Organic-inorganic hybrid composite diaphragm and preparation method thereof

Abstract

The invention discloses an organic-inorganic hybrid composite diaphragm and a preparation method thereof, and belongs to the field of battery diaphragms. The composite diaphragm comprises a base membrane and an organic-inorganic hybrid coating, the organic-inorganic hybrid coatings are coated on the two sides of the base membrane; the organic-inorganic hybrid coating comprises the following raw materials in parts by mass: 20-30 parts of modified branched polymethyl methacrylate, 10-20 parts of inorganic particles, 3-5 parts of a water-based adhesive, 1-2 parts of a dispersing agent and 40-65 parts of a solvent; and the molecular chain of the modified branched polymethyl methacrylate contains ether oxygen bonds. Modified branched polymethyl methacrylate can effectively prevent inorganic particles from falling off in the circulation process, a composite system is formed, the porosity of the diaphragm is improved, ether oxygen bonds are combined, the ion transmission efficiency is remarkably enhanced, and the performance of the diaphragm is improved by optimizing a physical channel, enhancing interface wettability and dynamically regulating and controlling an ion transmission path. And the rate capability and the cycling stability of the battery when the diaphragm is applied to the lithium ion battery are obviously improved.

Description

Technical Field

[0001] The present invention relates to the field of battery separators, and in particular to an organic-inorganic hybrid composite separator and a preparation method thereof. Background Art

[0002] Lithium-ion battery separators are key functional components located between the positive and negative electrodes. They enable the selective transmission of lithium ions, preventing direct electron conduction, and thus maintaining the stability of the battery's electrochemical reactions. To meet the application requirements of lithium-ion batteries, separators must balance ion transmission efficiency and mechanical properties. Separator performance directly impacts the battery's energy density, cycle life, and safety.

[0003] The commonly used diaphragms at present are polymer diaphragms and aqueous diaphragms. Among them, polymer diaphragms have good chemical stability, can withstand the chemical reaction environment inside the battery, and have good processability. However, polymer diaphragms have poor affinity for electrolytes, which will cause some micropores in the polymer diaphragms to be unable to be filled with electrolytes, thereby increasing the internal resistance of the battery and affecting the battery's cycle and rate performance.

[0004] To address the aforementioned issues with single polymer separators, studies have been conducted on improving the performance of single separators by applying modified coatings to the surface of polymer separators. Among these, the method of applying inorganic coatings to polymer separators has received widespread attention. Applying inorganic coatings to polymer separators can significantly improve the thermal performance of the separator by forming a rigid skeleton on the surface of the polymer separator, maintaining the structural integrity of the separator pores at high temperatures, and increasing the separator's affinity for the electrolyte, thereby inhibiting the migration of electrode side reaction products.

[0005] However, the nanoparticles in the inorganic coating can easily clog the diaphragm's micropores during the coating process, reducing the diaphragm's porosity, which in turn leads to a decrease in the ion transmission efficiency of the diaphragm, thereby affecting the battery's cycle performance and rate performance. Furthermore, the traditional adhesives in the inorganic coating are only bonded to the inorganic particles through physical adsorption, which can easily fall off during cycling, leading to interfacial peeling. Furthermore, poor dispersion of the inorganic particles in the coating can also lead to increased local interfacial impedance, thus affecting battery performance. Summary of the Invention

[0006] The present invention provides an organic-inorganic hybrid composite membrane and a preparation method thereof, which can solve the problem of the difficulty in balancing the ion transmission efficiency and mechanical strength of polymer membranes in the prior art.

[0007] In a first aspect, the present invention provides an organic-inorganic hybrid composite membrane, the composite membrane comprising a base membrane and an organic-inorganic hybrid coating; the organic-inorganic hybrid coating is coated on both sides of the base membrane;

[0008] The organic-inorganic hybrid coating comprises the following raw materials in parts by weight:

[0009] 20-30 parts of modified branched polymethyl methacrylate;

[0010] 10-20 parts of inorganic particles;

[0011] 3-5 parts of water-based adhesive;

[0012] 1-2 parts of dispersant;

[0013] 40-65 parts of solvent;

[0014] The molecular chain of the modified branched polymethyl methacrylate contains ether oxygen bonds.

