CN114551986A - High-conductivity composite solid electrolyte and preparation method thereof - Google Patents

High-conductivity composite solid electrolyte and preparation method thereof Download PDF

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CN114551986A
CN114551986A CN202110936112.8A CN202110936112A CN114551986A CN 114551986 A CN114551986 A CN 114551986A CN 202110936112 A CN202110936112 A CN 202110936112A CN 114551986 A CN114551986 A CN 114551986A
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peo
solid electrolyte
litfsi
pet
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宫娇娇
陈军
黄建根
郑利峰
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Wanxiang A123 Systems Asia Co Ltd
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Abstract

The invention relates to the technical field of solid electrolytes of fiber membranes of lithium batteries, in particular to a high-conductivity composite solid electrolyte and a preparation method thereof. The lithium ion canTo move within the free volume of the polymeric PET/PEO nanofiber for ion transport by inter-or intra-chain hopping of the polymer. LLTO nanowires and PET act to inhibit polymer crystallization process, improve interfacial stability properties of polymer matrix, to provide multiple Li+The ion transmission channel greatly improves the conductivity of the solid electrolyte. When the mass concentration of the added LLTO nano wire is 1 percent, the solid electrolyte has the best performance, and TiO2The nano-array substrate is additionally provided with a lithium ion transmission channel on the basis of the original substrate, so that the conductivity and the mechanical strength are obviously improved compared with those of the prior art.

Description

High-conductivity composite solid electrolyte and preparation method thereof
Technical Field
The invention relates to the technical field of lithium battery fiber membrane solid electrolytes, in particular to a high-conductivity composite solid electrolyte and a preparation method thereof.
Background
Lithium Ion Batteries (LIBs) have shown great market potential due to their high operating voltage, high energy density, fast charge and discharge speed, and long cycle life. However, the traditional lithium ion energy density based on liquid electrolyte is improved to the limit, and meanwhile, the liquid electrolyte is highly flammable and has potential safety hazards. In contrast, solid electrolytes can provide high energy density, inhibit dendritic growth, and have the advantages of thermal stability, mechanical strength, flexibility, and compactness. Among them, polyethylene oxide (PEO) is one of the most attractive solid electrolyte materials, which has excellent solubility to lithium ions, which can move in the free volume of PEO and transport ions through inter-chain or intra-chain hopping in PEO, but its poor conductivity and interfacial stability to the positive electrode material at high temperature have been one of the obstacles limiting its scale application.
In order to solve the problems, Chinese patent CN201911371784.8 discloses a fiber membrane solid electrolyte of a power lithium battery and a preparation method thereof, a lithium compound is encapsulated in an inner layer of a fiber through coaxial spinning, the surface of a composite fiber forms loose and micropores through gelation of lithium silicate, the conductivity is improved through the improved interface performance, but a lithium ion transmission channel is still limited in the solid electrolyte, and the actual requirements of the solid lithium battery cannot be effectively met. Chinese patent CN112151859A discloses a composite solid electrolyte with two surfaces, which is coated on a three-dimensional ceramic skeleton by two polymer electrolyte solutions with different electrochemical stability, and the interface stability is also improved, but there is still much room for improvement of the conductivity of the solid electrolyte. Chinese patent CN202110122226.9 discloses a method for modifying polymer solid polyelectrolyteThe method utilizes titanium dioxide nano particles to be compounded with polyalkylene oxide-polyphenylene ether copolymer, TiO2The nano particles are uniformly dispersed in the organic polymer matrix, the motion capability of a PEO chain segment is improved, the crystallinity of the polymer is effectively reduced, and the ionic conductivity of the polymer is improved.
Disclosure of Invention
Aiming at the problem that the conductivity of the solid electrolyte is to be improved in the prior art, the invention provides a high-conductivity composite solid electrolyte and a preparation method thereof, so as to increase multiple Li+The ion transmission channel greatly improves the conductivity of the solid electrolyte.
The object of the present invention is achieved by the following means.
A composite solid electrolyte with high conductivity comprises LLTO nano-wires, PET/PEO nano-fibers and lithium bis (trifluoromethane) sulfonimide, wherein the lithium bis (trifluoromethane) sulfonimide and the LLTO nano-wires are dispersed in the PET/PEO nano-fibers. Lithium ions can move in the free volume of the polymer PET/PEO nano-fiber and carry out ion transportation through interchain or intrachain jumping of the polymer. LLTO nanowires and PET act to inhibit polymer crystallization process, improve interfacial stability properties of polymer matrix, to provide multiple Li+The ion transmission channel greatly improves the conductivity of the solid electrolyte.
Further, the preparation method of the LLTO nanowire is as follows: adding polyvinylpyrrolidone PVP with the average molecular weight of 1000000-1800000 into dimethylformamide DMF, stirring and dissolving into a solution with the mass fraction of 10-15%, adding acetic acid and Ti (OC)4H9)4、La(NO3)3·6H2O and LiNO3Stirring at 45-55 deg.C for 4-6 hr, and ultrasonic dispersing for 1-2 hr to obtain transparent solution containing PVP, acetic acid, and Ti (OC)4H9)4、La(NO3)3·6H2O and LiNO3In a molar ratio of 0.4-0.8:0.1-0.3:1-1.1:0.5-0.7: 0.22-0.48; the transparent solution is used for obtaining a precursor by an electrostatic spinning method at the speed of 0.5-2.5mL/h at 10-35kV, the precursor is calcined for 1-3 hours at the high temperature of 850 ℃ in air at the heating rate of 2-4 ℃/min, and finally, the LLTO nanowire with the diameter of 10-50 nanometers is obtained by natural cooling to the room temperature. The higher the temperature rise speed during high-temperature calcination, the faster the sintering temperature, and the smaller the diameter of the LLTO nanowire. The fine LLTO nanowires are mixed in PEO, which is beneficial to inhibiting the crystallization of PEO, and the amorphous PEO is more beneficial to the transmission of lithium ions than the crystalline PEO.
