Silicon-carbon negative electrode material and preparation method thereof

Abstract

The present application provides a kind of silicon-carbon negative electrode material and its preparation method.The silicon-carbon negative electrode material includes carbon skeleton with pore structure and silicon-based material arranged in the pore structure, in the region from the surface of the silicon-carbon negative electrode material to the inside extending 10nm from the surface, the content of high-valence silicon is less than 25% relative to the total amount of low-valence silicon and high-valence silicon, wherein the low-valence silicon is 0-valence to 2-valence silicon, and the high-valence silicon is 3-valence to 4-valence silicon.Thereby, the lithium extraction gram capacity and the first coulomb efficiency of the silicon-carbon negative electrode material can be improved, and the discharge gram capacity and the first coulomb efficiency of the secondary battery can be improved.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to a silicon-carbon anode material and its preparation method. Background Technology

[0002] With the continuous increase in the power of electronic devices such as mobile phones, computers, power tools, and electric vehicles, the demand for energy density in rechargeable batteries is also increasing. Silicon-based anode materials have high specific capacity, and the industry has begun to improve the energy density of rechargeable batteries by incorporating silicon-based anode materials into the anode sheets. However, the increased volume expansion rate after lithium intercalation in silicon-based anode materials may lead to cracking of the anode sheets.

[0003] To address the issue of high volume expansion rates in silicon-based anode materials, current research often employs silicon-carbon anode materials formed by depositing silicon within porous carbon. This utilizes the voids within the porous carbon to mitigate the expansion of the silicon-based material. However, because the silicon in the silicon-carbon anode material is oxidized to high-valence silicon, the specific capacity of the silicon-carbon anode material decreases, impacting the initial coulombic efficiency of the secondary battery. Summary of the Invention

[0004] This application is made in view of the above-mentioned problems, and its purpose is to provide a silicon-carbon anode material and a method for preparing it. This silicon-carbon anode material has high lithium removal capacity and initial coulombic efficiency, thereby improving the discharge capacity and initial coulombic efficiency of secondary batteries.

[0005] To achieve the above objectives, a first aspect of this application provides a silicon-carbon anode material comprising a carbon framework having a porous structure and a silicon-based material disposed in the porous structure. In a region extending 10 nm from the surface of the silicon-carbon anode material inward from the surface, the content of high-valence silicon is less than 25% relative to the total amount of low-valence silicon and high-valence silicon, wherein the low-valence silicon is silicon with a valence of 0 to 2 and the high-valence silicon is silicon with a valence of 3 to 4.

[0006] The silicon-carbon anode material of this application suppresses the content of high-valence silicon to a low level, resulting in a high content of low-valence silicon, thereby improving the specific capacity and initial coulombic efficiency of the anode material, and effectively improving the discharge specific capacity and initial coulombic efficiency of the secondary battery.

[0007] In some embodiments, within a region extending 10 nm inward from the surface of the silicon-carbon anode material, the content of high-valence silicon is less than or equal to 20% relative to the combined amount of low-valence and high-valence silicon. Consequently, the anode material exhibits higher specific capacity after lithium removal and higher initial coulombic efficiency, resulting in a secondary battery with better specific capacity after discharge and higher initial coulombic efficiency.

[0008] In some embodiments, within a region extending from 10 nm to 20 nm from the surface of the silicon-carbon anode material, the content of high-valence silicon is less than or equal to 20% relative to the combined amount of low-valence and high-valence silicon, optionally less than or equal to 10%. Thus, the content of high-valence silicon in the silicon-carbon anode material of this application is further suppressed to a low level, which is more conducive to improving the lithium stripping capacity and first coulombic efficiency of the anode material.

[0009] In some embodiments, within a region extending from 20 nm to 30 nm from the surface of the silicon-carbon anode material, the content of high-valent silicon is less than or equal to 10%, and optionally less than or equal to 5%, relative to the combined amount of low-valent and high-valent silicon. Thus, the content of high-valent silicon in the silicon-carbon anode material of this application is further suppressed to a low level, which is more conducive to improving the lithium stripping capacity and initial coulombic efficiency of the anode material.

[0010] In some embodiments, the silicon-carbon anode material satisfies at least one of the following conditions: (1) the volume distribution particle size Dv50 of the silicon-carbon anode material is 5μm-10μm, optionally 6μm-9μm; (2) the specific surface area of ​​the silicon-carbon anode material is less than or equal to 5m². 2 / g, can be less than or equal to 2m 2 / g; (3) The compacted density of the silicon-carbon anode material under 3000N pressure is 0.8g / cm³. 3 -1.2g / cm 3 0.9g / cm³ is an option. 3 -1.2g / cm 3 (4) The tap density of the silicon-carbon anode material is 0.9 g / cm³. 3 -1.1g / cm 3 1.0g / cm can be selected. 3 -1.1g / cm 3 (5) The specific lithium removal capacity of the silicon-carbon anode material is 800mAh / g-2500mAh / g, and can be selected as 1000mAh / g-2000mAh / g. By keeping the particle size, compaction density, and tap density of the silicon-carbon anode material within the above range, the compaction density of the electrode sheet can be effectively improved, thereby increasing the energy density of the battery cell. In addition, by keeping the specific surface area within 5m²... 2 Below / g, the contact area between particles and electrolyte can be minimized as much as possible, thereby improving initial coulombic efficiency, cycle and storage performance.

[0011] In some embodiments, the pore volume of the carbon framework is 0.4 cm³. 3 / g-1.5cm 3 / g, can be selected as 0.6cm 3 / g-1.2cm 3 / g; and / or, relative to the pore volume, the volume ratio of micropores with a pore diameter of less than 2 nm is greater than or equal to 60%, optionally greater than or equal to 80%. This allows silicon-based material to be primarily deposited within the micropores; the higher the proportion of micropores, the more silicon-based material is deposited, and the higher the corresponding lithium removal capacity.

[0012] In some embodiments, the surface of the silicon-carbon anode material has a coating layer; optionally, the coating layer is a carbon coating layer. This application, through this coating layer, significantly reduces the risk of silicon in the anode material being oxidized to form high-valence silicon, thus reducing the content of high-valence silicon in the silicon-carbon anode material.

