Current collector-free short carbon fiber reinforced metal compound hard carbon composite sodium ion battery negative electrode material and preparation method thereof

Abstract

The invention relates to the technical field of preparation of sodium ion battery negative electrode materials, in particular to a current collector-free short carbon fiber reinforced metal compound hard carbon compounded sodium ion battery negative electrode material and a preparation method thereof. According to the preparation method, a metal compound and defibered short carbon fibers are added into phenolic resin, a short carbon fiber reinforced metal compound / phenolic resin molding compound sheet is prepared through a blade coating or pressing method, and then a short carbon fiber reinforced metal compound / phenolic resin composite material sheet is prepared through a hot-pressing curing molding process. And carrying out high-temperature sintering pyrolysis to obtain the current collector-free short carbon fiber reinforced metal compound hard carbon composite sodium ion battery negative electrode material. The preparation method provided by the invention is environment-friendly, saves resources, can effectively improve the sodium storage capacity and the electrode structure stability of the sodium ion battery negative electrode material, simplifies the preparation process, and is beneficial to the realization of industrial production.

Description

Technical Field

[0001] This application relates to the technical field of the preparation of negative electrode materials for sodium-ion batteries, and particularly relates to a negative electrode material for a sodium-ion battery prepared by short-cut carbon fiber reinforced metal compound hard carbon without a current collector and a preparation method thereof. Background Art

[0002] To solve the problems of limited reserves of traditional fossil energy and environmental pollution during its development, large-scale energy storage technologies have been developed. Among them, rechargeable secondary batteries represented by lithium-ion batteries (LIBs) have the advantages of high energy density, excellent rate performance, good cycle stability and thermal stability, environmental friendliness and no pollution, and portability, and have become widely used energy storage devices in daily life and industrial production, bringing great convenience to production and life. However, the content of lithium in the earth's crust is only 0.0065%, and 70% of the lithium is distributed in South America. Therefore, long-term large-scale application will be limited by the shortage of lithium resources.

[0003] Sodium and lithium are in the same main group and have the same physical and chemical properties, and the charge and discharge principles of the batteries are basically the same. Moreover, sodium-ion batteries (SIBs) have their unique advantages compared with LIBs. (1) Sodium-ion resources are rich in reserves and widely distributed on the earth; (2) Compared with LIBs, SIBs do not need to use high-priced rare metals such as lithium and cobalt. (3) SIBs have better safety performance compared with LIBs. SIBs have become a battery energy storage technology with great development potential in large-scale energy storage technologies.

[0004] The negative electrode, as one of the main components of SIBs, is divided into alloy type, conversion type and intercalation type.

[0005] The conversion type negative electrode materials can be divided into oxides, sulfides, selenides, phosphides and MOF-based materials. These materials will undergo insertion or alloying reactions during the conversion reaction, but there are problems such as voltage hysteresis, large volume change and slow reaction kinetics during the cycling process, resulting in low energy storage efficiency, poor cycle stability, poor rate performance and low initial Coulomb efficiency (ICE).

[0006] Alloy type negative electrode materials usually mix common alloy elements such as Sb, Sn and P with inert elements (Ni, Mo, Zn, Cu and F) or active elements (Sb, Bi) to prepare intermetallic alloy compounds as negative electrode materials. Among them, antimony (Sb) and bismuth (Bi) have been widely concerned due to their high theoretical specific capacities of 660 and 385 mAhg -1 respectively and moderate working potentials. However, during the cycling process, Sb and Bi will produce volume expansions of about 293% and about 352% respectively, resulting in the collapse of the electrode structure and the instability of the solid electrolyte interface (SEI film), leading to rapid capacity decay.

[0007] Intercalation-type anode materials are based on carbon-based materials. Carbon-based materials are the preferred anodes for SIBs due to their low cost, ease of preparation, low working potential (vs. Na + / Na), and high chemical and thermal stability. Current research on carbon materials mainly includes: graphite, soft carbon, and hard carbon. However, due to the limited storage sites in the crystal structures of most intercalation-type materials, they usually exhibit relatively small reversible capacities. In addition, most layered carbon-based oxides have poor electronic conductivity, which poses another obstacle to electron migration. These factors lead to slow Na + reaction kinetics, severely limiting the development of intercalation-type anodes in SIBs. Summary of the Invention

[0008] To solve the above technical problems, the present application provides a sodium-ion battery anode material composed of short carbon fibers reinforced with metal compounds without a current collector and its preparation method. The present application adds metal compounds and defibrated short carbon fibers to phenolic resin, prepares a short carbon fiber-reinforced metal compound / phenolic resin molding compound sheet by a doctor blade / pressing method, then prepares a short carbon fiber-reinforced metal compound / phenolic resin composite sheet through a hot pressing and curing process, and obtains a sodium-ion battery anode material composed of short carbon fibers reinforced with metal compounds without a current collector through high-temperature sintering and pyrolysis. Using the obtained sodium-ion battery anode material composed of short carbon fibers reinforced with metal compounds without a current collector as the sodium-ion anode eliminates the subsequent process of coating the pyrolyzate onto copper foil / aluminum foil, avoids the use of organic solvents and copper foil / aluminum foil materials in the current preparation process, saves resources, reduces environmental pollution caused by organic solvents, and more importantly, shortens the process flow, realizing the simple and scalable preparation of a sodium-ion battery anode with low volume expansion and high cycle stability. The introduction of metal compounds can increase the Na + storage sites in the hard carbon formed by the sintering of phenolic resin, which is beneficial to the improvement of the sodium storage capacity. Short carbon fibers themselves have conductivity, which not only has little impact on electron migration but also plays a reinforcing role in the hard carbon formed by the pyrolysis of phenolic resin, avoiding the collapse of the electrode structure caused by volume expansion during cycling and can be directly used as an anode to assemble a battery.

