Silicon-carbon composite materials and their preparation methods, secondary batteries and electrical devices

Abstract

This application provides a silicon-carbon composite material, a method for preparing the same, a secondary battery, and an electrical device. The silicon-carbon composite material comprises a porous carbon matrix and a silicon-based material, wherein at least a portion of the silicon-based material is distributed within the pores of the porous carbon matrix; and the silicon-carbon composite material satisfies Q2 / Q1≤0.7; wherein, when the silicon-carbon composite material is charged and discharged using a coin cell battery, the capacity during the charging process from 0.2V to 0.4V is Q1, and the capacity during the charging process from 0.4V to 0.6V is Q2.

Description

Technical Field

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

[0002] In recent years, with the increasingly wide application of secondary batteries, they have been widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric cars, military equipment, aerospace, and many other fields. Due to the significant development of secondary batteries, higher requirements have been placed on their performance and other aspects.

[0003] Silicon-carbon composite materials are commonly used as negative electrode active materials in secondary batteries and have a significant impact on battery performance. However, the performance of current negative electrode active materials in secondary batteries is still insufficient to meet the high cycle performance requirements. 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 method for preparing the same, which can improve the cycle performance of a secondary battery. Furthermore, this application also provides a secondary battery comprising the aforementioned silicon-carbon composite and an electrical device comprising the aforementioned secondary battery.

[0005] To achieve the above objectives, this application provides a silicon-carbon composite material, a method for preparing the same, a secondary battery, and an electrical device.

[0006] In a first aspect, this application provides a silicon-carbon composite material, the silicon-carbon composite material comprising:

[0007] A porous carbon matrix and a silicon-based material, wherein at least a portion of the silicon-based material is distributed in the pores of the porous carbon matrix;

[0008] Furthermore, the silicon-carbon composite material satisfies Q2 / Q1≤0.7; wherein, when the silicon-carbon composite material is charged and discharged using a coin cell battery, the capacity when the voltage during the charging process is from 0.2V to 0.4V is Q1, and the capacity when the voltage during the charging process is from 0.4V to 0.6V is Q2.

[0009] In this application, the silicon-carbon composite material satisfies Q2 / Q1≤0.7, which reflects that most of the silicon-based material is deposited in the pores of the porous carbon matrix, and only a small amount of silicon-based material is deposited on the surface of the porous carbon matrix. This can effectively improve the cycle performance of the secondary battery.

[0010] In some embodiments, the silicon-carbon composite material satisfies 0.3 ≤ Q2 / Q1 ≤ 0.7. In some embodiments, the silicon-carbon composite material satisfies 0.5 ≤ Q2 / Q1 ≤ 0.65.

[0011] In some embodiments, at least a portion of the surface of the silicon-carbon composite material has a coating layer; optionally, the thickness of the coating layer is from 2 nm to 100 nm.

[0012] The silicon-carbon composite material of this application has a coating layer on its surface, which can reduce the side reactions between the material surface and the electrolyte, thereby improving the first coulombic efficiency of the secondary battery.

[0013] In some embodiments, the silicon-carbon composite material satisfies Q3 / Q1≤0.37; wherein, the capacity during the charging process when the voltage changes from 0.6V to 0.8V is Q3.

[0014] Therefore, the silicon-carbon composite material of this application satisfies Q3 / Q1≤0.37, which can effectively improve the first coulombic efficiency of the secondary battery.

[0015] In some embodiments, the silicon-carbon composite material satisfies 0.25 ≤ Q3 / Q1 ≤ 0.37. In some embodiments, the silicon-carbon composite material satisfies 0.3 ≤ Q3 / Q1 ≤ 0.37.

[0016] In some embodiments, the porous carbon matrix includes micropores and mesopores. In some embodiments, the pore volume ratio of the micropores to the mesopores is 1 to 40; in some embodiments, the pore volume ratio of the micropores to the mesopores is 3 to 10.

[0017] In some embodiments, the silicon-carbon composite material satisfies at least one of the following:

[0018] The specific surface area (BET) of the silicon-carbon composite material is 0.1 m². 2 / g to 5m 2 / g, in some implementations 1m 2 / g to 3m 2 / g;

[0019] The silicon-based material content in the silicon-carbon composite material is 30% to 60%, and in some embodiments it is 40% to 50%.

[0020] The silicon-based material in the silicon-carbon composite material exists at least partially in the form of amorphous silicon.

[0021] Secondly, this application provides a method for preparing a silicon-carbon composite material, the method comprising the following steps:

[0022] A gas containing silane is introduced into a reactor containing the porous carbon matrix to deposit a silicon-based material in the pores of the porous carbon matrix;

[0023] The reaction tail gas is monitored. When the volume concentration of silane in the reaction tail gas is not higher than 5 vol%, the gas containing silane is stopped to obtain the silicon-carbon composite material. The silicon-carbon composite material includes a porous carbon matrix and a silicon-based material, wherein at least a portion of the silicon-based material is distributed in the pores of the porous carbon matrix, and the silicon-carbon composite material satisfies Q2 / Q1≤0.7. The silicon-carbon composite material is charged and discharged using a coin cell battery. The capacity during the charging process when the voltage is from 0.2V to 0.4V is Q1, and the capacity during the charging process when the voltage is from 0.4V to 0.6V is Q2.

[0024] In the preparation method of this application, by monitoring the volume concentration of silane in the exhaust gas to be no higher than 5 vol%, the silicon-based material is deposited on the surface of the porous carbon matrix as little as possible, so that the silicon-carbon composite material satisfies Q2 / Q1≤0.7, thereby effectively improving the cycle performance of the secondary battery.

[0025] In some embodiments, the total volume of silane in the silane-containing gas introduced per kilogram of the porous carbon matrix is ​​400 L to 1500 L. In some embodiments, the total volume of silane in the silane-containing gas introduced per kilogram of the porous carbon matrix is ​​650 L to 850 L.

[0026] In some embodiments, the temperature at which the silicon-based material is deposited is between 450°C and 600°C; and / or, the deposition time for each kilogram of the porous carbon matrix is ​​between 1.2 h and 37.5 h; and / or, the gas flow rate of the silane-containing gas is between 0.1 L / min and 10 L / min.

[0027] In some embodiments, the deposition time for each kilogram of the porous carbon matrix is ​​2.5 h to 20 h at 510 °C to 560 °C.

[0028] In some embodiments, depositing silicon-based materials in the pores of the porous carbon matrix includes an initial reaction phase, a middle reaction phase, and a final reaction phase. The amount of silane introduced per kilogram of the porous carbon matrix is ​​20 L to 170 L in the initial reaction phase, 390 L to 680 L in the middle reaction phase, and 20 L to 170 L in the final reaction phase. Optionally, the amount of silane introduced per kilogram of the porous carbon matrix is ​​150 L to 170 L in the initial reaction phase, 420 L to 490 L in the middle reaction phase, and 150 L to 170 L in the final reaction phase.

