High-performance positive electrode coating as well as preparation method and application thereof

Abstract

The invention belongs to the field of electrochemistry, and particularly relates to a high-performance positive electrode coating as well as a preparation method and application thereof. The coating comprises a micro-mesoporous material with an ion selective permeability function and a binder. Wherein the micro-mesoporous material has a continuous pore channel structure and an adjustable pore diameter, is rich in metal cation groups, has high ionic conductivity, and can be used for preparing a high-performance positive electrode coating. In addition, by regulating and controlling the structure-function relationship among the pore diameter X of the micro-mesoporous material, the cation diameter Y1, the anion diameter Y2 and the solvation group volume Y3, ions are selectively screened, and low-temperature desolvation is promoted. The high-performance positive electrode coating constructed by the invention can effectively improve the cycling stability and low-temperature performance of the lithium ion battery in a wide temperature range.

Description

Technical Field

[0001] The present invention belongs to the field of electrochemistry, and particularly relates to a high-performance cathode coating, a preparation method thereof, and an application thereof. Background Art

[0002] With the gradual in-depth application of lithium-ion batteries in fields such as electric vehicles, aerospace, and polar exploration, it is required that the cathode of lithium-ion batteries has high energy density, high low-temperature performance, and stable cycling in a wide temperature range. This requires that the cathode coating must have high ionic conductivity, rapid desolvation, and can form a stable film layer on the cathode surface. This is not easy to achieve for the current cathode coatings. The properties of the cathode coating include ionic conductivity, desolvation behavior, interfacial chemical properties, etc. How to adjust the interaction between the solvent-cation-anion and the cathode coating so that the cathode coating simultaneously has fast ion transport kinetics and forms a stable and effective interfacial film is still a challenge in the current cathode coating design. Summary of the Invention

[0003] To solve or partially solve the problems existing in the related technologies, the present application proposes a high-performance cathode coating, a preparation method thereof, and an application thereof, so as to reduce the side reactions at the electrolyte / cathode interface, promote the desolvation of lithium ions on the cathode side during low-temperature discharge, and thus effectively improve the cycling stability and low-temperature performance of lithium-ion batteries in a wide temperature range.

[0004] To achieve the above object, the present invention adopts the following technical solutions:

[0005] In a first aspect, the present application provides a cathode coating, comprising a micro-mesoporous material and a binder.

[0006] Preferably, the mass ratio of the micro-mesoporous material is 70-80 wt%, and the mass ratio of the binder is 20-30 wt%.

[0007] For the micro-mesoporous material M-MFI, the average pore diameter X, the diameter Y1 of the cation in the electrolyte, the diameter Y2 of the anion, and the volume Y3 of the solvation group of the cation satisfy Y1≤Y2≤X<1.24Y3 1 / 3 When this is the case, the pore diameter of M-MFI can effectively promote the removal of the solvation group of the cation or the shedding of part of the solvation sheath, and the pore structure, the rich metal cations, and the silanol groups of M-MFI can better bind the anions, promote the migration of cations, and significantly improve the ionic conductivity and low-temperature performance. In addition, the cathode coating of this micro-mesoporous material also reduces the contact between the high-energy solvation sheath and the cathode material, reduces the interfacial side reactions caused by excessive solvent, and improves the cycling stability. If the pore diameter of M-MFI is larger than the solvation group of the cation, that is, X>1.24Y3 1 / 3When the solvation group of the cation can freely pass through the M-MFI pores, the desolvation is difficult, and the interfacial side reactions are aggravated, resulting in poor battery cycling performance and low-temperature performance.

[0008] Preferably, the average thickness of the positive electrode coating is 2-5 μm, and the porosity is 30-50%.

[0009] Preferably, for the metal element doping of the micro-mesoporous material, the doping element is one or more of K, Na, Mn, Fe, Al, Cu, Zn, Ti, Sn, Mo, and W. The content of the doping element is 5-20 wt%. By controlling the content of the doping element and the difference in the atomic radii of different metal elements, a micro-mesoporous material with adjustable pore size is obtained.

[0010] Preferably, the carbon source for carbon-coated M-MFI@C is one of polydopamine, glucose, polyvinylpyrrolidone, and polyvinylidene fluoride. The thickness of the carbon coating layer is about 5-20 nm.

[0011] Preferably, the specific surface area of the micro-mesoporous material is 350-720 m 2 / g, and the pore diameter is The pore depth is 90-160 nm.

[0012] Preferably, the particle size of M-MFI@C is 130-200 nm.

