Silicon-oxygen-carbon composite material as well as preparation method and application thereof

Abstract

The invention provides a silicon-oxygen-carbon composite material as well as a preparation method and application thereof, the surface layer of a silicon-oxygen material of a bulk phase of the composite material is lithiated and reduced into silicon, meanwhile, a double-layer carbon structure ensures the conductivity of the material, a plasma carbon coating layer is formed on the surface of SiO by utilizing a PECVD (Plasma Enhanced Chemical Vapor Deposition) technology before pre-lithiation, and the conductivity of the material is improved. After pre-lithiation, a heteroatom porous carbon coating layer is constructed on the surface of the material, so that a surface conductive layer is kept in contact with the inside, and doping modification is realized while carbon coating is performed. According to the preparation method, the microstructure of the pre-lithiated SiO is optimized, the growth of silicon particles in the pre-lithiation process is reduced, a three-dimensional penetrating conductive network is formed by combining the external carbon layer and the internal carbon layer, a channel is provided for rapid transmission of lithium ions, the conductivity of the material is improved, and volume expansion is relieved. The preparation process is simple, the first efficiency of the material is high, the conductivity is good, and the cycle rate capability is good.

Description

Technical Field

[0001] The present invention relates to the technical field of negative electrode materials for lithium ion batteries, and in particular to a silicon-oxygen-carbon composite material, a preparation method and an application thereof. Background Art

[0002] SiO negative electrode materials have a wide range of application prospects in lithium-ion battery negative electrode materials due to their high theoretical capacity (2680mAh / g), low lithium insertion and extraction potential, and small volume expansion (~150%). Their commercial prospects are ahead of pure silicon negative electrodes, and their application in the field of power batteries is more mainstream. Compared with pure silicon negative electrodes, the volume change of silicon oxide during charging and discharging is small, but the coulomb efficiency of SiO negative electrode materials in the first cycle is only about 67%. This is because SiO will irreversibly form L2O and lithium silicate in the first cycle. This process consumes a large amount of lithium ions, resulting in a relatively low initial coulomb efficiency of SiO negative electrodes. In addition, silicon-oxygen negative electrodes also have disadvantages such as low intrinsic conductivity, poor chemical activity, and volume effect.

[0003] At present, researchers mainly modify SiO negative electrode materials through pre-lithiation, porosification, coating and doping. Pre-lithiation is the main method to improve the first effect of SiO negative electrode materials. Doping can improve the conductivity of SiO negative electrode materials, and coating can effectively improve its cycle rate performance. Most of the prior art directly contacts SiO with the pre-lithiation agent, resulting in a fast pre-lithiation reaction rate, enrichment of lithium silicate salts, material conductivity, and unstable structure. In patent CN117878274A, the cavity structure of the expanded SiO material during the pre-lithiation process is constructed in advance by an alkali dissolution method, which can effectively alleviate the volume expansion. However, the production of the cavity structure requires strong alkali etching, the production cost is too high, and the silicate is covered on the SiO surface after pre-lithiation. In the process of water homogenization, it is easy to cause slurry denaturation, gas production, poor coating quality and low yield. Summary of the invention

[0004] To solve the technical deficiencies of low initial efficiency, large volume change and poor conductivity of existing silicon-based negative electrode materials. The present invention provides a silicon-oxygen-carbon composite material and a preparation method thereof. The surface layer of the silicon-oxygen material of the composite material bulk phase prepared by the present invention is lithium-reduced to silicon, and the double-layer carbon structure ensures the conductive performance and cycle stability of the material. The present invention uses PECVD technology to form a plasma carbon coating layer on the SiO surface before lithiation, so that the carbon layer is in close contact with SiO, which is an effective buffer coating layer, and can significantly alleviate the growth and volume expansion of active silicon particles during the pre-lithiation process. At the same time, the alkalinity of the pre-lithiation SiO surface is reduced. After pre-lithiation, a heteroatom porous carbon coating layer is constructed on the surface of the material, and a three-dimensional penetrating conductive network is formed in combination with the internal carbon layer, so that the surface conductive layer is kept in contact with the interior, and doping modification is achieved while carbon coating. The preparation method optimizes the microstructure of pre-lithiation SiO, and the double-layer carbon coating reduces the growth of active Si during pre-lithiation and alleviates the volume expansion; at the same time, the three-dimensional penetrating conductive network provides a channel for the rapid transmission of lithium ions, thereby improving the conductivity of the material. The invention provides a method for preparing a silicon-oxygen-carbon composite material. The preparation process is simple, the material has high initial efficiency, good electrical conductivity and good cycle rate performance.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0006] A method for preparing a silicon-oxygen-carbon composite material, comprising:

