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

Abstract

A silicon composite material and a preparation method, a negative electrode sheet, a battery, and an electric device. The silicon composite material comprises a silicon-based material and a flexible material, wherein the hardness of the flexible material is less than the hardness of the silicon-based material. The silicon-based material comprises at least one of elemental silicon, a silicon-oxygen compound, a silicon-carbon composite, a silicon-nitrogen composite, and a silicon alloy. The flexible material is located on at least part of the surface of the silicon-based material. By means of the combination of the flexible material and the silicon-based material, the risk of a current collector being crushed during the preparation of an electrode sheet can be reduced, and the compacted density of the electrode sheet can be improved, thus increasing the energy density of a battery.

Description

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

[0001] Related applications

[0002] This application claims priority to Chinese patent application number 2023111434075, filed on September 6, 2023, entitled “Silicon composite material and preparation method, negative electrode sheet, 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 secondary batteries, and in particular to a silicon composite material and a preparation method thereof, a negative electrode sheet, a battery and an electrical device. Background Art

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

[0005] Silicon-based materials have high specific capacity, and their introduction into secondary batteries could potentially increase the battery's energy density. However, silicon-based materials are generally hard, making them prone to crushing the current collector during electrode sheet fabrication. This limits the improvement of the electrode sheet's compaction density, and thus, further increases in battery energy density.

[0006] Summary of the Invention

[0007] In order to achieve the above-mentioned purpose, the present application provides a silicon composite material, comprising a silicon-based material and a flexible material, wherein the hardness of the flexible material is less than the hardness of the silicon-based material. The silicon-based material comprises at least one of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites and silicon alloys. The flexible material is located on at least part of the surface of the silicon-based material. In the above-mentioned silicon composite material, through the cooperation of the flexible material and the silicon-based material, the flexible material can buffer the force of the silicon-based material on the current collector, which can reduce the risk of the current collector being crushed when preparing the electrode pole piece, which is beneficial to improving the compaction density of the electrode pole piece, thereby increasing the energy density of the battery.

[0008] In some embodiments, the flexible material comprises a flexible conductive material. The introduction of the flexible conductive material can improve the conductivity of the silicon composite material, thereby improving the electrical performance of the battery. Optionally, the flexible conductive material comprises at least one of graphite and soft carbon.

[0009] In some embodiments, the Dv50 of the flexible material is less than or equal to the Dv50 of the silicon-based material. The flexible material can be more evenly dispersed on the surface of the silicon-based material, which is conducive to further improving the buffering effect of the flexible material on the silicon-based material.

[0010] In some embodiments, the Dv50 of the flexible material is between 1 μm and 5 μm. A Dv50 of the flexible material within this range allows the flexible material to be more evenly dispersed on the surface of the silicon-based material, while also providing a suitable deformation space between the flexible materials. Suitable deformation space helps buffer the forces between the silicon-based material and the current collector, reducing the risk of damage to the current collector during electrode sheet preparation.

[0011] In some embodiments, the Dv50 of the silicon-based material is 2 μm to 7 μm. When the Dv50 of the silicon-based material is within this range, the electrode plate has a higher compaction density, which is beneficial to improving the energy density of the battery.

[0012] In some embodiments, both the silicon-based material and the flexible material are granular, and the flexible material is distributed in a granular form over at least a portion of the surface of the silicon-based material. The granular distribution of the flexible material can provide a better cushioning effect. When the silicon-based material has a low sphericity, i.e., when the silicon-based material has sharp protrusions, the granular distribution of the flexible material can better cooperate with the protrusions, reducing the risk of damage to the current collector caused by the protrusions. Optionally, the flexible material is distributed in a granular form over the entire surface of the silicon-based material.

[0013] In some embodiments, the mass ratio of the flexible material to the silicon-based material is (1-9):1. Within this range, the flexible material to silicon-based material mass ratio can fully utilize the flexible material's cushioning effect and reduce the risk of current collector damage. Furthermore, within this range, the flexible material to silicon-based material mass ratio is beneficial for increasing the compaction density of the electrode, thereby maintaining a high energy density in the battery.

[0014] In some embodiments, the silicon-carbon composite includes a porous carbon material and elemental silicon located within the pores of the porous carbon material. The pores within the porous carbon material can provide a certain amount of reserved expansion space for the elemental silicon, reducing the overall expansion of the silicon-carbon composite and improving the structural stability of the electrode during charge and discharge.

[0015] In some embodiments, the specific surface area of ​​the porous carbon material is 500 m 2 / g~1800m 2 The specific surface area of ​​porous carbon materials within this range can provide a larger space for the attachment of elemental silicon, thereby promoting the improvement of battery energy density.

[0016] In some embodiments, the pores of the porous carbon material have a pore diameter of 2 nm to 50 nm. The pore diameter of the porous carbon material within this range can provide a larger expansion space for the expansion of elemental silicon and enable the battery to have better cycle performance.

[0017] In some embodiments, the mass percentage of the elemental silicon in the silicon-carbon composite is 20% to 60%. When the mass percentage of the elemental silicon is within this range, the battery can have both high energy density and good cycle stability.

[0018] In some embodiments, the silicon composite material further includes a coating layer, the coating layer comprising at least one of carbon and a metal oxide, and the coating layer completely or partially covers the silicon-based material and the flexible material. The provision of the coating layer can provide a certain barrier to the electrolyte, further reducing the risk of direct contact between the electrolyte and the silicon-based material, and reducing side reactions between the electrolyte and the silicon-based material inside the battery, which is beneficial to improving the battery's cycling and fast charging performance. Optionally, the metal oxide includes at least one of aluminum oxide and titanium dioxide.

[0019] In some embodiments, the coating layer has a thickness of 5 nm to 60 nm. When the coating layer has a thickness within this range, the silicon composite material can have a suitable particle size while maintaining a good coating effect, which is beneficial for improving the compaction density of the electrode sheet.

[0020] In some embodiments, the silicon composite material has a Dv50 of 8 μm to 40 μm. The Dv50 of the silicon composite material within this range can provide a path of appropriate size for the diffusion of lithium ions and improve the transport kinetics of lithium ions.

[0021] In some embodiments, the tap density of the silicon composite material is 0.9 g / cm 3 ~1.2g / cm 3 The tap density of the silicon composite material within this range is conducive to improving the compaction density of the negative electrode sheet.

[0022] In some embodiments, the specific surface area of ​​the silicon composite material is 0.8 m 2 / g~1.5m 2 / g. The specific surface area of ​​the silicon composite material within this range can enable the electrode plate to have good dynamic performance.

