Preparation method of high-performance silicon-carbon negative electrode material

Abstract

The invention relates to the technical field of sodium-ion battery negative electrode materials, and discloses a preparation method of a high-performance silicon-carbon negative electrode material, which comprises the following steps: step 1, obtaining a porous silicon-carbon material; step 2, obtaining a porous silicon carbon dispersion liquid with positive charges; step 3, dispersing to obtain a surfactant modified porous silicon carbon material dispersion liquid with positive charges; step 4, obtaining single-layer MXene powder; step 5, obtaining an MXene dispersion liquid; step 6, obtaining a mixed solution; and 7, obtaining the MXene coated silicon carbon negative electrode material for the negative electrode of the lithium ion battery. Porous silicon carbon particles with positive charges are spontaneously inserted between single-layer MXene sheet layers by utilizing simple electrostatic interaction, the problem of volume expansion of silicon can be relieved by a porous silicon carbon structure, MXene has excellent hydrophilicity and electronic conductivity, and meanwhile, the problem of expansion of a silicon material can be effectively improved by MXene with a layered structure; and the cycling stability and the rate capability are enhanced.

Description

Technical Field

[0001] The invention relates to the technical field of sodium ion battery negative electrode materials, and in particular to a method for preparing a high-performance silicon-carbon negative electrode material. Background Art

[0002] In the small energy storage market, lithium-ion batteries are favored by portable electronic devices due to their high specific capacity, stable voltage, no memory effect and excellent safety performance. At the same time, with the widespread popularization of electric vehicles and the country's promotion of clean energy, lithium-ion batteries play an increasingly indispensable role in people's daily lives, and the requirements for lithium-ion battery energy density and cycle life are also getting higher and higher. As an important component of the battery, the capacity and cycle period of the negative electrode material itself will also have an important impact on the overall capacity, life and other key performance of the lithium-ion battery.

[0003] Currently, the mainstream lithium battery negative electrode material in the market is commercial graphite material, but with the increase in market demand, the specific capacity of graphite of 372mAh / g is far from meeting the demand for increasing the energy density of lithium battery negative electrodes.

[0004] Silicon has become the most promising candidate material for the negative electrode material of the next generation of lithium-ion batteries due to its high theoretical capacity (4200mAh / g), low discharge potential and rich storage capacity. However, silicon material also has a fatal disadvantage: the volume expansion rate is very serious during the lithium ion deintercalation process. A volume change of 300% will cause damage to the material structure and cause the material powder to fall off. In the battery cell, it is directly manifested as continuous consumption of active materials, increase in irreversible capacity, and continuous attenuation of capacity retention rate, resulting in rapid attenuation of battery capacity, extremely poor cycle performance, and finally cell failure.

[0005] At present, the methods to improve silicon materials include: nano-sizing, pore creation, composite carbon materials, etc. However, nano-sizing can only alleviate the problem of volume expansion, and the low electrical conductivity of silicon itself has not been improved; although pore creation technology can alleviate volume changes, the large specific surface area will cause serious interface problems; although composite carbon materials can appropriately alleviate volume expansion, there is still an obvious capacity attenuation problem after long-term cycling; in short, the above methods all improve a single problem, but carbon coating can not only enhance the electronic conductivity of the material, but also alleviate volume expansion, thereby improving kinetic performance and cycle life.

[0006] Two-dimensional layered transition metal carbon / nitride (MXene) is expected to become an ideal substrate for carbon composites due to its high specific surface area, excellent electronic conductivity and hydrophilicity, and adjustable surface structure.

[0007] The common technology is to combine MXene with nano-silicon to alleviate the volume effect of silicon materials and improve the cycle performance of batteries. However, the MXene layers will spontaneously collapse and stack, greatly reducing the specific surface area, reducing the adsorption sites of Li+, resulting in a decrease in capacity. Moreover, the collapse and stacking will cause a significant increase in the resistivity of the MXene in the vertical direction between the layers, further hindering the transmission of Li+ and affecting the rate performance of the material. Summary of the invention

[0008] The purpose of the present invention is to provide a method for preparing a high-performance silicon-carbon negative electrode material to solve the problems raised in the above background technology.

