Negative electrode material and preparation method thereof, negative electrode, lithium ion battery and electric equipment

Abstract

The invention relates to a negative electrode material and a preparation method thereof, a negative electrode, a lithium ion battery and electric equipment. The negative electrode material comprises a negative electrode active material and a coating layer coating the surface of the negative electrode active material, the coating layer comprises a covalent organic framework polymer; the covalent organic framework polymer comprises an imine type covalent organic framework polymer and / or a borate type covalent organic framework polymer. According to the invention, the storage performance and the cycling stability of the negative electrode of the lithium ion battery in a high-temperature and high-SOC state can be improved.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to the technical field of lithium ion batteries, in particular, to a negative electrode material and a preparation method thereof, a negative electrode, a lithium ion battery and an electric device. BACKGROUND

[0002] During the storage process (i.e. in the unused state) of the lithium iron phosphate battery at high temperature and high SOC (45-60℃), the lithium-embedded graphite negative electrode is in a low potential state for a long time, and the electrolyte reduction reaction will consume active lithium ions, eventually generating inorganic lithium salt; high temperature further increases the electrolyte reduction reaction rate, resulting in a large loss of active lithium ions. Therefore, the lithium iron phosphate battery will have irreversible capacity decay after being stored at high temperature for a long time (several months), resulting in a decrease in battery life and affecting the service life.

[0003] In order to improve the high-temperature storage life of the battery, common strategies include electrolyte additives, adjustment of the liquid injection process during formation, high-temperature baking, etc. to improve the thermal stability of the SEI film on the surface of the graphite negative electrode, and to ensure that the SEI remains highly stable at high temperature to avoid decomposition. However, the SEI composition is usually formed by the decomposition of solvents, additives, etc. and lithium-embedded graphite, and the decomposition products are complex, making it difficult to accurately control the composition and distribution on the surface of the graphite, and as the battery cycles and storage cross, the SEI will change in appearance, composition and be consumed and cannot be restored, resulting in a gradual decrease in the improvement of the high-temperature storage performance of the battery over time. SUMMARY

[0004] The purpose of the present disclosure is to provide a negative electrode material and a preparation method thereof, a negative electrode, a lithium ion battery and an electric device, in order to improve the storage performance and cycle stability of the lithium ion battery negative electrode at high temperature and high SOC.

[0005] In order to achieve the above-mentioned purpose, the first aspect of the present disclosure provides a negative electrode material, comprising a negative electrode active material and a coating layer coated on the surface of the negative electrode active material; the coating layer comprises a covalent organic framework polymer; The covalent organic framework polymer comprises an imine type covalent organic framework polymer and / or a borate type covalent organic framework polymer.

[0006] The present disclosure provides a negative electrode material, which is coated with a layer of covalent organic framework polymer (COFs) on the surface of particles of a conventional negative electrode active material. The COFs are crystalline porous organic polymers (imine type covalent organic framework polymers and / or borate type covalent organic framework polymers) formed by ordered connection through strong covalent bonds, have periodic pore structures, crystallinity and easy modification characteristics of functional groups, are not easily attacked by chemical reagents, are not easily dissociated at high temperatures, are not soluble, have high chemical stability and thermal stability, and have high thermal stability and electrical insulation (not allowing electrons to pass in a resting unused state) of the covalent organic framework of the COFs, which can block the reduction reaction between electrolyte molecules and graphite while not reacting with the negative electrode, and maintain long-term structural stability. In the cycle process of charging and discharging, the polar functional groups in the periodic pores of the covalent organic framework polymer material of the coating layer have strong affinity with lithium ions, can adsorb ions, can accelerate ion desolvation and conduction rate, and thus accelerate electrode reaction kinetics and improve battery rate performance.

[0007] In an embodiment, the covalent organic framework polymer is a two-dimensional covalent organic framework polymer, and the pore diameter of the covalent organic framework polymer is 2-5 nm, preferably 2.6-4.5 nm, which is beneficial to the ordered conduction performance of ions and improves ion conductivity.

[0008] In an embodiment, the imine type covalent organic framework polymer comprises aromatic imine structural units, and the borate type covalent organic framework polymer comprises aromatic borate structural units. The aromatic imine structural units are derived from the reaction product of an amino aromatic hydrocarbon monomer and an aldehyde aromatic hydrocarbon monomer, and the aromatic borate structural units are derived from the reaction product of a borate aromatic hydrocarbon monomer and a hydroxyl aromatic hydrocarbon monomer.

[0009] In an embodiment, the amino aromatic hydrocarbon monomer comprises one or more of the following compounds A-1-A-5:

[0010] The aldehyde aromatic hydrocarbon monomer comprises one or more of the following compounds B-1-B-5:

[0011] The borate aromatic hydrocarbon monomer comprises one or more of the following compounds C-1-C-5:

[0012] The hydroxyl aromatic hydrocarbon monomer comprises one or more of the following compounds D-1-D-4:

[0013] In one embodiment, the molar ratio of the moieties derived from the amino aromatic monomer to the moieties derived from the aldehyde aromatic monomer in the imine type covalent organic framework polymer is 1:0.8-2.0, preferably 1:0.9-1.6. In the borate type covalent organic framework polymer, the molar ratio of the moieties derived from the boronic acid aromatic monomer to the moieties derived from the hydroxyl aromatic monomer is 1:0.8-2.0, preferably 1:0.9-1.6. The molar ratio of the moieties derived from the two monomers in the polymer within the range of the present embodiment, especially within the preferred range, is more advantageous to improve the high-temperature storage performance and cycle stability of the battery.

[0014] In one embodiment, the negative electrode active material comprises one or more of carbon materials and silicon-oxygen materials. Optionally, the carbon material comprises one or more of graphite, hard carbon and silicon-carbon. Preferably, the negative electrode active material comprises one or more of graphite, silicon-carbon and silicon-oxygen. Optionally, the particle size of the negative electrode active material is 0.1-10 μm, preferably 0.2-8 μm.

