Preparation process of graphene powder for energy storage battery negative electrode

Abstract

This invention relates to the field of graphene powder preparation and discloses a process for preparing graphene powder for the negative electrode of an energy storage battery. The process includes: mixing graphene oxide powder, an inorganic eutectic salt precursor, and a strong reducing agent to prepare a reaction precursor; controlling the material system across the eutectic temperature range and maintaining a constant temperature; utilizing the latent heat of phase change in the melting salt component to absorb the exothermic deoxidation reduction, allowing the molten salt liquid phase to penetrate into the graphite interlayer; repairing the carbon lattice at high temperature and controlling the cooling rate to induce in-situ precipitation of submicron-sized microcrystals from the liquid phase. This invention ensures lattice integrity through a thermodynamic hedging mechanism and dissipates crystallization stress through a microcrystallization locking mechanism, preventing irreversible agglomeration of graphene sheets, ensuring the powder maintains a three-dimensional open topological morphology, and improving the initial discharge specific capacity of the energy storage electrode active material.

Description

Technical Field

[0001] This invention belongs to the field of graphene powder preparation technology, and particularly relates to a graphene powder preparation process for the negative electrode of an energy storage battery. Background Technology

[0002] Currently, graphene powder possesses high carrier mobility and chemical stability, making it a core material for high-performance energy storage battery anodes. Large-scale preparation typically employs an inorganic salt medium method, utilizing the high-temperature liquid fluidity of inorganic salts to provide the reaction environment and assist in intercalation and exfoliation. During the deoxidation and reduction stage, graphene oxide powder undergoes a violent exothermic reaction. Due to a temporal misalignment between the exothermic peak and the inorganic salt melting phase transition point in the conventional heating process, the exothermic reaction occurs before the formation of the molten salt liquid. This results in the inorganic salt remaining solid during the deoxidation and reconstruction of graphite sheets. At this point, the system lacks an effective in-situ heat transfer medium, leading to transient extreme heat causing thermal burn-through of the carbon-based lattice. Furthermore, the natural cooling during product recovery is a near-equilibrium thermodynamic process. Molten salt precipitates between graphene layers, forming large-sized macroscopic crystals. The expansion stress and shear force generated by crystallization physically sever the three-dimensional mesoporous network of graphene, leading to irreversible layer stacking and secondary agglomeration of the product.

[0003] Besides improvements in the morphology of inorganic salt media and basic exfoliation efficiency, existing technologies generally lack precise engineering methods for managing heat flow during deoxidation reduction and controlling crystallization kinetics during the cooling stage. For example, Chinese invention patent application CN116254098A discloses a molten salt-based reduced graphene composite material and its preparation method, which utilizes in-situ reduction in a molten salt environment to improve the dispersibility of nanomaterials. However, the selected nitrate system has strong oxidizing properties at high temperatures, and its coexistence with the strong reduction process in the same system induces intense redox exothermic reactions. The process logic lacks a decoupling and matching design for the reduction exothermic peak and the latent heat of molten salt phase transition. The thermodynamic preset premise is mismatched with the actual complex exothermic conditions, and the reduction instant cannot suppress the thermodynamic burn-through of the graphene lattice. In the cooling stage, the conventional cooling logic is used, which cannot block the physical compression of the primary graphene network by the macroscopic crystallization of molten salt. The final product still has problems of sheet aggregation and decreased porosity.

[0004] Therefore, the technical problem to be solved by this invention is how to achieve energy release and phase transition balance throughout the entire preparation cycle, and avoid physical interference of the cooling crystallization process on the microstructure, so as to produce graphene powder with high lattice integrity and open three-dimensional morphology. Summary of the Invention

[0005] The present invention aims to solve the problem of simultaneously maintaining lattice integrity and morphology fixation during the preparation of graphene powder.

[0006] In this technical solution, a process for preparing graphene powder for the negative electrode of an energy storage battery includes the following steps:

[0007] Step S1: Mix graphite oxide powder, inorganic eutectic salt precursor and a strong reducing agent at a mass of 5% to 12% of the graphite oxide powder to prepare a reaction precursor; wherein the mass ratio of graphite oxide powder to inorganic eutectic salt precursor is 1:5 to 1:15.

[0008] Step S2: Place the reaction precursor in a reactor under a protective atmosphere and heat it to 580°C to 600°C at a heating rate of 5°C / min to 8°C / min.

[0009] Step S3: Control the heating rate to be reduced to 0.5℃ / min to 1.5℃ / min so that the reaction precursor can cross the temperature range of 640℃ to 680℃ and be held at 660℃ for 60min to 90min. During the holding process, the inorganic eutectic salt precursor undergoes a melting phase transition. The latent heat of the phase transition absorbs the local heat generated by the deoxidation exothermic reaction of the strong reducing agent and clamps the temperature of the interlayer micro-region of the graphite oxide powder near the eutectic melting point of the inorganic eutectic salt precursor, so that the generated molten salt liquid phase enters the interlayer voids of the graphite oxide powder.

