Silicon-carbon composite material and preparation method therefor, and secondary battery and electric apparatus

Abstract

Provided are a silicon-carbon composite material and a preparation method therefor, and a secondary battery and an electric apparatus. 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 pores of the porous carbon matrix. In addition, the silicon-carbon composite material satisfies Q2 / Q1≤0.7. A button battery is used to charge and discharge the silicon-carbon composite material, the capacity of the silicon-carbon composite material is Q1 when the voltage is from 0.2V to 0.4V in a charging process, and the capacity of the silicon-carbon composite material is Q2 when the voltage is from 0.4V to 0.6V in the charging process.

Description

Silicon-carbon composite material, preparation method thereof, secondary battery and electrical device

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This disclosure is based on Chinese patent application number 202410122765.6, application date January 29, 2024, and invention name “Silicon-carbon composite material and preparation method thereof, secondary battery and electrical device”, and claims the priority of the Chinese patent application. The entire content of the Chinese patent application is hereby introduced into the present disclosure as a reference. Technical Field

[0003] The present disclosure relates to the field of battery technology, and in particular to a silicon-carbon composite material and a preparation method thereof, a secondary battery, and an electrical device. Background Art

[0004] In recent years, the application of secondary batteries has become increasingly widespread. They are widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power stations, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and other fields. As secondary batteries have achieved great development, higher requirements have been placed on their performance.

[0005] Silicon-carbon composites are commonly used as negative electrode active materials in secondary batteries and have a significant impact on their performance. However, the performance of negative electrode active materials in current secondary batteries cannot meet the requirements for high cycle performance.

[0006] Summary of the Invention

[0007] The present disclosure is made in view of the above-mentioned problems and aims to provide a silicon-carbon composite material and a preparation method thereof that can improve the cycle performance of a secondary battery. In addition, the present disclosure also provides a secondary battery including the silicon-carbon composite and an electrical device including the secondary battery.

[0008] In order to achieve the above objectives, the present disclosure provides a silicon-carbon composite material and a preparation method thereof, a secondary battery, and an electrical device.

[0009] In a first aspect, the present disclosure provides a silicon-carbon composite material, comprising:

[0010] 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;

[0011] And the silicon-carbon composite material satisfies Q2 / Q1≤0.7; wherein, the silicon-carbon composite material is charged and discharged using a button battery, and the capacity when the voltage is from 0.2V to 0.4V during the charging process is Q1, and the capacity when the voltage is from 0.4V to 0.6V during the charging process is Q2.

[0012] The silicon-carbon composite material disclosed in the present invention satisfies Q2 / Q1≤0.7, reflecting 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, which can effectively improve the cycle performance of the secondary battery.

[0013] 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.

[0014] In some embodiments, at least a portion of the surface of the silicon-carbon composite material has a coating layer; optionally, the coating layer has a thickness of 2 nm to 100 nm.

[0015] The silicon-carbon composite material disclosed herein has a coating layer on its surface, which can reduce side reactions between the material surface and the electrolyte, thereby improving the initial coulombic efficiency of the secondary battery.

[0016] In some embodiments, the silicon-carbon composite material satisfies Q3 / Q1≤0.37; wherein, the capacity when the voltage is from 0.6V to 0.8V during the charging process is Q3.

[0017] Therefore, the silicon-carbon composite material disclosed in the present invention satisfies Q3 / Q1≤0.37, and can effectively improve the first coulombic efficiency of the secondary battery.

[0018] 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.

[0019] In some embodiments, the porous carbon matrix comprises 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.

[0020] In some embodiments, the silicon-carbon composite material satisfies at least one of the following:

[0021] The specific surface area of ​​the silicon-carbon composite material is 0.1 m 2 / g to 5m 2 / g, in some embodiments 1m 2 / g to 3m 2 / g;

[0022] The silicon-carbon composite material has a silicon-based material content of 30% to 60%, and in some embodiments, 40% to 50%;

[0023] At least part of the silicon-based material in the silicon-carbon composite material exists in the form of amorphous silicon.

[0024] In a second aspect, the present disclosure provides a method for preparing a silicon-carbon composite material, the method comprising the following steps:

[0025] introducing a gas containing silane into a reactor containing the porous carbon substrate to deposit a silicon-based material in the pores of the porous carbon substrate;

[0026] Monitor the reaction exhaust gas. When the volume concentration of silane in the reaction exhaust gas is not higher than 5 vol%, stop introducing the gas containing silane to obtain the silicon-carbon composite material, wherein the silicon-carbon composite material includes: a porous carbon matrix and a silicon-based material, wherein at least part 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; wherein, a button battery is used to charge and discharge the silicon-carbon composite material, and the capacity when the voltage is from 0.2V to 0.4V during the charging process is Q1, and the capacity when the voltage is from 0.4V to 0.6V during the charging process is Q2.

[0027] In the preparation method disclosed herein, 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.

[0028] In some embodiments, the total volume of silane in the silane-containing gas introduced per kilogram of the porous carbon substrate 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 substrate is 650 L to 850 L.

[0029] In some embodiments, the temperature of depositing the silicon-based material is between 450°C and 600°C; and / or the deposition time per kilogram of the porous carbon matrix is ​​between 1.2 hours and 37.5 hours; and / or the ventilation rate of the silane-containing gas is between 0.1 L / min and 10 L / min.

[0030] In some embodiments, the deposition time is 2.5 h to 20 h per kilogram of the porous carbon substrate at 510° C. to 560° C.

[0031] In some embodiments, depositing silicon-based materials in the pores of the porous carbon matrix includes an initial reaction stage, a middle reaction stage, and a final reaction stage. Calculated by the amount of silane introduced per kilogram of the porous carbon matrix, the amount of silane introduced at the initial reaction stage is 20L to 170L, the amount of silane introduced in the middle reaction stage is 390L to 680L, and the amount of silane introduced at the final reaction stage is 20L to 170L; optionally, calculated by the amount of silane introduced per kilogram of the porous carbon matrix, the amount of silane introduced at the initial reaction stage is 150L to 170L, the amount of silane introduced in the middle reaction stage is 420L to 490L, and the amount of silane introduced at the final reaction stage is 150L to 170L.

[0032] Therefore, the present invention helps to make silane enter the pores of the porous carbon matrix as much as possible by controlling the amount of silane deposition at different stages of the reaction process of depositing silicon-based materials in the pores of the porous carbon matrix, thereby depositing silicon-based materials 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.

