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

Abstract

The application provides 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, and the hardness of the flexible material is less than that of the silicon-based material. The silicon-based material comprises at least one of elemental silicon, a silicon oxide 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. Through the cooperation of the flexible material and the silicon-based material, the risk of the current collector being crushed during the preparation of the electrode sheet can be reduced, the compaction density of the electrode sheet is improved, and the energy density of the battery is improved.

Description

Technical Field

[0001] This application relates to the field of secondary battery technology, and in particular to a silicon composite material and its preparation method, a negative electrode sheet, a battery, and an electrical device. Background Technology

[0002] The statements herein are provided only as background information in connection with this application and do not necessarily constitute prior art.

[0003] Silicon-based materials have high specific capacity, and their introduction into secondary batteries may improve the battery's energy density. However, silicon-based materials typically have high hardness, which can easily damage the current collector during electrode fabrication. This limits the improvement of electrode compaction density, and consequently, further limits the improvement of battery energy density. Summary of the Invention

[0004] To achieve the above objectives, this 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 that of the silicon-based material. The silicon-based material includes at least one of elemental silicon, silicon oxide compounds, 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 above-mentioned 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, reducing the risk of damage to the current collector during electrode fabrication, thus improving the compaction density of the electrode and consequently increasing the energy density of the battery.

[0005] In some embodiments, the flexible material includes a flexible conductive material. The introduction of a 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 includes at least one of graphite and soft carbon.

[0006] 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 uniformly dispersed on the surface of the silicon-based material, which is beneficial for further improving the buffering effect of the flexible material on the silicon-based material.

[0007] In some embodiments, the Dv50 of the flexible material is 1 μm to 5 μm. A Dv50 within this range allows the flexible material to be more uniformly dispersed on the surface of the silicon-based material, while also providing suitable deformation space between the flexible materials. This suitable deformation space helps buffer the interaction forces between the silicon-based material and the current collector, reducing the risk of damage to the current collector during electrode fabrication.

[0008] In some embodiments, the Dv50 of the silicon-based material is 2 μm to 7 μm. A Dv50 within this range allows the electrode sheets to have a high compaction density, which is beneficial for improving the energy density of the battery.

[0009] In some embodiments, both the silicon-based material and the flexible material are particulate materials, with the flexible material distributed in a particulate form on at least a portion of the surface of the silicon-based material. A particulate distribution of the flexible material provides better cushioning. When the silicon-based material has low sphericity, i.e., has sharp protrusions, the particulate flexible material can better conform to the protrusions, reducing the risk of damage to the current collector. Optionally, the flexible material is particulate across the entire surface of the silicon-based material.

[0010] 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's buffering effect is fully utilized, reducing the risk of current collector damage. Simultaneously, this mass ratio also helps increase the electrode's compaction density, thereby maintaining a high energy density in the battery.

[0011] In some embodiments, the silicon-carbon composite comprises a porous carbon material and elemental silicon located within the pores of the porous carbon material. The pores within the porous carbon material provide a certain amount of space for the elemental silicon to expand, reducing the overall expansion of the silicon-carbon composite and improving the structural stability of the electrode sheets during charging and discharging.

[0012] In some embodiments, the specific surface area of ​​the porous carbon material is 500 m². 2 / g~1800m 2 / g. The specific surface area of ​​porous carbon materials within this range can provide a large space for the adhesion of elemental silicon, thus promoting the improvement of battery energy density.

[0013] In some embodiments, the pore size of the porous carbon material is 2 nm to 50 nm. A pore size within this range provides ample expansion space for elemental silicon, while also giving the battery better cycle performance.

[0014] In some embodiments, the elemental silicon accounts for 20% to 60% of the mass percentage of the silicon-carbon composite. This range of elemental silicon mass percentage allows the battery to achieve both high energy density and good cycle stability.

[0015] In some embodiments, the silicon composite material further includes a coating layer comprising at least one of carbon and a metal oxide, which completely or partially covers the silicon-based material and the flexible material. The coating layer provides a barrier to the electrolyte, further reducing the risk of direct contact between the electrolyte and the silicon-based material, minimizing side reactions between the electrolyte and the silicon-based material inside the battery, and improving the battery's cycle and fast-charging performance. Optionally, the metal oxide includes at least one of aluminum oxide and titanium dioxide.

[0016] In some embodiments, the thickness of the coating layer is 5 nm to 60 nm. A coating layer thickness within this range can maintain a good coating effect while allowing the silicon composite material to have a suitable particle size, which is beneficial for improving the compaction density of the electrode sheet.

[0017] In some embodiments, the Dv50 of the silicon composite material is 8 μm to 40 μm. A Dv50 within this range can provide a suitable path size for lithium-ion diffusion, improving lithium-ion transport kinetics.

[0018] In some embodiments, the tap density of the silicon composite material is 0.9 g / cm³. 3 ~1.2g / cm 3 Within this range, the tap density of silicon composite materials is beneficial for improving the compaction density of the negative electrode sheet.

[0019] In some embodiments, the specific surface area of ​​the silicon composite material is 0.8 m². 2 / g~1.5m 2 / g. The specific surface area of ​​silicon composite materials within this range can enable electrode sheets to have good kinetic properties.

[0020] This 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 the hardness of the silicon-based material; and wherein the silicon-based material includes at least one of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The dispersion is then subjected to spray drying.

[0021] In some embodiments, the solid content of the dispersion is 1% to 40%.

