Positive electrode additive composition, positive electrode slurry and positive electrode plate

Abstract

The invention relates to the technical field of electrochemistry, and provides a positive electrode additive composition, positive electrode slurry and a positive electrode pole piece, the positive electrode additive composition comprises additive powder, a dispersing aid and a solvent; the additive powder is a metal organic framework material doped with metal elements; the metal element comprises at least one of Li, Na, K, Ca, Mg, Cu, Co, Ni, Fe, Cr, Ti, Zn and Mn, and the molar content of the metal element is 0-2.3 based on the amount of substance of the metal organic framework material doped with the metal element. The additive is fully wetted and dispersed to prepare the positive electrode additive composition in the form of the mixed glue solution, and then the positive electrode additive composition is added into the slurry, so that the problem that additive powder is easy to agglomerate can be effectively solved, and the stability of the positive electrode slurry is further improved. The positive electrode additive composition is in the form of a mixed glue solution, so that the additive is easier to mix with other materials, the preparation process of the positive electrode slurry can be simplified, and the production efficiency is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electrochemistry, and in particular to a positive electrode additive composition, a positive electrode slurry comprising the positive electrode additive composition, and a positive electrode sheet comprising the positive electrode additive composition. BACKGROUND

[0002] Lithium ion batteries are widely used in the fields of electronic products and electric vehicles due to their high energy density and long cycle life. Currently, various additives are usually added to the positive electrode to improve the fast charging performance and safety performance of the battery cell.

[0003] Existing additives, such as metal organic framework (MOF) or covalent organic framework (COF) materials, are usually added to the positive electrode slurry in the form of dry powder. MOF or COF has a high specific surface area and strong interaction force, and is easy to form agglomerates, which affects its dispersion in the matrix. In addition, the addition of additive powder in the slurry mixing process can absorb a large amount of solvent, which can cause the viscosity of the slurry to be too high. In order to ensure the appropriate discharge viscosity, more solvent must be added in the subsequent viscosity adjustment stage, and too much solvent will cause the solid content of the slurry to be too low. The low solid content of the slurry requires more solvent to be evaporated during the coating and drying process, which reduces the coating rate and increases the energy consumption of the equipment. At the same time, too low solid content of the slurry can cause quality problems such as edge lifting, coating cracking and adhesive floating during coating, which can reduce the adhesion of the electrode sheet. Therefore, how to solve the problem of easy agglomeration of additive powder material to improve the uniformity and stability of the positive electrode slurry has become a problem that needs to be solved by those skilled in the art. SUMMARY

[0004] The purpose of the present application is to provide a positive electrode additive composition, a positive electrode slurry comprising the positive electrode additive composition, and a positive electrode sheet comprising the positive electrode additive composition. By first wetting and dispersing the additive powder to form a positive electrode additive composition in the form of a mixed glue solution and then adding it to the slurry, the problem of easy agglomeration of additive powder can be effectively solved, and the stability of the positive electrode slurry can be improved. The positive electrode additive composition is in the form of a mixed glue solution, which makes it easier for the additive powder to mix with other materials, simplifies the preparation process of the positive electrode slurry, and improves the production efficiency. The specific technical solutions are as follows:

[0005] The first aspect of the present application provides a positive electrode additive composition comprising an additive powder, a dispersing aid and a solvent; the additive powder is a metal element doped metal organic framework material, and the molecular formula of the metal element doped metal organic framework material is M a Zr6O m (OH) n (OL) 6-(x+y) / 2 (sol) x (blank)y N b , 0≤a≤2.3, 4≤m≤6, 0≤n≤4, 0.09≤x≤0.92, 1.8≤y≤6.02, 0.9≤b≤9.24; wherein, M is a metallic element, including at least one of Li, Na, K, Ca, Mg, Cu, Co, Ni, Fe, Cr, Ti, Zn and Mn, OL is a dicarboxylic acid conjugated organic ligand, and sol includes acetate, formate, CH3-(CH2) p -COO - Any of the following, 1≤p≤6, blank is a ligand vacancy, and N is a counter ion.

[0006] In one embodiment of this application, the molar ratio of Zr to OL in the positive electrode additive composition is 6:(2.53~5.055).

[0007] In one embodiment of this application, the molar ratio of Zr to OL in the positive electrode additive composition is 6:(2.766~4.64).

[0008] In one embodiment of this application, the molar ratio of Zr to OL in the positive electrode additive composition is 6:(2.766~4.266).

[0009] In one embodiment of this application, the molar ratio of Zr to OL in the positive electrode additive composition is 6:(2.766~3.69).

[0010] In one embodiment of this application, the total defect rate of the metal-organic framework material doped with the metal element is Z, where 20% ≤ Z ≤ 53.5%.

[0011] In one embodiment of this application, the total defect rate of the metal-organic framework material doped with the metal element is Z, 30.7%≤Z≤53.5%.

[0012] In one embodiment of this application, the total defect rate of the metal-organic framework material doped with the metal element is Z, 40%≤Z≤53.5%.

[0013] In one embodiment of this application, the unsaturated coordination defect rate of the metal-organic framework material doped with the metal element is K, where 15% ≤ K ≤ 50.1%.

[0014] In one embodiment of this application, the unsaturated coordination defect rate of the metal-organic framework material doped with the metal element is K, where 27.1% ≤ K ≤ 50.1%.

[0015] In one embodiment of this application, the unsaturated coordination defect rate of the metal-organic framework material doped with the metal element is K, where 37% ≤ K ≤ 50.1%.

[0016] In one embodiment of this application, the molar content of the metal element doped with the metal-organic framework material is from 0.1 mol / mol to 2.3 mol / mol, based on the amount of the metal element.

[0017] In one embodiment of this application, based on the mass of the positive electrode additive composition, the mass percentage of the additive powder is W1, where 5% ≤ W1 ≤ 30%; the mass ratio of the additive powder to the dispersant is 1:0.01~0.5.

[0018] In one embodiment of this application, the counter ion includes PO4. 3- NO3 - Cl - SO4 2- ,Br - F - And any one of acetylacetonate.

[0019] In one embodiment of this application, the dispersing agent includes at least one of polyvinylpyrrolidone (PVP), hydrogenated nitrile butadiene rubber (HNBR), poly(ε-caprolactone), polyethylene, polyethylene glycol, and poly(hydroxyethyl methacrylate).

[0020] In one embodiment of this application, the positive electrode additive composition further includes a dehydrating agent, wherein the mass ratio of the dehydrating agent to the additive powder is 0.01~0.5:1, and the dehydrating agent includes at least one of hexamethyldisilazane (HMDS), heptamethyldisilazane (H7DMS), dicyclohexylcarbodiimide (DCC), diisopropylcarbodiimide (DIC), trimethylsilyl isocyanate (Si-NCO), and tert-butyl isocyanate (C-NCO).

[0021] In one embodiment of this application, the solvent includes at least one of N-methyl-2-pyrrolidone (NMP), diethylene glycol dimethyl ether (Diglyme), triethylene glycol dimethyl ether (Triglyme), and tetrahydrofuran (THF).

[0022] In one embodiment of this application, the specific surface area of ​​the additive powder is 400 m². 2 / g to 1040m 2 / g.

[0023] In one embodiment of this application, the average particle size of the metal-organic framework material doped with the metal element is 20 nm to 110 nm.

[0024] In one embodiment of this application, the average particle size of the metal-organic framework material doped with the metal element is 64 nm to 80 nm.

[0025] In one embodiment of this application, the metal-doped metal-organic framework material includes a dicarboxylic acid conjugated organic ligand, wherein the molecular skeleton of the dicarboxylic acid conjugated organic ligand includes any one of phenyl, imidazolyl, and pyridinyl.