[0033] In some embodiments, the method further comprises:

[0034] coating a carbon coating layer on at least a portion of the surface of the silicon-carbon composite material;

[0035] Optionally, coating at least a portion of the surface of the silicon-carbon composite material with a carbon coating layer comprises:

[0036] 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 to 10 hours; optionally, the reaction is carried out at 600° C. to 700° C. for 2 to 6 hours.

[0037] The present invention forms a carbon coating layer on the surface of the silane composite material to obtain a silicon-carbon composite material with reduced surface activity, thereby reducing the side reaction between the silicon-carbon 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.

[0038] In a third aspect, the present disclosure provides a secondary battery comprising a negative electrode plate, wherein the negative electrode plate comprises the silicon-carbon composite material of the first aspect of the present disclosure, or comprises a silicon-carbon composite material prepared by the method for preparing the silicon-carbon composite material of the second aspect of the present disclosure. The secondary battery has excellent cycle performance.

[0039] In a fourth aspect, the present disclosure provides an electric device, comprising the secondary battery according to the third aspect of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] FIG. 1 is a schematic diagram of a battery cell according to an embodiment of the present disclosure.

[0041] FIG. 2 is an exploded view of the battery cell according to the embodiment of the present disclosure shown in FIG. 1 .

[0042] FIG3 is a schematic diagram of a battery module according to an embodiment of the present disclosure.

[0043] FIG4 is a schematic diagram of a battery pack according to an embodiment of the present disclosure.

[0044] FIG. 5 is an exploded view of the battery pack shown in FIG. 4 according to an embodiment of the present disclosure.

[0045] FIG6 is a schematic diagram of an electric device using a secondary battery according to an embodiment of the present disclosure as a power source.

[0046] Description of reference numerals:

[0047] 1. Battery pack; 2. Upper box; 3. Lower box; 4. Battery module; 5. Battery cell; 51. Housing; 52. Electrode assembly; 53. Top cover assembly. DETAILED DESCRIPTION

[0048] Below, the embodiments of the silicon-carbon composite material and its preparation method, secondary battery and electrical device disclosed in the present invention are described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present disclosure and are not intended to limit the subject matter described in the claims.

[0049] " scope " disclosed in the present disclosure is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and selected lower limit and upper limit define the boundary of special scope.The scope that this mode limits can be to include end value or not include end value, and can be combined arbitrarily, and promptly any lower limit can form a scope with any upper limit combination.For example, if the scope of 60-120 and 80-110 is listed for specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected.In addition, if the minimum range value 1 and 2 listed, and if the maximum range value 3,4 and 5 listed, then the following scope can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5.In the present disclosure, unless otherwise specified, numerical range " ab " represents the abbreviation of any real number combination between a and b, and wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0050] Unless otherwise specified, all embodiments and optional embodiments of the present disclosure can be combined with each other to form new technical solutions.

[0051] Unless otherwise specified, all technical features and optional technical features disclosed herein can be combined with each other to form a new technical solution.

[0052] Unless otherwise specified, the terms used in the present disclosure have the common meanings that are generally understood by those skilled in the art.

[0053] Unless otherwise specified, the numerical values ​​of the parameters mentioned in the present disclosure can be measured using various test methods commonly used in the art, for example, they can be measured according to the test methods given in the present disclosure.

[0054] Silicon-based materials have higher theoretical gram capacity than carbon-based materials, but silicon-based materials expand significantly during the battery charge and discharge cycle, resulting in unsatisfactory cycle life.

[0055] Currently, silicon-based materials can be deposited into the pores of a porous carbon matrix through chemical vapor infiltration to produce silicon-carbon composite materials, which can, to a certain extent, solve the problem of cycle life. Silicon-carbon composite materials are commonly used as negative electrode active materials in secondary batteries and have a significant impact on the performance of secondary batteries. In current secondary batteries, the performance of silicon-carbon composite materials used as negative electrode active materials cannot meet the requirements of high cycle performance of secondary batteries.

[0056] Based on this, the present disclosure proposes a silicon-carbon composite material and a preparation method thereof, a secondary battery, and an electrical device.

[0057] In a first aspect, the present disclosure provides a silicon-carbon composite material, comprising:

[0058] 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;

[0059] And the silicon-carbon composite material satisfies Q2 / Q1≤0.7; wherein, the silicon-carbon composite material is charged and discharged using a button battery, and the capacity when the voltage is from 0.2V to 0.4V during the charging process is Q1, and the capacity when the voltage is from 0.4V to 0.6V during the charging process is Q2.

[0060] The silicon-carbon composite material disclosed in the present invention 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, which can effectively improve the cycle performance of the secondary battery.

[0061] The silicon-carbon composite material is prepared into a button-type half-cell, and the button-type half-cell is used for charge and discharge. During the charging process, the capacity charged to 0.2V is recorded as C1, the capacity charged to 0.4V is recorded as C2, the capacity charged to 0.6V is recorded as C3, and the capacity charged to 0.8V is recorded as C4; wherein, during the charging process, 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 the technical solution disclosed in the present invention, the silicon-carbon composite material satisfies Q2 / Q1≤0.7 to improve the cycle performance of the secondary battery. The above-mentioned button-type half-cell is composed of a working electrode using the silicon-carbon composite material provided by the present invention as the negative electrode active material and metallic lithium as the counter electrode.

[0062] It should be noted that the phase transition of silicon in silicon-carbon composite materials during lithium insertion is relatively complex, and the phase transition during lithium insertion can be summarized as Si→Li x Si→Li 15 Si4, the delithiation process is the opposite, and the phase change during the delithiation process can be summarized as Li 15 Si4→Li x Si→Si, where x is a value between 0 and 15.

[0063] During the charging process of the button half-charge, Q1 corresponds to a charging capacity of 0.2V to 0.4V, which comes from the phase change of silicon in the pores inside the porous carbon matrix. 15 Si4→Li xSi; Q2 corresponds to the charge capacity of 0.4V to 0.6V, which comes from the phase transition of silicon on the surface of the porous carbon matrix to Li 15 Si4→Li x Si→Si, and the phase transition of silicon inside the porous carbon matrix to Li x Si→Si; Q3 corresponds to a charge capacity of 0.6V to 0.8V, which is derived from the delithiation phase transition of oxygen defects and LiSi x C y The corresponding value represents the capacity contributed by each phase transition. The larger the value, the higher the contributed capacity, and the corresponding phase content is also higher.

