adjusting agent into an alcohol-water solution and thoroughly disperse it by ultrasonication to obtain a glacial acetic acid-alcohol-water solution. The mass ratio of alcohol solvent to deionized water in the alcohol-water solution is 90:10, and the concentration of glacial acetic acid is 2 mol / L. Ultrasonication conditions include a frequency of 30 kHz and a duration of 10 min.

[0171] S1.3 Mix the positive electrode material and the composite modifier: add 0.2g of diisostearyl ethyl titanate and 0.3g of ethyl orthosilicate as a composite modifier to the NCM811 positive electrode material dispersion obtained in S1.1, that is, the mass ratio of diisostearyl ethyl titanate and ethyl orthosilicate in the composite modifier is 4:6, and the mass ratio of NCM811 positive electrode material to the composite modifier is about 99.5:0.5, and then use ultrasonic dispersion to form a uniform mixed liquid, and the ultrasonic dispersion conditions are 50kHz and 20min.

[0172] S1.4 Adjust the pH value and dry: Use the glacial acetic acid alcohol aqueous solution in S1.2 to adjust the pH of the mixed solution in S1.3 to 4.5, continue stirring during the adjustment process, and then continue stirring for 1 hour and repeat the pH test to ensure that the pH range of the mixed solution is within 4.5, where the stirring speed is 1000r / min; after the pH of the mixed solution stabilizes, place it in an oven and dry it until the solvent is completely removed. The drying temperature is 60℃ and the drying time is 24h. Finally, the NCM811 positive electrode material modified with the composite modifier is obtained.

[0173] The order of S1.2 is not limited. It only needs to be performed before S1.4 to complete the preparation of the pH regulating solution.

[0174] Then, the positive electrode material modified by the composite modifier is used to prepare the positive electrode film by dry method:

[0175] S2.1 Prepare a premixed modified cathode mixture: Weigh 95g of composite modifier-modified NCM811 cathode material, 3g of acetylene black, and 2g of polytetrafluoroethylene (PTFE) and stir to obtain a premixed modified cathode mixture. The mass ratio of composite modifier-modified NCM811 cathode material, conductive agent acetylene black, and binder polytetrafluoroethylene is 95:3:2. Stir at a rate of 1500 rpm for 2 hours.

[0176] S2.2 Preparation of a Fiberized Modified Cathode Mixture: The premixed modified cathode mixture obtained in step S2.1 was crushed, dispersed, and fiberized using airflow milling to produce a fiberized modified NCM811 cathode mixture. The airflow milling speed was 50 m / s, the airflow pressure was 0.5 MPa, the feed pressure was 0.5 MPa, and the temperature was 30°C.

[0177] S2.3 Preparation of dry-modified positive electrode membrane: Under the conditions of pressure of 500 kPa and temperature of 250°C, the fiberized modified NCM811 positive electrode mixture was heated and calendered to obtain a dry-modified NCM811 positive electrode membrane with a thickness of 300 μm.

[0178] S2.4 Preparation of positive electrode film: At a temperature of 300°C, the dry-modified NCM811 positive electrode film obtained in S2.3 and the aluminum foil current collector are rolled to make the dry-modified NCM811 positive electrode film and the aluminum foil current collector composite to obtain a dry-modified NCM811 positive electrode film with a thickness of 50 μm.

[0179] Then, the above-mentioned positive electrode film is used to prepare a button-type lithium-ion battery:

[0180] S3.1 Select the negative electrode material (silicon-graphite composite material) and cut it into 16 mm diameter discs to serve as the negative electrode sheets.

[0181] S3.2 Cut the positive electrode film obtained in S2.4 into round pieces with a diameter of 14 mm to serve as positive electrode sheets;

[0182] S3.3 Cut the polyethylene homopolymer film into 19 mm diameter discs to serve as separators;

[0183] S3.4 In an argon-filled glove box, the positive electrode sheet, negative electrode sheet, and separator are stacked, electrolyte is added, and the battery is sealed to form a button-type lithium-ion battery. The electrolyte is 1M LiPF6 in FEC-DMC (volume ratio 1:4).

[0184] Example 6

[0185] An embodiment of the present application provides a lithium battery, wherein the positive electrode film is formed by combining a positive electrode film and a current collector, and the positive electrode material used in the positive electrode film is modified by a composite modifier, and the preparation method is as follows.

[0186] First, the surface of the cathode material is modified:

[0187] S1.1 Cathode Material Pretreatment: Weigh 100g of lithium nickel cobalt manganese oxide (LiNi0.8Co0.1Mn0.1O2, hereinafter referred to as NCM811) and disperse it in 500ml of ethanol solvent by ball milling to obtain a uniform NCM811 cathode material dispersion. The NCM811 concentration is 0.2g / ml. The ball milling process is performed at a rate of 300 rpm for 15 minutes.

[0188] S1.2 Prepare pH adjusting solution: Weigh 120 g of glacial acetic acid pH adjusting agent into an alcohol-water solution and thoroughly disperse it by ultrasonication to obtain a glacial acetic acid-alcohol-water solution. The mass ratio of alcohol solvent to deionized water in the alcohol-water solution is 90:10, and the concentration of glacial acetic acid is 2 mol / L. Ultrasonication conditions include a frequency of 30 kHz and a duration of 10 min.

[0189] S1.3 Mixing the positive electrode material and the composite modifier: Add 0.83g of isopropyl trioleyl titanate and 3.33g of ethyl orthosilicate as a composite modifier to the NCM811 positive electrode material dispersion obtained in S1.1, that is, the mass ratio of isopropyl trioleyl titanate and ethyl orthosilicate in the composite modifier is about 1:4, and the mass ratio of NCM811 positive electrode material to the composite modifier is about 96:4, and then use magnetic stirring to form a uniform mixed liquid, the stirring speed is 1000r / min, and the time is 30min.

