A method for simultaneously extracting lithium and removing fluorine from retired lithium battery waste electrolyte

Abstract

This invention relates to a method for simultaneously extracting lithium and removing fluoride from waste electrolyte of retired lithium batteries. The method includes: placing the waste electrolyte in an electrolysis device, using copper or a copper alloy as the cathode and graphite or copper as the anode for electrolysis; during electrolysis, Li... + Lithium metal is deposited at the cathode by reduction, PF6 ‑ The lithium metal is converted into a fluorine-containing solid compound through anodic oxidation; after electrolysis, the lithium metal and the fluorine-containing compound are separated to obtain an electrolyte in which lithium and fluorine have been removed. This method efficiently and simultaneously recovers lithium resources and removes fluorine contamination.

Description

Technical Field

[0001] This invention relates to a method for simultaneously extracting lithium and removing fluoride from waste electrolyte of retired lithium batteries. Background Technology

[0002] By 2035, the number of new energy vehicles will reach 170 million, of which 50-80 million will be out of warranty. Statistics show that in 2024, the domestic recycling volume of power batteries exceeded 300,000 tons. Retired lithium batteries contain strategic metal resources such as Li, Ni, Co, Cu, and Al, as well as harmful substances such as carbonate organic electrolytes and fluorine compounds. Recycling retired lithium batteries is of strategic significance. Currently, the recycling of retired lithium batteries focuses on the cathode material, while research on electrolyte recycling is limited. The electrolyte mainly consists of carbonate electrolytes, LiPF6, and trace additives. In current lithium battery recycling processes, the electrolyte is often not fully recovered and is discharged with exhaust gases during crushing or pyrolysis, not only wasting resources but also potentially causing safety accidents such as leaks or fires due to volatilization and combustion. In current retired lithium battery recycling processes, during the pyrolysis stage, the electrolyte volatilizes and decomposes upon heating, generating various fluorine-containing compounds such as LiF, HF, POF3, PF5, and fluorinated hydrocarbons (C2H5OCOOPF4, C2H5F). This is the main source of fluorine pollution during the pyrolysis process. Therefore, the treatment of electrolyte from retired lithium batteries is a key technical challenge and environmental priority in the industry. Developing an effective electrolyte treatment method is crucial for reducing environmental pollution and achieving resource recycling. Recycling electrolyte can reduce fluorine and organic pollution; therefore, the safe and efficient treatment of waste electrolyte remains one of the key challenges restricting the green development of the industry. According to statistics, my country's lithium battery electrolyte shipments in 2024 reached 1.527 million tons, with solvents accounting for an average of 80%. The potential recyclable electrolyte volume is approximately 1.2216 million tons, indicating a potential market demand and recycling space.

[0003] Currently, the main methods for treating electrolytes in retired lithium batteries are divided into physical and chemical methods. Physical methods involve low-temperature heating and condensation recovery under an inert atmosphere, while chemical methods can be further divided into high-temperature pyrolysis, wet processing, organic solvent extraction, and supercritical CO2 extraction. Physical methods primarily involve placing retired lithium batteries under inert gas protection for crushing and sorting, utilizing the differences in melting and boiling points between different carbonate solvents to separate different components. Because carbonate electrolytes have low boiling points, and the boiling points and saturated vapor pressures of the components differ, the low-boiling-point volatile organic solvents DMC and DEC can be separated from EC. DMC and EC have different saturated vapor pressures and a high separation coefficient. The most common chemical processing method is high-temperature pyrolysis. After the lithium battery has finished discharging, the positive and negative electrode sheets enter a high-temperature pyrolysis furnace. The pyrolysis temperature is typically 400℃-500℃. This high-temperature process causes varying degrees of decomposition of the electrolyte, with some electrolyte undergoing thermal decomposition into C7H at high temperatures. 14 LiPF6 in the electrolyte contains hydrocarbons such as C2H6O and other small molecule gases (H2, CO, CO, etc.). During the pyrolysis stage, LiPF6 in the electrolyte undergoes thermal decomposition to generate various fluorides. These fluorides are then introduced into the subsequent wet leaching process along with the battery black powder. The fluoride (F) concentration in the leaching solution gradually increases, exacerbating equipment corrosion, increasing the cost of defluorination in the leaching solution and wastewater, and posing a serious environmental hazard. Existing electrolyte treatment processes do not consider the removal of fluoride. Summary of the Invention

[0004] To address the aforementioned problems, the present invention aims to provide a method for simultaneously extracting lithium and removing fluoride from waste electrolyte of retired lithium batteries, which has the advantages of efficient simultaneous recovery of lithium resources and removal of fluoride pollution.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: This application provides a method for simultaneously extracting lithium and removing fluoride from waste electrolyte of retired lithium batteries, the technical solution of which is as follows: Includes the following steps: S1. Use waste electrolyte from retired lithium batteries containing LiPF6 as the electrolyte and place it in an electrolysis device; S2. Electrolysis is carried out in waste electrolyte using a copper or copper alloy electrode as the cathode and a graphite or copper electrode as the anode; S3. During the electrolysis process, Li + At the cathode, lithium is reduced to metallic lithium and deposited, while PF6 - It is oxidized at the anode and converted into a fluorine-containing solid compound that is insoluble in the waste electrolyte; S4. After electrolysis, the metallic lithium deposited on the cathode is separated, and the fluorine-containing solid compound is separated from the electrolyte to obtain an electrolyte in which lithium and fluorine have been removed.

[0006] Furthermore, this application also proposes that the waste electrolyte contains one or more carbonate organic solvents.

[0007] Furthermore, this application also proposes that the carbonate organic solvent is selected from one or more of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethylene carbonate, and propylene carbonate.

[0008] Furthermore, this application also proposes that the electrolysis is constant voltage electrolysis, with an electrolysis voltage of 2.5 V to 6 V.

[0009] Furthermore, this application also proposes that the electrolysis is constant current electrolysis with a current density of 5 mA / cm² to 100 mA / cm².

[0010] Furthermore, this application also proposes that the electrolysis time be from 1 hour to 10 hours.

[0011] Furthermore, this application also proposes that the electrolysis is carried out in an air atmosphere or an inert atmosphere, at an ambient temperature of 25°C to 30°C.

[0012] Furthermore, this application also proposes that when the anode is a graphite electrode, the graphite electrode is an artificial or natural graphite sheet with a layered structure and an interlayer spacing d(002) of 0.335 nm to 0.340 nm, and the graphite electrode is subjected to electrochemical or chemical expansion treatment before use.

[0013] Furthermore, this application also proposes that when the anode is a copper electrode, the copper electrode is a clean electrolytic copper foil or copper sheet, and is subjected to acid washing or electrochemical polishing treatment to remove the surface oxide layer before use.