[0026] In one embodiment of this application, the molecular skeleton of the dicarboxylated conjugated organic ligand is selected from phenyl, and the dicarboxylated conjugated organic ligand includes functional groups, which include any one of amino, hydroxyl, mercapto, methoxy, nitro, fluorine, and chlorine groups.

[0027] In one embodiment of this application, the dicarboxylic acid conjugated organic ligand includes any one of terephthalate, amino-modified terephthalate, fluoroterephthalate, and pyridinic acid dicarboxylate.

[0028] The second aspect of this application provides a positive electrode slurry comprising the positive electrode additive composition provided in the first aspect of this application; based on the total mass of solid matter in the positive electrode slurry, the mass percentage of metal-organic framework material doped with metal elements in the positive electrode slurry composition is 0.01%-20%, and the solid content of the positive electrode slurry is 40wt%~80wt%.

[0029] A third aspect of this application provides a positive electrode sheet, which includes a positive current collector and a first positive electrode material layer disposed on at least one surface of the positive current collector, wherein the first positive electrode material layer includes the positive electrode slurry provided in the second aspect of this application.

[0030] The fourth aspect of this application provides another positive electrode sheet, which includes a positive current collector, a second positive electrode material layer, and a coating. The second positive electrode material layer is disposed on at least one surface of the positive current collector, and the coating is disposed on at least one surface of the second positive electrode material layer. The coating includes the positive electrode additive composition provided in the first aspect of this application.

[0031] The beneficial effects of this application are:

[0032] This application provides a positive electrode additive composition, a positive electrode slurry including the positive electrode additive composition, and a positive electrode sheet including the positive electrode additive composition. The positive electrode additive composition includes additive powder, dispersant, and solvent. The additive powder is a metal-organic framework material doped with a metal element, and the molecular formula of the metal-organic framework material is M. a Zr6O m (OH) n (OL) 6-(x+y) / 2 (sol) x(blank) y N b , 0≤a≤2.3, 4≤m≤6, 0≤n≤4, 0.09≤x≤0.92, 1.8≤y≤6.02, 0.9≤b≤9.24; where M is a metallic element, including at least one of Li, Na, K, Ca, Mg, Cu, Co, Ni, Fe, Cr, Ti, Zn, and Mn; OL is a dicarboxylic acid conjugated organic ligand; and sol includes acetate, formate, and CH3-(CH2). p -COO - Any of the following, 1≤p≤6, blank represents a ligand vacancy, and N represents a counter ion. On the one hand, the inclusion of metal-organic framework materials doped with metal elements within the scope of this application in the cathode additive composition is beneficial for active metal ions (e.g., Li). + During interfacial transport, removing the coordination solvent increases the rate of active metal ion transport across the interface, thereby improving the fast-charging and cycle performance of the secondary battery. On the other hand, by first fully wetting and dispersing the additive powder to form a mixed colloidal solution for the positive electrode additive composition before adding it to the slurry, the problem of easy agglomeration of the additive powder can be effectively solved, thereby improving the stability of the positive electrode slurry.

[0033] 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. Detailed Implementation

[0034] 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.

[0035] The first aspect of this application provides a positive electrode additive composition comprising an additive powder, a dispersant, and a solvent; the additive powder is a metal-organic framework material doped with a metal element, wherein the molecular formula of the metal-organic framework material is M. a Zr6O m (OH) n (OL) 6-(x+y) / 2 (sol) x (blank) y N b, 0≤a≤2.3, 4≤m≤6, 0≤n≤4, 0.09≤x≤0.92, 1.8≤y≤6.02, 0.9≤b≤9.24, preferably, 0.1≤a≤2.3; wherein, M is a metallic element, including at least one of Li, Na, K, Ca, Mg, Cu, Co, Ni, Fe, Cr, Ti, Zn and Mn, OL is a dicarboxylic acid conjugated organic ligand, and sol is selected from acetate, formate, CH3-(CH2). p -COO - Any of the following, 1≤p≤6, blank is a ligand vacancy, and N is a counter ion. For example, the value of 'a' can be 0, 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 'x' can be 0.09, 0.15, 0.18, 0.2, 0.22, 0.25, 0.28, 0.3, 3, 0.35, 0.4, 0.45, 0.5, 0.6, 0.65, 0.7, 0.8, 0.85, 0.92, or a range of any two values; the value of 'y' can be 1.8, 2, 2.2, 2.5, 2.6, 2.8, 2.9, 3, 3.2, 3.5, 3.8, 4, 4.2, 4.5, 4.8, 5, 5.2, 5.5, 5.88. The values ​​of b can be 0.9, 1.2, 1.5, 1.8, 1.9, 2, 2.2, 2.5, 2.8, 3, 3.2, 3.5, 3.8, 4, 4.2, 4.5, 4.8, 5, 5.2, 5.48, 5.5, 5.8, 6, 6.2, 6.55, 6.8, 7.02, 7.55, 8, 8.5, 9.24, or any two of these values; the values ​​of m can be 4, 4.3, 4.6, 5, 5.2, 5.5, 5.8, 6, or any two of these values; the values ​​of n can be 0, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, or any two of these values.

[0036] 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 slurry includes a metal-organic framework material doped with the metal element described in this application, and the molar content of the metal element is controlled within the range of this application. On the one hand, the metal-doped metal-organic framework material has a porous structure, which is beneficial for the removal of active metal ions from the outer weakly coordinating solvent. On the other hand, the metal doping sites in the metal-doped metal-organic framework material promote the dissociation of the inner strong coordinating solvent of the active metal ions. This "assembly line" synergistic desolvation mechanism is beneficial for improving the rate of interfacial transport of active metal ions and improving the fast-charging and cycle performance of secondary batteries. Meanwhile, the abundant polar groups on the surface of metal-organic framework materials doped with metal elements have a high affinity for electrolytes, and the porous structure can quickly conduct electrolytes, which is beneficial for the electrolyte to wet the positive electrode.

[0037] 'a' represents the amount of substance of the metal-organic framework material based on metal element doping, specifically the molar content of the metal element. When 'a' is too large, for example, greater than 2.3, some metal elements are adsorbed into the pores of the metal-organic framework material in the form of physical adsorption. During the charging and discharging process of the secondary battery, these metal elements will detach from the pores of the metal-organic framework material and diffuse to the electrode interface with the electric field, catalyzing side reactions such as gas production, which will affect the electrochemical performance of the secondary battery.

[0038] 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 with other nanomaterials, MOFs have advantages such as larger specific surface area, tunable pore size and shape, and ease of doping. Activated MOFs can be used as additives in positive electrode slurries to 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. In addition, monodisperse metals have advantages such as high atom utilization, uniform site structure, and maximized metal-carrier interface, which can provide high-quality active sites for MOFs. Therefore, this application, by loading metal elements into MOFs, endows them with better conductivity, specific surface area, porosity, chemical tunability, active site abundance, and pore structure. Using MOFs within the scope of this application, after loading with metal elements, is beneficial to improving the rate of cross-interfacial transport of active metal ions, thereby improving the fast-charging performance and cycle performance of secondary batteries.

[0039] 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 widely accepted in the industry. 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≤a≤2.3, 4≤m≤6, 0≤n≤4, 0.09≤x≤0.92, 1.8≤y≤6.02, and 0.9≤b≤9.24.

[0040] In some embodiments of this application, the molar ratio of Zr to OL in the cathode additive composition is 6:(2.53~5.055), preferably 6:(2.766~4.64), more preferably 6:(2.766~4.266), and even more preferably 6:(2.766~3.69). For example, the molar ratio of Zr to OL can be 6:2.53, 6:2.766, 6:3.5, 6:3.69, 6:4266, 6:4.5, 6:4.64, 6:5.055, or a range of any two of these values. The molar ratio of Zr to OL actually reflects the total defect rate of the material. 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 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, cycle performance, and low-temperature performance of the secondary battery, and help improve the energy density of the secondary battery.