[0015] Preferably, the inorganic particles include one or more of zirconium dioxide, aluminum oxide, silicon dioxide and titanium dioxide.

[0016] Preferably, the base film includes any one of a polyethylene porous film, a polypropylene porous film and a polypropylene / polyethylene composite porous film.

[0017] More preferably, the base film has a thickness of 8 to 15 μm and a porosity of 40 to 60%.

[0018] Preferably, the water-based adhesive includes any one of polyvinyl alcohol, acrylic water-soluble adhesive and styrene-butadiene latex.

[0019] Preferably, the dispersant includes one or more combinations of polyoxyethylene dioleate, polyethylene glycol monostearate, polyethylene glycol monooleate, polyoxypropylene stearate, polyoxyethylene fatty acid, alkylbenzene sulfonate, polyoxyethylene alkyl ether and polyvinyl pyrrolidone.

[0020] Preferably, the solvent includes any one of dimethylformamide, dimethylacetamide, tetramethylurea, acetone, dimethylformamide, N-methylpyrrolidone, cyclohexane, water and ethanol.

[0021] By adopting the above technical solution, an organic-inorganic hybrid coating is coated on both sides of the base membrane, wherein the coating contains inorganic particles. The high temperature resistance of the inorganic particles can inhibit the high temperature shrinkage of the diaphragm and maintain the stability of the pore structure of the base membrane, thereby avoiding thermal shrinkage that may occur during the cycle. In addition, the rigid structure of the inorganic particles can enhance the puncture resistance of the diaphragm. However, the inorganic particles also have problems such as poor dispersion and easy falling off. In order to solve this problem, modified branched polymethyl methacrylate is also added to the organic-inorganic hybrid coating.

[0022] The modified branched polymethyl methacrylate has a three-dimensional network structure. On the one hand, it can prevent the agglomeration of inorganic particles through steric hindrance, thereby improving the dispersibility of the inorganic particles. In addition, the ether oxygen groups contained in the modified branched polymethyl methacrylate can form hydrogen bonds with the hydroxyl groups on the surface of the inorganic particles, thereby optimizing the bonding strength between the coating composition and the inorganic particles, which is beneficial to promoting the dispersion and wetting of the inorganic particles.

[0023] On the other hand, the molecular chain segments of the modified branched polymethyl methacrylate can form an interlocking structure with the inorganic particles. The molecular chain segments can wrap the inorganic particles to prevent them from falling off during the battery cycle, thereby improving the peel strength of the inorganic particles. In addition, the molecular chain segments of the branched structure have higher flexibility and can buffer the volume change stress generated during the cycle, effectively preventing the inorganic particles from falling off due to the influence of stress.

[0024] In addition to improving the binding force and dispersibility of inorganic particles, modified branched polymethyl methacrylate can also increase the ion transmission rate of the separator and its affinity for the electrolyte, while synergizing with inorganic particles to increase the porosity of the separator. Specifically:

[0025] The micropores formed between the inorganic particles can significantly reduce the curvature of the lithium ion migration path, and together with the modified branched polymethyl methacrylate, form multi-level channels, ensuring the three-dimensional connectivity of the pore network and the stability of the pore structure, optimizing the physical channels, enhancing the interface wettability and dynamically regulating the ion transmission path, significantly improving the rate performance and cycle stability of lithium-ion batteries.

[0026] Preferably, the raw materials of the modified branched polymethyl methacrylate include methyl methacrylate, branching monomer and polyethylene oxide in a molar ratio of 100:(1.6-1.8):(15-20).

[0027] Preferably, the branching monomer includes one or more of ethylene glycol dimethacrylate, tripropylene glycol diacrylate, 2-(2-bromoisobutyryloxy)ethyl methacrylate and divinylbenzene.

