CN115020802A - In-situ UV-curable nanofiber composite solid electrolyte and preparation method and application thereof - Google Patents

Abstract

The invention relates to an in-situ ultraviolet light curing nanofiber composite solid electrolyte and a preparation method and application thereof, and the preparation method comprises the following steps: s1, obtaining a nanofiber organic film by an electrostatic spinning method; s2, selecting an elastic organic polymer monomer, lithium salt, a plasticizer, a photosensitive curing agent and a cross-linking agent, and mixing to obtain a mixed solution; s3, placing the positive pole piece with the active material into a polytetrafluoroethylene mold, placing the nanofiber organic film on the pole piece, and flatly paving the mixed solution in the nanofibers and the pole piece; s4, vertically irradiating under an ultraviolet lamp for a certain time to obtain the composite solid electrolyte. The solid electrolyte material can be applied to a lithium metal gel solid lithium battery, has good electrochemical performance, and provides a technical reserve basis for the development of the future battery field.

Description

In-situ UV-curable nanofiber composite solid electrolyte and its preparation method and application

technical field

The invention relates to the technical field of solid-state batteries, in particular to an in-situ ultraviolet light-cured nanofiber composite solid-state electrolyte and a preparation method and application thereof.

Background technique

With the rapid development of industries around the world, carbon dioxide emissions have also increased sharply, and the most serious negative impact is the greenhouse effect. Among many renewable green energy systems, lithium-ion batteries are widely used in unmanned aerial vehicles, pure electric vehicles, Hybrid electric vehicles and industrial and residential energy storage are widely used. With the rapid development of batteries, the market has higher and higher requirements for the performance of lithium batteries, and the energy density of batteries is also increasing. However, the increase in energy density also brings a series of potential safety hazards. Battery explosion safety accidents emerge one after another, and the safety accidents caused by the explosion of lithium-ion batteries endanger the safety of users. Solid-state batteries are composed of solid electrolytes, positive electrode materials and negative electrode materials. Compared with liquid lithium-ion batteries, solid-state batteries have the following advantages:

(1) The solid-state battery replaces the flammable liquid electrolyte and separator with a solid electrolyte, which greatly reduces the risk of thermal runaway;

(2) Compared with the electrochemical window of 4.2V of liquid lithium battery, the electrochemical window of solid-state battery can reach more than 5V, and the high voltage window allows matching high-energy positive electrode and metal lithium negative electrode, which greatly improves the battery energy density;

(3) The solid-state battery has a simple packaging process, which can reduce the weight of the battery in a limited space, and the volumetric energy density is more than 70% higher than that of the liquid lithium battery (graphite negative electrode), reaching 500Wh/kg.

In order to obtain a lithium metal battery with high safety and high energy density, the positive electrode uses a positive electrode material with high specific capacity and high working voltage, and the negative electrode uses a high-quality/volume energy density, low-cost metal lithium, which is currently the hottest spot for solid-state batteries. . However, the low ionic conductivity of polymer electrolytes at room temperature and the interfacial problems between solid electrolytes/electrodes are the gaps between key materials and battery performance. This patent studies the interfacial characteristics and application modification of solid electrolyte to electrodes by means of in-situ polymerization of the positive electrode surface, introduction of nanofiber intermediate layer, surface modification and modification, and interface structure control, which has great research value and practical significance. These in-depth and systematic basic research will be beneficial to the development of solid-state ionics and energy storage materials in China.