[0013] The second aspect of this application provides a method for preparing the silicon-carbon anode material of the first aspect, comprising the following steps:

[0014] The silicon-carbon particle formation step involves reacting a porous carbon framework with a silicon source gas to form silicon-carbon particles containing silicon-based materials within the porous structure; and

[0015] The silicon carbon particle treatment step involves introducing a mixed gas, comprising a carbon source gas and an inert gas, into the silicon carbon particles at a flow rate greater than 0 L / min and less than or equal to 10 L / min under conditions of a temperature of 500℃-800℃ and a pressure of 0 kPa-1 kPa. The carbon source gas is selected from at least one of ethane, ethylene, acetylene, and methane.

[0016] The above preparation method can form a uniform and dense coating layer on the surface of silicon-carbon particles, which greatly reduces the risk of silicon being oxidized in the anode material to form high-valence silicon, and can obtain silicon-carbon anode materials with high lithium removal capacity and first coulombic efficiency.

[0017] In some embodiments, during the silicon-carbon particle processing step, the mixed gas is introduced into the silicon-carbon particles at a temperature of 550°C-650°C and a pressure of 0 kPa-0.5 kPa at a flow rate of 0.5 L / min-4 L / min. This allows for the formation of a more uniform and dense coating layer, which is beneficial for obtaining silicon-carbon anode materials with higher lithium removal capacity and initial coulombic efficiency.

[0018] In some embodiments, the mixed gas comprises 10-70 vol% acetylene, 0-20 vol% methane, and 10-90 vol% inert gas; optionally, it comprises 15-60 vol% acetylene, 5-10 vol% methane, and 30-80 vol% inert gas. Thus, by using a specific mixed gas, the decomposition rate can be controlled, allowing carbon to slowly coat the particle surface, resulting in a denser coating.

[0019] In some embodiments, the silicon-carbon particle formation step includes the following steps: evacuating the reaction apparatus and then introducing an inert gas. This removes oxygen from the reaction apparatus, significantly reducing the risk of the silicon deposited in the negative electrode material being oxidized by oxygen in the reaction apparatus to form high-valence silicon.

[0020] In some embodiments, the silicon-carbon particle formation step includes the following step: heating a porous carbon skeleton to 400°C-550°C in a reaction apparatus to remove oxygen from the carbon skeleton. This removes oxygen adsorbed by the carbon skeleton itself, significantly reducing the risk of silicon deposited in the anode material being oxidized by oxygen adsorbed by the carbon skeleton, thus forming high-valence silicon.

[0021] In some embodiments, the silicon-carbon particle formation step includes the following steps: introducing a mixture of silicon source gas and inert gas into the reaction apparatus, and depositing at a temperature of 400°C-550°C for 2 to 10 hours to form silicon-carbon particles. This allows silicon to be uniformly deposited inside the porous carbon.

[0022] In some embodiments, the silicon source gas is selected from one or more of silane, silane, dichlorosilane, and trichlorosilane; optionally, the silicon source gas is silane.

[0023] In some embodiments, the inert gas is argon. This prevents the silicon source gas from flamming and the silicon from being oxidized.

[0024] A third aspect of this application also provides a negative electrode sheet, comprising the silicon-carbon negative electrode material of the first aspect of this application or the silicon-carbon negative electrode material prepared by the second aspect.

[0025] A fourth aspect of this application also provides a secondary battery, including the negative electrode sheet of the third aspect of this application. This secondary battery exhibits excellent initial coulombic efficiency.

[0026] The fifth aspect of this application also provides an electrical device, including the secondary battery of the fourth aspect of this application. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of a battery cell according to one embodiment of this application.

[0028] Figure 2 yes Figure 1 An exploded view of a battery cell according to one embodiment of this application is shown.

[0029] Figure 3 This is a schematic diagram of a battery module according to one embodiment of this application.

[0030] Figure 4This is a schematic diagram of a battery pack according to one embodiment of this application.

[0031] Figure 5 yes Figure 4 An exploded view of a battery pack according to one embodiment of this application is shown.

[0032] Figure 6 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application.

[0033] Figure 7 This is an XPS image of the silicon-carbon anode material of Embodiment 1 of this application, analyzed from the surface to the region extending 10 nm inward from the surface.

[0034] Figure 8 This is an XPS image of the silicon-carbon anode material of Comparative Example 1 of this application, analyzed from the surface to the region extending 10 nm inward from the surface.

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

[0036] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Battery cell; 51 Housing; 52 Electrode assembly; 53 Cover plate. Detailed Implementation

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

[0038] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

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

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

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

[0042] Unless otherwise specified, the terms used in this application have the common meanings as commonly understood by those skilled in the art.

[0043] Unless otherwise specified, the values ​​of the parameters mentioned in this application can be determined using various testing methods commonly used in the art, such as the testing methods provided in this application.

[0044] With the extensive research on silicon-carbon anode materials, higher demands have been placed on their performance. Inventors have discovered that increasing the content of low-valent silicon in silicon-carbon anode materials helps improve their lithium removal capacity. However, in current silicon-carbon anode materials, low-valent silicon is inevitably oxidized to form high-valent silicon, leading to a decrease in lithium removal capacity and initial coulombic efficiency. Furthermore, this high-valent silicon readily forms irreversible lithium silicates with lithium ions, reducing the amount of active lithium that is repeatedly inserted and extracted between the positive and negative electrodes, resulting in lithium loss and consequently a decrease in the discharge capacity and initial coulombic efficiency of the secondary battery.

[0045] In view of this, this application proposes a silicon-carbon anode material, comprising a carbon framework having a porous structure and a silicon-based material disposed in the porous structure. In a region extending 10 nm from the surface of the silicon-carbon anode material to the interior, the content of high-valence silicon is less than 25% relative to the total amount of low-valence silicon and high-valence silicon. The low-valence silicon is silicon with a valence of 0 to 2, and the high-valence silicon is silicon with a valence of 3 to 4.

[0046] The silicon-carbon anode material of this application suppresses the content of high-valence silicon to a low level, so that the content of low-valence silicon is greater than or equal to 75%, which improves the specific capacity and first coulombic efficiency of the anode material. Moreover, the low content of high-valence silicon reduces the formation of lithium silicate and significantly reduces lithium loss, effectively improving the discharge specific capacity and first coulombic efficiency of the secondary battery.

