Flexible self-supporting porous electrode sheets for ion batteries, membrane assemblies, and methods of making

Abstract

The application discloses a flexible self-supporting porous electrode sheet for ion batteries, a film assembly and a preparation method. The porous electrode sheet is a porous positive electrode sheet or a porous negative electrode sheet, has an overall thickness of 9-150 um, and comprises a support framework, an active material and a conductive agent. The support framework is a porous fiber film made of ultrahigh molecular polyethylene, and the surface of the support framework is distributed with the active material and the conductive agent. The film assembly comprises the porous electrode sheet and a diaphragm layer which are connected and form an integrated structure. The diaphragm layer is one layer, and the porous electrode sheet is one layer or two layers. The preparation method is to prepare the porous electrode sheet through an extrusion-stretching mode, or to prepare the film assembly through a co-extrusion-stretching mode, and to perform high-temperature annealing after extraction, so as to obtain the porous electrode sheet or the film assembly with high performance. The porous electrode sheet and the film assembly have good flexibility, can keep the performance unchanged after being subjected to multiple foldings, effectively avoid the swelling problem in the charging and discharging process, and have strong thermal stability.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of flexible batteries, in particular to a flexible self-supporting porous electrode sheet for ion batteries based on ultra-high molecular weight polyethylene, a film assembly and a preparation method. BACKGROUND

[0002] In recent years, with the development of science and technology, people's demand for energy is growing, and ion batteries (IBs) have become the main energy storage equipment in modern society, and are one of the important electronic basic products supporting the development of new intelligent terminals, electric vehicles, new energy storage, etc. Ion batteries are secondary batteries composed of two ion compounds that can be reversibly inserted and de-inserted as positive and negative electrodes. When charging, ions de-insert from the positive electrode and insert into the negative electrode. When discharging, the reverse is true.

[0003] Ion batteries (IBs) include lithium ion batteries (LIBs), sodium ion batteries (SIBs), zinc ion batteries (ZIBs), and magnesium ion batteries (MIBs). Looking at the history of battery development, we can see three characteristics of the current world battery industry development. First, green and environmentally friendly batteries are developing rapidly, including ion batteries, hydrogen nickel batteries, etc. Second, primary batteries are being converted into storage batteries, which is in line with the sustainable development strategy. Third, batteries are further developing towards small, light, and thin. Among commercial rechargeable batteries, ion batteries have high specific energy, and the positive and negative electrodes are mainly composed of active materials, binders, and conductive agents. In particular, lithium ion batteries (LIBs) can achieve thin rechargeable batteries. Due to the special nature of the working principle of LIBs, there are special requirements for the structure of the positive and negative electrodes. With the increasing importance of energy density indicators, the electrode active load gradually increases, and the traditional binder begins to show the shortcomings of poor adhesion, uneven distribution, insufficient mechanical strength, and uneven thickness of the solid electrolyte interface (SEI). Therefore, research on binders has gradually increased, and binders have begun to have some new functions (such as improving electrical conductivity, stabilizing the interface, and inhibiting the volume expansion of active materials), and the importance of developing new binders has become increasingly prominent.

[0004] In order to solve the above-mentioned problems existing in traditional binders, in recent decades, domestic and foreign researchers have carried out a large amount of research work, among which modifying traditional binders or directly seeking a new type of binder to replace traditional binders is one of the most effective means to improve the comprehensive performance of the electrode sheet, which can have high adhesion and high mechanical strength, as well as inhibition of electrode sheet expansion. The binder plays a role in bonding the active material and the current collector, the active material and the active material, and the active material and the conductive agent.

[0005] In ion batteries, the positive electrode binder mainly includes oil-based polyvinylidene fluoride (PVDF), acrylic acid (PAA), polyacrylonitrile (PAN) and polyacrylate; the negative electrode binder is similar to the positive electrode, mainly including oil-based PVDF, water-based CMC, PAMAC, polyvinyl alcohol (PVA) and sodium alginate. The selection of the binder is crucial when preparing the positive and negative electrode sheets, although the current binder process is relatively mature and has some excellent properties, for example, PVDF has a relatively wide electrochemical stability window, and the electrochemical performance is stable at 0-5V (Li / Li+), and PVDF has good oxidation resistance and chemical reaction inertness and is not easy to deteriorate, but there are still some problems that are difficult to solve, for example: (1) the electronic and ionic conductivity of the binder itself is weak, which greatly reduces the performance of LIBs; (2) the adhesion of some binders is generally from the van der Waals force between molecules and the hydrogen bond formed by the C-F bond on the main chain and other substances of the electrode, especially when the binder is applied to the silicon negative electrode with large volume expansion, which is easy to cause capacity loss and fracture of the conductive network; (3) some binders need to use N-methyl pyrrolidone (NMP) as a solvent, and the volatilization temperature of the solvent is relatively high, which has certain environmental pollution and is expensive; (4) the Young's modulus is relatively high, and the flexibility of the electrode sheet is not good enough. In order to reduce the expansion problem of the positive and negative electrode sheets during the charging and discharging process, the binder cross-linking modification and surface high-temperature sintering methods are currently used to prepare the electrode sheets, so that the expansion ratio is reduced. Undoubtedly, the binder cross-linking modification method overcomes the expansion problem of the positive and negative electrode sheets during the charging and discharging process and improves the charging and discharging performance of the electrode sheet, but the technology is complex, the cost is high and it cannot be mass-produced, which hinders its large-scale promotion and application. SUMMARY

[0006] The present application aims to overcome the shortcomings of the prior art, and provides a flexible self-supporting porous electrode sheet for ion batteries, which has good flexibility and does not change in performance after being folded multiple times, effectively avoids the expansion problem during the charging and discharging process, has strong thermal stability, better absorption and adsorption of electrolyte, and can effectively improve the battery performance after application.

[0007] Another object of the present application is to provide a membrane assembly for ion batteries with the above-mentioned flexible self-supporting porous electrode sheet.

[0008] Still another object of the present application is to provide a preparation method of the above-mentioned flexible self-supporting porous electrode sheet.

[0009] Still another object of the present application is to provide a preparation method of the above-mentioned membrane assembly.

