CN112670479B - Sulfur and nitrogen co-doped coaxial core-shell silicon-carbon negative electrode material, preparation method thereof and lithium ion battery - Google Patents
Sulfur and nitrogen co-doped coaxial core-shell silicon-carbon negative electrode material, preparation method thereof and lithium ion battery Download PDFInfo
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Abstract
The invention discloses a sulfur and nitrogen co-doped coaxial core-shell silicon-carbon cathode material, a preparation method thereof and a lithium ion battery. The method comprises the following steps: 1) preparing a carbon nano tube coated by silicon oxide; 2) mixing the carbon nano tube coated by the silicon oxide with a reducing agent, calcining in an inert atmosphere, removing impurities from a calcined product, and drying to obtain a precursor; 3) and dissolving the precursor and thiourea in a solvent to obtain a mixed solution, and carrying out hydrothermal reaction to obtain the sulfur and nitrogen co-doped coaxial core-shell silicon-carbon material, wherein the sulfur and nitrogen co-doped coaxial core-shell silicon-carbon material has excellent cycle stability.
Description
Technical Field
The invention relates to the technical field of new energy material preparation, and relates to a sulfur and nitrogen co-doped coaxial core-shell silicon-carbon cathode material, a preparation method thereof and a lithium ion battery.
Background
The problems of volume expansion of lithium intercalation and lithium deintercalation inherent in a silicon electrode and poor conductivity are solved, and a large number of documents report that the size of silicon is reduced to a nano level or other materials are compounded into two effective strategies for adapting to volume change and limiting pulverization of the silicon anode in the charging/discharging process. Such as nanoparticles, nanospheres, nanowires, nanotube arrays, and the like. The one-dimensional silicon nanotube can generate hoop stress, and can relieve volume change in the charging/discharging process by reducing the thickness of the shell to a few nanometers, so that lithium ion and electron transmission paths are reduced, and the multiplying power and the cycle performance of the silicon-based anode are improved. Thus, by transitioning from nanoparticles (zero dimension) to nanotubes (one dimension), many of the negative problems associated with silicon anode materials can be reduced.
However, the fabrication of these one-dimensional Si nanotubes typically requires various metal oxide templates, such as MgO or ZnO. Silicon is then deposited by CVD or sol-gel methods, followed by removal of the template to obtain silicon nanotubes. CN102101670A discloses a method for preparing a crystalline silicon nanotube with controllable size and morphology, which uses an anodic oxidation method to obtain an alumina template with a hole shape of a straight-line through hole or a Y-branch-shaped through hole or a three-branch-shaped through hole or a two-generation Y-branch-shaped through hole, and prepares the crystalline silicon nanotube with controllable size and morphology by using the template. CN101284667B discloses a method for preparing a silicon nanotube, which adopts mixed powder of SiO, Si and the like as a starting material, takes a small amount of rare earth elements as an indirect catalyst, thermally evaporates the raw material under the conditions of higher temperature and lower gas pressure, and nucleates by the accumulation of silicon atoms at a proper deposition temperature to prepare the silicon nanotube with a hollow structure.
However, the synthesis method of silicon nanotubes disclosed in the prior art is not only complicated in process and high in cost, but also may use toxic precursors.
Disclosure of Invention
Aiming at the problems in the prior art, the invention aims to provide a sulfur and nitrogen co-doped coaxial core-shell silicon carbon negative electrode material, a preparation method thereof and a lithium ion battery negative electrode.
In order to achieve the purpose, the invention adopts the following technical scheme:
in a first aspect, the invention provides a preparation method of a sulfur and nitrogen co-doped coaxial core-shell silicon carbon material, which comprises the following steps:
(1) preparing a carbon nano tube coated by silicon oxide;
(2) mixing the carbon nano tube coated by the silicon oxide with a reducing agent, calcining in an inert atmosphere, removing impurities from a calcined product, and drying to obtain a precursor;
(3) and dissolving the precursor and thiourea in a solvent to obtain a mixed solution, and carrying out hydrothermal reaction to obtain the sulfur and nitrogen co-doped coaxial core-shell silicon-carbon material.
The kind of gas in the inert atmosphere is not particularly limited in the present invention, and may be at least one of argon, neon, helium, or xenon, for example. By heating and reducing in inert atmosphere, oxygen is isolated, and high-efficiency reaction is facilitated.
