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

Abstract

A composite silicon material and a preparation method therefor, a negative electrode sheet, a secondary battery, and an electric device. The composite silicon material comprises an inner core and a silicon-containing coating layer that covers the outer side of the inner core, wherein the inner core comprises a silicon-carbon material, the silicon-carbon material comprising a porous conductive material and a first silicon-based material, the outer surface of the porous conductive material being provided with pores, and at least part of the first silicon-based material being distributed in the pores; and the silicon-containing coating layer comprises an ion-conducting material and a second silicon-based material, the second silicon-based material being dispersed in the ion-conducting material. At least part of the first silicon-based material is embedded in the pores of the porous conductive material, which can effectively alleviate the problem of the expansion of silicon. Moreover, the ion-conducting material can increase ion transport paths, thereby effectively alleviating the problem of deteriorated dynamic performance caused by there being few ion transport paths in the silicon-carbon material. In addition, the fast charging capability and cycling performance of a secondary battery can also be improved.

Description

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

[0001] This application refers to Chinese patent application No. 202311146150.9 filed on September 6, 2023, entitled "Composite silicon material and preparation method thereof, negative electrode plate, secondary battery and electrical device", which is incorporated into this application in its entirety by reference. Technical Field

[0002] The present application relates to the technical field of secondary batteries, and in particular to a composite silicon material and a preparation method thereof, a negative electrode sheet, a secondary battery, and an electrical device. Background Art

[0003] Secondary batteries are widely used in various consumer electronics and electric vehicles due to their outstanding features such as light weight, no pollution, and no memory effect. With the continuous development of the new energy industry, people have put forward increasingly higher requirements for the energy density of secondary batteries.

[0004] Silicon-based anode materials are widely used in secondary batteries due to their high capacity. However, due to silicon's high expansion and poor conductivity, while silicon-based anode materials improve the energy density of secondary batteries, they also lead to expansion and poor kinetics, limiting the further development of battery technology.

[0005] Summary of the Invention

[0006] Based on this, it is necessary to provide a composite silicon material and a preparation method thereof, a negative electrode plate, a secondary battery and an electrical device to alleviate the expansion of the secondary battery and improve the dynamic performance of the secondary battery.

[0007] In order to achieve the above objectives, the first aspect of the present application provides a composite silicon material, comprising:

[0008] a core, the core comprising a silicon-carbon material, the silicon-carbon material including a porous conductive material and a first silicon-based material, the porous conductive material having pores on its outer surface, at least a portion of the first silicon-based material being distributed within the pores; and

[0009] The silicon-containing coating layer is coated on the outer side of the core, and the silicon-containing coating layer comprises an ion-conducting material and a second silicon-based material, wherein the second silicon-based material is dispersed in the ion-conducting material.

[0010] The composite silicon material of the present application includes a silicon-carbon material and a silicon-containing coating layer. The silicon-carbon material includes a porous conductive material with holes on the outer surface and a first silicon-based material. At least part of the first silicon-based material is embedded in the holes of the porous conductive material, which can effectively alleviate the problem of silicon expansion; at the same time, the silicon-containing coating layer contains an ion-conducting material, which can increase the ion transmission path, thereby effectively alleviating the problem of poor kinetic performance caused by the small number of ion transmission paths of the silicon-carbon material.

[0011] In some embodiments, the silicon-containing coating has at least one of the following characteristics:

[0012] (1) The thickness of the silicon-containing coating layer is 5 nm to 100 nm;

[0013] (2) The ion-conducting material includes one or more of hard carbon, soft carbon, graphite, transition metal nitride, silicon-based alloy, tin-based alloy and lithium metal;

[0014] (3) The ion-conducting material and the second silicon-based material are composited into silicon oxide;

[0015] (4) the volume average particle size Dv50 of the second silicon-based material is 2 nm to 20 nm;

[0016] (5) The second silicon-based material includes one or more of elemental silicon and silicon-tin alloy;

[0017] (6) The shape of the second silicon-based material includes one or more of granular, linear, spherical, quasi-spherical and flake-like.

[0018] In some embodiments, the silicon-containing coating layer has a thickness of 30 nm to 60 nm.

[0019] In some embodiments, the molar ratio of oxygen to silicon in the silicon oxide is denoted as x, where 0<x<2.

[0020] In some embodiments, 0<x≤0.6.

[0021] In some embodiments, the volume average particle size Dv50 of the second silicon-based material is 2 nm-9 nm.

[0022] In some embodiments, the silicon-carbon material has at least one of the following characteristics:

[0023] (1) The mass proportion of silicon element in the silicon-carbon material is 3%-25%;

[0024] (2) The pores have a diameter of 2 nm to 50 nm;

[0025] (3) The stacking height of the first silicon-based material in the hole is 1 nm to 35 nm;

[0026] (4) The shape of the silicon-carbon material includes one or more of granular, spherical, and quasi-spherical shapes;

[0027] (5) The first silicon-based material includes one or more of elemental silicon and silicon-tin alloy;

[0028] (6) The shape of the first silicon-based material includes one or more of granular, linear, spherical, quasi-spherical, and flake-shaped;

[0029] (7) The porous conductive material includes porous carbon.

[0030] In some embodiments, the mass proportion of silicon in the silicon-carbon material is 8%-10%.

[0031] In some embodiments, the pores have a diameter of 15 nm to 35 nm.

[0032] In some embodiments, the stacking height of the first silicon-based material in the hole is 15 nm-25 nm.

[0033] In some embodiments, at least 3% of the first silicon-based material is embedded in the pores.

[0034] In some embodiments, all of the first silicon-based material is embedded in the hole.

[0035] In some embodiments, the composite silicon material further includes a first carbon coating layer, wherein the first carbon coating layer is located between the substrate and the silicon-containing coating layer.

[0036] In some embodiments, the first carbon coating layer has at least one of the following characteristics:

[0037] (1) The thickness of the first carbon coating layer is 10 nm to 30 nm;

[0038] (2) The material of the first carbon coating layer includes amorphous carbon.

[0039] In some embodiments, the composite silicon material further includes a second carbon coating layer, wherein the second carbon coating layer is coated on an outer side of the silicon-containing coating layer.

[0040] In some embodiments, the second carbon coating layer has at least one of the following characteristics:

[0041] (1) The thickness of the second carbon coating layer is 10 nm to 30 nm;

[0042] (2) The material of the second carbon coating layer includes amorphous carbon.

[0043] In some embodiments, the composite silicon material has a shape including one or more of granular, spherical, and spheroidal.

[0044] In some embodiments, the volume average particle size Dv50 of the composite silicon material is 3 μm-22 μm.

[0045] In some embodiments, the volume average particle size Dv50 of the composite silicon material is 5 μm-10 μm.

[0046] The second aspect of the present application provides a method for preparing the composite silicon material of the first aspect of the present application, comprising the following steps:

[0047] preparing the silicon-carbon material;

[0048] The silicon-containing coating layer is formed on the outer side of the silicon-carbon material.

[0049] The third aspect of the present application provides a method for preparing the composite silicon material of the first aspect of the present application, comprising the following steps:

[0050] preparing the silicon-carbon material;

[0051] forming a silicon dioxide coating layer on the outer side of the silicon-carbon material to prepare an intermediate with a silicon dioxide coating layer;

[0052] The intermediate is reduced to form the silicon-containing coating layer on the outer side of the silicon-carbon material.

[0053] In some embodiments, the silicon-carbon material is prepared by a vapor deposition method; the vapor deposition method includes at least one of the following conditions:

[0054] (1) The raw materials for preparing the silicon-carbon material include a porous conductive material and a first silicon source;

[0055] The molar ratio of the porous conductive material to the first silicon source is (3-8):1;

[0056] The first silicon source includes monosilane;

[0057] The porous conductive material includes porous carbon;

[0058] (2) The reaction temperature of the vapor deposition method is 800°C-900°C, and the reaction time is 2h-8h;

[0059] (3) The reaction atmosphere of the vapor deposition method includes an inert gas.

[0060] In some embodiments, a hydrothermal method is used to form a silicon dioxide coating layer on the outside of the silicon-carbon material; the hydrothermal method includes at least one of the following conditions:

[0061] (1) The raw materials for preparing the silicon dioxide coating layer include a second silicon source;

[0062] The second silicon source includes ethyl orthosilicate;

[0063] The mass ratio of the silicon-carbon material to the second silicon source is 3:(1-5);

[0064] (2) The reaction temperature of the hydrothermal method is 110°C-130°C, and the reaction time is 0.5h-5h;

[0065] (3) The reaction medium of the hydrothermal method includes a mixture of ethanol and water;

[0066] The volume ratio of ethanol to water in the mixed solution is (2-4):1.

[0067] In some embodiments, the intermediate is reduced using a magnesium thermal reduction method; the magnesium thermal reduction method includes at least one of the following conditions:

[0068] (1) The reducing agent used includes magnesium powder;

[0069] The mass ratio of the intermediate to the magnesium powder is (2-4):1;

[0070] (2) The reaction temperature of the magnesium thermal reduction method is 600°C-750°C, and the reaction time is 0.5h-10h.

[0071] In some embodiments, before the step of forming a silicon dioxide coating layer on the outer side of the silicon-carbon material, the method further comprises: using a first carbon source to prepare a first carbon coating layer on the outer side of the silicon-carbon material;

[0072] The preparation of the first carbon coating layer includes at least one of the following conditions:

[0073] (1) The first carbon source includes acetylene;

[0074] (2) adding a first dilution gas when preparing the first carbon coating layer, wherein the first dilution gas includes argon;

[0075] The volume ratio of the first carbon source to the first dilution gas is (0.5-2):9;

[0076] (3) The reaction temperature is 600°C-800°C, and the reaction time is 0.5h-2h.

[0077] In some embodiments, the preparation method further comprises: using a second carbon source to form a second carbon coating layer on the outer side of the silicon-containing coating layer;

[0078] The preparation of the second carbon coating layer includes at least one of the following conditions:

[0079] (1) The second carbon source includes acetylene;

[0080] (2) adding a second dilution gas when preparing the second carbon coating layer, wherein the second dilution gas includes argon;

[0081] The volume ratio of the second carbon source to the second dilution gas is (0.5-2):9;

[0082] (3) The reaction temperature is 600°C-800°C, and the reaction time is 0.5h-2h.

