Magnesium-doped prelithiated silicon oxide composite material for lithium-ion batteries and its preparation method

Abstract

The present invention belongs to the field of preparation of lithium-ion battery materials, and particularly relates to a magnesium-doped prelithiated silicon oxide composite material used for lithium-ion batteries and a preparation method thereof. The preparation process is as follows: micron silicon, silicon dioxide and magnesium powder are reacted in a high-temperature furnace to generate magnesium-doped silicon monoxide, and then a lithium supplementing agent and a carbon source are sequentially deposited on its surface through atomic vapor deposition and vapor deposition to obtain the magnesium-doped prelithiated silicon oxide composite material. The beneficial effects of the present invention are as follows: The present invention uses silicon dioxide, silicon powder and magnesium powder to carry out sintering under argon conditions, and utilizes its own disproportionation reaction to generate silicon / silicon monoxide / magnesium silicate; at the same time, a lithium supplementing agent is coated on its outer surface through atomic vapor deposition, and lithium silicate is formed by the lithium ions released by the lithium supplementing agent during the charge and discharge process, reducing the irreversible capacity of the material and improving the first efficiency; at the same time, the released excessive lithium ions improve the cycle performance and power performance of the material.

Description

Technical Field

[0001] The present invention relates to the field of preparation of lithium - ion battery materials, and particularly relates to a magnesium - doped prelithiated silicon - oxygen composite material for lithium - ion batteries and a preparation method thereof. Background Art

[0002] At present, the research on silicon - oxygen anode materials mainly focuses on the disproportionation reaction of silicon and silicon dioxide by vacuum high - temperature sintering to obtain silicon monoxide, reducing the expansion of the material and improving its electronic conductivity. However, there are still problems such as poor rate performance and low initial efficiency. Although there are methods in the market to improve the initial efficiency of the material by doping with metals such as magnesium, the uniformity of magnesium doping is poor. At the same time, in terms of improving the rate performance of the material, mainly through liquid - phase / solid - phase methods to coat amorphous carbon and other compounds on the material surface to improve the interfacial performance of the material, reduce the impedance or increase the lithium - ion insertion / extraction rate of the material. However, there are defects such as poor consistency and unobvious improvement effect, resulting in a still relatively large impedance of the silicon - based material. Summary of the Invention

[0003] The purpose of the present invention is to address the above - mentioned defects existing in the prior art, and provide a magnesium - doped prelithiated silicon - oxygen composite material for lithium - ion batteries and a preparation method thereof. By doping with magnesium and coating a lithium - supplementing agent, a high - initial - efficiency silicon - oxygen composite material can be prepared, which can improve the power and cycling performance of the silicon - based material.

[0004] A magnesium - doped prelithiated silicon - oxygen composite material for lithium - ion batteries mentioned in the present invention has a core - shell structure. The inner core is magnesium - doped silicon - oxygen, and the outer shell is a composite composed of a lithium - supplementing agent and amorphous carbon. Calculated based on 100% of the mass ratio of the composite material, the mass ratio of the outer shell is 5 - 15%.

[0005] Preferably, calculated based on 100% of the mass of the inner core, the magnesium content is 1 - 5%.

[0006] Preferably, the content of the lithium - supplementing agent in the outer shell is 5 - 30%, and the rest is amorphous carbon.

[0007] The preparation method of the magnesium - doped prelithiated silicon - oxygen composite material for lithium - ion batteries mentioned in the present invention includes the following processes:

[0008] (1) Micron - sized silicon powder, silicon dioxide and magnesium powder are added to a ball mill and ball - milled at a rotation speed of 500 - 1000 RPM for 30 - 300 min; then asphalt solid is added, heated, and pressed into a block structure in a molten state; then it is transferred to a vacuum sintering furnace, and the reaction is carried out at a vacuum degree of 0 - 20 Pa and a temperature of 1500℃ - 2000℃ for 1 - 6 h, and then the heating is stopped and cooled to obtain a magnesium - containing silicon monoxide precursor.