[0015] In one embodiment, the particle size of the negative electrode material is 0.1-10 μm, preferably 0.2-8 μm. Optionally, the thickness of the coating layer is 2-10 nm, preferably 2.5-8 nm.

[0016] The second aspect of the present disclosure provides a method for preparing a negative electrode material, comprising the following steps: contacting the negative electrode active material, the first monomer, the second monomer and the solvent to perform a polycondensation reaction; The first monomer and the second monomer are polycondensed to form a covalent organic framework polymer, which comprises an imine type covalent organic framework polymer and / or a borate type covalent organic framework polymer.

[0017] The present disclosure provides a method for preparing a negative electrode material, so that the polycondensation reaction of the first monomer and the second monomer can form a high-molecular mesh structure (such as an imine type covalent organic framework polymer and / or a borate type covalent organic framework polymer) on the surface of the negative electrode active material, which has a periodic pore structure, crystallinity and easy modification characteristics of functional groups, is formed by a strong covalent bond and is not easy to be attacked by chemical reagents, is not easy to be dissociated at high temperature, is not soluble and has high chemical stability and thermal stability; and the preparation of the coating layer is controllable and uniform in coating and distribution on the surface of the negative electrode active material; the polar functional groups around the pores can interact with lithium ions to help the desolvation of lithium ions and accelerate the ion difference conduction.

[0018] In an embodiment, the covalent organic framework polymer is an imine type covalent organic framework polymer, the first monomer comprises an amino aromatic hydrocarbon monomer, and the second monomer comprises an aldehyde group aromatic hydrocarbon monomer; or, the covalent organic framework polymer is a borate type covalent organic framework polymer, the first monomer comprises a borate group aromatic hydrocarbon monomer, and the second monomer comprises a hydroxyl group aromatic hydrocarbon monomer.

[0019] In an embodiment, the amino aromatic hydrocarbon monomer comprises one or more of the following compounds A-1~A-5:

[0020] The aldehyde group aromatic hydrocarbon monomer comprises one or more of the following compounds B-1~B-5:

[0021] The borate group aromatic hydrocarbon monomer comprises one or more of the following compounds C-1~C-5:

[0022] The hydroxyl group aromatic hydrocarbon monomer comprises one or more of the following compounds D-1~D-4:

[0023] The covalent organic framework polymer obtained by the polycondensation reaction of the first monomer and the second monomer provided in the embodiment can have better performance, so as to improve the high-temperature storage performance and cycle stability of the battery.

[0024] In an embodiment, the negative electrode active material comprises one or more of carbon materials and silicon-oxygen materials; In an embodiment, the carbon material comprises one or more of graphite, hard carbon and silicon-carbon; In an embodiment, the negative electrode active material comprises one or more of graphite, silicon-carbon and silicon-oxygen; In an embodiment, the solvent comprises one or more of dioxane, mesitylene, 1,2-dichlorobenzene, 1-butanol and water; preferably comprises one or more of dioxane, mesitylene and water; the use of the solvent types in the embodiment can make the covalent organic framework have better crystallinity and more regular pore arrangement.

[0025] In an embodiment, the weight ratio of the first monomer to the second monomer is 0.1-10:1, preferably 0.2-8:1, and the first monomer and the second monomer are added according to the molar ratio or the weight ratio in the embodiment, especially according to the preferred weight ratio, so that the prepared covalent organic framework has better crystallinity. In an embodiment, the weight ratio of the total weight of the first monomer and the second monomer to the weight of the negative active material is 0.001-0.12:1, preferably 0.005-0.1:1, and the two monomers and the negative active material are added according to the weight ratio in the embodiment, especially according to the preferred weight ratio, so that the covalent organic framework has better crystallinity and coating effect. In an embodiment, the amount of the negative active material is 0.5-5 kg, preferably 0.6-3 kg, relative to 1 L of the solvent, so that the coating is more uniform and the thickness is controllable.

[0026] In an embodiment, the method further comprises adding a catalyst to improve the effect of the polycondensation reaction. In an embodiment, the catalyst comprises one or more of acetic acid, hydrochloric acid, malonic acid, succinic acid, and maleic acid; optionally, the concentration of the catalyst is 0.01-1 M, preferably 0.02-0.8 M. In a preferred embodiment, the weight ratio of the catalyst to the total weight of the first monomer and the second monomer is 0.001-0.1:1, preferably 0.005-0.08:1.

[0027] In an embodiment, the conditions of the polycondensation reaction include a reaction temperature of 90-150°C and a reaction time of 12-72 h; preferably, the reaction temperature is 100-140°C and the reaction time is 24-48 h; under the mild conditions, a coating layer of COFs can be formed on the surface of the negative active material, and according to the process conditions in the embodiment, especially according to the preferred process conditions, the polycondensation reaction can have the effects of controllable coating thickness and higher coating rate. In an embodiment, the method further comprises washing and drying the product obtained by the polycondensation reaction; optionally, the conditions of the drying treatment include a drying temperature of 45-90°C and a drying time of 2-24 h.

[0028] The third aspect of the present disclosure provides a negative material prepared by the method according to the second aspect of the present disclosure.

[0029] The fourth aspect of the present disclosure provides a negative electrode comprising the negative material according to the first aspect or the third aspect of the present disclosure.

[0030] The fifth aspect of the present disclosure provides a lithium ion battery comprising the negative electrode according to the fourth aspect of the present disclosure.

[0031] The sixth aspect of the present disclosure provides a power utilization device comprising the lithium ion battery of the fifth aspect of the present disclosure.

[0032] Other features and advantages of the present disclosure will be described in detail in the following detailed description. BRIEF DESCRIPTION OF DRAWINGS

[0033] The accompanying drawings are included to provide a further understanding of the present disclosure and constitute a part of the specification, which together with the detailed description, serve to explain the present disclosure. In the drawings: Figure 1 is a structural schematic diagram of the covalent organic framework polymer provided by the present disclosure. DETAILED DESCRIPTION

[0034] The following detailed description of the present disclosure is described in detail. It should be understood that the specific implementation described herein is only used to illustrate and explain the present disclosure, and is not used to limit the present disclosure.

