Method for preparing silicon-carbon material, silicon-carbon material, negative pole piece and battery

Abstract

The invention discloses a method for preparing a silicon-carbon material, the silicon-carbon material, a negative pole piece and a battery. The method for preparing the silicon-carbon material comprises the following steps: placing a porous carbon carrier in silicon deposition equipment; the porous carbon carrier is subjected to first treatment, second particles are obtained, and the first treatment comprises the steps that silicon source gas is introduced into the silicon deposition equipment for silicon deposition treatment, and first particles are obtained; introducing nitrogen source gas into the silicon deposition equipment to carry out etching treatment so as to obtain the second particles; and carrying out second treatment on the second particles to obtain the silicon-carbon material, the second treatment comprising: introducing a silicon source gas into the silicon deposition equipment to carry out silicon deposition treatment to obtain the silicon-carbon material. Therefore, the silicon-carbon material with a small volume expansion rate can be obtained through a simple and convenient process.

Description

Technical Field

[0001] The present application relates to the technical field of batteries, and specifically, to a method for preparing silicon-carbon materials, silicon-carbon materials, negative electrode sheets, and batteries. Background Art

[0002] With the continuous development of electric vehicles, the market has higher and higher requirements for power batteries, and lithium-ion batteries have also developed rapidly. The negative electrode active material is a key factor affecting the performance of lithium-ion batteries. Currently, the commercially available negative electrode active material is mainly graphite, with a theoretical specific capacity of 372 mAh / g, but it can no longer meet the usage requirements. Silicon-based materials are considered to be the next-generation negative electrode active materials with great application potential due to their excellent theoretical specific capacity (4200 mAh / g), suitable voltage platform, environmental friendliness, etc. However, the current silicon-based materials have problems such as large volume expansion, poor cycle stability, and low first charge-discharge efficiency during the charge-discharge cycle of the battery. Therefore, the current silicon-based 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 the first aspect of the present application, a method for preparing a silicon-carbon material is proposed, including: placing a porous carbon carrier in a silicon deposition device; performing a first treatment on the porous carbon carrier to obtain second particles, where the first treatment includes: introducing a silicon source gas into the silicon deposition device to perform silicon deposition treatment to obtain first particles; introducing a nitrogen source gas into the silicon deposition device to perform etching treatment to obtain the second particles; performing a second treatment on the second particles to obtain the silicon-carbon material, where the second treatment includes: introducing a silicon source gas into the silicon deposition device to perform silicon deposition treatment to obtain the silicon-carbon material. Thus, a silicon-carbon material with a smaller volume expansion rate can be obtained through a relatively simple process.

[0005] In some embodiments, the etching treatment satisfies at least one of the following conditions: the temperature of the etching treatment is 500°C - 800°C; the time of the etching treatment is 0.5 h - 5 h; the nitrogen source gas includes ammonia gas. Thus, small-sized microporous structures can be etched and formed inside the porous carbon carrier, reducing the volume expansion rate of the silicon-carbon material.

[0006] In some embodiments, the total mass of the nitrogen source gas introduced in the etching treatment in the first treatment is m1, and the mass of the porous carbon carrier is m2, and m1:m2 is 0.05 - 1. Thus, more small-sized microporous structures can be formed on the porous carbon carrier.

[0007] In some embodiments, the first treatment includes a plurality of alternately performed silicon deposition treatments and etching treatments. Thereby, the amount of silicon deposited inside the porous carbon carrier can be further increased, and a relatively large number of small-sized micropores can be formed inside the porous carbon carrier.

[0008] In some embodiments, the silicon deposition treatment satisfies at least one of the following conditions: the temperature of the silicon deposition treatment is 400°C - 800°C; the time of the silicon deposition treatment is 2h - 50h; the silicon source gas includes at least one of silane, disilane, tris(trimethylsilyl)silane, silicon tetrafluoride, trichlorosilane, chlorosilane; the total mass of the silicon source gas introduced in the silicon deposition treatment in the first treatment is m3, the mass of the porous carbon carrier is m2, and m3:m2 is 0.4 - 0.8; the total mass of the silicon source gas introduced in the silicon deposition treatment in the second treatment is m4, the mass of the porous carbon carrier is m2, and m4:m2 is 0.2 - 0.6; the sum of the total masses of the silicon source gas introduced in the silicon deposition treatments in the first treatment and the second treatment is m5, the mass of the porous carbon carrier is m2, and m5:m2 is 0.7 - 1.8. Thereby, it helps to form uniformly distributed elemental silicon inside the porous carbon carrier.

[0009] In the second aspect of the present application, the present application proposes a silicon-carbon material, which is prepared by the aforementioned method. Thereby, the silicon-carbon material has all the characteristics and advantages of the aforementioned method for preparing the silicon-carbon material. When this material is used as the negative electrode active material of a battery, during the charge and discharge cycle of the battery, the volume expansion of the negative electrode active material is relatively small, and the battery has relatively excellent cycle stability.

