A self-assembled modified polyolefin diaphragm and its preparation method and application

Abstract

The present invention relates to a self-assembled modified polyolefin diaphragm and a preparation method and application thereof, belonging to the field of electrochemical technology. The present invention solves the technical problems in the prior art such as poor thermal stability, poor mechanical properties, poor wettability, serious side reactions at the electrode-diaphragm interface, and the tendency of dendritic lithium dendrites to cause internal short circuits in batteries. The preparation method of the self-assembled modified polyolefin diaphragm of the present invention first performs deposition modification of layered hydroxides on the surface of the polyolefin diaphragm by vacuum filtration to obtain a modified layer, and then performs phase interface transformation on the modified layer by an electrochemical in-situ method to form a stable transition interface layer. The preparation method has the advantages of low production cost and simple operation process. The diaphragm prepared by the method has good thermal stability, mechanical properties and chemical activity, and can inhibit dendrite growth to achieve a long life cycle of the battery, and is suitable for large-scale production and industrial application.

Description

Technical Field

[0001] The present invention belongs to the field of electrochemical technology, and specifically relates to a self-assembled modified polyolefin diaphragm and a preparation method and application thereof, and especially relates to the application of the self-assembled modified polyolefin diaphragm in metal lithium batteries. Background Art

[0002] In lithium metal batteries, the separator's fundamental function is to prevent physical contact between the positive and negative electrodes while also acting as a carrier for the electrolyte, enabling ion transport. While the separator doesn't directly participate in the electrochemical reactions within the battery, its structure and properties significantly impact the battery's performance and lifespan.

[0003] Among existing lithium-ion batteries, the most widely used separators are made of polyolefins, mainly microporous polyethylene (PE) and polypropylene (PP) separators. Although polyolefin separators have good porosity, which allows the electrolyte to infiltrate and pass through the micropores, the thermal stability of polyolefin separators is relatively low, and they are prone to deformation under high temperature conditions, which can lead to short circuits in the battery. Secondly, the mechanical properties of polyolefin membranes are poor and cannot prevent the formation of metallic lithium dendrites. Under high current density, they are also easily pierced by metallic lithium dendrites, causing battery safety issues. In addition, since polyolefin separators have non-polar surfaces and low surface energy, the wettability and electrolyte retention rate of polyolefin separators are also limited. The electrolyte cannot fully fill the microporous structure of the separator, which increases the ion transfer resistance, thereby affecting the lithium ion transfer efficiency, resulting in a short battery cycle life and serious side reactions at the electrode-separator interface. Summary of the Invention

[0004] In view of this, the present invention aims to solve the technical problems in the prior art such as poor thermal stability, poor mechanical properties, poor wettability, serious side reactions at the electrode-membrane interface, and dendritic lithium dendrites that easily lead to internal short circuits in batteries. The present invention proposes a self-assembled modified polyolefin membrane and a preparation method and application thereof. The self-assembled modified polyolefin membrane has good chemical stability, good mechanical strength, high specific capacity, and excellent cycle performance. The preparation method has the advantages of low production cost and simple operation process, and is suitable for large-scale production and industrial application.

[0005] The present invention solves the above technical problems and adopts the following technical solutions.

[0006] The present invention provides a method for preparing a self-assembled modified polyolefin diaphragm, comprising the following steps:

[0007] Step 1: Preparation of modified precursor sol

[0008] First, a transition metal acetate hydrate and an alkali metal acetate are dissolved in anhydrous ethanol and mixed uniformly to obtain a reaction mixture; then, the reaction mixture is reacted at 40-80° C. under normal pressure, and after the reaction is complete, the mixture is filtered, dried, and crushed to obtain a solid powder; finally, the solid powder is dissolved in deionized water from which oxygen has been removed, and ultrasonication is performed until the solid powder is completely dissolved to obtain a modified precursor sol;

[0009] In the reaction mixture, the concentration of transition metal ions is 10-40 mmol / L, acetate (Ac - ) concentration is 2 to 2.4 times the concentration of transition metal ions;

[0010] Step 2: Self-assembly modification of the diaphragm

[0011] The modified precursor sol prepared in step 1 is mixed evenly with anhydrous ethanol to obtain a modified liquid, and the modified liquid is used as a filtrate by vacuum filtration using a polyolefin microporous filter membrane as a suction membrane to obtain a self-assembled membrane, and then vacuum dried at 40-60°C;

[0012] Step 3: Electrochemical phase transition of the diaphragm modification layer

[0013] The dried self-assembled membrane prepared in step 2 is placed in a lithium-lithium symmetrical battery, and a lithium insertion reaction is performed for 2-5 cycles at a scan rate of 0.5-3 mV / s and a voltage range of 3.0 V to -0.2 V to obtain a self-assembled modified polyolefin membrane;

[0014] In the lithium-lithium symmetrical battery, the lithium salt concentration of the electrolyte is controlled to be 0.5-1.5 mol / L.