[0047] In this application, the aforementioned high-valence silicon and low-valence silicon can be quantified using XPS. In the XPS plot, the binding energy of low-valence silicon is 98-102 eV, corresponding to valence states of 0, 1, and 2. The area enclosed by the curve and the baseline (S1) represents the atomic molar mass of low-valence silicon. The binding energy of high-valence silicon is 102-106 eV, corresponding to valence states of 3 and 4. The area enclosed by the curve and the baseline (S2) represents the atomic molar mass of high-valence silicon. Relative to the combined amount of low-valence and high-valence silicon, the content of high-valence silicon = S2 / (S1+S2)×100%, and the content of low-valence silicon = S1 / (S1+S2)×100%. The baseline is the line connecting two points on the test curve, namely X = 98 eV and X = 106 eV.

[0048] In some embodiments, the content of high-valence silicon (denoted as C) is specified in the region extending 10 nm from the surface of the silicon-carbon anode material inward. 10The percentage () is a range of values ​​between any two values, including but not limited to: 24%, 23%, 22%, 21%, 20%, 19%, 18%, 17%, 16%, 15%, 14%, 13%, 12%, 11%, 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%. In some embodiments, C is preferably used in the region extending 10 nm from the surface of the silicon-carbon anode material into the interior. 10 Less than or equal to 20%, therefore C is preferred. 10 Less than or equal to 10%. The smaller the content of high-valence silicon in the region extending 10 nm from the surface of the silicon-carbon anode material into the interior, the higher the content of low-valence silicon, and the higher the specific capacity of the silicon-carbon anode material for lithium removal. Moreover, the low content of high-valence silicon reduces the formation of lithium silicates, which greatly improves the discharge specific capacity and initial coulombic efficiency of the secondary battery.

[0049] In some embodiments, the content of high-valence silicon (denoted as C) is defined in the region from 10 nm to 20 nm from the surface of the silicon-carbon anode material. 20 The content of high-valence silicon is less than or equal to 20%. For example, the content of high-valence silicon can be 20%, 19%, 18%, 17%, 16%, 15%, 14%, 13%, 12%, 11%, 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, or any value within a range of two such values, but is not limited thereto. In some embodiments, C is preferably present in the region from 10 nm to 20 nm from the surface of the silicon-carbon anode material. 20 Less than 10%.

[0050] In some embodiments, the content of high-valence silicon (denoted as C) is specified in the region extending from 20 nm to 30 nm from the surface of the silicon-carbon anode material. 30 The content of high-valent silicon (C) is less than or equal to 10%. For example, the content of high-valent silicon (C) 30 The percentage (C) can be 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, or any range of two values, but is not limited thereto. Preferably, in the region from 20 nm to 30 nm from the surface of the silicon-carbon anode material, C 30 Less than or equal to 5%.

[0051] Regarding the above C 10 C 20 C 30 For specific determination methods, please refer to the description in the Examples section.

[0052] In some embodiments, the silicon-carbon anode material satisfies at least one of the following conditions: (1) the volume distribution particle size Dv50 of the silicon-carbon anode material is 5μm-10μm, for example, it can be 5μm, 6μm, 6.5μm, 7μm, 7.5μm, 8μm, 8.5μm, or 9μm, preferably 6μm-9μm; (2) the specific surface area of ​​the silicon-carbon anode material is less than or equal to 5m². 2 / g, for example, can be 5m 2 / g、4m 2 / g、3m 2 / g、2m 2 / g, 1.5m 2 / g、1m 2 / g, etc., preferably less than or equal to 2m 2 / g; (3) The compacted density of the silicon-carbon anode material under 3000N pressure is 0.8g / cm³. 3 -1.2g / cm 3 For example, it can be 0.8 g / cm³. 3 0.9g / cm 3 0.95g / cm 3 1.0g / cm 3 1.1g / cm 3 1.15g / cm 3 1.2g / cm 3 The preferred value is 0.9 g / cm³. 3 -1.2g / cm 3 (4) The tap density of the silicon-carbon anode material is 0.9 g / cm³. 3 -1.1g / cm 3 For example, it can be 0.9 g / cm³. 3 0.95g / cm 3 1.0g / cm 3 1.05g / cm 3 1.1g / cm 3 The preferred value is 1.0 g / cm³. 3 -1.1g / cm 3(5) The lithium removal capacity of the silicon-carbon anode material is 800mAh / g-2500mAh / g, for example, it can be 800mAh / g, 900mAh / g, 1000mAh / g, 1100mAh / g, 1200mAh / g, 1300mAh / g, 1400mAh / g, 1500mAh / g, 1600mAh / g, 1700mAh / g, 1800mAh / g, 1900mAh / g, 2000mAh / g, 2100mAh / g, etc., preferably 1000mAh / g-2000mAh / g. By keeping the particle size, compaction density and tap density of the silicon-carbon anode material within the above range, the compaction density of the electrode sheet can be effectively improved, and the energy density of the cell can be improved. In addition, by keeping the specific surface area within 5m², the specific surface area can be improved. 2 Below / g, the contact area between particles and electrolyte can be minimized, thereby improving initial coulombic efficiency, cycle and storage performance.

[0053] In this application, the volumetric particle size distribution (Dv50) of the material has a well-known meaning in the art, representing the particle size corresponding to a cumulative volumetric distribution percentage of 50%, which 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. The testing instrument can be a Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK.

[0054] In this application, the specific surface area of ​​the material has a meaning known in the art and can be determined using instruments and methods known in the art. For example, it can be tested using the nitrogen adsorption specific surface area analysis method according to GB / T 19587-2017, and calculated using the BET (Brunauer Emmett Teller) method. The testing instrument can be the Tri-Star 3020 specific surface area and pore size analyzer from Micromeritics, USA.

[0055] In this application, the compacted density of the powder is a term known in the art and can be determined using instruments and methods known in the art. For example, it can be determined using an electronic pressure testing machine (e.g., a UTM7305 type electronic pressure testing machine) in accordance with GB / T 24533-2009. An exemplary test method is as follows: Weigh 1g of sample powder, add it to a mold with a bottom area of ​​1.327cm2, pressurize to 300kg, hold the pressure for 30s, then release the pressure, hold for 10s, and then record and calculate the compacted density of the material under a pressure of 3000N.

[0056] In this application, the tap density of the material 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 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 measuring cylinder of 25mL.

[0057] In this application, the lithium removal capacity of the material has a meaning known in the art and can be tested using methods known in the art. Specific testing methods can be found in the embodiments described.

