Nano silicon material, preparation method, application and lithium ion battery

Abstract

The present invention discloses a nano silicon material, a preparation method, an application and a lithium ion battery. The method comprises: heating silicon carbon alloy powder and magnesium powder at 500-700°C for 0.5-8h under the protection of an inert gas, washing and drying after cooling to obtain the nano silicon material; the molar ratio of silicon in the silicon carbon alloy powder to the magnesium powder is 1:(1.0-3.5). The preparation method of the present invention can realize the gentle and controllable preparation of nano silicon material. The prepared nano silicon material has a smaller size and has a higher specific capacity and better cycle stability when applied to the negative electrode of a lithium ion battery.

Description

Technical Field

[0001] The invention specifically relates to a nano silicon material, a preparation method, an application and a lithium ion battery. Background Art

[0002] In lithium-ion battery technology, negative electrode materials are the key to achieving lithium ion storage and release and maintaining electrode stability. At present, mainstream manufacturers generally use graphite negative electrodes, which have excellent electrochemical properties, stable cycle performance and low cost. However, the energy density and power density of graphite are low, which to some extent restricts its application in long-range power batteries and fast charging fields.

[0003] In order to further improve the performance of lithium-ion batteries, researchers began to explore new negative electrode materials such as silicon-based materials, tin-based materials, oxides, alloys, and lithium metal. Among them, silicon currently has a high degree of industrialization. As an emerging negative electrode material with a theoretical specific capacity of 4200mAh / g, it far exceeds the 372mAh / g of graphite and has attracted widespread attention. The silicon negative electrode not only has excellent cycle stability, but also has a low discharge potential and abundant crustal reserves, making it the first choice for large-scale production and cost-effective battery manufacturing. In addition, the silicon negative electrode is still the main negative electrode technology route for future solid-state batteries. However, the silicon negative electrode will experience severe volume expansion (more than 300%) during the charging and discharging process, resulting in damage to the electrode structure, destruction of the conductive network, and reduced cycle stability. In addition, the poor conductivity of the silicon material itself will also affect the power density and charging and discharging efficiency of the electrode.

[0004] In order to overcome these problems, the commercial method of nano-silicon is usually used to increase the specific surface area, which is conducive to the storage of lithium ions, improve the specific capacity and reduce the impact of volume expansion and pulverization, thereby improving the cycle stability of the battery. However, the current processes used to produce nano-silicon, such as sand milling, vapor deposition and evaporation, have extremely strict equipment requirements, and have problems such as low production efficiency, difficult equipment maintenance and limited output. Therefore, it is particularly important to develop low-cost, simple and fast synthesis methods to prepare nano-silicon materials. Magnesium metal reduction of silicon dioxide is usually used for industrial crude silicon synthesis, which has the advantages of low cost and high output, but the reaction of magnesium and other metals reducing silicon dioxide is prone to self-propagating reaction, which instantly releases a large amount of heat and destroys the silicon micro-nano structure. In addition, impurities such as magnesium oxide are generated, which are difficult to remove. Summary of the invention

[0005] In order to overcome the problems of poor reaction controllability and uncontrollable silicon structure in the conventional reduction method for preparing silicon materials in the prior art, the present invention provides a nano silicon material and a preparation method, application and lithium ion battery. The preparation method of the present invention can realize the mild and controllable preparation of nano silicon materials, and the prepared nano silicon material has a small size and has a high specific capacity and good cycle stability when applied to the negative electrode of a lithium ion battery.

[0006] Silicon-carbon alloy is a powder made by mixing silicon powder and carbon powder in a certain proportion. It has low cost, and the properties and uses of silicon-carbon alloy and silicon carbide compounds are quite different. Silicon-carbon alloy powder is mainly used in the casting and metallurgical industries. It can be used as a flux and can also play a reducing role in slag.

[0007] The present invention prepares nano-silicon by using a low-cost silicon-carbon alloy to react with magnesium. Compared with the traditional magnesium thermal reaction, the amount of Mg consumed in the reaction is reduced, thereby reducing the production cost; the reaction process is more gentle, and the carbon in the silicon-carbon alloy can disperse the silicon. In addition, the carbon has a strong thermal conductivity, thereby slowing down the intensity of the reaction and inhibiting the self-propagating reaction of the usual magnesium thermal reduction method, so that the size of the nano-silicon is better controlled; the by-product magnesium carbide is easily hydrolyzed, easily reacts with an acid solution at the interface, and is easy to remove.

