Method for regenerating graphite from black powder leaching residues through double-pulse Joule heat flash evaporation

Abstract

The invention discloses a black powder leaching residue double-pulse Joule heat flash evaporation graphite regeneration method which comprises the following steps: pretreating raw materials, and quantitatively configuring leaching residues, a circulating conductive auxiliary agent and a carbon precursor according to a ratio; pressing the prepared mixed material into a continuous conductive thin layer; introducing a protective atmosphere formed by mixing N2, Ar and H2 according to a certain proportion into the reaction cavity, and adding an impurity trapping agent; performing double-pulse treatment on the continuous conductive thin layer, firstly applying a preheating pulse to perform preheating shaping on the thin layer material, and applying a main flash pulse to the preheated thin layer material after a certain time interval; quality judgment: judging the state of the material according to a criterion function, performing real-time judgment, stopping the machine if the material reaches the standard, and supplementing an auxiliary flash pulse if the material does not reach the standard; post-treatment and tail gas purification; and inspecting the finished product. The black powder leaching residue double-pulse Joule thermal flash graphite regeneration method provided by the invention has the advantages that the conductivity is reconstructed, and second-level re-graphitization and impurity removal are synchronously realized by integrating two pulses.

Description

Technical Field

[0001] This invention relates to the field of graphite regeneration and recycling technology, and in particular to a method for regenerating graphite from leaching residue by double-pulse Joule heat flash evaporation in the wet metal recovery of lithium battery black powder. Background Technology

[0002] The common route for lithium battery recycling is "mechanical pretreatment—wet leaching—metal extraction / precipitation—residue disposal / reuse". The residue (i.e., leaching residue) is mainly carbonaceous but has poor conductivity and complex impurities. Traditional graphitization uses high-temperature resistance furnaces / graphitization furnaces for long-term heat preservation to improve crystallinity, but its removal of non-metallic impurities such as F / P is limited, requiring strong acid washing. In the wet metal recovery of lithium battery black powder, the leaching residue suffers from disrupted conductive paths after leaching, increased overall material resistance, leading to uneven Joule heating flow and localized overheating / underheating. PVDF pyrolysis and wet residue result in the co-enrichment of F, P, S, and trace metallic impurities. Traditional graphitization requires hourly heat preservation at 2800–3000 ℃, resulting in high energy consumption and long cycles, making it difficult to match the cost and cycle time of the recycling industry. Product consistency and environmental (HF / POx) remediation are difficult to achieve simultaneously. Summary of the Invention

[0003] This invention is based on the inventor's discoveries and understanding of the following facts and problems: Graphite recycling suffers from both localized overheating and under-burning.

[0004] The present invention aims to at least partially solve one of the technical problems in the related art.

[0005] Therefore, embodiments of the present invention propose a method for regenerating graphite by dual-pulse Joule heat flash evaporation of black powder leaching residue, comprising the following steps: raw material pretreatment, wherein the leaching residue is quantitatively configured with a circulating conductive additive and a carbon precursor in a certain proportion; The prepared mixture is pressed into a continuous conductive thin layer; A protective atmosphere of N2 / Ar / H2 mixed in a certain proportion is introduced into the reaction chamber, and a scavenger is added; The continuous conductive thin film is subjected to dual-pulse processing. First, a preheating pulse is applied to preheat and shape the thin film material. After a certain interval, a main flash pulse is applied to the preheated thin film material. Quality assessment is performed based on a criterion function to determine the material condition in real time. If the condition meets the standard, the machine is stopped; otherwise, an auxiliary flash pulse is added. Post-treatment and exhaust gas purification, graded screening and acid washing to obtain the finished product, and exhaust gas is treated by cracking, adsorption and waste heat recovery; Inspect the finished products.

[0006] The present invention has the advantages and technical effects of reconstructing conductivity and achieving second-level re-graphitization and impurity removal through two pulse integration synchronizations.

[0007] In some embodiments, the leaching residue accounts for 70%-90%, the recycled conductive additive accounts for 10%-20%, and the carbon precursor accounts for 5%-15%, and the three are mixed quantitatively in weight ratio.

[0008] In some embodiments, the leaching residue is lithium battery black powder leaching residue, the circulating conductive additive is graphite powder or carbon black, and the carbon precursor is phenolic resin or asphalt.

