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

Abstract

The invention provides a silicon-carbon negative electrode material. The silicon-carbon negative electrode material comprises a porous carbon matrix and a silicon-based material existing in pores of the porous carbon matrix, wherein the volume V silicon of the silicon-based material in the unit mass of the silicon-carbon negative electrode material is 0.155 cm < 3 > / g-0. 175 cm < 3 > / g, the silicon-carbon negative electrode material internally comprises closed pores, and the volume PV closed of the closed pores in the unit mass of the silicon-carbon negative electrode material is greater than or equal to 0.250 cm < 3 > / g.

Description

Technical Field

[0001] This application relates to the technical field of lithium batteries, and particularly to a silicon-carbon negative electrode material, a preparation method thereof, a secondary battery, and an electrical device. Background Art

[0002] In recent years, with the increasingly wide application range of lithium-ion batteries, lithium-ion batteries are widely used in energy storage power systems such as hydro, thermal, wind, and solar power stations, as well as in multiple fields such as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, and aerospace. Due to the great development of lithium-ion batteries, higher requirements are also put forward for their performance.

[0003] Improving the specific capacity of electrode materials is one of the ways to improve the performance of lithium-ion batteries. Silicon-based negative electrode materials have become highly regarded lithium-ion battery negative electrode materials due to their high specific capacity. However, existing silicon-based negative electrode materials have problems such as a high volume expansion rate and a low initial Coulombic efficiency during charge and discharge processes. This greatly limits the wide use of silicon-based negative electrode materials in lithium-ion batteries. Summary of the Invention

[0004] This application is made in view of the above problems, and its purpose is to provide a silicon-carbon negative electrode material and a preparation method thereof. The negative electrode material has a small specific surface area and a low volume expansion rate, thereby improving the initial Coulombic efficiency of the material while having excellent cycle performance. Another purpose of this application is to provide a secondary battery and an electrical device including the negative electrode material.

[0005] To achieve the above purpose, a first aspect of this application provides a silicon-carbon negative electrode material, including 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 in the silicon-carbon negative electrode material per unit mass 硅 is 0.155 cm 3 / g to 0.175 cm 3 / g, the silicon-carbon negative electrode material includes closed pores inside, and the volume PV of the closed pores in the silicon-carbon negative electrode material per unit mass 闭 is greater than or equal to 0.250 cm 3 / g. Thus, while the silicon-carbon negative electrode material contains a certain volume of silicon-based material, it also has an appropriate amount of closed pore expansion space reserved for the expansion of the silicon-based material. Therefore, the negative electrode material has a small specific surface area and a low volume expansion rate, thereby improving the initial Coulombic efficiency of the material while having excellent cycle performance.

[0006] In some embodiments, the volume V of the silicon-based material in the silicon-carbon negative electrode material per unit mass 硅 is 0.159 cm 3 / g to 0.172 cm3 / g; and / or, the volume PV of closed pores in the silicon-carbon negative electrode material per unit mass 闭 is 0.253 cm 3 / g to 0.300 cm 3 / g.

[0007] In some embodiments, the open pore volume PV of the silicon-carbon negative electrode material 开 is 0.008 cm 3 / g to 0.040 cm 3 / g. Thus, the open pore volume of the silicon-carbon negative electrode material is small, resulting in a small contact area between the negative electrode material and the electrolyte, which is beneficial to improving the first Coulombic efficiency of the material.

[0008] In some embodiments, the porous carbon matrix includes mesopores, and the proportion of the mesopores in the total pore volume of the porous carbon matrix is 40% to 75%. By controlling the proportion of the pore volume of the mesopores within this range, it is beneficial to form an appropriate amount of closed pore expansion space.

[0009] In some embodiments, the total pore volume of the porous carbon matrix is 0.5 cm 3 / g to 1.02 cm 3 / g. Thus, there is more space in the porous carbon matrix to accommodate silicon grains and space reserved for the expansion of the silicon-based material, and at the same time, the porous carbon matrix has sufficient strength.

[0010] In some embodiments, relative to the total weight of the silicon-carbon negative electrode material, the content C of the silicon-based material 硅 is 36 wt% to 40 wt%; and / or, the content C of the porous carbon matrix 碳 is 50 wt% to 57 wt%.

[0011] 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. Thus, the silicon crystal clusters formed by the silicon grains can block the entrances of the irregular pores in the porous carbon matrix, which is beneficial to the silicon crystal clusters and the blocked pores together forming closed pore pores.

[0012] In some embodiments, the silicon-carbon negative electrode material includes one or more of the following characteristics:

[0013] The true density of the silicon-carbon negative electrode material is 1.8 g / cm 3 to 2.3 g / cm 3 ;

[0014] The tapped density of the silicon-carbon negative electrode material is 0.4 g / cm 3 to 0.9 g / cm3 ;

[0015] The specific surface area of the silicon-carbon negative electrode material is 2.5 m 2 / g to 12 m 2 / g;

[0016] The specific surface area of the porous carbon matrix is 1000 m 2 / g to 1800 m 2 / g.

[0017] In some embodiments, the silicon-carbon negative electrode material further includes a carbon coating layer. This carbon coating layer can improve the conductivity of the silicon-based material and also isolate the electrolyte from contacting the silicon-based material, reducing the occurrence of side reactions.

[0018] The second aspect of the present application provides a method for preparing a silicon-carbon negative electrode material, the method comprising:

[0019] Providing a porous carbon matrix, the porous carbon matrix includes mesopores, and the proportion of the mesopores in the total pore volume of the porous carbon matrix is less than or equal to 75%;

[0020] Placing the porous carbon matrix in a reactor;

[0021] Introducing a first mixed gas including a silicon source gas and a first inert gas into the reactor, the partial pressure of the silicon source gas is greater than or equal to 0.3, wherein, calculated by the mass of silicon element, the mass ratio of the introduced silicon source gas to the porous carbon matrix is less than or equal to 0.95; [[ID=3,2]]

[0022] Adjusting the gas hourly space velocity of the first mixed gas to be less than or equal to 1200 L / kg, and under this condition, depositing a silicon-based material in the pores of the porous carbon matrix, thereby obtaining the silicon-carbon negative electrode material,

[0023] 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 to 0.175 cm 3 / g, the silicon-carbon negative electrode material internally 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.

[0024] By controlling the proportion of the mesoporous pore volume 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-based material with a certain content and a silicon-carbon negative electrode material with an appropriate amount of closed-pore expansion space are prepared. This material has a small specific surface area and a low volume expansion rate, thereby improving the first Coulombic efficiency of the material while having excellent cycling performance.

[0025] In some embodiments, the proportion of the mesopores in the total pore volume of the porous carbon matrix is 40% to 75%.

[0026] In some embodiments, in the first mixed gas, the partial pressure of the silicon source gas is 0.3 to 0.7.

[0027] In some embodiments, the mass ratio of the introduced silicon source gas to the porous carbon matrix is 0.78 to 0.95.

[0028] In some embodiments, the gas hourly space velocity of the first mixed gas is adjusted to 500 L / kg to 1200 L / kg.

[0029] In some embodiments, the total pore volume of the porous carbon matrix is 0.5 cm 3 / g to 1.02 cm 3 / g; and / or, the specific surface area of the porous carbon matrix is 1000 m 2 / g to 1800 m 2 / g.

[0030] In some embodiments, the method satisfies one or more of the following conditions (1)-(4):

[0031] (1) Under a pressure of 1 kPa to 5 kPa, deposit the silicon-based material in the pores of the porous carbon matrix;

[0032] (2) The deposition time of the silicon-based material is 5 h to 12 h;

[0033] (3) The silicon source gas includes one or more of silane, disilane, trisilane, dichlorosilane, trichlorosilane, or tetrachlorosilane;

[0034] (4) The first inert gas includes one or more of nitrogen, argon, helium, or neon.

[0035] In some embodiments, the method further includes: after depositing the silicon-based material, introducing a second mixed gas including 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.

[0036] Optionally, the carbon source gas includes one or more of acetylene, ethylene, propylene, methane, ethane, or propane.

[0037] Optionally, the second inert gas includes one or more of nitrogen, argon, helium, or neon.

