A germanium-doped amorphous silicon monoxide composite material, a preparation method and application thereof

Abstract

The application belongs to the technical field of battery negative electrode materials, and particularly relates to a germanium-doped amorphous silicon monoxide composite material, which comprises amorphous silicon monoxide and germanium atoms at substitution sites of silicon. In addition, the application also comprises a preparation method of the material and application of the material in lithium secondary batteries. The preparation method of the application comprises the following steps: melting germanium and silicon and then cooling to form a silicon-germanium solid solution; performing a disproportionation reaction on the silicon-germanium solid solution and silicon dioxide under vacuum, and cooling the reaction gas to recover the germanium-doped amorphous silicon monoxide composite material. The material has excellent electrochemical performance, and in particular has excellent fast charging performance.

Description

Technical Field

[0001] This method relates to the field of negative electrode material technology, and in particular to a negative electrode active material for improving the fast charge and discharge performance of lithium-ion batteries. Background Technology

[0002] Lithium-ion batteries are a crucial type of rechargeable battery, widely used in new energy vehicles, consumer batteries, and large-scale grid energy storage. New energy vehicles, in particular, consume a large volume of batteries, and their growth rate is extremely rapid, resulting in power batteries accounting for over 60% of the entire lithium-ion battery market.

[0003] To improve battery energy density, silicon has become the most promising next-generation anode material due to its highest theoretical specific capacity. Among them, silicon suboxide anode has been widely used in the field of power batteries due to its much higher specific capacity (1600mAh / g vs 360mAh / g) and excellent cycle stability compared to graphite.

[0004] However, silicon suboxide itself has poor kinetic properties, specifically low electrical conductivity and Li+ conductivity, which makes its battery fast charge and discharge performance unable to meet consumer needs.

[0005] Jung-In Lee et al. (Chemical-assisted thermal disproportionation of porous silicon monoxide into silicon-based multicomponent systems, Angew. Chem. Int. Ed. 2012, 51, 2767-2771) prepared porous SiO using Ag-catalyzed chemical etching. This SiO exhibited higher capacity retention at 3C current rates compared to dense SiO. However, the porous SiO structure is brittle and cannot pass the high-strength rolling test required for electrode materials in the battery industry. Junying Zhang et al. (High-performance ball-milled SiO) x (Anodes for lithium ion batteries, Journal of PowerSources, 2017, 339, 86-92) Modifying SiO through high-energy ball milling resulted in improved rate performance. According to the data in the article, its 0.5C / 0.0625C capacity ratio was 79.3%, which is an improvement compared to the unmodified SiO, but still cannot meet the actual usage requirements of batteries.

[0006] Therefore, there is an urgent need to develop a method to improve the dynamic performance of silicon suboxide to meet the requirements of power batteries for rapid charging and discharging. Summary of the Invention

[0007] To address the issue that existing silicon suboxide active materials still have unsatisfactory fast-charging performance, the primary objective of this invention is to provide a germanium-doped amorphous silicon suboxide composite material (also referred to as the composite material in this invention) that aims to reduce internal resistance and improve fast-charging performance.

[0008] The second objective of this invention is to provide a method for preparing the germanium-doped amorphous silicon suboxide composite material, which aims to improve the fast-charging and other properties of the prepared material.

[0009] The third objective of this invention is to provide the application of the aforementioned germanium-doped amorphous silicon suboxide composite material in lithium secondary batteries and lithium secondary batteries containing the aforementioned composite material.

[0010] A germanium-doped amorphous silicon suboxide composite material includes amorphous silicon suboxide and germanium atoms located at substitution sites on silicon.

[0011] This invention has discovered that by innovatively using germanium to replace silicon at substitution sites in amorphous silicon suboxide, the various electrochemical properties of the material can be unexpectedly and effectively improved, especially the battery internal resistance and the fast-charging performance of the material.

