High-power lithium ion battery diaphragm for grafting acrylonitrile through electron beam irradiation as well as preparation method and application of high-power lithium ion battery diaphragm

Abstract

The invention discloses a high-power lithium ion battery diaphragm for grafting acrylonitrile through electron beam irradiation and a preparation method and application thereof, and the preparation method comprises the following steps: (1) dissolving acrylonitrile in acetone to form a monomer solution for grafting; (2) putting the polypropylene diaphragm subjected to ultrasonic cleaning and drying into the grafted monomer solution, and fully soaking; and (3) carrying out electron beam irradiation treatment on the soaked diaphragm and the grafted monomer solution, then putting the treated diaphragm into absolute ethyl alcohol to wash, removing residual unreacted monomers and homopolymers, and finally drying to prepare the diaphragm. After grafting monomer solution preparation, diaphragm cleaning and soaking and electron beam irradiation treatment, a contact angle lower than 5 degrees can be realized, excellent wettability is achieved, the ionic conductivity is enhanced, ion transfer is accelerated, the rate capability of the battery is improved, and good application prospects are achieved.

Description

Technical Field

[0001] The present invention relates to the field of lithium-ion batteries, and particularly to a high-power lithium-ion battery separator grafted with acrylonitrile by electron beam irradiation, a preparation method thereof, and an application thereof. Background Art

[0002] As a core component of renewable energy systems, energy storage technology plays a crucial role in the efficient utilization and stable supply of energy. Currently, common energy storage technologies include electrochemical energy storage, mechanical energy storage, gravitational energy storage, electrical energy storage, thermal energy storage, superconducting magnetic energy storage, and hybrid energy storage systems. However, some energy storage technologies are difficult to meet market demands due to material performance limitations or insufficient feasibility. Electrochemical energy storage technology has gradually become the mainstream choice in the energy storage field due to its high system efficiency, modular design, wide application range (from small portable devices to large industrial devices), and potential for reducing pollution and greenhouse gas emissions. Electrochemical energy storage realizes the efficient conversion and storage between electrical energy and chemical energy through chemical reaction cycles and is one of the most promising energy storage technologies currently.

[0003] In an electrochemical energy storage system, the separator is a key component that undertakes the important functions of isolating the positive and negative electrodes to prevent short circuits and allowing electrolyte ions to pass freely. An ideal separator needs to have excellent electrochemical stability, thermal stability, mechanical strength, a reasonable pore structure, and good wetting performance to ensure the stability, long life, and high safety of the battery. However, the currently widely used commercial polyolefin separators have poor wettability due to their strong surface hydrophobicity and insufficient electrolyte affinity, which severely limits the ion transport efficiency and thus affects the overall performance of the battery. To solve this problem, separator modification technology has become the research focus. Traditional modification methods, such as chemical grafting and surface coating, can partially improve the separator performance, but still have limitations such as complex operation, uneven modification, and difficulty in large-scale production. Therefore, developing an efficient, precise, and easy-to-implement separator modification technology has become a key issue that urgently needs to be broken through in the current electrochemical energy storage field.

[0004] The electron beam irradiation process has gradually received extensive attention due to its uniform modification process, process controllability, suitability for large-scale production, and efficient and precise modification effect. How to efficiently utilize the electron beam irradiation process to improve the separator performance is a topic worthy of exploration. Summary of the Invention

[0005] Due to the poor wettability of the polyolefin separator of the battery, resulting in low ionic conductivity, and then problems such as rapid capacity loss and thermal runaway during high-power charge and discharge, the purpose of the present invention is to provide a high-power lithium-ion battery separator grafted with acrylonitrile by electron beam irradiation, its preparation method and application. By preparing a graft monomer solution, soaking and treating the separator after cleaning, and then combining with electron beam irradiation, a separator with a contact angle lower than 5° is successfully obtained, that is, it has excellent wettability, thereby improving the ionic conductivity, and significantly improving the performance of the lithium-ion battery under high power after application.

[0006] To solve the problems of the existing technology, the technical solution adopted by the present invention is as follows:

[0007] A preparation method of a high-power lithium-ion battery separator grafted with acrylonitrile by electron beam irradiation, comprising the following steps:

[0008] 2) Prepare a graft monomer solution:

[0009] Dissolve acrylonitrile in acetone at 15-25 °C to obtain a graft monomer solution with a volume fraction of 5-30%, and seal it for later use;

[0010] 2) Immerse the ultrasonically cleaned and dried separator in the graft monomer solution for 1-3 h;

[0011] 3) Perform electron beam irradiation treatment on the monomer solution soaked with the separator, then rinse the separator with anhydrous ethanol 2-3 times to remove unreacted acrylonitrile monomers and homopolymers, and dry it at 40-60 °C to obtain a high-power lithium-ion battery separator grafted with acrylonitrile by electron beam irradiation.

