Composite positive electrode material and preparation method therefor, positive electrode sheet, secondary battery, and electrical apparatus

Abstract

A composite positive electrode material and a preparation method therefor, a positive electrode sheet, a battery, and an electrical apparatus. The composite positive electrode material comprises a nickel-containing positive electrode material and a functional film layer arranged on the surface of the nickel-containing positive electrode material. Components of the functional film layer comprise Li2MO4 and an organic lithium phosphonate compound, where M is selected from at least one of sulfur, selenium, and tellurium; and the organic lithium phosphonate compound contains a structure represented by formula (1): (I), where * represents sites where the structure represented by formula (1) is connected to other structures in the organic lithium phosphonate compound.

Description

Composite positive electrode material and preparation method thereof, positive electrode sheet, secondary battery and electrical device

[0001] Cross-references

[0002] This application refers to Chinese patent application No. 202310952564.4 filed on July 31, 2023, entitled “Composite positive electrode material and preparation method thereof, positive electrode sheet, secondary battery and electrical device”, which is incorporated into this application in its entirety by reference. Technical Field

[0003] The present application relates to the field of battery technology, and in particular to a composite positive electrode material and a preparation method thereof, a positive electrode sheet, a secondary battery, and an electrical device. Background Art

[0004] Secondary batteries are increasingly widely used due to their clean and renewable characteristics. They mainly rely on the movement of active ions such as lithium ions between the positive and negative electrodes to generate electricity. They have been widely used in electric vehicles, portable electronic devices, energy storage systems and other fields.

[0005] In recent years, with the rapid development of the new energy industry, people's demand for new energy vehicles such as electric cars and electric bicycles has increased, and their performance requirements have become increasingly higher.

[0006] As demand increases, the performance of traditional secondary batteries is increasingly unable to meet people's needs and needs to be further improved.

[0007] Summary of the Invention

[0008] According to various embodiments of the present application, the present application provides a composite positive electrode material and a preparation method thereof, a positive electrode sheet, a battery and an electrical device, aiming to improve the cycle performance and kinetic performance of a secondary battery.

[0009] In a first aspect of the present application, a composite positive electrode material is provided, comprising a nickel-containing positive electrode material and a functional film layer provided on a surface of the nickel-containing positive electrode material, wherein components of the functional film layer include Li2MO4 and an organic lithium phosphonate compound;

[0010] Wherein, M is selected from at least one of sulfur, selenium and tellurium; and the organic lithium phosphonate compound has a structure shown in formula (1):

[0011] * represents the site where the structure represented by formula (1) is connected to other structures in the organic lithium phosphonate compound.

[0012] In the above-mentioned composite positive electrode material, a functional film layer with specific components is formed on the surface of the positive electrode material. The components of the functional film layer include the inorganic component Li2MO4 and the organic component organic lithium phosphonate compound. The specific organic and inorganic components synergistically improve the strength and stability of the functional film layer, thereby reducing the probability of positive electrode material particle breakage; and, on the one hand, Li2MO4 and the organic component organic lithium phosphonate compound can effectively improve the kinetic properties of the positive electrode material as fast ion conductors; on the other hand, the organic lithium phosphonate compound has good thermal stability and good flame retardant function, which can improve the thermal stability of the battery; all aspects work together, so that when the composite positive electrode material is used to prepare a battery, it can improve the cycle stability and kinetic performance of the battery.

[0013] In some embodiments, in the functional film layer, MO4 in Li2MO4 2- The molar ratio of the group to the structure represented by formula (1) in the organic lithium phosphonate compound is (0.6-5):1;

[0014] Optionally, in the functional film layer, MO4 in Li2MO4 2- The molar ratio of the group to the structure represented by formula (1) in the organic lithium phosphonate compound is (1-5):1.

[0015] The ratio of each component in the functional membrane layer is regulated to synergistically form a structurally stable organic-inorganic hybrid functional membrane layer while reducing the negative impact on battery cycle performance.

[0016] In some embodiments, in the composite positive electrode material, the content of the element M is ≤0.1%.

[0017] The content of the residual M element in the functional film layer is regulated to reduce its negative impact on the conductive properties of the positive electrode material.

[0018] In some embodiments, the thickness of the functional film layer is 5 nm to 20 nm;

[0019] Optionally, the thickness of the functional film layer is 5 nm to 10 nm.

[0020] By regulating the thickness of the functional film layer, the stability of the positive electrode material can be further improved while reducing the negative impact on its cycle performance.

[0021] In some embodiments, the organic lithium phosphonate compound contains a group represented by formula (1-1):

[0022] Wherein, R1 is selected from any one of -OR2, a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms, a substituted or unsubstituted alkenyl group having 2 to 10 carbon atoms, and a substituted or unsubstituted alkynyl group having 2 to 10 carbon atoms; R2 is selected from any one of H, Li, a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms, a substituted or unsubstituted alkenyl group having 2 to 10 carbon atoms, a substituted or unsubstituted alkynyl group having 2 to 10 carbon atoms, and a substituted or unsubstituted alkylcarboxylic acid having 2 to 10 carbon atoms.

[0023] In some embodiments, the organic lithium phosphonate compound includes at least one of (a) to (c):

[0024] wherein, in (a), each R2 is not simultaneously selected from H;

[0025] Each R3 is independently selected from any one of a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms, a substituted or unsubstituted alkenyl group having 2 to 10 carbon atoms, a substituted or unsubstituted alkynyl group having 2 to 10 carbon atoms, a phosphonic acid group, and a group represented by formula (1-1), and at least one R3 is selected from a group represented by formula (1-1); L1 is selected from a substituted or unsubstituted alkane subunit having 1 to 10 carbon atoms and a substituted or unsubstituted alkene subunit having 2 to 10 carbon atoms;

[0026] Each L2 is independently selected from any one of a single bond, a substituted or unsubstituted alkane subunit having 1 to 10 carbon atoms, and a substituted or unsubstituted alkene subunit having 2 to 10 carbon atoms; each R4 is independently selected from a substituted or unsubstituted alkyl subunit having 1 to 10 carbon atoms, a substituted or unsubstituted alkenyl subunit having 2 to 10 carbon atoms, a substituted or unsubstituted alkynyl subunit having 2 to 10 carbon atoms, and -L 21 At least one of R5;

[0027] Each L 21 Each is independently selected from a single bond, a substituted or unsubstituted alkane subunit having 1 to 10 carbon atoms, R5 is selected from -N(R6)2, each R6 is independently selected from H, a substituted or unsubstituted alkane subunit having 1 to 10 carbon atoms, a phosphonic acid group and any one of the groups represented by formula (1-1); and (c) contains at least one group represented by formula (1-1).

[0028] In some embodiments, the organic lithium phosphonate compound satisfies at least one of the following conditions (3) to (5):

[0029] (3) Each R2 is independently selected from any one of H, Li, an alkyl group having 1 to 10 carbon atoms, an alkyl group having 1 to 10 carbon atoms substituted by a halogen, an alkyl group having 1 to 10 carbon atoms substituted by a hydroxyl group, an alkenyl group having 2 to 10 carbon atoms, an alkynyl group having 2 to 10 carbon atoms, an alkylcarboxylic acid having 2 to 10 carbon atoms, and an alkylcarboxylic acid having 2 to 10 carbon atoms substituted by a hydroxyl group;

[0030] (4) Each R3 is independently selected from any one of an alkyl group having 1 to 10 carbon atoms, an alkyl group having 1 to 10 carbon atoms substituted by a halogen, an alkyl group having 1 to 10 carbon atoms substituted by a hydroxyl group, an alkenyl group having 2 to 10 carbon atoms, an alkynyl group having 2 to 10 carbon atoms, a phosphonic acid group, and a group represented by formula (1-1);

[0031] (5) Each R4 is independently selected from an alkyl group having 1 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, an alkynyl group having 2 to 10 carbon atoms, and -L 21 At least one of R5; each R6 is independently selected from any one of an alkane subunit having 1 to 10 carbon atoms, a phosphonic acid group and a group represented by formula (1-1).

[0032] In some embodiments, the components of the functional film layer further include a metal oxide rock salt phase;

[0033] Optionally, the metal in the metal oxide type rock salt phase includes at least one of Ni, Co and Mn.

[0034] The metal oxide rock salt phase can further protect the nickel-containing positive electrode material, reduce the chance of it being corroded by organic phosphate compounds, and further improve the cycle stability of the composite positive electrode material.

[0035] In some embodiments, the composition of the nickel-containing positive electrode material satisfies: Li t Ni x Co y A h O z ;

[0036] Wherein, A is selected from at least one of manganese, aluminum, copper, zinc, tin, magnesium and iron, 0<x<1, 0<y<1, 1.5≤y≤2.5, 0<h<1, 0.8≤t≤1.5, 1.5≤z≤2.5.

[0037] In some embodiments, the residual lithium in the composite positive electrode material accounts for ≤2% by mass, and the residual lithium includes Li2CO3, LiOH and Li2O.

[0038] In a second aspect of the present application, a method for preparing a composite positive electrode material is provided, comprising the following steps:

[0039] The nickel-containing positive electrode material, M element and an organic phosphonic acid compound are mixed to prepare a prefabricated positive electrode material;

[0040] Performing a chemical conversion treatment on the prefabricated positive electrode material to prepare the composite positive electrode material;

[0041] The M element includes at least one of sulfur, selenium and tellurium; the organic phosphonic acid compound has a structure shown in formula (2):

[0042] * represents the site where the structure represented by formula (2) is connected to other structures in the organic phosphonic acid compound.

[0043] During the preparation of the above-mentioned composite positive electrode material, the M element reacts with the layered oxide in the nickel-containing positive electrode material to form Li2M2O3, and at the same time forms a metal oxide-type rock salt phase to protect the surface of the positive electrode material particles, so that the organic phosphonic acid compound preferentially reacts with the residual lithium such as LiOH and Li2CO3 on the surface of the positive electrode material to form an organic lithium phosphonate compound, thereby absorbing the residual lithium on the surface of the nickel-containing positive electrode material and preliminarily forming a coating layer on the surface of the positive electrode material; in the further formation process, Li2M2O3 further reacts with the residual lithium and is oxidized to Li2MO4, finally forming a functional film layer including the inorganic component Li2MO4 and the organic component organic lithium phosphonate compound. The specific organic and inorganic components synergistically improve the strength and stability of the functional film layer, thereby reducing the probability of breakage of the positive electrode material particles, and the organic-inorganic hybrid functional film layer generated in situ on the particle surface improves the kinetic properties, cycle stability and thermal stability of the material.

