A functionalized coated separator and lithium-ion battery

Abstract

A functionalized coated separator and lithium-ion battery, by grafting and modifying the polymer backbone PVDF of the coating layer with single-ion conductor lithium salt, effectively constructs a single-lithium-ion conduction ion transport layer at the electrode / electrolyte interface without changing the original function of the coating layer. In lithium-ion battery systems, only lithium ions actually participate in the electrochemical reaction and energy conversion process. The movement of anions in the electrolyte will cause their accumulation on the electrode surface, leading to increased battery polarization and interfacial side reactions. The PVDF coating layer itself can effectively improve the adhesion between the separator and the electrode and the wettability with the electrolyte. By introducing immobilized anionic groups on the PVDF backbone, the functionalization of interfacial single-lithium-ion transport provided by this invention can further optimize the performance of the coating layer, the separator, and the liquid lithium-ion battery.

Description

Technical Field

[0001] This invention relates to the field of new energy materials technology, specifically to a functionalized coated separator and a lithium-ion battery. Background Technology

[0002] Lithium-ion batteries have been widely used in portable devices due to their high energy density and good cycle performance. The separator is a multi-microporous membrane placed between the positive and negative electrodes, allowing ions to pass freely while preventing direct contact between the electrodes. Currently, the main commercial separator materials are porous polymer films based on polyolefins. However, polyolefin separators suffer from poor adhesion to the electrode plates and insufficient hydrophilicity with carbonate electrolytes. This leads to a series of problems, including poor cycle performance, low thermal stability, unstable electrode-separator interface, poor battery hardness, and difficulties in processing and transportation. These issues significantly limit the improvement of battery energy density and cycle life, as well as the development of high-performance ultra-thin batteries.

[0003] To improve the adhesion of polyolefin separators to electrodes and their wettability with electrolytes, the main solution currently is to coat the polyolefin separator with a polyvinylidene fluoride (PVDF) coating, constructing a so-called coated separator. Because the molecular chains of oil-based PVDF coatings are in an extended state, compared to the coiled state in water-based coatings, it is easier to make thinner and has higher peel strength. This coating layer can effectively improve the adhesion of the separator and also has good wettability with the electrolyte, which can greatly improve battery performance. However, the electrolytes used in currently commercial lithium-ion batteries are dual-ion systems, meaning that lithium ions and anions dissociated from lithium salts move simultaneously in the electrolyte. In reality, anions do not participate in the energy conversion reaction inside the battery; their migration and accumulation on the electrode surface can also cause the formation of a space charge layer at the electrode / electrolyte interface, increasing polarization and negatively impacting the battery's rate performance. Summary of the Invention

[0004] To address the technical deficiencies of existing technologies, this invention provides a functionalized coated separator and a lithium-ion battery. PVDF powder is first grafted to introduce a single-ion conductor lithium salt structure onto its chain segments, and then dissolved and coated onto the surface of a polyolefin separator. This functionalized coated separator can effectively solve battery polarization problems caused by anion enrichment on the electrode surface, further improving the performance of the coated separator and existing commercial liquid lithium-ion batteries.

[0005] The technical solution adopted in this invention is: a functionalized coated diaphragm, comprising a diaphragm substrate and a functionalized single-ion conductor modified coating layer coated on the diaphragm substrate, wherein the functionalized single-ion conductor modified coating layer is a polyvinylidene fluoride coating grafted with single-ion conductor lithium salt. The structure of the diaphragm substrate can be a single layer, or a double-layer or multi-layer structure composed of the above materials.

[0006] The thickness of the adhesive coating layer is 50nm-10μm, preferably 0.5nm-1μm.

[0007] The single-ion conductor lithium salt package is one or more of lithium acrylate, lithium vinyl sulfonate, lithium [(trifluoromethyl)(vinyl)]sulfonylimide, lithium vinyl borate, lithium allyl sulfonate, and 2-acrylamide-2-methylpropanesulfonic acid.

[0008] The grafting rate of the polyvinylidene fluoride coating grafted with lithium salt of single ion conductor is 5%-80%.

[0009] The membrane substrate is a polyolefin porous polymer membrane.

[0010] The polyolefin porous polymer membrane includes, but is not limited to, polymer membranes composed of at least one of the following polymers: polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyvinyl chloride, polyethylene terephthalate, polybutylene terephthalate, polymethyl methacrylate, polyacrylonitrile, polyimide, polyethylene oxide, or blends or copolymers derived from the above polymers.

[0011] A method for preparing a functionalized coated diaphragm includes the following steps:

[0012] (1) Preparation of polyvinylidene fluoride coating grafted with single-ion conductor lithium salt: PVDF powder was fully dispersed in a single-ion conductor lithium salt aqueous solution for surface grafting treatment. The final product was centrifuged, washed and dried to obtain PVDF powder grafted with single-ion lithium salt.

