Conductive material and preparation method thereof, battery pole piece and secondary battery

Abstract

The invention provides a conductive material and a preparation method thereof, a battery pole piece and a secondary battery. The conductive material comprises a one-dimensional carbon nanowire, nitrogen atoms are doped in the one-dimensional carbon nanowire, the one-dimensional carbon nanowire contains a nanopore structure, and the porosity of the one-dimensional carbon nanowire is that the length-diameter ratio of the one-dimensional carbon nanowire is 80-220. Compared with the prior art, the conductive material is doped with nitrogen atoms and has a porous structure, the conductivity of the carbon material can be improved, the energy efficiency and the rate capability can be effectively improved, and the rich gap structure can improve the liquid retention capability and improve the later cycle performance of a battery cell.

Description

Technical Field

[0001] The present invention relates to the field of secondary batteries, and particularly to a conductive material, a preparation method thereof, a battery electrode sheet, and a secondary battery. Background Art

[0002] As a new type of energy storage device, lithium-ion batteries are widely used in fields such as portable electronic devices, electric vehicles, and energy storage systems due to their high specific capacity, low self-discharge rate, and no memory effect. With the progress of technology and the continuous increase in market demand, the performance requirements for lithium-ion batteries are gradually increasing, especially the requirements for aspects such as the cycle life, energy efficiency, and charge-discharge rate performance of the batteries are becoming increasingly stringent.

[0003] In the design of lithium-ion batteries, the battery electrode sheet, as a key component, directly affects the comprehensive performance of the battery. The conductivity of the electrode is one of the important factors affecting the battery efficiency and cycle life. Insufficient conductivity of the electrode will lead to the occurrence of electrode polarization, which will in turn affect the charge-discharge efficiency of the battery, increase energy loss, and at the same time affect the later cycle stability of the battery. In addition, the liquid retention ability of the electrode sheet also has an important impact on the cycle performance and stability of the battery. How to improve the conductivity and liquid retention ability of the battery electrode sheet and reduce the polarization of the electrode sheet has become an important technical direction for improving the battery performance.

[0004] Currently, the common method to improve the conductivity of the electrode sheet is to add conductive materials such as carbon nanotubes. Due to their unique nanostructure and excellent conductivity, carbon nanotubes can effectively improve the conductivity of the battery electrode sheet, thereby reducing the polarization of the electrode sheet. However, the use of carbon nanotubes faces significant technical challenges, especially in terms of their dispersibility; uneven dispersion of carbon nanotubes in the electrode sheet material may lead to a decrease in conductivity, and their preparation process usually requires high temperatures and complex equipment, such as arc discharge method, chemical vapor deposition method, and laser ablation method, etc. These methods not only have high equipment costs but also have harsh operating conditions, which limit their large-scale application.

[0005] In view of this, it is indeed necessary to provide a technical solution to solve the above problems. Summary of the Invention

[0006] One of the purposes of the present invention is to: in view of the deficiencies of the prior art, provide a conductive material to solve the problems of poor conductivity and dispersibility of existing conductive materials.

[0007] To achieve the above purpose, the present invention adopts the following technical solutions:

[0008] A conductive material, the conductive material comprising one-dimensional carbon nanotubes, nitrogen atoms are doped in the one-dimensional carbon nanotubes, the one-dimensional carbon nanotubes contain a nano-porous structure, the porosity of the one-dimensional carbon nanotubes is 30%-80%, and the aspect ratio of the one-dimensional carbon nanotubes is 80 to 220.

[0009] Preferably, the synthesis raw materials of the one-dimensional nanowires include metal salts, metal ligands and nitrogen-containing organic ligands; wherein, the mass ratio of the metal salts, metal ligands and nitrogen-containing organic ligands is 0.7 to 1:2 to 3:4 to 5.

[0010] Preferably, the metal salts include one or more of iron acetate, ferrous acetate, iron oxalate, iron nitrate, iron sulfate, cobalt acetate, cobalt sulfate, cobalt nitrate, nickel acetate, nickel nitrate, nickel sulfate, zinc acetate, zinc sulfate, zinc nitrate.

