Silicon-carbon negative electrode material and preparation method therefor, secondary battery, and electrical device

Abstract

Provided is a silicon-carbon negative electrode material, comprising a porous carbon matrix and a silicon-based material present in pores of the porous carbon matrix, wherein the volume Vsilicon of the silicon-based material in the silicon-carbon negative electrode material per unit mass is 0.155 cm3 / g-0.175 cm3 / g, the interior of the silicon-carbon negative electrode material comprises closed holes, and the volume PVclosed of the closed holes in the silicon-carbon negative electrode material per unit mass is greater than or equal to 0.250 cm3 / g.

Description

Silicon-carbon negative electrode material and preparation method thereof, secondary battery and electric device

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This disclosure is based on Chinese patent application number 202410130127.9, application date January 30, 2024, and invention name “Silicon-carbon negative electrode 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 technical field of lithium batteries, and in particular to a silicon-carbon negative electrode material and a preparation method thereof, a secondary battery, and an electrical device. Background Art

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

[0005] Improving the specific capacity of electrode materials is one way to improve the performance of lithium-ion batteries. Silicon-based anode materials have attracted considerable attention due to their high specific capacity. However, existing silicon-based anode materials suffer from high volume expansion during charge and discharge, as well as low initial coulombic efficiency. This significantly limits their widespread use in lithium-ion batteries.

[0006] Summary of the Invention

[0007] The present disclosure addresses the aforementioned challenges and aims to provide a silicon-carbon anode material and its preparation method. This anode material exhibits a small specific surface area and low volume expansion rate, thereby improving the initial coulombic efficiency of the material while also exhibiting excellent cycling performance. The present disclosure also aims to provide a secondary battery and an electrical device comprising this anode material.

[0008] In order to achieve the above-mentioned object, the present disclosure provides a silicon-carbon negative electrode material in the first aspect, comprising a porous carbon matrix and a silicon-based material present in the pores of the porous carbon matrix; wherein the volume V of the silicon-based material per unit mass of the silicon-carbon negative electrode material is 硅 0.155cm 3 / g~0.175cm 3 / g, the silicon-carbon negative electrode material includes closed pores, and the volume PV of the closed pores per unit mass of the silicon-carbon negative electrode material is 闭 Greater than or equal to 0.250cm3 / g. As a result, the silicon-carbon anode material, while containing a certain volume of silicon-based material, also has an appropriate amount of closed-pore expansion space reserved for the expansion of the silicon-based material. As a result, the anode material has a small specific surface area and a low volume expansion rate, thereby improving the material's initial coulombic efficiency while also providing excellent cycling performance.

[0009] In some embodiments, the volume V of the silicon-based material per unit mass of the silicon-carbon negative electrode material is 硅 0.159cm 3 / g~0.172cm 3 / g; and / or, the volume PV of closed pores per unit mass of silicon-carbon negative electrode material 闭 0.253cm 3 / g~0.300cm 3 / g.

[0010] In some embodiments, the open pore volume PV of the silicon-carbon negative electrode material is 开 0.008cm 3 / g~0.040cm 3 As a result, the open pore volume of the silicon-carbon negative electrode material is small, which makes the contact area between the negative electrode material and the electrolyte also small, which is conducive to improving the first coulombic efficiency of the material.

[0011] In some embodiments, the porous carbon matrix includes mesopores, and the mesopores account for 40% to 75% of the total pore volume of the porous carbon matrix. By controlling the pore volume percentage of the mesopores within this range, an appropriate amount of closed-cell expansion space is formed.

[0012] In some embodiments, the total pore volume of the porous carbon matrix is ​​0.5 cm 3 / g~1.02cm 3 As a result, there is more space in the porous carbon matrix to accommodate silicon grains and space reserved for the expansion of silicon-based materials, and the porous carbon matrix has sufficient strength.

[0013] In some embodiments, the content of the silicon-based material C relative to the total weight of the silicon-carbon negative electrode material is 硅 36 wt% to 40 wt%; and / or, the content of the porous carbon matrix C 碳 It is 50wt% to 57wt%.

[0014] In some embodiments, the silicon-based material comprises amorphous silicon or crystalline silicon. In some embodiments, the silicon-based material comprises crystalline silicon, and the grain size of the crystalline silicon is 3 nm to 6 nm. Thus, silicon clusters formed by the silicon grains can block the entrances of irregular pores in the porous carbon matrix, facilitating the formation of closed pores by the silicon clusters and the pores they block.

[0015] In some embodiments, the silicon-carbon anode material includes one or more of the following features:

[0016] The true density of the silicon-carbon negative electrode material is 1.8g / cm 3 ~2.3g / cm 3 ;

[0017] The tap density of the silicon-carbon negative electrode material is 0.4g / cm 3 ~0.9g / cm 3 ;

[0018] The specific surface area of ​​silicon-carbon negative electrode material is 2.5m 2 / g~12m 2 / g;

[0019] The specific surface area of ​​the porous carbon matrix is ​​1000m 2 / g~1800m 2 / g.

[0020] In some embodiments, the silicon-carbon negative electrode material further includes a carbon coating layer, which can improve the conductivity of the silicon-based material and isolate the electrolyte from contact with the silicon-based material, thereby reducing the occurrence of side reactions.

[0021] A second aspect of the present disclosure provides a method for preparing a silicon-carbon negative electrode material, the method comprising:

[0022] Providing a porous carbon matrix, wherein the porous carbon matrix includes mesopores, and the mesopores account for less than or equal to 75% of the total pore volume of the porous carbon matrix;

[0023] placing the porous carbon substrate in a reactor;

[0024] Passing a first mixed gas comprising a silicon source gas and a first inert gas into the reactor, wherein the partial pressure of the silicon source gas is greater than or equal to 0.3, wherein the mass ratio of the silicon source gas to the porous carbon matrix, calculated on the mass of the silicon element, is less than or equal to 0.95;

[0025] The gas hourly space velocity of the first mixed gas is adjusted to be less than or equal to 1200 L / kg, and under this condition, the silicon-based material is deposited in the pores of the porous carbon matrix, thereby obtaining a silicon-carbon negative electrode material.

[0026] The silicon-carbon negative electrode material includes a porous carbon matrix and a silicon-based material present in the pores of the porous carbon matrix; wherein the volume of the silicon-based material per unit mass of the silicon-carbon negative electrode material is 0.155 cm 3 / g~0.175cm 3 / g, the silicon-carbon negative electrode material contains closed pores, and the volume of closed pores per unit mass of the silicon-carbon negative electrode material is greater than or equal to 0.250 cm 3 / g.

[0027] By controlling the mesopore volume fraction of the porous carbon matrix, the gas hourly space velocity of the first mixed gas, the partial pressure of the silicon source gas, and the mass ratio of the silicon source gas to the porous carbon matrix within specific ranges, a silicon-carbon anode material with a certain silicon-based content and an appropriate amount of closed-cell expansion space was prepared. This material has a small specific surface area and low volume expansion rate, thereby improving the material's initial coulombic efficiency while also providing excellent cycling performance.

[0028] In some embodiments, the mesopores account for 40% to 75% of the total pore volume of the porous carbon matrix.

[0029] In some embodiments, in the first mixed gas, the partial pressure of the silicon source gas is 0.3 to 0.7.

[0030] In some embodiments, the mass ratio of the introduced silicon source gas to the porous carbon matrix is ​​0.78 to 0.95.

[0031] In some embodiments, the gas hourly space velocity of the first mixed gas is adjusted to 500 L / kg to 1200 L / kg.

[0032] In some embodiments, the total pore volume of the porous carbon matrix is ​​0.5 cm 3 / g~1.02cm 3 / g; and / or, the specific surface area of ​​the porous carbon matrix is ​​1000m 2 / g~1800m 2 / g.

[0033] In some embodiments, the method satisfies one or more of the following conditions (1)-(4):

[0034] (1) Depositing the silicon-based material into the pores of the porous carbon matrix at a pressure of 1 kPa to 5 kPa;

[0035] (2) The deposition time of silicon-based materials is 5h to 12h;

[0036] (3) The silicon source gas includes one or more of monosilane, disilane, trisilane, dichlorosilane, trichlorosilane or tetrachlorosilane;

[0037] (4) The first inert gas includes one or more of nitrogen, argon, helium or neon.

[0038] In some embodiments, the method further comprises: after depositing the silicon-based material, introducing a second mixed gas comprising a carbon source gas and a second inert gas into the reactor to form a carbon coating layer on the surface of the silicon-carbon negative electrode material.

[0039] Optionally, the carbon source gas includes one or more of acetylene, ethylene, propylene, methane, ethane or propane.

[0040] Optionally, the second inert gas includes one or more of nitrogen, argon, helium or neon.

[0041] The third aspect of the present disclosure provides a secondary battery, comprising a negative electrode plate, the negative electrode plate comprising a negative electrode collector and a negative electrode film layer located on at least one surface of the negative electrode collector; the negative electrode film layer comprises the silicon-carbon negative electrode material of the first aspect of the present disclosure or the silicon-carbon negative electrode material prepared according to the method of the second aspect of the present disclosure.