[0038] The third aspect of the present application provides a secondary battery, including a negative electrode plate, where the negative electrode plate includes a negative electrode current collector and a negative electrode film layer located on at least one surface of the negative electrode current collector; the negative electrode film layer includes the silicon-carbon negative electrode material of the first aspect of the present application or the silicon-carbon negative electrode material prepared by the method according to the second aspect of the present application.

[0039] The fourth aspect of the present application provides an electrical device, including the secondary battery of the third aspect of the present application.

[0040] In the silicon-carbon negative electrode material in the embodiments of the present application, an appropriate amount of closed pore space for silicon expansion is reserved inside, so the negative electrode material has a smaller specific surface area and a lower volume expansion rate, thereby having excellent cycle performance while improving the first Coulomb efficiency of the material. Description of the Drawings

[0041] Figure 1 Shows a schematic structural diagram of a porous carbon matrix without deposited 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 an embodiment of the present application.

[0042] Figure 2 Is a schematic diagram of a battery cell in an embodiment of the present application.

[0043] Figure 3 Is Figure 2 The exploded view of the battery cell in an embodiment of the present application shown.

[0044] Figure 4 Is a schematic diagram of a battery module in an embodiment of the present application.

[0045] Figure 5 Is a schematic diagram of a battery pack in an embodiment of the present application.

[0046] Figure 6 Is Figure 5 The exploded view of the battery pack in an embodiment of the present application shown.

[0047] Figure 7 Is a schematic diagram of an electrical device using the secondary battery in an embodiment of the present application as a power source.

[0048] Description of the Reference Numerals:

[0049] 1 Battery pack; 2 Upper box body; 3 Lower box body; 4 Battery module; 5 Battery cell; 51 Shell; 52 Electrode assembly; 53 Top cover assembly Detailed implementation manners

[0050] Hereinafter, embodiments of the silicon-carbon negative electrode material, its preparation method, secondary battery, and electrical device of the present application will be specifically described in detail with reference to the accompanying drawings as appropriate. However, there may be cases where unnecessary details are omitted. For example, there may be cases where details of well-known matters are omitted and repeated descriptions of actually identical 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 accompanying drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter recited in the claims.

[0051] The "range" disclosed in the present application is defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a particular range. The ranges defined in this way can include the end values or not include the end values, and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60 - 120 and 80 - 110 are listed for a specific parameter, ranges of 60 - 110 and 80 - 120 are also contemplated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, then the following ranges are all contemplated: 1 - 3, 1 - 4, 1 - 5, 2 - 3, 2 - 4, and 2 - 5. In the present application, unless otherwise specified, the numerical range "a - b" represents an abbreviated representation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0 - 5" means that all real numbers between "0 - 5" have been fully listed herein, and "0 - 5" is only an abbreviated representation of these numerical combinations. Additionally, when it is stated that a certain parameter is an integer ≥2, it is equivalent to disclosing that the parameter is, for example, the integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0052] If there is no special instruction, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0053] If there is no special instruction, all technical features and optional technical features of the present application can be combined with each other to form a new technical solution.

[0054] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0055] Unless otherwise specified, the terms used in this application have the common meanings generally understood by those skilled in the art.

[0056] Unless otherwise specified, the values of the parameters mentioned in this application 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 this application.

[0057] Unless otherwise specified, in this application, 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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] Based on this, the present application proposes a silicon-carbon negative electrode material and a preparation method thereof, a secondary battery, and an electrical device. The present application and optional implementation methods are described in more detail below.

[0062] [Silicon-carbon anode material]

[0063] The first aspect of the present application proposes 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 0.155cm3 / g to 0.175 cm 3 / g, and the silicon-carbon negative electrode material includes closed pores inside, and the volume of the closed pores in the silicon-carbon negative electrode material per unit mass is greater than or equal to 0.250 cm 3 / g.

[0064] The volume V of the silicon-based material in the silicon-carbon negative electrode material per unit mass 硅 is calculated by the following formula (I):

[0065] V 硅 = C 硅 ÷ ρ 硅 (I)

[0066] In formula (I), C 硅 represents the content of the silicon-based material relative to the total weight of the silicon-carbon negative electrode material. For example, relative to the total weight of the silicon-carbon negative electrode material, the content of the silicon-based material is 40%, then C 硅 is equal to 40%. The content of the silicon-based material can be measured by methods well known in the art, such as inductively coupled plasma emission spectrometry.

[0067] 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. As is well known to those skilled in the art, the density of amorphous silicon or crystalline silicon is 2.33 g / cm 3 .

[0068] "C 硅 ÷ ρ 硅 " represents the volume of the silicon-based material present in the pores of the porous carbon matrix in the silicon-carbon negative electrode material per unit mass, corresponding to the volume V of the silicon-based material in the silicon-carbon negative electrode material per unit mass 硅 .

[0069] The silicon-carbon negative electrode material includes closed pores inside. Closed pores are closed pores existing inside the silicon-carbon negative electrode material that cannot be measured for their pore volume and specific surface area by the nitrogen adsorption method. The volume PV of the closed pores in the silicon-carbon negative electrode material 闭 can be calculated by the following formula (II):

[0070] PV 闭 = (C 碳 × PV 总 ) - PV 开 - V 硅 (II)

[0071] 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 the nitrogen adsorption method, and its unit is cm 3 / g.

[0072] “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 is equal to 55%. The content of the porous carbon matrix can be measured by methods well-known in the art, such as by testing with a carbon-sulfur analyzer.

[0073] “C 碳 ×PV 总 ” represents the total pore volume provided by the porous carbon matrix without deposited silicon-based material in the silicon-carbon negative electrode material per unit mass.

[0074] “PV 开 ” represents the pore volume of the open pores in the silicon-carbon negative electrode material per unit mass, in cm 3 / g. The “pore volume of the open pores in the silicon-carbon negative electrode material” refers to the pore volume that can be measured using the nitrogen adsorption method. Using this method, only the pore volume of the pores into which nitrogen can pass can be measured, and the pore volume of the pores into which nitrogen cannot pass cannot be measured. The pores that can be measured by the nitrogen adsorption method are referred to as open pores in this article. The pores that cannot be measured by the nitrogen adsorption method are referred to as closed pores in this article. In the silicon-carbon negative electrode material of the embodiments of the present application, there is a pore volume of closed pores that cannot be measured by the nitrogen adsorption method. Here, “PV 开 ” does not include the pore volume of the closed pores that cannot be measured by the nitrogen adsorption method.

[0075] V 硅 represents the volume of the silicon-based material in the silicon-carbon negative electrode material per unit mass, in cm 3 / g. As described above, V 硅 can be obtained through Equation (I).

[0076] In the silicon-carbon negative electrode material, a part of the pores in the porous carbon matrix is occupied by the deposited silicon-based material, and a part is blocked by the deposited silicon-based material during the deposition of the silicon-based material, thereby forming “closed pores”. The remaining pores in the porous carbon matrix form the open pore structure of the silicon-carbon negative electrode material, which can be measured using the nitrogen adsorption method.

[0077] Therefore, the volume of the closed pores PV 闭 in the silicon-carbon negative electrode material per unit mass 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 Equation (II) above.

[0078] Figure 1Schematically shown are the structural diagram of a porous carbon matrix without deposited silicon-based material in an embodiment of the present application (left figure) and the structural diagram of a silicon-carbon negative electrode material formed after depositing a silicon-based material in the porous carbon matrix (right figure). In Figure 1 In the left figure, the total pore volume of the porous carbon matrix used to form the negative electrode silicon-carbon negative electrode material is denoted as "PV 总 ". In Figure 1 In the right figure, the pore volume of the closed pores in the negative electrode silicon-carbon material per unit mass is denoted as PV 闭 , the pore volume of the open pores is denoted as PV 开 , and the volume occupied by the silicon-based material is denoted as V 硅 . As shown in Figure 1 , after depositing the silicon-based material, the pores of the porous carbon matrix are divided into three parts. One part is the closed pore pores that are not connected to the outside, and this part of the pores cannot be measured by the nitrogen adsorption method; one part is the volume V 硅 occupied by the deposited silicon-based material, and this part can be obtained by calculating the content and density of the silicon-based material; the remaining part is the open pore pores that are connected to the outside, and this part of the pores can be measured by the nitrogen adsorption method. Therefore, for the silicon-carbon negative electrode material per unit mass, the volume PV 闭 of the closed pores inside it can be obtained by subtracting the volume occupied by the silicon-based material and the volume PV 开 of the open pores from the pore volume of the porous carbon matrix.

