A diaphragm and a secondary battery

Abstract

This application relates to the field of electrochemical technology, and provides a separator and a secondary battery. The separator includes a substrate and a coating disposed on at least one surface of the substrate. The coating includes a metal-organic framework material doped with a metal element, wherein the metal element includes at least one selected from Li, Na, K, Ca, Mg, Cu, Co, Ni, Fe, Cr, Zn, and Mn. Based on the amount of the metal-doped metal-organic framework material, the molar content of the metal element is from 0.01 mol / mol to 2.3 mol / mol. The coating includes a metal-organic framework material doped with a metal element within the scope of this application, which is beneficial for the activity of metal ions (e.g., Li). + During interfacial transport, the removal of the coordination solvent increases the rate of interfacial transport of active metal ions, thereby improving the fast-charging performance, cycle performance, low-temperature performance, and energy density of the secondary battery.

Description

Technical Field

[0001] This application relates to the field of electrochemical technology, and in particular to a separator and a secondary battery. Background Technology

[0002] Secondary batteries, such as lithium-ion batteries, are characterized by high energy density, high operating voltage, low self-discharge rate, small size, and light weight, and are widely used in various fields such as energy storage, portable electronic devices, and electric vehicles. With the increasing demand for portable electronic devices and electric vehicles, battery anxiety is becoming more prominent, and the fast-charging performance of lithium-ion batteries is receiving increasing attention.

[0003] It is generally believed that the current bottleneck in fast charging of lithium-ion batteries lies in the obstructed transport of ions at the interface, which leads to kinetic polarization of the lithium-ion battery and lithium plating at the negative electrode. Therefore, how to improve the cross-interface transport rate of lithium ions to enhance the fast charging and cycle performance of lithium-ion batteries has become an urgent problem to be solved by those skilled in the art. Summary of the Invention

[0004] The purpose of this application is to provide a separator and a secondary battery to improve the activity of metal ions (e.g., Li). + This improves the cross-interface transmission rate, enhancing the fast-charging performance, cycle performance, and low-temperature performance of secondary batteries, while also increasing energy density. The specific technical solution is as follows:

[0005] A first aspect of this application provides a diaphragm comprising a substrate and a coating disposed on at least one surface of the substrate, the coating comprising a metal-organic framework material doped with a metal element, the metal-organic framework material having the molecular formula M a Zr6O m (OH) n (OL) 6-(x+y) / 2 (sol) x (blank) y N b , 0.01≤a≤2.3, 4≤m≤6, 0≤n≤4, 0.09≤x≤0.92, 1.8≤y≤6.02, 0.905≤b≤9.24; M is the metal element, which includes at least one of Li, Na, K, Ca, Mg, Cu, Co, Ni, Fe, Cr, Zn and Mn; OL is a dicarboxylic acid conjugated organic ligand; sol includes acetate, formate and CH3(CH2). p COO - At least one of the following, 1≤p≤6, blank is a ligand vacancy, and N is a counter ion.

[0006] In some embodiments of this application, the molar ratio of Zr to OL in the diaphragm is 6:(2.53~5.055).

[0007] In some embodiments of this application, the molar ratio of Zr to OL in the diaphragm is 6:(2.766~4.92).

[0008] In some embodiments of this application, the molar ratio of Zr to OL in the diaphragm is 6:(2.766~4.266).

[0009] In some embodiments of this application, the molar ratio of Zr to OL in the diaphragm is 6:(2.766~3.69).

[0010] In some embodiments of this application, the metal-doped metal-organic framework material includes a dicarboxylate conjugated organic ligand, the molecular skeleton of which includes any one of phenyl, imidazolyl, and pyridyl.

[0011] In some embodiments of this application, the molecular skeleton of the dicarboxylated conjugated organic ligand is selected from phenyl, and the dicarboxylated conjugated organic ligand includes a functional group X, which includes any one of amino, hydroxyl, mercapto, methoxy, nitro, fluorine, and chlorine groups.

[0012] In some embodiments of this application, the dicarboxylate conjugated organic ligand includes any one of terephthalate, amino-modified terephthalate, fluoroterephthalate, and pyridinic acid dicarboxylate.

[0013] In some embodiments of this application, 0.1≤a≤2.3, preferably, 0.21≤a≤2.3, and more preferably, 0.3≤a≤2.3.

[0014] In some embodiments of this application, the counterion includes NO3. - Cl - SO4 2- ,Br - F - At least one of acetylacetone radicals.

[0015] In some embodiments of this application, the mass percentage of the metal-organic framework material doped with metal elements is W1, based on the quality of the coating, with 65% ≤ W1 ≤ 94.4%; preferably, 75% ≤ W1 ≤ 90%.

[0016] In some embodiments of this application, the coating includes a binder, a wetting agent, and a dispersant. Based on the mass of the coating, the binder has a mass percentage content of W2, 2.7% ≤ W2 ≤ 32.8%, preferably 7.4% ≤ W2 ≤ 22.6%; the wetting agent has a mass percentage content of W3, 0.01% ≤ W3 ≤ 6%, preferably 0.01% ≤ W3 ≤ 1.5%; and the dispersant has a mass percentage content of W4, 0.1% ≤ W4 ≤ 6%, preferably 0.5% ≤ W4 ≤ 1.5%.

[0017] In some embodiments of this application, 41.8 ≤ W1 / W4 ≤ 650; preferably, 55.7 ≤ W1 / W4 ≤ 83.6.

[0018] In some embodiments of this application, the binder includes at least one of sodium carboxymethyl cellulose and polyacrylate; the wetting agent includes at least one of branched alcohols, sodium dodecyl sulfate, sodium dodecyl sulfonate, and acetylenic glycol polyoxyethylene ether; and the dispersant includes at least one of polyvinyl alcohol, polyacrylonitrile, and polyvinylpyrrolidone.

[0019] In some embodiments of this application, the coating thickness is from 0.3 μm to 6 μm; preferably, the coating thickness is from 0.5 μm to 3 μm.

[0020] In some embodiments of this application, the coating weight per unit area on the substrate is 0.12 g / m². 2 Up to 2.52g / m 2 Preferably, the coating weight per unit area on the substrate is 0.21 g / m². 2 Up to 1.26 g / m 2 .

[0021] In some embodiments of this application, the total defect rate Z of the metal-organic framework material doped with metal elements is 20% ≤ Z ≤ 53.5%; preferably, 25% ≤ Z ≤ 53.5%; more preferably, 29.6% to 53.5%; and even more preferably, 40% to 53.5%.

[0022] In some embodiments of this application, the unsaturated coordination defect rate K of the metal-organic framework material doped with metal elements is 15%≤K≤50.1%; preferably, 22%≤K≤50.1%; even more preferably, 26.1%≤K≤50.1%; and more preferably, 37%≤K≤50.1%.

[0023] In some embodiments of this application, the average particle size of the metal-organic framework material doped with metal elements is D, where 20 nm ≤ D ≤ 110 nm, and preferably 64 nm ≤ D ≤ 80 nm.

[0024] In some embodiments of this application, the XRD patterns of metal-organic framework materials doped with metal elements include diffraction peaks of the (200) and (111) crystal planes.

[0025] In some embodiments of this application, the coating further includes at least one of semiconductor oxides, oxide solid electrolytes, or covalent organic framework materials; and / or, the separator further includes other coatings, which include at least one of semiconductor oxides, oxide solid electrolytes, or covalent organic framework materials.

[0026] The second aspect of this application provides a secondary battery comprising a positive electrode, a negative electrode, an electrolyte, and a separator provided in the first aspect of this application.

[0027] The beneficial effects of this application are:

[0028] This application provides a separator and a secondary battery. The separator includes a substrate and a coating disposed on at least one surface of the substrate. The coating includes a metal-organic framework material doped with a metal element, wherein the metal element includes at least one selected from Li, Na, K, Ca, Mg, Cu, Co, Ni, Fe, Cr, Zn, and Mn. Based on the amount of the metal-organic framework material doped with the metal element, the molar content of the metal element is from 0.01 mol / mol to 2.3 mol / mol. The coating includes a metal-organic framework material doped with a metal element within the scope of this application, which is beneficial for the activity of metal ions (e.g., Li). + During interfacial transport, the removal of the coordination solvent increases the rate of interfacial transport of active metal ions, thereby improving the fast-charging performance, cycle performance, low-temperature performance, and energy density of secondary batteries.

[0029] Of course, implementing any product or method of this application does not necessarily require achieving all of the advantages described above at the same time. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other embodiments can be obtained based on these accompanying drawings.

[0031] Figure 1 The XRD patterns of the metal-doped metal-organic framework materials used in Examples 1-1, 1-6, 1-7, 1-8, and 1-9 of this application are shown.

[0032] Figure 2 This is a scanning electron microscope image of the diaphragm coating of Embodiment 1-1 of this application;

[0033] Figure 3 The XRD patterns of the metal-organic framework material doped with metal elements in Example 1-1 of this application and the membrane coating in Example 1-1 of this application are shown.

[0034] Figure 4 This is a cell structure diagram of a metal-organic framework material doped with metal elements according to one embodiment of this application, wherein 1 is a dicarboxylic acid conjugated organic ligand, 2 is an oxygen atom, 3 is a zirconium atom, 4 is a nitrogen atom, and 5 is a lithium atom. Detailed Implementation

[0035] The technical solutions of this application will be clearly and completely described below with reference to the embodiments and accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0036] It should be noted that, in the specific embodiments of this application, lithium-ion batteries are used as an example of secondary batteries to explain this application, but the secondary batteries in this application are not limited to lithium-ion batteries.

[0037] A first aspect of this application provides a diaphragm comprising a substrate and a coating disposed on at least one surface of the substrate, the coating comprising a metal-organic framework material doped with a metal element, the metal-organic framework material having the molecular formula M a Zr6O m (OH) n (OL) 6-(x+y) / 2 (sol) x (blank) y N b The 0.01≤a≤2.3, preferably 0.1≤a≤2.3, more preferably 0.21≤a≤2.3, and even more preferably 0.3≤a≤2.3, 4≤m≤6, 0≤n≤4, 0.09≤x≤0.92, 1.8≤y≤6.02, and 0.905≤b≤9.24; M is a metallic element, including at least one of Li, Na, K, Ca, Mg, Cu, Co, Ni, Fe, Cr, Zn, and Mn; OL is a dicarboxylic acid conjugated organic ligand; and sol includes acetate, formate, and CH3(CH2). p COO -At least one of the following, 1≤p≤6, blank represents a ligand vacancy, and N represents a counter ion. For example, in the molecular formula of the metal-organic framework material doped with the metal element, the value of a can be 0.01, 0.05, 0.1, 0.21, 0.3, 0.5, 1, 1.5, 2, 2.3, or a range of any two values ​​therein; the value of m can be 4, 4.3, 4.5, 4.8, 5, 5.3, 5.5, 5.8, 6, or a range of any two values ​​therein; the value of n can be 0, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, or a range of any two values ​​therein; and the value of x can be 0.09, 0.12, 0.15, 0.18, 0.2, 0.2. The values ​​of y can be 1.8, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.02, or any two of these values; the values ​​of b can be 0.905, 1, 1.5, 2, 2.1, 2.5, 2.8, 3, 3.5, 4, 4.5, 5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.24, or any two of these values. The term "coating disposed on at least one surface of the substrate" refers to a coating that can be disposed on one surface of the substrate along its thickness direction, or on two surfaces of the substrate along its thickness direction, or multiple layers of coating can be disposed on one or two surfaces of the substrate along its thickness direction. Active metal ions (e.g., Li) +In secondary batteries, interfacial migration of active metal ions requires the removal of coordinating solvents. This process necessitates overcoming a high energy barrier of 50 kJ / mol to 70 kJ / mol for interfacial charge transfer. Therefore, compared to bulk transport within the electrodes and electrolyte, desolvation is generally considered the main energy-consuming step in the transport of active metal ions. This application's research found that the membrane coating, comprising a metal-doped metal-organic framework (MOF) material with the molar content of the metal element controlled within the specified range, offers several advantages. First, the porous structure of the MOF facilitates the removal of active metal ions from the outer weakly coordinating solvent. Second, the metal doping sites within the MOF promote the dissociation of the inner strong coordinating solvent of the active metal ions. This "assembly line" synergistic desolvation mechanism enhances the rate of interfacial transport of active metal ions. Simultaneously, the abundant polar groups on the surface of the MOF material exhibit high affinity for the electrolyte, and the porous structure allows for rapid electrolyte conduction, facilitating electrolyte wetting. This is beneficial for improving the fast-charging performance, cycle performance, and low-temperature performance of secondary batteries. Furthermore, due to the pore-confining effect of the metal-organic framework material doped with metal elements, TFSI in the electrolyte can be anchored. - FSI - PF6 - The presence of anions can release more active lithium ions, and faster ion transport can reduce the thickness of the positive electrode interface film and adjust the composition of the negative electrode interface film, further reducing the loss of active lithium due to the formation of the positive and negative electrode interface films, thereby promoting the capacity utilization of the secondary battery and increasing the energy density of the secondary battery.