[0009] To achieve the above object, the present invention provides the following technical solution: a method for preparing a high-performance silicon-carbon negative electrode material, comprising the following steps:

[0010] Step 1: Mixing single crystal silicon material with graphite, uniformly dispersing the mixed powder in a pickling solvent for pickling, then ultrasonically centrifugally cleaning with ethanol and water for multiple times, and drying to obtain a porous silicon-carbon material;

[0011] Step 2: uniformly mix the porous silicon-carbon material and the organic carbon source, heat-treat under an inert gas atmosphere to obtain a carbon-encapsulated porous silicon-carbon material, mix the carbon-encapsulated porous silicon-carbon material with deionized water, and ultrasonically disperse for 30 minutes to obtain a positively charged porous silicon-carbon dispersion;

[0012] Step 3: Add the surfactant and porous silicon-carbon dispersion into a beaker, stir evenly, and then centrifuge and wash at 4000 r / min for 5 min each time until the pH of the supernatant is 7, and disperse to obtain a surfactant-modified porous silicon-carbon material dispersion with positive charge;

[0013] Step 4: Using HF etching method, the MAX precursor is etched with concentrated HF solution to obtain a multilayer MXene material, and then subjected to ultrasonic and high-speed centrifugal washing and drying treatment to obtain a single-layer MXene powder;

[0014] Step 5: Add the monolayer MXene powder into deionized water and ultrasonicate in an ice bath for 1 h to obtain a MXene dispersion;

[0015] Step 6: slowly add the positively charged porous silicon-carbon material dispersion obtained in step 3 into the MXene dispersion while stirring at a constant speed to obtain a mixed solution;

[0016] Step 7: The mixed solution is allowed to stand for 5 hours, washed by centrifugation with deionized water, and freeze-dried for 12 hours to obtain a MXene-coated silicon-carbon negative electrode material for a lithium-ion battery negative electrode.

[0017] In a specific embodiment, in step 1, the single crystal silicon material and graphite are mixed by ball milling, wherein the ball milling speed is 500-1000 r / min and the ball milling time is 2-10 h.

[0018] In a specific embodiment, in step 1, the pickling solvent is one of sulfuric acid, hydrochloric acid, nitric acid and hydrofluoric acid.

[0019] In a specific embodiment, in step 2, the organic carbon source is one or more of glucose, sucrose, citric acid, dopamine salt, formaldehyde, phenolic resin, xylenol, polyacrylonitrile, polypyrrole, polyaniline and polythiophene.

[0020] In a specific embodiment, in step 2, the heat treatment method is: uniformly mix the porous silicon carbon material and the organic carbon source, place them in a tube furnace for sintering, the sintering temperature is 500-1500°C, the time is 2-5h, and the inert gas is one of argon and nitrogen.

[0021] In a specific embodiment, in step three, the surfactant is a cationic surface modifier, specifically one of CTAB and PEI.

[0022] In a specific embodiment, in step three, the stirring conditions of the surfactant and the porous silicon carbon dispersion are: stirring speed is 100-500 r / min, stirring time is 5-15 h, and stirring temperature is 25-60°C.

[0023] In a specific embodiment, in step six, the uniform stirring conditions are: stirring temperature is 25-60° C., and stirring time is 2-10 h.

[0024] In a specific embodiment, in step six, the positively charged porous silicon-carbon material dispersion is mixed with the Ti3C2 dispersion. The principle is: due to the presence of functional groups on the surface of Ti3C2, it itself carries a negative charge. Under the effect of electrostatic adsorption, the porous silicon-carbon material will spontaneously adsorb in the Ti3C2 layer to form a structure in which particles are intercalated between the layers.

[0025] In a specific embodiment, in step five, the MXene powder is a single layer, M is a transition metal, X is C and / or N, wherein M is one or more of Ti, V, Nb, Ta, Cr, Zn, Ni and Mo.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] The present invention utilizes simple electrostatic effects to spontaneously insert positively charged porous silicon-carbon particles between single-layer MXene sheets. The porous silicon-carbon structure can alleviate the volume expansion problem of silicon. MXene has excellent hydrophilicity and electronic conductivity. At the same time, the layered structure of MXene can effectively improve the expansion problem of silicon materials, enhance cycle stability and rate performance. The functional groups on the surface of MXene can also react to form a passivation layer, effectively forming a stable SEI, reducing the consumption of active substances, and further improving the cycle life.