[0010] The technical scheme of the present application is: a flexible self-supporting porous electrode sheet for ion battery, comprising a support framework, an active material and a conductive agent, the support framework is a porous fiber membrane made of ultra-high molecular weight polyethylene, the surface of the support framework is distributed with the active material and the conductive agent, and the overall thickness of the porous electrode sheet is 9-150 um; the porous electrode sheet is a porous positive electrode sheet or a porous negative electrode sheet, that is, the flexible self-supporting porous electrode sheet can be used as a porous positive electrode sheet or a negative electrode sheet, and can be realized by using the corresponding type of active material.

[0011] In the porous electrode sheet, the mass fraction of each raw material is as follows: 2-20 parts of ultra-high molecular weight polyethylene, 55-96 parts of active material, and 2-25 parts of conductive agent.

[0012] When the porous electrode sheet is a porous positive electrode sheet, the active material is a lithium ion battery positive active material, a sodium ion battery positive active material, a zinc ion battery positive active material or a magnesium ion battery positive active material; wherein the lithium ion battery positive active material is one or more of lithium manganate (LiMnO4), lithium cobaltate (LiCoO2), lithium iron phosphate (LiFePO4) or ternary material (LiNiMnCoO2); the sodium ion battery positive active material is one or more of sodium manganate (NaMnO2), sodium cobaltate (NaCoO2), sodium nickelate (NaNiO2), sodium iron phosphate (NaFePO4), sodium sulfide (Na2S) or sodium iron sulfide (Na2FeS2); the zinc ion battery positive active material is one or more of manganese dioxide (MnO2), manganese oxide (Mn3O4), cobalt oxide (Co3O4) or lithium iron phosphate (LiFePO4); and the magnesium ion battery positive active material is one or more of manganese dioxide (MnO2), kaolin (KAlSi3O8), lithium iron phosphate (LiFePO4), molybdenum disulfide (MoS2) or titanium sulfide (TiS2).

[0013] When the porous electrode sheet is a porous negative electrode sheet, the active material is one or more of natural graphite, artificial graphite, soft carbon, hard carbon (HC), lithium titanate (LTO) or Si-based material.

[0014] The particle size of the active material ranges from 50 nm to 10 um.

[0015] The conductive agent is one or more of acetylene black (AB), graphite (KS), multi-walled carbon nanotubes, single-walled carbon nanotubes (CNTs), ketchen black (KB) or graphene.

[0016] The present application is a film assembly for ion battery with the above-mentioned flexible self-supporting porous electrode sheet, comprising a porous electrode sheet and a separator layer connected and forming an integrated structure, wherein the separator layer is one layer, and the porous electrode sheet is one or two layers.

[0017] When the porous electrode sheet is one layer, the porous electrode sheet is a porous positive electrode sheet, the porous positive electrode sheet and the separator layer form a double-layer integrated membrane assembly, and the overall thickness of the double-layer integrated membrane assembly is 10-150 mu m, wherein the thickness of the separator layer is 1-20 mu m, and the thickness of the porous positive electrode sheet is 9-130 mu m;

[0018] When the porous electrode sheet is two layers, one layer of the porous electrode sheet is a porous positive electrode sheet, and the other layer is a porous negative electrode sheet, the porous positive electrode sheet, the separator layer and the porous negative electrode sheet are sequentially connected to form a three-layer integrated membrane assembly, and the overall thickness of the three-layer integrated membrane assembly is 19-280 mu m, wherein the thickness of the separator layer is 1-20 mu m, the thickness of the porous positive electrode sheet is 9-130 mu m, and the thickness of the porous negative electrode sheet is 9-130 mu m;

[0019] Each layer of the double-layer integrated membrane assembly and the three-layer integrated membrane assembly uses a porous fiber membrane made of ultrahigh molecular polyethylene as a support skeleton, and the surface of the support skeleton of the separator layer is loaded with a ceramic material. In the double-layer integrated membrane assembly and the three-layer integrated membrane assembly, each layer is loaded with different functional materials, wherein the porous electrode sheet is highly loaded with active materials and conductive agents, and the separator is loaded with a ceramic material.

[0020] In the double-layer integrated membrane assembly or the three-layer integrated membrane assembly, the porosity of the porous positive electrode sheet and the porous negative electrode sheet is 20-50%, and the porosity of the separator layer is 40-80%.

[0021] In the double-layer integrated membrane assembly or the three-layer integrated membrane assembly, the molecular weight of the ultrahigh molecular weight polyethylene used in the porous positive electrode sheet and the porous negative electrode sheet is 3 million-9 million, and the molecular weight of the ultrahigh molecular weight polyethylene used in the separator layer is 0.8 million-2.5 million.

[0022] In the separator layer, the mass fraction of each raw material is: ultrahigh molecular weight polyethylene 50-99 parts, and ceramic material 1-50 parts;

[0023] The ceramic material is one or more of silicon dioxide (SiO2), aluminum oxide (Al2O3), zirconium oxide (ZrO2), and titanium dioxide (TiO2), and the particle size of the ceramic material is in the range of 5 nm-100 nm.

[0024] A preparation method of the above-mentioned flexible self-supporting porous electrode sheet, comprising the following steps:

[0025] (1) The active material, ultrahigh molecular weight polyethylene, conductive agent and diluent are added to the stirring kettle according to the predetermined ratio, stirred uniformly, then continuously plasticized and melt-blended through the extruder to form a homogeneous solution, then extruded through a single-layer film, and then cooled and shaped through a casting roller to form a single-layer gel film; wherein the roller temperature of the casting roller is 10-50 DEG C;

[0026] (2) the single-layer gel film obtained in step (1) is subjected to uniaxial stretching, asynchronous biaxial stretching or synchronous biaxial stretching, and then heat setting is performed to obtain a stretched fiber gel film with an ultra-high molecular weight polyethylene fiber skeleton; wherein the stretching temperature is 90-130℃, the transverse-to-longitudinal stretching ratio or the longitudinal stretching ratio is 1-10 times, the heat setting temperature is 90-130℃, and the heat setting time is 0.5-10 minutes;

[0027] (3) the diluent in the stretched fiber gel film obtained in step (2) is removed by using an extractant, and then drying and high-temperature annealing are performed to obtain a porous electrode sheet; wherein the high-temperature annealing temperature is 130-160℃, and the annealing time is 1-8 minutes.

