CN115117324A - Magnesium-doped hollow silicon-carbon composite material prepared by template method and preparation method thereof - Google Patents
Magnesium-doped hollow silicon-carbon composite material prepared by template method and preparation method thereof Download PDFInfo
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Abstract
The invention discloses a magnesium-doped hollow silicon-carbon composite material prepared by a template method and a preparation method thereof, wherein the preparation method comprises the following steps: obtaining a suspension by adopting a template method, adding a magnesium salt compound, a silicon-based material, a silane coupling agent, a carbon nano tube and a catalyst thereof into the suspension by a sol coprecipitation method, uniformly dispersing, carrying out hydrothermal reaction, drying in vacuum, removing the template by heat treatment at the temperature of 200-1100 ℃ respectively, and heating to the temperature of 700-1100 ℃ for chemical vapor deposition for 1-6h to obtain the product. The invention can improve the charge-discharge cycle performance, and has stable structure and high first efficiency.
Description
Technical Field
The invention belongs to the field of preparation of lithium ion battery materials, and particularly relates to a template method for preparing a magnesium-doped hollow silicon-carbon composite material, and a preparation method for preparing the magnesium-doped hollow silicon-carbon composite material by using the template method.
Background
The silicon material has the advantages of abundant resources, low price, high theoretical capacity (up to 4200mAh/g) in nature, safer performance as a lithium ion battery cathode compared with a graphite material and the like, so that the silicon material is widely concerned by researchers. However, the silicon material can generate serious volume change (volume expansion of 300%) in the charging and discharging processes, so that not only is the silicon material seriously pulverized, but also an SEI film is continuously formed at the position where the silicon is contacted with an electrolyte, and the capacity of a silicon electrode is rapidly attenuated in the circulating process. In addition, the poor conductivity of silicon hinders the improvement of the rate capability of the silicon anode material. In order to solve the problem that the silicon negative electrode material is easy to generate stress cracking in the charging and discharging process to cause volume expansion to cause cycle performance deterioration, the following improvement methods are mainly adopted at present: reducing the particle size of active silicon particles, and preparing a nano-grade material to reduce the internal stress of volume change; the volume expansion of silicon is relieved by utilizing the compound of the nano silicon material and other materials, such as a silicon-carbon composite material, so that the cycle life of the silicon is prolonged; the silicon-based material is doped to reduce impedance and improve the first efficiency, but the nano silicon is agglomerated, so that the cycle performance is easily deteriorated. For example, chinese patent CN201610893698.3 discloses a method for preparing a silicon-carbon composite material by using a magnesiothermic reduction method, which comprises mixing a silica source, an organic carbon source and a solvent, wherein the organic carbon source is polyvinylidene fluoride, polypyrrole, polyacrylonitrile or polyethylene, performing ball milling to obtain a homogenized mixture, and drying to obtain a silica/carbon precursor composite material; and mixing the silicon dioxide/carbon precursor composite material with magnesium powder, and carrying out a magnesiothermic reduction reaction at the temperature of 680-700 ℃ to obtain the silicon-carbon composite material. Although the efficiency is improved for the first time, the defects of poor power performance, poor structural stability and the like exist, and the problem of silicon expansion is not fundamentally solved. For example, chinese patent publication No. CN 110854379B discloses a silicon-carbon composite negative electrode material and a preparation method thereof, a negative electrode sheet, and a lithium ion battery, wherein the preparation method comprises the steps of preparing a mixed solution of a template agent, a dispersant, a carbon nanotube, and thioacetamide, mixing the mixed solution with a silicon acetate solution, performing a magnesium thermal reaction, washing, and drying, but the magnesium reduction reduces the first efficiency in a back-end process, and the silicon and magnesium reaction is slow in reaction process at a high temperature and low in efficiency.
Disclosure of Invention
The invention aims to overcome the defects and provide the template method for preparing the magnesium-doped hollow silicon-carbon composite material, which can improve the charge-discharge cycle performance, has a stable structure and high first efficiency.