[0028] The preparation method provided by the present invention utilizes a simple electrostatic self-assembly principle and only requires standing and waiting. It does not require a heating process of a hydrothermal process, nor does it need to consider the cost of CVD coating. The operation is simple, pollution-free, efficient and low-cost, and the cost in the preparation process of lithium-ion battery negative electrode materials is effectively reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 is a metallographic diagram of the porous silicon-carbon material of the present invention;

[0030] Figure 2 This is the metallographic diagram of the Ti3C2-coated silicon-carbon negative electrode material of the present invention. DETAILED DESCRIPTION

[0031] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0032] Example 1

[0033] A method for preparing a high-performance silicon-carbon negative electrode material comprises the following steps:

[0034] Step 1: 160 mg of single crystal silicon material and 40 mg of graphite were ground and mixed by ball milling, the ball milling speed was 1000 r / min, the ball milling time was 3 h, and the mixed powder was evenly dispersed in a sulfuric acid solution with a concentration of 5 mol / ml for pickling. The pickling conditions were magnetic stirring for 2 h at room temperature by a magnetic stirrer, and then ultrasonic centrifugal washing was performed three times with ethanol and water, and then dried to obtain a porous silicon-carbon material (such as Figure 1 shown);

[0035] Step 2: uniformly mix the porous silicon-carbon material and the organic carbon source-glucose, and sinter them in a tube furnace under an argon gas atmosphere at a sintering temperature of 800°C for 5 hours to obtain a carbon-encapsulated porous silicon-carbon material; 100 mg of the carbon-encapsulated porous silicon-carbon material is mixed with 50 ml of deionized water, and ultrasonically dispersed for 30 minutes to obtain a positively charged porous silicon-carbon dispersion;

[0036] Step 3, add 100 ml of 8 mg / ml CTAB (hexadecyltrimethylammonium bromide) aqueous solution and porous silicon-carbon dispersion into a beaker, stir evenly by magnetic force, the stirring speed is 500 r / min, the stirring time is 10 h, the stirring temperature is 40 ° C, and then centrifuge and wash at 4000 r / min, each time for 5 min, until the supernatant pH = 7, and disperse to obtain a CTAB (hexadecyltrimethylammonium bromide) modified positively charged porous silicon-carbon material dispersion;

[0037] Step 4: Using HF etching method, MAX precursor Ti3AlC2 is etched with concentrated HF solution to obtain multilayer Ti3C2 material, and then subjected to ultrasonic and high-speed centrifugal washing (4500r / min) and drying treatment to obtain single-layer Ti3C2 powder;

[0038] Step 5: Add 30 mg of single-layer Ti3C2 powder into 100 ml of deionized water and ultrasonicate in an ice bath for 1 h to obtain a Ti3C2 dispersion;

[0039] Step 6: slowly add the positively charged porous silicon-carbon material dispersion obtained in step 3 into the Ti3C2 dispersion while maintaining uniform stirring at a stirring speed of 500 r / min, a stirring temperature of 25° C., and a stirring time of 2 h to obtain a mixed solution;

[0040] Step 7: The mixed solution is allowed to stand for 5 hours, washed by centrifugation with deionized water, and freeze-dried for 12 hours to obtain a Ti3C2-coated silicon-carbon negative electrode material for a lithium-ion battery negative electrode (such as Figure 2 shown).

[0041] Example 2

[0042] A method for preparing a high-performance silicon-carbon negative electrode material comprises the following steps:

[0043] Step 1: Grind and mix 160 mg of single crystal silicon material and 40 mg of graphite by ball milling, the ball milling speed is 800 r / min, the ball milling time is 5 h, and the mixed powder is evenly dispersed in a nitric acid solution with a concentration of 5 mol / ml for pickling. The pickling condition is to stir magnetically for 2 h at room temperature by a magnetic stirrer, and then ultrasonically centrifuge and clean three times with ethanol and water, and dry to obtain a porous silicon-carbon material;

[0044] Step 2: uniformly mix the porous silicon-carbon material and the organic carbon source-glucose, and sinter them in a tube furnace under an argon gas atmosphere at a sintering temperature of 1000° C. for 3 hours to obtain a carbon-encapsulated porous silicon-carbon material; 100 mg of the carbon-encapsulated porous silicon-carbon material is mixed with 50 ml of deionized water, and ultrasonically dispersed for 30 minutes to obtain a positively charged porous silicon-carbon dispersion;

