CN115020802A - In-situ ultraviolet light curing 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 ultraviolet light curing nanofiber composite solid electrolyte and preparation method and application thereof

Technical Field

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

Background

With the rapid development of industries in all countries of the world, the emission of carbon dioxide is also increased dramatically, and the most serious negative effect is the greenhouse effect. In a plurality of renewable green energy systems, the lithium ion battery has the advantages of large energy density, good power performance, high voltage platform, long cycle life, good temperature adaptability, flexible size design and the like, and is widely applied to the fields of unmanned aerial vehicles, pure electric vehicles, hybrid electric vehicles, industrial and civil energy storage and the like. With the rapid development of batteries, the market has higher and higher requirements on the performance of lithium batteries, and the energy density of the batteries is also higher and higher. However, a series of potential safety hazards are also brought by the increase of the energy density, the safety accidents caused by battery explosion are endless, and the safety accidents caused by the lithium ion battery explosion endanger the safety of users. The solid-state battery is composed of a solid electrolyte, a positive electrode material and a negative electrode material, and has the following advantages compared with a liquid-state lithium ion battery:

(1) the solid-state battery replaces the combustible liquid electrolyte and the diaphragm with the solid electrolyte, so that the thermal runaway risk is greatly reduced;

(2) compared with an electrochemical window of 4.2V of a liquid lithium battery, the electrochemical window of the solid battery can reach more than 5V, and the high-voltage window allows the high-energy anode and the metal lithium cathode to be matched, so that the energy density of the battery is greatly improved;

(3) the solid-state battery packaging process is simple, the weight of the battery can be reduced in a limited space, and the volume energy density is improved by more than 70% compared with that of a liquid-state lithium battery (graphite cathode) and reaches 500 Wh/kg.

In order to obtain a lithium metal battery with high safety and high energy density, the anode adopts an anode material with high specific capacity and high working voltage, and the cathode adopts metal lithium with high quality/volume energy density and low price, which is the hottest hotspot of the current solid-state batteries. However, polymer electrolytes have low ionic conductivity at room temperature and the problem of solid electrolyte/electrode interface is a gap that spans between critical materials and battery performance. The method researches the interface characteristics and application modification of the electrode by solid electrolyte through the means of in-situ polymerization of the surface of the anode, introduction of a nanofiber intermediate layer, surface modification, interface structure regulation and the like, has great research value and practical significance, and the basic research of the deep system is beneficial to the development of the solid-state ionology and energy storage material discipline in China.

Aiming at the problem of interface contact of the solid-state battery in the solid-state battery, a Guan [ UV-Current interconnecting Networks of Single-ion connecting Polymer Electrolytes for Rechargeable Lithium Batteries [ J].ACS Applied Energy Materials, (2020).3(12)：12532–12539.]IN-situ polymerization is initiated by a simple ultraviolet light to prepare the single-ion conductive polymer electrolyte (IN-SCPE), so as to improve the interface problem between the positive electrode and the solid electrolyte. Mixing lithium salt, monomer, interface modifier, photoinitiator and cross-linking agent to prepare a cross-linked polymer gel network, and then exposing the cross-linked polymer gel network to ultraviolet light to initiate free radical polymerization. Tests show that the IN-situ formed polymer network improves the interface contact capacity of IN-SCPEs and the anode active material, reduces the activation energy of Li + conduction, and improves the room-temperature ionic conductivity (1.9 multiplied by 10) ^-4 S cm ^-1 ) The Li + ion transfer number (0.90) and electrochemical window (5.3V), mechanical tensile strength performance (0.5MPa), 200 cycles of long cycle life testing at room temperature at 0.5C rate. However, the mechanical tensile strength of the solid electrolyte membrane prepared by the method is only 0.5MPa which is too low to inhibit the growth of lithium dendrites, so that the potential safety hazard of battery short circuit exists, the battery has only 200 cycles of long charge-discharge cycle under 0.5C rate, and the performance cannot meet the requirement of long cycle life. The method adopts an in-situ ultraviolet light initiated polymerization mode as a means for improving the interface of the anode and the electrolyte, can realize the design of the integral structure of the anode and the solid 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 by using liquid and polymerizing in situ on the electrode, and can theoretically overcome the difficult problem of poor contact between the anode material and the electrolyte interface.

