Preparation method of magnesium-doped silicon monoxide composite negative electrode material

Abstract

This invention provides a method for preparing a magnesium-doped silicon suboxide composite anode material. The method involves pre-magnesifying, silica sol-coating, and etching fine silicon suboxide powder generated during air jet milling to obtain a magnesium-doped silicon suboxide composite anode material with voids between the inner and outer layers. This anode material exhibits multi-level volume buffering properties, effectively mitigating volume expansion during silicon suboxide charging and discharging. The preparation process is simple, production cost is low, and it demonstrates good electrical performance and stability.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion batteries, in particular to a preparation method of a magnesium-doped silicon monoxide composite negative electrode material of a lithium ion battery. BACKGROUND

[0002] Silicon-based negative electrode materials generally include elemental nanosilicon and silicon monoxide. The theoretical capacity of elemental silicon is high, but its volume expansion reaches 300% when lithium ions are inserted. Even if the elemental silicon is coated with carbon in various forms, material cracking and pulverization will occur during the cycling process. Although the theoretical capacity of silicon monoxide material is not as high as that of elemental silicon, its volume expansion is relatively small when lithium ions are inserted, and it is a silicon-based negative electrode material with great potential for large-scale application.

[0003] Even though the expansion coefficient of silicon monoxide is relatively low compared to elemental silicon, it still reaches 110%, which is much higher than that of mainstream graphite negative electrodes. During repeated de-insertion of ions, material cracking and pulverization will occur due to the large volume expansion, which greatly affects the cycle stability of silicon monoxide materials. In addition, during the first insertion of lithium ions, silicon monoxide materials will form Li2O and Li4SiO4, etc. irreversible inert substances, resulting in a low first coulombic efficiency. These factors restrict the commercial application of silicon monoxide materials. In addition, during the preparation of silicon monoxide negative electrode materials, a large amount of fine powder is generated during the airflow crushing process, which cannot be effectively utilized, resulting in a great waste of resources and an increase in preparation cost.

[0004] Therefore, we propose a method for preparing a silicon monoxide composite negative electrode material with high initial efficiency and long cycle stability using a low-cost method. SUMMARY

[0005] The purpose of the present application is to provide a magnesium-doped silicon monoxide material to solve the problems of silicon monoxide as a negative electrode material for lithium ion batteries.

[0006] To achieve the above purpose, the technical scheme adopted by the present application is as follows:

[0007] A preparation method of a magnesium-doped silicon monoxide composite negative electrode material of a lithium ion battery, comprising the following steps:

[0008] Step 1. Take silicon monoxide fine powder (such as silicon monoxide fine powder generated during the airflow crushing process) and metal magnesium powder in a certain mass ratio, mix uniformly, and perform high-temperature sintering. Crush the sintered material to obtain a precursor 1;

[0009] Step 2. Disperse the non-amorphous carbon material in the silica sol to obtain a silica sol composite material;

[0010] Step 3. The precursor 1 is uniformly dispersed in the silica sol composite material, spray-dried, sintered, and crushed to prepare the precursor 2 with a core-shell structure;

[0011] Step 4. The precursor 2 is etched with an HF solution, filtered, washed to neutral, and dried to obtain a magnesium-doped silicon monoxide composite negative electrode material.

[0012] Further, the particle size of the silicon monoxide fine powder used in step 1 satisfies 0.5um≤D50≤2um, and the particle size of the magnesium powder satisfies 0.5um≤D50≤2um.

[0013] Further, the mass ratio of the magnesium powder to the silicon monoxide fine powder in step 1 is (1-5):(19-28).

[0014] Further, in step 1, the sintering process is to increase the temperature from room temperature to 300-500℃ at a temperature increasing rate of 3-5℃ / min, keep the temperature for 1-3h, then increase the temperature to 950-1100℃ at a temperature increasing rate of 5-8℃ / min, keep the temperature for 1-3h, and finally increase the temperature to 1200-1500℃ at a temperature increasing rate of 1-3℃ / min, keep the temperature for 3-24h.

[0015] Further, the particle size of the precursor 1 after final crushing in step 1 satisfies 4um≤D50≤8um.

