Process for preparing nitrogen-doped silicon carbon high-performance negative electrode material through chemical vapor deposition

Abstract

The invention relates to a process for preparing a nitrogen-doped modified silicon carbon negative electrode material through chemical vapor deposition for a lithium ion battery. According to the method, the high-performance nitrogen-doped modified silicon-carbon negative electrode material is prepared through chemical vapor deposition in cooperation with a mechanical ball milling method and a heat treatment process, and the nitrogen-doped modified silicon-carbon negative electrode material has good cycling stability and rate performance in a lithium ion battery. The optimal addition mass ratio of the silicon-carbon negative electrode material to the melamine is 1: 1. Compared with a traditional silicon-carbon negative electrode material, the lithium intercalation and deintercalation rate and the volume expansion effect resistance of an electrode are obviously improved, the process complexity is reduced, the method is environment-friendly, and good industrial application prospects are shown. The method is simple in preparation process and easy to operate, the preparation process is high in expansibility, and large-scale industrial synthesis can be carried out.

Description

Technical Field

[0001] The present invention relates to a preparation method of a nitrogen-doped modified silicon-carbon anode material and its application in the anode of a lithium-ion battery, belonging to the technical field of lithium-ion battery anode materials. Background Art

[0002] With the widespread popularity of mobile terminal devices such as smart phones and tablet computers, as well as new energy transportation vehicles such as electric vehicles and electric bicycles, the market demand for high-performance energy storage devices is increasing day by day, especially for energy storage solutions with longer cycle life and higher energy density. To meet the social progress and the growing energy demand of mankind, developing new energy storage technologies has become an urgent task. As the most widely used energy storage device at present, the performance of lithium-ion batteries (LIBs) in terms of energy density and cycle life is mainly limited by the performance of electrode materials. Therefore, exploring new electrode materials with higher reversibility and cycle stability has become the focus of current research.

[0003] Anode materials with high theoretical capacity include silicon (4200 mAh·g -1 ), phosphorus (2596 mAh·g -1 ), germanium (1600 mAh·g -1 ), etc. The theoretical capacities of these materials far exceed that of commercially available graphite anodes (372 mAh·g -1 ). Among them, silicon-based materials with high capacity and low discharge platform show great application potential. Compared with pure Si, SiO x (1≤x<2) has a smaller volume expansion (<200%). In-situ generated lithium silicate (such as Li4SiO4 and Li2Si2O5) and Li2O formed in the initial cycle can mitigate the volume change of SiO x , which plays a crucial role in stabilizing the solid electrolyte layer, thereby improving the structural stability and reducing electrode cracking and pulverization, and thus improving the durability of the battery. These advantages make SiO x show broad prospects as an anode material for advanced lithium-ion batteries with high energy density and long cycle life.

[0004] Regarding SiO xProblems such as volume expansion and low conductivity during the insertion and extraction of lithium ions in the silicon-based anode can be addressed by introducing carbon materials to form composites with them. The silicon-based / carbon materials obtained in this way are an effective strategy to solve the drawbacks of silicon anode materials. The excellent properties of carbon materials can make up for the deficiencies of silicon-based materials, such as poor conductivity and low mechanical strength. Chemical vapor deposition (CVD) is a deposition technique in which gaseous precursors undergo chemical reactions in an activated environment such as heat, plasma, or photoexcitation to finally form solid materials. Compared with traditional carbon material preparation processes, CVD technology provides a highly controllable and scalable synthesis method, enabling the preparation of high-quality, large-area functional carbon materials at a reasonable cost.

[0005] However, in most of the currently published patents, on the one hand, only traditional sol-gel or mechanical ball milling methods are used to coat the silicon-based anode with carbon. The drawback of these methods is that the synthesized silicon-carbon anode is prone to agglomeration, and the uncontrollable silicon-carbon interface structure limits the battery capacity level. On the other hand, many CVD processes for synthesizing silicon-carbon anode materials require high-cost auxiliary facilities, such as plasma-enhanced chemical vapor deposition (PECVD) or the introduction of metal-organic chemical vapor deposition (MOCVD) with biotoxicity. Therefore, it is of great significance to study a simple, low-cost, and scalable CVD process for preparing silicon-carbon anodes to overcome problems such as poor conductivity, large volume expansion, and low initial Coulombic efficiency (ICE) of silicon-carbon anodes. Summary of the Invention

[0006] Aiming at the deficiencies of traditional silicon-carbon anode materials, such as low ICE and poor cycle stability, the purpose of the present invention is to provide a method for preparing a nitrogen-doped modified silicon-carbon anode material for lithium-ion batteries. This method designs the coating of silicon-based materials through chemical vapor deposition, optimizes the CVD reaction parameters, and regulates the amount of nitrogen source added to prepare a nitrogen-doped modified silicon-carbon anode material. This material has advantages such as good ICE and stable cycle performance, and is particularly suitable as a high-electrochemical-performance anode material for lithium-ion batteries.

