Core-shell structure composite, method for preparing the same, use thereof, secondary battery, and electric device

Abstract

The present application provides a core-shell structure composite material, a preparation method thereof, an application thereof, a secondary battery and an electric device. The core-shell structure composite material comprises a core layer and a shell layer at least partially covering the surface of the core layer, and the shell layer comprises a zero-strain material. An electrode active material prepared from the core-shell structure composite material can improve the cycle performance of a battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of secondary batteries, in particular to a core-shell structure composite material, a preparation method and application thereof, a secondary battery and an electric device. BACKGROUND

[0002] With the increasing prominence of energy and environmental problems, new energy industries have received more and more attention. In recent years, lithium secondary batteries have been widely used as an important new type of energy storage device due to their high energy density and good cycle performance.

[0003] As an important component of lithium ion batteries, positive active material provides lithium ions moving back and forth between the positive and negative electrodes during the charging and discharging process of the battery, so the positive active material is crucial to the performance of the battery. However, the positive active material is prone to side reactions and transition metal dissolution when it comes into contact with the electrolyte, which leads to the easy decay of battery capacity and makes it difficult to meet the market requirements for battery performance. SUMMARY

[0004] The present application is made in view of the above-mentioned problems, and aims to provide a core-shell structure composite material and its application as an electrode active material to improve the cycle performance of the battery.

[0005] The first aspect of the present application provides a core-shell structure composite material, which comprises a core layer and a shell layer at least partially covering the surface of the core layer, wherein the core layer comprises a lithium-containing transition metal oxide, and the shell layer comprises a zero-strain material.

[0006] The core-shell structure composite material of the present application can impart beneficial effects to the conventional material containing only a core layer, as a "shielding layer" and a "functional layer". The shell layer can "shield" the core layer from direct contact with the electrolyte, prevent the occurrence of battery side reactions and the dissolution of transition metals, and improve the cycle performance of the material. As a "functional layer", the shell layer contains a zero-strain material, which improves the structural stability of the material and improves the cycle performance of the material during the lithium ion intercalation and deintercalation process.

[0007] In any embodiment, the shell layer comprises a conductive material.

[0008] The coating of the zero-strain material on the surface of the core layer can easily lead to a decrease in the electronic transmission capacity of the electrode active material. The addition of a conductive material in the shell layer can effectively improve the conductivity of the active material, increase the electronic transmission rate, further improve the cycle performance of the battery, and improve the dynamic performance and voltage window of the battery.

[0009] In any embodiment, the shell layer comprises a first shell layer at least partially coated on the surface of the core layer and a second shell layer at least partially coated on the surface of the first shell layer, the first shell layer comprising a zero-strain material, and the second shell layer comprising a conductive material.

[0010] By the inner and outer arrangement of the first shell layer and the second shell layer, the core-shell structure composite material exhibits more excellent cycle performance when used as an electrode active material.

[0011] In any embodiment, the thickness ratio of the core layer to the first shell layer is 0.1-10:1, and optionally 0.2-5:1. When the thickness ratio of the core layer to the first shell layer is within this range, the structural stability of the material can be improved, and the cycle performance of the material can be improved.

[0012] In any embodiment, the thickness ratio of the first shell layer to the second shell layer is 0.1-10:1, and optionally 0.2-5:1. When the thickness ratio of the first shell layer to the second shell layer is within this range, the structural stability of the material can be improved, the cycle performance of the material can be improved, and the conductive performance of the material can be improved, and the battery cell kinetics performance can be improved.

[0013] In any embodiment, the zero-strain material comprises one or more of lithium titanate, lithium molybdate, and modified materials thereof.

[0014] In any embodiment, the conductive material comprises carbon nitride.

[0015] Carbon nitride itself has a suitable electron channel, which can further improve the conduction rate of electrons between the electrode material and the electrolyte, significantly widen the cycle voltage window, and compensate for the problem of voltage drop caused by the coating of the zero-strain material.

[0016] In any embodiment, the lithium-containing transition metal oxide comprises a lithium-containing manganese-based oxide, and is optionally at least one of LiMn2O4, aLi2MnO3·(1-a)LiAO2; wherein 0

[0017] The second aspect of the present application provides a use of the core-shell structure composite material of the first aspect of the present application as an electrode active material.

[0018] The third aspect of the present application provides a preparation method of a core-shell structure composite material, comprising: coating a shell layer containing a zero-strain material on the surface of a core layer to prepare a core-shell structure composite material, the core layer comprising a lithium-containing transition metal oxide.

[0019] In any embodiment, the preparation method specifically comprises: coating a first shell layer containing a zero-strain material on the surface of a core layer, and coating a second shell layer containing a conductive material on the surface of the first shell layer.

[0020] In any embodiment, the first shell layer is grown in situ on the surface of the core layer.

[0021] In any embodiment, the zero-strain material comprises lithium titanate, and the preparation method specifically comprises:

[0022] A core-shell structure composite material comprising a core layer containing a lithium-containing transition metal oxide and a shell layer containing lithium titanate is prepared by mixing a lithium-containing transition metal oxide, a lithium source, a titanium source, and a solvent for a hydrothermal reaction, and then spray drying.

