Silicon-carbon negative electrode material, preparation method thereof, negative electrode sheet and electrochemical device

Abstract

The application relates to the technical field of batteries, and discloses a silicon-carbon negative electrode material, a preparation method thereof, a negative electrode sheet and an electrochemical device. The silicon-carbon negative electrode material comprises a porous carbon base body, the oxygen content of the porous carbon base body is A, 0.3wt%<=A<=3wt%, nano-silicon, the nano-silicon is at least partially located in the pores of the porous carbon base body, and a carbon coating layer wraps at least part of the surface of the porous carbon base body. The silicon-carbon negative electrode material has relatively optimal electrochemical performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular, to a silicon-carbon negative electrode material, a preparation method thereof, a negative electrode sheet and an electrochemical device. BACKGROUND

[0002] With the global emphasis on clean energy and the rapid development of new energy industries such as electric vehicles, photovoltaic power generation and wind energy, the application demand of lithium batteries and other electrochemical devices in the field of energy storage presents an explosive growth trend. Although silicon negative electrode material has the advantage of high theoretical specific capacity, its volume will change significantly during the charging and discharging process of lithium batteries. This dramatic volume change will cause the active material to fall off, pulverize and even destroy the electrode structure, thereby causing rapid capacity decay of the battery. This technical bottleneck seriously restricts the widespread application of silicon negative electrode material in industrial production. Carbon negative electrode material has a small volume change during the charging and discharging process due to its stable structural characteristics, and exhibits excellent cycle stability. At the same time, carbon material has similar chemical properties to silicon and good compatibility. Therefore, the industry generally adopts the method of combining silicon and carbon material to prepare silicon-carbon negative electrode material. Silicon-carbon negative electrode material can effectively improve the volume effect of silicon and improve its electrochemical stability.

[0003] However, in the composite system of silicon and porous carbon, there are many disadvantages in the deposition of silicon source on the surface of porous carbon, such as the deposition of silicon on the surface causing silicon crystallization, exacerbating the expansion, blocking the pore channel of the porous carbon substrate, exacerbating the electrochemical performance defects, restricting the cycle stability, unstable SEI film, continuous consumption of lithium source and other adverse factors. These problems are intertwined and jointly restrict the practical application of gas-phase silicon-carbon negative electrode material in lithium ion batteries, and also become one of the key technical bottlenecks that need to be broken through in the field of new energy materials.

[0004] 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 the prior art. SUMMARY

[0005] In a first aspect of the present application, a silicon-carbon negative electrode material is provided, comprising: a porous carbon substrate, the oxygen content of the porous carbon substrate being A, 0.3wt%≤A≤3wt%; nano-silicon, the nano-silicon being at least partially located in the pores of the porous carbon substrate; and a carbon coating layer, the carbon coating layer wrapping at least part of the surface of the porous carbon substrate.

[0006] In some embodiments, the hydrogen content of the porous carbon substrate is B, wherein 0.05wt%≤B≤0.5wt% and A>B.

[0007] In some embodiments, 1.5 wt%≤A≤2wt% and 0.1wt%≤B≤0.25wt%.

[0008] In some embodiments, the specific surface area of the porous carbon matrix is 1600 m 2 / g~2400 m 2 / g.

[0009] In some embodiments, the microporosity of the porous carbon matrix is 80%~97%.

[0010] In some embodiments, the pore volume of the porous carbon matrix is 0.6 cm 3 / g-1.2 cm 3 / g.

[0011] In some embodiments, the average pore size of the porous carbon matrix is 1.5 nm-2.3 nm.

[0012] In some embodiments, the particle size of the porous carbon matrix is 3 μm≤Dv50≤10 μm.

[0013] In a second aspect of the present application, a method for preparing a silicon-carbon negative electrode material is provided, which comprises: performing a first carbonization treatment on a resin carbon source to obtain a first intermediate; performing an activation treatment on the first intermediate to obtain a second intermediate; performing a second carbonization treatment on the second intermediate to obtain a porous carbon matrix, wherein the temperature of the second carbonization treatment is 800°C~1000°C; and performing a gas phase deposition treatment on the porous carbon matrix using a silicon source and a carbon source to obtain the silicon-carbon negative electrode material.

