Modified negative electrode active material and preparation method thereof, electrode plate, battery and electric equipment

Abstract

The invention provides a modified negative electrode active material and a preparation method thereof, an electrode plate, a battery and electric equipment. The modified negative electrode active material comprises a negative electrode active material and a metal organic framework layer coating at least part of the surface of the negative electrode active material, the metal organic framework layer comprises a metal organic framework material, the metal organic framework material comprises metal ions and an organic ligand in coordination connection with the metal ions, and the metal ions comprise at least one of alkali metal ions, alkaline earth metal ions and transition metal ions. The modified negative electrode active material provided by the invention can reduce the generation of a negative electrode SEI membrane and reduce the loss of active metal ions, and can significantly improve the battery capacity when being used in a battery.

Description

Technical Field

[0001] The present invention relates to a modified negative electrode active material, in particular to a modified negative electrode active material and a preparation method thereof, an electrode sheet, a battery, and an electrical device, belonging to the field of secondary batteries. Background Art

[0002] Secondary batteries have shown broad development prospects in many fields. With the continuous development of technology, large-scale energy storage requires secondary batteries to have a sufficiently long cycle life and safety to meet actual usage needs and lower full life cycle costs, thereby improving the economic benefits of energy storage systems.

[0003] Usually, when the capacity of a secondary battery decays to a certain amount, the battery life is considered to have reached the end. During the cycle process of secondary battery capacity decay, the solvent molecules in the electrolyte will corrode the negative electrode layer, which may cause the negative electrode layer to peel off and induce further growth of SEI. The continuous rupture and regeneration of SEI leads to the continuous loss of active materials and electrolyte, which in turn causes the battery capacity to continue to decline.

[0004] Therefore, there is an urgent need to study technical solutions that can increase battery capacity. Summary of the Invention

[0005] The present invention provides a modified negative electrode active material, which can reduce the generation of negative electrode SEI film, reduce the loss of active metal ions, and can significantly improve the battery capacity when used in a battery.

[0006] The present invention also provides a method for preparing a modified negative electrode active material. The method is simple to operate and can prepare the modified negative electrode active material.

[0007] The present invention also provides an electrode sheet comprising the modified negative electrode active material.

[0008] The present invention also provides a battery comprising the electrode sheet and having excellent cycle performance.

[0009] The present invention also provides a lithium ion battery comprising the electrode sheet and having excellent cycle performance.

[0010] The present invention also provides a sodium ion battery comprising the electrode sheet and having excellent cycle performance.

[0011] The present invention also provides an electrical device comprising the battery.

[0012] In one aspect, the present invention provides a modified negative electrode active material, comprising a negative electrode active material and a metal organic framework layer coated on at least a portion of the surface of the negative electrode active material;

[0013] The metal organic framework layer includes a metal organic framework material, which includes metal ions and organic ligands coordinated with the metal ions. The metal ions include at least one of alkali metal ions, alkaline earth metal ions, and transition metal ions.

[0014] In the modified negative electrode active material as described above, the metal ions are selected from lithium ions or sodium ions.

[0015] In the modified negative electrode active material as described above, the mass percentage of the metal organic framework material is 0.01%-20% based on the modified negative electrode active material.

[0016] In the modified negative electrode active material as described above, the organic ligand includes a polycarboxylic acid ligand and / or an imidazole ligand.

[0017] In the modified negative electrode active material as described above, the organic ligand includes at least one of terephthalic acid, pyromellitic acid, 4,4'-biphenyldicarboxylic acid, 2,6-naphthalene dicarboxylic acid, 4,4'-sulfonylbis(methylbenzoic acid), L-aspartic acid, 1,2,3,4,5-penta(4-(carboxyphenyl))pyrrole, imidazole, and dimethylimidazole.

[0018] In the modified negative electrode active material as described above, the molar ratio of the metal ion to the organic ligand is (1-12):1.

[0019] In the modified negative electrode active material as described above, the thickness of the metal organic framework layer is 1 nm to 500 nm.

[0020] The modified negative electrode active material as described above has a specific surface area of ​​50m 2 / g~5000m 2 / g.