According to the method, the carbon nano tube coated with the silicon oxide is adopted, the silicon oxide is reduced by calcining the reducing agent in an inert atmosphere, a silicon coating shell can be formed on the surface of the carbon nano tube, the coating shell is tightly combined with the carbon nano tube, the purity of the silicon coating shell is guaranteed through impurity removal, the pores generated by the impurity removal are beneficial to doping of N and S to the internal carbon nano tube, the hydrothermal process realizes co-doping of the material N, S and has a repairing function, the conductivity and the ion transmission function of the material are improved, and therefore the circulation stability of the material is improved.
In the sulfur and nitrogen co-doped coaxial core-shell silicon-carbon material prepared by the method, the excellent mechanical stability of the carbon nano tube provides an ideal structural template and a stable structural support body for the carbon-silicon composite material, the coaxial core-shell structure effectively relieves the volume expansion of silicon in the charge and discharge processes of the composite material, and the formed SEI film is relatively stable when being contacted with a carbon layer; moreover, the carbon nanotube has good conductivity, the structure of the inner core of the carbon nanotube is compact with that of the silicon shell, and the S, N codoping on the composite material is mainly at the contact gap between the carbon nanotube and the silicon, so that the potential barrier can be effectively reduced, more defects and active centers are generated, the adsorption and transmission of lithium ions are facilitated, the conductivity and the transmission of the lithium ions and electrons are improved, and the cycle performance of the electrode material is improved.
The invention adopts the carbon nano tube as the template for preparing the silicon nano tube, the template does not need to be removed, the performance of the material can be enhanced, and the method is simple and convenient, reduces the cost for purchasing the nano silicon and reduces the production cost.
The following is a preferred technical solution of the present invention, but not a limitation to the technical solution provided by the present invention, and the technical objects and advantageous effects of the present invention can be better achieved and achieved by the following preferred technical solution.
Preferably, the preparation method of step (1) comprises:
(a) adding a surfactant into the water-alcohol mixed solution, then adding the carboxylated carbon nanotubes, and uniformly dispersing to obtain a first mixed solution;
(b) adding NH into the first mixed solution 3 ·H 2 And (3) stirring the mixture of O and ethyl orthosilicate for reaction, and drying to obtain the carbon nano tube coated by silicon oxide.
In this preferred embodiment, the surfactant is not limited to a specific type, and may be cetyltrimethylammonium bromide (CTAB), for example.
Preferably, said NH of step (b) 3 ·H 2 The volume ratio of O to tetraethoxysilane is 1 (1.5-4), such as 1:1.5, 1:1.8, 1:2, 1:2.5, 1:3, 1:3.5 or 1: 4.
Preferably, the mass ratio of the tetraethoxysilane to the carboxylated carbon nanotubes in the step (b) is (10-20): 1, for example, 10:1, 12:1, 14:1, 15:1, 18:1 or 20: 1. In the preferable range, S, N doping of the carbon nano tube is facilitated, and the structural stability of the coating shell is ensured, and the high conductivity and electrochemical performance of the material are ensured.
Preferably, the stirring reaction time in step (b) is 25 ℃ to 50 ℃, such as 25 ℃, 30 ℃, 32 ℃, 35 ℃, 40 ℃, 45 ℃ or 50 ℃.
Preferably, the stirring reaction time in step (b) is 8h to 24h, such as 8h, 10h, 12h, 15h, 16h, 18h, 20h or 24 h.
Preferably, the reducing agent in the step (2) is magnesium powder.
Preferably, the mass ratio of the silicon oxide-coated carbon nanotubes to the reducing agent in the step (2) is 1.0 to 1.15, such as 1.0, 1.05, 1.10 or 1.15.
In a preferred embodiment of the method of the present invention, sodium chloride and/or potassium chloride is further mixed in the step (2) of mixing the silica-coated carbon nanotubes with a reducing agent. By adding sodium chloride and/or potassium chloride, molten salt formed at high temperature can be used as a heat absorbent, heat generated in the reduction (such as magnesiothermic reduction) process can be absorbed, silicon carbon products are prevented from being formed due to overhigh temperature, silicon purity is improved, and silicon crystal grains can be prevented from being excessively grown.
Preferably, the mass of the sodium chloride and/or potassium chloride is 1.5 to 2.5 times, for example, 1.5 times, 1.7 times, 2 times, 2.2 times, 2.5 times, or the like, the mass of the silicon oxide-coated carbon nanotube.