[0014] In some embodiments, the temperature of the first carbonization treatment is 400°C~600°C.

[0015] In some embodiments, the activation agent comprises at least one of KOH, NaOH, CO2, and water vapor.

[0016] In some embodiments, the temperature of the activation treatment is 400°C~800°C.

[0017] In a third aspect of the present application, a negative electrode tab is provided, which comprises the silicon-carbon negative electrode material provided by the present application or prepared by the method provided by the present application.

[0018] In a fourth aspect of the present application, an electrochemical device is provided, which comprises the negative electrode tab provided by the present application.

[0019] The technical solutions provided by the present application have at least the following beneficial effects:

[0020] The silicon-carbon anode material proposed in this application exhibits high bonding strength between nano-silicon and the porous carbon matrix, with the nano-silicon possessing a suitable spatial distribution. This helps reduce the shedding of nano-silicon particles during lithium-ion battery cycling, thereby improving cycle stability. Furthermore, the carbon coating layer, combined with the aforementioned porous carbon matrix and nano-silicon, further enhances the conductivity and structural stability of the silicon-carbon anode material.

[0021] The method for preparing silicon-carbon anode materials proposed in this application achieves suitable micro-oxygen content and low hydrogen content in the porous carbon matrix through precise control of relevant process parameters. This is beneficial for preparing silicon-carbon anode materials with uniform nano-silicon distribution, small silicon volume effect, and good electrochemical stability. Attached Figure Description

[0022] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0023] Figure 1 This is a voltage-to-capacity curve of the silicon-carbon anode material prepared in one embodiment of this application;

[0024] Figure 2 This is a scanning electron microscope (SEM) image of the silicon-carbon anode material prepared in one embodiment of this application;

[0025] Figure 3 This is a pore size distribution diagram of the porous carbon matrix prepared in Example 7 of this application. Detailed Implementation

[0026] The embodiments of this application are described in detail below, with examples of these embodiments shown in the accompanying drawings. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0027] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used in this application is for the purpose of describing particular embodiments only and is not intended to limit this application; unless otherwise stated, the values ​​of the parameters mentioned in this application can be measured using various measurement methods commonly used in the art (e.g., they can be tested according to the methods given in the embodiments of this application).

[0028] The terms "comprising" and "having" and any variations thereof in the specification and claims of this application are open-ended, that is, they mean including, but not limited to, whatever follows the term.

[0029] In the description of the present application, all the numbers disclosed herein are approximate. Each numerical value has a tolerance of ± 10% or as understood by one skilled in the art, such as ± 1%, ± 2%, ± 3%, ± 4%, or ± 5%.

[0030] The ranges disclosed in the present application are defined by the lower limit and the upper limit in the form of a range, and the given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of the particular range. The ranges defined in this way can include or not include the end value, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a range. For example, if the ranges of 60-120 and 80-110 are listed for a particular parameter, it is understood that the ranges of 60-110 and 80-120 are also contemplated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4 and 5 are listed, the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise stated, the numerical range "a-b" represents a shorthand notation for any real combination of integers between a and b, where a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" have been listed herein, and "0-5" is only a shorthand notation for these numerical combinations. In addition, when a parameter is stated to be ≥2 integers, it is equivalent to disclose that the parameter is, for example, integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0031] If not specifically stated, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions.

[0032] If not specifically stated, all technical features and optional technical features of the present application can be combined with each other to form new technical solutions.

[0033] Taking lithium batteries as an example, when silicon-carbon material is used as negative active material, silicon will undergo a huge volume change after lithium intercalation, resulting in the rupture of the original SEI film, and the fresh silicon surface exposed will react with the electrolyte again, continuously generating new and thicker SEI films, thereby consuming a large amount of lithium and electrolyte, and further reducing the first coulombic efficiency of lithium ion batteries.

[0034] To this end, in a first aspect of the present application, the present application provides a silicon-carbon negative electrode material, comprising: a porous carbon matrix, the oxygen content of the porous carbon matrix being A, wherein 0.3wt%≤A≤3wt%; nano-silicon, the nano-silicon being at least partially located in the pores of the porous carbon matrix; and a carbon coating layer, the carbon coating layer wrapping at least part of the surface of the porous carbon matrix. Wherein the oxygen content of the porous carbon matrix is A, and the hydrogen content is B, the oxygen content being the percentage of oxygen in the porous carbon in the total weight of the porous carbon, and the hydrogen content being the percentage of hydrogen in the porous carbon in the total weight of the porous carbon.