[0009] In the first aspect, the present application provides a preparation method for a sodium-ion battery anode material composed of short carbon fibers reinforced with metal compounds without a current collector, adopting the following technical solutions: A preparation method for a sodium-ion battery anode material composed of short carbon fibers reinforced with metal compounds without a current collector, comprising the following steps: S1. Fix the reactor in an oil bath, equip an electric stirrer in the reactor, control the oil bath temperature at 58 - 62 °C, and add phenolic resin; S2. Add a metal compound to the reactor in step S1, start the stirrer at a rotation speed of 200 - 400 r / min, maintain the current temperature, and stir for 10 - 30 minutes to obtain a mixture for standby; S3. Add the chopped carbon fibers after fibrillation to the reactor in step S2, start the stirrer at a rotation speed of 200 - 400 r / min, maintain the current temperature, and stir for 30 - 60 minutes to obtain a chopped carbon fiber reinforced metal compound / phenolic resin mixture; S4. Coat the chopped carbon fiber reinforced metal compound / phenolic resin mixture heated to 58 - 62 °C prepared in step S3 onto a release paper by a doctor - blade method. After drying, obtain a coating with a thickness of 180 - 420 μm to prepare a chopped carbon fiber reinforced metal compound / phenolic resin molding compound sheet; or prepare a chopped carbon fiber reinforced metal compound / phenolic resin molding compound sheet by a pressing method; S5. Cut the chopped carbon fiber reinforced metal compound / phenolic resin molding compound sheet obtained in step S4 according to the size of the used mold, then put it into the mold, and then place the mold in a flat vulcanizing machine to thermally press and cure the chopped carbon fiber reinforced metal compound / phenolic resin molding compound sheet to obtain a chopped carbon fiber reinforced metal compound / phenolic resin composite sheet; S6. Under the protection of an inert atmosphere, perform high - temperature sintering on the chopped carbon fiber reinforced metal compound / phenolic resin composite sheet obtained in step S5 to obtain a sodium - ion battery negative electrode material of chopped carbon fiber reinforced metal compound hard carbon composite without a current collector.

[0010] By adopting the above technical solution, in the process of preparing the anode material of a sodium-ion battery with a current collector-free short-cut carbon fiber reinforced metal compound hard carbon composite, each step has its specific function, and there is also a synergistic effect among these steps. Step S1: This step mainly fixes the reactor in an oil bath and adds phenolic resin. Controlling the oil bath temperature at 58 - 62 °C is to ensure that the phenolic resin reacts at an appropriate temperature. This step provides guarantee for subsequent impregnation and mixing. Step S2: This step is to add the metal compound into the reactor and stir. Stirring enables the metal compound to be fully mixed with the phenolic resin to form a uniform mixture. Step S3: This step is to add the short-cut carbon fiber after defibration into the reactor and stir. The short-cut carbon fiber plays a reinforcing role in this step and is fully mixed with the phenolic resin and the metal compound at the same time. Step S4: This step is to coat the mixture on a release paper or prepare a molding compound sheet by the pressing method. Both coating and pressing are to make the mixture into the required shape and thickness. Step S5: This step is to perform hot pressing and curing on the molding compound sheet. Hot pressing and curing is to tightly bond the materials in the molding compound sheet to form the required composite material sheet. Step S6: The last step is to perform high-temperature sintering on the composite material sheet. High-temperature sintering is to remove the organic components in the material and form a hard carbon structure. The synergistic effect among these steps is mainly reflected in the following aspects: Material mixing and uniform distribution: By stirring and centrifugal filtration, it is ensured that the metal compound, phenolic resin, and short-cut carbon fiber can be evenly distributed, thus guaranteeing the performance consistency of the final material. Reinforcement and structure formation: The short-cut carbon fiber plays a reinforcing role in the composite material sheet and the hard carbon structure during hot pressing and curing and high-temperature sintering processes, which helps to improve the mechanical strength and electrochemical performance of the material, and hot pressing and curing forms a composite material sheet with a stable structure. Sintering: Through high-temperature sintering, the organic components are removed and a hard carbon structure is formed, while maintaining the conductivity and structural stability of the short-cut carbon fiber. In summary, each step not only independently completes specific tasks, but also jointly promotes the preparation process of the current collector-free short-cut carbon fiber reinforced metal compound hard carbon composite through synergistic effects, and finally realizes the preparation of the anode material of a high-performance sodium-ion battery.

[0011] Preferably, the mass ratio of the phenolic resin, the metal compound, and the short-cut carbon fiber after defibration is 100:1 - 10:1 - 8.