[0044] Furthermore, during the reaction of M to form Li2MO4, the Li + The released Li ions can be used to compensate for the loss of Li ions caused by the formation of the functional film layer. Taking the organic lithium phosphonate compound as hydroxyethylidene diphosphonic acid C2H8O7P2 (HEDP) and the M element as sulfur as an example, the main reaction processes that may be involved in the above preparation process are explained:

[0045] (1)4LiM1O2+2S→4M1O+Li2S2O3+Li2O;

[0046] (2)2Li2O+C2H8O7P2→Li4C2H4O7P2+2H2O;

[0047] (3)2Li2CO3+C2H8O7P2→Li4C2H4O7P2+2H2O+2CO2;

[0048] In reaction (1), the M element reacts with the layered oxide LiM1O2 in the nickel-containing positive electrode material to form Li2M2O3, and simultaneously generates a metal oxide-type rock salt phase M1O, where M1 is the metal in the nickel-containing positive electrode material, including but not limited to: Ni, Co or Mn; at the same time, the organic phosphonic acid compound preferentially reacts with residual lithium such as LiOH and Li2CO3 on the surface of the positive electrode material to form an organic lithium phosphonate compound.

[0049] (4)2LiMO2+S+2Li2O-4e - →2MO+Li2SO4+4Li + ;

[0050] (5)2LiMO2+S+2Li2CO3-4e - →2MO+Li2SO4+2CO2+4Li + ;

[0051] (6)Li2S2O3+5Li2O-8e - →2Li2SO4+8Li + ;

[0052] (7)Li2S2O3+Li2CO3-8e - →2Li2SO4+5CO2+8Li + ;

[0053] During the formation process, the main reactions are (4) to (7). Li2M2O3 further reacts with the residual lithium and is oxidized to Li2MO4, eventually forming a functional membrane layer including inorganic component Li2MO4 and organic component lithium phosphonate compound, and further absorbs the residual lithium, converting the Li in the residual lithium into Li + Release it.

[0054] In some embodiments, the mixing process comprises the following steps:

[0055] The nickel-containing positive electrode material and the M element are subjected to a first mixing process, and then the organic phosphonic acid compound is added to perform a second mixing process;

[0056] Optionally, the first mixing treatment time is 0.5h to 6h;

[0057] Optionally, the second mixing treatment lasts for 0.5 h to 3 h.

[0058] Research has found that when organic phosphonic acid compounds come into direct contact with layered oxides in nickel-containing cathode materials, a redox reaction occurs, releasing oxygen, thereby damaging the structure of the cathode material. Taking hydroxyethylidene diphosphonic acid C2H8O7P2 (HEDP) as an example, the reaction is as follows:

[0059] 4LiMO2+C2H8O7P2→Li4C2H4O7P2+4MO+2H2O+O2

[0060] Therefore, the nickel-containing positive electrode material and the M element are first mixed to deposit a metal oxide rock salt phase MO on the surface of the nickel-containing positive electrode material, which is equivalent to a "protective barrier" to reduce the probability of oxygen release due to redox reaction when the organic phosphonic acid compound directly contacts the layered oxide in the nickel-containing positive electrode material.

[0061] In some embodiments, the mixing process satisfies at least one of the following conditions (6) to (7):

[0062] (6) The mass ratio of the M element to the nickel-containing positive electrode material is (0.01-1):100;

[0063] Optionally, the mass ratio of the M element to the nickel-containing positive electrode material is (0.1-0.4):100;

[0064] (7) The mass ratio of the organic phosphonic acid compound to the nickel-containing positive electrode material is (0.01-1):100;

[0065] Optionally, the mass ratio of the organic phosphonic acid compound to the nickel-containing positive electrode material is (0.1-0.5):100.

[0066] The mass ratio of the M element, the organic phosphonic acid compound and the nickel-containing positive electrode material is controlled to absorb residual lithium while forming a stable inorganic-organic hybrid functional membrane layer, further avoiding the negative impact on the battery cycle performance.

[0067] In a third aspect of the present application, a positive electrode sheet is provided, comprising the composite positive electrode material of the first aspect or the composite positive electrode material prepared by the preparation method of the composite positive electrode material of the second aspect.

[0068] In a fourth aspect of the present application, a secondary battery is provided, comprising the composite positive electrode material of the first aspect or the composite positive electrode material prepared by the preparation method of the composite positive electrode material of the second aspect or the positive electrode sheet of the third aspect.

[0069] In a fifth aspect of the present application, an electrical device is provided, comprising the secondary battery according to the fourth aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0070] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments of the present application. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on the drawings without inventive work. In the drawings:

[0071] FIG1 is a schematic diagram of an embodiment of a battery cell;

[0072] Figure 2 is an exploded view of Figure 1;

[0073] FIG3 is a schematic diagram of an embodiment of a battery pack;

[0074] FIG4 is an exploded view of FIG3 ;

[0075] 5 is a schematic diagram of an embodiment of an electrical device using a secondary battery as a power source;

[0076] FIG6 is an electron microscope image of a composite positive electrode material according to one embodiment.

[0077] Reference numerals: 1. battery pack; 2. upper case; 3. lower case; 4. battery cell; 41. housing; 42. electrode assembly; 43. cover plate; 5. electrical device. DETAILED DESCRIPTION

[0078] To make the above-mentioned objects, features, and advantages of the present application more clearly understood, the specific embodiments of the present application are described in detail below. The following description sets forth many specific details to facilitate a full understanding of the present application. However, the present application can be implemented in many other ways than those described herein, and those skilled in the art can make similar modifications without violating the scope of the present application. Therefore, the present application is not limited to the specific embodiments disclosed below.

[0079] In this application, the terms "first" and "second" are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly specify the number of technical features indicated. Therefore, a feature specified as "first" or "second" may explicitly or implicitly include at least one of such features. In the description of this application, "plurality" means at least two, for example, two, three, etc., unless otherwise specifically defined.

[0080] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application pertains. The terms used herein in the specification of this application are for the purpose of describing specific embodiments only and are not intended to limit this application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0081] In this application, the term "alkyl" refers to a group formed when an alkane loses a hydrogen, such as methane loses a hydrogen to form a methyl group; "alkenyl or alkynyl" refers to a group formed when an alkene or alkyne loses a hydrogen, such as ethylene loses a hydrogen to form vinyl, and acetylene loses a hydrogen to form ethynyl.

[0082] The term "chain alkane" refers to an alkane in which the carbon atoms are connected by single carbon-carbon bonds and do not form a ring, and the remaining valence bonds are all hydrogen bonds, including straight-chain alkanes and branched-chain alkanes.

[0083] In the present application, the number of carbon atoms in the “alkyl group having 1 to 10 carbon atoms” may be 1 to 30, including 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10. Non-limiting examples include methane, ethyl, n-propyl, isopropyl, n-butane, isobutyl, 2-ethylbutane, 3,3-dimethylbutane, n-pentane, isopentane, neopentane, 1-methylpentane, 3-methylpentane, 2-ethylpentane, 4-methyl-2-pentane, n-hexane, 1-methylhexane, 2-ethylhexane, 2-butylhexane, n-heptane, 1-methylheptane, 2,2-dimethylheptane, 2-ethylheptane, n-octane, n-nonane, and n-decane.

[0084] In the present application, the term "substituted or unsubstituted" means that the functional group described after the term may or may not have a substituent.

[0085] In the present application, the halogen group includes chlorine, fluorine, bromine, and iodine.

[0086] In this application, when two groups are linked by a point of attachment, e.g. When R is selected from a single bond, it means that the two groups do not need to be connected through a specific group, but are directly connected by a single bond, that is,

[0087] In one embodiment of the present application, a composite positive electrode material is provided, which includes a nickel-containing positive electrode material and a functional film layer provided on the surface of the nickel-containing positive electrode material, wherein components of the functional film layer include Li2MO4 and an organic lithium phosphonate compound.

[0088] Wherein, M is selected from at least one of sulfur, selenium and tellurium; the organic lithium phosphonate compound has a structure shown in formula (1):

[0089] * represents the site where the structure represented by formula (1) is connected to other structures in the organic lithium phosphonate compound.

[0090] In the above-mentioned composite positive electrode material, a functional film layer with specific components is formed on the surface of the positive electrode material. The components of the functional film layer include the inorganic component Li2MO4 and the organic component organic lithium phosphonate compound. The specific organic and inorganic components synergistically improve the strength and stability of the functional film layer, thereby reducing the probability of positive electrode material particle breakage; and, on the one hand, Li2MO4 and the organic component organic lithium phosphonate compound can effectively improve the kinetic properties of the positive electrode material as fast ion conductors; on the other hand, the organic lithium phosphonate compound has good thermal stability and good flame retardant function, which can improve the thermal stability of the battery; all aspects work together, so that when the composite positive electrode material is used to prepare a battery, it can improve the cycle stability and kinetic performance of the battery.

[0091] It can be understood that “*” represents the site where the group represented by formula (1) is connected to other structures in the organic lithium phosphonate compound. In other words, there is at least one electron in the group represented by formula (1) that forms a covalent bond with an electron in other structures in the organic lithium phosphonate compound.

[0092] In the functional film layer, MO4 in Li2MO4 2- The molar ratio of the group to the structure represented by formula (1) in the organic lithium phosphonate compound is (0.6-5):1.

[0093] In some embodiments, in the functional film layer, MO4 in Li2MO4 2- The molar ratio of the group to the structure represented by formula (1) in the organic lithium phosphonate compound is (1 to 5):1.

[0094] In some embodiments, in the functional film layer, MO4 in Li2MO4 2- The molar ratio of the group to the structure represented by formula (1) in the organic lithium phosphonate compound is (1.5 to 5):1.

[0095] The ratio of each component in the functional membrane layer is regulated to synergistically form a structurally stable organic-inorganic hybrid functional membrane layer while reducing the negative impact on battery cycle performance.

[0096] It is understandable that the MO4 in Li2MO4 2- The molar ratio of the group to the structure represented by formula (1) in the organic lithium phosphonate compound directly reacts with the molar ratio of the structure represented by formula (1) in the Li2MO4 organic lithium phosphonate compound.

[0097] Specifically, the functional film layer can be directly tested by using X-ray photoelectron spectroscopy (XPS) to obtain an energy spectrum diagram and mark MO4 accordingly. 2- The ratio of the peak intensities of the characteristic peaks of the group and the group of the structure shown in formula (1) is MO4 2-The molar ratio of the group to the group of the structure represented by formula (1).

[0098] In the above “(0.6~5):1”, the values ​​include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Specific examples include but are not limited to the point values ​​in the embodiments and the following point values: 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1, 2:1, 2.1:1, 2.2:1, 2.3:1, 2.4, 2.5:1, 2.6:1, 2.7:1, 2.8:1, 2.9:1 , 3:1, 3.1:1, 3.2:1, 3.3:1, 3.4, 3.5:1, 3.6:1, 3.7:1, 3.8:1, 3.9:1, 4:1, 5:1; or a range consisting of any two values, for example: “(1.5-4):1, (1.5-3.5):1, (1.5-3):1, (1.5-2.5):1, (1.5-2):1, (2-4):1, (2-3.5):1, (2-3):1, (2-2.5):1, (2.5-4):1, (2.5-3.5):1, (2.5-3:1.

[0099] In some embodiments, the MO4 in Li2MO4 2- The molar ratio of the group to the structure represented by formula (1) in the organic lithium phosphonate compound is 2:1.

[0100] In some embodiments, in the composite positive electrode material, the content of the simple substance of the M element is ≤0.1%.

