Secondary battery, method for manufacturing the same, and electric device

Abstract

The application provides a secondary battery and a preparation method therefor, and an electric device. The secondary battery comprises a negative electrode sheet, the negative electrode sheet comprises a negative electrode current collector and a negative electrode active layer arranged on at least one side of the negative electrode current collector, the negative electrode active layer comprises a negative electrode active material, the negative electrode active material comprises a first silicon-carbon material, the sphericity of the first silicon-carbon material is 0.6-0.95, and the ratio of the minimum Feret diameter to the maximum Feret diameter of the first silicon-carbon material is 0.4-0.7. The secondary battery provided by the application has both cycle performance and kinetic performance.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to secondary batteries, their preparation methods, and electrical devices. Background Technology

[0002] In recent years, the application range of secondary batteries, such as lithium-ion batteries, has become increasingly wide. They are widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric cars, military equipment, aerospace, and many other fields. The development of secondary batteries has been tremendous, thus placing higher demands on their cycle performance and fast-charging dynamic performance. Summary of the Invention

[0003] In view of the above problems, this application provides a secondary battery and its preparation method and power device, which aims to balance the battery's cycle performance and dynamic performance such as fast charging.

[0004] The first aspect of this application provides a secondary battery, the secondary battery including a negative electrode sheet, the negative electrode sheet including a negative current collector and a negative active layer disposed on at least one side of the negative current collector, the negative active layer comprising a negative active material, the negative active material including a first silicon-carbon material, the first silicon-carbon material having a sphericity of 0.6 to 0.95, and the ratio of the minimum Feretta diameter to the maximum Feretta diameter of the first silicon-carbon material being 0.4 to 0.7.

[0005] In the technical solutions provided by the embodiments of this application, by controlling the sphericity of the first silicon-carbon material to be 0.6~0.95, the first silicon-carbon material can be made into a near-ellipsoidal morphology. Compared with a perfect sphere and / or a near-sphere, this near-ellipsoidal morphology has more areas with greater curvature on its surface, that is, more relatively convex parts, which can provide more contact area between materials, thereby increasing the transport channels of active ions and improving the kinetic performance of the battery, such as fast charging. At the same time, this near-ellipsoidal morphology also has the characteristics of a more rounded surface contour and almost no sharp edges, so that the first silicon-carbon material can be subjected to uniform stress during the pressure process and / or the cyclic expansion of the cell, and is not easy to break or fracture, thus possessing high pressure resistance, thereby reducing the consumption of irreversible lithium. While improving the kinetic performance of the battery, such as fast charging, it is also beneficial to take into account the cycle life. In summary, the technical solutions provided by this application are beneficial to taking into account both the kinetic performance of the battery, such as fast charging, and the cycle performance.

[0006] In some embodiments, the sphericity of the first silicon-carbon material is 0.7 to 0.86.

[0007] In some embodiments, the ratio of the minimum Feretta diameter to the maximum Feretta diameter of the first silicon-carbon material is 0.4 to 0.65, and optionally 0.5 to 0.65.

[0008] In some embodiments, the first silicon-carbon material has a near-ellipsoidal morphology.

[0009] In some embodiments, the roundness of the first silicon carbide material is 0.7 to 0.95, and optionally 0.75 to 0.9.

[0010] In some embodiments, the convexity of the first silicon carbide material is 0.8 to 0.95, and optionally 0.9 to 0.95.

[0011] In some implementations, one or more of the following conditions are met:

[0012] (1) The ID / IG ratio of the first silicon-carbon material is 0.4~1, and can be selected as 0.6~1;

[0013] (2) In the first silicon-carbon material, the mass ratio of silicon to carbon is (0.4~0.6):1.

[0014] In some embodiments, the negative electrode active material further includes a second silicon-carbon material, wherein the sphericity of the second silicon-carbon material is greater than or equal to 0.3 and less than 0.6, and optionally greater than or equal to 0.4 and less than 0.6.

[0015] In some embodiments, the roundness of the second silicon carbide material is greater than or equal to 0.4 and less than 0.7, and can be selected as 0.4 to 0.55.

[0016] In some embodiments, the convexity of the second silicon-carbon material is greater than or equal to 0.6 and less than 0.8, and can be selected as 0.6 to 0.7.

[0017] In some implementations, one or more of the following conditions are met:

[0018] (1) The ID / IG ratio of the second silicon-carbon material is 0.4~1, and can be selected as 0.6~1;

[0019] (2) In the second silicon-carbon material, the mass ratio of silicon to carbon is (0.4~0.6):1.

[0020] In some embodiments, the mass ratio of the first silicon-carbon material to the second silicon-carbon material in the negative electrode active layer is (3~9):(7~1), or optionally (5~9):(5~1).

[0021] In some embodiments, the negative electrode active material further includes graphite;

[0022] Optionally, the ID / IG ratio of the graphite is 0.1~0.6, and optionally 0.1~0.4;

[0023] Optionally, in the negative electrode active layer, the mass ratio of silicon-carbon material to graphite is (5~85):(95~15), wherein the silicon-carbon material includes the first silicon-carbon material and the second silicon-carbon material.

[0024] In some embodiments, the silicon content in the negative electrode active layer is 5% to 85% by mass, and can be selected as 20% to 85%.

[0025] In some embodiments, the compaction density of the negative electrode sheet is 1.0 g / cm³. 3 ~1.8g / cm 3 .

[0026] A second aspect of this application also provides a method for preparing a secondary battery, the secondary battery comprising a negative electrode sheet, the negative electrode sheet comprising a negative current collector and a negative active layer disposed on at least one side of the negative current collector, the negative active layer comprising a negative active material, the negative active material comprising a first silicon-carbon material, the first silicon-carbon material having a sphericity of 0.6 to 0.95, and the ratio of the minimum Feretta diameter to the maximum Feretta diameter of the first silicon-carbon material being 0.4 to 0.7;

[0027] The preparation steps of the first silicon-carbon material include:

[0028] An emulsion containing a morphology modifier and a resin carbon source is cured to form resin microspheres, wherein the weight-average molecular weight of the morphology modifier is less than the weight-average molecular weight of the resin carbon source.

[0029] The resin microspheres are carbonized to form ellipsoidal carbon material microspheres;

[0030] The first silicon-carbon material was prepared by vapor-phase silicon infiltration of the ellipsoidal carbon material microspheres.

[0031] In some implementations, one or more of the following conditions are met:

[0032] (1) The weight-average molecular weight of the morphology modifier is 5 × 10⁻⁶. 4 ~2×10 5 g / mol;

[0033] (2) The weight-average molecular weight of the carbon source in the resin is 5 × 10⁻⁶. 5 g / mol ~ 1×10 6 g / mol;

[0034] (3) The morphology modifier contains a flexible chain, which includes one or more of polyether chains, aliphatic polyester chains and polyolefin chains;

[0035] (4) The thermal decomposition temperature of the morphology modifier is lower than the thermal decomposition temperature of the resin carbon source;

[0036] (5) The glass transition temperature of the resin carbon source is less than or equal to the thermal decomposition temperature of the morphology modifier.

[0037] In some implementations, one or more of the following conditions are met:

[0038] (1) The morphology modifier comprises a polymer;

[0039] Optionally, the polymer includes one or more of polyethylene glycol, polyvinylpyrrolidone, polyacrylic acid, and polyurethane;

[0040] (2) The carbon source of the resin includes one or more of phenolic resin, epoxy resin, furan resin, cellulose resin, lignin resin and starch resin;

[0041] (3) In the emulsion, the mass ratio of the resin carbon source to the morphology modifier is (0.4~4.5):1;

[0042] (4) The curing process includes chemical crosslinking curing and / or heat curing;

[0043] A third aspect of this application provides an electrical device, including a secondary battery according to the first aspect of this application or a secondary battery prepared by the preparation method of the second aspect of this application.

[0044] The electrical device of this application includes the secondary battery provided in this application, and therefore has at least the same advantages as the secondary battery.

[0045] Details of one or more embodiments of this application are set forth in the following drawings and description. Other features, objects, and advantages of this application will become apparent from the specification, drawings, and claims. Attached Figure Description

[0046] To better describe and illustrate the embodiments or examples provided in this application, 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 applications, the currently described embodiments or examples, or the best mode of conduct of these applications as currently understood. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0047] Figure 1This is a scanning electron microscope image of the first silicon-carbon material and the second silicon-carbon material combined in the negative electrode of Embodiment 1 of this application.

[0048] Figure 2 This is a scanning electron microscope image of the first silicon-carbon material in the negative electrode sheet of Embodiment 1 of this application.

[0049] Figure 3 This is an argon ion polishing (CP) morphology diagram of the negative electrode sheet of Embodiment 1 of this application, in which the first silicon-carbon material and the second silicon-carbon material are combined.

[0050] Figure 4 This is an argon-ion polishing (CP) morphology image of the second silicon-carbon material in the negative electrode of Comparative Example 1 of this application.

[0051] Figure 5 This is a schematic diagram of a single cell of a secondary battery according to one embodiment of this application.

[0052] Figure 6 yes Figure 1 An exploded view of a battery cell according to one embodiment of this application is shown.

[0053] Figure 7 This is a schematic diagram of a battery device according to one embodiment of this application.

[0054] Figure 8 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0055] Figure 9 yes Figure 8 An exploded view of a battery pack according to one embodiment of this application is shown.

[0056] Figure 10 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.

[0057] Explanation of reference numerals in the attached figures:

[0058] 1. Battery pack; 2. Upper casing; 3. Lower casing; 4. Battery assembly; 5. Individual battery cell; 51. Housing; 52. Electrode assembly; 53. Cover plate; 6. Electrical device. Detailed Implementation

[0059] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0060] The "range" disclosed in this application can be defined in the form of 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. Any endpoint can be independently included or excluded, and they can be combined arbitrarily; 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 expected that ranges of 60~110 and 80~120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are also 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" and "5" have been listed in this document; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, stating that a parameter is an integer ≥2 is equivalent to disclosing that the parameter is, for example, an integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For instance, stating that a parameter is an integer selected from "2~10" is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0061] In this application, the terms "multiple" or "various" are used unless otherwise specified, referring to a quantity greater than or equal to 2. For example, "one or more" means one or more types.