[0079] In the silicon-carbon negative electrode material of the embodiment of the present application, for the silicon-based material with a volume of 0.155 cm 3 / g to 0.175 cm 3 / g, there is a closed pore volume of greater than or equal to 0.250 cm 3 / g. Thus, an appropriate closed pore expansion space is provided for the silicon-based material existing in the pores of the porous carbon matrix. Therefore, for the silicon-carbon negative electrode material containing a certain content of silicon-based material, the silicon-carbon negative electrode material of the embodiment of the present application has a smaller specific surface area and a lower volume expansion rate, thereby having excellent cycle performance while improving the first Coulomb efficiency of the material.

[0080] In the present application, the terms "pore volume", "hole volume", "volume of the hole", "volume of the pore" have the same meaning and can be used interchangeably.

[0081] In some embodiments, the volume V 硅 of the silicon-based material in the silicon-carbon negative electrode material per unit mass can be 0.155 cm 3 / g to 0.175 cm 3 / g, optionally 0.159 cm 3 / g to 0.172 cm 3 / g. For example, V硅 It can be 0.155 cm 3 / g, 0.159 cm 3 / g, 0.160 cm 3 / g, 0.163 cm 3 / g, 0.165 cm 3 / g, 0.167 cm 3 / g, 0.170 cm 3 / g, and 0.172 cm 3 / g, 0.175 cm 3 / g or a value between any two numerical values, but not limited to this.

[0082] In some embodiments, the volume PV of the closed pores in the silicon-carbon negative electrode material per unit mass 闭 It can be 0.253 cm 3 / g to 0.350 cm 3 / g, 0.253 cm 3 / g to 0.300 cm 3 / g, 0.255 cm 3 / g to 0.300 cm 3 / g. For example, PV 闭 It can be 0.253 cm 3 / g, 0.255 cm 3 / g, 0.260 cm 3 / g, 0.265 cm 3 / g, 0.266 cm 3 / g, 0.270 cm 3 / g, 0.274 cm 3 / g, 0.275 cm 3 / g, 0.280 cm 3 / g, 0.285 cm 3 / g, 0.287 cm 3 / g, 0.290 cm 3 / g, 0.295 cm 3 / g, 0.300 cm 3 / g, 0.349 cm 3 / g, 0.350 cm 3 / g or a value between any two numerical values, but not limited to this.

[0083] In some embodiments, the open pore volume PV of the silicon-carbon negative electrode material 开 It can be 0.008 cm 3 / g to 0.040 cm 3 / g, optionally 0.022 cm 3 / g to 0.038 cm 3 / g. For example, the open pore volume of the silicon-carbon negative electrode material can be 0.008 cm 3 / g, 0.009 cm 3 / g, 0.01 cm 3 / g, 0.015 cm 3 / g, 0.016 cm 3 / g, 0.017 cm 3 / g, 0.019 cm 3 / g, 0.02 cm 3 / g, 0.022 cm 3 / g, 0.025 cm 3 / g, 0.026 cm 3 / g, 0.03 cm 3 / g, 0.031 cm 3 / g, 0.034 cm 3 / g, 0.035 cm 3 / g, 0.038 cm 3 / g, 0.039 cm 3 / g, 0.040 cm 3 / g or a value within the range formed by any two values, but not limited to this.

[0084] The open pore volume of the silicon-carbon negative electrode material refers to the pore volume that can be measured using the nitrogen adsorption method. Using the nitrogen adsorption method, only the pore volume of the open pores through which nitrogen can pass can be measured, and the pore volume of the closed pores through which nitrogen cannot pass cannot be measured.

[0085] During the first charging process of the battery, a solid electrolyte interface film (SEI film) will form at the interface between the negative electrode material and the electrolyte. The formation of the SEI film will consume a part of the lithium ions, and the lithium ions will become inactivated lithium ions after participating in the SEI film formation reaction. The larger the contact area between the negative electrode material and the electrolyte, the larger the area of the formed SEI film, and the more inactivated lithium ions, resulting in a decrease in the first Coulombic efficiency of the battery. In the embodiments of the present application, the open pore volume of the silicon-carbon negative electrode material is small, so that the contact area between the negative electrode material and the electrolyte is also small, which is beneficial to improving the first Coulombic efficiency of the material.

[0086] By controlling the open pore volume of the silicon-carbon negative electrode material within the above range, on the one hand, an appropriate open pore expansion space can be provided 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, and it will not consume more Li to form a solid electrolyte film due to the too large contact area between the negative electrode material and the electrolyte, affecting the first Coulombic efficiency.

[0087] 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 can be 3 nm, 4 nm, 5 nm, or 6 nm, but is not limited thereto.

[0088] The size D of the silicon grains can be calculated by the Scherrer formula. The Scherrer formula can be expressed as D = 0.89λ / βcosθ, where λ is the wavelength of the X-ray, 0.154056 nm, β is the full width at half maximum of the diffraction peak, generally the first peak of silicon (about 28.6°), and θ is the diffraction angle. In the silicon-carbon anode material of the embodiments of the present application, the silicon grain size is relatively large. Referring to Figure 1 it can be seen that the silicon crystal clusters with a relatively large grain size block the entrances of the irregular pores of the porous carbon matrix, and the silicon crystal clusters and the pores blocked by them together form closed pores. On the one hand, this increases the number of closed pores in the material, and on the other hand, it reduces the specific surface area of the anode material, thereby providing an appropriate amount of closed pore space for the expansion of the silicon-based material and reducing the contact area between the anode material and the electrolyte. This is beneficial to reducing the volume expansion rate of the anode material and improving the first Coulomb efficiency of the anode material.

[0089] In some embodiments, the true density of the silicon-carbon anode material can be 1.8 g / cm 3 ~2.3 g / cm 3 , optionally 1.99 g / cm 3 ~2.2 g / cm 3 , optionally 2.0 g / cm 3 ~2.2 g / cm 3 . For example, the true density of the silicon-carbon anode material can be 1.8 g / cm 3 , 1.9 g / cm 3 , 2.0 g / cm 3 , 2.01 g / cm 3 , 2.02 g / cm 3 , 2.03 g / cm 3 , 2.1 g / cm 3 , 2.2 g / cm 3 , 2.3 g / cm 3 or a value between any two numerical values, but is not limited thereto.

[0090] The true density has the meaning well known in the art and can be tested by instruments and methods known in the art. For example, it can be tested by referring to the method described in GB / T 24586-2009.

[0091] In some embodiments, the tapped density of the silicon-carbon anode material can be 0.4 g / cm3 ~0.9g / cm 3 , optionally 0.5g / cm 3 ~0.71g / cm 3 For example, the tap density of the 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.

[0092] Tap density is a well-known term in the art and can be measured using instruments and methods known in the art, for example, as described in GB / T 5162-2006.

[0093] 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 the 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.

[0094] The specific surface area of the silicon-carbon negative electrode material refers to the surface area of the open pores that can be measured by the nitrogen adsorption method. The surface area inside the closed pores of the silicon-carbon negative electrode material cannot be measured by the nitrogen adsorption method.

[0095] In these embodiments, the silicon-carbon negative electrode material has a relatively small specific surface area. The relatively small specific surface area indicates that there are fewer open pores in the silicon-carbon negative electrode material. Although the mechanism is not yet clear, it is found in this application that the silicon-based material exists as relatively large silicon clusters in the porous carbon matrix. These relatively large silicon clusters block the entrances of the irregular pores in the porous carbon matrix, rather than depositing at the bottom of the pores through the entrances of these irregular pores. Therefore, the silicon-carbon negative electrode material has a relatively small specific surface area while having an appropriate amount of closed pores. Figure 1 The right figure shows a schematic structural diagram of the silicon-carbon negative electrode material formed after depositing silicon in the porous carbon matrix. Refer to Figure 1 , it can be seen that the silicon clusters with relatively large grain sizes block the entrances of the irregular pores in the porous carbon matrix, and the silicon clusters and the pores they block together form closed pores. Thus, on the one hand, the number of closed pores of the material is increased, and on the other hand, the specific surface area of the material is reduced.