[0041] In one embodiment of this application, thermogravimetric analysis is used to test the total defect rate Z of the metal-organic framework material doped with metal elements. The defect rate Z is 20% ≤ Z ≤ 53.5%, preferably 30.7% ≤ Z ≤ 53.5%, and more preferably 40% ≤ Z ≤ 53.5%. For example, the value of Z can be 20%, 22%, 25%, 29.6%, 30%, 30.7%, 32%, 34%, 36%, 38%, 40%, 42%, 45%, 47%, 49%, 50%, 53.5%, or a range of any two of these values. 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 increased, and the fast-charging performance and cycle performance of the secondary battery can be improved.

[0042] In one embodiment of this application, solid-state NMR phosphorus spectroscopy is used to determine the unsaturated coordination defect rate K of the metal-organic framework material doped with metal elements. K is 15% ≤ K ≤ 50.1%, preferably 27.1% ≤ K ≤ 50.1%, and more preferably 37% ≤ K ≤ 50.1%. For example, the value of K can be 15%, 18%, 20%, 22%, 25%, 27.1%, 28%, 29%, 30%, 32%, 35%, 37%, 38%, 40%, 42%, 45%, 48%, 49%, 50.1%, or a range of any two of these values. Compared with other types of defects, unsaturated coordination defects have higher activity; exposed unsaturated metal coordination sites have lower steric hindrance and higher site accessibility, which is more conducive to active metal ions (e.g., Li). + During interfacial transport, the coordination solvent is removed. Furthermore, unsaturated coordination sites typically have lower metal valence states, resulting in a charge distribution within the material and a charge transfer path with the substrate that differs significantly from saturated coordination structures. This unique charge distribution and transfer path are more conducive to molecular activation and electron migration, thereby increasing the rate of interfacial transport of active metal ions. Controlling the unsaturated coordination defect rate of metal-organic framework materials doped with metal elements within the range described in this application is beneficial for improving the rate of interfacial transport of active metal ions in secondary batteries, thereby improving the fast-charging performance and cycle performance of secondary batteries.

[0043] In one embodiment of this application, based on the mass of the cathode additive composition, the mass percentage of the additive powder is W1, where 5% ≤ W1 ≤ 30%; the mass ratio of the additive powder to the dispersing agent is 1:0.01~0.5. For example, the mass percentage of the metal-doped metal-organic framework material can be 5%, 10%, 15%, 20%, 25%, 30%, or any two of these values; the mass ratio of the additive powder to the dispersing agent can be 1:0.01, 1:0.1, 1:0.2, 1:0.3, 1:0.4, 1:0.5, or 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 promoting the metal-doped metal-organic framework material to remove 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.

[0044] In some embodiments of this application, the counter ion includes PO4. 3- NO3 - Cl - SO4 2- ,Br - F - And any one of acetylacetonate. Based on their charge characteristics, metal-organic frameworks (MOFs) can be classified into cationic frameworks, anionic frameworks, and neutral frameworks. Counterions are weakly bound to MOFs through non-covalent interactions and are essential for maintaining the charge neutrality of MOF materials. In this application, the metal-doped MOF material consists of a cationic framework and counterions. For the cationic framework of the metal-doped MOF material in this application, the counterions can originate from the MOF material preparation process or from the metal element loading process.

[0045] In one embodiment of this application, the dispersing agent includes at least one selected from polyvinylpyrrolidone, hydrogenated nitrile butadiene rubber, poly(ε-caprolactone), polyethylene, polyethylene glycol, and polyhydroxyethyl methacrylate. The cathode additive composition includes dispersing agents within the scope of this application, and the mass percentage of the dispersing agent is controlled within the range of this application. This helps to reduce the agglomeration of the additive powder, ensuring uniform dispersion of the metal-organic framework material doped with metal elements in the cathode additive composition, thereby improving the uniformity and stability of the cathode slurry.

[0046] In one embodiment of this application, the positive electrode additive composition further includes a dehydrating agent, wherein the mass ratio of the dehydrating agent to the additive powder is 0.01 to 0.5:1. For example, the mass ratio of the dehydrating agent to the additive powder can be 1:0.01, 1:0.1, 1:0.2, 1:0.3, 1:0.4, 1:0.5, or any two of these values. The dehydrating agent includes at least one of hexamethyldisilazane, heptamethyldisilazane, dicyclohexylcarbodiimide, diisopropylcarbodiimide, trimethylsilyl isocyanate, and tert-butyl isocyanate. The positive electrode additive composition includes a dehydrating agent within the scope of this application, and controlling the mass percentage of the dehydrating agent within this scope effectively removes moisture from the additive composition, thereby reducing the obstruction of moisture to electron transport and lithium-ion migration, improving the charge and discharge efficiency of the battery, enabling the battery to charge and discharge quickly, enhancing high-rate charge and discharge performance, and reducing internal side reactions, allowing the battery to maintain a high capacity retention rate after multiple cycles.

[0047] In one embodiment of this application, the solvent includes at least one selected from N-methyl-2-pyrrolidone, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetrahydrofuran.

[0048] In one embodiment of this application, the specific surface area of ​​the additive powder is 400 m². 2 / g to 1040m 2 / g. For example, the specific surface area of ​​the additive powder can be 400m². 2 / g、500m 2 / g、600m 2 / g、700m 2 / g、800m 2 / g、900m 2 / g, 1000m 2 / g、1040m 2 / g or a range consisting of any two of these values. A specific surface area of ​​the additive powder within the above range is beneficial for constructing suitable pore sizes, promoting the removal of coordination solvents from active metal ions, increasing the rate of cross-interface transport of active metal ions, and improving the fast-charging and cycle performance of secondary batteries.

[0049] In one embodiment of this application, the average particle size of the metal-doped metal-organic framework material is 20 nm to 110 nm, preferably 64 nm to 80 nm. For example, the average particle size of the metal-doped metal-organic framework material can be 20 nm, 40 nm, 60 nm, 80 nm, 100 nm, 110 nm, or any combination of two of these values. Limiting the average particle size of the metal-doped metal-organic framework material to the range specified in this application is beneficial for increasing the surface exchange sites per unit mass of the metal-doped metal-organic framework material, promoting the removal of coordination solvents by active metal ions, improving the rate of cross-interface transport of active metal ions, and improving the overall performance of the secondary battery.

[0050] When the particle size of a material is too large, the bulk diffusion pathways of its ions / molecules increase significantly, resulting in slow mass transfer kinetics; simultaneously, the specific surface area decreases sharply, leading to insufficient effective surface reaction sites. Both of these factors jointly limit the material's performance. Correspondingly, larger particle sizes generally 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 and significantly increased total defect rate and unsaturated coordination defect rate are present, the risks of agglomeration and structural instability are also introduced. In one embodiment of this application, the molecular skeleton of the dicarboxylic acid conjugated organic ligand includes any one of phenyl, pyridinyl, and imidazolyl groups. When the molecular skeleton of the dicarboxylated conjugated organic ligand is selected from imidazole and pyridinyl groups, the ligand skeleton itself contains heteroatoms, which is beneficial for regulating the polarity of the pore walls of the metal-doped metal-organic framework material. This enhances the interaction between the pore walls and lithium ions, solvents, and anions in the electrolyte, promotes the dissociation of these three components within the pores, and thus improves the migration efficiency of lithium ions. In one embodiment of this application, the molecular skeleton of the dicarboxylated conjugated organic ligand is selected from phenyl groups, 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 the metal-doped metal-organic framework material, and controlling the type of functional group X within the scope of this application, is beneficial for regulating the polarity of the pore walls of the metal-doped metal-organic framework material, thereby enhancing the interaction between the pore walls and lithium ions, solvents, and anions in the electrolyte, promoting the dissociation of these three components within the pores, and thus improving the migration efficiency of lithium ions.

