PVDF-LLZTO electrostatic spinning solution, and preparation method and application of solid electrolyte membrane

Abstract

The invention provides an electrostatic spinning solution which is prepared from the following raw materials: LLZTO modified by a silane coupling agent MEMO, PVDF-HFP and a solvent, the mass ratio of the silane coupling agent MEMO modified LLZTO to the PVDF-HFP is (15 to 20): 100. The invention also provides a preparation method of the solid-state electrolyte membrane, the PVDF-HFP matrix and the LLZTO filler in the prepared composite solid-state electrolyte membrane are uniformly dispersed by optimizing a formula of an electrostatic spinning solution, improving a lithium salt introduction mode and adopting a step-by-step drying process and a double-layer glass sheet capping process, so that a continuous and efficient ion transmission channel is formed; meanwhile, the lithium salt is uniformly distributed in the electrolyte membrane, so that the ionic conductivity is remarkably improved, the electrolyte membrane has relatively high compactness and stability and is in good interface contact with an electrode material, the charge-discharge performance of the battery is effectively improved, the cycle life of the battery is effectively prolonged, and powerful support is provided for development of a high-performance solid-state battery.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of LLZTO electrolyte modification, and relates to an electrostatic spinning liquid, a preparation method and application of a solid electrolyte membrane, in particular to an PVDF-LLZTO electrostatic spinning liquid, a preparation method and application of a solid electrolyte membrane. BACKGROUND

[0002] As a key component of solid-state batteries, the performance of solid-state electrolytes is directly related to the safety, energy density and cycle life of the batteries. With the development of the new energy field, the demand for high-performance solid-state electrolytes is increasingly urgent. The commonly used solid-state electrolyte preparation methods include physical mixing, in-situ polymerization, etc.

[0003] Among them, the physical mixing method is to simply mix the solid-state electrolyte powder with the polymer matrix and press into a film, but this method is difficult to achieve uniform dispersion of each component at the microscale, resulting in limited ion transport. The in-situ polymerization method is to form a polymer matrix by initiating the polymerization reaction of monomers in the electrolyte, which can improve the component dispersion to some extent, but the method requires high control of reaction conditions, and there are problems such as incomplete polymerization. With further research, the existing research scheme also discloses a method for preparing a composite solid-state electrolyte by electrospinning, the main steps of which are to prepare a spinning liquid containing PVDF and ceramic particles, to spin the spinning liquid into a film by electrospinning technology, and then to soak the spinning film in a lithium salt solution and obtain a composite solid-state electrolyte after drying. However, this method still has problems such as unstable solution and fiber breakage, and the performance of the electrolyte membrane is low, and the compactness and stability are poor.

[0004] Therefore, how to find a more suitable preparation method to overcome the above-mentioned defects in the preparation of solid-state electrolytes has become one of the focuses of many front-line researchers in the industry. SUMMARY

[0005] Therefore, the technical problem to be solved by the present application is to provide an electrostatic spinning liquid, a preparation method and application of a solid electrolyte membrane, in particular a preparation method of a solid electrolyte membrane. The present application successfully solves the problems of uneven component dispersion, low ionic conductivity, poor interface contact with the electrode, etc. in the existing solid-state electrolyte preparation method by optimizing the electrostatic spinning liquid formula, improving the lithium salt introduction method, adopting a step-by-step drying process and a double-layer glass sheet pressing process. The preparation method is simple, mild, controllable and easy to operate, and is more suitable for industrialization and application.

[0006] The application provides electrospinning liquid, which comprises, in terms of raw materials, silane coupling agent MEMO modified LLZTO, PVDF-HFP and solvent; the mass ratio of the silane coupling agent MEMO modified LLZTO and the PVDF-HFP is (15-20):100.

[0007] Preferably, the silane coupling agent MEMO is specifically 3-methacryloyloxypropyl trimethoxysilane;

[0008] The particle size of the LLZTO is 300-400 nm;

[0009] The surface of the silane coupling agent MEMO modified LLZTO has hydroxyl groups.

[0010] Preferably, the solvent comprises DMAC and acetone;

[0011] In the electrospinning liquid, the silane coupling agent MEMO modified LLZTO and the PVDF-HFP are connected by chemical bonds;

[0012] In the electrospinning liquid, the PVDF-HFP is a matrix, and the silane coupling agent MEMO modified LLZTO is a filler;

[0013] The mass concentration of the electrospinning liquid is 16%-20%.

[0014] Preferably, the preparation process of the electrospinning liquid comprises the following steps:

[0015] (1) mixing the silane coupling agent MEMO, the solvent and the pH value adjusting agent to obtain a mixed solution, then adding LLZTO powder, and stirring and reacting to obtain the silane coupling agent MEMO modified LLZTO;

[0016] The pH value of the mixed solution is 3.5-5;

[0017] The stirring and reaction comprises normal-temperature stirring and reaction and heating stirring and reaction;

[0018] The time of the normal-temperature stirring and reaction is 2-3 h;

[0019] The temperature of the heating stirring and reaction is 65-70 DEG C;

[0020] The time of the heating stirring and reaction is 6-8 h;

[0021] (2) mixing the PVDF-HFP and the solvent, adding the silane coupling agent MEMO modified LLZTO obtained in the above step, and then stirring and mixing after ultrasonic treatment to obtain the electrospinning liquid;

[0022] The time of the ultrasonic treatment is 20-30 min.