[0022] In some embodiments, the temperature of the hot air used in the spray drying process is 150°C to 200°C.

[0023] In some embodiments, the flow rate of the hot air used in the spray drying process is 0.08 m³ / s. 3 / min~0.2m 3 / min.

[0024] This application also provides a negative electrode sheet, including a negative current collector and a negative electrode film layer located on at least one surface of the negative current collector; the negative electrode film layer comprises the silicon composite material or the silicon composite material prepared by the preparation method.

[0025] In some embodiments, the compaction density of the negative electrode sheet is 1.3 g / cm³. 3 ~1.75g / cm 3 Within this range, the compaction density of the negative electrode sheet is beneficial for improving the energy density of the battery.

[0026] In some embodiments, the full-charge expansion rate of the negative electrode is 22% to 50%. A full-charge expansion rate within this range can give the battery better cycle stability.

[0027] This application also provides a secondary battery, including the negative electrode plate.

[0028] This application also provides an electrical device, including the secondary battery described herein. Attached Figure Description

[0029] To more clearly illustrate the technical solution of this application, the accompanying drawings used in this application will be briefly described below. Obviously, the drawings described below are merely some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without any creative effort.

[0030] Figure 1 This is a schematic diagram of a secondary battery according to one embodiment of this application.

[0031] Figure 2 for Figure 1 An exploded view of a secondary battery according to one embodiment of this application is shown.

[0032] Figure 3 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application.

[0033] Figure 4 This is a schematic diagram of the structure of a silicon composite material in one embodiment of this application.

[0034] Figure 5 This is a schematic diagram of the structure of the silicon composite material in another embodiment of this application.

[0035] Explanation of reference numerals in the attached figures:

[0036] 1. Secondary battery; 11. Casing; 12. Electrode assembly; 13. Cover plate; 2. Electrical device; 3. Silicon composite material; 31. Silicon-carbon composite; 32. Graphite; 33. Coating layer.

[0037] To better describe and illustrate embodiments and / or examples of the inventions disclosed herein, reference may be made to one or more accompanying drawings. Additional details or examples used to describe the drawings should not be considered as limiting the scope of any of the disclosed inventions, the currently described embodiments and / or examples, or the best mode of these inventions as currently understood. Detailed Implementation

[0038] To facilitate understanding of this application, a more complete description will be provided below with reference to the accompanying drawings. Preferred embodiments of this application are shown in the drawings. However, this application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of this application.

[0039] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0040] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints 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 60–120 and 80–110 are listed for a specific parameter, it is understood that ranges of 60–110 and 80–120 are also expected. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1–3, 1–4, 1–5, 2–3, 2–4, and 2–5. In this application, unless otherwise stated, the numerical range "a–b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0~5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0041] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0042] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0043] Unless otherwise specified, all steps in this 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 it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0044] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0045] Unless otherwise specified, the term "or" is inclusive in this application. 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 exists, and B is false or does not exist; A is false or does not exist, and B is true or exists; or both A and B are true, or both A and B exist.

[0046] Unless otherwise stated, the terms used in this application have their common meanings as commonly understood by those skilled in the art. Unless otherwise stated, the numerical values ​​of the parameters mentioned in this application can be measured using various measurement methods commonly used in the art. For example, they can be tested according to the methods given in the embodiments of this application.

[0047] One embodiment of this application provides a silicon composite material. The silicon composite material includes a silicon-based material and a flexible material, wherein the hardness of the flexible material is less than that 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, reducing the risk of damage to the current collector during electrode fabrication, thus improving the compaction density of the electrode and consequently increasing the energy density of the battery.

[0048] Alternatively, the flexible material may be located on the entire surface of the silicon-based material.

[0049] Furthermore, when silicon composite materials are applied to secondary batteries, 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 and improving the cycle performance of the battery.

[0050] In some embodiments, the flexible material includes a flexible conductive material. The introduction of a 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 graphite includes at least one of natural graphite and artificial graphite.

[0051] 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 uniformly dispersed on the surface of the silicon-based material, which is beneficial for further improving the buffering effect of the flexible material on the silicon-based material. Optionally, the Dv50 of the flexible material is less than the Dv50 of the silicon-based material.

[0052] It is understood that in this application, Dv50 refers to the particle size corresponding to the cumulative particle size distribution number reaching 50% in the volume cumulative distribution curve. Physically, it means that 50% of the particles are smaller (or larger) than Dv50. As an example, Dv50 can be obtained by referring to the test method in GB / T 19077-2016 and using the particle size distribution curve obtained by a Mastersizer3000 laser diffraction particle size distribution measuring instrument.

[0053] As some optional examples of the Dv50 of flexible materials, the Dv50 of the flexible materials is 1μm to 5μm. A Dv50 within this range allows the flexible materials to be more uniformly dispersed on the surface of the silicon-based material, while also providing suitable deformation space between the flexible materials. Suitable deformation space helps buffer the interaction forces between the silicon-based material and the current collector, reducing the risk of damage to the current collector during electrode fabrication. Optionally, the Dv50 of the flexible material can be 1μm, 2μm, 3μm, 4μm, 5μm, etc.

[0054] As some alternative examples of the Dv50 of silicon-based materials, the Dv50 of the silicon-based materials is 2μm to 7μm. Within this range, the Dv50 of the silicon-based materials can result in higher compaction density of the electrode sheets, which is beneficial for improving the energy density of the battery. Optionally, the Dv50 of the silicon-based materials can be 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, etc.

