A silicon-based material, its preparation method and application

Abstract

This invention relates to a silicon-based material, its preparation method, and its application. The preparation method of the silicon-based material includes: expanding graphite powder being fed into an explosion reaction chamber between two electrodes by a powder feeding device; one electrode being connected to one end of a capacitor via a gap gas switch, and the other electrode being connected to the other end of the capacitor; the explosion reaction chamber being evacuated and then a measured amount of gaseous silane material being introduced; the capacitor being charged, and when the voltage across the capacitor exceeds the voltage threshold of the gap gas switch, the gap gas switch is activated, generating a high-energy electrical pulse through capacitor discharge, causing the expanding graphite powder to vaporize, and the expanding graphite powder to peel off to form sheet graphene through the impact force of the explosion; the sheet graphene undergoes collision and heat exchange with the gaseous silane material in the explosion reaction chamber, causing the silane material to decompose to form nano-silicon; the sheet graphene and the decomposed nano-silicon then combine to form a silicon-carbon composite material.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of materials, in particular to a silicon-based material and a preparation method and application thereof. BACKGROUND

[0002] Materials containing graphite are widely used as negative active materials for lithium secondary batteries. The average potential of the materials containing graphite when releasing lithium is about 0.2 V (vs. Li / Li + ), and the potential changes relatively uniformly during discharging. This has the advantage that the voltage of the battery is high and constant. Although the specific capacity of the graphite material is as low as 372 mAh / g, the capacity of the graphite material has been improved and is currently close to the theoretical capacity, so it is difficult to further increase the capacity.

[0003] In order to achieve higher capacity for lithium secondary batteries, many negative active materials are being studied. As negative active materials with high capacity, materials that form intermetallic compounds with lithium (such as silicon or tin) are expected to be promising negative active materials. Silicon, as one of the currently more ideal commercial negative materials, has a theoretical specific capacity of 4200 mAh / g, which is 10 times that of graphite. However, the volume expansion effect caused by the deintercalation of lithium limits its application. Silicon-based materials containing silicon cause large volume changes (~300%) during charging and discharging, resulting in the physical contact between materials being broken and peeling off. As a result, ion conductivity and electronic conductivity, etc. are sharply reduced, so the actual initial life characteristics tend to be sharply reduced.

[0004] In order to improve the properties of silicon-based materials with high theoretical capacity, the industry has carried out some research on silicon / carbon composites. However, due to the complex manufacturing process and low yield, it is not sufficient to commercialize it. SUMMARY

[0005] The embodiment of the present application provides a preparation method of a silicon-based material. The expanded graphite powder is used as the electric explosion powder, and the silane gas is used as the medium. The expanded graphite powder is gasified by using the electric explosion method, and the reconstruction of carbon occurs in the explosion process. The expanded graphite can be peeled off into graphene under the impact of the electric explosion. The silane gas is cracked into nano-silicon in the heat exchange process and is compounded with the sheet graphene generated by the electric explosion method.

[0006] In a first aspect, the embodiment of the present application provides a preparation method of a silicon-based material, and the preparation method comprises the following steps:

[0007] The expanded graphite powder is sent into the explosion reaction chamber between two electrodes by a powder feeding device; one end of the electrode is connected to one end of a capacitor through a gap gas switch, and the other end of the electrode is connected to the other end of the capacitor;

[0008] After the explosion reaction chamber is vacuumed, a certain amount of gaseous silane material is introduced.

[0009] The capacitor is charged, and when the voltage across the capacitor exceeds the voltage threshold of the gap gas switch, the gap gas switch is turned on, a high-energy electric pulse is generated by discharging the capacitor, the expanded graphite powder is gasified, and the expanded graphite powder is exfoliated to form sheet graphite by the impact force of the explosion, the sheet graphite exchanges heat with the gaseous silane material in the explosion reaction chamber, so that the silane material is cracked to form nanosilicon, and the sheet graphite and the cracked nanosilicon are combined to form a silicon-carbon composite material.

