Negative electrode mixture, dry negative electrode sheet, and preparation method therefor and use thereof

Abstract

Disclosed in the present invention are a negative electrode mixture, a dry negative electrode sheet, and a preparation method therefor and a use thereof. The negative electrode mixture comprises a coated negative electrode material, a conductive agent and polytetrafluoroethylene. The coated negative electrode material comprises a negative electrode main material and a polymer coated on the surface of the negative electrode main material, the mass ratio of the negative electrode main material to the polymer being 90:10-99:1. The polymer is one or more of polyacrylic acid, polyvinylidene fluoride, polymethyl methacrylate, polyethylene, polypropylene or polybutylene succinate. In the present invention, by coating a negative electrode main material with a polymer, the contact between the negative electrode main material and a binder can be effectively avoided, so that the irreversible capacity loss caused by the decomposition of the binder is improved, thereby effectively improving the charging and discharging efficiency of a sodium-ion battery.

Description

A negative electrode mixture, dry negative electrode sheet and preparation method and application thereof TECHNICAL FIELD

[0001] The present application belongs to the technical field of sodium ion batteries, and particularly relates to a negative electrode mixture, a dry negative electrode sheet and a preparation method and application thereof. BACKGROUND

[0002] Sodium ion batteries have a wide application prospect in the energy storage field due to the advantages of abundant sodium resources, low cost and good safety performance. The working principle of sodium ion batteries is similar to that of lithium ion batteries, and the reversible embedding and extraction of sodium ions between the positive and negative electrodes is used to realize energy storage and release.

[0003] Traditional lithium / sodium ion batteries use a wet electrode process. A slurry is prepared by mixing powder materials and solvents, and an electrode is prepared through multiple processes such as coating, drying, solvent recovery and rolling. This method needs to handle harmful substances such as waste gas, and has problems such as glue floating, electrode cracking and solvent residue. In addition, there is a theoretical upper limit for the electrode compaction density and the coating surface density, which limits the improvement of energy density.

[0004] The dry electrode process eliminates the slurry preparation, drying and solvent recovery manufacturing links. At present, the fibrillation method of the binder is the mainstream dry electrode manufacturing process in the industry. The commonly used binder is polytetrafluoroethylene. However, polytetrafluoroethylene is prone to decomposition reaction when it comes into contact with the negative electrode. During the charging process of the battery, the potential of polytetrafluoroethylene decreases due to the embedding of sodium in the negative electrode, which causes decomposition and irreversible capacity loss, thereby limiting its application. SUMMARY

[0005] The purpose of the present application is to overcome the defects or deficiencies of the above-mentioned fibrillation method for preparing sodium ion battery negative electrode sheets, and to provide a negative electrode mixture. The application of the negative electrode mixture to the dry sodium ion battery negative electrode sheet can effectively improve the charge and discharge efficiency.

[0006] Another purpose of the present application is to provide a sodium ion battery negative electrode sheet.

[0007] Another purpose of the present application is to provide a sodium ion battery.

[0008] In order to achieve the above-mentioned purposes, the present application adopts the following technical solutions:

[0009] A negative electrode mixture comprises a coated negative electrode material, a conductive agent and polytetrafluoroethylene. The coated negative electrode material comprises a negative electrode main material and a polymer coated on the surface of the negative electrode main material. The mass ratio of the negative electrode main material to the polymer is 90:10 to 99:1. The polymer is one or more of polyacrylic acid, polyvinylidene fluoride, polymethyl methacrylate, polyethylene, polypropylene or polybutylene succinate.

[0010] In the present application, by adopting the polymer to coat the negative main material, the surface of the negative main material is coated with a passivation layer, which can effectively prevent the negative main material from contacting with polytetrafluoroethylene, avoid the decomposition of polytetrafluoroethylene due to too low potential in the negative electrode, and effectively improve the irreversible capacity loss caused by the decomposition of polytetrafluoroethylene when the coated negative material is applied to a sodium ion battery.

[0011] It should be noted that the mass ratio of the negative main material and the polymer in the present application is 90:10 to 99:1, for example, but not limited to 90:10, 91:9, 92:8, 93:7, 94:6, 95:5, 96:4, 97:3, 98:2 or 99:1, etc. can achieve the present application.

[0012] Further, the mass ratio of the negative main material and the polymer is 91:9 to 98:2.

[0013] Further, the mass ratio of the negative main material and the polymer is 91:9 to 95:5.

