Silicon-carbon negative electrode material and preparation method therefor

Abstract

A silicon-carbon negative electrode material and a preparation method therefor. The silicon-carbon negative electrode material comprises a carbon skeleton having a pore structure and a silicon-based material arranged in the pore structure, wherein within a region beginning at the surface of the silicon-carbon negative electrode material and ending at interior positions that are 10 nm away from the surface, the content of high-valence silicon is less than 25% relative to the total amount of low-valence silicon and high-valence silicon, the low-valence silicon being silicon with a valence of 0 to 2, and the high-valence silicon being silicon with a valence of 3 to 4. The silicon-carbon negative electrode material can improve the delithiation specific capacity and the initial coulombic efficiency of the silicon-carbon negative electrode material, and can enhance the specific discharge capacity and the initial coulombic efficiency of a secondary battery.

Description

Silicon-carbon negative electrode material and preparation method thereof

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This disclosure is based on the Chinese patent application with application number 202311619241.X, application date November 28, 2023, and invention name “Silicon-carbon negative electrode material and preparation method thereof”, 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 negative electrode material and a preparation method thereof. Background Art

[0004] As the power of electrical devices like mobile phones, computers, power tools, and electric vehicles continues to increase, the demand for energy density in secondary batteries is also increasing. Silicon-based anode materials have a high specific capacity, and the industry has begun to increase the energy density of secondary batteries by incorporating them into the anode plates. However, the increased volume expansion of silicon-based anode materials after lithium insertion can cause cracking in the anode plates.

[0005] To address the high volume expansion rate of silicon-based anode materials, silicon-carbon anode materials are currently commonly used. Silicon is deposited inside porous carbon, creating a structure that reduces the expansion of the silicon-based material by utilizing the voids within the porous carbon. However, because the silicon in the silicon-carbon anode material is oxidized into high-valent silicon, the specific capacity of the silicon-carbon anode material decreases, affecting the initial coulombic efficiency of the secondary battery.

[0006] Summary of the Invention

[0007] The present disclosure is made in view of the above problems, and its purpose is to provide a silicon-carbon negative electrode material and a preparation method, which has high lithium removal capacity and first coulomb efficiency, thereby improving the discharge capacity and first coulomb efficiency of the secondary battery.

[0008] In order to achieve the above-mentioned purpose, the first aspect of the present disclosure provides a silicon-carbon negative electrode material, which includes a carbon skeleton with a pore structure and a silicon-based material arranged in the pore structure. In the area from the surface of the silicon-carbon negative electrode material to the area extending 10 nm inward from the surface, the content of the high-valent silicon is less than 25% relative to the total amount of low-valent silicon and high-valent silicon, wherein the low-valent silicon is silicon with a valence of 0 to 2, and the high-valent silicon is silicon with a valence of 3 to 4.

[0009] The silicon-carbon negative electrode material disclosed herein suppresses the content of high-valent silicon to a low level, making the content of low-valent silicon high, thereby improving the lithium removal capacity and first coulombic efficiency of the negative electrode material, and effectively improving the discharge capacity and first coulombic efficiency of the secondary battery.

[0010] In some embodiments, within a region extending 10 nm inward from the surface of the silicon-carbon negative electrode material, the content of the high-valent silicon is less than or equal to 20% relative to the total amount of low-valent silicon and high-valent silicon. As a result, the negative electrode material has a higher delithiation gram capacity and first coulombic efficiency, and the resulting secondary battery has better discharge gram capacity and first coulombic efficiency.

[0011] In some embodiments, within the region from 10 nm to 20 nm from the surface of the silicon-carbon negative electrode material, the content of high-valent silicon is less than or equal to 20%, and optionally less than or equal to 10%, relative to the total amount of low-valent silicon and high-valent silicon. Thus, the content of high-valent silicon in the silicon-carbon negative electrode material of the present disclosure is further suppressed to a low level, which is more conducive to improving the lithium removal gram capacity and first coulombic efficiency of the negative electrode material.

[0012] In some embodiments, within the region from 20 nm to 30 nm from the surface of the silicon-carbon negative electrode material, the content of high-valent silicon is less than or equal to 10%, and optionally less than or equal to 5%, relative to the total amount of low-valent silicon and high-valent silicon. Thus, the content of high-valent silicon in the silicon-carbon negative electrode material of the present disclosure is further suppressed to a low level, which is more conducive to improving the lithium removal gram capacity and first coulombic efficiency of the negative electrode material.

[0013] In some embodiments, the silicon-carbon negative electrode material satisfies at least one of the following conditions: (1) the volume distribution particle size Dv50 of the silicon-carbon negative electrode material is 5 μm-10 μm, optionally 6 μm-9 μm; (2) the specific surface area of ​​the silicon-carbon negative electrode material is less than or equal to 5 m 2 / g, can be less than or equal to 2m 2 / g; (3) the powder compaction density of the silicon-carbon negative electrode material under a pressure of 3000N is 0.8g / cm 3 -1.2g / cm 3 , optional 0.9g / cm 3 -1.2g / cm 3 ;(4) The tap density of the silicon-carbon negative electrode material is 0.9g / cm 3 -1.1g / cm 3 , optional 1.0g / cm 3 -1.1g / cm 3(5) The lithium-free capacity of the silicon-carbon negative electrode material is 800mAh / g-2500mAh / g, and can be optionally 1000mAh / g-2000mAh / g. By making the particle size, compaction density and tap density of the silicon-carbon negative electrode material within the above range, the compaction density of the electrode sheet can be effectively increased, and the energy density of the battery cell can be increased. In addition, by making the specific surface area within 5m 2 / g or less, which can minimize the contact area between the particles and the electrolyte and improve the initial coulombic efficiency, cycle and storage performance.

[0014] In some embodiments, the pore volume of the carbon skeleton is 0.4 cm 3 / g-1.5cm 3 / g, optional 0.6cm 3 / g-1.2cm 3 / g; and / or, relative to the pore volume, the volume proportion of micropores with a pore diameter of less than 2 nm is greater than or equal to 60%, and optionally greater than or equal to 80%. As a result, the silicon-based material is mainly deposited in the micropores. The higher the micropore proportion, the more silicon-based material is deposited, and the corresponding delithiation capacity is higher.

[0015] In some embodiments, the surface of the silicon-carbon negative electrode material has a coating layer; optionally, the coating layer is a carbon coating layer. The present disclosure significantly reduces the risk of silicon in the negative electrode material being oxidized to form high-valent silicon through this coating layer, thereby reducing the content of high-valent silicon in the silicon-carbon negative electrode material.

