Composite fiber membrane and preparation method thereof, solid-state battery and preparation method thereof

Abstract

The application provides a composite fiber membrane, comprising a composite fiber base film with a cross-linked structure, the composite fiber base film comprising cellulose acetate, the cross-linked structure being formed by the reaction of a blocked aqueous isocyanate with the cellulose acetate, and the surface of the composite fiber base film being grafted with an acrylate structure. The cross-linked structure formed by the reaction of the cellulose acetate with the blocked aqueous isocyanate can accelerate the dissociation of lithium ions, promote the transmission of lithium ions, and thus increase the transmission rate of lithium ions; and the acrylate structure grafted on the surface of the composite fiber base film can reduce the crystallinity of the solid-state electrolyte and increase the ionic conductivity of the solid-state electrolyte. The application further discloses a preparation method of the composite fiber membrane and a solid-state battery and a preparation method thereof.

Description

Technical Field

[0001] This invention belongs to the field of solid-state battery preparation technology, specifically relating to a composite fiber membrane and its preparation method, and a solid-state battery and its preparation method. Background Technology

[0002] Lithium metal batteries, as an energy storage device, have attracted widespread attention and research due to their high energy density resulting from the low potential of the lithium anode and their extremely high theoretical specific capacity. However, traditional lithium metal batteries are prone to a series of safety risks, such as spontaneous combustion, due to the use of highly flammable polyolefin separators and liquid electrolytes with high ester or ether content. Furthermore, the uneven lithium deposition in the liquid electrolyte promotes the uncontrolled growth of lithium dendrites, leading to a reduction in the cycle life of lithium metal batteries.

[0003] To compensate for the shortcomings of liquid electrolytes, existing technologies use gel solid electrolytes to replace liquid electrolytes to obtain solid lithium metal batteries. However, due to the presence of polymer networks in gel solid electrolytes, the viscosity of the electrolyte increases, thereby reducing the ion transport rate of the membrane and resulting in the inability to obtain excellent room temperature electrochemical performance. Summary of the Invention

[0004] To address the shortcomings of the prior art, this invention provides a composite fiber membrane. Through the reaction of cellulose acetate with a blocked aqueous isocyanate to form a cross-linked structure, it accelerates the dissociation of lithium ions and promotes lithium ion transport. Simultaneously, the acrylate structure grafted onto the surface of the composite fiber membrane reduces the crystallinity of the solid electrolyte, thereby increasing the lithium ion transport rate and ultimately improving the ionic conductivity of the solid electrolyte. This invention also provides a method for preparing the composite fiber membrane and a solid-state battery and its preparation method.

[0005] The technical effects to be achieved by this invention are realized through the following technical aspects:

[0006] In a first aspect, the present invention provides a composite fiber membrane comprising a composite fiber base membrane having a cross-linked structure, the composite fiber base membrane comprising cellulose acetate, the cross-linked structure being formed by reacting a blocked aqueous isocyanate with the cellulose acetate, and the surface of the composite fiber base membrane being grafted with an acrylate structure.

[0007] In some embodiments, the blocked aqueous isocyanate is a polyisocyanate blocked with a hydrogen-containing compound, the polyisocyanate containing a hydrophilic group.

[0008] In some embodiments, the hydrogen-containing compound is one or more of methanol, ethanol, propanol, butanol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, propylene glycol monomethyl ether, or propylene glycol monoethyl ether.

[0009] In some embodiments, the polyisocyanate is one or more of isophorone diisocyanate, 1,6-hexane diisocyanate, 4,4-dicyclohexylmethane diisocyanate, phenylene diisocyanate, tetramethylphenyl diisocyanate, toluene diisocyanate, diphenylmethane diisocyanate, 1,5-naphthalene diisocyanate, or polymethylene polyphenyl polyisocyanate.

[0010] In some embodiments, the molar ratio of the hydrogen-containing compound to the polyisocyanate in the blocked aqueous isocyanate is (1.05~1.5):1.

[0011] Secondly, the present invention provides a method for preparing the composite fiber membrane, comprising the following steps:

[0012] S1. Dissolve cellulose acetate and blocked aqueous isocyanate in a first organic solvent, heat and stir to obtain a precursor solution;

[0013] S2. Electrospinning the precursor solution to obtain a composite fiber-based membrane with a cross-linked structure;

[0014] S3. Dissolve the acrylate-containing silane coupling agent in a second organic solvent to obtain a modified solution, drop the modified solution onto the composite fiber base membrane, and dry it to obtain the composite fiber membrane.