[0096] During the first charging process of the battery, a solid electrolyte interface film (SEI film) will be formed at the interface between the negative electrode material and the electrolyte. The formation of the SEI film will consume a part of the lithium ions, and the lithium ions become inactivated lithium ions after participating in the SEI film formation reaction. The larger the contact area between the negative electrode material and the electrolyte, the larger the area of the formed SEI film, and the more inactivated lithium ions, resulting in a decrease in the first Coulomb efficiency of the material. In the embodiments of this application, the specific surface area of the silicon-carbon negative electrode material is relatively small, so that the contact area between the negative electrode material and the electrolyte is also relatively small, which is beneficial to improving the first Coulomb efficiency of the material.

[0097] 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 proportion of the mesopores in the total pore volume of the porous carbon matrix is 40% - 75%, optionally 50% - 75%, optionally 60% - 75%.

[0098] 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 not limited to this. 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.

[0099] Generally speaking, the activation pore-forming process of porous carbon can only regulate the open pores, wherein the closed pores 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 embodiment of the present application are all closed pores formed during the silicon deposition process, and therefore, the closed pore volume is controllably formed by 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 an effect of a lower volume expansion rate of the silicon-carbon negative electrode material containing a certain content of silicon-based material.

[0100] In some embodiments, the proportion of the micropores in the total pore volume of the porous carbon matrix may be 15% to 50%. For example, the proportion of micropores in the total pore volume of the porous carbon matrix may 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.

[0101] In some embodiments, the proportion of the macropores in the total pore volume of the porous carbon matrix may be 1% to 10%. For example, the proportion of the macropores in the total pore volume of the porous carbon matrix may be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or a value between any two values, but not limited thereto. The proportion of the macropores in the total pore volume of the porous carbon matrix refers to the percentage of the macropore volume relative to the total pore volume of the porous carbon matrix. Optionally, the proportion of the macropores in the total pore volume of the porous carbon matrix is relatively low.

[0102] In some embodiments, the total pore volume of the porous carbon matrix is 0.5 cm 3 / g to 1.02 cm 3 / g, optionally 0.78 cm 3 / g to 0.89 cm 3 / g, optionally 0.78 cm 3 / g to 0.85 cm 3 / g. For example, the total pore volume of the porous carbon matrix may be 0.5 cm 3 / g, 0.6 cm 3 / g, 0.7 cm 3 / g, 0.8 cm 3 / g, 0.84 cm 3 / g, 0.89 cm 3 / g, 0.9 cm 3 / g, 0.92 cm 3 / g, 1.0 cm 3 / g, 1.02 cm 3 / g or a value between any two values, but not limited thereto.

[0103] 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 0.78 cm 3 / g, whereby there is more space in the porous carbon matrix to accommodate silicon clusters and space reserved for the expansion of the silicon-based material. The pore volume of the porous carbon matrix is less than or equal to 1.02 cm 3 / g, optionally less than or equal to 0.89 cm 3 / g, whereby the porous carbon matrix has sufficient strength and the negative electrode material will not break during the subsequent preparation process of the full cell, resulting in silicon dissolution.

[0104] In some embodiments, the specific surface area of the porous carbon matrix may be 1000 m 2 / g to 1800 m 2 / g, optionally 1200 m 2 / g to 1500 m 2 / g, optionally 1200 m 2 / g to 1400 m 2 / g. For example, the specific surface area of the porous carbon matrix can be 1000 m 2 / g, 1100 m 2 / g, 1200 m 2 / g, 1300 m 2 / g, 1310 m 2 / g, 1400 m 2 / g, 1423 m 2 / g, 1454 m 2 / g, 1500 m 2 / g, 1600 m 2 / g, 1700 m 2 / g, 1800 m 2 / g or values between any two numerical values, but not limited thereto.

[0105] 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 1800 m 2 / g, optionally less than or equal to 1500 m 2 / g, optionally less than or equal to 1400 m 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 1000 m 2 / g, optionally greater than or equal to 1200 m 2 / g, whereby there is more space in the porous carbon matrix to accommodate silicon clusters and space reserved for the expansion of the silicon-based material.

[0106] In some embodiments, relative to the total weight of the silicon-carbon negative electrode material, the content C of the silicon-based material 硅 can be 36 wt% to 41 wt%, optionally 36 wt% to 40 wt%; and / or, the content C of the porous carbon matrix 碳 can be 50 wt% to 57 wt%. For example, the content of the porous carbon matrix can be obtained by testing with a carbon-sulfur analyzer. For example, after surface passivation of the porous carbon matrix deposited with the silicon-based material, the carbon element content therein is tested with a carbon-sulfur analyzer, whereby the content of the porous carbon matrix is measured.

[0107] In some embodiments, the silicon-carbon negative electrode material further includes a carbon coating layer. This carbon coating layer can improve the electrical conductivity of the silicon-based material. In addition, the carbon coating layer can also isolate the electrolyte from contacting the silicon-based material, reduce the occurrence of side reactions, and is beneficial to the formation of a stable and uniform solid electrolyte interface film.

[0108] In some embodiments, relative to the total weight of the silicon-carbon negative electrode material, the content of the carbon coating layer can be 2 wt% to 5 wt%. For example, relative to the total weight of the silicon-carbon negative electrode material, the content of the carbon coating layer can be 2 wt%, 3 wt%, 4 wt%, 5 wt% or a value within the range composed of any two values, but not limited thereto. By controlling the content of the carbon coating layer within the above range, it is beneficial to form a complete carbon coating layer, thereby being able to better isolate the electrolyte and at the same time not having an adverse effect on the capacity of the silicon-carbon negative electrode material.

[0109] The content of the carbon coating layer can be measured by a carbon-sulfur analyzer, for example. For example, the content of carbon element in the silicon-carbon negative electrode material is measured by a carbon-sulfur analyzer, 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. Combining the content of the porous carbon matrix obtained by the above-mentioned test, the content of the carbon coating layer can be obtained through calculation.

[0110] [Method for preparing silicon-carbon negative electrode material]

[0111] The second aspect of the present application provides a method for preparing a silicon-carbon negative electrode material. The method includes:

[0112] Providing a porous carbon matrix, the porous carbon matrix includes mesopores, and the proportion of the mesopores in the total pore volume of the porous carbon matrix is less than or equal to 75%;

[0113] Placing the porous carbon matrix in a reactor;

[0114] Introducing a first mixed gas including a silicon source gas and a first inert gas into the reactor, the partial pressure of the silicon source gas is greater than or equal to 0.3, wherein, based on the mass of silicon element, the mass ratio M of the introduced silicon source gas to the porous carbon matrix Si / M C is less than or equal to 0.95;

[0115] Adjusting the gas hourly space velocity of the first mixed gas to be less than or equal to 1200 L / kg, and depositing a silicon-based material in the pores of the porous carbon matrix under this condition, thereby obtaining the silicon-carbon negative electrode material,

[0116] 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 in the silicon-carbon negative electrode material per unit mass is 0.155 cm3 / g to 0.175 cm 3 / g, and the silicon-carbon anode material includes closed pores inside, and the volume of the closed pores in the silicon-carbon anode material per unit mass is greater than or equal to 0.250 cm 3 / g.

[0117] Although the mechanism is not yet clear, it is found in this application that by selecting the proportion of the mesopore 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 crystal clusters with larger grain sizes. The silicon crystal clusters with larger grain sizes block the entrances of the irregular pores of the porous carbon matrix, and the silicon crystal clusters and the pores they block together form closed pore spaces. Thus, an appropriate amount of closed pore expansion space is reserved for the expansion of the silicon-based material, achieving the effect that for the silicon-carbon anode material containing a certain content of silicon-based material, the volume expansion rate of the silicon-carbon anode material is lower.

[0118] "Gas hourly space velocity" has the meaning well known in the art and can be measured by instruments and methods known in the art. For example, a mass flow meter is used to control the volume of gas passing through per unit time, and the gas hourly space velocity = the volume (L) of the first mixed gas passing through the porous carbon matrix within 1 hour / the mass (kg) of the porous carbon matrix.

[0119] 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, 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 value between any two values, but not limited thereto.

[0120] 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 then adjusting according to the test result. If the test result is greater than 1200 L / kg, the gas hourly space velocity of the first mixed gas is reduced.