[0014] In the present application, the commonly used negative main material can be selected according to the prior art, for example, but not limited to, the negative main material includes one or more of hard carbon, soft carbon, graphite, tin, bismuth, and phosphorus.

[0015] Further, the coated negative material is obtained by uniformly mixing the negative main material and the polymer at 95-200°C.

[0016] Specifically, the negative mixture includes 80-96 parts by weight of the coated negative material, 2-10 parts by weight of the conductive agent, and 2-10 parts by weight of polytetrafluoroethylene.

[0017] Specifically, the 80-96 parts by weight of the above coated negative material, for example, but not limited to 80 parts by weight, 82 parts by weight, 84 parts by weight, 86 parts by weight, 88 parts by weight, 90 parts by weight, 92 parts by weight, 94 parts by weight or 96 parts by weight, etc. can achieve the present application.

[0018] Specifically, the 2-10 parts by weight of the conductive agent, for example, but not limited to 2 parts by weight, 3 parts by weight, 4 parts by weight, 5 parts by weight, 6 parts by weight, 7 parts by weight, 8 parts by weight, 9 parts by weight or 10 parts by weight, etc. can achieve the present application.

[0019] Specifically, the 2-10 parts by weight of the binder, for example, but not limited to 2 parts by weight, 3 parts by weight, 4 parts by weight, 5 parts by weight, 6 parts by weight, 7 parts by weight, 8 parts by weight, 9 parts by weight or 10 parts by weight, etc. can achieve the present application.

[0020] In the present application, a common conductive agent can be selected by referring to the prior art, for example, the conductive agent includes but is not limited to one or more of carbon nanotubes, graphite, conductive carbon black, ketjen black, acetylene black, graphene or carbon fiber.

[0021] The present application also provides a preparation method of the negative electrode mixture, comprising the following steps:

[0022] The coated negative electrode material, the conductive agent and the polytetrafluoroethylene are mixed at room temperature, and a sodium ion battery negative electrode mixture is obtained by high-speed shearing.

[0023] Specifically, the rotating speed of the high-speed shearing is 1500-2000 revolutions per minute.

[0024] The present application also provides a sodium ion battery negative electrode sheet comprising the negative electrode mixture.

[0025] The present application also provides a preparation method of the sodium ion battery negative electrode sheet, comprising the following steps:

[0026] The negative electrode mixture is hot-pressed into a film and is compounded on a current collector to obtain a sodium ion battery negative electrode sheet.

[0027] Specifically, the temperature of the hot-pressing is 70-90 DEG C.

[0028] Specifically, the current collector comprises an aluminum foil and / or a copper foil.

[0029] The present application also provides a sodium ion battery comprising the sodium ion battery negative electrode sheet.

[0030] Compared with the prior art, the present application has the following beneficial effects:

[0031] The present application provides a negative electrode mixture comprising a coated negative electrode material, a conductive agent and polytetrafluoroethylene, wherein the coated negative electrode material is obtained by coating a negative electrode main material with a polymer, which effectively prevents the negative electrode main material from being in electrical contact with the polytetrafluoroethylene, avoids the problem that the polytetrafluoroethylene is decomposed due to too low potential in the negative electrode, effectively improves the irreversible capacity loss and the cell gas generation behavior caused by the decomposition of the polytetrafluoroethylene, and prevents the peeling of the negative electrode active material caused by the decrease in adhesion due to the decomposition of the polytetrafluoroethylene. BRIEF DESCRIPTION OF DRAWINGS

[0032] Fig. 1 is a first cycle charge-discharge curve of the sodium ion battery prepared in Example 1 and Comparative Example 1;

[0033] Fig. 2 is a 45 DEG C cycle performance effect diagram of Example 1, Comparative Examples 1, 3 and 5. DETAILED DESCRIPTION

[0034] The application will be further described in conjunction with specific examples, which are used to explain the application and are not intended to limit the scope of the application. The test methods used in the following examples are conventional methods unless otherwise specified. The materials, reagents, etc. used are commercially available unless otherwise specified.

[0035] Example 1

[0036] A sodium-ion battery negative electrode sheet is prepared by the following method:

[0037] S1. Hard carbon and polyacrylic acid are mixed uniformly at a mass ratio of 98:2 at 150°C to obtain a coated negative electrode material;

[0038] S2. The coated negative electrode material of S1, conductive carbon black, and polytetrafluoroethylene are mixed at room temperature at a mass ratio of 94:3:3, and a sodium-ion battery negative electrode mixture is obtained by shearing at a rotation speed of 2000 rpm to form a filament;

[0039] S3. The sodium-ion battery negative electrode mixture in S2 is hot-pressed into a film at 80°C, and the sodium-ion battery negative electrode sheet is obtained by compounding the film on an aluminum foil through conductive glue.