Aiming at the interfacial contact problem of solid-state batteries in solid-state batteries, Guan[UV-CuredInterpenetrating Networks of Single-ion Conducting Polymer Electrolytes for Rechargeable Lithium Metal Batteries[J].ACS Applied Energy Materials, (2020).3(12):12532–12539 .] et al. prepared a single-ion conducting polymer electrolyte (IN-SCPE) by a facile UV-induced in-situ polymerization method to improve the interface between the cathode and the solid electrolyte. A cross-linked polymer gel network was prepared by mixing lithium salts, monomers, interfacial modifiers, photoinitiators, and crosslinking agents, which were then exposed to UV light to initiate radical polymerization. Tests show that the in situ formed polymer network improves the interfacial contact between IN-SCPEs and the cathode active material, reduces the activation energy of Li+ conduction, and increases the room temperature ionic conductivity (1.9×10 ^-4 S cm ^-1 ) , Li+ ion transfer number (0.90) and electrochemical window (5.3V), mechanical tensile strength properties (0.5MPa), 200-cycle long cycle life test at room temperature 0.5C rate. However, the mechanical tensile strength of the solid electrolyte membrane prepared in this way is only 0.5MPa, which is not enough to inhibit the growth of lithium dendrites, and there is a potential safety hazard of battery short circuit, and the battery can be charged and discharged for a long time at a rate of 0.5C With only 200 cycles, the performance cannot meet the needs of long cycle life. In situ UV light-induced polymerization is used as a means to improve the interface between the positive electrode and the electrolyte. By improving the preparation method of the electrolyte, optimizing the distribution uniformity of the electrolyte material, preparing the composite electrolyte, infiltrating the electrode interface with liquid and in situ polymerizing the electrode, it can be achieved. The design of the integrated structure of the positive electrode and the solid electrolyte can theoretically overcome the problem of poor contact between the positive electrode material and the electrolyte interface.

Chinese patent CN112201847A discloses a composite solid-state electromembrane and its preparation method and application. In the composite solid-state electrolyte membrane, a flexible polymer is used as the skeleton of the polymer solid-state electrolyte, and the added organic nanofibers have high strength and tempering. , the mechanical properties are greatly improved, the inorganic oxide ceramic filler has a high specific surface area, and the surface is rich in Lewis acid sites, which increases the ability of the solid electrolyte membrane to capture TFSI ^- anion, inhibits polymer crystallization and promotes Li ⁺ dissociation, making the composite solid electrolyte membrane Has excellent electrochemical performance; organic nanofibers and inorganic oxide ceramic particles can synergistically reduce the crystallinity of the polymer, thereby promoting the dissociation of lithium salts, increasing the ion transport pathway at the interface, resulting in excellent ionic conductivity, combined with polymerization The flexibility of the material and the rigidity of the inorganic particles achieve good contact between the positive and negative electrodes, and the final composite solid electrolyte membrane has high electrochemical performance and high mechanical performance. However, the solid electrolyte prepared in this patent was tested at 60°C, but not at room temperature, because polyethylene oxide has too low ionic conductivity and poor ionic conductivity at room temperature, which limits the The application of the invention patent at room temperature. In addition, in the long-cycle charge-discharge test, the electrolyte was only tested for 100 charge-discharge cycles, which is not enough to prove that the electrolyte can be used in lithium batteries.

SUMMARY OF THE INVENTION

The purpose of the invention of the present invention is to provide a preparation method and application of an in-situ ultraviolet light-cured nanofiber composite solid electrolyte to overcome the problems existing in the prior art in view of the above-mentioned problems.

The technical scheme adopted in the present invention is as follows: an in-situ ultraviolet light curing nanofiber composite solid electrolyte preparation method, comprising the following steps:

S1, obtain the nanofiber organic matter precursor by the electrospinning method, after removing the nanofiber organic matter precursor spinning solvent, obtain the nanofiber organic matter film, standby;

S2, select the elastic organic polymer monomer, lithium salt, plasticizer, photosensitive curing agent and cross-linking agent into the mixing container in a certain proportion, stir and disperse evenly, and obtain a mixed solution;

S3, prepare a positive pole piece with active positive material, put it into a polytetrafluoroethylene mold, place the nanofiber organic film prepared by S1 on the pole piece, and then spread the mixed solution obtained by S2 according to a certain mass ratio. On the nanofiber organic film and the positive pole piece;

S4. Select a UV lamp with a certain power, and place the mold of S3 under the UV lamp for a certain period of time, that is, it is obtained.

In the present invention, the nanofiber organic precursor is selected from polyvinylidene fluoride, polyacrylonitrile, polyethylene oxide, polyvinylpyrrolidone, polymethyl methacrylate, polyvinyl alcohol, poly(vinylidene fluoride-co- One of hexafluoropropylene). The nanofiber organic precursor has the following technical advantages: 1. The nanofiber structure has a continuous 3D ion-conducting path, which can provide a good transport channel for lithium ions. The active site promotes the transport of lithium ions, which can effectively improve the ionic conductivity of the electrolyte; 2. The nanofiber structure has high mechanical strength and can effectively resist the destruction of lithium dendrites. At the same time, its flexibility and thickness are also excellent. The cycle stability and safety of lithium-ion batteries provide an effective guarantee; 3. The nanofiber structure has a very high porosity, which can more effectively absorb the elastic organic polymer monomer and avoid the elastic organic polymer monomer and the positive electrode of the pole piece. When the materials are in contact, the resulting surface tension affects the contact effect between the electrolyte and the negative electrode.