[0023] The stirring mixing time is 11-14h.

[0024] The application provides a preparation method of a solid electrolyte membrane, comprising the following steps:

[0025] 1) After electrospinning the electrospinning solution, a first drying is performed to obtain an electrospinning fiber membrane;

[0026] The electrospinning solution is the electrospinning solution in any one of the above technical solutions;

[0027] 2) The fiber membrane obtained in the above step is placed on a substrate, then a lithium salt solution is poured on the fiber membrane, the fiber membrane on which the lithium salt solution is poured is subjected to uniform coating, then the fiber membrane is covered with a substrate again and placed in a drying device, after a second drying and a third drying, a solid electrolyte membrane is obtained.

[0028] Preferably, the spinning voltage of the electrospinning is 15-20KV;

[0029] The electrospinning solution injection speed of the electrospinning is 0.5-0.8mL / min;

[0030] The first drying is performed by vacuum drying;

[0031] The first drying temperature is 65-70℃;

[0032] The first drying time is 12-15h.

[0033] Preferably, the lithium salt solution specifically comprises a mixed solution of lithium salt, succinonitrile, PVDF-HFP and solvent;

[0034] The mass concentration of the lithium salt solution is 4.5%-5%;

[0035] The amount of the lithium salt solution is 0.02-0.03g / cm 2 .

[0036] Preferably, the second drying is performed by vacuum drying;

[0037] The second drying temperature is 25-35℃;

[0038] The second drying time is 7-10h.

[0039] Preferably, the third drying is performed by vacuum drying;

[0040] The third drying temperature is 50-60℃;

[0041] The third drying time is 36-48 hours.

[0042] The application provides application of the electrospinning liquid or the solid electrolyte membrane prepared by the preparation method in a solid-state battery.

[0043] The application provides an electrospinning liquid, which comprises, in terms of raw materials, silane coupling agent MEMO modified LLZTO, PVDF-HFP and a solvent, and the mass ratio of the silane coupling agent MEMO modified LLZTO and the PVDF-HFP is (15-20):100. Compared with the prior art, although the electrospinning preparation of a composite solid electrolyte is an effective technical direction, there are still some aspects that need to be improved. According to the research of the application, in the prior art, firstly, the adaptability of the solvent and the solute is not fully considered in the electrospinning liquid formula, which leads to problems such as unstable solution and fiber fracture in the electrospinning process; secondly, after the lithium salt solution is soaked, the lithium salt is unevenly distributed in the electrospinning film, which affects the performance of the electrolyte film; and thirdly, the drying process is single, and it is difficult to effectively remove the solvent, so that residual solvent and pores are easily left in the electrolyte film, which reduces the compactness and stability of the electrolyte film.

[0044] In particular, the spinning solution formulation is unreasonable, due to the unreasonable spinning solution formulation, the interaction between the solvent and the solute is not coordinated, and problems such as unstable jetting and irregular fiber morphology are prone to occur in the spinning process, thereby causing uneven dispersion of the PVDF-HFP (polyvinylidene fluoride-hexafluoropropylene) matrix and the LLZTO (lithium lanthanum zirconium tantalum oxide) filler in the spinning film, forming discontinuous ion transmission channels, and reducing the ionic conductivity. For example, when the solvent evaporation rate is too fast or too slow, the forming quality of the fiber is affected, and the filler is aggregated in the matrix, hindering ion migration. At the same time, the fiber membrane is not properly post-processed, after the spinning film is immersed in a lithium salt solution, the lithium salt diffuses unevenly in the spinning film, especially in the interior and the interface of the fiber, the distribution of the lithium salt is obviously different, causing uneven distribution of ion concentration in the electrolyte membrane, affecting the transmission efficiency and stability of lithium ions, causing the polarization of the battery to increase during charging and discharging, and the cycle performance to deteriorate. Further, a single drying process cannot effectively remove the solvent in the spinning film, and the residual solvent occupies the space in the electrolyte membrane, forming pores and reducing the compactness of the electrolyte membrane. At the same time, in the subsequent use process, the residual solvent may react with other substances to produce gas, further damaging the structure of the electrolyte membrane, causing poor interface contact and high interface resistance. In addition, when using the solution casting method, the electrolyte solution is dried in the mold, and uneven evaporation of the solvent can cause ripples or uneven thickness on the surface of the film. In the preparation process, the existing technology usually does not use an effective surface restraint mechanism to ensure the flatness of the electrolyte membrane. For example, some methods only rely on natural drying or simple hot pressing after pouring the electrolyte solution, causing wrinkles or irregular undulations on the surface of the film. This lack of restraint in the preparation method causes uneven contact between the electrolyte membrane and the electrode material in the subsequent use, affecting the overall performance of the battery.

