A silicon monoxide / silicon oxynitride composite material, its preparation and application

Abstract

The present invention belongs to the technical field of anode materials for lithium secondary batteries, and specifically discloses a silicon monoxide / silicon oxynitride composite material, which is coated with a dense amorphous silicon oxynitride layer on the surface of silicon monoxide; in addition, the present invention also provides a preparation method and application of the composite material. The composite material of the present invention not only does not hinder the normal transmission of active ions such as Li+, but also helps to reduce the capacity loss of the battery under high-temperature storage conditions. When the material is assembled into a battery, the high-temperature storage performance of the battery can be significantly improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of anode materials, and particularly relates to a novel anode active material for lithium secondary batteries. Background Art

[0002] Lithium-ion batteries are an important type of secondary battery and are widely used in consumer electronics, new energy vehicles, and large-scale grid energy storage due to their high energy density, long cycle life, and other advantages. In recent years, the rapid popularization of new energy vehicles has not only strongly promoted the development of the battery industry but also put forward many new requirements for battery technology. For example, the current range anxiety of new energy vehicles requires people to further improve the energy density of the battery, and the anxiety about charging speed requires people to further improve the rate performance of the battery. At the same time, due to the usage conditions and service life of the vehicle, the high-temperature storage performance of power batteries is also very important. The high-temperature storage test of power batteries generally refers to charging the battery fully and then storing it at a high temperature of 60°C for a fixed number of days, and then testing the capacity recovery rate after recharging and discharging. Since the electrolyte that is active at high temperatures is very likely to undergo side reactions with the electrode material, improving the high-temperature storage performance requires further optimizing the composition and structure of the electrode material, especially the interface in contact with the electrolyte.

[0003] Silicon monoxide has received strong attention in the battery industry because its mass specific capacity is much higher than that of graphite (1600 mAh / g vs 360 mAh / g). Leading battery manufacturers have added silicon monoxide to the anode to improve the energy density of the battery. However, currently, the addition amount of silicon monoxide is generally less than 5%, and more addition will cause the deterioration of battery performance. Among them, the deterioration of the high-temperature storage performance (capacity recovery ability after high temperature) is one of the most important problems. Although commercial silicon monoxide is carbon-coated to change its surface properties, its high-temperature storage performance still cannot meet the requirements. Therefore, it is urgent to find a method to improve the high-temperature storage performance of silicon monoxide to meet the increasing demand for higher energy density of power batteries. Summary of the Invention

[0004] To solve the problem of poor high-temperature storage performance of silicon monoxide, the first object of the present invention is to provide a composite material of silicon monoxide / silicon oxynitride, aiming to provide a material with a novel structure and excellent high-temperature capacity recovery rate.

[0005] The second object of the present invention is to provide a preparation method for the composite material of silicon monoxide / silicon oxynitride described above.

[0006] The third object of the present invention is to further provide the application of the composite material of silicon monoxide / silicon oxynitride in lithium secondary batteries and the obtained lithium secondary batteries.

[0007] A silicon monoxide / silicon oxynitride composite material, comprising a silicon monoxide core and an amorphous silicon oxynitride layer coated in situ on its surface;

[0008] The coating integrity of the silicon oxynitride layer is ≥98%; the degree of amorphousness is ≥95%.

[0009] In the present invention, the high-amorphous silicon oxynitride layer is coated in situ and integrally on the surface of the silicon monoxide, so that the high-temperature storage stability of the material can be unexpectedly improved, and the capacity recovery rate after high temperature can be improved.

[0010] In the present invention, the combined action of the in-situ composite structure, the high coating integrity of the nitrogen oxide, and the high degree of amorphousness is the key to synergistically improving the high-temperature storage stability of the composite material. In the present invention, the in-situ composite means that the coating layer is directly formed by in-situ transformation of the material on the core surface, and the two are tightly combined and there is a material interface. The coating integrity described in the present invention refers to the degree of coating of the silicon oxynitride layer on the core.

[0011] In the present invention, the silicon oxynitride layer is coated in situ, integrally and densely on the surface of the silicon monoxide.

[0012] The silicon oxynitride layer of the present invention is a thin coating layer, and its thickness is preferably 5-20 nm, more preferably 8-15 nm. The mass fraction of the silicon oxynitride is, for example, 3-8%.