[0009] By mass ratio, micron silicon powder: silicon dioxide: magnesium powder: pitch = 20 - 25:40 - 50:5 - 20:20 - 35;

[0010] (2) Subsequently, through atomic vapor deposition, the lithium supplementing agent is deposited on the surface of the magnesium-containing silicon monoxide precursor; then the obtained material is transferred to a tube furnace, and by vapor deposition method, a carbon source is introduced and vaporized, and carbonization is carried out at a temperature of 700 - 1100 °C for 1 - 6 h, and then cooled to room temperature under an inert atmosphere and pulverized to obtain a magnesium-doped prelithiated silicon oxide composite material.

[0011] Preferably, the process of atomic vapor deposition in the above step (2) is as follows: The method of atomic vapor deposition in step (3) is: ① The lithium supplementing agent material for 1 second; ② Nitrogen purging for 60 seconds; ③ Oxygen source introduction for 5 seconds; ④ Nitrogen purging for 5 seconds; ⑤ Water introduction for 0.05 seconds; ⑥ Nitrogen purging for 50 seconds; ⑦ Cycle 100 times starting from step ①.

[0012] Preferably, the lithium supplementing agent in the above step (2) is one of lithium ferrite, lithium nickelate, lithium cobaltate, and lithium cuprate.

[0013] Preferably, the carbon source mentioned in the above step (2) is one of benzene, toluene, and xylene.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention uses silicon dioxide, silicon powder, and magnesium powder to sinter under argon conditions, and generates silicon, silicon monoxide, and magnesium silicate through its own disproportionation reaction; at the same time, a lithium supplementing agent is coated on its outer surface by atomic vapor deposition, and lithium silicate is formed by the lithium ions released by the lithium supplementing agent during the charge and discharge process, reducing the irreversible capacity of the material and improving the first efficiency; at the same time, excessive lithium ions are released to improve the cycle performance and power performance of the material. Description of the Drawings

[0015] Figure 1 SEM image of the magnesium-doped prelithiated silicon oxide composite material prepared in Example 1. Specific Embodiments

[0016] The following describes the preferred embodiments of the present invention with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0017] Example 1, The preparation method of the magnesium-doped prelithiated silicon oxide composite material used in the lithium-ion battery mentioned in the present invention includes the following processes:

[0018] (1) Add 20g of micron silicon powder, 40g of silicon dioxide and 10g of magnesium powder into a ball mill and mill at a speed of 800RPM for 60min; then add 25g of asphalt solid, mix, heat, and press into a block structure in a molten state; then transfer to a vacuum sintering furnace, and react at a vacuum degree of 10Pa and a temperature of 1800℃ for 3h, then stop heating and cool to obtain a magnesium-containing silicon monoxide precursor;

[0019] (2) Then, the lithium ferrite is deposited on the surface of the magnesium-containing silicon oxide precursor by atomic vapor deposition according to the following steps: ① lithium ferrite material for 1 second; ② nitrogen purge for 60 seconds; ③ introduction of oxygen source for 5 seconds; ④ nitrogen purge for 5 seconds; ⑤ introduction of water for 0.05 seconds; ⑥ nitrogen purge for 50 seconds; ⑦ 100 cycles starting from step ①; lithium ferrite is deposited on the surface of the magnesium-containing silicon oxide precursor; then the obtained material is transferred to a tubular furnace, and a benzene carbon source is introduced and gasified by vapor deposition, and carbonized at a temperature of 900°C for 3 hours, and then cooled to room temperature in an argon inert atmosphere, crushed, and a magnesium-doped pre-lithiated silicon-oxygen composite material is obtained.

