A solid electrolyte membrane with a skeleton film support and a method for manufacturing the same

Abstract

The application relates to a skeleton membrane supported solid-state electrolyte membrane and a preparation method thereof, which comprises a porous skeleton membrane and a fiberized composite electrolyte material located on the surface of the porous skeleton membrane and in the pores of the porous skeleton membrane. The skeleton membrane supported solid-state electrolyte membrane and the preparation method thereof provided by the application solve the technical problems of insufficient mechanical strength, uneven electrolyte distribution and unstable ion conduction of a traditional solid-state electrolyte membrane by virtue of in-situ embedding structure design of the porous skeleton membrane and the fiberized composite electrolyte material and combination of a hot roller pressing process, and have the advantages of improved mechanical strength, improved electrolyte distribution uniformity and enhanced ion conduction stability.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion battery solid-state electrolyte materials, in particular to a solid-state electrolyte membrane supported by a skeleton membrane and a preparation method thereof. BACKGROUND

[0002] Conventional liquid lithium / sodium ion batteries have been widely used in the fields of energy storage, electronic products, electric vehicles and the like. However, the traditional liquid electrolyte has environmental problems and performance limitations, which will hinder the improvement of battery performance and the application in certain specific places. Therefore, the research and development of solid-state batteries become particularly important, and the formation and preparation of solid-state electrolyte membranes, as a key part of solid-state batteries, are more prominent. Limited by solvents, the current solid-state electrolyte is mainly prepared in a dry method. The dry film preparation technology does not use toxic organic solvents and does not need a drying process, so it can better avoid pollution caused by organic solvents.

[0003] The main preparation and processing method of the existing dry solid-state electrolyte membrane is to perform fiberization treatment and roll pressing into a film after blending polytetrafluoroethylene (PTFE) with a solid-state electrolyte (oxide, sulfide, polymer, halide, etc.). However, the solid-state electrolyte membrane prepared by this method has low mechanical strength, and its strength depends on the content of PTFE. However, if the content of PTFE is too high, it will deteriorate the ionic conductivity of the electrolyte membrane. PTFE is an inert material and does not conduct ions. When the content of PTFE is less than 5wt.%, the tensile strength of the dry solid-state electrolyte membrane prepared is generally less than 1Mpa, which is difficult to withstand the tension in the roll-to-roll process, and cannot realize large-scale continuous production.

[0004] Therefore, the existing dry method technology is in a dilemma that cannot be reconciled: the pursuit of mechanical strength and the pursuit of high ionic conductivity form a contradictory relationship. High strength must be accompanied by high impedance, and low impedance means that the film body is fragile and fragile, and cannot realize large-scale roll-to-roll production. This inherent contradiction between'strength-conductivity' has become a fundamental technical bottleneck restricting the industrialization of high-performance, low-cost dry solid-state electrolyte membranes. SUMMARY

[0005] The purpose of the present application is to provide a solid-state electrolyte membrane supported by a skeleton membrane and a preparation method thereof, which has the advantages of improving mechanical strength, improving electrolyte distribution uniformity and enhancing ionic conduction stability.

[0006] A solid-state electrolyte membrane supported by a skeleton membrane, comprising:

[0007] A porous skeleton membrane and a fiberized composite electrolyte material located on the surface of the porous skeleton membrane and in the pores of the porous skeleton membrane.

[0008] The application provides a solid-state electrolyte membrane supported by a skeleton membrane and a preparation method thereof, and the core is that a composite electrolyte material pre-fiberized by airflow milling is in-situ embedded into an ultrathin porous skeleton membrane through electrostatic blanking and hot roller pressing.

[0009] The solid-state electrolyte membrane supported by the skeleton membrane provided by the application can achieve the following technical effects:

[0010] Through the composite structure design of the porous skeleton membrane and the fiberized composite electrolyte material and the hot roller pressing process, the technical problems of insufficient mechanical strength, uneven electrolyte distribution and unstable ion conduction of the traditional solid-state electrolyte membrane are solved, and the solid-state electrolyte membrane supported by the skeleton membrane has the advantages of improved mechanical strength, improved electrolyte distribution uniformity and enhanced ion conduction stability. BRIEF DESCRIPTION OF DRAWINGS

[0011] Figure 1 is a schematic diagram of a solid-state electrolyte membrane supported by a single-layer skeleton membrane provided by one of the embodiments of the application;

[0012] Figure 2 is a schematic diagram of a solid-state electrolyte membrane supported by a double-layer porous skeleton membrane provided by one of the embodiments of the application;

[0013] Figure 3 is a schematic diagram of a preparation device of a solid-state electrolyte membrane supported by a single-layer skeleton membrane provided by one of the embodiments of the application;

[0014] Figure 4 is a schematic diagram of a preparation device of a solid-state electrolyte membrane supported by a double-layer porous skeleton membrane provided by one of the embodiments of the application;

[0015] Figure 5 is a flow chart of preparation of a solid-state electrolyte membrane supported by a skeleton membrane provided by one of the embodiments of the application;

[0016] Figure 6 is a schematic diagram of a structure of a porous skeleton membrane under an electron microscope provided by one of the embodiments of the application;

[0017] Figure 7 is a schematic diagram of a structure of a solid-state electrolyte membrane supported by a skeleton membrane under an electron microscope (with a magnification of 1000 times) provided by one of the embodiments of the application;

[0018] The reference signs are explained as follows: 1, porous skeleton membrane; 2, composite electrolyte material; 3, unwinding roller; 4, electrostatic blanking device; 5, hot roller; 100, solid-state electrolyte membrane. DETAILED DESCRIPTION

[0019] The following will be described in detail with reference to the accompanying drawings. Figures 1-7The application further provides a solid electrolyte membrane supported by a skeleton membrane and a preparation process thereof.

[0020] In the prior art, the manufacturing of lithium ion battery electrode sheets mainly relies on wet and dry processes. Although the dry process has environmental advantages, it faces the core problem of insufficient dispersibility of the binder. In the traditional dry process, due to the lack of solvent medium, the binder is difficult to be uniformly distributed in the mixed powder, resulting in poor film forming quality, uneven film thickness, and reduced conductivity and mechanical properties. Some existing technologies attempt to use a high polymer substrate as a support structure, but there are problems such as excessively large surface resistance and low preparation efficiency, which cannot meet the needs of high-performance solid electrolyte membranes.

