Composite diaphragm capable of eliminating lithium dendrites, preparation method and lithium battery

Abstract

The invention belongs to the technical field of battery diaphragms, and particularly provides a composite diaphragm capable of eliminating lithium dendrites, a preparation method of the composite diaphragm and a lithium battery. The composite diaphragm capable of eliminating the lithium dendrites comprises a nanometer material interlayer, base membranes are arranged on the upper side and the lower side of the nanometer material coating, and the nanometer material interlayer contains metal oxide nanometer particles and a binding agent. The material of the metal oxide nanoparticles is selected from one or more of nickel oxide, titanium dioxide, zinc oxide, tin oxide, iron oxide and ferroferric oxide, and the particle size D50 of the metal oxide nanoparticles is less than 1 [mu] m. According to the composite diaphragm capable of eliminating the lithium dendrites, on one hand, the mechanical strength of the composite diaphragm is improved through the nanometer material interlayer to play a role of a physical barrier, and on the other hand, the tips of the dendrites are rapidly passivated through the redox reaction of the metal oxides and lithium, chemical elimination is achieved, and the situation that the dendrites pierce the diaphragm is avoided.

Description

Technical Field

[0001] This invention belongs to the field of battery separator technology, and more specifically, relates to a composite separator that can eliminate lithium dendrites and its preparation method, and a lithium battery. Background Technology

[0002] With the increasing demand for high-energy-density energy storage, semi-solid-state lithium batteries have become a research hotspot due to their combination of the high ionic conductivity of liquid batteries and the high safety of solid-state batteries.

[0003] However, lithium dendrites are prone to form during battery cycling, which can lead to separator puncture, internal short circuits, and capacity decay, severely affecting service life and safety.

[0004] In existing technologies, traditional polyolefin separators (such as polyethylene and polypropylene) possess basic mechanical strength and electrolyte wettability, but they can only rely on mechanical properties to block lithium dendrite growth, not eliminate existing lithium dendrites. The resulting dynamic interface mismatch and localized stress concentration are actually detrimental to the long-term stable cycling of lithium batteries.

[0005] Traditional methods enhance mechanical strength by adding ceramic coatings (such as Al2O3 or SiO2) or employing multilayer composite structures (PE / PP / PE). However, improving the puncture resistance and mechanical strength of the separator requires increasing the coating or composite structure thickness, which inevitably leads to a decrease in separator porosity. This, in turn, causes problems such as difficulty in ion migration, deterioration of electrolyte wettability, and increased interfacial impedance. Simultaneously, it increases the overall size and weight of the battery, and reduces its energy density.

[0006] Furthermore, in actual battery operation, there are charge-discharge cycles and heating-cooling cycles. These two cycles cause the separator to expand and contract, leading to a mismatch between the surface coating and the base film, resulting in microcracks. In this situation, lithium dendrites can grow along the direction of the cracks. Therefore, simply increasing the mechanical strength of the separator cannot fundamentally solve the problem of lithium dendrite growth. Unremoved lithium dendrites are very likely to break and form "dead lithium," which, once embedded in the separator pores, causes a double hazard. On the one hand, it blocks the separator pores, reducing effective ion transport channels and increasing the battery's internal resistance; on the other hand, the surface of the dead lithium continues to react with the electrolyte, generating byproducts, causing battery capacity loss and decreased cycle performance.

[0007] In other words, modifying the separator by enhancing its mechanical strength does not fundamentally eliminate lithium dendrites. Even if none of the above occurs, lithium dendrites will continue to grow during battery cycling, retaining the risk of exceeding the mechanical strength of the separator and puncturing it, which is unacceptable for the healthy and stable operation of lithium batteries. Summary of the Invention

[0008] In view of this, the present invention aims to provide a composite separator capable of eliminating lithium dendrites, a preparation method thereof, and a lithium battery.

