COF coated and modified positive electrode material precursor as well as preparation method and application thereof

Abstract

The invention relates to a COF coated and modified positive electrode material precursor and a preparation method and application thereof, the preparation method comprises the following steps: (1) mixing a first organic monomer, a second organic monomer, an organic solvent and an organic acid reagent to obtain a COF precursor solution; and (2) reacting a precursor material with the COF precursor solution, and then separating and drying to obtain the COF coated and modified positive electrode material precursor. According to the preparation method provided by the invention, in-situ growth of the COF is carried out on the precursor material, and close contact and uniform coating of a COF coating layer and the precursor material are realized by adopting the method, so that the interface stability and the ion / electron conduction capability of the positive electrode material prepared by taking the COF-coated positive electrode material precursor as a raw material are improved; further, the electrochemical performance of the positive electrode material is effectively improved.

Description

Technical Field

[0001] The present invention relates to the technical field of battery materials, and in particular to a COF-coated modified positive electrode material precursor, a preparation method thereof, and applications thereof. Background Art

[0002] Ternary cathode materials (such as NCM and NCA) are widely used in lithium-ion batteries due to their high energy density and good cycle performance. However, these materials suffer from structural instability, numerous interfacial side reactions, and short cycle life during charge and discharge.

[0003] To address the problems with the aforementioned ternary cathode materials, researchers have proposed a variety of surface modification methods, such as oxide coating and carbon coating. Prior art CN109713262A discloses a method for preparing a cobalt oxide-coated ternary cathode material, comprising placing a cobalt source and a high-nickel ternary cathode material in a container, stirring and mixing them at a speed of ≤700 rpm to obtain a corresponding mixed material; and subjecting the mixed material to a low-temperature solid-phase sintering treatment at 250°C to 550°C in an atmosphere of air or oxygen to obtain the corresponding cobalt oxide-coated ternary cathode material. The prior art CN114583125A discloses a preparation method of a carbon-coated nickel-cobalt-manganese ternary material, a carbon-coated nickel-cobalt-manganese ternary material, and a lithium-ion battery positive electrode material having the same, comprising: mixing the nickel-cobalt-manganese ternary material with a carbon source, subjecting the nickel-cobalt-manganese ternary material and the carbon source to plasma discharge-assisted high-energy ball milling, so that the nickel-cobalt-manganese ternary material and the carbon source undergo a chemical reaction to obtain the carbon-coated nickel-cobalt-manganese ternary material; the carbon source is obtained by high-temperature carbonization treatment of sugar-containing crops.

[0004] However, the surface modifications of the above-mentioned methods, such as oxide coating and carbon coating, have disadvantages such as uneven coating and weak interfacial bonding. Covalent organic framework (COF) materials are ideal coating materials due to their high specific surface area, controllable pore structure and excellent chemical stability. Traditional COF coating methods (such as mechanical mixing and solution impregnation) have difficulty in achieving a uniform and dense coating layer, and the interfacial bonding between the coating layer and the ternary precursor is weak.

[0005] Therefore, developing a new COF coating method to achieve uniform and dense growth of COF on the surface of the cathode material precursor, thereby improving the performance of the cathode material, is an urgent problem to be solved. Summary of the Invention

[0006] To address the above-mentioned technical problems, the present invention aims to provide a COF-coated modified cathode material precursor, its preparation method, and its application. The preparation method provided by the present invention performs in-situ growth of a covalent organic framework (COF) on the precursor material. The method used achieves close contact and uniform coating between the COF coating layer and the precursor material, thereby improving the interfacial stability and ion / electron conductivity of the cathode material prepared using the COF-coated cathode material precursor as raw material, thereby effectively improving the electrochemical performance of the cathode material.

[0007] To achieve this object, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides a method for preparing a COF-coated modified cathode material precursor, the preparation method comprising:

[0009] (1) mixing a first organic monomer, a second organic monomer, an organic solvent, and an organic acid reagent to obtain a COF precursor solution;

[0010] (2) reacting the precursor material with the COF precursor solution, and then separating and drying to obtain the COF-coated modified positive electrode material precursor.