[0007] The present invention provides a nitrogen-doped modified silicon-carbon anode material, using silicon monoxide as the silicon source, methane as the carbon source, and melamine as the nitrogen source. A nitrogen-doped modified silicon-carbon anode material is prepared by chemical vapor deposition in combination with mechanical ball milling and high-temperature pyrolysis. Further, the auxiliary gases in the CVD reaction process are hydrogen and argon.

[0008] The present invention also provides a method for preparing the nitrogen-doped modified silicon-carbon anode, and the steps thereof may be specifically as follows: (1) Uniformly disperse an appropriate amount of silicon suboxide powder on a clean corundum plate, send it into a cold-wall chemical vapor deposition system, and when the temperature is raised to the reaction temperature under a hydrogen-argon mixed gas according to the equipment operation process, adjust the flow rates of hydrogen and argon and introduce methane to carry out a chemical vapor deposition (CVD) reaction. After that, turn off methane and hydrogen, and cool down to room temperature in an argon environment to obtain the silicon-carbon anode material SiO x @Gr.

[0009] (2) Add the SiO x @Gr powder obtained in step (1) and melamine into a ball-milling tank, add ball-milling beads, grind them in a planetary ball mill, and then sieve them for standby; (3) Place the mixture obtained in step (2) in a corundum boat, send it into a single-temperature-zone high-temperature tube furnace, raise the temperature to the required temperature in an Ar atmosphere and keep it warm for a certain period of time. After the heat treatment is completed, naturally cool down to room temperature under the protection of an inert gas to obtain the nitrogen-doped modified silicon-carbon anode material SiO x @Gr-N.

[0010] (4) In step (2), by adjusting the mass ratios of different silicon-carbon materials SiO x @Gr and melamine, repeat steps (2)-(3) to prepare different nitrogen-doped modified silicon-carbon anode materials SiO x @Gr-NX.

[0011] Further, the carbon substance generated by the CVD reaction is mainly vertically oriented multi-layer graphene.

[0012] Further, the addition amount of the SiO x powder in step (1) is 0.5 g.

[0013] Further, the temperature-raising process in step (1) is as follows: After evacuating the air in the reaction chamber and purging the gas, at a flow rate of H2 / Ar = 30 / 70 sccm, raise the temperature to 900 °C at a temperature-raising rate of 5 °C·min -1 .

[0014] Further, the CVD reaction process in step (1) is as follows: When the temperature rises to 900 °C, adjust the flow rates of H2 and Ar to 20 and 400 sccm respectively, stabilize for 5 min, and then introduce 50 sccm of methane and keep it warm for reaction for 120 min.

[0015] Further, in step (2), add zirconia beads at a mass ratio of ball-to-material of 20:1, and grind for 5 h at a rotation speed of 500 r·min -1 .

[0016] Further, in step (2), SiO added before ball milling x @The mass ratio of Gr and melamine is any one of 1:0.5, 1:1 and 1:2.

[0017] Further, in step (3), in a single-temperature zone tube furnace with an Ar flow rate of 100 sccm, the heating rate is 5 °C·min -1 It is heated to 900 °C and then held for 3 h.

[0018] The present invention also provides an application of the above-prepared nitrogen-doped modified silicon-carbon anode material in the anode of a lithium-ion half-cell. First, a slurry is prepared by grinding and mixing according to a mass ratio of active material: conductive agent: binder = 8:1:1 (Super P is used as the conductive agent, PVDF is used as the binder, and N-methylpyrrolidone is used as the dispersant). It is coated on a copper foil with a coating thickness of 100 μm, sent to a vacuum drying oven and dried at 80 °C for 8 h, and then cut into circular anode sheets with a diameter of 12 mm using a slicer for standby. Then, it is assembled into a battery using a CR2032-type button battery case. In a glove box filled with an argon atmosphere (O2 < 0.01 ppm, H2O < 0.01 ppm), the battery is assembled, and the battery is tightly sealed with a sealing machine and left standing for 24 h to test the electrochemical performance of the battery. The electrochemical performance of the battery is mainly tested by constant current charge and discharge cycling, rate performance, and electrochemical impedance spectroscopy (EIS).

