Asphalt-based silicon-carbon porous sphere negative electrode material as well as preparation method and application thereof

Abstract

The invention provides an asphalt-based silicon-carbon porous sphere negative electrode material as well as a preparation method and application thereof, and relates to the technical field of battery materials. The preparation method comprises the following steps: performing spray drying on asphalt to obtain asphalt-based carbon microspheres; the preparation method comprises the following steps: dispersing asphalt-based carbon microspheres in an organic solvent, sequentially adding a template agent and a silicon source, carrying out a stirring reaction to obtain an intermediate, carrying out heat treatment on the intermediate in a reducing atmosphere, and then carrying out etching by using an etching agent to obtain the asphalt-based silicon-carbon porous sphere negative electrode material. According to the preparation method, asphalt is carbonized into spheres in one step, the obtained carbon microspheres have the characteristics of uniform morphology and high sphericity degree, then a certain pore structure is formed while low-activity SiO2 is reduced and removed, the asphalt-based SiOx / C porous sphere negative electrode material with the core-shell structure is obtained, volume expansion of an electrode material in the lithium ion charging and discharging process can be effectively inhibited, and the performance of the lithium ion battery is improved. And lithium ion diffusion is accelerated, so that the lithium ion battery negative electrode material with high reversible specific capacity and long cycle stability is obtained.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of battery materials, in particular to a pitch-based silicon-carbon porous spherical negative electrode material, a preparation method and application thereof. BACKGROUND

[0002] The development and application of renewable energy such as wind energy and solar energy have accelerated the replacement process of traditional fossil fuels, but due to the intermittency and diversity of clean energy, it is urgent to develop high-energy, high-power density and high-performance large-scale energy storage systems to effectively store renewable clean energy. In recent years, people's demand for portable energy storage has increased, and lithium ion batteries have the advantages of high voltage and high energy density, and are widely used. According to different application scenarios, lithium ion batteries usually need to be balanced between various performance parameters, including capacity, power, cycle life, cost, safety and environmental impact. Especially for the current lithium ion battery energy storage system applied in the field of electric vehicles and hybrid electric vehicles, improving the energy density has become the key to further optimizing the performance of the battery and improving the endurance of the vehicle. As an important part of lithium ion batteries, the development of high-performance negative electrode materials has become the key to promoting the development of battery performance.

[0003] Silicon-based negative electrode materials include elemental silicon, silicon monoxide, silicon dioxide and SiO x (0 < x < 2), which has the advantages of abundant reserves, high theoretical specific capacity and low cost, and is considered to be one of the most promising next-generation lithium ion battery negative electrode materials. The biggest problem of elemental silicon is poor electrical conductivity and too large volume expansion during charging and discharging, which leads to low first-cycle coulombic efficiency and poor cycle stability, while the volume expansion of SiO x is much smaller than that of elemental silicon, and the theoretical lithium storage capacity can reach 2200-3580 mAh / g. The silicon-carbon negative electrode formed by compounding SiO with carbon materials not only can make up for the low reversible specific capacity of single carbon material, but also can make up for the defect of low electrical conductivity of silicon-based negative electrode.

[0004] Existing methods for preparing silicon-carbon anodes typically use silicon as the main component, introducing a carbon source through surface coating, mechanical ball milling, etc.; or use carbon materials as the main component, introducing silicon through chemical vapor deposition, ball milling, etc. For example, Chinese patent application CN117497735A discloses a silicon-carbon anode material and its preparation method. This invention uses nano-silicon as raw material and obtains a silicon-carbon anode through steps such as coating nano-silicon material, coating anode material, carbonization, and sieving. It belongs to silicon-based and carbon-auxiliary silicon-carbon anode materials. Chinese patent application CN202310532964 discloses a method for preparing a pitch-based silicon-carbon anode material for lithium-ion batteries. This invention uses pitch as raw material, passes gas into a molecular sieve to form nano-gas, then passes it into a reaction vessel and controls the pressure and temperature inside the reaction vessel to further heat and carbonize to obtain a pitch-based porous carbon material. The silicon-carbon anode is obtained by silicon deposition. It belongs to carbon-based and silicon-auxiliary silicon-carbon anodes, but the preparation method is still a traditional deposition method. However, the doping and recombination of silicon and carbon in the above-mentioned preparation process is not thorough enough, resulting in low uniformity of the prepared anode material, weak ion diffusion rate and volume expansion suppression effect, and the cycle performance needs to be improved. Summary of the Invention

[0005] The main objective of this invention is to provide a pitch-based silicon-carbon porous spherical anode material, its preparation method, and its application, in order to solve the problem that existing anode materials are difficult to simultaneously achieve good material uniformity, ion diffusion rate, and volume expansion suppression, resulting in an inability to balance capacity performance and cycle performance.

[0006] To achieve the above objectives, according to one aspect of the present invention, a method for preparing a pitch-based silicon-carbon porous spherical anode material is provided, comprising the following steps: Step S1, spray drying pitch to obtain pitch-based carbon microspheres; Step S2, dispersing the pitch-based carbon microspheres in an organic solvent, sequentially adding a template agent and a silicon source, and stirring to obtain a reaction solution; sequentially filtering, washing, and drying the reaction solution to obtain an intermediate; Step S3, heat-treating the intermediate in a reducing atmosphere to obtain a reduction product; Step S4, etching the reduction product using an etchant to obtain the pitch-based silicon-carbon porous spherical anode material.

[0007] Furthermore, in step S1, the spray drying temperature is 700–1000°C, the pressure is 0.3–3 MPa, and the atmosphere is a nitrogen atmosphere.

[0008] Furthermore, in step S1, the particle size D of the pitch-based carbon microspheres... 50 The microspheres have a diameter of 500 nm to 10 μm; and / or the sphericity of the pitch-based carbon microspheres is ≥90%; and / or the contact angle of the pitch-based carbon microspheres is 91 to 115°.