[0038] The zirconium-oxygen cluster nodes of UiO series metal-organic composites are typically represented as Zr6O4(OH)4 (i.e., m=4, n=4), a designation that has gained industry consensus. However, during post-processing such as heating and vacuum treatment, the hydroxyl groups at the zirconium-oxygen cluster nodes may dehydrate and partially detach, potentially forming a Zr6O6 structure in extreme cases. Due to limitations in current characterization techniques, it is not yet possible to precisely quantify the hydroxyl content at the zirconium-oxygen cluster nodes. Therefore, in this application, the molecular formula of the metal-doped metal-organic composite is expressed as "M". a Zr6O m (OH) n (OL) 6(x+y) / 2 (sol) x (blank) y N b ", where 0.01≤a≤2.3, 4≤m≤6, 0≤n≤4, 0.09≤x≤0.92, 1.8≤y≤6.02, 0.905≤b≤9.24.

[0039] When metal elements are doped into metal-organic frameworks (MOFs), they act as additional Lewis acid sites, exhibiting strong affinity for typical solvents, anions, and free radicals. Simultaneously, the introduction of metal elements further alters the pore shape and reduces the pore volume; these changes in pore shape and solvent also enhance the confinement effect of the pores themselves.

[0040] In this application, metal doping does not destroy the crystal structure of the metal-organic framework material. Figure 4 This is a schematic diagram of a metal-organic framework material doped with a metal element (with metal element M represented by Li, dicarboxylic acid conjugated organic ligand molecular framework of phenyl, and counterion of NO3). - (For example), where 1 is a dicarboxylate conjugated organic ligand, 2 is an oxygen atom, 3 is a zirconium atom, 4 is a nitrogen atom, and 5 is a lithium atom. If no ligand is present, it indicates the absence of dicarboxylate conjugated organic ligand 1, resulting in an unsaturated coordination defect. Metal-doped metal-organic frameworks (MOFs) consist of zirconium atoms, oxygen atoms, dicarboxylate conjugated organic ligands, a metal element M, and counterions. The zirconium atoms, oxygen atoms, dicarboxylate conjugated organic ligands, and metal element M are connected by coordination bonds, while the counterions and small molecule ligands are weakly bonded to the metal framework through non-covalent interactions. Specifically, a single metal-doped MOF contains six zirconium atoms within its unit cell. These six zirconium atoms form octahedral zirconium-oxygen cluster nodes by bonding with bridging oxygen and bridging hydroxyl groups. Simultaneously, zirconium oxide clusters coordinate with dicarboxylic acid conjugated organic ligands to form an overall framework structure. In a defect-free perfect crystal, each metal-doped metal-organic framework material unit cell can coordinate with 12 dicarboxylic acid conjugated organic ligands, meaning each metal-doped metal-organic framework material unit cell can contain 6 dicarboxylic acid conjugated organic ligands. If the chemical bond to be coordinated on a zirconium atom does not coordinate with a dicarboxylic acid conjugated organic ligand, a defect is formed. The missing organic ligand is replaced by a solvent or template agent, i.e., a small molecule ligand (sol). If the missing organic ligand is not occupied by any molecule / ion, it becomes a ligand vacancy (blank). To make the charge properties of the unsaturated coordination defect electrically neutral, an antiion with the same number of charges, i.e., a counterion, needs to be introduced at the ligand-deficient site. Kinetic simulation (MD) shows that during the synthesis of metal-organic framework materials doped with metal elements, the metal element M is anchored near the defect sites of the metal-organic framework material and coordinated with the oxygen / carbon in the metal-organic framework material. At the same time, in order to conserve charge, counterions also participate in the stabilization of the metal element M, so that the metal element M exists in the coordination structure of M-O3C. One oxygen atom and carbon atom come from the organic ligand, and the other two oxygen atoms come from nitrate.

[0041] Based on the amount of metal element doped in the metal-organic framework (MOF) material, if the molar content of the metal element is too high, for example, higher than 2.3 mol / mol (i.e., a > 2.3), some of the metal element is adsorbed into the pores of the MOF material via physical adsorption. During the charging and discharging process of the secondary battery, this metal element will detach from the pores of the MOF material and diffuse to the electrode interface with the electric field, catalyzing side reactions such as gas production, thus affecting the electrochemical performance of the secondary battery. Based on the amount of metal element doped in the MOF material, if the molar content of the metal element is too low, for example, lower than 0.01 mol / mol (i.e., a < 0.01), it indicates that the amount of metal element doped in the MOF material is too small. The active lithium in the battery will be chemically adsorbed and bound within the framework, leading to the loss of active lithium, affecting the capacity utilization of the secondary battery, and reducing the energy density of the secondary battery.

[0042] In this application, the metal element-doped metal-organic framework (MOF) material is a compound containing a metal element, where the metal element is doped into the crystal structure of the MOF material. That is, the metal element is chemically modified into the crystal structure of the MOF material, and its crystal structure changes after doping. The metal element-doped MOF material provided in this application differs from physically adsorbing a metal element into the MOF material. If a metal element is physically adsorbed into the MOF material, during the charging and discharging process of the secondary battery, the physically adsorbed metal element will detach from the pores of the MOF material. As the electric field diffuses to the electrode interface, it can catalyze side reactions such as gas production, affecting the electrochemical performance of the secondary battery. The metal element-doped MOF material provided in this application also differs from physically mixing a metal compound with the MOF material. In physical mixing, the contact between the metal compound (such as oxides or nanoparticles) and the MOF material crystal is only a macroscopic interface, and molecular-scale bonding or electronic coupling cannot be formed. There is obvious phase separation between the two phases, and it is difficult for them to have molecular size coordination, which is not conducive to the transport of active metal ions between the two phases, thus hindering the improvement of the fast charging performance of the secondary battery.

[0043] In some embodiments of this application, the molar ratio of Zr to OL in the separator is 6:(2.53~5.055), preferably 6:(2.766~4.92), more preferably 6:(2.766~4.266), and even more preferably 6:(2.766~3.69). For example, the molar ratio of Zr to OL in the separator can be 6:2.53, 6:2.766, 6:3, 6:3.5, 6:3.69, 6:4, 6:4.266, 6:4.5, 6:4.92, 6:5.055, or a range consisting of any two of these values. In the separator, the molar ratio of Zr to OL actually reflects the total defect rate of the metal-organic framework material doped with metal elements. Theoretically, the total defect rate = 1 - n(OL) / n(Zr). Controlling the molar ratio of Zr to OL within the range of this application helps to ensure that the defect rate is within a suitable range, which can promote the removal of coordination solvents from active metal ions, improve the rate of cross-interface transport of active metal ions, improve the fast charging performance, cycle performance, and low-temperature performance of the secondary battery, and help to improve the energy density of the secondary battery.

[0044] In some embodiments of this application, thermogravimetric analysis is used to test the total defect rate Z of the metal-organic framework material doped with metal elements, which is 20% ≤ Z ≤ 53.5%; preferably, 25% ≤ Z ≤ 53.5%; more preferably, 29.6% ≤ Z ≤ 53.5%; and more preferably, 40% ≤ Z ≤ 53.5%. For example, the value of Z can be 20%, 22%, 25%, 29%, 29.6%, 30%, 32%, 34%, 36%, 38%, 40%, 42%, 45%, 47%, 49%, 50%, 53.5%, or a range of any two of these values. Defects in MOF materials have unique spatial structures and electronic properties, which can provide active sites for chemical reactions. The total defect rate refers to the ratio of the number of defects present in the structure of the metal-organic framework material to the number of corresponding linked ligands in the theoretically intact structure. If the ligand is not completely connected to the metal node or the structure of the ligand itself (such as length, functional groups, molecular skeleton, etc.) is changed, organic ligand defects will be formed. For example, in a metal-organic framework material with terephthalic acid as a ligand, terephthalic acid may be partially lacking in coordination or replaced by solvents and template agents, resulting in organic ligand defects. These defects are Lewis acid sites that interact strongly with solvents and anions in the electrolyte. By adjusting the value of Z within the range specified in this application, the removal of coordination solvents from active metal ions can be promoted, increasing the rate of cross-interface transport of active metal ions, improving the fast-charging performance, cycle performance, and low-temperature performance of secondary batteries, and contributing to higher energy density. For any bulk material, its performance is often constrained by both the diffusion rate within the bulk and the surface exchange rate. Reducing the particle size of the material can increase its specific surface area, thereby increasing the contact area between the material and the external environment per unit mass. The presence of defects can reduce steric hindrance and enhance diffusion capacity within the bulk phase; on the other hand, they can also serve as active sites, promoting desolvation processes and effectively removing byproducts. Among these, unsaturated coordination defects, compared to conventional defects, can significantly reduce steric hindrance while possessing higher reactivity.

[0045] In some embodiments of this application, solid-state NMR phosphorus spectroscopy is used to determine the unsaturated coordination defect rate K of the metal-organic framework material doped with metal elements, where 15% ≤ K ≤ 50.1%; preferably, 22% ≤ K ≤ 50.1%; more preferably, 26.1% ≤ K ≤ 50.1%; and even more preferably, 37% ≤ K ≤ 50.1%. For example, the value of K can be 15%, 18%, 20%, 22%, 24%, 25%, 26.1%, 28%, 29%, 30%, 32%, 35%, 37%, 38%, 40%, 42%, 45%, 48%, 49%, 50%, 50.1%, or a range of any two of these values. Unsaturated coordination defects refer to defect structures caused by the absence of ligands. Compared with other types of defects, unsaturated coordination defects have higher activity; exposed unsaturated metal sites have lower steric hindrance and higher site accessibility, which is more conducive to active metal ions (e.g., Li). + During interfacial transport, the coordination solvent is removed. Furthermore, unsaturated coordination sites typically have lower metal valence states, resulting in a charge distribution within the material and a charge transfer path with the substrate that differs significantly from saturated coordination structures. This unique charge distribution and transfer path are more conducive to molecular activation and electron migration, thereby increasing the rate of interfacial transport of active metal ions. Controlling the unsaturated coordination defect rate of metal-organic framework materials doped with metal elements within the range described in this application is beneficial for improving the rate of interfacial transport of active metal ions in secondary batteries, enhancing the fast-charging and cycle performance of secondary batteries, and simultaneously removing byproducts generated during battery operation, such as transition metals, gases, and free radicals.

[0046] In some embodiments of this application, the metal-doped metal-organic framework material includes a dicarboxylate conjugated organic ligand, the molecular skeleton of which includes any one of phenyl, imidazolyl, and pyridyl groups. When the molecular skeleton of the dicarboxylate conjugated organic ligand is selected from phenyl, the molecule itself has a certain rigidity, supporting only axial rotation, which is beneficial for exerting the confinement effect of the pore size. When the molecular skeleton of the dicarboxylate conjugated organic ligand is selected from imidazolyl and pyridyl groups, the organic ligand skeleton itself contains heteroatoms, which is beneficial for adjusting the polarity of the pore wall of the metal-doped metal-organic framework material, thereby enhancing the interaction between its pore wall and lithium ions, solvent, and anions in the electrolyte, promoting the dissociation of the three within the pore, and thus improving the migration efficiency of lithium ions.

[0047] In some embodiments of this application, the molecular skeleton of the dicarboxylated conjugated organic ligand is selected from phenyl, and the dicarboxylated conjugated organic ligand includes a functional group X, which includes any one of amino, hydroxyl, mercapto, methoxy, nitro, fluorine, and chlorine groups; preferably, the functional group X includes any one of amino, mercapto, and fluorine groups. Introducing functional group X into the metal-organic framework material doped with metal elements, and controlling the type of functional group X within the scope of this application, is beneficial to adjusting the polarity of the pore wall, thereby enhancing the interaction between the pore wall and lithium ions, solvent, and anions in the electrolyte, promoting the dissociation of the three within the pore, and thus improving the migration efficiency of lithium ions, improving the fast charging performance, cycle performance, low-temperature performance of the secondary battery, and increasing the energy density of the secondary battery.