[0051] In this application, the dicarboxylated conjugated organic ligand is selected from at least one of the following substances:

[0052] (1) When the functional group X is an amino group, the dicarboxylic acid conjugated organic ligand includes at least one of 2-aminoterephthalate, 2,5-diaminoterephthalate, 2,3-diaminoterephthalate, 2,3,5-triaminoterephthalate and 2,3,4,5-tetraaminoterephthalate; preferably at least one of 2-aminoterephthalate and 2,5-diaminoterephthalate.

[0053] (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;

[0054] (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;

[0055] (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;

[0056] (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;

[0057] (6) When the functional group X is a fluorine group, the dicarboxylic acid conjugated organic ligand includes at least one of 2,5-dicarboxyfluorobenzoate, 2,5-difluoroterephthalate, 2,3-difluoroterephthalate, 2,3,5-trifluoroterephthalate and 2,3,4,5-tetrafluoroterephthalate; preferably 2,5-dicarboxyfluorobenzoate;

[0058] (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.

[0059] In this application, the molecular skeleton is selected from either pyridyl or imidazolyl, and the dicarboxylate conjugated organic ligand includes at least one of the following substances:

[0060] (1) When the molecular skeleton is selected from pyridinyl, the dicarboxylic acid conjugated organic ligand includes 2,5-pyridinic acid dicarboxylate;

[0061] (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.

[0062] In one embodiment of this application, the dicarboxylic acid conjugated organic ligand includes any one of terephthalate, amino-modified terephthalate, fluoroterephthalate, and pyridinic acid dicarboxylate.

[0063] In this application, functional group X influences the steric hindrance of the metal-organic framework material doped with metal elements. 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 node; electron-withdrawing groups enhance the Lewis acidity of the node, 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.

[0064] In this application, sol refers to a small molecule ligand, and blank refers to a ligand vacancy appearing around Zr. The small molecule ligand (sol) is introduced during the preparation process using a template agent. It is understood that the small molecule ligand sol may be partially substituted by the solvent during the preparation process, for example, by polar molecules such as ethanol, dichloromethane, and water. It should be noted that when sol is selected from acetate in the embodiments of this application, it includes the case where it is partially substituted by the solvent.

[0065] 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.

[0066] In this application, there is no particular limitation on the source of the metal-doped metal-organic framework material; it can be obtained by purchase or by preparation. There are no particular limitations on the preparation method of the substrate metal-organic framework material, as long as it achieves the purpose of this application. For example, the preparation method of Zr-based metal-organic framework material may include, but is not limited to, the following steps: adding Zr source material and dicarboxylic acid conjugated organic ligand to deionized water and a template agent, stirring and refluxing, centrifuging to obtain a precipitate, soaking the precipitate in an organic solvent, and finally centrifuging to obtain the substrate metal-organic framework material. This application does not particularly limit the preparation method of metal-doped metal-organic framework materials. For example, the preparation method of metal-doped Zr-based metal-organic framework material may be: drying and activating the Zr-based metal-organic framework material prepared above; adding the activated Zr-based metal-organic framework material and the metal source material to a diffusion solvent, refluxing, centrifuging, washing, and vacuum drying to obtain the metal-doped Zr-based metal-organic framework material. Other metal-based metal-organic framework materials can be prepared using methods similar to the above process, or they can be prepared using methods known to those skilled in the art or purchased from commercially available products, and then loaded with metal elements.

[0067] For zirconium-based metal-organic framework materials, this application does not specifically limit the Zr source mentioned above, as long as it can achieve the purpose of this application. For example, the Zr source material may include, but is not limited to, at least one of zirconium oxynitrate, zirconium chloride, zirconium oxychloride, zirconium bromide, zirconium fluoride, zirconium acetylacetonate, and zirconium sulfate. This application also does not specifically limit the template agent mentioned above, as long as it can meet the purpose of this application; for example, the template agent is selected from glacial acetic acid, formic acid, hydrochloric acid, and CH3-(CH2). p At least one of -COOH, 1≤p≤6. This application does not particularly limit the above-mentioned organic solvents, which may include, but are not limited to, at least one of ethanol, acetone, or dichloromethane. This application does not particularly limit the metal element source material, as long as it can achieve the purpose of this application. For example, when the metal element is Li, Na, K, Ca, Mg, Cu, Co, Ni, Fe, Cr, Ti, Zn, or Mn, a nitrate compound containing the corresponding metal element, a chloride compound containing the corresponding metal element, a sulfate compound containing the corresponding metal element, or a phosphate compound containing the corresponding metal element can be added accordingly. The choice can be made according to actual needs, as long as the purpose of this application is achieved. This application does not particularly limit the diffusion solvent, as long as it can achieve the purpose of this application. For example, water, ethanol, methanol, n-hexane, cyclohexane, acetone, etc.

[0068] Typically, the molar content of metal elements in metal-organic framework materials doped with metal elements can be controlled by adjusting the concentration of the metal element source material; and the desired metal-doped metal-organic framework material can be selected by combining the "test of molar content of metal elements in metal-organic framework materials doped with metal elements" provided in this application.

[0069] The preparation method of the cathode additive composition of this application is not particularly limited; any method that can sufficiently disperse the cathode additive can be used. For example, an exemplary preparation method includes the following steps:

[0070] Additive powder, dispersant, dehydrating agent and solvent are placed in a ball mill or sand mill in proportion. The ball milling speed is 100 rpm to 1000 rpm and the ball milling time is 1 to 50 hours. After ball milling, the grinding balls and the glue are separated by filtration to obtain the positive electrode additive composition.

[0071] Another exemplary preparation method includes the following steps:

[0072] The additive powder, dispersant, and solvent are placed in a container and crushed using an ultrasonic cell disruptor with an ultrasonic power of 100-150W and a frequency of 40-60Hz. Simultaneously, a stirring rod is used to stir the mixture at a speed of 100-1000rpm for 1-50 hours. After stirring, the positive electrode additive composition is obtained.

[0073] The second aspect of this application provides a positive electrode slurry comprising the positive electrode additive composition provided in the first aspect of this application; based on the total mass of solid matter in the positive electrode slurry, the mass percentage of metal-organic framework material doped with metal elements in the positive electrode additive composition is 0.01%-20%, and the solid content of the positive electrode slurry is 40wt%~80wt%. For example, the mass percentage of metal-organic framework material doped with metal elements in the positive electrode additive composition can be 0.01%, 0.05%, 0.1%, 0.5%, 1%, 3%, 5%, 8%, 10%, 12%, 14%, 16%, 18%, 20%, or a range consisting of any two of these values; the solid content of the positive electrode slurry can be 40wt%, 45wt%, 50wt%, 55wt%, 60wt%, 65wt%, 70wt%, 75wt%, 80wt%, or a range consisting of any two of these values. By controlling the content of the positive electrode additive composition and the solid content of the positive electrode slurry within the range of this application, the fluidity and viscosity of the positive electrode slurry are moderate, which can reduce problems such as sedimentation and flocculation caused by storage and transportation, and improve the uniformity of the positive electrode slurry; at the same time, it is beneficial to the coating of the positive electrode active material layer in subsequent processes, thereby improving the capacity and charge-discharge performance of the secondary battery.

[0074] This application does not impose any particular limitation on the preparation method of the positive electrode slurry, as long as it can achieve the purpose of this application. For example, the preparation method of the positive electrode slurry can be as follows: dissolving a composition of binder and positive electrode additive in a positive electrode slurry solvent to prepare a colloid, then adding positive electrode active material and conductive agent to the above colloid, and stirring evenly to obtain the positive electrode slurry.

[0075] A third aspect of this application provides a positive electrode sheet, which includes a positive current collector and a first positive electrode material layer disposed on at least one surface of the positive current collector, wherein the first positive electrode material layer includes the positive electrode slurry provided in the second aspect of this application.

