Silicon-oxygen composite silicon-carbon material, preparation method and application thereof, and lithium ion battery

Abstract

This invention discloses a silicon-oxygen composite silicon-carbon material, its preparation method, application, and lithium-ion battery. The method includes: (1) calcining a mixture of metal A and silicon powder under inert gas protection to obtain a precursor; wherein metal A is an alkali metal and / or an alkaline earth metal; the calcination temperature is 300-800℃; (2) under inert gas protection, calcining a mixture of halogen-containing polymer, oxygen-containing polymer, and the precursor at 200-450℃ for 0.5-6h, then further heating to 600-1000℃ and holding for 20min-2h, cooling to room temperature, washing, and drying to obtain the silicon-oxygen composite silicon-carbon material. The silicon-oxygen composite silicon-carbon material prepared by this invention has excellent electrochemical performance, and the preparation method is simple.

Description

Technical Field

[0001] This invention specifically relates to a silicon-oxygen composite silicon-carbon material, its preparation method, applications, and lithium-ion batteries. Background Technology

[0002] With the continuous advancement of technology, the demand for lithium-ion batteries with high energy density, high power density, long lifespan, and safety is increasing. Silicon, as the anode material for lithium-ion batteries, is considered the next-generation anode material for long-lasting batteries due to its high theoretical specific capacity (approximately 4200 mAh / g, far exceeding the 372 mAh / g of traditional graphite anodes).

[0003] However, silicon undergoes significant volume expansion (up to 300% or more) during charging and discharging, leading to pulverization of electrode materials, damage to electrode structures, and repeated formation of the solid electrolyte interphase (SEI) film, thus affecting the battery's cycle stability and lifespan. Furthermore, silicon's low conductivity and the slow diffusion rate of lithium ions within it also limit its high-rate performance.

[0004] To overcome these problems, researchers have begun exploring nano-silicon anode materials. Due to its unique size effect, nano-silicon can alleviate the stress caused by volume expansion to some extent and provides a larger electrode-electrolyte contact area, thereby improving conductivity and lithium-ion diffusion rate. Furthermore, nano-silicon materials can be further enhanced in their electrochemical performance by being designed into porous structures or combined with other materials such as carbon.

[0005] Current methods for preparing nano-silicon, such as sand milling and silane deposition, suffer from drawbacks including reliance on expensive equipment like sand mills and tube furnaces, low batch yields, and high production costs, making it difficult to meet the demand for low-cost energy storage. Furthermore, while mass production of silicon anode materials is crucial for promoting green energy development in my country, the production process itself typically consumes significant amounts of energy and resources, necessitating the integration of environmental protection technologies to reduce environmental burden. Resource utilization of waste pollutants during the preparation process is a vital pathway to achieving green manufacturing, especially for halogenated waste plastics like PVC. Their production, use, and disposal all impact the environment, particularly due to their chlorine content, which can release harmful substances if improperly disposed of. Therefore, the green resource utilization of PVC-like polymers is particularly important. From both economic and environmental perspectives, there is an urgent need to develop green manufacturing technologies that are compatible with traditional anode material mass production processes and the resource utilization of waste pollutants, enabling the low-cost, high-volume, environmentally friendly, and simple preparation of silicon-carbon composite materials. Summary of the Invention

[0006] The technical problem solved by this invention is to overcome the problems of poor electrochemical performance, high preparation cost, low batch yield, low resource utilization, and lack of green environmental protection of silicon-carbon composite materials in the prior art, and to provide a silicon-oxygen composite silicon-carbon material, its preparation method, application and lithium-ion battery.

[0007] The preparation method of this invention can efficiently prepare silicon-oxygen composite silicon-carbon materials while achieving high-value-added green utilization of halogen-containing waste plastics such as PVC. First, a precursor is generated by reacting silicon powder with a metal. Then, HCl, generated from the dehalogenation of halogen-containing polymers at high temperature, reacts with the precursor to generate silicon and metal chlorides, achieving chlorine fixation and preventing the release of chlorine-containing gaseous pollutants into the environment. Simultaneously, oxygen-containing polymers undergo pyrolysis to generate highly reactive oxygen-containing free radicals, which react with silicon to form silicon oxide (SiOx) on the silicon surface. Finally, carbon coating is achieved by decomposing residual polymers at high temperature, resulting in silicon-oxygen composite silicon-carbon materials with excellent electrochemical performance. This preparation method requires no complex equipment; silicon-oxygen composite silicon-carbon materials can be prepared in large quantities using simple solid-phase reaction equipment, while simultaneously achieving the resource-based and environmentally friendly utilization of halogen-containing polymer (e.g., polyvinyl chloride) waste pollutants. Furthermore, the silicon oxide on the silicon surface prevents direct contact between active silicon and the electrolyte, avoiding side reactions.