[0011] The preparation method provided by the present invention adopts an in-situ growth method to coat a covalent organic framework (COF) on a cathode material precursor. The precursor material is reacted with a COF precursor solution, and the hydroxyl groups on the surface of the precursor material are used to undergo a covalent condensation reaction with the organic monomers in the COF precursor solution. The COF layer is in-situ grown on the surface of the precursor material, and in-situ chemical bonds are formed to enhance the interfacial bonding force between the coating layer and the material. The close contact and uniform coating of the COF coating layer and the precursor material can be achieved. The COF coating layer formed on the precursor material has regular pores, which can selectively transmit lithium-ion batteries and at the same time prevent the occurrence of harmful side reactions, thereby effectively improving the interface stability and ion / electron conductivity of the cathode material prepared using the COF-coated cathode material precursor as raw material, thereby improving the electrochemical performance and cycle stability of the cathode material.

[0012] Preferably, in step (1), the first organic monomer and the second organic monomer are of different types.

[0013] Preferably, in step (1), the first organic monomer and the second organic monomer independently include any one of an aldehyde monomer and an amino monomer.

[0014] In the present invention, when the first organic monomer is an aldehyde monomer, the second organic monomer is an amino monomer; when the first organic monomer is an amino monomer, the second organic monomer is an aldehyde monomer.

[0015] The present invention adopts aldehyde monomer and amino monomer to carry out imine condensation reaction to in situ grow COF coating layer on the surface of precursor material. The mechanism of its reaction with positive electrode material precursor is that: the hydroxyl group (-OH) on the surface of precursor material and transition metal coordination site (such as Ni 2+ 、Co 2+ ) First, the aldehyde / amino monomers in the COF precursor solution are adsorbed through hydrogen bonding and coordination to form a local high-concentration reaction zone; under weakly acidic conditions, the surface hydroxyl groups participate in proton transfer to catalyze the condensation reaction of aldehyde groups and amino groups, forming an imine bond (-C=N-) accompanied by the release of water molecules. At the same time, the nitrogen atoms in the newly formed imine bond further coordinate with the metal sites on the surface of the precursor material to achieve chemical bonding between the COF coating layer and the precursor material, thereby improving the close contact and uniform coating between the COF coating layer and the precursor material.

[0016] Preferably, the aldehyde monomer includes any one of 1,3,5-triformylbenzene, 2,4,6-triformylbenzaldehyde, terephthalaldehyde, 4,4'-biphenyldicarboxaldehyde or 2,5-diformylfuran, or a combination of at least two thereof.

[0017] Preferably, the amino monomer includes any one of 1,4-p-phenylenediamine, benzyl diamine, 2,5-diaminobenzenesulfonic acid or 1,3,5-triaminobenzene, or a combination of at least two thereof.

[0018] Preferably, during the mixing process in step (1), the molar ratio of the aldehyde monomer to the amino monomer is 1:(0.5-2), for example, 1:0.5, 1:0.6, 1:0.8, 1:1.0, 1:1.2, 1:1.4, 1:1.6, 1:1.8 or 1:2.0, etc.

[0019] Preferably, in the COF precursor solution of step (1), the total concentration of the first organic monomer and the second organic monomer is 0.5-2 mmol / mL, for example, 0.5 mmol / mL, 0.6 mmol / mL, 0.8 mmol / mL, 1.0 mmol / mL, 1.2 mmol / mL, 1.4 mmol / mL, 1.6 mmol / mL, 1.8 mmol / mL or 2.0 mmol / mL, etc.

[0020] Preferably, the volume ratio of the organic solvent to the organic acid reagent in step (1) is 1:(0.05-0.5), for example, 1:0.05, 1:0.1, 1:0.15, 1:0.20, 1:0.25, 1:0.30, 1:0.35, 1:0.40, 1:0.45 or 1:0.50, etc.

[0021] The organic acid reagent added in step (1) of the present invention serves as a catalyst for catalyzing the reaction between organic monomers and providing weakly acidic conditions for the reaction.

[0022] Preferably, the organic solvent in step (1) comprises any one or a combination of at least two of o-dichlorobenzene, n-butanol, dimethyl sulfoxide, dimethylacetamide, toluene, mesitylene, dichlorohexacyclopentane, chloroform or acetone, preferably a combination of o-dichlorobenzene and n-butanol.

[0023] Preferably, the volume ratio of the o-dichlorobenzene to the n-butanol is 1:(0.8-1.2), such as 1:0.8, 1:0.9, 1:1.0, 1:1.1 or 1:1.2.

[0024] Preferably, the organic acid reagent in step (1) comprises any one of acetic acid, trifluoroacetic acid, p-toluenesulfonic acid, trimesic acid or 2,5-dihydroxyterephthalic acid, or a combination of at least two thereof.