[0010] Preferably, the method further comprises: performing carbon coating treatment on the silicon-carbon composite material, and grading and removing magnetism to obtain the silicon-based material.

[0011] Preferably, the silane material specifically comprises one or more of trisilyl silane, monosilane, disilane, tetrafluorosilane, silicon trichloride, chlorosilane, hexamethyldisilane, methyl vinyl dichlorosilane, dimethyl vinyl chlorosilane, or vinyl trichlorosilane.

[0012] Preferably, the capacitor is charged so that the voltage of the capacitor is 5kV-100kV.

[0013] In a second aspect, the present application provides a silicon-based material prepared by the preparation method of the silicon-based material of the first aspect.

[0014] In a third aspect, the present application provides a lithium battery negative material comprising the silicon-based material of the second aspect.

[0015] In a fourth aspect, the present application provides a lithium battery pole piece comprising the lithium battery negative material of the third aspect.

[0016] In a fifth aspect, the present application provides a lithium battery comprising the lithium battery pole piece of the fourth aspect.

[0017] The preparation method of the silicon-based material provided by the present application uses expanded graphite powder as an electric explosion powder and silane gas as a medium, and uses an electric explosion method to gasify the expanded graphite powder and cause carbon reconstruction in the explosion process, so that the expanded graphite is exfoliated into graphite under the impact of the electric explosion. In the heat exchange process, the silane gas is cracked into nanosilicon and combined with the sheet graphite produced by the electric explosion method. Moreover, the extreme conditions of the electric explosion method provide an unbalanced structure in terms of thermodynamics for the expanded graphite powder and store excess energy, so that the silicon-carbon composite material obtained by the explosion has a certain activity. BRIEF DESCRIPTION OF DRAWINGS

[0018] The technical solutions of the embodiments of the present application will be further described in detail below with reference to the drawings and examples.

[0019] Figure 1 is a schematic diagram of a preparation device structure for preparing a silicon-based material according to an embodiment of the present application;

[0020] Figure 2 is a flow chart of a method for preparing a silicon-based material according to an embodiment of the present application. DETAILED DESCRIPTION

[0021] The present application will be further described by the accompanying drawings and specific embodiments, but it should be understood that these embodiments are only used for more detailed description and should not be understood as limiting the present application in any form, i.e. not intended to limit the scope of protection of the present application.

[0022] The present application proposes a method for preparing a silicon-based material by an electric explosion method. In order to better understand the preparation method of the present application, first, a brief introduction to the preparation device used for preparation is given.

[0023] Figure 1 is a schematic diagram of a preparation device structure for preparing a silicon-based material according to an embodiment of the present application. As shown in the figure, the device mainly comprises: a high-voltage generator 1, a high-voltage capacitor 2, a gap gas switch 3, an electrode 4, an explosion reaction chamber 5, a gas supply device 6, a vacuum pump 7 and a powder feeding device 8.

[0024] The high-voltage generator 1 is connected to both ends of the high-voltage capacitor 2, which is used to charge the high-voltage capacitor 2, so that the voltage of the high-voltage capacitor 2 can be charged to 5kV-100kV, reaching or exceeding the closing critical voltage of the gap gas switch 3.

[0025] The expanded graphite powder is loaded in the powder feeding device 8, which is located between the two electrodes 4 in the explosion reaction chamber 5. The top of the powder feeding device 8 is open, the bottom surface is parallel to the bottom surface of the explosion reaction chamber 5, and it can be controlled to move in and out of the explosion reaction chamber 5. There are corresponding closable openings on the side wall of the explosion reaction chamber 5 for the powder feeding device 8 to move in and out of the explosion reaction chamber 5, which facilitates the loading of the expanded graphite powder. Of course, the expanded graphite powder can also be manually loaded into the powder feeding device 8 in the explosion reaction chamber 5.

[0026] One end of the two electrodes is connected to one end of the high-voltage capacitor 4 through the gap gas switch 3, and the other end of the electrode is connected to the other end of the high-voltage capacitor 4.