[0010] In some embodiments, the silicon content in the silicon-carbon material is 35% - 60%, and / or, the true density of the silicon-carbon material is 1.65 g / cm 3 - 2.0 g / cm 3 . Thereby, it helps to improve the specific capacity of the silicon-carbon material.

[0011] In the third aspect of the present application, the present application proposes a negative electrode plate, which includes a negative electrode current collector and a negative electrode active material layer at least on one side of the negative electrode current collector. The negative electrode active material layer includes the silicon-carbon material prepared by the aforementioned method, or, the aforementioned silicon-carbon material. Thereby, the negative electrode plate has all the characteristics and advantages of the aforementioned silicon-carbon material and the method for preparing the silicon-carbon material, which will not be elaborated herein.

[0012] In some embodiments, the thickness of the negative electrode plate satisfies (D 100-(D0) / D0 is 35% - 60%, where, after the negative electrode sheet and the positive electrode sheet are assembled into a battery, the thickness of the negative electrode sheet when the battery is at 0% SOC is D0; after the battery is charged and discharged 100 times, the thickness of the negative electrode sheet when the battery is at 0% SOC is D 100 . Thus, the volume expansion of the negative electrode sheet during the charge and discharge cycle of the battery is small.

[0013] In the fourth aspect of the present application, a battery is proposed, including the aforementioned negative electrode sheet. Thus, the battery has all the characteristics and advantages of the aforementioned negative electrode sheet, which will not be elaborated here. Description of the Drawings

[0014] The above and / or additional aspects and advantages of the present application will become apparent and easy to understand from the description of the embodiments in conjunction with the following drawings, where:

[0015] Figure 1 is a schematic flow chart of a method for preparing a silicon-carbon material according to an embodiment of the present application;

[0016] Figure 2 is a schematic flow chart of a method for preparing a silicon-carbon material according to another embodiment of the present application. Detailed Description of the Embodiments

[0017] The embodiments of the present application will be described in detail below. The examples of the embodiments are shown in the drawings, but there may be cases where unnecessary details are omitted. For example, there may be cases where the detailed description of well-known matters is omitted and the repeated description of actually identical structures is omitted. This is to avoid the following description from becoming unnecessarily long and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter recited in the claims.

[0018] Unless otherwise defined, all technical and scientific terms used in the present application have the same meaning as commonly understood by those skilled in the art belonging to the technical field of the present application; the terms used in the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application; unless otherwise stated, the numerical values of the various parameters mentioned in the present application can be measured by various commonly used measurement methods in the art (for example, they can be tested according to the methods given in the embodiments of the present application).

[0019] The terms "including" and "having" and any variations thereof in the specification and claims of the present application are open expressions, that is, including the content specified in the present application, but not excluding other aspects.

[0020] In the description of this application, all the numbers disclosed herein are approximate values, whether or not words such as "about" or "approximately" are used. There may be a difference of less than 10% in the numerical value of each number or a reasonable difference considered by those skilled in the art, such as a difference of 1%, 2%, 3%, 4%, or 5%.

[0021] In the description of this application, the terms "first" and "second" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. The "first feature" and "second feature" may include one or more of such features.

[0022] In the description of this application, the meaning of "a plurality of" is two or more.

[0023] In the description of this application, "A and / or B" may include the case of A alone, the case of B alone, and any one of the cases of A and B, where A and B are only for example and may be any technical features connected by "and / or" in this application.

[0024] The lithium insertion platform of the silicon-based material is relatively high, and the lithium potential is about 0.5V. When the silicon-based material is used as the negative electrode active material, the possibility of lithium precipitation on the surface of the negative electrode plate during the charge and discharge process of the battery is relatively small. Moreover, the theoretical specific capacity of the silicon-based material can reach 4200 mAh / g, which is much higher than 372 mAh / g of the carbon-based material, and it has more excellent lithium storage performance. However, during the process of lithium insertion and extraction of the silicon-based negative electrode active material, there is an obvious volume change. Specifically, silicon inserts and extracts lithium in the form of forming a Li-Si alloy with lithium ions, and the volume expansion rate of the Li-Si alloy can reach 300%. The excessive stress will cause the fragmentation of the silicon-based material, resulting in the detachment of the silicon-based negative electrode active material from the negative electrode plate, and then significantly deteriorating the cycle performance of the battery.

