Composite negative electrode material, preparation method thereof, negative electrode sheet, secondary battery and electric device

Abstract

The application relates to a composite negative electrode material, a preparation method thereof, a negative electrode sheet, a secondary battery and an electric device. The composite negative electrode material comprises a carbon fiber composite material and a silicon material layer arranged on at least part of the surface of the carbon fiber composite material, wherein the carbon fiber composite material comprises carbon fibers with a three-dimensional fiber network structure and a fast ion conductor combined on the carbon fibers. The composite negative electrode material can reduce the expansion force of the battery, improve the ion conductivity of the negative electrode, and improve the cycle life of the lithium ion battery under high-rate fast charging and discharging conditions, thereby obtaining a lithium ion battery with relatively optimal comprehensive performance.

Description

TECHNICAL FIELD

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

[0002] Secondary batteries are widely used in various consumer electronic products and electric vehicles due to their light weight, no pollution and no memory effect. Lithium ion batteries have dominated many fields of the battery market due to their high energy density, long service life and no memory effect. With the great development of lithium ion batteries, especially with the wide application of lithium ion batteries in new energy electric vehicles, higher requirements are put forward for the energy density and rapid charging capacity of lithium ion batteries. However, the theoretical specific capacity of the currently commercialized graphite negative electrode material is only 372 mAh / g, which is relatively low and cannot meet the increasing demand for high capacity and high power. Therefore, finding a higher capacity electrode material to replace the commercialized graphite negative electrode has become an important exploration direction for the research of lithium ion battery negative electrodes.

[0003] Silicon is currently the material with the highest specific capacity for lithium intercalation (3579-4200 mAh / g), and has the advantages of low discharge potential and abundant natural reserves, and has become the most potential lithium ion battery negative electrode material to replace graphite. However, during the lithium ion intercalation and deintercalation process, the silicon material will have a volume change of up to 300%, which will cause problems such as electrode structure damage, electrical connection failure and continuous consumption of active materials, ultimately leading to the destruction of battery performance, such as cycle performance deterioration. The current common method to improve the volume change problem of silicon in battery cycling is to nanoize or composite silicon and carbon, but the improvement effect is not ideal, and the cycle stability problem under high-rate rapid charging and discharging conditions still cannot be effectively solved. Therefore, the existing negative electrode material still needs to be improved. SUMMARY

[0004] Therefore, it is necessary to provide a composite negative electrode material, a preparation method thereof, a negative electrode sheet, a secondary battery and an electric device to improve the cycle stability of the battery under high-rate rapid charging and discharging conditions.

[0005] To achieve the above-mentioned purpose, the first aspect of the present application provides a composite negative electrode material, comprising a carbon fiber composite material and a silicon material layer arranged on at least part of the surface of the carbon fiber composite material, wherein the carbon fiber composite material comprises carbon fibers with a three-dimensional fiber network structure and a fast ion conductor compounded on the carbon fibers.

[0006] In some embodiments, the fast ion conductor comprises one or more of a perovskite-type fast ion conductor, a garnet-type fast ion conductor and a NASICON-type fast ion conductor.

[0007] Optionally, the fast ion conductor comprises a perovskite-type fast ion conductor, a garnet-type fast ion conductor and a NASICON-type fast ion conductor.

[0008] Further optionally, the mass ratio of the perovskite-type fast ion conductor, the garnet-type fast ion conductor and the NASICON-type fast ion conductor is (1-2) : (1-2) : 1.

[0009] In some embodiments, the perovskite-type fast ion conductor has a chemical formula of Li 3x1 La 2 / 3- x1 M y1 TiD z1 O3, wherein M comprises one or more of Ba 2+ and Sr 2+ , D comprises one or more of Al 3+ and Zr 4+ , 0.04≤x1≤0.167, 0≤y1≤1, 0≤z1≤1, optionally Li 0.33 La 0.56 TiO3; and / or,

[0010] The garnet-type fast ion conductor has a chemical formula of Li 7-y2 La 3-x2 A x2 Zr 2-y2 B y2 O 12 , wherein 0≤x2≤3, 0≤y2≤2, A comprises one or more of Y, Nd and Gd, B comprises one or more of Nb and Ta, optionally Li7La3Zr2O 12 ; and / or,

[0011] The NASICON-type fast ion conductor has a chemical formula of Li 1+x3 M'2(PO4)3, M' comprises one or more of Al, Ti, Ge, Hf, 0.1≤x3≤0.5, optionally Li 1.3 Al 0.3 Ti 1.7 (PO4)3.

[0012] In some embodiments, the fast ion conductor is a ceramic particle, and the average volume particle size Dv50 of the ceramic particle is 10-70 nm, optionally 20-50 nm.

[0013] In some embodiments, the carbon fiber composite material satisfies at least one of the following features (1)-(3):

[0014] (1) the average diameter of the carbon fibers in the carbon fiber composite material is 0.1 μm to 1 μm;

[0015] (2) the porosity of the carbon fiber composite material is 20% to 70%;

[0016] (3) the mass ratio of the carbon fibers to the fast ion conductor in the carbon fiber composite material is (1-19): 1, or optionally (1.2-9): 1.

[0017] In some embodiments, the silicon material layer satisfies at least one of the following characteristics (4)-(5):

[0018] (4) the thickness of the silicon material layer is 5 nm to 100 nm, or optionally 10 nm to 80 nm;

[0019] (5) the average volume particle size Dv50 of the silicon material in the silicon material layer is 3 nm to 10 nm.

[0020] In some embodiments, the composite negative electrode material satisfies at least one of the following characteristics (6)-(10):

[0021] (6) the average volume particle size Dv50 of the composite negative electrode material is 5 μm to 20 μm;

[0022] (7) the specific surface area of the composite negative electrode material is 1 m 2 / g to 20 m 2 / g;

[0023] (8) the mass content of the silicon material in the silicon material layer is 1% to 70% based on the mass of the composite negative electrode material;

[0024] (9) the mass content of the fast ion conductor is 10% to 50% based on the mass of the composite negative electrode material;

[0025] (10) the mass content of the carbon fibers is 5% to 30% based on the mass of the composite negative electrode material.

[0026] The second aspect of the present application provides a preparation method of the composite negative electrode material, comprising:

[0027] providing the carbon fiber composite material;

[0028] forming the silicon material layer on the carbon fiber composite material.

[0029] In some embodiments, the preparation method of the carbon fiber composite material comprises the following steps:

[0030] S11, mixing an organic polymer, a fast ion conductor, a complexing agent and a solvent to obtain a mixed solution;

[0031] S12, heat treating the mixed solution to obtain a fiber preform solution;

[0032] S13, preparing a fiber structure material by electrospinning process of the fiber preform solution;

[0033] S14, sintering the fiber structure material to obtain a carbon fiber composite material.