[0101] The content of the residual M element in the functional film layer is regulated to reduce its negative impact on the conductive properties of the positive electrode material.

[0102] In some embodiments, the thickness of the functional film layer is 5 nm to 20 nm;

[0103] Optionally, the thickness of the functional film layer is 5 nm to 10 nm.

[0104] By regulating the thickness of the functional film layer, the stability of the positive electrode material can be further improved while reducing the negative impact on its cycle performance.

[0105] In the above-mentioned "5nm~20nm", the values ​​include the minimum and maximum values ​​of the range, and every value between the minimum and maximum values. Specific examples include but are not limited to the point values ​​in the embodiments and the following point values: 5nm, 6nm, 7nm, 8nm, 9nm, 10nm, 11nm, 12nm, 13nm, 14nm, 15nm, 16nm, 17nm, 18nm, 19nm, 20nm; or a range consisting of any two numerical values, for example: 5nm~20nm, 5nm~15nm, 5nm~10nm, 7nm~20nm, 7nm~20nm, 7nm~15nm, 7nm~10nm, 10nm~20nm, 10nm~15nm, 15nm~20nm.

[0106] In some embodiments, the organic lithium phosphonate compound contains a group represented by formula (1-1):

[0107] Wherein, R1 is selected from any one of -OR2, a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms, a substituted or unsubstituted alkenyl group having 2 to 10 carbon atoms, and a substituted or unsubstituted alkynyl group having 2 to 10 carbon atoms; R2 is selected from any one of H, Li, a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms, a substituted or unsubstituted alkenyl group having 2 to 10 carbon atoms, a substituted or unsubstituted alkynyl group having 2 to 10 carbon atoms, and a substituted or unsubstituted alkylcarboxylic acid having 2 to 10 carbon atoms.

[0108] In some embodiments, R1 is selected from any one of -OR2, an alkyl group having 1 to 10 carbon atoms, an alkyl group having 1 to 10 carbon atoms substituted by a halogen, an alkyl group having 1 to 10 carbon atoms substituted by a hydroxyl group, an alkenyl group having 2 to 10 carbon atoms, and an alkynyl group having 2 to 10 carbon atoms.

[0109] In some embodiments, R1 is selected from any one of -OR2, a chain alkyl group having 1 to 10 carbon atoms, a chain alkyl group having 1 to 10 carbon atoms substituted by halogen, a chain alkyl group having 1 to 10 carbon atoms substituted by hydroxyl, an alkenyl group having 2 to 10 carbon atoms, and an alkynyl group having 2 to 10 carbon atoms.

[0110] In some embodiments, R1 is selected from any one of -OR2, an alkyl group having 1 to 5 carbon atoms, an alkyl group having 1 to 5 carbon atoms substituted by a halogen, an alkyl group having 1 to 5 carbon atoms substituted by a hydroxyl group, an alkenyl group having 2 to 5 carbon atoms, and an alkynyl group having 2 to 5 carbon atoms.

[0111] In some embodiments, R1 is selected from any one of -OR2, a chain alkyl group having 1 to 5 carbon atoms, a chain alkyl group having 1 to 5 carbon atoms substituted by a halogen, a chain alkyl group having 1 to 5 carbon atoms substituted by a hydroxyl group, an alkenyl group having 2 to 5 carbon atoms, and an alkynyl group having 2 to 5 carbon atoms.

[0112] In some embodiments, R1 is selected from any one of -OR2, a chain alkyl group having 1 to 3 carbon atoms, a chain alkyl group having 1 to 3 carbon atoms substituted by a halogen, a chain alkyl group having 1 to 3 carbon atoms substituted by a hydroxyl group, an alkenyl group having 2 to 5 carbon atoms, and an alkynyl group having 2 to 5 carbon atoms.

[0113] In some embodiments, R2 is selected from any one of H, Li, an alkyl group having 1 to 10 carbon atoms, an alkyl group having 1 to 10 carbon atoms substituted by a halogen, an alkyl group having 1 to 10 carbon atoms substituted by a hydroxyl group, an alkenyl group having 2 to 10 carbon atoms, an alkynyl group having 2 to 10 carbon atoms, and an alkylcarboxylic acid having 2 to 10 carbon atoms.

[0114] It is understood that "alkyl carboxylic acid" refers to a group formed by replacing at least one hydrogen in an alkyl group with a carboxylic acid group.

[0115] In some embodiments, R2 is selected from any one of H, Li, an alkyl group having 1 to 10 carbon atoms, an alkyl group having 1 to 10 carbon atoms substituted by halogen, an alkyl group having 1 to 10 carbon atoms substituted by hydroxyl, an alkenyl group having 2 to 10 carbon atoms, an alkynyl group having 2 to 10 carbon atoms, and an alkylcarboxylic acid having 2 to 10 carbon atoms.

[0116] In some embodiments, R2 is selected from any one of H, Li, an alkyl group having 1 to 5 carbon atoms, an alkyl group having 1 to 5 carbon atoms substituted by a halogen, an alkyl group having 1 to 5 carbon atoms substituted by a hydroxyl group, an alkenyl group having 2 to 5 carbon atoms, an alkynyl group having 2 to 5 carbon atoms, and an alkylcarboxylic acid having 2 to 5 carbon atoms.

[0117] In some embodiments, R2 is selected from any one of H, Li, an alkyl group having 1 to 5 carbon atoms, an alkyl group having 1 to 5 carbon atoms substituted by a halogen, an alkyl group having 1 to 5 carbon atoms substituted by a hydroxyl group, an alkenyl group having 2 to 5 carbon atoms, an alkynyl group having 2 to 5 carbon atoms, and an alkylcarboxylic acid having 2 to 5 carbon atoms.

[0118] In some embodiments, R2 is selected from any one of H, Li, an alkyl group having 1 to 3 carbon atoms, an alkyl group having 1 to 3 carbon atoms substituted by a halogen, an alkyl group having 1 to 3 carbon atoms substituted by a hydroxyl group, an alkenyl group having 2 to 5 carbon atoms, an alkynyl group having 2 to 5 carbon atoms, and an alkylcarboxylic acid having 2 to 5 carbon atoms.

[0119] In some embodiments, the organophosphonate lithium compound includes at least one of (a) to (c):

[0120] Wherein, in (a), each R2 is not selected from H at the same time.

[0121] In some embodiments, each R3 is independently selected from any one of a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms, a substituted or unsubstituted alkenyl group having 2 to 10 carbon atoms, a substituted or unsubstituted alkynyl group having 2 to 10 carbon atoms, a phosphonic acid group and a group represented by formula (1-1), and at least one R3 is selected from the group represented by formula (1-1); L1 is selected from a substituted or unsubstituted alkane subunit having 1 to 10 carbon atoms and a substituted or unsubstituted alkene subunit having 2 to 10 carbon atoms.

[0122] In some embodiments, each R3 is independently selected from any one of an alkyl group having 1 to 10 carbon atoms, an alkyl group having 1 to 10 carbon atoms substituted by a halogen, an alkyl group having 1 to 10 carbon atoms substituted by a hydroxyl group, an alkenyl group having 2 to 10 carbon atoms, an alkynyl group having 2 to 10 carbon atoms, a phosphonic acid group, and a group represented by formula (1-1), and at least one R3 is selected from a group represented by formula (1-1).

[0123] In some embodiments, each R3 is independently selected from any one of a chain alkyl group having 1 to 10 carbon atoms, a chain alkyl group having 1 to 10 carbon atoms substituted by a halogen, a chain alkyl group having 1 to 10 carbon atoms substituted by a hydroxyl group, an alkenyl group having 2 to 10 carbon atoms, an alkynyl group having 2 to 10 carbon atoms, a phosphonic acid group, and a group represented by formula (1-1), and at least one R3 is selected from a group represented by formula (1-1).

[0124] In some embodiments, each R3 is independently selected from any one of a chain alkyl group having 1 to 5 carbon atoms, a chain alkyl group having 1 to 5 carbon atoms substituted by a halogen, a chain alkyl group having 1 to 5 carbon atoms substituted by a hydroxyl group, an alkenyl group having 2 to 5 carbon atoms, an alkynyl group having 2 to 10 carbon atoms, a phosphonic acid group, and a group represented by formula (1-1), and at least one R3 is selected from a group represented by formula (1-1).

[0125] In some embodiments, each L2 is independently selected from any one of a single bond, an alkane subunit having 1 to 10 carbon atoms, an alkane subunit having 1 to 10 carbon atoms substituted by a hydroxyl group, an alkane subunit having 1 to 10 carbon atoms substituted by a halogen, and an alkene subunit having 2 to 10 carbon atoms.

[0126] In some embodiments, each L2 is independently selected from any one of a single bond, a chain alkane subunit having 1 to 10 carbon atoms, a chain alkane subunit having 1 to 10 carbon atoms substituted by a hydroxyl group, a chain alkane subunit having 1 to 10 carbon atoms substituted by a halogen, and an alkene subunit having 2 to 10 carbon atoms.

[0127] In some embodiments, each L2 is independently selected from any one of a single bond, an alkane subunit having 1 to 5 carbon atoms, an alkane subunit having 1 to 5 carbon atoms substituted by a hydroxyl group, an alkane subunit having 1 to 5 carbon atoms substituted by a halogen, and an alkene subunit having 2 to 5 carbon atoms.

[0128] In some embodiments, each L2 is independently selected from any one of a single bond, a chain alkane subunit having 1 to 5 carbon atoms, a chain alkane subunit having 1 to 5 carbon atoms substituted by a hydroxyl group, a chain alkane subunit having 1 to 5 carbon atoms substituted by a halogen, and a chain alkene subunit having 2 to 5 carbon atoms.

[0129] In some embodiments, each R4 is independently selected from substituted or unsubstituted alkyl having 1 to 10 carbon atoms, substituted or unsubstituted alkenyl having 2 to 10 carbon atoms, substituted or unsubstituted alkynyl having 2 to 10 carbon atoms, and -L 21 At least one of R5.

[0130] Each L 21 Each is independently selected from a single bond, a substituted or unsubstituted alkane subunit with 1 to 10 carbon atoms, R5 is selected from -N(R6)2, each R6 is independently selected from H, a substituted or unsubstituted alkane subunit with 1 to 10 carbon atoms, a phosphonic acid group and any one of the structures represented by formula (1-1); and (c) contains at least one group represented by formula (1-1).

[0131] It is understood that (c) contains at least one group represented by formula (1-1) means that at least one R4 in formula (c) is selected from -L 21 R5, and at least one L 21 is -N(R6)2, and at least one R6 is a group represented by formula (1-1).

[0132] In some embodiments, each L 21 Each of them is independently selected from any one of a single bond, an alkanediyl group having 1 to 10 carbon atoms, an alkanediyl group having 1 to 10 carbon atoms substituted by a halogen, and an alkanediyl group having 1 to 10 carbon atoms substituted by a hydroxyl group.

[0133] In some embodiments, each L 21Each of them is independently selected from any one of a single bond, an alkane substituent having 1 to 10 carbon atoms, an alkane substituent having 1 to 10 carbon atoms substituted by a halogen, and an alkane substituent having 1 to 10 carbon atoms substituted by a hydroxyl group.