Chinese patent CN112201847A discloses a composite solid-state motor membrane, its preparation method and application, in the composite solid-state electrolyte membrane, flexible polymer is used as skeleton of polymer solid-state electrolyte, the added organic nano-fiber has high strength and high abrasion, the mechanical property is greatly improved, the inorganic oxide ceramic filler has high specific surface area, and the surface is rich in Lewis acidIncrease solid electrolyte Membrane Capture TFSI ^- Negative ion capacity, inhibition of polymer crystallization and promotion of Li ⁺ Dissociation is carried out, so that the composite solid electrolyte membrane has excellent electrochemical performance; the organic nano-fiber and the inorganic oxide ceramic particles can synergistically reduce the crystallinity of the polymer, so that the dissociation of lithium salt is promoted, the ion transmission path on an interface is increased, excellent ionic conductivity is obtained, good contact of a positive electrode and a negative electrode is realized by combining the flexibility of the polymer and the rigidity of the inorganic particles, and the finally prepared composite solid electrolyte membrane has high electrochemical performance and high mechanical performance. However, the solid electrolyte prepared in this patent is subjected to a battery test at a temperature of 60 ℃ and is not tested at room temperature, because polyethylene oxide has too low ionic conductivity and poor ionic conductivity at room temperature, thereby limiting the application of this patent at room temperature. In addition, when the electrolyte is subjected to long-cycle charge and discharge tests, the charge and discharge cycle tests are only performed for 100 times, and the fact that the electrolyte can be applied to lithium batteries is not enough proved.

Disclosure of Invention

The invention aims to: aiming at the problems, the preparation method and the application of the in-situ ultraviolet curing nanofiber composite solid electrolyte are provided to overcome the problems in the prior art.

The technical scheme adopted by the invention is as follows: a preparation method of an in-situ ultraviolet curing nanofiber composite solid electrolyte comprises the following steps:

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 stirring and dispersing uniformly 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.

In the invention, the nanofiber organic precursor is selected from one of polyvinylidene fluoride, polyacrylonitrile, polyethylene oxide, polyvinylpyrrolidone, polymethyl methacrylate, polyvinyl alcohol and poly (vinylidene fluoride-co-hexafluoropropylene). The nanofiber organic precursor mainly has the following technical advantages: 1. the nanofiber structure has a continuous 3D ion guide path, so that a transmission channel can be well provided for lithium ions, meanwhile, the strong polarity bond position of the nanofiber organic matter can also provide a large number of active sites, the transmission of the lithium ions is promoted, and the ion conductivity of an electrolyte can be effectively improved; 2. the nanofiber structure has high mechanical strength, can effectively resist the damage of lithium dendrites, has excellent flexibility and thickness, and provides effective guarantee for the cycle stability and safety of the lithium ion battery; 3. the nanofiber structure has very high porosity, can more effectively absorb the elastic organic polymer monomer, and avoids the influence of the generated surface tension on the contact effect of the electrolyte and the negative electrode when the elastic organic polymer monomer is contacted with the positive electrode material of the pole piece.

In the present invention, the elastic organic polymer monomer is selected from one of 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 (oxalato) borate, lithium difluoro (oxalato) phosphate, lithium tetrafluoro (oxalato) phosphate and lithium carbonate.

In the invention, the photoinitiator is one of 2-hydroxy-methyl phenyl propane-1-ketone, 1-hydroxycyclohexyl phenyl ketone, 2-methyl-1- (4-methylthiophenyl) -2-morpholinyl-1-acetone 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, triethyl phosphate, polycarbonate and diethyl carbonate. The plasticizer can be immersed into a solid polymer system, an amorphous area in the system is increased, the crystallinity of the system is reduced, and the glass transition temperature of the system is finally reduced, wherein the reduction of the glass transition temperature is accompanied by the improvement of the contact performance between the electrolyte and the electrodes under the room temperature condition, so that the battery performance is finally improved, the generation of lithium dendrites is reduced, the interface contact between the electrodes and the electrolyte is improved, and the safety performance of the battery is improved.