[0023] The present application also provides a method for preparing a silicon composite material, comprising the following steps: mixing a silicon-based material, a flexible material, and a solvent to obtain a dispersion; wherein the hardness of the flexible material is less than that of the silicon-based material; and wherein the silicon-based material comprises at least one of elemental silicon, a silicon-oxygen compound, a silicon-carbon composite, a silicon-nitrogen composite, and a silicon alloy; and spray drying the dispersion.

[0024] In some embodiments, the solid content of the dispersion is 1% to 40%.

[0025] In some embodiments, the temperature of the hot air in the spray drying process is 150°C to 200°C.

[0026] In some embodiments, the flow rate of the hot air for the spray drying process is 0.08m 3 / min~0.2m 3 / min.

[0027] The present application also provides a negative electrode plate, comprising a negative electrode current collector and a negative electrode film layer located on at least one surface of the negative electrode current collector; the negative electrode film layer comprises the silicon composite material or the silicon composite material prepared by the preparation method.

[0028] In some embodiments, the compacted density of the negative electrode sheet is 1.3 g / cm 3 ~1.75g / cm 3 The compaction density of the negative electrode sheet within this range is beneficial to improving the energy density of the battery.

[0029] In some embodiments, the full charge expansion rate of the negative electrode plate is 22% to 50%. A full charge expansion rate within this range can enable the battery to have good cycle stability.

[0030] The present application also provides a secondary battery, comprising the negative electrode plate.

[0031] The present application also provides an electrical device comprising the secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] To more clearly illustrate the technical solution of this application, the following is a brief introduction to the drawings used in this application. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without inventive effort.

[0033] FIG1 is a schematic diagram of a secondary battery according to one embodiment of the present application.

[0034] FIG. 2 is an exploded view of the secondary battery according to one embodiment of the present application shown in FIG. 1 .

[0035] FIG3 is a schematic diagram of an electric device using a secondary battery as a power source according to an embodiment of the present application.

[0036] FIG4 is a schematic structural diagram of a silicon composite material in one embodiment of the present application.

[0037] FIG5 is a schematic structural diagram of a silicon composite material in another embodiment of the present application.

[0038] Explanation of the reference numerals: 1. Secondary battery; 11. Housing; 12. Electrode assembly; 13. Cover plate; 2. Electric device; 3. Silicon composite material; 31. Silicon-carbon composite material; 32. Graphite; 33. Coating layer.

[0039] In order to better describe and illustrate the embodiments and / or examples of the inventions disclosed herein, 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 to limit the scope of the disclosed inventions, the presently described embodiments and / or examples, and any of the best modes currently understood for these inventions. DETAILED DESCRIPTION

[0040] To facilitate understanding of the present application, a more comprehensive description of the present application will be provided below with reference to the accompanying drawings. The accompanying drawings illustrate preferred embodiments of the present application. However, the present application may be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and comprehensive understanding of the disclosure of the present application.

[0041] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application pertains. The terms used herein in the specification of this application are for the purpose of describing specific embodiments only and are not intended to limit this application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0042] The "ranges" disclosed herein are defined in terms of lower and upper limits, where a given range is defined by selecting a lower limit and an upper limit, and the selected lower and upper limits define the boundaries of the particular range. Ranges defined in this manner can be inclusive or exclusive of the end values ​​and can be combined arbitrarily, i.e., 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 contemplated. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, the following ranges are all contemplated: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5. In this application, unless otherwise indicated, the numerical range "a to b" is a shorthand representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, a numerical range of "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 disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0043] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0044] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0045] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly. In some embodiments, they are performed sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or may include 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 may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0046] Unless otherwise specified, the terms "include" and "comprising" used in this application may be open-ended or closed-ended. For example, "include" and "comprising" may mean that other components not listed may also be included or that only the listed components are included.

[0047] Unless otherwise specified, the term "or" is used in this application to be inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true or present, and B is false or absent; A is false or absent, and B is true or present; or both A and B are true, or both A and B are present.

[0048] Unless otherwise indicated, the terms used in this application have the commonly understood meanings generally understood by those skilled in the art. Unless otherwise indicated, the numerical values ​​of the various parameters mentioned in this application can be measured using various measurement methods commonly used in the art. For example, the tests can be performed using the methods described in the examples of this application.

[0049] One embodiment of the present application provides a silicon composite material. The silicon composite material includes a silicon-based material and a flexible material, and the hardness of the flexible material is less than the hardness of the silicon-based material. The silicon-based material includes at least one of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The flexible material is located on at least a portion of the surface of the silicon-based material. In the silicon composite material, through the combination of the flexible material and the silicon-based material, the flexible material can buffer the force exerted by the silicon-based material on the current collector, which can reduce the risk of the current collector being crushed when preparing the electrode pole piece, which is beneficial to improving the compaction density of the electrode pole piece, thereby increasing the energy density of the battery.

[0050] Optionally, the flexible material is located on the entire surface of the silicon-based material.

[0051] Furthermore, when the silicon composite material is applied to a secondary battery, the flexible material is located on at least part of the surface of the silicon-based material. The flexible material can reduce the risk of direct contact between the electrolyte and the silicon-based material, thereby reducing the side reactions between the electrolyte and the silicon-based material inside the battery, which is beneficial to improving the cycle performance of the battery.

[0052] In some embodiments, the flexible material includes a flexible conductive material. The inclusion of the flexible conductive material can improve the conductivity of the silicon composite material, thereby improving the electrical performance of the battery. Optionally, the conductive material includes at least one of graphite and soft carbon. It is understood that the graphite includes at least one of natural graphite and artificial graphite.

[0053] In some embodiments, the Dv50 of the flexible material is less than or equal to the Dv50 of the silicon-based material. In this case, the flexible material can be more evenly dispersed on the surface of the silicon-based material, which helps further improve the buffering effect of the flexible material on the silicon-based material. Alternatively, the Dv50 of the flexible material is less than the Dv50 of the silicon-based material.

[0054] It is understood that in this application, Dv50 refers to the particle size corresponding to the 50% cumulative particle size distribution in the volume cumulative distribution curve. Its physical meaning is that particles with a smaller (or larger) size account for 50%. As an example, Dv50 can be obtained by referring to the GB / T 19077-2016 test method and using a laser diffraction particle size distribution analyzer Mastersizer3000 to obtain a particle size distribution curve.