[0014] Furthermore, this application also proposes that when the anode is a graphite electrode, the fluorine-containing solid compound is PF6. - C formed by intercalation of graphite X PF6; when the anode is a copper electrode, the fluorine-containing solid compound is Cu(PF6)2.

[0015] As can be seen from the above, this application provides a method for simultaneous lithium extraction and fluoride removal from waste electrolyte of retired lithium batteries. Considering that traditional high-temperature pyrolysis processes cannot effectively remove fluoride (F) from the electrolyte during the pretreatment stage, this invention aims to separate LiPF6 and carbonate electrolyte from the electrolyte, reduce Li loss and F pollution caused by improper electrolyte treatment in traditional battery recycling processes, and achieve electrolyte recycling and reuse. This invention proposes a method for directly separating Li and F elements from the electrolyte using an electrochemical method, utilizing graphite and copper as the active anode, and PF6...- Intercalation reactions can occur between graphite layers to generate C. X PF6 intercalation compound, Cu and PF6 - The reaction produces Cu(PF6)2, and Li+ can be directly electrochemically deposited as lithium metal on the Cu cathode. Based on this principle, a one-step electrochemical separation of Li and F can be achieved directly in the electrolyte. The specific reaction equations are shown in equations (1) to (3). LiPF6 is electrochemically decomposed in the electrolyte using electrochemical methods, and F can be converted to C using a graphite or Cu anode. X The F and Li elements are fixed in the form of PF6 and Cu(PF6)2, while metallic Li can be recovered at the cathode. By electrolyzing LiPF6 in the electrolyte, F and Li elements can be directly collected and fixed in the pretreatment stage, reducing the problem of F enrichment in the wet post-processing. Attached Figure Description

[0016] Figure 1 This is a schematic diagram illustrating the simultaneous lithium extraction and fluoride removal from waste electrolyte of retired lithium batteries, as provided in this application. Detailed Implementation

[0017] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. 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.

[0018] 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," "clockwise," and "counterclockwise," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not 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.

[0019] 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 indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more, unless explicitly defined otherwise.

[0020] 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 connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0021] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0022] Traditional recycling processes for retired lithium-ion batteries primarily focus on cathode materials, with limited research on electrolyte recovery. Electrolytes are often discharged with waste gases during crushing or pyrolysis, resulting in resource waste and potential safety hazards. Particularly during pyrolysis, LiPF6 in the electrolyte decomposes to form various fluorine compounds, causing severe fluoride pollution, exacerbating equipment corrosion, significantly increasing subsequent defluorination costs, and posing a threat to the environment. Current processes fail to effectively remove fluoride from electrolytes, making the safe and efficient treatment of waste electrolytes a critical challenge for the industry.

[0023] like Figure 1 As shown, this application proposes a method for simultaneous lithium extraction and fluoride removal from waste electrolyte of retired lithium batteries. This method uses waste electrolyte containing LiPF6 from retired lithium batteries as the electrolyte, places it in an electrolysis device, and performs electrolysis using a copper or copper alloy electrode as the cathode and a graphite or copper electrode as the anode. During the electrolysis process, Li… + At the cathode, lithium is reduced to metallic lithium and deposited, while PF6... - The lithium metal deposited on the cathode and the fluorine-containing solid compounds separated from the electrolyte are oxidized and converted into fluorine-containing solid compounds that are insoluble in the waste electrolyte. After electrolysis, the lithium metal deposited on the cathode and the fluorine-containing solid compounds separated from the electrolyte are separated to obtain an electrolyte in which lithium and fluorine have been removed.

[0024] For ease of understanding, the following explains some key terms in this embodiment: Retired lithium battery waste electrolyte: refers to the electrolyte extracted from lithium-ion batteries that have reached the end of their service life or have been phased out for other reasons. This electrolyte typically contains lithium hexafluorophosphate (LiPF6) as well as various carbonate organic solvents and additives, and serves as the initial reaction medium for lithium extraction and defluorination in this method.

[0025] Electrolysis apparatus: refers to equipment used to carry out electrochemical reactions, which typically includes an electrolytic cell, a pair of electrodes (cathode and anode), and a DC power supply. In this method, waste electrolyte is placed in the apparatus as an electrolyte, and the electrochemical reaction is driven by applying voltage or current.

[0026] Cathode: Refers to the electrode in an electrolysis device where the reduction reaction occurs. In this method, lithium ions (Li...) + The electrons are gained on the electrode surface and reduced to metallic lithium, which is then deposited on the cathode surface.

[0027] Anode: Refers to the electrode in an electrolytic device where the oxidation reaction occurs. In this method, hexafluorophosphate ions (PF6)... - The electrons are lost and oxidized on the surface of the electrode, and then transformed into a fluorine-containing solid compound that is insoluble in the electrolyte.

[0028] Metallic lithium: refers to elemental lithium recovered from waste electrolyte through electrochemical reduction. It is deposited in solid form on the cathode surface and has high recycling value.

[0029] Fluorine-containing solid compounds: refer to those produced by PF6 during anodic electrochemical oxidation. - The resulting solid substance is insoluble in the waste electrolyte. The formation of this compound achieves the fixation and removal of fluorine from the waste electrolyte.

[0030] This application provides a method for simultaneously extracting lithium and removing fluoride from waste electrolyte of retired lithium batteries, and its specific implementation may include the following steps: First, waste electrolyte from retired lithium-ion batteries containing LiPF6 is placed in an electrolysis device as the electrolyte. This waste electrolyte can be directly extracted and used from retired lithium-ion batteries without complex pretreatment. The electrolysis device can be a simple electrolytic cell containing the electrolyte and equipped with electrodes.

[0031] Secondly, electrolysis is carried out in the aforementioned waste electrolyte using a copper or copper alloy electrode as the cathode and a graphite or copper electrode as the anode. The cathode can be a pure copper sheet or copper foil, or an alloy electrode formed from copper and metals such as zinc or nickel. The anode can be a common graphite sheet or copper sheet. The electrolysis process can be driven by applying DC voltage or current from an external power source. For example, constant voltage or constant current electrolysis can be used. The electrolysis time can be set according to actual needs; for example, electrolysis can be carried out for several hours. The electrolysis environment can be in an open air atmosphere or in an inert atmosphere (such as argon or nitrogen), and the ambient temperature can be maintained near room temperature.

[0032] Furthermore, during the electrolysis process, Li + In the aforementioned cathode, lithium metal is reduced and deposited, while PF6... - The anode is oxidized and converted into a fluorine-containing solid compound insoluble in the waste electrolyte. Specifically, when direct current passes through the electrolyte, positively charged lithium ions move towards the cathode, gain electrons at the cathode surface, are reduced to metallic lithium, and adhere to the cathode. Simultaneously, negatively charged hexafluorophosphate ions move towards the anode, lose electrons at the anode surface, undergo an oxidation reaction, and generate a fluorine-containing solid substance insoluble in the electrolyte. For example, when the anode is a graphite electrode, PF6... - Fluorine-containing graphite compounds may be formed through intercalation reactions; when the anode is a copper electrode, PF6 - It may react with copper ions to form fluorine-containing copper compounds.