[0035] At present, a nitrogen-containing organic metal framework compound containing cobalt can be constructed on the surface of graphite to obtain a graphite material coated with a nitrogen-containing organic metal framework compound containing cobalt; the graphite material coated with the nitrogen-containing organic metal framework compound containing cobalt is subjected to pyrolysis treatment (650-950℃) to obtain the graphite negative electrode material for low temperature after coating. The graphite material is subjected to pyrolysis, which can fully carbonize the organic metal compound on the surface of the graphite to form porous carbon, and generate cobalt element at the same time. However, the present disclosure discloses that in the above process, the metal organic framework is carbonized, and the periodic and ordered porous structure is destroyed by high temperature, the pores are non-uniform and non-periodic, the channel is disordered in the process of lithium ion shuttling through the interface, and the tortuosity is high, which is not conducive to high-rate charging and discharging; and although the graphitized carbon and cobalt element after carbonization improve the electronic conductivity of the surface of the graphite negative electrode, the surface conductivity of the graphite is increased, the electronic insulation of the electrolyte cannot be fully achieved, and under high temperature, the potential difference between the electrolyte and the graphite and the existence of the cobalt element further catalyze the exchange of electrons with the electrolyte, and a reduction reaction continuously occurs, which causes the high-temperature storage performance of the graphite to be further deteriorated, and the effect of electronic insulation cannot be achieved.

[0036] The first aspect of the present disclosure provides a negative electrode material, comprising a negative electrode active material and a coating layer coated on the surface of the negative electrode active material; the coating layer comprises a covalent organic framework polymer. The covalent organic framework polymer comprises an imine type covalent organic framework polymer and / or a borate type covalent organic framework polymer.

[0037] The negative electrode material provided by the present disclosure is coated with a covalent organic framework polymer (COFs) on the surface of a traditional negative electrode active material, the COFs include a crystalline porous organic polymer (such as an imine type covalent organic framework polymer and / or a borate type covalent organic framework polymer) formed by ordered connection through strong covalent bonds, has a periodic pore structure, crystallinity, and easy modification characteristics of functional groups, is not easily attacked by chemical reagents, is not easily dissociated by high temperature, is not soluble, has high chemical stability and thermal stability; when the negative electrode is in a high lithium intercalation state and under high temperature conditions (for example, above 45℃), the covalent organic framework of the COFs has high thermal stability and electrical insulation (does not allow electrons to pass in a resting and unused state), can block the reduction reaction between electrolyte molecules and graphite, and at the same time will not react with the negative electrode, maintaining long-term structural stability. At the same time, in the cycle process of charging and discharging, the polar functional groups in the periodic pores of the covalent organic framework polymer material of the coating layer have strong affinity with lithium ions, can adsorb ions, can accelerate ion desolvation and conduction rate, and thus accelerate electrode reaction kinetics and improve battery rate performance.

[0038] In the present disclosure, the "covalent organic framework polymer (COFs)" refers to an organic polymer with a porous crystal structure and strong covalent bond connection, and the organic building units are connected together through covalent bonds (such as B-O, C-N, C-C, C-Si, etc.) to form a porous framework with a periodic structure.

[0039] In the present disclosure, the "imine type covalent organic framework polymer" refers to a covalent organic framework polymer in which the covalent bond that constructs the periodic structure includes a -N=C- bond; and the "borate type covalent organic framework polymer" refers to a covalent organic framework polymer in which the covalent bond that constructs the periodic structure includes a bond.

[0040] The structure schematic diagram of the negative electrode material provided by the present disclosure is shown in Figure 1 As can be seen from the structure schematic diagram, the negative electrode material has a coating layer on the surface of the negative electrode active material; the coating layer includes a covalent organic framework polymer (COFs) with an ordered grid structure; and the COFs has a periodic pore structure.

[0041] In an embodiment, the covalent organic framework polymer is a two-dimensional covalent organic framework polymer, and the pore channel diameter of the covalent organic framework polymer is 2-5 nm, preferably 2.6-4.5 nm, which is conducive to the ordered conduction performance of ions and improves the ion conductivity.

[0042] In the present disclosure, the "two-dimensional covalent organic framework polymer" refers to a layered structure formed by planar monomers through side-to-side or face-to-face π-π stacking, and the layers are stacked through weak forces (such as van der Waals forces, hydrogen bonds), and the pore channel extends along the layer plane.

[0043] In a preferred embodiment, the imine type covalent organic framework polymer comprises aromatic imine structural units, and the borate type covalent organic framework polymer comprises aromatic borate structural units. The aromatic imine structural units are derived from the reaction product of an amino aromatic hydrocarbon monomer and an aldehyde group aromatic hydrocarbon monomer; and the aromatic borate structural units are derived from the reaction product of a boronic acid group aromatic hydrocarbon monomer and a hydroxyl group aromatic hydrocarbon monomer.

[0044] In a specific embodiment, the number of amino groups in the amino aromatic hydrocarbon monomer is ≥ 2; the number of aldehyde groups in the aldehyde group aromatic hydrocarbon monomer is ≥ 3; the number of boronic acid groups in the boronic acid group aromatic hydrocarbon monomer is ≥ 2; and the number of hydroxyl groups in the hydroxyl group aromatic hydrocarbon monomer is ≥ 6.

[0045] In a preferred embodiment, the amino aromatic hydrocarbon monomer comprises one or more of the following compounds A-1 to A-5:

[0046] The aldehyde group aromatic hydrocarbon monomer comprises one or more of the following compounds B-1 to B-5:

[0047] The boronic acid group aromatic hydrocarbon monomer comprises one or more of the following compounds C-1 to C-5:

[0048] The hydroxyl group aromatic hydrocarbon monomer comprises one or more of the following compounds D-1 to D-4:

[0049] In a preferred embodiment, the amino aromatic hydrocarbon monomer comprises one or more of the following compounds A-1 (Pa-1), A-3 (TAPA), A-4 (TAPB) and A-5 (TAPT); the aldehyde group aromatic hydrocarbon monomer comprises one or more of the following compounds B-2 (TFPA), B-3 (TFPT), B-4 (2-CHO-TAT) and B-5 (TPT-CHO); the boronic acid group aromatic hydrocarbon monomer comprises one or more of the following compounds C-3 (BTPB), C-4 (TPEBA) and C-5 (TBPP); and the hydroxyl group aromatic hydrocarbon monomer comprises one or more of the following compounds D-1 (HPCT), D-3 (HHTP) and D-4 (MPc[OH]8). Covalent organic framework polymers composed of monomers derived from the present embodiment can have better performance to improve the high-temperature storage performance and cycle stability of the battery.

