Composite active material and related secondary battery and electric device

Abstract

The present application relates to a composite active material and related secondary battery and electric device. The composite active material comprises metal matrix particles and silicon nanoparticles, the metal matrix particles have a porous framework structure; the silicon nanoparticles are located in at least part of the pores of the porous framework structure. When the composite active material is applied to a secondary battery, the cycle performance and energy density of the secondary battery can be improved.

Description

Technical Field

[0001] This application relates to the field of battery technology, and more specifically, to composite active materials and related secondary batteries and electrical devices. Background Technology

[0002] Secondary batteries are widely used due to their reliable performance, lack of pollution, and absence of memory effect. For example, with increasing emphasis on environmental protection and the growing popularity of new energy vehicles, the demand for power-type secondary batteries will experience explosive growth.

[0003] To improve the performance of secondary batteries, materials within the battery, such as the negative electrode active material, are typically optimized and improved. As a carrier of metal ions and electrons in the secondary battery, the negative electrode active material plays a crucial role in energy storage and release, and thus has a significant impact on the battery's performance.

[0004] However, even with the improved negative electrode active materials, the cycle performance and energy density of secondary batteries are still relatively poor when applied. Summary of the Invention

[0005] This application provides a composite active material and related secondary batteries and power devices. When the composite active material is applied to a secondary battery, the cycle performance and energy density of the secondary battery can be improved.

[0006] In a first aspect, this application proposes a composite active material comprising metal matrix particles and silicon nanoparticles, wherein the metal matrix particles have a porous framework structure, and the silicon nanoparticles are located within at least a portion of the pores of the porous framework structure.

[0007] The metal matrix particles of this application possess a stable porous framework structure with strong support capabilities, exhibiting high stress resistance and excellent mechanical properties and conductivity. The porous framework structure provides ample space for silicon nanoparticles, enabling large-scale silicon storage. The silicon nanoparticles are uniformly dispersed within the porous structure. The combination of the metal matrix particles and silicon nanoparticles enhances the conductivity of the composite active material. Furthermore, the relatively high mechanical strength of the metal matrix particles provides effective mechanical support for the silicon nanoparticles, mitigating the volume expansion of silicon during lithium intercalation and effectively withstanding stress changes in the silicon nanoparticles. This ensures the structural stability of the composite active material, improving its cycle stability and lithium storage capacity. Consequently, when applied to secondary batteries, this enhances the cycle performance and energy density of the secondary battery.

[0008] In some embodiments, the average pore size of the porous framework structure is R, with units of nm, where 1 ≤ R ≤ 100; optionally, 1 ≤ R ≤ 8; and further optionally, 1 ≤ R ≤ 5. When the average pore size of the porous framework structure is within the above range, due to the pore size limitation of the porous framework structure, silicon nanoparticles are less likely to agglomerate and form large silicon grains, which is beneficial to the uniform dispersion of silicon nanoparticles.

[0009] In some embodiments, the pore volume of the porous framework structure is V, with units of cm. 3 / g, 0.5≤V≤0.8. When the pore volume of the porous framework structure is within the above range, due to the limitation of pore volume, silicon nanoparticles are less likely to agglomerate and form large silicon grains, which is conducive to the uniform dispersion of silicon nanoparticles.

[0010] In some embodiments, the BET specific surface area of ​​the metal matrix particles is S1, with units of m². 2 / g, 1000≤S1≤2000. When the BET specific surface area of ​​the metal matrix particles is within the above range, the metal matrix particles can provide a larger exposed area, which is conducive to the widespread dispersion of silicon nanoparticles and the uniform distribution of silicon nanoparticles.

[0011] In some embodiments, the volume distribution particle size Dv50 of the metal matrix particles is D1, with units of μm, and 3 ≤ D1 ≤ 8. When the volume distribution particle size of the metal matrix particles is within the above range, it has a richer three-dimensional cross-linked pore structure, which is beneficial for the uniform dispersion of silicon nanoparticles in the pore structure.

[0012] In some embodiments, the material of the metal matrix particles includes one or more of iron, nickel, and copper. When the metal matrix particles include multiple elemental metals, the multiple elemental metals can form an alloy, such as an iron-nickel alloy.

[0013] In some embodiments, the average particle size of the silicon nanoparticles is D. Si Its unit is nm, D si ≤100; optionally, 1≤D si ≤3. The relatively small particle size of silicon nanoparticles can significantly alleviate the high pressure caused by silicon volume changes, which is beneficial to ensuring the overall structural stability of the composite active material and improving the cycle stability of the secondary battery; it can also significantly shorten the lithium ion transport distance, which is beneficial to improving the kinetic performance of the composite active material.

[0014] In some embodiments, the silicon nanoparticles include one or more of silicon oxide compounds, pre-lithiated silicon oxide compounds, amorphous silicon, crystalline silicon, and silicon-carbon composites. Amorphous silicon can expand uniformly in all directions, thereby causing uniform compression of the metal matrix particles, which can effectively alleviate the volume expansion of amorphous silicon. Crystalline silicon has a relatively more stable structure, which is more conducive to fully utilizing its capacity characteristics. Silicon-carbon composites, which pre-combine carbon and silicon into a compound and form it in the pores of the metal matrix particles, have relatively small volume expansion, thereby reducing the stress on the porous carbon matrix particles.

[0015] In some embodiments, the mass percentage of silicon nanoparticles is A% based on the total mass of the composite active material; the mass percentage of metal matrix particles is B% based on the total mass of the composite active material; and the composite active material satisfies: 0.4 ≤ A / B ≤ 1.5; optionally, 30 ≤ A ≤ 55; and / or 45 ≤ B ≤ 70. When the mass percentage of silicon nanoparticles is within the above range, the capacity of the composite active material is relatively high.

[0016] In some embodiments, the composite active material further includes a conductive layer that covers at least a portion of the surface of the metal matrix particles. As a continuous layered structure, the conductive layer covers the outer surface of the metal matrix particles, thereby concealing the pores on the surface of the particles, reducing the specific surface area of ​​the metal matrix particles, and decreasing the risk of side reactions between the silicon nanoparticles and the electrolyte, thus improving the structural stability of the composite active material. Furthermore, the aforementioned substances possess excellent conductivity, thereby significantly improving the conductivity of the composite active material.