[0010] Step S4: Heat to 750°C to 850°C at a heating rate of 5°C / min to 10°C / min and hold for 2h to 4h to obtain the high-temperature reaction product;

[0011] Step S5: Remove the heat source and introduce a low-temperature inert gas with a flow rate of 10 L / min to 20 L / min into the protective atmosphere reactor, so that the cooling rate of the high-temperature reaction product in the range of 800℃ to 450℃ is maintained at 30℃ / min to 50℃ / min, inducing the precipitation of microcrystals with an average particle size of less than 500 nm in the molten salt liquid phase in the interlayer voids.

[0012] Step S6: Wash the material system after microcrystal precipitation with deionized water and dry it to obtain graphene powder.

[0013] Preferably, the inorganic eutectic salt precursor is composed of and The composition of the two components is such that the molar ratio is 0.4:0.6 to 0.6:0.4, and the eutectic melting point is 657℃.

[0014] Preferably, the strong reducing agent is or Particles.

[0015] Preferably, the inorganic eutectic salt precursor contains 2% to 5% by mass of a transition metal chloride, wherein the transition metal chloride is... or The washing process in step S6 includes acid washing with dilute hydrochloric acid.

[0016] Preferably, the specific surface area of ​​the obtained graphene powder is 600. g to 850 g.

[0017] Preferably, step S1 includes the following sub-steps: step S11, controlling the rotation speed of the mixing equipment to 300 r / min to 500 r / min; step S12, continuing to mix for 2 h to 4 h, so that the inorganic eutectic salt precursor particles are coated on the surface of the graphite oxide powder.

[0018] Preferably, during steps S2 to S4, the ambient pressure inside the protective atmosphere reactor is maintained at 0.02 MPa to 0.05 MPa.

[0019] Preferably, the Raman spectrum of the prepared graphene powder shows... Peak and Peak intensity ratio Less than 0.1.

[0020] Preferably, the graphene powder obtained has an initial discharge specific capacity of not less than 370 mAh / g at a 1C rate.

[0021] Compared with existing technologies, the graphene powder preparation process for the negative electrode of the energy storage battery of the present invention has the following advantages:

[0022] 1. In the graphene powder preparation process, by establishing a dynamic counterbalancing mechanism for heat absorption and release within a specific temperature range, the local exothermic runaway phenomenon during the reduction reaction is eliminated. In the critical stage of deoxidation and reduction of graphene oxide powder, the large amount of reaction heat released by the decomposition of strong reducing agent and the melting process of inorganic eutectic salt precursor are spatiotemporally overlapped. The latent heat absorbed by the inorganic salt precursor during the solid-liquid phase transition serves as an in-situ heat buffer, which equally offsets the transient extreme heat generated by the reduction reaction, thus clamping the highest temperature of the graphene micro-region near the eutectic melting point. This thermodynamic balance mechanism, based on the underlying physical laws, avoids carbon-based lattice burn-through and thermodynamic tearing caused by high temperature overheating, ensuring that the graphene powder has high lattice integrity and electrical conductivity.

[0023] 2. This invention utilizes the capillary wetting and rigid spatial wedging effect of the molten salt liquid phase to block the physical aggregation path of graphene sheets during the deoxidation and reconstruction period. The molten salt liquid phase generated in situ due to the absorption of local reduction heat has ultra-low viscosity characteristics. At the moment when the interlayer spacing of graphite is in the maximum expansion state due to deoxidation expansion, it spontaneously penetrates and fills the interlayer voids by relying on surface tension. This liquid phase physical barrier is completed before the van der Waals forces cause the sheets to recombine, isolating free single-layer or few-layer graphene, so that the obtained powder can still maintain an open three-dimensional topological morphology during desolvation and subsequent heat treatment.

[0024] 3. This invention eliminates the damage to the microstructure caused by macroscopic crystallization stress during the cooling process by constructing a microcrystallization locking path driven by deep supercooling. In the high-gradient gas phase quenching stage after the reaction, the material system quickly crosses the eutectic phase transition point and obtains a large thermodynamic supercooling. In this state, the molten salt liquid phase filled in the graphene channels exhibits the kinetic characteristics of greatly increased crystal nuclei and restricted crystal growth, thus freezing in situ in the form of a submicron-scale microcrystal array. This discontinuous solid matrix, which is divided into parts, effectively dissipates the volume expansion force and shear stress generated during the crystallization process, protects the fragile three-dimensional graphene network from compression damage, and improves the robustness of the powder structure. Attached Figure Description

[0025] Figure 1 This is a flowchart of the stepwise thermal reduction preparation process of graphene powder for the negative electrode of energy storage battery according to the present invention;

[0026] Figure 2 This is a schematic diagram illustrating the principle of the microscopic state evolution and thermodynamic hedging mechanism of the material system in this invention. Detailed Implementation

[0027] The technical solutions of the embodiments of this application will be clearly described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application are within the scope of protection of this application.