[0045] Step 3, add 100 ml of 8 mg / ml CTAB (hexadecyltrimethylammonium bromide) aqueous solution and porous silicon-carbon dispersion into a beaker, stir evenly by magnetic force, the stirring speed is 500 r / min, the stirring time is 10 h, the stirring temperature is 40 ° C, and then centrifuge and wash at 4000 r / min, each time for 5 min, until the supernatant pH = 7, and disperse to obtain a CTAB (hexadecyltrimethylammonium bromide) modified positively charged porous silicon-carbon material dispersion;

[0046] Step 4: Using HF etching method, MAX precursor Ti3AlC2 is etched with concentrated HF solution to obtain multilayer Ti3C2 material, and then subjected to ultrasonic and high-speed centrifugal washing (4500r / min) and drying treatment to obtain single-layer Ti3C2 powder;

[0047] Step 5: Add 30 mg of single-layer Ti3C2 powder into 100 ml of deionized water and ultrasonicate in an ice bath for 1 h to obtain a Ti3C2 dispersion;

[0048] Step 6: slowly add the positively charged porous silicon-carbon material dispersion obtained in step 3 into the Ti3C2 dispersion while maintaining uniform stirring at a stirring speed of 500 r / min, a stirring temperature of 30° C., and a stirring time of 2 h to obtain a mixed solution;

[0049] Step 7: The mixed solution is allowed to stand for 5 hours, washed by centrifugation with deionized water, and freeze-dried for 12 hours to obtain a Ti3C2-coated silicon-carbon negative electrode material for a lithium-ion battery negative electrode.

[0050] Example 3

[0051] A method for preparing a high-performance silicon-carbon negative electrode material comprises the following steps:

[0052] Step 1: Grind and mix 160 mg of single crystal silicon material and 40 mg of graphite by ball milling, the ball milling speed is 1000 r / min, the ball milling time is 3 h, and the mixed powder is evenly dispersed in a hydrofluoric acid solution with a concentration of 5 mol / ml for pickling. The pickling condition is to stir magnetically for 5 h at room temperature by a magnetic stirrer, and then ultrasonically centrifuge and clean three times with ethanol and water, and dry to obtain a porous silicon-carbon material;

[0053] Step 2: uniformly mix the above-mentioned porous silicon-carbon material and the organic carbon source-sucrose, and sinter them in a tube furnace under an argon gas atmosphere at a sintering temperature of 1500° C. for 3 hours to obtain a carbon-encapsulated porous silicon-carbon material. Mix 100 mg of the carbon-encapsulated porous silicon-carbon material with 50 ml of deionized water, and ultrasonically disperse for 30 minutes to obtain a positively charged porous silicon-carbon dispersion.

[0054] Step 3, add 100 ml of 8 mg / ml CTAB (hexadecyltrimethylammonium bromide) aqueous solution and porous silicon-carbon dispersion into a beaker, stir evenly by magnetic force, the stirring speed is 500 r / min, the stirring time is 10 h, the stirring temperature is 60 ° C, and then centrifuge and wash at 4000 r / min, each time for 5 min, until the supernatant pH = 7, and disperse to obtain a CTAB (hexadecyltrimethylammonium bromide) modified positively charged porous silicon-carbon material dispersion;

[0055] Step 4: Using HF etching method, MAX precursor Ti3AlC2 is etched with concentrated HF solution to obtain multilayer Ti3C2 material, and then subjected to ultrasonic and high-speed centrifugal washing (4500r / min) and drying treatment to obtain single-layer Ti3C2 powder;

[0056] Step 5: Add 30 mg of single-layer Ti3C2 powder into 100 ml of deionized water and ultrasonicate in an ice bath for 1 h to obtain a Ti3C2 dispersion;

[0057] Step 6: slowly add the positively charged porous silicon-carbon material dispersion obtained in step 3 into the Ti3C2 dispersion while maintaining uniform stirring at a stirring speed of 500 r / min, a stirring temperature of 25° C., and a stirring time of 2 h to obtain a mixed solution;

[0058] Step 7: The mixed solution is allowed to stand for 5 hours, washed by centrifugation with deionized water, and freeze-dried for 12 hours to obtain a Ti3C2-coated silicon-carbon negative electrode material for a lithium-ion battery negative electrode.

