Method for producing lithium iodide, solid-state battery

Abstract

A preparation method of lithium iodide and a solid-state battery, the preparation method comprising mixing a lithium source material, water, a first solvent and a quaternary amine base, reacting the quaternary amine base with carbon dioxide under a reaction atmosphere containing carbon dioxide to generate HCO3 ‑ , HCO3 ‑ reacting with lithium ions in the lithium source material to generate lithium bicarbonate, collecting an aqueous phase after the reaction; decomposing the lithium bicarbonate in the aqueous phase to generate lithium carbonate, collecting a solid phase, decomposing the lithium carbonate in the solid phase to generate lithium oxide to obtain an intermediate; dissolving a quaternary ammonium iodide salt in a second solvent and adding the intermediate, converting the lithium oxide into lithium hydroxide, and performing ion exchange between the lithium hydroxide and the quaternary ammonium iodide salt to generate lithium iodide, collecting a liquid phase; and collecting the lithium iodide in the liquid phase. Based on the characteristics of the specific quaternary amine base and the quaternary ammonium iodide salt, the application selectively enhances carbonization leaching of Li in the lithium source material, removes anion impurities in the lithium source material, and also realizes anion exchange in an organic phase and preparation of high-purity anhydrous lithium iodide.

Description

Technical Field

[0001] This application relates to the field of electrochemical energy storage technology, specifically to a method for preparing lithium iodide and a solid-state battery. Background Technology

[0002] Lithium salts are one of the core materials in rechargeable batteries (such as lithium-ion batteries), and their purity directly determines key performance characteristics such as energy density, safety, and cycle life. However, the lithium salts obtained by current production processes still have a high impurity content, and the purity of lithium salts needs to be improved. Summary of the Invention

[0003] In view of this, this application provides a method for preparing lithium iodide and a solid-state battery to solve the above-mentioned technical problems.

[0004] To achieve the above objectives, in a first aspect, this application provides a method for preparing lithium iodide, comprising: mixing lithium source materials, water, a first solvent, and a quaternary ammonium base, wherein the general chemical formula of the quaternary ammonium base is [(C n1 H 2n1+1 ) n2 N(CH3) n3 ] + OH - Where n1≥6, n2>0, n3≥0, n2+n3=4, the solubility of the quaternary ammonium base in the first solvent at 20 ℃ to 25 ℃ is greater than or equal to 10 g / L, a first mixture is obtained, and the quaternary ammonium base in the first mixture is reacted with carbon dioxide to generate HCO3 under a reaction atmosphere containing carbon dioxide. - and make HCO3 - Lithium bicarbonate is generated by reacting with lithium ions in the lithium source material, and the aqueous phase is collected after the reaction. The lithium bicarbonate in the aqueous phase is then decomposed to generate lithium carbonate, and the solid phase is collected. The lithium carbonate in the solid phase is then decomposed to generate lithium oxide, yielding an intermediate. A quaternary ammonium iodide salt is dissolved in a second solvent, and the intermediate is added to obtain a second mixture. The lithium oxide in the second mixture is converted to lithium hydroxide, and the lithium hydroxide undergoes ion exchange with the quaternary ammonium iodide salt to generate lithium iodide. The liquid phase is collected. The second solvent includes a polyol, and the general chemical formula of the quaternary ammonium iodide salt is [(C n H 2n+1 )4N] + I - (n≤4); Collect lithium iodide in the liquid phase.

[0005] Based on the first aspect, in some possible implementations, the mass ratio of lithium source material, water and first solvent is 1:(8~50):(4~25).

[0006] Based on the first aspect, in some possible implementations, the mass ratio of the second solvent to the quaternary ammonium iodide is (5~30):1.

[0007] Based on the first aspect, in some possible implementations, the flow rate of the reaction atmosphere is 1 m. 3 / h to 30 m 3 / h.

[0008] Based on the first aspect, in some possible implementations, the second mixture also includes lithium hydroxide, wherein the molar ratio of lithium oxide, lithium hydroxide and quaternary ammonium iodide is (0.05~0.3):(0.4~0.5):1.

[0009] Based on the first aspect, in some possible implementations, the first solvent includes one or more of dichloromethane, chloroform, and toluene.

[0010] Based on the first aspect, in some possible implementations, the liquid phase is extracted with an organic solvent to obtain a lithium-containing organic phase, and the lithium-containing organic phase is concentrated and crystallized to collect lithium iodide from the liquid phase.

