Lithium metal battery modified diaphragm based on aramid nanofiber as well as preparation method and application of lithium metal battery modified diaphragm

Abstract

The invention discloses a preparation method of a lithium metal battery modified diaphragm based on aramid nanofibers. The modified diaphragm has excellent mechanical strength, can effectively bear mechanical stress in the charging and discharging process of the battery, and reduces the risk of fracture. Meanwhile, the diaphragm material is subjected to modification treatment and shows excellent temperature resistance. The porous structure of the modified diaphragm is precisely designed, so that the resistance in the transmission process is reduced, the modified diaphragm has the capability of adsorbing heavy metal ions dissolved out from a positive electrode material, and the charge-discharge efficiency of the battery is remarkably improved. The preparation method of the modified diaphragm based on the aramid nanofiber is simple in process flow, easy for large-scale production, high in cost benefit and beneficial to reducing the manufacturing cost of the whole battery, and brings breakthrough progress for the development of a lithium metal battery technology.

Description

Technical Field

[0001] The present invention relates to a separator for a lithium metal battery based on aramid nanofibers and a preparation method thereof, belonging to the technical field of battery materials. Background Art

[0002] With the rapid development of technology, rechargeable batteries with high energy density have become increasingly widely used in fields such as portable electronic devices and electric vehicles. Lithium-ion batteries have become the mainstream of current battery technology due to their high energy density, long cycle life, and good safety performance. However, the performance of lithium-ion batteries is still limited by the physical and chemical properties of their components.

[0003] Lithium metal anodes are considered an ideal choice for improving the energy density of lithium-ion batteries because of their high theoretical specific capacity (3860 mAh / g) and low electrochemical potential (-3.04 V vs. standard hydrogen electrode). However, in practical applications, lithium metal anodes face many challenges. First, the interfacial instability between the lithium metal anode and the electrolyte leads to rapid capacity loss during charge-discharge cycles. The vigorous growth of lithium dendrites not only increases the risk of internal short circuits but may also pierce the separator, triggering thermal runaway and even combustion of the battery. In addition, the generation of "dead lithium" and the uncontrolled volume change of the battery during charge-discharge further limit the service life and safety of lithium metal anodes.

[0004] To overcome these limitations, the design of the modified layer of the separator is of great significance for improving battery performance. In addition to focusing on improving the wettability of the electrolyte and inhibiting the growth of lithium dendrites, the porous structure and chemical functions of the separator are also the focus of research. The introduction of the modified layer aims to enhance the physical and chemical properties of the separator to meet the stringent requirements of the lithium metal anode during charge-discharge processes. An ideal modified layer should have an optimized porosity and pore size distribution to ensure efficient lithium-ion transport while maintaining sufficient mechanical strength to resist the growth of lithium dendrites. In addition, the chemical functionality of the modified layer is also crucial. It should be able to effectively interact with the active substances in the battery, reduce the occurrence of harmful side reactions, and thus extend the cycle life of the battery. When exploring the application of the modified separator layer, attention should be paid to its impact on the overall performance of the battery, including but not limited to ion transport efficiency, thermal stability, and safety. Through the design of the modified separator, the charge-discharge efficiency and cycle stability of the battery can be significantly improved while reducing safety risks, which is of great value for promoting the development of lithium metal battery technology.

[0005] In addition to solving the limitations of lithium metal anodes, the research on cathode materials cannot be ignored. In recent years, cathode materials with a high nickel content (LiNi x M 1-xO2, M = Mn, Co, x ≥ 0.6) has been widely used in lithium metal batteries due to its high energy density characteristics. However, during the charge and discharge process, these materials will generate transition metal ions that dissolve into the electrolyte, and these ions will subsequently form an irreversible deposition layer on the anode, resulting in a loss of battery capacity. This phenomenon not only reduces the energy efficiency of the battery but also increases the risk of battery failure.

