A metal nano-oxide modified lithium ion battery diaphragm and its preparation method and application

Abstract

The present application belongs to the field of lithium ion battery, and particularly relates to a metal nano-oxide modified lithium ion battery diaphragm, a preparation method and application thereof. The metal nano-oxide modified layer on the surface of the lithium ion battery diaphragm has a thickness of 5-100 nm, and can modify one side or both sides of the diaphragm. The preparation method comprises the following steps: firstly, preparing a metal layer on at least one side of the diaphragm; then, completely immersing in deionized water; heating in the presence of an oxygen-containing atmosphere to make the metal layer on the surface fully react and in-situ synthesize metal oxide; and drying to obtain the metal nano-oxide modified diaphragm. The metal nano-oxide modified layer can improve the interface contact, strengthen the mechanical properties and thermal stability of the diaphragm, has flame retardancy, good wettability, can improve the cycle life and safety of the lithium battery, and has excellent interface contact and adhesion. The preparation method is simple and efficient, and has great commercialization potential.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of lithium ion batteries, and particularly relates to a metal nano-oxide modified lithium ion battery separator and a preparation method and application thereof. BACKGROUND

[0002] In recent years, the increasingly deteriorating environmental problems and the irreversible consumption of non-renewable fossil energy make the development of energy storage systems necessary. Lithium ion batteries are widely used in electronic devices, electric vehicles and aerospace engineering fields due to their excellent comprehensive performance, such as low self-discharge rate, excellent cycle life and high working voltage. Lithium ion batteries mainly include three parts: positive electrode, negative electrode and separator. The separator is sandwiched between the positive and negative electrodes, which plays a role in preventing internal short circuit, ensuring the conduction of lithium ions through the interconnected microporous structure, and avoiding thermal runaway of lithium ion batteries under abnormal heating conditions.

[0003] Commercialized separators prepared from polyolefin materials (such as polyethylene and polypropylene) have become the first choice for commercial lithium batteries due to their excellent performance and low cost. However, the inherent hydrophobic surface properties resulting from the low surface energy of polyolefins weaken the affinity to carbonate electrolyte, which damages the migration of lithium ions and further damages the overall performance of lithium ion batteries; polyolefins have poor thermal stability, which often shrinks at elevated temperatures, causing potential safety hazards such as internal short circuit, and even explosion. In order to improve the mechanical properties and thermal stability of the separator, so far there have been many studies by modifying the surface of the separator, such as coating ceramic materials on the surface, surface grafting functional groups, nanoparticle coating, etc. Among them, coating nano-inorganic particles on the surface of the separator has been proved to be a method that can improve the thermal stability, flame retardancy and mechanical properties of the separator.

[0004] In the relevant literature, such as patent CN110400898A, a polyolefin-based separator coated with a porous core-shell structure inorganic particle coating is proposed, which optimizes the wettability of the separator to the electrolyte and the thermal stability, but the process greatly increases the thickness of the separator (25%); similarly, patent CN106221480A proposes a coating filler of a polymer-coated silica core-shell structure, and the complex process of preparing the core-shell structure and the time-consuming characteristics are contradictory to the principle requirements of commercial manufacturing on a large scale and low cost. In addition, patent CN108819393A proposes a sandwich structure (polysulfonamide / titanium dioxide / polysulfonamide) lithium battery separator based on the combination of electrospinning technology and electrostatic spraying technology, which uses electrospinning to prepare a polysulfonamide film on the outer layer, and uses electrostatic spraying to prepare a nanometer titanium dioxide film on the middle layer, thereby forming a sandwich structure composite separator, but this technology still has the disadvantages of complex process and inability to mass production. In addition, patent CN104269509A proposes a ceramic-coated separator, which uses a water-based ceramic coating slurry to coat a ceramic protective layer structure on the separator substrate. This method has the disadvantage of high cost of ceramics, and the coating method increases the thickness of the separator from 16 to 20 and greatly increases the weight of the separator, which easily leads to the reduction of the energy density of the lithium battery.

