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

Abstract

The present invention discloses a high-first-efficiency silicon monoxide negative electrode material, a preparation method thereof and an application thereof, belonging to the technical field of preparation of silicon negative electrode materials. In the present invention, metallic lithium or a lithium salt is used as a solid source, and SF6 (or CF4, N2, etc.) is used as a gas source. A lithium-rich layer is in-situ constructed on the surface of silicon monoxide through plasma chemical vapor deposition to form a high-first-efficiency silicon monoxide negative electrode material. The present invention provides a new method for preparing a silicon monoxide-based composite material with a short reaction time, environmental friendliness and easy preparation. The silicon monoxide-based composite material provided by the present invention has the characteristic of high initial Coulomb efficiency as a negative electrode material for lithium ion batteries, and the initial Coulomb efficiency can be as high as 89.5%.

Description

Technical Field

[0001] The present invention belongs to the technical field of the preparation of silicon negative electrode materials, and particularly relates to a high first-efficiency silicon monoxide negative electrode material, a preparation method thereof, and an application thereof. Background Art

[0002] At present, the commercialized negative electrode materials of lithium-ion batteries are mainly graphite-based carbon materials. Although graphite negative electrodes have excellent cycle stability, their theoretical specific capacity is only 372 mAh / g, which cannot meet the application requirements of long-range power batteries for electric vehicles. Therefore, it is urgent to develop a new generation of negative electrode materials for lithium-ion batteries with high energy density.

[0003] Silicon monoxide negative electrode materials are recognized as new negative electrode materials that are most likely to replace traditional graphite at present due to their high theoretical capacity (2000 mAh / g), low cost, and less volume expansion effect, and have great potential for commercial development. However, during the first lithium intercalation process of silicon monoxide, an unstable SEI film will form on the surface, consuming active lithium ions. At the same time, lithium ions react with oxygen elements in the structure of silicon monoxide to generate Li2O and a large amount of lithium silicates (such as Li4SiO4, Li2SiO3, Li2Si2O5), etc. These reactions are irreversible, resulting in a large consumption of lithium sources, leading to a low first efficiency of silicon monoxide materials, affecting the performance of the positive electrode capacity, and it is difficult to obtain lithium-ion batteries with higher energy density. Therefore, the prelithiation technology of silicon monoxide is the key to realizing its commercial application. Commonly used prelithiation methods include electrochemical prelithiation, lithium metal prelithiation, and chemical prelithiation, etc. Electrochemical prelithiation is to form an electrochemical system with a lithium foil, an electrolyte, and a negative electrode, and Li + diffuses through the electrolyte to the negative electrode under the action of an external electric field to complete prelithiation. Lithium metal prelithiation is to add lithium powder to the negative electrode material to achieve prelithiation.

[0004] At present, the common prelithiation method of silicon monoxide is to introduce an organic or inorganic lithium source and achieve prelithiation through a solid-phase calcination method. However, during the high-temperature calcination process, a disproportionation reaction of silicon monoxide will occur, generating silicon grains and silicon dioxide; in addition, due to the uneven solid-phase reaction on the surface, it is difficult to control the uniformity and degree of lithium supplementation, affecting the electrochemical performance of the material.

[0005] For example, the patent application with the publication number CN108417814A provides a lithium battery negative electrode material with organic lithium salt prelithiation and a preparation method thereof. A lithium-rich organic matter is obtained by reacting a lithium source with an organic solvent containing hydroxyl and nitrile groups, and then the negative electrode material is coated with the lithium-rich organic matter to obtain a lithium battery negative electrode material with organic lithium salt prelithiation. However, in its prelithiation process, high-temperature hot melt coating is used to obtain the prelithiated lithium battery negative electrode material, the process is complex, the equipment requirements are high, the economic benefits are poor, and it is not conducive to large-scale commercial promotion.

