Semi-solid lithium battery diaphragm and preparation method thereof

Abstract

The invention belongs to the field of lithium ion batteries, and particularly relates to a semi-solid lithium battery diaphragm and a preparation method thereof.The semi-solid lithium battery diaphragm comprises a base membrane and gradient functional coatings coated on the two sides of the base membrane, the base membrane is a polyimide membrane, and each gradient functional coating comprises a bonding layer on the bottom layer, a regulating layer on the surface layer and a filling layer located between the bonding layer and the regulating layer; the bonding layer comprises a component A, and the component A comprises a polymer matrix, a disulfide bond-containing cross-linking agent, a coupling agent and a first solvent; the polymer matrix comprises polyimide and polyurethane; the filling layer comprises a component B and a component A, and the component B comprises core-shell particles and a dispersing agent, wherein the core-shell particles are formed by coating Li1. 3Al0. 3Ti1. 7 (PO4) 3 particles with ZrO2; the regulation and control layer comprises perfluorinated sulfonic acid resin, a plasticizer, an interface stabilizer, a second solvent and deionized water. Through the synergistic effect of all the layers in the gradient functional coating, the self-repairing performance of a damaged interface of the diaphragm can be achieved, and the strength of the diaphragm is improved.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion batteries, specifically relating to a semi-solid lithium battery separator and its preparation method. Background Technology

[0002] Compared to traditional liquid lithium batteries, semi-solid-state lithium batteries have an electrolyte that lies between liquid and solid states, typically in a gel-like or mixed state containing a small amount of liquid components. They offer advantages such as high energy density, high ion conductivity at low temperatures, strong safety, and fast charging speed. In the structure of a semi-solid-state lithium battery, the separator, serving as the physical isolation layer between the positive and negative electrodes, is one of the key internal components. The quality of the separator directly affects crucial characteristics of the semi-solid-state battery, including its interface structure, internal resistance, battery capacity, and safety performance.

[0003] However, during the charging and discharging process, the separator is prone to structural changes, such as the decomposition and embrittlement of the adhesive between the base film and the coating, the shedding of coating particles, and the separation and detachment of the base film and the coating. These changes lead to a decrease in the battery capacity and safety performance of the semi-solid lithium battery, reduce its durability, and pose certain safety hazards. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a semi-solid lithium battery separator and its preparation method. The present invention can achieve the self-repair performance of the damaged interface of the separator through the synergistic effect of each layer in the gradient functional coating, improve the strength of the separator, improve the conductivity while inhibiting the reaction between the electrolyte and the gradient functional coating, and improve the buffering capacity of the separator against volume stress, thereby improving the durability of the semi-solid lithium battery.

[0005] The technical solution adopted by the present invention to solve the above problems is as follows:

[0006] A semi-solid-state lithium battery separator includes a base film with a thickness of 4-6 μm and a gradient functional coating coated on both sides of the base film. The base film is a polyimide film. The gradient functional coating includes a bottom adhesive layer, a top regulating layer, and a filler layer located between the adhesive layer and the regulating layer. The adhesive layer, filler layer, and regulating layer each include the following components calculated in parts by weight:

[0007] The adhesive layer includes component A, which includes 12-20 parts of polymer matrix, 4-8 parts of crosslinking agent containing disulfide bonds, 2-4 parts of coupling agent, and 12-18 parts of first solvent; the polymer matrix includes polyimide and polyurethane, and the mass ratio of polyimide to polyurethane is 1.5:1.

[0008] The filling layer includes component B and component A, wherein component B comprises ZrO2-encapsulated Li. 1.3 Al 0.3 Ti 1.7(PO4)3 particles, core-shell particles 8-10 parts, dispersant 4-6 parts; ZrO2 and Li 1.3 Al 0.3 Ti 1.7 The mass ratio of (PO4)3 particles is 4:6, and the mass ratio of core-shell particles to component A is 1:2 to 3;

[0009] The control layer comprises 6-8 parts of perfluorosulfonic acid resin, 2-5 parts of plasticizer, 1-3 parts of interface stabilizer, 9-12 parts of second solvent, and 1-3 parts of deionized water.