[0012] In this invention, germanium atoms are uniformly distributed in amorphous silicon suboxide;

[0013] Preferably, the germanium content is 1-5 wt%;

[0014] Preferably, the degree of amorphization of the germanium-doped amorphous silicon suboxide composite material is ≥95%, and more preferably ≥99.5%.

[0015] A method for preparing a germanium-doped amorphous silicon suboxide composite material involves melting and cooling elemental germanium and silicon to form a silicon-germanium solid solution; subjecting the silicon-germanium solid solution and silicon dioxide to a disproportionation reaction under vacuum; cooling the reaction gas; and recovering the germanium-doped amorphous silicon suboxide composite material.

[0016] Early research by the inventors revealed that the differences in properties between silicon and germanium made it difficult to directly incorporate germanium into the disproportionation reaction of silicon and silicon dioxide to obtain germanium-silicon suboxide materials. Furthermore, the preparation process faced numerous challenges, including the tendency of germanium and silicon to crystallize and separate, poor dispersion uniformity, and low amorphization rate. To address these challenges, the inventors proposed an improved solution that innovatively pre-solutions elemental germanium and silicon, followed by a subsequent vacuum disproportionation reaction. This effectively solves the technical problems of mismatched volatilization temperatures of silicon and germanium, easy crystallization and separation of germanium and silicon, poor dispersion uniformity, and low amorphization rate. This results in a germanium-doped amorphous silicon suboxide composite material with germanium substitution, ultra-high amorphization content, and uniform dispersion. Research has shown that the material prepared using this technique effectively reduces internal resistance and improves fast-charging performance.

[0017] In this invention, the mass ratio of germanium to silicon can be adjusted according to the needs of the product. For example, the mass ratio can be 2-8:100.

[0018] In this invention, there are no special requirements for the melting temperature, as long as it can completely melt both materials. For example, the melting temperature is greater than or equal to 1420°C. Considering energy consumption, the preferred melting temperature is 1450-1500°C.

[0019] In this invention, there are no special requirements for the melting time; simply melting the two materials is sufficient. Considering energy efficiency, the preferred melting time is 1 to 10 hours.

[0020] In this invention, existing methods can be used to cool the molten liquid to form a solid solution.

[0021] Preferably, the molten germanium and silicon are rapidly quenched to obtain the silicon-germanium solid solution. Studies have found that using a rapid quenching process to obtain the solid solution facilitates subsequent disproportionation reactions and improves the fast-charging performance of the resulting composite material.

[0022] Preferably, the cooling rate of the melt is ≥50℃ / min, for example, it can be 50~100℃ / min.

[0023] In this invention, the obtained silicon-germanium solid solution can be crushed, for example, to obtain powder with a mesh size of 800 to 1200.

[0024] In this invention, the solid solution is then mixed with silicon dioxide and vaporized under vacuum to form a film.

[0025] In this invention, the particle size of the silicon dioxide is, for example, 800 to 1200 mesh.

[0026] In this invention, the amount of silicon dioxide is greater than the theoretical reaction amount. For example, the mass ratio of silicon dioxide to silicon-germanium solid solution is 210 to 270:100.

[0027] In this invention, the vacuum degree is ≤1 Pa;

[0028] Preferably, the disproportionation reaction temperature is 1300-1400℃;

[0029] Preferably, the disproportionation reaction time is 5-20 hours;

[0030] Preferably, the reactant gas is subjected to rapid cooling to obtain the germanium-doped amorphous silicon suboxide composite material. This invention has found that rapid cooling helps to further improve the electrochemical performance of the prepared material, particularly its fast-charging performance.

[0031] Preferably, the cooling rate of the reaction gas is ≥50℃ / min, for example, 50~100℃ / min.

[0032] In this invention, the collected products can be crushed to obtain a size suitable for use in batteries. For example, D50 is 1-10 micrometers.

[0033] A preferred preparation method of the present invention comprises the following steps:

[0034] First, elemental germanium and elemental silicon are mixed in a ratio of 2-8:100 and heated to above the melting point of silicon (1420℃), for example, 1450-1500℃, under an argon protective atmosphere. This temperature is maintained for 4-5 hours to ensure full fusion of silicon and germanium atoms. Then, the mixture is rapidly cooled to room temperature at a rate ≥50℃ / min to obtain a solid solution with uniformly distributed silicon and germanium.

