A polyionic liquid-based solid electrolyte, preparation method thereof and lithium ion battery

Abstract

The present invention discloses a polyionic liquid-based solid electrolyte, a preparation method thereof and a lithium ion battery, and belongs to the technical field of lithium ion batteries. The preparation method provided by the present invention is as follows: LLZTO nanoparticles are dispersed in a polyacrylonitrile solution to obtain a spinning solution; the spinning solution is subjected to electrostatic spinning to obtain a composite fiber membrane; poly(diallyldimethylammonium)bis(fluorosulfonyl)imide, lithium bis(fluorosulfonyl)imide and 1-methyl-1-propylpyrrolidinium bis(fluorosulfonyl)imide are mixed in a solvent to obtain a polyionic liquid electrolyte solution; the composite fiber membrane is immersed in the polyionic liquid electrolyte solution, taken out and left to stand, dried, and obtained. The solid electrolyte prepared by the present invention has high ionic conductivity and mechanical strength, good flexibility and flame retardancy, and the battery prepared by the present invention can be circulated for more than 200 cycles at a high rate current density.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to a polyionic liquid-based solid electrolyte, a preparation method thereof and a lithium ion battery. Background Art

[0002] The information disclosed in the background of the invention is only intended to enhance the understanding of the overall background of the invention and should not be necessarily regarded as an acknowledgment or any form of suggestion that the information constitutes the prior art already known to a person skilled in the art.

[0003] Traditional liquid lithium metal batteries have the problem of uncontrollable lithium dendrite growth, which can easily cause safety problems such as battery short circuit, fire and even explosion, thus limiting the widespread application of lithium metal batteries. Due to the higher safety and energy density of solid electrolytes, all-solid-state lithium metal batteries are widely regarded as the most promising next-generation rechargeable energy storage device. Solid electrolytes are generally divided into three categories: inorganic solid electrolytes, polymer solid electrolytes and composite solid electrolytes. Among them, inorganic solid electrolytes have the characteristics of high room temperature ionic conductivity, wide electrochemical window and high mechanical strength, but they are brittle and have large solid-solid contact resistance. Polymer solid electrolytes usually have good flexibility and processing properties and good interface contact, but have low ionic conductivity and relatively poor mechanical strength. Composite solid electrolytes combine the advantages of inorganic solid electrolytes and polymer solid electrolytes, not only having better ionic conductivity, but also excellent mechanical properties.

[0004] Polymer ionic liquid (PIL) poly(diallyldimethylammonium)bis(fluorosulfonyl)imide (PDADMAFSI) has good chemical stability and wide electrochemical stability and is often used as a polymer electrolyte matrix. However, the low ionic conductivity of PDADMAFSI at room temperature hinders its widespread application. Adding ionic liquid to it will increase its ionic conductivity, but will lead to a significant decrease in mechanical strength, making it difficult to curb the penetration of lithium dendrites. Adding inorganic fillers to PDADMAFSI-based polymer electrolytes can improve the mechanical strength of solid electrolytes. However, the compatibility of inorganic fillers and matrices is poor, which easily causes agglomeration, thereby affecting the transmission of lithium ions, causing uneven lithium ion deposition, and then triggering the formation and growth of lithium dendrites.

[0005] Therefore, how to provide a PDADMAFSI-based polymer electrolyte with high ionic conductivity, high mechanical strength and long cycle life is an urgent problem to be solved. Summary of the invention

[0006] In view of this, the present invention provides a polyionic liquid-based solid electrolyte, a preparation method thereof and a lithium-ion battery. The polyionic liquid-based solid electrolyte provided by the present invention has high mechanical strength and ionic conductivity, thereby being able to support a dendrite-free, stable, and long-life cycle of an all-solid-state battery.

[0007] In a first aspect, the present invention provides a method for preparing a polyionic liquid-based solid electrolyte, comprising the following steps:

[0008] Dispersing LLZTO nanoparticles in a polyacrylonitrile solution to obtain a spinning solution; electrospinning the spinning solution to obtain a composite fiber membrane;

[0009] Mixing poly(diallyldimethylammonium)bis(fluorosulfonyl)imide, lithium bis(fluorosulfonyl)imide and 1-methyl-1-propylpyrrolidinium bis(fluorosulfonyl)imide in a solvent to obtain a polyionic liquid electrolyte solution; wherein the ratio of the mass of poly(diallyldimethylammonium)bis(fluorosulfonyl)imide to the total mass of lithium bis(fluorosulfonyl)imide and 1-methyl-1-propylpyrrolidinium bis(fluorosulfonyl)imide is 1:(0.9-1.1);

[0010] The composite fiber membrane is immersed in the polyionic liquid electrolyte solution, taken out, left to stand, and dried to obtain the composite fiber membrane.