[0045] Based on this, the present application particularly designs an electrospinning solution with a specific component and ratio, introduces MEMO (silane coupling agent) small molecules into LLZTO (lithium lanthanum zirconium tantalum oxide), and modifies the surface of LLZTO, so that the surface of LLZTO molecules carries chemical bonds (-OH) that can be grafted with PVDF-HFP (polyvinylidene fluoride-hexafluoropropylene), thereby significantly enhancing the interaction between PVDF-HFP (polyvinylidene fluoride-hexafluoropropylene) and LLZTO (lithium lanthanum zirconium tantalum oxide), reducing the phenomenon of uneven deposition in the spinning process, ensuring the stability of the spinning process, and uniformly dispersing the PVDF-HFP (polyvinylidene fluoride-hexafluoropropylene) matrix and the LLZTO@MEMO (lithium lanthanum zirconium tantalum oxide@silane coupling agent) filler in the spinning film, forming continuous and efficient ion transmission channels, and improving the ionic conductivity.

[0046] The application also provides a preparation method of the solid electrolyte membrane, which adopts optimized electrostatic spinning parameters, in particular, an innovative design of post-treatment of the fiber membrane, (1) improving the lithium salt introduction method, adopting a process of coating and then uniformly coating to make the lithium salt solution uniformly distributed on the fiber membrane, and then through a step-by-step drying process, the uniform dispersion of the lithium salt in the electrolyte membrane is ensured, the lithium ion transmission efficiency and stability are improved, and the charge-discharge performance of the battery is improved, (2) optimizing the drying process, controlling the drying temperature and time in stages, effectively removing the solvent, reducing the pores in the electrolyte membrane, improving the compactness and stability of the electrolyte membrane, reducing the interface resistance with the electrode material, and enhancing the overall performance of the battery, and (3) improving the surface flatness, the electrolyte membrane is designed with a double glass sheet sandwich, and the flat and rigid characteristics of the glass sheet are used to apply uniform constraint force on the upper casting liquid and the fiber membrane, so that the prepared electrolyte membrane has good surface flatness.

[0047] The application successfully solves the problems of uneven composition dispersion, low ion conductivity, poor electrode interface contact and the like in the existing solid electrolyte preparation method by optimizing the electrostatic spinning liquid formula, improving the lithium salt introduction method, adopting a step-by-step drying process and a double-layer glass sheet pressing process. The prepared composite solid electrolyte thin film has uniform dispersion of the PVDF-HFP (polyvinylidene fluoride-hexafluoropropylene) matrix and the LLZTO (lithium lanthanum zirconium tantalum oxide) filler, forms a continuous and efficient ion transmission channel, and the lithium salt is uniformly distributed therein, which significantly improves the ion conductivity. The solid electrolyte membrane prepared by the method provided by the application has an ion conductivity of 1.39*10 -3 S / cm In addition, the step-by-step drying process effectively removes the solvent, so that the electrolyte membrane has high compactness and stability, has good interface contact with the electrode material, the interface resistance is reduced to 19.7Ω, and the charge-discharge performance and cycle life of the battery are effectively improved, which provides strong support for the development of high-performance solid-state batteries. BRIEF DESCRIPTION OF DRAWINGS

[0048] Figure 1 The preparation process flowchart of the solid electrolyte membrane provided by the application is shown in the figure;

[0049] Figure 2 The SEM scanning electron microscope images of the pure PVDF-HFP, the MEMO@LLZTO doped and the spinning fiber membrane prepared in Example 1 in the application are shown in the figure;

[0050] Figure 3 The impedance spectrograms of the PVDF-HFP, the PVDF-HFP / LLZTO and the PVDF-HFP / MEMO@LLZTO three kinds of electrolyte membranes in the application are shown in the figure;

[0051] Figure 4Rate performance of the PVDF-HFP / MEMO@LLZTO composite electrolyte film prepared for the embodiment 1 of the present application;

[0052] Figure 5 Electrochemical window of the PVDF-HFP / MEMO@LLZTO composite electrolyte film prepared for the embodiment 1 of the present application;

[0053] Figure 6 Cycle performance chart of the PVDF-HFP / MEMO@LLZTO composite electrolyte film prepared for the embodiment 1 of the present application;

[0054] Figure 7 Schematic diagram of the composition structure of the solid-state battery for testing the electrolyte film of the present application. DETAILED DESCRIPTION

[0055] In order to further understand the present application, the preferred embodiments of the present application are described below in combination with the embodiments, but it should be understood that these descriptions are only for further illustrating the features and advantages of the present application, and are not limitations to the claims of the present application.

[0056] All raw materials of the present application are not particularly limited in source, and can be purchased on the market or prepared according to the conventional methods well known to those skilled in the art.

[0057] All raw materials of the present application are not particularly limited in purity, and the analytical pure or the conventional purity used in the field of solid-state electrolyte film preparation is preferred in the present application.

[0058] In the description of the present application, PVDF-HFP (polyvinylidene fluoride-hexafluoropropylene) is abbreviated or written as PVDF.

[0059] The present application provides a electrospinning liquid, which comprises, by raw material: silane coupling agent MEMO modified LLZTO, PVDF-HFP and solvent.

[0060] The mass ratio of the silane coupling agent MEMO modified LLZTO and PVDF-HFP is (15-20):100.

[0061] In the present application, the mass ratio of the silane coupling agent MEMO modified LLZTO and PVDF-HFP is (15-20):100, which can be (17-20):100, can be (19-20):100, and specifically can be 20:100.