[0134] In some embodiments, each L 21 Each of the groups is independently selected from any one of a single bond, an alkanediyl group having 1 to 5 carbon atoms, an alkanediyl group having 1 to 5 carbon atoms substituted by a halogen, and an alkanediyl group having 1 to 5 carbon atoms substituted by a hydroxyl group.

[0135] In some embodiments, each L 21 Each of them is independently selected from any one of a single bond, an alkane substituent having 1 to 5 carbon atoms, an alkane substituent having 1 to 5 carbon atoms substituted by a halogen, and an alkane substituent having 1 to 5 carbon atoms substituted by a hydroxyl group.

[0136] In some embodiments, each L 21 Each of the groups is independently selected from any one of a single bond, an alkanediyl group having 1 to 3 carbon atoms, an alkanediyl group having 1 to 3 carbon atoms substituted by a halogen, and an alkanediyl group having 1 to 3 carbon atoms substituted by a hydroxyl group.

[0137] In some embodiments, each R6 is independently selected from H, an alkane subunit having 1 to 10 carbon atoms, an alkane subunit having 1 to 10 carbon atoms substituted by a halogen, an alkane subunit having 1 to 10 carbon atoms substituted by a hydroxyl group, a phosphonic acid group, and any one of the structures shown in formula (1-1).

[0138] In some embodiments, each R6 is independently selected from H, a chain alkane subunit with 1 to 10 carbon atoms, a chain alkane subunit with 1 to 10 carbon atoms substituted by a halogen, a chain alkane subunit with 1 to 10 carbon atoms substituted by a hydroxyl group, a phosphonic acid group, and any one of the structures shown in formula (1-1).

[0139] In some embodiments, each R6 is independently selected from H, an alkane subunit having 1 to 5 carbon atoms, an alkane subunit having 1 to 5 carbon atoms substituted by a halogen, an alkane subunit having 1 to 5 carbon atoms substituted by a hydroxyl group, a phosphonic acid group, and any one of the structures shown in formula (1-1).

[0140] In some embodiments, each R6 is independently selected from H, a chain alkane subunit with 1 to 5 carbon atoms, a chain alkane subunit with 1 to 5 carbon atoms substituted by a halogen, a chain alkane subunit with 1 to 5 carbon atoms substituted by a hydroxyl group, a phosphonic acid group, and any one of the structures shown in formula (1-1).

[0141] In some embodiments, the components of the functional film layer further include a metal oxide-type rock salt phase;

[0142] Optionally, the metal in the metal oxide type rock salt phase includes at least one of Ni, Co and Mn.

[0143] The metal oxide rock salt phase can further protect the nickel-containing positive electrode material, reduce the chance of it being corroded by organic phosphate compounds, and further improve the cycle stability of the composite positive electrode material.

[0144] It is understood that the nickel positive electrode material can be various nickel positive electrode materials commonly used in the art, such as lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, also referred to as NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM523), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (referred to as NCM811), lithium nickel cobalt aluminum oxide (such as LiNi 0.8 Co 0.15 Al 0.05 O2) and at least one of its modified compounds, etc.

[0145] It should be noted that the lithium content in the positive electrode material mentioned in the above example refers to its content when it is not in use. During the use of the battery, it will be repeatedly used as a battery, and the Li in the positive electrode active material will change during the charge and discharge process. That is, the molar subscript of Li in the positive electrode active material in the battery product will not always remain at 1, but will change.

[0146] In some embodiments, the composition of the nickel-containing positive electrode material satisfies: Li t Ni x Co y A h O z ;

[0147] Wherein, A is selected from at least one of manganese, aluminum, copper, zinc, tin, magnesium and iron, 0<x<1, 0<y<1, 1.5≤y≤2.5, 0<h<1, 0.8≤t≤1.5, 1.5≤z≤2.5.

[0148] In some embodiments, the residual lithium in the composite positive electrode material accounts for ≤2% by mass, and the residual lithium includes Li2CO3, LiOH and Li2O.

[0149] Another embodiment of the present application provides a method for preparing a composite positive electrode material, comprising the following steps S10 to S20.

[0150] S10, mixing the nickel-containing positive electrode material, M element and the organic phosphonic acid compound to prepare a prefabricated positive electrode material.

[0151] S20, performing a chemical conversion treatment on the prefabricated positive electrode material to prepare a composite positive electrode material.

[0152] The M element includes at least one of sulfur, selenium and tellurium; and the organic phosphonic acid compound has a structure represented by formula (2):

[0153] * represents the site where the structure represented by formula (2) is connected to other structures in the organic phosphonic acid compound.

[0154] During the preparation of the above-mentioned composite positive electrode material, the M element reacts with the layered oxide in the nickel-containing positive electrode material to form Li2M2O3, and at the same time forms a metal oxide-type rock salt phase to protect the surface of the positive electrode material particles, so that the organic phosphonic acid compound preferentially reacts with the residual lithium such as LiOH and Li2CO3 on the surface of the positive electrode material to form an organic lithium phosphonate compound, thereby absorbing the residual lithium on the surface of the nickel-containing positive electrode material and preliminarily forming a coating layer on the surface of the positive electrode material; in the further formation process, Li2M2O3 further reacts with the residual lithium and is oxidized to Li2MO4, finally forming a functional film layer including the inorganic component Li2MO4 and the organic component organic lithium phosphonate compound. The specific organic and inorganic components synergistically improve the strength and stability of the functional film layer, thereby reducing the probability of breakage of the positive electrode material particles, and the organic-inorganic hybrid functional film layer generated in situ on the particle surface improves the kinetic properties, cycle stability and thermal stability of the material.

[0155] It can be understood that the organic phosphonic acid compound containing the structure shown in formula (2) reacts with residual lithium such as LiOH and Li2CO3 on the surface of the positive electrode material to form an organic lithium phosphonate compound having the structure shown in formula (1).

[0156] Furthermore, during the reaction of M to form Li2MO4, the Li + The released Li ions can be used to compensate for the loss of Li ions caused by the formation of the functional film layer. Taking the organic lithium phosphonate compound as hydroxyethylidene diphosphonic acid C2H8O7P2 (HEDP) and the M element as sulfur as an example, the main reaction processes that may be involved in the above preparation process are explained:

[0157] (1)4LiM1O2+2S→4M1O+Li2S2O3+Li2O;

[0158] (2)2Li2O+C2H8O7P2→Li4C2H4O7P2+2H2O;

[0159] (3)2Li2CO3+C2H8O7P2→Li4C2H4O7P2+2H2O+2CO2;

[0160] In reaction (1), the M element reacts with the layered oxide LiM1O2 in the nickel-containing positive electrode material to form Li2M2O3, and simultaneously generates a metal oxide-type rock salt phase M1O, where M1 is the metal in the nickel-containing positive electrode material, including but not limited to: Ni, Co or Mn; at the same time, the organic phosphonic acid compound preferentially reacts with residual lithium such as LiOH and Li2CO3 on the surface of the positive electrode material to form an organic lithium phosphonate compound.

[0161] (4)2LiMO2+S+2Li2O-4e - →2MO+Li2SO4+4Li + ;

[0162] (5)2LiMO2+S+2Li2CO3-4e - →2MO+Li2SO4+2CO2+4Li + ;

[0163] (6)Li2S2O3+5Li2O-8e - →2Li2SO4+8Li + ;

[0164] (7)Li2S2O3+Li2CO3-8e - →2Li2SO4+5CO2+8Li + ;

[0165] During the formation process, the main reactions are (4) to (7). Li2M2O3 further reacts with the residual lithium and is oxidized to Li2MO4, eventually forming a functional membrane layer including inorganic component Li2MO4 and organic component lithium phosphonate compound, and further absorbs the residual lithium, converting the Li in the residual lithium into Li + Release it.

[0166] It is understandable that when the composite cathode material or the method for preparing the composite cathode material is used to prepare a secondary battery, the formation step in step S20 can be performed directly in the battery.

[0167] In some embodiments, the mixing process in step S10 includes the following step S11 .

[0168] Step S11: performing a first mixing treatment on the nickel-containing positive electrode material and the M element, and then adding an organic phosphonic acid compound to perform a second mixing treatment.

[0169] The researchers found that when organic phosphonic acid compounds come into direct contact with the layered oxides in nickel-containing cathode materials, a redox reaction occurs, releasing oxygen, which damages the structure of the cathode material. Taking hydroxyethylidene diphosphonic acid C2H8O7P2 (HEDP) as an example, the reaction is as follows:

[0170] 4LiMO2+C2H8O7P2→Li4C2H4O7P2+4MO+2H2O+O2

[0171] Therefore, the nickel-containing positive electrode material and the M element are first mixed to deposit a metal oxide rock salt phase MO on the surface of the nickel-containing positive electrode material, which is equivalent to a "protective barrier" to reduce the probability of oxygen release due to redox reaction when the organic phosphonic acid compound directly contacts the layered oxide in the nickel-containing positive electrode material.

[0172] Optionally, the first mixing treatment lasts for 0.5 h to 6 h.

[0173] Optionally, the second mixing treatment lasts for 0.5 h to 3 h.

[0174] In the above "0.5h~6h", the values ​​include the minimum and maximum values ​​of the range, and every value between the minimum and maximum values. Specific examples include but are not limited to the point values ​​in the embodiments and the following point values: 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, 6h; or a range consisting of any two values.

[0175] In the above "0.5h~3h", the values ​​include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Specific examples include but are not limited to the point values ​​in the embodiments and the following point values: 0.5h, 1h, 1.5h, 2h, 2.5h, 3h; or a range consisting of any two values.

[0176] In some embodiments, the first mixing process and the second mixing process are both performed under stirring conditions; further, the stirring speed is maintained at 400 r / s to 1000 r / s.

[0177] In some embodiments, the mass ratio of M element to the nickel-containing positive electrode material is (0.01-1):100.

[0178] Optionally, the mass ratio of M element to the nickel-containing positive electrode material is (0.1-0.4):100.

[0179] In some embodiments, the mass ratio of the organic phosphonic acid compound to the nickel-containing positive electrode material is (0.01-1):100.

[0180] Optionally, the mass ratio of the organic phosphonic acid compound to the nickel-containing positive electrode material is (0.1-0.5):100.

[0181] By controlling the mass ratio of M element, organic phosphonic acid compound and nickel-containing positive electrode material, a stable inorganic-organic hybrid functional membrane layer is formed while absorbing residual lithium, and further avoiding the negative impact on battery cycle performance.

[0182] In the above “(0.01~1):100”, the values ​​include the minimum and maximum values ​​of the range, and every value between the minimum and maximum values. Specific examples include but are not limited to the point values ​​in the embodiments and the following point values: 0.01:100, 0.05:100, 0.1:100, 0.15:100, 0.2:100, 0.25:100, 0.3:100, 0.35:100, 0.4:100, 0.45:100, 0.5:100, 0.55:100, 0.6:100, 0.65:100, 0.7:100, 0.75:100, 0.8:100, 0.85:100, 0.9:100, 0.95:100, 1:100; or a range consisting of any two values.