[0025] The silicon-carbon material using porous carbon as the dispersion carrier and silicon as the active substance can alleviate the volume expansion of silicon to a certain extent during the process of lithium insertion and extraction, but it still causes problems such as the thickness of the negative electrode plate changing greatly, the electrolyte being unable to flow back in time after being extruded, the wettability of the electrode plate deteriorating, and the cycle performance deteriorating significantly. Taking the pores with a pore diameter less than or equal to 1 nm as small-sized micropores and the pores with a pore diameter of 1 nm - 2 nm as large-sized micropores as an example, during the silicon deposition treatment on the porous carbon carrier, elemental silicon is not easy to deposit and grow in the small-sized micropores. Therefore, the small-sized micropores in the porous carbon carrier can serve as a buffer space to alleviate the volume expansion of the silicon-carbon material during the process of lithium insertion and extraction. However, the number of small-sized micropores in the porous carbon carrier itself is often small, and the effect of alleviating the volume expansion of the silicon-carbon material needs to be improved.

[0026] In the present application, after the porous carbon carrier is subjected to silicon deposition treatment, elemental silicon is deposited and formed in some pore structures inside the porous carbon carrier, such as large-sized micropores, mesopores, and macropores. Moreover, the small-sized micropore structure of the porous carbon carrier itself is not filled with elemental silicon, which can provide a buffer space for the expansion of elemental silicon. Subsequently, a nitrogen source gas is introduced to etch the porous carbon carrier, and then more small-sized micropore structures are formed on the porous carbon carrier, further providing a buffer space for the expansion of elemental silicon. Subsequently, elemental silicon is again deposited and formed in the large-sized micropores, mesopores, and macropores inside the porous carbon carrier that are not filled with elemental silicon through silicon deposition treatment. At this time, the small-sized micropore structures formed by etching with the nitrogen source gas are still not filled with elemental silicon, which can provide a buffer space for the expansion of elemental silicon. Thus, in the application, by performing the silicon deposition treatment step by step and adding an etching treatment with the nitrogen source gas between adjacent silicon deposition treatment steps, a silicon-carbon material with both a high silicon content and a large number of small-sized micropores can be obtained. This silicon-carbon material has both a high specific capacity and a low volume expansion rate. In addition, after etching the porous carbon carrier with the nitrogen source gas, nitrogen elements can be incorporated into the porous carbon carrier to form a nitrogen-doped porous carbon carrier. The nitrogen elements doped in the porous carbon carrier will change the atomic and electronic arrangements in the porous carbon carrier, increase its conductivity, thereby improving the overall conductivity of the porous carbon carrier and further improving the kinetic performance of the silicon-carbon material

[0027] In the first aspect of the present application, the present application proposes a method for preparing a silicon-carbon material, so that a silicon-carbon material with a small volume expansion rate can be obtained through a relatively simple process. Specifically, referring to Figure 1 , the method for preparing a silicon-carbon material includes:

[0028] S100: Place the porous carbon carrier in a silicon deposition device

[0029] In some embodiments, in this step, the porous carbon carrier is placed in the silicon deposition device at a certain filling rate. The silicon deposition device may include at least one of a rotary kiln and a fluidized bed.

[0030] In some embodiments, the filling rate of the porous carbon carrier in the rotary kiln may be 2%-20%, and the filling rate of the porous carbon carrier in the fluidized bed may be 25%-40%.

[0031] When the filling rate of the silicon deposition device is within the foregoing range, the filling rate is appropriate, which helps to control the reaction rate of the silicon source gas and reduce the occurrence of surface silicon coating and material caking.

[0032] In some embodiments, the porous carbon carrier includes at least one of a biomass-based porous carbon and an organic compound-based porous carbon.

[0033] In some embodiments, after placing the porous carbon support in the silicon deposition device, a first treatment is performed on the porous carbon support to obtain second particles, wherein the first treatment includes:

[0034] S210: Introduce a silicon source gas into the silicon deposition device

[0035] In some embodiments, in this step, a silicon source gas is introduced into the silicon deposition device, and the silicon deposition device is heated to perform silicon deposition treatment to obtain first particles.

[0036] According to some embodiments of the present application, the temperature of the silicon deposition treatment is 400°C - 800°C.

[0037] As an example, the temperature of the silicon deposition treatment can be 400°C, 410°C, 420°C, 430°C, 440°C, 450°C, 460°C, 470°C, 480°C, 490°C, 500°C, 510°C, 520°C, 530°C, 540°C, 550°C, 560°C, 570°C, 580°C, 590°C, 600°C, 610°C, 620°C, 630°C, 640°C, 650°C, 660°C, 670°C, 680°C, 690°C, 700°C, 710°C, 720°C, 730°C, 740°C, 770°C, 760°C, 770°C, 780°C, 790°C or 800°C.

[0038] When the temperature of the silicon deposition treatment is within the aforementioned range, it helps to form elemental silicon with a relatively high crystallinity within the pore structure of the porous carbon support, such that the first particles have a relatively high specific capacity.

[0039] According to some embodiments of the present application, the time of the silicon deposition treatment is 2h - 50h.

[0040] When the time of the silicon deposition treatment is within the aforementioned range, it helps to fully deposit elemental silicon within the pore structure of the porous carbon support.