[0013] (2) Preparation of functionalized coated diaphragm: The grafted PVDF is fully dissolved in an organic solvent, and the PVDF coating layer modified by single-ion conductor lithium salt grafting is applied to the polyolefin porous polymer diaphragm by casting or electrospinning. After drying, the functionalized coated diaphragm is obtained.

[0014] In step (1), surface grafting is performed by co-irradiation grafting or heating reaction.

[0015] A lithium-ion battery includes a positive electrode material, a negative electrode material, and a non-aqueous electrolyte, wherein the positive electrode material and the negative electrode material are separated by a functionalized coated separator as described in claim 1.

[0016] The lithium-ion battery mentioned includes a liquid lithium-ion battery.

[0017] The non-aqueous electrolyte secondary battery provided by the present invention only needs to have the ceramic separator with the above-mentioned multilayer composite structure. There are no particular restrictions on other components, and the components used in conventional non-aqueous electrolyte secondary batteries can be adopted.

[0018] The beneficial effects of this invention are as follows: This invention provides a functionalized coated separator and lithium-ion battery. By modifying the polymer skeleton PVDF of the coating layer through grafting with single-ion conductor lithium salt, a single-lithium-ion conduction ion transport layer is further constructed at the electrode / electrolyte interface without changing the original function of the coating layer. Since only lithium ions actually participate in the electrochemical reaction and energy conversion process in lithium-ion battery systems, the movement of anions in the electrolyte will cause their accumulation on the electrode surface, leading to increased battery polarization and the occurrence of interfacial side reactions. The PVDF coating layer itself can effectively improve the adhesion between the separator and the electrode and the wettability with the electrolyte. By introducing immobilized anionic groups on the PVDF skeleton, the functionalization of interfacial single-lithium-ion transport provided by this invention can further optimize the performance of the coating layer, the separator, and the liquid lithium-ion battery. Attached Figure Description

[0019] Figure 1 The functionalized coated diaphragm obtained in Example 2.

[0020] Figure 2 The image shows the infrared spectrum of the grafted modified PVDF powder obtained in Example 2.

[0021] Figure 3 The graph shows the battery cycle performance of Example 4 and Comparative Example 4. Detailed Implementation

[0022] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] Example 1:

[0024] Take 5 grams of PVDF powder and fully disperse it in a 30% (w / w) aqueous solution of lithium allyl sulfonate. Place the solution into... 60Co-irradiation grafting was performed in a Coγ-ray field with an irradiation dose of 15 kGy. After irradiation, the final product was centrifuged, washed, and dried to obtain PVDF powder grafted with single-ion lithium salt. Weight gain and infrared spectroscopy tests showed that lithium allyl sulfonate was successfully grafted onto the PVDF framework with a grafting rate of 20%.

[0025] 1 gram of grafted PVDF was fully dissolved in 10 g of N-methylpyrrolidone solution, and the solution was cast onto the surface of a polypropylene diaphragm. After drying with solvent, a functionalized coated diaphragm was obtained.

[0026] Example 2:

[0027] Take 5 grams of PVDF powder and place it in a 3 mol / L potassium hydroxide aqueous solution. o After being treated at C for 12 hours, the powder was centrifuged and then dispersed in a 30% (w / w) aqueous solution of lithium allyl sulfonate, and heated to 80°C. o C. Surface grafting treatment was performed. This process was carried out under a nitrogen protective atmosphere. The final product, after centrifugation, washing, and drying, yielded PVDF powder grafted with single-ion lithium salt. Weight gain and infrared spectroscopy tests showed that lithium allyl sulfonate was successfully grafted onto the PVDF framework, with a grafting rate of 9.6%.

[0028] 5g of grafted PVDF was dissolved in a mixed solution of 10g N,N-dimethylformamide and 15g acetone until fully dissolved. 10ml of this PVDF solution was transferred into a 30ml syringe. A 20cm × 80cm Asahi Kasei wet-process polyethylene diaphragm substrate was placed on a roller collector and secured with tape. The electrospinning parameters were adjusted as follows: positive voltage 10kV; negative voltage -2kV; syringe advance speed 0.2mm / min; collector rotation speed 50rpm; distance between syringe and collector 25cm. After electrospinning, a single-ion conductor lithium salt grafted modified PVDF coating layer with a thickness of approximately 1µm was obtained. This layer was then placed in a vacuum drying oven at 60℃ for 24h to obtain the functionalized coated diaphragm.

[0029] Example 3:

[0030] Take 5 grams of PVDF powder and fully disperse it in a lithium [(trifluoromethyl)(vinyl)]sulfonylimide solution. Place the solution into... 60 Co-irradiation grafting was performed in a Coγ-ray field with an irradiation dose of 10 kGy. After irradiation, the final product was extracted and separated into self-polymerized products, centrifuged, washed, and dried to obtain PVDF powder grafted with single-ion lithium salt. Weight gain and infrared spectroscopy tests showed that lithium allyl sulfonate was successfully grafted onto the PVDF framework with a grafting rate of 30%.

