A solid electrolyte membrane, its preparation method and application

Abstract

A solid electrolyte membrane, a preparation method thereof and an application thereof, belonging to the technical field of solid-state batteries; the solid electrolyte membrane includes: a thin film framework, the thin film framework includes interconnected pores, and the composition of the thin film framework includes polyacrylonitrile; an electrolyte composition, the electrolyte is filled in the pores of the thin film framework, and the electrolyte composition includes an oxide inorganic solid electrolyte, a binder and a lithium salt; it can take into account performances such as ion transport, energy density and cycle life.

Description

Technical Field

[0001] The present application relates to the technical field of solid-state batteries, and more particularly, to a solid electrolyte membrane, a preparation method thereof, and an application thereof. Background Art

[0002] The reserves of fossil energy are gradually depleted, and the use of fossil fuels has brought serious environmental pollution problems and the greenhouse effect. New energy sources represented by wind energy and solar energy are expected to alleviate the current energy shortage and also significantly reduce air pollution and greenhouse gas emissions. However, the randomness, volatility, and discontinuity of these new energy sources greatly limit their application in actual industries. Therefore, it is necessary to develop energy storage devices to store wind energy and solar energy, so energy storage devices play a very important role in the new energy system. As a relatively common energy storage device, lithium-ion batteries have the advantages of high energy density, easy to carry, and many application scenarios. Currently, the electrolyte of lithium-ion batteries widely used in electronic products and power batteries is mainly organic flammable electrolyte. The toxicity and flammability of organic flammable electrolyte seriously affect the safety in actual use. The leakage of electrolyte is likely to cause environmental pollution and explosion and fire accidents, and the theoretical energy density of lithium-ion batteries using electrolyte cannot meet the usage scenarios with higher requirements. Therefore, researchers have conducted a large number of studies on safer solid-state lithium batteries with higher theoretical energy density. Among them, one of the most important components of solid-state lithium batteries is solid electrolyte. Currently, solid electrolytes are mainly divided into pure polymer solid electrolytes, inorganic ceramic solid electrolytes, and composite solid electrolytes. Among them, inorganic ceramic solid electrolytes are mainly divided into three systems: oxides, sulfides, and halides. Among these materials, pure polymer solid electrolytes have good flexibility but low ionic conductivity (~10 -6 S / cm), and although inorganic ceramic solid electrolytes have good ionic conductivity (~10 -3 S / cm), problems such as difficulty in thinning, poor flexibility, fragility, and poor contact with the electrode interface have become the main reasons restricting their application and development. In addition, solid electrolytes in the sulfide system are prone to react with water and carbon dioxide in the air, and solid electrolytes in the halide system have poor compatibility with electrodes, which is not conducive to large-scale application. One of the representative materials of oxide ceramic materials is garnet-type LLZTO, which has high ionic conductivity, a wide electrochemical window, and a relatively stable matching with the lithium metal interface, so it is often used in the field of solid electrolytes, but its mechanical properties still need to be further improved.

[0003] To address the above problems, composite solid electrolytes developed by researchers by combining polymer and ceramic solid electrolytes retain both high ionic conductivity (10 -4(S / cm), while possessing the flexibility of polymers and the advantage of good interfacial contact. Its preparation routes are mainly divided into two categories: Mold casting method: The composite solid electrolyte slurry is dried according to certain specifications through a casting mold, and then cut for use; Coating and casting method: The composite solid electrolyte slurry is coated on the positive and negative electrodes, and then dried for direct use. Usually, when the thickness of the solid electrolyte is between 5 and 30 μm, better ion transport performance can be achieved. However, for the materials obtained by the mold casting method, due to the limitations of mold processing, the resulting solid electrolyte has a relatively large thickness, above 100 μm, which greatly reduces the energy density of the battery; Although the coating and casting method can reduce the thickness of the solid electrolyte, it will increase the possibility of side reactions at the interface due to the increased stress at the interface between the electrolyte material and the electrode during drying, making it still face certain challenges in improving the cycle performance. Summary of the Invention

[0004] The present application provides a solid electrolyte membrane, its preparation method and application, which can take into account performance such as ion transport, energy density, and cycle life.

[0005] In the first aspect, an embodiment of the present application provides a solid electrolyte membrane, which includes:

[0006] A thin film framework, the thin film framework includes interconnected pores, and the component of the thin film framework includes polyacrylonitrile;

[0007] An electrolyte composition, the electrolyte is filled in the pores of the thin film framework, and the electrolyte composition includes an oxide inorganic solid electrolyte, a binder, and a lithium salt.

