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

Abstract

The application provides a composite silicon material, a preparation method thereof, a negative electrode sheet, a secondary battery and an electric device; the composite silicon material comprises a core and a silicon-containing coating layer covering the outside of the core; the core comprises a silicon-carbon material, the silicon-carbon material comprises a porous conductive material and a first silicon-based material, the porous conductive material has pores on the outer surface thereof, and at least part of the first silicon-based material is distributed in the pores; the silicon-containing coating layer comprises an ion-conducting material and a second silicon-based material, and the second silicon-based material is 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 silicon expansion; meanwhile, the ion-conducting material can increase the ion transmission path, thereby effectively alleviating the problem of poor kinetic performance caused by the small ion transmission path of the silicon-carbon material. In addition, the fast-charging capacity and the cycle performance of the secondary battery can also be improved.

Description

TECHNICAL FIELD

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

[0002] Secondary batteries are widely used in various consumer electronic products and electric vehicles due to their light weight, no pollution, no memory effect and other outstanding characteristics. With the continuous development of the new energy industry, people have put forward higher and higher requirements for the energy density of secondary batteries.

[0003] Silicon-based negative electrode materials are widely used in secondary batteries due to their high capacity. However, due to the high expansion characteristics of silicon and its poor electrical conductivity, silicon-based negative electrode materials not only improve the energy density of secondary batteries, but also cause the secondary batteries to expand and have poor dynamics, which limits the further development of battery technology. SUMMARY

[0004] Therefore, it is necessary to provide a composite silicon material, a preparation method thereof, a negative electrode sheet, a secondary battery and an electric device to alleviate the expansion of the secondary battery and improve the dynamic performance of the secondary battery.

[0005] To achieve the above purpose, the first aspect of the present application provides a composite silicon material, comprising:

[0006] 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, and at least part of the first silicon-based material being distributed in the pores; and

[0007] a silicon-containing coating layer coated on the outside of the core, the silicon-containing coating layer comprising an ion-conductive material and a second silicon-based material, the second silicon-based material being dispersed in the ion-conductive material.

[0008] The composite silicon material of the present application includes a silicon-carbon material and a silicon-containing coating layer, the silicon-carbon material including a porous conductive material having pores on its outer surface and a first silicon-based material, and at least part of the first silicon-based material being embedded in the pores 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-conductive material, which can increase the ion transport path, thereby effectively alleviating the problem of poor dynamic performance caused by the lack of ion transport path of the silicon-carbon material.

[0009] In some embodiments, the silicon-containing coating layer has at least one of the following characteristics:

[0010] (1) the thickness of the silicon-containing coating layer is 5-100 nm, which can be optionally 30-60 nm;

[0011] (2) the ion-conductive material comprises one or more of hard carbon, soft carbon, graphite, transition metal nitride, silicon-based alloy, tin-based alloy, and lithium metal;

[0012] (3) the ion-conductive material and the second silicon-based material are compounded into silicon oxide;

[0013] Optionally, the molar ratio of oxygen element and silicon element contained in the silicon oxide is denoted as x, and 0 < x < 2, which can be 0 < x < 0.6;

[0014] (4) the volume average particle size Dv50 of the second silicon-based material is 2 nm-20 nm, which can be 2 nm-9 nm;

[0015] (5) the second silicon-based material comprises one or more of elemental silicon and silicon-tin alloy;

[0016] (6) the shape of the second silicon-based material comprises one or more of particle, wire type, spherical, quasi-spherical, and flaky.

[0017] In some embodiments, the silicon-carbon material has at least one of the following characteristics:

[0018] (1) the mass percentage of silicon element in the silicon-carbon material is 3%-25%, which can be 8%-10%;

[0019] (2) the pore size of the pores is 2 nm-50 nm, which can be 15 nm-35 nm;

[0020] (3) the stacking height of the first silicon-based material in the pores is 1 nm-35 nm, which can be 15 nm-25 nm;

[0021] (4) the shape of the silicon-carbon material comprises one or more of particle, spherical, and quasi-spherical;

[0022] (5) the first silicon-based material comprises one or more of elemental silicon and silicon-tin alloy;

[0023] (6) the shape of the first silicon-based material comprises one or more of particle, wire type, spherical, quasi-spherical, and flaky;

[0024] (7) the porous conductive material comprises porous carbon.

[0025] In some embodiments, at least 3% of the first silicon-based material is embedded in the pores;

[0026] Optionally, all the first silicon-based material is embedded in the pores.

[0027] In some embodiments, the composite silicon material further comprises a first carbon coating layer, the first carbon coating layer being located between the substrate and the silicon-containing coating layer;

[0028] Optionally, the first carbon coating layer has at least one of the following characteristics:

[0029] (1) the thickness of the first carbon coating layer is 10-30 nm;

[0030] (2) the material of the first carbon coating layer comprises amorphous carbon.

[0031] In some embodiments, the composite silicon material further comprises a second carbon coating layer, the second carbon coating layer being coated on the outside of the silicon-containing coating layer;

[0032] Optionally, the second carbon coating layer has at least one of the following characteristics:

[0033] (1) the thickness of the second carbon coating layer is 10-30 nm;

[0034] (2) the material of the second carbon coating layer comprises amorphous carbon.

[0035] In some embodiments, the shape of the composite silicon material comprises one or more of granular, spherical and spheroidal.

[0036] Optionally, the volume average particle size Dv50 of the composite silicon material is 3-22 μm, optionally 5-10 μm.

[0037] The second aspect of the present application provides a preparation method of the composite silicon material of the first aspect of the present application, comprising the following steps:

[0038] preparing the silicon-carbon material;

[0039] forming the silicon-containing coating layer on the outside of the silicon-carbon material.

[0040] The third aspect of the present application provides a preparation method of the composite silicon material of the first aspect of the present application, comprising the following steps:

[0041] preparing the silicon-carbon material;

[0042] forming a silicon dioxide coating layer on the outside of the silicon-carbon material, to prepare an intermediate with a silicon dioxide coating layer;

[0043] reducing the intermediate to form the silicon-containing coating layer on the outside of the silicon-carbon material.

[0044] In some embodiments, the silicon-carbon material is prepared by a gas phase deposition method;

[0045] Optionally, the vapor deposition method comprises at least one of the following conditions:

[0046] (1) the preparation raw material of the silicon-carbon material comprises a porous conductive material and a first silicon source;

[0047] Optionally, the molar ratio of the porous conductive material and the first silicon source is (3-8): 1;

[0048] Optionally, the first silicon source comprises monosilane;

[0049] Optionally, the porous conductive material comprises porous carbon;

[0050] (2) the reaction temperature of the vapor deposition method is 800-900℃, and the reaction time is 2-8h;

[0051] (3) the reaction atmosphere of the vapor deposition method comprises an inert gas.

[0052] In some embodiments, a hydrothermal method is used to form a silicon dioxide coating layer on the outside of the silicon-carbon material;

[0053] Optionally, the hydrothermal method comprises at least one of the following conditions:

[0054] (1) the preparation raw material of the silicon dioxide coating layer comprises a second silicon source;

[0055] Optionally, the second silicon source comprises tetraethyl orthosilicate;

[0056] Optionally, the mass ratio of the silicon-carbon material and the second silicon source is 3:(1-5);

[0057] (2) the reaction temperature of the hydrothermal method is 110-130℃, and the reaction time is 0.5-5h;

[0058] (3) the reaction medium of the hydrothermal method comprises a mixture of ethanol and water;

[0059] Optionally, the volume ratio of ethanol to water in the mixture is (2-4): 1.

[0060] In some embodiments, a magnesium hot reduction method is used to reduce the intermediate;

[0061] Optionally, the magnesium hot reduction method comprises at least one of the following conditions:

[0062] (1) the reducing agent used comprises magnesium powder;

[0063] Optionally, the mass ratio of the intermediate and the magnesium powder is (2-4): 1;

[0064] (2) the reaction temperature of the magnesium thermal reduction method is 600-750°C, and the reaction time is 0.5-10 h.

[0065] In some embodiments, before the step of forming the silicon dioxide coating layer on the outside of the silicon-carbon material, the method further comprises:

[0066] a first carbon source is used to prepare a first carbon coating layer on the outside of the silicon-carbon material;

[0067] Optionally, the preparation of the first carbon coating layer comprises at least one of the following conditions:

[0068] (1) the first carbon source comprises acetylene;

[0069] (2) a first dilution gas is added during the preparation of the first carbon coating layer, and the first dilution gas comprises an inert gas;

[0070] Optionally, the first dilution gas comprises argon;

[0071] Optionally, the volume ratio of the first carbon source to the first dilution gas is (0.5-2):9;

[0072] (3) the reaction temperature is 600-800°C, and the reaction time is 0.5-2 h.