[0013] Preferably, the binder is one or more of polyvinylidene fluoride, polytetrafluoroethylene, polyacrylic acid, polyimide, acrylonitrile, styrene-butadiene rubber, sodium carboxymethyl cellulose, and polyvinyl alcohol.

[0014] In a second aspect, the present application provides a method for preparing a positive electrode coating, including:

[0015] S1. Preparation of metal-doped M-MFI: Ultra-rapid high-temperature sintering is used for quantitative metal ion doping of MFI zeolite Silicalite-1. First, by the solution impregnation method, a certain mass of MFI zeolite Silicalite-1 support is immersed in saturated solutions of different metal chlorides (such as NaCl, KCl). When the pores in the MFI zeolite Silicalite-1 support come into contact with the liquid, capillary pressure is generated due to the surface tension, causing the liquid to penetrate into the pore channels, and the metal ions diffuse in the pores and adsorb on the surface of the support. Then, ultra-rapid high-temperature sintering is carried out, and the effects of different sintering times and temperatures on the density and microstructure of M-MFI are studied. The optimal sintering conditions are determined to be about 1500 K and 3-20 seconds. Excessive sintering time or too high temperature will cause closed pores in M-MFI. Different pore sizes of M-MFI are obtained by ultra-rapid high-temperature sintering of different metal ion-doped Silicalite-1.

[0016] S2. Preparation of Carbon-Coated M-MFI@C: Mix M-MFI and glucose (mass ratio of M-MFI:glucose = 0.5 - 10:0.2 - 5) evenly and transfer them to a tubular furnace. In the tubular furnace filled with inert gas (argon, nitrogen, helium), maintain at 550 - 700 °C for 2 - 6 hours. After the reaction, cool naturally to room temperature to obtain the target product, i.e., M-MFI@C material.

[0017] S3. Preparation of the positive electrode coating: Disperse M-MFI@C in a solvent, and then add a uniformly dispersed binder to it. After slowly stirring for 20 - 180 min and then quickly stirring for 0.5 - 3 h, a positive electrode coating slurry is obtained after mixing evenly. By one or more methods of blade coating, spin coating, casting, or pouring, the positive electrode coating slurry is coated on the surface of the positive electrode plate, and then dried at 80 - 150 °C for 6 - 24 h to remove the solvent molecules.

[0018] Preferably, the organic solvent includes at least one of methanol, ethanol, isopropanol, and N-methylpyrrolidone.

[0019] Beneficial effects: The coating is composed of a micro-mesoporous material with an ion-selective permeation function and a binder. Among them, the micro-mesoporous material has a continuous pore structure and adjustable pore size, is rich in metal cation groups, has high ionic conductivity, and can be used to prepare a high-performance positive electrode coating. In addition, by regulating the structure-activity relationship between the pore size X of the micro-mesoporous material and the cation diameter Y1, anion diameter Y2, and solvation group volume Y3, ions can be selectively screened and low-temperature desolvation can be promoted. The high-performance positive electrode coating constructed by the present invention can effectively improve the cycle stability and low-temperature performance of lithium-ion batteries in a wide temperature range. Description of the Drawings

[0020] Figure 1 It is a diagram showing the comparison items between the examples and the comparative examples and the performance test results of the lithium-ion battery.

[0021] Figure 2 It is a table showing the contents of M element and Si element obtained by ICPMS test. Detailed Embodiments

[0022] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0023] A high-performance cathode coating, the cathode coating comprising a micro-mesoporous material and a binder, wherein the mass ratio of the micro-mesoporous material is 70 to 85 wt%, and the mass ratio of the binder is 15 to 30 wt%;

[0024] The micro-mesoporous material is MFI-type Silicalite-1 zeolite doped with metal element M, and the pore structure can be regulated by metal element doping to achieve adjustable pore diameter and high ionic conductivity, denoted as M-MFI. In addition, by carbon coating M-MFI, the electronic conductivity is improved, denoted as M-MFI@C;

[0025] The average pore diameter of the M-MFI is denoted as The diameter of the cation in the electrolyte is denoted as The diameter of the anion is denoted as The volume of the solvation group of lithium ions is denoted as Among them, X, Y1, Y2, Y3 need to satisfy Y1 ≤ Y2 ≤ X < 1.24Y31 / 3.

[0026] The average thickness of the cathode coating is 0.5 to 20 μm, and the porosity is 20 to 60%.