[0008] In the technical solution of the embodiment of the present application, polyacrylonitrile is used as a template framework, and the electrolyte composition is filled therein. The oxide inorganic solid electrolyte and polyacrylonitrile form an ion transport network, which can better promote lithium ion transport, and at the same time can effectively reduce the thickness of the solid electrolyte membrane, thereby reducing the ion transport distance, which is beneficial to the ion transport performance of the solid electrolyte membrane and improves the rate performance of the battery. And the reduction of the thickness of the entire solid electrolyte membrane can reduce the mass of inactive materials, which is beneficial to the energy density of the battery. And the nitrile group (C≡N) of polyacrylonitrile in the thin film framework is a strong electron-withdrawing group with high electrochemical stability. The oxide inorganic solid electrolyte and polyacrylonitrile will undergo a dehydrogenation cyanation reaction at the contact interface, enhancing the interfacial interaction, which will help to promote the rapid and continuous Li +The establishment of the migration path is beneficial to the establishment of a stable lithium-ion transmission channel. Appropriately reducing the ionic conductivity through polyacrylonitrile can increase the resistance of electrons migrating between the lithium metal and the oxide inorganic solid electrolyte, thereby inhibiting the formation of lithium dendrites, and thus improving the rate performance and cycle life of the lithium-ion battery. In addition, the thin film framework can provide a flexible buffering area for the electrolyte composition, enabling the solid electrolyte membrane to have good anti-bending ability.

[0009] As an alternative embodiment, the mass of the electrolyte composition is 40% - 60% of the total mass of the solid electrolyte membrane.

[0010] In the above implementation process, the larger the mass ratio of the electrolyte composition, the more beneficial it is to the lithium-ion transmission performance of the solid electrolyte membrane. The smaller the mass ratio of the electrolyte composition, the more beneficial it is to the mechanical properties of the solid electrolyte membrane. By controlling the mass ratio of the electrolyte composition, the mechanical properties and lithium-ion transmission performance of the solid electrolyte membrane can be balanced.

[0011] As an alternative embodiment, the thickness of the solid electrolyte membrane is 10 - 30 μm.

[0012] In the above implementation process, the thicker the thickness of the solid electrolyte membrane, the more beneficial it is to the mechanical properties of the solid electrolyte membrane. The thinner the thickness of the solid electrolyte membrane, the more beneficial it is to the control of the mass of non-active substances in the solid electrolyte membrane, and thus beneficial to the energy density of the battery. By controlling the thickness of the solid electrolyte membrane to be 10 - 30 μm, the mechanical properties of the solid electrolyte membrane and the energy density of the battery can be balanced.

[0013] As an alternative embodiment, the porosity of the thin film framework is 40% - 60%; and / or

[0014] The pore diameter of the thin film framework is 1 - 10 μm.

[0015] In the above implementation process, by controlling the porosity of the thin film framework to be 40% - 60%, the mechanical properties of the thin film framework and the filling amount of the electrolyte composition can be balanced. By controlling the pore diameter of the thin film framework to be 1 - 10 μm, it is beneficial for the electrolyte composition to fill into the pores of the thin film framework.

[0016] As an alternative embodiment, the mass ratio of the oxide inorganic solid electrolyte, the binder, and the lithium salt is 1:(0.5 - 2):(0.1 - 2); and / or

[0017] The oxide inorganic solid electrolyte includes at least one of lithium lanthanum zirconium tantalum oxide and lithium titanium aluminum phosphate; and / or

[0018] The binder includes at least one of polyvinylidene fluoride, poly(ethylene oxide), styrene-butadiene rubber, and polyacrylic acid; and / or

[0019] The number-average molecular weight of the binder is 100,000 to 600,000; and / or

[0020] The lithium salt includes at least one of lithium bis(trifluoromethanesulfonyl)imide, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(oxalato)borate, and lithium difluoro(oxalato)borate.

[0021] In the above implementation process, the greater the proportion of the binder, the more beneficial it is to the bonding force between the electrolyte composition and the film framework. The smaller the proportion of the binder, the more beneficial it is to the ionic conductivity of the solid electrolyte membrane. And the greater the proportion of the lithium salt, the more beneficial it is to reducing the resistance of the solid electrolyte membrane. The smaller the proportion of the lithium salt, the more capable of reducing the probability of lithium dendrite formation, thereby increasing the cycle life of the battery. By controlling the mass ratio of the oxide inorganic solid electrolyte, the binder, and the lithium salt to be 1:(0.5 - 2):(0.1 - 2), the performance such as ion transport, energy density, and cycle life can be taken into account.

[0022] In a second aspect, an embodiment of the present application provides a method for preparing a solid electrolyte membrane, the method including:

[0023] Electrospinning a polyacrylonitrile solution to obtain a film framework with interconnected pores;

[0024] Mixing the oxide inorganic solid electrolyte, the binder, and the lithium salt in a solvent to obtain an electrolyte slurry;

[0025] Filling the electrolyte slurry into the pores of the film framework, and then drying and hot-pressing to obtain a solid electrolyte membrane.