[0012] As an improvement, in step 1), the volume ratio of acrylonitrile to acetone is 20%.

[0013] As an improvement, the specific operation of the cleaning and drying treatment of the separator in step 2) is to immerse the separator in anhydrous ethanol and ultrasonically clean it at 80-100 Hz for 15-60 min, the drying temperature is 40-60 °C, and the drying time is 360-720 min.

[0014] As an improvement, the time for the separator to be immersed in the graft monomer solution in step 2) is 2 h.

[0015] As an improvement, in step 3), the energy of the electron beam irradiation is 100-200 keV; the irradiation dose is 1-200 kGy, the nitrogen value introduced is 99%, and the irradiation time is 1-90 s;

[0016] As a further improvement, the irradiation dose in step 3) is 20-200 kGy.

[0017] As an improvement, the drying temperature in step 3) is 60 °C and the time is 720 min.

[0018] The high-power lithium-ion battery separator grafted with acrylonitrile by electron beam irradiation prepared by the above preparation method.

[0019] A negative electrode material suitable for lithium-ion batteries, comprising the high-power lithium-ion battery separator grafted with acrylonitrile by electron beam irradiation prepared by the above preparation method.

[0020] Application of the above high-power lithium-ion battery separator grafted with acrylonitrile by electron beam irradiation or the above negative electrode material suitable for lithium-ion batteries in the preparation of lithium-ion batteries.

[0021] Beneficial effects:

[0022] In the present invention, a high-power lithium-ion battery separator grafted with acrylonitrile by electron beam irradiation, its preparation method and application, by preparing a graft monomer solution, soaking and treating the separator after cleaning, and then irradiating with an electron beam, a contact angle lower than 5° can be achieved. The obtained separator has excellent wettability, thereby effectively improving the ionic conductivity of the separator. Compared with a commercial polypropylene separator (0.09 mS cm-1), it is greatly increased to 0.52 mS cm-1. After being applied to the battery, the performance and safety level under high-rate conditions of 50C are improved. At the same time, the thermal stability of the modified separator is not negatively affected, and it has good rate performance.

[0023] The present invention innovatively introduces electron beam irradiation technology, which can efficiently break polymer chains and generate a large number of active sites on the surface of the separator. These active sites can induce cross-linking reactions and trigger new chemical reactions, which helps to improve the mechanical strength and thermal stability of the separator. Compared with traditional chemical grafting or surface coating methods, the process flow is simplified, the efficiency is high, the operation is simple, and precise directional modification can be achieved, and it has high processing energy efficiency.

[0024] In addition, by grafting acrylonitrile on the surface of the polypropylene separator, the introduction of polar functional groups (C≡N and C=O) significantly improves the wettability of the separator and enhances the ionic conductivity at the same time, thereby accelerating the transmission rate of lithium ions and comprehensively improving the application performance of the separator in lithium-ion batteries. It still has a capacity retention rate of 55.5% at a high current density of 50C, providing a reliable solution for optimizing the rate performance of the battery and showing broad application value. Description of the drawings

[0025] Figure 1 SEM pattern of the modified polypropylene separator prepared in Example 1;

[0026] Figure 2 FTIR pattern of the modified polypropylene separator prepared in Example 1;

[0027] Figure 3Contact angle test diagram of the modified polypropylene separator prepared in Example 1;

[0028] Figure 4 DSC spectrum of the modified polypropylene separator prepared in Example 1;

[0029] Figure 5 EIS spectrum of the modified polypropylene separator prepared in Example 1;

[0030] Figure 6 Rate performance diagram of the modified polypropylene separator prepared in Example 1. Detailed implementation manners

[0031] To better understand the technical solution of this application, the embodiments of this application will be described in detail below with reference to the accompanying drawings.

[0032] It should be clear that the described embodiments are only a part of the embodiments of this application, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in this application without creative efforts belong to the scope of this application.

[0033] The terms used in the embodiments of this application are only for the purpose of describing specific embodiments, and are not intended to limit this application. The singular forms of "a", "the" and "said" used in the embodiments of this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0034] It should be understood that the term " / and" used herein is only a description of the associated relationship of the associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A alone, A and B existing simultaneously, and B alone. In addition, the character " / " herein generally represents an "or" relationship between the associated objects before and after.

