CN115425220B - A modified preparation method for a crystal domain petroleum coke-based silicon-carbon composite electrode material - Google Patents
A modified preparation method for a crystal domain petroleum coke-based silicon-carbon composite electrode material Download PDFInfo
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Abstract
The invention discloses a modification preparation method of a crystal domain petroleum coke-based silicon-carbon composite electrode material, which is characterized in that crystal domain petroleum coke is taken as an inner core, an oxygen-containing organic silicon compound is taken as a silicon source, the crystal domain petroleum coke and the oxygen-containing organic silicon compound are compounded through hydrothermal reaction, then the crystal domain petroleum coke coated with silicon is obtained through reduction through one-step magnesium thermal reaction, calcium carbonate is taken as a sacrificial layer, gaps are introduced into the material, and an amorphous carbon layer is coated on the outermost layer as an outer shell layer, so that the excessive expansion of silicon is effectively restrained. The carbon-void-silicon-carbon four-level yolk-eggshell silicon-carbon composite electrode material has the advantages of good conductivity, high reversible specific capacity, stable cycle performance and good multiplying power performance, the first-circle coulomb efficiency is more than 70%, the reversible specific capacity under the current density of 0.1C is more than 580mAh/g, and the specific capacity under the current density of 10C is more than 470 mAh/g.
Description
Technical Field
The invention belongs to the field of lithium ion battery electrode materials, and relates to a modification preparation method of a crystal domain petroleum coke-based silicon-carbon composite electrode material.
Background
In recent decades, lithium ion batteries have been widely studied and focused on their advantages of high voltage, high energy, long cycle life, no memory effect, and the like. However, graphite has low specific capacity and poor high-rate charge and discharge performance as an anode material, and is difficult to meet the increasing demands of human beings, so that materials with high energy density are required to be searched for to replace graphite anode materials. The silicon negative electrode has theoretical specific capacity as high as 4200mAh/g, is rich in reserves, and is completely hopeful to replace graphite to become a new commercial negative electrode material. But the volume expansion itself generated upon intercalation and deintercalation of lithium ions causes pulverization of the anode material and generation of an SEI film, resulting in deterioration of cycle stability and irreversible capacity loss. Meanwhile, the conductivity of silicon is low at normal temperature, so that lithium ions are difficult to diffuse in the silicon negative electrode. In order to mitigate the volume effect and improve the electrical conductivity, many strategies for designing silicon-based anode materials have been proposed, and silicon-carbon composite materials are being widely studied as one of the most successful strategies. However, most of the research is focused on structural design of silicon-carbon composite materials. In fact, the microstructure of the carbon component has a crucial influence on its electrochemical behaviour, thereby further affecting the cell performance.
The petroleum coke is a good carbon source for preparing the high-performance silicon/carbon composite material, the crystal domain petroleum coke is a petroleum coke which is coexistent in needle domain, wide area and inlaid polarized light structures and uniformly distributed and mixed, carbon layers in the needle domain and wide area structures of the material are more regularly arranged, the material has higher lithium storage capacity and better cycle stability, and the inlaid structure provides a certain disordered layer structure after carbonization and graphitization, so that the multiplying power performance of the material is improved. The crystal domain petroleum coke derived soft carbon material has outstanding electron transfer characteristics and structural elasticity, the relative contents of different polarized structures can be conveniently adjusted through the heat treatment temperature, and the crystallinity of the crystal domain petroleum coke derived soft carbon material can be further adjusted and controlled, so that the overall electrochemical performance of the material is adjusted. The nature of the active silicon particles requires that the surface of the carbon component has a certain anchoring point for fixation, and compared with the common petroleum coke, the crystal domain petroleum coke has a needle domain and wide area structure, and the activated active silicon particles can be provided with enough anchoring points and simultaneously maintain high lithium storage capacity and cycle performance. Therefore, the silicon-carbon composite electrode material with good performance is prepared by constructing a multi-layer silicon-carbon composite structure by using the crystal domain petroleum coke as a carbon source.