[0007] S1: Weigh a certain amount of SiO2 and load it into the PECVD equipment, evacuate and heat the PECVD equipment; introduce argon gas, and after the temperature rises to the set temperature, start the plasma excitation source, adjust the power, and introduce the carbon source gas into the PECVD equipment cavity. After a certain reaction time, turn off the plasma, stop introducing the carbon source gas, and cool the sample in the argon atmosphere to obtain the carbon-coated SiO2@C material;

[0008] S2: Mixing SiO@C material and pre-lithiation agent, and pre-lithiation under argon atmosphere to obtain pre-lithiation SiO@C / Li composite material;

[0009] S3: adding a carbon source containing heteroatoms into a solvent, adding a pre-lithiated SiO@C / Li composite material, stirring, centrifugal washing, freeze drying, and sintering to obtain a heteroatom carbon-coated pre-lithiated silicon oxygen carbon composite material SiO@C / Li@Cd.

[0010] Preferably, D of the SiO raw material S1 is 50 =5μm; set the temperature to 400-800°C, the power of the plasma excitation source to 50W-300W, and the reaction time to 10min-120min.

[0011] Preferably, the carbon source gas in S1 is any one or more of methane, acetylene, ethylene, and ethane, and the flow rate of the carbon source gas is 1-100 mL / min. The flow rate of argon is 50-300 mL / min.

[0012] Preferably, the mass ratio of the SiO@C material and the pre-lithium agent in S2 is (2-20):1; the pre-lithium agent is one or more of lithium hydride, lithium powder, lithium hydroxide, lithium trifluoromethanesulfonate, lithium chloride, lithium nitride, lithium aluminum hydride, and lithium borohydride.

[0013] Preferably, the pre-lithiation in S2 is specifically as follows: heating rate is 1-10°C / min, heating to 550-950°C, keeping the temperature for 1-20h and then cooling down.

[0014] Preferably, the carbon source in S3 includes one or more of dopamine hydrochloride, carboxymethyl cellulose, urea, melamine, ascorbic acid, sodium alginate, chitosan, asphalt, phenolic resin, pyridine, pyrrole, polyacrylonitrile, and polyaniline. The mass ratio of the pre-lithiated SiO@C / Li composite material to the carbon source is 1:(1-20).

[0015] Preferably, the solvent in S3 is one or more of water, ethanol, methanol, tris(hydroxymethylaminomethane) hydrochloride buffer solution, dimethyl sulfoxide, N-methylpyrrolidone, 1-butyl-3-methylimidazole chloride, and 1-ethyl-3-methylimidazole tetrafluoroborate.

[0016] Preferably, the sintering conditions are as follows: in an argon atmosphere, the temperature is raised to 450-750° C. at a heating rate of 1-10° C. / min, and the temperature is lowered after being kept at that temperature for 1-6 hours.

[0017] The present invention provides a silicon-oxygen-carbon composite material, which is obtained by the preparation method described in any one of the above technical solutions. The surface layer of the silicon-oxygen material in the bulk phase of the composite material is lithium-reduced to silicon, and the outside is composed of a plasma carbon layer and a porous carbon layer, wherein a plasma carbon coating layer is formed on the surface of SiO, and a heteroatom porous carbon coating layer is constructed on the surface of the material after pre-lithiation, so that the surface conductive layer is kept in contact with the inside, and doping modification is achieved while carbon coating, and the external and internal carbon layers are combined to form a three-dimensional through-conductive network, which provides a channel for the rapid transmission of lithium ions, improves the conductivity of the material, and alleviates volume expansion.

[0018] The silicon-oxygen-carbon composite material provided by the present invention can be used as a negative electrode active material for lithium ion batteries.

