Preparation method and application of low-voltage high-specific-capacity hard carbon and preparation device

Abstract

The application provides a preparation method and application and a preparation device of low-voltage and high-specific-capacity hard carbon. The application mainly synthesizes the hard carbon by applying a voltage pulse to a carbon-containing precursor. The synthesis method can be used for direct synthesis of the precursor into the low-working-voltage and high-platform-capacity hard carbon, and can also be used for modification of the finished hard carbon. The particle size of the hard carbon material prepared by the method does not change obviously, and it can be found through Raman testing that partial graphitization occurs in the treated material, and defects are optimized. The charge-discharge curve of the sodium ion battery assembled by using the material as a negative electrode presents the characteristics of low voltage and high platform capacity, and the sodium ion battery has good cycle stability and rate performance.

Description

Technical Field

[0001] This application relates to the field of materials technology, and in particular to a method for preparing low-voltage, high-specific-capacity hard carbon, its application, and a preparation apparatus. Background Technology

[0002] Hard carbon materials, as one of the main anode materials for sodium-ion batteries, hold a crucial position in the field. Currently, the common synthesis method for hard carbon materials mainly involves prolonged high-temperature treatment of the precursors. Commonly used precursors include biomass precursors, polymer precursors, and fossil fuel precursors.

[0003] As an anode material, the charge-discharge curve of hard carbon materials can be divided into a plateau region and a ramp region. The plateau region voltage is typically below 0.1V, while the ramp region voltage is above 0.1V. Currently, most hard carbon materials provide a significant proportion of capacity in both the plateau and ramp regions. As an anode material, a lower voltage window and a longer plateau region capacity are more conducive to improving the energy density of the entire battery. Therefore, it is necessary to improve the plateau region capacity and reduce the voltage window.

[0004] Traditional methods for synthesizing hard carbon are time-consuming and energy-intensive. Hard carbon materials synthesized using these methods often struggle to simultaneously achieve low operating voltage and high capacity. Lowering the operating voltage inevitably leads to a decrease in overall capacity, while increasing capacity necessitates a higher operating voltage. While hard carbon materials synthesized using phenolic resin as a precursor exhibit a high plateau region, their high cost and complex processes limit their potential for improvement. Therefore, a rapid synthesis technology for low-voltage, high-specific-capacity hard carbon is needed. Summary of the Invention

[0005] This application provides a technology that improves energy efficiency, reduces energy consumption, and shortens preparation time to the second level. It requires only one device to complete both pre-carbonization and the final preparation process, avoiding the drawbacks of traditional methods such as excessively long pyrolysis times, uneven heat distribution, and high energy consumption. The method provided by this invention can not only synthesize hard carbon from precursors but also perform secondary processing on the finished hard carbon to obtain hard carbon materials with lower voltage and higher plateau capacity. The product prepared by this invention differs from the steady-state products of traditional technologies; instead, it utilizes flash evaporation technology to "capture" the hard carbon material, fixing its state at its optimal condition. The technology used can fix the microstructure of hard carbon materials, allowing for precise control over the microstructure (size, number of layers, and number of closed-ring carbon domains, etc.) of hard carbon.

[0006] The particle size of the prepared hard carbon material does not change significantly. Raman testing reveals that partial graphitization occurs in the treated material, and defects are optimized. The charge-discharge curve of the sodium-ion battery assembled with this material as the negative electrode exhibits the characteristics of low voltage and high plateau capacity, and has good cycle stability and rate performance.

[0007] Typically, in one embodiment, the present invention is characterized by a method for preparing low-voltage, high-specific-capacity hard carbon, which includes synthesizing hard carbon by applying a voltage pulse to a carbon-containing precursor.

[0008] Embodiments of the present invention include one or more of the following features:

[0009] The duration of the voltage pulse can be from 0.1 to 1000 seconds.

[0010] The carbon-containing precursor includes at least one of all non-hard carbon-containing precursors and hard carbon precursors. Hard carbon precursors refer to finished hard carbon products. Traditional methods synthesize hard carbon from non-hard carbon-containing precursors, while the method of this application can synthesize hard carbon materials with superior performance based on hard carbon synthesized by traditional methods. Therefore, the hard carbon precursors mentioned in this application are finished hard carbon products or commercially available hard carbon.

[0011] The non-hard carbon carbon-containing precursors include at least one of the following: biomass-based precursors, synthetic polymer precursors, fossil fuel-based precursors, etc.

[0012] The biomass-based precursors include at least one of the following: recycled cotton, walnut shells, oak, cherry blossom petals, kelp, lignin, grapefruit peel, lotus root stems, chitosan, artichoke cysts, eggshell membranes, animal and plant tissues, cork, xylose, argan shells, mangosteen shells, and pine cones.

[0013] The synthetic polymer precursor includes at least one of the following: phenolic resin, polyacrylonitrile, polyvinylpyrrolidone, polyvinylpyrrole, polyaniline, polyethylene dioxythiophene, sodium polyacrylate, polyvinyl chloride, polyamic acid, triblock copolymer, etc.

[0014] Fossil fuel-based precursors include at least one of the following: bitumen, asphalt, coal tar, anthracite, petroleum, etc.

[0015] The processing methods for the non-hard carbon precursors include pre-carbonization and no pre-carbonization. The carbonization process of non-hard carbon precursors produces a lot of tar and gases, etc. Pre-carbonization can end these products in advance, thereby reducing similar products in the subsequent carbonization process.