[0016] A second aspect of the present disclosure provides a method for preparing the silicon-carbon negative electrode material of the first aspect, comprising the following steps:

[0017] a silicon-carbon particle forming step of reacting a carbon skeleton having a pore structure with a silicon source gas to form silicon-carbon particles having a silicon-based material in the pore structure; and

[0018] The silicon-carbon particle processing step is to introduce a mixed gas including a carbon source gas and an inert gas into the silicon-carbon particles at a ventilation rate greater than 0 L / min and less than or equal to 10 L / min under the conditions of a temperature of 500°C-800°C and a pressure of 0 kPa-1 kPa, wherein the carbon source gas is selected from at least one of ethane, ethylene, acetylene, and methane.

[0019] Through the above preparation method, a uniform and dense coating layer can be formed on the surface of the silicon-carbon particles, which greatly reduces the risk of silicon in the negative electrode material being oxidized to form high-valent silicon, and can obtain a silicon-carbon negative electrode material with high lithium removal capacity and first coulombic efficiency.

[0020] In some embodiments, during the silicon-carbon particle treatment step, the mixed gas is introduced into the silicon-carbon particles at a temperature of 550° C. to 650° C. and a pressure of 0 kPa to 0.5 kPa at a flow rate of 0.5 L / min to 4 L / min. This allows for the formation of a more uniform and dense coating layer, which is beneficial for obtaining a silicon-carbon anode material with a higher delithiation gram capacity and first coulombic efficiency.

[0021] In some embodiments, the gas mixture comprises 10% to 70% by volume of acetylene, 0% to 20% by volume of methane, and 10% to 90% by volume of an inert gas. Alternatively, the gas mixture comprises 15% to 60% by volume of acetylene, 5% to 10% by volume of methane, and 30% to 80% by volume of an inert gas. Thus, the specific gas mixture can control the decomposition rate, allowing carbon to slowly coat the particle surface, resulting in a denser coating.

[0022] In some embodiments, the step of forming silicon-carbon particles includes evacuating the reaction vessel and then introducing an inert gas. This removes oxygen from the reaction vessel, significantly reducing the risk of silicon deposited in the negative electrode material being oxidized by oxygen in the reaction vessel to form high-valent silicon.

[0023] In some embodiments, the step of forming silicon-carbon particles includes heating a porous carbon skeleton to 400°C-550°C in a reaction apparatus to remove oxygen from the carbon skeleton. This removes oxygen adsorbed by the carbon skeleton itself, significantly reducing the risk of silicon deposited in the negative electrode material being oxidized by oxygen adsorbed by the carbon skeleton itself to form high-valent silicon.

[0024] In some embodiments, the step of forming silicon-carbon particles includes the following steps: introducing a mixture of a silicon source gas and an inert gas into a reaction apparatus, and depositing the mixture at a temperature of 400° C. to 550° C. for 2 to 10 hours to form silicon-carbon particles. This allows silicon to be uniformly deposited within the porous carbon.

[0025] In some embodiments, the silicon source gas is selected from one or more of monosilane, disilane, dichlorosilane, and trichlorosilane. Optionally, the silicon source gas is monosilane.

[0026] In some embodiments, the inert gas is argon, thereby preventing the silicon source gas from being flammable and silicon from being oxidized.

[0027] The third aspect of the present disclosure further provides a negative electrode plate, comprising the silicon-carbon negative electrode material of the first aspect of the present disclosure or the silicon-carbon negative electrode material prepared by the second aspect.

[0028] The fourth aspect of the present disclosure further provides a secondary battery comprising the negative electrode sheet according to the third aspect of the present disclosure. The secondary battery has excellent first coulombic efficiency.

[0029] A fifth aspect of the present disclosure further provides an electrical device comprising the secondary battery according to the fourth aspect of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] FIG1 is a schematic diagram of a battery cell according to an embodiment of the present disclosure.

[0031] FIG. 2 is an exploded view of the battery cell according to the embodiment of the present disclosure shown in FIG. 1 .

[0032] FIG3 is a schematic diagram of a battery module according to an embodiment of the present disclosure.

[0033] FIG4 is a schematic diagram of a battery pack according to an embodiment of the present disclosure.

[0034] FIG. 5 is an exploded view of the battery pack shown in FIG. 4 according to an embodiment of the present disclosure.

[0035] 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.

[0036] FIG7 is an XPS graph of the silicon-carbon negative electrode material of Example 1 of the present disclosure, obtained by analyzing the region extending from the surface to the inner portion by 10 nm.

[0037] FIG8 is an XPS graph of the silicon-carbon negative electrode material of Comparative Example 1 of the present disclosure, obtained by analyzing the region extending from the surface to the inner portion by 10 nm.

[0038] Description of reference numerals:

[0039] 1 battery pack; 2 upper box; 3 lower box; 4 battery module; 5 battery cell; 51 shell; 52 electrode assembly; 53 cover plate. DETAILED DESCRIPTION

[0040] Below, the embodiments of the silicon-carbon negative electrode material and the preparation method thereof 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.

[0041] " 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.

[0042] Unless otherwise specified, all embodiments and optional embodiments of the present disclosure can be combined with each other to form new technical solutions.

[0043] Unless otherwise specified, all technical features and optional technical features disclosed herein can be combined with each other to form a new technical solution.

[0044] Unless otherwise specified, all steps of the present disclosure may be performed sequentially or randomly, preferably sequentially. For example, a method comprising steps (a) and (b) indicates that the method may comprise steps (a) and (b) performed sequentially, or may comprise steps (b) and (a) performed sequentially. For example, a method further comprising step (c) indicates that step (c) may be added to the method in any order, for example, the method may comprise steps (a), (b), and (c), or may comprise steps (a), (c), and (b), or may comprise steps (c), (a), and (b), etc.

[0045] Unless otherwise specified, the terms used in the present disclosure have the common meanings that are generally understood by those skilled in the art.

[0046] 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.