[0008] The present invention solves the above technical problems through the following technical solutions:

[0009] The invention provides a method for preparing a nano silicon material, which comprises the following steps: heating silicon-carbon alloy powder and magnesium powder at 500-700°C for reaction for 0.5-8h under the protection of an inert gas, washing and drying after cooling to obtain the nano silicon material; the molar ratio of silicon in the silicon-carbon alloy powder to the magnesium powder is 1:(1.0-3.5).

[0010] In the present invention, the particle size of the silicon-carbon alloy powder may be 2-500 mesh, such as 50 mesh, 100 mesh or 200 mesh.

[0011] In the present invention, the mass fraction of silicon in the silicon-carbon alloy powder may be 40%-80%, such as 50%, 60%, 70%, 75% or 78%, preferably 45% to 65%.

[0012] In the present invention, the silicon-carbon alloy powder can be prepared by high-temperature solid-phase reaction or purchased from the market.

[0013] In the present invention, the molar ratio of silicon in the silicon-carbon alloy powder to the magnesium powder is preferably 1:(1.0-2.5), for example, 1:1.1, 1:2.1, or 1:2.3.

[0014] In the present invention, before the heating reaction, the silicon-carbon alloy powder and the magnesium powder are generally mixed evenly.

[0015] In the present invention, the heating reaction is generally carried out in a tube furnace.

[0016] In the present invention, the inert gas may be conventional in the art, such as nitrogen or argon.

[0017] In the present invention, the temperature of the heating reaction is preferably 500-700° C., for example, 550° C., 600° C. or 680° C. The time of the heating reaction is preferably 0.5-4 h, for example, 1 h, 1.5 h, 2 h, 4 h or 6 h.

[0018] In the present invention, the washing may be carried out by acid washing. Preferably, the washing process includes first acid washing and then washing with a solvent. The acid may be acetic acid or hydrochloric acid. The concentration of the acetic acid may be 4-8M, for example 6M. The solvent may be deionized water or ethanol.

[0019] In the present invention, the number of washings can be conventional in the art, generally 3-6 times.

[0020] The present invention also provides a nano silicon material prepared by the above method.

[0021] In the present invention, the particle size of the nano-silicon material may be 50nm to 500nm.

[0022] The present invention also provides an application of the nano silicon material prepared by the above method in a lithium ion battery.

[0023] The present invention also provides a lithium ion battery, which comprises a positive electrode, a negative electrode, an electrolyte and a separator, wherein the negative electrode comprises the nano silicon material as described above.

[0024] On the basis of being in accordance with the common sense in the art, the above-mentioned preferred conditions can be arbitrarily combined to obtain the preferred embodiments of the present invention.

[0025] The reagents and raw materials used in the present invention are commercially available.

[0026] The positive and progressive effects of the present invention are:

[0027] The preparation method of the invention is simple, low-cost, and conducive to industrial production. By-product carbides such as magnesium carbide can be quickly removed in a solvent, thereby realizing mild, simple, and rapid preparation of nano silicon materials. The prepared nano silicon material is small in size and has the characteristics of high specific capacity, high cycle, etc. when used for the negative electrode of a lithium ion battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is the SEM image of the nano-silicon prepared in Example 1;

[0029] Figure 2This is a SEM image of the silicon material prepared in Comparative Example 1;

[0030] Figure 3 This is the XRD pattern of nano-silicon prepared in Example 1. DETAILED DESCRIPTION

[0031] The present invention is further described below by way of examples, but the present invention is not limited to the scope of the examples. The experimental methods in the following examples without specifying specific conditions are carried out according to conventional methods and conditions, or selected according to the product specifications.

[0032] Example 1

[0033] Silicon-carbon alloy powder (Jinsheng Metallurgy, 100 mesh) with a silicon content of 70wt% and magnesium powder are evenly mixed in a crucible at a molar ratio of silicon in the silicon-carbon alloy powder to metal magnesium powder of 1:2.1, and heated to 550°C at 2°C / min in a tubular furnace protected by high-purity argon, kept warm for 2 hours and then cooled; the product is washed three times with 6M acetic acid and then washed three times with deionized water, and then dried to obtain nano-silicon material.

