Cathode material, preparation method thereof, cathode sheet, secondary battery, and electric device

Abstract

The application relates to a positive electrode material and a preparation method thereof, a positive electrode sheet, a secondary battery and an electric device, and provides a positive electrode material which comprises positive electrode active material particles and a coating layer arranged on at least part of the surfaces of the positive electrode active material particles; wherein the positive electrode active material comprises at least one of the following group: lithium transition metal oxide, olivine type lithium-containing phosphate and a modified compound of each of the above; the coating layer comprises a covalent organic framework material containing nitrogen elements and sulfur elements and has a layered stacking structure. By coating and modifying the positive electrode active material, the generation of RLCs on the material surface can be inhibited, and the cycle stability, storage performance and rate performance of the battery can be significantly improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of secondary batteries, in particular to a positive electrode material, a preparation method thereof, a positive electrode sheet, a secondary battery and an electric device. BACKGROUND

[0002] In recent years, secondary batteries represented by lithium ion batteries are widely used in energy storage power systems such as hydroelectric, thermal, wind and solar power stations, and in many fields such as electric tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, etc. With the popularization of secondary batteries, higher requirements are put forward for their cycle performance, service life, etc.

[0003] During storage and use, the positive electrode material of the lithium ion battery can generate surface residual lithium compounds (RLCs) due to Li + and CO2 in the air, which has adverse effects including reducing the initial coulombic efficiency of the battery and degrading the storage performance of the battery. Moreover, when the positive electrode material is a high-nickel layered oxide, the negative effects caused by RLCs are more obvious, which poses a severe challenge to the preparation, storage and application of high-nickel layered positive electrode materials. SUMMARY

[0004] The purpose of the present application is to provide a positive electrode material, a preparation method thereof, a positive electrode sheet, a secondary battery and an electric device, which is coated and modified to inhibit the formation of RLCs on the surface of the material; when used in a secondary battery, it has good cycle stability, storage performance and rate performance.

[0005] To this end, the present application provides a positive electrode material, which comprises positive electrode active material particles and a coating layer; the coating layer is arranged on at least part of the surface of the positive electrode active material particles;

[0006] The positive electrode active material comprises one or a combination of two or more of the following group: lithium transition metal oxide, olivine-type lithium-containing phosphate and their respective modified compounds;

[0007] The coating layer comprises a covalent organic framework material, which contains nitrogen and sulfur elements and has a layered stacking structure.

[0008] The covalent organic framework material with a layered stacking structure can uniformly coat the positive electrode active material, and the structural units of the covalent organic framework material are orderly laid on the surface of the positive electrode active material. The S and N electronegativity and lone pair electrons in the coating layer can interact with the cations on the surface of the positive electrode active material, thereby inhibiting the migration and dissolution of transition metals, relieving voltage drop, reducing side reactions and RLCs, and reducing the volume change of the positive electrode material in the electrochemical reaction, thereby further improving the cycle stability of the battery. In addition, the covalent organic framework material has a N and S heteroatom carbon skeleton, which can improve the electronic conductivity, thereby improving the rate capability.

[0009] In some embodiments, the covalent organic framework material has an ordered pore structure, and the pore size of the pore is 1-4 nm.

[0010] According to the structural characteristics of the covalent organic framework material, it has an ordered crystal structure, and the structural units usually have a pore structure, so that the covalent organic framework material as a whole has an ordered pore structure. The use of the covalent organic framework material with an ordered pore structure as a coating layer can provide an ion transmission channel, improve the ion transmission performance, and be beneficial to the rate capability of the battery.

[0011] In some embodiments, the thickness of the coating layer is 2-10 nm.

[0012] In some embodiments, 75%-100% of the surface area of the positive electrode active material particles is coated by the coating layer. When the coated surface area is more than 75%, the material surface stability can be significantly improved.

[0013] In some embodiments, the mass of the coating layer is 0.2%-2% of the mass of the positive electrode active material particles. When the mass of the coating layer is within the above range, sufficient positive electrode active material capacity can be ensured, and the improvement effect on the storage, rate and cycle stability of the battery is better.

[0014] In some embodiments, the particle size Dv50 of the positive electrode active material particles is 3-8 μm. When the particle size of the positive electrode active material particles is within the above range, it is helpful to avoid the significant increase of direct current resistance (DCR) caused by too long ion transmission distance or too large specific surface area.

[0015] In some embodiments, the covalent organic framework material is obtained by connecting trivalent connecting monomers and divalent connecting monomers through Schiff base reaction in a two-dimensional plane by carbon-nitrogen double bond; at least one of the trivalent connecting monomers and the divalent connecting monomers contains sulfur element.

[0016] In some embodiments, the covalent organic framework material comprises a structural unit satisfying formula (1),

[0017]

[0018] wherein X is a trivalent linking group, Y is a divalent linking group, at least one of X and Y contains a sulfur element; the double bond indicated by = is a carbon-nitrogen double bond.

[0019] In some embodiments, the trivalent linking monomer has a planar triangular structure, and the divalent linking monomer has a linear structure.

[0020] the trivalent linking monomer has three amino end groups and the divalent linking monomer has two aldehyde end groups; or,

[0021] the trivalent linking monomer has three aldehyde end groups and the divalent linking monomer has two amino end groups.

[0022] In some embodiments, the trivalent linking monomer is selected from one of the following group:

[0023]

[0024]

[0025] In some embodiments, the divalent linking monomer is selected from one of the following group:

[0026]

[0027]

[0028] In some embodiments, the positive active material comprises one or a combination of two or more of the following group: lithium cobalt oxide (LCO), nickel cobalt manganese ternary material (NCM), nickel cobalt aluminum ternary material (NCA), nickel cobalt manganese aluminum quaternary material (NCMA), lithium iron phosphate (LFP), lithium manganese phosphate (LMP), lithium vanadium phosphate (LVP), lithium manganate (LMO).