[0190] S1.4 Adjust the pH value and dry: Use the glacial acetic acid alcohol aqueous solution in S1.2 to adjust the pH of the mixed solution in S1.3 to 4.5, continue stirring during the adjustment process, and then continue stirring for 1 hour and repeat the pH test to ensure that the pH of the mixed solution is 4.5, wherein the stirring speed is 1000r / min; after the pH of the mixed solution stabilizes, place it in an oven and dry it until the solvent is completely removed. The drying temperature is 60℃ and the drying time is 24h. Finally, the NCM811 positive electrode material modified with the composite modifier is obtained.

[0191] The order of S1.2 is not limited. It only needs to be performed before S1.4 to complete the preparation of the pH regulating solution.

[0192] Then, the positive electrode material modified by the composite modifier is used to prepare the positive electrode film by dry method:

[0193] S2.1 Prepare a premixed modified cathode mixture: Weigh 94 g of composite modifier-modified NCM811 cathode material, 3 g of acetylene black, and 3 g of polytetrafluoroethylene (PTFE) and mix them by ball milling to obtain a premixed modified cathode mixture. The mass ratio of composite modifier-modified NCM811 cathode material, conductive agent acetylene black, and binder polytetrafluoroethylene is 94:3:3. Ball milling is performed at 300 rpm for 2.5 hours.

[0194] S2.2 Preparation of a Fiberized Modified Cathode Mixture: The premixed modified cathode mixture obtained in step S2.1 was crushed, dispersed, and fiberized using airflow milling to produce a fiberized modified NCM811 cathode mixture. The airflow milling speed was 50 m / s, the airflow pressure was 0.5 MPa, the feed pressure was 0.5 MPa, and the temperature was 30°C.

[0195] S2.3 Preparation of dry-modified positive electrode membrane: Under the conditions of pressure of 500 kPa and temperature of 250°C, the fiberized modified NCM811 positive electrode mixture was heated and calendered to obtain a dry-modified NCM811 positive electrode membrane with a thickness of 300 μm.

[0196] S2.4 Preparation of positive electrode film: At a temperature of 300°C, the dry-modified NCM811 positive electrode film obtained in S2.3 and the aluminum foil current collector are rolled to make the dry-modified NCM811 positive electrode film and the aluminum foil current collector composite to obtain a dry-modified NCM811 positive electrode film with a thickness of 50 μm.

[0197] Next, a button-type lithium-ion battery was prepared using the above-mentioned positive electrode film:

[0198] S3.1 Select the negative electrode material (silicon-graphite composite material) and cut it into 16 mm diameter discs to serve as the negative electrode sheets.

[0199] S3.2 Cut the positive electrode film obtained in S2.4 into round pieces with a diameter of 14 mm to serve as positive electrode sheets;

[0200] S3.3 Cut the polyethylene homopolymer film into 19 mm diameter discs to serve as separators;

[0201] S3.4 In an argon-filled glove box, the positive electrode sheet, negative electrode sheet, and separator are stacked, electrolyte is added, and the battery is sealed to form a button-type lithium-ion battery. The electrolyte is 1M LiPF6 in FEC-DMC (volume ratio 1:4).

[0202] Example 7

[0203] An embodiment of the present application provides a lithium battery, wherein the positive electrode film is formed by combining a positive electrode film and a current collector, and the positive electrode material used in the positive electrode film is modified by a composite modifier, and the preparation method is as follows.

[0204] First, the surface of the cathode material is modified:

[0205] S1.1 Cathode Material Pretreatment: Weigh 100g of lithium nickel cobalt manganese oxide (LiNi0.8Co0.1Mn0.1O2, hereinafter referred to as NCM811) and disperse it in 500ml of ethanol solvent by ball milling to obtain a uniform NCM811 cathode material dispersion. The NCM811 concentration is 0.2g / ml. The ball milling process is performed at a rate of 300 rpm for 15 minutes.

[0206] S1.2 Prepare pH adjusting solution: Weigh 120 g of glacial acetic acid pH adjusting agent into an alcohol-water solution and thoroughly disperse it by ultrasonication to obtain a glacial acetic acid-alcohol-water solution. The mass ratio of alcohol solvent to deionized water in the alcohol-water solution is 90:10, and the concentration of glacial acetic acid is 2 mol / L. Ultrasonication conditions include a frequency of 30 kHz and a duration of 10 min.

[0207] S1.3 Mixing the positive electrode material and the composite modifier: Add 1.25g of tetrabutyl titanate and 2.51g of methyl orthosilicate as a composite modifier to the NCM811 positive electrode material dispersion obtained in S1.1, that is, the mass ratio of tetrabutyl titanate and methyl orthosilicate in the composite modifier is about 1:2, and the mass ratio of NCM811 positive electrode material to the composite modifier is about 96:4. Then use magnetic stirring to form a uniform mixed liquid, the stirring speed is 1000r / min, and the time is 30min.

[0208] S1.4 Adjust the pH value and dry: Use the glacial acetic acid alcohol aqueous solution in S1.2 to adjust the pH of the mixed solution in S1.3 to 4.5, continue stirring during the adjustment process, and then continue stirring for 1 hour and repeat the pH test to ensure that the pH of the mixed solution is 4.5, wherein the stirring speed is 1000r / min; after the pH of the mixed solution stabilizes, place it in an oven and dry it until the solvent is completely removed. The drying temperature is 60℃ and the drying time is 24h. Finally, the NCM811 positive electrode material modified with the composite modifier is obtained.