[0005] Therefore, a low-cost and low-technical barrier clever manufacturing technology is a necessary condition for producing a separator with excellent electrolyte affinity, high strength, and high flame retardancy. SUMMARY

[0006] In view of the poor wettability, poor thermal stability, poor flame retardancy of the lithium battery separator, and the high cost and high technical barrier of the separator modification technology in the prior art, the present application proposes a lithium ion battery separator modified by metal nano-oxide and a preparation method and application thereof, thereby obtaining an ultra-thin nano-oxide layer, which strengthens the mechanical properties of the separator, has excellent thermal stability, is flame retardant, has good wettability, and can improve the cycle life and safety of the lithium battery; and the preparation method is simple and efficient, has great commercialization potential and market application prospect.

[0007] To achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0008] A preparation method of a lithium ion battery separator modified by metal nano-oxide, the method comprises the following steps: depositing an ultra-thin metal layer on at least one side surface of the separator by physical vapor deposition; immersing the obtained separator with the surface-deposited metal layer in water and performing heating treatment, and completely oxidizing the metal layer on the surface of the separator to a metal oxide layer in the presence of an oxygen-containing atmosphere; and drying the obtained separator to obtain a lithium ion battery separator modified by metal nano-oxide.

[0009] Preferably, the water is deionized water.

[0010] Preferably, the oxygen-containing atmosphere is oxygen.

[0011] Preferably, the preparation method specifically comprises the following steps:

[0012] S1, depositing a layer of ultra-thin metal on at least one side of the surface of the diaphragm by physical vapor deposition;

[0013] S2, completely immersing the diaphragm with the surface-deposited metal layer obtained in step S1 into water, and performing heat treatment while introducing a certain amount of oxygen-containing atmosphere, so as to completely oxidize the metal layer on the surface of the diaphragm into a metal oxide layer after a certain period of time;

[0014] S3, drying the diaphragm obtained in step S2 to obtain a lithium ion battery diaphragm modified with metal nano-oxides.

[0015] Preferably, the physical vapor deposition method in step S1 is to plate a layer of metal on both sides (or one side) of the surface of the lithium battery diaphragm by magnetron sputtering, and more preferably the thickness is 5-100 nm, but it is not limited to the listed values, and other values not listed within this range are also applicable.

[0016] Preferably, during the magnetron sputtering process, the pressure is 0.4-1.2 Pa, more preferably 0.7-0.9 Pa, the sputtering power is 40-80 W, the sputtering time is 5-30 min, and the atmosphere is an inert atmosphere, more preferably at least one of argon or nitrogen; but it is not limited to the listed values, and other values not listed within this range are also applicable.

[0017] Preferably, the diaphragm in step S1 is at least one of a polyethylene diaphragm, a polypropylene diaphragm, a polyimide film, and a polyacrylonitrile film, but it is not limited to the listed ones, and other unlisted ones within this range are also applicable.

[0018] Preferably, the diaphragm in step S1 has a thickness of 10-30 μm, but it is not limited to the listed values, and other values not listed within this range are also applicable.

[0019] Preferably, the metal in step S1 is at least one of aluminum, tin, and indium, but it is not limited to the listed metals, and other unlisted ones within this range are also applicable.

[0020] Preferably, the heat treatment conditions in step S2 are 60-100℃ for 2-12 hours. The metal thin layer is relatively difficult to oxidize at room temperature, so it is preferred to perform the reaction more efficiently at the said temperature. But it is not limited to the listed values, and other values not listed within this range are also applicable.

[0021] Preferably, the oxygen-containing atmosphere in step S2 is oxygen, and more preferably, the oxygen flow rate is 3-10 mL / min, but is not limited to the listed values, and other values within the range are also applicable. By the technical solution, the reaction can be further completed; when the oxygen flow rate is higher, the metal surface will be rapidly oxidized to form metal oxide, and the internal metal will be difficult to contact with oxygen to react; meanwhile, when the oxygen flow rate is lower, the external metal is preferentially oxidized, and when the external reaction is completed, the internal metal is difficult to contact with oxygen to react.

[0022] Preferably, the drying in step S3 refers to that the water content of the separator reaches the requirement of ordinary lithium battery separators, and more preferably, the drying is performed to a water content of 200-350 ppm.

[0023] Preferably, the drying condition in step S3 is 60-80℃ for 8-12 hours, but is not limited to the listed values, and other values within the range are also applicable.

[0024] Another object of the present application is to provide a metal nano-oxide modified lithium ion battery separator prepared by any of the above preparation methods.

[0025] Still another object of the present application is to provide an application of the above metal nano-oxide modified lithium ion battery separator in the field of lithium ion batteries.