[0011] Based on the first aspect, in some possible implementations, the organic solvent includes ether-based organic solvents and chain-like carbonate-based organic solvents.

[0012] Based on the first aspect, in some possible implementations, the volume ratio of the liquid phase to the organic solvent is 1:(2~5).

[0013] Based on the first aspect, in some possible implementations, the extraction includes multi-stage extraction, where the number of extraction stages is greater than or equal to 3.

[0014] Based on the first aspect, in some possible implementations, the extraction temperature is 5 ℃ to 40 ℃ and the time is 10 min to 60 min.

[0015] Based on the first aspect, in some possible implementations, the temperature of the concentration crystallization process is between 30 °C and 100 °C.

[0016] Based on the first aspect, in some possible implementations, the reaction temperature for generating lithium bicarbonate is from 10 °C to 50 °C, and the reaction time is from 4 h to 24 h.

[0017] Based on the first aspect, in some possible implementations, the reaction temperature for ion exchange is from 5 °C to 40 °C, and the reaction time is from 30 min to 180 min.

[0018] Based on the first aspect, in some possible implementations, the aqueous phase is heated to decompose lithium bicarbonate in the aqueous phase to generate lithium carbonate, with the heating temperature being 85 ℃ to 100 ℃ and the time being 1.5 h to 4 h.

[0019] Based on the first aspect, in some possible implementations, the solid phase is heat-treated to decompose lithium carbonate in the solid phase into lithium oxide, and the heat treatment temperature is 600 ℃ to 1000 ℃ for 1 h to 6 h.

[0020] Based on the first aspect, in some possible implementations, the aqueous phase is collected by static stratification at a temperature of 5 ℃ to 40 ℃ for a time of 10 min to 60 min.

[0021] Based on the first aspect, in some possible implementations, before the lithium carbonate is decomposed to generate lithium oxide, the preparation method further includes: drying the solid phase at a temperature of 85 °C to 150 °C for 1.5 h to 4 h.

[0022] Based on the first aspect, in some possible implementations, after collecting lithium iodide from the liquid phase, the preparation method further includes: vacuum drying the lithium iodide at a temperature of 30 ℃ to 80 ℃ for 1 h to 4 h, and at a pressure less than or equal to -0.3 MPa.

[0023] Based on the first aspect, in some possible implementations, ion exchange is carried out in a protective gas atmosphere.

[0024] Based on the first aspect, in some possible implementations, the collection of lithium iodide in the liquid phase is carried out in a protective gas atmosphere.

[0025] Based on the first aspect, in some possible implementations, the lithium source material includes lithium hydroxide, and the molar ratio of lithium hydroxide to quaternary ammonium base in the lithium source material is 1:(0.05~0.5).

[0026] Based on the first aspect, in some possible implementations, the lithium source material includes lithium carbonate, and the molar ratio of lithium carbonate to quaternary ammonium base in the lithium source material is 1:(0.05~0.5).

[0027] Based on the first aspect, in some possible implementations, the lithium source material includes waste lithium iron phosphate cathode material, and the first mixture also includes an organothiol, which includes one or more of alkyl thiols, aromatic thiols and heteroaryl thiols, and the molar ratio of the organothiol to the quaternary ammonium base is (2~5):(0.05~0.5).

[0028] Based on the first aspect, in some possible implementations, the lithium source material includes waste lithium iron phosphate cathode material, and the reaction atmosphere also includes an oxidizing gas, which includes one or more of air, oxygen, and ozone.

[0029] Secondly, this application provides a solid-state battery comprising lithium iodide prepared by the above-described preparation method.

[0030] This application utilizes the CO2 capture characteristics and phase transfer characteristics of specific quaternary ammonium bases and the ion exchange characteristics of specific iodide quaternary ammonium salts to selectively enhance the carbonization leaching of Li in lithium source materials, while simultaneously reducing SO4 content in the lithium source materials. 2- PO4 3- The method achieves the goal of deep anion removal; furthermore, it enables anion exchange of lithium-containing intermediates in an organic phase to prepare high-purity anhydrous lithium iodide, avoiding the problems of difficult removal of lithium iodide crystal water and easy hydrolysis caused by aqueous systems. Tests show that the lithium salt yield according to the method of this invention is higher than 96%, and the purity of the lithium salt is higher than 99.9%. In addition, this invention has the advantages of simple operation process, environmental friendliness, controllable quality, and ease of industrialization, which can generate good economic and social benefits and has broad application prospects.