[0183] In the above “(0.01~1):100”, the values ​​include the minimum and maximum values ​​of the range, and every value between the minimum and maximum values. Specific examples include but are not limited to the point values ​​in the embodiments and the following point values: 0.01:100, 0.05:100, 0.1:100, 0.15:100, 0.2:100, 0.25:100, 0.3:100, 0.35:100, 0.4:100, 0.45:100, 0.5:100, 0.55:100, 0.6:100, 0.65:100, 0.7:100, 0.75:100, 0.8:100, 0.85:100, 0.9:100, 0.95:100, 1:100; or a range consisting of any two values.

[0184] In some embodiments, after the mixing step and before the forming step, a drying step is further included.

[0185] Furthermore, the drying temperature is 80° C. to 110° C., and the drying time is 0.01 h to 5 h.

[0186] In some embodiments, the mixing step is performed in a solvent; further, the solvent includes N-methylpyrrolidone and a small molecule alcohol having 2 to 5 carbon atoms.

[0187] Furthermore, the small molecule alcohol having 2 to 5 carbon atoms includes ethanol.

[0188] In some embodiments, the M element is added in the form of a solution; specifically, the M element and N-methylpyrrolidone are mixed to form a solution; further, the concentration of the M element is 0.5 mol / L to 2 mol / L.

[0189] In some embodiments, the organic phosphonic acid compound is added in the form of a solution; specifically, the organic phosphonic acid compound and a small molecule alcohol having 2 to 5 carbon atoms are mixed to form a solution; further, the concentration of the organic phosphonic acid compound is 0.5 mol / L to 2 mol / L.

[0190] In some embodiments, the organic phosphonic acid compound contains a group represented by formula (1-2):

[0191] Among them, R 1a Select from -OR 2a , any one of a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms, a substituted or unsubstituted alkenyl group having 2 to 10 carbon atoms, and a substituted or unsubstituted alkynyl group having 2 to 10 carbon atoms; R 2a Any one selected from H, Li, a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms, a substituted or unsubstituted alkenyl group having 2 to 10 carbon atoms, a substituted or unsubstituted alkynyl group having 2 to 10 carbon atoms, and a substituted or unsubstituted alkylcarboxylic acid having 2 to 10 carbon atoms.

[0192] In some embodiments, R 1a Select from -OR 2a , any one of an alkyl group having 1 to 10 carbon atoms, an alkyl group having 1 to 10 carbon atoms substituted by a halogen, an alkyl group having 1 to 10 carbon atoms substituted by a hydroxyl group, an alkenyl group having 2 to 10 carbon atoms, and an alkynyl group having 2 to 10 carbon atoms.

[0193] In some embodiments, R 1a Select from -OR 2a , any one of a chain alkyl group having 1 to 10 carbon atoms, a chain alkyl group having 1 to 10 carbon atoms substituted by a halogen, a chain alkyl group having 1 to 10 carbon atoms substituted by a hydroxyl group, an alkenyl group having 2 to 10 carbon atoms, and an alkynyl group having 2 to 10 carbon atoms.

[0194] In some embodiments, R 1a Select from -OR 2a, an alkyl group having 1 to 5 carbon atoms, an alkyl group having 1 to 5 carbon atoms substituted by a halogen, an alkyl group having 1 to 5 carbon atoms substituted by a hydroxyl group, an alkenyl group having 2 to 5 carbon atoms, and an alkynyl group having 2 to 5 carbon atoms.

[0195] In some embodiments, R 1a Select from -OR 2a , any one of a chain alkyl group having 1 to 5 carbon atoms, a chain alkyl group having 1 to 5 carbon atoms substituted by a halogen, a chain alkyl group having 1 to 5 carbon atoms substituted by a hydroxyl group, an alkenyl group having 2 to 5 carbon atoms, and an alkynyl group having 2 to 5 carbon atoms.

[0196] In some embodiments, R 1a Select from -OR 2a , any one of a chain alkyl group having 1 to 3 carbon atoms, a chain alkyl group having 1 to 3 carbon atoms substituted by a halogen, a chain alkyl group having 1 to 3 carbon atoms substituted by a hydroxyl group, an alkenyl group having 2 to 5 carbon atoms, and an alkynyl group having 2 to 5 carbon atoms.

[0197] In some embodiments, R 2a Any one selected from the group consisting of H, an alkyl group having 1 to 10 carbon atoms, an alkyl group having 1 to 10 carbon atoms substituted by a halogen, an alkyl group having 1 to 10 carbon atoms substituted by a hydroxyl group, an alkenyl group having 2 to 10 carbon atoms, an alkynyl group having 2 to 10 carbon atoms, and an alkylcarboxylic acid having 2 to 10 carbon atoms.

[0198] It is understood that "alkyl carboxylic acid" refers to a group formed by replacing at least one hydrogen in an alkyl group with a carboxylic acid group.

[0199] In some embodiments, R 2a Any one selected from the group consisting of H, an alkyl group having 1 to 10 carbon atoms, an alkyl group having 1 to 10 carbon atoms substituted by a halogen, an alkyl group having 1 to 10 carbon atoms substituted by a hydroxyl group, an alkenyl group having 2 to 10 carbon atoms, an alkynyl group having 2 to 10 carbon atoms, and an alkylcarboxylic acid having 2 to 10 carbon atoms.

[0200] In some embodiments, R 2a Any one selected from the group consisting of H, an alkyl group having 1 to 5 carbon atoms, an alkyl group having 1 to 5 carbon atoms substituted by a halogen, an alkyl group having 1 to 5 carbon atoms substituted by a hydroxyl group, an alkenyl group having 2 to 5 carbon atoms, an alkynyl group having 2 to 5 carbon atoms, and an alkylcarboxylic acid having 2 to 5 carbon atoms.

[0201] In some embodiments, R 2aAny one selected from the group consisting of H, an alkyl group having 1 to 5 carbon atoms, an alkyl group having 1 to 5 carbon atoms substituted by a halogen, an alkyl group having 1 to 5 carbon atoms substituted by a hydroxyl group, an alkenyl group having 2 to 5 carbon atoms, an alkynyl group having 2 to 5 carbon atoms, and an alkylcarboxylic acid having 2 to 5 carbon atoms.

[0202] In some embodiments, R 2a Any one selected from the group consisting of H, an alkyl group having 1 to 3 carbon atoms, an alkyl group having 1 to 3 carbon atoms substituted by a halogen, an alkyl group having 1 to 3 carbon atoms substituted by a hydroxyl group, an alkenyl group having 2 to 5 carbon atoms, an alkynyl group having 2 to 5 carbon atoms, and an alkylcarboxylic acid having 2 to 5 carbon atoms.

[0203] In some embodiments, the organic phosphonic acid compound includes at least one of (A) to (C):

[0204] Among them, in (a), each R 2a Not selected from H at the same time.

[0205] In some embodiments, each R 3a are independently selected from any one of a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms, a substituted or unsubstituted alkenyl group having 2 to 10 carbon atoms, a substituted or unsubstituted alkynyl group having 2 to 10 carbon atoms, a phosphonic acid group, and a group represented by formula (1-2), and at least one R 3a is selected from the group represented by formula (1-2); L 1a It is selected from substituted or unsubstituted alkane subunits having 1 to 10 carbon atoms and substituted or unsubstituted alkene subunits having 2 to 10 carbon atoms.

[0206] In some embodiments, each R 3a They are independently selected from any one of an alkyl group having 1 to 10 carbon atoms, an alkyl group having 1 to 10 carbon atoms substituted by a halogen, an alkyl group having 1 to 10 carbon atoms substituted by a hydroxyl group, an alkenyl group having 2 to 10 carbon atoms, an alkynyl group having 2 to 10 carbon atoms, a phosphonic acid group and a group represented by formula (1-2), and at least one R3 is selected from the group represented by formula (1-2).

[0207] In some embodiments, each R 3a They are independently selected from any one of a chain alkyl group having 1 to 10 carbon atoms, a chain alkyl group having 1 to 10 carbon atoms substituted by halogen, a chain alkyl group having 1 to 10 carbon atoms substituted by hydroxyl, an alkenyl group having 2 to 10 carbon atoms, an alkynyl group having 2 to 10 carbon atoms, a phosphonic acid group and a group represented by formula (1-2), and at least one R3 is selected from a group represented by formula (1-2).

[0208] In some embodiments, each R 3aThey are independently selected from any one of a chain alkyl group having 1 to 5 carbon atoms, a chain alkyl group having 1 to 5 carbon atoms substituted by a halogen, a chain alkyl group having 1 to 5 carbon atoms substituted by a hydroxyl group, an alkenyl group having 2 to 5 carbon atoms, an alkynyl group having 2 to 10 carbon atoms, a phosphonic acid group and a group represented by formula (1-2), and at least one R3 is selected from a group represented by formula (1-2).

[0209] In some embodiments, each L 2a Each of the groups is independently selected from a single bond, an alkane subunit having 1 to 10 carbon atoms, an alkane subunit having 1 to 10 carbon atoms substituted by a hydroxyl group, an alkane subunit having 1 to 10 carbon atoms substituted by a halogen, and an alkene subunit having 2 to 10 carbon atoms.

[0210] In some embodiments, each L 2a Each of the groups is independently selected from a single bond, an alkane subunit having 1 to 10 carbon atoms, an alkane subunit having 1 to 10 carbon atoms substituted by a hydroxyl group, an alkane subunit having 1 to 10 carbon atoms substituted by a halogen, and an alkene subunit having 2 to 10 carbon atoms.

[0211] In some embodiments, each L 2a Each is independently selected from any one of a single bond, an alkane subunit having 1 to 5 carbon atoms, an alkane subunit having 1 to 5 carbon atoms substituted by a hydroxyl group, an alkane subunit having 1 to 5 carbon atoms substituted by a halogen, and an alkene subunit having 2 to 5 carbon atoms.

[0212] In some embodiments, each L 2a Each of the groups is independently selected from a single bond, an alkane subunit having 1 to 5 carbon atoms, an alkane subunit having 1 to 5 carbon atoms substituted by a hydroxyl group, an alkane subunit having 1 to 5 carbon atoms substituted by a halogen, and an alkene subunit having 2 to 5 carbon atoms.

[0213] In some embodiments, each R 4a are independently selected from substituted or unsubstituted alkyl groups having 1 to 10 carbon atoms, substituted or unsubstituted alkenyl groups having 2 to 10 carbon atoms, substituted or unsubstituted alkynyl groups having 2 to 10 carbon atoms, and -L 21a R 5a At least one of .

[0214] Each L 21a are independently selected from single bonds, substituted or unsubstituted alkane substituents having 1 to 10 carbon atoms, R 5a Selected from -N(R 6a )2, each R 6aThey are independently selected from H, a substituted or unsubstituted alkane substituent having 1 to 10 carbon atoms, a phosphonic acid group, and any one of the structures represented by formula (1-1); and (c) contains at least one group represented by formula (1-2).