[0025] Preferably, the chemical formula of the precursor material in step (2) is Ni a Co b Mn c (OH)2, wherein a is 0.7-0.9, for example, 0.70, 0.72, 0.74, 0.76, 0.78, 0.80, 0.82, 0.84, 0.86, 0.88 or 0.90, b is 0.05-0.2, for example, 0.05, 0.06, 0.08, 0.10, 0.12, 0.14, 0.16, 0.18 or 0.20, c is 0.05-0.1, for example, 0.05, 0.06, 0.07, 0.08, 0.09 or 0.10, and a+b+c=1.

[0026] Preferably, the precursor material in step (2) is also pretreated before the reaction.

[0027] In the present invention, the order of the precursor material pretreatment process and the COF precursor solution preparation process is not specifically limited. The precursor material can be pretreated first, and then the COF precursor solution is prepared; the COF precursor solution can be prepared first, and then the precursor material pretreatment; or the precursor material pretreatment and COF precursor solution preparation can be performed simultaneously. Those skilled in the art can choose the appropriate method as needed.

[0028] Preferably, the pretreatment includes ultrasonic cleaning of the precursor material to remove impurities on the surface of the precursor material.

[0029] Preferably, the ultrasonic cleaning time is 40-60 min, for example, 40 min, 44 min, 48 min, 52 min, 56 min or 60 min.

[0030] Preferably, the reagent used in the ultrasonic cleaning includes ethanol.

[0031] Preferably, during the ultrasonic cleaning process, the mass ratio of the reagent used in the ultrasonic cleaning to the precursor material is (5-15):1, for example, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 11:1, 12:1, 13:1, 14:1 or 15:1, etc.

[0032] Preferably, the mass volume ratio of the precursor material in step (2) to the COF precursor solution is 1g:(40-55)mL, for example, 1g:40mL, 1g:41mL, 1g:42mL, 1g:43mL, 1g:44mL, 1g:45mL, 1g:46mL, 1g:47mL, 1g:48mL, 1g:49mL, 1g:50mL, 1g:51mL, 1g:52mL, 1g:53mL, 1g:54mL or 1g:55mL, etc.

[0033] Preferably, the reaction in step (2) is carried out under closed conditions.

[0034] Preferably, the reaction temperature in step (2) is 80-150°C, for example, 80°C, 85°C, 90°C, 95°C, 100°C, 105°C, 110°C, 115°C, 120°C, 125°C, 130°C, 135°C, 140°C, 145°C or 150°C, etc.

[0035] Preferably, the reaction time in step (2) is 12-48 h, for example, 12 h, 16 h, 20 h, 24 h, 28 h, 32 h, 36 h, 40 h, 44 h or 48 h.

[0036] Preferably, the separation method in step (2) includes centrifugation.

[0037] Preferably, the drying temperature in step (2) is 150-250°C, for example, 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, 210°C, 220°C, 230°C, 240°C or 250°C.

[0038] Preferably, the drying time in step (2) is 6-12 h, for example, 6 h, 7 h, 8 h, 9 h, 10 h, 11 h or 12 h.

[0039] In a second aspect, the present invention provides a COF-coated modified cathode material precursor, wherein the COF-coated modified cathode material precursor is prepared by the preparation method described in the first aspect.

[0040] The COF-coated modified positive electrode material precursor provided by the present invention is prepared by a specific preparation method. In the obtained positive electrode material precursor, the COF coating layer is tightly and evenly coated on the surface of the positive electrode material precursor. The COF coating layer has a regular pore structure, which can realize the selective transmission of lithium ions and prevent the occurrence of harmful side reactions, thereby effectively improving the interface stability and ion / electron conductivity of the positive electrode material prepared with the COF-coated positive electrode material precursor as raw material, thereby making the positive electrode material have excellent electrochemical performance and cycle stability.

[0041] In a third aspect, the present invention provides a method for preparing a positive electrode material, the method comprising the following steps:

[0042] The COF-coated modified cathode material precursor as described in the second aspect is mixed with a lithium source and then sintered to obtain the cathode material.

[0043] The preparation method of the positive electrode material provided by the present invention adopts the mixing of the COF-coated modified positive electrode material precursor and the lithium source, and then combines it with a sintering process. During the sintering process, the COF coating layer on the surface of the positive electrode material precursor can be carbonized to form a conductive network structure, while also retaining the polar functional groups on the surface of the coating layer. The synergistic effect of the two can improve the interface stability between the positive electrode material and the coating layer and the ion / electron conductivity, thereby improving the electrochemical performance of the positive electrode material.