[0035] A preparation method of a high-power lithium-ion battery separator grafted with acrylonitrile by electron beam irradiation includes the following steps:

[0036] 3) Prepare a grafting monomer solution:

[0037] Dissolve acrylonitrile in acetone at 15-25 °C to obtain a grafting monomer solution with a volume fraction of 5-30%, and seal it for later use;

[0038] 2) Immerse the ultrasonically cleaned and dried separator in the grafting monomer solution for 1-3 h;

[0039] 3) The monomer solution soaked with the separator is irradiated with electron beam, and then the separator is rinsed with anhydrous ethanol 2-3 times to remove unreacted acrylonitrile monomer and homopolymer, and dried at 40-60 °C to obtain a high-power lithium-ion battery separator grafted with acrylonitrile by electron beam irradiation.

[0040] Specifically, in step 1), the volume ratio of acrylonitrile to acetone is 20%.

[0041] In step 2), the specific operation of cleaning and drying the separator is to immerse the separator in anhydrous ethanol and ultrasonically clean it at 80-100 Hz for 15-60 min, and the drying temperature is 40-60 °C and the drying time is 360-720 min.

[0042] In step 2), the time for the separator to be immersed in the grafting monomer solution is 2 h.

[0043] In step 3), the energy of electron beam irradiation is 100-200 keV; the irradiation dose is 1-200 kGy, and the irradiation time is 1-90 s;

[0044] In step 3), the irradiation dose is 20-200 kGy.

[0045] In step 3), the drying temperature is 60 °C and the time is 720 min.

[0046] The high-power lithium-ion battery separator grafted with acrylonitrile by electron beam irradiation prepared by the above preparation method.

[0047] A negative electrode material suitable for lithium-ion batteries, comprising the high-power lithium-ion battery separator grafted with acrylonitrile by electron beam irradiation prepared by the above preparation method.

[0048] The application of the above high-power lithium-ion battery separator grafted with acrylonitrile by electron beam irradiation or the above negative electrode material suitable for lithium-ion batteries in the preparation of lithium-ion batteries.

[0049] Specifically, the above negative electrode consists of a carrier and a coating layer, wherein the carrier is in a sheet structure, and the coating layer uniformly covers the surface of the carrier. The components of the coating layer include a conductive agent, a binder, and the above-mentioned lithium-ion battery negative electrode active material. In practical applications, the ratio of these three components can be configured according to 1:1:8. The carrier can be copper foil, carbon-coated aluminum foil or carbon paper. The conductive agent is acetylene black, and the binder is PVDF (a solution with a mass fraction of 8%). However, it should be noted that those skilled in the art can flexibly adjust the ratio of each component according to specific needs, and this embodiment does not provide strict restrictions on this.

[0050] For better understanding, the technical solutions provided in this application will be described in detail below with reference to specific embodiments.

[0051] Example 1

[0052] A preparation method of a high-power lithium-ion battery separator grafted with acrylonitrile by electron beam irradiation, comprising the following steps:

[0053] (1) At 20 °C, dissolve 8 ml of AN (acrylonitrile) in an acetone solution with a mass fraction of 32% according to a volume ratio of 1:4, and stir for 1 h to obtain a grafting monomer solution. It should be particularly noted that acrylonitrile is a volatile organic compound. If the stirring and mixing time is too long, the concentration will not be accurate enough, and it will affect the environment and people.

[0054] (2) Place the commercial polypropylene separator (Celgard 3401) in absolute ethanol and ultrasonically clean it at 80 - 100 Hz for 30 min. After cleaning, place it in a vacuum drying oven and dry it at 60 °C for 720 min, and then soak it in the grafting monomer solution for 2 h.

[0055] (3) Perform electron beam irradiation treatment on the grafting monomer solution soaked with the polypropylene separator. Among them, the conditions of the electron beam irradiation process are: irradiation energy 200 KeV, irradiation dose 50 kGy, nitrogen gas value introduced 99%, and irradiation time 15 s. Then wash the treated separator with absolute ethanol 3 times to remove unreacted acrylonitrile monomers and homopolymers, and then place it in a vacuum drying oven and dry it at 60 °C for 720 min to obtain a polypropylene separator modified by electron beam irradiation grafted with acrylonitrile.

[0056] Example 2

[0057] Except that the electron beam irradiation dose is changed to 20 kGy, the rest is the same as in Example 1.

