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

Abstract

A silicon composite material and a preparation method therefor, a negative electrode sheet, a secondary battery, and an electric device. The silicon composite material comprises a core and a first coating layer covering the surface of the core; the core comprises a first core and a second core; the first core comprises a first conductive material; the first conductive material comprises a flexible conductive material; the second core comprises a silicon-based material of which the surface is coated with a second coating layer; and the second coating layer contains a second conductive material. The silicon composite material has the characteristics of good cycle performance and fast charging performance.

Description

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

[0001] Related applications

[0002] This application claims priority to Chinese patent application number 2023111458084, filed on September 6, 2023, entitled “Silicon composite material and preparation method thereof, negative electrode sheet, secondary battery and electrical device,” the entire text of which is hereby incorporated by reference. Technical Field

[0003] The present application relates to the technical field of battery materials, and in particular to a silicon composite material and a preparation method thereof, a negative electrode sheet, a secondary battery and an electrical device. Background Art

[0004] In recent years, the application of lithium-ion batteries has become increasingly widespread. They are widely used in energy storage systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and other fields. As lithium-ion batteries have achieved significant development, higher requirements have been placed on their energy density, cycle performance, and safety performance.

[0005] Silicon-based materials have attracted attention due to their significantly higher capacity than carbon-based materials, as higher capacity translates to higher energy density. However, silicon-based materials experience significant volume changes (>300%) during charge and discharge, which can cause material particles to break and the conductive network of the electrode to collapse, impacting the battery's cycling and fast-charging performance.

[0006] Summary of the Invention

[0007] The present application provides a silicon composite material with good cycle performance and fast charging performance and a preparation method thereof, as well as a negative electrode plate, a secondary battery and an electrical device using the silicon composite material.

[0008] In the first aspect of the present application, a silicon composite material is provided, comprising a core and a first coating layer coated on the surface of the core, wherein the core comprises a first core and a second core, the first core comprises a first conductive material, the first conductive material comprises a flexible conductive material, the second core comprises a silicon-based material with a second coating layer coated on the surface, and the second coating layer comprises a second conductive material.

[0009] The above-mentioned silicon composite material can have both good expansion inhibition and conductivity, thereby effectively improving the cycle performance and fast charging performance.

[0010] In some embodiments, the silicon-based material is a nanoscale or microscale silicon-based material;

[0011] Optionally, the Dv50 of the silicon-based material is 10 nm to 5 μm;

[0012] Optionally, the silicon-based material includes one or both of pure silicon and silicon monoxide;

[0013] Further optionally, the Dv50 of the pure silicon is 10nm to 150nm; further optionally, the Dv50 of the pure silicon is 50nm to 100nm;

[0014] Further optionally, the Dv50 of the silicon monoxide is 2 μm to 5 μm; further optionally, the Dv50 of the silicon monoxide is 2.5 μm to 3.5 μm.

[0015] In some embodiments, the flexible conductive material includes one or both of soft carbon and graphite; optionally, the flexible conductive material includes graphite.

[0016] In some embodiments, the graphite includes one or both of the following features:

[0017] (1) The Dv50 of the graphite is 1 μm to 5 μm; optionally, the Dv50 of the graphite is 1 μm to 3.5 μm;

[0018] (2) The graphite includes one or both of natural graphite and artificial graphite.

[0019] In some embodiments, the second conductive material includes a conductive carbon material; optionally, the conductive carbon material includes one or more of graphene, single-walled carbon nanotubes, or multi-walled carbon nanotubes.

[0020] In some embodiments, the thickness of the second cladding layer is 0.3 nm to 3 nm; optionally, the thickness of the second cladding layer is 1.2 nm to 3 nm.

[0021] In some embodiments, the mass percentage of the first conductive material and the silicon-based material whose surface is coated with the second coating layer is (10% to 90%): (90% to 10%); optionally, the mass percentage of the first conductive material and the silicon-based material whose surface is coated with the second coating layer is (40% to 90%): (60% to 10%).

[0022] In some embodiments, the first coating layer includes a carbon coating layer; optionally, the carbon coating layer includes one or both of the following features:

[0023] (1) The thickness is 5 nm to 60 nm; optionally, the thickness is 20 nm to 60 nm;

[0024] (2) The carbon coating layer includes amorphous carbon.

[0025] In some embodiments, the silicon composite material includes one or more of the following features:

[0026] (1) Tap density is 0.9g / cm 3 ~1.3g / cm 3 ;

[0027] (2) Specific surface area is 0.6m 2 / g~1.4m 2 / g;

[0028] (3) The Dv50 of the silicon composite material is 3 μm to 30 μm;

[0029] Optionally, the silicon-based material includes pure silicon, and the Dv50 of the silicon composite material is 3 μm to 15 μm;

[0030] Optionally, the silicon-based material includes silicon monoxide, and the Dv50 of the silicon composite material is 8 μm to 30 μm.

[0031] A second aspect of the present application provides a method for preparing a silicon composite material, comprising the following steps:

[0032] Mixing a first conductive material, a silicon-based material having a second coating layer on its surface, and water to prepare a dispersion; the second coating layer comprises a second conductive material, and the first conductive material comprises a flexible conductive material;

[0033] drying the dispersion to prepare a precursor;

[0034] The precursor is coated to form a first coating layer, which is coated on the surface of the core. The core includes a first core and a second core. The first core includes the first conductive material, and the second core includes a silicon-based material with a second coating layer coated on the surface.

[0035] The preparation method has simple steps and is easy to promote and apply in industrialization.

[0036] In some embodiments, the preparation method of the silicon-based material having the second coating layer coated on the surface comprises one or both of a gas phase reaction method and a liquid phase coating method, and the second coating layer comprises graphene;

[0037] Optionally, preparing the silicon-based material having the second coating layer coated on the surface by a gas phase reaction method comprises the following steps:

[0038] vapor-depositing the silicon-based material in a mixed gas of a second carbon source gas and carbon dioxide to form the second coating layer, thereby preparing the silicon-based material having the second coating layer coated on its surface;

[0039] Further optionally, the temperature of the vapor deposition is 600° C. to 800° C.;

[0040] Further optionally, the second carbon source gas includes a hydrocarbon gas; further optionally, the second carbon source gas includes one or both of CH4 or C2H4;

[0041] Optionally, the liquid phase coating method for preparing the silicon-based material having the second coating layer coated on the surface comprises the following steps:

[0042] Mixing the silicon-based material with a second dispersant, water, and graphene oxide to prepare a mixed solution;

[0043] Drying and calcining the mixed solution to prepare the silicon-based material with the second coating layer coated on the surface;

[0044] Further optionally, the second dispersant includes one or more of polyvinyl pyrrolidone, polyethylene glycol or sodium carboxymethyl cellulose;

[0045] Further optionally, the drying conditions include: a temperature of 60°C to 80°C;

[0046] Further optionally, the calcination conditions include: heating to 600° C. to 800° C. at a heating rate of 2° C. / min to 5° C. / min under a reducing atmosphere, and calcining for 1 hour to 3 hours.