[0033] The specific reaction equations are shown in equations (1) to (3): Cathode reaction: Formula (1) Anode reaction: Formula (2) Formula (3) Finally, after electrolysis, the metallic lithium deposited on the cathode and the fluorine-containing solid compounds are separated from the electrolyte, yielding an electrolyte free of lithium and fluorine. The metallic lithium deposited on the cathode can be collected by mechanical scraping or stripping. The fluorine-containing solid compounds in the electrolyte can be removed by simple physical separation methods such as filtration, centrifugation, or sedimentation. After separation, the lithium and fluorine content in the remaining electrolyte is significantly reduced, thus achieving electrolyte purification. This application achieves the simultaneous recovery and removal of lithium and fluorine from waste electrolytes from retired lithium batteries through an electrochemical method. This method effectively solves the problems of difficult fluorine removal, environmental pollution, and resource waste in existing electrolyte treatment processes. By reducing lithium ions to metallic lithium for recovery and simultaneously converting harmful fluoride ions into easily separable solid compounds, this method not only avoids the diffusion and corrosion problems of fluorides in subsequent treatment but also realizes the resource utilization of valuable metallic lithium, thereby reducing environmental risks and improving resource recycling efficiency.

[0034] Specifically, the waste electrolyte described in this application contains one or more carbonate organic solvents.

[0035] Carbonate organic solvents are a class of organic compounds containing carbonate functional groups. They are characterized by high dielectric constants, low viscosity, and good electrochemical stability, making them ideal components of lithium-ion battery electrolytes. During electrolysis, carbonate organic solvents serve as the solvent matrix for the electrolyte, primarily dissolving electrolyte salts (such as LiPF6) and providing Li... + Medium for ion migration.

[0036] Specifically, the carbonate organic solvent can be a linear carbonate, such as dimethyl carbonate, diethyl carbonate, or methyl ethyl carbonate. These solvents typically have low viscosity and high ionic conductivity, which is beneficial for Li... + Rapid migration. Furthermore, the carbonate organic solvent can also be a cyclic carbonate, such as ethylene carbonate or propylene carbonate. These solvents typically have a high dielectric constant, effectively promoting the dissociation of the electrolyte salt and increasing Li... +The concentration of the electrolyte is important. In practical applications, to balance the overall performance of the electrolyte, a mixture of one or more linear carbonates and one or more cyclic carbonates is usually used as a solvent to ensure ionic conductivity while also considering the solubility and electrochemical stability of the electrolyte salt. Specifically, the carbonate organic solvent is selected from one or more of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethylene carbonate, and propylene carbonate. The carbonate organic solvent is a core component of lithium battery waste electrolyte, and its selection directly affects the ionic conductivity, electrochemical stability, and wettability of the electrolyte to electrode materials. In the method of simultaneously extracting lithium and removing fluoride from retired lithium battery waste electrolyte, a suitable solvent system can ensure the effective migration and reduction of lithium ions at the cathode, while maintaining PF6. - The oxidative conversion at the anolyte provides a stable medium environment. Specifically, the carbonate organic solvent can be a single component, for example, using only dimethyl carbonate as the main solvent of the waste electrolyte. Dimethyl carbonate has low viscosity and high dielectric constant, which is beneficial for the rapid transport of lithium ions, and its boiling point is moderate, allowing for controllable volatility during electrolysis. Alternatively, the carbonate organic solvent can be a mixture of two or more components, for example, a mixture of dimethyl carbonate and ethylene carbonate. Ethyl carbonate has a high dielectric constant and can effectively dissolve LiPF6, while dimethyl carbonate can reduce the viscosity of the mixed solvent and improve ionic conductivity. Meanwhile, methyl ethyl carbonate, diethyl carbonate, and propylene carbonate are also commonly used in lithium battery electrolytes. They each have different physicochemical properties, and through proper proportioning, the overall performance of the electrolyte can be optimized, for example, increasing the flash point and lowering the freezing point, thereby widening the operating temperature range and enhancing safety.

[0037] In a preferred embodiment, the electrolysis is constant-voltage electrolysis, with an electrolysis voltage ranging from 2.5 V to 6 V. Specifically, constant-voltage electrolysis refers to maintaining the voltage across the electrolysis device at a preset constant value throughout the entire electrolysis process by precisely controlling the power output. This control mode differs from constant-current electrolysis (maintaining a constant current), its core being to provide a stable potential driving force for the electrochemical reaction. Methods for achieving constant-voltage electrolysis include: firstly, using a DC power supply with high-precision constant-voltage output function, which automatically adjusts the output current according to the real-time impedance changes of the electrolytic cell to maintain the set voltage value; secondly, using an intelligent power supply system integrating a voltage sensor and a feedback control unit, which monitors the electrolysis voltage in real time and responds and adjusts rapidly based on deviations from the set value, thereby ensuring voltage stability. The introduction of constant-voltage electrolysis aims to provide a continuous and stable potential environment for the electrochemical reaction, avoiding adverse effects on the reaction pathway, product selectivity, and overall efficiency caused by voltage fluctuations.

[0038] Meanwhile, the electrolysis voltage is set within the range of 2.5 V to 6 V. This voltage range is based on the Li content in the waste electrolyte. + The reduction potential and PF6 - The oxidation potential was studied in depth and determined by combining the electrochemical window characteristics of the electrolyte. Within this voltage range, Li can be effectively driven. + At the cathode, it is reduced to metallic lithium, which promotes PF6 - The electrolyte is converted into a fluorinated solid compound insoluble in the waste electrolyte through anodic oxidation. Achieving this voltage range can be achieved in two ways: first, by precisely adjusting the output voltage of the DC power supply to stabilize it at a specific value between 2.5 V and 6 V; second, by equipping the electrolysis unit with a high-precision voltmeter and a programmable power supply, allowing operators or automated control systems to select and maintain the optimal electrolysis voltage within this range based on the specific composition of the waste electrolyte and the target product requirements. Selecting this voltage range aims to ensure the efficient execution of the target reaction while avoiding side reactions caused by excessive voltage, such as electrolyte solvent decomposition, electrode material corrosion, or unnecessary product formation.

