Silicon-carbon composite material and negative electrode sheet comprising the same

Abstract

The present application relates to a silicon-carbon composite material, which is a particle including a porous carbon skeleton, a silicon-containing deposition layer in a pore of the porous carbon skeleton, and a carbon-containing coating layer on the silicon-containing deposition layer and / or a surface of the particle, the silicon-carbon composite material having an oil absorption value of 35 mL / 100 g to 80 mL / 100 g. The silicon-carbon composite material of the present application has a higher energy density and improved cycle life. In addition, the present application also relates to a negative electrode sheet including the material, a secondary battery, a battery module, a battery pack, and a power utilization device.

Description

Technical Field

[0001] This application relates to the field of lithium battery technology, and more particularly to a silicon-carbon composite material. This application also relates to negative electrode sheets, secondary batteries, battery modules, battery packs, and electrical devices incorporating the silicon-carbon composite material. Background Technology

[0002] Given the widespread application of lithium-ion rechargeable batteries in energy storage, the field has paid close attention to their energy density and long-term performance, and has conducted extensive research in this area, including material improvements. Silicon-carbon composite materials are favored due to their high energy density. However, because silicon-based materials have high interfacial activity, they are prone to side reactions upon contact with the electrolyte, which affect the interfacial stability of the electrode. Consequently, after multiple cycles, the capacity of the material is easily degraded, shortening the lifespan of both the material and the battery.

[0003] Therefore, there is an urgent need in this field for materials with high energy density and long cycle life. Summary of the Invention

[0004] This application was made in view of the aforementioned problems, and its object is to provide a silicon-carbon composite material and a negative electrode sheet comprising the material. The silicon-carbon composite material of this application has low side reactions and long cycle life, enabling secondary batteries to have good energy density and cycle life.

[0005] The first aspect of this application provides a silicon-carbon composite material comprising particles including a porous carbon framework, a silicon-containing deposited layer, and a carbon-containing coating layer. The silicon-containing deposited layer is located within the pores of the porous carbon framework, and the carbon-containing coating layer is located on the silicon-containing deposited layer and / or on the surface of the particles. The silicon-carbon composite material has an oil absorption value of 35 mL / 100 g to 80 mL / 100 g. The silicon-carbon composite material of this application can impart good energy density and cycle life to secondary batteries.

[0006] In any embodiment, the silicon-carbon composite material has an oil absorption value of 45 mL / 100g to 70 mL / 100g, optionally 48 mL / 100g to 62 mL / 100g. Controlling the oil absorption value of the material within the above range can further improve energy density and cycle life.

[0007] In any embodiment, the silicon-carbon composite material has a particle center silicon content of ≥10% by weight, optionally ≥15% by weight, and more preferably 20% to 35% by weight, based on the total weight of the particles; wherein the particle center silicon content is obtained by selecting a cross-section from the particle cross-section obtained by ion polishing of the material, where the major axis length is equal to the volume average particle size, and determining the silicon content at the midpoint of the major axis on the selected cross-section. The silicon-carbon composite material of this application is less prone to reacting with the electrolyte, thereby improving cycle life.

[0008] In any embodiment, the porous carbon framework has a through-pore structure and an oil absorption value of ≥100 mL / 100 g, optionally ≥120 mL / 100 g, more preferably ≥150 mL / 100 g, and ≤190 mL / 100 g; optionally, the porous carbon framework has an oil absorption value of 136 mL / 100 g to 179 mL / 100 g. Such a porous carbon framework facilitates the distribution of silicon deposited layers within the material particles, thereby contributing to improved energy density and cycle life.

[0009] In any embodiment, the silicon-carbon composite material comprises 20% to 60% by weight, optionally 30% to 50% by weight, and more preferably 35% to 45% by weight of silicon, based on the total weight of the silicon-carbon composite material. This enables the material to have good energy density and cycling performance.

[0010] In any embodiment, the carbon coating comprises 3% to 10% by weight, optionally 3.5% to 7% by weight, and more preferably 4% to 6% by weight, based on the total weight of the silicon-carbon composite material. Controlling the carbon coating content can further improve cycle life.

[0011] In any embodiment, the oil absorption value X1 of the porous carbon skeleton, the oil absorption value X2 of the silicon-carbon composite material, the weight percentage of silicon Y1 in the silicon-carbon composite material, and the weight percentage of carbon coating Y2 satisfy the following:

[0012] and

[0013] k is a value ranging from 100 to 250, optionally any value from 130 to 180. Such silicon-carbon composite materials combine good energy density and long cycle life.

[0014] A second aspect of this application also provides a silicon-carbon composite material, prepared by the following steps:

[0015] i) Provide a porous carbon framework having a through-pore structure and an oil absorption value of ≥100mL / 100g and ≤190mL / 100g;

[0016] ii) Chemical vapor deposition is performed using a silicon-containing gas source to form a silicon-containing deposition layer in the pores of the porous carbon framework, thereby obtaining an intermediate material;

[0017] iii) A carbon-containing coating layer is formed on the silicon-containing deposition layer of the intermediate material and / or on the particle surface of the porous carbon skeleton to obtain the granular silicon-carbon composite material, wherein the carbon-containing coating layer accounts for 3% to 10% by weight, based on the total weight of the silicon-carbon composite material;

[0018] The silicon-carbon composite material described herein has an oil absorption value of 35 mL / 100g to 80 mL / 100g. Such a silicon-carbon composite material imparts good energy density and cycle life to the secondary battery.

[0019] In any embodiment, the silicon-carbon composite material has an oil absorption value of 45 mL / 100g to 70 mL / 100g, optionally 48 mL / 100g to 62 mL / 100g. Controlling the oil absorption value of the material within the above range can further improve energy density and cycle life.

[0020] In any embodiment, the silicon-carbon composite material has a particle center silicon content of ≥10% by weight, optionally ≥15% by weight, and more preferably 20% to 35% by weight, based on the total weight of the particles; wherein the particle center silicon content is obtained by selecting a cross-section from the particle cross-section obtained by ion polishing of the material, where the major axis length is equal to the volume average particle size, and determining the silicon content at the midpoint of the major axis on the selected cross-section. This can further improve cycle life.

[0021] In any embodiment, the porous carbon framework has an oil absorption value of ≥120 mL / 100 g, optionally ≥150 mL / 100 g; optionally, the porous carbon framework has an oil absorption value of 136 mL / 100 g to 179 mL / 100 g. This helps to further improve energy density and cycle life.

[0022] In any embodiment, the silicon-carbon composite material comprises 20% to 60% by weight, optionally 30% to 50% by weight, and more preferably 35% to 45% by weight of silicon, based on the total weight of the silicon-carbon composite material. This enables the material to have good specific capacity and cycling performance.

