Nanosilicon material, preparation method, application and lithium ion battery thereof

Abstract

The application discloses a kind of nano silicon material and its preparation method, application and lithium ion battery.The method comprises: the mixture containing reducing metal, low melting point metal and silicon dioxide is heated under inert gas protection at 300-700 DEG C and reacts for 2-6h, after cooling to room temperature, low melting point metal and reaction product are separated, then reaction product is washed, dried and grinded again;Low melting point metal includes Ga, and the molar ratio of reducing metal and low melting point metal is 1: (4-50) ;When reducing metal is alkali earth metal element, the molar ratio of reducing metal and silicon dioxide is 1: (0.3-0.5) ;When reducing metal is alkali metal element, the molar ratio of reducing metal and silicon dioxide is 1: (0.2-0.25).The nano silicon material prepared by the preparation method has small size, and has high specific capacity, high cycle and other characteristics when used as anode of lithium ion battery.

Description

Technical Field

[0001] This invention specifically relates to a nano-silicon material, its preparation method, its application, and lithium-ion batteries. Background Technology

[0002] The anode material of lithium-ion batteries is one of the key factors affecting battery performance; therefore, the search and development of high-performance anode materials has always been a research hotspot. Silicon, as a novel anode material, possesses high theoretical specific capacity and good cycle stability, and is considered a potential anode material with enormous application potential. However, silicon exhibits significant volume expansion during charge and discharge, which can lead to electrode material cracking and detachment, thus affecting the battery's cycle performance and lifespan. To address this issue, researchers have proposed many methods, such as silicon nanostructuring and silicon-carbon composite materials.

[0003] Nanoscale silicon anode materials refer to silicon particles whose size is reduced to the nanoscale, thereby improving their electrochemical performance. Nanoscale silicon has a large specific surface area, which is beneficial for lithium storage and increases specific capacity. Furthermore, the size effect of nanoscale silicon can effectively alleviate the volume expansion problem of silicon during charge and discharge, thus improving the cycle stability of the battery. Industrial methods for preparing nanoscale silicon, such as sand milling and vapor deposition, rely on sand mills and precision vacuum equipment, respectively, which present challenges such as high equipment requirements, low production efficiency, difficult equipment maintenance, and limited yield. Therefore, developing controllable solid-phase synthesis methods for preparing nanoscale silicon is an important research direction for the industry.

[0004] Magnesium reduction is a chemical synthesis method for preparing silicon. It generates elemental silicon by reducing silicon dioxide with magnesium at high temperatures. It has advantages such as abundant raw materials, low cost, simple operation, and suitability for large-scale production. However, the magnesium reduction of silicon dioxide is exothermic, which can damage the micro / nano structure of silicon. Therefore, effective temperature and reaction rate control are crucial for the preparation of micron- and nano-sized silicon. Summary of the Invention

[0005] The technical problem solved by this invention is to overcome the shortcomings of conventional magnesium thermal reduction methods for silicon preparation, which cannot effectively control the reaction temperature and rate, leading to the destruction of the silicon structure and the inability to obtain small-sized silicon nanoparticles. This invention provides a nano-silicon material, its preparation method, applications, and lithium-ion batteries. The preparation method of this invention enables the mild and controllable preparation of nano-silicon materials, resulting in small-sized nano-silicon materials that exhibit high specific capacity and high cycle life when used as a negative electrode in lithium-ion batteries.

[0006] This invention introduces a low-melting-point metal (Ga) during the thermal reduction process. This Ga forms a low-melting-point alloy with the reducing metal during the reaction. This low-melting-point alloy exists in the reaction system as a liquid metal and acts as a medium to highly disperse the reducing metal. This allows the reducing metal to react and reduce silicon dioxide at a slower rate at the interface between silicon dioxide and the alloy. This overcomes the problems of the traditional magnesium thermal reduction reaction, which is characterized by its violent and highly exothermic nature, making it difficult to control the product morphology and reaction rate. This method enables the mild and controllable preparation of nano-silicon materials. After the reaction is complete, the low-melting-point metal can be separated from the nano-silicon in liquid form for recycling. This method can produce small-sized nano-silicon particles, which exhibit high specific capacity and high cycle life when used as a negative electrode in lithium-ion batteries.