[0064] Among these phase changes, it is mainly the silicon on the surface of the porous carbon matrix in Q2 that deteriorates the cycle performance of the silicon-carbon composite material. Therefore, in the process of depositing silicon, the silicon-based material should be deposited in the pores of the porous carbon matrix as much as possible to reduce the enrichment of the silicon-based material on the surface of the porous carbon matrix. In this way, the Q2 / Q1 of the silicon-carbon composite material can be reduced and its cycle life can be improved.

[0065] The silicon-carbon composite material provided by the present disclosure includes a porous carbon matrix and a silicon-based material distributed within the pores of the porous carbon matrix. The porous carbon matrix can improve the conductivity of the silicon-based material and also serve as a buffer for the volume expansion of the silicon-based material during charge and discharge, effectively alleviating the problem of increased volume of the secondary battery caused by the expansion of the silicon-based material. Furthermore, the silicon-carbon composite material satisfies Q2 / Q1≤0.7, which can effectively improve the cycle performance of the secondary battery.

[0066] In some embodiments, the silicon-carbon composite material satisfies 0.3≤Q2 / Q1≤0.7. In further embodiments, the silicon-carbon composite material satisfies 0.5≤Q2 / Q1≤0.65.

[0067] 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 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.

[0068] In some embodiments, at least a portion of the surface of the silicon-carbon composite material has a coating layer. Optionally, the coating layer has a thickness of 2 nm to 100 nm. The present disclosure does not particularly limit the thickness of the coating layer and can be adjusted according to actual needs. For example, the coating layer thickness can be 5 nm to 90 nm, 10 nm to 80 nm, 20 nm to 80 nm, 20 nm to 60 nm, etc., specifically 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, etc.

[0069] It should be noted that the Q3 capacity comes from the delithiation phase transition of oxygen defects and LiSi x C y After the silicon-carbon composite material is deposited, the activity of the silicon-based material is very high. By forming a coating layer on the surface of the silicon-carbon composite material, the reaction activity of the material surface can be reduced, thereby reducing the Q3 / Q1 of the silicon-carbon composite material and thus improving the first coulombic efficiency of the secondary battery.

[0070] 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.

[0071] According to a specific embodiment, the coating layer is a carbon coating layer.

[0072] In some embodiments, the silicon-carbon composite material having a carbon coating layer has a powder resistivity of less than 50 Ω·cm at 4 MPa. The silicon-carbon composite material has excellent electrical conductivity, which helps improve the dynamic performance of the secondary battery.

[0073] In some embodiments, the silicon-carbon composite material satisfies Q3 / Q1≤0.37; wherein, the capacity when the voltage is from 0.6V to 0.8V during the charging process is Q3.

[0074] The silicon-carbon composite material satisfies Q3 / Q1≤0.37, and can effectively improve the initial coulombic efficiency of the secondary battery.

[0075] In some embodiments, Q3 / Q1 of the silicon-carbon composite material may be greater than 0.37, for example, 0.38, 0.40, 0.42, 0.44, etc.

[0076] In some embodiments, the silicon-carbon composite material satisfies 0.25≤Q3 / Q1≤0.37. Alternatively, the silicon-carbon composite material satisfies 0.3≤Q3 / Q1≤0.37.

[0077] The silicon-carbon composite material satisfies the corresponding Q3 / Q1 range, which is more conducive to improving the initial coulombic efficiency of the secondary battery. For example, Q3 / Q1 can be 0.25, 0.28, 0.30, 0.31, 0.32, 0.33, 0.34, 0.35, 0.36 and 0.37, but is not limited thereto.

[0078] In some embodiments, the porous carbon matrix includes micropores and mesopores; optionally, a pore volume ratio of the micropores to the mesopores is 1 to 40; optionally, 3 to 10.

[0079] The porous carbon matrix includes pores of different pore sizes. For example, the porous carbon includes micropores, which refer to pores with a pore size of less than 2 nm (usually 0.5 nm to 2 nm). For another example, the porous carbon includes mesopores, which refer to pores with a pore size range of 2 nm to 50 nm. When the pore volume ratio of the micropores to the mesopores of the porous carbon matrix is ​​within the above range, it can provide suitable space for the deposition of silicon-based materials, thereby making the silicon-carbon material have a suitable capacity.

[0080] For example, the pore volume of the micropores and mesopores of the porous carbon matrix can be measured using methods known in the art. For example, the pore volume can be measured using a nitrogen adsorption specific surface area analysis method according to GB / T 19587-2017 and calculated using the BET method. The nitrogen adsorption specific surface area analysis test can be performed using a Tri Star 3020 specific surface area pore size analyzer from Micromeritics, USA.

[0081] In some embodiments, the silicon-carbon composite material satisfies at least one of the following:

[0082] The specific surface area of ​​the silicon-carbon composite material is 0.1 m 2 / g to 5m 2 / g; optionally 1m 2 / g to 3m 2 / g;

[0083] The silicon-carbon composite material contains 30% to 60% of silicon-based materials; optionally, 40% to 50%;

[0084] At least part of the silicon-based material in the silicon-carbon composite material exists in the form of amorphous silicon.

[0085] For example, the specific surface area of ​​the silicon-carbon composite material is well known in the art and can be measured using methods known in the art. For example, the specific surface area can be measured using the nitrogen adsorption specific surface area analysis test method according to GB / T 19587-2017 and calculated using the BET method. The nitrogen adsorption specific surface area analysis test can be performed using a Tri Star 3020 specific surface area pore size analyzer from Micromeritics, USA.

[0086] For example, the content of silicon-based material in the silicon-carbon composite material can be tested by inductively coupled plasma atomic emission spectroscopy (ICP-AES).

[0087] In a second aspect, the present disclosure provides a method for preparing the above-mentioned silicon-carbon composite material, the method comprising the following steps:

[0088] introducing a gas containing silane into a reactor containing the porous carbon substrate to deposit a silicon-based material in the pores of the porous carbon substrate;

[0089] The reaction tail gas is monitored, and when the volume concentration of silane in the reaction tail gas is not higher than 5 vol%, the introduction of the gas containing silane is stopped to obtain the silicon-carbon composite material.

[0090] The present invention controls the amount of silicon-based material deposited on the surface of the porous carbon matrix by controlling the volume concentration of silane in the reaction tail gas to be no more than 5 vol% during the process of depositing the silicon-based material in the pores of the porous carbon matrix. The silicon-carbon composite material prepared satisfies Q2 / Q1≤0.7, so that most of the silicon-based material is deposited in the pores of the porous carbon matrix, and as little silicon-based material as possible is enriched on the surface of the porous carbon matrix, which can effectively improve the cycle performance of the secondary battery.

