Method for preparing repairable regenerated black powder from retired lithium battery through fine heat treatment and product and application thereof

Abstract

The application discloses a method for preparing repairable regenerated black powder by fine heat treatment of retired lithium batteries, and products and applications thereof, and belongs to the technical field of lithium battery recycling, and comprises the following steps: (1) punching the retired batteries after discharge, and performing negative pressure distillation separation of electrolyte under a negative pressure condition, and pyrolyzing the remaining part under a nitrogen atmosphere to remove PVDF binder and a separator; (2) slowly oxidizing and releasing heat of the retired batteries after pyrolysis in a mixed gas of oxygen and nitrogen, detecting and recycling the high-temperature circulating tail gas after the oxidation reaction, and separating and crushing the positive and negative electrode materials to obtain the repairable regenerated black powder. The method provided by the application can process retired lithium batteries of different types and forms, is suitable for distributed workstation popularization requirements, can be embedded in a large-scale recycling factory or independently deployed, and has a wide popularization and application prospect.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery recycling technology, and in particular relates to a method for preparing repairable and regenerable black powder through refined thermal treatment of retired lithium batteries, as well as its products and applications. Background Technology

[0002] As the global energy structure accelerates its transformation towards low-carbon, clean, and electrified energy, lithium-ion batteries, as a high-efficiency energy storage medium, have demonstrated strong application potential in new energy vehicles, power storage, and consumer electronics. In 2024, my country's total lithium-ion battery production reached 1170 GWh, with its global market share rising to 76%. It is projected that by 2030, my country's annual output of end-of-life lithium-ion batteries will reach 4 million tons. As an important component of urban mining, the efficient recycling of retired lithium-ion batteries can not only achieve high-value regeneration of strategic metal resources such as lithium, cobalt, nickel, and copper, but also significantly reduce the safety and environmental pollution risks posed by discarded batteries. However, my country's lithium battery recycling system is currently underdeveloped, with generally low recycling rates, even below 10% in some areas. The recycling of retired lithium batteries still faces multiple challenges, including technological, economic, and environmental safety issues.

[0003] In existing technologies, the pretreatment for recycling retired lithium batteries mainly includes three technical paths: the crushing-then-pyrolysis path, the direct crushing and separation path without heat treatment, and the traditional pyrolysis path. Among them, the core process of the crushing-then-pyrolysis path is primary crushing and descaling, fine crushing and pulverizing, and pyrolysis treatment. The advantages of this path are that the crushing equipment is mature and the processing efficiency is high. Pyrolysis can quickly remove organic matter such as electrolyte, separator and PVDF binder. The process has strong continuity and is easy to scale up. However, its defects are also very obvious: after fine crushing, copper and aluminum current collectors are completely mixed with positive and negative electrode materials and impurities, which cannot be separated after pyrolysis, resulting in a high content of black powder impurities; the crushing process is very prone to short circuits and thermal runaway, posing serious safety hazards; fine crushing will also destroy the crystal structure of the positive electrode material, which seriously affects the subsequent repair and regeneration effect. Secondly, the core process of the direct crushing and separation path without heat treatment involves discharge, initial crushing and descaling, fine crushing, and physical sorting. This path has the simplest process, the lowest equipment investment cost, no high-temperature treatment, and no risk of flue gas pollution. However, its problems include the incomplete decomposition of organic binders, low separation efficiency between active materials and current collectors, and residual electrolyte, PVDF, and other organic matter in the black powder. Subsequent leaching or remediation requires additional impurity removal. Physical sorting cannot remove chemical impurities such as fluorides, resulting in low overall recovery efficiency. In addition, conventional pyrolysis in the traditional pyrolysis path can only remove organic impurities, leaving metallic impurities such as copper and aluminum in the black powder. This necessitates additional impurity removal steps in subsequent hydrometallurgical processes, significantly increasing processing costs. Under high-temperature conditions, it can also easily trigger an aluminothermic reaction, damaging the crystal structure of the cathode material and affecting the resource recycling value. Furthermore, the traditional fine crushing and pulverizing process easily causes impurities in the active material and current collector to mix, making it difficult to improve the purity of the black powder. Impurities such as fluorides cannot be removed by a single pyrolysis, requiring an additional defluorination process, increasing process complexity and environmental pressure.

[0004] The core defects of existing technologies for pre-processing retired lithium batteries can be summarized in four aspects. First, there is a high safety risk. Retired batteries still retain 30% to 80% of their remaining charge. Improper handling during pre-processing operations such as mechanical crushing and shearing can easily lead to short circuits and self-heating, potentially causing thermal runaway or even fires and explosions. Furthermore, the toxic, harmful, flammable, and explosive gases such as HF, CO, and VOCs released during pyrolysis can easily cause gas explosions in confined spaces. In recent years, numerous safety accidents involving retired lithium batteries have occurred, fully exposing the weaknesses in safety control within the current recycling system. Second, there is insufficient purity of the black powder. Mechanical crushing in traditional pre-processing technologies easily introduces metallic impurities such as copper and aluminum, damaging the crystal structure of the cathode material. Traditional heat treatment makes it difficult to precisely control reaction conditions, resulting in insufficient purity of the black powder and high levels of copper and aluminum impurities. Copper impurities can cause self-discharge in the repaired cathode material, severely affecting electrochemical performance. Furthermore, current technologies for recycling retired batteries are energy-intensive and involve lengthy processes. Pyrometallurgical processes typically involve high-temperature roasting above 1000℃, resulting in extremely high energy consumption and significant greenhouse gas emissions. Hydrometallurgical processing costs approximately $3360 to $4160 per ton in China and as high as $4780 to $5640 per ton in the United States. Finally, direct recycling technology faces industrialization bottlenecks. Existing direct recycling technologies are all based on the manual dismantling and separation of high-purity cathode materials in laboratory environments, failing to address the core challenge of large-scale processing of actual retired batteries: how to achieve precise and efficient industrial-scale separation of cathode and anode materials from current collectors, while ensuring that the separated products meet the requirements of low impurities and direct repairability. Current pretreatment technologies are not suitable for the large-scale application requirements of direct recycling.