[0040] Example 2

[0041] A sodium-ion battery negative electrode sheet is prepared by the following method:

[0042] S1. Hard carbon and polyacrylic acid are mixed uniformly at a mass ratio of 91:9 at 150°C to obtain a coated negative electrode material;

[0043] S2. The coated negative electrode material of S1, conductive carbon black, and polytetrafluoroethylene are mixed at room temperature at a mass ratio of 94:3:3, and a sodium-ion battery negative electrode mixture is obtained by shearing at a rotation speed of 2000 rpm to form a filament;

[0044] S3. The sodium-ion battery negative electrode mixture in S2 is hot-pressed into a film at 80°C, and the sodium-ion battery negative electrode sheet is obtained by compounding the film on an aluminum foil through conductive glue.

[0045] Example 3

[0046] A sodium-ion battery negative electrode sheet is prepared by the following method:

[0047] S1. Hard carbon and polyacrylic acid are mixed uniformly at a mass ratio of 95:5 at 150°C to obtain a coated negative electrode material;

[0048] S2. The coated anode material, conductive carbon black and polytetrafluoroethylene of S1 are mixed at room temperature in a mass ratio of 94:3:3, and a sodium ion battery anode mixture is obtained by shearing at a speed of 2000 revolutions per minute;

[0049] S3. The sodium ion battery anode mixture in S2 is hot-pressed into a film at 80°C, and a sodium ion battery anode sheet is obtained by being compounded on an aluminum foil through conductive glue.

[0050] Example 4

[0051] A sodium ion battery anode sheet is prepared by the following method:

[0052] S1. Hard carbon and polyvinylidene fluoride are mixed uniformly at a mass ratio of 98:2 at 200°C to obtain a coated anode material;

[0053] S2. The coated anode material, conductive carbon black and polytetrafluoroethylene of S1 are mixed at room temperature in a mass ratio of 94:3:3, and a sodium ion battery anode mixture is obtained by shearing at a speed of 2000 revolutions per minute;

[0054] S3. The sodium ion battery anode mixture in S2 is hot-pressed into a film at 80°C, and a sodium ion battery anode sheet is obtained by being compounded on an aluminum foil through conductive glue.

[0055] Example 5

[0056] A sodium ion battery anode sheet is prepared by the following method:

[0057] S1. Hard carbon and polymethyl methacrylate are mixed uniformly at a mass ratio of 98:2 at 180°C to obtain a coated anode material;

[0058] S2. The coated anode material, conductive carbon black and polytetrafluoroethylene of S1 are mixed at room temperature in a mass ratio of 94:3:3, and a sodium ion battery anode mixture is obtained by shearing at a speed of 2000 revolutions per minute;

[0059] S3. The sodium ion battery anode mixture in S2 is hot-pressed into a film at 80°C, and a sodium ion battery anode sheet is obtained by being compounded on an aluminum foil through conductive glue.

[0060] Example 6

[0061] A sodium ion battery anode sheet is prepared by the following method:

[0062] S1. Tin powder and polyacrylic acid are mixed uniformly at a mass ratio of 98:2 at 150°C to obtain a coated anode material;

[0063] S2. The coated negative material of S1, acetylene black and polytetrafluoroethylene were mixed at room temperature in a ratio of 94:3:3 by mass, and a sodium ion battery negative mixture was obtained by shearing spinning at a speed of 2000 revolutions per minute;

[0064] S3. The sodium ion battery negative mixture in S2 was hot-pressed into a film at 80°C, and a sodium ion battery negative sheet was obtained by compounding on an aluminum foil through conductive glue.

[0065] Comparative Example 1

[0066] A sodium ion battery negative sheet was prepared by the following method:

[0067] Hard carbon, conductive carbon black and polytetrafluoroethylene were mixed at room temperature in a ratio of 94:3:3 by mass, and a sodium ion battery negative mixture was obtained by shearing spinning at a speed of 2000 revolutions per minute;

[0068] The sodium ion battery negative mixture was hot-pressed into a film at 80°C, and a sodium ion battery negative sheet was obtained by compounding on an aluminum foil through conductive glue.