[0062] In the present application, the silane coupling agent MEMO is specifically preferably 3-methacryloyloxypropyltrimethoxysilane.

[0063] In the present application, the particle size of the LLZTO is preferably 300-400 nm, more preferably 320-380 nm, and more preferably 340-360 nm.

[0064] In the present application, the surface of the LLZTO modified by the silane coupling agent MEMO preferably has hydroxyl groups.

[0065] In the present application, the solvent preferably includes DMAC and acetone.

[0066] In the present application, in the electrospinning solution, the LLZTO modified by the silane coupling agent MEMO is preferably chemically bonded to the PVDF-HFP.

[0067] In the present application, in the electrospinning solution, the PVDF-HFP is preferably a matrix, and the LLZTO modified by the silane coupling agent MEMO is preferably a filler.

[0068] In the present application, the mass concentration of the electrospinning solution is preferably 16%-20%, more preferably 16.5%-19.5%, and more preferably 17%-19%, and specifically can be 18%.

[0069] In the present application, the preparation process of the electrospinning solution preferably includes the following steps:

[0070] (1) mixing the silane coupling agent MEMO, the solvent, and the pH value adjusting agent to obtain a mixed solution, then adding LLZTO powder, and stirring and reacting to obtain the LLZTO modified by the silane coupling agent MEMO;

[0071] (2) mixing the PVDF-HFP and the solvent, adding the LLZTO modified by the silane coupling agent MEMO obtained in the above step, and stirring and mixing after ultrasonic treatment to obtain the electrospinning solution.

[0072] In the present application, the silane coupling agent MEMO, the solvent, and the pH value adjusting agent are first mixed to obtain a mixed solution, then LLZTO powder is added, and stirring and reaction are performed to obtain the LLZTO modified by the silane coupling agent MEMO.

[0073] In the present application, the silane coupling agent MEMO is specifically 3-methacryloyloxypropyltrimethoxysilane MEMO organosilane coupling agent, i.e. MEMO 3-methacryloyloxypropyltrimethoxysilane.

[0074] In the present application, the pH value of the mixed solution is preferably 3.5-5, more preferably 3.8-4.7, and more preferably 4.1-4.4.

[0075] In the present application, the stirring reaction preferably comprises a normal temperature stirring reaction and a heated stirring reaction. Specifically, the normal temperature can be 15-40 DEG C, or 20-35 DEG C, or 25-30 DEG C.

[0076] In the present application, the time of the normal temperature stirring reaction is preferably 2-3h, more preferably 2.2-2.8h, more preferably 2.4-2.6h.

[0077] In the present application, the temperature of the heated stirring reaction is preferably 65-70 DEG C, more preferably 66-69 DEG C, more preferably 67-68 DEG C.

[0078] In the present application, the time of the heated stirring reaction is preferably 6-8h, more preferably 6.2-7.8h, more preferably 6.5-7.5h, more preferably 6.7-7.3h.

[0079] The present application then mixes PVDF-HFP and solvent, adds the silane coupling agent MEMO modified LLZTO obtained in the above step, and after ultrasonic treatment, is stirred and mixed to obtain an electrospinning solution.

[0080] In the present application, the time of the ultrasonic treatment is preferably 20-30min, more preferably 24-30min, more preferably 28-30min, and specifically can be 30min.

[0081] In the present application, the time of the stirring and mixing is preferably 11-14h, more preferably 11.5-13.5h, more preferably 12-13h, and specifically can be 12h.

[0082] The present application provides a preparation method of a solid-state electrolyte membrane, comprising the following steps:

[0083] 1) After electrospinning the electrospinning solution, a first drying is performed to obtain an electrospinning fiber membrane;

[0084] The electrospinning solution is the electrospinning solution of any one of the above technical solutions.

[0085] 2) The fiber membrane obtained in the above step is placed on a substrate, a lithium salt solution is poured on the fiber membrane, the fiber membrane on which the lithium salt solution is poured is subjected to uniform coating, then the fiber membrane is covered with a substrate and placed in a drying device, and after a second drying and a third drying, a solid-state electrolyte membrane is obtained.

[0086] The present application first electrospins the electrospinning solution, and after a first drying, an electrospinning fiber membrane is obtained;

[0087] The electrospinning solution is the electrospinning solution of any one of the above technical solutions.

[0088] In the present application, the spinning voltage of the electrospinning is preferably 15-20KV, more preferably 15-19KV, more preferably 15-17KV, and specifically can be 15KV.

[0089] In the present application, the electrospinning liquid injection speed of the electrospinning is preferably 0.5-0.8mL / min, more preferably 0.5-0.7mL / min, more preferably 0.5-0.6mL / min, and specifically can be 0.5ml / min.

[0090] In the present application, the mode of the first drying is preferably vacuum drying.

[0091] In the present application, the temperature of the first drying is preferably 65-70℃, more preferably 67-70℃, more preferably 69-70℃, and specifically can be 70℃.

[0092] In the present application, the time of the first drying is preferably 12-15h, more preferably 12-14h, more preferably 12-13h, and specifically can be 12h.