[0055] It is understood that flexible materials and silicon-based materials can be bonded together through the surface tension of the flexible and silicon-based materials. Optionally, the silicon composite material may also include a binder. The binder can further enhance the bonding force between the flexible and silicon-based materials, allowing them to be better integrated and thus improving the structural stability of the silicon composite material. Optionally, the binder may be at least one of polyvinylpyrrolidone, polyethylene glycol, and sodium carboxymethyl cellulose.

[0056] In some embodiments, both the silicon-based material and the flexible material are particulate, with the flexible material distributed in a particulate form on at least a portion of the surface of the silicon-based material. This particulate distribution of the flexible material provides better cushioning. When the silicon-based material has low sphericity, i.e., has sharp protrusions, the particulate flexible material can better conform to the protrusions, reducing the risk of damage to the current collector. Optionally, the flexible material is particulate across the entire surface of the silicon-based material.

[0057] In some embodiments, the mass ratio of flexible material to silicon-based material is (1–9):1. Within this range, the buffering effect of the flexible material is fully utilized, reducing the risk of current collector damage. Simultaneously, this mass ratio allows the battery to maintain a high energy density. Optionally, the mass ratio of flexible material to silicon-based material can be 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, etc.

[0058] In some embodiments, the silicon oxide compound includes the chemical formula SiO. x The material, wherein 0 < x < 2. Further optionally, 0.5 ≤ x ≤ 1.5. Further optionally, the silicon oxide compound includes SiO.

[0059] Further optionally, metal elements may be distributed on the surface and / or inside the silicon oxide compound to reduce the proportion of irreversible phase (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 can reduce the risk of damage to the silicon oxide compound and improve its lifetime. Optionally, 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.

[0060] Optionally, the silicon-nitrogen compound includes Si3N4.

[0061] In some embodiments, the silicon-carbon composite comprises a porous carbon material and elemental silicon located within the pores of the porous carbon material. The pores within the porous carbon material provide a certain amount of space for the elemental silicon to expand, reducing the overall expansion of the silicon-carbon composite and improving the structural stability of the electrode sheets during charging and discharging. Optionally, the elemental silicon includes nano-silicon.

[0062] Silicon-carbon composites typically have a relatively hard texture. When applied to electrode sheets, the hardness of the silicon-carbon composite during cold pressing can damage the current collector, thus adversely affecting the performance of the electrode sheet and the battery. In this application, a flexible material is used in conjunction with the silicon-carbon composite. The flexible material is softer than the silicon-carbon composite, which can disperse the stress introduced by the silicon-carbon composite during cold pressing, reducing its adverse effects on the current collector. This improves the structural stability of the electrode sheet and ultimately enhances battery performance.

[0063] Furthermore, silicon-carbon composites have poor compressive strength and are prone to breakage during cold pressing. In this application, by combining flexible materials with silicon-carbon composites, the silicon composite material can be made to have better compressive strength. When this silicon composite material is introduced into the electrode sheet, it is beneficial to further improve the compaction density of the electrode sheet.

[0064] In some embodiments, the specific surface area of ​​the porous carbon material is 500 m². 2 / g~1800m 2 / g. Within this range, the specific surface area of ​​porous carbon materials can provide ample space for the adhesion of elemental silicon, thus promoting an increase in battery energy density. Optionally, the specific surface area of ​​the porous carbon material can be 500m². 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.

[0065] In some embodiments, the pore size of the porous carbon material is 2 nm to 50 nm. This pore size range provides ample expansion space for elemental silicon, resulting in better cycle performance and storage capacity for the battery. Optionally, the pores of the porous carbon material are mesoporous.

[0066] In some embodiments, elemental silicon accounts for 20% to 60% of the mass percentage of the silicon-carbon composite. Within this range, the mass percentage of elemental silicon allows the battery to achieve both high energy density and good cycle stability. Optionally, the mass percentage of elemental silicon in the silicon-carbon composite can be 20%, 30%, 40%, 50%, 60%, etc.

[0067] In some embodiments, the flexible material includes graphite, and the silicon-based material includes silicon-carbon composites. See also... Figure 4 The diagram shows a schematic representation of the structure of a silicon composite material in one embodiment of this application. Figure 4 The corresponding silicon composite material 3 includes a silicon-carbon composite 31 and graphite 32, with graphite 32 located on at least a portion of the surface of the silicon-carbon composite 31. It is understood that, in Figure 4 The diagram illustrates the positional relationship between silicon composite material 3, silicon-carbon composite 31, and graphite 32, but does not represent the actual shapes of these components. Figure 4 The shapes shown are as indicated. In silicon composites, the shapes of the silicon composite, silicon-carbon composite, and graphite can be other shapes. For example, the shapes of the silicon composite, silicon-carbon composite, and graphite can each be independently selected from at least one of spherical and near-spherical shapes.

[0068] In some embodiments, the silicon composite material further includes a coating layer comprising at least one of carbon and metal oxides, which completely or partially covers the silicon-based material and the flexible material. The coating layer provides a barrier to the electrolyte, further reducing the risk of direct contact between the electrolyte and the silicon-based material, minimizing side reactions between the electrolyte and the silicon-based material inside the battery, and improving the battery's cycle and fast-charging performance. Optionally, the coating layer may be a carbon coating layer.