[0027] For the metal element doping of the micro-mesoporous material, the doping elements include one or more of Ge, K, Na, Mn, Fe, Al, Mg, Ag, Co, Cu, Zn, Ti, Sn, Mo, W, and the content of the doping elements is 1 to 25 wt%.

[0028] The carbon source for carbon coating in M-MFI@C is one or more of polydopamine, glucose, sucrose, polyvinylpyrrolidone, polyacrylonitrile, and polyvinylidene fluoride, and the thickness of the carbon coating layer is 5 to 80 nm.

[0029] The specific surface area of the micro-mesoporous material is 280 to 840 m2 / g, the pore diameter is adjustable within the range, and the pore depth is adjustable within the range of 50 to 400 nm.

[0030] The chemical formula of M-MFI is: (M)2 / nO·xSiO2·yH2O, where M is the metal doping ion, n is the valence state of the metal ion, x is the molar number of silicon, y is the molar number of water, x is adjustable within the range of 1 to 10,000, and y is adjustable within the range of 0 to 40.

[0031] The particle size of the M-MFI@C is 60 to 560 nm.

[0032] The binder includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, polyacrylic acid, polyimide, acrylonitrile, styrene-butadiene rubber, sodium carboxymethyl cellulose, and polyvinyl alcohol.

[0033] Preparation method of high-performance cathode coating, comprising the following steps:

[0034] S1. Preparation of metal-doped M-MFI: By a controllable metal element doping method, the metal element is uniformly doped into the silica structure of Silicalite-1 zeolite. The doping methods include one or more of ultra-rapid high-temperature sintering, chemical vapor deposition, atomic layer deposition, coprecipitation method, spray pyrolysis, hydrothermal / solvothermal method, and combustion method;

[0035] S2. Preparation of carbon-coated M-MFI@C: The M-MFI micro-mesoporous material and the carbon source are mixed evenly in a certain proportion, and the carbon-coated micro-mesoporous material is prepared by heat treatment; The heat treatment methods include one or more of spray drying, chemical vapor deposition, and solid-phase sintering;

[0036] S3. Preparation of cathode coating: Disperse M-MFI@C and the binder in an organic solvent, mix evenly, and coat on the surface of the cathode plate; The coating methods include one or more of blade coating, spin coating, casting, and pouring.

[0037] Application of the high-performance cathode coating: Apply the high-performance cathode coating to an electrochemical device, and the electrochemical device includes the high-performance cathode coating.

[0038] In the examples and comparative examples, the particle size of the Silicalite-1 zeolite nanocrystal raw material is ~300 nm, and it is calcined at 400 - 650 °C for 2 - 10 h for activation treatment.

[0039] In the examples and comparative examples, the contents of metal elements and silicon elements are measured by ICP MS.

[0040] Example 1

[0041] Preparation process of Na-MFI: Weigh 2 g of Silicalite-1 and disperse it in a saturated NaCl solution. After stirring for 15 h, filter it. Place the filter cake in an oven at 100 °C and dry it for 12 h. Then place it in a muffle furnace at 250 °C and calcine it for 4 h. Then adopt the ultra-rapid high-temperature sintering process and flash sinter at 1500 K for 5 s to obtain Na-MFI. Test the Na / Si element content by ICP MS.

[0042] Preparation of carbon-coated Na-MFI@C: Grind Na-MFI and glucose (Na-MFI:C 6 H 6 O 6 = 1:2, mass ratio) in a mortar, mix evenly, and transfer it to a tube furnace. In the tube furnace filled with argon, keep it at 600 °C for 3 h. After the reaction, cool it to room temperature naturally to obtain the target product, that is, the Na-MFI@C material.

[0043] Preparation of the positive electrode coating: Disperse Na-MFI@C in N-methylpyrrolidone, and then add uniformly dispersed polyvinylidene fluoride thereto (the mass ratio of Na-MFI@C to polyvinylidene fluoride is 8:2). After slowly stirring for 30 min, quickly stir for 1 h. After mixing evenly, a positive electrode coating slurry is obtained. By the doctor blade method, the positive electrode coating slurry is coated on the surface of the NCM811 positive electrode sheet, and then dried at 80 °C for 6 h to remove solvent molecules, thus obtaining a composite positive electrode sheet, and the thickness of the positive electrode coating is 5 μm.

[0044] Electrolyte: Ethylene carbonate and dimethyl carbonate are mixed at a volume ratio of 3:7, and lithium hexafluorophosphate is added to form an electrolyte, and the concentration of lithium hexafluorophosphate is 1 mol / L; Assemble a coin-type lithium-ion full battery in an inert atmosphere glove box in the assembly order of graphite negative electrode sheet - separator - electrolyte - composite positive electrode sheet.

