Negative electrode active materials, secondary batteries and electrical equipment

Abstract

This application provides a negative electrode active material, a secondary battery, and an electrical device. The silicon-carbon negative electrode material includes a silicon-carbon composite material, which comprises a first silicon-carbon composite particle and a second silicon-carbon composite particle. The first silicon-carbon composite particle comprises a first carbon matrix with a porous structure and a first silicon-based material disposed within the porous structure of the first carbon matrix. The second silicon-carbon composite particle comprises a second carbon matrix with a porous structure and a second silicon-based material disposed within the porous structure of the second carbon matrix. Furthermore, the mass percentage of silicon in the first silicon-carbon composite particle is greater than the mass percentage of silicon in the second silicon-carbon composite particle. This silicon-carbon negative electrode material exhibits both high specific capacity and good cycle stability, thereby improving the energy density and cycle performance of the battery.

Description

Technical Field

[0001] This application relates to the field of lithium battery technology, and in particular to a negative electrode active material, a secondary battery, and an electrical device. Background Technology

[0002] In recent years, with the increasingly widespread application of batteries, represented by lithium-ion batteries, they have been 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 vehicles, military equipment, aerospace, and many other fields. Due to the significant advancements in battery technology, higher requirements have been placed on their energy density, cycle performance, and safety performance. Silicon-based anode materials, due to their high specific capacity, are considered the best choice for meeting high energy density requirements.

[0003] However, silicon-based anode materials have a large volume expansion rate and poor cycle stability during cycling, which leads to a decrease in battery cycle performance. Therefore, silicon-based anode materials need further improvement. Summary of the Invention

[0004] This application provides a negative electrode active material, a secondary battery, and an electrical device. The silicon-carbon negative electrode material has both high specific capacity and good cycle stability.

[0005] In a first aspect, this application provides a negative electrode active material, comprising a silicon-carbon composite material, wherein the silicon-carbon composite material comprises a first silicon-carbon composite particle and a second silicon-carbon composite particle; the first silicon-carbon composite particle comprises a first carbon matrix having a porous structure and a first silicon-based material disposed in the porous structure of the first carbon matrix; the second silicon-carbon composite particle comprises a second carbon matrix having a porous structure and a second silicon-based material disposed in the porous structure of the second carbon matrix; and the mass percentage content of silicon in the first silicon-carbon composite particle is greater than the mass percentage content of silicon in the second silicon-carbon composite particle.

[0006] According to this application, the negative electrode active material includes a silicon-carbon composite material, comprising two silicon-carbon composite particles with different silicon contents. The first silicon-carbon composite particle with a higher silicon content is beneficial to improving the specific capacity of the silicon-carbon negative electrode material, while the second silicon-carbon composite particle with a lower silicon content is beneficial to improving the cycle stability of the silicon-carbon negative electrode material. The two work together to enable the silicon-carbon composite material to have both high specific capacity and good cycle stability, thereby improving the energy density and cycle performance of the battery.

[0007] In some embodiments, the mass percentage of silicon in the first silicon-carbon composite particles is ≥50%, optionally 50%-60%; and / or, the mass percentage of silicon in the second silicon-carbon composite particles is ≤47%, optionally 38%-47%. In this case, the silicon-carbon composite material as a whole has higher specific capacity and better cycle stability.

[0008] In some embodiments, the mass percentage of silicon in the first silicon-carbon composite particle is denoted as ω1, and the mass percentage of silicon in the second silicon-carbon composite particle is denoted as ω2. The negative electrode active material satisfies: 1.06 ≤ ω1 / ω2 ≤ 1.6, which can be selected as 1.1-1.3. In this case, the silicon-carbon composite material as a whole has higher specific capacity and better cycle stability.

[0009] In some embodiments, the first carbon matrix includes a microporous structure, wherein the pore volume of the microporous structure in the first carbon matrix is ​​V1 ≥ 0.6 cm³. 3 / g, can be selected as 0.6-0.75cm 3 / g; and / or, the second carbon matrix includes a microporous structure, wherein the pore volume of the microporous structure in the second carbon matrix is ​​V² ≥ 0.4 cm³. 3 / g, can be selected as 0.5-0.7cm 3 / g. At this point, the first silicon-carbon composite particles and / or the second silicon-carbon composite particles exhibit better cycle stability, which can further improve the overall cycle stability of the silicon-carbon composite material and further improve the cycle performance of the battery.

[0010] In some embodiments, both the first carbon matrix and the second carbon matrix include microporous structures, and the pore volume of the microporous structures in the first carbon matrix is ​​greater than the pore volume of the microporous structures in the second carbon matrix. The first and second silicon-carbon composite particles exhibit better cycle stability, further improving the overall cycle stability of the silicon-carbon composite material and thus further enhancing the cycle performance of the battery.

[0011] In some embodiments, the average pore size of the pore structure in the first carbon matrix is ​​d1≤5nm, optionally 1-4nm; and / or, the average pore size of the pore structure in the second carbon matrix is ​​d2≤10nm, optionally 3-5nm. Suitable pore sizes help reduce the volume change rate of the first silicon-carbon composite particles and / or the second silicon-carbon composite particles, resulting in better cycle stability and further improving the overall cycle stability of the silicon-carbon composite material, thus further improving the cycle performance of the battery.

[0012] In some embodiments, the average pore size of the pore structure in the first carbon matrix is ​​smaller than the average pore size of the pore structure in the second carbon matrix. In this case, the first silicon-carbon composite particles have better cycle stability, and the second silicon-carbon composite particles can reserve a larger expandable space, which can further improve the overall cycle stability of the silicon-carbon composite material and further improve the cycle performance of the battery.

[0013] In some embodiments, the specific surface area of ​​the first carbon matrix is ​​BET1≥1800m². 2 / g, selectable as 1800-2000m 2 / g; and / or, the specific surface area of ​​the second carbon matrix is ​​BET2≥1600m². 2 / g, selectable as 1600-1800m 2 / g. At this point, the porous structure of the first carbon matrix and / or the second carbon matrix can accommodate more silicon-based materials, and the cycle stability of the first silicon-carbon composite particles and the second silicon-carbon composite particles is better, which can further improve the overall cycle stability of the silicon-carbon composite material and further improve the cycle performance of the battery.

[0014] In some embodiments, the specific surface area of ​​the first carbon matrix is ​​greater than that of the second carbon matrix. In this case, the first silicon-carbon composite particles have better cycle stability, and the structure of the second silicon-carbon composite particles is more stable, which can further improve the overall cycle stability of the silicon-carbon composite material and further improve the cycle performance of the battery.

[0015] In some embodiments, based on the silicon-carbon composite material, the mass content of the first silicon-carbon composite particles is less than the mass content of the second silicon-carbon composite particles. In this case, the overall cycle stability of the silicon-carbon composite material is further improved, thus enhancing the cycle performance of the battery.

[0016] In some embodiments, based on the silicon-carbon composite material, the mass content of the first silicon-carbon composite particles is ≤10%, optionally 0.1%-5%; and / or, based on the silicon-carbon composite material, the mass content of the second silicon-carbon composite particles is ≥80%, optionally 80%-99.8%. In this case, the overall cycle stability of the silicon-carbon composite material further improves the cycle performance of the battery.

[0017] In some embodiments, at least a portion of the surface of the first silicon-carbon composite particles and / or the second silicon-carbon composite particles has a coating layer, optionally a carbon coating layer. In this case, the side reactions between the first and / or second silicon-carbon composite particles and the electrolyte are reduced, the overall cycle stability of the silicon-carbon composite material is better, and the initial efficiency and cycle performance of the battery are further improved.

[0018] In some embodiments, the silicon-carbon composite material further includes third silicon-carbon composite particles. These third silicon-carbon composite particles comprise a third carbon matrix with a porous structure and a third silicon-based material disposed within the porous structure of the third carbon matrix. The mass percentage of silicon in the third silicon-carbon composite particles is less than the mass percentage of silicon in the first silicon-carbon composite particles, and the mass percentage of silicon in the third silicon-carbon composite particles is less than the mass percentage of silicon in the second silicon-carbon composite particles. The third silicon-carbon composite particles can further improve the overall cycle stability of the silicon-carbon composite material and further improve the cycle performance of the battery.

[0019] In some embodiments, the silicon-carbon composite material further includes third silicon-carbon composite particles. The first silicon-carbon composite particles comprise a third carbon matrix with a porous structure and a third silicon-based material disposed within the porous structure of the third carbon matrix. The average pore size of the porous structure in the third carbon matrix is ​​smaller than the average pore size of the porous structure in the first carbon matrix, and the average pore size of the porous structure in the third carbon matrix is ​​smaller than the average pore size of the porous structure in the second carbon matrix. This improves the processing performance of the silicon-carbon composite material, increases the compaction density of the negative electrode sheet, and is beneficial for improving the energy density of the battery.

[0020] In some embodiments, the silicon-carbon composite material further includes third silicon-carbon composite particles. The first silicon-carbon composite particles comprise a third carbon matrix with a porous structure and a third silicon-based material disposed within the porous structure of the third carbon matrix. The specific surface area of ​​the third carbon matrix is ​​smaller than that of the first carbon matrix, and the specific surface area of ​​the third carbon matrix is ​​smaller than that of the second carbon matrix. This improves the processing performance of the silicon-carbon composite material, increases the compaction density of the negative electrode sheet, and is beneficial for improving the energy density of the battery.