[0026] The present application provides a metal nano-oxide modified lithium ion battery separator, wherein the metal nano-oxide modification layer can improve the interface contact, and strengthen the mechanical properties and thermal stability of the separator, has flame retardancy, good wettability, and can improve the cycle life and safety of the lithium battery; and the metal nano-oxide modification layer is synthesized in situ through a chemical conversion reaction, thus having excellent interface contact and adhesion.

[0027] Compared with the prior art, the present application has the following beneficial effects:

[0028] (1) The lithium ion battery separator prepared by the present application introduces an inorganic metal oxide nano layer, and compared with the traditional lithium ion battery separator, has higher strength, equivalent safety, and better electrolyte wettability; and has a simple structure, does not affect the weight of the battery, is low in cost, is easy to mass process, and has a broad market application prospect;

[0029] (2) In the reaction process for preparing the inorganic metal oxide nano layer, violent chemical reactions are avoided, and a low-temperature heat treatment method is used, and the inorganic metal oxide nano layer is synthesized in situ on the surface of the separator through a chemical conversion reaction, thus having excellent interface contact and adhesion, and being suitable for industrialized mass application. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 This is a schematic diagram of the structure of the lithium-ion battery separator modified with metal nano-oxides according to the present invention.

[0031] Figure 2 This is the XRD pattern of the diaphragm prepared in Example 1.

[0032] Figure 3 This is a stress-strain relationship diagram between the PP diaphragm prepared in Example 1 and the pure PP diaphragm.

[0033] Figure 4 This is a comparison of the thermal stability of the PP membrane prepared in Example 1 (right) and the pure PP membrane (left) at 80°C.

[0034] Figure 5 This is a graph showing the cycle life and discharge capacity of a lithium iron phosphate coin cell assembled with the PP separator prepared in Example 1 at a 0.5C rate. Detailed Implementation

[0035] The technical solution of the present invention will be further described in detail below through specific embodiments and in conjunction with the accompanying drawings.

[0036] Example 1:

[0037] First, using magnetron sputtering technology, a 15nm aluminum layer (Al@PP) was obtained by sputtering both sides of a 19mm diameter polypropylene (PP) separator for 5 minutes at 0.7Pa and 50W. Then, the obtained Al@PP was completely immersed in deionized water, heated to 60℃ and held for 6 hours, while oxygen was introduced at a rate of 3mL / min to completely oxidize the nano-aluminum layer on the surface of the PP separator into a nano-alumina layer, resulting in an alumina-coated PP separator (Al2O3@PP). After the reaction was completed, the separator was removed and transferred to a 70℃ oven for 8 hours to ensure complete removal of moisture. After complete drying, a lithium-ion battery separator modified with metal nano-oxide was obtained.

[0038] Figure 2 This is the XRD pattern of the diaphragm prepared in this embodiment.

[0039] Figure 3 This is a stress-strain diagram comparing the PP diaphragm prepared in Example 1 with the pure PP diaphragm (Comparative Example 1). The modified diaphragm exhibits better mechanical properties than the unmodified pure PP diaphragm.

[0040] Figure 4is a comparison diagram of the thermal stability of the PP separator prepared in Example 1 (right side of the figure) and the pure PP separator (left side of the figure, Comparative Example 1) at 80°C. Among them, the modified separator does not curl within 40 minutes at 80°C, while the unmodified pure PP separator is extremely prone to curling at 80°C, and curls greatly after about 5 minutes.

[0041] Figure 5 is a cycle number-discharge capacity diagram of the lithium iron phosphate-lithium button cell using the PP separator prepared in Example 1 and the unmodified separator of Comparative Example 1 (pure PP separator) at a 0.5C rate. Among them, the unmodified separator short-circuits at 680 cycles, while the modified battery still does not short-circuit after 700 cycles, and the discharge capacity and capacity retention are better than the half-cell prepared by the unmodified separator.

[0042] The preparation steps of the lithium-lithium button cell in this embodiment are as follows: sequentially place the gasket and the positive electrode sheet into the 2032 positive electrode shell; place the corresponding separator on the positive electrode sheet, use a rubber head dropper to absorb the electrolyte to wet the surface of the separator; place the lithium sheet in the middle of the separator, then place the gasket on the lithium sheet in alignment, and then cover it with a negative electrode shell matched with the positive electrode shell. Further, place the button cell on a battery sealing machine, adjust the pressure (generally 500 Pa) and press for 5 seconds to complete the assembly of the button cell.