[0023] In any embodiment, the conductive material comprises carbon nitride, and the preparation method further comprises:

[0024] A core-shell structure composite material comprising a core layer containing a lithium-containing transition metal oxide and a shell layer containing lithium titanate is prepared by mixing a lithium-containing transition metal oxide, a lithium source, a titanium source, and a solvent for a hydrothermal reaction, and then spray drying.

[0025] In any embodiment, the temperature of the hydrothermal reaction is 160-220°C, and / or the time of the hydrothermal reaction is 12-24h.

[0026] In any embodiment, the lithium source comprises at least one of lithium hydroxide, lithium hydroxide monohydrate, lithium carbonate, lithium acetate, and lithium nitrate.

[0027] In any embodiment, the titanium source comprises at least one of butyl titanate, titanium tetrachloride, titanium sulfate, and titanium dioxide.

[0028] The fourth aspect of the present application provides a secondary battery comprising a positive electrode sheet, wherein the positive electrode sheet comprises the core-shell structure composite material of the first aspect of the present application.

[0029] In any embodiment, the secondary battery comprises a lithium ion battery.

[0030] The fifth aspect of the present application provides an electric device comprising the secondary battery of the fourth aspect of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 is a structural schematic diagram of a core-shell structure composite material according to an embodiment of the present application;

[0032] Figure 2 is a schematic diagram of a secondary battery according to an embodiment of the present application;

[0033] Figure 3 is Figure 2 is an exploded view of a secondary battery according to an embodiment of the present application;

[0034] Figure 4 is a schematic view of a battery module according to an embodiment of the present application;

[0035] Figure 5 is a schematic view of a battery pack according to an embodiment of the present application;

[0036] Figure 6 is an exploded view of a battery pack according to an embodiment of the present application; Figure 5

[0037] Figure 7 is a schematic view of an electric device using a secondary battery according to an embodiment of the present application as a power source.

[0038] Explanation of Reference Numerals:

[0039] 1 battery pack; 2 upper case; 3 lower case; 4 battery module; 5 secondary battery; 51 case; 52 electrode assembly; 53 cover plate; 6 core-shell structure composite; 61 core layer; 62 first shell layer; 63 second shell layer. DETAILED DESCRIPTION

[0040] Hereinafter, embodiments of a core-shell structure composite, a manufacturing method thereof, applications thereof, a secondary battery, and an electric device according to the present application are specifically disclosed in detail with appropriate reference to the accompanying drawings. However, there can be cases where unnecessary detailed descriptions are omitted. For example, there can be cases where detailed descriptions of matters well known in the art, repetitive descriptions of substantially identical structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. In addition, the accompanying drawings and the following description are provided so that those skilled in the art can fully understand the present application, and are not intended to limit the subject matter recited in the claims.

[0041] ​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 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 "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0042] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0043] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0044] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0045] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0046] If not specifically stated, the term "or" in this application is inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, any of the following satisfy the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0047] Lithium-containing transition metal oxides are commonly used as positive active materials in secondary batteries. However, during the charge-discharge cycle of lithium ion batteries, the positive active material is prone to lattice distortion, leading to the dissolution of transition metals, which seriously reduces the capacity of the battery and significantly degrades the cycle performance.

[0048] [Core-shell structure composite material]

[0049] Based on this, the present application provides a core-shell structure composite material, which comprises a core layer and a shell layer at least partially covering the surface of the core layer, the core layer comprising a lithium-containing transition metal oxide, and the shell layer comprising a zero-strain material.

[0050] In this context, the term "zero-strain material" refers to a material whose crystal lattice constant or volume changes less than 1% when lithium ions are inserted or extracted. The "zero-strain property" of the material can be characterized by measuring the changes in the lattice constant and volume of the electrode material before and after cycling by X-ray diffraction (XRD).

[0051] In this context, the term "shell layer" refers to a portion covering the surface of the core layer, which can but does not necessarily completely cover the core layer. The use of "shell layer" is only for ease of description and is not intended to limit the present application.

[0052] When a zero-strain material is used as a shell layer to cover a lithium-containing transition metal oxide, on the one hand, it can avoid direct contact between the electrode active material in the core layer and the electrolyte, inhibit the occurrence of side reactions on the material surface and the dissolution of transition metal elements, and stabilize the chemical properties of the material surface. On the other hand, due to its own characteristics, the zero-strain material has a crystal lattice constant or volume change of less than 1% when lithium ions are inserted or extracted, which can inhibit the structural distortion of the core material during the charge-discharge process, reduce the dissolution of transition metal elements from the electrode active material, thereby improving the structural stability of the material and the cycle performance of the battery.

[0053] In some embodiments, the shell layer comprises a conductive material.

[0054] In this context, the term "conductive material" refers to a material used to transport and conduct electric current.

[0055] The coating of the zero-strain material on the surface of the core layer is likely to cause the decrease of the electron transport ability of the electrode active material. The addition of the conductive material in the shell layer can effectively improve the conductivity of the active material and the electron transport rate, further improve the cycle performance of the battery and the kinetic performance of the battery, and improve the voltage window of the battery.

