Negative active material and preparation method thereof, negative pole piece and battery

Abstract

The invention discloses a negative electrode active material and a preparation method thereof, a negative electrode plate, a battery, and the negative electrode active material, the negative electrode active material comprises a silicon carbon material, dQ / dV of a lithium removal curve of the silicon carbon material has a first characteristic peak in a range of 0.25 V to 0.35 V, the peak intensity of the first characteristic peak is IH, the unit of IH is mAh / V, and the unit of the first characteristic peak is mAh / V. The dQ / dV of the lithium removal curve of the negative electrode active material has a second characteristic peak in the range of 0.4 V-0. 5V, the peak intensity of the second characteristic peak is IS, the unit of IS is mAh / V, and IS / IH is less than or equal to 0.6. Therefore, the powder caking of the negative electrode active material can be reduced, and the volume expansion of the negative electrode active material in the charge-discharge cycle of the battery can be relieved.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular, to negative electrode active materials and preparation methods thereof, negative electrode plates, and batteries. Background Art

[0002] With the continuous development of electric vehicles, the market requirements for power batteries are getting higher and higher, and lithium-ion batteries are also developing rapidly. The negative electrode active material is a key factor affecting the performance of lithium-ion batteries. At present, the commercial negative electrode active material is mainly graphite, and its theoretical specific capacity is 372mAh / g, but it can no longer meet the use needs. Silicon-based materials are considered to be high-energy density negative electrode active materials with great application potential due to their excellent theoretical specific capacity (4200mAh / g), suitable voltage platform, and environmental friendliness. However, silicon-based materials have disadvantages such as severe volume expansion and easy pulverization during the battery charge and discharge cycle. Therefore, the current negative electrode active materials still need to be further improved.

[0003] It should be noted that the above statements are only used to provide background technical information related to the present application and do not necessarily constitute prior art. Summary of the invention

[0004] In one aspect of the present application, the present application provides a negative electrode active material, including a silicon-carbon material, wherein the dQ / dV of the lithium removal curve of the silicon-carbon material has a first characteristic peak in the range of 0.25V-0.35V, and the peak intensity of the first characteristic peak is 1 H , I H The unit is mAh / V, and the dQ / dV of the lithium removal curve of the negative electrode active material has a second characteristic peak in the range of 0.4V-0.5V, and the peak intensity of the second characteristic peak is I S , I S The unit is mAh / V, I S / I H Less than or equal to 0.6. Thus, the powder agglomeration of the negative electrode active material can be reduced, and the volume expansion of the negative electrode active material during the battery charge and discharge cycle can be alleviated.

[0005] According to an embodiment of the present application, the silicon-carbon material includes a porous carbon carrier and elemental silicon, the elemental silicon is located in the pore structure of the porous carbon carrier, and the mass fraction of silicon in the negative electrode active material is 30%-70%; optionally, the mass fraction of silicon in the negative electrode active material is 35%-55%. Thus, the specific capacity of the negative electrode active material can be increased.

[0006] According to an embodiment of the present application, the Dv50 particle size of the negative electrode active material is 4 μm-13 μm, which helps to improve the compaction density of the negative electrode sheet by mixing negative electrode active materials of different particle sizes.

[0007] According to an embodiment of the present application, the specific surface area of ​​the negative electrode active material is 1 m 2 / g-20m 2 / g. Thus, the specific capacity of the negative electrode active material can be further improved.

[0008] According to an embodiment of the present application, it further includes: a carbon coating layer, which at least partially covers the outer surface of the silicon-carbon material; optionally, the mass fraction of the carbon coating layer in the negative electrode active material is 2%-15%.

[0009] In another aspect of the present application, the present application proposes a method for preparing the aforementioned negative electrode active material, comprising: placing a porous carbon carrier in a silicon deposition device; introducing a mixed gas of a silicon source gas and hydrogen into the silicon deposition device, and performing a silicon deposition process to obtain the silicon-carbon material. Thus, the aforementioned negative electrode active material can be obtained by a relatively simple method.

[0010] According to an embodiment of the present application, the porous carbon carrier satisfies at least one of the following conditions: the specific surface area of ​​the porous carbon carrier is 600 m 2 / g-2000m 2 / g; the Dv50 particle size of the porous carbon carrier is 3μm-12μm; the minimum particle size of the porous carbon carrier is greater than or equal to 1.5μm; the particle size span value of the porous carbon carrier is 0.9-1.2. Thus, it is helpful for silicon to be deposited in the pore structure of the porous carbon carrier.

[0011] According to an embodiment of the present application, the silicon deposition process satisfies at least one of the following conditions: the temperature of the silicon deposition process is 400°C-800°C; the time of the silicon deposition process is 2h-50h; the silicon source gas includes at least one of silane, disilane, tri(trimethylsilyl)silane, tetrafluorosilane, silicon trichloride, and chlorosilane. Thus, it is helpful to fully deposit elemental silicon in the pore structure of the porous carbon carrier.

[0012] According to an embodiment of the present application, the silicon deposition equipment includes at least one of a rotary kiln and a fluidized bed; optionally, the filling rate of the porous carbon carrier in the rotary kiln is 2%-20%; optionally, the filling rate of the porous carbon carrier in the fluidized bed is 25%-40%; optionally, the silicon deposition equipment further includes: a knocking device, the knocking device includes at least one of an air hammer and a pendulum ball. This helps to improve the yield of the negative electrode active material.

[0013] According to an embodiment of the present application, the silicon deposition process includes n stages performed sequentially, n≥2, wherein the flow rate of the silicon source gas in the first stage is v, the flow rate of the hydrogen gas in the first stage is 0, and the first stage makes the silicon deposition amount in the silicon-carbon material reach 40%-50% of the preset deposition amount; the flow rate of the silicon source gas in the a stage is yv, y=-4.0089((a+n-1) / 2n) 2 +4.0068((a+n-1) / 2n), the flow rate of the hydrogen in the a stage is v(1-y), wherein a is greater than 1. This helps to control the deposition rate of elemental silicon, so that more elemental silicon is deposited in the pore structure of the porous carbon carrier.