[0027] By closing the gap gas switch 3, the high-voltage capacitor 2 can be discharged to generate a high-energy electric pulse to make the expanded graphite powder in the powder feeding device 8 gasify and explode to form sheet-like graphene.

[0028] The gas supply device 6 and the vacuum pump 7 are connected to the explosion reaction chamber 5 respectively. The vacuum pump 7 is used to vacuum the explosion reaction chamber 5, and the gas supply device 6 is used to introduce a certain amount of gaseous silane material into the explosion reaction chamber 5.

[0029] The silane material introduced can specifically include one or more of trisilyl silane, monosilane, disilane, tetrafluorosilane, silicon trichloride, chlorosilane, hexamethyldisilane, methyl vinyl dichlorosilane, dimethyl vinyl chlorosilane or vinyl trichlorosilane.

[0030] Based on the above preparation device, the preparation method of the silicon-based material proposed by the present application is shown in the figure, and mainly includes the following steps: Figure 2

[0031] Step 110: The expanded graphite powder is sent into the explosion reaction chamber between the two electrodes by the powder feeding device.

[0032] Step 120: After the explosion reaction chamber is evacuated, a certain amount of gaseous silane material is introduced.

[0033] In a specific embodiment, the volume of the explosion reaction chamber is 0.1 m 3 The pressure of the introduced silane gas in the explosion reaction chamber is 1 standard atmosphere, and the mass of the loaded expanded graphite powder is 5 mg-100 mg.

[0034] Step 130: The capacitor is charged, and when the voltage across the capacitor exceeds the voltage threshold value of the gap gas switch, the gap gas switch is turned on, a high-energy electric pulse is generated by discharging the capacitor, the expanded graphite powder is gasified, and the expanded graphite powder is peeled off to form sheet layer graphene by the impact force of the explosion, the sheet layer graphene collides with the gaseous silane material in the explosion reaction chamber to exchange heat, so that the silane material is cracked to form nanosilicon, and the sheet layer graphene and the cracked nanosilicon are combined to form a silicon-carbon composite material.

[0035] Specifically, the high-voltage capacitor is charged, so that the electrode voltage reaches or exceeds the minimum threshold value of the electrode breakdown voltage, the gas in the gap gas switch breaks down, the switch loses insulation, and the switch is turned on. At this time, the high-energy electric pulse acts on the expanded graphite powder through the electrode, the expanded graphite powder is gasified and exploded, and the impact force makes the expanded graphite powder peel off to form sheet layer graphene.

[0036] The gasification of the expanded graphite powder releases a large amount of heat energy. The silane absorbs the heat energy released by the gasification of the expanded graphite powder, and obtains the energy generated by the collision and heat exchange between the sheet layer graphene and the silane in the explosion reaction chamber, cracks to form silicon, and combines with the sheet layer graphene to form a silicon-carbon composite material through the excess energy.

[0037] Because the extreme conditions of the electric explosion method provide an unbalanced structure in the thermodynamics of the expanded graphite powder and store excess energy, the silicon-carbon composite material obtained by explosion has a certain activity.

[0038] ​Further, in order to obtain a silicon-based material with better performance, the material prepared above can be subjected to carbon coating treatment and graded magnetic removal to obtain the silicon-based material prepared by the application.

[0039] The preparation method of the silicon-based material provided by the application uses expanded graphite powder as the electric explosion powder and silane gas as the medium, gasifies the expanded graphite powder by using the electric explosion method, and causes carbon reconstruction during the explosion process. The expanded graphite can be peeled off into graphene under the impact of the electric explosion. The silane gas is cracked into nanosilicon during the heat exchange process and is compounded with the sheet graphene produced by the electric explosion method. Moreover, the extreme conditions of the electric explosion method provide an unbalanced structure in the thermal dynamics aspect for the expanded graphite powder and store excess energy, so that the silicon-carbon composite material obtained by the explosion has a certain activity.