[0209] The order of S1.2 is not limited. It only needs to be performed before S1.4 to complete the preparation of the pH regulating solution.

[0210] Then, the positive electrode material modified by the composite modifier is used to prepare the positive electrode film by dry method:

[0211] S2.1 Prepare a premixed modified cathode mixture: Weigh 94 g of composite modifier-modified NCM811 cathode material, 3 g of acetylene black, and 3 g of polytetrafluoroethylene (PTFE) and stir to obtain a premixed modified cathode mixture. The mass ratio of composite modifier-modified NCM811 cathode material, conductive agent acetylene black, and binder polytetrafluoroethylene is 94:3:3. Stir at a rate of 1500 rpm for 2 hours.

[0212] S2.2 Preparation of a Fiberized Modified Cathode Mixture: The premixed modified cathode mixture obtained in step S2.1 was crushed, dispersed, and fiberized using airflow milling to produce a fiberized modified NCM811 cathode mixture. The airflow milling speed was 50 m / s, the airflow pressure was 0.5 MPa, the feed pressure was 0.5 MPa, and the temperature was 30°C.

[0213] S2.3 Preparation of dry-modified positive electrode membrane: Under the conditions of pressure of 700 kPa and temperature of 290°C, the fiberized modified NCM811 positive electrode mixture was heated and calendered to obtain a dry-modified NCM811 positive electrode membrane with a thickness of 100 μm.

[0214] S2.4 Preparation of positive electrode film: At a temperature of 300°C, the dry-modified NCM811 positive electrode film obtained in S2.3 and the aluminum foil current collector are rolled to make the dry-modified NCM811 positive electrode film and the aluminum foil current collector composite to obtain a dry-modified NCM811 positive electrode film with a thickness of 50 μm.

[0215] Then, the above-mentioned positive electrode film is used to prepare a button-type lithium-ion battery:

[0216] S3.1 Select the negative electrode material (silicon-graphite composite material) and cut it into 16 mm diameter discs to serve as the negative electrode sheets.

[0217] S3.2 Cut the positive electrode film obtained in S2.4 into round pieces with a diameter of 14 mm to serve as positive electrode sheets;

[0218] S3.3 Cut the polyethylene homopolymer film into 19 mm diameter discs to serve as separators;

[0219] S3.4 In an argon-filled glove box, the positive electrode sheet, negative electrode sheet, and separator are stacked, electrolyte is added, and the battery is sealed to form a button-type lithium-ion battery. The electrolyte is 1M LiPF6 in FEC-DMC (volume ratio 1:4).

[0220] Example 8

[0221] An embodiment of the present application provides a lithium battery, wherein the positive electrode film is formed by combining a positive electrode film and a current collector, and the positive electrode material used in the positive electrode film is modified by a composite modifier, and the preparation method is as follows.

[0222] First, the surface of the cathode material is modified:

[0223] S1.1 Cathode Material Pretreatment: Weigh 100g of lithium nickel cobalt manganese oxide (LiNi0.8Co0.1Mn0.1O2, hereinafter referred to as NCM811) and disperse it in 500ml of ethanol solvent by ball milling to obtain a uniform NCM811 cathode material dispersion. The NCM811 concentration is 0.2g / ml. The ball milling process is performed at a rate of 300 rpm for 15 minutes.

[0224] S1.2 Prepare pH adjusting solution: Weigh 120 g of glacial acetic acid pH adjusting agent into an alcohol-water solution and thoroughly disperse it by ultrasonication to obtain a glacial acetic acid-alcohol-water solution. The mass ratio of alcohol solvent to deionized water in the alcohol-water solution is 90:10, and the concentration of glacial acetic acid is 2 mol / L. Ultrasonication conditions include a frequency of 30 kHz and a duration of 10 min.

[0225] S1.3 Mixing the positive electrode material and the composite modifier: Add 3.32g of tetrabutyl titanate and 0.83g of butyl orthosilicate as a composite modifier to the NCM811 positive electrode material dispersion obtained in S1.1, that is, the mass ratio of tetrabutyl titanate and butyl orthosilicate in the composite modifier is about 4:1, and the mass ratio of the NCM811 positive electrode material to the composite modifier is about 96:4. Then use magnetic stirring to form a uniform mixed liquid, the stirring speed is 1000r / min, and the time is 30min.

[0226] S1.4 Adjust the pH value and dry: Use the glacial acetic acid alcohol aqueous solution in S1.2 to adjust the pH of the mixed solution in S1.3 to 4.5, continue stirring during the adjustment process, and then continue stirring for 1 hour and repeat the pH test to ensure that the pH of the mixed solution is 4.5, wherein the stirring speed is 1000r / min; after the pH of the mixed solution stabilizes, place it in an oven and dry it until the solvent is completely removed. The drying temperature is 60℃ and the drying time is 24h. Finally, the NCM811 positive electrode material modified with the composite modifier is obtained.

[0227] The order of S1.2 is not limited. It only needs to be performed before S1.4 to complete the preparation of the pH regulating solution.

[0228] Then, the positive electrode material modified by the composite modifier is used to prepare the positive electrode film by dry method:

[0229] S2.1 Prepare a premixed modified cathode mixture: Weigh 94 g of composite modifier-modified NCM811 cathode material, 3 g of acetylene black, and 3 g of polytetrafluoroethylene (PTFE) and stir to obtain a premixed modified cathode mixture. The mass ratio of composite modifier-modified NCM811 cathode material, conductive agent acetylene black, and binder polytetrafluoroethylene is 94:3:3. Stir at a rate of 1500 rpm for 2 hours.