[0056] In some embodiments, the zero-strain material and the conductive material are located in the same shell layer.

[0057] In some embodiments, a structure diagram of the core-shell structure composite material is as shown in Figure 1 The core-shell structure composite material 6 includes a core layer 61 and a shell layer, the shell layer includes a first shell layer 62 at least partially coated on the surface of the core layer 61 and a second shell layer 63 at least partially coated on the surface of the first shell layer 62, the first shell layer 62 contains a zero-strain material, and the second shell layer 63 contains a conductive material.

[0058] The coating of the first shell layer 62 and the second shell layer 63 can effectively reduce the direct contact of the core layer 61 with the electrolyte, alleviate the occurrence of the battery side reaction and the dissolution of the transition metal, and improve the cycle performance of the material. The first shell layer 62 contains a zero-strain material, which can fully play the structural stability of the zero-strain material in close contact with the core layer, and inhibit the dissolution of the transition metal.

[0059] The second shell layer 63 contains a conductive material, which is coated outside the first shell layer, can improve the rate of electron exchange between the electrode material and the electrolyte, and further improve the cycle performance of the battery. Through the inside and outside collocation of the first shell layer and the second shell layer, compared with one coating layer, the core-shell structure composite material as an electrode active material shows more excellent cycle performance.

[0060] In some embodiments, the thickness ratio of the core layer to the first shell layer is 0.1 to 10:1. In some embodiments, the thickness ratio of the core layer to the first shell layer can be selected as 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 0.5:1, 1.5:1, 2.5:1, 3.5:1, 4.5:1, 5.5:1, 6.5:1, 7.5:1, 8.5:1, 9.5:1, 0.2:1, 0.4:1, 0.6:1, 0.8:1, 1.2:1, 1.4:1, 1.6:1, 1.8:1, 2.2:1, 2.4:1, 2.6:1, 2.8:1, 3.2:1, 3.4:1, 3.6:1, 3.8:1, 4.2:1, 4.4:1, 4.6:1, 4.8:1, 5.2:1, 5.4:1, 5.6:1, 5.8:1, 6.2:1, 6.4:1, 6.6:1, 6.8:1, 7.2:1, 7.4:1, 7.6:1, 7.8:1, 8.2:1, 8.4:1, 8.6:1, 8.8:1, 9.2:1, 9.4:1, 9.6:1, 9.8:1.

[0061] Within this range, the ratio of the core layer thickness to the first shell thickness helps to fully utilize the capacity performance of the core layer and avoids increased resistance and difficulty in achieving full capacity due to an excessively thick first shell.

[0062] In some embodiments, the thickness ratio of the first shell layer to the second shell layer is 0.1 to 10:1. In some embodiments, the thickness ratio of the first shell layer to the second shell layer can be selected as 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 0.5:1, 1.5:1, 2.5:1, 3.5:1, 4.5:1, 5.5:1, 6.5:1, 7.5:1, 8.5:1, 9.5:1, 0.2:1, 0.4:1, 0.6:1, 0.8:1, 1.2:1, 1.4:1, 1.6:1, 1.8:1, 2.2:1, 2.4:1. , 2.6:1, 2.8:1, 3.2:1, 3.4:1, 3.6:1, 3.8:1, 4.2:1, 4.4:1, 4.6:1, 4.8:1, 5.2:1, 5.4:1, 5.6:1, 5.8:1, 6.2:1, 6.4:1, 6.6:1, 6.8:1, 7.2:1, 7.4:1, 7.6:1, 7.8:1, 8.2:1, 8.4:1, 8.6:1, 8.8:1, 9.2:1, 9.4:1, 9.6:1, 9.8:1.

[0063] Within this range, the thickness ratio of the first shell to the second shell helps to ensure that the second shell tightly and uniformly coats the first shell, thus improving the structural stability and conductivity of the electrode material in a balanced manner.

[0064] In some embodiments, the lithium-containing transition metal oxide comprises a lithium-containing manganese-based oxide, optionally at least one of LiMn2O4, aLi2MnO3·(1-a)LiAO2, wherein 0

[0065] The lithium-containing manganese-based oxide has low cost, good safety and low temperature performance. However, the manganese element is prone to overflow, resulting in rapid capacity attenuation of the battery. The composite material provided in the application can effectively improve the poor structural stability of the lithium-containing manganese-based oxide, and effectively improve the structural stability and cycle performance of the electrode material.

[0066] In some embodiments, the zero-strain material comprises one or more of lithium titanate, lithium molybdate and modified materials thereof. In some embodiments, the zero-strain material comprises one or more of Li4Ti5O 12 , LiCrTiO4, LiY(MoO4)2.

[0067] The above zero-strain material not only has good structural stability, but also can provide a part of capacity, which can further reduce the capacity loss of the electrode active material during the charge and discharge cycle process.

[0068] In some embodiments, the conductive material comprises one or more of carbon nitride, graphene, nitrogen-doped carbon, and conductive polymer. In some embodiments, the conductive polymer comprises polypyrrole, polyaniline, etc. In some embodiments, the conductive material comprises carbon nitride.