[0062] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0063] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment or implementation of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments. The term "implementation" as used herein has a similar understanding.

[0064] Those skilled in the art will understand that the order in which the steps are written in the methods of various embodiments or examples does not imply a strict execution order and does not constitute any limitation on the implementation process. The detailed execution order of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps of this application may be performed sequentially or randomly, preferably sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if the method may also include step (c), it means that step (c) can 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.

[0065] In this application, unless otherwise specified, A (e.g., B) means that B is a non-limiting example of A, and it is understood that A is not limited to B.

[0066] In this application, "optionally," "optionally," and "optional" mean that something is optional, that is, it means that it is selected from either "with" or "without." If there are multiple "optional" entries in a technical solution, unless otherwise specified and there are no contradictions or mutual constraints, each "optional" entry shall be independent.

[0067] Currently, silicon-carbon materials are widely used in the negative electrode of rechargeable batteries due to their high theoretical specific capacity. However, traditional silicon-carbon materials are usually irregular in shape, often with many sharp edges. During the cold pressing process of the electrode and / or the cyclic expansion of the cell, the irregular material is subjected to pressure, and its sharp edges are prone to breakage, exposing new surfaces and forming new SEI films, consuming more irreversible lithium, and ultimately leading to a deterioration in battery cycle life. To address this, some solutions involve making silicon-carbon materials into spherical and / or near-spherical shapes to ensure uniform stress distribution during compression, reducing the risk of material breakage and thus improving cycle life. However, the contact between spherical and / or near-spherical particles is usually point contact. The small contact area of ​​point contacts limits the transport channels (number) of active ions, easily deteriorating the material's kinetic performance, such as fast charging.

[0068] In view of this, this application provides a secondary battery in which a first silicon-carbon material with a near-ellipsoidal morphology is used in the negative electrode to achieve a balance between cycle performance and kinetic performance such as fast charging. The following will describe this secondary battery in more detail.

[0069] Some embodiments of the first aspect of this application provide a secondary battery, the secondary battery including a negative electrode sheet, the negative electrode sheet including a negative current collector and a negative electrode active layer disposed on at least one side of the negative current collector, the negative electrode active layer including a negative electrode active material, the negative electrode active material including a first silicon-carbon material, the sphericity of the first silicon-carbon material being 0.6~0.95, optionally 0.7~0.86; the ratio of the minimum Feretta diameter to the maximum Feretta diameter of the first silicon-carbon material being 0.4~0.7, optionally 0.4~0.65.

[0070] In the above technical solutions provided by the embodiments of this application, the sphericity of the first silicon carbide material is 0.6 to 0.95. By controlling the sphericity to be no less than 0.6, the sphericity of the first silicon carbide material can be relatively high, thereby making it as far away from a blocky morphology with many edges and corners or an irregular polygonal morphology as possible. At the same time, by controlling the sphericity to be less than 1 and no more than 0.95, the first silicon carbide material can be made to be less close to a perfect sphere and / or a near-sphere. That is, by controlling the sphericity of the first silicon carbide material to be 0.6 to 0.95, the first silicon carbide material can be made closer to an ellipsoid and / or a near-ellipsoidal morphology; that is, by adjusting the sphericity of the first silicon carbide material to be 0.6 to 0.95, this application can make the first silicon carbide material have a near-ellipsoidal morphology.

[0071] Compared to spherical and / or near-spherical shapes, this quasi-ellipsoidal morphology has more areas with greater curvature, i.e., more relatively convex parts, providing a larger contact area between materials. In particular, under pressure, this quasi-ellipsoidal shape can increase the actual contact area through mechanical interlocking and local deformation, thus having a larger effective contact area compared to the point contact of spherical and / or near-spherical shapes. This increases the transport channels for active ions, which is beneficial for improving the battery's fast-charging and other kinetic performance. Simultaneously, this quasi-ellipsoidal morphology also has a relatively rounded surface profile with almost no sharp edges, allowing the first silicon-carbon material to be subjected to uniform stress during pressure and / or cell cyclic expansion, making it less prone to breakage or fracture, and possessing higher pressure resistance. This reduces the consumption of irreversible lithium, improving both the battery's fast-charging and other kinetic performance while also considering cycle life. In summary, the technical solution provided in this application is beneficial for balancing the battery's fast-charging and other kinetic performance with its cycle performance.

[0072] It should be noted that the "quasi-ellipsoidal morphology" in this application includes both perfectly regular, ideal ellipsoidal morphologies and approximate ellipsoidal morphologies whose overall three-dimensional contour is similar to an ideal ellipsoid, but whose surface or local details exhibit a certain degree of irregularity. Compared to perfect spheres, equilateral spheres, or near-spheres, this type of ellipsoidal morphology possesses spherical characteristics while also exhibiting a significant aspect ratio, such as less than 0.9, while the aspect ratio of a perfect sphere or equilateral sphere is 1, and the aspect ratio of a near-sphere is very close to 1 (e.g., ≥0.95). Compared to blocky or irregular morphologies, this type of ellipsoidal morphology does not possess the sharp-edged characteristics of blocky or irregular morphologies; for example, see [link to relevant documentation]. Figure 3 Comparison of ellipsoidal particle 1 and irregularly shaped particle 2.

[0073] It should be noted that "near-spherical" in this application refers to particles whose shape is very close to a perfect sphere, with a sphericity typically ≥0.95 (or even ≥0.98), and the ratio of the minimum Ferete diameter to the maximum Ferete diameter typically ≥0.9 (or even ≥0.95).

[0074] For example, the sphericity of the first silicon-carbon material can be 0.6, 0.62, 0.64, 0.66, 0.68, 0.7, 0.72, 0.74, 0.76, 0.78, 0.8, 0.82, 0.84, 0.86, 0.88, 0.9, 0.91, 0.93, 0.95 or within any of the above values.

[0075] Non-limitingly, the morphology and sphericity of the first silicon-carbon material in the negative electrode sheet can be tested using the following method: Disassemble the battery, remove the negative electrode sheet, and soak and clean it with a solvent such as dimethyl carbonate to remove residual electrolyte; scrape off the powder material of the negative electrode active layer, and fully soak the powder material extracted from the negative electrode active layer with a solvent (such as N-methylpyrrolidone (NMP)) to dissolve organic components such as binders in the solvent (ultrasonic dispersion can also be used to promote dissolution). After washing and filtering, collect the solid phase, and then use density difference to centrifuge to separate the relatively low-density conductive agent from the suspension. Collect the centrifuged precipitate to obtain the test powder of the negative electrode active material. At a certain test magnification (such as 5000x), the test powder of the negative electrode active material is tested by scanning electron microscopy (SEM) to observe the morphology of particles (such as ellipsoidal shape) within the field of view, and images are taken at this magnification. Then, the captured images are analyzed using ImageJ software.

[0076] Furthermore, the scanning electron microscope (SEM) images containing only the particles are imported into ImageJ software (e.g., version 1.46r, win64) for analysis. The scale settings are completed based on the SEM images, and the SEM images to be analyzed are loaded. The "Shape Description" and "Area" analysis functions are used to analyze the morphology and area of ​​the identified particles. According to the software manual (e.g., ImageJ User Guide IJ 1.46r), the "Area" parameter obtained from the analysis represents the projected area of ​​the particle. The projected circumference is obtained from the projected area. Sphericity is the ratio of the circumference of the equivalent projected circle of the particle to the actual circumference, sphericity = 2 × √π × A / Preal, where A = projected area, and Preal = actual circumference. According to the software manual (ImageJ UserGuideIJ 1.46r), after identifying and analyzing the "Feret diameter", "Area", "Circ" and "Round" of each ellipsoidal particle in the image, the corresponding parameters are given. From this, the sphericity of each ellipsoidal particle can be obtained. The average sphericity of multiple (e.g., 20 particles) ellipsoidal particles in the image can be used as the sphericity of the first silicon-carbon material.

[0077] In some embodiments, the ratio of the minimum Feretta diameter to the maximum Feretta diameter of the first silicon-carbon material is 0.4 to 0.7, optionally 0.4 to 0.65, and further optionally 0.5 to 0.65. For example, the ratio can be 0.4, 0.42, 0.46, 0.48, 0.5, 0.52, 0.56, 0.58, 0.6, 0.62, 0.66, 0.68, 0.7, or within any range of the above values.

[0078] Based on the sphericity range of the first silicon-carbon material mentioned above, a ratio of the minimum Feretta diameter to the maximum Feretta diameter of the first silicon-carbon material is set to 0.4 to 0.7. This further demonstrates that the first silicon-carbon material has a near-ellipsoidal morphology, rather than a perfectly spherical, near-spherical, blocky, or irregular morphology. Thus, by synergistically combining the appropriate range of sphericity and the appropriate range of the ratio of the minimum to the maximum Feretta diameter, the first silicon-carbon material can be made closer to a regular ellipsoidal morphology (in other words, the projection of the particles of the first silicon-carbon material is elliptical, such as a moderately elongated ellipse). This results in a larger contact area between the particles, which is beneficial for further increasing the transport channels of active ions. Furthermore, this improves the kinetic performance of the battery, such as fast charging, while also contributing to a longer cycle life.

[0079] Understandably, the Freret diameter of the first silicon-carbon material refers to the perpendicular distance between any two parallel tangents on the two-dimensional projected profile of the particles of the first carbon material; where the minimum Freret diameter and the maximum Freret diameter refer to the minimum and maximum values ​​of the perpendicular distance between any two parallel tangents, respectively.

[0080] Non-limiting, the Feret diameter of the first silicon-carbon material can be tested using the following method: Referring to the previous description, at a certain magnification (e.g., 5000x), the test powder of the negative electrode active material is subjected to scanning electron microscopy (SEM) to observe the morphology of the particles within the field of view (e.g., ellipsoidal shape). Images are captured at this magnification, and then the captured images are analyzed using ImageJ software. The analysis process is described above. According to the software manual (ImageJ User Guide IJ 1.46r), the "Feret diameter," "Area," "Round," and "Solidity" of each ellipsoidal particle in the image are identified and analyzed to provide corresponding parameters. From this, the ratio of the minimum Feret diameter to the maximum Feret diameter of each ellipsoidal particle can be obtained. The average of this ratio for multiple (e.g., 20 particles) ellipsoidal particles in the image can be used as the ratio of the minimum Feret diameter to the maximum Feret diameter of the first silicon-carbon material.