The invention also aims to provide a preparation method for preparing the magnesium-doped hollow silicon-carbon composite material by the template method.
The magnesium-doped hollow silicon-carbon composite material prepared by the template method is of a core-shell structure, the core is made of a magnesium-doped silicon-based material, the shell is amorphous carbon, the mass ratio of the shell is 1-5wt% according to 100% of the mass of the composite material, and the core is made of a silicon-based material: magnesium compound: the mass ratio of the carbon nano tubes is 100: 1-5: 0.5-2.
The invention relates to a preparation method for preparing a magnesium-doped hollow silicon-carbon composite material by a template method, which comprises the following steps of:
(1) according to the polystyrene microsphere: magnesium salt compound, silicon-based material, silane coupling agent, carbon nanotube: catalyst: the mass ratio of the organic solvent is 5-20: 1-5: 100:0.5-2: 1-5: 0.5-2: 500, a step of; adding polystyrene microspheres into an organic solvent to obtain a suspension, adding a magnesium salt compound, a silicon-based material, a silane coupling agent, 1-5wt% of carbon nanotube conductive liquid and a catalyst, uniformly dispersing, transferring into a high-pressure reaction kettle, reacting at 80-150 ℃ under 1-5Mpa for 1-6h, and vacuum drying at 80 ℃ under (-0.09Mpa) for 24h to obtain silicon-based/magnesium-based material coated polystyrene microspheres;
(2) transferring the silicon-based/magnesium-based material coated polystyrene microspheres into a tube furnace, heating to 200-fold-activated carbon at 300 ℃ in an inert atmosphere, preserving the heat for 1-6h, treating for 100-500 s under the conditions that the oxygen flow is 10-50 SCCM, the cavity pressure is 100-800 mtorr, the power is 100-400W, obtaining a magnesium-doped silicon-carbon material precursor, introducing a carbon source gas atmosphere, heating to 700-fold-activated carbon at 1100 ℃, and carbonizing for 1-6 h.
The magnesium salt compound in the step (1) is one of methoxy magnesium, ethoxy magnesium, propoxy magnesium, butoxy magnesium, isobutoxy magnesium or 2-ethylhexoxy magnesium; the organic solvent is one of carbon tetrachloride, cyclohexane or N-methyl pyrrolidone.
The silicon-based material in the step (1) is one of nano silicon and SiOx (X is more than 0 and less than 2).
The silane coupling agent in the step (1) is one of 3-aminopropyltrimethoxysilane, gamma-chloropropyltrimethoxysilane, bis (gamma-triethoxysilylpropyl) tetrasulfide, bis (triethoxysilylpropyl) disulfide, gamma-mercaptopropyltriethoxysilane or gamma-aminopropyltriethoxysilane.
The catalyst in the step (1) is one of nano nickel, nano cobalt or nano nickel, and the particle size is 100-500 nm.
The preparation method of the 1-5wt% carbon nano tube conductive liquid in the step (1) comprises the following steps: adding 1-5 parts of carbon nano tube into 100 parts of N-methyl pyrrolidone, and dispersing for 24-48 h by a sand mill under the condition that the rotating speed is 100-500RPM to obtain the 1-5wt% carbon nano tube conductive liquid.
