CN114843485B - Mesoporous silicon/carbon nano-sheet of long-cycle lithium ion battery cathode composite material and preparation method thereof - Google Patents
Mesoporous silicon/carbon nano-sheet of long-cycle lithium ion battery cathode composite material and preparation method thereof Download PDFInfo
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Abstract
The invention belongs to the technical field of preparation of lithium ion battery electrode materials, and particularly relates to a long-cycle lithium ion battery negative electrode composite material mesoporous silicon/carbon nano sheet and a preparation method thereof, wherein tetraethyl orthosilicate-32 is used as a silicon source, and a wet chemical method is adopted to synthesize a silicon dioxide nano sheet; taking 1, 4-bis (triethoxysilyl) benzene as an organosilicon source, wrapping the outer side of the obtained silicon dioxide nano-sheet with a layer of mesoporous organic silicon dioxide, and marking the obtained product as SiO 2 @mOSiO 2 NS. Preparation of uniformly distributed mSiO by carbonization at 900 ℃ under argon atmosphere 2 C NS; then preparing mSi/C NS through magnesia reduction at 650 ℃. The method is scientific and reasonable in design, the silicon-based material combines different carbon doping modes to achieve the complementary and synergistic effects of silicon-carbon functions, silicon has high specific capacity, carbon doping plays a role in buffering and protecting, and the volume change of silicon is reduced; the capacity attenuation condition of the lithium ion battery in the circulation process is improved, and the prepared lithium ion battery has good circulation performance, good multiplying power performance and large reversible capacity.
Description
Technical Field
The invention belongs to the technical field of preparation of electrode materials of lithium ion batteries, and particularly relates to a long-cycle lithium ion battery negative electrode composite material mesoporous silicon/carbon nano sheet and a preparation method thereof.
Background
Lithium ion batteries are ideal energy storage elements for tools such as mobile phones, notebook computers, new energy automobiles and the like due to the characteristics of high energy density, long cycle life, small volume, green pollution-free performance and the like. The lithium ion battery cathode material widely used at present is a carbon material, and the carbon material can not meet the demands of people because the theoretical specific capacity is only 375 mAh/g. Therefore, development of a novel lithium ion battery cathode material with large capacity, good safety and long service life is urgent. The novel lithium ion battery cathode material comprises transition metal oxide, transition metal sulfide, nano alloy, silicon material and the like. The theoretical specific capacity of the silicon material can reach 4200mAh/g, which is more than 10 times of that of the carbon material, thus providing possibility for the lithium ion battery with large capacity.
However, the silicon negative electrode material has poor conductivity, and the generation of volume expansion of approximately 300% in the process of lithium intercalation and deintercalation leads to poor cycle performance and rapid capacity decay in the use process, which limits the development of the silicon negative electrode material. The approach currently taken is to nanocrystallise the silicon material. The silicon nanomaterial with the two-dimensional mesoporous structure has high specific surface area, large transverse size and an effective buffer area, and provides a trigger for solving the problem of volume expansion, but lacks an effective preparation method. Furthermore, carbon doping will further promote long cycling of lithium ion batteries.
Therefore, the development of the mesoporous silicon-carbon composite material with the two-dimensional structure has important significance for energy storage.
Disclosure of Invention
The invention aims to provide a long-cycle lithium ion battery cathode composite material mesoporous silicon/carbon nano sheet and a preparation method thereof, which are used for solving the problem of capacity attenuation caused by volume expansion in the current silicon-based lithium ion battery recycling process.