[0028] The preparation method of the film assembly for the ion battery includes the following steps:

[0029] (1) the active material, the ultra-high molecular weight polyethylene, the conductive agent and the diluent are added into a stirring kettle according to a preset ratio, stirred uniformly, and then continuously plasticized and melt-blended by using an extruder to form a porous electrode sheet homogeneous solution; the ceramic material, the ultra-high molecular weight polyethylene and the diluent are added into a stirring kettle according to a preset ratio, stirred uniformly, and then continuously plasticized and melt-blended by using an extruder to form a separator layer homogeneous solution; then, multi-layer film co-extrusion is performed, and a cooling roll is used for cooling and setting to form a multi-layer gel film; wherein the roll temperature of the cooling roll is 10-50℃;

[0030] (2) the multi-layer gel film obtained in step (1) is subjected to uniaxial stretching, asynchronous biaxial stretching or synchronous biaxial stretching, and then heat setting is performed to obtain a stretched fiber gel film with an ultra-high molecular weight polyethylene fiber skeleton; wherein the stretching temperature is 90-130℃, the transverse-to-longitudinal stretching ratio or the longitudinal stretching ratio is 1-10 times, the heat setting temperature is 90-130℃, and the heat setting time is 0.5-10 minutes;

[0031] (3) the diluent in the stretched fiber gel film obtained in step (2) is removed by using an extractant, and then drying and high-temperature annealing are performed to obtain a film assembly; wherein the high-temperature annealing temperature is 130-160℃, and the annealing time is 1-8 minutes.

[0032] In the above method, when the double-layer integrated membrane assembly is prepared, in step (1), the raw materials of the porous positive electrode sheet are continuously plasticized and melt-blended by one extruder, and the raw materials of the diaphragm layer are continuously plasticized and melt-blended by another extruder, and correspondingly, the multi-layer die used for co-extrusion is a double-layer die; when the three-layer integrated membrane assembly is prepared, in step (1), the raw materials of the porous positive electrode sheet are continuously plasticized and melt-blended by a first extruder, the raw materials of the porous negative electrode sheet are continuously plasticized and melt-blended by a second extruder, and the raw materials of the diaphragm layer are continuously plasticized and melt-blended by a third extruder, and correspondingly, the multi-layer die used for co-extrusion is a three-layer die.

[0033] In step (1), the mass of the diluent in the homogeneous solution of the porous electrode sheet or the homogeneous solution of the diaphragm layer after mixing accounts for 50-90% of the total mass of the blend formed after mixing; the diluent can be a high-molecular diluent (such as PVP, PEG, PVA, etc.) or a small-molecule diluent (such as decalin, mineral oil, vegetable oil, etc.).

[0034] In the above flexible self-supporting porous electrode sheet, membrane assembly and preparation method for ion batteries, the principle is that the porous electrode sheet uses ultra-high molecular weight polyethylene as a binder, and due to its affinity with the active material and the conductive agent, the mixture is uniform, which can prolong the service life of the IBs. Meanwhile, in the ultra-high molecular polyethylene fiber membrane skeleton formed during the extrusion after blending, the active material and the conductive agent are adhered, which can form network-face contact, so that a more uniform, more stable and thinner SEI layer is formed during the charge and discharge cycle, which greatly improves the cycle performance of the ion battery. The self-supporting ultra-high molecular polyethylene fiber membrane skeleton has a three-dimensional porous network structure, so that the electrochemical active sites of the active material attached to the surface thereof are fully exposed as much as possible, and have a large specific surface area, which can effectively improve the electron transmission of the active material with poor conductivity, promote the effective transmission of carriers in the catalytic process, and form a strong interaction between the active material and the substrate (i.e. the supporting skeleton), so that the strong contact interface between the active material and the self-supporting substrate can efficiently transmit electrons and reduce the reaction potential barrier. In the preparation method, the porous electrode sheet and the diaphragm layer are compounded together by co-extrusion, which greatly reduces the production process and the surface resistance; at the same time, through the extrusion-stretching technology, the thickness of the porous electrode sheet and the membrane assembly, and the distribution of the microporous structure in the porous electrode sheet and the membrane assembly can be adjusted, so that the flexible battery electrode sheet and the membrane assembly meeting the requirements can be better obtained.

[0035] Compared with the prior art, the present application has the following beneficial effects:

[0036] The flexible self-supporting porous electrode sheet, membrane assembly and preparation method for the ion battery are proposed in view of the problems of low conductivity, poor electrolyte impregnation, low mechanical strength, complex process, high cost and the like in the existing manufacturing process of the positive and negative electrode sheets and membrane batteries of the polymer ion battery. The ultra-high molecular polyolefin (UHMWPE) is used as the binder, and the flexible self-supporting porous electrode sheet and the electrode sheet and membrane integrated co-extruded membrane assembly are prepared by the extrusion-stretching forming method. The strong interaction can be formed between the active material and the substrate (i.e. the supporting framework), and the strong contact interface between the active material and the self-supporting substrate can efficiently transmit electrons and reduce the reaction barrier. At the same time, due to the strong contact between the active material and the self-supporting substrate, the deficiency of easy falling off in the catalytic process of the binder is avoided, and therefore the good catalytic stability is shown. The new flexible battery and the manufacturing method thereof are formed, and the advantages of better performance of the flexible battery can be obtained.