[0028] Preferably, the modified branched polymethyl methacrylate is prepared according to the following method:

[0029] 80-90 wt% of methyl methacrylate, branching monomers and auxiliary agents are added to anisole, stirred and mixed, and reacted for 4-5 hours at 90-95° C. in an argon atmosphere. Then, the remaining amount of methyl methacrylate, polyethylene oxide and catalyst are added, and the reaction is continued at 80-85° C. for 4-6 hours. Finally, the product is washed, filtered and dried.

[0030] More preferably, the auxiliary agent comprises 2-bromoisobutyryl bromide, cuprous bromide and bipyridine in a molar ratio of (1.5-2):1:3; and the molar ratio of the auxiliary agent to methyl methacrylate is (5.5-6):100.

[0031] Preferably, the catalyst includes any one of azobisisobutyronitrile and cuprous chloride.

[0032] By adopting this technical solution, polyethylene oxide is introduced during the preparation of branched polymethyl methacrylate, and after grafting, ether oxygen bonds are introduced into the molecular chain of the branched polymethyl methacrylate. The branched structure improves the mechanical strength of polymethyl methacrylate. Compared with linear polymethyl methacrylate, branched polymethyl methacrylate maintains good interfacial bonding with the separator while improving its own mechanical strength, thereby improving the puncture resistance and strength of the separator.

[0033] The ether oxygen bonds in the modified branched polymethyl methacrylate can form dynamic coordination between the lone pair electrons contained in the polymethyl methacrylate and lithium ions, thereby promoting the dissociation of lithium salts and realizing rapid conduction of lithium ions. At the same time, the micropores between the inorganic particles can also improve the rapid ion migration channel. The two can work together to greatly improve the ion transmission efficiency of the diaphragm. In addition, the polar effect of the modified branched polymethyl methacrylate can improve the polarity of the organic-inorganic hybrid coating, thereby enhancing the compatibility with the electrolyte and reducing the interfacial impedance, thereby improving the cycle and rate performance of the lithium-ion battery.

[0034] Preferably, a nanocellulose fiber coating is further provided between one side surface of the base film and the organic-inorganic hybrid coating.

[0035] Preferably, the nanocellulose fiber coating comprises the following raw materials in parts by mass: 20-30 parts of nanocellulose fibers, 10-15 parts of chitosan and 40-60 parts of adhesive solution.

[0036] More preferably, the adhesive solution is an adhesive aqueous solution with a mass fraction of 10 to 20%; the adhesive includes a combination of one or more of polyvinyl alcohol, methyl cellulose, ethyl cellulose, vinyl cellulose and isopropyl cellulose.

[0037] Preferably, the side of the base membrane coated with the double-layer coating of nanocellulose fiber coating and organic-inorganic hybrid coating faces the negative electrode; the side of the base membrane coated with the single-layer coating of organic-inorganic hybrid coating faces the positive electrode.

[0038] By adopting the above technical solution, a layer of nanocellulose fiber coating is first coated on the surface of one side of the base membrane. The pore size formed by nanocellulose in the nanocellulose fiber coating is much smaller than the size of the lateral growth of dendrites. The network structure of the obtained nanocellulose fiber coating can form a physical barrier to block the growth of dendrites, further improve the puncture resistance of the diaphragm, and provide the diaphragm with higher tensile strength.

[0039] An organic-inorganic hybrid coating is then applied to both sides of the base membrane, resulting in a base membrane with high porosity on one side and low porosity on the other. The high porosity facilitates rapid ion transport, compensating for the transport resistance that low porosity may cause. The low porosity side significantly improves the mechanical strength and dendrite penetration resistance of the separator, resulting in a separator material with high ion transport efficiency and high puncture resistance. This structure also better balances the performance of both sides of the separator, and its application in batteries can improve the cycle and rate performance of lithium batteries.