[0121] 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 according to the test result. If the test result is less than 500 L / kg, the gas hourly space velocity of the first mixed gas is increased; if the test result is greater than 1200 L / kg, the gas hourly space velocity of the first mixed gas is reduced.

[0122] In the above method, based on the mass of silicon element in the silicon source gas, the mass ratio of the introduced silicon source gas to the porous carbon matrix may be 0.78 to 0.95, optionally 0.80 to 0.93, and optionally 0.80 to 0.86. For example, it may be 0.78, 0.80, 0.82, 0.84, 0.86, 0.88, 0.90, 0.92, 0.93, 0.95 or a value between any two numerical values, but not limited thereto.

[0123] The "partial pressure of the gas" has the meaning well-known in the art, which refers to the pressure ratio of a certain component gas in the mixed gas and can be measured by instruments and methods known in the art. For example, by controlling the flow rates of the component gas and the carrier gas introduced into the reactor per unit time, the partial pressure of the component gas can be regulated. The measurement and control of the flow rate can be performed using a mass flow meter (for example, model Alicat DODA). The partial pressure of the gas is related to the volume concentration of this component gas in the mixed gas. For example, when the volume concentration of a certain component gas in the mixed gas is 50%, the partial pressure of this component gas can be calculated as 0.5 according to the ideal gas state equation.

[0124] 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 any two numerical values, but not limited thereto. The partial pressure of the silicon source gas affects the deposition mode of the silicon source gas. In the case of a higher partial pressure, the self-nucleation deposition mode is mainly adopted. In the case of a lower partial pressure, the chemical growth deposition mode is mainly adopted, thereby affecting the silicon grain size and the size of the silicon crystal clusters. By controlling the partial pressure of the silicon source gas within the above range, the deposition mode is mainly self-nucleation deposition, which is beneficial to the formation of silicon grains of the required size, and then the closed pore volume can be controllably formed.

[0125] 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 proportion of the mesopores in the total pore volume of the porous carbon matrix may be 40% to 75%, optionally 50% to 75%, and optionally 60% to 75%.

[0126] 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 not limited to this. 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.

[0127] Generally speaking, the activation pore-forming process of porous carbon can only regulate the open pores, wherein the closed pores 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 embodiment of the present application are all closed pores formed during the silicon deposition process, and therefore, the closed pore volume is controllably formed by 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 an effect of a lower volume expansion rate of the silicon-carbon negative electrode material containing a certain content of silicon-based material.

[0128] In some embodiments, the proportion of the micropores in the total pore volume of the porous carbon matrix may be 15% to 50%. For example, the proportion of micropores in the total pore volume of the porous carbon matrix may 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.

[0129] In some embodiments, the proportion of the macropores in the total pore volume of the porous carbon matrix can be 1% to 10%. For example, the proportion of the 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 any two values, but not limited thereto. The proportion of the macropores in the total pore volume of the porous carbon matrix refers to the percentage of the macropore volume relative to the total pore volume of the porous carbon matrix. Optionally, the proportion of the macropores in the total pore volume of the porous carbon matrix is relatively low.

[0130] In some embodiments, the total pore volume of the porous carbon matrix is 0.5 cm 3 / g to 1.02 cm 3 / g, optionally 0.78 cm 3 / g to 0.89 cm 3 / g, optionally 0.78 cm 3 / g to 0.85 cm 3 / g. For example, the total pore volume of the porous carbon matrix can be 0.5 cm 3 / g, 0.6 cm 3 / g, 0.7 cm 3 / g, 0.8 cm 3 / g, 0.84 cm 3 / g, 0.89 cm 3 / g, 0.9 cm 3 / g, 0.92 cm 3 / g, 1.0 cm 3 / g, 1.02 cm 3 / g or a value between any two values, but not limited thereto.

[0131] 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 0.78 cm 3 / g, whereby there is more space in the porous carbon matrix to accommodate silicon clusters and space reserved for the expansion of the silicon-based material. The pore volume of the porous carbon matrix is less than or equal to 1.02 cm 3 / g, optionally less than or equal to 0.89 cm 3 / g, whereby the porous carbon matrix has sufficient strength and the negative electrode material will not break during the subsequent preparation process of the full cell, resulting in silicon dissolution.

[0132] In some embodiments, the specific surface area of the porous carbon matrix can be 1000 m 2 / g to 1800 m 2 / g, optionally 1200 m 2 / g to 1500 m 2 / g, optionally 1200 m 2 / g to 1400 m 2 / g. For example, the specific surface area of the porous carbon matrix can be 1000 m 2 / g, 1100 m 2 / g, 1200 m 2 / g, 1300 m 2 / g, 1310 m 2 / g, 1400 m 2 / g, 1423 m 2 / g, 1454 m 2 / g, 1500 m 2 / g, 1600 m 2 / g, 1700 m 2 / g, 1800 m 2 / g or a value between any two numerical values, but not limited thereto.

[0133] 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 1800 m 2 / g, optionally less than or equal to 1500 m 2 / g, optionally less than or equal to 1400 m 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 1000 m 2 / g, optionally greater than or equal to 1200 m 2 / g, whereby there is more space in the porous carbon matrix to accommodate silicon clusters and space reserved for the expansion of the silicon-based material.

[0134] In some embodiments, the silicon-based material can be deposited in the pores of the porous carbon matrix at a pressure of 1 kPa to 5 kPa. For example, the silicon-based material can be deposited in the pores of the porous carbon matrix at a pressure of 1 kPa to 2 kPa, but not limited thereto.

[0135] In some embodiments, the deposition time of the silicon-based material can be 5 h to 12 h. For example, the deposition time of the silicon-based material can be 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, 11 h, 12 h or a value between any two numerical values, but not limited thereto. The deposition time of the silicon-based material refers to the duration from the start of introducing the silicon source gas to the stop of introducing the silicon source gas.

[0136] 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 silane, disilane, trisilane, dichlorosilane, trichlorosilane, or tetrachlorosilane. Optionally, the silicon source gas may include or be silane.

[0137] 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.

[0138] In some embodiments, the silicon-based material may 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 may 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 value between any two values.

[0139] In some embodiments, the method further includes: after depositing the silicon-based material, introducing a second mixed gas including 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. Thus, a carbon coating layer can be formed on the porous carbon matrix deposited with the silicon-based material. The carbon coating layer can improve the conductivity of the silicon-based material. In addition, the carbon coating layer can also isolate the electrolyte from contacting the silicon-based material, reduce the occurrence of side reactions, and facilitate the formation of a stable and uniform solid electrolyte interface membrane.

[0140] 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.

[0141] In some embodiments, the gas hourly space velocity of the second mixed gas is adjusted to 100 L / kg to 300 L / kg, optionally 200 L / kg to 260 L / kg, and under this condition, carbon is coated on the porous carbon matrix with silicon-based material deposited in the pores. The gas hourly space velocity of the second mixed gas can be adjusted to 100 L / kg, 150 L / kg, 200 L / kg, 250 L / kg, 300 L / kg, or a value between any two values, but 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 ranges, it is beneficial to form a complete carbon coating layer, which can better isolate the electrolyte and at the same time will not have an adverse effect on the capacity of the silicon-carbon negative electrode material.

[0142] In some embodiments, the step of carbon coating may be carried out at a temperature of 580°C to 800°C, optionally 650°C to 750°C, but not limited thereto.

[0143] In some embodiments, the step of carbon coating may be carried out at a pressure of 100 Pa to 2000 Pa, optionally 200 Pa to 500 Pa, but not limited thereto.

[0144] In some embodiments, the duration of introducing the second mixed gas including the carbon source gas and the second inert gas may be 2 h to 12 h, optionally 2 h to 10 h, but not limited thereto.

[0145] Through the above steps, a uniform and dense carbon coating layer can be formed on the surface of the silicon-carbon negative electrode material. This carbon coating layer can improve the conductivity of the silicon-based material. In addition, the carbon coating layer can also isolate the contact between the electrolyte and the silicon-based material, reduce the occurrence of side reactions, and is beneficial to the formation of a stable and uniform solid electrolyte interface film.

[0146] In some embodiments, the carbon source gas may include one or more of acetylene, ethylene, propylene, methane, ethane or propane, but not limited thereto.

[0147] In some embodiments, the second inert gas may include one or more of nitrogen, argon, helium or neon, but not limited thereto.