[0059] Example 4

[0060] A method for preparing a high-performance silicon-carbon negative electrode material comprises the following steps:

[0061] Step 1: Grind and mix 160 mg of single crystal silicon material and 40 mg of graphite by ball milling, the ball milling speed is 1000 r / min, the ball milling time is 3 h, and the mixed powder is evenly dispersed in a sulfuric acid solution with a concentration of 5 mol / ml for pickling. The pickling condition is magnetic stirring for 2 h at room temperature by a magnetic stirrer, and then ultrasonically centrifuged and cleaned three times with ethanol and water, and dried to obtain a porous silicon-carbon material;

[0062] Step 2: uniformly mix the above-mentioned porous silicon-carbon material and the organic carbon source-polyaniline, and sinter them in a tube furnace under an argon gas atmosphere at a sintering temperature of 800° C. for 5 hours to obtain a carbon-encapsulated porous silicon-carbon material. Mix 100 mg of the carbon-encapsulated porous silicon-carbon material with 50 ml of deionized water, and ultrasonically disperse for 30 minutes to obtain a positively charged porous silicon-carbon dispersion.

[0063] Step 3, add 100 ml of 8 mg / ml CTAB (hexadecyltrimethylammonium bromide) aqueous solution and porous silicon-carbon dispersion into a beaker, stir evenly by magnetic force, the stirring speed is 500 r / min, the stirring time is 10 h, the stirring temperature is 40 ° C, and then centrifuge and wash at 4000 r / min, each time for 5 min, until the supernatant pH = 7, and disperse to obtain a CTAB (hexadecyltrimethylammonium bromide) modified positively charged porous silicon-carbon material dispersion;

[0064] Step 4: Using HF etching method, MAX precursor Ti2AlC is etched with concentrated HF solution to obtain multilayer Ti2C material, and then subjected to ultrasonic and high-speed centrifugal washing (4500r / min) and drying treatment to obtain single-layer Ti2C powder;

[0065] Step 5: Add 30 mg of single-layer Ti2C powder into 100 ml of deionized water and ultrasonicate in an ice bath for 1 h to obtain a Ti2C dispersion;

[0066] Step 6: slowly add the positively charged porous silicon-carbon material dispersion obtained in step 3 into the Ti2C dispersion while maintaining uniform stirring at a stirring speed of 500 r / min, a stirring temperature of 25° C., and a stirring time of 2 h to obtain a mixed solution;

[0067] Step 7: The mixed solution is allowed to stand for 5 hours, washed by centrifugation with deionized water, and freeze-dried for 12 hours to obtain a Ti2C-coated silicon-carbon negative electrode material for a lithium-ion battery negative electrode.

[0068] Example 5

[0069] A method for preparing a high-performance silicon-carbon negative electrode material comprises the following steps:

[0070] Step 1: Grind and mix 160 mg of single crystal silicon material and 40 mg of graphite by ball milling, the ball milling speed is 1200 r / min, the ball milling time is 5 h, and the mixed powder is evenly dispersed in a sulfuric acid solution with a concentration of 5 mol / ml for pickling. The pickling condition is to stir magnetically for 3 h at room temperature by a magnetic stirrer, and then ultrasonically centrifuge and clean three times with ethanol and water, and dry to obtain a porous silicon-carbon material;

[0071] Step 2: uniformly mix the above-mentioned porous silicon-carbon material and the organic carbon source-glucose, and sinter them in a tube furnace under an argon gas atmosphere at a sintering temperature of 900°C for 5 hours to obtain a carbon-encapsulated porous silicon-carbon material; 100 mg of the carbon-encapsulated porous silicon-carbon material is mixed with 50 ml of deionized water, and ultrasonically dispersed for 30 minutes to obtain a positively charged porous silicon-carbon dispersion;

[0072] Step 3, add 100 ml of 8 mg / ml CTAB (hexadecyltrimethylammonium bromide) aqueous solution and porous silicon-carbon dispersion into a beaker, stir evenly by magnetic force, the stirring speed is 500 r / min, the stirring time is 10 h, the stirring temperature is 50 ° C, and then centrifuge and wash at 4500 r / min, each time for 5 min, until the supernatant pH = 7, and disperse to obtain a CTAB (hexadecyltrimethylammonium bromide) modified positively charged porous silicon-carbon material dispersion;

[0073] Step 4: Using HF etching method, MAX precursor Nb2AlC is etched with concentrated HF solution to obtain multilayer Nb2C material, and then subjected to ultrasonic and high-speed centrifugal washing (4500r / min) and drying treatment to obtain single-layer Nb2C powder;

[0074] Step 5: Add 30 mg of monolayer Nb2C powder into 100 ml of deionized water and ultrasonicate in an ice bath for 1 h to obtain a Nb2C dispersion;

[0075] Step 6: slowly add the positively charged porous silicon-carbon material dispersion obtained in step 3 into the Nb2C dispersion while maintaining uniform stirring at a stirring speed of 500 r / min, a stirring temperature of 25° C., and a stirring time of 2 h to obtain a mixed solution;

[0076] Step 7: The mixed solution is allowed to stand for 5 hours, washed by centrifugation with deionized water, and freeze-dried for 12 hours to obtain the Nb2C-coated silicon-carbon negative electrode material for the negative electrode of a lithium-ion battery.