[0014] According to an embodiment of the present application, it further includes: after the silicon deposition process, a carbon source gas is introduced into the silicon deposition device, and a carbon coating process is performed, wherein the carbon coating process satisfies at least one of the following conditions: the temperature of the carbon coating process is 500°C-1000°C; the time of the carbon coating process is 1h-10h; the carbon source gas includes at least one of methane, acetylene, and propyne. Thus, a carbon coating layer can be formed on the surface of the silicon-carbon material by a simple method.

[0015] In another aspect of the present application, the present application proposes a negative electrode sheet, comprising a negative electrode current collector and a negative electrode active material layer located at least on one side of the negative electrode current collector, wherein the negative electrode active material layer comprises the aforementioned negative electrode active material, or the negative electrode active material prepared by the aforementioned method. Therefore, the negative electrode sheet has all the features and advantages of the aforementioned negative electrode active material and the method for preparing the negative electrode active material, which will not be described in detail here.

[0016] In another aspect of the present application, the present application provides a battery, comprising the aforementioned negative electrode sheet. Therefore, the battery has all the features and advantages of the negative electrode sheet, which will not be described in detail here. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The above and / or additional aspects and advantages of the present application will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0018] Figure 1 is a schematic structural diagram of a negative electrode active material according to an embodiment of the present application;

[0019] Figure 2 is a schematic structural diagram of a negative electrode active material in yet another embodiment of the present application;

[0020] Figure 3 is a schematic flow chart of a method for preparing a negative electrode active material according to an embodiment of the present application;

[0021] Figure 4is a schematic flow chart of a method for preparing a negative electrode active material according to another embodiment of the present application;

[0022] Figure 5 is a dQ / dV-V curve diagram of the negative electrode active material of Example 1 of the present application;

[0023] Figure 6 is a dQ / dV-V curve diagram of the negative electrode active material of Example 2 of the present application;

[0024] Figure 7 is a dQ / dV-V curve diagram of the negative electrode active material of Example 3 of the present application;

[0025] Figure 8 is a dQ / dV-V curve diagram of the negative electrode active material of Comparative Example 1 of the present application;

[0026] Fig. 9 is a dQ / dV-V curve diagram of the negative electrode active material of Comparative Example 2 of the present application;

[0027] Fig.10 is a cross-sectional EDS image of the negative electrode active material of Example 1 of the present application;

[0028] Fig.11 is a cross-sectional EDS image of the negative electrode active material of Comparative Example 1 of the present application;

[0029] Fig.12 is a powder image of the negative electrode active material of Example 1 of the present application;

[0030] Fig.13 This is a powder picture of the negative electrode active material of Comparative Example 1 of the present application.

[0031] Description of reference numerals:

[0032] Porous carbon carrier 10; elemental silicon 20; carbon coating layer 30. DETAILED DESCRIPTION

[0033] The embodiments of the present application are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present application, and cannot be understood as limiting the present application.

[0034] Unless otherwise defined, all technical and scientific terms used in this application have the same meanings as those commonly understood by technicians in the technical field to which this application belongs; the terms used in this application are only for the purpose of describing specific embodiments and are not intended to limit this application; unless otherwise specified, the numerical values ​​of the parameters mentioned in this application can be measured using various measurement methods commonly used in the art (for example, they can be tested according to the methods given in the embodiments of this application).

[0035] The terms "including" and "having" in the specification and claims of the present application and any modifications thereof are open expressions, that is, including the contents specified in the present application but not excluding other contents.

[0036] In the description of this application, regardless of whether the words "about" or "approximately" are used, all the numbers disclosed herein are approximate values. The value of each number may differ by less than 10% or a reasonable difference considered by those skilled in the art, such as 1%, 2%, 3%, 4% or 5%.

[0037] In the description of this application, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. "First feature" and "second feature" may include one or more of the features.

[0038] In the description of the present application, "A and / or B" may include the case of A alone, the case of B alone, or any of the cases of A and B, where A and B are only used for examples and may be any technical feature connected by "and / or" in the present application.

[0039] Compared with graphite, which is a good conductor, silicon, as a semiconductor, has a lower conductivity at room temperature. Its poor conductivity leads to the obstruction of electron transmission in the silicon bulk phase and the diffusion of lithium ions, and the poor kinetic performance of the material, making it difficult to increase the charge and discharge current when silicon is used as a negative electrode active material, which in turn leads to poor rate performance of the battery. Silicon undergoes significant volume changes during the process of lithium insertion and extraction. Specifically, silicon inserts and extracts lithium by forming a Li-Si alloy with lithium. The volume expansion rate of the Li-Si alloy can reach 300%. Excessive stress will cause silicon to break, causing the silicon negative electrode active material to fall off the negative electrode sheet, which in turn leads to a significant deterioration in the cycle performance of the battery. Silicon-carbon materials with porous carbon as a dispersion carrier and silicon as an active substance can not only buffer the volume change of silicon particles when lithium is inserted and extracted through the porous carbon carrier, maintain the structural integrity of the negative electrode sheet, but also use the porous carbon carrier as a conductive support to provide electron channels and ion channels for silicon, thereby improving the kinetic performance of silicon. The silicon-carbon material can be obtained by a deposition process. For example, elemental silicon can be deposited in the pores of a porous carbon support to obtain the silicon-carbon material.

[0040] The silicon content in the silicon-carbon material is positively correlated with the reversible specific capacity of the silicon-carbon material. In order to increase the silicon content in the silicon-carbon material, the silicon deposition process time is usually extended and the flow rate of the silicon source gas is increased. However, with the continuous deposition of silicon in the pore structure of the porous carbon carrier, the pore structure of the porous carbon carrier is continuously filled with elemental silicon, and the voids in the pore structure of the porous carbon carrier continue to decrease, causing the deposition rate of silicon in the pore structure of the porous carbon carrier to continue to decrease in the later stage of the process. Since the silicon source gas still maintains a relatively fast decomposition rate at this time, elemental silicon will tend to be deposited on the surface of the porous carbon carrier due to the slow rate of deposition into the pore structure, and the silicon-carbon material will undergo surface silicon coating. In addition, when the amount of elemental silicon deposited in the pore structure of the porous carbon carrier is already large, but the deposition process has not stopped, the amount of silicon deposition at this time exceeds the receiving capacity of the porous carbon carrier, which then causes the gas phase silicon to condense and nucleate on the surface of the porous carbon carrier, making the surface silicon coating problem of the silicon-carbon material more serious.