[0019] The cycle stability and rate performance of the battery are tested by a Neware battery test system CT-4008, and the electrochemical impedance spectroscopy is detected by a Chenhua electrochemical workstation CHI-660E.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention provides a preparation process for a high-performance nitrogen-doped modified silicon-carbon anode material for lithium-ion batteries. The preparation process of this method is simple and easy to operate, and the prepared nitrogen-doped modified silicon-carbon anode material has good cycle stability and rate performance in lithium-ion batteries. The capacity retention rate is more than 87% after 100 cycles of constant current cycling, and the electrode kinetics of this anode material is excellent. The electrochemical impedance spectroscopy shows that the charge transfer resistance is reduced from 523.4 Ω of the initial silicon monoxide to 182.0 Ω, that is, the electrode has good conductivity. The optimal mass ratio of the silicon-carbon anode material and melamine added before ball milling is 1:1. In addition, no catalyst needs to be introduced during the reaction process, which reduces the complexity and production cost of the preparation process. This process has strong scalability and is environmentally friendly, and is suitable for large-scale industrial applications. Description of the Drawings

[0021] Figure 1 is 0.5 A·g -1Cyclic charge-discharge curves of the nitrogen-doped modified silicon-carbon anode material sample group under current density.

[0022] Figure 2 For SiO x Rate performance test of SiO

[0023] Figure 3 For SiO x 、SiO x Electrochemical impedance spectra of SiO

[0024] Figure 4 For SiO x XPS full spectra and Si 2p, C 1s, N 1s fine spectra of SiO

[0025] Figure 5 TEM images of the nitrogen-doped modified silicon-carbon anode material.

[0026] Figure 6 For SiO x 、SiO x @Gr and SiO x XRD patterns of SiO Detailed implementation manners

[0027] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments, but the protection scope of the present invention is not limited. Unless otherwise specified, the experimental methods used in the present invention are all conventional methods, and the experimental equipment, materials, reagents, etc. used can all be obtained from commercial channels.

[0028] The silicon source in the following examples: silicon monoxide (SiO x ) is of AR grade with an average particle size of 1 μm; the nitrogen source: melamine, AR grade, both are produced by Shanghai Aladdin Biochemical Technology Co., Ltd. The carbon source: methane, auxiliary gases: hydrogen, argon, with a purity of ≥99.999%, all are produced by Jiuce Gas Sales (Fujian) Co., Ltd. The cold-wall chemical vapor deposition system is produced by Changzhou Guocheng New Materials Technology Co., Ltd.

[0029] Example 1 (1) Weigh 0.5 g of silicon monoxide powder and disperse it evenly on a clean corundum plate, then send it into the cold-wall chemical vapor deposition system. According to the equipment operation process, under the mixed gas flow of H2 / Ar = 30 / 70 ml·min -1 flow rate, at a rate of 5 °C·min -1The heating rate is increased to 900 °C. When the reaction temperature is reached, the flow rates of hydrogen and argon are adjusted to 20 and 400 sccm respectively. After stabilizing for 5 min, 50 sccm of methane is introduced and the chemical vapor deposition (CVD) reaction is carried out for 120 min. Then, the power supplies of methane, hydrogen, and the heater are turned off, and the argon is adjusted to 100 sccm. After water cooling to room temperature, the silicon-carbon anode material SiO x @Gr is obtained.

[0030] (2)The SiO x @Gr powder and melamine are added to the ball milling tank according to a certain mass ratio. Ball milling beads and the mixed powder are added according to a mass ratio of 20:1. It is ball milled in a planetary ball mill at 500 r·min -1 for 5 h and then sieved for standby; (3)The mixture in step (2) is placed in a corundum boat and sent into a single-temperature zone high-temperature tube furnace. It is heated to 900 °C at a rate of 5 °C·min -1 in an atmosphere of 100 sccm Ar and held for 3 h. After the heat treatment, it is naturally cooled to room temperature under the protection of inert gas to obtain a nitrogen-doped modified silicon-carbon anode material.

