Positive electrode material, secondary battery, and electric device

Abstract

The invention relates to the technical field of batteries, in particular to a positive electrode material, a secondary battery and a power utilization device. The positive pole piece comprises a positive current collector and a positive film layer arranged on at least one surface of the positive current collector; the positive electrode film layer comprises a positive electrode material, and the positive electrode material comprises a positive electrode active material and a coating material located on the surface of the positive electrode active material; the coating material comprises a cyano group-containing compound and a copolymer of acetoacetic acid ethylene glycol methacrylate. The positive pole piece in the secondary battery provided by the invention has high discharge capacity per gram, and the secondary battery has good cyclic storage performance.

Description

Technical Field

[0001] This application relates to the field of batteries, specifically to a positive electrode material, a secondary battery, and an electrical device. Background Technology

[0002] Under high voltage, the positive electrode of a secondary battery suffers from the dissolution of transition metals and the release of oxygen through numerous side reactions, which leads to a decrease in the battery's cycle life.

[0003] Therefore, it is crucial to develop a rechargeable battery that can solve the above problems. Summary of the Invention

[0004] In view of the above problems, this application provides a positive electrode material, a secondary battery, and an electrical device. The positive electrode sheet formed by the positive electrode material in the secondary battery of this application has a high discharge capacity, and the secondary battery has good cycle storage performance.

[0005] In a first aspect, this application provides a secondary battery, the secondary battery including a positive electrode sheet;

[0006] The positive electrode sheet includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector;

[0007] The positive electrode film layer includes a positive electrode material, which includes a positive electrode active material and a coating material located on the surface of the positive electrode active material;

[0008] The coating material comprises a copolymer of a cyano-containing compound and ethylene glycol acetoacetate methacrylate.

[0009] In the technical solution of this application, the copolymer of the cyano-containing compound and ethylene glycol acetoacetate methacrylate (AAEM) is used. The β-diketone bidentate chelate coordination in the structural unit formed by AAEM forms a stable six-membered chelate ring, which can stabilize transition metal ions in various oxidation states and coordination numbers. The structural unit formed by the cyano-containing compound provides strong electronegativity to the copolymer, which is beneficial to the stability of the six-membered chelate ring. The two work together to improve the problem of transition metal dissolution and large-scale oxygen release from side reactions, improve the discharge specific capacity of the positive electrode, and improve the cycle storage performance of the secondary battery.

[0010] In some embodiments, the cyanide-containing compound includes acrylonitrile (AN).

[0011] In the technical solution of this application, acrylonitrile has high reactivity and the structural unit formed after copolymerization has strong electronegativity, which further stabilizes the six-membered chelate ring. Together with the structural unit of AAEM, it further improves the problem of transition metal dissolution and large-scale oxygen release from side reactions, increases the discharge specific capacity of the positive electrode, and improves the cycle storage performance of the secondary battery, especially the high-temperature cycle storage performance.

[0012] In some embodiments, the copolymer comprises a six-membered ring, the six-membered ring including an N atom disposed on the ring and a *=NH substituent, wherein * represents a substituent linkage site.

[0013] In some embodiments, the six-membered ring in the copolymer is formed by a cyano group (-CN) in a cyano-containing compound, which provides strong electronegativity to the copolymer and is beneficial to the stability of the six-membered chelate ring. The two work together to improve the problem of transition metal dissolution and the release of oxygen by a large number of side reactions, improve the discharge specific capacity of the positive electrode, and improve the cycle storage performance of the secondary battery, especially the high-temperature cycle storage performance.

[0014] In some embodiments, the structure of the six-membered ring is shown in Equation 1:

[0015]

[0016] Where n≥2, and can be optionally selected from 2-4.

[0017] In some embodiments, the copolymer has the structural formula shown in Formula 2:

[0018]

[0019] Where n≥2, which can be optionally selected from 2-4; m≥2.

[0020] In some embodiments, the mass ratio of the coating material to the positive electrode active material is (0.5-2):100; and / or;

[0021] The thickness of the shell formed by the coating material is 2-10 nm.

[0022] In the technical solution of this application embodiment, the mass ratio of the coating material to the positive electrode active material is within the above range, which can effectively adjust the thickness of the shell layer; the reason why the thickness of the shell layer formed by the coating material is controlled within 2-10nm is that: within the thickness range, the positive electrode active material can be effectively coated, and the positive electrode active material has good conductivity, which is beneficial to improving the cycle storage performance and other properties of the secondary battery.

[0023] In some embodiments, the copolymer has a copolymer molar ratio of (40-80):(20-60) of the cyano-containing compound and ethylene glycol acetoacetate methacrylate.

[0024] In the technical solution of this application, the reason why the copolymerization molar ratio of the cyano-containing compound and the two monomers AAEM in the copolymer is controlled within the specified range is that: within the specified range, the β-diketone bidentate chelate coordination is stable, which ultimately helps to improve the cycle storage performance of the secondary battery.

[0025] In some embodiments, the copolymer has a weight-average molecular weight of 10,000-200,000.

[0026] In the technical solution of this application, the reason why the weight-average molecular weight of the copolymer is controlled within the specified range is that the weight-average molecular weight within the specified range facilitates the control of the shell thickness formed by the coating material, which is beneficial to industrial production, and also benefits the stability of the shell, reducing the risk of excessive swelling of the shell or even dissolution in the electrolyte.

