A lithium-ion battery silicon-carbon negative electrode material and preparation method thereof

Abstract

The present invention discloses a lithium-ion battery silicon-carbon negative electrode material and a preparation method thereof, which belongs to the technical field of lithium-ion batteries, and includes: (1) preparation of nitrogen-carbon-fluorine layer silicon dioxide: silicon dioxide powder is placed in a quartz cavity of a low-pressure inductively coupled plasma, and then a mixed gas of carbon tetrafluoride and ammonia is introduced, and plasma discharge treatment is performed to obtain silicon dioxide wrapped with a nitrogen-carbon-fluorine layer; (2) thermal reduction of silicon dioxide: silicon dioxide, metal powder and metal chloride wrapped with a nitrogen-carbon-fluorine layer are fully stirred and mixed, and then placed in a reactor, an inert gas is introduced, and heating reduction is performed; (3) cleaning: the generated product is rinsed with an inorganic acid. The present invention uses a mixed gas of carbon tetrafluoride and ammonia to modify silicon dioxide, and a uniform nitrogen-carbon-fluorine layer is formed on the surface and inside of the silicon dioxide, so as to better alleviate the volume expansion of nano-silicon, so that the first charge and discharge efficiency and cycle stability of the battery are greatly improved.

Description

Technical Field

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

[0002] Silicon-based materials have the advantages of high capacity and wide sources as negative electrodes for lithium-ion batteries, but due to the large volume expansion during the charge and discharge process, they have the disadvantages of poor stability and low initial efficiency. The preparation methods of silicon-carbon negative electrodes include carbon thermal reduction and aluminum thermal reduction. One of the commonly used methods is to modify the surface of nano-silicon with carbon materials to alleviate the volume expansion of silicon negative electrodes during the charge and discharge process. Common carbon coating methods include chemical vapor deposition, pyrolysis, and hydrothermal methods. Chemical vapor deposition and pyrolysis are methods that decompose organic gases into carbon sources under high temperature conditions and deposit them on the silicon surface to eventually form a carbon layer that coats the silicon material. This experimental method requires a high reaction temperature, harsh reaction conditions, and a low deposition rate. The hydrothermal method is a method in which organic matter such as glucose is partially carbonized and precipitated under high temperature and high pressure conditions and attached to the silicon surface to achieve carbon coating, but the carbon layer formed by this method is relatively thin, only 2~3nm. In addition, the silicon-carbon negative electrode obtained by the above preparation method has carbon material coated on the outer surface of silicon nanoparticles, while the silicon inside the silicon nanoparticles cannot coat the carbon material. Therefore, after multiple cycles, the silicon nanoparticles are pulverized due to the volume expansion of silicon, thereby reducing the cycle life of the battery. Summary of the invention

[0003] In view of the above-mentioned deficiencies in the prior art, the present invention provides a method for preparing a silicon-carbon negative electrode, which is based on plasma etching technology, using carbon tetrafluoride and ammonia as a mixed gas, and using carbon tetrafluoride plasma to react chemically with silicon dioxide while ammonia plasma reacts with it on the surface of silicon dioxide and inside its nanoparticles to generate a uniform and stable nitrogen-carbon-fluorine layer. The biggest difference between the present invention and the existing preparation technology is that the generated nitrogen-carbon-fluorine layer is chemically bonded to silicon dioxide and distributed in the internal structure of silicon dioxide. This preparation method not only improves the battery capacity, but also effectively alleviates the volume expansion of the silicon-carbon negative electrode material.

[0004] The present invention is achieved through the following technical solutions:

[0005] A method for preparing a lithium-ion battery silicon-carbon negative electrode material comprises the following steps:

[0006] Step 1, preparation of silicon dioxide containing nitrogen-carbon fluoride layer: placing silicon dioxide powder into a quartz chamber of low-pressure inductively coupled plasma, then introducing a mixture of carbon tetrafluoride and ammonia gas, and performing plasma discharge treatment to obtain silicon dioxide wrapped with a nitrogen-carbon fluoride layer;

[0007] Step 2, thermal reduction of silicon dioxide: the silicon dioxide coated with the nitrogen-carbon fluoride layer obtained in step 1, the metal powder and the metal chloride are fully stirred and mixed, and then placed in a reactor, and an inert gas is introduced, and heated for reduction;

[0008] Step 3: Cleaning: Wash the generated product with an inorganic acid.

[0009] Preferably, in step 1, the size of a single sphere in the silicon dioxide powder is 0.005-500 μm, the volume ratio of the carbon tetrafluoride and ammonia mixed gas is 1:1-1:100, the flow rate of the gas is 2-100 mL / min, the power of the plasma discharge is 80-1000 W, and the time of the plasma discharge is 10-30 min.