[0050] In a preferred embodiment, the molar ratio of the moieties derived from the amino aromatic hydrocarbon monomer to the moieties derived from the aldehyde aromatic hydrocarbon monomer in the imine type covalent organic framework polymer is 1:0.8-2.0, preferably 1:0.9-1.6; or, In the borate type covalent organic framework polymer, the molar ratio of the moieties derived from the boronic acid aromatic hydrocarbon monomer to the moieties derived from the hydroxyl aromatic hydrocarbon monomer is 1:0.8-2.0, preferably 1:0.9-1.6; the molar ratio of the moieties derived from the two monomers in the polymer is within the range of the present embodiment, and more preferably within the preferred range, which is more conducive to improving the high-temperature storage performance and cycle stability of the battery.

[0051] In a preferred embodiment, the weight ratio of the negative electrode active material to the coating layer in the negative electrode material is 1:0.005-0.02, preferably 1:0.008-0.015. According to the weight ratio in the present embodiment, and more preferably according to the preferred weight ratio, the negative electrode active material and the coating layer can be set to achieve a more optimal synergistic application effect, thereby improving the high-temperature storage performance and cycle stability of the negative electrode material.

[0052] In a specific embodiment, the negative electrode active material comprises one or more of carbon materials and silicon-oxygen materials; In a specific embodiment, the carbon material comprises one or more of graphite, hard carbon, and silicon-carbon; In a preferred embodiment, the negative electrode active material comprises one or more of graphite, silicon-carbon, and silicon-oxygen; In an embodiment, the particle size of the negative electrode active material is 0.1-10 μm, preferably 0.2-8 μm.

[0053] In an embodiment, the particle size of the negative electrode material is 0.1-10 μm, preferably 0.2-8 μm.

[0054] In a specific embodiment, the thickness of the coating layer is 2-10 nm, preferably 2.5-8 nm.

[0055] The second aspect of the present disclosure provides a method for preparing a negative electrode material, comprising the following steps: contacting the negative electrode active material, the first monomer, the second monomer, and the solvent to perform a polycondensation reaction; The first monomer and the second monomer are polycondensed to form a covalent organic framework polymer, which comprises an imine type covalent organic framework polymer and / or a borate type covalent organic framework polymer.

[0056] The present disclosure provides a method for preparing a negative electrode material, so that the polycondensation reaction of the first monomer and the second monomer can form a high molecular reticular structure (for example, an imine type covalent organic framework polymer and / or a borate type covalent organic framework polymer) on the surface of the negative electrode active material, which has a periodic pore structure, crystallinity, and a functional group easy modification characteristic, is connected by a strong covalent bond, is not easy to be attacked by a chemical reagent, is not easy to be dissociated at high temperature, is not soluble, has high chemical stability and thermal stability, and the preparation of the coating layer is controllable, the coating and distribution on the surface of the negative electrode active material are uniform, the polar functional groups around the pore can have a strong interaction with lithium ions, help the desolvation of lithium ions, and accelerate the ion difference conduction.

[0057] In an embodiment, the covalent organic framework polymer is an imine type covalent organic framework polymer, the first monomer includes an amino aromatic hydrocarbon type monomer, and the second monomer includes an aldehyde group aromatic hydrocarbon type monomer; or, The covalent organic framework polymer is a borate type covalent organic framework polymer, the first monomer includes a boronic acid group aromatic hydrocarbon type monomer, and the second monomer includes a hydroxyl group aromatic hydrocarbon type monomer.

[0058] In a preferred embodiment, the number of amino groups in the amino aromatic hydrocarbon type monomer is greater than or equal to 2, the number of boronic acid groups in the boronic acid group aromatic hydrocarbon type monomer is greater than or equal to 2, the number of aldehyde groups in the aldehyde group aromatic hydrocarbon type monomer is greater than or equal to 3, and the number of hydroxyl groups in the hydroxyl group aromatic hydrocarbon type monomer is greater than or equal to 6.

[0059] In a preferred embodiment, the amino aromatic hydrocarbon type monomer includes one or more of the following compounds A-1 to A-5:

[0060] The aldehyde group aromatic hydrocarbon type monomer includes one or more of the following compounds B-1 to B-5:

[0061] The boronic acid group aromatic hydrocarbon type monomer includes one or more of the following compounds C-1 to C-5:

[0062] The hydroxyl group aromatic hydrocarbon type monomer includes one or more of the following compounds D-1 to D-4:

[0063] The polycondensation reaction of the first monomer and the second monomer provided in the present embodiment can have better performance, so as to improve the high temperature storage performance and cycle stability of the battery.

[0064] In a preferred embodiment, the amino aromatic monomer includes one or more of compounds A-1 (Pa-1), A-3 (TAPA), A-4 (TAPB) and A-5 (TAPT); the aldehyde aromatic monomer includes one or more of compounds B-2 (TFPA), B-3 (TFPT), B-4 (2-CHO-TAT) and B-5 (TPT-CHO); the boronic acid aromatic monomer includes compounds C-3 (BTPB), C-4 (TPEBA) and C-5 (TBPP); and the hydroxyl aromatic monomer includes one or more of compounds D-1 (HPCT), D-3 (HHTP) and D-4 (MPc[OH]8). The use of the types of first monomer and second monomer in this embodiment is more conducive to the formation of a coating layer with better performance, thereby improving the performance of the lithium ion battery.