In the present invention, the elastic organic polymer monomer is selected from butyl acrylate, methyl acrylate, ethyl acrylate, and propyl acrylate; the lithium salt is selected from lithium bisfluorosulfonimide, bistri Lithium Fluoromethylsulfonimide, Lithium Hexafluorophosphate, Lithium Tetrafluoroborate, Lithium Perchlorate, Lithium Chloride, Lithium Tris(pentafluoroethyl)trifluorophosphate, Lithium Bisoxalate Borate, Lithium Difluorooxalate Borate, Difluoro One or more combinations of lithium dioxalate phosphate, lithium tetrafluorooxalate phosphate and lithium carbonate.

In the present invention, the photoinitiator is 2-hydroxy-methylphenylpropan-1-one, 1-hydroxycyclohexyl phenyl ketone, 2-methyl-1-(4-methylthiobenzene base)-2-morpholinyl-1-acetone and benzoin dimethyl ether BDK; the crosslinking agent is polyethylene glycol diacrylate; the plasticizer is fluoroethylene carbonate, carbonic acid One or more combinations of vinyl ester, dimethyl carbonate, triethyl phosphate, polycarbonate and diethyl carbonate. The addition of plasticizer can be immersed into the solid polymer system, increase the amorphous area in the system, reduce the crystallinity of the system, and finally reduce the glass transition temperature of the system. The reduction of glass transition temperature will be accompanied by the improvement of the contact performance between the electrolyte and the electrode at room temperature , and ultimately improve the battery performance, reduce the formation of lithium dendrites, improve the interface contact between the electrode and the electrolyte, and improve the safety performance of the battery.

In the present invention, the molar ratio of the polymer monomer and lithium salt is 10-20:1, for example, 10:1, 13:1, 15:1, 17:1, 18:1, 20:1 Wait. The mass ratio of the photoinitiator and the polymer monomer is 0.5-2:100, for example, 0.5:100, 0.7:100, 0.8:100, 1:100, 1.1:100, 1.3:100, 1.5:100, 2:100, etc., the amount of photoinitiator should not be too much or too little, too much will cause yellowing of the electrolyte membrane, and excessive photoinitiator will also have a certain impact on the electrochemical performance of the electrolyte membrane. Further, the mass ratio of the crosslinking agent and the polymer monomer is 0.5-2:100, for example, 0.5:100, 0.7:100, 0.8:100, 1:100, 1.1:100, 1.3:100, 1.5: 100, 2:100, etc. Further, the mass ratio of the plasticizer to the polymer monomer is 0.3-0.5:1, such as 0.3:1, 0.33:1, 0.35:1, 0.36:1, 0.38:1, 0.4:1, 0.42 :1, 0.45:1, 0.46:1, 0.47:1, 0.48:1, 0.5:1, etc., the amount of plasticizer should not be too much or too little, too little will lead to a higher glass transition temperature after polymer polymerization , the material becomes brittle; too much will cause the glass transition temperature of the electrolyte membrane to be low, become very viscous, and have poor mechanical properties.

In the present invention, the illumination power of the ultraviolet lamp is 200W, the illumination time is 5-15min, the specific illumination is selected according to actual needs, the vertical distance from the ultraviolet light source to the film is 20-30cm, and the wavelength is 365nm.

In the present invention, the process parameters of electrospinning are: static voltage 12-17kV, spinning distance 10-15cm, spinning solution flow rate 1-1.5mL/h, spinning drum rotation speed 100-350rpm.

Further, the thickness of the nanofiber organic film is not easy to be too thick or too thin, too thin will cause the electrolyte performance to fail to meet the requirements, and too thick will lead to higher bulk resistance, affecting the performance of the material battery. It is concluded from the experiment that the thickness of the nanofiber organic film is suitable to be 20-80 μm.

Further, the fiber diameter of the nanofiber organic film should not be too thin or too thick. It is concluded through experiments that the fiber diameter of the nanofiber organic film is 100-300 nm.