[0069] The zero-strain material, such as lithium titanate, will cause the problem of reduced cell voltage while improving structural stability. The carbon nitride itself has a suitable electron channel, which can further improve the conduction rate of electrons between the electrode material and the electrolyte, significantly widen the voltage window of the battery, and make up for the problem of voltage drop caused by the zero-strain material.

[0070] In some embodiments, the particle size of the core layer material is 1-100 nm, and optionally 5-20 nm. In some embodiments, the particle size of the zero-strain material in the shell layer is 1-100 nm, and optionally 5-20 nm. In some embodiments, the particle size of the conductive material in the shell layer is 1-50 nm, and optionally 2-50 nm.

[0071] Another aspect of the application provides an application of the core-shell structure composite material as an electrode active material.

[0072] In some embodiments, the core-shell structure composite material is a positive electrode active material.

[0073] In some embodiments, the core-shell structure composite material is a negative electrode active material.

[0074] In another aspect of the present application, a method for preparing a core-shell structure composite material is provided, the method comprising:

[0075] coating a shell layer containing a zero-strain material on the surface of the core layer to prepare a core-shell structure composite material, the core layer comprising a lithium-containing transition metal oxide.

[0076] In some embodiments, the method for preparing specifically comprises:

[0077] coating a first shell layer containing a zero-strain material on the surface of the core layer, and coating a second shell layer containing a conductive material on the surface of the first shell layer.

[0078] In some embodiments, the first shell layer is grown in situ on the surface of the core layer.

[0079] The first shell layer grown in situ on the surface of the core layer has a strong binding force between the core layer and the first shell layer, and has better structural stability and cycle stability.

[0080] In some embodiments, the zero-strain material comprises lithium titanate, and the method for preparing specifically comprises:

[0081] mixing a lithium-containing transition metal oxide, a lithium source, a titanium source, and a solvent to perform a hydrothermal reaction, and then performing spray drying to obtain a core-shell structure composite material, wherein the core layer comprises the lithium-containing transition metal oxide, and the shell layer comprises lithium titanate, the lithium source comprises at least one of a lithium-containing salt and a lithium-containing base, and the titanium source comprises at least one of a titanium-containing salt, a titanium-containing organic compound, and a titanium-containing oxide.

[0082] In some embodiments, the conductive material comprises carbon nitride, and the method for preparing further comprises:

[0083] dispersing the core-shell structure composite material, wherein the core layer comprises the lithium-containing transition metal oxide, and the shell layer comprises lithium titanate, into a solution containing carbon nitride (C3N4), and then performing stirring and drying to obtain a core-shell structure composite material, wherein the core layer comprises the lithium-containing transition metal oxide, the first shell layer comprises lithium titanate, and the second shell layer comprises C3N4.

[0084] In some embodiments, the temperature of the hydrothermal reaction is 160°C to 220°C, and / or the time of the hydrothermal reaction is 12h to 24h. In some embodiments, the temperature of the hydrothermal reaction is 160°C, 170°C, 180°C, 190°C, 200°C, 210°C, or 220°C. In some embodiments, the time of the hydrothermal reaction is 12h, 13h, 14h, 15h, 16h, 17h, 18h, 19h, 20h, 21h, 22h, 23h, or 24h.

[0085] In some embodiments, the lithium source comprises at least one of lithium hydroxide, lithium hydroxide monohydrate, lithium carbonate, lithium acetate, lithium nitrate.

[0086] In some embodiments, the titanium source comprises at least one of butyl titanate, titanium tetrachloride, titanium sulfate, titanium dioxide.

[0087] The core-shell structure composite prepared by the preparation method can improve the cycle performance and kinetic performance of the battery.

[0088] [Positive electrode sheet]

[0089] The positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode film layer comprises a positive electrode active material, and the positive electrode active material comprises the core-shell structure composite of any of the embodiments or the core-shell structure composite prepared by the preparation method of the core-shell structure composite of any of the embodiments.

[0090] For example, the positive electrode current collector has two opposite surfaces in the thickness direction of the positive electrode current collector, and the positive electrode film layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.

[0091] In some embodiments, the positive electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, an aluminum foil can be used. The composite current collector can comprise a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer material base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0092] In some embodiments, the positive electrode film layer can further optionally comprise a conductive agent. For example, the conductive agent can comprise at least one of super P, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0093] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the toughening agent, the binder, and any other components, in a solvent (such as N-methyl pyrrolidone) to form a positive electrode slurry, coating the positive electrode slurry on the positive electrode current collector, and then drying, cold pressing, etc. to obtain the positive electrode sheet.

[0094] [Negative electrode sheet]

[0095] In some embodiments, the negative electrode tab includes a negative current collector and a negative film layer disposed on at least one surface of the negative current collector.

[0096] As an example, the negative current collector has two surfaces opposite in the thickness direction thereof, and the negative film layer is disposed on either one or both of the two opposite surfaces of the negative current collector.

