Silicon active material for ultra-high capacity secondary battery and preparation method thereof

Abstract

The present invention discloses a silicon active material for ultra-high capacity secondary batteries, which uses nano-sized silicon dioxide particles as a matrix, and the surface of the silicon dioxide particles is directionally coated with a mixed solution, and silicon nanoparticles with a three-dimensional structure are formed after a high-temperature reduction reaction in a hydrogen environment. The obtained nanoparticles are coated with a surface conductive layer to obtain a silicon active material with a mechanically and electrochemically stable three-dimensional structure. The present invention also provides a preparation method and use of the above-mentioned silicon active material for ultra-high capacity secondary batteries. The silicon active material of the present invention has the characteristics of ultra-high specific capacity, stable cycle performance, and low cost, high flexibility in raw material selection, low price, and simple preparation process.

Description

Technical Field

[0001] The present invention relates to the technical field of rechargeable battery materials, and in particular to a silicon active material for ultra-high capacity secondary batteries and a preparation method thereof. Background Art

[0002] Modern society's demand for energy has greatly promoted the development of energy storage technology. As the most successful energy storage device, lithium-ion batteries have broad application prospects in portable electronic devices, electric vehicles, space technology, and other fields, and have become a research hotspot that has attracted widespread attention in recent years.

[0003] The loss of silicon active materials and poor electrical contact lead to slow kinetics and short cycle life, making the application of silicon active materials in lithium batteries not promising.

[0004] Silicon nanostructures such as nanotubes, nanowires, nanorods, nanosheets, porous, hollow or encapsulated silicon particles with protective coatings are usually used to improve the structure and electrical performance of silicon-based negative electrode materials. However, the methods for preparing these nanostructures have disadvantages such as complex technology and many steps. Therefore, it is very important to improve silicon active materials to have both good conductivity and mechanical strength.

[0005] Chinese patent CN106654271A discloses an ultra-high capacity lithium battery cathode material and preparation process, the raw materials include graphite, platinum powder, silicon carbide, titanium dioxide, lithium carbonate, tin powder, silicon dioxide, iron oxide, titanium dioxide. The patent has the advantages of good cycle performance, no reaction with electrolyte, high safety performance, stable charge and discharge platform, etc., but the raw materials are complex, the cost is high, and the process flow is relatively complicated. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a silicon active material for ultra-high capacity secondary batteries, which has the characteristics of ultra-high specific capacity, stable cycle performance and low cost.

[0007] The present invention provides a silicon active material for an ultra-high capacity secondary battery, which uses nano-sized silicon dioxide particles as a matrix, and the surface of the silicon dioxide particles is directionally coated with a mixed solution. After a high-temperature reduction reaction, silicon nanoparticles with a three-dimensional structure are formed, and the surface of the silicon nanoparticles with a three-dimensional structure is coated with a conductive layer.

[0008] Furthermore, the mixed solution is composed of the following components in weight percentage: 60wt% water, 20wt% propanol, 5wt% acetone, and 15wt% glucose.

[0009] Furthermore, the high-temperature reduction reaction is carried out in a mixed gas environment, wherein the mixed gas environment is composed of 20% by volume of hydrogen and 80% by volume of argon.

[0010] The present invention also provides a method for preparing the above-mentioned silicon active material for ultra-high capacity secondary battery, comprising the following steps:

[0011] (1) Through a high-energy mechanical ball milling process, high-purity silica material is ball milled at a speed of 500-1000 rpm for 36-48 hours to obtain nano-sized silica particles;

[0012] (2) pouring the obtained silica particles into a mixed solution, wherein the mixed solution is composed of the following components in weight percentage: 60wt% water, 20wt% propanol, 5wt% acetone, and 15wt% glucose, to carry out directional coating on the particle surface, stirring the mixture for more than 2h, and drying the mixture in a vacuum environment at a temperature above 90°C to obtain a coated composite particle material;

[0013] (3) Silicon nanoparticles with a three-dimensional structure are obtained by a high-temperature reduction reaction at 600-1200 degrees for 2h-4h in a hydrogen and argon environment. The reaction formula is as follows:

[0014] C6H 12 O6 = 6C + 6H2O

[0015] SiO2 + 2H2 -> Si + 2H2O

[0016] (4) The silicon nanoparticles and the conductive carbon nanoparticles obtained in step 3) are subjected to high-energy mechanical ball milling, wherein the mass ratio of the conductive carbon to the silicon nanoparticles is between 1:10 and 1:20, and the nanoparticles are coated with an additional surface conductive layer to obtain a three-dimensional silicon active material.