[0021] Therefore, the application provides a solid electrolyte membrane supported by a skeleton membrane 100, which comprises a porous skeleton membrane 1 and a composite electrolyte material 2.

[0022] The overall thickness of the solid electrolyte membrane 100 ranges from 10 to 50 microns. Preferably, the overall thickness of the solid electrolyte membrane 100 is between 15 microns and 30 microns.

[0023] The porous skeleton membrane 1 is an ultra-thin biaxially stretched porous polymer membrane. The material of the porous polymer membrane includes polyolefins, polyethylene (PE), especially ultra-high molecular weight polyethylene (UHMWPE), polypropylene (PP), polyvinylidene fluoride (PVDF) and its copolymer (such as PVDF-HFP), and fluoropolymers. PVDF has excellent electrochemical stability and good affinity for electrolyte. These polymer materials can be prepared into porous membranes by phase inversion or stretching method. Among them, the porous polymer membrane is preferably an ultra-thin polytetrafluoroethylene biaxially stretched porous membrane, which is a polytetrafluoroethylene-based porous thin film prepared by a biaxial stretching process. Specifically, a biaxial synchronous or step-by-step stretching process can be used to achieve a uniform distribution of microporous structure during the stretching process, and the chemical stability and mechanical strength can provide support for the composite electrolyte.

[0024] The composite electrolyte material 2 is formed on the surface and pores of the porous skeleton membrane 1 after fiberization and calendering.

[0025] The porosity of the porous skeleton membrane 1 is 65% to 95%, the pore size ranges from 50 nm to 500 nm, and the thickness ranges from 1 micron to 4 microns.

[0026] Among them, the porosity of 65% to 95% refers to the proportion of pore volume in the total volume of the porous polymer membrane. The porosity can be achieved by adjusting the stretching process parameters. The porosity in this range can accommodate enough electrolyte material while maintaining the structural integrity of the skeleton membrane.

[0027] The pore size of 50-500 nm refers to the average diameter range of the pores in the porous polymer film, which can be achieved by controlling the stretching temperature and stretching rate. The pore size range can promote lithium ion transmission and prevent excessive penetration of electrolyte material. Preferably, the pore size range is 50-150 nm. Specifically, the lower limit of 50 nm ensures that the pore is wide enough to build a low tortuosity ion high-speed transmission network, avoiding the performance bottleneck caused by excessive small pore size and uneven electrolyte filling; at the same time, the upper limit of 150 nm can generate sufficient mechanical resistance and interface energy barrier, thereby effectively inhibiting the growth and penetration of lithium dendrites. According to the famous "Sand's Time" model and Laplace pressure theory, the mechanical strength and pore size of the electrolyte are key to effectively inhibiting lithium dendrites. When the pore size is too large (e.g., more than 500 nm), even if the skeleton itself has a certain strength, it cannot form an effective pressure barrier to the lithium dendrite tip, and the dendrite can "grow wild" in the wide pore, eventually piercing the separator and causing a short circuit in the battery.

[0028] In the present embodiment, the mass ratio of the porous skeleton film 1 to the composite electrolyte material 2 is controlled so that the mass ratio of the porous skeleton film 1 in the prepared solid-state electrolyte film is 0.8-4%. By adjusting the ratio of the skeleton film to the composite material, the skeleton film pores are fully filled while maintaining a continuous ion transmission path.

[0029] Specifically, the porous skeleton film 1 serves as a three-dimensional carrier to guide the fibrous composite material to extend and distribute along the pore direction during the calendering process. In the fibrous composite material, the binder forms a micron-level fiber network, and the solid-state electrolyte particles form an interlocking structure. During the hot roller 5 calendering process, the composite material is pressed into the skeleton film pores and forms a continuous phase, and the mechanical strength of the skeleton film compensates for the brittleness defect of the pure electrolyte film. By precisely controlling the mass ratio, the skeleton film provides sufficient support while avoiding excessive use that causes pore blockage, allowing ions to be efficiently transmitted between the composite material and the porous skeleton film 1.

[0030] The fibrous composite electrolyte material 2 refers to a powder mixture subjected to mechanical shearing treatment, which can be achieved by uniformly mixing solid-state electrolyte powder, lithium salt, and binder and then performing fibrous processing on the powder using an air jet mill device. This treatment causes the binder to form a network fiber structure, enhancing the binding force with the active material.

[0031] The composite electrolyte material 2 includes solid-state electrolyte powder and lithium salt, and can also include a binder. The components include 7.5%-37.5% lithium salt and the balance of solid-state electrolyte powder in terms of mass ratio. When the binder is present, its mass ratio is greater than 0% and not higher than 0.5%.

[0032] The solid electrolyte powder refers to an inorganic or organic solid electrolyte material constituting the main structure of the electrolyte film, which can be implemented by using one or a combination of polymer solid electrolyte, oxide solid electrolyte, sulfide solid electrolyte, or halide solid electrolyte, for example, the mass ratio is controlled to be 65%-88% to maintain the mechanical support ability and ion conduction network of the electrolyte film.

[0033] The advantage of controlling the mass ratio of the solid electrolyte powder in the range of 65%-88% is that, on the one hand, the content of not less than 65% ensures that the powder concentration exceeds the percolation threshold, forming a three-dimensional continuous ion conduction network throughout the film, thereby obtaining extremely high ion conductivity; on the other hand, the content of not more than 88% leaves sufficient polymer matrix to provide excellent mechanical flexibility and interface wettability for the electrolyte film, solving the problems of brittleness and high interface impedance caused by ultra-high filling amount. This range optimizes the conductive path and mechanical / interface performance, enabling the composite solid electrolyte to achieve high conductivity while maintaining the mechanical stability and low interface impedance required for practical applications.

[0034] The lithium salt refers to an electrolyte additive that provides a lithium ion migration carrier, which can be one or several of LiClO4, LiBF4, LiAsF6, LiPF6, LiTFSI (lithium bis(trifluoromethanesulfonyl) imide), LiFSI (lithium bis(fluorosulfonyl) imide), LiCF3SO3, LiBOB, LiDFOB; the mass ratio is set to 7.5%-37.5% to supplement the ion conduction path while avoiding the increase of interface impedance caused by excessive crystallization. The selection of a single type of lithium salt in the prior art often cannot meet the ion conduction requirements of different electrolyte systems, and the combination of multiple types of lithium salts provided in the present scheme can be adapted and selected according to the characteristics of the electrolyte material, for example, lithium perchlorate with high thermal stability is preferred in the oxide electrolyte system. The addition amount of lithium salt is limited to 7.5%-37.5%, which supplements the lithium ion source while balancing the conductivity and chemical stability to prevent electrolyte decomposition side reactions.

