Silicon-carbon composite material and preparation method therefor, negative electrode sheet, secondary battery, and device

Abstract

A silicon-carbon composite material and a preparation method therefor, a negative electrode sheet, a secondary battery, and a device. The silicon-carbon composite material comprises a carbon matrix having a pore structure and a silicon-based material distributed in the pore structure of the carbon matrix, and the silicon-carbon composite material contains the element phosphorus. The silicon-based material in the silicon-carbon composite material increases the capacity of the carbon matrix, and the carbon matrix having the pore structure improves the conductivity of the silicon-based material, and can also be used as a buffer medium for volume expansion of the silicon-based material during charging and discharging, so that the problem of increase of the volume of a secondary battery due to silicon expansion is effectively relieved; in addition, the element phosphorus doped in the framework of the carbon matrix is beneficial to improving the electronic conductivity of the material, thus improving the cycle performance of the battery.

Description

Silicon-carbon composite material, preparation method thereof, negative electrode sheet, secondary battery and device

[0001] Related applications

[0002] This disclosure claims priority to Chinese patent application number 202311728656.0, filed on December 14, 2023, entitled “Silicon-carbon composite material, preparation method thereof, negative electrode sheet, secondary battery and device,” the entire text of which is hereby incorporated by reference. Technical Field

[0003] The present disclosure relates to the technical field of lithium-ion batteries, and in particular to a silicon-carbon composite material and a preparation method thereof, a negative electrode sheet, a secondary battery, and a device. Background Art

[0004] The statements herein merely provide background information related to the present disclosure and may not necessarily constitute prior art.

[0005] In recent years, as the application scope of lithium-ion batteries has become increasingly broad, lithium-ion batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power stations, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and other fields. With the continuous development of lithium-ion battery technology, users have placed increasingly higher demands on the energy density of lithium-ion batteries. Silicon-based materials are widely used in lithium-ion batteries due to their high capacity. However, due to the high expansion characteristics of silicon-based materials, the silicon-based material structure becomes powdery and detaches from the current collector during battery charging and discharging, thus losing its activity. In addition, silicon-based materials have poor conductivity. Therefore, while silicon-based materials improve the energy density of lithium-ion batteries, they also affect the cycle performance of secondary batteries, limiting the further development of lithium-ion battery technology.

[0006] Summary of the Invention

[0007] The present disclosure provides a silicon-carbon composite material and a preparation method thereof, a negative electrode plate, a secondary battery and a device to alleviate the expansion of silicon-based materials and improve the cycle performance of the battery.

[0008] In order to achieve the above objectives, the first aspect of the present disclosure provides a silicon-carbon composite material, comprising:

[0009] a carbon matrix having a porous structure; and

[0010] a silicon-based material distributed in the pore structure of the carbon matrix;

[0011] The silicon-carbon composite material contains phosphorus element.

[0012] Therefore, the silicon-based material in the silicon-carbon composite material disclosed in the present invention improves the capacity of the carbon matrix, and the carbon matrix with a pore structure not only improves the conductivity of the silicon-based material, but also can serve as a buffer medium for the volume expansion of the silicon-based material during charging and discharging, effectively alleviating the problem of the increase in volume of the secondary battery due to silicon expansion; and the phosphorus element contained in the silicon-carbon composite material helps to improve the electronic conductivity of the material, thereby improving the cycle performance of the silicon-carbon composite material.

[0013] In some embodiments, the mass proportion of the phosphorus element in the silicon-carbon composite material is 5 ppm-80 ppm; optionally 10 ppm-50 ppm.

[0014] In some embodiments, the silicon-carbon composite material further contains at least one of aluminum and potassium.

[0015] In some embodiments, the silicon-carbon composite material further contains aluminum, and the mass proportion of phosphorus in the silicon-carbon composite material is greater than the mass proportion of aluminum in the silicon-carbon composite material.

[0016] In some embodiments, the silicon-carbon composite material further contains potassium, and the mass proportion of phosphorus in the silicon-carbon composite material is greater than the mass proportion of potassium in the silicon-carbon composite material.

[0017] In some embodiments, the silicon-carbon composite material further contains aluminum and potassium, and the mass proportion of the aluminum in the silicon-carbon composite material is less than the mass proportion of the potassium in the silicon-carbon composite material.

[0018] In some embodiments, the silicon-carbon composite material further contains aluminum, and the mass proportion of the aluminum in the silicon-carbon composite material is 5ppm-80ppm; optionally 10ppm-40ppm.

[0019] In some embodiments, the silicon-carbon composite material further contains potassium, and the mass proportion of the potassium in the silicon-carbon composite material is 5ppm-80ppm; optionally 10ppm-70ppm.

[0020] In some embodiments, the silicon-based material has one or more of the following characteristics:

[0021] (1) The grain size of the silicon-based material is ≤8 nm, optionally ≤5 nm, and more preferably 1 nm to 4 nm;

[0022] (2) The silicon-based material includes one or more of silicon, silicon oxide, silicon carbon compound and silicon alloy;

[0023] (3) The shape of the silicon-based material includes one or more of spherical, quasi-spherical, flake and linear.

[0024] In some embodiments, the carbon matrix has one or more of the following characteristics:

[0025] (1) The average pore size of the pore structure is 0.5 nm to 8 nm, and can be optionally 0.5 nm to 5 nm;

[0026] (2) The pore structure includes micropores, and the average pore diameter d1 of the micropores satisfies: 0.5 nm ≤ d1 < 2 nm;

[0027] (3) The pore structure includes mesopores, and the average pore diameter d2 of the mesopores satisfies: 2nm≤d2≤8nm;

[0028] (4) The pore structure includes micropores, and the number of the micropores in the pore structure accounts for 60%-90%, and optionally 70%-80%;

[0029] (5) The specific surface area of ​​the carbon matrix is ​​500 m 2 / g-2000m 2 / g, optional 1000m 2 / g-1800m 2 / g.

[0030] In some embodiments, the silicon-carbon composite material has one or more of the following characteristics:

[0031] (1) The volume distribution particle size Dv50 of the silicon-carbon composite material is 3 μm-15 μm, and can be optionally 5 μm-12 μm;

[0032] (2) The volume distribution particle size Dv90 of the silicon-carbon composite material is ≤35 μm, and can be selected from 15 μm to 25 μm;

[0033] (3) The particle size distribution of the silicon-carbon composite material satisfies: 1≤(Dv90-Dv10) / Dv50≤3, which may be 1≤(Dv90-Dv10) / Dv50≤2;

[0034] (4) The specific surface area of ​​the silicon-carbon composite material is 1m 2 / g-10m 2 / g, optional 2m 2 / g-6m 2 / g;

[0035] (5) The tap density of the silicon-carbon composite material is 0.8 g / cm 3 -1.2g / cm 3 , optional 0.85g / cm 3 -1.0g / cm 3 ;

[0036] (6) The powder resistivity of the silicon-carbon composite material at 16 MPa is ≤5Ω·cm, and can be optionally ≤2Ω·cm;

[0037] (7) The mass proportion of silicon element in the silicon-carbon composite material is 20%-60%, and can be optionally 30%-50%.

[0038] In some embodiments, at least a portion of the surface of the silicon-carbon composite material has a coating layer; optionally, the coating layer is a carbon coating layer.

[0039] In some embodiments, the carbon coating layer has one or more of the following characteristics:

[0040] (1) The material of the carbon coating layer includes amorphous carbon;

[0041] (2) The thickness of the carbon coating layer is 50nm-200nm.

[0042] In some embodiments, the phosphorus element is distributed in the carbon matrix; and / or at least one of the aluminum element and the potassium element is distributed in the carbon matrix.

[0043] The second aspect of the present disclosure provides a method for preparing the silicon-carbon composite material of the first aspect of the present disclosure, comprising the following steps:

[0044] The carbon material precursor is mixed with a phosphorus-containing compound and sintered to prepare a carbon matrix with a porous structure;

[0045] The silicon-based material is deposited in the pore structure of the carbon matrix to prepare the silicon-carbon composite material.

[0046] The preparation method of the silicon-carbon composite material provided by the present disclosure has a simple process, can achieve one-step pore formation, and the obtained pore size is relatively uniform, and at the same time, phosphorus elements can be incorporated into the skeleton of the carbon matrix.

[0047] In some embodiments, the mass ratio of the carbon material precursor to the phosphorus-containing compound is 100:(3-15); optionally 100:(4-10).

[0048] In some embodiments, the sintering temperature is 600°C-1000°C; optionally 600°C-900°C.

[0049] In some embodiments, the sintering treatment time is 1 hour to 12 hours; optionally, 4 hours to 8 hours.

[0050] In some embodiments, the conditions for preparing the carbon matrix further include one or more of the following conditions:

[0051] (1) Mixing the carbon material precursor with the phosphorus-containing compound includes mixing the carbon material precursor with a solution containing the phosphorus-containing compound;

[0052] Optionally, the carbon material precursor is mixed with a solution containing the phosphorus-containing compound and then allowed to stand;

[0053] Further optionally, the standing time is 12h-24h;

[0054] (2) the phosphorus-containing compound includes one or more of phosphoric acid, potassium phosphate, sodium phosphate, calcium dihydrogen phosphate or potassium dihydrogen phosphate;

[0055] (3) The carbon material precursor includes one or more of biomass hard carbon or resin-based carbon materials;

[0056] (4) The carbon material precursor contains at least one of aluminum and potassium;

[0057] Optionally, the carbon material precursor contains aluminum element, and the mass proportion of the aluminum element in the carbon material precursor is 5ppm-80ppm; optionally 6ppm-60ppm;

[0058] Optionally, the carbon material precursor contains potassium, and the mass proportion of the potassium in the carbon material precursor is 5ppm-80ppn; optionally 6ppm-60ppm;

[0059] (5) The sintering atmosphere includes one or more of an inert gas and nitrogen;

[0060] Optionally, the atmosphere of the sintering process includes one or more of argon and nitrogen.