[0042] A fourth aspect of the present disclosure provides an electric device including the secondary battery according to the third aspect of the present disclosure.

[0043] The silicon-carbon negative electrode material in the embodiment of the present disclosure has an appropriate amount of closed-pore space reserved inside for silicon expansion, so the negative electrode material has a smaller specific surface area and a lower volume expansion rate, thereby improving the material's first coulombic efficiency while having excellent cycle performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] FIG1 shows a schematic structural diagram of a porous carbon matrix without depositing a silicon-based material and a schematic structural diagram of a silicon-carbon negative electrode material formed after depositing a silicon-based material in the porous carbon matrix in one embodiment of the present disclosure.

[0045] FIG. 2 is a schematic diagram of a battery cell according to an embodiment of the present disclosure.

[0046] FIG. 3 is an exploded view of the battery cell according to the embodiment of the present disclosure shown in FIG. 2 .

[0047] FIG. 4 is a schematic diagram of a battery module according to an embodiment of the present disclosure.

[0048] FIG5 is a schematic diagram of a battery pack according to an embodiment of the present disclosure.

[0049] FIG. 6 is an exploded view of the battery pack shown in FIG. 5 according to an embodiment of the present disclosure.

[0050] FIG. 7 is a schematic diagram of an electric device using a secondary battery according to an embodiment of the present disclosure as a power source.

[0051] Description of reference numerals:

[0052] 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

[0053] Below, the embodiments of the silicon-carbon negative electrode material and its preparation method, secondary battery and electric 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.

[0054] " 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.

[0055] Unless otherwise specified, all embodiments and optional embodiments of the present disclosure can be combined with each other to form new technical solutions.

[0056] Unless otherwise specified, all technical features and optional technical features disclosed herein can be combined with each other to form a new technical solution.

[0057] 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.

[0058] Unless otherwise specified, the terms used in the present disclosure have the common meanings that are generally understood by those skilled in the art.

[0059] 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.

[0060] Unless otherwise specified, in the present disclosure, the term "active ions" refers to ions that can be intercalated and extracted back and forth between the positive electrode and the negative electrode of a secondary battery, including but not limited to lithium ions.

[0061] In recent years, the application scope of lithium-ion batteries has become increasingly extensive. With the widespread application of lithium-ion batteries, higher requirements have been placed on the battery's energy density and cycle performance.

[0062] Improving the specific capacity of electrode materials is one approach to improving the performance of lithium-ion batteries. Silicon-based materials have attracted considerable attention as anode materials for lithium-ion batteries due to their high specific capacity. However, existing silicon-based anode materials suffer from high volume expansion during charge and discharge, as well as low initial coulombic efficiency. This significantly limits their widespread use in lithium-ion batteries.

[0063] Therefore, providing a silicon-based negative electrode material with low volume expansion rate and high first coulombic efficiency remains a technical problem that needs to be solved urgently.

[0064] Based on this, the present disclosure proposes a silicon-carbon negative electrode material and a preparation method thereof, a secondary battery, and an electrical device. The present disclosure and optional embodiments are described in more detail below.

[0065] [Silicon-carbon anode material]

[0066] The first aspect of the present disclosure provides a silicon-carbon negative electrode material. The silicon-carbon negative electrode material comprises a porous carbon matrix and a silicon-based material present in the pores of the porous carbon matrix; wherein the volume V of the silicon-based material per unit mass of the silicon-carbon negative electrode material is 硅 0.155cm 3 / g~0.175cm 3 / g, the silicon-carbon negative electrode material contains closed pores, and the volume of closed pores per unit mass of the silicon-carbon negative electrode material is greater than or equal to 0.250 cm 3 / g.

[0067] The volume V of silicon-based material per unit mass of silicon-carbon negative electrode material 硅 Calculated by the following formula (I):

[0068] V 硅 =C 硅÷ρ 硅 (I)

[0069] In formula (I), C 硅 Indicates the content of silicon-based materials relative to the total weight of silicon-carbon negative electrode materials. For example, if the content of silicon-based materials is 40% relative to the total weight of silicon-carbon negative electrode materials, then C 硅 The content of the silicon-based material can be measured using methods known in the art, such as inductively coupled plasma optical emission spectroscopy.

[0070] ρ 硅 Represents the density of the silicon-based material. For example, the silicon-based material present in the porous carbon matrix includes amorphous silicon or crystalline silicon. It is well known to those skilled in the art that the density of amorphous silicon or crystalline silicon is 2.33 g / cm 3 .

[0071] “C 硅 ÷ρ 硅 " represents the volume of silicon-based material in the pores of the porous carbon matrix per unit mass of silicon-carbon negative electrode material, corresponding to the volume V of silicon-based material per unit mass of silicon-carbon negative electrode material 硅 .

[0072] The silicon-carbon negative electrode material contains closed pores. Closed pores are closed pores that exist in the silicon-carbon negative electrode material and whose pore volume and specific surface area cannot be measured by nitrogen adsorption method. The volume PV of closed pores in silicon-carbon negative electrode material is 闭 It can be calculated by the following formula (II):

[0073] PV 闭 =(C 碳 ×PV 总 )-PV 开 -V 硅 (II)

[0074] In formula (II), “PV 总 " represents the total pore volume of all pores in the porous carbon matrix per unit mass that can be measured by nitrogen adsorption method, and its unit is cm 3 / g.

[0075] “C 碳 " represents the content of the porous carbon matrix relative to the total weight of the silicon-carbon negative electrode material. For example, if the content of the porous carbon matrix is ​​55%, then C 碳 The content of the porous carbon matrix can be measured using methods known in the art, such as using a carbon-sulfur analyzer.

[0076] “C 碳 ×PV 总” represents the total pore volume provided by the porous carbon matrix without depositing silicon-based materials in unit mass of silicon-carbon negative electrode material.

[0077] “PV 开 " represents the pore volume of the open pores in the unit mass of silicon-carbon negative electrode material, in cm 3 / g. "The pore volume of open pores in the silicon-carbon negative electrode material" refers to the pore volume that can be tested using the nitrogen adsorption method. Using this method, only the pore volume of pores that can pass nitrogen can be tested, and the pore volume of pores that cannot pass nitrogen cannot be tested. The pores that can be tested by the nitrogen adsorption method are referred to as open pores in this article. The pores that cannot be tested by the nitrogen adsorption method are referred to as closed pores in this article. There is a pore volume of closed pores in the silicon-carbon negative electrode material of the embodiment of the present disclosure that cannot be tested by the nitrogen adsorption method. Here, "PV 开 The pore volume of closed pores that cannot be measured by nitrogen adsorption method is not included.

[0078] V 硅 Indicates the volume of silicon-based material per unit mass of silicon-carbon negative electrode material, in cm 3 / g. As mentioned above, V 硅 It can be obtained from formula (I).

[0079] In the silicon-carbon negative electrode material, part of the pores in the porous carbon matrix are occupied by the deposited silicon-based material, and part of the pores are blocked by the deposited silicon-based material during the deposition process of the silicon-based material, thereby forming "closed pores". The remaining pores in the porous carbon matrix form the open pores of the silicon-carbon negative electrode material, which can be tested using the nitrogen adsorption method.

[0080] Therefore, the volume PV of closed pores in unit mass of silicon-carbon negative electrode material is 闭 It can be obtained by subtracting the volume of the deposited silicon-based material and the volume of the open pores in the silicon-carbon negative electrode material from the pore volume of the porous carbon matrix in the silicon-carbon negative electrode material per unit mass, as shown in the above formula (II).

[0081] FIG1 schematically shows a structure diagram of a porous carbon matrix without silicon-based material deposited thereon (left figure) and a structure diagram of a silicon-carbon negative electrode material formed after silicon-based material is deposited in the porous carbon matrix (right figure). In the left figure of FIG1 , the total pore volume of the porous carbon matrix used to form the negative electrode silicon-carbon negative electrode material is represented as “PV 总 In the right figure of Figure 1, the pore volume of closed pores per unit mass of negative electrode silicon-carbon material is expressed as PV 闭 , the pore volume of the open pores is expressed as PV 开 , the volume occupied by the silicon-based material is expressed as V 硅As shown in Figure 1, the pores of the porous carbon matrix are divided into three parts after the deposition of the silicon-based material. One part is the closed pores that are not connected to the outside world. This part of the pores cannot be tested by the nitrogen adsorption method; the other part is the volume V occupied by the deposited silicon-based material. 硅 This part can be calculated by the content and density of the silicon-based material; the remaining part is the open pores connected to the outside world, which can be tested by nitrogen adsorption. Therefore, for a unit mass of silicon-carbon negative electrode material, the closed pore volume PV inside it is 闭 The PV can be calculated by subtracting the volume occupied by the silicon-based material and the volume of the open pores from the pore volume of the porous carbon matrix. 开 Come to find out.