[0041] According to some embodiments of the present application, the silicon source gas includes at least one of silane, disilane, tris(trimethylsilyl)silane, silicon tetrafluoride, trichlorosilane, and chlorosilane.

[0042] In some embodiments, the gas in the silicon deposition device can be replaced with a carrier gas first, and then a mixture of the silicon source gas and the carrier gas is introduced at a certain temperature and in a certain ratio.

[0043] S220: Introduce a nitrogen source gas into the silicon deposition device

[0044] In some embodiments, after the silicon deposition process is completed, a nitrogen source gas is introduced into the silicon deposition equipment in this step to perform an etching process to obtain second particles. The nitrogen source gas etches the porous carbon carrier in the first particles, and then forms more small-sized microporous structures on the porous carbon carrier, thereby obtaining second particles with more small-sized microporous structures, providing a buffer space for the expansion of the elemental silicon loaded in the porous carbon carrier.

[0045] According to some embodiments of the present application, the temperature of the etching process is 500°C - 800°C.

[0046] As an example, the temperature of the etching process can be 500°C, 510°C, 520°C, 530°C, 540°C, 550°C, 560°C, 570°C, 580°C, 590°C, 600°C, 610°C, 620°C, 630°C, 640°C, 650°C, 660°C, 670°C, 680°C, 690°C, 700°C, 710°C, 720°C, 730°C, 740°C, 770°C, 760°C, 770°C, 780°C, 790°C or 800°C.

[0047] When the temperature of the etching process is within the aforementioned range, the temperature of the etching process is close to that of the silicon deposition process. While the etching effect of the nitrogen source gas on the porous carbon carrier is good, it can also reduce the waiting time for the equipment temperature to rise and the consumed time, greatly improving the production efficiency.

[0048] In some embodiments, the temperature of the etching process is the same as that of the silicon deposition process.

[0049] According to some embodiments of the present application, the time of the etching process is 0.5 h - 5 h.

[0050] When the time of the etching process is within the aforementioned range, more small-sized microporous structures can be formed on the porous carbon carrier, and the collapse of the small-sized microporous structures caused by too long etching time can be reduced, thereby forming large-sized micropores.

[0051] According to some embodiments of the present application, the nitrogen source gas includes ammonia.

[0052] It can be understood that the etching process in the first treatment should be carried out after the silicon deposition process, so that after elemental silicon fills the large-sized micropores of the original porous carbon support and closes the small-sized micropore structure of the original porous carbon support, a new small-sized micropore structure can be formed through the etching process, thereby realizing the increase in the total amount of small-sized micropores of the porous carbon support. If the porous carbon support is directly etched, the small-sized micropores of the porous carbon support itself will collapse due to etching, and then communicate with adjacent pore structures to form large-sized micropores, mesopores or macropore structures, which will still be filled with elemental silicon in the subsequent silicon deposition process and cannot provide a buffer space for the expansion of elemental silicon.

[0053] In some embodiments, the total mass of the nitrogen source gas introduced in the etching process in the first treatment is m1, and the mass of the porous carbon support is m2, and m1:m2 is 0.05 - 1. In other embodiments, m1:m2 is 0.1 - 0.6.

[0054] When the total mass of the nitrogen source gas introduced in the etching process is within the aforementioned range, more small-sized micropore structures with smaller pore diameters can be formed on the porous carbon support, and the porous carbon support can be doped with an appropriate amount of nitrogen elements.

[0055] In some embodiments, the first treatment may include a plurality of alternately performed silicon deposition processes and etching processes. For example, referring to Figure 2 , the first treatment may include alternately performing a silicon deposition process S210 and an etching process S220, so that the silicon deposition process can be divided into multiple steps, and an etching process is performed after each silicon deposition process to form a new small-sized micropore structure, thereby obtaining a silicon-carbon material with both a high silicon content and a low volume expansion rate.

[0056] As an example, the first treatment may include: first depositing silicon to 50% of the theoretical silicon deposition amount, and then introducing ammonia gas with m1 = 0.2m2.

[0057] As an example, the first treatment may include: first depositing silicon to 33% of the theoretical silicon deposition amount, and then introducing ammonia gas with m1 = 0.1m2; then depositing silicon to 66% of the theoretical silicon deposition amount, and introducing ammonia gas with m1 = 0.1m2 again.

[0058] In some embodiments, the total mass of the silicon source gas introduced in the silicon deposition process in the first treatment is m3, and the mass of the porous carbon support is m2, and m3:m2 is 0.4 - 0.8.

[0059] It should be noted that when the first treatment includes multiple alternately performed silicon deposition treatments and etching treatments, the silicon deposition amount of each silicon deposition treatment and the number of silicon deposition treatments are not particularly limited, as long as the sum of the silicon deposition amounts of the multiple silicon deposition treatments in the multiple first treatments can meet the total mass of the silicon source gas introduced in the required first treatment. Those skilled in the art can choose according to the actual situation.