[0017] In some embodiments, the thickness of the conductive layer is H, measured in nm, where 3 ≤ H ≤ 10. As a continuous layered structure, the conductive layer coats the outer surface of the metal matrix particles, covering the pores on the particle surface, reducing the specific surface area of ​​the metal matrix particles, and decreasing the risk of side reactions between the silicon nanoparticles and the electrolyte, thereby improving the structural stability of the composite active material. Furthermore, the aforementioned substance possesses excellent conductivity, thus significantly improving the conductivity of the composite active material.

[0018] In some embodiments, the conductive layer comprises a carbon layer and / or a conductive polymer layer; optionally, the conductive polymer layer comprises one or more of polyaniline, polypyrrole, polyacetylene, polythiophene, polyphenylene sulfide, and poly(p-phenylene).

[0019] In some embodiments, the volume distribution particle size Dv50 of the composite active material is D2, with units of μm, and 2 ≤ D2 ≤ 12; and / or the BET specific surface area of ​​the composite active material is S2, with units of m³. 2 / g, 800≤S2≤3000; and / or the porosity of the composite active material is P%, 0<P≤90.

[0020] Secondly, this application proposes a secondary battery, the secondary battery including a negative electrode sheet, the negative electrode sheet including the composite active material described in any embodiment of the first aspect of this application.

[0021] Thirdly, this application proposes an electrical device including a secondary battery as described in the second aspect of this application. Attached Figure Description

[0022] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0023] Figure 1 This is a graph showing the relationship between the pore volume and pressure of the porous framework structure in the composite active material of this application.

[0024] Figure 2 This is a schematic diagram of one embodiment of the secondary battery of this application.

[0025] Figure 3 yes Figure 2 An exploded view of the implementation method of the secondary battery.

[0026] Figure 4 This is a schematic diagram of one embodiment of the battery module of this application.

[0027] Figure 5 This is a schematic diagram of one embodiment of the battery pack of this application.

[0028] Figure 6 yes Figure 5 An exploded view of an embodiment of the battery pack shown.

[0029] Figure 7 This is a schematic diagram of one embodiment of an electrical device that uses a secondary battery as a power source, as described in this application.

[0030] Figure 8 This is a cross-sectional morphology diagram of the composite active material of Example 1 of this application.

[0031] The accompanying drawings may not be drawn to scale.

[0032] The annotations in the attached figures are explained as follows:

[0033] 1. Battery pack; 2. Upper casing; 3. Lower casing; 4. Battery module;

[0034] 5. Secondary battery; 51. Housing; 52. Electrode assembly;

[0035] 53. Cover plate;

[0036] 6. Electrical appliances. Detailed Implementation

[0037] The following detailed description, with appropriate reference to the accompanying drawings, specifically discloses embodiments of the composite active material and related secondary batteries and power-consuming devices of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0038] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is 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 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 "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0039] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0040] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0041] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0042] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0043] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0044] A secondary battery includes a positive electrode and a negative electrode. The positive electrode includes a positive electrode film containing positive active material, and the negative electrode includes a negative electrode film containing negative active material. During the charging and discharging process of the secondary battery, the electrolyte, which has ion conductivity, provides a pathway for active ions, allowing them to intercalate and deintercalate in the positive and negative electrode materials.

[0045] With the increasing application of rechargeable batteries, the requirements for their performance, such as energy density, are gradually increasing. The negative electrode active material has a significant impact on the performance of rechargeable batteries. Carbon and silicon, as commonly used negative electrode active materials, have been extensively studied. Carbon particles have a relatively low theoretical specific capacity and a low lithium intercalation potential, making them prone to lithium deposition and causing safety issues. Silicon can form a silicon-lithium alloy with lithium at room temperature, resulting in a relatively high theoretical specific capacity; furthermore, silicon's lithium intercalation potential is slightly higher than that of graphite, which can reduce the risk of lithium deposition. However, the volume change of micron-sized silicon materials during lithium insertion / extraction reactions can exceed 300%. This significant volume change and the continuous volume change of silicon particles can easily cause the solid-electrolyte interphase (SEI) film on the surface of the active material to rupture and regenerate. Repeated growth of the SEI film not only continuously consumes lithium and electrolyte but also restricts lithium-ion transport, reduces the electrical contact of the active material, and increases impedance. Furthermore, micron-sized silicon materials can also experience rupture and pulverization. After rupture and pulverization, fresh silicon surfaces are constantly exposed, forming new SEI films and increasing the thickness of the SEI film, which leads to a longer lithium-ion transport path.

[0046] Combining carbon particles and silicon particles into a core-shell structure, with carbon particles as the shell and silicon particles as the core, aims to improve the performance of secondary batteries. However, due to the low strength and compaction density of carbon particles, they are easily crushed, losing their structural advantages. Furthermore, silicon particles may still pulverize and crack during expansion, making it impossible for secondary batteries to simultaneously improve cycle performance and energy density.

[0047] To address the aforementioned issues, this application improves the negative electrode active material by employing metal matrix particles and forming silicon nanoparticles within the porous structure of the metal matrix particles. The silicon nanoparticles are uniformly dispersed within the porous structure. The composite of the metal matrix particles and silicon nanoparticles enhances the conductivity of the negative electrode active material. Furthermore, the relatively high mechanical strength of the metal matrix particles provides effective mechanical support for the silicon nanoparticles, mitigating the volume expansion of silicon during lithium intercalation and effectively withstanding stress changes in the silicon nanoparticles. This ensures the structural stability of the negative electrode active material and improves its cycle stability and lithium storage capacity. Consequently, when the negative electrode active material is applied to secondary batteries, it enhances the cycle performance and energy density of the secondary battery. The technical solution for the negative electrode active material will be described in detail below.

[0048] Composite active materials

[0049] In a first aspect, this application proposes a composite active material comprising metal matrix particles and silicon nanoparticles, wherein the metal matrix particles have a porous framework structure and the silicon nanoparticles are located within at least a portion of the pores of the porous framework structure.