[0093] The present application further places the fiber membrane obtained in the above steps on a substrate, then pours a lithium salt solution on the fiber membrane, uniformly coats the fiber membrane on which the lithium salt solution is poured, then covers the fiber membrane with a substrate and places it in a drying device, and after the second drying and the third drying, a solid-state electrolyte membrane is obtained.

[0094] In the present application, the lithium salt solution specifically preferably comprises a mixed solution of lithium salt, butanedinitrile, PVDF-HFP and solvent.

[0095] In the present application, the mass concentration of the lithium salt solution is preferably 4.5%-5%, more preferably 4.6%-4.9%, more preferably 4.7%-4.8%.

[0096] In the present application, the amount of the lithium salt solution is preferably 0.02-0.03g / cm 2 , more preferably 0.022-0.028g / cm 2 , and more preferably 0.024-0.026g / cm 2 .

[0097] In the present application, the mode of the second drying is preferably vacuum drying.

[0098] In the present application, the temperature of the second drying is preferably 25-35℃, more preferably 27-33℃, more preferably 29-31℃, and specifically can be 30℃.

[0099] In the present application, the time of the second drying is preferably 7-10h, more preferably 7-9h, more preferably 7-8h, and specifically can be 7h.

[0100] In the present application, the mode of the third drying is preferably vacuum drying.

[0101] In the present application, the temperature of the third drying is preferably 50-60℃, more preferably 50-56℃, more preferably 50-52℃, and specifically can be 50℃.

[0102] In the present application, the time of the third drying is preferably 36-48h, more preferably 36-43h, more preferably 36-38h, and specifically can be 36h.

[0103] The present application also provides the application of the electrospinning solution according to any one of the above technical solutions or the solid electrolyte membrane prepared by the preparation method according to any one of the above technical solutions in a solid-state battery.

[0104] The present application is a complete and detailed overall technical solution, which better guarantees the composition and properties of the electrospinning solution and further improves the electrical performance, compactness and stability of the solid electrolyte membrane. The above PVDF-LLZTO electrospinning solution, the preparation method of a solid electrolyte membrane and the application can specifically include the following contents:

[0105] Design and optimization of the formula of the electrospinning solution

[0106] (1) The electrospinning solution formula introduces a small molecule of MEMO (silane coupling agent) into LLZTO (lithium lanthanum zirconium tantalum oxide) for surface modification, so that the surface of the LLZTO molecules carries a chemical bond (-OH) that can be grafted with PVDF-HFP (polyvinylidene fluoride-hexafluoropropylene), thereby significantly enhancing the interaction between PVDF-HFP (polyvinylidene fluoride-hexafluoropropylene) and LLZTO (lithium lanthanum zirconium tantalum oxide), reducing the phenomenon of uneven deposition during the spinning process, ensuring the stability of the spinning process, and ensuring that the PVDF-HFP (polyvinylidene fluoride-hexafluoropropylene) matrix and the LLZTO@MEMO (lithium lanthanum zirconium tantalum oxide@silane coupling agent) filler are uniformly dispersed in the prepared spinning film, forming a continuous and efficient ion transmission channel and improving the ion conductivity.

[0107] Experimental samples: anhydrous ethanol, deionized water, glacial acetic acid and a silane coupling agent MEMO to prepare a precursor solution, and LLZTO powder.

[0108] Experimental process and results:

[0109] First, the precursor solution is prepared, using a graduated cylinder to weigh ethanol, deionized water, MEMO, stirring evenly, then adding acetic acid to adjust the pH of the solution, the pH is controlled between 3.5-5. Then add LLZTO powder, temperature adjustment, magnetic stirring, then increase the temperature, magnetic stirring, the solution appears milk white, then use ethanol to wash and centrifuge three times, get white solid, finally dried in a vacuum drying oven, get white solid powder.

[0110] (2) Preparation of fiber membrane:

[0111] Prepare a certain mass fraction of electrospinning solution. Use an electronic balance to weigh PVDF, LLZTO powder, and use a graduated cylinder to measure DMAC and acetone. Add the PVDF powder to the mixed solvent of DMAC and acetone, stir at room temperature until it dissolves evenly, then add the LLZTO powder to the above solution, stir for a period of time, then ultrasonic, then stir at room temperature. Put the prepared solution into a syringe for electrospinning. The obtained fiber membrane is vacuum dried.

[0112] Post-processing of fiber membrane

[0113] (1) Introduction of lithium salt solution and uniform coating process: improve the introduction method of lithium salt, adopt the process of coating first and then uniform coating to make the lithium salt solution uniformly distributed on the fiber membrane, and then through the step-by-step drying process, ensure the uniform dispersion of lithium salt in the electrolyte membrane, improve the lithium ion transmission efficiency and stability, and improve the charge and discharge performance of the battery.

[0114] Specifically, first, use a coating machine for overall uniform coating, then use a uniform coating machine for fine uniform coating treatment using its centrifugal force, reduce local thickness difference, ensure uniform distribution of lithium salt solution on the spinning membrane, solve the problem of uneven distribution of lithium salt in the prior art, and improve the lithium ion transmission efficiency.

[0115] (2) Optimize the drying process, control the drying temperature and time in stages, effectively remove the solvent, reduce the pores in the electrolyte membrane, improve the compactness and stability of the electrolyte membrane, reduce the interface resistance with the electrode material, and enhance the overall performance of the battery.