[0041] The elemental silicon on the surface of the porous carbon carrier will cause the adjacent porous carbon carriers to adhere to each other during the silicon deposition process, which will cause the final silicon-carbon material to agglomerate. When used as a negative electrode active material, the elemental silicon on the surface of the porous carbon carrier will cause cracks in the silicon-carbon material until it is pulverized due to its own huge volume expansion during the lithium insertion and extraction process, destroying the contact between the silicon-carbon material and the negative electrode current collector, causing the negative electrode active material to detach from the negative electrode plate, resulting in rapid decay of the battery capacity and a significant decrease in the cycle performance. In addition, the elemental silicon on the surface of the porous carbon carrier will also generate stress inside the battery after expansion, which will then squeeze the adjacent pole plates. As the charge and discharge cycle proceeds, the pole plates are at risk of breaking.

[0042] In the present application, the inventors discovered through a large number of experimental investigations and theoretical analyses that, for silicon-carbon materials, the differential capacitance curve (dQ / dV-V) of the negative electrode active material during the delithiation process will have a first characteristic peak in the range of 0.25V-0.35V, and the peak intensity of the first characteristic peak is positively correlated with the content of elemental silicon in the pore structure of the porous carbon carrier; there is a second characteristic peak in the range of 0.4V-0.5V, and the peak intensity of the second characteristic peak is positively correlated with the content of elemental silicon on the outer surface of the porous carbon carrier. When the ratio of the peak intensity of the second characteristic peak to the peak intensity of the first characteristic peak is small, the silicon-carbon material has a lower silicon content on the outer surface of the porous carbon carrier, a higher gram capacity and better cycle performance.

[0043] In one aspect of the present application, the present application provides a negative electrode active material, including a silicon-carbon material, wherein the dQ / dV of the lithium removal curve of the silicon-carbon material has a first characteristic peak in the range of 0.25V-0.35V, and the peak intensity of the first characteristic peak is 1 H , I HThe unit is mAh / V. The dQ / dV of the lithium removal curve of the negative electrode active material has a second characteristic peak in the range of 0.4V-0.5V. The peak intensity of the second characteristic peak is I S , I S The unit is mAh / V, I S / I H Less than or equal to 0.6. When the silicon-carbon material meets the above conditions, the silicon-carbon material powder is not easy to agglomerate because the porous carbon carrier of the silicon-carbon material has less silicon coverage on the surface. At the same time, less surface coverage can also effectively alleviate the volume expansion problem of the negative electrode active material during the battery charge and discharge cycle, thereby improving the cycle life of the battery.

[0044] As an example, the delithiation curve of silicon-carbon material, that is, the differential capacitance curve (dQ / dV-V) during the delithiation process, can be tested for electrochemical performance by the following method: the negative electrode active material: sodium carboxymethyl cellulose: conductive carbon black: styrene-butadiene rubber are mixed in a mass ratio of 94.5:1.5:1.5:2.5 to prepare a negative electrode slurry, which is then coated on a copper foil current collector and vacuum dried to obtain a negative electrode sheet; then the negative electrode sheet, lithium sheet, and 1 mol / L LiPF 6 The solution, Celgard2400 separator and shell are assembled into a button battery using conventional production processes. 6 The solvent of the solution is obtained by mixing ethylene carbonate: dimethyl carbonate: ethyl methyl carbonate in a volume ratio of 1:1:1. The charge and discharge test of the button battery was carried out on the LA ND battery test system of Wuhan Jinnuo Electronics Co., Ltd. The test conditions are: room temperature (for example, 25°C), charge and discharge voltage limit of 0.05-2V, 0.1C constant current charge and discharge. The differential value dQ / dV obtained by differentiating the charge and discharge capacity Q by the electrode potential V can be plotted with dQ / dV as the y-axis and the electrode potential V as the x-axis to obtain the differential capacitance curve of the negative electrode active material in the corresponding delithiation process.

[0045] As an example, the differential capacitance curve of the silicon-carbon material mentioned above can be obtained by testing the first-cycle lithium desorption curve of the silane material during the charge and discharge cycle; the differential capacitance curve of the silicon-carbon material mentioned above can also be obtained by testing the lithium desorption curve of any cycle of the silane material during the charge and discharge cycle.

[0046] As an example, the peak position of the first characteristic peak can be 0.25V, 0.26V, 0.27V, 0.28V, 0.29V, 0.30V, 0.31V, 0.32V, 0.33V, 0.34V or 0.35V; the peak position of the second characteristic peak can be 0.40V, 0.41V, 0.42V, 0.43V, 0.44V, 0.45V, 0.46V, 0.47V, 0.48V, 0.49V or 0.50V.

[0047] In some embodiments, the peak position of the first characteristic peak is 0.3V, and the peak position of the second characteristic peak is 0.45V.

[0048] As an example, I S / I H It can be 0.01, 0.03, 0.05, 0.08, 0.1, 0.13, 0.15, 0.18, 0.2, 0.23, 0.25, 0.28, 0.3, 0.33, 0.35, 0.38, 0.4, 0.43, 0.45, 0.48, 0.5, 0.53, 0.55, 0.58 or 0.6.

[0049] In some embodiments, reference Figure 1 The silicon-carbon material may include a porous carbon carrier 10 and elemental silicon 20. The elemental silicon 20 is located in the pore structure of the porous carbon carrier 10. The mass fraction of silicon element in the negative electrode active material is 30%-70%, so that the silicon-carbon material has a higher silicon content, which can effectively improve the specific capacity of the silicon-carbon material. Correspondingly, an appropriate amount of carbon content also helps to improve the conductivity of the silicon-carbon material and improve the kinetic performance.