[0028] It should be noted that all directional and positional terms used in this invention, such as: up, down, left, right, front, back, vertical, horizontal, inner, outer, top, bottom, transverse, longitudinal, center, etc., are only used to explain the relative positional relationship and connection between components in a specific state (as shown in the accompanying drawings). They are only for the convenience of describing this invention and do not require that this invention be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention. In addition, the descriptions of "first," "second," etc., in this invention are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated.

[0029] In the description of this invention, unless otherwise explicitly specified and limited, the terms installation, connection, and linking should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections; they can refer to direct connections or indirect connections through an intermediate medium; they can refer to the internal connection of two components. For those skilled in the art, the specific meaning of the above terms in this invention can be understood according to the specific circumstances.

[0030] In the description of this specification, references to the terms "an embodiment," "some embodiments," "illustrative embodiments," "examples," "specific examples," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example, and the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0031] A process for preparing graphene powder for the negative electrode of an energy storage battery, the stepwise thermal reduction preparation process flow is as follows: Figure 1 As shown, the evolution of the microscopic state of the material system and the principle of thermodynamic hedging mechanism during the preparation process are as follows: Figure 2 As shown, the preparation process specifically includes the following steps:

[0032] Step S1: Mix graphite oxide powder, inorganic eutectic salt precursor and a strong reducing agent at a mass of 5% to 12% of the graphite oxide powder to prepare a reaction precursor; wherein the mass ratio of graphite oxide powder to inorganic eutectic salt precursor is 1:5 to 1:15.

[0033] Step S2: Place the reaction precursor in a reactor under a protective atmosphere and heat it to 580°C to 600°C at a heating rate of 5°C / min to 8°C / min.

[0034] Step S3: Control the heating rate to be reduced to 0.5℃ / min to 1.5℃ / min so that the reaction precursor can cross the temperature range of 640℃ to 680℃ and be held at 660℃ for 60min to 90min. During the holding process, the inorganic eutectic salt precursor undergoes a melting phase transition. The latent heat of the phase transition absorbs the local heat generated by the deoxidation exothermic reaction of the strong reducing agent and clamps the temperature of the interlayer micro-region of the graphite oxide powder near the eutectic melting point of the inorganic eutectic salt precursor, so that the generated molten salt liquid phase enters the interlayer voids of the graphite oxide powder.

[0035] Step S4: Heat to 750°C to 850°C at a heating rate of 5°C / min to 10°C / min and hold for 2h to 4h to obtain the high-temperature reaction product;

[0036] Step S5: Remove the heat source and introduce a low-temperature inert gas with a flow rate of 10 L / min to 20 L / min into the protective atmosphere reactor, so that the cooling rate of the high-temperature reaction product in the range of 800℃ to 450℃ is maintained at 30℃ / min to 50℃ / min, inducing the precipitation of microcrystals with an average particle size of less than 500 nm in the molten salt liquid phase in the interlayer voids.

[0037] Step S6: Wash the material system after microcrystal precipitation with deionized water and dry it to obtain graphene powder.

[0038] Preferably, the inorganic eutectic salt precursor is composed of and The composition of the two components is such that the molar ratio is 0.4:0.6 to 0.6:0.4, and the eutectic melting point is 657℃.

[0039] Preferably, the strong reducing agent is or Particles.

[0040] Preferably, the inorganic eutectic salt precursor contains 2% to 5% by mass of a transition metal chloride, wherein the transition metal chloride is... or The washing process in step S6 includes acid washing with dilute hydrochloric acid.

[0041] Preferably, the specific surface area of ​​the obtained graphene powder is 600. g to 850 g.

[0042] Preferably, step S1 includes the following sub-steps: step S11, controlling the rotation speed of the mixing equipment to 300 r / min to 500 r / min; step S12, continuing to mix for 2 h to 4 h, so that the inorganic eutectic salt precursor particles are coated on the surface of the graphite oxide powder.

[0043] Preferably, during steps S2 to S4, the ambient pressure inside the protective atmosphere reactor is maintained at 0.02 MPa to 0.05 MPa.

[0044] Preferably, the Raman spectrum of the prepared graphene powder shows... Peak and Peak intensity ratio Less than 0.1.

[0045] Preferably, the graphene powder obtained has an initial discharge specific capacity of not less than 370 mAh / g at a 1C rate.