Further, the PET/PEO nanofibers were prepared as follows: dissolving PET and PEO in anhydrous DMF to obtain a polymer solution, wherein the mass ratio of PET to PEO is 0.5-1.0: 2.5-5.0; stirring the polymer solution at 50-80 ℃ for 10-40 hours, adding LiTFSI into the polymer solution, and performing ultrasonic dispersion at 30-50 ℃ for 10-30 hours, wherein the mass ratio of the LiTFSI to PEO is 5-10: 80-95; extruding the polymer solution by a spinneret at the constant speed of 0.1-0.6mL/h at normal temperature; the applied voltage between the spinneret and the collector was set at 5-35kV, the relative humidity was 2-15% RH, and the solution jet from the spinneret was attracted to a grounded calibrator and collected to obtain PET/PEO nanofibers. The diameter of the PET/PEO/LiTFSI fiber obtained by the method is not more than 0.5 μm. The fine PET/PEO/LiTFSI is intertwined with each other, a large number of extremely fine free volume cavities are formed between the fine PET/PEO/LiTFSI, and more lithium ion transmission channels can be provided in the same volume, so that the conductivity and the mechanical strength of the solid electrolyte are greatly improved. PET is mixed in PEO to inhibit crystallization of PEO, and non-crystalline PEO is more favorable for lithium ion transport than crystalline PEO.
Further, the polymer mass fraction of the polymer solution formed by dissolving the PET and the PEO in the anhydrous DMF is 20-60%. The polymer mass fraction directly influences the diameter of the PET/PEO nanofiber, the mass fraction is too high, the larger the intermolecular force between the PET and the PEO is, the thicker the formed nanofiber is, the free volume in the unit volume of the PET/PEO nanofiber is reduced, the mass fraction is too low, the preparation efficiency is too low, and the preparation cost is increased.
Further, the composite solid electrolyte also comprises a titanium dioxide nanotube array matrix, wherein the diameter of the titanium dioxide nanotube is 50-90 nanometers, the thickness of the tube wall is 15-30 nanometers, and the length of the tube is 30-50 micrometers. The technical effect is not obvious due to the fact that the diameter of the titanium dioxide nanotube is too thin, too thick or too short, the nanotube is too long and is easy to peel off from the titanium foil substrate, and the transmission performance of lithium ions is reduced due to too high or too low thickness of the nanotube. The titanium dioxide nanotube array is vertically arranged on one side of a titanium foil and is wrapped in the polymer matrix to form a lithium ion transmission channel with high mechanical strength, high specific surface area and shortest vertical length, so that the crystallinity of the polymer is effectively reduced, the lithium dendrite resistance and the number of the lithium ion transmission channels of the polymer composite electrolyte are greatly improved again on the basis of the original matrix, the conductivity is improved, the resistivity is effectively reduced, and the mechanical strength is further improved.
Further, the preparation method of the titanium dioxide nanotube array substrate comprises the following steps: the method comprises the steps of taking a titanium foil with a clean surface and a thickness of 5-15 mu m as a working electrode, taking a platinum sheet as a counter electrode, coating paraffin on one side of the titanium foil, aligning the side which is not coated with the paraffin to the platinum sheet counter electrode, placing a two-electrode system formed by the titanium foil and the platinum sheet in an inorganic sodium salt electrolyte solution for electrochemical oxidation to obtain the titanium foil with a titanium dioxide nanotube vertical array distributed on the surface of one side, taking out the titanium foil, and washing and airing the titanium foil by water to obtain the titanium dioxide nanotube array matrix. The reaction formula is as follows:
Ti-4e→Ti4+
Ti4++2H2O→TiO2+4H+
TiO2+6F-+4H+→TiF6 2-+2H2O。
further, the titanium foil is electrochemically oxidized in a two-electrode system, and the inorganic sodium salt electrolyte solution is Na added with NaF2SO4Solution of NaF 0.3-1.1 wt%, Na2SO4The mol concentration is 0.1-0.5mol/L, the oxidation voltage is 20-40V, and the oxidation time is 1-5 hours. The longer the oxidation time and the higher the oxidation voltage, the titanium dioxide is nanoThe larger the tube diameter, the longer the length. In inorganic sodium salt electrolyte solution F-When the concentration is too high, the titanium dioxide nanotube array can collapse.
Further, the preparation of the titanium dioxide nano array substrate also comprises the step of calcining the titanium foil with the titanium dioxide nano tube vertical array distributed on the surface of one side for 10-20 hours at the temperature of 400-500 ℃ in a nitrogen atmosphere to obtain the titanium dioxide nano tube array substrate doped with nitrogen element. Compared with the amorphous titanium dioxide nanotube, the titanium dioxide doped with nitrogen element can form a large amount of crystal defects, which is beneficial to the conduction of lithium ions between the titanium dioxide doped with nitrogen element and the amorphous titanium dioxide nanotube.
A preparation method of a high-conductivity composite solid electrolyte is disclosed, and the preparation method of the LLTO nanowire modified PET/PEO/LiTFSI solid electrolyte comprises the following steps: the weight ratio of bis (trifluoromethane) sulfimide lithium LiTFSI and LLTO nano-wire is 1-3% and 1-2% of the composite solid electrolyte respectively, adding into anhydrous acetonitrile, then adding PET/PEO nano-fiber into the anhydrous acetonitrile, the mass ratio of the PET/PEO nano-fiber to the LiTFSI is 16-20:1-2, stirring for 10-30 hours, then carrying out ultrasonic dispersion for 0.5-3.0 hours, introducing the mixed solution into a mold, drying for 10-30 hours at 30-50 ℃, and then carrying out vacuum drying at 60-80 ℃ until the solvent is removed, thus obtaining the LLTO nano-wire modified PET/PEO/LiTFSI solid electrolyte with the thickness of 100 and 200 mu m, namely the composite solid electrolyte with multiple Li + transmission channels. The energy density of the battery may increase with the thickness of the solid electrolyte, but the resistance may increase with the thickness exceeding 200 μm, which is disadvantageous in electrical conduction.
Further, TiO2The preparation method of the modified LLTO nanowire modified PET/PEO/LiTFSI composite solid electrolyte comprises the following steps: respectively taking the LiTFSI and LLTO nanowires as 1-3% and 1-2% of the composite solid electrolyte in weight ratio, adding anhydrous acetonitrile, adding PET/PEO nanofibers into the anhydrous acetonitrile, stirring for 10-30 hours, ultrasonically dispersing for 0.5-3.0 hours, introducing the mixed solution into a mold with a titanium dioxide nanotube array matrix paved at the bottom, enabling the side with the titanium dioxide nanotubes to face upwards, drying for 10-30 hours at 30-50 ℃, and drying in vacuum at 60-80 ℃ until the solvent is removed to obtain the titanium dioxide composite solid electrolyteThe LLTO nanowire modified PET/PEO/LiTFSI composite solid electrolyte with the thickness of 100-200 mu m and the nanotube array as the matrix is a composite solid electrolyte with multiple Li + transmission channels.