[0073] In some embodiments, the preparation method further comprises:

[0074] a second carbon source is used to form a second carbon coating layer on the outside of the silicon-containing coating layer;

[0075] Optionally, the preparation of the second carbon coating layer comprises at least one of the following conditions:

[0076] (1) the second carbon source comprises acetylene;

[0077] (2) a second dilution gas is added during the preparation of the second carbon coating layer, and the second dilution gas comprises an inert gas;

[0078] Optionally, the second dilution gas comprises argon;

[0079] Optionally, the volume ratio of the second carbon source to the second dilution gas is (0.5-2):9;

[0080] (3) the reaction temperature is 600-800°C, and the reaction time is 0.5-2 h.

[0081] A fourth aspect of the present application provides a negative electrode tab, comprising:

[0082] a negative electrode current collector; and

[0083] A negative active material layer is located on at least one side of the negative current collector, and the negative active material layer comprises 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.

[0084] The fifth aspect of the present application provides a secondary battery comprising the negative electrode sheet of the third aspect of the present application.

[0085] The sixth aspect of the present application provides an electric device comprising the secondary battery of the fourth aspect of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0086] Figure 1 is a schematic diagram of a secondary battery according to an embodiment of the present application.

[0087] Figure 2 is Figure 1 is an exploded view of the secondary battery according to an embodiment of the present application.

[0088] Figure 3 is a schematic diagram of an electric device using the secondary battery according to an embodiment of the present application as a power source.

[0089] Figure 4 is a SEM image of a cross section of the composite silicon material in Example 1.

[0090] BRIEF DESCRIPTION OF DRAWINGS

[0091] 1 secondary battery; 11 housing; 12 electrode assembly; 13 cover plate; 2 electric device. DETAILED DESCRIPTION

[0092] In order to facilitate the understanding of the present application, the present application will be described more fully below with reference to the accompanying drawings. The preferred embodiments of the present application are shown in the drawings. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, these embodiments are provided so that the disclosure of the present application can be more thoroughly and completely understood.

[0093] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present application belongs. The terminology used in the description of the present application herein only for the purpose of describing specific embodiments of the present application and is not intended to limit the present application.

[0094] In the present application, the technical features described in an open manner include both the closed technical solution consisting of the listed features and the open technical solution containing the listed features.

[0095] In this application, numerical ranges are referred to as continuous unless otherwise specified, and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0096] In this application, if the unit of a data range is only followed by the right endpoint, 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 (nanometer).

[0097] In this application, terms such as "multiple," "various," and "repeatedly" are used unless otherwise specified, referring to a quantity greater than or equal to 2. For example, "multiple" means two or more. This document only specifically discloses some numerical ranges. 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, just as any upper limit can be combined with any other upper limit to form an unspecified range. Furthermore, each individually disclosed point or single value can itself serve as a lower or upper limit and be combined with any other point or single value or with other lower or upper limits to form an unspecified range.

[0098] The "scope" disclosed in this application is defined by a lower limit and an upper limit. A given scope is defined by selecting a lower limit and an upper limit, which define the boundaries of the specific scope. The scope defined in this way may include end values ​​or not.

[0099] Unless otherwise specified, the temperature parameters in this application may be either constant temperature processing or processing within a certain temperature range. The constant temperature processing allows for temperature fluctuations within the precision range controlled by the instrument.

[0100] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions. Unless otherwise specified, all technical features and optional technical features of this application can be combined to form new technical solutions.

[0101] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, but sequentially is preferred.

[0102] Silicon-based anode materials are widely used in secondary batteries. However, due to the high expansion characteristics of silicon and its limited ion transport paths and poor conductivity, secondary batteries using silicon-based anode materials, while improving energy density, still suffer from problems of expansion and poor kinetic performance.

[0103] To address the aforementioned issues, this application combines a silicon-containing coating layer containing an ion-conducting material with a silicon-carbon material. The silicon-carbon material comprises a porous conductive material with pores on its outer surface and a first silicon-based material, with at least a portion of the first silicon-based material embedded within the pores. The pores provide space for the expansion of the first silicon-based material, mitigating the problem of increased overall volume of the composite silicon material due to the expansion of the first silicon-based material. Furthermore, the ion-conducting material in the silicon-containing coating layer located outside the silicon-carbon material increases the ion transport path, thereby improving the kinetic performance of the composite silicon material.

[0104] The first aspect of this application provides a composite silicon material, including a core and a silicon-containing coating layer covering the outside of the core; the 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 having pores, at least a portion of the first silicon-based material being distributed within the pores; 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.

[0105] It should be noted that the term "first silicon-based material" in this application is used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should it be construed as implicitly indicating the importance or quantity of the indicated technical features.

[0106] Porous conductive materials refer to conductive materials whose outer surface and / or interior have pores. The number of pores in a porous conductive material can be one or more. The first silicon-based material in silicon-carbon materials can be entirely distributed within the pores of the porous conductive material, or only a portion of the first silicon-based material can be distributed within the pores of the porous conductive material.

[0107] Ion-conducting materials can include materials that inherently possess ion-conducting capabilities, or materials that, through further reactions, can form compounds with ion-conducting properties; for example, ion-conducting materials can include materials that can form compounds with ion-conducting properties during battery charging, etc., and are not specifically limited. The silicon-containing coating layer can be a continuous and complete coating layer, or an incomplete coating layer; wherein, "complete" means that the material located inside the silicon-containing coating layer is completely covered by the silicon-containing coating layer, and the silicon-containing coating layer completely isolates the material inside from its outside. "Incomplete" means that the material located inside the silicon-containing coating layer is not completely covered by the silicon-containing coating layer, and at least partially, the material inside the silicon-containing coating layer can contact the outside of the silicon-containing coating layer. Preferably, the silicon-containing coating layer is a continuous and complete coating layer.

[0108] Understandably, the composite silicon material of this application includes silicon-carbon material and 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 ion transport paths, thereby effectively alleviating the problem of deteriorated kinetic performance caused by the limited ion transport paths of the silicon-carbon material. In addition, it can also improve the fast-charging capability and cycle performance of the secondary battery.

[0109] In some embodiments, the thickness of the silicon-containing coating layer is 5nm-100nm. When the thickness of the silicon-containing coating layer is less than the above range, the increase in ion transport paths is limited, resulting in poor kinetic performance of the composite silicon material. When the thickness of the silicon-containing coating layer is greater than the above range, the overall silicon content of the composite silicon material is too high, leading to excessive expansion of the composite silicon material. This may cause the SEI film on the surface of the composite silicon material to rupture, exposing new sites. The electrolyte continuously repairs the SEI film at the damaged interface, consuming active lithium and affecting the cycle performance of the cell. At the same time, the expansion of the composite silicon material will deteriorate the energy density of the 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 any two of the above values. Optionally, the thickness of the silicon-containing coating layer is 30nm-60nm.

[0110] As an example, the thickness of the silicon-containing coating mentioned above can be measured by transmission electron microscopy (TEM).

[0111] 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.

[0112] In some embodiments, the ion-conducting material and the second silicon-based material are combined to form a silicon oxide; a silicon oxide is a compound containing both silicon and oxygen elements; when the ion-conducting material and the second silicon-based material can be combined to form a silicon oxide, the ion-conducting material is silicon dioxide, and the second silicon-based material is dispersed within the ion-conducting material; during the charging process, silicon dioxide can undergo an electrochemical reaction with lithium extracted from the positive electrode active material to form lithium silicate with ion-conducting properties.

[0113] In some optional embodiments, the molar ratio of oxygen to silicon in the silicon oxide is denoted as x, where 0 < x < 2. When the molar ratio of oxygen to silicon in the silicon oxide is within the above range, the larger the value of x, the smaller the volume expansion of the silicon oxide, but its specific capacity is also lower; the smaller the value of x, the higher the specific capacity of the silicon oxide, but its volume expansion is also larger. As an example, the molar ratio of oxygen to silicon in the 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 any two of the above values. Optionally, 0 < x ≤ 0.6. As an example, the molar ratio of oxygen to silicon in the aforementioned silicon oxide can be determined by the following method: X-ray energy dispersive spectroscopy (EDS) is performed on the composite silicon material, and the silicon content in the silicon-carbon material is subtracted to qualitatively determine the x-value in the silicon oxide.

[0114] It should be noted that the term "second silicon-based material" in this application is used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should it be construed as implicitly indicating the importance or quantity of the indicated technical features.

[0115] 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 cracking. In addition, the second silicon-based material has a larger active surface area and relatively better kinetics. 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 any two of the above values. Optionally, the volume average particle size Dv50 of the second silicon-based material is 2nm-9nm.