[0048] In some embodiments of this application, the dicarboxylated conjugated organic ligand comprises at least one of the following substances:

[0049] (1) When the functional group X is an amino group, the dicarboxylic acid conjugated organic ligand includes at least one of 2-aminoterephthalate, 2,5-diaminoterephthalate, 2,3-diaminoterephthalate, 2,3,5-triaminoterephthalate and 2,3,4,5-tetraaminoterephthalate; preferably at least one of 2-aminoterephthalate and 2,5-diaminoterephthalate.

[0050] (2) When the functional group X is a hydroxyl group, the dicarboxylic acid conjugated organic ligand includes at least one of 2-hydroxyterephthalate, 2,5-dihydroxyterephthalate, 2,3-dihydroxyterephthalate, 2,3,5-trihydroxyterephthalate and 2,3,4,5-tetrahydroxyterephthalate;

[0051] (3) When the functional group X is a thiol group, the dicarboxylic acid conjugated organic ligand includes at least one of 2-mercaptoterephthalate, 2,5-dimercaptoterephthalate, 2,3-dimercaptoterephthalate, 2,3,5-trimercaptoterephthalate and 2,3,4,5-tetramercaptoterephthalate;

[0052] (4) When the functional group X is methoxy, the dicarboxylic acid conjugated organic ligand includes at least one of 2-methoxyterephthalate, 2,5-dimethoxyterephthalate, 2,3-dimethoxyterephthalate, 2,3,5-trimethoxyterephthalate and 2,3,4,5-tetramethoxyterephthalate;

[0053] (5) When the functional group X is a nitro group, the dicarboxylic acid conjugated organic ligand includes at least one of 2-nitroterephthalate, 2,5-dinitroterephthalate, 2,3-dinitroterephthalate, 2,3,5-trinitroterephthalate and 2,3,4,5-tetranitroterephthalate;

[0054] (6) When the functional group X is a fluorine group, the dicarboxylic acid conjugated organic ligand includes at least one of 2,5-dicarboxyfluorobenzoate, 2,5-difluoroterephthalate, 2,3-difluoroterephthalate, 2,3,5-trifluoroterephthalate and 2,3,4,5-tetrafluoroterephthalate; preferably 2,5-dicarboxyfluorobenzoate;

[0055] (7) When the functional group X is a chlorine group, the dicarboxylic conjugated organic ligand includes at least one of 2,5-dicarboxychlorophthalate, 2,5-dichloroterephthalate, 2,3-dichloroterephthalate, 2,3,5-trichloroterephthalate and 2,3,4,5-tetrachloroterephthalate.

[0056] In some embodiments of this application, the molecular skeleton is selected from either pyridyl or imidazolyl, and the dicarboxylated conjugated organic ligand comprises at least one of the following substances:

[0057] (1) When the molecular skeleton is selected from pyridinyl, the dicarboxylic acid conjugated organic ligand includes 2,5-pyridinic acid dicarboxylate;

[0058] (2) When the molecular skeleton is selected from imidazole, the dicarboxylic conjugated organic ligand includes at least one of 1H-imidazol-2,4-dicarboxylate and imidazol-4,5-dicarboxylate.

[0059] In some embodiments of this application, the dicarboxylic acid conjugated organic ligand includes any one of terephthalate, amino-modified terephthalate, fluoroterephthalate, and pyridinic acid dicarboxylate. The amino-modified terephthalate includes at least one of 2-aminoterephthalate, 2,5-diaminoterephthalate, 2,3-diaminoterephthalate, 2,3,5-triaminoterephthalate, and 2,3,4,5-tetraaminoterephthalate; preferably 2-aminoterephthalate or 2,5-diaminoterephthalate. The fluoroterephthalate ion includes at least one selected from 2,5-dicarboxyfluorobenzoate, 2,5-difluoroterephthalate, 2,3-difluoroterephthalate, 2,3,5-trifluoroterephthalate, and 2,3,4,5-tetrafluoroterephthalate; preferably 2,5-dicarboxyfluorobenzoate. The pyridine dicarboxylate ion includes 2,5-pyridine dicarboxylate. Metal-doped metal-organic framework materials including dicarboxylic acid conjugated organic ligands within the above-mentioned range are beneficial for further modulating the polarity of the pore walls of the metal-doped metal-organic framework materials, thereby enhancing the interaction between the pore walls and lithium ions, solvents, and anions in the electrolyte, promoting the dissociation of these three components within the pores, further improving the migration efficiency of lithium ions, and further improving the fast-charging performance, cycle performance, low-temperature performance, and energy density of the secondary battery.

[0060] In some embodiments of this application, the counterion includes NO3. - Cl - SO4 2- ,Br - F - And any one of acetylacetonate. Preferably, the counterion includes NO3. - and Cl - At least one of the following. Based on their charge characteristics, metal-organic frameworks (MOFs) can be classified into cationic frameworks, anionic frameworks, and neutral frameworks. Counterions weakly bind to the MOFs through non-covalent interactions and are essential for maintaining the charge neutrality of MOF materials. The role of counterions is to balance the charge of the cationic framework caused by defects. In this application, the metal-doped MOF material consists of a cationic framework and counterions. For the cationic framework of the metal-doped MOF material in this application, the counterions can originate from the MOF material preparation process or from the metal element loading process. In secondary batteries, the counterions in the metal-doped MOF material can dissolve and replace other ions with the same charge in the electrolyte, such as TFSI. - FSI - PF6 -Counterions can affect the formation of the negative electrode film. The solid electrolyte interphase (SEI) film formed is more conducive to ion transport, thereby improving the charge transfer at the interface and improving the fast charging performance, cycle performance and low temperature performance of the secondary battery.

[0061] In this application, sol refers to a small molecule ligand, and blank refers to a ligand vacancy appearing around Zr. This application does not specifically limit the small molecule ligand (sol) in metal-organic framework materials doped with metal elements, as long as it achieves the purpose of this application. For example, the small molecule ligand sol can include, but is not limited to, acetate, formate, chloride, and CH3-(CH2). n -COO - 1 ≤ n ≤ 6. The small molecule ligand (sol) is introduced during the preparation process via a template agent. It is understood that the small molecule ligand sol may be partially substituted by the solvent during the preparation process, for example, by polar molecules such as the template agent, ethanol, dichloromethane, and water. It should be noted that when sol is selected from acetate in the embodiments of this application, it includes the case where it is partially substituted by the solvent.

[0062] In some embodiments of this application, based on the quality of the coating, the mass percentage of the metal-doped metal-organic framework material is W1, where 65% ≤ W1 ≤ 94.4%, preferably 75% ≤ W1 ≤ 90%. For example, the value of W1 can be 65%, 68%, 70%, 73%, 75%, 78%, 80%, 83%, 85%, 88%, 90%, 92%, 94%, 94.4%, or a range of any two of these values. By adjusting the value of W1 within the range of this application, it is beneficial to promote the metal-doped metal-organic framework material to play a role in removing lithium-ion coordination solvents, improve the rate of lithium-ion cross-interface transport, and improve the fast-charging performance and cycle performance of the secondary battery. Excessive W1 can lead to coating detachment due to insufficient adhesion, and also increases the collision probability of the metal-doped metal-organic framework material, making it easier for the metal-doped metal-organic framework material in the slurry to settle.

[0063] In some embodiments of this application, the coating includes an adhesive, which includes at least one of sodium carboxymethyl cellulose and polyacrylate. Based on the mass of the coating, the mass percentage of the adhesive is W2, where 2.7% ≤ W2 ≤ 32.8%, preferably 7.4% ≤ W2 ≤ 22.6%. For example, the value of W2 can be 2.7%, 5%, 7.4%, 8%, 10%, 12%, 14%, 16%, 18%, 20%, 22%, 22.6%, 25%, 28%, 30%, 32.8%, or a range of any two of these values. The coating includes an adhesive within the scope of this application, and the mass percentage of the adhesive is controlled within this scope to facilitate the adhesive's bonding effect in the coating, resulting in good stability of the coating.

[0064] In some embodiments of this application, the coating includes a wetting agent, which includes at least one selected from branched alcohols, sodium dodecyl sulfate, sodium dodecyl sulfonate, and acetylenol polyoxyethylene ether. The branched alcohol may include, but is not limited to, at least one selected from 2-methyl-2,4-pentanediol, trimethylolpropane, and pentaerythritol. Based on the mass of the coating, the mass percentage of the wetting agent is W3, 0.01% ≤ W3 ≤ 6%, preferably 0.01% ≤ W3 ≤ 1.5%. For example, the value of W3 can be 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.1%, 0.3%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, or a range consisting of any two of these values. Including a wetting agent within the scope of this application and controlling the mass percentage of the wetting agent within the scope of this application is beneficial for the uniform distribution of the slurry on the diaphragm substrate during coating.

[0065] In some embodiments of this application, the coating includes a dispersant, which includes at least one of polyvinyl alcohol, polyacrylonitrile, and polyvinylpyrrolidone. Based on the mass of the coating, the mass percentage of the dispersant is W4, where 0.1% ≤ W4 ≤ 6%, preferably 0.5% ≤ W4 ≤ 1.5%. For example, the value of W4 can be 0.1%, 0.3%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, or a range of any two of these values. Including a dispersant within the scope of this application and controlling the mass percentage of the dispersant within the scope of this application is beneficial for stabilizing the metal-doped metal-organic framework material and reducing the agglomeration of the metal-doped metal-organic framework material in the slurry.

[0066] In some embodiments of this application, 41.8 ≤ W1 / W4 ≤ 650; preferably, 55.7 ≤ W1 / W4 ≤ 83.6. For example, the value of W1 / W4 can be 41.8, 45, 50, 55, 55.7, 60, 62, 65, 68, 70, 75, 80, 83.6, 90, 100, 110, 120, 130, 140, 150, 160, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, or a range of any two of these values. By controlling the ratio of the mass percentage of metal-organic framework material (W1) to the mass percentage of dispersant (W4) in the coating to the mass percentage of metal-organic framework material within the range of this application, it is beneficial to the uniform distribution of the metal-organic framework material in the coating and to reduce the agglomeration of the metal-organic framework material in the slurry. If the W1 / W4 ratio is too high, the metal-organic framework material doped with metal elements will agglomerate in the slurry due to the high probability of collision. If the ratio is too low, the metal-organic framework material doped with metal elements will be severely coated by polymers, increasing steric hindrance and preventing the pores from contacting the target object.

[0067] In some embodiments of this application, the coating thickness is from 0.3 μm to 6 μm, preferably from 0.5 μm to 3 μm. For example, the coating thickness can be 0.3 μm, 0.5 μm, 0.8 μm, 1 μm, 1.2 μm, 1.5 μm, 1.8 μm, 2 μm, 2.2 μm, 2.5 μm, 2.8 μm, 3 μm, 3.2 μm, 3.5 μm, 3.8 μm, 4 μm, 4.2 μm, 4.5 μm, 4.8 μm, 5 μm, 5.2 μm, 5.5 μm, 5.8 μm, 6 μm, or a range consisting of any two of these values. By adjusting the coating thickness within the range specified in this application, it is beneficial to promote the removal of coordination solvents from active metal ions, increase the rate of cross-interface transport of active metal ions, improve the fast-charging performance and cycle performance of the secondary battery, while also considering the energy density of the secondary battery. It should be noted that the thickness of the coating in this application refers to the total thickness of the coating on the substrate.

[0068] In some embodiments of this application, the coating weight per unit area on the substrate is 0.12 g / m². 2 Up to 2.52g / m 2 Preferably, the coating weight per unit area on the substrate is 0.21 g / m². 2 Up to 1.26 g / m 2 For example, the coating weight per unit area on the substrate can be 0.12 g / m². 2 0.21g / m 2 0.25g / m 2 0.3g / m 2 0.35g / m2 0.4g / m 2 0.45g / m 2 0.5g / m 2 0.55g / m 2 0.6g / m 2 0.65g / m 2 0.7g / m 2 0.75g / m 2 0.8g / m 2 0.84g / m 2 0.85g / m 2 1g / m 2 1.26g / m 2 1.5g / m 2 1.8g / m 2 2g / m 2 2.2g / m 2 2.52g / m 2 This can be a range consisting of any two of these values. By adjusting the unit coating weight on the substrate within the range specified in this application, it is beneficial to promote the removal of coordination solvents from active metal ions, increase the rate of cross-interface transport of active metal ions, improve the fast-charging performance and cycle performance of the secondary battery, while also considering the energy density of the secondary battery. It should be noted that the unit coating weight on the substrate in this application refers to the unit coating weight on one side of the substrate.