[0091] The volume concentration of silane in the reaction exhaust gas can be monitored by any conventional method, or using a commercially available silane detector. It should be understood that under normal process conditions, a trace amount of unreacted silane gas (e.g., a volume concentration of less than 0.01 vol%) may be emitted from the exhaust gas. During this period, the reaction is still ongoing, and the introduction of the silane-containing gas need not be stopped.

[0092] In some embodiments, the total volume of the silane in the silane-containing gas introduced per kilogram of the porous carbon substrate is 400 L to 1500 L. Alternatively, the total volume of the silane in the silane-containing gas introduced per kilogram of the porous carbon substrate is 650 L to 850 L. Exemplarily, the total volume of the silane in the silane-containing gas introduced per kilogram of the porous carbon substrate is 650 L, 680 L, 700 L, 720 L, 750 L, 780 L, 800 L, 820 L, 840 L, etc. The total volume of the silane in the silane-containing gas can be determined according to the amount of silicon to be deposited, and the present disclosure has no particular limitation thereto.

[0093] In the technical solution disclosed herein, in the process of depositing silicon-based materials in the pores of a porous carbon matrix, the total amount of silane introduced is an important process parameter. For each kilogram of porous carbon matrix, the total amount of silane introduced depends on the gas flow range of the gas containing silane and the duration of the reaction. Thus, the present disclosure is more conducive to making the prepared silicon-carbon composite material meet Q2 / Q1≤0.7 by limiting the total amount of silane introduced, thereby effectively improving the cycle performance of the secondary battery.

[0094] The silane-containing gas described herein includes, in addition to silane, a carrier gas, which is generally an inert gas such as nitrogen.

[0095] In some embodiments, the volume concentration of silane in the silane-containing gas ranges from greater than 5 to 100 vol%, and optionally from 20 vol% to 80 vol%. For example, 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%.

[0096] According to a specific embodiment, the silane is monosilane.

[0097] The present disclosure does not particularly limit the volume concentration range of silane in the silane-containing gas, and any conventional volume concentration range of silane may be used.

[0098] In some embodiments, the temperature for depositing the silicon-based material is between 450° C. and 600° C.; and / or the deposition time is between 1.2 hours and 37.5 hours per kilogram of the porous carbon substrate; and / or the aeration rate of the silane-containing gas is between 0.1 L / min and 10 L / min. Alternatively, at 510° C. and 560° C., the deposition time is between 2.5 hours and 20 hours per kilogram of the porous carbon substrate.

[0099] The present disclosure does not particularly limit the gas flow rate range of silane in the silane-containing gas, and any conventional silane gas flow rate range is acceptable. Exemplarily, the ventilation 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 ventilation 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.

[0100] Exemplarily, the temperature for depositing the silicon-based material ranges from 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.

[0101] Under the conditions of different determined reaction temperatures, ventilation rates and the proportion of silane in the silane-containing gas, the method disclosed in the present invention can terminate the reaction in a timely manner by monitoring the silane content in the exhaust gas, thereby avoiding excessive silicon deposition on the surface of the carbon matrix, thereby reducing the Q2 / Q1 value.

[0102] In the disclosed technical solution, during the process of depositing the silicon-based material in the pores of the 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 still depends on when the volume concentration of silane in the reaction exhaust gas can be monitored to be no higher than 5 vol%.

[0103] In some embodiments, depositing the silicon-based material in the pores of the porous carbon substrate comprises an initial reaction stage, an intermediate reaction stage, and an end reaction stage, wherein, based on the amount of silane introduced per kilogram of the porous carbon substrate, the amount of silane introduced in the initial reaction stage is 20 L to 170 L, the amount of silane introduced in the intermediate reaction stage is 390 L to 680 L, and the amount of silane introduced in the end reaction stage is 20 L to 170 L. In some specific embodiments, based on the amount of silane introduced per kilogram of the porous carbon substrate, the amount of silane introduced in the initial reaction stage is 150 L to 170 L, the amount of silane introduced in the intermediate reaction stage is 420 L to 490 L, and the amount of silane introduced in the end reaction stage is 150 L to 170 L.

[0104] The reaction process of depositing silicon-based materials in the pores of porous carbon matrix is ​​divided into initial stage of reaction, mid-stage of reaction and late stage of reaction. In the initial stage of reaction, the inner and outer surfaces of silicon-based materials and porous carbon matrix form silicon-carbon interface, and reaction speed is slow. Now, if the amount of silane in the initial stage of reaction is large, the utilization rate of silane is low. In the late stage of reaction, the reaction of depositing silicon-based materials in the pores of porous carbon matrix gradually reaches saturation. Now, if the amount of silane in the late stage of reaction is large, silane is more likely to be deposited on the surface of porous carbon matrix rather than being deposited in the pores of porous carbon matrix. Therefore, the amount of silane in the initial stage of reaction and late stage of reaction is less than the amount of silane in the mid-stage of reaction.

[0105] Therefore, the present disclosure is beneficial to improving the utilization efficiency of silane by dividing the reaction process of depositing silicon-based materials in the pores of the porous carbon matrix.

[0106] In some specific embodiments, the deposition amount of the silicon-based material in the pores of the porous carbon matrix at the initial stage, the middle stage and the final stage of the reaction can be controlled by controlling the deposition time, the concentration of the silane, the flow rate, etc. to control the amount of silane introduced in each period. For example, based on the total duration of the deposition of the silicon-based material, the duration of the initial stage of the reaction accounts for 10% to 20%, the duration of the middle stage of the reaction accounts for 60% to 80%, and the duration of the final stage of the reaction accounts for 10% to 20%. In particular, the volume concentration of silane in the initial stage of the reaction and the final stage of the reaction can be controlled to be less than the volume concentration of silane in the middle stage of the reaction, and / or the gas flow rate of the silane-containing gas in the initial stage of the reaction and the final stage of the reaction can be controlled to be less than the gas flow rate of the silane-containing gas in the middle stage of the reaction.

[0107] In some embodiments, during the deposition of the silicon-based material in the pores of the porous carbon matrix, the pressure in the reactor ranges from greater than 0 to 1 kPa; optionally, from 100 Pa to 500 Pa.

[0108] The present disclosure has no particular limitation on the reaction pressure, and the pressure during the deposition process can be a slightly positive pressure.

[0109] In some embodiments, the method further comprises:

[0110] coating a carbon coating layer on at least a portion of the surface of the silicon-carbon composite material;

[0111] Optionally, coating at least a portion of the surface of the silicon-carbon composite material with a carbon coating layer comprises:

[0112] 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 to 10 hours; optionally, the reaction is carried out at 600° C. to 700° C. for 2 to 6 hours.