[0029] Therefore, by controlling the amount of silane deposited at different stages of the reaction process of depositing silicon-based materials in the pores of the porous carbon matrix, this application is beneficial to allow silane to enter the pores of the porous carbon matrix as much as possible, so that silicon-based materials are deposited in the pores of the porous carbon matrix rather than on the surface; in addition, it is also beneficial to improve the utilization efficiency of silane.

[0030] In some embodiments, the method further includes:

[0031] At least a portion of the surface of the silicon-carbon composite material is coated with a carbon coating layer;

[0032] Optionally, coating at least a portion of the surface of the silicon-carbon composite material with a carbon coating layer includes:

[0033] A gas containing a carbon source is introduced into the reactor, and the reaction is carried out at 550°C to 900°C for 0.5 h to 10 h; optionally, the reaction is carried out at 600°C to 700°C for 2 h to 6 h.

[0034] This application obtains a silicon-carbon composite material with reduced surface activity by forming a carbon coating layer on the surface of a silane composite material, thereby reducing side reactions between the composite material and the electrolyte. The prepared silicon-carbon composite material satisfies Q3 / Q1≤0.37, which can effectively improve the first coulombic efficiency of the secondary battery.

[0035] Thirdly, this application provides a secondary battery comprising a negative electrode sheet, wherein the negative electrode sheet comprises a silicon-carbon composite material according to the first aspect of this application, or a silicon-carbon composite material prepared by the method for preparing the silicon-carbon composite material according to the second aspect of this application. The secondary battery exhibits excellent cycle performance.

[0036] Fourthly, this application provides an electrical device, which includes the secondary battery of the third aspect of this application. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of a battery cell according to one embodiment of this application.

[0038] Figure 2 yes Figure 1 An exploded view of a battery cell according to one embodiment of this application is shown.

[0039] Figure 3 This is a schematic diagram of a battery module according to one embodiment of this application.

[0040] Figure 4 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0041] Figure 5 yes Figure 4 An exploded view of a battery pack according to one embodiment of this application is shown.

[0042] 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.

[0043] Explanation of reference numerals in the attached figures:

[0044] 1. Battery pack; 2. Upper casing; 3. Lower casing; 4. Battery module; 5. Battery cell; 51. Housing; 52. Electrode assembly; 53. Top cover assembly. Detailed Implementation

[0045] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the silicon-carbon composite material, its preparation method, secondary battery, and electrical device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0046] 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.

[0047] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0048] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0049] Unless otherwise specified, the terms used in this application have the common meanings as commonly understood by those skilled in the art.

[0050] Unless otherwise specified, the values ​​of the parameters mentioned in this application can be determined using various testing methods commonly used in the art, for example, according to the testing methods given in this application.

[0051] Silicon-based materials have a higher theoretical specific capacity than carbon-based materials, but silicon-based materials expand significantly during battery charge-discharge cycles, resulting in less than ideal cycle life.

[0052] Currently, silicon-based materials can be deposited into the pores of porous carbon matrices via chemical vapor infiltration to generate silicon-carbon composites, which can address the cycle life issue to some extent. Silicon-carbon composites are commonly used as the negative electrode active material in secondary batteries and have a significant impact on battery performance. However, in current secondary batteries, the performance of silicon-carbon composites used as negative electrode active materials is still insufficient to meet the high cycle performance requirements of secondary batteries.

[0053] Based on this, this application proposes a silicon-carbon composite material, its preparation method, a secondary battery, and an electrical device.

[0054] In a first aspect, this application provides a silicon-carbon composite material, the silicon-carbon composite material comprising:

[0055] A porous carbon matrix and a silicon-based material, wherein at least a portion of the silicon-based material is distributed in the pores of the porous carbon matrix;

[0056] Furthermore, the silicon-carbon composite material satisfies Q2 / Q1≤0.7; wherein, when the silicon-carbon composite material is charged and discharged using a coin cell battery, the capacity when the voltage during the charging process is from 0.2V to 0.4V is Q1, and the capacity when the voltage during the charging process is from 0.4V to 0.6V is Q2.

[0057] The silicon-carbon composite material of this application satisfies Q2 / Q1≤0.7, which reflects that most of the silicon-based material is deposited in the pores of the porous carbon matrix, and a small amount of silicon-based material is deposited on the surface of the porous carbon matrix, thus effectively improving the cycle performance of the secondary battery.

[0058] A coin cell half-cell is fabricated using silicon-carbon composite material and then charged and discharged using it. During charging, the capacity at 0.2V is denoted as C1, the capacity at 0.4V as C2, the capacity at 0.6V as C3, and the capacity at 0.8V as C4. Specifically, during charging, the capacity from 0.2V to 0.4V is Q1 = (C2 - C1), the capacity from 0.4V to 0.6V is Q2 = (C3 - C2), and the capacity from 0.6V to 0.8V is Q3 = (C4 - C3). In this technical solution, the silicon-carbon composite material satisfies Q2 / Q1 ≤ 0.7 to improve the cycle performance of the secondary battery. The aforementioned coin cell half-cell is constructed using the silicon-carbon composite material provided in this application as the working electrode (negative electrode active material) and lithium metal as the counter electrode.

[0059] It should be noted that the phase transition of silicon in silicon-carbon composites during lithium intercalation is quite complex. The phase transition during lithium intercalation can be summarized as Si→Li. x Si→Li 15 The delithiation process of Si4 is the opposite; the phase transition during delithiation can be summarized as Li 15 Si4→Li x Si→Si, where x is a value between 0 and 15.

[0060] During the charging process of the coin cell, Q1 corresponds to a charging capacity of 0.2V to 0.4V, which originates from the Li phase transition of silicon in the pores of the porous carbon matrix. 15 Si4→Li x Si;Q2 corresponds to a charging capacity of 0.4V to 0.6V, which originates from the phase transition of silicon to Li on the surface of the porous carbon matrix. 15 Si4→Li x Si→Si, and the phase transition of silicon within the porous carbon matrix, Li x Si→Si; Q3 corresponds to a charging capacity of 0.6V to 0.8V, which originates from the delithiation phase transition due to oxygen defects and LiSi. x C y The delithiation phase transition. The corresponding values ​​represent the capacity contributed by each phase transition; the larger the value, the higher the capacity contribution, and the higher the content of that phase.