[0008] The present invention solves the above-mentioned technical problems through the following technical solutions:

[0009] This invention provides a method for preparing a silicon-oxygen composite silicon-carbon material, comprising the following steps:

[0010] (1) A precursor is prepared by calcining a mixture of metal A and silicon powder under an inert gas atmosphere; wherein the metal A is an alkali metal and / or an alkaline earth metal; and the calcination temperature is 300–800 °C.

[0011] (2) Under the protection of an inert gas, the mixture of halogen-containing polymer, oxygen-containing polymer and the precursor is first calcined at 200-450°C for 0.5-6 hours, and then the temperature is further increased to 600-1000°C and held for 20 minutes-2 hours. After cooling to room temperature, it is washed and dried to obtain the silicon-oxygen composite silicon-carbon material.

[0012] In step (1), the silicon powder can be conventional in the art, generally commercially available or prepared in-house, and the main component of the silicon powder is silicon dioxide. The purity of the silicon powder is >95%; the particle size can be 1-5μm.

[0013] In step (1), the alkali metal element is preferably one or more of Li, Na and K.

[0014] In step (1), the alkaline earth metal element is preferably one or more of Mg, Ca, Sr and Ba, and more preferably Mg.

[0015] In step (1), the molar ratio of the metal A to the silicon powder can be 1:(0.3-2), for example 1:0.5, 1:1 or 1:2.

[0016] In step (1), the chemical formula of the precursor can be A. x Si, preferably, 0.5 ≤ x ≤ 3, for example, 0.5, 1 or 2.

[0017] When the metal A is Mg, the A x Si can be Mg₂Si. When the metal A is Ca, the A... x Si can be Ca 0.5 Si, Ca₂Si, or CaSi. When the metal A is Na, the A... x Si can be Na₂Si or NaSi.

[0018] In steps (1) and (2), the inert gas can be a conventional industrial inert gas, such as nitrogen or argon.

[0019] In steps (1) and (2), the calcination is generally carried out in a tubular furnace.

[0020] In step (1), the rate of heating to the calcination temperature is preferably 2-10 °C / min, for example 5 °C / min.

[0021] In step (1), the calcination temperature is preferably 550 to 750°C, for example 600°C, 700°C or 750°C.

[0022] In step (1), the calcination time is preferably 3 to 12 hours, more preferably 4 to 10 hours, for example 4 hours, 6 hours or 10 hours.

[0023] In step (2), the halogenated polymer is preferably polyvinyl chloride and / or polyvinylidene chloride. The viscosity number (K) of the polyvinyl chloride can be 50-80, for example, 62-60. The halogenated polymer is preferably in powder form. Before use, the halogenated polymer can be cleaned and mechanically pulverized into powder.

[0024] In step (2), the mass ratio of the precursor to the halogenated polymer can be (2-5):1, for example 3:1, 4:1 or 5:1.

[0025] In step (2), the oxygen-containing polymer is preferably polyethylene glycol and / or polyvinyl alcohol. The average number-average molecular weight (Mn) of the polyethylene glycol can be 1000-20000 g / mol, preferably 5000-15000 g / mol, for example 8000 g / mol. The degree of alcoholysis of the polyvinyl alcohol can be above 70 mol%, preferably 90-100 mol%, for example 99.0-99.4 mol%; the viscosity of the polyvinyl alcohol can be 4-20 mPa·s, preferably 10-20 mPa·s, for example 12.0-16.0 mPa·s.

[0026] In step (2), the mass ratio of the halogenated polymer to the oxygen-containing polymer can be 1:(0.15-0.4), for example 1:0.2, 1:0.25 or 1:0.3.

[0027] In step (2), the rate of heating to the temperature of the first calcination is preferably 1-5 °C / min, for example 3 °C / min.

[0028] In step (2), the temperature of the first calcination is preferably 250-400℃, for example 300℃.

[0029] In step (2), the first calcination time is preferably 3-6 hours, for example 4 hours or 5 hours.

[0030] In step (2), preferably, the temperature is further increased to 700-900°C, for example, 700°C or 800°C, based on the temperature of the first calcination.

[0031] In step (2), after the temperature is increased further based on the temperature of the first calcination, it is preferable to keep the temperature for 20-60 minutes, for example, 30 minutes.

[0032] In step (2), the solvent used for washing can be conventional in the art, such as deionized water.