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

[0084] a negative electrode current collector; and

[0085] The 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 composite silicon material of the first aspect of the present application or the composite silicon material prepared by the method of the second aspect of the present application or the method of the third aspect of the present application.

[0086] The fifth aspect of the present application provides a secondary battery, comprising the negative electrode sheet of the fourth aspect of the present application.

[0087] A sixth aspect of the present application provides an electrical device comprising the secondary battery of the fifth aspect of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0088] To more clearly illustrate the technical solution of this application, the following is a brief introduction to the drawings used in this application. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without inventive effort.

[0089] FIG1 is a schematic diagram of a secondary battery according to an embodiment of the present application.

[0090] FIG. 2 is an exploded view of the secondary battery according to the embodiment of the present application shown in FIG. 1 .

[0091] FIG3 is a schematic diagram of an electric device using a secondary battery as a power source according to an embodiment of the present application.

[0092] FIG4 is a SEM image of a cross section of the composite silicon material in Example 1. FIG.

[0093] Description of reference numerals: 1 secondary battery; 11 housing; 12 electrode assembly; 13 cover plate; 2 power-consuming device. DETAILED DESCRIPTION

[0094] To facilitate understanding of the present application, a more comprehensive description of the present application will be provided below with reference to the accompanying drawings. The accompanying drawings illustrate preferred embodiments of the present application. However, the present application may be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and comprehensive understanding of the disclosure of the present application.

[0095] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application pertains. The terms used herein in the specification of this application are for the purpose of describing specific embodiments only and are not intended to limit this application.

[0096] In this application, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0097] In this application, when referring to numerical ranges, unless otherwise specified, the numerical ranges are considered continuous and include the minimum and maximum values ​​of the range, as well as every value between such minimum and maximum values. Further, when a range refers to an integer, every integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe a feature or characteristic, the ranges can be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges subsumed therein.

[0098] In this application, when referring to a range of units, if only the right endpoint is followed by a unit, it means that the units of the left and right endpoints are the same. For example, 10-1000nm means that the units of the left endpoint "10" and the right endpoint "1000" are both nm (nanometers).

[0099] In this application, references to "multiple," "multiple," and "multiple times," etc., unless otherwise specified, refer to a number greater than or equal to 2. For example, "multiple" means greater than or equal to two. Only some numerical ranges are specifically disclosed herein. However, any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range, and similarly, any upper limit can be combined with any other upper limit to form an unspecified range. In addition, each individually disclosed point or single value can itself be combined as a lower limit or upper limit with any other point or single value, or with other lower limits or upper limits, to form an unspecified range.

[0100] The "ranges" disclosed herein are defined in terms of lower and upper limits. A given range is defined by selecting a lower limit and an upper limit, and the selected lower and upper limits define the boundaries of the particular range. Ranges defined in this manner may be inclusive or exclusive of the end values.

[0101] The temperature parameters in this application, unless otherwise specified, allow for both constant temperature treatment and treatment within a certain temperature range. The constant temperature treatment allows for temperature fluctuations within the precision range of instrument control.

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

[0103] Unless otherwise specified, all steps of the present application can be performed sequentially or randomly, preferably sequentially.

[0104] Silicon-based negative electrode materials are widely used in secondary batteries. However, due to the high expansion characteristics of silicon, its few ion transmission paths and poor conductivity, secondary batteries using silicon-based negative electrode materials in related technologies have problems with expansion and poor kinetic performance while improving energy density.

[0105] Based on the above problems, the present application combines a silicon-containing coating layer containing an ion-conducting material and a silicon-carbon material. The silicon-carbon material includes a porous conductive material with holes on the outer surface and a first silicon-based material, and at least part of the first silicon-based material is embedded in the holes. The holes can provide space for the expansion of the first silicon-based material, thereby alleviating the problem of the overall volume of the composite silicon material increasing due to the expansion of the first silicon-based material; and the ion-conducting material in the silicon-containing coating layer located on the outside of the silicon-carbon material can increase the ion transmission path, thereby improving the kinetic performance of the composite silicon material.

[0106] The first aspect of the present application provides a composite silicon material, including an inner core and a silicon-containing coating layer coated on the outside of the inner core; the inner core contains a silicon-carbon material, the silicon-carbon material includes a porous conductive material and a first silicon-based material, the outer surface of the porous conductive material has holes, and at least part of the first silicon-based material is distributed in the holes; the silicon-containing coating layer contains an ion-conducting material and a second silicon-based material, and the second silicon-based material is dispersed in the ion-conducting material.

[0107] It should be noted that the "first silicon-based material" in this application is used for descriptive purposes only and cannot be understood as indicating or implying relative importance or quantity, nor can it be understood as implicitly indicating the importance or quantity of the indicated technical features.

[0108] A porous conductive material refers to a conductive material having pores on its surface and / or interior. The number of pores in a porous conductive material can be one or more. The first silicon-based material in the silicon-carbon material can be entirely distributed within the pores of the porous conductive material, or only partially distributed within the pores of the porous conductive material.

[0109] The ion-conducting material may include a material that has ion-conducting ability itself, or may include a material that can form a compound with ion-conducting properties after further reaction; for example, the ion-conducting material may include a material that can form a compound with ion-conducting properties during the battery charging process, etc., and is not specifically limited. The silicon-containing coating layer may be a continuous and complete coating layer, or it may be an incomplete coating layer; wherein, "complete" means that the substance located on the inner side of the silicon-containing coating layer is completely coated by the silicon-containing coating layer, and the silicon-containing coating layer completely isolates the substance inside it from the outside. "Incomplete" means that the substance located on the inner side of the silicon-containing coating layer is not completely coated by the silicon-containing coating layer, and the substance inside the silicon-containing coating layer can at least partially contact the outside of the silicon-containing coating layer. Preferably, the silicon-containing coating layer is a continuous and complete coating layer.

[0110] Understandably, the composite silicon material of this application includes a silicon-carbon material and an ion-conducting material. The silicon-carbon material includes a porous conductive material with pores on its outer surface and a first silicon-based material. At least a portion of the first silicon-based material is embedded in the pores of the porous conductive material, which can effectively alleviate the problem of silicon expansion. At the same time, the ion-conducting material can increase the ion transmission path, thereby effectively alleviating the problem of poor dynamic performance caused by the limited ion transmission path of the silicon-carbon material. In addition, it can also improve the fast charging capability and cycle performance of the secondary battery.

[0111] In some embodiments, the thickness of the silicon-containing coating layer is 5nm-100nm. When the thickness of the silicon-containing coating layer is lower than the above range, the increase in the ion transport path is limited, and the dynamic performance of the composite silicon material is poor; when the thickness of the silicon-containing coating layer is higher than the above range, the silicon content of the composite silicon material is too high, so that the composite silicon material expands too much, which may cause the SEI film on the surface of the composite silicon material to rupture, exposing new sites. The electrolyte continues to repair the SEI film at the damaged interface, consuming active lithium, affecting the cycle performance of the battery cell; at the same time, the expansion of the composite silicon material will deteriorate the energy density of the battery cell. As an example, the thickness of the silicon-containing coating layer can be, but is not limited to, 5nm, 10nm, 15nm, 20nm, 25nm, 30nm, 35nm, 40nm, 45nm, 50nm, 55nm, 60nm, 65nm, 70nm, 75nm, 80nm, 85nm, 90nm, 95nm, 100nm, or a range between any two of the above values. Optionally, the thickness of the silicon-containing coating layer is 30nm-60nm.

[0112] As an example, the thickness of the aforementioned silicon-containing coating layer can be measured by transmission electron microscopy (TEM).

[0113] In some embodiments, the ion-conducting material includes one or more of hard carbon, soft carbon, graphite, transition metal nitrides, silicon-based alloys, tin-based alloys, and lithium metal.

[0114] In some embodiments, the ion-conducting material and the second silicon-based material are compounded into silicon oxide; silicon oxide refers to a compound containing both silicon and oxygen elements; when the ion-conducting material and the second silicon-based material can be compounded into silicon oxide, the ion-conducting material is silicon dioxide, and the second silicon-based material is dispersed in the ion-conducting material; during the charging process, silicon dioxide can undergo an electrochemical reaction with lithium released from the positive electrode active material to form lithium silicate with ion conductive properties.

[0115] In some optional embodiments, the molar ratio of oxygen to silicon contained in silicon oxide is denoted as x, 0<x<2. When the molar ratio of oxygen to silicon contained in silicon oxide is within the above range, the larger the value of x, the smaller the volume expansion of silicon oxide, but its gram capacity is also lower; the smaller the value of x, the higher the gram capacity of silicon oxide, but its volume expansion is also larger. As an example, the molar ratio of oxygen to silicon contained in silicon oxide can be, but is not limited to, 0.01, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 1.95, 1.99 or a range between any two of the above values. Optionally, 0<x≤0.6. As an example, the molar ratio of oxygen and silicon in the silicon oxide mentioned above can be determined by the following method: performing X-ray energy dispersive spectroscopy (EDS) on the composite silicon material, deducting the silicon content in the silicon-carbon material, and qualitatively determining the x value in the silicon oxide.

[0116] It should be noted that the "second silicon-based material" in this application is used for descriptive purposes only and cannot be understood as indicating or implying relative importance or quantity, nor can it be understood as implicitly indicating the importance or quantity of the indicated technical features.

[0117] In some optional embodiments, the volume average particle size Dv50 of the second silicon-based material is 2nm-20nm; when the volume average particle size Dv50 of the second silicon-based material is within the above range, the strain caused by different lithium concentrations is smaller, and it can withstand greater strain without breaking; in addition, the second silicon-based material has a larger active specific surface area and relatively good dynamics. As an example, the volume average particle size Dv50 of the second silicon-based material can be, but is not limited to, 2nm, 3nm, 4nm, 5nm, 6nm, 7nm, 8nm, 9nm, 10nm, 11nm, 12nm, 13nm, 14nm, 15nm, 16nm, 17nm, 18nm, 19nm, 20nm, or a range between any two of the above values. Optionally, the volume average particle size Dv50 of the second silicon-based material is 2nm-9nm.