[0061] In some embodiments, the step of depositing the silicon-based material within the pore structure of the carbon matrix comprises:

[0062] The carbon substrate is placed in a mixed gas containing a silicon source and a first protective gas, and a first vapor deposition is performed to deposit the silicon-based material in the pore structure of the carbon substrate.

[0063] In some embodiments, the first vapor deposition comprises one or more of the following conditions:

[0064] (1) The temperature of the first vapor deposition is 400° C.-800° C., optionally 500° C.-700° C., and more preferably 500° C.-600° C.;

[0065] (2) The time of the first vapor deposition is 1 hour to 12 hours, and can be optionally 4 hours to 8 hours;

[0066] (3) The volume proportion of the silicon source in the mixed gas is 10%-50%;

[0067] (4) The volume proportion of the first protective gas in the mixed gas is 30%-85%;

[0068] (5) The positive difference between the pressure of the first vapor deposition and the atmospheric pressure is 200 Pa to 600 Pa;

[0069] (6) The silicon source includes one or more of monosilane, disilane and trisilane;

[0070] (7) The first protective gas includes one or more of nitrogen and argon.

[0071] In some embodiments, the mixed gas further comprises a first carbon source.

[0072] In some embodiments, the volume proportion of the first carbon source in the mixed gas is 5%-20%.

[0073] In some embodiments, the volume ratio of the silicon source to the first carbon source is (2-10):1.

[0074] In some embodiments, the first carbon source comprises one or more of methane, ethylene, and acetylene.

[0075] In some embodiments, after the step of depositing the silicon-based material in the pore structure of the carbon matrix, the method further comprises:

[0076] The carbon substrate is placed in a mixed gas containing a second carbon source and a second protective gas, and a second vapor deposition is performed to form the carbon coating layer on at least a portion of the outer surface of the carbon substrate.

[0077] In some embodiments, the second vapor deposition comprises one or more of the following conditions:

[0078] (1) The temperature of the second vapor deposition is 500° C.-900° C.;

[0079] (2) The second vapor deposition time is 1 hour to 6 hours;

[0080] (3) the volume proportion of the second carbon source in the mixed gas is 5%-50%, and the sum of the volume proportions of the second carbon source and the second protective gas in the mixed gas is 100%;

[0081] (4) the second carbon source comprises one or more of methane, ethylene and acetylene;

[0082] (5) The second protective gas includes one or more of nitrogen and argon.

[0083] A third aspect of the present disclosure provides a negative electrode plate, comprising:

[0084] a negative electrode current collector; and

[0085] A negative electrode active material layer is located on at least one side of the negative electrode current collector, and the negative electrode active material layer includes the silicon-carbon composite material of the first aspect of the present disclosure or the silicon-carbon composite material prepared by the method of the second aspect of the present disclosure.

[0086] A fourth aspect of the present disclosure provides a secondary battery comprising the negative electrode sheet according to the third aspect of the present disclosure.

[0087] The secondary battery disclosed herein comprises the silicon-carbon composite material provided herein and has excellent cycle performance.

[0088] A fifth aspect of the present disclosure provides an electric device including the secondary battery according to the fourth aspect of the present disclosure.

[0089] The electric device of the present disclosure includes the secondary battery provided by the present disclosure, and thus has at least the same advantages as the secondary battery.

[0090] The details of one or more embodiments of the present disclosure are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the present disclosure will become apparent from the description, drawings, and claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0091] In order to better describe and illustrate the embodiments or examples provided by the present disclosure, reference may be made to one or more of the accompanying drawings. The additional details or examples used to describe the accompanying drawings should not be considered as limiting the scope of the disclosed application, the embodiments or examples currently described, and any of the best modes currently understood for these applications. Moreover, the same reference numerals are used throughout the accompanying drawings to represent the same components. In the accompanying drawings:

[0092] FIG1 is a schematic diagram of a battery cell according to an embodiment of the present disclosure.

[0093] FIG. 2 is an exploded view of the battery cell according to one embodiment of the present disclosure shown in FIG. 1 .

[0094] FIG3 is a schematic diagram of a battery module according to an embodiment of the present disclosure.

[0095] FIG4 is a schematic diagram of a battery pack according to an embodiment of the present disclosure.

[0096] FIG. 5 is an exploded view of the battery pack shown in FIG. 4 according to an embodiment of the present disclosure.

[0097] FIG6 is a schematic diagram of an electric device using a secondary battery as a power source according to an embodiment of the present disclosure.

[0098] Explanation of reference numerals: 1 battery pack; 2 upper case; 3 lower case; 4 battery module; 5 battery cell; 51 housing; 52 electrode assembly; 53 cover plate; 6 electrical device. DETAILED DESCRIPTION

[0099] Hereinafter, some embodiments of the silicon-carbon composite material and its preparation method, negative electrode sheet, secondary battery and electrical device disclosed in the present invention are described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present disclosure and are not intended to limit the subject matter described in the claims.

[0100] " scope " disclosed in the present disclosure can adopt the form of lower limit and upper limit to limit, and given range is limited by selecting a lower limit and an upper limit, and selected lower limit and upper limit limit the boundary of special scope.The scope that this mode limits can be to include end value or not include end value, and any end value can be included or not included independently, and can be combined arbitrarily, and promptly any lower limit can form a scope with any upper limit combination.For example, if the scope of 60-120 and 80-110 is listed for specific parameter, it is also expected that the scope of 60-110 and 80-120 is understood to be.In addition, if the minimum range value 1 and 2 listed, and if also listed maximum range value 3,4 and 5, then the following scope can all be expected: 1-3,1-4,1-5,2-3,2-4 and 2-5.In the present disclosure, unless otherwise specified, numerical range " ab " represents the abbreviation of any real number combination between a and b, and wherein a and b are all real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is merely an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to listing the parameter as, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, and so on. For example, when a parameter is expressed as an integer selected from "2-10", this is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0101] In the present disclosure, "a plurality of" or "a plurality of" refers to a number greater than or equal to 2 unless otherwise specified. For example, "one or more" means one or more than or equal to two.

[0102] Unless otherwise specified, all embodiments and optional embodiments of the present disclosure can be combined with each other to form new technical solutions.

[0103] References to "embodiments" herein mean that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment or implementation of the present disclosure. The appearance of the phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it necessarily refer to independent or alternative embodiments that are mutually exclusive of other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments. References to "implementations" herein have a similar understanding.

[0104] It will be understood by those skilled in the art that, in the methods of each embodiment or example, the order in which the steps are written does not imply a strict order of execution and does not constitute any limitation on the implementation process, and the detailed order of execution of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps of the present disclosure can 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 steps (b) and (a) performed sequentially. For example, it is mentioned that the method may also include step (c), indicating that step (c) can be added to the method in any order, for example, the method may include steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0105] In the present disclosure, in the open technical features or technical solutions described with words such as "contain", "include", and "include", unless otherwise specified, additional members other than the listed members are not excluded, and it can be regarded as providing both closed features or solutions consisting of the listed members and open features or solutions including additional members in addition to the listed members. For example, A includes a1, a2, and a3. Unless otherwise specified, it may also include other members or may not include additional members. It can be regarded as providing both the feature or solution of "A consists of a1, a2, and a3", and the feature or solution of "A includes not only a1, a2, and a3, but also other members". In the present disclosure, unless otherwise specified, A (such as B) means that B is a non-limiting example of A, and it can be understood that A is not limited to B.

[0106] In this disclosure, the terms "optionally," "optional," and "optional" mean optional or dispensable, i.e., they refer to either option being selected from two parallel options: "with" or "without." If a technical solution contains multiple "optional" clauses, each "optional" clause is independent unless otherwise specified and there are no conflicts or constraints.

[0107] Silicon-based materials are widely used in secondary batteries. However, due to their high expansion characteristics and poor conductivity, while silicon-based materials improve the energy density of lithium-ion batteries, they also affect the cycle performance of secondary batteries.

[0108] Based on the above problems, the present invention adopts a method of mixing a carbon material precursor with a solution containing a phosphoric acid substance and heating and sintering. During the sintering process, the phosphoric acid substance helps to open the cell wall framework of the carbon source precursor, realize one-step pore formation, and obtain a relatively uniform pore size, thereby preparing a carbon matrix with a suitable pore structure; at the same time, phosphorus element is doped into the skeleton of the carbon matrix, which helps to improve the electronic conductivity of the silicon-carbon composite material and enhance the cycle performance of the material.

[0109] A first aspect of the present disclosure provides a silicon-carbon composite material, comprising a carbon matrix having a pore structure and a silicon-based material distributed in the pore structure of the carbon matrix, wherein the silicon-carbon composite material contains phosphorus.

[0110] It should be noted that the carbon matrix mentioned above refers to a carbon-based material having a pore structure on its outer surface and / or inside, and the number of pore structures contained in the carbon matrix can be one or more.

[0111] The silicon-carbon composite material includes a silicon-based material distributed in the pore structure of a carbon matrix, and may also include a silicon-based material distributed on the surface of a support of the carbon matrix.

[0112] It can be understood that the silicon-carbon composite material disclosed in the present invention includes a carbon matrix with a pore structure and a silicon-based material distributed in the pore structure. The silicon-based material improves the capacity of the carbon matrix, and the carbon matrix with a pore structure improves the conductivity of the silicon-based material. At the same time, it can also serve as a buffer medium for the volume expansion of the silicon-based material during charging and discharging; and the phosphorus element contained in the silicon-carbon composite material helps to improve the electronic conductivity of the material, thereby improving the cycle performance of the battery.

[0113] In some embodiments, the mass percentage of phosphorus in the silicon-carbon composite material is 5 ppm to 80 ppm; for example, it can be, but is not limited to, 3 ppm, 5 ppm, 10 ppm, 15 ppm, 20 ppm, 25 ppm, 30 ppm, 35 ppm, 40 ppm, 45 ppm, 50 ppm, 55 ppm, 60 ppm, 65 ppm, 70 ppm, 75 ppm, 80 ppm, or a range between any two of the foregoing values. When the mass percentage of phosphorus in the silicon-carbon composite material is within the above range, the cycling performance of the battery can be further improved.