[0058] In some embodiments, the pore volume of the carbon framework is 0.4 cm³. 3 / g-1.5cm 3 / g, can be selected as 0.6cm 3 / g-1.2cm 3 / g, and / or, relative to the aforementioned pore volume, the volume percentage of micropores with a diameter less than 2 nm is greater than or equal to 60%, optionally greater than or equal to 80%. This allows the silicon-based material to be primarily deposited within the micropores; the higher the proportion of micropores, the more silicon-based material is deposited, and the higher the corresponding lithium removal capacity. In some embodiments, the aforementioned silicon-based material can be amorphous hard carbon.

[0059] In some embodiments, the surface of the aforementioned silicon-carbon anode material has a coating layer; optionally, the coating layer is a carbon coating layer. By providing a uniform and dense coating layer, this application can further prevent oxygen in the air from entering the anode material, greatly reducing the risk of silicon in the silicon-carbon anode material being oxidized to form high-valence silicon, and reducing the content of high-valence silicon in the silicon-carbon anode material.

[0060] In addition, this application provides a method for preparing the above-mentioned silicon-carbon anode material, which includes a silicon-carbon particle forming step (step (a)), in which a carbon skeleton with a porous structure reacts with a silicon source gas to form silicon-carbon particles with silicon-based materials within the porous structure; and a silicon-carbon particle processing step (step (b)), in which a mixed gas including a carbon source gas and an inert gas is introduced into the silicon-carbon particles at a gas flow rate greater than 0 L / min and less than or equal to 10 L / min under the conditions of a temperature of 500℃-700℃ and a pressure of 0 kPa-1 kPa, wherein the carbon source gas is selected from at least one of ethane, ethylene, acetylene, and methane.

[0061] Therefore, by employing specific temperatures, pressures, ventilation rates, and mixed gases, the decomposition rate of the carbon source gas can be effectively controlled, which is beneficial for forming a uniform and dense coating layer on the surface of silicon-carbon particles. This effectively reduces the risk of silicon in the silicon-carbon particles being oxidized by oxygen in the air to form high-valence silicon, thus reducing the content of high-valence silicon in the particles and making C...10 C 20 and C 30 Within the aforementioned range, by selecting the aforementioned carbon source gas, uniform and complete coating can be achieved.

[0062] In some embodiments, in step (b), the temperature can be, for example, a value between 500°C, 550°C, 600°C, 650°C, 700°C, or any combination of these values. The pressure can be, for example, a value between 0 kPa, 50 Pa, 100 Pa, 150 Pa, 200 Pa, 250 Pa, 300 Pa, 350 Pa, 400 Pa, 450 Pa, 500 Pa, 550 Pa, 600 Pa, 650 Pa, 700 Pa, 750 kPa, 800 Pa, 850 Pa, 900 Pa, 950 Pa, 1000 Pa (1 kPa), or any combination of these values. By controlling the temperature and pressure within the aforementioned ranges, the decomposition rate of the carbon source gas can be effectively controlled, which is beneficial for forming a uniform and dense coating layer.

[0063] In some embodiments, in step (b), the ventilation rate can be, for example, 0.5 L / min, 1.0 L / min, 1.5 L / min, 2.0 L / min, 2.5 L / min, 3.0 L / min, 3.5 L / min, 4.0 L / min, 4.5 L / min, 5.0 L / min, 5.5 L / min, 6.0 L / min, 6.5 L / min, 7.0 L / min, 7.5 L / min, 8.0 L / min, 8.5 L / min, 9.0 L / min, 9.5 L / min, 10.0 L / min, or a value within a range of any two of these values. By controlling the ventilation rate within the above range, the carbon source gas can react fully, improving the utilization rate of the carbon source gas and facilitating the formation of a uniform and dense coating layer.

[0064] In some embodiments, in step (b), preferably, the mixed gas is introduced at a temperature of 550°C-650°C and a pressure of 0 kPa-500 Pa at a flow rate of 0.5 L / min-4 L / min. Under these conditions, a denser coating layer can be formed, further reducing the possibility of oxygen in the air entering the particle and oxidizing the silicon, and further reducing C. 10 C 20 and C 30 .

[0065] In some embodiments, preferably, the mixed gas comprises 10%-70% acetylene, 0%-20% methane, and 10%-90% inert gas; more preferably, the mixed gas comprises 15%-60% acetylene, 5%-10% methane, and 30%-80% inert gas. Acetylene has a low decomposition temperature and decomposes rapidly. Adding a certain amount of methane can control the decomposition rate of acetylene, allowing carbon to slowly coat the particle surface, resulting in a dense coating layer.

[0066] Inert gases are gases that do not react with silicon materials. Examples of inert gases include, but are not limited to, helium, neon, argon, krypton, xenon, and radon. Using inert gases as protective gases can reduce the formation of Si3N4.

[0067] In some implementations, step (a) above may include steps (a1) to (a3) ​​below.

[0068] Step (a1) In the reaction apparatus, a porous carbon skeleton is heated to 400℃-550℃ to remove oxygen from the carbon skeleton.

[0069] The above-mentioned reaction apparatus is not particularly limited and can be any commonly used apparatus in the field, such as: medium frequency furnace, roller kiln, rotary kiln, pusher kiln, vertical granulation kettle, horizontal granulation kettle, vertical reaction kettle, horizontal reaction kettle or drum furnace, etc.

[0070] In step (a1), the carbon skeleton is heated to 400℃-550℃. For example, it can be heated to 400℃, 410℃, 420℃, 430℃, 440℃, 450℃, 460℃, 470℃, 480℃, 490℃, 500℃, 510℃, 520℃, 530℃, 540℃, 550℃, or any value within a range of two such values, but is not limited thereto. Preferably, the carbon skeleton is heated to 450℃-550℃. By heating the carbon skeleton to the above range, the oxygen adsorbed by the carbon skeleton itself can be eliminated, which greatly reduces the risk of silicon deposited in the anode material being oxidized by the oxygen adsorbed by the carbon skeleton to form high-valence silicon. This keeps the content of low-valence silicon in the silicon-carbon anode material at a high level, which helps to reduce the content of high-valence silicon, making C... 10 C 20 C 30 Within the aforementioned range, a silicon-carbon anode material with high lithium removal capacity was obtained.

[0071] Step (a2) The reaction apparatus is evacuated, and then an inert gas is introduced.