[0118] As an example, the volume average particle size Dv50 of the second silicon-based material mentioned above can be measured with reference to GB / T 19077-2016 Particle Size Distribution Laser Diffraction Method using a laser particle size analyzer, such as the Mastersizer 2000E laser particle size analyzer produced by Malvern Instruments Ltd. in the United Kingdom.

[0119] In some embodiments, the second silicon-based material includes one or more of elemental silicon and a silicon-tin alloy.

[0120] In some embodiments, the second silicon-based material has a shape including one or more of particles, wires, spheres, spherical shapes, and flakes.

[0121] In some embodiments, the mass proportion of silicon in the silicon-carbon material is 3%-25%; when the mass proportion of silicon in the silicon-carbon material is within the above range, the silicon-carbon material has a higher gram capacity and its electrochemical performance is relatively stable, and the cycle life is better; when the content of silicon increases further, the conductivity of the silicon-carbon material particles drops sharply, thereby causing capacity decay. As an example, the mass proportion of silicon in the silicon-carbon material can be but is not limited to 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25% or a range between any two of the above values. Optionally, the mass proportion of silicon in the silicon-carbon material is 8%-10%.

[0122] As an example, the mass ratio of silicon element in silicon-carbon material can be qualitatively determined using EDS energy spectrum.

[0123] In some embodiments, the pores of the porous conductive material have a pore size of 2nm-50nm; when the pore size of the porous conductive material is within the above range, while providing expansion space, it can minimize the deterioration of the compaction density caused by the porous conductive material having internal reserved holes, thereby improving the energy density. As an example, the pore size of the porous conductive material can be, but is not limited to, 2nm, 5nm, 8nm, 10nm, 13nm, 15nm, 18nm, 20nm, 23nm, 25nm, 27nm, 30nm, 33nm, 35nm, 38nm, 40nm, 43nm, 45nm, 47nm, 50nm, or a range between any two of the above values. Optionally, the pore size of the porous conductive material is 15nm-35nm.

[0124] It should be noted that when the porous conductive material has only a single hole, the pore size of the hole refers to the pore size of the single hole; when the porous conductive material has multiple holes, the pore size of the hole refers to the average pore size of the holes.

[0125] As an example, the pore diameters mentioned above can be measured using a specific surface area analysis tester with reference to the gas adsorption BET method specified in GB / T 19587-2017.

[0126] In some embodiments, the stacking height of the first silicon-based material in the pore is 1nm-35nm; when the stacking height of the first silicon-based material in the pore is within the above range, the silicon-carbon material has a higher gram capacity while its electrochemical performance is relatively stable and the cycle life is better; when the stacking height of the first silicon-based material in the pore is further increased, the conductivity of the silicon-carbon material particles drops sharply, thereby causing capacity decay. As an example, the stacking height of the first silicon-based material in the pore can be, but is not limited to, 1nm, 3nm, 5nm, 8nm, 10nm, 13nm, 15nm, 17nm, 20nm, 23nm, 25nm, 28nm, 30nm, 33nm, 35nm or a range between any two of the above values. Optionally, the stacking height of the first silicon-based material in the pore is 15nm-25nm.

[0127] It should be noted that the accumulation height of the first silicon-based material within the hole refers to the accumulation thickness of the first silicon-based material along the depth of the hole. When all of the first silicon-based materials fall within the same hole, the accumulation height of the first silicon-based material within the hole is the height of the first silicon-based material accumulated in that hole. When the first silicon-based material falls within multiple holes, the accumulation height of the first silicon-based material within the hole refers to the average accumulation height of the first silicon-based material within the hole.

[0128] As an example, the stacking height of the aforementioned first silicon-based material in the pores can be measured using a transmission electron microscope (TEM).

[0129] As a possible implementation manner, the shape of the silicon-carbon material includes one or more of granular, spherical, and quasi-spherical shapes.

[0130] In some embodiments, the first silicon-based material includes one or more of elemental silicon and a silicon-tin alloy.

[0131] In some embodiments, the shape of the first silicon-based material includes one or more of particles, wires, spheres, spherical shapes, and flakes.

[0132] In some embodiments, the porous conductive material comprises porous carbon.

[0133] In some embodiments, at least 3% of the first silicon-based material is embedded in the pores.

[0134] Optionally, all of the first silicon-based materials are embedded in the holes; this can further reduce the volume expansion of the composite silicon material.

[0135] As a possible implementation, the composite silicon material also includes a first carbon coating layer, which is located between the substrate and the silicon-containing coating layer; the first carbon coating layer can act as a fast-charging ion ring, improve the kinetic properties of the composite silicon material, and reduce the contact between the silicon-carbon material and the electrolyte.

[0136] It should be noted that the “first carbon coating layer” in this application is used for descriptive purposes only and cannot be understood as indicating or implying relative importance or quantity, nor can it be understood as implicitly indicating the importance or quantity of the indicated technical features.

[0137] In some optional embodiments, the thickness of the first carbon coating layer is 10nm-30nm; when the thickness of the first carbon coating layer is within the above range, the silicon-carbon material has a higher gram capacity while its electrochemical performance is relatively stable and the cycle life is better; when the thickness of the first carbon coating layer is further increased, the conductivity of the silicon-carbon material particles drops sharply, thereby causing capacity decay. As an example, the thickness of the first carbon coating layer can be, but is not limited to, 10nm, 11nm, 12nm, 13nm, 14nm, 15nm, 16nm, 17nm, 18nm, 19nm, 20nm, 21nm, 22nm, 23nm, 24nm, 25nm, 26nm, 27nm, 28nm, 29nm, 30nm or a range between any two of the above values.

[0138] As an example, the thickness of the first carbon coating layer mentioned above can be measured using a transmission electron microscope (TEM).

[0139] In some optional embodiments, the material of the first carbon coating layer includes amorphous carbon. Using amorphous carbon as the material of the first carbon coating layer has better ionic conductivity and can also prevent the silicon-based material from directly contacting the electrolyte, thereby reducing side reactions.

[0140] In some embodiments, the composite silicon material further includes a second carbon coating layer, which is coated on the outside of the silicon-containing coating layer; the second carbon coating layer can act as a fast-charging ion ring, improve the kinetic properties of the composite silicon material, and reduce the contact between the silicon-containing coating layer and the electrolyte.

[0141] It should be noted that the “second carbon coating layer” in this application is used for descriptive purposes only and cannot be understood as indicating or implying relative importance or quantity, nor can it be understood as implicitly indicating the importance or quantity of the indicated technical features.

[0142] Optionally, the thickness of the second carbon coating layer is 10 nm to 30 nm. When the thickness of the second carbon coating layer is within the above range, the second carbon coating layer has good ionic conductivity and high mechanical strength, can tolerate the expansion of the silicon material to a large extent without cracking, and reduces the occurrence of side reactions. As an example, the thickness of the second carbon coating layer can be, but is not limited to, 10 nm, 11 nm, 12 nm, 13 nm, 14 nm, 15 nm, 16 nm, 17 nm, 18 nm, 19 nm, 20 nm, 21 nm, 22 nm, 23 nm, 24 nm, 25 nm, 26 nm, 27 nm, 28 nm, 29 nm, 30 nm, or a range between any two of the above values.

[0143] As an example, the thickness of the second carbon coating layer mentioned above can be measured using a transmission electron microscope (TEM).

[0144] Optionally, the material of the second carbon coating layer includes amorphous carbon. When amorphous carbon is used as the material of the second carbon coating layer, the second carbon coating layer has better ionic conductivity and can also block direct contact between the silicon-based material and the electrolyte, thereby reducing side reactions.

[0145] In some possible embodiments, the composite silicon material has a shape including one or more of granular, spherical, and quasi-spherical.

[0146] In some optional embodiments, the volume average particle size Dv50 of the composite silicon material is 3 μm-22 μm. When the volume average particle size Dv50 of the composite silicon material is within the above range, it has a greater compaction density and a larger active specific surface area. As an example, the volume average particle size Dv50 of the composite silicon material can be, but is not limited to, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, 21 μm, 22 μm, or a range between any two of the above values. Optionally, the volume average particle size Dv50 of the composite silicon material is 5 μm-10 μm.

[0147] Dv50 refers to the particle size at which the cumulative particle size distribution percentage reaches 50% by volume. For example, Dv50 can be conveniently measured using a laser particle size analyzer, such as the Mastersizer 2000E laser particle size analyzer from Malvern Instruments Ltd. in the United Kingdom, in accordance with GB / T 19077-2016, Particle Size Distribution - Laser Diffraction Method.

[0148] In some embodiments, the composite silicon material comprises:

[0149] The inner core comprises a silicon-carbon material, the silicon-carbon material comprises a porous conductive material and a first silicon-based material, the outer surface of the porous conductive material has holes, and at least part of the first silicon-based material is embedded in the holes; the mass proportion of silicon element in the silicon-carbon material is 3%-25%, and can be optionally 8%-10%; the pore diameter is 2nm-50nm, and can be optionally 15nm-35nm; the stacking height of the first silicon-based material in the hole is 1nm-35nm, and can be optionally 15nm-25nm; the shape of the silicon-carbon material includes one or more of granular, spherical and quasi-spherical; the first silicon-based material includes one or more of elemental silicon and silicon-tin alloy; the shape of the first silicon-based material includes one or more of granular, linear, spherical, quasi-spherical and flake; the porous conductive material includes porous carbon; at least 3% of the first silicon granular silicon-based material is embedded in the holes;

[0150] a first carbon coating layer, coating at least a portion of the outer surface of the substrate, the first carbon coating layer having a thickness of 10 nm to 30 nm, and the material of the first carbon coating layer includes amorphous carbon;

[0151] a silicon-containing coating layer coated on at least a portion of the outer surface of the first carbon coating layer, the silicon-containing coating layer comprising an ion-conducting material and a second silicon-based material, wherein the second silicon-based material is dispersed in the ion-conducting material; the silicon-containing coating layer has a thickness of 5 nm to 100 nm, optionally 30 nm to 60 nm; the volume average particle size Dv50 of the second silicon-based material is 2 nm to 20 nm, optionally 2 nm to 9 nm; the second silicon-based material comprises one or more of elemental silicon and a silicon-tin alloy; the shape of the second silicon-based material comprises one or more of particles, lines, spheres, quasi-spherical shapes, and flakes; the ion-conducting material comprises one or more of hard carbon, soft carbon, graphite, transition metal nitrides, silicon-based alloys, tin-based alloys, and lithium metal; or the ion-conducting material and the second silicon-based material are composited into silicon oxide, wherein the molar ratio of oxygen to silicon in the silicon oxide is denoted by x, 0<x<2, optionally 0<x≤0.6; and

[0152] a second carbon coating layer coated on at least a portion of the outer surface of the silicon-containing coating layer, the second carbon coating layer having a thickness of 10 nm to 30 nm, and the material of the second carbon coating layer comprising amorphous carbon;

[0153] The shape of the composite silicon material includes one or more of granular, spherical and quasi-spherical shapes; the volume average particle size Dv50 of the composite silicon material is 3 μm-22 μm, and can be optionally 5 μm-10 μm.