[0077] Comparative Example 1

[0078] A method for preparing a high-performance silicon-carbon negative electrode material, which differs from Example 1 in that this comparative example does not involve an electrostatic self-adsorption process, and the MXene-coated silicon-carbon negative electrode material is prepared using a conventional hydrothermal reaction. The method comprises the following steps:

[0079] Step 1: Grind and mix 160 mg of single crystal silicon material and 40 mg of graphite by ball milling, the ball milling speed is 1000 r / min, the ball milling time is 3 h, and the mixed powder is evenly dispersed in a sulfuric acid solution with a concentration of 5 mol / ml for pickling. The pickling condition is magnetic stirring for 2 h at room temperature by a magnetic stirrer, and then ultrasonically centrifuged and cleaned three times with ethanol and water, and dried to obtain a porous silicon-carbon material;

[0080] Step 2: uniformly mix the porous silicon-carbon material and the organic carbon source-glucose, and sinter them in a tube furnace under an argon gas atmosphere at a sintering temperature of 800° C. for 5 hours to obtain a carbon-encapsulated porous silicon-carbon material;

[0081] Step 3: Using HF etching method, MAX precursor Ti3AlC2 is etched with concentrated HF solution to obtain multilayer Ti3C2 material, and then subjected to ultrasonic and high-speed centrifugal washing (4500r / min) and drying treatment to obtain single-layer Ti3C2 powder;

[0082] Step 4: Mix the carbon-wrapped porous silicon-carbon material of step 2 and the single-layer Ti3C2 powder of step 3, and evenly disperse them in deionized water to obtain a C solution. Then, slowly pour the mixed solution C into a polytetrafluoroethylene reactor and maintain the hydrothermal condition at 200°C for 5 hours.

[0083] Step 5. Finally, the mixed solution in the above reaction kettle is centrifuged and washed with deionized water, and freeze-dried for 12 hours to obtain the Ti3C2-coated silicon-carbon negative electrode material for the negative electrode of the lithium-ion battery.

[0084] Comparative Example 2

[0085] A method for preparing a high-performance silicon-carbon negative electrode material, which differs from Example 5 in that this comparative example does not involve an electrostatic self-adsorption process, and the MXene-coated silicon-carbon negative electrode material is prepared using a conventional hydrothermal reaction. The method comprises the following steps:

[0086] Step 1: Grind and mix 160 mg of single crystal silicon material and 40 mg of graphite by ball milling, the ball milling speed is 1000 r / min, the ball milling time is 3 h, and the mixed powder is evenly dispersed in a sulfuric acid solution with a concentration of 5 mol / ml for pickling. The pickling condition is magnetic stirring for 2 h at room temperature by a magnetic stirrer, and then ultrasonically centrifuged and cleaned three times with ethanol and water, and dried to obtain a porous silicon-carbon material;

[0087] Step 2: uniformly mix the porous silicon-carbon material and the organic carbon source-glucose, and sinter them in a tube furnace under an argon gas atmosphere at a sintering temperature of 800° C. for 5 hours to obtain a carbon-encapsulated porous silicon-carbon material;

[0088] Step 3: Using HF etching method, MAX precursor Nb2AlC is etched with concentrated HF solution to obtain multilayer Nb2C material, and then subjected to ultrasonic and high-speed centrifugal washing (4500r / min) and drying treatment to obtain single-layer Nb2C powder;

[0089] Step 4: Mix the carbon-wrapped porous silicon-carbon material of step 2 and the single-layer Nb2C powder of step 3, and evenly disperse them in deionized water to obtain a C solution. Then, slowly pour the mixed solution C into a polytetrafluoroethylene reactor and maintain the hydrothermal condition at 200° C. for 5 hours.