[0148] This application also provides a silicon-carbon negative electrode material. The silicon-carbon negative electrode material is prepared by the method described in the second aspect of this application. The silicon-carbon negative electrode material has one or more of the same characteristics as the silicon-carbon negative electrode material described in the first aspect of this application and can produce the same technical effects.

[0149] In addition, the secondary battery and the electrical device of this application will be described below with appropriate reference to the drawings.

[0150] In some embodiments of this application, a secondary battery is provided.

[0151] The term "secondary battery" mentioned herein refers to a battery cell, a battery module or a battery pack. Descriptions will be given separately below.

[0152] Generally, a battery cell includes a positive electrode plate, a negative electrode plate, an electrolyte and a separator. During the charging and discharging process of the battery, active ions are embedded and extracted back and forth between the positive electrode plate and the negative electrode plate. The electrolyte plays a role in conducting ions between the positive electrode plate and the negative electrode plate. The separator is disposed between the positive electrode plate and the negative electrode plate, mainly to prevent short circuit between the positive and negative electrodes, and at the same time allows ions to pass through.

[0153] Positive electrode plate

[0154] The positive electrode tab includes a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector, and the positive electrode film layer includes a positive electrode active material.

[0155] As an example, the positive electrode current collector has two surfaces opposite to each other in its own thickness direction, and the positive electrode film layer is provided on either one or both of the two opposite surfaces of the positive electrode current collector.

[0156] In some embodiments, the positive electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, aluminum foil can be used. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (such as 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.).

[0157] In some embodiments, when the battery cell is a lithium-ion battery, the positive electrode active material can be a positive electrode active material known in the art for lithium-ion batteries. As an example, the positive electrode active material can 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 application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials can also be used. These positive electrode active materials can be used alone or in combination of two or more. Among them, examples of lithium transition metal oxides can 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 / 3Mn 1 / 3 O2 (which can also be abbreviated as NCM 333 )、LiNi 0.5 Co 0.2 Mn 0.3 O2 (which can also be abbreviated as NCM 523 )、LiNi 0.5 Co 0.25 Mn 0.25 O2 (which can also be abbreviated as NCM 211 )、LiNi 0.6 Co 0.2 Mn 0.2 O2 (which can also be abbreviated as NCM 622 )、LiNi0.8 Co 0.1 Mn 0.1 O2 (which can also be abbreviated as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.1 Al 0.05 O2), and one or more of its modified compounds, etc. Examples of olivine-structured lithium-containing phosphates may include, but are not limited to, lithium iron phosphate (such as LiFePO4 (which can also be abbreviated as LFP)), composites of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), composites of lithium manganese phosphate and carbon, lithium manganese iron phosphate, and composites of lithium manganese iron phosphate and carbon.

[0158] In some embodiments, during the charge and discharge process of the battery, the deintercalation and consumption of Li will occur, and the molar content of Li is different when the battery is discharged to different states. In the listing of the positive electrode active materials in this application, the molar content of Li is the initial state of the material, that is, the state before feeding. When the positive electrode active material is applied to the battery system, after charge and discharge cycles, the molar content of Li will change.

[0159] In the listing of the positive electrode active materials in this application, the molar content of O is only the theoretical state value. The release of oxygen from the lattice will cause the molar content of oxygen to change, and the actual molar content of O will show fluctuations.

[0160] In some embodiments, the positive electrode film layer may also optionally include a binder. As an example, the binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0161] In some embodiments, the positive electrode film layer may also optionally include a conductive agent. As an 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.

[0162] In some embodiments, the positive electrode plate can be prepared in the following manner: Disperse the components for preparing the positive electrode plate, such as the positive electrode active material, conductive agent, binder, and any other components, in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; coat the positive electrode slurry on the positive electrode current collector, and after processes such as drying and cold pressing, the positive electrode plate can be obtained.

[0163] Negative electrode plate

[0164] The negative electrode plate includes a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector. The negative electrode film layer includes the silicon-carbon negative electrode material of the first aspect of the present application or the silicon-carbon negative electrode material prepared by the method described in the second aspect of the present application as the negative electrode active material.

[0165] As an example, the negative electrode current collector has two surfaces opposite to each other in its own thickness direction, and the negative electrode film layer is provided on any one or both of the two opposite surfaces of the negative electrode current collector.

[0166] In some embodiments, the negative electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, copper foil can be used. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be formed by forming a metal material (such as copper, copper 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.).

[0167] In addition to the silicon-carbon negative electrode material of the first aspect of the present application or the silicon-carbon negative electrode material prepared by the method described in the second aspect of the present application, the negative electrode active material can also include negative electrode active materials known in the art for batteries. As an example, the negative electrode active material can 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 materials can be selected from one or more of elemental silicon, silicon oxides, silicon-carbon composites (referring to silicon-carbon composites other than the silicon-carbon negative electrode material of the present application), silicon-nitrogen composites, and silicon alloys. The tin-based materials can be selected from one or more of elemental tin, tin oxides, and tin alloys. However, the present application is not limited to these materials, and other conventional materials that can be used as battery negative electrode active materials can also be used. These negative electrode active materials can be used alone or in combination of two or more kinds.

[0168] In some embodiments, the negative electrode film layer may optionally include a binder. The binder can 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).

[0169] In some embodiments, the negative electrode film layer may optionally include a conductive agent. The conductive agent can be selected from one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0170] In some embodiments, the negative electrode film layer may also optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)), etc.

[0171] In some embodiments, the negative electrode plate can be prepared in the following manner: dispersing the components for preparing the negative electrode plate described above, such as the negative electrode active material, the conductive agent, the binder, and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry on the negative electrode current collector, and after processes such as drying and cold pressing, the negative electrode plate can be obtained.

[0172] Electrolyte

[0173] The electrolyte functions to conduct ions between the positive electrode plate and the negative electrode plate. There is no specific limitation on the type of the electrolyte in this application, and it can be selected according to requirements. For example, the electrolyte can be liquid, gel-like, or all-solid-state.

[0174] In some embodiments, the electrolyte uses an electrolytic solution. The electrolytic solution includes an electrolyte salt and a solvent.

[0175] In some embodiments, the electrolyte salt can 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 difluorooxalate borate, lithium bis(oxalato)borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0176] In some embodiments, the solvent can be selected from one or more of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl 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, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0177] In some embodiments, the electrolytic solution may also optionally include additives. For example, the additives can include negative electrode film-forming additives, positive electrode film-forming additives, and can also include additives that can improve certain battery performance, such as additives for improving the overcharge performance of the battery, additives for improving the high-temperature or low-temperature performance of the battery, etc.

[0178] Separator

[0179] In some embodiments, the battery cell also includes a separator. There is no particular limitation on the type of the separator in this application, and any well-known porous structure separator with good chemical stability and mechanical stability can be selected.

[0180] In some embodiments, the material of the separator membrane can be selected from one or more of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator membrane can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator membrane is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0181] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator membrane can be made into an electrode assembly by a winding process or a stacking process.

[0182] In some embodiments, the battery cell can include an outer package. The outer package can be used to encapsulate the above-mentioned electrode assembly and electrolyte.

[0183] In some embodiments, the outer package of the battery cell can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the battery cell can also be a soft package, such as a pouch-type soft package. The material of the soft package can be plastic. As plastics, polypropylene, polybutylene terephthalate, and polybutylene succinate can be listed, etc.

[0184] This application does not particularly limit the shape of the battery cell, and it can be cylindrical, square, or any other arbitrary shape. For example, Figure 2 is a battery cell 5 with a square structure as an example.

[0185] In some embodiments, referring to Figure 3 , the outer package can include a housing 51 and a top cover assembly 53. Among them, the housing 51 can include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose a receiving cavity. The housing 51 has an opening communicating with 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 separator membrane can form an electrode assembly 52 through a winding process or a stacking 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.

[0186] In some embodiments, the battery cells can be assembled into a battery module. The number of battery cells contained in the battery module can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0187] Figure 4 is a battery module 4 as an example. Referring to Figure 4 , in the battery module 4, a plurality of battery cells 5 can be arranged in sequence along the length direction of the battery module 4. Of course, they can also be arranged in any other arbitrary manner. Further, the plurality of battery cells 5 can be fixed by fasteners.