Further, it is more suitable that the mass ratio of the nanofiber organic matter film to the polymer monomer is 0.3-1:1.

Further, the present invention also includes an in-situ UV-curable nanofiber composite solid electrolyte prepared by the above-mentioned preparation method.

Further, the thickness of the in-situ UV-curable nanofiber composite solid electrolyte is suitable to be 150-300 μm, and the specific parameters can be selected according to actual production conditions. Correspondingly, the thickness of the composite solid electrolyte should not be too thin or too thick, too thin will lead to the decline of the mechanical properties of the whole system, lithium dendrites penetrate the film and lead to short circuit of the battery, and too thick will lead to higher bulk resistance, which will affect the performance of the material battery. .

Further, the present invention also includes the application of an in-situ UV-curable nanofiber composite solid electrolyte in a solid-state battery, wherein the electrolyte diaphragm of the solid-state battery is the above-mentioned in-situ UV-cured nanofiber composite solid electrolyte, and the positive electrode of the solid-state battery is active. The substance is one or more of lithium cobalt oxide, lithium iron phosphate, nickel-cobalt-manganese ternary material, nickel-cobalt-aluminum ternary material, spinel nickel-manganese-rich material and lithium-rich manganese material; negative electrode activity of solid-state battery One or more of the material graphite, silicon-based material, soft carbon, hard carbon and metal lithium, the solid-state battery adopts the traditional method to prepare the pole piece, and assembles to obtain the solid-state battery with the sandwich structure.

To sum up, due to the adoption of the above-mentioned technical solutions, the beneficial effects of the present invention are:

1. The present invention uses a nanofiber polymer membrane as a substrate, and its nanofiber structure has a continuous 3D ion-conducting path, which can provide a good transport channel for lithium ions, and the nanofiber membrane can also provide a large number of active sites, thereby promoting lithium ions. It can effectively improve the ionic conductivity of the electrolyte;

2. The present invention uses a nanofiber organic film as a substrate. The nanofiber structure has high mechanical strength and can effectively resist the destruction of lithium dendrites. At the same time, its flexibility and thickness are also excellent, which is the cycle stability and safety of lithium ion batteries. Sex provides an effective guarantee;

3. Aiming at the problem of poor solid-solid interface contact of traditional solid-state electrolytes, the present invention uses in-situ ultraviolet polymerization to prepare solid-state electrolytes and in-situ construction of interface layer bonding on the basis of in-situ ultraviolet light-initiated polymerization. The elastic-like organic polymer monomer was used as the precursor, and film-forming additives and inorganic substances were introduced to form the negative electrode interface layer and the positive electrode buffer layer in situ. The integrated solid-state battery lays a solid foundation for the analysis and control of solid-state batteries;

4. In the present invention, when the elastic organic polymer monomer solution is dripped on the positive electrode plate, the surface tension will cause the liquid to be unevenly distributed on the surface of the electrode plate, and there will be some gaps in contact with the negative electrode lithium plate, resulting in an increase in interface impedance. In the present invention, the electrospinning nanofiber membrane is used as the intermediate layer, and the dispersion uniformity of the precursor solution on the positive electrode plate can be studied by adsorbing the elastic organic polymer monomer solution, and the nanofiber membrane has high specific surface area and strong polarity. Based on the advantages of functional groups, the conduction behavior of lithium ions in the nanofiber membrane was studied, and the formation mechanism of the lithium ion conduction path model in the solid-state battery after nanofiber composite was clarified in principle. The application provides theoretical support.

Description of drawings

Fig. 1 is the electrochemical window diagram of embodiment 1;

Figure 2 is a charge-discharge curve diagram of the solid-state battery obtained in Example 1 at 25°C and a rate of 0.1C;

FIG. 3 is a physical view of the solid electrolyte membrane of Example 1. FIG.

Detailed ways

The present invention will be described in detail below with reference to the accompanying drawings.

In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, but not to limit the present invention.