In the present invention, the molar ratio of the polymer monomer to the lithium salt is 10 to 20:1, for example, may be 10:1, 13: 1. 15:1, 17:1, 18:1, 20:1, etc. The mass ratio of the photoinitiator to 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 the photoinitiator should not be too much or too little, which may cause yellowing of the electrolyte membrane, and the excessive photoinitiator may also have a certain influence on the electrochemical performance of the electrolyte membrane. Further, the mass ratio of the cross-linking agent to the polymer monomer is 0.5-2: 100, for example, can be 0.5:100, 0.7:100, 0.8:100, 1:100, 1.1:100, 1.3:100, 1.5:100, 2:100, and the like. Further, the mass ratio of the plasticizer to the polymer monomer is 0.3-0.5: 1, for example, can be 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 and the like, and the dosage of the plasticizer is not too much or too little, so that the glass transition temperature of the polymer after polymerization is higher and the material becomes brittle; too much results in a lower glass transition temperature of the electrolyte membrane, which becomes very viscous and poor mechanical properties.

In the 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 365 nm.

In the invention, the technological parameters of electrostatic spinning 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.

Furthermore, the thickness of the nanofiber organic film is not easy to be too thick or too thin, the electrolyte performance can not meet the requirement due to too thin, and the body resistance is higher due to too thick, so that the performance of the material battery is influenced. The thickness of the nanofiber organic film is 20-80 μm, which is obtained by experimental summary.

Furthermore, the fiber diameter of the nanofiber organic membrane is not too small or too thick, and the fiber diameter of the nanofiber organic membrane is more suitable for being 100-300nm as obtained by test summary.

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

Furthermore, the invention also comprises an in-situ ultraviolet curing nanofiber composite solid electrolyte prepared by the preparation method.

Further, the thickness of the in-situ ultraviolet curing nanofiber composite solid electrolyte is more suitable for being 150-300 μm, and specific parameters can be selected according to actual production conditions. Accordingly, the thickness of the composite solid electrolyte should not be too thin or too thick, the mechanical performance of the whole system is reduced due to the too thin thickness, the battery is short-circuited due to the penetration of lithium dendrites through the membrane, and the performance of the material battery is affected due to the higher bulk resistance due to the too thick thickness.

Furthermore, the invention also comprises an application of the in-situ ultraviolet light curing nanofiber composite solid electrolyte in a solid-state battery, wherein an electrolyte diaphragm of the solid-state battery is the in-situ ultraviolet light curing nanofiber composite solid electrolyte, and a positive active substance 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 material and a lithium-rich manganese material; the solid-state battery is characterized in that one or more of graphite, silicon-based materials, soft carbon, hard carbon and metal lithium are used as negative active materials of the solid-state battery, pole pieces are prepared by the solid-state battery through a traditional method, and the solid-state battery with a sandwich structure is obtained through assembly.

In summary, due to the adoption of the technical scheme, the invention has the beneficial effects that:

1. according to the invention, the nanofiber polymer film is used as a substrate, the nanofiber structure of the nanofiber polymer film has a continuous 3D ion guide path, a transmission channel can be well provided for lithium ions, and the nanofiber film can also provide a large number of active sites, so that the transmission of the lithium ions is promoted, and the ionic conductivity of an electrolyte can be effectively improved;

2. according to the invention, the nanofiber organic film is used as the substrate, the mechanical strength of the nanofiber structure is high, the damage of lithium dendrite can be effectively resisted, and meanwhile, the flexibility and the thickness of the nanofiber structure are excellent, so that the cycle stability and the safety of the lithium ion battery are effectively guaranteed;

3. aiming at the problem of poor solid-solid interface contact of the traditional solid electrolyte, on the basis of in-situ ultraviolet light initiated polymerization, a method for preparing the solid electrolyte and constructing an interface layer in situ is adopted, an olefine acid elastic organic polymer monomer is taken as a precursor, and a film-forming additive and an inorganic substance are introduced to form a negative interface layer and a positive buffer layer in situ, so that the integrated solid battery of 'negative electrode-interface protection layer-solid electrolyte-interface buffer layer-positive electrode' is constructed by a one-step method, and a solid foundation is laid for analysis and control of the solid battery;

4. according to the invention, when the elastic organic polymer monomer solution is dripped on the positive pole piece, the liquid is unevenly distributed on the surface of the pole piece due to surface tension, and the interface impedance is increased due to partial gaps when the elastic organic polymer monomer solution is contacted with a negative pole lithium piece.