[0015] In some embodiments, the precursor solution contains 15-20% cellulose acetate by mass and 1-3% blocked aqueous isocyanate by mass.

[0016] In some embodiments, in step S1, the heating temperature for heating and stirring is 50~70°C, and the stirring time is 6~10h.

[0017] In some embodiments, in S3, the acrylate-containing silane coupling agent is 3-(trimethoxysilyl)propyl-2-methyl-2-acrylate.

[0018] In some embodiments, in step S3, the mass fraction of the acrylate-containing silane coupling agent in the modified solution is 10-20%.

[0019] In some embodiments, in step S3, the amount of modified solution added to the composite fiber-based membrane is 0.2~0.5 mL / cm. 2 .

[0020] Thirdly, the present invention provides a solid-state battery, comprising a positive electrode, a separator, a negative electrode, and an electrolyte, wherein the separator is the composite fiber membrane.

[0021] In some embodiments, the electrolyte includes an electrolyte solution, a polymeric monomer, and an initiator, wherein the polymeric monomer includes an acrylate monomer, which is used to copolymerize with an acrylate structure grafted onto the surface of the composite fiber base membrane of the composite fiber membrane.

[0022] In some embodiments, the acrylate monomer includes one or more combinations of hexafluorobutyl methacrylate, polyethylene glycol diacrylate, or pentaerythritol acrylate.

[0023] Fourthly, the present invention provides a method for preparing a solid-state battery, comprising the following steps:

[0024] S4-1. Mix the electrolyte, polymerizing monomer and initiator to obtain a solid electrolyte;

[0025] S4-2. Using the composite fiber membrane as the separator and the solid electrolyte prepared in S4-1 as the electrolyte, assemble it with the positive electrode and the negative electrode to form a battery.

[0026] S4-3. The assembled battery is left to stand and solidify to obtain a solid-state battery.

[0027] In summary, the present invention has at least the following advantages:

[0028] 1. The composite fiber membrane provided by this invention has a cross-linked structure formed by the reaction of the hydroxyl groups of cellulose acetate on the composite fiber base membrane with the isocyanate groups on the blocked aqueous isocyanate. The aminomethyl ester and amide in the cross-linked structure act as Lewis bases, accelerating the dissociation of lithium ions in the electrolyte and promoting lithium ion transport. Furthermore, the acrylate structure grafted onto the surface of the composite fiber base membrane can copolymerize with the monomers in the solid electrolyte, resulting in a tight bond between the composite fiber membrane and the solid electrolyte, reducing the crystallinity of the solid electrolyte, thereby increasing the lithium ion transport rate and ultimately improving the ionic conductivity of the solid electrolyte. The composite fiber membrane of this invention has a large pore size and strong mechanical properties, including high tensile strength, enabling it to form well-ordered three-dimensional ion transport channels in the solid electrolyte.

[0029] 2. The method for preparing the composite fiber membrane provided by this invention involves reacting the hydroxyl groups on cellulose acetate with the isocyanate groups on a blocked aqueous isocyanate to form a cross-linked structure, which can accelerate the dissociation of lithium ions in the electrolyte and effectively improve the lithium ion transport rate. Modification of the composite fiber base membrane with an acrylate-containing silane coupling agent results in the grafting of acrylate structures onto the surface of the composite fiber base membrane. These acrylate structures can undergo copolymerization reactions with the polymer monomers in the solid electrolyte, causing the composite fiber membrane to bond tightly with the solid electrolyte, reducing the crystallinity of the solid electrolyte, and effectively improving the ionic conductivity of the solid electrolyte.

[0030] 3. The solid-state battery provided by the present invention uses the composite fiber membrane as the separator, which has good cycle stability, high ionic conductivity and cycle specific capacity, and the preparation method is simple and the preparation cost is low. Attached Figure Description

[0031] Figure 1 This is a scanning electron microscope image of the composite fiber membrane prepared in Example 1 of the present invention;

[0032] Figure 2 This is a schematic diagram of the charge-discharge cycle test results of each solid-state battery in Test Example 2 of the present invention at a rate of 0.5C. Detailed Implementation

[0033] To facilitate understanding of the present invention, a more comprehensive description will be given below with reference to specific embodiments and accompanying drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of the present invention.

[0034] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0035] In a first aspect, the present invention provides a composite fiber membrane, comprising a composite fiber base membrane having a cross-linked structure, the composite fiber base membrane comprising cellulose acetate (CA), the cross-linked structure being formed by the reaction of a blocked aqueous isocyanate (BIC) with cellulose acetate, and the surface of the composite fiber base membrane being grafted with an acrylate structure. The composite fiber membrane has a porous structure with a pore size of approximately 1 μm and a thickness of 30-40 μm.