[0011] In a second aspect, the present invention provides a polyionic liquid-based solid electrolyte prepared by the above preparation method.

[0012] In a third aspect, the present invention provides a lithium-ion battery, comprising a positive electrode, a negative electrode and a solid electrolyte, wherein the solid electrolyte is the above-mentioned polyionic liquid-based solid electrolyte.

[0013] Compared with the prior art, the present invention has achieved the following beneficial effects:

[0014] (1) The preparation method provided by the present invention is simple and easy to mass produce. It can prepare a thin (<100 μm) polyionic liquid-based solid electrolyte, which is beneficial to reduce battery weight and improve energy density;

[0015] (2) The polyionic liquid-based solid electrolyte prepared by the present invention uses LLZTO-polyacrylonitrile composite fiber membrane as a three-dimensional network skeleton, has good mechanical properties, and the LLZTO nanoparticles are evenly dispersed, which can further improve the ionic conductivity of the solid electrolyte and facilitate the rapid transmission of lithium ions inside and at the interface of the electrolyte; poly(diallyldimethylammonium)bis(fluorosulfonyl)imide (PDADMAFSI), lithium bis(fluorosulfonyl)imide (LiFSI) and 1-methyl-1-propylpyrrolidinium bis(fluorosulfonyl)imide (PyR 13The PDADMAFSI has good chemical stability and wide electrochemical stability. The binding energy between lithium ions and bis(fluorosulfonyl)imide anions in lithium bis(fluorosulfonyl)imide is weak, and it can form a stable interphase when in contact with metallic lithium. 1-Methyl-1-propylpyrrolidinium bis(fluorosulfonyl)imide as a plasticizer has relatively high conductivity, as well as extremely low volatility and flammability. The combination of the three makes the prepared solid electrolyte have high ionic conductivity, good processability and excellent flame retardancy, and also has excellent resistance to lithium dendrite growth. When applied to solid-state lithium metal batteries, it can be cycled for more than 200 times at a high rate current density. The prepared soft-pack batteries show ultra-high safety in various extreme test environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The drawings constituting part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their description are used to explain the present invention and do not constitute an improper limitation of the present invention. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative work.

[0017] Figure 1 1 is a plane scanning electron microscope image of the PAN-LLZTO composite fiber membrane of Example 1 of the present invention and an X-ray diffraction spectrum of the PAN-LLZTO composite fiber membrane and LLZTO, wherein a is a plane scanning electron microscope image, and b is an X-ray diffraction spectrum of the PAN-LLZTO composite fiber membrane and LLZTO;

[0018] Figure 2 1 is a planar scanning electron microscope image and a cross-sectional scanning electron microscope image of the PPL-PLF solid electrolyte of Example 1 of the present invention, wherein a is a planar scanning electron microscope image and b is a cross-sectional scanning electron microscope image;

[0019] Figure 3 is a tensile test result diagram of the solid electrolytes prepared in Example 1, Comparative Example 1 and Comparative Example 5 of the present invention;

[0020] Figure 4 1 is a comparison diagram of the electrochemical stability windows of the PPL-PLF solid electrolyte of Example 1 of the present invention and the PPL solid electrolyte of Comparative Example 1;

[0021] Figure 5 Graphs showing ionic conductivity of the PPL-PLF solid electrolyte of Example 1 of the present invention and the PPL solid electrolyte of Comparative Example 1 at different temperatures;

[0022] Figure 61 is a graph showing the results of lithium ion migration number determination of the PPL-PLF solid electrolyte of Example 1 of the present invention and the PPL solid electrolyte of Comparative Example 1; wherein a is a chronoamperometric curve of a symmetrical battery assembled with the PPL-PLF solid electrolyte, b is an electrochemical impedance spectrum of a symmetrical battery assembled with the PPL-PLF solid electrolyte before and after the test, c is a chronoamperometric curve of a symmetrical battery assembled with the PPL solid electrolyte, and d is an electrochemical impedance spectrum of a symmetrical battery assembled with the PPL solid electrolyte before and after the test;