[0026] In the technical solution of the embodiment of the present application, by using electrospinning to prepare the film framework, various parameters of electrospinning can be adjusted to control the properties such as the thickness, porosity, and pore size of the film framework for the filling of the electrolyte slurry. Secondly, the highly porous and ultrathin PAN film prepared by electrospinning technology is used for the composite solid electrolyte framework, providing a flexible buffer area for the ceramic electrolyte and endowing the composite solid electrolyte with good anti-bending ability. The ceramic and polymer electrolytes filled inside constitute a developed ion transport network, which can better promote lithium ion transport. At the same time, hot-pressing the solid electrolyte can further significantly reduce the thickness of the electrolyte film. The ultrathin thickness can reduce the ion transport distance and the mass of inactive materials, thereby facilitating the improvement of the rate performance and energy density of lithium batteries. Finally, the nitrile group (C≡N) in the PAN polymer chain is a strong electron-withdrawing group with high electrochemical stability. The oxide inorganic solid electrolyte in the electrolyte slurry will undergo a dehydrogenation cyanation reaction with the PAN film at the contact interface, enhancing the interfacial interaction, which will help promote the rapid and continuous Li +The establishment of the migration path is conducive to the establishment of a stable lithium-ion transmission channel. Appropriately reducing the ionic conductivity through PAN can increase the resistance of electrons migrating between the lithium metal and the oxide inorganic solid electrolyte, thereby inhibiting the formation of lithium dendrites and improving the rate performance and cycle life of lithium-ion batteries.

[0027] As an alternative implementation, the electrolyte slurry is filled into the pores of the thin film frame, and then dried and hot-pressed to obtain a solid electrolyte membrane, including:

[0028] Coat the electrolyte slurry on the surface of the thin film frame;

[0029] Perform suction filtration on the thin film frame coated with the electrolyte slurry to fill the electrolyte slurry into the pores of the thin film frame;

[0030] Dry and hot-press the thin film frame filled with the electrolyte slurry to obtain a solid electrolyte membrane;

[0031] Among them, the suction filtration time is 30 - 180 s, and the pressure of the suction filtration vacuum pump is 80 - 90 kPa.

[0032] As an alternative implementation, the mass concentration of polyacrylonitrile in the polyacrylonitrile solution is 5% - 15%; and / or

[0033] The positive voltage of electrospinning is +12 - +16 kV, the negative voltage of electrospinning is -1 - -3 kV, the spinning distance of electrospinning is 100 - 200 mm, the feeding rate of electrospinning is 0.6 - 1 mL / h, and the rotating speed of the electrospinning roller is 200 - 800 rpm.

[0034] In the above implementation process, by controlling the concentration of the spinning solution and various parameters of the electrospinning method, the performance such as the thickness, porosity, and mechanical properties of the thin film frame can be regulated.

[0035] As an alternative implementation, the solvent includes at least one of N-methylpyrrolidone, ethanol, acetonitrile, dichloroethane, chloroform, acetone, polyethylene glycol, and isopropanol.

[0036] In a third aspect, the embodiments of the present application further provide a solid-state lithium battery, and the solid-state lithium battery includes the solid electrolyte membrane provided in the first aspect or the solid electrolyte membrane obtained by the preparation method of the solid electrolyte membrane provided in the second aspect. Description of the Drawings

[0037] To more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the accompanying drawings required for the embodiments. It should be understood that the following drawings only show some embodiments of the present application, and therefore should not be regarded as limiting the scope. For those of ordinary skill in the art, without creative efforts, other related drawings can also be obtained based on these drawings.

[0038] Figure 1 is the flowchart of the method provided by the embodiments of the present application;

[0039] Figure 2 is the planar SEM image of the thin film frame provided by Embodiment 3 of the present application;

[0040] Figure 3 is the planar SEM image of the thin film frame provided by Embodiment 1 of the present application;

[0041] Figure 4 is the planar SEM image of the thin film frame provided by Embodiment 2 of the present application;

[0042] Figure 5 is the cross-sectional SEM image of the thin film frame provided by Embodiment 2 of the present application;

[0043] Figure 6 is the cross-sectional SEM image of the thin film frame provided by Embodiment 2 of the present application after hot pressing at 100°C and 0.4 MPa;

[0044] Figure 7 is the XRD pattern of the LLZTO ceramic powder provided by Embodiment 4 of the present application;

[0045] Figure 8 is the SEM image of the LLZTO ceramic powder provided by Embodiment 4 of the present application;

[0046] Figure 9 is the low-magnification planar SEM image of the solid electrolyte membrane obtained in Embodiment 5 of the present application;

[0047] Figure 10 is the high-magnification planar SEM image of the solid electrolyte membrane obtained in Embodiment 5 of the present application;

[0048] Figure 11 is the cross-sectional SEM image of the solid electrolyte membrane obtained in Embodiment 5 of the present application;

[0049] Figure 12 is the impedance curve graph of the solid electrolyte membrane obtained in Embodiment 5 of the present application at 30°C;

[0050] Figure 13 is the schematic diagram of the flexible test process of the solid electrolyte membrane obtained in Embodiment 5 of the present application;

[0051] Figure 14 is the cyclic voltammetry curve of the solid electrolyte membrane obtained in Example 5 of the present application at 60 °C and 0.1 mA / cm 2 for a lithium symmetric battery;

[0052] Figure 15 is the cyclic voltammetry curve of the solid electrolyte membrane obtained in Example 5 of the present application at 60 °C and 0.2 mA / cm 2 for a lithium symmetric battery;

[0053] Figure 16 is the cyclic voltammetry curve of the solid electrolyte membrane obtained in Example 5 of the present application at 60 °C and 0.5 mA / cm 2 for a lithium symmetric battery;