[0081] In some embodiments, the roundness of the first silicon carbide material is 0.7 to 0.95, optionally 0.75 to 0.9. For example, the roundness of the first silicon carbide material can be 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, or within any range of the above values. This indicates that the surface profile of the first silicon carbide material has a higher smoothness, more closely resembling a regular ellipsoidal morphology. Consequently, the first silicon carbide material can be subjected to uniform stress during compression, reducing the risk of material breakage and thus better ensuring cycle life.

[0082] Non-limiting, the roundness of the first silicon-carbon material can be tested using the following method: Referring to the previous description, at a certain magnification (e.g., 5000x), the test powder of the negative electrode active material is subjected to scanning electron microscopy (SEM) to observe the morphology of the particles within the field of view (e.g., ellipsoidal shape). Images are captured at this magnification, and then the captured images are analyzed using ImageJ software. The analysis process is described above. According to the software manual (ImageJ User Guide IJ 1.46r), the "Feret diameter," "Area," "Round," and "Solidity" of each ellipsoidal particle in the image are identified and analyzed. The average value of the radius of curvature of each protruding region in the particle relative to the radius of the particle's circumcircle is obtained and calculated. This yields the roundness value of each ellipsoidal particle. The average roundness value of multiple (e.g., 20 particles) ellipsoidal particles in the image is then used as the roundness of the first silicon-carbon material.

[0083] In some embodiments, the convexity of the first silicon-carbon material is 0.8 to 0.95, optionally 0.9 to 0.95. For example, the convexity of the first silicon-carbon material can be 0.8, 0.84, 0.88, 0.9, 0.92, 0.95, or within any range of the above values. This indicates that the surface profile of the first silicon-carbon material has fewer depressions, thereby reducing the non-contact area caused by surface depressions, increasing the contact area between the first silicon-carbon materials, increasing the transport channels for active ions, and thus enabling the battery to possess higher dynamic performance such as fast charging.

[0084] Non-limiting, the convexity of the first silicon-carbon material can be tested using the following method: Referring to the previous description, at a certain magnification (e.g., 5000x), the test powder of the negative electrode active material is subjected to scanning electron microscopy (SEM) to observe the morphology of the particles within the field of view (e.g., ellipsoidal shape), and images are captured at this magnification. The captured images are then analyzed using ImageJ software. According to the software manual (ImageJ User Guide IJ 1.46r), the "Area," "Round," and "Solidity" of each ellipsoidal particle in the image are identified and analyzed. The ratio of the convex hull area (minimum convex hull) of the ellipsoidal particle to its actual projected area is obtained and calculated, thus yielding the convexity value of each ellipsoidal particle. The average convexity value of multiple (e.g., 20 particles) ellipsoidal particles in the image is then used as the convexity of the first silicon-carbon material.

[0085] In some embodiments, the ID / IG ratio of the first silicon carbide material is 0.4 to 1, and optionally 0.6 to 1. For example, the ID / IG ratio of the first silicon carbide material can be 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, or within any range of the above values. This is advantageous for giving the first silicon carbide material higher capacity and higher pressure resistance.

[0086] Non-limiting, the ID / IG ratio of the first and second silicon-carbon materials can be tested using the following method: the test particles are uniformly dispersed on a substrate, and the target area is scanned at multiple points (usually at intervals of 1-5 μm) using a laser confocal Raman spectrometer, acquiring the Raman spectrum of each point; the D peak (~1350 cm⁻¹) is analyzed using software (such as WiRE or Origin). -1 ) and G peak (~1580 cm) -1 Perform Lorentz / Gaussian fitting and calculate the ratio of their integral areas, ID / IG.

[0087] In some embodiments, the negative electrode active material further includes a second silicon-carbon material, the second silicon-carbon material having a sphericity greater than or equal to 0.3 and less than 0.6, optionally greater than or equal to 0.4 and less than 0.6. A sphericity greater than or equal to 0.3 and less than 0.6 indicates that the second silicon-carbon material is closer to an irregular morphology. By combining a first silicon-carbon material with a near-ellipsoidal morphology and a second silicon-carbon material with a near-irregular morphology, more surface contact can be formed between the near-ellipsoidal and irregular materials. Therefore, while maintaining cycle life, the contact area between materials can be further increased, further increasing the transport channels for active ions, thereby better improving kinetic performance such as fast charging.

[0088] For example, the sphericity of the second silicon-carbon material can be 0.3, 0.32, 0.34, 0.36, 0.38, 0.4, 0.42, 0.44, 0.46, 0.48, 0.5, 0.52, 0.54, 0.56, 0.58, 0.59 or within any of the above values.

[0089] Non-limiting, the test methods for the morphology, sphericity, roundness, convexity, ID / IG, etc. of the second silicon carbide material are similar to the corresponding test methods for the first silicon carbide material described above, and will not be repeated here.

[0090] It is understood that the irregular morphology in this application refers to particles that deviate significantly from simple geometric shapes in shape, outline or surface and have no consistent regularity, such as particles with sharp edges, fracture surfaces, depressions or protrusions. Such particles cannot be classified into any regular category such as spheres, flakes, rods, fibers, etc.

[0091] In some embodiments, the roundness of the second silicon-carbon material is greater than or equal to 0.4 and less than 0.7, and can be selected from 0.4 to 0.55. For example, the roundness of the second silicon-carbon material can be 0.4, 0.43, 0.46, 0.5, 0.53, 0.56, 0.6, 0.63, 0.66, 0.69, or within any range of the above values. This indicates that the surface profile of the second silicon-carbon material has relatively low smoothness and is closer to an irregular morphology. Therefore, when combined with the first silicon-carbon material, it can further increase the contact area between the materials and further increase the transport channels for active ions, thereby better improving dynamic performance such as fast charging.

[0092] In some embodiments, the convexity of the second silicon-carbon material is greater than or equal to 0.6 and less than 0.8, and can be selected from 0.6 to 0.7. For example, the convexity of the second silicon-carbon material can be 0.6, 0.63, 0.67, 0.7, 0.73, 0.76, 0.79, or within any range of the above values. This indicates that the surface profile of the second silicon-carbon material has relatively more depressions, more closely resembling an irregular morphology. Therefore, when combined with the first silicon-carbon material, it can further increase the contact area between the materials, further increase the transport channels for active ions, and thus better improve kinetic performance such as fast charging.

[0093] In some embodiments, the ID / IG ratio of the second silicon carbide material is 0.4 to 1, and optionally 0.6 to 1. For example, the ID / IG ratio of the second silicon carbide material can be 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, or within any range of the above values. This is advantageous for giving the second silicon carbide material higher capacity and higher pressure resistance.

[0094] In some embodiments, the mass ratio of the first silicon-carbon material to the second silicon-carbon material in the negative electrode active layer is (3~9):(7~1), and can be selected as (5~9):(5~1). For example, the mass ratio of the first silicon-carbon material to the second silicon-carbon material in the negative electrode active layer can be 3:7, 4:6, 5:5, 6:4, 7:3, 8:2, 9:1, or within any range of the above values. This setting increases the contact area between materials, improves kinetic performance such as fast charging, and also helps to better balance cycle performance.

[0095] In some embodiments, the mass ratio of silicon to carbon in the first and second silicon-carbon materials is independently (0.4 to 0.6):1. For example, the mass ratio of silicon to carbon can be independently 0.4:1, 0.45:1, 0.5:1, 0.55:1, 0.6:1, or within any range of these values. Thus, the silicon content in the first or second silicon-carbon material is moderate and can be uniformly distributed in the porous carbon, resulting in higher initial efficiency compared to a lower silicon content and a lower expansion rate compared to a higher silicon content.

[0096] In some implementations, the negative electrode active material also includes graphite. Combining graphite with silicon-carbon materials helps to achieve a balance in battery capacity, cycle life, and energy density, resulting in better overall performance.

[0097] In some implementations, the ID / IG of graphite is 0.1 to 0.6, and may be 0.1 to 0.4. For example, the ID / IG of graphite may be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, or within any range of the above values.

[0098] In some embodiments, the mass ratio of silicon-carbon material to graphite in the negative electrode active layer is (5~85):(95~15), wherein the silicon-carbon material includes a first silicon-carbon material and a second silicon-carbon material. For example, the mass ratio of silicon-carbon material to graphite can be 5:95, 5:15, 6:10, 85:95, 85:15, or within any range of the above values. This setting is beneficial for achieving a better balance between capacity, cycle life, and energy density in the battery, resulting in better overall performance.

[0099] In some embodiments, the silicon mass percentage in the negative electrode active layer is 5% to 85%, and may be 10% to 85%. For example, the silicon mass percentage in the negative electrode active layer may be 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 85%, or any range of the above values.

[0100] In silicon-containing systems, especially those with a silicon content of 5% to 85%, the volume expansion during cell cycling is significant, which can easily lead to material breakage and a decrease in cycle life. Therefore, by employing a first silicon-carbon material with a near-ellipsoidal morphology, which imparts better stress uniformity during compression, the first silicon-carbon material can exhibit higher compressive strength, enabling it to withstand the larger expansion pressures during cyclic expansion and thus improving cycle life.

[0101] In some embodiments, the compaction density of the negative electrode sheet is 1.0 g / cm³.3 ~1.8g / cm 3 For example, the compaction density of the negative electrode sheet can be 1.0 g / cm³. 3 1.1g / cm 3 1.2g / cm 3 1.3g / cm 3 1.4g / cm 3 1.5g / cm 3 1.6g / cm 3 1.7g / cm 3 1.8g / cm 3 Or within any of the above values. The first silicon-carbon material with a near-ellipsoidal morphology can be subjected to uniform stress during the compression process (such as cold pressing) and has high compressive strength, thus it can withstand greater cold pressing pressure, thereby enabling the negative electrode sheet to obtain a higher compaction density.

[0102] Non-limiting, the compaction density of the negative electrode sheet can be tested using the following method: cut the dried negative electrode sheet to an area of ​​1540.25 mm². 2 Five negative electrode sheets were prepared. The thickness of each negative electrode sheet was measured using a micrometer and recorded as d0 cm. The negative active layer was scraped off from the negative electrode sheet using a scraper, and its mass was measured using a balance and recorded as m (mg). The thickness of the negative current collector after removing the negative active layer was measured using a micrometer and recorded as d cm. The compaction density of the negative active layer was calculated using the following formula: Compaction density = m / [154.025 × (d0 - d)]. The compaction density ρ1 of the negative electrode sheet is the average compaction density of the negative active layer in the five negative electrode sheets obtained above.