[0029] In some embodiments, the lithium transition metal oxide has a chemical formula of:

[0030] Li a (A b Co c Mn d Al e )O2, wherein A is selected from one of Ni and Fe or a mixture of the two; 0.2

[0031] In some embodiments, the lithium transition metal oxide is a high-nickel layered metal oxide having a chemical formula of Li a Ni b Co c Mn d O2, 0.2 < a < 1.2, 0.8 < b < 1, 0 < c < 0.1, 0 < d < 0.1, and b + c + d = 1.

[0032] In a second aspect of the present application, a preparation method of the positive electrode material of the first aspect of the present application is provided, which comprises: adding the positive electrode active material particles and monomers for preparing the covalent organic framework material into a solvent, so that the monomers are dissolved in the solvent and the positive electrode active material particles are uniformly dispersed in the solvent; and in-situ coating the covalent organic framework material on the surface of the positive electrode active material particles by heating reaction, so as to obtain the positive electrode material.

[0033] Thus, the coating layer of the covalent organic framework material is formed on the surface of the positive electrode active material particles by the in-situ coating method, which has a layered stacking structure and can be uniformly coated on the surface of the positive electrode active material.

[0034] In some embodiments, the monomers comprise trivalent connecting monomers and divalent connecting monomers; the trivalent connecting monomers and the divalent connecting monomers are connected by Schiff base reaction in a two-dimensional plane to obtain the covalent organic framework material through carbon-nitrogen double bonds; and at least one of the trivalent connecting monomers and the divalent connecting monomers contains sulfur elements.

[0035] In some embodiments, the trivalent connecting monomers have a planar triangular structure and the divalent connecting monomers have a linear structure.

[0036] The trivalent connecting monomers have three amino end groups and the divalent connecting monomers have two aldehyde end groups; or,

[0037] The trivalent connecting monomers have three aldehyde end groups and the divalent connecting monomers have two amino end groups.

[0038] In some embodiments, the trivalent connecting monomers are selected from one of the following groups:

[0039]

[0040]

[0041] In some embodiments, the divalent connecting monomers are selected from one of the following groups:

[0042]

[0043]

[0044] In some embodiments, the organic solvent is an aprotic solvent.

[0045] In some embodiments, the aprotic solvent includes one or more combinations of the following: acetonitrile, acetone, N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAC), dimethyl sulfoxide (DMOS), N-methylpyrrolidone (NMP), N-ethylpyrrolidone, N-propylpyrrolidone, and N-butylpyrrolidone.

[0046] In some embodiments, the heating reaction time is 2 to 6 hours; the heating reaction temperature is 120 to 150°C.

[0047] In some embodiments, the heating step is followed by washing and drying.

[0048] In some embodiments, the detergent used for washing is capable of solventizing the monomer and does not dissolve the covalent organic framework material.

[0049] In some embodiments, the method for preparing the positive electrode material includes: adding the positive electrode active material particles, a trivalent linker monomer, and a divalent linker monomer to a solvent, such that the trivalent linker monomer and the divalent linker monomer dissolve in the solvent, and the positive electrode active material particles are uniformly dispersed in the solvent; then, under an inert gas atmosphere, the covalent organic framework material is in situ coated on the surface of the positive electrode active material particles by heating reaction; and then the particles are washed and dried sequentially to obtain the positive electrode material.

[0050] A third aspect of this application provides a positive electrode sheet comprising the positive electrode material described in the first aspect of this invention.

[0051] A fourth aspect of this application provides a secondary battery comprising the positive electrode sheet described in the third aspect of this application.

[0052] In some embodiments, the secondary battery is a lithium-ion battery.

[0053] A fifth aspect of this application provides a battery module that includes the secondary battery of the fourth aspect of this application.

[0054] A sixth aspect of this application provides a battery pack that includes a secondary battery or a battery module as described in the fifth aspect of this application.

[0055] A seventh aspect of this application provides an electrical device comprising at least one of the secondary battery of the fourth aspect of this application, the battery module of the fifth aspect of this application, and the battery pack of the sixth aspect of this application.

[0056] Compared with the prior art, the beneficial effects of the technical solution of this application include:

[0057] This application provides a covalent organic framework (COF) coating layer containing N and S on at least a portion of the surface of the positive electrode active material particles. This COF has a layered stacking structure on the surface of the positive electrode active material, allowing the structural units of the COF to be laid flat on the surface. Through the electronegativity of S and N and the interaction of lone pairs with cations on the surface of the positive electrode active material, the migration and dissolution of transition metals are suppressed, thereby reducing side reactions and the generation of RLCs on the material surface. The coating layer also reduces the volume change of the positive electrode material during electrochemical reactions. Furthermore, the N and S heteroatomic carbon skeleton of the COF significantly improves conductivity. Therefore, the positive electrode material provided by this application significantly improves the cycle stability, storage performance, and rate performance of the battery. Attached Figure Description

[0058] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of the embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0059] FIG. 1 This is a schematic diagram of a secondary battery according to one embodiment of this application;

[0060] FIG. 2 yes FIG. 1 An exploded view of a secondary battery according to an embodiment of this application is shown.

[0061] FIG. 3 This is a schematic diagram of a battery module according to one embodiment of this application;

[0062] FIG. 4 This is a schematic diagram of a battery pack according to one embodiment of this application;

[0063] FIG. 5 yes FIG. 4 An exploded view of a battery pack according to one embodiment of this application is shown;

[0064] FIG. 6 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application;

[0065] FIG. 7 This is a scanning electron microscope (SEM) image of uncoated and unmodified positive electrode active material particles;

[0066] FIG. 8 This is a high-resolution transmission scanning microscope (HRTEM) image of uncoated and unmodified positive electrode active material particles;

[0067] FIG. 9 This is a high-resolution transmission scanning microscope (HRTEM) image of a cathode material prepared by in-situ coating according to an embodiment of this application; wherein, "SN-COF" is an abbreviation for covalent organic framework material;

[0068] FIG. 10 This is a diagram showing the pore structure of the coating layer of a cathode material prepared by in-situ coating according to an embodiment of this application; the left image is a high-resolution microscope image; the right image is a schematic diagram of the structure.