[0034] Example 2

[0035] Compared with Example 1, except that the silicon-carbon alloy powder with a silicon content of 70wt% (Jinsheng Metallurgy, 100 mesh) is replaced by the silicon-carbon alloy powder with a silicon content of 78wt% (Jinsheng Metallurgy, 100 mesh), the other parameters and conditions are the same as those in Example 1.

[0036] Example 3

[0037] Compared with Example 1, except that the silicon-carbon alloy powder with a silicon content of 70wt% (Jinsheng Metallurgy, 100 mesh) is replaced by the silicon-carbon alloy powder with a silicon content of 50wt% (Jinsheng Metallurgy, 100 mesh), the other parameters and conditions are the same as those in Example 1.

[0038] Example 4

[0039] Compared with Example 1, except that the heating temperature is replaced with 680° C., the other parameters and conditions are the same as those of Example 1.

[0040] Example 5

[0041] Compared with Example 1, except that the holding time is replaced with 1 h, the other parameters and conditions are the same as those in Example 1.

[0042] Example 6

[0043] Compared with Example 1, except that the holding time is replaced with 6 hours, the other parameters and conditions are the same as those in Example 1.

[0044] Example 7

[0045] Compared with Example 1, except that the molar ratio of silicon in the silicon-carbon alloy powder to the metal magnesium powder is changed to 1:1.1, the other parameters and conditions are the same as those in Example 1.

[0046] Example 8

[0047] Silicon-carbon alloy powder with a silicon content of 70wt% (Jinsheng Metallurgy, 100 mesh) and magnesium powder are evenly mixed in a crucible at a molar ratio of silicon in the silicon-carbon alloy powder to metal magnesium powder of 1:2.1, and heated to 550°C at 2°C / min in a tubular furnace protected by high-purity argon. After keeping warm for 2 hours, the mixture is cooled and the product is washed three times with 6M acetic acid and then three times with deionized water. After drying, nano-silicon material is obtained.

[0048] Comparative Example 1

[0049] Metal magnesium powder and silicon dioxide powder (3AChem, size 1-3μm, purity 99.9%) were placed in a crucible at a molar ratio of 2.1:1, and then heated to 550°C at 5°C / min in a high-purity argon atmosphere in a tubular furnace. After being kept warm for 2 hours, they were cooled to room temperature, and the products were washed with 0.5M dilute hydrochloric acid, 1%wt hydrofluoric acid, and a mixed solution of water and ethanol in a volume ratio of 1:1, respectively, and dried to obtain silicon material.

[0050] Effect Example

[0051] (1) Morphology characterization and XRD testing

[0052] Figure 1 This is a SEM image of the nano-silicon prepared in Example 1; Figure 2 This is a SEM image of the silicon prepared in Comparative Example 1. It can be seen that the size of the nano-silicon prepared in Example 1 is significantly smaller than that in Comparative Example 1. Figure 3 This is the XRD pattern of nano-silicon prepared in Example 1, and its composition is Si.

[0053] The particle sizes of the nano-silicon prepared in Examples 1-6 and Comparative Example 1 were statistically analyzed using a laser particle size distribution analyzer MS3000, as shown in Table 1:

[0054] Table 1

[0055]

[0056]

[0057] According to Examples 1-3, reducing the silicon content in the silicon-carbon alloy is beneficial to the preparation of nano-silicon materials with smaller particle sizes; according to Examples 1 and 4-6, lowering the reaction temperature and reaction time is beneficial to reducing the nano-silicon particle size, but may result in incomplete reaction.