[0015] Preferably, in step 1, the transition metal acetate hydrate includes one or more of cobalt acetate tetrahydrate (CoAc2·4H2O), nickel acetate tetrahydrate (NiAc2·4H2O), and ferrous acetate tetrahydrate (FeAc2·4H2O).

[0016] Preferably, in step 1, the alkali metal acetate includes one or more of potassium acetate, sodium acetate, and lithium acetate.

[0017] Preferably, in step 1, the mass ratio of the solid powder to the deionized water from which oxygen has been removed is 1:80 to 1:130.

[0018] Preferably, in step 2, the volume ratio of the modified precursor sol to anhydrous ethanol is 1:0.6 to 1:1.5.

[0019] Preferably, in step 2, the polyolefin microporous filter membrane includes one or more of a polyethylene membrane, a polypropylene membrane, a mixed polyolefin membrane, a cellulose membrane, a polyethersulfone membrane, and a polytetrafluoroethylene membrane.

[0020] Preferably, in step 2, the pore size of the polyolefin microporous filter membrane is 10 to 80 nm.

[0021] Preferably, in step 2, the vacuum drying is carried out at 40-60° C. for 12-24 hours.

[0022] Preferably, in step three, in the electrolyte of the Li-Li symmetrical battery, the lithium salt includes one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium bis(trifluoromethylsulfonyl imide) (LiTFSI), and lithium trifluoromethanesulfonate (LiSFI); the solvent includes one or more of dimethyl carbonate (DMC), ethylene carbonate (EC), propylene carbonate (PC), 1,4-dioxolane (DOL), diethyl carbonate (DEC), dimethyl ether (DME), ethylene glycol dimethyl ether (EGDME), and tetraethylene glycol dimethyl ether (TEGDME).

[0023] The present invention also provides a self-assembled modified polyolefin membrane prepared by the preparation method of the self-assembled modified polyolefin membrane.

[0024] The present invention also provides application of the self-assembled modified polyolefin separator in metal lithium batteries.

[0025] The principle of the present invention is: first, the surface of the polyolefin diaphragm is modified by layer-by-layer self-assembly to form a layered modified layer, and then an in-situ phase interface transformation is performed by an electrochemical method to convert the layered modified layer into an electrochemically active modified layer, thereby forming a stable interface layer on the surface of the polyolefin diaphragm, thereby improving the stability between the diaphragm and the metal negative electrode, and at the same time inhibiting dendrite growth to achieve a long life cycle of the battery.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] The present invention provides a method for preparing a self-assembled modified polyolefin membrane, which includes self-assembly modification and electrochemical phase transition. Layered hydroxides are deposited and modified on the surface of the polyolefin membrane using a vacuum filtration device, and the phase interface is transformed in situ using an electrochemical method. This method forms a stable transition interface layer on the polyolefin membrane surface, thereby inhibiting the growth of metallic lithium dendrites. This method also features simple processes, simple equipment, a short production cycle, environmental friendliness, low cost, and high repeatability, making it suitable for large-scale production and promising applications.

[0028] The self-assembled modified polyolefin membrane of the present invention is uniform and has good density; surface modification of the polyolefin membrane can effectively improve the wettability of the electrolyte on the surface of the polyolefin membrane, and improve the mechanical strength, thermal stability and chemical activity of the polyolefin membrane; strengthening the surface of the polyolefin membrane with a modified layer can also inhibit the generation of metallic lithium dendrites, thereby greatly improving the stability of the negative electrode and extending the battery life and rate performance.

[0029] The results of lithium symmetry experiments and lithium iron phosphate experiments show that the self-assembled modified polyolefin separator of the present invention exhibits excellent performance in lithium metal batteries, such as lower polarization, longer cycle time, and higher capacity. It can significantly improve the battery's capacity, cycle performance, and other characteristics, playing a significant role in improving the battery's overall performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some specific implementation plans of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0031] Figure 1 This is a SEM cross-sectional image of the self-assembled modified polyolefin membrane prepared in Example 1 of the present invention;

[0032] Figure 2 The AFM surface images of the self-assembled modified polyolefin membrane prepared in Example 1 of the present invention are shown. The left image is a surface roughness analysis image, and the right image is a surface morphology image.