[0016] Prior to the preparation method, the pre-carbonization temperature of the pre-carbonization treatment is 500–900°C.

[0017] Prior to the preparation method, the heating rate of the pre-carbonization temperature is 1–20 °C / min.

[0018] Prior to the preparation method, the holding time at the pre-carbonization temperature is 0.1 to 72 hours, which is the highest holding time.

[0019] Before the preparation method, the specific operation of the pre-carbonization treatment is to dry the product and place it in a tube furnace, heat it to the pre-carbonization temperature under an inert atmosphere and keep it at that temperature, and then let the tube furnace cool naturally to room temperature after completion.

[0020] Prior to the preparation method, the non-hard carbon precursor comprises a non-hard carbon-containing precursor with added conductive agent and a non-hard carbon-containing precursor without added conductive agent.

[0021] The conductive agent is selected from anthracite, biochar treated at higher temperatures, calcined petroleum coke, carbon nanotubes, graphene quantum dots, acetylene black, carbon black, sub-graphite, graphene, or mixtures thereof; the conductive precursor additive is added to the non-hard carbon-containing precursor material with lower electrical conductivity, so that the non-hard carbon-containing precursor material with lower electrical conductivity has sufficient electrical conductivity to obtain hard carbon products by the preparation method.

[0022] Prior to the preparation method, the mass ratio of the conductive agent in the mixture of the conductive agent and the non-hard carbon-containing precursor was 1% to 50%.

[0023] Prior to the preparation method, the carbon-containing precursor includes a composite carbon-containing precursor with added binder and a carbon-containing precursor without binder.

[0024] Prior to the preparation method, the binder used in the carbon-containing precursor with added binder includes at least one of the following: sodium carboxymethyl cellulose (CMC), hydroxypropyl methyl cellulose (HPMC), hydroxyethyl cellulose (HEC), methyl cellulose (MC), polyanionic cellulose (PAC), hydroxypropyl cellulose (HPC), polyvinyl alcohol (PVA), sodium polyacrylate (PAA), styrene-butadiene rubber (SBR), sodium alginate, starch, molasses, and asphalt.

[0025] Prior to the method, the binder contained in the carbon-containing precursor containing the binder had a mass fraction of 1 to 50%.

[0026] The method for processing the carbon-containing precursor is as follows: after changing the atmosphere, adjust the current and voltage of the power supply, use a voltage pulse method to rapidly heat up the carbon-containing precursor and maintain it for a period of time, disconnect the power supply, and take out the material after it cools down to room temperature.

[0027] The current across the sample can be 0.01 to 1000 A.

[0028] The voltage across the sample can be 1 to 500V.

[0029] The temperature at which the sample is heated can be 500–3000°C.

[0030] The sample atmosphere can be at least one of the following: low vacuum (<10 Pa), helium, argon, and nitrogen.

[0031] The synthesized sample can be hard carbon, and its collection yield can be 1-100%.

[0032] The collected product can be a low-voltage, high-platform-capacity hard carbon.

[0033] The method can be a continuous method.

[0034] The method can be an automated method.

[0035] The method can use alternating current.

[0036] The method can use direct current.

[0037] Typically, in another embodiment, the invention is characterized by a method comprising synthesizing hard carbon by applying a voltage pulse to a carbon-containing precursor, wherein heteroatoms are present when the voltage pulse is applied to the carbon-containing precursor to provide a doped or heteroatom-containing hard carbon product.

[0038] Embodiments of the present invention may include one or more of the following features:

[0039] The heteroatoms can be selected from nitrogen, phosphorus, boron, and mixtures thereof.

[0040] The heteroatoms can be selected from metals, half-metals, and mixtures thereof.

[0041] The heteroatom source can be selected from melamine, aminoborane, melamine-formaldehyde resin, phosphine, phosphate, metal salt, metal oxide and mixtures thereof.

[0042] Typically, in another embodiment, the present invention is characterized by an apparatus comprising a reaction chamber, positive and negative electrodes disposed within the reaction chamber, and a carrier or insulating tube supporting hard carbon, wherein the carrier is provided with retainers at both ends, the retainers being locked onto the positive and negative electrodes respectively, the positive and negative electrodes being connected to a pulse power supply disposed outside the reaction chamber via wires, and the reaction chamber being provided with a vacuum pump, an inlet valve, and an outlet valve.

[0043] Embodiments of the present invention include one or more of the following features:

[0044] The heating method can be direct heating, which involves applying the voltage directly to the electrodes connected to both ends of a conductive sample (such as a carbon material film) to complete the high-temperature heat treatment of the sample; or by rotating the electrodes to apply pressure, forming a circuit with the sample to be heated in contact, thus completing the direct heating of the sample.

[0045] The heating method can be indirect heating, which is achieved by loading or clamping the sample to be heated onto the surface or between layers of a conductive carrier and applying the voltage to the sample.

[0046] The electrode is equipped with a liquid cooling device. The coolant can be water, organic solvent, or a mixture thereof. The coolant passes through the positive and negative electrodes respectively. The coolant inlet and outlet are connected to the cooling device through water pipes, which ensures that the electrode will not overheat during the heating process, thus achieving heat preservation for more than 10 minutes.

[0047] The carrier can be a carbon material, such as carbon cloth, carbon felt, carbon paper, graphite sheet, etc., or a metal with a high melting point (above 1400℃), such as tungsten, molybdenum, tantalum, zirconium, niobium or their metal alloys.