Compared with the prior art, the invention has obvious beneficial effects, and the technical scheme can show that: the preparation method comprises the steps of doping magnesium salt compounds in silicon-based materials to perform magnesium doping of precursors, reacting under the condition of plasma, preparing a hollow core structure, depositing a carbon nanotube conductive liquid on the surface of the hollow core structure to form a uniform spherical structure, sintering at high temperature to remove a soft template to obtain the hollow magnesium-doped silicon-based materials, and reducing silicon expansion in the charging and discharging processes by using the hollow core structure, wherein the shell is made of the silicon-based materials containing reticular carbon nanotubes and magnesium doping; meanwhile, the reticular carbon nano tube can avoid the structural collapse of the material in the charge and discharge process to improve the cycle performance, and the catalyst is used for coating the amorphous carbon in the shell of the reticular carbon nano tube to reduce the direct contact of the core of the reticular carbon nano tube with the electrolyte to improve the high-temperature storage performance and the first efficiency. On the other hand, the carbon nanotube has high electronic conductivity and rate-increasing performance. Meanwhile, a liquid phase method is adopted, a magnesium salt compound is adopted, the magnesium-doped silicon-based material is obtained by connecting the silicon-based material with a silane coupling agent, magnesium silicate is formed in the charging and discharging process, and the magnesium silicate has the characteristics of stable structure, high first-time efficiency and the like.
Drawings
Fig. 1 is an SEM image of a silicon carbon composite material prepared in example 1.
Detailed Description
Example 1
A method for preparing a magnesium-doped hollow silicon-carbon composite material by a template method comprises the following steps:
(1) adding 10g of polystyrene microspheres into 500ml of carbon tetrachloride to obtain a suspension, then adding 3g of methoxy magnesium, 100g of nano silicon, 1g of 3-aminopropyltrimethoxysilane, 100ml of 3 wt% of carbon nanotube conductive liquid and 1g of nano nickel, uniformly dispersing, transferring into a high-pressure reaction kettle, carrying out hydrothermal reaction at the temperature of 120 ℃, reacting for 3h, under the pressure of 3MPa and under the temperature of 80 ℃ for 24h (the vacuum degree is-0.09 MPa), and obtaining the silicon-based/magnesium-based material coated polystyrene microspheres;
(2) transferring the silicon-based/magnesium-based material coated polystyrene microspheres into a tube furnace, heating to 250 ℃ and preserving heat for 3 hours under the inert atmosphere of argon, treating by plasma under the conditions of oxygen flow of 30SCCM, cavity pressure of 500mtorr, power of 200W and treatment time of 300s to obtain a magnesium-doped silicon-carbon material precursor, and heating to 900 ℃ to carbonize for 3 hours under the atmosphere of methane carbon source gas to obtain the magnesium-doped silicon-carbon material precursor.
Example 2
A preparation method for preparing a magnesium-doped hollow silicon-carbon composite material by a template method comprises the following steps:
(1) adding 5g of polystyrene microspheres into 500ml of cyclohexane to obtain a suspension, then adding 1g of magnesium ethoxide, 100g of SiO material, 0.5g of gamma-chloropropyltrimethoxysilane, 100ml of 1 wt% of carbon nanotube conductive liquid and 0.5g of nano cobalt thereof, uniformly dispersing, then transferring into a high-pressure reaction kettle, carrying out hydrothermal reaction at the temperature of 80 ℃, carrying out reaction for 6 hours, carrying out vacuum drying at the pressure of 1MPa and at the temperature of 80 ℃ for 24 hours (the vacuum degree is-0.09 MPa), and obtaining the silicon-based/magnesium-based material-coated polystyrene microspheres;
(2) transferring the silicon-based/magnesium-based material coated polystyrene microspheres into a tube furnace, heating to 200 ℃ and preserving heat for 6 hours in an argon inert atmosphere, carrying out plasma treatment for 500s at an oxygen flow of 10SCCM, a cavity pressure of 100mtorr, a power of 400W to obtain a magnesium-doped silicon-carbon material precursor, and heating to 700 ℃ for carbonization for 6 hours in an acetylene carbon source gas atmosphere to obtain the magnesium-doped silicon-carbon material precursor.