[0023] In any embodiment, the carbon coating comprises 3.5% to 7% by weight, more preferably 4% to 6% by weight, based on the total weight of the silicon-carbon composite material. Controlling the carbon coating content can further improve cycle life.

[0024] In any embodiment, the oil absorption value X1 of the porous carbon skeleton, the oil absorption value X2 of the silicon-carbon composite material, the weight percentage of silicon Y1 in the silicon-carbon composite material, and the weight percentage of carbon coating Y2 satisfy the following relationship:

[0025] and

[0026] k is a value ranging from 100 to 250, optionally any value from 130 to 180. Such silicon-carbon composite materials combine good energy density and long cycle life.

[0027] A third aspect of this application also provides a negative electrode sheet, comprising a current collector and a negative electrode material layer disposed on at least one surface of the current collector, the negative electrode material layer comprising the silicon-carbon composite material of this application. The negative electrode sheet of this application has good energy density and cycle performance.

[0028] In any embodiment, the negative electrode material layer comprises 5% to 50% by weight, optionally 10% to 30% by weight, and more preferably 15% to 25% by weight of the silicon-carbon composite material, based on the total weight of the negative electrode material layer. This further improves the electrode performance.

[0029] The fourth aspect of this application provides a secondary battery, including the silicon-carbon composite material of the first and second aspects of this application or the negative electrode sheet of the third aspect.

[0030] The fifth aspect of this application provides a battery module, including the secondary battery of the fourth aspect of this application.

[0031] A sixth aspect of this application provides a battery pack that includes the battery module of the fifth aspect of this application.

[0032] The seventh aspect of this application provides an electrical device comprising at least one selected from the fourth aspect of this application, the fifth aspect of this application, or the sixth aspect of this application.

[0033] The silicon-carbon composite material of this application has a high energy density and a significantly improved cycle life. Attached Figure Description

[0034] Figure 1 This is an ion-polished cross-sectional morphology analysis diagram of silicon-carbon composite material particles according to an embodiment of the present invention.

[0035] Figure 2 This is a schematic diagram of a secondary battery according to one embodiment of this application.

[0036] Figure 3 yes Figure 2 An exploded view of a secondary battery according to one embodiment of this application is shown.

[0037] Figure 4 This is a schematic diagram of a battery module according to one embodiment of this application.

[0038] Figure 5 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0039] Figure 6 yes Figure 5 An exploded view of a battery pack according to one embodiment of this application is shown.

[0040] Figure 7This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application.

[0041] Explanation of reference numerals in the attached figures:

[0042] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Secondary battery; 51 Casing; 52 Electrode assembly; 53 Top cover assembly Detailed Implementation

[0043] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the silicon-carbon composite material and its preparation method, negative electrode sheet, secondary battery, battery module, battery pack, 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.

[0044] 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.

[0045] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0046] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0047] 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.

[0048] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0049] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0050] Given the widespread application of lithium-ion rechargeable batteries in energy storage, the field has paid close attention to their energy density and long-term performance, and has conducted extensive research in this area, including material improvements. Silicon-carbon composite materials are favored due to their high energy density. However, silicon-based materials have high interfacial activity and are prone to side reactions upon contact with the electrolyte, affecting the stability of the electrode interface. Consequently, after multiple cycles, the material's capacity easily decays, shortening the lifespan of both the material and the battery.

[0051] Therefore, there is an urgent need in the art for anode active materials with high energy density and long cycle life. This invention meets this need and provides related advantages.

[0052] Silicon-carbon composite materials

[0053] In one embodiment of this application, a silicon-carbon composite material is provided, which comprises particles including a porous carbon skeleton, a silicon-containing deposited layer and a carbon-containing coating layer, wherein the silicon-containing deposited layer is in the pores of the porous carbon skeleton, and the carbon-containing coating layer is on the silicon-containing deposited layer and / or on the surface of the particles, and the silicon-carbon composite material has an oil absorption value of 35 mL / 100g to 80 mL / 100g.

[0054] The silicon-carbon composite material of this application can improve the energy density (e.g., specific capacity) and cycle life of lithium-ion secondary batteries. Without being bound by any theory, this is likely due to the fact that the silicon-carbon composite material of this application, particularly with a carbon coating and an oil absorption value within the aforementioned range, can effectively reduce the ingress of electrolyte and its contact with the silicon-containing deposited layer within the material pores, thus significantly improving the cycle life of lithium-ion secondary batteries.

[0055] In this article, the term "oil absorption value" refers to the volume (mL) of organic solvent (e.g., dibutyl phthalate, acrylate) absorbed by 100g of silicon-carbon composite material. The oil absorption value can be determined using the method described in GB / T3780.2-2007. The oil absorption value of porous materials reflects the patency of the material's pores. A higher oil absorption value indicates more unobstructed pores, allowing liquids (e.g., electrolytes) or gases (e.g., various gas sources, such as silane gas used for silicon deposition) to penetrate deeper into the material through the pores.

[0056] In some embodiments, the silicon-carbon composite material has an oil absorption value of 45 mL / 100g to 70 mL / 100g, optionally 48 mL / 100g to 62 mL / 100g. Controlling the oil absorption value of the material within the above range can further improve the cycle life of the lithium-ion secondary battery.

[0057] In some embodiments, the silicon-carbon composite material has a particle center silicon content of ≥10% by weight, optionally ≥15% by weight, and more preferably 20% to 35% by weight, based on the total weight of the particles; wherein the particle center silicon content is obtained by selecting a cross-section from the particle cross-section obtained by ion polishing of the material, wherein the cross-section with a major axis length equal to the volume average particle size is selected, and the silicon content at the midpoint of the major axis on the selected cross-section is determined.

[0058] In this paper, the silicon content at the particle center indicates the silicon content in the central region inside the material particle (i.e., the region furthest from the particle surface, for example). Compared to silicon-carbon composite materials in the prior art, the material of this application has a higher silicon content at the particle center while maintaining a similar overall silicon content. Therefore, the silicon-carbon composite material of this application is less likely to react with the electrolyte compared to similar materials in the prior art where the silicon deposition layer is mainly located in a shallower layer, which is beneficial for improving cycle life.

[0059] In some implementations, the value of silicon content at the particle center can be the average of the silicon content at the midpoint of the major axis on multiple selected cross sections.

[0060] In this text, "major axis" refers to the straight line connecting the two points furthest apart on the cross-section of the particle. In the case of a circular cross-section, the major axis is the diameter.