The invention has the following beneficial effects: the fine PEO nano-fiber produced by the electrostatic spinning method contains LLTO nano-filaments for preventing PEO from crystallizing and a LLTO/PET/PEO/LiTFSI composite solid electrolyte prepared from PET, and the structure of the fine PEO nano-fiber contains a large number of nano-scale free volume holes, and more lithium ion transmission channels can be provided in the same volume, so that the conductivity and the mechanical strength of the solid electrolyte are greatly improved. After the titanium dioxide nanotube array matrix is added, the lithium ion transmission channel with high mechanical strength, high specific surface area and shortest vertical length is formed, the crystallinity of the polymer is effectively reduced, the lithium dendrite resistance of the polymer composite electrolyte and the number of the lithium ion transmission channels are greatly improved again on the basis of the original matrix, the conductivity is improved, the resistivity is effectively reduced, and the mechanical strength is further improved. Meanwhile, the preparation process is simple and is beneficial to large-scale production.
Detailed Description
The following further describes the embodiments of the present invention.
The starting materials used in the present invention are commercially available or commonly used in the art, unless otherwise specified, and the methods in the following examples are conventional in the art, unless otherwise specified.
Example 1(PET/PEO/LiTFSI composite solid electrolyte with 0.5% LLTO nanowires added)
A composite solid electrolyte with high conductivity is prepared by the following steps:
(1) preparing LLTO nanowires: adding polyvinylpyrrolidone PVP with average molecular weight of 1800000 into DMF, stirring to dissolve into 15% mass fraction solution, adding acetic acid and Ti (OC)4H9)4、La(NO3)3·6H2O and LiNO3Stirring at 55 deg.C for 6 hr, and ultrasonic dispersing for 2 hr to obtain transparent solution containing PVP, acetic acid, and Ti (OC)4H9)4、La(NO3)3·6H2O and LiNO3The mass ratio of (1) is 0.8:0.3:1.1:0.7: 0.48; obtaining a precursor at the speed of 2.5mL/h at 35kV by using an electrostatic spinning method, calcining the precursor at the high temperature of 850 ℃ for 3 hours in the air at the heating rate of 4 ℃/min, and finally naturally cooling to the room temperature to obtain the LLTO nanowire.
(2) Preparation of PET/PEO/LiTFSI nanofibers: dissolving PET and PEO in anhydrous DMF at a mass fraction of 20% at a mass ratio of 0.5:2.5, stirring the solution at 50 ℃ for 10 hours, adding LiTFSI into the solution, and ultrasonically dispersing at 30 ℃ for 10 hours, wherein the mass ratio of the LiTFSI to the PEO is 5: 80; extruding the polymer solution by a spinneret at the constant speed of 0.1mL/h at normal temperature; the applied voltage between the spinneret and the collector was set at 5kV and the relative humidity was 2% RH, and the solution jet from the spinneret was attracted to a grounded calibrator and collected to obtain PET/PEO/LiTFSI nanofibers.
(3) Preparing LLTO/PET/PEO/LiTFSI solid composite electrolyte: preparing a LLTO nanowire modified PET/PEO/LiTFSI solid electrolyte by using a solution casting method, adding bis (trifluoromethane) sulfimide lithium LiTFSI and LLTO nanowires into anhydrous acetonitrile, wherein the weight ratio of the bis (trifluoromethane) sulfimide lithium LiTFSI and the LLTO nanowires is 1% and 0.5% of the weight ratio of the composite solid electrolyte respectively, then adding PET/PEO/LiTFSI nanofibers into the solution, the molar ratio of the PET/PEO/LiTFSI nanofibers to the weight of the LiTFSI is 16:1, mechanically stirring the solution for 10 hours, ultrasonically dispersing the solution for 0.5 hour, introducing the mixed solution into a mold, drying the solution at 30 ℃ for 10 hours, and drying the dried solution in a vacuum oven at 60 ℃ to remove the solvent to obtain the 0.5% LLTO/PET/PEO/LiTFSI solid electrolyte, namely the composite solid electrolyte with high conductivity.
Example 2(PET/PEO/LiTFSI composite solid electrolyte with 1% LLTO nanowires added)
A composite solid electrolyte with high conductivity is prepared by the following steps:
(1) preparing LLTO nanowires: adding polyvinylpyrrolidone PVP (polyvinylpyrrolidone) with average molecular weight of 1000000 into dimethyl formamide DMF, stirring to dissolve into 10% mass fraction solution, adding acetic acid and Ti (OC)4H9)4、La(NO3)3·6H2O and LiNO3Stirring at 45 deg.C for 4 hr, and ultrasonic dispersing for 1 hr to obtain transparent solution containing PVP, acetic acid, and Ti (OC)4H9)4、La(NO3)3·6H2O and LiNO3The mass ratio of (1) is 0.4:0.1:1:0.5: 0.22; obtaining a precursor at the speed of 0.5mL/h at 10kV by using an electrostatic spinning method, calcining the precursor at the high temperature of 600 ℃ for 1 hour in the air at the heating rate of 2 ℃/min, and finally naturally cooling to the room temperature to obtain the LLTO nanowire.
(2) Preparing PET/PEO/LiTFSI nano-fiber, namely dissolving PET and PEO in anhydrous DMF to form a solution with the mass fraction of 60%, wherein the mass ratio of the PET to the PEO is 1.0:5.0, stirring the solution at 80 ℃ for 40 hours, adding LiTFSI into the solution, and ultrasonically dispersing the solution at 50 ℃ for 30 hours, wherein the mass ratio of the LiTFSI to the PEO is 10: 95; extruding the polymer solution by a spinneret at the constant speed of 0.6mL/h at normal temperature; the applied voltage between the spinneret and the collector was set at 35kV and the relative humidity was 15% RH, and the solution jet from the spinneret was attracted to a grounded calibrator and collected to obtain PET/PEO/LiTFSI nanofibers.