Disclosure of Invention
In order to overcome the defects of the prior art, the invention provides a modification preparation method of a crystal domain petroleum coke-based silicon-carbon composite electrode material, which utilizes petroleum coke with a crystal domain structure and an oxygen-containing organosilicon compound to prepare a silicon-carbon composite material as an inner core through the steps of particle size screening, hydrothermal reaction, magnesia reduction and high-temperature carbonization, then sequentially coats calcium carbonate and an amorphous carbon layer on the outer layer of the silicon-carbon composite material, and finally carries out hydrochloric acid etching to obtain the yolk-eggshell silicon-carbon composite electrode material with a four-level structure, and the silicon-carbon composite electrode material has the advantages of good conductivity, high reversible specific capacity, stable cycle performance and good multiplying power performance.
The aim of the invention is achieved by the following technical scheme;
the modification preparation method of the crystal domain petroleum coke-based silicon-carbon composite electrode material comprises the following specific steps:
The method comprises the steps of 1, taking crystal domain petroleum coke as a raw material, crushing, screening by using a 600-1000 mesh screen to obtain crystal domain petroleum coke particles, adding the crystal domain petroleum coke particles into an organic acid solution with the concentration of 3-5mol/L, and stirring for 24 hours at 180-230 ℃ to obtain activated crystal domain petroleum coke particles, wherein the organic acid comprises trichloroacetic acid or p-toluenesulfonic acid;
Step 2, ultrasonically dispersing the activated crystal domain petroleum coke particles in deionized water, then dropwise adding an oxygen-containing organosilicon compound, continuing to ultrasonically disperse completely, transferring the dispersion liquid into a hydrothermal reaction kettle, and reacting for 6-15h at 160-200 ℃;
step 3, mixing the dried product with magnesium powder, placing the mixture in a stainless steel reactor, and carrying out magnesium thermal reaction for 4-8 hours at 600 ℃ in an argon atmosphere;
Step 4, dispersing the treated magnesium thermal reaction product in deionized water by ultrasonic, sequentially adding sodium carbonate and calcium chloride, and vigorously stirring to obtain white precipitate uniformly coated by the calcium carbonate, then adding the white precipitate into a solution of like asphalt, stirring for 24 hours, filtering, washing the precipitate with deionized water, drying, placing the dried precipitate in a tubular furnace, pre-oxidizing for 2-4 hours in 320 ℃ air atmosphere, and carbonizing for 2 hours at 800-1200 ℃ in argon atmosphere to obtain carbonized product;
And 5, placing the carbonized product in 0.1mol/L hydrochloric acid, fully washing to remove calcium carbonate precipitate, washing to neutrality by deionized water, and drying to obtain the carbon-void-silicon-carbon four-stage core-shell crystal domain petroleum coke-based silicon-carbon composite electrode material.
The polarizing structure of the crystal domain petroleum coke consists of a needle domain, a wide area and an inlaid structure, wherein the sizes of the needle domain and the wide area polarizing structure are 50-500 mu m, accounting for 70-85% of the total area, the size of the inlaid polarizing structure is 1-50 mu m, accounting for 15-30% of the total area, and the three polarizing structures coexist and are uniformly distributed and mixed, and the size of the polarizing structure refers to the length of a monochromatic area of anisotropic substances in the crystal domain petroleum coke under orthogonal polarized light.
In the invention, the oxygen-containing organosilicon compound is selected from one of triisopropyl silicon-based trifluoromethanesulfonate, 3-tertiary butyl dimethyl silyl-2-propyn-1-ol or (1, 1-dimethyl ethyl) dimethyl silicon-based trifluoromethanesulfonate.
In the invention, the silicon content of the product is controlled by the addition amount of the oxygen-containing organosilicon compound in the hydrothermal synthesis raw material, and the more the addition amount of the oxygen-containing organosilicon compound is, the higher the silicon content in the final product is, preferably, the dosage ratio of the crystal domain petroleum coke particles, the organic acid solution and the oxygen-containing organosilicon compound is 1g to 200mL (0.1-0.5) g;
the dosage ratio of the dried product obtained in the step 2 to magnesium powder, sodium carbonate and calcium chloride is 1g to 0.1g (1-1.5 g) (1.2-1.8 g);
the dosage ratio of the white sediment to the like asphalt in the step 4 is 1g (1-1.5 g).
In the step4, the temperature rising rate in the air atmosphere pre-oxidation process is 1 ℃ per minute.
