A two-dimensional oxide ultra-thin coating for lithium metal battery separator that can be synthesized on a large scale, and its preparation method and application

Abstract

The present invention discloses a two-dimensional oxide ultra-thin coating for lithium metal battery diaphragms that can be synthesized on a large scale, a preparation method and an application thereof, and belongs to the technical field of commercial diaphragm modification. The present invention uses two-dimensional oxide, a binder and an organic solvent as components of the coating and sprays them on the surface of the diaphragm to modify the diaphragm. The diaphragm can reduce the contact angle and heat shrinkage of the diaphragm, while improving the ionic conductivity.

Description

Technical Field

[0001] The present invention belongs to the technical field of commercial diaphragm modification, and in particular relates to a two-dimensional oxide ultra-thin coating for lithium metal battery diaphragms that can be synthesized on a large scale, and a preparation method and application thereof. Background Art

[0002] As a vital component of lithium metal batteries, the physical and electrochemical properties of the separator are closely related to the cycle life, interface structure, battery performance and safety of lithium metal batteries.

[0003] Currently, commercial polyolefin separators are often prepared using a dry process. The dry separator process is a method for preparing polymer films. The polymer, additives and other raw materials are mixed to form a uniform melt, and a lamellar structure is formed under tensile stress during extrusion. After heat treatment, a hard and elastic polymer film is obtained; then, it is stretched at a certain temperature to form slit-shaped micropores, and a microporous membrane is obtained after heat setting. However, since the process cannot accurately control the size of the pore size, when preparing commercial separators made of materials such as polypropylene (PP) and polyethylene (PE), the pore size after stretching may become larger, thereby affecting the battery performance. In addition, polypropylene (PP) and polyethylene (PE), as non-polar polymer materials, have low melting points and poor electrolyte wettability, which leads to an increase in the internal resistance of the battery. At the same time, the low porosity of the material will lead to lower ionic conductivity, which seriously limits the high-rate performance of the battery and makes it difficult to meet the requirements of the battery for fast charging and discharging with large currents.

[0004] In order to solve these problems, researchers mainly use modified treatments on polyolefin separators, including surface coating and chemical grafting. The chemical grafting method gives polymers new properties by introducing different functional groups or branches on the polymer chain. The chemical grafting method can be carried out by radiation-induced grafting, free radical-induced grafting, ion-induced grafting, etc. These methods can improve the surface properties, compatibility, mechanical properties, chemical stability, etc. of the polymer, thereby expanding the application of polymers in various fields. However, the chemical grafting method often has a complex manufacturing process, high manufacturing cost, and is difficult to mass produce. The surface coating method can improve the performance of the separator by covering a thin film on the surface of the separator or adding specific materials. The use of inorganic materials as surface coatings for modification is the most commonly used commercial separator coating method on the market, and its market share reaches nearly 90% of all coating methods. Because inorganic materials can improve the thermal stability and wettability of the separator, and have the advantages of low price and easy access, researchers often use surface coating methods to modify polyolefin separators. However, inorganic material surface coatings often reduce the porosity of the membrane and cannot ensure the integrity of the structure. In addition, if the surface coating is too thick, it is easy to fall off, affecting the cycle stability of the battery and cannot meet the growing usage needs.

[0005] Therefore, how to design a technology for large-scale synthesis of ultra-thin two-dimensional oxide coatings for lithium metal battery separators to solve the above problems is the main challenge currently faced. Summary of the invention

[0006] In view of the above technical problems, the present invention proposes a two-dimensional oxide ultra-thin coating for lithium metal battery separators that can be synthesized on a large scale, and a preparation method and application thereof. The method can synthesize a two-dimensional oxide ultra-thin coating on a large scale to modify lithium metal battery separators.

[0007] To achieve the above object, the present invention provides the following technical solutions:

[0008] A two-dimensional oxide ultra-thin coating for lithium metal battery separators which can be synthesized on a large scale comprises the following components in parts by mass: 10-40 parts of two-dimensional oxide, 0.5-2 parts of binder and 250-800 parts of organic solvent.