[0035] Within the foregoing range, the oxygen element in the porous carbon matrix is mostly in the form of polar functional groups such as hydroxyl (-OH), carboxyl (-COOH), carbonyl (C=O), etc. These functional groups can form chemical bonds with silicon elements or the silicon oxide layer SiO x The formation of Si-O-C covalent bonds or strong hydrogen bonds can significantly enhance the interfacial bonding force between the nano-silicon and the porous carbon matrix, reducing the shedding of nano-silicon during the charge-discharge cycle of the lithium battery. The combination of the aforementioned chemical bonds can also improve the direct bonding strength between the nano-silicon and the porous carbon matrix, reducing the multi-layer adsorption of nano-silicon. In addition, oxygen-containing functional groups such as carboxyl groups can be fully consumed in the bonding with silicon elements, thereby reducing the side reactions of active functional groups containing oxygen with substances such as electrolyte in lithium batteries. Including side reactions with lithium ions (Li + ) reaction -COOH+Li + →-COOLi+H + , and further reducing the additional consumption of lithium in lithium batteries. Thus, the aforementioned silicon-carbon negative electrode material can have better initial efficiency and lithium intercalation capacity in lithium batteries.

[0036] As an example, the oxygen content A is 0.3wt%, 0.5wt%, 0.7wt%, 1wt%, 1.3wt%, 1.5wt%, 1.7wt%, 2wt%, 2.3wt%, 2.5wt%, 2.7wt%, 3wt%, etc.

[0037] In some embodiments, the hydrogen content of the porous carbon matrix is B, wherein 0.05wt%≤B≤0.5wt%, and A>B.

[0038] The hydrogen element mainly exists in the form of non-polar C-H bonds in the porous carbon matrix, and the C-H bonds are connected with the silicon element through van der Waals force, and the interaction is weak, and the anchoring effect on the nanometer silicon is relatively limited. When the oxygen element is dominant in the porous carbon matrix relative to the hydrogen element, the "binding" ability of the porous carbon matrix to the nanometer silicon is stronger, which is beneficial to the silicon-carbon negative electrode material to maintain high structural stability. Therefore, the nanometer silicon is uniformly distributed in the pores of the porous carbon matrix, providing active sites for lithium ion storage, which is beneficial to reducing the shedding of nanometer silicon particles in the silicon-carbon negative electrode material during the cycle process of the lithium battery, improving the cycle stability and lithium intercalation capacity. Moreover, the carbon coating layer is combined with the aforementioned porous carbon matrix and nanometer silicon, further enhancing the conductivity and structural stability of the silicon-carbon negative electrode material.

[0039] For example, the hydrogen content B is 0.05wt%, 0.07wt%, 0.1wt%, 0.2wt%, 0.3wt%, 0.4wt%, 0.5wt%, etc.

[0040] In some embodiments, 1.5wt%≤A≤2wt%, 0.1wt%≤B≤0.25wt%.

[0041] Within the range of the aforementioned oxygen content and hydrogen content, it is beneficial to optimize the adsorption state of nanometer silicon, which can improve the uniformity of nanometer silicon distribution, enhance the stability of the silicon-carbon composite structure, and strengthen the bonding strength. Therefore, it is beneficial to improve the first charge-discharge efficiency and cycle performance of the silicon-carbon negative electrode material.

[0042] In some embodiments, the specific surface area of the porous carbon matrix is 1600m 2 / g~2400m 2 / g. Therefore, on the aforementioned porous carbon matrix, the nanometer silicon can have suitable dispersibility, which is beneficial to reducing the structural damage caused by local swelling stress concentration to the silicon-carbon negative electrode material.