[0027] In some embodiments, the positive electrode active material includes any one or a combination of at least two of ternary positive electrode materials, lithium-rich manganese-based materials, lithium manganese oxide, or lithium nickel manganese oxide; and / or;

[0028] The ternary cathode material includes a nickel-cobalt-manganese ternary cathode material; and / or;

[0029] The lithium-rich manganese-based cathode material includes Li2MnO3 and / or LiMnO2.

[0030] Secondly, this application provides a cathode material.

[0031] The positive electrode material includes a positive electrode active material and a coating material located on the surface of the positive electrode active material;

[0032] The coating material comprises a copolymer of a cyano-containing compound and ethylene glycol acetoacetate methacrylate.

[0033] In some embodiments, the cyanide-containing compound includes acrylonitrile.

[0034] In some embodiments, the copolymer comprises a six-membered ring, the six-membered ring including an N atom disposed on the ring and a *=NH substituent, wherein * represents a substituent linkage site.

[0035] In some embodiments, the structure of the six-membered ring is shown in Equation 1:

[0036]

[0037] Where n≥2, and can be optionally selected from 2-4.

[0038] In some embodiments, the copolymer has the structural formula shown in Formula 2:

[0039]

[0040] Where n≥2, which can be optionally selected from 2-4; m≥2.

[0041] In some embodiments, the thickness of the shell formed by the coating material is 2-10 nm.

[0042] In some embodiments, the copolymer has a copolymer molar ratio of (40-80):(20-60) of the cyano-containing compound and ethylene glycol acetoacetate methacrylate.

[0043] In some embodiments, the copolymer has a weight-average molecular weight of 10,000-200,000.

[0044] In some embodiments, the positive electrode active material includes any one or a combination of at least two of ternary positive electrode materials, lithium-rich manganese-based materials, lithium manganese oxide, or lithium nickel manganese oxide; and / or;

[0045] The ternary cathode material includes a nickel-cobalt-manganese ternary cathode material; and / or;

[0046] The lithium-rich manganese-based cathode material includes Li2MnO3 and / or LiMnO2.

[0047] Thirdly, this application provides a method for preparing a positive electrode material, the method comprising the following steps:

[0048] The coating material is deposited on the surface of the positive electrode active material to obtain the positive electrode material;

[0049] The coating material comprises a copolymer of a cyano-containing compound and ethylene glycol acetoacetate methacrylate.

[0050] In some embodiments, the method for preparing the copolymer includes the following steps:

[0051] The copolymer is obtained by copolymerizing a cyano-containing compound with ethylene glycol acetoacetate methacrylate.

[0052] In some embodiments, the copolymerization temperature is 70-90°C; and / or;

[0053] The copolymerization time is 1-20 hours.

[0054] In some embodiments, the copolymerization is carried out in a solvent, optionally including N-methylpyrrolidone.

[0055] In some embodiments, the copolymer is disposed on the surface of the positive electrode active material by spray drying.

[0056] In some embodiments, the spray drying process further includes pre-oxidation into rings; and / or;

[0057] The pre-oxidation cyclization temperature is 180-240℃; and / or;

[0058] The pre-oxidation cyclization time is 1-10 hours.

[0059] Fourthly, this application provides an electrical device comprising the secondary battery described in the first aspect, and / or the positive electrode material described in the second aspect, and / or the positive electrode material obtained by the preparation method described in the third aspect.

[0060] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0061] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, the same reference numerals denote the same parts throughout the drawings.

[0062] Figure 1 This is a structural characterization diagram of the prepolymer (PAN-AAEM prepolymer) of acrylonitrile and ethylene glycol acetoacetate methacrylate obtained in step (1) of Example 1 of this application;

[0063] Figure 2 This is a TEM image of the coated active material in Example 1 of this application at a scale of 10 nm;

[0064] Figure 3 This is a TEM image of the coated active material in Example 1 of this application at a scale of 50 nm.

[0065] Figure 4 This is a TEM image of the coated active material of Comparative Example 3 of this application at a scale of 10 nm. Detailed Implementation

[0066] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0067] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0068] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0069] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60–120 and 80–110 are listed for a specific parameter, it is also expected that ranges of 60–110 and 80–120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1–3, 1–4, 1–5, 2–3, 2–4, and 2–5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "2-10" indicates that all real numbers between "2-10" have been listed in this article; "2-10" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0070] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent three cases: A exists, A and B exist simultaneously, and B exists. In addition, the character " / " in this document generally indicates that the related objects before and after it have an "or" relationship.

[0071] Under high voltage (such as 4.5V), the dissolution of transition metals (such as Mn) and the release of oxygen by a large number of side reactions in the positive electrode (such as lithium-ion positive electrode active materials, such as lithium-rich manganese system) will cause a decrease in the performance of secondary batteries, such as cycle storage.