[0037] In the flexible self-supporting porous electrode sheet, membrane assembly and preparation method for the ion battery, the porous electrode sheet uses the ultra-high molecular weight polyethylene as the binder, and is formed with the active material and the conductive agent through the preferred ratio and forming process. The ultra-high molecular weight polyethylene plays the role of mechanical support, and enhances the mechanical properties and stability of the porous electrode sheet. In the membrane assembly, the ultra-high molecular weight polyethylene is also used as the substrate (i.e. the supporting structure of the membrane layer and the porous electrode sheet is made of the ultra-high molecular weight polyethylene), and the porous electrode sheet and the membrane layer are compounded together through the co-extrusion, which greatly reduces the production process and reduces the surface resistance. In the preparation method, the diluent is used in the extraction process, so that the microporous structure is formed in the porous electrode sheet and the membrane assembly, the specific surface area of the porous electrode sheet and the membrane assembly is increased, more electrolyte can be stored, the use performance of the battery is improved, and the performance of the battery is not greatly affected after folding and puncturing. The safety performance of the battery is greatly improved, and the ion conductivity requirement of the electrode sheet and the membrane assembly of the polymer ion battery can be completely met. In addition, in the preparation method of the porous electrode sheet and the membrane assembly, the thickness of the battery electrode sheet and the membrane assembly, and the distribution of the microporous structure in the battery electrode sheet and the membrane assembly can be adjusted through the extrusion-stretching technology, so that the flexible battery electrode sheet and the membrane assembly meeting the requirements can be better obtained. Under the conditions of the thickness and main components of the porous electrode sheet and the membrane assembly, the battery performance is not affected after folding multiple times.

[0038] In the flexible self-supporting porous electrode and membrane module used in this ion battery, the characteristics of ultra-high molecular weight polyethylene (UHMWPE) result in its affinity for active materials and conductive agents, ensuring uniform mixing and extending the lifespan of IBs (Integrated Biscalar Intakes). Simultaneously, the UHMWPE fiber membrane skeleton formed during co-extrusion adheres to the active materials and conductive agents, forming a network-surface contact. This results in a more uniform, stable, and thinner SEI layer during charge-discharge cycles, significantly improving the cycle performance of the ion battery. The self-supporting UHMWPE fiber membrane skeleton has a three-dimensional porous network structure, maximizing the exposure of electrochemical active sites of the active materials attached to its surface. It also possesses a large specific surface area, effectively improving electron transport in the less conductive active materials, promoting efficient carrier transport during catalysis, and fostering strong interactions between the active materials and the substrate. This strong contact interface between the active materials and the self-supporting substrate enables efficient electron transport and reduces the reaction barrier. Furthermore, the self-supporting characteristic allows for the application of a conductive layer to the electrode surface using a mesh current collector or by direct coating, significantly reducing the energy density and weight of the ion battery. Attached Figure Description

[0039] Figure 1 This is an electron microscope image of the cross-sectional structure of the porous positive electrode sheet prepared in Example 1.

[0040] Figure 2 The image shows a cross-sectional electron microscope (EM) image of the porous positive electrode sheet prepared in Example 1 after 200 cycles.

[0041] Figure 3 This is an electron microscope image of the cross-sectional structure of the porous positive electrode sheet prepared in Example 2.

[0042] Figure 4 The image shows a cross-sectional electron microscope (EM) image of the porous positive electrode sheet prepared in Example 2 after 200 cycles.

[0043] Figure 5 This is an electron microscope image of the cross-sectional structure of the porous negative electrode sheet prepared in Example 3.

[0044] Figure 6 This is a cross-sectional structural diagram of the membrane module prepared in Example 4.

[0045] Figure 7 The image shows a cross-sectional electron microscope image of a conventional electrode fabricated for comparison. Detailed Implementation

[0046] The present invention will be further described in detail below with reference to the embodiments, but the implementation of the present invention is not limited thereto.

[0047] Example 1

[0048] The embodiment provides a flexible self-supporting porous positive electrode sheet for an ion battery and a preparation method thereof.

[0049] The porous positive electrode sheet comprises a support framework, an active material and a conductive agent, the support framework is a porous fiber membrane made of ultra-high molecular weight polyethylene, the surface of the support framework is distributed with the active material and the conductive agent, and the overall thickness of the porous electrode sheet is 9-150 um. The mass fraction of each raw material is as follows: 2-20 parts of ultra-high molecular weight polyethylene, 55-96 parts of the active material and 2-25 parts of the conductive agent. The active material can be a lithium ion battery positive electrode active material, a sodium ion battery positive electrode active material, a zinc ion battery positive electrode active material or a magnesium ion battery positive electrode active material; wherein the lithium ion battery positive electrode active material is one or more of lithium manganate (LiMnO4), lithium cobaltate (LiCoO2), lithium iron phosphate (LiFePO4) or a ternary material (LiNiMnCoO2); the sodium ion battery positive electrode active material is one or more of sodium manganate (NaMnO2), sodium cobaltate (NaCoO2), sodium nickelate (NaNiO2), sodium iron phosphate (NaFePO4), sodium sulfide (Na2S) or sodium iron sulfide (Na2FeS2); the zinc ion battery positive electrode active material is one or more of manganese dioxide (MnO2), manganese oxide (Mn3O4), cobalt oxide (Co3O4) or lithium iron phosphate (LiFePO4); the magnesium ion battery positive electrode active material is one or more of manganese dioxide (MnO2), kaolin (KAlSi3O8), lithium iron phosphate (LiFePO4), molybdenum disulfide (MoS2) or titanium sulfide (TiS2); and the particle size of the active material ranges from 50 nm to 10 um. The conductive agent can be one or more of acetylene black (AB), graphite (KS), multi-walled carbon nanotubes, single-walled carbon nanotubes (CNTs), ketjen black (KB) or graphene.

[0050] In the embodiment, the preparation method of the porous positive electrode sheet is specifically as follows:

[0051] (1) The fiber framework is prepared by using ultra-high molecular weight polyethylene with a molecular weight of 7.8 million, the positive electrode active material is lithium iron phosphate (LiFePO4), and the conductive agent is conductive carbon black (Super P), and the diluent is liquid paraffin;

[0052] The lithium iron phosphate, the ultra-high molecular weight polyethylene and the conductive carbon black are weighed according to the mass fraction ratio of 80:10:10, liquid paraffin is added to form a mixture, the mass of the liquid paraffin accounts for 80% of the total mass of the formed mixture, and the mixture is stirred in a stirring kettle at 80 DEG C for 5 min until it is uniformly stirred;

[0053] (2) melt blending and plasticizing transportation of the mixture by a twin-screw extruder at 200℃, and then casting a single-layer gel film by an extrusion die, and then stretching the single-layer gel film to form a stretched fiber gel film, wherein the stretching ratio is 3x3, and the stretching temperature is 110℃; after the stretching, heat setting at 120℃ for 5min;

[0054] (3) extracting the stretched fiber gel film after heat setting in step (2) by using n-hexane as an extraction liquid to remove liquid paraffin to form a microporous structure;

[0055] (4) drying to remove n-hexane, and then annealing at a high temperature of 140℃ for 3min to obtain a flexible self-supporting porous positive electrode sheet for lithium ion batteries.