[0050] In some embodiments, the mass fraction of silicon in the negative electrode active material is 35%-55%.

[0051] As an example, the mass fraction of silicon in the negative electrode active material can be 30%, 32%, 35%, 37%, 40%, 42%, 45%, 47%, 50%, 52%, 55%, 57%, 60%, 62%, 65%, 67% or 70%.

[0052] As an example, the mass fraction of silicon in the negative electrode active material can be obtained by ICP-OES testing.

[0053] In some embodiments, the Dv50 particle size of the negative electrode active material is 4 μm-13 μm.

[0054] As an example, the Dv50 particle size of the negative electrode active material is 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm or 13 μm. By mixing negative electrode active materials of different particle sizes, the gaps in the negative electrode active material layer can be filled, thereby increasing the compaction density of the negative electrode sheet.

[0055] In some embodiments, the specific surface area of ​​the negative electrode active material is 1 m 2 / g-20m 2 / g.

[0056] As an example, the specific surface area of ​​the negative electrode active material can be 1 m 2 / g, 2m2 / g, 3m 2 / g, 4m 2 / g, 5m 2 / g, 6m 2 / g, 7m 2 / g, 8m 2 / g, 9m 2 / g、0m 2 / g, 10m 2 / g, 11m 2 / g, 12m 2 / g, 13m 2 / g, 14m 2 / g, 15m 2 / g, 16m 2 / g, 17m 2 / g, 18m 2 / g, 9m 2 / g or 20m 2 / g.

[0057] The porous carbon carrier has a high specific surface area. For example, the specific surface area of ​​the porous carbon carrier can be 600m 2 / g-2000m 2 / g. The specific surface area is mainly contributed by the inner surface of the pore structure inside the porous carbon carrier. When a large amount of elemental silicon in the silicon-carbon material is formed in the pore structure of the porous carbon carrier, that is, when the elemental silicon fills the pore structure of the porous carbon carrier, the inner surface of the pore structure of the porous carbon carrier is covered by elemental silicon, thereby causing the specific surface area of ​​the silicon-carbon material to be sharply reduced compared with the porous carbon carrier.

[0058] In some embodiments, reference Figure 2 The silicon-carbon material may further include: a carbon coating layer 30, wherein the carbon coating layer 30 at least partially covers the outer surface of the silicon-carbon material.

[0059] In some embodiments, the mass fraction of the carbon coating layer in the negative electrode active material is 2%-15%. In other embodiments, the mass fraction of the carbon coating layer in the negative electrode active material is 5%-10%.

[0060] As an example, the mass fraction of the carbon coating layer in the negative electrode active material can be 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14% or 15%.

[0061] The provision of a carbon coating layer can further enhance the conductivity of silicon-carbon materials and improve their dynamic properties. It can also reduce the failure of silicon-carbon materials caused by the spontaneous combustion of nano-silicon in the air, thereby broadening the processing window.

[0062] In some embodiments, the powder resistivity of the silicon carbon material may be 5 Ω·mm-3000 Ω·mm.

[0063] In another aspect of the present application, the present application proposes a method for preparing the aforementioned negative electrode active material, by placing a porous carbon carrier in a silicon deposition device, introducing a mixture of silicon source gas and hydrogen, increasing the hydrogen flow rate in stages, and reducing the silicon source gas flow rate in stages. Taking silane as an example, the thermal decomposition reaction of silane in the silicon deposition process is: SiH 4 =Si+2H 2 ↑, therefore, as silicon deposition proceeds, by increasing the hydrogen flow rate and reducing the silane flow rate, the thermal decomposition reaction of silane can be made to proceed in the opposite direction, thereby achieving control over the thermal decomposition reaction rate of silane. In this way, the decomposition rate of the silicon source gas can be adjusted to match the deposition rate of elemental silicon in the pore structure, and the deposition of elemental silicon can be controlled, which is conducive to more deposition of elemental silicon in the pore structure, reducing the surface silicon coverage of the silicon-carbon material, thereby improving the cycle performance of the silicon-carbon material and alleviating the volume expansion during the lithium insertion and extraction process. Specifically, see Figure 3 , the method for preparing the negative electrode active material may include the following steps:

[0064] S100: Placing porous carbon supports in silicon deposition equipment

[0065] In some embodiments, in this step, the porous carbon carrier is placed in a silicon deposition device at a certain filling rate, and the silicon deposition device may include at least one of a rotary kiln and a fluidized bed.

[0066] In some embodiments, the filling rate of the porous carbon carrier in the rotary kiln can be 2%-20%, and the filling rate of the porous carbon carrier in the fluidized bed can be 25%-40%. When the filling rate in the silicon deposition device is within the aforementioned range, the filling rate is moderate, which helps to control the reaction rate of the silicon source gas and reduce the occurrence of surface silicon coating and material agglomeration.

[0067] In some embodiments, the specific surface area of ​​the porous carbon support can be 600 m 2 / g-2000m 2 / g. When the specific surface area of ​​the porous carbon carrier is 600m 2 / g-2000m 2 / g, the porous carbon carrier has a rich pore structure inside, and a large number of pore structures help to increase the deposition amount of elemental silicon in the pore structure, thereby increasing the silicon content of the silicon-carbon material.

[0068] In some embodiments, the Dv50 particle size of the porous carbon carrier may be 3 μm-12 μm. When the Dv50 particle size of the porous carbon carrier is 3 μm-12 μm, it is helpful to form silicon-carbon materials of different particle sizes and optimize the particle size matching of the silicon-carbon materials.

[0069] In some embodiments, the minimum particle size of the porous carbon support may be greater than or equal to 1.5 μm, thereby helping to increase the number of pore structures inside the porous carbon support and increase the amount of silicon deposition.

[0070] In some embodiments, the particle size span of the porous carbon support may be 0.9-1.2, thereby helping to improve the particle size uniformity of the prepared silicon-carbon material.

[0071] In some embodiments, the porous carbon support may include at least one of biomass-based porous carbon and organic compound-based porous carbon.