[0021] The modified negative electrode active material as described above includes graphite, soft carbon, hard carbon, lithium titanate, titanium dioxide, lithium titanium phosphate, silicon-based materials, germanium-based materials, tin-based materials, lead-based materials, transition metal sulfide MS X , transition metal oxides MO X 、Transition metal phosphide MP X Conversion materials, transition metal nitrides MN X at least one of the conversion materials;

[0022] Wherein, M includes at least one of iron, cobalt, nickel, copper, zinc and molybdenum; and x>1.

[0023] Another aspect of the present invention provides a method for preparing the modified negative electrode active material as described above, comprising the following steps:

[0024] The first mixed solution including the negative electrode active material and the metal ions is mixed with the second mixed solution containing the organic ligand for reaction, and the mixture is collected and dried after filtration / centrifugation, or directly dried to obtain the negative electrode active material.

[0025] In another aspect, the present invention provides an electrode sheet, comprising the modified negative electrode active material as described above or the modified negative electrode active material prepared by the preparation method as described above.

[0026] In another aspect, the present invention provides a battery comprising the electrode sheet described above.

[0027] In another aspect, the present invention provides a lithium-ion battery comprising the electrode sheet described above.

[0028] In another aspect, the present invention provides a sodium ion battery comprising the electrode sheet described above.

[0029] In another aspect, the present invention provides an electrical device comprising at least one of the battery described above, the lithium-ion battery described above, and the sodium-ion battery described above.

[0030] The modified negative electrode active material provided by the present invention includes a negative electrode active material and a metal-organic framework layer coated on at least a portion of the surface of the negative electrode active material. By limiting the type of metal ions in the metal-organic framework layer and setting organic ligands, the modified negative electrode active material can be used as an artificial SEI coating layer of the corresponding secondary battery negative electrode active material, thereby reducing the generation of negative electrode SEI, reducing the loss of active metal ions, improving coulombic efficiency, and alleviating battery capacity decay. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is an SEM image of the modified negative electrode active material provided in Example 1 of the present invention;

[0032] Figure 2 The XRD pattern of the modified negative electrode active material provided in Example 1 of the present invention;

[0033] Figure 3 This is an SEM image of the modified negative electrode active material provided in Example 2 of the present invention;

[0034] Figure 4 This is the XRD pattern of the modified negative electrode active material provided in Example 2 of the present invention. DETAILED DESCRIPTION

[0035] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0036] Metal-organic framework (MOF) materials are a type of crystalline porous materials formed by self-assembly bridging of inorganic metal centers (metal ions or metal clusters) and organic ligands.

[0037] MOF materials are often used as carrier materials or gas adsorption materials due to their adjustable pore size and composition. Although modifying negative electrode active materials by coating them with MOF materials can improve ion transport rates, simply coating the negative electrode active materials with MOF materials cannot prevent the loss of active metal ions, leading to problems such as battery capacity decay.

[0038] In one aspect, the present invention provides a modified negative electrode active material, comprising a negative electrode active material and a metal organic framework layer coated on at least a portion of the surface of the negative electrode active material;

[0039] The metal organic framework layer includes a metal organic framework material. The metal organic framework material includes metal ions and organic ligands coordinated with the metal ions. The metal ions include at least one of alkali metal ions, alkaline earth metal ions, and transition metal ions.

[0040] The modified negative electrode active material provided by the present invention is a core-shell structure, wherein the negative electrode active material is the core and the metal organic framework layer is the shell.

[0041] The metal-organic framework material of the metal-organic framework layer serving as the outer shell includes metal ions and organic ligands. The organic ligands refer to organic molecules containing multiple coordinating atoms. The organic ligands form coordination bonds with the metal ions through their coordinating atoms, thereby constructing a three-dimensional network structure to form a metal-organic framework layer.

[0042] The metal ions in the present invention include at least one of alkali metal ions, alkaline earth metal ions, and transition metal ions, such as lithium, sodium, potassium, magnesium, calcium, zinc, and the like.

[0043] The modified negative electrode active material provided by the present invention can significantly improve the capacity decay of the battery after being applied to the battery. On the one hand, the metal organic framework layer with specific metal ions enables the MOF material to have a weak interaction or repulsion with certain solvent molecules. This chemical selectivity can further improve the filtering effect of the MOF layer on solvent molecules, reduce the erosion of the electrolyte on the negative electrode active material, and alleviate the capacity decay caused by the loss of active material. On the other hand, the metal organic framework layer with specific metal ions can provide specific metal ions when the SEI is formed, reducing the loss of active metal ions caused by SEI formation and further reducing capacity decay.

