Silicon-carbon composite negative electrode material, and preparation method therefor and use thereof

Abstract

A silicon-carbon composite negative electrode material, and a preparation method therefor and the use thereof. The silicon-carbon composite negative electrode material has a core-shell structure. The silicon-carbon composite negative electrode material comprises amorphous carbon, porous carbon and silicon nanosheets, wherein the silicon nanosheets are a core material, the porous carbon and the amorphous carbon are shell layer materials, and a cavity is present between the core material and the shell layer material. The method can solve the problem of volume expansion of the silicon-carbon composite negative electrode material, and can also improve the cycle performance and initial coulombic efficiency of the silicon-carbon composite negative electrode material.

Description

A silicon-carbon composite negative electrode material and its preparation method and application

[0001] This application claims priority to a prior application, patent application number 2024101940501, filed with the State Intellectual Property Office of China on February 21, 2024, entitled “A Silicon-Carbon Composite Anode Material, Preparation Method, and Application Thereof.” The entire text of that prior application is incorporated herein by reference. Technical Field

[0002] The present invention belongs to the technical field of negative electrode materials for lithium ion batteries, and specifically relates to a silicon-carbon composite negative electrode material and a preparation method and application thereof. Background Art

[0003] Lithium-ion batteries offer a host of advantages, including high specific capacity, stable operating voltage, excellent safety, and no memory effect. Consequently, they are widely used in a wide range of portable electronic devices, including laptops, mobile phones, and instrumentation. With the rapid development of various electronic devices and electric vehicles, the demand for lithium-ion batteries' energy density and cycle life is increasing. Anode materials are a crucial component of batteries. Together with cathode materials, they determine key lithium-ion battery properties, including cycle life, capacity, and safety, making them a key research focus worldwide.

[0004] Currently, commercial graphite-based anode materials have a low specific capacity of only approximately 372 mAh / g, which significantly limits the overall capacity of lithium-ion batteries and can no longer meet market demand. Silicon reportedly has a theoretical lithium storage capacity of approximately 4200 mAh / g, with a slightly higher lithium insertion platform than graphite and fewer safety risks, making it an excellent alternative to graphite-based anode materials. However, silicon exhibits a volume change of up to 300% during charge and discharge, which can easily lead to silicon particle pulverization, destruction of the electrode's internal conductive network, and poor electrical conductivity. Summary of the Invention

[0005] To address the serious volume expansion issues of existing silicon anode materials, the present invention provides a method for preparing a silicon-carbon composite anode material using montmorillonite, and the resulting silicon-carbon composite anode material. The method effectively addresses the volume expansion issue of the silicon-carbon composite anode material while also improving the cycling performance and initial coulombic efficiency of the silicon-carbon composite anode material. Montmorillonite, a renewable biomass resource, is green, non-toxic, environmentally friendly, abundant, and inexpensive, helping to reduce the production cost of the silicon-carbon composite anode material.

[0006] The object of the present invention is achieved through the following technical solutions:

[0007] A method for preparing a silicon-carbon composite negative electrode material, the preparation method comprising the following steps:

[0008] (1) mixing montmorillonite and sodium alginate to prepare a suspension;

[0009] (2) mixing the suspension of step (1) with an aqueous solution of zinc salt to carry out a cross-linking reaction to prepare a hydrogel;

[0010] (3) drying the hydrogel obtained in step (2) and then calcining the dried hydrogel to obtain porous carbon-coated two-dimensional montmorillonite nanosheets;

[0011] (4) mixing the porous carbon-coated two-dimensional montmorillonite nanosheets and magnesium powder in step (3) under anhydrous and inert atmosphere and placing them in a reaction vessel to perform a magnesium thermal reduction reaction to obtain an initial reaction product containing porous carbon-coated silicon nanosheets;

[0012] (5) grinding, washing, and acid-washing the initial reaction product of step (4) to prepare porous carbon@cavity@silicon nanosheets;

[0013] (6) The porous carbon@cavity@silicon nanosheets prepared in step (5) are sequentially subjected to carbon coating treatment and sintering treatment to prepare the silicon-carbon composite negative electrode material.

