Double-layer solid electrolyte membrane and preparation method and application thereof

Abstract

The invention belongs to the technical field of solid-state batteries, and relates to a double-layer solid-state electrolyte membrane, a preparation method thereof and application of the double-layer solid-state electrolyte membrane in a solid-state battery. The double-layer solid electrolyte membrane comprises a positive electrode membrane and a negative electrode membrane which are arranged in sequence; the positive electrode film is prepared from a positive electrode film solution, and the positive electrode film solution comprises 1-3 parts by weight of nano zinc oxide quantum dots; the negative electrode film is prepared from a negative electrode film solution, and the negative electrode film solution comprises 1-4 parts by weight of nano zinc oxide quantum dots. The nano zinc oxide quantum dots are added into the positive electrode film and the negative electrode film, so that the mechanical strength and the ionic conductivity of the positive electrode film can be effectively improved; meanwhile, the nano-zinc oxide quantum dots have relatively strong adsorbability on the DMF solvent, and a large amount of residual DMF solvent is adsorbed in the nano-zinc oxide quantum dots, so that the large amount of residual DMF solvent is prevented from directly generating side reaction with the positive electrode material, and the ionic conductivity of the solid electrolyte and the charge-discharge performance of the battery are improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of solid-state batteries and relates to a double-layer solid-state electrolyte membrane and a preparation method thereof and application in solid-state batteries. Background Art

[0002] The solid electrolyte in all-solid-state batteries has the advantage of being non-flammable, which can fundamentally solve this safety problem. Solid electrolytes can support the use of lithium metal anodes with higher theoretical specific capacity, thereby significantly improving the energy density of lithium batteries. However, single-layer solid electrolytes are difficult to be compatible with high-voltage positive electrode materials and lithium metal negative electrode materials at the same time, and their mechanical strength is not high.

[0003] Polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP) electrolyte is a special candidate material due to its superior thermal resilience, high Young's modulus and wide electrochemical stability window, which is very suitable for practical applications. However, after drying, about 10% of the N,N-dimethylformamide (DMF) solvent in the PVDF-HFP matrix has not evaporated. DMF will react with lithium metal negative and positive electrode materials, resulting in reduced ionic conductivity and decreased battery performance after solvent removal. Further research on the ion conduction mechanism found that the residual solvent DMF in the PVDF-HFP electrolyte strongly binds to lithium to form a complex, thereby affecting the performance of battery-related performance.

[0004] Chinese patent CN118763269A discloses a method for preparing a double-layer composite solid electrolyte, in which two different solid electrolytes are prepared separately, and then the two are uniformly contacted and extruded to obtain a double-layer composite solid electrolyte. However, since it is formed by physical contact and extrusion, the fit of the interface of the two solid electrolytes cannot be well controlled, resulting in poor interface fit or excessive contact.

[0005] Chinese patent CN 110504486 B relates to the application of a functional quantum dot composite solid electrolyte membrane in the field of all-solid-state lithium batteries. The functional quantum dot composite solid electrolyte membrane selects polyethylene oxide (PEO) as a polymer matrix, uses polyethylene glycol diglycidyl ether (PEGDGE), diethylenetriamine, and citric acid aqueous solution to mix microwave-assisted reaction to prepare PEGDGE functionalized carbon quantum dots as fillers, mixes PEGDGE functionalized carbon quantum dot dispersion, lithium bistrifluoromethanesulfonyl imide (LiTFSI), and PEO to prepare a casting solution, and prepares a solid electrolyte membrane by casting. However, there is poor compatibility between PEGDGE functionalized carbon quantum dots and the electrolyte membrane matrix, resulting in poor dispersibility in the electrolyte membrane.

[0006] Chinese patent CN 113394464 B discloses a highly conductive polymer solid electrolyte and a preparation method thereof, the preparation method comprising: adding PEO powder to a solution containing lithium salt, then adding perovskite quantum dots, heating and stirring at 50-70°C for 20-28h to obtain a uniform slurry, placing the slurry in a mold to form a film and removing the solvent, and finally vacuum drying to obtain a highly conductive polymer solid electrolyte membrane. However, the chemical stability of perovskite quantum dots in the electrolyte membrane is relatively weak, and the crystal structure of the perovskite quantum dots is easily destroyed in the electrolyte membrane. Summary of the invention

[0007] The purpose of the present invention is to provide a double-layer solid electrolyte and a preparation method and application thereof, so as to solve the problem that existing single-layer solid electrolytes are difficult to achieve simultaneous compatibility with high voltage and low ionic conductivity.

[0008] In order to achieve the above object, the technical solution of the present invention is as follows:

[0009] A double-layer solid electrolyte membrane comprises a positive electrode membrane and a negative electrode membrane which are arranged in sequence; the positive electrode membrane is prepared from a positive electrode membrane solution, wherein the positive electrode membrane solution comprises 1 to 3 parts by weight of nano zinc oxide quantum dots; the negative electrode membrane is prepared from a negative electrode membrane solution, wherein the negative electrode membrane solution comprises 1 to 4 parts by weight of nano zinc oxide quantum dots.

[0010] The present invention effectively improves the mechanical strength and ion conductivity of the positive electrode membrane by adding nano zinc oxide quantum dots to the positive electrode membrane solution and the negative electrode membrane solution. The nano zinc oxide quantum dots can promote the dissociation of lithium salts, promote the migration of ions, and improve ion conductivity.

[0011] In a preferred embodiment, the thickness of the positive electrode film is 40-60 μm, the thickness of the negative electrode film is 45-60 μm, and the thickness of the non-woven fabric is 15-20 μm.

[0012] In a preferred embodiment, the double-layer solid electrolyte membrane further includes a supporting skeleton.

[0013] In a preferred embodiment, the double-layer solid electrolyte membrane includes a positive electrode membrane, a supporting skeleton and a negative electrode membrane arranged in sequence.