[0009] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0010] According to a first aspect of the present invention, a composite separator (hereinafter sometimes referred to as a composite separator) capable of eliminating lithium dendrites is provided, comprising an upper base film and a lower base film, wherein a nanomaterial interlayer is formed between the upper base film and the lower base film, the nanomaterial interlayer containing metal oxide nanoparticles and a binder, wherein the metal oxide nanoparticles are selected from one or more of nickel oxide, titanium dioxide, zinc oxide, tin oxide, iron oxide, and iron(II,III) oxide, and the particle size D50 of the metal oxide nanoparticles is less than 1 μm.

[0011] In some embodiments of the present invention, the thickness of the nanomaterial interlayer is 1–5 μm.

[0012] In some embodiments of the present invention, the adhesive is one or more of polyvinyl alcohol, polyacrylic acid, styrene-butadiene rubber, and hydroxymethyl cellulose.

[0013] In some embodiments of the present invention, the binder accounts for 0.5%-15% of the total weight of the nanomaterial interlayer.

[0014] In some embodiments of the present invention, the material of the upper base film is selected from one or more of polypropylene, polyethylene, and polyimide, and the thickness of the base film is 6-12 μm.

[0015] In some embodiments of the present invention, the material of the lower base film is selected from one or more of polypropylene, polyethylene, and polyimide, and the thickness of the base film is 6-12 μm.

[0016] According to a second aspect of the present invention, a method for preparing a composite separator capable of eliminating lithium dendrites is provided, comprising:

[0017] Provide base film;

[0018] A nanomaterial slurry is provided, wherein the nanomaterial slurry contains metal oxide nanoparticles, a binder, and a solvent, wherein the metal oxide nanoparticles are selected from one or more of nickel oxide, titanium dioxide, zinc oxide, tin oxide, iron oxide, and iron(II,III) oxide, and the particle size D50 of the metal oxide nanoparticles is less than 1 μm.

[0019] The nanomaterial slurry is coated on the upper surface of the lower base film to form a nanomaterial coating. Then, the lower surface of the upper base film is covered on the nanomaterial coating, and the film is dried to remove the solvent, thus obtaining the composite membrane.

[0020] In some embodiments of the present invention, the content of the metal oxide nanoparticles in the nanomaterial slurry is 20wt%-45wt%, and the content of the binder is 0.2wt%-3.5wt%.

[0021] In some embodiments of the present invention, the solvent is deionized water, an alcohol solvent, or a mixture of deionized water and an alcohol solvent. The alcohol solvent includes one or more of methanol, ethanol, and isopropanol. The preparation of the nanomaterial slurry includes:

[0022] The metal oxide nanoparticles and binder are added to the solvent, and the nanomaterial slurry is obtained by stirring or ball milling.

[0023] In some embodiments of the present invention, the adhesive is one or more of polyvinyl alcohol, polyacrylic acid, styrene-butadiene rubber, and hydroxymethyl cellulose;

[0024] And / or, the materials of the upper base film and the lower base film are respectively selected from one of polypropylene, polyethylene, and polyimide;

[0025] And / or, the thickness of both the upper and lower base films is 6-12 μm.

[0026] According to a third aspect of the present invention, a lithium battery is provided, wherein the lithium battery includes a composite separator as described in any embodiment of the first aspect of the present invention, or includes a composite separator prepared by the preparation method described in any embodiment of the second aspect of the present invention.

[0027] The above-described technical solution of the present invention has at least one of the following beneficial effects:

[0028] The composite separator capable of eliminating lithium dendrites according to embodiments of the present invention comprises a nanomaterial interlayer (with the particle size of the metal oxide particles being at the nanometer level) sandwiched between two base films. On one hand, the nanomaterial interlayer enhances the mechanical strength of the composite separator, acting as a physical barrier. On the other hand, the redox reaction between these metal oxides and lithium rapidly passivates the dendrite tips, achieving chemical elimination. Furthermore, the double-layer separator design ensures that dendrites can penetrate at most one layer of the separator, reacting with the nanomaterial interlayer and being passivated and eliminated before growing into the other layer. In other words, by combining physical barrier and chemical elimination technologies, the passive defense mode relying solely on physical barriers is overcome, fundamentally solving the problems of dendrite elimination and dead lithium accumulation, providing technical support for the design and development of high-energy-density, high-safety, and long-life lithium batteries.