[0097] In some embodiments, the negative current collector can employ a metal foil or a composite current collector. For example, as the metal foil, a copper foil can be employed. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer material base layer such as a base layer of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0098] In some embodiments, the negative active material can employ a negative active material for a battery known in the art. As an example, the negative active material can include at least one of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based material, tin-based material, and lithium titanate, etc. The silicon-based material can be selected from at least one of elemental silicon, silicon oxide compound, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy. The tin-based material can be selected from at least one of elemental tin, tin oxide compound, and tin alloy. However, the present application is not limited to these materials, and other conventional materials that can be used as a negative active material for a battery can also be used. These negative active materials can be used alone or in combination of two or more.

[0099] In some embodiments, the negative film layer can further optionally include a binder. The binder 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).

[0100] In some embodiments, the negative film layer can further optionally include a conductive agent. The conductive agent can be selected from at least one of super conductive carbon, acetylene black, carbon black, ketjen black, carbon dot, carbon nanotube, graphene, and carbon nanofiber.

[0101] In some embodiments, the negative film layer can further optionally include other auxiliary agents, such as a thickening agent (e.g., sodium carboxymethyl cellulose (CMC-Na)) and the like.

[0102] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the 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 then drying, cold-pressing, or the like to obtain the negative electrode sheet.

[0103] [Electrolyte]

[0104] The electrolyte functions to conduct ions between the positive electrode sheet and the negative electrode sheet. The type of electrolyte is not particularly limited in the present application, and can be selected as needed. For example, the electrolyte can be liquid, gel, or all-solid.

[0105] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0106] In some embodiments, the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonylimide, lithium bis-trifluoromethanesulfonylimide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorobisoxalate borate, lithium bisoxalate borate, lithium difluorobisoxalate phosphate, and lithium tetrafluorobisoxalate phosphate.

[0107] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclobutane sulfone, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0108] In some embodiments, the electrolyte solution can optionally further include an additive. For example, the additive can include a negative electrode film-forming additive, a positive electrode film-forming additive, and can further include an additive capable of improving certain properties of the battery, such as an additive for improving overcharge performance of the battery, an additive for improving high-temperature or low-temperature performance of the battery, etc.

[0109] [Separator]

[0110] In some embodiments, the secondary battery further includes a separator. The type of separator is not particularly limited in the present application, and any known porous structure separator having good chemical stability and mechanical stability can be used.

[0111] In some embodiments, the material of the separator film can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator film can be a single layer film or a multi-layer composite film, and is not particularly limited. When the separator film is a multi-layer composite film, the materials of the layers can be the same or different, and are not particularly limited.

[0112] [Secondary battery]

[0113] In one embodiment of the present application, a secondary battery is provided, which includes a positive electrode sheet, a separator film, a negative electrode sheet, and an electrolyte, the positive electrode sheet including the toughening agent of any one of the embodiments or the binder of any one of the embodiments.

[0114] Generally, a secondary battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator film. During the charging and discharging of the secondary battery, active ions are inserted and extracted between the positive electrode sheet and the negative electrode sheet. The electrolyte functions to conduct ions between the positive electrode sheet and the negative electrode sheet. The separator film is disposed between the positive electrode sheet and the negative electrode sheet, and mainly functions to prevent short circuiting between the positive electrode and the negative electrode, while allowing ions to pass through.

[0115] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator film can be made into an electrode assembly by a roll-pressing process or a stacking process.

[0116] In some embodiments, the secondary battery can include an outer package. The outer package can be used to package the electrode assembly and the electrolyte described above.

[0117] In some embodiments, the outer package of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, or the like. The outer package of the secondary battery can also be a soft package, such as a pouch-type soft package. The material of the soft package can be plastic, and as the plastic, polypropylene, polybutylene terephthalate, polybutylene succinate, or the like can be exemplified.

[0118] The shape of the battery is not particularly limited in the present application, and can be cylindrical, square, or any other shape. For example, Figure 2 is a square structure of a secondary battery 5 as an example.

[0119] In some embodiments, with reference to Figure 3The outer package can include a housing 51 and a cover plate 53. The housing 51 can include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be arranged on the opening to close the receiving cavity. The positive electrode tab, the negative electrode tab, and the separator film can form the electrode assembly 52 through a winding process or a stacking process. The electrode assembly 52 is packaged in the receiving cavity. The electrolyte is impregnated in the electrode assembly 52. The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and a person skilled in the art can select according to the specific actual needs.

[0120] [Battery module]

[0121] In some embodiments, the secondary battery can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, and the specific number can be selected by a person skilled in the art according to the application and capacity of the battery module.

[0122] Figure 4 The battery module 4 is an example. Refer to Figure 4 In the battery module 4, a plurality of secondary batteries 5 can be arranged in sequence along the length direction of the battery module 4. Of course, other arbitrary arrangements can also be used. Further, the plurality of secondary batteries 5 can be fixed by fasteners.

[0123] Optionally, the battery module 4 can also include a housing having a receiving space, and the plurality of secondary batteries 5 are received in the receiving space.

[0124] [Battery pack]

[0125] In some embodiments, the above-mentioned battery module can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, and the specific number can be selected by a person skilled in the art according to the application and capacity of the battery pack.