[0082] In the silicon-carbon negative electrode material of the embodiment of the present disclosure, for a volume of 0.155 cm 3 / g~0.175cm 3 / g of silicon-based materials, there are greater than or equal to 0.250cm 3 / g of closed pore volume. This provides an appropriate amount of closed-pore expansion space for the silicon-based material present in the pores of the porous carbon matrix. Therefore, for silicon-carbon negative electrode materials containing a certain amount of silicon-based material, the silicon-carbon negative electrode material of the embodiment of the present disclosure has a smaller specific surface area and lower volume expansion rate, thereby improving the material's initial coulombic efficiency while also having excellent cycling performance.

[0083] In the present disclosure, the terms "pore volume", "pore volume", "pore volume", and "pore volume" have the same meaning and can be used interchangeably.

[0084] In some embodiments, the volume V of the silicon-based material per unit mass of the silicon-carbon negative electrode material is 硅 Can be 0.155cm 3 / g~0.175cm 3 / g, optionally 0.159cm 3 / g~0.172cm 3 / g. For example, V 硅 Can be 0.155cm 3 / g, 0.159cm 3 / g, 0.160cm 3 / g, 0.163cm 3 / g, 0.165cm 3 / g, 0.167cm 3 / g, 0.170cm 3 / g,0.172cm 3 / g, 0.175cm 3 / g or a value between any two values, but not limited thereto.

[0085] In some embodiments, the volume PV of closed pores in a unit mass of silicon-carbon negative electrode material is 闭 Can be 0.253cm 3 / g~0.350cm 3 / g,0.253cm 3 / g~0.300cm 3 / g,0.255cm 3 / g~0.300cm 3 / g. For example, PV 闭 Can be 0.253cm 3 / g, 0.255cm 3 / g, 0.260cm 3 / g, 0.265cm 3 / g, 0.266cm 3 / g, 0.270cm 3 / g, 0.274cm 3 / g, 0.275cm 3 / g, 0.280cm 3 / g, 0.285cm 3 / g, 0.287cm 3 / g, 0.290cm 3 / g, 0.295cm 3 / g, 0.300cm 3 / g, 0.349cm 3 / g, 0.350cm 3 / g or a value between any two values, but not limited thereto.

[0086] In some embodiments, the open pore volume PV of the silicon-carbon negative electrode material is 开 Can be 0.008cm 3 / g~0.040cm 3 / g, optionally 0.022cm 3 / g~0.038cm 3 / g. For example, the open pore volume of the silicon-carbon negative electrode material can be 0.008cm 3 / g, 0.009cm 3 / g, 0.01cm 3 / g, 0.015cm 3 / g, 0.016cm 3 / g, 0.017cm 3 / g, 0.019cm 3 / g, 0.02cm 3 / g, 0.022cm 3 / g, 0.025cm 3 / g, 0.026cm 3 / g, 0.03cm 3 / g, 0.031cm 3 / g, 0.034cm 3 / g, 0.035cm 3 / g, 0.038cm 3 / g, 0.039cm 3 / g, 0.040cm 3 / g or a value between any two values, but not limited thereto.

[0087] The open pore volume of silicon-carbon anode materials refers to the pore volume that can be measured using the nitrogen adsorption method. The nitrogen adsorption method can only measure the pore volume of open pores that can be penetrated by nitrogen, but cannot measure the pore volume of closed pores that cannot be penetrated by nitrogen.

[0088] During the first charging process of the battery, a solid electrolyte interface film (SEI film) will be formed at the interface of the negative electrode material and the electrolyte. The formation of the SEI film will consume a portion of the lithium ions, and the lithium ions will become inactivated lithium ions after participating in the reaction to form the SEI film. The larger the contact area between the negative electrode material and the electrolyte, the larger the area of ​​the SEI film formed, and the more lithium ions will be inactivated, resulting in a decrease in the first coulombic efficiency of the battery. The open pore volume of the silicon-carbon negative electrode material in the embodiment of the present disclosure is small, so that the contact area between the negative electrode material and the electrolyte is also small, which is conducive to improving the first coulombic efficiency of the material.

[0089] By controlling the open pore volume of the silicon-carbon negative electrode material within the above range, on the one hand, it can provide an appropriate amount of open pore expansion space for the silicon-based material, and on the other hand, it is beneficial to control the contact area between the negative electrode material and the electrolyte, so that the excessive contact area between the negative electrode material and the electrolyte will not lead to more consumption of Li to generate the solid electrolyte membrane, thereby affecting the first coulombic efficiency.

[0090] In some embodiments, the silicon-based material includes amorphous silicon or crystalline silicon. In some embodiments, the silicon-based material includes crystalline silicon, and the grain size of the crystalline silicon is 3 nm to 6 nm, optionally 3 nm to 5 nm. For example, the size of the silicon grains may be 3 nm, 4 nm, 5 nm, or 6 nm, but is not limited thereto.

[0091] The size D of the silicon grains can be calculated using the Scherrer formula. The Scherrer formula can be expressed as D = 0.89λ / βcosθ, where λ is the wavelength of the X-ray 0.154056nm, β is the half-width of the diffraction peak, generally the first peak of silicon (about 28.6°) is selected, and θ is the diffraction angle. In the silicon-carbon negative electrode material of the present disclosure, the silicon grain size is relatively large. Referring to Figure 1, it can be seen that silicon clusters with larger grain sizes are blocked at the entrance of the irregular pores of the porous carbon matrix, and the silicon clusters and the blocked pores together form closed pores. This increases the number of closed pores in the material on the one hand, and reduces the specific surface area of ​​the negative electrode material on the other hand, thereby providing an appropriate amount of closed pore space for the expansion of the silicon-based material, while reducing the contact area between the negative electrode material and the electrolyte. This is conducive to reducing the volume expansion rate of the negative electrode material and improving the first coulombic efficiency of the negative electrode material.

[0092] In some embodiments, the true density of the silicon-carbon negative electrode material can be 1.8 g / cm 3 ~2.3g / cm 3 , optionally 1.99 g / cm 3 ~2.2g / cm 3 , optionally 2.0 g / cm 3 ~2.2g / cm 3 For example, the true density of silicon-carbon anode material can be 1.8 g / cm 3 , 1.9g / cm 3 , 2.0g / cm 3 , 2.01g / cm 3 , 2.02g / cm 3 , 2.03g / cm 3 , 2.1g / cm 3 , 2.2g / cm 3 , 2.3g / cm 3 Or a value between any two values, but not limited to this.

[0093] True density is well known in the art and can be measured using instruments and methods known in the art, for example, the method in GB / T 24586-2009.

[0094] In some embodiments, the tap density of the silicon-carbon negative electrode material can be 0.4 g / cm 3 ~0.9g / cm 3 , optionally 0.5g / cm 3 ~0.71g / cm 3 For example, the tap density of silicon-carbon negative electrode material can be 0.4 g / cm 3 , 0.5g / cm 3 , 0.6g / cm 3, 0.61g / cm 3 , 0.62g / cm 3 , 0.63g / cm 3 , 0.64g / cm 3 , 0.65g / cm 3 , 0.66g / cm 3 , 0.67g / cm 3 , 0.68g / cm 3 , 0.69g / cm 3 , 0.70g / cm 3 , 0.71g / cm 3 , 0.8g / cm 3 , 0.9g / cm 3 Or a value between any two values, but not limited to this.

[0095] The tap density is well known in the art and can be measured using instruments and methods known in the art, for example, according to GB / T 5162-2006.

[0096] In some embodiments, the specific surface area of ​​the silicon-carbon negative electrode material can be 2.5 m 2 / g~12m 2 / g. For example, the specific surface area of ​​silicon-carbon negative electrode material can be 2.5m 2 / g、3m 2 / g、4m 2 / g、5m 2 / g, 5.4m 2 / g, 5.8m 2 / g、6m 2 / g, 6.3m 2 / g、7m 2 / g、8m 2 / g, 8.2m 2 / g, 8.8m 2 / g、9m 2 / g、10m 2 / g、11m 2 / g、12m 2 / g or a value between any two values, but not limited thereto.

[0097] The specific surface area of ​​silicon-carbon anode materials refers to the surface area of ​​open pores that can be measured by nitrogen adsorption. The surface area of ​​closed pores in silicon-carbon anode materials cannot be measured by nitrogen adsorption.

[0098] In these embodiments, the silicon-carbon negative electrode material has a smaller specific surface area. The smaller specific surface area indicates that the number of open pores present in the silicon-carbon negative electrode material is smaller. Although the mechanism is not yet clear, the present disclosure found that the silicon-based material exists in the porous carbon matrix as larger silicon crystal clusters. These larger silicon crystal clusters are blocked at the entrances of the irregular pores in the porous carbon matrix, and are not deposited at the bottom of the pores through the entrances of these irregular pores. Therefore, the silicon-carbon negative electrode material has a smaller specific surface area while having an appropriate amount of closed pores. The right figure of Figure 1 shows a schematic structural diagram of the silicon-carbon negative electrode material formed after silicon is deposited in the porous carbon matrix. Referring to Figure 1, it can be seen that silicon crystal clusters with larger grain sizes are blocked at the entrances of the irregular pores of the porous carbon matrix, and the silicon crystal clusters and the pores they block together form closed pores. This increases the number of closed pores in the material on the one hand, and reduces the specific surface area of ​​the material on the other hand.