[0033] Figure 3 This is the BET image of the self-assembled modified polyolefin membrane prepared in Example 1 of the present invention;

[0034] Figure 4 The electrochemical performance of a symmetrical battery containing the self-assembled modified polyolefin separator prepared in Example 1 of the present invention is compared with that of a symmetrical battery containing a commercial unmodified separator. DETAILED DESCRIPTION

[0035] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the embodiments and drawings.

[0036] In the following examples, various processes and methods not described in detail are conventional methods known in the art. Unless otherwise specified, the materials, reagents, devices, instruments, equipment, etc. used in the following examples can be obtained from commercial sources.

[0037] Example 1

[0038] Step 1: Preparation of modified precursor sol

[0039] Cobalt acetate tetrahydrate, sodium acetate, and anhydrous ethanol were first mixed and dissolved in a mass ratio of 1:0.2:80, and then reacted at 52°C under normal pressure. After the reaction was complete, the reaction solution was filtered, dried, and crushed to obtain a solid powder. Finally, the solid powder was dissolved in deionized water from which oxygen was removed, and ultrasonicated until the solid powder was completely dissolved to obtain a modified precursor sol. The mass ratio of the solid powder to the deionized water from which oxygen was removed was 1:95.

[0040] Step 2: Self-assembly modification of the diaphragm

[0041] The modified precursor sol prepared in step 1 was mixed evenly with anhydrous ethanol in a volume ratio of 1:1.2 to obtain a modified solution. The modified solution was filtered through a commercial Celgard-2500 microporous membrane as a suction membrane to obtain a self-assembled membrane, which was then vacuum dried at 40-60°C for 20 h.

[0042] Step 3: Electrochemical phase transition of the diaphragm modification layer

[0043] The dried self-assembled membrane prepared in step 2 was placed in a lithium-lithium symmetric battery, using metallic lithium as the electrode and an electrolyte prepared by dissolving 1M LiTFSI in DOL / DME (volume ratio 1:1) as the working electrolyte. Two cycles of lithium insertion reaction were performed at a voltage of 3.0V to -0.2V and a scan rate of 0.5mV / s to phase transform the self-assembled membrane, and finally a self-assembled modified polyolefin membrane capable of inhibiting dendrite formation was obtained.

[0044] Figure 1 This is a SEM cross-sectional image of the self-assembled modified polyolefin membrane prepared in Example 1 of the present invention; Figure 2 The AFM surface images of the self-assembled modified polyolefin membrane prepared in Example 1 of the present invention are shown. The left image is a surface roughness analysis image, and the right image is a surface morphology image. Figure 3 This is the BET image of the self-assembled modified polyolefin membrane prepared in Example 1 of the present invention.

[0045] Example 2

[0046] Step 1: Preparation of modified precursor sol

[0047] Nickel acetate tetrahydrate, lithium acetate, and anhydrous ethanol were first mixed and dissolved in a mass ratio of 0.3:0.2:80, and then reacted at 70°C under normal pressure. After the reaction was complete, the reaction solution was filtered, dried, and crushed to obtain a solid powder. Finally, the solid powder was dissolved in deionized water from which oxygen was removed, and ultrasonicated until the solid powder was completely dissolved to obtain a modified precursor sol. The mass ratio of the solid powder to the deionized water from which oxygen was removed was 1:100.

[0048] Step 2: Self-assembly modification of the diaphragm

[0049] The modified precursor sol prepared in step 1 was mixed evenly with anhydrous ethanol in a volume ratio of 1:1 to obtain a modified solution. The modified solution was filtered through a commercial Celgard-2500 microporous membrane as a suction membrane to obtain a self-assembled membrane, which was then vacuum dried at 40-60°C for 20 h.

[0050] Step 3: Electrochemical phase transition of the diaphragm modification layer

[0051] The dried self-assembled membrane prepared in step 2 was placed in a lithium-lithium symmetric battery, using metallic lithium as the electrode and an electrolyte prepared by dissolving 1M LiTFSI in DOL / DME (volume ratio 1:1) as the working electrolyte. Two cycles of lithium insertion reaction were performed at a voltage of 3.0V to -0.2V and a scan rate of 0.5mV / s to phase transform the self-assembled membrane, and finally a self-assembled modified polyolefin membrane capable of inhibiting dendrite formation was obtained.