[0012] Preferably, the phenolic resin is at least one of thermosetting phenolic resin, nitrogen-containing phenolic resin, phosphorus-containing phenolic resin, and phosphorus-nitrogen-containing phenolic resin; the metal compound is at least one of metal oxide, metal sulfide, and metal phosphide.

[0013] Preferably, the metal oxide is one of SnO2, Sb2O3, and Bi2O3; the metal sulfide is one of SnS2, MoS2, and SoS2; the metal phosphide is Sn4P3.

[0014] Preferably, in step S3, the method for preparing the defibrated short carbon fibers includes the following steps: S51. Add 2000 parts of the dispersion liquid and 2 parts of short carbon fibers to a fiber standard defibrator, and lock the lid of the fiber standard defibrator; S52. Set the rotation speed to 90000 revolutions, start the rotation speed switch, after the rotation speed reaches the set rotation speed, turn off the rotation speed switch, and when the rotation speed is 0, let it stand for another 60 minutes; S53. Set the rotation speed to 90000 revolutions again, start the rotation speed switch, after the rotation speed reaches the set rotation speed, turn off the rotation speed switch, and when the rotation speed is 0, let it stand for 60 - 240 minutes to obtain a mixed liquid; S54. Vacuum filter the mixed liquid, then rinse the short carbon fibers with ionized water 3 times, and then dry at 100 °C for 1 - 3 hours to obtain the defibrated short carbon fibers.

[0015] By adopting the above technical solution, the prepared defibrated short carbon fibers can make the carbon fibers evenly distributed in the composite material, thereby improving the overall mechanical strength of the material; can form an effective conductive path for the carbon fibers in the composite material to improve the electrical conductivity of the material; and can also reduce the thermal expansion coefficient of the material to improve the dimensional stability.

[0016] Preferably, in step S51, the dispersion liquid is an aqueous solution of polyvinyl alcohol with a mass concentration of 0.05%; the short carbon fibers are short carbon fibers with a length of 2 - 6 mm or a combination of short carbon fibers with multiple different lengths.

[0017] Preferably, in step S4, the process method for preparing the short carbon fiber reinforced metal compound / phenolic resin molded plastic sheet by the pressing method is to place the short carbon fiber reinforced metal compound / phenolic resin mixture obtained in step S3 between two layers of release paper, and at room temperature, press it into a sheet in a flat vulcanizing machine at 10 MPa, and the holding pressure time is 10 - 60 seconds. The thickness of the obtained short carbon fiber reinforced metal compound / phenolic resin molded plastic sheet is 150 - 350 μm.

[0018] Preferably, in step S5, the process conditions for hot pressing and curing are a curing temperature of 100 - 180 °C, a stepwise heat preservation time of 3 - 6 hours, and a molding pressure of 1 - 8 MPa.

[0019] Preferably, in step S6, the inert atmosphere is one of nitrogen and argon, and the process conditions for high-temperature sintering are as follows: heating from room temperature to 1200°C at a heating rate of 2-10°C / min. The specific heating method is stepwise heating. Heat from room temperature to 400°C and hold for 1 hour, heat from 400°C to 600°C and hold for 1 hour, heat from 600°C to 800°C and hold for 1 hour, heat from 800°C to 1000°C and hold for 1 hour, and heat from 1000°C to 1200°C and hold for 1 hour.

[0020] In a second aspect, the present application provides a negative electrode material for a sodium-ion battery with a non-current collector short-cut carbon fiber reinforced metal compound hard carbon composite, adopting the following technical solution: As a general technical concept, the present application also provides a negative electrode material for a sodium-ion battery with a non-current collector short-cut carbon fiber reinforced metal compound hard carbon composite, which is prepared by using the preparation method of the negative electrode material for a sodium-ion battery with a non-current collector short-cut carbon fiber reinforced metal compound hard carbon composite described above.

[0021] In summary, the beneficial technical effects of the present application are as follows: 1. Resource conservation and environmental protection: By omitting the processes of using binders and copper foils / aluminum foils, the use of organic solvents and environmental pollution are reduced. At the same time, the preparation process is simplified, resources are saved, and production costs are reduced.

[0022] 2. Improving the sodium storage capacity: The addition of metal compounds increases the Na+ storage sites of the hard carbon formed by the sintering of phenolic resin, thereby improving the sodium storage capacity of the material.

[0023] 3. Enhancing the structural stability of the electrode: The short-cut carbon fiber has good electrical conductivity and at the same time enhances the hard carbon formed by the pyrolysis of phenolic resin. This structural design helps to prevent the collapse of the electrode structure caused by volume expansion during cycling.

[0024] 4. Achieving simple and scalable preparation: The entire preparation process is simple and easy to scale up production, which is conducive to realizing industrial production.