[0099] During the first charging process of the battery, a solid electrolyte interface film (SEI film) will be formed at the interface of the negative electrode material and the electrolyte. The formation of the SEI film will consume a portion of lithium ions, and the lithium ions will become inactivated lithium ions after participating in the reaction to form the SEI film. The larger the contact area between the negative electrode material and the electrolyte, the larger the area of ​​the SEI film formed, and the more lithium ions will be inactivated, resulting in a decrease in the first coulombic efficiency of the material. The specific surface area of ​​the silicon-carbon negative electrode material in the embodiment of the present disclosure is small, so that the contact area between the negative electrode material and the electrolyte is also small, which is conducive to improving the first coulombic efficiency of the material.

[0100] In some embodiments, the porous carbon matrix includes mesopores. In some embodiments, the porous carbon matrix includes micropores, mesopores, and macropores. In some embodiments, the mesopores account for 40% to 75% of the total pore volume of the porous carbon matrix, optionally 50% to 75%, and optionally 60% to 75%.

[0101] Among them, micropores refer to pores with a pore diameter of less than 2nm, mesopores refer to pores with a pore diameter between 2nm and 50nm, and macropores refer to pores with a pore diameter greater than 50nm. The proportion of mesopores in the total pore volume of the porous carbon matrix refers to the percentage of the mesopore volume relative to the total pore volume of the porous carbon matrix. In some embodiments, the proportion of mesopores in the total pore volume of the porous carbon matrix can be 40% to 75%, optionally 50% to 75%, optionally 60% to 75%. For example, the proportion of mesopores in the total pore volume of the porous carbon matrix can be 40%, 45%, 50%, 55%, 60%, 62%, 65%, 70%, 74%, 75% or a value between the ranges consisting of any two values, but is not limited thereto. By controlling the proportion of mesopores in the total pore volume of the porous carbon matrix within the above range, it is beneficial to controllably form closed pores in the silicon-carbon negative electrode material.

[0102] Generally speaking, the activation pore-forming process of porous carbon can only regulate the open pores, and the closed pores therein are usually generated by the raw materials themselves or by carbon rearrangement under high-temperature treatment, and the consistency of the closed pore amount of the porous carbon matrix is ​​difficult to control. In some embodiments, the porous carbon matrix itself does not include closed pores. Therefore, the closed pores in the silicon-carbon negative electrode material of the present disclosure are all closed pores formed during the silicon deposition process, and therefore, the closed pore volume is controllably formed through the silicon deposition process. By controllably forming the closed pore volume, an appropriate amount of closed pore expansion space is reserved for the expansion of the silicon-based material, thereby achieving the effect of a lower volume expansion rate of the silicon-carbon negative electrode material containing a certain content of silicon-based material.

[0103] In some embodiments, the proportion of micropores in the total pore volume of the porous carbon matrix can be 15% to 50%. For example, the proportion of micropores in the total pore volume of the porous carbon matrix can be 15%, 20%, 30%, 40%, 50% or a value between the ranges consisting of any two numerical values, but is not limited thereto. The proportion of micropores in the total pore volume of the porous carbon matrix refers to the percentage of the pore volume of micropores relative to the total pore volume of the porous carbon matrix. By controlling the proportion of micropores in the total pore volume of the porous carbon matrix within a smaller range, it is beneficial for the porous carbon matrix to have stronger strength. On the other hand, micropores have a strong catalytic effect on the silicon source gas used to deposit silicon-based materials, and too many micropores lead to poor controllability of the decomposition reaction of the silicon source gas. Optionally, the proportion of micropores in the total pore volume of the porous carbon matrix is ​​low.

[0104] In some embodiments, the proportion of macropores in the total pore volume of the porous carbon matrix can be 1% to 10%. For example, the proportion of macropores in the total pore volume of the porous carbon matrix can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or a value between the ranges consisting of any two values, but is not limited thereto. The proportion of macropores in the total pore volume of the porous carbon matrix refers to the percentage of the pore volume of macropores relative to the total pore volume of the porous carbon matrix. Optionally, the proportion of macropores in the total pore volume of the porous carbon matrix is ​​low.

[0105] In some embodiments, the total pore volume of the porous carbon matrix is ​​0.5 cm 3 / g~1.02cm 3 / g, optionally 0.78cm 3 / g~0.89cm 3 / g, optionally 0.78cm 3 / g~0.85cm 3 For example, the total pore volume of the porous carbon matrix can be 0.5 cm 3 / g, 0.6cm 3 / g, 0.7cm 3 / g, 0.8cm 3 / g, 0.84cm 3 / g, 0.89cm 3 / g, 0.9cm 3 / g, 0.92cm 3 / g, 1.0cm 3 / g, 1.02cm 3 / g or a value between any two values, but not limited thereto.

[0106] The total pore volume of the porous carbon matrix includes the sum of the pore volumes of micropores, mesopores and macropores. The pore volume of the porous carbon matrix is ​​greater than or equal to 0.5 cm 3 / g, optionally greater than or equal to 0.78cm 3 / g, so that there is more space in the porous carbon matrix to accommodate silicon clusters and space reserved for the expansion of silicon-based materials. The pore volume of the porous carbon matrix is ​​less than or equal to 1.02cm 3 / g, optionally less than or equal to 0.89cm 3 / g, so that the porous carbon matrix has sufficient strength, and the negative electrode material will not be broken after being subjected to external force during the subsequent full battery preparation process, resulting in silicon dissolution.

[0107] In some embodiments, the specific surface area of ​​the porous carbon matrix can be 1000 m 2 / g~1800m 2 / g, optionally 1200m 2 / g~1500m 2 / g, optionally 1200m 2 / g~1400m 2 / g. For example, the specific surface area of ​​the porous carbon matrix can be 1000m 2 / g、1100m 2 / g、1200m 2 / g、1300m 2 / g、1310m 2 / g、1400m 2 / g、1423m 2 / g、1454m 2 / g、1500m 2 / g、1600m 2 / g、1700m 2 / g、1800m 2 / g or a value between any two values, but not limited thereto.

[0108] The specific surface area of ​​the porous carbon matrix includes the sum of the specific surface areas of micropores, mesopores and macropores. The specific surface area of ​​the porous carbon matrix is ​​less than or equal to 1800m 2 / g, optionally less than or equal to 1500m2 / g, optionally less than or equal to 1400m 2 / g, thereby reducing the surface energy of the porous carbon matrix and improving the controllability of the silicon source gas decomposition reaction. The specific surface area of ​​the porous carbon matrix is ​​greater than or equal to 1000m 2 / g, optionally greater than or equal to 1200m 2 / g, so that there is more space in the porous carbon matrix to accommodate silicon clusters and space reserved for the expansion of silicon-based materials.

[0109] In some embodiments, the content of the silicon-based material C relative to the total weight of the silicon-carbon negative electrode material is 硅 The content of the porous carbon matrix C may be 36 wt% to 41 wt%, optionally 36 wt% to 40 wt%; and / or 碳 The content of the porous carbon matrix can be 50 wt % to 57 wt %. For example, the content of the porous carbon matrix can be determined by testing using a carbon-sulfur analyzer. For example, after surface passivation of the porous carbon matrix on which the silicon-based material is deposited, the carbon content therein is tested using a carbon-sulfur analyzer to thereby determine the content of the porous carbon matrix.

[0110] In some embodiments, the silicon-carbon anode material further includes a carbon coating. This carbon coating can improve the conductivity of the silicon-based material. Furthermore, the carbon coating can isolate the electrolyte from the silicon-based material, reducing side reactions and facilitating the formation of a stable and uniform solid electrolyte interface film.

[0111] In some embodiments, the carbon coating layer may contain 2 wt% to 5 wt% of the total weight of the silicon-carbon negative electrode material. For example, the carbon coating layer may contain 2 wt%, 3 wt%, 4 wt%, 5 wt%, or a range of any two values ​​relative to the total weight of the silicon-carbon negative electrode material, but is not limited thereto. By controlling the carbon coating layer content within the above range, a complete carbon coating layer is formed, thereby effectively isolating the electrolyte without adversely affecting the capacity of the silicon-carbon negative electrode material.

[0112] The content of the carbon coating layer can be determined, for example, by testing with a carbon-sulfur analyzer. For example, the carbon content of the silicon-carbon negative electrode material is measured using a carbon-sulfur analyzer, i.e., the sum of the carbon content in the porous carbon matrix and the carbon coating relative to the content of the silicon-carbon negative electrode material. Combined with the content of the porous carbon matrix measured above, the content of the carbon coating layer can be calculated.