[0035] The binder can be one or several of polytetrafluoroethylene, ultra-high molecular weight polyethylene, polyimide, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polyethylene oxide, and polyacrylonitrile.

[0036] The mass ratio of the binder is limited to 0%-0.5%. As understood by those skilled in the art, when the binder content is zero, the physical anchoring of the three-dimensional network structure of the porous framework film 1 and the "cold welding effect" or interface diffusion caused by the particle interfacial diffusion of the hot pressing process form cohesion. When a small amount of binder within 0.5% is added, combined with the airflow fiberization treatment, the binder can form an efficient nanoscale fiber network that uniformly coats the particles.

[0037] This formula design completely subverts the concept of traditional dry process (usually 3%-5% binder). The traditional process is prone to ion conduction path blockage due to binder agglomeration, while the present scheme, through the use of extremely low amount + fiberization, maximizes the reduction of inert ingredients while improving interfacial bonding strength, and breaks through the conventional process limit of less than 5% lithium salt addition, and through optimized ratio, synergistically improves the electrical conductivity and interface stability, and fundamentally solves the problems of film cracking, thickness fluctuation and performance decline caused by uneven material dispersion.

[0038] In summary, the present application uses a dual strategy of "micro-preconstruction" and "macro-forced molding" to completely break through this bottleneck:

[0039] The first, micro-preconstruction - solve the adhesion problem at the powder stage. The present application uses high-energy shearing means such as air jet mill to stretch the fiberizable binder in situ between solid electrolyte particles into a nanoscale fiber network at a content of only 0.5% or even lower at the mixing stage. This makes the binder change from the "agglomerated block" form in traditional process to the efficient three-dimensional "spider web" form, achieving uniform coating and physical locking of active particles with very little amount. This step directly reduces the amount of inert "roadblock" - binder that hinders ion transmission by nearly an order of magnitude.

[0040] The second, macro-forced molding - realize ordered accumulation with skeleton as template. The micro-preconstructed fiberized composite powder is filled into the porous skeleton film 1 with high porosity and nanoscale pore size. This skeleton film plays the role of a three-dimensional molding template in this process, and its strong pore wall structure plays a "directional guiding" role during hot calendering, forcing the loose powder to arrange in an orderly and dense manner within the limited pore space, completely eliminating macroscopic defects (such as uneven thickness, holes, etc.) caused by free-flowing powder. More importantly, the mechanical strength of the film is completely borne by the skeleton itself, thereby completely decoupling the "mechanical support function" and the "ion conduction function".

[0041] The solid-state electrolyte film described in the present application can be flexibly implemented in two preferred structures according to process requirements and performance emphasis:

[0042] One is a single-layer skeleton structure, such as Figure 1 and the corresponding preparation equipment Figure 3As shown. In this structure, a single porous skeleton film 1 is delivered by a single unwinding roller 3, and the composite electrolyte material 2 is applied to one or both sides of the film by electrostatic dispensing device 4 and other means, and is embedded in the pores during subsequent hot pressing. The process flow of this structure is relatively simple, and is suitable for application scenarios with moderate mechanical strength requirements. As shown in Example 2, when the composite electrolyte layer is in direct contact with the electrode, the interface without the barrier of the skeleton may result in lower interface impedance.

[0043] The second is a "sandwich" structure, as shown in Figure 2 and the corresponding preparation equipment Figure 4 As shown. In this structure, two porous skeleton films 1 are synchronously delivered by two unwinding rollers 3, and the composite electrolyte material 2 is precisely fed between the two layers of skeleton films. During hot rolling 5, the constraining effect of this double-sided coating plays a key role: it acts as a moving mold, effectively preventing the powder from escaping laterally under high pressure, and forcing it to achieve more efficient densification in the vertical direction. Therefore, the sandwich structure not only gives the solid-state electrolyte film the ultimate mechanical strength and tear resistance, but also ensures higher compaction density and excellent thickness uniformity, fundamentally eliminating the risk of delamination, and is an ideal choice for preparing high-performance, ultra-thin solid-state electrolyte films.

[0044] Compared with the prior art, the uneven dispersion of the binder in the traditional dry process leads to loose film layer structure and increased resistance, while the present solution uses single-layer pore filling or double-layer sandwich structure design to force the uniform distribution of the composite material by the physical confinement effect of the skeleton film, and the fiberization process enhances the mechanical interlocking between the materials, solving the film formation defect problem from the structural level, without relying on solvent dispersion to achieve the balance between film layer densification and conductivity.

[0045] Please refer to Figure 5 The present application further provides a preparation method of the solid-state electrolyte film 100 supported by the skeleton film, comprising:

[0046] S1: providing a porous skeleton film 1, which is an ultra-thin biaxially stretched porous polymer film;

[0047] S2: providing a composite electrolyte material 2, and embedding the fiberized composite electrolyte material 2 into the porous skeleton film 1;

[0048] S3: hot rolling the porous skeleton film 1 embedded with the composite electrolyte material 2 by hot roller 5 to prepare a solid-state electrolyte film supported by the skeleton film. In this embodiment, by controlling the amount of the porous skeleton film 1 and the composite electrolyte material 2, the mass fraction of the porous skeleton film 1 in the prepared solid-state electrolyte film 100 is 0.8-4%. Preferably, the mass fraction of the porous skeleton film 1 is 0.8-2%.

[0049] In a preferred embodiment, the roll temperature of the calendering roll 5 can be controlled in the range of 80-150°C, the pressure intensity of the material in the roll contact zone can be set in the range of 100-1000 MPa, and the calendering speed can be controlled in the range of 1-15 m / min, so as to obtain a dense and uniform-thickness solid-state electrolyte film.

[0050] The composite electrolyte material 2 refers to a mixture composed of solid-state electrolyte powder, lithium salt and binder, which can be specifically treated by air-jet fiberization. The air-jet mill refers to a device that utilizes the impact force and shear force generated by high-speed airflow to crush and mix the powder, which can be specifically implemented by a fluidized bed type or a spiral type air-jet mill, and the binder is stretched into a fibrous structure by mechanical action.