[0009] Furthermore, the two-dimensional oxide is titanium iron oxide nanosheet or titanium dioxide nanosheet.

[0010] Furthermore, the binder is polyvinylidene fluoride.

[0011] Furthermore, the organic solvent is acetone.

[0012] The present invention also provides a method for preparing a two-dimensional oxide ultra-thin coating for lithium metal battery separators that can be synthesized on a large scale, comprising the following steps: mixing the two-dimensional oxide, a binder and an organic solvent according to a proportion, and stirring evenly to obtain a mixed solution; spraying the mixed solution on the surface of the lithium metal battery separator and heating the separator to obtain a coating.

[0013] Furthermore, the stirring parameters are: temperature 20-40°C, rotation speed 300-500rpm, and time 1-3h.

[0014] Furthermore, the parameters in the spraying process are: heating temperature 60-70°C, pressure 0.3-0.4MPa, and nozzle diameter 0.3mm.

[0015] Furthermore, the thickness of the lithium metal battery separator is 24-26 um, and the thickness of the coating is 0.5-2 um.

[0016] The present invention also provides a two-dimensional oxide ultra-thin coating for lithium metal battery separators that can be synthesized on a large scale and its application in lithium ion battery separators.

[0017] The present invention provides a technology for large-scale synthesis of a two-dimensional oxide ultra-thin coating for lithium metal battery separators. The main principle is to use a spraying device, control the gas flow rate by adjusting the gas pressure, and control the spray size by selecting nozzles of different diameters, and evenly spray a uniform mixed solution formed by dissolving the two-dimensional oxide and a polymer adhesive in an organic solvent on the surface of the lithium metal battery separator to form a surface coating. The present invention utilizes the characteristics of the organic solvent having a low boiling point and being volatile, and heats the lithium metal battery separator during the spraying process, so that the mixed solution quickly evaporates on the surface of the lithium metal battery separator to form a surface coating, and reduces the reduction in the separator porosity by reducing the penetration of the solution into the pores of the lithium metal battery separator.

[0018] Compared with the prior art, the present invention has the following advantages and technical effects:

[0019] The present invention uses two-dimensional oxide as the coating material, which has the advantages of small unit size, large specific surface area, and higher surface activity compared to one-dimensional oxide materials. These characteristics make the thickness of the membrane surface coating of the present invention have better size adjustability, excellent electrolyte wettability, and the internal structure of the coating provides more landing sites and ordered channels for lithium ion transmission. The use of spraying method to prepare the membrane surface coating also lays a technical foundation for subsequent large-scale synthesis. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The drawings constituting a part of the present application are used to provide a further understanding of the present application. The illustrative embodiments and descriptions of the present application are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0021] Figure 1 Graph showing the cycling test results of lithium metal full batteries for Example 1 and the control group. DETAILED DESCRIPTION

[0022] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0023] It should be understood that the terms described in the present invention are only for describing special embodiments and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. Each smaller range between the intermediate value in any stated value or stated range and any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0024] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0025] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to those skilled in the art. The present invention description and examples are exemplary only.

[0026] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0027] A two-dimensional oxide ultra-thin coating for lithium metal battery separators which can be synthesized on a large scale comprises the following components in parts by mass: 10-40 parts of two-dimensional oxide, 0.5-2 parts of binder and 250-800 parts of organic solvent.

[0028] In the following embodiments of the present invention, the two-dimensional oxide is titanium iron oxide nanosheet or titanium dioxide nanosheet, the binder is polyvinylidene fluoride, and the organic solvent is acetone.

[0029] The method for preparing a two-dimensional oxide ultra-thin coating for a lithium metal battery separator that can be synthesized on a large scale comprises the following steps: mixing a two-dimensional oxide, a binder and an organic solvent according to a proportion, and stirring on a magnetic stirrer for 1-3 hours to obtain a uniform mixed solution; using a spraying device to uniformly spray the mixed solution on the surface of the lithium metal battery separator and heating the separator to prepare a coating on the surface of the lithium metal battery separator, thereby achieving the purpose of modifying the surface coating of the lithium metal battery separator.