[0009] In some embodiments, the mixture is pressed into a continuous thin layer with a thickness of 0.5-5 mm.

[0010] In some embodiments, the protective atmosphere comprises N2, 80%-95% Ar, 5%-15% H2, and 1%-5% by volume.

[0011] In some embodiments, the impurity catcher is 0.1%-5 wt% of a B / Al-based impurity catcher.

[0012] In some embodiments, the preheating pulse has a duration of 0.2-20 ms and a pulse intensity of 10-200 A·cm. -2 Current density, 0.1-5 J·mg -1 Low-energy pulses with high energy density.

[0013] In some embodiments, the main flash pulse is applied for a duration of 5-2000 μs and a pulse intensity of 200-2000 A·cm. -2 Current density, 2-50 J·mg -1 High-energy pulses with high energy density.

[0014] In some embodiments, the criterion function f(Q) = α·I²D / IG + β·(1 / R) end )-γ·E m Based on the real-time monitoring of the I2D / IG peak intensity ratio of the material using an online Raman spectrometer, combined with the resistance value R collected by the resistance sensor at the end of the pulse... end , and E m If the single-pulse energy f(Q) is greater than the preset value, it is determined to meet the standard and the material is discharged. If it does not meet the standard, an auxiliary flash pulse is added until the standard is met.

[0015] In some embodiments, the preheating pulse is spaced 10-50 ms apart from the main flash pulse.

[0016] The leaching residue, circulating conductive additive, and carbon precursor reconstruct conductivity, while a 0.5–5 mm thin-layer flow path rebuilds a stable flow path framework. Dual-spectrum pulses sequentially remove bound gases, eliminate hot spots, and homogenize current, followed by main flash graphitization and deep impurity removal. In terms of control, online judgment enables immediate stop / refill pulses upon reaching the target, significantly reducing overtreatment and batch-to-batch fluctuations. Attached Figure Description

[0017] Figure 1 This is a flowchart of a method for regenerating graphite from black powder leaching residue using a dual-pulse Joule heat flash evaporation method, as described in an embodiment of the present invention. Detailed Implementation

[0018] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0019] The embodiments of the present invention propose a method for regenerating graphite by double-pulse Joule thermal flash evaporation of black powder leaching residue, comprising the following steps: raw material pretreatment, wherein the leaching residue is quantitatively configured with a circulating conductive additive and a carbon precursor in a certain proportion; the three are mixed in a weight ratio, and the leaching residue can be pre-dried to reduce the moisture content, ensuring that the resistivity of the configured material is reduced.

[0020] The prepared mixture is pressed into a continuous conductive thin layer; the width of the pressed continuous thin layer is adapted to the electrode array of the reaction chamber, and the edges should be neat and free of breakage to avoid local overheating caused by uneven current distribution during pulse heating.

[0021] A protective atmosphere of N2 / Ar / H2 mixed in a certain proportion is introduced into the reaction chamber, and a scavenger is added. The hydrogen concentration is strictly controlled below 5% to avoid the risk of explosion, while providing a reducing environment to remove trace metal impurities. The particle size of the scavenger must be smaller than that of the mixed materials to ensure full contact with the impurities in the leaching residue, generating stable compounds at high temperature to achieve in-situ fixation of impurities.

[0022] A dual-pulse treatment is applied to the continuous conductive thin film. First, a preheating pulse is applied to preheat and shape the thin film material. After a certain interval, a main flash pulse is applied to the preheated thin film material. The preheating pulse is a low-energy pulse designed to quickly remove residual moisture and bound gases from the material, eliminate local resistance differences, and improve the uniformity of current distribution within the thin film material. The main flash pulse instantly heats the material to 2500-3000℃, causing disordered carbon in the leaching residue to rapidly reconstruct into graphite crystals. This allows impurities such as F and P that are not fixed by the impurity catcher to escape in gaseous form or react with the impurity catcher to achieve millisecond-second crystallization enhancement and selective impurity removal.