[0017] Furthermore, before performing step (4), the silicon nanoparticles are washed with deionized water for 1 to 3 times and dried in a vacuum environment at a temperature above 90° C. for 12 to 36 hours to obtain high-purity silicon nanoparticles with a three-dimensional structure.

[0018] Furthermore, the silica material in step (1) contains silicon at a mass percentage concentration of more than 99%.

[0019] Furthermore, the vacuum degree in step (2) and step (4) is -0.05 MPa.

[0020] The present invention also provides the use of the silicon active material for ultra-high capacity secondary batteries in the preparation of secondary batteries.

[0021] The present invention uses nano-sized silicon dioxide particles as a matrix, and the surface of the silicon dioxide particles is directionally coated with a mixed solution. After a high-temperature reduction reaction in a hydrogen environment, silicon nanoparticles with a three-dimensional structure are formed, and the obtained nanoparticles are coated with a surface conductive layer to obtain a silicon active material with a mechanically and electrochemically stable three-dimensional structure. The present invention uses a reducing gas to simultaneously in-situ synthesize nanosilicon and in-situ coat the porous nanocarbon layer on the surface of the nanosilicon to form a practical active lithium ion battery negative electrode material. The silicon active material of the present invention has the characteristics of ultra-high specific capacity, stable cycle performance, and low cost, high flexibility in raw material selection, low price, and simple preparation process.

[0022] The beneficial effects of the present invention are:

[0023] (1) The present invention uses high-purity silica as raw material, which has high flexibility in raw material selection and low raw material price.

[0024] (2) The present invention uses nano-sized silicon dioxide particles as a matrix, and the surface is directionally coated with a mixed solution. After a high-temperature reduction reaction, silicon nanoparticles with a three-dimensional structure are formed and then coated with a conductive layer. The preparation process is simple.

[0025] (3) The present invention forms silicon nanoparticles with a three-dimensional structure after a high-temperature reduction reaction, which enhances the ion conduction ability and the electronic conductivity of the material.

[0026] (4) The present invention has both mechanical strength and excellent electrical conductivity, thereby improving the recycling performance of the material. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0028] Figure 1 Battery cycling data, charge and discharge gram capacity, and coulombic efficiency based on silicon active materials.

[0029] Figure 2 Voltage characteristics of lithium metal batteries based on silicon active materials at the 1st, 50th, and 100th cycles. DETAILED DESCRIPTION

[0030] The technical solution of the present invention will be clearly and completely described below through specific implementation methods.

[0031] The silicon active material for an ultra-high capacity secondary battery of the present invention adopts nano-sized silicon dioxide particles as a matrix, the surface of the silicon dioxide particles is directionally coated with a mixed solution, and silicon nanoparticles with a three-dimensional structure are formed after a high-temperature reduction reaction in a hydrogen environment, and the surface of the silicon nanoparticles with the three-dimensional structure is coated with a conductive layer.

[0032] The mixed solution is composed of the following components in weight percentage: 60wt% water, 20wt% propanol, 5wt% acetone, and 15wt% glucose.

[0033] The hydrogen atmosphere contains 20% by mass hydrogen and 80% by mass argon.

[0034] The silicon active material raw material of the present invention is easy to obtain, the raw material selection flexibility is high, and the raw material price is low. The present invention adopts the mixed solution directional coating to improve the dispersibility and compatibility between silicon dioxide nanoparticles, and after high temperature reduction reaction, silicon nanoparticles with three-dimensional structure are formed, the specific surface area of ​​silicon nanoparticles is increased, and the ion conduction ability and electrical conductivity are enhanced. Example 1

[0035] A method for preparing a silicon active material for an ultra-high capacity secondary battery in this embodiment includes the following steps:

[0036] (1) Through high-energy mechanical ball milling, 1 kg of high-purity silica material was ball milled at 500 rpm for 36 hours to obtain nano-sized silicon dioxide particles. The purity of the silica material used was over 99%;

[0037] (2) pouring the obtained silica particles into the mixed solution to carry out directional coating on the particle surface, stirring fully for more than 2 hours, and drying in a vacuum environment above 90 degrees with a vacuum degree of -0.05Mpa to obtain a coated composite particle material;

[0038] (3) In a mixed gas environment, the mixed gas environment is composed of 20% by volume of hydrogen and 80% by volume of argon. Silicon nanoparticles with a three-dimensional structure are prepared by a high temperature (1000°C) reduction reaction for 2 hours;

[0039] (4) Washing the obtained silicon nanoparticles with three-dimensional structure was performed by washing them twice with deionized water and drying them in a vacuum environment at a temperature of above 90 degrees for 24 hours with a vacuum degree of -0.05 MPa.