[0046] Example 1: In the large-scale thermal reduction preparation of graphene powder for high-rate energy storage battery anodes, the instantaneous exothermic reaction of graphene oxide powder during the deoxidation reduction stage often leads to local energy runaway, resulting in burn-through of the graphene lattice and irreversible stacking between layers. This is avoided in the practical simulation of the process of this invention through a thermodynamic hedging mechanism. In the actual process deployment, graphene oxide powder and an inorganic eutectic salt precursor are selected and mixed at a mass ratio of 1:12, with an additional 10% by mass of the graphene oxide powder. Particles, as strong reducing agents The inorganic eutectic salt precursor particles are initially contacted with graphite oxide powder in a reactor under a protective atmosphere. A controlled mixing device continuously applies mechanical shear force, causing plastic deformation of the particle surface and dense coating. The outer periphery of the particles forms a solid-phase physical barrier, blocking Mass transfer between the graphite oxide powder and the inorganic eutectic salt powder in the temperature range below the eutectic melting point delays the initiation threshold of the chemical reduction reaction to 657℃. When the system temperature rises above the eutectic point and triggers the inorganic salt melting phase transition, the strong reducing agent is released upon heating, triggering transient exothermic reactions. This smooths out the temporal and spatial scale differences between chemical kinetic heat release and physical phase transition endothermic reactions. The physical realization of this plastic deformation relies on the micro-frictional heating effect between powder particles. When the system operates within the conventional low-speed range of 300 r / min to 500 r / min, the high-frequency frictional collisions of the powder in the confined space of the mixing equipment convert mechanical energy into local heat energy. This causes the micro-temperature of the extremely thin surface area of ​​the inorganic eutectic salt precursor particles to jump instantaneously and approach its brittle-ductile transition temperature. Thus, without changing the bulk solid-state structure, the powder extends and spreads on the surface of the target particles under relatively mild mechanical shear force through the surface slip mechanism. The inorganic eutectic salt precursor contains a pre-added transition metal chloride with a mass fraction of 3%. Cobalt ions dissociate in the liquid phase system of the high-temperature region of lattice repair, relying on the space... orbitals and carbon atoms Hybridized electron clouds generate coordination adsorption, reducing the diffusion activation energy at the edges of residual carbon atoms, driving the thermodynamic healing process, and filling the carbon lattice vacancies left by deoxidation. In this thermodynamic healing process, the unique polar fluid environment of high-temperature molten salt enables positively charged free cobalt ions to conform to the electrostatic potential distribution on the graphene surface and spontaneously target and enrich themselves precisely along the electric field gradient towards the vacancy region with abnormally high electron density at the defect edge. At the same time, the nanoscale oligolayer graphite micro-regions and amorphous carbon fragments that inevitably fall off during the intense deoxidation process in the early stage of the system have critical solubility in the high-temperature eutectic salt liquid phase. These free structures, as in-situ free active carbon sources, under the efficient catalytic guidance of cobalt ions enriched at the lattice vacancies, carry out relay self-assembly filling of the damaged carbon network framework along the path with the lowest energy barrier.

[0047] The material system was heated to 590℃ at a rate of 7℃ / min, and the heating rate was switched to 1.2℃ / min to pass through the 640℃ to 680℃ range. It was then held at a constant temperature of 660℃ for 80 min. At this point, the inorganic eutectic salt precursor, which was near the eutectic melting point of 657℃, underwent a melting phase transition. The latent heat of the phase transition absorbed the local heat generated by the deoxidation exothermic reaction of the strong reducing agent in situ, thus clamping the highest temperature of the graphene micro-region near the eutectic melting point of the inorganic eutectic salt precursor. The capillary wetting effect of the molten salt liquid phase was used to wed into the graphite layers, and a liquid phase physical barrier was constructed at the moment of violent energy release during deoxidation and reduction. The lattice integrity of the graphene oxide powder was preserved under thermal shock.