[0103] Some embodiments of the second aspect of this application provide a method for preparing a secondary battery, which can be used to prepare the secondary battery of the first aspect of this application. The secondary battery includes a negative electrode sheet, the negative electrode sheet includes a negative current collector and a negative active layer disposed on at least one side of the negative current collector, the negative active layer includes a negative active material, the negative active material includes a first silicon-carbon material, the sphericity of the first silicon-carbon material is 0.6 to 0.95, and the ratio of the minimum Freret diameter to the maximum Freret diameter of the first silicon-carbon material is 0.4 to 0.7.

[0104] The preparation steps of the first silicon-carbon material include:

[0105] S1. The emulsion containing the morphology modifier and the resin carbon source is cured to form resin microspheres, wherein the weight-average molecular weight of the morphology modifier is less than the weight-average molecular weight of the resin carbon source.

[0106] S2. Carbonize the resin microspheres to form ellipsoidal carbon material microspheres.

[0107] S3. Vapor-phase silicon infiltration is performed on ellipsoidal carbon material microspheres to obtain the first silicon-carbon material.

[0108] In the preparation method provided in this application, after curing the emulsion containing the morphology modifier and the resin carbon source, the resin carbon source can be cross-linked and cured into a three-dimensional network structure to form resin microspheres. During the curing process, the morphology modifier can be encapsulated in the resin microspheres. When the resin microspheres are subsequently carbonized, since the weight-average molecular weight of the morphology modifier is smaller than that of the resin carbon source, the morphology modifier can decompose and evaporate earlier and faster than the resin carbon source during the carbonization process, resulting in a greater shrinkage (rate) in its direction. This allows the entire resin microsphere to be "stretched" into a quasi-ellipsoidal shape to form a quasi-ellipsoidal carbon material microsphere. Afterward, the quasi-ellipsoidal carbon material microsphere is subjected to vapor-phase silicon infiltration to obtain the first silicon-carbon material of this application.

[0109] In some embodiments, the thermal decomposition temperature of the morphology modifier is lower than that of the resin carbon source. Therefore, during the carbonization process, the morphology modifier can undergo thermal decomposition preferentially over the resin carbon source, and thus can preferentially (earlier) shrink in its direction, thereby facilitating the "stretching" of the resin microspheres into a near-ellipsoidal shape, thereby forming the first silicon-carbon material and giving it a near-ellipsoidal morphology.

[0110] In some embodiments, the glass transition temperature of the resin carbon source is less than or equal to the thermal decomposition temperature of the morphology modifier. This allows the resin microspheres to be in a softer, viscous state rather than a more rigid state before or at the onset of thermal decomposition, thus making the softened resin microspheres easier to "stretch" into a near-ellipsoidal shape.

[0111] In some embodiments, the morphology modifier contains flexible chains, including one or more of polyether chains, aliphatic polyester chains, and polyolefin chains. Flexible chains enable the morphology modifier to exhibit greater shrinkage during carbonization, thereby further promoting the formation of ellipsoidal morphologies. Furthermore, using different types of flexible chains allows the sphericity of the ellipsoidal morphology to be altered within the range of 0.6 to 0.95.

[0112] Terminology Explanation: In this application, the structural formula of the polyether chain includes -(R1-O-R2). n1 -、-(R'1-O-) n2 -、-(O-R'2) n3 - One of them, R1, R2, R'1, R'2 each independently includes substituted or unsubstituted aliphatic alkylene groups, n1≥2, n2≥2, n3≥2; further, R1, R2, R'1, R'2 each independently includes substituted or unsubstituted C1~C20 aliphatic alkylene groups.

[0113] Terminology Explanation: In this application, the structural formula of the aliphatic polyester chain is -(O-R3-C(O)). n4 - R3 includes substituted or unsubstituted aliphatic alkylene groups, n4≥2; further, R3 includes substituted or unsubstituted C1~C20 aliphatic alkylene groups.

[0114] Terminology Explanation: In this application, the structural formula of the polyolefin chain is -(CH2-CHR4). n5 - R4 includes alkyl or hydrogen, n5≥2; further, R4 includes C1~C20 alkyl or hydrogen.

[0115] In some embodiments, the polyether chain includes -(OCH2CH2). n1 -、-(OCH2CH(CH3) n1 -、-(OCH2CH2CH2CH2) n1 - one or more of the following.

[0116] In some embodiments, the aliphatic polyester chain includes polytrimethylene acetate segments.

[0117] In some embodiments, the polyolefin chain includes a polyethylene chain -(-CH2-CH2-). n3 Polypropylene chain -(CH2-CH(CH3)) n3 - one or more of the following.

[0118] In some embodiments, the morphology modifier comprises a polymer, including one or more of polyethylene glycol, polyvinylpyrrolidone, polyacrylic acid, and polyurethane.

[0119] In some embodiments, the resin carbon source includes one or more of phenolic resin, epoxy resin, and furan resin. Furthermore, the emulsion in step S1 may also contain one or more of cellulose, lignin, and starch, which can also serve as a carbon source for forming resin microspheres.

[0120] In some embodiments, the mass ratio of resin carbon source to morphology modifier in the emulsion of step S1 is (0.4~4.5):1. For example, the mass ratio of resin carbon source to morphology modifier can be 0.4:1, 0.7:1, 1:1, 1.3:1, 1.8:1, 2:1, 2.4:1, 2.7:1, 3:1, 3.4:1, 3.8:1, 4:1, 4.5:1, or within any range of the above values. Controlling the mass ratio of resin carbon source to morphology modifier within the above range allows the polymer phase to decompose or evaporate more quickly during the carbonization stage, resulting in greater shrinkage in its direction. This is beneficial for forming the ellipsoidal morphology of this application and allows its sphericity and the ratio of minimum Ferrette diameter to maximum Ferrette diameter to vary within the range of this application.

[0121] In some embodiments, the emulsion in step S1 further includes an emulsifier, and the mass ratio of the emulsifier to the resin carbon source is (0.1~5):100. For example, the mass ratio of the emulsifier to the resin carbon source can be 0.1:100, 0.5:100, 0.8:100, 1:100, 2:100, 3:100, 4:100, 5:100, or within any of the above values. Controlling the mass ratio of the emulsifier to the resin carbon source within the above range can reduce the stability of the emulsion particles during titration emulsification, making it more conducive to forming spherical, non-spherical, and / or near-spherical shapes. This makes it more conducive to forming the ellipsoidal morphology of this application in the subsequent curing and carbonization stages, and allows its sphericity and the ratio of the minimum Freret diameter to the maximum Freret diameter to vary within the range of this application.

[0122] In some embodiments, the emulsifier includes, but is not limited to, one or more of polyvinyl alcohol (PVA), sorbitan monooleate (Span-80), and sodium dodecyl sulfate (SDS).

[0123] In some embodiments, the emulsion in step S1 can be prepared by the following method: a mixture of resin carbon source and morphology modifier (dispersed phase) is titrated into a dispersion medium (continuous phase) containing emulsifier under stirring; then the mixture is added to a reaction vessel and stirred using a mechanical stirrer in the reaction vessel. The size of the emulsion particles is controlled by controlling the stirring rate. The higher the speed, the greater the shear force, the smaller the size of the emulsion particles formed, and the smaller the size of the resin microspheres and carbon material microspheres obtained in the end.

[0124] In some embodiments, the titration rate can be 10 drops / second to 50 drops / second to control the size of the emulsion particles; the stirring rate can be 200 rpm to 500 rpm to reduce the adhesion of emulsion particles.

[0125] In some embodiments, the mass ratio of the mixture of resin carbon source and morphology modifier in the emulsion to the dispersion medium is (0.01~0.1):1. For example, this mass ratio can be 0.01:1, 0.02:1, 0.04:1, 0.06:1, 0.08:1, 0.1:1, or within any range of the above values.

[0126] In some embodiments, the dispersion medium must be a liquid that is immiscible with the resin carbon source, including but not limited to silicone oil and / or mineral oil.

[0127] In some embodiments, the curing process includes chemical crosslinking curing and / or heat curing.

[0128] In some embodiments, chemical crosslinking curing may include the following step: adding a curing agent to the emulsion in step S1. Thus, a three-dimensional network structure can be formed by the reaction of the curing agent with the resin carbon source, resulting in resin microspheres.

[0129] In some embodiments, the mass ratio of curing agent to resin carbon source is (0.01~0.1):1. For example, this mass ratio can be 0.01:1, 0.02:1, 0.04:1, 0.06:1, 0.08:1, 0.1:1, or within any range of the above values. Controlling the mass ratio of curing agent to resin carbon source within the above range is more conducive to the formation of resin microspheres into spherical, rather than perfectly spherical and / or near-spherical shapes, thus facilitating the formation of ellipsoidal morphologies in subsequent curing and carbonization stages.

[0130] In some embodiments, the type of curing agent needs to be selected according to the type of resin carbon source used, so that the resin carbon source can react with the curing agent to form a three-dimensional network structure, thereby forming resin microspheres; including but not limited to formaldehyde, glutaraldehyde and acidic crosslinking agents; further, acidic crosslinking agents include but are not limited to hydrochloric acid and / or sulfuric acid.

[0131] In some embodiments, chemical crosslinking curing can be carried out at room temperature or under heating conditions; optionally, the heating temperature can be 60°C to 100°C to avoid emulsion rupture as much as possible. Heating conditions are beneficial for accelerating the crosslinking reaction.

[0132] In other embodiments, chemical crosslinking and curing can also be carried out under acidic conditions; furthermore, the pH value of the acidic conditions can be 2 to 4. This also helps to accelerate the crosslinking reaction.

[0133] In some embodiments, the chemical crosslinking curing reaction time can be 1 h to 24 h. This reaction time can be adjusted according to the activity of the curing agent until the reaction is complete.

[0134] In some embodiments, heat curing may include the following steps: heating the emulsion to a curing temperature, holding it at that temperature, and then cooling it to room temperature. In this way, the resin carbon source can undergo thermal crosslinking or polymerization by heating, forming a rigid structure. Further, the curing temperature may be 80°C to 200°C.