[0006] In this process, the role of the separator becomes particularly crucial. Metal ions dissolved from the cathode migrate towards the counter anode through the ion conduction channels of the separator. The existence of this chemical crosstalk problem not only exacerbates the growth of lithium dendrites but also may lead to internal short circuits in the battery, triggering safety issues. Therefore, the separator has great potential in solving the chemical crosstalk problem, and its design and material selection are crucial for improving the overall performance of the battery. Summary of the Invention

[0007] Aiming at the deficiencies existing in the prior art, the purpose of the present invention is to provide a modified separator for lithium batteries based on aramid nanofibers and its preparation method. This modified separator has excellent mechanical strength, ensuring that it can effectively withstand mechanical stress during the charge and discharge process of the battery and reducing the risk of rupture. At the same time, the separator material has been specially treated and exhibits excellent heat resistance, maintaining the stability of its structure and function even at extreme temperatures, thereby enhancing the thermal safety of the battery. The porous structure of the modified separator has been precisely designed to optimize the pore size and distribution, providing a fast and direct transmission path for lithium ions, reducing the resistance during the transmission process, and significantly improving the charge and discharge efficiency of the battery. In addition, the modified separator has high-efficient electron blocking ability, effectively preventing internal short circuits in the battery and ensuring safe use. In terms of chemical composition, the separator exhibits good chemical stability and thermal stability, being able to resist the erosion of electrolytes and active substances, and enhancing the long-term stability of the battery. The preparation method of the modified separator of the present invention has a simple technological process, is easy to scale up production, and has high cost-effectiveness, which is conducive to reducing the overall battery manufacturing cost, bringing a breakthrough in the development of lithium-ion battery technology, and at the same time improving the cycle performance and safety performance of the battery.

[0008] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0009] A modified separator for a lithium metal battery, which is composed of a polypropylene (PP) base film and a copolymer coating of aramid nanofibers (ANF) and polyacrylamide (PAM). The copolymer layer is formed by the in-situ reaction of aramid nanofibers and polyacrylonitrile in a solvent, and PAN is transformed into PAM in an alkaline DMSO environment.

[0010] The thickness of the polymer coating is 50 - 100 μm.

[0011] The preparation method of the lithium metal separator shown in the present invention is as follows:

[0012] (1) Place para-aramid short fiber (PPTA) and potassium hydroxide (KOH) in dimethyl sulfoxide (DMSO) and 4 ml of deionized water for dissolution, and stir evenly for 4 - 8 h at room temperature to obtain a dark red ANF solution;

[0013] (2) Add potassium persulfate powder to deionized water, stir until completely dissolved, then immerse the PP separator in the solution, keep it at 60 - 70 °C for 3 - 5 h, take it out after the reaction, wash and dry to obtain the surface-activated PP separator;

[0014] (3) Add PAN powder to dimethylformamide (DMF) solution, stir evenly at room temperature until completely dissolved to obtain a PAN solution;

[0015] (4) Add the PAN solution in step (3) to the ANF solution in step (1), and stir evenly at room temperature.

[0016] (5) Simply coat the mixed solution in step (4) onto the activated PP separator in step (2), and put it into an oven at 50 °C to dry for 24 h after coating. Then the target material can be obtained.

[0017] Further, in step (1), the concentration of the ANF solution is 0.02 - 0.2 g / ml.

[0018] Further, in step (2), the concentration of the potassium persulfate solution is 0.05 - 0.1 mol / L.

[0019] Further, in step (3), the concentration of the PAN solution is 0.05 - 0.01 g / ml.

[0020] Further, in step (4), in the ANF-PAN mixed solution, the mass ratio of ANF to PAN is 1:1 to 5:1.

[0021] Further, in step (5), the thickness of the scraper is set to 50 - 100 μm. After taking it out of the oven, lay the coated surface flat in water for 1 - 3 h and then dry it on a glass plate or directly place it on a glass plate.

[0022] The prepared separator has the following multi-functional advantages:

[0023] (1) The lithium battery separator described in the present invention has good film-forming property and extremely high chemical stability, provides more channels for the transmission of the electrolyte and the migration of lithium ions, and achieves the effects of preventing the generation of lithium dendrites and reducing the interfacial impedance.

[0024] (2) The aramid nanofibers have excellent thermal stability, which is significantly higher than that of PE and PP. This can effectively inhibit the thermal softening and shrinkage problems of the separator during battery heating, and improve the battery performance.

[0025] (3) The in-situ formed ANF-PAM layer on the separator has a uniform and flat surface structure. This uniform surface structure helps to provide a more stable lithium-ion transport path, reduce the formation of lithium dendrites caused by excessive local current density, and thus reduce the risk of internal short circuit in the battery.