[0035] The solid solution is then crushed and ground to 1000-1200 mesh, uniformly mixed with 1000-1200 mesh silica, and placed in a vacuum furnace. Grinding to this fine particle size ensures sufficient contact between silicon and silica. The vacuum furnace has a heating chamber and a cooling and collection chamber equipped with a water-cooling device. First, a vacuum of ≤1 Pa is applied, then the mixture is heated in the heating chamber to the reaction temperature of silicon and silica (1300-1400℃) and held for 5-20 hours. At this temperature, silicon and silica react to generate silicon suboxide gas, and germanium atoms dissolved in the silicon matrix also vaporize and enter the collection chamber. The reaction product is collected and cooled in the collection chamber using a water-cooling device, ensuring a cooling rate ≥50℃ / min. Rapid cooling "freezes" the uniformly mixed germanium atoms and silicon suboxide gas, helping to further improve the amorphous state, minimize the precipitation of silicon nanocrystals, and further improve performance. A blocky product is collected. The germanium content was tested to be 1-5%. The composite material was tested by XRD and calculated using Jade software, and the degree of amorphization was found to be 99.95%.

[0036] Beneficial effects

[0037] 1. This invention provides a novel germanium-doped amorphous silicon suboxide composite material, which innovatively utilizes Ge to replace the substitution sites of amorphous silicon suboxide, thereby effectively improving the internal resistance of the material and enhancing its fast-charging performance.

[0038] 2. In this invention, germanium and silicon are pre-solidified and then subjected to subsequent vacuum disproportionation. This solves the technical problem that germanium, silicon and silicon dioxide are difficult to directly disproportionate and dopant, and can effectively improve the electrochemical performance of the material, especially the fast charging performance. Attached Figure Description

[0039] Figure 1 The image shown is a scanning electron microscope image of the product from Example 1. It can be seen that the product consists of uniform particles with a D50 of 5 micrometers.

[0040] Figure 2 The EDS mapping of the product of Example 1 shows that germanium is very uniformly distributed in the particles.

[0041] Figure 3 The XRD pattern of the product in Example 1 shows no sharp peaks, indicating that the product is in an amorphous state. The 20-30° and 50-60° peaks correspond to the diffraction results of amorphous silicon suboxide.

[0042] Figure 4 The image shown is a high-resolution transmission electron microscope image of the product from Example 1, which clearly shows that the product is in a completely amorphous, non-crystalline state. Detailed Implementation

[0043] The present invention will be described in detail below with reference to embodiments, but the present invention is not limited thereto.

[0044] Example 1

[0045] First, elemental germanium and elemental silicon were mixed in a ratio of 2:100, heated to 1450℃ under an argon protective atmosphere, held at that temperature for 5 hours, and then rapidly cooled to room temperature at a rate of 50℃ / min to obtain a solid solution in which silicon and germanium are uniformly distributed.

[0046] The solid solution was crushed and ground to 1000 mesh, then uniformly mixed with 1000 mesh silica and placed in a vacuum furnace (solid solution to silica mass ratio 100:270). The vacuum furnace had a heating chamber and a cooling and collection chamber equipped with a water-cooling device. The vacuum was first evacuated to 0.5 Pa, then the mixture was heated to 1300°C in the heating chamber and held at that temperature for 15 hours. The reaction product was collected and cooled in the collection chamber using a water-cooling device, maintaining a cooling rate of 50°C / min. The collected bulk product was then crushed and ground into particles with a D50 of 10 micrometers to obtain the desired germanium-doped silicon suboxide material. Testing showed that the material contained 1.2% germanium and had an amorphization degree of 99.5%.