[0047] With the extensive research on silicon-carbon negative electrode materials, people have put forward higher requirements for the performance of silicon-carbon negative electrode materials. The inventors found that increasing the content of low-valent silicon in silicon-carbon negative electrode materials helps to improve the lithium-free gram capacity of silicon-carbon negative electrode materials. However, in the current silicon-carbon negative electrode materials, low-valent silicon is inevitably oxidized to form high-valent silicon, resulting in a decrease in the lithium-free gram capacity and the first coulombic efficiency of the silicon-carbon negative electrode materials. Moreover, these high-valent silicons easily form irreversible lithium silicates with lithium ions, which reduces the amount of active lithium embedded and extracted between the positive and negative electrode sheets, causing lithium loss, resulting in a decrease in the discharge gram capacity and the first coulombic efficiency of the secondary battery.

[0048] In view of this, the present disclosure proposes a silicon-carbon negative electrode material, which includes a carbon skeleton with a pore structure and a silicon-based material arranged in the pore structure. In the area from the surface of the above-mentioned silicon-carbon negative electrode material to the area extending 10 nm inward from the surface, the content of the high-valent silicon is less than 25% relative to the total amount of low-valent silicon and high-valent silicon. The low-valent silicon is silicon with a valence of 0 to 2, and the high-valent silicon is silicon with a valence of 3 to 4.

[0049] The content of high-valent silicon in the silicon-carbon negative electrode material disclosed herein is suppressed to a low level, so that the content of low-valent silicon is greater than or equal to 75%, thereby improving the lithium removal capacity and first coulombic efficiency of the negative electrode material. Moreover, the low content of high-valent silicon reduces the formation of lithium silicates and significantly reduces lithium loss, thereby effectively improving the discharge capacity and first coulombic efficiency of the secondary battery.

[0050] In the present disclosure, the above-mentioned high-valent silicon and low-valent silicon can be quantified by XPS. In the XPS graph, the binding energy of low-valent silicon is 98-102 eV, corresponding to valence states of 0, 1, and 2. The area (S1) enclosed by the curve and the baseline is the atomic molar amount of low-valent silicon. The binding energy of high-valent silicon is 102 eV-106 eV, corresponding to valence states of 3 and 4. The area (S2) enclosed by the curve and the baseline is the atomic molar amount of high-valent silicon. Relative to the total amount of low-valent silicon and high-valent silicon, the content of high-valent silicon = S2 / (S1+S2)×100%, and the content of low-valent silicon = S1 / (S1+S2)×100%. The baseline is the line connecting two points on the test curve, where X=98 eV and X=106 eV.

[0051] In some embodiments, the content of high-valent silicon (denoted as C 10) is: 24%, 23%, 22%, 21%, 20%, 19%, 18%, 17%, 16%, 15%, 14%, 13%, 12%, 11%, 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, etc. or a range between any two values, but is not limited thereto. In some embodiments, in the area from the surface of the silicon-carbon negative electrode material to the area extending 10 nm from the surface to the inside, it is preferred that C 10 Less than or equal to 20%, preferably C 10 Less than or equal to 10%. The smaller the content of high-valent silicon in the area extending 10nm from the surface of the silicon-carbon negative electrode material to the inside, the higher the content of low-valent silicon, and the higher the lithium removal capacity of the silicon-carbon negative electrode material. In addition, the low content of high-valent silicon reduces the formation of lithium silicates, greatly improving the discharge capacity and first coulombic efficiency of the secondary battery.

[0052] In some embodiments, the content of high-valent silicon (denoted as C 20 ) is less than or equal to 20%. For example, the content of high-valent silicon is: 20%, 19%, 18%, 17%, 16%, 15%, 14%, 13%, 12%, 11%, 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, etc. or a value between any two values, but not limited thereto. In some embodiments, in the area from 10 nm to 20 nm from the surface of the silicon-carbon negative electrode material, preferably C 20 Less than 10%.

[0053] In some embodiments, in the region from 20 nm to 30 nm from the surface of the silicon-carbon negative electrode material, the content of high-valent silicon (denoted as C 30 ) is less than or equal to 10%. For example, the content of high-valent silicon (C 30 ) can be 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, or a range between any two values, but is not limited thereto. Preferably, in the region from 20 nm to 30 nm from the surface of the silicon-carbon negative electrode material, C 30 Less than or equal to 5%.

[0054] Regarding the above C 10 、C 20 、C 30 For the specific determination method, see the description in the Examples section.

[0055] In some embodiments, the silicon-carbon negative electrode material satisfies at least one of the following conditions: (1) the volume distribution particle size Dv50 of the silicon-carbon negative electrode material is 5 μm-10 μm, for example, it can be 5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, preferably 6 μm-9 μm; (2) the specific surface area of ​​the silicon-carbon negative electrode material is less than or equal to 5 m 2 / g, for example, 5m 2 / g、4m 2 / g、3m 2 / g, 2m 2 / g, 1.5m 2 / g、1m 2 / g, etc., preferably less than or equal to 2m 2 / g; (3) the powder compaction density of the silicon-carbon negative electrode material under a pressure of 3000N is 0.8g / cm 3 -1.2g / cm 3 , for example, it can be 0.8 g / cm 3 , 0.9g / cm 3 , 0.95g / cm 3 , 1.0g / cm 3 , 1.1g / cm 3 , 1.15g / cm 3 , 1.2g / cm 3 , preferably 0.9 g / cm 3 -1.2g / cm 3 ;(4) The tap density of the silicon-carbon negative electrode material is 0.9g / cm 3 -1.1g / cm 3 , for example, it can be 0.9 g / cm 3 , 0.95g / cm 3 , 1.0g / cm 3 , 1.05g / cm 3 , 1.1g / cm 3 , preferably 1.0 g / cm 3 -1.1g / cm 3(5) The lithium-free gram capacity of the silicon-carbon negative electrode material is 800mAh / g-2500mAh / g, for example, it can be 800mAh / g, 900mAh / g, 1000mAh / g, 1100mAh / g, 1200mAh / g, 1300mAh / g, 1400mAh / g, 1500mAh / g, 1600mAh / g, 1700mAh / g, 1800mAh / g, 1900mAh / g, 2000mAh / g, 2100mAh / g, etc., preferably 1000mAh / g-2000mAh / g. By making the particle size, compaction density and tap density of the silicon-carbon negative electrode material within the above range, the compaction density of the pole piece can be effectively improved, and the energy density of the battery cell can be improved. In addition, by making the specific surface area within 5m 2 / g or less, which can minimize the contact area between the particles and the electrolyte and improve the initial coulombic efficiency, cycle and storage performance.