[0126] Figure 5 and Figure 6 The battery pack 1 is an example. Refer to Figure 5 and Figure 6 In the battery pack 1, a battery box and a plurality of battery modules 4 arranged in the battery box can be included. The battery box includes an upper box body 2 and a lower box body 3, and the upper box body 2 can be arranged on the lower box body 3 and form a closed space for receiving the battery module 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0127] [Electric device]

[0128] In addition, the application further provides a power utilization device comprising at least one of the secondary battery, the battery module, or the battery pack provided by the application. The secondary battery, the battery module, or the battery pack can be used as a power supply of the power utilization device, and can also be used as an energy storage unit of the power utilization device. The power utilization device can include a mobile device (such as a mobile phone, a notebook computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship and a satellite, an energy storage system, etc., but is not limited thereto.

[0129] As the power utilization device, the secondary battery, the battery module, or the battery pack can be selected according to the use requirement thereof.

[0130] Figure 7 The power utilization device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the requirement of high power and high energy density of the secondary battery for the power utilization device, the battery pack or the battery module can be used.

[0131] The device as another example can be a mobile phone, a tablet computer, a notebook computer, etc. The device usually requires thinning, and the secondary battery can be used as a power supply.

[0132] Example

[0133] Hereinafter, the embodiments of the application are described. The embodiments described below are exemplary and are only used to explain the application, and cannot be understood as a limitation of the application. If the specific technology or condition is not indicated in the embodiments, the technology or condition described in the literature in the art or according to the product instruction is used. If the reagent or instrument used is not indicated by the manufacturer, it is a conventional product that can be obtained by purchase.

[0134] Embodiment 1

[0135] 1) Preparation of positive active material

[0136] Lithium hydroxide 20 g and butyl titanate 50 g were respectively dissolved in 350 g of water and 650 g of ethanol, and the two solutions were uniformly mixed to prepare solution 1;

[0137] 100 g of lithium manganate was subjected to crushing treatment in a crusher, and the crushed polycrystalline lithium manganate was uniformly dispersed into 1 L of solution 1 and subjected to ultrasonic treatment, and the solution after ultrasonic treatment was used as solution 2;

[0138] Solution 2 was placed in a hydrothermal reaction kettle and subjected to hydrothermal reaction at 200 ℃ for 15 h. After the reaction was completed, the solution was subjected to spray drying to obtain a composite material A comprising lithium manganate in the core layer and lithium titanate in the shell layer.

[0139] Take 100 g of composite material A and disperse it in 0.1 mol of C3N4 aqueous solution, ultrasonic for 30 min, and continuously stir for 2 h to obtain solution 3. Vacuum filter, dry and grind solution 3 to obtain a positive electrode active material with a core layer containing lithium manganate, a first shell layer containing lithium titanate, and a second shell layer containing C3N4.

[0140] 2) Preparation of positive electrode sheet

[0141] Mix the positive electrode active material of Example 1 and carbon nanotubes in a mass ratio of 96:4, then add solvent N-methyl pyrrolidone (NMP) and stir to make the solid content of the positive electrode slurry 70%-80%; then uniformly coat the positive electrode slurry on the positive electrode current collector, and then go through drying, cold pressing, and slitting to obtain the positive electrode sheet.

[0142] 3) Preparation of negative electrode sheet

[0143] Dry mix the active material graphite and SUPER P in a weight ratio of 95:3, then add deionized water and stir to make the solid content of the negative electrode slurry 45%-55%, then add 2% binder styrene-butadiene rubber (SBR), mix uniformly to prepare the negative electrode slurry; uniformly coat the negative electrode slurry on the negative electrode current collector copper foil, and then go through drying, cold pressing, and slitting to obtain the negative electrode sheet.

[0144] 4) Separation film

[0145] Use a polypropylene film as the separation film.

[0146] 5) Preparation of electrolyte

[0147] In an argon atmosphere glove box (H2O <0.1 ppm, O2 <0.1 ppm), mix the organic solvent ethylene carbonate (EC) / ethyl methyl carbonate (EMC) uniformly in a volume ratio of 3 / 7, add LiPF6 lithium salt dissolved in the organic solvent, and stir uniformly to make the mass content of LiPF6 lithium salt 12.5%, to obtain the electrolyte of Example 1.

[0148] 6) Preparation of battery

[0149] Stack the positive electrode sheet, the separation film, and the negative electrode sheet of Example 1 in order, with the separation film between the positive and negative electrode sheets to play a separation role, then roll to obtain a bare cell, weld the tabs to the bare cell, and put the bare cell into an aluminum shell, and bake at 80°C to remove water, then inject electrolyte and seal to obtain a non-charged battery.

[0150] The non-charged battery goes through the processes of standing, hot and cold pressing, formation, shaping, and capacity testing in order to obtain the lithium ion battery product of Example 1.

[0151] The preparation parameters in Examples 2 to 13 are basically the same as those in Example 1. The specific parameters are shown in Table 1.