[0040] The application provides that the mass of the expanded graphite powder is 5 mg-100 mg. Because the applicant finds that, based on the explosion reaction chamber of the embodiment of the application, when the mass of the expanded graphite powder is less than 5 mg, the powder is discontinuously accumulated, and it is not easy to form a complete and good loop channel in the electrode, which affects the effect of the electric explosion method. When the mass of the expanded graphite powder is more than 100 mg, the accumulated graphite powder is too much, which on the one hand causes the graphite powder to easily produce accumulated heat release during the electric explosion process, and on the other hand affects the energy density of the negative electrode material after compounding.

[0041] The application provides that the capacitor voltage is 5-100 kV. Because the applicant finds that the energy deposition level is also an important factor affecting the particle size of the deposited particles. When the capacitor voltage is less than 5 kV, the graphite powder is mainly in the form of liquid phase particles after ionization, and the electric explosion product of the graphite powder is mainly graphite particles condensed from liquid phase particles. When the capacitor voltage is 5-100 kV, the input energy is greater than the gasification energy of the expanded graphite powder, and the shock wave produced by the powder electric explosion instantaneously can cause the expanded graphite to peel off, and the electric explosion product is mainly in the form of graphene sheet. When the capacitor voltage is greater than 100 kV, the particle size distribution is relatively narrow and the particle size is relatively small, and the energy consumption is also high.

[0042] The silicon-based material prepared above can be used as the active material of the negative electrode material of the lithium battery and used for preparing the negative electrode sheet of the lithium battery. The negative electrode sheet of the application also includes a negative electrode current collector, and the application does not have special limitations on the negative electrode current collector as long as the application purposes can be achieved. For example, it can include but is not limited to copper foil, copper alloy foil, nickel foil, stainless steel foil, foamed nickel, foamed copper or composite current collector and the like.

[0043] In the application, the lithium battery negative electrode material can also include a conductive agent, and the application does not have special limitations on the conductive agent as long as the application purposes can be achieved.

[0044] The lithium battery using the silicon-based material as the negative electrode material of the lithium battery can include, but is not limited to, a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery or a lithium ion polymer secondary battery and the like.

[0045] In order to better understand the technical solutions provided by the present application, the following describes the specific process of preparing the silicon-based material by using the method provided by the above embodiments of the present application, and the method and characteristics of applying the silicon-based material to the lithium battery.

[0046] Example 1

[0047] The explosion reaction chamber is vacuumized and silane gas is introduced into the chamber to 1 atmosphere, 10 mg of expanded graphite powder is sent into the explosion chamber by using a powder feeding device. The high-voltage capacitor is charged to 20 kV, the gap gas switch is connected, the electric explosion reaction occurs, and the silicon-carbon composite material is obtained after cooling after the reaction is completed.

[0048] The silicon-carbon composite material is sintered, nitrogen and acetylene with a volume ratio of 3:1 are introduced, sintering is carried out at 900℃ for 1 hour to form a carbon coating, and finally the silicon-based material is obtained by grading and removing the magnet.

[0049] The above obtained negative electrode material is used as the negative electrode active material, carbon black as the conductive additive, carboxymethyl cellulose sodium and butadiene rubber with a mass ratio of 1:1 as the binder, and the mass ratio of the above materials is 95%:2%:3%. The materials are weighed and put into a beater at room temperature to prepare a slurry. The prepared slurry is uniformly coated on a copper foil. After drying in a forced air drying oven at 50℃ for 2 hours, the electrode piece is cut into 8x8mm, and then vacuum drying is carried out at 100℃ for 10 hours in a vacuum drying oven. The dried electrode piece is then transferred into a glove box for use in assembling a battery.

