A high-capacity and high-first-efficiency silicon-based anode material, its preparation method and application

Abstract

The present invention relates to the field of anode materials for lithium-ion batteries, and discloses a preparation method of a silicon-based anode material with high capacity and high initial efficiency, comprising: (1) mixing silicon monoxide with glucose and gluconate to obtain precursor A; (2) dispersing precursor A in deionized water to dissolve glucose and gluconate in water to form a dispersion, and freeze-drying the dispersion to obtain a material to be sintered B; (3) placing the material to be sintered in an atmosphere of protective gas, heating and holding the temperature, and finally cooling to obtain a finished product of a silicon-oxygen anode material for a lithium-ion battery with high capacity and high initial efficiency. The silicon-oxygen anode material prepared by the present invention has the characteristics of high capacity and high initial efficiency. When at a voltage of 0.8V, the initial efficiency of the prepared silicon monoxide anode material reaches 85%, and the capacity is greater than 1300 mAh / g.

Description

Technical Field

[0001] The present invention relates to the field of negative electrode materials for lithium-ion batteries, and particularly relates to a high-capacity and high-first-efficiency silicon-based negative electrode material, a preparation method thereof, and an application thereof. Background Art

[0002] With the growing demand for electric vehicle (EV) applications, many types of negative electrode materials for lithium batteries (Si, Li metal, organic compounds) have been deeply studied to replace traditional graphite negative electrode materials. Among them, silicon has a specific capacity as high as 4200 mAh·g -1 , which is more than 10 times that of traditional carbon-based materials and is the ideal negative electrode material with the highest known specific capacity. The negative electrode material based on silicon monoxide (SiO X ) is the first batch of commercial high-capacity negative electrode materials. This material has a unique microstructure of randomly mixed small-sized Si and SiO2 phases, which alleviates the volume expansion caused by lithium insertion in silicon-based negative electrode materials, making it have the characteristics of large capacity and high first efficiency.

[0003] The advantages of silicon-oxygen electrodes are as follows: (1) The highest theoretical capacity of SiO X can reach 2650 mAh·g -1 , which is more than 5 times that of traditional graphite negative electrodes; (2) SiO X has a relatively high energy density, which can further reduce the volume of the battery; (3) The negative electrode material of SiO X has a long cycle life, has a smaller volume expansion compared with Si negative electrodes, and has more stable performance; (4) SiO X has a low voltage plateau of 0.5 V, and the assembly and use costs are lower; (5) Silicon materials have a wide source, rich reserves, are non-toxic themselves, and are environmentally friendly.

[0004] As the negative electrode of lithium battery materials, SiO X has a high capacity retention rate during cycling, but the initial performance of SiO X is not stable. The low initial coulomb efficiency may be due to the electrochemical reaction between silicon monoxide and Li + to generate irreversible Li-Si-O products. Therefore, a large irreversible capacity loss will occur during the first charge / discharge cycle. The traditional method to alleviate the volume expansion of silicon-oxygen negative electrodes and improve their initial coulomb efficiency is to use the liquid-phase coating C technology. Among them, silicon particles provide the lithium storage capacity, and carbon materials buffer the volume change, taking into account the balance between specific capacity and service life. In addition, the first cycle efficiency can also be improved by methods such as prelithiation and premagnesiation. The principle of improving the first cycle efficiency by prelithiation, premagnesiation, etc. is: forming a SEI film on the surface of the negative electrode material in advance, thereby reducing the Li source consumed during cycling, and at the same time preventing the co-insertion of solvent ions into the negative electrode to damage the negative electrode material.

[0005] The currently commonly used prelithiation method is to prelithiate the anode material with powder, that is, to mix the SiO X / C material with the prelithiation material and then perform heat treatment, so that the prelithiation reagent reacts on the surface of the silicon material to complete the prelithiation of the material, achieving the effect of lithium supplementation for the anode material, thereby making up for the irreversible capacity loss and greatly improving the first efficiency and cycle performance of the anode material. However, there is no solution that can both solve the problem of volume expansion of the silicon-oxygen anode and simultaneously form a SEI film on the surface of the anode material in advance. At the same time, in the prior art, the binder strength of the silicon-based material is not high, resulting in the inability of the electrode to shrink during cycling, and cracking often occurs during actual use, which also affects the service life of the battery. Summary of the Invention

[0006] In view of the problems existing in the prior art, the present invention provides a high-capacity and high-first-efficiency silicon-based anode material, its preparation method and application. The high-capacity and high-first-efficiency silicon-based anode material described in the present invention is a silicon monoxide material coated with a carbon-silicate composite shell.