[0135] In some embodiments, the heating rate of the emulsion to the curing temperature can be 5°C / min to 10°C / min to minimize the risk of emulsion cracking.

[0136] In some embodiments, the heat curing time can be 1h to 6h, and the heat curing time can be adjusted according to the thermal stability of the resin carbon source used.

[0137] In some embodiments, step S2, which involves carbonizing the resin microspheres, may include the following steps: in a temperature-controlled tube furnace or industrial kiln, the dried resin microspheres are placed in a crucible and heated to the carbonization temperature at a certain heating rate (e.g., 1°C / min to 5°C / min) under the protection of high-purity nitrogen or argon, and then held at that temperature to finally obtain ellipsoidal carbon material microspheres.

[0138] In some embodiments, the carbonization temperature is 500°C to 1000°C. For example, the carbonization temperature can be 500°C, 600°C, 700°C, 800°C, 900°C, 1000°C, or any range of the above values.

[0139] Understandably, the carbonization temperature needs to be greater than or equal to the thermal decomposition temperature of the resin carbon source and the morphology modifier, so that at this carbonization temperature, both the resin carbon source and the morphology modifier can decompose to generate carbon and other heteroatoms (such as oxygen, nitrogen and other heteroatoms). At this carbonization temperature, the other heteroatoms are easily evaporated after generation, thus achieving carbonization and forming pores in the carbon material microspheres generated after carbonization.

[0140] In some embodiments, prior to the vapor-phase silicon infiltration in step S3, the preparation step of the first silicon-carbon material may further include an alkali-based pore-forming step of the quasi-ellipsoidal carbon material microspheres obtained in step S2: the quasi-ellipsoidal carbon material microspheres are mixed with an alkaline reagent (mass ratio of (0.5~4):1), placed in a box furnace, and heated to 600℃~900℃ under an inert atmosphere (such as argon atmosphere), and held for 1h~12h to obtain porous carbon material microspheres. After alkali-based pore-forming, a large number of pores can be formed in the carbon material microspheres, facilitating the subsequent infiltration of silicon.

[0141] In some embodiments, the alkali-based pore-forming step may further include: adding an acidic solution to the alkali-based pore-forming material and mixing it evenly to remove residual alkaline reagents, followed by heating and drying.

[0142] In some embodiments, alkaline reagents include, but are not limited to, potassium hydroxide, sodium hydroxide, etc.

[0143] In some embodiments, the acidic solution includes, but is not limited to, hydrochloric acid solution, sulfuric acid solution, etc., and the concentration of the acidic solution can be 0.1 mol / L to 0.5 mol / L.

[0144] In some embodiments, step S3, which involves vapor-phase silicon infiltration of quasi-ellipsoidal carbon material microspheres, may include the following steps: placing the quasi-ellipsoidal carbon material microspheres into a rotary kiln or fluidized bed, introducing a mixture of silicon source gas, carrier gas, and reducing gas, and controlling the pressure inside the kiln within a slightly positive pressure range (i.e., 200 Pa to 600 Pa higher than atmospheric pressure) to deposit silicon, thereby obtaining quasi-ellipsoidal silicon-carbon microspheres.

[0145] In some embodiments, the vapor phase silicon infiltration time is 1h to 12h, and the temperature is 420℃ to 480℃.

[0146] In some embodiments, the mass ratio of silicon source gas to reducing gas in the above mixed gas is (0.05~0.2):1. For example, this mass ratio can be 0.05:1, 0.08:1, 0.1:1, 0.13:1, 0.16:1, 0.19:1, 0.2:1, or within any range of the above values. By adjusting the mass ratio of the introduced silicon source gas and reducing gas, the mass ratio of silicon to carbon elements in the first silicon-carbon material can be adjusted.

[0147] In some embodiments, the silicon source gas includes, but is not limited to, silane and / or tetramethylsilane.

[0148] In some embodiments, the carrier gas includes, but is not limited to, argon and / or nitrogen. The carrier gas can be used to dilute the reaction gases, control the reaction rate, and prevent localized overheating as much as possible.

[0149] In some embodiments, the reducing gas includes, but is not limited to, hydrogen. The reducing gas helps promote uniform silicon deposition.

[0150] In some embodiments, after the vapor-phase silicon infiltration in step S3, the preparation step of the first silicon-carbon material may further include a step of carbon coating treatment on the quasi-ellipsoidal silicon-carbon microspheres: placing the quasi-ellipsoidal silicon-carbon microspheres in a rotary kiln or fluidized bed, introducing a mixed gas of carbon source gas and dilution gas, and coating the surface of the quasi-ellipsoidal silicon-carbon microspheres with a carbon layer by vapor-phase deposition.

[0151] In some embodiments, the carbon source gas includes, but is not limited to, one or more of acetylene, methane, and propylene. In other embodiments, the diluent gas includes, but is not limited to, argon and / or nitrogen.

[0152] In some embodiments, the carbon coating treatment is carried out at a temperature of 400°C to 1000°C for a time of 30 min to 240 min.

[0153] In some embodiments, the preparation steps of the second silicon-carbon material are similar to those of the first silicon-carbon material described above. The main difference is that, before performing the vapor-phase silicon infiltration in step S3, the ellipsoidal carbon microspheres can be crushed to form an irregularly shaped carbon material. Alternatively, the morphology modifier in step S1 can be omitted, so that the carbon microspheres formed in step S2 are spheroidal carbon microspheres. Then, before performing the vapor-phase silicon infiltration in step S3 on these spheroidal carbon microspheres, they are also crushed to form an irregularly shaped carbon material. Subsequent processing, such as alkali pore formation, vapor-phase silicon infiltration, and carbon coating, is then performed on this irregularly shaped carbon material, resulting in the second silicon-carbon material.

[0154] In some embodiments, the crushing process includes, but is not limited to, impact crushing, airflow crushing, hammer crushing, and shear crushing. During the crushing process, by changing the crushing conditions (such as the rotational speed of impact crushing), parameters such as the sphericity, the ratio of the minimum to the maximum Feretta diameter, roundness, and convexity of the second silicon carbide material can be altered.

[0155] It should be noted that the preparation of the second silicon carbide material involves steps such as alkali pore formation, vapor phase silicon infiltration, and carbon coating, which are similar to the preparation process of the first silicon carbide material. Please refer to the previous description of the first silicon carbide material, which will not be repeated here.

[0156] It should also be noted that, in addition to being prepared by the method described above in this application, the second silicon carbide material can also be obtained directly by purchase. Therefore, the preparation method described above in this application does not constitute a limitation on the second silicon carbide material.

[0157] Another embodiment of this application provides an electrical device. This electrical device includes at least one of the above-described secondary battery and a secondary battery prepared by the above-described method.

[0158] The secondary battery and power-consuming device of this application will be described below with appropriate reference to the accompanying drawings.

[0159] 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.

[0160] Positive electrode sheet

[0161] 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.

[0162] As a non-limiting example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive active layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0163] 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 polymeric material substrate and a metal layer formed on at least one surface of the polymeric material substrate. The composite current collector can be obtained by forming a metal material on the polymeric material substrate. Non-limiting examples of the metal material in the positive electrode current collector may include one or more of aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. Non-limiting examples of the polymeric material substrate in the positive electrode current collector may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0164] In some embodiments, the positive electrode active material may be a known positive electrode active material for batteries. As a non-limiting example, the positive electrode active material may include one or more 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.

[0165] In some implementations, the positive electrode active material includes lithium phosphate.

[0166] Optionally, the chemical formula of the lithium phosphate is Li β Fe α M 2 (1-α) PO4, where 0.2≤α≤1, 1≤β≤1.1, M 2 It includes at least one of Ti, V, Mg, Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, and Sr.

[0167] In some embodiments, the lithium phosphate includes the chemical formula Li m A a Fe x D d P y E e O z G gThe material, A includes at least one element selected from Al, Na, K or Mg; D includes at least one element selected from Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, Ti or V; E includes at least one element selected from B, S, Si or N; G includes at least one element selected from S, F, Cl or Br; wherein, 0.5≤m≤1.5; 0≤a≤0.1; 0.5≤x≤1; 0≤d≤0.5; 0.5≤y≤1; 0≤e≤0.5; 3.5≤z≤4; 0≤g≤0.5.

[0168] Examples of lithium transition metal oxides include, but are not limited to, one or more of lithium cobalt oxides (such as LiCoO2), lithium nickel oxides, lithium manganese oxides, lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, lithium nickel cobalt manganese oxides, lithium nickel cobalt aluminum oxides, and their modified compounds. Non-limiting examples of lithium phosphates with an olivine structure include, but are not limited to, one or more of lithium iron phosphate, lithium iron phosphate and carbon composites, lithium manganese phosphate, lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0169] Non-limiting examples of lithium cobalt oxides may include LiCoO2; non-limiting examples of lithium nickel oxides may include LiNiO2; non-limiting examples of lithium manganese oxides may include LiMnO2, LiMn2O4, etc.; non-limiting examples of lithium nickel cobalt manganese oxides may include LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 Examples of lithium nickel cobalt aluminum oxides include LiNi, etc. 0.8 Co 0.15 Al 0.05 O2.

[0170] In some examples, lithium transition metal oxides include ternary cathode materials with the chemical formula Li. y (Ni a Co b Mn c ) 1-d M 1 d O 2-x A x y is 0.2~1.2, a+b+c=1, 0≤d≤1, 0≤x<2; M 1 It is one or more of Zr, Sr, B, Ti, Mg, Sn and Al, and A is one or more of S, N, F, Cl, Br and I.

[0171] Understandably, lithium (Li) is intercalated and deintercalated during the charging and discharging process of a battery, and the Li content in the positive electrode active material varies depending on the state of discharge. In the examples of positive electrode active materials listed in this application, unless otherwise specified, the Li content refers to the initial state of the material. When positive electrode active materials are applied to the positive electrode sheet in a battery system, the Li content in the positive electrode active material typically changes after charge-discharge cycles. The Li content can be measured using molar content, but is not limited to this. Regarding "Li content refers to the initial state of the material," the initial state of the material refers to its state before being added to the positive electrode slurry. It is understood that new materials obtained by appropriately modifying the listed positive electrode active materials are also within the scope of positive electrode active materials. The aforementioned appropriate modification refers to acceptable modification methods for positive electrode active materials, and non-limiting examples include coating modification.