[0039] The above technical solution, employing a constant-voltage electrolysis mode, ensures that the voltage remains within a preset stable range throughout the electrolysis process. This stability avoids current instability caused by voltage fluctuations, thereby optimizing the control of the electrochemical reaction. Operation is carried out within a specific electrolysis voltage range of 2.5 V to 6 V, a carefully selected range that effectively drives the Li in the waste electrolyte. + At the cathode, lithium is reduced to metallic lithium and deposited, while simultaneously promoting PF6. - At the anode, it is oxidized and converted into a fluorine-containing solid compound insoluble in the waste electrolyte. This precise voltage control not only improves lithium-ion reduction but also enhances PF6. - The efficiency and selectivity of the oxidation conversion also significantly reduce potential side reactions, such as the decomposition of the electrolyte solvent or the corrosion of the electrode materials. Therefore, this scheme can effectively improve the lithium recovery rate and fluorine removal efficiency, and ultimately obtain an electrolyte with lithium and fluorine removed, thus realizing a stable and efficient process for simultaneous lithium extraction and fluorine removal from waste electrolytes of retired lithium batteries.

[0040] In another embodiment, the electrolysis is constant current electrolysis, with a current density of 5 mA / cm² to 100 mA / cm². Specifically, constant current electrolysis means that during the electrolysis process, the current passing through the electrolysis device is kept constant through a control circuit. This electrolysis method can ensure the stability of the electrode reaction rate and effectively avoid problems such as interruption of lithium deposition or discontinuous electrode reaction caused by voltage fluctuations. Methods for achieving constant current electrolysis may include, but are not limited to: using a constant current power supply equipped with a feedback control system, which can monitor the electrolysis current in real time and automatically adjust the output voltage to maintain the current at a preset value; or using a high-precision current controller, combined with the electrochemical characteristics of the electrolytic cell, to precisely set and regulate the current.

[0041] Meanwhile, the current density is limited to the range of 5 mA / cm² to 100 mA / cm². Current density, the magnitude of the current passing through a unit electrode area, is a key parameter affecting electrode reaction rate, product morphology, and process efficiency. The selection of this range aims to balance the lithium deposition rate with the safety of the electrolysis process. For example, the current density can be precisely controlled within this range by adjusting the total output current of the constant current power supply and combining it with the effective surface area of ​​the cathode. In practical operation, the specific composition of the waste electrolyte (such as Li) can be considered. + Concentration, PF6 - The optimal current density value within this range was determined through preliminary experiments, taking into account the concentration and geometry of the electrolysis device.

[0042] The above technical solution, employing constant current electrolysis, provides a stable current input, ensuring a smooth lithium-ion reduction process at the cathode and promoting uniform lithium deposition. Simultaneously, controlling the current density within a specific range of 5 mA / cm² to 100 mA / cm² avoids problems such as excessively high current densities leading to overly rapid deposition, localized overheating, or side reactions, as well as excessively low current densities causing slow electrolysis and low efficiency. This enables PF6... - The oxidation process at the anode can be carried out efficiently and controllably, effectively converting the electrolyte into a fluorine-containing solid compound that is insoluble in the waste electrolyte. Overall, this technology significantly improves the efficiency and controllability of simultaneous lithium extraction and fluorine removal, ensuring the quality of lithium metal recovery and the effective removal of fluorine compounds, thereby optimizing the recycling and treatment of waste electrolyte from retired lithium batteries.

[0043] Furthermore, this application proposes an electrolysis time of 1 to 10 hours. Electrolysis time refers to the duration for which electrical energy is applied to drive the electrochemical reaction during electrolysis. Its purpose is to ensure that the electrolysis reaction proceeds sufficiently, allowing for the efficient formation of the target products (lithium metal and fluorine-containing solid compounds). Limiting the electrolysis time to the range of 1 to 10 hours allows for the reduction of lithium ions to metallic lithium at the cathode and its deposition, as well as the formation of PF6. - Sufficient reaction time is provided for the anode to be oxidized and converted into fluorine-containing solid compounds insoluble in the waste electrolyte. This time range effectively avoids the problems of incomplete lithium-ion reduction or insufficient fluorine compound oxidation caused by excessively short electrolysis time, thus ensuring the simultaneous and efficient removal of lithium and fluorine. At the same time, it also prevents energy waste and potential side reactions that may be caused by excessively long electrolysis time, optimizing the overall efficiency and economy of the electrolysis process. Combined with the above conditions of constant voltage electrolysis (electrolysis voltage of 2.5 V to 6 V) or constant current electrolysis (current density of 5 mA / cm² to 100 mA / cm²), this time range allows the electrolysis process to proceed stably and efficiently, thereby significantly improving the recovery effect and resource utilization efficiency of simultaneous lithium extraction and fluorine removal from retired lithium battery waste electrolyte.

[0044] In a further embodiment, the electrolysis is carried out in an air atmosphere or an inert atmosphere at an ambient temperature of 25°C to 30°C. This technical solution aims to control the gaseous environment during the electrolysis process to avoid or reduce undesirable side reactions between the electrolyte and electrode materials and reactive gases (such as oxygen and water vapor) in the external environment. Specifically, electrolysis in an air atmosphere means that the electrolysis device is in an open environment or connected to the air. This method is simple to operate, low in cost, and suitable for situations where the electrolyte components are not sensitive to oxygen and water vapor, or where electrolysis in air will not significantly affect the target reaction efficiency and product purity. On the other hand, electrolysis in an inert atmosphere typically refers to operation in a closed environment filled with an inert gas (such as nitrogen, argon, or helium). An inert atmosphere can effectively isolate oxygen and water vapor, which is crucial for electrolytes that are easily oxidized or hydrolyzed (such as LiPF6) and reduction products (such as metallic lithium), significantly improving the stability and safety of the electrolysis process and ensuring product purity. Inert atmosphere can be achieved by means of operation in a glove box or by continuously introducing inert gas into the electrolysis unit for protection.

[0045] Meanwhile, this technical solution aims to precisely control the ambient temperature of the electrolysis process within a narrow, suitable range. Specifically, controlling the ambient temperature between 25°C and 30°C ensures that components such as LiPF6 and carbonate solvents in the electrolyte maintain good stability, preventing electrolyte decomposition, volatilization, or the generation of harmful byproducts (such as fluorinated compounds like HF, POF3, and PF5) due to excessively high temperatures. This temperature range also coincides with the Li... + Reduction deposition at the cathode and PF6 - The oxidation conversion at the anode provides suitable reaction kinetics, which optimizes the efficiency of simultaneous lithium extraction and fluorine removal, and helps to form well-structured, high-purity lithium metal deposits and fluorine-containing solid compounds. This temperature control can be achieved, but is not limited to, using a constant-temperature water bath, a constant-temperature chamber, or an electrolytic cell equipped with a temperature control device (such as a heating / cooling circulator).