[0072] The particle size span value (Span) is a measure of the width of the particle size distribution, Span = (Dv90-Dv10) / Dv50. Dv10 refers to the particle size corresponding to 10% of the cumulative volume percentage of the negative electrode active material, Dv90 refers to the particle size corresponding to 90% of the cumulative volume percentage of the negative electrode active material, and Dv50 refers to the particle size corresponding to 50% of the cumulative volume percentage of the negative electrode active material, that is, the median particle size of the volume distribution.

[0073] In some embodiments, the silicon deposition device may further include: a knocking device, which may include at least one of an air hammer and a pendulum ball. The temperature of the silicon deposition device close to the tube wall is relatively high, which in turn makes the temperature of the material located at the tube wall of the silicon deposition device relatively high, which in turn makes the decomposition rate of the silicon source gas on the porous carbon carrier at the tube wall faster, making it difficult to control the deposition rate, and ultimately causing the silicon-carbon material to be coated with silicon on the surface and agglomerated and adhered to the wall. The knocking device can effectively reduce the adhesion of the porous carbon carrier to the wall, and reduce the surface coating of silicon and agglomeration of the silicon-carbon material.

[0074] S210: Introducing a mixed gas of silicon source gas and hydrogen into the silicon deposition equipment

[0075] In some embodiments, a mixed gas of silicon source gas and hydrogen is introduced into the silicon deposition device. Specifically, the atmosphere in the silicon deposition device may be replaced with an inert gas first, and then a mixed gas of silicon source gas, hydrogen and carrier gas is introduced in a certain proportion. The carrier gas includes at least one of nitrogen and an inert gas.

[0076] In some embodiments, the silicon deposition process may include n stages performed sequentially, n≥2, wherein the flow rate of the silicon source gas in the first stage is v, the flow rate of the hydrogen gas in the first stage is 0, and the silicon deposition amount in the silicon-carbon material in the first stage reaches 40%-50% of the preset deposition amount; the flow rate of the silicon source gas in the a stage is yv, y=-4.0089((a+n-1) / 2n) 2+4.0068((a+n-1) / 2n), the flow rate of hydrogen in the a stage is v(1-y), where a is greater than 1. This helps to control the deposition rate of elemental silicon, so that the silicon element is deposited more in the pore structure of the porous carbon support.

[0077] In some embodiments, the silicon deposition process may include five stages performed in sequence, specifically, silicon deposition to 50% of the designed deposition amount is the first stage, in which the silicon source gas flow rate is v; silicon deposition to 50-60% of the designed deposition amount is the second stage, in which the silicon source gas flow rate is 0.96v and the hydrogen flow rate is 0.04v; silicon deposition to 60-70% of the designed deposition amount is the third stage, in which the silicon source gas flow rate is 0.84v and the hydrogen flow rate is 0.16v; silicon deposition to 70-80% of the designed deposition amount is the fourth stage, in which the silicon source gas flow rate is 0.64v and the hydrogen flow rate is 0.36v; silicon deposition to 90-100% of the designed deposition amount is the third stage, in which the silicon source gas flow rate is 0.36v and the hydrogen flow rate is 0.64v. During the entire silicon deposition process, the flow rate of the inert gas is maintained at 1v-10v.

[0078] As an example, the silicon deposition process may include n stages performed sequentially, where n≥2, and specifically, n may be 2, 3, 4, 5 or 6.

[0079] It can be understood that the calculation model of the silicon source gas flow rate and the hydrogen flow rate in each stage is not limited to the aforementioned model. The decomposition rate of the silicon source gas is adjusted to match the deposition rate of elemental silicon in the pore structure, and the deposition of elemental silicon can be controlled. Those skilled in the art can make adjustments based on actual conditions. For example, based on the aforementioned model, the specific flow rate can be adjusted up and down to increase the hydrogen flow rate in stages and reduce the silicon source gas flow rate in stages accordingly.

[0080] In some embodiments, the silicon source gas may include at least one of silane, disilane, tris(trimethylsilyl)silane, tetrafluorosilane, silicon trichloride, and chlorosilane.

[0081] S230: Silicon deposition process

[0082] In some embodiments, a mixed gas of silicon source gas and hydrogen is introduced into the silicon deposition device to heat the silicon deposition device to perform a silicon deposition process. Further, after the silicon deposition process is completed, the collected material can be cooled under an inert gas to obtain a silicon-carbon material.

[0083] In some embodiments, the temperature of the silicon deposition process may be 400° C.-800° C., and / or the time of the silicon deposition process may be 2 h-50 h, thereby facilitating sufficient deposition of elemental silicon in the pore structure of the porous carbon support.

[0084] In some embodiments, the temperature of the silicon deposition process may be 460° C.-600° C., and / or the time of the silicon deposition process may be 4 h-20 h.

[0085] In some embodiments, reference Figure 4 , the method for preparing the negative electrode active material further comprises:

[0086] S310: Introducing carbon source gas into silicon deposition equipment

[0087] In some embodiments, after the silicon deposition process, a carbon source gas is introduced into the silicon deposition device to form a carbon coating layer. Specifically, a carrier may be used for secondary replacement to exhaust the hydrogen and silicon source gas in the silicon deposition device, and then the carbon source gas and the carrier are introduced in a certain ratio. The carrier gas includes at least one of nitrogen and an inert gas.

[0088] S320: Carbon coating treatment

[0089] In some embodiments, a carbon source gas is introduced into the silicon deposition device to heat the silicon deposition device to perform a carbon coating process, and after completion, the material is cooled and collected under a carrier atmosphere. Specifically, the temperature of the carbon coating process can be 500°C-1000°C, and / or the time of the carbon coating process can be 1h-10h, and / or the carbon source gas includes at least one of methane, acetylene, and propyne, so that a relatively complete carbon coating layer can be formed on the surface of the silicon-carbon material.

[0090] In some embodiments, the carbon source gas is acetylene, and / or the temperature of the carbon coating process is 580° C.-680° C., and / or the time of the carbon coating process is 1 h-5 h.