[0052] Example 3

[0053] Step 1: Preparation of modified precursor sol

[0054] Nickel acetate tetrahydrate, sodium acetate, and anhydrous ethanol were first mixed and dissolved in a mass ratio of 1:0.2:90, and then reacted at 70°C under normal pressure. After the reaction was complete, the reaction solution was filtered, dried, and crushed to obtain a solid powder. Finally, the solid powder was dissolved in deionized water from which oxygen was removed, and ultrasonicated until the solid powder was completely dissolved to obtain a modified precursor sol. The mass ratio of the solid powder to the deionized water from which oxygen was removed was 1:100.

[0055] Step 2: Self-assembly modification of the diaphragm

[0056] The modified precursor sol prepared in step 1 was mixed evenly with anhydrous ethanol in a volume ratio of 1:0.5 to obtain a modified solution. The modified solution was filtered using a commercial Celgard-2325 microporous membrane as a suction membrane and the filtrate was vacuum filtered to obtain a self-assembled membrane. The membrane was vacuum dried at 40°C for 16-18 hours.

[0057] Step 3: Electrochemical phase transition of the diaphragm modification layer

[0058] The dried self-assembled membrane prepared in step 2 was placed in a lithium-lithium symmetrical battery, using metallic lithium as the electrode and 1M LiClO4 dissolved in EC / DEC / PC (volume ratio 1:1:1) electrolyte as the working electrolyte. Four cycles of lithium insertion reaction were performed at a voltage of 3.0V to -0.2V and a scan rate of 0.5mV / s to phase transform the self-assembled membrane, and finally a self-assembled modified polyolefin membrane with the ability to inhibit dendrite formation was obtained.

[0059] Example 4

[0060] Step 1: Preparation of modified precursor sol

[0061] First, ferrous acetate tetrahydrate, lithium acetate, and anhydrous ethanol were mixed and dissolved in a mass ratio of 0.8:0.1:80, and reacted at 40°C under normal pressure. After the reaction was complete, the reaction solution was filtered, dried, and crushed to obtain a solid powder. Finally, the solid powder was dissolved in deionized water from which oxygen was removed, and ultrasonicated until the solid powder was completely dissolved to obtain a modified precursor sol. The mass ratio of the solid powder to the deionized water from which oxygen was removed was 1:89.

[0062] Step 2: Self-assembly modification of the diaphragm

[0063] The modified precursor sol prepared in step 1 was mixed evenly with anhydrous ethanol in a volume ratio of 1:1 to obtain a modified solution. The modified solution was filtered using a commercial Celgard-2325 microporous membrane as a suction membrane and the filtrate was vacuum-filtered to obtain a self-assembled membrane. The membrane was vacuum-dried at 40-60°C for 20 hours.

[0064] Step 3: Electrochemical phase transition of the diaphragm modification layer

[0065] The dried self-assembled membrane prepared in step 2 was placed in a lithium-lithium symmetric battery, using metallic lithium as the electrode and an electrolyte prepared by dissolving 1M LiTFSI in DOL / DME (volume ratio 1:1) as the working electrolyte. Three cycles of lithium insertion reaction were performed at a voltage of 3.0V to -0.2V, with a scan rate of 0.5mV / s, to phase transform the self-assembled membrane, and finally a self-assembled modified polyolefin membrane capable of inhibiting dendrite formation was obtained.

[0066] Example 5

[0067] Step 1: Preparation of modified precursor sol

[0068] First, nickel acetate tetrahydrate, potassium acetate and anhydrous ethanol are mixed and dissolved in a mass ratio of 1:0.1:90, and the reaction is carried out at 70°C under normal pressure. After the reaction is complete, the reaction solution is filtered, dried, and crushed to obtain a solid powder. Finally, the solid powder is dissolved in deionized water from which oxygen has been removed, and ultrasonication is performed until the solid powder is completely dissolved to obtain a modified precursor sol. The mass ratio of the solid powder to the deionized water from which oxygen has been removed is 1:108.

[0069] Step 2: Self-assembly modification of the diaphragm

[0070] The modified precursor sol prepared in step 1 was mixed evenly with anhydrous ethanol in a volume ratio of 1:1.3 to obtain a modified solution. A commercial cellulose microporous membrane was used as a suction filtration membrane, and the modified solution was used as the filtrate. Vacuum filtration was performed to obtain a self-assembled membrane, and the membrane was vacuum dried at 40-60°C for 20 hours.