[0069] FIG. 11 These are high-resolution transmission scanning microscope (HRTEM) images of a cathode material prepared by physical blending, taken at a scale of one proportion, as presented in this application; where "SN-COF" is an abbreviation for covalent organic framework material.

[0070] Explanation of reference numerals in the attached figures:

[0071] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Lithium-ion battery; 51 Housing; 52 Electrode assembly; 53 Top cover assembly. Detailed Implementation

[0072] Exemplary embodiments of this application will now be described in more detail. It should be understood that this application may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of this application and to fully convey the scope of this application to those skilled in the art.

[0073] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60–120 and 80–110 are listed for a specific parameter, it is expected that ranges of 60–110 and 80–120 are also included. Furthermore, if minimum range values ​​1 and 2 are listed, and maximum range values ​​3, 4, and 5 are listed, then the following ranges are all expected: 1–3, 1–4, 1–5, 2–3, 2–4, and 2–5. In this application, unless otherwise stated, the numerical range "a–b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0~5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0074] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0075] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0076] Unless otherwise specified, all steps of this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order; for example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0077] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0078] Li in the cathode material of lithium-ion batteries + When reacting with H2O and CO2 in the air, residual lithium compounds (RLCs) are formed on the surface. These impurities have various negative effects, including reducing the initial coulombic efficiency of the battery and degrading its storage performance. In particular, when the cathode material is a high-nickel layered oxide, surface side reactions are more likely to induce a sharp increase in RLCs such as LiOH / Li2CO3. Considering the various adverse effects of RLCs on the cathode material surface, it is necessary to suppress their formation.

[0079] This application modifies the positive electrode active material particles by using a covalent organic framework material containing N and S, and enables the covalent organic framework material to have a layered stacking structure on the surface of the positive electrode active material, thereby significantly suppressing the side reactions on the surface of the positive electrode material and inhibiting the formation of RLCs. Furthermore, by reducing the volume change of the positive electrode material in the electrochemical reaction and improving the conductivity, it further improves the cycle stability, storage performance and rate performance of the battery.

[0080] Positive electrode material

[0081] The first aspect of this application provides a positive electrode material, which includes positive electrode active material particles and a coating layer; wherein the coating layer is disposed on at least a portion of the surface of the positive electrode active material particles;

[0082] The positive electrode active material includes one or more combinations of the following: lithium transition metal oxides, olivine-type lithium-containing phosphates and their respective modified compounds;

[0083] The coating layer comprises a covalent organic framework material containing both nitrogen (N) and sulfur (S) elements, and has a layered stacked structure.

[0084] Covalent organic framework materials with layered stacking structures can uniformly coat the positive electrode active material, with the structural units in the covalent organic framework material spread evenly on the surface of the positive electrode active material. According to the technical solution of this application, the cycle stability of the positive electrode material can be improved in two ways: firstly, the electronegativity of S and N and the interaction of lone electron pairs with cations on the surface of the positive electrode active material can suppress transition metals (such as Fe). 3+ Ni 3+ / Ni 2+ Co 3+ Mn 4+ Al 3+ The migration and dissolution of substances such as sulfur and nitrogen (S and N) alleviate voltage drop, reduce side reactions and RLCs, and significantly improve battery cycle stability. On the other hand, covalent organic framework materials have a layered stacking structure, which allows them to be uniformly distributed at the molecular level on the surface of the positive electrode active material particles. The interaction between sulfur (S) and nitrogen (N) and cations on the material surface enhances the adhesion of the coating layer to the positive electrode active material particles. With good coating effect, the volume change of the positive electrode material during electrochemical reactions can be reduced, thereby improving battery cycle stability.

[0085] Furthermore, this coating layer can also improve the rate performance of the cathode material. This is because the N and S heteroatomic carbon skeleton can enhance electronic conductivity, thereby improving the rate performance of the battery.

[0086] The technical solutions described in the embodiments of this application are applicable to positive electrode materials, and also to methods for preparing positive electrode materials, positive electrode sheets containing positive electrode materials, secondary batteries using positive electrode sheets, battery modules using secondary batteries, battery packs using secondary batteries or battery modules, and electrical devices using at least one of secondary batteries, battery modules, and battery packs.

[0087] In some implementations, refer to FIG. 10 The covalent organic framework material has an ordered pore structure with a pore diameter of 1 to 4 nm, for example, about 1 nm, 1.5 nm, 2 nm, 2.5 nm, 3 nm, 3.5 nm, 4 nm, etc.

[0088] Based on the structural characteristics of covalent organic framework materials, they possess ordered crystalline structures, and their structural units typically contain porous structures, resulting in an overall ordered porous structure. Using covalent organic framework materials with ordered porous structures as coating layers can provide ion transport channels, improve ion transport performance, and benefit the rate performance of batteries.

[0089] In some embodiments, the thickness of the coating layer is 2 to 10 nm, for example, about 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, etc.

[0090] When the coating thickness is 2–10 nm, the coating thickness is moderate, which has a good lithium-ion conduction effect and has the advantages of high cycle retention rate, small DCR growth, high storage retention rate, and small voltage drop. If it is greater than 10 nm, the coating layer is too thick, which can easily lead to poor conduction effect and large voltage drop, thus hindering the improvement of cycle retention rate and storage retention rate, and may also cause a significant increase in DCR. If it is less than 2 nm, the coating layer is too thin, which may cause uneven coating and fail to protect the positive electrode active material.

[0091] In some embodiments, 75% to 100% of the surface area of ​​the positive electrode active material particles is covered by the coating layer; for example, the surface area of ​​the positive electrode active material particles covered by the coating layer is about 75%, 80%, 85%, 90%, 95%, 100%, etc.

[0092] Since the improvement of cathode material performance depends on the interaction between the coating layer and the cathode active material, at least a portion of the surface of the cathode active material particles needs to be coated. In some embodiments, when the coated surface area reaches 75% or more, it can significantly improve the surface stability of the material.