[0043] In some embodiments, the microporosity of the porous carbon matrix is 80%~97%. Micropores are pores with a pore size less than 2nm, which are the smallest among the three types of common pores (micropores <2nm, mesopores 2nm~50nm, macropores >50nm). Within the aforementioned microporosity range, the porous carbon matrix can accommodate a moderate amount of nanometer silicon deposition, which is beneficial to reducing the influence of silicon volume change on the stability of the silicon-carbon negative electrode material while achieving high lithium ion capacity. The calculation method of microporosity uses the "adsorption-desorption" behavior of small molecule gases (such as N2, CO2) in micropores at low temperature (such as N2 at -196℃), and calculates the pore parameters through adsorption isotherm, common models include t-plot method (t-plot method), DR (Dubinin-Radushkevich) method, HK (Horvath-Kawazoe) method, etc.

[0044] In some embodiments, the porous carbon matrix has a pore volume of 0.6 cm 3 / g-1.2 cm 3 / g. Thus, the influence of the volume change of the nanosilicon during lithium intercalation and deintercalation on the structural stability of the silicon-carbon anode material is reduced.

[0045] In some embodiments, the porous carbon matrix has an average pore size of 1.5 nm-2.3 nm. Thus, the uniform distribution of the nanosilicon in the pores is facilitated.

[0046] In some embodiments, the porous carbon matrix has a particle size of 3 μm≤Dv50≤10 μm. Thus, the porous carbon matrix has high structural stability and can buffer the volume change of the nanosilicon during lithium ion deintercalation.

[0047] In some embodiments, the silicon-carbon anode material has a specific surface area of 2 cm 2 / g~30 cm 2 / g. Thus, the silicon-carbon anode material has a proper contact area with the electrolyte in the lithium battery, and the deintercalation rate of lithium ions in the lithium battery is improved.

[0048] In a second aspect of the present application, a method for preparing a silicon-carbon anode material is provided, comprising: performing first carbonization treatment on a resin carbon source to obtain a first intermediate; performing activation treatment on the first intermediate to obtain a second intermediate; performing second carbonization treatment on the second intermediate to obtain a porous carbon matrix, wherein the temperature of the second carbonization treatment is 800°C~1000°C; and performing gas phase deposition treatment on the porous carbon matrix using a silicon source and a carbon source to obtain the silicon-carbon anode material.

[0049] In the method provided by the present application, in the first carbonization treatment, part of the oxygen-containing functional groups with low thermal stability contained in the resin carbon source are decomposed and removed, for example, carboxyl groups are decomposed into CO2 and H2O at 400°C~500°C, and hydroxyl groups are dehydrated at 500°C~600°C, so that a large number of ether bonds (-C-O-C-), carbonyl groups (C=O) and the like with high thermal stability are retained in the resin carbon source. Thus, the hydrogen content can be adjusted in the first carbonization treatment, and a first intermediate which is “lightly deoxidized” and retains strong bonding oxygen is obtained.

[0050] In the activation process, the first intermediate is chemically activated by an activating agent (such as KOH). At a low to medium activation temperature (400°C-800°C), the activating agent reacts with the carbon of the first intermediate to generate activated substances, which are beneficial to introducing hydroxyl (-OH), carboxyl (-COOH) and other groups on the surface of the carbon pore wall, and can improve the oxygen content of the second intermediate. The temperature of the second carbonization process is higher than that of the first carbonization process. During the second carbonization process, the second intermediate can remove heteroatoms in the porous structure and repair the carbon skeleton structure, thereby adjusting the pore structure of the prepared porous carbon matrix. The conditions of the second carbonization process are within the aforementioned range, which is beneficial to generating more abundant pore structures, improving the microporosity, and facilitating the deposition of nanosilicon. Thus, through the aforementioned process, a porous carbon matrix with moderate pore size, controllable oxygen content and hydrogen content can be prepared, so that the surface of the porous carbon matrix has sufficient reaction sites to bond with silicon elements, and the volume effect caused by excessive deposition of nanosilicon is reduced.