[0033] The present invention also provides a silicon-oxygen composite silicon-carbon material prepared by the preparation method described above.

[0034] In this invention, the silicon-oxygen composite silicon-carbon material can have a core-shell structure, with the core being a silicon material with a surface of silicon dioxide and the shell being a carbon layer. The particle size D of the silicon-oxygen composite silicon-carbon material... 50 The thickness can be 50-500 nm, preferably 100-200 nm. The thickness of the carbon layer can be 5-100 nm.

[0035] The present invention also provides an application of the silicon-oxygen composite silicon-carbon material as described above in lithium-ion batteries.

[0036] The present invention also provides a lithium-ion battery comprising a positive electrode, a negative electrode, an electrolyte, and a separator, wherein the negative electrode comprises a silicon-oxygen composite silicon-carbon material as described above.

[0037] Based on common knowledge in the field, the above-mentioned preferred conditions can be combined arbitrarily to obtain various preferred embodiments of the present invention.

[0038] The reagents and raw materials used in this invention are all commercially available.

[0039] The positive and progressive effects of this invention are as follows:

[0040] The preparation method of this invention does not rely on high-cost raw materials and equipment such as silanes and sand mills. Compared with current sand milling and vapor deposition methods, it can achieve large-scale production, and the process is compatible with traditional graphite anode production equipment. Furthermore, the preparation method can simultaneously achieve high-value-added green resource utilization of halogen-containing waste plastics such as PVC, combining environmental and economic benefits. When the prepared silicon-oxygen composite silicon-carbon material is applied to lithium-ion batteries, it exhibits excellent electrochemical performance, especially high specific capacity and cycle life. Attached Figure Description

[0041] Figure 1 This is a TEM image of the silicon-oxygen composite silicon-carbon material prepared in Example 1;

[0042] Figure 2 SEM image of the silicon-oxygen composite silicon-carbon material prepared in Example 1;

[0043] Figure 3 The images show the XRD patterns of the silicon-oxygen composite silicon-carbon materials prepared in Examples 1-2.

[0044] Figure 4 The image shows the XRD pattern of the precursor prepared in Example 1. Detailed Implementation

[0045] The present invention is further illustrated below by way of embodiments, but the invention is not limited to the scope of the embodiments described herein. Experimental methods in the following embodiments that do not specify specific conditions were performed according to conventional methods and conditions, or as selected according to the product instructions.

[0046] The commercial silicon powder used in the following examples and comparative examples was purchased from Aladdin and has a purity of 99.9% and a particle size of 1 μm.

[0047] Example 1

[0048] (1) Preparation: Mix magnesium powder and commercial silicon powder evenly in a molar ratio of 2:1 and place them in a crucible. Add the crucible to a tube furnace and heat it to 600°C in a nitrogen atmosphere at a heating rate of 5°C / min. Hold for 4 hours and then cool down to room temperature to obtain the precursor Mg2Si.

[0049] (2) The precursor, polyvinyl chloride powder (Aladdin, K62-60) and polyethylene glycol PEG (Aladdin, average number average molecular weight Mn of 8000 g / mol) were mixed in a mass ratio of 3:1:0.25. The mixture was heated to 300°C in a tube furnace under a nitrogen atmosphere at a heating rate of 3°C / min and held for 4 hours. Then, the mixture was heated to 800°C under a nitrogen atmosphere at a heating rate of 3°C / min and held for 30 minutes. The mixture was then cooled to room temperature, washed three times with deionized water, and dried to obtain silicon-oxygen composite silicon-carbon material.

[0050] Example 2

[0051] Compared with Example 1, except that the polyvinyl chloride powder was replaced with PVDC powder (Dow SARAN 516, extrusion type), all other operations and conditions were the same as in Example 1.

[0052] Example 3

[0053] Compared with Example 1, except that the magnesium powder was replaced with calcium powder, all other parameters and conditions were the same as in Example 1.

[0054] Example 4

[0055] Compared with Example 1, except that the magnesium powder was replaced with calcium powder and the molar ratio of calcium powder to commercial silicon powder was changed to 1:2, all other operations and conditions were the same as in Example 1.

[0056] Example 5

[0057] The precursor was prepared by uniformly mixing barium powder and commercial silicon powder at a molar ratio of 1:2 and placing them in a crucible. The crucible was then placed in a tube furnace and heated to 700°C at a heating rate of 5°C / min under a nitrogen atmosphere. After holding at this temperature for 6 hours, the mixture was cooled to room temperature. The precursor was then mixed with polyvinyl chloride powder (Aladdin, K62-60) at a mass ratio of 5:1 and heated to 300°C at a heating rate of 3°C / min under a nitrogen atmosphere in a tube furnace. After holding at this temperature for 4 hours, the mixture was further heated to 800°C at a heating rate of 3°C / min under a nitrogen atmosphere and held for 30 minutes. After cooling to room temperature, the mixture was washed three times with deionized water and dried to obtain the silicon-oxygen composite silicon-carbon material.