[0009] Further, in step S2, the template agent comprises one or more of cetyltrimethylammonium bromide, cetyltrimethylammonium chloride, octanol, isobutyl alcohol, isopropyl alcohol, isoamyl acetate, P123 and polyvinylpyrrolidone; preferably, the template agent comprises cetyltrimethylammonium bromide and / or cetyltrimethylammonium chloride; and / or the silicon source comprises one or more of tetraethyl silicate, tetramethyl silicate, methyl triethoxysilane, 3-aminopropyl triethoxysilane and tetrachlorosilane; preferably, the silicon source comprises tetraethyl silicate and / or tetramethyl silicate; and / or the organic solvent comprises ethanol and / or water.

[0010] Further, in step S2, the weight ratio of the pitch-based carbon microspheres to the template agent is 4:(1-50); and / or the liquid-solid ratio of the silicon source to the template agent is 1 mL:(0.3-2.5 g); and / or the temperature for stirring the reaction is 20-50°C, and the time is 0.5-24 h; and / or after the template agent is added, the pH of the solution is adjusted to 7-9 using an alkaline solvent, and then the silicon source is introduced; the alkaline solvent comprises ammonia water and / or an aqueous sodium hydroxide solution.

[0011] Further, in step S3, the reducing atmosphere comprises one or more of the following atmospheres: hydrogen, a mixed gas of hydrogen and argon, carbon dioxide; preferably, the reducing atmosphere is a mixed gas of hydrogen and argon, and the volume ratio of hydrogen to argon is (4-6):(94-96); preferably, the flow rate of the reducing atmosphere is 90-110 sccm; and / or the temperature for the heat treatment is 800-1200°C, and the time is 1-3 h.

[0012] Further, in step S4, the temperature for the etching is 20-80°C, and the time is 0.5-12 h; and / or the ratio of the amount of the reduction product to the etchant is 1 g:(0.03-0.3 mol).

[0013] Further, in step S4, the etchant comprises one or more of the following materials: hydrofluoric acid, sodium hydroxide, potassium hydroxide, hydrochloric acid and a mixture of fluorine-containing solid salts; preferably, the fluorine-containing solid salts comprise one or more of lithium fluoride, sodium fluoride, potassium fluoride, ammonium fluoride and dihydronium fluoride.

[0014] According to another aspect of the present application, there is provided a pitch-based silicon-carbon porous sphere negative electrode material, which is obtained by using the preparation method of the pitch-based silicon-carbon porous sphere negative electrode material described above.

[0015] According to another aspect of the present application, there is provided a lithium ion battery, which comprises a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, the negative electrode sheet comprises a current collector and a negative electrode active material coated on at least one side surface of the current collector, and the negative electrode active material comprises the pitch-based silicon-carbon porous sphere negative electrode material described above.

[0016] By using the technical solution of the present application, the pitch is carbonized into balls in one step by using a high-temperature spray method, and the obtained carbon microspheres have the characteristics of uniform morphology and high sphericity; then, silica is coated on the surface of the pitch-derived spherical carbon material by using a sol-gel method, and after subsequent high-temperature reduction and etching technology, the reduction and removal of low-activity SiO2 are performed at the same time to form a certain pore structure, so that the material has the triple structure characteristics of sphericity, porosity and "core-shell", and a pitch-based SiO x / C porous ball negative electrode material, so as to effectively inhibit the volume expansion of the electrode material in the lithium ion charging and discharging process, accelerate the diffusion of lithium ions, and thus obtain a lithium ion battery negative electrode material with high reversible specific capacity and long cycle stability. BRIEF DESCRIPTION OF DRAWINGS

[0017] The accompanying drawings, which form a part of the present application, are used to provide further understanding of the present application, and the illustrative embodiments of the present application and their descriptions are used to explain the present application, and do not constitute improper limitations on the present application. In the drawings:

[0018] Figure 1 A preparation process flow diagram according to embodiment 1 of the present application is shown.

[0019] Figure 2 An SEM image of pitch-based carbon microspheres according to embodiment 1 of the present application is shown. DETAILED DESCRIPTION

[0020] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0021] It should be noted that the reagents used in the present application can be conveniently purchased from the market or self-prepared by using conventional methods in the art, and the manufacturers and models of the used instruments are not limited.

[0022] As described in the background art of the present application, in the prior art, the negative electrode material is difficult to have good material uniformity, ion diffusion rate and volume expansion inhibition, which leads to the problem that the capacity performance and cycle performance cannot be considered. In order to solve the above problem, in a typical embodiment of the present application, a preparation method of pitch-based silicon-carbon porous ball negative electrode material is provided, comprising the following steps: step S1, spray drying pitch to obtain pitch-based carbon microspheres; step S2, dispersing the pitch-based carbon microspheres in an organic solvent, sequentially adding a template agent and a silicon source, and stirring to obtain a reaction solution; filtering, washing and drying the reaction solution to obtain an intermediate; step S3, heat treating the intermediate in a reducing atmosphere to obtain a reduction product; and step S4, etching the reduction product using an etching agent to obtain a pitch-based silicon-carbon porous ball negative electrode material.

[0023] Specifically, the present application first sprays and dries bitumen, and then sprays the bitumen into balls after the bitumen is heated to a molten state. The bitumen melt is atomized into small droplets at the nozzle. With the help of the surface tension of the droplets, the material is pyrolyzed and carbonized at the same time of free falling, and bitumen-based carbon microspheres are obtained. The byproduct bitumen commonly used in coal chemical industry is used as a precursor of carbon material. The spherical carbon (i.e. bitumen-based carbon microspheres) is prepared by high-temperature spraying of bitumen. The bitumen rich in small-sized aromatic molecular compounds can be ball-shaped based on the structural characteristics. The method of high-temperature spraying ball-shaping has a simple preparation process and can realize one-step carbonization and ball-shaping. The bitumen-based carbon microspheres obtained have the characteristics of uniform morphology and high sphericity. The production process is simple and continuous, and no subsequent treatment is required.

