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

Abstract

The application 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 one, obtaining a porous silicon-carbon material; step two, obtaining a positively-charged porous silicon-carbon dispersion solution; step three, dispersing to obtain a surfactant-modified positively-charged porous silicon-carbon material dispersion solution; step four, obtaining a single-layer MXene powder; step five, obtaining an MXene dispersion solution; step six, obtaining a mixed solution; and step seven, obtaining an MXene-coated silicon-carbon negative electrode material for a lithium ion battery negative electrode. The positively-charged porous silicon-carbon particles are spontaneously inserted between single-layer MXene layers by simple electrostatic action, the porous silicon-carbon structure can relieve the volume expansion problem of silicon, the MXene has excellent hydrophilicity and electronic conductivity, and the layered structure of the MXene can effectively improve the expansion problem of the silicon material, enhance the cycle stability and the rate performance.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of sodium ion battery negative electrode materials, in particular to a preparation method of a high-performance silicon-carbon negative electrode material. BACKGROUND

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

[0003] The mainstream lithium battery negative electrode material on the market is commercial graphite material, but as the market demand increases, the specific capacity of 372 mAh / g of graphite has far failed to meet the demand for the improvement of the energy density of the lithium battery negative electrode.

[0004] Silicon has become the most potential candidate material for the next generation of lithium ion battery negative electrode material due to its high theoretical capacity (4200 mAh / g), low discharge potential and abundant storage, etc. However, silicon material also has a fatal defect: the volume expansion rate is very serious during the lithium ion deintercalation process, and the 300% volume change will cause the destruction of the material structure, causing the material powder to fall off, directly showing the continuous consumption of active material in the battery, increasing the irreversible capacity, continuously decaying the capacity retention rate, causing the rapid decay of the battery capacity, the poor cycle performance, and finally leading to the failure of the battery.

[0005] The current methods for improving silicon material are nanocrystallization, pore making, composite carbon material, etc. However, nanocrystallization can only alleviate the volume expansion problem, and the low electrical conductivity of silicon itself has not been improved; the pore making technology can alleviate the volume change, but the large specific surface area will cause serious interface problems; the composite carbon material can appropriately alleviate the volume expansion, but there is still obvious capacity decay problem after long-term cycle; in summary, the above methods are all aimed at improving a single problem, however, carbon coating can not only enhance the electronic conductivity of the material, but also alleviate the volume expansion, thereby improving the kinetic performance and cycle life.

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

[0007] A common technique is to combine MXene with nano-silicon to mitigate the volume effect of silicon and improve battery cycling performance. However, MXene layers spontaneously collapse and stack, significantly reducing the specific surface area and the number of Li+ adsorption sites, leading to a decrease in capacity. Furthermore, this collapse and stacking can significantly increase the resistivity of the MXene in the direction perpendicular to the interlayers, further hindering Li+ transport and affecting the material's rate performance. Summary of the Invention

[0008] The object 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 an acid washing solvent for acid washing, then ultrasonically centrifugally washing 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-coated porous silicon-carbon material, mix the carbon-coated 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 at 4000 r / min for 5 minutes each time until the pH of the supernatant is 7, thereby obtaining a surfactant-modified positively charged porous silicon-carbon material dispersion;

[0013] Step 4: Using HF etching method, the MAX precursor is etched with concentrated HF solution to obtain a multilayer MXene material, which is then washed and dried by ultrasonication and high-speed centrifugation to obtain a single-layer MXene powder;

[0014] Step 5: Add the monolayer MXene powder to 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 to the MXene dispersion while maintaining constant stirring to obtain a mixed solution;

[0016] Step 7: The mixed solution was 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 one specific embodiment, in step one, the mixing method of the single crystal silicon material and graphite is ball milling, the ball milling speed is 500-1000 r / min, and the ball milling time is 2-10 h.

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

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

[0020] In one specific embodiment, in step two, the heat treatment method is to uniformly mix the porous silicon-carbon material and the organic carbon source, and then sinter in a tube furnace, the sintering temperature is 500-1500℃, the time is 2-5 h, and the inert gas is one of argon and nitrogen.