[0036] Blocked aqueous isocyanates are polyisocyanates blocked with hydrogen-containing compounds. Polyisocyanates contain hydrophilic groups. It should be noted that because polyisocyanates are inherently unstable, hydrogen-containing compounds are needed as blocking agents to form BICs (Bipolar Isocyanates). These can be deblocked by heating with CA (Carbon Dioxide). The hydrophilic groups in polyisocyanates can participate in lithium-ion transport, coordinating with and dissociating from lithium ions.

[0037] By using CA as the main body to form a composite fiber-based membrane, BIC is used to crosslink CA, causing the hydroxyl groups on CA to react with the isocyanate (-NCO) groups on BIC to form a crosslinked structure. The aminomethyl ester and amide in the crosslinked structure act as Lewis bases, which can accelerate the dissociation of lithium ions in the electrolyte and promote lithium ion transport. The acrylate structure grafted on the surface of the composite fiber-based membrane can undergo copolymerization with the polymer monomers in the solid electrolyte, making the composite fiber membrane tightly bonded to the solid electrolyte, reducing the crystallinity of the solid electrolyte, thereby increasing the lithium ion transport rate and thus improving the ionic conductivity of the solid electrolyte.

[0038] Specifically, the hydrogen-containing compound is one or more of methanol, ethanol, propanol, butanol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, propylene glycol monomethyl ether, or propylene glycol monoethyl ether.

[0039] Specifically, the polyisocyanate is one or more of the following: isophorone diisocyanate, 1,6-hexane diisocyanate, 4,4-dicyclohexylmethane diisocyanate, phenyl dimethylene diisocyanate, tetramethylphenyl diisocyanate, toluene diisocyanate, diphenylmethane diisocyanate, 1,5-naphthalene diisocyanate, or polymethylene polyphenyl polyisocyanate.

[0040] In blocked aqueous isocyanates, the molar ratio of hydrogen-containing compounds to polyisocyanates is (1.05~1.5):1. The higher molar proportion of hydrogen-containing compounds compared to polyisocyanates improves the stability of polyisocyanates at room temperature, allowing them to fully release active groups and initiate cross-linking reactions upon heating.

[0041] Secondly, the present invention provides a method for preparing a composite fiber membrane, comprising the following steps:

[0042] S1. Dissolve cellulose acetate and blocked aqueous isocyanate in a first organic solvent, heat and stir to obtain a precursor solution;

[0043] S2. The precursor solution is transferred to a syringe for electrospinning to form a film. When the film thickness reaches 30~40μm, the spinning is stopped to obtain a composite fiber-based film with a cross-linked structure.

[0044] S3. Dissolve the silane coupling agent containing acrylate in a second organic solvent to obtain a modified solution. Add the modified solution dropwise onto the composite fiber base membrane and dry it to obtain the composite fiber membrane.

[0045] The first organic solvent is one or a combination of DMF (N,N-dimethylformamide), acetone, NMP (N-methylpyrrolidone), or ethyl acetate. The second organic solvent is one or a combination of DMAC (N,N-dimethylacetamide), ethanol, or acetone.

[0046] In the precursor solution, the mass fraction of cellulose acetate is 15-20%, and the mass fraction of blocked aqueous isocyanate is 1-3%.

[0047] In S1, the heating temperature for heating and stirring is 50~70℃, and the stirring time is 6~10h. Magnetic stirring can be used for stirring. By setting appropriate heating temperature and stirring time, the blocked aqueous isocyanate is unblocked by heating and stirring, and reacts with cellulose acetate to form a cross-linked structure.

[0048] In S2, the specific process of electrospinning for film formation is as follows: the positive terminal of a high-voltage power supply is connected to the tip of a syringe needle, and a grounded stainless steel roller, wrapped in aluminum foil, is used as a collector and rotated at a speed of 50-60 rpm. The voltage for electrospinning is 20-25 kV, the constant distance between the syringe needle tip and the collector is 20-30 cm, preferably 25 cm, and the feed rate of the precursor solution is 1-1.2 mL / h.

[0049] In S3, the acrylate-containing silane coupling agent is 3-(trimethoxysilyl)propyl-2-methyl-2-acrylate (G-570). It should be noted that the acrylate-containing silane coupling agent is not limited to G-570, and can also be other acrylate-containing silane coupling agents.

[0050] In S3, the mass fraction of the acrylate-containing silane coupling agent in the modification solution is 10-20%, and the amount of the modification solution added to the composite fiber-based membrane is 0.2-0.5 mL / cm. 2 .