In the invention, the like asphalt is coal-series coated asphalt, petroleum-series coated asphalt or high-temperature coal asphalt with a softening point of 100-200 ℃, the solution preparation method of the like asphalt comprises the steps of dissolving the like asphalt into a solvent, wherein the solvent is one or more of tetrahydrofuran, toluene, N-methylpyrrolidone and pyridine, and the dosage ratio of the solvent to the like asphalt is 100mL (1-1.5) g.
In the four-stage core-shell crystal domain petroleum coke-based silicon-carbon composite electrode material of the carbon-gap-silicon-carbon, the preferable thickness of the silicon layer is 0.1-0.2 mu m, the thickness of the gap structure is 0.3-1 mu m, and the thickness of the amorphous carbon layer is 0.5-1 mu m.
The invention also provides the crystal domain petroleum coke-based silicon-carbon composite electrode material prepared by the method, which has a four-stage core-shell structure of carbon-gap-silicon-carbon, the first-ring coulomb efficiency is more than 70%, the reversible specific capacity under 0.1C current density is more than 580mAh/g, and the specific capacity under 10C high current density is more than 470 mAh/g.
According to the invention, the crystal domain petroleum coke is used as a carbon substrate with wide sources, the crystal domain petroleum coke is a petroleum coke which is coexistent in needle domain, wide area and inlaid polarized structures and uniformly distributed and mixed, the volume expansion of a silicon-based material is effectively buffered, and carbon layers in the needle domain and wide area structures are regularly arranged. The method avoids using hydrofluoric acid as an etchant compared with a common SiO 2 sacrificial layer, reduces the safety risk in the preparation process, is convenient for etching, and the generated gap layer reserves enough space for the volume expansion of inner silicon, and the outermost carbon coating layer further constrains the expansion of silicon for the volume change of silicon in the charging and discharging process, so that the carbon-gap-silicon-carbon four-level egg yolk-eggshell composite silicon-carbon electrode material is obtained. The dosages of sodium carbonate, calcium chloride and like asphalt are properly increased or decreased according to the dosage of the oxygen-containing organosilicon compound, so that the thicknesses of the gap layer and the coated carbon layer are increased or decreased simultaneously when the thickness of the silicon layer is increased or decreased, and the performance of the prepared silicon-carbon composite electrode material can be ensured to be optimal. Finally, the electrode material with high reversible specific capacity and stable cycle performance is prepared, the first circle coulomb efficiency is more than 70%, the reversible specific capacity under 0.1C current density is more than 580mAh/g, and the specific capacity under 10C high current density is more than 470 mAh/g.
Compared with the prior art, the invention has the following beneficial effects:
1. The carbon matrix in the composite material is the crystal domain petroleum coke prepared by heavy oil, wherein the crystal domain petroleum coke is used as a carbon substrate with wide sources, the volume expansion of the silicon-based material is effectively buffered, the arrangement of the needle domain and the wide area structure carbon layer is more regular, the composite material has higher lithium storage capacity and better cycle stability, and a plurality of active sites are provided for being connected with silicon after activation. The fewer mosaic structures distributed among the river basin structures provide a certain disordered layer structure after carbonization and graphitization, and are beneficial to improving the multiplying power performance of the material.
2. The calcium carbonate is used as the sacrificial layer, so that the use of hydrofluoric acid when SiO 2 is used as the sacrificial layer is avoided, the safety risk in the preparation process is reduced, the calcium carbonate is convenient to etch, and the etched gap layer reserves enough space for the volume expansion of inner silicon.
3. The amorphous carbon layer is coated on the outermost layer of the material by using the like asphalt, so that the volume expansion of silicon in the charge and discharge process is effectively restrained, and the cycling stability of the material is improved.
4. The organic acid solution is adopted to activate the carbon precursor, so that oxygen-containing functional groups on the crystal domain petroleum coke are increased, meanwhile, the organic silicon is adopted as a silicon source, the combination of the functional groups on the surface of the asphalt and the organic silicon is promoted through the interaction of the functional groups and the organic silicon, and then the combination of the silicon and the carbon is tighter compared with mechanical mixing through one-step magnesium thermal reaction reduction.