[0065] In an embodiment, the negative active material includes one or more of carbon material and silicon-oxygen material. In an embodiment, the carbon material includes one or more of graphite, hard carbon and silicon-carbon. In an embodiment, the negative active material includes one or more of graphite, silicon-carbon and silicon-oxygen. The present disclosure can use the types of conventional negative active materials.

[0066] In an embodiment, the solvent includes one or more of dioxane, mesitylene, 1,2-dichlorobenzene, 1-butanol and water; preferably, the solvent includes one or more of dioxane, mesitylene and water. The use of the types of solvent in this embodiment can make the covalent organic framework have better crystallinity and more regular pore arrangement.

[0067] In an embodiment, the weight ratio of the first monomer to the second monomer is 0.1-10:1, preferably 0.2-8:1. The use of the molar ratio or the weight ratio of the first monomer and the second monomer in this embodiment, especially the preferred weight ratio, can make the prepared covalent organic framework have better crystallinity.

[0068] In an embodiment, the total weight of the first monomer and the second monomer to the weight of the negative active material is 0.001-0.12:1, preferably 0.005-0.1:1. The use of the weight ratio of the two monomers and the negative active material in this embodiment, especially the preferred weight ratio, can make the covalent organic framework have better crystallinity and coating effect.

[0069] In an embodiment, the amount of the negative active material is 0.5-5 kg, preferably 0.6-3 kg, relative to 1 L of the solvent. This can have the effect of more uniform coating and controllable thickness.

[0070] In a preferred embodiment, the method further comprises adding a catalyst to improve the effect of the polycondensation reaction.

[0071] In a specific embodiment, the catalyst comprises one or more of acetic acid, hydrochloric acid, malonic acid, succinic acid and maleic acid; optionally, the concentration of the catalyst is 0.01-1 M, preferably 0.02-0.8 M. In a preferred embodiment, the ratio of the catalyst to the total weight of the first and second monomers is 0.001-0.1:1, preferably 0.005-0.08:1.

[0072] In an embodiment, the conditions of the polycondensation reaction comprise a reaction temperature of 90-150°C and a reaction time of 12-72 h; preferably, the reaction temperature is 100-140°C and the reaction time is 24-48 h; according to the process conditions in this embodiment, and especially according to the preferred process conditions, the polycondensation reaction can have the effect of forming a COF coating layer on the surface of the negative active material under mild conditions, and the coating thickness is controllable and the coating rate is higher.

[0073] In a specific embodiment, the method further comprises washing and drying the product obtained by the polycondensation reaction; optionally, the drying conditions comprise a drying temperature of 45-90°C and a drying time of 2-24 h.

[0074] The third aspect of the present disclosure provides a negative active material prepared by the method according to the second aspect of the present disclosure.

[0075] The fourth aspect of the present disclosure provides a negative electrode comprising the negative active material according to the third aspect of the present disclosure.

[0076] In a specific embodiment, the negative electrode comprises a negative electrode current collector and a negative electrode coating layer; the negative electrode coating layer comprises the negative active material, an optional negative electrode conductive agent and an optional negative electrode binder; wherein the material of the negative electrode current collector comprises but is not limited to copper foil, stainless steel, etc.; the negative electrode conductive agent comprises but is not limited to Super P, graphene, carbon nanotube, etc.; the negative electrode binder comprises but is not limited to sodium hydroxymethyl cellulose, butadiene rubber, etc.; and they can be purchased through conventional commercial channels or prepared by known methods.

[0077] In a preferred embodiment, the content of the negative active material is 90-98% by weight, preferably 92-97.5% by weight, based on the total weight (dry basis) of the negative electrode coating layer; the content of the negative electrode conductive agent is 1-4% by weight, preferably 1.2-3.6% by weight; and the content of the negative electrode binder is 0.5-4% by weight, preferably 0.6-3.5% by weight.

[0078] In one embodiment, the thickness of the negative electrode coating is 5-100 μm, preferably 8-60 μm.

[0079] In one embodiment, the negative electrode is prepared by a conventional process of slurry-making, coating, rolling and cutting.

[0080] In a fifth aspect, the present disclosure provides a lithium ion battery comprising the negative electrode of the fourth aspect.

[0081] In one embodiment, the lithium ion battery further comprises a positive electrode, an electrolyte and a separator.

[0082] In one embodiment, the positive electrode comprises a positive electrode current collector and a positive electrode coating; the positive electrode coating comprises a positive electrode material, an optional positive electrode conductive agent and an optional positive electrode binder; wherein the material of the positive electrode current collector comprises but is not limited to aluminum foil, stainless steel, etc.; the positive electrode material comprises but is not limited to lithium iron phosphate, lithium nickel cobalt manganese phosphate, lithium manganese iron phosphate, lithium-rich, etc.; the positive electrode conductive agent comprises but is not limited to Super P, graphene, carbon nanotube, etc.; the positive electrode binder comprises but is not limited to polytetrafluoroethylene, polyvinylidene fluoride, etc.; which can be purchased through conventional commercial channels or prepared by known methods.

[0083] In one preferred embodiment, the content of the positive electrode material is 90-98 wt%, preferably 92-97.5 wt%, based on the total weight (dry basis) of the positive electrode coating; the content of the positive electrode conductive agent is 1-4 wt%, preferably 1.2-3.6 wt%; the content of the positive electrode binder is 0.5-4 wt%, preferably 0.6-3.5 wt%.

[0084] In one embodiment, the thickness of the positive electrode coating is 5-100 μm, preferably 8-80 μm.

[0085] In one embodiment, the positive electrode is prepared by a conventional process of slurry-making, coating, rolling and cutting.

[0086] In one embodiment, the electrolyte comprises but is not limited to carbonate, ether, nitrile electrolyte; the electrolyte concentration is 0.6-1.5 mol / L, preferably 0.8-1.2 mol / L; the material of the separator comprises but is not limited to polyethylene, polypropylene, etc.