[0047] Example 2

[0048] First, elemental germanium and elemental silicon were mixed in a ratio of 5:100, heated to 1450℃ under an argon protective atmosphere, held at that temperature for 5 hours, and then rapidly cooled to room temperature at a rate of about 70℃ / min to obtain a solid solution in which silicon and germanium are uniformly distributed.

[0049] The solid solution was crushed and ground to 1000 mesh, then uniformly mixed with 1000 mesh silica and placed in a vacuum furnace (solid solution to silica mass ratio 100:240). The vacuum furnace had a heating chamber and a cooling and collection chamber equipped with a water-cooling device. The vacuum was first evacuated to 0.1 Pa, then the mixture was heated to 1350°C in the heating chamber and held at that temperature for 10 hours. The reaction product was collected and cooled in the collection chamber using a water-cooling device, maintaining a cooling rate of 70°C / min. The collected bulk product was then further crushed and ground into particles with a D50 of 5 micrometers to obtain the desired germanium-doped silicon suboxide material. Testing showed that the material contained 3% germanium and had an amorphization degree of 99.9%.

[0050] Example 3

[0051] First, elemental germanium and elemental silicon were mixed in a ratio of 8:100, heated to 1450℃ under an argon protective atmosphere, held at that temperature for 5 hours, and then rapidly cooled to room temperature at a rate of 100℃ / min to obtain a solid solution in which silicon and germanium are uniformly distributed.

[0052] The solid solution was crushed and ground to 1000 mesh, then uniformly mixed with 1000 mesh silica and placed in a vacuum furnace (solid solution to silica mass ratio 100:210). The vacuum furnace has a heating chamber and a cooling and collection chamber equipped with a water-cooling device. The vacuum was first evacuated to 0.05 Pa, then the mixture was heated to 1400°C in the heating chamber and held at that temperature for 5 hours. The reaction product was collected and cooled in the collection chamber using a water-cooling device, maintaining a cooling rate of 100°C / min. The collected bulk product was then crushed and ground into particles with a D50 of 3 micrometers to obtain the desired germanium-doped silicon suboxide material. Testing showed that the material had a germanium content of 4.8% and an amorphization degree of 99.95%.

[0053] Example 4

[0054] The adjustment between this embodiment and Embodiment 2 is that the cooling rate when obtaining the silicon-germanium solid solution is 20°C / min. The specific process is as follows:

[0055] First, elemental germanium and elemental silicon are mixed in a ratio of 5:100, heated to 1450℃ under an argon protective atmosphere, held at that temperature for 5 hours, and then rapidly cooled to room temperature at a rate of about 20℃ / min to obtain a silicon-germanium solid solution.

[0056] The solid solution was crushed and ground to 1000 mesh, then uniformly mixed with 1000 mesh silica and placed in a vacuum furnace (solid solution to silica mass ratio of 100:240). The vacuum furnace had a heating chamber and a cooling and collection chamber equipped with a water-cooling device. The vacuum was first evacuated to 0.1 Pa, then the mixture was heated to 1350°C in the heating chamber and held at that temperature for 10 hours. The reaction product was collected and cooled in the collection chamber using a water-cooling device, maintaining a cooling rate of 70°C / min. The collected bulk product was then crushed and ground into particles with a D50 of 5 micrometers to obtain the desired germanium-doped silicon suboxide material. Testing showed that the material contained 3% germanium and had an amorphization degree of 97.5%.

[0057] Example 5:

[0058] The adjustment between this embodiment and Embodiment 2 is that the cooling rate during product collection in the vacuum furnace is 20°C / min. The specific process is as follows:

[0059] First, elemental germanium and elemental silicon were mixed in a ratio of 5:100, heated to 1450℃ under an argon protective atmosphere, held at that temperature for 5 hours, and then rapidly cooled to room temperature at a rate of about 70℃ / min to obtain a solid solution in which silicon and germanium are uniformly distributed.