[0061] In these phase transitions, the silicon on the surface of the porous carbon matrix in Q2 is the main factor that deteriorates the cycle performance of silicon-carbon composites. Therefore, during the silicon deposition process, silicon-based materials should be deposited in the pores of the porous carbon matrix as much as possible to reduce the enrichment of silicon-based materials on the surface of the porous carbon matrix. In this way, the Q2 / Q1 ratio of silicon-carbon composites can be reduced and their cycle life can be improved.

[0062] The silicon-carbon composite material provided in this application includes a porous carbon matrix and silicon-based materials distributed in the pores of the porous carbon matrix. The porous carbon matrix can improve the conductivity of the silicon-based materials and also act as a buffer medium for the volume expansion of the silicon-based materials during charging and discharging, effectively alleviating the problem of increased secondary battery volume caused by silicon-based material expansion. Furthermore, the silicon-carbon composite material satisfies Q2 / Q1≤0.7, which can effectively improve the cycle performance of the secondary battery.

[0063] In some embodiments, the silicon-carbon composite material satisfies 0.3 ≤ Q2 / Q1 ≤ 0.7. In a further embodiment, the silicon-carbon composite material satisfies 0.5 ≤ Q2 / Q1 ≤ 0.65.

[0064] Silicon-carbon composite materials that meet the corresponding Q2 / Q1 range are more conducive to improving the cycle performance of secondary batteries. For example, Q2 / Q1 can be values ​​such as 0.51, 0.52, 0.53, 0.54, 0.55, 0.56, 0.57, 0.58, 0.59, 0.60, 0.61, 0.62, 0.63, and 0.64.

[0065] In some embodiments, at least a portion of the surface of the silicon-carbon composite material has a coating layer. Optionally, the thickness of the coating layer is from 2 nm to 100 nm. This application does not impose a particular limitation on the thickness of the coating layer, which can be adjusted according to actual needs. For example, the coating layer thickness can be from 5 nm to 90 nm, 10 nm to 80 nm, 20 nm to 80 nm, 20 nm to 60 nm, etc., specifically such as 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, etc.

[0066] It should be noted that the Q3 capacity originates from the delithiation phase transition due to oxygen vacancies and LiSi. x C y The delithiation phase transition. Typically, after the deposition of silicon-carbon composite materials, the silicon-based materials have very high activity. By forming a coating layer on the surface of the silicon-carbon composite material, the surface reactivity of the material can be reduced, thereby reducing the Q3 / Q1 ratio of the silicon-carbon composite material and thus improving the first coulombic efficiency of the secondary battery.

[0067] It should be noted that the coating layer can be a continuous and complete coating layer or an incomplete coating layer. "Continuous and complete" means that the entire surface of the silicon-carbon composite material is covered by the coating layer. "Incomplete" means that at least a portion of the surface of the silicon-carbon composite material is covered by the coating layer.

[0068] According to a specific implementation, the coating layer is a carbon coating layer.

[0069] In some embodiments, the silicon-carbon composite material with a carbon coating exhibits a powder resistivity of less than 50 Ω·cm at 4 MPa. The silicon-carbon composite material possesses excellent electrical conductivity, which in turn contributes to improving the kinetic performance of the secondary battery.

[0070] In some embodiments, the silicon-carbon composite material satisfies Q3 / Q1≤0.37; wherein, the capacity during the charging process when the voltage changes from 0.6V to 0.8V is Q3.

[0071] The silicon-carbon composite material satisfies Q3 / Q1≤0.37, which can effectively improve the initial coulombic efficiency of the secondary battery.

[0072] In some embodiments, the Q3 / Q1 ratio of the silicon-carbon composite material can be greater than 0.37, for example, it can be 0.38, 0.40, 0.42 and 0.44, etc.

[0073] In some embodiments, the silicon-carbon composite material satisfies 0.25 ≤ Q3 / Q1 ≤ 0.37. Optionally, the silicon-carbon composite material satisfies 0.3 ≤ Q3 / Q1 ≤ 0.37.

[0074] Silicon-carbon composite materials that meet the corresponding Q3 / Q1 range are more conducive to improving the initial coulombic efficiency of secondary batteries. For example, Q3 / Q1 can be values ​​such as 0.25, 0.28, 0.30, 0.31, 0.32, 0.33, 0.34, 0.35, 0.36 and 0.37, but are not limited to these.

[0075] In some embodiments, the porous carbon matrix includes micropores and mesopores; optionally, the pore volume ratio of the micropores to the mesopores is 1 to 40; optionally, it is 3 to 10.

[0076] Porous carbon matrices include pores of varying sizes. For example, porous carbon includes micropores, which are pores with a diameter less than 2 nm (typically 0.5 nm to 2 nm). Another example is mesopores, which are pores with a diameter ranging from 2 nm to 50 nm. When the pore volume ratio of micropores to mesopores in a porous carbon matrix is ​​within these ranges, it provides suitable space for the deposition of silicon-based materials, thereby giving the silicon-carbon material appropriate capacity.

[0077] For example, the pore volumes of micropores and mesopores in a porous carbon matrix can be tested using methods known in the art. For instance, the nitrogen adsorption specific surface area analysis method can be used, as specified in GB / T19587-2017, and the results can be calculated using the BET method. The nitrogen adsorption specific surface area analysis can be performed using a TriStar 3020 specific surface area and pore size analyzer from Micromeritics, Inc.

[0078] In some embodiments, the silicon-carbon composite material satisfies at least one of the following:

[0079] The specific surface area (BET) of the silicon-carbon composite material is 0.1 m². 2 / g to 5m 2 / g; optionally 1m 2 / g to 3m 2 / g;

[0080] The silicon-based material content in the silicon-carbon composite material is 30% to 60%; optionally, it is 40% to 50%.

[0081] The silicon-based material in the silicon-carbon composite material exists at least partially in the form of amorphous silicon.

[0082] For example, the specific surface area of ​​silicon-carbon composite materials has a well-known meaning in the art and can be tested using methods known in the art. For instance, it can be tested using the nitrogen adsorption specific surface area analysis method according to GB / T19587-2017 and calculated using the BET method. The nitrogen adsorption specific surface area analysis can be performed using a Tri Star 3020 specific surface area and pore size analyzer from Micromeritics, Inc.

[0083] For example, the content of silicon-based materials in silicon-carbon composite materials can be tested using inductively coupled plasma atomic emission spectrometry (ICP-AES).

[0084] Secondly, this application provides a method for preparing the above-mentioned silicon-carbon composite material, the method comprising the following steps:

[0085] A gas containing silane is introduced into a reactor containing the porous carbon matrix to deposit a silicon-based material in the pores of the porous carbon matrix;

[0086] Monitor the reaction tail gas, and when the volume concentration of silane in the reaction tail gas is not higher than 5 vol%, stop the introduction of the silane-containing gas to obtain the silicon-carbon composite material.