In order to achieve the technical purpose and the technical effect, the invention is realized by the following technical scheme:
the preparation method of the mesoporous silicon/carbon nano sheet of the long-cycle lithium ion battery cathode composite material comprises the following steps:
1) Using tetraethyl orthosilicate-32 as an organosilicon source, and synthesizing a silicon dioxide nano-sheet by adopting a wet chemical method; wherein tetraethyl orthosilicate is marked as TEOS-32, and the silicon dioxide nano-sheet is marked as SiO 2 NS；
2) Taking 1, 4-bis (triethoxysilyl) benzene as an organosilicon source, and obtaining SiO 2 The NS outside is wrapped with a layer of mesoporous organic silicon dioxide, and the obtained product is marked as SiO 2 @mOSiO 2 NS；SiO 2 @mOSiO 2 NS is carbonized at 900 ℃ under argon atmosphere to prepare uniformly distributed embedded carbon-doped mesoporous silica nanosheets; wherein, 1, 4-bis (triethoxysilyl) benzene is marked as BTEB, and the embedded carbon doped mesoporous silica nano-sheet is marked as mSiO 2 /C NS；
3) The obtained mSiO 2 Preparing carbon-doped mesoporous silicon nano-sheets by carrying out magnesia reduction at 650 ℃ on/C NS; wherein, the carbon doped mesoporous silicon nano sheet is marked as mSi/C NS. The chemical reaction formula is as follows:
SiO 2 +2Mg＝Si+2MgO
further, the specific operation of step 1) is that the aqueous NaOH solution is diluted with water, TEOS-32 is added under stirring and adjusting, then ethyl acetate is added, and the mixture is reacted for a period of time at room temperature; after the reaction is finished, centrifugally collecting a product, washing the product with deionized water and absolute ethyl alcohol, dispersing the product in the absolute ethyl alcohol to form SiO 2 NS dispersion; to remove SiO 2 Ethyl acetate on NS surface, stirred at room temperature, at SiO 2 Adding trisaminopropyl triethoxysilane, which is marked as APTES, into the NS dispersion; after a period of reaction, the product was centrifuged and washed once with absolute ethanol, and the product was dispersed in a certain amount of water.
Further, in step 1), 8mL of 2M NaOH aqueous solution was added to 1L of water, and 10mL of TEOS-32 was added at a stirring speed of 800rpm, followed by 10mL of ethyl acetate, and reacted at room temperature for 2.5 hours; after the reaction is finished, centrifugally collecting a product, washing the product with deionized water for 3 times, washing the product with absolute ethyl alcohol for two times, and dispersing the product inIn 10mL of absolute ethanol to form SiO 2 NS dispersion.
Further, to remove SiO 2 Ethyl acetate on NS surface, stirred at room temperature, at SiO 2 20. Mu.L APTES was added to the NS dispersion; after 24h of reaction, the product was centrifuged and washed once with absolute ethanol, the product was dispersed in 10mL of water.
Further, in the step 2), cetyltrimethylammonium bromide and aqueous NaOH solution are added to SiO 2 Stirring the NS dispersion for a period of time; the TEOS/BTEB ethanol solution is added dropwise for a plurality of times, and each time is separated for a period of time; after a reaction section, centrifugally collecting a product, washing the product by deionized water and ethanol, and drying to obtain SiO 2 @mOSiO 2 NS; siO is made of 2 @mOSiO 2 NS is placed in a tube furnace, and under the protection of argon, organic silicon doped in the material is carbonized through high-temperature heat treatment to obtain mSiO 2 C NS; wherein, cetyl trimethyl ammonium bromide is marked as CTAB, and TEOS/BTEB ethanol solution is formed by mixing TEOS-32, BTEB and ethanol.
Further, in step 2), 20mg of CTAB, 100. Mu.L of an aqueous NaOH solution having a concentration of 0.1M, was added to SiO 2 NS dispersion, stirring for 2h at 25 ℃; then adding 1mL of TEOS/BTEB ethanol dropwise in three times, wherein each time interval is 30min; after 24 hours of reaction, centrifugally collecting a product, washing the product with deionized water for 3 times, washing the product with ethanol for 1 time, and drying the product at 60 ℃ for 8 hours to obtain SiO 2 @mOSiO 2 NS; siO is made of 2 @mOSiO 2 Placing NS in a tube furnace, carbonizing the organic silicon doped in the material by heat treatment at 900 ℃ under the protection of argon, heating up at a speed of 2 ℃/min, and preserving the temperature for 3 hours to obtain mSiO 2 /C NS。
Further, the volume ratio of TEOS-32 to BTEB in the TEOS/BTEB ethanol solution is 0.1-5:1, and the total volume fraction of TEOS-32 to BTEB is 2%.
Further, in step 3), mSiO is added 2 Uniformly mixing/C NS and magnesium powder according to a certain proportion, placing into a stainless steel reactor, performing magnesian reduction in a tube furnace under the protection of argon, cooling, mixing the obtained product with HCl solution with the concentration of 1M, and placing into a chamberRemoving MgO and Mg by warm stirring 2 Si, unreacted magnesium powder; after centrifugal washing for a plurality of times, mixing with HF solution with the mass concentration of 1%, and stirring at room temperature for a period of time to remove unreacted silicon dioxide; washing with water for many times after the reaction is finished, and vacuum drying to obtain mSi/C NS.