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

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

[0023] In one specific embodiment, in step six, the uniform stirring conditions are as follows: the stirring temperature is 25-60℃, and the stirring time is 2-10 h.

[0024] In one specific embodiment, in step six, the mixing principle of the positively charged porous silicon-carbon material dispersion liquid and the Ti3C2 dispersion liquid is as follows: due to the existence of the surface functional groups of Ti3C2, it itself has a negative charge, under the action of electrostatic adsorption, the porous silicon-carbon material will spontaneously adsorb in the Ti3C2 layer, forming a structure in which the particles are intercalated between the layers.

[0025] In one specific embodiment, in step five, the MXene powder is single-layer, M is a transition metal, and 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 beneficial effects of the present application are:

[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 hydrothermal heating process, nor does it need to consider the cost of CVD coating. It is simple to operate, pollution-free, efficient and low-cost, effectively reducing the cost in the preparation process of lithium-ion battery negative electrode materials. 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 clearly and completely described 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 at a ball milling speed of 1000 r / min for 3 h. The mixed powder was evenly dispersed in a sulfuric acid solution with a concentration of 5 mol / ml and pickled. The pickling conditions were magnetic stirring for 2 h at room temperature by a magnetic stirrer, and then ultrasonically centrifuged and washed three times with ethanol and water, and dried to obtain a porous silicon-carbon material (such as Figure 1 shown);

[0035] Step 2: The porous silicon-carbon material and the organic carbon source - glucose are uniformly mixed, and sintered in a tube furnace under an argon gas atmosphere at a sintering temperature of 800 ° C for 5 hours to obtain a carbon-coated porous silicon-carbon material. 100 mg of the carbon-coated 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 three, 100 ml of CTAB (cetyltrimethylammonium bromide) aqueous solution with a concentration of 8 mg / ml and porous silicon carbon dispersion liquid are added to a beaker, uniformly stirred by magnetic stirring, the stirring speed is 500 r / min, the stirring time is 10 h, the stirring temperature is 40℃, then centrifugal washing is carried out under 4000 r / min, each time for 5 min, until the supernatant PH = 7, and the dispersion of the positively charged porous silicon carbon material modified by CTAB (cetyltrimethylammonium bromide) is obtained;

[0037] Step four, the MAX precursor Ti3AlC2 is etched by HF etching method to obtain a multi-layer Ti3C2 material, and the single-layer Ti3C2 powder is obtained through ultrasonic and high-speed centrifugal washing (4500 r / min) and drying treatment;

[0038] Step five, 30 mg of single-layer Ti3C2 powder is added to 100 ml of deionized water, and ice bath ultrasonic is carried out for 1 h to obtain a Ti3C2 dispersion liquid;

[0039] Step six, the positively charged porous silicon carbon material dispersion liquid obtained in step three is slowly added to the Ti3C2 dispersion liquid, while uniform stirring is maintained, the stirring speed is 500 r / min, the stirring temperature is 25℃, and the stirring time is 2 h to obtain a mixed solution;

[0040] Step seven, the above mixed solution is placed for 5 h, centrifuged and washed with deionized water, and freeze-dried for 12 h to obtain a Ti3C2 coated silicon carbon negative electrode material for lithium ion battery negative electrode (as shown in Figure 2 ).

[0041] Example 2

[0042] A preparation method of a high-performance silicon carbon negative electrode material, comprising the following steps:

[0043] Step one, 160 mg of single crystal silicon material and 40 mg of graphite are mixed by ball milling method, the ball milling speed is 800 r / min, the ball milling time is 5 h, the mixed powder is uniformly dispersed in a nitric acid solution with a concentration of 5 mol / ml for acid washing, the acid washing condition is that the magnetic stirring machine is magnetically stirred at room temperature for 2 h, then the ethanol and water are ultrasonically centrifuged and washed three times, and dried to obtain a porous silicon carbon material;