[0023] Quality assessment is performed in real-time based on a criterion function to determine the material's condition. If the condition meets the standard, the machine stops; otherwise, an additional flash pulse is added. This criterion function, utilizing multiple parameters for online feedback, overcomes the lag issues of offline detection and batch determination in traditional processes. Through online real-time monitoring and closed-loop control, precise quality control of each material segment is achieved. The automatic addition of additional flash pulses reduces human intervention and material loss due to parameter fluctuations, thereby improving production efficiency and cost control.

[0024] Post-treatment and exhaust gas purification: After grading, screening, and acid washing, the finished product is obtained. The exhaust gas undergoes pyrolysis, adsorption, and waste heat recovery treatment. Grading treatment can remove broken particles through vibrating sieving, combined with acid washing to remove residual impurities. After the exhaust gas undergoes high-temperature pyrolysis to decompose organic components, HF / POx is removed using an adsorption tower filled with calcium hydroxide. Heat is recovered from the exhaust gas through a heat exchanger to reduce system energy consumption and preheat the protective atmosphere.

[0025] Inspect the finished products.

[0026] In some embodiments, the leaching residue accounts for 70%-90%, the recycled conductive additive accounts for 10%-20%, and the carbon precursor accounts for 5%-15%, and the three are mixed quantitatively in weight ratio.

[0027] Specifically, the circulating conductive additive is essential for quickly establishing temporary conductive paths to meet the basic requirement of uniform pulse current conduction. An excessively high proportion will reduce the proportion of the primary carbon phase of graphite in the leaching residue, increasing costs. The carbon precursor carbonizes during the thermal process to form a stable carbon skeleton, fixing the leaching residue particles and preventing breakage during thin-layer pressing. An excessive proportion will cause large volume shrinkage, leading to thin-layer cracking. The leaching residue is first dried and crushed to ensure uniform mixing with the circulating conductive additive and carbon precursor. Leaching residue with excessively large particle sizes will result in insufficient encapsulation of the circulating conductive additive and carbon precursor, creating conductive blind spots. High moisture content will cause agglomeration, affecting the accuracy of the proportioning.

[0028] In some embodiments, the leaching residue is lithium battery black powder leaching residue, the circulating conductive additive is graphite powder or carbon black, and the carbon precursor is phenolic resin or asphalt.

[0029] Specifically, the leaching residue from lithium-ion battery black powder is the residue from the wet metal recovery of lithium-ion battery black powder. Due to metal leaching, the original conductive pathways are broken, the particles are loose and lack cohesion, and impurities are tightly bound to the carbon phase, directly limiting the feasibility of graphitization regeneration. Drying and crushing are used to process the particles, reducing moisture content and particle size. Graphite powder can build conductive pathways and improve the mechanical strength of thin layers. Carbon black has a large specific surface area, which can fill the voids in the leaching residue particles, solving the problem of uneven local conductivity. Its high adsorption capacity can pre-adsorb some F and P impurities, reducing the pressure of subsequent impurity removal. Phenolic resin can bind the loose particles into a whole, and after carbonization, it can form an amorphous carbon skeleton, introducing fewer additional impurities and ensuring the purity of the finished product. Asphalt is inexpensive and has high viscosity, which can encapsulate some of the remaining tiny impurities, preventing their migration and diffusion during graphitization.

[0030] In some embodiments, the mixture is pressed into a continuous thin layer with a thickness of 0.5-5 mm.

[0031] Specifically, when the thickness of a continuous thin layer pressed from a mixture is less than 0.5 mm, its mechanical strength is insufficient, making it prone to tearing and breakage. This can lead to current interruption during subsequent pulse heating, and excessive thinness can also cause overheating and ablation due to localized current concentration. When the thickness exceeds 5 mm, uneven heat dissipation can easily result in overheating of the outer layer and underheating of the core, failing to solve the problem. Furthermore, it increases the escape path length for internal gases such as moisture and PVDF decomposers. If these gases cannot be expelled in time, internal voids and cracks can occur. A double-roller tablet press is used for pressing, allowing for distributed pressing. Pre-pressing is performed first to initially compact the loose material, followed by a second pressing to precisely control the final thickness and density.

[0032] In some embodiments, the protective atmosphere consists of N2, 80%-95% Ar, 5%-15% H2, and 1%-5% by volume.

