Silicon-carbon negative active material, preparation method thereof, negative pole piece and battery

Abstract

The invention provides a silicon-carbon negative electrode active material and a preparation method thereof, a negative electrode pole piece and a battery, the method comprises the following steps: mixing phenolic resin, a conductive agent, a pore forming agent and a solvent to obtain a dispersion liquid, spray-drying the phenolic resin, the conductive agent and the pore forming agent according to a mass ratio of (60-90): (5-20): (5-20) to obtain a spherical modified phenolic resin precursor; sequentially carrying out aging treatment, carbonization treatment and activation treatment on the modified phenolic resin precursor under a protective gas condition to obtain a modified resin-based carbon skeleton; and placing the modified resin-based carbon skeleton in a protective gas condition, and introducing a silicon source for vapor deposition to obtain the silicon-carbon negative electrode active material. Therefore, the silicon-carbon negative electrode active material with relatively large micropore proportion, relatively low resistivity, relatively large pore volume and relatively large specific surface area is obtained, and the charge-discharge formation and cycle performance of the battery is improved.

Description

Technical Field

[0001] The present application relates to the field of batteries, and specifically, to a silicon-carbon negative electrode active material, a preparation method thereof, a negative electrode sheet, and a battery. Background Art

[0002] Lithium-ion batteries have become an important branch in multiple fields such as electric vehicles, power tools, and energy storage due to their high specific energy, high working voltage, wide application temperature range, low self-discharge rate, long cycle life, pollution-free, and good safety performance. With the rapid development of the new energy industry, higher requirements are put forward for the energy density, cycle life, etc. of lithium-ion batteries. Traditional lithium-ion batteries use graphite as the negative electrode active material, but the theoretical specific capacity of the graphite negative electrode active material is relatively low and cannot meet the requirements of high energy density of the battery. Compared with graphite-based negative electrode active materials, silicon negative electrode active materials have advantages such as high theoretical specific capacity (4200 mAh / g), low lithium deintercalation / insertion potential, high safety performance, and rich reserves, and are gradually used as negative electrode active materials for lithium-ion batteries. However, silicon negative electrode active materials have problems such as large volume expansion, low conductivity, and low initial efficiency, which limit the commercial application of silicon negative electrode materials.

[0003] Based on the above problems, the scientific research community usually uses the method of combining nano-scale silicon particles with carbon materials to prepare silicon-carbon negative electrode active materials, mainly including chemical vapor deposition (CVD), mechanical ball milling, hydrothermal method, and plasma evaporation condensation method. Among them, the chemical vapor deposition method can generate high-purity and highly uniform silicon-carbon composite materials through the ingenious design of a porous carbon skeleton. The production method requires less equipment and has a lower theoretical cost, making it the most competitive silicon-carbon negative electrode material product in the market.

[0004] The matrix materials of silicon-carbon negative electrode materials prepared by the CVD method mainly include natural graphite, artificial graphite, mesophase carbon microspheres, biomass, petroleum raw materials, polymer-based, coal-based, resins, etc. Among them, porous carbon with resin as the matrix material has advantages such as good chemical stability, large specific surface area, rich pore structure, simple process, and low cost, making it widely used in the fields of electrochemical energy storage devices and negative electrode materials for lithium-ion batteries.

[0005] However, the silicon-carbon negative electrode active material has a problem of relatively high volume expansion rate. Summary of the Invention

[0006] The present application aims to solve at least one of the technical problems in the related art to some extent.

[0007] The first aspect of the present application provides a method for preparing a silicon-carbon anode active material, the method comprising: mixing phenolic resin, a conductive agent, a pore-forming agent, and a solvent to obtain a dispersion, wherein the mass ratio of the phenolic resin, the conductive agent, and the pore-forming agent is (60-90):(5-20):(5-20), and spray-drying to obtain a spherical modified phenolic resin precursor; subjecting the modified phenolic resin precursor to aging treatment, carbonization treatment, and activation treatment in sequence under a protective gas condition to obtain a modified resin-based carbon framework; and placing the modified resin-based carbon framework under a protective gas condition and introducing a silicon source for chemical vapor deposition to obtain the silicon-carbon anode active material.