[0024] Secondly, the bitumen-based carbon microspheres are dispersed in an organic solvent, and a template agent and a silicon source are added in sequence. After ultrasonic dispersion, a mixed solution in which each component is uniformly dispersed is obtained. The mixed solution is stirred at high speed to perform a stirring reaction. The template agent plays the role of a surfactant to form micelles around the bitumen-based carbon microspheres. The hydrophobic tail is adsorbed on the surface of the bitumen-based carbon microspheres, and the hydrophilic head is directed outward to form a directional arrangement. After hydrolysis, the silicon source forms a hydrogen bond with the hydrophilic group, and then a condensation reaction is performed to complete the directional coating on the surface of the bitumen-based carbon microspheres. SiO2 grows on the surface of the bitumen-based carbon microspheres to obtain a reaction solution. The SiO2 coating layer belongs to a mesoporous structure, and the specific surface area of the core-shell silicon-carbon composite intermediate will be increased further after subsequent etching treatment.

[0025] The present application coats silicon oxide on the surface of the bitumen-based carbon microspheres with uniform morphology and high sphericity by using a simple sol-gel method. The uniform distribution of silicon oxide molecules at the molecular level can be realized, and the agglomeration problem of traditional solid-phase doping can be avoided. A core-shell silicon-carbon composite intermediate is formed, which has the advantages of easy Si element doping, simple equipment, low cost, etc., and is suitable for large-scale industrial production. The reaction solution is filtered, washed and dried in sequence to obtain the intermediate.

[0026] Then, the intermediate is heat-treated in a reducing atmosphere. The valence state of silicon in most silicon oxides in the material is effectively reduced by high-temperature thermal reduction, so that most of the SiO2 is reduced to SiO x , 0 < x < 2, to obtain a reduction product. The SiO x effectively improves the reversible battery capacity of a single carbon material, increases the energy density, and obtains high capacity and high rate. At the same time, the excess template agent is removed.

[0027] Finally, the reduction product is etched using an etchant to further remove the inactive SiO2 left in the silicon-carbon composite material in an etching manner, while leaving a rich pore structure on the surface, and the further morphology regulation of the silicon-oxygen shell on the surface of the silicon-carbon composite negative electrode is realized by etching pore making, to open sufficient diffusion channels for lithium ion insertion and extraction, reduce diffusion barrier, and improve diffusion rate. The pitch-based SiO x / C porous ball negative electrode material, which comprises an inner core and a coating layer, the inner core comprises pitch-based carbon microspheres, and the coating layer is a SiO x coating layer.

[0028] The good spherical morphology of the pitch-based carbon microspheres can be inherited to the final product, and the special porous core-shell structure can also buffer the volume expansion problem in the charging and discharging process, which is beneficial to increase the ion diffusion rate and reversible battery capacity in the charging and discharging process, so that the silicon-carbon composite negative electrode can improve the electrochemical energy storage efficiency while considering the cycle life, and prolong the life cycle of the battery.

[0029] It should be noted that the pitch used in the present application contains a super-high proportion of carbon atoms, is rich in small-size aromatic molecular compounds, has the advantages of rich yield, low price, high carbon content and high carbon yield, and the pitch-based carbon microspheres prepared by the spray method can complete atomization, ball formation and separation in one step, avoiding the separation and agglomeration problems existing in the conventional liquid phase ball formation method. The regular spherical morphology and relatively uniform structure and size can also lay a good foundation for subsequent structure regulation. The pitch-based carbon microspheres prepared by high-temperature spray drying in the present application have regular morphology, smooth surface and narrow particle size distribution, and are easy to be subjected to subsequent coating and structure modification in the present application, and are more suitable as lithium ion battery negative electrode materials. By regulating the pore structure, the application scenario can be further widened to the field of supercapacitors, which has a significant advantage compared with pitch powder or irregular pitch carbonization products.

[0030] Compared with common irregular silicon-carbon negative electrodes, the pitch-based silicon-carbon porous ball negative electrode material of the present application has a spherical morphology design, which can effectively improve the tap density of the electrode, is beneficial to reduce the area of the solid electrolyte membrane (SEI film), and improve the first cycle coulombic efficiency of the material. The porous and core-shell structure characteristics can also buffer the volume expansion in the charging and discharging process, increase the ion diffusion channels, and improve the ion diffusion rate, thereby greatly improving the battery energy density and endurance, and being much safer than traditional graphite negative electrodes in high-rate charging scenarios, and having a wide application prospect.

[0031] In a preferred embodiment, in step S1, the temperature of the spray drying is 700-1000°C, the pressure is 0.3-3 MPa, and the atmosphere is a nitrogen atmosphere. Under the above conditions, the pitch enters a molten state after reaching the softening point, and further heating causes the pitch to carbonize, thereby increasing the carbon content of the material by removing light components such as hydrogen, oxygen, and sulfur, and forming a carbon-based skeleton structure, thereby improving the electrical conductivity, heat resistance, and chemical stability. At the same time, the pitch-based carbon microspheres after carbonization still retain certain defects, which are more conducive to subsequent functional structure modification as a carbon matrix.

[0032] The size and morphology of the pitch-based carbon microspheres are the basis for subsequent effective structure control. In a preferred embodiment, in step S1, the particle size D 50 of the pitch-based carbon microspheres is 500 nm-10 μm; and / or the sphericity of the pitch-based carbon microspheres is ≥90%; and / or the contact angle (hydrophilic angle) of the pitch-based carbon microspheres is 91-115°. As a coating carrier, a suitable particle size of the pitch-based carbon microspheres is conducive to the formation of a complete core-shell structure of the silicon-carbon composite material, neither easily causing agglomeration of the material due to van der Waals forces because of too small a particle size, nor easily affecting the uniformity of surface coating and causing stress cracking of the shell material during the coating process because of too large a particle size. A higher sphericity is conducive to uniform distribution of stress at the core-shell interface of the negative electrode material, thereby further improving the uniformity of the spherical morphology of the material.

