A separator for lithium batteries containing an organic-inorganic coating and a method for its preparation

Abstract

The application discloses a kind of organic-inorganic coating lithium battery separators and preparation method thereof, to plant phenolic compound processing ceramic particles, later with isocyanate crosslinking reaction to obtain functionalized ceramic material, then with polyphosphine and its derivative self-crosslinking to form polyphosphine / functionalized ceramic composite coating, after the surface glyceride compound treatment, the separator coating prepared.The application introduces organic-inorganic coating on polyolefin separator single side or both sides, further improves the adhesion strength, mechanical properties and ionic conductivity of separator coating under the premise of not affecting other properties, and reduces the moisture content of separator;Further improve its electrochemical performance, so that it can better meet the performance requirements of lithium ion battery separator.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery technology, specifically relating to a separator for lithium batteries containing an organic-inorganic coating and its preparation method. Background Technology

[0002] In recent years, the strong demand for high-performance rechargeable batteries from the 3C (computers, communications, and consumer electronics) and new energy vehicle industries has driven the development of separator production technology. The separator is a crucial component of lithium-ion batteries, and its performance directly affects the battery's performance and lifespan. In the battery, the separator plays both the role of conducting lithium ions and isolating the positive and negative electrodes.

[0003] To improve the heat resistance of lithium batteries, ceramic-coated polyolefin separators are currently widely used commercially. However, ceramic coating technology suffers from problems such as poor coating adhesion, ionic conductivity, and mechanical properties (inorganic particles lack mechanical strength and are prone to powdering during electrolyte immersion). Furthermore, while ceramic-coated membranes are hydrophilic, they are also more prone to hydrophilicity, increasing the moisture content of the separator from ≤500ppm in the base membrane to ≥2000ppm after coating. In recent years, more and more battery manufacturers have imposed strict requirements on moisture content, as excessive moisture can lead to the decomposition of lithium salts in the electrolyte and corrode and damage the positive and negative electrode materials and current collectors. It also increases the battery's internal resistance, resulting in reduced cycle performance and safety. Therefore, addressing the problems of existing separators and developing new separators to meet market demands is now imperative. Summary of the Invention

[0004] The purpose of this invention is to provide a separator for lithium batteries containing an organic-inorganic coating, which has high adhesion performance, mechanical properties, ionic conductivity and low moisture content, and to provide a method for its preparation.

[0005] To achieve the above-mentioned objectives, the technical solution adopted by the present invention is as follows:

[0006] A method for preparing a lithium battery separator containing an organic-inorganic coating, wherein the separator comprises a battery base film and an organic-inorganic coating coated on one or both sides of the base film, characterized by comprising the following steps:

[0007] S1: Dissolve phenolic acid compounds in the first solvent under heating conditions, stir evenly to prepare a phenolic acid solution, then add ceramic particles, place in an ultrasonic bath, and treat the ceramic particles until there are no precipitated particles at the bottom of the beaker.

[0008] S2: Add isocyanate compounds to the above mixture and react under ultrasonic conditions for 3-5 hours to allow the isocyanate compounds to react with the hydroxyl and carboxyl groups on the ceramic surface to obtain a mixture of isocyanate-functionalized ceramic composites. Then wash with ethanol, filter and dry to obtain the isocyanate-functionalized ceramic composites.

[0009] S3: Dissolve the isocyanate-functionalized ceramic composite obtained in S2 in the second solvent, then add glycerol ester, dispersant and binder, and stir in a water bath at 50~60℃ for 20~28h to obtain organic-inorganic composite coating.

[0010] S4: The above organic-inorganic composite coating is applied to the polyolefin membrane to obtain a membrane with an organic-inorganic composite coating. After drying, the finished product is obtained. During the coating and drying process, the ambient humidity is controlled at 40~80RH.