[0093] In some embodiments, the mass of the coating layer is 0.2% to 2% of the mass of the positive electrode active material particles; for example, it can be about 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, etc.

[0094] When the mass of the coating layer is 0.2% to 2% of the positive electrode active material particles, it has a good effect on improving the storage capacity of the positive electrode material, the rate capability of the battery, and the cycle stability. When the mass of the coating layer is greater than 2% of the positive electrode active material particles, the capacity of the positive electrode active material will decrease relatively, resulting in poor ion conduction and thus hindering the improvement of cycle retention. When the mass of the coating layer is less than 0.2% of the positive electrode active material particles, it is difficult to form a uniform coating layer, so the effect on improving the cycle stability of the material is not significant.

[0095] In some embodiments, the particle size Dv50 of the positive electrode active material particles is 3 to 8 μm, for example, about 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, etc.

[0096] When the particle size (Dv50) of the positive electrode active material is 3–8 μm, the ion transport distance is moderate, which is beneficial for maintaining a good DCR. If it is larger than this range, the ion transport distance increases, which easily leads to a significant increase in DCR; if it is smaller than this range, the specific surface area increases accordingly, which easily leads to a significant increase in DCR at the electrolyte contact interface.

[0097] In some embodiments, the covalent organic framework material is obtained by connecting trivalent and divalent linkers in a two-dimensional plane via a Schiff base reaction with carbon-nitrogen double bonds; at least one of the trivalent and divalent linkers contains sulfur.

[0098] In some embodiments, the divalent linker contains an S-block, and the trivalent linker does not contain an S-block.

[0099] In some embodiments, the trivalent linker contains an S-block, and the divalent linker does not contain an S-block.

[0100] In some embodiments, the trivalent linker contains an S-block, and the divalent linker contains an S-block.

[0101] In some embodiments, the covalent organic framework material comprises structural units that satisfy formula (1).

[0102]

[0103] Wherein, X is a trivalent linker group, Y is a divalent linker group, and at least one of X and Y contains sulfur; the double bond shown by = is a carbon-nitrogen double bond.

[0104] The covalent organic framework material with structural unit as shown in formula (1) is flexible and has a conjugated structure and an ordered pore structure. It can not only effectively promote ion transport in the electrochemical process, but also effectively coat the positive electrode active material, thereby alleviating the volume change of the positive electrode active material in the electrochemical process, and further improving the conductivity and cycle performance of the positive electrode material.

[0105] In some embodiments, the trivalent linker has a planar triangular structure, and the divalent linker has a linear structure;

[0106] The trivalent linker has three amino terminal groups and the divalent linker has two aldehyde terminal groups; or...

[0107] The trivalent linker has three aldehyde end groups and the divalent linker has two amino end groups.

[0108] In some embodiments, the trivalent linker is selected from one of the following groups:

[0109]

[0110]

[0111] In some embodiments, the divalent linker is selected from one of the following groups:

[0112]

[0113]

[0114] In some embodiments, the structural units of the covalent organic framework material satisfy a structural formula selected from one of the following groups:

[0115] The covalent organic framework material obtained by connecting the trivalent monomer of formula A1 and the divalent monomer of formula B5 in a two-dimensional plane via Schiff base reaction with carbon-nitrogen double bonds has the structural formula of its structural unit as shown in formula (2).

[0116]

[0117] The covalent organic framework material obtained by connecting the trivalent monomer of formula A1 and the divalent monomer of formula B6 in a two-dimensional plane via Schiff base reaction with carbon-nitrogen double bonds has the structural formula of its structural unit as shown in formula (3).

[0118] The covalent organic framework material obtained by connecting the trivalent monomer of formula A8 and the divalent monomer of formula B2 in a two-dimensional plane via Schiff base reaction with carbon-nitrogen double bonds has the structural formula of its structural unit as shown in formula (4).

[0119]

[0120] The covalent organic framework material obtained by connecting the trivalent monomer of formula A6 and the divalent monomer of formula B2 in a two-dimensional plane via Schiff base reaction with carbon-nitrogen double bonds has the structural formula of its structural unit as shown in formula (5).

[0121] In some embodiments, the lithium-containing phosphate includes one or more combinations of the following: lithium iron phosphate (e.g., LiFePO4, abbreviated as LFP), lithium manganese phosphate (e.g., LiMnPO4), and lithium manganese iron phosphate.

[0122] In some embodiments, the lithium transition metal oxide includes one or more combinations selected from the group consisting of: lithium cobalt oxide (e.g., LiCoO2), lithium nickel oxide (e.g., LiNiO2), lithium manganese oxide (e.g., LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, and lithium nickel cobalt manganese oxide (e.g., LiNi1 / 3Co1 / 3Mn1 / 3O2, abbreviated as NCM333; LiNi 0.5 Co 0.2 Mn 0.3 O2, abbreviated as NCM523; LiNi 0.5 Co 0.25 Mn 0.25 O2, abbreviated as NCM211; LiNi 0.6 Co 0.2 Mn 0.2 O2, abbreviated as NCM622; LiNi 0.8 Co 0.1 Mn 0.1 O2, abbreviated as NCM811), lithium nickel cobalt aluminum oxide (e.g., LiNi) 0.85 Co 0.15 Al 0.05 O2).

[0123] In some embodiments, the chemical formula of the lithium transition metal oxide is: Li a (A b Co c Mn d Al e O2;

[0124] Where A is selected from either Ni or Fe or a mixture of both; 0.2 < a ≤ 1.2, 0 ≤ b ≤ 1, 0 ≤ c ≤ 0.2, 0 ≤ d ≤ 0.2, 0 ≤ e ≤ 0.2, and b + c + d + e = 1.

[0125] In some embodiments, the lithium transition metal oxide is a high-nickel layered metal oxide with the chemical formula Li. a Ni b Co c Mn d O2, 0.2<a≤1.2, 0.8≤b≤1, 0≤c≤0.1, 0≤d≤0.1, and b+c+d=1.