[0054] Figure 17 is the critical current test curve of the solid electrolyte membrane obtained in Example 5 of the present application at 60 °C and 0.09 - 1.8 mA / cm 2 for a lithium symmetric battery;

[0055] Figure 18 is the linear sweep voltammetry (LSV) curve of the solid electrolyte membrane obtained in Example 5 of the present application at room temperature;

[0056] Figure 19 is the charge - discharge curve of the solid electrolyte membrane obtained in Example 5 of the present application in a LiFePO4 / Li full battery at 60 °C and 0.05 C. Detailed Embodiments

[0057] The following will describe the implementation schemes of the present application in detail with reference to the embodiments. However, those skilled in the art will understand that the following embodiments are only used to illustrate the present application and should not be considered as limiting the scope of the present application. For those not specified in the embodiments, the conventional conditions or the conditions recommended by the manufacturer are followed. For the reagents or instruments not specified for the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0058] The solid electrolyte membranes prepared by the current methods usually have a thickness of more than 100 μm or have a large stress between the membrane and the electrode, resulting in poor performance such as ion transport, energy density, and cycle life. Therefore, the present application aims to provide a solid electrolyte membrane, its preparation method, and application to balance the performance such as ion transport, energy density, and cycle life.

[0059] The embodiments of the present application provide a solid electrolyte membrane, which includes: a thin - film framework and an electrolyte composition. The thin - film framework includes interconnected pores, and the component of the thin - film framework includes polyacrylonitrile; the electrolyte is filled in the pores of the thin - film framework, and the electrolyte composition includes an oxide inorganic solid electrolyte, a binder, and a lithium salt.

[0060] The solid electrolyte membrane uses polyacrylonitrile as a template framework and fills the electrolyte composition therein. The oxide inorganic solid electrolyte and polyacrylonitrile form an ion transport network, which can better promote lithium ion transport. At the same time, it can effectively reduce the thickness of the solid electrolyte membrane, thereby reducing the ion transport distance, which is beneficial to the ion transport performance of the solid electrolyte membrane and improves the rate performance of the battery. And the reduction of the thickness of the entire solid electrolyte membrane can reduce the mass of the inactive material, which is beneficial to the energy density of the battery. And the nitrile group (C≡N) of polyacrylonitrile in the thin film framework is a strong electron-withdrawing group with high electrochemical stability. The oxide inorganic solid electrolyte and polyacrylonitrile will undergo a dehydrogenation cyanation reaction at the contact interface, enhancing the interfacial interaction, which will help to promote the rapid and continuous Li + The establishment of the migration path is beneficial to the establishment of a stable lithium ion transport channel. Appropriately reducing the ionic conductivity through polyacrylonitrile can increase the resistance of electrons migrating between the lithium metal and the oxide inorganic solid electrolyte, thereby inhibiting the formation of lithium dendrites, and thus improving the rate performance and cycle life of the lithium ion battery. In addition, the thin film framework can provide a flexible buffer area for the electrolyte composition, making the solid electrolyte membrane have good anti-bending ability.

[0061] In some embodiments, the mass of the electrolyte composition is 40% - 60% of the total mass of the solid electrolyte membrane. The larger the mass ratio of the electrolyte composition, the more beneficial it is to the lithium ion transport performance of the solid electrolyte membrane. The smaller the mass ratio of the electrolyte composition, the more beneficial it is to the mechanical properties of the solid electrolyte membrane. By controlling the mass ratio of the electrolyte composition, the mechanical properties and lithium ion transport performance of the solid electrolyte membrane can be balanced.

[0062] In some embodiments, the thickness of the solid electrolyte membrane is 10 - 30 μm. The thicker the thickness of the solid electrolyte membrane, the more beneficial it is to the mechanical properties of the solid electrolyte membrane. The thinner the thickness of the solid electrolyte membrane, the more beneficial it is to the control of the mass of the inactive substances in the solid electrolyte membrane, and thus beneficial to the energy density of the battery. By controlling the thickness of the solid electrolyte membrane to be 10 - 30 μm, the mechanical properties of the solid electrolyte membrane and the energy density of the battery can be balanced.

[0063] In some embodiments, the porosity of the thin film framework is 40% - 60%. By controlling the porosity of the thin film framework to be 40% - 60%, the mechanical properties of the thin film framework and the filling amount of the electrolyte composition can be balanced.

[0064] In some embodiments, the pore diameter of the thin film framework is 1 - 10 μm. By controlling the pore diameter of the thin film framework to be 1 - 10 μm, it is beneficial for the electrolyte composition to fill into the pores of the thin film framework.

