Positive pole piece and secondary battery

Abstract

The invention relates to the technical field of secondary battery preparation, and provides a positive electrode plate and a secondary battery, a positive electrode material layer comprises a polyanion material, a conductive agent, a binder, a dispersant and a metal element doped metal organic framework material with a molecular formula of MaZr6Om (OH) n (OL) 6-(x + y) / 2 (sol) x (blank) yNb, 0.01 < = 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 comprises at least one of Li, Na, K, Ca, Mg, Cu, Co, Ni, Fe, Cr, Zn and Mn, OL is a dicarboxyl conjugated organic ligand, sol comprises at least one of acetate, formate and CH3-(CH2) p-COO-, p is greater than or equal to 1 and less than or equal to 6, bank is a ligand vacancy, and N is a counter ion.

Description

Technical Field

[0001] This application relates to the field of secondary battery preparation technology, and in particular to a positive electrode sheet and a secondary battery. Background Technology

[0002] Secondary batteries, such as lithium-ion batteries, possess numerous advantages including high energy density, long cycle life, high nominal voltage, and low self-discharge rate. In recent years, they have been widely used in energy storage power systems for hydropower, thermal power, wind power, and solar power plants, as well as in various fields such as electric bicycles, electric motorcycles, electric vehicles, military equipment, and aerospace, demonstrating broad application prospects. These new application areas also place higher demands on the energy density, cycle performance, and rate performance of lithium-ion batteries.

[0003] The positive electrode plays a crucial role in lithium-ion batteries. Generally, the quality of the positive electrode determines its microstructure, which in turn affects the battery's internal resistance, rate capability, and cycle life. Currently, commonly used polyanionic positive electrode active materials (such as lithium iron phosphate) have advantages in safety, cycle life, and cost, but their energy density, intrinsic conductivity, and rate performance still need improvement, and they also suffer from transition metal dissolution during long cycles. In some systems that improve rate capability and cycle performance, conductive agents such as carbon nanotubes (CNTs) and vapor-grown carbon fibers (VGCF) are often added to the positive electrode to increase its conductivity; however, these materials have low dispersion uniformity. Commonly used dispersion methods, such as ultrasonic dispersion, high-speed shearing, and electrostatic dispersion using ultrafine grinding beads, can damage the material itself or introduce non-energy storage materials to some extent, thereby reducing the energy density of the lithium-ion battery. Therefore, how to optimize the positive electrode to improve the energy density and charge-discharge performance of lithium-ion batteries has become one of the challenges and bottlenecks in lithium-ion battery design. Summary of the Invention

[0004] The purpose of this application is to provide a positive electrode and a secondary battery to improve the fast-charging performance and cycle performance of the secondary battery. The specific technical solution is as follows:

[0005] The first aspect of this application provides a positive electrode sheet, comprising a positive current collector and a positive electrode material layer disposed on at least one surface of the positive current collector. The positive electrode material layer comprises a positive electrode active material, a conductive agent, a binder, a dispersant, and a metal-organic framework material doped with a metal element, wherein the metal-organic framework material has the molecular formula M0. a Zr6O m (OH) n (OL) 6-(x+y) / 2 (sol) x (blank) y Nb , 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 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; 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; the positive electrode active material is a polyanionic material.

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

[0007] In some embodiments of this application, the molar ratio of Zr to OL in the cathode material layer is 6:(2.769~4.95).

[0008] In some embodiments of this application, the molar ratio of Zr to OL in the cathode material layer is 6:(2.769~4.266).

[0009] In some embodiments of this application, the molar ratio of Zr to OL in the cathode material layer is 6:(2.769~3.69).

[0010] In some embodiments of this application, the unsaturated coordination defect rate of the metal-organic framework material doped with the metal element is 15% to 50.1%, preferably 26.1% to 50.1%, and more preferably 37% to 50.1%.

[0011] In some embodiments of this application, the total defect rate of the metal-organic framework material doped with the metal element is 20% to 53.5%, preferably 29.6% to 53.5%, and more preferably 40% to 53.5%.

[0012] In some embodiments of this application, the polyanionic material includes at least one of lithium iron phosphate, lithium vanadium phosphate, lithium manganese iron phosphate, sodium iron phosphate composite, and sodium vanadium fluorophosphate.

[0013] In some embodiments of this application, the dicarboxylated conjugated organic ligand includes a molecular skeleton, which includes any one of phenyl, pyridyl, and imidazolyl groups.

[0014] 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.

[0015] In some embodiments of this application, the dicarboxylate conjugated organic ligand includes any one of terephthalate, amino-modified terephthalate, fluoroterephthalate, and pyridinic acid dicarboxylate.

[0016] In some embodiments of this application, the counterion includes NO3. - Cl - SO4 2- ,Br - F - At least one of acetylacetone radicals.

[0017] In some embodiments of this application, based on the total mass of the positive electrode material layer, the mass percentage of the metal-organic framework material doped with metal elements is 0.01% to 5%; the mass percentage of the positive electrode active material is 80% to 97.9899%; the mass percentage of the conductive agent is 1% to 5%; the mass percentage of the binder is 1% to 5%; and the mass percentage of the dispersant is 0.0001% to 5%.

[0018] In some embodiments of this application, based on the total mass of the positive electrode material layer, the mass percentage of the metal-organic framework material doped with metal elements is 0.1% to 3%; the mass percentage of the positive electrode active material is 89.9% to 96%; the mass percentage of the conductive agent is 1% to 3%; the mass percentage of the binder is 1% to 3%; and the mass percentage of the dispersant is 0.01% to 1.1%.

[0019] In some embodiments of this application, the positive electrode material layer includes a dehydrating agent, which includes at least one selected from hexamethyldisilazane, heptamethyldisilazane, dicyclohexylcarbodiimide, diisopropylcarbodiimide, trimethylsilyl isocyanate, and tert-butyl isocyanate; based on the total mass of the positive electrode material layer, the mass percentage of the dehydrating agent is 0.01% to 5%, preferably 0.1% to 1%.

[0020] In some embodiments of this application, 0.1 ≤ a ≤ 2.3, preferably 0.3 ≤ a ≤ 2.3.

[0021] In some embodiments of this application, the dispersant includes at least one selected from polyvinylpyrrolidone, hydrogenated nitrile butadiene rubber, poly(ε-caprolactone), polyethylene, polyethylene glycol, and poly(hydroxyethyl methacrylate).

[0022] In some embodiments of this application, the average particle size of the metal-organic framework material doped with the metal element is 20 nm to 110 nm, preferably 20 nm to 80 nm.

[0023] In some embodiments of this application, the areal density of the positive electrode material layer on one side is 100 g / m². 2 ~300 g / m 2 The thickness of the positive electrode material layer on one side is 35.7 μm to 136 μm.

[0024] In some embodiments of this application, the compaction density of the positive electrode material layer is 2.2 g / cm³. 3 ~2.8g / cm 3 .

[0025] The second aspect of this application provides a secondary battery, which includes the positive electrode, negative electrode, electrolyte and separator provided in the first aspect of this application.

[0026] The beneficial effects of this application are:

[0027] This application provides a positive electrode sheet and a secondary battery. The positive electrode sheet includes a positive current collector and a positive electrode material layer disposed on at least one surface of the positive current collector. The positive electrode material layer includes a positive electrode active material, a conductive agent, a binder, a dispersant, and a metal-organic framework material doped with a metal element. The metal-organic framework material doped with the metal element has 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 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; 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; the positive electrode active material is a polyanionic material. When the positive electrode active material in the secondary battery is a polyanionic material, the positive electrode sheet includes a metal-organic framework material doped with a metal element within the scope of this application, which is beneficial for active metal ions (e.g., Li). +During interfacial transport, the removal of the coordination solvent increases the rate of interfacial transport of active metal ions, inhibits the dissolution of transition metal elements (such as Mn and Fe), and improves the fast-charging and cycle performance of secondary batteries.

[0028] 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

[0029] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other embodiments can be obtained based on these drawings.

[0030] Figure 1 This is a schematic diagram of the structure 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.

[0031] Figure 2 The XRD patterns are of the metal-doped metal-organic framework materials used in Examples 1-1, 1-3, and 1-5 of this application. Detailed Implementation

[0032] The technical solutions of this application will be clearly and completely described below with reference to the embodiments of this application. 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.