[0007] The present invention specifically includes the following contents:

[0008] A preparation method of a high-capacity and high-first-efficiency silicon-based anode material, comprising the following steps:

[0009] (1) Mix silicon monoxide with glucose and gluconate to obtain precursor A;

[0010] (2) Disperse the precursor A obtained in step (1) in a solvent, heat and stir to obtain a dispersion, and freeze-dry the dispersion to obtain a material to be sintered B;

[0011] (3) Place the material to be sintered B obtained in step (2) in an atmosphere of protective gas, heat and keep warm, and finally cool naturally to obtain a silicon monoxide material coated with a carbon-silicate composite shell, that is, the finished product of the high-capacity and high-first-efficiency silicon-based anode material.

[0012] Specifically, the preparation method of the silicon monoxide in step (1) is: mix silicon and silicon dioxide evenly, heat to 1200-1500 °C under vacuum conditions, react for 6-10 hours to generate silicon monoxide vapor; then introduce a reducing gas to place the silicon monoxide product in an atmosphere of the reducing gas, keep the pressure at 0.1 MPa, and then cool down to 400-600 °C to deposit silicon monoxide. Specifically, the reaction temperature can be 1200 °C, 1300 °C, 1400 °C, or 1500 °C, etc., the reaction time can be 6 h, 7 h, 8 h, 9 h, 10 h, etc., and the cooling temperature is 400 °C, 450 °C, 500 °C, 550 °C, 600 °C, etc.

[0013] Specifically, the purity of the silicon and silicon dioxide is not less than 98%, and the D50 is 2-100 μm. Specifically, the D50 of the silicon and silicon dioxide can be 2 μm, 10 μm, 20 μm, 40 μm, 50 μm, 60 μm, 80 μm, 90 μm, or 100 μm; the reducing gas is hydrogen, carbon monoxide, sulfur monoxide or nitric oxide.

[0014] Specifically, in the step (1), the molar ratio of silicon monoxide to glucose is 100:(1-20). The specific molar ratio can be (100:1), (100:2), (100:5), (100:8), (100:10), (100:15), (100:18), or (100:20), etc.; the molar ratio of glucose to gluconate is 1:(0.01-100), and specifically can be (1:0.01), (1:0.1), (1:1), (1:10), (1:50), or (1:100), etc.

[0015] Specifically, the gluconate in the step (1) is one or a combination of several of sodium gluconate, lithium gluconate, calcium gluconate, zinc gluconate, magnesium gluconate, potassium gluconate or aluminum gluconate.

[0016] Specifically, in the step (1), the mixing method of silicon monoxide with glucose and gluconate is dry mixing, and the mixing time is 2-36 h. The specific mixing time can be 2 h, 4 h, 6 h, 8 h, 10 h, 15 h, 20 h, 30 h, 35 h, or 36 h, etc.; preferably, the equipment used for dry mixing is a ball mill, a sand mill or a dry mixer, and all particle sizes of the obtained precursor A are less than 10 μm.

[0017] Specifically, the solvent in the step (2) is deionized water. The volume ratio of the deionized water to the volume of the precursor A is 1:(0.5-5), the heating temperature is 25-80 °C, and the stirring time is 15 min-4 h. The specific volume ratio of the deionized water to the volume of the precursor A here can be (1:0.5), (1:0.8), (1:1), (1:2), (1:3.5), or (1:5), etc.; the heating temperature can be 25 °C, 30 °C, 40 °C, 50 °C, 60 °C, 70 °C, or 80 °C, etc.; the stirring time can be 15 min, 30 min, 1 h, 2 h, 3 h, or 4 h, etc.

[0018] Specifically, in the step (2), the temperature of freeze-drying is -100 to 10 °C, and the pressure is 0 - 101 kPa. The specific temperature can be -100 °C, -80 °C, -50 °C, -10 °C, 0 °C, 5 °C, or 10 °C, etc., and the pressure can be 0 kPa, 1 kPa, 5 kPa, 10 kPa, 50 kPa, 80 kPa, or 101 kPa, etc.