[0007] The present invention solves the above-mentioned technical problems through the following technical solutions:

[0008] This invention provides a method for preparing nano-silicon materials, comprising the following steps:

[0009] A mixture containing reducing metal, low-melting-point metal and silicon dioxide is heated and reacted at 300-700℃ for 2-6 hours under inert gas protection. After cooling to room temperature, the low-melting-point metal and the reaction product are separated. The reaction product is then washed, dried and ground to obtain nano-silicon material.

[0010] Wherein, the low-melting-point metal includes Ga, and the molar ratio of the reducing metal to the low-melting-point metal is 1:(4-50);

[0011] When the reducing metal is an alkaline earth metal, the molar ratio of the reducing metal to the silicon dioxide is 1:(0.3-0.5).

[0012] When the reducing metal is an alkali metal element, the molar ratio of the reducing metal to the silicon dioxide is 1:(0.2 to 0.25).

[0013] In this invention, the reducing metal and the low-melting-point metal can be commercially available or prepared in-house.

[0014] In this invention, the molar ratio of the reducing metal to the low melting point metal is preferably 1:(5-20), for example 1:5 or 1:10, and more preferably 1:(8-20).

[0015] In this invention, the alkaline earth metal element is preferably Mg and / or Ca.

[0016] In this invention, when the reducing metal is an alkaline earth metal, the molar ratio of the reducing metal to the silicon dioxide is, for example, 1:0.32 or 1:0.48, preferably 1:(0.4 to 0.5).

[0017] In this invention, the alkali metal element is preferably Na and / or K.

[0018] In this invention, when the reducing metal is an alkali metal element, the molar ratio of the reducing metal to the silicon dioxide is, for example, 1:0.22.

[0019] In this invention, the low-melting-point metal may further include In.

[0020] When the low-melting-point metal also includes In, the weight ratio of Ga to In can be (2-4):1, for example 3:1.

[0021] When the low-melting-point metal also includes In, the molar ratio of the reducing metal to the low-melting-point metal is preferably 1:(8-20), for example 1:5, 1:10 or 1:10.2.

[0022] In this invention, the silica can be commercially available or prepared in-house. The silica includes one or more of the following: microsilica powder, quartz sand, silica fume, fumed silica, nano-silica, and porous silica, preferably nano-silica.

[0023] The mesh size of the microsilica powder can be 325 mesh to 1000 mesh, for example, 325 mesh.

[0024] The mesh size of the quartz sand can be 2-600 mesh, for example 40-60 mesh.

[0025] The particle size of the nano-silica can be 5-50 nm, for example 15 nm.

[0026] The pore size of the porous silica can be 10-80 nm, for example, 50 nm.

[0027] In this invention, the preparation method of the mixture can be conventional in the art, such as conventionally grinding the reducing metal, the low-melting-point metal, and the silicon dioxide. The grinding time can be 2-20 minutes, for example, 5 minutes.

[0028] In this invention, the inert gas can be a conventional industrial inert gas, such as nitrogen or argon.

[0029] In this invention, the rate of heating to the heating temperature is preferably 2-5°C / min, for example 2°C / min.

[0030] In this invention, the heating temperature is preferably 500-600°C, for example 550°C.

[0031] In this invention, the heating time is preferably 3-5 hours, for example 4 hours.

[0032] In this invention, after cooling to room temperature, a mixture of the low-melting-point metal and the reaction product is obtained.