[0029] In addition, the Li2O generated by the redox reaction can repair the damaged SEI film, form a dense protective layer, greatly reduce the interfacial impedance and improve the stability of the negative electrode. Attached Figure Description

[0030] Figure 1 A schematic diagram of the composite membrane according to the present invention is shown;

[0031] Figure 2 Cycle curves of lithium symmetric batteries assembled using the separators of Example 1, Example 2, and the comparative example are shown.

[0032] Figure 3 Cycle curves of lithium metal half-cells assembled using the separators of Examples 1, 2, and the comparative example are shown. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention are within the scope of protection of the present invention.

[0034] The inventors of this application, through extensive research, discovered that while traditional polyolefin separators improve puncture resistance through ceramic coatings (such as Al2O3) or mechanical reinforcement layers, their essence remains a passive defense mechanism: dendrites continue to grow during cycling, eventually exceeding the separator's mechanical strength threshold. More seriously, broken dendrites form "dead lithium" deposits that accumulate in the separator pores. Experimental data shows that the proportion of dead lithium increases by 0.2-0.5% per cycle, resulting in a battery capacity decay rate of 0.8% / week (capacity retention <80% after 100 cycles).

[0035] Building upon this foundation, the inventors innovatively proposed an active defense system of "chemical reaction elimination-in-situ repair." This involves sandwiching a layer of nanomaterials containing certain metal oxide particles and a binder (the metal oxide particles have a nanometer-scale diameter, preferably D50 < 500 nm) between a bilayer base film such as a polyolefin film. Utilizing the redox reaction between these metal oxides and lithium (e.g., ZnO + 2Li → Li₂O + Zn), this reaction rapidly passivates dendrite tips, achieving chemical elimination and preventing dendrites from piercing the separator. Experiments have confirmed that while this reaction rapidly passivates dendrite tips, the generated Li₂O can also repair the damaged SEI film, forming a dense protective layer that significantly reduces interfacial impedance and improves negative electrode stability. This mechanism breaks through the passive defense mode that relies solely on physical barriers, fundamentally solving the problems of dendrite elimination and dead lithium accumulation, providing technical support for the design and development of high-energy-density, high-safety, and long-life lithium batteries.

[0036] The composite diaphragm and its preparation method according to embodiments of the present invention are described in detail below.

[0037] The composite separator according to embodiments of the present invention, such as Figure 1 As shown, it includes a nanomaterial interlayer 100 and a lower base film 200 and an upper base film 300 on the upper and lower sides of the interlayer.

[0038] The nanomaterial interlayer 100 contains metal oxide nanoparticles and a binder. The metal oxide nanoparticles can be selected from one or more of nickel oxide, titanium dioxide, zinc oxide, tin oxide, iron oxide, and iron(II,III) oxide.

[0039] Metal oxides such as nickel oxide, titanium dioxide, zinc oxide, tin oxide, iron oxide, and magnetite (Fe3O4) possess high mechanical strength. When coated between the lower and upper base films 200 and 300, they not only enhance the mechanical strength of the composite separator but also reduce its thermal shrinkage rate due to their significantly lower rate compared to the lower and upper base films 200 and 300. This physically inhibits the growth of lithium dendrites. Simultaneously, these metal oxides can undergo redox reactions with Li dendrites, chemically consuming them. In other words, the composite separator of this invention, when applied to lithium batteries, can prevent lithium dendrites from connecting to the positive and negative electrodes through a synergistic effect of physical barrier and chemical reaction, eliminating the generated lithium dendrites and improving the safety and cycle performance of the lithium battery.

[0040] The particle size D50 of the metal oxide nanoparticles is less than 1 μm, preferably between 50 nm and 500 nm. If the particle size of the metal oxide nanoparticles is too large, their specific surface area will decrease, which will be detrimental to the reaction with lithium dendrites; if the particle size is too small, on the one hand, they are prone to agglomeration, resulting in uneven distribution, and on the other hand, the cost will be high.