[0044] Step two, the above porous silicon carbon material and organic carbon source-glucose are uniformly mixed, sintered in a tube furnace under argon gas atmosphere, the sintering temperature is 1000℃, the time is 3 h, a carbon-coated porous silicon carbon material is obtained, 100 mg of the carbon-coated porous silicon carbon material is mixed with 50 ml of deionized water, and ultrasonic dispersion is carried out for 30 min to obtain a positively charged porous silicon carbon dispersion liquid;

[0045] Step three, 100 ml of CTAB (cetyltrimethylammonium bromide) aqueous solution with a concentration of 8 mg / ml and porous silicon carbon dispersion liquid are added to a beaker, uniformly stirred by magnetic stirring, the stirring speed is 500 r / min, the stirring time is 10 h, the stirring temperature is 40℃, then centrifugal washing is carried out under 4000 r / min, each time for 5 min, until the supernatant PH = 7, and the dispersion of the positively charged porous silicon carbon material modified by CTAB (cetyltrimethylammonium bromide) is obtained;

[0046] Step four, the MAX precursor Ti3AlC2 is etched by HF to obtain a multi-layer Ti3C2 material, and the single-layer Ti3C2 powder is obtained through ultrasonic and high-speed centrifugal washing (4500 r / min) and drying treatment;

[0047] Step five, 30 mg of single-layer Ti3C2 powder is added to 100 ml of deionized water, and ice bath ultrasonic is carried out for 1 h to obtain a Ti3C2 dispersion liquid;

[0048] Step six, the positively charged porous silicon carbon material dispersion liquid obtained in step three is slowly added to the Ti3C2 dispersion liquid, while uniform stirring is maintained, the stirring speed is 500 r / min, the stirring temperature is 30℃, and the stirring time is 2 h to obtain a mixed solution;

[0049] Step seven, the above mixed solution is placed for 5 h, centrifuged and washed with deionized water, and freeze-dried for 12 h to obtain a Ti3C2 coated silicon carbon negative electrode material for lithium ion batteries.

[0050] Example 3

[0051] A preparation method of a high-performance silicon carbon negative electrode material, comprising the following steps:

[0052] Step one, 160 mg of single crystal silicon material and 40 mg of graphite are mixed by ball milling, the ball milling speed is 1000 r / min, the ball milling time is 3 h, the mixed powder is uniformly dispersed in a hydrofluoric acid solution with a concentration of 5 mol / ml for acid washing, the acid washing condition is that the magnetic stirring machine is magnetically stirred at room temperature for 5 h, then the ethanol and water are ultrasonically centrifuged and washed three times, and dried to obtain a porous silicon carbon material;

[0053] Step two, the above porous silicon carbon material and an organic carbon source-sucrose are uniformly mixed, and sintered in a tube furnace under an argon gas atmosphere, the sintering temperature is 1500℃, and the time is 3 h to obtain a carbon-coated porous silicon carbon material, 100 mg of the carbon-coated porous silicon carbon material is mixed with 50 ml of deionized water, and ultrasonic dispersion is carried out for 30 min to obtain a positively charged porous silicon carbon dispersion liquid;

[0054] Step three, 100 ml of CTAB (cetyltrimethylammonium bromide) aqueous solution with a concentration of 8 mg / ml and porous silicon carbon dispersion liquid are added to a beaker, uniformly stirred by magnetic stirring, the stirring speed is 500 r / min, the stirring time is 10 h, the stirring temperature is 60℃, then centrifugal washing is carried out under 4000 r / min, each time for 5 min, until the supernatant PH = 7, and the dispersion of the positively charged porous silicon carbon material modified by CTAB (cetyltrimethylammonium bromide) is obtained;

[0055] Step four, the MAX precursor Ti3AlC2 is etched by HF to obtain a multi-layer Ti3C2 material, and the single-layer Ti3C2 powder is obtained through ultrasonic and high-speed centrifugal washing (4500 r / min) and drying treatment;

[0056] Step five, 30 mg of single-layer Ti3C2 powder is added to 100 ml of deionized water, and ice bath ultrasonic is carried out for 1 h to obtain a Ti3C2 dispersion liquid;