[0090] Step 5. Finally, the mixed solution in the above reaction kettle is centrifuged and washed with deionized water, and freeze-dried for 12 hours to obtain the Nb2C-coated silicon-carbon negative electrode material for the negative electrode of the lithium-ion battery.

[0091] Experimental Example 1

[0092] Method for testing the gram capacity and cycle number of the negative electrode material of the lithium-ion battery:

[0093] The MXene-coated silicon-carbon negative electrode material in Examples 1-5 and Comparative Examples 1 and 2 was used as the negative electrode, the metal sodium sheet was used as the positive electrode, and 1.0 mol / L LiPF6 / EC (ethylene carbonate) + DMC (dimethyl carbonate) + FEC (fluoroethylene carbonate) (EC, DMC and FEC volume ratio 4.5:4.5:1) was used as the electrolyte, and CR2032 button batteries were assembled in an argon glove box. The GCD was tested in the voltage window of 0.01-2V using the LAND battery test system. The test conditions and results are as follows:

[0094] Table 1

[0095]

[0096] The button cells were sequentially tested for constant current charge and discharge at a current density of 50 mA / g, with a voltage range of 0-2 V. The button half-cells of the MXene-coated silicon-carbon negative electrode materials prepared in Example 1 all have a high initial discharge capacity (over 1200 mAh / g), and the first inventory efficiency exceeds 89%, while the first discharge capacity of Comparative Example 1 is only 950.2 mAh / g, and the first coulombic efficiency is 80.6%. Due to the high specific capacity of silicon materials, the cycle life of MXene-coated silicon-carbon negative electrode materials is far superior to that of porous silicon-carbon materials. The MXene layer can not only buffer the volume expansion problem of silicon-carbon materials during charging and discharging, but the layer structure of MXene also provides a fast channel for the transmission of lithium ions between layers. Specific values ​​are shown in Table 1 (the first discharge capacity and first coulombic efficiency of button half-cells of electrode materials obtained in Examples 1-5 and Comparative Examples 1 and 2).

[0097] The button cell was subjected to constant current charge and discharge test at a current density of 50 mA / g, with a voltage range of 0-2 V and 200 cycles. The button half-cells of MXene-coated silicon-carbon negative electrode materials prepared in Examples 1-5 all had good cycle retention rates (greater than 80%), showing excellent cycle stability. The capacity retention rates of Comparative Examples 1 and 2 were only about 60%. Specific values ​​are shown in Table 2 (Capacity retention rates of button half-cells of electrode materials obtained in Examples 1-5 and Comparative Examples 1 and 2 after 200 cycles.)

[0098] Table 2

[0099] Current density 50mA / g 100 cycles capacity retention rate (%) Example 1 81.8 Example 2 81.2 Example 3 80.3 Example 4 82.2 Example 5 82.5 Comparative Example 1 60.4 Comparative Example 2 64.7

[0100] MXene materials can provide a continuous conductive framework, and the flexible sheet structure can be used as a buffer layer to improve the stress caused by silicon expansion during lithium ion extraction and insertion. By utilizing the characteristics of various materials, taking advantage of their strengths and making up for their weaknesses, the porous silicon carbon and MXene sheet electrostatic self-assembly are designed to prepare negative electrode materials, which not only brings out the high capacity characteristics of silicon alloy materials, but also has good cycle stability, improving the overall electrochemical performance of the electrode.

[0101] In summary, the present application utilizes simple electrostatic effects to spontaneously insert positively charged porous silicon-carbon particles between monolayer MXene sheets. The porous silicon-carbon structure can alleviate the volume expansion problem of silicon. MXene has excellent hydrophilicity and electronic conductivity. At the same time, the layered structure of MXene can effectively improve the expansion problem of silicon materials, enhance cycle stability and rate performance, and the functional groups on the surface of MXene can also react to form a passivation layer, effectively forming a stable SEI, reducing the consumption of active substances and further improving the cycle life. The preparation method provided by the present invention utilizes a simple electrostatic self-assembly principle, and only needs to be left standing and waiting. It does not require the heating process of the hydrothermal process, nor does it need to consider the cost of CVD coating. It is simple to operate, pollution-free, efficient and low-cost, and effectively reduces the cost in the preparation process of lithium-ion battery negative electrode materials.

[0102] The content of the present invention is not limited to the content of the above-mentioned examples. The combination of one or more of the examples can also achieve the purpose of the present invention.

[0103] In this specification, each embodiment is described in a progressive manner, and each example focuses on the differences from other embodiments. The same or similar parts between the examples can be referred to each other. For the method disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part description.