[0041] In some embodiments of the present invention, the thickness of the nanomaterial interlayer 100 is 1–5 μm. If the nanomaterial interlayer 100 is too thin, it is detrimental to improving the overall strength of the composite separator and insufficient to react fully with lithium dendrites; if it is too thick, it is detrimental to battery miniaturization. It should be noted that the present invention is not limited to the upper base film 300 and the lower base film 200 on both sides of the nanomaterial interlayer 100 having the same thickness and material. That is, the materials used for the upper base film 300 and the lower base film 200 can be the same or different, and their thicknesses can be the same or different.

[0042] In some embodiments of the present invention, the binder may be one or more of polyvinyl alcohol, polyacrylic acid, styrene-butadiene rubber, and hydroxymethyl cellulose. The binder fills the gaps between the metal oxide nanoparticles, firmly bonding them to the upper surface of the lower base film 200 and the lower surface of the upper base film 300, thereby improving the service life of the composite membrane. Furthermore, these binders themselves also play a certain dispersing role by adsorbing onto the surface of the metal oxide nanoparticles.

[0043] In some embodiments of the present invention, the binder accounts for 0.5%-15% of the total weight of the nanomaterial coating. If the proportion of binder is too low, it can easily cause problems such as uneven coating thickness and poor adhesion. If the proportion of binder is too high, there will be insufficient metal oxide nanoparticles, which may not be enough to chemically react with the dendrites, and the membrane strength will also be reduced, easily leading to a shorter battery life. Preferably, the binder accounts for 5%-12% of the total weight of the nanomaterial coating.

[0044] In some embodiments of the present invention, the materials of the lower base film 200 and the upper base film 300 are respectively selected from polypropylene, polyethylene, and polyimide, and the thickness of the base film is 6-12 μm. It should be noted that the materials of the lower base film 200 and the upper base film 300 can be the same or different, and their thicknesses can be the same or different, which can be selected according to the actual use environment, etc.

[0045] The composite membrane of the present invention introduces a three-in-one active protection mechanism of "chemical elimination - dynamic passivation - in-situ repair". Through the solid-phase redox reaction between metal oxide nanoparticles and lithium (such as ZnO + 2Li → Li2O + Zn), targeted elimination is achieved at the critical penetration stage of dendrite tips, which greatly reduces the risk of dendrite penetration compared with traditional physical blocking methods.

[0046] Furthermore, the metal oxide nanoparticles sandwiched between the two base films have their particle size limited to the nanometer level. This ensures sufficient porosity after the membrane is composited, while leveraging the large specific surface area of ​​the nanoparticles enhances their adsorption capacity for the electrolyte, significantly improving the electrolyte wetting rate and absorption rate. Test results show that the composite membrane not only eliminates lithium dendrites and increases the battery's safe cycle life, but also reduces interfacial impedance and improves the membrane's electrochemical performance.

[0047] The preparation method of the composite separator of the present invention will be further described in detail below through specific embodiments.

[0048] The method for preparing a composite separator according to an embodiment of the present invention includes:

[0049] A base film is provided, the base film comprising an upper base film and a lower base film;

[0050] A nanomaterial slurry is provided, the nanomaterial slurry containing metal oxide nanoparticles, a binder, and a solvent, wherein the metal oxide nanoparticles are selected from one or more of alumina, zinc oxide, and tin oxide, and the particle size D50 of the metal oxide nanoparticles is less than 1 μm.

[0051] The nanomaterial slurry is coated onto the upper surface of the lower base film to form a nanomaterial coating.

[0052] The upper base film is applied over the nanomaterial coating and dried to remove the solvent, thus obtaining the composite membrane.

[0053] In other words, by coating the upper surface of the lower base film with a nanomaterial slurry containing metal oxide nanoparticles such as nickel oxide, titanium dioxide, zinc oxide, tin oxide, iron oxide, and iron(II,III) oxide, binder, and solvent, and then covering it with the upper base film, a composite membrane with a nanomaterial interlayer can be formed after the solvent evaporates.