[0069] Please see Figure 5 The diagram illustrates the structure of a silicon composite material in another embodiment of this application. Figure 5 The corresponding silicon composite material 3 includes a silicon-carbon composite 31 and graphite 32, with graphite 32 located on at least a portion of the surface of the silicon-carbon composite 31. The silicon composite material 3 also includes a coating layer 33. The coating layer 33 completely coats the silicon-carbon composite 31 and graphite 32.

[0070] In some embodiments, the metal oxide includes at least one of aluminum oxide and titanium dioxide.

[0071] In some embodiments, the thickness of the coating layer is 5 nm to 60 nm. A coating layer thickness within this range can maintain a good coating effect while allowing the silicon composite material to have a suitable particle size, which is beneficial for improving the compaction density of the electrode sheet. Optionally, the thickness of the coating layer can be 5 nm, 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, etc.

[0072] Understandably, flexible materials, silicon-carbon composites, and coatings in silicon composite materials can be detected and distinguished using methods such as transmission electron microscopy (TEM) and X-ray diffraction (XRD).

[0073] In some embodiments, the Dv50 of the silicon composite material is 8 μm to 40 μm. A Dv50 within this range can provide a suitable path size for lithium-ion diffusion, improving lithium-ion transport kinetics. Optionally, the Dv50 of the silicon composite material can be 8 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, etc.

[0074] In some embodiments, the tap density of the silicon composite material is 0.9 g / cm³. 3 ~1.2g / cm 3 Within this range, the tap density of the silicon composite material is beneficial for improving the compaction density of the negative electrode sheet. Optionally, the tap density of the silicon composite material is 0.9 g / cm³. 3 1g / cm 3 1.1g / cm 3 1.2g / cm 3 It is understandable that the tap density of silicon composite materials can be measured using a tap density meter. A calibrated cylinder containing the silicon composite material is fixed to a mechanical vibration device. A vibration motor drives the device to vibrate vertically up and down, causing the cylinder to vibrate rhythmically. As the number of vibrations increases, the silicon composite material in the cylinder gradually compacts. After the set number of vibrations is reached, the device stops vibrating, and the volume of the cylinder is read. Based on the definition of density: mass divided by volume, the tap density of the silicon composite material can be calculated.

[0075] In some embodiments, the specific surface area of ​​the silicon composite material is 0.8 m². 2 / g~1.5m 2 / g. The specific surface area of ​​the silicon composite material within this range allows the electrode sheets to exhibit good kinetic properties. Optionally, the specific surface area of ​​the silicon composite material is 0.8m². 2 / g, 0.9m 2 / g, 1m 2 / g, 1.1m 2 / g, 1.2m 2 / g, 1.3m 2 / g, 1.4m 2 / g, 1.5m 2 / g etc.

[0076] In some implementations, the silicon composite material is in the form of spherical particles.

[0077] Another embodiment of this application provides a method for preparing a silicon composite material. The method includes the following steps: mixing a silicon-based material, a flexible material, and a solvent to obtain a dispersion; 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 oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The dispersion is then subjected to spray drying. This preparation method is simple and easy to implement, and the silicon composite material can be obtained through spray drying granulation.

[0078] Alternatively, spray drying is carried out in a dry, hot air atmosphere. It is understood that during spray drying, the dispersion is placed in a hot air atmosphere for drying.

[0079] In some embodiments, the temperature of the hot air used for spray drying is 150°C to 200°C. Optionally, the temperature of the hot air used for spray drying can be 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, etc.

[0080] In some embodiments, the flow rate of the hot air used in the spray drying process is 0.08 m³ / s. 3 / min~0.2m 3 / min. Optionally, the flow rate of the hot air for the spray drying process is 0.08m³ / min. 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.

[0081] In some embodiments, the solid content of the dispersion is 1% to 40%. Optionally, the solid content of the dispersion is 1%, 5%, 8%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, etc.

[0082] In some implementations, the solvent includes water.

[0083] In some embodiments, the preparation method of the 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 a dispersant can improve the dispersion effect of the silicon-based material and the flexible material in the solvent, which is beneficial to improving the uniformity of the silicon composite material.

[0084] 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). More preferably, the ratio can be 70:30, 75:25, 80:20, 85:15, 90:10, 95:5, etc. Even more preferably, the dispersant includes one or more of polyvinylpyrrolidone, polyethylene glycol, and sodium carboxymethyl cellulose.

[0085] In some embodiments, the preparation method of the 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 a binder can improve the bonding performance between the silicon-carbon composite and graphite, making the structure of the resulting silicon composite material more stable.

[0086] Alternatively, the binder may include one or more of polyvinylpyrrolidone, polyethylene glycol, and sodium carboxymethyl cellulose.

[0087] Understandably, a spray dryer can be used to spray dry the dispersion.

[0088] In some embodiments, the spray drying process further includes coating the solid material obtained from the spray drying process.

[0089] In some embodiments, the spray drying process further includes: carbon coating the solid material obtained from the spray drying process in a gaseous carbon source atmosphere. Carbon coating can improve the conductivity and fast-charging performance of the silicon composite material.

[0090] Optionally, the carbon coating process includes the following steps: placing the solid material obtained from spray drying into a ceramic boat, then placing the ceramic boat into a tube furnace with Ar gas as the protective gas, heating it to 600℃ to 800℃ at a heating rate of 2℃ to 10℃, and holding it at that temperature for 1h to 4h. Then, the Ar gas is replaced with a gaseous carbon source, and the process is continued for 15min to 30min, followed by cooling to room temperature. Further optionally, the gaseous carbon source includes at least one of CH4 and C2H2.