[0072] In the prior art, facing the above-mentioned technical problems, one traditional method is to dope inactive cations (such as T) into the coating layer formed on the outer surface of the positive electrode active material. i4+ Se 6+ 、Nb 5+ To enhance the binding with oxygen and thus inhibit oxygen release, the above-mentioned doped coating layer cannot isolate the positive electrode active material from the electrolyte, resulting in the dissolution of a large amount of transition metals. Another traditional method is to form an inert coating layer on the outer surface of the positive electrode active material. The inert coating layer is made of inorganic metal oxides (such as Al2O3, MgO, etc.) or phosphates (such as NaPO3, β-NaCaPO4, etc.). However, the above-mentioned inert coating layer has poor ion conductivity, and the expansion of the positive electrode active material will cause the coating layer to crack, affecting the performance of the secondary battery.

[0073] If the dissolution of transition metals and the occurrence of numerous side reactions can be reduced, and the ion conduction of the positive electrode active material can be maintained without cracking the coating layer, then the performance of the secondary battery can be further improved.

[0074] Based on the above considerations, in order to solve the problems of transition metal dissolution and large-scale oxygen release from side reactions in positive electrode sheets (such as lithium-ion positive electrode active materials, such as lithium-rich manganese systems) under high voltage, a positive electrode material, a secondary battery and an electrical device were developed through experimental research based on the above design concept.

[0075] [Rechargeable Battery]

[0076] This application provides a secondary battery, which includes a positive electrode plate;

[0077] The positive electrode sheet includes a positive current collector and a positive electrode film layer disposed on at least one (e.g., one or two) surface of the positive current collector;

[0078] The positive electrode film layer includes a positive electrode material, which includes a positive electrode active material and a coating material located on the surface of the positive electrode active material;

[0079] The coating material comprises a copolymer of a cyano-containing compound and ethylene glycol acetoacetate methacrylate;

[0080] In the technical solution of this application embodiment, the copolymer of the cyano-containing compound and ethylene glycol acetoacetate methacrylate (AAEM) has a certain degree of flexibility; wherein, the structural formula of AAEM is... Furthermore, the β-diketone bidentate chelate coordination in the structural unit formed by AAEM forms a stable six-membered chelate ring, which can stabilize transition metal ions in various oxidation states and coordination numbers. The structural unit formed by the cyano-containing compound provides strong electronegativity to the copolymer, which is beneficial to the stability of the six-membered chelate ring. The two work together to improve the problem of transition metal dissolution and the release of oxygen by a large number of side reactions, improve the discharge specific capacity of the positive electrode, and improve the cycle storage performance of the secondary battery.

[0081] In some embodiments, the cyano-containing compound includes acrylonitrile (AN). The structural formula of AN is:

[0082] In the technical solution of this application embodiment, acrylonitrile has high reactivity and the structural unit formed after copolymerization has strong electronegativity, which further stabilizes the six-membered chelate ring. Together with the structural unit of AAEM, it further improves the problem of transition metal dissolution and large amount of oxygen release from side reactions, improves the discharge specific capacity of the positive electrode, and improves the cycle storage performance of the secondary battery, especially the high-temperature cycle storage performance.

[0083] In some embodiments, the copolymer comprises a six-membered ring, the six-membered ring comprising an N atom disposed on the ring and a *=NH substituent, wherein * represents a substituent linkage site.

[0084] In this application, the asterisk (*) represents a substituent connection site, specifically referring to the connection site of the substituent on a six-membered ring.

[0085] In some embodiments, the six-membered ring in the copolymer is formed by a cyano group (-CN) in a cyano-containing compound, which provides strong electronegativity to the copolymer and is beneficial to the stability of the six-membered chelate ring. The two work together to improve the problem of transition metal dissolution and the release of oxygen by a large number of side reactions, improve the discharge specific capacity of the positive electrode, and improve the cycle storage performance of the secondary battery, especially the high-temperature cycle storage performance.

[0086] In the technical solution of this application embodiment, the structure of the six-membered ring is shown in Equation 1:

[0087]

[0088] Where n≥2, for example 3, 4, 5, 6, etc., can be optionally selected from 2-4.

[0089] In the technical solution of this application embodiment, the exemplary structural formula of the copolymer is shown in Formula 2:

[0090]

[0091] Where n≥2, for example 3, 4, 5, 6, etc., and can be optionally selected from 2-4;

[0092] m≥2, for example, 3, 4, 5, 6, etc.

[0093] The above structural formula is merely provided as an example and can be used to meet the actual needs of this application.

[0094] In the technical solution of this application embodiment, the β-diketone bidentate chelate coordination in the AAEM structural unit forms a stable six-membered chelate ring, and its exemplary structural formula is as follows:

[0095]

[0096] Where M represents a transition metal (e.g., Mn), and the wavy line represents an undefined structure in the middle.

[0097] In some embodiments, the mass ratio of the coating material to the positive electrode active material is (0.5-2):100, wherein 0.5-2 can be 0.6, 0.8, 1, 1.2, 1.4, 1.6, 1.8, etc.; and / or;

[0098] The thickness of the shell formed by the coating material is 2-10nm, such as 3nm, 4nm, 5nm, 6nm, 7nm, 8nm, 9nm, etc.

[0099] In the technical solution of this application embodiment, the mass ratio of the coating material to the positive electrode active material is within the above range, which can effectively adjust the thickness of the shell layer; the reason why the thickness of the shell layer formed by the coating material is controlled within 2-10nm is that: within the thickness range, the positive electrode active material can be effectively coated, and the positive electrode active material has good conductivity, which is beneficial to improving the cycle storage performance and other properties of the secondary battery.

