A method for preparing a porous silicon-carbon material of a silicon-copper alloy as a support structure, and products and applications thereof

Abstract

The present application belongs to the field of lithium ion battery, and particularly relates to a preparation method of a porous silicon-carbon material with a silicon-copper alloy as a supporting structure, a product thereof and application of the porous silicon-carbon material as a negative electrode material of a lithium ion battery. The porous silicon-carbon material with the silicon-copper alloy as the supporting structure introduces copper particles in the preparation process and makes silicon rivets on the copper, and generates a large number of pores by the silicon-copper alloy, thereby solving the problem of serious volume expansion effect of the silicon-based negative electrode material. Meanwhile, a carbon layer is coated on the surface of the silicon particles by a carbonization method, which greatly improves the poor conductivity of the material, and finally makes the prepared porous silicon-carbon material with the silicon-copper alloy as the supporting structure have excellent electrochemical performance and has great commercial value in the negative electrode of the lithium ion battery.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of lithium ion batteries, and particularly relates to a preparation method of a porous silicon-carbon material with a silicon-copper alloy as a supporting structure, a product thereof and application of the porous silicon-carbon material as a negative electrode material of a lithium ion battery. BACKGROUND

[0002] Since Sony first commercialized lithium ion batteries in 1991, lithium ion batteries have been recognized as the cornerstone of energy storage and conversion. In the past three decades, traditional lithium ion batteries have been striving to meet the growing demand of consumer electronics, electric vehicles and large-scale energy storage systems. However, the electrochemical performance of lithium ion batteries is limited by electrode materials, so seeking an electrode material with high specific capacity is the key to improving the energy density of the battery.

[0003] The theoretical specific capacity of the mainstream negative electrode material graphite on the market is only 372 mAh g-1, and the traditional graphite negative electrode has not been able to meet the commercial needs of existing lithium ion batteries. Among the existing negative electrode candidate materials, silicon is considered one of the most promising new negative electrode materials for high-energy-density lithium ion batteries due to its abundant crustal reserves, extremely high theoretical specific capacity (4200 mAh g-1) and good environmental compatibility. However, the large-scale application of silicon as a negative electrode material still faces great challenges. During the operation of the battery, i.e. lithium ion insertion and extraction, a huge volume change occurs, and the severe volume expansion causes a large stress inside the negative electrode, eventually leading to the pulverization of part of the electrode material and rapid capacity decay of the battery, which is the biggest obstacle to its commercial development.

[0004] Therefore, how to effectively suppress the expansion of the silicon negative electrode has become a difficult problem to be overcome in the lithium battery industry, and improvements need to be made in terms of materials and processes in this technical field. SUMMARY

[0005] Therefore, one of the purposes of the present application is to provide a preparation method of a porous silicon-carbon material with a silicon-copper alloy as a supporting structure; the second purpose of the present application is to provide a porous silicon-carbon material with a silicon-copper alloy as a supporting structure; and the third purpose of the present application is to provide application of the porous silicon-carbon material with a silicon-copper alloy as a supporting structure in the field of negative electrode materials of lithium ion batteries. The silicon-copper alloy obtained by the method cooperates with the pores of the heat treatment process to enable the material to have good cycle stability.

[0006] The technical scheme of the present application is as follows:

[0007] A preparation method of a porous silicon-carbon material with a silicon-copper alloy as a supporting structure, comprising the following steps:

[0008] (1) dispersing silicon powder and copper powder in anhydrous ethanol to form a suspension;

[0009] (2) adding ethylene glycol into the suspension in step (1) and mixing them uniformly by high-energy ball milling to make silicon particles rivet on copper particles;

[0010] (3) evaporating the anhydrous ethanol in the product in step (2) by water bath heating and removing the ethylene glycol by vacuum drying to obtain a silicon-copper mixture;

[0011] (4) heating the silicon-copper mixture in step (3) in a muffle furnace and cooling it in air to obtain a silicon-copper oxide mixture;

[0012] (5) dissolving polyacrylonitrile in N-N dimethylformamide by water bath heating and stirring to form a polyacrylonitrile solution;

[0013] (6) adding the silicon-copper oxide mixture in step (4) into the polyacrylonitrile solution prepared in step (5) and evaporating the N-N dimethylformamide by oil bath heating to obtain a precursor powder;

[0014] (7) carbonizing the precursor powder in step (6) in a tube furnace in an argon atmosphere to obtain a silicon-copper alloy as a silicon-carbon material with a supporting structure.