[0091] Another embodiment of this application provides a negative electrode sheet. The negative electrode sheet includes a negative current collector and a negative electrode film layer located on at least one surface of the negative current collector. The negative electrode film layer comprises the aforementioned silicon composite material or a silicon composite material prepared by the aforementioned method for preparing the silicon composite material.

[0092] In some embodiments, the compaction density of the negative electrode sheet is 1.3 g / cm³. 3 ~1.75g / cm 3 Within this range, the compaction density of the negative electrode sheet is beneficial for improving the energy density of the battery. For example, the compaction density of the negative electrode sheet can be 1.3 g / cm³. 3 1.4g / cm 3 1.5g / cm 3 1.6g / cm 3 1.7g / cm 3 wait.

[0093] In one embodiment, the full-charge expansion rate of the negative electrode is 22% to 50%. A full-charge expansion rate within this range allows the battery to have good cycle stability. Optionally, the full-charge expansion rate of the negative electrode can be 25%, 30%, 35%, 40%, 45%, etc. It is understood that the full-charge expansion rate of the negative electrode can be measured as follows: The full-charge expansion rate can be tested by measuring the original thickness of the negative electrode, denoted as W0. Then, after fully charging the assembled battery, it is disassembled, and the thickness of the negative electrode after full charging is measured, denoted as W1. The expansion rate α = (W1 - W0) / W0.

[0094] Another embodiment of this application provides a secondary battery. The secondary battery includes the aforementioned negative electrode plate.

[0095] Another embodiment of this application provides an electrical device. This electrical device includes the aforementioned secondary battery.

[0096] The secondary battery and power-consuming device of this application will be described below with appropriate reference to the accompanying drawings.

[0097] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0098] Positive electrode sheet

[0099] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including a positive electrode active material.

[0100] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive active material layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0101] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material on the polymer substrate. Optionally, the metal material may include, but is not limited to, one or more of aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. Optionally, the polymer 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).

[0102] As an example, the positive electrode active material may comprise positive electrode active materials known in the art for use in batteries. As an example, the positive electrode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides 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 / 3Mn 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 the following. Lithium nickel cobalt aluminum oxides include LiNi 0.85 Co 0.15 Al 0.05 O2. Examples of lithium phosphates with an olivine structure may include, but are not limited to, at least one of lithium iron phosphate, lithium iron phosphate and carbon composites, lithium manganese phosphate, lithium manganese phosphate and carbon composites, lithium iron manganese phosphate, and lithium iron manganese phosphate and carbon composites. Optionally, lithium iron phosphate includes LiFePO4 (LFP). Lithium manganese phosphate includes LiMnPO4. The positive electrode active material accounts for 80-100% by weight of the positive electrode film, based on the total weight of the positive electrode film.

[0103] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a terpolymer of PVDF-tetrafluoroethylene-propylene, a terpolymer of PVDF-hexafluoropropylene-tetrafluoroethylene, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorinated acrylate resin. The binder constitutes 0–20% by weight of the positive electrode film layer, based on the total weight of the positive electrode film layer.

[0104] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The conductive agent accounts for 0–20% by weight of the positive electrode film, based on the total weight of the positive electrode film.

[0105] In some embodiments, the positive electrode sheet can be prepared by dispersing the components used to prepare the positive electrode sheet, such as the positive active material, conductive agent, binder, and any other components, in a solvent to form a positive electrode slurry. Optionally, the solvent includes N-methylpyrrolidone. The positive electrode slurry has a solid content of 40–80 wt%, and its viscosity at room temperature is adjusted to 5000–25000 mPa·s. The positive electrode slurry is coated onto the surface of the positive current collector, dried, and then cold-pressed using a cold rolling mill to form the positive electrode sheet; the areal density of the positive electrode powder coating is 15–35 mg / cm². 2 The compaction density of the positive electrode sheet is 3.0-3.6 g / cm³. 3 The selectable value is 3.4-3.6 g / cm³. 3 The formula for calculating the compaction density is: Compaction density = Coating surface density / (Extreme electrode thickness after extrusion - Current collector thickness).

[0106] It is understood that, in the embodiments of this application, the positive electrode sheet may be made by using the above-mentioned positive electrode sheet as the main body of the positive electrode sheet and forming a solid electrolyte interface film on the surface of the main body of the positive electrode sheet.

[0107] Negative electrode sheet

[0108] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0109] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0110] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material on the polymer material substrate. Optionally, the metal material includes at least one of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. The polymer material includes at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0111] In some embodiments, the negative electrode active material may be a known battery negative electrode active material. As an example, the negative electrode active material may include the silicon composite material described in the embodiments of this 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 materials, and lithium titanate, etc. The tin-based material may be selected from at least one of elemental tin, tin oxides, and tin alloys. However, the negative electrode active material is not limited to these materials; other conventional materials that can be used as battery negative electrode active materials may also be used. These negative electrode active materials may be used alone or in combination of two or more. The weight percentage of the negative electrode active material in the negative electrode film is 70–100% by weight, based on the total weight of the negative electrode film.

[0112] As natural graphite, unprocessed natural graphite or spheroidal natural graphite, such as flake graphite, stamped graphite, and amorphous graphite, can be used. Flake graphite and stamped graphite exhibit almost complete crystals, while amorphous graphite has lower crystallinity. Considering electrode capacity, highly crystalline flake graphite and stamped graphite can be used. For example, flake graphite can be spheroidized before use. In the case of spheroidized natural graphite, the particle size can be 5 to 30 μm, preferably 10 to 25 μm.