[0010] Preferably, in step 2, the inert gas is one of nitrogen or argon or a mixture of the two, the metal powder is magnesium powder, the metal chloride is aluminum chloride or magnesium chloride, the heating reduction temperature is 200-550°C, the reaction time is 2-3 h, and the heating rate is 1-10°C / min.

[0011] Preferably, in step 3, the inorganic acid is one of hydrochloric acid, hydrofluoric acid and sulfuric acid, or a mixture of several of them.

[0012] A negative electrode material prepared by any of the above methods for preparing silicon-carbon negative electrode materials for lithium-ion batteries.

[0013] The benefits of the present invention are:

[0014] (1) The present invention is based on plasma etching technology and uses carbon tetrafluoride and ammonia as a mixed gas to react on the surface of silicon dioxide and inside its nanoparticles to generate a uniform and stable nitrogen-containing carbon fluorine layer, which effectively alleviates the volume expansion of the silicon negative electrode during the chemical cycle, thereby improving the cycle stability.

[0015] (2) Through the technical solution of the present invention, the etching rate is fast, and the thickness of the produced nitrogen-carbon fluoride layer can be adjusted with the etching time, and the process is simple. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in describing the embodiments are briefly introduced below.

[0017] Figure 1 : TEM-Mapping elemental diagram of SiO2-NH2.

[0018] Figure 2 : FTIR spectra of SiO2 and SiO2-NH2.

[0019] Figure 3: SEM image and XRD image of Si / C negative electrode.

[0020] Figure 4 : Charge and discharge curves of Si / C negative electrode.

[0021] Figure 5 : Cycle curves of Si / C negative electrode. DETAILED DESCRIPTION

[0022] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0023] Example 1

[0024] 5 g of silicon dioxide powder was placed in a low-pressure inductively coupled plasma quartz chamber, and a mixed gas of carbon tetrafluoride and ammonia was introduced. The gas flow rate was 9 mL / min, and the volume ratio of carbon tetrafluoride to ammonia was 1:1. The discharge was carried out at a discharge power of 120 W for 20 min to obtain silicon dioxide wrapped with a nitrogen-carbon fluoride layer. The silicon dioxide, magnesium powder and magnesium chloride wrapped with a nitrogen-carbon fluoride layer obtained in the above steps were fully stirred and mixed, and then placed in a reactor, nitrogen was introduced, and the mixture was heated to 550 ° C at a heating rate of 2 ° C / min, and maintained at this temperature for 3 h, and then cooled to room temperature. Finally, the generated product was rinsed with hydrofluoric acid to finally obtain a silicon-carbon negative electrode for lithium-ion batteries.

[0025] Example 2

[0026] 10 g of silicon dioxide powder was placed in a low-pressure inductively coupled plasma quartz chamber, and a mixed gas of carbon tetrafluoride and ammonia was introduced. The gas flow rate was 2 mL / min, and the volume ratio of carbon tetrafluoride to ammonia was 1:50. The discharge was carried out at a discharge power of 80 W for 10 min to obtain silicon dioxide wrapped with a nitrogen-carbon fluoride layer. The silicon dioxide, magnesium powder and magnesium chloride wrapped with a nitrogen-carbon fluoride layer obtained in the above steps were fully stirred and mixed, and then placed in a reactor, nitrogen was introduced, and the mixture was heated to 200 ° C at a heating rate of 1 ° C / min, and maintained at this temperature for 2 h, and then cooled to room temperature. Finally, the generated product was rinsed with hydrochloric acid to finally obtain a silicon-carbon negative electrode for lithium-ion batteries.

[0027] Example 3

[0028] 15 g of silicon dioxide powder was placed in a low-pressure inductively coupled plasma quartz chamber, and a mixed gas of carbon tetrafluoride and ammonia was introduced. The gas flow rate was 100 mL / min, and the volume ratio of carbon tetrafluoride to ammonia was 1:100. The mixture was discharged at a discharge power of 1000 W for 30 min to obtain silicon dioxide wrapped with a nitrogen-carbon fluoride layer. The silicon dioxide, magnesium powder and magnesium chloride wrapped with a nitrogen-carbon fluoride layer obtained in the above steps were fully stirred and mixed, and then placed in a reactor. Nitrogen was introduced, and the mixture was heated to 400 °C at a heating rate of 10 °C / min, and maintained at this temperature for 2.5 h, and then cooled to room temperature. Finally, the generated product was rinsed with sulfuric acid to obtain a silicon-carbon negative electrode for lithium-ion batteries.

[0029] Experimental Results

[0030] Figure 1 The electron scanning image (TEM) and element distribution map (Mapping) of the nitrogen-carbon fluorine layer silicon dioxide (SiO2-NH2) prepared in the above Example 1. TEM shows that the particle size of silicon dioxide is about 30μm. The TEM-Mapping element map further confirms that the distribution of carbon, fluorine and nitrogen is similar to that of Si and O, which indicates that these elements are deposited inside and on the surface of silicon dioxide.