[0019] Specifically, in the step (3), the heating rate is 2 - 20 °C / min, the heat preservation temperature is 700 - 1300 °C, and the heat preservation time is 1 h - 5 h. Preferably, both the heating and heat preservation are carried out under normal pressure. The specific heating rate can be 2 °C / min, 5 °C / min, 8 °C / min, 10 °C / min, 15 °C / min, or 20 °C / min, etc., the heat preservation temperature can be 700 °C, 800 °C, 900 °C, 1000 °C, 1200 °C, or 1300 °C, and the heat preservation time can be 1 h, 2 h, 3 h, 4 h, or 5 h, etc. The heating and heat preservation treatment in the step (3) is carried out in a high-temperature device, and the high-temperature device is a rotary kiln, a high-temperature fluidized bed, a box furnace, a tube furnace, an atmosphere furnace, a pit furnace, a roller hearth kiln, a tunnel kiln, or a pusher kiln; the carbon-silicate composite shell layer in the step (3) is obtained by an in-situ reaction of gluconate and glucose.

[0020] A high-capacity and high-first-efficiency silicon-based anode material prepared by using the preparation method of a high-capacity and high-first-efficiency silicon-based anode material disclosed in the present invention.

[0021] The beneficial effects of the present invention:

[0022] (1) The present invention simultaneously introduces glucose and gluconate. The main role of glucose is to serve as a carbon source. After glucose is dissolved and freeze-dried, it can uniformly adhere to the surface of silicon monoxide. Therefore, after calcination, glucose dehydrates and carbonizes, forming a uniform carbon layer on the surface of silicon monoxide, which improves the conductivity and interfacial stability, and reduces the influence of the volume expansion of the silicon-based material on the initial efficiency and cycling. At the same time, the in-situ generated silicate is evenly distributed, promoting the formation of a bonding network inside the particles, increasing the modulus in the lithiated state, thereby inhibiting the generation of cracks during the expansion process, ensuring the integrity of the micron-sized silicon-based composite material throughout its life cycle, and improving the structural strength of the material. When the gluconate is heat-treated, it mainly generates carbon and oxides (for example, magnesium gluconate and ordinary sugar coated on the surface of the silicon-based material will in-situ generate C and magnesium oxide during heating). For the selection of gluconate, in addition to requiring the gluconate ion to be used as a carbon source, it is also required that the metal salt ion has the effect of inhibiting the volume expansion and cracking caused during the first cycle of the silicon monoxide material. The present invention selects alkali metal salts of glucose such as sodium gluconate, lithium gluconate, calcium gluconate, zinc gluconate, magnesium gluconate, potassium gluconate or aluminum gluconate. Taking magnesium gluconate as an example, the mechanism of generating silicate during its preparation is: SiO + Mg 2+ →MgO + Si and MgO + SiO → Mg2SiO4 + Si. After the calcination is completed, a C-magnesium silicate composite shell layer will be formed on the surface of silicon monoxide. This shell layer has the following two functions: 1. It hinders the reaction between the inner core silicon raw material and the electrolyte, inhibits the reaction of silicon with the electrolyte to form the SEI film, and reduces the volume expansion and pulverization of the silicon negative electrode; 2. The metal oxides generated in this shell layer are dispersed in the shell layer and will react with SiO under the action of heat treatment to generate SiMg y O x , in SiMg y O x , MgSiO3 is evenly distributed, promoting the formation of a bonding network inside the particles, increasing the modulus in the lithiated state, and avoiding cracking inside the particles. Therefore, the silicon-based material prepared by the method disclosed in the present invention has the characteristics of high reversible capacity, stable cycling performance and low expansion rate. The silicon-oxygen negative electrode material prepared by the present invention has the characteristics of high capacity and high initial efficiency. When the voltage is 0.8V, the initial efficiency of the prepared silicon monoxide negative electrode material reaches 85%, the capacity is greater than 1300 mAh / g, and the capacity retention rate reaches 99.8% after 50 cycles.

[0023] (2) The present invention uses the method of freeze-drying to remove the water solvent in the dispersion. Compared with ordinary high-temperature drying, the advantages of freeze-drying are as follows: In the process of freeze-drying, free water directly evaporates from the surface of the silicon-based material. Therefore, uniform and dense glucose and gluconate can be deposited on the surface of the negative electrode. However, in traditional stirring drying and baking, free water evaporates from the liquid surface, and the deposited glucose and gluconate have a higher concentration at the bottom and a lower concentration on the surface. Therefore, the uniformity of freeze-drying is better, and the later coating effect is also better.