[0104] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a high-performance silicon-carbon negative electrode material, characterized in that: The following steps are involved: Step 1: Mixing single crystal silicon material with graphite, uniformly dispersing the mixed powder in a pickling solvent for pickling, then ultrasonically centrifugally cleaning with ethanol and water for multiple times, and drying to obtain a porous silicon-carbon material; Step 2: uniformly mix the porous silicon-carbon material and the organic carbon source, heat-treat under an inert gas atmosphere to obtain a carbon-encapsulated porous silicon-carbon material, mix the carbon-encapsulated porous silicon-carbon material with deionized water, and ultrasonically disperse for 30 minutes to obtain a positively charged porous silicon-carbon dispersion; Step 3: Add the surfactant and porous silicon-carbon dispersion into a beaker, stir evenly, and then centrifuge and wash at 4000 r / min for 5 min each time until the pH of the supernatant is 7, and disperse to obtain a surfactant-modified porous silicon-carbon material dispersion with positive charge; Step 4: Using HF etching method, the MAX precursor is etched with concentrated HF solution to obtain a multilayer MXene material, and then subjected to ultrasonic and high-speed centrifugal washing and drying treatment to obtain a single-layer MXene powder; Step 5: Add the monolayer MXene powder into deionized water and ultrasonicate in an ice bath for 1 h to obtain a MXene dispersion; Step 6: slowly add the positively charged porous silicon-carbon material dispersion obtained in step 3 into the MXene dispersion while stirring at a constant speed to obtain a mixed solution; Step 7: The mixed solution is allowed to stand for 5 hours, washed by centrifugation with deionized water, and freeze-dried for 12 hours to obtain a MXene-coated silicon-carbon negative electrode material for a lithium-ion battery negative electrode.

2. The method for preparing a high-performance silicon-carbon negative electrode material according to claim 1, characterized in that: In step 1, the single crystal silicon material and graphite are mixed by ball milling, the ball milling speed is 500-1000r / min, and the ball milling time is 2-10h.

3. The method for preparing a high-performance silicon-carbon negative electrode material according to claim 1, characterized in that: In step 1, the pickling solvent is one of sulfuric acid, hydrochloric acid, nitric acid and hydrofluoric acid.

4. The method for preparing a high-performance silicon-carbon negative electrode material according to claim 1, characterized in that: In step 2, the organic carbon source is one or more of glucose, sucrose, citric acid, dopamine salt, formaldehyde, phenolic resin, xylenol, polyacrylonitrile, polypyrrole, polyaniline and polythiophene.

5. The method for preparing a high-performance silicon-carbon negative electrode material according to claim 1, characterized in that: In step 2, the heat treatment method is: uniformly mix the porous silicon-carbon material and the organic carbon source, place them in a tube furnace for sintering, the sintering temperature is 500-1500° C., the time is 2-5 hours, and the inert gas is one of argon and nitrogen.

6. The method for preparing a high-performance silicon-carbon negative electrode material according to claim 1, characterized in that: In step three, the surfactant is a cationic surface modifier, specifically one of CTAB and PEI.

7. The method for preparing a high-performance silicon-carbon negative electrode material according to claim 1, characterized in that: In step three, the stirring conditions of the surfactant and the porous silicon carbon dispersion are: stirring speed is 100-500 r / min, stirring time is 5-15 h, and stirring temperature is 25-60°C.

8. The method for preparing a high-performance silicon-carbon negative electrode material according to claim 1, characterized in that: In step six, the uniform stirring conditions are: stirring temperature is 25-60° C., and stirring time is 2-10 h.

9. The method for preparing a high-performance silicon-carbon negative electrode material according to claim 1, characterized in that: In step six, the positively charged porous silicon-carbon material dispersion is mixed with the Ti3C2 dispersion based on the following principle: Due to the presence of functional groups on the surface of Ti3C2, which itself carries a negative charge, the porous silicon-carbon material will spontaneously adsorb in the Ti3C2 flakes under electrostatic adsorption, forming a structure in which particles are intercalated between the flakes.

10. The method for preparing a high-performance silicon-carbon negative electrode material according to claim 1, wherein The characteristics are: in step 5, the MXene powder is a single layer, M is a transition metal, X is C and / or N, in, M is one or more of Ti, V, Nb, Ta, Cr, Zn, Ni and Mo.

Images