[0116] As an example, the volume average particle size Dv50 of the aforementioned second silicon-based material can be determined using a laser particle size analyzer, for example, the Mastersizer 2000E laser particle size analyzer from Malvern Instruments Ltd., UK, in accordance with GB / T 19077-2016 Particle Size Distribution Laser Diffraction Method.

[0117] In some embodiments, the second silicon-based material includes one or more of elemental silicon and silicon-tin alloy.

[0118] In some embodiments, the shape of the second silicon-based material includes one or more of the following: granular, linear, spherical, near-spherical, and sheet-like.

[0119] In some embodiments, the mass percentage of silicon in the silicon-carbon material is 3%-25%. When the mass percentage of silicon in the silicon-carbon material is within the above range, the silicon-carbon material has a high specific capacity and relatively stable electrochemical performance, resulting in better cycle life. When the mass percentage of silicon increases further, the conductivity of the silicon-carbon material particles decreases sharply, leading to capacity decay. As an example, the mass percentage 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 any two of the above values. Optionally, the mass percentage of silicon in the silicon-carbon material is 8%-10%.

[0120] As an example, the mass percentage of silicon in silicon-carbon materials can be qualitatively determined using EDS energy dispersive spectroscopy.

[0121] In some embodiments, the pore size of the porous conductive material is 2nm-50nm. When the pore size of the porous conductive material is within the above range, it can minimize the deterioration of compaction density caused by the internal pre-reserved pores of the porous conductive material while providing expansion space, thereby improving 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 any two of the above values. Optionally, the pore size of the porous conductive material is 15nm-35nm.

[0122] It should be noted that when a porous conductive material has only a single pore, the pore diameter is the diameter of that single pore; when a porous conductive material has multiple pores, the pore diameter refers to the average pore diameter.

[0123] As an example, the pore size of the aforementioned holes can be determined using a specific surface area analyzer according to GB / T 19587-2017 Gas Adsorption BET Method.

[0124] In some embodiments, the packing height of the first silicon-based material within the pores is 1 nm to 35 nm. When the packing height of the first silicon-based material within the pores is within the above range, the silicon-carbon material exhibits high specific capacity, relatively stable electrochemical performance, and better cycle life. When the packing height of the first silicon-based material within the pores further increases, the conductivity of the silicon-carbon material particles decreases sharply, leading to capacity decay. As an example, the packing height of the first silicon-based material within the pores can be, but is not limited to, 1 nm, 3 nm, 5 nm, 8 nm, 10 nm, 13 nm, 15 nm, 17 nm, 20 nm, 23 nm, 25 nm, 28 nm, 30 nm, 33 nm, 35 nm, or any two of the above values. Optionally, the packing height of the first silicon-based material within the pores is 15 nm to 25 nm.

[0125] It should be noted that the stacking height of the first silicon-based material within the cavity refers to the stacking thickness of the first silicon-based material along the depth of the cavity. When all the first silicon-based materials fall within the same cavity, the stacking height of the first silicon-based material within the cavity is the height of the first silicon-based material stacked within that cavity. When the first silicon-based material falls within multiple cavities, the stacking height of the first silicon-based material within the cavity refers to the average stacking height of the first silicon-based material within the cavity.

[0126] As an example, the stacking height of the aforementioned first silicon-based material within the pores can be determined using a transmission electron microscope (TEM).

[0127] As one possible implementation, the silicon-carbon material may be in one or more of the following shapes: granular, spherical, and quasi-spherical.

[0128] In some embodiments, the first silicon-based material includes one or more of elemental silicon and silicon-tin alloy.

[0129] In some embodiments, the shape of the first silicon-based material includes one or more of the following: granular, linear, spherical, near-spherical, and sheet-like.

[0130] In some embodiments, the porous conductive material includes porous carbon.

[0131] In some implementations, at least 3% of the first silicon-based material is embedded within the pores.

[0132] Optionally, all the first silicon-based materials are embedded within the pores; this can further reduce the volume expansion of the composite silicon material.

[0133] As one possible implementation, the composite silicon material further includes a first carbon coating layer 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.

[0134] It should be noted that the term "first carbon coating layer" in this application is used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should it be construed as implicitly indicating the importance or quantity of the indicated technical features.

[0135] In some optional embodiments, the thickness of the first carbon coating layer is 10 nm to 30 nm. When the thickness of the first carbon coating layer is within the above range, the silicon-carbon material has a high specific capacity, relatively stable electrochemical performance, and better cycle life. When the thickness of the first carbon coating layer is further increased, the conductivity of the silicon-carbon material particles decreases sharply, resulting in capacity decay. As an example, the thickness of the first 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 any two of the above values.

[0136] As an example, the thickness of the first carbon coating layer mentioned above can be measured using transmission electron microscopy (TEM).

[0137] In some alternative embodiments, the material of the first carbon coating layer includes amorphous carbon. Using amorphous carbon as the material of the first carbon coating layer provides better ionic conductivity and also prevents direct contact between the silicon-based material and the electrolyte, reducing side reactions.

[0138] In some embodiments, the composite silicon material further includes a second carbon coating layer, which coats 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.

[0139] It should be noted that the term "second carbon coating layer" in this application is used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should it be construed as implicitly indicating the importance or quantity of the indicated technical features.

[0140] Optionally, the thickness of the second carbon coating layer is 10nm-30nm. 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, and can withstand the expansion of silicon material to a greater extent without cracking, reducing the occurrence of side reactions. As an example, the thickness of the second 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 any two of the above values.

[0141] As an example, the thickness of the aforementioned second carbon coating layer can be measured using transmission electron microscopy (TEM).

[0142] Optionally, the material of the second carbon coating layer includes amorphous carbon; using amorphous carbon as the material of the second carbon coating layer, the second carbon coating layer has better ionic conductivity, and at the same time can also prevent the silicon-based material from directly contacting the electrolyte, reducing side reactions.

[0143] In some possible embodiments, the shape of the composite silicon material includes one or more of granular, spherical, and quasi-spherical shapes.

[0144] 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 higher 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 any two of the above values. Optionally, the volume average particle size Dv50 of the composite silicon material is 5 μm-10 μm.

[0145] Dv50 refers to the particle size corresponding to a cumulative particle size distribution percentage of 50% in a sample. As an example, Dv50 can be conveniently determined using a laser particle size analyzer, such as the Mastersizer 2000E laser particle size analyzer from Malvern Instruments Ltd., UK, according to GB / T 19077-2016 Particle Size Distribution Laser Diffraction Method.

[0146] In some embodiments, the composite silicon material includes:

[0147] The core comprises a silicon-carbon material, which includes a porous conductive material and a first silicon-based material. The outer surface of the porous conductive material has pores, and at least a portion of the first silicon-based material is embedded within the pores. The mass percentage of silicon in the silicon-carbon material is 3%-25%, optionally 8%-10%. The pore diameter is 2nm-50nm, optionally 15nm-35nm. The stacking height of the first silicon-based material within the pores is 1nm-35nm, optionally 15nm-25nm. The shape of the silicon-carbon material includes one or more of granular, spherical, and near-spherical shapes. The first silicon-based material includes one or more of elemental silicon and silicon-tin alloys. The shape of the first silicon-based material includes one or more of granular, linear, spherical, near-spherical, and sheet-like shapes. The porous conductive material includes porous carbon. At least 3% of the first silicon particles and silicon-based material are embedded within the pores.

[0148] A first carbon coating layer is coated on at least a portion of the outer surface of the substrate. The thickness of the first carbon coating layer is 10 nm to 30 nm. The material of the first carbon coating layer includes amorphous carbon.

[0149] A silicon-containing coating layer is coated on at least a portion of the outer surface of a first carbon coating layer. The silicon-containing coating layer comprises an ion-conducting material and a second silicon-based material, the second silicon-based material being dispersed within the ion-conducting material. The thickness of the silicon-containing coating layer is 5 nm-100 nm, optionally 30 nm-60 nm. The volume average particle size (Dv50) of the second silicon-based material is 2 nm-20 nm, optionally 2 nm-9 nm. The second silicon-based material comprises one or more of elemental silicon and silicon-tin alloys. The shape of the second silicon-based material includes one or more of granular, linear, spherical, near-spherical, and sheet-like forms. 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. Alternatively, the ion-conducting material and the second silicon-based material are combined to form a silicon oxide, wherein the molar ratio of oxygen to silicon in the silicon oxide is denoted as x, 0 < x < 2, optionally 0 < x ≤ 0.6.