[0056] In this disclosure, the volume distribution particle size Dv50 of a material is generally known in the art and represents the particle size corresponding to 50% of the cumulative volume distribution percentage of the material. It can be measured using instruments and methods known in the art. For example, it can be measured using a laser particle size analyzer in accordance with GB / T 19077-2016. The testing instrument can be a Mastersizer 3000 laser particle size analyzer manufactured by Malvern Instruments Ltd. in the United Kingdom.

[0057] In this disclosure, the specific surface area of ​​a material is a term generally known in the art and can be measured using instruments and methods known in the art. For example, it can be measured using the nitrogen adsorption specific surface area analysis method in accordance with GB / T 19587-2017 and calculated using the BET (Brunauer Emmett Teller) method. The testing instrument can be a Tri-Star 3020 Specific Surface Area Pore Size Analyzer from Micromeritics, Inc., USA.

[0058] In the present disclosure, the powder compaction density of a material has a meaning well known in the art and can be measured using instruments and methods known in the art. For example, it can be measured using an electronic pressure testing machine (for example, a UTM7305 electronic pressure testing machine) with reference to GB / T 24533-2009. An exemplary test method is as follows: 1 g of sample powder is weighed, added to a mold with a bottom area of ​​1.327 cm2, pressurized to 300 kg, maintained for 30 seconds, then released, maintained for 10 seconds, and then recorded and calculated to obtain the powder compaction density of the material under a pressure of 3000 N.

[0059] In this disclosure, the tap density of a material is a term generally known in the art and can be measured using instruments and methods known in the art. For example, the tap density of a material can be measured using a powder tap density tester in accordance with GB / T 5162-2006. The test instrument can be a Dandong Baxter BT-301, with the following test parameters: a vibration frequency of 250 ± 15 times / minute, an amplitude of 3 ± 0.2 mm, a vibration count of 5000, and a 25 mL graduated cylinder.

[0060] In this disclosure, the lithium removal gram capacity of a material is a well-known term in the art and can be tested using methods known in the art. Specific testing methods can be found in the examples.

[0061] In some embodiments, the pore volume of the carbon skeleton is 0.4 cm 3 / g-1.5cm 3 / g, optional 0.6cm 3 / g-1.2cm 3 / g, and / or, relative to the pore volume, the volume of micropores with a pore diameter of less than 2 nm accounts for greater than or equal to 60%, optionally greater than or equal to 80%. Thus, the silicon-based material is primarily deposited within the micropores. The higher the micropore ratio, the more silicon-based material is deposited, and the corresponding delithiation capacity is higher. In some embodiments, the silicon-based material may be amorphous hard carbon.

[0062] In some embodiments, the surface of the silicon-carbon negative electrode material has a coating layer; optionally, the coating layer is a carbon coating layer. By providing a uniform and dense coating layer, the present disclosure further prevents oxygen from the air from entering the negative electrode material, significantly reducing the risk of silicon in the silicon-carbon negative electrode material being oxidized to form high-valent silicon, and reducing the content of high-valent silicon in the silicon-carbon negative electrode material.

[0063] In addition, the present disclosure provides a method for preparing the above-mentioned silicon-carbon negative electrode material, which includes a silicon-carbon particle forming step (step (a)), in which a carbon skeleton with a pore structure reacts with a silicon source gas to form silicon-carbon particles with a silicon-based material in the pore structure; and a silicon-carbon particle processing step (step (b)), in which a mixed gas including a carbon source gas and an inert gas is introduced into the silicon-carbon particles at a ventilation volume greater than 0 L / min and less than or equal to 10 L / min under the conditions of a temperature of 500°C-700°C and a pressure of 0 kpa-1 kpa, wherein the carbon source gas is selected from at least one of ethane, ethylene, acetylene, and methane.

[0064] Therefore, by adopting specific temperature, pressure, ventilation volume and mixed gas, the decomposition rate of the carbon source gas can be effectively controlled, which is conducive to forming a uniform and dense coating layer on the surface of the silicon-carbon particles. As a result, the risk of silicon in the silicon-carbon particles being oxidized by oxygen in the air to form high-valent silicon can be effectively reduced, and the content of high-valent silicon in the particles can be reduced, so that C10 、C 20 and C 30 By selecting the above carbon source gas, the coating can be uniform and complete.

[0065] In some embodiments, in step (b), the temperature may be, for example, 500°C, 550°C, 600°C, 650°C, 700°C, or a range consisting of any two of these values. The pressure may be, for example, 0 kPa, 50 Pa, 100 Pa, 150 Pa, 200 Pa, 250 Pa, 300 Pa, 350 Pa, 400 Pa, 450 Pa, 500 Pa, 550 Pa, 600 Pa, 650 Pa, 700 Pa, 750 kPa, 800 Pa, 850 Pa, 900 Pa, 950 Pa, 1000 Pa (1 kPa), or a range consisting of any two of these values. By controlling the temperature and pressure within the above ranges, the decomposition rate of the carbon source gas can be effectively controlled, which facilitates the formation of a uniform and dense coating layer.

[0066] In some embodiments, in step (b), the ventilation rate can be, for example, 0.5 L / min, 1.0 L / min, 1.5 L / min, 2.0 L / min, 2.5 L / min, 3.0 L / min, 3.5 L / min, 4.0 L / min, 4.5 L / min, 5.0 L / min, 5.5 L / min, 6.0 L / min, 6.5 L / min, 7.0 L / min, 7.5 L / min, 8.0 L / min, 8.5 L / min, 9.0 L / min, 9.5 L / min, 10.0 L / min, or a value within a range consisting of any two of these values. By controlling the ventilation rate within the above range, the carbon source gas can be fully reacted, the utilization rate of the carbon source gas can be improved, and a uniform and dense coating layer can be formed.

[0067] In some embodiments, in step (b), preferably, the mixed gas is introduced at a temperature of 550°C to 650°C and a pressure of 0kPa to 500Pa at a flow rate of 0.5L / min to 4L / min. Under the above conditions, a denser coating layer can be formed, further reducing the possibility of oxygen in the air entering the particles to oxidize silicon, and further reducing C 10 、C 20 and C 30 .

[0068] In some embodiments, the gas mixture preferably comprises 10%-70% acetylene, 0%-20% methane, and 10%-90% inert gas. More preferably, the gas mixture comprises 15%-60% acetylene, 5%-10% methane, and 30%-80% inert gas. Acetylene decomposes rapidly at a low temperature. Adding a certain amount of methane can control the decomposition rate of acetylene, allowing carbon to slowly coat the particle surface, resulting in a dense coating.