[0050] The pores in a porous framework structure refer to recessed structures that are recessed relative to the outer surface of the metal matrix particles and penetrate into the interior of the metal matrix particles, or through-pores that penetrate the metal matrix particles. A porous framework structure indicates that the composite active material contains multiple pores, which can be arranged in parallel and / or intersecting arrangements. Further, a porous framework structure can be a three-dimensional network cross-linked pore structure, i.e., a structure in which two or more pores are interconnected or intersected and share a pore volume. The components of a porous framework structure include pore size, pore length, and pore size distribution. The pore sizes of a porous framework structure include micropores, mesopores, and macropores. Micropores are pores with a diameter of less than approximately 2 nanometers. Mesopores are pores with a diameter of approximately 2 to approximately 5 nanometers. Macropores are pores with a diameter greater than 50 nanometers.

[0051] Silicon nanoparticles have a particle size at the nanometer level. When silicon nanoparticles are formed on a porous framework structure, they are more likely to adhere uniformly to the porous framework structure.

[0052] The metal matrix particles of this application possess a stable porous framework structure with strong support capabilities, exhibiting high stress resistance and excellent mechanical properties and conductivity. The porous framework structure provides ample space for silicon nanoparticles, enabling large-scale silicon storage. The silicon nanoparticles are uniformly dispersed within the porous structure. The combination of the metal matrix particles and silicon nanoparticles enhances the conductivity of the composite active material. Furthermore, the relatively high mechanical strength of the metal matrix particles provides effective mechanical support for the silicon nanoparticles, mitigating the volume expansion of silicon during lithium intercalation and effectively withstanding stress changes in the silicon nanoparticles. This ensures the structural stability of the composite active material, improving its cycle stability and lithium storage capacity. Consequently, when applied to secondary batteries, this enhances the cycle performance and energy density of the secondary battery.

[0053] In some embodiments, the porous framework structure is a three-dimensional network cross-linked porous structure. The three-dimensional network cross-linked porous structure enables more uniform deposition of silicon nanoparticles and provides better structural support and conductivity, thereby further improving the overall stability and conductivity of the composite active material and contributing to further improvements in the cycle performance of the secondary battery.

[0054] The pore structure of composite active materials can be tested using equipment and methods known in the art. For example, it can be tested using a scanning electron microscope (e.g., ZEISS Sigma 300). As an example, the following steps can be taken: First, cut the negative electrode containing the composite active material into a sample of a certain size (e.g., 6mm × 6mm). Clamp the sample between two conductive and thermally conductive sheets (e.g., copper foil). Secure the sample to the sheets with adhesive (e.g., double-sided tape). Press the sample with a flat iron block of a certain weight (e.g., about 400g) for a certain period of time (e.g., 1 hour) to minimize the gap between the sample and the copper foil. Then, trim the edges with scissors and attach the sample to a sample stage with conductive adhesive, ensuring the sample slightly protrudes from the edge of the sample stage. Then, the sample stage is installed and locked in place on the sample holder. The power of the argon ion section polisher (e.g., IB-19500CP) is turned on and a vacuum is drawn (e.g., 10Pa-4Pa). The argon flow rate (e.g., 0.15MPa), voltage (e.g., 8KV), and polishing time (e.g., 2 hours) are set. The sample stage is adjusted to swing mode to start polishing. After polishing, the ion polished cross-sectional morphology (CP) image of the sample is obtained using a scanning electron microscope (e.g., ZEISS Sigma 300).

[0055] In some embodiments, the porosity of the composite active material is P%, where 0 < P ≤ 90. Exemplarily, the porosity of the composite active material can be 10%, 20%, 30%, 50%, 60%, 70%, 80%, 90%, or a range of any two of the above values.

[0056] When the porosity of the composite active material is within the above range, the pores of the porous framework structure, in addition to being deposited by silicon nanoparticles, also retain some pores, which can leave space for the volume expansion of silicon nanoparticles, thereby further mitigating the volume effect of silicon during the lithium insertion / extraction process.

[0057] In this application, porosity refers to the ratio of the volume of pores within the particles to the total volume of the composite active material. Porosity can be measured using the gas displacement method according to GB / T24586. Porosity P% = (L1 - L2) / L1 * 100%, where L1 is the apparent volume of the sample and L2 is the actual volume of the sample.

[0058] P=0 indicates that the composite active material is basically poreless, meaning that the pores of the metal matrix particles are basically filled with silicon nanoparticles.

[0059] When the metal matrix particles of the composite active material of this application, in addition to satisfying the above design, optionally also satisfy one or more of the following parameters, the performance of the secondary battery can be further improved.

[0060] In some embodiments, the average pore size of the porous framework structure is R, in nm, where 1 ≤ R ≤ 100; optionally, 1 ≤ R ≤ 10; optionally, 1 ≤ R ≤ 8; optionally, 1 ≤ R ≤ 5; optionally, 1 ≤ R ≤ 3.

[0061] When the average pore size of the porous framework structure is within the above range, due to the pore size limitation of the porous framework structure, silicon nanoparticles are less likely to agglomerate and form large silicon grains, which is beneficial to the uniform dispersion of silicon nanoparticles.

[0062] In some embodiments, the pore volume of the porous framework structure is V, and its unit is cm. 3 / g, 0.5≤V≤0.8.

[0063] When the pore volume of the porous framework structure is within the above range, due to the limitation of pore volume, silicon nanoparticles are less likely to agglomerate and form large silicon grains, which is conducive to the uniform dispersion of silicon nanoparticles.

[0064] In this application, the average pore size and pore volume of the porous framework structure can be tested using the gas adsorption method, according to the testing standards GB / T19587-2017 & GB / T21650.2-2008, as follows: The composite active material is taken as a sample, and the sample tube is immersed in liquid nitrogen at -196℃. Nitrogen gas is adsorbed on the material under the relative pressure of 0-1 atmosphere (101 kPa). The pore size distribution of the porous material is characterized based on the relationship between the volume of each pore size and the corresponding partial pressure, and the pore volume of the porous framework structure is obtained. Figure 1 The graph shows the relationship between pore volume and corresponding partial pressure, where p / p0 represents the partial pressure and Va represents the pore volume in cm³. 3 (STP)g -1 .

[0065] In some embodiments, the BET specific surface area of ​​the metal matrix particles is S1, and its unit is m². 2 / g, 1000≤S1≤2000.

[0066] When the BET specific surface area of ​​the metal matrix particles is within the above range, the metal matrix particles can provide a larger exposed area, which is conducive to the widespread dispersion of silicon nanoparticles and the uniform distribution of silicon nanoparticles.