[0014] According to an embodiment of the present invention, in step (1), the montmorillonite has a lamellar structure, and the average thickness of the montmorillonite lamellar is 80nm-120nm, such as 80nm, 90nm, 100nm, 110nm or 120nm; the average length of the montmorillonite lamellar is 5μm-10μm, such as 5μm, 6μm, 7μm, 8μm, 9μm or 10μm.

[0015] According to an embodiment of the present invention, in step (1), the sources of the montmorillonite and sodium alginate are not particularly limited, and they can be obtained by methods known in the art.

[0016] According to an embodiment of the present invention, in step (1), the mass ratio of montmorillonite to sodium alginate is 1:(3-5), for example, 1:3, 1:3.5, 1:4, 1:4.5 or 1:5.

[0017] According to an embodiment of the present invention, in step (1), the suspension is a suspension of an aqueous system.

[0018] According to an embodiment of the present invention, in step (1), the concentration of montmorillonite in the suspension is 0.1%-0.3%, for example, 0.1%, 0.2% or 0.3%.

[0019] According to an embodiment of the present invention, step (1) includes the following steps: adding montmorillonite to water, stirring and ultrasonicating, then adding sodium alginate and stirring until it is completely dissolved, and then standing at room temperature for 12-24 hours to obtain the suspension.

[0020] Preferably, montmorillonite is added to deionized water, stirred and ultrasonicated for 10-30 minutes, and then sodium alginate is added and stirred at 60-100° C. until the sodium alginate is completely dissolved, and then allowed to stand at room temperature for 12-24 hours to obtain a uniformly dispersed suspension.

[0021] Preferably, the mass ratio of the montmorillonite to water is (0.1-0.3):100, for example, 0.1:100, 0.2:100 or 0.3:100.

[0022] Preferably, after standing for 4-6 hours, ultrasonication is performed for 1-2 hours, and then the steps of standing and ultrasonication are repeated.

[0023] According to an embodiment of the present invention, in step (2), the zinc salt is selected from at least one of zinc nitrate, zinc chloride, zinc sulfate and zinc acetate.

[0024] According to an embodiment of the present invention, in step (2), the concentration of the aqueous solution of the zinc salt is 10-50 g / L, for example, 10 g / L, 20 g / L, 30 g / L, 40 g / L or 50 g / L.

[0025] According to an embodiment of the present invention, in step (2), the mass ratio of the suspension to the aqueous solution of the zinc salt is (10-50):100, for example, 10:100, 20:100, 30:100, 40:100 or 50:100.

[0026] According to an embodiment of the present invention, in step (2), the temperature of the cross-linking reaction is room temperature, and the time of the cross-linking reaction is 16-28 hours, for example, 16 hours, 18 hours, 20 hours, 22 hours, 24 hours, 26 hours or 28 hours.

[0027] According to an embodiment of the present invention, in step (2), after the cross-linking reaction is completed, a post-treatment step is further included, and the post-treatment step includes washing. Exemplarily, the hydrogel is washed 2-5 times with deionized water. The purpose of the washing is to remove zinc ions adsorbed on the surface of the hydrogel to prevent them from affecting the performance of the silicon-carbon composite negative electrode material.

[0028] According to an embodiment of the present invention, in step (2), the mixing method can be to add the suspension of step (1) dropwise into the aqueous solution of zinc salt.

[0029] According to an embodiment of the present invention, in step (2), the hydrogel is in the form of a spherical hydrogel.

[0030] According to an embodiment of the present invention, in step (2), the diameter of the spherical hydrogel is 2 mm to 5 mm. Furthermore, the diameter of the spherical hydrogel can be controlled by controlling the size of the suspension droplets.

[0031] According to an embodiment of the present invention, in step (3), the drying temperature is 50° C.-100° C., for example, 50° C., 60° C., 70° C., 80° C., 90° C., or 100° C. The drying time is 8-24 hours, for example, 8 hours, 10 hours, 12 hours, 14 hours, 16 hours, 18 hours, 20 hours, or 24 hours.

[0032] According to an embodiment of the present invention, in step (3), the calcination includes a first calcination and a second calcination, the temperature of the first calcination is 500°C-800°C (such as 500°C, 550°C, 600°C, 650°C, 700°C, 750°C or 800°C), and the time of the first calcination is 2-6 hours (such as 2 hours, 3 hours, 4 hours, 5 hours or 6 hours); the temperature of the second calcination is 900°C-1100°C (such as 900°C, 950°C, 1000°C, 1050°C or 1100°C), and the time of the second calcination is 2-10 hours (such as 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours or 10 hours).