[0021] In some embodiments, the third silicon-carbon composite particles satisfy at least one of the following conditions: 1) the mass percentage of silicon in the third silicon-carbon composite particles is ≤25%, optionally 20%-25%; 2) the average pore size of the pore structure in the third carbon matrix is ​​d3≤4nm, optionally 1-3nm; 3) the third carbon matrix contains micropores with a pore size <2nm, wherein the percentage of micropore volume to total pore volume p is ≥60%, optionally 70%-85%; 4) the powder compaction density of the third carbon matrix under 49000N pressure is 0.4-1.1g / cm³. 3 The preferred concentration is 0.4-0.8 g / cm³. 3 ;5) The specific surface area BET3 of the third carbon matrix is ​​≥1000m² 2 / g, preferably 1000-1300m 2 / g. At this point, the battery's energy density and cycle performance are better.

[0022] In some embodiments, at least one of the first silicon-based material, the second silicon-based material, or the third silicon-based material includes silicon grains; optionally, the grain size of the silicon grains is less than or equal to 10 nm. In this case, the volume change rate of the first silicon-carbon composite particles, the second silicon-carbon composite particles, or the third silicon-carbon composite particles is smaller, the overall cycle stability of the silicon-carbon composite material is better, and the cycle performance of the battery is further improved.

[0023] In some embodiments, the silicon-carbon composite material satisfies at least one of the following conditions: 1) the specific surface area of ​​the silicon-carbon composite material is less than or equal to 6 m². 2 / g, optional ≤4m 2 1) The volume average particle size (Dv50) of the silicon-carbon composite material is 5-15 μm, optionally 5-10 μm; 2) Based on the total mass of the silicon-carbon composite material, the mass percentage content of silicon in the silicon-carbon composite material is 35%-50%, optionally 40%-50%; 3) The porosity of the silicon-carbon composite material is 45%-65%, optionally 45%-55%; 4) The powder compaction density of the silicon-carbon composite material under a pressure of 49000 N is 0.8-1.2 g / cm³. 3 The concentration can be selected as 0.9-1.1 g / cm³. 3 6) The tap density of the silicon-carbon composite material is 0.6-1.0 g / cm³. 3 The concentration can be selected as 0.7-0.9 g / cm³. 3 7) The powder resistivity of the silicon-carbon composite material is ≤5Ω·cm, and can be selected as ≤3Ω·cm; 8) The (Dv90-Dv10) / Dv50 of the silicon-carbon composite material is ≤5, and can be selected as ≤2.5. At this point, the battery has better energy density and cycle performance.

[0024] In a second aspect, this application provides a secondary battery, including a negative electrode sheet, the negative electrode sheet including a negative current collector and a negative electrode film layer, the negative electrode film layer including a negative electrode active material, the negative electrode active material including the silicon-carbon composite material described in any embodiment of the first aspect.

[0025] Thirdly, this application provides an electrical device including the secondary battery described in the second aspect. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of a battery cell according to one embodiment of this application.

[0027] Figure 2 yes Figure 1 An exploded view of a battery cell according to one embodiment of this application is shown.

[0028] Figure 3This is a schematic diagram of a battery module according to one embodiment of this application.

[0029] Figure 4 This is a schematic diagram of a battery according to one embodiment of this application.

[0030] Figure 5 yes Figure 4 An exploded view of a battery according to one embodiment of this application is shown.

[0031] Figure 6 This is a schematic diagram of an electrical device in which a single battery cell is used as a power source according to one embodiment of this application.

[0032] Explanation of reference numerals in the attached figures:

[0033] 1. Secondary battery; 2. Upper casing; 3. Lower casing; 4. Battery module; 5. Battery cell; 51. Housing; 52. Electrode assembly; 53. Top cover assembly. Detailed Implementation

[0034] The following detailed description, with appropriate reference to the accompanying drawings, specifically discloses embodiments of the silicon-carbon anode material, anode sheet, battery, and electrical device 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.

[0035] 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.

[0036] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0037] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0038] 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.

[0039] As described in the background section above, silicon-based anode materials have high specific capacity, but their volume expansion rate during cycling is large, resulting in poor cycle stability and deteriorating battery cycle performance.

[0040] In response, related technologies use a blend of silicon-based anode materials and carbon-based anode materials with good cycle stability as the anode material, or a direct composite of silicon-based anode materials and carbon-based anode materials as the anode material. However, the problem is that as the silicon content in the above-mentioned anode materials increases, the cycle performance of the battery also decreases, making it difficult to obtain a battery that simultaneously achieves good energy density and cycle performance.

[0041] Based on this, this application provides a negative electrode active material with high specific capacity and cycle stability, which can effectively improve the energy density and cycle performance of batteries when applied in batteries. The specific embodiments of this application are described in detail below.

[0042] Negative electrode active materials

[0043] In a first aspect, this application provides a negative electrode active material, including a silicon-carbon composite material, which includes a first silicon-carbon composite particle and a second silicon-carbon composite particle; the first silicon-carbon composite particle includes a first carbon matrix with a porous structure and a first silicon-based material disposed in the porous structure of the first carbon matrix; the second silicon-carbon composite particle includes a second carbon matrix with a porous structure and a second silicon-based material disposed in the porous structure of the second carbon matrix; and the mass percentage content of silicon in the first silicon-carbon composite particle is greater than the mass percentage content of silicon in the second silicon-carbon composite particle.

[0044] According to this application, the negative electrode active material includes a silicon-carbon composite material, which comprises two types of silicon-carbon composite particles with different silicon contents. Both types of silicon-carbon composite particles include a carbon matrix and silicon-based material disposed within the porous structure of the carbon matrix. It is understood that although the silicon-based material exhibits a large volume change rate during charge and discharge, the porous structure of the carbon matrix can limit the impact of its volume change on the overall volume of the silicon-carbon composite particles. Therefore, the two types of silicon-carbon composite particles have a smaller volume change rate, resulting in better cycle stability and improved battery cycle performance. Furthermore, the two types of silicon-carbon composite particles have different mass percentages of silicon. The first silicon-carbon composite particle... The first silicon-carbon composite particle has a higher mass percentage of silicon than the second silicon-carbon composite particle, resulting in a higher specific capacity and thus improving the overall specific capacity of the silicon-carbon composite material. The second silicon-carbon composite particle has a smaller volume change rate during charge and discharge. When the two are used together, space can be reserved for the volume change of the first silicon-carbon composite particle, thereby reducing the compression between particles during charge and discharge and alleviating particle breakage caused by volume expansion. This effectively improves the overall cycle stability of the silicon-carbon composite material. Therefore, using this silicon-carbon composite material as the negative electrode active material can improve the energy density and cycle performance of the battery.

[0045] It should also be noted that the first silicon-carbon composite particle and the second silicon-carbon composite particle are two different types of silicon-carbon composite particles. Although they are distinguished only by their silicon content, generally speaking, in silicon-carbon composite materials, the difference between the mass percentage of silicon in the first silicon-carbon composite particle and the mass percentage of silicon in the second silicon-carbon composite particle is not less than 0.5%. Prior to this application, silicon-carbon composite particles have been used as negative electrode active materials. However, usually, one type of silicon-carbon composite particle is used as the negative electrode active material. Silicon-carbon composite particles with a certain silicon content can be prepared by known methods (such as chemical vapor deposition). Although the silicon content of the silicon-carbon composite particles prepared under the same conditions may still have some differences, the differences are small and not enough to distinguish them as two different types of silicon-carbon composite particles, and therefore cannot meet the requirements of the embodiments of this application.

[0046] In some embodiments, the mass percentage of silicon in the first silicon-carbon composite particles is ≥50%; and / or, the mass percentage of silicon in the second silicon-carbon composite particles is ≤47%.

[0047] In some of the above embodiments, the mass percentage of silicon in the first silicon-carbon composite particles is not less than 50%, meaning that the first silicon-carbon composite particles have a higher specific capacity, which is beneficial for further improving the energy density of the battery. For example, the mass percentage of silicon in the first silicon-carbon composite particles can be 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, or any of the above values. Furthermore, the mass percentage of silicon in the first silicon-carbon composite particles can be 50%-60%. In this case, the first silicon-carbon composite particles have better stability and are less prone to breakage during charge and discharge, which can further improve the cycle stability of the silicon-carbon composite material and further improve the cycle performance of the battery.

[0048] The silicon content in the second silicon-carbon composite particles does not exceed 47% by mass. At this level, the volume change rate of the second silicon-carbon composite particles during charge and discharge is relatively small, allowing more space to accommodate the volume changes of the first silicon-carbon composite particles. This alleviates the mutual compression of the silicon-carbon composite materials during charge and discharge, thereby improving the overall cycle stability of the silicon-carbon composite material and further enhancing the cycle performance of the battery. For example, the silicon content in the second silicon-carbon composite particles can be 47%, 46%, 45%, 44%, 43%, 42%, 41%, 40%, 39%, 38%, 37%, 36%, 35%, or any value within the range mentioned above. Furthermore, the silicon content in the second silicon-carbon composite particles can be between 38% and 47% by mass. At this level, the second silicon-carbon composite particles have a higher specific capacity, which is beneficial for improving the energy density of the battery.

[0049] In some embodiments, the mass percentage of silicon in the first silicon-carbon composite particle is denoted as ω1, the mass percentage of silicon in the second silicon-carbon composite particle is denoted as ω2, and the negative electrode active material satisfies: 1.06≤ω1 / ω2≤1.6.

[0050] In some of the above embodiments, the relationship between the mass percentage of silicon in the first and second silicon-carbon composite particles is further defined. It is understood that in the silicon-carbon composite material, the two types of silicon-carbon composite particles work synergistically to achieve a balance between high specific capacity and cycle stability. When the negative electrode active material satisfies 1.06 ≤ ω1 / ω2 ≤ 1.6, the mutual compression forces between the two particles during charging and discharging can be further mitigated, thus ensuring particle stability. Simultaneously, the silicon-carbon composite material maintains a high specific capacity, further improving the battery's energy density and cycle performance. For example, ω1 / ω2 can be 1.06, 1.1, 1.15, 1.2, 1.25, 1.3, 1.35, 1.4, 1.45, 1.5, 1.55, 1.6, or any value within the range described above. Furthermore, ω1 / ω2 can be between 1.1 and 1.3, in which case the silicon-carbon composite material exhibits even higher specific capacity and better cycle stability, resulting in better energy density and cycle performance of the battery.