[0033] In this invention, the method for separating the low-melting-point metal and the reaction product can be conventional in the art, such as centrifugation. Preferably, before centrifugation, an appropriate amount of ethanol is added to the mixture of the low-melting-point metal and the reaction product to facilitate better stratification. After centrifugation, the low-melting-point metal and the reaction product will separate into layers, with the low-melting-point metal in the lower layer and the reaction product in the upper layer; the reaction product in the upper layer can be aspirated using a syringe.

[0034] In this invention, the washing is preferably performed sequentially using hydrochloric acid or nitric acid, hydrofluoric acid, and a solvent. The washing method can be conventional in the art, such as vacuum filtration. The washing process preferably includes: stirring the material to be washed for 5-20 minutes (e.g., 10 minutes), and then performing vacuum filtration.

[0035] The concentration of the hydrochloric acid or the nitric acid may be 0.05M-2M, preferably 0.1-0.5M, for example 0.2M, 0.3M or 0.5M.

[0036] The concentration of the hydrofluoric acid can be 0.01–10 wt%, preferably 0.5–5 wt%, for example 1 wt%, 2 wt%, or 5 wt%. The wt% refers to the mass ratio of the solute HF to the hydrofluoric acid.

[0037] The solvent may be one or more of deionized water, ethanol, isopropanol and acetone, preferably a mixed solvent of deionized water and ethanol, for example a mixed solvent of deionized water and ethanol in a volume ratio of 1:1.

[0038] In this invention, the number of washing cycles can be conventional in the art, such as 1-3 times.

[0039] In this invention, the drying operation and conditions can be conventional in the art.

[0040] In this invention, the grinding operation and conditions can be conventional in the art, generally using a mortar and pestle. The grinding time can be 1-10 minutes, for example, 5 minutes.

[0041] The present invention also provides a nano-silicon material prepared by the preparation method described above.

[0042] In this invention, the particle size of the nano-silicon material can be 30-500 nm.

[0043] The present invention also provides an application of the aforementioned nano-silicon material in lithium-ion batteries.

[0044] The present invention also provides a lithium-ion battery comprising a positive electrode, a negative electrode, an electrolyte, and a separator, wherein the negative electrode comprises the nano-silicon material as described above.

[0045] Based on common knowledge in the field, the above-mentioned preferred conditions can be combined arbitrarily to obtain various preferred embodiments of the present invention.

[0046] The reagents and raw materials used in this invention are all commercially available.

[0047] The positive and progressive effects of this invention are as follows:

[0048] The preparation method of this invention overcomes the problem that the product morphology and reaction rate are difficult to control due to the violent and highly exothermic characteristics of the traditional magnesium thermal reduction reaction. It can achieve mild and controllable preparation of nano-silicon materials, and the low-melting-point metal used in the reaction process can be recycled. This method can prepare small-sized nano-silicon particles, which have high specific capacity and high cycle life when used as a negative electrode for lithium-ion batteries. Attached Figure Description

[0049] Figure 1 TEM image of the nano-silicon prepared in Example 1;

[0050] Figure 2 This is a SEM image of the nano-silicon prepared in Example 1;

[0051] Figure 3 The images show the XRD patterns of nano-silicon prepared in Examples 1, 7 and Comparative Example 1. Detailed Implementation

[0052] The present invention is further illustrated below by way of embodiments, but the invention is not limited to the scope of the embodiments described herein. Experimental methods in the following embodiments that do not specify specific conditions were performed according to conventional methods and conditions, or as selected according to the product instructions.