[0024] (3) The present invention rapidly prepares silicon suboxide from silicon and silicon suboxide as raw materials in one step, and rapidly prepares a composite C-silicate coating shell in a liquid-phase environment with water as the solvent without introducing any organic solvents. The preparation process is simple, environmentally friendly, safe, highly operable, low in production cost, friendly to the environment, and suitable for large-scale industrial production. Brief Description of the Drawings

[0025] Figure 1 SEM comparison diagram of the silicon suboxide raw material (left) used in the present invention and the silicon suboxide material with carbon-silicate composite coating prepared in Example 5 (right);

[0026] Figure 2 XRD comparison diagram of the silicon suboxide raw material used in the present invention and the silicon suboxide material with carbon-silicate composite coating prepared in Example 5;

[0027] Figure 3 SEM comparison diagram of the initial thickness of the silicon suboxide raw material (left) and the thickness after 100 cycles at 0.8V (right);

[0028] Figure 4 SEM comparison diagram of the initial thickness of the silicon suboxide material with carbon-silicate composite coating prepared in Example 5 of the present invention (left) and the thickness after 100 cycles at 0.8V (right). Detailed Embodiments

[0029] The present invention will be described in detail below with reference to the drawings and specific embodiments. The following embodiments do not limit the content of the invention recorded in the claims in any way. In addition, all the contents shown in the following embodiments are not limited to those necessary for the solution of the invention recorded in the claims.

[0030] Example 1

[0031] This example relates to a preparation method of a high-capacity and high-first-efficiency silicon-oxygen negative electrode material for lithium-ion batteries, including the following specific steps:

[0032] (1) Mix elemental silicon and silicon dioxide evenly, place them in a vacuum environment, heat to 1250 °C, and at this temperature, a disproportionation reaction occurs. React for 6 hours to generate silicon monoxide vapor; then introduce a reducing gas to keep the silicon monoxide product in an atmosphere of the reducing gas, maintain a pressure of 0.1 MPa, and cool to 600 °C to deposit the silicon monoxide raw material.

[0033] (2) Take 100 g of the obtained silicon monoxide raw material and mix it with glucose and potassium gluconate in a molar ratio of 100:1:1 in a ball mill. Set the ball milling time of the ball mill to 24 hours and the rotational speed of the ball mill to 500 r / min to obtain precursor A, and the particle size of all particles in the precursor A is less than 10 μm.

[0034] (3) Disperse the obtained precursor A in deionized water and stir at room temperature for 2 hours to dissolve glucose and potassium gluconate to obtain a dispersion. Then place the dispersion under the conditions of a temperature of -40 °C and a pressure of 5 Pa for freeze-drying for 72 hours to obtain the material to be fired B.

[0035] (4) Heat-treat the obtained material to be fired B in a tube furnace. Under nitrogen protection, heat it to 700 °C at a rate of 2 °C / min, hold for 5 hours and then cool down to obtain a high-capacity and high-first-efficiency silicon negative electrode material for lithium-ion batteries.

[0036] Example 2

[0037] This example relates to the preparation of a high-capacity and high-first-efficiency silicon-oxygen negative electrode material for lithium-ion batteries, including the following specific steps:

[0038] (1) Mix elemental silicon and silicon dioxide evenly, place them in a vacuum environment, heat to 1400 °C, and at this temperature, a disproportionation reaction occurs. React for 8 hours to generate silicon monoxide vapor, then introduce a reducing gas to keep the silicon monoxide product in an atmosphere of the reducing gas, maintain a pressure of 0.1 MPa, and cool to 400 °C. After deposition, obtain the silicon monoxide raw material.

[0039] (2) Take 100 g of the obtained silicon monoxide raw material and mix it with glucose and potassium gluconate in a molar ratio of 100:10:1 in a ball mill. Set the ball milling time of the ball mill to 24 hours and the rotational speed of the ball mill to 500 r / min to obtain precursor A, and the particle size of all particles in the precursor A is less than 10 μm.

[0040] (3) Disperse precursor A in deionized water and stir at room temperature for 2 hours to dissolve glucose and potassium gluconate to obtain a dispersion. Then place the dispersion under the conditions of a temperature of -40 °C and a pressure of 5 Pa for freeze-drying for 72 hours to obtain the material to be fired B.

[0041] (4) Heat-treat the material to be fired B in a tube furnace. Under nitrogen protection, heat it up to 700 °C at a rate of 2 °C / min, hold for 5 h, and then cool down to obtain the finished high-capacity and high-first-efficiency silicon negative electrode material for lithium-ion batteries.

[0042] Example 3:

[0043] This example relates to the preparation of a high-capacity and high-first-efficiency silicon-oxygen negative electrode material for lithium-ion batteries, including the following specific steps:

[0044] (1) Mix elemental silicon and silicon dioxide evenly, place them in a vacuum environment, heat to 1500 °C, and a disproportionation reaction occurs at this temperature for 10 h to generate silicon monoxide vapor. Then introduce a reducing gas to place the silicon monoxide product in the atmosphere of the reducing gas, maintain the pressure at 0.1 MPa, cool down to 500 °C, and deposit to obtain the silicon monoxide raw material.