[0126] Because Li is extracted and consumed during the charging and discharging process, the molar content of Li varies when the battery is discharged to different states. The limitation of 'a' in the above chemical formula includes the molar content of Li under different charging and discharging states of the battery (usually the battery voltage is between 2-5V).

[0127] Compared to other cathode active materials with no nickel or low nickel content, high-nickel materials with a nickel content of over 80% are more prone to surface side reactions that induce a sharp increase in RLCs. One of the main reasons for this is that Ni... 3+ It is unstable and readily reduced to Ni during storage and electrochemical cycling. 2+ Oxygen in lattice 2- It will be oxidized to O - Ultimately, reactive oxygen species (O2) are formed on the material surface. 2 reactive oxygen species (O2) 2 Same as Li + Lithium oxides are formed and react with H2O and CO2 in the air to form lithium ions (RLCs). In some embodiments of this application, a high-nickel layered oxide with a nickel content greater than 80% is used as the positive electrode active material. After coating modification, the migration and dissolution of nickel ions can be significantly suppressed, reducing side reactions and the generation of RLCs.

[0128] Method for preparing a positive electrode material

[0129] The second aspect of this application provides a method for preparing a positive electrode material according to any embodiment of the first aspect of this application, wherein the positive electrode active material particles and the monomer for preparing the covalent organic framework material are added to a solvent, such that the monomer is dissolved in the solvent, and the positive electrode active material particles are uniformly dispersed in the solvent; the covalent organic framework material is in situ coated on the surface of the positive electrode active material particles by heating reaction, thereby preparing the positive electrode material.

[0130] Reference FIG. 9 The SN-COF is uniformly distributed on the material surface with a relatively uniform thickness and no significant defects. A covalent organic framework coating layer is formed on the surface of the positive electrode active material particles through an in-situ coating method. This layer has a layered stacking structure, is uniformly distributed on the surface of the positive electrode active material with a relatively uniform thickness, and no significant defects.

[0131] In some embodiments, the monomer includes a trivalent linker and a divalent linker; the trivalent linker and the divalent linker are linked in a two-dimensional plane by a Schiff base reaction to obtain the covalent organic framework material; at least one of the trivalent linker and the divalent linker contains sulfur.

[0132] In some embodiments, the trivalent linker has a planar triangular structure, and the divalent linker has a linear structure;

[0133] The trivalent linker has three amino terminal groups and the divalent linker has two aldehyde terminal groups; or...

[0134] The trivalent linker has three aldehyde end groups and the divalent linker has two amino end groups.

[0135] In some embodiments, the trivalent linker is selected from one of the group consisting of: 2,4,6-tris(3-aminophenyl)amino-1,3,5-triazine, 2,4,6-tris(4-aminophenyl)-1,3,5-triazine, and tris(4-aminophenyl)amine.

[0136]

[0137] In some embodiments, the divalent linker is selected from one of the following groups:

[0138]

[0139]

[0140] In some embodiments, the organic solvent is an aprotic solvent.

[0141] In some embodiments, the aprotic solvent includes one or more combinations of the following: acetonitrile, acetone, N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAC), dimethyl sulfoxide (DMOS), N-methylpyrrolidone (NMP), N-ethylpyrrolidone, N-propylpyrrolidone, and N-butylpyrrolidone.

[0142] In some embodiments, the heating reaction time is 2 to 6 hours; the heating reaction temperature is 100 to 120°C.

[0143] In some embodiments, the heating step is followed by washing and drying.

[0144] In some embodiments, the detergent used for washing is capable of solventizing the monomer and does not dissolve the covalent organic framework material.

[0145] In some embodiments, the method for preparing the positive electrode material includes: adding the positive electrode active material particles, a trivalent linker monomer, and a divalent linker monomer to a solvent, such that the trivalent linker monomer and the divalent linker monomer dissolve in the solvent, and the positive electrode active material particles are uniformly dispersed in the solvent; then, under an inert gas atmosphere, the covalent organic framework material is in situ coated on the surface of the positive electrode active material particles by heating reaction; and then the particles are washed and dried sequentially to obtain the positive electrode material.

[0146] Positive electrode sheet

[0147] A third aspect of this application provides a positive electrode sheet, comprising a positive electrode material according to any embodiment of the first aspect of this application, or a positive electrode material prepared by a method according to any embodiment of the second aspect of this application.

[0148] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including the positive electrode material of the first aspect of this application, or the positive electrode material prepared according to the method of the second aspect of this application.

[0149] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0150] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0151] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0152] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0153] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive electrode material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0154] Secondary battery

[0155] A fourth aspect of this application provides a secondary battery, including the positive electrode sheet described in the third aspect of this application.

[0156] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0157] [Positive electrode plate]

[0158] The positive electrode sheet described in the third aspect of this application is used.

[0159] [Negative electrode plate]

[0160] The negative electrode includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector. As an example, the negative current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative current collector.

[0161] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0162] In some embodiments, the negative electrode film layer includes a negative electrode active material, which may be a negative electrode active material known in the art for use in batteries. For example, the negative electrode active material includes one or more combinations selected from the group consisting of: natural graphite, artificial graphite, mesophase microcarbon spheres (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composites, Li-Sn alloys, Li-Sn-O alloys, Sn, SnO, SnO2, TiO2-Li4Ti5O 12 Li-Al alloys are used. However, this invention is not limited to these materials; other conventional materials that can be used as negative electrode active materials for lithium-ion batteries can also be used. These negative electrode active materials can be used alone or in combination of two or more.

[0163] In some embodiments, the negative electrode film layer may optionally include a binder. For example, the binder may include one or more combinations selected from the group consisting of: styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0164] In some embodiments, the negative electrode film may optionally include a conductive agent. For example, the conductive agent may include one or more combinations selected from the group consisting of: Super P, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0165] In some embodiments, the negative electrode film layer may optionally include other additives. For example, other additives may be thickeners (such as sodium carboxymethyl cellulose (CMC-Na)).

[0166] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0167] [Electrolytes]

[0168] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not specifically limit the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be selected from at least one of solid electrolytes and liquid electrolytes (i.e., electrolyte solutions).