[0060] The solid solution was crushed and ground to 1000 mesh, then uniformly mixed with 1000 mesh silica and placed in a vacuum furnace (solid solution to silica mass ratio 100:240). The vacuum furnace had a heating chamber and a cooling and collection chamber equipped with a water-cooling device. The vacuum was first evacuated to 0.1 Pa, then the mixture was heated to 1350°C in the heating chamber and held at that temperature for 10 hours. The reaction product was collected and cooled in the collection chamber using a water-cooling device, maintaining a cooling rate of 20°C / min. The collected bulk product was then further crushed and ground into particles with a D50 of 5 micrometers to obtain the desired germanium-doped silicon suboxide material. Testing showed that the material contained 3% germanium and had an amorphization degree of 95%.

[0061] Comparative Example 1

[0062] The only difference between this comparative example and Example 2 is that germanium is not added.

[0063] First, elemental silicon is heated to 1450°C under an argon protective atmosphere and held at that temperature for 5 hours. Then, it is rapidly cooled to room temperature at a rate of 70°C / min to obtain bulk silicon.

[0064] The block was crushed and ground to 1000 mesh, then uniformly mixed with 1000 mesh silica and placed in a vacuum furnace. This vacuum furnace has a heating chamber and a cooling and collection chamber equipped with a water-cooling device. The vacuum was first evacuated to 0.1 Pa, then the mixture was heated to 1350°C in the heating chamber and held at that temperature for 10 hours. The reaction product was collected and cooled in the collection chamber using a water-cooling device, maintaining a cooling rate of 70°C / min. The collected block product was then further crushed and ground into a powder material with a D50 of 5 micrometers. Testing showed that the amorphization degree of this material was 90.1%.

[0065] Comparative Example 2

[0066] Compared to Example 2, the only difference is that germanium and silicon were not pre-solidified; instead, elemental germanium, elemental silicon, and silicon dioxide were directly mixed. That is:

[0067] Germanium, silicon, and silicon dioxide were ground and collected into 1000-mesh powder, which was then placed in a vacuum furnace (composition ratio as in Example 2). This vacuum furnace had a heating chamber and a cooling and collection chamber equipped with a water-cooling device. The vacuum was first evacuated to 0.1 Pa, and then the mixture was heated to 1350°C in the heating chamber and held at that temperature for 10 hours. The reaction product was collected and cooled in the collection chamber using a water-cooling device, maintaining a cooling rate of 70°C / min. The collected bulk product was then further pulverized and ground into a powder material with a D50 of 5 micrometers. Testing showed that the amorphization degree of this material was 91.3%.

[0068] Performance testing

[0069] The materials prepared in Examples 1-5 and Comparative Examples 1-2 were used as electrode materials (active materials) to prepare electrode slurries and electrode sheets. The slurry ratio was electrode material: binder (PAA): conductive agent (SP) = 75:15:10. After the slurry was stirred evenly, it was coated onto copper foil and then dried under vacuum. The dried electrode sheet was used as the working electrode of the coin cell, and the lithium sheet was used as the counter electrode. The electrolyte was 1 mol / L lithium hexafluorophosphate (LiPF6) electrolyte dissolved in ethylene carbonate (EC) and diethyl carbonate (DEC) electrolyte in a volume ratio of 1:1. The initial delithiation specific capacity and initial coulombic efficiency of the above materials were tested at a current density of 0.2C, and the capacity was further tested at currents of 0.5C and 10C. The ratio of the capacity at 10C to 0.5C was used as an indicator of its fast charge and discharge performance. The larger the value, the stronger the fast charge and discharge capability of the material. The constant current charge and discharge voltage range was 0.01-1.5V.

[0070] As shown in Table 1, Examples 1-5 all exhibited lower battery internal resistance than Comparative Examples 1-2, indicating that the incorporation of germanium can improve the conductivity of silicon suboxide. Furthermore, Examples 1-5 all showed a higher 10C / 0.5C capacity ratio, indicating stronger capacity retention at high current rates, i.e., stronger kinetic performance. Therefore, the negative electrode material of this invention does indeed exhibit high kinetic performance.