[0013] The present invention also provides a method for preparing the silicon monoxide / silicon oxynitride composite material, wherein the silicon monoxide particles are subjected to liquid-phase surface oxidation treatment to form an oxide layer on the surface of the silicon monoxide; then ammoniation treatment is carried out in an ammonia atmosphere to in-situ convert the oxide layer into silicon oxynitride, thereby obtaining the silicon monoxide / silicon oxynitride composite material;

[0014] The temperature in the ammoniation treatment stage is 750-850 °C, and the partial pressure of ammonia is 0.05-0.2 atm.

[0015] In an earlier attempt of the present invention, a silicon oxynitride layer was formed on the surface of silicon suboxide by methods such as direct ammoniation and CVD. However, through extensive research, it was difficult to successfully obtain a material with good high-temperature storage performance. The main reasons for this were that the conditions during the treatment process were harsh and difficult to prepare, and during the coating process of silicon suboxide, there were problems such as excessive crystal transformation, increased aggregation of silicon nanocrystals, poor integrity of the silicon oxynitride coating and matrix binding ability, and unsatisfactory degree of amorphization. In view of this preparation difficulty, the inventor of the present invention, through in-depth research, found that by innovatively pre-treating silicon suboxide with liquid-phase surface oxidation, further combined with the combined control of low-pressure ammoniation and temperature, in-situ tight coating can be achieved under mild conditions, and it can effectively avoid the problems of silicon suboxide during the coating process, improve the coating integrity and the binding stability of the matrix, improve the degree of amorphization of the coating layer, effectively improve the high-temperature storage stability of the prepared material, and improve the capacity recovery rate after high temperature.

[0016] In the present invention, the combination of the liquid-phase surface oxidation-low-pressure ammoniation is the key to synergistically solving the problems of excessive crystal transformation of silicon suboxide and the increase of nanocrystals, improving the coating rate and the degree of amorphization of silicon oxynitride, improving the in-situ dense coating effect, and improving the high-temperature storage stability.

[0017] In the present invention, there is no special requirement for the particle size of the silicon suboxide particles, as long as they can meet the requirements for use as the anode material. For example, its D50 can be 2-8 microns.

[0018] In the present invention, the treatment solution for the liquid-phase surface oxidation is preferably an acid solution containing hydrogen peroxide. Preferably, in the treatment solution, the weight concentration of H2O2 in hydrogen peroxide is 10-35%; the acid is, for example, at least one of sulfuric acid and nitric acid. Further preferably, in the treatment solution, the volume content of hydrogen peroxide is, for example, 20-40%. The acid solution containing hydrogen peroxide can be, for example, a piranha solution.

[0019] Preferably, the temperature for the liquid-phase surface oxidation treatment is room temperature, and the temperature range of the room temperature is, for example, 5-45°C.

[0020] The time for the liquid-phase surface oxidation treatment can be adjusted as needed, and is preferably 2-10 minutes, for example.

[0021] In the present invention, after the liquid-phase surface oxidation treatment, an oxide layer modified with oxygen-containing groups such as hydroxyl groups can be formed on the silicon suboxide, which helps to carry out subsequent in-situ ammoniation and in-situ conversion coating at a lower temperature, and improves the coating degree and the degree of amorphization.

[0022] In the present invention, the ammoniation roasting is carried out in a conventional tube furnace.

[0023] In the present invention, the ammonia atmosphere in the ammoniation roasting stage is provided by the introduced ammonia, or a solid and / or liquid ammonia source that can release ammonia at the ammoniation temperature; preferably, it is provided by the introduced ammonia.

[0024] In the present invention, the silicon monoxide treated by liquid-phase surface oxidation is placed in the reaction chamber. The reaction chamber is evacuated in advance, and then ammonia is introduced and heated for ammoniation treatment. The degree of vacuum is, for example, less than or equal to 10 Pa.

[0025] In the present invention, under the said oxidation treatment, ammoniation roasting is further carried out under the said low pressure and at the said temperature, so that in-situ transformation of the oxide layer can be successfully achieved, and the coating integrity and the degree of amorphization can be improved.