[0011] Preferably, the metal ligands include one or more of potassium ferrocyanide, potassium ferrous cyanide, potassium cobalticyanide, potassium nickel cyanide, sodium ferrocyanide, sodium cobalticyanide.

[0012] Preferably, the nitrogen-containing organic ligands include one or more of imidazole, 2-methylimidazole, 2,4-dimethylimidazole, 2-ethyl-4-methylimidazole, ethylimidazole, 2-isopropylimidazole, 2-phenylimidazole.

[0013] The second object of the present invention is to provide a preparation method of a conductive material, comprising the following steps:

[0014] S1. Dissolve the metal salt and the metal ligand in an organic solution, stir ultrasonically until the solid is completely dissolved to obtain a mixed solution, add the nitrogen-containing organic ligand to the mixed solution, stir evenly, let the solution stand for aging, then filter the aged solution by suction, wash it repeatedly with an organic solvent, and place the obtained product in vacuum drying to obtain a dry powder.

[0015] S2. Take the above powder and calcine it in an inert atmosphere. After the calcination is completed, pickling the calcined product, then washing it with an organic solvent until it is neutral, and drying it to obtain the conductive material.

[0016] Preferably, in step S1, the aging time is 4 to 48 h.

[0017] Preferably, in step S2, the calcination temperature is 500 to 1000 °C, and the calcination time is 2 to 10 h.

[0018] The third object of the present invention is to provide a battery electrode plate, comprising the above conductive material, and the battery electrode plate comprises a positive electrode plate and a negative electrode plate.

[0019] A fourth object of the present invention is to provide a secondary battery, including the above battery electrode sheet, and the secondary battery further includes a separator and an electrolyte.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0021] 1) The one-dimensional carbon nanowires of the present invention are doped with nitrogen atoms and have a nano-porous structure, significantly improving the electrical conductivity of the carbon material; the doping of nitrogen atoms can optimize the electronic structure of the carbon nanowires, enhance their electrical conductivity, thereby improving the energy efficiency and rate performance of the battery;

[0022] 2) The rich porous structure of the one-dimensional carbon nanowires of the present invention provides more void space, effectively improving the liquid retention capacity of the material; this structure helps to improve the electrolyte permeability and ionic conduction performance of the battery cell, further enhancing the cycle stability of the battery during later charge and discharge processes and extending the service life of the battery;

[0023] 3) The one-dimensional carbon nanowires of the present invention have a high aspect ratio, resulting in better dispersion in the battery electrode sheet; good dispersion helps the one-dimensional carbon nanowires to be evenly distributed in the battery, enhancing the overall electrical conductivity of the electrode material and improving the electrochemical performance of the battery. Description of the Drawings

[0024] Figure 1 It is a SEM diagram of the conductive material of Example 1 of the present invention. Detailed Embodiments

[0025] To make the technical solutions and advantages of the present invention clearer, the present invention and its beneficial effects will be further described in detail below in conjunction with the specific embodiments and the drawings of the specification, but the embodiments of the present invention are not limited thereto.

[0026] The terms "first" and "second" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the present invention, "a plurality" means two or more, unless otherwise specifically defined.

[0027] A first aspect of the present invention aims to provide a conductive material, the conductive material includes one-dimensional carbon nanowires, the one-dimensional carbon nanowires are doped with nitrogen atoms, the one-dimensional carbon nanowires contain a nano-porous structure, the porosity of the one-dimensional carbon nanowires is 30%-80%, and the aspect ratio of the one-dimensional carbon nanowires is 80-220.

[0028] There is nitrogen element in the one-dimensional carbon nanotubes of the present invention, and the doping of heteroatoms has a beneficial effect on carbon conductivity. The typical characteristics of the carbon nanotubes of the present invention are very high aspect ratio, and have high strength, high chemical stability and low resistivity.