Example 3
A preparation method for preparing a magnesium-doped hollow silicon-carbon composite material by a template method comprises the following steps:
(1) adding 20g of polystyrene microspheres into 500ml of N-methyl pyrrolidone to obtain suspension, then adding 5g of propoxy magnesium, 100g of SiO silicon-based material, 2g of gamma-chloropropyltrimethoxysilane, 100ml of carbon nanotube conductive liquid with the concentration of 5wt% and 2g of nano iron, uniformly dispersing, transferring into a high-pressure reaction kettle, carrying out hydrothermal reaction at the temperature of 150 ℃, carrying out reaction for 1h, carrying out pressure of 5MPa and carrying out vacuum drying at the temperature of 80 ℃ for 24h (vacuum degree: -0.09MPa), and obtaining the polystyrene microspheres coated with the silicon-based/magnesium-based material;
(2) transferring the silicon-based/magnesium-based material coated polystyrene microspheres into a tube furnace, heating to 300 ℃ and preserving heat for 1h under the inert atmosphere of argon, treating by plasma at the oxygen flow of 50SCCM, the cavity pressure of 800mtorr, the power of 100W and the treatment time of 100s to obtain a magnesium-doped silicon-carbon material precursor, and introducing ethylene gas to the magnesium-doped silicon-carbon material precursor to heat to 1100 ℃ to carbonize for 1h to obtain the magnesium-doped silicon-carbon material precursor.
Comparative example 1:
a preparation method of a silicon-carbon composite material comprises the following steps:
adding 3g of methoxy magnesium, 100g of nano silicon, 1g of 3-aminopropyltrimethoxysilane, 100ml of 3% carbon nano tube conductive liquid and 1g of nano nickel into 500ml of carbon tetrachloride organic solvent, uniformly dispersing, transferring into a high-pressure reaction kettle, carrying out hydrothermal reaction at the temperature of 120 ℃, reacting for 3h, the pressure of 3Mpa and the temperature of 80 ℃ for 24h (the vacuum degree is-0.09 Mpa), obtaining a silicon-based/magnesium-based material, transferring into a tubular furnace, discharging air in the tube under the inert atmosphere of argon, introducing a methane carbon source gas, heating to 900 ℃ and carbonizing for 3h, and obtaining the silicon-carbon composite material.
Comparative example 2:
a preparation method of a silicon-carbon composite material comprises the following steps:
the silicon-based/magnesium-based material prepared in the step (1) in the example 1 is used to coat polystyrene microspheres as a precursor, oxygen is introduced at the temperature of 500 ℃ for oxidation treatment for 1h, and then methane carbon source gas is introduced to the precursor for carbonization for 3h after the temperature is raised to 900 ℃ to obtain the silicon-carbon composite material. Test example:
and (3) performance testing:
(1) topography testing
SEM tests were performed on the silicon carbon composite material of example 1, and the test results are shown in fig. 1. As can be seen from FIG. 1, the material has a hollow structure, and the particle size distribution of the material is uniform and reasonable, and the particle size of the particles is between 2 and 8 μm.
(2) Button cell test
The silicon-carbon composite materials in examples 1-3 and comparative examples 1-2 are used as negative electrode materials of lithium ion batteries to assemble button batteries, which are respectively marked as A1, A2, A3, B1 and B2.
The preparation method comprises the following steps: adding a binder, a conductive agent and a solvent into a lithium ion battery negative electrode material, stirring and pulping, coating the mixture on copper foil, and drying and rolling to prepare a negative electrode plate; the used binder is LA132, the conductive agent is SP, the solvent is NMP, and the proportion of the used negative electrode material, SP, PVDF and NMP is 95 g: 1 g: 4 g: 220 mL; LiPF in electrolyte 6 A mixture of EC and DEC with a volume ratio of 1:1 is used as an electrolyte; the metal lithium sheet is a counter electrode, and the diaphragm is a polypropylene (PP) film. Button cell assembly was performed in an argon-filled glove box. The electrochemical performance is carried out on a Wuhan blue electricity CT2001A type battery tester, the charging and discharging voltage range is 0.005V to 2.0V, and the charging and discharging rate is 0.1C.
The test results are shown in table 1.