[0051] In some embodiments, the first carbon matrix includes a microporous structure, wherein the pore volume of the microporous structure in the first carbon matrix is ​​V1 ≥ 0.6 cm³. 3 / g; and / or, the second carbon matrix includes a microporous structure, wherein the pore volume of the microporous structure in the second carbon matrix is ​​V² ≥ 0.4 cm³. 3 / g, can be selected as 0.5-0.7cm 3 / g.

[0052] In some of the above embodiments, the first carbon matrix includes a microporous structure, and the pore volume of the microporous structure is V1 ≥ 0.6 cm³. 3 / g, as understood, refers to micropores, which are pores with a diameter less than 2 nm, according to well-known principles in the field. Based on pore size, these pores can be further classified as mesopores and macropores, with mesopores having a diameter of 2-50 nm and macropores having a diameter greater than 50 nm. In microporous structures, the particle size of the first silicon-based material is smaller. Smaller particle sizes result in a smaller volume change rate during charge and discharge. Therefore, a larger pore volume in the microporous structure leads to better cycle stability of the first silicon-carbon composite particles, further improving the overall cycle stability of the silicon-carbon composite material and resulting in better battery cycle performance. For example, the pore volume V1 of the microporous structure in the first carbon matrix can be 0.6 cm³. 3 / g, 0.62cm 3 / g, 0.64cm 3 / g, 0.65cm 3 / g, 0.67cm 3 / g, 0.69cm 3 / g, 0.7cm 3 / g, 0.72cm 3 / g, 0.74cm 3 / g, 0.75cm 3 / g, 0.77cm 3 / g, 0.8cm 3 / g, or any of the values ​​mentioned above. Furthermore, the pore volume V1 of the microporous structure in the first carbon matrix can be 0.6-0.75 cm³. 3 / g, at this time, more first silicon-based material is set in the microporous structure, the first silicon-carbon composite particles have better cycle stability, the silicon-carbon composite material as a whole has better cycle stability, and further improves the cycle performance of the battery.

[0053] Similarly, the second carbon matrix includes a microporous structure, and the pore volume of the microporous structure in the second carbon matrix is ​​V² ≥ 0.4 cm³. 3 At a density of / g, the first silicon-carbon composite particles exhibit better cycle stability, further improving the overall cycle stability of the silicon-carbon composite material and resulting in better battery cycle performance. For example, the pore volume V2 of the microporous structure in the second carbon matrix can be 0.4 cm³. 3 / g, 0.42cm 3 / g, 0.45cm 3 / g, 0.48cm 3 / g, 0.5cm 3 / g, 0.52cm 3 / g, 0.55cm 3 / g, 0.58cm 3 / g, 0.6cm 3 / g, 0.62cm 3 / g, 0.65cm 3 / g, 0.69cm 3 / g, 0.7cm 3 / g, 0.72cm 3 / g, 0.74cm 3 / g, 0.75cm 3 / g, or any of the values ​​mentioned above. Furthermore, the pore volume V2 of the microporous structure in the second carbon matrix can be 0.5-0.7 cm³. 3 / g, at which point the silicon-carbon composite material exhibits better overall cycle stability, further improving the cycle performance of the battery.

[0054] In some embodiments, both the first carbon matrix and the second carbon matrix include microporous structures, and the pore volume of the microporous structures in the first carbon matrix is ​​greater than the pore volume of the microporous structures in the second carbon matrix.

[0055] In some of the above embodiments, both the first carbon matrix and the second carbon matrix include microporous structures. In this case, both the first silicon-carbon composite particles and the second silicon-carbon composite particles have good cycle stability. At the same time, the silicon content in the first silicon-carbon composite particles is higher than that in the second silicon-carbon composite particles, requiring a larger pore volume of the microporous structure to accommodate the silicon-based material within the microporous structure, thereby improving the cycle stability of the silicon-carbon composite particles. Thus, the pore volume of the microporous structure in the first carbon matrix is ​​greater than that in the second carbon matrix, which can further improve the overall cycle stability of the silicon-carbon composite material and further improve the cycle performance of the battery.

[0056] In some embodiments, the average pore size of the pore structure in the first carbon matrix is ​​d1≤5nm, which may be 1-4nm; and / or, the average pore size of the pore structure in the second carbon matrix is ​​d2≤10nm, which may be 3-5nm.

[0057] In some of the above embodiments, the average pore size d1 of the pore structure in the first carbon matrix does not exceed 5 nm. It is understood that the smaller the average pore size of the pore structure in the first carbon matrix, the smaller the average particle size of the first silicon-based material within the pore structure. This results in a smaller volume change rate of the first silicon-based material during charge and discharge, and better cycle stability of the first silicon-carbon composite particles. This further improves the overall cycle stability of the silicon-carbon composite material and the cycle performance of the battery. For example, the average pore size d1 of the pore structure in the first carbon matrix can be 5 nm, 4.5 nm, 4 nm, 3.5 nm, 3 nm, 2.5 nm, 2 nm, 1.5 nm, 1 nm, or any value within the range described above. Furthermore, the average pore size d1 of the pore structure in the first carbon matrix can be 1-4 nm. In this case, the cycle stability of the first silicon-carbon composite particles is even better, and the silicon-carbon composite material as a whole has better cycle stability, further improving the cycle performance of the battery.

[0058] Similarly, the average pore size d2 of the pore structure in the second carbon matrix does not exceed 10 nm. In this case, the volume change rate of the second silicon-based material during charge and discharge is smaller, and the cycle stability of the second silicon-carbon composite particles is better, which can further improve the overall cycle stability of the silicon-carbon composite material and further improve the cycle performance of the battery. For example, the average pore size d2 of the pore structure in the second carbon matrix can be 10 nm, 9.5 nm, 9 nm, 8.5 nm, 8 nm, 7.5 nm, 7 nm, 6.5 nm, 6 nm, 5.5 nm, 5 nm, 4.5 nm, 4 nm, 3.5 nm, 3 nm, or any value within the range of the above. Furthermore, the average pore size d2 of the pore structure in the second carbon matrix can be 3-4 nm. In this case, the cycle stability of the second silicon-carbon composite particles is even better, and the silicon-carbon composite material as a whole has better cycle stability, further improving the cycle performance of the battery.

[0059] In some embodiments, the average pore size of the pore structure in the first carbon matrix is ​​smaller than the average pore size of the pore structure in the second carbon matrix.

[0060] In some of the above embodiments, since the mass percentage of silicon in the first silicon-carbon composite particles is higher than that in the first silicon-carbon composite particles, the volume change rate of the first silicon-carbon composite particles can be reduced by further reducing the average pore size of the pore structure of the first carbon matrix, thereby improving its cycle stability. At the same time, it is understood that the second carbon matrix with a larger average pore size is less prone to cracking during extrusion, thus better adapting to the volume expansion of the first silicon-carbon composite particles, which can further improve the overall cycle stability of the silicon-carbon composite material and further improve the cycle performance of the battery.

[0061] In some embodiments, the specific surface area of ​​the first carbon matrix is ​​BET1≥1800m². 2 / g, selectable as 1800-2000m 2 / g; and / or, the specific surface area of ​​the second carbon matrix is ​​BET2≥1600m². 2 / g, selectable as 1600-1800m 2 / g.

[0062] In some of the above embodiments, the specific surface area BET1 of the first carbon matrix can be not less than 1800 m². 2 / g, at this point, the porous structure of the first carbon matrix has sufficient space to accommodate more of the first silicon-based material. The particle size of the first silicon-based material within the porous structure is limited, and the volume expansion of the first silicon-based material also restricts its impact on the first silicon-carbon composite particles. This results in the first silicon-carbon composite particles exhibiting both high specific capacity and better cycle stability. For example, the specific surface area BET1 of the first carbon matrix can be 1800-1800 m². 2 / g, 1850m 2 / g, 1900m 2 / g, 1950m 2 / g, 2000m 2 / g, 2050m 2 / g, 2100m 2 / g, 2200m 2 / g, 2300m 2 / g, 2400m 2 / g, or any of the values ​​mentioned above. Furthermore, the specific surface area BET1 of the first carbon matrix can be 1800-2000 m². 2 / g, at this point the first silicon-carbon composite particles have better cycle stability, the overall cycle stability of the silicon-carbon composite material is better, and the cycle performance of the battery is further improved.

[0063] Similarly, the specific surface area BET2 of the second carbon matrix can be no less than 1600 m². 2 / g, at this point, the second silicon-carbon composite particles exhibit better cycle stability, and the overall cycle stability of the silicon-carbon composite material is better, further improving the cycle performance of the battery. For example, the specific surface area BET2 of the second carbon matrix can be 1600m². 2 / g, 1650m 2 / g, 1700m 2 / g, 1750m 2 / g, 1800m 2 / g, 1850m 2 / g, 1900m 2 / g, 2000m 2 / g, 2100m 2 / g, 2200m 2 / g, or within any range of the above values. Preferably, the specific surface area BET2 of the second carbon matrix can be 1600-1800 m². 2 / g, at this point the second silicon-carbon composite particles have better cycle stability, the overall cycle stability of the silicon-carbon composite material is better, and the cycle performance of the battery is further improved.

[0064] In some embodiments, the specific surface area of ​​the first carbon matrix is ​​greater than that of the second carbon matrix.

[0065] In some of the above embodiments, the mass percentage of silicon in the first silicon-carbon composite particle is higher than that in the second silicon-carbon composite particle. The larger specific surface area of ​​the first carbon matrix is ​​conducive to the placement of silicon-based materials in the porous structure, thereby giving the first silicon-carbon composite particle better cycle stability. The smaller specific surface area of ​​the second carbon matrix is ​​conducive to improving the structural stability of the second silicon-carbon composite particle. In this case, the overall cycle stability of the silicon-carbon composite material is better, further improving the cycle performance of the battery.