[0031] (4)In step (2), by adjusting the mass ratios of different silicon-carbon materials SiO x @Gr and melamine, steps (2)-(3) are repeated to prepare different nitrogen-doped modified silicon-carbon anode materials SiO x @Gr-NX (X = 1, 2, 3, respectively indicating that the mass ratios of SiO x @Gr and melamine added before ball milling are 1:0.5, 1:1, and 1:2).

[0032] The materials are prepared into negative electrode sheets according to the method in the foregoing invention content and assembled into a CR2032 type button lithium-ion half-cell, which is left standing for 24 h for standby. The battery is subjected to a constant current charge-discharge cycle test and the results are plotted as Figure 1 .

[0033] The research results show that the first Coulombic efficiency of SiO x @Gr-N1 is 72.3%; while the ICEs of SiO x @Gr-N2 and SiO x @Gr-N3 are 76.7% and 72.7% respectively. After SiO x @Gr-NX is fully activated for 5 cycles at 0.1 A·g -1 and then cycled to 100 cycles at a current density of 0.5 A·g -1 , SiO x @Gr-N1, SiO x @Gr-N2, SiOx The capacity retention rates of @Gr-N3 compared to the 6th cycle are 106.4%, 89.7%, and 87.0% respectively. Generally speaking, for SiO x @Gr-N1 has the highest capacity retention rate. The capacity increase phenomenon is related to the formation and dissolution of the polymer gel-like film inside the electrode material. The capacity performances of the three electrode materials are not very different, and all show good cycle stability.

[0034] Application Example 1 The high-current charge and discharge ability of the nitrogen-doped modified silicon-carbon anode material is revealed by examining the rate performance of the battery. The test results are shown in Figure 2 .

[0035] The results show that the SiO x @Gr-NX electrodes are charged and discharged at different current densities: 0.1, 0.5, 1.0, 2.0, and 4.0 A·g -1 and then gradually restored to 0.1 A·g -1 After that, the capacity retention rate of SiO x @Gr-N1 is 93.7%, and the capacity retention rates of SiO x @Gr-N2 and SiO x @Gr-N3 are 97.9% and 70.8% respectively. The average Coulombic efficiency is above 98%. This shows that after the high-current charge and discharge process, the SiO x @Gr-NX sample group does not cause the collapse of the electrode structure due to the volume expansion of silicon substances, and the capacity retention rate is good.

[0036] To study the kinetic characteristics of the electrode, the assembled battery is tested for electrochemical impedance. After fitting through the equivalent circuit diagram corresponding to its characteristics, the curve is plotted. The results are shown in Figure 3 .

[0037] The results show that the nitrogen-doped silicon-carbon anode material effectively reduces the charge transfer resistance of SiO x (523.4 Ω), and the charge transfer resistance of the prepared SiO x @Gr-NX decreases with the increase of the nitrogen source addition amount. The charge transfer resistances of SiO x @Gr-N1, SiO x @Gr-N2, and SiO x @Gr-N3 are 416.7 Ω, 388.2 Ω, and 182.0 Ω respectively. This shows that increasing the nitrogen source content is beneficial to improving the charge transfer efficiency of the anode material.

[0038] To understand the chemical composition of the nitrogen-doped modified silicon-carbon anode material, the synthesized powder sample is tested and analyzed using XPS technology.

[0039] The results show that five characteristic peaks of Si 2p, Si 2s, C 1s, O 1s, and N 1s are detected in each material, and the binding energy positions correspond to 102.8, 153.8, 284.8, 532.8 eV, and 398.7 eV respectively, indicating the successful doping of N element. By using nitrogen doping to modify the material, the electronegativity and conductivity of the electrode can be effectively improved, and the diffusion barrier and adsorption energy of Li⁺ in the material can be reduced, thus having a positive impact on its storage and transmission processes.

[0040] To understand the microscopic morphology of the nitrogen-doped modified silicon-carbon anode material, a transmission electron microscope (TEM) was used to characterize the synthesized powder sample.

[0041] The results show that the graphene layer deposited by CVD has abundant wrinkles and a large number of burr-like edges, indicating its vertically oriented growth. The dense coating structure of graphene on SiO x can inhibit its huge volume expansion effect during the charge and discharge process of the lithium-ion battery, and the voids between the carbon layers can also provide reversible storage for some lithium ions, thereby improving the capacity performance of the battery.