[0008] In the method for preparing a silicon-carbon anode active material proposed by the present application, a conductive agent and a pore-forming agent are added simultaneously during the preparation of the modified resin precursor. The conductive agent can provide an excellent conductive network, improve the conductivity of the silicon-carbon anode active material, improve the adsorption and desorption ability of the silicon-carbon anode active material for active metal particles, and improve the rate performance of the silicon-carbon anode. During the subsequent carbonization treatment, the pore-forming agent can increase the content of micropores in the modified resin-based carbon framework. Under capillary action, the micropores in the modified resin-based carbon framework can effectively adsorb silane molecules and pyrolyze to form nanosilicon in the micropores. The abundant micropores in the modified resin-based carbon framework can effectively accommodate the volume change of silicon during charge and discharge and disperse the stress concentration caused by volume expansion, thereby enhancing the stability of the modified silicon-carbon anode material during charge and discharge. At the same time, through spray-drying technology, a spherical modified phenolic resin precursor can be obtained. The spherical modified phenolic resin precursor can significantly optimize the mechanical stability of the silicon-carbon anode material, increase the fit between particles, improve the filling performance and current distribution of the battery, so that the silicon-carbon material reacts more uniformly inside the battery and improves the overall performance of the battery. In summary, the silicon-carbon anode active material prepared by the method proposed by the present application can inhibit the volume effect during the insertion and extraction of active metal particles, and improve the Coulomb efficiency and cycle performance of the battery.

[0009] According to some embodiments of the present application, the method satisfies at least one of the following conditions: the conductive agent includes at least one of single-walled carbon nanotubes, multi-walled carbon nanotubes, conductive carbon black, and graphene; the pore-forming agent includes at least one of refined naphthalene, soluble starch, soluble carbon fiber, ammonium carbonate, ammonium bicarbonate, ammonium chloride, pulverized coal, carbon powder, polyoxyethylene polyoxypropylene ether triblock copolymer, and poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer.

[0010] According to some embodiments of the present application, the solid content of the dispersion is 10%-50%.

[0011] According to some embodiments of the present application, the method satisfies at least one of the following conditions: the inlet temperature of the spray drying is 160°C - 300°C, and the outlet temperature of the spray drying is 120°C - 230°C; the temperature of the aging treatment is 80°C - 250°C, and the time of the aging treatment is 1h - 36h; the temperature of the carbonization treatment is 500°C - 1000°C, and the time of the carbonization treatment is 1h - 12h; the temperature of the activation treatment is 500°C - 1200°C, and the time of the activation treatment is 1h - 12h.

[0012] According to some embodiments of the present application, the activation treatment includes at least one of steam activation, carbon dioxide activation, potassium hydroxide activation, sodium hydroxide activation, potassium carbonate activation, sodium hydrogen phosphate activation, zinc chloride activation, aluminum chloride activation, and phosphoric acid activation.

[0013] According to some embodiments of the present application, the temperature of the chemical vapor deposition is 500°C - 900°C, and the time of the chemical vapor deposition is 1h - 12h.

[0014] According to some embodiments of the present application, the method further includes: a step of carbon coating the modified silicon / porous carbon composite material.

[0015] The second aspect of the present application provides a silicon-carbon negative electrode active material, which is prepared by the method provided in the first aspect of the present application. The silicon-carbon negative electrode active material includes micropores, and the volume ratio of the micropores is 90% - 99%. The specific surface area of the silicon-carbon negative electrode active material is 2500m 2 / g - 3000m 2 / g, and the resistivity of the silicon-carbon negative electrode active material is 15Ω·cm - 90Ω·cm. Thus, the volume expansion rate of the silicon-carbon negative electrode active material is reduced, the Coulomb efficiency of the battery is improved, and the cycle performance of the battery is improved.

[0016] The third aspect of the present application provides a negative electrode sheet, which includes the silicon-carbon negative electrode active material provided in the second aspect of the present application.

[0017] The fourth aspect of the present application provides a battery, which includes the negative electrode sheet provided in the third aspect of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The above and / or additional aspects and advantages of the present application will become apparent and be readily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0019] Figure 1 A schematic flow chart of a method for preparing a silicon-carbon negative electrode active material according to an embodiment of the present application is shown.

