Regenerated cellulose-based composite metal organic framework diaphragm as well as preparation method and application thereof

Abstract

The invention relates to a regenerated cellulose-based composite metal organic framework diaphragm as well as a preparation method and application thereof. The diaphragm comprises: a substrate, which is made of regenerated cellulose; the surface of the regenerated cellulose is connected with a sulfonic acid group; the sulfonic acid group establishes a 3D sulfonic acid group network on the surface of the regenerated cellulose; the metal organic framework is arranged on the surface of the substrate; the metal organic framework and the regenerated cellulose can be connected at least through electrostatic interaction and coordination bond interaction. The technical problem to be solved is how to provide a composite diaphragm formed by tightly and stably combining regenerated fibers and a metal organic framework, so that the prepared diaphragm is good in mechanical property and electrochemical property.

Description

Technical Field

[0001] The invention belongs to the field of diaphragms, and in particular relates to a regenerated cellulose-based composite metal organic framework diaphragm and a preparation method and application thereof. Background Art

[0002] Aqueous zinc-ion supercapacitor batteries have the characteristics of small size, high density, good cycle performance, and long service life. They have become one of the most important energy storage devices and are widely used in small aircraft, wearable devices, electric vehicles, etc. With the development of the times, the application fields of aqueous zinc-ion supercapacitor batteries are also constantly expanding, which also puts higher requirements on aqueous zinc-ion supercapacitor battery separators. The development of high-performance aqueous zinc-ion supercapacitor battery separators has become a hot topic in current research.

[0003] At present, commercial diaphragms are still mainly glass fiber diaphragms. This is because glass fiber diaphragms have good electrochemical stability and pore size distribution. However, glass fiber has relatively poor mechanical properties and thermal stability. Therefore, batteries prepared with glass fiber diaphragms are prone to short circuits during the charging and discharging process, and may even cause battery fires and safety accidents.

[0004] There are documents disclosing a type of biomass-based battery separator, which is made of renewable biomass raw materials such as cellulose, sodium alginate, chitosan and other biopolymers. Although the thermal stability and mechanical strength of the separator are good, its pore size is far less than that of the glass fiber separator, and zinc dendrites are prone to pierce the separator, causing safety problems. Therefore, it is difficult to be accepted and used by the market. There are also documents disclosing a regenerated cellulose separator. Although it has good thermal stability, the regenerated cellulose separator has a low specific surface area, small pore size and low porosity, which makes it difficult for the electrolyte to penetrate and retain when the separator is used in the battery, increasing the internal impedance of the battery and causing a decrease in the electrochemical performance of the battery. Summary of the invention

[0005] The main purpose of the present invention is to provide a regenerated cellulose-based composite metal-organic framework diaphragm and its preparation method and application. The technical problem solved is how to provide a composite diaphragm that is tightly and stably combined with regenerated fiber and metal-organic framework, so that the prepared diaphragm has good mechanical properties and electrochemical properties.

[0006] The purpose of the present invention and the technical problem to be solved are achieved by adopting the following technical solutions. A regenerated cellulose-based composite metal organic framework diaphragm proposed in the present invention comprises:

[0007] A substrate, wherein the substrate material is regenerated cellulose; a sulfonic acid group is connected to the surface of the regenerated cellulose; the sulfonic acid group combines with the hydroxyl group (-OH) in the cellulose molecule to establish a 3D sulfonic acid group network in the cellulose;

[0008] The metal organic framework is arranged on the surface of the substrate; the metal organic framework and the regenerated cellulose can be connected at least through electrostatic action and coordination bond action.

[0009] The purpose of the present invention and the solution to its technical problems can be further achieved by adopting the following technical measures.

[0010] Preferably, in the aforementioned diaphragm, the metal organic framework is selected from any one of HKUST-1, ZIF-8 and MOF-5.

[0011] Preferably, in the aforementioned membrane, the molar ratio of the sulfonic acid group to the metal organic framework is 3:1 to 2.5.

[0012] Preferably, in the aforementioned diaphragm, the metal organic framework is HKUST-1, and the sulfonic acid group is further connected to a polyphenyl structure.

[0013] Preferably, in the aforementioned separator, the mass ratio of the HKUST-1 to the regenerated cellulose is 0 to 1.5:5.

[0014] Preferably, the aforementioned diaphragm has a pore size of 1 to 100 nm and a porosity of 45 to 90%.

[0015] The purpose of the present invention and the technical problem solved by the present invention are also achieved by adopting the following technical solutions. According to a method for preparing a regenerated cellulose-based composite metal organic framework diaphragm proposed by the present invention, the method comprises the following steps:

[0016] dissolving cellulose, a metal organic framework precursor, and a sulfonate in a dissolving system to form a co-solution;

[0017] The co-solution is subjected to a water bath coagulation treatment to form a hydrogel;

[0018] The hydrogel is immersed in an organic solvent coagulation bath for coagulation, washed with water, and dried to obtain a regenerated cellulose-based composite metal organic framework diaphragm.

[0019] The purpose of the present invention and the solution to its technical problems can be further achieved by adopting the following technical measures.

[0020] Preferably, in the aforementioned preparation method, the degree of polymerization of the cellulose is 700-1000.

[0021] Preferably, in the aforementioned preparation method, the dissolving system is an ionic liquid; the ionic liquid is selected from at least one of 1-allyl-3-methylimidazolium chloride, 1-ethyl-3-methylimidazolium acetate, 1-butyl-3-methylimidazolium chloride and 1-butyl-3-methylimidazolium chloride.