(3) Preparing a LLTO/PET/PEO/LiTFSI solid composite electrolyte: adding lithium bis (trifluoromethane) sulfonimide LiTFSI and LLTO nanowires which account for 3% and 1% of the composite solid electrolyte respectively in weight ratio into anhydrous acetonitrile, then adding PET/PEO nanofibers into the anhydrous acetonitrile, stirring for 30 hours with the mass ratio of the lithium bis (trifluoromethane) sulfonimide LiTFSI to LiTFSI being 20:2, then ultrasonically dispersing for 3.0 hours, introducing the mixed solution into a mold, drying for 30 hours at 50 ℃, and then drying in vacuum at 80 ℃ until the solvent is removed to obtain the LLTO nanowire modified PET/PEO/LiTFSI solid electrolyte, namely the high-conductivity composite solid electrolyte.
Example 3(PET/PEO/LiTFSI composite solid electrolyte with 1.5% addition of LLTO nanowires):
a composite solid electrolyte with high conductivity is prepared by the following steps:
(1) preparing LLTO nanowires: adding polyvinylpyrrolidone PVP (polyvinylpyrrolidone) with average molecular weight of 1400000 into dimethylformamide DMF, stirring to dissolve into 12.5% solution, adding acetic acid and Ti (OC)4H9)4、La(NO3)3·6H2O and LiNO3Stirring at 50 deg.C for 5 hr, and ultrasonic dispersing for 1.5 hr to obtain transparent solution containing PVP, acetic acid, and Ti (OC)4H9)4、La(NO3)3·6H2O and LiNO3In a molar ratio of 0.6:0.2:1.05:0.6: 0.35; and (3) obtaining a precursor from the transparent solution at the speed of 1.5mL/h at 22.5kV by using an electrostatic spinning method, calcining the precursor at high temperature for 2 hours at the temperature of 725 ℃ at the heating rate of 3 ℃/min in the air, and finally naturally cooling to the room temperature.
(2) Preparation of PET/PEO/LiTFSI nanofibers: dissolving PET and PEO in anhydrous DMF to obtain a polymer solution, wherein the mass ratio of PET to PEO is 0.75: 4.25; stirring the polymer solution at 65 ℃ for 25 hours, adding LiTFSI into the polymer solution, and ultrasonically dispersing at 30-50 ℃ for 20 hours, wherein the mass ratio of LiTFSI to PEO is 7.5: 87.5; extruding the polymer solution by a spinneret at the constant speed of 0.35mL/h at normal temperature; the applied voltage between the spinneret and the collector was set at 20kV and the relative humidity was 8.5% RH, and the solution jet from the spinneret was attracted to a grounded calibrator and collected to obtain PET/PEO nanofibers.
(3) Preparing a LLTO/PET/PEO/LiTFSI solid composite electrolyte: adding di (trifluoromethane) sulfimide lithium LiTFSI and LLTO nano-wires which account for 2% and 1.5% of the composite solid electrolyte respectively in weight ratio into anhydrous acetonitrile, then adding PET/PEO nano-fibers into the anhydrous acetonitrile, wherein the mass ratio of the PET/PEO nano-fibers to the LiTFSI is 18:1.5, stirring for 20 hours, then ultrasonically dispersing for 1.75 hours, introducing the mixed solution into a mold, drying for 20 hours at 40 ℃, and then drying in vacuum at 70 ℃ until the solvent is removed to obtain the LLTO nano-wire modified PET/PEO/LiTFSI solid electrolyte, namely the high-conductivity composite solid electrolyte.
Example 4 (PET/PEO/LiTFSI/TiO)2Addition of 0.5% LLTO nanowires to the composite solid electrolyte):
a composite solid electrolyte with high conductivity is prepared by the following steps:
(1) preparing a titanium dioxide nano array substrate: the surface is clean and the thickness is 1And taking a titanium foil with the diameter of 5 mu m as a working electrode, taking a platinum sheet as a counter electrode, coating paraffin on one side of the titanium foil, aligning one side which is not coated with the paraffin to the platinum sheet counter electrode, placing a two-electrode system formed by the titanium foil and the platinum sheet in an inorganic sodium salt electrolyte solution for electrochemical oxidation to obtain the titanium foil with the titanium dioxide nanotube vertical array distributed on the surface of one side, taking out the titanium foil, and washing and drying the titanium foil by water to obtain the titanium dioxide nanotube array matrix. The electrolyte solution of inorganic sodium salt is Na added with NaF2SO4Solution, NaF mass fraction 1.1 wt%, Na2SO4The molar concentration is 0.5mol/L, the oxidation voltage is 40V, and the oxidation time is 5 hours. Then, the titanium foil with the vertical array of the titanium dioxide nanotube distributed on the surface of the single side is calcined in nitrogen atmosphere at 500 ℃ for 20 hours to obtain the titanium dioxide nanotube array matrix doped with nitrogen element.
(2) The procedure for preparing LLTO nanowires was the same as in example 3.
(3) The procedure for making PET/PEO/LiTFSI nanofibers was the same as in example 3.
(4)0.5％LLTO/PET/PEO/LiTFSI/TiO2Preparing a solid composite electrolyte: preparing a LLTO nanowire modified PET/PEO/LiTFSI solid electrolyte by using a solution casting method, adding bis (trifluoromethane) sulfimide lithium LiTFSI and LLTO nanowires into anhydrous acetonitrile, wherein the weight ratio of the bis (trifluoromethane) sulfimide lithium LiTFSI and the LLTO nanowires is 1% and 0.5% of the weight ratio of the composite solid electrolyte respectively, then adding PET/PEO/LiTFSI nanofibers into the solution, the molar ratio of the PET/PEO/LiTFSI nanofibers to the weight of the LiTFSI is 16:1, mechanically stirring for 20 hours, ultrasonically dispersing for 0.5 hour, introducing the mixed solution into a mold with a titanium dioxide nano array matrix paved at the bottom, enabling the side with titanium dioxide nanotubes to face upwards, drying for 16 hours at 30 ℃, and then drying at 60 ℃ in vacuum to remove the solvent, thus obtaining the 0.5% LLTO/PET/PEO/LiTFSI solid electrolyte, namely the high-conductivity composite electrolyte.
