Silicon negative electrode material and preparation method thereof

Abstract

The application provides a silicon negative electrode material and a preparation method thereof, and relates to the technical field of lithium ion batteries.A preparation method of a silicon negative electrode material comprises the following steps: uniformly mixing a silicon source and a carbon source, performing high-speed ball milling to obtain a mixture, loading the mixture into a lithium metal bag, rubbing the lithium metal bag loaded with the mixture to obtain a composite material, and washing the composite material to obtain the silicon negative electrode material.The silicon negative electrode material provided by the application has excellent cycle performance.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a silicon anode material and its preparation method. Background Technology

[0002] With the development of the new energy industry, the energy density requirements for battery cells are becoming increasingly stringent. Traditional graphite anodes have reached their limits, while the high specific capacity of silicon anode materials meets the future energy density demands of battery cells. However, the cyclic stress expansion of silicon anodes severely restricts their further application. Current modifications to silicon anodes mainly involve nano-sizing, carbon coating, the use of silicon oxide, and oxide coating. Traditional silicon anode material coating with graphitized carbon materials is time-consuming, energy-intensive, and prone to poor coating properties and easy detachment. Summary of the Invention

[0003] Based on the technical problems existing in the background technology, the present invention proposes a method for preparing graphite material in situ coated on the surface of silicon source by lithium thermal reaction. The silicon anode material prepared by this method is economical and practical, and the prepared silicon anode material has excellent cycle performance.

[0004] The present invention proposes a method for preparing a silicon anode material, comprising the following steps:

[0005] The silicon source and carbon source are mixed evenly and then subjected to high-speed ball milling to obtain a mixture. The mixture is then placed in a lithium metal bag and rubbed to obtain a composite material. The composite material is then washed to obtain a silicon anode material.

[0006] This invention utilizes lithium thermal synthesis to prepare silicon anode materials in situ, forming a graphite coating on the silicon material surface in situ. The reaction conditions are mild, the operation is simple, and the industrialization feasibility is strong. The lithium thermal synthesis in this invention is carried out during the friction stage after heating a copper plate. The heated lithium bag melts, and the friction causes the molten lithium to collide and contact with the silicon and carbon source mixture, triggering the reaction to synthesize the silicon anode material.

[0007] Preferably, the silicon source is selected from one or more of elemental silicon and SiO2.

[0008] The role of the silicon source is to serve as the main material for silicon anode materials prepared from silicon.

[0009] Preferably, the carbon source is selected from one or more of PVDF and PTFE.

[0010] The role of the carbon source is to generate graphite that coats the surface of the silicon source during the lithium thermal synthesis reaction.

[0011] Preferably, the mass ratio of the silicon source to the carbon source is (4-5):(5-6).

[0012] Controlling the mass ratio of silicon source to carbon source within a certain range helps to improve the coating quality, resulting in silicon anode materials with excellent cycle performance.

[0013] Preferably, the ball milling parameters are: rotation speed of 800-1000 r / min, ball-to-material ratio of 15:1, and ball milling time of 6-12 h.

[0014] Adjusting the parameters of the ball mill helps to achieve uniform mixing of silicon and carbon sources, and allows for the in-situ uniform coating of graphite material on the surface of the silicon source.

[0015] Preferably, the mass ratio of the mixture to lithium metal is (1.5-2):1.

[0016] Within a certain range, the mass ratio of the mixture to lithium metal facilitates the occurrence of the lithium thermal reaction, thus preparing silicon anode materials.

[0017] Preferably, the friction of the lithium metal bag containing the mixture specifically involves placing the lithium metal bag containing the mixture in a plate heat compressor, heating a copper plate, and using the heated copper plate to rub the lithium metal bag containing the mixture.

[0018] More preferably, the heating temperature of the copper plate is 200-250°C.

[0019] Heating the copper plate to a certain temperature range helps ensure that the lithium metal bag can be completely melted. It is only necessary to heat the copper plate to 200-250℃; continuous heating is not required during the process, and the reaction time is short.