[0005] Therefore, how to provide a safe, simple, energy-efficient, and highly efficient method for recycling retired lithium batteries is a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention proposes a method for preparing repairable and regenerable black powder through refined thermal treatment of retired lithium batteries.

[0007] To achieve the above objectives, the present invention provides the following technical solution: A method for preparing repairable and regenerable black powder through refined thermal treatment of retired lithium batteries includes the following steps: (1) Drill holes in the discharged retired battery, place it under negative pressure conditions for negative pressure distillation to separate the electrolyte, and pyrolyze the remaining part under nitrogen atmosphere to remove PVDF binder and separator; (2) After the pyrolysis is completed, the retired battery is placed in a mixture of oxygen and nitrogen to slowly oxidize and release heat. After the oxidation reaction is completed, the high-temperature circulating tail gas is detected and recycled. The positive and negative electrode materials are separated and crushed to obtain repairable and regenerable black powder.

[0008] Beneficial Effects: This invention proposes a four-step synergistic and refined thermal treatment process: negative pressure distillation, gentle pyrolysis, low-oxygen flameless oxidation, and exhaust gas waste heat recovery. This process aims to mitigate the fire and explosion risks associated with the transportation, storage, disposal, and recycling of retired lithium batteries from the source. It produces high-purity, directly repairable and regenerable black powder with extremely low levels of copper, aluminum, and fluoride impurities, achieving a safe, efficient, clean, and low-carbon recycling process for retired lithium batteries. This invention integrates the safe disposal and resource recovery of retired lithium batteries, enabling efficient dissociation of organic impurities and simultaneous removal of copper and aluminum impurities. The entire process targets zero-charge retired lithium batteries. First, internal and external gas channels are established by perforating a safety valve. Then, the electrolyte is recovered by low-temperature distillation under negative pressure. Next, residual organic matter is decomposed by gentle pyrolysis under low-oxygen conditions. Then, low-oxygen flameless oxidation provides in-situ heating of the flue gas while mitigating explosion risks. Finally, exhaust gas waste heat recovery reduces overall energy consumption, yielding high-purity, repairable and regenerable black powder.

[0009] Preferably, the retired battery includes one or more of ternary lithium batteries (NCM), lithium iron phosphate batteries (LFP), and lithium cobalt oxide batteries (LCO).

[0010] Preferably, the discharge in step (1) is to discharge until SOC=0.

[0011] Preferably, the drilling in step (1) is performed at the location of the safety valve, with a hole diameter of 2-5 mm.

[0012] Preferably, the pressure of the negative pressure distillation in step (1) is -0.07~-0.09 MPa, and the temperature is 80-100℃.

[0013] Beneficial effects: Under negative pressure, the boiling points of organic solvents and lithium salts in the electrolyte are significantly reduced. This invention achieves low-temperature distillation by reducing pressure, avoiding the risk of thermal runaway caused by high temperatures. The distilled electrolyte vapor is liquefied and collected by a condensation and recovery device. A defluorination filter is installed at the front end of the condensation and fume collection tank to absorb hydrogen fluoride and water vapor, preventing hydrogen fluoride from corroding subsequent processing units. The negative pressure distillation stage in this invention can remove more than 90% of the electrolyte at temperatures below 100°C, eliminating the main flammable and explosive risks at the source.

[0014] Preferably, the pyrolysis temperature in step (1) is 400-500℃ and the time is 30-90min.

[0015] More preferably, when the retired battery is a ternary lithium battery (NCM), the pyrolysis temperature is 450~480℃ to prevent the reduction of lithium nickel cobalt manganese oxides; When the retired battery is a lithium iron phosphate battery (LFP), the pyrolysis temperature is 480~520℃, because its olivine structure has higher thermal stability. When the retired battery is a lithium cobalt oxide (LCO) battery, the pyrolysis temperature is 400~450℃ to avoid the decomposition of lithium cobalt oxide.

[0016] Beneficial effects: The pyrolysis in this invention is carried out under a nitrogen atmosphere. Low-oxygen pyrolysis controls the oxygen concentration to below 80% of the limiting oxygen concentration. Under this strictly controlled low-oxygen environment, the residual electrolyte, PVDF binder, separator, and other organic components undergo thermal decomposition. PVDF begins to decompose at 350℃ and almost completely decomposes at around 500℃. By controlling the temperature below 500℃, the aluminothermic reaction can be effectively avoided, protecting the lattice structure of the cathode material from damage. Simultaneously, by controlling the oxygen concentration below 80% of the limiting oxygen concentration, the combustible gases in the pyrolysis flue gas are prevented from reaching their explosive limits. The pyrolysis furnace temperature must also avoid the auto-ignition temperature sensitive range of major combustible gases such as hydrogen, methane, and carbon monoxide, between 550℃ and 610℃, ensuring the safety and controllability of the entire process.