Example 5 (PET/PEO/LiTFSI/TiO)2Addition of 1% LLTO nanowires in matrix):
high-conductivity LLTO/PET/PEO/LiTFSI/TiO2The preparation process of the solid composite electrolyte comprises the following steps:
(1) preparation of titanium dioxide nano array substrate: the method comprises the steps of taking a titanium foil with a clean surface and a thickness of 10 mu m as a working electrode, taking a platinum sheet as a counter electrode, coating paraffin wax on one side of the titanium foil, aligning the side which is not coated with the paraffin wax with the counter electrode of the platinum sheet, placing a two-electrode system formed by the titanium foil and the platinum sheet in an inorganic sodium salt electrolyte solution for electrochemical oxidation to obtain the titanium foil with a titanium dioxide nanotube vertical array distributed on the surface of one side, taking out the titanium foil, washing with water and drying in the air to obtain the titanium dioxide nanotube array matrix. The electrolyte solution of inorganic sodium salt is Na added with NaF2SO4Solution, NaF mass fraction 0.7 wt%, Na2SO4The molar concentration is 0.3mol/L, the oxidation voltage is 30V, and the oxidation time is 3 hours. And (3) calcining the titanium foil with the vertical array of the titanium dioxide nanotube distributed on the surface of one side at 450 ℃ in nitrogen atmosphere for 15 hours to obtain the nitrogen-doped titanium dioxide nanotube array substrate.
(2) The procedure for preparing LLTO nanowires is the same as in example 3.
(3) The procedure for making PET/PEO/LiTFSI nanofibers was the same as in example 3.
(4) Preparation of 1% LLTO/PET/PEO/LiTFSI/TiO2Solid composite electrolyte: respectively taking the weight ratio of the LiTFSI and the LLTO nanowires as 3 percent and 1 percent of the composite solid electrolyte, adding anhydrous acetonitrile, then adding the PET/PEO nanofibers into the anhydrous acetonitrile, wherein the mass ratio of the PET/PEO nanofibers to the LiTFSI is 20:2, stirring for 30 hours, then ultrasonically dispersing for 3.0 hours, introducing the mixed solution into a mold with a titanium dioxide nanotube array matrix paved at the bottom, enabling the side with the titanium dioxide nanotubes to face upwards, drying for 30 hours at 50 ℃, and then drying in vacuum at 80 ℃ until the solvent is removed, thus obtaining the LLTO nanowire modified PET/PEO/LiTFSI composite solid electrolyte with the titanium dioxide nanotube array as the matrix, namely the high-conductivity composite solid electrolyte.
Example 6 (PET/PEO/LiTFSI/TiO)2Addition of 1.5% LLTO nanowires in matrix):
high-conductivity LLTO/PET/PEO/LiTFSI/TiO2The preparation process of the solid composite electrolyte comprises the following steps:
(1) preparing a titanium dioxide nano array substrate: by drying on the surfaceThe clean titanium foil with the thickness of 5 mu m is taken as a working electrode, a platinum sheet is taken as a counter electrode, one side of the titanium foil is coated with paraffin, the side which is not coated with the paraffin is aligned to the platinum sheet counter electrode, a two-electrode system formed by the titanium foil and the platinum sheet is placed in an inorganic sodium salt electrolyte solution for electrochemical oxidation to obtain the titanium foil with the titanium dioxide nanotube vertical array distributed on the surface of one side, the titanium foil is taken out and washed by water for drying, and the titanium dioxide nanotube array matrix is obtained, wherein the inorganic sodium salt electrolyte solution is Na added with NaF2SO4Solution, NaF mass fraction 0.3 wt%, Na2SO4The molar concentration is 0.1mol/L, the oxidation voltage is 20V, the oxidation time is 1 hour, then the titanium foil with the vertical array of the titanium dioxide nano tube distributed on the surface of the single side is calcined in nitrogen atmosphere at 400 ℃, the calcination time is 10 hours, and the titanium dioxide nano tube array matrix doped with the nitrogen element is obtained.
(2) The procedure for preparing LLTO nanowires was the same as in example 5.
(3) The procedure for making PET/PEO/LiTFSI nanofibers was the same as in example 5.
(4) Preparation of 1.5% LLTO/PET/PEO/LiTFSI/TiO2Solid composite electrolyte: respectively taking the weight ratio of the LiTFSI and the LLTO nanowires as 2 percent and 1.5 percent of the composite solid electrolyte, adding anhydrous acetonitrile, then adding the PET/PEO nanofibers into the anhydrous acetonitrile, wherein the mass ratio of the PET/PEO nanofibers to the LiTFSI is 18:1.5, stirring for 20 hours, then ultrasonically dispersing for 1.75 hours, introducing the mixed solution into a mold with a titanium dioxide nanotube array matrix paved at the bottom, enabling the side with the titanium dioxide nanotubes to face upwards, drying for 20 hours at 40 ℃, and then drying in vacuum at 70 ℃ until the solvent is removed to obtain the LLTO nanowire modified PET/PEO/LiTFSI composite solid electrolyte with the titanium dioxide nanotube array as the matrix, namely the high-conductivity composite solid electrolyte.
Example 7 (PET/PEO/LiTFSI/TiO)2Adding 1% of LLTO nano wire and TiO in the matrix2Without nitrogen doping):
the preparation process of a high-conductivity composite solid electrolyte differs from that of example 5 only in that the titanium dioxide nanotube array substrate used is prepared by the following processes: to be provided withThe method comprises the steps of taking a titanium foil with a clean surface and a thickness of 10 mu m as a working electrode, taking a platinum sheet as a counter electrode, coating paraffin wax on one side of the titanium foil, aligning the side which is not coated with the paraffin wax with the counter electrode of the platinum sheet, placing a two-electrode system formed by the titanium foil and the platinum sheet in an inorganic sodium salt electrolyte solution for electrochemical oxidation to obtain the titanium foil with a titanium dioxide nanotube vertical array distributed on the surface of one side, taking out the titanium foil, washing with water and drying in the air to obtain the titanium dioxide nanotube array matrix. The electrolyte solution of inorganic sodium salt is Na added with NaF2SO4Solution, NaF mass fraction 0.7 wt%, Na2SO4The molar concentration is 0.3mol/L, the oxidation voltage is 30V, and the oxidation time is 3 hours.
Comparative example 1 (pure PEO/LiTFSI composite solid electrolyte without LLTO nanowires):
a composite solid electrolyte is prepared by the following steps:
(1) preparation of PEO/LiTFSI nanofibers: dissolving PEO in anhydrous DMF to obtain a 40% polymer solution, stirring the polymer solution at 65 ℃ for 25 hours, adding LiTFSI into the polymer solution, and ultrasonically dispersing at 40 ℃ for 20 hours, wherein the mass ratio of the LiTFSI to the PEO is 7.5: 87.5; extruding the polymer solution by a spinneret at the constant speed of 0.35mL/h at normal temperature; the applied voltage between the spinneret and the collector was set at 20kV and the relative humidity was 8.5% RH, and the solution jet from the spinneret was drawn into a grounded calibrator and collected to yield PEO/LiTFSI nanofibers.