[0020] Preferably, the washing solution used for washing is selected from one or more of methanol and hydrochloric acid.

[0021] Choosing the right detergent can help remove excess lithium metal and lithium fluoride impurities generated during the reaction.

[0022] More preferably, the concentration of the hydrochloric acid is 0.5-5M.

[0023] The present invention also proposes a silicon anode material prepared by the above preparation method.

[0024] The beneficial effects of this invention are as follows:

[0025] This invention utilizes the instantaneous high-temperature reaction of the lithium-thermal reaction to highly graphitize and coat the carbon source onto the silicon source surface, thereby preparing high-performance silicon anode materials. The lithium-thermal reaction process provided by this invention is a self-propagating high-temperature synthesis. This reaction can be initiated by directly immersing carbon source powder into molten Li in a transverse shear manner. The heat released by the strongly exothermic reaction generates a combustion wave, which spontaneously and self-sustainingly propagates to the remaining reactants. The graphite synthesized by the instantaneous carbon vaporization and condensation under high temperature simplifies the graphitization process of carbon materials. At the same time, graphite coating can be formed in situ on the silicon material surface. Furthermore, no continuous external energy input is required throughout the synthesis process, and the reaction time is short. This opens up an economical route for production and has advantages over traditional methods. Another important feature of the lithium-thermal strategy is its feasibility in industrial-scale material preparation, which can be achieved through tunnel kilns for large-scale production. Attached Figure Description

[0026] Figure 1 This is a SEM image of the silicon anode material prepared in Example 1 of the present invention.

[0027] Figure 2 This is a graph showing the cyclic capacity retention rate in Embodiment 1 of the present invention.

[0028] Figure 3 A schematic diagram simulating large-scale production using a tunnel kiln;

[0029] 1-Tunnel kiln, 2-Copper plate, 3-Lithium bag, 4-Mixture of silicon source and carbon source.

[0030] Figure 4 The first charge specific capacity is the silicon anode material prepared in Example 1. Detailed Implementation

[0031] The technical solution of the present invention will be described in detail through specific embodiments.

[0032] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0033] Example 1

[0034] A method for preparing a silicon anode material includes the following steps:

[0035] 4g of Si powder and 6g of PTFE powder were placed in the jar of a star-shaped high-energy ball mill, and then zirconium balls were added. The ball-to-powder ratio was 15:1. The mixture was ball-milled at 1000 r / min for 6 h to obtain a mixture. 5g of the mixture was weighed in a vacuum glove box and placed into a 9g lithium metal bag. The bag was placed in a plate heat compressor and the lithium bag was rubbed by heating a copper plate to 200°C to obtain a composite material. The composite material was washed with methanol and 1M HCl solution to obtain the silicon anode material Si@Gr.

[0036] Example 2

[0037] A method for preparing a silicon anode material includes the following steps:

[0038] 4g of SiO2 powder and 6g of PTFE powder were placed in the jar of a star-shaped high-energy ball mill, and then zirconium balls were added. The ball-to-powder ratio was 15:1. The mixture was ball-milled at 1000 r / min for 6 h to obtain a mixture. 5g of the mixture was weighed in a vacuum glove box and placed into a 9g lithium metal bag. The bag was placed in a plate heat compressor and the lithium bag was rubbed by heating a copper plate to 200°C to obtain a composite material. The composite material was washed with methanol and 1M HCl solution to obtain the silicon anode material SiO2@Gr.

[0039] Example 3

[0040] A method for preparing a silicon anode material includes the following steps:

[0041] 4g of Si powder and 6g of PVDF powder were placed in the jar of a star-shaped high-energy ball mill, and then zirconium balls were added. The ball-to-powder ratio was 15:1. The mixture was ball-milled at 1000 r / min for 6 h to obtain a mixture. 5g of the mixture was weighed in a vacuum glove box and placed into a 9g lithium metal bag. The bag was placed in a plate heat compressor and the lithium bag was rubbed by heating a copper plate to 200°C to obtain a composite material. The composite material was washed with methanol and 1M HCl solution to obtain the silicon anode material Si@Gr.