[0044] Preferably, the molar ratio of the COF-coated modified cathode material precursor to the lithium source is 1:(0.52-0.55), for example, 1:0.52, 1:0.53, 1:0.54 or 1:0.55.

[0045] Preferably, the lithium source includes any one of lithium hydroxide, lithium carbonate or lithium nitrate.

[0046] Preferably, the sintering temperature is 600-800°C, for example, 600°C, 620°C, 640°C, 660°C, 680°C, 700°C, 720°C, 740°C, 760°C, 780°C or 800°C.

[0047] The sintering temperature during the preparation of the positive electrode material provided by the present invention, on the one hand, ensures the preparation of the positive electrode material, and on the other hand, carbonizes the COF coating layer in the positive electrode material precursor while retaining the polar functional groups in the coating layer.

[0048] Preferably, the sintering time is 8-18 hours, for example, 8 hours, 10 hours, 12 hours, 14 hours, 16 hours or 18 hours.

[0049] In a fourth aspect, the present invention provides a positive electrode material, which is prepared using the positive electrode material preparation method described in the third aspect; the positive electrode material includes a positive electrode base material and a coating layer coated on the surface of the positive electrode base material.

[0050] In a fifth aspect, the present invention provides a lithium-ion battery, comprising a positive electrode plate, wherein the positive electrode plate comprises the positive electrode material described in the fourth aspect.

[0051] Compared with the prior art, the present invention has at least the following beneficial effects:

[0052] (1) The preparation method provided by the present invention performs in-situ growth of COF on a precursor material. The COF coating layer formed on the surface of the precursor material can achieve selective transmission of lithium ions. In addition, the method adopted achieves close contact and uniform coating of the COF coating layer and the precursor material, thereby improving the interface stability and ion / electron conductivity of the positive electrode material prepared with the COF-coated positive electrode material precursor as raw material, thereby effectively improving the electrochemical performance of the positive electrode material.

[0053] (2) The COF-coated modified positive electrode material precursor provided by the present invention is prepared by a specific preparation method. In the obtained positive electrode material precursor, the COF coating layer is tightly and evenly coated on the surface of the positive electrode material precursor. The COF coating layer has a regular pore structure, which can realize the selective transmission of lithium ions and prevent the occurrence of harmful side reactions, thereby effectively improving the interface stability and ion / electron conductivity of the positive electrode material prepared with the COF-coated positive electrode material precursor as raw material, thereby making the positive electrode material have excellent electrochemical performance and cycle stability.

[0054] (3) The preparation method of the positive electrode material provided by the present invention adopts a mixture of a COF-coated modified positive electrode material precursor and a lithium source, and then combines it with a sintering process. During the sintering process, the COF coating layer on the surface of the positive electrode material precursor can be carbonized to form a conductive network structure, while also retaining the polar functional groups on the surface of the coating layer. The synergistic effect of the two can improve the interface stability between the positive electrode material and the coating layer and the ion / electron conductivity, thereby improving the electrochemical performance of the positive electrode material. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 This is the EMPA diagram of the COF-coated modified cathode material precursor provided in Example 1. DETAILED DESCRIPTION

[0056] The technical solution of the present invention will be further described below with reference to the accompanying drawings and through specific embodiments. However, the following examples are merely simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention shall be subject to the claims.

[0057] Example 1

[0058] This embodiment provides a method for preparing a COF-coated modified cathode material precursor, comprising the following steps:

[0059] S1. Ni 0.8 Co 0.1 Mn 0.1 The (OH)2 precursor material was dispersed in ethanol with a mass ratio of the precursor material to ethanol being 1:10. Ultrasonic cleaning was performed for 60 minutes to remove impurities on the surface of the precursor material to obtain a pretreated precursor material.

[0060] S2. 1,3,5-triformylbenzene and 1,4-p-phenylenediamine were dissolved in an organic solvent at a molar ratio of 1:1.5, wherein the organic solvent consisted of o-dichlorobenzene and n-butanol in a volume ratio of 1:1. Acetic acid (with a concentration of 20 wt%) was added as a catalyst, and the ratio of the total volume of the organic solvent to the volume of the acetic acid was 1:0.2 to obtain a COF precursor solution. In the COF precursor solution, the total concentration of 1,3,5-triformylbenzene and 1,4-p-phenylenediamine was 1 mmol / mL.