[0087] This application controls the amount of silicon-based material deposited on the surface of the porous carbon matrix by monitoring the volume concentration of silane in the reaction tail gas to be no higher than 5 vol% during the process of depositing silicon-based materials in the pores of a porous carbon matrix. The resulting silicon-based composite material satisfies Q2 / Q1 ≤ 0.7, ensuring that most of the silicon-based material is deposited in the pores of the porous carbon matrix, with minimal silicon-based material accumulation on the surface. This effectively improves the cycle performance of the secondary battery.

[0088] The volume concentration of silane in the reaction tail gas can be monitored using any conventional method or a commercially available silane detection instrument. It should be understood that under normal process conditions, trace amounts of unreacted silane gas (e.g., a volume concentration less than 0.01 vol%) will be emitted from the tail gas; the reaction is still ongoing, and it is not necessary to stop the flow of silane-containing gas.

[0089] In some embodiments, the total volume of silane in the silane-containing gas introduced per kilogram of the porous carbon matrix is ​​400 L to 1500 L. Optionally, the total volume of silane in the silane-containing gas introduced per kilogram of the porous carbon matrix is ​​650 L to 850 L. Exemplarily, the total volume of silane in the silane-containing gas introduced per kilogram of the porous carbon matrix is ​​650 L, 680 L, 700 L, 720 L, 750 L, 780 L, 800 L, 820 L, 840 L, etc. The total volume of silane in the silane-containing gas can be determined based on the amount of silicon to be deposited, and this application does not impose any particular limitation on it.

[0090] In the technical solution of this application, the total amount of silane introduced during the deposition of silicon-based materials in the pores of a porous carbon matrix is ​​a crucial process parameter. The total amount of silane introduced per kilogram of porous carbon matrix depends on the flow rate range of the silane-containing gas and the reaction time. Therefore, by limiting the total amount of silane introduced, this application makes it easier to ensure that the prepared silicon-carbon composite material meets the requirement of Q2 / Q1≤0.7, thereby effectively improving the cycle performance of the secondary battery.

[0091] In addition to silane, the silane-containing gases described in this article also include carrier gases. The carrier gas is typically an inert gas, such as nitrogen.

[0092] In some embodiments, the volume concentration of silane in the silane-containing gas ranges from greater than 5 to 100 vol%; optionally, it is from 20 vol% to 80 vol%. Exemplarily, the volume concentration of silane in the silane-containing gas is 20 vol%, 30 vol%, 40 vol%, 50 vol%, 60 vol%, 70 vol%, or 80 vol%.

[0093] According to a specific implementation, the silane is methanesilane.

[0094] This application does not impose any particular limitation on the volume concentration range of silane in the silane-containing gas; any conventional silane volume concentration range is acceptable.

[0095] In some embodiments, the temperature for depositing the silicon-based material is between 450°C and 600°C; and / or, the deposition time for each kilogram of the porous carbon matrix is ​​between 1.2 h and 37.5 h; and / or, the gas flow rate containing silane is between 0.1 L / min and 10 L / min. Optionally, the deposition time for each kilogram of the porous carbon matrix is ​​between 510°C and 560°C, between 2.5 h and 20 h.

[0096] This application does not specifically limit the flow rate range of silane in the silane-containing gas; any conventional silane flow rate range is acceptable. For example, the gas flow rate of the silane-containing gas is in the range of 0.8 L / min to 8 L / min, 1 L / min to 6 L / min, 2 L / min to 8 L / min, or 3 L / min to 6 L / min. More specifically, the gas flow rate of the silane-containing gas is 0.8 L / min, 1 L / min, 2 L / min, 3 L / min, 3.5 L / min, 4 L / min, 4.5 L / min, 5 L / min, 6 L / min, 8 L / min, etc.

[0097] For example, the temperature range for depositing the silicon-based material is 500°C to 560°C, 510°C to 550°C, 520°C to 550°C, or 520°C to 540°C. More specifically, the temperature for depositing the silicon-based material is 480°C, 490°C, 500°C, 510°C, 515°C, 520°C, 525°C, 530°C, 535°C, 540°C, 550°C, 560°C, 570°C, etc.

[0098] Under the determined conditions of different reaction temperatures, gas flow rates, and the proportion of silane in the silane-containing gas, the method of this application can terminate the reaction in a timely manner by monitoring the silane content in the tail gas, thereby avoiding excessive silicon deposition on the surface of the carbon matrix and reducing the Q2 / Q1 value.

[0099] In the technical solution of this application, during the process of depositing silicon-based materials in the pores of a porous carbon matrix, deposition temperature and reaction time are important process parameters. Generally, the higher the deposition temperature, the shorter the reaction time. Of course, the determination of the reaction endpoint depends on when the volume concentration of silane in the reaction tail gas can be monitored to be no higher than 5 vol%.

[0100] In some embodiments, depositing silicon-based materials in the pores of the porous carbon matrix includes an initial reaction phase, a middle reaction phase, and a final reaction phase. The amount of silane introduced per kilogram of the porous carbon matrix is ​​20 L to 170 L in the initial reaction phase, 390 L to 680 L in the middle reaction phase, and 20 L to 170 L in the final reaction phase. In some specific embodiments, the amount of silane introduced per kilogram of the porous carbon matrix is ​​150 L to 170 L in the initial reaction phase, 420 L to 490 L in the middle reaction phase, and 150 L to 170 L in the final reaction phase.

[0101] The reaction process of depositing silicon-based materials in the pores of a porous carbon matrix is ​​divided into three stages: initial reaction, intermediate reaction, and final reaction. In the initial stage, a silicon-carbon interface forms between the silicon-based material and the inner and outer surfaces of the porous carbon matrix, resulting in a slow reaction rate. If the silane injection rate is high in the initial stage, the silane utilization rate is low. In the final stage, the deposition of silicon-based materials in the pores of the porous carbon matrix gradually reaches saturation. If the silane injection rate is high in the final stage, silane is more likely to deposit on the surface of the porous carbon matrix rather than in its pores. Therefore, the silane injection rate in the initial and final stages is lower than that in the intermediate stage.

[0102] Therefore, by dividing the reaction process of depositing silicon-based materials in the pores of a porous carbon matrix, this application is beneficial to improving the utilization efficiency of silanes.