[0061] In this article, "volume average particle size (Dv50)" has a meaning known in the art and can be determined using instruments and methods known in the art. For example, it can be determined using a laser particle size analyzer, referring to GB / T 19077-2016 Particle Size Distribution Laser Diffraction Method.

[0062] Unless otherwise specified, "weight%", "wt.%", "%" or other similar expressions have the same meaning and all refer to weight percentage.

[0063] The silicon content at any point in a material particle can be determined by a suitable method known in the art, such as X-ray energy dispersive spectroscopy (EDS).

[0064] In some embodiments, the porous carbon framework has a through-pore structure and an oil absorption value of ≥100 mL / 100 g, optionally ≥120 mL / 100 g, more preferably ≥150 mL / 100 g, and ≤190 mL / 100 g. In some embodiments, optionally, the porous carbon framework has an oil absorption value of ≤185 mL / 100 g, more preferably ≤180 mL / 100 g. In some embodiments, optionally, the porous carbon framework has an oil absorption value of 136 mL / 100 g to 179 mL / 100 g. The porous carbon framework having an oil absorption value within the above range indicates a high degree of pore openness in its particles, which is beneficial for silicon deposition within the particles. In this application, the silicon-containing deposition layer in the silicon-carbon composite material can advantageously be distributed throughout the bulk phase of the porous carbon framework material particles; advantageously, silicon precursors can more easily reach and deposit in the central region of the porous carbon framework particles. Compared to the existing technology where silicon is largely deposited on the surface of particles, the silicon-carbon composite material of this application is less prone to expansion and particle pulverization during charging, which is beneficial to improving the cycle life of the battery.

[0065] As those skilled in the art will understand, although it is desirable in this application that the porous carbon skeleton has the highest possible oil absorption value, considering factors such as the stability of the porous carbon skeleton's structure, the porous carbon skeleton may have an oil absorption value of no more than 190 mL / 100 g.

[0066] In this article, the term "through-hole structure" refers to a continuous network structure formed inside material particles by interconnected pores.

[0067] In some embodiments, the total pore volume of the porous carbon framework is ≥1 cm³. 3 / g. In some embodiments, the porous carbon framework has a macropore volume ≤0.2cm³. 3 / g, mesopore volume ≥0.5cm³ 3 / g, micropore volume ≤0.3cm 3 / g. In some embodiments, the porous carbon framework has a density of 700m. 2 / g to 1500m 2 The specific surface area (BET) is approximately 1 / g. Such porosity is more conducive to the deposition of silicon-containing deposits in the central region of the carbon framework, resulting in higher silicon content at the particle center, thereby improving the energy density and cycle performance of the material and the battery. In particular, the porous carbon framework has a greater number of mesopores, which facilitates the uniform distribution of silicon deposits within it and provides sufficient space for volume changes in the silicon material during cycling, thus contributing to improved cycle life.

[0068] In this application, the porous carbon skeleton can be obtained from agricultural byproducts (such as coconut shells, rice husks, straw, corn cobs, etc.), synthetic polymers (such as phenolic resins, epoxy resins) or natural polymers (such as starch, cellulose, lignin) through methods known in the art (such as carbonization).

[0069] In some embodiments, the silicon-carbon composite material comprises 20% to 60% by weight, optionally 30% to 50% by weight, more preferably 35% to 45% by weight, and more preferably 40% by weight of silicon, based on the total weight of the silicon-carbon composite material. The silicon-carbon composite material of this application, comprising the aforementioned amounts of silicon, ensures the material's specific capacity and facilitates the maintenance of a stable material structure (e.g., after charging and lithium intercalation, the volume expansion of silicon does not destroy the carbon framework structure and cause pulverization), thereby exhibiting good cycle performance.

[0070] In some embodiments, the carbon-containing coating layer accounts for 3% to 10% of the total weight of the silicon-carbon composite material, optionally 3.5% to 7% by weight, more preferably 4% to 6% by weight, and even more preferably 5% by weight. The silicon-carbon composite material of this application, having a carbon coating layer within the above-mentioned content range, is beneficial for controlling the oil absorption value within an ideal range, reducing the exposure of the pores of deposited silicon in the material, reducing irreversible consumption caused by the reaction between the silicon-containing deposited layer and the electrolyte, and thus improving the cycle performance of the material. Without being bound by any theory, the carbon coating reduces the electrolyte-accessible volume of the silicon-carbon composite material and reduces the exposure of the silicon-containing deposited layer to the electrolyte, thereby effectively reducing the contact between the electrolyte and the silicon material within the pores and improving cycle life.

[0071] In some embodiments, the oil absorption value X1 of the porous carbon skeleton, the oil absorption value X2 of the silicon-carbon composite material, the weight percentage Y1 of silicon in the silicon-carbon composite material, and the weight percentage Y2 of the carbon coating layer in the silicon-carbon composite material satisfy the following:

[0072] and

[0073] k is a value between 100 and 250, and optionally any value between 130 and 180.

[0074] Such silicon-carbon composite materials possess both good energy density (e.g., specific capacity) and long cycle life.

[0075] In some embodiments, the silicon-carbon composite material particles have a particle size of ≤0.6 cm as determined by nitrogen adsorption. 3 / g total pore volume. In some embodiments, the silicon-carbon composite material particles contain ≤0.1cm³. 3 / g micropores, ≤0.3cm 3 / g of mesopores, ≤0.1cm 3 The silicon-carbon composite material of this application has a relatively high content of mesopores and a uniformly distributed silicon-containing deposited layer. This structure encapsulates the silicon within the pores of the carbon framework through carbon coating. The relatively high content of mesopores provides space for silicon expansion, and the carbon coating prevents the electrolyte from entering the pores and contacting the silicon to cause side reactions, thereby improving cycle life.

[0076] In this article, "micropore" usually refers to a pore with a diameter of less than about 2 nanometers; "mesopore" (or "mesopore") usually refers to a pore with a diameter of about 2 nanometers to about 50 nanometers; and "macropore" usually refers to a pore with a diameter of more than about 50 nanometers.

[0077] In some embodiments, the silicon-carbon composite material particles have a particle size of 1m. 2 / g to 15m 2 / g, optionally 4m 2 / g to 10m 2 / g, or optionally 6.5m 2 / g to 7.5m 2 / g, or alternatively 7m 2 Specific surface area per g.

[0078] In some embodiments, the volume average particle size (Dv50) of the silicon-carbon composite material is from 5 μm to 15 μm, optionally from 8 μm to 12 μm. In some embodiments, the Dv50 of the silicon-carbon composite material is more preferably from 9.5 μm to 10.5 μm. In some embodiments, the Dv50 of the silicon-carbon composite material is optionally 10 μm.