(2) Preparing a PEO/LiTFSI solid composite electrolyte: preparing a PEO/LiTFSI solid composite electrolyte by using a solution casting method, adding lithium bis (trifluoromethane) sulfonimide LiTFSI into anhydrous acetonitrile, wherein the weight ratio of the lithium bis (trifluoromethane) sulfonimide LiTFSI is 1.5 percent of the weight of the composite solid electrolyte, adding PEO/LiTFSI nano fibers into the solution, wherein the molar ratio of the PEO/LiTFSI nano fibers to the weight of the LiTFSI is 18:1.5, mechanically stirring the solution for 25 hours, ultrasonically dispersing the solution for 0.75 hour, introducing the mixed solution into a mold, drying the mixed solution for 14 hours at 37.5 ℃, and drying the mixed solution in a vacuum oven at 65 ℃ for 13 hours to remove the solvent and water, so that the PEO/LiTFSI solid composite electrolyte is obtained, namely the composite solid electrolyte.
Comparative example 2 (pure PET/PEO/LiTFSI composite solid electrolyte without LLTO nanowires):
a composite solid electrolyte is prepared by the following steps:
(1) the procedure for making PET/PEO/LiTFSI nanofibers was the same as in example 3.
(2) Preparing a PET/PEO/LiTFSI solid composite electrolyte: adding bis (trifluoromethane) lithium sulfonimide LiTFSI which accounts for 2% of the composite solid electrolyte in weight ratio into anhydrous acetonitrile, adding PET/PEO nano-fibers into the anhydrous acetonitrile, stirring for 20 hours, then ultrasonically dispersing for 1.75 hours, introducing the mixed solution into a mold, drying for 20 hours at 40 ℃, and then drying in vacuum at 70 ℃ until the solvent is removed to obtain the LLTO nanowire modified PET/PEO/LiTFSI solid electrolyte, namely the composite solid electrolyte.
Comparative example 3 (addition of 0.5% LLTO nanowires to PEO/LiTFSI composite solid electrolyte):
a composite solid electrolyte is prepared by the following steps:
(1) preparing LLTO nanowires: adding polyvinylpyrrolidone PVP with average molecular weight of 1000000 into DMF, stirring to dissolve into 10% solution, adding acetic acid and Ti (OC)4H9)4、La(NO3)3·6H2O and LiNO3Stirring at 45 deg.C for 4 hr, and ultrasonic dispersing for 1 hr to obtain transparent solution containing PVP, acetic acid, and Ti (OC)4H9)4、La(NO3)36H2O and LiNO3The mass ratio of (1) is 0.4:0.1:1:0.5: 0.22; obtaining a precursor at the speed of 0.5mL/h at 10kV by using an electrostatic spinning method, calcining the precursor at the high temperature of 600 ℃ for 1 hour in the air at the heating rate of 2 ℃/min, and finally naturally cooling to the room temperature to obtain the LLTO nanowire.
(2) Preparation of PEO/LiTFSI nanofibers: dissolving PEO in anhydrous DMF to obtain a solution with the mass fraction of 20%, stirring the solution at 60 ℃ for 36 hours, adding LiTFSI into the solution, and ultrasonically dispersing the solution at 30 ℃ for 12 hours, wherein the mass ratio of the LiTFSI to the PEO is 5: 80; extruding the polymer solution by a spinneret at the constant speed of 0.2mL/h at normal temperature; the applied voltage between the spinneret and the collector was set at 15kV and the relative humidity was 5% RH, and the solution jet from the spinneret was drawn into a grounded calibrator and collected to yield PEO/LiTFSI nanofibers.
(3) Preparation of 0.5% LLTO nanowire modified PEO/LiTFSI solid electrolyte: preparing a LLTO nanowire modified PEO/LiTFSI solid electrolyte by using a solution casting method, adding bis (trifluoromethane) sulfimide lithium LiTFSI and a LLTO nanowire with the weight ratio of 1% and 0.5% of that of the composite solid electrolyte into anhydrous acetonitrile, then adding PEO/LiTFSI nanofibers into the solution with the molar ratio of 16:1 to that of the LiTFSI, mechanically stirring for 20 hours, ultrasonically dispersing for 0.5 hour, introducing the mixed solution into a mold, drying for 10 hours at 30 ℃, and drying in a vacuum oven at 60 ℃ to remove the solvent to obtain the 0.5% LLTO/PEO/LiTFSI solid electrolyte, namely the composite solid electrolyte.
Comparative example 4 (pure PEO/LiTFSI/TiO without LLTO nanowires2Composite solid electrolyte):
a composite solid electrolyte is prepared by the following steps:
(1) the procedure for preparing the titanium dioxide nano-array substrate was the same as in example 5.
(2) The procedure for making PEO/LiTFSI nanofibers was the same as in comparative example 1.
(3) Preparation of PEO/LiTFSI/TiO2Solid composite electrolyte: adding anhydrous acetonitrile into the composite solid electrolyte with the weight ratio of 2% of the LiTFSI, adding PEO nano-fibers into the anhydrous acetonitrile, stirring for 20 hours, performing ultrasonic dispersion for 1.75 hours, introducing the mixed solution into a mold with a titanium dioxide nanotube array matrix paved at the bottom, drying for 20 hours at 40 ℃, and then drying in vacuum at 70 ℃ until the solvent is removed to obtain the PEO/LiTFSI composite solid electrolyte with the titanium dioxide nanotube array as the matrix, namely the composite solid electrolyte.
Comparative example 5 (pure PET/PEO/LiTFS/TiO without LLTO nanowires2Solid composite electrolyte):
a composite solid electrolyte is prepared by the following steps:
(1) the procedure for preparing the titanium dioxide nano-array substrate was the same as in example 5.
(2) The procedure for making PET/PEO/LiTFSI nanofibers was the same as in example 3.