[0113] Artificial graphite is generally manufactured through graphitization, a process that involves sintering raw materials such as coal tar, coal tar pitch, and heavy petroleum oil at temperatures above 2500℃. After graphitization, the graphite is pulverized to form secondary particles. With adjustments, it can also be used as a negative electrode active material.

[0114] Generally, the crystals of synthetic graphite are randomly distributed within the particles, exhibiting lower sphericity and sharper shapes compared to natural graphite. Synthetic graphite can be in powder, flake, block, acid, plate, or rod form, but isotropic grain orientation is preferred to shorten the lithium-ion migration distance and improve output characteristics. Synthetic graphite can be in the form of sheets and / or plates.

[0115] Artificial graphite includes commercially widely used mesophase carbon microspheres (MCMB), mesophase pitch-based carbon fibers (MPCF), bulk graphitized artificial graphite, powdered graphitized artificial graphite, and graphite, etc. Furthermore, the particle size of artificial graphite can be 5–30 μm, preferably 10–25 μm.

[0116] The specific surface area of ​​synthetic graphite can be measured using the Brunauer-Emmett-Teller (BET) method. For example, using a porosity analyzer (Bell Japan Inc., Belserp-II mini), it can be measured via the BET 6-point method using nitrogen adsorption flow rate. The measurement of the specific surface area of ​​natural graphite, as described below, is also performed in this manner.

[0117] In some embodiments, the negative electrode film layer may optionally include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS). The binder accounts for 0–30% by weight of the negative electrode film layer, based on the total weight of the negative electrode film layer.

[0118] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The conductive agent accounts for 0 to 20% by weight of the negative electrode film, based on the total weight of the negative electrode film.

[0119] In some embodiments, the negative electrode film layer may optionally include other additives, such as thickeners. The other additives constitute 0-15% by weight of the negative electrode film layer, based on the total weight of the negative electrode film layer. Optionally, the thickener includes sodium carboxymethyl cellulose (CMC-Na).

[0120] In some implementations, the negative electrode film can be a single layer or multiple layers. When the negative electrode film is multilayered, the active materials of any two layers can be the same or different.

[0121] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder, and any other components, in a solvent to form a negative electrode slurry. Optionally, the solvent includes deionized water. The negative electrode slurry has a solid content of 30–70 wt% and its viscosity at room temperature is adjusted to 2000–10000 mPa·s. The obtained negative electrode slurry is coated onto a negative electrode current collector, and after drying and cold pressing, a negative electrode sheet is obtained. The areal density of the negative electrode powder coating is 75–220 mg / m³. 2 The compacted density of the negative electrode sheet is 1.2–2.0 g / m³. 3 .

[0122] It is understood that, in the embodiments of this application, the negative electrode sheet may be made by using the above-mentioned negative electrode sheet as the main body of the negative electrode sheet and forming a solid electrolyte interface film on the surface of the main body of the negative electrode sheet.

[0123] electrolytes

[0124] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0125] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0126] In some embodiments, the electrolyte salt may be selected from one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP). The concentration of the electrolyte salt is typically 0.5–5 mol / L.

[0127] In some embodiments, the solvent may be selected from one or more of fluoroethylene carbonate (FEC), ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl 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).

[0128] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0129] Separating membrane

[0130] In some embodiments, the secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0131] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0132] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0133] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the aforementioned electrode assembly and electrolyte.

[0134] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, aluminum shell, or steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate. This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 This is an example of a square-structured secondary battery 1.

[0135] In some implementations, refer to Figure 2 The outer packaging may include a shell 11 and a cover plate 13. The shell 11 may include a bottom plate and side plates connected to the bottom plate, the bottom plate and side plates forming a receiving cavity. The shell 11 has an opening communicating with the receiving cavity, and the cover plate 13 can be placed over the opening to close the receiving cavity. The positive electrode, negative electrode, and separator can be formed into an electrode assembly 12 by a winding process or a stacking process. The electrode assembly 12 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 12. The secondary battery 1 may contain one or more electrode assemblies 12, which can be selected by those skilled in the art according to specific practical needs.

[0136] In addition, this application also provides an electrical device, which includes the secondary battery provided in this 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, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., 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.

[0137] As the electrical device, a secondary battery can be selected according to its usage requirements.

[0138] Figure 3 Here is an example of an electrical device 2. This electrical device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of the secondary battery for this electrical device, a battery pack or battery module can be used.

[0139] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0140] Example

[0141] 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 embodiments and accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit this application or its applications. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0142] Where specific techniques or conditions are not specified in the examples, they shall be performed in accordance with the techniques or conditions described in the literature in this field or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0143] Example 1

[0144] The preparation method of the silicon composite material in this embodiment includes:

[0145] Silicon-based silicon-carbon composite and flexible graphite were added to deionized water and stirred until uniformly dispersed to obtain a dispersion. The dispersion was then spray-dried using a spray dryer. The solid material obtained after spray drying was then carbon-coated in a gaseous carbon source atmosphere to obtain the silicon composite material of this embodiment.

[0146] Examples 2 to 17

[0147] Compared with Example 1, Examples 2 to 17 differ in that the composition of the silicon composite material is different, as shown in Table 1.

[0148] Example 18

[0149] The difference between this embodiment and Example 1 is that graphite is replaced with soft carbon.