[0048] The carrier has a length of 1-20cm and a width of 1-10cm.

[0049] The insulating tube material can be quartz, mullite refractory, corundum refractory, alumina ceramic, magnesium oxide ceramic, zirconium oxide ceramic, aluminum nitride ceramic, silicon nitride ceramic, boron nitride ceramic, or silicon carbide ceramic.

[0050] The electrode rod material can be at least one of copper, tungsten, stainless steel, tungsten steel, and graphite.

[0051] The electrode is located in the center of the reaction chamber, and the high-transparency quartz window for external temperature measurement is placed in the center of the instrument for easy observation.

[0052] The inlet valve and outlet valve are located on the same side, opposite side, or adjacent side of the reaction chamber.

[0053] The connection between the reaction chamber and the wire is equipped with a mounting clip. When the electrode is placed in the chamber, the electrode can be connected to the chamber through the clip, thus sealing the chamber. The clip is a snap ring structure; after the electrode mounting plate and the chamber are connected, the snap ring clamps them together to achieve a sealed connection.

[0054] The volume of the reaction chamber can be 1 to 104 L.

[0055] The beneficial effects of this application are as follows: The method provided by this invention can synthesize hard carbon from precursors, and can also perform secondary processing on the finished hard carbon to obtain hard carbon materials with lower voltage and higher plateau capacity. The product prepared by this invention differs from the steady-state products of traditional technologies; instead, it utilizes flash evaporation technology to "capture" the hard carbon material, fixing its state to its optimal condition. The technology used can fix the microstructure of hard carbon materials, precisely controlling the microstructure of hard carbon (size, number of layers, and number of closed-ring carbon domains, etc.).

[0056] The particle size of the prepared hard carbon material does not change significantly. Raman testing reveals that partial graphitization occurs in the treated material, and defects are optimized. The charge-discharge curve of sodium-ion batteries assembled with this material as the negative electrode exhibits characteristics of low voltage and high plateau capacity, as well as good cycle stability and rate performance. Furthermore, the synthesis speed is fast and the energy consumption is low, enabling commercial mass production and facilitating its widespread application. Attached Figure Description

[0057] Figure 1 The image shows the XRD pattern of the hard carbon synthesized in Example 1 of this invention. Curve 1 is the XRD pattern of the hard carbon precursor, and curve 2 is the XRD pattern of the synthesized hard carbon material.

[0058] Figure 2 These are the laser Raman spectra before and after flash evaporation in Example 1 of the present invention. Curve 1 is the Raman spectrum of the hard carbon precursor, and curve 2 is the Raman spectrum of the synthesized hard carbon material.

[0059] Figure 3 The images show the SEM and TEM images of the hard carbon synthesized in Example 1 of this invention.

[0060] Figure 4 This is a graph showing the first charge-discharge curves of a battery assembled with hard carbon before and after synthesis, using the hard carbon as a sodium-ion anode material, as described in Example 2 of the present invention.

[0061] Figure 5 The graph shows the rate performance of batteries assembled with the hard carbon before and after the synthesis of hard carbon in Example 2 of this invention as sodium-ion anode materials at current densities of 30, 60, 150, 300, 600, and 1500 mA / g.

[0062] Figure 6 The graph shows the hard carbon synthesized in Example 2 of this invention before and after being used as a sodium ion anode material during long-cycle operation at a current density of 300 mA / g.

[0063] Figure 7 This is the first charge-discharge curve of the battery assembled using hard carbon obtained after polydopamine treatment as a sodium-ion anode material in Example 3 of the present invention.

[0064] Figure 8 The image shows the hard carbon synthesized from phenolic resin in Example 4 of this invention and its Raman spectroscopy.

[0065] Figure 9 This is a Raman diagram of anthracite and its processed form from Example 5 of the present invention.

[0066] Figure 10 This is a Raman diagram of hard carbon after being treated at the same temperature for different times in Example 7 of the present invention.

[0067] Figure 11 Raman diagrams of hard carbon treated at different temperatures in Example 6 of the present invention.

[0068] Figure 12 This is a schematic diagram of the apparatus for preparing low-voltage, high-specific-capacity hard carbon according to this application.

[0069] Figure 13 This is a schematic diagram of the heating of a conductor sample in the apparatus for preparing low-voltage, high-specific-capacity hard carbon according to this application.

[0070] Figure 14 This is a schematic diagram of the heating of a non-conductive sample in the apparatus for preparing low-voltage, high-specific-capacity hard carbon according to this application.

[0071] Figure 15 This is a schematic diagram of the heating of the rotating electrode in the apparatus for preparing low-voltage, high-specific-capacity hard carbon according to this application.

[0072] Figure 16 This is a schematic diagram of the electrode water cooling device of the apparatus for preparing low-voltage, high-specific-capacity hard carbon according to this application.

[0073] Figure 17 This is a schematic diagram of the apparatus structure for a continuous preparation method of low-voltage, high-specific-capacity hard carbon according to this application.