[0067] In this application, the specific surface area of ​​the material has a meaning known in the art, and the surface area is usually expressed in m². 2The unit / g is used for measurement and can be tested using methods and instruments known in the art. For example, it can be measured using the inert gas (e.g., nitrogen) adsorption specific surface area analysis method according to GB / T 19587-2017, and calculated using the BET (Brunauer Emmett Teller) method. The nitrogen adsorption specific surface area analysis can be performed using the Tri-Star 3020 specific surface area and pore size analyzer from Micromeritics, Inc., USA.

[0068] In some embodiments, the volume distribution particle size Dv50 of the metal matrix particles is D1, which is in μm, and 3≤D1≤8.

[0069] When the volume distribution particle size of the metal matrix particles is within the above range, it has a richer three-dimensional cross-linked pore structure, which is beneficial to the uniform dispersion of silicon nanoparticles in the pore structure.

[0070] In this application, Dv50 represents the particle size corresponding to a cumulative volume distribution percentage of 50%, which can be tested using methods known in the art. For example, it can be determined using a laser particle size analyzer (such as a Malvern Master Size 3000) in accordance with standard GB / T 19077.1-2016.

[0071] In some embodiments, the material of the metal matrix particles includes one or more of iron, nickel, and copper. When the metal matrix particles include multiple elemental metals, the multiple elemental metals can form an alloy, such as an iron-nickel alloy.

[0072] When the materials of the metal matrix particles include the above-mentioned materials, the metal matrix particles have good electrical conductivity and high mechanical strength, which can improve the support effect on silicon nanoparticles.

[0073] When the metal matrix particles of the composite active material of this application, in addition to satisfying the above design, optionally also satisfy one or more of the following parameters, the performance of the secondary battery can be further improved.

[0074] In some embodiments, the average particle size of the silicon nanoparticles is D Si Its unit is nm, D si ≤100; optionally, 1≤D si ≤3. Optionally, 1≤D si ≤2.

[0075] The relatively small particle size of silicon nanoparticles can significantly alleviate the high stress caused by silicon volume changes, which is beneficial to ensuring the overall structural stability of the composite active material and improving the cycle stability of the secondary battery. Furthermore, it can significantly shorten the lithium-ion transport distance, which is beneficial to improving the kinetic performance of the composite active material. For example, the particle size of the silicon nanoparticles can be 1 nm, 2 nm, 3 nm, 5 nm, 8 nm, 10 nm, 12 nm, 15 nm, 20 nm, 25 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, or any combination of two of the above values.

[0076] In this application, the particle size of silicon nanoparticles can be determined by testing the XRD pattern of the sample according to the JIS / K0131-1996 testing standard. Based on the XRD pattern of the sample, the full width at half maximum (FWHM) β and the diffraction angle θ of the Si(111) crystal plane diffraction peak are taken and substituted into the Debye-Scherrer formula to calculate the particle size of the silicon nanoparticles. The Debye-Scherrer formula is as follows: Dhkl=k·λ / (βcosθ), where Dhkl represents the particle size of the silicon nanoparticles in nm; k represents the Scherrer constant, 0.89; λ represents the incident X-ray wavelength, 0.15406 nm; β represents the FWHM of the diffraction peak in rad; and θ represents the diffraction angle in degrees.

[0077] In some embodiments, the silicon nanoparticles include one or more of silicon oxides, pre-lithiated silicon oxides, amorphous silicon, crystalline silicon, and silicon-carbon composites.

[0078] Amorphous silicon can expand uniformly in all directions, thereby causing uniform compression of the metal matrix particles, which effectively alleviates the volume expansion of amorphous silicon. Crystalline silicon has a more stable structure, which is more conducive to fully utilizing its capacity characteristics. Silicon-carbon composites, which pre-combine carbon and silicon into a compound and form it within the pores of the metal matrix particles, exhibit relatively small volume expansion, thus reducing the stress on the porous carbon matrix particles. For example, the silicon-carbon composite can be silicon carbide.

[0079] The crystal structure of composite active materials can be tested using equipment and methods known in the art. As an example, the following steps can be taken: Select a microgrid of a certain diameter (e.g., 3 mm), hold the edge of the microgrid with pointed tweezers, and gently place it flat on white filter paper with the film side facing upwards (the side that appears glossy under light is the film side); add an appropriate amount of silicon particle sample (e.g., 1 g) to a beaker containing an appropriate amount of ethanol and sonicate for 10-30 minutes; use a glass capillary tube to aspirate and then drop 2-3 drops of the sample onto the microgrid; after baking in an oven for 5 minutes, place the microgrid with the sample onto the sample stage and test it using a transmission electron microscope (e.g., Hitachi HF-3300S Cs-corrected STEM) at a certain magnification (e.g., 60,000x) to obtain a transmission electron microscope (TEM) image of the sample. If there are obvious lattice fringes (for example, the fringe spacing is about 0.331 nm), it is crystalline silicon; if no lattice fringes are observed, it is amorphous silicon.

[0080] In some embodiments, the mass percentage of silicon nanoparticles is A% based on the total mass of the composite active material; the mass percentage of metal matrix particles is B% based on the mass of the composite active material, and the composite active material satisfies: 10 ≤ A / B ≤ 80; optionally, 30 ≤ A / B ≤ 50. When the mass percentage of silicon nanoparticles is within the above range, the capacity of the composite active material is relatively high.

[0081] In some embodiments, the mass percentage of silicon nanoparticles is A%, based on the total mass of the composite active material, with 30 ≤ A ≤ 50. When the mass percentage of silicon nanoparticles is within the above range, the capacity of the composite active material is relatively high.

[0082] In this application, the mass percentage of silicon nanoparticles is a term known in the art. The mass percentage of silicon nanoparticles can be tested using methods and equipment known in the art, such as the determination according to EPA 6010D-2014 standard. Specifically, it can be tested using ICP-OES (elemental analysis-inductively coupled plasma atomic emission spectrometry). First, the solid to be tested is dissolved into a liquid with a strong acid. Then, the liquid is introduced into the ICP light source by atomization. Further, the gaseous atoms to be tested are ionized and excited in a strong magnetic field, and then recover from the excited state to the ground state. During the above process, energy is released and recorded as different characteristic spectral lines for trace element quantitative analysis.

[0083] To further improve the conductivity and other properties of the composite active material, in some embodiments, the composite active material may also include a conductive layer that covers at least a portion of the surface of the metal matrix particles.