[0172] In the examples of positive electrode active materials in this application, the oxygen (O) content is only a theoretical value. Lattice oxygen release will cause changes in the molar content of oxygen, and the actual O content will fluctuate. The O content can be measured in molar content, but is not limited to this.

[0173] In some embodiments, the positive electrode active layer may optionally include a binder. As a non-limiting example, the binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins.

[0174] In some embodiments, the positive electrode active layer may optionally include a conductive agent. As a non-limiting example, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0175] 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 electrode active material, conductive agent, binder, and any other components, in a solvent to form a positive electrode slurry; coating the positive electrode slurry onto at least one surface of the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing, and other processes. The solvent can be selected from, but is not limited to, any of the solvents in the foregoing embodiments, such as N-methylpyrrolidone (NMP). The surface of the positive electrode current collector coated with the positive electrode slurry can be a single surface of the positive electrode current collector or both surfaces of the positive electrode current collector. The solid content of the positive electrode slurry can be 40wt% to 80wt%. The viscosity of the positive electrode slurry at room temperature can be adjusted to 5000 mPa·s to 25000 mPa·s.

[0176] When coating the positive electrode slurry, the areal density per unit area of ​​the coating on one side, based on dry weight (excluding solvent), can be 15 mg / cm³. 2 ~35mg / cm 2 The compaction density of the positive electrode sheet can be 3.0 g / cm³. 3 ~3.6g / cm 3 3.3g / cm³ is an option. 3 ~3.5g / cm 3 .

[0177] Negative electrode sheet

[0178] The negative electrode sheet includes a negative current collector. Further, the negative electrode sheet may also include a negative active layer disposed on at least one surface of the negative current collector, the negative active layer comprising a negative active material.

[0179] As a non-limiting example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode active layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0180] 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 can be obtained by forming a metal material on the polymer material substrate. Non-limiting examples of the metal material in the negative electrode current collector may include one or more of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. Non-limiting examples of the polymer material substrate in the negative electrode current collector may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0181] In some embodiments, the negative electrode active layer may optionally include a binder. The binder may include one or more of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0182] In some embodiments, the negative electrode active layer may optionally include a conductive agent. The conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0183] In some embodiments, the negative electrode active layer may also optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0184] 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 (a non-limiting example of a solvent is deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto at least one surface of the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing, and other processes. The surface of the negative electrode current collector coated with the negative electrode slurry can be a single surface of the negative electrode current collector or both surfaces of the negative electrode current collector. The solid content of the negative electrode slurry can be 40wt% to 60wt%. The viscosity of the negative electrode slurry at room temperature can be adjusted to 2000 mPa·s to 10000 mPa·s.

[0185] When coating the negative electrode slurry, the areal density per unit area of ​​the single-sided coating, based on dry weight (excluding solvent), can be 7.5 mg / cm³. 2 ~22mg / cm 2 The compaction density of the negative electrode sheet can be 1.0 g / cm³. 3 ~ 1.8 g / cm 3 .

[0186] The compaction density of the positive or negative electrode sheet can be tested by the following method: disassemble the battery, remove the electrode sheet, and punch it into a piece with an area of ​​S = 1540.25 mm². 2 Take a small circular electrode, measure its weight M and thickness L, and then take another electrode. Remove the film layer from the surface of the electrode to remove the remaining empty current collector foil. Similarly, punch it to a diameter S = 1540.25 mm. 2 The small circular piece is weighed, and the mass M0 of the empty aluminum foil is measured. Then the compaction density PD = (M-M0) / S / (L-L0). L0 is the thickness of the current collector foil.

[0187] The areal density of the positive or negative electrode sheet can be tested by the following method: disassemble the battery, remove the electrode sheet, and punch it into a piece with an area of ​​S = 1540.25 mm². 2 Take a small circular electrode, measure its weight M, and then take another electrode. Remove the film layer from the surface of the electrode to remove the remaining empty current collector foil. Similarly, punch it to a diameter S = 1540.25 mm. 2 The small round piece is weighed, and the mass of the empty aluminum foil is M0. Then the areal density is (M-M0) / S / n, where n is the number of film layers coated on the current collector, which is 1 or 2, corresponding to single-sided coating or double-sided coating.

[0188] electrolytes

[0189] Electrolytes function to conduct ions between the positive and negative electrode plates. This application does not impose any particular restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or completely solid.

[0190] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0191] In some embodiments, the electrolyte salt may include an electrolyte lithium salt. Without limitation, the electrolyte salt may include 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 difluorophosphate (LiPO2F2), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0192] In some embodiments, the solvent includes at least one of ether solvents, ester solvents, and sulfone solvents.

[0193] As an example, the ether solvent may include at least one of ethylene glycol dimethyl ether (DME), diethylene glycol dimethyl ether (DEGDME), triethylene glycol dimethyl ether (TRGDME), tetraethylene glycol dimethyl ether (TEGDME), and 1,3-dioxolane (DOL);

[0194] As an example, the ester solvent may include at least one of ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), vinylene carbonate (VC), fluoroethylene carbonate (FEC), methyl ethyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), γ-butyrolactone (BL), 1,3-propanesulfonate lactone (1,3-PS), methyl propionate (MP), methyl butyrate (MB), ethyl acetate (EA), ethyl propionate (EP), propyl propionate (PP), and ethyl butyrate (EB).

[0195] 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.

[0196] Separating membrane

[0197] 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.

[0198] In some embodiments, the material of the separator may include one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer may be the same or different, without particular limitation.

[0199] In some embodiments, the thickness of the separator is 6 μm to 40 μm, and optionally 12 μm to 20 μm.

[0200] In some embodiments, the positive electrode, negative electrode, and separator are fabricated into an electrode assembly using a winding or stacking process. An electrolyte is used to wet the electrode assembly.

[0201] A secondary battery includes at least one battery cell. A secondary battery may include one or more battery cells.

[0202] In this application, unless otherwise specified, "battery cell" refers to the basic unit capable of converting chemical energy into electrical energy. Furthermore, a battery cell typically includes at least a positive electrode, a negative electrode, and an electrolyte. During battery charging and discharging, active ions repeatedly insert and extract between the positive and negative electrodes. The electrolyte acts as a conductor of active ions between the positive and negative electrodes. A battery cell includes one or more electrode components, and an electrolyte is used to wet these electrode components.

[0203] This application does not impose any particular limitation on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 5 The image shows a single battery cell, which serves as an example of a square-structured battery cell.

[0204] In some embodiments, the battery cell may include an outer packaging. This outer packaging can be used to encapsulate the electrode assembly and electrolyte described above. In some embodiments, the outer packaging of the battery cell may be a rigid shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the battery cell may also be a flexible package, such as a pouch. The material of the flexible package may be plastic; further, non-limiting examples of plastic may include one or more of polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0205] In some of these embodiments, reference is made to Figure 6 The outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed over the opening to close the receiving cavity. The positive electrode, negative electrode, and separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. The electrode assembly 52 is immersed in an electrolyte. The number of electrode assemblies 52 contained in a single battery cell 5 may be one or more, which can be selected by those skilled in the art according to actual needs.

[0206] In some embodiments, the secondary battery can be a battery device or a battery pack. A battery device includes at least one battery cell. The number of battery cells in a battery device can be one or more, and those skilled in the art can select an appropriate number based on the application and capacity of the battery device.

[0207] Figure 7 This is battery device 4, used as an example. (See reference...) Figure 7 In the battery assembly 4, multiple battery cells 5 can be arranged sequentially along the length of the battery assembly 4. Of course, they can also be arranged in any other manner. Furthermore, the multiple battery cells 5 can be fixed in place using fasteners.

[0208] Optionally, the battery device 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0209] In some embodiments, the battery devices described above can also be assembled into a battery pack, and the number of battery devices contained in the battery pack can be one or more. Those skilled in the art can select an appropriate number according to the application and capacity of the battery pack.

[0210] Figure 8 and Figure 9 This is battery pack 1 as an example. (See reference...) Figure 8 and Figure 9 The battery pack 1 may include a battery box and multiple battery devices 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery devices 4. The multiple battery devices 4 can be arranged in any manner within the battery box.

[0211] In some embodiments, multiple battery cells 5 can also be arranged in any way in the battery box to directly obtain the battery pack 1.

[0212] In addition, one embodiment of this application also provides an electrical device, which includes the secondary battery provided in this application. The secondary battery can be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device may include, but is not limited to, mobile devices, electric vehicles, electric trains, ships and satellites, energy storage systems, etc. Among them, mobile devices may be, for example, mobile phones, laptops, etc.; electric vehicles may be, for example, pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc., but are not limited to.

[0213] As an electrical device, a rechargeable battery can be selected based on its usage requirements.

[0214] Figure 10 Here is an example of an electrical device 6. 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 this electrical device for secondary batteries, the aforementioned battery pack or battery device can be used as the power source.

[0215] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can utilize the aforementioned battery cells as their power source.

[0216] 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.

[0217] 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.

[0218] Example 1

[0219] (1) Preparation of the first silicon-carbon material

[0220] (1.1) Emulsion preparation: The carbon source of the resin is phenolic resin (weight average molecular weight of 8×10⁻⁶). 5 g / mol, thermal decomposition temperature 350℃, glass transition temperature 120℃) and morphology modifier polyacrylic acid (weight average molecular weight 7×10⁻⁶ ... 4 A mixture with a concentration of g / mol, a thermal decomposition temperature of 250℃, and a glass transition temperature of 15℃ was titrated (at a rate of 30 drops / second) into a silicone oil dispersion medium containing polyvinyl alcohol (PVA) as an emulsifier to prepare a mixture. This mixture was then added to a reaction vessel and stirred using a mechanical stirrer (at a rate of 300 rpm) to prepare an emulsion. In the emulsion, the mass ratio of resin carbon source to morphology modifier was 5:5, the mass ratio of emulsifier to resin carbon source was 1:50, and the mass ratio of mixture to dispersion medium was 1:20.