[0015] Preferably, the particle size of the silicon powder in step (1) is 30-60 nm, the particle size of the copper powder is 5-20 μm, the mass ratio of the silicon powder and the copper powder is 2-10:1, and the volume ratio of the silicon powder, the copper powder and the anhydrous ethanol is 0.02-0.1 g:0.01-0.1 g:40-80 ml.

[0016] Preferably, in step (2), the volume ratio of the ethylene glycol and the suspension is 2-6 ml:40-80 ml, the high-energy ball milling time is 2-5 h, the rotating speed is 200-500 rpm, and the ball-to-material ratio is 30:1.

[0017] Preferably, in step (3), the water bath heating temperature is 85-95 °C, and the vacuum drying temperature is 70-90 °C for 8 h.

[0018] Preferably, in step (4), the muffle furnace heating temperature is 250-350 °C for 10-60 min.

[0019] Preferably, in step (5), the mass-to-volume ratio of the polyacrylonitrile and the N-N dimethylformamide solution is 20-100:10-50, mg:ml, the water bath heating temperature is 70-80 °C, and the stirring speed is 100-200 rpm.

[0020] Preferably, in step (6), the mass-volume ratio of the silicon-copper oxide mixture to the polyacrylonitrile solution is 0.05-0.15 g:10-30 ml, the oil bath heating temperature is 170-190 DEG C, and the stirring speed is 100-200 rpm.

[0021] Preferably, in step (7), the carbonization conditions are "carbonization for 1-2 h at a temperature of 300-400 DEG C and carbonization treatment for 2-4 h at a temperature of 750-900 DEG C in an inert atmosphere.

[0022] 2. The silicon-copper alloy as a porous silicon-carbon material with a support structure prepared by the above preparation method.

[0023] 3. Application of the silicon-copper alloy as a porous silicon-carbon material with a support structure to a negative electrode material of a lithium ion battery.

[0024] The present application has the beneficial effect that the present application discloses a silicon-copper alloy as a porous silicon-carbon material with a support structure, the preparation of the material first utilizes a commonly used high-energy ball milling method to obtain a silicon-copper mixture, which makes the silicon particles firmly riveted on the copper particles, which can appropriately improve the problem of low conductivity of the material. Then a heat treatment process is adopted to obtain a porous silicon-copper oxide material and generate a small amount of silicon-copper alloy. Subsequently, an oil bath heating is adopted to introduce a polyacrylonitrile layer, and finally a one-step carbonization method is adopted to convert the polyacrylonitrile layer into a polyacrylonitrile-derived carbon, reduce the copper oxide to copper and generate a silicon-copper alloy. The introduction of a large number of pore structures in the composite material can accelerate the insertion and extraction process of Li+ in the composite material and improve the transmission efficiency of Li+ between the electrode and the electrolyte interface. At the same time, it provides a buffer space for the volume expansion generated during the charging and discharging process, thereby significantly improving the electrochemical performance and structural stability of the material. More importantly, the silicon-copper alloy generated twice during the material preparation process ensures the stability of the electrode structure. According to the experimental results, the silicon-copper alloy as a porous silicon-carbon material with a support structure realizes a specific capacity of 1151 mAh g -1 at a current density of 1000 mA·g -1 after 120 cycles under the synergistic action of the internal pores and the support structure.

[0025] Other advantages, objects, and features of the present application will be better understood from the following specification and drawings.