[0026] In the present invention, the temperature of the ammoniation treatment is preferably 800 - 850 °C.

[0027] In the present invention, the time of the ammoniation treatment is 1 - 5 hours.

[0028] The present invention also provides an application of the silicon monoxide / silicon oxynitride composite material, which is used as the negative electrode active material of a lithium secondary battery.

[0029] In the present invention, using the said composite material as the negative electrode active material can effectively improve the high-temperature storage stability of the battery and the capacity recovery rate after high temperature.

[0030] In the present invention, the silicon monoxide / silicon oxynitride composite material can be prepared into a negative electrode material, a negative electrode slurry, a negative electrode sheet, and a lithium secondary battery based on existing means. The said lithium secondary battery is a lithium-ion battery.

[0031] The present invention also provides a lithium secondary battery, which includes the said silicon monoxide / silicon oxynitride composite material.

[0032] Preferably, the said silicon monoxide / silicon oxynitride composite material is compounded on the negative electrode sheet.

[0033] Advantageous effects:

[0034] 1. The present invention provides a composite material in which amorphous silicon oxynitride is formed by in-situ transformation on the surface of silicon monoxide, and this composite material has excellent high-temperature storage stability;

[0035] 2. Innovatively, through the combined process of liquid-phase surface oxidation and low-pressure ammoniation, the present invention can effectively solve many technical difficulties, such as the surface of silicon suboxide being difficult to successfully coat with silicon oxynitride, the silicon suboxide being prone to excessive crystal transformation and the nanocrystals being overly enlarged during the coating process, the coating integrity of the coating layer being not ideal, and the degree of amorphization being not high. Through the described preparation method, an amorphous silicon oxynitride can be in-situ transformed and formed on the surface of silicon suboxide, achieving a complete coating of the original state of silicon suboxide, and a new material with excellent high-temperature storage stability can be constructed. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a high-resolution transmission electron microscope photograph of the material obtained in Example 1. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0037] The present invention will be described in detail below with reference to the embodiments, but the present invention is not limited thereto.

[0038] In the following cases, the solution in the surface treatment (liquid-phase surface oxidation) stage takes the piranha solution as an example, which is a mixed solution of concentrated sulfuric acid and 30% hydrogen peroxide, and the volume ratio of the two is 7:3. The described surface treatment solution is only an example and does not constitute a necessary limitation of the surface treatment.

[0039] The temperature in the surface treatment stage is room temperature.

[0040] Example 1

[0041] 1) Select silicon suboxide with a particle size D50 of 8 microns for surface treatment, that is, soak it in the piranha solution for 2 minutes to make the surface of the silicon suboxide carry abundant hydroxyl groups.

[0042] 2) Place the surface-treated silicon suboxide in a rotatable rotary furnace and evacuate the furnace. Under vacuum conditions, heat it up to the specified temperature of 850 °C (ammoniation treatment temperature), and introduce a small flow of ammonia for reaction. During the reaction process, observe the pressure change in the furnace and timely adjust the ammonia flow rate to keep the pressure in the furnace at about 0.2 atmospheres.

[0043] 3) After reacting for 5 hours in the above state, stop introducing ammonia, replace the ammonia in the furnace with argon, and cool it down to room temperature under argon protection to obtain the obtained product. The TEM image is shown in Figure 1 , it can be seen that the silicon oxynitride is in an amorphous state and is densely and uniformly coated on the surface of the silicon suboxide. After testing, the thickness of the silicon oxynitride layer of this product is 15 nm, the mass fraction is 6%, the degree of amorphization is 96.5%, and the coating integrity reaches 98.2%.

[0044] Example 2

[0045] 1) Select silicon suboxide with a particle size D50 of 5 microns for surface treatment, that is, immerse it in piranha solution (a mixture of concentrated sulfuric acid and hydrogen peroxide) for 4 minutes to make the surface of silicon suboxide carry abundant hydroxyl groups.

[0046] 2) Place the surface-treated silicon suboxide in a rotatable rotary furnace and evacuate the furnace to vacuum. Heat it to the specified temperature of 800 °C under vacuum conditions and introduce a small flow of ammonia for reaction. During the reaction process, observe the change in the furnace pressure and adjust the ammonia flow rate in a timely manner to keep the furnace pressure at about 0.1 atmosphere.