[0230] S2.2 Preparation of a Fiberized Modified Cathode Mixture: The premixed modified cathode mixture obtained in step S2.1 was crushed, dispersed, and fiberized using airflow milling to produce a fiberized modified NCM811 cathode mixture. The airflow milling speed was 50 m / s, the airflow pressure was 0.5 MPa, the feed pressure was 0.5 MPa, and the temperature was 30°C.

[0231] S2.3 Preparation of dry-modified positive electrode membrane: Under the conditions of pressure of 500 kPa and temperature of 250°C, the fiberized modified NCM811 positive electrode mixture was heated and calendered to obtain a dry-modified NCM811 positive electrode membrane with a thickness of 300 μm.

[0232] S2.4 Preparation of positive electrode film: At a temperature of 300°C, the dry-modified NCM811 positive electrode film obtained in S2.3 and the aluminum foil current collector are rolled to make the dry-modified NCM811 positive electrode film and the aluminum foil current collector composite to obtain a dry-modified NCM811 positive electrode film with a thickness of 50 μm.

[0233] Then, the above-mentioned positive electrode film is used to prepare a button-type lithium-ion battery:

[0234] S3.1 Select the negative electrode material (silicon-graphite composite material) and cut it into 16 mm diameter discs to serve as the negative electrode sheets.

[0235] S3.2 Cut the positive electrode film obtained in S2.4 into round pieces with a diameter of 14 mm to serve as positive electrode sheets;

[0236] S3.3 Cut the polyethylene homopolymer film into 19 mm diameter discs to serve as separators;

[0237] S3.4 In an argon-filled glove box, the positive electrode sheet, negative electrode sheet, and separator are stacked, electrolyte is added, and the battery is sealed to form a button-type lithium-ion battery. The electrolyte is 1M LiPF6 in FEC-DMC (volume ratio 1:4).

[0238] Example 9

[0239] An embodiment of the present application provides a lithium battery, wherein the positive electrode film is formed by combining a positive electrode film and a current collector, and the positive electrode material used in the positive electrode film is modified by a composite modifier, and the preparation method is as follows.

[0240] First, the surface of the cathode material is modified:

[0241] S1.1 Cathode Material Pretreatment: Weigh 100g of lithium nickel cobalt manganese oxide (LiNi0.8Co0.1Mn0.1O2, hereinafter referred to as NCM811) and disperse it in 500ml of ethanol solvent by ball milling to obtain a uniform NCM811 cathode material dispersion. The NCM811 concentration is 0.2g / ml. The ball milling process is performed at a rate of 300 rpm for 15 minutes.

[0242] S1.2 Prepare pH adjusting solution: Weigh 120 g of glacial acetic acid pH adjusting agent into an alcohol-water solution and thoroughly disperse it by ultrasonication to obtain a glacial acetic acid-alcohol-water solution. The mass ratio of alcohol solvent to deionized water in the alcohol-water solution is 90:10, and the concentration of glacial acetic acid is 2 mol / L. Ultrasonication conditions include a frequency of 30 kHz and a duration of 10 min.

[0243] S1.3 Mixing the positive electrode material and the composite modifier: Add 2.50g of tetrabutyl titanate and 1.66g of isopropyl orthosilicate as a composite modifier to the NCM811 positive electrode material dispersion obtained in S1.1, that is, the mass ratio of tetrabutyl titanate and isopropyl orthosilicate in the composite modifier is about 3:2, and the mass ratio of NCM811 positive electrode material to composite modifier is about 96:4, and then use magnetic stirring to form a uniform mixed liquid, the stirring speed is 1000r / min, and the time is 30min.

[0244] S1.4 Adjust the pH value and dry: Use the glacial acetic acid alcohol aqueous solution in S1.2 to adjust the pH of the mixed solution in S1.3 to 4.5, continue stirring during the adjustment process, and then continue stirring for 1 hour and repeat the pH test to ensure that the pH of the mixed solution is 4.5, wherein the stirring speed is 1000r / min; after the pH of the mixed solution stabilizes, place it in an oven and dry it until the solvent is completely removed. The drying temperature is 60℃ and the drying time is 24h. Finally, the NCM811 positive electrode material modified with the composite modifier is obtained.

[0245] The order of S1.2 is not limited. It only needs to be performed before S1.4 to complete the preparation of the pH regulating solution.

[0246] Then, the positive electrode material modified by the composite modifier is used to prepare the positive electrode film by dry method:

[0247] S2.1 Prepare a premixed modified cathode mixture: Weigh 94 g of composite modifier-modified NCM811 cathode material, 3 g of acetylene black, and 3 g of polytetrafluoroethylene (PTFE) and stir to obtain a premixed modified cathode mixture. The mass ratio of composite modifier-modified NCM811 cathode material, conductive agent acetylene black, and binder polytetrafluoroethylene is 94:3:3. Stir at a rate of 1500 rpm for 2 hours.

[0248] S2.2 Preparation of fiberized modified positive electrode mixture: The premixed modified positive electrode mixture obtained in step S2.1 was crushed, dispersed and fiberized by high-speed dispersion to obtain a fiberized modified NCM811 positive electrode mixture. The high-speed dispersion rate was 15,000 m / s and the time was 100 min.

[0249] S2.3 Preparation of dry-modified positive electrode membrane: Under the conditions of pressure of 500 kPa and temperature of 250°C, the fiberized modified NCM811 positive electrode mixture was heated and calendered to obtain a dry-modified NCM811 positive electrode membrane with a thickness of 300 μm.