[0051] In S3, drying is performed using a vacuum drying oven for 5-8 hours at a temperature of 100-150°C, preferably 125°C.

[0052] Thirdly, the present invention provides a solid-state battery, comprising a positive electrode, a separator, a negative electrode, and an electrolyte, wherein the separator is a composite fiber membrane.

[0053] The electrolyte comprises an electrolyte solution, polymerizing monomers, and an initiator. The polymerizing monomers include acrylate monomers, which can copolymerize with acrylate structures grafted onto the surface of the composite fiber base membrane of the composite fiber membrane. The acrylate monomers include one or more combinations of hexafluorobutyl methacrylate, polyethylene glycol diacrylate, or pentaerythritol acrylate.

[0054] The electrolyte is a lithium-ion electrolyte, including one or more combinations of LB-037, LB-731, or LB-103. The initiator is one or more combinations of azobisisobutyronitrile, azobisisoheptanenitrile, benzoyl peroxide, or diethylhexyl peroxide.

[0055] Specifically, lithium-ion electrolyte LB-037 is composed of LiPF6 dissolved in EC, DEC, and EMC, with a LiPF6 concentration of 1 mol / L and an EC:DEC:EMC ratio of 1:1:1 (Vol%); lithium-ion electrolyte LB-731 is composed of LiPF6 dissolved in EC, EMC, and FEC, with a LiPF6 concentration of 1 mol / L and an EC:EMC:FEC ratio of 1:4:2 (Vol%); lithium-ion electrolyte LB-103 is composed of LiPF6 dissolved in DMC, EC, EMC, and FEC, with a LiPF6 concentration of 1 mol / L, an DMC:EC:EMC ratio of 1:1:1 (Vol%), and 10 wt% FEC.

[0056] In some embodiments, the electrolyte further includes an oxide, which is a doped filler, including one or more combinations of aluminum oxide, magnesium oxide, zinc oxide, or silicon dioxide.

[0057] Fourthly, the present invention provides a method for preparing a solid-state battery, comprising the following steps:

[0058] S4-1. Take 1~1.2 parts of electrolyte, 0.05~0.2 parts of polymer monomer, 0.003~0.008 parts of initiator and 0.01~0.03 parts of oxide and mix them to obtain a solid electrolyte;

[0059] S4-2: Using a composite fiber membrane as the separator and the solid electrolyte prepared in S4-1 as the electrolyte, a battery is assembled with a positive electrode and a negative electrode.

[0060] S4-3. After the assembled battery is left to stand for 6-8 hours, it is cured at a temperature of 60-80℃ for 3-5 hours to obtain a solid-state battery.

[0061] Example 1

[0062] This embodiment provides a composite fiber membrane, which is prepared by the following method:

[0063] S1. Weigh a certain amount of cellulose acetate (CA) and blocked isophorone diisocyanate (BIC) (methanol is used as the blocking agent, and the molar ratio of methanol to isophorone diisocyanate is 1.3:1), dissolve them together in DMF, and stir magnetically at 60°C for 8 hours to obtain the precursor solution.

[0064] Of these, CA had a mass fraction of 18%, and BIC had a mass fraction of 2%.

[0065] S2. Transfer the precursor solution into a plastic syringe. Connect the positive terminal of a high-voltage power supply to the syringe needle tip. Use a grounded stainless steel roller as a collector, wrapped in aluminum foil, and rotate it at 55 rpm. The electrospinning voltage is 22 kV, the constant distance between the syringe needle tip and the collector is 25 cm, and the precursor solution feed rate is 1 mL / h. Stop spinning when the membrane thickness reaches 35 μm to obtain a composite fiber-based membrane with a cross-linked structure.

[0066] S3. Dissolve 3-(trimethoxysilyl)propyl-2-methyl-2-acrylate (G-570) in DMAC (G-570 mass fraction is 15%), at a concentration of 0.3 mL / cm³. 2 The appropriate amount of solution was added dropwise to the composite fiber base membrane, and the membrane was dried in a vacuum drying oven at 125°C for 6 hours to obtain the composite fiber membrane. A scanning electron microscope image of the composite fiber membrane is shown below. Figure 1 As shown.