[0152] Specifically, in Examples 2-4, the thickness ratio of the first shell layer to the second shell layer of the core-shell structure is kept constant, while the thickness ratio of the core layer to the first shell layer is adjusted. The specific parameters are shown in Table 1.

[0153] In Examples 5-7, the thickness ratio of the core layer to the first shell layer was kept constant, and the thickness ratio of the first shell layer to the second shell layer was adjusted by regulating the time or temperature of the hydrothermal reaction and the mass of carbon nitride added. Specific parameters are shown in Table 1.

[0154] In Examples 8 and 9, the coating material of the first shell layer was changed, and the specific parameters are shown in Table 1.

[0155] Example 10

[0156] The difference between this embodiment and Embodiment 1 is that the first shell layer is made of Li4Ti5O. 12 After being mixed with C3N4, it was dispersed together with crushed polycrystalline lithium manganese oxide in an aqueous solution. After ultrasonic stirring, it was vacuum filtered, dried and ground to obtain Li4Ti5O with lithium manganese oxide as the core. 12 The mixture with C3N4 is the positive electrode active material of the shell.

[0157] Example 11

[0158] The process is basically the same as in Example 1, except that the lithium titanate coating is a mechanically mixed coating, and the specific preparation method is as follows:

[0159] 100g of lithium manganese oxide was crushed in a crusher, and the crushed polycrystalline lithium manganese oxide and lithium titanate were dispersed in a solvent. After stirring for 2 hours, the mixture was vacuum filtered, dried, and ground to obtain an intermediate with lithium manganese oxide as the core and lithium titanate as the shell.

[0160] 100g of the intermediate was dispersed in 0.1mol of C3N4 aqueous solution, sonicated for 30min and stirred continuously for 2h to obtain solution 3. Solution 3 was vacuum filtered, dried and ground to obtain a positive electrode active material with the intermediate as the core and C3N4 as the shell.

[0161] Example 12

[0162] Example 12 is basically the same as Example 1, except that C3N4 is replaced with graphene.

[0163] Example 13 is basically the same as Example 1, except that only lithium titanate is coated with lithium manganese oxide, and C3N4 coating is not performed. Comparative Example 1 is lithium manganese oxide without any coating.

[0164] In Comparative Example 1, lithium manganate was used as the positive active material, and no coating treatment was performed.

[0165] II. Test Methods

[0166] 1. Battery cycle capacity retention test

[0167] The battery capacity retention test procedure was as follows: at 25°C, the battery was charged at 1C constant current to 4.35V, then charged at 4.35V constant voltage to a current of 0.05C, rested for 10 min, then discharged at 1C to 2.8V, and the obtained capacity was recorded as the initial capacity CO. The above steps were repeated for the same battery, and the discharge capacity of the battery after the nth cycle Cn was recorded at the same time. Then, the battery capacity retention Pn = (Cn / CO) x 100% after each cycle, and the 1000-point values P1, P2, …, P1000 were taken as the ordinate, and the corresponding cycle number was taken as the abscissa, to obtain a graph of battery capacity retention versus cycle number.

[0168] In this test procedure, the first cycle corresponds to n = 1, the second cycle corresponds to n = 2, and the 1000th cycle corresponds to n = 1000. The battery capacity retention data corresponding to the examples and comparative examples in Table 1 were measured after 1000 cycles under the above test conditions, i.e., the value of P1000.

[0169] 2. Electrochemical stability window test

[0170] An electrochemical workstation was used to test the window of the electrolyte. The test temperature was 25°C, the voltage range was 1.0-5.0V, and the scan rate was 0.1 mV / s. The use window of the electrolyte was determined according to the starting position of the peak potential in the CV curve. The cyclic voltammetry (CV) test in this experiment was completed on a 1470 multi-channel electrochemical workstation from the British Solartron company.

[0171] III. Analysis of test results of examples and comparative examples

[0172] Table 1

[0173]

[0174] According to the above results, examples 1-13 all contain a core layer and a shell layer. The core layer contains a lithium-containing transition metal oxide, and the shell layer contains at least one of Li4Ti5O12, LiCrTiO4, and LiY(MoO4)2. From the comparison of examples 1-13 and comparative example 1, it can be seen that the core-shell structure composite material containing a zero-strain material in the shell layer can effectively improve the cycle performance of the battery. 12

[0175] ​From the comparison of Examples 1-12 and Example 13, it can be seen that the inclusion of C3N4 or graphene in the shell layer can more effectively improve the cycle performance of the battery; and the addition of C3N4 or graphene in the shell layer can improve the voltage window of the lithium manganate composite coated with zero-strain material.

[0176] From the comparison of Examples 1-11 and Example 12, it can be seen that C3N4 can more effectively improve the oxidation potential and widen the cycle voltage window of the positive active material than other conductive materials.

[0177] From the comparison of Examples 1-9, 11 and Example 10, it can be seen that the shell layer includes a first shell layer coated on the surface of the core layer and a second shell layer coated on the surface of the first shell layer, the first shell layer contains zero-strain material, and the second shell layer contains conductive material; compared with the core-shell structure with only one coating layer, the cycle performance of the battery can be more effectively improved.