[0025] 5. Improving battery performance: Since a short-cut carbon fiber reinforced metal compound hard carbon composite is used as the negative electrode material, the cycle stability and volume expansion control ability of the sodium-ion battery can be improved, thereby improving the overall battery performance. Description of the Drawings

[0026] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings used in the embodiments will be briefly introduced below: Figure 1Photograph of the sizes of the carbon fiber-reinforced MoS2 / phenolic resin composite sheet and the anode sheet prepared in Example 1; among them, (a) is a φ50 mm carbon fiber-reinforced MoS2 / phenolic resin composite sheet; (b) is a φ12.5 mm carbon fiber-reinforced MoS2 / phenolic resin composite sheet; (c) is a φ12.5 mm carbon fiber-reinforced MoS2 / hard carbon anode sheet; Figure 2 CV and impedance curves of the first three cycles of the sodium-ion half-button battery fabricated from the carbon fiber-reinforced MoS2 / hard carbon anode sheet prepared in Example 1; among them, (a) is the CV curve of the first three cycles of the sodium-ion half-button battery; (b) is the electrochemical impedance curve after 10 cycles of the sodium-ion half-button battery; Figure 3 Galvanostatic charge-discharge curve of the first cycle of the sodium-ion half-button battery fabricated from the carbon fiber-reinforced MoS2 / hard carbon anode sheet prepared in Example 1; Figure 4 Photograph of the sizes of the carbon fiber-reinforced Sb2O3 / phenolic resin composite sheet and the anode sheet prepared in Example 2; among them, (a) is a φ50 mm carbon fiber-reinforced Sb2O3 / phenolic resin composite sheet; (b) is a φ12.5 mm carbon fiber-reinforced Sb2O3 / phenolic resin composite sheet; (c) is a φ12.5 mm carbon fiber-reinforced Sb2O3 / hard carbon anode sheet; Figure 5 CV and impedance curves of the first three cycles of the sodium-ion half-button battery fabricated from the carbon fiber-reinforced Sb2O3 / hard carbon anode sheet prepared in Example 2; among them, (a) is the CV curve of the first three cycles of the sodium-ion half-button battery; (b) is the electrochemical impedance curve after 5 cycles of the sodium-ion half-button battery; Figure 6 Galvanostatic charge-discharge curve of the first cycle of the sodium-ion half-button battery fabricated from the carbon fiber-reinforced Sb2O3 / hard carbon anode sheet prepared in Example 2.

[0027] Figure 7 Electrochemical impedance curve after 5 cycles of the sodium-ion half-button battery fabricated from the carbon fiber-reinforced Sb2O3 / hard carbon anode sheet prepared in Comparative Example 1.

[0028] Figure 8 Galvanostatic charge-discharge curve of the first cycle of the sodium-ion half-button battery fabricated from the carbon fiber-reinforced Sb2O3 / hard carbon anode sheet prepared in Comparative Example 1. Detailed implementation mode

[0029] The implementation scheme of the present application will be described in detail below in conjunction with embodiments. However, those skilled in the art will understand that the following embodiments are only used to illustrate the present application and should not be regarded as limiting the scope of the present application. For those not specified in the embodiments, they are carried out under conventional conditions or conditions recommended by the manufacturer. For reagents or instruments not specified for the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0030] Preparation Example 1 Preparation of Short-Cut Carbon Fibers after Defibration The preparation method of short-cut carbon fibers after defibration includes the following steps: S51. Add 2000 g of an aqueous solution of polyvinyl alcohol with a mass concentration of 0.05% and 2 g of short-cut carbon fibers with a length of 2 - 6 mm to a fiber standard defibrator, and lock the lid of the fiber standard defibrator. S52. Set the rotation speed to 90000 revolutions, start the rotation speed switch. After the rotation speed reaches the set rotation speed, turn off the rotation speed switch. When the rotation speed is 0, let it stand for another 60 minutes. S53. Set the rotation speed to 90000 revolutions again, start the rotation speed switch. After the rotation speed reaches the set rotation speed, turn off the rotation speed switch. When the rotation speed is 0, let it stand for another 180 minutes to obtain a mixed solution. S54. Vacuum filter the mixed solution, then rinse the short-cut carbon fibers with ionized water 3 times, and then dry them at 100 °C for 3 hours to obtain short-cut carbon fibers after defibration.

[0031] Preparation Example 2 Preparation of Thermosetting Phenolic Resin Melt 1 mol (94.1 grams) of phenol in an oven at 60 °C, then add it to a three-necked flask equipped with a thermometer, a condenser (connected to a vacuum take-off tube), and a stirring device. While stirring, add 4.7 grams of aqueous ammonia solution, keep it at 55 °C for 5 minutes, then add 1.3 mol (41.9 grams, purity 93%) of paraformaldehyde, keep it at 60 °C for 1 hour, then raise the temperature to 85 °C and keep it for 3 hours, evacuate under -0.09 MPa for 30 minutes, and pour the synthesized product into a container at 60 °C and seal it and store it in a freezer.

[0032] Preparation Example 3 Preparation of Thermosetting Nitrogen-Containing Phenolic Resin (1) Synthesis of Melamine Formaldehyde Prepolymer Add 20.0 grams of deionized water, 28.2 grams of melamine, 0.14 grams of ammonia water, and 14.5 grams of paraformaldehyde to a three-necked flask equipped with a thermometer, a condenser, and a stirring device. Stir and heat up to 70 °C and keep it warm for 1.5 hours to obtain a melamine formaldehyde prepolymer for use.