[0221] (1.2) Curing treatment: The emulsion is slowly heated from room temperature (25℃) to 170℃ (heating rate is 8℃ / min), kept at the temperature for 3 hours and then cooled to room temperature to form resin microspheres. Then, the emulsion is filtered, washed and dried to obtain resin microspheres.

[0222] (1.3) Carbonization treatment: In a temperature-controlled tube furnace, the dried resin microspheres are placed in a crucible and heated to the carbonization temperature of 800°C at a heating rate of 5°C / min under argon (Ar) protection, and then held at the temperature to obtain ellipsoidal carbon material microspheres.

[0223] (1.4) Alkaliization and pore formation: Mix the ellipsoidal carbon material microspheres with the alkaline reagent potassium hydroxide (mass ratio of the two is 0.7:1), place them in a box furnace, heat them to 700℃ under an inert atmosphere (argon atmosphere), and keep them at that temperature for 6 hours; then add the alkali-formed material to a 0.1mol / L hydrochloric acid solution and mix evenly to remove the residual potassium hydroxide, and then heat and dry to obtain porous ellipsoidal carbon material microspheres;

[0224] (1.5) Vapor phase silicon infiltration: Porous ellipsoidal carbon microspheres are placed in a rotary furnace and a mixture of silicon source gas tetramethylsilane, carrier gas argon and reducing gas hydrogen is introduced (the mass ratio of silicon source gas to reducing gas is 0.14:1). The furnace pressure is controlled within a slightly positive pressure range (400 Pa higher than atmospheric pressure) to deposit silicon and obtain ellipsoidal silicon-carbon microspheres. The silicon deposition (i.e., vapor phase silicon infiltration) temperature is 450℃ and the time is 6h.

[0225] (1.6) Carbon coating treatment: Stop the introduction of silicon source gas and introduce a mixture of carbon source gas methane and dilution gas argon. Adjust the reaction temperature to 800℃ and react for 2 hours. After the reaction, cool and sieve to obtain the first silicon-carbon material.

[0226] The first silicon-carbon material has a near-ellipsoidal morphology with a sphericity of 0.79, a minimum Freret diameter to maximum Freret diameter ratio of 0.53, a roundness of 0.81, a convexity of 0.90, an ID / IG ratio of 0.74, and a silicon to carbon mass ratio of 0.52:1.

[0227] (2) Preparation of the second silicon-carbon material

[0228] (2.1) Emulsion preparation: The phenolic resin carbon source was titrated (at a rate of 30 drops / second) into silicone oil dispersion medium containing polyvinyl alcohol (PVA) emulsifier under stirring to obtain a mixture; then the mixture was added to a reaction vessel and stirred using a mechanical stirrer (at a stirring rate of 300 rpm) to obtain an emulsion. In the emulsion, the mass ratio of resin carbon source to dispersion medium was 5:5, and the mass ratio of emulsifier to resin carbon source was 1:50.

[0229] (2.2) Curing treatment: The emulsion is slowly heated from room temperature (25℃) to 170℃ (heating rate is 8℃ / min), kept at the temperature for 3 hours and then cooled to room temperature to form resin microspheres. Then, the emulsion is filtered, washed and dried to obtain resin microspheres.

[0230] (2.3) Carbonization treatment: In a temperature-controlled tube furnace, the dried resin microspheres are placed in a crucible and heated to the carbonization temperature of 800°C at a heating rate of 5°C / min under argon (Ar) protection, and then held at the temperature to obtain spherical carbon material microspheres.

[0231] (2.4) Crushing treatment: The spherical carbon material microspheres were crushed into irregularly shaped carbon materials using an impact crusher (speed of 1500 rpm);

[0232] (2.5) Alkaliization and pore formation: The irregularly shaped carbon material is mixed with the alkaline reagent potassium hydroxide (the mass ratio of the two is 2:1), placed in a box furnace, and heated to 700℃ under an inert atmosphere (argon atmosphere) and held for 6 hours; then the material after alkaliization and pore formation is added to 0.1mol / L hydrochloric acid solution and mixed evenly to remove the residual potassium hydroxide, and then heated and dried to obtain a porous irregularly shaped carbon material;

[0233] (2.6) Vapor-phase silicon infiltration: Porous irregularly shaped carbon material is placed in a rotary kiln and a mixture of silicon source gas tetramethylsilane, carrier gas argon and reducing gas hydrogen is introduced (the mass ratio of silicon source gas to reducing gas is 0.12:1). The pressure inside the furnace is controlled within a slightly positive pressure range (400 Pa higher than atmospheric pressure) to deposit silicon and obtain irregularly shaped silicon-carbon particles. The temperature of silicon deposition (i.e., vapor-phase silicon infiltration) is 450℃ and the time is 6h.

[0234] (2.7) Carbon coating treatment: Stop the introduction of silicon source gas and introduce a mixture of carbon source gas methane and dilution gas argon. Adjust the reaction temperature to 800℃ and react for 2 hours. After the reaction, cool and sieve to obtain the second silicon-carbon material.

[0235] The second silicon-carbon material has an irregular morphology with a sphericity of 0.54, a roundness of 0.45, a convexity of 0.64, an ID / IG ratio of 0.74, and a silicon to carbon mass ratio of 0.54:1.

[0236] (3) Preparation of negative electrode sheet

[0237] A first silicon-carbon material, a second silicon-carbon material, graphite (ID / IG = 0.26), sodium carboxymethyl cellulose thickener, styrene-butadiene rubber binder, and acetylene black conductive agent were mixed evenly in deionized water at a mass ratio of 17.78:2.22:77:1:1:1 to obtain a negative electrode slurry. The first and second silicon-carbon materials are collectively referred to as silicon-carbon materials. The negative electrode slurry was uniformly coated onto both sides of a copper foil. After drying the copper foil at room temperature, it was transferred to a 120°C oven for 1 hour, followed by cold pressing and slitting to obtain the negative electrode sheet. The coating weight per unit area on one side of the negative electrode sheet was 0.13 g / 1540.25 mm². 2 The mass ratio of the first silicon-carbon material to the second silicon-carbon material in the negative electrode active layer is 8:1 (see [reference]). Figures 1-3 The compaction density of the negative electrode sheet is 1.50 g / cm³. 3 .

[0238] (4) Preparation of positive electrode sheet

[0239] Lithium iron phosphate (LFP) as the positive electrode active material, carbon black (Super P) as the conductive agent, and polyvinylidene fluoride (PVDF) as the binder were mixed uniformly in N-methylpyrrolidone (NMP) at a mass ratio of 97.5:0.4:2.1 to obtain a positive electrode slurry. The positive electrode slurry was coated on both sides of the positive electrode current collector aluminum foil, and the positive electrode sheet was obtained through processes such as drying, cold pressing, slitting, and cutting. The coating amount per unit area on one side was 0.27 g / 1540.25 mm. 2 .

[0240] (5) Preparation of the separating membrane

[0241] Use a 7μm thick polypropylene diaphragm.

[0242] (6) Preparation of electrolyte

[0243] Ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed in a mass ratio of 30:70 to obtain an organic solvent. Fully dried LiPF6 was dissolved in the organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0244] (7) Preparation of lithium-ion batteries

[0245] The positive electrode, separator, and negative electrode are stacked and wound in sequence to obtain an electrode assembly. The electrode assembly is placed in an outer packaging, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping, a lithium-ion battery is obtained.

[0246] Examples 2-7

[0247] Similar to the preparation process of Example 1, the main difference is that in step (1), the mass ratio of the resin carbon source to the morphology modifier is changed to 45:55, 68:42, 78:22, 32:68, 59:41, and 81:19, respectively, so that the sphericity, the ratio of the minimum Feretta diameter to the maximum Feretta diameter, the roundness and the convexity of the first silicon carbide material are changed, as shown in Table 1 below.

[0248] Table 1

[0249]

[0250] As can be seen from the table above, when the sphericity of the first silicon-carbon material and the ratio of its minimum to maximum Feret diameter are both within the ranges specified in this application, it is beneficial to balance the battery's fast-charging and other kinetic and cycle performance. Furthermore, when the sphericity of the first silicon-carbon material is 0.7 to 0.86, the battery's cycle and kinetic performance are relatively better. Even further, when the ratio of the minimum to maximum Feret diameter of the first silicon-carbon material is 0.5 to 0.65, the battery's cycle and kinetic performance are relatively better.

[0251] Examples 8-11

[0252] Similar to the preparation process of Example 1, the main difference is that in step (3), the mass ratios of the first silicon carbide material, the second silicon carbide material, graphite, thickener sodium carboxymethyl cellulose, binder styrene-butadiene rubber, and conductive agent acetylene black are adjusted to 6:14:77:1:1:1, 10:10:77:1:1:1, 16:4:77:1:1:1, and 18:2:77:1:1:1, respectively, so that the mass ratios of the first silicon carbide material and the second silicon carbide material in the negative electrode active layer are 3:7, 5:5, 8:2, and 9:1, respectively, as shown in Table 2 below.

[0253] Example 12

[0254] Similar to the preparation process of Example 1, the main difference is that in step (3), the first silicon-carbon material of equal mass is used instead of the second silicon-carbon material (i.e., the silicon-carbon material is a pure ellipsoid), as shown in Table 2 below.

[0255] Table 2

[0256]

[0257] As can be seen from the table above, when the mass ratio of the first silicon-carbon material to the second silicon-carbon material is within the range specified in this application, it is beneficial to balance the battery's kinetic performance, such as fast charging, and cycle performance. Furthermore, when the mass ratio is (5~9):(5~1), the battery's cycle performance and kinetic performance are relatively better.

[0258] Comparative Example 1

[0259] The preparation process is similar to that of Example 1, with the main difference being that in step (3), an equal mass of second silicon-carbon material is used instead of the first silicon-carbon material (i.e., the silicon-carbon material is purely irregular in shape, see [reference]). Figure 4 (See Table 3 below).

[0260] Comparative Example 2

[0261] Similar to the preparation process in Example 1, the main difference is that in step (3), a near-spherical silicon-carbon material of equal mass is used instead of the first silicon-carbon material (i.e., the silicon-carbon material is a combination of near-spherical and irregular shapes); the sphericity of the near-spherical silicon-carbon material is 0.98, and the ratio of the minimum Feretta diameter to the maximum Feretta diameter is 0.95; as shown in Table 3 below. Among them, "mass percentage" refers to the mass percentage in the negative electrode active layer.