[0069] In this application, there is no particular limitation on the total thickness of the separator, as long as it achieves the purpose of this application. For example, the thickness of the separator is 9.3 μm to 16 μm, preferably 10 μm to 13 μm. By adjusting the thickness of the separator within the above range, it is beneficial to improve the fast charging performance and cycle performance of the secondary battery, while also taking into account the energy density of the secondary battery.

[0070] There is a significant correlation between the particle size of a material and its defect characteristics: generally, the lower the defect rate, the larger the particle size tends to be; conversely, the smaller the particle size, the higher the defect rate. Furthermore, the higher the degree of unsaturation of the defects, the more significant the impact on particle size. For example, materials can be broadly classified into two categories based on their defect characteristics: one is high unsaturated defect rate—high defect rate—small particle size samples; the other is low unsaturated defect rate—low defect rate—large particle size samples. Both higher defect rates and smaller particle sizes show a consistent trend in improving material properties.

[0071] In some embodiments of this application, the average particle size D of the metal-doped metal-organic framework material is 20 nm ≤ D ≤ 110 nm, preferably 64 nm ≤ D ≤ 80 nm. For example, the average particle size of the metal-doped metal-organic framework material can be 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm, 60 nm, 64 nm, 65 nm, 70 nm, 75 nm, 80 nm, 85 nm, 90 nm, 95 nm, 100 nm, 105 nm, 110 nm, or any combination of two of these values. By controlling the average particle size of the metal-doped metal-organic framework material within the above range, it is beneficial to increase the surface exchange sites per unit mass of the metal-doped metal-organic framework material, which is beneficial to promote the removal of coordination solvents by active metal ions, improve the rate of cross-interface transport of active metal ions, and improve the fast-charging performance and cycle performance of the secondary battery. When the particle size of a material is too large, the bulk diffusion paths of its ions / molecules increase significantly, resulting in slow mass transfer kinetics; simultaneously, the specific surface area decreases sharply, leading to an insufficient number of effective surface reaction sites. Both of these factors jointly limit the material's performance. Correspondingly, larger particle sizes usually mean higher crystallinity and a more complete structure, thus resulting in a lower total defect rate, especially a scarcity of highly reactive unsaturated coordination defects. When the particle size is too small, on the one hand, the surface energy is too high, making agglomeration highly likely, which reduces the effective surface area; on the other hand, excessively high defect density (especially a large number of unsaturated coordination defects) may disrupt the long-range ordered structure of the material, leading to decreased structural stability and potentially inducing the continuous occurrence of side reactions. Therefore, while small particle size significantly increases both the total defect rate and the unsaturated coordination defect rate, it also introduces the risks of agglomeration and structural instability.

[0072] In this application, there is no particular limitation on the specific surface area of ​​the metal-organic framework material doped with metal elements, as long as the purpose of this application can be achieved. For example, the specific surface area of ​​the metal-organic framework material doped with metal elements can be 400 m². 2 / g to 1040m 2 / g, the specific surface area of ​​metal-organic framework materials doped with metal elements is within the above range, which is conducive to constructing suitable pore sizes, promoting the removal of coordination solvents from active metal ions, improving the rate of cross-interface transport of active metal ions, and improving the fast charging performance and cycle performance of secondary batteries.

[0073] In some embodiments of this application, the XRD patterns of metal-doped metal-organic framework materials include diffraction peaks on the (200) and (111) crystal planes, such as... Figure 1As shown, the lower black vertical line (XRD standard card) in the figure represents the diffraction peaks simulated based on the UiO-66 single crystal, including diffraction peaks of the (200) and (111) crystal planes. The XRD pattern of the metal-doped metal-organic framework material includes diffraction peaks of the (200) and (111) crystal planes. On the one hand, this indicates that the metal-doped metal-organic framework material used in this application still maintains a good crystal structure; on the other hand, it indicates that the metal-doped metal-organic framework material used in this application has a porous structure, with 8 Å pores arranged in an orderly manner within the framework. During the charging and discharging process of the secondary battery, under the action of the electric field, solvated lithium ions in the electrolyte pass through the coating of this application. Under the confinement effect of the nanopores, the lithium ions undergo a gradient desolvation process. Compared with one-step desolvation on the positive and negative electrode surfaces, this gradient desolvation process requires overcoming a lower energy barrier.

[0074] In some embodiments of this application, the coating further includes at least one of a semiconductor oxide, an oxide solid electrolyte, or a covalent organic framework material. The inclusion of a semiconductor oxide in the coating is beneficial for improving the mechanical properties of the membrane and suppressing thermal shrinkage. Some materials (such as MnO2) possess catalytic activity, capable of decomposing electrolyte byproducts, reducing gas generation, and delaying thermal runaway. The oxide solid electrolyte itself is a fast ion conductor, which can promote Li... + In terms of transport, coatings including oxide solid electrolytes are beneficial for reducing interfacial impedance and improving rate performance. Coatings including covalent organic framework materials are beneficial for suppressing concentration polarization, promoting ion transport, and enhancing the thermal stability of the membrane. When metal-organic frameworks are co-constructed with semiconductor oxides, oxide solid electrolytes, or covalent organic frameworks (COFs), the nanoscale particle size of the metal-organic frameworks can act as a "structural lubricant," finely controlling the stacking pattern of each component, constructing a tight interface at the molecular scale, and significantly improving interphase compatibility and synergistic efficiency. This application does not have a particular limitation on the mass percentage of semiconductor oxides, oxide solid electrolytes, or covalent organic framework materials in the coating, as long as the purpose of this application is achieved. For example, based on the mass of the coating, the mass percentage of semiconductor oxides, oxide solid electrolytes, or covalent organic framework materials can be from 5% to 50%.

[0075] In some embodiments of this application, the separator further includes other coatings, which include at least one of semiconductor oxides, oxide solid electrolytes, or covalent organic framework materials. Including these other coatings in the separator is beneficial for improving mechanical properties and thermal stability. This application does not particularly limit the thickness of the other coatings, as long as they achieve the purpose of this application; for example, the thickness of the other coatings can be from 1 μm to 3 μm. This application does not particularly limit the coating location of the other coatings, as long as they achieve the purpose of this application; for example, the other coatings can be disposed on the same side of the metal-organic framework material coating containing metal elements; the other coatings can also be disposed on the other side of the metal-organic framework material coating containing metal elements; the other coatings can be directly adjacent to the substrate or directly adjacent to the metal-organic framework material coating containing metal elements. This application does not particularly limit the number of coating layers, as long as they achieve the purpose of this application; for example, one layer can be disposed on the surface of the separator substrate, or two layers can be disposed on the separator substrate.

[0076] In this application, there are no particular limitations on the aforementioned semiconductor oxides, oxide solid electrolytes, and covalent organic framework materials, as long as they can achieve the purpose of this application. For example, semiconductor oxides may include, but are not limited to, at least one of aluminum oxide, boehmite, titanium dioxide, and manganese oxide; oxide solid electrolytes may include, but are not limited to, Li. 1.3 Al 0.3 Ti 1.7 (PO4)3, Li 1.4 Al 0.4 Ti 1.6 (PO4)3, Li7La3Zr2O 12 Li .5 Al 0.5 Ge 1.5 P3O 12 Li 3x La 2 / 3-x At least one of TiO3 (0 < x < 0.16); the covalent organic framework material may include, but is not limited to, one of COF-1 (based on 1,4-phenylenediboronic acid and catechol), TAPB-COF (based on 1,3,5-tris(4-aminophenyl)benzene and terephthalaldehyde), COF-5 (based on 2,3,6,7,10,11-hexahydroxytriphenylene and mesitylene), CTF-1 (based on melamine and terephthalaldehyde), and COF-300 (CAS No. 1133843-97-6).

[0077] In this application, the source of the metal-doped metal-organic framework material is not particularly limited; it can be obtained by purchase or by preparation. The preparation method of the substrate metal-organic framework material is not particularly limited, as long as it achieves the purpose of this application. For example, the preparation method of the metal-organic framework material may include, but is not limited to, the following steps: adding Zr source material and dicarboxylic acid conjugated organic ligand to deionized water and a template agent, stirring and refluxing, centrifuging to obtain a precipitate, soaking the precipitate in an organic solvent, and finally centrifuging to obtain the substrate metal-organic framework material. The preparation method of the metal-modified metal-organic framework material is not particularly limited. For example, the preparation method of the metal-doped metal-organic framework material may be: drying and activating the metal-organic framework material prepared above; adding the activated metal-organic framework material and the metal source material to a diffusion solvent, refluxing, centrifuging, washing, and vacuum drying to obtain the metal-doped metal-organic framework material. Other metal-based metal-organic framework materials can be prepared using methods similar to the above process, or they can be prepared using methods known to those skilled in the art or purchased from commercially available products, and then loaded with metal elements.

[0078] For zirconium-based metal-organic framework materials, this application does not specifically limit the Zr source mentioned above, as long as it can achieve the purpose of this application. For example, the Zr source material may include, but is not limited to, at least one of zirconium oxynitrate, zirconium chloride, zirconium oxychloride, zirconium bromide, zirconium fluoride, zirconium acetylacetonate, and zirconium sulfate. This application also does not specifically limit the template agent mentioned above, as long as it can meet the purpose of this application; for example, the template agent includes glacial acetic acid, formic acid, hydrochloric acid, and CH3-(CH2). n At least one of -COOH, 1≤n≤6. This application does not particularly limit the above-mentioned organic solvents, which may include, but are not limited to, at least one of ethanol, acetone, or dichloromethane. This application does not particularly limit the metal element source material, as long as it can achieve the purpose of this application. For example, when the metal element is Li, Na, K, Ca, Mg, Cu, Co, Ni, Fe, Cr, Ti, Zn, or Mn, a nitrate compound containing the corresponding metal element, a chloride compound containing the corresponding metal element, a sulfate compound containing the corresponding metal element, or a phosphate compound containing the corresponding metal element can be added accordingly, as long as the purpose of this application is achieved. This application does not particularly limit the diffusion solvent, as long as it can achieve the purpose of this application. For example, water, ethanol, methanol, n-hexane, cyclohexane, acetone, etc.

[0079] Typically, the molar content of metal elements in metal-organic framework materials doped with metal elements can be controlled by adjusting the concentration of the metal element source material; and the desired metal-doped metal-organic framework material can be selected by combining the "test of molar content of metal elements in metal-organic framework materials doped with metal elements" provided in this application.

[0080] This application does not impose any particular limitation on the type of substrate, as long as it can achieve the purpose of this application. For example, the material of the substrate may include, but is not limited to, at least one of polyethylene (PE), polypropylene (PP), glass fiber, polyester (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), and polyamide (PA). The type of substrate may include, but is not limited to, at least one of woven membrane, nonwoven fabric, microporous membrane, composite membrane, rolled membrane, or spun membrane.

[0081] This application does not impose any particular limitation on the preparation method of the diaphragm, as long as it achieves the purpose of this application. For example, the preparation method of the diaphragm may include, but is not limited to, the following steps: adding the substances used in the coating (e.g., metal-organic framework materials doped with metal elements, binders, dispersants, and wetting agents) to a solvent and mixing them evenly to obtain a coating slurry; then coating the coating slurry onto the surface of a substrate; and finally drying it to obtain the diaphragm. This application does not impose any particular limitation on the solvents mentioned above, as long as they achieve the purpose of this application. For example, the solvent may include, but is not limited to, at least one of water and ethanol. This application does not impose any particular limitation on the coating method, as long as it achieves the purpose of this application, such as wire rod coating, microgravure coating, or spray coating.

[0082] The second aspect of this application provides a secondary battery comprising a positive electrode, a negative electrode, an electrolyte, and a separator provided in the first aspect of this application.