[0060] It should be noted that during the alternation of the silicon deposition treatment and the etching treatment in the first treatment, inert gas replacement can be performed according to the actual situation to reduce the generation of silicon nitride impurities.

[0061] In some embodiments, after obtaining the second particles, the second treatment is performed on the second particles to obtain a silicon-carbon material, wherein the second treatment includes:

[0062] S300: Introduce a silicon source gas into the silicon deposition equipment

[0063] In some embodiments, a silicon deposition treatment is performed in this step to further increase the silicon content in the silicon-carbon material to reach the theoretical silicon deposition amount, thereby obtaining a silicon-carbon material.

[0064] In some embodiments, the conditions of the silicon deposition treatment in the second treatment can be the same as those in the first silicon deposition treatment, which will not be elaborated here. Thus, when switching between the first treatment and the second treatment, the time consumption is less, and the production efficiency can be effectively improved.

[0065] In some embodiments, the total mass of the silicon source gas introduced in the silicon deposition treatment in the second treatment is m4, and the mass of the porous carbon carrier is m2, and m4:m2 is 0.2 - 0.6.

[0066] In some embodiments, the sum of the total masses of the silicon source gas introduced in the silicon deposition treatments in the first treatment and the second treatment is m5, and the mass of the porous carbon carrier is m2, and m5:m2 is 0.7 - 1.8.

[0067] In some embodiments, the total mass of the silicon source gas introduced in the first treatment is m3 = 0.5m2, the total mass of the silicon source gas introduced in the second treatment is m4 = 0.55m2, and the sum of the total masses of the silicon source gas introduced in the first treatment and the second treatment is m5 = 1.05m2.

[0068] It should be noted that those skilled in the art can choose the total silicon deposition amount in the first treatment according to the actual situation, as long as the sum m5 of the total amounts of the silicon source gas introduced in the first treatment and the second treatment can meet the requirement for the silicon content in the silicon-carbon material.

[0069] As an example, the first treatment may include: first depositing silicon to 33% of the theoretical silicon deposition amount, and then introducing ammonia gas with m1 = 0.1m2; subsequently, depositing to 100% of the theoretical silicon deposition amount through the second treatment.

[0070] As an example, the first treatment may include: first depositing silicon to 33% of the theoretical silicon deposition amount, and then introducing ammonia gas with m1 = 0.1m2; then depositing silicon to 66% of the theoretical silicon deposition amount, and introducing ammonia gas with m1 = 0.1m2 again; subsequently, depositing to 100% of the theoretical silicon deposition amount through the second treatment.

[0071] In some embodiments, after the second treatment is completed, the material can be cooled and collected under a carrier gas to obtain the silicon-carbon material.

[0072] In some embodiments, referring to Figure 2 , the method for preparing the silicon-carbon material may further include:

[0073] S400: Introduce a carbon source gas into the silicon deposition device

[0074] In some embodiments, after the second treatment, in this step, a carbon source gas is introduced into the silicon deposition device, the silicon deposition device is heated up, and a carbon coating treatment is performed. Specifically, a carrier gas can be used for secondary replacement first to exhaust the silicon source gas in the silicon deposition device, and then a mixture of the carbon source gas and the carrier gas is introduced in a certain proportion.

[0075] In some embodiments, the carrier gas includes at least one of nitrogen gas and inert gas.

[0076] In some embodiments, the carbon coating treatment satisfies at least one of the following conditions: the temperature of the carbon coating treatment is 500°C - 800°C; the time of the carbon coating treatment is 1h - 10h; 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.

[0077] In some embodiments, when the process switches between the silicon deposition treatment and the carbon coating treatment, a carrier gas can be first introduced into the silicon deposition device for gas replacement, and then the carbon source gas is introduced. For example, after introducing a mixture of the silicon source gas and the carrier gas in the second treatment to perform the silicon deposition treatment, a carrier gas can be introduced into the silicon deposition device for gas replacement, and then a mixture of the carbon source gas and the carrier gas is introduced to perform the carbon coating treatment.

[0078] In the second aspect of the present application, the present application provides a silicon-carbon material, which is prepared by the aforementioned method. Thus, the silicon-carbon material has all the characteristics and advantages of the aforementioned method for preparing the silicon-carbon material. When this material is used as the negative electrode active material of a battery, during the charge and discharge cycle of the battery, the volume expansion of the negative electrode active material is small, and the battery has better cycle stability.

[0079] The silicon-carbon material prepared by the foregoing method can not only effectively buffer the volume change during the insertion and extraction of lithium in silicon particles through the small-sized microporous structure in the porous carbon carrier, maintaining the structural integrity of the negative electrode sheet, but also use the nitrogen-doped porous carbon carrier as a conductive scaffold to provide an electron channel and an ion channel for silicon, improving the kinetic performance of silicon.