[0020] Figure 2Shows the SEM image of the silicon-carbon negative electrode active material prepared in Example 2 of the present application. Detailed implementation mode

[0021] The embodiments of the present application will be described in detail below. The following described embodiments are exemplary and are only used to explain the present application and should not be construed as a limitation to the present application. For those techniques or conditions not specified in the embodiments, they shall be carried out according to the techniques or conditions described in the literature in the art or according to the product specifications. For the reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0022] The first aspect of the present application provides a method for preparing a silicon-carbon negative electrode active material, the method comprising: mixing phenolic resin, conductive agent, pore-forming agent, and solvent to obtain a dispersion liquid, wherein the mass ratio of the phenolic resin, the conductive agent, and the pore-forming agent is (60-90):(5-20):(5-20), and spray drying to obtain a spherical modified phenolic resin precursor; subjecting the modified phenolic resin precursor to aging treatment, carbonization treatment, and activation treatment in sequence under a protective gas condition to obtain a modified resin-based carbon framework; placing the modified resin-based carbon framework in a protective gas condition and introducing a silicon source gas for chemical vapor deposition to obtain a silicon-carbon negative electrode active material.

[0023] In the method for preparing a silicon-carbon negative electrode active material proposed by the present application, a conductive agent and a pore-forming agent are added simultaneously during the preparation of the modified resin precursor. The conductive agent can improve the conductivity of the silicon-carbon negative electrode active material, and the pore-forming agent can increase the content of micropores in the modified resin-based carbon framework during the subsequent carbonization treatment. Under capillary action, the micropores in the modified resin-based carbon framework can effectively adsorb silane molecules and thermally crack to form nano-silicon in the micropores. The abundant micropores in the modified resin-based carbon framework can effectively accommodate the volume change of silicon during charge and discharge and disperse the stress concentration caused by volume expansion, thereby improving the stability of the modified silicon-carbon negative electrode material during charge and discharge. At the same time, through spray drying technology, a spherical modified phenolic resin precursor can be obtained. The spherical modified phenolic resin precursor can significantly optimize the mechanical stability of the silicon-carbon negative electrode material, increase the fit between particles, improve the filling performance and current distribution of the battery, so that the silicon-carbon material reacts more uniformly inside the battery and improves the overall performance of the battery. In summary, the silicon-carbon negative electrode active material prepared by the method proposed by the present application can inhibit the volume effect during the deintercalation and intercalation of active metal particles, and improve the Coulomb efficiency and cycle performance of the battery.

[0024] In the present application, micropores refer to pores with a pore diameter less than 2 nm.

[0025] The following will describe in detail each step of the method proposed by the present application, referring to Figure 1 , the method comprising:

[0026] S10: Mix phenolic resin, a conductive agent, a pore-forming agent, and a solvent to obtain a dispersion. The mass ratio of the phenolic resin, the conductive agent, and the pore-forming agent is (60 - 90):(5 - 20):(5 - 20). Spray dry to obtain spherical modified phenolic resin precursors.

[0027] According to some embodiments of the present application, the phenolic resin is a thermosetting phenolic resin with a solid content of 60% - 80%. The thermosetting phenolic resin has high heat resistance and acid resistance, good dimensional stability, and good flame retardancy, and is suitable for large-scale production.

[0028] According to some embodiments of the present application, the conductive agent includes at least one of single-walled carbon nanotubes, multi-walled carbon nanotubes, conductive carbon black, and graphene.

[0029] According to some embodiments of the present application, the pore-forming agent includes at least one of refined naphthalene, soluble starch, soluble carbon fiber, ammonium carbonate, ammonium bicarbonate, ammonium chloride, pulverized coal, carbon powder, polyoxyethylene polyoxypropylene ether triblock copolymer, and polyethylene oxide - polypropylene oxide - polyethylene oxide triblock copolymer. Thus, after high-temperature treatment, the pore-forming agent volatilizes, leaving pores inside the material.

[0030] According to some embodiments of the present application, the solid content of the dispersion is 10% - 50%. For example, it can be 10%, 20%, 30%, 40%, 50%, etc., or it can be a range composed of any of the above values.

[0031] According to some embodiments of the present application, the solvent includes at least one of methanol, absolute ethanol, propanol, butanol, isopropanol, ethylene glycol, vinyl alcohol, benzyl alcohol, n-butanol, cyclohexanehexol, n-butanol, and glycerol.

[0032] According to some embodiments of the present application, the mass ratio of the phenolic resin, the conductive agent, and the pore-forming agent can be (60 - 90):(5 - 20):(5 - 20).