[0054] In some embodiments of the present invention, the solvent may be, for example, deionized water, an alcohol solvent, or a mixture of deionized water and an alcohol solvent. The preparation of the nanomaterial slurry may, for example, include:

[0055] Metal oxide nanoparticles and binders are added to a solvent, and a nanomaterial slurry is obtained by stirring or ball milling.

[0056] There is no particular limitation on the amount of solvent added. In some embodiments of the present invention, the content of metal oxide nanoparticles in the nanomaterial slurry is 20wt%-45wt%, and the content of the binder is 0.2wt%-3.5wt%. If the solid content is too low, the slurry will be too thin, making it difficult to form a dense coating after coating and solvent evaporation. If the solid content is too high, the metal oxide nanoparticles may agglomerate, resulting in an uneven coating and unstable performance.

[0057] For information on adhesives, base membrane materials, and base membrane thickness, please refer to the above description of composite separators; further details will not be provided here.

[0058] The composite diaphragm of the present invention can be prepared by simply coating and stacking the base membrane, and the coating process has been optimized and simplified many times, resulting in low equipment modification costs for production units.

[0059] In addition, the use of water-based adhesives reduces the cost of solvent use and the harm of organic solvents to the environment and workers, thus meeting environmental protection requirements.

[0060] The composite separator prepared as described above can be applied to lithium batteries. As mentioned above, when the composite separator of the present invention is applied to a lithium battery, it can prevent lithium dendrites from connecting to the positive and negative electrodes of the battery through the synergistic effect of physical barrier and chemical reaction consumption, and eliminate the generated lithium dendrites, thereby improving the safety and cycle performance of the semi-solid-state battery.

[0061] The composite separator and its preparation method, as well as the lithium battery according to the present invention, will be further described in detail below with reference to specific embodiments.

[0062] It should be noted that in the following examples, both the upper and lower base films are made of polyethylene, and only deionized water is used as the solvent, in order to eliminate the influence of different base films and solvents. The composite separator of the present invention is not limited thereto.

[0063] Example 1

[0064] 1. Materials

[0065] Base film: The upper and lower base films are the same, both being 6μm thick polyethylene.

[0066] Metal oxide nanoparticles: Titanium dioxide particles, D50 = 200 nm

[0067] Adhesive: Polyvinyl alcohol

[0068] Solvent: Deionized water

[0069] 2. Preparation

[0070] Preparation of slurry: Add 20 parts by weight of titanium dioxide particles and 3 parts by weight of polyvinyl alcohol to 77 parts by weight of deionized water and disperse for 6 hours to obtain a uniform suspension.

[0071] Coating: The slurry is coated onto the lower base film with a coating thickness of 4μm. Then, the upper base film is placed on top of the lower base film coated with slurry. After vacuum drying at 60℃, a composite membrane is obtained.

[0072] Example 2

[0073] 1. Materials

[0074] Base film: The upper and lower base films are the same, both being 9μm thick polyethylene.

[0075] Metal oxide nanoparticles: Iron(III) oxide particles, D50 = 200 nm; Zinc oxide particles, D50 = 200 nm; Tin oxide particles, D50 = 200 nm

[0076] Adhesive: Polyvinyl alcohol

[0077] Solvent: Deionized water

[0078] 2. Preparation

[0079] Preparation of slurry: Add 15 parts by weight of iron oxide particles, 15 parts by weight of zinc oxide particles, 15 parts by weight of tin oxide particles and 3 parts by weight of polyvinyl alcohol to 52 parts by weight of deionized water and disperse for 6 hours to obtain a uniform suspension.

[0080] Coating: The above slurry is coated onto the base film with a coating thickness of 4μm. The upper base film is then placed on top of the lower base film coated with the slurry. After vacuum drying at 60℃, a composite separator is obtained.

[0081] Comparative Example

[0082] 1. Materials

[0083] Base film: 9μm thick polyethylene

[0084] Oxide nanoparticles: Alumina particles, D50 = 200 nm

[0085] Adhesive: Polyvinyl alcohol

[0086] Solvent: Deionized water

[0087] 2. Preparation

[0088] Preparation of slurry: Add 20 parts by weight of alumina particles and 3 parts by weight of polyvinyl alcohol to 77 parts by weight of deionized water and disperse for 6 hours to obtain a uniform suspension.