[0045] (2) Take 100 g of the obtained silicon monoxide raw material and mix it with glucose and potassium gluconate in a molar ratio of 100:10:10 in a ball mill. Set the ball milling time of the ball mill to 24 h and the rotation speed of the ball mill to 500 r / min to obtain precursor A, and the particle size of all particles in the precursor A is less than 10 μm.

[0046] (3) Disperse precursor A in deionized water and stir at room temperature for 2 h to dissolve glucose and potassium gluconate to obtain a dispersion. Place the dispersion under the conditions of a temperature of -40 °C and a pressure of 5 Pa for freeze-drying for 72 hours to obtain the material to be fired B.

[0047] (4) Heat-treat the obtained material to be fired B in a tube furnace. Under nitrogen protection, heat it up to 700 °C at a rate of 2 °C / min, hold for 5 h, and then cool down to obtain the high-capacity and high-first-efficiency silicon negative electrode material for lithium-ion batteries.

[0048] Example 4:

[0049] This example relates to the preparation of a high-capacity and high-first-efficiency silicon-oxygen negative electrode material for lithium-ion batteries, including the following specific steps:

[0050] (1) Mix elemental silicon and silicon dioxide evenly, place them in a vacuum environment, heat to 1300 °C, and a disproportionation reaction occurs at this temperature for 10 h to generate silicon monoxide vapor. Then introduce a reducing gas to place the silicon monoxide product in the atmosphere of the reducing gas, maintain the pressure at 0.1 MPa, cool down to 450 °C, and deposit to obtain the silicon monoxide raw material.

[0051] (2) Take 100 g of the obtained silicon monoxide raw material and mix it with glucose and potassium gluconate in a molar ratio of 100:1:1 in a ball mill. Set the ball milling time of the sand mill to 24 h and the rotation speed of the ball mill to 500 r / min to obtain precursor A, and the particle size of all particles in the precursor A is less than 10 μm.

[0052] (3) Disperse the obtained precursor A in deionized water and stir at room temperature for 2 h to dissolve glucose and potassium gluconate to obtain a dispersion. Place the dispersion under the conditions of a temperature of -40 °C and a pressure of 5 Pa for freeze-drying for 72 hours to obtain the material to be sintered B.

[0053] (4) Heat-treat the material to be sintered B in a tubular furnace. Under nitrogen protection, heat it to 800 °C at a rate of 2 °C / min, keep it at this temperature for 5 h, and then cool it down to obtain a high-capacity and high-first-cycle-efficiency silicon negative electrode material for lithium-ion batteries.

[0054] Example 5:

[0055] This example relates to the preparation of a high-capacity and high-first-cycle-efficiency silicon-based negative electrode material for lithium-ion batteries, including the following specific steps:

[0056] (1) Mix elemental silicon and silicon dioxide evenly, place them in a vacuum environment, heat to 1350 °C, and at this temperature, a disproportionation reaction occurs. React for 8 h to generate silicon monoxide vapor, and then introduce a reducing gas to place the silicon monoxide product in an atmosphere of the reducing gas. Keep the pressure at 0.1 MPa, cool down to 450 °C, and obtain the silicon monoxide raw material after deposition.

[0057] (2) Take 100 g of the obtained silicon monoxide raw material and mix it with glucose and magnesium gluconate in a molar ratio of 100:2:5 in a ball mill. Set the ball milling time of the ball mill to 36 h and the rotation speed of the ball mill to 500 r / min to obtain precursor A, and the particle size of all particles in the precursor A is less than 10 μm.

[0058] (3) Disperse precursor A in deionized water and stir at room temperature for 2 h to dissolve glucose and potassium gluconate to obtain a dispersion. Place the dispersion under the conditions of a temperature of -40 °C and a pressure of 5 Pa for freeze-drying for 72 hours to obtain the material to be sintered B.

[0059] (4) Heat-treat the material to be sintered B in a tubular furnace. Under nitrogen protection, heat it to 800 °C at a rate of 2 °C / min, keep it at this temperature for 5 h, and then cool it down to obtain a high-capacity and high-first-cycle-efficiency silicon negative electrode material for lithium-ion batteries.