[0014] In a preferred embodiment, the supporting frame is a non-woven fabric.

[0015] In a preferred embodiment, the positive electrode membrane solution also includes 5-15 parts of a polymer, 4-10 parts of a lithium salt and 30-50 parts of N,N-dimethylformamide (DMF); the lithium salt is one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide salt (LiFSI), lithium hexafluorophosphate (LiPF6), and lithium perchlorate (LiClO4), and the polymer is one or two of polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP) or polyacrylonitrile (PAN).

[0016] In a preferred embodiment, the positive electrode membrane solution also includes 7.5-12.5 parts of a polymer, 5-8 parts of a lithium salt and 30-50 parts of N,N-dimethylformamide (DMF); the lithium salt is one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide salt (LiFSI), lithium hexafluorophosphate (LiPF6), and lithium perchlorate (LiClO4), and the polymer is one or two of polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP) or polyacrylonitrile (PAN).

[0017] In a preferred embodiment, the negative electrode membrane solution also includes 3-8 parts of lithium salt, 0.5-1.5 parts of fluoroethylene carbonate (FEC), 5-15 parts of polyvinylidene fluoride-co-hexafluoropropylene and 30-50 parts of N,N-dimethylformamide (DMF); the lithium salt is one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide salt (LiFSI), lithium hexafluorophosphate (LiPF6), and lithium perchlorate (LiClO4).

[0018] In a preferred embodiment, the negative electrode membrane solution also includes 3.5-6.5 parts of lithium salt, 0.5-1.0 parts of fluoroethylene carbonate (FEC), 6-12 parts of polyvinylidene fluoride-co-hexafluoropropylene and 30-50 parts of N,N-dimethylformamide (DMF); the lithium salt is one or more of bistrifluoromethanesulfonic acid lithium imide, bisfluorosulfonyl imide lithium salt (LiFSI), lithium hexafluorophosphate (LiPF6), and lithium perchlorate (LiClO4).

[0019] Based on the same inventive concept, the present invention also claims protection for an electrode membrane solution comprising nano zinc oxide quantum dots, a polymer, a lithium salt and N,N-dimethylformamide.

[0020] In one preferred embodiment, when the electrode membrane solution is a positive electrode membrane solvent, the positive electrode membrane solution includes 1-3 parts of nano zinc oxide quantum dots, 5-15 parts of a polymer, 4-10 parts of a lithium salt and 30-50 parts of N,N-dimethylformamide (DMF); the lithium salt is one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide salt (LiFSI), lithium hexafluorophosphate (LiPF6), and lithium perchlorate (LiClO4), and the polymer is one or two of polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP) or polyacrylonitrile (PAN).

[0021] In one preferred embodiment, when the electrode membrane solution is the negative electrode membrane solvent, the negative electrode membrane solution includes 1-4 parts of nano zinc oxide quantum dots, 3-8 parts of lithium salt, 0.5-1.5 parts of fluoroethylene carbonate (FEC), 5-15 parts of polyvinylidene fluoride-co-hexafluoropropylene and 30-50 parts of N,N-dimethylformamide (DMF); the lithium salt is one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide salt (LiFSI), lithium hexafluorophosphate (LiPF6), and lithium perchlorate (LiClO4).

[0022] Too much PVDF-HFP in the positive electrode membrane solution and the negative electrode membrane solution will lead to a reduction in the space between the polymer chains, which will restrict the migration channel of lithium ions and thus reduce the overall ion conductivity; an appropriate amount of PVDF-HFP can improve the mechanical strength, while an excessive amount will make the material more fragile, affecting its durability and stability in long-term cycles; too little PVDF-HFP will not provide sufficient space and network structure to support the transmission of lithium ions, thereby significantly reducing ion conductivity; resulting in a significant decrease in the mechanical strength of the solid electrolyte, increasing the brittleness of the material, and affecting its stability during the charge and discharge process.

[0023] Too much lithium salt (LiTFSI, LiPF6) in the positive electrode membrane solution and the negative electrode membrane solution will inhibit the interaction of polymer chains, and the formed ion conduction channel may become blocked, thereby reducing the overall conductivity; too high lithium salt concentration will increase the interfacial reaction with the electrode, triggering side reactions, thus affecting the cycle stability and life of the battery. Too little lithium salt (LiTFSI, LiPF6) will reduce the ionic conductivity of the solid electrolyte; too little lithium salt cannot fully fill the space of the polymer matrix, resulting in an unstable electrolyte structure. Too low lithium salt concentration will lead to poor contact between the electrolyte and the electrode material, reduce the reactivity between the electrolyte and the electrode inside the battery, and lead to a decrease in battery performance.

[0024] Too much fluoroethylene carbonate (FEC) in the negative electrode membrane solution will block the lithium ion export channel in the polymer matrix, resulting in a decrease in ion conductivity; excessive FEC will increase the reaction between the electrode material, thereby increasing the interface resistance and reducing the battery's charge and discharge efficiency and cycle stability. Too little FEC will lead to uneven formation of the SEI film, increase the difficulty of the SEI film formation process, and increase the interface impedance.

[0025] In a preferred embodiment, the weight average molecular weight of the polyvinylidene fluoride-co-hexafluoropropylene is 400,000-600,000.

[0026] If the weight-average molecular weight of polyvinylidene fluoride-co-hexafluoropropylene is too large, the resistance to ion migration will increase and its flexibility will deteriorate. During the charge and discharge process of the battery, it will be difficult to adapt to the volume change of the electrode material, and stress concentration will easily occur, resulting in separation of the electrode and electrolyte interface, increasing the internal resistance of the battery and affecting the cycle stability of the battery. If the weight-average molecular weight of polyvinylidene fluoride-co-hexafluoropropylene is too small, the mechanical strength of the solid electrolyte membrane formed will be poor, and during the assembly and use of the battery, it will be prone to rupture and damage, affecting the safety and stability of the battery. The molecular weight is small, the number of molecular chain end groups is relatively large, and the chemical activity of the end groups is high. It is easy to react with lithium salts in the electrolyte, reducing the electrochemical stability of the solid electrolyte and affecting the cycle life and performance of the battery.