[0017] Preferably, the temperature of the mixed gas in step (2) is 100-200°C, and the volume concentration of oxygen is 5-10%.

[0018] Beneficial effects: This invention mixes fresh, room-temperature pure oxygen with high-temperature circulating exhaust gas in a certain proportion. After mixing, the oxygen concentration is controlled below 80% of the limiting oxygen concentration, and the combustible gas concentration is controlled below 80% of the lower explosive limit. This allows the combustible gas to undergo a slow oxidation reaction under flameless conditions, releasing heat. This flameless oxidation method replaces traditional open flame combustion, fundamentally avoiding the risk of flue gas explosions in confined spaces, while simultaneously achieving in-situ energy recovery and utilization.

[0019] Preferably, the temperature of the high-temperature circulating exhaust gas in step (2) is 200-400℃ and the concentration of combustible gas is >5 vol.

[0020] Preferably, the recycling process involves using high-temperature circulating exhaust gas to replace nitrogen and mix it with oxygen as a mixed gas for the slow oxidation and exothermic process of the decommissioned battery after pyrolysis.

[0021] More preferably, the recycling process involves replacing nitrogen with oxygen in the high-temperature circulating exhaust gas that does not meet emission standards (combustible gas concentration > 5 vol%) to create a mixed gas for waste heat recovery and slow oxidation heat release, providing a partial heat source for the pyrolysis process of retired batteries.

[0022] The exhaust gas that meets the standards (combustible gas concentration ≤5 vol%) is discharged after being absorbed by sodium hydroxide alkaline solution, etc.

[0023] Beneficial effects: High-temperature circulating exhaust gas can exchange heat with room-temperature pure oxygen in the mixing heat exchange device, transferring the residual heat in the high-temperature exhaust gas to fresh pure oxygen to achieve preheating. The preheated mixed gas enters the pyrolysis furnace for oxidation and heat release treatment, effectively reducing the energy consumption of electric heating and achieving low-carbon operation. Moreover, the carbon dioxide content in the high-temperature circulating exhaust gas reaches more than 90%, which has good inerting effect and heat carrier characteristics.

[0024] Preferably, the temperature of the oxidation exothermic process in step (2) is 300-500℃ and the time is 20-60min.

[0025] Beneficial effects: The flameless oxidation exothermic process is a slow gas-phase oxidation reaction, and the reaction rate is controlled by the concentration of combustible gas, oxygen concentration, and temperature. Under low oxygen concentration conditions (5~10 vol%), the reaction rate is moderate and will not cause violent combustion. As the combustible gas is consumed, the reaction automatically slows down. When the concentration drops below 5 vol%, the exothermic heat of oxidation is insufficient to maintain the high temperature, and the system enters a "self-limiting" steady state. At this point, the reaction can be judged to be over, and this time range is generally within 20-60 minutes.

[0026] A repairable and regenerable black powder prepared by the method described above, wherein the copper content in the repairable and regenerable black powder is 1-100 ppm and the aluminum content is 1-100 ppm.

[0027] Application of a repairable and regenerable black powder in the short-process direct recycling and preparation of high-purity lithium iron phosphate cathode materials.

[0028] More preferably, the application includes the following steps: The regenerable black powder is separated by flotation to achieve effective separation of the positive and negative electrode materials, thereby obtaining a high-purity positive electrode material that can be directly used for repair and regeneration.

[0029] Compared with the prior art, the present invention has the following advantages and technical effects: The integrated process of negative pressure distillation, low-temperature pyrolysis, and flameless exothermic oxidation in this invention completely solves the fire and explosion safety problem in the pretreatment process of retired lithium battery recycling, achieving a transformation from high safety risk to inherent safety. Simultaneously, the four-step synergistic process of negative pressure distillation, low-temperature pyrolysis, and flameless exothermic oxidation combined with the waste heat recovery process in this invention achieves efficient dissociation of organic impurities. Precise initial crushing avoids the mixing of copper and aluminum current collectors with positive and negative electrode materials. The copper and aluminum impurity content in the prepared black powder is controlled below 100 ppm, fully meeting the requirements for direct repair and regeneration. At the same time, it avoids the damage to the crystal structure of the positive electrode material caused by traditional fine crushing and pulverizing processes, maintaining the integrity of the layered or olivine structure of the positive electrode material, with uniform grain size distribution, allowing it to directly enter the repair and regeneration stage.