[0022] The purpose of the present invention and the technical problems solved therein are also achieved by the following technical solutions: According to an aqueous zinc ion supercapacitor battery proposed by the present invention, the battery comprises the regenerated cellulose-based composite metal organic framework diaphragm described in the above solution.

[0023] By means of the above technical solution, the present invention provides a regenerated cellulose-based composite metal organic framework diaphragm and a preparation method and application thereof, which have at least the following advantages:

[0024] The present invention provides a regenerated cellulose-based composite metal-organic framework diaphragm, which takes regenerated cellulose as a substrate, and further connects sulfonic acid groups on the surface of the regenerated cellulose to establish a 3D sulfonic acid group network. The 3D sulfonic acid group network not only provides an ion transmission channel for the diaphragm, but also contributes to the electrostatic interaction between the regenerated cellulose and the metal-organic framework to improve the stability of the metal-organic framework on the surface of the regenerated cellulose. Therefore, the diaphragm of the present invention not only retains the excellent tensile strength and other mechanical properties of the regenerated cellulose and the electrochemical stability, but also achieves close bonding of the metal-organic framework on the surface of the regenerated cellulose to significantly improve the mechanical properties and electrochemical stability of the diaphragm.

[0025] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention and implement it according to the contents of the specification, the following is a detailed description of the preferred embodiments of the present invention in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a scanning electron microscope image of the surface of the diaphragm prepared in Example 1 (5 micron scale);

[0027] Figure 2 This is a scanning electron microscope image of the surface of the diaphragm prepared in Example 1 (50 micron scale);

[0028] Figure 3 This is a scanning electron microscope image of the cross section of the diaphragm prepared in Example 1 (20 micron scale);

[0029] Figure 4 This is a graph of impedance data of the supercapacitor prepared in Example 1;

[0030] Figure 5 This is a long cycle capacity diagram of the supercapacitor prepared in Example 1. DETAILED DESCRIPTION

[0031] In order to further explain the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the following is a detailed description of a regenerated cellulose-based composite metal organic framework diaphragm and its preparation method and application proposed by the present invention in combination with the accompanying drawings and preferred embodiments. Its specific implementation, structure, characteristics and effects are described in detail as follows.

[0032] The inventors found that although the battery separator prepared by regenerated cellulose in the prior art has good electrochemical stability, the electrochemical performance of the separator is not high. The reason is that the regenerated cellulose swells after absorbing the electrolyte, which will lead to uneven ion flux. In addition, zinc ion batteries are prone to zinc dendrite growth and other side reactions during the charge and discharge process, which further affect ion transmission. This leads to a significant increase in the impedance inside the battery, which reduces the long cycle performance of the battery.

[0033] Metal-organic frameworks are a type of crystalline porous material with a periodic network structure formed by the self-assembly of inorganic metal centers (metal ions and metal clusters) and bridging organic ligands. They have good mechanical properties. The highly ordered pore configuration and uniform sub-nanometer channels within the framework can be used for molecular sieving, which is beneficial to improving ion transport capacity. However, in previous studies, metal framework materials were mostly directly coated on the polymer surface to obtain a composite diaphragm to inhibit the growth of zinc dendrites, which would weaken the inherent function of the metal framework material, resulting in large interfacial impedance and low Coulomb efficiency. In addition, the bonding force between the metal framework material and the polymer surface in the diaphragm formed by direct coating is weak, which may affect the electrochemical stability of the prepared battery.

[0034] Based on the characteristics of regenerated fibers and metal organic frameworks, the applicant attempted to closely combine the two to overcome the defects of the prior art, and to combine the metal organic framework on the surface of the regenerated cellulose membrane in an in-situ growth manner, so that coordination bonds and electrostatic effects were formed between the regenerated cellulose and the metal organic framework, so as to increase the close connection between the metal organic framework and the regenerated fibers and improve the ion transmission capacity of the cellulose membrane.

[0035] However, the applicant found that it is very challenging to stably combine the regenerated fiber with the metal organic framework without affecting the inherent properties of the regenerated fiber and the metal organic framework. Through research, the applicant found that by connecting sulfonic acid groups on the surface of the regenerated fiber, the sulfonic acid groups combine with the hydroxyl (-OH) in the cellulose molecules, and then establishing a 3D sulfonic acid group network in the cellulose, the 3D sulfonic acid group network is constructed in the pores of the diaphragm, and further ion transmission channels are provided for the diaphragm, thereby further improving the electrochemical properties of the diaphragm. The 3D sulfonic acid group network is beneficial to increase the electrostatic interaction between the regenerated fiber and the metal organic framework, which is beneficial to promote the stable combination of the regenerated fiber and the metal organic framework without affecting the inherent properties of the regenerated fiber and the metal organic framework, thereby maintaining the mechanical properties of the diaphragm and the good stability of the electrochemical properties of the prepared battery.

[0036] In view of the above, the present invention proposes a regenerated cellulose-based composite metal organic framework diaphragm, which includes: a substrate, the substrate material is regenerated cellulose; the regenerated cellulose surface is connected with sulfonic acid groups; the sulfonic acid groups establish a 3D sulfonic acid group network on the regenerated cellulose surface; a metal organic framework is arranged on the surface of the substrate; the metal organic framework and the regenerated cellulose can be closely combined at least through electrostatic action and coordination bond action. In the above scheme, in some embodiments, preferably, the metal organic framework added to the diaphragm is selected from HKUST-1 (copper-based metal organic framework), ZIF-8 (zeolite imidazole framework-8), MOF-5 (also known as ZIF-5, zeolite imidazole framework-5). The present invention prefers these metal organic frameworks because these metal organic framework materials do not need to be heated or raised in temperature during the synthesis process, so they are easy to grow on the surface of regenerated cellulose and do not affect the inherent properties of regenerated cellulose; in addition, these metals have very high specific surface area and rich pore structure, which can not only provide more charge storage sites for the diaphragm, improve the capacity of the battery, but also facilitate firm bonding with regenerated cellulose, improve the stability and electrochemical performance of the diaphragm.