[0051] The porous carbon matrix is subjected to a gas phase deposition process. Silane can react with the appropriate amount of oxygen-containing functional groups (such as -OH, -O-, etc.) on the surface of the porous carbon matrix to form stable Si-O covalent bonds, which is beneficial to improving the deposition efficiency of silane. Uniformly distributed and appropriately sized nanosilicon is prepared, and the volume effect of silicon is improved, thereby improving the electrochemical stability of the prepared silicon-carbon negative electrode material. In addition, organic functional groups, such as amino groups and epoxy groups, can be introduced into the silicon source during the silicon deposition process. The organic functional groups (such as amino groups and epoxy groups) in the silicon source extend outward and form a dense organic structure on the surface of the nanosilicon. The aforementioned organic structure can physically isolate the nanosilicon from direct contact with the electrolyte in the battery, thereby reducing side reactions (such as electrolyte decomposition, side reactions between nanosilicon and Li + Thus, the interaction between nanosilicon and the electrolyte is further reduced, which causes lithium ion consumption or damage to the structure of nanosilicon, thereby improving the initial efficiency and other electrical properties of the silicon-carbon negative electrode material.

[0052] As an example, the temperature of the second carbonization process is 1000°C.

[0053] As an example, the time of the second carbonization process is 20 min.

[0054] In some embodiments, the temperature of the first carbonization process is 400°C-600°C, and the time of the first carbonization process is 0.5h-2h. The conditions of the first carbonization process are within the aforementioned range, which is beneficial to adjusting the specific surface area and pore volume of the porous carbon matrix, thereby facilitating the generation of more abundant pore structures, improving the microporosity, facilitating the deposition of nanosilicon, and reducing the impact of the large volume expansion of nanosilicon during lithium extraction on the structure of the silicon-carbon negative electrode material through spatial buffering.

[0055] As an example, the temperature of the first carbonization treatment is 400°C, 450°C, 500°C, 550°C, 600°C.

[0056] As an example, the time of the first carbonization treatment is 0.5h, 1h, 1.5h, 2h.

[0057] In some embodiments, in the activation treatment, the molar ratio of the first intermediate to the activation agent is 1: (2~4), and the activation agent includes at least one of KOH, NaOH, CO2, and water vapor. Thus, the pore structure and the surface functional group composition of the carbon structure can be improved by the chemical action of the activation agent.

[0058] In some embodiments, the second intermediate is subjected to an acid washing treatment. Thus, the unreacted activation agent can be removed.

[0059] In some embodiments, the temperature of the activation treatment is 400°C~800°C, and the time of the activation treatment is 1h~2h.

[0060] As an example, the temperature of the activation treatment is 400°C, 450°C, 500°C, 550°C, 600°C, 650°C, 700°C, 750°C, 800°C.

[0061] In some embodiments, the vapor deposition treatment includes a silicon deposition treatment and a carbon deposition treatment.

[0062] As an example, the vapor deposition treatment includes:

[0063] S1: Start the fluidized bed, weigh a certain amount of porous carbon matrix and add it to the fluidized bed feed tank, send the material into the reactor while heating and passing the carrier gas, the carrier gas is inert gas (argon, etc.) or nitrogen, the heating rate is 3°C / min~10°C / min, and the weight of the porous carbon is 6kg~10kg;

[0064] S2: After rising to a certain temperature and keeping for a certain time, pass in silane for silicon deposition treatment after the temperature is stable, the temperature is raised to 480°C~530°C, the pressure maintaining time is 10min~50min, and the deposition reaction time is 4-8h;

[0065] S3: Close the silane for a period of time and continue to heat, pass in acetylene for carbon deposition treatment, the pressure maintaining time is 10min~30min, the temperature is raised to 600°C~700°C, the acetylene passing-in time is 1h~5h, and the target silicon-carbon negative electrode material is collected after being reduced to room temperature.

[0066] In some embodiments, the gas of the silicon deposition treatment includes silane.

[0067] In some embodiments, the carbon-coated gas includes at least one of methane, ethane, propane, butane, ethylene, propylene, butylene, acetylene, propyne, butyne, pentane, hexane, pentene, hexene, pentyne, or the like.

[0068] In a third aspect of the present application, a negative electrode tab is provided, which includes the silicon-carbon negative electrode material provided by the present application or the silicon-carbon negative electrode material prepared by the method provided by the present application.

[0069] The negative electrode tab includes a negative electrode current collector and a negative electrode film layer located on at least one side of the negative electrode current collector, the negative electrode film layer containing a negative electrode active material, the negative electrode active material including the silicon-carbon negative electrode material prepared by the method provided by the present application.

[0070] In some embodiments, the current collector includes any one of a copper foil, a nickel foil, a copper-nickel composite foil, an aluminum foil, a carbon-based current collector, a foam metal current collector, or the like.