[0033] Specifically, nitrogen is a low-cost inert gas and the main component of the protective atmosphere. Its high proportion allows for rapid replacement of air in the reaction chamber, creating a stable inert environment. Argon reduces heat convection losses within the reaction chamber, resulting in a more uniform temperature field during pulse heating. Ar has a high density; excessive addition increases gas circulation resistance and is costly. Hydrogen, as a weak reducing gas, reduces trace metal oxides remaining in the leaching residue, facilitating subsequent acid washing removal. It also catalyzes carbon skeleton reconstruction, improving graphitization efficiency. However, the hydrogen concentration has a safe threshold; excessively low concentrations will result in poor reduction.

[0034] In some embodiments, the impurity catcher is 0.1%-5wt% of a B / Al-based impurity catcher.

[0035] In some embodiments, the preheating pulse has a duration of 0.2-20 ms and an intensity of 10-200 A·cm. -2Current density, 0.1-5 J·mg -1 Low-energy pulses with high energy density.

[0036] Specifically, the lower limit of the low-energy pulse duration ensures sufficient pretreatment time for the material, achieving initial removal of surface and shallow moisture and weakly bound gases. Joule heating gently softens the carbon precursor, enhancing interparticle adhesion. The upper limit of the duration prevents excessively high material temperatures from causing localized disordered oxidation or premature carbonization of the precursor. The current density ensures sufficient Joule heating of the mixture while preventing localized overheating and ablation, which would affect heat transfer in the subsequent main flash evaporation process.

[0037] In some embodiments, the main flash pulse is applied for a duration of 5-2000 μs and a pulse intensity of 200-2000 A·cm. -2 Current density, 2-50 J·mg -1 High-energy pulses with high energy density.

[0038] Specifically, the lower limit of the main flash pulse duration ensures that the material receives a sufficient high temperature for a prolonged period, enabling rapid reconstruction of the graphite lattice. The upper limit of the duration prevents prolonged high-energy heating from damaging the graphite interlayer structure and causing carbon phase sublimation loss. The instantaneous high temperature of 2500-3000℃ promotes the rapid reconstruction of disordered carbon in the leaching residue into graphite crystals. Excessive current density can cause localized ablation and electrical breakdown, shortening equipment lifespan and affecting product quality. The steep rise and fall of the pulse waveform (square wave) ensures rapid and concentrated energy release, avoiding uneven heating caused by energy dispersion. In some embodiments, the criterion function f(Q) = α·I²D / IG + β·(1 / Rend) - γ·Em is based on the real-time monitoring of the I²D / IG peak intensity ratio of the material by an online Raman spectrometer, combined with the resistance value Rend collected by a resistance sensor at the end of the pulse, and E m If the single-pulse energy f(Q) is greater than the preset value, it is determined to meet the standard and the material is discharged. If it does not meet the standard, an auxiliary flash pulse is added until the standard is met.

[0039] Specifically, the peak intensity ratio is the ratio of the intensity of the 2D peak to the G peak in the Raman spectrum, reflecting the degree of crystallinity, with a target value ≥1.2, and the resistivity R... end Target value ≤ 10mΩ, R end Smaller conductivity indicates better conductivity and reflects structural compactness. Adding a pulse can salvage critically defective materials, increasing raw material utilization to ≥98% and reducing material loss costs. A limit of ≤2 pulse additions avoids meaningless energy waste. Online monitoring solves the lag problem of traditional offline detection, improving the pass rate. Multi-parameter fusion judgment ensures comprehensive product performance. α, β, and γ are used as weighting parameters to adjust the weights of various parameters in the criterion function, determined through experimental calibration.

[0040] In some embodiments, the interval between the preheating pulse and the main flash pulse is 10-50 ms.

[0041] Specifically, after the preheating pulse, the material rapidly loses moisture and some volatile organic compounds. These gases need to be discharged from the reaction chamber through a time interval. This interval allows for the smooth discharge of most of the removed gases, preventing them from being trapped inside the material by high temperatures during the main flash evaporation, which could lead to pores and cracks. Furthermore, the time interval allows the softened carbon precursor after preheating to initially cool and solidify, enhancing the material's structural stability and preventing particle splashing caused by the high-energy impact of the main flash evaporation. An excessively long interval can easily cause material degradation and a rise in resistivity, which is detrimental to subsequent main flash evaporation. The time interval also allows for a smooth temperature transition of the material, reducing structural damage caused by thermal stress.