[0034] In some embodiments, the organic polymer includes one or more of polyvinyl alcohol, polyacrylonitrile, polyethylene oxide, polyphenyl ether, polyethylene glycol, polymethyl propionate, and polyvinylidene fluoride hexafluoropropylene.

[0035] In some embodiments, the preparation method satisfies at least one of the following features (11)-(12):

[0036] (11) the concentration of the organic polymer in the mixed solution is 0.01-0.20 Kg / L, and optionally 0.08-0.18 Kg / L; and / or,

[0037] (12) the concentration of the fast ion conductor is 0.01-0.20 Kg / L, and optionally 0.08-0.15 Kg / L.

[0038] In some embodiments, the method for forming the silicon material layer includes at least one of chemical vapor deposition, physical vapor deposition, plasma spraying, and screen printing, and optionally chemical vapor deposition.

[0039] The third aspect of the present application provides a negative electrode tab including the composite negative electrode material of the first aspect of the present application or the composite negative electrode material prepared by the method of the second aspect of the present application.

[0040] The fourth aspect of the present application provides a secondary battery including the negative electrode tab of the third aspect of the present application.

[0041] The fifth aspect of the present application provides an electric device including the secondary battery of the fourth aspect of the present application.

[0042] Inventive effect

[0043] The composite negative electrode material provided by the present application includes a carbon fiber composite material and a silicon material layer arranged on the surface of the carbon fiber composite material, wherein the carbon fiber composite material takes carbon fiber as a matrix, the carbon fiber has a three-dimensional fiber network structure, and a fast ion conductor is loaded on the carbon fiber, the fast ion conductor has the ability to rapidly transport lithium ions, and thus the carbon fiber composite material not only has a conductive three-dimensional fiber network structure, but also increases the Li + transport path, and in combination with the silicon material layer, the Li+ The three-dimensional fiber network structure can be used for rapid transmission, greatly shortening the transmission path of lithium ions, improving the ionic conductivity of the negative electrode, and further improving the rate performance of the negative electrode and the cycle stability of the battery under high-rate fast charging and discharging conditions. BRIEF DESCRIPTION OF DRAWINGS

[0044] Figure 1 A schematic diagram of a secondary battery according to an embodiment of the present application.

[0045] Figure 2 A schematic diagram of a battery module according to an embodiment of the present application. Figure 1 An exploded view of a secondary battery according to an embodiment of the present application.

[0046] Figure 3 A schematic diagram of a battery pack according to an embodiment of the present application.

[0047] Figure 4 A schematic diagram of a battery pack according to an embodiment of the present application.

[0048] Figure 5 An exploded view of a battery pack according to an embodiment of the present application. Figure 4 An exploded view of a battery pack according to an embodiment of the present application.

[0049] Figure 6 A schematic diagram of an electrical device using a secondary battery according to an embodiment of the present application as a power source.

[0050] REFERENCE SIGNS:

[0051] 1 battery pack; 2 upper box; 3 lower box; 4 battery module; 5 secondary battery; 51 housing; 52 electrode assembly; 53 cover plate; 6 electrical device. DETAILED DESCRIPTION

[0052] Hereinafter, embodiments of the positive electrode active material and the manufacturing method thereof, the positive electrode sheet, the secondary battery, the battery module, the battery pack, and the electrical device according to the present application will be specifically disclosed with appropriate reference to the accompanying drawings. However, there will be cases where unnecessary detailed descriptions are omitted. For example, there will be cases where detailed descriptions of matters that are well known, repeated descriptions of substantially the same 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.

[0053] 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.

[0054] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0055] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0056] 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.

[0057] 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.

[0058] If not specifically stated, the term "or" is inclusive in this application. 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 present) and B is false (or not present); A is false (or not present) and B is true (or present); or both A and B are true (or present).

[0059] At present, in order to meet the market demand, the energy density of the secondary battery represented by the lithium ion battery is getting higher and higher, and with the continuous development of new energy electric vehicles, the problems of range anxiety and long charging time are highlighted, and in this case, the improvement of the rapid charging ability of high energy density battery has become the focus of the development of the next generation of batteries. At the same time, in order to improve the energy density, silicon-based materials are introduced in the selection of active materials of the secondary battery. The volume change of silicon-based materials is large during the cycle process of the secondary battery, and the volume change of silicon-based materials is larger during the high-rate rapid charging process, which can exceed 300%, resulting in the collapse of the structure of the negative electrode material. In order to solve the problem of volume change of silicon negative electrode material, the existing technology focuses on the research of developing suitable carriers, but based on the increasing demand for the rapid charging ability of the battery, the inventors find that only the carrier to ensure the expansion space of silicon has limited effect on the improvement of the high-rate rapid charging ability of the negative electrode material, and shortening the lithium ion transmission path can enable the anode to have the ability of rapid transmission of lithium ions, thereby greatly improving its rapid charging ability. Therefore, it is necessary to construct a negative electrode active material which can not only provide enough space to accommodate the volume change of silicon material but also shorten the lithium ion transmission path, to solve the problem of cycle stability of high energy density battery under the condition of high-rate rapid charging and discharging.

[0060] Composite negative electrode material

[0061] To this end, a first aspect of the embodiments of the present application provides a composite negative electrode material, comprising a carbon fiber composite material and a silicon material layer arranged on at least part of the surface of the carbon fiber composite material, wherein the carbon fiber composite material comprises carbon fibers having a three-dimensional fiber network structure and fast ion conductors compounded on the carbon fibers.

[0062] In the embodiments of the present application, the composite negative electrode material comprises a carbon fiber composite material and a silicon material layer arranged on the surface of the carbon fiber composite material, wherein the carbon fiber composite material takes carbon fibers as the matrix, the carbon fibers have a three-dimensional fiber network structure, and fast ion conductors are compounded on the carbon fibers, the fast ion conductors have the ability of rapid transmission of active ions such as lithium ions, and the carbon fiber composite material thus formed not only has the conductive three-dimensional fiber network structure, but also increases the Li + transport path, and in combination with the silicon material layer, the Li +The three-dimensional fiber network structure can be used for rapid transmission, greatly shortening the transmission path of lithium ions, improving the ionic conductivity of the negative electrode, and further improving the rate performance of the negative electrode and the cycle stability of the battery under high-rate fast charging and discharging conditions.

[0063] It should be noted that the silicon material layer can be arranged on part of the surface of the carbon fiber composite material, or on the entire surface of the carbon fiber composite material; preferably, the silicon material layer is arranged on the entire surface of the carbon fiber composite material, for example, the silicon material layer coats the three-dimensional fiber network structure skeleton of the carbon fiber composite material, and the three-dimensional fiber network structure skeleton of the carbon fiber composite material is entirely covered with the silicon material layer. Further, the surface formed by the silicon material layer can be a continuous surface or a discontinuous surface; preferably, the surface formed by the silicon material layer is a continuous surface.