[0030] Secondly, the oxidation process in this invention utilizes the high-temperature circulating tail gas recovered from the pyrolysis step. The combustible gas in this gas can release heat through oxidation, providing an auxiliary heat source for the pyrolysis furnace. Simultaneously, energy recovery is further achieved through heat exchange via mixing the high-temperature circulating tail gas with fresh pure oxygen. The battery thermal utilization rate within the system reaches over 80%, saving approximately 30% to 40% of energy compared to traditional heat treatment processes, significantly reducing operating costs. Furthermore, the four-step synergistic process in this invention organically integrates safe disposal with black powder preparation. The prepared repairable regenerable black powder can be directly used for flotation regeneration to prepare high-purity lithium iron phosphate cathode materials, eliminating the need for additional hydrometallurgical or pyrometallurgical steps. This significantly shortens the recycling process, providing high-purity repairable regenerable black powder for direct recycling technology, and propelling it from the laboratory to large-scale industrial application. Furthermore, the method provided by this invention achieves a high-efficiency recovery rate of over 90% for lithium battery electrolyte, avoiding pollution from the volatilization of organic solvents. Fluorine-containing gases such as hydrogen fluoride are captured in situ by calcium hydroxide and calcium oxide to form stable inorganic fluorides. The purification rate of combustible components in flue gas exceeds 95%, achieving emission standards without secondary pollution, fully complying with the requirements of green, low-carbon, and circular economic development. Finally, the method provided by this invention can process different types of retired lithium batteries, including ternary lithium, lithium iron phosphate, and lithium cobalt oxide, as well as batteries of different shapes, including cylindrical, prismatic, and pouch cells. It is suitable for the promotion of distributed workstations and can be embedded in large-scale recycling plants or deployed independently, demonstrating broad application prospects. Attached Figure Description

[0031] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 This is the four-step synergistic refined thermal treatment process for retired lithium batteries in Embodiment 1 of the present invention; Figure 2 The temperature-pressure-oxygen concentration synergistic control curves for the negative pressure distillation and mild pyrolysis stages in Example 1 are shown. Detailed Implementation

[0032] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0034] This invention provides a four-step synergistic refined thermal treatment process for preparing repairable regenerable black powder from retired lithium batteries. The core of this process lies in sequentially performing four stages: "negative pressure distillation - gentle pyrolysis - low-oxygen flameless oxidation - waste heat recovery from tail gas," followed by precise cutting and initial crushing and flotation separation after thermal treatment. The following is combined with... Figure 1 The process flow shown explains the optimal implementation parameters, equipment selection, and operational details for each stage.

[0035] 1. Pretreatment and safety valve drilling The retired lithium batteries to be processed must first be discharged to zero state of charge (SOC=0), which can be achieved using constant current discharge or short-circuit discharge, ensuring that the residual voltage of the battery is below 0.5V. Then, a special drilling device is used to drill a hole at the battery's safety valve location, with a hole diameter typically between 2 and 5 mm. The purpose is to establish a gas passage between the inside and outside of the battery, preventing explosions due to excessive internal pressure during subsequent heating. For pouch batteries, pressure can also be released using needle puncture or beveling methods.

[0036] 2. First stage: Negative pressure distillation The perforated battery is placed in a sealed pyrolysis furnace, connected to a vacuum system and a condensation recovery device. The furnace pressure is controlled at -0.07 to -0.09 MPa, and the battery is heated to 80 to 100°C at a heating rate of 5 to 10 K / min, held for 20 to 60 minutes. Under these conditions, the organic solvents (such as dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), etc.) and lithium salts (such as LiPF6) in the electrolyte vaporize and are liquefied into liquid electrolyte in a condenser (cooling medium is 5 to 10°C cold water or ethylene glycol solution), collected in a storage tank. A fluoride removal filter (containing calcium hydroxide, calcium oxide, or activated alumina) should be installed at the front end of the condenser to capture small amounts of HF and water vapor produced during decomposition, preventing corrosion of downstream equipment. The electrolyte recovery rate in this stage can reach over 90%.

[0037] 3. Second stage: Mild pyrolysis After negative pressure distillation, maintain a slight negative pressure or normal pressure inside the furnace, and introduce an inert gas (nitrogen, carbon dioxide, or recirculated tail gas) to control the oxygen concentration. Continue to raise the furnace temperature to 400-500℃ at a rate of 5-15 K / min, and hold for 30-90 minutes. Key control parameters: 1) The oxygen concentration should be controlled below 80% of the limiting oxygen concentration (LOC), which typically corresponds to ≤10 vol%. 2) The concentration of combustible gases (H2, CH4, CO, C2H4, etc.) in the pyrolysis flue gas is controlled to be below 80% of the lower explosive limit (LEL); 3) The pyrolysis temperature should avoid the auto-ignition temperature sensitive range (550~610℃) of major combustible gases such as hydrogen, methane, and carbon monoxide.

[0038] Under these conditions, residual electrolyte, diaphragm (PP / PE), PVDF binder, and other organic matter undergo complete thermal decomposition, generating small-molecule combustible gases, while the lattice structure of the cathode material remains intact, and the aluminum foil does not undergo an aluminothermic reaction. The pyrolysis furnace can be electrically heated, or the in-situ heating from subsequent flameless oxidation can be used as an auxiliary heat source.

[0039] 4. Third stage: Low-oxygen flameless oxidation exothermic Fresh, room-temperature pure oxygen (or oxygen-enriched air) is mixed with nitrogen (approximately 200-400℃) at a volume ratio of 1:3 to 1:5, resulting in an oxygen concentration of 5-10 vol%. The mixed gas enters a flameless oxidation chamber, where, under flameless conditions, the combustible gas undergoes a slow oxidation reaction, releasing heat. This released heat is fed back to the pyrolysis furnace via heat exchange or flue gas recirculation, providing an auxiliary heat source for the gentle pyrolysis stage and thus reducing energy consumption for electric heating. The key to this stage is maintaining the oxygen and combustible gas concentrations in the mixed gas below safe limits, fundamentally mitigating the risk of flue gas explosion.