[0031] When lithium iodide is used in solid-state batteries, its low water content and low impurity characteristics help reduce the blockage and damage of impurities to lithium-ion transport channels, which is conducive to building a more stable electrode-electrolyte interface with lower impedance, thereby synergistically improving the ionic conductivity, interface compatibility and long-term cycle performance of solid-state batteries. Detailed Implementation

[0032] To facilitate understanding of the technical solutions of this application, a more comprehensive description of the technical solutions will be provided below. However, the technical solutions of this application can be implemented in many different forms and are not limited to the embodiments described herein. Therefore, the purpose of providing these embodiments is to make the disclosure of the technical solutions of this application more thorough and comprehensive.

[0033] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0034] The efficiency of related technologies in preparing or purifying lithium salts from lithium source materials still needs improvement, reflected in the low purity of the obtained lithium salts and the difficulty in removing common residual impurities such as anions and water molecules. Based on this, the embodiments of this application improve the lithium salt preparation method to reduce the impurity content in the lithium salt and obtain higher purity lithium iodide, which can be used in solid-state batteries.

[0035] Based on this, one embodiment of this application provides a method for preparing lithium iodide. This method can process lithium source materials based on lithium compounds and reduce anionic impurities and moisture to obtain lithium salts with high yield and high purity. For example, the lithium source material (lithium compound) can be lithium hydroxide or lithium carbonate. The preparation method includes:

[0036] Step 1: Mix lithium source material, water, first solvent, and quaternary ammonium base. The general chemical formula of the quaternary ammonium base is [(C n1 H 2n1+1 ) n2 N(CH3) n3 ] + OH - Where n1≥6, n2>0, n3≥0, n2+n3=4, the solubility of the quaternary ammonium base in the first solvent at 20 ℃ to 25 ℃ is greater than or equal to 10 g / L, a first mixture is obtained, and the quaternary ammonium base in the first mixture is reacted with carbon dioxide to generate HCO3 under a reaction atmosphere containing carbon dioxide. - and make HCO3 - The lithium base reacts with lithium ions in the lithium source material to generate lithium bicarbonate, and the aqueous phase is collected after the reaction. For example, according to the above general chemical formula, the quaternary ammonium base of this application can be tetrahexylammonium hydroxide or tetraoctylammonium hydroxide, etc.

[0037] In the above steps, the lithium source material is mixed with a first solvent, a quaternary ammonium base, and water to form a first mixture of three phases: oil (organic phase), water (aqueous phase), and solid (raw material). The first solvent providing the oil phase is a good solvent for the quaternary ammonium base; therefore, the quaternary ammonium base exists in the organic phase. Furthermore, the quaternary ammonium base of this application has long-chain substituent groups (C...). n1 H 2n1+1 (n1≥6), which can further enhance its solubility and stability in the first solvent (oil phase). In this application, it plays a role in capturing CO2 at the oil-water interface and carrying out phase transfer, while the long-chain structure extracts anionic impurities (such as SO4). 2- PO4 3- The role of (etc.). Therefore, under the reaction atmosphere of carbon dioxide and oxidizing gases, some quaternary ammonium bases in the organic phase can capture CO2, forming water-soluble bicarbonate ion pairs. This substance can act as a phase transfer catalyst to enter the aqueous phase. In the aqueous phase, HCO3- - The lithium reacts with lithium in the lithium source material to form soluble lithium bicarbonate (LiHCO3), allowing lithium to selectively enter the aqueous phase. During this process, the quaternary ammonium base in the organic phase can react with anionic impurities (such as SO42-). 2- PO4 3- (etc.) form insoluble salts or ion pairs and are extracted and retained in the oil phase, thereby helping to separate anionic impurities from lithium in the aqueous phase.

[0038] Understandably, if n1 < 6 in the general chemical formula of the quaternary ammonium base, that is, when the long carbon chain substituents in the quaternary ammonium base are replaced with shorter carbon chain substituents, the partition coefficient and solubility stability of the quaternary ammonium base in the first solvent (hydrophobic organic phase) will be reduced, weakening its ability to effectively cycle between oil and water phases as a phase transfer catalyst, resulting in a decrease in CO2 capture efficiency and a decrease in lithium leaching rate. At the same time, the short carbon chain structure has insufficient affinity and extraction selectivity for anionic impurities, making it difficult to achieve deep removal, making it easier for impurities to enter the lithium-containing aqueous phase, ultimately affecting the purity of subsequent intermediates.