[0114] As an example, the mass proportion of phosphorus in the silicon-carbon composite material can be but is not limited to 10ppm-80ppm, 15ppm-80ppm, 20ppm-80ppm, 25ppm-70ppm, 30ppm-60ppm, 35ppm-50ppm, 35ppm-45ppm, 10ppm-60ppm, 10ppm-35ppm, 10ppm-45ppm, 45ppm-60ppm, 35ppm-60ppm, 35ppm-80ppm, 45ppm-80ppm, 60ppm-80ppm, 5ppm-10ppm, 5ppm-35ppm or 5ppm-45ppm, etc.

[0115] In some optional embodiments, the mass proportion of phosphorus in the silicon-carbon composite material is 10 ppm-50 ppm.

[0116] In some embodiments, at least one of aluminum and potassium is also distributed within the carbon matrix skeleton. Thus, the introduction of Al and / or potassium can improve the electronic conductivity of the carbon matrix and, at the same time, act as an attractant to improve the uniformity of silicon deposition.

[0117] In some embodiments, the silicon-carbon composite material further contains aluminum, and the mass proportion of phosphorus in the silicon-carbon composite material is greater than the mass proportion of aluminum in the silicon-carbon composite material.

[0118] In some embodiments, the silicon-carbon composite material further contains potassium, and the mass proportion of phosphorus in the silicon-carbon composite material is greater than the mass proportion of potassium in the silicon-carbon composite material.

[0119] In some embodiments, the silicon-carbon composite material further contains aluminum and potassium, and the mass proportion of the aluminum in the silicon-carbon composite material is less than the mass proportion of the potassium in the silicon-carbon composite material.

[0120] In some embodiments, the silicon-carbon composite material further contains aluminum, and the mass percentage of aluminum in the silicon-carbon composite material is 5ppm-80ppm; for example, it can be, but is not limited to, 5ppm, 7ppm, 10ppm, 13ppm, 15ppm, 17ppm, 20ppm, 23ppm, 25ppm, 27ppm, 30ppm, 33ppm, 35ppm, 37ppm, 40ppm, 43ppm, 45ppm, 47ppm, 50ppm, 53ppm, 55ppm, 57ppm, 60ppm, 63ppm, 65ppm, 67ppm, 70ppm, 73ppm, 75ppm, 77ppm, 80ppm, or a range between any two of the above values. When the mass percentage of aluminum in the silicon-carbon composite material is within the above range, it is beneficial to further improve the material's electrical conductivity and silicon deposition uniformity.

[0121] As an example, the mass proportion of aluminum element in the silicon-carbon composite material can be but is not limited to 5ppm-75ppm, 10ppm-70ppm, 10ppm-40ppm, 15ppm-65ppm, 20ppm-60ppm, 25ppm-55ppm, 30ppm-50ppm, 35ppm-45ppm, 10ppm-35ppm, 15ppm-30ppm or 20ppm-30ppm, etc.

[0122] In some embodiments, the silicon-carbon composite material further contains potassium, and the mass ratio of potassium in the silicon-carbon composite material is 5ppm-80ppm; for example, it can be but not limited to 5ppm, 7ppm, 10ppm, 13ppm, 15ppm, 17ppm, 20ppm, 23ppm, 25ppm, 27ppm, 30ppm, 33ppm, 35ppm, 37ppm, 40ppm, 43ppm, 45ppm, 47ppm, 50ppm, 53ppm, 55ppm, 57ppm, 60ppm, 63ppm, 65ppm, 67ppm, 70ppm, 73ppm, 75ppm, 77ppm, 80ppm or a range between any two of the above values. When the mass ratio of potassium in the silicon-carbon composite material is within the above range, it is beneficial to further improve the conductive properties of the material and the uniformity of silicon deposition.

[0123] As an example, the mass proportion of potassium in the silicon-carbon composite material can be but is not limited to 5ppm-75ppm, 10ppm-70ppm, 15ppm-65ppm, 20ppm-60ppm, 25ppm-55ppm, 30ppm-50ppm, 35ppm-45ppm, 10ppm-35ppm, 15ppm-40ppm or 20ppm-35ppm, etc.

[0124] The mass proportions of the various elements (such as silicon, phosphorus, aluminum or potassium) mentioned in the present disclosure in the silicon-carbon composite material can be referred to EPA-3052-1996 "Microwave Acid Digestion of Silicates" to digest the silicon-carbon composite material, and then the content of the target element is determined by using an inductively coupled plasma optical emission spectrometer (ICP-OES) in accordance with EPA 6010D-2014 "Inductively Coupled Plasma Atomic Emission Spectrometry"; for example, an ICAP-7000 inductively coupled plasma optical emission spectrometer from Thermo Fisher Scientific can be used.

[0125] As an example, the mass proportion of the above-mentioned phosphorus, aluminum or potassium elements in the silicon-carbon composite material can be determined by the following method: 0.5 g of the silicon-carbon composite material sample is microwave-digested with 10 mL of nitric acid and 10 mL of hydrofluoric acid, and after digestion, it is added to a 50 mL volumetric flask to make up the volume, and then the content of the target element is determined by ICAP-7000 ICP-OES.

[0126] In some embodiments, the grain size of the silicon-based material is ≤8nm; for example, it can be, but is not limited to, 0.01nm, 0.05nm, 0.1nm, 0.5nm, 1nm, 1.5nm, 2nm, 2.5nm, 3nm, 3.5nm, 4nm, 4.5nm, 5nm, 5.5nm, 6nm, 6.5nm, 7nm, 7.5nm, 8nm, or a range between any two of the above values. When the grain size of the silicon-based material is within the above range, the collapse of the silicon-carbon composite material structure caused by the expansion of the silicon-based material during the charge and discharge cycle can be prevented. Optionally, the grain size of the silicon-based material is ≤5nm. More optionally, the grain size of the silicon-based material is 1nm-4nm.

[0127] As an example, the grain size of the silicon-based material mentioned above can be calculated using an X-ray diffraction pattern or characterized by a transmission electron microscope to obtain the grain size of the silicon-based material.

[0128] In some embodiments, the silicon-based material includes one or more of silicon element, silicon-oxygen compound, silicon-carbon compound, and silicon alloy.

[0129] In some embodiments, the shape of the silicon-based material includes one or more of a sphere, a spherical shape, a flake shape, and a wire shape.

[0130] In some embodiments, the average pore diameter of the carbon matrix pore structure is between 0.5 nm and 8 nm; for example, it may be, but is not limited to, 2 nm, 2.5 nm, 3 nm, 3.5 nm, 4 nm, 4.5 nm, 5 nm, 5.5 nm, 6 nm, 6.5 nm, 7 nm, 7.5 nm, 8 nm, or a range between any two of the foregoing values. When the average pore diameter of the carbon matrix pore structure is within the foregoing range, the silicon-based material deposited within the pore structure can have a relatively uniform size, thereby reducing the probability of depositing oversized silicon-based material.

[0131] In some optional embodiments, the average pore diameter of the carbon matrix pore structure is 0.5 nm-5 nm.

[0132] In some embodiments, the pore structure includes micropores, and the average pore diameter d1 of the micropores satisfies 0.5 nm≤d1<2 nm.

[0133] In some embodiments, the pore structure includes mesopores, and the average pore diameter d2 of the mesopores satisfies: 2 nm ≤ d2 ≤ 8 nm.

[0134] In some embodiments, the pore structure includes micropores, and the number of micropores in the pore structure accounts for 60%-90%; for example, it can be, but is not limited to, 60%, 63%, 65%, 68%, 70%, 72%, 75%, 78%, 80%, 83%, 85%, 88%, 90%, or a range between any two of the above values. When the number of micropores in the pore structure accounts for within the above range, the probability of depositing large-sized silicon-based materials can be further reduced. Optionally, the number of micropores in the pore structure accounts for 70%-80%.

[0135] As an example, the average pore diameter of the carbon matrix pore structure mentioned above can be measured by nitrogen adsorption-desorption method.

[0136] In some embodiments, the carbon substrate has a specific surface area of ​​500 m 2 / g-2000m 2 / g; for example, but not limited to 500m 2 / g、600m 2 / g、700m 2 / g、800m 2 / g、900m 2 / g、1000m 2 / g、1100m 2 / g、1200m 2 / g、1300m 2 / g、1400m 2 / g、1500m 2 / g、1600m 2 / g、1700m2 / g、1800m 2 / g、1900m 2 / g、2000m 2 / g or a range between any two of the above values. When the specific surface area of ​​the carbon matrix is ​​within the above range, it is conducive to the deposition of the silicon-based material within the pore structure of the carbon matrix, while avoiding excessive deposition of the silicon-based material, thereby avoiding the collapse of the carbon matrix due to excessive volume expansion of the silicon-based material during charge and discharge cycles.

[0137] In some optional embodiments, the specific surface area of ​​the carbon matrix is ​​1000 m 2 / g-1800m 2 / g.

[0138] As an example, the specific surface area of ​​the carbon matrix mentioned above can be measured by nitrogen adsorption-desorption method.

[0139] In some embodiments, the volume distribution particle size Dv50 of the silicon-carbon composite material is 3 μm to 15 μm. When the volume distribution particle size Dv50 of the silicon-carbon composite material is within this range, it facilitates uniform deposition of the silicon-based material in the carbon matrix and improves secondary battery kinetics. As an example, the volume distribution particle size Dv50 of the aforementioned silicon-carbon composite material can be, but is not limited to, 3 μm, 5 μm, 7 μm, 10 μm, 12 μm, 15 μm, or a range between any two of the foregoing values.

[0140] In some optional embodiments, the volume distribution particle size Dv50 of the silicon-carbon composite material is 5 μm-12 μm.