[0069] Inert gases are gases that do not react with silicon materials. Examples include, but are not limited to, helium, neon, argon, krypton, xenon, and radon. Using an inert gas as a shielding gas can reduce the formation of Si3N4.

[0070] In some embodiments, the above step (a) may include the following steps (a1) to (a3).

[0071] Step (a1): In a reaction device, a carbon skeleton having a porous structure is heated to 400° C. to 550° C. to remove oxygen from the carbon skeleton.

[0072] The above-mentioned reaction device is not particularly limited, and commonly used devices in the field can be used, for example, it can be: medium frequency furnace, roller kiln, rotary kiln, pusher kiln, vertical granulation kettle, horizontal granulation kettle, vertical reactor, horizontal reactor or drum furnace and other equipment.

[0073] In the step (a1), the carbon skeleton is heated to 400°C-550°C, for example, it can be heated to: 400°C, 410°C, 420°C, 430°C, 440°C, 450°C, 460°C, 470°C, 480°C, 490°C, 500°C, 510°C, 520°C, 530°C, 540°C, 550°C or a value between any two values, but not limited thereto. Preferably, the carbon skeleton is heated to 450°C-550°C. By heating the carbon skeleton to the above range, the oxygen adsorbed by the carbon skeleton itself can be eliminated, which can greatly reduce the risk of silicon deposited in the negative electrode material being oxidized by the oxygen adsorbed by the carbon skeleton itself to form high-valent silicon, so that the content of low-valent silicon in the silicon-carbon negative electrode material is maintained at a high level, which helps to reduce the content of high-valent silicon, so that C 10 、C 20 、C 30 Within the above range, a silicon-carbon negative electrode material with high delithiation capacity is obtained.

[0074] Step (a2): The reaction apparatus is evacuated and then an inert gas is introduced.

[0075] Through this step, the oxygen in the reaction device can be removed, which can greatly reduce the risk of silicon deposited in the negative electrode material being oxidized by the oxygen in the reaction device to form high-valent silicon, and help maintain the content of low-valent silicon in the silicon-carbon negative electrode material at a high level, and help reduce the content of high-valent silicon, so that C 10 、C 20 、C 30 Within the above range.

[0076] In some embodiments, the vacuum degree in the reaction device is 1×10 -3 Pa~1×10 -6 Pa, for example, can be 1×10 -5 The smaller the pressure value in the reaction device, the less residual oxygen in the reaction device, and the lower the content of high-valent silicon in the prepared silicon-carbon negative electrode material.

[0077] In some embodiments, in step (a2), after the pressure in the reaction device reaches the aforementioned pressure value and is maintained for the aforementioned time, an inert gas is introduced into the reaction device to further reduce the residual amount of oxygen in the reaction device.

[0078] In some embodiments, the above step (a2) (vacuuming, maintaining pressure, and introducing inert gas) can be repeated in a cycle. The number of times this step can be performed includes but is not limited to: 1, 2, and 3.

[0079] In some embodiments, in step (a2), the oxygen content in the tail gas discharged from the reaction device can be detected at a set frequency. When the tail gas oxygen content is less than 200 ppm, step (a2) is terminated. For example, step (a2) can be terminated when the tail gas oxygen content is 0 ppm, 20 ppm, 40 ppm, 60 ppm, 80 ppm, 100 ppm, 120 ppm, 140 ppm, 160 ppm, 180 ppm, 190 ppm, or a range consisting of any two of these values.

[0080] The order of steps (a1) and (a2) is not particularly limited. Step (a1) can be performed first and then step (a2), or step (a2) can be performed first and then step (a1). These two steps can eliminate oxygen contained in the raw materials and the reaction apparatus to the greatest extent possible.

[0081] Step (a3): introducing a mixture of silicon source gas and inert gas into the reaction device, and depositing at a temperature of 400° C. to 550° C. for 2 to 10 hours to form silicon-carbon particles.

[0082] The silicon source gas includes a gas that can provide silicon atoms. For example, it can be one or more of monosilane, disilane, dichlorosilane, and trichlorosilane. Optionally, the silicon source gas is monosilane. The inert gas used in this step is defined the same as the inert gas in step (b) above, and argon is preferably used.

[0083] In some embodiments, a rotary kiln is used as the reaction apparatus. A mixture of monosilane and argon is introduced into the rotary kiln at a flow rate of 0.1 L / min to 4 L / min. The reaction is carried out under a slight positive pressure of 0-0.5 kPa and a rotation frequency of 0 Hz to 80 Hz. The rotation frequency of the reaction apparatus can be 0 Hz, 5 Hz, 10 Hz, 20 Hz, 30 Hz, 40 Hz, 50 Hz, 60 Hz, 70 Hz, 80 Hz, or a range consisting of any two of these values. By setting the rotation frequency within the above range, the powder can be fully rotated in the kiln, enhancing contact between the powder and the gas and ensuring a full reaction.

[0084] This step (a3) ​​is performed after the above-mentioned steps (a1) and (a2). Since the oxygen contained in the reaction materials and the reaction device has been excluded through the above-mentioned steps (a1) and (a2), the risk of oxidation of the silicon deposited in step (a3) ​​can be greatly reduced.

[0085] In addition, the present disclosure provides a negative electrode plate, which includes a negative electrode current collector and a negative electrode film layer arranged on at least one surface of the negative electrode current collector, wherein the negative electrode film layer includes a negative electrode active material, and the negative electrode active material includes the silicon-carbon negative electrode material disclosed in the present disclosure or the silicon-carbon negative electrode material prepared according to the preparation method disclosed in the present disclosure.

[0086] 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.

[0087] 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.).

[0088] 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).

[0089] 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.

[0090] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0091] 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.

[0092] In addition, the secondary battery and the electric device of the present disclosure will be described below with reference to the drawings as appropriate.

[0093] In one embodiment of the present disclosure, a secondary battery is provided.

[0094] The term "secondary battery" mentioned herein refers to a battery cell, a battery module, or a battery pack. Each of these is described below.

[0095] 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.

[0096] [Positive electrode]

[0097] 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 the positive electrode active material according to the first aspect of the present disclosure.

[0098] 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.

[0099] 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.).

[0100] 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 0.15 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.

[0101] 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.

[0102] 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.

[0103] 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.

[0104] [Electrolytes]

[0105] 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.

[0106] In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.

[0107] 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.

[0108] 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.

[0109] In some embodiments, the electrolyte may optionally 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.