[0033] After carbonization, the graphitization degree of the pitch increases, and the number of oxygen-containing functional groups decreases, and the contact angle formed with the plane is greater than 90°, exhibiting hydrophobicity. When participating in a reaction in a solution, the pitch needs to rely on the action of a template agent to reduce the interfacial energy, strengthen the contact between the solution and the solute, and ensure the full progress of the reaction. In a preferred embodiment, in step S2, the template agent includes one or more of cetyltrimethylammonium bromide, cetyltrimethylammonium chloride, octanol, isobutyl alcohol, isopropyl alcohol, isoamyl acetate, P123 (polyethylene ether-polypropylene ether-polyethylene ether triblock copolymer), and polyvinylpyrrolidone; preferably, the template agent includes cetyltrimethylammonium bromide and / or cetyltrimethylammonium chloride; and / or the silicon source includes one or more of tetraethyl orthosilicate (TEOS), tetramethyl orthosilicate, methyltriethoxysilane, 3-aminopropyltriethoxysilane, and tetrachlorosilane; preferably, the silicon source includes tetraethyl orthosilicate and / or tetramethyl orthosilicate; and / or the organic solvent includes ethanol and / or water.

[0034] The silicon source is used to coat the surface of the asphalt-based carbon microspheres with hydrophobic properties, and a template agent must be involved to improve the interface compatibility. In sol-gel chemistry, the selection of the template agent directly affects the morphology, size, pore structure, and dispersibility of the product. Cetyltrimethylammonium bromide and cetyltrimethylammonium chloride, as cationic surfactants, can further improve the mesoporous structure, and P123, as a non-ionic polymer, and octanol, as a long-chain alcohol, can also play a similar role. Isopropyl alcohol and isobutyl alcohol, as short-chain alcohols, are more conducive to size control and dispersibility improvement, and polyvinylpyrrolidone, as a non-ionic polymer, can also play a similar role. The above-mentioned template agents can more effectively induce the directional growth of the microstructure in the synthesis system, and thus more conducive to the stable formation of the core-shell structure. The above-mentioned types of silicon sources are different from silicone oil, which belongs to long-chain organosilicon polymers containing Si-O-Si backbone and methyl side chains, is inert, and needs to be treated by high-temperature oxidation or strong acid and other extreme conditions, with low efficiency; while the above-mentioned types of silicon sources are monomers, with mild reaction, more suitable for controlled synthesis and rapid industrial production.

[0035] In a preferred embodiment, in step S2, the weight ratio of the asphalt-based carbon microspheres to the template agent is 4:(1-50); and / or the liquid-solid ratio of the silicon source to the template agent is 1 mL:(0.3-2.5 g); and / or the temperature of the stirring reaction is 20-50°C, and the time is 0.5-24 h; and / or after the addition of the template agent, the pH of the solution is adjusted to 7-9 using an alkaline solvent, and then the silicon source is introduced; the alkaline solvent includes aqueous ammonia and / or aqueous sodium hydroxide solution.

[0036] The addition amount of the silicon source is related to the thickness of the formed SiO2 layer, and within the above-mentioned range, it can be ensured that the SiO2 can be successfully coated on the surface of the asphalt-based carbon microspheres and form a certain thickness, thereby improving the first turn Coulomb efficiency and specific capacity. The amount of the template agent is related to the amount of the silicon source and the coating effect, the amount of the silicon source is less, and the amount of the template agent is also less, and the SiO2 coated is less; the amount of the silicon source is more, and the amount of the template agent is also more, and the SiO2 coated is also more, and the above-mentioned addition amount of the template agent can further improve the coating effect. The above-mentioned stirring reaction conditions are more conducive to accelerating the reaction while reducing particle agglomeration. The solution within the above-mentioned pH range has a more suitable alkaline environment, and thus the material has a more suitable particle size and is not easy to agglomerate.

[0037] In a preferred embodiment, the reducing atmosphere in step S3 comprises one or more of the following atmospheres: hydrogen, a mixture of hydrogen and argon, carbon dioxide; preferably, the reducing atmosphere is a mixture of hydrogen and argon, and the volume ratio (flow ratio) of hydrogen to argon is (4-6):(94-96); preferably, the flow rate of the reducing atmosphere is 90-110 sccm (Standard Cubic Centimeter per Minute); and / or the temperature of the heat treatment is 800-1200℃, and the time is 1-3h.

[0038] Under the above heat reduction conditions, the reduction reaction of SiO2 is more likely to occur at high temperature and in a reducing atmosphere, and the valence of part of Si elements is reduced, so that the inactive SiO2 is converted into SiO x , SiO x can be further disproportionated to obtain Si, which further avoids the influence of excessive temperature on the graphitization degree of pitch-based carbon microspheres or the generation of by-products. Moreover, the above temperature range does not affect the pore structure, resulting in a decrease in micropores and an increase in macropores, thereby favoring the stability of the core-shell structure of the composite material.

[0039] For the purpose of further removing the inactive SiO2 left in the material and leaving more abundant pore structures on the surface, in a preferred embodiment, in step S4, the etching temperature is 20-80℃, and the time is 0.5-12h; and / or the usage ratio of the reduction product to the etchant is 1g:(0.03-0.3mol).

[0040] Based on similar reasons, in a preferred embodiment, in step S4, the etchant comprises one or more of the following materials: hydrofluoric acid, sodium hydroxide, potassium hydroxide, hydrochloric acid, and a mixture of fluorine-containing solid salts; preferably, the fluorine-containing solid salt comprises one or more of lithium fluoride, sodium fluoride, potassium fluoride, ammonium fluoride, and dihydrogen ammonium fluoride. Preferably, the etching is performed using an aqueous solution of the etchant. When an alkaline etchant with slightly weaker etching effect is used, the usage can be appropriately increased, such as 1g:(0.15-0.3mol), and when an acidic etchant with stronger etching effect is used, the usage can be appropriately reduced, such as 1g:(0.03-0.15mol).