[0019] Compared with the prior art, the surface layer of the silicon-oxygen material in the bulk phase of the composite material prepared by the present invention is lithium-reduced to silicon, and the double-layer carbon structure ensures the electrical conductivity and cycle rate performance of the material. The present invention forms a carbon coating structure on the SiO surface in advance through plasma, thereby avoiding the enrichment of lithium silicates caused by too fast reaction rate during the pre-lithiation process. After pre-lithiation, a heteroatom porous carbon coating layer is constructed on the surface of the material, which is combined with the internal carbon layer to form a three-dimensional penetrating conductive network, so that the surface conductive layer continues to maintain contact with the interior, and doping modification is achieved while the carbon is coated. This preparation method reduces the growth of active silicon particles and alleviates volume expansion; at the same time, the three-dimensional penetrating conductive network provides a channel for the rapid transmission of lithium ions, thereby improving the conductivity of the material. Therefore, compared with traditional pre-lithiation materials, the composite negative electrode material has a higher first effect, better conductivity, and good cycle rate performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is the XRD characterization test result of the material obtained in Example 1 of the present invention.

[0021] Figure 2 This is the charge and discharge curve of the material obtained in Example 1 of the present invention.

[0022] Figure 3 This is a cycle performance diagram of the material obtained in Example 1 of the present invention. DETAILED DESCRIPTION

[0023] In order to further illustrate the present invention, the silicon-oxygen-carbon composite material and the preparation method thereof provided by the present invention are described in detail below in conjunction with examples.

[0024] Example 1

[0025] The preparation method of the silicon-oxygen-carbon composite material in this embodiment is as follows

[0026] S1: Weigh 10 g SiO powder (D 50 =5μm) was loaded into a PECVD furnace, argon (200mL / min) was introduced, and the temperature was raised from room temperature to 550°C at 5°C / min. The plasma excitation source was started and the power was adjusted to 100W. Then acetylene gas (20mL / min) was introduced into the PECVD equipment cavity and reacted for 60min. Then the plasma emission source was turned off, the acetylene gas was stopped, and the sample was cooled in an argon atmosphere to obtain carbon-coated SiO@C.

[0027] S2: Weigh 2g of SiO@C in S1 and 0.2g of lithium hydride, put them into a degassing machine for high-energy mixing, heat them to 750°C at 2°C / min under argon atmosphere, keep them warm for 2h, and then cool them down with the furnace; wash them with water, and dry them in vacuum at 60°C to obtain pre-lithiated SiO@C / Li negative electrode material.

[0028] S3) Weigh 0.5g dopamine hydrochloride and dissolve it in 50mL tris(hydroxymethylaminomethane) hydrochloride buffer solution (0.1M, pH=~8.5) and stir for 10min. Weigh 1g pre-lithiated SiO@C / Li material in S2 and add it thereto, stir for 4h, wash it with deionized water and ethanol alternately by centrifugation, freeze-dry it, heat it to 550℃ at 5℃ / min in argon atmosphere, keep it warm for 2h, cool it down and take it out to obtain the prepared silicon-oxygen-carbon composite material.

[0029] Example 2

[0030] The difference from Example 1 is that the reaction temperature in S1 is increased from 550°C to 750°C; and the plasma power is adjusted to 150W.

[0031] Example 3

[0032] The difference from Example 1 is that the lithium hydride in S2 is replaced with lithium powder, the temperature is raised to 650° C. under the protection of argon atmosphere, and the holding time is 2 h.

[0033] Example 4

[0034] The difference from Example 1 is that the dopamine hydrochloride in S3 is replaced by carboxymethyl cellulose, and the tris(hydroxymethyl)aminomethane hydrochloride buffer solution is replaced by 1-ethyl-3-methylimidazole tetrafluoroborate solution.

[0035] Comparative Example 1

[0036] Compared with Example 1, heteroatom carbon coating doping is not performed, and the specific steps are as follows:

[0037] S1: Weigh 10 g SiO powder (D 50 =5μm) was loaded into a PECVD furnace, argon (200mL / min) was introduced, and the temperature was raised from room temperature to 550°C at 5°C / min. The plasma excitation source was started and the power was adjusted to 100W. Then acetylene gas (20mL / min) was introduced into the PECVD equipment cavity and reacted for 60min. Then the plasma emission source was turned off, the acetylene gas was stopped, and the sample was cooled in an argon atmosphere to obtain carbon-coated SiO@C.