(3) Preparation of PET/PEO/LiTFSI/TiO2Solid composite electrolyte process: adding anhydrous acetonitrile into LiTFSI which is 2 percent of the composite solid electrolyte in weight ratio respectively, then adding PET/PEO nano-fibers into the anhydrous acetonitrile, wherein the mass ratio of the PET/PEO nano-fibers to the LiTFSI is 18:1.5, stirring for 20 hours, then ultrasonically dispersing for 1.75 hours, introducing the mixed solution into a mold with a bottom paved with a titanium dioxide nanotube array matrix, drying for 20 hours at 40 ℃, and then drying in vacuum at 70 ℃ until the solvent is removed to obtain the PET/PEO/LiTFSI composite solid electrolyte with the titanium dioxide nanotube array as the matrix, namely the composite solid electrolyte.
Comparative example 6 (PEO/LiTFSI/TiO)2Addition of 0.5% LLTO nanowires to the composite solid electrolyte):
a composite solid electrolyte is prepared by the following steps:
(1) the procedure for preparing the titanium dioxide nanoarray substrate was the same as in example 5
(2) The procedure for preparing LLTO nanowires was the same as in example 3.
(3) Preparation of PEO/LiTFSI nanofibers: dissolving PEO in anhydrous DMF to obtain a solution with the mass fraction of 60%, stirring the solution at 80 ℃ for 40 hours, adding LiTFSI into the solution, and ultrasonically dispersing the solution at 50 ℃ for 30 hours, wherein the mass ratio of the LiTFSI to the PEO is 10: 95; extruding the polymer solution by a spinneret at the constant speed of 0.6mL/h at normal temperature; the applied voltage between the spinneret and the collector was set at 35kV and the relative humidity was 15% RH, and the solution jet from the spinneret was drawn into a grounded calibrator and collected to yield PEO/LiTFSI nanofibers.
(4) Preparation of 0.5% LLTO/PEO/LiTFSI/TiO2Solid composite electrolyte: preparing a LLTO nanowire modified PEO/LiTFSI solid electrolyte by using a solution casting method, and adding a di (tri) in anhydrous acetonitrileFluoromethane) lithium sulfonimide LiTFSI and LLTO nano-wires, the weight ratio of which is 3% and 0.5% of the composite solid electrolyte respectively, then PEO/LiTFSI nano-fibers are added into the solution, the molar ratio of the PEO/LiTFSI nano-fibers to the LiTFSI is 20:2, the mechanical stirring is carried out for 30 hours, then the ultrasonic dispersion is carried out for 3.0 hours, the mixed solution is led into a mold with the bottom paved with a titanium dioxide nano-array matrix, the side with titanium dioxide nano-tubes faces upwards, the drying is carried out for 30 hours at 50 ℃, then the solvent is dried and removed in a vacuum oven at 80 ℃, and 0.5% LLTO/PEO/LiTFSI solid electrolyte is obtained, namely the composite solid electrolyte.
Comparative example 7 (PET/PEO/LiTFSI/TiO)21% of LLTO nano wire and all TiO are added into the composite solid electrolyte2In the form of granules
A composite solid electrolyte is prepared by the following steps:
(1) the procedure for preparing LLTO nanowires was the same as in example 3.
(2) The procedure for making PET/PEO/LiTFSI nanofibers was the same as in example 3.
(3) Preparation of 1% LLTO/PET/PEO/LiTFSI/TiO2Particulate solid composite electrolyte: preparing a LLTO nanowire modified PET/PEO/LiTFSI solid electrolyte by using a solution casting method, adding lithium bis (trifluoromethane) sulfonimide LiTFSI, LLTO nanowires and titanium dioxide nanoparticles into anhydrous acetonitrile, wherein the average particle size is 200 nanometers, the weight ratio of the LiTFSI to the LLTO to the titanium dioxide nanoparticles is 2%, 1% and 1.3% of that of the composite solid electrolyte respectively, and then adding PET/PEO nanofibers into the solution, wherein the weight ratio of the PET/PEO nanofibers to the LiTFSI is 18:1.5, mechanically stirring for 20 hours, then ultrasonically dispersing for 1.75 hours, introducing the mixed solution into a mold, drying for 20 hours at 40 ℃, and then drying in a vacuum oven at 70 ℃ to remove the solvent, thus obtaining the PET/PEO/LiTFSI solid electrolyte modified by the LLTO and titanium dioxide nanoparticles, namely the composite solid electrolyte.
Performance test of the solid composite electrolyte obtained in each example and comparative example:
1. and (3) testing mechanical properties:
according to GB1040-92, Plastic tensile Property test method, tensile test is carried out under the condition of 10mm/min, each sample is 10 cm in length, 4 cm in width and 100-200 μm in thickness, the test is repeated for 5 times, and the average value of the middle three numbers is taken.
2. And (3) conductivity test:
the pressed solid electrolyte is subjected to alternating current internal resistance test at room temperature by adopting a double-probe method, and the frequency range is 1-106HZ, the alternating impedance, mainly reflects the lithium ion resistivity, the conductivity being the derivative of the resistivity. To reduce measurement errors, the samples were gold sprayed on the bottom and top prior to testing.
The data obtained for each of the examples and comparative examples are shown in table 1 below:
table 1: ionic conductivity, tensile strength and elongation at break data for each example and comparative example:
Figure BDA0003213220290000121
as shown in Table 1, the comparative examples 3, 6 to 7 and all the examples added with the LLTO nanowires are improved in conductivity, tensile strength and elongation at break compared with the comparative examples 1 to 2 and 4 to 5 without the material, the optimal mass concentration of the LLTO nanowires is 1%, and the conductivity, the tensile strength and the elongation at break all reach peak values; also with the LLTO nanowire modification, comparative example 7 with PET addition and all examples significantly improved conductivity, tensile strength and elongation at break over comparative examples 3 and 6 without PET addition; in the case of an equivalent 1% LLTO modification and addition of PET, TiO was added2Examples 5 and 7 of nanotube array substrates are better than no TiO2Example 2 of nanotube array substrate and incorporation of particulate nitrogen-doped TiO2Comparative example 7 of (a) is significantly improved in conductivity, tensile strength and elongation at break; no nitrogen doped TiO with equal 1% LLTO modification and addition of PET2Example 7 nanotube array substrate incorporating particulate nitrogen doped TiO2Comparative example 7 and addition of nitrogen-doped TiO2Example 5 comparison of nanotube array substrate with nitrogen doped TiO2Example 5 for nanotube array substrate modification has high conductivity and tensile strengthThe degree and the elongation at break are obviously improved compared with the former two.