[0066] In some embodiments, based on silicon-carbon composite materials, the mass content of the first silicon-carbon composite particles is ≤10%, optionally 0.1%-5%; and / or, based on silicon-carbon composite materials, the mass content of the second silicon-carbon composite particles is ≥80%, optionally 80%-99.8%.

[0067] In some of the above embodiments, the mass content of the first silicon-carbon composite particles does not exceed 10%. Due to its high silicon content, it exhibits a larger volume expansion rate during charge and discharge. This results in better overall cycle stability of the silicon-carbon composite particles and can improve the overall specific capacity to a certain extent, better balancing the battery's energy density and cycle performance. For example, the mass content of the first silicon-carbon composite particles can be 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.1%, or any of the above values. Furthermore, the mass content of the first silicon-carbon composite particles can be 0.1%-5%, which further improves the overall cycle stability of the silicon-carbon composite material and enhances the battery's cycle performance.

[0068] The second silicon-carbon composite particle has a mass content of not less than 80%. Due to its relatively low silicon content, it exhibits a smaller volume expansion rate during charge and discharge, making it suitable as the main material for the silicon-carbon composite material. It also better adapts to changes in the volume of the first silicon-carbon composite particle, improving the overall cycle stability of the silicon-carbon composite material and further enhancing the battery's cycle performance. For example, the mass content of the second silicon-carbon composite particle can be 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, 99.8%, or any value within the range described above. Furthermore, the mass content of the second silicon-carbon composite particle can be between 80% and 99.8%, resulting in even better overall cycle stability of the silicon-carbon composite material and further improving the battery's cycle performance.

[0069] In some embodiments, at least a portion of the surface of the first silicon-carbon composite particle and / or the second silicon-carbon composite particle has a coating layer.

[0070] In some of the above embodiments, at least a portion of the surface of the first silicon-carbon composite particles and / or the second silicon-carbon composite particles has a coating layer. This coating layer on the surface can reduce the specific surface area of ​​the carbon matrix, reduce side reactions with the electrolyte, and further improve the battery's initial efficiency and cycle performance. It should be noted that carbon coating of the first and / or second silicon-carbon composite particles will reduce the mass percentage of silicon in the first silicon-carbon composite particle to some extent, but the impact is small and will not significantly change the mass percentage of silicon in the silicon-carbon composite particle. Furthermore, the coating layer is a carbon coating layer, which has good conductivity and stability and will not significantly affect the electrical properties of the silicon-carbon composite material.

[0071] In some embodiments, the silicon-carbon composite material further includes third silicon-carbon composite particles, which include a third carbon matrix with a porous structure and a third silicon-based material disposed in the porous structure of the third carbon matrix. The mass percentage of silicon in the third silicon-carbon composite particles is less than the mass percentage of silicon in the first silicon-carbon composite particles, and the mass percentage of silicon in the third silicon-carbon composite particles is less than the mass percentage of silicon in the second silicon-carbon composite particles.

[0072] In some of the above embodiments, the silicon-carbon composite material also includes a third silicon-carbon composite particle, wherein the mass percentage of silicon element is less than that of the first and second silicon-carbon composite particles. Therefore, its volume change rate is smaller during charging and discharging. In the mixed system of silicon-carbon composite materials, more space can be reserved for the expansion of silicon-carbon composite particles, thereby alleviating the compression between composite particles, further improving the overall cycle stability of silicon-carbon composite materials, and thus improving the cycle performance and energy density of the battery.

[0073] In some embodiments, the silicon-carbon composite material further includes a third silicon-carbon composite particle, wherein the first silicon-carbon composite particle includes a third carbon matrix having a porous structure and a third silicon-based material disposed in the porous structure of the third carbon matrix, wherein the average pore size of the porous structure in the third carbon matrix is ​​smaller than the average pore size of the porous structure in the first carbon matrix, and the average pore size of the porous structure in the third carbon matrix is ​​smaller than the average pore size of the porous structure in the second carbon matrix.

[0074] In some of the above embodiments, the average pore size of the pore structure in the third carbon matrix is ​​smaller than the average pore size of the pore structure in the first and second carbon matrices. The smaller average pore size allows the third carbon matrix to have higher strength, improving the overall processability of the silicon-carbon composite material, reducing the likelihood of cracking during production, and increasing the compaction density of the negative electrode sheet, thereby improving the energy density of the battery. Furthermore, the higher strength and lower volume expansion rate also improve the overall cycle stability of the silicon-carbon composite material, thus improving the cycle performance of the battery.

[0075] In some embodiments, the silicon-carbon composite material further includes third silicon-carbon composite particles. The first silicon-carbon composite particles include a third carbon matrix with a porous structure and a third silicon-based material disposed in the porous structure of the third carbon matrix. The specific surface area of ​​the third carbon matrix is ​​smaller than that of the first carbon matrix, and the specific surface area of ​​the third carbon matrix is ​​smaller than that of the second carbon matrix.

[0076] In some of the above embodiments, the specific surface area of ​​the third carbon matrix is ​​smaller than that of the first carbon matrix and the second carbon matrix. Since the mass percentage of silicon in the third silicon-carbon composite particles is relatively smaller than that in the first and second silicon-carbon composite particles, the specific surface area of ​​the third carbon matrix can be appropriately reduced. The smaller specific surface area can improve the strength of the third silicon-carbon composite particles, thereby improving the processing performance of the silicon-carbon composite material, increasing the compaction density of the negative electrode sheet, and thus improving the energy density of the battery.

[0077] In some embodiments, the mass percentage of silicon in the third silicon-carbon composite particles is ≤25%, optionally 20-25%. This results in a smaller volume change rate during charge-discharge, further improving the overall cycle stability of the silicon-carbon composite material. For example, the mass percentage of silicon in the third silicon-carbon composite particles can be 25%, 24%, 23%, 22%, 21%, 20%, 19%, 18%, 17%, 16%, 15%, 14%, 13%, 12%, 11%, 10%, or any of the above values. Furthermore, the mass percentage of silicon in the third silicon-carbon composite particles can be 20%-25%, which better balances the overall specific capacity of the silicon-carbon composite material, thus improving the battery's energy density.

[0078] In some embodiments, the average pore size of the mesoporous structure in the third carbon matrix is ​​d3 ≤ 4 nm, and can be selected as 1-3 nm. In this case, the third silicon-carbon composite particles have high strength, which gives the silicon-carbon composite material good overall processability, improves the compaction density of the negative electrode sheet, and thus increases the energy density of the battery. Simultaneously, the smaller pore size helps limit the volume expansion of the third silicon-based material, thus giving the third silicon-carbon composite particles good cycle stability, thereby improving the overall cycle stability of the silicon-carbon composite material and improving the battery cycle performance. For example, the average pore size d3 of the mesoporous structure in the third carbon matrix can be 4 nm, 3.5 nm, 3 nm, 2.5 nm, 2 nm, 1.5 nm, 1 nm, or any value within the range described above. Furthermore, the average pore size of the mesoporous structure in the third carbon matrix can be 1-3 nm, which can further improve the energy density and cycle performance of the battery.

[0079] In some embodiments, the third carbon matrix comprises micropores with a pore size < 2 nm, wherein the percentage p of the micropore volume to the total pore volume is ≥ 60%, optionally 70%-85%. Since the micropores do not significantly reduce the strength of the particles, the third silicon-carbon composite material retains high porosity while also possessing high strength, which can alleviate the cracking of the silicon-carbon anode material during cold pressing, thereby improving the processability of the silicon-carbon composite material and contributing to increased battery energy density. Simultaneously, the majority of the third silicon-based material is disposed within the micropores, which helps reduce the volume change rate of the third silicon-carbon composite particles, thereby improving the battery's cycle performance. For example, the percentage p of the micropore volume to the total pore volume in the third carbon matrix can be 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or any value within the range described above. Further, p can be 70%-85%, which can further improve the battery's energy density and cycle performance.

[0080] In some embodiments, the compacted density of the third carbon matrix powder at a pressure of 49,000 N is 0.4-1.1 g / cm³. 3 The preferred concentration is 0.4-0.8 g / cm³. 3 At this point, the third silicon-carbon composite material exhibits higher strength, which can mitigate cracking of silicon-carbon composite materials during cold pressing, thereby improving the processability of silicon-carbon composite materials and contributing to increased battery energy density. For example, the compacted density of the third carbon matrix powder under 49000N pressure can reach 0.4 g / cm³. 3 0.5g / cm 3 0.6g / cm 3 0.7g / cm 3 0.8g / cm 3 0.9g / cm 3 1g / cm 3 1.1g / cm 3 Or, within any of the aforementioned values. Furthermore, the compacted density of the third carbon matrix powder at 49000N pressure is 0.4-0.8 g / cm³. 3 This allows for further improvement in the battery's energy density.

[0081] In some embodiments, the specific surface area BET3 of the third carbon matrix is ​​≥1000m². 2 / g, preferably 1000-1300m 2 / g. At this point, the porous structure of the third carbon matrix can accommodate more third silicon particles, resulting in better stability of the third silicon-based material within the porous structure. Consequently, the cycle stability of the third silicon-carbon composite particles is improved, further enhancing the overall cycle stability of the silicon-carbon composite material and thus the cycle performance of the battery. For example, the specific surface area BET3 of the third carbon matrix can be 1000 m². 2 / g, 1050m 2 / g, 1100m 2 / g, 1150m 2 / g, 1200m 2 / g, 1250m 2 / g, 1300m 2 / g, 1400m 2 / g, 1500m 2 / g, 1600m 2 / g, or any of the values ​​mentioned above. The specific surface area BET3 of the third carbon matrix can be 1000-1300 m². 2 / g, at which point the third silicon-carbon composite particles have better processability and can improve the energy density of the battery.