[0076] In this application, the aforementioned "first positive electrode material layer disposed on at least one surface of the positive electrode current collector" means that the first positive electrode material layer can be disposed on one surface of the positive electrode current collector along its own thickness direction, or it can be disposed on two surfaces of the positive electrode current collector along its own thickness direction. It should be noted that the "surface" here can be the entire surface area of ​​the positive electrode current collector, or it can be a partial surface area of ​​the positive electrode current collector. This application has no particular limitation, as long as the purpose of this application can be achieved. This application has no particular limitation on the positive electrode current collector, as long as the purpose of this application can be achieved. For example, the positive electrode current collector can be aluminum foil, aluminum alloy foil, or a composite current collector. The aforementioned composite 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), and 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, and nickel alloy. This application does not impose any particular limitation on the thickness of the positive electrode material layer and the positive electrode current collector, as long as the purpose of this application can be achieved. For example, the thickness of the single-sided positive electrode material layer is 50 μm to 250 μm, and the thickness of the positive electrode current collector is 7 μm to 16 μm.

[0077] The first positive electrode material layer includes a positive electrode active material. This application does not impose any particular limitation on the positive electrode active material, as long as it can achieve the purpose of this application. For example, the positive electrode active material may include, but is not limited to, lithium nickel cobalt manganese oxide (e.g., NCM811, NCM622, NCM523, NCM111), lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide (LiCoO2), lithium manganese oxide, lithium manganese iron phosphate, and lithium titanate.

[0078] The first positive electrode material layer also includes a conductive agent and a binder. This application does not impose any particular limitation on the types of conductive agents and binders, as long as they achieve the purpose of this application. For example, the conductive agent may include, but is not limited to, at least one of superconducting carbon black (SuperP), acetylene black, Ketjen black, carbon nanotubes, graphene, and carbon fiber. The binder may include, but is not limited to, at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin. This application does not impose any particular limitation on the mass ratio of the positive electrode active material, conductive agent, and binder in the first positive electrode material layer. Those skilled in the art can select according to actual needs, as long as the purpose of this application is achieved.

[0079] The fourth aspect of this application provides another positive electrode sheet, which includes a positive current collector, a second positive electrode material layer, and a coating. The second positive electrode material layer is disposed on at least one surface of the positive current collector, and the coating is disposed on at least one surface of the second positive electrode material layer. The coating includes the positive electrode additive composition provided in the first aspect of this application.

[0080] This application does not impose any particular limitation on the preparation method of the above-mentioned coating, as long as it can achieve the purpose of this application. For example, the preparation method of the coating can be: applying the positive electrode additive composition to the surface of the second positive electrode material layer by spraying or microgravure coating, and after coating and drying, cold pressing and cutting to obtain the positive electrode sheet coated with the coating. In this application, the second positive electrode material layer includes a positive electrode active material, a conductive agent, and a binder. This application does not impose any characteristic limitations on the types of positive electrode active material, conductive agent, and binder in the second positive electrode material layer, as long as it can achieve the purpose of this application. For example, it can be at least one of the positive electrode active material, conductive agent, and binder included in the first positive electrode material layer. This application does not impose any particular limitation on the mass ratio of positive electrode active material, conductive agent, and binder in the second positive electrode material layer. Those skilled in the art can choose according to actual needs, as long as it can achieve the purpose of this application.

[0081] Example:

[0082] 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.

[0083] Test methods and equipment:

[0084] Molar content test of metal elements in metal-organic framework materials doped with metal elements:

[0085] The contents of the framework metal Zr and the metal element M in the metal-doped metal-organic framework material were determined using inductively coupled plasma optical emission spectrometry (ICP-OES). The molar ratio of metal element M to Zr in the metal-doped metal-organic framework material was calculated and denoted as d. Based on the amount of substance of the metal-doped metal-organic framework material, the molar content of the metal element is represented by r, r = 6d. Specific procedures: Digestion was performed using BVIII grade nitric acid. 20 mg of sample and 15 mL of nitric acid were added to a polytetrafluoroethylene beaker, and the mixture was heated at 80°C for 20 min. After the solvent evaporated and approximately 2 mL remained, 15 mL of nitric acid was added, and heating continued for approximately 20 min. This process of adding nitric acid was repeated until the solid was completely dissolved and the residual liquid was clear and transparent. Acid removal was then initiated, and the mixture was diluted with ultrapure water before injection.

[0086] Total defect rate Z-test for metal-organic framework materials doped with metal elements:

[0087] 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.

[0088] 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. m O m / 2 Zr6O6(OL)6, the corresponding standardized weight is N (%), N (%) = MA (M m O m / 2 Zr6O6 (OL)6) / MA(6ZrO2+ M m O m / 2 ) )×100%, where MA(M m O m / 2 Zr6O6(OL)6) represents 1 mol M m O m / 2 The mass of Zr6O6(OL)6, MA(6ZrO2+ M m O m / 2 () represents 6 mol ZrO2 and 1 mol M m O m / 2The 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 that the internal OL connectors of the metal-organic framework material doped with defective metal elements are insufficient. The total defect rate is calculated using the formula: (w%(350°C)-100%) / (N-100%)=1-Z, where w%(350°C) is the normalized weight of the metal-organic framework material doped with defective metal elements at 350°C, i.e., w%(350°C) = weight of the remaining material at a test temperature of 350°C / weight of the remaining material at a test temperature of 600°C, and Z is the total defect rate of the metal-organic framework material doped with metal elements.

[0089] Test of the unsaturated coordination defect rate K of metal-organic frameworks doped with metal elements:

[0090] The unsaturated coordination defect rate K of metal-doped metal-organic frameworks (MOFs) was measured using solid-state NMR phosphorus spectrometry. The metal-doped MOFs were activated under vacuum at 150 °C for 4 h. 100 mg of 2,2,6,6-tetramethylpiperidine-1-oxo radical (TMPO) was dissolved in 15 mL of dichloromethane to obtain a TMPO solution. 50 mg of the activated metal-doped MOFs were added to the TMPO solution and immersed for 1 h. Defects in the metal-doped MOFs were labeled and identified using TMPO. The unsaturated coordination defect rate of the metal-doped MOFs was measured using a Bruker Avance NEO 600 MHz NMR spectrometer. A 3.2 mm MAS probe was used, with a rotation speed of 15 or 18 kHz. 31 The P signal was calibrated using the NH4H2PO4 signal. Peak fitting was performed on the data between 1 and 100 using Origin, and the fitted R value was... 2 ≥99.8%. The peaks near chemical shifts 62, 58, 55, and 53 represent Zr-blank, μ-OH(OL), μ-OH(sol), and Zr-sol sites, respectively. Zr-blank indicates an unsaturated coordination defect; μ-OH(OL) indicates a bridged hydroxyl group adjacent to the OL organic ligand; μ-OH(sol) indicates a bridged hydroxyl group adjacent to a coordination defect in a small molecule; and Zr-sol indicates a coordination defect in a small molecule. The relative proportions of the corresponding species can be obtained based on the peak area percentages.

[0091] Among them, the metal-organic framework material doped with metal elements has the molecular formula M m Zr6O4(OH)4(OL) 6-(x+y) / 2 (sol) x (blank) y N nIn this calculation, the value of x is obtained by calculating the peak area ratio of μ-OH(sol) and Zr-sol species, and the value of y is obtained by calculating the peak area ratio of Zr-blank. The unsaturated defect rate K is y / 12.

[0092] Counterion quantity b test:

[0093] 25 mg of metal-doped metal-organic framework material was added to 5 mL of NaOH solution with a concentration of 1 mol / L. The types and concentrations (mass fractions) of counterions in the sample solution were determined using an ion chromatograph (model: Dionex-7680). The mass fraction of the counterion is denoted as W(N), and the molar mass of the counterion is denoted as M(N).