[0071] In some embodiments, the active film layer further includes a binder and a conductive agent.

[0072] In some embodiments, the binder is sodium carboxymethyl cellulose (CMC), sodium alginate (SA), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylic acid (PAA), sodium polyacrylate (PAAS), styrene-butadiene rubber (SBR), polyimide (PI), polydopamine (PDA), polyvinyl alcohol (PVA), or any combination thereof.

[0073] In some embodiments, the conductive agent includes graphite, carbon black, acetylene black, ketjen black, graphene, metal powder, or any combination thereof.

[0074] In some embodiments, the negative electrode tab can be obtained by the following method:

[0075] The negative electrode active material, the conductive agent, and the binder are uniformly stirred in a solvent to prepare a negative electrode slurry, and the slurry is coated on the negative electrode current collector.

[0076] In some embodiments, the solvent is any one of deionized water or N-methyl pyrrolidone (NMP).

[0077] In a fourth aspect of the present application, an electrochemical device is provided, which includes the negative electrode tab provided by the present application.

[0078] The electrochemical device provided by the present application includes a lithium battery, which can include a lithium ion battery or other secondary battery. Thus, the silicon-carbon negative electrode material provided by the present application has excellent uniformity of volume expansion, which is beneficial to improving the stability of the electrode structure and thus improving the cycle performance and other electrical performance of the electrochemical device.

[0079] The scheme of the present application is illustrated below by 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. If a specific technique or condition is not specified in the examples, the technique or condition described in the literature in the art or according to the product manual is used. If the manufacturer of the reagent or instrument is not specified, it is a conventional product that can be obtained on the market.

[0080] Example 1

[0081] The thermoplastic resin was placed in a rotary kiln for a first carbonization treatment at 400°C for 1 h to obtain a first intermediate. The first intermediate (resin carbon powder) was mixed with KOH at a mass ratio of 1:2 and placed in a rotary kiln for an activation treatment at 700°C for 3 h to obtain a second intermediate. The second intermediate was subjected to an acid pickling treatment for 5 h, washed to neutral with water, and dried. The second intermediate was subjected to a second carbonization treatment to remove oxygen at a temperature of 800°C for 20 min to obtain a porous carbon matrix. The porous carbon matrix can be further subjected to a fine crushing treatment. The porous carbon matrix was placed in a fluidized bed for a gas phase deposition treatment. The reactor was replaced with nitrogen gas to replace the air inside the reactor, heated to 550°C, and a mixture of 50 L / min of silane and nitrogen gas was introduced for 6 h for a silicon deposition treatment. The introduction of silane was stopped, and a mixture of 50 L / min of acetylene and nitrogen gas was introduced for 4 h for a carbon deposition treatment to obtain a silicon-carbon negative electrode material.

[0082] Example 2

[0083] Example 2 is consistent with Example 1, except that the first carbonization treatment temperature is 500°C.

[0084] Example 3

[0085] Example 3 is consistent with Example 1, except that the first carbonization treatment temperature is 600°C.

[0086] Example 4

[0087] Example 4 is consistent with Example 1, except that the second carbonization treatment temperature is 900°C.

[0088] Example 5

[0089] Example 5 is consistent with Example 1, except that the second carbonization treatment temperature is 1000°C.

[0090] Example 6

[0091] Example 6 is consistent with Example 2, except that the second carbonization treatment temperature is 900°C.

[0092] Example 7

[0093] Example 7 is consistent with Example 2, except that the second carbonization treatment temperature is 1000°C.

[0094] Example 8

[0095] Example 8 is consistent with Example 3, except that the second carbonization treatment temperature is 900°C.

[0096] Example 9

[0097] Example 9 is consistent with Example 3, except that the second carbonization treatment temperature is 1000°C.

[0098] Comparative Example 1

[0099] Comparative Example 1 is consistent with Example 2, except that the second carbonization treatment temperature is 1100°C.

[0100] Comparative Example 2

[0101] Comparative Example 2 is consistent with Example 2, except that the second carbonization treatment temperature is 1200°C.