[0100] In some embodiments, the copolymer has a copolymer molar ratio of (40-80):(20-60) for the cyano-containing compound and ethylene glycol acetoacetate methacrylate, such as 50:50, 60:40, 70:30, etc.

[0101] In the technical solution of this application embodiment, the reason why the copolymerization molar ratio of the cyano-containing compound and the two monomers AAEM in the copolymer is controlled within the specified range is that: within the specified range, the β-diketone bidentate chelate coordination is stable, which ultimately helps to improve the cycle storage performance and other properties of the secondary battery.

[0102] In some embodiments, the weight-average molecular weight of the copolymer is 10,000-200,000, such as 20,000, 40,000, 60,000, 80,000, 100,000, 120,000, 140,000, 160,000, 180,000, etc.

[0103] In this application, the weight-average molecular weight is determined using gel permeation chromatography (GPC), also known as volume exclusion chromatography (SEC). The testing instrument is a Malvern OMNISEC multi-detector GPC / SEC gel permeation chromatography system. The specific testing method is as follows: the copolymer sample concentration is diluted to 2–5 mg / mL, filtered through a 0.22 μm–0.45 μm filter membrane into an autosampler vial, the equipment is started to begin the automatic testing process, and the weight-average molecular weight of the copolymer is calculated upon completion.

[0104] In the technical solution of this application embodiment, the reason why the weight-average molecular weight of the copolymer is controlled within the specified range is that the weight-average molecular weight within the specified range facilitates the control of the shell thickness formed by the coating material, which is beneficial to industrial production, and also benefits the stability of the shell, reducing the risk of excessive swelling of the shell or even dissolution in the electrolyte.

[0105] In some embodiments, the positive electrode active material includes any one or a combination of at least two of ternary positive electrode materials, lithium-rich manganese-based materials, lithium manganese oxide, or lithium nickel manganese oxide; and / or;

[0106] The ternary cathode material includes a nickel-cobalt-manganese ternary cathode material; and / or;

[0107] The lithium-rich manganese-based cathode material includes Li2MnO3 and / or LiMnO2.

[0108] In some embodiments, the nickel-cobalt-manganese ternary cathode material may be, for example, NCM333, NCM523, NCM622, and NCM811.

[0109] In some embodiments, the positive current collector can be made of any known material, for example, the positive current collector includes a metal foil or a composite current collector.

[0110] In some embodiments, the metal foil includes aluminum foil.

[0111] In some embodiments, the composite current collector includes a polymer material substrate layer and a metal layer disposed on at least one side of the polymer material substrate layer, wherein the polymer material substrate layer is made of, but is not limited to, any one or a combination of at least two of polyethylene, polypropylene, polystyrene, or polyethylene terephthalate; the metal layer is made of any one or a combination of at least two of aluminum, nickel, titanium, silver, aluminum alloy, nickel alloy, titanium alloy, or silver alloy.

[0112] In some embodiments, the positive electrode film layer further includes a binder and / or a conductive agent.

[0113] In some embodiments, the adhesive includes any one or a combination of at least two of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, or fluorinated acrylate resin.

[0114] In some embodiments, the conductive agent includes any one or a combination of at least two of acetylene black, Ketjen black, carbon dots, carbon nanotubes, graphene, or carbon nanofibers.

[0115] This application provides a method for preparing the positive electrode sheet described above, the method comprising the following steps:

[0116] The raw material of the positive electrode film is coated onto at least one surface of the positive electrode current collector and dried to obtain the positive electrode sheet;

[0117] The raw materials for the positive electrode film include positive electrode active materials and coating materials;

[0118] The coating material comprises a copolymer of acrylonitrile and ethylene glycol acetoacetate methacrylate.

[0119] In some embodiments, the raw materials for the positive electrode film include, for example, positive electrode active materials, coating materials, binders, conductive agents, any other components, and solvents (e.g., N-methylpyrrolidone NMP).

[0120] In some embodiments, the drying process may further include operations such as cold pressing and slitting.

[0121] In some embodiments, the positive electrode material includes a positive electrode active material and a coating material located on the surface of the positive electrode active material;

[0122] The coating material comprises a copolymer of a cyano-containing compound and ethylene glycol acetoacetate methacrylate.

[0123] In some embodiments, the method for preparing the positive electrode material includes the following steps:

[0124] The coating material is deposited on the surface of the positive electrode active material to obtain the positive electrode material;

[0125] The coating material comprises a copolymer of a cyano-containing compound and ethylene glycol acetoacetate methacrylate.

[0126] In some embodiments, the method for preparing the copolymer includes the following steps:

[0127] The copolymer is obtained by copolymerizing a cyano-containing compound with ethylene glycol acetoacetate methacrylate.

[0128] In some embodiments, the copolymerization temperature is 70-90°C, for example 75°C, 80°C, 85°C, etc.; and / or,

[0129] The copolymerization time is 1-20 hours, for example, 2 hours, 4 hours, 6 hours, 8 hours, 10 hours, 12 hours, 14 hours, 16 hours, 18 hours, etc.

[0130] In some embodiments, the copolymerization is carried out in a solvent, optionally including N-methylpyrrolidone.