TABLE 1
As can be seen from the data in table 1, the specific capacity and the first efficiency of the silicon-carbon composite material prepared in the example of the present invention are significantly better than those of the comparative examples 1 and 2. Compared with the comparative example 1, the method has no polystyrene template and no plasma treatment of the polystyrene template, can reduce the defect promotion capacity and the first efficiency of the surface due to the plasma treatment, improves the conductivity of the material, and promotes the specific surface area of the material by the holes left after the polystyrene template is carbonized, thereby being beneficial to the liquid absorption and retention of the material and the gram capacity exertion of the material. Compared with the example 1, the comparative example 2 does not adopt oxygen plasma treatment, namely, the silicon-based material contains more nano silicon and less silicon oxygen, the first efficiency is reduced, and the powder conductivity is also reduced.
(3) Testing the soft package battery:
the silicon-based composite materials in examples 1-3 and comparative examples 1-2 were doped with 90% artificial graphite as a negative electrode material to prepare a negative electrode sheet, and NCM532 was used as a positive electrode material; LiPF in electrolyte 6 A mixture of EC and DEC with a volume ratio of 1:1 is used as an electrolyte; 5Ah pouch cells, labeled C1, C2, C3, D1, and D2, were prepared with Celgard 2400 membrane as the separator. And respectively testing the liquid absorption and retention capacity, the rebound elasticity and the cycle performance of the negative pole piece.
a. Imbibition ability test
And (3) adopting a 1mL burette, sucking the electrolyte VmL, dripping a drop on the surface of the pole piece, timing until the electrolyte is completely absorbed, recording the time t, and calculating the liquid absorption speed V/t of the pole piece. The test results are shown in table 2.
b. Liquid retention test
Calculating the theoretical liquid absorption amount m of the pole piece according to the pole piece parameters 1 And weighing the weight m of the pole piece 2 Then, the pole piece is placed in electrolyte to be soaked for 24 hours, and the weight of the pole piece is weighed to be m 3 Calculating the amount m of the pole piece liquid absorption 3 -m 2 And calculated according to the following formula: retention rate ═ m 3 -m 2 ) 100%/m 1. The test results are shown in table 2.
TABLE 2
As can be seen from Table 2, the liquid and liquid absorbing abilities of the silicon carbon composite materials obtained in examples 1-3 are significantly higher than those of comparative examples 1 and 2. Experimental results show that the silicon-carbon composite material obtained by the soft template method has a high specific surface area, so that the liquid absorption and retention capacity of the material is improved.
c. Pole piece rebound rate test
Firstly, testing the average thickness of the pole piece to be D1 by using a thickness gauge, then placing the pole piece in a vacuum drying oven at 80 ℃ for drying for 48h, testing the thickness of the pole piece to be D2, and calculating according to the following formula: the rebound rate was (D2-D1) × 100%/D1. The test results are shown in table 3.
d. Pole piece resistivity testing
The resistivity of the pole piece was measured using a resistivity tester, and the results are shown in table 3.
TABLE 3
As can be seen from the data in table 3, the rebound resilience and resistivity of the negative electrode sheets prepared from the silicon-carbon composites obtained in examples 1 to 3 are significantly lower than those of comparative examples 1 and 2, i.e., the negative electrode sheets prepared from the silicon-carbon composites of the present invention have lower rebound resilience and resistivity. The reason for this may be: the silicon-carbon composite material obtained by the soft template method reduces the expansion of the silicon-carbon composite material, and meanwhile, the silicon-carbon composite material in the embodiment has higher electronic conductivity and reduces the resistivity of the pole piece.
e. Cycle performance test
The cycle performance of the battery is tested at the temperature of 25 +/-3 ℃ with the charge-discharge multiplying power of 1C/1C and the voltage range of 2.5V-4.2V. The test results are shown in table 4.
TABLE 4
As can be seen from table 4, the cycle performance of the battery prepared from the silicon-carbon composite material of the present invention is significantly better than that of the comparative example, and the reason for this is probably that the electrode plate prepared from the silicon-carbon composite material of the present invention has a lower expansion rate and a porous structure thereof, and reduces the expansion and improves the liquid absorption and retention capability of the material during the charging and discharging processes, thereby improving the cycle performance.