[0023] Figure 7 1 is an impedance diagram of the PPL-PLF solid electrolyte of Example 1 of the present invention and the solid electrolyte of Comparative Example 3;

[0024] Figure 8 1 is a macroscopic picture of the bending experiment of the PPL-PLF solid electrolyte of Example 1 of the present invention, wherein a is the original picture, b is the picture after folding, and c is the picture after folding and unfolding;

[0025] Fig. 9 The flame retardant experimental macroscopic pictures of the PPL-PLF solid electrolyte of Example 1 of the present invention, wherein a is the picture before ignition, b is the picture during ignition, and c is the picture after ignition;

[0026] Fig.10 The symmetrical battery assembled with the PPL-PLF solid electrolyte of Example 1 of the present invention is 0.2 mA / cm 2 Cyclic voltage curve at current density of ;

[0027] Fig.11 The symmetrical battery assembled with the PPL solid electrolyte of Comparative Example 1 of the present invention has a conductivity of 0.2 mA / cm 2 Cyclic voltage curve at current density of ;

[0028] Fig.12 The symmetrical battery assembled with the solid electrolyte of Comparative Example 2 of the present invention has a conductivity of 0.2 mA / cm 2 Cyclic voltage curve at current density of ;

[0029] Fig.13 3 is a comparison of the surface morphology of lithium metal after 200 cycles of the symmetrical battery assembled with the PPL-PLF solid electrolyte of Example 1 of the present invention and the solid electrolyte of Comparative Example 4, wherein a is a scanning electron microscope image of the surface morphology of lithium metal after 200 cycles of the symmetrical battery assembled with the solid electrolyte of Comparative Example 4, and b is a scanning electron microscope image of the surface morphology of lithium metal after 200 cycles of the symmetrical battery assembled with the solid electrolyte of Example 1;

[0030] Fig.14This is the electrochemical performance cycle curve of the full battery assembled with the PPL-PLF solid electrolyte of Example 1 of the present invention;

[0031] Fig.15 This is the electrochemical performance cycle curve of the full battery assembled with the PPL solid electrolyte of Comparative Example 1 of the present invention;

[0032] Fig.16 These are lighting test pictures of the soft-pack batteries assembled with the PPL-PLF solid electrolyte of Example 1 of the present invention under different treatment conditions, wherein a is the initial lighting test picture, b is the lighting test picture after folding, c is the lighting test picture after bending, and d is the lighting test picture after shearing damage. DETAILED DESCRIPTION

[0033] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0034] The present invention provides a method for preparing a polyionic liquid-based solid electrolyte, comprising the following steps:

[0035] Dispersing LLZTO nanoparticles in a polyacrylonitrile solution to obtain a spinning solution; electrospinning the spinning solution to obtain a composite fiber membrane;

[0036] Mixing poly(diallyldimethylammonium)bis(fluorosulfonyl)imide, lithium bis(fluorosulfonyl)imide and 1-methyl-1-propylpyrrolidinium bis(fluorosulfonyl)imide in a solvent to obtain a polyionic liquid electrolyte solution; wherein the ratio of the mass of poly(diallyldimethylammonium)bis(fluorosulfonyl)imide to the total mass of lithium bis(fluorosulfonyl)imide and 1-methyl-1-propylpyrrolidinium bis(fluorosulfonyl)imide is 1:(0.9-1.1);

[0037] The composite fiber membrane is immersed in the polyionic liquid electrolyte solution, taken out, left to stand, and dried to obtain the composite fiber membrane.

[0038] In the present invention, LLZTO is lithium lanthanum zirconium tantalum oxide, which has high ionic conductivity and good compatibility with metal Li; the composite fiber membrane constructed by electrostatic spinning of LLZTO nanoparticles and polyacrylonitrile (PAN) is used as a three-dimensional network skeleton, which can effectively enhance the mechanical strength of PDADMAFSI-based polymer electrolyte, and by adopting the above method, LLZTO nanoparticles can be evenly dispersed inside the composite fiber membrane, avoiding the problem of lithium dendrite formation and growth caused by agglomeration; at the same time, the LLZTO-PAN composite fiber membrane has good flexibility and high elongation at break, and is suitable for preparing flexible batteries.