[0131] In some embodiments, the amount of solvent added is 50%-400%, for example, 100%, 150%, 200%, 250%, 300%, 350%, etc., based on the total molar amount of the cyano-containing compound and ethylene glycol acetoacetate as 100%. In some embodiments, the molecular weight of the resulting copolymer of the cyano-containing compound and ethylene glycol acetoacetate can be adjusted by adjusting the amount of solvent added.

[0132] In some embodiments, the copolymerization is carried out under the action of an initiator, which may optionally include a peroxide initiator (e.g., benzoyl peroxide) and / or an azo initiator (e.g., azobisisobutyronitrile, azobisisoheptanenitrile, or dimethyl azobisisobutyrate).

[0133] In some embodiments, the copolymer is disposed on the surface of the positive electrode active material by spray drying.

[0134] For example, an industrial solvent-based spray drying device is used to mix the positive electrode active material, copolymer and solvent evenly, spray dry, collect the cyclone-separated material, and form a shell layer on the outer surface of the positive electrode active material to obtain the positive electrode material.

[0135] In some embodiments, the spray drying process further includes pre-oxidation into rings; and / or;

[0136] The pre-oxidation cyclization temperature is 180-240℃ (e.g., 190℃, 200℃, 210℃, 220℃, 230℃, etc.); and / or;

[0137] The pre-oxidation cyclization time is 1-10 hours (e.g., 2 hours, 4 hours, 6 hours, 8 hours, etc.).

[0138] In some embodiments, the method for preparing the positive electrode material includes the following steps:

[0139] (1) A cyano-containing compound with a molar ratio of (40-80):(20-60) and ethylene glycol acetoacetate methacrylate are copolymerized in a solvent using an initiator, wherein the copolymerization temperature is 70-90℃ and the copolymerization time is 1-20h, to obtain a first copolymer;

[0140] (2) The first copolymer is spray-dried onto the surface of the positive electrode active material to form a shell layer, thereby obtaining the positive electrode material; optionally, after spray drying, it is pre-oxidized at 180-240℃ for 1-10 hours to obtain the second copolymer.

[0141] In this application, the first copolymer can be directly used as a coating material to form a shell on the surface of the positive electrode active material to obtain the positive electrode material; alternatively, the first copolymer can be pre-oxidized and cyclized on the surface of the positive electrode active material to obtain a second copolymer containing a six-membered ring, which can then be used as a coating material, completing the pre-oxidation process while forming the shell to obtain the positive electrode material. The difference between the first copolymer and the second copolymer lies in whether or not pre-oxidation and cyclization have been performed.

[0142] In the technical solution of this application embodiment, the six-membered ring is formed by at least two (e.g., three, four, five, etc.) cyano groups in a cyano-containing compound such as acrylonitrile; the formation path of acrylonitrile is exemplarily shown below:

[0143]

[0144] Where n≥2, for example 3, 4, 5, 6, etc., can be optionally selected from 2-4.

[0145] Taking n=4 as an example, the path of the six-membered ring, using acrylonitrile as an example, is as follows:

[0146] (1) Forming AN repeating units from AN

[0147]

[0148] (2) Pre-oxidation of AN repeating units into rings

[0149]

[0150] In this application, the above-mentioned AN forming AN repeating unit is only illustrated for the convenience of showing the six-membered ring formation process. In fact, in the structure of intermediate 1, the number of cyano groups is ≥2, and 2-4 is more preferred.

[0151] In this application, during the pre-oxidation cyclization process of the AN repeating unit, intermediate 1 first forms intermediate 2, which can directly form the six-membered ring structure at a pre-oxidation temperature >180℃, such as 180℃ < pre-oxidation temperature ≤240℃; alternatively, intermediate 3 can be formed first, followed by the formation of the six-membered ring structure. In this case, the pre-oxidation temperature for intermediate 3 to form from intermediate 2 is 180-220℃, and the pre-oxidation temperature for the formation of the six-membered ring structure is >220℃, such as 220℃ < pre-oxidation temperature ≤240℃.

[0152] In some embodiments, the positive electrode sheet can be obtained by the following preparation method: forming a shell layer on the surface of the positive electrode active material with a coating material to obtain the positive electrode material; then dissolving the raw materials of the positive electrode film layer, namely the positive electrode material, binder, conductive agent and other arbitrary additives, in a solvent to form a positive electrode slurry; coating the positive electrode slurry on one or both sides of the positive electrode current collector, drying it to form a positive electrode film layer to obtain the positive electrode sheet. Optionally, after drying, cold pressing, slicing or other operations are performed.

[0153] [Negative electrode plate]

[0154] As the negative electrode, this application does not have any particular restrictions, and any known negative electrode can be selected according to actual needs.

[0155] In some embodiments, the method for preparing the negative electrode sheet includes: dissolving a negative electrode material, such as a negative electrode active material (e.g., graphite), a conductive agent (e.g., acetylene black), a binder (e.g., styrene-butadiene rubber), and other arbitrary components (e.g., thickeners, such as sodium carboxymethyl cellulose) in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto a negative electrode current collector (e.g., copper foil); and then drying, cold pressing, and slitting to obtain the negative electrode sheet.

[0156] Electrolyte

[0157] In some embodiments, the secondary battery further includes an electrolyte.