[0010] The thickness of the adhesive layer is 2.5–3.5 μm, the thickness of the filler layer is 5–8 μm, and the thickness of the regulating layer is 0.5–2 μm.

[0011] Through the above technical solutions, this invention combines a base film with a gradient functional coating. The adhesive layer introduces disulfide bonds to form a dynamic cross-linked network. After the chemical bonds between the base film and the adhesive layer break, reversible recombination of SS bonds can be initiated, thereby achieving dynamic repair of the damaged interface, improving the bonding strength of the interface, and making the coating less prone to peeling. The filling layer, through core-shell particles, can inhibit the reaction between the electrolyte and the core material of the core-shell particles, and can also form continuous lithium-ion transport channels through ZrO2, enhancing the stability of the semi-solid lithium battery while improving its conductivity. The perfluorosulfonic acid resin in the regulation layer can selectively adsorb free lithium ions in the electrolyte through sulfonic acid groups. Combined with the plasticizer to form a flexible network structure, it can effectively buffer the volume stress during charging and discharging, stabilize the electrode interface, and improve the durability of the semi-solid lithium battery.

[0012] Furthermore, the crosslinking agent includes at least one of succinimid-disulfide active ester-succinimid, polyethylene glycol dithiodipropionate, dimethyl 3,3'-dithiodipropionate, and dithiodibenzoate.

[0013] Furthermore, the coupling agent includes at least one of silane coupling agents, titanate coupling agents, and sulfur-containing coupling agents.

[0014] Further, the silane coupling agent includes at least one of titanylaminopropyltriethoxysilane, methacryloxypropyltrimethoxysilane, and vinyltrimethoxysilane; the titanate coupling agent includes at least one of isopropyltris(dioctylphosphoyloxy)titanate and bis(dioctylpyrophosphoyloxy)ethylene titanate; the sulfur-containing coupling agent includes at least one of bis-[3-(triethoxysilyl)propyl]-disulfide and 3-mercaptopropyltrimethoxysilane.

[0015] Through the above technical solutions, the coupling agent can enhance the anchoring strength between the base film and the coating, thereby further improving the stability of the diaphragm.

[0016] Furthermore, the dispersant includes at least one of polyacrylamide and polyvinylpyrrolidone.

[0017] Furthermore, the plasticizer includes at least one of polyethylene glycol dimethyl ether, dioctyl phthalate, triethyl citrate, diisononyl adipate, and polyethylene oxide.

[0018] By using the above technical solutions, adding plasticizers can improve the flexibility of the coating, making the diaphragm less prone to breakage and improving the stability of the diaphragm.

[0019] Furthermore, the interface stabilizer includes at least one of perfluoropolyether ammonium carboxylate, lithium dioxaborate, fluoroethylene carbonate, and lithium difluorophosphate.

[0020] Further, the first solvent includes at least one of N-methylpyrrolidone, dimethyl sulfoxide, and propylene carbonate, and the second solvent includes at least one of N-methylpyrrolidone, dimethyl sulfoxide, and propylene carbonate.

[0021] Furthermore, the method for preparing the core-shell particles includes the following steps:

[0022] A1. Mix zirconium oxychloride with a 70% ethylene glycol solution, with a mass ratio of zirconium oxychloride to ethylene glycol solution of 1:5-8. Then add polyethylene glycol at a total mass of 0.1% of zirconium oxychloride and ethylene glycol solution, and stir until homogeneous to obtain zirconium sol.