[0250] S2.4 Preparation of positive electrode film: At a temperature of 300°C, the dry-modified NCM811 positive electrode film obtained in S2.3 and the aluminum foil current collector are rolled to make the dry-modified NCM811 positive electrode film and the aluminum foil current collector composite to obtain a dry-modified NCM811 positive electrode film with a thickness of 50 μm.

[0251] Then, the above-mentioned positive electrode film is used to prepare a button-type lithium-ion battery:

[0252] S3.1 Select the negative electrode material (silicon-graphite composite material) and cut it into 16 mm diameter discs to serve as the negative electrode sheets.

[0253] S3.2 Cut the positive electrode film obtained in S2.4 into round pieces with a diameter of 14 mm to serve as positive electrode sheets;

[0254] S3.3 Cut the polyethylene homopolymer film into 19 mm diameter discs to serve as separators;

[0255] S3.4 In an argon-filled glove box, the positive electrode sheet, negative electrode sheet, and separator are stacked, electrolyte is added, and the battery is sealed to form a button-type lithium-ion battery. The electrolyte is 1M LiPF6 in FEC-DMC (volume ratio 1:4).

[0256] Comparative Example 1

[0257] Comparative Example 1 is basically the same as Example 1, except that the NCM811 positive electrode used in this example has not been surface modified, that is:

[0258] (1) Preparation of a premixed cathode mixture: Weigh 94 g of NCM811 cathode material, 3 g of acetylene black, and 3 g of polytetrafluoroethylene (PTFE) and mix them by stirring to obtain a premixed cathode mixture. The mass ratio of NCM811 cathode material, conductive agent acetylene black, and binder polytetrafluoroethylene is 94:3:3. The stirring rate is 1500 rpm and the mixing time is 2 h.

[0259] (2) Preparation of a fiberized cathode mixture: The premixed cathode mixture obtained in step (1) was crushed, dispersed, and fiberized using a jet milling method to obtain a fiberized NCM811 cathode mixture. The jet milling speed was 50 m / s, the air flow pressure was 0.5 MPa, the feed pressure was 0.5 MPa, and the temperature was 30°C.

[0260] (3) Preparation of dry-process cathode membrane: The fiberized NCM811 cathode mixture was heated and rolled under a pressure of 500 kPa and a temperature of 250 °C to obtain a dry-process NCM811 cathode membrane with a thickness of 300 μm.

[0261] (4) Preparation of positive electrode film: The dry-process NCM811 positive electrode film obtained in step (3) was rolled with the aluminum foil current collector at a temperature of 300° C. to composite the dry-process NCM811 positive electrode film with the aluminum foil current collector to obtain a dry-process NCM811 positive electrode film with a thickness of 50 μm.

[0262] (5) Select the negative electrode material (silicon-graphite composite material) and cut the negative electrode material into discs with a diameter of 16 mm to serve as the negative electrode sheet;

[0263] (6) Cutting the positive electrode film obtained in step (4) into discs with a diameter of 14 mm to serve as positive electrode sheets;

[0264] (7) Cut the polyethylene homopolymer film into discs with a diameter of 19 mm to serve as the diaphragm;

[0265] (8) In an argon-filled glove box, the positive electrode sheet, negative electrode sheet, and separator are stacked, electrolyte is added, and the battery is sealed to form a button-type lithium-ion battery. The electrolyte is 1M LiPF6 in FEC-DMC (volume ratio 1:4).

[0266] Comparative Example 2

[0267] Comparative Example 2 is basically the same as Example 1, except that the positive electrode material is only modified by a titanate coupling agent. The specific method is as follows:

[0268] (1) Cathode material pretreatment: 100 g of lithium nickel cobalt manganese oxide (LiNi0.8Co0.1Mn0.1O2, hereinafter referred to as NCM811) was weighed and dispersed in 500 ml of ethanol solvent by ball milling to obtain a uniform NCM811 cathode material dispersion. The concentration of NCM811 was 0.2 g / ml; the ball milling speed was 300 rpm and the time was 15 min.

[0269] (2) Preparation of pH adjusting solution: Weigh 120 g of glacial acetic acid pH adjusting agent into an alcohol-water solution and disperse it thoroughly by ultrasonication to obtain an acetic acid-alcohol-water solution. The mass ratio of the alcohol solvent to deionized water in the alcohol-water solution is 90:10, and the concentration of glacial acetic acid is 2 mol / L. The ultrasonication conditions include a frequency of 30 kHz and a duration of 10 min.

[0270] (3) Mixing the positive electrode material and the modifier: 4.16 g of tetrabutyl titanate coupling agent was added to the NCM811 positive electrode material dispersion obtained in (1) so that the mass ratio of the NCM811 positive electrode material to the tetrabutyl titanate coupling agent was approximately 96:4. Then, a magnetic stirring method was used to form a uniform mixed solution at a stirring speed of 1000 r / min for 30 min.

[0271] (4) Adjusting the pH value and drying: Use the glacial acetic acid alcohol aqueous solution in (2) to adjust the pH of the mixed solution in (3) to 4.5, stir continuously during the adjustment process, and then continue stirring for 1 hour and repeat the pH test to ensure that the pH of the mixed solution is 4.5, wherein the stirring speed is 1000r / min; after the pH of the mixed solution stabilizes, place it in an oven and dry it until the solvent is completely removed, the drying temperature is 60℃, and the drying time is 24h, and finally the NCM811 positive electrode material modified with tetrabutyl titanate is obtained.