[0051] The air-jet mill device can adopt a fluidized bed type or a spiral type air-jet mill. In order to avoid material moisture absorption or side reactions, dry air with a dew point lower than -40°C or high-purity nitrogen is preferably used as the grinding gas. The inlet pressure of the grinding gas can be controlled in the range of 0.5-1.2 MPa. Higher pressure helps to provide stronger shear force to promote the sufficient fiberization of PTFE. According to the model and processing capacity of the air-jet mill, the feeding rate can be controlled in the range of 0.5-10 kg / h.

[0052] Generally, a lower feeding rate helps the material to obtain a longer residence time in the mill cavity and a more sufficient fiberization effect. If an air-jet mill with a dynamic classification wheel is used, the rotational speed of the classification wheel can be set between 3000-12000 rpm, and the particle size distribution of the discharge can be effectively controlled by adjusting the rotational speed, so as to ensure that the main part of the powder can smoothly enter the micron or sub-micron pore channels of the porous skeleton film 1, and the retained fibrous morphology is beneficial to form an effective mechanical interlocking and ion conductive network in the pores.

[0053] The entire fiberization and mixing process is carried out in a low-humidity environment (relative humidity less than 15%) and a temperature-controlled environment (for example, 5-25°C), so as to ensure the chemical stability of the lithium salt and the solid-state electrolyte. The low-humidity condition refers to a dry atmosphere with a relative humidity less than 15%, which can be specifically implemented by using a nitrogen circulation system or a dehumidification device, to avoid the agglomeration or deliquescence of the lithium salt due to moisture absorption.

[0054] Fiberization mixing refers to the process of forming a continuous network of fibers in the binder through physical action. Specifically, the rotational speed of the jet mill and the processing time can be adjusted to achieve uniform coating of the solid electrolyte particles by the binder. Fiberization mixing enables the composite electrolyte material 2 to transform from the original particle morphology to a microcosmic, interwoven three-dimensional fiber network. This fiber network can physically capture and uniformly disperse the solid electrolyte particles and lithium salt, thereby forming a uniformly fiberized composite electrolyte material as a whole, laying the foundation for subsequent preparation of a thin film with excellent mechanical properties and continuous ion conductive pathways.

[0055] Hot roller calendering technology refers to a process of densifying materials by applying pressure through heated rollers. Specifically, a double-roller calendering machine can be used to perform calendering at a set temperature, utilizing heat and mechanical pressure to promote the densification of the electrode film structure.

[0056] In a specific preparation process, a solid electrolyte film preparation device can be used. The device can include one or two unwinding rollers 3 for unwinding the porous framework film 1, an electrostatic feeding device 4 located between the unwinding rollers 3 and the hot rollers 5, and two oppositely arranged hot rollers 5. The electrostatic feeding device 4 is used to sprinkle the fiberized composite electrolyte material onto the surface of the porous framework film 1 released by the unwinding rollers 3, and the hot rollers 5 are used to calender the porous framework film 1 covered with the fiberized composite electrolyte material.

[0057] When the unwinding rollers 3 are one, the solid electrolyte film includes a single-layer porous framework film 1 and the fiberized composite electrolyte material 2 located on the surface of the single-layer porous framework film 1 and within the pores of the porous framework film 1. When the unwinding rollers 3 are two, the solid electrolyte film includes a sandwich structure formed by the double-layer porous framework film sandwiching the composite electrolyte material 2.

[0058] Among them, the unwinding roller 3 refers to a roller structure for continuously conveying the porous framework film 1, which can be specifically implemented by a metal roller driven by a servo motor. Its role is to maintain the stability of the tension of the porous framework film 1 and continuously feed. The hot roller refers to a roller group for hot pressing the porous framework film 1 covered with powder, which can be specifically implemented by a steel roller plated with chromium in combination with a heating system. Its role is to form a dense bond between the fiberized composite electrolyte material 2 and the porous framework film 1 through hot pressing.

[0059] The electrostatic feeding device 4 refers to a device for quantitatively sprinkling the fiberized composite electrolyte material 2 onto the surface of the porous framework film 1, which can be specifically implemented by a vibrating sieve-type distributor. Its role is to achieve uniform coverage and directional penetration of the powder. The fiberized composite electrolyte material 2 serves to enhance the filling property and conductive continuity of the material in the pores of the framework film.

[0060] The single-layer structure refers to a skeleton film supporting the composite electrolyte material 2 on one side, which can be achieved by a single unwinding roller 3 combined with one-side powdering. The function is to simplify the process steps and maintain the uniformity of the electrolyte layer. The double-layer structure refers to a sandwich structure with the composite electrolyte material 2 sandwiched between two skeleton films, which can be achieved by two unwinding rollers 3 synchronously conveying the skeleton films and powdering in the middle. The function is to enhance the interlayer bonding force and reduce the interface impedance.

[0061] Specifically, during the continuous conveying of the porous skeleton film 1 by the unwinding roller 3, the electrostatic feeding device 4 uniformly spreads the fibrous composite electrolyte material onto the film surface. When a single unwinding roller 3 is used, the powder penetrates into the interior through the skeleton film pores, and then forms a single-layer composite structure through hot pressing by the hot roller 5. This method reduces material accumulation and improves interface bonding efficiency.

[0062] When two unwinding rollers 3 are used, the composite electrolyte material 2 is sandwiched between two porous skeleton films 1, and the powder penetrates into the pores of the upper and lower films at the same time through the bidirectional pressure of the hot roller 5, forming a three-dimensional interpenetrating network structure. The vibrating screen function of the electrostatic feeding device 4 can control the powder spreading density, avoiding the powder scattering problem caused by air flow disturbance in traditional spraying process. The hot pressing temperature of the hot roller 5 can be adjusted to be lower than the melting point of the binder, so that the fibrous composite electrolyte material is combined with the skeleton film through physical entanglement, reducing the amount of binder.

[0063] Please refer to Figure 6 which directly shows the microstructure of the porous skeleton film 1 as the mechanical support body of the present application in the form of a scanning electron microscope (SEM) image. As can be clearly seen from the figure, the skeleton film is composed of a large number of micron or sub-micron polymer fibers interlaced with each other and connected by nodes, thus forming a three-dimensional network structure with high porosity.