[0060] Example 6:

[0061] This example relates to the preparation of a high-capacity and high-first-cycle-efficiency silicon-based negative electrode material for lithium-ion batteries, including the following specific steps:

[0062] (1) Mix elemental silicon and silicon dioxide evenly, place them in a vacuum environment, heat to 1450 °C, at this temperature, a disproportionation reaction occurs, react for 9 h to generate silicon monoxide vapor, then introduce a reducing gas to place the silicon monoxide product in an atmosphere of the reducing gas, maintain the pressure at 0.1 MPa, cool down to 550 °C, and obtain silicon monoxide raw material after deposition.

[0063] (2) Take 100 g of the obtained silicon monoxide raw material and mix it with glucose and magnesium gluconate in a molar ratio of 100:1:1 in a ball mill. Set the ball milling time of the ball mill to 24 h and the rotation speed of the ball mill to 500 r / min to obtain precursor A, and the particle size of all particles in the precursor A is less than 10 μm.

[0064] (3) Disperse precursor A in deionized water, stir at room temperature for 2 h to dissolve glucose and potassium gluconate to obtain a dispersion. Place the dispersion under the conditions of -60 °C and 5 Pa for freeze-drying for 48 hours to obtain the material to be sintered B.

[0065] (4) Heat-treat the material to be sintered B in a tube furnace. Under nitrogen protection, heat it to 900 °C at a rate of 2 °C / min, keep it warm for 5 h and then cool down to obtain a high-capacity and high-first-efficiency silicon negative electrode material for lithium-ion batteries.

[0066] Example 7:

[0067] This example relates to the preparation of a high-capacity and high-first-efficiency silicon-oxygen negative electrode material for lithium-ion batteries ， including the following specific steps:

[0068] (1) Mix elemental silicon and silicon dioxide evenly, place them in a vacuum environment, heat to 1200 °C, at this temperature, a disproportionation reaction occurs, react for 10 h to generate silicon monoxide vapor, then introduce a reducing gas to place the silicon monoxide product in an atmosphere of the reducing gas, maintain the pressure at 0.1 MPa, cool down to 420 °C, and obtain silicon monoxide raw material after deposition.

[0069] (2) Take 100 g of the obtained silicon monoxide raw material and mix it with glucose and lithium gluconate in a molar ratio of 100:1:1 in a ball mill. Set the ball milling time of the ball mill to 24 h and the rotation speed of the ball mill to 500 r / min to obtain precursor A with a particle size less than 10 microns.

[0070] (3) Disperse precursor A in deionized water, stir at room temperature for 2 h to dissolve glucose and potassium gluconate to obtain a dispersion. Place the dispersion at -40 °C and 5 Pa for freeze-drying for 72 hours to obtain the material to be sintered B.

[0071] (4) Heat-treat the material to be sintered B in a tube furnace. Under nitrogen protection, heat it up to 900 °C at a rate of 2 °C / min, keep it at this temperature for 5 h, and then cool it down to obtain a high-capacity and high-first-cycle-efficiency silicon negative electrode material for lithium-ion batteries.

[0072] Example 8:

[0073] This example relates to the preparation of a high-capacity and high-first-cycle-efficiency silicon-oxygen negative electrode material for lithium-ion batteries, including the following specific steps:

[0074] (1) Mix elemental silicon and silicon dioxide evenly, place them in a vacuum environment, heat to 1300 °C, and at this temperature, a disproportionation reaction occurs. React for 8 h to generate silicon monoxide vapor, and then introduce a reducing gas to place the silicon monoxide product in the atmosphere of the reducing gas. Keep the pressure at 0.1 MPa, cool down to 580 °C, and obtain silicon monoxide raw materials after deposition.

[0075] (2) Take 100 g of the obtained silicon monoxide raw materials and mix them with glucose and magnesium gluconate in a molar ratio of 100:1:1 in a ball mill. Set the ball milling time of the ball mill to 24 h and the rotation speed of the ball mill to 500 r / min to obtain precursor A with a particle size less than 10 microns.

[0076] (3) Disperse precursor A in deionized water and stir at room temperature for 2 h to dissolve glucose and potassium gluconate to obtain a dispersion. Place the dispersion under the conditions of -40 °C and 5 Pa for freeze-drying for 72 hours to obtain the material to be sintered B.

[0077] (4) Heat-treat the material to be sintered B in a tube furnace. Under nitrogen protection, heat it up to 700 °C at a rate of 2 °C / min, keep it at this temperature for 5 h, and then cool it down to obtain a high-capacity and high-first-cycle-efficiency silicon negative electrode material for lithium-ion batteries.

