A method for preparing magnesium-containing silicon oxide negative electrode material for lithium-ion batteries

Abstract

The present invention relates to a method for preparing a magnesium-containing silicon oxide negative electrode material for lithium-ion batteries. The technical solution comprises the following steps: (1) mixing silicon oxide powder and metallic magnesium powder in proportion, adding a solid organic carbon source, and then placing the mixture into a nitrogen-protected VC mixer for mixing; (2) adding an inert gas for reaction; (3) introducing a gaseous organic carbon source into a chemical vapor deposition furnace for secondary carbon coating; after coating, cooling the mixture to room temperature, removing the mixture, and obtaining a magnesium-containing silicon oxide negative electrode material for lithium-ion batteries after grading. The beneficial effect is that the present invention simultaneously achieves pre-magnesium and double-layer carbon coating of the silicon oxide negative electrode material through a one-pot process. The resulting material not only exhibits good properties and has a smaller silicon grain size, but also has a simple, convenient, and easy-to-implement process, greatly reducing energy loss in the production process, and facilitating mass production and industrial application.

Description

Technical Field

[0001] The present invention relates to the field of negative electrode materials for lithium ion batteries, and in particular to a method for preparing a negative electrode material containing magnesium silicon oxide for lithium ion batteries. Background Art

[0002] With the national strategic goals of achieving carbon neutrality and peak carbon emissions, my country's new energy industry has ushered in new development opportunities, but also presents a significant challenge. To achieve carbon neutrality, it is imperative to develop new energy sources with low carbon emissions. Currently, lithium-ion batteries, a key component of new energy technology development, are widely used in electric vehicles, mobile phones, and laptops. However, as the market demands for higher energy density in lithium-ion batteries, traditional graphite anode materials (theoretical specific capacity: 372 mAh / g) are no longer able to meet the demand for high-energy-density batteries. Silicon-based materials, as a new type of lithium-ion battery anode material, have attracted considerable attention due to their high theoretical specific capacity (4200 mAh / g). However, they suffer from volume expansion of up to 300% during the charge and discharge process, resulting in low initial charge and discharge efficiency, poor rate performance, and even pulverization and shedding of the active material, seriously affecting their cycle life. Compared with nano-silicon, silicon oxide negative electrode material, as a silicon-based material, reduces the volume expansion of silicon during lithium insertion to a certain extent (200%) due to the presence of silicon dioxide. However, silicon dioxide is an inactive substance that does not participate in electrochemical reactions, which makes the initial efficiency of silicon oxide material low, seriously affecting its application in the field of electric vehicles.

[0003] Through extensive experiments and research, researchers have discovered that introducing an appropriate amount of magnesium can improve the initial coulombic efficiency of silicon oxide materials. For example, patent CN110311120A discloses a method for synthesizing magnesium silicide from silicon powder and magnesium powder, then mixing it with silicon monoxide, heating it, and then carbon-coating it to produce a magnesium-containing silicon oxide anode material. Patent CN113410448A utilizes a molten salt magnesium thermal reaction to mix silicon oxide with metallic magnesium powder and molten salt, ultimately producing a silicon oxide composite anode material with a core-shell structure consisting of a carbon outer layer and a silicate inner shell. Patent CN114068902A heat-treats the mixed silicon oxide and magnesium powder, then coats it with asphalt and then an organic gas, resulting in a silicon oxide anode material with three outer layers: a magnesium silicate layer, a carbon layer, and a carbon layer, from the inside out.

[0004] Although the above methods all obtain magnesium-containing silicon 2 oxide negative electrode materials, the process is relatively complicated and difficult to industrialize. In addition, the preparation process requires multiple intermittent material changes and heat treatments, resulting in large energy losses. Summary of the Invention

[0005] The purpose of the present invention is to address the above-mentioned defects in the prior art and provide a method for preparing a magnesium-containing silicon oxide negative electrode material for a lithium-ion battery. The method completes the pre-magnesium and two carbon coating processes of the silicon oxide negative electrode material in one pot, thereby obtaining a double-layer carbon-coated magnesium-containing silicon oxide negative electrode material. The preparation process is simple, convenient and easy to industrialize. In addition, by strictly controlling the heating rate and holding time during the preparation process, the influence of the magnesium thermal reaction process on the silicon grain size can be effectively reduced.