[0064] On the contrary, please refer to Figure 7 which shows the surface electron microscope image of the final skeleton film supported solid-state electrolyte film (100) prepared according to the present application. Unlike the open porous structure of the pure skeleton film in Figure 6 , Figure 7 the surface presents a highly dense state. This indicates that the particles of the composite electrolyte material 2 are uniformly and tightly filled in the surface and internal pores of the porous skeleton film 1 under the hot calendering process, and almost no obvious holes or defects can be seen. This directly proves that the preparation method of the present application can realize effective penetration of the composite material into the skeleton film and high compactness, forming a continuous conductive network of tight contact between electrolyte particles, which is the key structural basis for realizing high ionic conductivity and excellent mechanical properties.

[0065] Compared with the prior art, the traditional dry process adopts a spraying mode to attach electrode raw materials to the surface of the substrate, and there is a problem of uneven dispersion of the powder, which leads to excessively high porosity of the film layer, thereby increasing the surface resistance. The present scheme combines directional scattering by the electrostatic discharging device 4 and synchronous hot pressing by the hot roller 5, so that the fibrous composite electrolyte material uniformly fills the skeleton film pores and forms a continuous conductive path, and the double unwinding roller 3 structure further reduces the interface contact resistance by interlayer pressing. Compared with the multiple spraying and drying steps in the traditional process, the single powder scattering and calendering process of the present scheme significantly shortens the preparation period.

[0066] The beneficial effects of the present application are demonstrated by the following examples and comparative examples.

[0067] Example 1

[0068] In a low humidity environment (in this example, in an extremely dry environment with a humidity of less than 1%), LLZO (lithium lanthanum zirconium oxide) solid electrolyte powder, lithium salt LiTFSI, and binder PTFE are weighed in a ratio of 80:18.5:0.5, and then uniformly mixed by a mixer in a 5°C environment to obtain a premixed material; the premixing is carried out in a 5°C low temperature environment, which mainly utilizes the low temperature to greatly inhibit the agglomeration of lithium salt due to moisture absorption, and ensures that various powders can be extremely uniformly dispersed at the micro level, laying a key foundation for subsequent obtaining high-performance and uniform solid electrolyte film.

[0069] The mixed premixed material is also subjected to fibrous treatment by an air jet mill under low humidity conditions to obtain a fibrous composite electrolyte material.

[0070] Two rolls of porous skeleton film 1 made of PTFE material are introduced into the double roller calender machine in a V-shaped manner by the active unwinding roller 3, and then the above-prepared fibrous composite electrolyte material 2 is uniformly scattered from the upper opening of the V-shaped structure. Subsequently, the calendering is carried out by setting the hot roller temperature to 85°C, and after gradually thinning and edge cutting by multiple compression rollers, a "sandwich" structure solid electrolyte film 100 with a final thickness of 30 microns is obtained.

[0071] Through the above fibrous mixing treatment, a small amount of PTFE binder forms a micro three-dimensional fiber network in situ in the powder, and the LLZO particles and LiTFSI lithium salt are uniformly captured and fixed in the fibrous network, which lays the foundation for preparing a composite electrolyte film with high mechanical strength and high ionic conductivity.

[0072] Example 2

[0073] Different from Example 1, in the roller pressing section, there is only one unwinding, and the powder scattering becomes from both sides of the film into the double roller machine, so that the fibrous composite electrolyte material 2 is formed on the opposite sides of the porous skeleton film 1 and in the pores of the porous skeleton film 1, respectively.

[0074] The single-skeleton structure of Example 2, due to the partial exposure of the composite electrolyte material 2 to one side of the membrane, does not have the overall symmetry of the sandwich structure of Example 1, and thus exhibits lower strength and elongation in macroscopic tensile tests. However, this asymmetric structure can bring unexpected advantages at the electrochemical level: when the composite electrolyte layer on one side is in contact with the electrode, there is no barrier of the skeleton layer in the middle, forming a more direct and continuous ion transport interface, which can help to reduce the local interfacial impedance and improve the cycle stability. This further demonstrates the diversity and adjustability of the structural design of the present application.

[0075] Example 3

[0076] Unlike Example 1, the formulation does not contain PTFE binder, and the ratio of LLZO solid-state electrolyte powder to lithium salt LiTFSI is 80:19.

[0077] In this example, although there is no binder, under the huge mechanical pressure of hot roll stretching, the LLZO and LiTFSI particles undergo close packing and a certain degree of plastic deformation. Especially at the contact points of the particles, high pressure can cause a 'cold welding' effect, forming a strong inter-particle cohesion. Combined with the strong three-dimensional network physical anchoring effect of the porous skeleton membrane 1, it is sufficient to prepare a mechanically stable solid-state electrolyte membrane without the need for a binder.

[0078] Example 3A

[0079] The formulation and preparation process of this example are similar to Example 3, with the difference being that the solid-state electrolyte powder uses a sulfide solid-state electrolyte (such as Li6PS5Cl) with higher surface energy, and also does not add any binder.

[0080] According to the principles of materials science, it can be reasonably predicted that sulfide solid-state electrolytes generally have lower hardness and better plasticity than oxides (such as LLZO), and some sulfide material particles have higher surface energy. Therefore, without adding a binder, when the mixed powder of Li6PS5Cl and lithium salt is embedded in the porous skeleton membrane 1 made of PTFE in an inert atmosphere, and subjected to hot roll stretching, the particles are more likely to undergo plastic deformation and close packing. Under the action of pressure, their contact points will produce more significant 'cold welding effect' or interfacial reaction, forming stronger inter-particle bonding than the oxide system. Therefore, this scheme can also obtain a mechanically stable composite solid-state electrolyte membrane without the need for a binder, and is expected to exhibit excellent ionic conductivity due to the intrinsic high conductivity of sulfide materials.

[0081] Example 4

[0082] The formulation of this example is similar to Example 1, the main difference is that the solid electrolyte powder is replaced by sulfide solid electrolyte Li6PS5Cl with higher intrinsic ionic conductivity. Considering the sensitivity of sulfide materials to humidity and air, all preparation steps from powder mixing to hot-pressing into film are carried out in an argon glove box with water and oxygen content less than 0.1 ppm.