Preferably, the temperature of the calcination in step (2) is 650 ℃ to 900 ℃, such as 650 ℃, 675 ℃, 700 ℃, 750 ℃, 800 ℃, 850 ℃ or 900 ℃, etc., preferably 650 ℃ to 800 ℃.
Preferably, the calcination time in step (2) is 1.5h to 5h, such as 1.5h, 2h, 2.5h, 3h, 3.5h, 4h or 5h, etc.
Preferably, the impurity removal in the step (2) is as follows: water washing, HCl washing and HF washing are respectively carried out to remove the generated molten salt, MgO and SiO 2 Impurities. For example, the metal layer may be washed with hydrochloric acid, hydrofluoric acid, and water. The water washing can be replaced by the water-alcohol mixed solution washing, or the water washing can be replaced by the water washing and the alcohol washing which are respectively carried out.
Preferably, the mass of the thiourea in the step (3) is 2.5 to 5 times, for example, 2.5, 3, 3.5, 4, or 5 times, etc., of the mass of the precursor.
Preferably, the temperature of the hydrothermal reaction in step (3) is 160 ℃ to 200 ℃, such as 160 ℃, 170 ℃, 175 ℃, 180 ℃, 190 ℃ or 200 ℃ and the like.
Preferably, the hydrothermal reaction time in step (3) is 8h to 16h, such as 8h, 9h, 10h, 12h, 13h, 15h or 16 h.
As a further preferred technical solution of the method of the present invention, the method comprises the steps of:
step 1: weighing a certain amount of hexadecyl trimethyl bromideAdding ammonium chloride into a container containing mixed solution of ethanol and deionized water, placing the container on a magnetic stirrer, stirring until cetyl trimethyl ammonium bromide is dissolved, weighing a certain amount of carboxylated carbon nanotubes, adding, continuously stirring and ultrasonically treating for 2h, and adding NH (NH) in a volume ratio of 1:2 3 ·H 2 And stirring O and tetraethoxysilane for 12 hours, centrifugally collecting, drying the finally obtained product in a vacuum drying oven at 60 ℃ for later use at the rotating speed of 12000r/min, and obtaining powder A.
Step 2: mixing the powder A with magnesium powder in the same mass proportion and sodium chloride in an amount which is 2 times the mass of the powder A, uniformly grinding the mixture, placing the mixture in a tubular furnace in an argon atmosphere, and calcining the mixture for 4 hours at a high temperature of between 650 and 800 ℃ for reduction. Washing the calcined product with distilled water, HCl and HF to remove the molten salt, MgO and SiO 2 And drying impurities in a vacuum box at 60 ℃ for 12 hours to obtain powder B.
And step 3: and adding the powder B into 80mL of deionized water, performing ultrasonic dispersion for 30min, adding thiourea with the mass of 3 times, continuously stirring until the thiourea is dissolved, transferring the mixture into a stainless steel autoclave, keeping the stainless steel autoclave at 180 ℃ for 10h, naturally cooling the mixture to room temperature under a high pressure, sequentially washing the mixture by using distilled water and ethanol for several times, and drying the washed mixture in a vacuum drying oven at 60 ℃ to obtain the final sulfur and nitrogen co-doped coaxial core-shell silicon-carbon material.
In the present invention, the water used may be distilled water or deionized water, and those skilled in the art may select the water according to the need, and is not particularly limited.
In a second aspect, the invention provides a sulfur and nitrogen co-doped coaxial core-shell silicon-carbon material prepared by the method according to the first aspect, the core-shell silicon-carbon material is co-doped with sulfur and nitrogen, the core-shell silicon-carbon material comprises a carbon nanotube core and a silicon shell coated on the surface of the carbon nanotube core, and the silicon shell is tubular and coaxial with the carbon nanotube core.
The sulfur and nitrogen co-doped coaxial core-shell silicon-carbon material prepared by the method has excellent cycle performance.
In a third aspect, the invention provides a lithium ion battery, and a negative electrode of the lithium ion battery comprises the sulfur-nitrogen co-doped coaxial core-shell silicon-carbon material of the second aspect.
