Front pre-magnesium silicon monoxide negative electrode material and preparation method thereof

Abstract

The invention belongs to the technical field of lithium ion batteries, and relates to a silicon-oxygen negative electrode material, in particular to a front pre-magnesium silicon monoxide negative electrode material and a preparation method thereof.The preparation method comprises the following steps that S1, silicon, silicon dioxide and magnesium oxide are mixed and react under the vacuum heating condition, and a pre-precursor is generated; the heating temperature is 1200 DEG C to 1500 DEG C; the reaction time is 10 to 30 hours; s2, grinding the pre-precursor prepared in the step S1, then carrying out heat treatment in inert gas circulation flow, and cooling to obtain a finished product, wherein the heat treatment temperature is 700-900 DEG C; according to the invention, the initial coulombic efficiency and the long-term use capacity retention rate of the prepared silicon monoxide negative electrode material are improved, and the cycle life of the prepared battery is prolonged.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries and relates to silicon-oxygen negative electrode materials, and in particular to a pre-pre-magnesium silicon oxide negative electrode material and a preparation method thereof. Background Art

[0002] Lithium-ion batteries have achieved rapid development due to their high energy density and good cycle stability. In order to pursue high capacity density of lithium-ion batteries, the selection of negative electrodes is critical. Therefore, negative electrode materials are also an important area of ​​current research. As lithium-ion batteries pursue high capacity density, graphite negative electrode materials have limited their further development due to their low specific capacity and low capacity retention rate. Silicon-based materials have attracted widespread attention due to their extremely high theoretical specific capacity. Silicon oxide, as a type of silicon-based material, is a battery negative electrode material with high theoretical specific capacity. However, with the deepening of research, it was found that using silicon oxide directly as a negative electrode material has problems such as low conductivity, low first coulombic efficiency, and large volume expansion. Therefore, silicon oxide is rarely used directly now, but pre-magnesium silicon oxide is used. Usually, the industry prepares pre-magnesium silicon oxide by mixing silicon and magnesium to obtain pre-magnesium silicon oxide material, which is used to improve the charge and discharge cycle performance, first coulombic efficiency and capacity retention rate of silicon oxide as a negative electrode material. However, the structural arrangement of the pre-magnesium silicon oxide negative electrode material prepared by this method is not dense enough, and the first coulombic efficiency and capacity retention rate still have room for improvement.

[0003] Therefore, the present application proposes a pre-magnesium silicon oxide negative electrode material and a preparation method thereof, the purpose of which is to improve the first coulombic efficiency and capacity retention rate of the pre-magnesium silicon oxide negative electrode material. Summary of the Invention

[0004] In view of this, the object of the present invention is to provide a pre-magnesium silicon oxide negative electrode material and a preparation method thereof, so as to improve the first coulombic efficiency and capacity retention rate of the pre-magnesium silicon oxide negative electrode, thereby improving its cycle life.

[0005] In the first aspect, to achieve the above-mentioned purpose, the present invention discloses a method for preparing a pre-pre-magnesium silicon oxide negative electrode material, the technical solution adopted is:

[0006] A method for preparing a pre-pre-magnesium silicon oxide negative electrode material comprises the following steps:

[0007] S1: Silicon, silicon dioxide and magnesium oxide are mixed and reacted under vacuum heating conditions to generate a pre-precursor; the heating temperature is 1200°C-1500°C; the reaction time is 10-30 hours;

[0008] S2: Grinding the pre-precursor obtained in step S1, and then heat-treating it in a circulating inert gas at a temperature of 700° C.-900° C., taking it out and cooling it to obtain a finished product.

[0009] Beneficial effect: In order to improve the charge-discharge cycle performance, first coulomb efficiency and capacity retention rate after multiple uses of silicon oxide as a negative electrode material, pre-magnesium silicon oxide is prepared; by mixing silicon dioxide, silicon and magnesium oxide, in the process of generating silicon oxide at vacuum and high temperature, magnesium oxide is reduced to magnesium element through redox reaction, and then incorporated into the finished silicon oxide block through vapor deposition to form a pre-magnesium silicon oxide precursor block. The surface of the pre-magnesium silicon oxide precursor block generated at this time has a pore structure, and then the pre-magnesium silicon oxide precursor block is crushed and ground into powder and heat-treated under an inert atmosphere. The amorphous active silicon dioxide in the silicon oxide is consumed by the magnesium thermal reduction reaction to produce a magnesium silicate crystal phase. At the same time, the heat generated by the magnesium thermal reaction is promptly dissipated through the pores on the surface of the pre-magnesium silicon oxide precursor block to produce a magnesium silicate crystal phase, so that the prepared finished product has good first coulomb efficiency and multiple The capacity retention rate after the first use; at the same time, the present application uses magnesium oxide as the magnesium source, which is lower in cost compared to magnesium powder, and the high activity of metallic magnesium easily leads to the heat released in the reaction process being difficult to control, and the reaction rate is also fast and difficult to control. The present application scheme uses magnesium oxide to slow down the reaction rate, making the reaction rate easy to control and the performance of the finished product more stable; in addition, the present application prepares pre-magnesium silicon dioxide by mixing silicon dioxide with silicon. The procurement cost of silicon dioxide is lower than the price of silicon, which makes the cost of the finished product lower. At the same time, silicon dioxide in the present application is used as a direct oxygen source, and the oxygen content in the product can be accurately controlled by adjusting its addition amount, thereby adjusting the high specific capacity and high conductivity of the finished product. At the same time, the addition of silicon dioxide can inhibit the agglomeration of silicon particles, reduce pores, and form a tighter composite structure, thereby improving the initial coulombic efficiency and capacity retention rate of the subsequent silicon dioxide negative electrode material when used.