[0038] S2: Weigh 2g of SiO@C in S1 and 0.2g of lithium hydride, then put them into a degassing machine for high-energy mixing, heat them to 750℃ at 2℃ / min under argon atmosphere, keep them warm for 2h, and then cool them down with the furnace; wash them with water, and dry them in vacuum at 60℃ to obtain pre-lithiated SiO@C / Li negative electrode material.

[0039] Comparative Example 2

[0040] Compared with Example 1, pre-lithiation is performed first and then plasma coating is performed. The specific steps are as follows:

[0041] S1: Weigh 10 g of SiO powder (D 50 =5μm) and 1g lithium hydride, then put into a degassing machine for high-energy mixing, heat to 750°C at 2°C / min under argon atmosphere, keep warm for 2h, cool down with the furnace; wash with water, and dry in vacuum at 60°C to obtain a pre-lithiated SiO / Li negative electrode material.

[0042] S2: Weigh 10g of pre-lithiated SiO / Li powder in S1 and put it into the PECVD furnace, introduce argon (200mL / min), increase the temperature from room temperature to 550℃ at 5℃ / min, start the plasma excitation source, adjust the power to 100W, and then introduce acetylene gas (20mL / min) into the PECVD equipment cavity for 60min. Then turn off the plasma emission source, stop introducing acetylene gas, and cool the sample in an argon atmosphere to obtain carbon-coated SiO / Li@C.

[0043] S3: Weigh 0.5g dopamine hydrochloride and dissolve it in 50mL tris(hydroxymethylaminomethane) hydrochloride buffer solution (0.1M, pH=~8.5) and stir for 10min. Weigh 1g carbon-coated SiO / Li@C material in S2 and add it, stir for 4h, wash it with deionized water and ethanol by centrifugation alternately, freeze-dry it, heat it to 550℃ at 5℃ / min under argon atmosphere, keep it warm for 2h, cool it down and take it out to obtain the prepared silicon-oxygen-carbon composite material.

[0044] Comparative Example 3

[0045] Compared with Example 1, plasma is not enabled, and the specific steps are as follows:

[0046] S1: Weigh 10 g SiO powder (D 50 =5μm) was placed in a tube furnace, argon (200mL / min) was introduced, and the temperature was raised from room temperature to 550°C at 5°C / min, and then acetylene gas (20mL / min) was introduced and reacted for 60min. The sample was cooled in an argon atmosphere to obtain carbon-coated SiO@C.

[0047] S2: Weigh 2g of SiO@C in S1 and 0.2g of lithium hydride, then put them into a degassing machine for high-energy mixing, heat them to 750℃ at 2℃ / min under argon atmosphere, keep them warm for 2h, and then cool them down with the furnace; wash them with water, and dry them in vacuum at 60℃ to obtain pre-lithiated SiO@C / Li negative electrode material.

[0048] S3: Weigh 0.5g dopamine hydrochloride and dissolve it in 50mL tris(hydroxymethylaminomethane) hydrochloride buffer solution (0.1M, pH=~8.5) and stir for 10min. Weigh 1g pre-lithiated SiO@C / Li material in S2 and add it, stir for 4h, wash it with deionized water and ethanol by centrifugation alternately, freeze-dry it, heat it to 550℃ at 5℃ / min in argon atmosphere, keep it warm for 2h, cool it down and take it out to obtain the prepared silicon-oxygen-carbon composite material.

[0049] Comparative Example 4

[0050] Compared with Example 1, no pre-lithiation was performed, and the specific steps were as follows:

[0051] S1: Weigh 10 g SiO powder (D 50 =5μm) was loaded into a PECVD furnace, argon (200mL / min) was introduced, and the temperature was raised from room temperature to 550°C at 5°C / min. The plasma excitation source was started and the power was adjusted to 100W. Then acetylene gas (20mL / min) was introduced into the PECVD equipment cavity and reacted for 60min. Then the plasma emission source was turned off, the acetylene gas was stopped, and the sample was cooled in an argon atmosphere to obtain carbon-coated SiO@C.