[0030] In the following embodiments of the present invention, the stirring parameters are: temperature 20-40°C (preferably 25°C), rotation speed 300-500rpm (preferably 350rpm), time 1-3h (preferably 1h). The parameters in the spraying process are: heating temperature 60-70°C (preferably 65°C), gas pressure 0.3-0.4MPa (preferably 0.3MPa), nozzle diameter 0.3mm. The thickness of the lithium metal battery separator is 24-26um, preferably 25um, and the thickness of the coating is 0.5-2um.

[0031] The spraying on the surface of the lithium metal battery separator mentioned in the present invention means that both sides of the separator need to be sprayed, that is, both sides have coatings.

[0032] The two-dimensional oxide ultra-thin coating for the lithium metal battery separator that can be synthesized on a large scale can be used as a separator for a lithium metal battery using lithium metal as a negative electrode.

[0033] The "room temperature" in the present invention refers to 20-30°C unless otherwise specified.

[0034] The "parts" described in the present invention, unless otherwise specified, refer to parts by mass.

[0035] The titanium iron oxide nanosheets in the present invention are homemade, and the other raw materials are purchased from the market.

[0036] The preparation method of the titanium iron oxide nanosheet is as follows: synthesizing the precursor K 0.4 Ti 0.67 Fe 0.3 Li 0.02 O2. The raw materials were weighed and mixed in a molar ratio of K2CO3, TiO2, Fe2O3 and Li2CO3 of 0.2:0.67:0.15:0.01, and the mixture was ground in a mortar for 30 minutes, and then heated in a muffle furnace at 900°C for 1 hour in an air environment to decarbonize the mixture. The cooled powder was ground for 30 minutes, and then heated in air at 1000°C for 24 hours and cooled. The weight of the final product was weighed. The main H was synthesized through the protonation process. 0.42 Ti 0.67 Fe 0.3 O2. The precursor K 0.4 Ti 0.67 Fe 0.3 Li 0.02 O2 dissolved in 1 mol L -1 The mixture was stirred for 7 days. Most of the H 0.42 Ti 0.67 Fe 0.3 O2 and washed repeatedly with deionized water. Finally, large pieces of H 0.42 Ti 0.67 Fe 0.3 Before using the two-dimensional oxide, it is necessary to wash it repeatedly with deionized water to remove residual TBAOH.

[0037] The technical solution of the present invention is further illustrated by the following embodiments.

[0038] Example 1

[0039] Preparation of ultrathin two-dimensional oxide coatings for lithium metal battery separators that can be synthesized on a large scale:

[0040] 1) titanium iron oxide nanosheets, polyvinylidene fluoride and acetone were mixed in a mass ratio of 20:1:785, and stirred on a magnetic stirrer at a speed of 350 rpm and a heating temperature of 25°C for 1 h to obtain a uniform mixed solution;

[0041] 2) Use a spraying device to evenly spray 4 mL of the mixed solution on the upper and lower surfaces of the lithium metal battery separator (made of polypropylene) and heat the separator to prepare a coating on the surface of the lithium metal battery separator. The parameters during the spraying process are: heating temperature 65°C, gas pressure 0.3 MPa, nozzle diameter 0.3 mm. The thickness of the lithium metal battery separator is 25 um, and the total thickness of the obtained coating is 1.41 um (when the coating is sprayed on both the upper and lower surfaces, the thickness refers to the sum of the coating thickness on the upper and lower surfaces, the same below).

[0042] Example 2

[0043] Preparation of ultrathin two-dimensional oxide coatings for lithium metal battery separators that can be synthesized on a large scale:

[0044] 1) titanium iron oxide nanosheets, polyvinylidene fluoride and acetone were mixed in a mass ratio of 15:0.8:523, and stirred on a magnetic stirrer at a speed of 350 rpm and a heating temperature of 25° C. for 1 h to obtain a uniform mixed solution;

[0045] 2) Use a spraying device to evenly spray 2 mL of the mixed solution on the upper and lower surfaces of a lithium metal battery separator (made of polypropylene) and heat the separator to prepare a coating on the surface of the lithium metal battery separator. The parameters during the spraying process are: heating temperature 65°C, gas pressure 0.3 MPa, and nozzle diameter 0.3 mm. The thickness of the lithium metal battery separator is 25 um, and the total thickness of the obtained coating is 0.69 um.