[0057] Step six, the positively charged porous silicon carbon material dispersion liquid obtained in step three is slowly added to the Ti3C2 dispersion liquid, while uniform stirring is maintained, the stirring speed is 500 r / min, the stirring temperature is 25℃, and the stirring time is 2 h to obtain a mixed solution;

[0058] Step seven, the above mixed solution is placed for 5 h, centrifuged and washed with deionized water, and freeze-dried for 12 h to obtain a Ti3C2 coated silicon carbon negative electrode material for lithium ion batteries.

[0059] Example 4

[0060] A preparation method of a high-performance silicon carbon negative electrode material, comprising the following steps:

[0061] Step one, 160 mg of single crystal silicon material and 40 mg of graphite are mixed by ball milling, the ball milling speed is 1000 r / min, the ball milling time is 3 h, the mixed powder is uniformly dispersed in a sulfuric acid solution with a concentration of 5 mol / ml for acid washing, the acid washing condition is that the mixed powder is magnetically stirred by a magnetic stirrer at room temperature for 2 h, then the mixed powder is ultrasonically centrifuged with ethanol and water for three times, and dried to obtain a porous silicon carbon material;

[0062] Step two, the porous silicon carbon material and an organic carbon source-polyaniline are uniformly mixed, and sintered in a tube furnace under an argon gas atmosphere, the sintering temperature is 800℃, and the time is 5 h to obtain a carbon-coated porous silicon carbon material, 100 mg of the carbon-coated porous silicon carbon material is mixed with 50 ml of deionized water, and ultrasonic dispersion is carried out for 30 min to obtain a positively charged porous silicon carbon dispersion liquid;

[0063] Step three, 100 ml of CTAB (cetyltrimethylammonium bromide) aqueous solution with a concentration of 8 mg / ml and porous silicon carbon dispersion liquid are added to a beaker, uniformly stirred by magnetic stirring, the stirring speed is 500 r / min, the stirring time is 10 h, the stirring temperature is 40℃, then centrifugal washing is carried out under 4000 r / min, each time for 5 min, until the supernatant PH = 7, and the dispersion of the positively charged porous silicon carbon material modified by CTAB (cetyltrimethylammonium bromide) is obtained;

[0064] Step four, the MAX precursor Ti2AlC is etched by HF to obtain a multi-layer Ti2C material, and the single-layer Ti2C powder is obtained through ultrasonic and high-speed centrifugal washing (4500 r / min) and drying treatment;

[0065] Step five, 30 mg of single-layer Ti2C powder is added to 100 ml of deionized water, and ice bath ultrasonic is carried out for 1 h to obtain a Ti2C dispersion liquid;

[0066] Step six, the positively charged porous silicon carbon material dispersion liquid obtained in step three is slowly added to the Ti2C dispersion liquid, while uniform stirring is maintained, the stirring speed is 500 r / min, the stirring temperature is 25℃, and the stirring time is 2 h to obtain a mixed solution;

[0067] Step seven, the above mixed solution is placed for 5 h, centrifugally washed by deionized water, and freeze-dried for 12 h to obtain a Ti2C coated silicon carbon negative electrode material for lithium ion battery negative electrode.

[0068] Example 5

[0069] A preparation method of a high-performance silicon carbon negative electrode material, comprising the following steps:

[0070] Step one, 160 mg of single crystal silicon material and 40 mg of graphite are mixed by ball milling, the ball milling speed is 1200 r / min, the ball milling time is 5 h, the mixed powder is uniformly dispersed in a sulfuric acid solution with a concentration of 5 mol / ml for acid washing, the acid washing condition is that the magnetic stirring machine is magnetically stirred at room temperature for 3 h, then the ethanol and water are ultrasonically centrifugally washed three times, and dried to obtain a porous silicon carbon material;