[0044] In one embodiment, the metal ion is selected from lithium ion or sodium ion.

[0045] When the metal ion is selected from lithium ions, the metal ion of the modified negative electrode active material is Li and the outer shell is Li-MOF. In this case, the modified negative electrode active material can not only fully exert the protective effect of the metal-organic framework layer, but also provide an additional lithium source during the formation of the negative electrode SEI, replenishing lithium loss and improving the initial coulombic efficiency. When the metal ion is selected from sodium ions, the outer shell is Na-MOF, and the modified negative electrode active material can also play a role in replenishing sodium ion loss.

[0046] In practical applications, the cost of metal-organic framework materials is also a factor that needs to be considered. By controlling the content of the metal-organic framework material, a balance can be found between performance improvement and cost. In one embodiment, the weight percentage of the metal-organic framework material is 0.01% to 20% based on the weight of the modified negative electrode active material.

[0047] The mass of the metal-organic framework material can be measured by common methods in the art, such as thermogravimetric analysis, X-ray diffraction, elemental analysis, and nuclear magnetic resonance spectroscopy, thereby calculating the mass content of the metal-organic framework material.

[0048] In detail, the mass percentage of the metal organic framework material includes but is not limited to 0.01%, 0.1%, 1%, 5%, 10%, 15%, 20% or any range between two thereof.

[0049] When the metal-organic framework material mass content is within the above range, it can not only effectively protect the negative electrode active material, prevent the electrolyte from corroding the internal negative electrode active material, and limit the growth of the negative electrode SEI, but also effectively regulate the energy density of the negative electrode active material, control product costs, and improve the economic viability of the commercial application of the modified negative electrode active material.

[0050] Organic ligands in metal-organic frameworks not only provide structural support, but the type of organic ligand can further enhance the adsorption capacity of the metal-organic framework material and increase the selectivity of the metal-organic framework. In one embodiment, the organic ligand includes at least one of a polycarboxylic acid ligand and an imidazole ligand.

[0051] The polycarboxylic acid ligand refers to a ligand containing at least two carboxyl functional groups.

[0052] Polycarboxylic acid ligands and imidazole ligands can form stable coordination bonds with metal ions, and then synthesize MOF materials with large specific surface area in specific solutions. The open metal sites, strong polar functional groups and aromatic ring structures in MOF materials can effectively adsorb polar or weakly polar gas molecules (such as carbon dioxide) through hydrogen bonds and dipole-dipole interactions, thereby more effectively capturing and adsorbing gases such as carbon dioxide, hydrogen, and alkanes, thereby alleviating battery flatulence.

[0053] In one embodiment, the organic ligand includes at least one of terephthalic acid, pyromellitic acid, 4,4'-biphenyldicarboxylic acid, 2,6-naphthalene dicarboxylic acid, 4,4'-sulfonylbis(methylbenzoic acid), L-aspartic acid, 1,2,3,4,5-penta(4-(carboxyphenyl))pyrrole, imidazole, and dimethylimidazole.

[0054] When the organic ligand is of the above type, it can react with the aforementioned metal ions under certain conditions to form a stable metal-organic framework material.

[0055] In metal-organic frameworks (MOFs), the molar ratio of metal ions to organic ligands is an important parameter that determines the structure and properties of MOFs. In one embodiment, the molar ratio of metal ions to organic ligands is (1-12):1.

[0056] In detail, the molar ratio of the metal ion to the organic ligand includes but is not limited to 1:1, 2:1, 4:1, 6:1, 8:1, 10:1, 12:1 or any range therebetween.

[0057] When the molar ratio of metal ions to organic ligands is within the above range, a stable MOF structure and a relatively ideal MOF material yield can be achieved. Depending on the particle size of the substrate negative electrode active material, the above molar ratio can be adjusted to control the particle size of the MOF coating layer and achieve a relatively ideal coating effect. Generally speaking, the larger the molar ratio of metal ions to organic ligands, the smaller the MOF particle size.

[0058] As a core-shell structure, the thickness of the metal organic framework layer as the outer shell will also have a certain impact on the interface stability and ion and electron conductivity of the modified negative electrode active material. In one embodiment, the thickness of the metal organic framework layer is 1nm-500nm.