[0041] In another typical embodiment of the present application, an asphalt-based silicon-carbon porous spherical negative electrode material is also provided, which is obtained by using the above-mentioned preparation method of the asphalt-based silicon-carbon porous spherical negative electrode material of the present application, and is a SiO xThe porous ball negative electrode material can balance good material uniformity, ion diffusion rate and volume expansion inhibition effect, reasonable structure regulation helps to improve the electrochemical performance of lithium ion batteries, and at the same time, widens the application scenarios of coal chemical byproduct pitch, and realizes high value-added utilization of pitch.

[0042] In another typical embodiment of the present application, a lithium ion battery is also provided, which comprises a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, the negative electrode sheet comprises a current collector and a negative active material coated on at least one side surface of the current collector, and the negative active material comprises the pitch-based silicon-carbon porous ball negative electrode material of the present application, which has significantly improved capacity performance and cycle performance.

[0043] Typically but not limitedly, in step S1, the temperature of spray drying is 700 DEG C, 750 DEG C, 800 DEG C, 850 DEG C, 900 DEG C, 950 DEG C, 1000 DEG C or a range value composed of any two of them, and the pressure is 0.3 MPa, 0.5 MPa, 1 MPa, 1.5 MPa, 2 MPa, 2.5 MPa, 3 MPa or a range value composed of any two of them.

[0044] Typically but not limitedly, the particle size D 50 of the pitch-based carbon microspheres is 500 nm, 1 mu m, 2 mu m, 3 mu m, 4 mu m, 5 mu m, 6 mu m, 7 mu m, 8 mu m, 9 mu m, 10 mu m or a range value composed of any two of them.

[0045] Typically but not limitedly, the sphericity of the pitch-based carbon microspheres is 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% or a range value composed of any two of them.

[0046] Typically but not limitedly, the contact angle of the pitch-based carbon microspheres is 91 DEG, 95 DEG, 100 DEG, 105 DEG, 110 DEG, 115 DEG or a range value composed of any two of them.

[0047] Typically but not limitedly, in step S2, the weight ratio of the pitch-based carbon microspheres to the template agent is 4:1, 4:5, 4:10, 4:15, 4:20, 4:25, 4:30, 4:35, 4:40, 4:45, 4:50 or a range value composed of any two of them.

[0048] Typically but not limitedly, in step S2, the liquid-solid ratio of the silicon source to the template agent is 1 mL:0.3 g, 1 mL:0.5 g, 1 mL:1.0 g, 1 mL:1.5 g, 1 mL:2.0 g, 1 mL:2.5 g or a range value composed of any two of them.

[0049] Typically but not limitedly, in step S3, the flow rate of the reducing atmosphere is 90sccm, 92sccm, 95sccm, 98sccm, 100sccm, 102sccm, 105sccm, 108sccm, 110sccm or any range value formed by any two of them.

[0050] Typically but not limitedly, in step S3, the temperature of the heat treatment is 800℃, 850℃, 900℃, 950℃, 1000℃, 1050℃, 1100℃, 1150℃, 1200℃ or any range value formed by any two of them, and the time is 1h, 1.2h, 1.5h, 1.8h, 2.0h, 2.2h, 2.5h, 2.8h, 3h or any range value formed by any two of them.

[0051] Typically but not limitedly, in step S4, the temperature of the etching is 20℃, 30℃, 40℃, 50℃, 60℃, 70℃, 80℃ or any range value formed by any two of them, and the time is 0.5h, 1h, 2h, 5h, 8h, 10h, 12h or any range value formed by any two of them.

[0052] Typically but not limitedly, in step S4, the ratio of the reducing product to the etchant is 1g:0.03mol, 1g:0.05mol, 1g:0.1mol, 1g:0.15mol, 1g:0.2mol, 1g:0.25mol, 1g:0.3mol or any range value formed by any two of them.

[0053] The application will be further described in detail below in conjunction with specific examples, which cannot be understood as limiting the scope of the application claimed.

[0054] Example 1

[0055] In step S1, after the pitch is heated to 700℃ to reach a molten state, it is sprayed into balls. The operating pressure is 0.3Mpa. The pitch melt is atomized into small droplets at the nozzle. The droplets fall freely in hot nitrogen while pyrolysis and carbonization are completed at one step to form pitch-based carbon microspheres.

[0056] In step S2, 4g of carbon microspheres and 25g of hexadecyl trimethyl ammonium bromide are dispersed in ethanol and deionized water, and ultrasonic dispersion is performed to obtain a mixed solution in which each component is uniformly dispersed. The mixed solution is stirred at high speed, 8mL of ammonia solution is added, the pH of the system is adjusted to 8, 12mL of a mixed solution of tetraethyl orthosilicate and 40mL of ethanol is added in portions, and stirring is performed at 50℃ for 12 hours. After the stirring is completed, centrifugal filtration, washing and drying are performed to obtain a powder of the intermediate.

[0057] Step S3, the powder of the intermediate is placed in a crucible and heat-reduced at 1000°C for 3 hours in a hydrogen / argon mixed atmosphere with a flow ratio of 5:95, a gas flow rate of 100 sccm, and cooling, to obtain a reduction product.

[0058] Step S4, etching with hydrofluoric acid at room temperature for 3 hours (the usage ratio of the reduction product to the etchant is 1 g:0.15 mol), and washing and drying to obtain the pitch-based silicon-carbon porous ball negative electrode material with a core-shell structure.

[0059] The preparation process flow chart is shown in Figure 1 , and the SEM image of the pitch-based carbon microspheres is shown in Figure 2 .