[0065] In some embodiments, the mass ratio of the oxide inorganic solid electrolyte, the binder, and the lithium salt is 1:(0.5 - 2):(0.1 - 2); the oxide inorganic solid electrolyte includes at least one of lithium lanthanum zirconium tantalum oxide (LLZTO) and lithium aluminum titanium phosphate (LATP), for example: Li 6.5 La3Zr 1.5 Ta 0.5 O 12 、Li 1.3 AI 0.3 Ti 1.7 (PO4)3, etc.; the binder includes at least one of polyvinylidene fluoride (PVDF), polyethylene oxide (PEO), styrene-butadiene rubber, and polyacrylic acid (PAA); the average number-average molecular weight of the binder is 100,000 - 600,000; the lithium salt includes at least one of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium bis(oxalato)borate (LiBOB), and lithium difluoro(oxalato)borate (LiDFOB). The greater the proportion of the binder, the more beneficial it is to the bonding force between the electrolyte composition and the film frame. The smaller the proportion of the binder, the more beneficial it is to the ionic conductivity of the solid electrolyte membrane. And the greater the proportion of the lithium salt, the more beneficial it is to reduce the resistance of the solid electrolyte membrane. The smaller the proportion of the lithium salt, the more the probability of lithium dendrite formation can be reduced, thereby increasing the cycle life of the battery. By controlling the mass ratio of the oxide inorganic solid electrolyte, the binder, and the lithium salt to be 1:(0.5 - 2):(0.1 - 2), performance such as ion transport, energy density, and cycle life can be balanced.

[0066] Figure 1 is a flowchart of the method provided by the embodiments of the present application. As Figure 1 shown, the embodiments of the present application provide a method for preparing a solid electrolyte membrane. The method includes:

[0067] S1. Electrospinning a polyacrylonitrile-containing solution to obtain a film frame with interconnected pores;

[0068] In some embodiments, the mass concentration of polyacrylonitrile in the polyacrylonitrile-containing solution is 5% - 15%; too low a mass fraction of polyacrylonitrile will cause a decrease in the strength of the spun fibers, and too high a mass fraction will cause the spun fibers to be discontinuous, thereby affecting the mechanical properties of the film frame. The positive voltage of electrospinning is +12 - +16 kV, the negative voltage of electrospinning is -1 - -3 kV, the spinning distance of electrospinning is 100 - 200 mm, the feeding rate of electrospinning is 0.6 - 1 mL / h, and the roller rotation speed of electrospinning is 200 - 800 rpm. By adjusting the spinning time and the concentration of polyacrylonitrile in the solution, the thickness and porosity of the film frame can be more accurately controlled.

[0069] S2. Mix the oxide inorganic solid electrolyte, binder, and lithium salt in a solvent to obtain an electrolyte slurry;

[0070] In some embodiments, the solvent includes at least one of N-methylpyrrolidone, ethanol, acetonitrile, dichloroethane, chloroform, acetone, polyethylene glycol, and isopropanol.

[0071] Among them, the oxide inorganic solid electrolyte can be obtained by purchasing from the market or by preparation. Here, the preparation of LLZTO is taken as an example: Lithium carbonate, lanthanum oxide, zirconium oxide, and tantalum oxide with a certain stoichiometric ratio are used as raw materials for synthesizing LLZTO. Among them, lithium carbonate is in excess. Add the raw materials to a planetary ball mill jar and ball mill at a certain speed, then heat to a certain temperature in a muffle furnace to make the raw materials react fully, and then perform high-speed ball milling under argon protection and sieve to prepare LLZTO with controllable particle size. Among them, the ratio of lithium carbonate, lanthanum oxide, zirconium oxide, and tantalum oxide can be (6-7.5):(2-3):(1-2):(0.3-0.7). During the high-temperature sintering process, lithium elements are likely to volatilize, so 10wt%-30wt% of lithium carbonate is additionally added under the rated ratio. The ball milling speed is 200-600 rpm, and the ball milling time is 6-36 hours. Generally, during the ball milling process, too low a speed will require a longer ball milling time, and too high a speed will generate a large amount of heat in a short time, which has certain safety hazards. In addition, too short a ball milling time will result in insufficient ball milling, and too long a time will affect the service life of the instrument. The reaction temperature is 750-1200°C, where the heating and cooling rates are both 3°C / min, and the holding time is 12-18 hours. During the high-temperature solid-phase synthesis of LLZTO, too high or too low a reaction temperature will cause other side reactions to affect the cubic-phase LLZTO structure. Too high a heating and cooling rate will cause uneven heating of the sample, and too low a heating and cooling rate will cause an increase in side reactions. Too short a holding time will result in insufficient reaction, and too long a holding time will cause excessive volatilization loss of lithium elements. The prepared LLZTO has a size below 10 μm, which is beneficial for filling it into the pores of the framework film.

[0072] S3. Fill the electrolyte slurry into the pores of the film framework, and then perform drying and hot pressing to obtain a solid electrolyte membrane.

[0073] In some embodiments, filling the electrolyte slurry into the pores of the film framework and then performing drying and hot pressing to obtain a solid electrolyte membrane includes:

[0074] S3.1. Coat the electrolyte slurry on the surface of the film framework;

[0075] S3.2. Perform suction filtration on the thin film frame coated with the electrolyte slurry so that the electrolyte slurry fills the pores of the thin film frame; wherein, the suction filtration time is 30 - 180 s, the vacuum pump pressure for suction filtration is 80 - 90 kPa, and the suction filtration is carried out in an argon atmosphere.