[0016] Further, the non-amorphous carbon material in step 2 can be one of one-dimensional, two-dimensional, and three-dimensional structures, and is preferably graphene, carbon nanotube, carbon fiber, or vapor-grown carbon fiber reinforcement; further, the thickness of the graphene sheet is 1-20nm, preferably 2-10nm; the diameter of the carbon nanotube is 20-40nm, and the length is 10-30μm; the length of the carbon fiber and the vapor-grown carbon fiber reinforcement is 10-100μm.

[0017] Further, the solid content of the silica sol in step 2 is 20-60%, and the particle size of the silica particles in the silica sol is 6-50nm.

[0018] The mass ratio of the carbon material to the silica sol is 1:(10-50), preferably 1:(15-35).

[0019] Further, the mass ratio of the precursor 1 to the silica sol composite material in step 3 is 1:(1-5).

[0020] Further, in step 3, the sintering is performed at 200-1000℃ for 8-24h, and is preferably high-temperature treatment at 700-900℃ in a N2 atmosphere.

[0021] Further, the particle size of the precursor 2 satisfies 4.5um≤D50≤8um.

[0022] Furthermore, in step 4, the concentration of the HF solution is 4 mol / L-8 mol / L, the etching time is 0.2 h-2 h, and the mass ratio of the HF solution to the precursor 2 is (1-4):(1-2).

[0023] Another objective of this invention is to provide a magnesium-doped silicon suboxide composite anode material.

[0024] A magnesium-doped silicon suboxide composite anode material is prepared by the above method. The magnesium-doped silicon suboxide composite anode material includes an inner core and an outer shell, wherein the inner core is a magnesium-doped silicon suboxide material and the outer shell is a non-amorphous carbon material conductive layer.

[0025] Furthermore, the magnesium in the material exists mainly in one or more of the forms of Mg, MgO, MgSiO3, and Mg2SiO4, with a magnesium content of 5%-15% by mass, preferably 5%-10%.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] 1. This invention can use silica fine powder generated during air jet milling as raw material to prepare magnesium-doped silica composite anode material, providing a brand-new concept and technical route for the high-value-added utilization of silica fine powder, which can greatly reduce the manufacturing cost of silica materials.

[0028] 2. This invention employs front-end pre-magnesification for the preparation of magnesium-doped silicon suboxide composite anode materials. Magnesium incorporation can be achieved in a single high-temperature sintering process. Compared to back-end secondary sintering for pre-magnesification and pre-lithiation, this significantly reduces energy consumption and production costs while improving the initial coulombic efficiency. Furthermore, its smaller particle size and higher specific surface area allow for the loading of more silica sol composite materials and the coating of more conductive carbon materials, effectively improving the conductivity of silicon-based anode materials.

[0029] 3. The silicon suboxide composite anode material prepared by this invention adopts a multi-level buffer structure to alleviate its volume expansion during charge and discharge, providing support for the long-term cycle stability of the material and improving its cycle life: First, the introduction of inert materials such as MgO and MgSiO3 by doping with magnesium can play a certain role in buffering volume expansion; second, by etching the outer layer of silicon dioxide, a gap is constructed between the core silicon suboxide matrix and the outer conductive carbon layer, further reserving space for volume expansion; third, the outermost carbon conductive layer not only improves the conductivity of the material but also restricts the expansion of the silicon suboxide matrix.

[0030] 4. This invention replaces the traditional method by using silica sol liquid phase coating. This method offers a simple and low-cost preparation process, eliminating the need for acid-base catalytic hydrolysis of tetraethyl orthosilicate and reducing damage to the surface of silicon-based anode materials. Non-amorphous carbon materials such as graphene, carbon nanotubes, carbon fibers, and vapor-grown carbon fiber reinforcements can interlock on the silicon suboxide surface to form a conductive network, significantly improving the conductivity of silicon-based materials. Furthermore, graphene, carbon nanotubes, carbon fibers, and vapor-grown carbon fiber reinforcements all possess high strength and thermal conductivity, which can significantly improve the system's electron mobility and safety performance, preventing particle breakage. Detailed Implementation

[0031] The following embodiments will further illustrate the method provided by the present invention, but the present invention is not limited to the listed embodiments, and should also include any other known modifications within the scope of the claims of the present invention.