[0071] Step two, the above porous silicon carbon material and organic carbon source-glucose are uniformly mixed, sintered in a tube furnace under an argon gas atmosphere, the sintering temperature is 900℃, the time is 5 h, a carbon-coated porous silicon carbon material is obtained, 100 mg of the carbon-coated porous silicon carbon material is mixed with 50 ml of deionized water, ultrasonic dispersion is carried out for 30 min to obtain a positively charged porous silicon carbon dispersion liquid;

[0072] Step three, 100 ml of CTAB (cetyltrimethylammonium bromide) aqueous solution with a concentration of 8 mg / ml and porous silicon carbon dispersion liquid are added to a beaker, uniformly stirred by magnetic stirring, the stirring speed is 500 r / min, the stirring time is 10 h, the stirring temperature is 50℃, then centrifugal washing is carried out under 4500 r / min, each time for 5 min, until the supernatant PH = 7, and the dispersion liquid of the positively charged porous silicon carbon material modified by CTAB (cetyltrimethylammonium bromide) is obtained by dispersion;

[0073] Step four, the MAX precursor Nb2AlC is etched by HF to obtain a multi-layer Nb2C material, and the single-layer Nb2C powder is obtained by ultrasonic and high-speed centrifugal washing (4500 r / min) and drying treatment;

[0074] Step five, 30 mg of single-layer Nb2C powder is added to 100 ml of deionized water, and ice bath ultrasonic is carried out for 1 h to obtain a Nb2C dispersion liquid;

[0075] Step six, the positively charged porous silicon carbon material dispersion liquid obtained in step three is slowly added to the Nb2C dispersion liquid, while uniform stirring is maintained, the stirring speed is 500 r / min, the stirring temperature is 25℃, and the stirring time is 2 h to obtain a mixed solution;

[0076] Step seven, the above mixed solution is placed for 5 h, centrifugally washed by deionized water, and freeze-dried for 12 h to obtain a Nb2C coated silicon carbon negative electrode material for lithium ion battery negative electrode.

[0077] Comparative example 1

[0078] A preparation method of a high-performance silicon carbon negative electrode material, which is different from example 1 in that the process of electrostatic self-adsorption is not involved, and the MXene coated silicon carbon negative electrode material is prepared by using a conventional hydrothermal reaction. It includes the following steps:

[0079] Step one, 160 mg of single crystal silicon material and 40 mg of graphite are mixed by ball milling method, the ball milling speed is 1000 r / min, the ball milling time is 3 h, the mixed powder is uniformly dispersed in a sulfuric acid solution with a concentration of 5 mol / ml for acid washing, the acid washing condition is magnetic stirring for 2 h at room temperature by a magnetic stirrer, then the ethanol and water are ultrasonically centrifugally washed three times, and dried to obtain a porous silicon carbon material;

[0080] Step two, the above porous silicon carbon material and organic carbon source-glucose are uniformly mixed, and sintered in a tube furnace under argon gas atmosphere, the sintering temperature is 800℃, and the time is 5 h to obtain a carbon wrapped porous silicon carbon material;

[0081] Step three, etching MAX precursor Ti3AlC2 with concentrated HF solution to obtain multi-layer Ti3C2 material, and then drying by ultrasonic and high-speed centrifugal washing (4500 r / min) to obtain single-layer Ti3C2 powder;

[0082] Step four, mixing the carbon-coated porous silicon-carbon material in step two and the single-layer Ti3C2 powder in step three, and uniformly dispersing them in deionized water to obtain solution C, then slowly pouring the mixed solution C into a polytetrafluoroethylene reaction kettle, and keeping the hydrothermal condition at 200°C for 5h;

[0083] Step five, finally, centrifugally washing the mixed solution in the above reaction kettle with deionized water, and freeze-drying for 12h to obtain the Ti3C2-coated silicon-carbon negative electrode material for lithium ion battery negative electrode.