[0042] The composition and phase information of the nitrogen-doped modified silicon-carbon anode material were characterized by XRD.

[0043] The results show that the wide diffraction peak range of 18° - 30° corresponds to amorphous silicon suboxide. After CVD deposition for 120 min, the diffraction peaks of SiO x @Gr at 28.4°, 47.3°, 56.1°, 69.1°, 76.4°, and 88.0° positions correspond to the (111), (220), (311), (400), (331), (422) crystal planes of the Si crystal phase respectively. After adding melamine and ball milling and then thermal cracking, the Si crystal planes in the SiO x @Gr-NX material show no significant changes, showing diffraction peaks similar to those of SiO x @Gr, indicating that the mechanical ball milling and high-temperature decomposition processes did not change the crystal phase structure of SiO x and the free Si generated by its disproportionation. In addition, no N-related element and phase information were detected in the SiO x @Gr-NX sample group, probably because the nitrogen-doped carbon layer belongs to an amorphous substance.

[0044] The above is only a specific embodiment with relatively good creativity of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, makes equivalent substitutions or changes, and should be covered within the protection scope of the present invention.

Claims

1. A process for preparing a high-performance anode material of nitrogen-doped silicon carbide by chemical vapor deposition, characterized in that, Chemical vapor deposition is carried out on the silicon source, and a carbon source gas and an auxiliary gas are introduced to grow multi-layer vertically oriented graphene. Then, it is mixed with a nitrogen source material and ball-milled, and the ground powder is heat-treated to obtain a nitrogen-doped modified silicon-carbon anode material.

2. The method for preparing the nitrogen-doped modified silicon-carbon anode material according to claim 1, wherein The silicon source belongs to silicon monoxide SiO x ; the carbon source gas is selected as methane; the auxiliary gas is any one or two of hydrogen and argon; the nitrogen source material is melamine.

3. The method for preparing the nitrogen-doped modified silicon-carbon anode material according to claim 2, wherein, Specifically, it includes the following steps: (1) Uniformly disperse silicon monoxide powder SiO x on a clean corundum plate, feed it into a cold-wall chemical vapor deposition system. When the temperature is raised to the reaction temperature under a hydrogen-argon mixed gas according to the equipment operation process, adjust the flow rates of hydrogen and argon and introduce methane to carry out a chemical vapor deposition CVD reaction. Then, turn off methane and hydrogen, and cool down to room temperature in an argon environment to obtain a silicon-carbon anode material SiO x @Gr; (2) Add the SiO x @Gr powder and melamine into the ball milling jar, add ball milling beads, grind in a planetary ball mill and then sieve for standby; (3) Place the mixture from step (2) in a corundum boat and send it into a single-temperature-zone high-temperature tube furnace. Heat it up to the required temperature in an Ar atmosphere and hold for a certain time. After the heat treatment, let it cool down to room temperature naturally under the protection of inert gas to obtain the nitrogen-doped modified silicon-carbon anode material SiO x @Gr-N.

4. The preparation method according to claim 3, characterized in that, The addition amount of the SiO powder described in step (1) x is 0.5 g.

5. The preparation method according to claim 3, wherein The temperature-rising process in step (1) is as follows: After evacuating the air in the reaction chamber and purging the gas, at a flow rate of H2 / Ar = 30 / 70 sccm, the temperature is raised to 900 °C at a temperature-rising rate of 5 °C·min -1 -1.

6. The preparation method according to claim 3, characterized in that, The CVD reaction process in step (1) is as follows: after the temperature rises to 900 °C, the flow rates of H2 and Ar are adjusted to 20 and 400 sccm respectively. After stabilizing for 5 min, 50 sccm of methane is introduced and the reaction is carried out under insulation for 120 min.

7. The preparation method according to claim 3, characterized in that, In step (2), zirconia beads are added at a mass ratio of the ball-to-material ratio of 20:1, and ground for 5 h at a rotational speed of 500 r·min -1 -1.

8. The preparation method according to claim 3, characterized in that, In step (2), SiO added before ball milling x @The mass ratio of Gr to melamine is any one of 1:0.5, 1:1, and 1:

2.

9. The preparation method according to claim 3, characterized in that, Step (3) The single-zone tube furnace is heated at a heating rate of 5 °C·min⁻¹ with an Ar flow rate of 100 sccm. -1 After heating to 900 °C, it is held at this temperature for 3 h.

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