[0032] Example 1

[0033] The preparation method of the magnesium-doped silicon suboxide composite anode material includes the following steps:

[0034] (1) 900g of silica fume powder (D50 = 0.8µm) and 100g of magnesium powder (D50 = 1.3µm) produced during air jet milling were weighed and mixed evenly, and then placed in a high-temperature vacuum furnace. The temperature was increased from room temperature to 400℃ at a rate of 3℃ / min and held for 1h. Then the temperature was increased to 950℃ at a rate of 5℃ / min and held for 1.5h. Finally, the temperature was increased to 1350℃ at a rate of 1℃ / min and held for 5h. The collected samples were subjected to jaw crusher, roller crusher, and air jet milling. The resulting precursor 1 had a D50 of 4.9µm and a magnesium content of 9.6%.

[0035] (2) Carbon nanotubes are dispersed in a silica sol with a solid content of 30% and a silica particle size of 20 nm, wherein the mass ratio of carbon nanotubes to silica sol is 1:25. Ultrasonic vibration is used to make the carbon nanotubes disperse evenly in the silica sol to obtain a silica sol composite material.

[0036] (3) 500g of precursor 1 was uniformly dispersed in 1000g of silica sol composite material and impregnated for 5h. The solvent was evaporated by spray drying. Then, it was kept at 800℃ and N2 atmosphere for 12h, crushed and pulverized to prepare precursor 2 with a particle size D50 of 5.0um.

[0037] (4) Add 500g of precursor 2 to 1.8L of hydrofluoric acid solution with a concentration of 8mol / L and treat for 2h. After filtration and washing with ethanol aqueous solution until neutral, dry to obtain magnesium-doped silicon suboxide composite material with core-shell buffer structure.

[0038] Example 2

[0039] (1) Weigh 850g of fine silica powder (D50 = 0.8µm) and 150g of metallic magnesium powder (D50 = 1.5µm), mix them evenly, and place them in a high-temperature vacuum furnace. Increase the temperature from room temperature to 500℃ at a rate of 3℃ / min, hold for 2 hours, then increase the temperature to 950℃ at a rate of 5℃ / min, hold for 3 hours, and finally increase the temperature to 1350℃ at a rate of 1℃ / min, hold for 12 hours. The collected samples were subjected to jaw crusher, roller crusher, and air jet milling to obtain precursor 1, which had a D50 of 7.3µm and a magnesium content of 14.3%.

[0040] (2) Graphene is dispersed in a silica sol with a solid content of 30% and a silica particle size of 40 nm, wherein the mass ratio of graphene to silica sol is 1:30. Ultrasonic vibration is used to make the graphene dispersed evenly in the silica sol to obtain a silica sol composite material.

[0041] (3) 500g of precursor 1 was uniformly dispersed in 1000g of silica sol composite material and impregnated for 8h. The solvent was evaporated by spray drying. Then, it was kept at 800℃ and N2 atmosphere for 16h, crushed and pulverized to prepare precursor 2 with a particle size D50 of 7.5um.

[0042] (4) Add 500g of precursor 2 to 1.5L of hydrofluoric acid solution with a concentration of 6mol / L and treat for 1h. After filtration and washing with ethanol aqueous solution until neutral, dry to obtain magnesium-doped silicon suboxide composite material with core-shell buffer structure.

[0043] Example 3

[0044] (1) Weigh 900g of fine silica powder (D50 = 1.5µm) and 100g of magnesium powder (D50 = 1.3µm), mix them evenly, and place them in a high-temperature vacuum furnace. Increase the temperature from room temperature to 400℃ at a rate of 5℃ / min, hold for 1h, then increase the temperature to 1000℃ at a rate of 6℃ / min, hold for 1.5h, and finally increase the temperature to 1400℃ at a rate of 1℃ / min, hold for 10h. The collected samples were subjected to jaw crusher, roller crusher, and air jet milling. The resulting precursor 1 had a D50 of 5.5µm and a magnesium content of 9.5%.

[0045] (2) The vapor-grown carbon fiber reinforcement is dispersed in a silica sol with a solid content of 45% and a particle size of 30 nm, wherein the mass ratio of the vapor-grown carbon fiber reinforcement to the silica sol is 1:20. Ultrasonic vibration is used to make the vapor-grown carbon fiber reinforcement uniformly dispersed in the silica sol to obtain a silica sol composite material.