[0026] (4) The extremely high mechanical properties of the ANF-PAM layer slow down the growth of Li dendrites on the lithium metal anode. Its strength is sufficient to resist the mechanical stress caused by the growth of lithium dendrites, thereby protecting the separator from being pierced and enhancing the structural integrity and safety of the battery.

[0027] (5) The amide groups on the PAM layer have the ability to form coordination bonds with the dissolved heavy metal ions in the high-nickel cathode material, thereby effectively chelating these ions. This chelation can reduce the migration of heavy metal ions in the electrolyte, prevent them from forming a deposition layer on the lithium metal anode, improve the structural stability of the cathode material, reduce capacity loss, and extend the cycle life of the battery.

[0028] (6) The extremely thin thickness of the ANF-PAM layer has little impact on the overall volume of the battery, which helps to maintain or increase the volume energy density of the lithium metal full battery. It provides the possibility to achieve a higher energy density battery without sacrificing safety and stability.

[0029] (7) The preparation method of the lithium battery separator described in the present invention has a simple process, is easy to prepare and industrialize, and fully meets the requirements of large-scale preparation. Description of the Drawings

[0030] Figure 1 It is a scanning electron microscope (SEM) image of the modified separator of the aramid nanofiber-based lithium metal battery prepared in Example 1.

[0031] Figure 2 It is a comparison chart of the cycling performance of the modified separator of the aramid nanofiber-based lithium metal battery in the lithium metal symmetric battery in Example 1. Detailed Embodiments

[0032] The present invention will be further described below in conjunction with the drawings and specific embodiments. Among them, the methods are conventional methods unless otherwise specified, and the raw materials can be obtained from public commercial channels unless otherwise specified.

[0033] The main reagents and instrument information involved in the following examples are shown in Table 1 in detail.

[0034] Table 1

[0035]

[0036] In the following examples and comparative examples, the lithium-lithium pair batteries were assembled and tested: both the positive electrode and the negative electrode were lithium metal sheets, the electrolyte was composed of 1 mol / L lithium hexafluorophosphate and a mixed solvent of ethylene carbonate and diethyl carbonate with a volume ratio of 1:1, a Celgard separator was used, and CR2025 type lithium-lithium pair batteries were assembled in a glove box; an electrochemical performance test was carried out on the assembled lithium-lithium pair batteries using a BlueTEC test system, and the test temperature was 30 °C.

[0037] Example 1

[0038] (1) 0.2 g of para-aramid short-cut fibers (PPTA), 0.3 g of potassium hydroxide (KOH), 100 ml of dimethyl sulfoxide (DMSO) and 4 ml of deionized water were successively added to a 250 ml beaker, and then evenly stirred at room temperature for 4 h to obtain a dark red ANF solution;

[0039] (2) 10.8 g of potassium persulfate powder was added to 400 ml of water and stirred until completely dissolved. The PP separator was immersed in the solution and maintained at 70 °C for three hours. After the reaction, it was taken out, washed, and dried to obtain a surface-activated PP separator;

[0040] (3) 0.3 g of PAN powder was added to 30 ml of dimethylformamide (DMF) solution and stirred until completely dissolved to obtain a PAN solution;

[0041] (4) 2 ml of the PAN solution in step (3) was taken and added to 10 ml of the ANF solution in step (1), and evenly stirred at room temperature.

[0042] (5) The above mixture was coated on the activated PP separator in step (2), the blade thickness was set to 100 μm, and after coating, it was placed in an oven at 50 °C and dried for 24 h. After taking out, the coated surface was laid flat in water for 1 h, and finally dried on a glass plate. The target material was obtained.

[0043] Two lithium-lithium symmetric batteries were assembled, with the only difference being that one was a lithium-lithium symmetric battery assembled with the prepared composite separator, and the other was a lithium-lithium symmetric battery assembled with a PP separator. The two lithium-lithium symmetric batteries were subjected to a cycling test at a current density of 2.0 mAh / cm 2 . The cycle life of the symmetric battery assembled with the PP separator was less than 150 h; the cycle life of the symmetric battery assembled with the composite separator was not less than 800 h. This shows that the modified composite separator has a great improvement in the cycling performance and can significantly extend the cycle life of the battery.