[0059] The thickness of the metal-organic framework layer in the present invention refers to the average thickness, and the thickness of the metal-organic framework layer can be detected by common methods, such as transmission electron microscopy, scanning electron microscopy, atomic force microscopy, etc.

[0060] In detail, the thickness of the metal organic framework layer includes but is not limited to 1 nm, 50 nm, 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm, or a range between any two thereof.

[0061] When the thickness of the metal-organic framework layer is within the above range, it can better balance ion conductivity and energy density. It can not only prevent the inability to effectively isolate the electrolyte, replenish active ions, and reduce the capacity retention rate of the battery due to too low thickness; but also avoid excessively high interface impedance due to excessive thickness, affecting ion conduction and avoiding reducing the overall energy density.

[0062] Since the metal organic framework as the shell is a porous structure, the specific surface area of ​​the modified negative electrode active material has a significant impact on the electrochemical performance, cycle life and overall efficiency of the battery. In one embodiment, the specific surface area is 50 to 5000 m 2 / g.

[0063] The specific surface area of ​​the modified negative electrode active material can be tested using common testing methods in the art, such as the BET method, the BJH method, the chemical adsorption method, the microscopy method, and the like.

[0064] In one embodiment, the negative electrode active material includes graphite, soft carbon, hard carbon, lithium titanate, titanium dioxide, lithium titanium phosphate, silicon-based materials, germanium-based materials, tin-based materials, lead-based materials, transition metal sulfides MS X , transition metal oxides MO X 、Transition metal phosphide MP X Conversion materials, transition metal nitrides MN X at least one of the conversion materials;

[0065] Wherein, M includes at least one of iron, cobalt, nickel, copper, zinc and molybdenum; and x>1.

[0066] When the negative electrode active material is selected from the above types, it is helpful for the embedding and extraction of active metal ions, improves the conductivity, and can provide higher energy density and stable structure.

[0067] Another aspect of the present invention provides a method for preparing the modified negative electrode active material as described above, comprising the following steps:

[0068] The first mixed solution including the negative electrode active material and the metal ions is mixed with the second mixed solution containing the organic ligand for reaction, and the mixture is collected and dried after filtration / centrifugation, or directly dried to obtain the negative electrode active material.

[0069] In a specific embodiment, a metal ion source and a solvent are mixed to obtain a first mixed solution, an organic ligand and a solvent are mixed to obtain a second mixed solution, the negative electrode active material, the first mixed solution and the second mixed solution are mixed to react, and after the reaction, the mixture is filtered / centrifuged and collected, and dried to obtain a modified negative electrode active material.

[0070] A common solvent in the art can be selected according to actual needs, such as deionized water, dimethylformamide (DMF), methanol, ethanol, ethers and esters, preferably a mixed liquid of water and DMF.

[0071] Among them, in order to improve the uniformity of mixing and improve the efficiency of the mixing reaction, the first mixed liquid can also include a surfactant. A suitable surfactant can be selected according to actual conditions. For example, the surfactant is selected from polyvinylpyrrolidone (PVP), hexadecyltrimethylammonium bromide (CTAB), sodium dodecyl sulfate (SDS), sodium dodecylbenzene sulfonate (SDBS), etc.

[0072] In order to improve the efficiency of the reaction, after the first mixed liquid and the second mixed liquid are mixed, the obtained mixed solution can be subjected to ultrasonic treatment. After the ultrasonic treatment, the raw materials can be further fully contacted with each other, thereby improving the reaction efficiency.

[0073] In one embodiment, the metal ion is lithium metal, and the metal ion source is selected from LiCl, CH3COOLi, LiNO3, Li2C2O4, LiOH, etc.

[0074] In another specific embodiment, the metal ion is sodium metal, and the metal ion source is selected from NaCl, CH3COONa, NaNO3, NaNO2, Na2C2O4, NaOH, etc.

[0075] In another specific embodiment, the metal ion is zinc metal, and the metal ion source is selected from Zn(NO3)2·6H2O, Zn(CH3COO)2·2H2O, ZnCl2, etc.

[0076] The present invention does not limit the drying temperature and time, as long as a solid powder of negative electrode active material can be obtained for subsequent use. For example, the drying temperature is 60-180°C.