[0141] In some embodiments, the volume distribution particle size Dv90 of the silicon-carbon composite material is ≤ 35 μm; for example, it may be, but is not limited to, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, or a range between any two of the foregoing values. When the volume distribution particle size Dv90 of the silicon-carbon composite material is within the foregoing range, the probability of the negative electrode plate piercing the separator can be reduced.

[0142] In some optional embodiments, the volume distribution particle size Dv90 of the silicon-carbon composite material is 15 μm-25 μm.

[0143] In some embodiments, the particle size distribution of the silicon-carbon composite material satisfies: 1≤(Dv90-Dv10) / Dv50≤3. When the particle size distribution of the silicon-carbon composite material satisfies the above relationship, it is beneficial to improve the compaction density of the negative electrode sheet and the cycle performance of the material. As an example, (Dv90-Dv10) / Dv50 can be, but is not limited to, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3 or a range between any two of the above values.

[0144] In some optional embodiments, the particle size distribution Dv90 of the silicon-carbon composite material satisfies: 1≤(Dv90-Dv10) / Dv50≤2.

[0145] The Dv10, Dv50, and Dv90 of a material are well known in the art and can be measured using methods known in the art, for example, by using a laser particle size analyzer (such as the Malvern Master Size 3000) in accordance with standard GB / T 19077-2016.

[0146] The physical definitions of Dv10, Dv50, and Dv90 are as follows:

[0147] Dv10: The particle size corresponding to when the cumulative volume distribution percentage of the material reaches 10%;

[0148] Dv50: The particle size corresponding to when the cumulative volume distribution percentage of the material reaches 50%;

[0149] Dv90: The particle size corresponding to when the cumulative volume distribution percentage of the material reaches 90%.

[0150] As a possible embodiment, the specific surface area of ​​the silicon-carbon composite material is 1m 2 / g-10m 2 When the specific surface area of ​​the silicon-carbon composite material is within the above range, it is beneficial to improve the initial efficiency of the secondary battery. As an example, the specific surface area of ​​the silicon-carbon composite material can be, but is not limited to, 1m 2 / g, 2m 2 / g、3m 2 / g、4m 2 / g、5m 2 / g、6m 2 / g、7m 2 / g、8m 2 / g、9m 2 / g、10m 2 / g or the range between any two of the above values.

[0151] In some optional embodiments, the specific surface area of ​​the silicon-carbon composite material is 2m 2 / g-6m 2 / g.

[0152] As an example, the pore size of the pore structure of the carbon matrix and the specific surface area of ​​the silicon-carbon composite material mentioned above are well known in the art and can be measured using methods known in the art. For example, they can be measured using the nitrogen adsorption specific surface area analysis test method in accordance with GB / T 19587-2017 and calculated using the BET (Brunauer Emmett Teller) method. The nitrogen adsorption specific surface area analysis test can be performed using a Tri-Star 3020 specific surface area pore size analyzer from Micromeritics, USA.

[0153] In some embodiments, the tap density of the silicon-carbon composite material is 0.8 g / cm 3 -1.2g / cm 3 As an example, the tap density of the silicon-carbon composite material may be, but is not limited to, 0.8 g / cm 3 , 0.83g / cm 3 , 0.85g / cm 3 , 0.87g / cm 3 , 0.9g / cm 3 , 0.92g / cm 3 , 0.95g / cm 3 , 0.98g / cm 3 , 1g / cm 3 , 1.02g / cm 3 , 1.05g / cm 3 、1.08g / cm 3 , 1.1g / cm 3 , 1.12g / cm 3 , 1.15g / cm 3 , 1.18g / cm 3 , 1.2g / cm 3 Or the range between any two of the above values.

[0154] In some optional embodiments, the tap density of the silicon-carbon composite material is 0.85 g / cm 3 -1.0g / cm 3 .

[0155] It should be noted that the tap density of the silicon-carbon composite material mentioned above refers to the mass per unit volume of the silicon-carbon composite material powder in a container measured after being tapped under specified conditions.

[0156] The tap density of the negative electrode active material is well known in the art and can be measured using methods known in the art. For example, it can be measured using a powder tap density tester in accordance with GB / T 5162-2006. For example, a tap density tester model FZS4-4B from the Beijing Iron and Steel Research Institute can be used, with the following test parameters: vibration frequency: 250 ± 15 times / minute, amplitude: 3 ± 0.2 mm, number of vibrations: 5000, and a 25 mL graduated cylinder.

[0157] In some embodiments, the powder resistivity of the silicon-carbon composite material at 16 MPa is ≤5 Ω·cm. When the powder resistivity of the silicon-carbon composite material at 16 MPa is within the above range, the silicon-carbon composite material has excellent electrical conductivity, thereby helping to improve the dynamic performance of the battery. Optionally, the powder resistivity of the silicon-carbon composite material at 16 MPa is ≤2 Ω·m. More preferably, the powder resistivity of the silicon-carbon composite material at 16 MPa is ≤1 Ω·m.

[0158] As an example, the powder resistivity of the silicon-carbon composite material mentioned above at 16 MPa can be measured by the following method: place an appropriate amount of the sample to be tested in the feeding cup of the resistivity tester, apply pressure, manually collect data, and record the powder resistivity test results at different pressure points. The test pressure is 16 MPa.

[0159] In some embodiments, the mass proportion of silicon in the silicon-carbon composite material is 20%-60%. When the mass proportion of silicon in the silicon-carbon composite material is within the above range, the capacity, first efficiency and cycle performance of the silicon-carbon composite material can be improved. As an example, the mass proportion of silicon in the silicon-carbon composite material can be, but is not limited to, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60% or a range between any two of the above values.

[0160] In some optional embodiments, the mass proportion of silicon in the silicon-carbon composite material is 30%-50%.In some embodiments, at least a portion of the surface of the silicon-carbon composite material has a coating layer.

[0161] Optionally, the coating layer is a carbon coating layer; by providing a carbon coating layer, the conductivity of the material surface can be improved, which helps to exert the capacity and improve the cycle performance of the silicon-carbon composite material. The carbon coating layer can also reduce the contact between the silicon-based material and the electrolyte, reduce battery side reactions, and improve the stability and safety of the material.

[0162] It should be noted that the carbon coating layer can be a continuous and complete coating layer or an incomplete coating layer; wherein "complete" means that the substance located on the inner side of the carbon coating layer is completely covered by the carbon coating layer, and the carbon coating layer completely isolates the substance on the inner side from the substance on the outer side. "Incomplete" means that the substance located on the inner side of the carbon coating layer is not completely covered by the carbon coating layer, and the substance on the inner side of the carbon coating layer can at least partially contact the outer side of the carbon coating layer. Preferably, the carbon coating layer is a continuous and complete coating layer.

[0163] In some optional embodiments, the material of the carbon coating layer includes amorphous carbon; the amorphous carbon can act as a fast-charging ion ring, improve the kinetic properties of the silicon-carbon composite material, and reduce the contact between the silicon-based material and the electrolyte.

[0164] In some optional embodiments, the thickness of the carbon coating layer is 50 nm to 200 nm; for example, it can be, but is not limited to, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 110 nm, 120 nm, 130 nm, 140 nm, 150 nm, 160 nm, 170 nm, 180 nm, 190 nm, 200 nm, or a range between any two of the foregoing values. If the thickness of the carbon coating layer exceeds the foregoing range, the capacity of the secondary battery may be reduced; if the thickness of the carbon coating layer is below the foregoing range, the silicon-based material may be exposed, affecting processing performance.

[0165] As an example, the thickness of the carbon coating layer mentioned above can be measured using a transmission electron microscope.

[0166] In some embodiments, phosphorus is distributed in the carbon matrix.

[0167] In some embodiments, at least one of aluminum and potassium is distributed in the carbon matrix.

[0168] A second aspect of the present disclosure provides a method for preparing a silicon-carbon composite material, comprising the following steps:

[0169] The carbon material precursor is mixed with a phosphorus-containing compound and sintered to prepare a carbon matrix with a porous structure;

[0170] Silicon-based materials are deposited in the pore structure of the carbon matrix to prepare silicon-carbon composite materials.

[0171] It should be noted that the phosphorus-containing compound can be used as both a pore-forming additive and a phosphorus-doping raw material.

[0172] The present disclosure provides a method for preparing a silicon-carbon composite material, which has a simple process, can achieve one-step pore formation, and the obtained pore size is relatively uniform, and at the same time, phosphorus elements can be incorporated into the skeleton of the carbon matrix.

[0173] In some embodiments, mixing the carbon material precursor with the phosphorus-containing compound includes mixing the carbon material precursor with a solution containing the phosphorus-containing compound. Optionally, the solvent of the solution containing the phosphorus-containing compound is water.

[0174] In some optional embodiments, the carbon material precursor is mixed with the solution containing the phosphorus-containing compound and then allowed to stand; standing is beneficial for the solution containing the phosphorus-containing compound to infiltrate the carbon material precursor.

[0175] In some optional embodiments, the standing time is 12h-24h; for example, it can be but not limited to 12h, 13h, 14h, 15h, 16h, 17h, 18h, 19h, 20h, 21h, 22h, 23h, 24h or a range before any two of the above times.

[0176] In some embodiments, the phosphorus-containing compound includes one or more of phosphoric acid, potassium phosphate, sodium phosphate, calcium dihydrogen phosphate, and potassium dihydrogen phosphate.

[0177] As a possible implementation, the carbon material precursor includes one or more of biomass hard carbon and resin-based carbon materials.

[0178] Optionally, the biomass hard carbon includes one or more of coconut shell, lignin, bamboo powder and starch.

[0179] It should be noted that bamboo powder is a powder prepared using bamboo as raw material.

[0180] Optionally, the resin-based carbon material includes one or more of phenolic resin, epoxy resin, urea-formaldehyde resin and furan resin.

[0181] In some embodiments, the carbon material precursor contains at least one of aluminum and potassium.