[0044] Example 2

[0045] (1) Add 0.2 g of chopped para-aramid fiber (PPTA), 0.3 g of potassium hydroxide (KOH), 100 ml of dimethyl sulfoxide (DMSO), and 4 ml of deionized water into a 250 ml beaker in sequence, and then stir evenly for 4 h at room temperature to obtain a dark red ANF solution;

[0046] (2) Add 10.8 g of potassium persulfate powder into 400 ml of water, stir until completely dissolved, immerse the PP separator into the solution, keep it at 70 °C for three hours, take it out after the reaction, wash and dry to obtain the surface-activated PP separator;

[0047] (3) Add 0.3 g of PAN powder into 30 ml of dimethylformamide (DMF) solution, stir until completely dissolved to obtain a PAN solution;

[0048] (4) Take 2 ml of the PAN solution in step (3) and add it into 10 ml of the ANF solution in step (1), and stir evenly at room temperature.

[0049] (5) Coat the above mixture onto the activated PP separator in step (2), set the blade thickness to 100 μm, put it into an oven at 50 °C after coating and dry for 24 h, take it out and place it on a glass plate. The target material is obtained.

[0050] Assemble two lithium-lithium symmetric batteries, the difference is only that: one is a lithium-lithium symmetric battery assembled with the prepared composite separator, and the other is a lithium-lithium symmetric battery assembled with a PP separator. The two lithium-lithium symmetric batteries are subjected to a cycling test at a current density of 2.0 mAh / cm 2 The cycle life of the symmetric battery assembled with the PP separator is less than 150 h; the cycle life of the symmetric battery assembled with the composite separator is not less than 850 h. This shows that the protective interlayer on the lithium metal sheet can greatly improve the cycling performance and can significantly extend the cycle life of the battery.

[0051] Example 3

[0052] (1) Add 0.2 g of chopped para-aramid fiber (PPTA), 0.3 g of potassium hydroxide (KOH), 100 ml of dimethyl sulfoxide (DMSO), and 4 ml of deionized water into a 250 ml beaker in sequence, and then stir evenly for 4 h at room temperature to obtain a dark red ANF solution;

[0053] (2) Add 10.8 g of potassium persulfate powder into 400 ml of water, stir until completely dissolved, immerse the PP separator into the solution, keep it at 70 °C for three hours, take it out after the reaction, wash and dry to obtain the surface-activated PP separator;

[0054] (3) Add 0.3 g of PAN powder into 30 ml of dimethylformamide (DMF) solution, and stir until it is completely dissolved to obtain a PAN solution.

[0055] (4) Take 1 ml of the PAN solution in step (3) and add it into 10 ml of the ANF solution in step (1), and stir evenly at room temperature.

[0056] (5) Coat the above-mentioned mixed solution onto the activated PP separator in step (2), set the blade thickness to 100 μm, after coating, put it into an oven at 50 °C and dry for 24 h. After taking it out, lay the coated surface flat in water for 1 h, and finally dry it on a glass plate. The target material is obtained.

[0057] Assemble two lithium-lithium symmetric cells, the only difference being that one is a lithium-lithium symmetric cell assembled with the prepared composite separator, and the other is a lithium-lithium symmetric cell assembled with a PP separator. The two lithium-lithium symmetric cells are subjected to a cycling test at a current density of 2.0 mAh / cm 2 The cycle life of the symmetric cell assembled with the PP separator is less than 150 h; the cycle life of the symmetric cell assembled with the composite separator is not less than 850 h. This shows that the protective interlayer on the lithium metal sheet can greatly improve the cycling performance and can significantly extend the cycle life of the battery.

[0058] Example 4

[0059] (1) Add 0.2 g of para-aramid short fiber (PPTA), 0.3 g of potassium hydroxide (KOH), 100 ml of dimethyl sulfoxide (DMSO) and 4 ml of deionized water into a 250 ml beaker in sequence, and then stir evenly for 4 h at room temperature to obtain a dark red ANF solution.