[0010] Furthermore, the method for preparing the pre-pre-Mg-SiO negative electrode material according to claim 1 is characterized in that the reaction temperature in step S1 is preferably 1250°C-1350°C.

[0011] Furthermore, in step S1, silicon and silicon dioxide are composed according to a molar ratio of (0.9-1.2): (1.6-2.0).

[0012] Furthermore, in step S1, the silicon, silicon dioxide and magnesium oxide are uniformly mixed in a molar ratio of (0.9-1.2): (1.6-2.0): (0.24-0.5).

[0013] Furthermore, the reaction time in step S1 is preferably 15-25 hours.

[0014] Furthermore, during the heat treatment in step S2, the flow rate of the inert gas is 1 L-5 L / min.

[0015] Furthermore, when heat treatment is performed in step S2, the treatment time is 1-10 hours.

[0016] Furthermore, the finished product obtained in step S2 is post-processed, which includes placing the finished product in an inert gas environment, adding carbon source gas, setting the heating temperature to 500-1000° C., keeping the temperature for 1-10 hours, and cooling to obtain the finished product.

[0017] Furthermore, the carbon source gas is at least one of acetylene, methane, etc.

[0018] In a second aspect, the present application provides a pre-pre-magnesium silicon oxide negative electrode material, which is prepared according to the preparation method of the pre-pre-magnesium silicon oxide negative electrode material.

[0019] Beneficial effect: In order to improve the initial coulombic efficiency and capacity retention rate of silicon dioxide as a negative electrode, the present application prepares pre-magnesium silicon dioxide, and mixes silicon dioxide, silicon, and magnesium oxide. Under vacuum and high temperature conditions, silicon dioxide is generated and an oxidation-reduction reaction occurs, which reduces magnesium oxide to a single magnesium substance. In this process, it is deposited into silicon dioxide to form a pre-magnesium silicon dioxide precursor. By mixing silicon and silicon dioxide, silicon dioxide can also be used as an oxygen source in the reaction, thereby promoting the generation of pre-magnesium silicon dioxide and inhibiting the agglomeration of silicon particles, thereby further promoting the generation of the pre-magnesium silicon dioxide precursor. There are pores on the surface of the pre-magnesium silicon dioxide precursor. After being ground into powder, it is heat-treated in an inert atmosphere to consume the amorphous active silicon dioxide therein and produce a magnesium silicate crystal phase. At the same time, the heat generated by the magnesium thermal reaction is promptly dissipated through the pores, thereby preparing a negative electrode material with good initial coulombic efficiency and capacity retention rate. DETAILED DESCRIPTION

[0020] The following is a further detailed description of the pre-pre-Mg-SiO negative electrode material and its preparation method of the present invention in conjunction with specific embodiments 1-9:

[0021] Example 1:

[0022] A method for preparing a pre-pre-magnesium silicon oxide negative electrode material comprises the following steps:

[0023] S1: After uniformly mixing silica, silicon, and magnesium oxide in a molar ratio of 1:1.8:0.24, the mixture is placed in a reaction tank, and the reaction tank is vacuum-heated to allow the silica, silicon, and magnesium oxide mixture to react under vacuum heating conditions to generate a pre-precursor; wherein the heating temperature is 1200°C and the reaction time is 20 hours;

[0024] S2: The pre-precursor prepared in step S1 is placed in a jet mill for grinding, and then placed in a heated reaction box. Nitrogen is circulated in the reaction box at a nitrogen flow rate of 1 L / min. At the same time, the reaction box is heat-treated at a temperature of 800°C for 10 hours, and then cooled.

[0025] Example 2

[0026] The difference between this embodiment and embodiment 1 is that the heating temperature in step S1 is 1500° C., and the rest is the same as in embodiment 1.

[0027] Example 3

[0028] The difference between this embodiment and embodiment 1 is that the heating temperature in step S1 is 1300° C., and the rest is the same as in embodiment 1.

[0029] Example 4

[0030] The difference between this embodiment and embodiment 3 is that in step S1, silicon, silicon dioxide, and magnesium oxide are mixed in a molar ratio of 1:1.8:0.5, and the rest are the same as in embodiment 3.

[0031] Example 5

[0032] The difference between this embodiment and embodiment 3 is that in step S1, silicon, silicon dioxide, and magnesium oxide are uniformly mixed in a molar ratio of 1:1.8:0.37, and the rest are the same as in embodiment 3.

[0033] Example 6

[0034] The difference between this embodiment and embodiment 5 is that the gas flow rate of nitrogen in step S2 is 3 L / min, and the rest is the same as that in embodiment 5.