[0047] 3) After reacting for 3 hours under the above conditions, stop introducing ammonia, replace the ammonia in the furnace with argon, and cool it to room temperature under argon protection to obtain the resulting product. After testing, the thickness of the silicon oxynitride layer of this product is 12 nm, the mass fraction is 5%, the degree of amorphization is 97.7%, and the coating integrity reaches 98.5%.

[0048] Example 3

[0049] 1) Select silicon suboxide with a particle size D50 of 3 microns for surface treatment, that is, immerse it in piranha solution (a mixture of concentrated sulfuric acid and hydrogen peroxide) for 8 minutes to make the surface of silicon suboxide carry abundant hydroxyl groups.

[0050] 2) Place the surface-treated silicon suboxide in a rotatable rotary furnace and evacuate the furnace to vacuum. Heat it to the specified temperature of 750 °C under vacuum conditions and introduce a small flow of ammonia for reaction. During the reaction process, observe the change in the furnace pressure and adjust the ammonia flow rate in a timely manner to keep the furnace pressure at about 0.05 atmosphere.

[0051] 3) After reacting for 1.5 hours under the above conditions, stop introducing ammonia, replace the ammonia in the furnace with argon, and cool it to room temperature under argon protection to obtain the resulting product. After testing, the thickness of the silicon oxynitride layer of this product is 8 nm, the mass fraction is 4%, the degree of amorphization is 98.3%, and the coating integrity reaches 98.9%.

[0052] Comparative Example 1

[0053] Use the same silicon suboxide as in Example 1 without any treatment.

[0054] Comparative Example 2

[0055] Compared with Example 1, the difference is only that no silicon oxynitride coating is made, but carbon coating is made in the same way as the current commercial method. The difference is that acetylene is used to replace the ammonia, acetylene is introduced after 800 °C, and the introduction of acetylene is stopped after reacting for 3 hours. Cool it to room temperature in an argon atmosphere to obtain the required product.

[0056] Comparative Example 3:

[0057] Compared with Example 1, the difference is that the surface treatment of silicon suboxide is carried out by gas-phase thermal oxidation. Specifically:

[0058] 1) First, place the silicon suboxide in a heat treatment furnace and heat it to 650 °C in an air atmosphere, and keep it warm for 30 min.

[0059] 2) Place the surface-treated silicon suboxide in a rotatable rotary furnace, and evacuate the furnace to vacuum. Heat it to the specified temperature of 850 °C under vacuum conditions, and introduce a small flow of ammonia for reaction. During the reaction process, observe the change of the pressure in the furnace and timely adjust the ammonia flow rate so that the pressure in the furnace is maintained at about 0.2 atmospheres.

[0060] 3) After reacting for 5 hours in the above state, stop introducing ammonia, replace the ammonia in the furnace with argon, and cool it to room temperature under argon protection to obtain the obtained product. After testing, the thickness of the silicon oxynitride layer of this product is 1 nm, the mass fraction is 1.2%, the degree of amorphization is 96.1%, and the coating integrity is 65.7%.

[0061] Comparative Example 4:

[0062] Compared with Example 1, the difference is that a layer of silicon oxide is covered on the surface of silicon suboxide in a non-in-situ manner. Specifically:

[0063] 1) Adopt the simple and reproducible stober method, that is, dissolve the silicon suboxide in deionized water and anhydrous ethanol solution. Then add ammonia water (25 wt.%) and stir, and then slowly add TEOS (tetraethyl orthosilicate solution, 10 vol.%) with a pipette, and stir evenly at room temperature. After the reaction, wash by centrifugation with anhydrous ethanol and dry in vacuum to cover a layer of silicon oxide on the surface of silicon suboxide.

[0064] 2) Place the surface-treated silicon suboxide in a rotatable rotary furnace, and evacuate the furnace to vacuum. Heat it to the specified temperature of 850 °C under vacuum conditions, and introduce a small flow of ammonia for reaction. During the reaction process, observe the change of the pressure in the furnace and timely adjust the ammonia flow rate so that the pressure in the furnace is maintained at about 0.2 atmospheres.