[0215] It is understood that (C) contains at least one group represented by formula (1-2) means that at least one R in formula (C) 4a Selected from -L 21a R 5a , and at least one L 21a -N(R 6a )2, and at least one R 6a It is a group represented by formula (1-2).

[0216] In some embodiments, each L 21a Each of them is independently selected from any one of a single bond, an alkanediyl group having 1 to 10 carbon atoms, an alkanediyl group having 1 to 10 carbon atoms substituted by a halogen, and an alkanediyl group having 1 to 10 carbon atoms substituted by a hydroxyl group.

[0217] In some embodiments, each L 21a Each of them is independently selected from any one of a single bond, an alkane substituent having 1 to 10 carbon atoms, an alkane substituent having 1 to 10 carbon atoms substituted by a halogen, and an alkane substituent having 1 to 10 carbon atoms substituted by a hydroxyl group.

[0218] In some embodiments, each L 21a Each of the groups is independently selected from any one of a single bond, an alkanediyl group having 1 to 5 carbon atoms, an alkanediyl group having 1 to 5 carbon atoms substituted by a halogen, and an alkanediyl group having 1 to 5 carbon atoms substituted by a hydroxyl group.

[0219] In some embodiments, each L 21a Each of them is independently selected from any one of a single bond, an alkane substituent having 1 to 5 carbon atoms, an alkane substituent having 1 to 5 carbon atoms substituted by a halogen, and an alkane substituent having 1 to 5 carbon atoms substituted by a hydroxyl group.

[0220] In some embodiments, each L 21a Each of the groups is independently selected from any one of a single bond, an alkane group having 1 to 3 carbon atoms, an alkane group having 1 to 3 carbon atoms substituted by a halogen, and an alkane group having 1 to 3 carbon atoms substituted by a hydroxyl group.

[0221] In some embodiments, each R 6a Each of them is independently selected from H, an alkane subunit having 1 to 10 carbon atoms, an alkane subunit having 1 to 10 carbon atoms substituted by a halogen, an alkane subunit having 1 to 10 carbon atoms substituted by a hydroxyl group, a phosphonic acid group, and any one of the structures represented by formula (1-2).

[0222] In some embodiments, each R 6a Each of them is independently selected from H, a chain alkane subunit having 1 to 10 carbon atoms, a chain alkane subunit having 1 to 10 carbon atoms substituted by a halogen, a chain alkane subunit having 1 to 10 carbon atoms substituted by a hydroxyl group, a phosphonic acid group, and any one of the structures represented by formula (1-2).

[0223] In some embodiments, each R 6a Each of them is independently selected from H, an alkane subunit having 1 to 5 carbon atoms, an alkane subunit having 1 to 5 carbon atoms substituted by a halogen, an alkane subunit having 1 to 5 carbon atoms substituted by a hydroxyl group, a phosphonic acid group, and any one of the structures represented by formula (1-2).

[0224] In some embodiments, each R 6a Each of them is independently selected from H, a chain alkane subunit having 1 to 5 carbon atoms, a chain alkane subunit having 1 to 5 carbon atoms substituted by a halogen, a chain alkane subunit having 1 to 5 carbon atoms substituted by a hydroxyl group, a phosphonic acid group, and any one of the structures represented by formula (1-2).

[0225] In some embodiments, the organic lithium phosphonate compound includes at least one of hydroxyethylidene diphosphonic acid, amino trimethylene phosphonic acid, ethylenediamine tetramethylene phosphonic acid, hexamethylene diamine tetramethylene phosphonic acid, and diethylene triamine penta methylene phosphonic acid.

[0226] In one embodiment of the present application, a positive electrode sheet is further provided, which includes the composite positive electrode material as described above or the composite positive electrode material prepared by the method for preparing the composite positive electrode material as described above.

[0227] When the positive electrode sheet is used to prepare a battery, the cycle stability and dynamic performance of the battery can be improved.

[0228] Specifically, the positive electrode sheet includes a current collector and a positive electrode active layer provided on the surface of the current collector. The components of the positive electrode active layer include the composite positive electrode material as described above or the composite positive electrode material prepared by the method for preparing the composite positive electrode material as described above.

[0229] In any embodiment of the present application, in the positive electrode active layer, the mass proportion of the composite positive electrode material is 70% to 100%.

[0230] In any embodiment of the present application, the components of the positive electrode active layer further include a conductive agent and a binder.

[0231] The conductive agent may be any commonly used conductive agent in the art, including but not limited to at least one of graphite, carbon nanotubes, nanofibers, carbon black, and graphene. Specifically, the conductive agent may be selected from at least one of SP, KS-6, acetylene black, branched Ketjen black ECP, SFG-6, vapor-grown carbon fiber VGCF, carbon nanotubes CNTs, graphene, and composite conductive agents thereof.

[0232] The binder of the binder can be polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, hydrogenated nitrile rubber, styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), carboxymethyl chitosan (CMCS) and at least one of fluorine-containing acrylate resin.

[0233] Optionally, in the positive electrode active layer, the conductive agent accounts for 1% to 20% by mass.

[0234] Optionally, in the positive electrode active layer, the binder accounts for 1% to 10% by mass.

[0235] In any embodiment of the present application, the 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 on a polymer substrate.

[0236] In some embodiments, the metal material is selected from any one of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy.

[0237] In some embodiments, the polymer material substrate includes at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0238] In any embodiment of the present application, a positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing a positive electrode sheet in a solvent to form a positive electrode active slurry; coating the positive electrode active slurry on a current collector, and performing drying, cold pressing, and other steps to obtain a positive electrode sheet. The positive electrode slurry has a solid content of 40 wt% to 80 wt%, a viscosity at room temperature adjusted to 5000 mPa·s to 25000 mPa·s, and after drying, is cold-pressed on a cold rolling mill to form a positive electrode sheet.

[0239] In some embodiments, the solvent includes N-methylpyrrolidone.

[0240] In some embodiments, the surface density of the composite positive electrode material contained in the positive electrode sheet is 0.018 g / cm 2 ~0.05g / cm 2 .

[0241] The surface density of the composite positive electrode material = the mass of the composite positive electrode material / the area of ​​the positive electrode sheet.

[0242] Another embodiment of the present application provides a secondary battery, which includes the above-mentioned composite positive electrode material or the composite positive electrode material prepared by the above-mentioned method for preparing the composite positive electrode material or the above-mentioned positive electrode sheet.

[0243] In some embodiments, the secondary battery further comprises a negative electrode sheet, a separator, and an electrolyte, which are described herein as non-limiting.

[0244] [Negative electrode]

[0245] The negative electrode sheet includes a current collector and a negative electrode active layer loaded on the surface of the current collector.

[0246] The components of the negative electrode active layer include a negative electrode active material.

[0247] The negative electrode active material may be any commonly used negative electrode active material in this application.

[0248] In any embodiment of the present application, the above-mentioned negative electrode active material includes at least one of mesocarbon microbeads, graphite, glassy carbon, carbon nanotubes, carbon-carbon composite materials, carbon fibers, hard carbon, soft carbon, silicon-based materials, tin-based materials, magnesium-based materials and iron-based materials.

[0249] Optionally, specific examples of the above-mentioned negative electrode active material include, but are not limited to: at least one of mesocarbon microbeads, natural graphite, artificial graphite, graphene, glassy carbon, carbon nanotubes, carbon fiber, hard carbon, soft carbon, iron oxide, tin oxide, silicon oxide, magnesium oxide, and silicon-carbon composites.

[0250] In any embodiment of the present application, the battery is a lithium battery, and the mass proportion of the negative electrode active material in the negative electrode active layer is 70% to 100%.

[0251] In any embodiment of the present application, the components of the negative electrode active layer further include a negative electrode conductive agent and a negative electrode binder.

[0252] In any embodiment of the present application, the negative electrode conductive agent may be a conductive material commonly used in the art, including but not limited to at least one of graphite, carbon nanotubes, nanofibers, carbon black, and graphene. Specifically, the negative electrode conductive agent may be selected from at least one of SP, KS-6, acetylene black, branched Ketjen black ECP, SFG-6, vapor-grown carbon fiber VGCF, carbon nanotubes CNTs, graphene, and composite conductive agents thereof.

[0253] The weight ratio of the negative electrode conductive agent in the negative electrode active layer is 0 to 20 wt % based on the total weight of the negative electrode active layer.

[0254] The negative electrode binder can be a binder commonly used in the art, and can be selected from at least one 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).

[0255] The weight ratio of the negative electrode binder in the negative electrode active layer is 0 to 30 wt % based on the total weight of the negative electrode active layer.

[0256] In any embodiment of the present application, the negative electrode active layer may further optionally include other additives, such as a thickener, such as sodium carboxymethyl cellulose (CMC-Na), etc. Based on the total weight of the negative electrode active layer, the weight ratio of the other additives in the negative electrode active layer is 0 to 15 wt%.

[0257] In any embodiment of the present application, the current collector in the negative electrode sheet may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil.

[0258] 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 on a polymer substrate.

[0259] In some embodiments, the metal material is selected from any one of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy.

[0260] In some embodiments, the polymer material substrate includes at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0261] In any embodiment of the present application, a negative electrode sheet can be prepared by the following method: dispersing the above-mentioned components for preparing a negative electrode sheet, such as a negative electrode active material, a conductive agent, a binder, and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry on a negative electrode current collector, and performing drying, cold pressing, and other processes to obtain a negative electrode sheet. The negative electrode slurry has a solid content of 30 wt% to 70 wt%, and a viscosity at room temperature adjusted to 2000 mPa·s to 10000 mPa·s; coating the obtained negative electrode slurry on a negative electrode current collector, drying, and cold pressing, such as with a roller, to obtain a negative electrode sheet.

[0262] In some embodiments, the surface density of the negative electrode active material contained in the negative electrode sheet is 0.005 g / cm 2 ~0.03g / cm 2 .

[0263] The area density of the negative electrode active material = the mass of the negative electrode active material / the area of ​​the negative electrode sheet.

[0264] [Electrolyte]

[0265] The electrolyte includes electrolyte salt and solvent

[0266] In some embodiments, the electrolyte salt may be selected from lithium ion electrolyte salts commonly used in the art.

[0267] As an example, the lithium ion electrolyte salt includes, but is not limited to, one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalatoborate (LiDFOB), lithium dioxalatoborate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorobis(oxalatophosphate) (LiDFOP) and lithium tetrafluorooxalatophosphate (LiTFOP).

[0268] In some embodiments, the solvent can be selected from one or more of fluoroethylene carbonate (FEC), ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS) and diethyl sulfone (ESE).

[0269] In some embodiments, the concentration of the electrolyte salt in the electrolyte solution is generally 0.5 mol / L to 15 mol / L.

[0270] In some embodiments, the electrolyte may optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, and additives that improve battery high or low temperature performance.

[0271] [Isolation film]

[0272] The separator is provided between the positive electrode sheet and the negative electrode sheet.

[0273] The present application has no particular limitation on the type of isolation membrane, and any known isolation membrane with a porous structure having good chemical stability and mechanical stability can be selected.