Drawings
FIG. 1 is a schematic structural diagram of a crystal domain petroleum coke based silicon-carbon composite electrode material prepared by the invention.
FIG. 2 is a polarized light photograph of the domain petroleum coke used in the present invention.
Detailed Description
The modification preparation method of the crystal domain petroleum coke-based silicon-carbon composite electrode material is described in detail below by combining examples.
Example 1:
the embodiment provides a modification preparation method of a crystal domain petroleum coke-based silicon-carbon composite electrode material, which comprises the following specific steps:
(1) Crushing crystal domain petroleum coke, sieving by a 1000-mesh screen, adding 1g of crystal domain petroleum coke particles into 200mL of trichloroacetic acid solution with the concentration of 5mol/L, and stirring for 24 hours at 200 ℃ to obtain activated crystal domain petroleum coke particles;
(2) Dispersing activated crystal domain petroleum coke particles in deionized water, carrying out ultrasonic treatment for 1h, then dropwise adding 20mL of 0.01g/mL ethanol solution of triisopropyl silicon-based trifluoro methane sulfonate, continuing ultrasonic treatment for 1.5h to completely disperse, transferring the dispersion liquid into a hydrothermal reaction kettle, reacting for 8h at 160 ℃, filtering a product of the hydrothermal reaction, washing precipitate with ethanol and deionized water for three times respectively, and drying in an oven at 80 ℃ for 24h to obtain a dried product;
(3) Mixing 1g of dried product with 0.1g of magnesium powder, placing the mixture in a stainless steel reactor, reacting for 6 hours at 600 ℃ under argon atmosphere, washing the product to neutrality by 0.5mol/L dilute hydrochloric acid, ethanol and deionized water respectively, and vacuum drying for 24 hours at 100 ℃ to obtain a treated magnesium thermal reaction product;
(4) Dispersing the treated magnesium thermal reaction product in deionized water by ultrasonic, sequentially adding 1.4g of sodium carbonate and 1.6g of calcium chloride, and vigorously stirring to obtain white precipitate uniformly coated by the calcium carbonate, completely dissolving 1.4g of high-temperature coal tar pitch in 100mL of toluene to obtain a solution of the same-polarity pitch, adding 1g of white precipitate into the solution, stirring for 24 hours, filtering, washing the precipitate with deionized water, drying, placing the dried precipitate in a tubular furnace, pre-oxidizing for 2 hours in an air atmosphere at 320 ℃ and carbonizing for 2 hours at 1000 ℃ in an argon atmosphere to obtain a carbonized product, wherein the temperature rising rate in the pre-oxidizing process is 1 ℃ per minute;
(5) And (3) placing the carbonized product in 0.1mol/L hydrochloric acid, fully washing to remove calcium carbonate precipitate, washing to neutrality by deionized water, and drying to obtain the four-stage core-shell crystal domain petroleum coke-based silicon-carbon composite electrode material A of carbon-gap-silicon-carbon, wherein the thickness of the silicon layer is 0.1 mu m, the thickness of the gap structure is 0.5 mu m, and the thickness of the amorphous carbon layer is 0.7 mu m.