[0053] Example 1

[0054] Magnesium powder (Nanjing Reagent, 99.5% purity), gallium (Aladdin, 99.99% purity), and microsilica powder (Hebei Jianshi New Material Technology Co., Ltd., silica purity >99%, 325 mesh) were ground in a molar ratio of 1:10:0.48 for 5 minutes using conventional grinding. The mixture was then placed in a crucible and heated to 550℃ at 2℃ / min in a tube furnace under a high-purity argon atmosphere, held for 4 hours, and then cooled to room temperature. An appropriate amount of ethanol was added to the cooled product (ethanol to Ga volume ratio 1:1), and centrifuged at 3000 r / min for 3 minutes. After centrifugation, stratification occurred. The lower layer is Ga, and the rest of the material remains in the upper layer. The upper layer is extracted using a syringe, and then washed once each with 0.5M dilute hydrochloric acid, 1% wt hydrofluoric acid, and a 1:1 mixture of deionized water and ethanol (washing process: stirring at 200 rpm for 10 minutes on a magnetic stirrer, followed by filtration; during the dilute hydrochloric acid washing process, the volume ratio of the material to be washed to dilute hydrochloric acid is 1:5; the volumes of the hydrofluoric acid, deionized water, and ethanol mixture are all the same as the volume of the dilute hydrochloric acid). After drying, it is ground in a mortar for 5 minutes to obtain the nano-silicon material.

[0055] Example 2

[0056] Compared with Example 1, except that the silica powder was replaced with quartz sand (West Asia reagent, 40-60 mesh), all other parameters and conditions were the same as in Example 1.

[0057] Example 3

[0058] Compared with Example 1, except that the silica powder was replaced with silica (Sias Reagent), all other parameters and conditions were the same as in Example 1.

[0059] Example 4

[0060] Compared with Example 1, except that the micro silica powder was replaced with nano silica (Sias Reagent, particle size 15nm), all other parameters and conditions were the same as in Example 1.

[0061] Example 5

[0062] Compared with Example 1, except that the microsilica powder was replaced with porous silica (Hanzhong Jikang Biological Reagent Co., Ltd., pore size 50nm), all other parameters and conditions were the same as in Example 1.

[0063] Example 6

[0064] Compared with Example 1, except that the molar ratio of magnesium powder:gallium powder:silicon powder was changed to 1:10:0.32, all other parameters and conditions were the same as in Example 1.

[0065] Example 7

[0066] Compared with Example 1, except that the molar ratio of magnesium powder:gallium powder:silicon powder was changed to 1:5:0.48, all other parameters and conditions were the same as in Example 1.

[0067] Example 8

[0068] Compared with Example 1, except that the magnesium powder was replaced with calcium powder (Maclean, 99%), all other parameters and conditions were the same as in Example 1.

[0069] Example 9

[0070] Magnesium powder, gallium powder (Aladdin, 99.9% purity), In powder (Aladdin, 99.99% purity), and microsilica powder (Jianshi, silica purity >99%, 325 mesh) were weighed and ground for 5 minutes. The molar ratio of magnesium powder, gallium powder, and microsilica powder was 1:10:0.48, and the weight ratio of gallium powder to In powder was 3:1. After grinding, the powder was placed in a crucible and heated to 550°C at 2°C / min in a tube furnace under a high-purity argon atmosphere. After holding at this temperature for 4 hours, the powder was cooled to room temperature. An appropriate amount of ethanol was added to the cooled product. The mixture (the ratio of ethanol volume to the sum of Ga and In volumes is 1:1) was centrifuged at 3000 r / min for 3 min. After centrifugation, the mixture separated into layers. The lower layer was a GaIn alloy, while the remaining material remained in the upper layer. The upper layer was aspirated using a syringe. The aspirated material was then washed once each with 0.5 M dilute hydrochloric acid, 1% wt hydrofluoric acid, and a 1:1 mixture of water and ethanol. After drying, the mixture was ground in a mortar for 5 minutes to obtain the nano-silicon material.

[0071] Example 10

[0072] Compared with Example 1, except that magnesium powder was replaced with Na and the molar ratio of Na:gallium:silicon powder was changed to 1:10:0.22, all other parameters and conditions were the same as in Example 1.

[0073] Example 11

[0074] Compared with Example 9, except that the micro silica powder was replaced with nano silica (Siamese reagent, particle size 15nm), all other parameters and conditions were the same as in Example 9.