[0072] This step removes oxygen from the reaction apparatus, significantly reducing the risk of deposited silicon in the anode material being oxidized by oxygen and forming high-valence silicon. This helps maintain a high level of low-valence silicon in the silicon-carbon anode material and reduces the content of high-valence silicon, thus improving the C... 10 C 20 C 30 Within the aforementioned range.

[0073] In some embodiments, the vacuum level inside the reaction apparatus is 1×10⁻⁶ by evacuation. -3 Pa ~ 1×10 -6 Pa, for example, can be 1×10 -5 Pa. The lower the pressure inside the reaction apparatus, the less residual oxygen is inside the apparatus, and the lower the content of high-valence silicon in the prepared silicon-carbon anode material.

[0074] In some embodiments, after the pressure value in the reaction device reaches the aforementioned pressure value and is maintained for the aforementioned time in step (a2), an inert gas is introduced into the reaction device to further reduce the residual amount of oxygen in the reaction device.

[0075] In some implementations, the above steps (a2) (vacuuming, pressure holding, and introducing inert gas) can be repeated cyclically, and the number of times this step can be performed includes, but is not limited to, 1, 2, and 3.

[0076] In some embodiments, step (a2) may involve detecting the oxygen content in the exhaust gas discharged from the reaction device at a set frequency. Step (a2) is terminated when the oxygen content in the exhaust gas is below 200 ppm. For example, step (a2) may be terminated when the oxygen content in the exhaust gas is 0 ppm, 20 ppm, 40 ppm, 60 ppm, 80 ppm, 100 ppm, 120 ppm, 140 ppm, 160 ppm, 180 ppm, 190 ppm, or any combination of these values.

[0077] The order of steps (a1) and (a2) is not particularly limited; step (a1) can be performed before step (a2), or step (a2) can be performed before step (a1). Through these two steps, oxygen contained in the raw materials and reaction apparatus is eliminated to the greatest extent possible.

[0078] Step (a3) A mixture of silicon source gas and inert gas is introduced into the reaction device, and silicon-carbon particles are formed by deposition at a temperature of 400℃~550℃ for 2 to 10 hours.

[0079] The silicon source gas mentioned above includes gases that can provide silicon atoms. For example, it can be one or more of silane, disilane, dichlorosilane, and trichlorosilane. Optionally, the silicon source gas is silane. The definition of the inert gas used in this step is the same as that in step (b) above, and argon is preferred.

[0080] In some embodiments, a rotary kiln is used as the reaction apparatus. A mixture of silane and argon is introduced into the rotary kiln at a flow rate of 0.1 L / min to 4 L / min, and the reaction is carried out under a slightly positive pressure of 0-0.5 kPa and a rotation frequency of 0 Hz to 80 Hz. The rotation frequency of the reaction apparatus can be 0 Hz, 5 Hz, 10 Hz, 20 Hz, 30 Hz, 40 Hz, 50 Hz, 60 Hz, 70 Hz, 80 Hz, or any combination of these values. By setting the rotation frequency within the above range, the powder can be fully rotated within the kiln, enhancing the contact between the powder and the gas, and ensuring a complete reaction.

[0081] This step (a3) ​​is performed after the above steps (a1) and (a2) because the oxygen contained in the reaction materials and reaction apparatus has been eliminated by the above steps (a1) and (a2), so the risk of oxidation of the silicon deposited in step (a3) ​​can be greatly reduced.

[0082] In addition, this application provides a negative electrode sheet, which includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector. The negative electrode film layer includes a negative electrode active material, which includes the silicon-carbon negative electrode material of this application or the silicon-carbon negative electrode material prepared according to the preparation method of this application.

[0083] 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.

[0084] 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.).

[0085] In some embodiments, the negative electrode film layer may optionally include an adhesive. The adhesive 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).

[0086] 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.

[0087] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0088] 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.

[0089] In addition, the secondary battery and power-consuming device of this application will be described below with appropriate reference to the accompanying drawings.

[0090] In one embodiment of this application, a secondary battery is provided.

[0091] The term "secondary battery" used in this article refers to a single battery cell, a battery module, or a battery pack. These will be explained separately below.

[0092] Typically, a single secondary battery cell includes 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.

[0093] [Positive electrode plate]

[0094] 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.

[0095] 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.

[0096] 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.).

[0097] In some embodiments, when the battery cell is a lithium-ion battery, the positive electrode active material may be a positive electrode active material known in the art for lithium-ion batteries. As an example, the positive electrode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as 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 / 3Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05At 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.

[0098] 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.

[0099] 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.

[0100] 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.

[0101] [Electrolytes]

[0102] 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.

[0103] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0104] 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.

[0105] 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.

[0106] 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.

[0107] [Isolation membrane]

[0108] This application does not impose any particular restrictions on the type of separator membrane; any known porous separator membrane with good chemical and mechanical stability can be selected.

[0109] 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.

[0110] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0111] 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.

[0112] 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.

[0113] 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.

[0114] In some implementations, refer to Figure 2The outer packaging may include a housing 51 and a top cover assembly 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 top cover assembly 53 can cover 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 the battery cell 5 can be one or more, which can be selected by those skilled in the art according to specific practical needs.

[0115] In some implementations, individual battery cells can be assembled into a battery module. The number of individual battery cells contained in a battery module can be one or more, and the specific number can be selected by those skilled in the art based on the application and capacity of the battery module.

[0116] 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.

[0117] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0118] 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.

[0119] Figure 4 and Figure 5 This is battery pack 1 as an example. (See reference...) Figure 4 and Figure 5 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.

[0120] In addition, this application also provides an electrical device, which includes the secondary battery provided in this application. The secondary battery can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0121] As the electrical device, a single battery cell, a battery module, or a battery pack can be selected according to its usage requirements.

[0122] Figure 6 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.

[0123] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a single battery cell as their power source.

[0124] Example

[0125] 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.

[0126] Example 1

[0127] Preparation of silicon-carbon anode materials

[0128] Step (a1): Weigh 500g of porous carbon and place it in a rotary kiln. Heat it to 500℃ (T1) under argon protection and keep it at that temperature for 2 hours to desorb the air adsorbed in the porous carbon.