[0046] (3) 500g of precursor 1 was uniformly dispersed in 1500g of silica sol composite material and impregnated for 6h, spray dried, and then kept at 600℃ for 8h, crushed and pulverized to prepare precursor 2 with a particle size D50 of 5.6um.

[0047] (4) Add 500g of precursor 2 to 1L of hydrofluoric acid solution with a concentration of 5mol / L and treat for 30min. After filtration and washing with ethanol aqueous solution until neutral, dry to obtain magnesium-doped silicon suboxide composite material with core-shell buffer structure.

[0048] Example 4

[0049] (1) Weigh 950g of fine silica powder (D50 = 1.5µm) and 50g of magnesium powder (D50 = 0.9µm), mix them evenly, and place them in a high-temperature vacuum furnace. Increase the temperature from room temperature to 400℃ at a rate of 5℃ / min, hold for 1h, then increase the temperature to 1000℃ at a rate of 6℃ / min, hold for 1.5h, and finally increase the temperature to 1400℃ at a rate of 1℃ / min, hold for 10h. The collected samples were subjected to jaw crusher, roller crusher, and air jet milling. The resulting precursor 1 had a D50 of 5.5µm and a magnesium content of 4.9%.

[0050] (2) The vapor-grown carbon fiber reinforcement is dispersed in a silica sol with a solid content of 20% and a particle size of 30 nm, wherein the mass ratio of the vapor-grown carbon fiber reinforcement to the silica sol is 1:20. Ultrasonic vibration is used to make the vapor-grown carbon fiber reinforcement uniformly dispersed in the silica sol to obtain a silica sol composite material.

[0051] (3) 500g of precursor 1 was uniformly dispersed in 800g of silica sol composite material and impregnated for 6h, spray dried, and then kept at 700℃ for 8h, crushed and pulverized to prepare precursor 2 with a particle size D50 of 5.6um.

[0052] (4) Add 500g of the driver 2 to 1L of hydrofluoric acid solution with a concentration of 5mol / L and treat for 30min. After filtration and washing with ethanol aqueous solution until neutral, dry to obtain magnesium-doped silicon suboxide composite material with core-shell buffer structure.

[0053] Comparative Example 1

[0054] (1) Weigh 1000g of silica powder (D50 = 0.8µm) produced during air jet milling and place it in a high-temperature vacuum furnace. Increase the temperature from room temperature to 400℃ at a rate of 3℃ / min and hold for 1h. Then increase the temperature to 950℃ at a rate of 5℃ / min and hold for 1.5h. Finally, increase the temperature to 1350℃ at a rate of 1℃ / min and hold for 5h. The collected sample was subjected to jaw crusher, roller crusher, and air jet milling to obtain precursor 1 with a D50 = 5µm.

[0055] (2) Carbon nanotubes are dispersed in a silica sol with a solid content of 30% and a silica particle size of 20 nm, wherein the mass ratio of carbon nanotubes to silica sol is 1:25. Ultrasonic vibration is used to make the carbon nanotubes disperse evenly in the silica sol to obtain a silica sol composite material.

[0056] (3) 500g of precursor 1 was uniformly dispersed in 1000g of silica sol composite material and impregnated for 5h. The solvent was evaporated by spray drying. Then, it was kept at 800℃ and N2 atmosphere for 12h, crushed and pulverized to prepare precursor 2 with a particle size D50 of 5.0um.

[0057] (4) Add 500g of precursor 2 to 1.8L of hydrofluoric acid solution with a concentration of 8mol / L and treat for 2h. After filtration and washing with ethanol aqueous solution until neutral, dry to obtain magnesium-doped silicon suboxide composite material with core-shell buffer structure.

[0058] Comparative Example 2

[0059] (1) 900g of silica fume powder (D50 = 0.8µm) and 100g of magnesium powder (D50 = 1.3µm) produced during air jet milling were weighed and mixed evenly, and then placed in a high-temperature vacuum furnace. The temperature was increased from room temperature to 400℃ at a rate of 3℃ / min and held for 1h. Then the temperature was increased to 950℃ at a rate of 5℃ / min and held for 1.5h. Finally, the temperature was increased to 1350℃ at a rate of 1℃ / min and held for 5h. The collected samples were subjected to jaw crusher, roller crusher and air jet milling. The resulting precursor 1 had a D50 of 4.9µm and a magnesium content of 9.6%.