[0033] According to an embodiment of the present invention, in step (3), after the first calcination is completed, the temperature is continued to be raised to the second calcination temperature for the second calcination.

[0034] According to an embodiment of the present invention, in step (3), the calcination is carried out under a nitrogen atmosphere or an argon atmosphere.

[0035] According to an embodiment of the present invention, in step (3), during the first calcination process, zinc oxide and carbon generated by the decomposition of zinc alginate peel off the montmorillonite into two-dimensional montmorillonite nanosheets; during the second calcination process, the carbon reduces the zinc oxide to generate a zinc vapor escape reaction system, thereby obtaining porous carbon-coated two-dimensional montmorillonite nanosheets.

[0036] According to an embodiment of the present invention, in step (4), the weight ratio of the magnesium powder to the porous carbon-coated two-dimensional montmorillonite nanosheets is (0.8-1):1, for example, 0.8:1, 0.9:1 or 1:1.

[0037] According to an embodiment of the present invention, in step (4), the mixing is performed under grinding conditions, for example.

[0038] According to an embodiment of the present invention, in step (4), the magnesium thermal reduction reaction is carried out under an inert atmosphere, which is an argon atmosphere.

[0039] According to an embodiment of the present invention, in step (4), the temperature of the magnesium thermal reduction reaction is 800°C-1000°C (such as 800°C, 850°C, 900°C, 950°C or 1000°C), and the time of the magnesium thermal reduction reaction is 2-6 hours (such as 2 hours, 3 hours, 4 hours, 5 hours or 6 hours).

[0040] According to an embodiment of the present invention, in step (5), the water washing is to use deionized water to wash the ground reaction product, the purpose of which is to remove water-soluble impurity components in the reaction product.

[0041] According to an embodiment of the present invention, in step (5), the pickling includes a first pickling and a second pickling; wherein, the purpose of the first pickling is to remove impurity components such as aluminum oxide and magnesium oxide in the reaction product; the purpose of the second pickling is to remove impurity components such as cristobalite in montmorillonite in the reaction product; the removal of impurity components will form a cavity between the silicon nanosheets and the porous carbon, and the formation of the cavity is conducive to further alleviating the volume expansion of silicon.

[0042] According to an embodiment of the present invention, in step (5), the acid used in the first pickling includes one or more of hydrochloric acid, sulfuric acid and nitric acid, the pH of the acid solution used in the first pickling is 2-4, and the stirring time during the first pickling is 30min-10h; the acid used in the second pickling is hydrofluoric acid, the mass percentage concentration of the acid solution used in the second pickling is 0.1%-5%, and the stirring time during the second pickling is 30min-1h.

[0043] According to an embodiment of the present invention, in step (5), after the pickling is completed, post-processing steps such as filtration and drying are also included.

[0044] According to an embodiment of the present invention, in step (6), the carbon coating treatment and sintering treatment are methods known in the art, wherein the method used for the carbon coating treatment includes but is not limited to at least one of chemical vapor deposition, solid-phase mixing of carbon sources, or liquid-phase mixing of carbon sources.

[0045] Exemplarily, the carbon coating treatment method is to uniformly mix the porous carbon@cavity@silicon nanosheets of step (5) with asphalt, so that the asphalt is coated on the surface of the porous carbon@cavity@silicon nanosheets to obtain a mixture;

[0046] Illustratively, the sintering method is to sinter the carbon-coated mixture, and then break it up and screen it after cooling to obtain the silicon-carbon composite negative electrode material.

[0047] The present invention also provides a silicon-carbon composite negative electrode material prepared by the above method.

[0048] According to an embodiment of the present invention, the silicon-carbon composite negative electrode material has a core-shell structure.

[0049] According to an embodiment of the present invention, the silicon-carbon composite negative electrode material includes amorphous carbon, porous carbon and silicon nanosheets; the silicon nanosheets are core materials, the porous carbon and amorphous carbon are shell materials, and there is a cavity between the core material and the shell material.

[0050] Preferably, in the shell material, the amorphous carbon is located in the outermost layer, and the porous carbon is located in the second outermost layer.