[0060] (2) Add 10.8 g of potassium persulfate powder into 400 ml of water, stir until it is completely dissolved, immerse the PP separator into the solution, keep it at 70 °C for three hours, take it out after the reaction is over, wash it, and dry it to obtain a surface-activated PP separator.

[0061] (3) Add 0.3 g of PAN powder into 30 ml of dimethylformamide (DMF) solution, and stir until it is completely dissolved to obtain a PAN solution.

[0062] (4) Take 1 ml of the PAN solution in step (3) and add it into 10 ml of the ANF solution in step (1), and stir evenly at room temperature.

[0063] (5) Coat the above-mentioned mixed solution onto the activated PP separator in step (2), set the blade thickness to 100 μm, put it in an oven at 50 °C for drying for 24 h after coating, and finally place it on a glass plate after taking it out. The target material is obtained.

[0064] Assemble two lithium-lithium symmetric cells, with the only difference being that one is a lithium-lithium symmetric cell assembled with the prepared composite separator and the other is a lithium-lithium symmetric cell assembled with a PP separator. The two lithium-lithium symmetric cells are subjected to a cycling test at a current density of 2.0 mAh / cm 2 The cycling life of the symmetric cell assembled with the PP separator is less than 150 h; the cycling life of the symmetric cell assembled with the composite separator is not less than 750 h. This shows that the protective interlayer on the lithium metal sheet can significantly improve the cycling performance and can significantly extend the cycling life of the battery.

[0065] Example 5

[0066] (1) Add 0.2 g of para-aramid short fibers (PPTA), 0.3 g of potassium hydroxide (KOH), 100 ml of dimethyl sulfoxide (DMSO) and 4 ml of deionized water to a 250 ml beaker in sequence, and then stir evenly for 4 h at room temperature to obtain a dark red ANF solution;

[0067] (2) Add 10.8 g of potassium persulfate powder to 400 ml of water, stir until completely dissolved, immerse the PP separator in the solution, keep it at 70 °C for three hours, take it out after the reaction is over, wash and dry it to obtain a surface-activated PP separator;

[0068] (3) Add 0.3 g of PAN powder to 30 ml of dimethylformamide (DMF) solution, stir until completely dissolved to obtain a PAN solution;

[0069] (4) Take 0.5 ml of the PAN solution in step (3) and add it to 10 ml of the ANF solution in step (1), and stir evenly at room temperature.

[0070] (5) Coat the above-mentioned mixed solution onto the activated PP separator in step (2), set the blade thickness to 100 μm, put it in an oven at 50 °C for drying for 24 h after coating, and then place the coated surface flat in water for 1 h, and finally place it on a glass plate for drying. The target material is obtained.

[0071] Assemble two lithium-lithium symmetric cells, with the only difference being that one is a lithium-lithium symmetric cell assembled with the prepared composite separator and the other is a lithium-lithium symmetric cell assembled with a PP separator. The two lithium-lithium symmetric cells are subjected to a cycling test at a current density of 2.0 mAh / cm 2The cyclic test was carried out at a current density of []. The cycle life of the symmetric cell assembled with the PP separator was less than 150 h; the cycle life of the symmetric cell assembled with the composite separator was not less than 750 h. This shows that the protective interlayer on the lithium metal sheet can greatly improve the cycling performance and significantly extend the cycle life of the battery.

[0072] Example 6

[0073] (1) 0.2 g of para-aramid short fibers (PPTA), 0.3 g of potassium hydroxide (KOH), 100 ml of dimethyl sulfoxide (DMSO) and 4 ml of deionized water were successively added to a 250 ml beaker, and then evenly stirred in a room temperature environment for 4 h to obtain a dark red ANF solution;

[0074] (2) 10.8 g of potassium persulfate powder was added to 400 ml of water and stirred until completely dissolved. The PP separator was immersed in the solution and kept at 70 °C for three hours. After the reaction, it was taken out, washed and dried to obtain a surface-activated PP separator;

[0075] (3) 0.3 g of PAN powder was added to 30 ml of dimethylformamide (DMF) solution and stirred until completely dissolved to obtain a PAN solution;

[0076] (4) 0.5 ml of the PAN solution in step (3) was added to 10 ml of the ANF solution in step (1) and evenly stirred at room temperature.