[0071] Step 3: Electrochemical phase transition of the diaphragm modification layer

[0072] The dried self-assembled membrane prepared in step 2 was placed in a lithium-lithium symmetric battery, using metallic lithium as the electrode and an electrolyte prepared by dissolving 0.5M LiTFSI in DOL / DME (volume ratio 1:1) as the working electrolyte. Three cycles of lithium insertion reaction were performed at a voltage of 3.0V to -0.2V, with a scan rate of 0.5mV / s, to phase transform the self-assembled membrane, and finally a self-assembled modified polyolefin membrane capable of inhibiting dendrite formation was obtained.

[0073] Example 6

[0074] Step 1: Preparation of modified precursor sol

[0075] First, cobalt acetate tetrahydrate, potassium acetate and anhydrous ethanol are mixed and dissolved in a mass ratio of 1:0.4:85, and reacted at 47°C under normal pressure. After the reaction is complete, the reaction solution is filtered, dried, and crushed to obtain a solid powder. Finally, the solid powder is dissolved in deionized water from which oxygen has been removed, and ultrasonicated until the solid powder is completely dissolved to obtain a modified precursor sol. The mass ratio of the solid powder to the deionized water from which oxygen has been removed is 1:110.

[0076] Step 2: Self-assembly modification of the diaphragm

[0077] The modified precursor sol prepared in step 1 was mixed evenly with anhydrous ethanol in a volume ratio of 0.8:1 to obtain a modified solution. The modified solution was filtered using a commercial Celgard-2301 microporous membrane as a suction membrane and the filtrate was vacuum filtered to obtain a self-assembled membrane. The self-assembled membrane was vacuum dried at 40-60°C for 17 hours.

[0078] Step 3: Electrochemical phase transition of the diaphragm modification layer

[0079] The dried self-assembled membrane prepared in step 2 was placed in a lithium-lithium symmetrical battery, using metallic lithium as the electrode and 1M LiClO4 dissolved in EC / DEC / PC (volume ratio 1:1) electrolyte as the working electrolyte. Two cycles of lithium insertion reaction were performed at a voltage of 3.0V to -0.2V and a scan rate of 1.5mV / s to phase transform the self-assembled membrane, and finally a self-assembled modified polyolefin membrane with the ability to inhibit dendrite formation was obtained.

[0080] Example 7

[0081] Step 1: Preparation of modified precursor sol

[0082] First, ferrous acetate tetrahydrate, potassium acetate, and anhydrous ethanol were mixed and dissolved in a mass ratio of 0.9:0.4:80, and the mixture was reacted at 52°C under normal pressure. After the reaction was complete, the reaction solution was filtered, dried, and crushed to obtain a solid powder. Finally, the solid powder was dissolved in deionized water from which oxygen was removed, and ultrasonicated until the solid powder was completely dissolved to obtain a modified precursor sol. The mass ratio of the solid powder to the deionized water from which oxygen was removed was 1:100.

[0083] Step 2: Self-assembly modification of the diaphragm

[0084] The modified precursor sol prepared in step 1 was mixed evenly with anhydrous ethanol in a volume ratio of 1:1 to obtain a modified solution. The modified solution was filtered through a commercial Celgard-2400 microporous membrane as a suction membrane to obtain a self-assembled membrane, which was then vacuum dried at 40-60°C for 20 h.

[0085] Step 3: Electrochemical phase transition of the diaphragm modification layer

[0086] The dried self-assembled membrane prepared in step 2 was placed in a lithium-lithium symmetric battery, using metallic lithium as the electrode and an electrolyte prepared by dissolving 1M LiTFSI in DOL / DME (volume ratio 1:1) as the working electrolyte. Two cycles of lithium insertion reaction were performed at a voltage of 3.0V to -0.2V and a scan rate of 0.5mV / s to phase transform the self-assembled membrane, and finally a self-assembled modified polyolefin membrane capable of inhibiting dendrite formation was obtained.

[0087] Example 8

[0088] The battery performance test was performed on the self-assembled modified polyolefin separators prepared in Examples 1 to 7:

[0089] Button cells were assembled in an argon-filled glove box in the order of lithium sheet, self-assembled modified polyolefin separator (Ø16-14 mm), 60 μL commercial lithium-sulfur electrolyte (1 M LiTFSI dissolved in DOL / DME (volume ratio 1:1), and 1 wt% lithium nitrate added), and lithium sheet (Ø14-12 mm) to test the electrochemical performance.