[0047] In some embodiments, the solid content of the dispersion is 1% to 40%.

[0048] In some embodiments, the process of preparing the dispersion further comprises the step of adding a first dispersant;

[0049] Optionally, the first dispersant includes one or more of polyvinyl pyrrolidone, polyethylene glycol or sodium carboxymethyl cellulose;

[0050] Optionally, the percentage between the mass of the first dispersant and the total mass of the first conductive material and the silicon-based material whose surface is coated with the second coating layer is (70% to 95%): (30% to 5%); further optionally, the percentage between the mass of the first dispersant and the total mass of the first conductive material and the silicon-based material whose surface is coated with the second coating layer is (20% to 5%): (80% to 95%).

[0051] In some embodiments, the drying comprises spray drying; optionally, the spray drying comprises one or both of the following conditions:

[0052] (1) Temperature is 150℃~200℃;

[0053] (2) Air volume is 0.08m 3 / min~0.2m 3 / min.

[0054] In some embodiments, the first coating layer includes a carbon coating layer, and the steps of forming the first coating layer include: placing the precursor in a reaction container, introducing a first carbon source gas for vapor deposition to form the first coating layer;

[0055] Optionally, the conditions for introducing the first carbon source gas for vapor deposition include one or both of the following conditions:

[0056] (1) The first carbon source gas includes one or both of CH4 and C2H2;

[0057] (2) First, the temperature is raised to 600-800°C at a heating rate of 2°C / min-10°C / min, and kept at this temperature for 1h-4h, and then the first carbon source gas is introduced for 15min-30min.

[0058] In a third aspect of the present application, a negative electrode plate is provided, comprising a negative electrode current collector and a negative electrode active material layer arranged on at least one surface of the negative electrode current collector, wherein the negative electrode active material layer comprises one or more of the silicon composite material described in the first aspect or the silicon composite material prepared by the preparation method described in the second aspect.

[0059] In a fourth aspect of the present application, a secondary battery is provided, comprising the negative electrode sheet described in the third aspect.

[0060] In a fifth aspect of the present application, an electrical device is provided, comprising one or more of the negative electrode sheet described in the third aspect or the secondary battery described in the fourth aspect.

[0061] The details of one or more embodiments of the present application are set forth in the following drawings and description. Other features, objects, and advantages of the present application will become apparent from the description, drawings, and claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] In order to better describe and illustrate the embodiments or examples provided in this application, reference may be made to one or more of the accompanying drawings. The additional details or examples used to describe the accompanying drawings should not be considered as limiting the scope of the disclosed application, the embodiments or examples currently described, and any of the best modes currently understood for these applications. Moreover, the same reference numerals are used throughout the drawings to represent the same components. In the accompanying drawings:

[0063] FIG1 is a schematic diagram of a battery cell according to an embodiment of the present application;

[0064] FIG2 is an exploded view of a battery cell according to an embodiment of the present application shown in FIG1 ;

[0065] FIG3 is a schematic diagram of a battery module according to an embodiment of the present application;

[0066] FIG4 is a schematic diagram of a battery pack according to an embodiment of the present application;

[0067] FIG5 is an exploded view of the battery pack shown in FIG4 according to an embodiment of the present application;

[0068] FIG6 is a schematic diagram of an electrical device using a secondary battery as a power source according to an embodiment of the present application;

[0069] Explanation of reference numerals: 1 battery pack; 2 upper case; 3 lower case; 4 battery module; 5 battery cell; 51 housing; 52 electrode assembly; 53 cover plate; 6 electrical device. DETAILED DESCRIPTION

[0070] Below, some embodiments of the silicon composite material and its preparation method, negative electrode plate, secondary battery and electrical device of the present application are described in detail with appropriate reference to the drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0071] The "ranges" disclosed in this application can be defined in the form of lower limits and upper limits. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of the particular range. Ranges defined in this way can be inclusive or exclusive of the end values, any end value can be included or excluded independently, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60 to 120 and 80 to 110 are listed for a particular parameter, it is understood that ranges of 60 to 110 and 80 to 120 are also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4, and 5 are also listed, the following ranges are all expected: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5. In this application, unless otherwise specified, the numerical range "a to b" is an abbreviation for any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to listing the parameter as, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, and so on. For example, when a parameter is expressed as an integer selected from "2-10," this is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0072] In this application, "a plurality of" or "a plurality of" refers to a number greater than or equal to 2 unless otherwise specified. For example, "one or more" means one or more than or equal to two.

[0073] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0074] References to "embodiments" herein mean that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment or implementation of the present application. The appearance of such phrases in various locations in the specification does not necessarily refer to the same embodiment, nor does it necessarily refer to independent or alternative embodiments that are mutually exclusive with other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments. References to "implementations" herein have a similar understanding.

[0075] It will be appreciated by those skilled in the art that, in the methods of various embodiments or examples, the order in which the steps are written does not imply a strict order of execution and does not constitute any limitation on the implementation process, and the detailed order of execution of each step should be determined by its function and possible inherent logic. Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0076] In this application, in the open technical features or technical solutions described with words such as "contain", "include", and "include", unless otherwise specified, additional members other than the listed members are not excluded, and it can be regarded as providing both closed features or solutions consisting of the listed members and open features or solutions that also include additional members in addition to the listed members. For example, A includes a1, a2, and a3. Unless otherwise specified, it may also include other members or may not include additional members. It can be regarded as providing both the feature or solution of "A consists of a1, a2, and a3" and the feature or solution of "A includes not only a1, a2, and a3, but also other members". In this application, unless otherwise specified, A (such as B) means that B is a non-limiting example of A, and it can be understood that A is not limited to B.

[0077] In this application, the terms "optionally," "optional," and "optional" are optional and refer to either option being present or absent. If a technical solution contains multiple "options," each option is considered independent unless otherwise specified and there are no conflicts or constraints.

[0078] In some examples of the present application, a silicon composite material is provided, including a core and a first coating layer coated on the surface of the core, the core including a first core and a second core, the first core including a first conductive material, the first conductive material including a flexible conductive material, the second core including a silicon-based material with a second coating layer coated on the surface, and the second coating layer including a second conductive material.