[0083] According to the principles of material science, it can be reasonably expected that this replacement will produce significant synergistic effects:

[0084] In terms of mechanical properties: compared with the hard and brittle oxide ceramic powder used in Example 1, Li6PS5Cl particles are softer with excellent ductility and plasticity. Therefore, during hot stretching, these soft sulfide particles not only easily embed into the pores of the PTFE porous framework film, but more importantly, they themselves will undergo significant plastic deformation, forming a "cold welding" type of tight physical bonding between particles. This self-compaction and self-bonding effect due to the softness of the material greatly enhances the inter-particle cohesion, thereby forming a mechanically stable, dense and defect-free composite electrolyte film without relying on any binder.

[0085] In terms of electrochemical performance: due to the tight particle packing caused by the above-mentioned plastic deformation, continuous and low impedance ion transport channels are formed between Li6PS5Cl particles, effectively eliminating the grain boundary resistance caused by poor particle contact. This structural advantage, combined with the ultra-high intrinsic ionic conductivity of Li6PS5Cl itself, can be expected to produce a composite solid electrolyte film with extremely high room temperature ionic conductivity significantly better than Example 1 based on oxide electrolyte.

[0086] Example 5

[0087] Unlike Example 1, the lithium salt is LiAsF6, and the rest of the components and preparation methods are the same. The purpose of this replacement is to take advantage of the wider electrochemical stability window of LiAsF6. Therefore, it can be expected that the solid electrolyte film obtained in this example will also exhibit excellent cycle stability when matched with high-voltage cathodes.

[0088] Example 6

[0089] Unlike Example 1, the ratio of LLZO solid electrolyte powder, lithium salt LiTFSI, and binder PTFE micro powder is 85:13.5:0.5.

[0090] The preparation method of this example is as follows:

[0091] First step, 85 parts by weight of LLZO solid-state electrolyte powder, 13.5 parts by weight of LiTFSI lithium salt powder, and 0.5 parts by weight of PTFE micro powder are uniformly mixed to obtain a pre-mixed material. Under the same low humidity conditions as in Example 1, the pre-mixed material is mixed by air flow grinding to obtain a final fiberized composite electrolyte material.

[0092] Second step, provide a PTFE porous skeleton film. The fiberized composite electrolyte material is scattered by the electrostatic discharging device 4 to the pores of the PTFE porous skeleton film.

[0093] Third step, heat pressing to obtain the final composite solid-state electrolyte film.

[0094] Example 7

[0095] Different from Example 1, the binder is polyethylene oxide. Although the fiberization degree of polyethylene oxide is not as good as PTFE, the key is that through high-energy mixing of air flow grinding, nanoscale uniform dispersion and particle coating are also achieved. This highly dispersed state enables PEO to achieve efficient 'in-situ bonding' at a very low dosage during subsequent hot pressing due to its low glass transition temperature, achieving similar effects of reducing dosage and enhancing bonding force as the PTFE system.

[0096] Comparative Example 1

[0097] In a low humidity environment (humidity less than 1% glove box), LLZO solid-state electrolyte powder, lithium salt LiTFSI, and binder PTFE are weighed in a mass ratio of 80:17:3, then mixed by a V-type mixer for 2 hours at 5°C and a speed of 40 rpm to obtain a pre-mixed powder;

[0098] The mixed material is also fiberized and mixed by air flow grinding under low humidity conditions to obtain a fiberized composite electrolyte material. Specifically, the pre-mixed powder can also be fiberized and mixed by a circulating tube air flow grinder. Nitrogen is set as the working gas, the gas pressure is controlled at 0.6 MPa, and the powder feeding rate is 5 kg / h; the fiberized powder is placed on a double roller machine (roller diameter 150 mm) for roller pressing to form a film. The roller temperature is set to 105°C and the roller pressing line speed is 0.5 m / min. Two pressing processes are performed: the first roller pressing gap is set to 150 microns, and the second roller pressing gap is set to 80 microns, finally obtaining a solid-state electrolyte film with uniform thickness of 80 microns. Of course, it can be understood that in other ways, it is not limited to two pressing processes, but can be three or even more to ensure the desired thickness.

[0099] The PTFE (polytetrafluoroethylene) binder has the property of "fiberization" when subjected to shear force. It forms a three-dimensional fiber network that physically binds and adheres the LLZO ceramic powder (conductive filler) and LiTFSI lithium salt (ion source) like a spider web.

[0100] In the present application, lithium ion batteries were prepared using different solid electrolyte membranes in Examples 1-7 and Comparative Example 1, and the ion conductivity, elongation at break of the solid electrolyte membranes and the room temperature cycle performance of the lithium ion batteries were tested.

[0101] Room temperature ion conductivity test

[0102] The solid electrolyte membrane prepared in Example 1 of the present application was cut into a circular piece with a diameter of 16 mm, and its thickness (L) was measured. The membrane was placed between two polished stainless steel electrodes with a diameter of 14 mm and assembled in a coin cell shell to form a SS / SSE / SS symmetric battery. After standing in a constant temperature oven at 25°C for 2 hours, the electrochemical workstation was used for alternating current impedance test (EIS). The frequency range of the test was 1 MHz to 0.1 Hz, and the applied alternating current disturbance voltage was 10 mV. According to the intersection of the high frequency region semicircle and the real axis (Z') in the obtained Nyquist plot, the bulk resistance (R) of the membrane was read. The room temperature ion conductivity was calculated by the formula σ = L / (R*A), where A is the electrode area (π*(0.7cm) 2 )。

[0103] Mechanical property test

[0104] The mechanical properties of the solid electrolyte membrane were tested according to GB / T 1040.2-2022 "Determination of tensile properties of plastics - Part 2: test conditions for moulded and extruded plastics". The prepared membrane was cut into dumbbell-shaped samples, and a universal material testing machine was used to test at 25°C with a tensile rate of 5 mm / min until the sample broke, and the elongation at break was recorded.

[0105] Full cell long cycle performance test

[0106] To verify the electrochemical performance of the solid electrolyte membrane, the solid electrolyte membranes prepared in Examples 1-7 and Comparative Example 1 of the present application were used as separators, NCM811 was used as the positive electrode, and lithium metal / graphite was used as the negative electrode to assemble coin cells. The environmental temperature was controlled at 25±2°C, and the electrochemical performance of the battery was tested.