[0084] The conductive layer, as a continuous layered structure, coats at least a portion of the outer surface of the metal matrix particles. It can cover the pores on the surface of the metal matrix particles, reduce the specific surface area of ​​the metal matrix particles, and decrease the risk of side reactions between the silicon nanoparticles and the electrolyte, thereby improving the structural stability of the composite active material. Furthermore, the aforementioned substance possesses excellent conductivity, thus significantly improving the conductivity of the composite active material.

[0085] In some embodiments, the thickness of the conductive layer is H, measured in nm, where 3 ≤ H ≤ 10. When the thickness of the conductive layer meets the above range, the overall conductivity of the composite active material can be improved; and the smooth migration of active ions, such as lithium ions, within the composite active material can be ensured. For example, the thickness of the conductive layer can be 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 10 nm, or any combination of two of the above values.

[0086] In this application, the thickness of the conductive layer was measured using scanning electron microscopy. The ion-polished cross-sectional morphology of the sample was tested according to the JY / T010-1996 test standard, and the thickness of the conductive layer outside the material body was measured based on the cross-sectional morphology.

[0087] In some embodiments, the conductive layer includes a carbon layer and / or a conductive polymer layer; optionally, the conductive polymer layer includes one or more of polyaniline, polypyrrole, polyacetylene, polythiophene, polyphenylene sulfide, and poly(p-phenylene). The carbon layer facilitates uniform dispersion on the surface of the metal matrix particles, thereby improving the overall conductivity of the composite active material. The conductive polymer layer has a strong bond with the metal matrix particles and is not easily peeled off, thus improving the structural stability of the composite active material; and can further improve the conductivity of the composite active material.

[0088] In some embodiments, the volumetric particle size distribution Dv50 of the composite active material is D2, with units of μm, where 2 ≤ D2 ≤ 12. When the average particle size Dv50 of the composite active material meets the above range, the structure of the composite active material is relatively stable, and its kinetic performance is relatively good, which is beneficial to improving the first coulombic efficiency of the composite active material. For example, the volumetric particle size distribution Dv50 of the composite active material can be 2 μm, 3 μm, 5 μm, 7 μm, 8 μm, 10 μm, 12 μm, or any combination of two of the above values.

[0089] In some embodiments, the BET specific surface area of ​​the composite active material is S², with units of m². 2 / g, 800≤S2≤3000. When the BET specific surface area of ​​the composite active material meets the above range, the specific surface area range is relatively moderate, the kinetic performance of the composite active material is good, and it is beneficial to the first coulombic efficiency of the composite active material. For example, the BET specific surface area of ​​the composite active material can be 800m² / g. 2 / g, 1000m 2 / g、1200m 2 / g, 1500m 2 / g, 1700m 2 / g、1800m 2 / g、2000m 2 / g、2500m 2 / g、3000m 2 / g or a range consisting of any two of the above values.

[0090] Methods for preparing composite active materials

[0091] Secondly, this application also provides a method for preparing composite active materials. The method can be used to prepare the composite active materials according to any embodiment of the first aspect of this application. The method includes:

[0092] S100 provides a gas containing a silicon precursor to metal matrix particles with a porous framework structure;

[0093] S200, through chemical vapor deposition, silicon nanoparticles are generated from the silicon precursor and attached to at least some of the pores of the porous framework structure to obtain a composite active material.

[0094] Silicon precursors are deposited in at least some pores of a porous framework structure via chemical vapor deposition to form silicon nanoparticles, thereby enabling the metal matrix particles and silicon nanoparticles to work synergistically. While improving the conductivity and capacity of the composite active material, the metal matrix particles can limit the volume expansion of the silicon nanoparticles to a certain extent, thus ensuring the structural stability of the composite active material.

[0095] In step S100, the metal substrate particles can be placed in the heating chamber of the vapor deposition furnace beforehand, and the heating chamber is evacuated using a vacuum pump. A protective gas is introduced into the heating chamber, and after the protective gas fills the heating chamber, a gas containing the silicon precursor is introduced into the heating chamber, and the heating chamber is maintained at a certain pressure.

[0096] In this application, an inert gas and / or hydrogen can be used as a protective gas, and the protective gas and the gas containing the silicon precursor are jointly introduced onto the metal matrix particles. Exemplarily, the inert gas may include one or more of nitrogen, argon, and helium. Exemplarily, the gas containing the silicon precursor includes one or more of silane, dichlorosilane, trichlorosilane, and tetrachlorosilane.

[0097] In this application, deposition conditions can be controlled to improve deposition efficiency. Specifically, when the metal matrix particles contain a porous framework structure, the uniformity of silicon nanoparticle deposition within the pores of the porous framework can be adjusted. This allows the porous framework to better reduce the expansion volume of the silicon nanoparticles, thereby improving the cycle performance of the secondary battery. Furthermore, the silicon nanoparticles deposited on the porous framework do not aggregate significantly, thus ensuring the cycle performance of the secondary battery.

[0098] In step S200, during the chemical vapor deposition process, the silicon precursor can be decomposed into silicon nanoparticles by heating and deposited within the porous framework structure.

[0099] After the heating chamber is heated to a suitable temperature, the gas containing the silicon precursor is stopped, and the protective gas is stopped after the formed silicon nanoparticles have cooled naturally. The composite formed in step S200 can be used as the final composite active material. Of course, after step S200, other processes such as step S300 can be performed to further improve the performance of the composite active material.

[0100] In some embodiments, the method may further include: S300, forming a conductive layer on the surface of the metal matrix particles. By forming a conductive layer on the surface of the metal matrix particles and coating them, the overall conductivity and cycle performance of the composite active material can be improved.

[0101] The composite formed in step S300 can be used as the final composite active material. Of course, after step S300, other processes such as particle size screening can be performed.

[0102] As examples, when forming a carbon layer, a carbon layer can be generated by chemical vapor deposition, using a hydrocarbon gas as a carbon source to coat the surface of metal matrix particles. In some embodiments, the hydrocarbon gas may include C1-C3 straight-chain alkanes, cyclopropane, C2-C3 olefins, and C2-C3 alkynes. Exemplarily, C1-C3 straight-chain alkanes may include one or more of methane, ethane, and propane. C2-C3 olefins may include ethylene and / or propylene. C2-C3 alkynes may include acetylene and / or propyne.