[0045] Example 2

[0046] The main differences from Example 1 mainly include: The raw material for the preparation of K-MFI is saturated KCl solution.

[0047] Example 3

[0048] The main differences from Example 1 mainly include: The raw material for the preparation of Al-MFI is saturated AlCl 3 solution. When preparing the AlCl 3 solution, its hydrolysis property needs to be considered. During the preparation process, a small amount of hydrochloric acid is added to inhibit the hydrolysis of AlCl 3 .

[0049] Example 4

[0050] The main differences from Example 1 mainly include: The raw material for the preparation of Fe-MFI is saturated FeCl 3 solution.

[0051] Example 5

[0052] The main differences from Example 1 mainly include: The raw material for the preparation of Fe-MFI is saturated FeCl 3 solution. The electrolyte is different. The lithium salt of the electrolyte in Example 5 is lithium tetrafluoroborate, and the concentration of lithium tetrafluoroborate is 1 mol / L.

[0053] Example 6

[0054] The main differences from Example 1 mainly include: The raw material for the preparation of Fe-MFI is saturated FeCl 3 solution. The electrolyte is different. The lithium salt of the electrolyte in Example 6 is lithium bis(fluorosulfonyl)imide, and the concentration of lithium bis(fluorosulfonyl)imide is 1 mol / L.

[0055] Comparative Example 1

[0056] The differences between Comparative Example 1 and Example 1 mainly include: the positive electrode coating does not contain M-MFI@C, N-methylpyrrolidone and polyvinylidene fluoride are mixed evenly according to the mass ratio of 85:15, and directly coated into a positive electrode coating with a thickness of 5 μm.

[0057] Comparative Example 2

[0058] The differences between Comparative Example 2 and Example 1 mainly include: the micro-mesoporous material in the positive electrode coating is unmodified Silicalite-1, Silicalite-1, N-methylpyrrolidone and polyvinylidene fluoride are mixed evenly, and directly coated into a positive electrode coating with a thickness of 5 μm.

[0059] The comparison items of Examples 1 to 6 and Comparative Examples 1 to 2 and the performance test results of the lithium-ion battery are shown in Figure 1 。

[0060] The contents of M-MFI metal elements and silicon elements in Example 1, Example 2, Example 3, Example 4 and Comparative Example 2 are shown in Figure 2 。

[0061] From the contents of metal elements and silicon elements in the tested M-MFI, it can be seen that the concentrations of doped metal elements in the examples have no obvious difference, and the Si / M mass ratio is 5.4 to 5.7.

[0062] From the results of the above Examples 1 to 6 and Comparative Examples 1 to 2, it can be seen that in Comparative Example 1, the positive electrode coating made of polyvinylidene fluoride has no pore structure, low electronic conductivity and ionic conductivity, and poor low-temperature cycle performance. In Comparative Example 2, when Silicalite-1 is used as the positive electrode coating, its electronic conductivity is low, and there is still a large gap between its pore size and ionic conductivity compared with the materials that can be commercially applied, and the cycle performance is still poor, making it difficult to meet the actual requirements.

[0063] Furthermore, in the examples, doping metal elements into Silicalite-1 can further improve the pore size, conductivity, and high and low temperature performance. By constructing a suitable size ratio among the pore size X of the micro-mesoporous material, the cation diameter Y1, the anion diameter Y2, and the cation solvation group Y3, the ionic conductivity and high and low temperature cycling performance can be significantly improved. In Examples 1 to 4, different metal elements were doped, and the pore size of the micro-mesoporous material increased with the increase of the doped atomic radius. Among them, Al-MFI has the most suitable pore structure to match the lithium hexafluorophosphate / ethylene carbonate / dimethyl carbonate electrolyte system, thus obtaining the most excellent performance. In Examples 4 to 6, different lithium salts were added to the electrolyte. As the anion diameter in the lithium salt decreased and the size of the cation solvation group decreased, the ionic conductivity and cycling performance improved. Among them, the lithium bis(fluorosulfonyl)imide / ethylene carbonate / dimethyl carbonate electrolyte system has the most excellent performance in the Fe-MFI cathode coating.

[0064] In summary, this application uses a micro-mesoporous material with high ionic conductivity, high electronic conductivity, and high electrochemical stability, which exhibits excellent high and low temperature cycling performance when used in lithium-ion batteries.