[0107] First, the battery was activated for 3 cycles at a constant current charge / discharge rate of 0.1C / 0.1C, and the discharge capacity of the 3rd cycle was taken as the reference capacity (100%).

[0108] Subsequently, long cycle performance tests were conducted, with each cycle's charge and discharge regime being: charging to 4.35 V at a constant current (CC) of 1C, then switching to constant voltage (CV) 4.35 V charging until the charging current dropped to 0.05C (C / 20) cutoff; resting for 10 minutes, then discharging to 2.8 V at a constant current (CC) of 1C.

[0109] The discharge capacity of each cycle was recorded, and when the discharge capacity first decreased to 80% of the reference capacity, the test was terminated, and the number of cycles recorded at this time was the number of cycles at room temperature for the battery. Please refer to Table 1 below, which is the performance test results of lithium-ion batteries in Examples 1-7 and Comparative Example 1.

[0110] Table 1

[0111]

[0112] Through comparative analysis of the comparative examples and examples, the following conclusions can be drawn:

[0113] 1. Mechanical property comparison

[0114] Comparative Example: The tensile strength is only 0.65 MPa, and the elongation at break is only 15%, indicating that its mechanical properties are extremely poor and difficult to withstand mechanical stress during battery assembly and use.

[0115] Example: The tensile strength of Examples 1-7 is significantly higher than that of the comparative example, with the lowest being 4.36 MPa (Example 2) and the highest being 9.15 MPa (Example 4). The elongation at break is also greatly improved, with the lowest being 62% (Example 2) and the highest being 185% (Example 7).

[0116] Conclusion: By combining the porous framework film with the fibrous composite electrolyte material, the mechanical properties of the solid-state electrolyte film are significantly improved, making it better able to adapt to the mechanical requirements during battery assembly and use.

[0117] 2. Ion conductivity comparison

[0118] Example: The ion conductivity of Examples 1-7 is significantly improved, with the lowest being 2.44 mS / cm (Example 6) and the highest being 5.94 mS / cm (Example 4).

[0119] Conclusion: By optimizing the formulation and fibrous treatment of the composite electrolyte material, the examples significantly improve the ion conductivity, improving the performance and efficiency of the battery.

[0120] 3. Cycle performance comparison Comparative example: In the room temperature cycle test, only 256 cycles can be maintained, indicating poor cycle stability and short battery life.

[0121] Examples: The cycle number of examples 1-7 is significantly increased, the lowest is 1123 cycles (example 6), and the highest reaches 1687 cycles (example 4).

[0122] Conclusion: By optimizing the material formula and preparation process, the cycle stability of the solid-state electrolyte membrane is significantly improved, and the service life of the battery is prolonged.

[0123] 4. Film thickness comparison

[0124] Comparative example: The film thickness is 80 microns, and the thicker film will increase the internal resistance and weight of the battery.

[0125] Examples: The film thickness of examples 1-7 is 30 microns, which is significantly lower than the comparative example.

[0126] Conclusion: By optimizing the preparation process, the example realizes a thinner film thickness, reduces the internal resistance and weight of the battery, and maintains good mechanical properties and electrochemical properties.

[0127] 5. Adhesive dosage comparison Comparative example: The adhesive dosage is 3%, and higher adhesive dosage may hinder ion transmission and reduce conductivity.

[0128] Examples: The adhesive dosage in the example is only 0.5%, which is significantly lower than the comparative example.

[0129] Conclusion: Through the fiberization treatment and the support of the porous skeleton film, the example reduces the adhesive dosage while still maintaining good mechanical properties and electrochemical properties, further optimizing the comprehensive performance of the material.

[0130] 6. Structure design comparison Comparative example: The traditional dry process lacks effective three-dimensional support structure, resulting in uneven material distribution, uneven film thickness, and discontinuous ion transmission path.

[0131] Examples:

[0132] Through the combination of porous skeleton film and fiberized composite electrolyte material, a uniform three-dimensional network structure is formed, significantly improving the material distribution uniformity and ion transmission efficiency. Conclusion: The structure design of the example optimizes the dispersibility and ion transmission path of the material, improving the overall performance of the solid-state electrolyte membrane.

[0133] By comparing the examples with the comparative examples, it can be clearly seen that the application significantly improves the mechanical properties, ion conductivity and cycle stability of the solid-state electrolyte membrane by combining the porous skeleton film with the fiberized composite electrolyte material, while realizing a thinner film thickness and a smaller adhesive dosage.

[0134] It is worth emphasizing that the inherent contradiction of the conventional dry process (as shown in Comparative Example 1) is the reason why it is difficult to produce a thin film (e.g. 30 pm) with comparable performance to the present application. Due to the lack of skeleton support, in order to ensure that the film does not break during winding and operation, it is necessary to maintain a high thickness (e.g. 80 pm) and binder content (e.g. 3%), but this inevitably sacrifices the electrochemical performance. One of the core values of the'skeleton support' structure of the present application is that it gives the film unprecedented mechanical robustness, making it possible to'manufacture 30 pm or even thinner, low binder content, mass producible' dry solid electrolyte film.

[0135] The present application solves the performance and process bottlenecks of the prior art through the synergistic design of 'porous skeleton film support' and 'in-situ embedding of fiberized powder'. In terms of performance, this structure forces the uniform distribution of powder, eliminating local current concentration, while its physical bonding method greatly reduces the amount of binder, greatly unblocking the ion transmission channel; the dense bonding formed by calendering reduces the particle interface impedance, which together realizes the significant improvement of ionic conductivity. The physical bonding method of the fiberized composite electrolyte material and the porous skeleton film reduces the amount of binder added, avoiding the blockage of the ion transmission channel by excessive binder. As shown in Example 1 and Comparative Example 1, with a binder content of only 0.5% (vs 3%) and a thinner film thickness (30 pm vs 80 pm), the tensile strength jumps from 0.65 MPa to 8.64 MPa (more than 13 times), and the ionic conductivity is also greatly improved from 0.51 mS / cm to 2.67 mS / cm (more than 5 times).

[0136] Through the comparison of examples and comparative examples, it can be clearly seen that the present application, through the combination of porous skeleton film 1 and fiberized composite electrolyte material 2, has achieved overwhelming advantages in mechanical properties, ionic conductivity and cycle stability, while realizing thinner film thickness and less binder content.