[0272] (5) Preparation of premixed modified cathode mixture: 94 g of tetrabutyl titanate-modified NCM811 cathode material, 3 g of acetylene black, and 3 g of polytetrafluoroethylene were weighed and mixed by stirring to obtain a premixed modified cathode mixture. The mass ratio of tetrabutyl titanate-modified NCM811 cathode material, conductive agent acetylene black, and binder polytetrafluoroethylene was 94:3:3; the stirring mixing rate was 1500 rpm, and the mixing time was 2 h.

[0273] (6) Preparation of a fiberized modified cathode mixture: The premixed modified cathode mixture obtained in step (5) was crushed, dispersed, and fiberized using a jet milling process to obtain a fiberized modified NCM811 cathode mixture. The jet milling speed was 50 m / s, the air flow pressure was 0.5 MPa, the feed pressure was 0.5 MPa, and the temperature was 30°C.

[0274] (7) Preparation of dry-process modified cathode membrane: The fiberized modified NCM811 cathode mixture was heated and rolled at a pressure of 500 kPa and a temperature of 250 °C to obtain a dry-process modified NCM811 cathode membrane with a thickness of 300 μm.

[0275] (8) Preparation of positive electrode film: The dry-process modified NCM811 positive electrode film obtained in S2.3 was rolled with the aluminum foil current collector at a temperature of 300°C to composite the dry-process modified NCM811 positive electrode film with the aluminum foil current collector to obtain a dry-process modified NCM811 positive electrode film with a thickness of 50 μm.

[0276] (9) Select the negative electrode material (silicon-graphite composite material) and cut the negative electrode material into discs with a diameter of 16 mm to serve as the negative electrode sheet;

[0277] (10) Cut the positive electrode film obtained in S2.4 into discs with a diameter of 14 mm to serve as positive electrode sheets;

[0278] (11) Cut the polyethylene homopolymer film into discs with a diameter of 19 mm to serve as a separator;

[0279] (12) In an argon-filled glove box, the positive electrode sheet, negative electrode sheet, and separator are stacked, electrolyte is added, and the battery is sealed to form a button-type lithium-ion battery. The electrolyte is 1M LiPF6 in FEC-DMC (volume ratio 1:4).

[0280] Comparative Example 3

[0281] Comparative Example 3 is basically the same as Example 1, except that the positive electrode material is modified only with orthosilicate, and the specific method is as follows:

[0282] (1) Cathode material pretreatment: 100 g of lithium nickel cobalt manganese oxide (LiNi0.8Co0.1Mn0.1O2, hereinafter referred to as NCM811) was weighed and dispersed in 500 ml of ethanol solvent by ball milling to obtain a uniform NCM811 cathode material dispersion. The concentration of NCM811 was 0.2 g / ml; the ball milling speed was 300 rpm and the time was 15 min.

[0283] (2) Preparation of pH adjusting solution: Weigh 120 g of glacial acetic acid pH adjusting agent into an alcohol-water solution and disperse it thoroughly by ultrasonication to obtain an acetic acid-alcohol-water solution. The mass ratio of the alcohol solvent to deionized water in the alcohol-water solution is 90:10, and the concentration of glacial acetic acid is 2 mol / L. The ultrasonication conditions include a frequency of 30 kHz and a duration of 10 min.

[0284] (3) Mixing the positive electrode material and the modifier: Add 4.16 g of ethyl orthosilicate to the NCM811 positive electrode material dispersion obtained in S1.1, so that the mass ratio of NCM811 positive electrode material to ethyl orthosilicate is about 96:4, and then use magnetic stirring to form a uniform mixed solution at a stirring speed of 1000 r / min for 30 min.

[0285] (4) Adjusting the pH value and drying: Use the glacial acetic acid alcohol aqueous solution in (2) to adjust the pH of the mixed solution in (3) to 4.5, stir continuously during the adjustment process, and then continue stirring for 1 hour and repeat the pH test to ensure that the pH of the mixed solution is 4.5, wherein the stirring speed is 1000r / min; after the pH of the mixed solution is stable, put it into an oven and dry it until the solvent is completely removed, the drying temperature is 60℃, and the drying time is 24h, and finally the NCM811 positive electrode material modified with ethyl orthosilicate modifier is obtained.

[0286] (5) Preparation of premixed modified cathode mixture: 94 g of NCM811 cathode material modified with ethyl orthosilicate, 3 g of acetylene black, and 3 g of polytetrafluoroethylene were weighed and mixed by stirring to obtain a premixed modified cathode mixture. The mass ratio of the NCM811 cathode material modified with ethyl orthosilicate modifier, the conductive agent acetylene black, and the binder polytetrafluoroethylene was 94:3:3. The stirring mixing rate was 1500 rpm and the mixing time was 2 h.

[0287] (6) Preparation of a fiberized modified cathode mixture: The premixed modified cathode mixture obtained in step (5) was crushed, dispersed, and fiberized using a jet milling process to obtain a fiberized modified NCM811 cathode mixture. The jet milling speed was 50 m / s, the air flow pressure was 0.5 MPa, the feed pressure was 0.5 MPa, and the temperature was 30°C.

[0288] (7) Preparation of dry-process modified cathode membrane: The fiberized modified NCM811 cathode mixture was heated and rolled at a pressure of 500 kPa and a temperature of 250 °C to obtain a dry-process modified NCM811 cathode membrane with a thickness of 300 μm.