[0056] A cross-sectional SEM image of the flexible self-supporting porous positive electrode sheet for lithium ion batteries obtained by the above preparation method is shown in Figure 1 , and the thickness thereof is 35μm, the tensile strength is 4.23MPa, and the conductivity is 2.45x10 -3 S / cm. After assembling the battery, a cycle test was performed, and a cross-sectional SEM image of the obtained flexible self-supporting porous positive electrode sheet for lithium ion batteries after 200 cycles is shown in Figure 2 .

[0057] Example 2

[0058] The present embodiment provides a flexible self-supporting porous positive electrode sheet for ion batteries and a preparation method thereof.

[0059] The porous positive electrode sheet comprises a support framework, an active material and a conductive agent, the support framework is a porous fiber membrane made of ultra-high molecular weight polyethylene, the surface of the support framework is distributed with the active material and the conductive agent, and the overall thickness of the porous electrode sheet is 9-150 um. The mass fraction of each raw material is as follows: 2-20 parts of ultra-high molecular weight polyethylene, 55-96 parts of active material, and 2-25 parts of conductive agent. The active material can be a lithium ion battery positive electrode active material, a sodium ion battery positive electrode active material, a zinc ion battery positive electrode active material or a magnesium ion battery positive electrode active material; wherein the lithium ion battery positive electrode active material is one or more of lithium manganate (LiMnO4), lithium cobaltate (LiCoO2), lithium iron phosphate (LiFePO4) or ternary material (LiNiMnCoO2); the sodium ion battery positive electrode active material is one or more of sodium manganate (NaMnO2), sodium cobaltate (NaCoO2), sodium nickelate (NaNiO2), sodium iron phosphate (NaFePO4), sodium sulfide (Na2S) or sodium iron sulfide (Na2FeS2); the zinc ion battery positive electrode active material is one or more of manganese dioxide (MnO2), manganese oxide (Mn3O4), cobalt oxide (Co3O4) or lithium iron phosphate (LiFePO4); the magnesium ion battery positive electrode active material is one or more of manganese dioxide (MnO2), kaolin (KAlSi3O8), lithium iron phosphate (LiFePO4), molybdenum disulfide (MoS2) or titanium sulfide (TiS2); and the particle size of the active material ranges from 50 nm to 10 um. The conductive agent can be one or more of acetylene black (AB), graphite (KS), multi-walled carbon nanotubes, single-walled carbon nanotubes (CNTs), ketchen black (KB) or graphene.

[0060] In this embodiment, the preparation method of the porous positive electrode sheet is as follows:

[0061] (1) The fiber framework is made of ultra-high molecular weight polyethylene with a molecular weight of 7.8 million, the positive electrode active material is lithium iron phosphate (LiFePO4), and the conductive agent is conductive carbon black (Super P), and the diluent is liquid paraffin;

[0062] The lithium iron phosphate, the ultra-high molecular weight polyethylene and the conductive carbon black are weighed according to the mass fraction ratio of 80:10:10, then liquid paraffin is added to form a mixture, the mass of the liquid paraffin accounts for 80% of the total mass of the formed mixture, and the mixture is stirred in a stirring kettle at 80℃ for 5 min until it is uniformly stirred;

[0063] (2) melt-blending and plasticizing the mixture by a twin-screw extruder at 200℃, and then casting a single-layer gel membrane by an extrusion die, and then stretching the single-layer gel membrane in a unidirectional longitudinal direction to form a stretched fiber gel membrane, wherein the stretching ratio is 3 and the stretching temperature is 110℃; after the stretching, heat setting is performed at 120℃ for 5min;

[0064] (3) extracting the stretched fiber gel membrane after heat setting in step (2) by using n-hexane as an extraction liquid to remove liquid paraffin to form a microporous structure;

[0065] (4) drying to remove n-hexane, and then annealing at a high temperature of 140℃ for 3min to obtain a flexible self-supporting porous positive electrode sheet for lithium ion batteries.

[0066] The cross-sectional SEM image of the flexible self-supporting porous positive electrode sheet for lithium ion batteries obtained by the above preparation method is shown in Figure 3 , and the thickness thereof is 102μm, the tensile strength is 3.5MPa, and the conductivity is 5.47×10 -3 S / cm. After assembling the battery, the cycle test is performed, and the cross-sectional SEM image of the obtained flexible self-supporting porous positive electrode sheet for lithium ion batteries after 200 cycles is shown in Figure 4 .

[0067] Example 3

[0068] The present embodiment provides a flexible self-supporting porous negative electrode sheet for ion batteries and a preparation method thereof.

[0069] The porous negative electrode sheet comprises a support skeleton, an active material and a conductive agent, the support skeleton is a porous fiber membrane made of ultra-high molecular polyethylene, the surface of the support skeleton is distributed with the active material and the conductive agent, and the overall thickness of the porous electrode sheet is 9-150μm. The mass fraction of each raw material is as follows: 2-20 parts of ultra-high molecular weight polyethylene, 55-96 parts of active material, and 2-25 parts of conductive agent. The active material can be one or more of natural graphite, artificial graphite, soft carbon, hard carbon (HC), lithium titanate (LTO) or Si-based material; the particle size of the active material ranges from 50nm to 10μm. The conductive agent can be one or more of acetylene black (AB), graphite (KS), multi-walled carbon nanotubes, single-walled carbon nanotubes (CNTs), ketchen black (KB) or graphene.