[0060] Example 2

[0061] Step S1, after the pitch is heated to 1000°C to reach a molten state, spray balling is performed, the operating pressure is 3 Mpa, the pitch melt is atomized into small droplets at the nozzle, and pyrolysis and carbonization are completed at the same time in the free falling of the droplets in hot nitrogen, to form pitch-based carbon microspheres.

[0062] Step S2, 4 g of carbon microspheres and 50 g of cetyltrimethylammonium chloride are dispersed in ethanol and deionized water, and ultrasonic dispersion is performed, to obtain a mixed solution in which the components are uniformly dispersed. The mixed solution is stirred at high speed, a 0.25 mol / L sodium hydroxide solution is added, the pH of the system is adjusted to 8, a mixed solution of 20 mL of tetraethyl orthosilicate and 40 mL of methanol is added in portions, and stirring is performed at 50°C for 24 hours. After the stirring is completed, centrifugal filtration, washing, and drying are performed, to obtain the powder of the intermediate.

[0063] Step S3, the powder of the intermediate is placed in a crucible and heat-reduced at 1000°C for 3 hours in a hydrogen / argon mixed atmosphere with a flow ratio of 5:95, a gas flow rate of 100 sccm, and cooling, to obtain a reduction product.

[0064] Step S4, etching with hydrofluoric acid at room temperature for 3 hours (the usage ratio of the reduction product to the etchant is 1 g:0.15 mol), and washing and drying to obtain the pitch-based silicon-carbon porous ball negative electrode material with a core-shell structure.

[0065] Example 3

[0066] Step S1, after the pitch is heated to 1000°C to reach a molten state, spray balling is performed, the operating pressure is 3 Mpa, the pitch melt is atomized into small droplets at the nozzle, and pyrolysis and carbonization are completed at the same time in the free falling of the droplets in hot nitrogen, to form pitch-based carbon microspheres.

[0067] Step S2, 4g of carbon microspheres and 1g of cetyltrimethylammonium bromide were dispersed in ethanol and deionized water, and ultrasonic dispersion was performed to obtain a mixed solution in which the components were uniformly dispersed. The mixed solution was stirred at high speed, and a 0.05 mol / L sodium hydroxide solution was added to adjust the pH of the system to 8. A mixed solution of 4 mL of tetraethyl orthosilicate and 40 mL of methanol was added in portions, and stirring was performed at room temperature for 12 hours. After the stirring was completed, centrifugal filtration, washing, and drying were performed to obtain a powder of an intermediate.

[0068] Step S3, the powder of the intermediate was placed in a crucible, and heat reduction was performed at 800°C for 1 hour in a hydrogen atmosphere with a gas flow rate of 100 sccm. After cooling, a reduction product was obtained.

[0069] Step S4, etching was performed using a sodium hydroxide solution at 60°C for 10 hours (the ratio of the amount of the reduction product to the amount of the etchant was 1g:0.15 mol). After washing and drying, an asphalt-based silicon-carbon porous spherical negative electrode material with a core-shell structure was obtained.

[0070] Example 4

[0071] Step S1, after the asphalt was heated to 800°C to reach a molten state, spray balling was performed. The operating pressure was 0.5 MPa. The asphalt melt was atomized into small droplets at the nozzle. Pyrolysis and carbonization were completed in one step while the droplets freely fell in hot nitrogen.

[0072] Step S2, 4g of carbon microspheres and 25g of cetyltrimethylammonium bromide were dispersed in ethanol and deionized water, and ultrasonic dispersion was performed to obtain a mixed solution in which the components were uniformly dispersed. The mixed solution was stirred at high speed, and 8 mL of an ammonia solution was added to adjust the pH of the system to 8. A mixed solution of 10 mL of tetraethyl orthosilicate and 40 mL of ethanol was added in portions, and stirring was performed at 50°C for 16 hours. After the stirring was completed, centrifugal filtration, washing, and drying were performed to obtain a powder of an intermediate.

[0073] Step S3, the powder of the intermediate was placed in a crucible, and heat reduction was performed at 1000°C for 2 hours in a hydrogen / argon mixed atmosphere with a flow ratio of 5:95, with a gas flow rate of 100 sccm. After cooling, a reduction product was obtained.

[0074] Step S4, etching was performed using a hydrofluoric acid solution at 50°C for 1 hour (the ratio of the amount of the reduction product to the amount of the etchant was 1g:0.15 mol). After washing and drying, an asphalt-based silicon-carbon porous spherical negative electrode material with a core-shell structure was obtained.

[0075] Example 5

[0076] Step S1, after heating and warming the pitch to 700℃ to achieve a molten state, spray into balls, the operating pressure is 0.5Mpa, pitch melt is atomized into small droplets at the nozzle, free falling in hot nitrogen gas, while completing pyrolysis, carbonization in one step, forming pitch-based carbon microspheres.

[0077] Step S2, take 4g carbon microspheres, 20g P123 dispersed in ethanol and deionized water, ultrasonic dispersion, get a mixed solution of uniform dispersion of each component. The above mixed solution is stirred at high speed, add 12mL ammonia solution, adjust the system pH to 9, add 12mL of a mixed solution of tetrachlorosilane and 40mL ethanol, stir at 50℃ for 12 hours. After stirring, centrifugal filtration, washing, drying, get the intermediate powder.

[0078] Step S3, the above intermediate powder is placed in a crucible, in a hydrogen / argon mixed atmosphere with a flow ratio of 5:95 at 1000℃ for 3 hours, the gas flow rate is 100sccm, cooling, get the reduction product.

[0079] Step S4, using 10mL 9M hydrochloric acid and 0.8g lithium fluoride mixed solution etching at room temperature for 12 hours (the amount ratio of reduction product to etchant is 1g:0.3mol), after washing and drying, get pitch-based silicon-carbon porous ball negative electrode material with core-shell structure.