[0042] In some embodiments, during the raw material pretreatment step, the various materials are dried and crushed to produce a mixture.

[0043] Specifically, drying and crushing unify the material morphology and moisture content, avoiding the problems of poor conductivity and easy agglomeration of leaching residue. It can accurately control the particle size and mixing uniformity, ensuring sufficient contact between particles during thin-layer pressing and avoiding uneven heating caused by local pores.

[0044] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0045] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0046] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between them; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0047] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0048] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0049] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for regenerating graphite from black powder leaching residue using a dual-pulse Joule thermal flash evaporation technique, characterized in that, Includes the following steps: Raw material pretreatment involves quantitatively configuring leaching residue with recycled conductive additives and carbon precursors in a specific ratio. The prepared mixture is pressed into a continuous conductive thin layer; A protective atmosphere of N2 / Ar / H2 mixed in a certain proportion is introduced into the reaction chamber, and a scavenger is added; The continuous conductive thin film is subjected to dual-pulse processing. First, a preheating pulse is applied to preheat and shape the thin film material. After a certain interval, a main flash pulse is applied to the preheated thin film material. Quality assessment is performed based on a criterion function to determine the material condition in real time. If the condition meets the standard, the machine is stopped; otherwise, an auxiliary flash pulse is added. Post-treatment and exhaust gas purification, graded screening and acid washing to obtain the finished product, and exhaust gas is treated by cracking, adsorption and waste heat recovery; Inspect the finished products.

2. The method for regenerating graphite from black powder leaching residue using a dual-pulse Joule thermal flash evaporation according to claim 1, characterized in that, The leaching residue accounts for 70%-90%, the recycled conductive additive accounts for 10%-20%, and the carbon precursor accounts for 5%-15%, and the three are mixed quantitatively according to the weight ratio.

3. The method for regenerating graphite from black powder leaching residue using a dual-pulse Joule thermal flash evaporation according to claim 2, characterized in that, The leaching residue is lithium battery black powder leaching residue, the circulating conductive additive is graphite powder or carbon black, and the carbon precursor is phenolic resin or asphalt.

4. The method for regenerating graphite from black powder leaching residue using a dual-pulse Joule thermal flash evaporation according to claim 1, characterized in that, The mixture is pressed into a continuous thin layer with a thickness of 0.5-5 mm.

5. The method for regenerating graphite from black powder leaching residue using a dual-pulse Joule thermal flash evaporation according to claim 1, characterized in that, The protective atmosphere consists of N2, 80%-95% Ar, 5%-15% H2, and 1%-5% by volume.

6. The method for regenerating graphite from black powder leaching residue using dual-pulse Joule thermal flash evaporation according to claim 1, characterized in that, The impurity catcher is 0.1%-5 wt% of a B / Al-based impurity catcher.

7. The method for regenerating graphite from black powder leaching residue using dual-pulse Joule thermal flash evaporation according to claim 1, characterized in that, The preheating pulse has a duration of 0.2-20 ms and an intensity of 10-200 A·cm. -2 Current density, 0.1-5 J·mg -1 Low-energy pulses with high energy density.

8. The method for regenerating graphite from black powder leaching residue using dual-pulse Joule thermal flash evaporation according to claim 1, characterized in that, The main flash pulse is applied for a duration of 5-2000 μs and a pulse intensity of 200-2000 A·cm. -2 Current density, 2-50 J·mg -1 High-energy pulses with high energy density.

9. The method for regenerating graphite from black powder leaching residue using a dual-pulse Joule thermal flash evaporation according to claim 1, characterized in that, The criterion function f(Q) = α·I²D / IG + β·(1 / Rend) - γ·Em is based on the real-time monitoring of the I²D / IG peak intensity ratio of the material by an online Raman spectrometer, combined with the resistance value R collected by a resistance sensor at the end of the pulse. end , and E m If the single-pulse energy f(Q) is greater than the preset value, it is determined to meet the standard and the material is discharged. If it does not meet the standard, an auxiliary flash pulse is added until the standard is met.

10. The method for regenerating graphite from black powder leaching residue using a dual-pulse Joule thermal flash evaporation according to claim 1, characterized in that, The preheating pulse and the main flash pulse are spaced 10-50 ms apart.

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