[0033] (2) Thermosetting Nitrogen-Containing Phenolic Resin Melt 1 mol (94.1 g) of phenol in an oven at 60 °C, then add it to a three-necked flask equipped with a thermometer, a condenser (connected to a vacuum take-off adapter), and a stirring device. While stirring, add 4.7 g of aqueous ammonia solution, keep it at 55 °C for 5 minutes, then add 1.3 mol (41.9 g, purity 93%) of paraformaldehyde, keep it at 60 °C for 2 hours, then add the melamine formaldehyde prepolymer synthesized in step (1), and raise the temperature to 85 °C and keep it for 1.5 hours. Evacuate at -0.09 MPa for 45 minutes, and pour the synthesized product into a container at 60 °C and store it sealed in a freezer.

[0034] Example 1 A preparation method of a negative electrode material for a sodium-ion battery with a current collector-free short carbon fiber reinforced metal compound hard carbon composite, comprising the following steps: (1) Fix a stainless steel cup equipped with a stirring device in an oil bath at 60 °C, add 16.9 g of thermosetting nitrogen-containing phenolic resin and 1.69 g of MoS2, turn on the stirrer, set the rotation speed to 300 r / min, and stir for 30 minutes at the current temperature; (2) Add 1.2 g of dispersed short carbon fibers to the mixed system in step (1), set the rotation speed to 200 r / min, keep the current temperature, and stir for 30 minutes to obtain a short carbon fiber reinforced MoS2 / phenolic resin mixture; (3) Coat the 60 °C mixture obtained in step (2) onto a release paper by a doctor blade method to control the coating thickness to 300 μm to obtain a short carbon fiber reinforced MoS2 / phenolic resin molding compound sheet; (4) Cut the molding compound sheet obtained in step (3) into circular sheets with a size of φ50 mm, then put them into a mold coated with a release agent, and place the mold in a flat vulcanizing machine to cure and mold the molding compound sheet. The curing process is to keep the temperature at 130 °C for 20 minutes, then apply a pressure of 2 MPa, continue to keep the temperature for 40 minutes, increase the pressure to 5 MPa, then raise the temperature to 150 °C and keep the pressure for 1 hour, then raise the temperature to 170 °C and keep the pressure for 2 hours, cool down to room temperature with the press maintaining the pressure, relieve the pressure and demold to obtain a short carbon fiber reinforced MoS2 / phenolic resin composite sheet with a thickness of 204 μm; (5) Cut the φ50 mm composite sheet obtained in step (4) into φ12.5 mm circular sheets with a cutter, place them in a corundum pot, and put them into a tube furnace, introduce argon, and the flow rate is 0.02 m 3 / min, heating from room temperature to 400 °C, holding for 1 hour, heating from 400 °C to 600 °C and holding for 1 hour, heating from 600 °C to 800 °C and holding for 1 hour, heating from 800 °C to 1000 °C and holding for 1 hour, heating from 1000 °C to 1200 °C and holding for 1 hour, with a heating rate of 5 °C / min. Cooling to room temperature with the furnace to obtain a pyrolysis sheet, i.e., a carbon fiber reinforced MoS2 / hard carbon negative electrode sheet with a thickness of 212 μm.

[0035] Example 2 A preparation method of a sodium-ion battery negative electrode material composed of short-cut carbon fiber reinforced metal compound and hard carbon without a current collector includes the following steps: (1) Fix a stainless-steel cup equipped with a stirring device in an oil bath at 62 °C, add 18.25 g of thermosetting phenolic resin and 0.35 g of Sb2O3, turn on the stirrer, set the rotation speed to 250 r / min, and stir for 20 minutes at the current temperature; (2) Add 1.2 g of defibrated short-cut carbon fiber to the mixed system in step (1), set the rotation speed to 250 r / min, keep the current temperature, and stir for 30 minutes to obtain a short-cut carbon fiber reinforced Sb2O3 / phenolic resin mixture; (3) Place the mixture obtained in step (2) between two layers of release paper, place it on a flat vulcanizer at room temperature, and under a pressure of 10 MPa, hold the pressure for 20 seconds to press it into a short-cut carbon fiber reinforced Sb2O3 / phenolic resin molding compound sheet with a thickness of 200 μm; (4) Cut the molding compound sheet obtained in step (3) into circular sheets with a diameter of φ50 mm, then put them into a mold coated with a release agent, and place the mold in a flat vulcanizer to cure and form the molding compound sheet. The curing process is to hold at 100 °C for 30 minutes, then apply a pressure of 2 MPa and continue to hold for 30 minutes, increase the pressure to 5 MPa, then raise the temperature to 130 °C and hold for 20 minutes, increase the pressure to 7 MPa, continue to hold for 40 minutes, then raise the temperature to 160 °C and hold the pressure for 2 hours, cool to room temperature with the press holding the pressure, release the pressure and demold to obtain a short-cut carbon fiber reinforced Sb2O3 / phenolic resin composite sheet.

[0036] (5) Cut the φ50 mm composite sheet obtained in step (4) into circular sheets with a diameter of φ12.5 mm with a cutting machine, place them in a corundum pot, put them into a tube furnace, introduce argon, with a flow rate of 0.02 m 3 / min, heating from room temperature to 400 °C, holding for 1 hour, heating from 400 °C to 600 °C and holding for 1 hour, heating from 600 °C to 800 °C and holding for 1 hour, heating from 800 °C to 1000 °C and holding for 1 hour, heating from 1000 °C to 1200 °C and holding for 1 hour, with a heating rate of 5 °C / min. Cooling to room temperature with the furnace to obtain a pyrolysis sheet, i.e., a carbon fiber reinforced Sb2O3 / hard carbon negative electrode sheet.