[0048] The system was heated to 820℃ at a heating rate of 7℃ / min and held for 3 hours to repair the carbon lattice. After the reaction, the heat source was removed and low-temperature nitrogen gas at a flow rate of 18L / min was introduced into the reactor under a protective atmosphere. The cooling rate of the high-temperature reaction product was maintained at 45℃ / min within the range of 800℃ to 450℃. The high supercooling induced the precipitation of granular microcrystals with an average particle size of less than 500nm from the molten salt liquid phase in the interlayer voids. This microcrystallization locking mechanism dissipated the macroscopic crystallization stress generated during the cooling process, preventing the three-dimensional graphene network from being physically compressed and destroyed. The specific surface area of ​​the produced graphene powder was 785m² / g, and the intensity ratio of its D peak to G peak in the Raman spectrum was... With a value of 0.07, the synergistic effect of phase change thermal control and stress locking maintains the three-dimensional open topological morphology while ensuring lattice quality. Although such high-gradient rapid cooling often induces a non-equilibrium transformation of liquid salt directly to the amorphous glass phase in macroscopic free and open systems, in the extremely narrow two-dimensional geometrically confined micro-regions between graphene layers in this scheme, the numerous structural topological grooves remaining on the carbon-based surface serve as heterogeneous nucleation centers with extremely high abundance. Driven by the supercooled thermodynamic potential, they induce explosive transient multi-point nucleation of the salt liquid phase. At the same time, the rapid increase in system viscosity caused by rapid cooling and the narrow capillary resistance of the confined space are superimposed, cutting off the material supply path for the primary crystal nuclei to cross the nanoscale barrier to adsorb surrounding solute molecules for secondary size growth. Thus, the subsequent stages of crystal growth are precisely intervened by utilizing the kinetic resistance effect, forcibly freezing the crystal morphology at the submicron array scale with high rigidity and physical support strength.

[0049] Example 2: In the industrial-scale thermal reduction preparation of graphene powder for the negative electrode of a simulated energy storage battery, to address the energy runaway and sheet stacking problems existing in the deoxidation and reduction stage of graphene oxide powder, a machine with zoned temperature control function and temperature control accuracy superior to [previous technology / equipment] was used. A 1℃ protective atmosphere reactor was used as the experimental platform. This reactor was equipped with a mass flow controller with a flow accuracy of 0.1 L / min to simulate the gas flow environment under high-purity nitrogen protection conditions. The selected graphite oxide powder had an oxygen content between 42.5% and 45.2%, and the inorganic eutectic salt precursor was selected from... and The eutectic mixture has a eutectic melting point set to 657℃. The mass ratio of the inorganic eutectic salt precursor to the graphene oxide powder is set to balance the absorption efficiency of the latent heat of phase change on the exothermic deoxidation and the liquid phase treatment load of the washing process. When the oxygen content of the graphene oxide powder is in the aforementioned range, the mass ratio is set to 1:12 in order to keep the local temperature near the eutectic melting point. The cooling rate is set to balance the grain size and thermal stress distribution. In order to form granular microcrystals inside the graphene framework and avoid thermal cracking, the cooling rate in the range of 800℃ to 450℃ is set to 45℃ / min.

[0050] Three sample groups were set up in the experiment. Control group 1 operated the thermal reduction procedure without adding the inorganic eutectic salt precursor. Control group 2 added the inorganic eutectic salt precursor and set the cooling rate to 5℃ / min. To simulate the thermal field fluctuations in industrial production, a random temperature disturbance with an amplitude of ±8℃ was introduced into the material system during the isothermal residence stage at 660℃, and the system's response to the disturbance was monitored. Observations showed that in control group 1, spark discharge occurred after the temperature exceeded 600℃, and the material underwent local sintering and presented a dense blocky shape due to the exothermic oxidation. In control group 2, after cooling, the interlayer... and The molten salt liquid phase grows into micron-sized cubic crystals, which exert compressive stress on the overall graphene framework, causing partial collapse of the three-dimensional porous structure.

[0051] The data characterization results reflect the influence of different process routes on the product properties. The graphene powder produced by the control group has a specific surface area of ​​132 m² / g, and its Raman spectrum shows... The value was 0.42, indicating that the exothermic deoxidation caused lattice defects; the specific surface area of ​​control group II was 356 m² / g, and its mesopore volume was reduced due to the destruction caused by large-size crystallization stress; the interlayer precipitation of the sample group of this invention at a cooling rate of 45℃ / min and The average grain size, as observed by scanning electron microscopy, is 325 nm. These granular microcrystals support and lock in the three-dimensional space generated by deoxidation expansion, resulting in graphene powder with a specific surface area of ​​785 m² / g. The value is 0.07; when a strong reducing agent is used... When the addition amount was increased from 10% to 15% of the graphite oxide powder mass, the specific surface area decreased to 520 m² / g because the instantaneous heat release exceeded the upper limit of the latent heat absorption of the inorganic eutectic salt precursor. Reaching 0.15, this performance inflection point defines the effective boundary of the reducing agent ratio range. The results of this experiment show that by controlling the heating rate of 1.2℃ / min and the isothermal hold at 660℃ in the range of 640℃ to 680℃, the inorganic eutectic salt precursor generates latent heat of phase change, absorbs the deoxygenation exothermic reaction of the strong reducing agent, and ensures the integrity of the carbon lattice. Combined with a cooling rate of 45℃ / min to induce microcrystallization transformation of the liquid phase, the three-dimensional pores of graphene are effectively locked, which solves the technical contradiction between specific surface area loss and lattice quality degradation during the preparation process. The produced graphene powder exhibits low defect density and a highly developed three-dimensional open topology, which meets the performance requirements of high-performance energy storage battery anode materials for ion diffusion channels.