[0040] 5. Fourth stage: Exhaust gas waste heat recovery The concentration of combustible gases in the exhaust gas discharged from the flameless oxidation chamber is detected online. 1) If >5 vol% (not up to standard), it shall be sent back to the pyrolysis furnace or flameless oxidation chamber for secondary treatment by circulating fan; 2) If ≤5vol% (meets the standard), it is sent to an alkaline absorption tower (the absorption liquid is 5~10wt% NaOH or Ca(OH)2 suspension) for purification to remove acidic gases such as HF and CO2, and then discharged in compliance with the standard.

[0041] Simultaneously, high-temperature circulating exhaust gas (200~400℃) is mixed with room-temperature pure oxygen in a heat exchanger, preheating the pure oxygen to 100~200℃ before it enters the flameless oxidation chamber. This improves the oxidation reaction efficiency and recovers the waste heat from the exhaust gas. This stage can achieve an overall system thermal utilization rate of over 80%, saving 30~40% of energy compared to traditional heat treatment processes.

[0042] 6. Cutting, crushing and sorting after heat treatment After four heat treatment steps, the overall battery structure is fully disintegrated (the outer shell becomes brittle, the separator carbonizes, the binder disappears, and the copper / aluminum foil naturally separates from the active materials). Precision cutting equipment (such as laser cutting or disc shears) is used to remove the battery casing (aluminum, steel, or aluminum-plastic film). Then, light crushing (such as a hammer crusher or roller crusher, controlling the particle size to 1-5mm) further separates the copper and aluminum foil from the black powder. Through sieving (80-200 mesh) or air separation, repairable regenerable black powder (mainly a mixture of positive and negative electrode active materials) is obtained. The copper and aluminum impurity content in the repairable regenerable black powder can be controlled below 20ppm.

[0043] To further obtain high-purity cathode materials, recyclable black powder can be separated by flotation. The flotation medium is deionized water, with the addition of appropriate collectors (such as kerosene or pine oil) and modifiers (such as lime or sodium carbonate). By adjusting the pH and aeration rate, the cathode material (relatively hydrophobic) is effectively separated from the anode material (graphite, which is more hydrophilic). The flotation separation rate can reach over 95%, and the obtained cathode material can be directly used in lithium replenishment, repair, and other regeneration processes.

[0044] The above four-step synergistic process of the present invention can be appropriately adjusted according to different battery types and processing scales. For example, (1) High-temperature circulating tail gas replaces nitrogen as an inert medium: In the pyrolysis stage, the high-temperature circulating tail gas (CO2 content > 90%) of the fourth stage can be directly used to replace the purchased nitrogen, which reduces operating costs and utilizes the waste heat of the tail gas.

[0045] (2) Step-by-step equipment configuration: For small and medium scale processing (<1000 tons / year), negative pressure distillation and mild pyrolysis can be carried out in the same multi-functional pyrolysis furnace in different time periods; for large-scale continuous production (>5000 tons / year), a rotary kiln series design can be adopted, with the first kiln section being the negative pressure distillation section and the second kiln section being the mild pyrolysis section, with gas seal isolation in between.

[0046] (3) Flotation: If the copper and aluminum impurities in the black powder are below 20 ppm and only mixed powder is needed, the flotation step can be omitted and the black powder can be directly used for hydrometallurgical leaching. If it is necessary to recover the positive and negative electrodes separately, centrifugal gravity separation or electrostatic separation can be used in addition to flotation.

[0047] (4) Parameter adaptation for different battery types: 1) Ternary lithium battery (NCM): pyrolysis temperature 450~480℃, to prevent the reduction of lithium nickel cobalt manganese oxides.

[0048] 2) Lithium iron phosphate battery (LFP): The pyrolysis temperature can be increased to 480~520℃ due to its higher thermal stability due to its olivine structure.

[0049] 3) Lithium cobalt oxide (LCO) batteries: The pyrolysis temperature should be controlled at 400~450℃ to avoid the decomposition of lithium cobalt oxide.

[0050] Unless otherwise specified, all raw materials used in the embodiments of this invention were purchased through commercial channels; Unless otherwise specified, room temperature or normal temperature in the embodiments of the present invention refers to 25±3℃.

[0051] Example 1 A method for preparing repairable and regenerable black powder through refined thermal treatment of retired lithium batteries, such as... Figure 1As shown, a new energy vehicle uses a soft-pack ternary lithium battery, model NCM523, with a nominal capacity of 50Ah, a weight of approximately 2.5kg, and dimensions of approximately 300mm × 100mm × 12mm. The retired state of charge (SOC) is zero or close to zero. The process includes the following steps: (1) The battery SOC was reduced to 0 by constant current discharge. Then, a 3mm hole was drilled at the safety valve position using a special drilling tool to establish a gas communication channel between the inside and outside of the battery. The drilled battery was placed in a sealed box furnace and heated to 90℃ at a rate of 5K / min under a negative pressure of -0.08MPa for 30min for negative pressure distillation. During this process, the electrolyte vapor was liquefied and recovered by a condenser with a recovery rate of 92%. At the same time, the calcium hydroxide filter at the front end of the condenser was used to effectively capture hydrogen fluoride gas.