[0083] In this application, the secondary battery includes a negative electrode sheet, which includes a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector. The phrase "the negative electrode material layer is disposed on at least one surface of the negative electrode current collector" means that the negative electrode material layer can be disposed on one surface of the negative electrode current collector along its thickness direction, or on two surfaces of the negative electrode current collector along its thickness direction. It should be noted that the "surface" here can be the entire surface area of ​​the negative electrode current collector, or only a portion of it; this application has no particular limitation, as long as the purpose of this application is achieved. This application also has no particular limitation on the negative electrode current collector, as long as the purpose of this application is achieved. For example, the negative electrode current collector can be copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, foamed nickel or foamed copper, aluminum foil, or a composite negative electrode current collector. The aforementioned composite negative electrode current collector can be a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The material of the polymer material base layer can be, but is not limited to, at least one of polypropylene (PP), polyethylene terephthalate (PET), or polybutylene terephthalate (PBT). The material of the metal layer can be, but is not limited to, at least one of copper, copper alloy, nickel, or nickel alloy. This application does not impose any particular limitation on the thickness of the negative electrode material layer and the negative electrode current collector, as long as the purpose of this application can be achieved. For example, the thickness of the single-sided negative electrode material layer can be from 50 μm to 180 μm, and the thickness of the negative electrode current collector can be from 3 μm to 10 μm.

[0084] The negative electrode material layer includes a negative electrode active material. This application does not have a particular limitation on the type of negative electrode active material, as long as it can achieve the purpose of this application. For example, the negative electrode active material may include, but is not limited to, graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, etc. Graphite may include, but is not limited to, at least one of natural graphite or artificial graphite; the aforementioned silicon-based materials may include, but are not limited to, at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, or silicon alloys; the aforementioned tin-based materials may include, at least one of elemental tin, tin oxide compounds, or tin alloys.

[0085] The negative electrode material layer may further include a negative electrode conductive agent and a negative electrode binder. This application does not impose any particular limitation on the types of negative electrode conductive agents and negative electrode binders, as long as they achieve the purpose of this application. For example, the negative electrode conductive agent may include, but is not limited to, at least one of superconducting carbon black (Super P), acetylene black, Ketjen black, carbon nanotubes, graphene, or carbon fibers. The aforementioned carbon nanotubes may include, but are not limited to, single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The aforementioned carbon fibers may include, but are not limited to, vapor-grown carbon fibers (VGCF) and / or carbon nanofibers. For example, the negative electrode binder may include, but is not limited to, at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), sodium carboxymethyl cellulose (CMC), polymethyl methacrylate (PMAA), or carboxymethyl chitosan (CMCS). This application does not impose any particular limitation on the mass ratio of the negative electrode active material, conductive agent, and binder in the negative electrode material layer. Those skilled in the art can select according to actual needs, as long as the purpose of this application is achieved.

[0086] In this application, the secondary battery includes a positive electrode sheet, which includes a positive current collector and a positive electrode material layer disposed on at least one surface of the positive current collector. The phrase "positive electrode material layer disposed on at least one surface of the positive current collector" means that the positive electrode material layer can be disposed on one surface of the positive current collector along its thickness direction, or on two surfaces of the positive current collector along its thickness direction. It should be noted that the "surface" here can be the entire surface area of ​​the positive current collector, or only a portion thereof; this application does not have any particular limitation, as long as the purpose of this application is achieved. This application does not have any particular limitation on the positive current collector, as long as the purpose of this application is achieved; for example, the positive current collector can be an aluminum foil, an aluminum alloy foil, or a composite positive current collector. The aforementioned composite positive electrode current collector can be a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The material of the polymer material base layer can be, but is not limited to, at least one of polypropylene (PP), polyethylene terephthalate (PET), or polybutylene terephthalate (PBT). The material of the metal layer can be, but is not limited to, at least one of aluminum, aluminum alloy, nickel, or nickel alloy. This application does not impose any particular limitation on the thickness of the positive electrode material layer and the positive electrode current collector, as long as the purpose of this application can be achieved. For example, the thickness of the single-sided positive electrode material layer can be from 50 μm to 250 μm, and the thickness of the positive electrode current collector can be from 7 μm to 16 μm.

[0087] The positive electrode material layer includes a positive electrode active material. This application does not impose any particular limitation on the positive electrode active material, as long as it can achieve the purpose of this application. For example, the positive electrode active material may include, but is not limited to, lithium nickel cobalt manganese oxide (e.g., NCM811, NCM622, NCM622, NCM523, NCM111), lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide (LiCoO2), lithium manganese oxide, lithium manganese iron phosphate, or lithium titanate.

[0088] The positive electrode material layer may further include a positive electrode conductive agent and a positive electrode binder. This application does not impose any particular limitation on the types of positive electrode conductive agents and positive electrode binders, as long as they achieve the purpose of this application. For example, the positive electrode conductive agent may include, but is not limited to, at least one of superconducting carbon black (Super P), acetylene black, Ketjen black, carbon nanotubes, graphene, or carbon fiber. For example, the positive electrode binder may include, but is not limited to, at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, or fluorinated acrylate resin. This application does not impose any particular limitation on the mass ratio of the positive electrode active material, conductive agent, and binder in the positive electrode material layer. Those skilled in the art can select according to actual needs, as long as the purpose of this application is achieved.

[0089] In this application, the secondary battery also includes an electrolyte, which includes an electrolyte and a non-aqueous solvent.

[0090] This application does not impose any particular restrictions on the electrolyte, as long as it achieves the purpose of this application. For example, the electrolyte may include, but is not limited to, at least one of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, Li2SiF6, lithium bis(oxalato)borate (LiBOB), or lithium difluoroborate. This application also does not impose any particular restrictions on the content of the electrolyte in the electrolyte solution, as long as it achieves the purpose of this application.

[0091] This application does not impose any particular restrictions on non-aqueous solvents, as long as they can achieve the purpose of this application. For example, non-aqueous solvents may include, but are not limited to, at least one of carbonate compounds, carboxylic acid ester compounds, ether compounds, or other organic solvents.

[0092] The aforementioned carbonate compounds may include, but are not limited to, at least one of chain carbonate compounds, cyclic carbonate compounds, or fluorocarbonate compounds. The aforementioned chain carbonate compounds may include, but are not limited to, at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), or methyl ethyl carbonate (EMC). The aforementioned cyclic carbonates may include, but are not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), or vinyl ethylene carbonate (VEC). Fluorocarbonate compounds may include, but are not limited to, at least one of fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, or trifluoromethylethylene carbonate. The aforementioned carboxylic acid ester compounds may include, but are not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolactone, valproic acid lactone, or caprolactone. The aforementioned ether compounds may include, but are not limited to, at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran, or tetrahydrofuran. Other organic solvents may include, but are not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolium ketone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, or trioctyl phosphate. This application does not impose any particular limitation on the content of non-aqueous solvents in the electrolyte, as long as the purpose of this application is achieved.

[0093] In this application, the secondary battery also includes a casing for housing the positive electrode, separator, negative electrode, and electrolyte, as well as other components known in the field of secondary batteries. This application does not limit the scope of these other components. This application does not impose any particular limitation on the casing; it can be a casing known in the art, as long as it achieves the purpose of this application. For example, the casing can be a rigid casing or a flexible casing. The material of the rigid casing can be metal; this application does not limit the type of metal and can use known metal rigid casings, as long as they achieve the purpose of this application. The flexible casing can be a metal plastic film, such as aluminum-plastic film, steel-plastic film, etc.

[0094] The secondary battery described in this application is not particularly limited and may include any device in which an electrochemical reaction occurs. In one embodiment of this application, the secondary battery may include, but is not limited to, lithium-ion secondary batteries (lithium-ion batteries), sodium-ion secondary batteries (sodium-ion batteries), etc.

[0095] The preparation process of the secondary battery described in this application is well known to those skilled in the art, and this application does not impose any particular limitations. For example, the preparation process of the secondary battery may include, but is not limited to, the following steps: stacking the positive electrode, separator, and negative electrode in sequence, and performing operations such as winding and folding as needed to obtain a wound electrode assembly; placing the electrode assembly into a housing; injecting electrolyte into the housing and sealing it to obtain the secondary battery. Alternatively, stacking the positive electrode, separator, and negative electrode in sequence, and then fixing the four corners of the entire stacked structure with tape to obtain a stacked electrode assembly; placing the electrode assembly into a housing; injecting electrolyte into the housing and sealing it to obtain the secondary battery. In addition, overcurrent protection elements, conductive plates, etc., may be placed in the housing as needed to prevent pressure rise and overcharging / discharging inside the secondary battery. In this application, the side of the separator including the coating may be adjacent to the positive electrode or the negative electrode, preferably the side of the separator including the coating is adjacent to the positive electrode.

[0096] Example:

[0097] The embodiments and comparative examples provided below illustrate the implementation of this application in more detail. Various tests and evaluations were conducted according to the methods described below. Furthermore, unless otherwise specified, "parts" and "%" are quality standards.

[0098] Test methods and equipment:

[0099] Test of the molar content of metal elements in metal-organic framework materials doped with metal elements:

[0100] The contents of the framework metal Zr and the metal element M in the metal-doped metal-organic framework material were determined using inductively coupled plasma optical emission spectrometry (ICP-OES). The molar ratio of metal element M to Zr in the metal-doped metal-organic framework material was calculated and denoted as c. Based on the amount of substance of the metal-doped metal-organic framework material, the molar content of the metal element is represented by a, where a = 6c. Specific procedures: Digestion was performed using BVIII grade nitric acid. 20 mg of sample and 15 mL of nitric acid were added to a polytetrafluoroethylene beaker, and the mixture was heated at 80°C for 20 min. After the solvent evaporated and approximately 2 mL remained, 15 mL of nitric acid was added, and heating continued for approximately 20 min. This process of adding nitric acid was repeated until the solid was completely dissolved and the residual liquid was clear and transparent. Acid removal was then initiated, and the mixture was diluted with ultrapure water before injection.

[0101] Test of the number of counterions (b) in metal-organic framework materials doped with metal elements:

[0102] 25 mg of metal-doped metal-organic framework material was added to 5 mL of 1 mol / L NaOH solution. The sample was then subjected to ion chromatography (model: Dionex-7680) to determine the type and concentration (mass fraction) of counterions in the sample solution. The mass fraction of the counterion is denoted as W(N), and the molar mass of the counterion is denoted as M(N).

[0103] The mass fraction of Zr in the metal-organic framework material doped with metal elements was determined to be W(Zr), and the molar mass of Zr was determined to be M(Zr) using inductively coupled plasma optical emission spectrometry (ICP-OES). The molecular formula of the metal-organic framework material doped with metal elements is M. a Zr6O m (OH) n (OL) 6-(x+y) / 2 (sol) x (blank) y N b middle, .

[0104] Testing the total defect rate Z of metal-organic framework materials doped with metal elements:

[0105] The total defect rate of metal-organic framework materials doped with metal elements was tested using thermogravimetric analysis (TGA) in a temperature range of 50℃-600℃, a heating rate of 3℃ / min, and an air atmosphere.

[0106] The results were processed as follows: The mass of the remaining material (zirconia-M) from the TGA test at 600℃ was used as a baseline, and normalization was performed, recorded as 100%. Under ideal conditions, in defect-free metal-organic framework materials, the chemical formula of the metal-organic framework material at 350°C is M. a O a / 2 Zr6O6(OL)6, the corresponding standardized weight is N (%), N (%) = MA (M a O a / 2 Zr6O6 (OL)6) / MA(6ZrO2+ M a O a / 2 ) )×100%, where MA(M a O a / 2Zr6O6(OL)6) represents 1 mol M a O a / 2 The mass of Zr6O6(OL)6, MA(6ZrO2+M a Oa / 2 () represents 6 mol ZrO2 and 1 mol M a O a / 2 The sum of their masses. At 350°C, the normalized weight of metal-organic framework materials doped with defective metal elements is less than N%, indicating insufficient internal OL connectors when defects are present. The total defect rate is calculated using the formula: Where w% (350℃) is the standardized weight of metal-organic framework material with defects at 350℃, i.e., w% (350℃) = weight of remaining material at test temperature of 350℃ / weight of remaining material at test temperature of 600℃, and Z is the total defect rate of metal-organic framework material with metal elements.