Further, in step 4), mSiO is added to the reaction mixture 2 Uniformly mixing/C NS and magnesium powder according to the mass ratio of 10:7, placing the mixture into a stainless steel reactor, carrying out magnesian reduction at 650 ℃ in a tube furnace under the protection of argon, heating at a speed of 2 ℃/min, and preserving heat for 5 hours; after cooling, the obtained product is mixed with HCl with the concentration of 1M, stirred for 2 hours at room temperature to remove MgO and Mg 2 Si, unreacted magnesium powder; after centrifugal washing for three times, mixing with HF with the mass concentration of 1%, and stirring for 30min at room temperature to remove unreacted silicon dioxide; washing with water for three times after the reaction is finished, and drying for 8 hours at 70 ℃ in a vacuum drying oven to obtain mSi/C NS.
The long-cycle lithium ion battery cathode composite material is prepared by the preparation method.
The beneficial effects of the invention are as follows:
1. the preparation method provided by the invention is scientific and reasonable in design, and the silicon-based material is of a two-dimensional structure, has large specific surface area and small volume change; the complementary and synergistic effects of silicon-carbon functions are achieved by combining different carbon doping modes, silicon has high specific capacity, carbon doping plays a role in buffering and protecting, and the volume change of silicon is reduced; the state of the art of capacity fade of the lithium ion battery in the circulation process is greatly improved; the prepared silicon/carbon composite lithium ion battery has good cycle performance, good rate capability and large reversible capacity.
2. The preparation process of the material is easy to realize, does not pollute the environment, and has low cost of the used silicon source and conventional equipment.
Of course, it is not necessary for any one product to practice the invention to achieve all of the advantages set forth above at the same time.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings that are needed for the description of the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a schematic diagram showing the preparation process of mSi/C NS in example 1 of the present invention;
FIG. 2 is a TEM image of mSi/C NS of example 1 of the present invention;
FIG. 3 is a diagram of SiO in example 1 of the present invention 2 TEM images of NS;
FIG. 4 is a diagram of SiO in example 1 of the present invention 2 @mSiO 2 TEM images of NS;
fig. 5 is a diagram of a lithium ion battery LED lamp with mSi/C NS as the negative electrode assembly in example 1 of the present invention.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
Specific embodiments of the invention are as follows:
example 1
The preparation method of the long-cycle lithium ion battery cathode composite material mesoporous silicon/carbon nano sheet specifically comprises the following steps:
1)SiO 2 preparation of NS: 8mL of aqueous NaOH (2M) was added to 1L of water, and 10mL of tetraethyl orthosilicate-32 (TEOS-32) was added at a stirring speed of 800rpm, followed by 10mL of ethyl acetate, and reacted at room temperature for 2.5 hours. After the reaction was completed, the product was collected by centrifugation, washed with deionized water 3 times, washed twice with absolute ethanol, and dispersed in 10mL of absolute ethanol. To remove SiO 2 Ethyl acetate on NS surface was stirred at room temperature, 20 μl of triaminopropyl triethoxysilane (APTES) was added, reacted for 24 hours, centrifuged and 1 time was washed with absolute ethanol to disperse in 10mL of waterIs a kind of medium. The TEM image is shown in FIG. 3, with a transverse dimension of 3-5 μm.
2)SiO 2 @mOSiO 2 Preparation of NS: 20mg of cetyltrimethylammonium bromide (CTAB) and 100. Mu.L of aqueous NaOH (0.1M) were added to the above SiO 2 The NS dispersion was stirred at 25℃for 2h. Subsequently, 1mL of TEOS/BTEB (6:4) ethanol (V/V2%) was added dropwise in three portions, each at 30min intervals. After 24h of reaction, the product was collected by centrifugation, washed 3 times with deionized water, washed 1 time with ethanol, and dried at 60℃for 8h. The TEM image is shown in FIG. 4, the mesoporous structure is clearly visible, and the pore diameter is about 4nm.
3)mSiO 2 Preparation of/C NS: siO is made of 2 @mOSiO 2 And (3) placing NS in a tube furnace, and carbonizing the organic silicon doped in the material through heat treatment at 900 ℃ under the protection of argon, wherein the heating speed is 2 ℃/min, and the heat preservation time is 3h.