[0113] [Method for preparing silicon-carbon negative electrode material]

[0114] The second aspect of the present disclosure provides a method for preparing a silicon-carbon negative electrode material. The method comprises:

[0115] Providing a porous carbon matrix, wherein the porous carbon matrix includes mesopores, and the mesopores account for less than or equal to 75% of the total pore volume of the porous carbon matrix;

[0116] placing the porous carbon substrate in a reactor;

[0117] A first mixed gas comprising a silicon source gas and a first inert gas is introduced into the reactor, wherein the partial pressure of the silicon source gas is greater than or equal to 0.3, wherein the mass ratio M of the silicon source gas to the porous carbon matrix is ​​calculated based on the mass of the silicon element. Si / M C Less than or equal to 0.95;

[0118] The gas hourly space velocity of the first mixed gas is adjusted to be less than or equal to 1200 L / kg, and under this condition, the silicon-based material is deposited in the pores of the porous carbon matrix, thereby obtaining a silicon-carbon negative electrode material.

[0119] The silicon-carbon negative electrode material includes a porous carbon matrix and a silicon-based material present in the pores of the porous carbon matrix; wherein the volume of the silicon-based material per unit mass of the silicon-carbon negative electrode material is 0.155 cm 3 / g~0.175cm 3 / g, the silicon-carbon negative electrode material contains closed pores, and the volume of closed pores per unit mass of the silicon-carbon negative electrode material is greater than or equal to 0.250 cm 3 / g.

[0120] Although the mechanism is not yet clear, the present disclosure has found that by selecting the proportion of mesoporous pore volume, adjusting the gas hourly space velocity of the first mixed gas to a specific range, controlling the partial pressure of the silicon source gas, and controlling the mass ratio of the silicon source gas to the porous carbon matrix, the size of the silicon grains can be adjusted to form silicon clusters with larger grain sizes. Silicon clusters with larger grain sizes are blocked at the entrances of the irregular pores of the porous carbon matrix, and the silicon clusters and the pores they block together form closed pores. This reserves an appropriate amount of closed-pore expansion space for the expansion of the silicon-based material, thereby achieving a lower volume expansion rate for the silicon-carbon negative electrode material containing a certain content of silicon-based material.

[0121] "Gas hourly space velocity" is a well-known term in the art and can be measured using instruments and methods known in the art. For example, a mass flow meter can be used to control the volume of gas passing through the porous carbon substrate per unit time. Gas hourly space velocity = volume (L) of the first mixed gas passing through the porous carbon substrate in 1 hour / mass (kg) of the porous carbon substrate.

[0122] In the above method, the gas hourly space velocity of the first mixed gas can be adjusted to 500 L / kg to 1200 L / kg, and optionally 550 L / kg to 1100 L / kg. For example, the gas hourly space velocity of the first mixed gas can be adjusted to 500 L / kg, 600 L / kg, 700 L / kg, 800 L / kg, 900 L / kg, 1000 L / kg, 1050 L / kg, 1100 L / kg, 1200 L / kg, or a range between any two values, but is not limited thereto.

[0123] In the above method, the step of adjusting the gas hourly space velocity of the first mixed gas to be less than or equal to 1200 L / kg may include: testing the gas hourly space velocity of the first mixed gas and adjusting the gas hourly space velocity based on the test result. If the test result is greater than 1200 L / kg, reducing the gas hourly space velocity of the first mixed gas.

[0124] In the above method, the step of adjusting the gas hourly space velocity of the first mixed gas to 500 L / kg to 1200 L / kg may include: testing the gas hourly space velocity of the first mixed gas and then adjusting the gas hourly space velocity based on the test result. If the test result is less than 500 L / kg, increasing the gas hourly space velocity of the first mixed gas; if the test result is greater than 1200 L / kg, decreasing the gas hourly space velocity of the first mixed gas.

[0125] In the above method, the mass ratio of the silicon source gas introduced to the porous carbon substrate can be 0.78 to 0.95, optionally 0.80 to 0.93, or optionally 0.80 to 0.86, based on the mass of silicon element in the silicon source gas. For example, the mass ratio can be 0.78, 0.80, 0.82, 0.84, 0.86, 0.88, 0.90, 0.92, 0.93, 0.95, or a range between any two values, but is not limited thereto.

[0126] "Gas partial pressure" has a well-known meaning in the art, which refers to the pressure ratio of a certain component gas in a mixed gas, and can be measured using instruments and methods known in the art. For example, the partial pressure of the component gas can be regulated by controlling the flow rate of the component gas and the carrier gas introduced into the reactor per unit time. The flow rate can be tested and controlled using a mass flow meter (for example, model Alicat DODA). The gas partial pressure is related to the volume concentration of the component gas in the mixed gas. For example, when the volume concentration of a component gas in the mixed gas is 50%, the gas partial pressure of the component gas can be calculated to be 0.5 according to the ideal gas state equation.

[0127] In some embodiments, in the first mixed gas, the partial pressure of the silicon source gas may be 0.3 to 0.7, optionally 0.3 to 0.5. For example, the partial pressure of the silicon source gas may be 0.3, 0.33, 0.4, 0.5, 0.6, 0.7, or a value between a range of any two values, but is not limited thereto. The partial pressure of the silicon source gas affects the deposition mode of the silicon source gas. When the partial pressure is high, the self-nucleation deposition mode is dominant, and when the partial pressure is low, the chemical growth deposition mode is dominant, thereby affecting the silicon grain size and the size of the silicon cluster. By controlling the partial pressure of the silicon source gas within the above range, the deposition mode is dominated by self-nucleation deposition, which is conducive to the formation of silicon grains of the desired size, thereby controllably forming a closed pore volume.

[0128] In some embodiments, the porous carbon matrix includes mesopores. In some embodiments, the porous carbon matrix includes micropores, mesopores, and macropores. In some embodiments, the mesopores may account for 40% to 75% of the total pore volume of the porous carbon matrix, optionally 50% to 75%, and optionally 60% to 75%.

[0129] Among them, micropores refer to pores with a pore diameter of less than 2nm, mesopores refer to pores with a pore diameter between 2nm and 50nm, and macropores refer to pores with a pore diameter greater than 50nm. The proportion of mesopores in the total pore volume of the porous carbon matrix refers to the percentage of the mesopore volume relative to the total pore volume of the porous carbon matrix. In some embodiments, the proportion of mesopores in the total pore volume of the porous carbon matrix can be 40% to 75%, optionally 50% to 75%, optionally 60% to 75%. For example, the proportion of mesopores in the total pore volume of the porous carbon matrix can be 40%, 45%, 50%, 55%, 60%, 62%, 65%, 70%, 74%, 75% or a value between the ranges consisting of any two values, but is not limited thereto. By controlling the proportion of mesopores in the total pore volume of the porous carbon matrix within the above range, it is beneficial to controllably form closed pores in the silicon-carbon negative electrode material.

[0130] Generally speaking, the activation pore-forming process of porous carbon can only regulate the open pores, and the closed pores therein are usually generated by the raw materials themselves or by carbon rearrangement under high-temperature treatment, and the consistency of the closed pore amount of the porous carbon matrix is ​​difficult to control. In some embodiments, the porous carbon matrix itself does not include closed pores. Therefore, the closed pores in the silicon-carbon negative electrode material of the present disclosure are all closed pores formed during the silicon deposition process, and therefore, the closed pore volume is controllably formed through the silicon deposition process. By controllably forming the closed pore volume, an appropriate amount of closed pore expansion space is reserved for the expansion of the silicon-based material, thereby achieving the effect of a lower volume expansion rate of the silicon-carbon negative electrode material containing a certain content of silicon-based material.

[0131] In some embodiments, the proportion of micropores in the total pore volume of the porous carbon matrix can be 15% to 50%. For example, the proportion of micropores in the total pore volume of the porous carbon matrix can be 15%, 20%, 30%, 40%, 50% or a value between the ranges consisting of any two numerical values, but is not limited thereto. The proportion of micropores in the total pore volume of the porous carbon matrix refers to the percentage of the pore volume of micropores relative to the total pore volume of the porous carbon matrix. By controlling the proportion of micropores in the total pore volume of the porous carbon matrix within a smaller range, it is beneficial for the porous carbon matrix to have stronger strength. On the other hand, micropores have a strong catalytic effect on the silicon source gas used to deposit silicon-based materials, and too many micropores lead to poor controllability of the decomposition reaction of the silicon source gas. Optionally, the proportion of micropores in the total pore volume of the porous carbon matrix is ​​low.

[0132] In some embodiments, the proportion of macropores in the total pore volume of the porous carbon matrix can be 1% to 10%. For example, the proportion of macropores in the total pore volume of the porous carbon matrix can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or a value between the ranges consisting of any two values, but is not limited thereto. The proportion of macropores in the total pore volume of the porous carbon matrix refers to the percentage of the pore volume of macropores relative to the total pore volume of the porous carbon matrix. Optionally, the proportion of macropores in the total pore volume of the porous carbon matrix is ​​low.