[0046] Example 3

[0047] Preparation of ultrathin two-dimensional oxide coatings for lithium metal battery separators that can be synthesized on a large scale:

[0048] 1) titanium iron oxide nanosheets, polyvinylidene fluoride and acetone were mixed in a mass ratio of 40:1.33:262, and stirred on a magnetic stirrer at a speed of 350 rpm and a heating temperature of 25° C. for 1 h to obtain a uniform mixed solution;

[0049] 2) Use a spraying device to evenly spray 4 mL of the mixed solution on the upper and lower surfaces of a lithium metal battery separator (made of polypropylene) and heat the separator to prepare a coating on the surface of the lithium metal battery separator. The parameters during the spraying process are: heating temperature 65°C, gas pressure 0.3 MPa, nozzle diameter 0.3 mm. The thickness of the lithium metal battery separator is 25 um, and the thickness of the resulting coating is 1.5 um.

[0050] Example 4

[0051] Preparation of ultrathin two-dimensional oxide coatings for lithium metal battery separators that can be synthesized on a large scale:

[0052] 1) titanium dioxide nanosheets, polyvinylidene fluoride and acetone were mixed in a mass ratio of 30:1.5:393, and stirred on a magnetic stirrer at a speed of 350 rpm and a heating temperature of 25°C for 1 h to obtain a uniform mixed solution;

[0053] 2) Use a spraying device to evenly spray 4 mL of the mixed solution on the upper and lower surfaces of a lithium metal battery separator (made of polypropylene) and heat the separator to prepare a coating on the surface of the lithium metal battery separator. The parameters during the spraying process are: heating temperature 65°C, gas pressure 0.3 MPa, nozzle diameter 0.3 mm. The thickness of the lithium metal battery separator is 25 um, and the thickness of the resulting coating is 1.44 um.

[0054] Example 5

[0055] The same as Example 1, except that only 2 mL of the mixed solution is evenly sprayed on a single surface of the lithium metal battery separator (made of polypropylene), and the specific steps are to use a spraying device to evenly spray 2 mL of the mixed solution on the upper surface of the lithium metal battery separator (made of polypropylene) and heat the separator to prepare a coating on the surface of the lithium metal battery separator. The parameters during the spraying process are: heating temperature 65°C, gas pressure 0.3MPa, nozzle diameter 0.3mm. The thickness of the lithium metal battery separator is 25um, and the total thickness of the obtained coating is 0.71um.

[0056] Control group

[0057] Lithium metal battery separator, made of polypropylene.

[0058] Comparative Example 1

[0059] The same as Example 1, except that the titanium iron oxide nanosheets, polyvinylidene fluoride and acetone are mixed in a mass ratio of 20:3:785. The thickness of the obtained coating is 1.83 um.

[0060] Comparative Example 2

[0061] Same as Example 1, except that the volume of the mixed solution added for spraying is 3 mL. Specific step 2) is to use a spraying device to evenly spray 6 mL of the mixed solution on the upper and lower surfaces of the lithium metal battery separator (made of polypropylene) and heat the separator to prepare a coating on the surface of the lithium metal battery separator. The parameters during the spraying process are: heating temperature 65°C, gas pressure 0.3MPa, nozzle diameter 0.3mm. The thickness of the lithium metal battery separator is 25um, and the total thickness of the obtained coating is 2.1um.

[0062] Comparative Example 3

[0063] Same as Example 1, except that the mass of the organic solvent acetone (boiling point 56° C. at room temperature) is replaced by NMP (N-methylpyrrolidone, boiling point 202° C. at room temperature).