[0129] Step (a2): Evacuate the rotary kiln to a vacuum level of 1×10⁻⁶. -5 After maintaining the pressure at 100 Pa for 5 minutes, argon gas is introduced. The process of evacuating and introducing argon gas is repeated until the oxygen content in the exhaust gas is below 200 ppm.

[0130] Step (a3): A mixture of silane and argon gas (volume ratio of silane to argon 1:4) is introduced into the rotary kiln at a flow rate of 4 L / min, maintaining a slight positive pressure of 200 Pa, and the rotary kiln is rotated at a rotation frequency of 40 Hz to obtain silicon-carbon particles.

[0131] Step (b): The rotary kiln temperature is raised to 500℃ (T2), and a mixture of acetylene, methane and argon gas is introduced at a pressure (P) of 0.2 kPa and a gas flow rate (V) of 3 L / min. The rotary kiln is rotated at a rotation frequency of 40 Hz to coat the silicon carbide particles.

[0132] Then, after natural cooling, the silicon-carbon anode material is obtained by passing it through a 200-mesh sieve.

[0133] Determination of the content of high-valent silicon in silicon-carbon negative electrode materials 10 20 30 Determination of the content of high-valent silicon in silicon-carbon negative electrode materials​​

[0134] (1) Using X-rays as the excitation source, the surface of the silicon-carbon anode material was subjected to X-rays, and the region from the surface to a depth of 10 nm was detected. Figure 7 The XPS plot shown uses the area S1 enclosed by the curve corresponding to the 98-102 eV energy range and the baseline to represent the amount of low-valence silicon, and the area S2 enclosed by the curve corresponding to the 102-106 eV energy range and the baseline to represent the amount of high-valence silicon. The content C of high-valence silicon is calculated based on S2 / (S1+S2). 10 It is 17.5%.

[0135] (2) The surface of the silicon-carbon anode material described in (1) was etched using an argon ion gun at a etching rate of approximately 4 nm / min. By adjusting the etching time to 2.5 min, the analytical region described in (1) (i.e., the region from the surface to a depth of 10 nm) was etched away. Then, X-rays were used as the excitation source to act on the new surface of the silicon-carbon anode material after the above etching. The distribution information of photoelectron information at a depth of 10 nm was obtained. The silicon valence state information in the region from 10 nm to 20 nm from the surface was obtained using the same method as described in (1). 20 It is 9.6%.

[0136] (3) The surface of the silicon-carbon anode material described in (2) was further etched using an argon ion gun at a rate of approximately 4 nm / min, with the etching time adjusted to 2.5 min. The analytical region described in (2) was etched away, and then X-rays were used as the excitation source to act on the new surface of the etched silicon-carbon anode material. The distribution information of photoelectron information at a depth of 10 nm was obtained. The silicon valence state information in the region from 20 nm to 30 nm from the surface was obtained using the same method as described in (1). 30 It is 4.2%.

[0137] Preparation of secondary batteries

[0138] (a) Preparation of negative electrode sheet

[0139] The silicon-carbon composite material, conductive carbon black, thickener sodium carboxymethyl cellulose (CMC), and binder styrene-butadiene rubber emulsion (SBR) obtained above are thoroughly mixed in an appropriate amount of deionized water at a weight ratio of 96.5:1.0:1.0:1.5 to form a uniform negative electrode slurry. The negative electrode slurry is coated onto the negative electrode current collector, and after drying and other processes, the negative electrode sheet is obtained.

[0140] (b) Preparation of the positive electrode sheet

[0141] An 8μm thick aluminum foil was used as the positive electrode current collector. The positive electrode active material, LiNi, was used. 0.8 Co 0.1 Mn 0.1 O2 (NCM811), conductive agent acetylene black, and binder polyvinylidene fluoride (PVDF) are dissolved in solvent N-methylpyrrolidone (NMP) at a weight ratio of 93:2:5. After thorough stirring and mixing, a positive electrode slurry is obtained. The positive electrode slurry is then uniformly coated onto the positive electrode current collector, and after drying, cold pressing, and slitting, a positive electrode sheet is obtained.

[0142] (c) Preparation of electrolyte

[0143] The electrolyte is a mixture of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC), with a volume ratio of EC:20:20:60. LiPF6 is then dissolved in the above organic solvent, and fluoroethylene carbonate (FEC) is added as an additive. The concentration of LiPF6 is 1 mol / L, and the mass percentage of FEC in the electrolyte is 5%.

[0144] (d) Battery fabrication

[0145] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The resulting bare cell is then wound, tabs are welded onto it, and the cell is placed in an aluminum casing. It is then baked at 80°C to remove moisture, followed by the injection of electrolyte and sealing to obtain a non-charged battery. This non-charged battery then undergoes a series of processes including settling, hot and cold pressing, formation, shaping, and capacity testing to obtain the lithium-ion secondary battery of Example 1.

[0146] Examples 2-5 and Comparative Examples 1-2

[0147] The silicon-carbon anode material was prepared in the same manner as in Example 1, except that the temperature (T2) in step (b) was changed as shown in Table 1 below, and C was measured. 10 C 20 C30 This leads to the development of secondary batteries.

[0148] For the silicon-carbon anode material of Comparative Example 1, X-rays were used as the excitation source to act on the surface of the silicon-carbon anode material, and the region from the surface to a depth of 10 nm was detected, yielding... Figure 8 The XPS graph shown. Calculations were performed in the same manner as in Example 1, and the content of high-valent silicon C... 10 It is 30.3%.

[0149] The following performance tests were conducted on the above embodiments and comparative examples.

[0150] <Performance Testing>

[0151] (1) Lithium removal capacity and initial coulombic efficiency of silicon-carbon anode materials

[0152] a. Preparation of coin cell batteries: The above-mentioned silicon-carbon anode material, conductive carbon black, and binder polyacrylic acid were mixed at a mass ratio of 8:1:1. Deionized water was added as a solvent, and the mixture was stirred under the action of a high-speed stirrer until the system was homogeneous, obtaining a negative electrode slurry with a solid content of 45%. The negative electrode slurry was uniformly coated on the negative electrode current collector copper foil and dried at 85°C. After cold pressing, the electrode sheet was obtained. Using lithium metal as the counter electrode, a Celgard 2400 separator was used, and electrolyte was injected to assemble a coin cell battery. The electrolyte was a mixture of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC), wherein the volume ratio of EC, EMC, and DEC was 20:20:60. Then, LiPF6 was dissolved in the above-mentioned organic solvent, and fluoroethylene carbonate (FEC) was added as an additive, wherein the concentration of LiPF6 was 1 mol / L, and the mass percentage of FEC in the electrolyte was 5%.