[0150] A second carbon coating layer is coated on at least a portion of the outer surface of the silicon-containing coating layer. The thickness of the second carbon coating layer is 10 nm to 30 nm. The material of the second carbon coating layer includes amorphous carbon.

[0151] The shape of the composite silicon material includes one or more of granular, spherical and near-spherical shapes; the volume average particle size Dv50 of the composite silicon material is 3μm-22μm, and can be selected as 5μm-10μm.

[0152] The second aspect of this application provides a method for preparing a composite silicon material according to the first aspect, comprising the following steps: preparing a silicon-carbon material; forming a silicon-containing coating layer on the outside of the silicon-carbon material.

[0153] The third aspect of this application provides a method for preparing a composite silicon material according to 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; reducing the intermediate to form a silicon-containing coating layer on the outside of the silicon-carbon material.

[0154] In some embodiments, silicon-carbon materials are prepared using vapor deposition. Using vapor deposition to prepare silicon-carbon materials is advantageous in increasing the proportion of the first silicon-based material embedded within the pores of the porous conductive material in the final prepared silicon-carbon material, and may even allow all of the first silicon-based material to be deposited within the pores of the porous conductive material.

[0155] In some embodiments, the raw materials for preparing silicon-carbon materials include porous conductive materials and a first silicon source.

[0156] In some alternative 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 any two of the above ratios.

[0157] In some alternative implementations, the first silicon source includes silane.

[0158] In some alternative implementations, the porous conductive material includes porous carbon.

[0159] In some embodiments, the reaction temperature of the vapor deposition method is 800℃-900℃; for example, it can be, but is not limited to, 800℃, 810℃, 820℃, 830℃, 840℃, 850℃, 860℃, 870℃, 880℃, 890℃, 900℃, or any range between two of the above values. The reaction time is 2h-8h; for example, it can be, but is not limited to, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, 6h, 6.5h, 7h, 7.5h, 8h, or any range between two of the above values.

[0160] In some embodiments, the reaction atmosphere of the vapor deposition process includes an inert gas; alternatively, the reaction atmosphere of the vapor deposition process includes argon.

[0161] In some embodiments, a silica coating layer is formed on the outside of the silicon-carbon material using a hydrothermal method.

[0162] In some alternative embodiments, the raw materials for preparing the silica coating layer include a second silicon source.

[0163] Optionally, the second silicon source includes tetraethyl orthosilicate.

[0164] Optionally, the mass ratio of 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 any two of the above ratios.

[0165] As one possible implementation, the reaction temperature of the hydrothermal method is 110℃-130℃; for example, it can be, but is not limited to, 110℃, 112℃, 115℃, 118℃, 120℃, 122℃, 125℃, 128℃, 130℃, or any range between two of the above values. The reaction time is 0.5h-5h; for example, it can be, but is not limited to, 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, or any range between two of the above values.

[0166] In some embodiments, the reaction medium for the hydrothermal method includes a mixture of ethanol and water.

[0167] 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 any two of the above ratios.

[0168] In some implementations, the intermediate is reduced using a magnesothermic reduction method.

[0169] As one possible implementation method, the reducing agent used includes magnesium powder.

[0170] 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 any two of the above ratios.

[0171] As one possible implementation, the reaction temperature of the magnesothermic reduction method is 600℃-750℃; for example, but not limited to 600℃, 610℃, 620℃, 630℃, 640℃, 650℃, 660℃, 670℃, 680℃, 690℃, 700℃, 710℃, 720℃, 730℃, 740℃, 750℃, or any range between two of the above values. The reaction time is 0.5h-10h; for example, but not limited to 0.5h, 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, or any range between two of the above values.

[0172] In some embodiments, prior to the step of forming a silicon dioxide coating layer on the outside of the silicon-carbon material, the method further includes: preparing a first carbon coating layer on the outside of the silicon-carbon material using a first carbon source.

[0173] Optionally, the first carbon source includes acetylene.

[0174] In some alternative embodiments, a first diluting gas, including an inert gas, is also added during the preparation of the first carbon coating layer.

[0175] Optionally, the first diluting gas includes argon.

[0176] 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 any two of the above values.

[0177] In some embodiments, the reaction temperature for preparing the first carbon coating layer is 600℃-800℃; for example, it can be, but is not limited to, 600℃, 620℃, 650℃, 680℃, 700℃, 730℃, 750℃, 770℃, 800℃, or any range between two of the above values. The reaction time is 0.5h-2h; for example, it can be, but is not limited to, 0.5h, 0.7h, 1h, 1.3h, 1.5h, 1.8h, 2h, or any range between two of the above values.

[0178] In some embodiments, a silica coating layer is formed on the outside of the first carbon coating layer using a hydrothermal method.

[0179] In some alternative embodiments, the raw materials for preparing the silica coating layer include a second silicon source.

[0180] Optionally, the second silicon source includes tetraethyl orthosilicate.

[0181] Optionally, the mass ratio of the silicon-carbon material coated with the first carbon coating layer 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 any two of the above ratios.

[0182] As one possible implementation, the reaction temperature of the hydrothermal method is 110℃-130℃; for example, it can be, but is not limited to, 110℃, 112℃, 115℃, 118℃, 120℃, 122℃, 125℃, 128℃, 130℃, or any range between two of the above values. The reaction time is 0.5h-5h; for example, it can be, but is not limited to, 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, or any range between two of the above values.

[0183] In some embodiments, the reaction medium for the hydrothermal method includes a mixture of ethanol and water.

[0184] 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 any two of the above ratios.

[0185] In some embodiments, the preparation method further includes: forming a second carbon coating layer on the outside of the silicon-containing coating layer using a second carbon source.

[0186] Optionally, the second carbon source includes acetylene.

[0187] In some alternative embodiments, a second diluent gas, including an inert gas, is also added during the preparation of the second carbon coating layer.

[0188] Optionally, the second diluent gas includes argon.

[0189] 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 is not limited to, 0.5:9, 0.8:9, 1:9, 1.3:9, 1.5:9, 1.7:9, 2:9 or any range between the two values ​​mentioned above.

[0190] In some embodiments, the reaction temperature for preparing the second carbon coating layer is 600℃-800℃; for example, it can be, but is not limited to, 600℃, 620℃, 650℃, 680℃, 700℃, 730℃, 750℃, 770℃, 800℃, or any range between two of the above values. The reaction time is 0.5h-2h; for example, it can be, but is not limited to, 0.5h, 0.7h, 1h, 1.3h, 1.5h, 1.8h, 2h, or any range between two of the above values.

[0191] It should be noted that the terms "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 should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features.

[0192] It should be noted that when the ion-conducting material and the second silicon-based material can be combined to form silicon oxide, before the step of preparing the second carbon coating layer, after coating the silicon-containing coating layer, it can be mixed with a lithium supplementing agent so that the silicon dioxide in the silicon-containing coating layer reacts with the lithium supplementing agent to form lithium silicate with ionic conductivity.

[0193] In some embodiments, the method for preparing the composite silicon material includes:

[0194] Silicon-carbon materials are prepared by vapor deposition using porous conductive materials and a first silicon source as raw materials. The molar ratio of porous conductive materials to the first silicon source is (3-8):1. The first silicon source includes silane. The reaction temperature of the vapor deposition method is 800℃-900℃, the reaction time is 2h-8h, and the reaction atmosphere of the vapor deposition method includes an inert gas.

[0195] A first carbon coating layer is prepared on the outside of a silicon-carbon material using a first carbon source, the first carbon source including acetylene; preparation; a first dilution gas is also added during the preparation of the first carbon coating layer, the first dilution gas including an inert gas; the first dilution gas including argon, the volume ratio of the first carbon source to the first dilution gas is (0.5-2):9; the reaction temperature is 600℃-800℃, and the reaction time is 0.5h-2h;

[0196] An intermediate with a silica coating layer was prepared by forming a silica coating layer on the outside of a silicon-carbon material coated with a first carbon coating layer using a hydrothermal method. The raw materials for preparing the silica coating layer included a second silicon source, which included tetraethyl orthosilicate. The mass ratio of the silicon-carbon material coated with the first carbon coating layer to the second silicon source was 3:(1-5). The reaction temperature of the hydrothermal method was 110℃-130℃, and the reaction time was 0.5h-5h. The reaction medium of the hydrothermal method included a mixture of ethanol and water, with a volume ratio of ethanol to water of (2-4):1.

[0197] The intermediate was reduced by the magnesothermic reduction method to form a silicon-containing coating layer on the outside of the first carbon coating layer; the reducing agent used included magnesium powder, and the mass ratio of the intermediate to magnesium powder was (2-4):1; the reaction temperature of the magnesothermic reduction method was 600℃-750℃, and the reaction time was 0.5h-10h.