[0107] Testing of the unsaturated coordination defect rate K of metal-organic framework materials doped with metal elements:

[0108] The unsaturated coordination defect rate K of metal-doped metal-organic frameworks (MOFs) was measured using solid-state NMR phosphorus spectrometry. The metal-doped MOFs were activated under vacuum at 150 °C for 4 h. 100 mg of 2,2,6,6-tetramethylpiperidine-1-oxo radical (TMPO) was dissolved in 15 mL of dichloromethane to obtain a TMPO solution. 50 mg of the activated metal-doped MOFs were added to the TMPO solution and immersed for 1 h. Defects in the metal-doped MOFs were labeled and identified using TMPO. The unsaturated coordination defect rate of the metal-doped MOFs was measured using a Bruker AvanceNEO 600 MHz NMR spectrometer. A 3.2 mm MAS probe was used, with a rotation speed of 15 or 18 kHz. 31 The P signal was calibrated using the NH4H2PO4 signal. Peak fitting was performed on the data between 1 and 100 using Origin, and the fitted R value was... 2 ≥99.8%. The peaks near chemical shifts 62, 58, 55, and 53 represent Zr-blank, μ-OH(OL), μ-OH(sol), and Zr-sol sites, respectively. Zr-blank indicates an unsaturated coordination defect; μ-OH(OL) indicates a bridged hydroxyl group adjacent to the OL organic ligand; μ-OH(sol) indicates a bridged hydroxyl group adjacent to a coordination defect in a small molecule; and Zr-sol indicates a coordination defect in a small molecule. The relative proportions of the corresponding species can be obtained based on the peak area percentages.

[0109] In this study, the peak area ratio of Zr-blank species represents the unsaturated coordination defect rate, denoted as K; the sum of the peak area ratios of Zr-blank, μ-OH(sol), and Zr-sol species represents the total defect rate, denoted as S. The molecular formula of metal-organic framework materials doped with metal elements is M0. a Zr6O m (OH) n (OL) 6-(x+y) / 2 (sol) x (blank) y N b In (0.01≤a≤2.3, 4≤m≤6, 0≤n≤4, 0.09≤x≤0.92, 1.8≤y≤6.02, 0.905≤b≤9.24), x=12(SK), y=12K.

[0110] Test of the molar ratio of Zr to OL in the diaphragm:

[0111] Zr content test in the diaphragm: Take a diaphragm sample weighing between 1.2 and 1.4 g. Considering the volume of the digestion vessel (the amount of sample added and acid added are limited), accurately weigh the sample and record its weight m. Divide it into 10 portions (record the weight of each of the 10 portions, with the largest being used for the control vessel), cut them into small pieces, and place them into 10 digestion vessels. Add 6 mL of concentrated nitric acid and 1 mL of 30% H2O2 solution to each of the 10 digestion vessels. Heat at 140℃ for 0.5 h (after the diaphragm has softened). Remove the heater, and then add 3 mL of 30% H2O2 solution to each digestion vessel. After cooling to approximately room temperature (or when it is not hot to the touch, the digestion vessels can be shaken appropriately during this period), add another 3 mL of concentrated nitric acid. Assemble the digestion apparatus and digest according to the specific program. After digestion, combine the results in a 500 mL volumetric flask (PP material) and dilute to volume with ultrapure water. After adjusting the volume, shake well and then filter through a 0.22μm filter to obtain the prepared test solution.

[0112] (1) Open the instrument according to the operating procedure of the inductively coupled plasma atomic emission spectrometer. After the instrument is in a stable state, measure the standard curve solution. Plot the standard curve with zirconium ion concentration as the abscissa and the corresponding response value as the ordinate. The correlation coefficient r2≥0.9995.

[0113] (2) Under the same instrument conditions, the response value of zirconium ions in the test solution is measured, and the mass concentration (ug / mL) of the zirconium ions in the test solution is found on the standard curve. From this, the molar amount of Zr in the diaphragm can be calculated.

[0114] (3) The standard curve is tested by sequentially injecting samples from low concentration to high concentration. The standard solution and QC (initial calibration verification) are washed with water for 2 minutes before injection. The test solution needs to be washed with 5% nitric acid for 2 minutes and then washed with water for 2 minutes before injection.

[0115] Test for OL content in diaphragm:

[0116] Sample pretreatment: 25 mg of sample was placed in 5 mL of NaOH aqueous solution (1 mol / L), sonicated for 1 h, and after complete decomposition of the coated sample, filtered and detected by liquid chromatography. Column: Agilent ZORBAX SB-C18 column, 4.6 x 150 mm, 5 μm; flow rate: 0.8 mL / min; injection volume: 10 μL; column temperature: 30℃; mobile phase elution program: gradient elution of 85% acetonitrile and 15% formic acid aqueous solution (0.1%), run time 12 min; detector: DAD, wavelength 230 nm, bandwidth 4 nm.

[0117] Testing of the average particle size D of metal-organic framework materials doped with metal elements:

[0118] 2 mg of metal-doped metal-organic framework material was dispersed in 20 mL of methanol and sonicated for 20-60 min. A portion of the suspension was then dropped onto a copper grid and dried. The average particle size of the sample was measured using a transmission electron microscope (TEM) at a magnification of 1 million times. The particle size of the metal-doped metal-organic framework material particles in the TEM image was measured using Processing-Velox software, and the average particle size D was obtained by Gaussian fitting.

[0119] X-ray diffraction pattern test:

[0120] Metal-organic framework (MOF) powder samples or diaphragms coated with MOFs were placed in the X-ray diffractometer stage. Using Cu target Kα rays, a scanning rate of 5° / min and a scanning angle range of 2° to 40° were employed to obtain XRD patterns. The corresponding diffraction peaks were read and their positions recorded. Figure 3 The XRD patterns are of the metal-organic framework material doped with metal elements in Example 1-1 of this application and the membrane coating in Example 1-1 of this application.

[0121] Coating thickness testing:

[0122] The lithium-ion battery was disassembled to obtain the separator. The separator was dried to remove residual electrolyte. The cross-section of the coating was observed and the coating thickness was tested using a scanning electron microscope.

[0123] DC resistance (DCR) testing:

[0124] The lithium-ion battery was placed in a 25°C environment and charged at a constant current of 1C until the voltage reached 3.65V. Then it was charged at a constant voltage of 3.65V until the current reached 0.05C. After resting for 30 minutes, it was discharged at a constant current of 1C for 30 minutes (adjusted to 50% SOC, where SOC refers to the state of charge of the battery). The ending voltage was recorded as V1. After resting for 1 hour, it was discharged at a constant current of 2C for 10 seconds. The ending voltage was recorded as V2. The DC resistance DCR of the lithium-ion battery was calculated as DCR = (V1-V2) / (2C-1C).

[0125] AC resistance (ACR) testing:

[0126] The lithium-ion battery is placed in a 25°C environment, and a constant AC current of 100Hz / 10mA is passed into the lithium-ion battery. The battery's AC internal resistance (ACR) is then obtained by rectification and filtering.

[0127] The values ​​of DCR and ACR can qualitatively determine the fast charging performance of secondary batteries. Generally, the smaller the values ​​of DCR and ACR, the better the rate performance of the lithium-ion battery, that is, the better the fast charging performance.

[0128] Ratio performance test:

[0129] The lithium-ion battery was placed in a 25°C environment and charged at a constant current of 1C to the upper limit voltage of 3.65V, and then discharged at a constant current of 1C to the cutoff voltage of 2V. The discharge capacity was recorded as C1. Then, it was charged at a constant current of 4C to the upper limit voltage of 3.65V, and then discharged at a constant current of 4C to the cutoff voltage of 2V. The discharge capacity was recorded as C2. The capacity retention rate R = C2 / C1 × 100%. R represents the rate performance. The larger the R value, the better the rate performance, that is, the better the fast charging performance of the lithium-ion battery.

[0130] Cyclic performance test:

[0131] The lithium-ion battery was placed in an environment of 25°C, and then charged at a constant current of 4C to a voltage of 3.65V. It was then charged at a constant voltage of 3.65V to a current of 0.05C, and then discharged at a constant current of 4C to a voltage of 2V. The initial discharge capacity was recorded as Q1. This was considered one charge-discharge cycle. The above charge-discharge cycle was repeated for 2000 cycles. The discharge capacity after the 2000th cycle was recorded as Q2, in mAh.

[0132] Cycle capacity retention rate (%) = Q2 / Q1 × 100%; Cycle capacity retention rate and discharge capacity Q2 are used to evaluate the cycle performance of lithium-ion batteries. The larger the cycle capacity retention rate and the larger Q2, the better the cycle performance of lithium-ion batteries.

[0133] Discharge capacity testing:

[0134] The lithium-ion battery was placed in an environment of 25℃, then charged at a constant current of 1C to a voltage of 3.65V, then charged at a constant voltage of 3.65V to a current of 0.05C, and finally discharged at a constant current of 1C to a voltage of 2V. The discharge capacity was recorded. The discharge specific capacity D1 = discharge capacity / mass of the positive electrode active material. The mass of the positive electrode active material refers to the mass of the positive electrode active material in the positive electrode sheet of the lithium-ion battery.

[0135] The increase rate of discharge capacity is calculated based on the discharge capacity D2 of Comparative Example 3. The increase rate of discharge capacity is calculated as (D1-D2) / D2×100%.

[0136] Low temperature performance test:

[0137] Place the lithium-ion battery in a 25°C environment, then charge it at a constant current of 0.5C until the voltage reaches 3.65V, then charge it at a constant voltage of 3.65V until the current reaches 0.05C, then place the lithium-ion battery in a -10°C environment and let it stand for 30 minutes. Then discharge it at a constant current of 0.5C until the voltage reaches 2V. Record the discharge capacity in mAh.

[0138] Example 1-1:

[0139] <Preparation of Metal-Organic Framework Materials>

[0140] 21.38 g (85.8 mmol) of hydrated zirconium nitrate and 23.31 g (128.7 mmol) of 2-aminoterephthalic acid were added to a 1000 mL two-necked flask, followed by 205 mL of deionized water and 81 mL of glacial acetic acid to obtain the first suspension system.

[0141] The first suspension system was mechanically stirred at a rate of 600 r / min. Simultaneously, the reaction system was heated to 100℃ for 24 hours. Subsequently, the crude metal-organic framework material was obtained by centrifugation at 10000 r / min for 60 min.

[0142] The crude metal-organic complex was washed using the following steps: soaking in ethanol for 12 h, acetone for 12 h, dichloromethane for 12 h, then soaking in ethanol for 12 h, acetone for 12 h, and dichloromethane for 12 h, for a total of 6 soakings in different liquids. After each soaking, the supernatant was separated by centrifugation, and then fresh solvent was added. The centrifugation rate was 10000 r / min, and the centrifugation time was 15 min to obtain the metal-organic framework material.

[0143] Based on the volume of the first suspension system, the molar concentration of zirconium salt is 300 mmol / L, the molar ratio of zirconium salt to organic ligand is 1:1.5, and the molar ratio of zirconium salt to template agent is 0.06:1.

[0144] <Preparation of Metal-Organic Framework Materials Doped with Metal Elements>

[0145] 1 g of lithium nitrate and 30 g of water were added to a 350 mL pressure-resistant bottle to obtain a metal salt solution. Then, 7.75 g of the aforementioned metal-organic framework material was added, and the mixture was sonicated for 20 min to ensure thorough mixing. The solution was then heated at 100 °C for 6 h to obtain a second suspension. The second suspension was centrifuged at 10000 r / min for 5 min to obtain a solid. The solid was washed five times with water and then vacuum dried at 120 °C for 12 h to obtain the metal element-doped metal-organic framework material.

[0146] <Preparation of the diaphragm>

[0147] The metal-organic framework material doped with metal elements prepared above was added to deionized water along with the dispersant polyvinylpyrrolidone (PVP). The mixture was ultrasonically stirred at 25°C for 3 hours to obtain a slurry with a solid content of 6.88%. Then, an aqueous solution of polyacrylate (polyacrylate solid content of 19.8%), sodium carboxymethyl cellulose (CMC) binder, and sodium dodecyl sulfate (SDS) wetting agent were added. The mixture was ultrasonically stirred for 5 hours to obtain a slurry with a solid content of 7.69%. This slurry was then uniformly coated to a thickness of 9 mm using a microgravure coating method. A single-sided coated diaphragm was obtained by drying one side of a µm porous polyethylene (PE) substrate (PE porous substrate provided by Shenzhen Xingyuan Material Technology Co., Ltd.) at 90℃. The coating composition, based on mass, includes: 83.6% metal-organic framework material (doped with metal elements), 1.3% PVP dispersant, 12.6% polyacrylate binder, 1.3% CMC binder, 13.9% total binder mass, and 1.2% SDS wetting agent. The coating thickness is 2 μm, and the coating weight per unit area on the substrate is 0.8 g / m². 2 The membrane thickness is 11 μm.