Drawings

FIG. 1 is a diagram of an electrochemical window of example 1;

FIG. 2 is a charge-discharge curve diagram of the solid-state battery obtained in example 1 at 25 ℃ and a magnification of 0.1C;

fig. 3 is a schematic view of a solid electrolyte membrane according to example 1.

Detailed Description

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

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

Example 1

An in-situ ultraviolet light curing nanofiber composite solid electrolyte is prepared by the following steps:

s1.1, adding PVDF powder with a certain mass into a mixed solvent of DMAc and acetone with a volume ratio of 7:3 to prepare a PVDF spinning solution with the concentration of 12 wt%;

s1.2, stirring the prepared PVDF spinning solution for 12 hours by using a magnetic stirrer, and then performing ultrasonic defoaming for 1 hour by using an ultrasonic cleaner to obtain a transparent uniformly mixed spinning solution;

s1.3, extracting a certain amount of spinning solution by using an injector, placing the spinning solution on an injection pump, selecting a flat-mouth needle with the inner diameter of 0.5mm, connecting the anode of a high-voltage electrostatic generator with the needle, connecting the cathode or a grounding wire with a receiving screen, adjusting the distance between the needle and the receiving screen to be 12cm, slowly raising the pressure to 15KV, adjusting the flow rate of the injection pump to be 1.1mL/h, ejecting the spinning solution from the needle under the action of a high-voltage electric field, performing processes such as stretching and splitting and the like, finally depositing the spinning solution on the receiving screen, controlling the thickness of an electrospinning membrane to be 50 mu m by using spinning time, and finally placing the obtained non-spinning fiber membrane in an oven to dry for more than 24h at the temperature of 60 ℃ so as to completely volatilize a spinning solvent to obtain a nanofiber PVDF membrane, wherein the fiber diameter is controlled to be 100-300 nm;

s2.1, drying the nano-fiber PVDF membrane in a vacuum drying oven for 12 hours at the temperature of 60 ℃ for later use;

s2.2, in order to avoid lithium salt hydrolysis, storing the LiTFSI in gloves for storage for later use;

s2.3, weighing a certain mass of LiTFSI, dissolving a plasticizer (the mass ratio of fluoroethylene carbonate, triethyl phosphate and a monomer is 0.5: 1) in Butyl Acrylate (BA), stirring at room temperature for 1h, adding a crosslinking agent PEGDA and an ultraviolet initiator 2-hydroxy-2-methyl-1-phenyl-1-propyl ketone (HMPP) into the BA solution, and continuously stirring for 1h, wherein the amount of the initiator HMPP is 1% of the mass of the butyl acrylate, and the amount of the PEGDA is 1% of the mass of the butyl acrylate, so as to obtain a uniformly stirred PEGDA/BA/LiTFSI mixture;

s3, placing the positive pole piece with the positive active material on a Polytetrafluoroethylene (PTFE) mould, then flatly laying the nano-fiber PVDF membrane of S2.1 on the positive pole piece, and pouring the mixture of PEGDA/BA/LiTFSI into the polytetrafluoroethylene mould, wherein the mass ratio of the nano-fiber PVDF membrane to BA is 0.5: 1;

s4, placing the polytetrafluoroethylene mould in a dark box to irradiate for 10min under ultraviolet light with the wavelength of 365nm, placing the mould in a vacuum drying box after irradiation, and continuously drying for 24h at 45 ℃ to obtain the in-situ ultraviolet curing nanofiber composite solid electrolyte with the thickness of about 200 mu m.

Preparation of solid-state batteries

Taking the prepared in-situ ultraviolet light curing nanofiber composite solid electrolyte as an electrolyte membrane, preparing a positive electrode plate by adopting a lithium iron phosphate active material, taking a lithium metal sheet as a negative electrode plate for a negative electrode, cutting the lithium metal sheet into round sheets with the diameters of 18mm, 16mm and 16mm by using a slicing machine, and assembling the button solid battery with the sandwich structure. And (3) assembling the solid-state battery with the sandwich structure by adopting a stainless steel sheet with the diameter of 16mm to test the alternating-current impedance of the solid-state electrolyte. And (3) assembling the solid-state battery with the sandwich structure by adopting a lithium metal sheet with the diameter of 16mm to test the room-temperature ionic conductivity of the solid electrolyte.