[0026] Additional advantages, objects, and features of the application will be apparent to those skilled in the art upon examination of the following specification. It is intended that the application not be limited by any of the details of the specification. Accordingly, the BRIEF DESCRIPTION OF DRAWINGS

[0027] In order to make the objectives, technical solutions, and advantages of the present application clearer, the preferred embodiments of the present application will be described in detail below with reference to the accompanying drawings, in which:

[0028] Figure 1 X-ray diffraction pattern of the material (Si / Cu@C) prepared in Example 1.

[0029] Figure 2 Specific surface area test graph and pore size distribution graph of the material (Si / Cu@C) prepared in Example 1, in which (a) is the specific surface area test graph, and (b) is the pore size distribution test graph.

[0030] Figure 3 Transmission electron microscope (TEM) pattern of the material (Si / Cu@C) prepared in Example 1.

[0031] Figure 4 Comparison graph of cycle performance test curves of lithium ion half-batteries constructed by using the material (Si / Cu@C-1) prepared in Example 1, the material (Si / Cu@C-2) prepared in Example 2, and the material (Si / Cu@C-3) prepared in Example 3 as negative electrode materials under a current density of 1000 mA / g.

[0032] Figure 5 Comparison graph of cycle performance test curves of lithium ion half-batteries constructed by using the material (Si / Cu@C-1) prepared in Example 1, the material (Si@Cu) prepared in Comparative Example 1, and the material (Si@C) prepared in Comparative Example 2 as negative electrode materials under a current density of 1000 mA / g. DETAILED DESCRIPTION

[0033] The present application is herein described in particularity to provide a thorough understanding of the application. It will be apparent, however, to one skilled in the art that the application can be practiced without resorting to the details presented herein. The following detailed description is made in connection with the accompanying drawings.

[0034] The drawings are only used for exemplary illustration, and the representation is only a schematic diagram, not a physical diagram, and cannot be understood as a limitation on the present application; in order to better illustrate the embodiments of the present application, some components of the drawings may be omitted, enlarged or reduced, and do not represent the size of the actual product; it is understandable to those skilled in the art that some well-known structures and their descriptions in the drawings may be omitted.

[0035] Example 1

[0036] A silicon-copper alloy as a porous silicon-carbon material with a support structure, and the specific preparation method is as follows:

[0037] (1) 0.1 g of silicon powder and 0.025 g of copper powder were placed in 50 ml of anhydrous ethanol to obtain suspension A; 3 ml of ethylene glycol was added to suspension A to obtain suspension B;

[0038] (2) B was ball milled at a speed of 300 rpm, a ball-to-material ratio of 30 to 1, and for 4 h to obtain product 1. Product 1 was placed in a water bath at a temperature of 90°C and stirred at a speed of 300 rpm for 30 min to obtain product 2. Product 2 was dried in a vacuum oven at 80°C for 8 h to obtain a silicon-copper mixture.

[0039] (3) The silicon-copper mixture obtained in step (2) was placed in a muffle furnace at 600°C and heated for 30 min, then cooled in air to obtain a silicon-copper oxide mixture with a porous structure.

[0040] (4) 0.068 g of polyacrylonitrile was placed in 34 ml of N-N dimethylformamide, then stirred at 200 rpm at 70°C for 20 min, then the silicon-copper oxide mixture obtained in step (3) was added, and stirring was continued for 20 min to obtain product 3.

[0041] (5) Product 3 was stirred at 175°C at a speed of 200 rpm, and after the liquid evaporated, a silicon-copper oxide material coated with a layer of polyacrylonitrile was obtained.

[0042] (6) The silicon-copper oxide material coated with a layer of polyacrylonitrile obtained in step (5) was placed in a tube furnace with argon flowing in, then heated to 300°C at a heating rate of 5°C / min, and held for 2 h. Then heated to 850°C at a heating rate of 5°C / min to obtain a silicon-copper alloy as a porous silicon-carbon material with a support structure. Marked as (Si / Cu@C)1.