[0058] Example 6

[0059] The precursor was prepared by uniformly mixing sodium metal and commercial silicon powder at a molar ratio of 2:1 and placing the mixture in a crucible. The crucible was then placed in a tube furnace and heated to 750°C at a heating rate of 5°C / min in a high-purity argon atmosphere. After holding the mixture for 10 hours, the mixture was cooled to room temperature. The precursor was then mixed with polyvinyl chloride powder (Aladdin, K62-60) at a mass ratio of 3:1 and heated to 300°C at a heating rate of 3°C / min in a tube furnace under a nitrogen atmosphere. After holding the mixture at this temperature for 5 hours, the mixture was further heated to 700°C at a heating rate of 3°C / min in a nitrogen atmosphere and held for 30 minutes. After cooling to room temperature, the mixture was washed three times with deionized water and dried to obtain the silicon-oxygen composite silicon-carbon material.

[0060] Example 7

[0061] Compared with Example 1, except that polyethylene glycol was replaced with polyvinyl alcohol PVA (Aladdin, degree of hydrolysis: 99.0-99.4 mol%, viscosity: 12.0-16.0 mPa·s), all other operations and conditions were the same as in Example 1.

[0062] Comparative Example 1

[0063] Commercial crude silicon was milled to the particle size limit in an ethanol medium to obtain nano-silicon with a diameter of about 200 nm.

[0064] Comparative Example 2

[0065] Compared with Example 1, except that polyvinyl chloride powder is not added in step (2), all other operations and conditions are the same as in Example 1.

[0066] Comparative Example 3

[0067] Compared with Example 1, except that polyethylene glycol is not added in step (2), all other operations and conditions are the same as in Example 1.

[0068] Effect Example

[0069] (1) Morphological characterization and XRD testing

[0070] Figure 1 The image shows a TEM image of the silicon-oxygen composite silicon-carbon material prepared in Example 1, which shows that the material surface is uniformly coated with a multilayer carbon structure. Figure 2 SEM image of the silicon-oxygen composite silicon-carbon material prepared in Example 1; Figure 3 The images show the XRD patterns of the silicon-oxygen composite silicon-carbon materials prepared in Examples 1-2. Figure 4 The image shows the XRD pattern of the precursor prepared in Example 1, which has the composition Mg2Si.

[0071] The particle size of the silicon-oxygen composite silicon-carbon materials prepared in Examples 1-7 and the nano-silicon prepared in Comparative Examples 1-3 was statistically analyzed using a laser particle size analyzer MS3000, as shown in Table 1:

[0072] Table 1

[0073]

[0074]

[0075] (2) Electrochemical performance testing

[0076] The silicon-oxygen composite silicon-carbon materials prepared in Examples 1 to 7 and the materials prepared in Comparative Examples 1-3 were subjected to half-cell tests. The test method was as follows: the above materials were uniformly mixed with binder CMC (sodium carboxymethyl cellulose) and conductive carbon black in a mass ratio of 80:10:10 to form a slurry, which was then coated onto copper foil to a thickness of 100 micrometers. The slurry was then dried under vacuum at 80°C for 12 hours to prepare a lithium-ion battery negative electrode. Simulated battery assembly was performed in an argon-filled glove box using a 1 mol / L LiPF6 electrolyte (solvents were EC, DMC, and FEC, EC:DMC = 1:1 (volume ratio), FEC accounting for 5% of the total solvent volume). A polypropylene microporous membrane was used as the separator, and a lithium metal sheet was used as the counter electrode. Electrochemical performance tests were conducted on a Land CT2001A battery tester at 20°C, with a charge / discharge voltage range of 0.01 to 1.5V (1C = 250 mAh g). -1 The test results are shown in Table 2.

[0077] Table 2

[0078]

[0079]

[0080] Based on the above experimental results, it can be seen that the silicon-oxygen composite silicon-carbon material prepared by the present invention has excellent electrochemical performance, especially specific capacity and cycle life.