[0113] In a specific embodiment, after the introduction of the silane-containing gas is stopped, the reactor does not need to be replaced, and a gas containing a carbon source is immediately introduced into the reactor for surface coating.

[0114] Thus, the present disclosure forms a carbon coating layer on the surface of the silane composite material to obtain a silicon-carbon composite material. In this case, the prepared silicon-carbon composite material satisfies Q3 / Q1≤0.37, which can effectively improve the first coulombic efficiency of the secondary battery.

[0115] In some embodiments, the carbon source is selected from at least one of the following: methane, ethylene, acetylene, and propane.

[0116] The present disclosure has no particular limitation on the choice of carbon source, and any conventional carbon source can be used.

[0117] 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 of the carbon source can optionally range from 20 vol % to 80 vol %.

[0118] The present disclosure does not particularly limit the volume concentration range of the carbon source in the gas containing the carbon source, and any conventional volume concentration range of the carbon source can be used.

[0119] In some embodiments, the gas flow rate of the carbon source in the gas containing the carbon source ranges from greater than 0.1 L / min to 10 L / min; the gas flow rate of the carbon source can optionally range from greater than 0.1 L / min to 4 L / min.

[0120] The present disclosure does not particularly limit the gas flow rate range of the carbon source in the gas containing the carbon source, and any conventional gas flow rate range of the carbon source can be used.

[0121] In a third aspect, the present disclosure provides a secondary battery comprising a negative electrode plate, wherein the negative electrode plate comprises the silicon-carbon composite material of the first aspect of the present disclosure, or comprises a silicon-carbon composite material prepared by the method for preparing the silicon-carbon composite material of the second aspect of the present disclosure. The secondary battery has excellent cycle performance.

[0122] In addition, the secondary battery and the electric device of the present disclosure will be described below with reference to the drawings as appropriate.

[0123] In one embodiment of the present disclosure, a secondary battery is provided.

[0124] The term "secondary battery" mentioned herein refers to a battery cell, a battery module, or a battery pack. Each of these is described below.

[0125] Typically, a secondary battery cell consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During the battery's charge and discharge processes, active ions are inserted and removed between the positive and negative electrodes. The electrolyte conducts ions between the positive and negative electrodes. The separator, located between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0126] Negative electrode

[0127] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector. The negative electrode film layer includes a negative electrode active material. The negative electrode active material may include the silicon-carbon composite material according to the first aspect of the present disclosure.

[0128] As an example, the negative electrode current collector has two surfaces opposite to each other in its 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.

[0129] 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 base layer and a metal layer formed on at least one surface of the polymer base material. 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 base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0130] In some embodiments, the negative electrode active material may further employ negative electrode active materials for batteries known in the art. For 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. The silicon-based material may be selected from at least one of elemental silicon, silicon oxides, silicon-carbon complexes, silicon-nitrogen complexes, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxides, and tin alloys.

[0131] In some embodiments, the negative electrode film layer may further 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).

[0132] In some embodiments, the negative electrode film layer may further include a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0133] In some embodiments, the negative electrode film layer may optionally further include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0134] In some embodiments, the negative electrode sheet can be prepared by the following method: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0135] Positive electrode

[0136] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector, wherein the positive electrode film layer includes a positive electrode active material.

[0137] As an example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive electrode current collector.

[0138] In some embodiments, the positive electrode 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 material base and a metal layer formed on at least one surface of the polymer material base. 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 material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0139] In some embodiments, when the battery cell is a lithium-ion battery, the positive electrode active material may adopt the positive electrode active material for lithium-ion batteries known in the art. As an example, the positive electrode active material may include at least one of the following materials: lithium-containing phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, the present disclosure is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.1 Al 0.05O2) and its modified compounds. Examples of olivine-structured lithium-containing phosphates may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

[0140] The battery's charge and discharge processes involve the intercalation and deintercalation of lithium, leading to different molar Li contents at different discharge states. The molar Li contents listed in this disclosure for positive electrode active materials refer to the material's initial state, i.e., before addition. When a positive electrode active material is used in a battery system, its molar Li content will change over the course of charge and discharge cycles.

[0141] In the list of positive electrode active materials in this disclosure, the molar content of O is only a theoretical value. Oxygen release from the lattice will cause the molar content of oxygen to change, and the actual molar content of O will fluctuate.

[0142] In some embodiments, when the battery cell is a sodium-ion battery, the positive electrode active material may be a positive electrode active material known in the art for 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, the present disclosure is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials may also be used.

[0143] As an optional technical solution of the present disclosure, in the sodium transition metal oxide, the transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce. Sodium transition metal oxide is, for example, Na x MO2, wherein M is one or more of Ti, V, Mn, Co, Ni, Fe, Cr and Cu, and 0<x≤1. For example, sodium iron composite oxide (NaFeO2), sodium cobalt composite oxide (NaCoO2), sodium chromium composite oxide (NaCrO2), sodium manganese composite oxide (NaMnO2), sodium nickel composite oxide (NaNiO2), sodium nickel titanium composite oxide (NaNiO2), ... 1 / 2 Ti 1 / 2 O2), sodium nickel manganese composite oxide (NaNi 1 / 2 Mn 1 / 2 O2), sodium iron manganese composite oxide (Na 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).

[0144] As an optional technical solution of the present disclosure, the polyanionic compound can be a compound having sodium ions, transition metal ions and tetrahedral (YO4) 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- valence.

[0145] Polyanionic compounds can also be sodium ions, transition metal ions, tetrahedral (YO4) n- A class of compounds containing anion units and halogen 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- valence state; the halogen may be at least one of F, Cl and Br.

[0146] Polyanionic compounds can also be sodium ions, tetrahedral (YO4) n- Anion unit, polyhedron unit (ZO y ) m+ and an optional halogen anion. Y can be at least one of P, S and Si, and n represents (YO4) n- valence state; Z represents a transition metal, which may be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce, and m represents (ZO y ) m+ valence state; the halogen may be at least one of F, Cl and Br.

[0147] Polyanionic compounds include NaFePO4, Na3V2(PO4)3, NaM'PO4F (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).