[0067] The composite fiber membrane prepared by S3 is applied to the fabrication of solid-state lithium metal batteries, specifically including the following steps:

[0068] S4-1. Mix 1g of lithium-ion electrolyte LB-037, 0.1g of hexafluorobutyl methacrylate, 0.005g of azobisisobutyronitrile and 0.02g of alumina to obtain the electrolyte;

[0069] S4-2. Using the composite fiber membrane prepared in S3 as the separator, the electrolyte prepared in S4-1 as the electrolyte, lithium iron phosphate electrode sheet as the positive electrode sheet (the mass ratio of lithium iron phosphate, conductive carbon black and sodium carboxymethyl cellulose (CMC) is 96:1.5:2.5), and lithium metal electrode sheet as the negative electrode sheet, the composite fiber membrane, positive electrode sheet and negative electrode sheet are cut into 18mm, 16mm and 16mm round pieces respectively by a slicer and assembled into a sandwich structure lithium metal button battery;

[0070] S4-3. After the assembled lithium metal button cell is left to stand for 7 hours, it is cured at 70°C for 4 hours to obtain a solid-state lithium metal button cell.

[0071] Example 2

[0072] This embodiment provides a composite fiber membrane, which is prepared by the following method:

[0073] S1. Weigh a certain amount of cellulose acetate (CA) and blocked 1,6-hexamethylene diisocyanate (BIC) (ethylene glycol monomethyl ether is used as the blocking agent, and the molar ratio of ethylene glycol monomethyl ether to 1,6-hexamethylene diisocyanate is 1.05:1), dissolve them together in NMP, and stir magnetically at 50°C for 6 hours to obtain the precursor solution.

[0074] Of which, CA has a mass fraction of 20%, and BIC has a mass fraction of 1%;

[0075] S2. Transfer the precursor solution into a plastic syringe. Connect the positive terminal of a high-voltage power supply to the syringe needle tip. Use a grounded stainless steel roller as a collector, wrapped in aluminum foil, and rotate it at 50 rpm. The electrospinning voltage is 20 kV, the constant distance between the syringe needle tip and the collector is 25 cm, and the precursor solution feed rate is 1 mL / h. Stop spinning when the membrane thickness reaches 30 μm to obtain a composite fiber-based membrane with a cross-linked structure.

[0076] S3. Dissolve 3-(trimethoxysilyl)propyl-2-methyl-2-acrylate (G-570) in ethanol (G-570 mass fraction is 10%), at a concentration of 0.2 mL / cm³. 2 The amount of the solution was added dropwise to the composite fiber base membrane, and then dried in a vacuum drying oven at 100°C for 5 hours to obtain the composite fiber membrane.

[0077] The composite fiber membrane prepared by S3 is applied to the fabrication of solid-state lithium metal batteries, specifically including the following steps:

[0078] S4-1. Mix 1g of lithium-ion electrolyte LB-731, 0.05g of polyethylene glycol diacrylate, 0.003g of azobisisobutyronitrile and 0.01g of silicon dioxide to obtain the electrolyte;

[0079] S4-2. Using the composite fiber membrane prepared in S3 as the separator, the electrolyte prepared in S4-1 as the electrolyte, lithium iron phosphate electrode sheet as the positive electrode sheet (the mass ratio of lithium iron phosphate, conductive carbon black and sodium carboxymethyl cellulose (CMC) is 96:1.5:2.5), and lithium metal electrode sheet as the negative electrode sheet, the composite fiber membrane, positive electrode sheet and negative electrode sheet are cut into 18mm, 16mm and 16mm round pieces respectively by a slicer and assembled into a sandwich structure lithium metal button battery;

[0080] S4-3. After the assembled lithium metal button battery is left to stand for 6 hours, it is cured at 60°C for 3 hours to obtain a solid-state lithium metal button battery.

[0081] Example 3

[0082] This embodiment provides a composite fiber membrane, which is prepared by the following method:

[0083] S1. Weigh a certain amount of cellulose acetate (CA) and blocked 4,4-dicyclohexylmethane-diisocyanate (BIC) (propanol is used as the blocking agent, and the molar ratio of propanol to 4,4-dicyclohexylmethane-diisocyanate is 1.5:1), dissolve them together in acetone, and stir magnetically at 70°C for 10 hours to obtain the precursor solution.

[0084] Of which, CA has a mass fraction of 20%, and BIC has a mass fraction of 3%;

[0085] S2. Transfer the precursor solution into a plastic syringe. Connect the positive terminal of a high-voltage power supply to the syringe needle tip. Use a grounded stainless steel roller as a collector, wrapped in aluminum foil, and rotate it at 60 rpm. The electrospinning voltage is 25 kV, the constant distance between the syringe needle tip and the collector is 25 cm, and the precursor solution feed rate is 1.2 mL / h. Stop spinning when the membrane thickness reaches 40 μm to obtain a composite fiber-based membrane with a cross-linked structure.