[0011] Furthermore, step S3 further includes the following steps: mixing and dissolving polyphosphazene with the isocyanate-functionalized ceramic composite obtained in S2 in a second solvent, placing it in a ball mill, and under ball milling conditions, the N and P on the inorganic main chain polymer polyphosphazene crosslink with the polar groups on the isocyanate-functionalized ceramic composite to form a polyphosphazene / isocyanate-functionalized ceramic composite structure.

[0012] Furthermore, the polyphosphazene is one or more of linear polyphosphazene, amino polyphosphazene, and fluoroalkoxy polyphosphazene, and the weight of the polyphosphazene is 1 to 15% of the second solvent.

[0013] Furthermore, the weight ratio of the first solvent, phenolic acid compound, ceramic particles, and isocyanate compound is 1:(0.01~0.15):(0.2~0.5):(0.02~0.2).

[0014] The weight ratio of the second solvent, isocyanate-functionalized ceramic composite, glycerol ester, dispersant, and binder is 1:(0.1~0.5):(0.005~0.05):(0.005~0.05):(0.01~0.08).

[0015] Furthermore, the phenolic acid compound in S1 is one or more of tea polyphenols, ferulic acid, chlorogenic acid, cinnamic acid, etc.; the first solvent is one or more of water, ethanol, glycerol, THF, NMP, or NMF.

[0016] Furthermore, the ceramic particles in S1 are one or more of SiO2, Al2O3, TiO2, boehmite, sepiolite, hydroxyapatite, etc., and the particle size D of the ceramic particles is... 50 ≤2μm.

[0017] Furthermore, the isocyanate compound in S2 is one or more of cyclopentyl isocyanate, 3-thiophene isocyanate, p-toluene isocyanate, vinyl isocyanate, etc.

[0018] Furthermore, in step S3, the glyceride is one or more of glyceryl laurate, glyceryl monooleate, glyceryl linoleate, and glyceryl linolenic acid, and the second solvent is one or more of water, ethanol, and acetone.

[0019] Furthermore, in step S3, the dispersant is one or more of polyvinyl alcohol, polyvinylpyrrolidone, polyacrylamide, polyacrylic acid, sodium polyacrylate, and ammonium polyacrylate, and the binder is one or more of epoxy resin, polyurethane, polyacrylic acid, PVP, PVDF, PTFE, and PMMA.

[0020] The above method was used to prepare a separator for lithium batteries containing an organic-inorganic coating.

[0021] This invention treats ceramic particles with plant phenolic acid compounds, followed by a cross-linking reaction with isocyanate to obtain a functionalized ceramic material. The resulting membrane coating, after treatment with glycerol ester compounds, possesses an organic-inorganic cross-linked porous structure with a hydrophobic yet hydrophilic surface. Furthermore, polyphosphazene and its derivatives can be added to cross-link with the functionalized ceramic material to form a polyphosphazene / functionalized ceramic composite coating, which is then further treated with glycerol ester compounds to obtain the membrane coating. However, to save costs, polyphosphazene and its derivatives can be omitted. The isocyanate-modified ceramic particles possess extremely strong liquid absorption and conductivity properties, which, in synergy with the high-temperature resistance of polyphosphazene, improve the membrane prepared by addressing issues such as poor adhesion, ionic conductivity, mechanical properties, and high moisture content in commercial ceramic membranes, thereby enhancing their electrochemical performance and enabling them to better meet the performance requirements of lithium-ion battery membranes.

[0022] Ferulic acid, cinnamic acid, chlorogenic acid, and tea polyacids are widely found in nature, are inexpensive, and contain a large number of oxygen-containing functional groups such as hydroxyl and carboxyl groups. Treating ceramic particles with these oxygen-containing functional groups makes them easier to cross-link. This not only avoids the environmental pollution and operational hazards associated with strong acid and alkali treatments, but also modifies the hydroxyl and carboxyl groups of the ceramic particles, making them easier to combine with organic molecules and improving the biocompatibility of ceramic materials. This, in turn, increases the proton conductivity and ionic conductivity of the membrane material.