[0006] The present invention provides a method for preparing a negative electrode material containing magnesium silicon oxide for lithium ion batteries, the technical solution of which comprises the following steps:

[0007] (1) Silicon oxide powder and magnesium powder are mixed in a mass ratio of 1:0.03-1:0.2, and a solid organic carbon source is added to mix with them. The ratio of SiO powder and magnesium powder to solid organic carbon source is 1:0.02-0.15, and then placed together in a nitrogen-protected VC mixer for mixing for 1-5 hours;

[0008] (2) adding the mixed materials in step (1) into a chemical vapor deposition furnace protected by inert gas for reaction, heating the temperature to 400-700°C at a certain heating rate and keeping the temperature constant for 1-12 hours; then continuing to heat the temperature to 800-1000°C and keeping the temperature constant for 1-10 hours;

[0009] (3) After the constant temperature in step (2) is completed, a gaseous organic carbon source is introduced into the chemical vapor deposition furnace to perform a secondary carbon coating on the substance after the reaction in step (2); after the coating is completed, the substance is cooled to room temperature and taken out, and after graded treatment, a magnesium silicon oxide negative electrode material for lithium ion batteries is obtained.

[0010] Preferably, the solid organic carbon source in step (1) is one or more of sucrose, glucose, fructose, polyvinyl alcohol and citric acid.

[0011] Preferably, the heating rate in the above step (2) to 400-700°C and 800-1000°C is 0.01-5°C / min.

[0012] Preferably, the step of performing carbon coating treatment in the above step (3) is as follows: after the constant temperature in step (2) is completed, the furnace is not stopped, and a gaseous organic carbon source is continuously introduced into the chemical vapor deposition furnace to perform secondary carbon coating on the material in the chemical vapor deposition furnace.

[0013] Preferably, the gaseous organic carbon source in the above step (3) is one or more of methane, ethane, propane, ethylene, propylene, and acetylene.

[0014] Preferably, in the above step (3), the temperature of the secondary carbon coating is 500-1000°C, and the carbon content in the final magnesium silicon oxide negative electrode material for lithium ion batteries is 0.5-10%.

[0015] Preferably, the magnesium-containing silicon oxide negative electrode material for lithium-ion batteries obtained in the above step (3) has a core-shell structure: the core includes magnesium silicate, magnesium metasilicate and silicon particles between the two, and the outer shell is a double-layer carbon coating layer, wherein the inner layer is a relatively loose carbon layer formed by thermal decomposition of a solid organic carbon source, and the outer layer is a dense carbon layer formed by thermal decomposition of a gaseous organic carbon source.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0017] The preparation method of the present invention utilizes a one-pot process to simultaneously perform magnesium pre-treatment and double-layer carbon coating of silicon dioxide, rather than the prior art method of first synthesizing magnesium silicate and then subjecting it to a series of treatments before carbon coating. This makes the production process of the present invention simpler, easier to operate, and more controllable. Furthermore, the present invention fully utilizes the effects of the magnesium thermal reaction to reduce energy consumption throughout the production process, enabling mass production and industrial application.

[0018] Silicon oxide and metallic magnesium are heat-treated in a chemical vapor deposition (CVD) furnace, causing at least a portion of the silicon oxide to react with metallic magnesium powder to produce magnesium silicate and silicon element, thereby obtaining a magnesium-containing silicon oxide negative electrode material. Since the magnesium-containing silicate is chemically inert and does not have the ability to deintercalate or deintercalate lithium, it can form a stable chemical structure and inhibit the volume expansion of the silicon oxide material. At the same time, by utilizing the magnesium thermal mechanism and controlling the heating rate, the heat released by the magnesium thermal process is slowly released during the heating process, thereby avoiding the enlargement of silicon grains in the silicon oxide during the magnesium thermal process. The formation of smaller silicon grains is beneficial to improving the cycle performance of the negative electrode material.

[0019] In addition, while controlling the magnesium thermal reaction, the magnesium thermal reaction is simultaneously used to complete the carbon coating of the silicon oxide material with a solid organic carbon source, making full use of the heat released by the magnesium thermal reaction. At the same time, in the one-pot method, the product after the magnesium thermal reaction is subsequently coated with a gaseous organic carbon source, thereby forming a double-layer carbon coating on the surface of the material. The inner layer is a loose carbon layer formed by the thermal decomposition of the solid organic carbon source, and the outer layer is a dense carbon layer formed by the thermal cracking of the gaseous organic carbon source. This will make the material have better structural stability and improve the service life of the negative electrode material.