[0051] According to an embodiment of the present invention, the silicon-carbon composite negative electrode material includes amorphous carbon, porous carbon and silicon nanosheets; the silicon nanosheets are core materials, the porous carbon and amorphous carbon are shell materials, the amorphous carbon is located in the outermost layer, and the porous carbon is located in the second outermost layer; and there is a cavity between the silicon nanosheets and the porous carbon.

[0052] According to an embodiment of the present invention, in the silicon-carbon composite negative electrode material, the mass percentage of porous carbon is 3-8% (such as 3%, 4%, 5%, 6%, 7% or 8%).

[0053] According to an embodiment of the present invention, in the silicon-carbon composite negative electrode material, the mass percentage of amorphous carbon is 1-5% (such as 1%, 2%, 3%, 4% or 5%).

[0054] According to an embodiment of the present invention, in the silicon-carbon composite negative electrode material, the mass percentage of silicon nanosheets is 87-96% (such as 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95% or 96%).

[0055] According to an embodiment of the present invention, in the silicon-carbon composite negative electrode material, the average thickness of the silicon nanosheets is 15-50 nm, for example, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm or 50 nm; the average length of the silicon nanosheets is 150-500 nm, for example, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm or 500 nm.

[0056] According to an embodiment of the present invention, the silicon-carbon composite negative electrode material is -1 The first discharge capacity at a current density of ≥2200mAh / g, and the first charge and discharge efficiency ≥90.0%.

[0057] According to an embodiment of the present invention, the silicon-carbon composite negative electrode material is -1 The capacity retention rate after 100 cycles at a current density of ≥80%.

[0058] The present invention also provides use of the silicon-carbon composite negative electrode material in a lithium-ion battery, preferably as a negative electrode material for a lithium-ion battery.

[0059] Beneficial effects of the present invention:

[0060] The present invention utilizes the sodium ions on the negatively charged sodium alginate and the positive ions (Ca 2+ ) exchange effect, inserting sodium alginate into the interlayer of montmorillonite, and then weakening the interlayer force of montmorillonite through electrostatic repulsion, so that the interlayer distance of montmorillonite is increased; then using the cation (Na + ) and Zn 2+ A hydrogel is formed by a displacement crosslinking reaction. After drying, the hydrogel is calcined. During the first calcination at 500-800°C, zinc alginate decomposes to produce zinc oxide and carbon, which exfoliate the montmorillonite into two-dimensional montmorillonite nanosheets. The temperature is then raised to 900-1100°C for a second calcination, where the carbon reduces the zinc oxide to form a zinc vapor-emission reaction system, resulting in porous carbon-coated two-dimensional montmorillonite nanosheets. This process addresses the difficulty in dispersing silicon nanosheets. A magnesium-thermal reduction reaction then occurs, reducing the two-dimensional montmorillonite nanosheets to form a mixture of silicon nanosheets, aluminum oxide, and magnesium oxide. After removing impurities such as aluminum oxide and magnesium oxide through water washing and acid washing, cavities are formed between the silicon nanosheets and the porous carbon, resulting in porous carbon@cavity@silicon nanosheets. The presence of the cavity mitigates the volume expansion of silicon, addressing the low cycling performance of the silicon nanosheets. Finally, amorphous carbon is coated on the porous carbon surface to improve the initial coulombic efficiency of the silicon-carbon composite anode material. DETAILED DESCRIPTION

[0061] The technical solutions of the present invention will be described in further detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanations of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are encompassed within the scope of protection that the present invention is intended to protect.

[0062] Unless otherwise specified, the experimental methods used in the following examples are conventional methods; the reagents, materials, etc. used in the following examples are all commercially available unless otherwise specified.

[0063] Example 1

[0064] (1) 1 g of montmorillonite (average thickness 80 nm, average length 5 μm) was added to 1000 g of deionized water, stirred and ultrasonicated for 10 min, and then 3 g of sodium alginate was added and stirred at 70 °C until completely dissolved. The mixture was then allowed to stand for 14 h to obtain a uniformly dispersed suspension.