[0133] In some embodiments, the total pore volume of the porous carbon matrix is ​​0.5 cm 3 / g~1.02cm 3 / g, optionally 0.78cm 3 / g~0.89cm 3 / g, optionally 0.78cm 3 / g~0.85cm 3 For example, the total pore volume of the porous carbon matrix can be 0.5 cm 3 / g, 0.6cm 3 / g, 0.7cm 3 / g, 0.8cm 3 / g, 0.84cm 3 / g, 0.89cm 3 / g, 0.9cm 3 / g, 0.92cm 3 / g, 1.0cm 3 / g, 1.02cm 3 / g or a value between any two values, but not limited thereto.

[0134] The total pore volume of the porous carbon matrix includes the sum of the pore volumes of micropores, mesopores and macropores. The pore volume of the porous carbon matrix is ​​greater than or equal to 0.5 cm 3 / g, optionally greater than or equal to 0.78cm 3 / g, so that there is more space in the porous carbon matrix to accommodate silicon clusters and space reserved for the expansion of silicon-based materials. The pore volume of the porous carbon matrix is ​​less than or equal to 1.02cm 3 / g, optionally less than or equal to 0.89cm 3 / g, so that the porous carbon matrix has sufficient strength, and the negative electrode material will not be broken after being subjected to external force during the subsequent full battery preparation process, resulting in silicon dissolution.

[0135] In some embodiments, the specific surface area of ​​the porous carbon matrix can be 1000 m 2 / g~1800m 2 / g, optionally 1200m 2 / g~1500m 2 / g, optionally 1200m 2 / g~1400m 2 / g. For example, the specific surface area of ​​the porous carbon matrix can be 1000m 2 / g、1100m 2 / g、1200m 2 / g、1300m 2 / g、1310m 2 / g、1400m 2 / g、1423m 2 / g、1454m 2 / g、1500m 2 / g、1600m 2 / g、1700m 2 / g、1800m 2 / g or a value between any two values, but not limited thereto.

[0136] The specific surface area of ​​the porous carbon matrix includes the sum of the specific surface areas of micropores, mesopores and macropores. The specific surface area of ​​the porous carbon matrix is ​​less than or equal to 1800m 2 / g, optionally less than or equal to 1500m 2 / g, optionally less than or equal to 1400m 2 / g, thereby reducing the surface energy of the porous carbon matrix and improving the controllability of the silicon source gas decomposition reaction. The specific surface area of ​​the porous carbon matrix is ​​greater than or equal to 1000m 2 / g, optionally greater than or equal to 1200m 2 / g, so that there is more space in the porous carbon matrix to accommodate silicon clusters and space reserved for the expansion of silicon-based materials.

[0137] In some embodiments, the silicon-based material may be deposited in the pores of the porous carbon matrix under a pressure of 1 kPa to 5 kPa. For example, the silicon-based material may be deposited in the pores of the porous carbon matrix under a pressure of 1 kPa to 2 kPa, but is not limited thereto.

[0138] In some embodiments, the deposition time of the silicon-based material may be 5 hours to 12 hours. For example, the deposition time of the silicon-based material may be 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, or a range between any two values, but is not limited thereto. The deposition time of the silicon-based material refers to the time elapsed from the start of the introduction of the silicon source gas to the cessation of the introduction of the silicon source gas.

[0139] In some embodiments, the silicon source gas may be a silicon-containing substance commonly used in the art for depositing silicon-based materials. In some embodiments, the silicon source gas may include one or more of monosilane, disilane, trisilane, dichlorosilane, trichlorosilane, or tetrachlorosilane. Alternatively, the silicon source gas may include or be monosilane.

[0140] The first inert gas may be an inert gas commonly used in the art. For example, the first inert gas may include one or more of nitrogen, argon, helium, or neon. In some embodiments, the first inert gas may include or be nitrogen.

[0141] In some embodiments, the silicon-based material can be deposited in the pores of the porous carbon matrix at a temperature of 500° C. to 800° C. For example, the silicon-based material can be deposited in the pores of the porous carbon matrix at a temperature of 500° C., 550° C., 600° C., 700° C., 800° C., or a range between any two of these values.

[0142] In some embodiments, the method further comprises: after depositing the silicon-based material, passing a second mixed gas comprising a carbon source gas and a second inert gas into the reactor to form a carbon coating layer on the surface of the silicon-carbon negative electrode material. In this manner, a carbon coating layer can be formed on the porous carbon substrate on which the silicon-based material is deposited. The carbon coating layer can improve the conductivity of the silicon-based material. Furthermore, the carbon coating layer can isolate the electrolyte from contact with the silicon-based material, reducing the occurrence of side reactions and facilitating the formation of a stable and uniform solid electrolyte interface film.

[0143] In some embodiments, the partial pressure of the carbon source gas in the second mixed gas is greater than or equal to 0.3, optionally greater than or equal to 0.4, optionally greater than or equal to 0.5, and optionally 0.45 to 0.7.

[0144] In some embodiments, the gas hourly space velocity of the second mixed gas is adjusted to 100L / kg to 300L / kg, optionally 200L / kg to 260L / kg, under which conditions the carbon is coated on a porous carbon matrix in which silicon-based materials are deposited in the pores. The gas hourly space velocity of the second mixed gas can be adjusted to 100L / kg, 150L / kg, 200L / kg, 250L / kg, 300L / kg or a value between the ranges consisting of any two values, but is not limited thereto. By adjusting the partial pressure of the carbon source gas and / or the gas hourly space velocity of the second mixed gas within the above range, it is beneficial to form a complete carbon coating layer, which can better isolate the electrolyte without adversely affecting the capacity of the silicon-carbon negative electrode material.

[0145] In some embodiments, the carbon coating step may be performed at a temperature of 580° C. to 800° C., optionally 650° C. to 750° C., but is not limited thereto.

[0146] In some embodiments, the carbon coating step may be performed at a pressure of 100 Pa to 2000 Pa, optionally 200 Pa to 500 Pa, but is not limited thereto.

[0147] In some embodiments, the duration of introducing the second mixed gas including the carbon source gas and the second inert gas may be 2 hours to 12 hours, or alternatively 2 hours to 10 hours, but is not limited thereto.

[0148] Through the above steps, a uniform and dense carbon coating can be formed on the surface of the silicon-carbon negative electrode material. This carbon coating can improve the conductivity of the silicon-based material. In addition, the carbon coating can also isolate the electrolyte from the silicon-based material, reducing the occurrence of side reactions and facilitating the formation of a stable and uniform solid electrolyte interface film.

[0149] In some embodiments, the carbon source gas may include one or more of acetylene, ethylene, propylene, methane, ethane, or propane, but is not limited thereto.

[0150] In some embodiments, the second inert gas may include one or more of nitrogen, argon, helium, or neon, but is not limited thereto.

[0151] This disclosure also provides a silicon-carbon anode material. The silicon-carbon anode material is prepared by the method of the second aspect of this disclosure. The silicon-carbon anode material has one or more of the same properties as the silicon-carbon anode material of the first aspect of this disclosure and can produce the same technical effects.

[0152] In addition, the secondary battery and the electric device of the present disclosure will be described below with reference to the drawings as appropriate.

[0153] In some embodiments of the present disclosure, a secondary battery is provided.

[0154] The term "secondary battery" mentioned herein refers to a battery cell, a battery module, or a battery pack. Each of these is described below.

[0155] Typically, a 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.

[0156] Positive electrode

[0157] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector, and the positive electrode film layer includes a positive electrode active material.

[0158] 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.

[0159] 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.).

[0160] 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 one or more 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 NCM333 ), 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 0.05 O2) and its modified compounds, etc. Examples of olivine-structured lithium-containing phosphates may include, but are not limited to, one or more 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.

[0161] In some embodiments, the battery's charge and discharge processes are accompanied by Li intercalation and deintercalation, resulting in 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., the state before addition. When the positive electrode active material is used in a battery system, the molar Li content will change after charge and discharge cycles.

[0162] 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.

[0163] In some embodiments, the positive electrode film layer may further optionally include a binder. As an example, the binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorinated acrylate resin.

[0164] In some embodiments, the positive electrode film layer may further include a conductive agent. For example, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0165] 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.

[0166] Negative electrode

[0167] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer arranged on at least one surface of the negative electrode current collector, and the negative electrode film layer includes the silicon-carbon negative electrode material of the first aspect of the present disclosure or the silicon-carbon negative electrode material prepared by the method of the second aspect of the present disclosure as the negative electrode active material.

[0168] 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.

[0169] 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.).

[0170] In addition to the silicon-carbon negative electrode material of the first aspect of the present disclosure or the silicon-carbon negative electrode material prepared by the method of the second aspect of the present disclosure, the negative electrode active material may also include negative electrode active materials for batteries that are well known in the art. As an example, the negative electrode active material may further include one or more of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials and lithium titanate, etc. The silicon-based material can be selected from one or more of elemental silicon, silicon oxide compounds, silicon-carbon composites (referring to silicon-carbon composites other than the silicon-carbon negative electrode material of the present disclosure), silicon-nitrogen composites and silicon alloys. The tin-based material can be selected from one or more of elemental tin, tin oxide compounds and tin alloys. However, the present disclosure is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries can also be used. These negative electrode active materials can be used alone or in combination of two or more.