[0169] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0170] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0171] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0172] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0173] [Isolation membrane]

[0174] The separator is positioned between the positive and negative electrodes to provide isolation. This application does not impose any particular restriction on the type of separator; any known porous separator with good chemical and mechanical stability can be selected. The material of the separator can be selected from one or more combinations of the following: glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular restriction. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular restriction.

[0175] [Preparation of Lithium-ion Batteries]

[0176] A lithium-ion battery can be prepared by winding or stacking positive electrode sheets, negative electrode sheets, and separators to form an electrode assembly, which is then packaged and injected with electrolyte.

[0177] The outer packaging can be a hard shell, such as a hard plastic shell, aluminum shell, or steel shell. It can also be a flexible package, such as a pouch. The material of the flexible package can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0178] This invention does not impose any particular limitation on the shape of the lithium-ion battery; it can be cylindrical, square, or any other arbitrary shape. For example, FIG. 1 This is an example of a square-structured lithium-ion battery 5.

[0179] In some implementations, refer to FIG. 2 The outer packaging may include a housing 51 and a cover plate 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be placed over the opening to close the receiving cavity. Positive electrode sheets, negative electrode sheets, and a separator can be formed into an electrode assembly 52 through a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. The electrolyte is immersed in the electrode assembly 52. ​​The lithium-ion battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0180] Battery module, battery pack, power utilization device

[0181] In some implementations, the secondary batteries can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0182] FIG. 3 This is battery module 4, used as an example. (See reference...) FIG. 3 In battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary batteries 5 can be fixed in place using fasteners.

[0183] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0184] In some implementations, the secondary batteries can also be assembled into a battery pack.

[0185] In some embodiments, the battery module 4 can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0186] FIG. 4 and FIG. 5 This is battery pack 1 as an example. (See reference...) FIG. 4 and FIG. 5 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0187] In addition, this application also provides an electrical device, which includes the secondary battery provided in this application. In some embodiments, the electrical device includes at least one of the battery module or battery pack provided in this application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but is not limited thereto.

[0188] As the electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0189] FIG. 6 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0190] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0191] (I) Cathode Materials

[0192] Example 1

[0193]

[0194] A solution system containing monomers of formula A1 and B5 was prepared using DMF and DMSO at a volume ratio of 1:1. The total volume of the solution system was 1 L, with a molar ratio of formula A1 to formula B5 of 2:3 and a total molar concentration of 0.5 mol / L. 100 g of LiNi cathode active material with a particle size Dv50 of 5 μm was then used. 0.8 Co 0.1 Mn 0.1 O2 is uniformly dispersed in the solution system. Under an inert gas atmosphere, the mixture is stirred and heated for 4 hours, and then cooled, filtered, washed, and dried in sequence to obtain a covalent organic framework material in situ coated on the surface of the positive electrode active material particles, thus preparing the positive electrode material I-1.

[0195] In cathode material I-1, approximately 80% of the surface area of ​​the cathode active material particles is covered by the coating layer; the coating layer has an ordered pore structure with a pore diameter of approximately 2.3 nm, a coating layer thickness of approximately 6 nm, and a coating layer mass percentage of 1.0%.

[0196] Preparation Example 2

[0197]

[0198] Except for the following conditions, the cathode material I-2 was prepared according to the method of Example 1;

[0199] Monomer of formula B6 is used instead of monomer of formula B5; in the solution system, the total molar concentration of monomers of formula A1 and formula B6 is 0.2 mol / L.

[0200] In cathode material I-2, approximately 80% of the surface area of ​​the cathode active material particles is covered by the coating layer; the coating layer has an ordered pore structure with a pore diameter of approximately 2.3 nm, a coating layer thickness of approximately 2 nm, and a coating layer mass percentage of 0.2%.

[0201] Example 3

[0202]

[0203] Except for the following conditions, the cathode material I-3 was prepared according to the method of Example 1;

[0204] Monomer of formula A8 is used instead of monomer of formula A1, and monomer of formula B2 is used instead of monomer of formula B5; in the solution system, the total molar concentration of monomers of formula A8 and B2 is 1 mol / L.

[0205] In cathode material I-3, approximately 80% of the surface area of ​​the cathode active material particles is covered by the coating layer; the coating layer has an ordered pore structure with a pore diameter of approximately 2.2 nm, a coating layer thickness of approximately 8 nm, and a coating layer mass percentage of 2%.

[0206] Example 4

[0207]

[0208] Except for the following conditions, the cathode material I-4 was prepared according to the method of Example 1;

[0209] Monomer of formula A6 is used instead of monomer of formula A1, and monomer of formula B2 is used instead of monomer of formula B5; the total molar concentration of monomers of formula A6 and B2 in the solution system is 2 mol / L.

[0210] In cathode material I-4, approximately 80% of the surface area of ​​the cathode active material particles is covered by the coating layer; the coating layer has an ordered pore structure with a pore diameter of approximately 2.3 nm, a coating layer thickness of approximately 10 nm, and a coating layer mass ratio of 4%.

[0211] Example 5

[0212]

[0213] Except for the following conditions, the cathode material I-5 was prepared according to the method of Example 1;

[0214] The A4 monomer is used instead of the A1 monomer, and the B4 monomer is used instead of the B5 monomer.

[0215] In cathode material I-5, approximately 80% of the surface area of ​​the cathode active material particles is covered by a coating layer; the coating layer has an ordered pore structure with a pore diameter of approximately 1.4 nm, a coating layer thickness of approximately 6 nm, and a coating layer mass percentage of 1.0%.

[0216] Example 6

[0217]

[0218] Except for the following conditions, the cathode material I-6 was prepared according to the method of Example 1;

[0219] The A7 monomer is used instead of the A1 monomer, and the B2 monomer is used instead of the B5 monomer.

[0220] In cathode material I-6, approximately 80% of the surface area of ​​the cathode active material particles is covered by a coating layer; the coating layer has an ordered pore structure with a pore diameter of approximately 3.5 nm, a coating layer thickness of approximately 6 nm, and a coating layer mass percentage of 1.0%.