[0033] The first aspect of this application provides 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 positive electrode material layer includes a positive electrode active material, a conductive agent, a binder, a dispersant, and a metal-organic framework material doped with a metal element, wherein the metal-organic framework material has 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 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; 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; preferably, 0.1≤a≤2.3, more preferably, 0.3≤a≤2.3. For example, the value of 'a' can be 0.01, 0.05, 0.1, 0.3, 0.5, 0.8, 1, 1.2, 1.5, 1.8, 2, 2.3, or a range of any two values; 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; 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; the value of 'x' can be 0.09, 0.12, 0.15, 0.16, 0.18, 0.2, 0.22, 0.25, 0.28, 0.3, 0.35, 0.4, 0.45, 0.5, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, The values ​​of y can be 0.9, 0.92, or any two of these values; the values ​​of y can be 1.8, 2, 2.2, 2.6, 2.8, 3, 3.3, 3.5, 3.8, 4, 4.3, 4.5, 4.8, 5, 5.3, 5.5, 6, 6.02, or any two of these values; the values ​​of b can be 0.905, 1, 1.3, 1.8, 2.1, 2.2, 2.5, 2.8, 3, 3.2, 3.5, 3.8, 4, 4.2, 4.5, 4.8, 5, 5.2, 5.5, 5.8, 6, 6.3, 6.5, 6.8, 7, 7.3, 7.5, 7.8, 8, 8.3, 8.5, 8.8, 9, 9.24, or any two of these values; the positive electrode active material is a polyanionic material.

[0034] Polyanion refers to non-metallic atoms forming negatively charged anions with oxygen through covalent bonds. These anions possess high structural stability and good coordination ability with transition metals. In secondary batteries, polyanion materials include lithium iron phosphate, lithium vanadium phosphate, lithium manganese iron phosphate, and composite sodium iron phosphate. Typical polyanion systems, such as lithium iron phosphate, suffer from poor rate performance and low-temperature performance due to the sluggish Li insertion / extraction kinetics. Furthermore, long-cycle cycling presents the problem of Fe dissolution, leading to exacerbated side reactions and significant capacity decay. The lithium manganese iron phosphate system suffers from the dissolution of both Mn and Fe under operating conditions, with harsh conditions (such as high temperatures) further intensifying the dissolution of transition metals. Composite sodium iron phosphate exhibits problems such as Fe dissolution and high solubility of the SEI (solid electrolyte interface) / CEI (chemical-electrochemical interface) film. Adding metal-organic framework materials to the cathode material layer can effectively capture dissolved metals in situ, reduce catalytic side reactions, and improve the composition of SEI / CEI by improving ion cross-interface transport kinetics, thereby optimizing the composition and enhancing the capacity performance of the secondary battery.

[0035] In addition, 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 electrode and electrolyte, desolvation is generally considered the main energy-consuming step in the transport of active metal ions. The inventors of this application have discovered that the positive electrode material layer includes a metal-organic framework (MOF) material doped with metal elements. On one hand, the porous structure of the MOF material facilitates the removal of active metal ions from the weakly coordinating solvent on the outer layer. On the other hand, the metal doping sites within the MOF material promote the dissociation of the strongly coordinating solvent in the inner layer of the active metal ions. This "assembly line" synergistic desolvation mechanism improves the rate of interfacial transport of active metal ions, enhancing the fast-charging and cycle performance of the secondary battery. Simultaneously, the abundant polar groups on the surface of the metal-doped MOF material exhibit high affinity for the electrolyte, and the porous structure allows for rapid electrolyte conduction, facilitating the wetting of the positive electrode by the electrolyte. Furthermore, due to the pore-confining effect of metal-organic framework materials 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 improving the energy density of the secondary battery.

[0036] The positive electrode of this application includes metal-organic framework materials doped with metal elements within the aforementioned scope. On the one hand, the metal-doped metal-organic framework material has a porous structure, which is conducive to the removal of active metal ions from the outer weak coordination solvent. On the other hand, the metal doping sites in the metal-doped metal-organic framework material are conducive to promoting the dissociation of active metal ions from the inner strong coordination solvent. This "assembly line" synergistic desolvation mechanism is beneficial to improving the rate of cross-interface transport of active metal ions and improving the fast charging performance and cycle performance of the secondary battery. At the same time, the abundant polar groups on the surface of the metal-doped metal-organic framework material have a high affinity for the electrolyte, and the porous structure can quickly conduct the electrolyte, which is beneficial to the wetting of the positive electrode by the electrolyte.

[0037] Metal-organic frameworks (MOFs) are crystalline framework materials with intramolecular pores formed by the self-assembly of metal ions or clusters with organic ligands under certain conditions through coordination bonds. Compared to other nanomaterials, MOFs have advantages such as larger specific surface area, tunable pore size and shape, and ease of modification. Applying activated MOFs to the positive electrode active material layer can enhance the transport of active metal ions by enabling the interaction between the electrolyte and unsaturated open metal sites, thereby reducing the interfacial resistance of the positive electrode. Furthermore, monodisperse metals offer advantages such as high atom utilization, uniform site structure, and maximized metal-carrier interface, providing high-quality active sites for MOFs. Therefore, this application endows metal-organic framework materials with superior conductivity, specific surface area, porosity, chemical tunability, abundance of active sites, and pore structure by loading metal elements into them. Using metal-organic framework materials within the scope of this application, after loading metal elements, it is beneficial to capture metal ions dissolved from polyanionic materials in situ, reduce side reactions catalyzed by metal ions, improve the rate of cross-interface transport of active metal ions, and improve the fast-charging performance and cycle performance of secondary batteries.

[0038] Zirconium-oxygen cluster nodes in UiO series metal-organic frameworks 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, the hydroxyl content at the zirconium-oxygen cluster nodes cannot be precisely quantified. Therefore, in this application, the molecular formula of the metal-doped metal-organic framework material 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] Figure 1 This is a schematic diagram of the structure of a metal-organic 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. The absence of a ligand indicates the absence of dicarboxylate conjugated organic ligand 1, forming 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.

[0040] In some embodiments of this application, the molar ratio of Zr to OL in the cathode material layer is 6:(2.53~5.055), preferably 6:(2.769~4.95), or preferably 6:(2.769~4.266), or preferably 6:(2.769~3.69). For example, in metal-organic framework materials, the molar ratio of Zr to OL can be 6:2.53, 6:2.769, 6:3, 6:3.5, 6:3.69, 6:4, 6:4.266, 6:4.5, 6:4.95, 6:5, 6:5.055, or a range of any two of these values. The molar ratio of Zr to OL in the cathode material layer actually reflects the total defect rate of the material; theoretically, the total defect rate = 1 - n(OL) / n(Zr). Controlling the molar ratio of Zr to OL within the range specified in this application helps ensure that the defect rate is within a suitable range, which can guarantee sufficient lithium storage sites, effectively promote lithium-ion transport, improve interfacial contact with cathode material particles or electrolyte, reduce charge transfer impedance, increase the energy density of the secondary battery, and improve the rate and cycle performance of the secondary battery.

[0041] In some embodiments of this application, solid-state NMR phosphorus spectroscopy is used for testing. The unsaturated coordination defect rate of the metal-doped metal-organic framework material is 15%~50.1%, preferably 26.1%~50.1%, and more preferably 37%~50.1%. For example, the unsaturated coordination defect rate of the metal-doped metal-organic framework material is 15%, 20%, 22%, 25%, 26.1%, 28%, 29%, 30%, 32%, 35%, 37%, 38%, 40%, 42%, 45%, 48%, 49%, 50%, 50.1%, or a range of two of these values. Unsaturated coordination defects refer to defect structures caused by the absence of dicarboxyl conjugated organic 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 in-situ capture of dissolved metals in polyanionic materials, reducing catalytic side reactions, and simultaneously increasing the rate of interfacial transport of active metal ions in secondary batteries, thus improving the fast-charging and cycling performance of secondary batteries.