[0082] In some embodiments, at least one of the first, second, or third silicon-based materials includes silicon grains. Since silicon grains in the silicon-based material have a higher specific capacity, the silicon-carbon composite material as a whole has a higher specific capacity, which can further improve the energy density of the battery. Furthermore, since the silicon grains are disposed within the porous structure of the carbon matrix, the volume expansion of the silicon grains can be effectively limited, so the silicon grains do not significantly affect the overall cycle stability of the silicon-carbon composite material. Further, the grain size of the silicon grains is less than or equal to 10 nm. Since the smaller the grain size of silicon particles, the smaller their anisotropy, the lower the volume expansion rate of the silicon grains during charge and discharge, resulting in better cycle stability of the first, second, or third silicon-carbon composite particles, further improving the overall cycle stability of the silicon-carbon composite material and further improving the cycle performance of the battery. For example, the grain size of the silicon grains can be 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, or any of the values ​​described above.

[0083] In some of the above embodiments, at least a portion of the surface of the third silicon-carbon composite particles has a coating layer. This coating layer on the surface can reduce the specific surface area of ​​the carbon matrix, reduce side reactions with the electrolyte, and further improve the battery's initial efficiency and cycle performance. It should be noted that carbon coating of the third silicon-carbon composite particles will reduce the mass percentage of silicon in the first silicon-carbon composite particles to some extent, but the impact is small and will not significantly change the mass percentage of silicon in the silicon-carbon composite particles. Furthermore, the coating layer is a carbon coating layer, which has good conductivity and stability and will not significantly affect the electrical properties of the silicon-carbon composite material.

[0084] In some embodiments, the specific surface area of ​​the silicon-carbon composite material is ≤6m². 2 / g. Since silicon particles readily react with the electrolyte to form a solid electrolyte film, they consume active ions in the electrolyte. Simultaneously, the volume expansion of silicon particles can damage the solid electrolyte film, leading to further reaction with the electrolyte. The specific surface area of ​​the silicon-carbon composite material should be controlled to not exceed ≤6m². 2 At this ratio, the silicon-carbon composite material has a smaller contact area with the electrolyte in the battery, reducing the loss of active ions and minimizing side reactions, thus further improving the battery's initial efficiency and cycle performance. For example, the specific surface area of ​​the silicon-carbon composite material can be 1 m². 2 / g, 2m 2 / g, 3m 2 / g, 4m 2 / g, 5m 2 / g, 6m 2 / g, or within the range of any of the above-mentioned values. Furthermore, the specific surface area of ​​the silicon-carbon composite material is ≤4m². 2 / g, at which point the battery's initial efficiency and cycle performance are better.

[0085] In some embodiments, the volume average particle size (Dv50) of the silicon-carbon composite material is 5-15 μm. Since the particle size of the silicon-carbon composite material affects the intercalation / deintercalation of active ions and has a certain influence on the relative surface area, controlling the volume average particle size (Dv50) of the silicon-carbon composite material to be 5-15 μm facilitates the intercalation / deintercalation of active ions, resulting in better kinetic performance and further improving the cycle performance of the battery. For example, the Dv50 of the silicon-carbon composite material can be 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, or any of the values ​​described above. Furthermore, a Dv50 of 5-10 μm results in even better cycle performance of the battery.

[0086] In some embodiments, the silicon content in the silicon-carbon composite material is 35%-50% by mass. Generally, the higher the silicon content, the greater the specific capacity of the silicon-carbon composite material, but the worse its cycle stability. Controlling the silicon content in the silicon-carbon composite material to 35%-50% by mass allows for a better balance between specific capacity and cycle stability, further improving the battery's energy density and cycle performance. For example, the silicon content in the silicon-carbon composite material can be 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, or any of the values ​​mentioned above. Furthermore, a silicon content of 40%-50% by mass in the silicon-carbon composite material results in even better energy density and cycle performance of the battery.

[0087] In some embodiments, the porosity of the silicon-carbon composite material is 45%-65%. Because silicon particles expand significantly during cycling, to reduce the volume expansion rate of the negative electrode during cycling and improve the cycle stability of the silicon-carbon composite material, the composite material should have an appropriate porosity to allow space for silicon particle expansion and alleviate the stress generated by silicon expansion within the composite material, thereby improving the battery's cycle performance. Furthermore, an appropriate porosity can increase the compaction density of the negative electrode, improving the battery's energy density. For example, the porosity of the silicon-carbon composite material can be 45%, 47%, 49%, 50%, 52%, 54%, 55%, 56%, 58%, 60%, 62%, 64%, 65%, or any of the values ​​described above. Further, a porosity of 45%-55% in the silicon-carbon composite material results in better energy density and cycle performance in the battery.

[0088] In some embodiments, the powder compaction density of the silicon-carbon composite material at a pressure of 49,000 N is 0.8-1.2 g / cm³. 3 The concentration can be selected as 0.9-1.1 g / cm³. 3 At this point, the silicon-carbon composite material exhibits better processability, which is beneficial for increasing the compaction density of the negative electrode sheet, thereby resulting in a higher energy density of the battery. For example, the powder compaction density of the silicon-carbon composite material under a pressure of 49000N can reach 0.8 g / cm³. 3 0.85g / cm 3 0.9g / cm 3 0.95g / cm 3 1.00g / cm 3 1.05g / cm 3 1.1g / cm 3 1.15g / cm 3 1.2g / cm 3 The value can be within the range of any of the values ​​described above. Furthermore, the powder compaction density of the silicon-carbon composite material under 49000N pressure can be 0.9-1.1 g / cm³. 3 This allows for further improvement in the battery's energy density.

[0089] In some embodiments, the tap density of the silicon-carbon composite material is 0.6-1.0 g / cm³. 3 The concentration can be selected as 0.7-0.9 g / cm³. 3 At this point, the silicon-carbon composite material exhibits better processability, which is beneficial for increasing the tap density of the negative electrode sheet, thereby resulting in a higher energy density of the battery. For example, the tap density of the silicon-carbon composite material can be 0.6 g / cm³. 3 0.65g / cm 3 0.7g / cm 30.75g / cm 3 0.8g / cm 3 0.85g / cm 3 0.9g / cm 3 0.95g / cm 3 1g / cm 3 The value can be within the range of any of the values ​​described above. Furthermore, the tap density of the silicon-carbon composite material can be 0.7-0.9 g / cm³. 3 This allows for further improvement in the battery's energy density.

[0090] In some embodiments, the powder resistivity of the silicon-carbon composite material is ≤5 Ω·cm. This results in better conductivity of the silicon-carbon composite material, allowing for full utilization of its specific capacity and further improving the battery's energy density and cycle performance. For example, the powder resistivity of the silicon-carbon composite material can be 5 Ω·cm, 4.5 Ω·cm, 4 Ω·cm, 3.5 Ω·cm, 3 Ω·cm, 2.5 Ω·cm, 2 Ω·cm, 1.5 Ω·cm, 1 Ω·cm, 0.5 Ω·cm, or any of the values ​​described above. Furthermore, the powder resistivity of the silicon-carbon composite material can be ≤3 Ω·cm, resulting in even better energy density and cycle performance of the battery.

[0091] In some embodiments, the ratio of (Dv90-Dv10) / Dv50 of the silicon-carbon composite material is ≤5. This results in a narrower particle size distribution of the silicon-carbon composite material, which can increase the porosity of the negative electrode film in the negative electrode sheet, thereby alleviating the compression of the silicon-carbon composite material during charge and discharge and improving the battery's cycle performance. For example, the ratio of (Dv90-Dv10) / Dv50 of the silicon-carbon composite material can be 5, 4, 3, 2, 1, or any of the values ​​described above. Furthermore, the ratio of (Dv90-Dv10) / Dv50 of the silicon-carbon composite material can be ≤3, resulting in even better battery cycle performance.

[0092] In the context of this application, the mass percentage of the first, second, and third silicon-carbon composite particles in the silicon-carbon composite material has a meaning known in the art and can be detected by known methods.

[0093] The grain size of silicon has a well-known meaning in the art and can be detected by known methods. For example, the XRD pattern of the sample is tested according to the JIS / K0131-1996 test standard. Based on the XRD pattern of the sample, the full width at half maximum (FWHM) β and diffraction angle θ of the Si(111) crystal plane are taken and substituted into the Debye-Scherrer formula to calculate the grain size of the silicon particles.

[0094] Debye-Scherrer formula: Dhkl=kλ / βcosθ;

[0095] Dhkl—Grain size, in nm; k—Scherrer constant, 0.89; λ—Incident X-ray wavelength, 0.15406 nm; β—Full width at half maximum (FWHM) of the diffraction peak, in rad; θ—Diffraction angle, in degrees.

[0096] The specific surface area of ​​the first carbon matrix, second carbon matrix, third carbon matrix, and silicon-carbon composite material has a well-known meaning in the art and can be detected by known methods. For example, the specific surface area can be tested using the gas adsorption method according to the GB / T19587-2017 test standard, as follows: The analyte is taken as the sample, and the sample tube is immersed in liquid nitrogen at -196℃. The amount of nitrogen adsorbed on the solid surface at different pressures of 0.05-0.30 is measured. Based on the BET multilayer adsorption theory and its formula, the monolayer adsorption amount of the sample is obtained, and thus the specific surface area of ​​the solid is calculated.