[0052] Example 3: In the preparation of graphite oxide powder with varying oxygen content between batches, the instantaneous heat flux released by the material system during deoxidation and reduction varies with the oxygen content. This invention's process determines core control parameters by establishing an energy matching relationship; the initial oxygen content of the graphite oxide powder is measured; when the measured oxygen content is 45.2%, the total exothermic heat flux density of the system during the strong reducing agent reaction is calculated based on the exothermic enthalpy of the decomposition of oxygen-containing functional groups in the graphite oxide powder. To offset the instantaneous heat flux with the latent heat of phase change from the inorganic eutectic salt precursor, a quantitative procedure for dynamic thermal equilibrium of the system is constructed using the energy conservation mechanism of the first law of thermodynamics, based on the equation... Determine the baseline ingredient weights, where the mass of graphite oxide powder is... The oxygen mass fraction is calculated as follows: The exothermic enthalpy of the corresponding deoxygenation ratio determined by differential scanning calorimetry is expressed as a percentage. The inorganic eutectic salt precursor mass is calculated as follows: The latent heat value of phase change is calculated as follows: The measured oxygen content data is input into the above equation for solution, and the result is obtained. and The theoretical ratio is 1:14.8. To compensate for the boundary loss caused by thermal radiation from the reactor inner wall, the mass ratio of graphite oxide powder to inorganic eutectic salt precursor was set to 1:15 after rounding up the system threshold. Based on the heat transfer efficiency at 660℃, the isothermal residence time was set to 90 min to ensure that the interlayer liquid phase wetting depth reaches the submicron scale. In specific operation, to accurately decouple and purify the target enthalpy from the complex heat flow interweaving of differential scanning calorimetry, the system introduced pure graphite oxide powder of the same batch without reducing agent as a benchmark control group to execute the heating program, and completely collected the baseline heat flow data spectrum of the intrinsic thermal decomposition of its internal oxygen-containing groups. In the test group operation with added strong reducing agent, the global total exothermic response matrix was captured simultaneously. By performing strict point-by-point signal subtraction operation at the algorithm terminal, the spontaneous decomposition dissipation background was eliminated, and the isolated pure chemical deoxygenation reaction independent heat flow peak was integrated and normalized to obtain the deoxygenation specific exothermic enthalpy after removing substrate interference. This demonstrates the physical feasibility of accurately calculating the macroscopic energy balance equation.

[0053] The material system was passed through the eutectic temperature range of 640℃ to 680℃ at a rate of 0.8℃ / min from 600℃ in a reactor under a protective atmosphere. Temperature fluctuations at the center of the material were monitored by an online thermal compensation unit. The inorganic eutectic salt precursor underwent a phase transition and absorbed heat near 657℃, which offset the exothermic peak generated by the strong reducing agent and graphene oxide powder in the early stage of deoxidation and suppressed the merging of defects caused by overheating in the graphene crystal structure. The system was then heated to 820℃ and held for 3 hours to induce carbon atom diffusion and repair residual vacancy defects. This process was designed to overcome the millisecond-level transient exothermic reaction of deoxidation reduction and the second-level macroscopic phase transition absorption of bulk inorganic salts. The spatiotemporal dynamic mismatch between heats leads to the inorganic eutectic salt precursor, which is pre-uniformly coated on the surface of graphite oxide powder, being in a pre-melted state at the interface when the temperature rises to the critical state of crossing the eutectic point. This nanometer-thick pre-melted layer, as an ultra-high thermal conductivity physical medium, can rapidly conduct and distribute the transient extreme heat generated by chemical reduction to the surrounding unmelted solid bulk salt matrix at a microsecond-level response speed. By activating the bulk melting endothermic mechanism of the surrounding large-volume salt crystals, the microscopic local thermal shock wave is transformed into macroscopic thermal capacity storage, achieving an energy offset balance across several orders of magnitude of time scales.

[0054] The average cooling rate of the high-temperature product from 800℃ to 450℃ was maintained at 50℃ / min. The supercooling generated by the cooling was used to suppress the growth of crystal nuclei in the molten salt liquid phase and induce interlayer precipitation. and The grains exhibit a granular morphology with an average grain size of 210 nm. The small-particle microcrystalline structure dissipates crystallization stress while forming a distribution density of not less than [missing information]. Each flexible support node per cubic centimeter produces graphene powder with a specific surface area of ​​815 m² / g and an electrical conductivity of [missing information]. S / m achieves physical maintenance of the three-dimensional structure of high-performance graphene powder through the synergistic effect of energy flow control and microcrystallization topological support.