[0198] A second carbon coating layer is formed on the outside of the silicon-containing coating layer using a second carbon source; the second carbon source includes acetylene; a second dilution gas is also added when preparing the second carbon coating layer, the second dilution gas includes an inert gas; the second dilution gas includes argon; the volume ratio of the second carbon source and the second dilution gas is (0.5-2):9; the reaction temperature is 600℃-800℃, and the reaction time is 0.5h-2h.

[0199] In some embodiments, the method for preparing the composite silicon material includes:

[0200] The porous conductive material is placed in a rotary furnace, and the rotation speed is adjusted to 1 r / min-15 r / min. The first silicon source is injected at a flow rate of 0.1 L / min-0.6 L / min for 10 min-40 min. After heating to 800℃-900℃, the temperature is held for 2 h-8 h to obtain silicon-carbon material. After cooling, the rotary furnace is purged with argon gas for 30 min. The temperature is then increased to 600℃-800℃ at 5℃ / min-15℃ / min and held for 0.5 h-2 h. Then the gas is switched to a mixture of the first carbon source and the first diluent gas with a volume ratio of (0.5-2):9. The mixture is held for 30 min-120 min and cooled to obtain C@Si-C.

[0201] 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 min. Then, the mixture was added to a 200 ml high-pressure autoclave lined with polytetrafluoroethylene. The autoclave was heated to 110℃-130℃ and held at that temperature for 0.5 h-5 h. The autoclave was then allowed to cool naturally to room temperature. The resulting solution was centrifuged, washed repeatedly with anhydrous ethanol, and vacuum dried at 60℃ for 12 h to obtain SiO2@C@Si-C.

[0202] SiO2@first carbon coating layer@silicon carbide material and Mg powder were mixed at a mass ratio of (2-4):1 and thoroughly ground in a mortar. The mixture was heated in a tube furnace at 600℃-750℃ under an inert gas atmosphere for 0.5h-10h. After cooling to room temperature, MgO and unreacted Mg were removed by washing with 0.5M hydrochloric acid, followed by washing with deionized water until neutral. The mixture was then vacuum dried at 70℃ for 12h. It was then placed in a rotary furnace and purged with argon gas for 30min. The temperature was increased to 700℃ at 10℃ / min. The gas was then switched to a mixture of second carbon source and second dilution gas with a volume ratio of (0.5-2):9. The mixture was kept at this temperature for 30min-120min and then cooled to obtain the C / SiOx@C / Si-C composite material.

[0203] It should be noted that C@Si-C indicates that a first carbon coating layer is applied to the outside of the silicon-carbon material; SiO2@C@Si-C indicates that a silicon dioxide coating layer is applied to the outside of the first carbon coating layer; C / SiOx@C / Si-C indicates that a silicon-containing coating layer is formed on the outside of the first carbon coating layer, and a second carbon coating layer is formed on the outside of the silicon-containing coating layer.

[0204] The fourth aspect of this application provides a negative electrode sheet, comprising: a negative current collector and a negative active material layer located on at least one side of the negative current collector, wherein the negative active material layer comprises a composite silicon material of the first aspect of this application or a composite silicon material prepared by the method of the second aspect of this application.

[0205] The negative electrode sheet using the above-mentioned composite silicon material in this application exhibits a significantly reduced rebound rate after full charging, indicating a significant decrease in the volume expansion of the negative electrode sheet.

[0206] As an example, the negative electrode current collector has two surfaces opposite each other in its own 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.

[0207] 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 substrate 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 the polymer material substrate. 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), etc.

[0208] In some embodiments, the negative electrode active material may also simultaneously employ negative electrode active materials known in the art for use in batteries. 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 may be selected from at least one of elemental silicon, silicon-nitrogen compounds, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more. The weight percentage of the negative electrode active material in the negative electrode film layer is 70-100% by weight, based on the total weight of the negative electrode film layer.

[0209] In some embodiments, the negative electrode film layer may optionally 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 accounts for 0-30% by weight of the negative electrode film layer, based on the total weight of the negative electrode film layer.

[0210] In some embodiments, the negative electrode film may optionally 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 conductive agent accounts for 0-20% by weight of the negative electrode film, based on the total weight of the negative electrode film.

[0211] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)). The other additives constitute 0-15% by weight of the negative electrode film, based on the total weight of the negative electrode film.

[0212] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder, and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry, wherein the solid content of the negative electrode slurry is 30-70 wt%, and the viscosity at room temperature is 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, it is cold-pressed, for example, by rollers, to obtain the negative electrode sheet. The areal density of the negative electrode powder coated on one side is 75-160 g / 1540.25 cm². 2 The compacted density of the negative electrode sheet is 1.2-2.0 g / cm³. 3 .

[0213] The fifth aspect of this application provides a secondary battery, including the negative electrode sheet of the fourth aspect of this application.

[0214] The secondary battery using the aforementioned composite silicon material in this application has improved fast charging capability and cycle performance.

[0215] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0216] Positive electrode sheet

[0217] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including the positive electrode active material of the first aspect of this application.

[0218] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0219] In some embodiments, the positive 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 substrate 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 the polymer material substrate. The metal material includes, but is not limited to, aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. 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).

[0220] In some embodiments, the lithium-ion cathode active material may comprise cathode active materials known in the art for use in batteries. As an example, the cathode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as battery cathode active materials may also be used. These cathode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05 At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites. The positive electrode active material accounts for 80-100% by weight in the positive electrode film, based on the total weight of the positive electrode film.

[0221] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a terpolymer of PVDF-tetrafluoroethylene-propylene, a terpolymer of PVDF-hexafluoropropylene-tetrafluoroethylene, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorinated acrylate resin. The binder constitutes 0-20% by weight of the positive electrode film layer, based on the total weight of the positive electrode film layer.

[0222] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The conductive agent accounts for 0-20% by weight of the positive electrode film, based on the total weight of the positive electrode film.

[0223] In some embodiments, the positive electrode sheet can be prepared by dispersing the components used to prepare the positive electrode sheet, such as the positive active material, conductive agent, binder, and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry, wherein the solid content of the positive electrode slurry is 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 current collector, dried, and then cold-pressed using a cold rolling mill to form the positive electrode sheet; the areal density of the positive electrode powder coated on one side is 180-400 g / 1540.25 cm³. 2 The compaction density of the positive electrode sheet is 3.0-3.6 g / cm³. 3 The concentration can be selected as 3.3-3.5 g / cm³. 3 The formula for calculating the compaction density is as follows:

[0224] Compacted density = Coated surface density / (Extreme electrode thickness after extrusion - Current collector thickness).

[0225] electrolytes

[0226] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0227] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0228] 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 difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP). The concentration of the electrolyte salt is typically 0.5-5 mol / L.

[0229] In some embodiments, the solvent may be selected from one or more of fluoroethylene carbonate (FEC), ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl 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).

[0230] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0231] Separating membrane

[0232] In some embodiments, the secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0233] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven 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.

[0234] In some embodiments, the thickness of the isolation membrane is 6-40 μm, optionally 12-20 μm.

[0235] In some embodiments, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly by a winding process or a stacking process; the electrode assembly and electrolyte are packaged using the battery cell packaging material of the first aspect of this application.

[0236] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 This is an example of a square-structured secondary battery 1.

[0237] In some embodiments, refer to Figure 2 The outer packaging may include a shell 11 and a cover plate 13. The shell 11 may include a bottom plate and side plates connected to the bottom plate, the bottom plate and side plates forming a receiving cavity. The shell 11 has an opening communicating with the receiving cavity, and the cover plate 13 can be placed on the opening to close the receiving cavity.

[0238] The positive electrode, negative electrode, and separator can be formed into electrode assembly 12 by a winding or stacking process. Electrode assembly 12 is encapsulated within the receiving cavity. Electrolyte is immersed in electrode assembly 12. The lithium-ion battery 1 can contain one or more electrode assemblies 12, which can be adjusted according to requirements.

[0239] In some embodiments, secondary batteries can be assembled into battery modules, and the number of secondary batteries contained in a battery module can be multiple, the specific number of which can be adjusted according to the application and capacity of the battery module.

[0240] In a battery module, multiple secondary batteries can be arranged sequentially along the length of the module. Of course, they can also be arranged in any other manner. Furthermore, these multiple lithium-ion batteries can be secured using fasteners.

[0241] Optionally, the battery module may also include a housing with a receiving space in which multiple secondary batteries are housed.

[0242] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0243] The battery pack may include a battery box and multiple battery modules disposed within the battery box. The battery box includes an upper body and a lower body, with the upper body covering the lower body to form a closed space for accommodating the battery modules. The multiple battery modules can be arranged in any manner within the battery box.