[0097] The average pore size, micropore volume, and percentage of micropore volume to total pore volume of a carbon matrix have well-known meanings in the art and can be detected by known methods. For example, the pore size can be tested using the gas adsorption method according to the testing standards GB / T19587-2017 & GB / T21650.2-2008, as follows: The porous material sample tube is immersed in liquid nitrogen at -196℃, and nitrogen gas is adsorbed onto the material under a relative pressure of 0-1. The pore size distribution of the porous material is characterized by the relationship between the volume (i.e., pore volume) of each pore size and the corresponding partial pressure, thus obtaining the average pore size of the carbon matrix.

[0098] The Dv90, Dv50, and Dv10 of silicon-carbon composite materials have meanings known in the art, namely, the particle sizes corresponding to a cumulative particle size distribution of 90%, 50%, and 10% respectively on a volume basis, which can be detected by known methods. For example, using a laser diffraction particle size distribution measuring instrument (Malvern Mastersizer 3000), according to the particle size distribution laser diffraction method GB / T19077-2016, the particle size distribution can be measured to obtain Dv90, Dv50, and Dv10.

[0099] The mass percentage of silicon in the first, second, and third silicon-carbon composite particles and the silicon-carbon composite material has a meaning known in the art and can be detected by known methods. For example, the mass percentage of silicon can be determined using inductively coupled plasma (ICP) emission spectroscopy, as follows: the material to be tested is taken as a sample, digested with aqua regia and hydrofluoric acid (HF), the silicon content of the digested solution is tested, and the mass percentage of silicon in the silicon-carbon composite material is calculated.

[0100] The porosity of silicon-carbon composite materials has a well-known meaning in the art and can be detected by known methods. For example, according to the GB / T24586 test standard, the porosity P = (V2 - V1) / V2 * 100%, and the apparent volume V2 = S * H ​​* A, where S is the area in cm². 2 H is the thickness in cm; A is the number of samples in EA; V1 is the true volume of the sample in cm³. 3 V2 is the apparent volume of the sample, in cm³. 3 The true volume V1 of the sample is calculated as follows: The sample is placed in a true density analyzer (Accu Pyc II 1340 analyzer), the test system is sealed, and helium gas is introduced according to the procedure. By detecting the gas pressure in the sample chamber and the expansion chamber, and then according to the ideal gas law (v = nRT / P), the gas volumes in the sample chamber and the expansion chamber are obtained respectively. Thus, the volume of gas displaced by the sample under certain temperature and pressure conditions is obtained, which is the true volume V1 of the sample.

[0101] The resistivity of silicon-carbon composite powder has a well-known meaning in the art and can be detected by known methods. For example, the four-probe method can be used, specifically referring to GB / T30835-1994, and measured using a powder resistivity tester (ST2722-SZ): a certain amount of the sample powder to be tested is placed in a special mold, and different pressures are set to obtain the powder resistivity under a certain pressure. In this application, the pressure can be 16 MPa.

[0102] The compaction density of third-dimensional carbon matrix and silicon-carbon composite materials under different pressures has a meaning known in the art, and the compaction density can be determined using methods known in the art. For example, according to GB / T 24533-2009, an electronic pressure testing machine (e.g., UTM7305) can be used for testing: a specific amount of powder is placed in a dedicated compaction mold, different pressures are set, the powder thickness at different pressures is read on the equipment, and the compaction density at different pressures is calculated. In this application, the pressure can be 49000N.

[0103] The tap density of silicon-carbon composite materials has a meaning known in the art, and powder compaction density can be determined using methods known in the art. For example, it can be determined using a powder tap density tester according to GB / T 5162-2006. The testing instrument can be Dandong Baite BT-301, with the following test parameters: vibration frequency 250±15 times / minute, amplitude 3±0.2mm, number of vibrations 5000 times, and a 25mL graduated cylinder.

[0104] In some embodiments, the first silicon-carbon composite particles can be prepared by vapor deposition on a first carbon matrix at 350-800°C using a silicon source gas and a protective gas with an air-to-gas ratio of 1:1-6 for 8-15 hours, so as to deposit the first silicon-based material in the porous structure of the first carbon matrix to obtain the first silicon-carbon composite particles.

[0105] It should be noted that by adjusting the gas flow ratio, deposition temperature, and deposition time within the above range, and by using different first carbon matrices, first silicon-carbon composite particles of different specifications can be obtained. Furthermore, the first silicon-carbon composite particles are not limited to those prepared by the above methods; other known methods and conditions can also be used to obtain them.

[0106] In some embodiments, the second silicon-carbon composite particles can be prepared by vapor deposition on a second carbon matrix at 350-800°C using a silicon source gas and a protective gas with an air-to-gas ratio of 1:1-6 for 6-12 hours, so as to deposit a second silicon-based material in the pore structure of the second carbon matrix to obtain the second silicon-carbon composite particles.

[0107] It should be noted that by adjusting the gas flow ratio, deposition temperature, and deposition time within the above range, and by using different second carbon matrices, second silicon-carbon composite particles of different specifications can be obtained. Furthermore, the second silicon-carbon composite particles are not limited to those prepared by the above methods; other known methods and conditions can also be used to obtain them.

[0108] In some embodiments, the third silicon-carbon composite particles can be prepared by vapor deposition on a third carbon matrix at 350-800°C using a silicon source gas and a protective gas with an air-to-gas ratio of 1:1-6 for 3-7 hours, so as to deposit the third silicon-based material in the pore structure of the third carbon matrix to obtain the third silicon-carbon composite particles.

[0109] It should be noted that by adjusting the gas flow ratio, deposition temperature, and deposition time within the above range, and by using different third carbon matrices, third silicon-carbon composite particles of different specifications can be obtained. Third silicon-carbon composite particles are not limited to those prepared by the above methods; other known methods and conditions can also be used to obtain them.

[0110] In some embodiments, the carbon coating layer on the surface of the first silicon-carbon composite particle, the second silicon-carbon composite particle, or the third silicon-carbon composite particle can be prepared by the following method: at 400-800°C, a carbon source gas and a protective gas with an air-gas ratio of 1:1.5-10 are used for vapor phase deposition on a carbon substrate on which silicon-based materials are deposited for 0.2-2 hours, so that a carbon coating layer is deposited on the surface of the carbon substrate on which silicon-based materials are deposited.

[0111] It should be noted that the carbon coating is not limited to the methods described above; other known methods and conditions can also be used to obtain the carbon coating.

[0112] In some embodiments, the silicon source gas includes, but is not limited to, at least one of silane-containing hydrocarbons such as silane, dichlorosilane, trichlorosilane, and tetrachlorosilane.

[0113] In some embodiments, the protective gas includes, but is not limited to, at least one of nitrogen, argon, and hydrogen.

[0114] In some embodiments, the carbon source gas includes, but is not limited to, at least one of hydrocarbon gases such as methane, ethylene, and acetylene.

[0115] In some embodiments, silicon-carbon composite materials can be obtained by mixing first silicon-carbon composite particles, second silicon-carbon composite particles, and third silicon-carbon composite particles in a certain mass ratio.

[0116] It is understandable that silicon-carbon composite materials of different specifications can be obtained by adjusting the types and mass ratios of the first, second, and third silicon-carbon composite particles.

[0117] In some embodiments, the negative electrode active material may also include graphite.

[0118] Secondary batteries

[0119] In a second aspect, this application provides a secondary battery, including a negative electrode sheet, the negative electrode sheet including a negative current collector and a negative electrode film layer, the negative electrode film layer including a negative electrode active material, and the negative electrode active material including a negative electrode active material according to any embodiment of the first aspect.

[0120] According to this application, the negative electrode sheet in the battery includes the negative electrode active material of any embodiment of the first aspect, and therefore the secondary battery has the beneficial effects of the first aspect.

[0121] [Negative electrode plate]

[0122] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0123] 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 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 (copper, copper 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.).

[0124] In some embodiments, the negative electrode film layer may optionally include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0125] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0126] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0127] 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 (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.

[0128] Typically, a battery also includes a positive 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 of ions 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.

[0129] [Positive electrode plate]

[0130] 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.

[0131] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0132] 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.).

[0133] In some embodiments, the positive electrode active material may be a known battery positive electrode active material. 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 battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides 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 Al0.05 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.

[0134] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0135] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0136] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive 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 the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0137] [Electrolytes]

[0138] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0139] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0140] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0141] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0142] 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.

[0143] [Isolation membrane]

[0144] In some embodiments, the battery cell 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.

[0145] 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.

[0146] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0147] In some embodiments, the secondary battery may include a battery cell, which includes the electrode assembly described above.

[0148] 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.

[0149] In some embodiments, the outer packaging of the battery cell can be a rigid shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the battery cell can also be a flexible package, such as a pouch. The material of the flexible package can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0150] 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 1 The example shown is a square-structured battery cell 5.

[0151] In some implementations, refer to Figure 2 The outer packaging may include a housing 51 and a cover plate 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 plate 53 can be placed over the opening to close the receiving cavity. The positive electrode sheet, negative electrode sheet, and separator can 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. Electrolyte is immersed in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in a single battery cell 5 can be one or more, which can be selected by those skilled in the art according to specific practical needs.

[0152] In some embodiments, the secondary battery may also include a housing; individual battery cells are housed within the housing.

[0153] The battery may contain one or more individual cells, and the specific number may be selected by those skilled in the art based on the application and capacity of the battery.

[0154] Furthermore, in the aforementioned secondary battery, multiple battery cells exist in the form of battery modules assembled together. Figure 3 This is battery module 4, used as an example. (See reference...) Figure 3 In battery module 4, multiple battery cells 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 battery cells 5 can be fixed in place using fasteners.

[0155] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0156] Figure 4 and Figure 5 This is a secondary battery 1 used as an example. (See reference...) Figure 4 and Figure 5 The secondary battery 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, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0157] Electrical appliances

[0158] Fifthly, this application also provides an electrical device including a secondary battery according to any embodiment of the second aspect.

[0159] The battery can be used as a power source for the electrical device or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0160] As the electrical device, the aforementioned secondary battery can be selected according to its usage requirements.