[0079] In another embodiment of this application, a silicon-carbon composite material is proposed, which is prepared by the following steps:

[0080] i) Provide a porous carbon skeleton with a through-pore structure, wherein the porous carbon skeleton has a through-pore structure and has an oil absorption value of ≥100mL / 100g and ≤190mL / 100g;

[0081] ii) A silicon-containing deposition layer is formed in the pores of the porous carbon framework by chemical vapor deposition to obtain an intermediate material;

[0082] iii) A carbon-containing coating layer is formed on the silicon-containing deposited layer of the intermediate material and / or on the particle surface of the porous carbon skeleton to obtain the silicon-carbon composite material, wherein the carbon-containing coating layer accounts for 3% to 10% by weight, based on the total weight of the silicon-carbon composite material;

[0083] The silicon-carbon composite material described herein has an oil absorption value of 35 mL / 100g to 80 mL / 100g. The silicon-carbon composite material of this application can impart good cycle life to secondary batteries.

[0084] Without being bound by any theory, in this application, the advantage of using a porous carbon framework with a high oil absorption value as a raw material lies in the higher pore openness. Therefore, compared to similar materials in the prior art that do not possess such an oil absorption value, the high oil absorption value carbon framework in this application is more conducive to uniformly and thoroughly depositing silicon into the depths of the carbon framework's pores, even at the particle center, via vapor deposition. Subsequently, carbon coating is applied to the particle surface to seal the silicon deposition layer within the pores, significantly reducing the oil absorption value of the final material, resulting in a silicon-carbon composite material with a lower oil absorption value. The porous characteristics of the carbon framework in this silicon-carbon composite material provide space for possible volume changes in the silicon-containing deposition layer during cycling, without substantially affecting the structural stability of the material; while the lower oil absorption value of the carbon coating layer and the final material (i.e., lower pore openness) effectively reduces the amount of electrolyte entering the pores (especially inside the particles) and interacting with the silicon-containing deposition layer, thus reducing the side reactions. In summary, the silicon-carbon composite material of this application, due to the structural characteristics of its raw material carbon skeleton and the final material itself, can mitigate (or avoid) structural instability caused by silicon expansion within the material, while also reducing side reactions occurring when the electrolyte comes into contact with the silicon material. Therefore, the material of this application has improved cycle life.

[0085] In this article, "chemical vapor deposition (CVD)" refers to the use of gaseous compounds or mixtures thereof to produce a non-volatile coating on a heated surface of a substrate (e.g., a porous carbon framework) through a chemical reaction.

[0086] In some embodiments, the silicon-carbon composite material has an oil absorption value of 45 mL / 100g to 70 mL / 100g, optionally 48 mL / 100g to 62 mL / 100g. Controlling the oil absorption value of the material within the above range can further improve the cycle life of the lithium-ion secondary battery.

[0087] In some embodiments, the silicon-carbon composite material has a core silicon content of ≥10% by weight, optionally ≥15% by weight, and more preferably 20% to 35% by weight, based on the total weight of the particles; wherein the core silicon content is obtained by selecting a cross-section of the particles obtained by ion polishing of the material, where the major axis length is equal to the volume average particle size, and determining the silicon content at the midpoint of the major axis of the selected cross-section. The silicon-carbon composite material of this application has a high internal silicon content in its particles, making it less prone to reacting with the electrolyte, thereby improving cycle life.

[0088] In some embodiments, the porous carbon framework has an oil absorption value of ≥120 mL / 100 g, optionally ≥150 mL / 100 g; alternatively, the porous carbon framework has an oil absorption value of 136 mL / 100 g to 179 mL / 100 g. Such a porous carbon framework facilitates the distribution of silicon deposits within the material particles, thereby contributing to improved energy density and cycle life.

[0089] In some embodiments, the silicon-carbon composite material comprises 20% to 60% by weight, optionally 30% to 50% by weight, and more preferably 35% to 45% by weight of silicon. This enables the material to have good energy density and cycling performance.

[0090] In some embodiments, the carbon coating comprises 3.5% to 7% by weight, optionally 4% to 6% by weight, based on the total weight of the silicon-carbon composite material. Controlling the carbon coating content can further improve cycle life.

[0091] In some embodiments, the oil absorption value X1 of the porous carbon skeleton, the oil absorption value X2 of the silicon-carbon composite material, the weight percentage of silicon Y1 in the silicon-carbon composite material, and the weight percentage of carbon coating Y2 satisfy the following relationship:

[0092] and

[0093] k is a value ranging from 100 to 250, optionally any value from 130 to 180. Such silicon-carbon composite materials combine good energy density and long cycle life.

[0094] In another embodiment of this application, a method for preparing silicon-carbon composite materials is proposed, comprising the following steps:

[0095] i) Provide a porous carbon skeleton with a through-pore structure, wherein the porous carbon skeleton has a through-pore structure and has an oil absorption value of ≥100mL / 100g and ≤190mL / 100g;

[0096] ii) A silicon-containing deposition layer is formed in the pores of the porous carbon framework by chemical vapor deposition to obtain an intermediate material;

[0097] iii) A carbon-containing coating layer is formed on the silicon-containing deposited layer of the intermediate material and / or on the particle surface of the porous carbon skeleton to obtain the silicon-carbon composite material, wherein the carbon-containing coating layer accounts for 3% to 10% by weight, based on the total weight of the silicon-carbon composite material;

[0098] The silicon-carbon composite material described herein has an oil absorption value of 35 mL / 100 g to 80 mL / 100 g. The method of this application can prepare silicon-carbon composite materials with significantly improved cycle life and good energy density.

[0099] In some embodiments, the silicon-carbon composite material has an oil absorption value of 45 mL / 100g to 70 mL / 100g, and optionally 48 mL / 100g to 62 mL / 100g.

[0100] In some embodiments, the porous carbon framework has an oil absorption value of ≥120 mL / 100 g, optionally ≥150 mL / 100 g, and ≤190 mL / 100 g. In some embodiments, the porous carbon framework has an oil absorption value of 136 mL / 100 g to 179 mL / 100 g. Such a carbon framework facilitates the deposition of a large amount of silicon precursor within the porous carbon framework (even in the central region) in step ii), thereby enabling the final material to achieve good specific capacity and improving the cycle performance of the battery.