[0043] Among them, the material type of the positive electrode sheet is shown in Table 1.

[0044] Example 2:

[0045] First, a 30 nm layer of metallic tin (Sn@PE) was sputtered on one side of a polyethylene (PE) separator using a magnetron sputtering technique at a power of 60 W under the condition of 0.8 Pa for 5 min. Then, the obtained Sn@PE was completely immersed in deionized water, heated to 80°C and kept for 10 h, while oxygen was introduced at a rate of 5 mL / min, so that the nano-metallic tin layer on the surface of the PE separator was completely oxidized to a nano-tin oxide layer, obtaining a tin oxide coated PE separator (SnO2@PE). After the reaction was completed, the obtained separator was transferred to an 80°C oven for 12 h to ensure complete removal of moisture. After complete drying, a lithium ion battery separator modified with metal nano-oxides was obtained.

[0046] The obtained separator was assembled into a lithium nickel cobalt manganese oxide (811)-lithium button cell, wherein the tin oxide side corresponds to the lithium nickel cobalt manganese oxide side (metallic lithium is easy to react with tin oxide). The initial discharge capacity at 0.5C is 182mAhg -1 , and the capacity remains 82% of the discharge capacity after 100 cycles.

[0047] Example 3:

[0048] First, using magnetron sputtering technology, a 40 nm indium layer (In@PI) was sputtered on both sides of a polyimide (PI) membrane for 10 min at 0.7 Pa and a power of 80 W to obtain the desired layer. Then, the obtained In@PI was completely immersed in deionized water, heated to 100 °C and held at that temperature for 10 h, while oxygen was simultaneously introduced at a rate of 10 mL / min. This caused the nano-indium layer on the surface of the polyimide membrane to be completely oxidized into a nano-indium oxide layer, resulting in an indium oxide-coated PI membrane (In₂O₃@PI). After the reaction was complete, the membrane was removed and transferred to an 80 °C oven for 10 h to ensure complete removal of moisture. After complete drying, the lithium-ion battery membrane modified with metal nano-oxide was obtained.

[0049] The obtained separator was assembled into a lithium iron phosphate-lithium coin cell, with an initial discharge capacity of 157 mAh g at 0.2C. -1 After 100 cycles, the capacity still retains 94% of the discharge capacity.

[0050] Example 4:

[0051] First, a 30 nm aluminum layer (Al@PAN) was obtained by sputtering a polyacrylonitrile (PAN) separator at 50 W for 10 min under 0.7 Pa conditions. Then, the obtained Al@PAN was completely immersed in deionized water, heated to 60 °C and held for 12 h, while oxygen was introduced at a rate of 3 mL / min to completely oxidize the nano-aluminum layer on the surface of the PAN separator into a nano-alumina layer, resulting in an alumina-coated PAN separator (Al2O3@PAN). After the reaction was completed, the separator was removed and transferred to an 80 °C oven for 8 h to ensure complete removal of moisture. After complete drying, a lithium-ion battery separator modified with metal nano-oxide was obtained.

[0052] The resulting separator was assembled into a lithium nickel manganese oxide (64)-lithium coin cell, with an initial discharge capacity of 170 mAh g at 0.2C. -1 After 50 cycles, the capacity still retains 82% of the discharge capacity.

[0053] Example 5:

[0054] First, a 45 nm metal aluminum layer (Al@PP / PE) was obtained by sputtering a PP / PE double-layer separator for 15 min at a power of 50 W under the condition of 0.7 Pa using a magnetron sputtering technique. Then, the Al@PP / PE was completely immersed in deionized water, heated to 70°C and kept for 8 h, while oxygen was introduced at a rate of 4 mL / min, so that the nano-metal aluminum layer on the surface of the PP / PE separator was completely oxidized into a nano-aluminum oxide layer, obtaining an aluminum oxide coated PP / PE separator (Al2O3@PP / PE). After the reaction was completed, the obtained separator was transferred to an 80°C oven for 8 h to ensure complete removal of moisture. After complete drying, a lithium ion battery separator modified with metal nano-oxides was obtained.