[0221] Example 7

[0222]

[0223] Except for the following conditions, the cathode material I-7 was prepared according to the method of Example 1;

[0224] Monomer of formula A5 was used instead of monomer of formula A1, and monomer of formula B2 was used instead of monomer of formula B5. The reaction time was controlled at 2 hours.

[0225] In cathode material I-7, approximately 70% of the surface area of ​​the cathode active material particles is covered by a coating layer; the coating layer has an ordered pore structure with a pore diameter of approximately 2.3 nm, a coating layer thickness of approximately 6 nm, and a coating layer mass percentage of 0.8%.

[0226] Example 8

[0227]

[0228] Except for the following conditions, the cathode material I-8 was prepared according to the method of Example 1;

[0229] The A5 monomer was used instead of the A1 monomer, and the reaction time was controlled at 8 hours.

[0230] In cathode material I-8, approximately 90% of the surface area of ​​the cathode active material particles is covered by a coating layer; the coating layer has an ordered pore structure with a pore diameter of approximately 2.3 nm, a coating layer thickness of approximately 6 nm, and a coating layer mass ratio of approximately 2.0%.

[0231] Comparative Example 1

[0232] This comparative example uses a physical blending method to coat the surface of the positive electrode active material.

[0233] A solution system containing monomers of formula A1 and B5 was prepared using DMF and DMSO in a volume ratio of 1:1 as solvents. The total volume of the solution system was 1 L, with a molar ratio of formula A1 to formula B5 of 2:3 and a total molar concentration of 0.5 mol / L. The mixture was stirred and heated for 4 h under an inert gas atmosphere, followed by cooling, filtration, washing, and drying to obtain a covalent organic framework material with an ordered pore structure and a pore diameter of approximately 2.3 nm.

[0234] 100g of positive electrode active material LiNi with a particle size Dv50 of 5μm was used. 0.8 Co 0.1 Mn 0.1 O2 was mixed with the above covalent organic framework material and ball-milled for 4 hours to prepare cathode material II-1. Approximately 80% of the surface area of ​​the cathode active material particles was coated with a coating layer, and the coating layer accounted for approximately 1% of the mass.

[0235] Comparative Example 2

[0236] This comparative example uses the positive electrode active material from Example 1 as positive electrode material II-2, without any other modifications.

[0237] Comparative Example 3

[0238] This comparative example uses a linear polymer containing sulfur to coat the surface of positive electrode active material particles.

[0239] A solution system containing sulfur and polyacrylonitrile was prepared using toluene / DMSO at a volume ratio of 1:1. The total volume of this solution system was 1 L, with a molar ratio of sulfur to polyacrylonitrile of 1:1. 100 g of LiNi cathode active material with a particle size Dv50 of 5 μm was then used. 0.8 Co 0.1 Mn 0.1 O2 was uniformly dispersed in the solution system. Under an inert atmosphere, the mixture was stirred and heated for 6 hours, followed by cooling, filtration, washing, and drying to prepare linearly vulcanized polyacrylonitrile-coated cathode material II-3. Approximately 80% of the surface area of ​​the cathode active material particles was coated by the coating layer, which accounted for approximately 1% of the total mass.

[0240] (II) Lithium-ion batteries

[0241] Using the cathode materials prepared in the above embodiments and comparative examples, lithium-ion batteries were prepared according to the following steps.

[0242] 1) Preparation of positive electrode sheet

[0243] The positive electrode material, superconducting carbon black SP as a conductive agent, and polyvinylidene fluoride (PVDF) as a binder are dispersed in N-methylpyrrolidone (NMP) as a solvent at a mass ratio of 96:2:2 and mixed evenly to obtain a positive electrode slurry. The positive electrode slurry is uniformly coated on the positive electrode current collector aluminum foil, and after drying, cold pressing, slitting, and cutting, a positive electrode sheet is obtained.

[0244] 2) Preparation of negative electrode sheet

[0245] The negative electrode active material graphite, superconducting carbon black SP as a conductive agent, SBR as a binder, and CMC-Na as a thickener are dispersed in deionized water as a solvent at a mass ratio of 96:1:1:2 and mixed evenly to obtain a negative electrode slurry. The negative electrode slurry is then uniformly coated onto a negative electrode current collector copper foil. After drying, cold pressing, slitting, and cutting, a negative electrode sheet is obtained.

[0246] 3) Separating membrane

[0247] Polyethylene film is used as the separation membrane.

[0248] 4) Preparation of electrolyte

[0249] Ethyl carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC) were mixed uniformly in a volume ratio of 1:1:1 to obtain an organic solvent. Then, fully dried lithium salt LiPF6 was dissolved in the mixed organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0250] 5) Preparation of lithium-ion batteries

[0251] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrodes. The cells are then wound to obtain a bare cell. The bare cell is placed in an outer packaging shell, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping, a lithium-ion battery cell is obtained.

[0252] (III) Related Tests

[0253] The cathode materials prepared in the above embodiments and comparative examples, and the lithium-ion batteries prepared therefrom, were subjected to the following tests.

[0254] (1) Mass content test of the coating layer

[0255] Take a small amount of positive electrode material powder sample, its mass is recorded as m1, add it to the sample cell of the organic elemental analyzer, introduce He gas for 10 min, introduce oxygen, ignite and heat to 980℃, test the percentage of C, H, N and S elements in the collected tail gas; the mass of the obtained residue is recorded as m2, then the coating layer content is (m1-m2) / m2×100%.

[0256] (2) Capacity retention test

[0257] The assembled battery cell was placed in the electrochemical test channel and cycled 1000 times at a current of 0.5C and a room temperature of 25°C. The capacity value C was then read. 1 1000 Compared to the initial first-lap capacity C 1 0, according to the formula: Capacity retention rate = C 1 1000 / C 1 0×100% yields the capacity retention rate.