[0137] In summary, the core inventive concept of the present application is to solve the fundamental contradiction of the prior art through the synergistic effect of two key steps: first, use an air jet mill to pretreat the powder containing a small amount of fiberizable binder during the mixing stage, to prepare the binder into a highly dispersed nanofiber network in-situ in the powder, which enables the full and effective coating of the electrolyte particles with only 1 / 10 of the conventional amount of binder (e.g. 0.5%); second, fill this pre-fiberized powder into a porous skeleton film with high mechanical strength, and then realize densification through mild hot pressing.

[0138] The above are all preferred embodiments of the present application, and do not limit the protection scope of the present application, so that: all equivalent changes made according to the structure, shape, principle of the present application should be covered in the protection scope of the present application.

Claims

1. A solid electrolyte membrane supported by a skeleton film, characterized by, It comprises: a porous skeleton film (1) which is an ultra-thin biaxially stretched porous polymer film, the porous skeleton film (1) is an ultra-thin polytetrafluoroethylene biaxially stretched porous film, the porosity ranges from 65-95%, the pore size ranges from 50-500 nm, the mass of the porous skeleton film (1) accounts for 0.8-4% of the mass of the solid-state electrolyte film; and a fiberized composite electrolyte material (2) located on the surface of the porous skeleton film (1) and in the pores of the porous skeleton film (1), the composition of the composite electrolyte material (2) includes solid-state electrolyte powder and lithium salt, and can also include a binder; wherein each component accounts for 7.5%-37.5% of the lithium salt and the balance of the solid-state electrolyte powder in terms of mass percentage; when the binder is present, its mass percentage is greater than 0% and not higher than 0.5%.

2. The skeletonized membrane supported solid state electrolyte membrane of claim 1, wherein: The mass percentage of the solid-state electrolyte powder is 65%-88%; The solid-state electrolyte powder includes one or more of polymer solid-state electrolyte, oxide solid-state electrolyte, sulfide solid-state electrolyte, and halide solid-state electrolyte; The lithium salt is one or more of LiClO4, LiBF4, LiAsF6, LiPF6, LiTFSI, LiFSI, LiCF3SO3, LiBOB, LiDFOB; The binder includes one or more of the following fiberizable polymers: polytetrafluoroethylene, ultra-high molecular weight polyethylene, polyimide, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polyethylene oxide, polyacrylonitrile.

3. The solid-state electrolyte membrane with skeleton film support according to claim 1, characterized in that: The thickness of the porous skeleton film (1) ranges from 1 micron to 4 microns.

4. The solid-state electrolyte membrane with skeleton film support according to claim 1, characterized in that: The solid-state electrolyte film includes a single-layer porous skeleton film (1) and a fiberized composite electrolyte material (2) located on the surface of the single-layer porous skeleton film (1) and in the pores of the single-layer porous skeleton film (1), or The solid-state electrolyte film is a double-layer porous skeleton film (1) and a sandwich structure formed by the composite electrolyte material (2) sandwiched between the double-layer porous skeleton film (1).

5. A method for producing a solid electrolyte membrane with a skeleton membrane support, characterized by, It comprises: providing a porous skeleton film (1) which is an ultra-thin biaxially stretched porous polymer film, the porous skeleton film (1) is an ultra-thin polytetrafluoroethylene biaxially stretched porous film, the porosity ranges from 65-95%, the pore size ranges from 50-500 nm, the mass of the porous skeleton film (1) accounts for 0.8-4% of the mass of the solid-state electrolyte film; providing a composite electrolyte material (2), the composition of the composite electrolyte material (2) includes solid-state electrolyte powder and lithium salt, and can also include a binder; wherein each component accounts for 7.5%-37.5% of the lithium salt and the balance of the solid-state electrolyte powder in terms of mass percentage; when the binder is present, its mass percentage is greater than 0% and not higher than 0.5%, and embedding the treated composite electrolyte material (2) into the porous skeleton film (1); and calendering the porous skeleton film (1) embedded with the composite electrolyte material (2) by a hot roller (5) to prepare a solid-state electrolyte film supported by a skeleton film.

6. The method of claim 5, wherein: The method further comprises a mixing treatment of fiberizing the composite electrolyte material (2) by airflow milling under low humidity conditions before embedding the composite electrolyte material (2) into the porous framework film (1), to obtain a fiberized composite electrolyte material (2).

7. The method of claim 6, wherein: The mass ratio of the solid-state electrolyte powder is 65%-88%; The solid-state electrolyte powder comprises one or more of a polymer solid-state electrolyte, an oxide solid-state electrolyte, a sulfide solid-state electrolyte, and a halide solid-state electrolyte. The lithium salt is one or more of LiClO4, LiBF4, LiAsF6, LiPF6, LiTFSI, LiFSI, LiCF3SO3, LiBOB, and LiDFOB. The binder comprises one or more of a fiberizable polymer selected from the group consisting of polytetrafluoroethylene, ultra-high molecular weight polyethylene, polyimide, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polyethylene oxide, and polyacrylonitrile.

8. The method of claim 6, wherein the method further comprises: The thickness of the porous framework film (1) ranges from 1 micrometer to 4 micrometers.

9. The method of claim 6, wherein the method further comprises, The step of embedding the composite electrolyte material (2) into the porous framework film (1) and the step of calendering the porous framework film (1) embedded with the composite electrolyte material (2) by the hot roller (5) to prepare a solid-state electrolyte film supported by a framework film are implemented by a solid-state electrolyte film preparation device, which comprises: One unwinding roller (3) or two oppositely arranged unwinding rollers (3) to unwind the porous framework film (1); Two oppositely arranged hot rollers (5) and an electrostatic discharging device (4) between the unwinding roller (3) and the hot roller (5), the electrostatic discharging device (4) being used to sprinkle the fiberized composite electrolyte material onto the surface of the porous framework film (1) released by the unwinding roller (3), and the hot roller (5) being used to calender the porous framework film (1) covered with the fiberized composite electrolyte material; When the unwinding roller (3) is one, the solid-state electrolyte film comprises a single-layer porous framework film (1) and the fiberized composite electrolyte material (2) on the surface of the single-layer porous framework film (1) and in the pores of the porous framework film (1), or When the unwinding roller (3) is two, the solid-state electrolyte film is a sandwich structure formed by a double-layer porous framework film and the composite electrolyte material (2) sandwiched between the double-layer porous framework film (1).

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