[0101] In some embodiments, the chemical vapor deposition in step ii) is performed in the presence of a silicon-containing gas source. In some embodiments, the silicon-containing gas source may be any silicon-containing gas source commonly used in the art for chemical vapor deposition. In some embodiments, the silicon-containing gas source is selected from at least one of silane and silicon tetrachloride, optionally silane. In some embodiments, the silicon-containing gas source may also be used in combination with an inert gas (e.g., nitrogen). In the case of a mixed gas, the silane content is from about 5% by weight to 100% by weight, based on the total weight of the mixed gas. In some embodiments, the inlet rate of the silicon-containing gas source in step ii) is 2-8 L / min, optionally 3-5 L / min, and more preferably 4 L / min.

[0102] In some embodiments, the chemical vapor deposition in step ii) is performed at a deposition temperature of 300°C to 800°C. In some embodiments, the chemical vapor deposition in step ii) is performed for 5-15 hours, optionally 8-12 hours, optionally 10 hours.

[0103] In some embodiments, the chemical vapor deposition in step ii) is performed under agitation conditions.

[0104] In some embodiments, the method of this application further includes a step of surface micro-oxidation of the intermediate material after step ii) and before step iii). The surface micro-oxidation is performed by introducing at least one of air, carbon dioxide, carbon monoxide, and water vapor into the intermediate material at a high temperature. This temperature is determined by those skilled in the art.

[0105] In some implementations, step iii) is performed by coating or chemical vapor deposition.

[0106] In the case of coating, the coating is to coat the surface of the intermediate material particles with a layer of, for example, graphite, graphene, hard carbon, or soft carbon. Alternatively, a coating of a precursor material (e.g., bitumen) known in the art can be sprayed onto the surface of the intermediate material particles, followed by carbonization. In some embodiments, the amount of the precursor material coating added is 5-15% by weight, optionally 7-9% by weight, and more preferably 8% by weight, based on the total weight of the intermediate material. Coating amounts within the above range are beneficial for achieving better coating effects.

[0107] In some embodiments, the precursor material is asphalt, optionally asphalt with a softening point not exceeding 200°C, and more preferably asphalt with a softening point of 150-160°C. Asphalt with a softening point within this range spreads more easily on the particle surface during the coating process, contributing to a better coating effect. In the case of chemical vapor deposition, the chemical vapor deposition is carried out in the presence of a carbon-containing gas source. In some embodiments, the carbon-containing gas source can be selected from any carbon-containing gas source commonly used in chemical vapor deposition in the art. In some embodiments, the carbon-containing gas source is selected from at least one of methane, ethane, ethylene, and acetylene.

[0108] Chemical vapor deposition is carried out in reactors known in the art, such as fluidized bed reactors, static bed reactors, etc.

[0109] In some embodiments, the chemical vapor deposition in step iii) is performed at a temperature of 800°C to 1200°C. In some embodiments, the inlet rate of the carbon-containing gas source in the chemical vapor deposition in step iii) is 1-5 L / min, optionally 1-3 L / min, and more preferably 2 L / min. In some embodiments, the chemical vapor deposition in step iii) is performed for 1-3 hours.

[0110] Negative electrode sheet

[0111] In another embodiment of this application, a negative electrode sheet is provided, including a current collector and a negative electrode material layer disposed on at least one surface of the current collector, wherein the negative electrode material layer includes the silicon-carbon composite material of this application or the silicon-carbon composite material obtained according to the method of this application.

[0112] In some embodiments, the negative electrode material layer comprises 5% to 50% by weight, optionally 15% to 25% by weight, and more preferably 20% by weight of the silicon-carbon composite material, based on the total weight of the negative electrode material layer. The inclusion of carbon-based negative electrode active material within this range in the negative electrode material layer enables the secondary battery to possess both long cycle life and good energy density.

[0113] In some embodiments, the negative electrode material layer further includes 5% to 50% by weight of carbon-based negative electrode active material, based on the total weight of the negative electrode material layer. Including this range of carbon-based negative electrode active material in the negative electrode material layer enables the secondary battery to possess both a long cycle life and good energy density.

[0114] 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.

[0115] 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.).

[0116] This application is not limited to these materials, and other conventional materials that can be used as battery negative electrode active materials may also be used.

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

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

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

[0120] In some embodiments, the negative electrode sheet can be prepared by dispersing the 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.

[0121] Secondary batteries, battery modules, battery packs and electrical devices

[0122] In another embodiment of this application, a secondary battery is provided, which includes the silicon-carbon composite material of this application or the negative electrode sheet of this application.

[0123] In another embodiment of this application, a battery module is provided, which includes the secondary battery of this application.

[0124] In another embodiment of this application, a battery pack is provided, which includes the battery module of this application.

[0125] In another embodiment of this application, an electrical device is provided, which includes at least one selected from the secondary battery, battery module, or battery pack of this application.

[0126] In addition, the secondary battery, battery module, battery pack and power device of this application will be described below with appropriate reference to the accompanying drawings.

[0127] In one embodiment of this application, a secondary battery is provided.

[0128] In some embodiments, the secondary battery is a lithium-ion secondary battery.

[0129] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0130] [Positive electrode plate]

[0131] 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 the positive electrode active material of the first aspect of this application.

[0132] 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.

[0133] 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.).

[0134] 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.

[0135] 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.

[0136] 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.

[0137] 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.

[0138] [Electrolytes]

[0139] 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.

[0140] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0141] 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.

[0142] 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.

[0143] 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.

[0144] [Isolation membrane]

[0145] In some embodiments, the secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0146] 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.

[0147] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0148] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

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

[0150] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 2 This is an example of a square-structured secondary battery 5.

[0151] In some implementations, refer to Figure 3The outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed over the opening to close the receiving cavity. A positive electrode, a negative electrode, and a separator can be formed into an electrode assembly 52 using a winding or stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0152] In some implementations, the secondary batteries can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0153] Figure 4 This is battery module 4, used as an example. (See reference...) Figure 4 In battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary batteries 5 can be fixed in place using fasteners.

[0154] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0155] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0156] Figure 5 and Figure 6 This is battery pack 1 as an example. (See reference...) Figure 5 and Figure 6 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, 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] In addition, this application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided in this application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may 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.

[0158] As the electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0159] Figure 7 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0160] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0161] Example

[0162] 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.

[0163] Example 1

[0164] 1. Preparation of silicon-carbon composite materials

[0165] Provides a specific surface area of ​​1440m² 2 A porous carbon framework with an oil absorption value of 160 mL / 100 g and a total pore volume of 1.1 cm³. 3 / g, macropores 0.17cm 3 / g, mesopore 0.65cm 3 / g and micropores 0.28cm 3 / g). A porous carbon framework was heated to 600°C, and silane gas was introduced at a rate of 4 L / min for vapor deposition for 10 h to obtain an intermediate material after silane deposition. Then, the temperature was maintained at 600°C, and CO2 gas was introduced while monitoring the temperature change. During this process, the temperature was observed to first rise to approximately 605°C, and then decrease. When the temperature dropped below 605°C, the CO2 gas introduction was stopped, thus completing the surface micro-oxidation of the intermediate material. Finally, acetylene gas was introduced at 950°C at a rate of 2 L / min for vapor deposition for 2 h to obtain a 5% carbon coating layer. The silicon-carbon composite material of this application was thus obtained.