[0070] In the present embodiment, the preparation method of the porous negative electrode sheet is as follows:

[0071] (1) The fiber skeleton is prepared by using ultra-high molecular weight polyethylene with a molecular weight of 9 million, the negative electrode active material is graphite, the conductive agent is conductive carbon black (Super P), and the diluent is liquid paraffin;

[0072] The graphite, ultra-high molecular weight polyethylene and conductive carbon black are weighed according to the mass fraction ratio of 80:10:10, then liquid paraffin is added to form a mixture, the mass of the liquid paraffin accounts for 80% of the total mass of the formed mixture, the mixture is stirred in a stirred tank at 80℃ for 20min, and the stirring is uniform;

[0073] (2) The mixture is melt-blended and plasticized by a twin-screw extruder at 200℃, and a single-layer gel film is obtained by casting through an extrusion die, then the single-layer gel film is bidirectionally stretched to form a stretched fiber gel film, wherein the stretching ratio is 2x2 and the stretching temperature is 110℃; after the stretching is completed, heat setting is performed at 120℃ for 5min;

[0074] (3) The stretched fiber gel film after heat setting in step (2) is extracted by using n-hexane as an extraction liquid to remove the liquid paraffin to form a microporous structure;

[0075] (4) The n-hexane is dried and removed, and annealing treatment is performed at a high temperature of 150℃ for 2min to obtain a flexible self-supporting porous negative electrode sheet for lithium ion batteries.

[0076] The cross-sectional SEM image of the flexible self-supporting porous negative electrode sheet for lithium ion batteries obtained by the above preparation method is shown in Figure 5 , and the thickness thereof is 98μm, the tensile strength is 3.16MPa, and the electrical conductivity is 2.45x10 -3 S / cm.

[0077] Example 4

[0078] The present embodiment provides a membrane assembly for ion batteries and a preparation method thereof.

[0079] The film assembly of the embodiment is a double-layer integrated film assembly, which comprises a porous positive electrode sheet and a separator layer connected and forming an integrated structure. The overall thickness of the double-layer integrated film assembly is 10-150 μm, wherein the thickness of the separator layer is 1-20 μm and the thickness of the porous positive electrode sheet is 9-130 μm. In the film assembly, each layer adopts a porous fiber film made of ultra-high molecular polyethylene as a support skeleton, but each layer is loaded with different functional materials, wherein the porous electrode sheet is highly loaded with active materials and conductive agents, and the separator is loaded with ceramic materials. The porosity of the porous positive electrode sheet is 20-50%, and the porosity of the separator layer is 40-80%. The molecular weight of the ultra-high molecular polyethylene used in the porous positive electrode sheet is 3-9 million, and the molecular weight of the ultra-high molecular polyethylene used in the separator layer is 0.8-2.5 million. In the separator layer, the mass fraction of each raw material is: 50-99 parts of ultra-high molecular polyethylene and 1-50 parts of ceramic material. The ceramic material is one or more of silicon dioxide (SiO2), aluminum oxide (Al2O3), zirconium oxide (ZrO2), and titanium dioxide (TiO2), and the particle size of the ceramic material ranges from 5 nm to 100 nm.

[0080] In the embodiment, the preparation method of the film assembly is as follows:

[0081] (1) In the porous positive electrode sheet, the fiber skeleton is prepared by using ultra-high molecular polyethylene with a molecular weight of 7.8 million, the positive electrode active material is lithium iron phosphate (LiFePO4), the conductive agent is conductive carbon black (Super P), and the diluent is liquid paraffin;

[0082] In the separator layer, the fiber skeleton is prepared by using ultra-high molecular polyethylene with a molecular weight of 1.8 million, the inorganic ceramic particles are gas-phase SiO2, and the diluent is liquid paraffin;

[0083] Preparation of porous electrode sheet mixture: lithium iron phosphate, ultra-high molecular polyethylene and conductive carbon black are weighed according to the mass fraction ratio of 80:10:10, liquid paraffin is added to form a porous electrode sheet mixture, the mass of liquid paraffin accounts for 80% of the total mass of the formed porous electrode sheet mixture, and the porous electrode sheet mixture is stirred in a stirred tank at 80°C for 20 min until it is uniformly stirred;

[0084] Preparation of separator layer mixture: SiO2, ultra-high molecular polyethylene and conductive carbon black are weighed according to the mass fraction ratio of 80:20, liquid paraffin is added to form a separator layer mixture, the mass of liquid paraffin accounts for 80% of the total mass of the formed separator layer mixture, and the separator layer mixture is stirred in a stirred tank at 80°C for 5 min until it is uniformly stirred;

[0085] (2) Under the condition of 200℃, melt blend and plasticize transport of the porous cathode mixture and the separator layer mixture respectively by two twin-screw extruders, then flow cast by multi-layer co-extrusion die to obtain a double-layer gel film, and then stretch the double-layer gel film in two directions to obtain a stretched fiber gel film, wherein the stretching ratio is 4x4 and the stretching temperature is 110℃; after stretching, heat set at 120℃ for 5min;

[0086] (3) Extract the stretched fiber gel film after heat setting in step (2) using n-hexane as the extraction liquid to remove liquid paraffin to form a microporous structure;

[0087] (4) Dry to remove n-hexane, and anneal at high temperature of 150℃ for 2min to obtain a double-layer integrated film assembly of porous cathode and separator layer;

[0088] The cross-sectional SEM image of the double-layer integrated film assembly obtained by the above preparation method is shown in Figure 6 The film assembly has a thickness of 180μm, a tensile strength of 50.4MPa, and an electrical conductivity of 2.45x10 -3 S / cm.