[0060] Comparative Example 3

[0061] (1) 900g of silica fume powder (D50 = 0.8µm) and 100g of magnesium powder (D50 = 1.3µm) produced during air jet milling were weighed and mixed evenly, and then placed in a high-temperature vacuum furnace. The temperature was increased from room temperature to 400℃ at a rate of 3℃ / min and held for 1h. Then, the temperature was increased to 950℃ at a rate of 5℃ / min and held for 1.5h. Finally, the temperature was increased to 1350℃ at a rate of 1℃ / min and held for 5h. The collected samples were subjected to jaw crusher, roller crusher, and air jet milling. The resulting precursor 1 had a D50 of 4.9µm and a magnesium content of 9.3%.

[0062] (2)Use Precursor 1 was coated with silica using the following method: 800g of precursor 1 was stirred and dispersed in 5L of a mixed solution of ethanol and water in a ratio of 4:1. The pH was adjusted to 9-10 with ammonia (28%), 500mL of TEOS was added, and the mixture was reacted at room temperature for 6h. After centrifugation, the mixture was washed until neutral and dried under vacuum at -50℃ for 24h to obtain precursor 2.

[0063] (3) Take 500g of precursor 2 and place it in a rotary kiln. The rotary kiln speed is 0.5r / min. Acetylene is used as the carbon source gas and nitrogen is used as the inert gas protective atmosphere. The total gas flow rate is 0.5L / min, where the acetylene flow rate: nitrogen flow rate is 1:8. The temperature is raised to 900℃ at a rate of 5℃ / min and held for 3h to obtain precursor 3.

[0064] (4) Add 500g of precursor 3 to 1L of hydrofluoric acid solution with a concentration of 8mol / L and treat for 1h. After filtration and washing with ethanol aqueous solution until neutral, dry to obtain magnesium-doped silicon suboxide composite material with core-shell buffer structure.

[0065] Comparative Example 4

[0066] (1) 900g of silica fume powder (D50 = 0.8µm) and 100g of magnesium powder (D50 = 1.3µm) produced during air jet milling were weighed and mixed evenly, and then placed in a high-temperature vacuum furnace. The temperature was increased from room temperature to 400℃ at a rate of 3℃ / min and held for 1h. Then the temperature was increased to 950℃ at a rate of 5℃ / min and held for 1.5h. Finally, the temperature was increased to 1350℃ at a rate of 1℃ / min and held for 5h. The collected samples were subjected to jaw crusher, roller crusher and air jet milling. The resulting precursor 1 had a D50 of 4.9µm and a magnesium content of 9.6%.

[0067] (2) Take 800g of precursor 1 and place it in a rotary kiln. The rotary kiln speed is 0.5r / min. Acetylene is used as the carbon source gas and nitrogen is used as the inert gas protective atmosphere. The total gas flow rate is 0.5L / min, where the acetylene flow rate: nitrogen flow rate is 1:10. The temperature is raised to 900℃ at a rate of 5℃ / min and held for 3h to obtain magnesium-doped silicon suboxide material.

[0068] Performance testing:

[0069] The electrochemical cycling performance of the silicon-based anode materials for lithium-ion batteries prepared in Examples 1-4 and Comparative Examples 1-4 was tested using the following methods:

[0070] The negative electrode active material is prepared by mixing sodium carboxymethyl cellulose (CMC), conductive carbon black (SP), and styrene-butadiene rubber (SBR) in a mass ratio of 94.5:1.5:1.5:2.5. The working electrode is coated on a copper foil current collector and vacuum dried to obtain the negative electrode sheet. Then, the lithium sheet, electrolyte (1 mol / L LiPF6 mixed with solvent EC:DMC:EMC = 1:1:1 (v / v)), Celgard 2400 separator, and shell are assembled into a button cell using conventional production processes.