[0087] The battery of the present disclosure can be prepared and assembled by conventional methods. Specifically, the battery of the present disclosure can include a battery cell form, a battery module form, and a battery pack form. The battery cell includes a shell, an electrode core, and an electrolyte, the shell is formed with a receiving space, the electrode core and the electrolyte are arranged in the receiving space, the electrode core can include a positive electrode, a negative electrode, and a separator, and the positive electrode, the negative electrode, and the separator are arranged in a laminated or wound manner. In some embodiments, the battery cell can be assembled into a battery module, and the number of battery cells contained in the battery module can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery module. In some embodiments, the battery module can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery pack. The positive electrode, the electrolyte, and the separator of the battery of the present disclosure can be conventional types in the art.

[0088] The sixth aspect of the present disclosure provides a power consumption device comprising the lithium ion battery of the fifth aspect of the present disclosure.

[0089] In the present disclosure, the power consumption device can be a vehicle, a mobile phone, a portable device, a notebook computer, a ship, a spacecraft, and an electric toy, etc. The vehicle can be a fuel automobile, a gas automobile, or a new energy automobile, and the new energy automobile can be a pure electric automobile, a hybrid electric automobile, or an extended range automobile, etc. The spacecraft includes an airplane, a rocket, a space shuttle, and a spacecraft, etc. The electric toy includes a fixed or mobile electric toy, for example, a game console, an electric automobile toy, an electric ship toy, and an electric airplane toy, etc.

[0090] In a preferred embodiment, the power consumption device includes but is not limited to a vehicle, a mobile phone, a portable device, a notebook computer, etc.

[0091] The present disclosure is further illustrated in detail by the following examples. The raw materials used in the examples can be obtained by commercial channels.

[0092] In the negative electrode material obtained in the following examples and comparative examples: The molar ratio of the imine type covalent organic framework polymer derived from the amino aromatic hydrocarbon monomer part: the aldehyde group aromatic hydrocarbon monomer part, or the molar ratio of the borate type covalent organic framework polymer derived from the boronic acid group aromatic hydrocarbon monomer part: the hydroxyl group aromatic hydrocarbon monomer part is calculated by weight and reaction degree and the relative molecular mass of the monomer; the COFs pore channel diameter is obtained by BET specific surface area test; the carbon material particle size is obtained by field emission electron microscope test; and the coating layer thickness is obtained by high-magnification transmission electron microscope test.

[0093] Example 1 This example is used to illustrate the preparation method of the negative electrode material, which includes the following steps: (1) TAPT (compound A-5, first monomer), TFPT (compound C-3, second monomer), dioxane and 1,3,5-trimethylbenzene (solvent, volume ratio 2:1), graphite powder (carbon material, particle size 2 μm) are loaded into a reaction kettle; wherein the weight ratio of the first monomer to the second monomer is 1.2:1, the weight ratio of the total weight of the first monomer and the second monomer to the carbon material is 0.1:1, and the amount of the carbon material is 2 kg relative to 1 L of the solvent; (2) After ultrasonic treatment for 30 min, 1.5 M acetic acid solution (catalyst, the weight ratio of the catalyst to the total weight of the first monomer and the second monomer is 0.01:1) is added; (3) The reaction is continuously stirred at 120°C for 48 h (polycondensation reaction); (4) After the reaction is completed, the powder product is taken out and washed with acetone and deionized water for 3 times under vacuum filtration; (5) The product is dried in a 60°C air oven for 6 h (drying treatment).

[0094] The structures of the first monomer, the second monomer and the obtained COFs material in this example are shown below.

[0095]

[0096] Comparative Example 1 In this comparative example, a commercial graphite material is directly used as the negative electrode material without covalent organic framework polymer coating.

[0097] Example 2 This example refers to the preparation method in Example 1, and the difference from Example 1 is that: The structures of the first monomer, the second monomer and the obtained COFs material are shown below.

[0098]

[0099] Example 3 This example refers to the preparation method in Example 1, and the difference from Example 1 is that: The weight ratio of the first monomer to the second monomer is 0.15:1; the rest of the process is the same as Example 1.

[0100] Example 4 This example refers to the preparation method in Example 1, and the difference from Example 1 is that: The weight ratio of the first monomer to the second monomer is 15:1; the rest of the process is the same as Example 1.

[0101] Example 5 This example refers to the preparation method in Example 1, which is different from Example 1 in that: The total weight of the first monomer and the second monomer: the weight ratio of the carbon material is 0.12:1; the rest of the process is the same as Example 1.

[0102] Example 6 This example refers to the preparation method in Example 1, which is different from Example 1 in that: The total weight of the first monomer and the second monomer: the weight ratio of the carbon material is 5:1; the rest of the process is the same as Example 1.

[0103] Example 7 This example refers to the preparation method in Example 1, which is different from Example 1 in that: The amount of the carbon material is 5 kg relative to 1 L of the solvent; the rest of the process is the same as Example 1.

[0104] Example 8 This example refers to the preparation method in Example 1, which is different from Example 1 in that: The conditions of the polycondensation reaction include: the reaction temperature is 90°C, and the reaction time is 72 h; the rest of the process is the same as Example 1.

[0105] Table 1

[0106] In Table 1, "molar ratio of structural units": in imine-type covalent organic framework polymers (such as Examples 1, 3-8), the molar ratio of structural units refers to the molar ratio of the part derived from the amino aromatic hydrocarbon monomer: the part derived from the aldehyde group aromatic hydrocarbon monomer; in borate-type covalent organic framework polymers (such as Example 2), the molar ratio of structural units refers to the molar ratio of the part derived from the boronic acid group aromatic hydrocarbon monomer: the part derived from the hydroxyl group aromatic hydrocarbon monomer.

[0107] Battery test example This test example is used to illustrate the application effect of the negative electrode materials obtained in the above examples and comparative examples in lithium ion batteries.

[0108] Taking a soft package battery as an example, the negative electrode material obtained in the above examples and comparative examples and the lithium iron phosphate positive electrode material are subjected to the processes of slurry preparation-coating-rolling- cutting- laminating-micro short circuit test-spot welding tab-aluminum plastic sealing-liquid injection-vacuum standing-formation-aging-final sealing-performance test, to obtain a soft package battery with a capacity of 2 Ah.