[0042] In some embodiments of this application, thermogravimetric analysis is used to test the total defect rate of the metal-doped metal-organic framework material, which is 20% to 53.5%, preferably 29.6% to 53.5%, and more preferably 40% to 53.5%. For example, the total defect rate of the metal-doped metal-organic framework material can be 20%, 22%, 25%, 29%, 29.6%, 30%, 32%, 34%, 36%, 38%, 40%, 42%, 45%, 47%, 49%, 50%, 53%, 53.5%, or a range of any two of these values. The defects in MOF materials possess 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-doped metal-organic composite to the number of corresponding connected dicarboxyl conjugated organic ligands in the theoretically intact structure. The defects are Lewis acid sites, which have strong interactions with the solvent and anions in the electrolyte. By controlling the total defect rate of the metal-organic framework material doped with metal elements within the range of this application, the removal of coordination solvents by active metal ions can be promoted, the rate of cross-interface transport of active metal ions can be improved, and the fast charging performance and cycle performance of the secondary battery can be improved.

[0043] In some embodiments of this application, the polyanionic material includes at least one of lithium iron phosphate, lithium vanadium phosphate, lithium manganese iron phosphate, and sodium iron phosphate composite. Compared with other types of positive electrode active materials, polyanionic materials have higher safety, cycle life, and good high-temperature performance, while also being less expensive. Including polyanionic materials and metal-organic framework materials doped with metal elements in the positive electrode sheet facilitates the insertion and extraction of lithium ions during charging and discharging, while enabling the secondary battery to possess both high theoretical capacity and theoretical specific capacity, and low production cost.

[0044] In some embodiments of this application, the molar content of the metal element-doped metal-organic framework material is from 0.01 mol / mol to 2.3 mol / mol, preferably from 0.1 mol / mol to 2.3 mol / mol, based on the amount of metal element-doped metal-organic framework material. For example, the molar content of the metal element can be 0.01 mol / mol, 0.05 mol / mol, 0.08 mol / mol, 0.1 mol / mol, 0.3 mol / mol, 0.5 mol / mol, 0.8 mol / mol, 1 mol / mol, 1.3 mol / mol, 1.5 mol / mol, 1.8 mol / mol, 2 mol / mol, 2.3 mol / mol, or a range of any two of these values, based on the amount of metal element-doped metal-organic framework material. When the value of 'a' is too small, the metal loading is too low to produce an approximate effect; when the value of 'a' is too large, the metal loading is too high, and the metal will mainly exist in the form of physical adsorption, easily forming aggregates. It is also easy for the metal to detach from the pores of the metal-doped organometallic complex, and excessive metal will also occupy the pores, rendering them ineffective. Controlling the value of 'a' within the range specified in this application can further improve the abundance of active sites, pore structure, and electrical properties of the metal-doped organometallic complex.

[0045] 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.

[0046] Based on the molar amount of the metal element-doped metal-organic framework (MOF), if the molar content of the metal element is too high, some metal elements will be adsorbed into the pores of the MOF via physical adsorption. During the charging and discharging process of the secondary battery, these metal elements will detach from the pores of the MOF 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. Conversely, if the molar content of the metal element in the MOF is too low, it indicates a low loading of metal elements in the MOF. Active lithium in the battery will be chemically adsorbed and bound within the framework, leading to the loss of active lithium and affecting the capacity utilization of the secondary battery. Controlling the molar amount of metal elements in the metal element-doped MOF within the range specified in this application is beneficial to further improve the rate of cross-interface transport of active metal ions, thereby improving the fast-charging performance and cycle performance of the secondary battery.

[0047] In some embodiments of this application, the dicarboxylated conjugated organic ligand includes a molecular skeleton comprising any one of phenyl, pyridyl, and imidazole groups. When the molecular skeleton of the dicarboxylated conjugated organic ligand is selected from imidazole and pyridyl groups, the dicarboxylated conjugated organic ligand skeleton itself contains heteroatoms, which is beneficial for adjusting the polarity of the pore walls of the metal-organic framework material doped with metal elements. This enhances the interaction between the pore walls and lithium ions, solvent, and anions in the electrolyte, promotes the dissociation of these three components within the pores, and thus improves the migration efficiency of lithium ions.

[0048] In some embodiments of this application, the molecular skeleton is 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. Introducing functional group X into metal-organic framework materials doped with metal elements, and controlling the type of functional group X within the scope of this application, is beneficial for adjusting the polarity of the pore walls of the metal-doped metal-organic framework material, thereby enhancing the interaction between its pore walls and lithium ions, solvent, and anions in the electrolyte, promoting the dissociation of these three components within the pores, and thus improving the migration efficiency of lithium ions.

[0049] In some embodiments of this application, the dicarboxylate conjugated organic ligand is selected from terephthalate.

[0050] In some embodiments of this application, the dicarboxylic acid conjugated organic ligand is selected from any one of the following substances:

[0051] (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.

[0052] (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;

[0053] (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;

[0054] (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;

[0055] (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;

[0056] (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;

[0057] (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.

[0058] In some embodiments of this application, the molecular skeleton comprises either a pyridyl group or an imidazole group, and the dicarboxylated conjugated organic ligand comprises at least one of the following substances:

[0059] (1) When the molecular skeleton is selected from pyridinyl, the dicarboxylic acid conjugated organic ligand is selected from 2,5-pyridinic acid dicarboxylate;

[0060] (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.

[0061] In this application, functional group X influences the steric hindrance of the metal-organic framework material. Simultaneously, functional group X itself acts as an active site for Lewis acids or bases, altering the affinity of the pores for lithium ions, solvents, and anions in the electrolyte. Furthermore, functional group X is electronegative, affecting the electronic structure at the nodes; electron-withdrawing groups enhance the Lewis acidity of the nodes, and vice versa. Within the scope of this application, suitable functional groups and dicarboxylic acid conjugated organic ligands can be selected according to actual application requirements to achieve optimal electronic and spatial structures, thereby improving the fast-charging and cycle performance of the secondary battery.

[0062] 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, and CH3-(CH2). n -COO - , 1≤n≤6. The small molecule ligand (sol) is introduced through a template agent during the preparation process. It is understood that the small molecule ligand sol may be partially replaced by the solvent during the preparation process, for example, by polar molecules such as template agents, ethanol, methanol, acetone, tetrahydrofuran, chloroform, dichloromethane, and water.

[0063] In some embodiments of this application, the metal-doped metal-organic framework material consists of a cationic framework and counterions, wherein the counterions include PO4. 3- NO3 - Cl - SO4 2- ,Br - acetylacetone and F - At least one of the following. Based on the charge characteristics of the metal framework, metal frameworks in metal-doped metal-organic framework materials can be classified into cationic frameworks, anionic frameworks, and neutral frameworks. Counter ions are weakly bound to the metal framework through non-covalent interactions and are essential for maintaining the charge neutrality of metal-doped metal-organic framework materials. For cationic frameworks in metal-doped metal-organic framework materials, the counter ion is PO4. 3- NO3 - Cl - SO4 2- ,Br - acetylacetone and F -Counterions are used to balance the charge of the cationic framework caused by defects. In this application, for the cationic framework of the metal-doped metal-organic framework material, the counterions can originate from the metal-organic framework material preparation process or from the metal element loading process. The metal-doped metal-organic framework material includes the counterions of this application, which 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 interface film formed is more conducive to ion transport, thereby improving the charge transfer at the interface and improving the fast charging performance and cycle performance of the secondary battery.

[0064] In this application, since the metal-doped metal-organic framework material uses raw materials such as solvents and template agents in the preparation process, the prepared metal-doped metal-organic framework material also includes other adsorbed components, which include adsorbed solvents and / or adsorbed template agents; this application does not specifically limit the types and contents of other adsorbed components.

[0065] In some embodiments of this application, based on the total mass of the cathode material layer, the mass percentage of the metal-doped metal-organic framework material is 0.01% to 5%, preferably 0.1% to 3%; for example, the mass percentage of the metal-doped metal-organic framework material can be 0.01%, 0.05%, 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or a range of any two of these values. Controlling the mass percentage of the metal-doped metal-organic framework material within the range specified in this application is beneficial for in-situ capture of dissolved metals in polyanionic materials, reducing their catalytic side reactions, and simultaneously promoting the role of the metal-doped metal-organic framework material in removing lithium-ion coordination solvents, improving the rate of lithium-ion cross-interface transport, and improving the fast-charging performance and cycle performance of the secondary battery.