Compared with the prior art, the invention has the following beneficial effects:
according to the method, the carbon nano tube coated with the silicon oxide is adopted, the silicon oxide is reduced by calcining the reducing agent in an inert atmosphere, a silicon coating shell can be formed on the surface of the carbon nano tube, the coating shell is tightly combined with the carbon nano tube, the purity of the silicon coating shell is guaranteed through impurity removal, the pores generated by the impurity removal are beneficial to doping of N and S to the internal carbon nano tube, the hydrothermal process realizes co-doping of the material N, S and has a repairing function, the conductivity and the ion transmission function of the material are improved, and therefore the circulation stability of the material is improved.
Drawings
FIG. 1 is XRD patterns of a sulfur and nitrogen co-doped coaxial core-shell silicon carbon anode material prepared in example 1 and an anode material of a comparative example 2, wherein SNC @ Si @ CNTs corresponds to example 1, SiO is 2 @ CNTs corresponds to comparative example 2;
FIG. 2 is a Scanning Electron Microscope (SEM) image of the sulfur and nitrogen co-doped coaxial core-shell silicon carbon cathode material prepared in example 1;
FIG. 3 is a cycle chart of the sulfur and nitrogen co-doped coaxial core-shell silicon carbon anode material prepared in example 1 at a current density of 100 mA/g.
Detailed Description
The technical scheme of the invention is further explained by the specific implementation mode in combination with the attached drawings.
Example 1
The embodiment provides a preparation method of a sulfur and nitrogen co-doped coaxial core-shell silicon carbon material, which specifically comprises the following steps:
(1) preparing the silicon oxide coated carbon nano tube:
(a) adding cetyl trimethyl ammonium bromide into a water-alcohol mixed solution (the mass ratio of water to ethanol is 5:1), then adding a carboxylated carbon nanotube, and continuously stirring and ultrasonically treating for 2 hours to uniformly disperse the materials to obtain a first mixed solution;
(b) to the firstAdding NH into the mixed solution 3 ·H 2 Mixture of O and Ethyl orthosilicate (NH) 3 ·H 2 The volume ratio of O to tetraethoxysilane is 1:2, the mass ratio of tetraethoxysilane to carboxylated carbon nano-tubes is 15:1), stirring and reacting for 12 hours at the temperature of 30 ℃, centrifugally collecting, the centrifugal rotating speed is 9000r/min, drying the products centrifugally collected in a vacuum drying oven at the temperature of 60 ℃, and obtaining the carbon nano-tubes coated with silicon oxide, which are marked as powder A.
(2) Uniformly grinding the powder A obtained in the step (1), magnesium powder and sodium chloride, and then placing the mixture into a tube furnace, wherein the powder A: magnesium powder: calcining sodium chloride (mass ratio) 1:1:2 at 680 deg.C for 4 hr under argon atmosphere, washing the calcined product with distilled water, HCl solution and HF solution to remove the molten salt, MgO and SiO 2 Drying impurities in a vacuum drying oven at 60 ℃ for 12 hours to obtain a precursor, and marking as powder B;
(3) dissolving the powder B obtained in the step (2) in 80mL of water, performing ultrasonic dispersion for 30min, then adding 3 times of thiourea by mass, continuously stirring until the thiourea is dissolved to obtain a mixed solution, transferring the mixed solution into a reaction kettle, performing hydrothermal reaction at 170 ℃ for 15h, washing the mixed solution with distilled water and ethanol for several times after the high-pressure reaction kettle is naturally cooled to room temperature, and drying the washed solution in a vacuum drying oven at 60 ℃ to obtain the sulfur and nitrogen co-doped coaxial core-shell silicon-carbon material.
Example 2
The difference from example 1 is that the mass ratio of tetraethoxysilane to carboxylated carbon nanotubes is 6: 1.
Example 3
The difference from example 1 is that the mass ratio of tetraethoxysilane to carboxylated carbon nanotubes is 30: 1.
Example 4
The difference from example 1 is that sodium chloride is not added, and the calcination temperature in step (2) is 900 ℃.
Comparative example 1
The difference from example 1 is that thiourea was not added in step (3) and other preparation methods and conditions were the same as example 1 to obtain a negative electrode material.
Comparative example 2
The difference from example 1 is that step (2) and step (3) were not performed, and powder a was used as the anode material.
And (3) detection:
firstly, the sulfur and nitrogen co-doped coaxial core-shell silicon carbon cathode material prepared in example 1 is subjected to crystalline phase characterization, and an XRD (X-ray diffraction) pattern of the material is shown in FIG. 1.