[0080] Example 6

[0081] Step S1, after heating and warming the pitch to 700℃ to achieve a molten state, spray into balls, the operating pressure is 0.5Mpa, pitch melt is atomized into small droplets at the nozzle, free falling in hot nitrogen gas, while completing pyrolysis, carbonization in one step, forming pitch-based carbon microspheres.

[0082] Step S2, take 4g carbon microspheres, 20g P123 dispersed in ethanol and deionized water, ultrasonic dispersion, get a mixed solution of uniform dispersion of each component. The above mixed solution is stirred at high speed, add 12mL ammonia solution, adjust the system pH to 9, add 12mL of a mixed solution of tetrachlorosilane and 40mL ethanol, stir at 50℃ for 12 hours. After stirring, centrifugal filtration, washing, drying, get the intermediate powder.

[0083] Step S3, the above intermediate powder is placed in a crucible, in a hydrogen / argon mixed atmosphere with a flow ratio of 5:95 at 1000℃ for 3 hours, the gas flow rate is 100sccm, cooling, get the reduction product.

[0084] Step S4, using 10mL 9M hydrochloric acid and 0.8g lithium fluoride mixed solution etching at room temperature for 12 hours (the amount ratio of reduction product to etchant is 1g:0.3mol), after washing and drying, get pitch-based silicon-carbon porous ball negative electrode material with core-shell structure.

[0085] Comparative Example 1

[0086] The pitch was heated to 700°C to reach a molten state and then sprayed into balls. The operating pressure was 0.3 MPa. The pitch melt was atomized into small droplets at the nozzle. The droplets fell freely in hot nitrogen gas while pyrolysis and carbonization were completed in one step to form pitch-based carbon microspheres.

[0087] Comparative Example 2

[0088] Step S1, the pitch was heated to 700°C to reach a molten state and then sprayed into balls. The operating pressure was 0.3 MPa. The pitch melt was atomized into small droplets at the nozzle. The droplets fell freely in hot nitrogen gas while pyrolysis and carbonization were completed in one step to form pitch-based carbon microspheres.

[0089] Step S2, 4 g of carbon microspheres and 25 g of cetyltrimethylammonium bromide were dispersed in ethanol and deionized water, and ultrasonic dispersion was performed to obtain a mixed solution in which the components were uniformly dispersed. The mixed solution was stirred at high speed, 8 mL of an ammonia solution was added, the pH of the system was adjusted to 8, a mixed solution of 12 mL of tetraethyl orthosilicate and 40 mL of ethanol was added in portions, and stirring was performed at 50°C for 12 hours. After the stirring was completed, centrifugal filtration, washing, and drying were performed to obtain a powder of an intermediate.

[0090] Step S3, the powder of the intermediate was placed in a crucible, and hot reduction was performed at 1000°C for 3 hours in a hydrogen / argon mixed atmosphere with a flow ratio of 5:95, the gas flow rate was 100 sccm, and cooling was performed to obtain a negative electrode material.

[0091] Comparative Example 3

[0092] Step S1, 4 g of pitch powder (material obtained by crushing and sieving block pitch) and 25 g of cetyltrimethylammonium bromide were dispersed in ethanol and deionized water, and ultrasonic dispersion was performed to obtain a mixed solution in which the components were uniformly dispersed. The mixed solution was stirred at high speed, 8 mL of an ammonia solution was added, the pH of the system was adjusted to 8, a mixed solution of 12 mL of tetraethyl orthosilicate and 40 mL of ethanol was added in portions, and stirring was performed at 50°C for 12 hours. After the stirring was completed, centrifugal filtration, washing, and drying were performed to obtain a powder of an intermediate.

[0093] Step S2, the powder of the intermediate was placed in a crucible, and hot reduction was performed at 1000°C for 3 hours in a hydrogen / argon mixed atmosphere with a flow ratio of 5:95, the gas flow rate was 100 sccm, and cooling was performed to obtain a reduction product.

[0094] Step S3, etching was performed using hydrofluoric acid at room temperature for 3 hours (the amount ratio of the reduction product to the etchant was 1 g:0.15 mol), and after washing and drying, a pitch-based silicon-carbon porous ball negative electrode material with a core-shell structure was obtained.

[0095] Performance test:

[0096] D50 of pitch-based carbon microspheres: Malvern particle size analyzer.

[0097] Sphericity of pitch-based carbon microspheres: dynamic image particle analyzer.

[0098] Contact angle of pitch-based carbon microspheres: contact angle measuring instrument.

[0099] Electrochemical performance: The material prepared in the above examples and comparative examples was coated on the surface of a copper foil with a conductive agent (conductive carbon black + carbon nanotube, weight ratio 1:1), a binder (sodium alginate) at a mass ratio of 7:2:1 to prepare an electrode sheet, with a lithium metal sheet as a counter electrode, and sufficient electrolyte (silicon-carbon negative electrode electrolyte, such as 1 mol / L LiPF6, EC: EMC: DMC = 1:1:1) was added to ensure that the positive and negative electrodes and the separator were fully immersed, and then packaged into a CR2032 button cell. In the voltage range of 0.01-3V, the charge and discharge test was carried out in a constant current density (0.5A / g) manner, first discharged and then charged, and the initial specific capacity, the first cycle coulombic efficiency, the reversible specific capacity after 500 cycles and the capacity retention rate of 500 cycles were recorded, wherein the first cycle coulombic efficiency = initial specific capacity ÷ initial charge specific capacity × 100%, and the capacity retention rate = 500th cycle reversible specific capacity ÷ (initial specific capacity × first cycle coulombic efficiency) × 100%.

[0100] The test results are shown in Table 1.