[0027] In a preferred embodiment, the particle size of the nano zinc oxide quantum dots is 5-10 nm.

[0028] If the particle size of nano zinc oxide quantum dots is too large, they are prone to agglomeration when added to solid electrolytes, making it difficult to evenly distribute in the electrolyte and affecting the performance of the battery. If the particle size is too small, it is difficult to prepare and the cost is high.

[0029] In a preferred embodiment, the mass fraction of N,N-dimethylformamide in the positive electrode film is 10%-15%.

[0030] In a preferred embodiment, the mass fraction of N,N-dimethylformamide in the negative electrode film is 9.8%-14.6%.

[0031] Although a certain amount of DMF helps to improve ionic conductivity, when it is too high, it will destroy the structural stability of the electrolyte, block the channel for ion migration, and reduce ionic conductivity. Too much DMF will affect the crystallinity of PVDF and the interaction between molecular chains, resulting in a decrease in the mechanical strength of the electrolyte. During the battery charging and discharging process, it is difficult to maintain the structural stability of the electrode material, affecting the performance and life of the battery. If the residual amount is too low, the contact at the interface may not be tight enough, increase the interface resistance, affect the transmission dynamics of lithium ions at the interface, and cause a decrease in the battery's charge and discharge performance.

[0032] Based on the same inventive concept, the present invention also claims a method for preparing the double-layer solid electrolyte membrane, comprising the following steps:

[0033] Step 1: coating the cathode film solution on one side of the support frame, vacuum drying, and obtaining the cathode film@non-woven fabric electrolyte;

[0034] Step 2: coating the negative electrode film solution on the other side of the support frame, and vacuum drying to obtain a double-layer solid electrolyte.

[0035] In a preferred embodiment, the vacuum drying temperature is 45-60° C. and the time is 6-12 h.

[0036] In a preferred embodiment, the thickness of the double-layer solid electrolyte membrane is 100-150 μm.

[0037] Based on the same inventive concept, the present invention also claims protection for a solid-state battery comprising the above-mentioned double-layer solid-state electrolyte membrane.

[0038] In solid-state lithium batteries, double-layer solid electrolytes replace electrolytes and separators.

[0039] In a preferred embodiment, the solid-state lithium battery also includes a negative electrode.

[0040] In a preferred embodiment, the negative electrode is lithium metal.

[0041] In a preferred embodiment, the raw materials of the positive electrode include 70-80 parts of lithium iron phosphate (LiFePO4), 5-15 parts of polyvinylidene fluoride (PVDF), 5-15 parts of conductive carbon black (SuperP) and 30-60 parts of N-methylpyrrolidone (NMP) by weight.

[0042] In a preferred embodiment, the raw material of the positive electrode includes 70-80 parts by weight of lithium nickel cobalt manganese oxide (LiNi 0.92 Co 0.04 Mn 0.04O2), 5-15 parts of polyvinylidene fluoride (PVDF), 5-15 parts of conductive carbon black (SuperP) and 30-60 parts of N-methylpyrrolidone (NMP).

[0043] Compared with the prior art, the present invention has the following beneficial effects:

[0044] (1) The double-layer electrolyte membrane prepared by the present invention is obtained by coating the positive electrode membrane solution and the negative electrode membrane solution on the front and back surfaces of the non-woven fabric respectively, so as to obtain a positive electrode membrane @ non-woven fabric @ negative electrode membrane solid electrolyte with a sandwich structure. Compared with preparing two solid electrolyte membranes separately and then pressing them together, preparing a double-layer solid electrolyte on the non-woven fabric not only improves the mechanical strength of the double-layer solid electrolyte, which can effectively inhibit the puncture of lithium dendrites, but also improves the degree of adhesion between the double-layer electrolyte membranes; the positive electrode membrane and the negative electrode membrane are separated by the non-woven fabric, so that they can play related roles independently on the positive and negative electrodes, thereby avoiding the components in the positive and negative electrode membranes from having negative effects on the positive and negative electrodes.

[0045] (2) Adding nano zinc oxide quantum dots to the positive electrode membrane can effectively improve the mechanical strength and ionic conductivity of the positive electrode membrane; zinc oxide can induce PVDF segments to form a β-phase structure. The β-phase is the most polar phase with a fully trans (TTTT) conformation. Since the β-phase PVDF has the best dielectric properties, it can promote the dissociation of lithium salts and the migration of ions; at the same time, nano zinc oxide quantum dots have strong polarity, and a large number of polar sites have strong adsorption for DMF solvent, which adsorbs a large amount of residual DMF solvent into themselves, avoiding a large amount of residual DMF solvent directly reacting with the positive electrode material. The small amount of DMF solvent that remains can increase the interfacial wettability between the positive electrode and the positive electrode membrane, effectively reducing the interfacial impedance and improving the ionic conductivity of the solid electrolyte and the battery charge and discharge performance. However, when the residual amount of DMF is too low, it is not conducive to the migration of lithium ions in the electrolyte. When the zinc oxide particle size is too large, it is easy to agglomerate when added to the solid electrolyte, making it difficult to be evenly distributed in the electrolyte and affecting the performance of the battery. Therefore, zinc oxide particles of quantum dot size are selected.

[0046] (3) Adding nano zinc oxide quantum dots to the negative electrode membrane increases the amorphous region of PVDF-HFP, reduces the crystallinity of the negative electrode membrane, and improves the ionic conductivity of the negative electrode membrane; at the same time, it can adsorb residual DMF and weaken the binding strength between lithium ions and DMF, thereby adjusting the solvation structure. The resulting anion-rich solvation structure is conducive to the formation of a stable SEI layer, has excellent lithium ion migration kinetics, promotes uniform lithium deposition, weakens the volume change during lithium deposition and lithium stripping, and inhibits the growth of lithium dendrites.