Example 2

An in-situ ultraviolet light curing nanofiber composite solid electrolyte is prepared by the following steps:

s1.1, adding PEO powder with a certain mass into a water solvent to prepare a PEO spinning solution with the concentration of 8 wt%;

s1.2, stirring the prepared PEO spinning solution for 12 hours by using a magnetic stirrer, and then performing ultrasonic defoaming for 1 hour by using an ultrasonic cleaner to obtain a transparent uniformly mixed spinning solution;

s1.3, extracting a certain amount of spinning solution by using an injector, placing the spinning solution on an injection pump, selecting a flat-mouth needle with the inner diameter of 0.5mm, connecting the anode of a high-voltage electrostatic generator with the needle, connecting the cathode or a grounding wire with a receiving screen, adjusting the distance between the needle and the receiving screen to be 15cm, slowly raising the pressure to 13KV, adjusting the flow rate of the injection pump to be 1.2mL/h, ejecting the spinning solution from the needle under the action of a high-voltage electric field, performing processes such as stretching and splitting, and the like, finally depositing the spinning solution on the receiving screen, controlling the thickness of an electrospinning membrane to be about 40 mu m by using spinning time, and finally placing the obtained non-spinning fiber membrane in an oven to be dried for more than 24h at the temperature of 60 ℃ so as to completely volatilize a spinning solvent to obtain a nanofiber PEO membrane, wherein the fiber diameter is controlled to be 100-300 nm;

s2.1, drying the nanofiber PEO film in a vacuum drying oven for 12 hours at the temperature of 60 ℃ for later use;

s2.2, in order to avoid lithium salt hydrolysis, storing the LiTFSI in gloves for storage for later use;

s2.3, weighing certain mass of LiTFSI, fluoroethylene carbonate and triethyl phosphate (the mass ratio of the LiTFSI to the monomer is 0.5: 1) to be dissolved in Butyl Acrylate (BA), stirring for 1h at room temperature, adding a crosslinking agent PEGDA and an ultraviolet photoinitiator 2-hydroxy-2-methyl-1-phenyl-1-propyl ketone (HMPP) into the BA solution, and continuously stirring for 1h, wherein the amount of the initiator HMPP is 1% of the mass of the butyl acrylate, and the amount of the PEGDA is 1% of the mass of the butyl acrylate, so as to obtain a uniformly stirred PEGDA/BA/LiTFSI mixture;

s3, placing the positive pole piece with the positive active material on a Polytetrafluoroethylene (PTFE) mould, then flatly laying the nanofiber PEO film of S2.1 on the positive pole piece, and pouring the PEGDA/BA/LiTFSI mixture into the polytetrafluoroethylene mould, wherein the mass ratio of the nanofiber PEO film to BA is 0.6: 1;

s4, placing the polytetrafluoroethylene mold in a dark box to irradiate for 10min under ultraviolet light, wherein the wavelength of the used ultraviolet light is 365nm, placing the mold in a vacuum drying box after irradiation, and continuously drying the mold for 24h at the temperature of 45 ℃ to obtain the in-situ ultraviolet curing nanofiber composite solid electrolyte with the thickness of about 200 microns.

Preparation of solid-state batteries

Preparing the in-situ ultraviolet curing nanofiber composite solid electrolyte prepared by the method, preparing a positive electrode plate by adopting a lithium cobaltate active material, cutting a negative electrode plate by adopting a lithium metal sheet, cutting the negative electrode plate into round sheets with diameters of 18mm, 16mm and 16mm by using a slicing machine, and assembling the button solid battery with a sandwich structure.

Example 3

Preparation of solid-state batteries

The in-situ ultraviolet curing nanofiber composite solid electrolyte obtained in the embodiment 1 is used as an electrolyte membrane, a lithium cobaltate active material is used for preparing a positive electrode plate, a lithium metal plate is used as a negative electrode plate for a negative electrode, and the negative electrode plate is cut into round pieces with diameters of 18mm, 16mm and 16mm by a slicing machine, so that the button solid battery with the sandwich structure is assembled.

Comparative example 1

Comparative example 1 is the same as example 1 except that comparative example 1 does not have a nanofiber PVDF membrane added and is otherwise the same as example 1.

Comparative example 2

Comparative example 2 is the same as example 1 except that comparative example 2 adds the same mass of common PVDF polymer particles as the nanofiber PVDF membrane, and the others are the same as example 1.