[0077] The preparation method provided by the present invention is simple to operate. By in-situ synthesizing a metal organic framework layer on the surface of the negative electrode active material, in-situ coating of the negative electrode active material is achieved. The prepared modified negative electrode active material can be used in a battery to significantly improve the capacity of the battery.

[0078] In another aspect, the present invention provides an electrode sheet, comprising the modified negative electrode active material as described above or the modified negative electrode active material prepared by the preparation method as described above.

[0079] Since the electrode sheet provided by the present invention includes the modified negative electrode active material, the electrode sheet can effectively improve the battery capacity retention rate when used in a battery.

[0080] The electrode sheet of the present invention specifically includes a negative electrode current collector and a negative electrode active layer formed of a modified negative electrode active material and arranged on the surface of the negative electrode current collector.

[0081] To prepare the electrode sheet, the negative electrode active material, conductive agent, and binder can be dispersed in an appropriate amount of deionized water and thoroughly stirred to form a uniform negative electrode slurry. The negative electrode slurry is then evenly coated on the negative electrode current collector, dried, rolled, and slit to obtain the electrode sheet. In one embodiment, the negative electrode active layer comprises, by weight, 70-99% negative electrode active material, 0.5-15% conductive agent, and 0.5-15% binder. Furthermore, the negative electrode active layer comprises 80-98% negative electrode active material, 1-10% conductive agent, and 1-10% binder.

[0082] Among them, the material of the negative electrode current collector layer can be at least one of copper foil, nickel foam, and copper foam; the conductive agent can be selected from at least one of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, and graphene; the binder can be selected from at least one of carboxymethyl cellulose, styrene-butadiene rubber, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyvinyl alcohol, and sodium polyacrylate.

[0083] In another aspect, the present invention provides a battery comprising the electrode sheet described above.

[0084] It is conceivable that the battery of the present invention includes, in addition to the above-mentioned electrode sheet, a positive electrode sheet, an electrolyte and a separator.

[0085] The present invention does not strictly limit the positive electrode active material in the positive electrode sheet. Taking lithium-ion batteries as an example, the positive electrode active material can be any commonly used positive electrode active material in current lithium-ion batteries, such as at least one composite oxide of lithium and a metal selected from the group consisting of cobalt, manganese, nickel, and combinations thereof. Specifically, the positive electrode active material can be at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium manganese oxide, nickel-cobalt-manganese ternary materials, nickel-cobalt-aluminum ternary materials, lithium iron phosphate (LFP), lithium nickel manganese oxide, and lithium-rich manganese-based materials.

[0086] The present invention is not strictly limited to the selection of electrolyte. Taking lithium-ion batteries as an example, it can include one or more solvents commonly used in lithium-ion battery electrolytes and electrolyte lithium salts commonly used in lithium-ion electrolytes. For example, the solvent can be ethylene carbonate, propylene carbonate, butylene carbonate, fluoroethylene carbonate (FEC), dimethyl carbonate (DMC), diethyl carbonate (DEC), difluoroethylene carbonate (DFEC), dipropyl carbonate, ethyl methyl carbonate (EMC), ethyl acetate, ethyl propionate, propyl acetate, propyl propionate, sulfolane, γ-butyrolactone, etc.; the lithium salt can be, for example, one or more of lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium bis(trifluoromethylsulfonyl)imide (LiTFSI).

[0087] The present invention does not strictly limit the material selection of the diaphragm. Taking lithium-ion batteries as an example, it can be a diaphragm material commonly used in lithium-ion batteries, such as polypropylene diaphragm (PP), polyethylene diaphragm (PE), polypropylene / polyethylene double-layer composite film (PP / PE), polyimide electrospun diaphragm (PI), polypropylene / polyethylene / polypropylene three-layer composite film (PP / PE / PP), cellulose non-woven fabric diaphragm, and one of the diaphragms with ceramic coating.

[0088] During battery preparation, the positive electrode sheet, separator, and negative electrode sheet are wound or stacked to form a bare cell. This cell is then encapsulated in a pre-stamped aluminum-plastic film bag or a square aluminum shell. The encapsulated cells are dried at 85°C, and then the electrolyte is injected into the dried cells. After the cells are stored, formed, and resealed, the battery is complete.