[0089] Coating: The slurry is coated onto the base film with a coating thickness of 4μm. After vacuum drying at 60℃, a composite membrane is obtained.

[0090] Electrochemical performance testing

[0091] Using the separators obtained in Examples 1, 2, and the comparative examples above, batteries were prepared using the same methods and configurations, and their performance was evaluated.

[0092] 1. Assembly and cycle testing of lithium-ion symmetric batteries

[0093] The separators obtained in Examples 1, 2, and the comparative example were cut into 16mm diameter discs, each sandwiched between two 12mm diameter lithium metal discs, and 70μL of electrolyte was added. The electrolyte composition was EC, DEC, EMC in a volume ratio of 1:1:1, and 1M lithium hexafluorophosphate. The above system was placed in a battery case, sealed, and assembled into a lithium symmetric battery.

[0094] The above-mentioned lithium symmetric battery was tested at a capacity of 0.5 mAh cm⁻¹. -2 Cycling at a certain current density yields a cycling curve. Figure 2The cycling curves of lithium symmetric batteries assembled from the separators of Examples 1, 2, and the comparative example are shown. It can be seen that the separator obtained in the comparative example 1 was punctured by lithium dendrites after 315 hours of cycling, resulting in a short circuit. In contrast, the separators of Examples 1 and 2 can be cycled stably for more than 500 hours, and the overpotential is much smaller than that of the comparative example.

[0095] 2. Assembly and Cycle Testing of Lithium Metal Half-Batteries

[0096] The separators obtained in Examples 1, 2, and the comparative example were cut into circular pieces with a diameter of 16 mm. Using lithium iron phosphate as the positive electrode and lithium metal as the negative electrode, they were assembled with the above separators to form a lithium metal half-cell, and 70 μL of electrolyte was added. The electrolyte composition was EC, DEC, EMC in a volume ratio of 1:1:1, and 1M lithium hexafluorophosphate was added. The battery was placed in a battery case, sealed, and cycled at a rate of 0.5C within a range of 2.5-3.8V. Figure 3 The cycling curves of lithium metal half-cells assembled with the separators of Examples 1, 2 and the comparative example are shown. It can be seen that the capacity of the comparative example decreases significantly after 160 cycles, and the capacity retention rate is only 23.5% after 300 cycles. In contrast, the capacity retention rates of Examples 1 and 2 after 300 cycles are 54.5% and 70.0%, respectively.

[0097] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A composite separator capable of eliminating lithium dendrite, characterized in that, The composite diaphragm comprises an upper base film and a lower base film, and a nanomaterial interlayer is interposed between the upper base film and the lower base film, the nanomaterial interlayer contains metal oxide nanoparticles and a binder, the material of the metal oxide nanoparticles is selected from one or more of nickel oxide, titanium dioxide, zinc oxide, tin oxide, iron oxide and magnetite, and the particle size D50 of the metal oxide nanoparticles is less than 1 μm.

2. The composite separator of claim 1, wherein The thickness of the nanomaterial interlayer is 1-5 μm.

3. The composite separator of claim 1, wherein The binder is one or more of polyvinyl alcohol, polyacrylic acid, butadiene-styrene rubber and hydroxymethyl cellulose.

4. The composite separator of claim 1, wherein The binder accounts for 0.5%-15% of the total weight of the nanomaterial interlayer.

5. The composite separator of claim 1, wherein The material of the upper base film is selected from one of polypropylene, polyethylene and polyimide, and the thickness of the base film is 6-12 μm.

6. The composite separator of claim 1, wherein The material of the lower base film is selected from one of polypropylene, polyethylene and polyimide, and the thickness of the base film is 6-12 μm.