[0043] Example 2

[0044] A silicon-copper alloy as a porous silicon-carbon material with a support structure, and the specific preparation method is as follows:

[0045] (1) 0.1 g of silicon powder and 0.025 g of copper powder were placed in 50 ml of anhydrous ethanol to obtain suspension A; 3 ml of ethylene glycol was added to suspension A to obtain suspension B;

[0046] (2) B was ball milled at a speed of 300 rpm, a ball-to-material ratio of 30 to 1, and for 4 h to obtain product 1. Product 1 was placed in a water bath at a temperature of 90°C and stirred at a speed of 300 rpm for 30 min to obtain product 2. Product 2 was dried in a vacuum oven at 80°C for 8 h to obtain a silicon-copper mixture.

[0047] (3) The silicon-copper mixture obtained in step (2) was placed in a muffle furnace at 600°C and heated for 30 min and then cooled in air to obtain a silicon-copper oxide mixture with a porous structure.

[0048] (4) 0.058 g of polyacrylonitrile was placed in 29 ml of N-N dimethylformamide, and then stirred at 200 rpm at 70°C for 20 min, and then the silicon-copper oxide mixture obtained in step (3) was added, and stirring was continued for 20 min to obtain product 3.

[0049] (5) Product 3 was stirred at 175°C at a speed of 200 rpm, and after the liquid evaporated, a polyacrylonitrile layer-coated silicon-copper oxide material was obtained.

[0050] (6) The polyacrylonitrile layer-coated silicon-copper oxide material obtained in step (5) was placed in a tube furnace with argon gas flowing in, and then heated to 300°C at a heating rate of 5°C / min, and held for 2 h. Then heated to 850°C at a heating rate of 5°C / min to obtain a silicon-copper alloy as a support structure porous silicon-carbon material. Marked as (Si / Cu@C)2.

[0051] Example 3

[0052] A silicon-copper alloy as a support structure porous silicon-carbon material, and the specific preparation method is as follows:

[0053] (1) 0.1 g of silicon powder and 0.025 g of copper powder were placed in 50 ml of anhydrous ethanol to obtain suspension A; 3 ml of ethylene glycol was added to suspension A to obtain suspension B;

[0054] (2) B was ball milled at a speed of 300 rpm, a ball-to-material ratio of 30 to 1, and for 4 h to obtain product 1. Product 1 was placed in a water bath at a temperature of 90°C and stirred at a speed of 300 rpm for 30 min to obtain product 2. Product 2 was dried in a vacuum oven at 80°C for 8 h to obtain a silicon-copper mixture.

[0055] (3) The silicon-copper mixture obtained in step (2) was heated in a muffle furnace at 600 °C for 30 min and then cooled in air to obtain a silicon-copper oxide mixture having a porous structure.

[0056] (4) 0.078 g of polyacrylonitrile was placed in 39 ml of N-N dimethylformamide and then stirred at 200 rpm at 70 °C for 20 min. Then the silicon-copper oxide mixture obtained in step (3) was added and stirring was continued for 20 min to obtain product 3.

[0057] (5) Product 3 was stirred at 175 °C at 200 rpm until the liquid evaporated to obtain a polyacrylonitrile layer-coated silicon-copper oxide material.

[0058] (6) The polyacrylonitrile layer-coated silicon-copper oxide material obtained in step (5) was placed in a tube furnace purged with argon and then heated to 300 °C at a heating rate of 5 °C / min and held for 2 h. Then the temperature was increased to 850 °C at a heating rate of 5 °C / min to obtain a silicon-copper alloy as a support structure porous silicon-carbon material. Marked as (Si / Cu@C)3.

[0059] Comparative Example 1

[0060] A lithium ion battery Si / Cu anode material (abbreviated as Si / Cu) was prepared by ball milling to rivet silicon particles on copper particles. The specific preparation method is as follows:

[0061] (1) 0.1 g of silicon powder and 0.025 g of copper powder were placed in 50 ml of anhydrous ethanol to obtain suspension A; 3 ml of ethylene glycol was added to suspension A to obtain suspension B;

[0062] (2) B was ball milled at a speed of 300 rpm for 4 h with a ball-to-material ratio of 30 to 1 to obtain product 1. Product 1 was placed in a water bath at a temperature of 90 °C and stirred at a speed of 300 rpm for 30 min to obtain product 2. Product 2 was dried in a vacuum oven at 80 °C for 8 h to obtain a silicon-copper mixture. Marked as Si / Cu.