[0161] Figure 6 This is an example of an electrical device. The electrical device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc.

[0162] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a battery that consists of only a single battery cell as its power source.

[0163] Example

[0164] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0165] Preparation Example 1-1 :

[0166] Hard carbon was used as the carbon matrix, and the pore volume of the micropores in the hard carbon substrate was 0.72 cm³. 3 / g, with an average pore size of 3.2nm and a specific surface area of ​​1870m². 2 / g.

[0167] The hard carbon substrate was vapor-deposited at 455°C using silane and nitrogen gas with an air-to-gas ratio of 1:5 for 10 hours; then, at 660°C, ethylene and nitrogen gas with an air-to-gas ratio of 1:2 were vapor-deposited on the hard carbon substrate for 0.5 hours to form a carbon coating layer, resulting in silicon-carbon composite particles with a silicon content of 55%.

[0168] By controlling the type of carbon matrix, gas flow ratio, deposition temperature, and deposition time, corresponding silicon-carbon composite particles can be obtained.

[0169] The carbon substrate parameters and deposition processes for Preparation Examples 1-2, 2-1, and 2-2 are detailed in Table 1.

[0170] Table 1

[0171]

[0172] Preparation Example 3-1 :

[0173] Hard carbon is used as the carbon matrix, and the specific surface area of ​​the hard carbon substrate is 1200 m². 2 The hard carbon substrate has an average pore size of 2.1 nm and a porosity of 82%, and its compaction density is 0.61 g / cm³ when tested under 49000 N pressure. 3 .

[0174] The hard carbon substrate was vapor-deposited at 465°C using silane and nitrogen gas with an air-to-gas ratio of 1:6 for 3.5 h; then, at 660°C, ethylene and nitrogen gas with an air-to-gas ratio of 1:2 were vapor-deposited on the first carbon substrate for 0.5 h to form a carbon coating layer, resulting in silicon-carbon composite particles with a silicon content of 25%.

[0175] By controlling the type of carbon matrix, gas flow ratio, deposition temperature, and deposition time, silicon-carbon composite particles with different properties can be obtained.

[0176] The carbon matrix parameters and deposition process for Preparation Example 3-2 are detailed in Table 2 of the Examples.

[0177] Table 2

[0178]

[0179] Example 1

[0180] 1) Preparation of negative electrode sheet

[0181] Silicon-carbon composite material (silicon-carbon composite particles from Preparation Example 1-1 and Preparation Example 2-1 mixed at a mass ratio of 5:95), artificial graphite, conductive carbon black, styrene-butadiene rubber (SBR) binder, and sodium carboxymethyl cellulose (CMC-Na) thickener were thoroughly mixed in a deionized water solvent system at a mass ratio of 20:75:2:2:1 to obtain a negative electrode slurry. The negative electrode slurry was uniformly coated onto the negative electrode current collector copper foil. Then, the negative electrode sheet was obtained by drying, cold pressing, and slitting.

[0182] 2) Preparation of positive electrode sheet

[0183] The positive electrode active material Li(Ni) 0.8 Co 0.1 Mn 0.1 O2, conductive carbon black, and binder polyvinylidene fluoride (PVDF) are thoroughly mixed in an N-methylpyrrolidone solvent system at a mass ratio of 96:2:2 to obtain a positive electrode slurry. The positive electrode slurry is then uniformly coated onto a positive electrode current collector aluminum foil. After drying, cold pressing, and slitting, a positive electrode sheet is obtained.

[0184] 3) Preparation of electrolyte

[0185] In an argon-atmospheric glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), lithium hexafluorophosphate (LiPF6) was dissolved in a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 3:7. The mixture was stirred until homogeneous to obtain an electrolyte with a lithium salt concentration of 1 mol / L. Then, FEC was added, with the FEC content being 5% of the total electrolyte mass.

[0186] 4) Separating membrane

[0187] Polypropylene (PP) film is used as the separator.

[0188] 5) Battery manufacturing

[0189] The positive electrode, separator, and composite negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to isolate them. The electrode assembly is then wound up and placed in an outer package. Electrolyte is then injected, and after processes such as settling, cold pressing, formation, and shaping, a lithium-ion secondary battery is prepared.

[0190] Examples 2 to 9

[0191] Similar to the preparation method in Example 1, the difference lies in the use of different mass percentages and different types of silicon-carbon composite particles to obtain silicon-carbon composite materials, and the specific parameters are shown in Table 3.

[0192] Comparative Example 1

[0193] Similar to the preparation method of Example 1, the difference is that only the silicon-carbon composite particles of Preparation Example 2-1 are used as silicon-carbon composite materials, and the specific parameters are shown in Table 3.

[0194] Comparative Example 2

[0195] Similar to the preparation method of Example 1, the difference is that only the silicon-carbon composite particles of Preparation Example 1-1 are used as silicon-carbon composite materials, and the specific parameters are shown in Table 3.

[0196] In addition, the silicon-carbon composite materials and lithium-ion secondary batteries obtained in Examples 1-9 and Comparative Examples 1 and 2 were subjected to performance tests. The test results are shown in Table 3.

[0197] 1. Material capacity testing

[0198] Making a button battery:

[0199] The silicon-carbon composite material, conductive carbon black, styrene-butadiene rubber (SBR) binder, and sodium carboxymethyl cellulose (CMC-Na) thickener prepared above were thoroughly mixed in a deionized water solvent system at a mass ratio of 95:2:2:1 to obtain a negative electrode slurry. The negative electrode slurry was uniformly coated on a copper foil current collector, and then dried and cold-pressed to obtain a negative electrode sheet. Then, using a lithium metal sheet as the counter electrode and a polypropylene (PP) film as the separator, a CR2430 coin cell was assembled in an argon-protected glove box. The electrolyte formulation was as follows: In an argon-atmosphere glove box (H2O content <0.1ppm, O2 content <0.1ppm), lithium hexafluorophosphate (LiPF6) was dissolved in a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) (volume ratio 3:7) and stirred until homogeneous to obtain an electrolyte with a lithium salt concentration of 1 mol / L.

[0200] Test procedure: Under normal temperature conditions, the coin cell battery is left to stand for 3 hours, then discharged at a constant current of 0.05C to a voltage of 0.005V, and further discharged at a constant current of 50μA to a voltage of 0.005V. After standing for 5 minutes, it is charged at a rate of 0.1C to a voltage of 0.8V. The capacity at this time is recorded as the delithiation capacity, which is the 0.8V capacity of the silicon-carbon composite material.

[0201] 2. Battery cycle life test

[0202] (1) Cyclic performance test at 25℃

[0203] Test conditions: At 25℃, the battery was left to stand for 30 minutes, then charged at a 0.5C rate to a voltage of 4.2V, further charged at a constant voltage of 4.2V to a current of 0.05C, left to stand for 5 minutes, and then discharged at a 0.5C rate to a voltage of 2.8V. This constitutes one charge-discharge cycle. The discharge capacity was recorded at each cycle.

[0204] Capacity retention rate (%) after n cycles = (Discharge capacity of the nth cycle / Discharge capacity of the first cycle) × 100%.

[0205] (2) Cyclic performance test at 45℃

[0206] Test conditions: At 45℃, the battery was left to stand for 30 minutes, then charged at a 1C rate to a voltage of 4.2V, and further charged at a constant voltage of 4.2V to a current of 0.05C. After standing for 5 minutes, it was discharged at a 1C rate to a voltage of 2.8V. This is one charge-discharge cycle. The discharge capacity was recorded at each cycle.

[0207] The capacity retention rate (%) of a secondary battery after n cycles = (discharge capacity of the nth cycle / discharge capacity of the first cycle) × 100%.

[0208] 3. Expansion Test

[0209] Take the negative electrode sheet and secondary battery prepared in the above embodiments and comparative examples.

[0210] Testing process: Record the thickness T0 of the negative electrode sheet after cold pressing for each embodiment and comparative example; charge the batteries of each embodiment and comparative example at a rate of 0.5C to a voltage of 4.2V, disassemble the negative electrode sheet at this point, and test the thickness of the negative electrode sheet again, recording it as T1. The electrode sheet expansion calculation formula is as follows:

[0211] Electrode expansion rate (%) = (T1-T0) / T0 × 100%.

[0212]

[0213]

[0214] According to Table 2, the higher the cycle number of the lithium-ion secondary batteries obtained in each embodiment and comparative example, the better the cycle performance of the corresponding silicon-carbon composite material. Compared with Comparative Example 1, the silicon-carbon composite materials obtained in each embodiment have better cycle performance. The silicon-carbon composite materials in Comparative Example 1 and Comparative Example 2 contain only one type of silicon-carbon composite particles. The silicon-carbon composite particles in Comparative Example 2 have a higher mass percentage of silicon, and although their specific capacity increases accordingly, their cycle performance deteriorates significantly, and they also result in a higher electrode expansion rate.

[0215] As can be seen from Examples 1-3 and Comparative Example 1, by adding a certain amount of silicon-carbon composite particles with higher silicon content, the specific capacity of the material can be increased while improving cycle performance, without significantly worsening the expansion of the electrode.

[0216] As can be seen from Examples 4 to 6, the mass percentage of silicon in different silicon-carbon composite particles has a certain influence on the performance of silicon-carbon composite materials. When 1.06≤ω1 / ω2≤1.6, the silicon-carbon composite material has better cycle performance and a smaller expansion rate.

[0217] As can be seen from Examples 1, 7-9, adding a certain amount of silicon-carbon composite particles with a low silicon content can further improve the cycle performance of silicon-carbon composite materials and reduce their expansion rate.