[0023] Cyano-containing compounds can exist stably at 4.5V and possess high lithium-ion transference numbers, meeting the charge-discharge requirements of commercial cathode materials. A novel flexible ion transport material system based on polycyanoacrylate, combining a "rigid-flexible" design concept, enhances the electrochemical stability of the all-solid-state polymer electrolyte through Lewis acid-base interactions, effectively constructing an all-solid-state polymer electrolyte with excellent overall performance. Simultaneously, it synergistically improves battery interface safety, interface stability, and compatibility, exhibiting good rate capability and long-cycle stability in all-solid-state polymer lithium batteries.

[0024] Phosphazene compounds are a class of compounds whose main chain consists of alternating single and double bonds of nitrogen and phosphorus atoms, with two side groups attached to the phosphorus atom. Different side groups attached to the phosphorus atom yield phosphazene compounds with different properties. Because polyphosphazene systems do not form a longwall conjugation, the main chain exhibits excellent flexibility, a common characteristic of all polyphosphazenes—a flexible NP backbone chain. This gives the polymer chain a high degree of freedom and a low glass transition temperature, allowing for uniform crosslinking with oxygen-containing functional groups on the particle surface, unaffected by the steric hindrance typically associated with polymers. In the solid state, it can withstand structural changes. Polyphosphazenes have high phosphorus and nitrogen content; the high phosphorus-nitrogen content forms a synergistic system with excellent heat resistance and flame retardant properties. Therefore, this inorganic main-chain polymer possesses excellent properties such as radiation resistance, high and low temperature resistance, non-combustibility and flame retardancy, good optical transparency, and high light and thermal stability.

[0025] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0026] (1) This invention proposes to treat ceramic particles with plant phenolic acid compounds, introduce active functional groups (such as hydroxyl, carboxyl, etc.) on the ceramic surface, and react with isocyanate groups (-NCO) to obtain isocyanate functionalized ceramic materials. The introduction of electronegative groups cyano and ester groups increases the oxidation stability of the membrane and improves the high voltage resistance of the membrane. In addition, the polar cyano group can coordinate with lithium salt in the electrolyte to promote the dissociation of lithium salt, increase the peristaltic ability of polymer chain segments, promote the transport of lithium ions along the polymer chain, and lead to the improvement of lithium ion conductivity.

[0027] (2) Glyceryl esters are often used to prepare drug-loaded nanoparticles with hydrophobic and biocompatible surfaces. Isocyanate-functionalized ceramic materials (or composite materials formed by self-crosslinking with polyphosphazene and its derivatives) are treated in a solution containing glyceryl esters to obtain a hydrophobic surface. After coating, an isocyanate-functionalized ceramic coating membrane (or a polyphosphazene / isocyanate composite functionalized ceramic coating membrane) is obtained. The surface of the organic-inorganic crosslinked porous coating of this membrane is hydrophobic and has extremely strong liquid absorption and conductivity. Moreover, the interaction between the isocyanate-functionalized ceramic material (or the polyphosphazene / isocyanate composite functionalized ceramic material) and the binder and polyolefin-based membrane is enhanced, improving the mechanical and adhesive properties of the membrane. Therefore, the membrane prepared by this invention has high lithium-ion conductivity, mechanical properties, adhesive properties and low moisture content. Detailed Implementation

[0028] The following embodiments further illustrate a lithium battery separator with an organic-inorganic coating according to the present invention. The lithium battery base film used in the embodiments is a commercially available PP or PE film manufactured in-house.

[0029] Example 1

[0030] (1) First, weigh 100g of THF solvent into a 250mL beaker, then quickly weigh 2g of tea polyphenols and add them to the above THF solvent. Heat at 60℃ and stir with a magnetic stirrer until the tea polyphenols are completely dissolved to prepare a tea polyphenol / THF solution. Add 25g of Al2O3 to the above solution and place it in an ultrasonic bath. There are no precipitated particles at the bottom of the beaker when tilted.