[0033] By making the content of the conductive agent within the above range, the dispersion is easier to disperse, preventing the excessive content of the conductive agent from affecting the uniformity of the dispersion.

[0034] By making the content of the pore-forming agent within the above range, an appropriate number of micropores are formed on the modified resin-based carbon skeleton, preventing too many micropores and a large amount of deposited silicon, and increasing the volume expansion rate of the silicon-carbon negative electrode active material.

[0035] According to some embodiments of the present application, the inlet temperature of the spray drying is 160°C - 300°C, and the outlet temperature of the spray drying is 120°C - 230°C.

[0036] For example, the inlet temperature of spray drying can be 160°C, 180°C, 200°C, 220°C, 240°C, 260°C, 280°C, 300°C, etc., or can be a range composed of any of the above values.

[0037] For example, the outlet temperature of spray drying is 120°C, 150°C, 180°C, 210°C, 230°C, etc., or can be a range composed of any of the above values.

[0038] S20: Subject the modified phenolic resin precursor to aging treatment, carbonization treatment, and activation treatment in sequence under a protective gas condition to obtain a modified resin-based carbon skeleton

[0039] According to some embodiments of the present application, the protective gas includes at least one of nitrogen, argon, helium, and neon.

[0040] According to some embodiments of the present application, the temperature of the aging treatment is 80°C - 250°C, and the time of the aging treatment is 1h - 36h. Thus, by making the temperature and time of the aging treatment within the above range, the spherical morphology of the modified phenolic resin is maintained.

[0041] As an example, the temperature of the aging treatment can be 80°C, 110°C, 140°C, 170°C, 200°C, 230°C, 250°C, etc., or can be a range composed of any of the above values.

[0042] As an example, the temperature of the carbonization treatment is 500°C - 1000°C, and the time of the carbonization treatment is 1h - 12h. By making the temperature and time of the carbonization treatment within the above range, the pore-forming agent volatilizes, forming more micropores to adsorb silicon. During the battery cycling process, the volume expansion of silicon can be controlled, and the volume expansion rate of the silicon-carbon negative electrode active material can be reduced.

[0043] For example, the temperature of the carbonization treatment can be 500°C, 600°C, 700°C, 800°C, 900°C, 1000°C, etc., or can be a range composed of any of the above values.

[0044] For example, the time of the carbonization treatment can be 1h, 3h, 5h, 7h, 9h, 12h, etc., or can be a range composed of any of the above values, or can be a range composed of any of the above values.

[0045] According to some embodiments of the present application, the temperature of the activation treatment is 500°C - 1200°C, and the time of the activation treatment is 1h - 12h. Thus, by making the temperature and time of the activation treatment within the above range, more pores are formed on the modified resin-based carbon skeleton, increasing the specific surface area of the material, providing more active sites, and improving the charge-discharge capacity of the battery.

[0046] According to some embodiments of the present application, the activation treatment includes at least one of steam activation, carbon dioxide activation, potassium hydroxide activation, sodium hydroxide activation, potassium carbonate activation, sodium hydrogen phosphate activation, zinc chloride activation, aluminum chloride activation, and phosphoric acid activation.

[0047] According to some embodiments of the present application, the equipment used for the aging treatment and the carbonization treatment includes at least one of a rotary kiln, a roller hearth kiln, a fluidized bed, and an electric furnace.

[0048] S30: Place the modified resin-based carbon skeleton under a protective gas condition, and introduce a silicon source for chemical vapor deposition to obtain a silicon-carbon negative electrode active material.

[0049] According to some embodiments of the present application, the temperature of the chemical vapor deposition is 500°C - 900°C, and the time of the chemical vapor deposition is 1h - 12h. By making the temperature and time of the chemical vapor deposition within the above ranges, the deposition rate of silicon is controlled within an appropriate range, the crystallization quality of silicon is improved, and the formation of good chemical bonds between silicon atoms and carbon atoms is promoted.

[0050] As an example, the temperature of the chemical vapor deposition can be 500°C, 600°C, 700°C, 800°C, 900°C, etc., or can be a range composed of any of the above values.

[0051] As an example, the time of the chemical vapor deposition can be 1h, 3h, 5h, 7h, 9h, 11h, 12h, etc., or can be a range composed of any of the above values.