[0052] S2: Weigh 0.5g dopamine hydrochloride and dissolve it in 50mL tris(hydroxymethylaminomethane) hydrochloride buffer solution (0.1M, pH=~8.5) and stir for 10min. Weigh 1g SiO@C material in S1 and add it, stir for 4h, wash it with deionized water and ethanol alternately by centrifugation, freeze-dry it, heat it to 550℃ at 5℃ / min under argon atmosphere, keep it warm for 2h, cool it down and take it out to obtain the prepared silicon-oxygen-carbon composite material.

[0053] The SiO raw materials and the composite materials obtained in Examples 1-4 and Comparative Examples 1-4 were used as negative electrode active materials for lithium-ion batteries and assembled into half cells for electrochemical performance testing.

[0054] The specific experimental process is as follows: the prepared active material is mixed with the conductive agent (Super P), the binder CMC and SBR (mass ratio 6:4) in a mass ratio of 8:1:1 to form a slurry, which is coated on the copper foil. The pole piece is vacuum dried at 100°C for 12 hours and punched into a disc with a diameter of 12mm. The lithium sheet is used as the counter electrode, Celgard 2500 is used as the diaphragm, and 1M LiPF6 is used as the electrolyte. The CR2025 button battery is assembled in the glove box. The assembled battery is left to stand at room temperature for 10 hours, and a constant current charge and discharge test is performed on the Wuhan Blue Electric electrochemical test channel. The current density is 0.1C (1C = 1000mAh / g), the charge cut-off voltage is 2.00V, and the discharge cut-off voltage is 0.005V.

[0055] Table 1: Electrochemical performance of SiO raw materials, Examples 1-4 and Comparative Examples 1-4 silicon-oxygen-carbon composite materials.

[0056]

[0057] As can be seen from Table 1, in Comparative Example 1, no heteroatom carbon coating and doping was performed, the conductivity of the material was poor, the solid-liquid interface between the electrode material and the electrolyte was unstable, and the cycle performance was poor. In Comparative Example 2, pre-lithiation was performed first, the reaction rate was too fast, the silicon particles continued to grow, and more lithium silicates were generated while generating active silicon. The material capacity was limited, the initial efficiency was low, and the expansion was severe. In Comparative Example 3, plasma was not enabled to form a carbon coating layer. After pre-lithiation, the particles grew, the volume expansion of the material was severe, and the cycle stability was poor. In Comparative Example 4, no pre-lithiation was performed, and the silicon and oxygen in the bulk phase of the material failed to combine with lithium in advance to generate silicon, lithium oxide, and lithium silicates, and the initial efficiency of the material was low.

[0058] The material preparation method described in the present invention uses plasma to form a carbon coating structure on the surface of SiO in advance, so that the carbon layer is in close contact with SiO. As an effective buffer coating, it can significantly alleviate the growth and volume expansion of active silicon particles during the pre-lithiation process; avoid the enrichment of lithium silicates caused by too fast reaction rate during the pre-lithiation process, and at the same time alleviate the problems caused by high alkalinity during the pre-lithiation process. After pre-lithiation, a heteroatom porous carbon coating layer is constructed on the surface of the material, which is combined with the internal carbon layer to form a three-dimensional conductive network, providing a channel for the rapid transmission of lithium ions, improving the conductivity of the material, and alleviating volume expansion; improving the interface stability between the electrode material and the electrolyte, and ensuring that the material has high ion and electron transmission efficiency. The preparation method is simple and the process is controllable. The surface layer of the silicon-oxygen material of the prepared composite material phase is lithium-reduced to silicon, and the double-layer carbon structure ensures the conductive performance of the material. The prepared material has high initial efficiency, good cycle performance and rate performance.

[0059] The above description is only a preferred embodiment of the present invention. It should be pointed out that a person skilled in the art can make several improvements without departing from the principle of the present invention, and these improvements should also be regarded as within the protection scope of the present invention.