[0039] Understandably, if the solubility of the first solvent for the quaternary ammonium base is low, for example, if the solubility of the first solvent for the quaternary ammonium base is less than 10 g / L, for example, if acetone is chosen as the first solvent, the strong miscibility of acetone with water will disrupt the clear separation of the oil and water phases, resulting in the quaternary ammonium base and the chelated metal impurities not being effectively confined in an independent organic phase. At the same time, acetone has poor solubility for the aforementioned quaternary ammonium salt, which will reduce the effective concentration of the quaternary ammonium salt in the system and weaken the impurity removal effect based on phase distribution.

[0040] In some embodiments, the first solvent includes one or more of dichloromethane, chloroform, and toluene.

[0041] In some embodiments, the mass ratio of lithium source material, water, and the first solvent is 1:(8~50):(4~25). For example, taking 1 part by mass of lithium source material, the mass part of water can be 8, 11, 14, 17, 20, 23, 26, 29, 32, 35, 38, 41, 44, 47, 50, or any value within the range of any two of the above values. The mass part of the first solvent can be 4, 7, 10, 13, 16, 19, 22, 25, or any value within the range of any two of the above values. Controlling the mass ratio of lithium source material, water, and the first solvent within the above range helps the first mixture form a suitable proportion of oil (organic phase) - water (aqueous phase) - solid (raw material) three phases, promoting the reaction process of the aqueous phase and the organic phase in the above process. An optimized mass ratio helps to establish a more stable and efficient oil-water blending system with better phase transfer capabilities, which helps to promote lithium leaching. At the same time, through sufficient oil-water partitioning, it helps to promote the extraction of target anionic impurities into the oil phase and fix polyvalent cations in the solid or oil phase, thereby further improving the yield and purity of lithium salts.

[0042] In some embodiments, the molar ratio of lithium source material to quaternary ammonium base is 1:(0.05~0.5). For example, taking 1 molar amount of lithium source material as the basis, the molar amount of quaternary ammonium salt can be 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, or any value within the range of any two of the above values. Controlling the molar ratio of lithium source material to quaternary ammonium salt within the above range helps to fully utilize the role of quaternary ammonium base in the above process, further promoting the leaching reaction and impurity removal process, thereby further improving the yield and purity of lithium salt.

[0043] In some embodiments, the flow rate of the reaction atmosphere is 1 m. 3 / h to 30 m 3 / h. For example, the flow rate of the reaction atmosphere can be 1 m. 3 / h、3 m 3 / h、6 m 3 / h、9 m 3 / h、12 m 3 / h, 15 m 3 / h、18 m 3 / h、21 m 3 / h、24 m 3 / h、27 m 3 / h, 30m 3 / h or any value within the range of any two of the above values. Controlling the flow rate of the reaction atmosphere within the above range helps to regulate the mass transfer efficiency of the gas-liquid-solid three-phase interface. Sufficient flow rate helps to promote the effective concentration of CO2 in the liquid phase to continuously generate bicarbonate for lithium leaching. At the same time, it helps the reaction atmosphere to fully contact the solid raw materials, thereby further improving the yield and purity of lithium salts.

[0044] In some embodiments, the reaction temperature for generating lithium bicarbonate is between 10 °C and 50 °C, and the reaction time is between 4 h and 24 h. For example, the reaction temperature can be 10 °C, 15 °C, 20 °C, 25 °C, 30 °C, 35 °C, 40 °C, 45 °C, 50 °C, or any value within the range of any two of the above values, and the reaction time can be 4 h, 6 h, 8 h, 10 h, 12 h, 14 h, 16 h, 18 h, 20 h, 22 h, 24 h, or any value within the range of any two of the above values. Controlling the reaction temperature and reaction time within the above range helps to regulate the reaction rate, gas solubility, and mass diffusion rate, while promoting the reaction to reach or approach equilibrium, ensuring a complete reaction, and thus contributing to further improving the yield and purity of lithium salts.

[0045] In some embodiments, the aqueous phase is collected by settling and stratification at a temperature of 5°C to 40°C for a time of 10 min to 60 min. For example, the settling and stratification temperature can be 5°C, 10°C, 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, or any value within the range of any two of the above values, and the settling time can be 10 min, 15 min, 20 min, 25 min, 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, 60 min, or any value within the range of any two of the above values. Controlling the settling and stratification temperature and time within the above ranges helps to achieve clear separation of the oil and water phases. Appropriate temperature can maintain a suitable liquid phase viscosity, promoting the coalescence of dispersed droplets. Sufficient settling time ensures that the density difference-driven stratification process reaches equilibrium, which helps to reduce the entrainment of organic phase in the aqueous phase and reduce contamination of the lithium-containing solid phase, thereby further improving the yield and purity of lithium salts.