[0055] As some optional examples of Dv50 of flexible materials, the Dv50 of flexible materials is 1 micron (μm) to 5μm. The Dv50 of flexible materials within this range can make the flexible materials more evenly dispersed on the surface of the silicon-based material, and at the same time can provide a more suitable deformation space between the flexible materials. The suitable deformation space is conducive to buffering the force between the silicon-based material and the current collector, reducing the risk of damage to the current collector during the preparation of the electrode sheet. Optionally, the Dv50 of the flexible material can be 1μm, 2μm, 3μm, 4μm, 5μm, etc.

[0056] As some optional examples of Dv50 of silicon-based materials, the Dv50 of silicon-based materials is 2μm to 7μm. The Dv50 of silicon-based materials within this range can enable the electrode plates to have a higher compaction density, which is beneficial for improving the energy density of the battery. Alternatively, the Dv50 of the silicon-based material can be 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, etc.

[0057] It is understood that the flexible material and the silicon-based material can be bonded together by surface tension between the flexible material and the silicon-based material. Optionally, the silicon composite material may further include a binder. The binder can further enhance the bonding strength between the flexible material and the silicon-based material, allowing the flexible material and the silicon-based material to be better bonded together, thereby further improving the structural stability of the silicon composite material. Optionally, the binder can be at least one of polyvinyl pyrrolidone, polyethylene glycol, and sodium carboxymethyl cellulose.

[0058] In some embodiments, both the silicon-based material and the flexible material are granular, and the flexible material is distributed in a granular form over at least a portion of the surface of the silicon-based material. The granular distribution of the flexible material can provide a better cushioning effect. When the silicon-based material has a low degree of sphericity, that is, when the silicon-based material has relatively sharp protrusions, the granular distribution of the flexible material can better cooperate with the protrusions, reducing the risk of damage to the current collector caused by the protrusions. Optionally, the flexible material is distributed in a granular form over the entire surface of the silicon-based material.

[0059] In some embodiments, the mass ratio of the flexible material to the silicon-based material is (1-9):1. The mass ratio of the flexible material to the silicon-based material within this range can fully exert the buffering effect of the flexible material and reduce the risk of current collector damage. At the same time, the mass ratio of the flexible material to the silicon-based material within this range can enable the battery to maintain a high energy density. Optionally, the mass ratio of the flexible material to the silicon-based material can be 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, etc.

[0060] In some embodiments, the silicon oxide compound comprises a compound having the chemical formula SiO x wherein 0<x<2. Further optionally, 0.5≤x≤1.5. Further optionally, the silicon oxide compound comprises SiO.

[0061] Further optionally, metal elements may be distributed on the surface of the silicon oxide compound and / or inside the silicon oxide compound to reduce the proportion of irreversible phases (e.g., SiO2) and improve the efficiency of the active material. The metal may be at least one selected from Li, Mg, and Al. The introduction of these metal elements may reduce the risk of damage to the silicon oxide compound and improve the life of the silicon oxide compound. Alternatively, the metal may be at least one of Li and Mg. The mass percentage of the metal element may be 0.1% to 25%, optionally 3% to 15%, based on the mass percentage of the silicon oxide compound.

[0062] Optionally, the silicon nitrogen compound includes Si3N4.

[0063] In some embodiments, a silicon-carbon composite includes a porous carbon material and elemental silicon located within the pores of the porous carbon material. The pores within the porous carbon material can provide a certain amount of reserved expansion space for the elemental silicon, reducing the overall expansion of the silicon-carbon composite and improving the structural stability of the electrode during charge and discharge. Optionally, the elemental silicon includes nanosilicon.

[0064] Silicon-carbon composites typically have a relatively hard texture. When applied to electrode plates, the hard silicon-carbon composite may cause certain damage to the current collector during the cold pressing process, thereby adversely affecting the performance of the electrode plate and the battery. In this application, by combining a flexible material with the silicon-carbon composite, the flexible material is softer than the silicon-carbon composite and can disperse the stress caused by the silicon-carbon composite during the cold pressing process, reducing the adverse effects of the silicon-carbon composite on the current collector during the cold pressing process, thereby improving the structural stability of the electrode plate and thus improving the performance of the battery.

[0065] Furthermore, silicon-carbon composites have poor pressure-bearing capacity and are prone to breakage during cold pressing. In this application, by combining a flexible material with the silicon-carbon composite, the silicon composite material can be given improved pressure-bearing capacity. When this silicon composite material is incorporated into an electrode plate, it can further increase the compaction density of the electrode plate.

[0066] In some embodiments, the specific surface area of ​​the porous carbon material is 500 m2 / g (m 2 / g)~1800m 2 / g. The specific surface area of ​​the porous carbon material within this range can provide a larger space for the attachment of elemental silicon, thereby promoting the improvement of battery energy density. Optionally, the specific surface area of ​​the porous carbon material can be 500m 2 / g、600m 2 / g、700m 2 / g、800m 2 / g、900m 2 / g、1000m 2 / g、1100m 2 / g、1200m 2 / g、1300m 2 / g、1400m 2 / g、1500m 2 / g、1600m 2 / g、1700m 2 / g、1800m 2 / g, etc.

[0067] In some embodiments, the pores of the porous carbon material have a pore diameter of 2 nanometers (nm) to 50 nm. Within this range, the pores of the porous carbon material provide ample space for the expansion of elemental silicon, while also enabling the battery to have better cycling and storage performance. Optionally, the pores of the porous carbon material are mesopores.

[0068] In some embodiments, the mass percentage of elemental silicon in the silicon-carbon composite is 20% to 60%. Within this range, the mass percentage of elemental silicon can achieve both high energy density and good cycling stability in the battery. Alternatively, the mass percentage of elemental silicon in the silicon-carbon composite can be 20%, 30%, 40%, 50%, 60%, etc.

[0069] In some embodiments, the flexible material includes graphite, and the silicon-based material includes a silicon-carbon composite. Please refer to Figure 4, which shows a schematic diagram of the structure of the silicon composite material in one embodiment of the present application. The silicon composite material 3 corresponding to Figure 4 includes a silicon-carbon composite 31 and graphite 32, and the graphite 32 is located on at least a portion of the surface of the silicon-carbon composite 31. It can be understood that in Figure 4, the positional relationship of the silicon composite material 3, the silicon-carbon composite 31 and the graphite 32 is schematically shown, which does not mean that the actual shape of the silicon composite material 3, the silicon-carbon composite 31 and the graphite 32 is the shape shown in Figure 4. In the silicon composite material, the shapes of the silicon composite material, the silicon-carbon composite and the graphite can be other shapes. For example, the shapes of the silicon composite material, the silicon-carbon composite and the graphite can be independently selected from at least one of a spherical shape and a spherical-like shape.