[0040] The raw material of the nanocellulose fiber coating uses nanocellulose fibers as the matrix, which can form a three-dimensional interconnected pore network, which can reduce the pore size and porosity, but still maintain connectivity and will not affect ion transmission. The polar groups it contains will not affect the affinity of the diaphragm to the electrolyte, and can ensure that the pore channels are fully filled with the electrolyte, reducing the interfacial impedance. Moreover, its high crystallinity and rigid network can further improve the tensile strength and puncture resistance of the diaphragm, thereby improving the mechanical properties of the diaphragm.

[0041] The coating also contains chitosan, which can help improve the interfacial bonding strength between the membrane and the coating. It can also act as a volume filler to fill some of the pores, achieve a low-porosity design on one side of the membrane, improve density, and effectively inhibit dendrite penetration.

[0042] In a second aspect, the present invention provides a method for preparing an organic-inorganic hybrid composite membrane, comprising the following process steps:

[0043] S1 weighed the corresponding parts by mass of the raw materials of the nanocellulose fiber coating, stirred and mixed, and coated on one side of the base film surface, after drying to form a nanocellulose fiber coating on one side of the base film to obtain a pretreated base film;

[0044] S2. A water-based adhesive and a dispersant were added to the solvent, and after stirring to dissolve, modified branched polymethyl methacrylate and inorganic particles were added, and stirring was continued to obtain an organic - inorganic hybrid slurry;

[0045] S3. Soak the pretreated base membrane in the organic-inorganic hybrid slurry for 5 to 10 minutes, then take it out and dry it to obtain the organic-inorganic hybrid composite membrane.

[0046] Preferably, the technical effect of the present invention can be achieved without forming a nanocellulose fiber coating on the surface of the base film.

[0047] Preferably, the thickness of the nanocellulose fiber coating is 0.5 to 2 μm.

[0048] Preferably, the thickness of the organic-inorganic hybrid coating is 1 to 8 μm.

[0049] Beneficial effects of the present invention:

[0050] 1. The organic-inorganic hybrid composite membrane of the present invention includes an organic-inorganic hybrid coating. The inorganic particles in the coating work synergistically with the modified branched polymethyl methacrylate to effectively prevent the inorganic particles from falling off during the cycle and improve the dispersibility of the inorganic particles. Simultaneously, the ion transmission efficiency of the membrane and its affinity for the electrolyte can be improved. The inorganic particles and the modified branched polymethyl methacrylate can form multi-level pores, increasing the porosity of the membrane. Combined with ether oxygen bonds, the ion transmission efficiency is significantly enhanced. The three-dimensional connectivity of the pore network and the stability of the pore structure are also ensured. This optimizes physical channels, enhances interfacial wettability, and dynamically regulates ion transmission paths, significantly improving the rate performance and cycle stability of lithium-ion batteries.

[0051] 2. A nanocellulose fiber coating can be added to one side of the organic-inorganic hybrid composite membrane of the present invention to form a composite membrane with a high porosity on one side and a low porosity on the other side. The low-porosity side faces the negative electrode. Through the action of the nanocellulose fiber coating, a physical barrier can be formed to block the growth of dendrites, further improving the puncture resistance of the membrane. The network structure formed by the nanocellulose fibers still has connectivity and will not affect ion transmission, thereby obtaining a membrane material with high ion transmission efficiency and high puncture resistance. DETAILED DESCRIPTION

[0052] The specific embodiments of the present invention are described in detail below, but it should be understood that the protection scope of the present invention is not limited by the specific embodiments.

[0053] Preparation Example

[0054] Preparation Example 1: A modified branched polymethyl methacrylate was prepared according to the following method:

[0055] 85 mmol of methyl methacrylate, 1.7 mmol of ethylene glycol dimethacrylate and 6 mmol of an auxiliary agent were added to 50 mmol of anisole, wherein the auxiliary agent included 2-bromoisobutyryl bromide, cuprous bromide and bipyridine in a molar ratio of 2:1:3, stirred and mixed, and reacted under an argon atmosphere at 90°C for 5 h. Then, 15 mmol of methyl methacrylate and 18 mmol of polyethylene oxide (average molecular weight 6.0×10 5) and a catalyst, and continue the reaction at 80°C for 5 hours, and finally wash, filter and dry to obtain the product.