[0218] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A negative electrode active material, characterized in that, The silicon-carbon composite material includes a first silicon-carbon composite particle and a second silicon-carbon composite particle. The first silicon-carbon composite particle includes a first carbon matrix having a porous structure and a first silicon-based material disposed in the porous structure of the first carbon matrix; The second silicon-carbon composite particle includes a second carbon matrix having a porous structure and a second silicon-based material disposed in the porous structure of the second carbon matrix; Furthermore, the mass percentage of silicon in the first silicon-carbon composite particle is greater than the mass percentage of silicon in the second silicon-carbon composite particle. Based on the silicon-carbon composite material, the mass content of the first silicon-carbon composite particles is 0.1%-5%; Based on the silicon-carbon composite material, the mass content of the second silicon-carbon composite particles is 80%-99.8%.

2. The negative electrode active material according to claim 1, characterized in that, The silicon content of the first silicon-carbon composite particles is ≥50% by mass; and / or, The mass percentage of silicon in the second silicon-carbon composite particles is ≤47%.

3. The negative electrode active material according to claim 1, characterized in that, The silicon content in the first silicon-carbon composite particles is 50%-60% by mass; and / or, The silicon content in the second silicon-carbon composite particles is 38%-47% by mass.

4. The negative electrode active material according to claim 1, characterized in that, The mass percentage of silicon in the first silicon-carbon composite particle is denoted as ω1, and the mass percentage of silicon in the second silicon-carbon composite particle is denoted as ω2. The negative electrode active material satisfies: 1.06≤ω1 / ω2≤1.

6.

5. The negative electrode active material according to claim 1, characterized in that, The mass percentage of silicon in the first silicon-carbon composite particle is denoted as ω1, and the mass percentage of silicon in the second silicon-carbon composite particle is denoted as ω2. The negative electrode active material satisfies: 1.1≤ω1 / ω2≤1.

3.

6. The negative electrode active material according to claim 1, characterized in that, The first carbon matrix includes a microporous structure, and the pore volume of the microporous structure in the first carbon matrix is ​​V1 ≥ 0.6 cm³. 3 / g; and / or, The second carbon matrix includes a microporous structure, and the pore volume of the microporous structure in the second carbon matrix is ​​V² ≥ 0.4 cm³. 3 / g.

7. The negative electrode active material according to claim 1, characterized in that, The first carbon matrix includes a microporous structure, and the pore volume V1 of the microporous structure in the first carbon matrix is ​​0.6-0.75 cm³. 3 / g; and / or, The second carbon matrix includes a microporous structure, and the pore volume V2 of the microporous structure in the second carbon matrix is ​​0.5-0.7 cm³. 3 / g.

8. The negative electrode active material according to claim 1, characterized in that, Both the first carbon matrix and the second carbon matrix include microporous structures, and the pore volume of the microporous structures in the first carbon matrix is ​​greater than the pore volume of the microporous structures in the second carbon matrix.

9. The negative electrode active material according to claim 1, characterized in that, The average pore size of the pore structure in the first carbon matrix is ​​d1≤5nm; and / or, The average pore size of the pore structure in the second carbon matrix is ​​d2≤10nm.

10. The negative electrode active material according to claim 1, characterized in that, The average pore size of the pore structure in the first carbon matrix is ​​1-4 nm; and / or, The average pore size of the pore structure in the second carbon matrix is ​​3-5 nm.

11. The negative electrode active material according to claim 1, characterized in that, The average pore size of the pore structure of the first carbon matrix is ​​smaller than the average pore size of the pore structure of the second carbon matrix.

12. The negative electrode active material according to claim 1, characterized in that, The specific surface area of ​​the first carbon matrix is ​​BET1≥1800m² 2 / g; and / or, The specific surface area of ​​the second carbon matrix is ​​BET2 ≥ 1600 m² 2 / g.

13. The negative electrode active material according to claim 1, characterized in that, The specific surface area of ​​the first carbon matrix is ​​1800-2000 m². 2 / g; and / or, The specific surface area of ​​the second carbon matrix is ​​1600-1800 m². 2 / g.

14. The negative electrode active material according to claim 1, characterized in that, The specific surface area of ​​the first carbon matrix is ​​greater than that of the second carbon matrix.

15. The negative electrode active material according to claim 1, characterized in that, The first silicon-carbon composite particle and / or the second silicon-carbon composite particle have a coating layer on at least a portion of their surfaces.

16. The negative electrode active material according to claim 1, characterized in that, The first silicon-carbon composite particle and / or the second silicon-carbon composite particle have a carbon coating layer on at least a portion of their surfaces.

17. The negative electrode active material according to claim 1, characterized in that, The silicon-carbon composite material further includes third silicon-carbon composite particles, which include a third carbon matrix with a porous structure and a third silicon-based material disposed in the porous structure of the third carbon matrix. The mass percentage of silicon in the third silicon-carbon composite particles is less than the mass percentage of silicon in the first silicon-carbon composite particles, and the mass percentage of silicon in the third silicon-carbon composite particles is less than the mass percentage of silicon in the second silicon-carbon composite particles.

18. The negative electrode active material according to claim 1, characterized in that, The silicon-carbon composite material further includes a third silicon-carbon composite particle. The first silicon-carbon composite particle includes a third carbon matrix with a porous structure and a third silicon-based material disposed in the porous structure of the third carbon matrix. The average pore size of the porous structure in the third carbon matrix is ​​smaller than the average pore size of the porous structure in the first carbon matrix, and the average pore size of the porous structure in the third carbon matrix is ​​smaller than the average pore size of the porous structure in the second carbon matrix.

19. The negative electrode active material according to claim 1, characterized in that, The silicon-carbon composite material further includes third silicon-carbon composite particles. The first silicon-carbon composite particles include a third carbon matrix with a porous structure and a third silicon-based material disposed in the porous structure of the third carbon matrix. The specific surface area of ​​the third carbon matrix is ​​smaller than that of the first carbon matrix, and the specific surface area of ​​the third carbon matrix is ​​smaller than that of the second carbon matrix.

20. The negative electrode active material according to any one of claims 17-19, characterized in that, The third silicon-carbon composite particles satisfy at least one of the following conditions: 1) The mass percentage of silicon in the third silicon-carbon composite particles is ≤25%; 2) The average pore size of the pore structure in the third carbon matrix is ​​d3≤4nm; 3) The third carbon matrix contains micropores with a pore size of <2nm, wherein the percentage of micropore volume to total pore volume p is ≥60%; 4) The compacted density of the third carbon matrix powder under 49000N pressure is 0.4-1.1 g / cm³. 3 ; 5) The specific surface area BET3 of the third carbon matrix is ​​≥1000m² 2 / g.

21. The negative electrode active material according to any one of claims 17-19, characterized in that, The third silicon-carbon composite particles satisfy at least one of the following conditions: 1) The mass percentage of silicon in the third silicon-carbon composite particles is 20%-25%; 2) The average pore size of the pore structure in the third carbon matrix is ​​1-3 nm; 3) The third carbon matrix contains micropores with a pore size < 2 nm, wherein the percentage p of the micropore volume to the total pore volume is 70%-85%; 4) The compacted density of the third carbon matrix powder under 49000N pressure is 0.4-0.8 g / cm³. 3 ; 5) The specific surface area (BET3) of the third carbon matrix is ​​1000-1300 m². 2 / g.

22. The negative electrode active material according to any one of claims 17-19, characterized in that, At least one of the first silicon-based material, the second silicon-based material, or the third silicon-based material comprises silicon grains.

23. The negative electrode active material according to any one of claims 17-19, characterized in that, At least one of the first silicon-based material, the second silicon-based material, or the third silicon-based material includes silicon grains, wherein the grain size of the silicon grains is less than or equal to 10 nm.

24. The negative electrode active material according to any one of claims 1-19, characterized in that, The silicon-carbon composite material satisfies at least one of the following conditions: 1) The specific surface area of ​​the silicon-carbon composite material is less than or equal to 6 m². 2 / g; 2) The volume average particle size Dv50 of the silicon-carbon composite material is 5-15 μm; 3) Based on the total mass of the silicon-carbon composite material, the mass percentage of silicon in the silicon-carbon composite material is 35%-50%; 4) The porosity of the silicon-carbon composite material is 45%-65%; 5) The compacted density of the silicon-carbon composite material under a pressure of 49000N is 0.8-1.2 g / cm³. 3 ; 6) The tap density of the silicon-carbon composite material is 0.6-1.0 g / cm³. 3 ; 7) The resistivity of the silicon-carbon composite powder is ≤5Ω·cm; 8) The ratio of (Dv90-Dv10) / Dv50 of the silicon-carbon composite material is ≤5.

25. The negative electrode active material according to any one of claims 1-19, characterized in that, The silicon-carbon composite material satisfies at least one of the following conditions: 1) The specific surface area of ​​the silicon-carbon composite material is ≤4m². 2 / g; 2) The volume average particle size Dv50 of the silicon-carbon composite material is 5-10 μm; 3) Based on the total mass of the silicon-carbon composite material, the mass percentage of silicon in the silicon-carbon composite material is 40%-50%; 4) The porosity of the silicon-carbon composite material is 45%-55%; 5) The compacted density of the silicon-carbon composite material under a pressure of 49000N is 0.9-1.1 g / cm³. 3 ; 6) The tap density of the silicon-carbon composite material is 0.7-0.9 g / cm³. 3 ; 7) The resistivity of the silicon-carbon composite material powder is ≤3Ω·cm; 8) The ratio of (Dv90-Dv10) / Dv50 of the silicon-carbon composite material is ≤2.

5.

26. A secondary battery, characterized in that, The invention includes a negative electrode sheet, which comprises a negative current collector and a negative electrode film layer, wherein the negative electrode film layer comprises a negative electrode active material, and the negative electrode active material comprises the silicon-carbon composite material according to any one of claims 1-25.

27. An electrical appliance, characterized in that, Includes the secondary battery as described in claim 26.

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