[0089] In another aspect, the present invention provides a lithium-ion battery comprising the electrode sheet described above.

[0090] It can be understood that lithium-ion batteries use lithium ions as charge carriers and realize charge and discharge cycles through the insertion and extraction of lithium ions.

[0091] When the metal ions in the modified negative electrode active material in the electrode sheet of a lithium-ion battery are selected from lithium ions, the metal ions of the modified negative electrode active material are Li and the outer shell is Li-MOF. The modified negative electrode active material can not only give full play to the protective effect of the metal organic framework layer, but also provide additional lithium source when the negative electrode SEI is generated, replenish lithium loss, and improve the first coulombic efficiency.

[0092] In another aspect, the present invention provides a sodium ion battery comprising the electrode sheet described above.

[0093] Sodium-ion batteries use sodium ions as charge carriers and achieve charge and discharge cycles through the insertion and extraction of sodium ions.

[0094] When the metal ions in the modified negative electrode active material in the electrode sheet of the sodium ion battery are selected from sodium ions, the outer shell is Na-MOF, and the modified negative electrode active material can play a role in replenishing the loss of sodium ions and improving the first coulombic efficiency.

[0095] In another aspect, the present invention provides an electrical device comprising the battery as described above.

[0096] The present invention is not limited to the specific types of electrical equipment, and can include large energy storage systems, electric vehicles, mobile phones, smart homes, robots, drones, electronic cigarettes, speakers, and any other equipment that requires batteries to power it.

[0097] The electrical equipment provided by the present invention includes the above-mentioned battery or the above-mentioned battery pack, and thus has good performance.

[0098] Hereinafter, the modified negative electrode active material provided by the present invention will be described in detail through specific examples.

[0099] Unless otherwise specified, the reagents, materials, and instruments used in the following examples are conventional reagents, conventional materials, and conventional instruments in the art and can be obtained commercially. The reagents involved can also be synthesized by conventional methods in the art.

[0100] Example 1

[0101] The method for preparing the modified negative electrode active material provided in this embodiment includes the following steps:

[0102] 1. Dissolve 300 mg of graphite, 160 mg of polyvinylpyrrolidone (PVP), and 300 mg of Zn(NO3)2·6H2O in 30 mL of methanol solvent to obtain a first mixed solution;

[0103] 2. Dissolve 350 mg of dimethylimidazole in 30 mL of methanol to obtain a second mixed solution;

[0104] 3. Slowly adding the second mixed solution to the first mixed solution under stirring to obtain a mixed solution;

[0105] 4. The obtained mixed solution was dried in an oven at 80° C. for 24 h to obtain a dry solid powder, which was then ground and crushed to obtain the modified negative electrode active material.

[0106] The modified negative electrode active material provided in this embodiment was subjected to SEM testing. Figure 1 For SEM images, Figure 1 It can be seen that through the above steps, a layer of uniform and dense particles (ie, Zn-MOF) is in situ coated on the surface of the graphite negative electrode particles, the particle size of which is about 100 nm, and the coating layer has good integrity.

[0107] The modified negative electrode active material provided in this embodiment was subjected to XRD testing. Figure 2 is the XRD pattern, Figure 2 It can be seen that a series of diffraction peaks of ZIF-8 were observed between 10° and 25°, and the characteristic peak of graphite was observed at about 26.5°, confirming the successful synthesis of graphite@ZIF-8 modified negative electrode materials.

[0108] Example 2

[0109] The method for preparing the modified negative electrode active material provided in this embodiment includes the following steps:

[0110] 1. Dissolve 250 mg of graphite, 60 mg of PVP, and 170 mg of LiCl in 30 ml of a DMF / water mixed solvent, where the volume ratio of DMF to water is 4:1, to obtain a first mixed solution;

[0111] 2. Dissolve 160 mg of terephthalic acid in 30 ml of a DMF / water mixed solvent, wherein the volume ratio of DMF to water is 4:1, to obtain a second mixed solution;

[0112] 3. Slowly adding the second mixed solution to the first mixed solution under stirring to obtain a mixed solution;

[0113] 4. The obtained mixed solution was dried in an oven at 100° C. for 4 days to obtain a dry solid powder, which was then ground and crushed to obtain the modified negative electrode active material.