[0037] Example 3 A preparation method of a negative electrode material for a sodium-ion battery with a short-cut carbon fiber reinforced metal compound hard carbon composite without a current collector, comprising the following steps: (1) Fix a stainless steel cup equipped with a stirring device in an oil bath at 58 °C, add 30 g of thermosetting phenolic resin and 3 g of Sn4P3, turn on the stirrer, set the rotation speed to 400 r / min, and stir at the current temperature for 10 minutes; (2) Add 2.4 g of defibrated short-cut carbon fiber to the mixed system in step (1), set the rotation speed to 400 r / min, maintain the current temperature, and stir for 60 minutes to obtain a short-cut carbon fiber reinforced Sn4P3 / phenolic resin mixture; (3) Place the mixture prepared in step (2) between two layers of release paper, place it on a flat vulcanizer at room temperature, and under a pressure of 10 MPa, hold the pressure for 60 seconds to press it into a short-cut carbon fiber reinforced Sn4P3 / phenolic resin molding compound sheet with a thickness of 350 μm; (4) Cut the molding compound sheet obtained in step (3) into a circular sheet with a size of φ50 mm, then put it into a mold coated with a release agent, and place the mold in a flat vulcanizer to cure and form the molding compound sheet. The curing process is to keep the temperature at 100 °C for 30 minutes, then apply a pressure of 2 MPa, continue to keep the temperature for 30 minutes, increase the pressure to 5 MPa, then raise the temperature to 130 °C and keep the temperature for 20 minutes, increase the pressure to 7 MPa, continue to keep the temperature for 40 minutes, then raise the temperature to 180 °C and keep the pressure for 1 hour, and then cool down to room temperature with the press maintaining the pressure, release the pressure and demold to obtain a short-cut carbon fiber reinforced Sn4P3 / phenolic resin composite sheet.

[0038] (5) Cut the φ50 mm composite sheet obtained in step (4) into circular sheets with a size of φ12.5 mm using a cutting machine, place them in a corundum pot, put them into a tube furnace, introduce argon, with a flow rate of 0.02 m 3 / min, rise from room temperature to 400 °C, keep the temperature for 1 hour, rise from 400 °C to 600 °C and keep the temperature for 1 hour, rise from 600 °C to 800 °C and keep the temperature for 1 hour, rise from 800 °C to 1000 °C and keep the temperature for 1 hour, rise from 1000 °C to 1200 °C and keep the temperature for 1 hour, and the heating rate is 2 °C / min. Cool down to room temperature with the furnace to obtain a pyrolysis sheet, that is, a carbon fiber reinforced Sn4P3 / hard carbon negative electrode sheet.

[0039] Comparative Example 1 Same as Example 2, except that short-cut carbon fibers with a length of 2 - 6 mm of equal mass are used instead of defibrated short-cut carbon fibers.

[0040] Performance Test The negative electrode sheets prepared in Example 1, Example 2, and Comparative Example 1 were respectively fabricated into sodium-ion coin cells. The assembly method of the sodium-ion coin cells is as follows: (1) Use a slicing machine to cut the negative electrode sheet into a φ12.5 mm circular sheet, which is the negative electrode material of the sodium-ion battery, and cut the polypropylene separator into a φ19 mm circular sheet; (2) Place the negative electrode material cut in step (1) in the middle of the positive electrode case; (3) Add the electrolyte into the positive electrode case in two times, 75 μL each time. The electrolyte is: 1.5 M NaPF6 in EC / DMC / EMC = 1 / 2 / 2 VOL; (4) Place the separator on the negative electrode material, and then add 150 μL of the electrolyte; (5) Place a sodium sheet, a gasket, and a shrapnel on the separator in sequence; (5) Fasten the negative electrode case, and use a coin cell sealer to encapsulate the assembled battery; (6) Use a lint-free cloth to wipe off the electrolyte extruded and overflowed on the battery.

[0041] Steps (2-6) are all carried out in a glove box filled with an Ar atmosphere.

[0042] The sodium-ion coin cells were subjected to CV, impedance tests, and constant current charge-discharge tests at a rate of 0.1 C. The test results are as shown in Figure 2 、 Figure 3 、 Figure 5 、 Figure 6 、 Figure 7 and Figure 8 shown.

[0043] Figure 1 Figure is a photograph of the dimensions of the carbon fiber-reinforced MoS2 / phenolic resin composite sheet and the negative electrode sheet prepared in Example 1. Among them, (a) is a φ50 mm carbon fiber-reinforced MoS2 / phenolic resin composite sheet; (b) is a φ12.5 mm carbon fiber-reinforced MoS2 / phenolic resin composite sheet; (c) is a φ12.5 mm carbon fiber-reinforced MoS2 / hard carbon negative electrode sheet; the mass of the φ12.5 mm carbon fiber-reinforced MoS2 / phenolic resin composite sheet is 28.0 mg, and the thickness is 204 μm; the mass of the φ12.5 mm carbon fiber-reinforced MoS2 / hard carbon negative electrode sheet is 20.3 mg, and the thickness is 212 μm.