[0020] Therefore, the first coulombic efficiency of the lithium battery prepared by the negative electrode material of the present invention is greatly improved, so that the negative electrode material produced by the present invention is expected to become the most promising high-capacity negative electrode material for lithium-ion batteries in industrialization. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1The XRD pattern of the negative electrode material prepared in Example 1 of the present invention;

[0022] Figure 2 This is the SEM image of the negative electrode material prepared in Example 1 of the present invention;

[0023] Figure 3 The first charge and discharge curves of the negative electrode materials prepared in Example 1 of the present invention and the comparative example. DETAILED DESCRIPTION

[0024] The preferred embodiments of the present invention are described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0025] Example 1, a method for preparing a negative electrode material containing magnesium silicon oxide for a lithium ion battery mentioned in the present invention, comprising the following steps:

[0026] (1) Mix 1 kg of SiO powder and 80 g of magnesium powder, add 25 g of sucrose and mix with them, and put them into a nitrogen-protected VC mixer for mixing for 1 hour;

[0027] (2) adding the mixed materials in step (1) into a chemical vapor deposition (CVD) furnace protected by inert gas for reaction, heating the temperature to 550°C at a heating rate of 0.03°C / min and keeping the temperature constant for 2 hours; then continuing to heat the temperature to 850°C at a heating rate of 0.03°C / min and keeping the temperature constant for 2 hours;

[0028] (3) After the constant temperature in step (2) is completed, acetylene gas is introduced into the CVD furnace to perform a secondary carbon coating on the material after the reaction in step (2); the coating temperature is 850°C and the carbon coating amount is 5%; after the coating is completed, the material is cooled to room temperature and taken out, and after grading treatment, a magnesium-containing silicon oxide negative electrode material for lithium-ion batteries is obtained.

[0029] The final magnesium silicon oxide negative electrode material has a first specific capacity of 1345 mAh / g and a first coulombic efficiency of 82.4%.

[0030] Figure 1 The XRD spectrum of the negative electrode material prepared in Example 1 of the present invention shows obvious diffraction peaks of silicon and magnesium silicate and weaker diffraction peaks of silicon dioxide, indicating that the magnesium thermal reaction has a good reducing effect and forms magnesium silicate with silicon dioxide. At the same time, the grain size of silicon does not increase significantly. Figure 2 This is the SEM image of the negative electrode material prepared in this example. It can be seen from the figure that the particle size of the prepared negative electrode material is almost all less than 10μm, which indicates that magnesium doping has no obvious effect on the morphology and particle size of the negative electrode material. Figure 3The first charge-discharge curves of the negative electrode materials prepared in this embodiment and the comparative example are shown in FIG. Compared with the comparative example, the first specific capacity and coulombic efficiency of the negative electrode material prepared in this embodiment are greatly improved, indicating that the negative electrode material prepared in this embodiment has good performance.

[0031] Example 2, a method for preparing a magnesium silicon oxide negative electrode material for a lithium ion battery mentioned in the present invention, comprising the following steps:

[0032] (1) Mix 1 kg of SiO powder and 120 g of magnesium powder, add 30 g of sucrose and mix with them, and put them into a VC mixer protected by nitrogen and mix for 1 hour;

[0033] (2) The mixed materials in step (1) were added to a chemical vapor deposition (CVD) furnace protected by inert gas for reaction, and the temperature was increased to 550°C at a heating rate of 0.3°C / min and kept at this temperature for 2 hours; then the temperature was increased to 850°C at a heating rate of 0.3°C / min and kept at this temperature for 2 hours;

[0034] (3) After the constant temperature in step (2) is completed, acetylene gas is introduced into the CVD furnace to perform a secondary carbon coating on the material after the reaction in step (2); the coating temperature is 850°C and the carbon coating amount is 5%; after the coating is completed, the material is cooled to room temperature and taken out, and after grading treatment, a magnesium-containing silicon oxide negative electrode material for lithium-ion batteries is obtained.