[0182] In some optional embodiments, the mass proportion of aluminum in the carbon material precursor is 5ppm-80ppm; for example, it can be but not limited to 5ppm, 10ppm, 15ppm, 20ppm, 25ppm, 30ppm, 35ppm, 40ppm, 45ppm, 50ppm, 55ppm, 60ppm, 65ppm, 70ppm, 75ppm, 80ppm, or a range between any two of the above values. As an example, the mass proportion of aluminum in the carbon material precursor can be but not limited to 5ppm-75ppm, 10ppm-70ppm, 15ppm-65ppm, 20ppm-60ppm, 25ppm-55ppm, 30ppm-50ppm, 35ppm-45ppm, 10ppm-35ppm, 15ppm-30ppm, or 20ppm-30ppm, etc.

[0183] In some optional embodiments, the mass proportion of aluminum in the carbon material precursor is 6ppm-60ppm.

[0184] In some optional embodiments, the carbon material precursor further contains potassium, and the mass proportion of potassium in the carbon material precursor is 5ppm-80ppm; for example, it can be but not limited to 5ppm, 7ppm, 10ppm, 13ppm, 15ppm, 17ppm, 20ppm, 23ppm, 25ppm, 27ppm, 30ppm, 33ppm, 35ppm, 37ppm, 40ppm, 43ppm, 45ppm, 47ppm, 50ppm, 53ppm, 55ppm, 57ppm, 60ppm, 63ppm, 65ppm, 67ppm, 70ppm, 73ppm, 75ppm, 77ppm, 80ppm or a range between any two of the above values.

[0185] As an example, the mass proportion of potassium in the carbon material precursor can be but is not limited to 5ppm-75ppm, 10ppm-70ppm, 15ppm-65ppm, 20ppm-60ppm, 25ppm-55ppm, 30ppm-50ppm, 35ppm-45ppm, 10ppm-35ppm, 15ppm-40ppm or 20ppm-35ppm, etc.

[0186] In some optional embodiments, the mass proportion of potassium in the carbon material precursor is 10 ppm-70 ppm.

[0187] In some embodiments, the mass ratio of the carbon precursor to the phosphorus-containing compound is 100:(3-15); for example, it can be, but is not limited to, 100:3, 100:4, 100:5, 100:6, 100:7, 100:8, 100:9, 100:10, 100:11, 100:12, 100:13, 100:14, 100:15 or a range between any two of the above values. When the mass ratio of the carbon precursor to the phosphorus-containing compound is within the above range, the P element can be within the required range.

[0188] In some optional embodiments, the mass ratio of the carbon material precursor to the phosphoric acid substance is 100:(4-10).

[0189] In some embodiments, the sintering temperature is 600°C-1000°C; for example, but not limited to, 600°C, 650°C, 700°C, 750°C, 800°C, 850°C, 900°C, 950°C, 1000°C, or a range between any two of the foregoing values. Optionally, the sintering temperature is 600°C-900°C.

[0190] In some embodiments, the sintering time is 1 hour to 12 hours; for example, it can be, but is not limited to, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, or a range between any two of the above values. Optionally, the sintering time is 4 hours to 8 hours.

[0191] When the sintering temperature and time are controlled within the above ranges, if the treatment time is too long, the P element will be incorporated beyond the requirement.

[0192] In some embodiments, the sintering process atmosphere includes one or more of an inert gas and nitrogen. Alternatively, the sintering process atmosphere includes one or more of argon and nitrogen.

[0193] As one possible embodiment, the step of depositing a silicon-based material within the pore structure of the carbon matrix includes placing the carbon matrix in a mixed gas containing a silicon source and a first protective gas, and performing a first vapor deposition process to deposit the silicon-based material within the pore structure of the carbon matrix. Using vapor deposition to deposit the silicon-based material within the pore structure can increase the proportion of the silicon-based material embedded within the pore structure.

[0194] In some optional embodiments, the temperature of the first vapor deposition is 400°C-800°C; for example, it can be but not limited to 400°C, 430°C, 450°C, 480°C, 500°C, 530°C, 550°C, 570°C, 600°C, 630°C, 650°C, 680°C, 700°C, 730°C, 750°C, 770°C, 800°C, or a range between any two of the above values. When the temperature of the first vapor deposition is within the above range, it is beneficial to control the grain size of the silicon-based material to be within an appropriate range. It can be 500°C-700°C, and more preferably 500°C-600°C.

[0195] In some optional embodiments, the first vapor deposition time is 1 hour to 12 hours; for example, it can be, but is not limited to, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, or a range between any two of the foregoing values. It can optionally be 4 hours to 8 hours. The first vapor deposition time within the above range is conducive to obtaining a silicon-based material with an appropriate particle size and is conducive to controlling the silicon-based material to achieve an appropriate mass proportion in the silicon-carbon composite material.

[0196] In some optional embodiments, the volume proportion of the silicon source in the mixed gas is 10%-50%.

[0197] In some optional embodiments, the volume proportion of the first protective gas in the mixed gas is 30%-85%.

[0198] As a possible embodiment, the positive difference between the pressure of the first vapor deposition and the atmospheric pressure is 200Pa-600Pa; for example, it can be but not limited to 200Pa, 250Pa, 300Pa, 350Pa, 400Pa, 450Pa, 500Pa, 550Pa, 600Pa or a range between any two of the above values.

[0199] It should be noted that the positive difference refers to how much the pressure of the first vapor deposition is higher than the atmospheric pressure.

[0200] In some embodiments, the silicon source includes one or more of monosilane, disilane, and trisilane.

[0201] In some embodiments, the first protective gas includes one or more of nitrogen and argon.

[0202] In some embodiments, the mixed gas further includes a first carbon source, thereby promoting the decomposition of the silicon source.

[0203] In some optional embodiments, the volume proportion of the first carbon source in the mixed gas is 5%-20%.

[0204] In some optional embodiments, the volume ratio of the silicon source to the first carbon source is (2-10):1; for example, it can be but not limited to 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, or a range between any two of the above values. When the volume ratio of the silicon source to the first carbon source is higher than the above range, the carbon content decomposition ratio is high and the capacity improvement effect is general; when the volume ratio of the silicon source to the first carbon source is lower than the above range, the silicon-based material content on the surface of the carbon matrix will increase, and slurry processing will cause problems.

[0205] As a possible implementation manner, the first carbon source includes one or more of methane, ethylene and acetylene.

[0206] As a possible implementation manner, after the step of depositing the silicon-based material in the pore structure of the carbon matrix, the method further includes:

[0207] The carbon substrate is placed in a mixed gas containing a second carbon source and a second protective gas, and a second vapor deposition process is performed to form a carbon coating layer on at least a portion of the outer surface of the carbon substrate. Using vapor deposition to prepare the carbon coating layer facilitates the control of the coating amount to enhance the surface conductivity of the silicon-carbon composite material, improve the material's capacity, and maintain the stability and safety of the silicon-carbon composite material.

[0208] In some optional embodiments, the temperature of the second vapor deposition is 500°C-900°C; for example, it can be but is not limited to 500°C, 530°C, 550°C, 580°C, 600°C, 630°C, 650°C, 680°C, 700°C, 730°C, 750°C, 770°C, 800°C, 830°C, 850°C, 880°C, 900°C or a range between any two of the above values.

[0209] In some optional embodiments, the time of the second vapor deposition is 1 hour to 6 hours; for example, it can be but is not limited to 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours or a range between any two of the above values.

[0210] In some optional embodiments, the volume proportion of the second carbon source in the mixed gas is 5%-50%, and the sum of the volume proportions of the second carbon source and the second protective gas in the mixed gas is 100%.

[0211] In some alternative embodiments, the second carbon source comprises one or more of methane, ethylene, and acetylene.

[0212] In some optional embodiments, the second protective gas includes one or more of nitrogen and argon.

[0213] It should be noted that the above-mentioned "first carbon source", "second carbon source", "first protective gas", "second protective gas", "first vapor deposition" and "second vapor deposition" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or quantity, nor can they be understood as implicitly indicating the importance or quantity of the indicated technical features.

[0214] In some embodiments, the method for preparing the silicon-carbon composite material comprises the following steps:

[0215] The carbon precursor is mixed with a solution containing a phosphorus-containing compound and then allowed to stand for 12-24 hours, followed by sintering to prepare a carbon matrix with a porous structure. The phosphorus-containing compound includes one or more of phosphoric acid, potassium phosphate, sodium phosphate, calcium dihydrogen phosphate and potassium dihydrogen phosphate. The carbon precursor includes one or more of biomass hard carbon and resin-based carbon materials. The biomass hard carbon includes one or more of coconut shell, lignin, bamboo powder and starch. The resin-based carbon material includes one or more of phenolic resin, epoxy resin, urea-formaldehyde resin and furan resin. The mass ratio of the carbon precursor to the phosphorus-containing compound is 100:(3-15), and can be optionally 100:(4-10). The carbon precursor contains at least one of aluminum and potassium; the mass proportion of aluminum in the carbon precursor is 5ppm-80ppm; optionally 6ppm-60ppm; the mass proportion of potassium in the carbon precursor is 5ppm-80ppm; optionally 6ppm-60ppm. The sintering temperature is 600°C to 1000°C, optionally 600°C to 900°C. The sintering time is 1 hour to 12 hours, optionally 4 hours to 8 hours. The sintering atmosphere includes one or more of argon and nitrogen.

[0216] The carbon substrate is placed in a mixed gas containing a silicon source, a first carbon source, and a first protective gas, and a first vapor deposition is performed to deposit a silicon-based material within the pore structure of the carbon substrate. The temperature of the first vapor deposition is 400°C-800°C, optionally 500°C-700°C, and more optionally 500°C-600°C. The time of the first vapor deposition is 1 hour-12 hours, optionally 4 hours-8 hours. The volume proportion of the silicon source in the mixed gas is 10%-50%, the volume proportion of the first carbon source in the mixed gas is 5%-20%, and the volume proportion of the first protective gas in the mixed gas is 30%-85%. The sum of the volume proportions of the silicon source, the first carbon source, and the first protective gas in the mixed gas is 100%; the volume ratio of the silicon source to the first carbon source is (2-10):1. The positive difference between the pressure of the first vapor deposition and atmospheric pressure is 200 Pa-600 Pa. The silicon source includes one or more of monosilane, disilane, and trisilane. The first carbon source includes one or more of methane, ethylene and acetylene. The first protective gas includes one or more of nitrogen and argon.