[0074] Explanation of reference numerals in the attached figures:

[0075] 1-Pulse power supply; 2-Reaction chamber; 3-Fixer; 4-Carrier; 5-Electrode; 6-Wire; 7-Snap-on; 8-Outlet valve; 9-Inlet valve; 10-Vacuum pump; 11-Sample; 12-Water cooling device. Detailed Implementation

[0076] The following detailed description, with appropriate reference to the accompanying drawings, discloses an embodiment of a method for preparing low-voltage, high-specific-capacity hard carbon, its application, and a preparation apparatus. However, unnecessary details may be omitted. For example, detailed descriptions of well-known facts and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0077] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0078] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0079] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0080] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0081] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0082] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0083] This invention discloses a novel method for synthesizing low-voltage, high-platform-capacity hard carbon using flash evaporation technology. The method can be completed in less than 1 minute. The technology allows for precise control of the microstructure of hard carbon materials, including the size, number of layers, and number of closed-ring carbon domains in graphitized carbon. The carbon-containing precursors used can be derived from any stage in the traditional hard carbon material synthesis process.

[0084] For heating purposes, non-hard carbon precursors with poor electrical conductivity can be ground with a conductive agent (such as carbon) to improve the conductivity of the mixture. Non-hard carbon precursors with good electrical conductivity can skip this process. The mixed carbon precursors can be mixed with a binder and pressed into tablets or used directly, depending on the requirements. The proportion of binder used depends on the particle size and physical properties of the carbon material.

[0085] This application utilizes rapid heating and cooling to induce novel structures containing nano-graphite crystallites in hard carbon materials. Due to the different growth rates of the La and Lc graphite crystallites, the optimal value of their combined influence is found using flash evaporation technology. This method employs the Joule heating principle, controlling the temperature by adjusting the pulse current magnitude. During this process, the maximum pulse current is limited by voltage, and the upper limit of the pulse current can be adjusted by regulating the voltage. This method is primarily optimized through time; excessively short heating times cannot achieve high plateau capacity in hard carbon materials, while excessively long times lead to a simultaneous decrease in both plateau capacity and overall capacity. Unlike existing technologies that employ hour-level steady-state heating to produce steady-state results, this method uses second-level transient heating to achieve transient structures in hard carbon materials.

[0086] In this application, the voltage pulse treatment of the material is greatly affected by time. Since the synthesized product is a kinetic product, the time cannot be too long, and a good material can only be obtained within a specific time period.

[0087] A device for preparing low-voltage, high-specific-capacity hard carbon includes a reaction chamber 2, positive and negative electrodes 5 disposed within the reaction chamber 2, and a carrier 4 clamping a thin film sample 11. The carrier 4 has retainers 3 at both ends, which are respectively locked onto the positive and negative electrodes 5. The positive and negative electrodes 5 are connected to a pulse power supply 1 disposed outside the reaction chamber 2 via wires 6. The reaction chamber 2 is equipped with a vacuum pump 10, an inlet valve 9, and an outlet valve 8. Figure 12 As shown.

[0088] When the sample is conductive, direct heating can be used, such as for carbon material thin films. In this case, the fixture 3 and the support 4 are not necessary, or either the fixture 3 or the support 4 can be used. Figure 13 As shown; during assembly, corresponding electrodes are connected to both ends of the sample to apply the voltage, completing the high-temperature heat treatment of the sample; or pressure is applied by rotating the electrodes, such as... Figure 15 It forms a circuit with the sample to be heated in contact with it, thus completing the direct heating of the sample.

[0089] When the sample is non-conductive, indirect heating is used. This is achieved by loading or clamping the sample to be heated onto the surface or between layers of a conductive carrier and applying the voltage, i.e., through a fixture and carrier. Figure 14 This completes the indirect heating of the sample.

[0090] It also includes fixing the conductive sample 11 with a fixture 3, the fixture 3 being locked onto the positive and negative electrodes 5 respectively, and the positive and negative electrodes 5 being connected to the pulse power supply 1 set outside the reaction chamber 2 via wires 6.

[0091] It also includes directly contacting the conductive sample 11 by rotating the positive and negative electrodes 5, which are connected to the pulse power supply 1 located outside the reaction chamber 2 via wires 6.

[0092] A liquid cooling device 12 was added to electrode 5. Coolant passes through both electrodes 5, and the inlet and outlet of the coolant are connected to the cooling device, ensuring that the electrodes do not overheat during the heating process. Figure 16 As shown. Therefore, heat preservation for more than a few minutes can be achieved, which is expected to enable the rapid preparation of high-quality hard carbon.

[0093] The fixture 3 consists of two clamping plates, and the carrier 4 is fixed between the two clamping plates.

[0094] The carrier 4 can be a carbon material, such as carbon cloth, carbon felt, carbon paper, graphite sheet, graphene film, etc., or a metal with a high melting point (above 1400℃), such as tungsten, molybdenum, tantalum, or their metal alloys, or it can be the conductive sample itself. The sample is directly fixed between the fixtures to form a circuit.

[0095] The electrode 5 is located at the center of the reaction chamber 2, and the external temperature measuring instrument window is placed at the center of the instrument for easy observation.

[0096] The inlet valve 9 and the outlet valve 8 are located on the same side, opposite side, or adjacent side of the reaction chamber 2.

[0097] The connection between the reaction chamber 2 and the wire 6 is provided with a mounting buckle 7. When the electrode 5 is placed in the chamber, the electrode 5 can be connected to the chamber through the mounting buckle 7, and the chamber can be sealed.