[0289] (8) Preparation of positive electrode film: The dry-process modified NCM811 positive electrode film obtained in S2.3 was rolled with the aluminum foil current collector at a temperature of 300°C to composite the dry-process modified NCM811 positive electrode film with the aluminum foil current collector to obtain a dry-process modified NCM811 positive electrode film with a thickness of 50 μm.

[0290] (9) Select the negative electrode material (silicon-graphite composite material) and cut the negative electrode material into discs with a diameter of 16 mm to serve as the negative electrode sheet;

[0291] (10) Cut the positive electrode film obtained in S2.4 into discs with a diameter of 14 mm to serve as positive electrode sheets;

[0292] (11) Cut the polyethylene homopolymer film into discs with a diameter of 19 mm to serve as a separator;

[0293] (12) In an argon-filled glove box, the positive electrode sheet, negative electrode sheet, and separator are stacked, electrolyte is added, and the battery is sealed to form a button-type lithium-ion battery. The electrolyte is 1M LiPF6 in FEC-DMC (volume ratio 1:4).

[0294] The cycle performance and discharge capacity retention rate of the batteries of Examples 1 to 9 and Comparative Examples 1 to 3 were tested using the Xinwei charge and discharge test system. The first efficiency and discharge capacity retention rate of the batteries of Examples 1 to 9 and Comparative Examples 1 to 3 were shown in Table 1. At the same time, the test curves of Example 1 and Comparative Example 1 were exemplarily shown: the first cycle charge and discharge curves of the batteries of Example 1 and Comparative Example 1 (as shown in Figure 1), and the cycle curves of the discharge capacity retention rate of the batteries of Example 1 and Comparative Example 1 (as shown in Figure 2) were obtained.

[0295] Table 1

[0296] First effect (%) Discharge capacity retention rate after 100 cycles (%) Example 1 85.82 83.36 Example 2 83.39 82.43 Example 3 83.47 82.21 Example 4 82.15 80.03 Example 5 78.33 69.51 Example 6 85.14 82.12 Example 7 85.53 82.75 Example 8 84.52 80.36 Example 9 84.98 81.55 Comparative Example 1 77.85 67.77 Comparative Example 2 83.12 78.35 Comparative Example 3 83.55 79.12

[0297] As can be seen from Table 1, the first efficiency and capacity retention rate of the batteries of different embodiments and comparative examples after 100 cycles were tested and the results were summarized. Compared with the results of comparative example 1, Example 1, Example 2 and Example 3 showed higher first efficiency and capacity retention rate, indicating that the composite modifier makes the contact between the materials inside the dry-process positive electrode membrane closer, the positive electrode layer structure more stable, and can adapt to the volume expansion of the positive electrode material caused by the cycle, thus showing better performance; at the same time, the composite modifier is also applicable to other positive electrode materials, and the amount of the composite modifier can be flexibly adjusted within a certain range. The comparison of the results of Example 1 and Comparative Examples 1-3 shows that the additive can significantly improve the battery performance, and the comprehensive performance of the composite modifier is better than that of a single additive. The amount of binder is reduced in the positive electrode formula in Examples 4 and 5. Compared with Comparative Example 1, the results of Example 4 show that the battery system with an appropriate amount of composite modifier added can still maintain a high first efficiency and capacity retention rate when the amount of binder in the positive electrode formula is reduced, and the composite modifier added in Example 5 is only 0.5% and can still play its role. Comparison of the results of Examples 6-9 shows that the addition ratio of the two types of modifiers in the composite modifier can be flexibly adjusted within a certain range, and better improvement effects are exhibited when the proportion of orthosilicate is higher.

[0298] The accompanying drawings of the present application specification exemplarily show the test curves of Example 1 and Comparative Example 1. Figure 1 is a first-cycle charge and discharge curve of the battery of Example 1 and the battery of Comparative Example 1, wherein the test voltage range is 2.7V to 4.2V, and the charge and discharge current is 0.1C. As can be seen from Figure 1, compared with the battery of Comparative Example 1, the battery of Example 1 has smaller charge and discharge polarization and higher first charge and discharge efficiency. The first efficiency of the battery of Example 1 is 85.82%, while the first efficiency of the battery of the comparative example is 77.85%. This result shows that the internal material contact of the dry-modified NCM811 positive electrode membrane prepared in Example 1 of the present application is good, and the battery prepared in Example 1 of the present application exhibits higher charge and discharge efficiency and lower polarization.

[0299] Figure 2 shows the capacity retention of the battery of Example 1 and the battery of Comparative Example 1 after 100 charge and discharge cycles. The test voltage range is 2.7V to 4.2V, the activation current for the first three charge and discharge cycles is 0.1C, and then the battery is cycled at 0.2C charge / 0.5C discharge for 100 cycles. Example 1 exhibits higher capacity retention than Comparative Example 1, indicating that the dry electrode preparation strategy of pre-surface modification of the positive electrode material can significantly improve the battery's cycling stability.

[0300] At the same time, a scanning electron microscope test was performed on the cross section of the dry-process modified NCM811 positive electrode membrane in Example 1, and the distribution and morphology of the various materials inside the electrode are shown in Figures 3 and 4. As shown in Figure 3, the fibrous binder is evenly distributed inside the electrode in a spider web-like state. Although the binder fibers are not densely distributed, Figure 4 shows that the various materials inside the positive electrode are evenly distributed and have good contact. Therefore, after the surface treatment of the positive electrode material in advance, even if less binder is used, uniform mixing and close contact between the materials can be achieved.

Claims

1. A method for modifying a positive electrode material, comprising: S1.1: preparing positive electrode material dispersion; S1.2: adding a composite modifier to the positive electrode material dispersion to form a mixed solution to modify the positive electrode material, wherein the composite modifier includes a titanate coupling agent and an orthosilicate.