[0188] Optionally, the battery module 4 may further include a housing having an accommodation space, and a plurality of battery cells 5 are accommodated in the accommodation space.

[0189] In some embodiments, the above battery module may also be assembled into a battery pack. The number of battery modules included in the battery pack may be one or more, and those skilled in the art can select the specific number according to the application and capacity of the battery pack.

[0190] Figure 5 and Figure 6 is a battery pack 1 as an example. Refer to Figure 5 and Figure 6 , in the battery pack 1, a battery box and a plurality of battery modules 4 disposed in the battery box may be included. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 can cover the lower box body 3 and form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0191] In addition, the present application also provides an electrical device, and the electrical device includes the secondary battery provided by the present application. The secondary battery can be used as a power source of the electrical device or as an energy storage unit of the electrical device. The electrical device may include mobile devices (such as mobile phones, laptop computers, 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., but is not limited thereto.

[0192] As the electrical device, the secondary battery, battery module or battery pack can be selected according to its usage requirements.

[0193] Figure 7 is an electrical device as an example. The electrical device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the high power and high energy density requirements of the electrical device for the secondary battery, a battery pack or a battery module can be adopted.

[0194] Another example of the device may be a mobile phone, a tablet computer, a laptop computer, etc. This device generally requires thinning, and a battery cell can be used as a power source.

[0195] Embodiment

[0196] The embodiments of the present application will be described below. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as a limitation to the present application. For those without specific technologies or conditions noted in the embodiments, the technologies or conditions described in the literature in this field or according to the product specifications are followed. For reagents or instruments without the manufacturer noted, they are all conventional products that can be obtained through commercial purchase.

[0197] Example 1: Preparation of silicon-carbon anode material

[0198] 1) Take 2000 g of biomass porous carbon matrix and place it in a CVD deposition furnace. Heat up the temperature in the CVD deposition furnace to 550 °C at a heating rate of 5 °C / min and keep it warm for 30 min. Pass a first mixed gas including silane and nitrogen with a silane gas partial pressure of 0.33, adjust the gas hourly space velocity of the first mixed gas to 700 L / kg, and the furnace pressure is in the range of 1 kPa to 2 kPa. The gas passing time is about 9 h.

[0199] 2) After about 9 h of gas passing time, stop passing silane. Then continue to heat up the temperature in the CVD deposition furnace to 700 °C at a heating rate of 5 °C / min. Pass a second mixed gas including acetylene and nitrogen with an acetylene gas partial pressure of 0.5, adjust the gas hourly space velocity of the second mixed gas to 240 L / kg, and the furnace pressure is in the range of 200 Pa to 250 Pa. The gas passing time is about 2 h. Cool and discharge the material and sieve it through 325 meshes to obtain the target silicon-carbon anode material.

[0200] The total pore volume, macropore pore volume ratio, mesopore pore volume ratio, micropore pore volume ratio, M Si / M C , the silicon source gas partial pressure, the gas hourly space velocity of the first mixed gas and other parameters are shown in Table 1.

[0201] Examples 2 to 11

[0202] Examples 2 to 11 are the same as the steps of Example 1 except that the parameters are adjusted as shown in Table 1.

[0203] Comparative Examples 1 to 4

[0204] Comparative Examples 1 to 4 are the same as the steps of Example 1 except that the parameters are adjusted as shown in Table 1.

[0205] Performance test of silicon-carbon anode material

[0206] 1. Test of tap density

[0207] The tap density of the silicon-carbon anode materials of each example and comparative example was measured using a BT-301 powder tap density tester from Dandong BETTER, with reference to GB / T 5162-2006.

[0208] 1) After loading 21 - 24 ml of the powder sample into a 25-ml graduated cylinder of known mass, the total weight was measured. Then the mouth of the cylinder was sealed with a sealing film.

[0209] 2) The graduated cylinder containing the powder was fixed on a mechanical vibration device. The motor drove the mechanical vibration device to vibrate vertically up and down. The powder was gradually compacted. When the set number of vibrations was reached, the vibration stopped, and the volume of the graduated cylinder was read. According to the definition of density: mass divided by volume, the density of the compacted powder was calculated. Amplitude: 3.0 + 0.1 mm, vibration frequency: 250 ± 15 times / min, number of vibrations: 5000 times.

[0210] 2. Measurement of specific surface area

[0211] With reference to the standard of GB / T 19587-2017 for the determination of specific surface area of solid materials by gas adsorption BET method, the specific surface area of the material was measured using the nitrogen adsorption specific surface area analysis test method and calculated by the BET (Brunauer Emmett Teller) method. Among them, the nitrogen adsorption specific surface area analysis test was carried out using a Tri Star II 3020 specific surface area and pore size analyzer from Micromeritics, USA.

[0212] 3. Measurement of the content of porous carbon matrix

[0213] With reference to GB / T 20123-2006 / ISO 15350:2000, the carbon element content in the material was measured. The test instrument was an HCS-140 high-frequency infrared carbon-sulfur analyzer from Shanghai Dekai Instrument Co., Ltd.

[0214] After surface passivation of the product obtained in step 1), it was taken out from the deposition furnace, and the carbon element content in the product was measured using a carbon-sulfur analyzer. Thus, the content of the porous carbon matrix relative to the product was measured. The silicon-carbon anode material obtained in step 2) was tested using a carbon-sulfur analyzer. Thus, the carbon element content in the silicon-carbon anode material was measured, that is, the sum of the carbon contents in the porous carbon matrix and the carbon coating layer relative to the silicon-carbon anode material. By calculation, the content of the porous carbon matrix relative to the silicon-carbon anode material can be obtained.

[0215] 4. Measurement of silicon content

[0216] With reference to EPA6010D-2014, the silicon element content in the material was measured by inductively coupled plasma atomic emission spectrometry.

[0217] 5. Measurement of true density

[0218] The true density of the silicon-carbon anode material was tested according to the method described in GB / T 24586-2009.

[0219] Weigh a certain mass of the sample into a sample cup with a known volume. Place the sample cup containing the sample in a true density tester (AccuPyc II 1340). Seal the test system and introduce helium gas according to the procedure. By detecting the gas pressure in the sample chamber and the expansion chamber, and then based on the gas law, the true volume of the sample is obtained. Then, the true density is calculated by dividing the sample mass by the sample volume.

[0220] Preparation of coin cells

[0221] Mix the above-mentioned silicon-carbon anode material, conductive carbon black, and binder polyacrylic acid in a mass ratio of 8:1:1. Then add deionized water as the solvent and stir under a high-speed mixer until the system becomes homogeneous to obtain a negative electrode slurry with a solid content of 45%. Uniformly coat the negative electrode slurry on the negative electrode current collector copper foil and dry it at 85 °C. After cold pressing, an electrode sheet is obtained. Using metallic lithium as the counter electrode, a Celgard 2400 separator membrane is adopted, and the electrolyte is injected to assemble a coin cell. The electrolyte is an organic solvent mixture of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC). Among them, the volume ratio of EC, EMC, and DEC is 20:20:60. Then dissolve LiPF6 in the above-mentioned organic solvent and add an additive fluoroethylene carbonate (FEC). The concentration of LiPF6 is 1 mol / L, and the mass proportion of FEC in the electrolyte is 5%.

[0222] Testing of the initial Coulombic efficiency

[0223] After the assembled coin cell is left standing for 60 min, it is tested according to the procedure of constant current discharge at 0.05C to 5 mV, discharge at 50 μA to 5 mV, standing for 10 min, and charging at 0.1C to 0.8V. Among them, the lithium intercalation capacity of the silicon-carbon anode material is the capacity C1 discharged to 5 mV, the lithium deintercalation capacity of the silicon-carbon anode material is the capacity C2 charged to 0.8V, and the initial Coulombic efficiency of the silicon-carbon anode material is C2 / C1.

[0224] Preparation of secondary batteries

[0225] 1. Preparation of the positive electrode sheet

[0226] Mix the positive electrode active material LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM 811) The conductive carbon black and the binder polyvinylidene fluoride (PVDF) are fully stirred and mixed in an appropriate amount of N-methylpyrrolidone (NMP) solvent according to a weight ratio of 93:2:5 to form a uniform positive electrode paste. The positive electrode paste is coated on the surface of the positive electrode current collector, and after processes such as drying, the positive electrode plate is obtained.