[0046] Step 2: Decompose lithium bicarbonate in the aqueous phase to generate lithium carbonate, collect the solid phase, and decompose lithium carbonate in the solid phase to generate lithium oxide to obtain an intermediate.

[0047] In the above steps, lithium bicarbonate (LiHCO3) in the aqueous phase decomposes to form lithium carbonate (Li2CO3) precipitate, thereby transferring lithium from the aqueous phase to the solid phase. This precipitation process can further remove trace amounts of alkaline earth metal ions (Ca) that may coexist. 2+ Mg 2+ (If applicable). Lithium carbonate in the solid phase decomposes to form lithium oxide (Li₂O), thereby removing CO₂. Simultaneously, this heat treatment further decomposes residual trace organic matter (such as quaternary ammonium bases) and volatile impurities. Therefore, the main component of the resulting intermediate is high-purity lithium oxide (Li₂O). It should be noted that in cases of incomplete calcination or the presence of trace amounts of moisture in the environment, a small amount of lithium hydroxide (LiOH) may be generated on the surface of the intermediate.

[0048] In some embodiments, the aqueous phase is heated to decompose lithium bicarbonate in the aqueous phase to form lithium carbonate. The heating temperature is from 85°C to 100°C, and the heating time is from 1.5 h to 4 h. For example, the heating temperature can be 85°C, 86°C, 87°C, 88°C, 89°C, 90°C, 91°C, 92°C, 93°C, 94°C, 95°C, 96°C, 97°C, 98°C, 99°C, 100°C, or any value within the range of any two of the above values. The heating time can be 1.5 h, 1.8 h, 2.1 h, 2.4 h, 2.7 h, 3 h, 3.3 h, 3.6 h, 3.9 h, 4 h, or any value within the range of any two of the above values. Controlling the heating temperature and time within the above range helps to promote the decomposition of lithium bicarbonate (LiHCO3) dissolved in the aqueous phase to form lithium carbonate (Li2CO3) precipitate, reducing the risk of incomplete decomposition when the temperature or time is insufficient, and the risk of severe water evaporation affecting the crystal form of the precipitate when the temperature or time is excessive.

[0049] In some embodiments, the solid phase is heat-treated to decompose lithium carbonate in the solid phase to generate lithium oxide. The heat treatment temperature is from 600 °C to 1000 °C, and the time is from 1 h to 6 h. For example, the heat treatment temperature can be 600 °C, 650 °C, 700 °C, 750 °C, 800 °C, 850 °C, 900 °C, 950 °C, 1000 °C, or any value within the range of any two of the above values, and the time can be 1 h, 1.5 h, 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h, 5 h, 5.5 h, 6 h, or any value within the range of any two of the above values. Controlling the temperature and time of heat treatment within the above range helps to promote the complete decomposition of lithium carbonate (Li2CO3) into the desired intermediate lithium oxide (Li2O), and also helps to promote the pyrolysis of residual trace organic matter and the removal of volatile inorganic impurities, reducing the risk of incomplete reaction when the temperature or time is insufficient, and the risk of side reactions caused when the temperature or time is excessive.

[0050] In some embodiments, before decomposing lithium carbonate to generate lithium oxide (e.g., before heat treatment), the preparation method further includes: drying the solid phase at a temperature of 85°C to 150°C for a time of 1.5 h to 4 h. For example, the drying temperature can be 85°C, 90°C, 95°C, 100°C, 105°C, 110°C, 115°C, 120°C, 125°C, 130°C, 135°C, 140°C, 145°C, 150°C, or any value within the range of any two of the above values, and the time can be 1.5 h, 1.8 h, 2 h, 2.2 h, 2.5 h, 2.8 h, 3 h, 3.2 h, 3.5 h, 3.8 h, 4 h, or any value within the range of any two of the above values. Controlling the drying temperature and time within the above-mentioned range helps to reduce free water and some adsorbed water in the solid phase before lithium carbonate decomposition (or high-temperature calcination). Water vapor at high temperatures reacts with subsequently generated lithium oxide (Li₂O) to reversely generate lithium hydroxide, affecting the uniformity and controllability of the intermediate composition and potentially introducing impurities.