[0166] 2. Preparation of negative electrode sheet

[0167] Using water as a solvent, the silicon-carbon composite material prepared as described above, graphite, styrene-butadiene rubber (SBR) binder, acrylic acid-acrylonitrile-acrylamide copolymer binder, and conductive agents Super P, carbon nanotubes, and sodium carboxymethyl cellulose were mixed in a mass ratio of 20:80:0.8:1:1:1:0.5 to prepare a negative electrode slurry (solid content approximately 55%). The above negative electrode slurry was then uniformly coated onto a current collector copper foil (loading capacity 7.2 mg / cm²). 2 The negative electrode sheet is obtained by drying, cold pressing, and slitting.

[0168] 3. Preparation of the positive electrode sheet

[0169] A positive electrode slurry (solid content 76%) was prepared by mixing lithium nickel cobalt manganese oxide (NCM811), conductive carbon (SP), and binder polyvinylidene fluoride (PVDF) at a mass ratio of 97:1.5:1.5 using methylpyrrolidone (NMP) as a solvent. The above positive electrode slurry was then uniformly coated onto a current collector aluminum foil (loading capacity 18.7 mg / cm²). 2 After drying, cold pressing, and slitting, positive electrode sheets are obtained.

[0170] 4. Battery manufacturing

[0171] LiPF6 was added to a mixed solution of ethylene carbonate (EC) / diethyl carbonate (DEC) (volume ratio 1:1 at room temperature) to obtain a 1M solution as the electrolyte. Using a polyethylene (PE) separator, the positive and negative electrode sheets prepared above were stacked and wound in the order of "positive electrode sheet - separator - negative electrode sheet" in a low-humidity, constant-temperature chamber, then filled with electrolyte to assemble a lithium-ion secondary battery.

[0172] 5. Oil absorption value test

[0173] Referring to the method described in the national standard GB / T 3780.2-2007, the instrumental method A was adopted, with a sample amount of 20g and dibutyl phthalate (DBP) as the reagent.

[0174] 6. X-ray energy dispersive spectroscopy (EDS) test

[0175] Cut the electrode to be tested into a 6mm×6mm sample and place it on the ion polishing (CP) sample stage (the sample should protrude within 1mm of the sample stage). Cut it with a voltage of 7.5KV for about 30 minutes (the time can be adjusted appropriately according to the material and sample thickness) to obtain the ion polished sample.

[0176] Referring to the method described in GB / T 17359-2012, the silicon content in the central region of silicon-carbon composite particles was measured: the ion-polished electrode samples were tested using a field emission scanning electron microscope (Zeiss Sigma 300). Four silicon-carbon composite particle cross-sections with a major axis length equal to the material's Dv50 were randomly selected within the microscope's field of view. The silicon content at the midpoint of the major axis on each cross-section was then measured using EDS, and the average value was calculated.

[0177] Figure 1 The diagram shows the ion-polished cross-sectional morphology analysis of the electrode sample, where four particle cross-sections with a major axis equal to Dv50 were selected, and the silicon content at the center of the particle center was measured at the center of the major axis of each selected cross-section (the test points correspond to...). Figure 1 The spectrum marked in the middle Figure 1-4 ).

[0178] 7. Inductively Coupled Plasma Emission Spectroscopy (ICP) Test – Overall Silicon Content of Silicon-Carbon Composites

[0179] The material sample was placed in a digestion vessel, and a mixture of concentrated nitric acid and hydrofluoric acid was added. The sample was then digested in a microwave digester. The silicon content of the digested sample solution was determined using inductively coupled plasma atomic emission spectrometry (ICP-AES).

[0180] 8. Material density test

[0181] The negative electrode sheet is coated on one side using the above method, punched into a small circular sheet with a diameter of 14mm, and assembled with a separator and lithium sheet to form a button battery. The specific capacity is tested using the following method, based on 1C = 600mAh / g:

[0182] The above-mentioned button cell battery was discharged at a rate of 0.05C to 5mV, then discharged at 50μA to 5mV, and then discharged again at 10μA to 5mV. After standing for 5 minutes, the battery was charged at 0.1C to 2V. The battery capacity at this point was measured. The ratio of this capacity to the weight of the active material in the electrode was calculated, which gives the specific capacity of the active material.

[0183] 9. Cyclic life test

[0184] At an ambient temperature of 25℃, first discharge the battery at a constant current rate of 0.33C to 2.7V, let it stand for 5 minutes, then charge it at a constant current rate of 0.5C to 4.2V, then charge it at a constant voltage of 4.2V to 0.05C, let it stand for 5 minutes, and then discharge it at a constant current rate of 0.33C to 2.7V. This is the first cycle. The battery capacity at this point is measured as C1. Repeat the above steps until the capacity decays to 80% of C1. The number of cycles at this point is the cycle life.

[0185] 10. Volume average particle size (Dv50) test

[0186] Take a clean beaker, add an appropriate amount of the sample to be tested, add a surfactant, then add a dispersant, and sonicate at 120W / 5min to ensure complete dispersion of the sample in the dispersant. The particle size distribution characteristics of the sample are tested using a Malvern 3000 laser particle size analyzer to obtain Dv50.

[0187] Example 2

[0188] The preparation and testing methods were the same as in Example 1. The difference was that the specific surface area of ​​the porous carbon framework was 750 m². 2 / g, oil absorption value 155mL / 100g, total pore volume 1.02cm³ 3 / g, macropore 0.16cm 3 / g, mesopore 0.6cm 3 / g and micropores 0.26cm 3 / g.

[0189] Example 3

[0190] The preparation and testing methods were the same as in Example 1. The difference was that the specific surface area of ​​the porous carbon framework was 1100 m². 2 / g, oil absorption value 158mL / 100g, total pore volume 1.15cm³ 3 / g, macropore 0.18cm 3 / g, mesopore size 0.68cm 3 / g and micropores 0.29cm 3 / g.

[0191] Example 4

[0192] The same porous carbon framework, preparation method, and testing method as in Example 2 were used. The difference was that after obtaining the intermediate material after silane deposition, 8% by weight of softening point pitch with a softening point of 160°C was added based on the total weight of the intermediate material, mixed well, and then carbonized under a nitrogen atmosphere to obtain a silicon-carbon composite material with 5% carbon coating.