[0079] The above-mentioned silicon composite material comprehensively improves the expansion properties and conductive network of the silicon composite material through two aspects: first, a second coating layer containing a second conductive material is coated on the surface of the silicon-based material. The presence of the second conductive material can improve the conductivity of the silicon-based material on the one hand, and on the other hand, it can also make the silicon-based material, especially the small-particle silicon-based material, uniformly dispersed and easily coated by the first coating layer; secondly, the first conductive material containing a flexible conductive material is mixed with the silicon-based material with the second coating layer on the surface as the core. The presence of the flexible conductive material can buffer the expansion of the silicon-based material and has good conductivity. In this way, the above-mentioned silicon composite material can have both good expansion inhibition and conductivity, thereby effectively improving the cycle performance and fast charging performance.

[0080] In addition, the presence of the coating layer can protect the internal particles and better isolate the electrolyte from corroding the internal part of the material during the cycle.

[0081] It is understandable that the silicon-based material may be pre-lithiated or non-pre-lithiated.

[0082] In some examples, the silicon-based material is nanoscale or microscale. Using a small-particle silicon-based material can further reduce expansion. It is understood that "nanoscale" means that the Dv50 of the silicon-based material satisfies 1 nanometer (nm) ≤ Dv50 < 100nm, and "microscale" means that the Dv50 of the silicon-based material satisfies 1 micrometer (μm) ≤ Dv50 < 10μm.

[0083] In some examples, the Dv50 of the silicon-based material is 10nm to 5μm. Reasonable control of the particle size of the silicon-based material is conducive to improving fast charging performance and cycle life. It is also beneficial to the molding and dispersion of particles. Specifically, the Dv50 of the silicon-based material includes but is not limited to: 10nm, 20nm, 30nm, 40nm, 50nm, 70nm, 80nm, 90nm, 100nm, 110nm, 115nm, 120nm, 150nm, 200nm, 400nm, 600nm, 800nm, 1μm, 2μm, 3μm, 4μm, 5μm or a range between any two of the foregoing.

[0084] In some examples, the silicon-based material includes one or both of pure silicon and silicon monoxide (SiOx, 0<x<2).

[0085] Furthermore, the Dv50 of the pure silicon is between 10nm and 150nm. Specifically, the Dv50 of the pure silicon includes, but is not limited to, 10nm, 20nm, 30nm, 40nm, 50nm, 70nm, 80nm, 90nm, 100nm, 110nm, 115nm, 120nm, 150nm, or a range between any two of the foregoing. Furthermore, the Dv50 of the pure silicon is between 50nm and 100nm.

[0086] Furthermore, the Dv50 of the silicon 2 oxide is 2 μm to 5 μm. Specifically, the Dv50 of the silicon 2 oxide includes but is not limited to: 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 5 μm, or a range between any two of the foregoing. Furthermore, the Dv50 of the silicon 2 oxide is 2.5 μm to 3.5 μm.

[0087] In some examples, the flexible conductive material includes one or both of soft carbon and graphite. Furthermore, the flexible conductive material includes graphite. Using graphite as the flexible conductive material effectively buffers the expansion of the silicon-based material and provides excellent conductivity. Furthermore, the graphite is not limited in form and may be spherical, granular, flake, or a combination thereof.

[0088] In some examples, the Dv50 of the graphite is 1μm to 5μm. Reasonable control of the Dv50 of the graphite is conducive to improving fast charging performance and cycle life. Specifically, the Dv50 of the graphite includes but is not limited to: 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm, 5μm or a range between any two of the foregoing. Furthermore, the Dv50 of the graphite is 1μm to 3.5μm.

[0089] In some examples, the graphite includes one or both of natural graphite and artificial graphite. Furthermore, the graphite includes artificial graphite. This is beneficial for improving cycle life.

[0090] In some examples, the second conductive material includes a conductive carbon material. Furthermore, the conductive carbon material includes one or more of graphene, single-walled carbon nanotubes, or multi-walled carbon nanotubes. Furthermore, the conductive carbon material includes graphene. Using graphene as the second conductive material to coat the silicon-based material provides a good coating effect, which is beneficial for improving conductivity.

[0091] In some examples, the thickness of the second coating layer is 0.3nm to 3nm. Reasonable control of the thickness of the graphene layer makes the material relatively soft and easy to achieve complete coating of the silicon-based material, which is beneficial to the improvement of the cycle life. Specifically, the thickness of the second coating layer includes but is not limited to: 0.3nm, 0.8nm, 1nm, 1.2nm, 1.5nm, 2nm, 2.5nm, 3nm or a range between any two of the foregoing. Furthermore, the thickness of the second coating layer is 1.2nm to 3nm.

[0092] In some examples, the mass percentage of the first conductive material and the silicon-based material with the second coating layer on the surface is (10% to 90%): (90% to 10%). This is beneficial to reducing the expansion of the material on the one hand, and on the other hand, it can also make the material have a higher capacity, further improving the fast charging performance and cycle performance. A higher proportion of silicon-based materials can increase the capacity of the material. However, in traditional methods, when the proportion of silicon-based materials reaches 90%, the material expands significantly. For example, the anode full charge rebound can reach more than 300%. The solution of the present application can effectively improve the expansion of the material. Within the range of the mass percentage of the first conductive material and the silicon-based material with the second coating layer on the surface is (10% to 90%): (90% to 10%), a low anode full charge rebound can be maintained.

[0093] Specifically, the mass percentage includes, but is not limited to, 10%:90%, 20%:80%, 30%:70%, 40%:60%, 50%:50%, 60%:40%, 70%:30%, 80%:20%, 90%:10%, or a range between any two of the foregoing. Furthermore, the mass percentage of the first conductive material and the silicon-based material coated with the second coating layer is (40% to 90%):(60% to 10%).

[0094] In some examples, the first coating layer includes a carbon coating layer. Coating the core with the carbon coating layer can further buffer the expansion of the silicon-based material and improve the conductivity between the particles.

[0095] In some examples, the thickness of the carbon coating layer is 5nm to 60nm. This can better isolate the corrosion of the electrolyte on the inside of the material during the cycle, improve the cycle performance, and also improve the conductivity of the material. Specifically, the thickness of the carbon coating layer includes but is not limited to 5nm, 10nm, 15nm, 20nm, 25nm, 30nm, 35nm, 40nm, 45nm, 50nm, 55nm, 60nm or a range between any two of the foregoing. Furthermore, the thickness of the carbon coating layer is 20nm to 60nm.

[0096] Without limitation, the carbon coating layer includes amorphous carbon.

[0097] In some examples, the tap density of the silicon composite material is 0.9 g / cm3 (g / cm 3 )~1.3g / cm 3 .

[0098] In some examples, the specific surface area of ​​the silicon composite material is 0.6 m2 / g (m 2 / g)~1.4m 2 / g;

[0099] In some examples, the silicon composite material has a Dv50 of 3 μm to 30 μm.