[0058] Example 3

[0059] Except that the electron beam irradiation dose is changed to 100 kGy, the rest is the same as in Example 1.

[0060] Example 4

[0061] Except that the electron beam irradiation dose is changed to 150 kGy, the rest is the same as in Example 1.

[0062] Example 5

[0063] Except that the electron beam irradiation dose is changed to 200 kGy, the rest is the same as in Example 1.

[0064] Example 6

[0065] Except that the concentration of the acrylonitrile solution is changed to 10% (volume fraction), the rest is the same as in Example 1.

[0066] Comparative Example 1

[0067] Except changing the electron beam irradiation to ultraviolet radiation and irradiating with a 300W ultraviolet lamp at 30 cm for 40 min, the rest is the same as in Example 1.

[0068] The modified polypropylene separator prepared in Example 1 of the present invention was characterized as follows:

[0069] Figure 1 It is the SEM pattern of the high-power lithium-ion battery separator with acrylonitrile grafted by electron beam irradiation. It can be seen from the figure that acrylonitrile monomers were successfully grafted onto the surface of the separator, and the pores increased, and the overall morphology remained good.

[0070] Figure 2 It is the FTIR pattern of the high-power lithium-ion battery separator with acrylonitrile grafted by electron beam irradiation. Compared with the polypropylene separator before irradiation grafting modification, it contains a large number of polar groups such as C≡N and C=O, which are typical characteristics of acrylonitrile and free radicals generated by the cleavage of the polymer chain by electron beam irradiation, proving that acrylonitrile was successfully grafted onto the polypropylene separator by the electron beam irradiation process and a lot of active sites were generated.

[0071] Figure 3 It is the contact angle test pattern of the high-power lithium-ion battery separator with acrylonitrile grafted by electron beam irradiation. In Example 1, the contact angle of the polypropylene separator modified by electron beam irradiation grafting decreased significantly, proving that the increased polar groups of the polypropylene separator after grafting acrylonitrile improved the affinity of the electrolyte and its wettability.

[0072] Figure 4 It is the DSC pattern of the high-power lithium-ion battery separator with acrylonitrile grafted by electron beam irradiation. It can be seen from the figure that the melting temperature of Example 1 of the present invention did not change, indicating that the thermal stability of the separator after grafting acrylonitrile by irradiation was not negatively affected.

[0073] Figure 5 It is the EIS pattern of the high-power lithium-ion battery separator with acrylonitrile grafted by electron beam irradiation. It can be seen from the figure that the ionic conductivity of Example 1 of the present invention is higher, indicating that the separator after grafting acrylonitrile by irradiation, due to the increased C≡N and C=O polar groups, enhanced the electrolyte affinity and accelerated the ion transport speed, and thus the ionic conductivity was greatly improved.

[0074] Example 7

[0075] Weigh 240 mg of lithium vanadate material, 30 mg of acetylene black as a conductive agent, and 375 mg of an 8% mass fraction PVDF solution as a binder. Mix these three materials and stir them into a uniform slurry. Subsequently, coat the slurry evenly on the surface of a copper foil with a diameter of 1.2 cm, and use the copper foil coated with the active material as the negative electrode of the lithium-ion battery.

[0076] Rate performance test: Under normal temperature conditions, the prepared battery was tested on a LAND battery test system. The charge-discharge voltage range was 0.2 - 3V, and the specific capacity of the battery was tested at current densities of 0.2C, 0.5C, 1C, 2C, 5C, 10C, 20C, 30C, 40C, and 50C respectively.

[0077] Figure 6 This is the rate performance graph of the modified polypropylene separator prepared in Example 1 of the present invention matching the half-cell of lithium vanadate. From Figure 6 it can be seen that for the lithium vanadate half-cell matched with the irradiated and grafted modified separator, at 0.2C, it was 431 mAh / g; at a high current density of 50C, it had a high specific capacity of 239 mAh / g, demonstrating that the polypropylene separator modified by electron beam irradiation grafting acrylonitrile has excellent electrochemical performance.

[0078] The separators prepared in the above examples were tested for ionic conductivity, thermal shrinkage rate, and contact angle characterization, and were assembled with lithium vanadate materials and lithium metal sheets into button cells for rate performance evaluation. The test methods were all conventional technical means in the art, and the obtained experimental data are listed in Table 1.