[0103] This application allows for the formation of a carbon layer under a protective atmosphere; the protective gas can be nitrogen or argon.

[0104] This application can improve the deposition effect by controlling the deposition conditions, cover the pores on the surface of the metal matrix particles, reduce the specific surface area of ​​the composite active material, and improve the conductivity of the composite active material.

[0105] As other examples, when forming the conductive polymer layer, the organic polymer can be dissolved in a solvent using a solvent method, then mixed uniformly with the metal matrix particles, and the solvent removed, resulting in the organic polymer forming a conductive polymer layer coating the surface of the metal matrix particles. Exemplarily, the organic polymer may include one or more of polyaniline, polypyrrole, polyacetylene, polythiophene, polyphenylene sulfide, and poly(p-phenylene). The solvent may include acetone or methanol, etc. This application can improve the coating effect by controlling the coating conditions, covering the pores on the surface of the metal matrix particles, reducing the specific surface area of ​​the composite active material, and improving the conductivity of the composite active material.

[0106] In some embodiments, the metal matrix particles can be deposited using a porous framework structure via electrochemical deposition, specifically using a hydrogen bubble template method. The base plating solution consists of 0.4 mol / L copper sulfate and 1 mol / L sulfuric acid. Additives include polyethylene glycol (PEG) (80 mg / L), thiourea (10 mg / L), acetic acid (20 mg / L), and cetyltrimethylammonium bromide (CTAB) (15 mg / L). The working electrode is a copper-nickel alloy, and the current density is 1.5 to 2 A / cm². 2 The plating solution temperature is 20 to 70℃.

[0107] Because the electrodeposition potentials of copper and nickel are higher than the water decomposition potential, the deposition potential can be adjusted to be below the water decomposition potential during the preparation process. This generates hydrogen gas during metal deposition, resulting in a porous framework structure. The pore size can be adjusted by adding template agents such as PEG, thiourea, acetic acid, and CTAB, and the porosity and density of the metal deposition can be controlled by adjusting the current density.

[0108] Secondary batteries

[0109] Thirdly, this application proposes a secondary battery. The secondary battery may further include a positive electrode, a negative electrode, a separator, and an electrolyte. The separator is disposed between the positive and negative electrode to separate them.

[0110] [Negative electrode plate]

[0111] The negative electrode sheet includes a negative current collector and a negative active material layer disposed on at least one surface of the negative current collector, wherein the negative active material layer includes a negative active material.

[0112] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode active material layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0113] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0114] In some embodiments, the negative electrode active material may include the composite active material of any embodiment of the first aspect of this application, or it may be a composite active material prepared by the method of any embodiment of the second aspect of this application. Active ions, such as lithium ions, can enter the interior of the composite active material through the porous structure of the composite active material and undergo an alloying reaction with silicon nanoparticles to provide capacity; and the metal matrix particles can serve as the substrate of the negative electrode to receive lithium ions.

[0115] In some embodiments, the negative electrode active material may include, in addition to the composite active material of any embodiment of the first aspect of this application or the composite active material prepared by the method of any embodiment of the second aspect of this application, other negative electrode active materials, such as a second active material, may also be included. Exemplarily, the second active material may include, but is not limited to, at least one of natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. The silicon-based material may include at least one of elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy. The tin-based material may include at least one of elemental tin, tin oxide, and tin alloy. In this case, multiple negative electrode active materials may be mixed into the same slurry and coated onto the negative electrode current collector, resulting in a single-layer structure of negative electrode active material; alternatively, they may be prepared separately as slurries and coated onto the negative electrode current collector, resulting in a multi-layer structure of negative electrode active material.

[0116] Furthermore, the mass percentage ratio of the composite active material to the second active material is (9-1):1. The combined use of the composite active material and the second active material improves cycle performance and increases capacity performance. For example, the mass percentage ratio of the composite active material to the second active material is 9:1, 8:1, 7:1, 6:1, 5:1, 4:1, 3:1, 2:1, 1:1, or any range of two of these values.

[0117] In some embodiments, the negative electrode active material layer may optionally include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0118] In some embodiments, the negative electrode active material layer may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0119] In some embodiments, the negative electrode active material layer may also optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0120] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0121] [Positive electrode plate]

[0122] The positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector, the positive active material layer including a positive active material.

[0123] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive active material layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0124] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0125] In some embodiments, the positive electrode active material may be a known positive electrode active material for batteries. As an example, the positive electrode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05 At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0126] In some embodiments, the positive electrode active material layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0127] In some embodiments, the positive electrode active material layer may optionally include a conductive agent. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. 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 (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto a positive electrode current collector, and then performing processes such as drying and cold pressing to obtain the positive electrode sheet.

[0128] Electrolyte

[0129] Secondary batteries also include electrolytes.

[0130] During the charging and discharging process of a secondary battery, active ions repeatedly insert and extract between the positive and negative electrode plates, while the electrolyte acts as a conductor for these active ions. This application does not impose any particular restrictions on the type of electrolyte; it can be selected according to actual needs.

[0131] The electrolyte comprises an electrolyte salt and a solvent. The types of electrolyte salt and solvent are not specifically limited and can be selected according to actual needs.

[0132] As an example, the electrolyte salt may include, but is not limited to, at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0133] As an example, the solvent may include, but is not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl ester carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0134] In some embodiments, the electrolyte may optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, and additives that improve battery low-temperature power performance.

[0135] [Isolation membrane]

[0136] Secondary batteries also include a separator.

[0137] 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.

[0138] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0139] In some embodiments, the positive electrode, the separator, and the negative electrode can be fabricated into an electrode assembly using a winding process and / or a stacking process.

[0140] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0141] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic, such as at least one of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0142] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. Figure 2 This is an example of a square-structured secondary battery 5.

[0143] In some embodiments, such as Figure 3As shown, 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 enclosing a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 is used to cover 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 and / or a stacking process. The electrode assembly 52 is encapsulated in the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be adjusted according to requirements.

[0144] The method for preparing the secondary battery described in this application is well known. In some embodiments, a positive electrode, a separator, a negative electrode, and an electrolyte can be assembled to form a secondary battery. As an example, the positive electrode, separator, and negative electrode can be formed into an electrode assembly through a winding process and / or a stacking process. The electrode assembly is placed in an outer packaging, dried, and then injected with an electrolyte. After vacuum sealing, settling, formation, and shaping processes, a secondary battery is obtained.