[0064] The performance tests of the samples obtained from Examples 1-5, Comparative Examples 1-3 and the control group were performed as follows:

[0065] 1. Electrolyte contact angle: refer to the provisions of GB / T 30693-2014, and use the electrolyte formula: 1.0 mol / L lithium hexafluorophosphate, the solvent system is ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate, mixed in a volume ratio of 1:1:1.

[0066] 2. Thermal shrinkage:

[0067] 1) Required test equipment: a) high temperature box furnace, accuracy ±1℃; b) aluminum foil, thickness 1mm; c) brown high temperature resistant tape, thickness 50um; d) vernier caliper, accuracy 0.02mm.

[0068] 2) Sample: Cut three square diaphragms of 50mm×50mm in the longitudinal direction of the diaphragm. When cutting the diaphragm, one edge should be parallel to the longitudinal edge of the diaphragm, and the maximum deviation angle should not exceed 5°. Make longitudinal and transverse markings.

[0069] 3) Test steps: a) Apply two layers of brown high-temperature resistant tape around the aluminum foil to ensure it is flat; b) Cut the diaphragm into a square and use a vernier caliper to measure the longitudinal and transverse lengths, marking them as x and y respectively; c) Place the cut diaphragm sample flat in the center of the aluminum foil and stick it with another piece of aluminum foil so that the diaphragm is between the two pieces of aluminum foil; d) Control the temperature of the high-temperature box furnace to 140±1℃, put the aluminum foil with the sample in the middle of the high-temperature box furnace, close the high-temperature box furnace, and start calculating the time. The baking time is 1h±2min; e) After heating, take out the diaphragm, and after the diaphragm returns to room temperature, measure the longitudinal and transverse lengths again, and calculate the thermal shrinkage of the diaphragm according to the following formula.

[0070]

[0071] Among them, S0 is the original diaphragm area, and S1 is the diaphragm area after heat treatment.

[0072] 3. Ionic conductivity:

[0073] Assemble the stainless steel sheet symmetrical battery (SS / Separator / SS) to obtain the battery body resistance Rb, the test frequency range is 0.1-10 6 Hz, 10mv AC sinusoidal disturbance voltage, and then the ionic conductivity σ is calculated according to the following formula. The electrolyte formula used is: 1.0mol / L lithium hexafluorophosphate, and the solvent system is ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate, mixed in a volume ratio of 1:1:1.

[0074]

[0075] Where, d is the thickness of the diaphragm, R b is the volume resistance, and S is the effective area of ​​the diaphragm.

[0076] Table 1

[0077]

[0078] The test results show that the contact angle of the electrolyte of the lithium metal battery separator modified by the ultra-thin two-dimensional oxide coating prepared by the present invention is significantly reduced compared with the original separator. At the same time, the results of the 140℃ / 1h thermal shrinkage test show that the lithium metal battery separator modified by the ultra-thin two-dimensional oxide coating is significantly improved compared with the original separator, and the ion conductivity is also significantly improved.

[0079] Conventional materials spraying on both sides may cause the pores of the original diaphragm to be blocked, resulting in a decrease in performance. However, from the comparison between Example 1 and Example 5, it can be found that Example 1 and Example 5 have equally excellent performance in terms of contact angle and ionic conductivity, which shows that the coating sprayed on both sides does not block the pores of the original diaphragm and thus cause a decrease in performance. At the same time, the coating structure on both sides can help the diaphragm better resist thermal deformation and improve the safety of the diaphragm.

[0080] Compared with Example 1, the ability of Comparative Example 1 to resist thermal deformation is enhanced due to the increase in the adhesive ratio, but too much adhesive will cause the pores of the original diaphragm to be blocked, thereby reducing the contact angle and ionic conductivity.

[0081] Compared with Example 1, the volume of the sprayed mixed solution is increased in Comparative Example 2, resulting in an increase in the coating thickness. Too large a coating thickness will affect the adhesion stability between the coating and the original separator, thereby affecting the contact angle and ionic conductivity performance, but will also enhance the ability to resist thermal deformation.