[0023] A2. Li 1.3 Al 0.3 Ti 1.7 (PO4)3 particles were soaked in 0.1 mol / L oxalic acid for 20–40 min, filtered through a 0.25–0.35 μm microporous membrane, and then the treated Li... 1.3 Al 0.3 Ti 1.7 (PO4)3 particles were added to the zirconium sol, and Li 1.3 Al 0.3 Ti 1.7 The mass ratio of (PO4)3 particles to zirconium sol is 1:6-8. The mixture is ultrasonically dispersed for 30-50 min, and then ammonia is added to adjust the pH to 9-9.5. The mixture is then aged at 60-65℃ and a stirring speed of 60-120 rpm for 2-3 h to obtain the crude coating solution.

[0024] A3. Filter the coarse coating solution through a microporous membrane of 0.25-0.35 μm, collect the particles, anneal them at 550℃ for 3-4 h, then cool them down to 200℃, remove the particles, and allow them to cool naturally to room temperature to obtain core-shell particles.

[0025] Furthermore, the thickness of the adhesive layer is 7–9 μm, the thickness of the filler layer is 13–17 μm, and the thickness of the regulating layer is 2–3 μm.

[0026] This invention provides a method for preparing the above-mentioned semi-solid lithium battery separator, comprising the following steps:

[0027] S1. The base film is subjected to corona treatment, and the power density of the corona treatment is adjusted to 3-4 W / cm². 2 The time is 4-6 seconds, and then the base film is ultrasonically cleaned with isopropanol at a power of 30-50 kHz for 8-12 minutes to obtain the pretreated base film.

[0028] S2. Mix polyimide, polyurethane, crosslinking agent, coupling agent and first solvent, disperse at 1800-2200 rpm for 20-40 min to obtain component A, coat component A on both sides of the pretreated base film, dry with hot air at 75-80℃ for 5-10 min to form an adhesive layer, and obtain semi-finished diaphragm 1.

[0029] S3. Mix the core-shell particles, dispersant and component A evenly. The mass ratio of core-shell particles to component A is 1:2 to 3 to obtain slurry 2. Coat slurry 2 on both sides of the semi-finished diaphragm 1 and then perform gradient drying. The initial drying temperature is 60°C, and the temperature is increased by 20°C per minute until it reaches 120°C. Then cool it to room temperature to form a filling layer to obtain the semi-finished diaphragm 2.

[0030] S4. Mix the perfluorosulfonic acid resin, plasticizer, interface stabilizer, second solvent and deionized water evenly, and then spray it on both sides of the semi-finished diaphragm 2. The spraying pressure is 0.3-0.4 MPa. Then, vacuum dry at 70-90℃ for 2-5 minutes to form a control layer and obtain the finished product.

[0031] The present invention has the following beneficial effects:

[0032] 1. This invention achieves self-repair performance of the damaged interface of the separator through the synergistic effect of each layer in the gradient functional coating, improves the strength of the separator, enhances the conductivity while inhibiting the reaction between the electrolyte and the gradient functional coating, and improves the buffering capacity of the separator against volume stress, thereby improving the durability of the semi-solid lithium battery.

[0033] 2. The preparation method of the present invention is simple to operate and can improve the bonding ability of each layer in the gradient functional coating, thereby further improving the stability of the diaphragm. Detailed Implementation

[0034] To make the technical problems, solutions, and advantages of this invention clearer, a detailed description will be provided below with reference to specific examples. However, the scope of protection of this invention is not limited to the following specific embodiments. The described embodiments are merely some, not all, of the embodiments of this invention, and are not intended to limit the invention. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0035] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0036] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0037] In the quantitative experiments in the following examples, three replicate experiments were set up, and the data are the average of the three replicate experiments or the average ± standard deviation.

[0038] The semi-solid lithium battery separators of the present invention are respectively provided in Examples 1 to 3 and Comparative Examples 1 to 4. The specific components and contents are shown in Table 1, and the units are parts by weight.