[0006] The invention disclosed in the authorization number CN112701267B discloses a composite structure with an inner layer of Li2SiO3, a middle layer of Li2Si2O5, and an outermost layer of a carbon layer, which reduces the surface pH value of the material and improves the processing performance and cycling performance of the material. However, the material prelithiation uses organic lithium salts, and the prelithiation conditions are demanding, toxic, and costly.

[0007] There are still many difficulties to be overcome in the current prelithiation methods in practical applications, such as a series of problems including complex processes, harsh preparation conditions, poor compatibility with existing battery systems, and poor operability, which are problems that need to be urgently solved by those skilled in the art. Summary of the Invention

[0008] In view of the deficiencies of the prior art, the present invention provides a rapid prelithiation method for a high initial efficiency silicon monoxide negative electrode material. Using metallic lithium or lithium salt as a solid source and SF6 (or CF4, N2, etc.) as a gas source, a lithium-rich layer is in-situ constructed on the surface of silicon monoxide through plasma chemical vapor deposition to form a high initial efficiency silicon monoxide negative electrode material. The preparation process of the present invention is simple, low-cost, and environmentally friendly, and the obtained silicon monoxide negative electrode material has excellent electrochemical performance.

[0009] In order to achieve the above object, the specific technical solution of the present invention is as follows:

[0010] The present invention uses metallic lithium (or lithium salt) as a solid source and SF6 (or CF4, N2, etc.) as a gas source, and a lithium-rich layer is in-situ constructed on the surface of silicon monoxide through plasma chemical vapor deposition to obtain a high initial efficiency silicon monoxide negative electrode material. The specific preparation method includes the following steps:

[0011] Under an inert gas, the lithium source and silicon monoxide are mixed, and then under a vacuum state of 20 - 80 Pa, a pyrolysis gas source with a gas flow rate of 40 - 100 sccm is introduced, the radio frequency power is adjusted to 200 - 400 W, the reaction temperature is controlled at 300 - 500 °C, and the reaction time is 30 - 120 s to obtain a high initial efficiency silicon monoxide negative electrode material.

[0012] In some embodiments of the present invention, the lithium source is at least one of metallic lithium, lithium tetrafluoroborate, lithium difluorooxalate borate, lithium difluorodioxalate phosphate, lithium hydride, lithium acetate, lithium oxalate, and lithium carbonate.

[0013] Preferably, the pyrolysis gas source is at least one of SF6, CF4, and N2.

[0014] More preferably, the pyrolysis gas source is SF6.

[0015] Preferably, in the preparation method, under a vacuum state of 40 - 80 Pa, a pyrolysis gas source with a gas flow rate of 40 - 100 sccm is introduced, the radio frequency power is adjusted to 200 - 300 W, the reaction temperature for heat treatment is 400 - 500 °C, and the reaction time is 30 - 120 s.

[0016] More preferably, in the prelithiation method, under a vacuum state of 60 Pa, a pyrolysis gas source with a gas flow rate of 80 sccm is introduced, the radio frequency power is adjusted to 300 W, the reaction temperature for heat treatment is 400 °C, and the reaction time is 90 s.

[0017] In some embodiments of the present invention, the molar ratio of lithium ions in the lithium source to silicon suboxide is 1:20.

[0018] The lithium source can react with the gas source plasma to generate a lithium-rich layer such as LiF and Li2S and deposit on the surface of silicon suboxide. At the same time, the lithium source and silicon suboxide will generate lithium silicate salts under heating conditions. Both the lithium-rich layer and lithium silicate salts can compensate for the lithium loss during the cycling of the battery, achieving the effect of improving the initial Coulomb efficiency.

[0019] The present invention also provides a high-first-efficiency silicon suboxide negative electrode material prepared by the above-mentioned preparation method.

[0020] The present invention also provides the application of the high-first-efficiency silicon suboxide negative electrode material in the preparation of a negative electrode material for a lithium-ion battery.