[0052] (2) After the negative pressure distillation is completed, vacuum is continued, and nitrogen is introduced to maintain an oxygen concentration of 6 vol% > 5 vol%. Then, the temperature is increased to 450℃ at 5 K / min and held for 60 min for mild pyrolysis for 1 h. During the pyrolysis process, the oxygen concentration is monitored and controlled in real time to be 3~5 vol%, and the combustible gas concentration is 8~12 vol% (far below 80% of the lower explosive limit). During this process, the PVDF binder and the separator are completely decomposed, and the highest temperature in the furnace is 452℃ (below the 500℃ safety threshold). The layered structure of the positive electrode material is not damaged.

[0053] (3) After pyrolysis, nitrogen supply is stopped, and a mixed gas of pure oxygen (2L / min) and nitrogen (8L / min) at a volume ratio of 1:4 is used for gas supply. The oxygen concentration in the mixed gas is about 8 vol%. The combustible gas in the pyrolysis flue gas slowly oxidizes and releases heat under flameless conditions. The furnace temperature is maintained at 440~460℃ and the oxidation time is 45 min. No additional electric heating is required in this stage. The measured electric heating power is reduced by 65%. At the same time, after pyrolysis, the overall structure of the battery has been fully disintegrated. The aluminum-plastic film shell is precisely cut and removed, and the copper foil, aluminum foil and positive and negative electrode active materials are naturally separated. The positive and negative electrode active materials are lightly crushed to obtain black powder.

[0054] (4) During the oxidation process in step (3), the exhaust gas is recycled according to the concentration and temperature of combustible gas in the exhaust gas. The exhaust gas that does not meet the standard (combustible gas concentration > 5 vol%) is returned to the pyrolysis furnace through the circulation loop for the secondary flameless oxidation reaction in step (3). The exhaust gas that meets the standard (combustible gas concentration ≤ 5 vol%) is discharged after being absorbed by sodium hydroxide alkaline solution. The measured purification rate of combustible components in the flue gas is 97%. The high-temperature circulating exhaust gas (about 350°C) is mixed with room temperature pure oxygen (25°C) in the heat exchanger. After mixing, the gas supply temperature is about 120°C, which is used to preheat the gas entering the pyrolysis furnace to realize waste heat recovery.

[0055] According to ICP-OES testing, the copper content in the black powder was 8 ppm and the aluminum content was 12 ppm (both below 20 ppm).

[0056] Application Example 1 The black powder obtained in Example 1 was processed according to the above flotation separation process, wherein the amount of collector was 1.0 kg per ton of black powder, the amount of graphite inhibitor was 0.5 kg per ton of black powder, and the pH of the flotation medium was adjusted to 9. After flotation, the recovery rate of the cathode material reached 96%, and the obtained high-purity NCM523 cathode material had a complete layered structure and could be directly used for repair and regeneration.

[0057] Example 2 A method for preparing repairable and regenerable black powder from retired lithium batteries through refined thermal treatment, using cylindrical lithium iron phosphate batteries, model 18650, with a nominal capacity of 2.5Ah and a weight of approximately 45g, and batch processing 30 batteries to verify the scalability, includes the following steps: (1) The battery SOC was reduced to 0 by constant current discharge. Then, a hole with a diameter of 2 mm was drilled at the safety valve position using a special drilling tool to establish a gas communication channel between the inside and outside of the battery. The drilled battery was placed in a sealed box furnace and heated to 85°C at a heating rate of 8 K / min under a negative pressure of -0.07 MPa for 20 min for negative pressure distillation. During this process, the electrolyte vapor was liquefied and recovered by a condenser with a recovery rate of 91%. At the same time, the calcium hydroxide filter at the front end of the condenser was used to effectively capture hydrogen fluoride gas.

[0058] (2) After the negative pressure distillation is completed, vacuum is continued and nitrogen is introduced to maintain the oxygen concentration <6 vol%. Then, the temperature is increased to 480℃ at 5 K / min for mild pyrolysis for 1.5 h. During the pyrolysis process, the oxygen concentration is monitored and controlled in real time to be 3~5 vol%, and the combustible gas concentration is 8~12 vol% (far below the lower explosive limit of 75%). No aluminothermic reaction occurs. During this process, the PVDF binder and the separator are completely decomposed, and the highest temperature in the furnace is 480℃ (below the safety threshold of 500℃). The layered structure of the positive electrode material is not damaged.

[0059] (3) After pyrolysis, nitrogen supply is stopped, and a mixed gas of pure oxygen (0.5L / min) and nitrogen (2.5L / min) at a volume ratio of 1:5 is used for gas supply. The oxygen concentration in the mixed gas is about 9 vol%. The combustible gas in the pyrolysis flue gas slowly oxidizes and releases heat under flameless conditions. The furnace temperature is maintained at 470-485℃ and the oxidation time is 35 min. No additional electric heating is required in this stage. The measured electric heating power is reduced by 60%. At the same time, after pyrolysis, the overall structure of the battery has been fully disintegrated. The steel shell is precisely cut and removed, and the copper foil, aluminum foil and positive and negative electrode active materials are naturally separated. The positive and negative electrode active materials are lightly crushed to obtain black powder.