[0148] Prussian blue compounds can be 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. Prussian blue compounds are, for example, 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。

[0149] In some embodiments, the positive electrode film layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0150] In some embodiments, the positive electrode film layer may further include a conductive agent. For example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0151] In some embodiments, the positive electrode sheet can be prepared by the following method: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0152] electrolytes

[0153] The electrolyte conducts ions between the positive and negative electrodes. This disclosure does not specifically limit the type of electrolyte, and the electrolyte can be selected based on needs. For example, the electrolyte can be liquid, gel, or solid.

[0154] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0155] 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 difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0156] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0157] In some embodiments, the electrolyte may further include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, and additives that improve battery high or low temperature performance.

[0158] Isolation film

[0159] In some embodiments, the battery cell further includes a separator. The present disclosure has no particular limitation on the type of separator, and any known porous separator with good chemical and mechanical stability can be selected.

[0160] In some embodiments, the material of the separator can be selected from at least one of glass fiber, non-woven 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.

[0161] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0162] In some embodiments, the battery cell may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0163] In some embodiments, the outer packaging of the battery cell may be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. Alternatively, the outer packaging of the battery cell may be a soft shell, such as a pouch-type soft shell. The soft shell may be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0164] The present disclosure has no particular limitation on the shape of the battery cell, which may be cylindrical, square, or any other shape. For example, FIG1 shows a battery cell 5 with a square structure as an example.

[0165] In some embodiments, referring to Figure 2, the outer packaging may include a shell 51 and a top cover assembly 53. The shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the top cover assembly 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can form an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0166] In some embodiments, battery cells may be assembled into a battery module. The battery module may contain one or more battery cells. The specific number may be selected by those skilled in the art based on the application and capacity of the battery module.

[0167] FIG3 shows an example battery module 4. Referring to FIG3 , within the battery module 4, multiple battery cells 5 may be arranged sequentially along the length of the battery module 4. Of course, they may also be arranged in any other manner. Furthermore, the multiple battery cells 5 may be secured together using fasteners.

[0168] Optionally, the battery module 4 may further include a housing having an accommodation space, and the plurality of battery cells 5 are accommodated in the accommodation space.

[0169] In some embodiments, the battery modules described above may also be assembled into a battery pack. The battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art based on the application and capacity of the battery pack.

[0170] Figures 4 and 5 illustrate an example battery pack 1. Referring to Figures 4 and 5 , the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box comprises an upper case 2 and a lower case 3. The upper case 2 can be placed over the lower case 3 to form an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0171] In a fourth aspect, the present disclosure provides an electric device, comprising the secondary battery according to the third aspect of the present disclosure.

[0172] The secondary battery can be used as a power source or 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, satellites, and energy storage systems.

[0173] As the electrical device, a battery cell, a battery module or a battery pack can be selected according to its usage requirements.

[0174] Figure 6 shows an example of an electric device. This device is 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, a battery pack or battery module can be used.

[0175] Another example device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be lightweight and thin, and may use a battery cell as a power source.

[0176] Example

[0177] The following examples are provided. The examples described below are illustrative and are intended only to explain the present disclosure and are not to be construed as limiting the present disclosure. Where specific techniques or conditions are not specified in the examples, the methods were performed according to those described in the literature in the art or according to the product specifications. Reagents or instruments used without manufacturer's indication are all commercially available conventional products.

[0178] Preparation of silicon-carbon composite materials

[0179] Example 1

[0180] a. Place 1 kg of porous hard carbon substrate (micropore to mesopore pore volume ratio of 6.5) in a rotary kiln and heat to 500 ° C under nitrogen protection for 2 hours to fully desorb the air adsorbed in the porous carbon matrix;

[0181] b. Vacuum the rotary kiln to a vacuum degree of 1×10 -5 Pa, maintain the pressure for 5 minutes and then introduce nitrogen until the pressure in the kiln returns to normal;

[0182] c. Repeat step b until the oxygen content in the exhaust gas is less than 200 ppm;

[0183] d. A mixture of monosilane and nitrogen is introduced, the ratio of the mixed gas is monosilane: nitrogen = 1:4, the ventilation rate is 4L / min, the kiln maintains a slightly positive pressure of 200Pa, and the rotary kiln rotation frequency is 40Hz;

[0184] e chromatograph (model: Agilent Lab Gc 8860) to monitor the concentration of monosilane in the reaction exhaust gas, stop the introduction of a mixture of monosilane and nitrogen, the concentration of monosilane in the reaction exhaust gas was 4.8vol%, the total amount of monosilane introduced was 780L;

[0185] f. The temperature in the rotary kiln was raised to 600°C, and a mixture of acetylene and nitrogen was introduced for 5 hours. The ratio of the mixed gas was acetylene: nitrogen = 1:4, the ventilation rate was 2 L / min, a slight positive pressure of 200 Pa was maintained in the kiln, and the rotary kiln rotation frequency was 40 Hz to obtain a silicon-carbon composite material having a carbon coating layer with a thickness of about 10 nm; wherein the total amount of acetylene introduced was 600 L.

[0186] Example 2

[0187] The silicon-carbon composite material of Example 2 was prepared similarly to Example 1, except that the total amount of monosilane introduced was 720 L; and when the introduction of the mixed gas of monosilane and nitrogen was stopped, the concentration of monosilane in the reaction tail gas was 2.5 vol%.

[0188] Example 3

[0189] The silicon-carbon composite material of Example 3 was prepared similarly to Example 1, except that the ventilation rate of the mixed gas of monosilane and nitrogen was 3.8 L / min, and when the ventilation of the mixed gas of monosilane and nitrogen was stopped, the concentration of monosilane in the reaction exhaust gas was 3.7 vol%.

[0190] Example 4

[0191] The silicon-carbon composite material of Example 4 was prepared similarly to Example 1, except that no carbon coating layer was formed on the surface of the silicon-carbon composite material. When the introduction of the mixed gas of monosilane and nitrogen was stopped, the concentration of monosilane in the reaction exhaust gas was 4.7 vol%.

[0192] Comparative Example 1

[0193] The silicon-carbon composite material of Comparative Example 1 was prepared similarly to Example 1, except that when the introduction of the mixed gas of monosilane and nitrogen was stopped, the concentration of monosilane in the reaction tail gas was 5.5 vol%.

[0194] Preparation of button cells

[0195] The negative electrode sheet was prepared according to the following method: the silicon-carbon composite material, conductive agent carbon black, and binder polyacrylic acid prepared above were mixed in a mass ratio of 8:1:1, deionized water solvent was added, and the mixture was stirred in a rapid mixer until the system became uniform to obtain a negative electrode slurry; the negative electrode slurry was evenly coated on the negative electrode current collector copper foil and dried at 85°C, and then cold pressed to obtain a negative electrode sheet.