[0100] Furthermore, the silicon-based material includes pure silicon, and the Dv50 of the silicon composite material is 3 μm to 15 μm;

[0101] Furthermore, the silicon-based material includes silicon monoxide, and the Dv50 of the silicon composite material is 8 μm to 30 μm.

[0102] Some other examples of the present application provide a method for preparing a silicon composite material, comprising the following steps:

[0103] Mixing a first conductive material, a silicon-based material having a second coating layer on its surface, and water to prepare a dispersion; the second coating layer comprises a second conductive material, and the first conductive material comprises a flexible conductive material;

[0104] drying the dispersion to prepare a precursor;

[0105] The precursor is coated to form a first coating layer, which is coated on the surface of the core. The core includes a first core and a second core. The first core includes the first conductive material, and the second core includes a silicon-based material with a second coating layer coated on the surface.

[0106] The preparation method has simple steps and is easy to promote and apply in industrialization.

[0107] It can be understood that the silicon composite material prepared by the above preparation method has the same or similar scheme and effect as the aforementioned silicon composite material, and will not be described in detail here.

[0108] In some examples, the method for preparing the silicon-based material having the second coating layer on its surface comprises one or both of a gas phase reaction method and a liquid phase coating method. Without limitation, the equipment for the gas phase reaction method can be any equipment suitable for gas condensation method, hydrogen arc plasma method, sputtering method, vacuum deposition method, hybrid plasma method, gas phase decomposition method, plasma heating physical vapor synthesis, wire electric explosion technology, laser-induction composite heating method, or laser-induced chemical vapor deposition method.

[0109] Furthermore, the second coating layer comprises graphene, and the gas phase reaction method for preparing the silicon-based material having the second coating layer coated on the surface comprises the following steps:

[0110] The silicon-based material is vapor-deposited in a mixed gas of a second carbon source gas and carbon dioxide to form the second coating layer, thereby preparing the silicon-based material with the surface coated with the second coating layer.

[0111] In some examples, the vapor deposition temperature is 600 degrees Celsius (° C.) to 800° C.;

[0112] In some examples, the second carbon source gas includes a hydrocarbon gas. Without limitation, the second carbon source gas includes one or both of CH4 and C2H4.

[0113] Furthermore, the second coating layer comprises graphene, and the liquid phase coating method for preparing the silicon-based material having the second coating layer coated on the surface comprises the following steps:

[0114] Mixing the silicon-based material with a second dispersant, water, and graphene oxide to prepare a mixed solution;

[0115] The mixed liquid is dried and calcined to prepare the silicon-based material with the second coating layer coated on the surface.

[0116] In some examples, the second dispersant includes one or more of polyvinyl pyrrolidone (PVP), polyethylene glycol, or sodium carboxymethyl cellulose (CMC).

[0117] In some examples, the drying conditions include a temperature of 60°C to 80°C.

[0118] In some examples, the calcination conditions include: heating to 600°C to 800°C at a heating rate of 2°C / min to 5°C / min under a reducing atmosphere, and calcining for 1 to 3 hours. Without limitation, the inert gas includes argon and hydrogen, and the volume ratio of argon to hydrogen can be (90 to 98): (10 to 2). It is understood that a cooling step is included after the calcination, such as natural cooling to room temperature.

[0119] In addition, in some examples, the solid content of the dispersion is 1% to 40%.

[0120] In some examples, the process of preparing the dispersion further includes the step of adding a first dispersant. The introduction of the first dispersant enables the first conductive material and the silicon-based material coated with the second coating layer to be evenly dispersed, thereby improving the cycling performance and fast charging performance.

[0121] In some examples, the first dispersant includes one or more of polyvinyl pyrrolidone (PVP), polyethylene glycol, or sodium carboxymethyl cellulose (CMC).

[0122] In some examples, the percentage of the mass of the first dispersant to the total mass of the first conductive material and the silicon-based material coated with the second coating layer is (30% to 5%):(70% to 95%). Specifically, the percentage includes, but is not limited to, 30%:70%, 25%:75%, 20%:80%, 15%:85%, 10%:90%, 5%:95%, or a range between any two of the foregoing. Furthermore, the percentage is (20% to 5%):(80% to 95%).

[0123] In some examples, the drying comprises spray drying.

[0124] In some examples, the spray drying temperature is 150°C to 200°C.

[0125] In some examples, the air volume of the spray drying is 0.08 cubic meters per minute (m 3 / min)~0.2m 3 / min.

[0126] In some examples, the first coating layer includes a carbon coating layer, and the step of forming the first coating layer includes: placing the precursor in a reaction container, introducing a first carbon source gas for vapor deposition, and forming the first coating layer.

[0127] In some examples, during the process of introducing the first carbon source gas for vapor deposition, the first carbon source gas includes one or both of CH4 and C2H2.

[0128] In some of the examples, during the process of introducing the first carbon source gas for vapor deposition, the temperature is first raised to 600°C to 800°C at a heating rate of 2°C / min to 10°C / min, kept for 1h to 4h, and then the first carbon source gas is introduced for 15 minutes (min) to 30 minutes.

[0129] Some other examples of the present application provide a negative electrode plate, including a negative electrode current collector and a negative electrode active material layer arranged on at least one surface of the negative electrode current collector, wherein the negative electrode active material layer includes one or more of the silicon composite materials as described above or the silicon composite materials prepared by the preparation method as described above.

[0130] Some other examples of the present application provide a secondary battery including the negative electrode sheet as described above.

[0131] Some other examples of the present application provide an electrical device including one or more of the negative electrode sheet described above or the secondary battery described above.

[0132] In addition, the secondary battery and the electric device of the present application will be described below with reference to the drawings as appropriate.

[0133] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During the battery's charge and discharge processes, active ions are inserted and removed between the positive and negative electrodes. The electrolyte conducts ions between the positive and negative electrodes. The separator, located between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0134] Positive electrode

[0135] It is understandable that the battery will be accompanied by lithium (Li) deintercalation and consumption during the charge and discharge process, and the Li content in the positive electrode plate is different when the battery is discharged to different states. In the list of positive electrode materials in this application, unless otherwise specified, the Li content is the initial state of the material. The positive electrode material is applied to the positive electrode plate in the battery system, and after the charge and discharge cycle, the Li content in the positive electrode material contained in the plate will usually change. Among them, the Li content can be measured by molar content, but is not limited to this. Regarding "the Li content is the initial state of the material", the initial state of the material refers to the state before the material is added to the positive electrode slurry. It is understandable that new materials obtained by appropriate modification on the basis of the listed positive electrode materials are also within the scope of positive electrode materials. The aforementioned appropriate modification refers to acceptable modification methods for positive electrode materials, and non-limiting examples include coating modification.