[0078] Comparative Example 1

[0079] (1) Mix elemental silicon and silicon dioxide evenly, place them in a vacuum environment, heat to 1350 °C, and at this temperature, a disproportionation reaction occurs. React for 8 h to generate silicon monoxide vapor, and then introduce a reducing gas to place the silicon monoxide product in the atmosphere of the reducing gas. Keep the pressure at 0.1 MPa, cool down to 600 °C, and obtain silicon monoxide raw materials after deposition.

[0080] (2) Take 100 g of the obtained silicon monoxide raw materials and mix them with glucose and magnesium gluconate in a molar ratio of 100:0:1 in a ball mill. Set the ball milling time of the ball mill to 15 h and the rotation speed of the ball mill to 500 r / min to obtain precursor A.

[0081] (3)Disperse precursor A in deionized water and stir at room temperature for 2 h to dissolve glucose and potassium gluconate, obtaining a dispersion. Place the dispersion at -40°C and freeze-dry it under a pressure of 5 Pa for 24 hours to obtain the material B to be sintered.

[0082] (4)Perform heat treatment on the material B to be sintered in a tube furnace. Under nitrogen protection, heat it at a rate of 2°C / min to 800°C, hold for 5 h, and then cool down to obtain the silicon negative electrode material for lithium-ion batteries.

[0083] Comparative Example 2

[0084] (1)Mix elemental silicon and silicon dioxide evenly, place them in a vacuum environment, heat to 1300°C, and a disproportionation reaction occurs at this temperature for 10 h to generate vapor of silicon monoxide. Then introduce a reducing gas to place the silicon monoxide product in an atmosphere of the reducing gas, maintain the pressure at 0.1 MPa, and cool down to 450°C. After deposition, obtain the silicon monoxide raw material.

[0085] (2)Take 100 g of the obtained silicon monoxide raw material and mix it with glucose and magnesium gluconate in a molar ratio of 100:1:0 in a ball mill. Set the ball milling time of the ball mill to 24 h and the rotation speed of the ball mill to 2500 r / min to obtain precursor A.

[0086] (3)Disperse precursor A in deionized water and stir at room temperature for 2 h to dissolve glucose and potassium gluconate, obtaining a dispersion. Place the dispersion at -40°C and freeze-dry it under a pressure of 5 Pa for 72 hours to obtain the material B to be sintered.

[0087] (4)Perform heat treatment on the material B to be sintered in a tube furnace. Under nitrogen protection, heat it at a rate of 2°C / min to 800°C, hold for 5 h, and then cool down to obtain the silicon negative electrode material for lithium-ion batteries.

[0088] Figure 1 SEM comparison diagram of the silicon monoxide raw material used in the present invention (left) and the carbon-silicate composite-coated silicon monoxide material prepared in Example 5 (right). Figure 2 XRD comparison diagram of the silicon monoxide raw material used in the present invention and the carbon-silicate composite-coated silicon monoxide material prepared in Example 5. Among them, the curve at the upper part is the XRD curve of the carbon-silicate composite-coated silicon monoxide material, and the curve at the lower part is the XRD curve of the silicon monoxide raw material. From Figure 1 and Figure 2 it can be seen that there are differences in the morphologies of the silicon monoxide raw material and the carbon-silicate composite-coated silicon monoxide material prepared in Example 5, and the XRD characterization curves are significantly different, indicating that the method disclosed in the present invention can successfully coat a carbon-silicate composite shell on the surface of silicon monoxide.

[0089] Electrochemical performance test: The samples prepared in Examples 1, 4, 5 and Comparative Examples 1 and 2 were assembled into coin cells to test the electrochemical performance of the samples. The assembly and testing methods are as follows:

[0090] The high-capacity and high-first-efficiency silicon-oxygen negative electrode material of the present invention was mixed with 20 wt% of a binder (styrene-butadiene rubber-sodium carboxymethyl cellulose emulsion with a solid content of 2 wt% or N-methylpyrrolidone solution of polyvinylidene fluoride with a concentration of 0.02 g / mL) and 20 wt% of a conductive agent (Super P conductive carbon black), stirred evenly and then coated on copper foil, and dried in an oven at 60 - 80 °C. Then, it was punched into electrode sheets with a punch of 12 - 16 mm in diameter, dried in a vacuum oven at 60 - 120 °C for 8 - 12 hours, and then transferred to a glove box filled with argon. Using a lithium metal sheet as the counter electrode, an ENTEK PE porous membrane as the separator, and a mixed solution of ethylene carbonate and dimethyl carbonate (volume ratio 1:1) of 1 mol / L lithium hexafluorophosphate as the electrolyte, and adding 10% (volume fraction) of fluoroethylene carbonate to this electrolyte, a CR2016 coin cell was assembled and the constant current charge-discharge performance test was carried out on a LAND battery test system (provided by Wuhan Jinnuo Electronics Co., Ltd.). The charge-discharge cut-off voltage was relative to Li / Li + is 0.05 - 2 V.