[0020] Embodiment 2, the preparation method of the magnesium-doped pre-lithiated silicon-oxygen composite material used in the lithium-ion battery mentioned in the present invention comprises the following process:

[0021] (1) Add 25g of micron silicon powder, 50g of silicon dioxide and 20g of magnesium powder into a ball mill and mill at a speed of 500RPM for 300min; then add 35g of asphalt solid, mix, heat, and press into a block structure in a molten state; then transfer to a vacuum sintering furnace, and react at a vacuum degree of 10Pa and a temperature of 1500℃ for 1h, then stop heating and cool to obtain a magnesium-containing silicon monoxide precursor;

[0022] (2) Then, the lithium nickel oxide is deposited on the surface of the magnesium-containing silicon oxide precursor by atomic vapor deposition according to the following steps: ① lithium nickel oxide material for 1 second; ② nitrogen purge for 60 seconds; ③ introduction of oxygen source for 5 seconds; ④ nitrogen purge for 5 seconds; ⑤ introduction of water for 0.05 seconds; ⑥ nitrogen purge for 50 seconds; ⑦ 100 cycles starting from step ①; lithium nickel oxide is deposited on the surface of the magnesium-containing silicon oxide precursor; then the obtained material is transferred to a tubular furnace, and toluene carbon source is introduced and gasified by vapor deposition, and carbonized at a temperature of 700°C for 6 hours, and then cooled to room temperature in an argon inert atmosphere, crushed, and a magnesium-doped pre-lithiated silicon oxide composite material is obtained.

[0023] Embodiment 3, the preparation method of the magnesium-doped pre-lithiated silicon-oxygen composite material used in the lithium-ion battery mentioned in the present invention comprises the following process:

[0024] (1) Add 25 g of micron-sized silicon powder, 40 g of silicon dioxide, and 5 g of magnesium powder to a ball mill, and ball mill for 30 min at a rotation speed of 1000 RPM; then add it to 20 g of solid asphalt and mix, heat, and press it into a block structure in a molten state; then transfer it to a vacuum sintering furnace, and react for 1 h at a vacuum degree of 20 Pa and a temperature of 2000 °C, then stop heating, cool, and obtain a magnesium-containing silicon monoxide precursor;

[0025] (2) Then, through atomic vapor deposition, follow the steps as follows: ① Lithium cobaltate material for 1 second; ② Nitrogen purge for 60 seconds; ③ Introduce oxygen source for 5 seconds; ④ Nitrogen purge for 5 seconds; ⑤ Introduce water for 0.05 seconds; ⑥ Nitrogen purge for 50 seconds; ⑦ Cycle 100 times starting from step ①; Deposit lithium cobaltate on the surface of the magnesium-containing silicon monoxide precursor; then transfer the obtained material to a tube furnace, and use vapor deposition method to introduce xylene carbon source and vaporize it, and carbonize it at a temperature of 1100 °C for 1 h, then cool it to room temperature in an argon inert atmosphere, and pulverize it to obtain a magnesium-doped prelithiated silicon oxy composite material.

[0026] Comparative example:

[0027] (1) Add 20 g of micron-sized silicon powder and 40 g of silicon dioxide to a ball mill, and ball mill for 60 min at a rotation speed of 800 RPM; then add it to 25 g of solid asphalt and mix, heat, and press it into a block structure in a molten state; then transfer it to a vacuum sintering furnace, and react for 3 h at a vacuum degree of 10 Pa and a temperature of 1800 °C, then stop heating, cool, and obtain a silicon monoxide precursor;

[0028] (2) Then mix 100 g of the silicon monoxide precursor material and 10 g of the lithium ferrate material evenly and transfer it to a tube furnace, and use vapor deposition method to introduce benzene carbon source and vaporize it, and carbonize it at a temperature of 900 °C for 3 h, then cool it to room temperature in an argon inert atmosphere, and pulverize it to obtain a prelithiated silicon oxy composite material.

[0029] Performance test:

[0030] (1) Morphology test

[0031] Conduct SEM test on the prelithiated silicon oxy composite material in Example 1, and the test results are as Figure 1 shown. It can be Figure 1 seen that the material presents a granular structure, and the particle size distribution of the material is uniform and reasonable. The white substances on the surface are residual lithium salts, and the particle size is between 2 - 10 μm.

[0032] (2) Button battery test

[0033] The prelithiated silicon-oxygen composite materials in Examples 1-3 and the comparative examples were assembled into coin cells as the anode materials of lithium-ion batteries, denoted as A1, A2, A3, and B1 respectively.