[0066] In some embodiments of this application, based on the total mass of the positive electrode material layer, the mass percentage of the positive electrode active material is 80% to 97.9899%, preferably 89.9% to 96%; for example, the mass percentage of the positive electrode active material can be 80%, 85%, 87%, 89.9%, 90%, 95%, 96%, 97%, 97.9899%, or a range consisting of any two of these values. Controlling the mass percentage of the positive electrode active material within the range of this application is beneficial for the insertion and extraction of lithium ions during charging and discharging, while enabling the secondary battery to have both high theoretical capacity and theoretical specific capacity and low production cost.

[0067] In some embodiments of this application, based on the total mass of the positive electrode material layer, the mass percentage content of the conductive agent is 1% to 5%, preferably 1% to 3%; for example, the mass percentage content of the conductive agent can be 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or a range consisting of any two of these values. Controlling the mass percentage content of the conductive agent within the range specified in this application is beneficial for increasing the electron transport path, increasing the conductivity of the positive electrode, and promoting the electrochemical reaction; simultaneously, the positive electrode has better processability and electrolyte wettability.

[0068] In some embodiments of this application, the mass percentage of the binder is 1% to 5%, preferably 1% to 3%, based on the total mass of the positive electrode material layer; for example, the mass percentage of the binder can be 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or a range of any two values ​​therein. Controlling the mass percentage of the binder within the range of this application is beneficial for the binder to play a bonding role in the positive electrode material layer, enhancing the contact between the positive electrode active material and the conductive agent and current collector, stabilizing the positive electrode structure, and thus improving the fast charging performance and cycle performance of the secondary battery.

[0069] In some embodiments of this application, the mass percentage of the dispersant is 0.0001% to 5%, preferably 0.01% to 1.1%, based on the total mass of the positive electrode material layer. For example, the mass percentage of the dispersant can be 0.0001%, 0.0005%, 0.01%, 0.05%, 0.1%, 0.3%, 0.5%, 0.8%, 1%, 1.1%, 2%, 3%, 4%, 5%, or a range of any two of these values. Controlling the mass percentage of the dispersant within the range specified in this application helps to reduce the uniform dispersion of the positive electrode active material and the metal-organic framework material doped with metal elements in the positive electrode material layer, improving the uniformity and consistency of the positive electrode sheet, and thus improving the charge-discharge efficiency and cycle stability of the secondary battery.

[0070] In some embodiments of this application, the positive electrode material layer includes a dehydrating agent, which includes at least one selected from hexamethyldisilazane, heptamethyldisilazane, dicyclohexylcarbodiimide, diisopropylcarbodiimide, trimethylsilyl isocyanate, and tert-butyl isocyanate; based on the total mass of the positive electrode material layer, the mass percentage of the dehydrating agent is 0.01% to 5%, preferably 0.1% to 1%; for example, the mass percentage of the dehydrating agent can be 0.01%, 0.05%, 0.1%, 0.3%, 0.5%, 0.8%, 1%, 2%, 3%, 4%, 5%, or a range consisting of any two of these values. The positive electrode material layer includes a dehydrating agent within the scope of this application, and the mass percentage of the dehydrating agent is controlled within the scope of this application. This can effectively remove moisture, ensure the stability and performance of the material, thereby reducing the obstruction of moisture to electron transport and lithium ion migration, improving the charging and discharging efficiency of the battery, enabling the battery to charge and discharge quickly, improving high-rate charging and discharging performance, and reducing internal side reactions of the battery, allowing the battery to maintain a high capacity retention rate after multiple cycles.

[0071] In some embodiments of this application, the dispersant includes polyvinylpyrrolidone (PVP), hydrogenated nitrile butadiene rubber (HNBR), poly(ε-caprolactone), polyethylene, polyethylene glycol, and polyhydroxyethyl methacrylate. The inclusion of dispersants within the scope of this application in the positive electrode sheet helps reduce the agglomeration of solid materials in the positive electrode sheet, ensuring uniform dispersion of the positive electrode active material and metal-organic framework material doped with metal elements within the positive electrode sheet, thereby improving the uniformity and consistency of the positive electrode sheet, and ultimately enhancing the charge-discharge efficiency and cycle stability of the secondary battery.

[0072] The positive electrode sheet described in this application includes a conductive agent, a binder, and a solvent. This application does not impose any particular limitation on the types of conductive agents, binders, and solvents, as long as they achieve the purpose of this application. For example, the conductive agent includes, but is not limited to, at least one of conductive carbon black (Super P), acetylene black, Ketjen black, graphite (such as SFG-6), carbon fiber, single-walled and multi-walled carbon nanotubes, and graphene. The binder includes, but is not limited to, at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyethylene oxide (PEO), polyvinyl chloride, polyacryl alcohol, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins. The solvent includes, but is not limited to, at least one of N-methyl-2-pyrrolidone (NMP), diethylene glycol dimethyl ether (Diglyme), triethylene glycol dimethyl ether (Triglyme), and tetrahydrofuran (THF).

[0073] In some embodiments of this application, the average particle size of the metal-doped metal-organic framework material is 20 nm to 110 nm, preferably 20 nm to 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 particles 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, capture dissolved metals in polyanionic materials, reduce side reactions catalyzed by dissolved metals, and improve the fast-charging performance and cycle performance of secondary batteries. 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.

[0074] In some embodiments of this application, the XRD pattern of the metal-doped metal-organic framework material includes diffraction peaks on the (200) and (111) crystal planes. The inclusion of diffraction peaks on the (200) and (111) crystal planes in the XRD pattern of the metal-doped metal-organic framework material indicates that the metal-doped metal-organic framework material used in this application has a good crystal structure.

[0075] In some embodiments of this application, when the metal element is selected from Li, the electron energy loss spectrum of the metal-organic framework material doped with the metal element has coordination characteristic peaks at 59.5±0.2eV and 56.5±0.2eV.

[0076] In some embodiments of this application, when the metal element is selected from Na, the electron energy loss spectrum of the metal-organic framework material doped with the metal element has a coordination characteristic peak at 32.9 ± 0.2 eV.

[0077] In some embodiments of this application, when the metal element is selected from K, the electron energy loss spectrum of the metal-organic framework material doped with the metal element has coordination characteristic peaks at 297.8±0.2 eV and 301.9±0.2 eV.

[0078] This application does not impose a particular limitation on the specific surface area of ​​metal-organic framework materials doped with metal elements, as long as the purpose of this application can be achieved. For example, the specific surface area of ​​a 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.

[0079] This application does not impose any particular limitation on the preparation method of metal-organic framework materials doped with metal elements, as long as it achieves the purpose of this application. For example, the preparation method of metal-organic framework materials doped with metal elements may include, but is not limited to, the following steps: adding zirconium salt and dicarboxylic acid conjugated organic ligand to a mixed solution of deionized water and template agent to obtain a reaction system; heating at 60℃~120℃ for 1h~168h, centrifuging to obtain a precipitate, washing and separating the precipitate with a low-boiling-point organic solvent to obtain a metal-organic framework material. Drying and activating the metal-organic framework material obtained above. Mixing the activated metal-organic framework material with a metal element source solution uniformly to obtain a suspension system; heating the suspension system at 69℃~105℃ for 2h~24h, centrifuging, washing, and vacuum drying to obtain the metal-organic framework material doped with metal elements.

[0080] In this application, based on the volume of the reaction system, the molar concentration of the zirconium salt is 300 mmol / L to 600 mmol / L; the molar ratio of the zirconium salt to the dicarboxylic acid conjugated organic ligand is 1:(0.6~2), and the molar ratio of the zirconium salt to the template agent is (0.05~0.3):1.

[0081] This application does not specifically limit the zirconium salts mentioned above, as long as they achieve the purpose of this application; for example, the zirconium salt 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 agents mentioned above, as long as they meet the purpose of this application; for example, the template agents include glacial acetic acid, formic acid, hydrochloric acid, and CH3-(CH2). nAt least one of -COOH, 1≤n≤6. This application does not particularly limit the type of low-boiling-point organic solvent, as long as it can achieve the purpose of this application; for example, low-boiling-point solvents include at least one of methanol, ethanol, tetrahydrofuran, acetone, dichloromethane and chloroform.

[0082] Typically, the molar content of metal elements in metal-organic framework materials doped with metal elements can be controlled by adjusting the concentration of metal elements in the metal element source solution; 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.