[0150] Example 19

[0151] Compared with Example 1, the difference in this example is that the silicon-carbon composite is replaced with a silicon oxide compound, wherein the silicon oxide compound contains 50% silicon by mass.

[0152] Example 20

[0153] Compared with Example 1, the difference in this example is that the silicon-carbon composite is replaced with a silicon-nitrogen compound, wherein the silicon-nitrogen compound contains 50% silicon by mass.

[0154] The preparation method of secondary batteries is as follows:

[0155] (1) Preparation of positive electrode sheet.

[0156] LiNi cathode material 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 prepare a positive electrode slurry. The positive electrode slurry is evenly coated on the positive electrode current collector aluminum foil, dried at 85°C, cold pressed, and then die-cut and slit to form a positive electrode sheet.

[0157] (2) Preparation of negative electrode sheet.

[0158] The negative electrode active material, conductive agent acetylene black, thickener sodium carboxymethyl cellulose, and binder styrene-butadiene rubber were added to water at a mass ratio of 96:2:1:1 and mixed evenly to form a negative electrode slurry. The negative electrode slurry was uniformly coated onto the negative electrode current collector copper foil, dried at 85℃, and then cold-pressed under 40 tons of pressure. The cold pressing was performed using cylindrical cold pressing rollers at a speed of 20 m / min and a temperature of 25℃ to form the negative electrode sheet.

[0159] In this embodiment, the negative electrode active material is the silicon composite material in the corresponding embodiment.

[0160] In Comparative Example 1, the negative electrode active material is a silicon-carbon composite.

[0161] In Comparative Example 2, the negative electrode active material is graphite.

[0162] (3) Preparation of the isolation membrane.

[0163] Using polyethylene microporous film as the porous separator film substrate, inorganic alumina powder, polyvinylpyrrolidone, and acetone solvent are mixed evenly 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 the separator film.

[0164] (4) Preparation of electrolyte.

[0165] Lithium LiPF6 salt was dissolved in a mixed solvent of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate (volume ratio of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate: 1:2:1), and fluoroethylene carbonate (FEC) additive was added to obtain the electrolyte. The concentration of LiPF6 in the electrolyte was 1 mol / L, and the mass percentage of FEC was 5 wt%.

[0166] (5) Preparation of secondary batteries.

[0167] The positive electrode sheet, positive electrode sheet and separator are wound together to obtain a bare cell. Then, after processes such as encapsulation, liquid injection, formation and degassing, the corresponding secondary battery is obtained.

[0168] Test example:

[0169] (1) The structural stability of the negative electrode in the examples and comparative examples was tested.

[0170] a: The vertical cross-section of the negative electrode in the examples and comparative examples was observed using SEM (Scanning Electron Microscopy), and the depth H of the active material embedded in the current collector was measured. The measurement results are shown in Table 1. H can be used to represent the degree of damage to the negative electrode current collector; the larger the H value, the more severe the damage to the negative electrode current collector.

[0171] b: The elongation at break was tested on the negative electrode sheets in the examples and comparative examples. The cold-pressed negative electrode sheets were cut into 50mm*15mm strips using a die-cutting tool, with the 50mm direction representing the processing direction of the electrode sheet, i.e., the direction of movement of the electrode sheet relative to the cold-pressing roller. A high-speed rail tensile testing machine was used for the tensile test. Both ends of the tensile testing machine were sealed with anti-wrinkle adhesive to prevent the electrode sheet from loosening and falling off during stretching. The sample was kept perpendicular and taut during stretching. The sample needed to break at a point in the middle; data from breakage at either end of the fixture were discarded. The stretching speed was 2mm / min. The initial length of the negative electrode sheet was L0, i.e., 50mm, and the length at which it broke under tension in the length direction was L1. The elongation at break was λ = (L1 - L0) / L0. The test results are shown in Table 1.

[0172] (2) The volumetric energy density (VED) of the secondary batteries in the examples and comparative examples was tested. The batteries were left to stand at a constant temperature of 25°C for 2 hours, then charged at 0.33C to 4.2V at a range of 2.8V to 4.2V, and then charged at a constant voltage at 4.2V until the current ≤0.05C. After standing for 10 minutes, the batteries were discharged at 0.33C to 2.8V, and the capacity C0 of the battery was recorded. VED is the ratio of C0 to the battery casing volume. The test results are shown in Table 1.

[0173] (3) The cycle performance of the secondary batteries in the examples and comparative examples was tested. The test method was as follows: at 25°C, the battery under test was continuously charged and discharged at 0.5C in the 0-100% SOC range, and allowed to rest for 30 minutes after each charge and discharge cycle. This was continued until the battery had cycled 300 times, and the discharge capacity of the nth cycle was recorded as C. n The discharge capacity of the first cycle is denoted as C1, and the capacity retention rate of the nth cycle is = (C1 / C2) / ( ... 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.

[0174] Table 1

[0175]

[0176]

[0177] In Table 1, BET represents the specific surface area of ​​porous carbon materials, in m². 2 / g. Pore size indicates the pore size of the porous carbon material, in nm. Silicon percentage indicates the mass percentage of silicon in the silicon-based material. Dv50 of silicon-based materials is in μm. Dv50 of graphite is in μm. Graphite:silicon-based material indicates the mass ratio of graphite to silicon-based material. Carbon coating thickness is in nm. Dv50 of silicon composites is in μm. Tap density of silicon composites is in g / cm³. 3 The unit for the specific surface area of ​​silicon composite materials is m². 2 / g. The unit of compacted density of the negative electrode sheet is g / cm³. 3 The embedding depth represents the depth to which the active material is embedded in the current collector, and its unit is μm. The volumetric energy density of a secondary battery is expressed in W·h / L.