[0069] Comparative Example 2

[0070] A sodium ion battery negative sheet was prepared by the following method:

[0071] Hard carbon, polyacrylic acid, conductive carbon black and polytetrafluoroethylene were mixed at room temperature in a ratio of 92.1:1.9:3:3 by mass, and a sodium ion battery negative mixture was obtained by shearing spinning at a speed of 2000 revolutions per minute;

[0072] The sodium ion battery negative mixture was hot-pressed into a film at 80°C, and a sodium ion battery negative sheet was obtained by compounding on an aluminum foil through conductive glue.

[0073] Comparative Example 3

[0074] A sodium ion battery negative sheet was prepared by the following method:

[0075] S1. Hard carbon and polyacrylic acid were mixed uniformly at 150°C in a ratio of 89:11 by mass to obtain a coated negative material;

[0076] S2. The coated negative material of S1, conductive carbon black and polytetrafluoroethylene were mixed at room temperature in a ratio of 94:3:3 by mass, and a sodium ion battery negative mixture was obtained by shearing spinning at a speed of 2000 revolutions per minute;

[0077] S3. The sodium ion battery negative mixture in S2 was hot-pressed into a film at 80°C, and a sodium ion battery negative sheet was obtained by compounding on an aluminum foil through conductive glue.

[0078] Comparative Example 4

[0079] A sodium ion battery negative electrode sheet is prepared by the following method:

[0080] S1. Hard carbon and polyacrylic acid are mixed uniformly at a mass ratio of 99.8:0.2 at 150°C to obtain a coated negative electrode material;

[0081] S2. The coated negative electrode material of S1, conductive carbon black, and polytetrafluoroethylene are mixed at a mass ratio of 94:3:3 at room temperature, and a sodium ion battery negative electrode mixture is obtained by shearing at a rotation speed of 2000 revolutions / minute;

[0082] S3. The sodium ion battery negative electrode mixture in S2 is hot-pressed into a film at 80°C, and a sodium ion battery negative electrode sheet is obtained by compounding the film on an aluminum foil through conductive glue.

[0083] Comparative Example 5

[0084] A sodium ion battery negative electrode sheet is prepared by the following method:

[0085] S1. Hard carbon and polyacrylic acid are mixed uniformly at a mass ratio of 99.2:0.8 at 150°C to obtain a coated negative electrode material;

[0086] S2. The coated negative electrode material of S1, conductive carbon black, and polytetrafluoroethylene are mixed at a mass ratio of 94:3:3 at room temperature, and a sodium ion battery negative electrode mixture is obtained by shearing at a rotation speed of 2000 revolutions / minute;

[0087] S3. The sodium ion battery negative electrode mixture in S2 is hot-pressed into a film at 80°C, and a sodium ion battery negative electrode sheet is obtained by compounding the film on an aluminum foil through conductive glue.

[0088] Comparative Example 6

[0089] A sodium ion battery negative electrode sheet is prepared by the following method:

[0090] S1. Hard carbon and polyacrylic acid are mixed uniformly at a mass ratio of 99.2:0.8 at 150°C to obtain a coated negative electrode material;

[0091] S2. The coated negative electrode material of S1, conductive carbon black, and polytetrafluoroethylene are mixed at a mass ratio of 94:3:3 at room temperature, and a sodium ion battery negative electrode mixture is obtained by shearing at a rotation speed of 2000 revolutions / minute;

[0092] Performance Test

[0093] 1. Test Method

[0094] The sodium-ion battery anode sheets prepared in the above embodiments and comparative examples were used as anodes, and Na4Fe3(PO4)2P2O7 was used as the main material for the cathode. The cathode material was mixed, coated, and baked according to a mass ratio of super-P:PVDF = 90:5:5 to obtain the cathode sheet. The bare cells were assembled in the order of cathode, separator, anode, and separator again, with the anode capacity:cathode capacity = 1.2. Then, electrolyte was injected, encapsulated, formed, and capacity tested to obtain the sodium-ion battery.

[0095] The formation process involves constant current charging at 0.1C to 3.0V at 55°C.

[0096] The capacity test is performed at room temperature (25℃) by charging at 0.2C to a full charge of 3.4V, and then discharging at 0.2C to 1.5V.

[0097] The initial charge capacity is the sum of the charging capacities during formation and capacity grading processes, the initial discharge capacity is the discharge capacity during capacity grading processes, and the initial efficiency = initial discharge capacity ÷ initial charge capacity.