Claims

1. A method for preparing a silicon-oxygen-carbon composite material, characterized in that: The following steps are involved: S1: Weigh a certain amount of SiO2 and load it into the PECVD equipment, evacuate and heat the PECVD equipment; introduce argon gas, and after the temperature rises to the set temperature, start the plasma excitation source, adjust the power, and introduce the carbon source gas into the PECVD equipment cavity. After a certain reaction time, turn off the plasma, stop introducing the carbon source gas, and cool the sample in the argon atmosphere to obtain the carbon-coated SiO2@C material; S2: Mixing SiO@C material and pre-lithiation agent, pre-lithiation under argon atmosphere, washing with water, and drying to obtain pre-lithiation SiO@C / Li composite material; S3: Add the carbon source containing heteroatoms into the solvent, add the pre-lithiated SiO@C / Li composite material in S2, stir, centrifuge, wash, freeze-dry and sinter to obtain the heteroatom carbon-coated pre-lithiated silicon-oxygen-carbon composite material SiO@C / Li@Cd.

2. The method for preparing the silicon-oxygen-carbon composite material according to claim 1, characterized in that: The carbon source gas in S1 is any one or more of methane, acetylene, ethylene, and ethane, the flow rate of the carbon source gas is 1-100 mL / min, and the flow rate of the argon gas in S1 is 50-300 mL / min.

3. The method for preparing the silicon-oxygen-carbon composite material according to claim 1, characterized in that: The setting temperature in S1 is 400-800° C., the power of the plasma excitation source is 50W-300W, and the reaction time is 10min-120min.

4. The method for preparing the silicon-oxygen-carbon composite material according to claim 1, characterized in that: The mass ratio of SiO@C material and pre-lithium agent in S2 is (2-20):1; the pre-lithium agent is one or more of lithium hydride, lithium powder, lithium hydroxide, lithium trifluoromethanesulfonate, lithium chloride, lithium nitride, lithium aluminum hydride, and lithium borohydride.

5. The method for preparing the silicon-oxygen-carbon composite material according to claim 1, characterized in that: The specific operation of the pre-lithiation in S2 is: heating up to 550-950° C. at a heating rate of 1-10° C. / min, keeping the temperature for 1-20 hours and then cooling down.

6. The method for preparing the silicon-oxygen-carbon composite material according to claim 1, characterized in that: The carbon source in S3 includes one or more of dopamine hydrochloride, carboxymethyl cellulose, urea, melamine, ascorbic acid, sodium alginate, chitosan, asphalt, phenolic resin, pyridine, pyrrole, polyacrylonitrile, and polyaniline, and the mass ratio of the pre-lithiated SiO@C / Li composite material to the carbon source is 1:(1-20).

7. The method for preparing the silicon-oxygen-carbon composite material according to claim 1, characterized in that: The solvent in S3 is one or more of water, ethanol, methanol, tris(hydroxymethyl)aminomethane hydrochloride buffer solution, dimethyl sulfoxide, N-methylpyrrolidone, 1-butyl-3-methylimidazole chloride, and 1-ethyl-3-methylimidazole tetrafluoroborate.

8. The method for preparing the silicon-oxygen-carbon composite material according to claim 1, characterized in that: The specific sintering conditions in S3 are: in an argon atmosphere, the temperature is increased to 450-750°C at a heating rate of 1-10°C / min, and the temperature is reduced after being kept for 1-6 hours.

9. The silicon-oxygen-carbon composite material obtained by the method for preparing the silicon-oxygen-carbon composite material according to any one of claims 1 to 8, characterized in that: The surface layer of the silicon-oxygen material in the bulk phase of the composite material is lithium-reduced to silicon, and the outside is composed of a plasma carbon layer and a porous carbon layer. A plasma carbon coating layer is formed on the SiO surface, and a heteroatom porous carbon coating layer is constructed on the surface of the material after pre-lithiation, so that the surface conductive layer maintains contact with the interior, and doping modification is achieved while the carbon is coated. The external and internal carbon layers jointly form a three-dimensional through-conductive network, which provides a channel for the rapid transmission of lithium ions, improves the conductivity of the material, and alleviates volume expansion.

10. Use of the silicon-oxygen-carbon composite material according to claim 9 as a negative electrode active material for lithium-ion batteries.

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