[0136] In the examples of positive electrode materials in this application, the oxygen (O) content is only a theoretical value. Lattice oxygen release will cause the molar content of oxygen to change, and the actual O content will fluctuate. The O content can be measured by molar content, but is not limited to this.

[0137] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode active material layer includes a positive electrode active material.

[0138] As a non-limiting example, the positive electrode current collector has two surfaces facing each other in its thickness direction, and the positive electrode active material layer is disposed on either or both of the two facing surfaces of the positive electrode current collector.

[0139] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector may be obtained by forming a metal material on a polymer material substrate. In the positive electrode current collector, non-limiting examples of the metal material may include one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy. In the positive electrode current collector, non-limiting examples of the polymer material substrate may include one or more of substrates such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0140] In some embodiments, the positive electrode active material may be a positive electrode active material for a battery that is well known in the art. As a non-limiting example, the positive electrode active material may include one or more of the following materials: an olivine-structured lithium-containing phosphate, a lithium transition metal oxide, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides may include, but are not limited to, one or more of lithium cobalt oxide (such as LiCoO2), lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their modified compounds. Non-limiting examples of olivine-structured lithium-containing phosphates may include, but are not limited to, one or more of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon. Non-limiting examples of lithium cobalt oxides may include LiCoO2; non-limiting examples of lithium nickel oxides may include LiNiO2; non-limiting examples of lithium manganese oxides may include LiMnO2, LiMn2O4, etc.; non-limiting examples of lithium nickel cobalt manganese oxides may include LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM 523 ), LiNi 0.5 Co0.25 Mn 0.25 O2 (also referred to as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM 811 ) etc. Non-limiting examples of lithium nickel cobalt aluminum oxide may include LiNi 0.80 Co 0.15 Al 0.05 O2.

[0141] In some embodiments, the positive electrode active material layer may further optionally include a binder. As non-limiting examples, the binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0142] In some embodiments, the positive electrode active material layer may further include a conductive agent. As non-limiting examples, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0143] In some embodiments, the positive electrode sheet can be prepared by the following method: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder, and any other components, are dispersed in a solvent to form a positive electrode slurry; the positive electrode slurry is coated on at least one side of the positive electrode current collector, and after drying, cold pressing, and other processes, the positive electrode sheet can be obtained. The type of solvent can be selected from, but not limited to, any of the aforementioned embodiments, such as N-methylpyrrolidone (NMP). The surface of the positive electrode current collector coated with the positive electrode slurry can be on a single surface of the positive electrode current collector or on both surfaces of the positive electrode current collector. The surface of the positive electrode current collector coated with the positive electrode slurry can be on a single surface of the positive electrode current collector or on both surfaces of the positive electrode current collector. The solid content of the positive electrode slurry can be 40 wt% to 80 wt%. The viscosity of the positive electrode slurry at room temperature can be adjusted to 5000 millipascals per second (mPa·s) to 25000 mPa·s. When applying the positive electrode slurry, the coating unit area density based on dry weight (excluding solvent) can be 15 mg / cm2 (mg / cm 2 )~35mg / cm 2 The compacted density of the positive electrode can be 3.0 g / cm3 (g / cm3 )~3.6g / cm 3 , optional 3.3g / cm 3 ~3.5g / cm 3 .

[0144] Negative electrode

[0145] The negative electrode plate is as described above.

[0146] As a non-limiting example, the negative electrode current collector has two surfaces facing each other in its thickness direction, and the negative electrode active material layer is disposed on either or both of the two facing surfaces of the negative electrode current collector.

[0147] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be obtained by forming a metal material on a polymer material substrate. In the negative electrode current collector, non-limiting examples of the metal material may include one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy. In the negative electrode current collector, non-limiting examples of the polymer material substrate may include one or more of substrates such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0148] In some embodiments, the negative electrode active material layer may also include other negative electrode active materials for batteries that are well known in the art. As non-limiting examples, the negative electrode active material may include one or more of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc. Silicon-based materials may include one or more of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may include one or more of elemental tin, tin oxides, and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0149] In some embodiments, the negative electrode active material layer may further include a binder. The binder may include one or more of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0150] In some embodiments, the negative electrode active material layer may further include a conductive agent, which may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0151] In some embodiments, the negative electrode active material layer may optionally further include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0152] In some embodiments, the negative electrode sheet can be prepared in the following manner: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (a non-limiting example of the solvent is deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on at least one side of the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained. The surface of the negative electrode current collector coated with the negative electrode slurry can be a single surface of the negative electrode current collector or on both surfaces of the negative electrode current collector. The solid content of the negative electrode slurry can be 40wt% to 60wt%. The viscosity of the negative electrode slurry at room temperature can be adjusted to 2000mPa·s to 10000mPa·s. When coating the negative electrode slurry, the coating unit surface density on a dry weight basis (excluding the solvent) can be 75g / m 2 ~220g / m 2 The compaction density of the negative electrode can be 1.0g / cm 3 ~1.8g / cm 3 .

[0153] electrolytes

[0154] The electrolyte conducts ions between the positive and negative electrodes. This application does not specifically limit the type of electrolyte, and the electrolyte can be selected based on the needs. For example, the electrolyte can be liquid, gel, or solid.

[0155] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0156] In some embodiments, the electrolyte salt may include one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bisfluorosulfonyl imide (LiFSI), lithium bistrifluoromethanesulfonyl imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorophosphate (LiPO2F2), lithium difluorooxalatoborate (LiDFOB), lithium dioxalatoborate (LiBOB), lithium difluorodioxalatophosphate (LiDFOP) and lithium tetrafluorooxalatophosphate (LiTFOP).

[0157] In some embodiments, the solvent may include ethylene carbonate (EC, ), propylene carbonate (PC, ), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate One or more of fluoroethylene carbonate (FEC), methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0158] In some embodiments, the electrolyte may optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, and additives that improve battery high or low temperature performance.

[0159] In some embodiments, the additives in the electrolyte may include, but are not limited to, one or more of fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), trifluoromethylethylene carbonate (TFPC), and the like.

[0160] Isolation film

[0161] In some embodiments, the secondary battery further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical and mechanical stability can be selected.

[0162] In some embodiments, the material of the separator may include one or more of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer may be the same or different, without particular limitation.

[0163] In some embodiments, the isolation film has a thickness of 6 to 40 μm, and may optionally be 12 to 20 μm.

[0164] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0165] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0166] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery can also be a soft shell, such as a pouch-type soft shell. The material of the soft shell can be plastic. Further, non-limiting examples of plastic can include one or more of polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0167] A secondary battery includes at least one battery cell. A secondary battery may include one or more battery cells.