[0094] 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, .

[0095] Test of the molar ratio of Zr to OL in the cathode additive composition:

[0096] Zr content test in cathode additive composition: Take 50g of cathode additive composition sample and place it in an aluminum pan, place it on a heating plate at 110℃, and bake it. The resulting powder is then fed into a digester and digested and tested according to the following steps: 1) Heat approximately 0.03g of sample + 4mL nitric acid + 1mL hydrochloric acid at 140℃ for 40min with an electric heater, and cool to room temperature. 2) Add 3mL nitric acid + 2mL concentrated sulfuric acid and then microwave digest. The microwave digestion program is: 120℃-3min; 150℃-3min; 180℃-3min; 200℃-10min; 220℃-15min. 3) After bringing the volume to 100mL with ultrapure water, dilute 100 times and then test.

[0097] (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.

[0098] (2) Under the same instrument conditions, the response value of zirconium ions in the test solution is measured, and the mass concentration (ug / mL) of the zirconium ions in the test solution is found on the standard curve. From this, the molar amount of Zr in the diaphragm can be calculated.

[0099] (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.

[0100] Test of OL content in positive electrode additive composition:

[0101] Sample pretreatment: 25 mg of sample was placed in 5 mL of NaOH aqueous solution (1 mol / L), sonicated for 1 h, and after complete decomposition of the positive electrode additive composition, filtered and detected by liquid chromatography. Column: Agilent ZORBAX SB-C18 column, 4.6 x 150 mm, 5 μm; flow rate: 0.8 mL / min; injection volume: 10 μL; column temperature: 30°C; mobile phase elution program: gradient elution of 85% acetonitrile and 15% formic acid aqueous solution (0.1%), run time 12 min; detector: DAD, wavelength 230 nm, bandwidth 4 nm.

[0102] Viscosity testing of the cathode additive composition:

[0103] The viscosity of the cathode slurry was tested using a Brookfield dial rotational viscometer. First, the sample was placed in a container. Rotor #5 was selected, and the chosen rotor was screwed counterclockwise onto the shaft connecting rod. The lifting knob was rotated to slowly lower the instrument, immersing the rotor in the sample. The motor was turned on to start the rotor rotation, which was set to 20 rpm. After one minute, once the viscosity index stabilized, the sample viscosity was read. The viscosity of the freshly discharged cathode additive composition was tested using the same method and recorded as η0. Then, the viscosity of the cathode additive composition after standing for 3 months was tested and recorded as η3. The viscosity change rate = (η3 - η0) / η0 × 100%.

[0104] Testing of solid content in cathode additive compositions:

[0105] First, accurately weigh the dried and constant-weight container (denoted as m0). Then, take an appropriate amount of the positive electrode additive composition sample and place it into the container, and weigh the total mass of the container and the positive electrode additive composition again (denoted as m1). Place the sample and container together in an oven and dry them at the set temperature (120℃) until the sample is completely dry and reaches a constant weight. Subsequently, remove the container and cool it to room temperature, then weigh the total mass of the dried container and solid again (denoted as m2). According to the formula: Solid content of the positive electrode additive composition = [(m2-m0) / (m1-m0)]×100%.

[0106] Test of solid content difference:

[0107] Take a portion of the positive electrode additive composition with a height of 30 mm or more and place it in a 50 ml centrifuge tube. Store it vertically and let it stand for 3 months. Then test the solid content in the top 10 mm and bottom 10 mm of the positive electrode additive composition. Take a small amount of the upper and lower layers of slurry respectively and spread them evenly on a centrifuge tube with a mass of m. 上 and m 下 The total weights recorded on the aluminum foil are M. 上 and M 下 After baking in a 120℃ oven for 30 minutes, the total weight of the aluminum foil was M' 上 and M' 下 The solid content of the upper cathode additive composition was calculated to be (M' 上 -m 上 ) / (M 上 -m 上 The solid content of the lower cathode additive composition is (M')×100%. 下 -m 下 ) / (M 下 -m 下 )×100%, and the difference between the solid content of the upper layer and the solid content of the lower layer is denoted as △B.

[0108] Conductivity test of positive electrode:

[0109] 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.

[0110] Heat release test:

[0111] Weigh 3 mg of the positive electrode sheet and 5 μL of the corresponding electrolyte and place them in a DSC high-pressure crucible (model: 27 μL, manufacturer: Netzsch). Then use a press to seal the crucible to obtain a sample. After that, perform differential scanning calorimetry (DSC) testing on the sample. The testing instrument model is Netzsch differential scanning calorimeter DSC214. The heating range is from 25 °C to 400 °C, the heating rate is 10 °C / min, record the temperature of the main exothermic peak, and calculate the peak area from 150 °C to 350 °C to obtain the heat release from 150 °C to 350 °C.

[0112] Example 1-1:

[0113] <Preparation of Zr-based metal-organic framework materials>

[0114] Add 21.38 g (85.8 mmol) of zirconium oxynitrate hydrate and 23.31 g (128.7 mmol) of 2-aminoterephthalic acid to a 1000 mL two-necked flask, add 205 mL of deionized water and 81 mL of glacial acetic acid. Reflux at a stirring rate of 600 rpm / min and a temperature of 100 °C for 24 hours, then centrifuge at 10000 r / min for 60 min to separate the crude metal-organic framework material.

[0115] Wash the crude metal-organic complex. The specific steps are as follows: soak in ethanol for 12 h, soak in acetone for 12 h, soak in dichloromethane for 12 h, then soak in ethanol for 12 h, soak in acetone for 12 h, soak in dichloromethane for 12 h. A total of 6 times of soaking with different liquids, centrifuge at a rate of 10000 r / min for 15 min to separate the Zr-based metal-organic framework material.

[0116] <Preparation of lithium-doped Zr-based metal-organic framework materials>

[0117] Add 1 g of lithium nitrate and 30 g of water to a 350 mL pressure-resistant bottle to obtain a metal salt solution, then add 7.75 g of the above Zr-based metal-organic framework material, and ultrasonically mix for 20 min. Heat at 100 °C for 6 h to obtain a second suspension. Centrifuge the second suspension at 10000 r / min for 5 min to obtain a solid substance. Wash the solid substance 5 times with water and dry it in vacuum at 120 °C for 12 h to obtain the lithium-doped Zr-based metal-organic framework material Li 0.3 Zr6O4(OH)4(OL) 4.266 (CH3COO - ) 0.216 (blank) 3.252 (NO3) 3.552 .

[0118] The lithium-doped Zr-based metal-organic framework material Li obtained above 0.3 Zr6O4(OH)4(OL) 4.266 (CH3COO - ) 0.216 (blank) 3.252 (NO3) 3.552 The total defect rate Z is 30.7%, the unsaturated defect rate K is 27.1%, the average particle size is 70 nm, the molar content m of the metal element Li is 0.3 mol / mol, sol is acetate, and the dicarboxylic acid conjugated organic ligand OL is 2-aminoterephthalate, meaning the molecular skeleton of the dicarboxylic acid conjugated organic ligand is phenyl and the functional group is amino. The metal-doped metal-organic framework materials used in the other examples are similar to the above-mentioned Li 0.3 Zr6O4(OH)4(OL) 4.266 (CH3COO - ) 0.216 (blank) 3.252 (NO3) 3.552 The preparation is similar, and will not be described in detail in this application.