[0061] S3. The pretreated precursor material obtained in step S1 is mixed with the COF precursor solution obtained in step S2, and the mixture is reacted under closed conditions at 100°C for 24 hours. The mass volume ratio of the precursor material to the COF precursor solution is 1g:50mL. The product obtained after the reaction is centrifuged for solid-liquid separation, and the solid product is dried at 200°C for 8 hours to obtain a COF-coated modified positive electrode material precursor.

[0062] This embodiment also provides a method for preparing a positive electrode material, comprising the following steps:

[0063] The COF-coated modified cathode material precursor prepared above was mixed with lithium hydroxide at a molar ratio of 1:0.53, and then sintered at 700° C. for 12 h to obtain a cathode material.

[0064] Example 2

[0065] This embodiment provides a method for preparing a COF-coated modified cathode material precursor, comprising the following steps:

[0066] S1. 2,4,6-triformylbenzaldehyde and diphenylenediamine are dissolved in an organic solvent at a molar ratio of 1:1.5, wherein the organic solvent is composed of o-dichlorobenzene and n-butanol in a volume ratio of 1:0.8, and acetic acid (with a concentration of 20 wt%) is added as a catalyst. The ratio of the total volume of the organic solvent to the volume of the acetic acid is 1:0.05 to obtain a COF precursor solution. In the COF precursor solution, the total concentration of 2,4,6-triformylbenzaldehyde and diphenylenediamine is 0.5 mmol / mL.

[0067] S2. Ni 0.7 Co 0.2 Mn 0.1 The (OH)2 precursor material was dispersed in ethanol with a mass ratio of the precursor material to ethanol being 1:5. Ultrasonic cleaning was performed for 40 minutes to remove impurities on the surface of the precursor material to obtain a pretreated precursor material.

[0068] S3. The COF precursor solution obtained in step S1 is mixed with the pretreated precursor material obtained in step S2, and the mixture is reacted under closed conditions at 80°C for 48 hours. The mass volume ratio of the precursor material to the COF precursor solution is 1g:40mL. The product obtained after the reaction is centrifuged for solid-liquid separation, and the solid product is dried at 150°C for 12 hours to obtain a COF-coated modified positive electrode material precursor.

[0069] This embodiment also provides a method for preparing a positive electrode material, comprising the following steps:

[0070] The COF-coated modified cathode material precursor prepared above was mixed with lithium hydroxide at a molar ratio of 1:0.52, and then sintered at 600° C. for 18 h to obtain a cathode material.

[0071] Example 3

[0072] This embodiment provides a method for preparing a COF-coated modified cathode material precursor, comprising the following steps:

[0073] S1. Terlene dicarboxaldehyde and 1,3,5-triaminobenzene are dissolved in an organic solvent at a molar ratio of 1:0.6, wherein the organic solvent is composed of o-dichlorobenzene and n-butanol in a volume ratio of 1:1.2. Acetic acid (with a concentration of 10 wt%) is added as a catalyst, and the ratio of the total volume of the organic solvent to the volume of the acetic acid is 1:0.5 to obtain a COF precursor solution. In the COF precursor solution, the total concentration of terephthalaldehyde and 1,3,5-triaminobenzene is 2 mmol / mL.

[0074] S2. Ni 0.9 Co 0.05 Mn 0.05The (OH)2 precursor material was dispersed in ethanol with a mass ratio of the precursor material to ethanol being 1:15. Ultrasonic cleaning was performed for 60 minutes to remove impurities on the surface of the precursor material to obtain a pretreated precursor material.

[0075] S3. The COF precursor solution obtained in step S1 is mixed with the pretreated precursor material obtained in step S2, and the mixture is reacted under closed conditions at 150°C for 12 hours. The mass volume ratio of the precursor material to the COF precursor solution is 1g:55mL. The product obtained after the reaction is centrifuged for solid-liquid separation, and the solid product is dried at 250°C for 6 hours to obtain a COF-coated modified positive electrode material precursor.

[0076] This embodiment also provides a method for preparing a positive electrode material, comprising the following steps:

[0077] The COF-coated modified cathode material precursor prepared above was mixed with lithium carbonate at a molar ratio of 1:0.55, and then sintered at 800° C. for 8 h to obtain a cathode material.