[0080] In some embodiments, the silicon content in the silicon-carbon material is 35%-60%.

[0081] When the content of elemental silicon in the silicon-carbon material is within the foregoing range, the silicon-carbon material has a high specific capacity, and the elemental silicon is mainly deposited in the pore structure of the porous carbon carrier, reducing the poor silicon coating on the surface of the porous carbon carrier caused by excessive silicon content, and then improving the agglomeration, over-expansion and other defects in the silicon-carbon material.

[0082] In some embodiments, the true density of the silicon-carbon material is 1.65 g / cm 3 -2.0 g / cm 3 .

[0083] The true density refers to the actual mass of the solid substance per unit volume in the absolutely dense state of the material, that is, the density after removing the internal pores or the voids between particles. For the silicon-carbon material, the true density can reflect the silicon deposition amount in the silicon-carbon material. When the true density of the silicon-carbon material is within the foregoing range, the silicon-carbon material has a large number of internal small-sized microporous structures while still having a high silicon deposition amount, and both the specific capacity and the expansion inhibition performance of the silicon-carbon material are excellent.

[0084] In some embodiments, the nitrogen content in the silicon-carbon material is 0.5%-5%, and / or the mass fraction of the carbon coating layer in the silicon-carbon material is 2%-15%.

[0085] When the nitrogen content and / or carbon content of the silicon-carbon material is within the foregoing range, the doped nitrogen element in the porous carbon carrier will change the atomic and electron arrangements in the porous carbon carrier, increasing its conductivity, thereby improving the overall conductivity of the porous carbon carrier, and further making the silicon-carbon material have better conductivity and improving the kinetic performance.

[0086] In the third aspect of the present application, the present application provides a negative electrode sheet, including a negative electrode current collector and a negative electrode active material layer at least on one side of the negative electrode current collector. The negative electrode active material layer includes the silicon-carbon material prepared by the foregoing method, or the foregoing silicon-carbon material. Thus, the negative electrode sheet has all the characteristics and advantages of the foregoing silicon-carbon material and the method for preparing the silicon-carbon material, which will not be elaborated herein.

[0087] In some embodiments, the thickness of the negative electrode sheet satisfies (D 100-(D0) / D0 is 35% - 60%, where, after the negative electrode sheet and the positive electrode sheet are assembled into a battery, the thickness of the negative electrode sheet when the battery is at 0% SOC is D0; after the battery is charged and discharged 100 times, the thickness of the negative electrode sheet when the battery is at 0% SOC is D 100 .

[0088] When the thickness of the negative electrode sheet satisfies (D 100 -D0) / D0 is 35% - 60%, the thickness change of the negative electrode sheet after charge and discharge cycling is relatively small, so that the internal stress on the negative electrode sheet is small, and the small stress has little influence on the structural stability of the silicon-carbon material, and the cycle performance of the battery is improved.

[0089] In the fourth aspect of the present application, the present application proposes a battery including the aforementioned negative electrode sheet. Thus, the battery has all the features and advantages of the aforementioned negative electrode sheet, which will not be elaborated here.

[0090] The solution of the present application will be described below through specific examples. It should be noted that the following examples are only used to illustrate the present application and should not be regarded as limiting the scope of the present application. For those not specifying specific techniques or conditions in the examples, they shall be carried out according to the techniques or conditions described in the literature in this field or according to the product specifications. For reagents or instruments not indicating the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0091] Example 1

[0092] 1. Take 1 kg of a porous carbon carrier with a BET of 1853 m 2 / g and a Dv50 particle size of 6.1 μm in a rotary kiln, with a filling rate of 15%, and displace with nitrogen.

[0093] 2. The first treatment includes:

[0094] (1) Heat the rotary kiln to 550 °C, turn on the pneumatic hammer to strike, with a striking interval of 60 s; the rotation speed of the rotary kiln is 0.75 r / min; introduce a mixture of 2 L / min of silane and 2 L / min of nitrogen, and carry out silicon deposition treatment for 3.5 h.

[0095] (2) Keep the temperature and rotation speed of the rotary kiln unchanged, introduce a mixture of 2 L / min of ammonia and 2 L / min of nitrogen, and introduce a total of 0.2 kg of ammonia for etching treatment, and the etching treatment time is 2.5 h.

[0096] 3. The second treatment includes:

[0097] Keep the temperature and rotation speed of the rotary kiln unchanged, introduce a mixture of 2 L / min of silane and 2 L / min of nitrogen, and carry out silicon deposition treatment for 4 h.

[0098] 4. Keep the rotation speed of the rotary kiln unchanged, and use argon to conduct a secondary gas replacement on the rotary kiln. Raise the temperature of the rotary kiln to 650 °C, and introduce a mixture of 2 L / min of nitrogen and 2 L / min of acetylene to carry out carbon coating treatment for 2 h.