[0060] (4) During the oxidation process in step (3), the exhaust gas is recycled according to the concentration and temperature of combustible gas in the exhaust gas. The exhaust gas that does not meet the standard (combustible gas concentration > 5 vol%) is returned to the pyrolysis furnace through the circulation loop for secondary flameless oxidation in step (3). The exhaust gas that meets the standard (combustible gas concentration ≤ 5 vol%) is discharged after being absorbed by sodium hydroxide alkaline solution. The measured purification rate of combustible components in the flue gas is 95%. The high-temperature circulating exhaust gas (about 320°C) is mixed with room temperature pure oxygen (25°C) in the heat exchanger. After mixing, the gas supply temperature is about 110°C, which is used to preheat the gas entering the pyrolysis furnace to realize waste heat recovery.

[0061] According to ICP-OES testing, the copper content in the black powder was 6 ppm and the aluminum content was 9 ppm (both below 20 ppm).

[0062] Application Example 2 The black powder obtained in Example 2 was processed according to the above flotation separation process, wherein the amount of collector was 1.2 kg per ton of black powder, the amount of graphite inhibitor was 0.6 kg per ton of black powder, and the pH of the flotation medium was adjusted to 8.5. After flotation separation, the recovery rate of the cathode material reached 95%, and the obtained lithium iron phosphate cathode material had a complete olivine structure and could be directly used for repair and regeneration.

[0063] Comparative Example 1 The only difference from Example 1 is that step (2) uses a conventional pyrolysis process, specifically including the following steps: Step (1) is the same as in Example 1; (2) Traditional pyrolysis: After the negative pressure distillation was completed, the vacuum was stopped, and the atmosphere was restored to normal atmospheric pressure. The temperature was then directly increased to 550℃ at a rate of 10K / min and held for 60 minutes. Oxygen concentration was not controlled during pyrolysis; under natural air convection conditions, the oxygen concentration was approximately 21 vol%, and the concentration of combustible gases was not monitored. A violent aluminothermic reaction occurred during pyrolysis, causing the furnace temperature to rise rapidly to 680℃. The layered structure of the cathode material was severely damaged, and a significant sintering phase transformation occurred. A large amount of black smoke and dust was generated inside the furnace, and some material splashed onto the furnace walls.

[0064] Steps (3)-(4) are the same as in Example 1.

[0065] According to ICP-OES testing, the copper content in the black powder was 185 ppm and the aluminum content was 320 ppm.

[0066] Comparative Example 2 The only difference from Example 1 is that the exothermic oxidation process in step (3) is heated by open flame combustion, specifically including the following steps: Steps (1)-(2) are the same as in Example 1; (3): Open flame combustion heating: After pyrolysis, the pyrolysis flue gas generated during the pyrolysis process is directly introduced into the combustion chamber, and air (oxygen concentration ~21 vol%) is introduced to mix with the pyrolysis flue gas. An igniter is used to ignite the mixture, forming an open flame combustion. The combustion chamber temperature rapidly rises to 850~920℃, producing a violent flame and significant pressure fluctuations (maximum pressure rise rate approximately 15 kPa / s). A detonation occurs during combustion, and a momentary flame backflow is observed through the combustion chamber observation window. The heat released by the open flame combustion is transferred to the pyrolysis furnace through radiative heat exchange. However, due to low heat exchange efficiency and large temperature fluctuations, the pyrolysis furnace temperature fluctuates violently between 380~510℃, requiring continuous electric heating compensation. The electric heating power is reduced by only 15%. During combustion, some high-temperature flue gas is directly discharged without recirculation treatment.

[0067] Step (4) is the same as in Example 1.

[0068] According to ICP-OES testing, the copper content in the black powder was 42 ppm and the aluminum content was 58 ppm.

[0069] Comparative Example 3 The only difference from Example 1 is that, except for the exhaust gas recovery process in step (4), the remaining process steps and parameters are the same as in Example 1.

[0070] Specifically: steps (1)-(3) are the same as in Example 1; (4) Direct exhaust gas discharge: The exhaust gas after flameless oxidation is not treated by recirculation and is directly discharged after purification by the alkaline absorption tower. There is no heat exchange device for mixing high-temperature circulating exhaust gas and room-temperature pure oxygen. Fresh pure oxygen enters the flameless oxidation chamber directly at room temperature (25°C). The pyrolysis furnace relies entirely on electric heating to maintain the temperature, with no waste heat recovery compensation.

[0071] According to ICP-OES testing, the copper content in the black powder was 22 ppm and the aluminum content was 26 ppm.

[0072] Technical effects: 1. Figure 2 The curves represent the temperature-pressure-oxygen concentration synergistic control during the negative pressure distillation and mild pyrolysis stages in Example 1. The horizontal axis represents time, and the vertical axis represents the temperature, pressure, and oxygen concentration curves, respectively.

[0073] As can be seen, during the negative pressure distillation stage, the pressure rapidly drops to the target negative pressure value, the temperature slowly rises to around 90℃, and the oxygen concentration remains at a low level. During the mild pyrolysis stage, the pressure gradually recovers to near atmospheric pressure, the temperature rises to around 450℃, and the oxygen concentration is strictly controlled below the safety threshold. Throughout the entire process, the changes in temperature and oxygen concentration are stable and orderly, without drastic fluctuations, ensuring the safety and controllability of the heat treatment process.