[0196] 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 uniformly dissolved in the above solution, and fluoroethylene carbonate (FEC) was added as an additive to obtain an electrolyte. The concentration of LiPF6 was 1 mol / L, and the weight proportion of FEC in the electrolyte was 5%.

[0197] The button battery is prepared according to the following method: the above-mentioned negative electrode sheet is used as the working electrode, the metallic lithium is used as the counter electrode, and a polypropylene film is used as the isolation membrane. The negative electrode sheet, the isolation membrane and the metallic lithium are stacked in order so that the isolation membrane is between the working electrode and the counter electrode, and the electrolyte is injected to assemble the button battery.

[0198] Preparation of secondary batteries

[0199] The negative electrode sheet was prepared as follows: the negative electrode active material (the silicon-carbon composite material prepared above was mixed with artificial graphite in a ratio of 1:9), the conductive carbon nanotube and SP mixture, the binder styrene-butadiene rubber, and the thickener sodium carboxymethyl cellulose were thoroughly stirred in an appropriate amount of deionized water as a solvent at a weight ratio of 95.5:1:2:1.5 to form a negative electrode slurry. The negative electrode slurry was applied to both surfaces of the negative electrode current collector copper foil, dried, and cold pressed to obtain the negative electrode sheet.

[0200] The positive electrode sheet was prepared as follows: the positive electrode active material LiNi 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. An appropriate amount of NMP solvent is added and stirred evenly to obtain a positive electrode slurry. The positive electrode slurry is coated on both surfaces of the positive electrode current collector aluminum foil. After drying and cold pressing, the positive electrode sheet is obtained.

[0201] The electrolyte was prepared according to the following method: a mixture of ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) was used as an organic solvent, wherein the volume ratio of EC, EMC and DEC was 20:20:60. In an oxygen atmosphere glove box with a water content of <10ppm, a fully dried lithium salt (LiPF6) was dissolved in the above organic solvent, and an additive, fluoroethylene carbonate (FEC), was added to obtain an electrolyte. In this electrolyte, the concentration of LiPF6 was 1 mol / L, and the mass proportion of FEC in the electrolyte was 5%.

[0202] Polypropylene film is used as the isolation membrane.

[0203] The secondary battery is prepared according to the following method: the positive electrode sheet, separator and negative electrode sheet prepared above are placed in order, so that the separator (i.e., polypropylene film) is placed between the positive electrode sheet and the negative electrode sheet to play an isolating role, and then the electrode assembly is obtained by winding; the electrode assembly is placed in an outer package, dried, and then the electrolyte prepared above is injected, and the secondary battery is obtained through vacuum packaging, standing, formation, capacity separation and other processes.

[0204] Button battery performance test

[0205] 1. Q2 / Q1 and Q3 / Q1

[0206] The button cell prepared above was left to rest for 60 minutes, then discharged at a constant current of 0.05C to 5mV, discharged at 50μA to 5mV, left to rest 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. Q2 / Q1 and Q3 / Q1 were calculated.

[0207] 2. First Coulombic efficiency test

[0208] After the button battery assembled above 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 charged to 0.8V using 0.1C for testing. The delithiation capacity at 0.8V represents the capacity of the silicon-carbon composite material, corresponding to the delithiation capacity / lithiation capacity when the first effect = 0.08V.

[0209] Performance testing of secondary batteries

[0210] Cycle performance test

[0211] At 25°C, let the secondary battery rest for 30 minutes. Then, charge it at a rate of 0.5C to 4.25V. Further charge it at a constant voltage of 4.25V to a current of 0.05C, let it rest for 5 minutes, and then discharge it at a rate of 0.5C to a voltage of 2.5V. The resulting capacity is recorded as the initial capacity C0. This constitutes one charge-discharge cycle. Repeat these steps for the same secondary battery, recording the discharge capacity Cn after each cycle. The battery capacity retention rate after each cycle, Pn, is calculated as Cn / C0*100%. The test is stopped until Pn ≤ 80%. The number of cycles at this point is recorded.

[0212] For the button batteries prepared in Examples 1 to 4 and Comparative Example 1, Q2 / Q1, Q3 / Q1 and the first coulombic efficiency were tested; for the secondary batteries prepared in Examples 1 to 4 and Comparative Example 1, the cycle performance was tested, and the specific results are shown in Table 1.

[0213] Table 1

[0214] 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.

[0215] Example 5

[0216] The silicon-carbon composite material of Example 5 was prepared similarly to Example 1, except that the deposition temperature was 450° C., and the introduction of the mixed gas of monosilane and nitrogen was stopped, and the concentration of monosilane in the reaction tail gas was 3.4 vol%.

[0217] Example 6

[0218] The silicon-carbon composite material of Example 6 was prepared similarly to Example 1, except that the deposition temperature was 520° C. and when the introduction of the mixed gas of monosilane and nitrogen was stopped, the concentration of monosilane in the reaction tail gas was 3.4 vol%.

[0219] Example 7

[0220] The silicon-carbon composite material of Example 7 was prepared similarly to Example 1, except that the deposition temperature was 550° C. and when the introduction of the mixed gas of monosilane and nitrogen was stopped, the concentration of monosilane in the reaction tail gas was 3.4 vol%.

[0221] Example 8

[0222] The silicon-carbon composite material of Example 8 was prepared similarly to Example 1, except that the deposition temperature was 600° C. and when the introduction of the mixed gas of monosilane and nitrogen was stopped, the concentration of monosilane in the reaction tail gas was 3.4 vol%.

[0223] For the button batteries prepared by the same method as above for the silicon-carbon composite materials prepared in Examples 5 to 8, Q2 / Q1, Q3 / Q1 and first coulombic efficiency were tested. For the secondary batteries prepared by the same method as above for the silicon-carbon composite materials prepared in Examples 5 to 8, the cycle performance was tested. The specific results are shown in Table 2.

[0224] Table 2

[0225] As shown in Table 2, the Q2 / Q1 ratio of button cells made of silicon-carbon composite materials changes with the deposition temperature, and the corresponding cycling performance of secondary batteries made of silicon-carbon composite materials also changes. In general, the deposition temperature has little effect on the cycling performance of secondary batteries made of silicon-carbon composite materials.

[0226] Example 9

[0227] The silicon-carbon composite material of Example 9 was prepared similarly to Example 1, except that the amount of monosilane introduced at the initial stage of the reaction was 155 L, the amount of monosilane introduced at the middle stage of the reaction was 470 L, and the amount of monosilane introduced at the end of the reaction was 155 L; and when the introduction of the mixed gas of monosilane and nitrogen was stopped, the concentration of monosilane in the reaction exhaust gas was 2.3 vol%.