[0079] Table 1 Ionic conductivity, thermal shrinkage rate, contact angle, and rate performance data of the separators obtained in different examples

[0080]

[0081]

[0082] From the results in Table 1, it can be seen that the concentration of the grafting monomer solution should be matched with the dose of electron beam irradiation. If the concentration of the grafting monomer solution is too low and the irradiation dose is low, it may cause acrylonitrile to fail to be successfully grafted onto the polypropylene separator, thus not achieving the modification effect; while if the concentration of the grafting monomer solution is too high and the irradiation dose is high, it will result in excessive acrylonitrile grafted onto the polypropylene separator, blocking the pores on the separator and affecting the ion transport. Appropriate monomer concentration and irradiation dose play a crucial role in obtaining the best wetting performance and ionic conductivity. In addition, through the test of the thermal shrinkage rate, it can be seen that the separator of the present invention has a thermal shrinkage rate of only 45% at a high temperature of 150°C, which is higher than that of commercial polypropylene separators (81%).

[0083] In summary, the polypropylene separator modified by electron beam irradiation grafting acrylonitrile in the present invention exhibits higher safety performance, ion transport efficiency, and rate performance as a lithium-ion battery separator. Electron beam irradiation can more effectively improve the ion transport speed of the separator compared to the ultraviolet radiation process, and the grafted acrylonitrile significantly improves the wettability of the separator.

[0084] The above has schematically described the present invention and its embodiments. This description is not restrictive. What is shown in the drawings is only one of the embodiments of the present invention, and the actual structure is not limited thereto. Therefore, if those of ordinary skill in the art are inspired by it and, without departing from the purpose of the present invention, design similar structural forms and embodiments to this technical solution without creative efforts, they shall fall within the protection scope of the present invention.

Claims

1. A method for preparing a high-power lithium-ion battery separator by electron beam irradiation grafted acrylonitrile, characterized in that: The following steps are involved: Preparation of grafting monomer solution: Dissolve acrylonitrile in acetone at 15-25°C to obtain a grafting monomer solution with a volume fraction of 5-30%, and seal and store for later use; 2) Soak the ultrasonically cleaned and dried diaphragm in the grafting monomer solution for 1-3 hours; 3) The monomer solution in which the diaphragm is soaked is subjected to electron beam irradiation treatment, and then the diaphragm is rinsed with anhydrous ethanol 2-3 times to remove unreacted acrylonitrile monomer and homopolymer, and dried at 40-60° C. to obtain a high-power lithium-ion battery diaphragm grafted with electron beam irradiation acrylonitrile.

2. The method for preparing a high-power lithium-ion battery separator by electron beam irradiation grafted acrylonitrile according to claim 1, characterized in that: In step 1), the volume ratio of acrylonitrile to acetone is 20%.

3. The method for preparing a high-power lithium-ion battery separator of electron beam irradiation grafted acrylonitrile according to claim 1, characterized in that: Step 2) The specific operation of cleaning and drying the middle diaphragm is to immerse the diaphragm in anhydrous ethanol and ultrasonically clean it at 80-100 Hz for 15-60 minutes, with a drying temperature of 40-60°C and a drying time of 360-720 minutes.

4. The method for preparing a high-power lithium-ion battery separator by electron beam irradiation grafted acrylonitrile according to claim 1, characterized in that: In step 2), the membrane is immersed in the grafting monomer solution for 2 hours.

5. The method for preparing a high-power lithium-ion battery separator by electron beam irradiation grafted acrylonitrile according to claim 1, characterized in that: In step 3), the energy of the electron beam irradiation is 100-200 KeV; the irradiation dose is 1-200 kGy, the nitrogen value is 99%, and the irradiation time is 1-90 s.

6. The method for preparing a high-power lithium-ion battery separator by electron beam irradiation grafted acrylonitrile according to claim 5, characterized in that: The irradiation dose in step 3) is 20 to 200 kGy.

7. The method for preparing a high-power lithium-ion battery separator by electron beam irradiation grafted acrylonitrile according to claim 1, characterized in that: The drying temperature in step 3) is 60°C and the drying time is 720 minutes.

8. A high-power lithium-ion battery separator prepared by the preparation method according to any one of claims 1 to 7 and grafted with acrylonitrile by electron beam irradiation.

9. A negative electrode material suitable for lithium-ion batteries, comprising the high-power lithium-ion battery separator of electron beam irradiated acrylonitrile grafted thereon according to claim 8.

10. Use of the electron beam irradiated acrylonitrile grafted high-power lithium ion battery separator according to claim 8 or the negative electrode material suitable for lithium ion battery according to claim 9 in the preparation of lithium ion batteries.

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