[0274] In some embodiments, the material of the separator can be selected from at least one of 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 limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0275] The thickness of the diaphragm is controlled to be 2 μm to 15 μm; optionally, the thickness of the diaphragm is controlled to be 2 μm to 13 μm.

[0276] In some embodiments, the battery is a secondary battery; specifically, the battery is a lithium-ion battery.

[0277] The shape of the secondary battery of the present application is not particularly limited, and it can be cylindrical, square, or any other shape. For example, FIG1 shows a battery cell 4 with a square structure as an example.

[0278] In some embodiments, referring to FIG2 , the housing may include a shell 41 and a cover 43. Shell 41 may include a bottom plate and side plates connected to the bottom plate, with the bottom plate and side plates enclosing a receiving cavity. Shell 41 may have an opening communicating with the receiving cavity, and cover 43 may be positioned over the opening to seal the receiving cavity.

[0279] The positive electrode sheet, negative electrode sheet, and separator can be wound or laminated to form an electrode assembly 42. The electrode assembly 42 is enclosed in a housing. Electrolyte is infiltrated into the electrode assembly 42. The number of electrode assemblies 42 included in a battery cell 4 can be one or more, and can be adjusted based on demand.

[0280] The secondary battery includes one or more battery cells 4 .

[0281] The secondary battery can be a battery module or a battery pack; the battery module or battery pack includes at least one battery cell. The number of battery cells 4 included in the battery module can be one or more, and those skilled in the art can select an appropriate number based on the application and capacity of the battery module.

[0282] Figures 3 and 4 illustrate an exemplary battery pack 1. Battery pack 1 includes a battery case and one or more battery cells 4 disposed within the battery case. The battery case comprises an upper case 2 and a lower case 3. The upper case 2 can be placed over the lower case 3 to form an enclosed space for the battery cells 4.

[0283] The plurality of battery cells 4 can be arranged in the battery box in any manner.

[0284] The present application also provides an electrical device, which includes the above-mentioned secondary battery.

[0285] Furthermore, in the above-mentioned electrical device, the battery may exist in the form of a battery cell, or may be further assembled into a battery pack.

[0286] The secondary battery pack can be used as a power source for an electrical device or as an energy storage unit for the electrical device.

[0287] The above-mentioned electrical devices may be, but are not limited to, mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as 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.

[0288] Figure 5 shows an example of an electric device 5. The electric device 5 is 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 electric device 5, a battery pack can be used.

[0289] As another example, the power-consuming device may be a mobile phone, a tablet computer, a laptop computer, etc. Such a device is usually required to be light and thin, and may use a battery as a power source.

[0290] The present application will be described below in conjunction with specific embodiments, but the present application is not limited to the following embodiments. It should be understood that the attached claims summarize the scope of the present application. Under the guidance of the concept of the present application, those skilled in the art should realize that certain changes made to the various embodiments of the present application will be covered by the spirit and scope of the claims of the present application.

[0291] The following are specific examples.

[0292] Example 1

[0293] (1) Preparation of positive electrode

[0294] S1: Adding M elemental (sulfur) additive to organic solvent N-methylpyrrolidone (NMP),

[0295] Stir at a speed of 400r / s to 1000r / s for 0.5h to dissolve and prepare a 1mol / L M elemental solution;

[0296] S2: Add the organic phosphoric acid compound hydroxyethylidene diphosphonic acid to the organic solvent ethanol, and stir at a speed of 400 r / s to 1000 r / s for 0.5 h to dissolve it, to prepare an organic phosphoric acid solution with a concentration of 0.5 mol / L.

[0297] S3: LiNi containing nickel cathode material 0.9 Co 0.7 Mn 0.3 O2 (NCM9 series material), binder polyvinylidene fluoride (PVDF) and conductive agent SP are configured in a mass ratio of (97:1:2) and mixed with solvent N-methylpyrrolidone (NMP) to obtain a prefabricated cathode slurry with a solid content of 75%.

[0298] S3: Add the M elemental solution to the prefabricated cathode slurry and stir for 1 hour. After uniform mixing, add the organic phosphoric acid solution and stir for 0.5 hour to obtain a uniformly mixed cathode composite slurry.

[0299] The mass ratio of the M element to the nickel-containing positive electrode material is recorded as X1, and the mass ratio of the organic phosphoric acid compound to the nickel-containing positive electrode material is recorded as X2.

[0300] S4: The cathode composite slurry is coated on the current collector aluminum foil and dried at 110° C. for 30 minutes to form an active layer to obtain a prefabricated positive electrode sheet.

[0301] The compaction density of the prefabricated positive electrode sheet is 3.5g / cm 3, the calculation formula of compaction density is:

[0302] Compacted density = surface density / (pole thickness - current collector thickness).

[0303] The above-mentioned compaction density and areal density are well-known in the art. The areal density of the electrode refers to the weight of the active layer loaded per unit area of ​​the electrode. Unit areal density = weight of the active layer / area of ​​the active layer. As an example, the compaction density can be obtained by testing as follows:

[0304] The positive electrode sheet is cut into 1000mm long sheets; the negative electrode sheet is rolled under a certain pressure and then punched into 1540.25mm 2 By measuring the weight and thickness of the small disc, the compacted density can be calculated.

[0305] (2) Preparation of negative electrode

[0306] Silicon oxide material SiOx, artificial graphite, conductive agent carbon black, binder styrene-butadiene rubber SBR, and thickener sodium hydroxymethyl cellulose CMC are added to deionized water in a weight ratio of 40:57:0.5:1.25:1.25, mixed and stirred for 6 hours to obtain a negative electrode slurry; the slurry is evenly coated on the negative electrode current collector and dried to obtain a negative electrode sheet.

[0307] The compaction density of the negative electrode sheet is 1.6g / cm 3 The test method refers to the test of the compaction density of the positive electrode as above.

[0308] (3) Preparation of electrolyte

[0309] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a volume ratio of EC:EMC:DEC = 1:1:1 to obtain an organic solvent, and then fully dried lithium salt LiPF6 is dissolved in the above organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0310] (4) Isolation membrane: Polyethylene film is selected as the isolation membrane of lithium-ion batteries.

[0311] (5) Assembly of lithium-ion batteries: The positive electrode sheet, separator, and negative electrode sheet to be assembled are stacked in sequence, with the separator placed between the positive and negative electrode sheets to act as an insulator. Bare cells are then produced by winding. The bare cells are placed in a battery housing, dried, and then injected with electrolyte. After vacuum packaging, standing, forming, and shaping, the lithium-ion battery to be tested is obtained. The formation process is: constant current charging at a current of 0.05C until the cell voltage reaches 3.7V, then cut-off.

[0312] During the formation process, the nickel-containing positive electrode material in the prefabricated positive electrode sheet reacts with the M element and the organic phosphate compound, forming a functional film layer on the surface of the nickel-containing positive electrode material to obtain a composite positive electrode material.

[0313] (6) Testing:

[0314] S1. Disassemble the lithium-ion battery to obtain the positive electrode sheet, and separate the active layer components by the following method to obtain a nickel-containing positive electrode material, i.e., a composite positive electrode material:

[0315] The positive electrode sheet was soaked in DMC for 30 minutes to remove the electrolyte solvent and lithium salt, and then the powder was scraped to peel off the positive electrode active layer powder and the aluminum current collector. The collected powder was dissolved in NMP and stirred for 30 minutes to obtain a mixed slurry. The mixed slurry was then placed in a centrifugal device and centrifuged for 15 minutes to remove the lower layer component, which is the composite positive electrode material.

[0316] The obtained composite cathode material is placed under a transmission electron microscope (TEM) for observation, whereby distinct stratification can be observed, including a nickel-containing cathode material and a functional film layer disposed on the surface of the nickel-containing cathode material. The thickness of the functional film layer can be obtained based on the transmission electron microscope image information, which is recorded as H.

[0317] Specifically, when obtaining the thickness of the functional film layer, 5 areas of the composite positive electrode material are marked for test thickness, and the average value is taken.

[0318] S2. Use XPS to conduct qualitative testing on the components of the functional film layer of the composite positive electrode material to confirm the main component types.

[0319] XPS test results show that the functional film layer contains MO4 in Li2MO4 2- Group characteristic peak (175Ev, when M is S) and phosphate LiPO2 2- Characteristic peak (55.8eV), and the MO4 in Li2MO4 was calculated based on the ratio of the characteristic peak intensities 2- The molar ratio of the group to the phosphate group in the organic lithium phosphonate compound is recorded as Y1.

[0320] S3. Determine the residual lithium content Y2 of the composite positive electrode material using acid-base titration. The residual lithium includes Li2CO3, LiOH, and Li2O. The specific steps are as follows:

[0321] Pretreatment: Weigh 30g of composite cathode material powder, add 100mL of pure water and stir for 30min, let it stand for 10min, filter and remove a certain amount of filtrate;

[0322] Test: The filtrate was titrated with 0.05 mol / L hydrochloric acid standard solution and the residual lithium amount Y2 was calculated based on the titration results. The test and analysis method was in accordance with GB / T 9736-2008.

[0323] S4. Characterize the residual amount Y3 of M element in the composite positive electrode material through DSC thermogravimetric analysis.

[0324] S5. Battery rate cycle test

[0325] (1) 0.33C cycle capacity retention test

[0326] At 25°C, the secondary ion battery is first charged to 4.25V at a constant current of 0.33C, then further charged at a constant voltage of 4.25V to a current of 0.05C, left for 30 minutes, and then discharged to 2.8V at a constant current of 0.33C. This is a charge and discharge cycle process. The discharge capacity this time is the discharge capacity of the first cycle, recorded as Cap4.

[0327] The secondary battery was subjected to a cyclic charge-discharge test as described above. The discharge capacity at the 100th cycle was recorded as Cap5. The capacity retention rate of the lithium-ion battery after 100 cycles, M3, was calculated as [Cap5 / Cap4] × 100%. A larger M3 value indicates a smaller capacity loss and better rate cycling performance.

[0328] (2) Cyclic capacity retention test at 1C

[0329] At 25°C, the lithium-ion battery is first charged to 4.25V at a constant current of 1C, then further charged to a current of 0.05C at a constant voltage of 4.25V, left for 30 minutes, and then discharged to 2.8V at a constant current of 1C. This is a charge and discharge cycle process. The discharge capacity of this time is the discharge capacity of the first cycle, recorded as Cap6. The lithium-ion battery is subjected to a cyclic charge and discharge test in the above manner, and the discharge capacity of the 100th cycle is taken, recorded as Cap7. The capacity retention rate (%) of the lithium-ion battery after 100 cycles is M4 = [Cap7 / Cap6] × 100%.

[0330] The larger the M4 value, the smaller the battery capacity loss and the better the rate cycle performance.

[0331] S8, battery impedance test

[0332] At 25°C, the prepared secondary battery was charged at a constant current of 1 / 3C to 4.25V, and then charged at a constant voltage of 4.25V to a current of 0.05C. After standing for 30 minutes, the voltage U1 was recorded; then it was discharged at 1 / 3C for 30 seconds, and the voltage U2 was recorded. The internal resistance DCR of the secondary battery before storage was calculated based on the formula DCR = (U2-U1) / 1 / 3C.