[0058] (2) Electrochemical performance test

[0059] The nano-silicon materials prepared in Examples 1 to 8 and Comparative Example 1 were subjected to half-cell tests. The test method is: the nano-silicon materials were uniformly mixed with a binder, CMC (sodium carboxymethyl cellulose), and conductive carbon black in a mass ratio of 80:10:10, and the slurry was coated on a copper foil with a coating thickness of 100 microns, and then dried at 80°C in vacuum for 12 hours to prepare a lithium battery negative electrode sheet. The simulated battery assembly was carried out in an argon-filled glove box, using 1 mol / L LiPF 6 The electrolyte (solvents are EC, DMC and FEC, EC:DMC=1:1 (volume ratio), FEC accounts for 5% of the total volume of the solvent), polypropylene microporous membrane as the separator, metal lithium sheet as the counter electrode, and the electrochemical performance test is carried out on a Land CT2001A battery tester at 20 °C. The charge and discharge voltage range is 0.01 to 1.5 V (1C=250 mAh g -1 ). The test results are shown in Table 2.

[0060] Table 2

[0061]

[0062]

[0063] According to the above experimental results, the nano-silicon material prepared by the present invention has excellent specific capacity and cycle life. According to Examples 1-3, when the silicon content in the silicon-carbon alloy is reduced, the first charge specific capacity is significantly improved; according to Examples 1 and 4, when the reaction temperature is reduced, the first charge specific capacity is significantly improved.

[0064] In Comparative Example 1, during the preparation process, the direct reduction of silicon dioxide by metallic magnesium will release high heat in a short time due to the self-propagating reaction, which will destroy the silicon micro-nano structure, resulting in larger product particles and reduced specific capacity. Compared with nano-silicon, the problem of silicon expansion and powdering is more serious. Therefore, the electrochemical performance is poor, and the first charge capacity and cycle performance are far worse than those of the embodiment.

[0065] Although the specific embodiments of the present invention are described above, it should be understood by those skilled in the art that this is only for illustration and the protection scope of the present invention is defined by the appended claims. Those skilled in the art may make various changes or modifications to these embodiments without departing from the principles and essence of the present invention, but these changes and modifications all fall within the protection scope of the present invention.

Claims

1. A method for preparing nano-silicon material, characterized in that: It consists of the following steps: The silicon-carbon alloy powder and magnesium powder are heated to react at 500-600°C for 0.5-4h under the protection of inert gas, and washed and dried after cooling to obtain the nano-silicon material; the molar ratio of silicon in the silicon-carbon alloy powder to the magnesium powder is 1:(2.1-2.5); the mass fraction of silicon in the silicon-carbon alloy powder is 45%-70%.

2. The method for preparing nano-silicon material according to claim 1, characterized in that: The particle size of the silicon-carbon alloy powder is 2-500 meshes.

3. The method for preparing nano-silicon material according to claim 2, characterized in that: The particle size of the silicon-carbon alloy powder is 50 mesh, 100 mesh or 200 mesh.

4. The method for preparing nano-silicon material according to claim 1, characterized in that: The mass fraction of silicon in the silicon-carbon alloy powder is 50%, 60% or 70%.

5. The method for preparing nano-silicon material according to claim 1, characterized in that: The mass fraction of silicon in the silicon-carbon alloy powder is 45% to 65%.

6. The method for preparing nano-silicon material according to claim 1, characterized in that: The molar ratio of silicon in the silicon-carbon alloy powder to the magnesium powder is 1:2.

3.

7. The method for preparing nano-silicon material according to claim 1, characterized in that: The temperature of the heating reaction is 550°C or 600°C; And / or, the heating reaction time is 1 h, 1.5 h, 2 h, 4 h or 6 h.

8. The method for preparing nano-silicon material according to claim 1, characterized in that: The washing is acid washing.

9. The method for preparing nano-silicon material according to claim 8, characterized in that: The acid is acetic acid or hydrochloric acid.

10. The method for preparing nano-silicon material according to claim 9, characterized in that: The concentration of the acetic acid is 4-8M.

11. The method for preparing nano-silicon material according to claim 10, characterized in that: The concentration of the acetic acid is 6M.

12. A nano-silicon material, characterized in that: The nano-silicon material is prepared according to the method for preparing the nano-silicon material according to any one of claims 1 to 11.

13. The nano-silicon material according to claim 12, characterized in that: The particle size of the nano-silicon material is 50nm-500nm.

14. Use of the nano-silicon material according to claim 12 or 13 in a lithium-ion battery.

15. A lithium ion battery, characterized in that: The invention comprises a positive electrode, a negative electrode, an electrolyte and a separator, wherein the negative electrode comprises the nano silicon material as claimed in claim 12 or 13.

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