[0258] (3) High-temperature storage performance test

[0259] The assembled battery cells were placed on the electrochemical test channel and subjected to 5 cycles of 1 / 3C charge-discharge, charged to 97% of the upper limit voltage, and stored at 60°C. The capacity was tested every 15 days, and the capacity value (C) was recorded after 150 days. 2 150 Comparing the initial first-cycle capacity C at 60℃ 2 0, according to the formula: Capacity retention rate = C 2 150 / C 2 0×100% yields the capacity retention rate at high temperatures.

[0260] (4) DCR growth rate test

[0261] The assembled battery cell was placed on the electrochemical test channel and circulated 1000 times at a current of 0.5C and a temperature of 60°C. An external DC impedance meter was connected to read the DC impedance value R. 1000 Comparing the initial DC impedance value R0 at 60℃, the growth rate of DCR is calculated using the formula: DCR growth rate = (R0 / R0) / R0. 1000 The growth rate of DCR can be obtained by calculating (-R0) / R0×100%.

[0262] (5) Voltage drop test

[0263] The assembled battery cell was placed in the electrochemical test channel and cyclically charged to 4.25V at 0.5C current and 60℃ for 1000 cycles. The voltage was then maintained for 1 hour, and the voltage value (V) was recorded. 1000Comparing the initial first-cycle voltage value V0 at 60℃, the voltage drop is calculated using the formula: Voltage drop = (V0 - V 1000 The voltage drop can be obtained by calculating V0 × 100%.

[0264] The results of the above tests are shown in Table 1.

[0265] Table 1 Test Results

[0266]

[0267] Based on the above test results, it can be seen that compared to the unmodified cathode active material in Comparative Example 2, the cathode material provided by this application shows significant improvements in capacity retention, high-temperature storage performance, DCR growth rate after multiple cycles, and voltage drop. Comparative Example 3 used a linear polymer containing sulfur for coating, which had a relatively small effect on improving the above performance. Comparative Example 1 used a physical coating method, such as... FIG. 11 FIG. 11 As shown, through physical coating, covalent organic framework materials failed to form a uniform layered stacking structure on the surface of the positive electrode active material, and even exhibited uneven thickness and uneven coverage distribution. Therefore, the performance improvement effect was small compared to the unmodified positive electrode active material, and it was significantly worse than the technical solution of this application in terms of cycle performance and storage performance.

[0268] The above description is merely a preferred embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A positive electrode material, characterized by, The positive electrode active material particle includes a positive electrode active material particle, a coating layer; the coating layer is arranged on at least part of the surface of the positive electrode active material particle; The positive electrode active material includes at least one of the following group: lithium transition metal oxide, olivine type lithium-containing phosphate and its respective modified compound; The coating layer includes a covalent organic framework material, the covalent organic framework material contains nitrogen element and sulfur element, and has a layered stacking structure; The covalent organic framework material contains a structure unit satisfying formula (1), ， wherein X is a trivalent linking group, Y is a divalent linking group, and at least one of X and Y contains a sulfur element; and the double bond shown is a carbon-nitrogen double bond.

2. The positive electrode material of claim 1, wherein, The covalent organic framework material has an ordered pore structure, and the pore size of the pore is 1-4 nm.

3. The positive electrode material of claim 1, wherein, The thickness of the coating layer is 2-10 nm.

4. The positive electrode material of claim 1, wherein, 75%-100% of the surface area of the positive electrode active material particle is coated by the coating layer.

5. The cathode material of claim 1, wherein, The mass of the coating layer is 0.2%-2% of the mass of the positive electrode active material particle.

6. The cathode material of claim 1, wherein, The particle size Dv50 of the positive electrode active material particle is 3-8 μm.

7. The cathode material according to any one of claims 1 to 6, characterized in that, The positive electrode active material includes at least one of the following group: lithium cobaltate, nickel-cobalt-manganese ternary material, nickel-cobalt-aluminum ternary material, nickel-cobalt-manganese-aluminum quaternary material, lithium iron phosphate, lithium manganese phosphate, lithium vanadium phosphate, lithium manganate.

8. The positive electrode material according to any one of claims 1 to 6, wherein The chemical formula of the lithium transition metal oxide is: Li a (A b Co c Mn d Al e )O2, wherein A is selected from one of Ni and Fe or a mixture of both; 0.2 < a < 1.2, 0 < b < 1, 0 < c < 0.2, 0 < d < 0.2, 0 < e < 0.2, and b + c + d + e = 1.

9. The positive electrode material according to any one of claims 1 to 6, wherein The lithium transition metal oxide is a high-nickel layered metal oxide having a chemical formula of Li a Ni b Co c Mn d O2, 0.2 < a < 1.2, 0.8 < b < 1, 0 < c < 0.1, 0 < d < 0.1, and b + c + d = 1.

10. The method of producing the positive electrode material according to any one of claims 1 to 9, characterized by, The positive electrode material is prepared by the following method: The positive electrode active material particle, the monomer for preparing the covalent organic framework material are added into a solvent, so that the monomer is dissolved in the solvent, and the positive electrode active material particle is uniformly dispersed in the solvent; the covalent organic framework material is coated on the surface of the positive electrode active material particle in situ by heating reaction, so as to prepare the positive electrode material.

11. The production method according to claim 10, wherein The monomer includes trivalent connecting monomer and divalent connecting monomer; the trivalent connecting monomer and the divalent connecting monomer are connected by carbon-nitrogen double bond in two-dimensional plane through Schiff base reaction to obtain the covalent organic framework material; at least one of the trivalent connecting monomer and the divalent connecting monomer contains sulfur element.

12. A positive electrode sheet characterized by comprising: The positive electrode material includes the positive electrode material according to any one of claims 1-9.

13. A secondary battery characterized by comprising: The positive electrode sheet includes the positive electrode sheet according to claim 12.

14. A battery module, characterized by The secondary battery includes the secondary battery according to claim 13.

15. A battery pack, characterized by The secondary battery or the battery module according to claim 14.

16. An electrical device, comprising: The secondary battery, the battery module and the battery pack according to claims 13-15.

Images