[0148] <Preparation of the positive electrode>

[0149] Lithium iron phosphate (LiFePO4), a positive electrode active material, Super P, carbon nanotubes, and polyvinylidene fluoride (PVDF), a positive electrode binder, were mixed in a mass ratio of 95.5:2:0.5:2. N-methylpyrrolidone (NMP) was added as a solvent to prepare a slurry with a solid content of 55 wt%. After vacuum stirring, the slurry was obtained. The positive electrode slurry was uniformly coated onto one surface of a 16 μm thick aluminum foil used as a positive electrode current collector and dried at 90 °C to obtain a single-sided coated positive electrode sheet with a coating weight of 15 mg / mm². 2 Then, the above steps are repeated on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided coating of positive electrode material. After drying at 85°C, it is rolled, then slit and welded with tabs to obtain a positive electrode sheet with a size of 70mm×54mm for later use. The thickness of the single-sided positive electrode material layer is 141μm.

[0150] <Preparation of Negative Electrode Sheets>

[0151] Artificial graphite (anode active material), Super P (conductive agent), sodium carboxymethyl cellulose (CMC) (binder), and styrene-butadiene rubber (SBR) were mixed at a mass ratio of 92.2:2:1.5:4.3. Deionized water was added as a solvent to prepare a slurry with a solid content of 49 wt%. The slurry was stirred evenly in a vacuum mixer to obtain the anode slurry. The anode slurry was uniformly coated onto one surface of a 9 μm thick copper foil current collector and dried at 90 °C to obtain a single-sided coated anode electrode sheet with a coating weight of 7 mg / mm². 2 Then, the above steps are repeated on the other surface of the copper foil to obtain a negative electrode sheet with a double-sided coating of negative electrode material. After drying at 85°C, it is rolled, then slit and welded with tabs to obtain a negative electrode sheet with a size of 74mm×58mm for later use. The thickness of the single-sided negative electrode material layer is 99μm.

[0152] <Preparation of Electrolyte>

[0153] In an inert atmosphere with a water content of less than 0.1 ppm and an oxygen content of less than 1 ppm, organic solvents ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) are mixed in a mass ratio of EC:EMC:DMC=2:1:7. Then, lithium salt lithium hexafluorophosphate (LiPF6) is added to the organic solvent, dissolved, and mixed evenly to obtain an electrolyte with a LiPF6 concentration of 1 mol / L.

[0154] <Preparation of Lithium-ion Batteries>

[0155] The prepared positive electrode, separator, and negative electrode are stacked sequentially, with the separator positioned between the positive and negative electrodes to act as a separator. The side of the separator including the coating is adjacent to the positive electrode. The electrode assembly is then wound to form an electrode assembly. The electrode assembly is placed in an aluminum-plastic film packaging bag and dehydrated at 85°C. The electrolyte prepared above is then injected, and the battery undergoes vacuum sealing, settling, formation, and shaping processes to obtain a lithium-ion battery. The settling time is 48 hours, the formation current is 0.1C, the upper limit of the formation voltage is 3.65V, and the formation temperature is 45°C.

[0156] Examples 1-2 to 1-32:

[0157] Except for the substitution of the metal-doped metal-organic framework materials according to Tables 1 and 2-1 in the section on <Preparation of the Separator>, the rest is the same as in Example 1-1. The preparation of the metal-doped metal-organic framework materials is as follows:

[0158] Examples 1-1 to 1-10 and 1-12 to 1-16, <Preparation of Metal-Organic Framework Materials>, are the same as in Example 1-1. The remaining examples are identical to Example 1-1 except for adjustments to the amounts of zirconium salt, dicarboxylic acid conjugated organic ligand, deionized water, and template agent, the types of zirconium salt and dicarboxylic acid conjugated organic ligand, and the reaction conditions as shown in Table 2-2. In Example 1-14, water in the first suspension system is replaced with N,N-dimethylformamide, and the stirring rate in Example 1-27 is 900 r / min. In the <Preparation of Metal-Organic Framework Materials Doped with Metal Elements> method, Examples 1-2 to 1-32 are identical to Example 1-1 except for adjustments to the types of metal salt, the mass ratio of metal salt to solvent, the mass ratio of metal-organic framework material to metal salt solution, the heating temperature, and the heating time as shown in Table 2-3.

[0159] Examples 2-1 to 2-14:

[0160] Except for the following in <Preparation of the diaphragm>, where the mass percentages of the metal-doped metal-organic framework material W1, the binder W2, and the dispersant W4 in the diaphragm coating are adjusted according to Table 3, and the mass percentage of the wetting agent W3 remains unchanged, the rest is the same as in Example 1-1.

[0161] Examples 2-15 to 2-18:

[0162] Except for adjusting the coating thickness according to Table 3 in the <Preparation of the Separator> section, the rest is the same as in Example 1-1.

[0163] Example 3-1:

[0164] <Preparation of the diaphragm>

[0165] The metal-organic framework material doped with metal elements prepared in Examples 1-1, alumina, and the dispersant polyvinylpyrrolidone (PVP) were added to deionized water and ultrasonically stirred at 25°C for 3 hours to obtain a slurry with a solid content of 6.88%. Then, an aqueous solution of polyacrylate (polyacrylate solid content of 19.8%), sodium carboxymethyl cellulose (CMC) binder, and sodium dodecyl sulfate (SDS) wetting agent were added and ultrasonically stirred for 5 hours to obtain a slurry with a solid content of 7.69%. The above slurry was then uniformly coated to a thickness of 9 mm using a microgravure coating method. One side of a µm porous polyethylene (PE) substrate (PE porous substrate provided by Shenzhen Xingyuan Material Technology Co., Ltd.) is dried at 90℃ to obtain a single-sided coated diaphragm. The coating composition, based on mass, includes 65% lithium-doped metal-organic framework material, 18.6% alumina, 1.3% PVP dispersant, 12.6% polyacrylate binder, 1.3% CMC binder, 13.9% total binder mass, and 1.2% SDS wetting agent. The coating thickness is 2 μm, and the coating weight per unit area on the substrate is 0.8 g / m². 2 The membrane thickness is 11 μm.

[0166] Except for the preparation of the diaphragm, which is carried out according to the above process, the rest is the same as in Example 1-1.

[0167] Example 3-2:

[0168] Except in the section on "Preparation of the Separator", where aluminum oxide is replaced with Li 1.3 Al 0.3 Ti 1.7 Except for (PO4)3, the rest is the same as in Example 3-1.

[0169] Example 3-3:

[0170] Except for replacing aluminum oxide with covalent organic framework material TAPB-COF (based on 1,3,5-tris(4-aminophenyl)benzene and terephthalaldehyde, CAS No. 1800490-22-5) in the <Preparation of the Separator> section, the rest is the same as in Example 3-1.

[0171] Examples 3-4:

[0172] The metal-doped metal-organic framework material prepared in Examples 1-1 was added to deionized water along with the dispersant polyvinylpyrrolidone (PVP). The mixture was ultrasonically stirred at 25°C for 3 hours to obtain a slurry with a solid content of 6.88%. Then, an aqueous solution of polyacrylate (polyacrylate solid content 19.8%), sodium carboxymethyl cellulose (CMC), and sodium dodecyl sulfate (SDS) were added, and the mixture was ultrasonically stirred for 5 hours to obtain a slurry with a solid content of 7.69%. This slurry was then uniformly coated to a thickness of 9 mm using a microgravure coating method. A single-sided coated diaphragm was obtained by drying one side of a µm porous polyethylene (PE) substrate (PE porous substrate provided by Shenzhen Xingyuan Material Technology Co., Ltd.) at 90℃. The coating composition, based on mass, includes: 83.6% metal-organic framework material (doped with metal elements), 1.3% PVP dispersant, 12.6% polyacrylate binder, 1.3% CMC binder, 13.9% total binder mass, and 1.2% SDS wetting agent. The coating thickness is 2 μm, and the coating weight per unit area on the substrate is 0.8 g / m². 2 Then, aluminum oxide, sodium carboxymethyl cellulose (CMC) binder, and SDS wetting agent were added to deionized water at a mass ratio of 13:2:1 to prepare a slurry with a solid content of 32.9%. The slurry was then uniformly coated onto the uncoated surface of the diaphragm using a micro-gravure coating method and dried at 90°C. This resulted in a diaphragm with a metal-organic framework material doped with metal elements on one side and another coating containing aluminum oxide on the other side. The thickness of the other coating containing aluminum oxide was 3 μm, resulting in a total diaphragm thickness of 14 μm.

[0173] Except for the preparation of the diaphragm, which is carried out according to the above process, the rest is the same as in Example 1-1.

[0174] Comparative Example 1:

[0175] Except for the fact that no coating was applied to the substrate in the <Preparation of the Separator> section, the rest is the same as in Example 1-1.

[0176] Comparative Example 2:

[0177] Except for the section on "Preparation of the Separator," where the metal-doped metal-organic framework material is replaced with an undoped metal-organic framework material, the rest of the process is the same as in Examples 1-1. The molecular formula of the undoped metal-organic framework material can be represented as M... a Zr6O m (OH) n (OL) 6-(x+y) / 2 (sol) x (blank)y N b Where a=0, x=0.216, y=3.252, b=3.252, and sol is acetate.

[0178] Comparative Example 3:

[0179] Except for replacing the diaphragm with a commercially available ceramic diaphragm (Shenzhen Xingyuan Material Technology Co., Ltd., model: SP312J3020H), the rest is the same as in Example 1-1.

[0180] Comparative Example 4:

[0181] Except for the substitution of the metal-doped metal-organic framework material according to Tables 1 and 2-1 in the <Preparation of the Separator> section, the rest is the same as in Example 1-1.

[0182] In Comparative Example 4, the preparation of metal-organic framework materials was the same as in Example 1-1, except that the relevant parameters were adjusted according to Table 2-2. In the preparation of metal-organic framework materials doped with metal elements, the preparation of metal-organic framework materials was the same as in Example 1-1, except that the relevant parameters were adjusted according to Table 2-3.

[0183] The relevant parameters in the molecular formula of the metal-organic framework material doped with metal elements are shown in Table 1, the molecular formula is shown in Table 2-1, the preparation parameters of the metal-organic framework material are shown in Table 2-2, and the preparation parameters of the metal-organic framework material doped with metal elements are shown in Table 2-3.

[0184] The preparation and performance parameters of each embodiment and comparative example are shown in Tables 1 to 4.

[0185] Table 1:

[0186]

[0187] Note: In Table 1, " / " indicates that the corresponding preparation parameter or substance does not exist; "Z" represents the total defect rate of metal-organic framework materials doped with metal elements, in %; "K" represents the unsaturated coordination defect rate of metal-organic framework materials doped with metal elements, in %; "D" represents the average particle size of metal-organic framework materials doped with metal elements, in %; Zr:OL refers to the ratio of the amount of Zr to the amount of dicarboxylic acid conjugated organic ligand in metal-organic framework materials doped with metal elements.

[0188] Table 2-1:

[0189]

[0190] Note: In Table 2-1, " / " indicates that the corresponding preparation parameters or substances do not exist.

[0191] Table 2-2:

[0192]

[0193] Table 2-3:

[0194]

[0195] As can be seen from Examples 1-1 to 1-32 and Comparative Examples 1 to 4, the separators of the secondary batteries in each embodiment of this application include metal-organic framework materials doped with metal elements within the scope of this application, and the molar content of the metal elements is within the scope of this application. However, the separator in Comparative Example 1 does not include a coating, the metal-organic framework material in Comparative Example 2 is not modified with metal, Comparative Example 3 is a commercially available ceramic separator, and the molar content of the metal elements in the metal-organic framework material doped with metal elements in Comparative Example 4 is lower than that in this application. It can be seen that the secondary batteries obtained in the embodiments of this application have lower DC resistance and AC resistance, higher capacity retention rate R, higher cycle capacity retention rate, higher discharge capacity Q2, higher discharge specific capacity improvement rate, and higher -10℃ discharge capacity, indicating that the secondary batteries have good fast charging performance, cycle performance, low temperature performance, and high energy density.

[0196] Figure 1 The XRD patterns of the metal-doped metal-organic framework materials used in Examples 1-1, 1-6, 1-7, 1-8, and 1-9 are shown in the figures. As can be seen from the figures, the metal-doped metal-organic framework materials all include diffraction peaks of the (200) and (111) crystal planes. After testing, the metal-doped metal-organic framework materials used in Examples 1-1 to 1-32 all include diffraction peaks of the (200) and (111) crystal planes, indicating that the metal-organic framework materials used in the above examples still have good crystal structure after loading metal elements.