[0075] Comparative Example 1

[0076] Magnesium powder and microsilica powder (keystone, silica purity >99%, 325 mesh) were placed in a crucible at a molar ratio of 1:0.48. The crucible was heated to 550°C at a rate of 2–5°C / min in a tube furnace under a high-purity argon atmosphere and held at that temperature for 4 hours. After cooling to room temperature, the crucible was washed once each with 0.5M dilute hydrochloric acid, 1% wt hydrofluoric acid, and a 1:1 mixture of water and ethanol. After drying, the crucible was ground in a mortar for 5 minutes to obtain the silicon material.

[0077] Effect Example

[0078] (1) Morphological characterization and XRD testing

[0079] Figure 1 The image shows a TEM image of the nano-silicon prepared in Example 1, which shows that the size of the prepared silicon particles is about 50 nm. Figure 2 This is a SEM image of the nano-silicon prepared in Example 1, showing that the particles are in an aggregated state; Figure 3 The XRD patterns of nano-silicon prepared in Examples 1, 7, and Comparative Example 1 show obvious elemental silicon peaks.

[0080] (2) Particle size test

[0081] The particle size of the nano-silicon prepared in Examples 1-11 and Comparative Example 1 was measured using a laser particle size analyzer MS3000. The particle size information is shown in Table 1.

[0082] Table 1

[0083] sample Particle size D50 / nm Example 1 60 Example 2 53 Example 3 48 Example 4 43 Example 5 46 Example 6 82 Example 7 353 Example 8 64 Example 9 58 Example 10 65 Example 11 41 Comparative Example 1 655

[0084] (3) Electrochemical performance testing:

[0085] The nano-silicon materials prepared in Examples 1 to 11 and Comparative Example 1 were subjected to half-cell tests. The test method was as follows: the above-mentioned nano-silicon materials were uniformly mixed with binder CMC (sodium carboxymethyl cellulose) and conductive carbon black in a mass ratio of 80:10:10 to form a slurry. This slurry was coated onto copper foil to a thickness of 100 micrometers and then dried under vacuum at 80°C for 12 hours to prepare a lithium-ion battery negative electrode. Simulated battery assembly was performed in an argon-filled glove box using a 1 mol / L LiPF6 electrolyte (solvents were EC, DMC, and FEC, EC:DMC = 1:1 (volume ratio), FEC accounting for 5% of the total solvent volume). A polypropylene microporous membrane was used as the separator, and a lithium metal sheet was used as the counter electrode. Electrochemical performance tests were conducted on a Land CT2001A battery tester at a temperature of 20°C, a charge / discharge voltage range of 0.01 to 1.5V, a charge / discharge current of 200 mA / g, and 1C = 250 mAh g. -1 The test results are shown in Table 1.

[0086] Table 1

[0087]

[0088] Based on the above experimental results, it can be seen that the nano-silicon material prepared by the present invention has excellent electrochemical performance, especially specific capacity and cycle life.

[0089] In Comparative Example 1, during the preparation process, the direct reduction of silicon dioxide by metallic magnesium releases a large amount of heat in a short time, which destroys the silicon micro-nano structure. This results in larger product particles with increased specific surface area and decreased specific capacity. Compared with nano-silicon, the silicon expansion and differentiation problem is more serious, resulting in poorer electrochemical performance. The initial charge capacity and cycle performance are far worse than those of the Example.

[0090] While specific embodiments of the present invention have been described above, those skilled in the art should understand that these are merely illustrative examples, and the scope of protection of the present invention is defined by the appended claims. Those skilled in the art can make various changes or modifications to these embodiments without departing from the principles and essence of the present invention, but all such changes and modifications fall within the scope of protection of the present invention.