[0153] b. Coin Cell Testing Procedure: After the assembled coin cells are left to stand for 60 minutes, they are tested using a process of constant current discharge at 0.05C to 5mV, discharge at 50μA to 5mV, stand for 10 minutes, and charge at 0.1C to 2.0V. The lithium insertion capacity of the silicon-carbon anode material is the specific capacity C1 when discharged to 5mV, the lithium removal capacity of the silicon-carbon anode material is the specific capacity C2 when charged to 2.0V, and the initial coulombic efficiency of the silicon-carbon anode material is C2 / C1.

[0154] (2) Discharge capacity and initial coulombic efficiency of the secondary battery

[0155] The secondary batteries obtained through the above embodiments and comparative examples were kept at 25°C for 60 minutes, then charged with a constant current of 0.1C to 4.25V, and then charged with a constant voltage of 4.25V to 0.05C. The charging specific capacity at this time was recorded as Q1. After standing for 10 minutes, they were discharged with a constant current of 0.1C to 2.5V, and then discharged with a constant voltage of 2.5V to 0.05C. The discharge specific capacity at this time was recorded as Q2. The initial coulombic efficiency of the secondary battery was Q2 / Q1.

[0156] Table 1

[0157]

[0158] Note: The volume ratio of the mixed gases in Table 1 is the volume ratio of acetylene, methane, and argon.

[0159] As shown in Table 1, in step (b), by ensuring that the temperature, pressure, air flow rate, and mixed gas of the rotary kiln meet specific conditions, C can be obtained. 10 Less than 25% silicon-carbon anode material. Examples 1-5 show that controlling the rotary kiln temperature at 500℃-700℃ results in silicon-carbon anode materials with low high-valence silicon content and C. 10 All values ​​are less than 25%. The silicon-carbon anode material exhibits high lithium removal specific capacity and initial coulombic efficiency, resulting in high discharge specific capacity and initial coulombic efficiency in the derived secondary battery. In particular, when the rotary kiln temperature is controlled at 550℃-650℃, the C values ​​of the obtained silicon-carbon anode material are significantly increased. 10 Further reductions, all below 20%, and C 20 and C 30 It also further reduces costs, resulting in even better performance of the secondary battery.

[0160] Compared to Examples 1-5, in Comparative Examples 1 and 2, the temperature inside the rotary kiln was either too low (200°C) or too high (1000°C), affecting the C content of the silicon-carbon anode material. 10 If the percentage is greater than 30%, the technical effect of this application cannot be obtained.

[0161] Examples 6-8 and Comparative Example 3

[0162] The pressure (P) in step (b) was changed as shown in Table 2 below. Otherwise, the silicon-carbon anode material was prepared in the same manner as in Example 3, and C was measured. 10 C 20 C 30 This leads to the development of secondary batteries.

[0163] The performance evaluation was performed in the same manner as in Example 3, as shown in Table 2.

[0164] Table 2

[0165]

[0166] As shown in Table 2, by controlling the pressure of the rotary kiln within the range of 0 kPa-1 kPa in step (b), the resulting silicon-carbon anode material has a low content of high-valence silicon and C. 10 All were less than 25%. In particular, when the pressure of the rotary kiln was controlled within the range of 0 kPa-0.5 kPa, the C content of the obtained silicon-carbon anode material was significantly reduced. 10 Further reduction, below 20%, and C 20 and C 30 This further reduces the specific capacity and initial coulombic efficiency of silicon-carbon anode materials, resulting in high discharge specific capacity and initial coulombic efficiency of the secondary batteries.

[0167] In Comparative Example 3, the pressure inside the rotary kiln was too high (5 kPa), affecting the C content of the silicon-carbon anode material. 10 If the ratio is greater than 25%, the technical effect of this application cannot be achieved.

[0168] Examples 9-11 and Comparative Examples 4 and 5

[0169] The gas flow rate (V) in step (b) was changed as shown in Table 3 below. Otherwise, the silicon-carbon anode material was prepared in the same manner as in Example 3, and C was measured. 10 C 20 C 30 This leads to the development of secondary batteries.

[0170] The performance evaluation was performed in the same manner as in Example 3, as detailed in Table 3.

[0171] Table 3

[0172]

[0173] As shown in Table 3, by controlling the air flow rate (V) of the rotary kiln in step (b) within the range of greater than 0 L / min and less than or equal to 10 L / min, the resulting silicon-carbon anode material has a low content of high-valence silicon and C. 10 Less than 25%. In Comparative Examples 4 and 5, the technical effect of this application could not be achieved either because the ventilation rate was too high or no mixed gas was introduced.

[0174] Examples 12-15 and Comparative Example 6

[0175] The composition of the mixed gas in step (b) was changed as shown in Table 4 below. Otherwise, the silicon-carbon anode material was prepared in the same manner as in Example 3, and C was measured. 10 C 20 C 30 This leads to the development of secondary batteries.

[0176] The performance evaluation was performed in the same manner as in Example 3, as shown in Table 4.

[0177] Table 4

[0178]

[0179] As shown in Table 4, in step (b), by selecting at least one of ethane, ethylene, acetylene, and methane as the carbon source gas, the resulting silicon-carbon anode material has a low content of high-valence silicon. 10 Less than 25%. In Comparative Example 6, a mixture of propane, methane, and argon was used. However, because the decomposition temperature of propane was too high, the uniformity and integrity of the coating were poor, resulting in an excessively high content of high-valence silicon, which failed to achieve the technical effect of this application.

[0180] 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 anode material, characterized in that, The silicon-carbon anode material includes a carbon skeleton with a porous structure and a silicon-based material disposed in the porous structure. In a region extending 10 nm from the surface of the silicon-carbon anode material to the interior, the content of high-valence silicon is less than 25% relative to the total amount of low-valence silicon and high-valence silicon. The content of high-valence silicon gradually decreases in the direction extending from the surface of the silicon-carbon anode material to the interior. The low-valence silicon is silicon with a valence of 0 to 2, and the high-valence silicon is silicon with a valence of 3 to 4.