[0244] Electrical appliances

[0245] A sixth aspect of this application provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack described in the fifth aspect of this 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, mobile devices, electric vehicles, electric trains, ships and satellites, energy storage systems, etc.; wherein, mobile devices may include, but are not limited to, at least one of mobile phones, laptops, etc.; electric vehicles may include, but are not limited to, at least one of pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.

[0246] The device can be configured to use a secondary battery, battery module, or battery pack, depending on its usage requirements.

[0247] Figure 3 This is an example of an electrical device 2. This electrical device 2 is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the device's requirements for high power and high energy density of the secondary battery, a battery pack or battery module can be used.

[0248] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use lithium-ion batteries as their power source.

[0249] The beneficial effects of this application are further illustrated below with reference to the embodiments.

[0250] To make the technical problems, technical solutions, and beneficial effects solved by this application clearer, the following will provide a more detailed description in conjunction with the embodiments and accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit this application or its applications. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this application.

[0251] Where specific techniques or conditions are not specified in the examples, they shall be performed in accordance with the techniques or conditions described in the literature in this field or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0252] I. Preparation of Composite Silicon Materials

[0253] Example 1

[0254] Porous carbon was placed in a rotary kiln, and the rotation speed was adjusted to 6 r / min. Under an argon atmosphere, silane with a purity of 99.99% (as the first silicon source) was injected at a flow rate of 0.2 L / min for 30 min. The molar ratio of porous carbon to the first silicon source was 4:1. After heating to 850℃, the temperature was maintained for 4 h to carry out a vapor deposition reaction to obtain silicon-carbon material. After cooling, the rotary kiln was purged with argon for 30 min, and the temperature was increased to 700℃ at 10℃ / min. Then, the gas was switched to a mixture of acetylene (as the first carbon source) and argon (as the first dilution gas) with a volume ratio of 1:9. The mixture was maintained for 30 min, and after cooling, a first carbon coating layer was formed on the outside of the silicon-carbon material.

[0255] Weigh 3g of the silicon-carbon material coated with the first carbon coating layer and dissolve it in 100mL of a mixed solution of ethanol and water with a volume ratio of 2:1. Add 2g of tetraethyl orthosilicate (as a second silicon source), stir thoroughly for 30min, and then add it to a 200mL high-pressure reactor lined with polytetrafluoroethylene. Heat to 120℃ and keep warm for 1h, then cool naturally to room temperature. Centrifuge the obtained solution and wash it repeatedly with anhydrous ethanol. Dry it under vacuum at 60℃ for 12h to form a silica coating layer on the outside of the first carbon coating layer, thus obtaining an intermediate with a silica coating layer.

[0256] The above intermediate was mixed with magnesium powder (as a reducing agent) at a mass ratio of 3:1 and thoroughly ground in a mortar. The mixture was then heated in a tube furnace at 650°C for 2 hours under an inert gas atmosphere to carry out a magnesothermic reduction reaction. After cooling to room temperature, MgO and unreacted magnesium powder were removed by washing with 0.5M hydrochloric acid. The mixture was then washed with deionized water until neutral and vacuum dried at 70°C for 12 hours to form a silicon-containing coating layer on the outside of the first coating layer. The mixture was then placed in a rotary furnace and purged with argon gas for 30 minutes. The temperature was increased to 700°C at a rate of 10°C / min. The gas was then switched to a mixture of acetylene (as a second carbon source) and argon (as a second dilution gas) at a volume ratio of 1:9. The mixture was kept at this temperature for 30 minutes and then cooled to form a second carbon coating layer on the outside of the silicon-containing coating layer, thus obtaining the composite silicon material.

[0257] The cross-sectional SEM image of the composite silicon material prepared in Example 1 is shown below. Figure 4 As shown. By Figure 4It is known that the composite silicon material has a coating structure, with a silicon-containing coating layer covering the outside of the silicon-carbon material, and the core material is a load structure. The porous carbon pores contain elemental silicon (i.e., the first silicon-based material), while the coating layer has a dispersion structure, with elemental silicon (i.e., the second silicon-based material) dispersed in the silica matrix.

[0258] Example 2-35

[0259] The preparation methods of the composite silicon materials in Examples 2-35 are basically similar to those in Example 1. The main differences are: the type of the first silicon source, the molar ratio of porous carbon to 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 to the first diluent gas, the reaction temperature and / or time for 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 to the second silicon source, the reaction temperature and / or time for preparing the silica coating layer, the type of reducing agent in the magnesia reduction reaction, the mass ratio of the intermediate with the silica coating layer to the reducing agent, the temperature and / or time of the magnesia reduction reaction, the type of the second carbon source, the type of the second diluent gas, the volume ratio of the second carbon source to the second diluent gas, and the reaction temperature and / or time for preparing the second carbon coating layer are different. See Table 1 for details.

[0260] Comparative Example 1

[0261] The difference between Comparative Example 1 and Example 4 is that only silicon-carbon material and a first coating layer covering the outside of the silicon-carbon material were prepared, as detailed in Tables 1-1 and 1-2.

[0262] Table 1-1

[0263]

[0264] Table 1-2

[0265]

[0266] Wherein, n1 represents the molar ratio of porous carbon to the first silicon source, n2 represents the mass ratio of silicon-carbon material coated with the first carbon layer to the second silicon source, n3 represents the mass ratio of intermediate with silica coating to 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 silicon-containing material and a second carbon coating layer covering the outside of the silicon-containing material were prepared, without silicon-carbon material and a first carbon coating layer covering the outside of the silicon-carbon material. The specific preparation process is as follows:

[0269] Pure SiO2 and Mg powder were mixed (mixing mass ratio 3:1) and thoroughly ground in a mortar. The mixture was heated in a tube furnace at 650℃ for 2 hours under an inert gas atmosphere. After cooling to room temperature, MgO and unreacted Mg were removed by washing with 0.5M hydrochloric acid. The mixture was then washed with deionized water until neutral and vacuum dried at 70℃ for 12 hours. The mixture was then placed in a rotary furnace and purged with argon gas for 30 minutes. The temperature was increased to 700℃ at a rate of 10℃ / min. The gas was then switched to an acetylene / Ar mixture (acetylene to argon volume ratio of 1:9) and held at that temperature for 30 minutes. After cooling, a C / SiOx composite material with a carbon coating layer thickness of 10nm was obtained.

[0270] Comparative Example 3

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

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

[0273] Step 3: The solid powder obtained above is activated in a 50% KOH solution for 12 hours (impregnation ratio 1:3), then dried at 60°C, and then placed in a tube furnace and kept at 700°C for 2 hours under an argon atmosphere. After cooling, it is washed multiple times with 1.0 mol / L HCl to remove inorganic impurities, and then washed with deionized water until the filtrate is neutral. Finally, it is vacuum dried at 60°C for 12 hours to obtain the 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 specific details of the silicon mass percentage in the silicon-carbon material, the pore size of the porous carbon pores, the stacking height of the first silicon-based material in the pores, the thickness of the first coating layer, the thickness of the silicon-containing coating layer, the molar ratio of oxygen to silicon 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 shown in Table 2.

[0276] Table 2

[0277]

[0278]

[0279] Where w1 represents the mass percentage of silicon in the silicon-carbon material, w2 represents the molar ratio of oxygen to silicon in the silicon oxide, d1 represents the pore size of the 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 the 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.

[0280] It should be noted that the mass percentage of silicon in the silicon-carbon materials mentioned above was determined using EDS energy dispersive spectroscopy.

[0281] The pore size of the porous carbon pores mentioned above was determined using a specific surface area analyzer in accordance with GB / T 19587-2017 Gas Adsorption BET Method.

[0282] The stacking height of the first silicon-based material mentioned above within the pores was measured using transmission electron microscopy (TEM).

[0283] The thickness of the first carbon coating layer mentioned above was measured using transmission electron microscopy (TEM).

[0284] The molar ratio of oxygen to silicon in the aforementioned silicon oxide was determined using the following method: X-ray energy dispersive spectroscopy analysis was performed on the composite silicon material, and the silicon content in the silicon-carbon material was subtracted to qualitatively determine the X value in the silicon oxide.

[0285] The volume average particle size Dv50 of the second silicon-based material contained in the aforementioned silicon oxide was determined using a Mastersizer 2000E laser particle size analyzer from Malvern Instruments Ltd., UK, in accordance with GB / T19077-2016 Particle Size Distribution Laser Diffraction Method.

[0286] The thickness of the silicon-containing coating mentioned above was measured using transmission electron microscopy (TEM).

[0287] The thickness of the aforementioned second carbon coating layer was measured using transmission electron microscopy (TEM).