[0065] 3) After reacting for 5 hours in the above state, stop introducing ammonia, replace the ammonia in the furnace with argon, and cool it to room temperature under argon protection to obtain the obtained product. After testing, the thickness of the silicon oxynitride layer of this product is 12 nm, the mass fraction is 13%, the degree of amorphization is 93.1%, and the coating integrity is 57.7%.

[0066] Comparative Example 5:

[0067] Compared with Example 1, the only difference is that the pressure of ammonia gas in the ammoniation treatment stage is maintained at 0.5 atm. The degree of amorphization of the silicon oxynitride layer is 91.4%, and the coating integrity is 72.6%.

[0068] Comparative Example 6:

[0069] Compared with Example 1, the only difference is that the temperature of the ammoniation treatment is 1000 °C. The degree of amorphization of the silicon oxynitride layer is 39.2%, and the coating integrity is 92.9%.

[0070] Comparative Example 7:

[0071] Compared with Example 1, the only difference is that no liquid-phase surface treatment is carried out, but it is directly treated under the said temperature and ammonia gas atmosphere. Phase analysis of the product shows that no silicon oxynitride component is detected.

[0072] Performance Test

[0073] The electrode active materials (negative electrode active materials) of Examples 1 to 3 and those of Comparative Examples 1 to 6 are made into a negative electrode material with a capacity of 500 mAh / g by mixing with the same commercial graphite material for lithium-ion batteries, and a soft-pack battery with a capacity of 1.5 Ah (size: 60 * 40 * 2 mm) is designed for battery performance testing. The ratio of the negative electrode slurry is electrode material: thickener (CMC): binder (SBR): conductive agent (SP) = 95:2:1.5:1.5. After the slurry is stirred evenly, it is coated on the copper foil and then dried under vacuum. The positive electrode is the coated ternary NCM622 material, and the N / P ratio is 1.1:1. The electrolyte is 1 mol / L lithium hexafluorophosphate (LiPF6) electrolyte dissolved in an electrolyte composed of ethylene carbonate (EC) and diethyl carbonate (DEC) with a volume ratio of 1:1. The battery is placed in a constant-temperature oven at 60 °C in a fully charged state, and the capacity of the battery is tested after storing for seven days. The capacity retention rate is obtained by dividing this capacity by the initial capacity. Then, after the battery is charged and discharged once at a current of 0.2C / 0.5C, the capacity recovery rate of the battery at this time is obtained by dividing the capacity by the initial capacity. The capacity retention rate represents the capacity retention degree of the battery after high-temperature storage, and the capacity recovery rate represents the capacity retention rate of the battery under normal charge and discharge conditions after high-temperature storage.

[0074] Table 1: Test Results of Examples and Comparative Examples

[0075] Material Capacity retention rate Capacity recovery rate Example 1 99.1％ 99.5％ Example 2 98.8％ 99.3％ Example 3 98.7％ 99.2％ Comparative example 1 91.1％ 93.2％ Comparative example 2 94.3％ 95.3％ Comparative example 3 92.5％ 94.1％ Comparative example 4 93.9％ 95.3％ Comparative example 5 96.1％ 96.8％ Comparative example 6 90.8％ 92.5％ Comparative example 7 90.3％ 92.1％

[0076] As can be seen from Table 1, when the initial capacity of the battery is 1.5 Ah, Examples 1 - 3 all show higher capacity retention rates and capacity recovery rates than Comparative Examples 1 - 7. It can be seen that the negative electrode material of the present invention indeed exhibits better high-temperature storage performance.

Claims

1. A silicon suboxide / silicon oxynitride composite material, characterized in that, It includes a silicon monoxide core and an amorphous silicon oxynitride layer coated on its surface in-situ; The coating integrity of the silicon oxynitride layer is ≥98%; the degree of amorphousness is ≥95%; The silicon monoxide / silicon oxynitride composite material is prepared by the following method: performing liquid-phase surface oxidation treatment on silicon monoxide particles to form an oxide layer on the surface of silicon monoxide; then performing ammoniation treatment in an ammonia atmosphere to in-situ convert the oxide layer into silicon oxynitride, thereby obtaining the silicon monoxide / silicon oxynitride composite material; The temperature in the ammoniation treatment stage is 750 - 850 °C, and the partial pressure of ammonia is 0.05 - 0.2 atm.