[0052] According to some embodiments of the present application, the method further includes: a step of carbon coating the silicon-carbon negative electrode active material.

[0053] According to some embodiments of the present application, under a protective gas condition, the silicon-carbon negative electrode active material is placed at a certain temperature, and a carbon source gas is introduced for chemical vapor deposition to form a carbon coating layer on the surface of the silicon-carbon negative electrode active material.

[0054] As an example, the carbon source includes at least one of methane, acetylene, propylene, ethylene, ethane, acetone, butane, benzene, natural gas, toluene, and propyne.

[0055] The second aspect of the present application provides a silicon-carbon negative electrode active material, which is prepared by the method provided in the first aspect of the present application. The silicon-carbon negative electrode active material includes micropores, the volume ratio of the micropores is 90% - 99%, and the specific surface area of the silicon-carbon negative electrode active material is 2500m 2 / g - 3000m 2 / g, and the resistivity of the silicon-carbon negative electrode active material is 15 Ω·cm - 90 Ω·cm. Thus, the volume expansion rate of the silicon-carbon negative electrode active material is reduced, the Coulomb efficiency of the battery is improved, and the cycle performance of the battery is improved.

[0056] The third aspect of the present application provides a negative electrode sheet, including the silicon-carbon negative electrode active material provided by the second aspect of the present application.

[0057] The fourth aspect of the present application provides a battery, the negative electrode sheet provided by the third aspect of the present application, and the first de-lithiation specific capacity of the battery is 500 mAh / g - 3000 mAh / g.

[0058] The embodiments of the present application are described in detail below. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as a limitation to the present application. For those specific technologies or conditions not specified in the embodiments, they shall be carried out according to the technologies or conditions described in the literature in the field or according to the product specifications. For the reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0059] Example 1

[0060] Weigh 20 kg of thermosetting phenolic resin with a solid content of 70%, 0.5 kg of carbon nanotubes, and 1.5 kg of ammonium carbonate, dissolve them in 18 kg of ethanol dispersion liquid, and prepare a mixed solution with a solid content of 40%. Spray-dry the mixed solution under the conditions that the inlet temperature is 230 °C and the outlet temperature is 160 °C to obtain a modified spherical phenolic resin precursor;

[0061] Place the modified spherical phenolic resin precursor in a rotary kiln, age it for 10 h under a nitrogen atmosphere at 150 °C, then raise the temperature to 900 °C for carbonization treatment for 3 h to obtain a modified carbon precursor. Mix the modified carbon precursor material and potassium hydroxide evenly according to a mass ratio of 1:4, and then place the mixed material in a rotary kiln, and activate it for 6 h under a nitrogen atmosphere at 900 °C to obtain a modified porous carbon matrix;

[0062] Pass silane gas into the modified porous carbon matrix under a nitrogen atmosphere at 600 °C for 8 h for chemical vapor deposition to obtain a modified resin-based carbon skeleton;

[0063] Place the modified resin-based carbon skeleton at 600 °C under a nitrogen atmosphere, and pass acetylene gas for 6 h for chemical vapor deposition to obtain a silicon-carbon negative electrode active material with a carbon coating layer.

[0064] Example 2

[0065] The preparation method of the silicon-carbon negative electrode active material is the same as that in Example 1, except that:

[0066] Weigh 20 kg of thermosetting phenolic resin with a solid content of 70%, 1 kg of carbon nanotubes, and 1.5 kg of ammonium carbonate, dissolve them in 18.75 kg of ethanol dispersion, and prepare a mixed solution with a solid content of 40%. Spray-dry the mixed solution at an inlet temperature of 230 °C and an outlet temperature of 160 °C to obtain a modified spherical phenolic resin precursor.

[0067] Example 3

[0068] The preparation method of the silicon-carbon negative electrode active material is the same as that of Example 1, except that:

[0069] Weigh 20 kg of thermosetting phenolic resin with a solid content of 70%, 0.5 kg of carbon nanotubes, and 2.5 kg of ammonium carbonate, dissolve them in 19.5 kg of ethanol dispersion, and prepare a mixed solution with a solid content of 40%. Spray-dry the mixed solution at an inlet temperature of 230 °C and an outlet temperature of 160 °C to obtain a modified spherical phenolic resin precursor.