[0110] [Isolation film]

[0111] The present disclosure has no particular limitation on the type of isolation membrane, and any known isolation membrane with a porous structure having good chemical stability and mechanical stability can be selected.

[0112] 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.

[0113] 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.

[0114] In some embodiments, the battery cell may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0115] 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.

[0116] 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.

[0117] 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.

[0118] 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.

[0119] 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.

[0120] 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.

[0121] 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.

[0122] 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.

[0123] In addition, the present disclosure further provides an electrical device, the electrical device including the secondary battery provided in the present disclosure. 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 (such as mobile phones, laptops, etc.), electric vehicles (such as 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.

[0124] As the electrical device, a battery cell, a battery module or a battery pack can be selected according to its usage requirements.

[0125] 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.

[0126] 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.

[0127] Example

[0128] 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.

[0129] Example 1

[0130] Preparation of silicon-carbon anode materials

[0131] Step (a1): 500 g of porous carbon was weighed and placed in a rotary kiln. The kiln was heated to 500° C. (T1) under argon protection and kept at this temperature for 2 h to desorb the air adsorbed in the porous carbon.

[0132] Step (a2): Evacuate the rotary kiln to a vacuum degree of 1×10 -5 Pa, maintain the pressure for 5 minutes, then introduce argon. Repeat the steps of evacuating and introducing argon until the oxygen content in the tail gas is less than 200 ppm.

[0133] Step (a3): a mixed gas of monosilane and argon (the volume ratio of monosilane to argon is 1:4) is introduced into the rotary kiln at a ventilation rate of 4 L / min, a slightly positive pressure of 200 Pa is maintained, and the rotary kiln is rotated at a rotation frequency of 40 Hz to obtain silicon-carbon particles.

[0134] Step (b): The temperature of the rotary kiln is raised to 500°C (T2), a mixed gas of acetylene, methane and argon is introduced at a pressure (P) of 0.2 kPa and a ventilation volume (V) of 3 L / min, and the rotary kiln is rotated at a rotation frequency of 40 Hz to coat the above-mentioned silicon-carbon particles.

[0135] Then, after natural cooling, the product was passed through a 200-mesh sieve to obtain the silicon-carbon negative electrode material.

[0136] The content of high-valent silicon in silicon-carbon negative electrode materials C10 、C 20 、C 30 Determination of.

[0137] (1) Using X-rays as an excitation source to act on the surface of the silicon-carbon negative electrode material, the area from the surface to a depth of 10 nm was detected to obtain the XPS graph shown in Figure 7. The area S1 enclosed by the curve corresponding to the binding energy of 98-102 eV and the baseline is the amount of low-valent silicon, and the area S2 enclosed by the curve corresponding to the binding energy of 102 eV-106 eV and the baseline is the amount of high-valent silicon. The content C of high-valent silicon was calculated based on S2 / (S1+S2). 10 It is 17.5%.

[0138] (2) The surface of the silicon-carbon negative electrode material (1) is etched using an argon ion gun at an etching rate of about 4 nm / min. By adjusting the etching time to 2.5 min, the analysis area (i.e., the area from the surface to a depth of 10 nm) of the above (1) is etched away. Then, X-rays are used as an excitation source to act on the new surface of the silicon-carbon negative electrode material after the above etching, and the distribution information of photoelectron information is obtained at a depth of 10 nm. The silicon valence information in the area from 10 nm to 20 nm from the surface is obtained in the same manner as in (1) above. 20 It is 9.6%.

[0139] (3) The surface of the silicon-carbon negative electrode material in (2) is further etched using an argon ion gun at an etching rate of about 4 nm / min. The etching time is adjusted to 2.5 min. The analysis area in (2) is etched away, and then X-rays are used as an excitation source to act on the new surface of the etched silicon-carbon negative electrode material. The distribution information of photoelectron information is obtained at a depth of 10 nm. The silicon valence information in the area from 20 nm to 30 nm from the surface is obtained in the same manner as in (1). 30 It is 4.2%.

[0140] Preparation of secondary batteries

[0141] (a) Preparation of negative electrode sheet

[0142] The silicon-carbon composite material, conductive carbon black, thickener sodium carboxymethyl cellulose (CMC), and binder styrene-butadiene rubber latex (SBR) obtained above are fully stirred and mixed in an appropriate amount of deionized water in a weight ratio of 96.5:1.0:1.0:1.5 to form a uniform negative electrode slurry; the negative electrode slurry is coated on the negative electrode collector, and after drying and other processes, a negative electrode sheet is obtained.

[0143] (b) Preparation of positive electrode sheet

[0144] Aluminum foil with a thickness of 8 μm was used as the positive electrode current collector. 0.8 Co 0.1 Mn 0.1 O2 (NCM811), conductive agent acetylene black, and binder polyvinylidene fluoride (PVDF) are dissolved in solvent N-methylpyrrolidone (NMP) in a weight ratio of 93:2:5, and the mixture is fully stirred and mixed to obtain a positive electrode slurry; the positive electrode slurry is then evenly coated on the positive electrode collector, and then dried, cold pressed, and cut to obtain a positive electrode sheet.

[0145] (c) Preparation of electrolyte

[0146] The electrolyte is a mixture of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC), with the volume ratio of EC, EMC, and DEC being 20:20:60. LiPF6 is then dissolved in the aforementioned organic solvent, and fluoroethylene carbonate (FEC) is added as an additive. The concentration of LiPF6 is 1 mol / L, and the weight ratio of FEC in the electrolyte is 5%.

[0147] (d) Preparation of batteries

[0148] The positive electrode sheet, separator, and negative electrode sheet were stacked in order, with the separator positioned between the positive and negative electrode sheets to provide isolation. The cells were then wound to form a bare cell. The tabs were welded to the bare cell and placed in an aluminum casing. The cells were then baked at 80°C to remove moisture. The electrolyte was then injected and sealed to produce an uncharged battery. The uncharged battery then underwent a series of steps, including resting, hot and cold pressing, formation, shaping, and capacity testing, to obtain the lithium-ion secondary battery of Example 1.

[0149] Examples 2-5 and Comparative Examples 1-2

[0150] The temperature (T2) in step (b) was changed as shown in Table 1 below. Otherwise, the silicon-carbon negative electrode material was prepared in the same manner as in Example 1. The C 10 、C 20 、C 30 , and then made into a secondary battery.

[0151] For the silicon-carbon negative electrode material of Comparative Example 1, X-rays were used as the excitation source to act on the surface of the silicon-carbon negative electrode material, and the area from the surface to a depth of 10 nm was detected to obtain the XPS graph shown in Figure 8. The calculation was performed in the same way as in Example 1, and the content of high-valent silicon C 10 It is 30.3%.