[0029] The one-dimensional carbon nanotubes have a high aspect ratio and can form a good conductive network with the cathode material, prevent the material from cracking and falling off, and improve the cycle life; and the addition amount of carbon nanotubes in the battery is 1 / 6 to 1 / 2 of the addition amount of traditional carbon black compared with traditional carbon black, which is equivalent to reducing the overall mass of the electrode, increasing the mass ratio of the active material, and thus improving the energy density.

[0030] In some embodiments of the present invention, the synthesis raw materials of the one-dimensional nanowires include metal salts, metal ligands and nitrogen-containing organic ligands; wherein, the mass ratio of the metal salt, the metal ligand and the nitrogen-containing organic ligand is 0.7-1:2-3:4-5.

[0031] In some embodiments of the present invention, the metal salt includes one or more of iron acetate, ferrous acetate, iron oxalate, iron nitrate, iron sulfate, cobalt acetate, cobalt sulfate, cobalt nitrate, nickel acetate, nickel nitrate, nickel sulfate, zinc acetate, zinc sulfate, zinc nitrate.

[0032] In some embodiments of the present invention, the metal ligand includes one or more of potassium ferrocyanide, potassium ferrous cyanide, potassium cobalticyanide, potassium nickel cyanide, sodium ferrocyanide, sodium cobalticyanide.

[0033] In some embodiments of the present invention, the nitrogen-containing organic ligand includes one or more of imidazole, 2-methylimidazole, 2,4-dimethylimidazole, 2-ethyl-4-methylimidazole, ethylimidazole, 2-isopropylimidazole, 2-phenylimidazole.

[0034] There is nitrogen element in the organic ligand of the present invention, and N atom doping will be evenly introduced during the pyrolysis preparation process, which can improve the conductivity of the carbon material; at the same time, the metal ligand will be reduced to nano-metal particles under the action of carbon due to the confinement effect during the pyrolysis process. After the metal particles are removed by pickling subsequently, a rich pore structure will be formed in-situ, and the pore structure has a certain promoting effect on the liquid retention and lithium ion transport of the battery.

[0035] The second aspect of the present invention aims to provide a preparation method of a conductive material, including the following steps:

[0036] S1. Dissolve the metal salt and the metal ligand in an organic solution, stir ultrasonically to completely dissolve the solid to obtain a mixed solution, add the nitrogen-containing organic ligand to the mixed solution, stir evenly, let the solution stand for aging, then filter the aged solution, wash it repeatedly with an organic solvent, and place the obtained product in vacuum drying to obtain a dry powder.

[0037] S2. Take the above powder and calcine it under an inert atmosphere. After the calcination is completed, perform pickling on the calcined product, then wash it with an organic solvent until it is neutral, and dry it to obtain the conductive material.

[0038] In some embodiments of the present invention, in step S1, the aging time is 4 - 48 h.

[0039] In some embodiments of the present invention, in step S2, the calcination temperature is 600 - 1000 °C, and the calcination time is 2 - 10 h.

[0040] The preparation method of the conductive material of the present invention is MOF synthesis. MOF synthesis is a self - assembly chemical synthesis, in which an inorganic metal center (metal ion or metal cluster) and a bridging organic ligand are interconnected through self - assembly to form a class of crystalline porous materials with a periodic network structure. This method does not require special organic solvents and synthesis environments. It only needs to be mixed and dissolved in an ethanol / water solvent and then left standing at normal temperature and pressure to be synthesized. Moreover, the length of the synthesized nanowires can be regulated by adjusting the reactant concentration and reaction time.

[0041] The third aspect of the present invention aims to provide a battery electrode sheet, including the above - mentioned conductive material; wherein, the battery electrode sheet is a positive electrode sheet and / or a negative electrode sheet.

[0042] The fourth aspect of the present invention aims to provide a secondary battery, including a positive electrode sheet, a negative electrode sheet, and a separator disposed between the positive electrode sheet and the negative electrode sheet; wherein, the positive electrode sheet and / or the negative electrode sheet are the above - mentioned battery electrode sheets.