[0021] Compared with the prior art, the beneficial effects of the present invention are mainly reflected in:

[0022] (1) The present invention provides a new method for preparing a silicon suboxide-based composite material with a short reaction time, environmental friendliness, and easy preparation.

[0023] (2) The silicon suboxide-based composite material provided by the present invention has the characteristic of a high initial Coulomb efficiency as a negative electrode material for a lithium-ion battery, and the initial Coulomb efficiency can be as high as 89.5%. Description of the Drawings

[0024] Figure 1 It is a schematic diagram of a silicon suboxide prelithiation plasma chemical reaction device that can isolate air.

[0025] Figure 2 It is a scanning electron microscope (SEM) image of the high-first-efficiency silicon suboxide negative electrode material prepared in Example 1 of this application.

[0026] Figure 3 It is the first charge-discharge curve of the silicon suboxide negative electrode material prepared in Example 1 of this application and the silicon suboxide without prelithiation. Detailed Embodiments

[0027] The technical solution of the present invention is further described below with reference to specific embodiments, but the protection scope of the present invention is not limited thereto.

[0028] Example 1

[0029] In an argon protective atmosphere, take an appropriate amount of metallic lithium powder, silicon dioxide (where n Li / n siO =1:20) in a quartz boat, place the quartz boat in a quartz tube, seal both ends and keep aside.

[0030] The quartz tube is installed in the plasma reactor ( Figure 1 ), after evacuating the chamber, SF6 was introduced, the gas flow rate was adjusted to 80 sccm, the vacuum degree of the reaction chamber was 60 Pa, the RF power was 300 W, the reaction temperature was 400 ° C, and the reaction time was controlled to 90 s.

[0031] After the reaction is completed, the powder is taken out and fully ground to obtain a high-efficiency silicon dioxide negative electrode material.

[0032] Figure 2 This is a scanning electron microscope image of the high first-efficiency silicon iodine oxide negative electrode material prepared in Example 1 of the present application. The obtained material is micron-sized silicon iodine oxide.

[0033] Example 2

[0034] In an argon protective atmosphere, take an appropriate amount of metallic lithium powder, silicon dioxide (where n Li / n SiO =1:20) in a quartz boat, place the quartz boat in a quartz tube, seal both ends and keep aside.

[0035] The quartz tube was installed in the plasma reactor, and CF4 was introduced after vacuuming. The gas flow rate was adjusted to 40 sccm, the vacuum degree of the reaction chamber was 80 Pa, the RF power was 200 W, the reaction temperature was 500°C, and the reaction time was controlled to 30 s.

[0036] After the reaction is completed, the powder is taken out and fully ground to obtain a high-efficiency silicon dioxide negative electrode material.

[0037] Example 3

[0038] In an argon atmosphere, take appropriate amounts of lithium difluorooxalate borate and silicon dioxide (where n L i / n SiO =1:20) in a quartz boat, place the quartz boat in a quartz tube, seal both ends and keep aside.

[0039] The quartz tube was installed in the plasma reactor, and CF4 was introduced after vacuuming. The gas flow rate was adjusted to 60 sccm, the vacuum degree of the reaction chamber was 20 Pa, the RF power was 400 W, the reaction temperature was 400°C, and the reaction time was controlled to 60 s.

[0040] After the reaction is completed, take out the powder and grind it thoroughly to obtain the high-first-efficiency silicon monoxide negative electrode material.

[0041] Example 4

[0042] Under an argon protection atmosphere, take appropriate amounts of lithium hydride and silicon monoxide (where n Li / n SiO = 1:20) in a quartz boat, place the quartz boat in a quartz tube, and seal both ends for later use.

[0043] Install the quartz tube in a plasma reactor, evacuate it and then introduce N2, adjust the gas flow rate to 100 sccm, the reaction chamber vacuum degree to 40 Pa, the radio frequency power to 300 W, the reaction temperature to 400 °C, and control the reaction time to 120 s.