[0091] Those skilled in the art will appreciate that, in the above method of a specific embodiment, the order in which the steps are written does not imply a strict execution order and does not constitute any limitation on the implementation process. The specific execution order of the steps should be determined by their functions and possible internal logic.

[0092] In another aspect of the present application, the present application proposes a negative electrode sheet, comprising a negative electrode current collector and a negative electrode active material layer located at least on one side of the negative electrode current collector, wherein the negative electrode active material layer comprises the aforementioned negative electrode active material, or the negative electrode active material prepared by the aforementioned method. Therefore, the negative electrode sheet has all the features and advantages of the aforementioned negative electrode active material and the method for preparing the negative electrode active material, which will not be described in detail here.

[0093] In another aspect of the present application, the present application provides a battery, comprising the aforementioned negative electrode sheet. Therefore, the battery has all the features and advantages of the negative electrode sheet, which will not be described in detail here.

[0094] The scheme of the present application is described below by specific examples. It should be noted that the following examples are only used to illustrate the present application and should not be considered as limiting the scope of the present application. If no specific technology or conditions are specified in the examples, the technology or conditions described in the literature in this area or the product instructions are used. The reagents or instruments used are not specified by the manufacturer, and are all conventional products that can be obtained commercially.

[0095] Example 1

[0096] Source of raw materials: Silane was purchased from Dalian Date Gas Co., Ltd., and acetylene was purchased from Dalian Date Gas Co., Ltd.

[0097] 1. Take 2kg and the specific surface area is 1253m 2 / g, and a porous carbon carrier with a Dv50 of 6.1μm was placed in a rotary kiln with a filling rate of 15% and replaced with argon.

[0098] 2. The rotary kiln is heated to 500°C, and the air hammer is turned on to knock. The knocking interval is 60s. The rotary kiln speed is 0.75r / min. The designed silicon deposition amount is 45% by mass fraction of silicon element in silicon-carbon material. The silicon deposition to 50% of the designed deposition amount is the first stage, and the silane flow rate in the first stage is 2L / min. The silicon deposition to 50%-60% of the designed deposition amount is the second stage, and the silane flow rate in the second stage is 1.9L / min and the hydrogen flow rate is 0.1L / min. The silicon deposition to the designed deposition amount is 1.2L / min, and the hydrogen flow rate is 0.1L / min. 60%-70% is the third stage, in which the silane flow rate is 1.7L / min and the hydrogen flow rate is 0.3L / min; the silicon is deposited to 70%-80% of the designed deposition amount is the fourth stage, in which the silane flow rate is 1.3L / min and the hydrogen flow rate is 0.7L / min; the silicon is deposited to 90%-100% of the designed deposition amount is the fifth stage, in which the silane flow rate is 0.7L / min and the hydrogen flow rate is 1.3L / min; the nitrogen flow rate is 2L / min throughout the whole process.

[0099] 3. Use argon for secondary replacement. The temperature of the rotary kiln is raised to 650℃, the speed of the rotary kiln remains unchanged, and 2L / min of argon and 2L / min of acetylene are introduced to reach 8% of the designed carbon deposition amount.

[0100] 4. Stop heating, adjust the speed of the rotary kiln to 0.3r / min, turn off acetylene, and adjust the argon to 0.3L / min; wait for cooling and collecting the material to obtain the silicon-carbon material.

[0101] Example 2

[0102] 1. Take 1.5kg and the specific surface area is 1253m 2 / g, and a porous carbon carrier with a Dv50 of 6.1 μm was placed in a fluidized bed with a filling rate of 30% and replaced with nitrogen.

[0103] 2. The designed silicon deposition amount is consistent with that in Example 1. The fluidized bed is heated to 550°C, and the air hammer is turned on to knock, with an interval of 60s; silicon deposition to 50% of the designed deposition amount is the first stage, and the silane flow rate in the first stage is 4L / min; silicon deposition to 50%-60% of the designed deposition amount is the second stage, and the silane flow rate in the second stage is 3.8L / min and the hydrogen flow rate is 0.2L / min; silicon deposition to 60%-70% of the designed deposition amount is the third stage, and the silane flow rate in the third stage is 3.4L / min and the hydrogen flow rate is 0.6L / min; silicon deposition to 70%-80% of the designed deposition amount is the fourth stage, and the silane flow rate in the fourth stage is 2.6L / min and the hydrogen flow rate is 1.4L / min; silicon deposition to 90%-100% of the designed deposition amount is the fifth stage, and the silane flow rate in the fourth stage is 1.4L / min and the hydrogen flow rate is 2.6L / min; the nitrogen flow rate in the whole process is 12L / min.

[0104] 3. Secondary replacement with nitrogen. The temperature of the fluidized bed is raised to 650°C, and 5L / min of argon and 10L / min of acetylene are introduced to reach 8% of the designed carbon deposition amount.

[0105] 4. Stop heating, turn off acetylene, and adjust nitrogen to 5L / min; wait for cooling and collecting the material to obtain silicon-carbon material.

[0106] Example 3

[0107] 1. Take 2kg and the specific surface area is 1253m 2 / g, and a porous carbon carrier with a Dv50 of 6.1μm was placed in a rotary kiln with a filling rate of 15% and replaced with argon.

[0108] 2. The temperature of the rotary kiln was raised to 500° C. The rotation speed of the rotary kiln was 0.75 r / min. 2 L / min of silane and 2 L / min of argon were introduced to carry out silicon deposition to 35% of the designed silicon deposition amount in Comparative Example 1.

[0109] 3. Use argon for secondary replacement. The temperature of the rotary kiln is raised to 650℃, the speed of the rotary kiln remains unchanged, and 2L / min of argon and 2L / min of acetylene are introduced to reach 8% of the designed carbon deposition amount.

[0110] 4. Stop heating, turn off acetylene, and adjust nitrogen to 5L / min; wait for cooling and collecting the material to obtain silicon-carbon material.

[0111] Comparative Example 1

[0112] 1. Take 2kg and the specific surface area is 1253m 2 / g, and a porous carbon carrier with a Dv50 of 6.1μm was placed in a rotary kiln with a filling rate of 15% and replaced with argon.