[0082] Compared with Example 1, Comparative Example 3 replaces the organic solvent acetone with NMP (N-methylpyrrolidone). However, due to the high boiling point of the NMP solvent, the solvent is difficult to evaporate quickly during spraying, which will lead to uneven formation of the coating structure, thereby making the coating thickness inconsistent; at the same time, the residual NMP solvent will also affect the performance of the diaphragm, and ultimately affect the contact angle and ionic conductivity performance and the ability to resist thermal deformation.

[0083] Compared with the comparative examples using other one-dimensional materials and coating preparation methods, the results are shown in Table 2 below.

[0084] Table 2

[0085]

[0086] Application Examples

[0087] The diaphragm with ultra-thin two-dimensional oxide coating prepared in Example 1 and the original diaphragm (control group) were applied to lithium metal full batteries. The full battery material system is lithium iron phosphate-metal lithium, the battery structure is a round button battery, and the standard specific capacity of the lithium iron phosphate full battery is 170 mAh g -1 The battery was subjected to a 25°C room temperature cycle test with a charge and discharge rate of 1C. The test results are as follows: Figure 1 As shown. It can be seen that the discharge specific capacity of the lithium metal full battery after using the ultra-thin two-dimensional oxide coating modified diaphragm described in Example 1 in the cycle test is higher than that of the control group, and after 400 cycles, the capacity retention rate is 89.6%, which is an improvement over the 85.2% of the original diaphragm. It can be seen that the ultra-thin two-dimensional oxide coating modified diaphragm described in the present invention has a significant improvement in the battery cycle performance.

[0088] The above are only preferred specific implementations of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A two-dimensional oxide ultra-thin coating for lithium metal battery separator that can be synthesized on a large scale, characterized in that: The method comprises the following raw material components in parts by weight: 10-40 parts of two-dimensional oxide, 0.5-2 parts of binder and 250-800 parts of organic solvent; The two-dimensional oxide is titanium iron oxide nanosheets; The binder is polyvinylidene fluoride; The organic solvent is acetone; The method for preparing the two-dimensional oxide ultra-thin coating for lithium metal battery separators that can be synthesized on a large scale comprises the following steps: mixing the two-dimensional oxide, a binder and an organic solvent according to a proportion, and stirring to obtain a mixed solution; spraying the mixed solution on the surface of the lithium metal battery separator and heating the separator to obtain the coating; The parameters in the spraying process are: heating temperature 60-70°C, pressure 0.3-0.4MPa, nozzle diameter 0.3mm; During the spraying process, the volume of the mixed solution is 2 mL or 4 mL; The thickness of the lithium metal battery separator is 24-26 um, and the thickness of the coating is 0.5-2 um; The preparation method of the titanium iron oxide nanosheets is as follows: weighing and mixing raw materials according to the molar ratio of K2CO3, TiO2, Fe2O3 and Li2CO3 of 0.2:0.67:0.15:0.01, grinding the mixture in a mortar for 30 minutes, and then heating the mixture at 900°C in a muffle furnace under air environment for 1 hour to decarbonize the mixture; grinding the cooled powder for 30 minutes, and then heating it in air at 1000°C for 24 hours, and cooling it to obtain a precursor K 0.4 Ti 0.67 Fe 0.3 Li 0.02 O2; the precursor K 0.4 Ti 0.67 Fe 0.3 Li 0.02 O2 dissolved in 1 mol L -1 The mixture was stirred for 7 days and most of the HCL was collected by filtration. 0.42 Ti 0.67 Fe 0.3 O2, and repeatedly washed with deionized water, and finally, large pieces of H 0.42 Ti 0.67 Fe 0.3 O2 to obtain titanium iron oxide nanosheets.

2. The two-dimensional oxide ultra-thin coating for lithium metal battery separator that can be synthesized on a large scale according to claim 1, characterized in that: The stirring parameters are: temperature 20-40°C, rotation speed 300-500rpm, and time 1-3h.

3. An application of a two-dimensional oxide ultra-thin coating for lithium metal battery separators that can be synthesized on a large scale as described in any one of claims 1-2 in lithium-ion battery separators.

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