[0102] Test Methods:

[0103] 1. Scanning Electron Microscope (SEM) Test:

[0104] The scanning electron microscope characterization was recorded by a Philips XL-30 type field emission scanning electron microscope, and the detection was carried out under the condition of 10 kV, 10 mA.

[0105] 2. Specific Surface Area Characterization:

[0106] The JW-BK100C specific surface area and pore size analyzer was used to test the specific surface area of the prepared silicon-carbon negative electrode material, and the specific surface area data of the negative electrode material after deposition was obtained.

[0107] 3. Particle Size Distribution Characterization:

[0108] The Malvern Mastersizer 2000 / 3000 laser particle size analyzer was used to test the particle size distribution of the prepared fumed silicon-carbon negative electrode material, and the particle size distribution curve and key parameters were obtained.

[0109] 4. Electrochemical Performance Test:

[0110] (1) Preparation of Button Lithium Batteries

[0111] Preparation of negative electrode sheet: The mass ratio of silicon-carbon negative electrode material active substance, conductive agent (carbon black or carbon nanotube) and binder lithium polyacrylate (PAALi) is set to (6-8): 1: 1, a proper amount of deionized water is added, and the mixture is homogenized in a ball mill for 1-3 hours to ensure that the homogenization effect reaches the best state. A copper foil with a width of 10 cm and a length of 20 cm is cut out with a scalpel, placed on a heated flat coating machine for coating, and then the copper foil loaded with the slurry is placed in a vacuum drying oven with a drying temperature of 60-80°C and a drying time of 12-24 hours. The dried electrode sheet is taken out and punched into a 12-14 mm negative electrode sheet.

[0112] Preparation of electrolyte: First, seal the ethylene carbonate (EC) solvent in a constant temperature blast drying oven at 50°C and heat until it becomes liquid. Measure the required EC and propylene carbonate (PC) solvents respectively, and add the corresponding amount of fluoroethylene carbonate (FEC) additive according to the formula requirements, and place it in a magnetic stirrer for 4-6 hours. Take an appropriate amount of LiPF6 salt and add it to a glass bottle to prepare a 1M LiPF6 solution of EC: PC (n: n = 1: 1) + 5% FEC electrolyte.

[0113] Separator: The lithium battery separator is made of polyolefin polyethylene (PE) or polypropylene (PP) separator.

[0114] Battery assembly:

[0115] (a) Wipe the operating table in the glove box clean with a paper towel, use a metal tweezers to pick up the negative shell onto the operating table, then pick up the spring sheet and gasket in turn and place them in the center of the negative shell.

[0116] (b) Use a metal lithium sheet as the counter electrode. To avoid sliding of the metal lithium sheet, add one drop of electrolyte to the center of the gasket using a pipette, then pick up the metal lithium sheet and place it on the gasket.

[0117] (c) First, add 40 μL of electrolyte to the metal lithium sheet, then place the PP or PE separator, and then add another 40 μL of electrolyte.

[0118] (d) Place the negative electrode sheet with the active substance side facing the separator, and finally put on the positive shell.

[0119] (e) Then, package the assembled button cell. Finally, let the packaged battery stand at room temperature for 10 hours, and then perform electrochemical tests after the electrolyte is fully soaked with the active substance and the separator.

[0120] (2) Performance test method

[0121] The battery is tested by LAND system, and after standing for 10 h, discharged to 0.005 V at 0.05 C, and after standing for five minutes, discharged to 0.005 V at 50 μA; after standing for 5 min, discharged to 0.005 V at 10 μA, and finally charged to 2 V at 0.05 C constant current; repeat the above steps once; the charge-discharge capacity curve is obtained, wherein the first efficiency calculation method is the capacity of the lithium insertion cutoff voltage of 2 V / the capacity corresponding to the lithium extraction voltage cutoff of 0.005 V. Specifically, the electrochemical characteristics of the negative electrode material are explored within a defined voltage range through constant current charge-discharge test. This test procedure aims to obtain a series of key data, including specific capacity, coulombic efficiency, charge-discharge voltage curve and cycle stability, etc., so as to preliminarily and comprehensively evaluate the electrochemical performance of the negative electrode material.