[0051] Step 3: Dissolve the quaternary ammonium iodide salt in the second solvent, add the intermediate to obtain the second mixture, convert the lithium oxide in the second mixture to lithium hydroxide, and then allow the lithium hydroxide to undergo ion exchange with the quaternary ammonium iodide salt to generate lithium iodide. Collect the liquid phase. The second solvent includes a polyol, and the general chemical formula of the quaternary ammonium iodide salt is [(C n H 2n+1 )4N] + I - (n≤4). For example, according to the above general chemical formula, the quaternary ammonium iodide salt of this application can be tetramethylammonium iodide or tetraethylammonium iodide, etc., and the polyol includes one or more of ethylene glycol, propylene glycol and glycerol.

[0052] In the above steps, the polyol in the second mixture has a high boiling point and good solubility, and can serve as a reaction medium to dissolve the quaternary ammonium iodide salt and promote the heterogeneous reaction. Furthermore, this application uses a short-chain substituent group (C... n H 2n+1The quaternary ammonium iodide salt (n≤4) helps reduce its steric hindrance and viscosity in the second solvent (polyol), thus promoting the rate and completeness of the ion exchange reaction in this application. The intermediate first reacts with trace amounts of water in the polyol or with itself to generate lithium hydroxide (if LiOH is insufficient, it is supplemented). The lithium hydroxide (LiOH) then undergoes an ion exchange reaction with the quaternary ammonium iodide salt in the polyol medium, generating lithium iodide (LiI) which dissolves in the polyol. The exchanged quaternary ammonium base may precipitate or remain in the solution. In this process, the quaternary ammonium iodide salt acts as an iodine source and phase transfer promoter, converting lithium from an inorganic solid to an organically compatible iodide. The polyol provides the anhydrous or low-water environment required for this exchange reaction, avoiding the premature introduction of large amounts of water.

[0053] Understandably, if n > 4 in the general chemical formula of the above-mentioned quaternary ammonium iodide salt, that is, when the short carbon chain substituents in the quaternary ammonium iodide salt are replaced with longer carbon chain substituents, the larger molecular volume and hydrophobicity will increase the dissolution resistance and system viscosity in the second solvent (polyol), thereby inhibiting the mass transfer rate and reaction completeness of the ion exchange reaction, resulting in a decrease in lithium conversion efficiency. At the same time, the long carbon chain structure is more likely to remain in the lithium-containing organic phase in the subsequent extraction steps, and is difficult to completely remove through phase separation, thus being introduced into the final product as an organic impurity, which damages the crystal purity and chemical stability of lithium iodide.

[0054] Understandably, if the second solvent is not a polyol, for example, if ethanol is used, it is difficult to maintain a stable reaction environment at higher temperatures due to the low boiling point and weak polarity of ethanol, which may lead to incomplete reaction. At the same time, ethanol has limited solubility for the intermediate lithium oxide and the reaction product lithium iodide, and cannot provide an effective homogeneous reaction system, which will reduce the rate and conversion efficiency of the ion exchange reaction, resulting in a decrease in lithium recovery rate. It will also introduce organic impurities into the final product, which will damage the crystal purity and chemical stability of lithium iodide.

[0055] In some embodiments, the mass ratio of the second solvent to the quaternary ammonium iodide is (5~30):1. For example, with 1 part by mass of the quaternary ammonium iodide, the mass part of the second solvent can be 5, 9, 11, 13, 15, 17, 19, 21, 23, 25, 27, 29, 30, or any value within the range of any two of the above values. Controlling the mass ratio of the second solvent to the quaternary ammonium iodide within the above range helps to provide a homogeneous or well-dispersed reaction medium with suitable concentration and viscosity for the ion exchange reaction. A suitable solvent ratio ensures that the quaternary ammonium iodide is fully dissolved and the solid intermediate is well dispersed, promoting a stable, rapid, and thorough reaction, and reducing side reactions such as the decomposition of organic matter that may be caused by uneven reaction or excessive residence time, thereby contributing to further improvement in the yield and purity of lithium salts.