[0039] In the present invention, the mass ratio of the LLZTO nanoparticles to polyacrylonitrile is 1: (8-12); the amount of LLZTO nanoparticles added should not be too much, otherwise it will affect the electrospinning process and will not be conducive to the preparation of a three-dimensional network skeleton with good mechanical properties; too little LLZTO nanoparticles added will result in low ionic conductivity of the PDADMAFSI-based polymer electrolyte.

[0040] In the present invention, the concentration of the polyacrylonitrile solution is 8-15wt%, and the appropriate concentration can ensure that the spinning solution has an appropriate viscosity, thereby facilitating the smooth progress of the electrospinning process. The solvent of the polyacrylonitrile solution of the present invention is selected from one or more of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide or sulfolane.

[0041] The present invention does not impose any special restrictions on the dispersion process of LLZTO nanoparticles in polyacrylonitrile solution, and a uniformly dispersed spinning solution can be obtained by using a dispersion method commonly used in the art. The present invention does not impose any special restrictions on the electrospinning process, and a commonly used electrospinning method in the art can be used.

[0042] In the present invention, the thickness of the composite fiber membrane is 30-70 μm. The appropriate thickness can ensure better mechanical properties and help reduce the weight of the battery and improve the energy density. The present invention does not impose any special restrictions on the shape of the composite fiber membrane, and it can be cut into a specific size according to the size and shape of the battery.

[0043] In the present invention, after the composite fiber membrane is obtained by electrospinning, the obtained composite fiber membrane is further dried and rolled. The present invention does not impose any special restrictions on the drying process, and preferably 50-80° C. is dried for 20-50 hours to ensure complete volatilization of the solvent. The present invention does not impose any special restrictions on the equipment and rolling steps used for rolling, and rolling is to make the obtained composite fiber membrane more dense and smooth.

[0044] In the present invention, the molar ratio of lithium bis(fluorosulfonyl)imide to 1-methyl-1-propylpyrrolidinium bis(fluorosulfonyl)imide is 1:(1-2). Lithium bis(fluorosulfonyl)imide (LiFSI) has high lithium ion transport capacity, which helps to improve the ionic conductivity of polyionic liquids; 1-methyl-1-propylpyrrolidinium bis(fluorosulfonyl)imide (PyR 13 FSI) as a plasticizer can reduce the crystallinity of polyionic liquids and improve the molding processability of electrolytes. Too low a content of LiFSI will limit its effect on ionic conductivity, while too high a content will make it difficult to form a PyR 13 Dissolve completely in FSI.

[0045] In the step of mixing in a solvent of the present invention, the solvent is selected from one or more of acetonitrile, tetrahydrofuran or propylene carbonate, and the stirring and mixing time is 5 to 30 hours. 13 The order of mixing the FSI is not particularly limited.

[0046] In the polyionic liquid electrolyte solution of the present invention, the mass ratio of poly(diallyldimethylammonium)bis(fluorosulfonyl)imide to the solvent is 1:(2-3).

[0047] In the present invention, the immersion time of the composite fiber membrane in the polyionic liquid electrolyte solution is 30 to 90 seconds; the standing time is 10 to 30 hours, and the standing time is to evaporate the solvent slowly and evenly to avoid the evaporation rate being too fast and affecting the flatness of the electrolyte surface; the drying temperature is 50 to 80°C, and the drying is preferably carried out by vacuum drying.

[0048] The present invention also provides a polyionic liquid-based solid electrolyte prepared by the above preparation method.

[0049] The polyionic liquid-based solid electrolyte provided by the present invention has good mechanical strength, a tensile strength of more than 2.8 MPa, and an elongation at break of more than 160%; and has high ionic conductivity, and the ionic conductivity at room temperature can reach 5×10 -4 S cm -1 Above, the ionic conductivity at 70℃ can reach 10 -3 S cm -1 above.

[0050] The present invention also provides a lithium ion battery, comprising a positive electrode, a negative electrode and a solid electrolyte, wherein the solid electrolyte is the above-mentioned polyionic liquid-based solid electrolyte.

[0051] The present invention has no special restrictions on the types of the positive electrode and the negative electrode. In the present invention, the positive electrode is preferably a lithium iron phosphate positive electrode, a lithium cobalt oxide positive electrode, a lithium manganese oxide positive electrode or a nickel-cobalt-manganese ternary positive electrode material, and the negative electrode is preferably a lithium sheet.

[0052] The present invention does not impose any special restrictions on the preparation method of the lithium ion battery, and the preparation method of the solid-state lithium metal battery commonly used in the art can be adopted.