[0071] The charge / discharge tests of the button batteries were conducted on the LAND battery testing system of Wuhan Jinno Electronics Co., Ltd. The charge / discharge voltage was limited to 0.05–1.5V. Cycle performance testing was performed at room temperature. The initial charge / discharge performance test was also performed at room temperature, using a 0.1C constant current charge / discharge cycle for 10 cycles, followed by a 0.5C constant current charge / discharge cycle for 100 cycles. Capacity retention was then calculated. The relevant physicochemical properties and electrical performance test results of the above examples and comparative samples are shown in the table below:

[0072]

[0073] It should be noted that the embodiments described herein are only some embodiments of the present invention, and not all implementations of the present invention. These embodiments are merely illustrative and are intended only to provide a more intuitive and clear way to understand the content of the present invention, not to limit the technical solutions described herein. All other implementation methods that can be conceived by those skilled in the art without creative effort, as well as other simple substitutions and variations of the technical solutions of the present invention, without departing from the concept of the present invention, are within the protection scope of the present invention.

Claims

1. A method for preparing a magnesium-doped silicon suboxide composite anode material, characterized in that, Includes the following steps: Step 1. Weigh out fine silica powder and magnesium powder in a certain mass ratio, mix them evenly, and sinter them at high temperature. Then crush the sintered material to obtain precursor 1. Step 2. Disperse non-amorphous carbon materials in silica sol to obtain silica sol composite materials; Step 3. Precursor 1 is uniformly dispersed in silica sol composite material, spray dried, sintered, and pulverized to prepare precursor 2 with core-shell structure; Step 4. Etch precursor 2 with HF solution, filter, wash until neutral, and then dry to obtain a magnesium-doped silicon suboxide composite anode material.

2. The preparation method according to claim 1, wherein, The particle size of the silica powder in step 1 is 0.5um≤D50≤2um, and the particle size of the magnesium powder is 0.5um≤D50≤2um.

3. The preparation method according to claim 2, wherein, In step 1, the mass ratio of magnesium powder to silica powder is (1-5):(19-28).

4. The preparation method according to claim 1, wherein, The sintering process in step 1 is as follows: the temperature is increased from room temperature to 300℃ to 500℃ at a heating rate of 3℃ / min to 5℃ / min, and held for 1h to 3h. Then the temperature is increased to 950℃ to 1100℃ at a heating rate of 5℃ / min to 8℃ / min, and held for 1h to 3h. Finally, the temperature is increased to 1200℃ to 1500℃ at a heating rate of 1℃ / min to 3℃ / min, and held for 3h to 24h.

5. The preparation method according to any one of claims 1-4, wherein, The particle size of precursor 1 satisfies 4µm≤D50≤8µm.

6. The preparation method according to claim 1, wherein, The silica sol in step 2 has a solid content of 20-60% and the silica particles in the silica sol have a particle size of 6-50 nm.

7. The preparation method according to claim 1, wherein, In step 2, the non-amorphous carbon material is at least one of one-dimensional, two-dimensional, and three-dimensional structures; The mass ratio of carbon material to silica sol is 1:(10-50).

8. The preparation method according to claim 7, wherein, In step 2, the non-amorphous carbon material is at least one of graphene, carbon nanotubes, carbon fibers, and vapor-grown carbon fiber reinforcement. The mass ratio of carbon material to silica sol is 1:(15-35).

9. The preparation method according to any one of claims 1, 6-8, wherein, In step 3, the mass ratio of precursor 1 to silica sol composite material is 1:(1-5).

10. The preparation method according to claim 1, wherein, In step 3, sintering is carried out at 200-1000℃ for 8-24 hours.

11. The preparation method according to claim 10, wherein, In step 3, sintering is carried out at a high temperature of 700-900℃ under a N2 atmosphere.

12. The preparation method according to claim 1, wherein, The concentration of the HF solution in step 4 is 4 mol / L-8 mol / L, and the etching time is 0.2 h-2 h.

13. The preparation method according to claim 12, wherein, In step 4, the mass ratio of HF solution to precursor 2 is (1-4):(1-2).

14. A magnesium-doped silicon suboxide composite anode material prepared by the preparation method according to any one of claims 1-13, characterized in that, The magnesium-doped silicon suboxide composite anode material includes an inner core and an outer shell. The inner core is a magnesium-doped silicon suboxide material, and the outer shell is a non-amorphous carbon material conductive layer.

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