[0039] Table 1

[0040]

[0041]

[0042] Specifically, the preparation method of core-shell particles in the above embodiments and comparative examples includes the following steps:

[0043] A1. Mix zirconium oxychloride with a 70% ethylene glycol solution at a mass ratio of 1:7. Then add polyethylene glycol at a mass ratio of 0.1% of the total mass of zirconium oxychloride and ethylene glycol solution, and stir until homogeneous to obtain zirconium sol.

[0044] A2. Li 1.3 Al 0.3 Ti 1.7 (PO4)3 particles were soaked in 0.1 mol / L oxalic acid for 30 min, filtered through a 0.25 μm microporous membrane, and then the treated Li... 1.3 Al 0.3 Ti 1.7 (PO4)3 particles were added to the zirconium sol, Li 1.3 Al 0.3 Ti 1.7The mass ratio of (PO4)3 particles to zirconium sol was 1:8. The mixture was ultrasonically dispersed for 50 min, and then ammonia was added to adjust the pH to 9. The mixture was aged at 60℃ and 60 rpm for 2 h to obtain the crude coating solution.

[0045] A3. Filter the coarse coating solution through a 0.25μm microporous membrane, collect the particles, anneal at 550℃ for 3h, then cool to 200℃, remove the particles, and allow them to cool naturally to room temperature to obtain core-shell particles.

[0046] Specifically, the method for preparing the semi-solid lithium battery separator in the embodiment includes the following steps:

[0047] S1. A 5μm thick polyimide film is subjected to corona treatment, with the power density of the corona treatment adjusted to 3W / cm². 2 The time is 5s, and then the polyimide film is ultrasonically cleaned with isopropanol at a power of 40kHz for 10min to obtain the pretreated base film.

[0048] S2. Polyimide, polyurethane, succinimide-disulfide bond active ester-succinimide, vinyltrimethoxysilane and N-methylpyrrolidone are mixed and dispersed at 2000 rpm for 30 min to obtain component A. Component A is coated on both sides of the pretreated base membrane and dried with hot air at 80℃ for 10 min to form an adhesive layer with a thickness of 3 μm to obtain semi-finished membrane 1.

[0049] S3. Mix the core-shell particles, polyvinylpyrrolidone and component A evenly, with the mass ratio of core-shell particles to component A being 1:2, to obtain slurry 2. Coat slurry 2 on both sides of the semi-finished diaphragm 1 and perform gradient drying. The initial drying temperature is 60°C, and the temperature is increased by 20°C per minute until it reaches 120°C. Then cool it to room temperature to form a filling layer with a thickness of 6μm, to obtain the semi-finished diaphragm 2.

[0050] S4. Mix perfluorosulfonic acid resin, polyethylene glycol dimethyl ether, lithium difluorophosphate, propylene carbonate and deionized water evenly, and then spray it on both sides of the semi-finished diaphragm 2 at a pressure of 0.3 MPa. Then, vacuum dry at 80°C for 2-5 minutes to form a control layer with a thickness of 1 μm to obtain the finished product.

[0051] Similarly, the preparation method for the comparative proportion can be obtained. If there are substances that are not added or replaced, they can be deleted or replaced in the corresponding preparation steps.

[0052] Experimental test:

[0053] Tensile strength (refer to GB / T 1040.3-2006), interfacial peel strength (refer to GB / T8808-1988), heat shrinkage rate (refer to GB / T 36363-2018), ionic conductivity (refer to GB / T 36363-2018), interfacial resistance (refer to GB / T 18287-2013), and cycle performance (refer to GB / T 18287-2013) were tested for the examples and comparative examples. Specific test data are shown in Table 2.

[0054] Table 2

[0055]

[0056]

[0057] The test results of Examples 1 to 3 show that the diaphragm of the present invention has excellent tensile strength and peel strength, demonstrating that the diaphragm of the present invention has high strength and self-healing performance, while also having good thermal stability and ionic conductivity, high cycle retention rate, and excellent stability.