Comparative example 3

Comparative example 3 is the same as example 1 except that comparative example 3 does not add a plasticizer.

Comparative example 4

Comparative example 4 is the same as example 1 except that the plasticizer of comparative example 4 is added in an amount of 100% by mass of butyl acrylate.

Comparative example 5

Comparative example 5 is the same as example 1 except that the electrospun membrane of comparative example 5 has a thickness of 150 μm.

Comparative example 6

Comparative example 6 is the same as example 1 except that the fiber diameter of the nanofiber organic membrane in comparative example 6 is 500-600 nm.

Test results

Table 1 results of ionic conductivity tests of example 1 and comparative examples 1 to 6

Sample(s)	Ionic conductivity	Test temperature
			Example 1	5.1*10 -4 S/cm	25℃
Comparative example 1	4.2*10 -5 S/cm	25℃
			Comparative example 2	8.7*10 -5 S/cm	25℃
Comparative example 3	5.2*10 -7 S/cm	25℃
			Comparative example 4	2.8*10 -4 S/cm	25℃
Comparative example 5	4.8*10 -4 S/cm	25℃
			Comparative example 6	2.5*10 -4 S/cm	25℃

As can be seen from Table 1, the room-temperature conductivity of example 1 was 5.1X 10 ^-4 S/cm, comparative example 1 compared to the examples, the conductivity was 4.2X 10 without the addition of a nanofiber PVDF membrane ^-5 S/cm, lower than example 1, thus demonstrating that the introduction of the nanofiber PVDF membrane can significantly improve the ionic conductivity, and at the same time, the inventors' cause analysis leads to the following conclusions: the addition of the nanofiber PVDF membrane can improve the amorphous region of the whole electrolyte, the nanofiber PVDF membrane has a plurality of active sites, can provide certain ionic conductivity, and can effectively improve the ionic conductivity when being added into a matrix, so that the conductivity of example 1 is higher than that of comparative example 1.

Further, in comparative example 3, since no plasticizer was added, the glass transition temperature of the system was too high, the crystalline phase region increased, and the conduction of lithium ions in the system was hindered in comparative example 3, and thus the ionic conductivity was greatly decreased. Comparative example 4 added to mass of monomer 2:1, the ionic conductivity is improved, but the system presents a viscous flow state, the mechanical property is greatly reduced, and the film can not be effectively formed.

Further, comparative example 5 selects a nanofiber membrane having a large thickness, and only the thickness is increased compared to example 1, having no influence on ion conductivity, and thus lithium ion conductivity is not much changed. Comparative example 6, a nanofiber membrane with a larger fiber diameter was selected, and the ion conductivity decreased as the diameter became larger and the active sites of the whole system decreased.

Further, by comparing example 1 and comparative example 2, it is possible to obtain: first, in the preparation process, the general P in comparative example 2The VDF polymer particles are prone to agglomeration, resulting in a non-uniform membrane, and ultimately have an ionic conductivity of only 8.7 x 10 ^-5 S/cm, although higher than comparative example 1, the improvement in ionic conductivity was not significant; meanwhile, compared with the nano-fiber PVDF, the traditional particle PVDF has the advantages of low specific surface area, less active sites and reduced ion conduction sites, and compared with the embodiment 1 of the invention, the ionic conductivity of the traditional particle PVDF is lower.

Further, a wide electrochemical window is an important indicator of high energy density lithium metal batteries. As shown in fig. 1, the electrochemical window of example 1 was 5.0V according to the results of Linear Sweep Voltammetry (LSV) performed at 25 ℃, which indicates that the electrolyte has electrochemical stability of 5.0V or less and thus can be applied to a lithium metal battery.

Further, as can be seen from fig. 2, in the button cell using 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 can be effectively applied to a lithium iron phosphate battery.

Further, the results of the glass transition temperature test of the solid-state battery systems of example 1 and comparative examples 3 and 4 are shown in table 2:

table 2 results of solid state battery glass transition temperature test of example 1 and comparative examples 3 and 4

Sample (I)	Glass transition temperature
		Example 1	-32℃
Comparative example 3	52℃
		Comparative example 4	-70℃

As can be seen from Table 2, comparative example 3 has a higher glass transition temperature than examples 1 and 4 because no plasticizer is added. While comparative example 4 added an excess of plasticizer, having a lower glass transition temperature than example 1.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.

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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