4) Preparation of mSi/C NS: the mSiO is prepared 2 Uniformly mixing/C NS and magnesium powder according to the mass ratio of 10:7, placing the mixture into a stainless steel reactor, carrying out magnesian reduction at 650 ℃ in a tube furnace under the protection of argon, heating at a speed of 2 ℃/min, and preserving heat for 5h. After cooling, the sample is mixed with HCl solution with the concentration of 1M, and stirred for 2 hours at room temperature to remove unreacted magnesium powder, mgO and Mg 2 Si. After 3 times of centrifugal water washing, the mixture was mixed with an HF solution having a mass concentration of 1%, and the mixture was stirred at room temperature for 30 minutes to remove unreacted silica. Washing with water for three times after the reaction is finished, and drying for 8 hours at 70 ℃ in a vacuum drying oven. The TEM image is shown in FIG. 2.
5) The lithium ion battery is assembled in a glove box, materials, polytetrafluoroethylene (PVDF) adhesive and acetylene black conductive agent are ground for 30min according to the mass ratio of 7:2:1, and are uniformly mixed, and N-methylpyrrolidone (NMP) solvent is added for grinding for 10min to prepare slurry. Uniformly and flatly coating the slurry on a copper sheet with the diameter of 10mm, vacuum drying and assembling the copper sheet into a button cell, wherein a counter electrode is a lithium sheet, and an electrolyte is LiPF 6 。
6) The obtained lithium ion battery anode material silicon/graphene has a lamellar structure, and the size is 300nm-2 mu m. And the performance test of the lithium ion battery shows that the specific capacity of the first lithium intercalation reaches 2948mAh/g, the capacity of the second cycle is 1843mAh/g, and the specific capacity after 30 cycles is still more than 1650 mAh/g. The assembled battery is shown in fig. 5.
Example 2
SiO synthesized as in example 1 2 NS was dispersed in 10mL of water, and 20mg of cetyltrimethylammonium bromide (CTAB) and 100. Mu.L of aqueous NaOH (0.1M) were added thereto, followed by stirring at 25℃for 2 hours. Subsequently, 1mL of TEOS/BTEB (7:3) ethanol (V/V2%) was added dropwise in three portions, each at 30min intervals. After 24 hours of reaction, centrifugally collecting the product, washing 3 times with deionized water, washing 1 time with ethanol, drying 8 hours at 60 ℃, and carrying out SiO 2 @mOSiO 2 NS。
Preparation of mSi/C and cell Assembly the electrochemical performance was tested as in case 1. The specific capacity of the first lithium intercalation is 3206mAh/g, the capacity of the second ring is 1243mAh/g, and the specific capacity after 30 circles of circulation is 942mAh/g.
Example 3
SiO synthesized as in example 1 2 NS was dispersed in 10mL of water, and 20mg of cetyltrimethylammonium bromide (CTAB) and 100. Mu.L of aqueous NaOH (0.1M) were added thereto, followed by stirring at 25℃for 2 hours. Subsequently, 1mL of TEOS/BTEB (5:5) ethanol (V/V2%) was added dropwise in three portions, each at 30min intervals. After 24 hours of reaction, centrifugally collecting a product, washing the product with deionized water for 3 times, washing the product with ethanol for 1 time, and drying the product at 60 ℃ for 8 hours to prepare SiO 2 @mOSiO 2 NS。
Preparation of mSi/C and cell Assembly the electrochemical performance was tested as in case 1. The specific capacity of the first lithium intercalation is 1693mAh/g, the capacity of the second ring is 1148mAh/g, and the specific capacity after 30 circles of circulation is 826mAh/g.
Example 4
SiO synthesized as in example 1 2 @mOSiO 2 Placing NS in a tube furnace, carbonizing the organic silicon doped in the material by heat treatment at 800 ℃ under the protection of argon, heating up at a speed of 2 ℃/min, and preserving the temperature for 3 hours to prepare mSiO 2 /C NS。
Preparation of mSi/C and cell Assembly the electrochemical performance was tested as in case 1. The specific capacity of the first lithium intercalation is 4013mAh/g, the capacity of the second ring is 1243mAh/g, and the specific capacity after 30 circles of circulation is 405mAh/g.
Example 5
Will be faithfulExample 1 SiO synthesized by 2 @mOSiO 2 Placing NS in a tube furnace, carbonizing the organic silicon doped in the material by heat treatment at 1000 ℃ under the protection of argon, heating up at a speed of 2 ℃/min, and preserving the temperature for 3 hours to prepare mSiO 2 /C NS。
Preparation of mSi/C and cell Assembly the electrochemical performance was tested as in case 1. The specific capacity of the first lithium intercalation is 3206mAh/g, the capacity of the second ring is 1243mAh/g, and the specific capacity after 30 circles of circulation is 942mAh/g.