[0065] (2) Add 20g of the suspension from step (1) dropwise to 90g of Zn(NO3)2 . After the cross-linking reaction was stirred in 6H2O aqueous solution (20 g / L) for 16 h, the hydrogel spheres with a diameter of 3 mm were obtained by filtration and washed twice with deionized water;

[0066] (3) drying the hydrogel spheres from step (2) at 60° C. for 12 hours, calcining them at 600° C. in an argon atmosphere for 6 hours, then heating them to 950° C. for 6 hours, and cooling them to obtain porous carbon-coated two-dimensional montmorillonite nanosheets;

[0067] (4) mixing 0.8 g of the porous carbon-coated two-dimensional montmorillonite nanosheets from step (3) and 1 g of magnesium powder in anhydrous conditions and in the presence of argon, and grinding the mixture to obtain a uniformly mixed powder; placing the powder in a tubular furnace in the presence of argon at 850° C. for a magnesium thermal reduction reaction for 6 hours to obtain an initial reaction product containing porous carbon-coated silicon nanosheets;

[0068] (5) The initial product of step (4) was ground, dissolved in deionized water, and then pickled in a nitric acid solution with a pH of 4 for 2 h, followed by pickling in a hydrofluoric acid solution with a mass percentage concentration of 2.0% for 40 min, filtered, and dried to obtain porous carbon@cavity@silicon nanosheets;

[0069] (6) 100 g of the porous carbon@cavity@silicon nanosheets prepared in step (5) and 5 g of asphalt were mixed, treated at 1000 °C for 4 h under N2 protection, and then cooled to room temperature and then broken up, sieved, and demagnetized to obtain a silicon-carbon composite negative electrode material.

[0070] The silicon-carbon composite anode material has a core-shell structure of amorphous carbon, porous carbon, cavity, and silicon nanosheets. The outermost layer is amorphous carbon, the next outermost layer is porous carbon, and the core is a silicon nanosheet. There is a cavity between the silicon nanosheet and the porous carbon. The silicon nanosheets in the silicon-carbon composite anode material have an average thickness of 34 nm and an average length of 200 nm. The porous carbon accounts for 4% by weight, and the amorphous carbon accounts for 2% by weight.

[0071] Example 2

[0072] (1) 2 g of montmorillonite (average thickness of 120 nm, average length of 10 μm) was added to 1000 g of deionized water, stirred and ultrasonicated for 30 min, and then 8 g of sodium alginate was added and stirred at 90 °C until completely dissolved. The mixture was then allowed to stand for 24 h to obtain a uniformly dispersed suspension.

[0073] (2) 30 g of the suspension obtained in step (1) was added dropwise to 100 g of a Zn(NO3)2·6H2O aqueous solution (40 g / L) and stirred for a cross-linking reaction for 24 hours. The resulting hydrogel spheres were filtered to obtain hydrogel spheres with a diameter of 5 mm, which were then washed four times with deionized water.

[0074] (3) drying the hydrogel spheres prepared in step (2) at 70° C. for 20 hours, calcining them at 700° C. in an argon atmosphere for 4 hours, then heating them to 1000° C. for 3 hours, and cooling them to obtain porous carbon-coated two-dimensional montmorillonite nanosheets;

[0075] (4) mixing 0.9 g of the porous carbon-coated two-dimensional montmorillonite nanosheets from step (3) and 1 g of magnesium powder in anhydrous conditions and in the presence of argon, and grinding the mixture to obtain a uniformly mixed powder; placing the powder in a tubular furnace in the presence of argon at 950° C. for a magnesium thermal reduction reaction for 3 hours to obtain an initial reaction product containing porous carbon-coated silicon nanosheets;

[0076] (5) The initial product of step (4) was ground, dissolved in deionized water, and then pickled in a nitric acid solution with a pH of 3 for 2 h, followed by pickling in a hydrofluoric acid solution with a mass percentage concentration of 4% for 30 min, filtered, and dried to obtain porous carbon@cavity@silicon nanosheets;

[0077] (6) 100 g of the porous carbon@cavity@silicon nanosheets prepared in step (5) and 10 g of asphalt were mixed, treated at 1100 °C for 4 h under N2 protection, and then cooled to room temperature, broken up, sieved, and demagnetized to obtain a silicon-carbon composite negative electrode material.

[0078] The silicon-carbon composite anode material has a core-shell structure of amorphous carbon, porous carbon, cavity, and silicon nanosheets. The outermost layer is amorphous carbon, the next outermost layer is porous carbon, and the core is a silicon nanosheet. There is a cavity between the silicon nanosheet and the porous carbon. The silicon nanosheets in the silicon-carbon composite anode material have an average thickness of 25 nm and an average length of 350 nm. The porous carbon accounts for 6% by weight, and the amorphous carbon accounts for 4% by weight.