[0158] This application does not impose any particular restrictions on the electrolyte; any known electrolyte with ion-conducting properties can be selected according to actual needs. The electrolyte includes electrolyte salts, solvents, and any additives.

[0159] In some embodiments, the electrolyte salt is selected from lithium salts, including but not limited to lithium hexafluorophosphate (LiPF6).

[0160] In some embodiments, the solvent includes, but is not limited to, any one or a combination of at least two of ethylene carbonate (EC), ethyl methyl carbonate (EMC), or diethyl carbonate (DEC).

[0161] [Isolation membrane]

[0162] As for the separator, this application does not have any particular limitations, and any known porous structure separator with electrochemical and mechanical stability can be selected according to actual needs. For example, the separator can be a single-layer or multi-layer film containing one or more of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride.

[0163] In some embodiments, the secondary battery can be prepared by the following method: stacking and winding the above-mentioned positive electrode sheet, separator, and negative electrode sheet in sequence to obtain a battery cell; placing the battery cell in an outer packaging, adding electrolyte, and then performing processes such as encapsulation, standing, formation, and aging to obtain a secondary battery.

[0164] [Battery module, battery pack]

[0165] In some embodiments, the batteries can be assembled into a battery module, and the number of batteries contained in the battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0166] In some embodiments, the batteries can also be assembled into a battery pack.

[0167] In some embodiments, the battery modules can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0168] [ Electrical appliances ]

[0169] This application provides an electrical device, which includes the aforementioned secondary battery.

[0170] In some embodiments, the electrical device includes at least one of the battery modules or battery packs provided in any embodiment of this application.

[0171] The secondary battery, battery module, or battery pack described in this application can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., including but not limited to these.

[0172] [Example]

[0173] Example 1

[0174] Positive electrode sheet: The positive electrode sheet is obtained by the following preparation method:

[0175] (1) AN and AAEM were added to NMP solvent at a copolymerization molar ratio of 80:20 (the molar ratio of solvent to the two monomers was 86:1). The mixture was stirred, heated to 75°C, and nitrogen gas was introduced for 1 hour. Then, 0.1% of the monomer molar ratio of initiator (azobisisobutyronitrile) was added and the mixture was reacted for 12 hours. After that, the temperature was raised to 85°C and 0.1% of the monomer molar ratio of initiator was added again and the mixture was reacted for 2 hours to obtain PAN-AAEM prepolymer with a weight-average molecular weight of 200,000. The structural characterization diagram is shown below. Figure 1 As shown, 2242.83 is the characteristic peak of cyano group and 1737.6 is the characteristic peak of ester carbonyl group, proving that the PAN-AAEM prepolymer was successfully synthesized.

[0176] (2) Using an industrial solvent-based spray drying equipment, the positive electrode active material (lithium-rich manganese Li2MnO3) and NMP are mixed evenly at a mass ratio of 1:1. After stirring for 1 hour, 1% mass fraction of PAN-AAEM prepolymer (calculated based on 100% solid content) of the positive electrode active material is added. After stirring for another 30 minutes, the material is fed in and spray dried in a nitrogen environment at 180℃. Then, it is pre-oxidized at 230℃ for 3 hours to obtain PAN-AAEM copolymer. The material separated by cyclone is collected to obtain the positive electrode material. The PAN-AAEM copolymer forms a 5.7nm shell on the outer surface of the positive electrode active material.

[0177] (3) Dissolve the positive electrode material, binder PVDF and conductive agent acetylene black in solvent NMP at a mass ratio of 97.3:2.4:0.3 and stir thoroughly to obtain a positive electrode slurry. Coat the positive electrode slurry evenly on the positive electrode current collector aluminum foil, dry it to obtain a coated positive electrode current collector, and then dry, cold press and cut it to obtain a positive electrode sheet.

[0178] Negative electrode sheet: The negative electrode active material artificial graphite, conductive agent acetylene black, binder styrene-butadiene rubber, and thickener sodium carboxymethyl cellulose are dissolved in deionized water at a mass ratio of 95:2:1:2 and thoroughly stirred to obtain a negative electrode slurry. The negative electrode slurry is coated on the negative electrode current collector copper foil, and then dried, cold-pressed, and slit to obtain the negative electrode sheet.

[0179] Separating membrane: Polyethylene film is used as the separating membrane.

[0180] Electrolyte: Ethyl carbonate, methyl ethyl carbonate, and diethyl carbonate are mixed in a volume ratio of 1:1:1. LiPF6 is then uniformly dissolved in this mixture to obtain the electrolyte. The concentration of LiPF6 in this electrolyte is 1 mol / L.

[0181] Assembly: The positive electrode, separator, and negative electrode are stacked and wound in sequence to obtain a battery cell; the battery cell is placed in an outer packaging, the electrolyte prepared above is added, and after processes such as encapsulation, standing, formation, and aging, the secondary battery is obtained.

[0182] Examples 2-10 and Comparative Examples 1-3

[0183] Except for the parameters in Tables 1 and 2, secondary batteries were prepared according to the method of Example 1.