[0064] It should be further noted that the combination of the fast ion conductor and the carbon fiber is not particularly limited, and the fast ion conductor can be combined with the carbon fiber in the form of particles, and the carbon fiber can be used as a matrix, and the fast ion conductor particles can be located on the surface of the carbon fiber or in the interior of the carbon fiber.

[0065] In this application, the fast ion conductor refers to an ion conductor having the ion conductivity of a molten salt or a liquid electrolyte in a solid state, and the basic feature distinguishing it from a general ion conductor is that it has an ion conductivity comparable to that of a liquid electrolyte and a low ion conductivity activation energy in a certain temperature range. The ion (including vacancy) conductivity of the fast ion conductor can be greater than or equal to 10 -2 Ω -1 cm -1 , the activation energy is less than or equal to 0.5 eV order of magnitude, further, the ion (including vacancy) migration number is greater than 99%, and it is a conductor for ions and an insulator for electrons.

[0066] In some embodiments, the fast ion conductor includes one or more of a perovskite-type fast ion conductor, a garnet-type fast ion conductor, and a NASICON-type fast ion conductor.

[0067] In some preferred embodiments, the fast ion conductor includes a perovskite-type fast ion conductor, a garnet-type fast ion conductor, and a NASICON-type fast ion conductor.

[0068] In some embodiments, the perovskite-type fast ion conductor has a chemical formula of Li 3x1 La 2 / 3-x1 M y1 TiD z1 O3, wherein M includes one or more of Ba 2+ and Sr 2+ , and D includes Al 3+ and Zr 4+one or more of Y, Nd, Gd, 0.04 < x1 < 0.167, 0 < y1 < 1, 0 < z1 < 1. Without being bound by any theory, specific examples of perovskite-type fast ion conductors include Li 0.33 La 0.56 TiO3.

[0069] In some embodiments, the garnet-type fast ion conductor has a chemical formula of Li 7-y2 La 3-x2 A x2 Zr 2-y2 B y2 O 12 wherein 0 < x2 < 3, 0 < y2 < 2, A includes one or more of Y, Nd, Gd, and B includes one or more of Nb, Ta. Without being bound by any theory, specific examples of garnet-type fast ion conductors include Li7La3Zr2O 12 .

[0070] In some embodiments, the NASICON-type fast ion conductor has a chemical formula of Li 1+x3 M'2(PO4)3, M' includes one or more of Al, Ti, Ge, Hf, 0.1 < x3 < 0.5. Without being bound by any theory, specific examples of NASICON-type fast ion conductors include Li 1.3 Al 0.3 Ti 1.7 (PO4)3.

[0071] In some alternative embodiments, the fast ion conductor includes a perovskite-type fast ion conductor, a garnet-type fast ion conductor, and a NASICON-type fast ion conductor. Without being bound by any theory, the three types of fast ion conductors work in concert to further improve the lithium ion transport speed of the composite anode material, further improving the ionic conductivity of the anode. Alternatively, the mass ratio of the perovskite-type fast ion conductor, the garnet-type fast ion conductor, and the NASICON-type fast ion conductor is (1 ~ 2) : (1 ~ 2) : 1, which can be understood to be 1:1:1, 1:2:1, 2:1:1, 2:2:1, etc., without being limited in particular. The mass ratio of the perovskite-type fast ion conductor, the garnet-type fast ion conductor, and the NASICON-type fast ion conductor within the above range can have a better synergistic effect.

[0072] In some specific embodiments, the fast ion conductor includes Li 0.33 La 0.56 TiO3, Li7La3Zr2O 12 and Li 1.3 Al 0.3 Ti 1.7 (PO4)3.

[0073] In some embodiments, the fast ion conductor is ceramic particles having an average volume particle size Dv50 of 10 nm to 70 nm, such as 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm, 60 nm, 65 nm, and any value therebetween. The fast ion conductor ceramic particles having an average volume particle size Dv50 within the above range have better uniformity of distribution and ion transport distance, which can further improve the fast ion transport performance thereof. Optionally, the fast ion conductor ceramic particles have an average volume particle size Dv50 of 20 nm to 50 nm.

[0074] In some embodiments, the carbon fibers have an average diameter of 0.1 μm to 1 μm, such as 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, and any value therebetween. The carbon fibers having an average diameter within the above range have better mechanical and electrical properties. Optionally, the carbon fibers have an average diameter of 0.1 μm to 0.5 μm.

[0075] The average diameter of the carbon fibers has the meaning known in the art and can be tested by using instruments and methods known in the art. For example, the average diameter of the carbon fibers can be characterized by transmission electron microscopy.

[0076] In some embodiments, the carbon fiber composite has a porosity of 20% to 70%, such as 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, and any value therebetween. The carbon fiber composite having a porosity within the above range has better specific surface area and structural stability, which can further increase the deposition amount of silicon and has higher energy density. Optionally, the carbon fiber composite has a porosity of 30% to 50%.

[0077] The carbon fiber composite is a mixed ionic-electronic conductor. In some embodiments, the mass ratio of the carbon fibers to the fast ion conductor in the carbon fiber composite is (1-19): 1, such as 2: 1, 4: 1, 6: 1, 8: 1, 9: 1, 10: 1, 12: 1, 14: 1, 16: 1, 18: 1, and any ratio therebetween. The carbon fiber composite having a mass ratio of the fast ion conductor to the carbon fibers within the range has better electrical conductivity and ionic conductivity, which can further improve the cycle performance of the battery at high rate. Optionally, the mass ratio of the carbon fibers to the fast ion conductor in the carbon fiber composite is (1.2-9): 1.

[0078] In some embodiments, the thickness of the silicon material layer is 5 nm to 100 nm, for example, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, 75 nm, 80 nm, 85 nm, 90 nm, 95 nm, and any value therebetween. With the thickness of the silicon material layer in this range, the negative active material has a better silicon content, which can improve its specific capacity, and better conductivity and cycle performance. Alternatively, the thickness of the silicon material layer is 10 nm to 80 nm.

[0079] In some embodiments, the volume average particle size Dv50 of the silicon material in the silicon material layer is 2 nm to 20 nm, for example, 3 nm, 5 nm, 7 nm, 9 nm, 11 nm, 13 nm, 15 nm, 17 nm, 19 nm, and any value therebetween. Alternatively, the volume average particle size Dv50 of the silicon material in the silicon material is 3 nm to 10 nm.

[0080] The volume average particle size Dv50 of the silicon material in the silicon material layer is a meaning known in the art, which represents the particle size corresponding to the cumulative volume distribution percentage of 50%, and can be tested by instruments and methods known in the art. For example, GB / T 19077-2016 Particle Size Distribution Laser Diffraction Method can be referred to, and a laser particle size analyzer, such as Mastersizer 2000E laser particle size analyzer of Malvern Instruments Ltd., UK, can be conveniently used for testing.