[0070] In some embodiments, the silicon composite material further includes a coating layer comprising at least one of carbon and a metal oxide, and the coating layer completely or partially coats the silicon-based material and the flexible material. The coating layer can provide a certain barrier to the electrolyte, further reducing the risk of direct contact between the electrolyte and the silicon-based material, and reducing side reactions between the electrolyte and the silicon-based material within the battery, thereby improving the battery's cycling and fast-charging performance. Optionally, the coating layer can be a carbon coating layer.

[0071] Please refer to Figure 5, which shows a schematic structure of a silicon composite material according to another embodiment of the present application. Silicon composite material 3 shown in Figure 5 includes a silicon-carbon composite 31 and graphite 32, with graphite 32 located on at least a portion of the surface of silicon-carbon composite 31. Silicon composite material 3 also includes a coating layer 33. Coating layer 33 completely encapsulates silicon-carbon composite 31 and graphite 32.

[0072] In some embodiments, the metal oxide includes at least one of aluminum oxide and titanium dioxide.

[0073] In some embodiments, the coating layer has a thickness of 5 nm to 60 nm. Within this range, the coating layer maintains a good coating effect while ensuring the silicon composite material has an appropriate particle size, which helps improve the compaction density of the electrode sheet. Alternatively, the coating layer may have a thickness of 5 nm, 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, etc.

[0074] It is understood that the flexible material, silicon-carbon composite and coating layer in the silicon composite material can be detected and distinguished by means of transmission electron microscopy (TEM) and X-ray diffraction (XRD).

[0075] In some embodiments, the silicon composite material has a Dv50 of 8 μm to 40 μm. Within this range, the silicon composite material can provide a path of suitable size for lithium ion diffusion, thereby improving lithium ion transport kinetics. Alternatively, the silicon composite material can have a Dv50 of 8 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, etc.

[0076] In some embodiments, the tap density of the silicon composite material is 0.9 g / cm3 (g / cm 3 )~1.2g / cm 3 The tap density of the silicon composite material within this range is conducive to improving the compaction density of the negative electrode. Optionally, the tap density of the silicon composite material is 0.9 g / cm 3 , 1g / cm 3 , 1.1g / cm 3 , 1.2g / cm 3 etc. It is understood that the tap density of a silicon composite material can be measured using a tap density meter. A graduated cylinder containing the silicon composite material is mounted on a mechanical vibrator. A vibration motor drives the vibrator to vibrate vertically up and down, causing the graduated cylinder containing the silicon composite material to vibrate rhythmically with the mechanical vibrator. As the number of vibrations increases, the silicon composite material in the graduated cylinder gradually becomes compacted. After the set number of vibrations is reached, the mechanical vibrator stops, and the volume of the graduated cylinder is read. Based on the definition of density: mass divided by volume, the tap density of the silicon composite material can be calculated.

[0077] In some embodiments, the silicon composite material has a specific surface area of ​​0.8 m 2 / g~1.5m 2 / g. The specific surface area of ​​the silicon composite material within this range can make the electrode plate have good dynamic performance. Optionally, the specific surface area of ​​the silicon composite material is 0.8m 2 / g, 0.9m 2 / g、1m 2 / g, 1.1m2 / g, 1.2m 2 / g, 1.3m 2 / g, 1.4m 2 / g, 1.5m 2 / g, etc.

[0078] In some embodiments, the silicon composite material is in the form of spherical particles.

[0079] Another embodiment of the present application provides a method for preparing a silicon composite material. The method comprises the following steps: mixing a silicon-based material, a flexible material, and a solvent to obtain a dispersion; the flexible material has a hardness less than that of the silicon-based material; and the silicon-based material comprises at least one of elemental silicon, a silicon-oxygen compound, a silicon-carbon complex, a silicon-nitrogen complex, and a silicon alloy. The dispersion is then spray-dried. This method is simple and easy to implement, and the silicon composite material can be obtained through spray-drying granulation.

[0080] Optionally, spray drying is carried out in a dry hot air atmosphere. It will be appreciated that during spray drying, the dispersion is placed in a hot air atmosphere for drying.

[0081] In some embodiments, the temperature of the hot air during the spray drying process is 150 degrees Celsius (° C.) to 200° C. Alternatively, the temperature of the hot air during the spray drying process can be 150° C., 160° C., 170° C., 180° C., 190° C., 200° C., etc.

[0082] In some embodiments, the flow rate of hot air for spray drying is 0.08 cubic meters per minute (m 3 / min)~0.2m 3 / min. Optionally, the flow rate of the hot air for spray drying is 0.08m 3 / min、0.09m 3 / min、0.1m 3 / min、0.11m 3 / min、0.12m 3 / min、0.13m 3 / min、0.14m 3 / min、0.15m 3 / min、0.16m 3 / min、0.17m 3 / min、0.18m 3 / min、0.19m 3 / min、0.2m 3 / min, etc.

[0083] In some embodiments, the solid content of the dispersion is 1% to 40%. Alternatively, the solid content of the dispersion is 1%, 5%, 8%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, etc.

[0084] In some embodiments, the solvent comprises water.

[0085] In some embodiments, a method for preparing a silicon composite material includes the following steps: mixing a silicon-based material, a flexible material, a dispersant, and a solvent to obtain a dispersion; and spray-drying the dispersion. The addition of the dispersant can improve the dispersion of the silicon-based material and the flexible material in the solvent, thereby improving the uniformity of the silicon composite material.

[0086] Optionally, the ratio of the total mass of the silicon-based material and the flexible material to the mass of the dispersant is (70-95):(5-30). Further optionally, the ratio of the total mass of the silicon-based material and the flexible material to the mass of the dispersant can be 70:30, 75:25, 80:20, 85:15, 90:10, 95:5, etc. Further optionally, the dispersant includes one or more of polyvinyl pyrrolidone, polyethylene glycol, and sodium carboxymethyl cellulose.

[0087] In some embodiments, a method for preparing a silicon composite material includes the following steps: mixing a silicon-based material, a flexible material, a dispersant, a binder, and a solvent to obtain a dispersion; and spray drying the dispersion. The addition of the binder can improve the bonding between the silicon-carbon composite and the graphite, making the resulting silicon composite material more structurally stable.

[0088] Optionally, the binder includes one or more of polyvinyl pyrrolidone, polyethylene glycol and sodium carboxymethyl cellulose.