[0098] The operating procedure is as follows: First, the hard carbon-binder composite film sample 11 is clamped and fixed to the fixture 3 using the carrier 4. The fixture 3 is then fixed between the two electrodes 5 with screws. The electrodes 5 are placed in the center of the reaction chamber 2, and the buckle 7 is installed to seal the reaction chamber 2. The inside of the reaction chamber 2 is evacuated to a vacuum using the vacuum pump 10. Argon gas is introduced through the inlet valve 9, and after the gas pressure reaches atmospheric pressure, it is closed. This operation is repeated twice. Finally, the argon gas supply is kept constant, and the outlet valve 8 is opened. The outer side of the electrode 5 is connected to the pulse power supply 1 using the wire 6, and the required pre-carbonization and graphitization reaction parameters are set on the pulse power supply. After the settings are completed, the pulse power supply 1 is started. The carrier instantly reaches a high temperature, the reaction is completed, and the hard carbon material is obtained.

[0099] In the preparation method of this application, the pre-carbonization temperature is below 1000 degrees Celsius, and the graphitization temperature is above 1000 degrees Celsius. Graphitization will occur when the material is heated at high temperatures for a certain period of time. All operations described in this method are conditional steps for graphitization; short-term, low-temperature treatment will generally not result in graphitization, while long-term high-temperature treatment will. In fact, the pre-carbonization step essentially occurs during the graphitization process. The pre-carbonization process involves gas generation and other behaviors, essentially extending the holding time at low temperatures before high-temperature treatment. Direct graphitization, on the other hand, is direct high-temperature treatment. Generally, whether or not pre-carbonization is performed during the operation is mainly to ensure more complete decomposition of the material.

[0100] To achieve the continuous and automated preparation method described in this application, the apparatus comprises a carbon raw material; a non-conductive container operable to confine the carbon-containing precursor; and electrodes operable to apply voltage pulses to the carbon-containing precursor within the non-conductive container for continuous and automated synthesis of hard carbon.

[0101] It also includes one or more of the following structures:

[0102] The device further includes a conduit through which carbon-containing precursors can be transported into a non-conductive container.

[0103] The device further includes a chamber in which a non-conductive container can be positioned when a voltage pulse is applied to the electrodes.

[0104] Non-conductive containers contain quartz or ceramic materials.

[0105] The non-conductive container contains a quartz tube.

[0106] The apparatus includes a plurality of non-conductive containers; further includes a belt or screw and a collection box; the belt or screw is operable to convey containers of the plurality of non-conductive containers into the chamber after the carbon-containing precursor has been filled into the non-conductive containers; and to convey the non-conductive containers out of the chamber so that the synthesized hard carbon can be collected in the collection box.

[0107] For industrial production, the preparation method can be automated for continuous hard carbon synthesis. Figure 17 This is a continuous, automated method for preparing hard carbon, featuring a belt 20 and gears (first gear 13 and second gear 14). The rotational movement of gears 13-14 is synchronized with the movement of the belt 20, and each gear has separate components for preheating and flash evaporation. Specifically, the first gear 13 has electrodes 25 for compression and preheating, and the second gear 14 has electrodes 26 for FJH pulses. The line speed can be at least 60 pps. The belt 20 has a quartz (or ceramic) tube 17 that can be removed and replaced. Figure 14As shown, the quartz tube 17 can be mounted on a spring with a weak frictional engagement away from gears 13, 14, and protrudes beyond the cylindrical electrodes. This forms a cup with electrode 24 at the bottom of the quartz tube 17, and the precursor powder feed 16 is measured into the quartz cup 17. The measured feed can be a screw, gear, or piston feed, and is typically straight-line, thus a variety of powder feeds are available. The belt 20 can be moved by a roller 19, which may be metal. When electrode 25 in the first gear 13 engages, it protrudes into the top of the quartz cup 17, compressing the precursor powder. When electrode 26 in the second gear 14 engages, an electrical pulse converts the sample into hard carbon. The apparatus includes a series of gas jets 15 that can blow cold air onto the electrodes (electrodes 24, 25, 26). The air blown from the gas jets 15 can also be used to clean the quartz cup 17 and remove particles (spraying water is also optional). To remove hard carbon from the quartz cup, the quartz cup can be lowered (it is lowered by...) Figure 14 The quartz cup 21 (represented by nozzle 22) is used to remove hard carbon from the quartz cup 21 and collect it in a collection box 23. Since hot carbon atoms are highly reducing and corrosive, they can damage the quartz cup 17. A wheel or robotic arm 18 can remove, for example, one-tenth of the quartz cup for cleaning or replacement, and the newly provided clean cup is further rotated along the belt 20. Using such a simple replacement scheme, low-expansion borosilicate (Pyrex) can be suitable (Pyrex has been tested and it performs well), and the cost is far lower than that of a quartz tube / cup. Since damage tends to be cumulative, frequent cleaning of the quartz cup allows for many cycles of reuse.

[0108] The apparatus for preparing the hard carbon of this application also includes one or more of the following technical features:

[0109] The device includes a plurality of capacitors operable to apply the voltage pulse.

[0110] The device includes a controller and a mechanical relay operable to control the application of the voltage pulse.

[0111] The device includes an inductor and a diode operably connected to a controller and a mechanical relay.

[0112] The device further includes a cut-off switch.

[0113] The apparatus is operable for a continuous method of synthesizing hard carbon from the carbon-containing precursor.

[0114] The apparatus is operable to perform an automated method for synthesizing hard carbon from the carbon-containing precursor.

[0115] Typically, in another embodiment, the invention is characterized by an apparatus that includes the apparatus described above.