[0053] The technical solution of the present invention is further described below in conjunction with specific embodiments. The present invention has no special restrictions on the sources of the reagents in the following embodiments, and commercially available products known to those skilled in the art can be used.

[0054] In the following examples, PAN represents polyacrylonitrile; DMF represents N,N-dimethylformamide; LLZTO represents lithium lanthanum zirconium tantalum oxide, and its chemical formula is Li6.4 LqCy 1.4 Ta 0.6 O 12 ; LiFSI stands for lithium bis(fluorosulfonyl)imide; PyR 13 FSI stands for 1-methyl-1-propylpyrrolidinium bis(fluorosulfonyl)imide; PDADMAFSI stands for poly(diallyldimethylammonium)bis(fluorosulfonyl)imide.

[0055] Example 1

[0056] This embodiment provides a method for preparing a polyionic liquid-based solid electrolyte PPL-PLF.

[0057] (1) Weigh 1.76 g of PAN powder to prepare a 13 wt% PAN / DMF solution and dissolve it under magnetic stirring at room temperature.

[0058] (2) Weigh 0.176 g of LLZTO powder, add 100 μL of oxalic acid dropwise to the PAN / DMF solution of step (1), then add the weighed LLZTO powder, ultrasonicate for 3 h, and then magnetically stir for 24 h to obtain a PAN-LLZTO / DMF solution.

[0059] (3) 5 mL of the prepared PAN-LLZTO / DMF solution was extracted and spun into a PAN-LLZTO composite fiber membrane using an electrospinning device. The electrospinning process parameters were set as follows: spinning voltage was 12 kV; the distance between the needle and the receiving roller was 16 cm; the solution propulsion speed was 0.9 mL / h; the roller speed was 370 rpm; and the electrospinning time was 5 h.

[0060] (4) The spun PAN-LLZTO composite fiber membrane was placed in a vacuum drying oven at 60°C for 24 hours to evaporate the solvent, and then rolled by a roller machine to make the surface smoother. Finally, it was cut into discs with a diameter of 16 mm and rectangular membranes with a length of 5 cm and a width of 4 cm and placed in a glove box for later use.

[0061] (5) Weigh 0.38 g of LiFSI (2.0 mmol) and 1 g of PyR 13 FSI (3.2 mmol) was mixed to form an ionic liquid electrolyte.

[0062] (6) Weigh 1.38 g of PDADMAFSI, add the ionic liquid electrolyte prepared in step (5) so that the mass ratio of PDADMAFSI to the ionic liquid electrolyte is 1:1, and add 3 g of anhydrous acetonitrile. Stir magnetically for 24 h to obtain a uniformly mixed polyionic liquid electrolyte solution.

[0063] (7) The PAN-LLZTO composite fiber membrane disc and rectangular membrane obtained in step (4) are immersed in the polyionic liquid electrolyte solution obtained in step (6). After complete immersion (about 1 min), they are taken out and placed on a glass plate to evaporate the solvent. After standing for 24 h, they are moved to a vacuum drying oven and dried at 60 ° C for 48 h to obtain a polyionic liquid-based solid electrolyte, which is recorded as PPL-PLF.

[0064] Figure 1 a and b in the figure are respectively the plane scanning electron microscope image of the PAN-LLZTO composite fiber membrane obtained in step (4) of this embodiment and the X-ray diffraction (XRD) spectrum of the PAN-LLZTO composite fiber membrane and LLZTO. It can be seen from the figure that the fibers are interlaced to form a three-dimensional network skeleton. The XRD spectrum proves that the crystal structure of the LLZTO particles in the fiber membrane is in a cubic phase and no other impurity peaks appear.

[0065] Figure 2 a and b are respectively the planar scanning electron micrograph and cross-sectional scanning electron micrograph of the PPL-PLF solid electrolyte prepared in this embodiment. It can be seen from the figure that the surface of the electrolyte membrane is relatively flat, and the fiber structure can be clearly seen. The thickness of the PPL-PLF solid electrolyte is only about 40 microns. The thin electrolyte helps to reduce the volume and mass of the battery and improve the energy density.

[0066] Comparative Example 1

[0067] The difference between this comparative example and Example 1 is that this comparative example does not include the preparation of the PAN-LLZTO composite fiber membrane, and the specific preparation process is as follows:

[0068] (1) Weigh 0.38 g of LiFSI (2.0 mmol) and 1 g of PyR 13 FSI (3.2 mmol) was mixed to form an ionic liquid electrolyte.