[0217] The carbon substrate after the silicon-based material is deposited is placed in a mixed gas containing a second carbon source and a second protective gas, and a second vapor deposition is performed to form a carbon coating layer on at least a portion of the outer surface of the carbon substrate. The temperature of the second vapor deposition is 500°C-900°C. The time of the second vapor deposition is 1h-6h. The volume proportion of the second carbon source in the mixed gas is 5%-50%, and the sum of the volume proportions of the second carbon source and the second protective gas in the mixed gas is 100%. The second carbon source includes one or more of methane, ethylene and acetylene. The second protective gas includes one or more of nitrogen and argon.

[0218] The third aspect of the present disclosure provides a negative electrode plate, comprising a negative electrode current collector and a negative electrode active material layer located on at least one side of the negative electrode current collector, the negative electrode active material layer comprising the silicon-carbon composite material of the first aspect of the present disclosure or the silicon-carbon composite material prepared by the method of the second aspect of the present disclosure.

[0219] The negative electrode plate disclosed herein comprises the silicon-carbon composite material provided herein, and its volume conversion rate during the charge and discharge process is significantly reduced.

[0220] As a non-limiting example, the negative electrode current collector has two surfaces facing each other in its thickness direction, and the negative electrode active material layer is disposed on either or both of the two facing surfaces of the negative electrode current collector.

[0221] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be obtained by forming a metal material on a polymer material substrate. In the negative electrode current collector, non-limiting examples of the metal material may include one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy. In the negative electrode current collector, non-limiting examples of the polymer material substrate may include one or more of substrates such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0222] In some of these embodiments, the negative electrode active material may also adopt negative electrode active materials for batteries that are well known in the art. As non-limiting examples, the negative electrode active material may include one or more of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc. Silicon-based materials may include one or more of elemental silicon, silicon oxides, silicon nitrogen complexes, and silicon alloys. Tin-based materials may include one or more of elemental tin, tin oxides, and tin alloys. However, the present disclosure is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0223] In some embodiments, the negative electrode active material layer may further include a binder. The binder may include one or more 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).

[0224] In some embodiments, the negative electrode active material layer may further include a conductive agent, which may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0225] In some embodiments, the negative electrode active material layer may optionally further include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0226] In some embodiments, the negative electrode sheet can be prepared in the following manner: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (a non-limiting example of the solvent is deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on at least one side of the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained. The surface of the negative electrode current collector coated with the negative electrode slurry can be a single surface of the negative electrode current collector or on both surfaces of the negative electrode current collector. The solid content of the negative electrode slurry can be 40wt% to 60wt%. The viscosity of the negative electrode slurry at room temperature can be adjusted to 2000mPa·s-10000mPa·s. When coating the negative electrode slurry, the coating unit surface density on a dry weight basis (excluding the solvent) can be 75g / m 2 -220 g / m 2 The compaction density of the negative electrode can be 1.3g / cm 3 -1.8g / cm 3 .

[0227] A fourth aspect of the present disclosure provides a secondary battery comprising the negative electrode sheet according to the third aspect of the present disclosure.

[0228] The secondary battery disclosed herein comprises the silicon-carbon composite material provided herein and has excellent cycle performance.

[0229] In addition, the secondary battery and the electric device of the present disclosure will be described below with reference to the drawings as appropriate.

[0230] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During the battery's charge and discharge processes, active ions are inserted and removed between the positive and negative electrodes. The electrolyte conducts ions between the positive and negative electrodes. The separator, located between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0231] Positive electrode

[0232] 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, wherein the positive electrode active material layer includes a positive electrode active material.

[0233] As a non-limiting example, the positive electrode current collector has two surfaces facing each other in its thickness direction, and the positive electrode active material layer is disposed on either or both of the two facing surfaces of the positive electrode current collector.

[0234] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector may be obtained by forming a metal material on a polymer material substrate. In the positive electrode current collector, non-limiting examples of the metal material may include one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy. In the positive electrode current collector, non-limiting examples of the polymer material substrate may include one or more of substrates such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0235] The positive electrode active material may be any positive electrode active material for secondary batteries known in the art.

[0236] When the secondary battery of the present disclosure is a lithium-ion battery, the positive electrode active material for the lithium-ion battery may include, but is not limited to, one or more of lithium-containing transition metal oxides and lithium-containing phosphates. Examples of the lithium transition metal oxides may include, but are not limited to, one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide or their respective modified compounds. Examples of the lithium-containing phosphates may include, but are not limited to, one or more of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, a composite material of lithium manganese iron phosphate and carbon or their respective modified compounds.

[0237] In some embodiments, in order to further improve the energy density of the secondary battery, the positive electrode active material for the lithium-ion battery may include Li a Ni b Co c M d O e A f , where 0.5 ≤ a ≤ 1.2, 0.5 ≤ b < 1, 0 < c < 1, 0 < d < 1, 1 ≤ e ≤ 2, 0 ≤ f ≤ 1, M includes one or more of Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti and B, and A includes one or more of N, F, S and Cl.

[0238] In some embodiments, by way of example, the positive electrode active material for the lithium-ion battery may include LiCoO2, LiNiO2, LiMnO2, LiMn2O4, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O2 (NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811), LiNi 0.80 Co 0.15 Al 0.05 O2, LiFePO4 and LiMnPO4, or one or more of them.

[0239] In the present disclosure, the modified compounds of the above positive electrode active materials may be doping modification and / or surface coating modification of the positive electrode active materials.

[0240] In some embodiments, the positive electrode active material layer may further optionally include a binder. As non-limiting examples, the binder may include one or more 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 acrylate resin.

[0241] In some embodiments, the positive electrode active material layer may further include a conductive agent. As non-limiting examples, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0242] In some embodiments, the positive electrode sheet can be prepared by the following method: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder, and any other components, are dispersed in a solvent to form a positive electrode slurry; the positive electrode slurry is coated on at least one side of the positive electrode current collector, and after drying, cold pressing, and other processes, the positive electrode sheet can be obtained. The type of solvent can be selected from but not limited to any of the aforementioned embodiments, such as N-methylpyrrolidone (NMP). The surface of the positive electrode current collector coated with the positive electrode slurry can be on a single surface of the positive electrode current collector or on both surfaces of the positive electrode current collector. The surface of the positive electrode current collector coated with the positive electrode slurry can be on a single surface of the positive electrode current collector or on both surfaces of the positive electrode current collector.

[0243] electrolytes

[0244] The electrolyte conducts ions between the positive and negative electrodes. The present disclosure does not specifically limit the type of electrolyte, and the electrolyte can be selected based on the needs. For example, the electrolyte can be liquid, gel, or solid.

[0245] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0246] In some embodiments, the electrolyte salt may include one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bisfluorosulfonyl imide (LiFSI), lithium bistrifluoromethanesulfonyl imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorophosphate (LiPO2F2), lithium difluorooxalatoborate (LiDFOB), lithium dioxalatoborate (LiBOB), lithium difluorodioxalatophosphate (LiDFOP) and lithium tetrafluorooxalatophosphate (LiTFOP).

[0247] In some embodiments, the solvent may include ethylene carbonate (EC, ), propylene carbonate (PC, ), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate One or more of fluoroethylene carbonate (FEC), 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.

[0248] In some embodiments, the electrolyte may optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, and additives that improve battery high or low temperature performance.

[0249] In some embodiments, the additives in the electrolyte may include, but are not limited to, one or more of fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), trifluoromethylethylene carbonate (TFPC), and the like.

[0250] Isolation film

[0251] In some embodiments, the secondary battery further includes a separator. The present disclosure has no particular limitation on the type of separator, and any known porous separator with good chemical and mechanical stability can be selected.

[0252] In some embodiments, the material of the separator may include one or more of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer may be the same or different, without particular limitation.

[0253] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0254] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0255] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery can also be a soft shell, such as a pouch-type soft shell. The material of the soft shell can be plastic. Further, non-limiting examples of plastic can include one or more of polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0256] A secondary battery includes at least one battery cell. A secondary battery may include one or more battery cells.

[0257] In this disclosure, unless otherwise specified, a "battery cell" refers to a basic unit capable of converting chemical energy into electrical energy. Furthermore, it generally includes at least a positive electrode, a negative electrode, and an electrolyte. During the battery's charge and discharge process, active ions are intercalated and released back and forth between the positive and negative electrodes. The electrolyte conducts the active ions between the positive and negative electrodes.

[0258] The present disclosure has no particular limitation on the shape of the battery cell, which may be cylindrical, square, or any other shape. For example, FIG1 shows a battery cell 5 with a square structure as an example.

[0259] In some embodiments, referring to Figure 2, the outer packaging may include a shell 51 and a cover plate 53. The shell 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can be formed into an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is impregnated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell 5 can be one or more, and those skilled in the art can select according to actual needs.

[0260] The secondary battery may be a battery module 4 or a battery pack 1 .

[0261] A battery module includes at least one battery cell. The number of battery cells contained in a battery module can be one or more, and those skilled in the art can select an appropriate number based on the application and capacity of the battery module.

[0262] FIG3 shows an example battery module 4. Referring to FIG3 , within the battery module 4, multiple battery cells 5 may be arranged sequentially along the length of the battery module 4. Of course, they may also be arranged in any other manner. Furthermore, the multiple battery cells 5 may be secured together using fasteners.

[0263] Optionally, the battery module 4 may further include a housing having an accommodation space, and the plurality of battery cells 5 are accommodated in the accommodation space.

[0264] In some embodiments, the battery modules may be assembled into a battery pack. The battery pack may contain one or more battery modules. Those skilled in the art may select an appropriate number based on the application and capacity of the battery pack.