[0071] Table 1: Test Results of Examples and Comparative Examples

[0072]

[0073]

[0074] As shown in Table 1, the pre-solution followed by vacuum reaction of the present invention can produce a highly amorphous material with germanium substitution at the sites. This material exhibits lower internal resistance and higher fast-charging performance. Furthermore, by combining it with the aforementioned rapid cooling process, the internal resistance and fast-charging performance of the material can be further improved.

Claims

1. A method for producing a germanium-doped amorphous silicon monoxide composite material of a negative electrode active material for a lithium secondary battery, characterized by, The germanium single element and silicon single element are subjected to quenching treatment to obtain a silicon-germanium solid solution; the silicon-germanium solid solution and silicon dioxide are subjected to disproportionation reaction under vacuum, and the reaction gas is subjected to quenching treatment to recover the germanium-doped amorphous silicon monoxide composite material. The mass ratio of the germanium single element to the silicon single element is 2-8:

100. The cooling rate of the quenching of the molten liquid is ≥50℃ / min. The temperature of the disproportionation reaction is 1300-1400℃. The cooling rate of the quenching of the reaction gas is ≥50℃ / min.

2. The method for preparing a germanium-doped amorphous silicon monoxide composite material for a negative electrode active material of a lithium secondary battery according to claim 1, characterized by, The melting temperature is greater than or equal to 1420℃.

3. The method for preparing a germanium-doped amorphous silicon monoxide composite material for a negative electrode active material of a lithium secondary battery according to claim 2, characterized by, The melting temperature is 1450-1500℃.

4. The method for preparing a germanium-doped amorphous silicon monoxide composite material for a negative electrode active material of a lithium secondary battery according to claim 2, characterized by, The melting treatment time is 1-10h.

5. The method for preparing a germanium-doped amorphous silicon monoxide composite material for a negative electrode active material of a lithium secondary battery according to claim 1, characterized by, The cooling rate of the quenching of the molten liquid is 50-100℃ / min.

6. The method for preparing a germanium-doped amorphous silicon monoxide composite material for a negative electrode active material of a lithium secondary battery according to claim 1, characterized by, The vacuum degree of the vacuum is ≤1Pa.

7. The method for preparing a germanium-doped amorphous silicon monoxide composite material for a negative electrode active material of a lithium secondary battery according to claim 1, characterized by, The disproportionation reaction time is 5-20h.

8. The method for preparing a germanium-doped amorphous silicon monoxide composite material for a negative electrode active material of a lithium secondary battery according to claim 1, characterized by, The cooling rate of the quenching of the reaction gas is 50-100℃ / min.

9. The germanium-doped amorphous silicon monoxide composite material for lithium secondary batteries produced by the production method according to any one of claims 1 to 8, characterized by, The germanium-doped amorphous silicon monoxide composite material comprises amorphous silicon monoxide and germanium atoms at the substitution sites of silicon. The germanium atoms are uniformly distributed in the amorphous silicon monoxide. The germanium content is 1-5wt%. The amorphization degree of the germanium-doped amorphous silicon monoxide composite material is ≥95%.

10. Use of a germanium-doped amorphous silicon monoxide composite material produced by the production method according to any one of claims 1 to 8, characterized in that It is used as a negative electrode active material of a lithium secondary battery.

11. Use according to claim 10, wherein the compound is ###0002### It is used as a negative electrode active material, and a conductive agent and a binder are compounded to prepare a negative electrode material of a lithium secondary battery.

12. The use according to claim 11, wherein the compound is ###00010### or a pharmaceutically acceptable salt thereof. The negative electrode material is coated on a current collector to form a negative electrode sheet of a lithium secondary battery.

13. The use according to claim 12, wherein the compound is ###00010### or a pharmaceutically acceptable salt thereof. The negative electrode sheet is used to assemble a lithium secondary battery.

14. Use according to claim 13, wherein The lithium secondary battery is a lithium ion battery.

15. A lithium secondary battery, characterized by comprising: The germanium-doped amorphous silicon monoxide composite material is prepared by the preparation method of any one of claims 1-8.

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