[0069] (2) Weigh 1.38 g of PDADMAFSI, add the ionic liquid electrolyte prepared in step (1), and add 3 g of anhydrous acetonitrile, and stir magnetically for 24 h to obtain a uniformly mixed polyionic liquid electrolyte solution.

[0070] (3) The polyionic liquid electrolyte solution obtained in step (2) was poured into a PTFE mold, allowed to stand for 24 hours, and then moved to a vacuum drying oven and dried at 60° C. for 48 hours to obtain a polyionic liquid-based solid electrolyte (denoted as PPL) having a thickness of about 40 μm.

[0071] Comparative Example 2

[0072] The difference between this comparative example and Example 1 is that in step (6) of this comparative example, PDADMAFSI is replaced by polyethylene oxide (PEO), and the finally obtained solid electrolyte is recorded as PEOPL-PLF.

[0073] Comparative Example 3

[0074] Compared with Example 1, the difference between this comparative example and Example 1 is that 1-methyl-1-propylpiperidinium bis(trifluoromethylsulfonyl)imide salt (PP13TFSI) is used to replace PyR 13 In this comparative example, the mass of LiFSI is 0.38 g, the mass of PP13TFSI is 1 g, and the remaining steps are the same as those in Example 1.

[0075] Comparative Example 4

[0076] The difference between this comparative example and Example 1 is that in this comparative example, 0.38 g of LiFSI in step (5) is replaced by 0.38 g of lithium bis(trifluorosulfonyl)imide (LiTFSI), and the remaining steps are the same as those in Example 1.

[0077] Comparative Example 5

[0078] The difference between this comparative example and Example 1 is that in this comparative example, the mass of PDADMAFSI in step (6) is adjusted to 0.92 g, so that the mass ratio of PDADMAFSI to the ionic liquid electrolyte is 4:6, and the obtained solid electrolyte is recorded as PPL-PLF (4:6).

[0079] Test example

[0080] Assembly of symmetrical batteries: Place two lithium sheets with a diameter of 10 mm symmetrically on both sides of a solid electrolyte with a diameter of 16 mm, and place them in a 2032-type battery shell in the order of gasket, lithium sheet, solid electrolyte, lithium sheet, gasket, and shrapnel, and finally seal it using a battery packaging machine.

[0081] Assembly of button batteries: A lithium sheet with a diameter of 10 mm is used as the negative electrode, a solid electrolyte with a diameter of 16 mm is used as the electrolyte, and a lithium iron phosphate electrode with a diameter of 10 mm is used as the positive electrode. The 1 mm thick gasket, negative electrode, electrolyte, positive electrode, gasket, and spring are placed in order from bottom to top, and then packaged in a 2023 type battery shell by a battery packaging machine.

[0082] Assembly of soft-pack batteries: The dimensions of the negative lithium electrode sheet and the positive lithium iron phosphate electrode sheet are both 4 cm long and 3 cm wide. The negative electrode and the positive electrode are then placed on both sides of a rectangular electrolyte membrane that is 5 cm long and 4 cm wide, respectively, packaged in an aluminum-plastic bag, and sealed with a vacuum packaging machine.

[0083] 1. Solid electrolyte performance test:

[0084] (1) Mechanical properties measurement:

[0085] The solid electrolytes prepared in Example 1, Comparative Example 1 and Comparative Example 5 were subjected to tensile tests. The test results are as follows: Figure 3 As shown in the figure, it can be seen that the tensile strength of the solid electrolyte of Example 1 can reach 2.92 MPa, and the elongation at break can reach 170%, while the tensile strength of the solid electrolyte of Comparative Example 5 is slightly weaker, which is 2.01 MPa, and the elongation at break is 117%, indicating that LiFSI and PyR 13 Too high FSI content will cause the mechanical strength of the electrolyte to decrease, while the PPL solid electrolyte of Comparative Example 1 is only 0.68 MPa, and the elongation at break is only 10%; this shows that the LLZTO-PAN composite fiber membrane significantly improves the mechanical properties of the solid electrolyte, and the high mechanical strength is beneficial to resisting lithium dendrite piercing, thereby improving the safety and cycle life of the battery.