[0116] Specifically, by first vacuum drying the spinning membrane at 70°C for 12h, then drying the spinning membrane with composite lithium salt solution at 30°C for 7h and 50°C for 36h in turn, the solvent is effectively removed, the pores in the electrolyte membrane are reduced, the compactness and stability of the membrane are improved, and the interface resistance with the electrode material is reduced.

[0117] (3) Improve the surface flatness, design the electrolyte membrane with double glass sheet sandwich, use the flat and rigid characteristics of the glass sheet to apply uniform restraint force to the upper layer of casting liquid and fiber membrane, ensure that the prepared electrolyte membrane has good surface flatness.

[0118] Specifically, the double-layer glass sheet capping process: the fiber membrane poured with lithium salt solution is placed between two glass sheets, and the uniform constraint force is applied to the fiber membrane by taking advantage of the flat and rigid characteristics of the glass sheet. Under the uniform coating and drying process conditions, the upper glass sheet transmits effective pressure to the lithium salt solution, promotes the lithium salt solution to fully penetrate into the fiber layer, and then makes the fiber membrane fully contact and tightly combine with the lithium salt solution, so as to ensure that the prepared electrolyte membrane has good surface flatness, and then improve the interface contact quality between the electrolyte membrane and the electrode material, and enhance the electrochemical performance of the solid-state battery.

[0119] Referring to Figure 1 , Figure 1 The preparation process flow diagram of the solid-state electrolyte membrane provided by the present application is shown in the figure.

[0120] The above content of the present application provides a PVDF-LLZTO electrostatic spinning liquid, a preparation method and application of a solid-state electrolyte membrane. The electrostatic spinning liquid with a specific component and ratio designed by the present application introduces MEMO (silane coupling agent) small molecules into LLZTO (lithium lanthanum zirconium tantalum oxide), and performs surface modification on the LLZTO molecules, so that the surface of the LLZTO molecules carries chemical bonds (-OH) that can be grafted with PVDF-HFP (polyvinylidene fluoride-hexafluoropropylene), thereby significantly enhancing the interaction between PVDF-HFP (polyvinylidene fluoride-hexafluoropropylene) and LLZTO (lithium lanthanum zirconium tantalum oxide), reducing the phenomenon of uneven deposition in the spinning process, ensuring the stability of the spinning process, and ensuring that the PVDF-HFP (polyvinylidene fluoride-hexafluoropropylene) matrix and the LLZTO@MEMO (lithium lanthanum zirconium tantalum oxide@silane coupling agent) filler in the prepared spinning membrane are uniformly dispersed, forming a continuous and efficient ion transmission channel, and improving the ionic conductivity.

[0121] The present application also provides a preparation method of a solid-state electrolyte membrane, which adopts optimized electrostatic spinning parameters, and particularly creatively designs the post-treatment of the fiber membrane, (1) improves the lithium salt introduction method, adopts the process of coating first and then uniform coating to make the lithium salt solution uniformly distributed on the fiber membrane, and then through a step-by-step drying process, ensures that the lithium salt is uniformly dispersed in the electrolyte membrane, improves the lithium ion transmission efficiency and stability, and improves the charge and discharge performance of the battery. (2) Optimize the drying process, control the drying temperature and time in stages, effectively remove the solvent, reduce the pores in the electrolyte membrane, improve the density and stability of the electrolyte membrane, reduce the interface resistance with the electrode material, and enhance the overall performance of the battery. (3) Improve the surface flatness, and design the electrolyte membrane with a double-glass sheet sandwich, and apply uniform constraint force to the upper casting liquid and the fiber membrane by taking advantage of the flat and rigid characteristics of the glass sheet, so as to ensure that the prepared electrolyte membrane has good surface flatness.

[0122] The present application successfully solves the problems of uneven composition dispersion, low ionic conductivity, poor electrode interface contact and the like in the existing solid-state electrolyte preparation method by optimizing the electrospinning liquid formula, improving the lithium salt introduction method, adopting a step-by-step drying process and a double-layer glass sheet capping process. The prepared composite solid-state electrolyte film has uniform dispersion of the PVDF-HFP (polyvinylidene fluoride-hexafluoropropylene) matrix and the LLZTO (lithium lanthanum zirconium tantalum oxide) filler, forming a continuous and efficient ion transmission channel, and the lithium salt is uniformly distributed therein, which significantly improves the ionic conductivity. The solid-state electrolyte film prepared by the method provided by the present application has an ionic conductivity of 1.39 x 10 -3 S / cm after electrochemical performance test. In addition, the step-by-step drying process effectively removes the solvent, so that the electrolyte film has high compactness and stability, good interface contact with the electrode material, and the interface resistance is reduced to 19.7Ω, effectively improving the charge-discharge performance and cycle life of the battery, and providing strong support for the development of high-performance solid-state batteries.

[0123] In order to further illustrate the present application, the electrospinning liquid, the preparation method and application of the solid-state electrolyte film provided by the present application are described in detail below in conjunction with the examples, but it should be understood that these examples are implemented on the premise of the technical scheme of the present application, and detailed implementation modes and specific operation processes are given, which are only for further illustrating the features and advantages of the present application, and are not a limitation on the claims of the present application, and the protection scope of the present application is not limited to the following examples.