[0043] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer coated on at least one surface of the positive electrode current collector. The positive electrode current collector can be various materials in the art suitable for use as the positive electrode current collector of a lithium - ion battery. For example, the positive electrode current collector can include, but is not limited to, metal foils, etc., and more specifically can include, but is not limited to, aluminum foils, etc.

[0044] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer coated on at least one surface of the negative electrode current collector. The negative electrode active material layer can include one or several of, but is not limited to, graphite, soft carbon, hard carbon, carbon fiber, mesophase carbon microspheres, silicon - based materials, tin - based materials, lithium titanate, or other metals that can form alloys with lithium, etc. Among them, graphite can be selected from one or several of artificial graphite, natural graphite, and modified graphite; the silicon - based material can be selected from one or several of elemental silicon, silicon oxides, silicon - carbon composites, and silicon alloys; the tin - based material can be selected from one or several of elemental tin, tin oxides, and tin alloys. The negative electrode current collector is usually a structure or part for collecting current, and the negative electrode current collector can be various materials in the art suitable for use as the negative electrode current collector of a lithium - ion battery. For example, the negative electrode current collector can include, but is not limited to, metal foils, etc., and more specifically can include, but is not limited to, copper foils, etc.

[0045] The separator can be various materials suitable for lithium-ion battery separators in the art. For example, it can be a combination of one or more of polyethylene, polypropylene, polyvinylidene fluoride, aramid, polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, polyester, and natural fibers, etc.

[0046] The secondary battery further includes an electrolyte, which includes an organic solvent, an electrolyte lithium salt, and an additive. Among them, the electrolyte lithium salt can be LiPF6 and / or LiBOB used in high-temperature electrolytes; it can also be at least one of LiBF4, LiBOB, and LiPF6 used in low-temperature electrolytes; it can also be at least one of LiBF4, LiBOB, LiPF6, and LiTFSI used in overcharge-preventing electrolytes; it can also be at least one of LiClO4, LiAsF6, LiCF3SO3, and LiN(CF3SO2)2. The organic solvent can be a cyclic carbonate, including PC and EC; it can also be a chain carbonate, including DFC, DMC, or EMC; it can also be a carboxylic acid ester, including MF, MA, EA, MP, etc. The additive includes at least one of, but not limited to, a film-forming additive, a conductive additive, a flame retardant additive, an overcharge-preventing additive, an additive for controlling the content of H2O and HF in the electrolyte, an additive for improving low-temperature performance, and a multifunctional additive.

[0047] To make the technical solutions and advantages of the present invention clearer, the present invention and its beneficial effects will be further described in detail below in conjunction with specific embodiments and the accompanying drawings of the specification. However, the embodiments of the present invention are not limited thereto.

[0048] Example 1

[0049] The preparation method of the conductive material is as follows:

[0050] 1) Dissolve 40 g of anhydrous cobalt acetate and 100 g of potassium cobalt cyanide in a mixed solution of 5 L of deionized water and 5 L of ethanol, and ultrasonically stir for 30 min to completely dissolve the solid crystals; add 160 g of dimethylimidazole to the above mixed solution, and after stirring for 10 min, the solution turns blue-violet; let the solution stand and age for 24 h, then perform suction filtration, and repeatedly wash three times with deionized water and ethanol. The obtained product is placed in a vacuum oven and dried at 60 °C to finally obtain a purple powder product;

[0051] 2) Take 50 g of the above purple powder and calcine it at 800 °C for 8 h in high-purity argon. After the calcination is completed, pickle the carbon / metal product with hydrochloric acid, and finally wash it with ethanol / water until it is neutral, and then dry it to obtain the required one-dimensional carbon nanowires.

[0052] Preparation of the positive electrode sheet: The conductive material prepared above was added to the positive electrode slurry at a mass ratio of 0.2%, and the final mass ratio of the obtained slurry was: active material: binder: conductive material = 97.8%: 2%: 0.2%. The slurry was coated on aluminum foil, baked, rolled, and slit to obtain the positive electrode sheet.