[0171] In some embodiments, the negative electrode film layer may further include a binder. The binder may be selected from one or more 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).

[0172] In some embodiments, the negative electrode film layer may further include a conductive agent, which may be selected from one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0173] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0174] 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.

[0175] electrolytes

[0176] 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.

[0177] In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.

[0178] In some embodiments, the electrolyte salt may be selected from one or more 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.

[0179] In some embodiments, the solvent may be selected from one or more 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.

[0180] 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.

[0181] Isolation film

[0182] 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.

[0183] In some embodiments, the material of the separator can be selected from one or more 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.

[0184] 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.

[0185] In some embodiments, the battery cell may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0186] 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.

[0187] 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, FIG2 shows a battery cell 5 with a square structure as an example.

[0188] In some embodiments, referring to Figure 3, 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 be formed into 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.

[0189] 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.

[0190] FIG4 illustrates an exemplary battery module 4. Referring to FIG4 , within the battery module 4, multiple battery cells 5 may be arranged sequentially along the length of the battery module 4. Alternatively, the arrangement may be arranged in any other manner. Furthermore, the multiple battery cells 5 may be secured together using fasteners.

[0191] 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.

[0192] 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.

[0193] Figures 5 and 6 illustrate an example battery pack 1. Referring to Figures 5 and 6 , 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 positioned 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.

[0194] In addition, the present disclosure further provides an electrical device, which includes the secondary battery provided by 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 can 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, satellites, energy storage systems, etc.

[0195] As an electrical device, a secondary battery, a battery module or a battery pack can be selected according to its usage requirements.

[0196] Figure 7 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.

[0197] 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.

[0198] Example

[0199] 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.

[0200] Example 1: Preparation of silicon-carbon negative electrode material

[0201] 1) Place 2000 g of the biomass porous carbon substrate into a CVD deposition furnace. Raise the temperature in the CVD deposition furnace to 550°C at a heating rate of 5°C / min and maintain for 30 minutes. A first gas mixture comprising monosilane and nitrogen is introduced at a monosilane partial pressure of 0.33. The gas hourly space velocity of the first gas mixture is adjusted to 700 L / kg, and the furnace pressure is maintained between 1 kPa and 2 kPa. The aeration time is approximately 9 hours.

[0202] 2) After approximately 9 hours of ventilation, the introduction of monosilane was stopped. The temperature in the CVD deposition furnace was then further increased to 700°C at a heating rate of 5°C / min. A second gas mixture comprising acetylene and nitrogen was introduced at an acetylene partial pressure of 0.5. The gas hourly space velocity of the second gas mixture was adjusted to 240 L / kg, and the furnace pressure was within the range of 200 Pa to 250 Pa. The ventilation period was approximately 2 hours. The material was cooled and sieved through a 325 mesh screen to obtain the target silicon-carbon anode material.

[0203] The total pore volume, macropore volume fraction, mesopore volume fraction and micropore volume fraction of the porous carbon matrix used in step 1) of Example 1, M Si / M C , silicon source gas partial pressure, gas hourly space velocity of the first mixed gas and other parameters are shown in Table 1.

[0204] Example 2 to Example 11

[0205] Except for adjusting the parameters as shown in Table 1, the other steps of Examples 2 to 11 are the same as those of Example 1.

[0206] Comparative Examples 1 to 4

[0207] Comparative Examples 1 to 4 are the same as Example 1 except that the parameters are adjusted as shown in Table 1.

[0208] Performance test of silicon-carbon anode materials

[0209] 1. Tap density test

[0210] The tap density of the silicon-carbon negative electrode materials of the embodiments and comparative examples was tested using a Dandong Better BT-301 powder tap density tester in accordance with GB / T 5162-2006.

[0211] 1) Place 21-24 ml of powder sample into a 25 ml graduated cylinder of known mass and weigh the total weight. Seal the tube with parafilm.

[0212] 2) Mount the graduated cylinder containing the powder on a mechanical vibrator. The motor drives the vibrator to vibrate vertically up and down, gradually compacting the powder. After the set number of vibrations, stop the vibrations and read the volume of the graduated cylinder. Calculate the density of the compacted powder using the definition of density: mass divided by volume. Amplitude: 3.0 ± 0.1 mm, frequency: 250 ± 15 vibrations / min, number of vibrations: 5000.

[0213] 2. Specific surface area test

[0214] Referring to GB / T 19587-2017, the BET method for determining the specific surface area of ​​solid substances by gas adsorption, the specific surface area of ​​the material was measured using nitrogen adsorption specific surface area analysis and calculated using the BET (Brunauer Emmett Teller) method. The nitrogen adsorption specific surface area analysis was performed using a Micromeritics Tri Star II 3020 Surface Area and Porosity Analyzer.

[0215] 3. Content test of porous carbon matrix

[0216] The carbon content of the test materials was determined according to GB / T 20123-2006 / ISO 15350:2000. The test instrument used was the HCS-140 high-frequency infrared carbon and sulfur analyzer from Shanghai Dekai Instrument Co., Ltd.

[0217] After surface passivation of the product obtained in step 1), it is taken out of the deposition furnace and the carbon content in the product is tested with a carbon-sulfur analyzer, thereby measuring the content of the porous carbon matrix relative to the product. The silicon-carbon negative electrode material obtained in step 2) is tested with a carbon-sulfur analyzer to measure the carbon content in the silicon-carbon negative electrode material, that is, the sum of the carbon contents in the porous carbon matrix and the carbon coating layer relative to the content of the silicon-carbon negative electrode material. By calculation, the content of the porous carbon matrix relative to the silicon-carbon negative electrode material can be obtained.

[0218] 4. Silicon content test

[0219] The silicon content in the material was tested using the inductively coupled plasma atomic emission spectrometry method according to EPA 6010D-2014.

[0220] 5. True density test

[0221] The true density of the silicon-carbon negative electrode material was tested according to the method in GB / T 24586-2009.

[0222] Weigh a sample of a specified mass into a sample cup of known volume. This cup is then placed in a true density tester (AccuPyc II 1340). The test system is sealed and helium is introduced as programmed. The gas pressures in the sample chamber and expansion chamber are measured, and the true volume of the sample is determined according to gas laws. The true density is then calculated by dividing the sample mass by the sample volume.

[0223] Preparation of button cells

[0224] The 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, resulting in a negative electrode slurry with a solid content of 45%. The negative electrode slurry was evenly coated onto a negative electrode current collector copper foil, 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 an organic solvent 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 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%.

[0225] First test of Coulombic efficiency

[0226] After the assembled button cell rested for 60 minutes, it was tested using a constant current discharge process of 0.05C to 5mV, 50μA to 5mV, rested for 10 minutes, and then charged at 0.1C to 0.8V. The lithium insertion capacity of the silicon-carbon anode material is the gram capacity (C1) at discharge to 5mV, the lithium removal capacity (C2) at charge to 0.8V, and the first coulombic efficiency (C2 / C1) of the silicon-carbon anode material.

[0227] Preparation of secondary batteries

[0228] 1. Preparation of positive electrode sheet

[0229] The positive electrode active material LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM 811), conductive carbon black, and binder polyvinylidene fluoride (PVDF) are thoroughly stirred in an appropriate amount of N-methylpyrrolidone (NMP) solvent at a weight ratio of 93:2:5 to form a uniform positive electrode slurry. The positive electrode slurry is applied to the surface of the positive electrode current collector and dried to obtain a positive electrode sheet.

[0230] 2. Preparation of negative electrode sheet

[0231] The silicon-carbon negative electrode materials prepared in the above examples or comparative examples, artificial graphite, conductive carbon black, thickener sodium carboxymethyl cellulose (CMC-Na), and binder styrene-butadiene rubber latex (SBR) were thoroughly stirred and mixed in an appropriate amount of deionized water at a weight ratio of 18:77.5:1.3:1.2:2 to form a uniform negative electrode slurry. The negative electrode slurry was applied to the negative electrode current collector and dried to obtain a negative electrode sheet.

[0232] 3. Preparation of Electrolyte

[0233] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1 to obtain an organic solvent. Then, fully dried lithium salt LiPF6 is dissolved in the mixed organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0234] 4. Isolation film

[0235] The isolation membrane is a 12 μm thick polypropylene (PP) porous membrane.

[0236] 5. Preparation of Secondary Batteries

[0237] The positive electrode sheet, separator, and negative electrode sheet are stacked in sequence, then wound into an electrode assembly and placed in an outer package, injected with the above-mentioned electrolyte, and then undergo sealing, standing, hot and cold pressing, formation and other processes to obtain a secondary battery.