Claims (7)
1. A magnesium-doped hollow silicon-carbon composite material prepared by a template method is of a core-shell structure, a core is made of a magnesium-doped silicon-based material, a shell is made of amorphous carbon, the mass ratio of the shell is 1-5wt% according to 100% of the mass of the composite material, and the magnesium-doped hollow silicon-carbon composite material is prepared from the following silicon-based materials in the core: magnesium compound: the mass ratio of the carbon nano tubes is 100: 1-5: 0.5-2.
2. A method for preparing a magnesium-doped hollow silicon-carbon composite material by a template method comprises the following steps:
(1) according to the polystyrene microsphere: magnesium salt compound, silicon-based material, silane coupling agent, carbon nanotube: catalyst: the mass ratio of the organic solvent is 5-20: 1-5: 100:0.5-2: 1-5: 0.5-2: 500, a step of; adding polystyrene microspheres into an organic solvent to obtain a suspension, adding a magnesium salt compound, a silicon-based material, a silane coupling agent, 1-5wt% of carbon nanotube conductive liquid and a catalyst, uniformly dispersing, transferring into a high-pressure reaction kettle, reacting at 80-150 ℃ under 1-5Mpa for 1-6h, and vacuum drying at 80 ℃ under (-0.09Mpa) for 24h to obtain silicon-based/magnesium-based material coated polystyrene microspheres;
(2) transferring the silicon-based/magnesium-based material coated polystyrene microspheres into a tube furnace, heating to 200-fold-activated carbon at 300 ℃ in an inert atmosphere, preserving the heat for 1-6h, treating for 100-500 s under the conditions that the oxygen flow is 10-50 SCCM, the cavity pressure is 100-800 mtorr, the power is 100-400W, obtaining a magnesium-doped silicon-carbon material precursor, introducing a carbon source gas atmosphere, heating to 700-fold-activated carbon at 1100 ℃, and carbonizing for 1-6 h.
3. The method for preparing the magnesium-doped hollow silicon-carbon composite material according to the template method of claim 2, wherein: the magnesium salt compound in the step (1) is one of magnesium methoxide, magnesium ethoxide, magnesium propoxide, magnesium butoxide, magnesium isobutoxide or 2-ethylhexyloxy magnesium; the organic solvent is one of carbon tetrachloride, cyclohexane or N-methyl pyrrolidone.
4. The method for preparing the magnesium-doped hollow silicon-carbon composite material according to the template method of claim 2, wherein: the silicon-based material in the step (1) is one of nano silicon and SiOx (X is more than 0 and less than 2).
5. The method for preparing the magnesium-doped hollow silicon-carbon composite material according to the template method of claim 2, wherein: the silane coupling agent in the step (1) is one of 3-aminopropyltrimethoxysilane, gamma-chloropropyltrimethoxysilane, bis (gamma-triethoxysilylpropyl) tetrasulfide, bis (triethoxysilylpropyl) disulfide, gamma-mercaptopropyltriethoxysilane or gamma-aminopropyltriethoxysilane.
6. The method for preparing the magnesium-doped hollow silicon-carbon composite material according to the template method of claim 2, wherein: the catalyst in the step (1) is one of nano nickel, nano cobalt or nano nickel, and the particle size is 100-500 nm.
7. The preparation method of the magnesium-doped hollow silicon-carbon composite material by the template method according to claim 2, wherein the preparation method of the 1-5wt% carbon nanotube conductive liquid in the step (1) comprises the following steps: adding 1-5 parts of carbon nano tube into 100 parts of N-methyl pyrrolidone, and dispersing for 24-48 h by a sand mill under the condition that the rotating speed is 100-500RPM to obtain the 1-5wt% carbon nano tube conductive liquid.
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