Example 1

An in-situ ultraviolet light-cured nanofiber composite solid electrolyte, the preparation method comprising the following steps:

S1.1, adding a certain mass of PVDF powder into a mixed solvent of DMAc and acetone with a volume ratio of 7:3 to prepare a PVDF spinning solution with a concentration of 12 wt%;

S1.2. Stir the prepared PVDF spinning solution with a magnetic stirrer for 12 hours, and then use an ultrasonic cleaner to perform ultrasonic defoaming for 1 hour to obtain a transparent and evenly mixed spinning solution;

S1.3. Use a syringe to extract a certain amount of spinning solution, put it on the syringe pump, use a flat needle with an inner diameter of 0.5mm, connect the positive electrode of the high-voltage electrostatic generator to the needle, and connect the negative electrode or ground wire to the receiving screen , adjust the distance between the needle and the receiving screen to 12cm, slowly increase the pressure to 15KV, adjust the flow rate of the syringe pump to 1.1mL/h, the spinning solution is ejected from the needle by the action of a high-voltage electric field, and is finally stretched and split. It was deposited on the receiving screen, and the thickness of the electrospun membrane was controlled by the spinning time to 50 μm. Finally, the obtained non-woven fiber membrane was placed in an oven at 60 ° C to dry for more than 24 hours, so that the spinning solvent was completely volatilized, and a nanofiber PVDF membrane was obtained. , in which the fiber diameter is controlled at 100-300nm;

S2.1. Put the nanofiber PVDF membrane in a vacuum drying oven at 60°C for 12h, and set aside;

S2.2. In order to avoid the hydrolysis of lithium salt, store LiTFSI in gloves for future use;

S2.3. Weigh a certain mass of LiTFSI, dissolve the plasticizer (the mass ratio of fluoroethylene carbonate and triethyl phosphate to the monomer is 0.5:1) in butyl acrylate (BA) and stir at room temperature for 1 h , add the cross-linking agent PEGDA and the ultraviolet photoinitiator 2-hydroxy-2-methyl-1-phenyl-1-propyl ketone (HMPP) into the BA solution, and stir continuously for 1 h. The amount of the initiator HMPP is acrylic acid 1% of the mass of butyl ester, and the amount of PEGDA is 1% of the mass of butyl acrylate to obtain a uniformly stirred PEGDA/BA/LiTFSI mixture;

S3. Place the positive pole piece with the positive active material on the polytetrafluoroethylene (PTFE) mold, then spread the nanofiber PVDF film of S2.1 on the positive pole piece, and pour the PEGDA/BA/LiTFSI mixture into In the above-mentioned polytetrafluoroethylene mold, the mass ratio of the nanofiber PVDF film to BA is 0.5:1;

S4. Irradiate the polytetrafluoroethylene mold under the ultraviolet light in the dark box for 10min. The wavelength of the ultraviolet light used is 365nm. After irradiation, place it in a vacuum drying box and continue drying at 45°C for 24h. It is a 200 μm in-situ UV-curable nanofiber composite solid electrolyte.

Preparation of solid-state batteries

The in-situ ultraviolet light-cured nanofiber composite solid electrolyte prepared above was used as the electrolyte membrane, the positive electrode sheet was prepared by using lithium iron phosphate active material, and the negative electrode was made of lithium metal sheet as the negative electrode sheet, which was cut into diameters of 18mm and 16mm with a slicer. and 16mm wafers to assemble a sandwich structure button solid-state battery. A sandwich-structure solid-state battery was assembled with a stainless steel sheet with a diameter of 16 mm to test the AC impedance of the solid-state electrolyte. The ionic conductivity of the solid electrolyte at room temperature was tested by assembling a sandwich-structure solid-state battery with a lithium metal sheet with a diameter of 16 mm.

Example 2

An in-situ ultraviolet light-cured nanofiber composite solid electrolyte, the preparation method comprising the following steps:

S1.1. Add a certain mass of PEO powder into a water solvent to prepare a PEO spinning solution with a concentration of 8 wt%;

S1.2. Stir the prepared PEO spinning solution with a magnetic stirrer for 12 hours, and then use an ultrasonic cleaner for ultrasonic defoaming for 1 hour to obtain a transparent and evenly mixed spinning solution;