2. The silicon-carbon anode material according to claim 1, characterized in that, In the region extending 10 nm from the surface of the silicon-carbon anode material to the interior, the content of high-valence silicon is less than or equal to 20% relative to the total amount of low-valence silicon and high-valence silicon.

3. The silicon-carbon anode material according to claim 1, characterized in that, In the region defined by a distance of 10 nm from the surface of the silicon-carbon anode material to a distance of 20 nm from the surface of the silicon-carbon anode material, the content of high-valence silicon is less than 20% relative to the total amount of low-valence silicon and high-valence silicon.

4. The silicon-carbon anode material according to claim 3, characterized in that, In the region defined by a distance of 10 nm from the surface of the silicon-carbon anode material to a distance of 20 nm from the surface of the silicon-carbon anode material, the content of high-valence silicon is less than or equal to 10% relative to the total amount of low-valence silicon and high-valence silicon.

5. The silicon-carbon anode material according to claim 1, characterized in that, In the region defined by a distance of 20 nm from the surface of the silicon-carbon anode material to a distance of 30 nm from the surface of the silicon-carbon anode material, the content of high-valence silicon is less than 10% relative to the total amount of low-valence silicon and high-valence silicon.

6. The silicon-carbon anode material according to claim 5, characterized in that, In the region defined by a distance of 20 nm from the surface of the silicon-carbon anode material to a distance of 30 nm from the surface of the silicon-carbon anode material, the content of high-valence silicon is less than or equal to 5% relative to the total amount of low-valence silicon and high-valence silicon.

7. The silicon-carbon anode material according to any one of claims 1 to 6, characterized in that, The silicon-carbon anode material satisfies at least one of the following conditions: (1) The volume distribution particle size Dv50 of the silicon-carbon anode material is 5μm-10μm; (2) The specific surface area of ​​the silicon-carbon anode material is less than or equal to 5 m². 2 / g; (3) The compacted density of the silicon-carbon anode material under a pressure of 3000N is 0.8 g / cm³. 3 -1.2g / cm 3 ; (4) The tap density of the silicon-carbon anode material is 0.9 g / cm³. 3 -1.1g / cm 3 ; (5) The specific capacity for delithiation of the silicon-carbon anode material is 800mAh / g - 2500mAh / g.

8. The silicon-carbon anode material according to claim 7, characterized in that, The silicon-carbon anode material satisfies at least one of the following conditions: (1) The volume distribution particle size Dv50 of the silicon-carbon anode material is 6μm-9μm; (2) The specific surface area of ​​the silicon-carbon anode material is less than or equal to 2m². 2 / g; (3) The compacted density of the silicon-carbon anode material under a pressure of 3000 N is 0.9 g / cm³. 3 -1.2g / cm 3 ; (4) The tap density of the silicon-carbon anode material is 1.0 g / cm³. 3 -1.1g / cm 3 ; (5) The delithiation capacity of the silicon-carbon anode material is 1000mAh / g-2000mAh / g.

9. The silicon-carbon anode material according to any one of claims 1 to 6, characterized in that, The pore volume of the carbon skeleton is 0.4 cm³. 3 / g -1.5cm 3 / g; and / or, The volume of micropores with a diameter of less than 2 nm accounts for more than 60% of the total volume.

10. The silicon-carbon anode material according to claim 9, characterized in that, The carbon skeleton has a pore volume of 0.6 cm³. 3 / g-1.2cm 3 / g; and / or, The volume of micropores with a diameter of less than 2 nm accounts for more than 80% of the total pore volume.

11. The silicon-carbon anode material according to any one of claims 1 to 6, characterized in that, The surface of the silicon-carbon anode material has a coating layer.

12. The silicon-carbon anode material according to claim 11, characterized in that, The coating layer is a carbon coating layer.

13. A method for preparing a silicon-carbon anode material according to any one of claims 1 to 12, characterized in that, Includes the following steps: The silicon-carbon particle formation step involves reacting a porous carbon framework with a silicon source gas to form silicon-carbon particles containing silicon-based materials within the porous structure; and The silicon carbon particle treatment step involves introducing a mixed gas, comprising a carbon source gas and an inert gas, into the silicon carbon particles at a flow rate greater than 0 L / min and less than or equal to 10 L / min under conditions of a temperature of 500℃-700℃ and a pressure of 0 kPa-1 kPa. The carbon source gas is selected from at least one of ethane, ethylene, acetylene, and methane.

14. The preparation method according to claim 13, characterized in that, In the silicon-carbon particle treatment step, the mixed gas is introduced into the silicon-carbon particles at a flow rate of 0.5 L / min to 4 L / min under conditions of temperature 550℃-650℃ and pressure 0 kPa-0.5 kPa.

15. The preparation method according to claim 13, characterized in that, The mixed gas comprises 10-70 vol% acetylene, 0-20 vol% methane, and 10-90 vol% inert gas.

16. The preparation method according to claim 15, characterized in that, The mixed gas comprises 15-60 vol% acetylene, 5-10 vol% methane, and 30-80 vol% inert gas.

17. The preparation method according to claim 16, characterized in that, The silicon-carbon particle forming step includes the following steps: The reaction apparatus was evacuated, and then an inert gas was introduced.

18. The preparation method according to any one of claims 13 to 17, characterized in that, The silicon-carbon particle forming step includes the following steps: In the reaction apparatus, a porous carbon skeleton is heated to 400°C-550°C to remove oxygen from the carbon skeleton.

19. The preparation method according to any one of claims 13 to 17, characterized in that, The silicon-carbon particle forming step includes the following steps: A mixture of silicon source gas and inert gas is introduced into the reaction device, and silicon-carbon particles are formed by deposition at a temperature of 400℃~550℃ for 2 to 10 hours.

20. The preparation method according to any one of claims 13 to 17, characterized in that, The silicon source gas is selected from one or more of silane, silane, dichlorosilane, and trichlorosilane.

21. The preparation method according to claim 20, characterized in that, The silicon source gas is silane.

22. The preparation method according to any one of claims 13 to 17, characterized in that, The inert gas is argon.

23. A negative electrode sheet, characterized in that, The silicon-carbon anode material includes any one of claims 1 to 12 or a silicon-carbon anode material prepared by any one of claims 13 to 22.

24. A secondary battery, characterized in that, Includes the negative electrode sheet as described in claim 23.

25. An electrical appliance, characterized in that, Includes the secondary battery as described in claim 24.

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