[0044] After the reaction is completed, take out the powder and grind it thoroughly to obtain the high-first-efficiency silicon monoxide negative electrode material.

[0045] Test Example 1

[0046] Assemble the lithium-ion half-cell with the materials prepared in the above examples according to the following method.

[0047] Using water as a solvent, prepare a slurry by mixing the conductive agent conductive carbon black (super-P), the binder polyacrylic acid (PAA), and the active material (the above materials) in a mass percentage of 20:20:60, then uniformly coat it on a copper foil, dry it under vacuum at 120 °C for 12 h and then cut it into electrode sheets for later use. Then assemble the above electrode sheets into a lithium-ion half-cell in a glove box under an argon atmosphere. First, stack the positive electrode shell, the above electrode sheet, the separator, the lithium sheet, the stainless steel gasket, the spring piece, and the negative electrode shell in sequence, and then drop an appropriate amount of electrolyte and seal it. Among them, the battery shell used is of the CR2032 type, the separator is Celgard 2500, and the electrolyte is 1 mol / L LiPF6 / EC-EMC-DEC (1:1:1) + 5% FEC + 1% VC.

[0048] Perform charge-discharge tests on the above battery at a current density of 0.2 A / g. The test results are shown in Table 1.

[0049] Table 1

[0050]

[0051] From Table 1 and Figure 3 it can be seen that it is found that the silicon monoxide negative electrode material prepared in Example 1 shows an initial discharge specific capacity of 1971.9 mAh / g when used as the negative electrode material of a lithium-ion battery, and the Coulomb efficiency is increased from 69.6% to 89.5%, demonstrating excellent electrochemical performance.

Claims

1. A preparation method of a high-first-efficiency silicon monoxide negative electrode material, characterized in that, Under an inert gas, a lithium source and silicon monoxide are mixed at a molar ratio of lithium ions in the lithium source to silicon monoxide of 1:

20. Then, under a vacuum of 20 - 80 Pa, a pyrolysis gas source with a gas flow rate of 40 - 100 sccm is introduced. The radio frequency power is adjusted to 200 - 400 W, the reaction temperature is controlled at 300 - 500 °C, and the reaction time is 30 - 120 s to obtain a high-first-efficiency silicon monoxide negative electrode material.

2. The preparation method of the high-first-efficiency silicon monoxide negative electrode material according to claim 1, wherein The lithium source is at least one of metallic lithium, lithium tetrafluoroborate, lithium difluorooxalate borate, lithium difluorodioxalate phosphate, lithium hydride, lithium acetate, lithium oxalate, and lithium carbonate.

3. The preparation method of the high-first-efficiency silicon monoxide negative electrode material according to claim 1, characterized in that, The pyrolysis gas source is at least one of SF6, CF4, and N2.

4. The preparation method of the high-first-efficiency silicon monoxide negative electrode material according to claim 3, characterized in that The pyrolysis gas source is SF6.

5. The preparation method of the high-first-efficiency silicon monoxide negative electrode material according to claim 1, characterized in that, In the preparation method, under a vacuum of 40 - 80 Pa, a pyrolysis gas source with a gas flow rate of 40 - 100 sccm is introduced. The radio frequency power is adjusted to 200 - 300 W, the reaction temperature for heat treatment is 400 - 500 °C, and the reaction time is 30 - 120 s.

6. The preparation method of the high-first-efficiency silicon monoxide negative electrode material according to claim 5, wherein, In the preparation method, under a vacuum of 60 Pa, a pyrolysis gas source with a gas flow rate of 80 sccm is introduced. The radio frequency power is adjusted to 300 W, the reaction temperature for heat treatment is 400 °C, and the reaction time is 90 s.

7. A high-first-efficiency silicon monoxide negative electrode material prepared by the preparation method according to any one of claims 1 - 6.

8. Use of the high-first-efficiency silicon monoxide negative electrode material according to claim 7 in the preparation of a negative electrode material for a lithium-ion battery.

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