[0103] In some specific embodiments, the deposition amount of silicon-based material in the pores of the porous carbon matrix during the initial, middle, and final stages of the reaction can be controlled by adjusting the deposition time, silane concentration, and flow rate. For example, based on the total deposition time of the silicon-based material, the initial reaction period accounts for 10% to 20%, the middle reaction period accounts for 60% to 80%, and the final reaction period accounts for 10% to 20%. Specifically, the volume concentration of silane in the initial and final stages of the reaction can be controlled to be lower than that in the middle stage, and / or the flow rate of silane-containing gas in the initial and final stages of the reaction can be lower than that in the middle stage.

[0104] In some embodiments, during the deposition of silicon-based material in the pores of the porous carbon matrix, the pressure in the reactor is greater than 0 to 1 kPa; optionally, it is 100 Pa to 500 Pa.

[0105] This application does not impose any special restrictions on the reaction pressure; a slightly positive pressure is sufficient during the deposition process.

[0106] In some embodiments, the method further includes:

[0107] At least a portion of the surface of the silicon-carbon composite material is coated with a carbon coating layer;

[0108] Optionally, coating at least a portion of the surface of the silicon-carbon composite material with a carbon coating layer includes:

[0109] A gas containing a carbon source is introduced into the reactor, and the reaction is carried out at 550°C to 900°C for 0.5 h to 10 h; optionally, the reaction is carried out at 600°C to 700°C for 2 h to 6 h.

[0110] In a specific embodiment, after stopping the introduction of the silane-containing gas, the reactor does not need to be replaced; instead, a carbon-source-containing gas is immediately introduced into the reactor for surface coating.

[0111] Therefore, this application obtains a silicon-carbon composite material by forming a carbon coating layer on the surface of a silane composite material. The prepared silicon-carbon composite material satisfies Q3 / Q1≤0.37, which can effectively improve the initial coulombic efficiency of the secondary battery.

[0112] In some embodiments, the carbon source is selected from at least one of the following: methane, ethylene, acetylene, and propane.

[0113] This application does not impose any special restrictions on the selection of carbon source; any conventional carbon source is acceptable.

[0114] In some embodiments, the volume concentration of the carbon source in the gas containing the carbon source ranges from greater than 0 to 100 vol%; the volume concentration range of the carbon source may be selected from 20 vol% to 80 vol%.

[0115] This application does not impose any special limitation on the volume concentration range of the carbon source in the gas containing the carbon source; any conventional carbon source volume concentration range is acceptable.

[0116] In some embodiments, the gas flow rate of the carbon source in the gas containing the carbon source is in the range of greater than 0.1 L / min to 10 L / min; the gas flow rate of the carbon source may be selected as greater than 0.1 L / min to 4 L / min.

[0117] This application does not impose any special limitation on the gas flow rate range of the carbon source in the gas containing the carbon source; any conventional carbon source gas flow rate range is acceptable.

[0118] Thirdly, this application provides a secondary battery comprising a negative electrode sheet, wherein the negative electrode sheet comprises a silicon-carbon composite material according to the first aspect of this application, or a silicon-carbon composite material prepared by the method for preparing the silicon-carbon composite material according to the second aspect of this application. The secondary battery exhibits excellent cycle performance.

[0119] In addition, the secondary battery and power-consuming device of this application will be described below with appropriate reference to the accompanying drawings.

[0120] In one embodiment of this application, a secondary battery is provided.

[0121] 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.

[0122] 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.

[0123] Negative electrode sheet

[0124] The negative electrode sheet 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 may include the silicon-carbon composite material of the first aspect of this application.

[0125] 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.

[0126] 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.).

[0127] In some embodiments, the negative electrode active material may further employ negative electrode active materials known in the art for use in batteries. As an example, the negative electrode active material may further include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys.

[0128] 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).

[0129] 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.

[0130] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0131] 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.

[0132] Positive electrode sheet

[0133] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including a positive electrode active material.

[0134] 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.

[0135] 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.).

[0136] 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 0.1 Al 0.05 At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0137] During the charging and discharging process of a battery, Li undergoes insertion / extraction and consumption, resulting in varying molar Li content at different discharge states. In the examples of positive electrode active materials in this application, the molar Li content refers to the initial state of the material, i.e., before feeding. When the positive electrode active material is applied to the battery system, the molar Li content changes after charge-discharge cycles.

[0138] In the examples of positive electrode active materials in this application, the molar content of O is only a theoretical value. Oxygen release from the crystal lattice will cause changes in the molar content of oxygen, and the actual molar content of O will fluctuate.

[0139] In some embodiments, when the battery cell is a sodium-ion battery, the positive electrode active material can be any positive electrode active material known in the art for use in sodium-ion batteries. As examples, the positive electrode active material may include sodium transition metal oxides, polyanionic compounds (phosphates, fluorophosphates, pyrophosphates, sulfates), Prussian blue compounds, etc. However, this application is not limited to these materials, and other conventional materials that can be used as positive electrode active materials for batteries may also be used.

[0140] As an optional technical solution in this application, the transition metal in the sodium transition metal oxide can be at least one selected from Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. For example, the sodium transition metal oxide is Na. x MO2, where M is one or more of Ti, V, Mn, Co, Ni, Fe, Cr, and Cu, and 0 < x ≤ 1. Examples include sodium-iron composite oxides (NaFeO2), sodium-cobalt composite oxides (NaCoO2), sodium-chromium composite oxides (NaCrO2), sodium-manganese composite oxides (NaMnO2), and sodium-nickel composite oxides.

[0141] (NaNiO2), sodium nickel titanium composite oxide (NaNi) 1 / 2 Ti 1 / 2 O2), sodium nickel manganese composite oxide (NaNi) 1 / 2 Mn 1 / 2O2), sodium iron manganese composite oxide (Na2O2), 2 / 3 Fe 1 / 3 Mn 2 / 3 O2), sodium nickel cobalt manganese composite oxide (NaNi) 1 / 3 Co 1 / 3 Mn 1 / 3 O2).

[0142] As an optional technical solution in this application, the polyanionic compound can be a compound containing sodium ions, transition metal ions, or a tetrahedral (YO4) structure. n- A class of compounds with anionic units. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y can be at least one of P, S, and Si; n represents (YO4). n- The price state.

[0143] Polyanionic compounds can also contain sodium ions, transition metal ions, or tetrahedral (YO4) ions. n-A class of compounds containing anionic units and halide anions. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y can be at least one of P, S, and Si, and n represents (YO4). n- The valence state; the halogen can be at least one of F, Cl and Br.

[0144] Polyanionic compounds can also be sodium-containing tetrahedral (YO4) compounds. n- Anionic unit, polyhedral unit (ZO) y ) m+ And a class of compounds with optional halide anions. Y can be at least one of P, S, and Si, and n represents (YO4). n- The valence state; Z represents a transition metal, which can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; m represents (ZO) y ) m+ The valence state; the halogen can be at least one of F, Cl and Br.