[0046] By employing the aforementioned technical solutions, the environmental atmosphere of the electrolysis process is limited to air or an inert atmosphere, and the ambient temperature is precisely controlled between 25°C and 30°C, effectively solving problems such as electrolyte oxidation, decomposition, and side reactions that may occur during electrolysis. Specifically, electrolysis under an air or inert atmosphere can selectively avoid the oxidative degradation of the electrolyte by oxygen and water vapor, based on the sensitivity of the electrolyte and the stability of the target product, thereby ensuring the stability and safety of the electrolysis process. This is particularly important for waste electrolytes containing LiPF6 and carbonate organic solvents, effectively inhibiting the generation of harmful substances due to oxidation during electrolysis and maintaining the stability of the electrolyte composition. Simultaneously, controlling the ambient temperature between 25°C and 30°C avoids excessive decomposition and volatilization of the electrolyte at high temperatures, significantly reducing the generation of harmful fluorinated compounds such as HF, POF3, and PF5, thereby reducing the risk of equipment corrosion and the difficulty of subsequent treatment. This suitable temperature range also helps optimize Li… + The efficiency and deposition quality of cathode reduction to metallic lithium, and the promotion of PF6 - The efficient oxidation at the anode converts the lithium into an insoluble fluorine-containing solid compound, ensuring the simultaneous and efficient removal of both lithium and fluorine. Combined with the aforementioned electrolysis method, and through precise control of the electrolysis atmosphere and temperature, this application significantly improves the efficiency and selectivity of simultaneous lithium extraction and fluorine removal from retired lithium-ion battery electrolytes, reduces side reactions, and thus obtains higher purity metallic lithium and a more thorough fluorine removal effect, while ensuring operational safety and environmental friendliness.

[0047] In a specific embodiment, when the anode is a graphite electrode, the graphite electrode is a sheet of artificial or natural graphite with a layered structure and an interlayer spacing d(002) of 0.335 nm to 0.340 nm, and the graphite electrode undergoes electrochemical or chemical expansion treatment before use. Specifically, the core of the graphite electrode as an anode material lies in its unique layered structure, which is PF6. - The intercalation (intercalation) of ions provides the necessary space and channels. Graphite is a two-dimensional layered structure formed by carbon atoms arranged in a hexagonal grid, with these layers bonded together by van der Waals forces. When PF6... - When ions are oxidized during electrolysis and enter the graphite interlayer, they form intercalation compounds C. X PF6. To ensure PF6 - For efficient and stable ion intercalation, the interlayer spacing d(002) of graphite is crucial. This application limits the interlayer spacing d(002) to the range of 0.335 nm to 0.340 nm, a range that provides a suitable channel size that is neither too small nor too small to impede PF6. - The introduction of ions will not cause instability in the intercalation structure due to excessive size. Both artificial graphite and natural graphite sheets have good electrical conductivity and chemical stability, making them ideal electrode materials. For example, artificial graphite is usually produced by graphitizing carbonaceous raw materials such as petroleum coke or pitch coke at high temperatures, resulting in high purity and crystallinity; natural graphite sheets are extracted directly from minerals and then purified and processed.

[0048] To further improve PF6 - To improve ion intercalation efficiency and electrode stability, this application describes an expansion treatment of the graphite electrode before use. The expansion treatment aims to increase the distance between graphite layers or activate the graphite surface, thereby promoting PF6… - Rapid and uniform intercalation of ions. One expansion treatment method is electrochemical expansion. This method typically places a graphite electrode in a solution containing a specific electrolyte. By applying a certain voltage or current, certain ions in the electrolyte (such as sulfate ions, nitrate ions, etc.) intercalate between the graphite layers, thereby increasing the interlayer spacing and forming expanded graphite. In subsequent electrolysis, these pre-intercalated ions may be absorbed by PF6. - Ion substitution or synergistic effects further promote PF6 -Intercalation. Another expansion treatment method is chemical expansion. This method usually involves immersing the graphite electrode in a strong oxidizing agent solution, such as concentrated sulfuric acid, concentrated nitric acid, or mixtures thereof, and sometimes other oxidizing agents such as potassium permanganate are added. Oxidizing agent molecules or ions intercalate between the graphite layers and react with the graphite layers to produce gas or increase the interlayer spacing, thereby achieving graphite expansion. Graphite that has undergone chemical expansion treatment has increased interlayer spacing and more surface active sites, which is beneficial for PF6. - Rapid intercalation of ions.

[0049] Through the above technical solution, this application effectively solves the problems of low intercalation efficiency and unstable electrode performance caused by improper structure or lack of treatment during the defluorination process of graphite electrodes. Specifically, artificial or natural graphite sheets with a specific interlayer spacing d(002) are used as the anode, ensuring that there are suitable channel sizes between the graphite layers, achieving PF6. - The smooth entry and stable intercalation of ions provide a foundation. Building upon this, electrochemical or chemical expansion treatment of the graphite electrode before use further increases the interlayer distance of the graphite and activates the graphite surface, thereby significantly promoting PF6. - Rapid and uniform ion intercalation. This makes PF6 - The ions can be efficiently oxidized at the anode and converted into fluorine-containing solid compounds C that are insoluble in the waste electrolyte. X PF6. Overall, these measures worked synergistically, not only improving PF6. - The improved conversion efficiency ensures effective fluoride removal, enhances electrode stability, and extends electrode lifespan. This results in a more efficient and stable removal of fluoride from waste electrolytes of retired lithium batteries, further enhancing the recycling value of waste electrolytes.

[0050] In another embodiment, when the anode is a copper electrode, the copper electrode is a clean electrolytic copper foil or sheet, which undergoes acid washing or electrochemical polishing to remove the surface oxide layer before use. Here, the clean electrolytic copper foil or sheet refers to high-purity copper material prepared through electrolytic refining, characterized by extremely low impurity content, thus ensuring excellent conductivity and chemical stability. This can be achieved by selecting commercially available electrolytic copper foil or sheet with a purity of 99.9% or higher, or by strictly controlling the impurity content during preparation to ensure the cleanliness of its surface and body. Simultaneously, surface cleanliness means that the electrode surface is free of visible oil, dust, and other contaminants. This can be achieved through preliminary physical or chemical cleaning before use, such as wiping with organic solvents (e.g., acetone, ethanol) to remove oil, or rinsing with deionized water to remove water-soluble impurities.