[0077] (5) The above mixture was coated on the activated PP separator in step (2), the blade thickness was set to 100 μm, and after coating, it was placed in an oven at 50 °C and dried for 24 h, and then taken out and placed on a glass plate. The target material was obtained.

[0078] Two lithium-lithium symmetric cells were assembled, with the only difference being that one was a lithium-lithium symmetric cell assembled with the prepared composite separator and the other was a lithium-lithium symmetric cell assembled with the PP separator. The two lithium-lithium symmetric cells were subjected to a cyclic test at a current density of 2.0 mAh / cm 2 The cycle life of the symmetric cell assembled with the PP separator was less than 150 h; the cycle life of the symmetric cell assembled with the composite separator was not less than 700 h. This shows that the protective interlayer on the lithium metal sheet can greatly improve the cycling performance and significantly extend the cycle life of the battery.

Claims

1. A preparation method of an aramid nanofiber-based modified separator for lithium metal batteries, characterized in that, The modified separator includes a base film, and at least one side surface of the base film is coated with a modified layer. The modified layer is polymerized from aramid nanofibers and polyacrylamide, and the copolymer layer is formed by in-situ reaction of aramid nanofibers and polyacrylonitrile in a solvent.

2. The modified separator for lithium metal battery based on aramid nanofibers according to claim 1, wherein The solvent is dimethyl sulfoxide.

3. The modified separator for lithium metal battery based on aramid nanofibers according to claim 1, characterized in that, The thickness of the polymer modified coating is 10μm - 100μm; Further preferably, the thickness of the polymer modified coating is 50μm - 100μm.

4. A method for preparing the modified separator according to any one of claims 1 to 3, characterized in that, It includes the following steps: S1: Put para-aramid short fibers and potassium hydroxide into dimethyl sulfoxide and deionized water for dissolution, and stir evenly at room temperature to obtain a dark red aramid nanofiber solution; S2: Add potassium persulfate powder into deionized water, stir to dissolve, then immerse the base film into the solution for activation treatment, take it out, wash and dry to obtain the surface-activated base film; S3: Add polyacrylonitrile powder into dimethylformamide solution, and stir evenly at room temperature until completely dissolved to obtain a polyacrylonitrile solution; S4: Add the polyacrylonitrile solution obtained in S3 into the aramid nanofiber solution obtained in S1, and stir evenly at room temperature to obtain a mixed solution; S5: Simply coat the mixed solution onto the surface-activated base film, put it into an oven at 50°C after coating and dry for 24h, then cool to obtain the required modified separator for lithium metal batteries.

5. The preparation method of the modified separator for lithium metal battery based on aramid nanofibers according to claim 4, wherein The concentration of the aramid nanofiber solution in S1 is 0.02 - 0.2g / ml.

6. The preparation method of the modified separator for lithium metal battery based on aramid nanofibers according to claim 4, characterized in that, The concentration of the potassium persulfate solution in S2 is 0.05 - 0.01g / ml.

7. The preparation method of the modified separator for lithium metal battery based on aramid nanofibers according to claim 4, wherein, The concentration of the polyacrylonitrile solution in S3 is 0.05 - 0.01g / ml.

8. The preparation method of the modified separator for lithium metal battery based on aramid nanofibers according to claim 4, characterized in that, The mass ratio of aramid nanofibers and polyacrylonitrile in the mixed solution in S4 is 1:1 to 10:

1. Further preferably, the mass ratio of aramid nanofibers and polyacrylonitrile in the mixed solution in S4 is 1:1 to 5:

1.

9. The preparation method of the modified separator for lithium metal battery based on aramid nanofibers according to claim 4, characterized in that, The stirring time in S1 is 4 - 8h.

10. The preparation method of the modified separator for lithium metal battery based on aramid nanofibers according to claim 4, characterized in that, The activation treatment temperature in S2 is maintained at 60 - 70°C for 3 - 5h.

11. The preparation method of the modified separator for lithium metal battery based on aramid nanofibers according to claim 4, characterized in that, The cooling in S5 is to lay it flat in water for 1 - 3h and then dry it on a glass plate or directly place it on a glass plate.

12. A battery, an electrochemical device or an electrical equipment using the modified separator described in any one of claims 1 - 3 and the modified separator prepared by the preparation method described in any one of claims 4 - 11.

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