[0047] (4) The double-layer electrolyte membrane prepared by the present invention has a simple preparation process, the membrane thickness can be adjusted, the cost is controllable, and it has practical promotion significance. It is also easy to realize large-scale industrial production and commercial application of solid electrolyte membranes. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 This is a SEM image of nano zinc oxide quantum dots in Example 1 of the present invention;

[0049] Figure 2 This is a SEM image of the positive electrode film on the non-woven fabric in Example 1 of the present invention;

[0050] Figure 3 This is a SEM image of the negative electrode film on the non-woven fabric in Example 1 of the present invention. DETAILED DESCRIPTION

[0051] The present invention is not limited to the following specific embodiments. A person skilled in the art can implement the present invention in various other specific embodiments according to the contents disclosed in the present invention, or any simple changes or modifications made by adopting the design structure and ideas of the present invention fall within the protection scope of the present invention. It should be noted that the embodiments of the present invention and the features in the embodiments can be combined with each other without conflict. Various raw materials, reagents, instruments and equipment used in the present invention can be purchased on the market or prepared by existing methods. The weight average molecular weight of the polyvinylidene fluoride-co-hexafluoropropylene is 600000.

[0052] Example 1

[0053] A method for preparing a double-layer solid electrolyte for a lithium battery is carried out according to the following steps:

[0054] (1) Preparation of positive electrode film: 0.5 g of lithium bis(trifluoromethanesulfonyl)imide LiTFSI, 0.75 g of poly(vinylidene fluoride-co-hexafluoropropylene) PVDF-HFP, 0.14 g of nano zinc oxide quantum dot powder, and 5 mL of N,N-dimethylformamide DMF solvent were weighed in a glove box and stirred on a magnetic stirrer at 45°C and 400 r / min for 12 h to obtain a positive electrode film solution. The particle size of the nano oxidative quantum dots was 10 nm.

[0055] (2) The cathode film solution was evenly coated on one side of the non-woven fabric by a scraper with a specification of 1000 μm to prepare a cathode film@non-woven fabric solid electrolyte membrane, which was then vacuum dried at a drying temperature of 50°C for 8 hours. After drying, the mass of DMF accounted for 12.8% of the mass of the cathode film. The thickness of the cathode film was 40 μm.

[0056] (3) Preparation of negative electrode film: 0.38 g lithium hexafluorophosphate LiPF6, 0.64 g polyvinylidene fluoride-co-hexafluoropropylene PVDF-HFP, 0.12 g nano zinc oxide quantum dot powder, and 5 mL of N,N-dimethylformamide DMF solvent were weighed in a glove box and stirred on a magnetic stirrer at 45°C and 450 r / min for 12 h to obtain a negative electrode film solution. The particle size of the nano oxidative quantum dots was 10 nm.

[0057] (4) The negative electrode film solution was evenly coated on the other side of the non-woven fabric using a scraper with a specification of 1000 μm to prepare a positive electrode film @ non-woven fabric @ negative electrode film solid electrolyte, which was then vacuum dried at a temperature of 50°C for 10 hours. After drying, the mass of DMF accounted for 11.6%. The thickness of the negative electrode film was 60 μm. The thickness of the non-woven fabric was 20 μm. The microscopic morphology of the nano zinc oxide quantum dots, positive electrode film, and negative electrode film was observed. The results are as follows: Figure 1-Figure 3 shown. Figure 1 This is a SEM image of nano zinc oxide quantum dots in Example 1 of the present invention; Figure 2 This is a SEM image of the positive electrode film on the non-woven fabric in Example 1 of the present invention; Figure 3 This is a SEM image of the negative electrode film on the non-woven fabric in Example 1 of the present invention.

[0058] (5) 1.6g lithium iron phosphate, 0.2g PVDF, 0.2g SuperP and 10g N-methylpyrrolidone (NMP) were uniformly mixed to prepare a positive electrode sheet, and the positive electrode sheet, the double-layer solid electrolyte and the lithium metal negative electrode were assembled into a lithium solid-state battery. The battery was subjected to a constant current charge and discharge cycle test at 25°C in the voltage range of 2.5-4.2V using a NEWARE multi-channel tester. At a current density of 1C, the battery had an initial discharge specific capacity of 162.6mAh / g, and a capacity retention rate of 82.6% after 100 cycles.

[0059] Example 2

[0060] A method for preparing a double-layer solid electrolyte for a lithium battery is carried out according to the following steps:

[0061] (1) Preparation of positive electrode film: 0.60 g LiTFSI, 0.75 g PVDF-HFP, 0.2 g nano zinc oxide quantum dot powder, and 5 mL DMF solvent were weighed in a glove box and stirred on a magnetic stirrer at 45° C. and 400 r / min for 12 h to obtain a positive electrode film solution. The particle size of the nano oxidative quantum dots was 5 nm.

[0062] (2) The cathode film solution was evenly coated on one side of the non-woven fabric by a scraper with a specification of 1000 μm to prepare a cathode film@non-woven fabric solid electrolyte membrane, which was then vacuum dried at a drying temperature of 50°C for 8 hours. After drying, the mass of DMF accounted for 12.5% ​​of the mass of the cathode film. The thickness of the cathode film was 40 μm.

[0063] (3) Preparation of negative electrode film: 0.65 g LiPF6, 0.64 g PVDF-HFP, 0.2 g nano zinc oxide quantum dot powder, and 5 mL DMF solvent were weighed in a glove box and stirred on a magnetic stirrer at 45°C and 450 r / min for 12 h to obtain a negative electrode film solution. The particle size of the nano oxidative quantum dots was 5 nm.