[0089] It is understood that the dispersion can be spray-dried using a spray dryer.

[0090] In some embodiments, the spray drying process further comprises: coating the solid material obtained by the spray drying process.

[0091] In some embodiments, after the spray drying process, the method further includes: performing a carbon coating process on the solid material obtained by the spray drying process in a gaseous carbon source atmosphere. The carbon coating process can improve the conductivity and fast charging performance of the silicon composite material.

[0092] Optionally, the carbon coating treatment includes the following steps: placing the solid material obtained by the spray drying treatment in a porcelain boat, then placing the porcelain boat in a tubular furnace with Ar gas as the protective gas, heating it to 600°C to 800°C at a heating rate of 2°C to 10°C, and keeping it warm for 1 hour (h) to 4 hours. Then, the Ar gas is replaced with a gaseous carbon source for 15 minutes (min) to 30 minutes, and then cooled to room temperature. Further optionally, the gaseous carbon source includes at least one of CH4 and C2H2.

[0093] Another embodiment of the present application provides a negative electrode plate. The negative electrode plate includes a negative electrode current collector and a negative electrode film layer located on at least one surface of the negative electrode current collector. The negative electrode film layer includes the aforementioned silicon composite material or a silicon composite material prepared by the aforementioned method for preparing the silicon composite material.

[0094] In some embodiments, the compacted density of the negative electrode sheet is 1.3 g / cm 3 ~1.75g / cm 3 The compaction density of the negative electrode sheet within this range is beneficial to improving the energy density of the battery. For example, the compaction density of the negative electrode sheet can be 1.3g / cm 3 , 1.4g / cm 3 , 1.5g / cm 3 , 1.6g / cm 3 , 1.7g / cm 3 wait.

[0095] In one embodiment, the full charge expansion rate of the negative electrode plate is 22% to 50%. A full charge expansion rate within this range can enable the battery to have good cycle stability. Optionally, the full charge expansion rate of the negative electrode plate can be 25%, 30%, 35%, 40%, 45%, etc. It is understood that the full charge expansion rate of the negative electrode plate can be measured as follows: The full charge expansion rate can be tested by the following method: Measure the original thickness of the negative electrode plate, recorded as W0. Then, disassemble the assembled battery after full charge, and measure the thickness of the negative electrode plate after full charge, recorded as W1. Expansion rate α = (W1-W0) / W0.

[0096] Another embodiment of the present application provides a secondary battery comprising the above-mentioned negative electrode plate.

[0097] Another embodiment of the present application provides an electric device, which includes the aforementioned secondary battery.

[0098] The secondary battery and the electric device of the present application will be described below with reference to the accompanying drawings as appropriate.

[0099] 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.

[0100] Positive electrode

[0101] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector, wherein the positive electrode film layer includes a positive electrode active material.

[0102] As an example, the positive electrode current collector has two surfaces facing each other in its thickness direction, and the positive electrode active material layer is provided on either or both of the two facing surfaces of the positive electrode current collector.

[0103] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector may be formed by forming a metal material on a polymer material substrate. Alternatively, the metal material may include but is not limited to one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy. Alternatively, the polymer material substrate may include but is not limited to one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS) and polyethylene (PE).

[0104] As an example, the positive electrode active material may include positive electrode active materials for batteries that are well known in the art. As an example, the positive electrode active material may include at least one of the following materials: lithium-containing phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Among them, examples of lithium transition metal oxides may include but are not limited to at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their modified compounds. Optionally, lithium cobalt oxide includes LiCoO2. Lithium nickel oxide includes LiNiO2. Lithium manganese oxide includes at least one of LiMnO2 and LiMn2O4. Lithium nickel cobalt manganese oxide includes LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2(NCM333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2(NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2(NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2(NCM 622 ) and LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM 811 ) at least one of. Lithium nickel cobalt aluminum oxide includes LiNi 0.85 Co 0.15 Al 0.05 O2. Examples of olivine-structured lithium-containing phosphates may include, but are not limited to, at least one of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, and a composite material of lithium manganese iron phosphate and carbon. Optionally, the lithium iron phosphate includes LiFePO4 (LFP). The lithium manganese phosphate includes LiMnPO4. The weight ratio of the positive electrode active material in the positive electrode film layer is 80 weight percent (wt%) to 100 wt%, based on the total weight of the positive electrode film layer.

[0105] In some embodiments, the positive electrode film layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin. The weight ratio of the binder in the positive electrode film layer is 0 to 20 wt%, based on the total weight of the positive electrode film layer.

[0106] In some embodiments, the positive electrode film layer may also optionally include a conductive agent. For example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The weight ratio of the conductive agent in the positive electrode film layer is 0 to 20 wt%, based on the total weight of the positive electrode film layer.

[0107] 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. Optionally, the solvent includes N-methylpyrrolidone. The positive electrode slurry has a solid content of 40 wt% to 80 wt%, and the viscosity at room temperature is adjusted to 5000 mPa·s (mPa·s) to 25000 mPa·s. The positive electrode slurry is coated on the surface of the positive electrode collector, dried, and then cold-pressed by a cold rolling mill to form a positive electrode sheet; the positive electrode powder coating unit area density is 15 mg / cm2 (mg / cm 2 )~35mg / cm 2 The compaction density of the positive electrode is 3.0g / cm 3 ~3.6g / cm 3 , optional 3.4g / cm 3 ~3.6g / cm 3 The calculation formula of the compaction density is: compaction density = coating surface density / (thickness of the electrode after extrusion - thickness of the current collector).

[0108] It is understandable that the positive electrode sheet in the embodiment of the present application can be made by using the above-mentioned positive electrode sheet as the positive electrode sheet body and forming a solid electrolyte interface film on the surface of the positive electrode sheet body.

[0109] Negative electrode

[0110] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector, wherein the negative electrode film layer includes a negative electrode active material.

[0111] As an example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0112] 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 base layer and a metal layer formed on at least one surface of the polymer base material. The composite current collector may be formed by forming a metal material on a polymer base material. Optionally, the metal material includes at least one of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy. The polymer material includes at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS) and polyethylene (PE).

[0113] In some embodiments, the negative electrode active material may adopt the negative electrode active material for batteries that is well known in the art. As an example, the negative electrode active material may include the silicon composite material in the embodiment of the present application. The negative electrode active material may also include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, tin-based material and lithium titanate, etc. The tin-based material may be selected from at least one of elemental tin, tin oxide and tin alloy. However, the negative electrode active material 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. The weight ratio of the negative electrode active material in the negative electrode film layer is 70wt% to 100wt%, based on the total weight of the negative electrode film layer.