Secondly, the appearance of the sulfur and nitrogen co-doped coaxial core-shell silicon carbon negative electrode material prepared in example 1 is characterized, and an SEM image of the material is shown in FIG. 2.
Thirdly, the sulfur and nitrogen co-doped coaxial core-shell silicon carbon materials of the embodiments and the cathode materials of the comparative examples 1 to 2 are analyzed in electrochemical performance, and fig. 3 is a circulation diagram of the sulfur and nitrogen co-doped coaxial core-shell silicon carbon cathode material prepared in the embodiment 1 under a current density of 400 mA/g.
The electrochemical performance analysis comprises the following steps:
(1) preparing a negative pole piece:
the sulfur and nitrogen co-doped coaxial core-shell silicon-carbon material of each example and the negative electrode material of comparative examples 1-2 are used as negative electrode active materials, the conductive agent SP and the binder PAA are dissolved in a solvent according to the mass percentage of 83:7:10 and mixed, the solid content is controlled to be 46%, the mixture is coated on a copper foil current collector, and vacuum drying is carried out to prepare a negative electrode plate.
(2) The negative pole piece is adopted to be assembled into a button cell in an argon atmosphere glove box, the diaphragm is a polypropylene microporous membrane, and the electrolyte is 1mol/L LiPF 6 And the counter electrode is a metal lithium sheet.
The button cell was subjected to a cycling test using a blue cell test system CT2001C at room temperature (25 ℃) and 100mA/g current density for 100 weeks, as shown in table 1.
TABLE 1
And (3) analysis:
as is clear from the comparison between example 1 and example 2, if the amount of tetraethoxysilane added is too small, the coating effect of tetraethoxysilane is not good, the integrity of the silicon layer is lowered, the capacity is lowered, and the cycle stability is also lowered.
It is understood from the comparison between example 1 and example 3 that if the addition amount of the carboxylated carbon nanotubes is too small and the addition amount of the tetraethoxysilane is too large, the uniformity of the silicon-based material is reduced, the agglomeration is increased, the doping effect of S, N is affected, the electrochemical performance of the material is further reduced, and the improvement of the capacity and the cycle performance is not facilitated.
It can be seen from the comparison between example 1 and example 4 that the calcination temperature is higher without adding sodium chloride, and the capacity and cycle performance are reduced, which may be caused by the formation of carbon silicon product due to too high temperature, and the reduction of purity, and may also be caused by the too large growth of silicon crystal grains and the larger volume expansion during the cycle.
As can be seen from the comparison of example 1 and comparative example 1, without addition of thiourea, S, N co-doping was not performed, resulting in a great decrease in cycle performance.
It can be seen from the comparison of example 1 and comparative example 2 that the capacity of the silica-coated carbon nanotubes is drastically decreased, the cycle performance is inferior to that of the composite anode material of the present invention, and the silica obtained by hydrolysis of tetraethoxysilane does not provide additional capacity, but rather further prevents lithium ions from being intercalated into the carbon nanotubes.
The applicant states that the present invention is illustrated in detail by the above examples, but the present invention is not limited to the above detailed methods, i.e. it is not meant that the present invention must rely on the above detailed methods for its implementation. It should be understood by those skilled in the art that any modification of the present invention, equivalent substitutions of the raw materials of the product of the present invention, addition of auxiliary components, selection of specific modes, etc., are within the scope and disclosure of the present invention.
Claims (18)
1. A preparation method of a sulfur and nitrogen co-doped coaxial core-shell silicon carbon material is characterized by comprising the following steps:
(1) preparing a carbon nano tube coated by silicon oxide;
(2) mixing the carbon nano tube coated by the silicon oxide with a reducing agent, calcining in an inert atmosphere, removing impurities from a calcined product, and drying to obtain a precursor;
(3) dissolving the precursor and thiourea in a solvent to obtain a mixed solution, and carrying out hydrothermal reaction to obtain a sulfur and nitrogen co-doped coaxial core-shell silicon-carbon material;
mixing the carbon nano tube coated by the silicon oxide with a reducing agent, and mixing sodium chloride and/or potassium chloride;
the impurity removal in the step (2) is as follows: water washing, HCl washing, and HF washing were performed, respectively.