[0116] Embodiments of the present invention include one or more of the following features:

[0117] The device can be operatively connected to a DC voltage source.

[0118] The device can be operatively connected to an AC voltage source.

[0119] The device can be operatively connected to a power source that uses three-phase power.

[0120] The power supply can use three-phase power, followed by full-wave rectification.

[0121] The power supply can use a zero-crossing relay to control the duration of the voltage pulse.

[0122] The power supply may further include computer control, wherein the computer control is operable to select the duration of the voltage pulse based on the number of half-cycles allowed to pass through the zero-crossing relay.

[0123] The power supply is operable to use one of the following: 120, 208, 277, or 480 volts AC (RMS) three-phase.

[0124] The power source may include a three-phase generator operable to provide AC power.

[0125] The three-phase generator can be mechanically connected to the AC motor.

[0126] The three-phase generator may include a rotor. The three-phase generator may be operable to rapidly convert mechanical power into electric current to provide AC power through the inertia of the rotor.

[0127] The three-phase generator may include a flywheel. The three-phase generator may be operable to use the flywheel to provide AC power in order to provide longer duration and stable voltage and current output.

[0128] The device may include a plurality of capacitors operable to apply voltage pulses. The device may also include a controller and a mechanical relay operable to control the application of the voltage pulses.

[0129] A low-voltage, high-specific-capacity hard carbon preparation technique involves loading a carbon-containing precursor into a reaction chamber, activating a pulsed power supply, and heating the carbon-containing precursor sample using a temperature program that includes:

[0130] (1) Set the working voltage to 10-500V, the working current to 0.01-1000A, and the room temperature to 500-3000℃;

[0131] (2) Keep warm in a vacuum environment for 0.1–1000 s;

[0132] (3) Let it cool to room temperature;

[0133] In some embodiments, the aforementioned carrier is a carbon material, such as carbon cloth, carbon felt, carbon paper, graphite sheet, graphene film, etc., or it can be a metal with a high melting point, preferably carbon felt.

[0134] In some embodiments, the aforementioned applied voltage is 10 to 500V, preferably 40 to 70V.

[0135] In some embodiments, the pulse duration is 0.1 to 1000 s, preferably 10 to 40 s.

[0136] In some embodiments, the applied current is 0.01 to 1000 A, preferably 50 to 100 A.

[0137] In some embodiments, the heating temperature is 500–3000°C, preferably 1300–1700°C.

[0138] In some embodiments, the carbon-containing precursor is placed in a certain atmosphere, such as at least one of low vacuum (<10 Pa), helium, argon, and nitrogen, preferably argon.

[0139] The carbon-containing precursor is at least one of a non-hard carbon-containing precursor and a hard carbon precursor.

[0140] The non-hard carbon carbon-containing precursors include at least one of the following: biomass-based precursors, synthetic polymer precursors, fossil fuel-based precursors, etc.

[0141] The biomass-based precursors include at least one of the following: recycled cotton, walnut shells, oak, cherry blossom petals, kelp, lignin, grapefruit peel, lotus root stems, chitosan, artichoke cysts, eggshell membranes, animal and plant tissues, cork, xylose, argan shells, mangosteen shells, and pine cones.

[0142] The synthetic polymer precursor includes at least one of the following: phenolic resin, polyacrylonitrile, polyvinylpyrrolidone, polyvinylpyrrole, polyaniline, polyethylene dioxythiophene, sodium polyacrylate, polyvinyl chloride, polyamic acid, triblock copolymer, etc.

[0143] Fossil fuel-based precursors include at least one of the following: bitumen, asphalt, coal tar, anthracite, petroleum, etc.

[0144] The processing methods for the non-hard carbon precursors include pre-carbonization and no pre-carbonization. The carbonization process of non-hard carbon precursors produces a lot of tar and gases, etc. Pre-carbonization can end these products in advance, thereby reducing similar products in the subsequent carbonization process.

[0145] Pre-carbonization is not necessary, and most materials will go through the process of material-amorphous carbon material-hard carbon at temperatures of 0-1500℃ or even higher. Pre-carbonization is to stay in the second process for a longer time.

[0146] Prior to the preparation method, the non-hard carbon precursor comprises a non-hard carbon-containing precursor with added conductive agent and a non-hard carbon-containing precursor without added conductive agent.

[0147] The conductive agent is selected from anthracite, biochar treated at higher temperatures, calcined petroleum coke, carbon nanotubes, graphene quantum dots, acetylene black, carbon black, sub-graphite, graphene, or mixtures thereof; the conductive precursor additive is added to the non-hard carbon-containing precursor material with lower electrical conductivity, so that the non-hard carbon-containing precursor material with lower electrical conductivity has sufficient electrical conductivity to obtain hard carbon products by the preparation method.

[0148] Prior to the preparation method, the mass ratio of the conductive agent in the mixture of the conductive agent and the non-hard carbon-containing precursor was 1% to 50%.

[0149] Prior to the preparation method, the carbon-containing precursor includes a composite carbon-containing precursor with added binder and a carbon-containing precursor without binder.

[0150] In practical applications, conductive agents or binders can be mixed together and then ground.

[0151] Prior to the preparation method, the binder used in the carbon-containing precursor with added binder includes at least one of the following: sodium carboxymethyl cellulose (CMC), hydroxypropyl methyl cellulose (HPMC), hydroxyethyl cellulose (HEC), methyl cellulose (MC), polyanionic cellulose (PAC), hydroxypropyl cellulose (HPC), polyvinyl alcohol (PVA), sodium polyacrylate (PAA), styrene-butadiene rubber (SBR), sodium alginate, starch, molasses, and asphalt.