[0031] (2) Then take 5g of cyclopentyl isocyanate and add it to the above mixture. Under ultrasonic conditions, react with the hydroxyl and carboxyl groups on the ceramic surface for 3 hours to obtain the isocyanate functionalized ceramic composite mixture. Then wash with ethanol, filter and dry to obtain the isocyanate functionalized ceramic composite.

[0032] (3) Weigh 100g of a mixed solvent of water and ethanol (water: ethanol = 1:1), disperse the prepared isocyanate functionalized ceramic composite in the mixed solvent under ultrasonic conditions, add 1g of sodium polyacrylate dispersant, 1g of glyceryl laurate and 3g of polyacrylic acid binder to the mixture and stir in a 50℃ water bath for 24h.

[0033] (4) The above mixture is coated on a 16μm PP base film for lithium batteries. The coated wet film is placed in deionized water for 2 minutes and then removed and dried.

[0034] Example 2

[0035] (1) First, weigh 100g of NMP solvent into a 250mL beaker, then quickly weigh 1g of ferulic acid and add it to the above NMP solvent. Heat at 60℃ and stir with a magnetic stirrer until the ferulic acid is completely dissolved to prepare a ferulic acid / NMP solution. Add 20g of SiO2 to the above solution and place it in an ultrasonic bath. The ultrasonic frequency is 60HZ. Continue the ultrasonic treatment until the SiO2 is basically completely modified and no precipitate particles are visible at the bottom of the solution.

[0036] (2) Then take 2g of 3-thiophene isocyanate and add it to the above mixture. Under ultrasonic conditions, react with the hydroxyl and carboxyl groups on the ceramic surface for 3 hours to obtain the isocyanate functionalized ceramic composite mixture. Then wash with ethanol, filter and dry to obtain the isocyanate functionalized ceramic composite.

[0037] (3) Weigh 100g of a mixed solvent of water and ethanol (water: ethanol = 1:1), disperse the prepared isocyanate functionalized ceramic composite in the mixed solvent under ultrasonic conditions, add 0.5g of ammonium polyacrylate dispersant, 0.5g of glyceryl monooleate and 1g of polyurethane binder to the mixture and stir in a 50℃ water bath for 24h.

[0038] (4) The above mixture is coated on a 16μm PP base film for lithium batteries. The coated wet film is placed in deionized water for 2 minutes and then removed and dried.

[0039] Example 3

[0040] (1) First, weigh 100g of glycerol solvent into a 250mL beaker, then quickly weigh 15g of chlorogenic acid and add it to the above glycerol solvent. Heat at 60℃ and stir with a magnetic stirrer until the chlorogenic acid is completely dissolved to prepare a chlorogenic acid / glycerol solution. Add 50g of titanium dioxide to the above solution and place it in an ultrasonic bath. The ultrasonic frequency is 60HZ. Under ultrasonic conditions, the titanium dioxide is basically completely modified and no precipitate particles are visible at the bottom of the solution.

[0041] (2) Then take 20g of vinyl isocyanate and add it to the above mixture. Under ultrasonic conditions, react with the hydroxyl and carboxyl groups on the surface of titanium oxide for 3 hours to obtain the isocyanate functionalized titanium oxide complex mixture. Then wash with ethanol, filter and dry to obtain the isocyanate functionalized titanium oxide complex.

[0042] (3) Weigh 100g of a mixed solvent of water and ethanol (water: ethanol = 1:1), disperse the prepared isocyanate functionalized ceramic composite in the mixed solvent under ultrasonic conditions, add 5g of polyacrylamide dispersant, 5g of linoleic acid glyceride and 4g of polyacrylic acid binder to the mixture and stir in a 50℃ water bath for 24h.

[0043] (4) The above mixture is coated on a 16μm PP base film for lithium batteries. The coated wet film is placed in deionized water for 2 minutes and then removed and dried.