[0050] The battery assembly is simulated in a glove box containing high-purity Ar atmosphere, using metallic lithium as the counter electrode, a dispersion of 1 mol LiPF6 in ethylene carbonate (EC) / dimethyl carbonate (DMC) (volume ratio v:v=1:1) as the electrolyte, and assembling into a battery. A constant current charge-discharge tester is used to test the battery in a constant current charge-discharge mode, with the discharge cut-off voltage being 0.005 V and the charge cut-off voltage being 1.5 V. The first week of charge-discharge test is carried out at a current density of C / 10, and the second week of discharge test is carried out at a current density of C / 10.

[0051] Under the above conditions, a cycle test is carried out, and the capacity retention rate is 93% after 100 cycles.

[0052] Example 2

[0053] The specific operation steps are the same as those of Example 1, except that the capacitor voltage is 30 kV and the mass of the expanded graphite powder is 25 mg.

[0054] The battery assembly and cycle test were carried out according to the parameters and test conditions of Example 1 above, and the capacity retention rate was 93% after 100 cycles.

[0055] Example 3

[0056] The specific operation steps were the same as those of Example 1, except that the capacitor voltage was 15 kV and the mass of the expanded graphite powder was 12 mg.

[0057] The battery assembly and cycle test were carried out according to the parameters and test conditions of Example 1 above, and the capacity retention rate was 93% after 100 cycles.

[0058] Example 4

[0059] The specific operation steps were the same as those of Example 1, except that the capacitor voltage was 60 kV and the mass of the expanded graphite powder was 30 mg.

[0060] The battery assembly and cycle test were carried out according to the parameters and test conditions of Example 1 above, and the capacity retention rate was 94% after 100 cycles.

[0061] Example 5

[0062] The specific operation steps were the same as those of Example 1, except that the capacitor voltage was 9 kV and the mass of the expanded graphite powder was 8 mg.

[0063] The battery assembly and cycle test were carried out according to the parameters and test conditions of Example 1 above, and the capacity retention rate was 93% after 100 cycles.

[0064] Example 6

[0065] The specific operation steps were the same as those of Example 1, except that the capacitor voltage was 60 kV and the mass of the expanded graphite powder was 40 mg.

[0066] The battery assembly and cycle test were carried out according to the parameters and test conditions of Example 1 above, and the capacity retention rate was 94% after 100 cycles.

[0067] Example 7

[0068] The specific operation steps were the same as those of Example 1, except that the capacitor voltage was 26 kV and the mass of the expanded graphite powder was 17 mg.

[0069] The battery assembly and cycle test were carried out according to the parameters and test conditions of Example 1 above, and the capacity retention rate was 93% after 100 cycles.

[0070] The present application also provides some comparative examples for comparison with the above examples.

[0071] Comparative Example 1

[0072] The specific operation steps are the same as those in Example 1, except that the capacitor voltage is 3 kV, and the mass of the expanded graphite powder is 10 mg.

[0073] The battery assembly and cycle test are carried out according to the parameters and test conditions of Example 1, and the capacity retention rate after 100 cycles is 45%.

[0074] Comparative Example 2

[0075] The specific operation steps are the same as those in Example 1, except that the capacitor voltage is 20 kV, and the mass of the expanded graphite powder is 200 mg.

[0076] The battery assembly and cycle test are carried out according to the parameters and test conditions of Example 1, and the capacity retention rate after 100 cycles is 10%.

[0077] Comparative Example 3

[0078] An appropriate amount of nano-silicon and expanded graphite is selected and compounded according to the specific capacity of Example 1, and sintering is carried out at 1200 DEG C for 6 hours under a vacuum atmosphere of 50 Pa to form a silicon-carbon composite material. The material is cooled to room temperature and discharged and broken and sieved. The sieved material is coated with carbon according to the method of Example 1, and the negative electrode material is obtained after grading and magnetic removal.

[0079] The battery assembly and cycle test are carried out according to the parameters and test conditions of Example 1, and the capacity retention rate after 100 cycles is 62%.