[0064] (4) The negative electrode film solution was evenly coated on the other side of the non-woven fabric by a scraper with a specification of 1000 μm to prepare a positive electrode film @ non-woven fabric @ negative electrode film solid electrolyte, which was then vacuum dried at a drying temperature of 50°C for 10 h. After drying, the mass of DMF accounted for 11.9%. The thickness of the negative electrode film was 45 μm. The thickness of the non-woven fabric was 20 μm.

[0065] (5) 1.6g lithium iron phosphate, 0.2g PVDF, 0.2g SuperP and 10g N-methylpyrrolidone (NMP) were uniformly mixed to prepare a positive electrode sheet, and the positive electrode sheet, the double-layer solid electrolyte and the lithium metal negative electrode were assembled into a lithium solid-state battery. The battery was subjected to a constant current charge and discharge cycle test at 25°C in the voltage range of 2.5-4.2V using a NEWARE multi-channel tester. At a current density of 1C, the battery had an initial discharge specific capacity of 158.7mAh / g, and a capacity retention rate of 84.3% after 100 cycles.

[0066] Example 3

[0067] A method for preparing a double-layer solid electrolyte for a lithium battery is carried out according to the following steps:

[0068] (1) Preparation of positive electrode film: 0.8 g LiTFSI, 1.25 g PVDF-HFP, 0.14 g nano zinc oxide quantum dot powder, and 5 mL DMF solvent were weighed in a glove box and stirred on a magnetic stirrer at 45° C. and 400 r / min for 12 h to obtain a positive electrode film solution. The particle size of the nano oxidative quantum dots was 8 nm.

[0069] (2) The cathode film solution was evenly coated on one side of the non-woven fabric by a scraper with a specification of 1000 μm to prepare a cathode film@non-woven fabric solid electrolyte membrane, which was then vacuum dried at a drying temperature of 50°C for 8 hours. After drying, the mass of DMF accounted for 13.1% of the mass of the cathode film. The thickness of the cathode film was 40 μm.

[0070] (3) Preparation of negative electrode film: 0.50 g LiPF6, 0.86 g PVDF-HFP, 0.2 g nano zinc oxide quantum dot powder, and 5 mL DMF solvent were weighed in a glove box and stirred on a magnetic stirrer at 45°C and 450 r / min for 12 h to obtain a negative electrode film solution. The particle size of the nano oxidative quantum dots was 5 nm.

[0071] (4) The negative electrode film solution was evenly coated on the other side of the non-woven fabric by a scraper with a specification of 1000 μm to prepare a positive electrode film @ non-woven fabric @ negative electrode film solid electrolyte, which was then vacuum dried at a drying temperature of 50°C for 10 h. After drying, the mass of DMF accounted for 11.2%. The thickness of the negative electrode film was 50 μm. The thickness of the non-woven fabric was 20 μm.

[0072] (5) 1.6g lithium iron phosphate, 0.2g PVDF, 0.2g SuperP and 10g N-methylpyrrolidone (NMP) were uniformly mixed to prepare a positive electrode sheet, and the positive electrode sheet, the double-layer solid electrolyte and the lithium metal negative electrode were assembled into a lithium solid-state battery. The battery was subjected to a constant current charge and discharge cycle test at 25°C in the voltage range of 2.5-4.2V using a NEWARE multi-channel tester. At a current density of 1C, the battery had an initial discharge specific capacity of 150.8mAh / g, and a capacity retention rate of 80.5% after 100 cycles.

[0073] Example 4

[0074] A method for preparing a double-layer solid electrolyte for a lithium battery is carried out according to the following steps:

[0075] (1) Preparation of positive electrode film: 0.8 g LiTFSI, 1.2 g PVDF-HFP, 0.14 g nano zinc oxide quantum dot powder, and 5 mL DMF solvent were weighed in a glove box and stirred on a magnetic stirrer at 45° C. and 400 r / min for 12 h to obtain a positive electrode film solution. The particle size of the nano oxidative quantum dots was 10 nm.

[0076] (2) The cathode film solution was evenly coated on one side of the non-woven fabric by a scraper with a specification of 1000 μm to prepare a cathode film@non-woven fabric solid electrolyte membrane, which was then vacuum dried at a drying temperature of 50°C for 8 hours. After drying, the mass of DMF accounted for 12.8% of the mass of the cathode film. The thickness of the cathode film was 60 μm.

[0077] (3) Preparation of negative electrode film: 0.62 g LiPF6, 1.2 g PVDF-HFP, 0.3 g nano zinc oxide quantum dot powder, and 5 mL DMF solvent were weighed in a glove box and stirred on a magnetic stirrer at 45°C and 450 r / min for 12 h to obtain a negative electrode film solution. The particle size of the nano oxidative quantum dots was 5 nm.

[0078] (4) The negative electrode film solution was evenly coated on the other side of the non-woven fabric by a scraper with a specification of 1000 μm to prepare a positive electrode film @ non-woven fabric @ negative electrode film solid electrolyte, which was then vacuum dried at a drying temperature of 50°C for 10 h. After drying, the mass of DMF accounted for 11.6%. The thickness of the negative electrode film was 45 μm. The thickness of the non-woven fabric was 20 μm.

[0079] (5) 1.6 g LiNi 0.92 Co 0.04 Mn 0.04 O2, 0.2g PVDF, 0.2g SuperP and 10g N-methylpyrrolidone (NMP) were uniformly mixed to prepare a positive electrode sheet, and the positive electrode sheet, the double-layer solid electrolyte and the lithium metal negative electrode were assembled into a lithium solid-state battery. The battery was subjected to a constant current charge and discharge cycle test at 25°C in the voltage range of 3.0-4.2V by a NEWARE multi-channel tester. At a current density of 0.5C, the battery had an initial discharge capacity of 190.3mAh / g, and a capacity retention rate of 85.1% after 100 cycles.