[0051] Before use, the surface oxide layer is removed by pickling or electrochemical polishing. Pickling is a chemical method that uses an acidic solution to dissolve the oxide layer on the metal surface. For example, a dilute sulfuric acid solution (concentration range of 5% to 15%) can be used to immerse the copper electrode at a temperature of room temperature to 60°C. The treatment time can be adjusted according to the thickness of the oxide layer, usually from 5 to 30 minutes, followed by thorough rinsing with deionized water. Another pickling method uses a mixed acid solution containing nitric acid or hydrochloric acid to more effectively remove stubborn oxide layers, but process parameters must be strictly controlled to avoid excessive corrosion. Electrochemical polishing is a fine treatment method that removes microscopic unevenness and oxide layers from the metal surface through electrochemical dissolution. Specifically, the copper electrode is used as the anode and placed in an electrolyte containing phosphoric acid, sulfuric acid, etc. A certain current density (e.g., 1 A / dm² to 10 A / dm²) is applied, and the treatment is carried out at a specific temperature (e.g., 20°C to 50°C) for a time usually of 1 to 5 minutes. This method achieves a smoother, brighter surface and completely removes the oxide layer, thereby significantly improving the surface activity of the electrode. The above technical solution effectively solves the problem of the oxide layer on the copper electrode surface hindering the electrolytic reaction. Specifically, using clean electrolytic copper foil or copper sheet as the anode ensures the high purity and excellent conductivity of the electrode material itself. Furthermore, by acid washing or electrochemical polishing before use, the insulating oxide layer on the copper electrode surface is completely removed, exposing fresh, highly active copper atoms. This activated surface significantly reduces PF6. - The activation energy for the oxidation reaction at the anode promotes the oxidation of PF6. - The rapid and efficient conversion accelerates the formation of insoluble fluorine-containing solid compounds. This not only improves the removal efficiency of fluorine in waste electrolyte but also ensures the stability and continuity of the electrolysis process, avoiding reaction interruption or efficiency reduction due to electrode passivation. Ultimately, in the method of simultaneous lithium extraction and fluorine removal, this treatment method ensures the smooth progress of the anodic fluorine removal process and works synergistically with the efficient reduction of metallic lithium at the cathode, jointly achieving efficient and simultaneous recovery and removal of lithium and fluorine from waste electrolytes of retired lithium batteries.

[0052] In this regard, this application further clarifies the specific form of the fluorine-containing solid compound: when the anode is a graphite electrode, the fluorine-containing solid compound is PF6. - C formed by intercalation of graphite X PF6; when the anode is a copper electrode, the fluorine-containing solid compound is Cu(PF6)2.

[0053] Specifically, when the anode is a graphite electrode, PF6 - C formed by intercalation of graphite X PF6 is a type of PF6- A stable compound formed by the intercalation of anions between graphite layers. Graphite electrodes possess a unique layered structure, PF6. - The electrochemical intercalation of PF6 provides a natural host space. During electrolysis, PF6... - The graphite anode surface is oxidized and embedded between graphite layers to form C with a specific stoichiometric ratio. X PF6. This intercalation compound exhibits good chemical stability and is insoluble in the waste electrolyte, thus effectively immobilizing fluorine in the solid phase for subsequent separation and recovery. Furthermore, C... X The formation mechanism of PF6 can be understood as PF6 - Under the influence of an electric field, fluorine interacts with the graphite lattice through an oxidation reaction, eventually intercalating between graphite layers to form a stable intercalation compound. This intercalation process ensures that fluorine exists in a non-volatile and non-soluble form, preventing the accumulation of fluorides in the electrolyte or their release into the environment.

[0054] When the anode is a copper electrode, the fluorinated solid compound is Cu(PF6)2. Cu(PF6)2 is a copper fluorophosphate compound, and its formation mechanism involves the oxidation of the copper electrode during electrolysis, where the generated copper ions react with PF6 in the electrolyte. - The anions combine to form a solid precipitate insoluble in the waste electrolyte. Specifically, during electrolysis, the copper anode undergoes an oxidation reaction, losing electrons to form copper ions. These copper ions then combine with PF6 in the electrolyte. - The anions undergo a chemical reaction to generate a stable Cu(PF6)2 solid. This compound also exhibits good chemical stability and is insoluble in the waste electrolyte, enabling efficient removal of fluorine from the electrolyte and recovery in solid form.

[0055] Through the above technical solution, this application effectively solves the problems of unstable compounds, difficulty in effective separation, or environmental risks that may occur during the fluorine fixation process by specifying the specific forms of fluorine-containing solid compounds generated under different anode types. Specifically, when a graphite electrode is used as the anode, PF6... - Intercalated graphite forming C X PF6, this intercalation structure fully utilizes the layered properties of graphite, making PF6... - It is stably embedded therein, forming an insoluble and easily separable compound. When a copper electrode is used as the anode, it is formed by the interaction of copper and PF6. -The direct reaction forms a highly stable Cu(PF6)2 solid, thus avoiding the formation of soluble fluorides. This precise control of compound form ensures that fluorine is fixed in a specific, harmless, and stable solid form, significantly improving the removal efficiency and recovery purity of fluorine while reducing environmental risks. This provides a more reliable and efficient approach for simultaneous lithium extraction and fluorine removal from waste electrolytes of retired lithium batteries.

[0056] The implementation process of this plan is as follows: First, the collected waste electrolyte from retired lithium-ion batteries containing LiPF6 was used as the electrolyte and injected into a specially designed electrolysis device. This device was equipped with electrodes: a clean copper sheet was selected as the cathode, and an artificial graphite sheet with a layered structure and an interlayer spacing d(002) of 0.335 nm was selected as the anode. The graphite anode underwent electrochemical expansion treatment before use to improve its PF6 uptake resistance. - Its intercalation capability.

[0057] Subsequently, electrolysis was carried out in an electrolysis apparatus. To ensure the stability and efficiency of the electrolysis process, a constant voltage electrolysis mode was adopted, and the electrolysis voltage was set to 3.5 V. The entire electrolysis process was carried out in an inert atmosphere (such as argon), the ambient temperature was maintained at 28°C, and the electrolysis duration was 6 hours.

[0058] During the electrolysis process, lithium ions (Li) in the waste electrolyte... + The electrolyte gains electrons on the copper cathode surface, is reduced to metallic lithium, and gradually deposited on the cathode. Simultaneously, hexafluorophosphate ions (PF6) in the waste electrolyte... - PF6 migrates towards the graphite anode. On the anode surface, PF6 - It is oxidized and intercalated into the layered structure of graphite to form a fluorine-containing solid compound C that is insoluble in the waste electrolyte. X PF6. Unlike existing technologies where fluorides escape in gaseous form or accumulate in the liquid phase, this method fixes fluorine into a solid compound, effectively avoiding the generation and spread of fluorine pollution.

[0059] After electrolysis, the copper cathode with deposited lithium metal is first removed from the electrolysis unit. High-purity lithium metal can be easily separated from the cathode surface using methods such as mechanical scraping, thus achieving lithium resource recovery. Next, the remaining electrolyte in the electrolysis unit undergoes solid-liquid separation, for example, through filtration to remove insoluble fluorine-containing solid compounds C. X PF6 was separated from the electrolyte. The separated C... XPF6 solid compounds can be centrally processed or utilized as resources, rather than being uncontrollable pollutants. After the simultaneous removal of lithium and fluorine, the remaining electrolyte is mainly a carbonate organic solvent, and its purity is significantly improved. Further refining and recycling can be considered, or it can be safely disposed of as a low-pollution waste liquid.

[0060] Using the above method, the processing center successfully recovered valuable metallic lithium from the waste electrolyte of retired lithium batteries simultaneously and efficiently removed harmful fluorine, converting it into an easily processed solid form. This avoids the problems of lithium resource waste and fluorine pollution associated with traditional methods. This integrated electrochemical treatment solution not only recovers valuable metals but also solves the problem of fluorine pollution in waste electrolytes, improving resource utilization and environmental friendliness.