[0114] The modified negative electrode active material provided in this embodiment was subjected to SEM testing. Figure 3 For SEM images, Figure 3 It can be seen that through the above steps, a Li-MOF coating layer is in situ formed on the surface of the graphite particles, the particle size is about 50 to 100 nm, and the coating layer is relatively complete.

[0115] The modified negative electrode active material provided in this embodiment was subjected to XRD testing. Figure 4 is the XRD pattern, Figure 4 It can be seen that a series of diffraction peaks of Li-MOF were observed between 15° and 25°, as well as the characteristic peak of graphite at 26.5°, confirming the synthesis of graphite@Li-MOF modified negative electrode materials.

[0116] Example 3

[0117] The method for preparing the modified negative electrode active material provided in this embodiment includes the following steps:

[0118] 1. Dissolve 300 mg of graphite, 150 mg of PVP, and 340 mg of LiNO3 in 30 ml of DMF solvent to obtain a first mixed solution;

[0119] 2. Dissolve 1.25 g of 4,4'-biphenyldicarboxylic acid in 65 ml of DMF solvent to obtain a second mixed solution;

[0120] 3. Slowly adding the second mixed solution to the first mixed solution under stirring to obtain a mixed solution;

[0121] 4. The mixed solution was transferred to a hydrothermal kettle containing a Teflon liner, and after standing in a 180°C forced air drying oven for 4 days, it was filtered and then dried to obtain a solid powder. After grinding and crushing, the modified negative electrode active material was obtained.

[0122] Example 4

[0123] The preparation method of the modified negative electrode active material provided in this embodiment is basically the same as that in Example 3, except that:

[0124] In step 1), the mass of LiNO3 is 2.0 g.

[0125] In step 2), the mass of 4,4'-biphenyldicarboxylic acid is 5.0 g.

[0126] Example 5

[0127] The preparation method of the modified negative electrode active material provided in this embodiment is basically the same as that in Example 3, except that:

[0128] In step 2), the mass of 4,4'-biphenyldicarboxylic acid is 2.5 g.

[0129] Example 6

[0130] The preparation method of the modified negative electrode active material provided in this embodiment is basically the same as that in Example 3, except that:

[0131] In step 1), the mass of graphite is 80 mg.

[0132] Comparative Example 1

[0133] The negative electrode active material provided in this comparative example is graphite.

[0134] Test Case

[0135] 1. Physical property test

[0136] The modified negative electrode active materials provided in all the examples were tested, including the following steps:

[0137] (1) Observing the samples prepared in the above examples and comparative examples under a transmission electron microscope (TEM) to obtain information on the thickness and particle size of the metal organic framework layer;

[0138] (2) Measure the specific surface area of ​​the sample by nitrogen adsorption-desorption method;

[0139] (3) Thermogravimetric analysis of the samples was performed using a Diamond DSC differential scanning calorimeter: the sample to be tested was placed in a differential scanning calorimeter and heated from room temperature to 700°C in a flowing air atmosphere to allow the surface coating to fully react, obtain the sample mass loss information, and obtain the mass ratio of the metal organic framework layer.

[0140] 2. Electrochemical performance test

[0141] The modified negative electrode active material provided in the examples or the negative electrode active material provided in the comparative examples, carbon black, and PVDF were mixed in a mass ratio of 8:1:1, and an appropriate amount of the organic solvent N-methylpyrrolidone (NMP) was added. The mixed slurry was thoroughly ground and uniformly coated on the surface of copper foil. The mixture was then dried in a vacuum oven at 60°C for 12 hours. The dried electrode sheet was then cut into 12 mm diameter electrode sheets to obtain electrode sheets.

[0142] Using metallic lithium sheets as counter electrodes, 1M LiPF6 EC-DEC-EMC solution as electrolyte, and PE / PP separators, the above-mentioned electrode sheets were assembled into CR2032 button half-cells in an argon-filled glove box. After assembly, the cells were left to stand for 12 hours to allow the electrolyte to fully infiltrate, and then charge and discharge tests were performed. The test results are shown in Table 1.