2. The method according to claim 1, wherein the preparation method of step (1) comprises:
(a) adding a surfactant into the water-alcohol mixed solution, then adding the carboxylated carbon nanotubes, and uniformly dispersing to obtain a first mixed solution;
(b) adding NH into the first mixed solution 3 ·H 2 And (3) stirring the mixture of O and ethyl orthosilicate for reaction, and drying to obtain the carbon nano tube coated by silicon oxide.
3. The method of claim 2, wherein the NH of step (b) 3 ·H 2 The volume ratio of the O to the tetraethoxysilane is 1 (1.5-4).
4. The method according to claim 2, wherein the mass ratio of the tetraethoxysilane to the carboxylated carbon nanotubes in the step (b) is (10-20): 1.
5. The process of claim 2, wherein the temperature of the stirred reaction of step (b) is from 25 ℃ to 50 ℃.
6. The method of claim 2, wherein the stirring reaction time in step (b) is 8-24 h.
7. The method of claim 1, wherein the reducing agent of step (2) is magnesium powder.
8. The method according to claim 1, wherein the mass ratio of the silicon oxide-coated carbon nanotubes to the reducing agent in the step (2) is 1.0 to 1.15.
9. The method according to claim 1, wherein the mass of the sodium chloride and/or potassium chloride is 1.5 to 2.5 times the mass of the silicon oxide-coated carbon nanotube.
10. The method of claim 1, wherein the temperature of the calcining in step (2) is 650 ℃ to 900 ℃.
11. The method of claim 10, wherein the temperature of the calcining in step (2) is 650 ℃ to 800 ℃.
12. The method of claim 1, wherein the calcination time in step (2) is 1.5h to 5 h.
13. The method according to claim 1, wherein the mass of the thiourea in the step (3) is 2.5 to 5 times that of the precursor.
14. The method according to claim 1, wherein the temperature of the hydrothermal reaction in the step (3) is 160 ℃ to 200 ℃.
15. The method according to claim 1, wherein the hydrothermal reaction time in step (3) is 8-16 h.
16. Method according to claim 1, characterized in that it comprises the following steps:
step 1: weighing a certain amountAdding a certain amount of cetyl trimethyl ammonium bromide into a container filled with a mixed solution of ethanol and deionized water, placing the container on a magnetic stirrer, stirring until the cetyl trimethyl ammonium bromide is dissolved, weighing a certain amount of carboxylated carbon nanotubes, adding, continuously stirring and ultrasonically treating for 2 hours, and then adding NH (NH) with the volume ratio of 1:2 3 ·H 2 Stirring O and tetraethoxysilane for 12 hours, centrifugally collecting at the rotating speed of 8000-12000 r/min, and drying the finally obtained product in a vacuum drying oven at the temperature of 60 ℃ for later use to obtain powder A;
step 2: mixing the powder A with magnesium powder in the same mass proportion and sodium chloride in an amount which is 2 times the mass of the powder A, uniformly grinding the mixture, placing the mixture in a tubular furnace in an argon atmosphere, and calcining the mixture at a high temperature of between 650 and 800 ℃ for 4 hours to reduce the mixture; washing the calcined product with distilled water, HCl solution and HF solution to remove the molten salt, MgO and SiO 2 Drying impurities in a vacuum box at 60 ℃ for 12 hours to obtain powder B;
and step 3: and adding the powder B into 80mL of deionized water, performing ultrasonic dispersion for 30min, adding thiourea with the mass of 3 times, continuously stirring until the thiourea is dissolved, transferring the mixture into a stainless steel autoclave, keeping the stainless steel autoclave at 180 ℃ for 10h, naturally cooling the mixture to room temperature under a high pressure, sequentially washing the mixture by using distilled water and ethanol for several times, and drying the washed mixture in a vacuum drying oven at 50-70 ℃ for 10-16 h to obtain the final sulfur and nitrogen co-doped coaxial core-shell silicon-carbon material.
17. The sulfur and nitrogen co-doped coaxial core-shell silicon-carbon material prepared according to any one of claims 1 to 16, which is characterized in that the core-shell silicon-carbon material is co-doped with sulfur and nitrogen, the core-shell silicon-carbon material comprises a carbon nanotube core and a silicon shell coated on the surface of the carbon nanotube core, and the silicon shell is tubular and coaxial with the carbon nanotube core.
18. A lithium ion battery, characterized in that the sulfur and nitrogen co-doped coaxial core-shell silicon carbon material of claim 17 is included in the negative electrode of the lithium ion battery.
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