[0119] <Preparation of Cathode Additive Composition>

[0120] 10g of metal-organic framework material doped with metal elements (molecular formula Li) 0.3 Zr6O4(OH)4(OL) 4.266 (CH3COO - ) 0.216 (blank) 3.252 (NO3) 3.552 Specific surface area is 600m² 2 0.5 g of polyvinylpyrrolidone (PVP) dispersant and 89.5 g of N-methyl-2-pyrrolidone solvent were added to a 250 ml ball mill jar, followed by 400 g of 1 mm diameter zirconia grinding balls. The ball mill jar was placed in a planetary ball milling system and milled at 500 rpm for 5 hours. After milling, the grinding balls and the colloid were separated by vacuum filtration to obtain the positive electrode additive composition.

[0121] Examples 1-2 to 1-38:

[0122] Except for adjusting the type of metal-organic framework material doped with metal elements, the molar content of metal elements (based on the amount of substance of the metal-doped metal-organic framework material), counter ions, specific surface area of ​​the metal-doped metal-organic framework material, W1, the mass ratio of additive powder / dispersant, and the mass ratio of additive powder / dehydrating agent according to Table 1, everything else is the same as in Example 1. The solvent content varies with changes in W1, the mass ratio of additive powder / dispersant, and the mass ratio of additive powder / dehydrating agent.

[0123] The dicarboxyl conjugated organic ligand of the metal-doped metal-organic framework materials in Examples 1-27 is 2,5-dichloroterephthalate; the dicarboxyl conjugated organic ligand of the metal-doped metal-organic framework materials in Examples 1-32 is 2,5-pyridinedicarboxylate; the dicarboxyl conjugated organic ligand of the metal-doped metal-organic framework materials in Examples 1-33 is imidazole-4,5-dicarboxylate; the dicarboxyl conjugated organic ligand of the metal-doped metal-organic framework materials in Examples 1-34 is 2,5-difluoroterephthalate; the dicarboxyl conjugated organic ligand of the metal-doped metal-organic framework materials in Examples 1-35 is 2,5-dimethoxyterephthalate; the dicarboxyl conjugated organic ligand of the metal-doped metal-organic framework materials in Examples 1-36 is 2,5-dimercaptoterephthalate; and the dicarboxyl conjugated organic ligand of the metal-doped metal-organic framework materials in Examples 1-37 is terephthalate.

[0124] Example 2-1:

[0125] <Preparation of Positive Electrode Slurry>

[0126] The positive electrode additive composition prepared in Example 1-1 and the binder polyvinylidene fluoride (PVDF) were added to N-methylpyrrolidone (NMP), and then the positive electrode active material LiNi was added. 0.8 Co 0.1 Mn 0.1 O2 (NCM811) and conductive agent Super P were stirred evenly to obtain a positive electrode slurry. The solid content of the positive electrode slurry was 70 wt%. Based on the total mass of solid matter in the positive electrode slurry, the mass percentage of the metal-organic framework material modified and doped with metal elements in the positive electrode additive composition was 5%, and the positive electrode active material was LiNi. 0.8 Co 0.1 Mn 0.1 The mass percentage of O2 (NCM811) is 91%, the mass percentage of conductive agent Super P is 2%, and the mass percentage of binder PVDF is 2%.

[0127] <Preparation of the positive electrode>

[0128] The above-mentioned positive electrode slurry was uniformly coated onto one surface of a 13+1+1μm pre-coated aluminum foil current collector (Topwin Technology, 13+1+1μm × 160mm), and dried at 105℃ to obtain a positive electrode sheet with a single-sided coating of the first positive electrode 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 single-sided coating of the first positive electrode 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 specification 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 first positive electrode material layer is 3.5 g / cm³. 3 .

[0129] Examples 2-2 to 2-3:

[0130] Except for adjusting the relevant parameters according to Table 2 in <Preparation of Positive Electrode Slurry>, the rest is the same as in Example 2-1.

[0131] Example 3-1:

[0132] <Preparation of the positive electrode>

[0133] LiNi, the positive electrode active material 0.8 Co 0.1 Mn 0.1 O2 (NCM811), conductive agent Super P, and binder polyvinylidene fluoride were mixed in a mass ratio of 97.9:0.9:1.2. N-methylpyrrolidone (NMP) was added as a solvent to prepare a slurry with a solid content of 75 wt%. The slurry was then stirred uniformly under vacuum. This slurry was uniformly coated onto one surface of a 13+1+1 μm pre-coated aluminum foil current collector (Tuoyingfengke, 13+1+1 μm × 160 mm) and dried at 105 °C to obtain a positive electrode sheet with a single-sided coating of the second positive electrode material layer. The above steps were repeated on the other surface of the pre-coated aluminum foil current collector to obtain a positive electrode sheet with a single-sided coating of the second positive electrode material layer, ready for use. The areal density of the coated surface was 141.66 g / m². 2 .

[0134] The positive electrode additive composition prepared in Example 1-1 was uniformly sprayed onto the surfaces of the two second positive electrode material layers of the above-mentioned positive electrode sheet using a spraying device to form a coating. After drying at 105°C, the coating was rolled and then dried in a vacuum drying oven at 105°C for 12 hours. The coating was then slit and the tabs were welded to obtain a positive electrode sheet with dimensions of 54mm × 70mm. The metal-organic framework material doped with metal elements had a mass percentage of 10% based on the coating mass. The coating thickness h was 43μm, and the coating compaction density was 3.5g / cm³. 3.

[0135] Examples 3-2 to 3-3:

[0136] Except for adjusting the relevant parameters according to Table 3 in the <Preparation of Positive Electrode Sheet> section, the rest is the same as in Example 3-1. That is, the coating of Example 3-2 is prepared from the positive electrode additive composition of Examples 1-21, and the coating of Example 3-3 is prepared from the positive electrode additive composition of Examples 1-22.

[0137] Comparative Examples 1-1 to 1-4:

[0138] Except for adjusting the mass ratio of W1 and additive powder / dispersant according to Table 1, everything else is the same as in Example 1. The solvent content varies with the mass ratio of W1 and additive powder / dispersant.

[0139] Comparative Example 3-1:

[0140] Except for the fact that the above-mentioned coating slurry was not sprayed onto the surface of the second positive electrode material layer in the <Preparation of Positive Electrode Sheet>, the rest is the same as in Example 3-1.

[0141] The preparation parameters and performance parameters of each embodiment and comparative example are shown in Tables 1 to 3.

[0142] Table 1:

[0143] Note: Z (%) represents the total defect rate of metal-organic framework materials doped with metal elements, K (%) represents the unsaturated defect rate of metal-organic framework materials doped with metal elements, D (nm) represents the average particle size of metal-organic framework materials doped with metal elements, and Zr:OL refers to the ratio of the amount of Zr to the amount of dicarboxylic acid conjugated organic ligand in metal-organic framework materials doped with metal elements.

[0144] Table 2:

[0145] Table 3:

[0146] As can be seen from Examples 1-1 to 1-38 and Comparative Examples 1-1 to 1-4, when the additive powder is selected from the metal-organic framework material doped with metal elements provided in this application, and the mass percentages of the additive powder, dispersant, and solvent are controlled within the range of this application, the viscosity change rate of the prepared cathode additive composition after discharge and after standing for 3 months is within 27%; the difference in solid content between the upper and lower layers of the cathode additive composition after standing for 3 months is small, all less than 14%, indicating that the cathode additive composition has good uniformity and stability. When the content of metal-organic framework material doped with metal elements in the cathode additive composition is too small, such as in Comparative Examples 1-4, although the cathode additive composition also has a low viscosity change rate and solid content difference, it is not conducive to the subsequent preparation of the cathode electrode sheet. When the content of metal-organic framework material doped with metal elements in the cathode additive composition is too small, there is more solvent in the cathode additive composition, the cost of the cathode additive composition increases, and it will also lead to the cathode slurry discharge having too low solid content, making coating difficult.