[0143] Table 1

[0144]

[0145]

[0146] As shown in the above experimental results, Comparative Example 1 uses pure graphite as the negative electrode active material without a surface coating layer. During the first cycle, due to the large amount of SEI layer generated, lithium ions are consumed, resulting in a low coulombic efficiency; Example 1 uses ZIF-8 (Zn-MOF) as an artificial SEI layer coated on the graphite surface, which reduces the direct contact between the electrolyte / graphite negative electrode during the first cycle, reduces the interface side reaction, and improves the first coulombic efficiency; Examples 2 and 3 use Li-MOF with both artificial SEI and lithium supplementation as the coating layer, which can not only reduce the interface side reaction, but also improve the coulombic efficiency. Providing a lithium source to replenish the lithium ions consumed during SEI formation, the first coulombic efficiency improvement is most obvious. In Examples 4 and 6, the metal-organic framework layer is too thick and the mass percentage content is too high. On the one hand, it causes the transmission path of ions to the graphite matrix to be too long, thereby increasing the interface impedance and reducing the coulombic efficiency. On the other hand, it causes the proportion of active material matrix to be reduced, affecting the battery energy density. In Example 5, the particle size of the metal-organic framework material is too large, resulting in incomplete coverage on the surface of the matrix graphite material, and the inability to form an effective coating layer, and the effect of improving the coulombic efficiency is not obvious.

[0147] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A modified negative electrode active material, characterized in that: The invention comprises a negative electrode active material and a metal organic framework layer coated on at least a portion of the surface of the negative electrode active material; The metal organic framework layer includes a metal organic framework material, which includes metal ions and organic ligands coordinated with the metal ions. The metal ions include at least one of alkali metal ions, alkaline earth metal ions, and transition metal ions.

2. The modified negative electrode active material according to claim 1, characterized in that The metal ions are selected from lithium ions or sodium ions.

3. The modified negative electrode active material according to claim 1, characterized in that Based on the modified negative electrode active material, the mass percentage of the metal organic framework material is 0.01%-20%.

4. The modified negative electrode active material according to claim 1 or 2, characterized in that The organic ligand includes a polycarboxylic acid ligand and / or an imidazole ligand.

5. The modified negative electrode active material according to any one of claims 1 to 4, characterized in that: The organic ligand includes at least one of terephthalic acid, pyromellitic acid, 4,4'-biphenyldicarboxylic acid, 2,6-naphthalene dicarboxylic acid, 4,4'-sulfonylbis(methylbenzoic acid), L-aspartic acid, 1,2,3,4,5-penta(4-(carboxyphenyl))pyrrole, imidazole, and dimethylimidazole.

6. The modified negative electrode active material according to claim 4 or 5, characterized in that The molar ratio of the metal ion to the organic ligand is (1-12):

1.

7. The modified negative electrode active material according to claim 1, characterized in that The thickness of the metal organic framework layer is 1 nm to 500 nm.

8. The modified negative electrode active material according to any one of claims 1 to 6, characterized in that: The modified negative electrode active material has a specific surface area of ​​50 m 2 / g~5000m 2 / g.

9. The modified negative electrode active material according to claim 1, characterized in that The negative electrode active material includes graphite, soft carbon, hard carbon, lithium titanate, titanium dioxide, lithium titanium phosphate, silicon-based materials, germanium-based materials, tin-based materials, lead-based materials, transition metal sulfide MS X , transition metal oxides MO X 、Transition metal phosphide MP X Conversion materials, transition metal nitrides MN X at least one of the conversion materials; Wherein, M includes at least one of iron, cobalt, nickel, copper, zinc and molybdenum; and x>1.

10. A method for preparing the modified negative electrode active material according to any one of claims 1 to 9, characterized in that: The following steps are involved: A first mixed solution including the negative electrode active material and the metal ions is mixed with a second mixed solution containing the organic ligand for reaction, and then dried to obtain the modified negative electrode active material.

11. An electrode sheet, characterized in that: The modified negative electrode active material comprises the modified negative electrode active material according to any one of claims 1 to 9 or the modified negative electrode active material prepared by the preparation method according to claim 10.

12. A battery, characterized in that: Including the electrode sheet according to claim 11.

13. A lithium ion battery, characterized in that: Including the electrode sheet according to claim 11.

14. A sodium ion battery, characterized in that: Including the electrode sheet according to claim 11.

15. An electrical device, characterized in that: The method comprises at least one of the battery according to claim 12, the lithium-ion battery according to claim 13, and the sodium-ion battery according to claim 14.

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