[0193] Examples 5-10

[0194] The preparation and testing methods used in Example 1 were employed. The difference lies in the oil absorption values ​​of the carbon skeleton in Examples 5-10 (see Table 2 below), resulting in different oil absorption values ​​for the obtained silicon-carbon composite materials. Table 1 below lists the relevant parameters of the carbon skeleton in each of the above examples:

[0195] Table 1

[0196]

[0197] Comparative Examples 1-2

[0198] The preparation and testing methods were as described in Example 1. The difference was that Comparative Example 1 used 18% by weight of asphalt for carbonization, resulting in a silicon-carbon composite material with approximately 10.8% carbon coating and a low oil absorption value; while Comparative Example 2 used 5% by weight of asphalt for coating and had an excessively high skeleton oil absorption value, thus resulting in a silicon-carbon composite material with approximately 3% carbon coating and a high oil absorption value.

[0199] Comparative Example 3

[0200] The preparation and testing methods were the same as in Example 1. The difference was that the specific surface area of ​​the porous carbon framework was 20 m². 2 / g, oil absorption value 80mL / 100g, total pore volume 0.22cm³ 3 / g, macropores 0.07cm 3 / g, mesopore size 0.09cm 3 / g and micropores 0.06cm 3 / g.

[0201] Comparative Example 4

[0202] The porous carbon framework, preparation method, and testing method used in Example 1 were employed. The difference was that the resulting silicon-carbon composite material was not carbon-coated.

[0203] Comparative Example 5

[0204] The same porous carbon framework, preparation method, and testing method as in Example 1 were used. The difference was that after obtaining the intermediate material after silane deposition, CO2 gas was introduced to micro-oxidize the material. Finally, 2% by weight of asphalt with a softening point of 250°C was added based on the total weight of the intermediate material, mixed thoroughly, and carbonized under a nitrogen atmosphere to obtain a silicon-carbon composite material with approximately 1.2% carbon coating.

[0205] Comparative Example 6

[0206] 60nm nano-silicon powder and emulsified asphalt were mixed and sprayed at 180°C to obtain 10µm cured particles. These particles were then placed in asphalt with a softening point of 90°C to impregnate and densify the asphalt. Finally, they were carbonized at 1150°C to obtain a silicon-carbon composite material with a diameter of 10µm encapsulating nano-silicon particles.

[0207] Table 2 shows the various embodiments and comparative examples described above.

[0208] Table 2

[0209]

[0210] *The silicon content at the particle center was obtained as follows: From the cross-sections of particles obtained by ion polishing of the material, a cross-section with a major axis length equal to the average particle volume diameter was selected, and the silicon content at the midpoint of the major axis of the selected cross-section was determined. The silicon content at the particle center was measured at four cross-sections, and the average value was calculated. The average value is shown in the table. In the table above, the particle size of the silicon-carbon composite material is approximately 10 μm.

[0211] Where X1 is the oil absorption value of the porous carbon framework, and X2 is the oil absorption value of the silicon-carbon composite material.

[0212] Y1 represents the total weight percentage of silicon in the silicon-carbon composite material, and Y2 represents the weight percentage of the carbon coating layer.

[0213] As can be seen from Table 2, in the silicon-carbon composite material of this application, the porous carbon skeleton has a large oil absorption value, while the final composite material has a small oil absorption value; furthermore, in the silicon-carbon composite material particles of this application, the silicon distribution is relatively uniform, especially the silicon content in the central region is high, thus exhibiting good comprehensive performance—high specific capacity and long cycle life.

[0214] Examples 11-14

[0215] Following Example 1, the porous carbon framework shown in Table 3 and the silicon-carbon composite material prepared therefrom were used, and their performance was tested. Table 3 shows the effect of the overall silicon content in the material on the performance.

[0216] Table 3

[0217]

[0218] As shown in Table 3, when the total silicon content in the silicon-carbon composite material is between 20-60% by weight, the amount of silicon-carbon composite material required for its compounding with graphite is moderate, thereby reducing side reactions and improving cycle performance.

[0219] The silicon content in the central region of the silicon-carbon composite particles is within the range of this application. The carbon skeleton can restrain the expansion of silicon, which is beneficial to improving cycle performance.

[0220] Examples 15-19

[0221] Silicon-carbon composite materials were prepared using a method similar to that in Example 1. However, by controlling the vapor deposition time of acetylene gas in the third step, silicon-carbon composite materials with different carbon coating amounts were obtained. Table 4 shows the effect of different carbon coating amounts on performance.

[0222] Table 4

[0223]

[0224] As shown in Table 4, the silicon-carbon composite material of this application has good energy density and cycle life when it has the above-mentioned carbon coating amount.

[0225] In addition, Table 5 shows Embodiment 1 of this application (reference). Figure 1 The silicon content test results of the silicon-carbon composite particles in Comparative Examples 3 and 6, including the determination of the silicon content (wt%) in the center of the particles at four randomly selected cross sections with a major axis length equal to particle Dv50, and the calculation of the average value.

[0226] Table 5

[0227]

[0228] As shown in Table 5, the silicon-carbon composite material of Example 1 of this application has a higher silicon content at the particle center, and the silicon content distribution at the particle center of different particles is more uniform. The material of Comparative Example 3 has a lower silicon content at the particle center, which indicates that, while the overall silicon content is comparable to that of the material of Example 1, the silicon deposition layer is more distributed in the shallow part of the material particles. As shown in Table 2, its specific capacity and cycle life are both lower. Although Comparative Example 6 also has a high silicon content at the particle center, it lacks a carbon coating layer, and therefore, as shown in Table 2, its cycle life is poor.

[0229] 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 silicon-carbon composite material which is a particle comprising a porous carbon skeleton, a silicon-containing deposited layer in the pores of the porous carbon skeleton, and a carbon-containing coating layer on the silicon-containing deposited layer and / or on the surface of the particle, the silicon-carbon composite material having an oil absorption value of 35 mL / 100 g to 80 mL / 100 g. The porous carbon skeleton has a through-hole structure, and an oil absorption value of > 100 mL / 100 g and < 190 mL / 100 g.

2. The silicon-carbon composite material according to claim 1, wherein the silicon-carbon composite material has an oil absorption value of 45 mL / 100 g to 70 mL / 100 g.

3. The silicon-carbon composite material according to claim 2, having an oil absorption value of 48 mL / 100 g to 62 mL / 100 g.