[0288] The volume average particle size Dv50 of the aforementioned composite silicon material was determined using a Mastersizer 2000E laser particle size analyzer from Malvern Instruments Ltd., UK, in accordance with GB / T 19077-2016 Particle Size Distribution Laser Diffraction Method.

[0289] It should be noted that since the volume average particle size Dv50 of the composite silicon material is at the micrometer level, while the thicknesses of the first carbon coating layer, the silicon-containing coating layer, and the second carbon coating layer are only at the nanometer level, the fluctuations in the thicknesses of the first carbon coating layer, the silicon-containing coating layer, and the second carbon coating layer have a very small impact on the volume average particle size Dv50 of the composite silicon material and can be ignored.

[0290] II. Preparation of negative electrode sheet and secondary battery

[0291] 1. Preparation of negative electrode sheet

[0292] The silicon-based materials prepared in the above embodiments and comparative examples were mixed with conductive carbon, sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) at a mass ratio of 10:85:1:1. Water was added, and the mixture was stirred evenly to obtain a negative electrode slurry. The negative electrode slurry was uniformly coated on both sides of a copper foil with a thickness of 6 μm, and the coating surface density on one side was 130 mg / 1540.25 mm. 2 After being dried in an oven and cold-pressed, the material is die-cut with a slit width of 43.5mm to produce lithium-ion battery negative electrode sheets.

[0293] 2. Preparation of the positive electrode sheet

[0294] 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 then uniformly coated onto an aluminum foil with a thickness of 15 μm and an areal density of 320 mg / 1540.25 mm. 2 After drying, the material is cold-pressed and then die-cut to a width of 40mm to produce lithium-ion battery positive electrode sheets.

[0295] 3. Preparation of the separating membrane

[0296] A 3μm thick aluminum oxide coating was applied to polyethylene as the base film to obtain the separator.

[0297] 4. Preparation of electrolyte

[0298] Ethyl carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1. LiPF6 was then uniformly dissolved in this solution to obtain the electrolyte. The concentration of LiPF6 in the electrolyte was 1 mol / L.

[0299] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. After processes such as encapsulation, electrolyte injection, and formation, a lithium-ion battery is produced.

[0300] It should be noted that the formation process in the above lithium-ion battery preparation process is as follows: 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.

[0301] III. Performance Testing of Negative Electrode Sheets and Secondary Batteries

[0302] 1. Electrode rebound rate test

[0303] After fully charging the secondary battery, it was disassembled, and the rebound rate of the negative electrode was tested. The electrode rebound rate = (fully charged electrode thickness / cold-pressed electrode thickness - 1) * 100%. The results are detailed in Table 3.

[0304] Full charge process: Let the battery rest for 30 minutes, then charge it at a 0.5C rate until the voltage is 4.25V, then charge it at a constant voltage of 4.25V until the current is 0.05C, and let it rest for 5 minutes.

[0305] 2. Fast charging capability test

[0306] The negative electrode sheets prepared in the above embodiments and comparative examples were assembled with single-sided positive electrode sheets into three-electrode stacks, and their lithium plating window was tested to calculate their fast charging capability (10-80% SOC).

[0307] Fast charging capability = 60 * 0.1 / (C) 20％ +C 30％ +C 40％ +C 50％ +C 60％ +C 70％ +C 80％ )

[0308] Among them, C xx％ This indicates the maximum charging rate corresponding to the SOC; for example, C. 20％ This indicates the maximum charging rate at 20% SOC. See Table 3 for detailed results.

[0309] 3. Cyclic capacity retention test

[0310] Test conditions: Under normal temperature conditions, the system performs 300 full charge and discharge cycles at a 0.5C rate.

[0311] Test procedure: Let the battery rest for 30 minutes, then charge it at a 0.5C rate to a voltage of 4.25V, then charge it at a constant voltage of 4.25V to a current of 0.05C, let it rest for 5 minutes, and then discharge it at a 0.5C rate to a voltage of 2.5V. This is one charge-discharge cycle. Record the discharge capacity at each cycle.

[0312] Capacity retention rate (%) after 300 cycles = (Discharge capacity of the 300th cycle / Discharge capacity of the first cycle) × 100%.

[0313] The results are detailed in Table 3.

[0314] Table 3

[0315]

[0316]

[0317] As can be seen from the comparison of the results of Examples 1-35 and Comparative Examples 1-3 in Table 3, in this application, by using silicon-carbon material in combination with a silicon-containing coating layer containing 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 sheet can be reduced, and the fast charging performance and cycle performance of the secondary battery can be improved.

[0318] The difference between Examples 1-7 lies in the thickness of the silicon-containing coating layer. In Example 1, the thickness of the silicon-containing coating layer is the smallest, while in Example 7, the thickness is the largest. Compared with Examples 2-6, the fast charging time in Example 1 is prolonged. Technicians analyzed that this may be because when the thickness of the silicon-containing coating layer is too low, the ion transport path may increase only slightly, 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 in Example 7 is significantly increased, and the cycle capacity retention rate is significantly reduced. Technicians analyzed that this may be because 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 lead to excessive expansion of the composite silicon material, which may in turn lead to damage to the SEI film on the surface of the composite silicon material. The electrolyte consumes active lithium to continuously repair the SEI film at the damaged interface, thus deteriorating the cycle performance.

[0319] The main differences between Examples 4 and Examples 8-13 lie in the mass percentage of silicon in the silicon-carbon material and the stacking height of the first silicon-based material within the pores. Example 8 has the lowest mass percentage of silicon in the silicon-carbon material and the lowest stacking height of the first silicon-based material within the pores, while Example 13 has the highest mass percentage of silicon in the silicon-carbon material and the highest stacking height of the first silicon-based material within the pores. Compared to Examples 4 and Examples 9-12, Example 13 exhibits a longer fast-charging time and a significantly reduced cycle capacity retention rate. Technical personnel analyzed that this may be due to the excessively high mass percentage of silicon in the silicon-carbon material, which could lead to a sharp decrease in the conductivity of the silicon-carbon material particles, thus... This results in decreased fast-charging performance and capacity decay, as well as reduced cycle performance. Compared to Examples 4 and 9-12, the cycle capacity retention rate in Example 8 is significantly lower. The technicians analyzed that the reason may be that: when the mass proportion of silicon in the silicon-carbon material is too small, the internal space of the silicon-carbon material particles after lithium intercalation may be large, and the mechanical strength of the silicon-carbon material particles is low. Under long-term high expansion during cycling, the composite silicon material may be prone to cracking, which leads to contact between the electrolyte and the internal silicon, increasing side reactions and reducing the cycle capacity retention rate. It should be noted that because the mass proportion of silicon in the silicon-carbon material in Example 8 is small, the specific capacity and energy density of the final prepared composite silicon material are reduced.

[0320] The main difference between Example 4 and Examples 14-18 lies in the different molar ratios of oxygen and silicon in the silicon oxide. As can be seen from the results of Examples 4 and 14-18, when the molar ratio x of oxygen and silicon in the silicon oxide is 0.6, the silicon oxide has a relatively high specific capacity and a small volume expansion during cycling, fewer side reactions, excellent cycling performance, and can provide more ion channels. Therefore, when x is 0.6, the composite silicon material can balance volume expansion, cycling performance, and fast charging performance.

[0321] The main difference between Examples 4 and Examples 19-22 lies in the different volume average particle size Dv50 of the second silicon-based material contained in the silicon oxide. In Example 22, the volume average particle size Dv50 of the second silicon-based material is the largest. As can be seen from the results of Examples 4 and Examples 19-23, when the volume average particle size Dv50 of the second silicon-based material contained in the silicon oxide is 2-20 nm, 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 cracking, with fewer side reactions. Therefore, the composite silicon material has better fast charging capability and cycle performance, and excellent kinetic performance.

[0322] The main difference between Examples 4 and Examples 23-28 lies in the volume average particle size Dv50 of the composite silicon material. In Example 23, the volume average particle size Dv50 of the composite silicon material is the smallest, while in Example 28, the volume average particle size Dv50 of the composite silicon material is the largest. Compared with Examples 4 and Examples 24-27, the cycle capacity retention rate is reduced in Example 23, and the fast charging time is prolonged in Example 28. From the above comparison, 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 performance. At the same time, due to its small particle size, it can withstand greater strain without cracking, with fewer side reactions, thus the composite silicon material has excellent cycle performance and fast charging performance.

[0323] The main difference between Example 4 and Examples 33-35 is that the setting of the first carbon coating layer and / or the second carbon coating layer is different. As can be seen from the comparison of the results of Example 4 and Examples 33-35, 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.