[0113] 2. The designed silicon deposition amount is consistent with that in Example 1. The rotary kiln is heated to 500° C. and the rotary kiln speed is 0.75 r / min; 2 L / min of silane and 2 L / min of argon are introduced to deposit silicon until the designed silicon deposition amount reaches 100%.

[0114] 3. Use argon for secondary replacement. The temperature of the rotary kiln is raised to 650℃, the speed of the rotary kiln remains unchanged, and 2L / min of argon and 2L / min of acetylene are introduced to reach 8% of the designed carbon deposition amount.

[0115] 4. Stop heating, turn off acetylene, and adjust nitrogen to 5L / min; wait for cooling and collecting the material to obtain silicon-carbon material.

[0116] Comparative Example 2

[0117] 1. Take 2kg and the specific surface area is 1253m 2 / g、D V 50 A porous carbon carrier with a diameter of 6.1 μm was placed in a rotary kiln with a filling rate of 15% and replaced with argon.

[0118] 2. The temperature of the rotary kiln was raised to 500° C. and the rotation speed of the rotary kiln was 0.75 r / min. 2 L / min of silane and 2 L / min of argon were introduced to carry out silicon deposition to 130% of the designed silicon deposition amount in Comparative Example 1.

[0119] 3. Use argon for secondary replacement. The temperature of the rotary kiln is raised to 650℃, the speed of the rotary kiln remains unchanged, and 2L / min of argon and 2L / min of acetylene are introduced to reach 8% of the designed carbon deposition amount.

[0120] 4. Stop heating, turn off acetylene, and adjust nitrogen to 5L / min; wait for cooling and collecting the material to obtain silicon-carbon material.

[0121] The silicon-carbon materials in Examples 1-3 and Comparative Examples 1-2 were subjected to electrochemical testing, and the testing method was as follows:

[0122] The negative electrode active material: sodium carboxymethyl cellulose: conductive carbon black: styrene butadiene rubber were mixed in a mass ratio of 94.5:1.5:1.5:2.5 to prepare a negative electrode slurry, which was coated on a copper foil current collector and vacuum dried to obtain a negative electrode sheet; then the negative electrode sheet, lithium sheet, 1 mol / L LiPF 6 The solution, Celgard2400 separator and shell are assembled into a button battery using conventional production processes. 6The solvent of the solution is obtained by mixing ethylene carbonate: dimethyl carbonate: ethyl methyl carbonate in a volume ratio of 1:1:1. The charge and discharge test of the button battery was carried out on the LAND battery test system of Wuhan Jinnuo Electronics Co., Ltd. The test conditions are: room temperature, charge and discharge voltage limit of 0.05-2V, 0.1C constant current charge and discharge. The differential value dQ / dV obtained by differentiating the charge and discharge capacity Q by the electrode potential V can be plotted with dQ / dV as the y-axis and the electrode potential V as the x-axis to obtain the differential capacitance curve of the negative electrode active material in the corresponding delithiation process.

[0123] The test results show that Figure 5-Figure 7 , in Example 1 I S / I H is 0.565, in Example 2 I S / I H The second characteristic peak was not observed in Example 3. S / I H Approaches 0. See Figure 8 and Fig. 9 , in Comparative Example 1, S / I H is 1.278, and in Comparative Example 2, S / I H is 3.33. S / I H Both are less than 0.6.

[0124] In Comparative Example 1, the silane decomposition rate was not adjusted during the silicon deposition process, resulting in surface silicon coating. S / I H The amount of silicon deposited in Comparative Example 2 far exceeds the amount of silicon deposited that can be filled in the pore structure of the porous carbon carrier, resulting in a large amount of elemental silicon deposited on the surface of the porous carbon carrier, resulting in a serious surface silicon coating phenomenon, making the second characteristic peak in Comparative Example 2 extremely strong. S / I H Too large.

[0125] See also Fig.10 and Fig.11 It can be seen from the EDS image of the cross-section of the silicon-carbon material particles that the surface silicon content of the silicon-carbon material in Example 1 is basically consistent with that in the interior, while the surface silicon content in Comparative Example 1 is different from the internal silicon content, less silicon is deposited in the pore structure inside the porous carbon carrier, and a higher silicon content is deposited on the surface of the porous carbon carrier.

[0126] See also Fig.12 and Fig.13 The silicon-carbon material sample in Example 1 is in powder form and does not have agglomeration. The silicon-carbon material sample in Comparative Example 1 has a large number of agglomerates of different sizes, and the uneven agglomeration phenomenon is very serious.

[0127] For Examples 1-3 and Comparative Example 1-2, the negative electrode materials were assembled into button-type full batteries, and the cycle performance test was performed:

[0128] Preparation of positive electrode sheet: LiNi 0.8 Co 0.1 Mn 0.1 O 2 , conductive carbon black, binder polyvinylidene fluoride, and carbon nanotubes are mixed in a mass ratio of 96.5:1:2:0.5, and then an appropriate amount of N-methylpyrrolidone (NMP) is added to obtain a positive electrode slurry under the action of a vacuum mixer, wherein the solid content of the positive electrode slurry is 70wt%. The positive electrode slurry is coated on a 9μm thick aluminum foil and dried at 120°C to obtain a positive electrode sheet coated with a positive electrode active material layer with a thickness of 45μm on one side. After cold pressing and cutting, a positive electrode sheet of the required specifications is obtained.

[0129] Preparation of electrolyte: In an argon atmosphere glove box with a water content of less than 10 ppm, dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), and fluoroethylene carbonate (FEC) were mixed in a mass ratio of 60:12:15:3:10 to obtain an organic solvent, and then lithium salt LiPF was added to the organic solvent. 6 , and obtain an electrolyte, wherein LiPF 6 The concentration is 1.2 mol / L.