[0184] Table 1: Material and structural information of cathode materials

[0185]

[0186]

[0187] Table 2: Process parameters for preparing positive electrode sheets

[0188]

[0189]

[0190] In the table, polymers refer to PAN-AAEM copolymers, PAN homopolymers, or PAAEM homopolymers, consistent with the shell material in the examples or comparative examples.

[0191] "——" indicates data that is not involved.

[0192] Performance testing

[0193] (1) Coating effect test:

[0194] 1) Transmission electron microscopy (TEM) was used for testing. The testing procedure was as follows: a small amount of powder sample was placed in a vial, ethanol was added to about 2 / 3 of the vial, the sample was ultrasonically dispersed for about 15 minutes, and allowed to stand for about 5 minutes. 1-2 drops of the supernatant were transferred to a copper grid and baked with an infrared lamp to complete the sample preparation. Finally, the sample was sent to the TEM (Thermo Scientific-Talos F200S G2) for testing.

[0195] 2) The electron beam accelerated by high voltage in the TEM equipment is projected onto a thin sample (nm). The electrons interact with the atoms in the sample and are scattered. By collecting the scattered electrons after transmission and analyzing their angle, intensity and energy, the sample size, morphology, structure and composition information can be obtained.

[0196] Test results are as follows Figure 2-4 .analyze Figure 2-4 It can be seen that, according to Figure 2-3 and Figure 4As can be seen from the comparison, the embodiments described in this application successfully coated the surface of the positive electrode active material with a shell layer.

[0197] (2) 60℃ High-Temperature Cyclic Storage Performance Test: In a constant temperature environment of 60℃, the secondary battery was charged from 2.5V to the upper limit cutoff voltage (4.4V) at 0.33C, then charged at a constant voltage until the current ≤0.05mA, and discharged at 0.33C to 2.5V. The discharge capacity D0 was recorded. Then, it was charged at the upper limit cutoff voltage (4.4V) at a constant voltage until the current ≤0.05mA. The secondary battery was left to stand for 150 days. During the standing period, three cycles were performed every 15 days. In each cycle, the battery was first discharged at 0.33C to 2.5V and then charged at a constant voltage of 4.4V until the current ≤0.05mA. The discharge capacity of the third cycle was recorded as D. n (n = 1, 2, 3...), where n represents the nth 15-day resting period. D n Divide by D0 to get the capacity retention rate, which is used as an evaluation index of the cell degradation degree on the nth 15-day high-temperature storage. Record the capacity retention rate on the 90th day.

[0198] (3) Initial Coulomb Efficiency: According to the embodiments of this application, the steps for determining the rated capacity include: using a charge / discharge machine at 25°C, first charging to 4.4V at 1 / 3C, then charging at a constant voltage of 4.4V until the current decreases to 0.05C, and using this total charging capacity as the charging capacity; then discharging to 2.5V at 1 / 3C, and the discharged capacity at this time is the battery's discharge capacity, and dividing the charging capacity by the discharge capacity is the initial Coulomb efficiency.

[0199] (4) Discharge specific capacity: According to the embodiments of this application, the steps for determining the rated capacity include: charging the battery at 1 / 3C to 4.25V using a charge / discharge machine at 25°C, then charging it at a constant voltage of 4.25V until the current decreases to 0.05C; then discharging it at 1 / 3C to 2.5V. The capacity discharged at this point is the discharge capacity of the battery. The discharge specific capacity is obtained by dividing the discharge capacity by the total mass of the active material.

[0200] The test results are summarized in Table 3.

[0201] Table 3

[0202]

[0203] In the table, Fading EOL, or End of Life, refers to the state in which a secondary battery can no longer safely and effectively provide the required power.

[0204] Analysis of the data in Table 3 shows that the discharge specific capacity of the positive electrode in the secondary battery described in this application is above 181.06 mAh / g, and the initial coulombic efficiency of the secondary battery is above 82.98%. Under the test conditions of 60℃ and 0.33C, after 90 days of cell decay, the capacity retention rate is above 81.76%, that is, the high-temperature storage days are above 90 days. The positive electrode in the secondary battery described in this application has a high discharge specific capacity, and the secondary battery also has a high capacity retention rate after 90 days of cell decay under the test conditions of 60℃ and 0.33C, exhibiting excellent cycle storage performance, especially excellent high-temperature cycle storage performance.

[0205] Analysis of Comparative Examples 1-3 and Example 1 shows that the performance of Comparative Examples 1-3 is not as good as that of Comparative Example 1, proving that the positive electrode sheet formed by the shell described in this application is more conducive to improving the performance of secondary batteries.

[0206] Analysis of Examples 4-7 shows that the performance of Examples 6-7 is not as good as that of Examples 4-5, proving that a shell thickness of 2-10nm formed by using coating materials is more conducive to improving the performance of secondary batteries.

[0207] Analysis of Examples 8-9 and Example 1 shows that the performance of Examples 8-9 is not as good as that of Example 1, proving that the positive electrode formed by the copolymerization molar ratio of cyano-containing compounds and AAEM in the copolymer described in this application of (40-80):(20-60) is more conducive to improving the performance of secondary batteries.

[0208] Analysis of Example 10 and Example 1 shows that the performance of Example 10 is not as good as that of Example 1, proving that the presence of a six-membered ring in the copolymer described in this application is more conducive to improving the performance of secondary batteries.