[0078] Example 4

[0079] The only difference between this embodiment and embodiment 1 is that the pretreatment process of the positive electrode material precursor in step S1 is omitted. The rest of the contents are the same as those in embodiment 1.

[0080] Example 5

[0081] The only difference between this embodiment and embodiment 1 is that the reaction temperature of the pretreated precursor material and the COF precursor solution in step S3 is 70° C. The rest of the contents are the same as those in embodiment 1.

[0082] Example 6

[0083] The only difference between this embodiment and embodiment 1 is that the reaction temperature of the pretreated precursor material and the COF precursor solution in step S3 is 160° C. The rest of the contents are the same as those in embodiment 1.

[0084] Example 7

[0085] The only difference between this embodiment and embodiment 1 is that in step S2, 1,3,5-triformylbenzene and 1,4-p-phenylenediamine are dissolved in an organic solvent at a molar ratio of 1:0.3. The rest of the contents are the same as those in embodiment 1.

[0086] Example 8

[0087] The only difference between this embodiment and embodiment 1 is that in step S2, 1,3,5-triformylbenzene and 1,4-p-phenylenediamine are dissolved in an organic solvent at a molar ratio of 1:2.5. The rest of the contents are the same as those in embodiment 1.

[0088] Example 9

[0089] The only difference between this embodiment and embodiment 1 is that in step S3, the mass volume ratio of the precursor material to the COF precursor solution is 1 g:35 mL. The rest of the contents are the same as those in embodiment 1.

[0090] Example 10

[0091] The only difference between this embodiment and embodiment 1 is that in step S3, the mass volume ratio of the precursor material to the COF precursor solution is 1 g:60 mL. The rest of the contents are the same as those in embodiment 1.

[0092] Example 11

[0093] The only difference between this embodiment and embodiment 1 is that in the preparation method of the positive electrode material provided in this embodiment, the sintering temperature of the product obtained by mixing the COF-coated modified positive electrode material precursor and lithium hydroxide is 550° C. The rest of the contents are the same as those in embodiment 1.

[0094] Example 12

[0095] The only difference between this embodiment and embodiment 1 is that in the preparation method of the positive electrode material provided in this embodiment, the sintering temperature of the product obtained by mixing the COF-coated modified positive electrode material precursor and lithium hydroxide is 850° C. The rest of the contents are the same as those in embodiment 1.

[0096] Comparative Example 1

[0097] The difference between this comparative example and Example 1 is that the modification of the precursor material by COF is omitted in this comparative example, and the positive electrode precursor provided is only Ni 0.8 Co 0.1 Mn 0.1 (OH) 2. The rest of the contents are the same as in Example 1.

[0098] The positive electrode material obtained in the above embodiment and comparative example was used as the positive electrode active material, and was mixed with conductive carbon and PVDF in a mass ratio of 8:1:1. The mixture was then dispersed in methyl pyrrolidone (NMP) as a solvent to obtain a positive electrode slurry, which was evenly coated on an aluminum foil. Then, the positive electrode was vacuum-dried at 120°C for 12 hours to obtain a positive electrode sheet. Metallic lithium was selected as the negative electrode, and 1 mol / L LiPF6 was dissolved in EC and DMC solvents (volume ratio of 3:7) as the electrolyte. The positive electrode, negative electrode, and separator were wound to prepare a battery cell, which was then assembled into a lithium-ion battery through packaging, liquid injection, formation, and capacity division.

[0099] The prepared lithium-ion battery was subjected to electrochemical performance testing. The specific test parameters were as follows: after the battery was assembled, it was allowed to stand at room temperature for 10 hours and then tested after the voltage stabilized. The test was carried out on an Autolab (model PGSTAT302N) electrochemical workstation, and the battery was charged to 4.3V (relative to the potential of Li) at a rate of 0.1C (1C = 200mAh / g), allowed to stand, and then discharged to 2.5V, and also allowed to stand. Subsequent cycles were repeated as needed, and the cycle performance was tested at room temperature (25°C) at 1.9V-4.3V, 0.1C and 1C rates. The coulombic efficiency of the first charge and discharge at 0.1C, the capacity retention rate after 100 cycles at 0.1C, and the discharge specific capacity after 100 cycles at 0.1C and 1C were recorded.