[0080] Example 5

[0081] A method for preparing a double-layer solid electrolyte for a lithium battery is carried out according to the following steps:

[0082] (1) Preparation of positive electrode film: 0.6 g LiTFSI, 0.9 g PVDF-HFP, 0.2 g nano zinc oxide quantum dot powder, and 5 mL DMF solvent were weighed in a glove box and stirred on a magnetic stirrer at 45° C. and 400 r / min for 12 h to obtain a positive electrode film solution. The particle size of the nano oxidative quantum dots was 5 nm.

[0083] (2) The cathode film solution was evenly coated on one side of the non-woven fabric by a scraper with a specification of 1000 μm to prepare a cathode film@non-woven fabric solid electrolyte membrane, which was then vacuum dried at a drying temperature of 50°C for 8 hours. After drying, the mass of DMF accounted for 12.5% ​​of the mass of the cathode film. The thickness of the cathode film was 60 μm.

[0084] (3) Preparation of negative electrode film: 0.5 g LiPF6, 0.8 g PVDF-HFP, 0.12 g nano zinc oxide quantum dot powder, and 5 mL DMF solvent were weighed in a glove box and stirred on a magnetic stirrer at 45°C and 450 r / min for 12 h to obtain a negative electrode film solution. The particle size of the nano oxidative quantum dots was 10 nm.

[0085] (4) The negative electrode film solution was evenly coated on the other side of the non-woven fabric by a scraper with a specification of 1000 μm to prepare a positive electrode film @ non-woven fabric @ negative electrode film solid electrolyte, which was then vacuum dried at a drying temperature of 50°C for 10 h. After drying, the mass of DMF accounted for 11.9%. The thickness of the negative electrode film was 60 μm. The thickness of the non-woven fabric was 20 μm.

[0086] (5) 1.6 g LiNi 0.92 Co 0.04 Mn 0.04 O2, 0.2g PVDF, 0.2g SuperP and 10g N-methylpyrrolidone (NMP) were uniformly mixed to prepare a positive electrode sheet, and the positive electrode sheet, the double-layer solid electrolyte and the lithium metal negative electrode were assembled into a lithium solid-state battery. The battery was subjected to a constant current charge and discharge cycle test at 25°C in the voltage range of 3.0-4.2V by a NEWARE multi-channel tester. At a current density of 0.5C, the battery had an initial discharge capacity of 182.3mAh / g, and a capacity retention rate of 81.4% after 100 cycles.

[0087] Example 6

[0088] A method for preparing a double-layer solid electrolyte for a lithium battery is carried out according to the following steps:

[0089] (1) Preparation of positive electrode film: 0.7 g LiTFSI, 1.0 g PVDF-HFP, 0.14 g nano zinc oxide quantum dot powder, and 5 mL DMF solvent were weighed in a glove box and stirred on a magnetic stirrer at 45° C. and 400 r / min for 12 h to obtain a positive electrode film solution. The particle size of the nano oxidative quantum dots was 8 nm.

[0090] (2) The cathode film solution was evenly coated on one side of the non-woven fabric by a scraper with a specification of 1000 μm to prepare a cathode film@non-woven fabric solid electrolyte membrane, which was then vacuum dried at a drying temperature of 50°C for 8 hours. After drying, the mass of DMF accounted for 13.1% of the mass of the cathode film. The thickness of the cathode film was 50 μm.

[0091] (3) Preparation of negative electrode film: 0.6 g LiPF6, 0.9 g PVDF-HFP, 0.2 g nano zinc oxide quantum dot powder, and 5 mL DMF solvent were weighed in a glove box and stirred on a magnetic stirrer at 45°C and 450 r / min for 12 h to obtain a negative electrode film solution. The particle size of the nano oxidative quantum dots was 8 nm.

[0092] (4) The negative electrode film solution was evenly coated on the other side of the non-woven fabric by a scraper with a specification of 1000 μm to prepare a positive electrode film @ non-woven fabric @ negative electrode film solid electrolyte, which was then vacuum dried at a drying temperature of 50°C for 10 hours. After drying, the mass of DMF accounted for 11.2%. The thickness of the negative electrode film was 50 μm. The thickness of the non-woven fabric was 15 μm.

[0093] (5) 1.6 g LiNi 0.92 Co 0.04 Mn 0.04 O2, 0.2g PVDF, 0.2g SuperP and 10g N-methylpyrrolidone (NMP) were uniformly mixed to prepare a positive electrode sheet, and the positive electrode sheet, the double-layer solid electrolyte and the lithium metal negative electrode were assembled into a lithium solid-state battery. The battery was subjected to a constant current charge and discharge cycle test at 25°C in the voltage range of 3.0-4.2V by a NEWARE multi-channel tester. At a current density of 0.5C, the battery had an initial discharge capacity of 178.8mAh / g, and a capacity retention rate of 79.4% after 100 cycles.

[0094] It can be seen from Examples 1-6 that the prepared double-layer solid electrolyte has a wide adaptability to positive electrode materials.

[0095] Comparative Example 1

[0096] In step 1 of Example 1, nano zinc oxide quantum dot powder is not added, and the rest is the same as Example 1. The assembled LFP battery is subjected to constant current charge and discharge cycle test in the voltage range of 2.5-4.2V at 25°C by a NEWARE multi-channel tester. At a current density of 1C, the battery has an initial discharge specific capacity of 134.1mAh / g, and a capacity retention rate of 67.4% after 100 cycles.

[0097] Comparative Example 2

[0098] In step 3 of Example 1, nano zinc oxide quantum dot powder is not added, and the rest is the same as Example 1. The assembled LFP battery is subjected to constant current charge and discharge cycle test at 25° C. in the voltage range of 2.5-4.2 V by a NEWARE multi-channel tester. At a current density of 1C, the battery has an initial discharge specific capacity of 142.9 mAh / g, and a capacity retention rate of 70.3% after 100 cycles.