[0083] In the suspension system described in this application, the mass ratio of the metal-organic framework material to the metal element source solution is 1:3.5 to 1:40. The metal element source solution is a solution of a salt compound containing a metal element, and the solvent is any one of n-hexane, ethanol, and water.

[0084] In some embodiments of this application, the areal density of the positive electrode material layer on one side is 100 g / m². 2 ~300 g / m 2 The thickness of the positive electrode material layer on one side is 35.7 μm to 136 μm; for example, the areal density of the positive electrode material layer on one side can be 100 g / m³. 2 150g / m 2 200g / m 2 250g / m 2 300g / m 2 The thickness of the positive electrode material layer can be 35.7 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 110 μm, 120 μm, 130 μm, 136 μm, or any two of these values. By controlling the areal density and thickness of the positive electrode material layer within the scope of this application, it is beneficial to promote the removal of coordination solvents by 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.

[0085] In some embodiments of this application, the compaction density of the positive electrode material layer is 2.2 g / cm³. 3 ~2.8g / cm 3 For example, the compaction density of the positive electrode material layer can be 2.2 g / cm³. 3 2.3g / cm 3 2.4g / cm 3 2.5g / cm 32.6g / cm 3 2.7g / cm 3 2.8g / cm 3 Or it can be a range consisting of any two of these values. By adjusting the compaction density of the cathode material layer within the range of 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 taking into account the energy density of the secondary battery.

[0086] In some embodiments of this application, the conductivity of the positive electrode is 10. -2 S / cm~10 0 For example, the conductivity of the positive electrode can be 0.01 S / cm, 0.05 S / cm, 0.1 S / cm, 0.3 S / cm, 0.5 S / cm, 0.7 S / cm, 0.9 S / cm, 1 S / cm, or a range of any two values ​​therein. By using the positive electrode of this application, the internal resistance of the secondary battery can be reduced, and the charging and discharging efficiency and performance of the secondary battery can be improved.

[0087] In this application, the positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector. The phrase "positive active material layer disposed on at least one surface of the positive current collector" means that the positive active 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 "surface" here can be the entire surface area of ​​the positive current collector, or only a portion of the surface area; 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 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 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 aforementioned 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 aforementioned metal layer can be, but is not limited to, at least one of aluminum, aluminum alloy, nickel, or nickel alloy.

[0088] The second aspect of this application provides a secondary battery, which includes the positive electrode, negative electrode, electrolyte and separator provided in the first aspect of this application.

[0089] 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 "surface" here can refer to 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.

[0090] 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.

[0091] 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.

[0092] In this application, the secondary battery also includes an electrolyte, which includes an electrolyte and a non-aqueous solvent.

[0093] 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.

[0094] 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.

[0095] 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.

[0096] The secondary battery of this application also includes a separator to separate the positive and negative electrode plates, prevent internal short circuits, allow ions to pass freely, and not affect the electrochemical charging and discharging process. This application does not impose any particular limitation on the type of separator; any porous structure separator with good chemical and mechanical stability can be selected. For example, the separator material can include at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator type can include, but is not limited to, at least one of woven membrane, nonwoven membrane (nonwoven fabric), microporous membrane, composite membrane, rolled membrane, or spun membrane. The separator can be a single-layer thin film or a multi-layer composite thin film. In this application, the thickness of the separator is not particularly limited, as long as it achieves the purpose of this application; for example, the thickness can be from 10 μm to 25 μm.

[0097] 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.

[0098] 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.

[0099] 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.

[0100] Example:

[0101] 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.

[0102] Test methods and equipment:

[0103] Molar content test of metal elements in metal-organic framework materials doped with metal elements:

[0104] The contents of Zr and M in the metal-organic framework material doped with metal elements were determined using inductively coupled plasma optical emission spectrometry (ICP-OES). The molar ratio of M to Zr in the 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.

[0105] Specific procedures: Digest with BVIII grade nitric acid. Add 20 mg of sample and 15 mL of nitric acid to a polytetrafluoroethylene beaker. Heat at 80°C for 20 min. After the solvent has evaporated and about 2 mL remains, add 15 mL of nitric acid and continue heating for 20 min. Repeat the addition of nitric acid until the solid is completely dissolved and the residual liquid is clear and transparent. Start removing the acid, dilute with ultrapure water, and inject the sample.

[0106] Test of the number of counterions (b) in metal-organic framework materials doped with metal elements:

[0107] 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).

[0108] 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, .

[0109] Testing the total defect rate Z of metal-organic framework materials doped with metal elements:

[0110] 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.

[0111] 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+Li a O a / 2 )×100%, where MA(M a O a / 2 Zr6O6(OL)6) represents 1 mol M a O a / 2 The mass of Zr6O6(OL)6, MA(6ZrO2+M a O a / 2 () represents 6 mol ZrO2 and 1 mol M a O a / 2 The sum of the masses. At 350°C, the normalized weight of the metal-organic framework material doped with defective metal elements is less than N (%), indicating insufficient OL connectors within the metal-organic framework material doped with defective metal elements. 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.

[0112] Testing the unsaturated coordination defect rate K of metal-organic frameworks doped with metal elements:

[0113] The unsaturated coordination defect rate (K) of metal-doped metal-organic frameworks (MOFs) was measured using solid-state phosphorus NMR spectroscopy. 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 total defect rate and unsaturated coordination defect rate of the metal-doped MOFs were 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 are identified as Zr-blank, μ-OH(OL), μ-OH(sol), and Zr-sol sites, respectively. Zr-blank represents unsaturated coordination defects; μ-OH(OL) represents bridged hydroxyl groups adjacent to OL organic ligands; μ-OH(sol) represents bridged hydroxyl groups adjacent to coordination defects in small molecules; and Zr-sol represents coordination defects in small molecules. The relative proportions of the corresponding species can be obtained based on the peak area percentages.

[0114] 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, 0.15≤x≤0.65, 3≤y≤6.02, 1.8≤b≤6.02), x=12(SK), y=12K.

[0115] Test of the molar ratio of Zr to OL in the positive electrode:

[0116] Zr content test in positive electrode sheet: Take 40g of positive electrode sheet and cut it into small pieces (less than 5×5mm), then add 100g of NMP solvent and ultrasonically stir for 1 hour. After stirring, pass it through a 200-mesh sieve to separate the aluminum sheet and the solution. After drying the solution at 120℃ to constant weight, grind it into fine powder. Take a sample weighing between 1 and 2 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 the sample into 10 portions (record the weight of each of the 10 portions; the largest portion is 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, then remove the heater. Add another 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 the sample 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 dilution, shake well and then filter through a 0.22 μm filter to obtain the processed test solution.

[0117] (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.

[0118] (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 positive electrode can be calculated.

[0119] (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.

[0120] Test of OL content in positive electrode sheet:

[0121] Take 40g of positive electrode sheet and cut it into small pieces (less than 5×5mm). Then add 100g of NMP solvent and sonicate for 1 hour. After stirring, pass the mixture through a 200-mesh sieve to separate the aluminum sheet and the solution. Dry the solution at 120℃ to constant weight, then grind it into a fine powder. Accurately weigh 100mg of the sample into a 50mL centrifuge tube, add 10mL of 5M H2SO4, sonicate in a 60°C water bath for 60min, and then centrifuge at 11000 rpm for 10min. Take 1mL of the supernatant, add 1.8mL of 5M sodium hydroxide and mix well. Add ultrapure water to make up to 10mL, measure the pH to be approximately 2, filter through a 0.22μm filter membrane, and detect 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 °C; mobile phase elution program: gradient elution of 85% acetonitrile and 15% formic acid aqueous solution (0.1%), run time 12 minutes; detector: DAD, wavelength 230 nm, bandwidth 4 nm.

[0122] X-ray diffraction pattern analysis of metal-organic framework materials doped with metal elements in the positive electrode:

[0123] Take 40g of positive electrode sheet and cut it into small pieces (less than 5×5mm). Then add 100g of NMP solvent and ultrasonically stir for 1 hour. After stirring, pass the mixture through a 200-mesh sieve to separate the aluminum sheet and the solution. Centrifuge the solution at 5000 r / min for 5 min, collect the supernatant solid, dry it at 120℃ to constant weight, grind it into a fine powder, place it in the sample stage of an X-ray diffractometer, use Cu target Kα rays, a scanning rate of 2° / min, a scanning angle range of 3° to 80°, a step size of 0.02, and XRF detector mode to obtain the XRD diffraction pattern. Read the corresponding diffraction peaks and record their positions.