[0114] As natural graphite, unprocessed natural graphite such as flake graphite, stamped graphite, and earthy graphite, or spherical natural graphite can be used. Flake graphite and stamped graphite exhibit nearly complete crystals, while earthy graphite has a low degree of crystallinity. Considering electrode capacity, flake graphite and stamped graphite with high crystallinity can be used. For example, flake graphite can be spheroidized before use. In the case of spheroidized natural graphite, the particle size can range from 5 μm to 30 μm, and optionally from 10 μm to 25 μm.

[0115] Artificial graphite is generally produced by graphitization, which involves sintering raw materials such as coal tar, coal tar pitch, and heavy petroleum oil at temperatures above 2500°C. After graphitization, the material is pulverized to form secondary particles. These particles can also be used as negative electrode active materials after conditioning.

[0116] Generally speaking, artificial graphite crystals are randomly distributed within the particles, resulting in lower sphericity and sharper shapes compared to natural graphite. Artificial graphite can be in the form of powder, flakes, blocks, plates, or rods, but isotropic grain orientation is preferred to minimize lithium ion travel distance and improve output characteristics. Artificial graphite can be in the form of flakes and / or plates.

[0117] Artificial graphite includes commercially widely used mesocarbon microbeads (MCMB), mesophase pitch-based carbon fibers (MPCF), bulk graphitized artificial graphite, powdered graphitized artificial graphite, graphite, etc. In addition, the particle size of the artificial graphite can be 5 μm to 30 μm, optionally 10 μm to 25 μm.

[0118] The specific surface area of ​​artificial graphite can be measured by the Brunauer-Emmett-Teller (BET) method. For example, using a porosity analyzer (Bell Japan Inc, Belsorp-II mini), it can be measured by the BET 6-point method using a nitrogen adsorption flow method. The same is true for the measurement of the specific surface area of ​​natural graphite described below.

[0119] In some embodiments, the negative electrode film layer may further include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS). The weight ratio of the binder in the negative electrode film layer is 0 to 30 wt%, based on the total weight of the negative electrode film layer.

[0120] In some embodiments, the negative electrode film layer may further include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The weight ratio of the conductive agent in the negative electrode film layer is 0 to 20 wt%, based on the total weight of the negative electrode film layer.

[0121] In some embodiments, the negative electrode film layer may further include other additives, such as a thickener. The weight ratio of the other additives in the negative electrode film layer is 0-15 wt%, based on the total weight of the negative electrode film layer. Optionally, the thickener includes sodium carboxymethylcellulose (CMC-Na).

[0122] In some embodiments, the negative electrode film layer can be a single layer or multiple layers. When the negative electrode film layer is multiple layers, the active materials of any two layers can be the same or different.

[0123] In some embodiments, the negative electrode sheet can be prepared by the following method: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent to form a negative electrode slurry. Optionally, the solvent includes deionized water. The solid content of the negative electrode slurry is 30wt% to 70wt%, and the viscosity at room temperature is adjusted to 2000mPa·s to 10000mPa·s; the obtained negative electrode slurry is coated on the negative electrode current collector, and after drying and cold pressing, the negative electrode sheet is obtained. The negative electrode powder coating unit area density is 75 mg / m2 (mg / m 2 )~220mg / m 2 , the compaction density of the negative electrode is 1.2g / m 3 ~2.0g / m 3 .

[0124] It can be understood that the negative electrode sheet in the embodiment of the present application can be made by using the above-mentioned negative electrode sheet as the negative electrode sheet body and forming a solid electrolyte interface film on the surface of the negative electrode sheet body.

[0125] electrolytes

[0126] The electrolyte conducts ions between the positive and negative electrodes. This application does not specify the type of electrolyte, and the electrolyte can be selected based on the needs. For example, the electrolyte can be liquid, gel, or solid.

[0127] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0128] In some embodiments, the electrolyte salt may be selected from one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalatoborate (LiDFOB), lithium bis(oxalatoborate) (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorobis(oxalatophosphate) (LiDFOP), and lithium tetrafluorooxalatophosphate (LiTFOP). The concentration of the electrolyte salt is typically 0.5 mol / L to 5 mol / L.

[0129] In some embodiments, the solvent can be selected from one or more of fluoroethylene carbonate (FEC), ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS) and diethyl sulfone (ESE).

[0130] In some embodiments, the electrolyte may further include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, and additives that improve battery high or low temperature performance.

[0131] Isolation film

[0132] 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.

[0133] In some embodiments, the material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0134] 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.

[0135] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0136] 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 package, such as a bag-type soft package. The material of the soft package can be plastic. Examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate. This application does not particularly limit the shape of the secondary battery, which can be cylindrical, square, or any other shape. For example, Figure 1 shows a secondary battery 1 with a square structure as an example.

[0137] In some embodiments, referring 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 a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 11 has an opening connected to the receiving cavity, and the cover plate 13 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 12 through a winding process or a lamination process. The electrode assembly 12 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 12. The number of electrode assemblies 12 contained in the secondary battery 1 can be one or more, and those skilled in the art can select according to specific actual needs.

[0138] 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 may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but is not limited thereto.

[0139] As the electrical device, a secondary battery can be selected according to its usage requirements.

[0140] Fig. 3 shows an example of an electric device 2. The electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle.

[0141] As another example, the device may be a mobile phone, a tablet computer, a laptop computer, etc.

[0142] Example

[0143] In order to make the technical problems, technical solutions and beneficial effects solved by this application clearer, the application will be further described in detail below with reference to the embodiments and drawings. Obviously, the described embodiments are only a part of the embodiments of this application, rather than all the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is in no way intended to limit the present application and its applications. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0144] If no specific techniques or conditions are specified in the examples, the experiments were carried out according to the techniques or conditions described in the literature in the field or according to the product instructions. All reagents or instruments used without specifying the manufacturer are commercially available conventional products.

[0145] Example 1

[0146] The preparation method of the silicon composite material in this embodiment includes:

[0147] A silicon-based material, a silicon-carbon composite, and a flexible material, graphite, were added to deionized water and stirred to uniformly disperse to obtain a dispersion. The dispersion was spray-dried using a spray dryer. The solid material obtained by the spray drying process was carbon-coated in a gaseous carbon source atmosphere to obtain the silicon composite material of this embodiment.

[0148] Example 2 to Example 17

[0149] Compared with Example 1, Examples 2 to 17 differ in that the compositions of the silicon composite materials are different, as specifically shown in Table 1.