[0070] Comparative Example 1

[0071] The preparation method of the silicon-carbon negative electrode active material is the same as that of Example 1, except that:

[0072] Weigh 20 kg of thermosetting phenolic resin with a solid content of 70% and 1.5 kg of ammonium carbonate, dissolve them in 17.25 kg of ethanol dispersion, and prepare a mixed solution with a solid content of 40%. Spray-dry the mixed solution at an inlet temperature of 230 °C and an outlet temperature of 160 °C to obtain a modified spherical phenolic resin precursor.

[0073] Comparative Example 2

[0074] The preparation method of the silicon-carbon negative electrode active material is the same as that of Example 1, except that:

[0075] Weigh 20 kg of thermosetting phenolic resin with a solid content of 70% and 0.5 kg of carbon nanotubes, dissolve them in 15.75 kg of ethanol dispersion, and prepare a mixed solution with a solid content of 40%. Spray-dry the mixed solution at an inlet temperature of 230 °C and an outlet temperature of 160 °C to obtain a modified spherical phenolic resin precursor.

[0076] Comparative Example 3

[0077] The preparation method of the silicon-carbon negative electrode active material is the same as that of Example 1, except that:

[0078] Weigh 20 kg of thermosetting phenolic resin with a solid content of 70% and dissolve it in 15 kg of ethanol dispersion, prepare a mixed solution with a solid content of 30%. Spray-dry the mixed solution at an inlet temperature of 230 °C and an outlet temperature of 160 °C to obtain a modified spherical phenolic resin precursor.

[0079] Performance Test

[0080] 1. Resistivity

[0081] The resistivity test method of the present invention is carried out in accordance with the standard of GB / T 31838.3.

[0082] 2. Specific Surface Area

[0083] The specific surface area test method of the present invention is carried out in accordance with the standard of GB / T 19587-2017.

[0084] 3. Pore Volume

[0085] The pore volume test method of the present invention is carried out in accordance with the standard of GB / T 19587-2017.

[0086] 4. Micropore Ratio

[0087] The micropore ratio test method of the present invention is carried out in accordance with the standard of GB / T 19587-2017.

[0088] The test results of the silicon-carbon negative electrode active materials prepared in Examples 1-3 and Comparative Examples 1-3 are shown in Table 1.

[0089] Table 1

[0090]

[0091] It can be seen from Table 1 that in the process of preparing the silicon-carbon negative electrode active material, if only the pore-forming agent is added, the micropore ratio of the silicon-carbon negative electrode active material is relatively high, but the resistivity of the material is relatively large; if only the conductive agent is added, the resistivity of the silicon-carbon negative electrode active material is relatively low, but the micropore ratio is relatively low. If neither the pore-forming agent nor the conductive agent is added, the resistivity of the material is relatively large and the micropore ratio is relatively low. In this application, by adding the conductive agent and the pore-forming agent simultaneously, a silicon-carbon negative electrode active material with a large micropore ratio, a low resistivity, a large pore volume and a large specific surface area can be obtained.

[0092] Battery Preparation

[0093] Mix the above-prepared silicon-carbon negative electrode active material with conductive carbon black and binder in a ratio of 88:6:6, add an appropriate amount of deionized water, and use a homogenizer to prepare it into a paste. The paste is evenly scraped on the copper foil with a thickness of 200 μm, and then baked in an oven to prepare a pole piece.

[0094] The baked electrode sheets are pressed and cut into circular electrodes with a diameter of 14 mm. The above-mentioned circular electrodes are stacked neatly in the order of negative electrode case, spring piece, gasket, lithium sheet, separator, electrode sheet, and positive electrode case in a glove box filled with argon atmosphere, and electrolyte is injected, and then encapsulated to obtain a CR2025 button-type lithium-ion battery.

[0095] Performance Test

[0096] Unless otherwise specified, the initial lithium deintercalation specific capacity, initial Coulombic efficiency, and capacity retention rate of the present invention are all obtained by performing charge and discharge tests on the CR2025 button-type lithium-ion battery using a Blue Energy series battery test system.

[0097] 1. Initial lithium deintercalation specific capacity

[0098] The above CR2025 battery is discharged at a current of 0.05C until the voltage < 0.001V to obtain the initial lithium intercalation specific capacity of the silicon-carbon material. Then, the above CR2025 battery is charged at a current of 0.05C until the voltage ≥ 2V to obtain the initial lithium deintercalation specific capacity.