[0262] Table 3

[0263]

[0264] As can be seen from the comparison of the examples and Comparative Examples 1-2 in the table above, compared with the silicon-carbon material using a second silicon-carbon material with a pure irregular morphology (Comparative Example 1) or the combination of the silicon-carbon material using a second silicon-carbon material with an irregular morphology and a near-spherical silicon-carbon material (Comparative Example 2), the silicon-carbon material of this application using a first silicon-carbon material with a near-ellipsoidal morphology (Examples 1-11) or the silicon-carbon material using a first silicon-carbon material with a near-ellipsoidal morphology and a second silicon-carbon material with an irregular morphology (Example 12) is beneficial for the battery to take into account both cycle performance and fast charging dynamic performance.

[0265] Performance testing:

[0266] 1. Cyclic performance (60D storage capacity retention)

[0267] The electrodes were fabricated into stacked cells. The battery was discharged at a constant current rate of 0.33C to the cutoff voltage of 2.5V, allowed to stand for 30 minutes, and then charged at a constant current rate of 0.33C to the charging cutoff voltage of 4.25V. Afterward, it was charged at a constant voltage until the current ≤0.05C. After standing for 30 minutes, the initial capacity was recorded as C0. The battery was stored in a 60℃ constant temperature chamber for 60 days. After 60 days, the battery was removed and allowed to stand at room temperature for 60 minutes before capacity testing. The specific procedure was as follows: discharge at a constant current rate of 0.33C to the cutoff voltage of 2.5V, allowed to stand for 30 minutes, then charge at a constant current rate of 0.33C to the charging cutoff voltage of 4.25V, and then charged at a constant voltage until the current ≤0.05C. The capacity was recorded as C1. The 60-day (Day, D) storage capacity retention rate = C1 / C0 * 100%.

[0268] 2. Dynamic performance (charging (fast charging) time)

[0269] At 35°C, the batteries of the above embodiments and comparative examples were charged and discharged for the first time at a current of 1C (i.e., the current value at which the theoretical capacity is completely discharged within 1 hour). Specifically, the batteries were charged at a constant current rate of 1C to the charging cutoff voltage V1, then charged at a constant voltage until the current ≤0.05C, left to stand for 5 minutes, and then discharged at a constant current rate of 0.33C to the discharge cutoff voltage V2. The actual capacity was recorded as C0. Then, the battery is sequentially charged at constant currents of 2.8C0, 3C0, 3.2C0, 3.5C0, 3.8C0, 4.1C0, 4.4C0, 4.7C0, 5C0, 5.3C0, 5.6C0, and 5.9C0 until it reaches the full battery charging cutoff voltage V1 or the 0V negative terminal cutoff potential (whichever comes first). After each charging cycle, it is discharged at 1C0 until it reaches the full battery discharge cutoff voltage V2. The charging rates at different states of charge (10%, 20%, 30%, 40%, 50%, 60%, 70%, and 80%) are recorded. The negative electrode potential corresponding to the state of charge (SOC) is plotted, and the charging rate-negative electrode potential curves are drawn for different SOC states. After linear fitting, the charging rate corresponding to the negative electrode potential of 0V under different SOC states is obtained. This charging rate is the charging window under that SOC state, denoted as C10%SOC, C20%SOC, C30%SOC, C40%SOC, C50%SOC, C60%SOC, C70%SOC, and C80%SOC. The charging time T for the battery to charge from 10%SOC to 80%SOC is calculated according to the formula (60 / C20%SOC + 60 / C30%SOC + 60 / C40%SOC + 60 / C50%SOC + 60 / C60%SOC + 60 / C70%SOC + 60 / C80%SOC) × 10%, in minutes. The shorter the charging time, the better the battery's fast charging performance.

[0270] The description of the various embodiments above tends to emphasize the differences between the various embodiments. The similarities or similarities between them can be referred to, and for the sake of brevity, they will not be repeated here.

[0271] It is understood that the above embodiments are merely illustrative examples, and those skilled in the art may also use other preparation methods to obtain the first silicon-carbon material of this application. For example, without adding a morphology modifier, the morphology of the first silicon-carbon material may be changed to a near-ellipsoidal morphology by adjusting other process parameters or using different process conditions to obtain the secondary battery protected by the first aspect of this application. This application does not limit the preparation method of the secondary battery protected by the first aspect.

[0272] 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.

[0273] The above embodiments merely illustrate 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, and the specification and drawings can be used to interpret the scope of the claims.

Claims

1. A secondary battery, characterized in that, The secondary battery includes a negative electrode sheet, the negative electrode sheet includes a negative current collector and a negative active layer disposed on at least one side of the negative current collector, the negative active layer contains a negative active material, the negative active material includes a first silicon-carbon material, the sphericity of the first silicon-carbon material is 0.6~0.95, and the ratio of the minimum Feretta diameter to the maximum Feretta diameter of the first silicon-carbon material is 0.4~0.

7.

2. The secondary battery according to claim 1, characterized in that, The sphericity of the first silicon-carbon material is 0.7~0.

86.

3. The secondary battery according to claim 1, characterized in that, The ratio of the minimum Ferete diameter to the maximum Ferete diameter of the first silicon-carbon material is 0.4 to 0.

65.

4. The secondary battery according to any one of claims 1 to 3, characterized in that, The ratio of the minimum Ferete diameter to the maximum Ferete diameter of the first silicon-carbon material is 0.5 to 0.

65.

5. The secondary battery according to any one of claims 1 to 3, characterized in that, The first silicon-carbon material has a near-ellipsoidal morphology.

6. The secondary battery according to any one of claims 1 to 3, characterized in that, The roundness of the first silicon-carbon material is 0.7~0.

95.

7. The secondary battery according to any one of claims 1 to 3, characterized in that, The convexity of the first silicon-carbon material is 0.8~0.

95.

8. The secondary battery according to any one of claims 1 to 3, characterized in that, One or more of the following conditions must be met: (1) The ID / IG ratio of the first silicon-carbon material is 0.4~1; (2) In the first silicon-carbon material, the mass ratio of silicon to carbon is (0.4~0.6):

1.

9. The secondary battery according to any one of claims 1 to 3, characterized in that, The negative electrode active material further includes a second silicon-carbon material, wherein the sphericity of the second silicon-carbon material is greater than or equal to 0.3 and less than 0.

6.

10. The secondary battery according to claim 9, characterized in that, The roundness of the second silicon-carbon material is greater than or equal to 0.4 and less than 0.

7.

11. The secondary battery according to claim 9, characterized in that, The convexity of the second silicon-carbon material is greater than or equal to 0.6 and less than 0.

8.

12. The secondary battery according to claim 9, characterized in that, One or more of the following conditions must be met: (1) The ID / IG ratio of the second silicon-carbon material is 0.4~1; (2) In the second silicon-carbon material, the mass ratio of silicon to carbon is (0.4~0.6):

1.

13. The secondary battery according to claim 9, characterized in that, In the negative electrode active layer, the mass ratio of the first silicon-carbon material to the second silicon-carbon material is (3~9):(7~1).

14. The secondary battery according to claim 13, characterized in that, The mass ratio of the first silicon-carbon material to the second silicon-carbon material is (5~9):(5~1).

15. The secondary battery according to claim 9, characterized in that, The negative electrode active material also includes graphite.

16. The secondary battery according to claim 15, characterized in that, One or more of the following conditions must be met: (1) The ID / IG ratio of the graphite is 0.1~0.6; (2) In the negative electrode active layer, the mass ratio of silicon carbon material to graphite is (5~85):(95~15), wherein the silicon carbon material includes the first silicon carbon material and the second silicon carbon material.

17. The secondary battery according to any one of claims 1 to 3, characterized in that, The silicon content in the negative electrode active layer is 5% to 85% by mass.

18. The secondary battery according to any one of claims 1 to 3, characterized in that, The compaction density of the negative electrode sheet is 1.0 g / cm³. 3 ~1.8g / cm 3 .

19. A method for preparing a secondary battery, characterized in that, The secondary battery includes a negative electrode sheet, the negative electrode sheet includes a negative current collector and a negative active layer disposed on at least one side of the negative current collector, the negative active layer contains a negative active material, the negative active material includes a first silicon-carbon material, the sphericity of the first silicon-carbon material is 0.6~0.95, and the ratio of the minimum Freret diameter to the maximum Freret diameter of the first silicon-carbon material is 0.4~0.7; The preparation steps of the first silicon-carbon material include: An emulsion containing a morphology modifier and a resin carbon source is cured to form resin microspheres, wherein the weight-average molecular weight of the morphology modifier is less than the weight-average molecular weight of the resin carbon source. The resin microspheres are carbonized to form ellipsoidal carbon material microspheres; The first silicon-carbon material was prepared by vapor-phase silicon infiltration of the ellipsoidal carbon material microspheres.

20. The preparation method according to claim 19, characterized in that, One or more of the following conditions must be met: (1) The weight-average molecular weight of the morphology modifier is 5 × 10⁻⁶. 4 ~2×10 5 g / mol; (2) The weight-average molecular weight of the carbon source in the resin is 5 × 10⁻⁶. 5 g / mol ~ 1×10 6 g / mol; (3) The morphology modifier contains a flexible chain, which includes one or more of polyether chains, aliphatic polyester chains and polyolefin chains; (4) The thermal decomposition temperature of the morphology modifier is lower than the thermal decomposition temperature of the resin carbon source; (5) The glass transition temperature of the resin carbon source is less than or equal to the thermal decomposition temperature of the morphology modifier.

21. The preparation method according to claim 19 or 20, characterized in that, One or more of the following conditions must be met: (1) The morphology modifier comprises a polymer; Optionally, the polymer includes one or more of polyethylene glycol, polyvinylpyrrolidone, polyacrylic acid, and polyurethane; (2) The carbon source of the resin includes one or more of phenolic resin, epoxy resin and furan resin; (3) In the emulsion, the mass ratio of the resin carbon source to the morphology modifier is (0.4~4.5):1; (4) The curing process includes chemical crosslinking curing and / or heat curing; Optionally, the curing temperature for heat curing is 80℃~200℃.

22. An electrical appliance, characterized in that, This includes the secondary battery as described in any one of claims 1 to 18 or the secondary battery prepared by the preparation method described in any one of claims 19 to 21.

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