[0081] In some embodiments, the volume average particle size Dv50 of the composite negative electrode material is 3 μm to 30 μm, for example, 4 μm, 6 μm, 8 μm, 10 μm, 12 μm, 14 μm, 15 μm, 16 μm, 18 μm, 20 μm, 22 μm, 24 μm, 26 μm, 28 μm, and any value therebetween. Alternatively, the volume average particle size Dv50 of the composite negative electrode material is 5 μm to 20 μm.

[0082] The volume average particle size Dv50 of the composite negative electrode material is a meaning known in the art, which represents the particle size corresponding to the cumulative volume distribution percentage of 50%, and can be tested by instruments and methods known in the art. For example, GB / T 19077-2016 Particle Size Distribution Laser Diffraction Method can be referred to, and a laser particle size analyzer, such as Mastersizer 2000E laser particle size analyzer of Malvern Instruments Ltd., UK, can be conveniently used for testing.

[0083] In some embodiments, the specific surface area of the composite negative electrode material is 1 m 2 / g to 20 m 2 / g, for example, 2 m 2 / g, 4m 2 / g, 6m 2 / g, 8m 2 / g, 10m 2 / g, 12m 2 / g, 14m 2 / g, 15m 2 / g, 16m 2 / g, 18m 2 / g, and any value therebetween. Optionally, the specific surface area of the composite negative electrode material is 2m 2 / g ~ 15m 2 / g.

[0084] In some embodiments, the mass content of silicon is 1% ~ 70%, for example, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, and any value therebetween, based on the mass of the composite negative electrode material.

[0085] In some embodiments, the mass content of the fast ion conductor is 10% ~ 50%, for example, 12%, 15%, 18%, 20%, 22%, 25%, 28%, 30%, 32%, 35%, 38%, 40%, 42%, 45%, 48%, and any value therebetween, based on the mass of the composite negative electrode material.

[0086] In some embodiments, the mass content of the carbon fiber is 5% ~ 30%, for example, 6%, 8%, 10%, 12%, 15%, 18%, 20%, 22%, 25%, 28%, and any value therebetween, based on the mass of the composite negative electrode material.

[0087] In the present application, a cross-section polisher (such as an argon ion cross-section polisher of IB-09010CP type from JEOL) can be used to prepare a cross-section of the composite negative electrode material particle, which passes through the core of the composite negative electrode material particle; then an element distribution map in the cross-section can be obtained by EDX or EDS element analysis combined with TEM or SEM (such as EDS of X-Max type from Oxford Instruments Group combined with SEM of Sigma-02-33 type from ZEISS) face scanning test; and the structure, composition, and characteristics and content of each composition of the composite negative electrode material can be further obtained by combining methods known in the art.

[0088] For example, the mass content of silicon, the mass content of fast ion conductor and the mass content of carbon fiber, a cross-section of the negative electrode active material particle is prepared by a cross-section polisher (such as an argon ion cross-section polisher of IB-09010CP type of JEOL company), the cross-section passes through the core of the negative electrode active material particle; then an element distribution map in the cross-section is obtained by EDX or EDS element analysis combined with TEM or SEM (such as EDS of X-Max type of Oxford Instruments Group of the United Kingdom combined with SEM of Sigma-02-33 type of ZEISS of Germany) surface scanning test; in a region in the cross-section, the Si content or the specific element content of the fast ion conductor or the carbon content can be obtained by integrating the silicon element distribution or the specific element distribution of the fast ion conductor or the carbon element distribution. In order to improve the accuracy of the test, a plurality of regions (for example, 10) can be counted, and the average value is taken as the test result.

[0089] For another example, the thickness of the silicon material layer, a cross-section of the negative electrode active material particle is prepared by a cross-section polisher (such as an argon ion cross-section polisher of IB-09010CP type of JEOL company), the cross-section passes through the core of the negative electrode active material particle; then an element distribution map in the cross-section is obtained by EDX or EDS element analysis combined with TEM or SEM (such as EDS of X-Max type of Oxford Instruments Group of the United Kingdom combined with SEM of Sigma-02-33 type of ZEISS of Germany) surface scanning test; the thickness of the silicon material layer is obtained according to the element distribution of the cross-section. More accurately, the thickness values of the silicon material layer at a plurality of (more than 3, such as 8, 10, 12, etc.) different positions on the cross-section can be tested, and the average value is taken as the thickness of the silicon material layer.

[0090] Preparation method of composite negative electrode material

[0091] The second aspect of the embodiments of the present application provides a preparation method of a negative electrode material, comprising:

[0092] S10, providing a carbon fiber composite material; and

[0093] S20, forming a silicon material layer on the carbon fiber composite material.

[0094] In some embodiments, the preparation method of the carbon fiber composite material comprises the following steps:

[0095] S11, mixing an organic polymer, a fast ion conductor, a complexing agent and a solvent to obtain a mixed solution;

[0096] S12, heat-treating the mixed solution to obtain a fiber pre-liquid;

[0097] S13, preparing a fiber structure material by an electrospinning process from the fiber pre-liquid;

[0098] S14, sintering the fibrous structural material to obtain a carbon fiber composite material.

[0099] Optionally, in step S11, the organic polymer comprises one or more of polyvinyl alcohol, polyacrylonitrile, polyethylene oxide, polyphenylene ether, polyethylene glycol, polymethyl propionate, polyvinylidene fluoride hexafluoropropylene.

[0100] Optionally, in step S11, the fast ion conductor comprises one or more of any of the fast ion conductors mentioned above. In some embodiments, the fast ion conductor comprises Li 0.33 La 0.56 TiO3, Li7La3Zr2O 12 and Li 1.3 Al 0.3 Ti 1.7 (PO4)3.

[0101] Optionally, in step S11, the complexing agent comprises one or more of citric acid, malic acid, malonic acid, succinic acid, succinic acid, glycolic acid, aminoacetic acid, lactic acid, tartaric acid, EDTA (Chinese name: ethylenediamine tetraacetic acid).

[0102] Optionally, in step S11, the solvent is water.

[0103] Optionally, in step S12, the temperature of the heat treatment is 500-1000°C, and the time of the heat treatment is 1-5h.

[0104] In some embodiments, the concentration of the organic polymer in the mixed solution is 0.01-0.20 Kg / L, and optionally 0.08-0.18 Kg / L.

[0105] In some embodiments, the concentration of the fast ion conductor is 0.01-0.20 Kg / L, and optionally 0.08-0.15 Kg / L.

[0106] In some embodiments, the method for forming the layer of silicon material comprises chemical vapor deposition, physical vapor deposition, plasma spraying, or screen printing, and optionally chemical vapor deposition.

[0107] The negative electrode tab

[0108] The third aspect of the embodiments of the present application provides a negative electrode tab, which comprises a negative electrode current collector and a negative electrode active material layer arranged on at least one surface of the negative electrode current collector, wherein the negative electrode active material layer comprises a negative electrode active material, and the negative electrode active material comprises the composite negative electrode material of the first aspect of the present application or the composite negative electrode material prepared by the method of the second aspect of the present application. As an example, the negative electrode current collector has two surfaces opposite in the thickness direction of the negative electrode current collector, and the negative electrode active material layer is arranged on any one or both of the two opposite surfaces of the negative electrode current collector.