[0034] The specific preparation method is as follows: Add a binder, a conductive agent, and a solvent to the anode material of the lithium-ion battery, stir to make a slurry, coat it on a copper foil, and obtain the anode sheet through drying and rolling; the binder used is LA132, the conductive agent is SP, the solvent is NMP, and the dosage ratio of the anode material, SP, PVDF, and NMP is 95 g: 1 g: 4 g: 220 mL; LiPF6 is used as the electrolyte in the electrolyte, and a mixture of EC and DEC with a volume ratio of 1:1 is used as the solvent; a lithium metal sheet is used as the counter electrode, and a polypropylene (PP) membrane is used as the separator. The coin cell assembly is carried out in a glove box filled with argon. The electrochemical performance is tested on a Wuhan Blue Electric CT2001A battery tester, and the charge-discharge voltage range is 0.005 V to 2.0 V, and the charge-discharge rate is 0.1 C.

[0035] The test results are shown in Table 1.

[0036] Table 1

[0037]

[0038] It can be seen from the data in Table 1 that the specific capacity and the first efficiency of the prelithiated silicon-oxygen composite material prepared in the examples of the present invention are significantly better than those of the comparative examples. The reason is that: the surface lithium supplement agent is added by atomic vapor deposition method, so that sufficient lithium ions are provided during the charge-discharge process to reduce its irreversible capacity loss and improve the first efficiency; at the same time, the atomic vapor deposition method has the advantages of high density and strong consistency of the deposited material, thus improving the powder conductivity and tap density of the material.

[0039] (3) Soft-pack battery test:

[0040] The anode sheets were prepared by using the prelithiated silicon-oxygen composite materials doped with 90% artificial graphite in Examples 1-3 and the comparative examples as the anode materials, using NCM532 as the cathode material; LiPF6 was used as the electrolyte in the electrolyte, and a mixture of EC and DEC with a volume ratio of 1:1 was used as the solvent; a Celgard 2400 membrane was used as the separator to prepare 5 Ah soft-pack batteries, denoted as C1, C2, C3, and D1. The liquid absorption and retention capacity, the resilience of the electrode sheet, and the cycle performance of the anode sheets were tested respectively.

[0041] a. Liquid absorption capacity test

[0042] A 1 mL burette was used, and V mL of the electrolyte was sucked, and a drop was added on the surface of the electrode sheet and timed until the electrolyte was completely absorbed. The time t was recorded, and the liquid absorption speed V / t of the electrode sheet was calculated. The test results are shown in Table 2.

[0043] b. Liquid retention rate test

[0044] Calculate the theoretical liquid absorption capacity m1 of the electrode sheet according to the electrode sheet parameters, and weigh the weight m2 of the electrode sheet. Then immerse the electrode sheet in the electrolyte for 24 h, weigh the weight of the electrode sheet as m3, calculate the liquid absorption capacity of the electrode sheet m3 - m2, and calculate according to the following formula: Liquid retention rate = (m3 - m2) * 100% / m1. The test results are shown in Table 2.

[0045] Table 2

[0046]

[0047] It can be seen from Table 2 that the liquid absorption and retention capacity of the prelithiated silicon oxide composite materials obtained in Examples 1 - 3 is significantly higher than that of the comparative examples. The experimental results show that the reason is that the lithium supplementing agent deposited by the atomic vapor deposition method has a high specific surface area, which improves the liquid absorption and retention capacity of the prelithiated silicon oxide composite material.

[0048] c. Electrode sheet rebound rate test

[0049] First, use a thickness gauge to measure the average thickness of the electrode sheet as D1. Then place the electrode sheet in a vacuum drying oven at 80 °C for 48 h, measure the thickness of the electrode sheet as D2, and calculate according to the following formula: Rebound rate = (D2 - D1) * 100% / D1. The test results are shown in Table 3.

[0050] d. Electrode sheet resistivity test

[0051] Use a resistivity tester to measure the resistivity of the electrode sheet. The test results are shown in Table 3.