[0035] The final magnesium silicon oxide negative electrode material has a first specific capacity of 1285 mAh / g and a first coulombic efficiency of 83.7%.

[0036] Example 3, a method for preparing a negative electrode material containing magnesium silicon oxide for a lithium ion battery mentioned in the present invention, comprising the following steps:

[0037] (1) Mix 1 kg of SiO powder and 150 g of magnesium powder, add 30 g of glucose and mix them together, and put them into a VC mixer protected by nitrogen and mix for 1 hour;

[0038] (2) The mixed materials in step (1) were added to a chemical vapor deposition (CVD) furnace protected by inert gas for reaction, and the temperature was increased to 550°C at a heating rate of 0.5°C / min and kept at this temperature for 2 hours; then the temperature was increased to 850°C at a heating rate of 0.5°C / min and kept at this temperature for 2 hours;

[0039] (3) After the constant temperature in step (2) is completed, methane gas is introduced into the CVD furnace to perform a secondary carbon coating on the material after the reaction in step (2); the coating temperature is 850°C and the carbon coating amount is 5%; after the coating is completed, the material is cooled to room temperature and taken out, and after grading treatment, a magnesium silicon oxide negative electrode material for lithium ion batteries is obtained.

[0040] The final magnesium silicon oxide negative electrode material has a first specific capacity of 1248 mAh / g and a first coulombic efficiency of 82.7%.

[0041] Example 4, a method for preparing a magnesium silicon oxide negative electrode material for a lithium ion battery mentioned in the present invention, comprising the following steps:

[0042] (1) Mix 1 kg of SiO powder and 180 g of magnesium powder, add 35 g of fructose, and mix them in a nitrogen-protected VC mixer for 1 h.

[0043] (2) adding the mixed materials in step (1) into a chemical vapor deposition (CVD) furnace protected by inert gas for reaction, heating the temperature to 550°C at a heating rate of 1°C / min and keeping the temperature constant for 2 hours; then continuing to heat the temperature to 850°C at a heating rate of 1°C / min and keeping the temperature constant for 2 hours;

[0044] (3) After the constant temperature in step (2) is completed, ethane gas is introduced into the CVD furnace to perform a secondary carbon coating on the material after the reaction in step (2); the coating temperature is 850°C and the carbon coating amount is 5%; after the coating is completed, the material is cooled to room temperature and taken out, and after grading treatment, a magnesium-containing silicon oxide negative electrode material for lithium-ion batteries is obtained.

[0045] The final magnesium silicon oxide negative electrode material has a first specific capacity of 1448 mAh / g and a first coulombic efficiency of 78.6%.

[0046] Example 5, a method for preparing a negative electrode material containing magnesium silicon oxide for a lithium ion battery mentioned in the present invention, comprising the following steps:

[0047] (1) Mix 1 kg of SiO powder and 30 g of magnesium powder, add 20.6 g of polyvinyl alcohol and mix them together, and put them into a VC mixer protected by nitrogen and mix for 1 hour;

[0048] (2) The mixed materials in step (1) were added to a chemical vapor deposition (CVD) furnace protected by inert gas for reaction, and the temperature was increased to 400°C at a heating rate of 0.01°C / min and kept constant at that temperature for 1 hour; then the temperature was continued to be increased to 800°C at a heating rate of 0.01°C / min and kept constant at that temperature for 1 hour;

[0049] (3) After the constant temperature in step (2) is completed, propane gas is introduced into the CVD furnace to perform a secondary carbon coating on the material after the reaction in step (2); the coating temperature is 500°C, and the carbon coating amount is 0.5%; after the coating is completed, the material is cooled to room temperature and taken out, and after grading treatment, a magnesium-containing silicon oxide negative electrode material for lithium-ion batteries is obtained.

[0050] The final magnesium silicon oxide negative electrode material has a first specific capacity of 1330 mAh / g and a first coulombic efficiency of 80.6%.