[0089] Comparative Example

[0090] This comparative example provides a dry method for preparing a traditional cathode sheet using polyvinylidene fluoride as a binder, as follows:

[0091] (1) Using polyvinylidene fluoride (PVDF) as a binder, lithium iron phosphate (LiFePO4) as a positive active material, and conductive carbon black (Super P) as a conductive agent;

[0092] Lithium iron phosphate, polyvinylidene fluoride, and conductive carbon black are weighed according to the mass fraction ratio of 80:10:10, then 50% of the lithium iron phosphate, conductive carbon black, binder PVDF, and 50% of the lithium iron phosphate are sequentially added to a blender, and the revolution speed is maintained at (5±1) r / min during the feeding process. After feeding is completed, start dry mixing and pre-stirring, set the revolution speed to (7±1) r / min, and do not start the rotation dispersion. After 5min, switch to normal dry mixing and stirring, set the revolution speed to (13±1) r / min, and the rotation speed to (400±2) r / min. Stir for 0.5h. This process needs to ensure that the dry mixing can fully mix the powder of lithium iron phosphate, conductive carbon black, and binder PVDF;

[0093] (2) Spraying N-methyl pyrrolidone (NMP) solvent on the uniformly dispersed powder, adding part of the NMP solvent first, controlling at about 70% of the total amount of NMP solvent; then entering the powder wetting step, mainly using revolution stirring, setting the revolution speed at (15±5) r / min, supplemented by (150±2) r / min of rotation, stirring for 1.5 h, at this time the slurry presents a high viscosity thick liquid, adding the remaining NMP solvent, diluting and stirring for 10-15 min;

[0094] (3) Entering the high-speed dispersion and viscosity reduction step: keeping the revolution speed unchanged at (15±5) r / min, increasing the rotation dispersion speed to (1200±50) r / min, stirring for 2 h, then slowly reducing the speed (revolution speed (10±1) r / min, rotation speed (200±5) r / min) for cooling, completing the preparation of the slurry;

[0095] (4) Coating the slurry obtained in step (3) on the foil, and uniformly scraping the slurry with a scraper, then placing the scraped aluminum foil in a blast oven for drying for 10 hours, and punching to the appropriate size;

[0096] (5) Placing the treated pole piece in step (4) into a vacuum oven for drying for 2 hours, removing excess water, and storing in an inert atmosphere for dry preservation for use, obtaining the LFP positive electrode.

[0097] The cross-sectional SEM image of the positive electrode pole piece with polyvinylidene fluoride as the binder obtained by the above preparation method is shown in Figure 7 , and the thickness thereof is 48.56 μm, the tensile strength is 2.4 MPa, and the conductivity is 2.45×10 -3 s / cm.

[0098] The porous positive electrode pole piece, negative electrode pole piece or membrane assembly prepared in the above Examples 1-4 and the positive electrode pole piece prepared in the Comparative Example were assembled into full cells according to the battery assembly process, and the electrochemical performance of the battery was tested at room temperature and 1C, and the charge-discharge voltage was set to 2.5-4.3V, and the electrochemical performance test results are shown in Table 1.

[0099] Table 1. Electrochemical performance test results of samples in each example and comparative example

[0100]

[0101] As shown in Table 1, in the present application, the ultra-high molecular polyethylene is used as a base, the fiber skeleton with a porous structure is used as a support structure, the fiber skeleton is stretched, and excellent mechanical properties can be provided for the finally formed flexible self-supporting porous electrode sheet and the multi-layer film battery; at the same time, the active material and the conductive agent are loaded on the surface of the fiber skeleton of the porous electrode sheet to form a network-surface contact, which can effectively inhibit the crack phenomenon of the electrode sheet in the charging and discharging process; the diluent is used to form micropores in the extraction and drying process, increase the specific surface area of the electrode sheet, store more electrolyte, and improve the use performance of the battery; the film assembly is compounded with a separator layer on the basis of the porous electrode sheet preparation method, which greatly simplifies the preparation method, and the porous electrode sheet and the separator layer are the same base, which are well contacted together, reduces the internal resistance of the battery, and under the condition of the thickness and main components of the electrode sheet, the battery performance is not affected under multiple folding, and the safety performance is improved.

[0102] As described above, the present application can be better realized, and the above-mentioned embodiments are only the preferred embodiments of the present application, and are not intended to limit the implementation scope of the present application; that is, all equivalent changes and modifications made according to the content of the present application are covered by the scope of the claims of the present application.

Claims

1. A flexible, self-supporting porous electrode for ion batteries, characterized in that, It includes a support framework, active materials, and conductive agents. The support framework is a porous fiber membrane made of ultra-high molecular weight polyethylene. The surface of the support framework is distributed with active materials and conductive agents. The overall thickness of the porous electrode is 9~150um. The porous electrode can be a porous positive electrode or a porous negative electrode. Flexible self-supporting porous electrode sheets are prepared by the following method: (1) The active material, ultra-high molecular weight polyethylene, conductive agent and diluent are added to the mixing tank according to the preset ratio and stirred evenly. Then, the mixture is continuously plasticized and melt-blended through an extruder to form a homogeneous solution. The solution is then extruded through a single-layer film extruder and cooled and shaped by a casting roller to form a single-layer gel film. The temperature of the casting roller is 10~50℃. (2) After the monolayer gel film obtained in step (1) is stretched uniaxially, asynchronously biaxially or synchronously, it is then heat-set to obtain a stretched fiber gel film with an ultra-high molecular weight polyethylene fiber skeleton; wherein, the stretching temperature is 90-130℃, the transverse and longitudinal stretching ratio or the longitudinal stretching ratio is 1 to 10 times, the heat setting temperature is 90-130℃, and the heat setting time is 0.5 to 10 minutes; (3) Use an extractant to remove the diluent from the stretched fiber gel membrane obtained in step (2), then dry it, and then perform high-temperature annealing to obtain a porous electrode sheet; wherein, the high-temperature annealing temperature is 130~160℃ and the annealing time is 1~8 minutes.

2. The flexible self-supporting porous electrode for an ion battery according to claim 1, characterized in that, The porous electrode sheet contains the following mass fractions of each raw material: 2-20 parts of ultra-high molecular weight polyethylene, 55-96 parts of active material, and 2-25 parts of conductive agent.