[0124] Testing of the average particle size D of metal-organic framework materials doped with metal elements:

[0125] 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 was obtained by Gaussian fitting.

[0126] Single-sided thickness test of positive / negative electrode material layers:

[0127] Disassemble the lithium-ion battery to obtain the positive / negative electrode sheets. Dry the positive / negative electrode sheets to remove residual electrolyte. Use a scanning electron microscope to observe the positive active material layer and test the single-sided thickness of the positive / negative electrode material layer.

[0128] Single-sided areal density test of positive / negative electrode material layers:

[0129] The areal density of the positive / negative electrode material layer was tested using a gravimetric method. The specific steps are as follows: First, the negative / positive electrode material layer of the secondary battery was separated from the electrode sheet. Then, the mass of the positive / negative electrode material layer was weighed using a balance. Next, the area of ​​the positive active material layer on the positive / negative electrode sheet was measured using vernier calipers. Finally, the mass of the positive / negative electrode material layer was divided by the area of ​​the positive active material layer on the positive / negative electrode sheet to obtain the areal density σg / m² of the positive / negative electrode material layer. 2 .

[0130] Compaction density test of the cathode material layer:

[0131] The surface density of a single surface measured by the above method is σg / m³. 2 The thickness of the positive electrode material layer on one side is measured to be D μm. Therefore, the compaction density of the positive / negative electrode material layer is σ / D, with units of g / cm³. 3 .

[0132] Conductivity test of positive electrode:

[0133] The rolled electrode was cut into 50mm×50mm square samples and placed in the sample placement area of ​​the Yuaneng Technology BER1050 electrode resistance meter. The MRMS 2.0 software was started to begin the measurement. The test was repeated 3 times to obtain the electrode conductivity data.

[0134] Cathode material specific capacity testing:

[0135] The lithium-ion battery was placed in a 25°C environment and left to stand for 2 hours. It was then charged at a constant current of 1C to a voltage of 3.65V, and then charged at a constant voltage at 3.65V until the cutoff current reached 0.05C. Finally, it was discharged at a constant current of 1C to 2.0V. This constitutes one charge-discharge cycle, and the initial discharge capacity was recorded as C. The specific capacity of the material is calculated as C / (σ×N×S×W2), where σ is the areal density of the positive electrode material layer measured by the above method, N is the number of positive electrode layers in a single cell, S is the coating area of ​​the positive electrode material layer on one side, and W2 is the mass percentage of the positive electrode active material based on the total mass of the positive electrode material layer.

[0136] Rate charge / discharge test:

[0137] The secondary battery was placed in a 25℃ environment and left to stand for 2 hours. It was then charged at a constant current of 1C to a voltage of 3.65V, and then charged at a constant voltage at 3.65V to a cutoff current of 0.05C. After standing for 1 hour, it was discharged at a constant current of 1C to 2.0V and left to stand for 1 hour. The discharge capacity was recorded as C1. The battery was then charged at a constant current of 5C to a voltage of 3.65V, and then charged at a constant voltage at 3.65V to a cutoff current of 0.05C. After standing for 1 hour, it was discharged at a constant current of 5C to 2.0V and left to stand for 1 hour. The discharge capacity was recorded as C5. The 5C capacity retention rate was calculated as C5 / C1.

[0138] High-temperature cycling performance test:

[0139] The secondary battery was placed in a 45℃ environment and left to stand for 2 hours. It was then charged at a constant current of 2.5C to a voltage of 3.65V, and then charged at a constant voltage at 3.65V until the cutoff current reached 0.05C. After standing for 30 minutes, it was discharged at a constant current of 2.5C to 2.0V and left to stand for 30 minutes. This constitutes one charge-discharge cycle. The initial discharge capacity was recorded as C0. This charge-discharge cycle was repeated for 1500 cycles, and the discharge capacity C on the 1500th cycle was recorded. 1500 High-temperature cycling capacity retention rate = (C 1500 / C0)×100%.

[0140] Example 1-1:

[0141] <Preparation of Metal-Organic Framework Materials>

[0142] 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.

[0143] 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.

[0144] The crude metal-organic framework material 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 for 15 min to obtain the metal-organic framework material. The unsaturated coordination defect rate of the metal-organic framework material is shown in Table 1-1.

[0145] 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.

[0146] <Preparation of Metal-Organic Framework Materials Doped with Metal Elements>

[0147] 1 g of lithium nitrate and 30 g of water were added to a 350 mL pressure-resistant bottle, followed by 6.2 g of metal-organic framework material. The mixture was sonicated for 20 min to ensure thorough mixing, and then heated at 105 °C for 24 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-doped metal-organic framework material.

[0148] <Preparation of Positive Electrode Slurry>

[0149] Step 1: Place 18g of metal-doped metal-organic framework material, 2g of dispersant hydrogenated nitrile butadiene rubber (HNBR), and 180g of N-methylpyrrolidone (NMP) in a ball mill jar and ball mill at 500 rpm for 5 hours to obtain mixture 1. Place 800g of NMP in a dispersion vessel, add 40g of binder polyvinylidene fluoride (PVDF), and disperse under vacuum at 2500 rpm for 3 hours to obtain mixture 2.

[0150] Step 2: Mix system 1 and system 2 evenly and add them to the dispersion vessel. Set the rotation speed of the dispersion vessel to 40 rpm and the dispersion speed to 5500 rpm. After dispersing in the dispersion vessel for 3 hours, add 40g of conductive agent Super P and 500g of NMP. Set the rotation speed of the dispersion vessel to 40 rpm and the dispersion speed to 5500 rpm. After dispersing in the dispersion vessel for 3 hours, add 1900g of positive electrode active material lithium iron phosphate (LiFePO4). Set the rotation speed of the dispersion vessel to 25 rpm and the dispersion speed to 500 rpm. Knead in the dispersion vessel for 3 hours. Add 520g of NMP to adjust the solid content of the positive electrode slurry to 50wt%. Set the rotation speed to 40 rpm and the dispersion speed to 5500 rpm. After dispersing in the dispersion vessel for 3 hours, the positive electrode slurry is obtained.

[0151] <Preparation of the positive electrode>

[0152] The above-mentioned positive electrode slurry was uniformly coated onto one surface of a 13+1+1μm pre-coated aluminum foil current collector (Tuoyingfengke, 13+1+1μm×160mm), and dried at 105℃ to obtain a positive electrode sheet with a single-sided coating of the positive electrode material active material layer. The above steps were then repeated on the other surface of the pre-coated aluminum foil current collector to obtain a positive electrode sheet with a double-sided coating of the positive electrode active material layer. After drying at 105℃, the sheet was rolled, then dried in a vacuum drying oven at 105℃ for 12 hours. Afterwards, the sheet was slit and the tabs were welded to obtain a positive electrode sheet with a size of 54mm×70mm for later use. The surface density of the single-sided coating of the positive electrode slurry was 150g / m³. 2 The compaction density of the positive electrode material layer is 2.4 g / cm³. 3 .

[0153] <Preparation of Negative Electrode Sheets>

[0154] 945g of graphite (negative electrode active material), 20g of Super P (conductive agent), 20g of SBR (binder), and 15g of CMC (thickener) were added to deionized water as a solvent to prepare a slurry with a solid content of 50wt%. The slurry was then stirred evenly in a vacuum mixer to obtain the negative electrode slurry. The negative electrode slurry was uniformly coated onto one surface of a 6μm thick copper foil used as a negative electrode current collector and dried at 90℃ to obtain a negative electrode sheet with a single-sided negative electrode material layer. The above steps were repeated on the other surface of the copper foil to obtain a negative electrode sheet with a double-sided negative electrode material layer. After drying at 85℃, the sheet was rolled, then slit and had tabs welded to obtain a negative electrode sheet with a size of 58mm × 74mm for later use. The areal density of the single-sided negative electrode material layer was 95g / m³. 2 The compaction density of the negative electrode material layer is 1.5 g / cm³. 3 .

[0155] <Preparation of the diaphragm>

[0156] The diaphragm used in this application is a ceramic-coated diaphragm (Xingyuan 7+3+1μm), wherein the thickness of the alumina ceramic layer is 3μm and the thickness of the polyvinylidene fluoride (PVDF) coating layer is 1μm.