[0228] Example 10

[0229] The silicon-carbon composite material of Example 10 was prepared similarly to Example 1, except that the amount of monosilane introduced at the initial stage of the reaction was 170 L, the amount of monosilane introduced at the middle stage of the reaction was 440 L, and the amount of monosilane introduced at the end of the reaction was 170 L; and the introduction of the mixed gas of monosilane and nitrogen was stopped, and the concentration of monosilane in the reaction exhaust gas was 2.3 vol%.

[0230] The button cells prepared from the silicon-carbon composite materials prepared in Example 9 and Example 10 by the same method as above were tested to obtain the initial coulombic efficiency. The secondary batteries prepared from the silicon-carbon composite materials prepared in Example 9 and Example 10 by the same method as above were tested to obtain the cycle performance. The specific results are shown in Table 3.

[0231] Table 3

[0232] As shown in Table 3, the reaction process is divided into the initial, mid, and final stages. As the amount of monosilane introduced changes in each reaction stage, the Q2 / Q1 ratio of the button-type battery prepared from the silicon-carbon composite material also changes, and the corresponding cycling performance of the secondary battery prepared from the silicon-carbon composite material also changes. In general, dividing the reaction process into three stages and controlling the amount of monosilane introduced in each reaction stage is more conducive to controlling the Q2 / Q1 ratio of the button-type battery prepared from the silicon-carbon composite material within a selectable range.

[0233] It should be noted that the present disclosure is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and within the scope of the technical solution of the present disclosure, embodiments having substantially the same structure as the technical concept and exerting the same effects are all included in the technical scope of the present disclosure. In addition, within the scope of the present disclosure, various modifications that can be imagined by those skilled in the art to the embodiments, and other methods constructed by combining some of the constituent elements of the embodiments are also included in the scope of the present disclosure.

Claims

1. A silicon-carbon composite material, comprising: 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; wherein, the silicon-carbon composite material is charged and discharged using a button battery, and the capacity when the voltage is from 0.2V to 0.4V during the charging process is Q1, and the capacity when the voltage is from 0.4V to 0.6V during the charging process is Q2.

2. The silicon-carbon composite material according to claim 1, wherein The silicon-carbon composite material satisfies 0.3≤Q2 / Q1≤0.7; optionally, 0.5≤Q2 / Q1≤0.

65.

3. The silicon-carbon composite material according to claim 1 or 2, wherein At least part of the surface of the silicon-carbon composite material has a coating layer; optionally, the coating layer has a thickness of 2 nm to 100 nm.

4. The silicon-carbon composite material according to claim 3, wherein The silicon-carbon composite material satisfies Q3 / Q1≤0.37; wherein, during the charging process, the capacity when the voltage is from 0.6V to 0.8V is Q3.

5. The silicon-carbon composite material according to claim 4, wherein The silicon-carbon composite material satisfies 0.25≤Q3 / Q1≤0.37; optionally, 0.3≤Q3 / Q1≤0.

37.

6. The silicon-carbon composite material according to any one of claims 1 to 5, wherein The porous carbon matrix includes micropores and mesopores; optionally, a pore volume ratio of the micropores to the mesopores is 1 to 40.

7. The silicon-carbon composite material according to any one of claims 1 to 6, wherein The silicon-carbon composite material satisfies at least one of the following: The specific surface area of ​​the silicon-carbon composite material is 0.1 m 2 / g to 5m 2 / g; The silicon-carbon composite material contains 30% to 60% silicon-based material; At least part of the silicon-based material in the silicon-carbon composite material exists in the form of amorphous silicon.

8. A method for preparing a silicon-carbon composite material, the method comprising the following steps: introducing a gas containing silane into a reactor containing the porous carbon substrate to deposit a silicon-based material in the pores of the porous carbon substrate; Monitoring the reaction tail gas, and when the volume concentration of silane in the reaction tail gas is not higher than 5 vol%, stopping the introduction of the gas containing silane to obtain the silicon-carbon composite material, wherein 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, and the silicon-carbon composite material satisfies Q2 / Q1≤0.7; wherein a button battery is used to charge and discharge the silicon-carbon composite material, and the capacity when the voltage is from 0.2V to 0.4V during the charging process is Q1, and the capacity when the voltage is from 0.4V to 0.6V during the charging process is Q2.

9. The preparation method according to claim 8, wherein The total volume of the silane in the gas containing silane introduced is 400 L to 1500 L per kilogram of the porous carbon substrate.

10. The preparation method according to claim 8 or 9, wherein The temperature of depositing the silicon-based material is 450° C. to 600° C.; and / or, The deposition time per kilogram of the porous carbon substrate is 1.2 hours to 37.5 hours; and / or, The ventilation rate of the silane-containing gas is 0.1 L / min to 10 L / min; Optionally, the deposition temperature is 510° C. to 560° C., and the deposition time is 2.5 h to 20 h per kilogram of the porous carbon substrate.

11. The preparation method according to any one of claims 8 to 10, wherein The deposition of silicon-based materials in the pores of the porous carbon matrix includes an initial reaction stage, a middle reaction stage and a final reaction stage. Calculated by the amount of silane introduced per kilogram of the porous carbon matrix, the amount of silane introduced at the initial reaction stage is 20L to 170L, the amount of silane introduced at the middle reaction stage is 390L to 680L, and the amount of silane introduced at the final reaction stage is 20L to 170L; optionally, calculated by the amount of silane introduced per kilogram of the porous carbon matrix, the amount of silane introduced at the initial reaction stage is 150L to 170L, the amount of silane introduced at the middle reaction stage is 420L to 490L, and the amount of silane introduced at the final reaction stage is 150L to 170L.

12. The preparation method according to any one of claims 8 to 11, wherein The method further comprises: coating a carbon coating layer on at least a portion of the surface of the silicon-carbon composite material; Optionally, coating at least a portion of the surface of the silicon-carbon composite material with a carbon coating layer comprises: 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 to 10 hours; optionally, the reaction is carried out at 600° C. to 700° C. for 2 to 6 hours.

13. A secondary battery, comprising a negative electrode plate, wherein the negative electrode plate comprises the silicon-carbon composite material according to any one of claims 1 to 7, or comprises the silicon-carbon composite material prepared by the preparation method according to any one of claims 8 to 12. 14 . An electric device comprising the secondary battery according to claim 13 .

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