[0168] In this application, unless otherwise specified, a "battery cell" refers to a basic unit that can achieve the mutual conversion of chemical energy and electrical energy. Further, generally speaking, it includes at least a positive electrode plate, a negative electrode plate, and an electrolyte. During the battery's charge and discharge process, active ions are embedded in and out of the positive and negative electrode plates. The electrolyte plays the role of conducting active ions between the positive and negative electrode plates.

[0169] The present application has no particular limitation on the shape of the battery cell, which can be cylindrical, square, or any other shape. For example, FIG1 shows a battery cell 5 with a square structure as an example.

[0170] In some embodiments, referring to Figure 2, the outer packaging may include a shell 51 and a cover plate 53. The shell 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can be formed into an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is impregnated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell 5 can be one or more, and those skilled in the art can select according to actual needs.

[0171] The secondary battery may be a battery module 4 or a battery pack 1 .

[0172] A battery module includes at least one battery cell. The number of battery cells contained in a battery module can be one or more, and those skilled in the art can select an appropriate number based on the application and capacity of the battery module.

[0173] FIG3 shows an example battery module 4. Referring to FIG3 , within the battery module 4, multiple battery cells 5 may be arranged sequentially along the length of the battery module 4. Of course, they may also be arranged in any other manner. Furthermore, the multiple battery cells 5 may be secured together using fasteners.

[0174] Optionally, the battery module 4 may further include a housing having an accommodation space, and the plurality of battery cells 5 are accommodated in the accommodation space.

[0175] In some embodiments, the battery modules may be assembled into a battery pack. The battery pack may contain one or more battery modules. Those skilled in the art may select an appropriate number based on the application and capacity of the battery pack.

[0176] Figures 4 and 5 illustrate an example battery pack 1. Referring to Figures 4 and 5 , the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box comprises an upper case 2 and a lower case 3. The upper case 2 can be placed over the lower case 3 to form an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0177] In addition, the present application also provides an electrical device, which includes the secondary battery provided in the present application. The secondary battery can be used as a power source for the electrical device or as an energy storage unit for the electrical device. The electrical device can include, but is not limited to, mobile devices, electric vehicles, electric trains, ships, satellites, energy storage systems, etc. Among them, mobile devices can be, for example, mobile phones, laptops, etc.; electric vehicles can be, for example, pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc., but are not limited to these.

[0178] As an electrical device, a secondary battery can be selected according to its usage requirements.

[0179] Figure 6 shows an example of an electric device 6. The electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the electric device's requirements for high power and high energy density of secondary batteries, a battery pack or battery module may be used.

[0180] Another example device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be lightweight and thin, and may use a battery cell as a power source.

[0181] Below, the embodiment of the present application is described. The embodiment described below is exemplary, is only used to explain the present application, and is not to be construed as limiting the present application. Where the technology or conditions are not specified in the embodiment, the technology or conditions described in the literature in this area or the product instructions are used. Where the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be obtained commercially.

[0182] Example 1

[0183] 1) Preparation of positive electrode sheet

[0184] The positive electrode active material NCM811, conductive carbon black SP and binder PVDF were dispersed in the solvent NMP in a weight ratio of 98:1:1 and mixed evenly to obtain a positive electrode slurry. The positive electrode slurry was evenly coated on both sides of the positive electrode current collector aluminum foil, and after drying and cold pressing, a positive electrode sheet was obtained. The coating amount per unit area on both sides was 0.27g / 1540.25mm 2 .

[0185] 2) Preparation of negative electrode sheet

[0186] 2.1 Preparation of negative electrode active materials

[0187] Preparation of silicon-based materials with graphene layers on the surface:

[0188] Si nanoparticles (Dv50 = 80 nm) and a secondary dispersant, PVP, were uniformly dispersed in deionized water at a ratio of 1:2 to form a solution containing 5 wt% Si nanoparticles. Graphene oxide powder was then added at 10% by weight of the Si nanoparticles, mixed evenly, and dried at 80°C. The solution was then transferred to a tube furnace, where the air was evacuated using a vacuum oil pump. Argon and hydrogen (argon:hydrogen = 95:5) were then slowly introduced as a protective gas. The temperature was raised to 700°C at a rate of 3°C / min. After calcination for two hours and then naturally cooled, a pure silicon material (graphene@silicon-based material) with a surface-coated graphene layer of 1 nm was prepared.

[0189] Preparation of silicon composite material precursor:

[0190] The main material and the first dispersant PVP are added to deionized water in a weight ratio of 80%:20%, stirred and dispersed evenly to obtain a standby suspension. The main material includes natural graphite particles and a silicon-based material with a graphene layer coated on the surface, wherein the weight ratio of natural graphite particles to the silicon-based material with a graphene layer coated on the surface is 50%:50%, and the solid content of the standby suspension is 20%; the standby suspension is spray-dried using a spray dryer, the temperature is set to 180°C, and the drying air volume is set to 0.15m 3 / min, to obtain a spherical precursor of the composite silicon material;

[0191] Preparation of carbon coating: The precursor is placed in a clean porcelain boat, and then the porcelain boat is placed in a tubular furnace with Ar gas as the protective gas. The temperature is raised to 700°C at a heating rate of 5°C and kept warm for 2 hours. Then the Ar gas is replaced with CH4 gas for 20 minutes, and then cooled to room temperature to prepare a carbon coating with a thickness of 25 nm. The core of the carbon coating includes natural graphite and a silicon-based material with a graphene layer coated on the surface to obtain a silicon composite material.

[0192] 2.2. The negative electrode active material prepared in step 2.1, the thickener sodium carboxymethyl cellulose, the binder styrene butadiene rubber, and the conductive agent acetylene black were mixed in a mass ratio of 97:1:1:1, deionized water was added, and a negative electrode slurry was obtained under the action of a vacuum mixer; the negative electrode slurry was evenly coated on both sides of the copper foil; the copper foil was dried at room temperature and then transferred to a 120°C oven for drying for 1 hour, and then supercooled pressed and cut to obtain a negative electrode sheet, wherein the coating amount per unit area on both sides was 0.17 g / 1540.25 mm 2 .

[0193] 3) Isolation film

[0194] A 12μm thick polypropylene isolation film was selected.

[0195] 4) Preparation of electrolyte

[0196] The organic solvent is a mixture of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC), with the volume ratio of EC, EMC, and DEC being 20:20:60. In an argon atmosphere glove box with a water content of <10 ppm, fully dried lithium salt LiPF6 is dissolved in the organic solvent and mixed thoroughly to obtain an electrolyte solution. The concentration of the lithium salt is 1 mol / L.