[0157] <Preparation of Electrolyte>

[0158] 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), dimethyl carbonate (DMC), and diethyl carbonate (DEC) are mixed in a mass ratio of 25:50:20. Then, lithium salt LiPF6 is added to the organic solvent to dissolve and mix evenly to obtain an electrolyte with a lithium salt concentration of 1 mol / L.

[0159] <Preparation of Secondary Batteries>

[0160] The prepared positive electrode, separator, and negative electrode are stacked sequentially, with the separator positioned between the positive and negative electrodes to provide insulation. The electrode assembly is then wound to obtain the 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 24 hours, the formation current is 0.05C, the upper limit of the formation voltage is 3.65V, and the formation temperature is 45°C.

[0161] Examples 1-2 to 1-23:

[0162] Except for the section on "Preparation of Positive Electrode Slurry," where the type of metal-doped metal-organic framework material was replaced according to Tables 1-1 and 1-2, the rest of the content is the same as in Example 1-1. Specifically, in "Preparation of Metal-Organic Framework Materials," except for adjusting the preparation parameters according to Table 1-3, the rest of the content is the same as in Example 1-3. In "Preparation of Metal-Doped Metal-Organic Framework Materials," except for adjusting the preparation parameters according to Table 1-4, the rest of the content is the same as in Example 1-3.

[0163] Examples 1-24:

[0164] Except for replacing the positive electrode active material with lithium manganese iron phosphate (LiMn6Fe4PO4) in the <Preparation of Positive Electrode Slurry> section, and using a voltage range of 2.5~4.3V for the specific capacity test, rate charge-discharge test, and high-temperature cycle performance test of the positive electrode material, everything else is the same as in Examples 1-2. Here, 815Cycle@80%EOL means that in the high-temperature cycle performance test, after 815 cycles, the battery retains 80% of its capacity.

[0165] Examples 1-25:

[0166] Except for replacing the type of positive active material with sodium iron pyrophosphate (Na4Fe3(PO4)2P2O7) in the <Preparation of Positive Electrode Slurry>, and using a voltage range of 2.0~3.6V in the specific capacity test, rate charge-discharge test and high temperature cycling performance test of the positive electrode material, the rest are the same as in Examples 1-2.

[0167] Examples 2-1 to 2-8:

[0168] Except for adjusting the mass percentages of the metal-organic framework material, positive electrode active material, conductive agent, binder, and dispersant according to Table 2 during the preparation of the positive electrode slurry, the rest is the same as in Examples 1-3. Specifically, based on the total mass of solid matter in the positive electrode slurry, the mass percentages W1 (metal-organic framework material), W2 (positive electrode active material), W3 (conductive agent), W4 (binder), and W5 (dispersant) are as shown in Table 2.

[0169] Examples 2-9 to 2-10:

[0170] Except for adjusting the type and quality of the dispersant added during the preparation of the positive electrode slurry, the rest is the same as in Examples 1-3.

[0171] In Examples 2-9, the dispersant is PVP, and in Examples 2-10, the dispersant is a mixture of PVP and HNBR (the mass ratio of PVP to HNBR is 1:1).

[0172] Examples 2-11 to 2-13:

[0173] Except for adjusting the surface density of the positive electrode slurry coating on one side as shown in Table 2 during the preparation of the positive electrode sheet, the rest is the same as in Examples 1-3.

[0174] Examples 2-14 to 2-15:

[0175] Except for adjusting the compaction density of the positive electrode active material layer as shown in Table 2 during the <Preparation of Positive Electrode Sheet> process, the rest is the same as in Examples 1-3.

[0176] Example 2-16:

[0177] Except for the following steps in the <Preparation of Positive Electrode Slurry>: adding 10g of dehydrating agent hexamethyldisilazane to the mixing system 1 in step 1, adjusting the mass of lithium iron phosphate (LiFePO4) added to 1890g in step 2, and adjusting the mass percentage of metal-doped metal-organic framework material, positive electrode active material, conductive agent, binder, and dispersant according to Table 2, the rest are the same as in Examples 1-3.

[0178] Among them, based on the total mass of solid matter in the cathode slurry, the mass percentage of metal-organic framework material doped with metal elements is 0.5%.

[0179] The preparation method of mixed system 1 is as follows:

[0180] 18g of metal-doped metal-organic framework material, 2g of dispersant hydrogenated nitrile butadiene rubber (HNBR), 10g of hexamethyldisilazane and 180g of N-methylpyrrolidone (NMP) were placed in a ball mill jar and ball-milled at 500 rpm for 5 hours to obtain mixed system 1.

[0181] Comparative Example 1:

[0182] Except for the fact that in the <Preparation of Positive Electrode Slurry> process, metal-organic framework materials doped with metal elements are not used, and the metal-organic framework materials doped with metal elements are replaced by lithium iron phosphate, the rest is the same as in Examples 1-3.

[0183] Comparative Example 2:

[0184] Except for the replacement of the metal-doped metal-organic framework material with undoped metal-organic framework material in the <Preparation of Positive Electrode Slurry> process, the rest is the same as in Examples 1-3. The molecular formula of the metal-organic framework material is Zr6O4(OH)4(OL). 4.266 (sol) 0.216 (blank) 3.252 (NO3) 3.252 .

[0185] Comparative Example 3:

[0186] Except for the fact that in the <Preparation of Positive Electrode Slurry> process, metal-organic framework materials doped with metal elements are not used, and the metal-organic framework materials doped with metal elements are replaced by an equal mass of positive electrode active material lithium manganese iron phosphate, the rest is the same as in Examples 1-24.

[0187] Comparative Example 4:

[0188] Except for the fact that in the <Preparation of Positive Electrode Slurry> process, metal-organic framework materials doped with metal elements are not used, and the metal-organic framework materials doped with metal elements are replaced by sodium iron pyrophosphate of phosphate at equal mass, the rest is the same as in Examples 1-25.

[0189] The preparation and performance parameters of each embodiment and comparative example are shown in Tables 1-1 to 1-4 and Table 2.

[0190] Table 1-1:

[0191] In Table 1-1, " / " indicates that the corresponding preparation parameters or substances do not exist; "A" represents the amount of substance of the metal-organic framework material doped with the metal element, specifically the molar content of the metal element, in mol / mol; "Z" represents the total defect rate of the metal-organic framework material doped with the metal element, in %; "K" represents the unsaturated coordination defect rate of the metal-organic framework material doped with the metal element, in %; "D" represents the average particle size of the metal-organic framework material doped with the metal element, in %; Zr:OL refers to the ratio of the amount of Zr to the amount of dicarboxyl conjugated organic ligand in the metal-organic framework material doped with the metal element.

[0192] Table 1-2:

[0193] Table 1-3:

[0194] Table 1-4:

[0195] Table 2:

[0196] In Table 2, based on the total mass of the cathode material layer, the mass percentage of the metal-organic framework material doped with metal elements is represented as "W1", the mass percentage of the cathode active material is represented as "W2", the mass percentage of the conductive agent is represented as "W3", the mass percentage of the binder is represented as "W4", and the mass percentage of the dispersant is represented as "W5".

[0197] As can be seen from Examples 1-1 to 1-25 and Comparative Examples 1 to 4, the positive electrode sheets of 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. The prepared positive electrode sheets have high conductivity, and the secondary batteries assembled from the positive electrode sheets have high specific capacity, high rate charge-discharge performance, and high-temperature cycle capacity retention. The positive electrode sheets of Comparative Examples 1, 3, and 4 do not contain metal-organic framework materials doped with metal elements, and the positive electrode slurry of Comparative Example 2 uses metal-organic framework materials that are not doped with metal elements. The prepared positive electrode sheets have low conductivity, and the secondary batteries have low specific capacity, high rate charge-discharge performance, and high-temperature cycle capacity retention.