[0040] (5) The conductive carbon and the obtained silicon nanoparticles are subjected to high-energy mechanical ball milling (500-1000 rpm, 5 h), with the mass ratio of the conductive carbon to the silicon nanoparticles being 1:10, and the nanoparticles are coated with an additional surface conductive layer to obtain a three-dimensional structured silicon active material.

[0041] The battery cycle tester was used to test the constant current and constant voltage cycle test method commonly used for lithium batteries, with a voltage range of 0.01-1V and a current of 1C, measured at room temperature and pressure. The electrochemical capacity of the silicon active material prepared in this embodiment was 2200 mAh / g. After 500 cycles, 85.7% of the capacity was still retained. Example 2

[0042] (1) Through high-energy mechanical ball milling, 2 kg of high-purity silica material was ball milled at 600 rpm for 48 hours to obtain nano-sized silicon dioxide particles. The purity of the silica material used was over 99%;

[0043] (2) pouring the obtained silica particles into the mixed solution to carry out directional coating on the particle surface, stirring fully for more than 2 hours, and drying in a vacuum environment above 90 degrees with a vacuum degree of -0.05Mpa to obtain a coated composite particle material;

[0044] (3) In a mixed gas environment, the mixed gas environment is composed of 20% by volume of hydrogen and 80% by volume of argon. Silicon nanoparticles with a three-dimensional structure are prepared by a high temperature (900°C) reduction reaction for 4 hours;

[0045] (4) By subjecting the conductive carbon and the obtained silicon nanoparticles to high-energy mechanical ball milling (600 rpm, 5 h), the mass ratio of the conductive carbon to the silicon nanoparticles was 1:20, and the nanoparticles were coated with an additional surface conductive layer to obtain a three-dimensional structured silicon active material.

[0046] refer to Figure 1 and 2 , using a battery cycle tester, adopting the constant current and constant voltage cycle test method commonly used for lithium batteries, with a voltage range of 0.01-1V and a current of 1C, measured in a normal temperature and pressure environment.

[0047] The electrochemical capacity of the silicon active material prepared in this embodiment is 3000 mAh / g, and it can still maintain a capacity of 2700 mAh / g after 300 cycles. In comparison, the electrochemical capacity of graphite material is 300 mAh / g, and the electrochemical capacity of silicon-carbon mixed material is 450 mAh / g. The electrochemical capacity of silicon-carbon material of SiC-I in the national standard GB / T38823-2020 is 400-600.

[0048] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art may make various modifications or equivalent substitutions to the present invention within the essence and protection scope of the present invention, and such modifications or equivalent substitutions should also be deemed to fall within the protection scope of the technical solution of the present invention.

Claims

1. A method for preparing a silicon active material for an ultra-high capacity secondary battery, characterized in that: The steps include: (1) Through a high-energy mechanical ball milling process, high-purity silica material is ball milled at a speed of 500-1000 rpm for 36-48 hours to obtain nano-sized silica particles; (2) pouring the obtained silica particles into a mixed solution, wherein the mixed solution is composed of the following components in weight percentage: 60wt% water, 20wt% propanol, 5wt% acetone, and 15wt% glucose, to carry out directional coating on the particle surface, stirring the mixture for more than 2h, and drying the mixture in a vacuum environment at a temperature above 90°C to obtain a coated composite particle material; (3) Silicon nanoparticles with a three-dimensional structure are obtained by a high-temperature reduction reaction at 600-1200 degrees for 2h-4h in a hydrogen and argon environment. The reaction formula is as follows: C6H 12 O6 = 6C + 6H2O SiO2 + 2H2 -> Si + 2H2O (4) The silicon nanoparticles and the conductive carbon nanoparticles obtained in step 3) are subjected to high-energy mechanical ball milling, wherein the mass ratio of the conductive carbon to the silicon nanoparticles is between 1:10 and 1:20, and the nanoparticles are coated with an additional surface conductive layer to obtain a three-dimensional silicon active material.

2. The method for preparing a silicon active material for an ultra-high capacity secondary battery according to claim 1, characterized in that: Before performing step (4), the silicon nanoparticles with high purity and a three-dimensional structure are obtained by washing with deionized water for 1 to 3 times and drying in a vacuum environment at a temperature above 90° C. for 12 to 36 hours.

3. The method for preparing a silicon active material for an ultra-high capacity secondary battery according to claim 1, characterized in that: The silica material in step (1) contains silicon in a mass percentage concentration of more than 99%.

4. The method for preparing a silicon active material for an ultra-high capacity secondary battery according to claim 1, characterized in that: The vacuum degree in step (2) is -0.05Mpa.

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