[0076] S3.3. Dry and hot press the thin film frame filled with the electrolyte slurry to obtain a solid electrolyte membrane;

[0077] This method prepares the thin film frame by using electrospinning. By adjusting various parameters of electrospinning, properties such as the thickness, porosity, and pore size of the thin film frame can be controlled to facilitate the filling of the electrolyte slurry. Secondly, the highly porous and ultra-thin PAN film prepared by the electrospinning technique is used as the composite solid electrolyte frame, providing a flexible buffer region for the ceramic electrolyte and endowing the composite solid electrolyte with good anti-bending ability. The ceramic and polymer electrolyte filled inside form a well-developed ion transport network, which can better promote the lithium ion transport. At the same time, hot pressing the solid electrolyte can further significantly reduce the thickness of the electrolyte film. The ultra-thin thickness can reduce the ion transport distance and the mass of inactive materials, thus facilitating the improvement of the rate performance and energy density of the lithium battery. Finally, the nitrile group (C≡N) in the PAN polymer chain is a strong electron-withdrawing group with high electrochemical stability. The oxide inorganic solid electrolyte in the electrolyte slurry will undergo a dehydrogenation cyanation reaction with the PAN film at the contact interface, enhancing the interfacial interaction, which will help promote the establishment of a fast and continuous Li + migration path, which is beneficial to establishing a stable lithium ion transport channel. Appropriately reducing the ionic conductivity through PAN can increase the resistance of electrons migrating between the lithium metal and the oxide inorganic solid electrolyte, thereby inhibiting the formation of lithium dendrites, and thus improving the rate performance and cycle life of the lithium ion battery.

[0078] The embodiment of the present application provides a solid-state lithium battery, which includes the solid electrolyte membrane provided above. Specifically, lithium metal is used as the negative electrode, lithium iron phosphate is used as the positive electrode, and the battery is assembled with the solid electrolyte membrane.

[0079] The following further describes the solid electrolyte membrane of the present application in detail in combination with embodiments.

[0080] Example 1

[0081] Prepare an ultra-thin porous PAN thin film frame using a 10 wt% mass fraction of PAN in DMF solution. The specific preparation process is as follows:

[0082] Prepare a 30 g spinning solution by adding 3 g PAN to DMF. Set the positive electrode voltage to 16 kV, the negative electrode voltage to -2 kV, the roller speed to 400 rpm, the spinning distance to 100 mm, and the micro-pump rate to 0.8 mL / h for electrospinning. Dry at 60 °C to obtain a PAN porous film framework.

[0083] Example 2

[0084] Prepare an ultra-thin porous PAN film framework using a 10 wt% PAN DMF solution. The specific preparation process is as follows:

[0085] Prepare a 30 g spinning solution by adding 3 g PAN to DMF. Set the positive electrode voltage to 16 kV, the negative electrode voltage to -2 kV, the roller speed to 600 rpm, the spinning distance to 100 mm, and the micro-pump rate to 0.8 mL / h for electrospinning. Dry at 60 °C to obtain a PAN porous film framework.

[0086] Example 3

[0087] Prepare an ultra-thin porous PAN film framework using a 10 wt% PAN DMF solution. The specific preparation process is as follows:

[0088] Prepare a 30 g spinning solution by adding 3 g PAN to DMF. Set the positive electrode voltage to 16 kV, the negative electrode voltage to -2 kV, the roller speed to 1200 rpm, the spinning distance to 100 mm, and the micro-pump rate to 0.8 mL / h for electrospinning. Dry at 60 °C to obtain a PAN porous film framework.

[0089] Perform SEM tests on the film frameworks provided in Examples 1 to 3. Figure 2 is the planar SEM image of the film framework provided in Example 3 of this application; from Figure 2 It can be seen that the PAN fibers obtained by the collection roller at a higher speed have stronger orientation, and there are obvious differences in the mechanical structures in all directions. Figure 3 is the planar SEM image of the film framework provided in Example 1 of this application; from Figure 3 It can be seen that the PAN fibers obtained by the collection roller at a lower speed are looser. Figure 4 is the planar SEM image of the film framework provided in Example 2 of this application. From Figure 4 It can be seen that the PAN fibers obtained by the collection roller at a speed of 600 rpm have relatively uniform orientation, and the fibers are relatively straight and continuous. Figure 5 and Figure 6 are the cross-sectional SEM images of the film framework before and after hot pressing at 100 °C and 0.4 MPa respectively. From Figure 5 It can be seen that the thickness of the PAN film obtained by the collection roller at a speed of 600 rpm without hot pressing is about 180 μm; and from Figure 6It can be seen that the thickness of the PAN film obtained by the hot-pressed collecting roller at a rotational speed of 600 rpm is about 20 μm, making it possible for the total thickness of the composite solid electrolyte to be less than 30 μm.

[0090] Example 4

[0091] Sinter the LLZTO ceramic powder at 900 °C. The specific preparation process is as follows:

[0092] Add lithium carbonate, lanthanum oxide, tantalum oxide, and zirconium oxide with masses of 2.604 g, 4.887 g, 1.848 g, and 1.104 g respectively. After wet ball milling for 12 h, evaporate to dryness, and then sinter in a muffle furnace. The heating and cooling rates are set at 3 °C / min, the holding time is 12 h, the sintering temperature is 900 °C. After cooling, take out and grind, and sieve through 1000- and 2000-mesh sieves in sequence to obtain LLZTO ceramic materials with particle sizes in the range of 0.1-10 μm.