[0099] Comparative Example 3

[0100] In step 1 of Example 1, 0.50 g of nano zinc oxide quantum dot powder was added instead, and in step 3, 0.50 g of nano zinc oxide quantum dot powder was added instead, and the rest was the same as in Example 1. The assembled LFP battery was subjected to a constant current charge and discharge cycle test at 25° C. in a voltage range of 2.5-4.2 V using a NEWARE multi-channel tester. At a current density of 1 C, the battery had an initial discharge specific capacity of 99.0 mAh / g, and a capacity retention rate of 42.0% after 100 cycles.

[0101] Comparative Example 4

[0102] In step 1 of Example 1, 0.50 g of nano zinc oxide quantum dot powder was added instead, and the rest was the same as Example 1. The assembled LFP battery was subjected to constant current charge and discharge cycle test at 25° C. in the voltage range of 2.5-4.2 V by a NEWARE multi-channel tester. At a current density of 1C, the battery had an initial discharge specific capacity of 118.4 mAh / g, and a capacity retention rate of 48.7% after 100 cycles.

[0103] Comparative Example 5

[0104] In step 3 of Example 1, 0.60 g of nano zinc oxide quantum dot powder was added instead, and the rest was the same as in Example 1. The assembled LFP battery was subjected to constant current charge and discharge cycle test at 25° C. in the voltage range of 2.5-4.2 V by a NEWARE multi-channel tester. At a current density of 1C, the battery had an initial discharge specific capacity of 128.1 mAh / g, and a capacity retention rate of 53.8% after 100 cycles.

[0105] Comparative Example 6

[0106] In step 1 of Example 1, 0.14 g of nano titanium dioxide quantum dot powder was added instead, and in step 3, 0.12 g of nano titanium dioxide quantum dot powder was added instead, and the rest was the same as in Example 1. The assembled LFP battery was subjected to a constant current charge and discharge cycle test at 25° C. in a voltage range of 2.5-4.2 V using a NEWARE multi-channel tester. At a current density of 1 C, the battery had an initial discharge specific capacity of 125.6 mAh / g, and a capacity retention rate of 66.0% after 100 cycles.

[0107] Comparative Example 7

[0108] In step 1 of Example 1, 0.14 g of nano titanium dioxide quantum dot powder was added, and the rest was the same as Example 1. The assembled LFP battery was subjected to constant current charge and discharge cycle test at 25° C. in the voltage range of 2.5-4.2 V by a NEWARE multi-channel tester. At a current density of 1C, the battery had an initial discharge specific capacity of 120.8 mAh / g, and a capacity retention rate of 52.4% after 100 cycles.

[0109] Comparative Example 8

[0110] In step 3 of Example 1, 0.12 nanometer titanium dioxide quantum dot powder was added, and the rest was the same as Example 1. The assembled LFP battery was subjected to constant current charge and discharge cycle test at 25° C. in the voltage range of 2.5-4.2 V by a NEWARE multi-channel tester. At a current density of 1C, the battery had an initial discharge specific capacity of 134.2 mAh / g, and a capacity retention rate of 48.8% after 100 cycles.

[0111] Comparative Example 9

[0112] In step 1 of Example 4, nano zinc oxide quantum dot powder is not added, and the rest is the same as Example 4. The assembled NCM92 battery is subjected to constant current charge and discharge cycle test in the voltage range of 3.0-4.2V at 25°C by NEWARE multi-channel tester. At a current density of 0.5C, the battery has an initial discharge specific capacity of 120.3mAh / g, and a capacity retention rate of 40.6% after 100 cycles.

[0113] Comparative Example 10

[0114] In step 3 of Example 4, nano zinc oxide quantum dot powder is not added, and the rest is the same as Example 4. The assembled NCM92 battery is subjected to constant current charge and discharge cycle test at 25° C. in the voltage range of 3.0-4.2 V by a NEWARE multi-channel tester. At a current density of 0.5C, the battery has an initial discharge specific capacity of 95 mAh / g, and a capacity retention rate of 36.8% after 100 cycles.

[0115] Comparative Example 11

[0116] In step 1 of Example 4, 0.50 g of nano zinc oxide quantum dot powder was added instead, and in step 3, 0.50 g of nano titanium dioxide quantum dot powder was added instead, and the rest was the same as in Example 4. The assembled NCM92 battery was subjected to constant current charge and discharge cycle test at 25° C. in the voltage range of 3.0-4.2 V by a NEWARE multi-channel tester. At a current density of 0.5 C, the battery had an initial discharge specific capacity of 76.2 mAh / g, and a capacity retention rate of 21.7% after 100 cycles.

[0117] Comparative Example 12

[0118] In step 1 of Example 4, 0.50 g of nano zinc oxide quantum dot powder was added instead, and the rest was the same as in Example 4. The assembled NCM92 battery was subjected to a constant current charge and discharge cycle test at 25° C. in the voltage range of 3.0-4.2 V by a NEWARE multi-channel tester. At a current density of 0.5 C, the battery had an initial discharge specific capacity of 82.4 mAh / g, and a capacity retention rate of 38.1% after 100 cycles.

[0119] Comparative Example 13

[0120] In step 3 of Example 4, 0.50 g of nano zinc oxide quantum dot powder was added instead, and the rest was the same as Example 4. The assembled NCM92 battery was subjected to constant current charge and discharge cycle test at 25° C. in the voltage range of 3.0-4.2 V by a NEWARE multi-channel tester. At a current density of 0.5 C, the battery had an initial discharge specific capacity of 70.9 mAh / g, and a capacity retention rate of 28.4% after 100 cycles.

[0121] Comparative Example 14

[0122] In step 1 of Example 4, 0.14 g of nano titanium dioxide quantum dot powder was added instead, and in step 3, 0.12 g of nano titanium dioxide quantum dot powder was added instead, and the rest was the same as in Example 4. The assembled NCM92 battery was subjected to a constant current charge and discharge cycle test at 25° C. in a voltage range of 3.0-4.2 V using a NEWARE multi-channel tester. At a current density of 0.5 C, the battery had an initial discharge specific capacity of 109.2 mAh / g, and a capacity retention rate of 51.7% after 100 cycles.