[0154] The second aspect of the present application provides a method for preparing the composite silicon material of the first aspect, comprising the following steps: preparing a silicon-carbon material; and forming a silicon-containing coating layer on the outside of the silicon-carbon material.

[0155] The third aspect of the present application provides a method for preparing the composite silicon material of the first aspect, comprising the following steps: preparing a silicon-carbon material; forming a silicon dioxide coating layer on the outside of the silicon-carbon material to prepare an intermediate with a silicon dioxide coating layer; and reducing the intermediate to form a silicon-containing coating layer on the outside of the silicon-carbon material.

[0156] In some embodiments, the silicon-carbon material is prepared using a vapor deposition method. This method can help increase the proportion of the first silicon-based material embedded in the pores of the porous conductive material in the final silicon-carbon material, and can even allow all of the first silicon-based material to be deposited in the pores of the porous conductive material.

[0157] In some embodiments, the raw materials for preparing the silicon-carbon material include a porous conductive material and a first silicon source.

[0158] In some optional embodiments, the molar ratio of the porous conductive material to the first silicon source is (3-8):1; as an example, the molar ratio of the porous conductive material to the first silicon source can be but is not limited to 3:1, 3.5:1, 4:1, 4.5:1, 5:1, 5.5:1, 6:1, 6.5:1, 7:1, 7.5:1, 8:1 or a range between any two of the above ratios.

[0159] In some alternative embodiments, the first silicon source comprises monosilane.

[0160] In some alternative embodiments, the porous conductive material comprises porous carbon.

[0161] In some embodiments, the reaction temperature of the vapor deposition method is 800° C.-900° C., such as, but not limited to, 800° C., 810° C., 820° C., 830° C., 840° C., 850° C., 860° C., 870° C., 880° C., 890° C., 900° C., or a range between any two of the foregoing values. The reaction time is 2 h-8 h, such as, but not limited to, 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h, 5 h, 5.5 h, 6 h, 6.5 h, 7 h, 7.5 h, 8 h, or a range between any two of the foregoing values.

[0162] In some embodiments, the reaction atmosphere of the vapor deposition method includes an inert gas; alternatively, the reaction atmosphere of the vapor deposition method includes argon.

[0163] In some embodiments, a hydrothermal method is used to form a silicon dioxide coating layer on the outside of the silicon-carbon material.

[0164] In some optional embodiments, the raw materials for preparing the silicon dioxide coating layer include a second silicon source.

[0165] Optionally, the second silicon source includes tetraethyl orthosilicate.

[0166] Optionally, the mass ratio of the silicon-carbon material to the second silicon source is 3:(1-5); for example, it can be but is not limited to 3:1, 3:1.5, 3:2, 3:2.5, 3:3, 3:3.5, 3:4, 3:4.5, 3:5 or a range between any two of the above ratios.

[0167] As a possible embodiment, the reaction temperature of the hydrothermal method is 110°C-130°C; for example, it can be, but not limited to, 110°C, 112°C, 115°C, 118°C, 120°C, 122°C, 125°C, 128°C, 130°C, or a range between any two of the above values. The reaction time is 0.5h-5h; for example, it can be, but not limited to, 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, or a range between any two of the above values.

[0168] In some embodiments, the reaction medium of the hydrothermal method includes a mixture of ethanol and water.

[0169] Optionally, the volume ratio of ethanol to water in the mixture is (2-4): 1. As an example, the volume ratio of ethanol to water in the mixture can be, but is not limited to, 2:1, 2.3:1, 2.5:1, 2.7:1, 3:1, 3.3:1, 3.5:1, 3.8:1, 4:1, or a range between any two of the above ratios.

[0170] In some embodiments, the intermediate is reduced using magnesium thermal reduction.

[0171] As a possible implementation, the reducing agent used includes magnesium powder.

[0172] Optionally, the mass ratio of the intermediate to the magnesium powder is (2-4):1; as an example, the mass ratio of the intermediate to the magnesium powder can be but is not limited to 2:1, 2.3:1, 2.5:1, 2.7:1, 3:1, 3.3:1, 3.5:1, 3.8:1, 4:1 or a range between any two of the above ratios.

[0173] As a possible embodiment, the reaction temperature of the magnesium thermal reduction method is 600°C-750°C; for example, it can be but not limited to 600°C, 610°C, 620°C, 630°C, 640°C, 650°C, 660°C, 670°C, 680°C, 690°C, 700°C, 710°C, 720°C, 730°C, 740°C, 750°C, or a range between any two of the above values. The reaction time is 0.5h-10h; for example, it can be but not limited to 0.5h, 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, or a range between any two of the above values.

[0174] In some embodiments, before the step of forming a silicon dioxide coating layer on the outer side of the silicon-carbon material, the method further includes: using a first carbon source to prepare a first carbon coating layer on the outer side of the silicon-carbon material.

[0175] Optionally, the first carbon source comprises acetylene.

[0176] In some optional embodiments, a first dilution gas is further added when preparing the first carbon coating layer, and the first dilution gas includes an inert gas.

[0177] Optionally, the first dilution gas includes argon.

[0178] Optionally, the volume ratio of the first carbon source to the first dilution gas is (0.5-2):9; for example, it can be but is not limited to 0.5:9, 0.8:9, 1:9, 1.3:9, 1.5:9, 1.7:9, 2:9 or a range between any two of the above values.

[0179] In some embodiments, the reaction temperature for preparing the first carbon coating layer is 600° C.-800° C., for example, but not limited to, 600° C., 620° C., 650° C., 680° C., 700° C., 730° C., 750° C., 770° C., 800° C., or a range between any two of the foregoing values. The reaction time is 0.5 h-2 h, for example, but not limited to, 0.5 h, 0.7 h, 1 h, 1.3 h, 1.5 h, 1.8 h, 2 h, or a range between any two of the foregoing values.

[0180] In some embodiments, a hydrothermal method is used to form a silicon dioxide coating layer on the outside of the first carbon coating layer.

[0181] In some optional embodiments, the raw materials for preparing the silicon dioxide coating layer include a second silicon source.

[0182] Optionally, the second silicon source includes tetraethyl orthosilicate.

[0183] Optionally, the mass ratio of the silicon-carbon material coated with the first carbon coating layer and the second silicon source is 3:(1-5); for example, it can be but is not limited to 3:1, 3:1.5, 3:2, 3:2.5, 3:3, 3:3.5, 3:4, 3:4.5, 3:5 or a range between any two of the above ratios.

[0184] As a possible embodiment, the reaction temperature of the hydrothermal method is 110°C-130°C; for example, it can be, but not limited to, 110°C, 112°C, 115°C, 118°C, 120°C, 122°C, 125°C, 128°C, 130°C, or a range between any two of the above values. The reaction time is 0.5h-5h; for example, it can be, but not limited to, 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, or a range between any two of the above values.

[0185] In some embodiments, the reaction medium of the hydrothermal method includes a mixture of ethanol and water.

[0186] Optionally, the volume ratio of ethanol to water in the mixture is (2-4): 1. As an example, the volume ratio of ethanol to water in the mixture can be, but is not limited to, 2:1, 2.3:1, 2.5:1, 2.7:1, 3:1, 3.3:1, 3.5:1, 3.8:1, 4:1, or a range between any two of the above ratios.

[0187] In some embodiments, the preparation method further comprises: using a second carbon source to form a second carbon coating layer on the outside of the silicon-containing coating layer.

[0188] Optionally, the second carbon source comprises acetylene.

[0189] In some optional embodiments, a second dilution gas is further added when preparing the second carbon coating layer, and the second dilution gas includes an inert gas.

[0190] Optionally, the second dilution gas includes argon.

[0191] Optionally, the volume ratio of the second carbon source and the second dilution gas is (0.5-2):9; for example, it can be but not limited to 0.5:9, 0.8:9, 1:9, 1.3:9, 1.5:9, 1.7:9, 2:9 or a range between any two of the above values.

[0192] In some embodiments, the reaction temperature for preparing the second carbon coating layer is 600° C.-800° C., for example, but not limited to, 600° C., 620° C., 650° C., 680° C., 700° C., 730° C., 750° C., 770° C., 800° C., or a range between any two of the foregoing values. The reaction time is 0.5 h-2 h, for example, but not limited to, 0.5 h, 0.7 h, 1 h, 1.3 h, 1.5 h, 1.8 h, 2 h, or a range between any two of the foregoing values.

[0193] It should be noted that the “first silicon source”, “second silicon source”, “first carbon source”, “second carbon source”, “first dilution gas” and “second dilution gas” in this application are used for descriptive purposes only 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.

[0194] It should be noted that when the ion-conducting material and the second silicon-based material can be compounded into silicon oxide, before the step of preparing the second carbon coating layer, after the silicon-containing coating layer is coated, it can be mixed with a lithium replenisher so that the silicon dioxide in the silicon-containing coating layer and the lithium replenisher undergo an electrochemical reaction to form lithium silicate with ion conductivity.