[0051] Example 6, a method for preparing a negative electrode material containing magnesium silicon oxide for a lithium ion battery mentioned in the present invention, comprising the following steps:

[0052] (1) Mix 1 kg of SiO powder and 200 g of magnesium powder, add 180 g of citric acid and mix them together, and put them into a nitrogen-protected VC mixer and mix for 1 hour;

[0053] (2) The mixed materials in step (1) were added to a chemical vapor deposition (CVD) furnace protected by inert gas for reaction, and the temperature was increased to 700°C at a heating rate of 5°C / min and kept constant at that temperature for 12 hours; then the temperature was continued to be increased to 1000°C at a heating rate of 5°C / min and kept constant at that temperature for 10 hours;

[0054] (3) After the constant temperature in step (2) is completed, ethylene and propylene gases are introduced into the CVD furnace, and the ethylene and propylene gases are mixed in a ratio of 1:1, and the material after the reaction in step (2) is subjected to secondary carbon coating; the coating temperature is 1000°C, and the carbon coating amount is 10%; after the coating is completed, the material is cooled to room temperature and taken out, and after grading treatment, a magnesium silicon oxide negative electrode material for lithium ion batteries is obtained.

[0055] The final magnesium silicon oxide negative electrode material has a first specific capacity of 1475 mAh / g and a first coulombic efficiency of 78.8%.

[0056] Comparative Example:

[0057] This comparative example provides a method for preparing a magnesium powder-doped silicon oxide negative electrode material, which mainly includes the following steps:

[0058] (1) 1 kg of SiO powder and 180 g of magnesium powder were mixed in a nitrogen-protected VC mixer and mixed for 1 h.

[0059] (2) adding the mixed materials in step (1) into a chemical vapor deposition (CVD) furnace protected by inert gas to react at a heating rate of 1°C / min to 850°C and maintaining the temperature for 2 hours;

[0060] (3) The material after the reaction in step (2) is subjected to carbon coating treatment using acetylene at a coating temperature of 850°C and a carbon coating amount of 5%. After the carbon coating is completed, the material is cooled to room temperature and taken out, and after crushing and grading, a magnesium-containing silicon oxide negative electrode material for lithium-ion batteries is obtained.

[0061] The resulting magnesium-silicon oxide-containing negative electrode material had an initial specific capacity of 1172 mAh / g and an initial coulombic efficiency of 74.5%. Compared with Examples 1-6, the initial specific capacity and initial coulombic efficiency of the negative electrode material in this comparative example were not as high. Furthermore, the use of a relatively fast heating rate for the magnesium thermal reduction reaction prevented a good reaction between the magnesium powder and silicon oxide, resulting in the generation of impurities such as additional magnesium oxide, which affected the performance of the negative electrode material.

[0062] The above descriptions are merely some preferred embodiments of the present invention. Anyone skilled in the art may be able to modify the above-described technical solutions or convert them into equivalent technical solutions. Therefore, any corresponding simple modifications or equivalent transformations based on the technical solutions of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A method for preparing a negative electrode material containing magnesium silicon oxide for lithium ion batteries, characterized by: The following steps are involved: (1) Mix 1 kg of SiO powder and 80 g of magnesium powder, add 25 g of sucrose and mix with them, and put them into a nitrogen-protected VC mixer for mixing for 1 hour; (2) Add the mixed materials in step (1) into a chemical vapor deposition furnace protected by inert gas for reaction, heat the temperature to 550°C at a heating rate of 0.03°C / min, and keep the temperature constant for 2 hours; then continue to heat the temperature to 850°C at a heating rate of 0.03°C / min, and keep the temperature constant for 2 hours; (3) After the constant temperature in step (2) is completed, acetylene gas is introduced into the chemical vapor deposition furnace to perform a secondary carbon coating on the material after the reaction in step (2), the coating temperature is 850°C, and the carbon coating amount is 5%; after the coating is completed, the material is cooled to room temperature and taken out, and after grading treatment, a magnesium silicon oxide negative electrode material for lithium ion batteries is obtained; The final magnesium silicon oxide negative electrode material has an initial specific capacity of 1345 mAh / g and an initial coulombic efficiency of 82.4%. The magnesium-containing silicon oxide negative electrode material for lithium-ion batteries obtained in step (3) has a core-shell structure: the core includes magnesium silicate, magnesium metasilicate and silicon particles between the two, and the shell is a double-layer carbon coating layer, wherein the inner layer is a relatively loose carbon layer formed by thermal decomposition of a solid organic carbon source, and the outer layer is a dense carbon layer formed by thermal decomposition of a gaseous organic carbon source.

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