[0093] Perform XRD testing on the LLZTO ceramic powder provided in Example 4. Figure 7 is the XRD pattern of the LLZTO ceramic powder provided in Example 4 of this application; it can be seen from Figure 7 that the obtained LLZTO can show the corresponding characteristic diffraction peaks, so the experimentally obtained cubic-phase LLZTO has a high purity.

[0094] Perform SEM testing on the LLZTO ceramic powder provided in Example 4. Figure 8 is the SEM image of the LLZTO ceramic powder provided in Example 4 of the present invention; it can be seen from Figure 8 that the particle size of the LLZTO powder prepared by this solution is between 0.1-10 μm.

[0095] Example 5

[0096] Preparation of the solid electrolyte membrane. The specific preparation process is as follows:

[0097] Select the film frame provided in Example 2 and the LLZTO prepared in Example 4 for use. Prepare an electrolyte slurry with a total mass of 26 g, using acetonitrile as the solvent, and with 2 g each of LLZTO / PEO / LiTFSI. Coat the prepared slurry evenly on the surface of the PAN film frame obtained at a roller speed of 600 rpm and let it stand for 30 s. Then use a sand core suction filtration device to filter for 60 s until the electrolyte slurry passes through the pores of the PAN film. Then dry it in vacuum at 60 °C, cut into pieces, and hot press to obtain the solid electrolyte membrane.

[0098] Perform SEM testing on the solid electrolyte membrane provided in Example 5. Figure 9 and Figure 10 are the low-magnification and high-magnification plane SEM images of the solid electrolyte membrane obtained in Example 5 of this application respectively. It can be seen fromFigure 9 It can be seen that the electrolyte slurry is evenly distributed in the PAN film framework, and the interface of the composite solid electrolyte is flat, which can provide good interface contact. From Figure 10 It can be seen that the slurry containing LLZTO electrolyte is coated on the surface of the PAN polymer fiber framework, facilitating the interaction between the electrolyte distributed along the continuous spinning fibers and the nitrile groups in PAN to generate a built-in electric field. Figure 11 This is the cross-sectional SEM image of the solid electrolyte membrane obtained in Example 5 of this application. From Figure 11 It can be seen that the thickness of the ultra-thin composite solid electrolyte is about 25 μm, meeting the requirement of being ultra-thin.

[0099] The impedance test was carried out on the solid electrolyte membrane provided in Example 5. Figure 12 This is the impedance curve graph of the solid electrolyte membrane obtained in Example 5 of this application at 30 °C. From Figure 12 It can be seen that the charge transfer resistance of the solid electrolyte of the present invention at room temperature is relatively low, about 1200 Ω. The low charge transfer resistance is conducive to the transmission of ions.

[0100] The flexibility test was carried out on the solid electrolyte membrane provided in Example 5. Figure 13 This is a schematic diagram of the flexibility test process of the solid electrolyte membrane obtained in Example 5 of this application. The composite solid electrolyte can be folded in half at room temperature without breaking, indicating that the composite solid electrolyte obtained by the present invention has good flexibility.

[0101] The CR2032 battery case was selected for battery assembly. In the symmetric battery test, one lithium metal sheet has a diameter of 16 mm and the other lithium metal sheet has a diameter of 12 mm, both with a thickness of 0.2 mm, and the composite solid electrolyte prepared in the above steps. In the full battery test, the positive electrode is a slurry prepared by dispersing lithium iron phosphate (LiFePO4), polyvinylidene fluoride (PVDF), and conductive carbon black in NMP with a mass ratio of 8:1:1, coated on an aluminum foil and dried. The diameter of the electrode sheet is 12 mm, and the negative electrode is a lithium metal sheet with a diameter of 16 mm. The electrochemical performance test was completed on a NEWARE battery test system. The current range of the symmetric battery test is 0.09 - 1.8 mA / cm 2 . The current range of the full battery test is 0.05 - 1C (1C = 170 mA / g).

[0102] For the solid electrolyte membrane provided in Example 5 at 0.1 mA / cm 2 、0.2 mA / cm 2 、0.5 mA / cm 2 、the battery cycle tests were carried out at the currents respectively, and the results are as Figures 14 - 15 shown. From Figure 14 It can be seen that at 0.1 mA / cm2 Under the cyclic current, the lithium symmetric battery can stably cycle for more than 1000 h, indicating its good cycling stability. From Figure 15 It can be seen that under the cyclic current of 0.2 mA / cm 2 , the lithium symmetric battery can stably cycle for 200 h, and the initial overpotential is about 60 mV, indicating its good cycling stability. From Figure 16 It can be seen that under 0.5 mA / cm 2 , the lithium symmetric battery can stably cycle for 60 cycles and 20 h, indicating that it still has good cycling stability at a large current density.