Claims

1. A method for preparing nano-silicon materials, characterized in that, It consists of the following steps: a mixture containing reducing metal, low melting point metal and silicon dioxide is heated and reacted at 500-600℃ for 3-5 hours under inert gas protection, cooled to room temperature, the low melting point metal and the reaction product are separated, and the reaction product is washed, dried and ground to obtain the nano silicon material. The silica includes one or more of microsilica, silica, fumed silica, nano-silica, and porous silica; the low-melting-point metal includes Ga; and the molar ratio of the reducing metal to the low-melting-point metal is 1:(8-20). When the reducing metal is an alkaline earth metal, the molar ratio of the reducing metal to the silicon dioxide is 1:(0.3~0.5). When the reducing metal is an alkali metal element, the molar ratio of the reducing metal to the silicon dioxide is 1:(0.2~0.25).

2. The method for preparing nano-silicon materials according to claim 1, characterized in that, The silicon dioxide is nano-silicon dioxide.

3. The method for preparing nano-silicon materials according to claim 1, characterized in that, The microsilica powder has a mesh size of 325-1000 mesh; And / or, the particle size of the nano-silica is 5-50 nm; And / or, the porous silica has a pore size of 10-80 nm.

4. The method for preparing nano-silicon materials according to claim 3, characterized in that, The microsilica powder has a mesh size of 325.

5. The method for preparing nano-silicon materials according to claim 3, characterized in that, The particle size of the nano-silica is 15 nm.

6. The method for preparing nano-silicon materials according to claim 3, characterized in that, The porous silica has a pore size of 50 nm.

7. The method for preparing nano-silicon materials according to claim 1, characterized in that, The molar ratio of the reducing metal to the low-melting-point metal is 1:10; And / or, the alkaline earth metal is Mg and / or Ca; And / or, the alkali metal element is Na and / or K.

8. The method for preparing nano-silicon materials according to claim 1, characterized in that, When the reducing metal is an alkaline earth metal, the molar ratio of the reducing metal to the silicon dioxide is 1:(0.4~0.5).

9. The method for preparing nano-silicon materials according to claim 1, characterized in that, When the reducing metal is an alkaline earth metal, the molar ratio of the reducing metal to the silicon dioxide is 1:0.32 or 1:0.

48.

10. The method for preparing nano-silicon materials according to claim 1, characterized in that, When the reducing metal is an alkali metal element, the molar ratio of the reducing metal to the silicon dioxide is 1:0.

22.

11. The method for preparing nano-silicon materials according to claim 1, characterized in that, The low-melting-point metal also includes In.

12. The method for preparing nano-silicon materials according to claim 11, characterized in that, The weight ratio of Ga to In is (2-4):

1.

13. The method for preparing nano-silicon materials according to claim 11, characterized in that, The weight ratio of Ga to In is 3:

1.

14. The method for preparing nano-silicon materials according to claim 1, characterized in that, The heating temperature is 550°C; And / or, the heating time is 4 hours; And / or, the low-melting-point metal and reaction products are separated by centrifugation.

15. The method for preparing nano-silicon materials according to claim 1, characterized in that, The washing process involves sequentially using hydrochloric acid or nitric acid, hydrofluoric acid, and a solvent.

16. The method for preparing nano-silicon materials according to claim 15, characterized in that, The concentration of the hydrochloric acid or the nitric acid is 0.05M-2M.

17. The method for preparing nano-silicon materials according to claim 15, characterized in that, The concentration of the hydrofluoric acid is 0.01~10wt%.

18. The method for preparing nano-silicon materials according to claim 15, characterized in that, The solvent is one or more of deionized water, ethanol, isopropanol, and acetone.

19. The application of the nano-silicon material prepared by the method described in any one of claims 1-18 in lithium-ion batteries.

20. A lithium-ion battery, characterized in that, It includes a positive electrode, a negative electrode, an electrolyte, and a separator, wherein the negative electrode comprises nano-silicon material prepared by the method for preparing nano-silicon material as described in any one of claims 1-18.

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