[0086] (2) Electrochemical stability window determination:

[0087] Figure 4 By comparing the electrochemical stability windows of the PPL-PLF solid electrolyte of Example 1 and the PPL solid electrolyte of Comparative Example 1, it can be seen that the PPL-PLF solid electrolyte of Example 1 has a wider electrochemical stability window, which can reach 5.2 V.

[0088] (3) Determination of ionic conductivity and lithium ion transference number:

[0089] Figure 5 The Arrhenius curves of the PPL-PLF solid electrolyte of Example 1 and the PPL solid electrolyte of Comparative Example 1 are shown. It can be seen from the figure that the ionic conductivity of the PPL solid electrolyte of Comparative Example 1 at room temperature is only 1.9×10 -4 S cm -1 , it can rise to 4.6×10 at 70℃ -4 S cm -1 In comparison, the ionic conductivity of PPL-PLF can be increased by 2 times, reaching 5×10 -4 S cm -1 , at 70℃ it can reach 1×10 -3 S cm -1 .

[0090] Figure 6The lithium ion migration numbers of the PPL-PLF solid electrolyte of Example 1 and the PPL solid electrolyte of Comparative Example 1 are shown. a is the time-current curve measured by the chronoamperometry of the symmetrical battery assembled using the PPL-PLF solid electrolyte, b is the impedance of the symmetrical battery assembled using the PPL-PLF solid electrolyte before and after the test, c is the time-current curve measured by the chronoamperometry of the symmetrical battery assembled using the PPL solid electrolyte, and d is the impedance of the symmetrical battery assembled using the PPL solid electrolyte before and after the test. From the data obtained in the figure, it can be concluded that the lithium ion migration number of the PPL electrolyte is 0.58, while the lithium ion migration number of the PPL-PLF using the three-dimensional network skeleton can be increased to 0.62.

[0091] The above measurements proved that the LLZTO-PAN three-dimensional network skeleton is beneficial to increase the lithium ion transmission channels inside the electrolyte.

[0092] (4) Impedance value determination:

[0093] The impedance values ​​of the PPL-PLF solid electrolyte of Example 1 and the solid electrolyte of Comparative Example 3 were measured. The results are as follows: Figure 7 As shown in the figure, it can be seen that the body resistance of the solid electrolyte of Comparative Example 3 is about twice that of the PPL-PLF solid electrolyte of Example 1, which indicates that PYR 13 Compared with PP13TFSI, FSI plays a better plasticizing role in the polyionic liquid matrix and is more helpful in improving the ionic conductivity of the electrolyte.

[0094] (5) Flexibility and flame retardancy test:

[0095] Figure 8 This is a bending experiment of the PPL-PLF solid electrolyte of Example 1. It can be seen that the solid electrolyte does not break or crack after being bent and unfolded, indicating that it has good flexibility. Fig. 9 This is a flame retardant experiment of the PPL-PLF solid electrolyte of Example 1. It can be seen that the PPL-PLF is not ignited during direct contact with the flame, and its morphology does not change significantly, indicating that it has excellent flame retardancy.

[0096] 2. Battery performance test:

[0097] (1) Evaluation of electrolyte interfacial stability:

[0098] Fig.10 The symmetrical battery assembled with the PPL-PLF solid electrolyte of Example 1 is 0.2 mA / cm 2 From the cyclic voltage curve at a current density of , it can be seen that its polarization voltage remains stable during the cycle process of more than 2500 hours, and the value is only 30 mV. Fig.11The symmetrical battery assembled with the PPL solid electrolyte of Example 1 at 0.2 mA cm -2 From the cyclic voltage curve under a current density of , it can be seen that the polarization voltage gradually increases during the cycle, the interface stability of the surface gradually deteriorates with the cycle, and due to insufficient mechanical strength, a short circuit occurs after 120 hours of cycling. Fig.12 The symmetrical battery of the PEOPL-PL solid electrolyte of Comparative Example 2 at 0.2 mA cm -2 It can be seen from the long cycle at a current density of 1.5 , that an obvious short circuit phenomenon occurs after 83 hours of cycling, and the polarization voltage before short circuit is about 100 mV, which is more than three times the polarization voltage of the symmetrical battery assembled with the PPL-PLF solid electrolyte in Example 1. It can be seen that the symmetrical battery based on polyionic liquid has a lower polarization voltage and a significantly longer cycle life than the symmetrical battery based on PEO.