[0197] 5) Preparation of batteries

[0198] The positive electrode sheet, isolation film, and negative electrode sheet are stacked in order, with the isolation film placed between the positive and negative electrode sheets to serve as an isolation. After winding into a square bare battery cell, an aluminum-plastic film is placed in it. After baking at 80°C to remove water, 10g of the corresponding non-aqueous electrolyte is injected and sealed. After standing, hot and cold pressing, formation, clamping, capacity division and other processes, a finished battery with a capacity of 4000mAh is obtained.

[0199] The secondary batteries of Examples 2 to 30 are prepared in a similar manner to the secondary battery of Example 1, with the main differences being the types and proportions of materials, as shown in Table 1 below.

[0200] The preparation method of the secondary battery of Comparative Example 1 is similar to that of the secondary battery of Example 1, the main difference being that the surface of the silicon-based material is not coated with a graphene layer.

[0201] The preparation method of the secondary battery of Comparative Example 2 is similar to that of the secondary battery of Example 1, the main difference being that natural graphite is not used as the main material.

[0202] Table 1

[0203] In addition, the tap density, specific surface area and Dv50 of the silicon composite materials prepared in Examples 1 to 30 and Comparative Examples 1 to 2 are summarized in Table 2 below:

[0204] Table 2

[0205] Test example:

[0206] Test method:

[0207] (1) Anode full charge rebound:

[0208] Use a micrometer to measure the thickness H1 of the negative electrode sheet obtained by cold pressing and cutting, then fully charge the battery cell and disassemble it, and then use a micrometer to measure the thickness H2 of the negative electrode sheet. The negative electrode full charge rebound = (H2 / H1-1)*100%.

[0209] (2) DC internal resistance:

[0210] Adjust the battery cell to 50% SoC and record the DC internal resistance value after 4C discharge for 30s.

[0211] (3) Fast charging performance:

[0212] At 25°C, take the battery with the pre-embedded copper wire and charge it at a constant current of 0.33C to 4.2V. Continue to charge it at a constant voltage until the current reaches 0.05C. At this point, the battery is fully charged. The charge capacity at this point is recorded, which is the charge capacity of the first cycle. After the battery is left to rest for 30 minutes, it is discharged at a constant current of 0.33C to 2.8V. This is a cycle of charge and discharge. The discharge capacity at this point is recorded, which is the discharge capacity of the first cycle. Then, lithium plating begins. Connect the charging device to the copper wire and the positive electrode and charge it at a constant current of 20uA for 2 hours. Then connect the charging device to the copper wire and the negative electrode and charge it at a constant current of 20uA for 2 hours. The copper wire after lithium plating serves as the reference electrode, and the reference electrode potential defaults to 0mV. After lithium plating, charge the battery at a constant current of 2C and record the potential difference between the anode and reference electrode. When the potential difference reaches 0mV, record the ratio of the charged capacity to the charge capacity of the first cycle. This ratio represents the fast charging performance of the battery cell.

[0213] (4) Cycle performance:

[0214] At 25°C, charge the battery at a constant current of 0.5C to 4.2V. Continue charging at a constant voltage until the current reaches 0.05C. At this point, the battery is fully charged. Record the charge capacity at this point, which is the charge capacity of the first cycle. After the battery is allowed to rest for 30 minutes, discharge it at a constant current of 1C to 2.8V. This is a cycle of charge and discharge. Record the discharge capacity at this point, which is the discharge capacity of the first cycle. Perform a cyclic charge and discharge test on the battery according to the above method, recording the discharge capacity after each cycle until the battery's discharge capacity decays to 80% of the discharge capacity of the first cycle. The number of cycles at this point is used to represent the cycle life of the battery.

[0215] The test results are shown in Table 3 below:

[0216] Table 3

[0217] From the comparison between Examples 1 to 30 and Comparative Examples 1 to 2, it can be seen that the present application comprehensively improves the expansibility and conductive network of the silicon composite material by coating the surface of the silicon-based material with a conductive material graphene layer and combining the conductive material natural graphene with the silicon-based material with the surface coated with the conductive material graphene layer, thereby effectively improving the cycle performance and fast charging performance.

[0218] From the comparison between Examples 1 to 5, it can be seen that reasonable control of the Dv50 of the graphite is conducive to further improvement of the fast charging performance and cycle life.

[0219] From the comparison between Example 1 and Example 4, it can be seen that the use of artificial graphite can further optimize the cycle life.

[0220] A comparison between Example 1 and Examples 5 to 8 shows that by properly controlling the mass percentage of the first conductive material and the silicon-based material coated with the second coating layer, the fast charging performance and cycle performance can be further improved. In addition, a comparison between Example 1 and Examples 5 to 8 also shows that when the mass percentage of graphite and graphene@silicon-based material varies within the range of (10% to 90%): (90% to 10%), the anode full charge rebound can be maintained at a low level.

[0221] From the comparison between Example 1 and Examples 9 to 17, it can be seen that reasonable control of the particle size of the silicon-based material is beneficial to the improvement of fast charging performance and cycle life.

[0222] From the comparison between Example 1 and Examples 18 to 20, it can be seen that reasonable control of the thickness of the graphene layer is beneficial to the improvement of the cycle life.

[0223] From the comparison between Example 1 and Examples 21 to 24, it can be seen that the fast charging performance and cycle life can be improved by reasonably controlling the thickness of the carbon coating layer.

[0224] From the comparison between Example 1 and Examples 25 to 30, it can be seen that the cycle performance and fast charging performance can be improved by reasonably controlling the amount of the first dispersant.

[0225] The above description of the various embodiments tends to emphasize the differences between the various embodiments. The same or similar aspects can be referenced with each other and will not be repeated herein for the sake of brevity.

[0226] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and within the scope of the technical solution of the present application, embodiments having substantially the same structure as the technical concept and exerting the same effects are all included in the technical scope of the present application. In addition, within the scope of the subject matter of the present application, various modifications that can be conceived by those skilled in the art to the embodiments, and other methods constructed by combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A silicon composite material, comprising a core and a first coating layer coated on the surface of the core, wherein the core comprises a first core and a second core, the first core comprises a first conductive material, the first conductive material comprises a flexible conductive material, the second core comprises a silicon-based material with a second coating layer coated on the surface, and the second coating layer comprises a second conductive material.

2. The silicon composite material according to claim 1, wherein: The silicon-based material is a nano-scale or micro-scale silicon-based material.

3. The silicon composite material according to claim 2, wherein: The Dv50 of the silicon-based material is 10 nm to 5 μm.

4. The silicon composite material according to any one of claims 1 to 3, wherein: The silicon-based material includes one or both of pure silicon and silicon monoxide.