S1.3. Use a syringe to extract a certain amount of spinning solution, put it on the syringe pump, use a flat needle with an inner diameter of 0.5mm, connect the positive electrode of the high-voltage electrostatic generator to the needle, and connect the negative electrode or ground wire to the receiving screen , adjust the distance between the needle and the receiving screen to 15cm, slowly increase the pressure to 13KV, adjust the flow rate of the syringe pump to 1.2mL/h, the spinning solution is ejected from the needle by the action of the high-voltage electric field, and finally through the process of stretching and splitting, finally Deposited on the receiving screen, the thickness of the electrospun film was controlled by the spinning time to about 40 μm, and finally the obtained non-woven fiber film was placed in an oven at 60 ° C to dry for more than 24 hours, so that the spinning solvent was completely volatilized, and the nanofiber PEO was obtained Membrane, wherein the fiber diameter is controlled at 100-300nm;

S2.1. Put the nanofiber PEO film in a vacuum drying oven at 60°C for 12h and use it for later use;

S2.2. In order to avoid the hydrolysis of lithium salt, store LiTFSI in gloves for future use;

S2.3. Weigh a certain mass of LiTFSI, fluorinated ethylene carbonate and triethyl phosphate (with a mass ratio of 0.5:1) dissolved in butyl acrylate (BA) and stir at room temperature for 1 h. The linking agent PEGDA and the ultraviolet photoinitiator 2-hydroxy-2-methyl-1-phenyl-1-propyl ketone (HMPP) were added to the BA solution and stirred continuously for 1 h. The amount of the initiator HMPP was the mass of butyl acrylate. 1% of PEGDA, and the amount of PEGDA is 1% of the mass of butyl acrylate to obtain a well-stirred PEGDA/BA/LiTFSI mixture;

S3. Place the positive pole piece with the positive active material on the polytetrafluoroethylene (PTFE) mold, then spread the nanofiber PEO film of S2.1 on the positive pole piece, and pour the PEGDA/BA/LiTFSI mixture into In the above-mentioned polytetrafluoroethylene mold, the mass ratio of the nanofiber PEO film to BA is 0.6:1;

S4. Irradiate the polytetrafluoroethylene mold under the ultraviolet light in the dark box for 10min. The wavelength of the ultraviolet light used is 365nm. After irradiation, place it in a vacuum drying box and continue drying at 45°C for 24h. It is a 200 μm in-situ UV-curable nanofiber composite solid electrolyte.

Preparation of solid-state batteries

The in-situ ultraviolet light-cured nanofiber composite solid electrolyte prepared above was prepared by using lithium cobalt oxide active material to prepare a positive electrode sheet, and a lithium metal sheet was used as the negative electrode sheet for the negative electrode. The wafer is assembled into a sandwich structure button-type solid-state battery.

Example 3

Preparation of solid-state batteries

The in-situ UV-curable nanofiber composite solid electrolyte obtained in Example 1 was used as the electrolyte membrane, and the positive electrode sheet was prepared by using lithium cobalt oxide active material, and the negative electrode was made of lithium metal sheet as the negative electrode sheet, which was cut with a slicer to a diameter of 18 mm, 16mm and 16mm wafers to assemble a sandwich structure button solid-state battery.

Comparative Example 1

Comparative Example 1 is the same as Example 1, except that the nanofiber PVDF membrane is not added in Comparative Example 1, and the others are the same as Example 1.

Comparative Example 2

Comparative Example 2 is the same as Example 1, except that ordinary PVDF polymer particles of the same quality as the nanofiber PVDF membrane are added in Comparative Example 2, and the others are the same as Example 1.

Comparative Example 3

Comparative Example 3 is the same as Example 1, except that no plasticizer is added to Comparative Example 3.

Comparative Example 4

Comparative Example 4 is the same as Example 1, except that the amount of plasticizer added in Comparative Example 4 is 100% of the mass of butyl acrylate.

Comparative Example 5

Comparative Example 5 was the same as Example 1, except that the thickness of the electrospun membrane of Comparative Example 5 was 150 µm.