[0052] Table 3

[0053]

[0054] It can be seen from the data in Table 3 that the rebound rate and resistivity of the negative electrode sheets prepared from the prelithiated silicon oxide composite materials obtained in Examples 1 - 3 are significantly lower than those of the comparative examples. The reason may be that: the materials deposited by the atomic vapor deposition method have advantages such as high density and high integrity, thus reducing the resistivity of the electrode sheet.

[0055] e. Cycle performance test

[0056] Test the cycle performance of the battery at a charge-discharge rate of 1C / 1C and a voltage range of 2.5V - 4.2V at a temperature of 25 ± 3 °C. The test results are shown in Table 4.

[0057] Table 4

[0058]

[0059] As can be seen from Table 4, the cycle performance of the battery prepared from the prelithiated silicon oxide composite material of the present invention is significantly better than that of the comparative example. The reason may be that the electrode sheet prepared from the prelithiated silicon oxide composite material of the present invention has a lower expansion rate and its porous structure, which reduces the expansion during charge and discharge and improves the liquid absorption and retention capacity of the material, thereby improving its cycle performance.

[0060] The above are only some preferred embodiments of the present invention. Any person skilled in the art may modify the above-described technical solutions or modify them into equivalent technical solutions. Therefore, any corresponding simple modification or equivalent transformation made according to the technical solutions of the present invention falls within the scope of the present invention's claims.

Claims

1. A preparation method of a magnesium-doped prelithiated silicon oxide composite material for a lithium-ion battery, characterized in that: The composite material presents a core-shell structure, with the inner core being magnesium-doped silicon oxide and the outer shell being a composite composed of a lithium supplement agent and amorphous carbon; calculated based on 100% of the mass of the composite material, the mass ratio of the outer shell is 5-15%; In the inner core, calculated based on 100% of the mass, the magnesium content is 1-5%; In the outer shell, the content of the lithium supplement agent is 5-30%, and the rest is amorphous carbon; The preparation method of the magnesium-doped prelithiated silicon oxide composite material used in the lithium-ion battery includes the following processes: (1) Micron silicon powder, silicon dioxide and its magnesium powder are added to a ball mill and ball milled at a rotation speed of 500-1000 RPM for 30-300 min; then asphalt solid is added and mixed, heated, and pressed into a block structure in a molten state; then transferred to a vacuum sintering furnace, and the reaction is carried out at a vacuum degree of 0-20 Pa and a temperature of 1500 °C - 2000 °C for 1-6 h, and then the heating is stopped and cooled to obtain a magnesium-containing silicon monoxide precursor; By mass ratio, micron silicon powder: silicon dioxide: magnesium powder: asphalt = 20-25:40-50:5-20:20-35; (2) Then, through atomic vapor deposition, the lithium supplement agent is deposited on the surface of the magnesium-containing silicon monoxide precursor; then the obtained material is transferred to a tube furnace, and by vapor deposition method, a carbon source is introduced and gasified, and carbonized at a temperature of 700-1100 °C for 1-6 h, and then cooled to room temperature in an inert atmosphere and pulverized to obtain a magnesium-doped prelithiated silicon oxide composite material; The process of atomic vapor deposition in step (2) is as follows: ① The lithium supplement agent material for 1 second; ② Nitrogen purging for 60 seconds; ③ Oxygen source introduction for 5 seconds; ④ Nitrogen purging for 5 seconds; ⑤ Water introduction for 0.05 seconds; ⑥ Nitrogen purging for 50 seconds; ⑦ Cycle 100 circles starting from step ①.

2. The preparation method of the magnesium-doped prelithiated silicon oxide composite material used in the lithium-ion battery according to claim 1, characterized in that: The lithium supplement agent in step (2) is one of lithium ferrite, lithium nickelate, lithium cobaltate, and lithium cuprate.

3. The preparation method of the magnesium-doped prelithiated silicon oxide composite material for the lithium-ion battery according to claim 1, wherein: The carbon source mentioned in step (2) is one of benzene, toluene, and xylene.

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