[0084] Comparative example 2

[0085] A preparation method of a high-performance silicon-carbon negative electrode material, which is different from example 5 in that the present comparative example does not involve the process of electrostatic self-adsorption, and the MXene-coated silicon-carbon negative electrode material is prepared by using a conventional hydrothermal reaction. It comprises the following steps:

[0086] Step one, grinding and mixing 160mg of single-crystal silicon material with 40mg of graphite by ball milling at a speed of 1000r / min for 3h, uniformly dispersing the mixed powder in a sulfuric acid solution with a concentration of 5mol / ml for acid washing by magnetic stirring at room temperature for 2h, and then performing three times of ultrasonic centrifugal washing with ethanol and water, and drying to obtain a porous silicon-carbon material;

[0087] Step two, uniformly mixing the above porous silicon-carbon material with an organic carbon source-glucose, and sintering in a tube furnace under an argon gas atmosphere at a sintering temperature of 800°C for 5h to obtain a carbon-coated porous silicon-carbon material;

[0088] Step three, etching MAX precursor Nb2AlC with concentrated HF solution to obtain multi-layer Nb2C material, and then drying by ultrasonic and high-speed centrifugal washing (4500 r / min) to obtain single-layer Nb2C powder;

[0089] Step four, mixing the carbon-coated porous silicon-carbon material in step two and the single-layer Nb2C powder in step three, and uniformly dispersing them in deionized water to obtain solution C, then slowly pouring the mixed solution C into a polytetrafluoroethylene reaction kettle, and keeping the hydrothermal condition at 200°C for 5h;

[0090] Step five, finally, centrifugally washing the mixed solution in the above reaction kettle with deionized water, and freeze-drying for 12h to obtain the Nb2C-coated silicon-carbon negative electrode material for lithium ion battery negative electrode.

[0091] Experimental Example 1

[0092] The method for testing the specific capacity and cycle number of the lithium ion battery negative electrode material is as follows:

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

[0094] Table 1

[0095] Current density 100 (mA / g) First discharge capacity (mAh / g) First charge capacity (mAh / g) First coulombic efficiency (%) Example 1 1291.6 1152.1 89.2 Example 2 1350.3 1195.0 88.5 Example 3 1296.5 1176.0 90.7 Example 4 1281.7 1148.4 89.6 Example 5 1250.9 1144.6 91.5 Comparative Example 1 950.2 765.8 80.6 Comparative Example 2 856.6 695.6 81.2

[0096] The button cells were subjected to constant current charge and discharge tests at a current density of 50 mA / g, and the voltage interval was 0-2 V. The button half-cells of the MXene-coated silicon-carbon negative electrode material prepared in Example 1 all had a high initial discharge capacity (more than 1200 mAh / g), and the first storage efficiency was more than 89%, while the first discharge capacity of Comparative Example 1 was only 950.2 mAh / g, and the first coulombic efficiency was 80.6%. Because of the high specific capacity of the silicon material, the cycle life of the MXene-coated silicon-carbon negative electrode material was much better than that of the porous silicon-carbon material. The MXene sheet layer not only buffered the volume expansion problem of the silicon-carbon material during the charge and discharge process, but also provided a fast channel for the transmission of lithium ions between the layers. The specific values are shown in Table 1 (the first discharge capacity and the first coulombic efficiency of the electrode material of the button half-cells of Examples 1-5 and Comparative Examples 1 and 2).

[0097] The button cells were subjected to constant current charge and discharge tests at a current density of 50 mA / g, and the voltage interval was 0-2 V, and the cycle was 200 times. The button half-cells of the MXene-coated silicon-carbon negative electrode material prepared in Examples 1-5 all had a good capacity retention rate (more than 80%), and exhibited excellent cycle stability. The capacity retention rates of Comparative Examples 1 and 2 were only about 60%. The specific values are shown in Table 2 (the capacity retention rate of the electrode material of the button half-cells of Examples 1-5 and Comparative Examples 1 and 2 after 200 cycles).

[0098] Table 2

[0099] Current density 50 mA / g 100 cycle capacity retention (%) 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] The MXene material can provide a continuous conductive framework, and the flexible sheet structure can serve as a buffer layer to improve the stress generated by the expansion of silicon during lithium ion deintercalation. By utilizing the characteristics of various materials, the porous silicon-carbon and MXene sheet electrostatic self-assembly preparation of the negative electrode material not only has the characteristics of high capacity of silicon alloy materials, but also has good cycle stability, and improves the overall electrochemical performance of the electrode.