[0123] Comparative Example 15

[0124] In step 1 of Example 4, 0.14 g of nano titanium dioxide quantum dot powder was added instead, and the rest was the same as in Example 4. The assembled NCM92 battery was subjected to a constant current charge-discharge cycle test at 25° C. in the voltage range of 3.0-4.2 V by a NEWARE multi-channel tester. At a current density of 0.5 C, the battery had an initial discharge specific capacity of 94.4 mAh / g, and a capacity retention rate of 48.4% after 100 cycles.

[0125] Comparative Example 16

[0126] In step 3 of Example 4, 0.12 g of nano titanium dioxide quantum dot powder was added instead, and the rest was the same as in Example 4. The assembled NCM92 battery was subjected to a constant current charge and discharge cycle test at 25° C. in the voltage range of 3.0-4.2 V by a NEWARE multi-channel tester. At a current density of 0.5 C, the battery had an initial discharge specific capacity of 76.4 mAh / g, and a capacity retention rate of 32.9% after 100 cycles.

[0127] In summary, it can be seen that after adding non-woven fabrics and nano zinc oxide quantum dots to the double-layer solid electrolyte membrane prepared by the present invention, the ionic conductivity of the solid electrolyte and the battery charge and discharge performance are improved. From Examples 2 to 3, Examples 5 to 6, Comparative Examples 3 to 5, and Comparative Examples 11 to 13, it can be seen that with the increase in the amount of nano zinc oxide quantum dots added, the battery performance slightly decreases. Excessive addition of nano zinc oxide quantum dots will cause them to agglomerate in the solid electrolyte membrane, thereby reducing the ionic conductivity and thus reducing the battery charge and discharge performance.

[0128] It should be noted that the above embodiments are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is impossible to list all the embodiments here. Any obvious changes or modifications derived from the technical solution of the present invention are still within the scope of protection of the present invention.

Claims

1. A double-layer solid electrolyte membrane, characterized in that: It comprises a positive electrode film and a negative electrode film arranged in sequence; the positive electrode film is prepared from a positive electrode film solution, and the positive electrode film solution comprises 1-3 parts of nano zinc oxide quantum dots by weight; the negative electrode film is prepared from a negative electrode film solution, and the negative electrode film solution comprises 1-4 parts of nano zinc oxide quantum dots by weight.

2. The double-layer solid electrolyte membrane according to claim 1, characterized in that: The positive electrode membrane solution also includes 5-15 parts of a polymer, 4-10 parts of a lithium salt and 30-50 parts of N,N-dimethylformamide (DMF); the lithium salt is one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide salt (LiFSI), lithium hexafluorophosphate (LiPF6), and lithium perchlorate (LiClO4), and the polymer is one or two of polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP) or polyacrylonitrile (PAN).

3. The double-layer solid electrolyte membrane according to claim 1, characterized in that: The negative electrode membrane solution also includes 3-8 parts of lithium salt, 0.5-1.5 parts of fluoroethylene carbonate (FEC), 5-15 parts of polyvinylidene fluoride-co-hexafluoropropylene and 30-50 parts of N,N-dimethylformamide (DMF); the lithium salt is one or more of bis(trifluoromethanesulfonic acid) lithium imide, bis(fluorosulfonyl)imide lithium salt (LiFSI), lithium hexafluorophosphate (LiPF6), and lithium perchlorate (LiClO4).

4. The double-layer solid electrolyte membrane according to claim 1, characterized in that: The particle size of the nano zinc oxide quantum dots is 5-10 nm.

5. The double-layer solid electrolyte membrane according to claims 1-4, characterized in that: The mass fraction of N,N-dimethylformamide in the positive electrode film is 10%-15%; the mass fraction of N,N-dimethylformamide in the negative electrode film is 9.8%-14.6%.

6. The method for preparing a double-layer solid electrolyte membrane according to claims 1-5, characterized in that: The following steps are involved: Step 1: coating the cathode film solution on one side of the support frame, vacuum drying, and obtaining the cathode film@non-woven fabric electrolyte; Step 2: coating the negative electrode film solution on the other side of the support frame, and vacuum drying to obtain a double-layer solid electrolyte.

7. A solid-state battery, characterized in that: It comprises the double-layer solid electrolyte membrane described in claims 1-5.

8. The solid-state battery according to claim 7, characterized in that: The solid-state lithium battery also includes a negative electrode; The negative electrode is lithium metal.

9. An electrode membrane solution, characterized in that: It includes nano zinc oxide quantum dots, polymers, lithium salts and N,N-dimethylformamide.

10. The electrode membrane solution according to claim 9, characterized in that: When the electrode film solution is a positive electrode film solvent, the positive electrode film solution includes 1-3 parts of nano zinc oxide quantum dots, 5-15 parts of a polymer, 4-10 parts of a lithium salt and 30-50 parts of N,N-dimethylformamide (DMF); the lithium salt is one or more of bis(trifluoromethylsulfonic acid) imide lithium, bis(fluorosulfonyl)imide lithium salt (LiFSI), lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), and the polymer is polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP) or polyacrylonitrile (PAN ) one or two of; when the electrode membrane solution is the negative electrode membrane solvent, the negative electrode membrane solution includes 1-4 parts of nano zinc oxide quantum dots, 3-8 parts of lithium salt, 0.5-1.5 parts of fluoroethylene carbonate (FEC), 5-15 parts of polyvinylidene fluoride-co-hexafluoropropylene and 30-50 parts of N,N-dimethylformamide (DMF); the lithium salt is one or more of bistrifluoromethanesulfonic acid lithium imide, bisfluorosulfonyl imide lithium salt (LiFSI), lithium hexafluorophosphate (LiPF6), and lithium perchlorate (LiClO4).

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