[0037] In the aforementioned scheme, in some embodiments, preferably, the molar ratio of the sulfonic acid group to the metal organic framework is 3:1-2.5. Under this condition, the sulfonic acid group can generate enough ion channels on the surface of regenerated cellulose and stabilize the metal organic framework, and reduce or even avoid excessive influence of the sulfonic acid group on the binding of the metal organic framework, thereby avoiding affecting the various properties of the membrane; in other embodiments, the molar ratio of the sulfonic acid group to the metal organic framework is 3:1.2-2.3. The membrane prepared under this condition has better performance.

[0038] In the above scheme, in some embodiments, preferably, the metal organic framework is HKUST-1, and the sulfonic acid group is also connected to a polyphenyl structure. The use of this technical solution can not only form coordination bonds and electrostatic interactions between regenerated cellulose and the metal organic framework, but also the hydroxyl group (-OH) in the cellulose molecule can form hydrogen bonds with the carboxyl group (-COOH) in the ligand BTC of HKUST-1, further improving the tightness of the combination of regenerated cellulose and the metal organic framework, and the electrochemical performance stability of the battery prepared using the diaphragm is better; the 3D sulfonic acid group network structure established by the polyphenylene sulfonic acid group on the surface of the regenerated cellulose is more stable, providing a more stable ion transmission channel, and the polyphenylene sulfonic acid group can better stabilize the HKUST-1 bound to the cellulose surface, which is conducive to maintaining the mechanical properties of the diaphragm and the good stability of the electrochemical performance of the prepared battery.

[0039] In the aforementioned scheme, preferably, in order to reduce or even avoid excessive content of metal organic framework precursor leading to large-scale polymerization on the surface of regenerated cellulose, so as to cover the ion transport channel of the diaphragm and affect the electrochemical properties of the diaphragm, in some embodiments, preferably, the mass ratio of HKUST-1 to regenerated cellulose is 0 to 1.5:5; further preferably, in other embodiments, the mass ratio of HKUST-1 to regenerated cellulose is 0.8 to 1.2:5; the present invention optimizes the mass ratio of HKUST-1 to regenerated cellulose to ensure that the addition of HKUST-1 can improve the electrochemical and mechanical properties of the diaphragm.

[0040] Since the size of the diaphragm pore size directly affects the ion conduction rate. A diaphragm with a moderate pore size can ensure sufficient porosity, thereby supporting the smooth flow of ions and ensuring the efficient operation of the battery. If the pore size is too small, the speed of ion migration will be limited, affecting the performance of the battery; while a pore size that is too large may cause unstable electrolyte fluidity and even cause an internal short circuit in the battery. Therefore, the pore size of the diaphragm must be precisely controlled to ensure efficient ion conduction. In some preferred embodiments of the present invention, the pore size of the diaphragm is 1 to 100 nm; the porosity is 45 to 90%.

[0041] In some embodiments of the above-mentioned scheme, the thickness of the diaphragm is 10-40 μm. Under this condition, the electrochemical and mechanical properties of the diaphragm are better.

[0042] The present invention also provides a method for preparing a regenerated cellulose-based composite metal organic framework diaphragm, which comprises the following steps:

[0043] S1: dissolving cellulose, a metal organic framework precursor and a sulfonate in a dissolving system to form a co-solution; the dissolving system is a solvent system for dissolving cellulose, a metal organic framework precursor and a sulfonate together.

[0044] In the above scheme, the cellulose is preferably plant cellulose. In some embodiments, corn, bamboo and cotton are selected as the raw material for preparing the cellulose; in other embodiments, it is further preferred that the degree of polymerization of the cellulose is 700 to 1000. The present invention optimizes the cellulose raw material to obtain a higher cellulose content, which is further conducive to providing sufficient fiber specific surface area to combine more metal organic framework materials, so that the prepared diaphragm has good electrical and mechanical properties.

[0045] In the above scheme, preferably, in some embodiments, the metal organic framework precursor is copper nitrate trihydrate, ethanolamine and trimesic acid, which can form HKUST-1 in the dissolution system; in other embodiments, the metal organic framework precursor is zinc nitrate hexahydrate, dimethylformamide, 2-methylimidazole, which can form ZIF-8 in the dissolution system; in other embodiments, the metal organic framework precursor is zinc chloride, ethanolamine, imidazole, which can form MOF-5 in the dissolution system. The preferred metal organic framework precursor of the present invention is simple to synthesize in the dissolution system, can be well dissolved uniformly with cellulose and sulfonate, and does not require high temperature heating, which can avoid the problem of high temperature heating causing cellulose aggregation or even destroying the inherent characteristics of cellulose. The metal organic framework in the finally prepared diaphragm is well distributed uniformly in the regenerated fiber, the electrochemical properties and mechanical properties of the formed diaphragm are stable and good, and the quality of the diaphragm is good.

[0046] In some embodiments of the above scheme, the dissolving system is any new solvent system such as high-concentration inorganic salt, ionic liquid, lithium chloride / dimethylacetamide, etc., so as to achieve the co-dissolution of cellulose and metal organic framework precursor.