[0150] Example 18

[0151] Compared with Example 1, the difference of this embodiment is that graphite is replaced by soft carbon.

[0152] Example 19

[0153] Compared with Example 1, the difference of this embodiment is that the silicon-carbon composite is replaced by a silicon-oxygen compound, wherein the mass percentage of silicon in the silicon-oxygen compound is 50%.

[0154] Example 20

[0155] Compared with Example 1, the difference of this embodiment is that the silicon-carbon composite is replaced by a silicon-nitrogen compound, wherein the mass percentage of silicon in the silicon-nitrogen compound is 50%.

[0156] The preparation method of the secondary battery is as follows:

[0157] (1) Preparation of positive electrode sheets.

[0158] The positive electrode material LiNi 0.8 Co 0.1 Mn 0.1 O2, conductive agent acetylene black, and binder polyvinylidene fluoride (PVDF) are mixed evenly in a mass ratio of 97:2:1 and added to the solvent N-methylpyrrolidone (NMP) to make a positive electrode slurry; the positive electrode slurry is evenly coated on the positive electrode current collector aluminum foil, dried at 85°C and cold pressed, and then die-cut and slit to make positive electrode sheets.

[0159] (2) Preparation of negative electrode sheets.

[0160] The negative electrode active material, conductive agent acetylene black, thickener sodium hydroxymethyl cellulose, and binder styrene-butadiene rubber were added to the solvent water at a mass ratio of 96:2:1:1 and mixed evenly to form a negative electrode slurry. The negative electrode slurry was evenly coated on the negative electrode current collector copper foil, dried at 85°C, and then cold-pressed with a 40-ton pressure using cylindrical cold press rollers at a speed of 20 meters per minute (m / min) and a temperature of 25°C to form the negative electrode sheet.

[0161] The negative electrode active material in the embodiment is the silicon composite material in the corresponding embodiment.

[0162] In Comparative Example 1, the negative electrode active material is a silicon-carbon composite.

[0163] In Comparative Example 2, the negative electrode active material is graphite.

[0164] (3) Preparation of isolation membrane.

[0165] A polyethylene microporous film is used as a porous isolation membrane substrate, and inorganic alumina powder, polyvinylpyrrolidone, and acetone solvent are evenly mixed in a weight ratio of 3:1.5:5.5 to form a slurry, which is then coated on one side of the substrate and dried to obtain an isolation membrane.

[0166] (4) Preparation of electrolyte.

[0167] LiPF6 lithium salt was dissolved in a mixed solvent of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate (the volume ratio of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate was 1:2:1), and fluoroethylene carbonate (FEC) was added as an additive to obtain an electrolyte. The concentration of LiPF6 in the electrolyte was 1 mol / L, and the mass percentage of FEC was 5 wt%.

[0168] (5) Preparation of secondary batteries.

[0169] The positive electrode sheet, the positive electrode sheet and the separator are wound to obtain a bare battery cell, which is then packaged, injected, formed, vented and other processes to obtain the corresponding secondary battery.

[0170] Test example:

[0171] (1) The structural stability of the negative electrode sheets in the examples and comparative examples was tested.

[0172] a: Vertical cross-sections of the negative electrode sheets in the Examples and Comparative Examples were observed using a scanning electron microscope (SEM) to measure the depth H of the active material embedded in the current collector. The measurement results are shown in Table 1. H can be used to indicate the degree of damage to the negative electrode current collector; a larger H value indicates more severe damage to the negative electrode current collector.

[0173] b: The elongation at break was tested on the negative electrode sheets in the examples and comparative examples. Take the cold-pressed negative electrode sheet and use a die-cutting knife to punch out samples into 50 mm (mm) * 15 mm long strips, where the 50 mm direction is the processing direction of the sheet, that is, the direction of movement of the sheet relative to the cold-pressing roller. A high-speed rail tensile test machine was used to conduct the tensile test. The two ends of the tensile machine needed to be tightly attached with wrinkle glue to prevent the sheet from loosening and falling off during stretching. The sample was kept vertical and straight during stretching. The sample needed to break somewhere in the middle, and the data of the break at both ends of the fixture was discarded. The stretching speed was 2 mm / min. The initial length of the negative electrode sheet was L0, i.e. 50 mm. The length when it was stretched to break in the length direction was L1, and the elongation at break λ = (L1-L0) / L0. The test results are shown in Table 1.

[0174] (2) The volume energy density (VED) of the secondary batteries in the examples and comparative examples was tested. The batteries were left at a constant temperature of 25°C for 2 hours, then charged to 4.2V at 0.33 coulombs (C) at 2.8V to 4.2V, then charged at a constant voltage of 4.2V to a current ≤ 0.05C, left at rest for 10 minutes, and then discharged to 2.8V at 0.33C. The battery capacity C0 was recorded. VED is the ratio of C0 to the volume of the battery case. The test results are shown in Table 1.

[0175] (3) The cycle performance of the secondary batteries in the embodiment and the comparative example was tested. The test method is as follows: at 25°C, the battery to be tested was continuously charged and discharged at 0.5C in the range of 0-100% SOC, and each charge and discharge was left to stand for 30 minutes. The battery cycled to 300 cycles, and the discharge capacity of the nth cycle was recorded as C n The first cycle discharge capacity is recorded as C1, and the capacity retention rate of the nth cycle = (C n / C1)×100%, where the capacity retention rate after 300 cycles at 25℃=(C 300 / C1)×100. The test results are shown in Table 1.

[0176] Table 1

[0177] In Table 1, BET represents the specific surface area of ​​porous carbon materials, with the unit being m 2 / g. Pore size refers to the pore size of the porous carbon material, and the unit is nm. The percentage of silicon refers to the mass percentage of silicon in the silicon-based material. The unit of Dv50 of silicon-based material is μm. The unit of Dv50 of graphite is μm. Graphite:silicon-based material refers to the mass ratio of graphite to silicon-based material. The unit of carbon coating thickness is nm. The unit of Dv50 of silicon composite material is μm. The unit of tap density of silicon composite material is g / cm 3 The unit of specific surface area of ​​silicon composite material is m 2 / g. The unit of compaction density of negative electrode is g / cm 3 The embedding depth indicates the depth to which the active material is embedded in the current collector, and is measured in μm. The volumetric energy density of a secondary battery is measured in watt-hours per liter (Wh / L).