[0195] In some embodiments, a method for preparing a composite silicon material includes:

[0196] A silicon-carbon material is prepared by vapor deposition using a porous conductive material and a first silicon source as raw materials; the molar ratio of the porous conductive material to the first silicon source is (3-8):1, the first silicon source includes monosilane, the reaction temperature of the vapor deposition method is 800° C.-900° C., the reaction time is 2 h-8 h, and the reaction atmosphere of the vapor deposition method includes an inert gas;

[0197] A first carbon coating layer is prepared on the outer side of the silicon-carbon material using a first carbon source; the first carbon source includes acetylene; a first diluent gas is added during the preparation of the first carbon coating layer, the first diluent gas includes an inert gas; the first diluent gas includes argon, and the volume ratio of the first carbon source to the first diluent gas is (0.5-2):9; the reaction temperature is 600° C.-800° C., and the reaction time is 0.5 h-2 h;

[0198] A silica coating layer is formed on the outer side of a silicon-carbon material coated with a first carbon coating layer by a hydrothermal method to prepare an intermediate with a silica coating layer; the raw materials for preparing the silica coating layer include a second silicon source; the second silicon source includes ethyl orthosilicate; the mass ratio of the silicon-carbon material coated with the first carbon coating layer to the second silicon source is 3:(1-5); the reaction temperature of the hydrothermal method is 110° C.-130° C., and the reaction time is 0.5 h-5 h; the reaction medium of the hydrothermal method includes a mixture of ethanol and water, and the volume ratio of ethanol to water in the mixture is (2-4):1;

[0199] The intermediate is reduced by a magnesium thermal reduction method to form a silicon-containing coating layer on the outer side of the first carbon coating layer; the reducing agent used includes magnesium powder, and the mass ratio of the intermediate to the magnesium powder is (2-4):1; the reaction temperature of the magnesium thermal reduction method is 600°C-750°C, and the reaction time is 0.5h-10h;

[0200] A second carbon source is used to form a second carbon coating layer on the outside of the silicon-containing coating layer; the second carbon source includes acetylene; a second dilution gas is also added when preparing the second carbon coating layer, and the second dilution gas includes an inert gas; the second dilution gas includes argon; the volume ratio of the second carbon source to the second dilution gas is (0.5-2):9; the reaction temperature is 600°C-800°C, and the reaction time is 0.5h-2h.

[0201] In some embodiments, a method for preparing a composite silicon material includes:

[0202] The porous conductive material is placed in a rotary kiln, the rotation speed is adjusted to 1r / min-15r / min, and the first silicon source is injected at a flow rate of 0.1L / min-0.6L / min for 10min-40min. After heating to 800℃-900℃, the temperature is kept for 2h-8h to obtain a silicon-carbon material; after cooling, argon is introduced into the rotary kiln for 30min, and the temperature is increased to 600℃-800℃ at 5℃ / min-15℃ / min, and the temperature is kept for 0.5h-2h; then the gas is switched to a mixed gas of the first carbon source and the first dilution gas with a volume ratio of (0.5-2):9, and the mixture is kept for 30min-120min. After cooling, C@Si-C is obtained;

[0203] The silicon-carbon material coated with the first carbon coating layer was dissolved in 100 ml of an ethanol-water solution with a volume ratio of (2-4):1, a second silicon source was added, and the mixture was stirred thoroughly for 30 minutes. The mixture was then added to a 200 ml polytetrafluoroethylene-lined autoclave, heated to 110°C-130°C, kept warm for 0.5-5 hours, and then naturally cooled to room temperature. The resulting solution was centrifuged, repeatedly washed with anhydrous ethanol, and vacuum-dried at 60°C for 12 hours to obtain SiO2@C@Si-C.

[0204] SiO2@first carbon coating layer@silicon-carbon material and Mg powder are mixed in a mass ratio of (2-4):1, fully ground and mixed in a mortar, heated in a 600℃-750℃ tube furnace in an inert gas atmosphere for 0.5h-10h, cooled to room temperature, washed with 0.5M hydrochloric acid to remove MgO and unreacted Mg, and then washed with deionized water until neutral, and then vacuum dried at 70℃ for 12h; then placed in a rotary kiln, purged with argon for 30min, heated to 700℃ at 10℃ / min, and then the gas was switched to a mixed gas of the second carbon source and the second dilution gas with a volume ratio of (0.5-2):9, kept warm for 30min-120min, and cooled to obtain a C / SiOx@C / Si-C composite material.

[0205] It should be noted that C@Si-C means that a first carbon coating layer is coated on the outside of the silicon-carbon material; SiO2@C@Si-C means that a silicon dioxide coating layer is further coated on the outside of the first carbon coating layer; C / SiOx@C / Si-C means that a silicon-containing coating layer is formed outside the first carbon coating layer, and a second carbon coating layer is formed outside the silicon-containing coating layer.

[0206] The fourth aspect of the present application 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 composite silicon material of the first aspect of the present application or the composite silicon material prepared by the method of the second aspect of the present application.

[0207] The negative electrode plate made of the composite silicon material mentioned above is used in this application, and its plate rebound rate after full charge is significantly reduced, indicating that the volume expansion degree of the negative electrode plate is significantly reduced.

[0208] As an example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0209] 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 formed by forming a metal material on a polymer material substrate. Among them, the metal material includes but is not limited to copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver and silver alloys, etc., and the polymer material substrate includes but is not limited to polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE) and other substrates.

[0210] In some embodiments, the negative electrode active material can also simultaneously adopt the negative electrode active materials for batteries that are well known in the art. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials and lithium titanate, etc. The silicon-based material can be selected from at least one of elemental silicon, silicon-nitrogen complexes and silicon alloys. The tin-based material can be selected from at least one of elemental tin, tin oxide compounds and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries can also be used. These negative electrode active materials can be used alone or in combination of two or more. The weight ratio of the negative electrode active material in the negative electrode film layer is 70-100 weight%, based on the total weight of the negative electrode film layer.

[0211] In some embodiments, the negative electrode film layer may further include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS). The binder may be present in the negative electrode film layer in an amount of 0-30% by weight, based on the total weight of the negative electrode film layer.

[0212] In some embodiments, the negative electrode film layer may further include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The weight ratio of the conductive agent in the negative electrode film layer is 0-20% by weight, based on the total weight of the negative electrode film layer.

[0213] In some embodiments, the negative electrode film layer may further include other additives, such as a thickener (e.g., sodium carboxymethyl cellulose (CMC-Na)). The weight ratio of the other additives in the negative electrode film layer is 0-15% by weight, based on the total weight of the negative electrode film layer.

[0214] In some embodiments, the negative electrode sheet can be prepared by the following method: 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 (such as deionized water) to form a negative electrode slurry, wherein the negative electrode slurry has a solid content of 30-70 wt % and a viscosity at room temperature adjusted to 2000-10000 mPa·s; the obtained negative electrode slurry is coated on both sides of the negative electrode current collector, and after a drying process, cold pressing, such as with a roller, is performed to obtain the negative electrode sheet. The negative electrode powder is coated on one side with a unit area density of 75-160 g / 1540.25 cm 2 , the compaction density of the negative electrode is 1.2-2.0g / cm 3 .

[0215] The fifth aspect of the present application provides a secondary battery, comprising the negative electrode sheet of the fourth aspect of the present application.

[0216] The secondary battery using the composite silicon material described above in this application has improved fast charging capability and cycle performance.

[0217] 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.

[0218] Positive electrode

[0219] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector, wherein the positive electrode film layer includes the positive electrode active material of the first aspect of the present application.

[0220] As an example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive electrode current collector.

[0221] 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 formed by forming a metal material on a polymer material substrate. Among them, the metal material includes but is not limited to aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc. The polymer material substrate includes but is not limited to one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS) and polyethylene (PE).

[0222] In some embodiments, the lithium ion positive electrode active material may include a positive electrode active material for a battery that is well known in the art. As an example, the positive electrode active material may include at least one of the following materials: a lithium-containing phosphate with an olivine structure, a lithium transition metal oxide, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM622 ), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.80 Co 0.15 Al 0.05 O2) and its modified compounds. Examples of olivine-structured lithium-containing phosphates may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon. The weight ratio of the positive electrode active material in the positive electrode film layer is 80-100 weight%, based on the total weight of the positive electrode film layer.

[0223] In some embodiments, the positive electrode film layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin. The weight ratio of the binder in the positive electrode film layer is 0-20 weight%, based on the total weight of the positive electrode film layer.

[0224] In some embodiments, the positive electrode film layer may further optionally include a conductive agent. For example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The weight ratio of the conductive agent in the positive electrode film layer is 0-20% by weight, based on the total weight of the positive electrode film layer.

[0225] 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 (such as N-methylpyrrolidone) to form a positive electrode slurry, wherein the positive electrode slurry has a solid content of 40-80 wt %, and the viscosity at room temperature is adjusted to 5000-25000 mPa·s, the positive electrode slurry is coated on both sides of the positive electrode current collector, and after drying, the positive electrode sheet is formed by cold rolling; the unit surface density of the positive electrode powder coated on one side is 180-400 g / 1540.25 cm 2 The compaction density of the positive electrode is 3.0-3.6g / cm 3 , optional 3.3-3.5g / cm 3 The calculation formula of the compacted density is

[0226] Compaction density = coating surface density / (thickness of the electrode after extrusion - thickness of the current collector).

[0227] electrolytes

[0228] The electrolyte conducts ions between the positive and negative electrodes. This application does not specify the type of electrolyte, and the electrolyte can be selected based on the needs. For example, the electrolyte can be liquid, gel, or solid.

[0229] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0230] In some embodiments, the electrolyte salt may be selected from one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalatoborate (LiDFOB), lithium bis(oxalatoborate) (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorobis(oxalatophosphate) (LiDFOP), and lithium tetrafluorooxalatophosphate (LiTFOP). The concentration of the electrolyte salt is typically 0.5-5 mol / L.

[0231] In some embodiments, the solvent can be selected from one or more of fluoroethylene carbonate (FEC), ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS) and diethyl sulfone (ESE).

[0232] In some embodiments, the electrolyte may further 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.

[0233] Isolation film

[0234] In some embodiments, the secondary battery further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical and mechanical stability can be selected.

[0235] In some embodiments, the material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0236] In some embodiments, the isolation film has a thickness of 6-40 μm, and optionally 12-20 μm.

[0237] In some embodiments, the positive electrode sheet, the negative electrode sheet and the separator can be made into an electrode assembly through a winding process or a lamination process; the electrode assembly and the electrolyte are packaged using the battery cell packaging material of the first aspect of the present application.

[0238] The present application has no particular limitation on the shape of the secondary battery, which may be cylindrical, square, or any other shape. For example, FIG1 shows a secondary battery 1 with a square structure as an example.