[0047] In order to achieve co-solubility of cellulose and metal organic framework precursor, it is further preferred that the dissolving system is an ionic liquid; in some embodiments, the ionic liquid is selected from [Amim]Cl (1-allyl-3-methylimidazolium chloride), [Emim]Ac (1-ethyl-3-methylimidazolium acetate), [Bmim]Cl (1-butyl-3-methylimidazolium chloride), [C 4mim]Cl (1-butyl-3-methylimidazolium chloride), under this condition, on the one hand, the co-solubility of cellulose, metal organic framework and sulfonate is better; on the other hand, it is also conducive to the in-situ growth of metal organic framework in the cellulose regeneration process. This is because the ionic liquid and solvent replacement effect is stronger in the cellulose regeneration process, which is more conducive to the metal organic framework to smoothly combine with the hydroxyl group on the cellulose surface to form coordination bonds and hydrogen bonds, so that the in-situ growth of the metal organic framework on the cellulose surface proceeds smoothly; in addition, because the ionic liquid is easy to detach from the cellulose surface, the electrostatic effect between the cellulose surface and the metal organic framework is enhanced, the binding force between the regenerated cellulose and the metal organic framework is improved, and the electrochemical and mechanical stability of the diaphragm is improved. In other embodiments, it is further preferred that the purity of the ionic liquid is above 98%. The use of ionic liquids under this condition can accelerate the dissolution of cellulose and has better co-solubility with cellulose and metal organic framework.

[0048] In some embodiments of the above scheme, it is further preferred that cellulose and sulfonate are first dissolved and mixed evenly in an ionic liquid to form a semi-liquid state, and then a metal organic framework precursor is added and further mixed evenly to form a co-solution of cellulose, metal organic framework precursor and sulfonate. The present invention adopts the technical solution to prepare a diaphragm with better electrochemical performance and stability, and the metal organic framework on the surface of the regenerated fiber is more evenly distributed. The reason may be that during the mixing process of sulfonate and cellulose, the sulfonic acid group cross-links with the hydroxyl group (-OH) in the cellulose molecule, thereby binding the sulfonate to the cellulose surface to modify the cellulose, so as to establish a 3D sulfonic acid group network on the cellulose surface, which can reduce or even avoid the subsequent aggregation and growth of the metal organic framework on the surface of the regenerated cellulose, and the 3D sulfonic acid group network established on the cellulose surface helps to improve the electrostatic interaction between the regenerated cellulose and the metal organic framework, so as to help stabilize the metal organic framework on the surface of the regenerated cellulose.

[0049] In the above scheme, it is further preferred that the sulfonate is polybenzenesulfonate. In some embodiments, the polybenzenesulfonate used is sodium polybenzenesulfonate or potassium polybenzenesulfonate. The electrochemical performance of the prepared diaphragm is better. The reason may be that the electron cloud density of the benzene ring in the polybenzenesulfonic acid group is large, which helps to increase the electron cloud density on the surface of the regenerated cellulose, and then helps to increase the electrostatic interaction between the regenerated cellulose and the metal organic framework, which has a better stabilizing effect on the metal organic framework grown on the surface of the regenerated cellulose.

[0050] In the aforementioned scheme, during the co-dissolution process of cellulose, metal organic framework materials and sulfonates in the ionic liquid, some embodiments preferably have a temperature of the dissolution system of 70 to 90°C and a stirring speed of 50 to 300 rpm; further preferably, the temperature of the dissolution system is 70 to 90°C and the stirring speed is 60 to 200 rpm; the present invention limits the temperature and stirring speed of the dissolution system so that cellulose, metal organic framework materials and sulfonates can be quickly and evenly dissolved in the ionic liquid to achieve co-dissolution, and avoid the influence of excessive temperature on the inherent properties of cellulose, while avoiding excessive breakage of hydrogen bonds in cellulose when the temperature is too high and the stirring speed is too fast, because excessive breakage of hydrogen bonds in cellulose may affect the tensile strength, tear resistance, compression resistance and other properties of the finally prepared diaphragm; in addition, if the temperature of the dissolution system exceeds the range required by the present invention, the pore size and distribution uniformity of the prepared diaphragm are affected, thereby affecting the electrochemical properties and mechanical properties of the diaphragm.

[0051] In the aforementioned scheme, some embodiments preferably dissolve cellulose and sulfonate in the ionic liquid and stir for 20 to 40 minutes. Under this condition, cellulose can be uniformly dissolved in the ionic liquid, and the sulfonic acid groups can be bound to the cellulose surface. It can also avoid that the cellulose reacts in the ionic liquid for too long, causing a large number of hydrogen bonds in the cellulose to break and recombine, forming a large number of regenerated fibers with a low degree of polymerization, which affects the tensile strength, tear resistance and other properties of the prepared diaphragm.

[0052] In some embodiments of the aforementioned scheme, after cellulose is uniformly dissolved in the ionic liquid, the metal organic framework precursor is added and stirring is continued for 50 to 70 minutes at the temperature and stirring speed of the aforementioned scheme.

[0053] In the above scheme, some embodiments further preferably have an absolute dry mass percentage of cellulose in the co-solution of 1 to 5%. The present invention strictly limits the absolute dry mass of cellulose in the co-solution to make the strength and uniformity of the prepared diaphragm good. Cellulose has high tensile strength and rigidity, and an appropriate cellulose mass concentration helps to form a diaphragm with good mechanical properties and is beneficial to improving the electrochemical properties of the diaphragm. When the cellulose content in the co-solution is too low, the prepared diaphragm may have an incomplete structure, and it will also lead to a reduction in the content of cellulose effectively combined with the metal organic framework, so that the tensile resistance, compression resistance and tear resistance of the prepared diaphragm will be affected, and the electrochemical performance may also be affected; if the cellulose content in the co-solution is too high, the high-quality cellulose is not easy to dissolve evenly in the ionic solution, and it will also lead to uneven combination of cellulose with the metal organic framework material, which will affect the pore size and porosity of the diaphragm, and the quality and stability of the electrochemical and mechanical properties may also be affected; in other embodiments, it is further preferred that the absolute dry mass percentage of cellulose in the co-solution is 3 to 4%, and the mechanical properties and electrochemical properties of the diaphragm prepared under this condition are kept good.