[0152] Prior to the method, the binder contained in the carbon-containing precursor containing the binder had a mass fraction of 1 to 50%.

[0153] Example 1

[0154] Combining the above steps, the sample is loaded into the reaction chamber, and the pulse power supply is started. The temperature program for heating the carbon-containing precursor includes:

[0155] The operating voltage was set to 50V and the operating current to 100A. The temperature was increased from room temperature to 1500℃ and held for 15 seconds. The XRD patterns of the carbon-containing precursor and the resulting sample are shown below. Figure 1 As shown, X-ray diffraction reveals a rightward shift of the 002 peak at 25°. In contrast, the 002 peak in crystalline carbon materials shows no significant change. Further analysis of the XRD data reveals that the interlayer spacing of the heat-treated carbon materials has decreased.

[0156] Raman spectra of carbon-containing precursors and the resulting samples are shown below. Figure 2 As shown, compared with the untreated sample (Comparative Example 1), the treated hard carbon showed a significant 2D peak, indicating that the treated sample underwent partial graphitization.

[0157] SEM and TEM images of the carbon-containing precursor and the resulting sample are as follows: Figure 3 As shown. From top to bottom and left to right, the images are: SEM of carbon-containing precursor, TEM of carbon-containing precursor, SEM of product, and TEM of product.

[0158] Example 2

[0159] The other operating steps in this embodiment 2 are the same as those in embodiment 1, except for the battery test.

[0160] The electrochemical performance of hard carbon was tested in a CR2032 battery. All batteries were assembled in a glove box under an argon atmosphere. The CR2032 sodium-ion battery comprises sodium foil as the counter electrode, a glass fiber separator (G / D) as the separator, 1M sodium hexafluorophosphate (NaPF6) dissolved in dimethyl carbonate (DMC) as the electrolyte, and hard carbon as the anode. The anode was prepared by casting a slurry (containing 95 wt% active material in deionized water (H2O) and 5 wt% sodium carboxymethyl cellulose (CMC; Kroeder)) onto an Al / Cu foil. Constant current discharge / charge tests were performed within a voltage range of 0.005–3.0 V (compared to Na / Na) for the anode.

[0161] The long-cycle test results are as follows: After activation at a current density of 0.1C (30mA / g) for two cycles, the current density was switched to 1C (300mA / g) for further testing (e.g.). Figure 6 ).

[0162] The rate testing procedure is as follows: After activation at a current density of 0.1C (30mA / g) for two cycles, the current density is switched once to 0.2, 0.5, 1, 2, 5C (60, 150, 300, 600, 1500mA / g), and finally the current density is switched back to 0.1C (e.g., ...). Figure 5 ).

[0163] like Figure 4The first charge-discharge curves of hard carbon activated at a current density of 0.1C (30mA / g) before and after heat treatment are shown. It can be clearly observed from the curves that the voltage plateau of hard carbon decreased significantly after heat treatment, while the specific capacity did not decrease significantly compared with that before treatment.

[0164] The modified hard carbon also exhibits excellent long-cycle performance as a sodium-ion anode material, retaining 93% of its capacity after 400 cycles. Its rate performance also shows no significant decrease compared to before treatment.

[0165] Example 3

[0166] Combining the above steps, polydopamine is loaded into the reaction chamber, and the pulse power supply is started. The temperature program for heating the polydopamine includes:

[0167] The operating voltage is set to 50V and the operating current to 100A. The temperature is raised from room temperature to 1500℃ and held for 2 seconds.

[0168] The method for assembling sodium-ion batteries with the obtained hard carbon material is the same as in Example 2.

[0169] The test used a current density of 0.1C (30mA / g) for activation. The resulting first charge-discharge curves are shown below. Figure 7 As shown, its charge-discharge curves are similar to those of commercial hard carbon, both exhibiting high slope capacity.

[0170] Example 4

[0171] Combining the above steps, the hard carbon precursor prepared using phenolic resin as a precursor is loaded into the reaction chamber. The pulse power supply is then activated, and the temperature program for heating the sample includes:

[0172] The operating voltage is set to 50V and the operating current to 100A. The temperature is raised from room temperature to 1500℃ and held for 2 seconds.

[0173] The Raman spectra of the obtained hard carbon material are as follows Figure 8 As shown.

[0174] Example 5

[0175] Combining the above steps, anthracite is loaded into the reaction chamber, and the pulse power supply is started. The temperature program for heating the anthracite includes:

[0176] The operating voltage was set to 50V and the operating current to 80A. The temperature was increased from room temperature to 1500℃ and held for 15 seconds. The Raman spectrum of the resulting hard carbon material is shown below. Figure 9 As shown.

[0177] Example 6

[0178] The other operating steps in this embodiment are the same as in Embodiment 1, except that the temperature reaches 1400, 1500, 1600, 1700, and 1800℃.

[0179] Raman testing was performed, and the Raman spectrum is as follows: Figure 11 As shown in the Raman spectrum analysis, the proportion of the 2D peak increases with increasing temperature, which corresponds to the increase in the graphitization degree of the hard carbon material after heating.