[0109] The composite negative electrode material provided by the present application is included in the negative electrode tab, and the composite negative electrode material can improve the cycle stability of the battery under high-rate fast charging and discharging conditions.

[0110] In some embodiments, the negative current collector can be a metal foil or a composite current collector. For example, as the metal foil, a copper foil can be used. 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 on a polymer material base layer. The metal material includes, but is not limited to, copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc., and the polymer material base layer includes, but is not limited to, polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0111] In some embodiments, the negative active material does not exclude other negative active materials in addition to the composite negative active material provided by the present application. The other negative active material can use a negative active material known in the art for a secondary battery. As an example, the other negative active material can include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, other silicon-based materials, tin-based materials, and lithium titanate, etc. The other silicon-based material can be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material can be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, the present application is not limited to these materials, and other conventional materials that can be used as a battery negative active material can also be used. These negative active materials can be used alone or in combination with two or more. The weight ratio of the negative active material in the negative active material layer is 70-100% by weight, based on the total weight of the negative active material layer.

[0112] In some embodiments, the negative active material layer can also 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). The weight ratio of the binder in the negative active material layer is 0-30% by weight, based on the total weight of the negative active material layer.

[0113] In some embodiments, the negative active material layer can further optionally include a conductive agent. The conductive agent can be selected from at least one of super P, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The weight ratio of the conductive agent in the negative active material layer is 0-20% by weight, based on the total weight of the negative active material layer.

[0114] In some embodiments, the negative active material layer can further optionally include other auxiliary agents, such as thickening agents (e.g., sodium carboxymethyl cellulose (CMC-Na)) and the like. The weight ratio of the other auxiliary agents in the negative active material layer is 0-15% by weight, based on the total weight of the negative active material layer.

[0115] 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 active material provided herein, the optional other negative active material, the optional binder, the optional conductive agent, 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 current collector, and after drying, cold pressing, and the like, a negative electrode sheet is obtained. The solid content of the negative electrode slurry can be 30-70% by weight, the viscosity at room temperature can be adjusted to 2000-10000 mPa·s, and the compaction density of the negative electrode sheet can be 1.2-2.0 g / m2. 3 The thickness of the negative active material layer can be 34 μm-143 μm.

[0116] The thickness T of the negative active material layer can be measured using a micrometer, for example, a micrometer with a model number of Mitutoyo 293-100 and a precision of 0.1 μm. It should be noted that the thickness of the negative active material layer as described herein refers to the thickness of the negative active material layer in the negative electrode sheet after cold pressing and compaction and used for assembling a battery.

[0117] The negative electrode sheet provided herein does not exclude other additional functional layers other than the negative active material layer. For example, in some embodiments, the negative electrode sheet provided herein further includes a conductive primer layer (e.g., composed of a conductive agent and a binder) disposed on the surface of the negative current collector and sandwiched between the negative current collector and the negative active material layer. In some other embodiments, the negative electrode sheet provided herein further includes a protective layer covering the surface of the negative active material layer.

[0118] In addition, the secondary battery, the battery module, the battery pack, and the power utilization device provided herein are described below with appropriate reference to the accompanying drawings.

[0119] In one embodiment of the present application, a secondary battery is provided.

[0120] Generally, a secondary battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. During charging and discharging of the battery, active ions are intercalated and deintercalated 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 is disposed between the positive electrode sheet and the negative electrode sheet and functions to prevent short circuiting between the positive and negative electrodes while allowing ions to pass through.

[0121] The positive electrode sheet

[0122] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector, the positive electrode active material layer including the positive electrode active material of the first aspect of the present application.

[0123] As an example, the positive electrode current collector has two surfaces opposite in the thickness direction thereof, and the positive electrode active material layer is disposed on either one or both of the two opposite surfaces of the positive electrode current collector.

[0124] 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 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 (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer material base material (e.g., a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0125] In some embodiments, the positive electrode active material can use a positive electrode active material for a battery known in the art. As an example, the positive electrode active material can include at least one of a lithium-containing phosphate having an olivine structure, a lithium transition metal oxide, and a modified compound of each thereof. However, the present application is not limited to these materials, and other conventional materials that can be used as a positive electrode active material for a battery can also be used. These positive electrode active materials can be used alone only one or in combination of two or more. Among them, examples of the lithium transition metal oxide can include, but are not limited to, lithium cobalt oxide (e.g., LiCoO2), lithium nickel oxide (e.g., LiNiO2), lithium manganese oxide (e.g., LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (e.g., LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (which can also be referred to as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2 (which can also be referred to as NCM 523LiNi 0.5 Co 0.25 Mn 0.25 O2(also can be referred to as NCM 211 LiNi 0.6 Co 0.2 Mn 0.2 O2(also can be referred to as NCM 622 LiNi 0.8 Co 0.1 Mn 0.1 O2(also can be referred to as NCM 811 lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05 O2) and modified compounds thereof. Examples of lithium-containing phosphates of olivine structure can include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4(also can be referred to as LFP)), a composite of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite of lithium manganese phosphate and carbon, lithium manganese iron phosphate, a composite of lithium manganese iron phosphate and carbon. The weight ratio of the positive electrode active material in the positive electrode active material layer is 80-100 wt.%, based on the total weight of the positive electrode active material layer.

[0126] In some embodiments, the positive electrode active material layer can also optionally include a binder. As an example, the binder can include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene-fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene-fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylic ester resin. The weight ratio of the binder in the positive electrode active material layer is 0-20 wt.%, based on the total weight of the positive electrode active material layer.

[0127] In some embodiments, the positive electrode active material layer can also optionally include a conductive agent. As an example, the conductive agent can include at least one of super P carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The weight ratio of the conductive agent in the positive electrode active material layer is 0-20 wt.%, based on the total weight of the positive electrode active material layer.

[0128] In some embodiments, the positive electrode sheet can be prepared by dispersing the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder, and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry on a positive electrode current collector; and drying, cold-pressing, and the like to obtain the positive electrode sheet. In this case, the positive electrode slurry has a solid content of 40-80 wt%, a viscosity of 5000-25000 mPa·s at room temperature, and a positive electrode sheet compaction density of 3.0-3.6 g / cm 3 , and optionally 3.3-3.5 g / cm 3 . The thickness of the positive electrode active material layer is 51-152 μm.

[0129] The thickness T of the positive electrode active material layer can be measured using a micrometer, for example, a micrometer with a model number of Mitutoyo 293-100 and a precision of 0.1 μm. It should be noted that the thickness of the positive electrode active material layer as described herein refers to the thickness of the positive electrode active material layer in the positive electrode sheet after cold-pressing and compaction and used for assembling a battery.