[0103] The critical current of the solid electrolyte membrane provided in Example 5 was tested. Figure 17 is the critical current test curve of the solid electrolyte membrane obtained in Example 5 of this application at 60 °C and 0.09 - 1.8 mA / cm 2 of the lithium symmetric battery. From Figure 17 it can be seen that the critical current density of the composite solid electrolyte prepared by this scheme is about 1.7 mA / cm 2 , indicating that the electrolyte can cycle at a large current density.

[0104] The linear sweep voltammetry test was carried out on the solid electrolyte membrane provided in Example 5. Figure 18 is the linear sweep voltammetry (LSV) curve of the solid electrolyte membrane obtained in Example 5 of this application at room temperature. From Figure 18 it can be seen that the composite solid electrolyte prepared in the present invention has a relatively high decomposition voltage close to 5 V, and is expected to match the cathode material with a higher voltage.

[0105] The charge-discharge test was carried out on the solid electrolyte membrane provided in Example 5. Figure 19 is the charge-discharge curve of the solid electrolyte membrane obtained in Example 5 of this application in the LiFePO4 / Li full cell at 60 °C and 0.05 C. From Figure 19 it can be seen that the LiFePO4 / Li full cell using the composite solid electrolyte prepared in the present invention has a specific capacity of 110 mAh / g at 60 °C and 0.05 C, indicating that the electrolyte has good cycling performance in the full cell.

[0106] Example 6

[0107] In this example, except for using the thin film frame provided in Example 1, the rest of the content is the same as that in Example 5.

[0108] Example 7

[0109] In this example, except for using the thin film frame provided in Example 3, the rest of the content is the same as that in Example 5.

[0110] The above are only specific embodiments of the present application and are not intended to limit the present application. For those skilled in the art, various modifications and changes can be made to the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included within the protection scope of the present application.

Claims

1. A method for preparing a solid electrolyte membrane, characterized in that The method includes: Electrospinning a polyacrylonitrile solution to obtain a thin film framework with interconnected pores; Mixing an oxide inorganic solid electrolyte, a binder, and a lithium salt in a solvent to obtain an electrolyte slurry; Filling the electrolyte slurry into the pores of the thin film framework, followed by drying and hot pressing to obtain a solid electrolyte membrane; Among them, the positive voltage of the electrospinning is +12 to +16 kV, the negative voltage of the electrospinning is -1 to -3 kV, the spinning distance of the electrospinning is 100 to 200 mm, the feeding rate of the electrospinning is 0.6 to 1 mL / h, and the roller rotation speed of the electrospinning is 600 to 800 rpm; The step of filling the electrolyte slurry into the pores of the thin film framework, followed by drying and hot pressing to obtain a solid electrolyte membrane includes: coating the electrolyte slurry on the surface of the thin film framework; performing suction filtration on the thin film framework coated with the electrolyte slurry to fill the electrolyte slurry into the pores of the thin film framework; drying and hot pressing the thin film framework filled with the electrolyte slurry to obtain a solid electrolyte membrane; among them, the time of the suction filtration is 30 to 180 s, and the vacuum pump pressure of the suction filtration is 80 to 90 kPa; The solid electrolyte membrane includes: A thin film framework, the thin film framework includes interconnected pores, and the component of the thin film framework includes polyacrylonitrile; An electrolyte composition, the electrolyte is filled in the pores of the thin film framework, and the electrolyte composition includes an oxide inorganic solid electrolyte, a binder, and a lithium salt.

2. The method for preparing a solid electrolyte membrane according to claim 1, wherein, The mass of the electrolyte composition is 40% to 60% of the total mass of the solid electrolyte membrane.

3. The method for preparing a solid electrolyte membrane according to claim 1, wherein The thickness of the solid electrolyte membrane is 10 to 30 μm.

4. The method for preparing a solid electrolyte membrane according to claim 1, wherein, The porosity of the thin film framework is 40% to 60%; and / or The pore size of the thin film framework is 1 to 10 μm.

5. The method for preparing a solid electrolyte membrane according to any one of claims 1 to 4, characterized in that, The mass ratio of the oxide inorganic solid electrolyte, the binder, and the lithium salt is 1:(0.5 to 2):(0.1 to 2); and / or The oxide inorganic solid electrolyte includes at least one of lithium lanthanum zirconium tantalum oxide and lithium titanium aluminum phosphate; and / or The binder includes at least one of polyvinylidene fluoride, polyethylene oxide, styrene-butadiene rubber, and polyacrylic acid; and / or The average number average molecular weight of the binder is 100,000 to 600,000; and / or The lithium salt includes at least one of lithium bis(trifluoromethanesulfonyl)imide, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(oxalato)borate, and lithium difluoro(oxalato)borate.

6. The method for preparing a solid electrolyte membrane according to claim 1, wherein The mass concentration of polyacrylonitrile in the polyacrylonitrile solution is 5% to 15%.

7. The method for preparing a solid electrolyte membrane according to claim 1, wherein, The solvent includes at least one of N-methylpyrrolidone, ethanol, acetonitrile, dichloroethane, chloroform, acetone, polyethylene glycol, and isopropanol.

8. A solid-state lithium battery, characterized in that, The solid-state lithium battery includes a solid electrolyte membrane prepared by the method for preparing a solid electrolyte membrane according to any one of claims 1 to 7.

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