[0239] In some embodiments, referring to FIG2 , the outer packaging may include a housing 11 and a cover 13 . The housing 11 may include a bottom plate and side plates connected thereto, the bottom plate and side plates together forming a receiving cavity. The housing 11 may have an opening communicating with the receiving cavity, and the cover 13 may be positioned over the opening to seal the receiving cavity.

[0240] The positive electrode sheet, the negative electrode sheet, and the separator can be wound or laminated to form an electrode assembly 12. The electrode assembly 12 is encapsulated in the housing. The electrolyte is infiltrated into the electrode assembly 12. The number of electrode assemblies 12 included in the lithium-ion battery 1 can be one or more, and can be adjusted according to needs.

[0241] In some embodiments, secondary batteries can be assembled into a battery module. The battery module can contain multiple secondary batteries, and the specific number can be adjusted according to the application and capacity of the battery module.

[0242] In a battery module, multiple secondary batteries can be arranged in sequence along the length of the battery module. Of course, they can also be arranged in any other manner. Further, the multiple lithium-ion batteries can be fixed using fasteners.

[0243] Optionally, the battery module may further include a housing having an accommodation space, and the plurality of secondary batteries are accommodated in the accommodation space.

[0244] In some embodiments, the battery modules described above may also be assembled into a battery pack, and the number of battery modules contained in the battery pack may be adjusted according to the application and capacity of the battery pack.

[0245] A battery pack may include a battery box and multiple battery modules disposed within the box. The battery box comprises an upper case and a lower case. The upper case can be placed over the lower case to form an enclosed space for accommodating the battery modules. The multiple battery modules can be arranged in any manner within the battery box.

[0246] Electrical devices

[0247] In a sixth aspect, the present application provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack on the fifth side of the present application. The secondary battery, battery module, or battery pack can be used as a power source for the device, or as an energy storage unit for the device. The device may be, but is not limited to, a mobile device, an electric vehicle, an electric train, a ship, a satellite, an energy storage system, etc.; wherein the mobile device may include, but is not limited to, at least one of a mobile phone, a laptop computer, etc.; the electric vehicle may include, but is not limited to, at least one of a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.

[0248] The device can select a secondary battery, a battery module or a battery pack according to its usage requirements.

[0249] Figure 3 shows an example of an electric device 2. The electric device 2 is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the device's requirements for high power and high energy density of secondary batteries, a battery pack or battery module can be used.

[0250] Another example device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be lightweight and thin, and may use a lithium-ion battery as a power source.

[0251] The beneficial effects of the present application are further illustrated below with reference to the examples.

[0252] In order to make the technical problems, technical solutions and beneficial effects solved by this application clearer, the following will be further described in detail with reference to the embodiments and drawings. Obviously, the described embodiments are only a part of the embodiments of this application, rather than all the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is in no way intended to limit this application and its applications. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0253] If no specific techniques or conditions are specified in the examples, the experiments were carried out according to the techniques or conditions described in the literature in the field or according to the product instructions. All reagents or instruments used without specifying the manufacturer are commercially available conventional products.

[0254] 1. Preparation of composite silicon materials

[0255] Example 1

[0256] The porous carbon was placed in a rotary furnace, the speed was adjusted to 6r / min, and under an argon atmosphere, 99.99% pure silane (as the first silicon source) was sprayed at a flow rate of 0.2L / min for 30 minutes. The molar ratio of the porous carbon and the first silicon source was 4:1. After heating to 850°C, the temperature was kept for 4 hours for vapor deposition reaction to obtain a silicon-carbon material. After cooling, argon was introduced into the rotary furnace for 30 minutes, and the temperature was increased to 700°C at 10°C / min. The gas was then switched to a mixed gas of acetylene (as the first carbon source) and argon (as the first dilution gas) with a volume ratio of 1:9. The temperature was kept for 30 minutes, and the first carbon coating layer was formed on the outside of the silicon-carbon material after cooling.

[0257] Weigh 3 g of the silicon-carbon material coated with the first carbon coating layer, dissolve it in 100 mL of a mixed solution of ethanol and water with a volume ratio of 2:1, add 2 g of ethyl orthosilicate (as a second silicon source), stir thoroughly for 30 minutes, and then add it to a 200 mL polytetrafluoroethylene-lined autoclave, heat it to 120°C and keep it warm for 1 hour, and then cool it naturally to room temperature; the resulting solution is centrifuged and repeatedly washed with anhydrous ethanol, and vacuum dried at 60°C for 12 hours to form a silica coating layer on the outside of the first carbon coating layer, thereby obtaining an intermediate with a silica coating layer.

[0258] The above intermediate was mixed with magnesium powder (as a reducing agent) in a mass ratio of 3:1, fully ground and mixed in a mortar, heated in a 650°C tubular furnace in an inert gas atmosphere for 2 hours to perform a magnesium thermal reduction reaction, cooled to room temperature, washed with 0.5M hydrochloric acid to remove MgO and unreacted magnesium powder, washed with deionized water until neutral, and then vacuum dried at 70°C for 12 hours to form a silicon-containing coating layer on the outside of the first coating layer; placed in a rotary kiln, purged with argon for 30 minutes, heated to 700°C at 10°C / min, and then switched to a mixed gas of acetylene (as a second carbon source) and argon (as a second dilution gas) with a volume ratio of 1:9, kept warm for 30 minutes, and formed a second carbon coating layer on the outside of the silicon-containing coating layer after cooling to obtain a composite silicon material.

[0259] A cross-sectional SEM image of the composite silicon material prepared in Example 1 is shown in Figure 4. As shown in Figure 4, the composite silicon material has a coating structure, with a silicon-containing coating layer coating the outside of the silicon-carbon material. The core material is a supporting structure, with elemental silicon (i.e., the first silicon-based material) contained in the pores of the porous carbon. The coating layer has a dispersed structure, with elemental silicon (i.e., the second silicon-based material) dispersed in a silicon dioxide matrix.

[0260] Example 2-35

[0261] The preparation method of the composite silicon material in Examples 2-35 is basically similar to the preparation method of the composite silicon material in Example 1, with the main differences being: the type of the first silicon source, the molar ratio of the porous carbon and the first silicon source, the temperature of the vapor deposition reaction, the time of the vapor deposition reaction, the type of the first carbon source, the type of the first diluent gas, the volume ratio of the first carbon source and the first diluent gas, the reaction temperature and / or time when preparing the first carbon coating layer, the type of the second silicon source, the mass ratio of the silicon-carbon material coated with the first carbon coating layer and the second silicon source, the reaction temperature and / or time when preparing the silica coating layer, the type of the reducing agent for the magnesium thermal reduction reaction, the mass ratio of the intermediate with the silica coating layer to the reducing agent, the temperature and / or time of the magnesium thermal reduction reaction, the type of the second carbon source, the type of the second diluent gas, the volume ratio of the second carbon source and the second diluent gas, and at least one of the reaction temperature and / or time when preparing the second carbon coating layer is different. See Table 1 for details.

[0262] Comparative Example 1

[0263] The difference between Comparative Example 1 and Example 4 is that only the silicon-carbon material and the first coating layer coated on the outside of the silicon-carbon material are prepared. For details, see Table 1-1 and Table 1-2.

[0264] Table 1-1

[0265] Table 1-2

[0266] Wherein, n1 represents the molar ratio of porous carbon to the first silicon source, n2 represents the mass ratio of the silicon-carbon material coated with the first carbon coating layer and the second silicon source, n3 represents the mass ratio of the intermediate with the silica coating layer to the reducing agent, v1 represents the volume ratio of the first carbon source to the first dilution gas, and v2 represents the volume ratio of the second carbon source to the second dilution gas.

[0267] Comparative Example 2

[0268] The difference between Comparative Example 2 and Example 4 is that only the silicon-containing material and the second carbon coating layer coated on the outside of the silicon-containing material are prepared, and the silicon-carbon material and the first carbon coating layer coated on the outside of the silicon-carbon material are not included. The specific preparation process is as follows:

[0269] Pure SiO2 and Mg powder were mixed (mixing mass ratio 3:1), thoroughly ground and mixed in a mortar, heated in a 650℃ tube furnace in an inert gas atmosphere for 2h, cooled to room temperature, washed with 0.5M hydrochloric acid to remove MgO and unreacted Mg, and then washed with deionized water until neutral. Then, vacuum dried at 70℃ for 12h, placed in a rotary kiln, purged with argon for 30min, heated to 700℃ at 10℃ / min, and then switched to acetylene / Ar mixed gas (the volume ratio of acetylene to argon is 1:9), kept warm for 30min, and cooled to obtain a C / SiOx composite material with a carbon coating layer deposition thickness of 10nm.

[0270] Comparative Example 3

[0271] Step 1: Mix pure SiO2 and Mg powder (mixing mass ratio 3:1), grind and mix them thoroughly in a mortar, heat them in a 650℃ tube furnace in an inert gas atmosphere for 2h, cool to room temperature, wash with 0.5M hydrochloric acid to remove MgO and unreacted Mg, and then wash with deionized water until neutral, then vacuum dry at 70℃ for 12h, then place it in a rotary furnace, pass argon gas to purge for 30min, heat to 700℃ at 10℃ / min, then switch the gas to acetylene / Ar mixed gas (the volume ratio of acetylene to argon is 1:9), keep warm for 30min, and after cooling, obtain a C / SiOx composite material with a silicon oxide layer deposition thickness of 10nm.

[0272] Step 2: Add 2 g of o-aminobenzenesulfonic acid and 2 g of lignin powder to the C / SiOx composite material obtained above, disperse it in 150 mL of deionized water, mix thoroughly, transfer it to a hydrothermal reactor at 110°C and react for 8 hours. The resulting solution is centrifuged and washed, and dried in a vacuum drying oven at 60°C overnight.

[0273] Step 3: The solid powder obtained above was activated in a 50% by mass KOH solution for 12 h (impregnation ratio 1:3), then dried at 60°C, and then placed in a tube furnace and kept at 700°C for 2 h under an argon atmosphere. After cooling, it was washed several times with 1.0 mol / L HCl to remove inorganic impurities, and then washed with deionized water until the filtrate was neutral. Finally, it was vacuum dried at 60°C for 12 h to obtain a C / Si-C@C / SiOx composite material.