[0124] Example 1

[0125] Experimental sample:

[0126] Anhydrous ethanol, deionized water, glacial acetic acid and silane coupling agent MEMO were used to prepare the precursor solution, and LLZTO powder was used.

[0127] Experimental process:

[0128] First, the precursor solution was prepared. 36 mL of ethanol, 2 mL of deionized water and 1 mL of MEMO were weighed using a graduated cylinder, and 1 mL of acetic acid was added after stirring to adjust the pH of the solution to 3.5-5.

[0129] Then, 1.5 g of LLZTO powder was added, the temperature was adjusted to 35℃, and magnetic stirring was performed for about 2 h, and then the temperature was adjusted to 70℃, and magnetic stirring was performed for 7 h. The solution was milky white, and then the white solid was obtained by washing and centrifuging three times with ethanol. Finally, the white solid powder was dried in a vacuum drying oven at 70℃ for 12 h.

[0130] Preparation of fiber film:

[0131] The electrospinning solution with a mass fraction of 18% was prepared. 0.55 g of PVDF, 0.11 g of LLZTO powder and 1 mL of DMAC and 2 mL of acetone were weighed and measured by using an electronic balance and a measuring cylinder respectively.

[0132] The PVDF powder was added into the mixed solvent of DMAC and acetone, and stirred at room temperature until uniformly dissolved, then the LLZTO powder was added into the above solution, and stirred for a period of time, and then ultrasonic for 30 min, and then stirred at room temperature for 12 h.

[0133] The prepared solution was placed into a syringe for electrospinning. The electrospinning solution was electrospun at a spinning voltage of 15 KV and a push-in speed of 0.5 ml / min, and then the above spinning film was vacuum dried at 70℃ for 12 h to obtain a spinning fiber film. Subsequently, the spinning fiber film was cut into a square with a size of 5 cm x 5 cm, and placed on a glass sheet.

[0134] A lithium salt solution (0.23 mol / L) was prepared by using DMSO (dimethyl sulfoxide) as a solvent and PVDF-HFP (polyvinylidene fluoride-hexafluoropropylene), butanedinitrile and lithium salt as solutes, the lithium salt solution was poured on the fiber film, and then the whole was uniformly coated by using a coating machine, and then the spinning film on which the lithium salt solution was poured was placed on a film applicator, and fine uniform coating treatment was performed by using the centrifugal force of the film applicator. The amount of the lithium salt solution was 0.03 g / cm 2 .

[0135] Subsequently, another glass sheet was covered on the upper layer to ensure the flatness of the surface of the prepared electrolyte film, and finally the electrolyte film was placed in a vacuum drying oven, and dried at 30℃ for 7 h and then at 50℃ for 36 h, to obtain a solid electrolyte film.

[0136] The solid electrolyte film prepared in Example 1 was characterized and performance detection was performed.

[0137] Referring to Figure 2 , Figure 2 are SEM scanning electron microscope images of the pure PVDF-HFP, the MEMO@LLZTO doped and the spinning fiber film prepared in Example 1 in the present application. Among them, (a) is the surface morphology of the pure PVDF-HFP, (b) is the MEMO@LLZTO doped, and (c) is the composite electrolyte film formed after pouring the lithium salt solution on the PVDF-HFP / MEMO@LLZTO fiber film and drying.

[0138] From Figure 2 It can be seen from the comparison that in the composite electrolyte film prepared in the present application, the fillers are uniformly dispersed, and a continuous and efficient ion transmission channel can be formed, so that the ion conductivity is improved.

[0139] Referring to Figure 3 ,Figure 3 The impedance spectrum of the PVDF-HFP, PVDF-HFP / LLZTO and PVDF-HFP / MEMO@LLZTO electrolyte films in the application is shown in Figure 1. The ion conductivity and interface resistance of the electrolyte films are shown in Table 1.

[0140] Referring to Table 1, the parameters and electrochemical performance of the solid electrolyte films prepared in the application, the pure PVDF-HFP solid electrolyte film and the PVDF-HFP / LLZTO solid electrolyte film are compared.

[0141] Table 1

[0142]

[0143] Referring to Figure 4 , Figure 4 The rate performance of the PVDF-HFP / MEMO@LLZTO composite electrolyte film prepared in Example 1 of the application is shown in Figure 2.

[0144] As shown in Figure 2, the specific capacity of the PVDF-HFP / MEMO@LLZTO composite electrolyte film prepared in Example 1 of the application is 148 mAh / g under the condition of 1C. Figure 4

[0145] Referring to Figure 5 , Figure 5 The electrochemical window of the PVDF-HFP / MEMO@LLZTO composite electrolyte film prepared in Example 1 of the application is shown in Figure 3.

[0146] As shown in Figure 3, the electrochemical window of the PVDF-HFP / MEMO@LLZTO composite electrolyte film prepared in Example 1 of the application is also improved compared to the composite electrolyte film prepared by using the filler modified by the silane coupling agent MEMO. Figure 5

[0147] Referring to Figure 6 , Figure 6 The cycle performance of the PVDF-HFP / MEMO@LLZTO composite electrolyte film prepared in Example 1 of the application is shown in Figure 4.