5. The silicon composite material according to claim 4, wherein: The Dv50 of the pure silicon is 10nm to 150nm; the Dv50 of the silicon monoxide is 2μm to 5μm.

6. The silicon composite material according to claim 5, wherein: The Dv50 of the pure silicon is 50nm-100nm; the Dv50 of the silicon monoxide is 2.5μm-3.5μm.

7. The silicon composite material according to any one of claims 1 to 6, wherein: The flexible conductive material includes one or both of soft carbon and graphite.

8. The silicon composite material according to claim 7, wherein: The graphite includes one or two of the following characteristics: (1) The Dv50 of the graphite is 1 μm to 5 μm; (2) The graphite includes one or both of natural graphite and artificial graphite.

9. The silicon composite material according to claim 8, characterized in that: The Dv50 of the graphite is 1 μm to 3.5 μm.

10. The silicon composite material according to any one of claims 1 to 9, wherein: The second conductive material includes one or more of graphene, single-walled carbon nanotubes or multi-walled carbon nanotubes.

11. The silicon composite material according to any one of claims 1 to 10, wherein: The thickness of the second coating layer is 0.3 nm to 3 nm.

12. The silicon composite material according to claim 11, wherein: The thickness of the second coating layer is 1.2 nm to 3 nm.

13. The silicon composite material according to any one of claims 1 to 12, wherein: The mass percentage of the first conductive material and the silicon-based material whose surface is coated with the second coating layer is (10% to 90%): (90% to 10%).

14. The silicon composite material according to claim 13, wherein: The mass percentage of the first conductive material and the silicon-based material whose surface is coated with the second coating layer is (40% to 90%): (60% to 10%).

15. The silicon composite material according to any one of claims 1 to 14, wherein: The first coating layer includes a carbon coating layer.

16. The silicon composite material according to claim 15, wherein: The carbon coating layer includes one or two of the following features: (1) Thickness is 5nm to 60nm; (2) The carbon coating layer includes amorphous carbon.

17. The silicon composite material according to claim 16, wherein: The thickness of the carbon coating layer is 20nm to 60nm.

18. The silicon composite material according to any one of claims 1 to 17, characterized in that: The silicon composite material comprises one or more of the following features: (1) Tap density is 0.9 g / cm 3 ~1.3g / cm 3 ; (2) Specific surface area is 0.6m 2 / g~1.4m 2 / g; (3) The Dv50 of the silicon composite material is 3 μm to 30 μm.

19. A method for preparing a silicon composite material, comprising the following steps: Mixing a first conductive material, a silicon-based material having a second coating layer on its surface, and water to prepare a dispersion; the second coating layer comprises a second conductive material, and the first conductive material comprises a flexible conductive material; Drying the dispersion to prepare a precursor; The precursor is coated to form a first coating layer, wherein the first coating layer is coated on the surface of the inner core, the inner core comprises a first inner core and a second inner core, the first inner core comprises the first conductive material, and the second inner core comprises a silicon-based material whose surface is coated with the second coating layer.

20. The method for preparing the silicon composite material according to claim 19, wherein: The method for preparing the silicon-based material with the second coating layer coated on the surface comprises one or both of a gas phase reaction method and a liquid phase coating method, and the second coating layer comprises graphene.

21. The method for preparing the silicon composite material according to claim 20, wherein: The gas phase reaction method for preparing the silicon-based material having the second coating layer on the surface comprises the following steps: The silicon-based material is vapor-deposited in a mixed gas of a second carbon source gas and carbon dioxide to form the second coating layer, thereby preparing the silicon-based material with the second coating layer coated on the surface.

22. The method for preparing the silicon composite material according to claim 21, wherein: The gas phase reaction method includes one or more of the following features: (1) The temperature of the vapor deposition is 600° C. to 800° C.; (2) The second carbon source gas includes a hydrocarbon gas.

23. The method for preparing the silicon composite material according to claim 20, wherein: The liquid phase coating method for preparing the silicon-based material having the second coating layer on the surface comprises the following steps: Mixing the silicon-based material with a second dispersant, water, and graphene oxide to prepare a mixed solution; The mixed solution is dried and calcined to prepare the silicon-based material with the second coating layer coated on the surface.

24. The method for preparing the silicon composite material according to claim 23, wherein: The liquid phase coating method includes one or more of the following features: (1) the second dispersant comprises one or more of polyvinyl pyrrolidone, polyethylene glycol or sodium carboxymethyl cellulose; (2) The drying conditions include: a temperature of 60°C to 80°C; (3) The calcination conditions include: heating to 600° C. to 800° C. at a heating rate of 2° C. / min to 5° C. / min under a reducing atmosphere, and calcining for 1 h to 3 h.

25. The method for preparing the silicon composite material according to any one of claims 19 to 24, wherein: The solid content of the dispersion is 1% to 40%.

26. The method for preparing a silicon composite material according to any one of claims 19 to 25, wherein: The process of preparing the dispersion also includes the step of adding a first dispersant; The first dispersant includes one or more of polyvinyl pyrrolidone, polyethylene glycol or sodium carboxymethyl cellulose; The percentage between the mass of the first dispersant and the total mass of the first conductive material and the silicon-based material with the second coating layer coated on the surface is (70% to 95%): (30% to 5%).

27. The method for preparing a silicon composite material according to any one of claims 19 to 26, wherein: The drying comprises spray drying, and the spray drying comprises one or two of the following conditions: (1) The temperature is 150℃~200℃; (2) Air volume is 0.08m 3 / min~0.2m 3 / min.

28. The method for preparing a silicon composite material according to any one of claims 19 to 27, wherein: The first coating layer includes a carbon coating layer, and the step of forming the first coating layer includes: placing the precursor in a reaction container, introducing a first carbon source gas for vapor deposition, and forming the first coating layer.

29. The method for preparing the silicon composite material according to claim 28, wherein: The conditions for introducing the first carbon source gas for vapor deposition include one or two of the following conditions: (1) The first carbon source gas includes one or both of CH4 and C2H2; (2) First, the temperature is raised to 600-800° C. at a heating rate of 2° C. / min-10° C. / min, and kept at this temperature for 1 h-4 h, and then the first carbon source gas is introduced for 15 min-30 min.

30. A negative electrode plate, comprising a negative electrode current collector and a negative electrode active material layer arranged on at least one surface of the negative electrode current collector, wherein the negative electrode active material layer comprises one or more of the silicon composite material according to any one of claims 1 to 18 or the silicon composite material prepared by the preparation method according to any one of claims 19 to 29.

31. A secondary battery comprising the negative electrode sheet according to claim 30.

32. An electrical device comprising one or more of the negative electrode sheet according to claim 30 or the secondary battery according to claim 31.

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