[0031] Figure 2 The following are Fourier transform infrared spectra (FTIR) of the nitrogen-fluorinated carbon layer silicon dioxide (SiO2-NH2) and the original silicon dioxide prepared in Example 1. The Fourier transform infrared spectroscopy (FTIR) studied the changes in the functional groups in SiO2 and SiO2-NH2. As shown in the figure, compared with the FTIR spectrum of silicon dioxide, the -1 and 3163 cm -1 The new peak at 1425 cm-1 is attributed to the stretching vibration of the NH bond, indicating the formation of an amino group. -1 and 1381 cm -1 The peaks at 1100 cm -1 and 795 cm -1 The intensity of the peak at 2923 cm increased significantly, further confirming the formation of the fluorocarbon layer. -1 and 2851 cm -1 The peak at 795 cm is the CH stretching vibration absorption peak. The symmetric and antisymmetric stretching vibration absorption peaks of Si-O-Si appear at 795 cm -1 and 1103 cm -1 This indicates that after plasma treatment, nitrogen-carbon-fluorine layers appeared on the surface and inside of the silica spheres, but the bulk phase of silica was not changed.

[0032] Figure 3The SEM image and XRD image of the silicon-carbon negative electrode (Si / C) prepared in Example 1 above are shown. Figure 3 The SEM image in a shows that the size of silicon carbon is about 20~30μm. Figure 3 The diffraction peaks at 28.5°, 47.3°, 56.2°, 69.2°, 76.4°, 88°, etc. in the XRD image of middle b prove the presence of elemental silicon.

[0033] Figure 4 , Figure 5 The charge-discharge curves and cycle curves of the silicon-carbon (Si / C) negative electrode and the silicon negative electrode (Si) without carbon coating prepared by the present invention are shown in FIG. Figure 4 The first charge and discharge curves show that the discharge specific capacities of the silicon-carbon anode (Si / C) and the silicon anode without carbon coating (Si) are 1166 mAh / g and 860 mAh / g, respectively, and the first efficiencies are 75.8% and 66.1%, respectively. Figure 5 It was proved that the capacity retention rates of silicon-carbon anode (Si / C) and silicon anode without carbon coating (Si) after 300 cycles were 960 mAh / g and 646.7 mAh / g, respectively, and their capacity retention rates were 82.3% and 74.5%, respectively.

[0034] Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments, or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a lithium-ion battery silicon-carbon negative electrode material, characterized in that: The following steps are involved: Step 1, preparation of silicon dioxide containing nitrogen-carbon fluoride layer: placing silicon dioxide powder into a quartz cavity of low-pressure inductively coupled plasma, wherein the quartz cavity of the low-pressure inductively coupled plasma provides low pressure conditions, and then introducing a mixed gas of carbon tetrafluoride and ammonia to perform plasma discharge treatment to obtain silicon dioxide wrapped with a nitrogen-carbon fluoride layer; Step 2, thermal reduction of silicon dioxide: the silicon dioxide coated with the nitrogen-carbon fluoride layer obtained in step 1, the metal powder and the metal chloride are fully stirred and mixed, and then placed in a reactor, and an inert gas is introduced, and heated for reduction; Step 3, cleaning: washing the generated product with an inorganic acid; In step 1, the power of the plasma discharge is 80-1000 W, and the time of the plasma discharge is 10-30 min.

2. The method for preparing a lithium-ion battery silicon-carbon negative electrode material according to claim 1, characterized in that: In step 1, the size of a single sphere in the silica powder is 0.005-500 μm.

3. The method for preparing a lithium-ion battery silicon-carbon negative electrode material according to claim 1, characterized in that: In step 1, the volume ratio of carbon tetrafluoride to ammonia is 1:1-1:100, and the flow rate of the gas is 2-100 mL / min.

4. The method for preparing a lithium-ion battery silicon-carbon negative electrode material according to claim 1, characterized in that: In step 2, the inert gas is nitrogen or argon, or a mixture of the two.

5. The method for preparing a lithium-ion battery silicon-carbon negative electrode material according to claim 1, characterized in that: In step 2, the metal powder is magnesium powder or aluminum powder, and the metal chloride is aluminum chloride or magnesium chloride.

6. The method for preparing a lithium-ion battery silicon-carbon negative electrode material according to claim 1, characterized in that: In step 2, the temperature of heating reduction is 200-550°C, the reaction time is 2-3 h, and the heating rate is 1-10°C / min.

7. The method for preparing a lithium-ion battery silicon-carbon negative electrode material according to claim 1, characterized in that: In step 3, the inorganic acid is one of hydrochloric acid, hydrofluoric acid and sulfuric acid or a mixture of several of them.

8. A negative electrode material prepared by the method for preparing a lithium ion battery silicon-carbon negative electrode material as claimed in any one of claims 1 to 7.

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