[0056] Preparation Example 2, a modified branched polymethyl methacrylate, differs from Preparation Example 1 only in that the added amount of ethylene glycol dimethacrylate is 1.6 mmol; the added amount of polyethylene oxide is 15 mmol.

[0057] Preparation Example 3, a modified branched polymethyl methacrylate, differs from Preparation Example 1 only in that the added amount of ethylene glycol dimethacrylate is 1.8 mmol; the added amount of polyethylene oxide is 20 mmol.

[0058] Preparation Example 4, a modified branched polymethyl methacrylate, is different from Preparation Example 1 only in that the amount of polyethylene oxide added is 10 mmol.

[0059] Preparation Example 5, a modified branched polymethyl methacrylate, is different from Preparation Example 1 only in that the amount of polyethylene oxide added is 25 mmol.

[0060] Preparation Example 6: A branched polymethyl methacrylate was prepared according to the following method:

[0061] 100 mmol of methyl methacrylate, 1.7 mmol of ethylene glycol dimethacrylate and 6 mmol of an auxiliary agent were added to 50 mmol of anisole, wherein the auxiliary agent included 2-bromoisobutyryl bromide, cuprous bromide and bipyridine in a molar ratio of 2:1:3, and the mixture was stirred and reacted under an argon atmosphere at a temperature of 90°C for 7 hours. Finally, the mixture was washed, filtered and dried to obtain the product.

[0062] Preparation Example 7, a modified polymethyl methacrylate, was prepared according to the following method:

[0063] 85 mmol of methyl methacrylate and 6 mmol of an auxiliary agent were added to 50 mmol of anisole, wherein the auxiliary agent included 2-bromoisobutyryl bromide, cuprous bromide and bipyridine in a molar ratio of 2:1:3, stirred and mixed, and reacted under an argon atmosphere at 90°C for 5 h. Then, 15 mmol of methyl methacrylate and 18 mmol of polyethylene oxide (average molecular weight 6.0×10 5 ) and a catalyst, and continue the reaction at 80°C for 5 hours, and finally wash, filter and dry to obtain the product.

[0064] Preparation Example 8: Polymethyl methacrylate was prepared according to the following method:

[0065] 100 mmol of methyl methacrylate and 6 mmol of an auxiliary agent are added to 50 mmol of anisole, wherein the auxiliary agent includes 2-bromoisobutyryl bromide, cuprous bromide and bipyridine in a molar ratio of 2:1:3. After stirring and mixing, the mixture is reacted under an argon atmosphere at a temperature of 90°C for 7 hours, and finally washed, filtered and dried to obtain the product.

[0066] Example

[0067] Example 1, an organic-inorganic hybrid composite membrane, was prepared according to the following method:

[0068] S1. 4 parts of polyvinyl alcohol and 1.5 parts of polyethylene glycol monostearate were added to 50 parts of dimethyl amide, stirred and dissolved, and then 25 parts of the modified branched polymethyl methacrylate prepared in Preparation Example 1 and 15 parts of zirconium dioxide (average particle size of 0.5 μm) were added, and stirring and mixing were continued to obtain an organic-inorganic hybrid slurry;

[0069] S2. Soak a polypropylene porous film (thickness of 10 μm, porosity of 45%) in the organic-inorganic hybrid slurry for 6 minutes, then take it out and dry it to obtain an organic-inorganic hybrid composite membrane.