[0055] Example 4: In a workshop environment with fluctuating temperature and humidity, the heating inertia of the material system shifts with changes in the reactor's internal state and the material's bulk density. The switching critical point of the heating program is corrected by measuring the heat capacity. In actual operation, a preheating test is conducted at a nitrogen flow rate of 18 L / min. The temperature rise curve is monitored by a temperature sensor installed at the center of the reactor, and the response time of the system from 500°C to 600°C is recorded. And according to the formula Calculate the equivalent heat capacity of the system ,in, The change in temperature For the effective input power of the heating element, For response time, For heat capacity, when the temperature of the graphite oxide powder is switched from 580℃ to a low-rate heating, the output slope of the temperature sensor will be... As a switching criterion, when the output slope When the deviation rate of three consecutive sampling values ​​is less than 5%, the system switches to the isothermal holding program, so that the interlayer state of the graphite oxide powder exhibits a thermodynamically uniform distribution before the material enters the eutectic temperature zone of 640℃ to 680℃.

[0056] In raw material switching scenarios where the specific surface area of ​​graphite oxide powder fluctuates, the amount of inorganic eutectic salt precursor added changes with the physical properties of the powder. The mixing ratio is determined by calculating the loose packing density. In actual production, the loose packing density of graphite oxide powder is measured. and the loose packing density of inorganic eutectic salt precursors According to the formula Determine the quality of precursor salt addition. ,in, For the quality of precursor salts, For the quality of graphite oxide powder, For the precursor salt packing density, The loose packing density of graphite oxide powder, As a volume correction factor, the Andreassen packing model of porous particle systems was applied to determine the average porosity inside batches of graphite oxide powder using a nitrogen adsorption analyzer. Substitute the relation The measured porosity value of the batch was 0.2, and the correction factor was calculated and output. The value is 1.25. Subsequently, the mixed reaction precursor is laid in the carrier boat with a stacking thickness of 2.5 cm, and a mixed gas consisting of 0.5% hydrogen and 99.5% nitrogen by volume is injected into the reactor. The mixed gas assists in lowering the wetting angle of the liquid-phase molten salt on the graphene sheet surface, allowing the molten salt liquid phase to spontaneously undergo capillary permeation into the carbon-based micropores. The final graphene powder exhibits a morphology with a consistent pore size distribution. In the parameter conversion logic of the aforementioned Andreassen packing model, the continuous particle distribution modulus defined by this model is... In this system, the boundary extreme value of 0.37 is constantly constrained to specifically characterize the microscopic particle aggregation characteristics under the densest packing state within a confined reactor. The system derives the macroscopic gradation equation under this extreme condition in a limiting manner, making the overall volume expansion rate of the particles equivalent to the geometric series expansion of the pore volume. Thus, the system parameters originally describing the multidimensional particle size distribution are accurately reduced in dimension to the average porosity. In the single-variable relationship, it is ensured that the dimensions of the correction coefficient are not only consistent in mathematical derivation, but also directly correspond to the limit expansion critical point when the interlayer voids are completely filled by the molten phase in engineering applications.

[0057] Example 5: In the production scenario of graphene powder with high crystallinity requirements and frequent batch fluctuations of raw materials, the exfoliation effect of the material system is controlled by the liquid phase viscosity and penetration rate of the inorganic eutectic salt precursor. The system determines the compatibility relationship of the eutectic system by establishing a melting point calibration method based on the molar ratio of components; and analyzes the inorganic eutectic salt precursor. and The purity index is used to calculate the eutectic temperature based on the binary phase diagram. As the mole fraction of the components evolves, in order to make Stabilize at 657℃, and The molar ratio was selected as 50.6:49.4, and the particle size was selected accordingly. No larger than 50μm The particles, acting as a strong reducing agent, were contacted with graphite oxide powder in a three-dimensional mixer at 300 rpm for 20 minutes. The results were verified by measuring the volume density fluctuation of the mixture at five different sampling points within the mixing vessel. The uniformity of coating on the surface of graphite oxide powder, when the volume density dispersion coefficient at the sampling points... When the value is below 0.05, the system determines that each micro-reaction zone has the ability to offset the latent heat of phase change.