[0130] Electrolyte

[0131] The electrolyte functions to conduct ions between the positive electrode sheet and the negative electrode sheet. The type of the electrolyte is not particularly limited and can be selected as needed. For example, the electrolyte can be in a liquid state, a gel state, or a full solid state.

[0132] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0133] 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. The concentration of the electrolyte salt is generally 0.5-5 mol / L.

[0134] 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, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0135] 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 performance of the battery, such as an additive capable of improving overcharge performance of the battery, an additive capable of improving high-temperature or low-temperature performance of the battery, etc.

[0136] Separation film

[0137] In some embodiments, a separation film is further included in the secondary battery. The type of the separation film is not particularly limited in the present application, and any known porous structure separation film having good chemical stability and mechanical stability can be used.

[0138] In some embodiments, the material of the separation film can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separation film can be a single layer film or a multi-layer composite film, and is not particularly limited. When the separation film is a multi-layer composite film, the materials of the respective layers can be the same or different, and are not particularly limited.

[0139] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separation film can be formed into an electrode assembly through a winding process or a stacking process.

[0140] 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 solution described above.

[0141] 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, etc. 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, etc. can be listed.

[0142] The shape of the secondary battery is not particularly limited in the present application, and can be cylindrical, square, or any other shape. For example, Figure 1 is a square structure secondary battery 5 as an example.

[0143] In some embodiments, with reference to Figure 2 , the outer package can include a shell 51 and a cover plate 53. The shell 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 shell 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be provided on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet, and the separation film can be formed into an electrode assembly 52 through a winding process or a stacking process. The electrode assembly 52 is packaged in the receiving cavity. The electrolyte solution is impregnated in the electrode assembly 52. The number of the electrode assemblies 52 contained in the secondary battery 5 can be one or more, and can be selected by a person skilled in the art according to specific actual needs.

[0144] In some embodiments, the secondary battery can be assembled into a battery module, and the number of secondary batteries included in the battery module can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0145] Figure 3 The battery module 4 is an example. Referring to FIG. 1, the battery module 4 includes a plurality of secondary batteries 5 and a housing 6. Figure 3 In the battery module 4, the 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.

[0146] Optionally, the battery module 4 can further include a housing having an accommodation space, and the plurality of secondary batteries 5 are accommodated in the accommodation space.

[0147] In some embodiments, the above-mentioned battery module can also be assembled into a battery pack, and the number of battery modules included in the battery pack can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0148] Figure 4 and Figure 5 The battery pack 1 is an example. Referring to FIG. 2, the battery pack 1 includes a plurality of battery modules 4 and a battery box 7. Figure 4 and Figure 5 In the battery pack 1, the battery box and the plurality of battery modules 4 disposed 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 covered on the lower box body 3 to form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0149] In addition, the application also provides a power utilization device, which includes 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, or can be used as an energy storage unit of the power utilization device. The power utilization device can include a mobile device, an electric vehicle, an electric train, a ship and a satellite, an energy storage system, etc., but is not limited thereto. Among them, the mobile device can be a mobile phone, a notebook computer, etc.; the electric vehicle can be 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., but is not limited thereto.

[0150] As the power utilization device, the secondary battery, the battery module, or the battery pack can be selected according to the use requirements thereof.

[0151] Figure 6The electric device 6 is an example. The electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the demand of the electric device for high power and high energy density of the secondary battery, a battery pack or a battery module can be used.

[0152] The device as another example can be a mobile phone, a tablet, a notebook, etc. The device generally requires thinning, and a secondary battery can be used as a power source.

[0153] Embodiments

[0154] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are for the purpose of explanation of the present application only and are not to be understood as a limitation of the present application. In the embodiments, the specific techniques or conditions not mentioned are performed according to the techniques or conditions described in the literature in the field or according to the product manual. The reagents or instruments not mentioned by the manufacturer are all conventional products that can be obtained commercially.

[0155] The English abbreviations referred to below are explained as follows:

[0156] LLTO represents Li 0.33 La 0.56 TiO3;

[0157] LLZO represents Li7La3Zr2O 12 ;

[0158] LATP represents Li 1.3 Al 0.3 Ti 1.7 (PO4)3.

[0159] I. Preparation of Embodiments

[0160] Preparation of Embodiment 1

[0161] 1. LLZO, LLTO and LATP ceramic nanoparticles in a mass ratio of 2:2:1 were added to a polyvinyl alcohol aqueous solution with a concentration of 0.12 Kg / L, and the concentration of the ceramic nanoparticles in the solution was 0.12 Kg / L. An amount of citric acid equivalent to the ceramic nanoparticles was added as a complexing agent. The solution was stirred at 95°C for 5h under water bath conditions to obtain a transparent and uniform spinning solution.

[0162] 2. The above solution was used for electrospinning to obtain a three-dimensional fiber network structure material. The spinning voltage was 12kV, the injection speed of the syringe needle was 0.4ml / h, the distance between the syringe needle and the aluminum foil receiver was 15cm, and the spinning time was 3h.

[0163] 3. The three-dimensional fiber network structure material is placed in a tube furnace, calcined in an Ar inert atmosphere, and calcined at 700 DEG C for 2 h to obtain a carbon fiber composite material.

[0164] 4. The carbon fiber composite material is placed in a tube furnace to deposit a layer of nano-silicon material, and Ar inert gas is passed at 900 DEG C for 2 h. The reaction gas source is SiH4 and C2H2 in a volume ratio of 2:1, the flow rate is 50 mL / min, the deposition temperature is 900 DEG C, and the deposition time is 30 min. A three-dimensional fiber network material with amorphous silicon deposition is obtained, which is a negative electrode active material.

[0165] The composite negative electrode material is tested by SEM scanning electron microscopy and has a three-dimensional fiber network structure with a three-dimensional network skeleton.

[0166] Preparation Examples 2-30

[0167] The preparation method of Preparation Examples 2-30 is similar to that of Preparation Example 1. The difference is that the related parameters of the composite negative electrode material and its preparation process are adjusted. The specific parameters are shown in Table 1 below. "-" indicates that the corresponding parameter does not exist.

[0168] Preparation Comparative Example 1

[0169] The preparation method of Preparation Comparative Example 1 is different from that of Preparation Example 1 in that the addition of LLZO, LLTO and LATP ceramic nanoparticles is omitted in step 1, i.e., the spinning solution is only polyvinyl alcohol aqueous solution without LLZO, LLTO and LATP ceramic nanoparticles.

[0170] II. Application Examples

[0171] Example 1

[0172] 1) Preparation of positive electrode sheet

[0173] The prepared positive electrode active material ternary material nickel-cobalt-manganese (NCM811), conductive carbon black SP and binder PVDF are dispersed into the solvent NMP in a weight ratio of 97:2:1, mixed uniformly, and a positive electrode slurry is obtained. The positive electrode slurry is uniformly coated on the positive electrode current collector aluminum foil, and after drying, cold pressing, die cutting and slitting, a positive electrode sheet is obtained. The coating amount per unit area is 0.27 g / 1540.25 mm 2 .