Example 2:
the embodiment provides a modification preparation method of a crystal domain petroleum coke-based silicon-carbon composite electrode material, which comprises the following specific steps:
(1) Crushing crystal domain petroleum coke, sieving by a 800-mesh screen, adding 1g of crystal domain petroleum coke particles into 200mL of p-toluenesulfonic acid solution with the concentration of 5mol/L, and activating and stirring for 24 hours at 200 ℃ to obtain activated crystal domain petroleum coke particles;
(2) Dispersing activated crystal domain petroleum coke particles in deionized water for 1h by ultrasonic treatment, then dropwise adding 30mL of 0.01g/mL ethanol solution of triisopropyl silicon-based trifluoro methane sulfonate, continuing ultrasonic dispersion for 1.5h to complete dispersion, transferring the dispersion into a hydrothermal reaction kettle for reaction at 160 ℃ for 8h, filtering a product of the hydrothermal reaction, washing precipitate with ethanol and deionized water for three times respectively, and drying the precipitate in an oven at 80 ℃ for 24h to obtain a dried product;
(3) Mixing 1g of dried product with 0.1g of magnesium powder, placing the mixture in a stainless steel reactor, reacting for 6 hours at 600 ℃ under argon atmosphere, washing the product to neutrality by 0.5mol/L dilute hydrochloric acid, ethanol and deionized water respectively, and vacuum drying for 24 hours at 100 ℃ to obtain a treated magnesium thermal reaction product;
(4) Dispersing the treated magnesium thermal reaction product in deionized water by ultrasonic, sequentially adding 1.4g of sodium carbonate and 1.6g of calcium chloride, and stirring vigorously to obtain white precipitate uniformly coated by the calcium carbonate, completely dissolving 1.4g of high-temperature coal tar pitch in 100mL of toluene to obtain a solution of the same-polarity pitch, adding 1g of white precipitate into the solution, stirring for 24 hours, filtering, washing the precipitate with deionized water, drying, placing the dried precipitate in a tubular furnace, pre-oxidizing for 2 hours in an air atmosphere at 320 ℃ and carbonizing for 2 hours at 1000 ℃ in an argon atmosphere to obtain a carbonized product, wherein the temperature rising rate in the pre-oxidation process is 1 ℃ per minute;
(5) And (3) placing the carbonized product in 0.1mol/L hydrochloric acid, fully washing to remove calcium carbonate precipitate, washing to neutrality by deionized water, and drying to obtain the carbon-void-silicon-carbon four-stage core-shell crystal domain petroleum coke-based silicon-carbon composite electrode material B, wherein the thickness of a silicon layer is 0.18 mu m, the thickness of a void structure is 0.8 mu m, and the thickness of an amorphous carbon layer is 0.8 mu m.
Example 3:
the embodiment provides a modification preparation method of a crystal domain petroleum coke-based silicon-carbon composite electrode material, which comprises the following specific steps:
(1) Crushing crystal domain petroleum coke, sieving by a 1000-mesh screen, adding 1g of crystal domain petroleum coke particles into 200mL of trichloroacetic acid solution with the concentration of 3mol/L, and activating and stirring for 24 hours at 200 ℃ to obtain activated crystal domain petroleum coke particles;
(2) Dispersing activated crystal domain petroleum coke particles in deionized water for 1h by ultrasonic treatment, then dropwise adding 30mL of 0.01g/mL ethanol solution of 3-tert-butyldimethylsilyl-2-propyn-1-ol, continuing ultrasonic dispersion for 1.5h to complete dispersion, transferring the dispersion into a hydrothermal reaction kettle, reacting for 8h at 160 ℃, filtering the product of the hydrothermal reaction, washing the precipitate with ethanol and deionized water for three times respectively, and drying for 24h at 80 ℃ in an oven to obtain a dried product;
(3) Mixing 1g of dried product with 0.1g of magnesium powder, placing the mixture into a stainless steel reactor, reacting for 6 hours at 600 ℃ under argon atmosphere, then washing the product to neutrality by 0.5mol/L dilute hydrochloric acid, ethanol and deionized water respectively, and vacuum drying for 24 hours at 100 ℃ to obtain a treated magnesium thermal reaction product;
(4) Dispersing the treated magnesium thermal reaction product in deionized water by ultrasonic, sequentially adding 1.5g of sodium carbonate and 1.8g of calcium chloride, and stirring vigorously to obtain white precipitate uniformly coated by the calcium carbonate, completely dissolving 1.5g of high-temperature coal tar pitch in 100mL of toluene to obtain a solution of the same-polarity pitch, adding 1g of white precipitate into the solution, stirring for 24 hours, filtering, washing the precipitate with deionized water, drying, placing the dried precipitate in a tubular furnace, pre-oxidizing for 2 hours in an air atmosphere at 320 ℃ and carbonizing for 2 hours at 1000 ℃ in an argon atmosphere to obtain a carbonized product, wherein the temperature rising rate in the pre-oxidation process is 1 ℃ per minute;
(5) And (3) placing the carbonized product in 0.1mol/L hydrochloric acid, fully washing to remove calcium carbonate precipitate, washing to neutrality by deionized water, and drying to obtain the carbon-void-silicon-carbon four-stage core-shell crystal domain petroleum coke-based silicon-carbon composite electrode material C, wherein the thickness of a silicon layer is 0.2 mu m, the thickness of a void structure is 1 mu m, and the thickness of an amorphous carbon layer is 1 mu m.