[0180] Example 7

[0181] The sample preparation process in this embodiment is the same as in Example 1, except that the holding time is modified to 5, 10, 20, 30, 45, and 60 seconds. Raman spectroscopy is then performed, and the Raman spectra are shown below. Figure 10 As shown in the figure, Raman spectroscopy analysis revealed that the 2D peak began to appear and intensify with increasing heat preservation time, which corresponds to the change in the degree of graphitization of the hard carbon material during long-term heat preservation.

[0182] Comparative Example 1:

[0183] The pretreated coconut shell precursor was crushed and then heated in a tube furnace. The temperature was raised to 800℃ at a rate of 5℃ / min and held for 2 hours for pre-carbonization. The temperature was then further raised to 1500℃ at a rate of 5℃ / min and held for 3 hours, followed by natural cooling to room temperature. The results were... Figures 1-6 The original sample, before heating, before processing, or before Joule heating.

[0184] Examples 4 and 5 both involve the synthesis of different types of precursors. Examples 3 and 4 are polymer precursors, while Example 5 is a fossil fuel-based precursor. Example 4 involves sintering the finished hard carbon using conventional methods and then subjecting it to pulse treatment. Example 5 involves direct pulse treatment.

[0185] In Example 2 Figure 4 The comparison of charge-discharge curves shows that the hard carbon material synthesized by this method is a material with high plateau capacity and low voltage; the cycle diagram in Example 2 (as shown in the figure) Figure 6 This indicates that the remaining properties of the material synthesized by this method are not affected, that is, optimization does not affect other properties; Example 3 shows that this method can synthesize high-performance hard carbon materials as well as hard carbon materials that can be synthesized by conventional methods.

[0186] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A method for preparing low-voltage, high-specific-capacity hard carbon, characterized in that, This includes the synthesis of hard carbon by applying voltage pulses to carbon-containing precursors; The carbon-containing precursor is at least one of a non-hard carbon-containing precursor and a hard carbon precursor, wherein the hard carbon precursor is a finished hard carbon product, and the non-hard carbon-containing precursor includes at least one of a biomass-based precursor, a synthetic polymer precursor, and a fossil fuel-based precursor; when the carbon-containing precursor is a non-hard carbon-containing precursor, the non-hard carbon-containing precursor is subjected to a pre-carbonization treatment, the pre-carbonization temperature is 500~900℃, the heating rate is 1~20℃ / min, and the holding time is 0.1~72h; The specific method of voltage pulse synthesis is as follows: before processing, the atmosphere is changed, and the atmosphere environment includes at least one of helium, argon, and nitrogen or a low vacuum of less than 10 Pa; the current and voltage of the power supply are adjusted, the current is DC or AC, the magnitude is 0.01~1000A, and the voltage is 1~500V; the carbon-containing precursor is rapidly heated to 500~3000℃ and held for 0.1~1000s using a voltage pulse, then the power supply is disconnected, and the material is taken out after cooling to room temperature.

2. The method for preparing low-voltage, high-specific-capacity hard carbon according to claim 1, characterized in that, The biomass-based precursors include at least one of the following: recycled cotton, walnut shells, oak, cherry blossom petals, kelp, lignin, grapefruit peel, lotus root stems, chitosan, artichoke cysts, eggshell membranes, animal and plant tissues, cork, xylose, argan shells, mangosteen shells, and pine cones; the synthetic polymer precursors include at least one of the following: phenolic resin, polyacrylonitrile, polyvinylpyrrolidone, polyvinylpyrrole, polyaniline, polyethylene dioxythiophene, sodium polyacrylate, polyvinyl chloride, polyamic acid, and triblock copolymers; the fossil fuel-based precursors include at least one of the following: asphalt, coal tar, anthracite, and petroleum.

3. The method for preparing low-voltage, high-specific-capacity hard carbon according to claim 1, characterized in that, The non-hard carbon-containing precursor contains a conductive agent, and the mass fraction of the conductive agent in the mixture of the conductive agent and the non-hard carbon-containing precursor is 1% to 50%. a) The conductive agent is one or more of the following: anthracite, calcined petroleum coke, carbon nanotubes, graphene quantum dots, acetylene black, carbon black, sub-graphite, and graphene. b) The conductive agent is added to the non-hard carbon-containing precursor so that the mixed non-hard carbon-containing precursor can be used in the preparation method.

4. The method for preparing low-voltage, high-specific-capacity hard carbon according to claim 1, characterized in that, The carbon-containing precursor is supplemented with a binder, and the mass fraction of the binder in the carbon-containing precursor with added binder is 1-50%. The adhesive comprises at least one of the following: sodium carboxymethyl cellulose, hydroxypropyl methylcellulose, hydroxyethyl cellulose, methylcellulose, polyanionic cellulose, hydroxypropyl cellulose, polyvinyl alcohol, sodium polyacrylate, styrene-butadiene rubber, sodium alginate, starch, molasses, and asphalt.

5. The method for preparing low-voltage, high-specific-capacity hard carbon according to claim 1, characterized in that, When a voltage pulse is applied to a carbon-containing precursor, heteroatoms are present to synthesize doped or heteroatom-containing hard carbon; the heteroatoms are nitrogen, phosphorus, boron, metals or mixtures thereof; the heteroatom source of the heteroatoms is melamine, aminoborane, melamine-formaldehyde resin, phosphine, phosphate, metal salt, metal oxide or mixtures thereof.

6. The application of a hard carbon material prepared according to any one of claims 1-5 as a negative electrode in sodium-ion, lithium-ion and potassium-ion batteries.

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