[0035] Example 7

[0036] The difference between this embodiment and embodiment 6 is that the heat treatment time in step S2 is 5 hours, and the rest is the same as in embodiment 6.

[0037] Example 8

[0038] The difference between this embodiment and embodiment 7 is that the finished product obtained in step S2 is post-processed, and the post-processing includes placing the finished product in an inert gas environment, introducing a carbon source gas, setting the heating temperature to 800°C, keeping the temperature for 6 hours, and cooling the finished product. In this embodiment, the carbon source gas is selected as acetylene, and the rest is the same as in embodiment 7.

[0039] Example 9

[0040] The difference between this embodiment and embodiment 8 is that the carbon source gas in this embodiment is acetylene and methane mixed in a volume ratio of 1:1, and the rest is the same as in embodiment 8.

[0041] Comparative Example 1:

[0042] The difference between this comparative example and Example 1 is that silicon dioxide is not added in this comparative example, and the rest is the same as in Example 1.

[0043] Experimental data:

[0044] The pre-magnesium silicon oxide materials prepared in Examples 1-9 and Comparative Example 1 were coated onto copper foil, dried, and roll-pressed to form negative electrode sheets. A metallic lithium sheet served as the positive electrode, and a polypropylene microporous membrane served as the separator. 1 mol / L LiPF6 was dissolved in a 1:1 volume ratio of ethylene carbonate (EC) and dimethyl carbonate (DEC). An electrolyte containing 5% fluoroethylene carbonate (FEC) was added to the EC / DEC mixture. The negative electrode sheets were assembled into CR2032 button cells in an argon-filled inert gas glove box. The CR2032 button cells were allowed to stand at room temperature for 12 hours before undergoing charge and discharge tests on a battery testing system.

[0045] The test conditions are: discharge to 0.005V at a discharge rate of 0.1C, discharge to 0.005V at a discharge rate of 0.02C, and charge to 1.5V at a charge rate of 0.1C. The first coulombic efficiency and 100-week capacity retention rate are measured through electrochemical testing.

[0046]

[0047]

[0048] Data Analysis

[0049] By comparison, it can be analyzed that the pre-magnesium silicon oxide negative electrode material prepared by mixing silicon dioxide with silicon and reacting with magnesium oxide has better high initial efficiency, which also means that the irreversible loss of active lithium ions in the first cycle of the material is small, and the subsequent capacity retention rate is also high, which proves that the subsequent cycle stability of the negative electrode material is also good. Compared with the method of using only silicon and magnesium oxide to react in the comparative example, the prepared negative electrode material is better; by further limiting the reaction conditions and post-treatment methods, the high initial efficiency and capacity retention rate of the prepared negative electrode material are further improved.

Claims

1. A method for preparing a pre-prepared magnesium silicon oxide negative electrode material, characterized in that: The following steps are involved: S1: Silicon, silicon dioxide and magnesium oxide are mixed and reacted under vacuum heating conditions to generate a pre-precursor; the heating temperature is 1200°C-1500°C; the reaction time is 10-30 hours; S2: Grinding the pre-precursor obtained in step S1, and then heat-treating it in a circulating inert gas at a temperature of 700° C.-900° C., and obtaining a finished product after cooling.

2. The method for preparing a pre-pre-Mg-SiO negative electrode material according to claim 1, characterized in that: The heating temperature in step S1 is further set to 1250°C-1350°C.

3. The method for preparing a pre-pre-Mg-SiO negative electrode material according to claim 1, characterized in that: In step S1, silicon and silicon dioxide are composed according to a molar ratio of (0.9-1.2): (1.6-2.0).

4. The method for preparing a pre-pre-Mg-SiO negative electrode material according to claim 3, characterized in that: In step S1, the silicon, silicon dioxide and magnesium oxide are uniformly mixed in a molar ratio of (0.9-1.2): (1.6-2.0): (0.24-0.5).

5. The method for preparing a pre-pre-Mg-SiO negative electrode material according to claim 1, characterized in that: During the heat treatment in step S2, the flow rate of the inert gas is 1 L-5 L / min.

6. The method for preparing the pre-pre-Mg-SiO negative electrode material according to claim 1, characterized in that: The reaction time in step S1 is preferably 15-25 hours.

7. The method for preparing the pre-pre-Mg-SiO negative electrode material according to claim 1, characterized in that: When heat treatment is performed in step S2, the treatment time is 1-10 hours.

8. The method for preparing the pre-pre-Mg-SiO negative electrode material according to claim 1, characterized in that: The finished product obtained in step S2 is post-processed, which includes placing the finished product in an inert gas environment, introducing a carbon source gas, setting the heating temperature to 500-1000° C., keeping the temperature for 1-10 hours, and cooling the finished product.

9. The method for preparing the pre-pre-Mg-SiO negative electrode material according to claim 8, characterized in that: The carbon source gas is at least one of acetylene, methane, etc.

10. A pre-pre-magnesium silicon oxide negative electrode material, characterized in that: It is prepared according to the method for preparing the pre-pre-magnesium silicon oxide negative electrode material according to any one of claims 1 to 9.

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