[0054] S2: subjecting the co-solution to water bath coagulation treatment to form a hydrogel;

[0055] In the above scheme, the co-solution is coagulated in a water coagulation bath. During this process, the metal organic framework grows in situ on the surface of the regenerated cellulose through coordination bonds and electrostatic effects to form a regenerated cellulose-based composite metal organic framework hydrogel. The pore size of the hydrogel is dense and fine, and the pore distribution is uniform.

[0056] S3: The hydrogel is immersed in an organic solvent coagulation bath for coagulation, washed with water, and dried to obtain a regenerated cellulose-based composite metal organic framework membrane.

[0057] In the aforementioned scheme, the hydrogel formed by S2 is solidified in an organic solvent coagulation bath to form a diaphragm, and the performance of the diaphragm is better. The reason may be that the aforementioned scheme accelerates the process of solidification of the hydrogel to form a diaphragm, and the pore structure of the formed diaphragm is stable, and the size and distribution of the pores may be more uniform. Although the hydrogel can be formed into a diaphragm material by extending the water bath coagulation time, however, during the long-term coagulation of the hydrogel in the water coagulation bath to form a diaphragm, the cellulose in the diaphragm may be excessively dissolved or expanded, resulting in the breakage of the cellulose molecular chain or loose structure, which in turn leads to a decrease in the strength of the fiber, a deterioration in toughness, and even possible breakage. In addition, it will also lead to poor stability of the pore structure of the fiber, poor pore size and distribution uniformity, affecting the electrochemical properties of the diaphragm.

[0058] In the aforementioned scheme, in some embodiments, the organic solvent coagulation bath is preferably ethanol, ethylene glycol, propylene glycol, or isopropanol; the present invention optimizes the organic solvent coagulation bath, which not only enables the hydrogel to coagulate as quickly as possible, but also avoids affecting the metal organic framework or polyphenylene sulfonic acid group on the hydrogel.

[0059] The regenerated cellulose formed by cellulose in a water coagulation bath has good pore density and uniform pore size distribution, but the specific surface area of ​​the regenerated fiber is low, while the regenerated cellulose formed by an organic solvent coagulation bath has rough and large pores, which can increase the specific surface area of ​​cellulose. When the specific surface area of ​​cellulose is increased, it is beneficial to promote the formation of van der Waals force and electrostatic effect between the cellulose surface and the metal organic framework, thereby facilitating the improvement of the binding force of the metal organic framework on the cellulose surface. In order to make the pore size distribution of the prepared diaphragm uniform and the pore size appropriate, and to increase the specific surface area of ​​cellulose, some embodiments of the present invention preferably soak the co-solution in a water coagulation bath for 20 to 40 minutes to form a hydrogel, and further soak it in an organic solvent coagulation bath for 30 to 60 minutes to form a diaphragm.

[0060] Finally, water washing is used to wash away organic substances from the membrane to form a wet diaphragm, so as to avoid alcohol organic solvents on the membrane that affect the electrochemical performance of the battery when the prepared diaphragm is used in a battery. In some embodiments, the membrane is washed with water and the membrane is soaked in water for 6 to 12 hours.

[0061] Preferably, in the aforementioned technical scheme, the present invention freeze-dries the washed wet diaphragm, thereby achieving low-temperature drying and avoiding cracking of the prepared diaphragm during the drying process; in some embodiments, the freeze-drying is carried out by drying with liquid nitrogen or drying in a refrigerator; in other embodiments, the low-temperature freezing temperature is -60 to -80°C, and the time is ≥12h.

[0062] The regenerated cellulose-based composite metal-organic framework diaphragm prepared by the present invention is prepared by introducing a metal-organic framework material into the regenerated cellulose diaphragm by an in-situ growth method to prepare a composite diaphragm with high porosity and a sub-nanometer channel structure. The composite diaphragm not only retains the high strength and thermal stability of the regenerated cellulose material diaphragm, but also retains the sub-nanometer channels existing in the metal-organic framework itself to achieve uniform and stable ion transmission of the diaphragm during application, and has a high porosity. When using the composite diaphragm described in the present invention, the metal-organic framework material can effectively support the diaphragm under charge and discharge conditions, prevent the diaphragm from heating up and shrinking, and reduce or even avoid the situation where the ion transmission performance of the regenerated cellulose diaphragm inhibits the generation of zinc dendrites.

[0063] The present invention also proposes an application of the diaphragm prepared by the above-mentioned scheme in an aqueous zinc ion supercapacitor battery.

[0064] The aqueous zinc ion supercapacitor battery described in the aforementioned solution of the present invention can be applied to small aircraft, wearable devices, electric vehicles and other fields.

[0065] The present invention will be further described below in conjunction with specific embodiments, but this should not be construed as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made to the present invention by technicians in this field based on the above-mentioned contents of the present invention still fall within the scope of protection of the present invention.

[0066] Unless otherwise specified, the materials, reagents, etc. involved below are all commercially available products well known to those skilled in the art; unless otherwise specified, the methods described are all methods well known in the art. Unless otherwise defined, the technical terms or scientific terms used should have the common meanings understood by ordinary technicians in the field to which the present invention belongs.