[0044] Example 4

[0045] (1) First, weigh 100g of THF solvent into a 250mL beaker, then quickly weigh 2g of tea polyphenols and add them to the above THF solvent. Stir with a magnetic stirrer at 60℃ until the tea polyphenols are completely dissolved to prepare a tea polyphenol / THF solution. Add 25g of boehmite to the above solution and place it in an ultrasonic bath. There are no precipitated particles at the bottom of the beaker when tilted.

[0046] (2) Then take 5g of cyclopentyl isocyanate and add it to the above mixture. Under ultrasonic conditions, react with the hydroxyl and carboxyl groups on the ceramic surface for 3 hours to obtain the isocyanate functionalized ceramic composite mixture. Then wash with ethanol, filter and dry to obtain the isocyanate functionalized ceramic composite.

[0047] (3) Next, 2g of aminopolyphosphazene and 25g of the above-mentioned isocyanate-modified ceramic particles were mixed in a solvent (water: ethanol = 1:1) and placed in a ball mill. Under ball milling conditions, the N and P of aminopolyphosphazene and the polar groups of isocyanate compounds crosslinked to form polyphosphazene / isocyanate functionalized ceramic composite material.

[0048] (4) Add 1g of glyceryl laurate and 3g of polyacrylic acid binder to the above mixture and stir in a 50°C water bath for 24 hours. Then coat the above mixture onto a 16μm PP base film for lithium batteries. Place the coated wet film in deionized water for 2 minutes and then take it out and dry it to obtain the final product.

[0049] Comparative Example 1

[0050] 16μm PP base film for commercial lithium batteries.

[0051] Comparative Example 2

[0052] Ceramic coating film for commercial lithium batteries.

[0053] The diaphragms of Examples 1-4 and Comparative Examples 1 and 2 were subjected to relevant performance tests, and the results are shown in Table 1.

[0054]

[0055] Commercial lithium-ion battery PP base films are uncoated, making peel strength undetectable. Table 1 shows that the peel strength and mechanical properties (tensile and puncture) of Examples 1-4 are significantly improved compared to the commercial base film and ceramic-coated film. This is because the interaction between the isocyanate-functionalized ceramic material and the binder and polyolefin base film is enhanced, resulting in more -NCO groups, which also facilitates obtaining an ideal chemical bonding interface, thus significantly improving the membrane peel strength (i.e., characterizing adhesion performance). Although the commercial ceramic-coated film has a higher ionic conductivity than the commercial PP base film, it adsorbs more water molecules, leading to... The present invention addresses a series of problems such as electrolyte hydrolysis failure, but the diaphragm coating does not suffer from these issues. The diaphragm not only reduces surface energy, giving it a larger hydrophobic angle and thus reducing moisture content, but also incorporates cyano groups, ester groups, and oxygen, which synergistically promote the dissociation of lithium ions in lithium hexafluorophosphate in the electrolyte. This increases the creeping ability of polymer chains, promoting lithium ion transport along the polymer chains and leading to improved lithium ion conductivity. Furthermore, multiple experiments revealed a correlation between the peel strength (adhesion) of the coated diaphragm and relative humidity; the peel strength increases when the relative humidity varies between 40% and 80%. Experiments also showed that the amount of glycerol ester added affects the film-forming properties of the coated membrane. When the amount of glycerol ester added is 1%, the mechanical and adhesive properties of the diaphragm are optimal. Further increases in the amount of glycerol ester weaken the bonding of various forces in the coating, resulting in poorer mechanical and adhesive properties of the composite membrane.

[0056] The above embodiments are merely preferred embodiments of the present invention. It should be noted that those skilled in the art can make several improvements and equivalent substitutions without departing from the principle of the present invention. All such improvements and equivalent substitutions to the claims of the present invention fall within the protection scope of the present invention.