[0070] Example 2 and Example 3 are organic-inorganic hybrid composite membranes. The only difference between Example 1 and Example 1 is that the raw materials of the organic-inorganic hybrid coating are adjusted, as shown in Table 1:

[0071] Table 1 Raw material ratio of organic-inorganic hybrid coating

[0072] Example 1 Example 2 Example 3 Dimethylamide / part 50 45 65 Polyvinyl alcohol / part 4 5 3 Polytetraethylene glycol monostearate / part 1.5 2 1 Modified branched polymethyl methacrylate / part 25 20 30 Zirconium dioxide / part 15 20 10

[0073] The modified branched polymethyl methacrylate used was the modified branched polymethyl methacrylate prepared in Preparation Example 1.

[0074] Example 4, an organic-inorganic hybrid composite membrane, is the same as Example 1 except that the modified branched polymethyl methacrylate prepared in Preparation Example 1 is replaced by an equal amount of the modified branched polymethyl methacrylate prepared in Preparation Example 2.

[0075] Example 5, an organic-inorganic hybrid composite membrane, is the same as Example 1 except that the modified branched polymethyl methacrylate prepared in Preparation Example 1 is replaced by an equal amount of the modified branched polymethyl methacrylate prepared in Preparation Example 3.

[0076] Example 6, an organic-inorganic hybrid composite membrane, is the same as Example 1 except that the modified branched polymethyl methacrylate prepared in Preparation Example 1 is replaced by an equal amount of the modified branched polymethyl methacrylate prepared in Preparation Example 4.

[0077] Example 7, an organic-inorganic hybrid composite membrane, is the same as Example 1 except that the modified branched polymethyl methacrylate prepared in Preparation Example 1 is replaced by an equal amount of the modified branched polymethyl methacrylate prepared in Preparation Example 5.

[0078] Example 8, an organic-inorganic hybrid composite membrane, was prepared according to the following method:

[0079] S1. Weigh 25 parts of nanocellulose fibers (4-10 nm in diameter and 1-3 μm in length), 12 parts of chitosan, and 50 parts of a 15% aqueous solution of ethyl cellulose, stir and mix, and then apply the mixture to one side of a polypropylene porous film (10 μm thick, 45% porosity). After drying, a nanocellulose fiber coating is formed on one side of the base film to obtain a pretreated base film.

[0080] S2. 4 parts of polyvinyl alcohol and 1.5 parts of polyethylene glycol monostearate were added to 50 parts of dimethyl amide, stirred and dissolved, and then 25 parts of the modified branched polymethyl methacrylate prepared in Preparation Example 1 and 15 parts of zirconium dioxide (average particle size of 0.5 μm) were added, and stirring and mixing were continued to obtain an organic-inorganic hybrid slurry;

[0081] S3. Soak the pretreated base membrane in the organic-inorganic hybrid slurry for 6 minutes, then take it out and dry it to obtain the organic-inorganic hybrid composite membrane.

[0082] Example 9, an organic-inorganic hybrid composite membrane, is different from Example 8 only in that the added amount of cellulose nanofibers is 15 parts.

[0083] Example 10, an organic-inorganic hybrid composite membrane, is different from Example 8 only in that the added amount of cellulose nanofibers is 35 parts.

[0084] Comparative Example

[0085] Comparative Example 1 is an organic-inorganic hybrid composite membrane, which is different from Example 1 only in that the amount of modified branched polymethyl methacrylate prepared in Preparation Example 1 added is 10 parts.

[0086] Comparative Example 2 is an organic-inorganic hybrid composite membrane, which is different from Example 1 only in that the amount of modified branched polymethyl methacrylate prepared in Preparation Example 1 added is 40 parts.

[0087] Comparative Example 3, an organic-inorganic hybrid composite membrane, is the same as Example 1 except that the modified branched polymethyl methacrylate prepared in Preparation Example 1 is replaced by an equal amount of the branched polymethyl methacrylate prepared in Preparation Example 6.

[0088] Comparative Example 4, an organic-inorganic hybrid composite membrane, is similar to Example 1 except that the modified branched polymethyl methacrylate prepared in Preparation Example 1 is replaced by an equal amount of the modified polymethyl methacrylate prepared in Preparation Example 7.