[0053] Preparation of the negative electrode sheet: Graphite, conductive agent carbon nanotubes, binder styrene-butadiene rubber, and thickening agent sodium carboxymethyl cellulose were stirred and mixed evenly in deionized water according to a mass ratio of 96.5:1.5:1:1. After mixing evenly, the negative electrode slurry was coated on Cu foil, baked, rolled, and slit to obtain the negative electrode sheet.

[0054] Preparation of the separator: A polyethylene (PE) polymer film was used as the separator.

[0055] Preparation of the electrolyte: Organic solvents were uniformly mixed according to a mass ratio to obtain a mixed organic solvent solution. The detailed mass ratio was: ethylene carbonate (EC): propyl propionate (PP): vinylene carbonate (VC): diethyl carbonate (DEC): propylene carbonate (PC) = 20:28:2:30:20. Lithium salt LiPF6 was added to the mixed organic solvent solution, and the mass ratio of LiPF6 to the mixed organic solvent solution was 9:91. After mixing evenly, the electrolyte of the lithium-ion battery was obtained.

[0056] Preparation of the lithium-ion battery: The positive electrode sheet, separator, and negative electrode sheet were stacked in sequence, wound to obtain an electrode assembly. When folding the electrode sheets, it should be noted that the separator completely isolates the positive and negative electrode sheets. The electrode assembly was placed in a packaging case, the electrolyte was injected into the packaging case and sealed, and finally the lithium-ion battery was obtained. The specification of this lithium-ion battery is 5Ah.

[0057] Example 2

[0058] The difference from Example 1 is that the addition amount of potassium cyanocobaltate in Step 1 is 10 g.

[0059] The rest is the same as in Example 1 and will not be elaborated here.

[0060] Example 3

[0061] The difference from Example 1 is that the aging time in the preparation step is 6 h.

[0062] The rest is the same as in Example 1 and will not be elaborated here.

[0063] Example 4

[0064] The difference from Example 1 is that cobalt acetate anhydrous in the preparation step is zinc acetate.

[0065] The rest is the same as in Example 1 and will not be elaborated here.

[0066] Example 5

[0067] Different from Example 1, the calcination temperature in the preparation step is 500 °C.

[0068] The rest is the same as in Example 1 and will not be elaborated here.

[0069] Example 6

[0070] Different from Example 1, the calcination time in the preparation step is 2 h.

[0071] The rest is the same as in Example 1 and will not be elaborated here.

[0072] Comparative Example 1

[0073] Different from Example 1, potassium hexacyanoferrate is not added.

[0074] The rest is the same as in Example 1 and will not be elaborated here.

[0075] Comparative Example 2

[0076] Different from Example 1, the conductive material is conductive carbon black.

[0077] The rest is the same as in Example 1 and will not be elaborated here.

[0078] Comparative Example 3

[0079] Different from Example 1, hydrochloric acid pickling is not performed in step 2).

[0080] The rest is the same as in Example 1 and will not be elaborated here.

[0081] The batteries obtained in Examples 1 to 7 and Comparative Examples 1 to 3 above were respectively subjected to performance tests.

[0082] Among them, the test results are shown in Table 1 below.

[0083] Table 1

[0084]

[0085] As can be seen from Table 1 above, by comparing Example 1 and Example 2, reducing the dosage of potassium cobalt cyanide will reduce the aspect ratio of the final product and affect the electrical conductivity of the battery cell. By comparing Example 1 and Example 3, reducing the aging time of precursor synthesis will reduce the aspect ratio of the final product, thus affecting the electrical performance of the battery cell. Changing the metal precursor in Example 4 has no significant effect on the synthesis of carbon nanotubes and the performance of the battery cell. In Example 5, reducing the calcination temperature results in a smaller degree of carbonization shrinkage of the precursor, but a low carbonization temperature leads to a small degree of graphitization of the material, affecting its electrical conductivity and thus the resistance and electrical performance of the battery cell. It can be seen from Comparative Example 1 that without adding potassium cobalt cyanide, only conventional polyhedral materials rather than one-dimensional nanowires can be obtained, and the derived carbon materials lack long-range electrical conductivity, affecting the performance of the battery cell. In Comparative Example 2, an equal amount of conductive carbon black is added, and its electrical conductivity and the performance of the battery cell are worse than those in Example 1, indicating that the one-dimensional carbon nanotubes exhibit better long-range electrical conductivity and liquid retention performance brought by the porous high specific surface area compared with conductive carbon black.