[0031] 1 gram of grafted PVDF was fully dissolved in a mixed solution of 1 g n-butanol and 6 g acetone. The solution was then coated onto the surface of a three-layer polyolefin membrane and dried with the solvent to obtain a functionalized coated membrane.

[0032] Comparative Example 1:

[0033] 5g of PVDF was dissolved in a mixed solution of 10g N,N-dimethylformamide and 15g acetone until fully dissolved. 10ml of this PVDF solution was then transferred to a 30ml syringe. A 20cm × 80cm Asahi Kasei wet-process polyethylene diaphragm substrate was placed on a roller collector and secured with tape. The electrospinning parameters were adjusted as follows: positive voltage 10kV; negative voltage -2kV; syringe advance speed 0.2mm / min; collector rotation speed 50rpm; distance between syringe and collector 25cm. After electrospinning, a single-ion conductor lithium salt grafted modified PVDF coating layer with a thickness of approximately 1µm was obtained. This layer was then placed in a vacuum drying oven at 60℃ for 24h to obtain the coated diaphragm.

[0034] Comparative Example 2:

[0035] 1 gram of PVDF was fully dissolved in 10 g of N-methylpyrrolidone solution, and the solution was cast onto the surface of a polypropylene diaphragm. After drying with solvent, the coated diaphragm was obtained.

[0036] Example 4:

[0037] A battery includes a positive electrode material and a negative electrode material, with a functionalized coated separator prepared in Example 1 between the positive electrode material and the negative electrode material.

[0038] Example 5:

[0039] A battery includes a positive electrode material and a negative electrode material, with a functionalized coated separator prepared in Example 2 between the positive electrode material and the negative electrode material.

[0040] Example 6:

[0041] A battery includes a positive electrode material and a negative electrode material, with a functionalized coated separator prepared in Example 3 between the positive electrode material and the negative electrode material.

[0042] Comparative Example 3:

[0043] A battery includes a positive electrode material and a negative electrode material, with a coated separator prepared in Comparative Example 1 between the positive electrode material and the negative electrode material.

[0044] Comparative Example 4:

[0045] A battery includes a positive electrode material and a negative electrode material, with a coated separator prepared in Comparative Example 2 between the positive electrode material and the negative electrode material.

[0046] Through append Figure 3 It is evident that the liquid lithium-ion battery using the functionalized coated separator of this invention exhibits superior performance compared to the coated separator using a PVDF coating without grafted single-ion conductor lithium salt.

[0047] Please note to all technical personnel: Although the present invention has been described according to the specific embodiments above, the inventive concept of the present invention is not limited to this invention. Any modifications that utilize the inventive concept will be included within the scope of protection of this patent.

[0048] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A functionalized gelled separator, characterized in that, The functionalized single-ion conductor modified adhesive layer coated on the diaphragm substrate is a polyvinylidene fluoride coating layer grafted with a single-ion conductor lithium salt.

2. The functionalized gelled separator of claim 1, wherein, The adhesive layer has a thickness of 0.5 nm to 1 μm.

3. The functionalized gelled separator of claim 1, wherein, The single-ion conductor lithium salt is one or more of lithium acrylate, lithium vinyl sulfonate, lithium [(trifluoromethyl)(vinyl)] sulfonimide, lithium vinyl borate, and lithium allyl sulfonate.

4. The functionalized gelled separator of claim 1, wherein, The grafting rate of the polyvinylidene fluoride coating layer grafted with the single-ion conductor lithium salt is 5% to 80%.

5. The functionalized gelled separator of claim 1, wherein, The diaphragm substrate is a polyolefin porous polymer diaphragm.

6. The functionalized gelled separator of claim 5, wherein, The polyolefin porous polymer diaphragm is a polymer film composed of at least one of polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyvinyl chloride, polyethylene terephthalate, polybutylene terephthalate, polymethyl methacrylate, polyacrylonitrile, polyimide, polyethylene oxide, or a blended or copolymerized system derived from the above polymers.

7. A method of preparing the functionalized gummed separator according to claim 1, characterized by, The method comprises the following steps: (1) preparing a single-ion conductor lithium salt grafted polyvinylidene fluoride coating layer: dispersing PVDF powder in a single-ion conductor lithium salt aqueous solution to perform surface grafting treatment, and obtaining a single-ion lithium salt grafted PVDF powder after centrifugation, washing, and drying of the final product; (2) preparing a functionalized adhesive diaphragm: dissolving the grafted PVDF in an organic solvent, and obtaining a single-ion conductor lithium salt grafted PVDF adhesive layer on a polyolefin porous polymer diaphragm by means of flow coating or electrospinning, and obtaining a functionalized adhesive diaphragm after drying.

8. The production method according to claim 7, characterized by, The surface grafting in step (1) is performed by co-irradiation grafting or heating reaction.

9. A lithium ion battery comprising a positive electrode material, a negative electrode material and a nonaqueous electrolyte, characterized in that, The functionalized adhesive diaphragm is arranged between the positive electrode material and the negative electrode material.

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