[0099] 5. Stop heating the rotary kiln, adjust the rotation speed of the rotary kiln to 0.3 r / min, turn off acetylene, and adjust nitrogen to 0.3 L / min; wait for cooling and material collection to obtain the new silicon-carbon material.

[0100] Example 2

[0101] Example 2 is the same as Example 1, except that in the first treatment, a total of 0.1 kg of ammonia gas is introduced for etching treatment, and the etching treatment time is 1.25 h.

[0102] Example 3

[0103] Example 3 is the same as Example 1, except that the first treatment includes alternately performing the first silicon deposition treatment, the first etching treatment, the second silicon deposition treatment, and the second etching treatment, where the time of the first silicon deposition treatment is 2.5 h, the time of the first etching treatment is 1.25 h, the time of the second silicon deposition treatment is 2.5 h, the time of the second etching treatment is 1.25 h, and the silicon deposition time of the second treatment is 2.5 h.

[0104] Example 4

[0105] Example 4 is the same as Example 1, except that in the second treatment, the time of the silicon deposition treatment is 3.5 h.

[0106] Comparative Example 1

[0107] Comparative Example 1 is the same as Example 4, except that no etching treatment is performed.

[0108] Assemble the silicon-carbon materials in the above examples and comparative examples into coin-shaped full cells, and the assembly method is as follows:

[0109] Preparation of the positive electrode sheet: Mix the positive electrode active material LiNi 0.8 Co 0.1 Mn 0.1 O2, conductive carbon black, binder polyvinylidene fluoride, and carbon nanotubes in a mass ratio of 96.5:1:2:0.5, and then add an appropriate amount of N-methylpyrrolidone (NMP). Obtain the positive electrode slurry under the action of a vacuum mixer, where the solid content of the positive electrode slurry is 70 wt%. Coat the positive electrode slurry on an aluminum foil with a thickness of 9 μm and dry it at 120 °C to obtain a positive electrode sheet with a single-sided coating of a positive electrode active material layer with a thickness of 45 μm. After cold pressing and cutting, obtain the positive electrode sheet with the required specifications.

[0110] Preparation of electrolyte: In a glove box under an argon atmosphere 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. Then, lithium salt LiPF6 was added to the above-mentioned mixed organic solvent to obtain an electrolyte. Among them, the concentration of LiPF6 in the electrolyte was 1.2 mol / L.

[0111] Preparation of the negative electrode sheet: The above-mentioned silicon-carbon material, conductive carbon black, carbon nanotubes, sodium carboxymethyl cellulose, 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. Under the action of a vacuum mixer, a negative electrode slurry was obtained, and the solid content of the negative electrode slurry was 45 wt%. The negative electrode slurry was coated on a 9-μm-thick copper foil and dried at 80°C to obtain a negative electrode sheet with a single-sided coating of negative electrode active material with a thickness of 40 μm. After cold pressing and cutting, negative electrode sheets of the required specifications were obtained.

[0112] Selection of the separator: A porous polyethylene film (Celgard company) with a thickness of 7 μm was used.

[0113] Assembly of the battery: The positive electrode shell, positive electrode sheet, separator, negative electrode sheet, gasket, shrapnel, and negative electrode shell were assembled in sequence to obtain a button-type full battery. The battery shell was of the LIR2025 model.

[0114] The negative electrode active materials in the above-mentioned examples and comparative examples were assembled into button-type half cells, and the assembly method was as follows:

[0115] The silicon-carbon material, acetylene black, and binder were mixed in a mass ratio of 80:1:1, where the binder was a mixed binder of carboxymethyl cellulose and styrene-butadiene rubber with a mass ratio of 5:5. Using 1 mol / L LiPF6 as the electrolyte, the solvent of the electrolyte was a mixed solvent of EC:EMC:DMC with a volume ratio of 1:1:1, and a metal lithium sheet was used as the counter electrode. A CR2032 button-type half cell was assembled in a glove box.

[0116] The button-type full cells and button-type half cells in the above-mentioned examples and comparative examples were tested, and the test method was as follows. The test results are shown in Table 1:

[0117] Swelling rate test: The button-type full cell was tested on a LAND battery test system of Wuhan Jinnuo Electronics Co., Ltd. The test conditions were: at 25°C, the charge-discharge voltage limit was 0.005 V - 2 V, and 1C constant current charge-discharge was performed. Specifically, it was charged at a 1C rate to a voltage of 2 V, and then discharged at a 1C rate to a voltage equal to 0.005 V. After cycling 100 times according to the above charge-discharge process, the battery was disassembled, and the thickness of the negative electrode sheet was measured as D100 , the initial thickness of the negative electrode sheet is D0, and the swelling rate n of the negative electrode sheet after the battery is cycled 100 times at 25 °C is n = (D 100 - D0) / D0 × 100%.