[0145] In some embodiments of this application, the secondary battery according to this application can be assembled into a battery module. The number of secondary batteries contained in the battery module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module.

[0146] Figure 4 This is a schematic diagram of battery module 4 as an example. Figure 4 As shown, in battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary batteries 5 can be fixed in place using fasteners.

[0147] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0148] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0149] Figure 5 and Figure 6 This is a schematic diagram of battery pack 1 as an example. Figure 5 and Figure 6 As shown, the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3. The upper body 2 covers the lower body 3, forming a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0150] Electrical appliances

[0151] A third aspect of this application provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack described in this application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device or as an energy storage unit for the electrical device. The electrical device may be, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0152] The electrical device can be equipped with a secondary battery, battery module, or battery pack according to its usage requirements.

[0153] Figure 7 This is a schematic diagram of an example electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the device's requirements for high power and high energy density, a battery pack or battery module can be used.

[0154] Another example of an electrical device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use rechargeable batteries as their power source.

[0155] Example

[0156] The following embodiments describe the disclosure of this application in more detail. These embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on mass, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0157] Example

[0158] Example 1

[0159] 1. Preparation of negative electrode sheet

[0160] 1.1 Preparation of composite active materials

[0161] (1) Preparation of metal matrix particles with porous framework structure:

[0162] The base plating solution consisted of 0.4 mol / L copper sulfate and 1 mol / L sulfuric acid. Additives included polyethylene glycol (PEG) (80 mg / L), thiourea (10 mg / L), acetic acid (20 mg / L), and cetyltrimethylammonium bromide (CTAB) (15 mg / L). The working electrode was a copper-nickel alloy, and the current density was 1.5 to 2 A / cm². 2 The plating solution temperature is 20 to 70℃.

[0163] (2) Preparation of composite active materials

[0164] Nitrogen gas is introduced into the heating chamber. After the heating chamber is filled with nitrogen, silane gas is introduced into the heating chamber. The gas flow ratio of silane gas to protective gas is 5:1.

[0165] The heating chamber is heated to 600℃ and protected for 5 hours, while the vapor deposition furnace is kept under positive pressure; silane gas is decomposed into silicon nanoparticles and deposited in the pores of various framework structures.

[0166] After the heating chamber is heated to a suitable temperature, the silane gas supply is stopped, allowing the silicon nanoparticles to cool naturally. Nitrogen gas supply is then stopped, resulting in the composite active material. Figure 8 As shown, it displays a SEM image of the composite active material.

[0167] 1.2 Preparation of negative electrode sheet

[0168] The negative electrode active material (55% of the above-prepared composite material + 45% artificial graphite), conductive carbon black, thickener sodium carboxymethyl cellulose (CMC-Na), and binder styrene-butadiene rubber emulsion (SBR) are thoroughly mixed in an appropriate amount of deionized water at a weight ratio of 96.5:1.0:1.0:1.5 to form a uniform negative electrode slurry. The negative electrode slurry is coated onto the negative electrode current collector, and after drying and other processes, the negative electrode sheet is obtained.

[0169] 1.3 Preparation of the positive electrode sheet

[0170] LiNi, the positive electrode active material 0.98 Co 0.0125 Mn 0.0075 O2 (NCM98), conductive carbon black SP, carbon nanotubes SWCNT, and binder PVDF are dissolved in N-methylpyrrolidone (NMP) at a mass ratio of 96:2:0.6:0.2:1.2 and thoroughly mixed to prepare a positive electrode slurry. The positive electrode slurry is then uniformly coated onto the positive electrode current collector aluminum foil, followed by drying, cold pressing, and slitting to obtain the positive electrode sheet.

[0171] 1.4 Separating membrane

[0172] Polypropylene film is used.

[0173] 1.5 Preparation of Electrolyte

[0174] Ethyl carbonate (EC), methyl ethyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1. LiPF6 was then uniformly dissolved in this solution to obtain the electrolyte. The concentration of LiPF6 in the electrolyte was 1 mol / L.

[0175] 1.6 Preparation of Secondary Batteries

[0176] 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, and the electrolyte prepared above is added. After processes such as encapsulation, standing, formation, and aging, a secondary battery is obtained.

[0177] Examples 2-1 to 2-3

[0178] The secondary battery was prepared using a method similar to that of Example 1. The difference from Example 1 is that the average pore size of the metal matrix particles was adjusted in Examples 2-1 to 2-3.

[0179] Examples 3-1 and 3-2

[0180] Secondary batteries were prepared using a method similar to that of Example 1. The difference from Example 1 is that the pore volume of the metal matrix particles was adjusted in Examples 3-1 and 3-2.

[0181] Examples 4-1 and 4-2

[0182] The secondary battery was prepared using a method similar to that of Example 1. The difference from Example 1 is that the volume distribution particle size of the metal matrix particles was adjusted in Examples 4-1 and 4-2.

[0183] Examples 5-1 to 5-3

[0184] The secondary battery was prepared using a method similar to that of Example 1. The difference from Example 1 is that the average particle size of the silicon nanoparticles was adjusted in Examples 5-1 to 5-3.

[0185] Example 6

[0186] The secondary battery was prepared using a method similar to that of Example 1. However, unlike Example 1, Example 6 further deposited a carbon layer on the metal matrix particles via chemical vapor deposition. The specific preparation process of the composite active material is as follows:

[0187] Nitrogen gas is introduced into the heating chamber. After the heating chamber is filled with nitrogen, silane gas is introduced into the heating chamber. The gas flow ratio of silane gas to protective gas is 5:1.

[0188] The heating chamber is heated to 600℃ and protected for 5 hours, while the vapor deposition furnace is kept under positive pressure; silane gas is decomposed into silicon nanoparticles and deposited in the pores of various framework structures.

[0189] After the heating chamber is heated to a suitable temperature, the silane gas supply is stopped, allowing the silicon nanoparticles to cool naturally.

[0190] Methane gas is introduced into a heating chamber, and the chamber is heated. The methane gas decomposes into carbon and deposits on the surface and in the pores of the metal matrix particles, thus obtaining a composite active material.