[0079] Example 3

[0080] (1) 1 g of montmorillonite (average thickness of 100 nm, average length of 8 μm) was added to 1000 g of deionized water, stirred and ultrasonicated for 20 min, and then 5 g of sodium alginate was added and stirred at 80 °C until completely dissolved. The mixture was then allowed to stand for 20 h to obtain a uniformly dispersed suspension.

[0081] (2) 30 g of the suspension from step (1) was added dropwise to 100 g of a 30 g / L Zn(NO3)2·6H2O aqueous solution and stirred for 20 hours for cross-linking reaction. The resulting hydrogel spheres were filtered to obtain a diameter of 4 mm and washed three times with deionized water.

[0082] (3) drying the hydrogel spheres prepared in step (2) at 90° C. for 20 hours, calcining them at 800° C. in an argon atmosphere for 2 hours, then heating them to 1050° C. for 3 hours, and cooling them to obtain porous carbon-coated two-dimensional montmorillonite nanosheets;

[0083] (4) mixing 1 g of the porous carbon-coated two-dimensional montmorillonite nanosheets from step (3) and 1 g of magnesium powder in anhydrous conditions and in the presence of argon, and grinding the mixture to obtain a uniformly mixed powder; subjecting the powder to a magnesium thermal reduction reaction at 900° C. in a tubular furnace in the presence of argon for 4 hours to obtain an initial reaction product containing porous carbon-coated silicon nanosheets;

[0084] (5) The initial reaction product of step (4) was ground, dissolved in deionized water, and then pickled in a nitric acid solution with a pH of 4 for 2 h, followed by pickling in a hydrofluoric acid solution with a mass percentage concentration of 5.0% for 60 min, filtered, and dried to obtain porous carbon@cavity@silicon nanosheets;

[0085] (6) 100 g of the porous carbon@cavity@silicon nanosheets prepared in step (5) and 10 g of asphalt were mixed, treated at 1000° C. for 7 h under N2 protection, and then cooled to room temperature and then broken up, sieved, and demagnetized to obtain a silicon-carbon composite negative electrode material.

[0086] The silicon-carbon composite anode material has a core-shell structure of amorphous carbon, porous carbon, cavity, and silicon nanosheets. The outermost layer is amorphous carbon, the next outermost layer is porous carbon, and the core is a silicon nanosheet. There is a cavity between the silicon nanosheet and the porous carbon. The silicon nanosheets in the silicon-carbon composite anode material have an average thickness of 20 nm and an average length of 280 nm. The porous carbon accounts for 7% by weight, and the amorphous carbon accounts for 3% by weight.

[0087] Electrochemical performance test:

[0088] Half-cell test method: The silicon-carbon composite negative electrode material prepared in the example: conductive carbon black (SP): carboxymethyl cellulose (CMC): styrene-butadiene rubber (SBR) = 95:1:1.5:2.5 (mass ratio) were mixed evenly and applied on copper foil. The coated electrode was placed in a vacuum drying oven at 120°C and dried for 12 hours. A simulated battery assembly was performed in an argon-protected Braun glove box. The electrolyte was 1M-LiPF6+EC:DEC:DMC (volume ratio of 1:1:1). The metal lithium sheet was used as the counter electrode. The simulated battery test was performed in a 5V, 10mA Xinwei battery test cabinet. The charge and discharge voltage was 0.01-1.5V, 200mAg -1 The first discharge capacity and first coulombic efficiency were tested at a current density of , and the test results are listed in Table 1.

[0089] Full battery test method: The silicon-carbon composite negative electrode material prepared in the example was used as the negative electrode, lithium cobalt oxide was used as the positive electrode, and 1M-LiPF6+EC:DEC:DMC (volume ratio 1:1:1) solution was used as the electrolyte to assemble a full battery. -1 The charge and discharge were carried out at room temperature at a current density of 1.5 V and a voltage range of 3.0-4.2 V. The cycle performance obtained from the test is listed in Table 1.