[0100] The test results are shown in Table 1:

[0101] Table 1

[0102]

[0103] The test results show that:

[0104] (1) It can be seen from Examples 1 to 3 that the preparation method provided by the present invention performs in-situ growth of COF on a precursor material, and the COF coating layer formed on the surface of the precursor material can achieve selective transmission of lithium ions. In addition, the method adopted achieves close contact and uniform coating of the COF coating layer and the precursor material, thereby improving the interface stability and ion / electron conductivity of the positive electrode material prepared with the COF-coated positive electrode material precursor as raw material, thereby effectively improving the electrochemical performance of the positive electrode material.

[0105] Figure 1 This is the EMPA diagram of the COF-coated modified cathode material precursor provided in Example 1. As can be seen from the figure, the preparation method provided in Example 1 achieves COF coating on the cathode material precursor.

[0106] (2) By comparing Example 1 and Example 4, it can be seen that if the pretreatment of the cathode material precursor is omitted in the present invention, impurities will exist on the surface of the cathode material precursor, affecting the subsequent in situ growth of COF on the surface of the precursor material, thereby affecting the electrochemical performance of the prepared cathode material.

[0107] (3) By comparing Example 1 with Examples 5-6, it can be seen that if the reaction temperature of the precursor material and the COF precursor solution of the present invention is too low, the imine condensation reaction rate of the organic monomer will be reduced, resulting in incomplete COF crystallization and the formation of an amorphous coating layer, thereby affecting the electrochemical properties of the resulting positive electrode material; if the reaction temperature of the precursor material and the COF precursor solution is too high, the imine bond will break when the temperature is too high, causing the COF framework to collapse and generate an amorphous polymer. The coating layer is dense but the ion transmission capacity is reduced, and the electrochemical performance of the resulting positive electrode material is reduced.

[0108] (4) By comparing Example 1 with Examples 7-8, it can be seen that if the molar ratio of the aldehyde monomer to the amino monomer is too large, the residual monomer will react with the lithium source during the subsequent sintering process to generate lithium salt impurities, affecting the electrochemical properties of the positive electrode material; if the molar ratio of the aldehyde monomer to the amino monomer is too small, the imine bond formation rate will be low, resulting in easy cracking of the COF layer, discontinuous carbon coating after sintering, and a significant decrease in the cycle stability of the lithium-ion battery.

[0109] (5) By comparing Example 1 with Examples 9-10, it can be seen that if the mass-to-volume ratio of the precursor material to the COF precursor solution is too low and the amount of COF precursor solution added is relatively too high, it will not only grow on the surface of the precursor, but also self-aggregate in the solution to form independent COF particles, which will clog the pores of the positive electrode particles after sintering, inhibit lithium ion transmission, and cause the electrochemical performance of the battery to decline; if the mass-to-volume ratio of the precursor material to the COF precursor solution is too high and the amount of precursor material added is relatively too low, it will lead to the inability to completely cover the active sites on the precursor surface, resulting in local non-coating and poor battery cycle performance.

[0110] (6) By comparing Example 1 with Examples 11-12, it can be seen that if the sintering temperature in the preparation process of the positive electrode material of the present invention is too low, it will lead to incomplete reaction, insufficient sintering of the primary particles, and a loose porous structure, which will aggravate the side reaction of the electrolyte and cause the cycle performance of the battery to deteriorate significantly; if the sintering temperature in the preparation process of the positive electrode material is too high, it will cause excessive growth of the primary particles and rupture of the secondary particles, resulting in the presence of fine powder during the cycle, which will affect the electrochemical properties of the positive electrode material.

[0111] (7) It can be seen from the comparison between Example 1 and Comparative Example 1 that, compared with conventional precursors, the present invention achieves close contact and uniform coating of the COF coating layer and the precursor material by in-situ growth of COF on the surface of the precursor material, thereby improving the interface stability and ion / electron conductivity between the positive electrode material and the coating layer, and further improving the electrochemical performance of the positive electrode material. If the COF coating layer is lacking in coating the precursor material, the electrochemical performance of the positive electrode material prepared using conventional precursor materials is poor.