[0130] Preparation of negative electrode sheet: The aforementioned silicon-carbon material, conductive carbon black, carbon nanotubes, carboxymethyl cellulose lithium, and styrene-butadiene rubber were mixed in a mass ratio of 96:1:0.1:1:1.9, and then an appropriate amount of deionized water was added to obtain a negative electrode slurry under the action of a vacuum mixer, wherein the solid content of the negative electrode slurry was 45wt%. The negative electrode slurry was coated on a 9μm thick copper foil and dried at 80°C to obtain a negative electrode sheet coated with a negative electrode active material with a thickness of 40μm on one side. After cold pressing and cutting, a negative electrode sheet of the required specifications was obtained.

[0131] Selection of isolation membrane: A porous polyethylene film with a thickness of 7 μm (Celgard Company) was used.

[0132] Battery assembly: Assemble the positive electrode shell, positive electrode sheet, separator, negative electrode sheet, gasket, spring and negative electrode shell in sequence to obtain a button-type full battery. The battery shell adopts LIR2025 model.

[0133] Cyclic performance test: The charge and discharge test was conducted on the LAND battery test system of Wuhan Jinnuo Electronics Co., Ltd. The test conditions were: at 25°C, the charge and discharge voltage was limited to 0.05-2V, and 1C constant current charge and discharge was performed. Specifically, the battery was charged at a rate of 1C to a voltage of 2V, and then discharged at a rate of 1C to a voltage of 0.5V. The reversible capacity was measured to be E 0 The above charge and discharge process is cycled 100 times to obtain the reversible capacity and recorded as E n , where n = 100, the capacity retention rate of the battery after 100 cycles at 25°C is ε = E n / E 0 ×100%.

[0134] The test results are as follows:

[0135] serial number Capacity retention after 100 cycles Example 1 96.1％ Example 2 96.8％ Example 3 96.4％ Comparative Example 1 92.1％ Comparative Example 2 85.3％

[0136] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and the same effect as the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A negative electrode active material, characterized in that: A silicon-carbon material is included, wherein the dQ / dV of the lithium removal curve of the silicon-carbon material has a first characteristic peak in the range of 0.25V-0.35V, and the peak intensity of the first characteristic peak is 1 H , I H The unit is mAh / V, and the dQ / dV of the lithium removal curve of the negative electrode active material has a second characteristic peak in the range of 0.4V-0.5V, and the peak intensity of the second characteristic peak is I S , I S The unit is mAh / V, I S / I H Less than or equal to 0.

6.

2. The negative electrode active material according to claim 1, characterized in that The silicon-carbon material comprises a porous carbon carrier and elemental silicon, wherein the elemental silicon is located in the pore structure of the porous carbon carrier, and the mass fraction of silicon in the negative electrode active material is 30%-70%; Optionally, the mass fraction of silicon in the negative electrode active material is 35%-55%.

3. The negative electrode active material according to claim 1, characterized in that The Dv50 particle size of the negative electrode active material is 4 μm-13 μm.

4. The negative electrode active material according to claim 1, characterized in that The specific surface area of ​​the negative electrode active material is 1 m 2 / g-20m 2 / g.

5. The negative electrode active material according to any one of claims 1 to 4, characterized in that: Further including: A carbon coating layer, wherein the carbon coating layer at least partially covers the outer surface of the silicon-carbon material; Optionally, the mass fraction of the carbon coating layer in the negative electrode active material is 2%-15%.

6. A method for preparing the negative electrode active material according to any one of claims 1 to 5, characterized in that: include: placing the porous carbon support in a silicon deposition apparatus; A mixed gas of silicon source gas and hydrogen is introduced into the silicon deposition equipment, and a silicon deposition process is performed to obtain the silicon-carbon material.

7. The method according to claim 6, characterized in that The porous carbon support satisfies at least one of the following conditions: The specific surface area of ​​the porous carbon carrier is 600 m 2 / g-2000m 2 / g; The Dv50 particle size of the porous carbon carrier is 3 μm-12 μm; The minimum particle size of the porous carbon carrier is greater than or equal to 1.5 μm; The particle size span of the porous carbon carrier is 0.9-1.

2.

8. The method according to claim 6, characterized in that The silicon deposition process satisfies at least one of the following conditions: The temperature of the silicon deposition process is 400°C-800°C; The silicon deposition treatment time is 2h-50h; The silicon source gas includes at least one of silane, disilane, tri(trimethylsilyl)silane, tetrafluorosilane, silicon trichloride, and chlorosilane.

9. The method according to claim 8, characterized in that The silicon deposition equipment includes at least one of a rotary kiln and a fluidized bed; Optionally, the filling rate of the porous carbon carrier in the rotary kiln is 2%-20%; Optionally, the filling rate of the porous carbon carrier in the fluidized bed is 25%-40%; Optionally, the silicon deposition equipment further comprises: a knocking device, wherein the knocking device comprises at least one of an air hammer and a pendulum ball.

10. The method according to any one of claims 6 to 9, characterized in that: The silicon deposition process comprises n stages, n≥2, performed in sequence, wherein: The flow rate of the silicon source gas in the first stage is v, the flow rate of the hydrogen gas in the first stage is 0, and the first stage makes the silicon deposition amount in the silicon-carbon material reach 40%-50% of the preset deposition amount; The flow rate of the silicon source gas in the first stage a is yv, y = -4.0089 ((a + n - 1) / 2n) 2 +4.0068((a+n-1) / 2n), the flow rate of the hydrogen in the ath stage is v(1-y), wherein a is greater than 1.

11. The method according to any one of claims 6 to 9, characterized in that: Further including: After the silicon deposition process, a carbon source gas is introduced into the silicon deposition device, and a carbon coating process is performed, wherein the carbon coating process satisfies at least one of the following conditions: The temperature of the carbon coating treatment is 500°C-1000°C; The carbon coating treatment time is 1h-10h; The carbon source gas includes at least one of methane, acetylene and propyne.

12. A negative electrode plate, characterized in that: The invention comprises a negative electrode current collector and a negative electrode active material layer at least located on one side of the negative electrode current collector, wherein the negative electrode active material layer comprises the negative electrode active material according to any one of claims 1 to 5, or a negative electrode active material prepared by the method according to any one of claims 6 to 11.

13. A battery, characterized in that: Including the negative electrode sheet as described in claim 12.

Images