[0067] Example 1

[0068] This embodiment provides a regenerated cellulose-based composite metal organic framework membrane and a preparation method and application thereof, as follows:

[0069] 1. Preparation of regenerated cellulose-based composite metal-organic framework membrane

[0070] Preparation of a co-solution: Cotton pulp cellulose with a degree of polymerization of 800 and sodium polybenzene sulfonate are added to the ionic liquid amimcl, and stirred at 80°C (stirring speed 100 rpm) for 30 minutes to form a semi-liquid mixed solution, and copper nitrate trihydrate, ethanolamine and trimesic acid are further added, and stirring is continued at the same temperature and stirring speed for 60 minutes, copper nitrate trihydrate, ethanolamine and trimesic acid are synthesized in the dissolving system to synthesize the metal organic framework HKUST-1; the mixture is allowed to stand to eliminate bubbles, and a co-solution is obtained;

[0071] The absolute dry mass percentage of cellulose in the co-solution is 3.5%, the mass ratio of the metal organic framework to the cellulose is 1:5; and the molar ratio of the sulfonic acid group to the synthesized metal organic framework in the co-solution is 3:2.

[0072] Co-solution film formation

[0073] The co-solution was scraped onto the surface of the glass, and then quickly placed in deionized water for 30 minutes to form a hydrogel. The hydrogel was further immersed in an ethanol solution (purity 98%) for 60 minutes, and then immersed in deionized water for 12 hours to form a wet membrane.

[0074] The wet membrane was taken out and placed in a -80°C ultra-low temperature freezer for freeze-drying to obtain a regenerated cellulose-based composite metal-organic framework membrane having a thickness of 20 μm.

[0075] 2. Application of regenerated cellulose-based composite metal-organic framework membranes

[0076] The separator prepared in this example is assembled with the positive electrode sheet and the negative electrode sheet to form a lithium battery. The negative electrode sheet, separator and positive electrode are stacked in an arrangement manner, and then placed in an aluminum-plastic film packaging bag, a small amount of electrolyte is injected and vacuum sealed to obtain an aqueous zinc ion supercapacitor battery ACL-1.

[0077] Index detection

[0078] 1) Scanning electron microscopy was used to scan the membrane prepared in this example. The results are shown in the attached Figure 1-5 .

[0079] 2) The pore size and porosity of the diaphragm are tested by using a fully automatic specific surface area and porosity analyzer to draw a nitrogen adsorption-desorption curve test to obtain the pore size and distribution data.

[0080] 3) The ion conductivity (25° C.), interface resistance, tensile strength and contact angle of the diaphragm prepared in this example were tested respectively, and the testing methods were in accordance with the corresponding national standards.

[0081] The test results of this embodiment are shown in Table 1.

[0082] Example 2

[0083] This embodiment provides a regenerated cellulose-based composite metal organic framework membrane and its preparation method and application. The difference from Example 1 is that the molar ratio of sulfonic acid groups to the synthesized metal organic framework in the co-solution is 3:1, and the remaining process steps and methods are the same as Example 1.

[0084] The pore size, porosity, ionic conductivity (25° C.), interface resistance, tensile strength and contact angle of the diaphragm prepared in this example were tested in the same manner as in Example 1. The test results of each item in this example are shown in Table 1.

[0085] Example 3

[0086] This embodiment provides a regenerated cellulose-based composite metal organic framework membrane and its preparation method and application. The difference from Example 1 is that the molar ratio of sulfonic acid groups to synthesized metal organic framework in the co-solution is 3:2.5, and the remaining process steps and methods are the same as Example 1.

[0087] The pore size, porosity, ionic conductivity (25° C.), interface resistance, tensile strength and contact angle of the diaphragm prepared in this example were tested in the same manner as in Example 1. The test results of each item in this example are shown in Table 1.

[0088] Example 4

[0089] This embodiment provides a regenerated cellulose-based composite metal organic framework membrane and its preparation method and application. The difference from Example 1 is that the molar ratio of sulfonic acid groups to synthesized metal organic framework in the co-solution is 3:1.2, and the remaining process steps and methods are the same as Example 1.

[0090] The pore size, porosity, ionic conductivity (25° C.), interface resistance, tensile strength and contact angle of the diaphragm prepared in this example were tested in the same manner as in Example 1. The test results of each item in this example are shown in Table 1.

[0091] Example 5

[0092] This embodiment provides a regenerated cellulose-based composite metal organic framework diaphragm and its preparation method and application. The difference from Example 1 is that the molar ratio of sulfonic acid groups to synthesized metal organic framework in the co-solution is 3:2.3, and the remaining process steps and methods are the same as Example 1.

[0093] The pore size, porosity, ionic conductivity (25° C.), interface resistance, tensile strength and contact angle of the diaphragm prepared in this example were tested in the same manner as in Example 1. The test results of each item in this example are shown in Table 1.

[0094] Example 6

[0095] This embodiment provides a regenerated cellulose-based composite metal organic framework membrane and a preparation method and application thereof. The difference from Example 1 is that the mass ratio of the metal organic framework and cellulose synthesized in the co-solution is 0.8:5, and the remaining process steps and methods are the same as Example 1.

[0096] The pore size, porosity, ionic conductivity (25° C.), interface resistance, tensile strength and contact angle of the diaphragm prepared in this example were tested in the same manner as in Example 1. The test results of each item in this example are shown in Table 1.

[0097] Example 7

[0098] This embodiment provides a regenerated cellulose-based composite metal-organic framework membrane and a preparation method and application thereof. The difference from Example 1 is that the mass ratio of the metal-organic framework and cellulose synthesized in the co-solution is 1.2:5, and the remaining process steps and methods are the same as Example 1.