[0197] The type of organic ligands in metal-organic framework materials doped with metal elements affects the fast-charging performance, cycle performance, low-temperature performance, and energy density of secondary batteries. As can be seen from Examples 1-1, 1-17 to 1-18, when the organic ligands in the metal-organic framework materials doped with metal elements are within the scope of this application, the resulting secondary batteries have lower DC and AC resistance, higher capacity retention R, higher cycle capacity retention, higher discharge capacity Q2, higher discharge capacity improvement rate, and higher -10℃ discharge capacity, indicating that the secondary batteries have good fast-charging performance, cycle performance, low-temperature performance, and high energy density.

[0198] The total defects, unsaturated coordination defects, and average particle size of metal-organic framework materials doped with metal elements affect the fast-charging performance, cycle performance, low-temperature performance, and energy density of secondary batteries. As can be seen from Examples 1-1, 1-11, 1-24 to 1-28, when the total defect rate, unsaturated coordination defect rate, and average particle size in the metal-organic framework materials doped with metal elements are within the range of this application, the resulting secondary batteries have lower DC and AC resistance, higher capacity retention rate R, higher cycle capacity retention rate, higher discharge capacity Q2, higher discharge specific capacity improvement rate, and higher -10℃ discharge capacity, indicating that the secondary batteries have good fast-charging performance, cycle performance, low-temperature performance, and high energy density.

[0199] The types of counterions in metal-organic framework materials doped with metal elements affect the fast-charging performance, cycle performance, low-temperature performance, and energy density of secondary batteries. As can be seen from Examples 1-1, 1-29 to 1-30, when the types of counterions in the metal-organic framework materials doped with metal elements are within the scope of this application, the resulting secondary batteries have lower DC and AC resistance, higher capacity retention R, higher cycle capacity retention, higher discharge capacity Q2, higher discharge capacity improvement rate, and higher -10℃ discharge capacity, indicating that the secondary batteries have good fast-charging performance, cycle performance, low-temperature performance, and high energy density.

[0200] Table 3:

[0201]

[0202] Table 4:

[0203]

[0204] The mass percentage W1 of the metal-organic framework material doped with metal elements affects the fast-charging performance, cycle performance, low-temperature performance, and energy density of the secondary battery. As can be seen from Examples 1-1, 2-1 to 2-5, when the mass percentage of the metal-organic framework material doped with metal elements in the separator coating is within the range of this application, the obtained secondary battery has lower DC resistance and AC resistance, higher capacity retention R, higher cycle capacity retention, higher discharge capacity Q2, higher discharge capacity improvement rate, and higher -10℃ discharge capacity, indicating that the secondary battery has good fast-charging performance, cycle performance, low-temperature performance, and high energy density. Figure 2 The image shows a scanning electron microscope (SEM) image of the diaphragm coating of Example 1-1 of this application. It can be seen from the image that the diaphragm coating is evenly applied to the substrate and no cracking or other phenomena are observed.

[0205] The ratio of the mass percentage W1 of the metal-organic framework material doped with metal elements to the mass percentage W4 of the dispersant affects the fast-charging performance, cycle performance, low-temperature performance, and energy density of the secondary battery. As can be seen from Examples 1-1, 2-6 to 2-14, when the value of W1 / W4 is within the range of this application, the obtained secondary battery has lower DC resistance and AC resistance, higher capacity retention R, higher cycle capacity retention, higher discharge capacity Q2, higher discharge capacity improvement rate, and higher -10℃ discharge capacity. This indicates that the fast-charging performance, cycle performance, and low-temperature performance of the secondary battery are further improved, and the energy density of the secondary battery is further increased.

[0206] The thickness of the separator coating affects the fast-charging performance, cycle performance, low-temperature performance, and energy density of the secondary battery. As can be seen from Examples 1-1, 2-15 to 2-18, when the thickness of the separator coating is within the range of this application, the obtained secondary battery has lower DC resistance and AC resistance, higher capacity retention rate R, higher cycle capacity retention rate, higher discharge capacity Q2, higher discharge capacity improvement rate, and higher -10℃ discharge capacity, indicating that the secondary battery has good fast-charging performance, cycle performance, low-temperature performance, and high energy density.

[0207] As can be seen from Examples 3-1 to 3-3, the coating includes the metal-doped metal-organic framework material provided in this application, and also includes at least one of semiconductor oxides, oxide solid electrolytes, or covalent organic framework materials. The resulting secondary battery has lower DC and AC resistance, higher capacity retention R, higher cycle capacity retention, higher discharge capacity Q2, higher discharge capacity improvement rate, and higher -10°C discharge capacity, indicating that the secondary battery has good fast-charging performance, cycle performance, low-temperature performance, and high energy density. As can be seen from Examples 3-4, the separator includes a coating containing metal-doped metal-organic framework material provided in this application, and also includes other coatings containing semiconductor oxides. The resulting secondary battery also has lower DC and AC resistance, higher capacity retention R, higher cycle capacity retention, higher discharge capacity Q2, higher discharge capacity improvement rate, and higher -10°C discharge capacity, indicating that the secondary battery has good fast-charging performance, cycle performance, low-temperature performance, and high energy density.

[0208] The above description is only a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A diaphragm, characterized in that, The membrane includes a substrate and a coating disposed on at least one surface of the substrate, the coating comprising a metal-organic framework material doped with a metal element, the metal-organic framework material having the molecular formula M. a Zr6O m (OH) n (OL) 6-(x+y) / 2 (sol) x (blank) y N b , 0.01≤a≤2.3, 4≤m≤6, 0≤n≤4, 0.09≤x≤0.92, 3≤y≤6.02, 0.905≤b≤9.24; M is a metallic element, including at least one of Li, Na, K, Ca, Mg, Cu, Co, Ni, Fe, Cr, Zn, and Mn; OL is a dicarboxylic acid conjugated organic ligand, the molecular skeleton of which includes any one of phenyl, imidazolyl, and pyridinyl; sol includes acetate, formate, and CH3(CH2). p COO - At least one of the following, 1≤p≤6, blank is a ligand vacancy, and N is a counter ion.

2. The diaphragm according to claim 1, characterized in that, In the diaphragm, the molar ratio of Zr to OL is 6:(2.766~4.329).

3. The diaphragm according to claim 1, characterized in that, In the diaphragm, the molar ratio of Zr to OL is 6:(2.766~4.266).

4. The diaphragm according to claim 1, characterized in that, In the diaphragm, the molar ratio of Zr to OL is 6:(2.766~3.69).

5. The diaphragm according to claim 1, characterized in that, In the diaphragm, the molar ratio of Zr to OL is 6:(2.766~3.5).

6. The diaphragm according to claim 1, characterized in that, In the diaphragm, the molar ratio of Zr to OL is 6:(2.766~2.94).

7. The diaphragm according to claim 1, characterized in that, The total defect rate Z of the metal-organic framework material doped with the metal element was obtained by thermogravimetric analysis, and was 29.6% ≤ Z ≤ 53.5%.

8. The diaphragm according to claim 7, characterized in that, The total defect rate of the metal-organic framework material doped with the metal element is Z, 40%≤Z≤53.5%.

9. The diaphragm according to claim 7, characterized in that, The total defect rate of the metal-organic framework material doped with the metal element is Z, 42%≤Z≤53.5%.

10. The diaphragm according to claim 7, characterized in that, The total defect rate of the metal-organic framework material doped with the metal element is Z, 47%≤Z≤53.5%.

11. The diaphragm according to claim 7, characterized in that, The total defect rate of the metal-organic framework material doped with the metal element is Z, where 50% ≤ Z ≤ 53.5%.

12. The diaphragm according to claim 1, characterized in that, The unsaturated coordination defect rate K of the metal-organic framework material doped with the metal element was obtained by solid-state NMR phosphorus spectroscopy, where 25% ≤ K ≤ 50.1%.

13. The diaphragm according to claim 12, characterized in that, The unsaturated coordination defect rate of the metal-organic framework material doped with the metal element is K, where 26.1% ≤ K ≤ 50.1%.

14. The diaphragm according to claim 12, characterized in that, The unsaturated coordination defect rate of the metal-organic framework material doped with the metal element is K, where 37% ≤ K ≤ 50.1%.

15. The diaphragm according to claim 12, characterized in that, The unsaturated coordination defect rate of the metal-organic framework material doped with the metal element is K, where 40% ≤ K ≤ 50.1%.

16. The diaphragm according to claim 12, characterized in that, The unsaturated coordination defect rate of the metal-organic framework material doped with the metal element is K, where 45% ≤ K ≤ 50.1%.

17. The diaphragm according to claim 12, characterized in that, The unsaturated coordination defect rate of the metal-organic framework material doped with the metal element is K, where 48% ≤ K ≤ 50.1%.

18. The diaphragm according to claim 1, characterized in that, The molecular skeleton of the dicarboxylated conjugated organic ligand is selected from phenyl, and the dicarboxylated conjugated organic ligand includes a functional group X, which includes any one of amino, hydroxyl, mercapto, methoxy, nitro, fluorine, and chlorine groups.

19. The diaphragm according to claim 1, characterized in that, The dicarboxylic acid conjugated organic ligand includes any one of terephthalate, amino-modified terephthalate, fluoroterephthalate, and pyridinic acid dicarboxylate.

20. The diaphragm according to claim 1, characterized in that, 0.1≤a≤2.3。 21. The diaphragm according to claim 1, characterized in that, 0.21≤a≤2.3。 22. The diaphragm according to claim 1, characterized in that, 0.3≤a≤2.3。 23. The diaphragm according to claim 1, characterized in that, The counterions include NO3. - Cl - SO4 2- ,Br - F - At least one of acetylacetone radicals.

24. The diaphragm according to claim 1, characterized in that, Based on the quality of the coating, the mass percentage of the metal-organic framework material doped with the metal element is W1, 65%≤W1≤94.4%.

25. The diaphragm according to claim 1, characterized in that, Based on the quality of the coating, the mass percentage of the metal-organic framework material doped with the metal element is W1, where 75% ≤ W1 ≤ 90%.

26. The diaphragm according to claim 1, characterized in that, The coating comprises a binder, a wetting agent, and a dispersant. Based on the mass of the coating, the mass percentage of the binder is W2, 2.7% ≤ W2 ≤ 32.8%, the mass percentage of the wetting agent is W3, 0.01% ≤ W3 ≤ 6%, and the mass percentage of the dispersant is W4, 0.1% ≤ W4 ≤ 6%.

27. The diaphragm according to claim 26, characterized in that, 7.4%≤W2≤22.6%, 0.01%≤W3≤1.5%, 0.5%≤W4≤1.5%.

28. The diaphragm according to claim 26, characterized in that, 41.8≤W1 / W4≤650.

29. The diaphragm according to claim 26, characterized in that, 55.7≤W1 / W4≤83.

6.

30. The diaphragm according to claim 26, characterized in that, The binder includes at least one of sodium carboxymethyl cellulose and polyacrylate; the wetting agent includes at least one of branched alcohol, sodium dodecyl sulfate, sodium dodecyl sulfonate, and acetylenic diol polyoxyethylene ether; and the dispersant includes at least one of polyvinyl alcohol, polyacrylonitrile, and polyvinylpyrrolidone.

31. The diaphragm according to any one of claims 1 to 30, characterized in that, The coating thickness is from 0.3 μm to 6 μm.

32. The diaphragm according to claim 31, characterized in that, The coating thickness is 0.5 μm to 3 μm.

33. The diaphragm according to any one of claims 1 to 30, characterized in that, The coating weight per unit area on the substrate is 0.12 g / m². 2 Up to 2.52g / m 2 .

34. The diaphragm according to claim 33, characterized in that, The coating weight per unit area on the substrate is 0.21 g / m². 2 Up to 1.26 g / m 2 .

35. The diaphragm according to any one of claims 1 to 30, characterized in that, The average particle size of the metal-organic framework material doped with the metal element is D, where 20nm ≤ D ≤ 110nm.

36. The diaphragm according to any one of claims 1 to 30, characterized in that, 64nm≤D≤80nm.

37. The diaphragm according to any one of claims 1 to 30, characterized in that, The XRD pattern of the metal-organic framework material doped with metal elements includes diffraction peaks on the (200) and (111) crystal planes.

38. The diaphragm according to any one of claims 1 to 30, characterized in that, The coating further includes at least one of semiconductor oxides, oxide solid electrolytes, or covalent organic framework materials; and / or, the membrane further includes other coatings, which include at least one of semiconductor oxides, oxide solid electrolytes, or covalent organic framework materials.

39. A secondary battery, characterized in that, The secondary battery includes a positive electrode, a negative electrode, an electrolyte, and a separator according to any one of claims 1 to 38.

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