4. The silicon-carbon composite material of any one of claims 1 to 3, wherein the silicon-carbon composite material has a particle center silicon content of > 15 wt.%, based on the total weight of the particle; wherein, The particle center silicon content is obtained by selecting a cross section having a major axis length equal to the volume average particle diameter from the cross section of the material obtained by ion polishing, and determining the silicon content at the midpoint of the major axis on the selected cross section.

5. The silicon-carbon composite material according to claim 4, wherein the particle center silicon content of the silicon-carbon composite material is 20% to 35% by weight.

6. The silicon-carbon composite material according to any one of claims 1 to 3, wherein the porous carbon skeleton has an oil absorption value of > 120 mL / 100 g and < 190 mL / 100 g.

7. The silicon-carbon composite material according to claim 6, wherein the porous carbon skeleton has an oil absorption value of > 150 mL / 100 g and < 190 mL / 100 g.

8. The silicon-carbon composite material according to claim 7, wherein the porous carbon skeleton has an oil absorption value of 136 mL / 100 g to 179 mL / 100 g.

9. The silicon-carbon composite material according to any one of claims 1 to 3, wherein the silicon-carbon composite material comprises 20% to 60% by weight of silicon, based on the total weight of the silicon-carbon composite material.

10. The silicon-carbon composite material according to claim 9, comprising 30% to 50% by weight of silicon.

11. The silicon-carbon composite material according to claim 10, comprising 35% to 45% by weight of silicon.

12. The silicon-carbon composite material according to any one of claims 1 to 3, wherein the carbon-containing coating layer accounts for 3% to 10% by weight, based on the total weight of the silicon-carbon composite material.

13. The silicon-carbon composite material according to claim 12, wherein the carbon-containing coating layer accounts for 3.5% to 7% by weight.

14. The silicon-carbon composite material according to claim 13, wherein the carbon-containing coating layer accounts for 4% to 6% by weight.

15. The silicon-carbon composite material of claims 1-3, wherein, The oil absorption value X1 of the porous carbon skeleton, the oil absorption value X2 of the silicon-carbon composite material, the weight percentage Y1 of silicon in the silicon-carbon composite material, and the weight percentage Y2 of the carbon coating layer satisfy: k = 1 and k is an arbitrary value of 100 to 250.

16. The silicon-carbon composite material according to claim 15, wherein K is an arbitrary value of 130 to 180.

17. A silicon-carbon composite material prepared by the following steps: i) providing a porous carbon skeleton, wherein the porous carbon skeleton has a through-pore structure and has an oil absorption value of > 100 mL / 100 g and < 190 mL / 100 g; ii) forming a silicon-containing deposition layer in the pores of the porous carbon skeleton by chemical vapor deposition using a silicon-containing gas source to obtain an intermediate material; iii) forming a carbon-containing coating layer on the silicon-containing deposition layer of the intermediate material and / or on the particle surface of the porous carbon skeleton to obtain the particulate silicon-carbon composite material, wherein the carbon-containing coating layer accounts for 3 wt% to 10 wt% based on the total weight of the silicon-carbon composite material; wherein the silicon-carbon composite material has an oil absorption value of 35 mL / 100 g to 80 mL / 100 g.

18. The silicon-carbon composite material according to claim 17, wherein the silicon-carbon composite material has an oil absorption value of 45 mL / 100 g to 70 mL / 100 g.

19. The silicon-carbon composite material according to claim 18, having an oil absorption value of 48 mL / 100 g to 62 mL / 100 g.

20. The silicon-carbon composite material of any one of claims 17-19, wherein the silicon-carbon composite material has a particle center silicon content of > 15 wt.%, based on the total weight of the particle; wherein, The particle center silicon content is obtained by selecting a cross section with a major axis length equal to the volume average particle size from the cross section of the particles obtained by ion polishing of the material, and determining the silicon content at the midpoint of the major axis on the selected cross section.

21. The silicon-carbon composite material according to claim 20, having a particle center silicon content of 20 wt% to 35 wt%.

22. The silicon-carbon composite material according to any one of claims 17 to 19, wherein the porous carbon skeleton has an oil absorption value of > 120 mL / 100 g and < 190 mL / 100 g.

23. The silicon-carbon composite material according to claim 22, wherein the porous carbon skeleton has an oil absorption value of > 150 mL / 100 g and < 190 mL / 100 g.

24. The silicon-carbon composite material according to claim 23, wherein the porous carbon skeleton has an oil absorption value of 136 mL / 100 g to 179 mL / 100 g.

25. The silicon-carbon composite material according to any one of claims 17 to 19, wherein the silicon-carbon composite material comprises 20 wt% to 60 wt% silicon based on the total weight of the silicon-carbon composite material.

26. The silicon-carbon composite material according to claim 25, wherein the silicon-carbon composite material comprises 30 wt% to 50 wt% silicon.

27. The silicon-carbon composite material according to claim 26, wherein the silicon-carbon composite material comprises 35 wt% to 45 wt%.

28. The silicon-carbon composite material according to any one of claims 17 to 19, wherein the carbon-containing coating layer accounts for 3.5 wt% to 7 wt% based on the total weight of the silicon-carbon composite material.

29. The silicon-carbon composite material according to claim 28, wherein the carbon-containing coating layer accounts for 4 wt% to 6 wt%.

30. The silicon-carbon composite material of claims 17-19, wherein, The oil absorption value of the porous carbon skeleton X1, the oil absorption value of the silicon-carbon composite material X2, the weight percentage of silicon in the silicon-carbon composite material Y1 and the weight percentage of the carbon coating layer Y2 satisfy the following relationship: k = 1 and k is any value from 100 to 250.

31. The silicon-carbon composite material of claim 30, k is any value from 130 to 180.

32. A negative electrode sheet comprising a current collector and a negative electrode material layer disposed on at least one surface of the current collector, the negative electrode material layer comprising the silicon-carbon composite material of any one of claims 1 to 31.

33. The negative electrode sheet of claim 32, wherein the negative electrode material layer comprises 5 wt% to 50 wt% of the silicon-carbon composite material, based on the total weight of the negative electrode material layer.

34. The negative electrode sheet of claim 33, wherein the negative electrode material layer comprises 10 wt% to 30 wt% of the silicon-carbon composite material.

35. The negative electrode sheet of claim 34, wherein the negative electrode material layer comprises 15 wt% to 25 wt% of the silicon-carbon composite material.

36. A secondary battery comprising the silicon-carbon composite material of any one of claims 1 to 31, or the negative electrode sheet of any one of claims 32 to 35.

37. A battery module comprising the secondary battery of claim 36.

38. A battery pack comprising the battery module of claim 37.

39. An electric device comprising at least one selected from the secondary battery of claim 36, the battery module of claim 37 or the battery pack of claim 38.

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