Example 6
When the mSi/C NS prepared in the embodiment 1 is used for lithium ion battery assembly, materials, PVDF binder and acetylene black conductive agent are ground for 30min according to the mass ratio of 8:2:1, and then NMP solvent is added for grinding for 10min to prepare slurry. Uniformly and flatly coating the slurry on a copper sheet with the diameter of 10mm, vacuum drying and assembling the copper sheet into a button cell, wherein a counter electrode is a lithium sheet, and an electrolyte is LiPF 6 . The electrochemical properties were tested. The specific capacity of the first lithium intercalation is 3845mAh/g, the capacity of the second circle is 1856mAh/g, and the specific capacity after 30 circles of circulation is 569mAh/g.
Example 7
When the mSi/C NS prepared in the example 1 is used for lithium ion battery assembly, materials, PVDF binder and acetylene black conductive agent are ground for 30min according to the mass ratio of 7:1.5:1.5, and are uniformly mixed, and then NMP solvent is added for grinding for 10min to prepare slurry. Uniformly and flatly coating the slurry on a copper sheet with the diameter of 10mm, vacuum drying and assembling the copper sheet into a button cell, wherein a counter electrode is a lithium sheet, and an electrolyte is LiPF 6 . The electrochemical properties were tested. The specific capacity of the first lithium intercalation is 2473mAh/g, the capacity of the second ring is 1460mAh/g, and the specific capacity after 30 circles of circulation is 853mAh/g.
The preferred embodiments of the invention disclosed above are intended only to assist in the explanation of the invention. The preferred embodiments are not exhaustive or to limit the invention to the precise form disclosed. Obviously, many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and the practical application, to thereby enable others skilled in the art to best understand and utilize the invention. The invention is limited only by the claims and the full scope and equivalents thereof.
Claims (7)
1. The preparation method of the mesoporous silicon/carbon nano-sheet of the long-cycle lithium ion battery cathode composite material is characterized by comprising the following steps:
1) Using tetraethyl orthosilicate-32 as a silicon source, and synthesizing a silicon dioxide nano-sheet by adopting a wet chemical method; wherein tetraethyl orthosilicate-32 is marked as TEOS-32, and the silicon dioxide nano-sheet is marked as SiO 2 NS；
Specifically, naOH aqueous solution is diluted by water, TEOS-32 is added under stirring and adjustment, ethyl acetate is then added, and the mixture is reacted for a period of time at room temperature; after the reaction is finished, centrifugally collecting a product, washing the product with deionized water and absolute ethyl alcohol, dispersing the product in the absolute ethyl alcohol to form SiO 2 NS dispersion; to remove SiO 2 Ethyl acetate on NS surface, stirred at room temperature, at SiO 2 Adding trisaminopropyl triethoxysilane, which is marked as APTES, into the NS dispersion; after a period of reaction, centrifuging and washing the product once with absolute ethanol, the product being dispersed in a certain amount of water;
2) Taking 1, 4-bis (triethoxysilyl) benzene as an organosilicon source, and obtaining SiO 2 The NS outside is wrapped with a layer of mesoporous organic silicon dioxide, and the obtained product is marked as SiO 2 @mOSiO 2 NS；SiO 2 @mOSiO 2 NS is carbonized at 900 ℃ under argon atmosphere to prepare uniformly distributed embedded carbon-doped mesoporous silica nanosheets; wherein, 1, 4-bis (triethoxysilyl) benzene is marked as BTEB, and the embedded carbon doped mesoporous silica nano-sheet is marked as mSiO 2 /C NS；
Specifically, cetyltrimethylammonium bromide and NaOH aqueous solution are added to SiO 2 Stirring the NS dispersion for a period of time; the TEOS/BTEB ethanol solution is added dropwise for a plurality of times, and each time is separated for a period of time; after reacting for a period of time, centrifugally collecting a product, washing the product by deionized water and ethanol, and drying to obtain SiO 2 @mOSiO 2 NS; siO is made of 2 @mOSiO 2 NS is placed in a tube furnace, and under the protection of argon, organic silicon doped in the material is carbonized through high-temperature heat treatment to obtain mSiO 2 C NS; wherein, cetyl trimethyl ammonium bromide is marked as CTAB, and TEOS/BTEB ethanol solution is formed by mixing TEOS-32, BTEB and ethanol;
3) The obtained mSiO 2 Preparing carbon-doped mesoporous silicon nano-sheets by carrying out magnesia reduction at 650 ℃ on/C NS; wherein, the carbon doped mesoporous silicon nano sheet is marked as mSi/C NS;
specifically, mSiO is used as 2 Uniformly mixing/C NS and magnesium powder according to a certain proportion, placing into a stainless steel reactor, performing magnesian reduction in a tube furnace under the protection of argon, cooling, mixing the obtained product with HCl solution with the concentration of 1M, and stirring at room temperature to remove unreacted magnesium powder, mgO and Mg 2 Si; after centrifugal washing for a plurality of times, mixing with HF solution with the mass concentration of 1%, and stirring at room temperature for a period of time to remove unreacted silicon dioxide; washing with water for many times after the reaction is finished, and vacuum drying to obtain mSi/C NS.