[0109] The preparation process of the negative electrode includes the following steps: the formula is prepared from the following raw materials by weight: 97 parts of natural graphite, 1.6 parts of sodium hydroxymethyl cellulose and butadiene rubber in total, and 1.4 parts of Super P. The solid content of the solution prepared from the above formula is 39-41% by weight, the solvent is deionized water, and the solid content refers to the weight percentage of solute in the solution prepared from the above formula. The coating process includes the following steps: (1) batching, the weight percentage of each component of the above formula is batched; (2) emulsifier stirring, the slurry prepared by the above configuration is placed in the emulsifier for stirring, and after stirring is completed, it is placed; (3) setting the coating speed and oven temperature; (4) roller; (5) coating. The preparation process of the positive electrode includes the following steps: the formula is prepared from the following raw materials by weight: 96.5 parts of lithium iron phosphate, 2.0 parts of polytetrafluoroethylene, and 1.5 parts of Super P. The solid content of the solution prepared from the above formula is 45-55% by weight, the solvent is nitrogen methyl pyrrolidone, and the solid content refers to the weight percentage of solute in the solution prepared from the above formula. The coating process includes the following steps: (1) batching, the weight percentage of each component of the above formula is batched; (2) emulsifier stirring, the slurry prepared by the above configuration is placed in the emulsifier for stirring, and after stirring is completed, it is placed; (3) setting the coating speed and oven temperature; (4) roller; (5) coating. The electrolyte uses 1M LiPF6, the solvent is DEC:EC=1:1Vol%, and the separator uses a polypropylene separator with a thickness of 12μm.

[0110] The assembled soft package battery is tested for performance according to the following method: 1) 25℃ 1C / 1C cycle + 45℃ 100% SOC storage: the battery is first cycled at 25℃ 1C charge / 1C discharge for 200 cycles, then the battery is fully charged and placed in a 45℃ environment for 3 days of storage, then the above cycle and storage are repeated until the battery capacity decays to 80% of the initial capacity.

[0111] 2) 60℃ 100% SOC storage: the battery is stored in a 45℃ environment until the battery capacity decays to 80% of the initial capacity, and the corresponding storage days are recorded.

[0112] 3) 6C charge capacity retention rate / %: the battery is fully charged at 25℃ 0.33C, then discharged at 0.33C, then fully charged at 6C, and the ratio of 6C full charge capacity to 0.33C charge full charge capacity (capacity retention rate) is recorded.

[0113] The test results are listed in Table 2 below.

[0114] Table 2

[0115] According to the data in Table 2, it can be seen that: Compared with the commercialized graphite material of Comparative Example 1, the negative electrode material provided in Examples 1-8 has more cycles required to decay to 80% SOH, longer storage days at 100% SOC at 60°C, and higher 6C charge capacity retention, indicating that the battery performance of the negative electrode material provided in the present disclosure with a COFs coating layer is more excellent; Comparing Example 3 with Example 4, the weight ratio of the first monomer to the second monomer in the preparation of the negative electrode material in Example 3 is within the optimization range provided in the present disclosure, and the negative electrode material obtained in Example 3 has more cycles required to decay to 80% SOH, longer storage days at 100% SOC at 60°C, and higher 6C charge capacity retention, indicating that the performance of the negative electrode material is more excellent; Comparing Example 1 with Example 3, the weight ratio of the first monomer to the second monomer in the preparation of the negative electrode material in Example 1 is within the further preferred range provided in the present disclosure, and the negative electrode material obtained in Example 1 has more cycles required to decay to 80% SOH, longer storage days at 100% SOC at 60°C, and higher 6C charge capacity retention, indicating that the performance of the negative electrode material is more excellent; Comparing Example 5 with Example 6, the weight ratio of the total weight of the first monomer and the second monomer to the carbon material in the preparation of the negative electrode material in Example 5 is within the optimization range provided in the present disclosure, and the negative electrode material obtained in Example 5 has more cycles required to decay to 80% SOH, longer storage days at 100% SOC at 60°C, and higher 6C charge capacity retention, indicating that the performance of the negative electrode material is more excellent; Comparing Example 1 with Example 5, the weight ratio of the total weight of the first monomer and the second monomer to the carbon material in the preparation of the negative electrode material in Example 1 is within the further preferred range provided in the present disclosure, and the negative electrode material obtained in Example 1 has more cycles required to decay to 80% SOH, longer storage days at 100% SOC at 60°C, and higher 6C charge capacity retention, indicating that the performance of the negative electrode material is more excellent; Comparing Example 1 with Example 7, the amount of the carbon material relative to 1 L of solvent in the preparation of the negative electrode material in Example 1 is within the preferred range, and the negative electrode material obtained in Example 1 has more cycles required to decay to 80% SOH, longer storage days at 100% SOC at 60°C, and higher 6C charge capacity retention, indicating that the performance of the negative electrode material is more excellent; Comparing Example 1 with Example 8, the polycondensation reaction conditions in Example 1 are within the preferred range, and the negative electrode material obtained in Example 1 has more cycles required to decay to 80% SOH, longer storage days at 100% SOC at 60°C, and higher 6C charge capacity retention, indicating that the performance of the negative electrode material is more excellent.

[0116] The preferred embodiments of the present disclosure are described in detail above, but the present disclosure is not limited to the specific details described in the above embodiments. Within the technical concept of the present disclosure, various simple modifications can be made to the technical solutions of the present disclosure, and these simple modifications all belong to the protection scope of the present disclosure.

[0117] In addition, it should be noted that each specific technical feature described in the above specific embodiments can be combined in any appropriate manner without contradiction. In order to avoid unnecessary repetition, various possible combinations are not described again in the present disclosure.

[0118] In addition, any combination of various different embodiments of the present disclosure can also be made, as long as it does not deviate from the idea of the present disclosure, and it should also be considered as disclosed by the present disclosure.