[0145] Polyanionic compounds include, for example, NaFePO4, Na3V2(PO4)3, NaM'PO4F (where M' is one or more of V, Fe, Mn, and Ni) and Na3(VO y )2(PO4)2F 3-2y At least one of (0≤y≤1).

[0146] Prussian blue compounds can be a class of compounds containing sodium ions, transition metal ions, and cyanide ions (CN-). The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. Examples of Prussian blue compounds include Na. a Me b Me' c (CN)6, wherein Me and Me' are each independently at least one of Ni, Cu, Fe, Mn, Co, and Zn, 0 <a≤2,0<b<1,0<c<1。

[0147] 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.

[0148] 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.

[0149] 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.

[0150] electrolytes

[0151] 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.

[0152] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0153] 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.

[0154] 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.

[0155] 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.

[0156] Separating membrane

[0157] In some embodiments, the battery cell also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0158] 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.

[0159] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0160] 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.

[0161] 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.

[0162] 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.

[0163] In some implementations, refer to Figure 2 The 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. A positive electrode sheet, a negative electrode sheet, and a separator can be formed into an electrode assembly 52 through a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in a single battery cell 5 can be one or more, which can be selected by those skilled in the art according to specific practical needs.

[0164] 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.

[0165] 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.

[0166] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0167] 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.

[0168] 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.

[0169] Fourthly, this application provides an electrical device, which includes the secondary battery of the third aspect of this application.

[0170] 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.

[0171] As the electrical device, a single battery cell, a battery module, or a battery pack can be selected according to its usage requirements.

[0172] 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.

[0173] 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.

[0174] Example

[0175] 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.

[0176] Preparation of silicon-carbon composite materials

[0177] Example 1

[0178] a. Place 1 kg of porous hard carbon matrix (the pore volume ratio of micropores to mesopores is 6.5) in a rotary kiln, heat it to 500℃ under nitrogen protection and hold it for 2 hours to allow the air adsorbed in the porous carbon matrix to be fully desorbed.

[0179] b. Evacuate the rotary kiln to a vacuum level of 1×10⁻⁶. -5 After maintaining the pressure for 5 minutes, nitrogen gas is introduced until the pressure inside the kiln returns to normal.

[0180] c. Repeat step b until the oxygen content in the exhaust gas is below 200 ppm;

[0181] d. A mixture of silane and nitrogen is introduced, with a silane:nitrogen ratio of 1:4, a gas flow rate of 4L / min, a slight positive pressure of 200Pa maintained inside the kiln, and a rotary kiln rotation frequency of 40Hz.

[0182] e. The concentration of silane in the reaction tail gas was monitored using a chromatograph (model: Agilent Lab Gc 8860). When the mixture of silane and nitrogen was stopped, the concentration of silane in the reaction tail gas was 4.8 vol%, and the total amount of silane introduced was 780 L.

[0183] f. Raise the temperature in the rotary kiln to 600℃, and introduce a mixture of acetylene and nitrogen gas for 5 hours. The ratio of the mixed gas is acetylene:nitrogen = 1:4, the gas flow rate is 2L / min, the kiln is kept under a slight positive pressure of 200Pa, and the rotary kiln is rotated at a frequency of 40Hz to obtain a silicon-carbon composite material with a carbon coating layer of about 10nm thickness; wherein, the total amount of acetylene introduced is 600L.

[0184] Example 2

[0185] The silicon-carbon composite material of Example 2 was prepared similarly to that of Example 1, except that the total amount of silane introduced was 720 L; and the concentration of silane in the reaction tail gas was 2.5 vol when the mixed gas of silane and nitrogen was stopped.

[0186] Example 3

[0187] The silicon-carbon composite material of Example 3 was prepared in a similar manner to Example 1, except that the gas flow rate of the silane and nitrogen mixture was 3.8 L / min, and the concentration of silane in the reaction tail gas was 3.7 vol when the gas flow of the silane and nitrogen mixture was stopped.

[0188] Example 4

[0189] The silicon-carbon composite material of Example 4 was prepared similarly to that of Example 1, except that no carbon coating layer was formed on the surface of the silicon-carbon composite material, and the concentration of silane in the reaction tail gas was 4.7 vol when the mixed gas of silane and nitrogen was stopped.

[0190] Comparative Example 1

[0191] The silicon-carbon composite material of Comparative Example 1 was prepared similarly to that of Example 1, except that the concentration of silane in the reaction tail gas was 5.5 vol when the mixed gas of silane and nitrogen was stopped.

[0192] Preparation of button cells

[0193] The negative electrode sheet was prepared according to the following method: the silicon-carbon composite material, conductive carbon black, and binder polyacrylic acid prepared above were mixed in a mass ratio of 8:1:1, and deionized water was added as a solvent. The mixture was stirred under the action of a high-speed mixer until the system was homogeneous to obtain a negative electrode slurry. The negative electrode slurry was uniformly coated on the negative electrode current collector copper foil and dried at 85°C. After cold pressing, the negative electrode sheet was obtained.

[0194] The electrolyte was prepared as follows: ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 20:20:60. LiPF6 was then uniformly dissolved in the solution, and fluoroethylene carbonate (FEC) was added as an additive to obtain the electrolyte. The concentration of LiPF6 was 1 mol / L, and the mass percentage of FEC in the electrolyte was 5%.

[0195] The coin cell was prepared by means of the following method: using the above-mentioned negative electrode as the working electrode, lithium metal as the counter electrode, and a polypropylene film as the separator, the negative electrode, the separator and the lithium metal were stacked in sequence, with the separator positioned between the working electrode and the counter electrode, and electrolyte was injected to assemble the coin cell.

[0196] Preparation of secondary batteries

[0197] The negative electrode sheet was prepared as follows: The negative electrode active material (a mixture of the prepared silicon-carbon composite material and artificial graphite at a ratio of 1:9), the conductive agent (a mixture of carbon nanotubes and SP), the binder (styrene-butadiene rubber), and the thickener (sodium carboxymethyl cellulose) were thoroughly mixed in an appropriate amount of deionized water at a weight ratio of 95.5:1:2:1.5 to form a negative electrode slurry. The negative electrode slurry was coated onto both surfaces of the negative electrode current collector copper foil, and after drying and cold pressing, the negative electrode sheet was obtained.

[0198] The positive electrode sheet is prepared according to the following method: The positive electrode active material LiNi is... 0.8 Co 0.l Mn 0.1 O2 (NCM811) is mixed with conductive carbon black and polyvinylidene fluoride in a weight ratio of 97.5:1.2:1.3, and an appropriate amount of NMP solvent is added. The mixture is stirred until homogeneous to obtain a positive electrode slurry. The positive electrode slurry is coated onto both surfaces of the positive electrode current collector aluminum foil, and after drying and cold pressing, a positive electrode sheet is obtained.