[0056] In some embodiments, the second mixture further includes lithium hydroxide, and the molar ratio of lithium oxide, lithium hydroxide, and quaternary ammonium iodide is (0.05~0.3):(0.4~0.5):1. For example, with the molar ratio of quaternary ammonium iodide being 1, the molar ratio of lithium oxide can be 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, or any value within the range of any two of the above values, and the molar ratio of lithium hydroxide can be 0.4, 0.41, 0.42, 0.43, 0.44, 0.45, 0.46, 0.47, 0.48, 0.49, 0.5, or any value within the range of any two of the above values. Controlling the molar ratio of the three components within the above range provides sufficient active lithium to fully react with the quaternary ammonium iodide, which helps to promote the ion exchange reaction, thereby further improving the yield and purity of the lithium salt.

[0057] In some embodiments, the reaction temperature for ion exchange is from 5 °C to 40 °C, and the reaction time is from 30 min to 180 min. For example, the reaction temperature for ion exchange can be 5 °C, 10 °C, 15 °C, 20 °C, 25 °C, 30 °C, 35 °C, 40 °C, or any value within the range of any two of the above values, and the reaction time can be 30 min, 40 min, 50 min, 60 min, 70 min, 80 min, 90 min, 100 min, 120 min, 140 min, 160 min, 180 min, or any value within the range of any two of the above values. Controlling the reaction temperature and time within the above ranges helps to optimize the ion exchange process kinetically and thermodynamically. A suitable temperature provides sufficient activation energy to accelerate the reaction rate while reducing the decomposition and carbonization of polyols or organic quaternary ammonium salts. Sufficient time helps to promote the reaction to reach or approach equilibrium, further promoting the conversion of LiOH to LiI.

[0058] In some embodiments, ion exchange is carried out in a protective gas atmosphere. Controlling the reaction to occur in a protective gas atmosphere (such as nitrogen or argon) helps reduce side reactions caused by air components, thereby contributing to further improvements in the yield and purity of lithium salts.

[0059] Step 4: Collect lithium iodide from the liquid phase.

[0060] In some embodiments, the liquid phase is extracted with an organic solvent to obtain a lithium-containing organic phase, which is then concentrated and crystallized to collect lithium iodide from the liquid phase. The change in the partition coefficient of LiI in the mixed solvent system can be utilized to extract it from the more polar polyol phase to the less polar organic phase, thereby separating residual trace amounts of quaternary ammonium salts, polyols, and other organic impurities. Finally, the lithium-containing organic phase is concentrated and crystallized under reduced pressure. Because the entire crystallization process is carried out in a strictly anhydrous organic system, anhydrous lithium iodide crystals are directly precipitated, which helps reduce the formation of difficult-to-remove hydrates during crystallization from aqueous solutions and hydrolysis during high-temperature dehydration, thus contributing to the acquisition of high-purity, high-yield lithium iodide.

[0061] In some embodiments, the organic solvents include ether-based organic solvents and chain carbonate-based organic solvents. Ether-based (e.g., diethyl ether) or chain carbonate-based (e.g., propyl formate, methyl acetate, ethyl acetate, propyl acetate, etc.) organic solvents are chosen because they have moderate partition coefficients for lithium iodide (LiI) and limited miscibility with polyols (the second solvent), facilitating phase separation. Ether-based solvents have lower polarity and high extractive selectivity for LiI, effectively separating organic impurities; carbonate-based solvents have slightly higher polarity and stronger solubility for LiI, which is beneficial for improving single-stage extraction efficiency. Controlling the use of these solvents helps to efficiently and selectively extract LiI from a liquid phase rich in polyols and reaction byproducts (such as quaternary ammonium bases), thereby achieving primary purification and enrichment of the product, laying the foundation for subsequent crystallization to obtain a high-purity product, and thus contributing to further improvements in the purity and yield of lithium salts.

[0062] In some embodiments, the volume ratio of the liquid phase to the organic solvent is 1:(2~5). For example, with the volume of the liquid phase as 1, the volume of the organic solvent can be 2, 2.3, 2.6, 2.9, 3.2, 3.5, 3.8, 4.1, 4.4, 4.7, 5, or any value within the range of any two of the above values. Controlling the volume ratio of the liquid phase to the organic solvent within the above range helps to optimize the mass transfer driving force of the extraction process. An optimized volume ratio can improve extraction efficiency while maintaining a high LiI concentration in the organic phase, which is beneficial for subsequent crystallization.

[0063] In some embodiments, the extraction includes multi-stage extraction, wherein the number of extraction stages is greater than or equal to 3. For example, the number of extraction stages in multi-stage extraction can be 3, 4, 5, 6, or any value within the range of any two of the above values. Using multi-stage extraction, through multiple equilibrium contacts, helps to further improve the recovery rate and purity of lithium iodide products and reduce the potential contamination risks associated with complex systems.