2. The method for preparing the mesoporous silicon/carbon nano-sheet of the long-cycle lithium ion battery cathode composite material, which is characterized by comprising the following steps of: in step 1), 8mL aqueous NaOH solution with concentration of 2M is added into 1L of water, 10mL of TEOS-32 is added at stirring speed of 800rpm, 10mL of ethyl acetate is added, and the mixture is reacted for 2.5h at room temperature; after the reaction is finished, centrifugally collecting a product, washing the product with deionized water for 3 times and washing the product with absolute ethyl alcohol for two times, dispersing the product in 10mL of absolute ethyl alcohol to form SiO 2 NS dispersion.
3. The method for preparing the mesoporous silicon/carbon nano-sheet of the long-cycle lithium ion battery cathode composite material according to claim 2, which is characterized in that: to remove SiO 2 Ethyl acetate on NS surface, stirred at room temperature, at SiO 2 20. Mu.L APTES was added to the NS dispersion; after 24h of reaction, the product was centrifuged and washed once with absolute ethanol, the product was dispersed in 10mL of water.
4. According to claimThe method for preparing the mesoporous silicon/carbon nano-sheet of the long-cycle lithium ion battery cathode composite material, which is characterized by comprising the following steps of: in step 2), 20mg of CTAB, 100. Mu.L of aqueous NaOH solution having a concentration of 0.1M are added to SiO 2 NS dispersion, stirring for 2h at 25 ℃; then adding 1mL of TEOS/BTEB ethanol dropwise in three times, wherein each time interval is 30min; after 24 hours of reaction, centrifugally collecting a product, washing the product with deionized water for 3 times, washing the product with ethanol for 1 time, and drying the product at 60 ℃ for 8 hours to obtain SiO 2 @mOSiO 2 NS; siO is made of 2 @mOSiO 2 Placing NS in a tube furnace, carbonizing the organic silicon doped in the material by heat treatment at 900 ℃ under the protection of argon, heating up at a speed of 2 ℃/min, and preserving the temperature for 3 hours to obtain mSiO 2 /C NS。
5. The method for preparing the mesoporous silicon/carbon nano-sheet of the long-cycle lithium ion battery cathode composite material, which is characterized in that: the volume ratio of TEOS-32 to BTEB in the TEOS/BTEB ethanol solution is 0.1-5:1, and the total volume fraction of the TEOS-32 and the BTEB is 2%.
6. The method for preparing the mesoporous silicon/carbon nano-sheet of the long-cycle lithium ion battery cathode composite material, which is characterized in that: in step 3), mSiO is added 2 Uniformly mixing/C NS and magnesium powder according to the mass ratio of 10:7, placing the mixture into a stainless steel reactor, carrying out magnesian reduction at 650 ℃ in a tube furnace under the protection of argon, heating at a speed of 2 ℃/min, and preserving heat for 5 hours; after cooling, the obtained product is mixed with HCl solution with the concentration of 1M, and stirred for 2 hours at room temperature to remove MgO and Mg 2 Si, unreacted magnesium powder; after centrifugal washing for three times, mixing with HF solution with the mass concentration of 1%, and stirring at room temperature for 30min to remove unreacted silicon dioxide; washing with water for three times after the reaction is finished, and drying for 8 hours at 70 ℃ in a vacuum drying oven to obtain mSi/C NS.
7. The mesoporous silicon/carbon nano-sheet of the long-cycle lithium ion battery cathode composite material, which is prepared by the preparation method according to any one of claims 1-6.
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