[0080] From Examples 1-7, it can be seen that the electric explosion method used in the present application has good effect, the silicon-carbon composite is uniform, and the cycle performance is good. From Comparative Example 1, it can be seen that when the capacitor voltage is low, the input energy is not enough, only part of the expanded graphite is dissociated and restructured, and the composite effect is poor. From Comparative Example 2, it can be seen that the amount of expanded graphite is too much, and the input energy is not enough to cause the expanded graphite to be peeled off and ionized, so that only nano-silicon is present in the structure. From Comparative Example 3, it can be seen that the cycle retention rate of the traditional silicon-carbon composite material after 100 cycles is also unsatisfactory.

[0081] The present application uses expanded graphite powder as the electric explosion powder, and silane gas as the medium, and uses the electric explosion method to gasify the expanded graphite powder, and carbon restructuring occurs in the process, and the huge electric explosion impact force can make the expanded graphite peel off into the layered graphene. The silane gas is cracked into nano-silicon in the heat exchange process and is compounded with the layered graphene produced by the electric explosion method. Moreover, the extreme conditions of the electric explosion method provide an unbalanced structure in the thermodynamics for the expanded graphite powder and store excess energy, so that the silicon-carbon composite material obtained by explosion has a certain activity. Due to the in-situ silicon-carbon composite, the peeled layered graphene will wrap the produced nano-silicon layer by layer, and the silicon-carbon composite is good. Under the treatment of carbon coating, the cycle performance of the silicon-carbon composite negative electrode is further improved. The electric explosion method used in the present application has rapid energy burst and short preparation time, greatly shortening the process time, and has good industrial application prospect.

[0082] The above specific embodiments further specifically describe the purposes, technical solutions and beneficial effects of the present application, and it should be understood that the above description is only a specific embodiment of the present application and is not used to limit the protection scope of the present application, and any modification, equivalent replacement, improvement, etc. within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. A method of preparing a silicon-based material, characterized by, The preparation method comprises: The expanded graphite powder is sent into the explosion reaction chamber between two electrodes by a powder feeding device; one end of the electrode is connected to one end of a capacitor through a gap gas switch, and the other end of the electrode is connected to the other end of the capacitor; After the explosion reaction chamber is vacuumized, a certain amount of gaseous silane material is introduced; The capacitor is charged, and when the voltage across the capacitor exceeds the voltage threshold of the gap gas switch, the gap gas switch is turned on, a high-energy electric pulse is generated by discharging the capacitor, the expanded graphite powder is gasified, and the expanded graphite powder is exfoliated to form sheet layer graphene by the impact force of the explosion; the sheet layer graphene collides with the gaseous silane material in the explosion reaction chamber to exchange heat, so that the silane material is cracked to form nanosilicon, and the sheet layer graphene and the cracked nanosilicon are combined to form a silicon-carbon composite material.

2. The method of claim 1, wherein the silicon-based material is prepared by a method comprising: The method further comprises: The silicon-carbon composite material is subjected to carbon coating treatment and graded magnetic removal to obtain the silicon-based material.

3. The method of claim 1, wherein the silicon-based material is prepared by a process comprising: The silane material specifically comprises one or more of trisilyl silane, monosilane, disilane, tetrafluorosilane, chlorosilane, and hexamethyldisilane.

4. The method of claim 1, wherein the silicon-based material is prepared by a process comprising: The silane material specifically comprises one or more of silicon trichloride, methylvinyl dichlorosilane, dimethylvinyl chlorosilane, or vinyltrichlorosilane.

5. The method of claim 1, wherein the silicon-based material is prepared by a process comprising: The capacitor is charged so that the voltage of the capacitor reaches 5kV-100kV.

6. A silicon-based material prepared by the preparation method of any one of claims 1-5.

7. A lithium battery anode material, characterized in that, The lithium battery negative electrode material comprises the silicon-based material of claim 6.

8. A lithium battery pole piece, characterized by, The lithium battery pole piece comprises the lithium battery negative electrode material of claim 7.

9. A lithium battery, characterized by The lithium battery comprises the lithium battery pole piece of claim 8.

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