[0044] Figure 2 Figure shows the CV and impedance curves of the first three cycles of the carbon fiber-reinforced MoS2 / hard carbon negative electrode sheet prepared in Example 1 fabricated into a sodium-ion coin cell. As can be seen from Figure 2 when the scanning rate is 0.2 mVs -1 Figure 2 ​(a)The three CV curves overlap, indicating that the sodium-ion half-cell has good reversibility and stable electrochemical performance. Figure 2 (b)The results show that the impedance of the sodium-ion half-cell is 327 Ω.

[0045] Figure 3 The first-cycle galvanostatic charge-discharge curve of the carbon fiber-reinforced MoS2 / hard carbon negative electrode sheet prepared in Example 1 was fabricated into a sodium-ion half-cell. As can be seen from Figure 3 , the initial discharge specific capacity is 135.73 mAhg -1 .

[0046] Figure 4 Photographs of the dimensions of the carbon fiber-reinforced Sb2O3 / phenolic resin composite sheet and the negative electrode sheet prepared in Example 2 are shown. Among them, (a) is a φ50 mm carbon fiber-reinforced Sb2O3 / phenolic resin composite sheet; (b) is a φ12.5 mm carbon fiber-reinforced Sb2O3 / phenolic resin composite sheet; (c) is a φ12.5 mm carbon fiber-reinforced Sb2O3 / hard carbon negative electrode sheet. The mass of the φ12.5 mm carbon fiber-reinforced Sb2O3 / phenolic resin composite sheet is 12.8 mg, and the thickness is 108 μm. The mass of the φ12.5 mm carbon fiber-reinforced Sb2O3 / hard carbon negative electrode sheet is 10.4 mg, and the thickness is 127 μm.

[0047] Figure 5 The CV and impedance curves of the first three cycles of the carbon fiber-reinforced Sb2O3 / hard carbon negative electrode sheet prepared in Example 2 were fabricated into a sodium-ion half-cell. As can be seen from Figure 5 , when the scanning rate is 0.2 mVs -1 Figure 5 (a)The CV curves in the first three cycles highly overlap, indicating that the sodium-ion half-cell has good reversibility and stable electrochemical performance. Figure 5 (b)The electrochemical impedance results show that the impedance of the sodium-ion half-cell is 128 Ω, which is due to the improved conductivity of the exfoliated carbon fiber, reducing the interfacial resistance.

[0048] Figure 6 The first-cycle galvanostatic charge-discharge curve of the carbon fiber-reinforced Sb2O3 / hard carbon negative electrode sheet prepared in Example 2 was fabricated into a sodium-ion half-cell. As can be seen from Figure 6 , the initial discharge specific capacity is 272.87 mAhg -1 , and the exfoliated short carbon fibers significantly improve the integrity of the conductive network, avoiding the coverage of active sites, thus greatly improving the sodium storage capacity.

[0049] Figure 7The electrochemistry impedance curve after 5 cycles of the sodium ion half-button battery fabricated from the carbon fiber reinforced Sb2O3 / hard carbon negative electrode sheet prepared in Comparative Example 1 was processed. As can be seen from Figure 7 that the impedance of the half-button battery is 232 Ω.

[0050] Figure 8 The first cycle constant current charge-discharge curve of the sodium ion half-button battery fabricated from the carbon fiber reinforced Sb2O3 / hard carbon negative electrode sheet prepared in Comparative Example 1 was processed. As can be seen from Figure 8 that the initial discharge specific capacity is 2.95 mAhg -1 . This is because the uncombed carbon fiber causes the fracture of the conductive network and the active sites are covered, resulting in a very low initial discharge specific capacity.

[0051] The above embodiments are only used to explain the technical solutions of the present application rather than to limit them. Although the above embodiments have specifically described the present application, those skilled in the art should understand that the specific implementation manners of the present application can still be modified or equivalently replaced. Any modification and equivalent replacement without departing from the spirit and scope of the present application shall be covered by the protection scope of the present application.

Claims

1. A method for preparing a negative electrode material for a sodium ion battery without a current collector and reinforced with short carbon fiber and a metal compound hard carbon composite, characterized in that: The following steps are involved: S1. Fix the reactor in an oil bath pot, equip the reactor with an electric stirrer, control the oil bath temperature at 58-62°C, and add phenolic resin; S2, adding the metal compound to the reactor in step S1, starting the stirrer at a speed of 200-400 r / min, maintaining the current temperature, stirring for 10-30 minutes to obtain a mixture for standby use; S3, adding the decomposed chopped carbon fibers to the reactor in step S2, starting the agitator at a speed of 200-400 r / min, maintaining the current temperature, and stirring for 30-60 minutes to obtain a chopped carbon fiber reinforced metal compound / phenolic resin mixture; S4, coating the chopped carbon fiber reinforced metal compound / phenolic resin mixture heated to 58-62° C. obtained in step S3 onto release paper by a doctor blade method, and drying to obtain a coating with a thickness of 180-420 μm, thereby obtaining a chopped carbon fiber reinforced metal compound / phenolic resin molding compound sheet; Alternatively, a chopped carbon fiber reinforced metal compound / phenolic resin molding compound sheet is prepared by a pressing method; S5, cutting the chopped carbon fiber reinforced metal compound / phenolic resin molding material sheet obtained in step S4 to a size according to the mold used, and then putting it into the mold, and then putting the mold into a flat vulcanizer to perform hot pressing and curing molding on the chopped carbon fiber reinforced metal compound / phenolic resin molding material sheet to obtain a chopped carbon fiber reinforced metal compound / phenolic resin composite material sheet; S6. Under the protection of an inert atmosphere, the chopped carbon fiber reinforced metal compound / phenolic resin composite material sheet obtained in step S5 is subjected to high-temperature sintering to obtain a current collector-free chopped carbon fiber reinforced metal compound hard carbon composite sodium ion battery negative electrode material.