[0086] S3. Dissolve 3-(trimethoxysilyl)propyl-2-methyl-2-acrylate (G-570) in acetone (G-570 mass fraction is 20%), at a concentration of 0.5 mL / cm³. 2 The amount of the solution was added dropwise to the composite fiber base membrane, and the membrane was dried at 150°C for 8 hours in a vacuum drying oven to obtain the composite fiber membrane.

[0087] The composite fiber membrane prepared by S3 is applied to the fabrication of solid-state lithium metal batteries, specifically including the following steps:

[0088] S4-1. Mix 1.2g of lithium-ion electrolyte LB-103, 0.2g of pentaerythritol acrylate, 0.008g of diethylhexyl peroxide and 0.03g of magnesium oxide to obtain the electrolyte;

[0089] S4-2. Using the composite fiber membrane prepared in S3 as the separator, the electrolyte prepared in S4-1 as the electrolyte, lithium iron phosphate electrode sheet as the positive electrode sheet (the mass ratio of lithium iron phosphate, conductive carbon black and sodium carboxymethyl cellulose (CMC) is 96:1.5:2.5), and lithium metal electrode sheet as the negative electrode sheet, the composite fiber membrane, positive electrode sheet and negative electrode sheet are cut into 18mm, 16mm and 16mm round pieces respectively by a slicer and assembled into a sandwich structure lithium metal button battery;

[0090] S4-3. After the assembled lithium metal button battery is left to stand for 8 hours, it is cured at 80℃ for 5 hours to obtain a solid-state lithium metal button battery.

[0091] Comparative Example 1

[0092] This comparative example provides a composite fiber membrane, which is prepared by the following method:

[0093] S1. Weigh a certain amount of cellulose acetate (CA), dissolve it in DMF, and stir magnetically at 60℃ for 8 hours to obtain a precursor solution, wherein the mass fraction of CA is 18%.

[0094] S2. Transfer the precursor solution into a plastic syringe. Connect the positive terminal of a high-voltage power supply to the syringe needle tip. Use a grounded stainless steel roller as a collector, wrapped in aluminum foil, and rotate it at 55 rpm. The electrospinning voltage is 22 kV, the constant distance between the syringe needle tip and the collector is 25 cm, and the precursor solution feed rate is 1 mL / h. Stop spinning when the membrane thickness reaches 35 μm to obtain a fiber-based membrane.

[0095] S3. Dissolve 3-(trimethoxysilyl)propyl-2-methyl-2-acrylate (G-570) in DMAC (G-570 mass fraction is 15%), at a concentration of 0.3 mL / cm³. 2 The amount of the solution was added dropwise to the fiber-based membrane, and then dried in a vacuum drying oven at 125°C for 6 hours to obtain the composite fiber membrane.

[0096] The composite fiber membrane prepared by S3 is applied to the fabrication of solid-state lithium metal batteries, specifically including the following steps:

[0097] S4-1. Mix 1g of lithium-ion electrolyte LB-037, 0.1g of hexafluorobutyl methacrylate, 0.005g of azobisisobutyronitrile and 0.02g of alumina to obtain the electrolyte;

[0098] S4-2. Using the composite fiber membrane prepared in S3 as the separator, the electrolyte prepared in S4-1 as the electrolyte, lithium iron phosphate electrode sheet as the positive electrode sheet (the mass ratio of lithium iron phosphate, conductive carbon black and sodium carboxymethyl cellulose (CMC) is 96:1.5:2.5), and lithium metal electrode sheet as the negative electrode sheet, the composite fiber membrane, positive electrode sheet and negative electrode sheet are cut into 18mm, 16mm and 16mm round pieces respectively by a slicer and assembled into a sandwich structure lithium metal button battery;

[0099] S4-3. After the assembled lithium metal button cell is left to stand for 7 hours, it is cured at 70°C for 4 hours to obtain a solid-state lithium metal button cell.

[0100] Comparative Example 2

[0101] This comparative example provides a composite fiber membrane, which is prepared by the following method:

[0102] S1. Weigh a certain amount of cellulose acetate (CA) and blocked isophorone diisocyanate (BIC) (methanol is used as the blocking agent, and the molar ratio of methanol to isophorone diisocyanate is 1.3:1), dissolve them together in DMF, and stir magnetically at 60°C for 8 hours to obtain the precursor solution.

[0103] Of these, CA had a mass fraction of 18%, and BIC had a mass fraction of 2%.