[0198] The total defect rate, unsaturated coordination defect rate, and average particle size of metal-organic framework (MOF) materials doped with metal elements affect the conductivity of the cathode electrode and the specific capacity, rate charge-discharge performance, and high-temperature cycle capacity retention of the secondary battery. As can be seen from Examples 1-19 to 1-23, when the total defect rate, unsaturated coordination defect rate, and average particle size of the metal-organic framework material doped with metal elements are within the range of this application, the prepared cathode electrode exhibits high conductivity, and the secondary battery exhibits high specific capacity, rate charge-discharge performance, and high-temperature cycle capacity retention. As can be seen from Examples 24 and 25, when the metal-organic framework material doped with metal elements within the range of this application is used in cathode electrodes with lithium manganese iron phosphate and sodium iron pyrophosphate as the cathode active material, the cathode electrode exhibits high conductivity, and the secondary battery assembled from the cathode electrode exhibits high specific capacity, rate charge-discharge performance, and high-temperature cycle capacity retention.

[0199] from Figure 2 It can be seen that the XRD patterns of the metal-organic framework materials doped with metal elements in Examples 1-1, 1-3, and 1-5 include diffraction peaks of the (200) and (111) crystal planes. The black vertical line in the lower part of the figure (XRD standard card) is the diffraction peak simulated based on UiO-66 single crystal, which includes diffraction peaks of the (200) and (111) crystal planes. The fact that the XRD patterns of the metal-doped metal-organic framework materials include diffraction peaks of the (200) and (111) crystal planes indicates, on the one hand, that the metal-doped metal-organic framework materials used in this application still maintain a good crystal structure; on the other hand, it can be shown that the metal-doped metal-organic framework materials used in this application have a porous structure, with 8 Å pores arranged in an orderly manner in the framework. The XRD patterns of the metal-doped metal-organic framework materials in the positive electrode sheets of Examples 1-1 to 1-23 of this application all include diffraction peaks of the (200) and (111) crystal planes.

[0200] The types and mass percentages of each component in the positive electrode material layer affect the conductivity of the positive electrode and the performance of the secondary battery. As can be seen from Examples 2-1 to 2-8, when the mass percentage of the metal-organic framework material doped with metal elements in the positive electrode material layer is within the range of this application, the prepared positive electrode has high conductivity, and the secondary battery has high specific capacity, high rate charge-discharge performance, and high-temperature cycle capacity retention.

[0201] As can be seen from Examples 2-9 to 2-10, when the type and mass percentage of the dispersant in the positive electrode material layer are within the range of this application, the prepared positive electrode sheet has high conductivity, and the secondary battery has high specific capacity, high rate charge-discharge performance, and high-temperature cycle capacity retention. As can be seen from Examples 2-11 to 2-15, when the areal density and compaction density of the positive electrode material layer are within the range of this application, the prepared positive electrode sheet has high conductivity, and the secondary battery has high specific capacity, high rate charge-discharge performance, and high-temperature cycle capacity retention. As can be seen from Example 2-16, adding a dehydrating agent to the positive electrode material layer results in a positive electrode sheet with high conductivity, and a secondary battery with high rate charge-discharge performance and high-temperature cycle capacity retention.

[0202] 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 positive electrode plate, characterized in that, The positive electrode includes a positive current collector and a positive electrode material layer disposed on at least one surface of the positive current collector. The positive electrode material layer includes a positive electrode active material, a conductive agent, a binder, a dispersant, and a metal-organic framework material doped with a metal element. The metal-organic framework material doped with the metal element has 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 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; 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; the positive electrode active material is a polyanionic material.

2. The positive electrode sheet according to claim 1, characterized in that, In the cathode material layer, the molar ratio of Zr to OL is 6:(2.53~5.055).

3. The positive electrode sheet according to claim 1, characterized in that, In the cathode material layer, the molar ratio of Zr to OL is 6:(2.769~4.95).

4. The positive electrode sheet according to claim 1, characterized in that, In the cathode material layer, the molar ratio of Zr to OL is 6:(2.769~4.266).

5. The positive electrode sheet according to claim 1, characterized in that, In the cathode material layer, the molar ratio of Zr to OL is 6:(2.769~3.69).

6. The positive electrode sheet according to claim 1, characterized in that, The unsaturated coordination defect rate of the metal-organic framework material doped with the metal element is 15%~50.1%.

7. The positive electrode sheet according to claim 1, characterized in that, The unsaturated coordination defect rate of the metal-organic framework material doped with the metal element is 26.1%~50.1%.

8. The positive electrode sheet according to claim 1, characterized in that, The unsaturated coordination defect rate of the metal-organic framework material doped with the metal element is 37%~50.1%.

9. The positive electrode sheet according to claim 1, characterized in that, The total defect rate of the metal-organic framework material doped with the metal element is 20% to 53.5%.

10. The positive electrode sheet according to claim 6, characterized in that, The total defect rate of the metal-organic framework materials doped with the metal elements is 29.6% to 53.5%.

11. The positive electrode sheet according to claim 7, characterized in that, The total defect rate of the metal-organic framework material doped with the metal element is 40% to 53.5%.

12. The positive electrode sheet according to claim 1, characterized in that, 0.1≤a≤2.3。 13. The positive electrode sheet according to claim 1, characterized in that, 0.3≤a≤2.3。 14. The positive electrode sheet according to claim 1, characterized in that, The polyanionic material includes at least one of lithium iron phosphate, lithium vanadium phosphate, lithium manganese iron phosphate, sodium iron phosphate composite, and sodium vanadium fluorophosphate.

15. The positive electrode sheet according to claim 1, characterized in that, The dicarboxylated conjugated organic ligand includes a molecular skeleton, which includes any one of phenyl, pyridyl, and imidazole groups.

16. The positive electrode sheet according to claim 15, 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.

17. The positive electrode sheet according to claim 15, characterized in that, The dicarboxylic acid conjugated organic ligand includes any one of terephthalate, amino-modified terephthalate, fluoroterephthalate, and pyridinic acid dicarboxylate.

18. The positive electrode sheet according to claim 1, characterized in that, The counterions include NO3. - Cl - SO4 2- ,Br - F - At least one of acetylacetone radicals.

19. The positive electrode sheet according to claim 1, characterized in that, Based on the total mass of the positive electrode material layer, the mass percentage of the metal-organic framework material doped with metal elements is 0.01%~5%; the mass percentage of the positive electrode active material is 80%~97.9899%; the mass percentage of the conductive agent is 1%~5%; the mass percentage of the binder is 1%~5%; and the mass percentage of the dispersant is 0.0001%~5%.

20. The positive electrode sheet according to claim 1, characterized in that, Based on the total mass of the positive electrode material layer, the mass percentage of the metal-organic framework material doped with metal elements is 0.1% to 3%; the mass percentage of the positive electrode active material is 89.9% to 96%; the mass percentage of the conductive agent is 1% to 3%; the mass percentage of the binder is 1% to 3%; and the mass percentage of the dispersant is 0.01% to 1.1%.

21. The positive electrode sheet according to claim 1, characterized in that, The positive electrode material layer includes a dehydrating agent, which includes at least one of hexamethyldisilazane, heptamethyldisilazane, dicyclohexylcarbodiimide, diisopropylcarbodiimide, trimethylsilyl isocyanate, and tert-butyl isocyanate; based on the total mass of the positive electrode material layer, the mass percentage of the dehydrating agent is 0.01% to 5%.

22. The positive electrode sheet according to claim 21, wherein the mass percentage of the dehydrating agent is 0.1% to 1% based on the total mass of the positive electrode material layer.

23. The positive electrode sheet according to claim 1, characterized in that, The dispersant includes at least one of polyvinylpyrrolidone, hydrogenated nitrile butadiene rubber, poly(ε-caprolactone), polyethylene, polyethylene glycol, and poly(hydroxyethyl methacrylate).

24. The positive electrode sheet according to any one of claims 1 to 23, characterized in that, The average particle size of the metal-organic framework material doped with the metal element is 20 nm to 110 nm.

25. The positive electrode sheet according to claim 24, characterized in that, The average particle size of the metal-organic framework material doped with the metal element is 20 nm to 80 nm.

26. The positive electrode sheet according to claim 1, characterized in that, The surface density of the positive electrode material layer is 100 g / m². 2 ~300 g / m 2 The thickness of the positive electrode material layer on one side is 35.7 μm to 136 μm.

27. The positive electrode sheet according to claim 1, characterized in that, The compaction density of the positive electrode material layer is 2.2 g / cm³. 3 ~2.8g / cm 3 .

28. A secondary battery, characterized in that, The secondary battery comprises a positive electrode, a negative electrode, an electrolyte, and a separator, as described in any one of claims 1 to 27.

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