[0058] By comparing the test results of Example 2 with those of Comparative Examples 1 and 2, it can be seen that, compared with the absence of a crosslinking agent containing disulfide bonds or the absence of a crosslinking agent, the addition of a crosslinking agent containing disulfide bonds can improve the tensile strength and interfacial peel strength of the diaphragm, and significantly reduce the heat shrinkage rate and cycle retention rate. This indicates that the crosslinking agent containing disulfide bonds can improve the strength, stability and self-healing performance of the diaphragm.

[0059] A comparison of the test results of Example 2 and Comparative Example 3 shows that replacing the core-shell particles used in this invention with an equal amount of Li... 1.3 Al 0.3 Ti 1.7 The (PO4)3 particles significantly reduced the ionic conductivity of the membrane, while also decreasing the tensile strength and interfacial peel strength, and increasing the thermal shrinkage rate and interfacial resistance. This indicates that the core-shell particles of the present invention can improve the strength and stability of the membrane, while maintaining the integrity of the ion channel and optimizing the transport of lithium ions at the interface.

[0060] By comparing the test results of Example 2 and Comparative Example 4, it can be seen that when the perfluorosulfonic acid resin used in this invention is replaced with polyvinylidene fluoride without sulfonic acid groups, the interfacial resistance of the diaphragm increases significantly, indicating that the perfluorosulfonic acid resin can stabilize the electrode interface and improve the interfacial compatibility and durability of the diaphragm.

[0061] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0062] It should also be noted that the various specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0063] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A semi-solid lithium battery separator, characterized in that, The system comprises a base film with a thickness of 4–6 μm and gradient functional coatings coated on both sides of the base film. The base film is a polyimide film. The gradient functional coatings include a bottom adhesive layer, a top regulating layer, and a filler layer located between the adhesive layer and the regulating layer. The adhesive layer, filler layer, and regulating layer each comprise the following components calculated in parts by weight: The adhesive layer includes component A, which includes 12-20 parts of polymer matrix, 4-8 parts of crosslinking agent containing disulfide bonds, 2-4 parts of coupling agent, and 12-18 parts of first solvent; the polymer matrix includes polyimide and polyurethane, and the mass ratio of polyimide to polyurethane is 1.5:

1. The filling layer includes component B and component A, wherein component B comprises ZrO2-encapsulated Li. 1.3 Al 0.3 Ti 1.7 (PO4)3 particles, core-shell particles 8-10 parts, dispersant 4-6 parts; ZrO2 and Li 1.3 Al 0.3 Ti 1.7 The mass ratio of (PO4)3 particles is 4:6, and the mass ratio of core-shell particles to component A is 1:2 to 3; The control layer comprises 6-8 parts of perfluorosulfonic acid resin, 2-5 parts of plasticizer, 1-3 parts of interface stabilizer, 9-12 parts of second solvent, and 1-3 parts of deionized water. The thickness of the adhesive layer is 2.5–3.5 μm, the thickness of the filler layer is 5–8 μm, and the thickness of the regulating layer is 0.5–2 μm.

2. The semi-solid lithium battery separator according to claim 1, characterized in that, The crosslinking agent includes at least one of succinimide-disulfide bond active ester-succinimide, polyethylene glycol dithiodipropionate, dimethyl 3,3'-dithiodipropionate, and dithiodibenzoate.

3. The semi-solid lithium battery separator according to claim 1, characterized in that, The coupling agent includes at least one of silane coupling agents, titanate coupling agents, and sulfur-containing coupling agents.

4. The semi-solid lithium battery separator according to claim 3, characterized in that, The silane coupling agent includes at least one of titanylaminopropyltriethoxysilane, methacryloxypropyltrimethoxysilane, and vinyltrimethoxysilane; the titanate coupling agent includes at least one of isopropyltris(dioctylphosphoyloxy)titanate and bis(dioctylpyrophosphoyloxy)ethylene titanate; the sulfur-containing coupling agent includes at least one of bis-[3-(triethoxysilyl)propyl]-disulfide and 3-mercaptopropyltrimethoxysilane.