[0274] The parameters of the composite silicon materials prepared in the above embodiments and comparative examples were measured, specifically including:

[0275] The mass proportion of silicon in the silicon-carbon material, the pore size of the porous carbon, the stacking height of the first silicon-based material in the pore, the thickness of the first coating layer, the thickness of the silicon-containing coating layer, the molar ratio of oxygen and silicon contained in the silicon oxide, the volume average particle size Dv50 of the second silicon-based material contained in the silicon oxide, the thickness of the second carbon coating layer, and the volume average particle size Dv50 of the composite silicon material are specifically shown in Table 2.

[0276] Table 2

[0277] Among them, w1 represents the mass proportion of silicon element in silicon-carbon material, w2 represents the molar ratio of oxygen element to silicon element contained in silicon oxide, d1 represents the pore size of porous carbon pores, d2 represents the stacking height of the first silicon-based material in the pores, d3 represents the volume average particle size Dv50 of the second silicon-based material contained in silicon oxide, d4 represents the volume average particle size Dv50 of the composite silicon material, L1 represents the thickness of the first carbon coating layer, L2 represents the thickness of the silicon-containing coating layer, and L3 represents the thickness of the second carbon coating layer.

[0278] It should be noted that the mass proportion of silicon element in the above-mentioned silicon-carbon materials is determined by EDS energy spectrum.

[0279] The pore size of the porous carbon mentioned above is measured using a specific surface area analysis tester with reference to the gas adsorption BET method in GB / T 19587-2017.

[0280] The stacking height of the aforementioned first silicon-based material in the pores is measured using a transmission electron microscope (TEM).

[0281] The thickness of the first carbon coating layer mentioned above is measured using a transmission electron microscope (TEM).

[0282] The molar ratio of oxygen to silicon in the aforementioned silicon oxide is determined by performing X-ray energy spectrum analysis on the composite silicon material, deducting the silicon content in the silicon-carbon material, and qualitatively determining the X value in the silicon oxide.

[0283] The volume average particle size Dv50 of the second silicon-based material contained in the silicon oxide mentioned above is measured with reference to the particle size distribution laser diffraction method of GB / T19077-2016 using a Mastersizer 2000E laser particle size analyzer from Malvern Instruments Ltd., UK.

[0284] The thickness of the silicon-containing coating layer mentioned above is measured using a transmission electron microscope (TEM).

[0285] The thickness of the second carbon coating layer mentioned above is measured using a transmission electron microscope (TEM).

[0286] The volume average particle size Dv50 of the composite silicon material mentioned above is measured with reference to GB / T 19077-2016 particle size distribution laser diffraction method using a Mastersizer 2000E laser particle size analyzer from Malvern Instruments Ltd., UK.

[0287] It should be noted that since the volume average particle size Dv50 of the composite silicon material is at the micron level, the thickness of the first carbon coating layer, the thickness of the silicon-containing coating layer, and the thickness of the second carbon coating layer are only at the nanometer level. Therefore, fluctuations in the thickness of the first carbon coating layer, the thickness of the silicon-containing coating layer, and the thickness of the second carbon coating layer have very little effect on the volume average particle size Dv50 of the composite silicon material and can be ignored.

[0288] 2. Preparation of negative electrode and secondary battery

[0289] 1. Preparation of negative electrode sheet

[0290] The silicon-based materials prepared in the above examples and comparative examples were mixed with conductive carbon, sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) in a mass ratio of 10:85:1:1, and water was added and stirred to obtain a negative electrode slurry. The negative electrode slurry was evenly coated on both sides of a copper foil with a thickness of 6 μm, and the single-side coating surface density was 130 mg / 1540.25 mm 2 After drying in an oven and cold pressing, it is die-cut with a slitting width of 43.5 mm to make lithium-ion battery negative electrode sheets.

[0291] 2. Preparation of positive electrode sheet

[0292] The positive electrode active material ternary material nickel cobalt manganese (NCM811), conductive agent acetylene black, and binder polyvinylidene fluoride (PVDF) were added to N-methylpyrrolidone (NMP) at a mass ratio of 97:2:1 and stirred evenly to prepare a positive electrode slurry; the positive electrode slurry was evenly coated on an aluminum foil with a thickness of 15 μm, and the surface density was 320 mg / 1540.25 mm 2 After drying, cold pressing is performed, and then die-cutting is performed, and the width of the strips is 40mm to make the positive electrode sheets of lithium-ion batteries.

[0293] 3. Preparation of Isolation Membrane

[0294] Polyethylene is used as a base film, and aluminum oxide with a thickness of 3 μm is coated on the base film to obtain an isolation film.

[0295] 4. Preparation of Electrolyte

[0296] Ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1, and then LiPF6 was uniformly dissolved in the above solution to obtain an electrolyte solution. The concentration of LiPF6 in the electrolyte solution was 1 mol / L.

[0297] The positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator placed between the positive and negative electrode sheets to play an isolating role. After that, the lithium-ion battery is manufactured through the processes of packaging, liquid injection, and formation.

[0298] It should be noted that the formation process in the preparation process of the above lithium-ion battery is: first charge to 3.0V at 0.02C, then charge to 3.4V at 0.1C, and finally charge to 3.9V at 0.2C.

[0299] 3. Negative electrode and secondary battery performance test

[0300] 1. Electrode rebound rate test

[0301] After fully charging the secondary battery, the battery was disassembled and the negative electrode plate rebound rate was measured. The rebound rate was calculated as follows: (full charge plate thickness / cold pressed plate thickness-1)*100%. The results are shown in Table 3.

[0302] Full charge process: Let the battery rest for 30 minutes, then charge at a rate of 0.5C to a voltage of 4.25V, then charge at a constant voltage of 4.25V to a current of 0.05C, and let it rest for 5 minutes.

[0303] 2. Fast charging capability test

[0304] The negative electrode sheets and single-sided positive electrode sheets prepared in the above embodiments and comparative examples were assembled into three-electrode small stacks, and their lithium deposition windows were tested and their fast charging capabilities (10-80% SOC) were calculated.

[0305] Fast charging capability = 60*0.1 / (C 20％ +C 30％ +C 40％ +C 50％ +C 60％ +C 70％ +C 80％ )

[0306] Among them, C xx％ Indicates the maximum charge rate corresponding to the SOC; for example, C 20％ The maximum charge rate at 20% SOC is shown in Table 3.

[0307] 3. Cycle capacity retention test

[0308] Test conditions: At room temperature, the battery was charged at a rate of 0.5C and discharged at a rate of 0.5C for 300 full charge and discharge cycles.

[0309] Test procedure: The battery was left to rest for 30 minutes, then charged at a rate of 0.5C to a voltage of 4.25V. Further constant voltage charging at 4.25V to a current of 0.05C was performed, followed by a rest for 5 minutes, and then discharged at a rate of 0.5C to a voltage of 2.5V. This constituted one charge-discharge cycle. The discharge capacity was recorded after each cycle.

[0310] Capacity retention after 300 cycles (%)=(discharge capacity at the 300th cycle / discharge capacity at the first cycle)×100%.

[0311] The results are shown in Table 3.

[0312] Table 3

[0313] From the comparison of the results of Examples 1-35 and Comparative Examples 1-3 in Table 3, it can be seen that in the present application, by combining a silicon-carbon material with a silicon-containing coating layer comprising an ion-conducting material and a second silicon-based material, and coating the silicon-containing coating layer on the outside of the silicon-carbon material to form a composite silicon material, the volume expansion of the negative electrode plate can be reduced, and the fast charging performance and cycle performance of the secondary battery can be improved.

[0314] The difference between Examples 1-7 lies in the thickness of the silicon-containing coating layer. The thickness of the silicon-containing coating layer in Example 1 is the smallest, and the thickness of the silicon-containing coating layer in Example 7 is the largest. Compared with Examples 2-6, the fast charging time in Example 1 is prolonged. Technicians analyzed that the reason may be that: when the thickness of the silicon-containing coating layer is too low, the ion transmission path may increase limitedly, and the kinetic performance of the composite silicon material may be correspondingly poor. Compared with Examples 2-6, the rebound rate of the negative electrode plate in Example 7 is significantly increased, and the cycle capacity retention rate is significantly reduced. Technicians analyzed that the reason may be that: when the thickness of the silicon-containing coating layer is too high, the overall silicon content of the loaded silicon material is too high, which may cause the composite silicon material to expand too much, and further may cause the SEI film on the surface of the composite silicon material to be damaged. The electrolyte consumes active lithium to continuously repair the SEI film at the damaged interface, thereby deteriorating the cycle performance.

[0315] The main difference between Example 4 and Examples 8-13 lies in the mass percentage of silicon in the silicon-carbon material and the stacking height of the first silicon-based material in the pores. The mass percentage of silicon in the silicon-carbon material and the stacking height of the first silicon-based material in the pores of Example 8 are the smallest, and the mass percentage of silicon in the silicon-carbon material and the stacking height of the first silicon-based material in the pores of Example 13 are the largest. Compared with Examples 4 and 9-12, the fast charging time in Example 13 is longer and the cycle capacity retention rate is significantly reduced. The technicians analyzed that the reason may be that the mass percentage of silicon in the silicon-carbon material is too large, which may cause the conductivity of the silicon-carbon material particles to drop sharply, and then This results in a decrease in fast charging performance and capacity attenuation, and a decrease in cycle performance; compared with Example 4 and Examples 9-12, the cycle capacity retention rate in Example 8 is significantly reduced. Technicians analyzed that the reason may be due to: when the mass proportion of silicon element in the silicon-carbon material is too small, the internal space of the silicon-carbon material particles may be larger after lithium insertion, and the mechanical strength of the silicon-carbon material particles is low. The composite silicon material may be easily broken under long-term high expansion during cycling, resulting in contact between the electrolyte and the internal silicon, increased side reactions, and a decrease in the cycle capacity retention rate; it should be noted that since the mass proportion of silicon element in the silicon-carbon material of Example 8 is relatively small, the gram capacity and energy density of the composite silicon material finally prepared are reduced.

[0316] The main difference between Example 4 and Examples 14-18 lies in the different molar ratios of oxygen and silicon contained in silicon oxide. From the results of Examples 4 and 14-18, it can be seen that when the molar ratio x of oxygen and silicon contained in silicon oxide is 0.6, the specific capacity of silicon oxide is relatively high and the volume expansion of silicon oxide during the cycle is small, there are fewer side reactions, the cycle performance is excellent, and more ion channels can be provided. Therefore, when x is 0.6, the composite silicon material can take into account volume expansion, cycle performance and fast charging performance.