[0265] Figures 4 and 5 illustrate an example battery pack 1. Referring to Figures 4 and 5 , the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box comprises an upper case 2 and a lower case 3. The upper case 2 can be placed over the lower case 3 to form an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0266] In addition, the present disclosure further provides an electrical device, comprising the secondary battery provided herein. The secondary battery can serve as a power source for the electrical device or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices, electric vehicles, electric trains, ships, satellites, energy storage systems, and the like. Examples of mobile devices include, but are not limited to, mobile phones and laptop computers; and examples of electric vehicles include, but are not limited to, pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, and electric trucks.

[0267] As an electrical device, a secondary battery can be selected according to its usage requirements.

[0268] Figure 6 shows an example of an electric device 6. The electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the electric device's requirements for high power and high energy density of secondary batteries, a battery pack or battery module may be used.

[0269] Another example device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is generally required to be lightweight and thin, and may use a secondary battery as a power source.

[0270] Example

[0271] The following examples are provided. The examples described below are illustrative and are intended only to explain the present disclosure and are not to be construed as limiting the present disclosure. Where techniques or conditions are not specified in the examples, the techniques or conditions described in the literature in the art or in the product specifications were used. Reagents or instruments used without manufacturer specified are all commercially available conventional products.

[0272] 1. Preparation of silicon-carbon composite materials

[0273] Example 1

[0274] Take 1 kg of bamboo powder (as a carbon material precursor), add 0.3 kg of 10 wt% phosphoric acid solution (as a phosphoric acid substance), use a VC mixer to mix evenly, let it stand for 24 hours, then increase the temperature to 800 ° C at a rate of 5 ° C / min, keep warm for 4 hours, and obtain a carbon matrix with a porous structure. After the furnace cools down, take it out for use; wherein, the mass ratio of the carbon material precursor and the phosphoric acid substance is 100:5; the mass proportion of aluminum in the carbon material precursor is 60 ppm, and the mass proportion of potassium is 65 ppm; the average pore size of the carbon matrix is ​​1.8 nm, the number of micropores accounts for 80%, the number of mesopores accounts for 20%, and the specific surface area of ​​the carbon matrix is ​​1600 m 2 / g;

[0275] The carbon substrate was placed in a fluidized bed deposition furnace and heated to 500°C at a rate of 5°C / min. A mixed gas of monosilane (as a silicon source) and nitrogen (as a first protective gas) was introduced at a volume ratio of 2:8 with a total gas flow rate of 5 L / min. The pressure in the furnace was controlled to be slightly higher than atmospheric pressure by 200 Pa, and the deposition was carried out for 4 hours.

[0276] Stop the introduction of monosilane, continue to raise the temperature to 600 ° C, and introduce a mixed gas of acetylene (as the second carbon source) and nitrogen (as the second protective gas) in a volume ratio of 4:6. Deposition is carried out for 2 hours. After cooling, the material is discharged and sieved to obtain a silicon-carbon composite material. In the silicon-carbon composite material, the silicon-based material (elemental silicon) is deposited in the pore structure of the carbon matrix. The mass proportion of silicon in the silicon-carbon composite material is about 50%, the content of phosphorus is about 4ppm, the content of aluminum is about 30ppm, and the content of potassium is about 32ppm. The deposited silicon grain size is about 2nm, and the volume distribution particle size Dv50 of the silicon-carbon composite material is about 7.8μm.

[0277] The preparation methods of Examples 2-9 are similar to those of Example 1, and the differences are detailed in Table 1.

[0278] Comparative Example 1

[0279] 1 kg of phenolic resin (as a carbon precursor) was mixed evenly with 0.93 kg of a 15 wt% KOH solution, and then sintered under nitrogen atmosphere at a heating rate of 1°C / min and a heat treatment temperature of 800°C for 4 h. After cooling, the mixture was washed with water to remove impurities and dried to obtain a carbon matrix for later use.

[0280] The carbon substrate was placed in a fluidized bed deposition furnace and heated to 500°C at a rate of 5°C / min. A mixed gas of monosilane (as a silicon source) and nitrogen (as a first protective gas) was introduced at a volume ratio of 2:8 with a total gas flow rate of 5 L / min. The pressure in the furnace was controlled to be slightly higher than atmospheric pressure by 200 Pa, and the deposition was carried out for 4 hours.

[0281] Stop introducing monosilane, continue to raise the temperature to 600°C, introduce a mixed gas of acetylene (as the second carbon source) and nitrogen (as the second protective gas) in a volume ratio of 4:6, and deposit for 2 hours. After cooling, discharge the material and sieve it through 325 mesh to obtain a silicon-carbon composite material.

[0282] Comparative Example 2

[0283] The preparation method of Comparative Example 2 is similar to that of Example 1, except that no phosphorus source is added when preparing the carbon matrix. The specific preparation method is as follows: 1 kg of bamboo powder (as a carbon material precursor) is taken, the mass proportion of aluminum in the carbon material precursor is 60 ppm, and the mass proportion of potassium is 65 ppm; 340 g of KOH solid is added, mixed evenly using a VC mixer, and allowed to stand for 24 hours, and then the temperature is increased to 800 ° C at a rate of 5 ° C / min, and kept at this temperature for 4 hours to obtain a carbon matrix with a porous structure. After the furnace cools down, it is taken out for use;

[0284] The carbon substrate was placed in a fluidized bed deposition furnace and heated to 500°C at a rate of 5°C / min. A mixed gas of monosilane (as a silicon source) and nitrogen (as a first protective gas) was introduced at a volume ratio of 2:8 with a total gas flow rate of 5 L / min. The pressure in the furnace was controlled to be slightly higher than atmospheric pressure by 200 Pa, and the deposition was carried out for 4 hours.

[0285] Stop introducing monosilane, continue to raise the temperature to 600°C, introduce a mixed gas of acetylene (as the second carbon source) and nitrogen (as the second protective gas) in a volume ratio of 4:6, and deposit for 2 hours. After cooling, discharge the material and sieve to obtain a silicon-carbon composite material.

[0286] The parameter settings in the above embodiments are shown in Table 1.

[0287] Table 1

[0288] The phosphorus content, potassium content, aluminum content, silicon grain size and volume distribution particle size Dv50 of the silicon-carbon composite materials prepared in the above examples and comparative examples were measured. The results are shown in Table 2.

[0289] It should be noted that the phosphorus content, aluminum content and potassium content in the above-mentioned silicon-carbon composite materials were determined by the following method: 0.5 g of silicon-carbon composite material sample was microwave-digested with 10 mL of nitric acid and 10 mL of hydrofluoric acid, and after digestion, the sample was added to a 50 mL volumetric flask to make up the volume, and then the content of the target element was determined by ICAP-7000 ICP-OES.

[0290] The grain size of the silicon-based materials mentioned above was characterized by transmission electron microscopy.

[0291] The volume distribution particle size Dv50 of the silicon-carbon composite material mentioned above is measured using a laser particle size analyzer Malvern Master Size 3000 with reference to the standard GB / T 19077-2016.

[0292] 2. Preparation of Secondary Batteries (Full Batteries)

[0293] 1. Negative electrode

[0294] The prepared silicon-carbon composite material, the conductive carbon nanotube and SP mixture, the binder styrene-butadiene rubber, and the thickener sodium carboxymethyl cellulose were thoroughly stirred and mixed in an appropriate amount of deionized water at a weight ratio of 95.5:1:2:1.5 to form a negative electrode slurry. The negative electrode slurry was coated on both surfaces of the negative electrode current collector copper foil, dried, and cold pressed to obtain a negative electrode sheet.

[0295] 2. Positive electrode

[0296] The positive electrode active material LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811) is mixed with conductive carbon black and polyvinylidene fluoride in a weight ratio of 97.5:1.2:1.3. An appropriate amount of NMP solvent is added and stirred evenly to obtain a positive electrode slurry. The positive electrode slurry is coated on both surfaces of the positive electrode current collector aluminum foil. After drying and cold pressing, the positive electrode sheet is obtained.

[0297] 3. Electrolyte:

[0298] A mixture of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) was used as the organic solvent, with the volume ratio of EC, EMC, and DEC being 20%:20%:60%. In an argon atmosphere glove box with a water content of <10ppm, fully dried lithium salt (LiPF6) was dissolved in the above organic solvent, and the additive fluoroethylene carbonate (FEC) was added to obtain an electrolyte. The concentration of LiPF6 in the electrolyte was 1 mol / L, and the mass proportion of FEC in the electrolyte was 5%.

[0299] 4. Isolation film

[0300] Polypropylene film is used as the isolation membrane.

[0301] 5. Preparation of Secondary Batteries

[0302] Place the isolation film and the positive electrode sheet and negative electrode sheet prepared above in order, so that the isolation film is located between the positive electrode sheet and the negative electrode sheet to play an isolating role, and then wind them to obtain an electrode assembly; place the electrode assembly in an outer package, dry it, and then inject the electrolyte prepared above, and go through vacuum packaging, standing, formation, capacity and other processes to obtain a secondary battery.

[0303] 3. Battery performance test

[0304] 1. Cyclic performance test

[0305] At 25°C, the prepared secondary battery was charged at 0.5C to 4.25V and then discharged at 1C to 2.5V. This constituted one charge-discharge cycle, and the discharge capacity at this point was recorded as the initial discharge capacity. The secondary battery was subjected to further cyclic charge-discharge testing using the above method, recording the discharge capacity after each cycle until the discharge capacity of the secondary battery decayed to 80% of the initial discharge capacity. The number of cycles at this point was then recorded. The results are shown in Table 2.

[0306] Table 2

[0307] From the comparison of the results of Examples 1-29 and Comparative Examples 1-2, it can be seen that the silicon-carbon composite material with a specific structure disclosed in the present invention contains phosphorus, which effectively improves the cycle performance of the battery.

[0308] The above description of the various embodiments tends to emphasize the differences between the various embodiments. The same or similar aspects can be referenced with each other and will not be repeated herein for the sake of brevity.