[0324] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above 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.

[0325] The embodiments described above are merely illustrative of several implementation methods of this application, and 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 those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A composite silicon material, characterized in that, include: The 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 having pores, and at least a portion of the first silicon-based material being distributed within the pores; and A silicon-containing coating layer is applied to the outside of the core. 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. The ion-conducting material and the second silicon-based material are combined to form a silicon oxide.

2. The composite silicon material as described in claim 1, characterized in that, 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 nitrides, silicon-based alloys, tin-based alloys and lithium metal; (3) The molar ratio of oxygen to silicon in the silicon oxide is denoted as x, where 0 < x < 2; (4) The volume average particle size Dv50 of the second silicon-based material is 2nm-20nm; (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 the following: granular, linear, spherical, near-spherical, and sheet-like.

3. The composite silicon material as described in claim 2, characterized in that, The thickness of the silicon-containing coating layer is 30nm-60nm.

4. The composite silicon material as described in claim 2, characterized in that, The molar ratio of oxygen to silicon in the silicon oxide is denoted as x, where 0 < x ≤ 0.

6.

5. The composite silicon material as described in claim 2, characterized in that, The volume average particle size Dv50 of the second silicon-based material is 2nm-9nm.

6. The composite silicon material as described in claim 1, characterized in that, The silicon-carbon material has at least one of the following characteristics: (1) The mass percentage of silicon in the silicon-carbon material is 3%-25%; (2) The aperture of the hole is 2nm-50nm; (3) The stacking height of the first silicon-based material in the pore is 1nm-35nm; (4) The shape of the silicon-carbon material includes one or more of the following: granular, spherical, and near-spherical. (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 the following: granular, linear, spherical, near-spherical, and sheet-like. (7) The porous conductive material includes porous carbon.

7. The composite silicon material as described in claim 6, characterized in that, The mass percentage of silicon in the silicon-carbon material is 8%-10%.

8. The composite silicon material as described in claim 6, characterized in that, The aperture of the hole is 15nm-35nm.

9. The composite silicon material as described in claim 6, characterized in that, The first silicon-based material has a stacking height of 15nm-25nm within the pores.

10. The composite silicon material as described in claim 1, characterized in that, At least 3% of the first silicon-based material is embedded in the pores.

11. The composite silicon material as described in claim 10, characterized in that, All of the first silicon-based material is embedded within the holes.

12. The composite silicon material according to any one of claims 1 to 4, characterized in that, The composite silicon material further includes a first carbon coating layer, which is located between the core and the silicon-containing coating layer.

13. The composite silicon material as described in claim 12, characterized in that, The first carbon coating layer has at least one of the following characteristics: (1) The thickness of the first carbon coating layer is 10nm-30nm; (2) The material of the first carbon coating layer includes amorphous carbon.

14. The composite silicon material according to any one of claims 1 to 4, characterized in that, The composite silicon material further includes a second carbon coating layer, which covers the outside of the silicon-containing coating layer.

15. The composite silicon material as described in claim 14, characterized in that, The second carbon coating layer has at least one of the following characteristics: (1) The thickness of the second carbon coating layer is 10nm-30nm; (2) The material of the second carbon coating layer includes amorphous carbon.

16. The composite silicon material according to any one of claims 1 to 4, characterized in that, The composite silicon material has one or more of the following shapes: granular, spherical, and near-spherical.

17. The composite silicon material as described in claim 16, characterized in that, The volume average particle size Dv50 of the composite silicon material is 3μm-22μm.

18. The composite silicon material as described in claim 17, characterized in that, The volume average particle size Dv50 of the composite silicon material is 5μm-10μm.

19. A method for preparing a composite silicon material as described in any one of claims 1 to 18, characterized in that, Includes the following steps: Prepare the silicon-carbon material; The silicon-containing coating layer is formed on the outside of the silicon-carbon material.

20. A method for preparing a composite silicon material as described in any one of claims 1 to 18, characterized in that, Includes the following steps: Prepare the silicon-carbon material; A silica coating layer is formed on the outside of the silicon-carbon material to prepare an intermediate with a silica coating layer. The intermediate is reduced to form the silicon-containing coating layer on the outside of the silicon-carbon material.

21. The method for preparing the composite silicon material as described in claim 20, characterized in that, The silicon-carbon material was prepared by vapor deposition.

22. The method for preparing the composite silicon material as described in claim 21, characterized in that, The vapor deposition method includes at least one of the following conditions: (1) The raw materials for preparing the silicon-carbon material include porous conductive materials and a first silicon source; (2) The reaction temperature of the vapor deposition method is 800℃-900℃ 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 the composite silicon material as described in claim 22, characterized in that, The molar ratio of the porous conductive material to the first silicon source is (3-8):

1.

24. The method for preparing the composite silicon material as described in claim 22, characterized in that, The first silicon source includes silane.

25. The method for preparing the composite silicon material as described in claim 22, characterized in that, The porous conductive material includes porous carbon.

26. The method for preparing the composite silicon material as described in claim 20, characterized in that, A silica coating layer is formed on the outside of the silicon-carbon material using a hydrothermal method.

27. The method for preparing the composite silicon material as described in claim 26, characterized in that, The hydrothermal method includes at least one of the following conditions: (1) The raw materials for preparing the silica coating layer include a second silicon source; (2) The reaction temperature of the hydrothermal method is 110℃-130℃, and the reaction time is 0.5h-5h; (3) The reaction medium of the hydrothermal method includes a mixture of ethanol and water.

28. The method for preparing the composite silicon material as described in claim 27, characterized in that, The second silicon source includes tetraethyl orthosilicate.

29. The method for preparing the composite silicon material as described in claim 27, characterized in that, The mass ratio of the silicon-carbon material to the second silicon source is 3:(1-5).

30. The method for preparing the composite silicon material as described in claim 27, characterized in that, The volume ratio of ethanol to water in the mixture is (2-4):

1.

31. The method for preparing the composite silicon material as described in claim 20, characterized in that, The intermediate was reduced using a magnesothermic reduction method.

32. The method for preparing the composite silicon material as described in claim 31, characterized in that, The magnesium thermal reduction method includes at least one of the following conditions: (1) The reducing agent used includes magnesium powder; (2) The reaction temperature of the magnesium thermal reduction method is 600℃-750℃ and the reaction time is 0.5h-10h.

33. The method for preparing the composite silicon material as described in claim 32, characterized in that, The mass ratio of the intermediate to the magnesium powder is (2-4):

1.

34. The method for preparing the composite silicon material according to any one of claims 20 to 33, characterized in that, Prior to the step of forming a silicon dioxide coating layer on the outside of the silicon-carbon material, the method further includes: A first carbon coating layer is prepared on the outside of the silicon-carbon material using a first carbon source.

35. The method for preparing the composite silicon material as described in claim 34, characterized in that, The preparation of the first carbon coating layer includes at least one of the following conditions: (1) The first carbon source includes acetylene; (2) When preparing the first carbon coating layer, a first dilution gas is also added, the first dilution gas including an inert gas; (3) The reaction temperature is 600℃-800℃ and the reaction time is 0.5h-2h.

36. The method for preparing the composite silicon material as described in claim 35, characterized in that, The first diluting gas includes argon.

37. The method for preparing the composite silicon material as described in claim 35, characterized in that, The volume ratio of the first carbon source to the first diluting gas is (0.5-2):

9.

38. The method for preparing the composite silicon material according to any one of claims 20 to 33, characterized in that, The preparation method further includes: A second carbon coating layer is formed on the outside of the silicon-containing coating layer using a second carbon source.

39. The method for preparing the composite silicon material as described in claim 38, characterized in that, The preparation of the second carbon coating layer includes at least one of the following conditions: (1) The second carbon source includes acetylene; (2) A second diluting gas is also added when preparing the second carbon coating layer, the second diluting gas including an inert gas; (3) The reaction temperature is 600℃-800℃ and the reaction time is 0.5h-2h.

40. The method for preparing the composite silicon material as described in claim 39, characterized in that, The second diluting gas includes argon.

41. The method for preparing the composite silicon material as described in claim 40, characterized in that, The volume ratio of the second carbon source to the second diluting gas is (0.5-2):

9.

42. A negative electrode sheet, characterized in that, include: Negative electrode current collector; as well as A negative electrode active material layer is located on at least one side of the negative electrode current collector, the negative electrode active material layer comprising a composite silicon material as described in any one of claims 1 to 18 or a composite silicon material prepared by the method described in any one of claims 19 to 41.

43. A secondary battery, characterized in that, Includes the negative electrode sheet as described in claim 42.

44. An electrical appliance, characterized in that, Includes the secondary battery as described in claim 43.

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