[0238] Performance testing of secondary batteries

[0239] 1. Cycle performance test

[0240] At 45°C, the secondary batteries prepared in each example and comparative example were charged at a constant current rate of 1C to a charge cutoff voltage of 4.25V. They were then charged at a constant voltage to a current of ≤0.05C, allowed to rest for 5 minutes, and then discharged at a constant current rate of 0.33C to a discharge cutoff voltage of 2.5V, allowed to rest for 5 minutes. This constituted one charge-discharge cycle. The batteries were subjected to cyclic charge-discharge testing using this method until the battery capacity decayed to 80%. The number of cycles at this point is the battery's cycle life.

[0241] 2. Full charge expansion rate test

[0242] The thickness of the negative electrode sheet of the secondary battery prepared in each embodiment and comparative example was measured and recorded as D0. The secondary battery prepared in each embodiment and comparative example was charged at a constant current rate of 1C to a cut-off voltage of 4.25V, and the thickness of the negative electrode sheet at this time was measured and recorded as D1.

[0243] Here, the first full charge expansion rate = (D1-D0) / D0×100%.

[0244] Table 1: Process parameters used in step 1) of the preparation of silicon-carbon anode materials

[0245] In Table 1, M Si / M C It represents the mass ratio of the silicon source gas introduced to the porous carbon matrix, calculated based on the mass of silicon element.

[0246] Table 2: Performance parameters of silicon-carbon anode materials

[0247] In Table 2, ρ 振 represents the tap density of silicon-carbon negative electrode material, ρ 真 Indicates the true density of silicon-carbon negative electrode material.

[0248] Table 3: Electrical performance parameter test results

[0249] According to the above results, the silicon-carbon negative electrode materials prepared in Examples 1-11 all meet the requirements of the present disclosure, and the batteries can simultaneously achieve high first coulombic efficiency and high-temperature cycle life, as well as low cycle expansion rate.

[0250] However, the silicon-carbon negative electrode materials prepared in Comparative Examples 1-4 cannot simultaneously meet the structural characteristics of the present disclosure, and therefore cannot make the battery have both high initial coulombic efficiency and high temperature cycle life, as well as low cycle expansion rate. Specifically, in Comparative Example 1, PV 闭 Less than 0.250cm 3 / g, mainly because the partial pressure of the silicon source gas is less than 0.3; in Comparative Example 2, PV 闭 Less than 0.250cm 3 / g, mainly because the gas hourly space velocity of the first mixed gas including monosilane and nitrogen is greater than 1200 L / kg; in Comparative Example 3, PV 闭 Less than 0.250cm 3 / g, and V 硅 Greater than 0.175cm 3 / g, mainly because the mass ratio of the introduced monosilane to the porous carbon matrix is ​​greater than 0.95; in Comparative Example 4, PV 闭 Less than 0.250cm 3 / g, mainly because the mesopore volume in the porous carbon matrix accounts for more than 75%. Therefore, the materials of Comparative Examples 1 to 4 cannot achieve both high initial coulombic efficiency and high temperature cycle life, as well as low cycle expansion rate.

[0251] 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 negative electrode material comprising a porous carbon matrix and a silicon-based material present in the pores of the porous carbon matrix; wherein: The volume V of silicon-based material per unit mass of silicon-carbon negative electrode material 硅 0.155cm 3 / g~0.175cm 3 / g, the silicon-carbon negative electrode material includes closed pores, and the volume PV of the closed pores per unit mass of the silicon-carbon negative electrode material is 闭 Greater than or equal to 0.250cm 3 / g.

2. The silicon-carbon negative electrode material according to claim 1, wherein The volume V of silicon-based material per unit mass of silicon-carbon negative electrode material 硅 0.159cm 3 / g~0.172cm 3 / g; and / or, Volume PV of closed pores per unit mass of silicon-carbon anode material 闭 0.253cm 3 / g~0.300cm 3 / g.

3. The silicon-carbon negative electrode material according to claim 1 or 2, wherein: The open pore volume PV of the silicon-carbon negative electrode material 开 0.008cm 3 / g~0.040cm 3 / g.

4. The silicon-carbon negative electrode material according to any one of claims 1 to 3, wherein The porous carbon matrix includes mesopores, and the mesopores account for 40% to 75% of the total pore volume of the porous carbon matrix.

5. The silicon-carbon negative electrode material according to any one of claims 1 to 4, wherein The total pore volume of the porous carbon matrix is ​​0.5 cm 3 / g~1.02cm 3 / g.

6. The silicon-carbon negative electrode material according to any one of claims 1 to 5, wherein Relative to the total weight of the silicon-carbon negative electrode material, the content of the silicon-based material C 硅 is 36 wt% to 40 wt%; and / or, the content of the porous carbon matrix C 碳 It is 50wt% to 57wt%.

7. The silicon-carbon negative electrode material according to any one of claims 1 to 6, wherein The silicon-based material includes amorphous silicon or crystalline silicon.

8. The silicon-carbon negative electrode material according to claim 7, wherein: The silicon-based material includes crystalline silicon, and the grain size of the crystalline silicon is 3 nm to 6 nm.

9. The silicon-carbon negative electrode material according to any one of claims 1 to 8, wherein The silicon-carbon negative electrode material includes one or more of the following features: The true density of the silicon-carbon negative electrode material is 1.8 g / cm 3 ~2.3g / cm 3 ; The tap density of the silicon-carbon negative electrode material is 0.4 g / cm 3 ~0.9g / cm 3 ; The specific surface area of ​​the silicon-carbon negative electrode material is 2.5 m 2 / g~12m 2 / g; The specific surface area of ​​the porous carbon matrix is ​​1000 m 2 / g~1800m 2 / g.

10. The silicon-carbon negative electrode material according to any one of claims 1 to 9, wherein The silicon-carbon negative electrode material further includes a carbon coating layer.

11. A method for preparing a silicon-carbon negative electrode material, the method comprising: Providing a porous carbon matrix, wherein the porous carbon matrix includes mesopores, and the mesopores account for less than or equal to 75% of the total pore volume of the porous carbon matrix; placing the porous carbon substrate in a reactor; Passing a first mixed gas comprising a silicon source gas and a first inert gas into the reactor, wherein the partial pressure of the silicon source gas is greater than or equal to 0.3, wherein the mass ratio of the silicon source gas to the porous carbon matrix, calculated on the basis of the mass of the silicon element, is less than or equal to 0.95; The gas hourly space velocity of the first mixed gas is adjusted to be less than or equal to 1200 L / kg, and under this condition, the silicon-based material is deposited in the pores of the porous carbon matrix, thereby obtaining the silicon-carbon negative electrode material. The silicon-carbon negative electrode material comprises a porous carbon matrix and a silicon-based material present in the pores of the porous carbon matrix; wherein the volume of the silicon-based material per unit mass of the silicon-carbon negative electrode material is 0.155 cm 3 / g~0.175cm 3 / g, the silicon-carbon negative electrode material includes closed pores, and the volume of the closed pores per unit mass of the silicon-carbon negative electrode material is greater than or equal to 0.250 cm 3 / g.

12. The method according to claim 11, wherein The mesopores account for 40% to 75% of the total pore volume of the porous carbon matrix.

13. The method according to claim 11 or 12, wherein: In the first mixed gas, the partial pressure of the silicon source gas is 0.3 to 0.

7.

14. The method according to any one of claims 11 to 13, wherein The mass ratio of the introduced silicon source gas to the porous carbon matrix is ​​0.78 to 0.

95.

15. The method according to any one of claims 11 to 14, wherein The gas hourly space velocity of the first mixed gas is adjusted to 500 L / kg to 1200 L / kg.

16. The method according to any one of claims 11 to 15, wherein The total pore volume of the porous carbon matrix is ​​0.5 cm 3 / g~1.02cm 3 / g; and / or, The specific surface area of ​​the porous carbon matrix is ​​1000 m 2 / g~1800m 2 / g.

17. The method according to any one of claims 11 to 16, wherein The method satisfies one or more of the following conditions (1)-(4): (1) depositing the silicon-based material in the pores of the porous carbon matrix at a pressure of 1 kPa to 5 kPa; (2) The deposition time of the silicon-based material is 5 h to 12 h; (3) The silicon source gas includes one or more of monosilane, disilane, trisilane, dichlorosilane, trichlorosilane or tetrachlorosilane; (4) The first inert gas includes one or more of nitrogen, argon, helium or neon.

18. The method according to any one of claims 11 to 17, wherein The method further comprises: after depositing the silicon-based material, introducing a second mixed gas comprising a carbon source gas and a second inert gas into the reactor to form a carbon coating layer on the surface of the silicon-carbon negative electrode material; Optionally, the carbon source gas includes one or more of acetylene, ethylene, propylene, methane, ethane or propane; Optionally, the second inert gas includes one or more of nitrogen, argon, helium or neon.

19. A secondary battery, comprising a negative electrode plate, wherein the negative electrode plate comprises a negative electrode current collector and a negative electrode film layer located on at least one surface of the negative electrode current collector, wherein the negative electrode film layer comprises the silicon-carbon negative electrode material according to any one of claims 1 to 10 or the silicon-carbon negative electrode material prepared by the method according to any one of claims 11 to 18.

20. An electric device comprising the secondary battery according to claim 19.

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