[0122] 5. Silane utilization rate test

[0123] The silicon deposition ratio is set to C, the deposited silicon-carbon negative electrode material is weighed as x g, placed in a tube furnace, and burned at 900 °C for 8 h, and after cooling, the weight after burning is set as y g, wherein the silane utilization rate = [(y ÷ 60 × 28) / x%] ÷ C.

[0124] Test results:

[0125] The characteristic test results of the silicon-carbon negative electrode material are shown in Table 1.

[0126] The electrical performance test results of the silicon-carbon negative electrode material are shown in Table 2.

[0127] Table 1

[0128]

[0129] Table 2

[0130]

[0131] From Tables 1 and 2, it can be seen that the silicon-carbon negative electrode material proposed in the present application has relatively optimal electrochemical performance.

[0132] In the description of the present application, the terms "first", "second" are only for the purpose of description, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. "First feature", "second feature" can include one or more of the features.

[0133] In the description of the present application, "A and / or B" can include any one of the cases of A alone, B alone, A and B, wherein A, B are only for example, which can be any technical feature connected by "and / or" in the present application.

[0134] In the present application, the order of writing each step does not mean a strict execution order and constitute any limitation to the implementation process, and the specific execution order of each step should be determined by its function and possible inherent logic. If not specifically stated, all steps of the present application can be sequentially or randomly performed, and preferably sequentially performed. For example, the method comprises steps (a) and (b), which means that the method can comprise sequentially performed steps (a) and (b), or sequentially performed steps (b) and (a). For example, the method can also comprise step (c), which means that step (c) can be added to the method in any order, for example, the method can comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0135] It should be noted that the present application is not limited to the above embodiments. The above embodiments are only examples, and embodiments having substantially the same configuration and playing the same role and effect as the technical idea within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, within the scope of the main idea of the present application, various modifications of the embodiments that can be thought of by those skilled in the art, other ways constructed by combining part of the elements of the embodiments are also included in the scope of the present application.

Claims

1. A silicon-carbon negative electrode material, characterized by, The silicon-carbon negative electrode material comprises: a porous carbon matrix, the oxygen content of the porous carbon matrix being A, 0.3wt%≤A≤3wt%; the hydrogen content of the porous carbon matrix being B, wherein, 0.05wt%≤B≤0.5wt%, and A>B; nano-silicon, the nano-silicon being at least partially located in the pores of the porous carbon matrix; a carbon coating layer, the carbon coating layer wrapping at least part of the surface of the porous carbon matrix; The method for preparing the silicon-carbon negative electrode material comprises: performing a first carbonization treatment on a resin carbon source to obtain a first intermediate; performing an activation treatment on the first intermediate to obtain a second intermediate; performing a second carbonization treatment on the second intermediate to obtain a porous carbon matrix, the temperature of the second carbonization treatment being 800°C~1000°C; performing a gas phase deposition treatment on the porous carbon matrix using a silicon source and a carbon source to obtain the silicon-carbon negative electrode material.

2. The silicon-carbon negative electrode material of claim 1, wherein, 1.5wt%≤A≤2wt%, 0.1wt%≤B≤0.25wt%.

3. The silicon-carbon negative electrode material according to claim 1 or 2, wherein, The specific surface area of ​​the porous carbon matrix is ​​1600 m². 2 / g~2400m 2 / g; and / or, the microporosity of the porous carbon matrix is 80%~97%.

4. The silicon-carbon negative electrode material according to claim 1 or 2, characterized in that, at least one of the following conditions is met: The porous carbon matrix has a pore volume of 0.6 cm 3 / g-1.2 cm 3 / g; the average pore size of the porous carbon matrix is 1.5nm-2.3nm; the particle size of the porous carbon matrix is 3μm≤Dv50≤10μm.

5. The silicon-carbon negative electrode material according to claim 1 or 2, wherein, the temperature of the first carbonization treatment is 400°C~600°C.

6. The silicon-carbon negative electrode material according to claim 1 or 2, wherein, in the activation treatment, the activation agent used comprises at least one of KOH, NaOH, CO2, and water vapor; the temperature of the activation treatment is 400°C~800°C.

7. A negative electrode sheet characterized by comprising: The negative electrode sheet comprises the silicon-carbon negative electrode material according to any one of claims 1~6.

8. An electrochemical device, characterized by, The electrochemical device comprises the negative electrode sheet according to claim 7.

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