[0148] As shown in Figure 4, the PVDF-HFP / MEMO@LLZTO composite electrolyte film prepared by using the electrostatic spinning process can be stably cycled for 230 cycles under 1C, and the coulombic efficiency can also be stably above 90%. Figure 6

[0149] The specific composition of the solid-state battery is: negative electrode shell-elastic sheet-gasket-lithium sheet-electrolyte film-lithium iron phosphate-gasket-positive electrode shell.

[0150] Referring to Figure 7 , Figure 7 The schematic diagram of the composition structure of the solid-state battery for testing the electrolyte film in the application is shown in Figure 5.

[0151] ​​​The above has carried out the detailed introduction to the PVDF-LLZTO electrostatic spinning liquid, the preparation method and the application of the solid electrolyte membrane provided by the application, the principle and the implementation mode of the present application are described in this paper by applying specific examples, the above example is only used to help understanding the method of the present application and its core idea, including the best mode, and also enable any person skilled in the art to practice the present application, including manufacturing and using any device or system, and implementing any combined method. It should be pointed out that for ordinary skilled in the art, without departing from the principles of the present application, the present application can be improved and modified, and these improvements and modifications also fall within the protection scope of the claims of the present application. The scope of the patent protection of the present application is limited by the claims, and can include other embodiments that can be thought by those skilled in the art. If these other embodiments have structural elements that are not different from the language expression of the claims, or if they include equivalent structural elements that are not substantially different from the language expression of the claims, then these other embodiments should also be included in the scope of the claims.

Claims

1. An electrospinning solution, characterized in that, According to the raw material, the silane coupling agent MEMO modified LLZTO, PVDF-HFP and solvent are included. The mass ratio of the silane coupling agent MEMO modified LLZTO and PVDF-HFP is (15-20):

100.

2. The electrospinning solution of claim 1, wherein, The silane coupling agent MEMO is specifically 3-methacryloyloxypropyl trimethoxysilane. The particle size of the LLZTO is 300-400 nm. The surface of the silane coupling agent MEMO modified LLZTO has hydroxyl groups.

3. The electrospinning solution of claim 1, wherein, The solvent includes DMAC and acetone. In the electrospinning solution, the silane coupling agent MEMO modified LLZTO and PVDF-HFP are connected by chemical bonds. In the electrospinning solution, PVDF-HFP is the matrix and the silane coupling agent MEMO modified LLZTO is the filler. The mass concentration of the electrospinning solution is 16%-20%.

4. The electrospinning solution of claim 1, wherein, The preparation process of the electrospinning solution includes the following steps: (1) After mixing the silane coupling agent MEMO, the solvent and the pH value regulator, a mixed solution is obtained, then the LLZTO powder is added, and after stirring and reaction, the silane coupling agent MEMO modified LLZTO is obtained. The pH value of the mixed solution is 3.5-5. The stirring and reaction includes normal temperature stirring and reaction and heating stirring and reaction. The time of the normal temperature stirring and reaction is 2-3 h. The temperature of the heating stirring and reaction is 65-70℃. The time of the heating stirring and reaction is 6-8 h. (2) After mixing the PVDF-HFP and the solvent, the silane coupling agent MEMO modified LLZTO obtained in the above step is added, and after ultrasonic treatment and stirring and mixing, the electrospinning solution is obtained. The time of the ultrasonic treatment is 20-30 min. The time of the stirring and mixing is 11-14 h.

5. A method of producing a solid-state electrolyte film, characterized by, The process includes the following steps: 1) After electrospinning the electrospinning solution and the first drying, the electrospinning fiber membrane is obtained. The electrospinning solution is the electrospinning solution according to any one of claims 1-4. 2) The fiber membrane obtained in the above step is placed on a substrate, then a lithium salt solution is poured on the fiber membrane, the fiber membrane on which the lithium salt solution is poured is subjected to uniform coating, then the fiber membrane is covered with a substrate and placed in a drying device, after the second drying and the third drying, the solid electrolyte membrane is obtained.

6. The production method according to claim 5, wherein The spinning voltage of the electrospinning is 15-20 KV. The electrospinning solution injection speed of the electrospinning is 0.5-0.8 mL / min. The first drying is vacuum drying. The temperature of the first drying is 65-70℃. The time of the first drying is 12-15 h.

7. The preparation method according to claim 5, characterized in that, The lithium salt solution is specifically a mixed solution including a lithium salt, butanedinitrile, PVDF-HFP and a solvent. The mass concentration of the lithium salt solution is 4.5%-5%. The amount of the lithium salt solution is 0.02 to 0.03 g / cm 2 .

8. The preparation method according to claim 5, characterized in that, The second drying is vacuum drying. The temperature of the second drying is 25-35℃. The time of the second drying is 7-10 h.

9. The preparation method according to claim 5, characterized in that, The third drying is vacuum drying. The temperature of the third drying is 50-60℃. The time of the third drying is 36-48 h.

10. Use of the electrospinning solution according to any one of claims 1 to 4 or the solid-state electrolyte membrane prepared by the preparation method according to any one of claims 5 to 9 in a solid-state battery.

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