[0042] Example 4

[0043] A method for preparing a silicon anode material includes the following steps:

[0044] 4g of SiO2 powder and 6g of PVDF powder were placed in the jar of a star-shaped high-energy ball mill, and then zirconium balls were added. The ball-to-powder ratio was 15:1. The mixture was ball-milled at 1000 r / min for 6 h to obtain a mixture. 5g of the mixture was weighed in a vacuum glove box and placed into a 9g lithium metal bag. The bag was placed in a plate heat compressor and the lithium bag was rubbed by heating a copper plate to 200°C to obtain a composite material. The composite material was washed with methanol and 1M HCl solution to obtain the silicon anode material SiO2@Gr.

[0045] The above-mentioned negative electrode material was used to prepare a negative electrode sheet, which was then assembled with a positive electrode sheet, a separator, and an electrolyte to obtain a lithium-ion battery. The capacity retention rate of the lithium-ion battery after 200 cycles was tested. Two parallel experiments were conducted, and the test results are shown in Table 1. The test method was as follows: charging at a rate of 0.5C from 2.8V to 4.35V, then maintaining a constant current of 4.35V until the current was cut off at 0.05C, and discharging at a rate of 1C back to 2.8V. This cycle was repeated for 200 cycles.

[0046] Table 1

[0047]

[0048] The assembled lithium-ion batteries were tested for their initial charge specific capacity and initial coulombic efficiency. The test method was as follows: first, the batteries were left to rest for 5 minutes, then discharged at a constant current of 0.06C to 0.005V, followed by a constant current discharge at 0.01C to 0.005V, then left to rest for 5 minutes, and finally charged at a constant current of 0.1C to 1.5V. The test results are shown in Table 2.

[0049] Table 2

[0050]

[0051]

[0052] From Table 1, Table 2 and Figure 2 , Figure 4 The data shows that the silicon anode material prepared by this invention has a high cycle capacity retention rate, indicating that the silicon anode material has excellent cycle performance and excellent first coulombic efficiency.

[0053] Figure 3 The schematic diagram for simulating large-scale production using a tunnel kiln shows that a mixture of milled silicon and carbon sources is placed in a lithium metal bag, which is then placed in a copper plate inside the tunnel kiln, and subsequently heated.

[0054] In summary, the silicon anode material provided by this invention has excellent cycle performance.

[0055] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for producing a silicon negative electrode material, characterized by, The method comprises the following steps: The silicon source and the carbon source are mixed uniformly, and then high-speed ball milling is performed to obtain a mixture; the mixture is loaded into a lithium metal bag, the lithium metal bag loaded with the mixture is rubbed, and a composite material is obtained; and the composite material is washed to obtain a silicon negative electrode material; The rubbing of the lithium metal bag loaded with the mixture is specifically as follows: the lithium metal bag loaded with the mixture is placed in a plate-type thermal compressor, the copper plate is heated, and the heated copper plate is used to rub the lithium metal bag loaded with the mixture; The mass ratio of the silicon source to the carbon source is (4-5):(5-6); and the mass ratio of the mixture to lithium metal is (1.5-2):

1. The silicon negative electrode material is Si@Gr or SiO2@Gr.

2. The production method according to claim 1, characterized by, The silicon source is selected from one or more of elemental silicon and SiO2.

3. The preparation method according to claim 1, characterized in that, The carbon source is selected from one or more of PVDF and PTFE.

4. The method of claim 1, wherein, The ball milling parameters are as follows: the rotation speed is 800-1000 r / min, the ball-to-material ratio is 15:1, and the ball milling time is 6-12 h.

5. The preparation method according to claim 1, characterized in that, The washing liquid used for washing is selected from one or more of methanol and hydrochloric acid.

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