[0118] Cycling performance test: The coin-type full battery was tested for cycling performance on the LAND battery test system of Wuhan Jinnuo Electronics Co., Ltd. The test conditions were as follows: at 25 °C, the charge-discharge voltage was limited to 0.005 - 2 V, and 1C constant current charge-discharge was carried out. Specifically, it was charged at a 1C rate to a voltage of 2 V, and then discharged at a 1C rate to a voltage equal to 0.005 V, and the reversible capacity was measured as E0. After cycling 100 times according to the above charge-discharge process, the reversible capacity was obtained and denoted as E n , where n = 100, and the capacity retention rate ε of the battery after being cycled 100 times at 25 °C is ε = E n / E0 × 100%.

[0119] 0.8V charge capacity test: The coin-type half battery was tested on the LAND battery test system of Wuhan Jinnuo Electronics Co., Ltd. The test conditions were as follows: at 25 °C, the charge-discharge voltage was limited to 0.005 V - 2 V, and 0.1C constant current charge-discharge was carried out. Specifically, it was discharged at a 0.1C rate to a voltage equal to 0.005 V, and then charged at a 0.1C rate to a voltage equal to 0.8 V, and the charge capacity was measured as E.

[0120] Table 1

[0121]

[0122] It should be noted that this 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 this application are included in the technical scope of this application. In addition, within the scope of not departing from the gist of this application, various modifications that can be thought of by those skilled in the art to the embodiments, and other ways constructed by combining some constituent elements of the embodiments are also included in the scope of this application.

Claims

1. A method for preparing a silicon-carbon material, characterized in that, Comprising: Placing a porous carbon support in a silicon deposition device; Performing a first treatment on the porous carbon support to obtain second particles, wherein the first treatment includes: introducing a silicon source gas into the silicon deposition device to perform a silicon deposition treatment to obtain first particles; introducing a nitrogen source gas into the silicon deposition device to perform an etching treatment to obtain the second particles; Performing a second treatment on the second particles to obtain the silicon-carbon material, wherein the second treatment includes: introducing a silicon source gas into the silicon deposition device to perform a silicon deposition treatment to obtain the silicon-carbon material.

2. The method according to claim 1, wherein The etching treatment satisfies at least one of the following conditions: The temperature of the etching treatment is 500°C - 800°C; The time of the etching treatment is 0.5 h - 5 h; The nitrogen source gas includes ammonia gas.

3. The method according to claim 1 or 2, characterized in that, In the first treatment, the total mass of the nitrogen source gas introduced in the etching treatment is m1, and the mass of the porous carbon support is m2, and m1:m2 is 0.05 - 1.

4. The method according to claim 1, wherein The first treatment includes multiple alternating silicon deposition treatments and etching treatments.

5. The method according to claim 1, wherein The silicon deposition treatment satisfies at least one of the following conditions: The temperature of the silicon deposition treatment is 400°C - 800°C; The time of the silicon deposition treatment is 2 h - 50 h; The silicon source gas includes at least one of silane, disilane, tris(trimethylsilyl)silane, silicon tetrafluoride, trichlorosilane, and chlorosilane; In the first treatment, the total mass of the silicon source gas introduced in the silicon deposition treatment is m3, and the mass of the porous carbon support is m2, and m3:m2 is 0.4 - 0.8; In the second treatment, the total mass of the silicon source gas introduced in the silicon deposition treatment is m4, and the mass of the porous carbon support is m2, and m4:m2 is 0.2 - 0.6; The sum of the total masses of the silicon source gas introduced in the silicon deposition treatments in the first treatment and the second treatment is m5, and the mass of the porous carbon support is m2, and m5:m2 is 0.7 - 1.

8.

6. A silicon-carbon material, characterized in that, The silicon-carbon material is prepared by the method according to any one of claims 1 - 5.

7. The silicon-carbon material according to claim 6, characterized in that, The silicon content in the silicon-carbon material is 35%-60%, and / or, the true density of the silicon-carbon material is 1.65 g / cm 3 -2.0 g / cm 3 .

8. A negative electrode sheet, characterized in that, Comprising a negative electrode current collector and at least a negative electrode active material layer on one side of the negative electrode current collector, wherein the negative electrode active material layer includes the silicon-carbon material prepared by the method according to any one of claims 1 - 5, or the silicon-carbon material according to claim 6 or 7.

9. The negative electrode sheet according to claim 8, characterized in that, The thickness of the negative electrode sheet satisfies that (D 100 - D0) / D0 is 35% - 60%, where, after the negative electrode sheet and the positive electrode sheet are assembled into a battery, the thickness of the negative electrode sheet when the battery is at 0% SOC is D0; after the battery is charged and discharged 100 times, the thickness of the negative electrode sheet when the battery is at 0% SOC is D 100 .

10. A battery, characterized in that, Comprising the negative electrode plate according to claim 8 or 9.

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