[0174] 2) Preparation of negative electrode sheet

[0175] The composite negative electrode material of Preparation Example 1, the conductive agent conductive carbon, the thickening agent sodium hydroxymethyl cellulose (CMC), and the binder styrene-butadiene rubber (SBR) are mixed in a weight ratio of 96:2:1:1, deionized water is added, and a negative electrode slurry is obtained under the action of a vacuum stirrer; the negative electrode slurry is uniformly coated on a copper foil; the copper foil is dried at room temperature, then transferred to an oven at 85°C for drying, and then cold-pressed, cut to obtain a negative electrode sheet, and the coating amount per unit area is 0.17 g / 1540.25 mm 2 .

[0176] 3) Isolation film

[0177] A porous isolation film with a thickness of 12 μm is selected.

[0178] The preparation of the porous isolation film includes: using a polyethylene microporous film as a porous isolation film substrate, mixing inorganic aluminum oxide powder, polyvinylpyrrolidone, and acetone solvent in a weight ratio of 3:1.5:5.5 to obtain a slurry, coating the slurry on one side of the substrate, and drying to obtain the porous isolation film.

[0179] 4) Preparation of electrolyte

[0180] The organic solvent is a mixture containing ethylene carbonate, dimethyl carbonate, and methyl ethyl carbonate, wherein the volume ratio of ethylene carbonate, dimethyl carbonate, and methyl ethyl carbonate is 1:2:1. In an argon glove box with a water content of <10 ppm, a fully dried lithium salt LiPF6 is dissolved in the organic solvent, mixed uniformly, and an electrolyte is obtained. The concentration of the lithium salt is 1 mol / L.

[0181] 5) Preparation of battery

[0182] The positive electrode sheet, the isolation film, and the negative electrode sheet are stacked in order, the isolation film is between the positive electrode sheet and the negative electrode sheet to play a role of isolation, then the square bare cell is wound, is placed in an aluminum plastic film, is baked at 80°C to remove water, is injected with 320 g of the corresponding electrolyte, is sealed, and after processes such as standing, hot and cold pressing, formation, clamping, and capacity distribution, a finished battery with a capacity of 180 Ah is obtained, and the first charge N / P of the battery is 1.05. N / P = negative electrode gram capacity * negative electrode active material mass / positive electrode gram capacity * positive electrode active material mass

[0183] The secondary batteries of Examples 2-30 and the secondary battery of Comparative Example 1 are prepared in a similar manner to the secondary battery of Example 1, but the composite negative electrode material of the corresponding preparation example is used.

[0184] III. Test method

[0185] 1. Specific surface area and porosity test

[0186] The specific surface area and pore size distribution of the composite negative electrode material, carbon fiber composite material and other materials in the examples and comparative examples were tested by nitrogen adsorption / desorption method using a specific surface area analyzer (Tristar II 3020M). Among them, the specific test was carried out in accordance with the national standard GB / T 19587-2017.

[0187] 2. Particle size distribution test

[0188] The particle size distribution of the negative electrode active material, silicon material layer of silicon material in the examples and comparative examples was tested using a Malvern particle size tester, and the average volume particle size Dv50 of the composite negative electrode material, silicon material layer of silicon material and fast ion conductor was obtained. Among them, the specific test was carried out in accordance with the national standard GB / T19077-2016.

[0189] 3. Silicon material layer thickness

[0190] The cross section of the negative electrode active material particle was prepared by a cross section polisher (such as argon ion cross section polisher of IB-09010CP type of Japan Electronics (JEOL) Co., Ltd.), which passed through the core of the negative electrode active material particle. Then, the element distribution map in the cross section was obtained by X-Max type EDS of British Oxford Instrument Group combined with Sigma-02-33 type SEM surface scanning test of Germany ZEISS, and the thickness of the silicon material layer was tested according to the element distribution of the cross section. The thickness values of the silicon material layer at three different positions on the cross section were taken, and the average value was taken as the thickness of the silicon material layer.

[0191] 4. Mass content of silicon in negative electrode active material, mass content of fast ion conductor and mass content of carbon fiber test

[0192] The cross section of the negative electrode active material particle was prepared by a cross section polisher (such as argon ion cross section polisher of IB-09010CP type of Japan Electronics (JEOL) Co., Ltd.), which passed through the core of the negative electrode active material particle. Then, the element distribution map in the cross section was obtained by X-Max type EDS of British Oxford Instrument Group combined with Sigma-02-33 type SEM surface scanning test of Germany ZEISS, and the thickness of the silicon material layer was tested according to the element distribution of the cross section. The thickness values of the silicon material layer at three different positions on the cross section were taken, and the average value was taken as the thickness of the silicon material layer.

[0193] 5. Negative electrode ion conductivity test

[0194] The negative electrode ion conductivity was characterized by alternating current impedance method. The negative electrode material was placed between two stainless steel gaskets, and the frequency was 0.01 Hz-10 6HZ, amplitude 5 mV, the ionic conductivity of the sample was calculated.

[0195] 6. Energy density and cycle life test of lithium ion battery

[0196] The cycle test temperature was 25℃, the battery was charged at 3C constant current to the upper limit voltage, charged at constant voltage to 0.05C, and then discharged at 0.33C to the lower limit voltage after standing for 5 minutes. The capacity obtained in this step was the initial capacity. The capacity was multiplied by the average discharge voltage, and then divided by the volume of the cell, and the energy density was obtained. The 3C charge / 0.33C discharge cycle test was carried out, and the cycle number corresponding to the capacity decay to 80% SOH was recorded to obtain the corresponding life data.

[0197] 7. Battery swelling force test

[0198] Before test 7, the battery was fixed in the clamp of the pressure sensor, clamped at a fixed pressure, and the capacity calibration and cycle test were carried out according to the process in test 7. The change of swelling force was monitored during the cycle process. The ratio of the swelling force increment when the capacity decayed to 80% to the initial swelling force was the change of swelling force.

[0199] Table 2 shows the negative electrode active material and battery performance test results of examples 1 to 30 and comparative example 1.

[0200] Table 1

[0201]

[0202]

[0203] Table 2

[0204]

[0205]

[0206] Through the comparison of examples and comparative examples, it can be seen that the composite negative electrode material obtained by setting a silicon material layer on the surface of the carbon fiber composite material with a three-dimensional fiber network structure can reduce the swelling force of the battery and improve the ionic conductivity of the lithium ion battery and the cycle life under high rate. By controlling the related condition parameters in the preparation process of the negative electrode active material, the performance of the negative electrode sheet and the lithium ion battery can be adjusted, so that lithium ion batteries with better comprehensive performance can be obtained according to the actual application requirements.