3. The flexible self-supporting porous electrode for an ion battery according to claim 1, characterized in that, When the porous electrode sheet is a porous positive electrode sheet, the active material is a positive electrode active material for lithium-ion batteries, sodium-ion batteries, zinc-ion batteries, or magnesium-ion batteries; wherein, the positive electrode active material for lithium-ion batteries is one or more of lithium manganese oxide, lithium cobalt oxide, lithium iron phosphate, or ternary materials; the positive electrode active material for sodium-ion batteries is one or more of sodium manganese oxide, sodium cobalt oxide, sodium nickel oxide, sodium iron phosphate, sodium sulfide, or sodium iron sulfide; the positive electrode active material for zinc-ion batteries is one or more of manganese dioxide, manganese oxide, cobalt oxide, or lithium iron phosphate; and the positive electrode active material for magnesium-ion batteries is one or more of manganese dioxide, kaolin, lithium iron phosphate, molybdenum disulfide, or titanium sulfide. When the porous electrode sheet is a porous negative electrode sheet, the active material is one or more of natural graphite, artificial graphite, soft carbon, hard carbon, lithium titanate, or Si-based materials. The particle size range of the active material is 50 nm to 10 μm.

4. The flexible self-supporting porous electrode for an ion battery according to claim 1, characterized in that, The conductive agent is one or more of acetylene black, graphite, multi-walled carbon nanotubes, single-walled carbon nanotubes, Ketjen black, or graphene.

5. A membrane assembly for an ion battery having the flexible self-supporting porous electrode sheet according to any one of claims 1 to 4, characterized in that, It includes a porous electrode sheet and a separator layer that are connected to form an integrated structure, wherein the separator layer is one layer and the porous electrode sheet is one or two layers. When the porous electrode is a single layer, the porous electrode is a porous positive electrode. The porous positive electrode and the separator layer form a double-layer integrated membrane module. The overall thickness of the double-layer integrated membrane module is 10~150μm, of which the thickness of the separator layer is 1~20μm and the thickness of the porous positive electrode is 9~130μm. When the porous electrode has two layers, one layer is a porous positive electrode and the other layer is a porous negative electrode. The porous positive electrode, the separator layer and the porous negative electrode are sequentially connected to form a three-layer integrated membrane module. The overall thickness of the three-layer integrated membrane module is 19~280μm, of which the thickness of the separator layer is 1~20μm, the thickness of the porous positive electrode is 9~130μm, and the thickness of the porous negative electrode is 9~130μm. Each layer of the dual-layer integrated membrane module and the triple-layer integrated membrane module uses a porous fiber membrane made of ultra-high molecular weight polyethylene as a support skeleton, and the surface of the support skeleton of the diaphragm layer is loaded with ceramic material.

6. The membrane module for an ion battery according to claim 5, characterized in that, In the dual-layer integrated membrane module or the three-layer integrated membrane module, the porosity of the porous positive electrode and the porous negative electrode is 20-50%, and the porosity of the separator layer is 40-80%.

7. The membrane module for an ion battery according to claim 5, characterized in that, In the aforementioned dual-layer integrated membrane module or triple-layer integrated membrane module, the porous positive electrode and the porous negative electrode are made of ultra-high molecular weight polyethylene with a molecular weight of 3 million to 9 million, and the membrane layer is made of ultra-high molecular weight polyethylene with a molecular weight of 800,000 to 2.5 million.

8. The membrane module for an ion battery according to claim 5, characterized in that, The mass fractions of each raw material in the membrane layer are: 50-99 parts of ultra-high molecular weight polyethylene and 1-50 parts of ceramic material. The ceramic material is one or more of silicon dioxide (SiO2), aluminum oxide (Al2O3), zirconium oxide (ZrO2), and titanium dioxide (TiO2), and the particle size range of the ceramic material is 5nm~100nm.

9. A method for preparing a flexible self-supporting porous electrode sheet according to any one of claims 1 to 4, characterized in that, Includes the following steps: (1) The active material, ultra-high molecular weight polyethylene, conductive agent and diluent are added to the mixing tank according to the preset ratio and stirred evenly. Then, the mixture is continuously plasticized and melt-blended through an extruder to form a homogeneous solution. The solution is then extruded through a single-layer film extruder and cooled and shaped by a casting roller to form a single-layer gel film. The temperature of the casting roller is 10~50℃. (2) After the monolayer gel film obtained in step (1) is stretched uniaxially, asynchronously biaxially or synchronously, it is then heat-set to obtain a stretched fiber gel film with an ultra-high molecular weight polyethylene fiber skeleton; wherein, the stretching temperature is 90-130℃, the transverse and longitudinal stretching ratio or the longitudinal stretching ratio is 1 to 10 times, the heat setting temperature is 90-130℃, and the heat setting time is 0.5 to 10 minutes; (3) Use an extractant to remove the diluent from the stretched fiber gel membrane obtained in step (2), then dry it, and then perform high-temperature annealing to obtain a porous electrode sheet; wherein, the high-temperature annealing temperature is 130~160℃ and the annealing time is 1~8 minutes.

10. A method for preparing a membrane module for an ion battery according to any one of claims 5 to 8, characterized in that, Includes the following steps: (1) The active material, ultra-high molecular weight polyethylene, conductive agent and diluent are added to the mixing tank according to the preset ratio and stirred evenly. Then, they are continuously plasticized and melt-blended through an extruder to form a porous electrode homogeneous solution. The ceramic material, ultra-high molecular weight polyethylene and diluent are added to the mixing tank according to the preset ratio and stirred evenly. Then, they are continuously plasticized and melt-blended through an extruder to form a diaphragm layer homogeneous solution. Then, the membrane layer is co-extruded through a multi-layer film extruder and cooled and shaped by a casting roller to form a multi-layer gel film. The roller temperature of the casting roller is 10~50℃. (2) After the multilayer gel film obtained in step (1) is stretched uniaxially, asynchronously biaxially or synchronously, it is then heat-set to obtain a stretched fiber gel film with an ultra-high molecular weight polyethylene fiber skeleton; wherein, the stretching temperature is 90-130℃, the transverse and longitudinal stretching ratio or the longitudinal stretching ratio is 1 to 10 times, the heat setting temperature is 90-130℃, and the heat setting time is 0.5 to 10 minutes; (3) Use an extractant to remove the diluent from the stretched fiber gel membrane obtained in step (2), then dry it, and then perform high-temperature annealing to obtain the membrane module; wherein the high-temperature annealing temperature is 130~160℃ and the annealing time is 1~8 minutes.

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