[0089] Comparative Example 5, an organic-inorganic hybrid composite membrane, is the same as Example 1 except that the modified branched polymethyl methacrylate prepared in Preparation Example 1 is replaced by an equal amount of polymethyl methacrylate prepared in Preparation Example 8.

[0090] Comparative Example 6, an organic-inorganic hybrid composite membrane, is similar to Example 1 except that the modified branched polymethyl methacrylate prepared in Preparation Example 1 is not added.

[0091] Performance testing

[0092] 1. Puncture resistance test: According to the relevant records in GB / T 23318-2019 "Determination of puncture strength of textiles", the puncture strength of the diaphragms obtained in the examples and comparative examples was tested.

[0093] 2. Interface Adhesion Strength Test: The composite membranes obtained in the Examples and Comparative Examples were cut into 1.5 cm × 7 cm pieces as test specimens. The specimens were adhered to glass plates using transparent double-sided tape (3M). The force required to separate the coatings was measured using a tensile strength tester, yielding the peel strength (gf / cm) between the membrane and the coating.

[0094] The above test structure is shown in Table 2.

[0095] 3. Electrical performance test: The diaphragms obtained in the examples and comparative examples were used as lithium battery diaphragms, a LiNiCoMnO2 electrode was used as the positive electrode, a graphite electrode was used as the negative electrode, and an electrolyte based on ethylene carbonate / ethyl methyl carbonate / diethyl carbonate (EC / EMC / DEC=3:2:5) dissolved in lithium hexafluorophosphate (LiPF6) was used to prepare lithium ion battery samples;

[0096] The obtained lithium-ion battery sample was charged and discharged at a rate of 0.5C at 25°C for 500 cycles, and the capacity retention rate before and after the cycle was tested.

[0097] The above test results are shown in Table 3.

[0098] Table 2 Puncture resistance and interface adhesion test results

[0099]

[0100]

[0101] Table 3 Electrical performance test results

[0102]

[0103] According to Table 2 and Table 3, combined with Example 1 and Example 8, it can be seen that adding a nanocellulose fiber coating on one side of the base membrane can significantly improve the puncture strength of the diaphragm. When applied to a lithium battery, it can also significantly improve the cycle performance of the battery without affecting the ion transmission capacity of the diaphragm, and can improve the stability and capacity retention rate of the battery.

[0104] Combining Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 6, it can be seen that the various properties of Comparative Examples 1, Comparative Example 2, and Comparative Example 6 are all reduced compared to Example 1. The reason is that Comparative Examples 1, Comparative Example 2, and Comparative Example 6 adjust the content of modified branched polymethyl methacrylate in the organic-inorganic hybrid coating. A small amount of addition reduces the improvement effect of the inorganic particles, and the effect of the synergistic inorganic particles on the ion transport efficiency of the diaphragm and the electrolyte affinity is reduced, resulting in a decrease in various properties. In Comparative Example 6, no modified branched polymethyl methacrylate is added, and the performance degradation is more obvious. Increasing the addition amount will cause the organic molecular chains in the coating to entangle, reduce flexibility, and reduce the porosity of the coating, resulting in a subsequent decrease in performance.

[0105] Combining Example 1, Comparative Example 3, Comparative Example 4 and Comparative Example 5, it can be seen that the various properties of Comparative Example 3, Comparative Example 4 and Comparative Example 5 are all reduced compared to Example 1. The reason is that in Comparative Example 3, branched polymethyl methacrylate is added, and the molecular chain does not contain ether oxygen bonds, which greatly reduces the effect of improving the ion transmission efficiency and the bonding force with the diaphragm. In Comparative Example 4, modified linear polymethyl methacrylate is added. Compared with the branched structure, the linear polymethyl methacrylate has low mechanical strength and poor puncture resistance, resulting in a decrease in the cycle performance when applied to the battery. In Comparative Example 5, no branching treatment is performed and no ether oxygen bonds are grafted, and the performance degradation is more obvious.