Claims (10)

1. A high conductivity composite solid electrolyte, comprising Lithium Lanthanum Titanate (LLTO) nanowires, PET/PEO nanofibers and lithium bis (trifluoromethane) sulfonimide (LiTFSI), wherein the LiTFSI, LLTO nanowires are dispersed in the PET/PEO nanofibers.
2. The composite solid electrolyte having high conductivity as claimed in claim 1, wherein the LLTO nanowire is prepared by the following process: adding polyvinylpyrrolidone PVP with the average molecular weight of 1000000-1800000 into dimethylformamide DMF, stirring and dissolving into a solution with the mass fraction of 10-15%, adding acetic acid and Ti (OC)4H9)4、La(NO3)3·6H2O and LiNO3Stirring at 45-55 deg.C for 4-6 hr, and ultrasonic dispersing for 1-2 hr to obtain transparent solution containing PVP, acetic acid, and Ti (OC)4H9)4、La(NO3)3·6H2O and LiNO3The molar ratio of (1) - (0.4-0.8) - (0.1-0.3) - (1.1) - (0.5-0.7) - (0.22-0.48); the transparent solution is used for obtaining a precursor by an electrostatic spinning method at the speed of 0.5-2.5mL/h at 10-35kV, the precursor is calcined for 1-3 hours at the high temperature of 850 ℃ in air at the heating rate of 2-4 ℃/min, and finally, the LLTO nanowire with the diameter of 10-50 nanometers is obtained by natural cooling to the room temperature.
3. The composite solid electrolyte having high conductivity according to claim 1, wherein the PET/PEO nanofibers are produced by: dissolving PET and PEO in anhydrous DMF to obtain a polymer solution, wherein the mass ratio of PET to PEO is 0.5-1.0: 2.5-5.0; stirring the polymer solution at 50-80 ℃ for 10-40 hours, adding LiTFSI into the polymer solution, and ultrasonically dispersing at 30-50 ℃ for 10-30 hours, wherein the mass ratio of LiTFSI to PEO is 5-10: 80-95; extruding the polymer solution by a spinneret at the constant speed of 0.1-0.6mL/h at normal temperature; the applied voltage between the spinneret and the collector was set at 5-35kV, the relative humidity was 2-15% RH, and the solution jet from the spinneret was attracted to a grounded calibrator and collected to obtain PET/PEO nanofibers.
4. The composite solid electrolyte having high conductivity according to claim 3, wherein the polymer mass fraction of the polymer solution formed by dissolving PET and PEO in anhydrous DMF is 20% to 60%.
5. The composite solid electrolyte with high conductivity according to claim 1, wherein the composite solid electrolyte further comprises a titanium dioxide nanotube array matrix, the diameter of the titanium dioxide nanotube is 50-90 nm, the thickness of the tube wall is 15-30 nm, and the length of the tube is 30-50 μm.
6. The composite solid electrolyte having high conductivity according to claim 5, wherein the titanium dioxide nano-array substrate is prepared by: the method comprises the steps of taking a titanium foil with a clean surface and a thickness of 5-15 mu m as a working electrode, taking a platinum sheet as a counter electrode, coating paraffin on one side of the titanium foil, aligning the side which is not coated with the paraffin to the platinum sheet counter electrode, placing a two-electrode system formed by the titanium foil and the platinum sheet in an inorganic sodium salt electrolyte solution for electrochemical oxidation to obtain the titanium foil with a titanium dioxide nanotube vertical array distributed on the surface of one side, taking out the titanium foil, washing with water, and airing to obtain the titanium oxide nanotube array matrix.
7. The composite solid electrolyte with high conductivity according to claim 6, wherein the titanium foil is electrochemically oxidized in a two-electrode system, and the inorganic sodium salt electrolyte solution is Na added with NaF2SO4Solution of NaF 0.3-1.1 wt%, Na2SO4The mol concentration is 0.1-0.5mol/L, the oxidation voltage is 20-40V, and the oxidation time is 1-5 hours.
8. The composite solid electrolyte with high conductivity as claimed in claim 6, wherein the preparation of the titanium dioxide nano array substrate further comprises calcining the titanium foil with the vertical array of titanium dioxide nanotubes distributed on the surface of one side at 500 ℃ in a nitrogen atmosphere for 10-20 hours to obtain the nitrogen-doped titanium dioxide nanotube array substrate.
9. A method for preparing a high-conductivity composite solid electrolyte as claimed in any one of claims 1 to 4, wherein the preparation process comprises: adding lithium bis (trifluoromethane) sulfonimide LiTFSI and LLTO nanowires which account for 1-3 wt% and 1-2 wt% of the composite solid electrolyte respectively into anhydrous acetonitrile, then adding PET/PEO nanofibers into the anhydrous acetonitrile, wherein the mass ratio of the PET/PEO nanofibers to the LiTFSI is 16-20:1-2, stirring for 10-30 hours, then ultrasonically dispersing for 0.5-3.0 hours, introducing the mixed solution into a mold, drying at 30-50 ℃ for 10-30 hours, and then drying at 60-80 ℃ in vacuum until the solvent is removed, thereby obtaining the composite solid electrolyte with a thickness of 100 LLTO nanowire modified PET/PEO/LiTFSI nanowire of 200 mu m, namely the composite solid electrolyte with a Li + transmission channel.
10. A method for preparing a high-conductivity composite solid electrolyte as claimed in any one of claims 1 to 8, wherein the preparation process comprises: adding anhydrous acetonitrile into LiTFSI and LLTO nanowires which are respectively 1-3% and 1-2% of the composite solid electrolyte in weight ratio, and then adding PET/PEO nanofibers into the anhydrous acetonitrile, the mass ratio of the PET/PEO nano-fiber to the LiTFSI is 16-20:1-2, the mixture is stirred for 10-30 hours, and then ultrasonically dispersing for 0.5-3.0 hours, introducing the mixed solution into a mold with a titanium dioxide nanotube array matrix paved at the bottom, enabling the side with the titanium dioxide nanotubes to face upwards, drying for 10-30 hours at 30-50 ℃, and then drying in vacuum at 60-80 ℃ until the solvent is removed, thereby obtaining the PET/PEO/LiTFSI composite solid electrolyte which is modified by the LLTO nanowires with the titanium dioxide nanotube array as the matrix and has the thickness of 100 plus materials and 200 mu m, namely the composite solid electrolyte with multiple Li + transmission channels.
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