Claims

1. A method for preparing a separator for lithium batteries containing an organic-inorganic coating, wherein the separator comprises a battery base film and an organic-inorganic coating coated on one or both sides of the base film, characterized in that, Includes the following steps: S1: Dissolve plant phenolic acid compounds in the first solvent under heating conditions, stir evenly to prepare a plant phenolic acid solution, then add ceramic particles, place in an ultrasonic bath, and treat the ceramic particles until there are no precipitated particles at the bottom of the beaker. S2: Add isocyanate compounds to the above mixture and react under ultrasonic conditions for 3-5 hours to obtain a mixture of isocyanate-functionalized ceramic composites. Then wash with ethanol, filter and dry to obtain isocyanate-functionalized ceramic composites. S3: The isocyanate-functionalized ceramic composite obtained in S2 is dispersed in the second solvent, and then glycerol ester, dispersant and binder are added. After stirring in a water bath at 50~60℃ for 20~28h, an organic-inorganic composite coating is obtained. S4: The above organic-inorganic composite coating is applied to a polyolefin separator to obtain a separator with an organic-inorganic coating. After drying, the finished product is obtained. During the coating and drying process, the ambient humidity is controlled at 40-80% RH%. S3 further includes the following steps: mixing and dispersing polyphosphazene with the isocyanate-functionalized ceramic composite obtained in S2 in a second solvent, placing it in a ball mill, and crosslinking under ball milling conditions to form a polyphosphazene / isocyanate-functionalized ceramic composite solution; the plant phenolic acid compound in S1 is one or more of tea polyphenols, ferulic acid, chlorogenic acid, and cinnamic acid.

2. The method for preparing a separator for lithium batteries containing an organic-inorganic coating according to claim 1, characterized in that, The polyphosphazene is one or more of linear polyphosphazene, amino polyphosphazene, and fluoroalkoxy polyphosphazene, and the weight of the polyphosphazene is 1 to 15% of the second solvent.

3. The method for preparing a separator for lithium batteries containing an organic-inorganic coating according to claim 1, characterized in that, The weight ratio of the first solvent, phenolic acid compound, ceramic particles, and isocyanate compound is 1:(0.01~0.15):(0.2~0.5):(0.02~0.2). The weight ratio of the second solvent, isocyanate-functionalized ceramic composite, glycerol ester, dispersant, and binder is 1:(0.1~0.5):(0.005~0.05):(0.005~0.05):(0.01~0.08).

4. The method for preparing a separator for lithium batteries containing an organic-inorganic coating according to claim 1, characterized in that: The first solvent is one or more of water, ethanol, glycerol, THF, NMP, or NMF.

5. The method for preparing a separator for lithium batteries containing an organic-inorganic coating according to claim 1, characterized in that: The ceramic particles in S1 are one or more of SiO2, Al2O3, TiO2, boehmite, sepiolite, and hydroxyapatite, and the particle size D of the ceramic particles is... 50 ≤2μm.

6. The method for preparing a lithium battery separator containing an organic-inorganic coating according to claim 1, characterized in that: The isocyanate compound in S2 is one or more of cyclopentyl isocyanate, 3-thiophene isocyanate, p-toluene isocyanate, and vinyl isocyanate.

7. The method for preparing a separator for lithium batteries containing an organic-inorganic coating according to claim 1, characterized in that: In step S3, the glyceride is one or more of glyceryl laurate, glyceryl monooleate, glyceryl linoleate, and glyceryl linolenic acid, and the second solvent is one or more of water, ethanol, and acetone.

8. The method for preparing a separator for lithium batteries containing an organic-inorganic coating according to claim 1, characterized in that: In step S3, the dispersant is one or more of polyvinyl alcohol, polyvinylpyrrolidone, polyacrylamide, polyacrylic acid, sodium polyacrylate, and ammonium polyacrylate, and the binder is one or more of epoxy resin, polyurethane, polyacrylic acid, PVP, PVDF, PTFE, and PMMA.

9. A separator for lithium batteries containing an organic-inorganic coating is prepared by the method described in any one of claims 1-8.

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