[0199] The electrolyte was prepared as follows: a mixture of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) was used as the organic solvent, with a volume ratio of EC:20:20:60. Thoroughly dried lithium salt (LiPF6) was dissolved in the above organic solvent in an oxygen-atmospheric glove box with a water content of <10 ppm, and fluoroethylene carbonate (FEC) was added as an additive to obtain the electrolyte. In this electrolyte, the concentration of LiPF6 was 1 mol / L, and the mass percentage of FEC in the electrolyte was 5%.

[0200] Polypropylene film is used as the separator.

[0201] The secondary battery is prepared according to the following method: the positive electrode, separator and negative electrode prepared above are arranged in order, with the separator (i.e., polypropylene film) placed between the positive electrode and the negative electrode to play a separating role, and then wound to obtain the electrode assembly; the electrode assembly is placed in the outer packaging, dried and then injected with the electrolyte prepared above, and after vacuum sealing, standing, formation and capacity testing, the secondary battery is obtained.

[0202] Performance testing of button cells

[0203] 1. Q2 / Q1 and Q3 / Q1

[0204] After the prepared coin cells were left to stand for 60 minutes, they were discharged at a constant current of 0.05C to 5mV, then discharged at 50μA to 5mV, left to stand for 10 minutes, and then charged at 0.1C to 0.8V for testing. The capacity during the charging process from 0.2V to 0.4V was recorded as Q1, the capacity from 0.4V to 0.6V as Q2, and the capacity from 0.6V to 0.8V as Q3. The ratios Q2 / Q1 and Q3 / Q1 were then calculated.

[0205] 2. First Coulomb efficiency test

[0206] After the assembled coin cell was left to stand for 60 minutes, it was discharged to 5mV using a constant current of 0.05C, discharged to 5mV using 50μA, left to stand for 10 minutes, and then charged to 0.8V using 0.1C for testing. The delithiation capacity of 0.8V represents the capacity of the silicon-carbon composite material, corresponding to the delithiation capacity / lithiation capacity at the first efficiency of 0.08V.

[0207] Performance testing of secondary batteries

[0208] Cyclic performance testing

[0209] At 25℃, the secondary battery was left to stand for 30 minutes, then charged at a rate of 0.5C to 4.25V, and further charged at a constant voltage of 4.25V to a current of 0.05C. It was then left to stand for 5 minutes, and finally discharged at a rate of 0.5C to a voltage of 2.5V. The resulting capacity was recorded as the initial capacity C0. This constitutes one charge-discharge cycle. The above steps were repeated for the same secondary battery, recording the discharge capacity Cn at each cycle. The battery capacity retention rate after each cycle was Pn = Cn / C0 * 100%, continuing until Pn ≦ 80%, at which point the test was stopped, and the number of cycles was recorded.

[0210] For the coin cells prepared in Examples 1 to 4 and Comparative Example 1, the Q2 / Q1, Q3 / Q1 and initial coulombic efficiency were tested; for the secondary cells prepared in Examples 1 to 4 and Comparative Example 1, the cycle performance was tested, and the specific results are shown in Table 1.

[0211] Table 1

[0212]

[0213] As shown in Table 1, by controlling the silicon-carbon composite material to satisfy Q2 / Q1≤0.7, the cycle life of the secondary battery is significantly improved.

[0214] Example 5

[0215] The silicon-carbon composite material of Example 5 was prepared similarly to that of Example 1, except that the deposition temperature was 450°C and the introduction of the mixed gas of silane and nitrogen was stopped, and the concentration of silane in the reaction tail gas was 3.4 vol%.

[0216] Example 6

[0217] The silicon-carbon composite material of Example 6 was prepared similarly to that of Example 1, except that the deposition temperature was 520°C and the concentration of silane in the reaction tail gas was 3.4 vol% when the mixed gas of silane and nitrogen was stopped.

[0218] Example 7

[0219] The silicon-carbon composite material of Example 7 was prepared similarly to that of Example 1, except that the deposition temperature was 550°C and the concentration of silane in the reaction tail gas was 3.4 vol% when the mixed gas of silane and nitrogen was stopped.

[0220] Example 8

[0221] The silicon-carbon composite material of Example 8 was prepared similarly to that of Example 1, except that the deposition temperature was 600°C and the concentration of silane in the reaction tail gas was 3.4 vol when the mixed gas of silane and nitrogen was stopped.

[0222] For the coin cells prepared by the silicon-carbon composite materials prepared in Examples 5 to 8 using the same method as above, the Q2 / Q1, Q3 / Q1 and initial coulombic efficiency were tested. For the secondary cells prepared by the silicon-carbon composite materials prepared in Examples 5 to 8 using the same method as above, the cycle performance was tested. The specific results are shown in Table 2.

[0223] Table 2

[0224] Example 1 500℃ 0.691 0.362 93.4％ 2539 Example 5 450℃ 0.695 0.363 93.2％ 2550 Example 6 520℃ 0.664 0.362 93.5％ 2671 Example 7 550℃ 0.681 0.361 93.3％ 2639 Example 8 600℃ 0.696 0.363 93.1％ 2543

[0225] As shown in Table 2, the Q2 / Q1 ratio of the coin cell prepared from silicon-carbon composite materials changes with the deposition temperature, and the corresponding cycle performance of the secondary cell prepared from silicon-carbon composite materials also changes. Overall, the deposition temperature has little effect on the cycle performance of the secondary cell prepared from silicon-carbon composite materials.

[0226] Example 9

[0227] The silicon-carbon composite material of Example 9 was prepared in a similar manner to Example 1, except that the amount of silane introduced at the beginning of the reaction was 155 L, the amount of silane introduced in the middle of the reaction was 470 L, and the amount of silane introduced at the end of the reaction was 155 L; and when the mixed gas of silane and nitrogen was stopped, the concentration of silane in the reaction tail gas was 2.3 vol.

[0228] Example 10

[0229] The silicon-carbon composite material of Example 10 was prepared in a similar manner to Example 1, except that the amount of silane introduced at the beginning of the reaction was 170 L, the amount of silane introduced in the middle of the reaction was 440 L, and the amount of silane introduced at the end of the reaction was 170 L; and the introduction of the mixed gas of silane and nitrogen was stopped, and the concentration of silane in the reaction tail gas was 2.3 vol.