[0086] In summary, the conductive material prepared by the present invention is doped with nitrogen atoms and has a porous structure, which can improve the electrical conductivity of the carbon material, effectively improve the energy efficiency and rate performance, and the rich pore structure can improve the liquid retention ability and the later cycle performance of the battery cell.

[0087] According to the disclosure and teachings of the above specification, those skilled in the art to which the present invention pertains can also make changes and modifications to the above embodiments. Therefore, the present invention is not limited to the above specific embodiments, and any obvious improvements, substitutions or variations made by those skilled in the art based on the present invention all fall within the protection scope of the present invention. In addition, although some specific terms are used in this specification, these terms are only for convenience of description and do not constitute any limitation to the present invention.

Claims

1. A conductive material, characterized in that, The conductive material includes one-dimensional carbon nanotubes doped with nitrogen atoms, the one-dimensional carbon nanotubes having a nano-porous structure, the porosity of the one-dimensional carbon nanotubes being 30%-80%, and the aspect ratio of the one-dimensional carbon nanotubes being 80-220.

2. The conductive material according to claim 1, wherein The synthesis raw materials of the one-dimensional nanowires include metal salts, metal ligands and nitrogen-containing organic ligands; wherein, the mass ratio of the metal salts, metal ligands and nitrogen-containing organic ligands is 0.7-1:2-3:4-5.

3. The conductive material according to claim 2, characterized in that, The metal salts include one or more of iron acetate, ferrous acetate, iron oxalate, iron nitrate, iron sulfate, cobalt acetate, cobalt sulfate, cobalt nitrate, nickel acetate, nickel nitrate, nickel sulfate, zinc acetate, zinc sulfate, zinc nitrate.

4. The conductive material according to claim 3, wherein, The metal ligands include one or more of potassium ferrocyanide, potassium ferrous cyanide, potassium cobalticyanide, potassium nickel cyanide, sodium ferrocyanide, sodium cobalticyanide.

5. The conductive material according to claim 3, wherein The nitrogen-containing organic ligands include one or more of imidazole, 2-methylimidazole, 2,4-dimethylimidazole, 2-ethyl-4-methylimidazole, ethylimidazole, 2-isopropylimidazole, 2-phenylimidazole.

6. A method for preparing the conductive material according to any one of claims 1 to 5, characterized in that, It includes the following steps: S1. Dissolve the metal salts and metal ligands in an organic solution, ultrasonically stir to completely dissolve the solids to obtain a mixed solution, add the nitrogen-containing organic ligand to the mixed solution, stir evenly, let the solution stand for aging, then filter the aged solution, wash it repeatedly with an organic solvent, and place the obtained product in vacuum for drying to obtain a dry powder. S2. Take the above powder and calcine it under an inert atmosphere. After the calcination is completed, pickle the calcined product, then wash it with an organic solvent until it is neutral, and dry it to obtain the conductive material.

7. The method for preparing the conductive material according to claim 6, wherein In step S1, the aging time is 4-48 h.

8. The preparation method of the conductive material according to claim 6, characterized in that, In step S2, the calcination temperature is 500-1000 °C, and the calcination time is 2-10 h.

9. A battery electrode plate, characterized in that, It includes the conductive material according to any one of claims 1-5.

10. A secondary battery, characterized in that, It includes the battery electrode plate according to claim 9.

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