Example 4:
the embodiment provides a modification preparation method of a crystal domain petroleum coke-based silicon-carbon composite electrode material, which comprises the following specific steps:
(1) Crushing crystal domain petroleum coke, sieving by a 1000-mesh screen, adding 1g of crystal domain petroleum coke particles into 200mL of trichloroacetic acid solution with the concentration of 3mol/L, and activating and stirring for 24 hours at 200 ℃ to obtain activated crystal domain petroleum coke particles;
(2) Dispersing activated crystal domain petroleum coke particles in deionized water for 1h by ultrasonic treatment, then dropwise adding 30mL of 0.01g/mL ethanol solution of 3-tert-butyldimethylsilyl-2-propyn-1-ol, continuing ultrasonic dispersion for 1.5h to complete dispersion, transferring the dispersion into a hydrothermal reaction kettle, reacting for 8h at 160 ℃, filtering the product of the hydrothermal reaction, washing the precipitate with ethanol and deionized water for three times respectively, and drying for 24h at 80 ℃ in an oven to obtain a dried product;
(3) Mixing 1g of dried product with 0.1g of magnesium powder, placing the mixture into a stainless steel reactor, reacting for 6 hours at 600 ℃ under argon atmosphere, then washing the product to neutrality by 0.5mol/L dilute hydrochloric acid, ethanol and deionized water respectively, and vacuum drying for 24 hours at 100 ℃ to obtain a precipitate of magnesium thermal reaction;
(4) 1.2g of high-temperature coal tar pitch is completely dissolved in 100mL of toluene to obtain a solution of the same-polarity pitch, 0.8g of magnesium thermal reaction precipitate is added into the solution, the solution is stirred for 24 hours and then filtered, washed by deionized water and then dried;
(5) And (3) placing the dried precipitate in a tube furnace, pre-oxidizing for 2 hours in 320 ℃ air atmosphere and carbonizing for 2 hours at 1000 ℃ in argon atmosphere, wherein the temperature rising rate in the pre-oxidizing process is 1 ℃ per minute, and obtaining the carbon-silicon-carbon three-stage core-shell crystal domain petroleum coke-based silicon-carbon composite electrode material D, wherein the thickness of the silicon layer is 0.2 mu m, and the thickness of the amorphous carbon layer is 1 mu m.
Example 5:
The embodiment provides a modification preparation method of a petroleum common Jiao Jigui carbon composite electrode material, wherein raw material petroleum coke is I-grade petroleum common coke which accords with GB/T24533-2019, and the technical indexes are shown in table 1.
Table 1 main technical index of grade I petroleum common coke
The method comprises the following specific steps:
(1) Pulverizing petroleum common coke, sieving with 1000 mesh sieve, adding 1g of petroleum common coke particles into 200mL trichloroacetic acid solution with concentration of 3mol/L, and activating and stirring at 200deg.C for 24h to obtain activated petroleum common coke particles;
(2) Dispersing activated petroleum general coke particles in deionized water for 1h by ultrasonic treatment, then dropwise adding 30mL of 0.01g/mL of 3-tert-butyldimethylsilyl-2-propyn-1-ol ethanol solution, continuing ultrasonic dispersion for 1.5h to complete dispersion, transferring the dispersion into a hydrothermal reaction kettle for reaction at 160 ℃ for 8h, filtering the product of the hydrothermal reaction, washing the precipitate with ethanol and deionized water for three times respectively, and drying at 80 ℃ for 24h to obtain a dried product;
(3) Mixing 1g of the dried product with 0.1g of magnesium powder, placing the mixture into a stainless steel reactor, reacting for 6 hours at 600 ℃ under argon atmosphere, then washing the product to neutrality by 0.5mol/L dilute hydrochloric acid, ethanol and deionized water respectively, and vacuum drying for 24 hours at 100 ℃ to obtain a magnesium thermal reaction product;
(4) Dispersing the treated magnesium thermal reaction product in deionized water by ultrasonic, sequentially adding 1.5g of sodium carbonate and 1.8g of calcium chloride, and stirring vigorously to obtain white precipitate uniformly coated by the calcium carbonate, completely dissolving 1.5g of high-temperature coal tar pitch in 100mL of toluene to obtain a solution of the same-polarity pitch, adding 1g of white precipitate into the solution, stirring for 24 hours, filtering, washing the precipitate with deionized water, drying, placing the dried precipitate in a tubular furnace, pre-oxidizing for 2 hours in an air atmosphere at 320 ℃ and carbonizing for 2 hours at 1000 ℃ in an argon atmosphere to obtain a carbonized product, wherein the temperature rising rate in the pre-oxidation process is 1 ℃ per minute;
(5) And (3) placing the carbonized product in 0.1mol/L hydrochloric acid, fully washing to remove calcium carbonate precipitate, washing to neutrality by deionized water, and drying to obtain the four-stage core-shell type petroleum coke-based silicon-carbon composite electrode material E with the thickness of a silicon layer of 0.2 mu m, the thickness of a void structure of 1 mu m and the thickness of an amorphous carbon layer of 1 mu m.