[0147] As can be seen from Examples 1-1 to 1-20 and Comparative Examples 1-1 and 1-4, when the metal-organic framework material doped with metal elements provided in this application is used as the additive powder and the mass percentage of the metal-organic framework material doped with metal elements is controlled within the range of this application, the resulting cathode additive composition has moderate discharge viscosity and viscosity after standing for 3 months, and the difference in solid content between the upper and lower layers after standing for 3 months is small, indicating that the cathode additive composition has good dispersibility and stability.

[0148] As can be seen from Examples 1, 1-21 to 1-22 and Comparative Examples 1-2 and 1-3, by adjusting the mass ratio of additive powder to dispersant within the range of this application, the discharge viscosity and viscosity after standing for 3 months of the positive electrode additive composition can be moderate, and the difference in solid content between the upper and lower layers after standing for 3 months of the composition is small, indicating that the positive electrode additive composition has good uniformity and stability.

[0149] The dehydrating agent can effectively remove moisture from the additive composition, reducing residual moisture during the positive electrode homogenization process. This reduces side reactions during battery charging and discharging, allowing the battery to maintain a high capacity retention rate after multiple cycles. As can be seen from Examples 1-23 to 1-24, by adjusting the mass ratio of additive powder to dehydrating agent within the range of this application, the discharge viscosity and the viscosity after standing for 3 months of time of the positive electrode additive composition can be made moderate, and the difference in solid content between the upper and lower layers after standing for 3 months is small, indicating that the positive electrode additive composition has good dispersibility and stability.

[0150] As can be seen from Examples 1-1, 1-25 and 1-26, by adjusting the specific surface area of ​​the metal-organic framework material doped with metal elements within the range of this application, the discharge viscosity and the viscosity after standing for 3 months of the cathode additive composition can be moderate, and the difference in solid content between the upper and lower layers after standing for 3 months of the composition is small, indicating that the cathode additive composition has good uniformity and stability.

[0151] As can be seen from Examples 2-1 to 2-3, Examples 3-1 to 3-3 and Comparative Example 3-1, the positive electrode sheet containing the positive electrode additive composition of this application has a high electrical conductivity and a low heat release, indicating that the battery containing the positive electrode sheet of this application has good electrical performance and flame retardant performance, and the severity of thermal runaway is small, with a low risk of explosion / combustion.

[0152] 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 additive composition, characterized in that, The product comprises additive powder, dispersant, and solvent, wherein the additive powder is a metal-organic framework material doped with a metal element, and the molecular formula of the metal-organic framework material is M. a Zr6O m (OH) n (OL) 6-(x+y) / 2 (sol) x (blank) y N b , 0≤a≤2.3, 4≤m≤6, 0≤n≤4, 0.09≤x≤0.92, 1.8≤y≤6.02, 0.9≤b≤9.24; wherein, M is a metallic element, including at least one of Li, Na, K, Ca, Mg, Cu, Co, Ni, Fe, Cr, Ti, Zn and Mn, OL is a dicarboxylic acid conjugated organic ligand, and sol includes acetate, formate, CH3-(CH2) p -COO - Any of the following, 1≤p≤6, blank is a ligand vacancy, and N is a counter ion.

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

3. The positive electrode additive composition according to claim 1, characterized in that, In the cathode additive composition, the molar ratio of Zr to OL is 6:(2.766~4.64).

4. The positive electrode additive composition according to claim 1, characterized in that, In the positive electrode additive composition, the molar ratio of Zr to OL is 6:(2.766~4.266).

5. The positive electrode additive composition according to claim 1, characterized in that, In the positive electrode additive composition, the molar ratio of Zr to OL is 6:(2.766~3.69).

6. The positive electrode additive composition according to claim 1, characterized in that, The total defect rate of the metal-organic framework material doped with the metal element is Z, where 20% ≤ Z ≤ 53.5%.

7. The positive electrode additive composition according to claim 1, characterized in that, The total defect rate of the metal-organic framework material doped with the metal element is Z, 30.7%≤Z≤53.5%.

8. The positive electrode additive composition according to claim 1, characterized in that, The total defect rate of the metal-organic framework material doped with the metal element is Z, 40%≤Z≤53.5%.

9. The positive electrode additive composition according to claim 1, characterized in that, The unsaturated coordination defect rate of the metal-organic framework material doped with the metal element is K, where 15% ≤ K ≤ 50.1%.

10. The positive electrode additive composition according to claim 1, characterized in that, The unsaturated coordination defect rate of the metal-organic framework material doped with the metal element is K, where 27.1% ≤ K ≤ 50.1%.

11. The positive electrode additive composition according to claim 1, characterized in that, The unsaturated coordination defect rate of the metal-organic framework material doped with the metal element is K, where 37% ≤ K ≤ 50.1%.

12. The positive electrode additive composition according to claim 1, characterized in that, 0.1≤a≤2.3。 13. The positive electrode additive composition according to claim 1, characterized in that, Based on the mass of the cathode additive composition, the mass percentage of the additive powder is W1, where 5% ≤ W1 ≤ 30%; the mass ratio of the additive powder to the dispersant is 1:0.01~0.

5.

14. The positive electrode additive composition according to claim 1, characterized in that, The counterions include PO4. 3- NO3 - Cl - SO4 2- ,Br - F - And any one of acetylacetonate.

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

16. The positive electrode additive composition according to claim 1, characterized in that, The positive electrode additive composition further includes a dehydrating agent, wherein the mass ratio of the dehydrating agent to the additive powder is 0.01~0.5:1, and the dehydrating agent includes at least one of hexamethyldisilazane, heptamethyldisilazane, dicyclohexylcarbodiimide, diisopropylcarbodiimide, trimethylsilyl isocyanate and tert-butyl isocyanate.

17. The positive electrode additive composition according to claim 1, characterized in that, The solvent includes at least one of N-methyl-2-pyrrolidone, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetrahydrofuran.

18. The positive electrode additive composition according to claim 1, characterized in that, The specific surface area of ​​the additive powder is 400 m². 2 / g to 1040m 2 / g.

19. The positive electrode additive composition according to claim 1, characterized in that, The average particle size of the metal-organic framework material doped with the metal element is 20 nm to 110 nm.

20. The positive electrode additive composition according to claim 1, characterized in that, The average particle size of the metal-organic framework material doped with the metal element is 64 nm to 80 nm.

21. The positive electrode additive composition according to claim 1, characterized in that, The metal-doped metal-organic framework material includes a dicarboxylic acid conjugated organic ligand, the molecular skeleton of which includes any one of phenyl, imidazolyl, and pyridinyl.

22. The positive electrode additive composition according to claim 21, characterized in that, The molecular skeleton of the dicarboxylated conjugated organic ligand is selected from phenyl, and the dicarboxylated conjugated organic ligand includes functional groups, which include any one of amino, hydroxyl, mercapto, methoxy, nitro, fluorine, and chlorine groups.

23. The positive electrode additive composition according to claim 21, characterized in that, The dicarboxylic acid conjugated organic ligand includes any one of terephthalate, amino-modified terephthalate, fluoroterephthalate, and pyridinic acid dicarboxylate.

24. A positive electrode slurry, characterized in that, The cathode additive composition includes any one of claims 1 to 23; based on the total mass of solid matter in the cathode slurry, the mass percentage of metal-organic framework material doped with metal elements in the cathode slurry is 0.01%-20%, and the solid content of the cathode slurry is 40wt% to 80wt%.

25. A positive electrode plate, characterized in that, It includes a positive current collector and a first positive electrode material layer disposed on at least one surface of the positive current collector, the first positive electrode material layer comprising the positive electrode slurry as described in claim 24.

26. A positive electrode plate, characterized in that, The device includes a positive current collector, a second positive electrode material layer, and a coating, wherein the second positive electrode material layer is disposed on at least one surface of the positive current collector, and the coating is disposed on at least one surface of the second positive electrode material layer, wherein the coating comprises the positive electrode additive composition according to any one of claims 1 to 23.

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