[0074] 2. Energy Consumption Comparison The energy consumption of Examples 1-2 and Comparative Examples 1-3 is shown in Table 1: Table 1 As can be seen from Table 1, the energy consumption levels of Example 1 and Example 2 are similar, approximately 0.85 kWh / kg battery and 0.88 kWh / kg battery, respectively. The difference between the two is mainly due to the different processing objects and scales. Example 2 has a slightly higher unit energy consumption due to the batch processing of 30 cylindrical batteries and a slightly higher pyrolysis temperature, but it still remains at a low level. This verifies the energy consumption stability of the four-step synergistic process of the present invention under different battery types and processing scales.

[0075] In contrast, the energy consumption of all three comparative examples deteriorated significantly: Comparative Example 1 used a traditional pyrolysis process, but the elimination of low-oxygen atmosphere control induced an aluminothermic reaction, leading to a surge in heat loss due to temperature runaway. Simultaneously, the quality of the black powder was downgraded, making it only suitable for high-energy-consuming hydrometallurgical processes, resulting in a total energy consumption of 1.42 kWh / kg battery, an increase of 67% compared to Example 1; Comparative Example 2 changed flameless oxidation to open flame combustion. Although the combustion heat release was intense, large temperature fluctuations led to frequent electric heating compensation in the pyrolysis furnace, and some high-temperature flue gas was directly discharged, causing heat loss, resulting in a total energy consumption of 1.28 kWh / kg battery, an increase of 51%; Comparative Example 3 eliminated waste heat recovery from tail gas, and the direct discharge of high-temperature tail gas prevented preheating with fresh pure oxygen, reducing the heat release efficiency of flameless oxidation. Electric heating accounted for 70%, resulting in a total energy consumption of 1.35 kWh / kg battery, an increase of 59%. It is worth noting that, compared with Comparative Example 1, Example 2 reduced the total energy consumption by about 38% and the single battery processing cycle was about 120 minutes. This is highly consistent with the energy saving of about 30% to 40% compared with the traditional heat treatment process. This shows that the three elements of mild pyrolysis with low oxygen atmosphere control, safe in-situ heating with flameless oxidation, and closed-loop recovery of exhaust gas waste heat are indispensable and together constitute the core support for the energy efficiency advantage of this invention.

[0076] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing repairable and regenerable black powder through refined thermal treatment of retired lithium batteries, characterized in that, Includes the following steps: (1) Drill holes in the discharged retired battery, place it under negative pressure conditions for negative pressure distillation to separate the electrolyte, and pyrolyze the remaining part under nitrogen atmosphere to remove PVDF binder and separator; (2) After the pyrolysis is completed, the retired battery is placed in a mixture of oxygen and nitrogen to slowly oxidize and release heat. After the oxidation reaction is completed, the high-temperature circulating tail gas is detected and recycled. The positive and negative electrode materials are separated and crushed to obtain repairable and regenerable black powder.

2. The method for preparing repairable and regenerable black powder through refined thermal treatment of retired lithium batteries according to claim 1, characterized in that, The discharge mentioned in step (1) is to discharge until SOC=0.

3. The method for preparing repairable and regenerable black powder through refined thermal treatment of retired lithium batteries according to claim 1, characterized in that, The drilling mentioned in step (1) refers to drilling a hole at the location of the safety valve, with a hole diameter of 2-5mm.

4. The method for preparing repairable and regenerable black powder through refined thermal treatment of retired lithium batteries according to claim 1, characterized in that, The pressure of the negative pressure distillation in step (1) is -0.07~-0.09 MPa, and the temperature is 80-100℃.

5. The method for preparing repairable and regenerable black powder through refined thermal treatment of retired lithium batteries according to claim 1, characterized in that, The pyrolysis temperature in step (1) is 400-500℃ and the time is 30-90min.

6. The method for preparing repairable and regenerable black powder through refined thermal treatment of retired lithium batteries according to claim 1, characterized in that, The temperature of the mixed gas in step (2) is 100-200℃, and the volume concentration of oxygen is 5-10%.

7. The method for preparing repairable and regenerable black powder through refined thermal treatment of retired lithium batteries according to claim 1, characterized in that, The temperature of the high-temperature circulating exhaust gas in step (2) is 200-400℃, and the concentration of combustible gas is >5 vol%. The recycling process involves replacing nitrogen with oxygen in the high-temperature circulating exhaust gas to create a mixed gas for waste heat recovery and slow oxidation heat release, thus providing a partial heat source for the pyrolysis process of retired batteries.

8. The method for preparing repairable and regenerable black powder through refined thermal treatment of retired lithium batteries according to claim 1, characterized in that, The temperature of the exothermic oxidation in step (2) is 300-500℃ and the time is 20-60min.

9. A reparable and regenerable black powder prepared by the method according to any one of claims 1-8, characterized in that, The copper content and aluminum content in the reparable and regenerable black powder are 1-100 ppm.

10. The application of the repairable regenerable black powder as described in claim 8 in the short-process direct recycling and preparation of high-purity lithium iron phosphate cathode materials.

Images