[0152] The following performance tests were performed on the above embodiments and comparative examples.

[0153] Performance Testing

[0154] (1) Lithium removal capacity and first coulombic efficiency of silicon-carbon anode materials

[0155] a. Preparation of a button cell: The aforementioned silicon-carbon anode material, conductive carbon black, and binder polyacrylic acid were mixed in a mass ratio of 8:1:1. Deionized water was added as a solvent and stirred in a high-speed blender until the mixture was homogeneous, yielding a 45% solids anode slurry. The anode slurry was evenly coated onto a copper foil anode current collector, dried at 85°C, and cold-pressed to produce an electrode sheet. A button cell was assembled using metallic lithium as the counter electrode, a Celgard 2400 separator, and an electrolyte. The electrolyte was a mixture of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC), with a volume ratio of EC, EMC, and DEC of 20:20:60. LiPF6 was then dissolved in the aforementioned organic solvent, and fluoroethylene carbonate (FEC) was added as an additive. The LiPF6 concentration was 1 mol / L, and the mass fraction of FEC in the electrolyte was 5%.

[0156] b. Button cell test process: After the assembled button cell is allowed to rest for 60 minutes, it is tested using a constant current discharge process of 0.05C to 5mV, 50μA discharge to 5mV, rest for 10 minutes, and 0.1C charge to 2.0V. The lithium insertion capacity of the silicon-carbon negative electrode material is the gram capacity (C1) when discharged to 5mV, the lithium removal capacity (C2) when charged to 2.0V, and the first coulombic efficiency (C2 / C1) of the silicon-carbon negative electrode material is measured.

[0157] (2) Discharge capacity and initial coulombic efficiency of secondary batteries

[0158] The secondary batteries obtained by the above embodiments and comparative examples were kept at a constant temperature of 25°C for 60 minutes, and then charged to 4.25V at a constant current of 0.1C, and then charged to 0.05C at a constant voltage of 4.25V. The charged capacity in grams at this time was recorded as Q1. After standing for 10 minutes, the batteries were discharged to 2.5V at a constant current of 0.1C, and then discharged to 0.05C at a constant voltage of 2.5V. The discharged capacity in grams at this time was recorded as Q2. The first coulombic efficiency of the secondary battery was Q2 / Q1.

[0159] Table 1

[0160] Note: The volume ratio of the mixed gas in Table 1 is: the volume ratio of acetylene, methane and argon

[0161] From the results in Table 1, it can be seen that in step (b), by making the temperature, pressure, ventilation volume and mixed gas of the rotary kiln meet specific conditions, C 10Less than 25% of silicon-carbon negative electrode material. Examples 1-5 show that by controlling the temperature of the rotary kiln at 500℃-700℃, the content of high-valent silicon in the obtained silicon-carbon negative electrode material is low, and C 10 The delithiation gram capacity and the first coulomb efficiency of the silicon-carbon negative electrode material are high, and the discharge gram capacity and the first coulomb efficiency of the obtained secondary battery are high. In particular, when the temperature of the rotary kiln is controlled at 550℃-650℃, the C 10 further reduced to less than 20%, and C 20 and C 30 It is also further reduced, and the performance of the secondary battery is better.

[0162] Compared with Examples 1 to 5, in Comparative Examples 1 and 2, the temperature in the rotary kiln was too low (200°C) or too high (1000°C), and the C 10 If the ratio is greater than 30%, the technical effect of the present disclosure cannot be achieved.

[0163] Examples 6-8 and Comparative Example 3

[0164] The pressure (P) in step (b) was changed as shown in Table 2 below. Otherwise, the silicon-carbon negative electrode material was prepared in the same manner as in Example 3. The C 10 、C 20 、C 30 , and then made into a secondary battery.

[0165] The performance evaluation was carried out in the same manner as in Example 3, as shown in Table 2.

[0166] Table 2

[0167] From the results in Table 2, it can be seen that by controlling the pressure of the rotary kiln in the range of 0kPa-1kPa in step (b), the content of high-valent silicon in the obtained silicon-carbon negative electrode material is low, and C 10 In particular, when the pressure of the rotary kiln is controlled within the range of 0kPa-0.5kPa, the C of the silicon-carbon negative electrode material obtained is 10 Further reduction, below 20%, and C 20 and C 30 The silicon-carbon negative electrode material has high lithium removal capacity and first coulombic efficiency, and the resulting secondary battery has high discharge capacity and first coulombic efficiency.

[0168] In Comparative Example 3, the pressure in the rotary kiln was too high (5 kPa), and the C 10 If it is greater than 25%, the technical effect of the present disclosure cannot be achieved.

[0169] Examples 9-11 and Comparative Examples 4 and 5

[0170] The silicon-carbon negative electrode material was prepared in the same manner as in Example 3 except that the ventilation volume (V) in step (b) was changed as shown in Table 3 below. The C 10 、C 20 、C 30 , and then made into a secondary battery.

[0171] The performance evaluation was carried out in the same manner as in Example 3, as shown in Table 3.

[0172] Table 3

[0173] From the results in Table 3, it can be seen that by controlling the ventilation volume (V) of the rotary kiln in the range of greater than 0 L / min and less than or equal to 10 L / min in step (b), the content of high-valent silicon in the obtained silicon-carbon negative electrode material is low, and C 10 In Comparative Examples 4 and 5, the ventilation volume was too high or no mixed gas was introduced, and the technical effect of the present disclosure could not be achieved.

[0174] Examples 12-15 and Comparative Example 6

[0175] The composition of the mixed gas in step (b) was changed as shown in Table 4 below. Otherwise, the silicon-carbon negative electrode material was prepared in the same manner as in Example 3. The C 10 、C 20 、C 30 , and then made into a secondary battery.

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

[0177] Table 4

[0178] From the results in Table 4, it can be seen that in step (b), by selecting the carbon source gas from at least one of ethane, ethylene, acetylene, and methane, the content of high-valent silicon in the obtained silicon-carbon negative electrode material is low, and C 10 In Comparative Example 6, a mixed gas of propane, methane, and argon was used. However, due to the high decomposition temperature of propane, the coating uniformity and integrity were poor, resulting in an excessively high content of high-valent silicon and the inability to achieve the technical effects of the present disclosure.