[0191] Comparative Example 1

[0192] The secondary battery was prepared using a method similar to that of Example 1. The difference from Example 1 is that silicon nanoparticles were deposited on carbon particles in Comparative Example 1. The specific preparation process of the composite active material is as follows:

[0193] Nitrogen gas is introduced into the heating chamber. After the heating chamber is filled with nitrogen, silane gas is introduced into the heating chamber. The gas flow ratio of silane gas to protective gas is 5:1.

[0194] The heating chamber is heated to 600℃ and protected for 5 hours, while the vapor deposition furnace is kept under positive pressure; silane gas is decomposed into silicon nanoparticles and deposited in the pores of various framework structures.

[0195] After the heating chamber is heated to a certain temperature, the silane gas supply is stopped, allowing the silicon nanoparticles to cool naturally, thus obtaining the composite active material.

[0196] Comparative Example 2

[0197] The secondary battery was prepared using a method similar to that of Example 1. The difference from Example 1 is that Comparative Example 2 used nano-silicon as the negative electrode active material.

[0198] The data for the examples and comparative examples are shown in Table 1.

[0199] Test section

[0200] 1. Cycle performance of lithium-ion batteries

[0201] Loop count test:

[0202] The lithium-ion batteries prepared in the various examples and comparative examples were charged at a constant current rate of 0.5C to the charging cutoff voltage of 4.25V at 25°C. Then, they were charged at a constant voltage until the current ≤0.05C, allowed to stand for 5 minutes, and then discharged at a constant current rate of 0.33C to the discharge cutoff voltage of 2V, allowed to stand for 5 minutes. This constitutes one charge-discharge cycle. The batteries were subjected to cyclic charge-discharge tests according to this method until the battery capacity decreased to 80%. The number of cycles at this point is the cycle life of the battery at 25°C.

[0203] 2. Energy density of lithium-ion batteries

[0204] After the lithium-ion battery is shipped, it is charged at a constant current of 1C to 4.25V, then charged at a constant voltage of 0.05C, left to stand for 30 minutes, and then discharged at 1C to 2.8V. The discharge capacity D0 is recorded. The battery is weighed and the mass m0 of the positive electrode film of the lithium-ion battery is recorded. The energy density of the lithium-ion battery is D0 / m0 (capacity per unit mass).

[0205] Table 1

[0206]

[0207] As shown in Table 1, Comparative Example 1 uses a carbon skeleton structure. Due to the low strength of carbon particles and the low compaction density of the powder, they are easily crushed, resulting in limited improvement in the cycle performance and energy density of the secondary battery. Comparative Example 2 uses silicon nanoparticles as the negative electrode active material, thus achieving a higher energy density. However, due to their volume expansion, the structure becomes unstable, leading to poor cycle performance.

[0208] The embodiments of this application adopt a metal framework structure. After the metal matrix particles and silicon nanoparticles are combined, the conductivity of the negative electrode active material can be improved. Furthermore, due to the relatively high mechanical strength of the metal matrix particles, it can provide effective mechanical support for the silicon nanoparticles, while alleviating the volume effect of silicon during the lithium insertion / extraction process. It can also fully withstand the stress changes of the silicon nanoparticles, ensuring the structural stability of the negative electrode active material, improving the cycle stability and lithium storage capacity of the negative electrode active material, and improving the cycle performance and energy density of the secondary battery.

[0209] Although illustrative embodiments have been demonstrated and described, those skilled in the art should understand that the above embodiments should not be construed as limiting the present application, and that changes, substitutions and modifications can be made to the embodiments without departing from the spirit, principles and scope of the present application.

Claims

1. A composite active material, comprising: Metal matrix particles, the metal matrix particles having a porous framework structure; and Silicon nanoparticles, wherein the silicon nanoparticles are located within at least a portion of the pores of the porous framework structure. in, The average pore size of the porous framework structure is R, and its unit is nm, where 1≤R≤8; The average particle size of the silicon nanoparticles is D. Si Its unit is nm, 1≤D si ≤3.

2. The composite active material according to claim 1, wherein, 1≤R≤5。 3. The composite active material according to claim 1 or 2, wherein, The pore volume of the porous framework structure is V, and its unit is cm. 3 / g, 0.5≤V≤0.

8.

4. The composite active material according to claim 1, wherein, The BET specific surface area of ​​the metal matrix particles is S1, and its unit is m. 2 / g, 1000≤S1≤2000.

5. The composite active material according to claim 1, wherein, The volume distribution particle size Dv50 of the metal matrix particles is D1, with units of μm, and 3≤D1≤8.

6. The composite active material according to claim 1, wherein, The material of the metal matrix particles includes one or more of iron, nickel, and copper.

7. The composite active material according to claim 1, wherein, The silicon nanoparticles include one or more of silicon oxides, pre-lithiated silicon oxides, amorphous silicon, crystalline silicon, and silicon-carbon composites.

8. The composite active material according to claim 1, wherein, Based on the total mass of the composite active material, the mass percentage of the silicon nanoparticles is A%; based on the total mass of the composite active material, the mass percentage of the metal matrix particles is B%; and the composite active material satisfies: 0.4 ≤ A / B ≤ 1.

5.

9. The composite active material according to claim 8, wherein, 30≤A≤55; and / or 45≤B≤70.

10. The composite active material according to claim 1, wherein the composite active material further comprises a conductive layer, the conductive layer covering at least a portion of the surface of the metal matrix particles.

11. The composite active material according to claim 10, wherein the thickness of the conductive layer is H, and its unit is nm, 3≤H≤10.

12. The composite active material according to claim 10 or 11, wherein, The conductive layer includes a carbon layer and / or a conductive polymer layer.

13. The composite active material according to claim 12, wherein, The conductive polymer layer includes one or more of polyaniline, polypyrrole, polyacetylene, polythiophene, polyphenylene sulfide, and poly(p-phenylene).

14. The composite active material according to claim 1, wherein, The volume distribution particle size Dv50 of the composite active material is D2, with units of μm, and 2≤D2≤12; and / or The BET specific surface area of ​​the composite active material is S², and its unit is m². 2 / g, 800≤S2≤3000; and / or The porosity of the composite active material is P%, 0 < P ≤ 90.

15. A secondary battery, comprising a negative electrode, said negative electrode comprising a composite active material as described in any one of claims 1 to 14.

16. An electrical device comprising the secondary battery as described in claim 15.

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