2. The method for preparing a current collector-free chopped carbon fiber reinforced metal compound hard carbon composite sodium ion battery negative electrode material according to claim 1, characterized in that: The mass ratio of the phenolic resin, the metal compound and the decomposed short-cut carbon fibers is 100:1-10:1-8.

3. The method for preparing a current collector-free chopped carbon fiber reinforced metal compound hard carbon composite sodium ion battery negative electrode material according to claim 1, characterized in that: The phenolic resin is at least one of thermosetting phenolic resin, nitrogen-containing phenolic resin, phosphorus-containing phenolic resin and phosphorus-containing and nitrogen-containing phenolic resin; the metal compound is at least one of metal oxide, metal sulfide and metal phosphide.

4. The method for preparing a current collector-free chopped carbon fiber reinforced metal compound hard carbon composite sodium ion battery negative electrode material according to claim 3, characterized in that: The metal oxide is one of SnO2, Sb2O3 and Bi2O3; the metal sulfide is one of SnS2, MoS2 and SoS2; and the metal phosphide is Sn4P3.

5. The method for preparing a current collector-free chopped carbon fiber reinforced metal compound hard carbon composite sodium ion battery negative electrode material according to claim 1, characterized in that: In step S3, the method for preparing the debonded chopped carbon fibers comprises the following steps: S51, adding 2000 parts of dispersion liquid and 2 parts of chopped carbon fibers into the fiber standard disintegrator, and locking the cover of the fiber standard disintegrator; S52, set the speed to 90,000, start the speed switch, and when the speed reaches the set speed, turn off the speed switch. When the speed reaches 0, let it stand for another 60 minutes; S53, set the speed to 90,000 again, start the speed switch, and when the speed reaches the set speed, turn off the speed switch. When the speed reaches 0, let it stand for 60-240 minutes to obtain a mixed solution; S54, vacuum-filtering the mixed solution, washing the chopped carbon fibers three times with ionized water, and then drying at 100° C. for 1-3 hours to obtain debonded chopped carbon fibers.

6. The method for preparing a current collector-free chopped carbon fiber reinforced metal compound hard carbon composite sodium ion battery negative electrode material according to claim 5, characterized in that: In step S51, the dispersion liquid is a polyvinyl alcohol aqueous solution with a mass concentration of 0.05%; the chopped carbon fibers are chopped carbon fibers with a length of 2-6 mm or a combination of chopped carbon fibers with a plurality of different lengths.

7. The method for preparing a current collector-free chopped carbon fiber reinforced metal compound hard carbon composite sodium ion battery negative electrode material according to claim 1, characterized in that: In step S4, the process method for preparing the chopped carbon fiber reinforced metal compound / phenolic resin molding material sheet by pressing is to place the chopped carbon fiber reinforced metal compound / phenolic resin mixture obtained in step S3 between two layers of release paper, and grind it into a sheet in a flat vulcanizer at room temperature and 10 MPa, and the holding time is 10-60 seconds. The thickness of the obtained chopped carbon fiber reinforced metal compound / phenolic resin molding material sheet is 150-350 μm.

8. The method for preparing a current collector-free chopped carbon fiber reinforced metal compound hard carbon composite sodium ion battery negative electrode material according to claim 1, characterized in that: In step S5, the process conditions of the hot pressing curing molding are curing temperature of 100-180°C, step insulation time of 3-6 hours, and molding pressure of 1-8 MPa.

9. The method for preparing a current collector-free chopped carbon fiber reinforced metal compound hard carbon composite sodium ion battery negative electrode material according to claim 1, characterized in that: In step S6, the inert atmosphere is one of nitrogen and argon, and the process conditions of high-temperature sintering are: heating from room temperature to 1200°C at a heating rate of 2-10°C / min. The specific heating method is step-by-step heating, from room temperature to 400°C, keeping warm for 1 hour, from 400°C to 600°C, keeping warm for 1 hour, from 600°C to 800°C, keeping warm for 1 hour, from 800°C to 1000°C, keeping warm for 1 hour, and from 1000°C to 1200°C, keeping warm for 1 hour.

10. A current collector-free chopped carbon fiber reinforced metal compound hard carbon composite sodium ion battery negative electrode material, characterized in that: The current collector-free chopped carbon fiber reinforced metal compound hard carbon composite sodium ion battery negative electrode material is prepared by the preparation method of the current collector-free chopped carbon fiber reinforced metal compound hard carbon composite sodium ion battery negative electrode material according to any one of claims 1 to 9.

Images