2. The cathode material modification method according to claim 1, wherein: The mass ratio of the positive electrode material to the composite modifier is (99.5:0.5)-(90:10); and / or the mass ratio of the titanate coupling agent to the orthosilicate is (1:9)-(9:1).

3. The cathode material modification method according to claim 1, wherein: The titanate coupling agent includes one or more of tetrabutyl titanate, diisostearyl ethyl titanate, triisostearyl isopropyl titanate, tetraisopropyl di(dioctyl phosphite) titanate, isopropoxy tri(dodecylbenzenesulfonyloxy) titanate, isopropyl trioleyl titanate, isopropyl dioleyl (dioctyl phosphate) titanate; and / or the orthosilicate includes one or more of methyl orthosilicate, ethyl orthosilicate, butyl orthosilicate, and isopropyl orthosilicate.

4. The method for modifying the positive electrode material according to claim 1, wherein: In S1.2, after adding the composite modifier to the positive electrode material dispersion, an ultrasonic frequency of 30-50 kHz is applied for 5-20 min, or magnetic stirring is performed at a speed of 300-1000 r / min for 10-30 min to fully mix the positive electrode material and the composite modifier.

5. The cathode material modification method according to claim 1, further comprising: S1.3: adding a pH regulating solution to adjust the pH value of the mixed solution to 4-5, and drying the mixed solution with a pH value of 4-5 to obtain a positive electrode material modified by a composite modifier.

6. The method for modifying the positive electrode material according to claim 5, wherein: Before S1.3, a pH adjusting agent is added to the alcohol aqueous solution and fully dispersed to prepare the pH adjusting solution with a concentration of 1-3 mol / L.

7. The method for modifying the positive electrode material according to claim 6, wherein: The pH regulator includes at least one of formic acid, glacial acetic acid and oxalic acid; and / or the alcohol aqueous solution includes an alcohol solvent and deionized water in a mass ratio of (90:10)-(70:30); and / or the alcohol solvent includes at least one of methanol, ethanol, ethylene glycol and isopropanol.

8. The method for modifying the positive electrode material according to claim 5, wherein: In S1.3, the pH regulating liquid is added to the mixed liquid while stirring, and stirring is continued after the pH regulating liquid is completely added. The pH value is measured once at a set interval, and after the pH value stabilizes between 4 and 5, the mixed liquid is dried to obtain a positive electrode material modified with a composite modifier.

9. The method for modifying the positive electrode material according to claim 8, wherein: In S1.3, stirring is performed at a rotation speed of 200-1200 r / min, and the set time is 0.5-1 h.

10. A method for preparing a positive electrode film of a lithium battery by a dry process, comprising: S2.1, mixing a positive electrode material modified by a composite modifier with a conductive agent and a binder to prepare a premixed modified positive electrode mixture, wherein the positive electrode material modified by the composite modifier is prepared by the positive electrode material modification method according to any one of claims 1 to 9; S2.2, crushing, dispersing and fiberizing the premixed modified positive electrode mixture to obtain a fiberized modified positive electrode mixture; S2.3, heating and calendering the fiberized modified cathode mixture to obtain a dry modified cathode film; S2.4, compounding the dry modified positive electrode film with a current collector to obtain a positive electrode film.

11. The method for preparing a positive electrode film for a lithium battery by a dry process according to claim 10, wherein: In S2.1, the conductive agent includes at least one of conductive carbon black, Ketjen black, acetylene black, carbon fiber and carbon nanotubes; and / or the binder includes at least one of ethylene-tetrafluoroethylene copolymer, polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymer; and / or the mass ratio of the positive electrode material modified by the composite modifier, the conductive agent and the binder is (90-96): (2-5): (2-5).

12. The method for preparing a positive electrode film for a lithium battery by a dry process according to claim 10, wherein: In S2.1, the positive electrode material modified by the composite modifier, the conductive agent and the binder are ball-milled and mixed at a rate of 100-350rpm for 0.5-3h, or stirred and mixed at a rate of 500-2500rpm for 0.5-3h to prepare a premixed modified positive electrode mixture; and / or the high-speed dispersion rate is 10000-20000rpm, the dispersion time is 5-120min, the air flow crushing speed is 20-100m / s, the air flow pressure is 0.3-1.2MPa, the feeding pressure is 0.3-1.0MPa, and the temperature is 20-60°C; and / or the fibrous modified positive electrode mixture is heated and calendered at a pressure of 80-800kPa and a temperature of 40-300°C to prepare the dry-modified positive electrode film with a thickness of 100-500μm.

13. The method for preparing a positive electrode film for a lithium battery by a dry process according to claim 10, wherein: In S2.4, the dry modified positive electrode film is composited with the current collector to form a positive electrode film with a thickness of 50-100 μm, and the composite method includes heating calendering or high-temperature rolling. The pressure of heating calendering is 200-600 kPa and the temperature is 40-300°C. The temperature of high-temperature rolling is 200-300°C.

14. A positive electrode material, the surface of which is coated with a titanate coupling agent and an orthosilicate; or the positive electrode material is formed by the positive electrode material modification method according to any one of claims 1 to 9.

15. A positive electrode film: It comprises a positive electrode film and a current collector, wherein the positive electrode film is made of the positive electrode material according to claim 14; Alternatively, the positive electrode film is formed by the dry method for preparing a positive electrode film for a lithium battery as described in any one of claims 10 to 13.

16. A lithium ion battery comprising: The positive electrode material according to claim 14; Or, the positive electrode film according to claim 15.

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