[0063] Comparative Example 2

[0064] A lithium ion battery Si / C anode material (abbreviated as Si / C) was prepared by introducing a polyacrylonitrile layer outside the silicon particles and then carbonizing the polyacrylonitrile by a one-step carbonization method. The specific preparation method is as follows:

[0065] (1) 0.068 g of polyacrylonitrile was placed in 34 ml of N-N dimethylformamide and then stirred at 200 rpm at 70 °C for 20 min. Then 0.125 g of silicon powder was added and stirring was continued for 20 min to obtain a dispersion.

[0066] (2) The dispersion obtained in step (1) was stirred at 175°C at 200 rpm, and after the liquid was evaporated, a precursor powder with a polyacrylonitrile layer was obtained.

[0067] (3) The polyacrylonitrile layer-coated precursor powder obtained in step (2) was placed in a tube furnace with argon flowing, and then heated to 300°C at a heating rate of 5°C / min, and held for 2 h. Then, the temperature was raised to 850°C at a heating rate of 5°C / min, and a polyacrylonitrile-derived carbon-coated silicon material, labeled as Si@C, was obtained.

[0068] Performance test

[0069] The prepared silicon copper carbon material Si / Cu@C1 was subjected to X-ray diffraction analysis, Figure 1 It can be seen from the composite that a silicon copper alloy is formed.

[0070] The prepared silicon copper carbon material Si / Cu@C1 was subjected to specific surface area and pore size distribution test. Figure 2 In (a), the specific surface area of Si / Cu@C is shown, and it can be seen that the composite has a smaller specific surface area (33.758 m 2 / g); Figure 2 In (b), the pore size distribution of the material is shown, and it can be seen that there are a large number of micropores around 0.5 nm and a small number of micropores between 0.5 nm and 1 nm in the material.

[0071] The prepared silicon copper carbon material Si / Cu@C1 was subjected to TEM test, Figure 3 It can be seen that there are many light and dark stripes in the material, which is the pore structure produced by the special heat treatment process.

[0072] Exploring the electrochemical performance of the porous silicon carbon material Si / Cu@C prepared by the silicon copper alloy as a support structure in examples 1-3

[0073] The materials prepared in examples 1-3 and comparative examples 1-2 were used as negative materials of lithium ion batteries, and lithium metal sheets were used as positive materials of lithium ion batteries to construct lithium ion half-batteries (wherein the separator was celgard 2500, and the electrolyte was composed of 1.0M LiPF6(EC:DMC:DEC=25:30:45) dissolved in EC, DMC and DEC, 3% fluoroethylene carbonate (FEC) and 0.5% vinylene carbonate (VC) for stabilizing SEI film, and the amount of electrolyte used in the process of assembling a battery was about 60μL), and then the prepared lithium ion half-batteries were subjected to discharge specific capacity test at a current density of 1000mA / g, and the experimental results corresponded to Figure 4 and Figure 5 The test data were arranged into table 1:

[0074] Table 1 first and after cycling discharge specific capacity of half-cells constructed based on different negative materials at a certain current density

[0075]

[0076] From Table 1, it can be seen that the capacity retention rate of Example 1 after 120 cycles is as high as 92.94%, that of Comparative Example 1 is 27.72%, and that of Comparative Example 2 is 53.97%. The above results show that the introduction of copper into the material and the generation of silicon-copper alloy and porous structure through a special heat treatment process are of great significance to improving the cycle stability of the material. The problem of serious volume expansion effect of the silicon-based negative material is solved, and the poor conductivity of the material is greatly improved by coating a carbon layer on the outer surface of the silicon particles through the carbonization method, so that the prepared porous silicon-carbon negative material has excellent electrochemical performance and great commercial value in the lithium ion battery negative electrode

[0077] In summary, the present application provides a preparation method and application of a porous silicon-carbon material with silicon-copper alloy as a support structure. In the preparation process, copper particles are introduced and silicon rivets are generated on the copper, and a large number of pores are generated by the silicon-copper alloy, solving the problem of serious volume expansion effect of the silicon-based negative material. At the same time, a carbon layer is coated on the surface of the silicon particles through the carbonization method, greatly improving the poor conductivity of the material, so that the prepared porous silicon-carbon material with silicon-copper alloy as a support structure has excellent electrochemical performance and great commercial value in the lithium ion battery negative electrode.