[0209] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and not to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application, and they should all be covered within the scope of the claims and specification of this application. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any way. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A secondary battery, characterized in that, The secondary battery includes a positive electrode plate; The positive electrode sheet includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector; The positive electrode film layer includes a positive electrode material, which includes a positive electrode active material and a coating material located on the surface of the positive electrode active material; The coating material comprises a copolymer of a cyano-containing compound and ethylene glycol acetoacetate methacrylate.

2. The secondary battery according to claim 1, characterized in that, The cyanide-containing compounds include acrylonitrile.

3. The secondary battery according to claim 1 or 2, characterized in that, The copolymer includes a six-membered ring, the six-membered ring including an N atom disposed on the ring and a *=NH substituent, wherein * represents a substituent linkage site.

4. The secondary battery according to claim 3, characterized in that, The structural formula of the six-membered ring is shown in Equation 1: Where n≥2, and can be optionally selected from 2-4.

5. The secondary battery according to any one of claims 1-4, characterized in that, The structural formula of the copolymer is shown in Formula 2: Where n≥2, which can be optionally selected from 2-4; m≥2.

6. The secondary battery according to any one of claims 1-5, characterized in that, The mass ratio of the coating material to the positive electrode active material is (0.5-2):100; and / or; The thickness of the shell formed by the coating material is 2-10 nm.

7. The secondary battery according to any one of claims 1-6, characterized in that, In the copolymer, the molar ratio of the cyano-containing compound and ethylene glycol acetoacetate methacrylate is (40-80):(20-60).

8. The secondary battery according to any one of claims 1-7, characterized in that, The copolymer has a weight-average molecular weight of 10,000-200,000.

9. The secondary battery according to any one of claims 1-8, characterized in that, The positive electrode active material includes any one or a combination of at least two of the following: ternary positive electrode material, lithium-rich manganese-based material, lithium manganese oxide, or lithium nickel manganese oxide; and / or; The ternary cathode material includes a nickel-cobalt-manganese ternary cathode material; and / or; The lithium-rich manganese-based cathode material includes Li2MnO3 and / or LiMnO2.

10. A positive electrode material, characterized in that, The positive electrode material includes a positive electrode active material and a coating material located on the surface of the positive electrode active material; The coating material comprises a copolymer of a cyano-containing compound and ethylene glycol acetoacetate methacrylate.

11. The cathode material according to claim 10, characterized in that, The cyanide-containing compounds include acrylonitrile.

12. The cathode material according to claim 10 or 11, characterized in that, The copolymer includes a six-membered ring, the six-membered ring including an N atom disposed on the ring and a *=NH substituent, wherein * represents a substituent linkage site.

13. The cathode material according to claim 12, characterized in that, The structural formula of the six-membered ring is shown in Equation 1: Where n≥2, and can be optionally selected from 2-4.

14. The cathode material according to any one of claims 10-13, characterized in that, The structural formula of the copolymer is shown in Formula 2: Where n≥2, and can be optionally selected from 2-4; m≥2。 15. The cathode material according to any one of claims 10-14, characterized in that, The thickness of the shell formed by the coating material is 2-10 nm.

16. The cathode material according to any one of claims 10-15, characterized in that, In the copolymer, the molar ratio of the cyano-containing compound and ethylene glycol acetoacetate methacrylate is (40-80):(20-60).

17. The cathode material according to any one of claims 10-16, characterized in that, The copolymer has a weight-average molecular weight of 10,000-200,000.

18. The cathode material according to any one of claims 10-17, characterized in that, The positive electrode active material includes any one or a combination of at least two of the following: ternary positive electrode material, lithium-rich manganese-based material, lithium manganese oxide, or lithium nickel manganese oxide; and / or; The ternary cathode material includes a nickel-cobalt-manganese ternary cathode material; and / or; The lithium-rich manganese-based cathode material includes Li2MnO3 and / or LiMnO2.

19. A method for preparing a positive electrode material, characterized in that, The preparation method includes the following steps: The coating material is deposited on the surface of the positive electrode active material to obtain the positive electrode material; The coating material comprises a copolymer of a cyano-containing compound and ethylene glycol acetoacetate methacrylate.

20. The preparation method according to claim 19, characterized in that, The method for preparing the copolymer includes the following steps: The copolymer is obtained by copolymerizing a cyano-containing compound with ethylene glycol acetoacetate methacrylate.

21. The preparation method according to claim 20, characterized in that, The copolymerization temperature is 70-90℃; and / or; The copolymerization time is 1-20 hours.

22. The preparation method according to claim 20 or 21, characterized in that, The copolymerization is carried out in a solvent, optionally including N-methylpyrrolidone.

23. The preparation method according to any one of claims 20-22, characterized in that, The copolymer is disposed on the surface of the positive electrode active material by means of spray drying.

24. The preparation method according to any one of claims 20-23, characterized in that, The spray drying process further includes pre-oxidation into rings; and / or; The pre-oxidation cyclization temperature is 180-240℃; and / or; The pre-oxidation cyclization time is 1-10 hours.

25. An electrical appliance, characterized in that, The electrical device includes a secondary battery according to any one of claims 1-9, and / or a positive electrode material according to any one of claims 10-18, and / or a positive electrode material obtained by the preparation method according to any one of claims 19-24.

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