[0227] 2. Preparation of the negative electrode plate

[0228] The silicon-carbon negative electrode material, artificial graphite, conductive carbon black, thickener sodium carboxymethyl cellulose (CMC-Na), and binder styrene-butadiene rubber latex (SBR) prepared in the above-mentioned respective examples or comparative examples are fully stirred and mixed in an appropriate amount of deionized water according to a weight ratio of 18:77.5:1.3:1.2:2 to form a uniform negative electrode paste. The negative electrode paste is coated on the negative electrode current collector, and after processes such as drying, the negative electrode plate is obtained.

[0229] 3. Preparation of the electrolyte

[0230] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed according to a volume ratio of 1:1:1 to obtain an organic solvent. Then, the fully dried lithium salt LiPF6 is dissolved in the mixed organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0231] 4. Separator

[0232] The separator is a 12-μm-thick polypropylene (PP) porous membrane.

[0233] 5. Preparation of the secondary battery

[0234] The positive electrode plate, separator, and negative electrode plate are stacked in sequence, then wound into an electrode assembly and placed in an outer package, and the above-mentioned electrolyte is injected. After processes such as sealing, standing, hot and cold pressing, and formation, the secondary battery is obtained.

[0235] Performance test of the secondary battery

[0236] 1. Test of the cycle performance

[0237] At 45 °C, the secondary batteries prepared in the respective examples and comparative examples are charged at a constant current of 1C to a charging cut-off voltage of 4.25V, then charged at a constant voltage until the current ≤ 0.05C, and left standing for the current ≤ 0.05C, and left standing for 5 minutes. Then, it is discharged at a constant current of 0.33C to a discharging cut-off voltage of 2.5V and left standing for 5 minutes. This is one charge-discharge cycle. The battery is tested for cyclic charge and discharge according to this method until the battery capacity decays to 80%. The number of cycles at this time is the cycle life of the battery.

[0238] 2. Test of the full charge expansion rate

[0239] Take the secondary batteries prepared in each example and comparative example, and measure the thickness of the negative electrode sheet, denoted as D0. Charge the secondary batteries prepared in each example and comparative example at a constant current of 1C to the cut-off voltage of 4.25V, and measure the thickness of the negative electrode sheet at this time, denoted as D1.

[0240] Among them, the first full charge expansion rate = (D1 - D0) / D0 × 100%.

[0241] Table 1: Process parameters used in step 1) of the preparation of the silicon-carbon negative electrode material

[0242]

[0243] In Table 1, M Si / M C represents the mass ratio of the silicon source gas introduced to the porous carbon matrix in terms of the mass of silicon element.

[0244] Table 2: Performance parameters of the silicon-carbon negative electrode material

[0245]

[0246] In Table 2, ρ 振 represents the tap density of the silicon-carbon negative electrode material, and ρ 真 represents the true density of the silicon-carbon negative electrode material.

[0247] Table 3: Test results of electrical performance parameters

[0248]

[0249]

[0250] According to the above results, it can be seen that the silicon-carbon negative electrode materials prepared in Examples 1-11 all meet the requirements of this application, and the battery can simultaneously achieve a relatively high first Coulomb efficiency, high-temperature cycle life, and low cycle expansion rate.

[0251] However, the silicon-carbon negative electrode materials prepared in Comparative Examples 1-4 cannot simultaneously meet the structural feature limitations of this application, so the battery cannot simultaneously achieve a relatively high first Coulomb efficiency, high-temperature cycle life, and low cycle expansion rate. Specifically, in Comparative Example 1, PV 闭 is less than 0.250 cm 3 / g, mainly because the partial pressure of the silicon source gas is less than 0.3; in Comparative Example 2, PV 闭 is less than 0.250 cm 3 / g, mainly because the gas hourly space velocity of the first mixed gas including silane and nitrogen is greater than 1200 L / kg; in Comparative Example 3, PV 闭 is less than 0.250 cm 3 / g, and V 硅Greater than 0.175 cm 3 / g, mainly because the mass ratio of the introduced silane to the porous carbon matrix is greater than 0.95; in Comparative Example 4, PV 闭 Less than 0.250 cm 3 / g, mainly because the proportion of the mesopore volume in the porous carbon matrix is greater than 75%. Therefore, the materials of Comparative Example 1 to Comparative Example 4 cannot enable the battery to simultaneously achieve a high initial Coulomb efficiency, a high-temperature cycle life, and a low cycle expansion rate.

[0252] It should be noted that the present application is not limited to the above embodiments. The above embodiments are only examples, and embodiments having the same structure and the same effect as the technical idea within the technical scope of the present application are included in the technical scope of the present application. In addition, within the scope not departing from the gist of the present application, various modifications that can be conceived by those skilled in the art to the embodiments, and other embodiments constructed by combining some of the constituent elements of the embodiments are also included in the scope of the present application.

Claims

1. A silicon-carbon anode 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 the silicon-based material in the silicon-carbon negative electrode material per unit mass 硅 is 0.155 cm 3 / g to 0.175 cm 3 / g. The silicon-carbon negative electrode material includes closed pores inside, and the volume PV of the closed pores in the silicon-carbon negative electrode material per unit mass 闭 is greater than or equal to 0.250 cm 3 / g.

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

3. The silicon-carbon anode material according to claim 1 or 2, characterized in that, The open pore volume PV of the silicon-carbon negative electrode material 开 is 0.008 cm 3 / g to 0.040 cm 3 / g.

4. The silicon-carbon negative electrode material according to any one of claims 1 to 3, characterized in that, the porous carbon matrix includes mesopores, and the proportion of the mesopores in the total pore volume of the porous carbon matrix is 40% to 75%.

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

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

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

8. The silicon-carbon anode material according to claim 7, characterized in that, 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 anode material according to any one of claims 1 to 8, characterized in that, 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 ~2.3 g / cm 3 ; The tap density of the silicon-carbon negative electrode material is 0.4 g / cm 3 to 0.9 g / cm 3 ; The specific surface area of the silicon-carbon negative electrode material is 2.5 m 2 / g to 12 m 2 / g; The specific surface area of the porous carbon matrix is 1000 m 2 / g to 1800 m 2 / g.

10. The silicon-carbon anode material according to any one of claims 1 to 9, characterized in that, the silicon-carbon negative electrode material further includes a carbon coating layer.

11. A method for preparing a silicon-carbon anode material, characterized in that, The method includes: providing a porous carbon matrix, the porous carbon matrix includes mesopores, and the proportion of the mesopores in the total pore volume of the porous carbon matrix is less than or equal to 75%; placing the porous carbon matrix in a reactor; introducing a first mixed gas including a silicon source gas and a first inert gas into the reactor, the partial pressure of the silicon source gas is greater than or equal to 0.3, wherein, based on the mass of silicon element, the mass ratio of the introduced silicon source gas to the porous carbon matrix is less than or equal to 0.95; adjusting the gas hourly space velocity of the first mixed gas to be less than or equal to 1200 L / kg, and depositing the silicon-based material in the pores of the porous carbon matrix under this condition, thereby obtaining the silicon-carbon negative electrode material, 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 in the silicon-carbon negative electrode material per unit mass is 0.155 cm 3 / g to 0.175 cm 3 / g, the silicon-carbon negative electrode material internally includes closed pores, and the volume of the closed pores in the silicon-carbon negative electrode material per unit mass is greater than or equal to 0.250 cm 3 / g.

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

13. The method according to claim 11 or 12, characterized in that, 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, characterized in that, 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, characterized in that Adjust the gas hourly space velocity of the first mixed gas to be 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 to 1.02 cm 3 / g; and / or, The specific surface area of the porous carbon matrix is 1000 m 2 / g to 1800 m 2 / g.

17. The method according to any one of claims 11 to 16, characterized in that, 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 under 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 silane, 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, characterized in that The method further includes: after depositing the silicon-based material, introducing a second mixed gas including 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, characterized in that, The secondary battery includes a negative electrode sheet, the negative electrode sheet includes a negative electrode current collector and a negative electrode film layer located on at least one surface of the negative electrode current collector, and the negative electrode film layer includes 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 electrical device, characterized in that, The electrical device includes the secondary battery according to claim 19.

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