[0091] Table 1 Electrochemical performance test data of Si / SiOx example samples and comparative samples

[0092] Sample Specific discharge capacity upon delithiation (mAh / g) Coulombic efficiency (%) Example 1 1422.6 83.84 Example 4 1524.5 85.12 Example 5 1760.1 88.45 Comparative Example 1 1165.8 68.55 Comparative Example 2 1196.5 70.24

[0093] Electrochemical cycling performance test of the high-capacity and high-first-efficiency silicon-based negative electrode material: The high-capacity and high-first-efficiency silicon-based negative electrode material prepared by the present invention was cycled 50 times at 0.8 V, and the capacity retention rate reached 99.8%. SEM observations were carried out on the high-capacity and high-first-efficiency silicon-based negative electrode material before and after cycling, and the results are as Figure 4 shown. In addition, the silicon monoxide raw material was subjected to a cycling experiment under the same experimental conditions, and the SEM comparison diagrams before and after cycling are as Figure 3 shown. Combining Figure 3 and Figure 4 It can be known through calculation and analysis that the volume expansion of the silicon-based negative electrode material prepared by the method disclosed in the present invention is only 26.2% after 100 cycles, while the volume expansion of the uncoated silicon monoxide raw material is as high as 220%. Thus, it can be proved that the high-capacity and high-first-efficiency silicon-based negative electrode material prepared by the present invention has excellent cycling performance, which shows that the C-silicate composite shell can not only play the role of inhibiting the formation of the SEI film, but also inhibit the volume expansion of the silicon monoxide negative electrode material.

[0094] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these 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 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 preparation method of a silicon-based anode material with high capacity and high initial efficiency, characterized in that, It includes the following steps: (1) Mix silicon monoxide with glucose and gluconate to obtain precursor A. The molar ratio of silicon monoxide to glucose is 100:(1 - 20), and the molar ratio of glucose to gluconate is 1:(0.01 - 100). The gluconate is one or a combination of several of sodium gluconate, lithium gluconate, calcium gluconate, zinc gluconate, magnesium gluconate, potassium gluconate, or aluminum gluconate; (2) Disperse the precursor A obtained in step (1) in deionized water, heat and stir to obtain a dispersion, and freeze-dry the dispersion to obtain the material to be sintered B; the volume ratio of the deionized water to the volume of the precursor A is 1:(0.5 - 5); the heating temperature is 25 - 80 °C, and the stirring time is 15 min - 4 h; (3) Place the material to be sintered B obtained in step (2) in an atmosphere of protective gas, heat and keep warm, and finally cool naturally to obtain a silicon monoxide material coated with a carbon-silicate composite shell, that is, the finished product of the high-capacity and high-first-cycle-efficiency silicon-based anode material; the heating rate is 2 - 20 °C / min, the heat preservation temperature is 700 - 1300 °C, and the heat preservation time is 1 h - 5 h.

2. The preparation method of a high-capacity and high-first-efficiency silicon-based anode material according to claim 1, characterized in that, The preparation method of the silicon monoxide in step (1) is: mix silicon and silicon dioxide, heat to 1200 - 1500 °C under vacuum conditions, react for 6 - 10 hours to generate silicon monoxide vapor; then introduce a reducing gas, maintain the pressure at 0.1 MPa, and then cool down to 400 - 600 °C to deposit silicon monoxide.

3. The preparation method of a high-capacity and high-first-efficiency silicon-based anode material according to claim 2, characterized in that The purity of the silicon and silicon dioxide is not less than 98%, and the D50 is 2 - 100 μm; the reducing gas is at least one of hydrogen, carbon monoxide, or nitric oxide.

4. The preparation method of the high-capacity and high-first-efficiency silicon-based anode material according to any one of claims 1-3, characterized in that, In step (1), the mixing method of silicon monoxide with glucose and gluconate is dry mixing, and the dry mixing time is 2 - 36 h.

5. The preparation method of the high-capacity and high-first-efficiency silicon-based anode material according to any one of claims 1-3, characterized in that, In step (2), the temperature of freeze-drying is -100 to 10 °C, and the pressure of freeze-drying is 0 - 101 kPa.

6. A high-capacity and high-first-cycle-efficiency silicon-based anode material prepared by using the preparation method of a high-capacity and high-first-cycle-efficiency silicon-based anode material described in claim 1.

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