[0178] From Examples 1-4, it can be seen that when the thickness ratio of the core layer to the shell layer is 0.2-5, the cycle performance of the battery can be effectively improved.

[0179] From Examples 5-7, it can be seen that when the thickness ratio of the first shell layer to the second shell layer is 0.2-5, the cycle performance of the battery can be effectively improved.

[0180] From Examples 1, 8-9, it can be seen that when the zero-strain material is one of Li4Ti5O 12 , LiCrTiO4, and LiY(MoO4)2, the cycle performance of the battery can be effectively improved.

[0181] From the comparison of Example 1 and Examples 10-11, it can be seen that the use of in-situ growth to prepare the first shell layer can make the connection between the first shell layer and the core layer more close, and can effectively improve the cycle performance of the battery.

[0182] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and embodiments having the same technical idea and playing the same role and effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, within the scope of the main idea of the present application, various modifications of the embodiments, combination of part of the constituent elements in the embodiments to construct other ways can also be included in the scope of the present application.

Claims

1. A core-shell structure composite material, characterized by, The core-shell structure composite material comprises a core layer and a shell layer at least partially covering the surface of the core layer, the core layer comprises a lithium-containing transition metal oxide, and the shell layer comprises a zero strain material and a conductive material.

2. The core-shell structure composite material according to claim 1, characterized in that, The shell layer comprises a first shell layer at least partially covering the surface of the core layer and a second shell layer at least partially covering the surface of the first shell layer, the first shell layer comprises a zero strain material, and the second shell layer comprises a conductive material.

3. The core-shell structure composite material according to claim 2, characterized in that, The thickness ratio of the core layer to the first shell layer is 0.1-10.

4. The core-shell structure composite material according to claim 3, characterized in that, The thickness ratio of the core layer to the first shell layer is 0.2-5.

5. The core-shell structure composite material according to claim 3 or 4, characterized in that, The thickness ratio of the first shell layer to the second shell layer is 0.1-10.

6. The core-shell structure composite of claim 5, wherein, The thickness ratio of the first shell layer to the second shell layer is 0.2-5.

7. The core-shell structure composite material according to any one of claims 1 to 6, characterized in that, The zero strain material comprises one or more of lithium titanate, lithium molybdate and modified materials thereof.

8. The core-shell structure composite material according to any one of claims 1 to 7, characterized in that, The conductive material comprises carbon nitride.

9. The core-shell structure composite material according to any one of claims 1 to 8, characterized in that, The lithium-containing transition metal oxide comprises a lithium-containing manganese-based oxide.

10. The core-shell structure composite of claim 9, wherein, The lithium-containing transition metal oxide comprises at least one of LiMn2O4 and aLi2MnO3·(1-a)LiAO2; wherein 0 11. A method for producing a core-shell structure composite material, characterized by, The preparation method comprises: The core-shell structure composite material comprises a core layer and a shell layer at least partially covering the surface of the core layer, the core layer comprises a lithium-containing transition metal oxide, and the shell layer comprises a zero strain material and a conductive material.

12. The method of claim 11, wherein, The preparation method specifically comprises: The core-shell structure composite material comprises a core layer and a shell layer at least partially covering the surface of the core layer, the core layer comprises a lithium-containing transition metal oxide, and the shell layer comprises a zero strain material and a conductive material. The preparation method specifically comprises: The core-shell structure composite material comprises a core layer and a shell layer at least partially covering the surface of the core layer, the core layer comprises a lithium-containing transition metal oxide, and the shell layer comprises a zero strain material and a conductive material.

14. The production method according to any one of claims 11 to 13, characterized by, The preparation method specifically comprises: The core-shell structure composite material comprises a core layer and a shell layer at least partially covering the surface of the core layer, the core layer comprises a lithium-containing transition metal oxide, and the shell layer comprises a zero strain material and a conductive material.

15. The preparation method according to claim 14, characterized in that, The preparation method specifically comprises: The core-shell structure composite material comprises a core layer and a shell layer at least partially covering the surface of the core layer, the core layer comprises a lithium-containing transition metal oxide, and the shell layer comprises a zero strain material and a conductive material.

16. The production method according to claim 14 or 15, characterized by, The temperature of the hydrothermal reaction is 160-220°C, and / or the time of the hydrothermal reaction is 12-24h.

17. The production method according to any one of claims 14 to 16, characterized by, The lithium source comprises at least one of lithium hydroxide, lithium hydroxide monohydrate, lithium carbonate, lithium acetate and lithium nitrate.

18. The production method according to any one of claims 14 to 17, characterized by, The titanium source comprises at least one of butyl titanate, titanium tetrachloride, titanium sulfate and titanium dioxide.

19. A secondary battery characterized by comprising: The positive electrode sheet comprises the core-shell structure composite material of any one of claims 1-10 or the core-shell structure composite material prepared by the preparation method of any one of claims 11-18.

20. The secondary battery according to claim 19, characterized by The secondary battery comprises a lithium ion battery.

21. An electrical device, comprising: The secondary battery comprises the secondary battery of claim 19 or 20.

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