[0101] In summary, the application utilizes simple electrostatic interaction to spontaneously insert positively charged porous silicon-carbon particles between single-layer MXene sheets. The porous silicon-carbon structure can relieve the volume expansion problem of silicon. MXene has excellent hydrophilicity and electronic conductivity, and the layered structure of MXene can effectively improve the expansion problem of silicon materials, enhance the 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 materials, and further improving the cycle life. The preparation method provided by the application utilizes the simple principle of electrostatic self-assembly, and only needs to be left to wait, without the need for a heating process of a hydrothermal process, and without the need to consider the cost problem of CVD coating. The operation is simple, pollution-free, efficient and low-cost, and effectively reduces the cost in the preparation process of the lithium ion battery negative electrode material.

[0102] The content of the application is not limited to the above-mentioned examples, and one or several examples can also achieve the purpose of the application.

[0103] The embodiments in the specification are 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 embodiments, since it corresponds to the method disclosed in the embodiments, the description is relatively simple, and the related parts can be referred to the method part.

[0104] The above description of the disclosed embodiments enables a person skilled in the art to implement or use the application. Various modifications to the embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the application. Therefore, the application will not be limited to the embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing high-performance silicon-carbon negative electrode material, characterized in that, Comprising the following steps: Step one, 160 mg of single crystal silicon material is mixed with 40 mg of graphite by ball milling, the ball milling speed is 1200 r / min, the ball milling time is 5 h, the mixed powder is uniformly dispersed in a sulfuric acid solution with a concentration of 5 mol / ml for acid washing, the acid washing condition is room temperature for 3 h by magnetic stirring, then three times of ultrasonic centrifugal washing with ethanol and water, and drying to obtain a porous silicon-carbon material; Step two, the porous silicon-carbon material is uniformly mixed with an organic carbon source-glucose, and sintered in a tube furnace under an argon gas atmosphere, the sintering temperature is 900 DEG C, and the time is 5 h, to obtain a carbon-coated porous silicon-carbon material, 100 mg of the carbon-coated porous silicon-carbon material is mixed with 50 ml of deionized water, and ultrasonic dispersion is performed for 30 min to obtain a positively charged porous silicon-carbon dispersion; Step three, 100 ml of a cetyltrimethylammonium bromide aqueous solution with a concentration of 8 mg / ml and the porous silicon-carbon dispersion are added to a beaker and uniformly stirred by magnetic stirring, the stirring speed is 500 r / min, the stirring time is 10 h, and the stirring temperature is 50 DEG C, then centrifugal washing is performed at 4500 r / min for 5 min each time until the supernatant pH is 7, and a cetyltrimethylammonium bromide modified positively charged porous silicon-carbon material dispersion is obtained by dispersion; Step four, HF etching is used to etch the MAX precursor Nb2AlC with a concentrated HF solution to obtain a multi-layer Nb2C material, which is ultrasonically washed and high-speed centrifuged at a speed of 4500 r / min, and then dried to obtain a single-layer Nb2C powder; Step five, 30 mg of the single-layer Nb2C powder is added to 100 ml of deionized water, and ice-bath ultrasonic treatment is performed for 1 h to obtain a Nb2C dispersion; Step six, the positively charged porous silicon-carbon material dispersion obtained in step three is slowly added to the Nb2C dispersion while maintaining uniform stirring, the stirring speed is 500 r / min, the stirring temperature is 25 DEG C, and the stirring time is 2 h, to obtain a mixed solution, wherein the positively charged porous silicon-carbon material and the single-layer Nb2C are electrostatically self-adsorbed; Step seven, the mixed solution is left to stand for 5 h, centrifugally washed with deionized water, and freeze-dried for 12 h to obtain a Nb2C-coated silicon-carbon negative electrode material for a lithium ion battery negative electrode.

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