Comparative Example 6

Comparative Example 6 is the same as Example 1, except that the fiber diameter of the nanofiber organic film in Comparative Example 6 is 500-600 nm.

test results

Table 1 The ionic conductivity test results of Example 1 and Comparative Examples 1-6

sample Ionic conductivity test temperature Example 1 5.1*10^-4S/cm 25℃ Comparative Example 1 4.2*10^-5S/cm 25℃ Comparative Example 2 8.7*10^-5S/cm 25℃ Comparative Example 3 5.2*10^-7S/cm 25℃ Comparative Example 4 2.8*10^-4S/cm 25℃ Comparative Example 5 4.8*10^-4S/cm 25℃ Comparative Example 6 2.5*10^-4S/cm 25℃

It can be obtained from Table 1 that the room temperature conductivity of Example 1 is 5.1×10 ^-4 S/cm. Compared with Example 1, the conductivity of Comparative Example 1 is 4.2×10 without adding nanofiber PVDF membrane. ^-5 S/cm, which is lower than that of Example 1, which indicates that the introduction of nanofiber PVDF membrane can significantly improve the ionic conductivity. At the same time, the inventors have obtained the following conclusions through genetic analysis: the addition of nanofiber PVDF membrane can improve the overall electrolyte conductivity. In the amorphous region, the nanofiber PVDF membrane itself has many active sites, which can provide a certain ionic conductivity. Adding it into the matrix can effectively improve the ionic conductivity. Therefore, the conductivity of Example 1 is higher than that of Comparative Example 1.

Further, in Comparative Example 3, because no plasticizer was added in Comparative Example 3, the glass transition temperature of the system was too high, the crystal phase region increased, and the conduction of lithium ions in the system was hindered, so the ionic conductivity was greatly reduced. In Comparative Example 4, the amount of 2:1 with the mass of the monomer was added. Although the ionic conductivity was improved, the system showed a viscous flow state, the mechanical properties were greatly reduced, and the film could not be formed effectively.

Further, in Comparative Example 5, a nanofiber membrane with a larger thickness was selected. Compared with Example 1, only the thickness was increased, which had no effect on the ion conductivity, so the lithium ion conductivity did not change much. In Comparative Example 6, a nanofiber membrane with a larger fiber diameter was selected. Due to the larger diameter, the active sites of the entire system decreased, so the ionic conductivity decreased.

Further, by comparing Example 1 and Comparative Example 2, it can be obtained: First, during the preparation process, the common PVDF polymer particles in Comparative Example 2 are prone to agglomeration, resulting in uneven film, and finally its ionic conductivity is only 8.7×10 ^-5 S/cm, although higher than that of Comparative Example 1, the ionic conductivity is not significantly improved; at the same time, compared with nanofiber PVDF, traditional particle PVDF has lower specific surface area, fewer active sites, and ion conduction sites. decreased, and its ionic conductivity was lower compared to Example 1 of the present invention.

Further, a wide electrochemical window is an important indicator for high energy density Li metal batteries. As shown in Figure 1, according to the results of linear sweep voltammetry (LSV) performed at 25°C, the electrochemical window of Example 1 is 5.0V, which indicates that the electrolyte is electrochemically stable below 5.0V, so Can be used in lithium metal batteries.

Further, as can be seen from Figure 2, in the button battery with lithium iron phosphate as the positive electrode, the discharge capacity of Example 1 is 163mAh/g, which is close to the theoretical capacity of lithium iron phosphate of 170mAh/g, and the electrolyte on the surface is in lithium iron phosphate. Can be effectively used in batteries.

Further, the glass transition temperature test results of the solid-state battery systems of Example 1 and Comparative Examples 3 and 4 are shown in Table 2:

Table 2 Test results of glass transition temperature of solid-state batteries in Example 1 and Comparative Examples 3 and 4

sample glass transition temperature Example 1 -32℃ Comparative Example 3 52℃ Comparative Example 4 -70℃

It can be obtained from Table 2 that the glass transition temperature of Comparative Example 3 is higher than that of Example 1 and Comparative Example 4 because no plasticizer is added. However, the glass transition temperature of Comparative Example 4 was lower than that of Example 1 with the addition of an excessive amount of plasticizer.

The above descriptions are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention shall be included in the protection of the present invention. within the range.

Claims (10)

1. The preparation method of the in-situ ultraviolet curing nanofiber composite solid electrolyte is characterized by comprising the following steps of:

s1, obtaining a nanofiber organic precursor through an electrostatic spinning method, and removing a nanofiber organic precursor spinning solvent to obtain a nanofiber organic film for later use;

s2, adding an elastic organic polymer monomer, lithium salt, a plasticizer, a photosensitive curing agent and a cross-linking agent into a mixing container according to a certain proportion, and uniformly stirring and dispersing to obtain a mixed solution;

s3, preparing a positive pole piece with an active positive pole material, putting the positive pole piece into a polytetrafluoroethylene mold, placing the nanofiber organic substance membrane prepared in the S1 on the pole piece, and then flatly spreading the mixed solution obtained in the S2 on the nanofiber organic substance membrane and the positive pole piece according to a certain mass ratio;

and S4, selecting an ultraviolet lamp with certain power, and placing the mold of S3 under the ultraviolet lamp for a certain time to obtain the product.