[0104] S2. Transfer the precursor solution into a plastic syringe. Connect the positive terminal of a high-voltage power supply to the syringe needle tip. Use a grounded stainless steel roller as a collector, wrapped in aluminum foil, and rotate it at 55 rpm. The electrospinning voltage is 22 kV, the constant distance between the syringe needle tip and the collector is 25 cm, and the precursor solution feed rate is 1 mL / h. Stop spinning when the membrane thickness reaches 35 μm to obtain a composite fiber-based membrane with a cross-linked structure.

[0105] S3. The composite fiber base membrane is dried in a vacuum drying oven at 125°C for 6 hours to obtain the composite fiber membrane.

[0106] The composite fiber membrane prepared by S3 is applied to the fabrication of solid-state lithium metal batteries, specifically including the following steps:

[0107] S4-1. Mix 1g of lithium-ion electrolyte LB-037, 0.1g of hexafluorobutyl methacrylate, 0.005g of azobisisobutyronitrile and 0.02g of alumina to obtain the electrolyte;

[0108] S4-2. Using the composite fiber membrane prepared in S3 as the separator, the electrolyte prepared in S4-1 as the electrolyte, lithium iron phosphate electrode sheet as the positive electrode sheet (the mass ratio of lithium iron phosphate, conductive carbon black and sodium carboxymethyl cellulose (CMC) is 96:1.5:2.5), and lithium metal electrode sheet as the negative electrode sheet, the composite fiber membrane, positive electrode sheet and negative electrode sheet are cut into 18mm, 16mm and 16mm round pieces respectively by a slicer and assembled into a sandwich structure lithium metal button battery;

[0109] S4-3. After the assembled lithium metal button cell is left to stand for 7 hours, it is cured at 70°C for 4 hours to obtain a solid-state lithium metal button cell.

[0110] Test Example 1

[0111] Composite fiber membranes prepared in Examples 1-3 and Comparative Examples 1-2 were used as separators, and electrolytes prepared in Examples 1-3 and Comparative Examples 1-2 were used as electrolytes. Stainless steel (Fe) was used as the blocking electrode to assemble Fe / electrolyte / Fe symmetric cells. The specific method is as follows:

[0112] Place a stainless steel sheet in the battery casing, add two drops of electrolyte to the stainless steel sheet, place the separator on the stainless steel sheet, add two more drops of electrolyte to the separator, after wetting, place the stainless steel sheet in, assemble into an Fe / electrolyte / Fe symmetrical battery, place in a 60℃ oven, cure for 3 hours and then use for impedance testing.

[0113] The test was conducted using the AC impedance method on a CHI760e electrochemical workstation. During the test, the perturbation was 5 mV, and the frequency range was 10...-2 Hz~10 6 Hz. Substitute the test data into the following formula to calculate the ionic conductivity of the electrolyte:

[0114] σ = l / RS;

[0115] Where σ is the conductivity, with units of S / cm;

[0116] l represents the thickness of the electrolyte sheet, in cm;

[0117] R is the resistance of the Fe / electrolyte / Fe symmetrical cell, in Ω;

[0118] S represents the test area of ​​the blocking electrode sheet, in cm². 2 .

[0119] The conductivity test results are shown in Table 1.

[0120] Table 1. Test results of conductivity

[0121]

[0122] The results show that the composite fiber membranes prepared in Examples 1, 2 and 3 have higher lithium-ion conductivity than those in Comparative Examples 1 and 2. This demonstrates that crosslinking modification of CA with BIC and modification of the composite fiber base membrane with acrylate-containing silane coupling agents can accelerate the lithium-ion transport rate in the solid electrolyte, thereby improving the ionic conductivity of the solid electrolyte.

[0123] Test Example 2

[0124] The cycle performance of the solid-state lithium metal coin cells prepared in Examples 1-3 and Comparative Examples 1-2 was tested using the following methods:

[0125] Each battery was subjected to two charge-discharge cycles at a rate of 0.1C using a battery charge-discharge tester (CT3002A) from Wuhan Landian Company, with a voltage range of 2.2~3.6V. Then, a charge-discharge cycle test was performed at a rate of 0.5C, with a test temperature of 25℃ and a voltage range of 2.2~3.6V.

[0126] The schematic diagram of the charge-discharge cycle test results of each battery at a 0.5C rate is shown below. Figure 2As shown in the figure, the initial discharge specific capacity of Examples 1, 2, 3, Comparative Example 1, and Comparative Example 2 were 155.8 mAh / g, 154.0 mAh / g, 154.5 mAh / g, 143.8 mAh / g, and 141.8 mAh / g, respectively. After 100 cycles, the discharge specific capacity remained at 149.8 mAh / g, 147.7 mAh / g, 148.1 mAh / g, 126.8 mAh / g, and 127.8 mAh / g, respectively. It is evident that Examples 1, 2, and 3 exhibited good capacity retention, while Comparative Example 1 and Comparative Example 2 showed lower initial discharge specific capacity, and the capacity decay rate increased significantly with increasing cycle number.