[0178] In Table 1, it can be seen from the comparison between Example 1 and Comparative Example 1 that, compared with the case where the silicon-carbon composite is used as the negative electrode active material, when the negative electrode active material includes the silicon-carbon composite and graphite, the damage to the negative electrode current collector is less during the preparation of the negative electrode sheet, and the volume energy density of the battery is higher.

[0179] It can be seen from the comparison between Example 1 and Comparative Example 2 that, compared with graphite as the negative electrode active material, when the negative electrode active material includes the silicon-carbon composite and graphite, the volume energy density of the battery is higher.

[0180] From the comparison between Example 1 and Example 7, it can be seen that when the Dv50 of the silicon-carbon composite in Example 7 is less than the Dv50 of graphite, the negative electrode current collector has certain damage and the cycle performance is low.

[0181] From the comparison among Example 1, Example 8 and Example 9, it can be seen that when the Dv50 of the silicon-carbon composite is larger or the Dv50 of graphite is smaller, the damage to the negative electrode current collector is greater when preparing the negative electrode sheet.

[0182] Comparing Examples 1 and 14, the battery in Example 14 exhibits lower cycling performance. This is likely due to the larger specific surface area of ​​the silicon-carbon composite, which exacerbates side reactions due to its large pores, leading to reduced cycling performance. Furthermore, the larger specific surface area of ​​the silicon-carbon composite in Example 14 results in a lower compaction density and, consequently, a lower volumetric energy density.

[0183] From the comparison between Example 1 and Example 15, it can be seen that the corresponding cycle performance of the battery in Example 15 is lower. The possible reason is that the specific surface area of ​​the silicon-carbon composite is small, and part of the elemental silicon is located on the particle surface of the silicon-carbon composite. The activity of elemental silicon is relatively high, which may deteriorate the cycle performance to a certain extent.

[0184] From the comparison between Example 1 and Example 16, it can be seen that when the pore size of the porous carbon in the silicon-carbon composite is larger, the compaction density is smaller and the volume energy density of the battery is smaller.

[0185] From the comparison between Example 1 and Example 17, it can be seen that when the thickness of the carbon coating layer is larger, the cycle performance of the battery is lower.

[0186] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0187] The above-described embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art could make various modifications and improvements without departing from the spirit of the present application, all of which fall within the scope of protection of the present application. Therefore, the scope of protection of the present patent application shall be determined by the appended claims.

Claims

1. A silicon composite material, comprising a silicon-based material and a flexible material, wherein the hardness of the flexible material is less than the hardness of the silicon-based material; the silicon-based material comprises at least one of elemental silicon, silicon-oxygen compounds, silicon-carbon composites, silicon-nitrogen composites and silicon alloys; and the flexible material is located on at least a portion of the surface of the silicon-based material.

2. The silicon composite material according to claim 1, wherein: The flexible material includes a flexible conductive material.

3. The silicon composite material according to claim 2, wherein: The flexible conductive material includes at least one of graphite and soft carbon.

4. The silicon composite material according to any one of claims 1 to 3, wherein The Dv50 of the flexible material is ≤ the Dv50 of the silicon-based material.

5. The silicon composite material according to claim 4, wherein: The Dv50 of the flexible material is 1 μm to 5 μm.

6. The silicon composite material according to claim 4 or 5, wherein: The Dv50 of the silicon-based material is 2 μm to 7 μm.

7. The silicon composite material according to any one of claims 1 to 6, wherein The silicon-based material and the flexible material are both granular materials, and the flexible material is distributed in granular form on at least a portion of the surface of the silicon-based material.

8. The silicon composite material according to any one of claims 1 to 7, wherein The mass ratio of the flexible material to the silicon-based material is (1-9):

1.

9. The silicon composite material according to any one of claims 1 to 8, wherein The silicon-carbon composite includes a porous carbon material and elemental silicon located in pores of the porous carbon material.

10. The silicon composite material according to claim 9, wherein: The specific surface area of ​​the porous carbon material is 500 m 2 / g~1800m 2 / g.

11. The silicon composite material according to claim 9 or 10, wherein: The pores of the porous carbon material have a pore diameter of 2 nm to 50 nm.

12. The silicon composite material according to any one of claims 9 to 11, wherein The mass percentage of the elemental silicon in the silicon-carbon composite is 20% to 60%.

13. The silicon composite material according to any one of claims 1 to 12, wherein: The silicon composite material further includes a coating layer, wherein the coating layer contains at least one of carbon and metal oxide, and the coating layer completely or partially covers the silicon-based material and the flexible material.

14. The silicon composite material according to claim 13, wherein: The metal oxide includes at least one of aluminum oxide and titanium dioxide.

15. The silicon composite material according to claim 13 or 14, wherein: The coating layer has a thickness of 5 nm to 60 nm.

16. The silicon composite material according to any one of claims 1 to 15, wherein The Dv50 of the silicon composite material is 8 μm to 40 μm.

17. The silicon composite material according to any one of claims 1 to 16, wherein The tap density of the silicon composite material is 0.9 g / cm 3 ~1.2g / cm 3 .

18. The silicon composite material according to any one of claims 1 to 17, wherein The specific surface area of ​​the silicon composite material is 0.8 m 2 / g~1.5m 2 / g.

19. A method for preparing a silicon composite material, comprising the following steps: A silicon-based material, a flexible material and a solvent are mixed to obtain a dispersion; the hardness of the flexible material is less than the hardness of the silicon-based material; the silicon-based material comprises at least one of elemental silicon, silicon-oxygen compounds, silicon-carbon compounds, silicon-nitrogen compounds and silicon alloys; The dispersion is spray dried.

20. The method for preparing the silicon composite material according to claim 19, wherein: The solid content of the dispersion is 1% to 40%.

21. The method for preparing the silicon composite material according to claim 19 or 20, wherein: The temperature of the hot air in the spray drying process is 150°C to 200°C.

22. The method for preparing a silicon composite material according to any one of claims 19 to 21, wherein: The flow rate of the hot air in the spray drying process is 0.08m 3 / min~0.2m 3 / min.

23. A negative electrode plate, comprising a negative electrode current collector and a negative electrode film layer located on at least one surface of the negative electrode current collector; the negative electrode film layer comprises 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 22.

24. The negative electrode sheet according to claim 23, wherein: The compaction density of the negative electrode sheet is 1.3 g / cm 3 ~1.75g / cm 3 .

25. The negative electrode sheet according to claim 23 or 24, wherein: The full charge expansion rate of the negative electrode plate is 22% to 50%.

26. A secondary battery comprising the negative electrode sheet according to any one of claims 23 to 25.

27. An electrical device comprising the secondary battery according to claim 26.

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