Example 6 Battery Performance test
1. Electrode preparation the electrode materials prepared in examples 1-5 were mixed with acetylene black, PVDF in a mass ratio of 8:1:1, NMP (azamethylpyrrolidone) as a solvent, ground to form a uniform slurry and coated on copper foil, dried in vacuo at 90 ℃ for 24 hours, and rolled to obtain an electrode sheet.
2. Cell performance test the resulting electrode sheet was cut to a diameter of 12mm for cell assembly. The assembly process was carried out in an argon filled glove box with less than 0.01ppm water oxygen. The battery adopts a CR2032 button battery, a metal lithium sheet is used as a counter electrode, a polypropylene film is used as a diaphragm, and 1M lithium hexafluorophosphate (the solvent is mixed liquid of ethylene carbonate and dimethyl carbonate with the volume ratio of 1:1, and 5% fluoroethylene carbonate is added) is used as electrolyte. The assembled button cell was subjected to a 0.1C charge-discharge cycle performance test and a 10C heavy current discharge performance test at 25 ℃ over a voltage range of 0.05V-2.2V. The measured first-turn specific capacity (mAh/g), first-charge-discharge efficiency (%) and reversible cycle specific capacity (mAh/g, 500 turns) of the battery were recorded while giving the silicon content in each electrode material, and the results are shown in table 2.
TABLE 2 comparison of electrode Material Properties
As can be seen from the data in the table, compared with the existing graphite cathode (360 mAh/g), the silicon-carbon composite electrode materials A, B and C prepared by the methods of the embodiments 1-3 of the invention have higher charge-discharge cycle performance (more than 580 mAh/g). Furthermore, it was found by comparison that the initial coulombic efficiency of the cell increased with increasing silicon content in the electrode material, but the initial specific capacity showed a tendency to increase and decrease with increasing silicon content, because of the increase in silicon ratio, which increased the capacity provided, whereas too high a silicon content resulted in a decay of the specific capacity due to the huge volume expansion of the silicon material. Thus, electrode material B has optimal properties, with a silicon content of 7.1wt% being optimal.
The electrode material D prepared in example 4 does not introduce a void structure, and the reversible cycle specific capacity is obviously lower than that of examples 1-3, which indicates that the electrode materials A, B and C well form a void structure, and the volume expansion of silicon in the composite material is well relieved.
In the embodiment 5, the I-grade petroleum common coke which accords with GB/T24533-2019 is adopted as the raw material, the first circle coulomb efficiency and the reversible circulation specific capacity are lower than those of the embodiments 1-3, which shows that the structure that needle domain, wide area and inlaid polarized light structures coexist and are uniformly distributed and mixed in the crystal domain petroleum coke can ensure that the material has better circulation stability, multiplying power performance and reversible capacity, and a large number of active sites are provided for silicon connection. In addition, by controlling the amount of added sodium carbonate and calcium chloride, the void layers with different thicknesses can be prepared, and the void layers can be flexibly regulated and controlled according to different silicon loading amounts.