7. A method of preparing a composite separator that can eliminate lithium dendrite, characterized by, The composite diaphragm comprises an upper base film and a lower base film, and a nanomaterial interlayer is interposed between the upper base film and the lower base film, the nanomaterial interlayer contains metal oxide nanoparticles and a binder, the material of the metal oxide nanoparticles is selected from one or more of nickel oxide, titanium dioxide, zinc oxide, tin oxide, iron oxide and magnetite, and the particle size D50 of the metal oxide nanoparticles is less than 1 μm. The thickness of the nanomaterial interlayer is 1-5 μm. The binder is one or more of polyvinyl alcohol, polyacrylic acid, butadiene-styrene rubber and hydroxymethyl cellulose. The binder accounts for 0.5%-15% of the total weight of the nanomaterial interlayer. The material of the upper base film is selected from one of polypropylene, polyethylene and polyimide, and the thickness of the base film is 6-12 μm.

8. The method of claim 7, wherein the composite separator is prepared by a method comprising: The material of the lower base film is selected from one of polypropylene, polyethylene and polyimide, and the thickness of the base film is 6-12 μm.

9. The method of claim 7, wherein the composite separator is prepared by a method comprising: The composite diaphragm comprises an upper base film and a lower base film, and a nanomaterial interlayer is interposed between the upper base film and the lower base film, the nanomaterial interlayer contains metal oxide nanoparticles and a binder, the material of the metal oxide nanoparticles is selected from one or more of nickel oxide, titanium dioxide, zinc oxide, tin oxide, iron oxide and magnetite, and the particle size D50 of the metal oxide nanoparticles is less than 1 μm. The thickness of the nanomaterial interlayer is 1-5 μm. The binder is one or more of polyvinyl alcohol, polyacrylic acid, butadiene-styrene rubber and hydroxymethyl cellulose. The binder accounts for 0.5%-15% of the total weight of the nanomaterial interlayer.

10. A lithium battery, characterized by, The material of the upper base film is selected from one of polypropylene, polyethylene and polyimide, and the thickness of the base film is 6-12 μm. The material of the lower base film is selected from one of polypropylene, polyethylene and polyimide, and the thickness of the base film is 6-12 μm. The composite diaphragm comprises an upper base film and a lower base film, and a nanomaterial interlayer is interposed between the upper base film and the lower base film, the nanomaterial interlayer contains metal oxide nanoparticles and a binder, the material of the metal oxide nanoparticles is selected from one or more of nickel oxide, titanium dioxide, zinc oxide, tin oxide, iron oxide and magnetite, and the particle size D50 of the metal oxide nanoparticles is less than 1 μm. The thickness of the nanomaterial interlayer is 1-5 μm. The binder is one or more of polyvinyl alcohol, polyacrylic acid, butadiene-styrene rubber and hydroxymethyl cellulose. The binder accounts for 0.5%-15% of the total weight of the nanomaterial interlayer. The material of the upper base film is selected from one of polypropylene, polyethylene and polyimide, and the thickness of the base film is 6-12 μm. The material of the lower base film is selected from one of polypropylene, polyethylene and polyimide, and the thickness of the base film is 6-12 μm. The composite diaphragm comprises an upper base film and a lower base film, and a nanomaterial interlayer is interposed between the upper base film and the lower base film, the nanomaterial interlayer contains metal oxide nanoparticles and a binder, the material of the metal oxide nanoparticles is selected from one or more of nickel oxide, titanium dioxide, zinc oxide, tin oxide, iron oxide and magnetite, and the particle size D50 of the metal oxide nanoparticles is less than 1 μm. The thickness of the nanomaterial interlayer is 1-5 μm. The binder is one or more of polyvinyl alcohol, polyacrylic acid, butadiene-styrene rubber and hydroxymethyl cellulose. The binder accounts for 0.5%-15% of the total weight of the nanomaterial interlayer. The material of the upper base film is selected from one of polypropylene, polyethylene and polyimide, and the thickness of the base film is 6-12 μm. The material of the lower base film is selected from one of polypropylene, polyethylene and polyimide, and the thickness of the base film is 6-12 μm. The lithium battery comprises the composite diaphragm of any one of claims 1-6 or the composite diaphragm prepared by the preparation method of any one of claims 7-9.

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