[0106] The above disclosures are only a few specific embodiments of the present invention. However, the embodiments of the present invention are not limited thereto. Any changes that can be conceived by those skilled in the art should fall within the scope of protection of the present invention.

Claims

1. An organic-inorganic hybrid composite membrane, characterized in that: The composite membrane includes a base membrane and an organic-inorganic hybrid coating; the organic-inorganic hybrid coating is coated on both sides of the base membrane; The organic-inorganic hybrid coating comprises the following raw materials in parts by mass: 20-30 parts of modified branched polymethyl methacrylate; 10-20 parts of inorganic particles; 3-5 parts of water-based adhesive; 1-2 parts of dispersant; 40-65 parts of solvent; The molecular chain of the modified branched polymethyl methacrylate contains ether oxygen bonds.

2. The organic-inorganic hybrid composite membrane according to claim 1, characterized in that The raw materials of the modified branched polymethyl methacrylate include methyl methacrylate, branching monomer and polyethylene oxide in a molar ratio of 100:(1.6-1.8):(15-20).

3. The organic-inorganic hybrid composite membrane according to claim 2, characterized in that: The branching monomer includes one or more of ethylene glycol dimethacrylate, tripropylene glycol diacrylate, 2-(2-bromoisobutyryloxy)ethyl methacrylate and divinylbenzene.

4. The organic-inorganic hybrid composite membrane according to claim 2, characterized in that The modified branched polymethyl methacrylate is prepared according to the following method: 80-90 wt% of methyl methacrylate, branching monomers and auxiliary agents are added to anisole, stirred and mixed, and reacted for 4-5 hours at 90-95° C. in an argon atmosphere. Then, the remaining amount of methyl methacrylate, polyethylene oxide and catalyst are added, and the reaction is continued at 80-85° C. for 4-6 hours. Finally, the product is washed, filtered and dried.

5. The organic-inorganic hybrid composite membrane according to claim 1, characterized in that: The inorganic particles include one or more of zirconium dioxide, aluminum oxide, silicon dioxide and titanium dioxide.

6. The organic-inorganic hybrid composite membrane according to claim 1, characterized in that: A nanocellulose fiber coating is further provided between one side surface of the base film and the organic-inorganic hybrid coating.

7. The organic-inorganic hybrid composite membrane according to claim 6, characterized in that: The nano-cellulose fiber coating comprises the following raw materials in parts by mass: 20 to 30 parts of nano-cellulose fibers, 10 to 15 parts of chitosan and 40 to 60 parts of adhesive solution.

8. The organic-inorganic hybrid composite membrane according to claim 6, characterized in that: The side of the base film coated with the double-layer coating of nanocellulose fiber coating and organic-inorganic hybrid coating faces the negative electrode; the side of the base film coated with the single-layer coating of organic-inorganic hybrid coating faces the positive electrode.

9. The organic-inorganic hybrid composite membrane according to claim 1, characterized in that: The base film includes any one of a polyethylene porous film, a polypropylene porous film and a polypropylene / polyethylene composite porous film.

10. A method for preparing an organic-inorganic hybrid composite membrane according to any one of claims 1 to 9, characterized in that: The process steps include: S1 weighed the corresponding parts by mass of the raw materials of the nanocellulose fiber coating, stirred and mixed, and coated on one side of the base film surface, after drying to form a nanocellulose fiber coating on one side of the base film to obtain a pretreated base film; S2. A water-based adhesive and a dispersant were added to the solvent, and after stirring to dissolve, modified branched polymethyl methacrylate and inorganic particles were added, and stirring was continued to obtain an organic - inorganic hybrid slurry; S3. Soak the pretreated base membrane in the organic-inorganic hybrid slurry for 5 to 10 minutes, then take it out and dry it to obtain the organic-inorganic hybrid composite membrane.

Images