[0090] Table 1 Electrochemical performance test results

[0091] The above describes the embodiments of the present invention. However, the present invention is not limited to the above embodiments. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included in the scope of protection of the present invention.

Claims

1. A method for preparing a silicon-carbon composite negative electrode material, the method comprising the following steps: (1) mixing montmorillonite and sodium alginate to prepare a suspension; (2) mixing the suspension of step (1) with an aqueous solution of zinc salt to carry out a cross-linking reaction to prepare a hydrogel; (3) drying the hydrogel obtained in step (2) and then calcining the dried hydrogel to obtain porous carbon-coated two-dimensional montmorillonite nanosheets; (4) mixing the porous carbon-coated two-dimensional montmorillonite nanosheets and magnesium powder in step (3) under anhydrous and inert atmosphere and placing them in a reaction vessel to perform a magnesium thermal reduction reaction to obtain an initial reaction product containing porous carbon-coated silicon nanosheets; (5) grinding, washing, and acid-washing the initial reaction product of step (4) to prepare porous carbon@cavity@silicon nanosheets; (6) The porous carbon@cavity@silicon nanosheets prepared in step (5) are sequentially subjected to carbon coating treatment and sintering treatment to prepare the silicon-carbon composite negative electrode material.

2. The preparation method according to claim 1, wherein In step (1), the montmorillonite has a lamellar structure, the average thickness of the montmorillonite lamellar is 80nm-120nm; the average length of the montmorillonite lamellar is 5μm-10μm; And / or, in step (1), the mass ratio of montmorillonite to sodium alginate is 1:(3-5); And / or, in step (1), the concentration of montmorillonite in the suspension is 0.1%-0.3%.

3. The preparation method according to claim 1 or 2, wherein In step (2), the zinc salt is selected from at least one of zinc nitrate, zinc chloride, zinc sulfate and zinc acetate; and / or, in step (2), the concentration of the aqueous solution of the zinc salt is 10-50 g / L; And / or, in step (2), the mass ratio of the suspension to the aqueous solution of the zinc salt is (10-50):100; and / or, in step (2), the mixing method is to add the suspension of step (1) dropwise to the aqueous solution of zinc salt; and / or, in step (2), the hydrogel is in the form of a spherical hydrogel; And / or, in step (2), the diameter of the spherical hydrogel is 2 mm to 5 mm.

4. The preparation method according to any one of claims 1 to 3, wherein In step (3), the calcination includes a first calcination and a second calcination, the temperature of the first calcination is 500°C-800°C, and the time of the first calcination is 2-6 hours; the temperature of the second calcination is 900°C-1100°C, and the time of the second calcination is 2-10 hours.

5. The preparation method according to any one of claims 1 to 4, wherein In step (4), the weight ratio of the magnesium powder to the porous carbon-coated two-dimensional montmorillonite nanosheets is (0.8-1):1; And / or, in step (4), the temperature of the magnesium thermal reduction reaction is 800° C.-1000° C., and the time of the magnesium thermal reduction reaction is 2-6 hours.

6. The preparation method according to any one of claims 1 to 5, wherein In step (5), the pickling includes a first pickling and a second pickling; the acid used in the first pickling includes one or more of hydrochloric acid, sulfuric acid and nitric acid, the pH of the acid solution used in the first pickling is 2-4, and the stirring time during the first pickling is 30min-10h; the acid used in the second pickling is hydrofluoric acid, the mass percentage concentration of the acid solution used in the second pickling is 0.1%-5%, and the stirring time during the second pickling is 30min-1h.

7. A silicon-carbon composite negative electrode material prepared by the method according to any one of claims 1 to 6.

8. The silicon-carbon composite negative electrode material according to claim 7, wherein: The silicon-carbon composite negative electrode material includes amorphous carbon, porous carbon and silicon nanosheets; the silicon nanosheets are core materials, the porous carbon and amorphous carbon are shell materials, and there is a cavity between the core material and the shell material.

9. The silicon-carbon composite negative electrode material according to claim 7 or 8, wherein: In the silicon-carbon composite negative electrode material, the mass percentage of porous carbon is 3-8%; and / or the mass percentage of amorphous carbon is 1-5%; and / or the mass percentage of silicon nanosheets is 87-96%.

10. Use of the silicon-carbon composite negative electrode material according to any one of claims 7 to 9 in a lithium-ion battery.

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