[0061] The following example will provide a more detailed explanation of the above technical solution: Example 1: Simultaneous Lithium Extraction and Fluorine Removal on Graphite Anodes 1. Electrolyte preparation: Take 100 mL of waste electrolyte recovered from retired ternary lithium batteries as the electrolyte. Its main component is 1.0 M LiPF6 dissolved in a mixed solvent of ethylene carbonate (EC) and dimethyl carbonate (DMC) (EC:DMC volume ratio = 3:7).

[0062] 2. Electrode preparation: Cathode: Use a pure copper sheet with a size of 2cm×4cm and a thickness of 0.2mm. Clean it ultrasonically with acetone, ethanol and deionized water in sequence, and then dry it with nitrogen gas for later use.

[0063] Anode: A 2cm × 4cm artificial graphite sheet with a thickness of 2mm was used. The interlayer spacing d(002) was determined to be 0.337nm by X-ray diffraction (XRD). Before use, the graphite sheet was placed in a 1.0M H2SO4 solution and subjected to constant current anodizing treatment at a current density of 5mA / cm² for 30 minutes to perform electrochemical expansion. Afterward, it was washed with deionized water and dried.

[0064] 3. Electrolysis process: Inject the above electrolyte into a 100mL glass electrolytic cell. Install the electrodes, controlling the electrode spacing to be 1.5cm. Place the electrolytic cell in a 25°C constant temperature water bath. Connect a DC regulated power supply, and under argon atmosphere protection, adopt constant voltage electrolysis mode, setting the electrolysis voltage to 4.0V and the electrolysis time to 5h.

[0065] 4. Post-processing: After electrolysis, remove the cathode, and a grayish-silver metallic lithium deposit layer can be observed. Carefully collect the deposited lithium metal with a stainless steel scraper and weigh it. Filter the remaining electrolyte to separate the anode surface and suspended solid residue (mainly carbon). XPF6), washed with a small amount of DMC, dried and weighed. Collect the filtrate (i.e., the treated electrolyte).

[0066] 5. Detection and Calculation: Before and after the electrolysis process, 250 μL of electrolyte was taken. The sampled electrolyte was added to 1 M HNO3 solution, mixed thoroughly, and then diluted. Subsequently, the Li content before and after electrolysis was measured. + Concentration change (C) Li / mgL -1 ), calculate the Li deposition rate R during electrolysis. Li As shown in formula (4): Formula (4) The concentration of Li in the electrolyte before electrolysis is R. Li1 After electrolysis, the concentration of Li in the electrolyte is R. Li2 Lithium deposition rate W Li With F fixed efficiency W F The calculations are shown in formulas (5) and (6): Formula (5) Formula (6) After calculation: Initial lithium ion concentration R in the electrolyte before electrolysis Li1 =6940mg / L (calculated based on 1.0MLiPF6).

[0067] Lithium ion concentration R in the filtrate after electrolysis Li2 =760mg / L.

[0068] Calculate the lithium deposition rate W using the formula. Li = = ≈89.0% According to the present invention, the fluorine fixation efficiency W F =W Li ≈89.0%. Example 2: Simultaneous Lithium Extraction and Fluorine Removal at Copper Anode 1. Electrolyte preparation: Same as in Example 1.

[0069] 2. Electrode preparation: Cathode: Same as in Example 1.

[0070] Anode: Use electrolytic copper foil with dimensions of 2cm × 4cm and a thickness of 0.2mm. Before use, soak it in a 10% (v / v) dilute sulfuric acid solution for 5 minutes to remove the surface oxide layer, then wash it with deionized water, dehydrate it with ethanol, and dry it with nitrogen.

[0071] 3. Electrolysis process: The apparatus is the same as in Example 1. Under air atmosphere, constant current electrolysis mode is adopted, the current density is set to 20mA / cm², and the electrolysis time is 3h.

[0072] 4. Post-processing: Same as in Example 1. Lithium metal was collected at the cathode. Filtration yielded a reddish-brown solid residue (mainly Cu(PF6)2).

[0073] 5. Detection and Calculation: The lithium ion concentration R in the filtrate after electrolysis was measured. Li2 =1390mg / L.

[0074] Lithium deposition rate W Li = = ≈80.0% Fluorine fixation efficiency W F =W Li ≈80.0%. Comparative Example 1 (Control Group without Electrochemical Treatment) Take 100 mL of the same waste electrolyte as in Example 1, place it in the same electrolytic cell, and add the same pretreated copper sheet (simulated cathode) and graphite sheet (simulated anode), but without applying any voltage. Let it stand for 5 hours under an argon atmosphere. After standing, the solution becomes clear, and there are no obvious changes on the electrode surface. Sampling and analysis show that the lithium ion concentration in the electrolyte remains almost unchanged before and after electrolysis (R...). Li2 ≈6.92 mg / L), calculated W Li ≈0.3%. This proves that LiPF6 cannot spontaneously decompose without an electric field, and neither lithium deposition nor fluorine fixation reactions occur. Comparative Example 2 (Control Group with Different Anode Materials) The operating procedures were exactly the same as in Example 1, except that the anode was replaced with a platinum sheet of the same size (Pt, inert anode). After 5 hours of electrolysis, a small amount of lithium was deposited at the cathode, but no obvious solid was formed at the anode. The filtrate after electrolysis was turbid, with white flocculent matter suspended in it. Analysis revealed that the lithium ion concentration R in the filtrate after electrolysis was... Li2 ≈4.51 mg / L, W Li ≈35.0%. The fluorine fixation efficiency was significantly lower than in Example 1. Analysis showed that the platinum anode could not effectively fix PF6. - Part of PF6 - During electrolysis, fluoride may decompose into soluble fluorides or hydrogen fluoride, leading to low defluorination efficiency and potential equipment corrosion. This comparison demonstrates that graphite anodes are less effective at fixing fluoride to form insoluble C. X The key role of PF6. Comparative Example 3 (Traditional pyrolysis treatment reference group) 100 mL of the same waste electrolyte was placed in a tube furnace and pyrolyzed at 500°C at a rate of 10°C / min for 2 hours under argon protection. After pyrolysis, the condensed organic liquid and residual solids were collected. Analysis showed a significant fluorine content in the condensate, indicating the formation of a large amount of volatile fluorides (such as HF and POF3); the residual solids contained fluorides such as LiF. This process failed to recover metallic lithium and converted fluorine into various volatile and easily migratable forms, increasing the difficulty of subsequent collection and treatment and raising environmental risks, in stark contrast to the one-step fixation and simultaneous recovery method of this invention. Example 3: Verification of process parameter range and investigation of boundary effects This embodiment aims to systematically verify the effectiveness and optimization of the process parameter range (voltage 2.5-6V, current density 5-100mA / cm², time 1-10h, temperature 25-30°C) claimed in the present invention, and to clarify its technical boundaries by setting up a control group that exceeds the range. 1. Verification of electrolysis voltage range (2.5V-6V): Using the basic conditions of Example 1 (graphite anode), with a fixed electrolysis time of 3 hours, the effects of different voltages were investigated, and a control group was set up for voltages that exceeded the range.