[0055] The obtained separator was assembled into a lithium iron phosphate-lithium button cell, and the initial discharge capacity at 1C was 140 mA h g -1 After 100 cycles, the capacity remained 89% of the discharge capacity.

[0056] Example 6: The preparation method was basically the same as that of Example 1, except that the radio frequency magnetron sputtering time was 20 minutes, and a 60 nm thick metal aluminum layer was obtained.

[0057] Example 7: The preparation method was basically the same as that of Example 1, except that the radio frequency magnetron sputtering time was 25 minutes, and a 75 nm thick metal aluminum layer was obtained.

[0058] Example 8: The preparation method was basically the same as that of Example 1, except that the radio frequency magnetron sputtering time was 30 minutes, and a 90 nm thick metal aluminum layer was obtained.

[0059] Example 9: The preparation method was basically the same as that of Example 1, except that the radio frequency magnetron sputtering was only prepared on one side of the separator to obtain a 15 nm thick metal aluminum layer.

[0060] Comparative Example 1: The polypropylene (PP) separator was not treated in Example 1.

[0061] Comparative Example 2: Compared with Example 1, it is a conventional aluminum oxide ceramic modified PP separator.

[0062] Comparative Example 3: Compared with Example 1, it is a conventional lithium lanthanum zirconium oxide (LLZO) ceramic modified PP separator.

[0063] Test Example 1:

[0064] The separators obtained in Examples 1-9 and Comparative Examples 1-3 are assembled into button lithium ion batteries, and the button lithium ion batteries are prepared according to the method for preparing the lithium-lithium button battery in Example 1. The assembled batteries are subjected to charge-discharge performance tests using different constant current densities, and the time, voltage and capacity during the charge-discharge process are collected to obtain the charge-discharge curve and the charge-discharge capacity. In this test, the charge-discharge interval of the battery with lithium iron phosphate as the positive electrode is 2.5-3.8V, and the charge-discharge interval of the battery with lithium nickel cobalt manganese oxide as the positive electrode is 2.5-4.2V. The test instrument is a battery performance tester from Shenzhen Xinwei, and the performance parameters obtained are shown in Table 1.

[0065] Table 1: Battery performance test table of each example and comparative example

[0066]

[0067]

[0068] In summary, the metal nano-oxide modified lithium ion battery separator and the preparation method thereof provided by the present application can improve the interface contact, increase the adhesion between the metal oxide and the separator, and strengthen the mechanical properties and thermal stability of the separator, and the separator has flame retardancy, good wettability, improved interface stability, and can improve the cycle life and safety of the lithium battery. The preparation method is simple and efficient, and has great commercialization potential.

[0069] The above-described examples are only preferred schemes of the present application, and do not limit the present application in any form. Other variants and modifications can be made without departing from the technical solutions recited in the claims.

Claims

1. A method for preparing a metal nano-oxide modified lithium-ion battery separator, characterized in that, The method is to deposit a metal layer on at least one side surface of the diaphragm by vapor deposition; immerse the obtained diaphragm in water, and completely oxidize the metal layer on the surface of the diaphragm into a metal oxide layer under a heating condition and in the presence of an oxygen-containing atmosphere; and obtain a metal nano-oxide modified lithium ion battery diaphragm after drying.

2. The method for preparing a lithium-ion battery separator modified with metal nano-oxides according to claim 1, characterized in that, The vapor deposition method is to deposit the metal layer by magnetron sputtering, wherein the pressure is 0.4-1.2 Pa, the sputtering power is 40-80 W, and the sputtering time is 5-30 min.

3. The method for preparing a lithium-ion battery separator modified with metal nano-oxides according to claim 1, characterized in that, The diaphragm is at least one of a polyethylene diaphragm, a polypropylene diaphragm, a polyimide film, and a polyacrylonitrile film.

4. The method for preparing a lithium-ion battery separator modified with metal nano-oxides according to claim 1, characterized in that, The oxygen-containing atmosphere is introduced at a flow rate of 3-10 mL / min.

5. The method for preparing a lithium-ion battery separator modified with metal nano-oxides according to claim 1, characterized in that, The drying refers to the water content of the diaphragm meeting the requirements of ordinary lithium batteries.

6. A metal nano-oxide modified lithium ion battery diaphragm prepared by the preparation method of any one of claims 1-5.

7. Use of the metal nano-oxide modified lithium ion battery diaphragm of claim 6 in the field of lithium ion batteries.

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