[0230] The initial coulombic efficiency was tested for the coin cells prepared by the silicon-carbon composite materials prepared in Examples 9 and 10 using the same method as above. The cycle performance was tested for the secondary cells prepared by the silicon-carbon composite materials prepared in Examples 9 and 10 using the same method as above. The specific results are shown in Table 3.

[0231] Table 3

[0232]

[0233] As shown in Table 3, the reaction process is divided into three stages: initial reaction, middle reaction, and final reaction. With changes in the amount of silane introduced in each reaction stage, the Q2 / Q1 ratio of the coin cell prepared from the silicon-carbon composite material also changes, consequently affecting the cycle performance of the secondary battery. In summary, dividing the reaction process into three stages and controlling the amount of silane introduced in each stage is more conducive to keeping the Q2 / Q1 ratio of the coin cell prepared from the silicon-carbon composite material within a selectable range.

[0234] 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 method for producing a silicon-carbon composite material, characterized by, The method includes the following steps: A gas containing silane is introduced into a reactor containing a porous carbon matrix to deposit a silicon-based material in the pores of the porous carbon matrix; the temperature at which the silicon-based material is deposited is between 500°C and 600°C. The reaction tail gas is monitored. When the volume concentration of silane in the reaction tail gas is not higher than 5 vol%, the gas containing silane is stopped to obtain the silicon-carbon composite material. The silicon-carbon composite material includes a porous carbon matrix and a silicon-based material, wherein at least a portion of the silicon-based material is distributed in the pores of the porous carbon matrix, and the silicon-carbon composite material satisfies Q2 / Q1≤0.

7. The silicon-carbon composite material is charged and discharged using a coin cell battery. The capacity during the charging process when the voltage is from 0.2V to 0.4V is Q1, and the capacity during the charging process when the voltage is from 0.4V to 0.6V is Q2.

2. The production method according to claim 1, characterized by, The total volume of the silane-containing gas introduced into each kilogram of the porous carbon matrix is ​​400 L to 1500 L.

3. The preparation method according to claim 1, characterized in that, The deposition time for each kilogram of the porous carbon matrix is ​​from 1.2 h to 37.5 h; and / or, The gas flow rate containing silane is from 0.1 L / min to 10 L / min; Optionally, the deposition time for each kilogram of the porous carbon matrix is ​​2.5 h to 20 h at 510 °C to 560 °C.

4. The production method according to any one of claims 1 to 3, characterized by, The deposition of silicon-based material in the pores of the porous carbon matrix includes an initial reaction, a middle reaction, and a final reaction. The amount of silane introduced per kilogram of the porous carbon matrix is ​​20 L to 170 L in the initial reaction, 390 L to 680 L in the middle reaction, and 20 L to 170 L in the final reaction.

5. The preparation method according to claim 4, characterized in that, The amount of silane introduced per kilogram of the porous carbon matrix is ​​150 L to 170 L in the initial stage of the reaction, 420 L to 490 L in the middle stage of the reaction, and 150 L to 170 L in the final stage of the reaction.

6. The preparation method according to any one of claims 1 to 3, characterized in that, The method further includes: At least a portion of the surface of the silicon-carbon composite material is coated with a carbon coating layer; Optionally, coating at least a portion of the surface of the silicon-carbon composite material with a carbon coating layer includes: A gas containing a carbon source is introduced into the reactor, and the reaction is carried out at 550°C to 900°C for 0.5 h to 10 h.

7. The preparation method according to claim 6, characterized in that, The carbon coating layer covering at least a portion of the surface of the silicon-carbon composite material includes: A gas containing a carbon source is introduced into the reactor, and the reaction is carried out at 600°C to 700°C for 2 to 6 hours.

8. A silicon-carbon composite material, characterized in that, The silicon-carbon composite material is prepared by the method according to any one of claims 1 to 7; the silicon-carbon composite material comprises: a porous carbon matrix and a silicon-based material, wherein at least a portion of the silicon-based material is distributed in the pores of the porous carbon matrix; Furthermore, the silicon-carbon composite material satisfies Q2 / Q1≤0.7; wherein, the silicon-carbon composite material is charged and discharged using a coin cell: using a negative electrode sheet including the silicon-carbon composite material as the working electrode, and lithium metal as the counter electrode, such that a separator is located between the working electrode and the counter electrode, and an electrolyte is injected to assemble the coin cell; after the coin cell is left to stand for 60 minutes, it is discharged to 5mV using a constant current of 0.05C, discharged to 5mV using 50μA, left to stand for 10 minutes, and charged to 0.8V using 0.1C for testing; the capacity when the voltage during the charging process is from 0.2V to 0.4V is Q1, and the capacity when the voltage during the charging process is from 0.4V to 0.6V is Q2.

9. The silicon-carbon composite material according to claim 8, characterized in that, The silicon-carbon composite material satisfies 0.3≤Q2 / Q1≤0.

7.

10. The silicon-carbon composite material according to claim 9, characterized in that, The silicon-carbon composite material satisfies 0.5≤Q2 / Q1≤0.

65.

11. The silicon-carbon composite material according to claim 8, characterized in that, At least a portion of the surface of the silicon-carbon composite material has a coating layer; optionally, the thickness of the coating layer is from 2 nm to 100 nm.

12. The silicon-carbon composite material according to claim 11, characterized in that, The silicon-carbon composite material satisfies Q3 / Q1≤0.37; wherein, the capacity when the voltage changes from 0.6V to 0.8V during the charging process is Q3.

13. The silicon-carbon composite material according to claim 12, characterized in that, The silicon-carbon composite material satisfies 0.25≤Q3 / Q1≤0.

37.

14. The silicon-carbon composite material according to claim 13, characterized in that, The silicon-carbon composite material satisfies 0.3≤Q3 / Q1≤0.

37.

15. The silicon-carbon composite material according to any one of claims 8 to 14, characterized in that, The porous carbon matrix includes micropores and mesopores; optionally, the pore volume ratio of the micropores to the mesopores is 1 to 40.

16. The silicon-carbon composite material according to any one of claims 8 to 14, characterized in that, The silicon-carbon composite material satisfies at least one of the following: The specific surface area BET of the silicon-carbon composite material is between 0.1 m 2 / g and 5 m 2 / g; The silicon-based material content in the silicon-carbon composite material is 30% to 60%; The silicon-based material in the silicon-carbon composite material exists at least partially in the form of amorphous silicon.

17. A secondary battery, the secondary battery comprising a negative electrode sheet, the negative electrode sheet comprising a silicon-carbon composite material according to any one of claims 8 to 16, or comprising a silicon-carbon composite material prepared by any one of claims 8 to 16.

18. An electrical appliance, characterized in that, The electrical device includes the secondary battery as described in claim 17.

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