[0101] Table 1

[0102]

[0103] Among them, comparative example 1 directly uses pitch-based carbon microspheres as negative electrode material, and since silicon is not introduced, although the first cycle coulombic efficiency and cycle capacity retention rate can be maintained at a high level, the capacity performance is significantly reduced. Comparative example 2 does not perform alkali etching, and the silicon coating layer does not form a rich pore structure, resulting in slow lithium ion insertion and extraction, reduced diffusion rate, and reduced first cycle coulombic efficiency and cycle capacity retention rate. Comparative example 3 directly uses pitch powder without preparing pitch-based carbon microspheres, and since the powder form is prone to agglomeration, the non-spherical structure has poor stability, resulting in poor uniformity of the material, poor silicon material coating effect, and significantly reduced capacity performance and cycle performance of the negative electrode material.

[0104] From the above, compared with the comparative examples, each embodiment of the present application uses high-temperature spray method to carbonize pitch into balls in one step, and the obtained carbon microspheres have the characteristics of uniform morphology and high sphericity; then the sol-gel method is used to coat silicon oxide on the surface of the pitch-derived spherical carbon material, and through subsequent high-temperature reduction and etching technology, the reduction and removal of low-activity SiO2 are realized at the same time to form a certain pore structure, so that the material has the characteristics of spherical, porous and "core-shell" triple structure, and a pitch-based SiO x / C porous ball negative electrode material, so as to effectively inhibit the volume expansion of the electrode material in the lithium ion charging and discharging process, accelerate the diffusion of lithium ions, and thus obtain a lithium ion battery negative electrode material with high reversible specific capacity and long cycle stability.

[0105] In addition, it can be seen that when each process parameter is within the preferred range of the present application, the comprehensive effect is better.

[0106] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing a pitch-based silicon-carbon porous spherical anode material, characterized in that, Includes the following steps: Step S1: Spray dry the asphalt to obtain asphalt-based carbon microspheres; Step S2: Disperse the asphalt-based carbon microspheres in an organic solvent, add a template agent and a silicon source in sequence, and stir to react to obtain a reaction solution; The reaction solution was sequentially filtered, washed, and dried to obtain an intermediate. Step S3: The intermediate is heat-treated in a reducing atmosphere to obtain a reduction product; Step S4: The reduction product is etched using an etchant to obtain the pitch-based silicon-carbon porous spherical anode material.

2. The method for preparing the pitch-based silicon-carbon porous spherical anode material according to claim 1, characterized in that, In step S1, the spray drying temperature is 700–1000°C, the pressure is 0.3–3 MPa, and the atmosphere is nitrogen.

3. The method for preparing the pitch-based silicon-carbon porous spherical anode material according to claim 1 or 2, characterized in that, In step S1 The particle size D of the asphalt-based carbon microspheres 50 500nm~10μm; and / or The sphericity of the asphalt-based carbon microspheres is ≥90%; and / or The contact angle of the pitch-based carbon microspheres is 91–115°.

4. The method for preparing the pitch-based silicon-carbon porous spherical anode material according to any one of claims 1 to 3, characterized in that, In step S2 The template agent comprises one or more of hexadecyltrimethylammonium bromide, hexadecyltrimethylammonium chloride, octanol, isobutanol, isopropanol, isoamyl acetate, P123, and polyvinylpyrrolidone; preferably, the template agent comprises hexadecyltrimethylammonium bromide and / or hexadecyltrimethylammonium chloride; and / or The silicon source includes one or more of tetraethyl silicate, tetramethyl silicate, methyltriethoxysilane, 3-aminopropyltriethoxysilane, and tetrachlorosilane; preferably, the silicon source includes tetraethyl silicate and / or tetramethyl silicate; and / or The organic solvents include ethanol and / or water.

5. The method for preparing the pitch-based silicon-carbon porous spherical anode material according to any one of claims 1 to 4, characterized in that, In step S2 The weight ratio of the asphalt-based carbon microspheres to the template agent is 4:(1-50); and / or The liquid-to-solid ratio of the silicon source to the template agent is 1 mL:(0.3–2.5 g); and / or The stirring reaction is carried out at a temperature of 20–50°C for a time of 0.5–24 h; and / or After adding the template agent, the pH of the solution is adjusted to 7-9 using an alkaline solvent, and then the silicon source is introduced; the alkaline solvent includes ammonia and / or an aqueous solution of sodium hydroxide.

6. The method for preparing the pitch-based silicon-carbon porous spherical anode material according to any one of claims 1 to 5, characterized in that, In step S3 The reducing atmosphere includes one or more of the following atmospheres: hydrogen, a mixture of hydrogen and argon, and carbon dioxide; preferably, the reducing atmosphere is a mixture of hydrogen and argon, with a volume ratio of hydrogen to argon of (4-6):(94-96); preferably, the flow rate of the reducing atmosphere is 90-110 sccm; and / or The heat treatment is performed at a temperature of 800–1200°C for 1–3 hours.

7. The method for preparing the pitch-based silicon-carbon porous spherical anode material according to any one of claims 1 to 6, characterized in that, In step S4 The etching temperature is 20–80°C, and the etching time is 0.5–12 h; and / or The ratio of the reduction product to the etching agent is 1 g:(0.03-0.3 mol).

8. The method for preparing the pitch-based silicon-carbon porous spherical anode material according to any one of claims 1 to 7, characterized in that, In step S4 The etching agent includes one or more of the following materials: hydrofluoric acid, sodium hydroxide, potassium hydroxide, hydrochloric acid, and a mixture of fluorine-containing solid salts; Preferably, the fluorine-containing solid salt includes one or more of lithium fluoride, sodium fluoride, potassium fluoride, ammonium fluoride, and ammonium dihydrogen fluoride.

9. A pitch-based silicon-carbon porous spherical anode material, characterized in that, The anode material was prepared using the method described in any one of claims 1 to 8.

10. A lithium-ion battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the negative electrode comprises a current collector and a negative electrode active material coated on at least one surface of the current collector, characterized in that, The negative electrode active material includes the pitch-based silicon-carbon porous sphere negative electrode material as described in claim 9.

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