[0058] When the system enters the high-temperature lattice repair stage, the rearrangement kinetics of carbon atoms are controlled by the residual oxygen partial pressure in the protective atmosphere. The system monitors the exhaust gas through an online analyzer. The dynamic endpoint of the 820℃ holding program is determined by the change in the content of oxygen. An initial replacement standard for the nitrogen scrubbing cycle is set; high-purity nitrogen is injected into the protective atmosphere reactor before heating until the oxygen volume fraction at the outlet is below 5 ppm. As the reaction temperature rises to 820℃, trace amounts of water vapor are generated due to the chemical reconstruction of oxygen vacancies and reduction products within the graphene lattice. This water vapor is converted into an electrical signal output by a sensor. The system records the dynamic value of the water vapor concentration based on the decay curve. When the water vapor concentration in the tail gas... The mole fraction was below 20 min for 20 minutes. When the degree of repair of the carbon lattice reaches thermodynamic equilibrium, the system automatically switches to a cooling program driven by low-temperature nitrogen. This method enables precise adjustment of the defect density in graphene, resulting in a more accurate Raman spectrum of the final graphene powder. The deviation remained within 0.01.

[0059] The embodiments of this application have been described above with reference to the accompanying drawings. Unless otherwise specified, the embodiments and features in the embodiments of this application can be combined with each other. This application is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of this application without departing from the spirit of this application and the scope of protection of this invention, and all of these forms are within the protection scope of this application.

Claims

1. A process for preparing graphene powder for the negative electrode of an energy storage battery, characterized in that, Includes the following steps: Step S1: Mix graphite oxide powder, inorganic eutectic salt precursor and a strong reducing agent at a mass of 5% to 12% of the graphite oxide powder to prepare a reaction precursor; wherein the mass ratio of graphite oxide powder to inorganic eutectic salt precursor is 1:5 to 1:

15. Step S2: Place the reaction precursor in a reactor under a protective atmosphere and heat it to 580°C to 600°C at a heating rate of 5°C / min to 8°C / min. Step S3: Control the heating rate to be reduced to 0.5℃ / min to 1.5℃ / min so that the reaction precursor can cross the temperature range of 640℃ to 680℃ and be held at 660℃ for 60min to 90min. During the holding process, the inorganic eutectic salt precursor undergoes a melting phase transition. The latent heat of the phase transition absorbs the local heat generated by the deoxidation exothermic reaction of the strong reducing agent and clamps the temperature of the interlayer micro-region of the graphite oxide powder near the eutectic melting point of the inorganic eutectic salt precursor, so that the generated molten salt liquid phase enters the interlayer voids of the graphite oxide powder. Step S4: Heat to 750°C to 850°C at a heating rate of 5°C / min to 10°C / min and hold for 2h to 4h to obtain the high-temperature reaction product; Step S5: Remove the heat source and introduce a low-temperature inert gas with a flow rate of 10 L / min to 20 L / min into the protective atmosphere reactor, so that the cooling rate of the high-temperature reaction product in the range of 800℃ to 450℃ is maintained at 30℃ / min to 50℃ / min, inducing the precipitation of microcrystals with an average particle size of less than 500 nm in the molten salt liquid phase in the interlayer voids. Step S6: Wash the material system after microcrystal precipitation with deionized water and dry it to obtain graphene powder.

2. The graphene powder preparation process for the negative electrode of an energy storage battery according to claim 1, characterized in that, Inorganic eutectic salt precursor is composed of and The composition of the two components is such that the molar ratio is 0.4:0.6 to 0.6:0.4, and the eutectic melting point is 657℃.

3. The graphene powder preparation process for the negative electrode of an energy storage battery according to claim 1, characterized in that, Strong reducing agent is or Particles.

4. The graphene powder preparation process for the negative electrode of an energy storage battery according to claim 1, characterized in that, The inorganic eutectic salt precursor contains 2% to 5% by mass of transition metal chlorides, which are... or The washing process in step S6 includes acid washing with dilute hydrochloric acid.

5. The graphene powder preparation process for the negative electrode of an energy storage battery according to claim 1, characterized in that, The specific surface area of ​​the obtained graphene powder is 600. g to 850 g.

6. The process for preparing graphene powder for the negative electrode of an energy storage battery according to claim 1, characterized in that, Step S1 includes the following sub-steps: Step S11, controlling the rotation speed of the mixing equipment to 300 r / min to 500 r / min; Step S12, continuing to mix for 2 h to 4 h, so that the inorganic eutectic salt precursor particles are coated on the surface of the graphite oxide powder.

7. The process for preparing graphene powder for the negative electrode of an energy storage battery according to claim 1, characterized in that, During steps S2 to S4, the ambient pressure inside the protective atmosphere reactor is maintained between 0.02 MPa and 0.05 MPa.

8. The graphene powder preparation process for the negative electrode of an energy storage battery according to claim 1, characterized in that, The Raman spectrum of the prepared graphene powder Peak and Peak intensity ratio Less than 0.

1.

9. The process for preparing graphene powder for the negative electrode of an energy storage battery according to claim 1, characterized in that, The obtained graphene powder has an initial discharge specific capacity of no less than 370 mAh / g at a 1C rate.

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