[0309] It should be noted that the present disclosure is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and within the scope of the technical solution of the present disclosure, embodiments having substantially the same structure as the technical concept and exerting the same effects are all included in the technical scope of the present disclosure. In addition, within the scope of the present disclosure, various modifications that can be imagined by those skilled in the art to the embodiments, and other methods constructed by combining some of the constituent elements of the embodiments are also included in the scope of the present disclosure.

Claims

1. A silicon-carbon composite material comprising: a carbon matrix having a porous structure; as well as a silicon-based material distributed in the pore structure of the carbon matrix; The silicon-carbon composite material contains phosphorus element.

2. The silicon-carbon composite material according to claim 1, wherein The mass proportion of the phosphorus element in the silicon-carbon composite material is 5ppm-80ppm; optionally 10ppm-50ppm.

3. The silicon-carbon composite material according to any one of claims 1 to 2, wherein: The silicon-carbon composite material further contains at least one of aluminum and potassium.

4. The silicon-carbon composite material according to any one of claims 1 to 3, wherein: The silicon-carbon composite material further contains aluminum and potassium elements, and the mass proportion of the aluminum element in the silicon-carbon composite material is smaller than the mass proportion of the potassium element in the silicon-carbon composite material.

5. The silicon-carbon composite material according to any one of claims 1 to 4, wherein: The silicon-carbon composite material further contains aluminum element, and the mass proportion of the aluminum element in the silicon-carbon composite material is 5ppm-80ppm; optionally 10ppm-40ppm.

6. The silicon-carbon composite material according to any one of claims 1 to 5, wherein: The silicon-carbon composite material further contains potassium element, and the mass proportion of the potassium element in the silicon-carbon composite material is 5ppm-80ppm; optionally 10ppm-70ppm.

7. The silicon-carbon composite material according to any one of claims 1 to 6, wherein: The silicon-based material has one or more of the following characteristics: (1) The grain size of the silicon-based material is ≤8 nm, optionally ≤5 nm, and more preferably 1 nm to 4 nm; (2) The silicon-based material includes one or more of silicon, silicon oxide, silicon carbon compound and silicon alloy; (3) The shape of the silicon-based material includes one or more of spherical, quasi-spherical, flake and linear.

8. The silicon-carbon composite material according to any one of claims 1 to 7, wherein: The carbon matrix has one or more of the following characteristics: (1) The average pore size of the pore structure is 0.5 nm to 8 nm, and can be optionally 0.5 nm to 5 nm; (2) The pore structure includes micropores, and the average pore diameter d1 of the micropores satisfies: 0.5 nm ≤ d1 < 2 nm; (3) The pore structure includes mesopores, and the average pore diameter d2 of the mesopores satisfies: 2nm≤d2≤8nm; (4) The pore structure includes micropores, and the number of the micropores in the pore structure accounts for 60%-90%, and optionally 70%-80%; (5) The specific surface area of ​​the carbon matrix is ​​500 m 2 / g-2000m 2 / g, optional 1000m 2 / g-1800m 2 / g.

9. The silicon-carbon composite material according to any one of claims 1 to 8, wherein: The silicon-carbon composite material has one or more of the following characteristics: (1) The volume distribution particle size Dv50 of the silicon-carbon composite material is 3 μm-15 μm, and can be optionally 5 μm-12 μm; (2) The volume distribution particle size Dv90 of the silicon-carbon composite material is ≤35 μm, and can be selected from 15 μm to 25 μm; (3) The particle size distribution of the silicon-carbon composite material satisfies: 1≤(Dv90-Dv10) / Dv50≤3, which may be 1≤(Dv90-Dv10) / Dv50≤2; (4) The specific surface area of ​​the silicon-carbon composite material is 1m 2 / g-10m 2 / g, optional 2m 2 / g-6m 2 / g; (5) The tap density of the silicon-carbon composite material is 0.8 g / cm 3 -1.2g / cm 3 , optional 0.85g / cm 3 -1.0g / cm 3 ; (6) The powder resistivity of the silicon-carbon composite material at 16 MPa is ≤5Ω·cm, and can be optionally ≤2Ω·cm; (7) The mass proportion of silicon element in the silicon-carbon composite material is 20%-60%, and can be optionally 30%-50%.

10. The silicon-carbon composite material according to any one of claims 1 to 9, wherein: At least a portion of the surface of the silicon-carbon composite material has a coating layer, and the coating layer is a carbon coating layer.

11. The silicon-carbon composite material according to claim 10, wherein: The carbon coating layer has one or more of the following characteristics: (1) The material of the carbon coating layer includes amorphous carbon; (2) The thickness of the carbon coating layer is 50nm-200nm.

12. The silicon-carbon composite material according to any one of claims 10 to 11, wherein: The phosphorus element is distributed in the carbon matrix.

13. The silicon-carbon composite material according to any one of claims 10 to 12, wherein: At least one of the aluminum element and the potassium element is distributed in the carbon matrix.

14. A method for preparing the silicon-carbon composite material according to any one of claims 1 to 13, comprising the following steps: The carbon material precursor is mixed with a phosphorus-containing compound and sintered to prepare a carbon matrix with a porous structure; The silicon-based material is deposited in the pore structure of the carbon matrix to prepare the silicon-carbon composite material.

15. The method for preparing the silicon-carbon composite material according to claim 14, wherein: The mass ratio of the carbon material precursor to the phosphorus-containing compound is 100:(3-15); optionally 100:(4-10).

16. The method for preparing the silicon-carbon composite material according to any one of claims 14 to 15, wherein: The temperature of the sintering treatment is 600°C-1000°C; optionally 600°C-900°C.

17. The method for preparing the silicon-carbon composite material according to any one of claims 14 to 16, wherein: The sintering treatment time is 1 hour to 12 hours, and can be optionally 4 hours to 8 hours.

18. The method for preparing the silicon-carbon composite material according to any one of claims 14 to 17, wherein: The conditions for preparing the carbon matrix also include one or more of the following conditions: (1) The mixing of the carbon material precursor and the phosphorus-containing compound includes mixing the carbon material precursor with the phosphorus-containing compound. The carbon material precursor and the solution containing the phosphorus-containing compound are mixed and then allowed to stand for 12 hours to 24 hours; (2) the phosphorus-containing compound includes one or more of phosphoric acid, potassium phosphate, sodium phosphate, calcium dihydrogen phosphate or potassium dihydrogen phosphate; (3) The carbon material precursor includes one or more of biomass hard carbon or resin-based carbon materials; (4) The carbon material precursor contains at least one of aluminum and potassium; (5) The atmosphere of the sintering treatment includes one or more of an inert gas and nitrogen.

19. The method for preparing the silicon-carbon composite material according to any one of claims 14 to 18, wherein: The carbon material precursor contains aluminum element, and the mass proportion of the aluminum element in the carbon material precursor is 5ppm-80ppm; optionally 6ppm-60ppm.

20. The method for preparing the silicon-carbon composite material according to any one of claims 14 to 19, wherein: The carbon material precursor contains potassium element, and the mass proportion of the potassium element in the carbon material precursor is 5ppm-80ppm; optionally 6ppm-60ppm.

21. The method for preparing the silicon-carbon composite material according to any one of claims 14 to 20, wherein: The step of depositing the silicon-based material in the pore structure of the carbon matrix comprises: The carbon substrate is placed in a mixed gas containing a silicon source and a first protective gas, and a first vapor deposition is performed to deposit the silicon-based material in the pore structure of the carbon substrate.

22. The method for preparing the silicon-carbon composite material according to claim 21, wherein: The first vapor deposition comprises one or more of the following conditions: (1) The temperature of the first vapor deposition is 400° C.-800° C., optionally 500° C.-700° C., and more preferably 500° C.-600° C.; (2) The time of the first vapor deposition is 1 hour to 12 hours, and can be optionally 4 hours to 8 hours; (3) The volume proportion of the silicon source in the mixed gas is 10%-50%; (4) The volume proportion of the first protective gas in the mixed gas is 30%-85%; (5) The positive difference between the pressure of the first vapor deposition and the atmospheric pressure is 200 Pa to 600 Pa; (6) The silicon source includes one or more of monosilane, disilane and trisilane; (7) The first protective gas includes one or more of nitrogen and argon.

23. The method for preparing the silicon-carbon composite material according to any one of claims 21 to 22, wherein: The mixed gas also contains a first carbon source, the volume ratio of the first carbon source in the mixed gas is 5%-20%, the volume ratio of the silicon source to the first carbon source is (2-10):1, and the first carbon source includes one or more of methane, ethylene and acetylene.

24. The method for preparing the silicon-carbon composite material according to any one of claims 14 to 23, wherein: After the step of depositing the silicon-based material in the pore structure of the carbon matrix, the method further comprises: The carbon substrate is placed in a mixed gas containing a second carbon source and a second protective gas, and a second vapor deposition is performed to form the carbon coating layer on at least a portion of the outer surface of the carbon substrate.

25. The method for preparing the silicon-carbon composite material according to claim 24, wherein: The second vapor deposition comprises one or more of the following conditions: (1) The temperature of the second vapor deposition is 500° C.-900° C.; (2) The second vapor deposition time is 1 hour to 6 hours; (3) the volume proportion of the second carbon source in the mixed gas is 5%-50%, and the sum of the volume proportions of the second carbon source and the second protective gas in the mixed gas is 100%; (4) the second carbon source comprises one or more of methane, ethylene and acetylene; (5) The second protective gas includes one or more of nitrogen and argon.

26. A negative electrode plate, comprising: negative electrode current collector; as well as A negative electrode active material layer is located on at least one side of the negative electrode current collector, wherein the negative electrode active material layer comprises the silicon-carbon composite material according to any one of claims 1 to 13 or the silicon-carbon composite material prepared by the method according to any one of claims 14 to 25.

27. A secondary battery comprising the negative electrode sheet according to claim 26.

28. An electric device comprising the secondary battery according to claim 27.

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