[0099] 2. Initial Coulombic efficiency

[0100] The initial Coulombic efficiency is calculated based on the above initial lithium deintercalation specific capacity and initial lithium intercalation specific capacity. Initial Coulombic efficiency = initial lithium deintercalation specific capacity / initial lithium intercalation specific capacity × 100%.

[0101] 3. Capacity retention rate

[0102] The above CR2025 battery is subjected to cyclic charge and discharge at a current of 0.2C, and the capacity of the first cycle C 1 and the capacity of the 50th cycle C 2 are recorded respectively. Capacity retention rate = C 2 / C 1 × 100%.

[0103] The test results of the batteries assembled with the negative electrode active materials of Examples 1 - 3 and Comparative Examples 1 - 3 are shown in Table 2.

[0104] Table 2

[0105]

[0106] As can be seen from Table 2, the silicon-carbon negative electrode active material obtained by the present application, which simultaneously has a large micropore ratio, a low resistivity, a large pore volume, and a large specific surface area, can improve the initial lithium deintercalation specific capacity, initial Coulombic efficiency, and capacity retention rate of the battery simultaneously.

[0107] Although the embodiments of the present application have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present application. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present application.

Claims

1. A method for preparing a silicon-carbon negative electrode active material, characterized in that: include: Mixing a phenolic resin, a conductive agent, a pore-forming agent, and a solvent to obtain a dispersion, wherein the mass ratio of the phenolic resin, the conductive agent, and the pore-forming agent is (60-90):(5-20):(5-20), and spray drying to obtain a spherical modified phenolic resin precursor; The modified phenolic resin precursor is subjected to an aging treatment, a carbonization treatment, and an activation treatment in sequence under protective gas conditions to obtain a modified resin-based carbon skeleton; The modified resin-based carbon skeleton is placed under protective gas conditions, and a silicon source is introduced for vapor deposition to obtain a silicon-carbon negative electrode active material.

2. The method according to claim 1, characterized in that At least one of the following conditions is met: The conductive agent includes at least one of single-walled carbon nanotubes, multi-walled carbon nanotubes, conductive carbon black, and graphene; The pore-forming agent includes at least one of refined naphthalene, soluble starch, soluble carbon fiber, ammonium carbonate, ammonium bicarbonate, ammonium chloride, coal powder, carbon powder, polyoxyethylene polyoxypropylene ether triblock copolymer, and polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer.

3. The method according to claim 1, characterized in that The solid content of the dispersion is 10%-50%.

4. The method according to any one of claims 1 to 3, characterized in that At least one of the following conditions is met: The inlet temperature of the spray drying is 160°C-300°C, and the outlet temperature of the spray drying is 120°C-230°C; The temperature of the aging treatment is 80°C-250°C, and the time of the aging treatment is 1h-36h; The temperature of the carbonization treatment is 500°C-1000°C, and the time of the carbonization treatment is 1h-12h; The temperature of the activation treatment is 500° C.-1200° C., and the time of the activation treatment is 1 h-12 h.

5. The method according to any one of claims 1 to 3, characterized in that: The activation treatment includes at least one of water vapor activation, carbon dioxide activation, potassium hydroxide activation, sodium hydroxide activation, potassium carbonate activation, sodium hydrogen phosphate activation, zinc chloride activation, aluminum chloride activation, and phosphoric acid activation.

6. The method according to any one of claims 1 to 3, characterized in that The temperature of the vapor deposition is 500° C.-900° C., and the time of the vapor deposition is 1 h-12 h.

7. The method according to any one of claims 1 to 3, characterized in that The method further comprises: a step of carbon coating the silicon-carbon negative electrode active material.

8. A silicon-carbon negative electrode active material, characterized in that: The silicon-carbon negative electrode active material is prepared by the method according to any one of claims 1 to 7, wherein the silicon-carbon negative electrode active material comprises micropores, the volume proportion of the micropores is 90% to 99%, and the specific surface area of ​​the silicon-carbon negative electrode active material is 2500 m 2 / g-3000m 2 / g, and the resistivity of the silicon-carbon negative electrode active material is 15Ω·cm-90Ω·cm.

9. A negative electrode plate, characterized in that: Comprising the silicon-carbon negative electrode active material as described in claim 8.

10. A battery, characterized in that: Including the negative electrode sheet as described in claim 9.

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