[0065] This application discloses a high-performance cathode coating and a preparation method thereof. The coating is composed of a micro-mesoporous material with an ion-selective permeation function and a binder. Among them, the micro-mesoporous material has a continuous pore structure and adjustable pore size, is rich in metal cation groups, has high ionic conductivity, and can be used to prepare a high-performance cathode coating. In addition, by regulating the structure-activity relationship among the pore size X of the micro-mesoporous material, the cation diameter Y1, the anion diameter Y2, and the volume of the solvation group Y3, ions can be selectively screened and low-temperature desolvation can be promoted. The high-performance cathode coating constructed by the present invention can effectively improve the cycling stability and low-temperature rate performance of lithium-ion batteries in a wide temperature range.

[0066] In the description of this specification, the description with reference to terms such as "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0067] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A high-performance cathode coating, characterized in that: The positive electrode coating comprises a micro-mesoporous material and a binder, wherein the mass ratio of the micro-mesoporous material is 70-85wt%, and the mass ratio of the binder is 15-30wt%; The micro-mesoporous material is a MFI-type Silicalite-1 zeolite doped with a metal element M, which can be doped with a metal element to adjust the pore structure, thereby achieving adjustable pore size and high ion conductivity, which is denoted as M-MFI. In addition, the electronic conductivity is improved by carbon coating the M-MFI, which is denoted as M-MFI@C. The average pore diameter of the M-MFI is recorded as The diameter of the cation in the electrolyte is recorded as The anion diameter is recorded as The solvation group volume of lithium ions is denoted by Among them, X, Y1, Y2, and Y3 must satisfy Y1≤Y2≤X<1.24Y3 1 / 3 .

2. The high performance cathode coating according to claim 1, characterized in that: The average thickness of the positive electrode coating is 0.5 to 20 μm, and the porosity is 20 to 60%.

3. The high performance cathode coating according to claim 1, characterized in that: The metal element doping of the micro-mesoporous material includes one or more of Ge, K, Na, Mn, Fe, Al, Mg, Ag, Co, Cu, Zn, Ti, Sn, Mo, and W, and the content of the doping element is 1 to 25 wt%.

4. The high performance cathode coating according to claim 1, characterized in that: The carbon source of the carbon coating in the carbon-coated M-MFI@C is one or more of polydopamine, glucose, sucrose, polyvinyl pyrrolidone, polyacrylonitrile and polyvinylidene fluoride, and the thickness of the carbon coating layer is 5 to 80 nm.

5. The high performance cathode coating according to claim 1, characterized in that: The specific surface area of ​​micro-mesoporous materials is 280~840m 2 / g, pore size The hole depth is adjustable within the range of 50 to 400 nm.

6. The high-performance cathode coating according to claim 1, characterized in that: The chemical formula of M-MFI is: (M) 2 / n O·xSiO2·yH2O, wherein M is a metal doping ion, n is a metal ion valence state, x is the molar number of silicon, y is the molar number of water, x is adjustable in the range of 1 to 10000, and y is adjustable in the range of 0 to 40.

7. The high performance cathode coating according to claim 1, characterized in that: The particle size of the M-MFI@C is 60 to 560 nm.

8. The high performance cathode coating according to claim 1, characterized in that: The binder includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, polyacrylic acid, polyimide, acrylonitrile, styrene-butadiene rubber, sodium carboxymethyl cellulose, and polyvinyl alcohol.

9. The method for preparing the high-performance positive electrode coating according to claims 1 to 8, characterized in that: The steps include: S1. Preparation of metal-doped M-MFI: metal elements are uniformly doped into the silica structure of Silicalite-1 zeolite by a controllable metal element doping method, wherein the doping method includes one or more of ultra-fast high temperature sintering, vapor deposition, atomic layer deposition, co-precipitation, spray pyrolysis, hydrothermal / solvothermal method and combustion method; S2. Preparation of carbon-coated M-MFI@C: M-MFI micro-mesoporous material and carbon source are uniformly mixed in a certain proportion, and carbon-coated micro-mesoporous material is prepared by heat treatment; the heat treatment method includes one or more of spray drying, vapor deposition, and solid phase sintering; S3. Preparation of positive electrode coating: Disperse M-MFI@C and a binder in an organic solvent, mix them evenly, and apply them on the surface of the positive electrode sheet; the coating method includes one or more of scraping, spin coating, casting, and casting.

10. An application of the high-performance cathode coating according to any one of claims 1 to 9, characterized in that: The high-performance positive electrode coating is applied to an electrochemical device, and the electrochemical device comprises the high-performance positive electrode coating.

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