Claims

1. A negative electrode material, characterized in that The invention comprises a negative electrode active material and a coating layer coated on the surface of the negative electrode active material; the coating layer comprises a covalent organic framework polymer; The covalent organic framework polymer includes an imine-type covalent organic framework polymer and / or a borate-type covalent organic framework polymer.

2. The negative electrode material according to claim 1, characterized in that The covalent organic framework polymer is a two-dimensional covalent organic framework polymer, and the pore diameter of the covalent organic framework polymer is 2-5 nm, preferably 2.6-4.5 nm.

3. The negative electrode material according to claim 1, characterized in that The imine type covalent organic framework polymer includes an aromatic imine structural unit, and the borate type covalent organic framework polymer includes an aromatic borate structural unit; The aromatic imine structural unit is derived from the reaction product of an amino aromatic hydrocarbon monomer and an aldehyde aromatic hydrocarbon monomer; the aromatic borate structural unit is derived from the reaction product of a boronic acid aromatic hydrocarbon monomer and a hydroxy aromatic hydrocarbon monomer.

4. The negative electrode material according to claim 3, characterized in that The amino aromatic hydrocarbon monomers include one or more of the following compounds A-1 to A-5: The aldehyde aromatic hydrocarbon monomers include one or more of the following compounds B-1 to B-5: The boric acid aromatic hydrocarbon monomers include one or more of the following compounds C-1 to C-5: The hydroxy aromatic hydrocarbon monomer includes one or more of the following compounds D-1 to D-4: 。 5. The negative electrode material according to claim 3, characterized in that In the imine-type covalent organic framework polymer, the molar ratio of the portion derived from amino aromatic hydrocarbon monomers to the portion derived from aldehyde aromatic hydrocarbon monomers is 1:0.8-2.0, preferably 1:0.9-1.6; In the borate ester covalent organic framework polymer, the molar ratio of the portion derived from the boronic acid aromatic hydrocarbon monomer to the portion derived from the hydroxy aromatic hydrocarbon monomer is 1:0.8-2.0, preferably 1:0.9-1.

6.

6. The negative electrode material according to claim 1, characterized in that The negative electrode active material includes one or more of carbon materials and silicon-oxygen materials; Optionally, the carbon material includes one or more of graphite, hard carbon and silicon carbon; Preferably, the negative electrode active material includes one or more of graphite, silicon carbon and silicon oxide; Optionally, the particle size of the negative electrode active material is 0.1-10 μm, preferably 0.2-8 μm.

7. The negative electrode material according to claim 1, characterized in that The particles of the negative electrode material are 0.1-10 μm, preferably 0.2-8 μm; Optionally, the coating layer has a thickness of 2 to 10 nm, preferably 2.5 to 8 nm.

8. A method for preparing a negative electrode material, characterized in that: The following steps are involved: contacting the negative electrode active material, the first monomer, the second monomer and the solvent to carry out a condensation reaction; The first monomer and the second monomer are polycondensed to generate a covalent organic framework polymer, and the covalent organic framework polymer includes an imine-type covalent organic framework polymer and / or a borate-type covalent organic framework polymer.

9. The method according to claim 8, characterized in that The covalent organic framework polymer is an imine-type covalent organic framework polymer, the first monomer includes an amino aromatic hydrocarbon monomer, and the second monomer includes an aldehyde aromatic hydrocarbon monomer; or The covalent organic framework polymer is a borate ester covalent organic framework polymer, the first monomer includes a boronic acid aromatic hydrocarbon monomer, and the second monomer includes a hydroxy aromatic hydrocarbon monomer.

10. The method according to claim 9, characterized in that The amino aromatic hydrocarbon monomers include one or more of the following compounds A-1 to A-5: The aldehyde aromatic hydrocarbon monomers include one or more of the following compounds B-1 to B-5: The boric acid aromatic hydrocarbon monomers include one or more of the following compounds C-1 to C-5: The hydroxy aromatic hydrocarbon monomer includes one or more of the following compounds D-1 to D-4: 。 11. The method according to claim 8, characterized in that The negative electrode active material includes one or more of a carbon material and a silicon-oxygen material; optionally, the carbon material includes one or more of graphite, hard carbon and silicon-carbon; Optionally, the solvent includes one or more of dioxane, 1,3,5-trimethylbenzene, 1,2-dichlorobenzene, 1-butanol and water; preferably, the solvent includes one or more of dioxane, 1,3,5-trimethylbenzene and water.

12. The method according to claim 8, characterized in that The weight ratio of the first monomer to the second monomer is 0.1 to 10:1, preferably 0.2 to 8:1; Optionally, the weight ratio of the total weight of the first monomer and the second monomer to the negative electrode active material is 0.001 to 0.12:1, preferably 0.005 to 0.1:1; Optionally, relative to 1 L of the solvent, the amount of the negative electrode active material used is 0.5-5 kg, preferably 0.6-3 kg.

13. The method according to claim 8, characterized in that The method further comprises adding a catalyst; Optionally, the catalyst comprises one or more of acetic acid, hydrochloric acid, malonic acid, succinic acid and maleic acid; optionally, the concentration of the catalyst is 0.01 to 1 M, preferably 0.02 to 0.8 M; Preferably, the weight ratio of the catalyst to the total weight of the first monomer and the second monomer is 0.001-0.1:1, preferably 0.005-0.08:

1.

14. The method according to claim 8, characterized in that The conditions of the polycondensation reaction include: reaction temperature of 90-150°C, reaction time of 12-72h; preferably, reaction temperature of 100-140°C, reaction time of 24-48h; Optionally, the method further comprises: washing and drying the product obtained from the polycondensation reaction; optionally, the drying conditions comprise: a drying temperature of 45-90° C. and a drying time of 2-24 hours.

15. A negative electrode material prepared according to the method according to any one of claims 8 to 14.

16. A negative electrode, characterized in that The negative electrode material comprises the negative electrode material according to any one of claims 1 to 7 and 15.

17. A lithium ion battery, characterized in that: Comprising the negative electrode according to claim 16.

18. An electrical device, characterized in that: Including the lithium ion battery according to claim 17.

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