[0099] The pore size, porosity, ionic conductivity (25° C.), interface resistance, tensile strength and contact angle of the diaphragm prepared in this example were tested in the same manner as in Example 1. The test results of each item in this example are shown in Table 1.

[0100] Example 8

[0101] This embodiment provides a regenerated cellulose-based composite metal-organic framework membrane and a preparation method and application thereof. The difference from Example 1 is that the mass ratio of the metal-organic framework and cellulose synthesized in the co-solution is 0.5:5, and the remaining process steps and methods are the same as Example 1.

[0102] The pore size, porosity, ionic conductivity (25° C.), interface resistance, tensile strength and contact angle of the diaphragm prepared in this example were tested in the same manner as in Example 1. The test results of each item in this example are shown in Table 1.

[0103] Example 9

[0104] This embodiment provides a regenerated cellulose-based composite metal organic framework membrane and a preparation method and application thereof. The difference from Example 1 is that the mass ratio of the metal organic framework and cellulose synthesized in the co-solution is 1.5:5, and the remaining process steps and methods are the same as Example 1.

[0105] The pore size, porosity, ionic conductivity (25° C.), interface resistance, tensile strength and contact angle of the diaphragm prepared in this example were tested in the same manner as in Example 1. The test results of each item in this example are shown in Table 1.

[0106] Example 10

[0107] This embodiment provides a regenerated cellulose-based composite metal-organic framework diaphragm and its preparation method and application. The difference from Example 1 is that the metal-organic framework precursor is zinc nitrate hexahydrate, dimethylformamide, and 2-methylimidazole, and ZIF-8 is synthesized in a dissolving system. The remaining process steps and methods are the same as Example 1.

[0108] The pore size, porosity, ionic conductivity (25° C.), interface resistance, tensile strength and contact angle of the diaphragm prepared in this example were tested in the same manner as in Example 1. The test results of each item in this example are shown in Table 1.

[0109] Embodiment 11

[0110] This embodiment provides a regenerated cellulose-based composite metal organic framework membrane and a preparation method and application thereof, which is different from Embodiment 1 in that the prepared wet membrane is dried at room temperature.

[0111] The pore size, porosity, ionic conductivity (25° C.), interface resistance, tensile strength and contact angle of the diaphragm prepared in this example were tested in the same manner as in Example 1. The test results of each item in this example are shown in Table 1.

[0112] Example 12

[0113] This embodiment provides a regenerated cellulose-based composite metal organic framework membrane and a preparation method and application thereof. The difference from Embodiment 1 is that bamboo cellulose with a degree of polymerization of 800 is used, and the remaining process steps and methods are the same as those in Embodiment 1.

[0114] The pore size, porosity, ionic conductivity (25° C.), interface resistance, tensile strength and contact angle of the diaphragm prepared in this example were tested in the same manner as in Example 1. The test results of each item in this example are shown in Table 1.

[0115] Embodiment 13

[0116] This embodiment provides a regenerated cellulose-based composite metal organic framework diaphragm and a preparation method and application thereof, which is different from Embodiment 1 in that:

[0117] In the process of preparing the co-solution, cotton pulp cellulose with a degree of polymerization of 700 and potassium polybenzenesulfonate were added to the ionic liquid [Emim]Ac, stirred at 90°C (stirring speed 300 rpm) for 20 minutes to form a semi-liquid mixture. After adding the metal precursor, stirring was continued for 70 minutes. The absolute dry mass percentage of cellulose in the formed co-solution was 5%.

[0118] During the co-solution film formation process, the co-solution was placed in deionized water for 40 minutes, the formed hydrogel was immersed in ethylene glycol (purity 98%) for 40 minutes, and then immersed in deionized water for 10 hours to form a wet membrane.

[0119] The thickness of the membrane obtained after freeze drying was 40 μm.

[0120] The remaining process steps and methods are the same as in Example 1.

[0121] The pore size, porosity, ionic conductivity (25° C.), interface resistance, tensile strength and contact angle of the diaphragm prepared in this example were tested in the same manner as in Example 1. The test results of each item in this example are shown in Table 1.

[0122] Embodiment 14

[0123] This embodiment provides a regenerated cellulose-based composite metal organic framework diaphragm and a preparation method and application thereof, which is different from Embodiment 1 in that:

[0124] In the process of preparing the co-solution, cotton pulp cellulose with a degree of polymerization of 1000 and potassium polybenzenesulfonate were added to the ionic liquid [Bmim]Cl, stirred at 70°C (stirring speed 50 rpm) for 40 minutes to form a semi-liquid mixed solution, and the metal precursor was added and stirred for 50 minutes. The absolute dry mass percentage of cellulose in the formed co-solution was 1%.

[0125] During the co-solution film formation process, the co-solution was placed in deionized water for 20 minutes, the formed hydrogel was soaked in ethylene glycol (purity 98%) for 30 minutes, and then placed in deionized water for 6 hours to form a wet membrane.

[0126] The thickness of the membrane obtained after freeze drying was 10 μm.

[0127] The remaining process steps and methods are the same as in Example 1.

[0128] The pore size, porosity, ionic conductivity (25° C.), interface resistance, tensile strength and contact angle of the diaphragm prepared in this example were tested in the same manner as in Example 1. The test results of each item in this example are shown in Table 1.

[0129] Comparative Example 1

[0130] This comparative example provides a regenerated cellulose separator and a preparation method and application thereof, as follows:

[0131] 1. Preparation of regenerated cellulose membrane

[0132] Cotton pulp cellulose with a degree of polymerization of 800 was added to the ionic liquid amimcl, stirred at 80°C (stirring speed 100 rpm) for 90 minutes, and allowed to stand to eliminate bubbles to obtain a cellulose solution. The absolute dry mass percentage of cellulose in the cellulose solution was 3.5%.