[0179] 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. Industrial Applicability

[0180] The present disclosure provides a silicon-carbon negative electrode material and a preparation method thereof. The silicon-carbon negative electrode material includes a carbon skeleton having a pore structure and a silicon-based material arranged in the pore structure. In the area from the surface of the silicon-carbon negative electrode material to the area extending 10nm inward from the surface, the content of the high-valent silicon is less than 25% relative to the total amount of low-valent silicon and high-valent silicon, wherein the low-valent silicon is silicon with a valence of 0 to 2, and the high-valent silicon is silicon with a valence of 3 to 4. As a result, the lithium removal gram capacity and the first coulomb efficiency of the silicon-carbon negative electrode material can be improved, and the discharge gram capacity and the first coulomb efficiency of the secondary battery can be improved.

Claims

1. A silicon-carbon negative electrode material, comprising a carbon skeleton having a porous structure and a silicon-based material disposed in the porous structure, wherein within a region extending from a surface of the silicon-carbon negative electrode material to a region extending 10 nm inward from the surface, the content of the high-valent silicon is less than 25% relative to the total amount of low-valent silicon and high-valent silicon, wherein: The low-valent silicon is silicon with a valence of 0 to 2, and the high-valent silicon is silicon with a valence of 3 to 4.

2. The silicon-carbon negative electrode material according to claim 1, wherein In a region extending from the surface of the silicon-carbon negative electrode material to 10 nm inward from the surface, the content of the high-valent silicon is less than or equal to 20% relative to the total amount of low-valent silicon and high-valent silicon.

3. The silicon-carbon negative electrode material according to claim 1 or 2, wherein: In the area from 10 nm to 20 nm from the surface of the silicon-carbon negative electrode material, the content of the high-valent silicon is less than or equal to 20% relative to the total amount of low-valent silicon and high-valent silicon, optionally, less than or equal to 10%.

4. The silicon-carbon negative electrode material according to any one of claims 1 to 3, wherein In the area from 20 nm to 30 nm from the surface of the silicon-carbon negative electrode material, the content of the high-valent silicon is less than or equal to 10% relative to the total amount of low-valent silicon and high-valent silicon, optionally, less than or equal to 5%.

5. The silicon-carbon negative electrode material according to any one of claims 1 to 4, wherein The silicon-carbon negative electrode material satisfies at least one of the following conditions: (1) The volume distribution particle size Dv50 of the silicon-carbon negative electrode material is 5 μm-10 μm, and Dv50 can be optionally 6 μm-9 μm; (2) The specific surface area of the silicon-carbon negative electrode material is less than or equal to 5m 2 / g, can be less than or equal to 2m 2 / g; (3) The powder compaction density of the silicon-carbon negative electrode material under a pressure of 3000N is 0.8g / cm 3 -1.2g / cm 3 , optional 0.9g / cm 3 -1.2g / cm 3 ; (4) The tap density of the silicon-carbon negative electrode material is 0.9 g / cm 3 -1.1g / cm 3 , optional 1.0g / cm 3 -1.1g / cm 3 ; (5) The lithium-free capacity of the silicon-carbon negative electrode material is 800mAh / g-2500mAh / g, and can be optionally 1000mAh / g-2000mAh / g.

6. The silicon-carbon negative electrode material according to any one of claims 1 to 5, wherein The pore volume of the carbon skeleton is 0.4 cm 3 / g-1.5cm 3 / g, optional 0.6cm 3 / g-1.2cm 3 / g; and / or, Relative to the pore volume, the volume proportion of micropores with a pore diameter less than 2 nm is greater than or equal to 60%, and can be optionally greater than or equal to 80%.

7. The silicon-carbon negative electrode material according to any one of claims 1 to 6, wherein The surface of the silicon-carbon negative electrode material has a coating layer; optionally, the coating layer is a carbon coating layer.

8. A method for preparing the silicon-carbon negative electrode material according to any one of claims 1 to 7, wherein: The steps include: a silicon-carbon particle forming step of reacting a carbon skeleton having a pore structure with a silicon source gas to form silicon-carbon particles having a silicon-based material in the pore structure; and The silicon carbon particle processing step is to process the silicon carbon particles at a temperature of 500°C-700°C and a pressure of 0kPa-1kPa at a flow rate greater than 0L / min and less than or equal to 10L / min. A mixed gas including a carbon source gas and an inert gas is introduced into the silicon-carbon particles at a ventilation rate of , wherein the carbon source gas is selected from at least one of ethane, ethylene, acetylene, and methane.

9. The preparation method according to claim 8, wherein In the silicon-carbon particle treatment step, the mixed gas is introduced into the silicon-carbon particles at a flow rate of 0.5 L / min to 4 L / min under the conditions of a temperature of 550° C. to 650° C. and a pressure of 0 kPa to 0.5 kPa.

10. The preparation method according to claim 8 or 9, wherein The mixed gas comprises 10% to 70% by volume of acetylene, 0% to 20% by volume of methane, and 10% to 90% by volume of an inert gas; Optionally, the mixed gas includes 15% to 60% by volume of acetylene, 5% to 10% by volume of methane, and 30% to 80% by volume of inert gas.

11. The preparation method according to any one of claims 8 to 10, wherein The step of forming silicon-carbon particles includes the following steps: The reaction apparatus was evacuated and then filled with inert gas.

12. The preparation method according to any one of claims 8 to 11, wherein The step of forming silicon-carbon particles includes the following steps: In a reaction device, a carbon skeleton with a porous structure is heated to 400° C.-550° C. to remove oxygen from the carbon skeleton.

13. The preparation method according to any one of claims 8 to 12, wherein The step of forming silicon-carbon particles includes the following steps: A mixed gas of silicon source gas and inert gas is introduced into the reaction device, and deposition is carried out at a temperature of 400° C. to 550° C. for 2 to 10 hours to form silicon-carbon particles.

14. The preparation method according to any one of claims 8 to 13, wherein The silicon source gas is selected from one or more of monosilane, disilane, dichlorosilane, and trichlorosilane. Optionally, the silicon source gas is monosilane.

15. The preparation method according to any one of claims 8 to 14, wherein The inert gas is argon.

16. A negative electrode plate, comprising the silicon-carbon negative electrode material according to any one of claims 1 to 7 or the silicon-carbon negative electrode material prepared by the preparation method according to any one of claims 8 to 15.

17. A secondary battery comprising the negative electrode sheet according to claim 16.

18. An electric device comprising the secondary battery according to claim 17.

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