5. The semi-solid lithium battery separator according to claim 1, characterized in that, The dispersant includes at least one of polyacrylamide and polyvinylpyrrolidone.

6. The semi-solid lithium battery separator according to claim 1, characterized in that, The plasticizer includes at least one of polyethylene glycol dimethyl ether, dioctyl phthalate, triethyl citrate, diisononyl adipate, and polyethylene oxide.

7. The semi-solid lithium battery separator according to claim 1, characterized in that, The interface stabilizer includes at least one of perfluoropolyether ammonium carboxylate, lithium dioxaborate, fluoroethylene carbonate, and lithium difluorophosphate.

8. The semi-solid lithium battery separator according to claim 1, characterized in that, The first solvent includes at least one of N-methylpyrrolidone, dimethyl sulfoxide, and propylene carbonate, and the second solvent includes at least one of N-methylpyrrolidone, dimethyl sulfoxide, and propylene carbonate.

9. The semi-solid lithium battery separator according to claim 1, characterized in that, The method for preparing the core-shell particles includes the following steps: A1. Mix zirconium oxychloride with a 70% ethylene glycol solution, with a mass ratio of zirconium oxychloride to ethylene glycol solution of 1:5-8. Then add polyethylene glycol at a total mass of 0.1% of zirconium oxychloride and ethylene glycol solution, and stir until homogeneous to obtain zirconium sol. A2. Li 1.3 Al 0.3 Ti 1.7 (PO4)3 particles were soaked in 0.1 mol / L oxalic acid for 20–40 min, filtered through a 0.25–0.35 μm microporous membrane, and then the treated Li... 1.3 Al 0.3 Ti 1.7 (PO4)3 particles were added to the zirconium sol, Li 1.3 Al 0.3 Ti 1.7 The mass ratio of (PO4)3 particles to zirconium sol is 1:6-8. The mixture is ultrasonically dispersed for 30-50 min, and then ammonia is added to adjust the pH to 9-9.

5. The mixture is then aged at 60-65℃ and a stirring speed of 60-120 rpm for 2-3 h to obtain the crude coating solution. A3. Filter the coarse coating solution through a microporous membrane of 0.25-0.35 μm, collect the particles, anneal them at 550℃ for 3-4 h, then cool them down to 200℃, remove the particles, and allow them to cool naturally to room temperature to obtain core-shell particles.

10. A method for preparing a semi-solid lithium battery separator according to any one of claims 1 to 9, characterized in that, Includes the following steps: S1. The base film is subjected to corona treatment, and the power density of the corona treatment is adjusted to 3-4 W / cm². 2 The time is 4-6 seconds, and then the base film is ultrasonically cleaned with isopropanol at a power of 30-50 kHz for 8-12 minutes to obtain the pretreated base film. S2. Mix polyimide, polyurethane, crosslinking agent, coupling agent and first solvent, disperse at 1800-2200 rpm for 20-40 min to obtain component A, coat component A on both sides of the pretreated base film, dry with hot air at 75-80℃ for 5-10 min to form an adhesive layer, and obtain semi-finished diaphragm 1. S3. Mix the core-shell particles, dispersant and component A evenly. The mass ratio of core-shell particles to component A is 1:2 to 3 to obtain slurry 2. Coat slurry 2 on both sides of the semi-finished diaphragm 1 and then perform gradient drying. The initial drying temperature is 60°C, and the temperature is increased by 20°C per minute until it reaches 120°C. Then cool it to room temperature to form a filling layer to obtain the semi-finished diaphragm 2. S4. Mix the perfluorosulfonic acid resin, plasticizer, interface stabilizer, second solvent and deionized water evenly, and then spray it on both sides of the semi-finished diaphragm 2. The spraying pressure is 0.3-0.4 MPa. Then, vacuum dry at 70-90℃ for 2-5 minutes to form a control layer and obtain the finished product.

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