Claims

1. A method for preparing a porous silicon-carbon material with a silicon-copper alloy as the supporting structure, characterized in that, Includes the following steps: (1) Disperse silicon powder and copper powder in anhydrous ethanol to form a suspension; (2) Add ethylene glycol to the suspension described in step (1) and mix it evenly by high-energy ball milling to rivet the silicon particles onto the copper particles. (3) The product obtained in step (2) is heated in a water bath to evaporate anhydrous ethanol, and ethylene glycol is removed by vacuum drying to obtain a silicon-copper mixture; (4) The silicon-copper mixture obtained in step (3) is heated in a muffle furnace and cooled in air to obtain a silicon-copper oxide mixture; (5) Dissolve polyacrylonitrile in N,N dimethylformamide and heat and stir in a water bath to form a polyacrylonitrile solution; (6) Add the silicon copper oxide mixture in step (4) to the polyacrylonitrile solution prepared in step (5), and evaporate N,N dimethylformamide by heating in an oil bath to obtain the precursor powder; (7) The precursor powder obtained in step (6) is carbonized in a tube furnace under an argon atmosphere to obtain silicon-copper alloy as the supporting structure of silicon-carbon material.

2. The method for preparing a porous silicon-carbon material with a silicon-copper alloy as a supporting structure according to claim 1, characterized in that, The silicon powder in step (1) has a particle size of 30-60 nm and the copper powder has a particle size of 5-20 μm. The mass ratio of silicon powder to copper powder is 2-10:1, and the mass ratio of silicon powder to copper powder and the volume ratio of anhydrous ethanol is 0.02-0.1 g: 0.01-0.1 g: 40-80 ml.

3. The method for preparing a porous silicon-carbon material with a silicon-copper alloy as a supporting structure according to claim 1, characterized in that, In step (2), the volume ratio of ethylene glycol to suspension is 2-6 ml: 40-80 ml, the high-energy ball milling time is 2-5 h, the rotation speed is 200-500 rpm, and the ball-to-material ratio is 30:

1.

4. The method for preparing a porous silicon-carbon material with a silicon-copper alloy as a supporting structure according to claim 1, characterized in that, Step (3) The water bath heating temperature is 85-95℃, and the vacuum drying temperature is 70-90℃ for 8 hours.

5. The method for preparing a porous silicon-carbon material with a silicon-copper alloy as a supporting structure according to claim 1, characterized in that, In step (4), the temperature of the muffle furnace is 250-350℃ and the time is 10-60min.

6. The preparation method according to claim 1, characterized in that, In step (5), the mass-to-volume ratio of the polyacrylonitrile and N,N dimethylformamide solution is 20-100:10-50 (mg:ml), the water bath heating temperature is 70-80℃, and the stirring speed is 100-200 rpm.

7. The preparation method according to claim 1, characterized in that, In step (6), the mass-to-volume ratio of the copper oxide mixture to the polyacrylonitrile solution is 0.05–0.15 g: 10–30 ml, the oil bath heating temperature is 170–190 °C, and the stirring speed is 100–200 rpm.

8. The preparation method according to claim 1, characterized in that, In step (7), the carbonization conditions are: "carbonization for 1 to 2 hours in an inert atmosphere at a temperature of 300 to 400°C, and carbonization for 2 to 4 hours at a temperature of 750 to 900°C".

9. A porous silicon-carbon material with a supporting structure, which is a silicon-copper alloy prepared by any one of claims 1 to 8.

10. The application of the porous silicon-carbon material with silicon-copper alloy as a supporting structure as described in claim 9 in the negative electrode material of lithium-ion batteries.

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