2. The method for preparing the in-situ ultraviolet curing nanofiber composite solid electrolyte as claimed in claim 1, wherein the nanofiber organic precursor is one selected from polyvinylidene fluoride, polyacrylonitrile, polyethylene oxide, polyvinylpyrrolidone, polymethyl methacrylate, polyvinyl alcohol, and poly (vinylidene fluoride-co-hexafluoropropylene).

3. The method for preparing the in-situ ultraviolet-curing nanofiber composite solid electrolyte as claimed in claim 1, wherein the elastic organic polymer monomer is one selected from butyl acrylate, methyl acrylate, ethyl acrylate and propyl acrylate; the lithium salt is selected from one or more of lithium bis (fluorosulfonyl) imide, lithium bis (trifluoromethyl) sulfonyl imide, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium chloride, lithium tris (pentafluoroethyl) trifluorophosphate, lithium bis (oxalate) borate, lithium difluorooxalate borate, lithium difluorobis (oxalate) phosphate, lithium tetrafluorooxalate phosphate and lithium carbonate.

4. The method for preparing the in-situ ultraviolet curing nanofiber composite solid electrolyte as claimed in claim 1, wherein the photoinitiator is one of 2-hydroxy-methylphenylpropane-1-one, 1-hydroxycyclohexyl phenyl ketone, 2-methyl-1- (4-methylthiophenyl) -2-morpholinyl-1-propanone and benzoin dimethyl ether BDK; the cross-linking agent is polyethylene glycol diacrylate; the plasticizer is one or more of fluoroethylene carbonate, ethylene carbonate, dimethyl carbonate, polycarbonate and diethyl carbonate.

5. The method for preparing the in-situ ultraviolet curing nanofiber composite solid electrolyte as claimed in claim 1, wherein the molar ratio of the polymer monomer to the lithium salt is 10-20: 1; the mass ratio of the photoinitiator to the polymer monomer is 0.5-2: 100, respectively; the mass ratio of the cross-linking agent to the polymer monomer is 0.5-2: 100, respectively; the mass ratio of the plasticizer to the polymer monomer is 0.3-0.5: 1.

6. the method as claimed in claim 1, wherein in step S4, the UV lamp has a power of 100-300W, a time of 5-15min, and a vertical distance from the UV source to the membrane of 20-30 cm.

7. The method for preparing the in-situ ultraviolet curing nanofiber composite solid electrolyte as claimed in claim 1, wherein the electrostatic spinning process parameters are as follows: the static voltage is 12-17kV, the spinning distance is 10-15cm, the flow rate of the spinning solution is 1-1.5mL/h, and the rotating speed of the spinning drum is 100-350 rpm; the thickness of the nanofiber organic film is 20-80 μm, the fiber diameter is 100-300nm, and the mass ratio of the nanofiber organic film to the polymer monomer is 0.3-1: 1.

8. an in-situ ultraviolet light curing nanofiber composite solid electrolyte, which is prepared by the preparation method of any one of claims 1 to 7.

9. The in-situ uv-curing nanofiber composite solid electrolyte as claimed in claim 8, wherein the thickness of the in-situ uv-curing nanofiber composite solid electrolyte is 150-300 μm.

10. The application of the in-situ ultraviolet light curing nanofiber composite solid electrolyte in a solid-state battery is characterized in that an electrolyte membrane of the solid-state battery is the in-situ ultraviolet light curing nanofiber composite solid electrolyte as claimed in claim 8 or 9, and a positive active material of the solid-state battery is one or more of lithium cobaltate, lithium iron phosphate, a nickel-cobalt-manganese ternary material, a nickel-cobalt-aluminum ternary material, a spinel lithium nickel manganese oxide material and a lithium-rich manganese material; one or more of graphite, silicon-based materials, soft carbon, hard carbon and metallic lithium, which are negative active materials of the solid-state battery.

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