[0207] Note that the present application is not limited to the above-described embodiments. The above-described embodiments are merely examples, and embodiments having substantially the same configuration, function, and effect as the technical idea of the present application are included in the technical scope of the present application. Furthermore, various modifications of the embodiments that can be conceived by those skilled in the art, and other modes of embodiments constructed by combining part of the constituent elements of the embodiments within the scope of the present application without departing from the gist of the present application are also included in the scope of the present application.

Claims

1. A composite negative electrode material, characterized in that, The invention includes a carbon fiber composite material and a silicon material layer disposed on at least a portion of the surface of the carbon fiber composite material, wherein the carbon fiber composite material includes carbon fibers having a three-dimensional fiber network structure and a fast ion conductor composited on the carbon fibers; the fast ion conductor includes one or more of perovskite fast ion conductors, garnet fast ion conductors, and NASICON fast ion conductors.

2. The composite negative electrode material according to claim 1, characterized in that, The fast ion conductors include perovskite-type fast ion conductors, garnet-type fast ion conductors, and NASICON-type fast ion conductors.

3. The composite negative electrode material according to claim 2, characterized in that, The mass ratio of the perovskite-type fast ion conductor, the garnet-type fast ion conductor, and the NASICON-type fast ion conductor is (1~2):(1~2):

1.

4. The composite negative electrode material according to claim 1, characterized in that, The chemical formula of the perovskite-type fast ion conductor is Li. 3x1 La 2 / 3-x1 M y1 TiD z1 O3, where M includes Ba 2+ and Sr 2+ One or more of them, D includes Al 3+ and Zr 4+ One or more of the following, 0.04≤x1≤0.167, 0≤y1≤1, 0≤z1≤1; and / or, The chemical formula of the garnet-type fast ion conductor is Li. 7-y2 La 3-x2 A x2 Zr 2-y2 B y2 O 12 Where 0 ≤ x² ≤ 3, 0 ≤ y² ≤ 2, A includes one or more of Y, Nd, and Gd, and B includes one or more of Nb and Ta; and / or, The chemical formula of the NASICON-type fast ion conductor is Li. 1+x3 M'2(PO4)3, where M' includes one or more of Al, Ti, Ge, and Hf, and 0.1≤x3≤0.

5.

5. The composite negative electrode material according to claim 1, characterized in that, The chemical formula of the perovskite-type fast ion conductor is Li. 0.33 La 0.56 TiO3.

6. The composite negative electrode material according to claim 1, characterized in that, The chemical formula of the garnet-type fast ion conductor is Li7La3Zr2O 12 .

7. The composite negative electrode material according to claim 1, characterized in that, The chemical formula of the NASICON-type fast ion conductor is Li. 1.3 Al 0.3 Ti 1.7 (PO4)3.

8. The composite negative electrode material according to any one of claims 1 to 7, characterized in that, The fast ion conductor is a ceramic particle, and the average volumetric particle size Dv50 of the ceramic particle is 10nm~70nm.

9. The composite negative electrode material according to claim 8, characterized in that, The average volumetric particle size Dv50 of the ceramic particles is 20nm~50nm.

10. The composite negative electrode material according to any one of claims 1 to 7, 9, characterized in that, The carbon fiber composite material satisfies at least one of the following characteristics (1)-(3): (1) The average diameter of the carbon fibers in the carbon fiber composite material is 0.1 μm to 1 μm; (2) The porosity of the carbon fiber composite material is 20%~70%; (3) The mass ratio of carbon fiber and fast ion conductor in the carbon fiber composite material is (1~19):

1.

11. The composite negative electrode material according to any one of claims 1 to 7, 9, characterized in that, The mass ratio of carbon fiber to fast ion conductor in the carbon fiber composite material is (1.2~9):

1.

12. The composite negative electrode material according to any one of claims 1 to 7, 9, characterized in that, The silicon material layer satisfies at least one of the following characteristics (4)-(5): (4) The thickness of the silicon material layer is 5nm~100nm; (5) The average volumetric particle size Dv50 of the silicon material in the silicon material layer is 3nm~10nm.

13. The composite negative electrode material according to any one of claims 1 to 7, 9, characterized in that, The thickness of the silicon material layer is 10nm~80nm.

14. The composite negative electrode material according to any one of claims 1 to 7, 9, characterized in that, The composite anode material satisfies at least one of the following characteristics (6)-(10): (6) The average volumetric particle size Dv50 of the composite negative electrode material is 5μm~20μm; (7) The specific surface area of ​​the composite negative electrode material is 1m². 2 / g~20m 2 / g; (8) Based on the mass meter of the composite negative electrode material, the mass content of silicon material in the silicon material layer is 1%~70%; (9) Based on the mass meter of the composite negative electrode material, the mass content of the fast ion conductor is 10%~50%; (10) Based on the mass of the composite negative electrode material, the mass content of the carbon fiber is 5%~30%.

15. A method for preparing a composite negative electrode material as described in any one of claims 1 to 14, characterized in that, include: Provide the carbon fiber composite material; The silicon material layer is formed on the carbon fiber composite material.

16. The method for preparing the composite negative electrode material according to claim 15, characterized in that, The preparation method of the carbon fiber composite material includes the following steps: S11. Mix the organic polymer, fast ion conductor, complexing agent and solvent to obtain a mixture; S12. The mixture is heat-treated to obtain a fiber preform solution; S13. The fiber prepreg solution is used to prepare fiber structural material by electrospinning process; S14. The fiber structure material is sintered to obtain a carbon fiber composite material.

17. The method for preparing the composite negative electrode material according to claim 16, characterized in that, The organic polymer includes one or more of polyvinyl alcohol, polyacrylonitrile, polyethylene oxide, polyphenylene ether, polyethylene glycol, polymethyl methacrylate, and polyvinylidene fluoride hexafluoropropylene.

18. The method for preparing the composite negative electrode material according to claim 17, characterized in that, It satisfies at least one of the following characteristics (11)-(12): (11) The concentration of the organic polymer in the mixture is 0.01~0.20 kg / L; (12) The concentration of the fast ion conductor is 0.01~0.20Kg / L.

19. The method for preparing the composite negative electrode material according to claim 17, characterized in that, The concentration of the organic polymer in the mixture is 0.08~0.18 kg / L.

20. The method for preparing the composite negative electrode material according to claim 17, characterized in that, The concentration of the fast ion conductor is 0.08~0.15Kg / L.

21. The method for preparing the composite negative electrode material according to any one of claims 15 to 20, characterized in that, The method for forming the silicon material layer includes at least one of chemical vapor deposition, physical vapor deposition, plasma spraying, and screen printing.

22. A negative electrode sheet, characterized in that, This includes the composite anode material according to any one of claims 1-14 or the composite anode material prepared by the method according to any one of claims 15-21.

23. A secondary battery, characterized in that, Includes the negative electrode sheet as described in claim 22.

24. An electrical appliance, characterized in that, Includes the secondary battery as described in claim 23.

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