[0112] In summary, the preparation method provided by the present invention adopts an in-situ growth method to coat a covalent organic framework (COF) on a positive electrode material precursor, by reacting the precursor material with a COF precursor solution, utilizing the hydroxyl groups on the surface of the precursor material to undergo a covalent condensation reaction with the organic monomer in the COF precursor solution, and in-situ growing a COF layer on the surface of the precursor material, forming an in-situ chemical bond to enhance the interfacial bonding force between the coating layer and the material, and achieving close contact and uniform coating between the COF coating layer and the precursor material. The COF coating layer formed on the precursor material has regular pores, which can selectively transmit lithium-ion batteries and at the same time prevent the occurrence of harmful side reactions, thereby effectively improving the interface stability and ion / electron conductivity of the positive electrode material prepared with the COF-coated positive electrode material precursor as raw material, thereby improving the electrochemical performance and cycle stability of the positive electrode material.

[0113] The applicant declares that the above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the scope of protection and disclosure of the present invention.

Claims

1. A method for preparing a COF-coated modified cathode material precursor, characterized in that: The preparation method comprises: (1) mixing a first organic monomer, a second organic monomer, an organic solvent, and an organic acid reagent to obtain a COF precursor solution; (2) reacting the precursor material with the COF precursor solution, and then separating and drying to obtain the COF-coated modified positive electrode material precursor.

2. The preparation method according to claim 1, characterized in that In step (1), the first organic monomer and the second organic monomer are of different types; Preferably, in step (1), the first organic monomer and the second organic monomer independently include any one of an aldehyde monomer or an amino monomer; Preferably, the aldehyde monomer includes any one or a combination of at least two of 1,3,5-triformylbenzene, 2,4,6-triformylbenzaldehyde, terephthalaldehyde, 4,4'-biphenyldicarboxaldehyde or 2,5-diformylfuran; Preferably, the amino monomer includes any one or a combination of at least two of 1,4-p-phenylenediamine, benzyl diamine, 2,5-diaminobenzenesulfonic acid or 1,3,5-triaminobenzene; Preferably, during the mixing process of step (1), the molar ratio of the aldehyde monomer to the amino monomer is 1:(0.5-2).

3. The preparation method according to claim 1 or 2, characterized in that In the COF precursor solution of step (1), the total concentration of the first organic monomer and the second organic monomer is 0.5-2 mmol / mL; Preferably, the volume ratio of the organic solvent to the organic acid reagent in step (1) is 1:(0.05-0.5); Preferably, the organic solvent in step (1) comprises any one or a combination of at least two of o-dichlorobenzene, n-butanol, dimethyl sulfoxide, dimethylacetamide, toluene, mesitylene, dichlorohexacyclopentane, chloroform or acetone, preferably a combination of o-dichlorobenzene and n-butanol; Preferably, the volume ratio of the o-dichlorobenzene to the n-butanol is 1:(0.8-1.2); Preferably, the organic acid reagent in step (1) comprises any one of acetic acid, trifluoroacetic acid, p-toluenesulfonic acid, trimesic acid or 2,5-dihydroxyterephthalic acid, or a combination of at least two thereof.

4. The preparation method according to any one of claims 1 to 3, characterized in that The chemical formula of the precursor material in step (2) is Ni a Co b Mn c (OH)2, wherein a is 0.6-0.9, b is 0.05-0.2, c is 0.05-0.1, and a+b+c=1; Preferably, the precursor material in step (2) is also pretreated before the reaction; Preferably, the pretreatment includes ultrasonic cleaning of the precursor material to remove impurities on the surface of the precursor material.

5. The preparation method according to any one of claims 1 to 4, characterized in that The mass volume ratio of the precursor material in step (2) to the COF precursor solution is 1 g: (40-55) mL; Preferably, the reaction in step (2) is carried out under closed conditions; Preferably, the reaction temperature in step (2) is 80-150°C; Preferably, the reaction time in step (2) is 12-48 hours.

6. A COF-coated modified cathode material precursor, characterized in that: The COF-coated modified positive electrode material precursor is prepared by the preparation method according to any one of claims 1 to 5.

7. A method for preparing a positive electrode material, characterized in that: The preparation method comprises the following steps: The COF-coated modified cathode material precursor as claimed in claim 6 is mixed with a lithium source and then sintered to obtain the cathode material.

8. The preparation method according to claim 7, characterized in that The sintering temperature is 600-800°C; Preferably, the sintering time is 8-18 hours.

9. A positive electrode material, characterized in that The positive electrode material is prepared by the method for preparing the positive electrode material according to claim 7 or 8; the positive electrode material comprises a positive electrode base material and a coating layer coated on the surface of the positive electrode base material.

10. A lithium ion battery, characterized in that: The lithium-ion battery includes a positive electrode plate, and the positive electrode plate includes the positive electrode material according to claim 9.

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