[0098] Cyclic test: At an ambient temperature of 45℃, charge the battery cell at 0.5C to 3.4V according to its rated capacity, and then discharge it at 1C to 1.5V; repeat the above steps until the remaining capacity reaches 80% of the rated capacity.

[0099] 2. Test Results

[0100] The test results of each embodiment and comparative example are shown in Figures 1-2 and Table 1.

[0101] Table 1 Test results for each embodiment and comparative example

[0102] As can be seen from Table 1, the sodium-ion battery prepared by the negative electrode mixture described in this invention has significantly improved charge and discharge efficiency compared to sodium-ion batteries prepared with the same material system, and its cycle stability at 45°C is significantly higher than that of the comparative example.

[0103] Specifically, as can be seen from Examples 1 to 5, the present invention uses hard carbon as the main negative electrode material, and the resulting negative electrode material has a good coating effect, while ensuring sodium ion transport, with an initial coulombic efficiency of >80%, and can achieve 3500 cycles at 45°C.

[0104] Comparing Example 1 and Comparative Example 1, as well as Example 6 and Comparative Example 6, it can be seen that if sodium-ion batteries are prepared directly using uncoated negative electrode materials, the initial efficiency of the prepared sodium-ion batteries is significantly lower.

[0105] As can be seen from Comparative Example 2, directly mixing the polymer, the main anode material, polytetrafluoroethylene, and the conductive agent during the preparation of the sodium-ion battery anode sheet cannot significantly improve the charge and discharge efficiency.

[0106] As can be seen from the comparative example 3, if the polymer addition amount in the coated negative electrode material is too much, the negative electrode ion conductivity is insufficient, the negative electrode releases metal sodium, and the cycle attenuation is rapid.

[0107] As can be seen from the comparative examples 4 and 5, if the polymer addition amount in the coated negative electrode material is too little, the negative electrode main material is not completely coated, the first efficiency and cycle performance of the battery cell show gradient attenuation.

[0108] Obviously, the above embodiments of the present application are merely exemplary and are not intended to limit the embodiments of the present application. Based on the above description, other different forms of changes or variations can be made by those skilled in the art. Here, it is not necessary and impossible to exhaust all the embodiments. Any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the claims of the present application.

Claims

1. A negative electrode mixture comprising a coated negative electrode material, a conductive agent, and polytetrafluoroethylene, characterized in that, The coated negative electrode material comprises a negative electrode main material and a polymer coated on the surface of the negative electrode main material, the mass ratio of the negative electrode main material and the polymer is 90:10-99:1; the polymer is one or more of polyacrylic acid, polyvinylidene fluoride, polymethyl methacrylate, polyethylene, polypropylene or polybutylene succinate.

2. The negative mixture of claim 1, wherein, The negative electrode main material is one or more of hard carbon, soft carbon, graphite, tin, bismuth and phosphorus.

3. The negative mixture of claim 1, wherein, The coated negative electrode material is obtained by uniformly mixing the negative electrode main material and the polymer at 95-200℃.

4. The negative mixture of claim 1, wherein, The negative electrode mixture comprises 80-96 parts of the coated negative electrode material, 2-10 parts of a conductive agent and 2-10 parts of polytetrafluoroethylene.

5. The negative mixture of claim 1, wherein, The conductive agent comprises one or more of carbon nanotubes, graphite, conductive carbon black, ketjen black, acetylene black, graphene or carbon fiber.

6. A method for producing a negative electrode mixture, characterized by, The method comprises the following steps: The coated negative electrode material, the conductive agent and the polytetrafluoroethylene are mixed at room temperature, and a negative electrode mixture is obtained by high-speed shearing.

7. The method of claim 6, wherein the negative electrode mixture is prepared by mixing the lithium metal oxide, the carbon material, and the binder solution. The rotation speed of the high-speed shearing is 1500-2000 rpm.

8. A sodium-ion battery anode sheet, characterized by, The method comprises the negative electrode mixture of any one of claims 1-5.

9. A method for producing a sodium-ion battery negative electrode sheet, characterized by, The method comprises the following steps: The negative electrode mixture of any one of claims 1-5 is hot-pressed into a film, which is then compounded on a current collector to obtain a sodium ion battery negative electrode sheet.

10. A sodium-ion battery, characterized in that, The method comprises the sodium ion battery negative electrode sheet of claim 8.

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