[0333] Please see Table 1 for specific parameters and test results.

[0334] Examples 2 to 5

[0335] Examples 2 to 5 are substantially the same as Example 1, with the only difference being that in step (1) of preparing the positive electrode sheet, the type and amount of the organic phosphoric acid compound used are different from those in Example 1, as shown in Table 1. An electron micrograph of the composite positive electrode material prepared in Example 4 is shown in FIG6 .

[0336] The other steps and conditions are the same as those in Example 1.

[0337] Examples 6-7

[0338] Examples 6 to 7 are basically the same as Example 1, except that in step (1) the preparation of the positive electrode sheet, the type and amount of the M element used are different from those in Example 1. Please see Table 1 for details.

[0339] The other steps and conditions are the same as those in Example 1.

[0340] Examples 8 to 15

[0341] Examples 8 to 15 are basically the same as Example 1, except that in step (1) of preparing the positive electrode sheet, the amount of the M element and the organic phosphoric acid compound is regulated differently from that in Example 1. See Table 1 for details.

[0342] The other steps and conditions are the same as those in Example 1.

[0343] Comparative Example 1

[0344] Comparative Example 1 is basically the same as Example 1, except that: in the preparation of the positive electrode sheet in step (1), no M element is added. For details, please see Table 1.

[0345] The other steps and conditions are the same as those in Example 1.

[0346] Comparative Example 2

[0347] Comparative Example 2 is basically the same as Example 1, except that: in step (1) of preparing the positive electrode sheet, no organic phosphoric acid compound is added. For details, please see Table 1.

[0348] The other steps and conditions are the same as those in Example 1.

[0349] The process conditions and test results of each embodiment and comparative example are shown in Table 1, where the mass ratio of the M element and the nickel-containing positive electrode material is recorded as X1, the mass ratio of the organophosphate compound and the nickel-containing positive electrode material is recorded as X2, the molar ratio of Li2MO4 to the organophosphonate lithium compound is recorded as Y1, the residual lithium amount of the composite positive electrode material is Y2, the residual amount of the S element in the composite positive electrode material is Y3, and the thickness of the functional film layer in the composite positive electrode material is recorded as H.

[0350] Table 1

[0351] Note: " / " indicates the absence of the substance or parameter. When "Y3 < 0.01%", it means that the residual lithium content is extremely low and has fallen below the lower limit that can be accurately determined by acid-base titration.

[0352] By analyzing the data in Table 1 and comparing the test results of Examples 1 to 15 with those of Comparative Examples 1 to 2, it can be seen that: by using the composite positive electrode material of the present application, a functional film layer having specific components is formed on the surface of the positive electrode material substrate: the inorganic component Li2MO4 and the organic component lithium organophosphonate compound work together to improve the cycle stability of the battery and reduce the internal resistance of the battery, that is, it can promote the transmission and diffusion of ions or electrons between the two poles in the battery, reduce the energy consumed during charging and discharging the battery, and thus improve the battery kinetic performance.

[0353] It can be seen that the technical solution of the present application can improve the cycle life of the battery while maintaining good dynamic performance.

[0354] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0355] The above-described embodiments merely represent several implementation methods of the present application, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the patent application. It should be noted that a person of ordinary skill in the art may make a number of variations and improvements without departing from the concept of the present application, and these variations and improvements fall within the scope of protection of the present application. Therefore, the scope of protection of the patent application shall be based on the appended claims, and the description and drawings may be used to interpret the content of the claims.

Claims

1. A composite positive electrode material, comprising a nickel-containing positive electrode material and a functional film layer disposed on the surface of the nickel-containing positive electrode material, wherein the components of the functional film layer include Li2MO4 and an organic lithium phosphonate compound; in, M is selected from at least one of sulfur, selenium and tellurium; the organic lithium phosphonate compound has a structure shown in formula (1): * represents the site where the structure represented by formula (1) is connected to other structures in the organic lithium phosphonate compound.

2. The composite cathode material according to claim 1, wherein In the functional film layer, MO4 in Li2MO4 2- The molar ratio of the group to the structure represented by formula (1) in the organic lithium phosphonate compound is (0.6-5):1; Optionally, in the functional film layer, MO4 in Li2MO4 2- The molar ratio of the group to the structure represented by formula (1) in the organic lithium phosphonate compound is (1-5):

1.

3. The composite cathode material according to claim 1, wherein In the composite positive electrode material, the content of the single substance of the M element is ≤0.1%.

4. The composite positive electrode material according to any one of claims 1 to 3, wherein The thickness of the functional film layer is 5nm to 20nm; Optionally, the thickness of the functional film layer is 5nm to 10nm.

5. The composite positive electrode material according to any one of claims 1 to 4, wherein The organic lithium phosphonate compound contains a group represented by formula (1-1): Among them, R1 is selected from any one of -OR2, substituted or unsubstituted alkyl having 1 to 10 carbon atoms, substituted or unsubstituted alkenyl having 2 to 10 carbon atoms, and substituted or unsubstituted alkynyl having 2 to 10 carbon atoms; R2 is selected from any one of H, Li, substituted or unsubstituted alkyl having 1 to 10 carbon atoms, substituted or unsubstituted alkenyl having 2 to 10 carbon atoms, substituted or unsubstituted alkynyl having 2 to 10 carbon atoms, and substituted or unsubstituted alkylcarboxylic acid having 2 to 10 carbon atoms.

6. The composite cathode material according to claim 5, wherein: The organic lithium phosphonate compound includes at least one of (a) to (c): Wherein, in (a), each R2 is not simultaneously selected from H; Each R3 is independently selected from any one of a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms, a substituted or unsubstituted alkenyl group having 2 to 10 carbon atoms, a substituted or unsubstituted alkynyl group having 2 to 10 carbon atoms, a phosphonic acid group, and a group represented by formula (1-1), and at least one R3 is selected from a group represented by formula (1-1); L1 is selected from a substituted or unsubstituted alkane subunit having 1 to 10 carbon atoms and a substituted or unsubstituted alkene subunit having 2 to 10 carbon atoms; Each L2 is independently selected from any one of a single bond, a substituted or unsubstituted alkane subunit having 1 to 10 carbon atoms, and a substituted or unsubstituted alkene subunit having 2 to 10 carbon atoms; each R4 is independently selected from a substituted or unsubstituted alkyl subunit having 1 to 10 carbon atoms, a substituted or unsubstituted alkenyl subunit having 2 to 10 carbon atoms, a substituted or unsubstituted alkynyl subunit having 2 to 10 carbon atoms, and -L 21 At least one of R5; Each L 21 They are independently selected from a single bond, a substituted or unsubstituted alkane subunit with 1 to 10 carbon atoms, R5 is selected from -N(R6)2, and each R6 is independently selected from H, a substituted or unsubstituted alkane subunit with 1 to 10 carbon atoms, a phosphonic acid group and any one of the structures shown in formula (1-1); and (c) contains at least one group shown in formula (1-1).

7. The composite cathode material according to claim 6, wherein The organic lithium phosphonate compound satisfies at least one of the following conditions (3) to (5): (3) each R2 is independently selected from any one of H, Li, an alkyl group having 1 to 10 carbon atoms, an alkyl group having 1 to 10 carbon atoms substituted by a halogen, an alkyl group having 1 to 10 carbon atoms substituted by a hydroxyl group, an alkenyl group having 2 to 10 carbon atoms, an alkynyl group having 2 to 10 carbon atoms, an alkylcarboxylic acid having 2 to 10 carbon atoms, and an alkylcarboxylic acid having 2 to 10 carbon atoms substituted by a hydroxyl group; (4) Each R3 is independently selected from any one of an alkyl group having 1 to 10 carbon atoms, an alkyl group having 1 to 10 carbon atoms substituted by a halogen, an alkyl group having 1 to 10 carbon atoms substituted by a hydroxyl group, an alkenyl group having 2 to 10 carbon atoms, an alkynyl group having 2 to 10 carbon atoms, a phosphonic acid group, and a group represented by formula (1-1); (5) Each R4 is independently selected from an alkyl group having 1 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, an alkynyl group having 2 to 10 carbon atoms, and -L 21 At least one of R5; each R6 is independently selected from any one of an alkane subunit having 1 to 10 carbon atoms, a phosphonic acid group and a group represented by formula (1-1).

8. The composite cathode material according to any one of claims 1 to 7, wherein: The components of the functional film layer also include a metal oxide type rock salt phase; Optionally, the metal in the metal oxide type rock salt phase includes at least one of Ni, Co and Mn.

9. The composite cathode material according to any one of claims 1 to 8, wherein: The components of the nickel-containing positive electrode material satisfy: Li t Ni x Co y A h O z ; Among them, A is selected from at least one of manganese, aluminum, copper, zinc, tin, magnesium and iron, 0<x<1, 0<y<1, 1.5≤y≤2.5, 0<h<1, 0.8≤t≤1.5, 1.5≤z≤2.

5.

10. The composite cathode material according to any one of claims 1 to 9, wherein: The mass proportion of residual lithium in the composite positive electrode material is ≤2%, and the residual lithium includes Li2CO3, LiOH and Li2O.

11. A method for preparing a composite positive electrode material, comprising the following steps: The nickel-containing positive electrode material, M element and an organic phosphonic acid compound are mixed to prepare a prefabricated positive electrode material; The prefabricated positive electrode material is subjected to a chemical formation treatment to prepare the composite positive electrode material; The M element includes at least one of sulfur, selenium and tellurium; the organic phosphonic acid compound has a structure shown in formula (2): * represents the site where the structure represented by formula (2) is connected to other structures in the organic phosphonic acid compound.

12. The method for preparing a composite positive electrode material according to claim 11, wherein: The mixing process comprises the following steps: The nickel-containing positive electrode material and the M element are subjected to a first mixing treatment, and then the organic phosphonic acid compound is added to perform a second mixing treatment; Optionally, the first mixing treatment time is 0.5h to 6h; Optionally, the second mixing treatment time is 0.5h to 3h.

13. The method for preparing a composite positive electrode material according to any one of claims 11 to 12, wherein: The mixing process satisfies at least one of the following conditions (6) to (7): (6) The mass ratio of the M element to the nickel-containing positive electrode material is (0.01-1):100; Optionally, the mass ratio of the M element to the nickel-containing positive electrode material is (0.1-0.4):100; (7) The mass ratio of the organic phosphonic acid compound to the nickel-containing positive electrode material is (0.01-1):100; Optionally, the mass ratio of the organic phosphonic acid compound to the nickel-containing positive electrode material is (0.1-0.5):

100.

14. A positive electrode sheet, comprising the composite positive electrode material according to any one of claims 1 to 10 or the composite positive electrode material prepared by the method for preparing the composite positive electrode material according to any one of claims 11 to 13.

15. A secondary battery, comprising the composite positive electrode material according to any one of claims 1 to 10 or the composite positive electrode material prepared by the method for preparing the composite positive electrode material according to any one of claims 11 to 13 or the positive electrode sheet according to claim 14. 16 . An electric device comprising the secondary battery according to claim 15 .

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