Claims (6)
1. The modification preparation method of the crystal domain petroleum coke-based silicon-carbon composite electrode material is characterized by comprising the following steps of:
The method comprises the steps of 1, taking crystal domain petroleum coke as a raw material, crushing, screening by using a 600-1000 mesh screen to obtain crystal domain petroleum coke particles, adding the crystal domain petroleum coke particles into an organic acid solution with the concentration of 3-5mol/L, and stirring for 24 hours at 180-230 ℃ to obtain activated crystal domain petroleum coke particles, wherein the polarizing structure of the crystal domain petroleum coke consists of a needle domain, a wide area and an inlaid structure, and the three polarizing structures coexist and are uniformly distributed and mixed;
Step 2, ultrasonically dispersing the activated crystal domain petroleum coke particles in deionized water, then dropwise adding an oxygen-containing organosilicon compound, continuing to ultrasonically disperse completely, transferring the dispersion liquid into a hydrothermal reaction kettle, and reacting for 6-15h at 160-200 ℃;
step 3, mixing the dried product with magnesium powder, placing the mixture in a stainless steel reactor, and carrying out magnesium thermal reaction for 4-8 hours at 600 ℃ in an argon atmosphere;
Step 4, dispersing the treated magnesium thermal reaction product in deionized water by ultrasonic, sequentially adding sodium carbonate and calcium chloride, and vigorously stirring to obtain white precipitate uniformly coated by the calcium carbonate, then adding the white precipitate into a solution of like asphalt, stirring for 24 hours, filtering, washing the precipitate with deionized water, drying, placing the dried precipitate in a tubular furnace, pre-oxidizing for 2-4 hours in 320 ℃ air atmosphere, and carbonizing for 2 hours at 800-1200 ℃ in argon atmosphere to obtain carbonized product;
And 5, placing the carbonized product in 0.1mol/L hydrochloric acid, fully washing to remove calcium carbonate precipitate, washing to neutrality by deionized water, and drying to obtain the carbon-void-silicon-carbon four-stage core-shell crystal domain petroleum coke-based silicon-carbon composite electrode material.
2. The modified preparation method of the crystal domain petroleum coke-based silicon-carbon composite electrode material is characterized in that in the polarizing structure of the crystal domain petroleum coke, the needle domain and wide area polarizing structure have the dimensions of 50-500 mu m, accounting for 70-85% of the total area, the inlaid polarizing structure has the dimensions of 1-50 mu m, accounting for 15-30% of the total area.
3. The modified preparation method of the crystal domain petroleum coke-based silicon-carbon composite electrode material is characterized in that the organic acid comprises trichloroacetic acid or p-toluenesulfonic acid, and the oxygen-containing organosilicon compound is selected from one of triisopropyl silicon-based trifluoromethanesulfonate, 3-tert-butyldimethylsilyl-2-propyn-1-ol or (1, 1-dimethylethyl) dimethylsilyl-trifluoromethanesulfonate.
4. The modified preparation method of the crystal domain petroleum coke-based silicon-carbon composite electrode material is characterized in that the like asphalt is coal-based coated asphalt, petroleum-based coated asphalt or high-temperature coal asphalt with a softening point of 100-200 ℃, the solution preparation method of the like asphalt is that the like asphalt is dissolved into a solvent, the solvent is selected from one or more of tetrahydrofuran, toluene, N-methylpyrrolidone and pyridine, and the dosage ratio of the solvent to the like asphalt is 100mL (1-1.5) g.
5. The modified preparation method of the crystal domain petroleum coke-based silicon-carbon composite electrode material according to claim 1, wherein the dosage relationship of crystal domain petroleum coke particles, organic acid solution and oxygen-containing organosilicon compound is 1g:200mL (0.1-0.5 g);
the dosage ratio of the dried product obtained in the step 2 to magnesium powder, sodium carbonate and calcium chloride is 1g to 0.1g (1-1.5 g) (1.2-1.8 g);
the dosage ratio of the white sediment to the like asphalt in the step 4 is 1g (1-1.5 g).
6. The crystal domain petroleum coke-based silicon-carbon composite electrode material prepared by the method of any one of claims 1-5 is characterized by having a four-stage core-shell structure of carbon-gap-silicon-carbon, wherein the thickness of a silicon layer is 0.1-0.2 μm, the thickness of a gap structure is 0.3-1 μm, and the thickness of an amorphous carbon layer is 0.5-1 μm.
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