[0133] After the obtained cellulose solution was scraped onto the surface of the glass, it was quickly placed in a deionized water bath for 30 minutes, then soaked in an ethanol solution for 30 minutes, and then soaked in deionized water for 12 hours to form a wet membrane. The wet membrane was taken out and placed in a -80°C ultra-low temperature refrigerator for freeze drying to obtain a regenerated cellulose membrane. The prepared membrane had a thickness of 20 μm.

[0134] The same process steps and parameters as in Example 1 were used to prepare an aqueous zinc ion supercapacitor battery.

[0135] The pore size, porosity, ionic conductivity (25° C.), interface resistance, tensile strength and contact angle of the diaphragm prepared in this comparative example were tested in the same manner as in Example 1. The test results of each item of this comparative example are shown in Table 1.

[0136] Table 1 Test results of embodiments and comparative examples

[0137]

[0138] By attaching Figures 1 to 3It can be seen that the membrane prepared by the method for preparing the regenerated cellulose-based composite metal-organic framework membrane provided by the present invention realizes the in-situ growth of the metal-organic framework onto the surface of the regenerated cellulose, and the degree of polymerization of the metal-organic framework on the cellulose surface is moderate, thereby avoiding the blockage of the ion transport channel of the membrane by the metal-organic framework.

[0139] Combined with the embodiments, comparative examples and Table 1, and the attached Figures 4 to 5 It can be seen that the membrane prepared by the present invention realizes the in-situ growth of the metal organic framework on the surface of the regenerated fiber, greatly improves the stability of the regenerated cellulose membrane, and provides uniform ion transmission channels, thereby improving the electrochemical performance of the composite membrane. The interface resistance of the membrane prepared by the present invention is in the range of 70 to 134Ω, the ion conductivity is in the range of 97 to 220μS / cm, the tensile strength is in the range of 70 to 125MPa, and the membrane is easily penetrated and wetted by the electrolyte. It can be seen that the membrane prepared by the present invention is excellent in mechanics and electrochemistry, and is suitable for preparing aqueous zinc ion supercapacitor batteries.

[0140] From the analysis of Examples 1 to 14, it can be seen that when the membrane is freeze-dried, the porosity of the membrane is significantly higher than that of room temperature drying, and it has good lyophilicity. This is because when the wet membrane is dried by the natural drying method, the cellulose drying rate is slow, causing the cellulose to shrink and the porosity to decrease, thus causing the ionic conductivity to decrease.

[0141] From the analysis of the examples, it can be seen that the prepared membrane preferably has a molar ratio of sulfonic acid groups to HKUST-1 of 3:1.2-2.3, and a mass ratio of HKUST-1 to the regenerated cellulose of 0.8-1.2:5.

[0142] The technical features in the claims and / or the specification of the present invention may be combined, and the combination is not limited to the combination obtained by reference in the claims. The technical solution obtained by combining the technical features in the claims and / or the specification is also within the protection scope of the present invention.

[0143] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any simple modification, equivalent change and modification made to the above embodiment according to the technical essence of the present invention still falls within the scope of the technical solution of the present invention.

Claims

1. A regenerated cellulose-based composite metal-organic framework membrane, characterized in that: It includes: A substrate, wherein the substrate material is regenerated cellulose; the surface of the regenerated cellulose is connected with sulfonic acid groups; the sulfonic acid groups establish a 3D sulfonic acid group network on the surface of the regenerated cellulose; A metal organic framework is disposed on the surface of the substrate; The metal organic framework and the regenerated cellulose can be connected at least through electrostatic interaction and coordination bond interaction.

2. The diaphragm according to claim 1, characterized in that The metal organic framework is selected from any one of HKUST-1, ZIF-8 and MOF-5.

3. The diaphragm according to claim 1, characterized in that The molar ratio of the sulfonic acid group to the metal organic framework is 3:1 to 2.

5.

4. The diaphragm according to claim 1, characterized in that The metal organic framework is HKUST-1, and the sulfonic acid group is further connected with a polyphenyl structure.

5. The diaphragm according to claim 4, characterized in that The mass ratio of the HKUST-1 to the regenerated cellulose is 0-1.5:

5.

6. The diaphragm according to any one of claims 1 to 5, characterized in that: The pore size of the diaphragm is 1-100 nm, and the porosity is 45-90%.

7. A method for preparing a regenerated cellulose-based composite metal-organic framework membrane, characterized in that: It includes the following steps: dissolving cellulose, a metal organic framework precursor, and a sulfonate in a dissolving system to form a co-solution; The co-solution is subjected to a water bath coagulation treatment to form a hydrogel; The hydrogel is immersed in an organic solvent coagulation bath for coagulation, washed with water, and dried to obtain a regenerated cellulose-based composite metal organic framework diaphragm.

8. The preparation method according to claim 7, characterized in that: The polymerization degree of the cellulose is 700-1000.

9. The preparation method according to claim 8, characterized in that: The dissolving system is an ionic liquid; the ionic liquid is selected from at least one of 1-allyl-3-methylimidazolium chloride, 1-ethyl-3-methylimidazolium acetate, 1-butyl-3-methylimidazolium chloride and 1-butyl-3-methylimidazolium chloride.

10. An aqueous zinc ion supercapacitor battery, characterized in that: The battery comprises the regenerated cellulose-based composite metal-organic framework separator according to any one of claims 1 to 6.

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