[0178] As can be seen from the comparison between Example 1 and Comparative Example 1 in Table 1, when the negative electrode active material includes silicon-carbon composite and graphite, the damage to the negative electrode current collector is smaller during the preparation of the negative electrode sheet, and the volumetric energy density of the battery is higher than that of silicon-carbon composite as the negative electrode active material.

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

[0180] As can be seen from the comparison between Example 1 and Example 7, when the Dv50 of the silicon-carbon composite in Example 7 is less than that of graphite, the negative electrode current collector is damaged to a certain extent and the cycle performance is low.

[0181] As can be seen from the comparison of Examples 1, 8 and 9, when the Dv50 of the silicon-carbon composite is large or the Dv50 of the graphite is small, the damage to the negative current collector is greater when preparing the negative electrode sheet.

[0182] Comparing Example 1 and Example 14, it can be seen that the cycle performance of the battery in Example 14 is lower. This may be because the silicon-carbon composite has a larger specific surface area, and the excessively large pores exacerbate side reactions, thus reducing the battery's cycle performance. Additionally, the silicon-carbon composite in Example 14 has a larger specific surface area, resulting in a lower compaction density and consequently a lower volumetric energy density.

[0183] As can be seen from the comparison between Example 1 and Example 15, the 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 some elemental silicon is located on the surface of the silicon-carbon composite particles. Since elemental silicon has high activity, it may deteriorate the cycle performance to some extent.

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

[0185] As can be seen from the comparison between Example 1 and Example 17, the battery cycle performance is lower when the carbon coating layer is thicker.

[0186] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0187] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A silicon composite material, characterized in that, The material includes a silicon-based material and a flexible material, wherein the hardness of the flexible material is less than that of the silicon-based material; the silicon-based material includes at least one of silicon-carbon composite, silicon-nitrogen composite, and silicon alloy; the flexible material is located on at least a portion of the surface of the silicon-based material; the flexible material is distributed in a particulate form on at least a portion of the surface of the silicon-based material.

2. The silicon composite material according to claim 1, characterized in that, The flexible material includes a flexible conductive material.

3. The silicon composite material according to claim 2, characterized in that, 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, characterized in that, The Dv50 of the flexible material is less than or equal to the Dv50 of the silicon-based material.

5. The silicon composite material according to claim 4, characterized in that, The Dv50 of the flexible material is 1μm~5μm.

6. The silicon composite material according to claim 4, characterized in that, The Dv50 of the silicon-based material is 2μm~7μm.

7. The silicon composite material according to any one of claims 1 to 6, characterized in that, Both the silicon-based material and the flexible material are granular materials.

8. The silicon composite material according to any one of claims 1 to 7, characterized in that, 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, characterized in that, The silicon-carbon composite comprises a porous carbon material and elemental silicon located in the pores of the porous carbon material.

10. The silicon composite material according to claim 9, characterized in that, The porous carbon material has a specific surface area of ​​500 m². 2 / g~1800m 2 / g.

11. The silicon composite material according to claim 9, characterized in that, The pore size of the porous carbon material is 2nm~50nm.

12. The silicon composite material according to claim 9, characterized in that, The elemental silicon accounts for 20% to 60% of the mass of the silicon-carbon composite.

13. The silicon composite material according to any one of claims 1 to 12, characterized in that, The silicon composite material further includes a coating layer comprising at least one of carbon and metal oxides, the coating layer completely or partially covering the silicon-based material and the flexible material.

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

15. The silicon composite material according to claim 13, characterized in that, The thickness of the coating layer is 5nm~60nm.

16. The silicon composite material according to any one of claims 1 to 15, characterized in that, The Dv50 of the silicon composite material is 8μm~40μm; and / or, The tap density of the silicon composite material is 0.9 g / cm³. 3 ~1.2g / cm 3 ; and / or, The specific surface area of ​​the silicon composite material is 0.8 m². 2 / g~1.5m 2 / g.

17. A method for preparing a silicon composite material, characterized in that, Includes the following steps: A dispersion is obtained by mixing a silicon-based material, a flexible material, and a solvent; 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 silicon-carbon composite, silicon-nitrogen composite, and silicon alloy. The dispersion is subjected to spray drying; the flexible material is distributed in particulate form on at least a portion of the surface of the silicon-based material.

18. The method for preparing the silicon composite material according to claim 17, characterized in that, The dispersion has a solid content of 1% to 40%; and / or, The temperature of the hot air used in the spray drying process is 150℃~200℃; and / or, The flow rate of the hot air used in the spray drying process is 0.08 m³ / s. 3 / min~0.2m 3 / min.

19. A negative electrode sheet, characterized in that, It 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 comprises a silicon composite material according to any one of claims 1 to 16 or a silicon composite material prepared by the preparation method according to any one of claims 17 to 18.

20. The negative electrode sheet according to claim 19, characterized in that, The compaction density of the negative electrode sheet is 1.3 g / cm³. 3 ~1.75g / cm 3 ; and / or, The full-charge expansion rate of the negative electrode is 22%~50%.

21. A secondary battery, characterized in that, Includes the negative electrode sheet as described in any one of claims 19 to 20.

22. An electrical appliance, characterized in that, Includes the secondary battery as described in claim 21.

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