[0081] Comparative Example 1: Due to the difficulty in further reducing the size during the sand milling process, the stress during the lithium-ion intercalation / deintercalation process is difficult to release due to deformation, making it more prone to pulverization and capacity decay. Furthermore, the lack of a silicon carbide / carbon coating layer to isolate the electrolyte leads to significant electrochemical side reactions, resulting in poor electrochemical performance. The initial discharge capacity and cycle performance are inferior to the example. Comparative Example 2: Due to the lack of polyvinyl chloride, the silicon precursor cannot complete the dehalogenation reaction to generate nano-silicon. The sample size is large, and the lithium storage is achieved using magnesium silicide and a small amount of carbon as the negative electrode. Therefore, the specific capacity and cycle life of the nano-silicon material are significantly reduced. Comparative Example 3: Due to the lack of polyethylene glycol, the surface of the generated nano-silicon cannot generate surface silicon oxide through oxygen free radical reaction. This leads to easy contact between the electrolyte and active silicon, causing side reactions and resulting in a decrease in initial charge specific capacity and cycle life.

[0082] While specific embodiments of the present invention have been described above, those skilled in the art should understand that these are merely illustrative examples, and the scope of protection of the present invention is defined by the appended claims. Those skilled in the art can make various changes or modifications to these embodiments without departing from the principles and essence of the present invention, but all such changes and modifications fall within the scope of protection of the present invention.

Claims

1. A method for preparing a silicon-oxygen composite silicon-carbon material, characterized in that, Includes the following steps: (1) A precursor is prepared by calcining a mixture of metal A and silicon powder under an inert gas atmosphere; wherein the metal A is an alkali metal and / or an alkaline earth metal; and the calcination temperature is 300–800 °C. (2) Under the protection of inert gas, the mixture of halogen-containing polymer, oxygen-containing polymer and the precursor is first calcined at 200-450°C for 0.5-6 hours, and then the temperature is further increased to 600-1000°C and held for 20 minutes-2 hours. After cooling to room temperature, it is washed and dried to obtain the silicon-oxygen composite silicon-carbon material.

2. The method for preparing the silicon-oxygen composite silicon-carbon material according to claim 1, characterized in that, The particle size of the silicon powder is 1-5 μm; And / or, the alkali metal is one or more of Li, Na, and K; And / or, the alkaline earth metal is one or more of Mg, Ca, Sr and Ba, preferably Mg.

3. The method for preparing the silicon-oxygen composite silicon-carbon material according to claim 1, characterized in that, In step (1), the molar ratio of metal A to silicon powder is 1:(0.3-2), for example 1:0.5, 1:1 or 1:2; And / or, in step (1), the precursor has the chemical formula A x Si, preferably, 0.5 ≤ x ≤ 3, for example, 0.5, 1 or 2.

4. The method for preparing silicon-oxygen composite silicon-carbon material according to claim 1, characterized in that, In step (1), the rate of heating to the calcination temperature is 2-10℃ / min; And / or, in step (1), the calcination temperature is 550–750°C; And / or, in step (1), the calcination time is 3 to 12 hours, preferably 4 to 10 hours.

5. The method for preparing the silicon-oxygen composite silicon-carbon material according to claim 1, characterized in that, In step (2), the halogenated polymer is polyvinyl chloride and / or polyvinylidene chloride; And / or, in step (2), the mass ratio of the precursor to the halogenated polymer is (2-5):1; And / or, in step (2), the oxygen-containing polymer is polyethylene glycol and / or polyvinyl alcohol; And / or, in step (2), the mass ratio of the halogenated polymer to the oxygen-containing polymer is 1:(0.15-0.4).

6. The method for preparing the silicon-oxygen composite silicon-carbon material according to claim 1, characterized in that, In step (2), the rate of heating to the temperature of the first calcination is 1-5℃ / min; And / or, in step (2), the temperature of the first calcination is 250-400℃; And / or, in step (2), the first calcination time is 3-6 hours.

7. The method for preparing the silicon-oxygen composite silicon-carbon material according to claim 1, characterized in that, In step (2), the temperature is further increased to 700-900℃ based on the temperature of the first calcination; And / or, in step (2), after further heating based on the temperature of the first calcination, hold the temperature for 20-60 minutes.

8. A silicon-oxygen composite silicon-carbon material, characterized in that, It is prepared according to the preparation method of silicon-oxygen composite silicon-carbon material as described in any one of claims 1-7.

9. The application of the silicon-oxygen composite silicon-carbon material as described in claim 8 in lithium-ion batteries.

10. A lithium-ion battery, characterized in that, It includes a positive electrode, a negative electrode, an electrolyte, and a separator, wherein the negative electrode includes the silicon-oxygen composite silicon-carbon material as described in claim 8.

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