[0317] The main difference between Example 4 and Examples 19-22 is that the volume average particle size Dv50 of the second silicon-based material contained in the silicon oxide is different. The volume average particle size Dv50 of the second silicon-based material in Example 22 is the largest; from the results of Examples 4 and Examples 19-23, it can be seen that when the volume average particle size Dv50 of the second silicon-based material contained in the silicon oxide is 2-20nm, the active specific surface area of ​​the second silicon-based material is large and the kinetic performance is better; at the same time, due to the smaller particle size of the second silicon-based material, the strain caused by different lithium concentrations is smaller, and the silicon oxide can withstand greater strain without breaking, and there are fewer side reactions, so that the composite silicon material has better fast charging capability and cycle performance, and excellent kinetic performance.

[0318] The main difference between Example 4 and Examples 23-28 lies in the different volume average particle size Dv50 of the composite silicon material. The volume average particle size Dv50 of the composite silicon material in Example 23 is the smallest, and the volume average particle size Dv50 of the composite silicon material in Example 28 is the largest; compared with Example 4 and Examples 24-27, the cycle capacity retention rate in Example 23 is reduced, and the fast charging time in Example 28 is extended; from the comparison of the above results, it can be seen that when the volume average particle size Dv50 of the composite silicon material is in the range of 3μm-22μm, the composite silicon material has a large active specific surface area and good kinetic properties; at the same time, due to its small particle size, it can withstand greater strain without breaking, and has fewer side reactions, and thus the composite silicon material has excellent cycle performance and fast charging performance.

[0319] The main difference between Example 4 and Examples 33-35 is that the settings of the first carbon coating layer and / or the second carbon coating layer are different; from the comparison of the results of Example 4 and Examples 33-35, it can be seen that by setting the first carbon coating layer and / or the second carbon coating layer, the cycle performance and fast charging performance of the composite silicon material can be improved.

[0320] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0321] The above-described embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that a person of ordinary skill in the art may make various modifications and improvements without departing from the spirit of the present application, and these modifications and improvements fall within the scope of protection of the present application. Therefore, the scope of protection of the present patent application shall be determined by the appended claims.

Claims

1. A composite silicon material, comprising: A core, the core comprising a silicon-carbon material, the silicon-carbon material comprising a porous conductive material and a first silicon-based material, the porous conductive material having holes on its outer surface, at least a portion of the first silicon-based material being distributed in the holes; and The silicon-containing coating layer is coated on the outer side of the inner core, and the silicon-containing coating layer comprises an ion-conducting material and a second silicon-based material, wherein the second silicon-based material is dispersed in the ion-conducting material.

2. The composite silicon material according to claim 1, wherein: The silicon-containing coating layer has at least one of the following characteristics: (1) The thickness of the silicon-containing coating layer is 5nm-100nm; (2) The ion-conducting material includes one or more of hard carbon, soft carbon, graphite, transition metal nitride, silicon-based alloy, tin-based alloy and lithium metal; (3) The ion-conducting material and the second silicon-based material are composited into silicon oxide; (4) the volume average particle size Dv50 of the second silicon-based material is 2 nm-20 nm; (5) The second silicon-based material includes one or more of elemental silicon and silicon-tin alloy; (6) The shape of the second silicon-based material includes one or more of particles, lines, spheres, quasi-spheres and flakes.

3. The composite silicon material according to claim 2, wherein: The thickness of the silicon-containing coating layer is 30nm-60nm.

4. The composite silicon material according to any one of claims 2 to 3, wherein: The molar ratio of oxygen element to silicon element contained in the silicon oxide is denoted as x, where 0<x<2.

5. The composite silicon material according to claim 4, wherein: 0＜x≤0.6。 6. The composite silicon material according to any one of claims 2 to 5, wherein: The volume average particle size Dv50 of the second silicon-based material is 2nm-9nm.

7. The composite silicon material according to any one of claims 1 to 6, wherein: The silicon-carbon material has at least one of the following characteristics: (1) The mass proportion of silicon in the silicon-carbon material is 3%-25%; (2) The pore diameter is 2nm-50nm; (3) The stacking height of the first silicon-based material in the hole is 1 nm-35 nm; (4) The shape of the silicon-carbon material includes one or more of granular, spherical and quasi-spherical shapes; (5) The first silicon-based material includes one or more of elemental silicon and silicon-tin alloy; (6) The shape of the first silicon-based material includes one or more of particles, lines, spheres, quasi-spheres and flakes; (7) The porous conductive material includes porous carbon.

8. The composite silicon material according to claim 7, wherein: The mass proportion of silicon element in the silicon-carbon material is 8%-10%.

9. The composite silicon material according to any one of claims 7 to 8, wherein: The pores have a diameter of 15 nm to 35 nm.

10. The composite silicon material according to any one of claims 7 to 8, wherein: The stacking height of the first silicon-based material in the hole is 15nm-25nm.

11. The composite silicon material according to any one of claims 1 to 10, wherein: At least 3% of the first silicon-based material is embedded in the holes.

12. The composite silicon material according to claim 11, wherein: All of the first silicon-based materials are embedded in the holes.

13. The composite silicon material according to any one of claims 1 to 12, wherein: The composite silicon material further includes a first carbon coating layer, wherein the first carbon coating layer is located between the core and the silicon-containing coating layer.

14. The composite silicon material according to claim 13, wherein: The first carbon coating layer has at least one of the following characteristics: (1) The thickness of the first carbon coating layer is 10 nm to 30 nm; (2) The material of the first carbon coating layer includes amorphous carbon.

15. The composite silicon material according to any one of claims 1 to 14, wherein: The composite silicon material further includes a second carbon coating layer, which is coated on the outer side of the silicon-containing coating layer.

16. The composite silicon material according to claim 15, wherein: The second carbon coating layer has at least one of the following characteristics: (1) The thickness of the second carbon coating layer is 10 nm to 30 nm; (2) The material of the second carbon coating layer includes amorphous carbon.

17. The composite silicon material according to any one of claims 1 to 16, wherein: The composite silicon material may have a shape of one or more of granular, spherical and quasi-spherical.

18. The composite silicon material according to claim 17, wherein: The volume average particle size Dv50 of the composite silicon material is 3 μm-22 μm.

19. The composite silicon material according to claim 18, wherein: The volume average particle size Dv50 of the composite silicon material is 5 μm-10 μm.

20. A method for preparing the composite silicon material according to any one of claims 1 to 19, comprising the following steps: preparing the silicon-carbon material; The silicon-containing coating layer is formed on the outer side of the silicon-carbon material.

21. A method for preparing the composite silicon material according to any one of claims 1 to 19, comprising the following steps: preparing the silicon-carbon material; Forming a silicon dioxide coating layer on the outer side of the silicon-carbon material to prepare an intermediate with a silicon dioxide coating layer; The intermediate is reduced to form the silicon-containing coating layer on the outer side of the silicon-carbon material.

22. The method for preparing a composite silicon material according to claim 20 or 21, wherein: The silicon-carbon material is prepared by a vapor deposition method; the vapor deposition method includes at least one of the following conditions: (1) The raw materials for preparing the silicon-carbon material include a porous conductive material and a first silicon source; The molar ratio of the porous conductive material to the first silicon source is (3-8):1; The first silicon source includes monosilane; The porous conductive material comprises porous carbon; (2) The reaction temperature of the vapor deposition method is 800°C-900°C, and the reaction time is 2h-8h; (3) The reaction atmosphere of the vapor deposition method includes an inert gas.

23. The method for preparing a composite silicon material according to any one of claims 21 to 22, wherein: A silicon dioxide coating layer is formed on the outer side of the silicon-carbon material by a hydrothermal method; the hydrothermal method includes at least one of the following conditions: (1) The raw materials for preparing the silicon dioxide coating layer include a second silicon source; The second silicon source includes tetraethyl orthosilicate; The mass ratio of the silicon-carbon material to the second silicon source is 3:(1-5); (2) The reaction temperature of the hydrothermal method is 110°C-130°C, and the reaction time is 0.5h-5h; (3) The reaction medium of the hydrothermal method includes a mixture of ethanol and water; the volume ratio of ethanol to water in the mixture is (2-4):

1.

24. The method for preparing a composite silicon material according to any one of claims 21 to 23, wherein: The intermediate is reduced by a magnesium thermal reduction method; the magnesium thermal reduction method comprises at least one of the following conditions: (1) The reducing agent used includes magnesium powder; the mass ratio of the intermediate to the magnesium powder is (2-4):1; (2) The reaction temperature of the magnesium thermal reduction method is 600°C-750°C, and the reaction time is 0.5h-10h.

25. The method for preparing a composite silicon material according to any one of claims 21 to 24, wherein: Before the step of forming a silicon dioxide coating layer on the outer side of the silicon-carbon material, the method further includes: using a first carbon source to prepare a first carbon coating layer on the outer side of the silicon-carbon material; The preparation of the first carbon coating layer comprises at least one of the following conditions: (1) The first carbon source includes acetylene; (2) adding a first dilution gas when preparing the first carbon coating layer, wherein the first dilution gas includes argon; The volume ratio of the first carbon source to the first dilution gas is (0.5-2):9; (3) The reaction temperature is 600°C-800°C, and the reaction time is 0.5h-2h.

26. The method for preparing a composite silicon material according to any one of claims 21 to 25, wherein: The preparation method further comprises: using a second carbon source to form a second carbon coating layer on the outer side of the silicon-containing coating layer; The preparation of the second carbon coating layer comprises at least one of the following conditions: (1) The second carbon source includes acetylene; (2) adding a second dilution gas when preparing the second carbon coating layer, wherein the second dilution gas includes argon; The volume ratio of the second carbon source to the second dilution gas is (0.5-2):9; (3) The reaction temperature is 600°C-800°C, and the reaction time is 0.5h-2h.

27. A negative electrode sheet, comprising: Anode current collector; as well as 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 comprises the composite silicon material according to any one of claims 1 to 19 or the composite silicon material prepared by the method according to any one of claims 20 to 26.

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

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

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