[0090] The cycling performance test was carried out using a NEWARE system (CT-4008T, Shenzhen NEWARE Electronics Co., Ltd.). The current density was 0.25 mA / cm 2 , with a capacity of 0.5 mAh / cm 2 First, activate for 3 cycles. Test using 1mA / cm 2 The current density of the cycle test is carried out, and the test results corresponding to Example 1 are as follows Figure 4 As shown. Figure 4 It can be seen that in the electrochemical test, the Li||Li battery equipped with the self-assembled separator of the present invention has excellent performance such as smaller polarization and longer cycle time.

[0091] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the embodiments. Those skilled in the art will readily appreciate that other variations or modifications based on the above descriptions are possible. It is not necessary and impossible to enumerate all embodiments here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A method for preparing a self-assembled modified polyolefin membrane, characterized in that: The following steps are involved: Step 1: Preparation of modified precursor sol First, a transition metal acetate hydrate and an alkali metal acetate are dissolved in anhydrous ethanol and mixed uniformly to obtain a reaction mixture; then, the reaction mixture is reacted at 40-80°C under normal pressure. After the reaction is complete, the mixture is filtered, dried, and crushed to obtain a solid powder; finally, the solid powder is dissolved in deionized water from which oxygen has been removed, and ultrasonication is performed until the solid powder is completely dissolved to obtain a modified precursor sol; In the reaction mixture, the concentration of transition metal ions is 10-40 mmol / L, and the concentration of acetate is 2-2.4 times the concentration of transition metal ions; The transition metal acetate hydrate includes one or more of cobalt acetate tetrahydrate, nickel acetate tetrahydrate, and ferrous acetate tetrahydrate; Step 2: Self-assembly modification of the diaphragm The modified precursor sol prepared in step 1 is mixed evenly with anhydrous ethanol to obtain a modified liquid, and the modified liquid is used as a filtrate by vacuum filtration using a polyolefin microporous filter membrane as a suction membrane to obtain a self-assembled membrane, and then vacuum dried at 40-60°C; Step 3: Electrochemical phase transition of the diaphragm modification layer The dried self-assembled membrane prepared in step 2 is placed in a lithium-lithium symmetrical battery, and a lithium insertion reaction is performed for 2 to 5 cycles at a scan rate of 0.5 to 3 mV / s and a voltage range of 3.0 V to -0.2 V to obtain a self-assembled modified polyolefin membrane; In the lithium-lithium symmetrical battery, the lithium salt concentration of the electrolyte is controlled to be 0.5-1.5 mol / L.

2. The method for preparing the self-assembled modified polyolefin membrane according to claim 1, wherein In step 1, the alkali metal acetate includes one or more of potassium acetate, sodium acetate, and lithium acetate.

3. The method for preparing the self-assembled modified polyolefin membrane according to claim 1, wherein In step 1, the mass ratio of the solid powder to the deionized water from which oxygen has been removed is 1:80 to 1:

130.

4. The method for preparing the self-assembled modified polyolefin membrane according to claim 1, wherein In step 2, the volume ratio of the modified precursor sol to anhydrous ethanol is 1:0.6 to 1:1.

5.

5. The method for preparing the self-assembled modified polyolefin membrane according to claim 1, wherein In step 2, the polyolefin microporous filter membrane includes one or more of a polyethylene membrane, a polypropylene membrane, and a mixed polyolefin membrane; And / or, the pore size of the polyolefin microporous filter membrane is 10-80 nm.

6. The method for preparing the self-assembled modified polyolefin membrane according to claim 1, wherein: In step 2, vacuum drying is performed at 40-60° C. for 12-24 hours.

7. The method for preparing the self-assembled modified polyolefin membrane according to claim 1, wherein: In step three, in the electrolyte of the lithium-lithium symmetrical battery, the lithium salt includes one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium bis(trifluoromethylsulfonylimide), and lithium trifluoromethanesulfonate; and the solvent includes one or more of dimethyl carbonate, ethylene carbonate, propylene carbonate, 1,4-dioxolane, diethyl carbonate, dimethyl ether, ethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.

8. A self-assembled modified polyolefin membrane prepared according to the method for preparing a self-assembled modified polyolefin membrane according to any one of claims 1 to 7.

9. Use of the self-assembled modified polyolefin separator according to claim 8 in metal lithium batteries.

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