2. The silicon suboxide / silicon oxynitride composite material according to claim 1, characterized in that, The thickness of the silicon oxynitride layer is 5 - 20 nm, and the mass fraction is 3 - 8%.

3. A method for preparing the silicon suboxide / silicon oxynitride composite material according to claim 1 or 2, characterized in that, Perform liquid-phase surface oxidation treatment on silicon monoxide particles to form an oxide layer on the surface of silicon monoxide; then perform ammoniation treatment in an ammonia atmosphere to in-situ convert the oxide layer into silicon oxynitride, thereby obtaining the silicon monoxide / silicon oxynitride composite material; The temperature in the ammoniation treatment stage is 750 - 850 °C, and the partial pressure of ammonia is 0.05 - 0.2 atm.

4. The method for preparing the silicon suboxide / silicon oxynitride composite material according to claim 3, characterized in that, The D50 of the silicon monoxide particles is 2 - 8 microns.

5. The method for preparing the silicon suboxide / silicon oxynitride composite material according to claim 3, characterized in that, The treatment liquid for liquid-phase surface oxidation is an acid solution containing hydrogen peroxide.

6. The method for preparing the silicon suboxide / silicon oxynitride composite material according to claim 5, characterized in that, In the treatment liquid, the weight concentration of H2O2 in hydrogen peroxide is 10 - 35%; the acid is at least one of sulfuric acid and nitric acid.

7. The method for preparing the silicon suboxide / silicon oxynitride composite material according to claim 6, characterized in that, In the treatment liquid, the volume content of hydrogen peroxide is 20 - 40%.

8. The method for preparing the silicon suboxide / silicon oxynitride composite material according to claim 5, characterized in that, The acid solution containing hydrogen peroxide is a piranha solution.

9. The method for preparing the silicon suboxide / silicon oxynitride composite material according to claim 3, characterized in that, The temperature of the liquid-phase surface oxidation treatment is room temperature.

10. The method for preparing the silicon suboxide / silicon oxynitride composite material according to claim 3, characterized in that, The time of the liquid-phase surface oxidation treatment is 2 - 10 minutes.

11. The method for preparing the silicon suboxide / silicon oxynitride composite material according to claim 3, characterized in that, The ammonia atmosphere in the ammoniation roasting stage is provided by the introduced ammonia, or a solid and / or liquid ammonia source that can release ammonia at the ammoniation temperature.

12. The method for preparing the silicon suboxide / silicon oxynitride composite material according to claim 11, characterized in that, The ammonia atmosphere in the ammoniation roasting stage is provided by the introduced ammonia.

13. The method for preparing the silicon suboxide / silicon oxynitride composite material according to claim 3, characterized in that, Place the silicon monoxide subjected to liquid-phase surface oxidation treatment in the reaction chamber, evacuate the reaction chamber in advance, and then introduce ammonia and heat for ammoniation treatment.

14. The method for preparing the silicon suboxide / silicon oxynitride composite material according to claim 13, characterized in that, The vacuum degree is less than or equal to 10 Pa.

15. The method for preparing a silicon monoxide / silicon oxynitride composite material according to claim 3, characterized in that The time of the ammoniation treatment is 1 - 5 hours.

16. An application of the silicon monoxide / silicon oxynitride composite material according to any one of claims 1 to 2 or the silicon monoxide / silicon oxynitride composite material prepared by the preparation method according to any one of claims 3 to 15, characterized in that Use it as the negative electrode active material of a lithium secondary battery.

17. The application according to claim 16, characterized in that Use it to prepare the negative electrode of a lithium secondary battery.

18. The application according to claim 16 or 17, characterized in that The lithium secondary battery is a lithium-ion battery.

19. A lithium secondary battery, characterized in that It includes the silicon monoxide / silicon oxynitride composite material described in any one of claims 1 - 2 or the silicon monoxide / silicon oxynitride composite material prepared by the preparation method described in any one of claims 3 - 15.

20. The lithium secondary battery according to claim 19, characterized in that The negative electrode sheet is compounded with the silicon monoxide / silicon oxynitride composite material.

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