[0127] In summary, the solid-state battery prepared using the composite fiber membrane provided by this invention exhibits good cycle stability, high ionic conductivity and cycle specific capacity, and excellent electrochemical performance.

[0128] The above description is merely an example and illustration of the structure of this invention, and while the description is specific and detailed, it should not be construed as limiting the scope of this invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this invention, and these obvious substitutions all fall within the protection scope of this invention.

Claims

1. A solid-state battery, characterized in that, It includes a positive electrode, a separator, a negative electrode, and an electrolyte, wherein the separator is a composite fiber membrane; The composite fiber membrane includes a composite fiber base membrane with a cross-linked structure, the composite fiber base membrane includes cellulose acetate, the cross-linked structure is formed by the reaction of a blocked aqueous isocyanate with the cellulose acetate, and the surface of the composite fiber base membrane is grafted with an acrylate structure. The electrolyte includes an electrolyte solution, a polymeric monomer, and an initiator. The polymeric monomer includes an acrylate monomer, which is used to copolymerize with the acrylate structure grafted onto the surface of the composite fiber base membrane of the composite fiber membrane.

2. The solid-state battery according to claim 1, characterized in that, The blocked aqueous isocyanate is a polyisocyanate blocked by a hydrogen-containing compound, and the polyisocyanate contains hydrophilic groups.

3. The solid-state battery according to claim 2, characterized in that, The hydrogen-containing compound is one or more of methanol, ethanol, propanol, butanol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, propylene glycol monomethyl ether, or propylene glycol monoethyl ether.

4. The solid-state battery according to claim 2, characterized in that, The polyisocyanate is one or more of the following: isophorone diisocyanate, 1,6-hexane diisocyanate, 4,4-dicyclohexylmethane diisocyanate, phenyl dimethyl diisocyanate, tetramethylphenyl dimethyl diisocyanate, toluene diisocyanate, diphenylmethane diisocyanate, 1,5-naphthalene diisocyanate, or polymethylene polyphenyl polyisocyanate.

5. The solid-state battery according to claim 2, characterized in that, In the closed-type aqueous isocyanate, the molar ratio of the hydrogen-containing compound to the polyisocyanate is (1.05~1.5):

1.

6. The solid-state battery according to claim 1, characterized in that, The acrylate monomers include one or more combinations of hexafluorobutyl methacrylate, polyethylene glycol diacrylate, or pentaerythritol acrylate.

7. A method for preparing a solid-state battery according to any one of claims 1-6, characterized in that, Includes the following steps: S4-1. Mix the electrolyte, polymerizing monomer and initiator to obtain a solid electrolyte; S4-2. Using a composite fiber membrane as the separator and the solid electrolyte prepared in S4-1 as the electrolyte, a battery is assembled with a positive electrode and a negative electrode. S4-3. The assembled battery is left to stand and solidify to obtain a solid-state battery.

8. The method for preparing a solid-state battery according to claim 7, characterized in that, The method for preparing the composite fiber membrane includes the following steps: S1. Dissolve cellulose acetate and blocked aqueous isocyanate in a first organic solvent, heat and stir to obtain a precursor solution; S2. Electrospinning the precursor solution to obtain a composite fiber-based membrane with a cross-linked structure; S3. Dissolve the acrylate-containing silane coupling agent in a second organic solvent to obtain a modified solution, drop the modified solution onto the composite fiber base membrane, and dry it to obtain the composite fiber membrane.

9. The method for preparing a solid-state battery according to claim 8, characterized in that, In the precursor solution, the mass fraction of cellulose acetate is 15-20%, and the mass fraction of blocked aqueous isocyanate is 1-3%.

10. The method for preparing a solid-state battery according to claim 8, characterized in that, In step S1, the heating temperature for heating and stirring is 50~70℃, and the stirring time is 6~10h.

11. The method for preparing a solid-state battery according to claim 8, characterized in that, In S3, the silane coupling agent containing acrylate is 3-(trimethoxysilyl)propyl-2-methyl-2-acrylate.

12. The method for preparing a solid-state battery according to claim 8, characterized in that, In S3, the mass fraction of the acrylate-containing silane coupling agent in the modified solution is 10-20%.

13. The method for preparing a solid-state battery according to claim 8, characterized in that, In step S3, the amount of modified solution added to the composite fiber-based membrane is 0.2~0.5 mL / cm. 2 .

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