[0075] Electrolysis voltage (V) state Lithium deposition rate WL (%) Phenomena and Problems 2.0 Below the range <5 The reaction could barely start, and the current was extremely weak. 2.5 Lower limit of range ~55 The reaction is initiated, and deposition begins, but at a slow rate. 4.0 Within the preferred range ~86 The reaction is stable and efficient, and the deposited layer is dense and uniform. 6.0 upper limit of range ~88 Efficiency increased slightly, but the electrolyte heated slightly and produced a small amount of gas. 7.0 Above the range ~85 The electrolyte exhibits significant heat generation and discoloration, produces numerous bubbles, and results in a deterioration in the morphology of deposited lithium, posing a serious risk of side reactions such as solvent decomposition. Conclusion: When the voltage is below 2.5V, the driving force is insufficient and the reaction is difficult to proceed; within the range of 2.5-6V, the reaction is efficient and controllable; when the voltage exceeds 6V (such as 7V), it will cause significant side reactions and safety risks, proving that 6V is the upper limit to ensure the safe and stable operation of this system. 2. Verification of current density range (5-100mA / cm²): Using the basic conditions of Example 2 (copper anode, constant current), with a fixed electrolysis time of 3 hours, the effect of different current densities was investigated.

[0076] Current density (mA / cm²) state Lithium deposition rate WL (%) Phenomena and Problems 1 Below the range ~20 The reaction rate is too slow to have practical application value. 5 Lower limit of range ~65 The reaction was stable and the anode dissolved uniformly, but the overall processing rate was low. 50 Within the preferred range ~85 The reaction rate is fast, the anodic dissolution and product formation are well matched, and the efficiency is high. 100 upper limit of range ~89 The reaction rate is fast, but the local dissolution of the anode is too rapid, so attention should be paid to heat dissipation. 120 Above the range ~88 The anode dissolves violently, the electrolyte heats up rapidly, posing a risk of fumes, and the lithium deposits on the cathode are in a loose dendritic form, posing a significant safety hazard. Conclusion: Efficiency is too low when the current density is below 5 mA / cm²; safe and efficient electrolysis can be achieved in the range of 5-100 mA / cm²; exceeding 100 mA / cm² will bring serious temperature rise, safety and product morphology problems, confirming the necessity of this upper limit.

[0077] 3. Discussion on the advantages of electrolysis time range (1h-10h) and room temperature: Time Range Validity: Under the preferred conditions (4.0V) of Example 1, the lithium deposition rates after 1 hour, 5 hours, and 10 hours of electrolysis were approximately 45%, 89%, and 93%, respectively. This demonstrates that 1 hour is sufficient for effective startup and partial recovery, 5 hours for efficient recovery, and 10 hours for deep purification. This range covers different needs from rapid pretreatment to deep recovery.

[0078] Advantages of room temperature (25-30℃) operation: All embodiments of this invention were successfully carried out at room temperature. This is in stark contrast to the traditional process in the background art, which requires high-temperature pyrolysis of 400-500℃. Room temperature operation avoids the huge energy consumption caused by high temperature, the safety risks of the violent decomposition of LiPF6 producing toxic hydrogen fluoride (HF) and other gases, and the stringent requirements for equipment corrosion resistance. This is the key to the safety, economy and environmental friendliness of this method.

[0079] In conclusion, the process parameter range defined in this invention is an effective and safe operating window determined after thorough research into the electrochemical behavior of the specific system of retired lithium battery waste electrolyte. Experiments have shown that exceeding this range will lead to reaction failure, low efficiency, or serious side reactions and safety hazards. These parameters, in conjunction with specific electrode materials (graphite / copper) and the core reaction pathway of "one-step electrochemical decomposition-separation," constitute a complete, optimized, and industrially feasible technical solution, successfully solving the industry challenge of simultaneously recovering lithium and removing fluoride from complex waste liquids.

[0080] In the description of this specification, references to terms such as "one embodiment," "some embodiments," "example," "specific example," 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 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.

[0081] 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 without departing from the principles and spirit of the present invention.

Claims

1. A method for simultaneously extracting lithium and removing fluoride from waste electrolyte of retired lithium batteries, characterized in that, Includes the following steps: S1. Use waste electrolyte from retired lithium batteries containing LiPF6 as the electrolyte and place it in an electrolysis device; S2. Electrolysis is performed in the waste electrolyte using a copper or copper alloy electrode as the cathode and a graphite or copper electrode as the anode; S3. During the electrolysis process, Li + At the cathode, lithium is reduced to metallic lithium and deposited, while PF6... - The anode is oxidized and converted into a fluorine-containing solid compound that is insoluble in the waste electrolyte; S4. After electrolysis, the metallic lithium deposited on the cathode is separated, and the fluorine-containing solid compound is separated from the electrolyte to obtain an electrolyte in which lithium and fluorine have been removed.

2. The method according to claim 1, characterized in that, The waste electrolyte contains one or more carbonate organic solvents.

3. The method according to claim 2, characterized in that, The carbonate organic solvent is selected from one or more of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethylene carbonate, and propylene carbonate.

4. The method according to claim 1, characterized in that, The electrolysis is constant voltage electrolysis, with an electrolysis voltage of 2.5 V to 6 V.

5. The method according to claim 1, characterized in that, The electrolysis is constant current electrolysis, with a current density of 5 mA / cm² to 100 mA / cm².

6. The method according to claim 1, 4, or 5, characterized in that, The electrolysis time is from 1 h to 10 h.

7. The method according to claim 1, characterized in that, The electrolysis is carried out in an air atmosphere or an inert atmosphere, with an ambient temperature of 25°C to 30°C.

8. The method according to claim 1, characterized in that, When the anode is a graphite electrode, the graphite electrode is an artificial or natural graphite sheet with a layered structure and an interlayer spacing d(002) of 0.335 nm to 0.340 nm, and the graphite electrode is subjected to electrochemical or chemical expansion treatment before use.

9. The method according to claim 1, characterized in that, When the anode is a copper electrode, the copper electrode is a clean electrolytic copper foil or copper sheet, and is subjected to acid washing or electrochemical polishing treatment to remove the surface oxide layer before use.

10. The method according to claim 1, characterized in that, When the anode is a graphite electrode, the fluorine-containing solid compound is PF6. - C formed by intercalation of graphite X PF6; when the anode is a copper electrode, the fluorine-containing solid compound is Cu(PF6)2.

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