[0099] (2) Lithium deposition phenomenon:

[0100] The symmetrical cell assembled with the PPL-PLF solid electrolyte of Example 1 and the solid electrolyte of Comparative Example 4 was tested at 0.1 mA cm -2 After cycling for 200 hours at a current density of , the lithium sheet was disassembled and the surface morphology of the obtained lithium sheet was as follows Fig.13 As shown, it can be seen that the surface of the lithium negative electrode ( Fig.13 b) in the figure is flatter and smoother, which is mainly because LiFSI is easier to form an interfacial phase rich in LiF and Li3N on the surface of the lithium negative electrode than LiTFSI, thereby achieving uniform lithium flux and promoting lithium deposition.

[0101] (3) Cyclic performance test:

[0102] The full battery (i.e., the button battery) assembled with the PPL-PLF solid electrolyte of Example 1 and the PPL solid electrolyte of Comparative Example 1 was subjected to cycle performance tests respectively, with the charge and discharge voltage range of 2.8-4V, the temperature of 30°C, and the current density of 1C (170mA / g), and then constant rate charge and discharge were performed to evaluate the discharge capacity retention rate and coulombic efficiency during the cycle. The results are as follows: Fig.14 and Fig.15 As shown, from Fig.14 It can be seen that the full battery using the PPL-PLF solid electrolyte of Example 1 can be stably cycled for 200 cycles, while the full battery using the PPL solid electrolyte of Comparative Example 1 has a significant capacity decay after 60 cycles and fails quickly.

[0103] (4) Safety testing:

[0104] Fig.16This is a safety (lighting) test photo of a soft-pack battery assembled with the PPL-PLF solid electrolyte of Example 1. Fig.16 It can be seen that the soft-pack battery can still work normally when folded, bent, or sheared, indicating that it has excellent safety.

[0105] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a polyionic liquid-based solid electrolyte, characterized in that: The steps include: Dispersing LLZTO nanoparticles in a polyacrylonitrile solution to obtain a spinning solution; electrospinning the spinning solution to obtain a composite fiber membrane; Mixing poly(diallyldimethylammonium)bis(fluorosulfonyl)imide, lithium bis(fluorosulfonyl)imide and 1-methyl-1-propylpyrrolidinium bis(fluorosulfonyl)imide in a solvent to obtain a polyionic liquid electrolyte solution; wherein the ratio of the mass of poly(diallyldimethylammonium)bis(fluorosulfonyl)imide to the total mass of lithium bis(fluorosulfonyl)imide and 1-methyl-1-propylpyrrolidinium bis(fluorosulfonyl)imide is 1:(0.9-1.1); The composite fiber membrane is immersed in the polyionic liquid electrolyte solution, taken out, left to stand, and dried to obtain the composite fiber membrane; The mass ratio of the LLZTO nanoparticles to polyacrylonitrile is 1: (8-12); The molar ratio of the lithium bis(fluorosulfonyl)imide to 1-methyl-1-propylpyrrolidinium bis(fluorosulfonyl)imide is 1:(1-2); In the polyionic liquid electrolyte solution, the mass ratio of poly(diallyldimethylammonium)bis(fluorosulfonyl)imide to the solvent is 1:(2-3).

2. The preparation method according to claim 1, characterized in that The concentration of the polyacrylonitrile solution is 8-15wt%, and the solvent of the polyacrylonitrile solution is selected from one or more of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide or sulfolane.

3. The preparation method according to claim 1, characterized in that: The thickness of the composite fiber membrane is 30-70 μm.

4. The preparation method according to claim 1, characterized in that: After the composite fiber membrane is obtained by electrostatic spinning, the method further includes the steps of drying and rolling the obtained composite fiber membrane.

5. The preparation method according to claim 1, characterized in that: In the step of mixing in a solvent, the solvent is selected from one or more of acetonitrile, tetrahydrofuran or propylene carbonate, and the stirring and mixing time is 5 to 30 hours.

6. The preparation method according to claim 1, characterized in that: The immersion time of the composite fiber membrane in the polyionic liquid electrolyte solution is 30-90 seconds; the standing time is 10-30 hours; and the drying temperature is 50-80°C.

7. A polyionic liquid-based solid electrolyte prepared by the preparation method according to any one of claims 1 to 6.

8. A lithium ion battery comprising a positive electrode, a negative electrode and a solid electrolyte, characterized in that: The solid electrolyte is the polyionic liquid-based solid electrolyte according to claim 7.

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