[0064] In some embodiments, the extraction temperature is from 5 °C to 40 °C, and the extraction time is from 10 min to 60 min. For example, the extraction temperature is 5 °C, 10 °C, 15 °C, 20 °C, 25 °C, 30 °C, 35 °C, 40 °C, or any value within the range of any two of the above values, and the extraction time can be 10 min, 15 min, 20 min, 25 min, 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, 60 min, or any value within the range of any two of the above values.

[0065] Controlling the extraction temperature and time within the aforementioned range helps regulate the mass transfer rate, the miscibility of the two phases, and the viscosity. Suitable temperature and time further optimize the partitioning behavior of LiI between the polyol phase and the organic extractant phase, increasing the mass transfer rate while reducing liquid phase viscosity, promoting phase separation, and minimizing cross-contamination caused by emulsification or entrainment. This, in turn, contributes to further improving the purity and yield of lithium salts.

[0066] In some embodiments, the concentration crystallization process is carried out at a temperature of 30°C to 100°C. For example, the concentration crystallization process temperature can be 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, 100°C, or any value within the range of any two of the above values. Controlling the concentration crystallization temperature within the above range helps to regulate the crystallization kinetics and thermodynamics of anhydrous lithium iodide. After removing most of the organic solvent through vacuum concentration, controlling the crystallization temperature (e.g., cooling crystallization) helps to control the supersaturation of LiI, promoting the formation of crystals with uniform particle size and high purity. It reduces the risk of potential impurities from the mother liquor being trapped during rapid crystallization, or lithium residue remaining in the mother liquor during incomplete crystallization, thereby contributing to further improvements in the purity and yield of lithium salts.

[0067] In some embodiments, after collecting lithium iodide from the liquid phase (e.g., after concentration and crystallization), the preparation method further includes vacuum drying of the lithium iodide (or the crystalline product) at a temperature of 30°C to 80°C for 1 to 4 hours and at a pressure less than or equal to -0.3 MPa. For example, the vacuum drying temperature can be 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, or any value within the range of any two of the above values; the time can be 1 hour, 1.3 hours, 1.6 hours, 1.9 hours, 2.2 hours, 2.5 hours, 2.8 hours, 3.1 hours, 3.3 hours, 3.7 hours, 4 hours, or any value within the range of any two of the above values. Controlling the temperature, time, and pressure of the vacuum drying within the above ranges helps to further reduce trace amounts of organic solvents and water molecules adsorbed on the crystal surface and possibly in the crystal lattice, and this is carried out under these mild conditions. Vacuum conditions help lower the boiling point of the solvent, enabling efficient desorption at relatively low temperatures. This reduces the oxidation, decomposition, or reaction with residual impurities of lithium iodide at high temperatures, thus further improving the purity and yield of lithium salts.

[0068] In some embodiments, the collection of lithium iodide from the liquid phase (e.g., concentration and crystallization) is carried out in a protective gas atmosphere. Controlling the collection of lithium iodide from the liquid phase (e.g., concentration and crystallization) in a protective gas atmosphere (e.g., nitrogen, argon) helps reduce side reactions caused by air components, which can lead to product contamination, such as reducing oxygen oxidation of iodide ions or reducing moisture deliquescence or hydrolysis of lithium iodide, thereby contributing to further improvements in the purity and yield of lithium salts.

[0069] Therefore, this application selectively enhances the carbonization leaching of Li in lithium source materials based on the CO2 capture characteristics, phase transfer characteristics of specific quaternary ammonium bases, and ion exchange characteristics of specific iodide quaternary ammonium salts, while simultaneously reducing SO4 content in the lithium source materials. 2- PO4 3- The method achieves the goal of deep anion removal; furthermore, it enables anion exchange of lithium-containing intermediates in an organic phase to prepare high-purity anhydrous lithium iodide, avoiding the problems of difficult removal of lithium iodide crystal water and easy hydrolysis caused by aqueous systems. Tests show that the lithium salt yield according to the method of this invention is higher than 96%, and the purity of the lithium salt is higher than 99.9%. In addition, this invention has the advantages of simple operation process, environmental friendliness, controllable quality, and ease of industrialization, which can generate good economic and social benefits and has broad application prospects.

[0070] This application also provides a method for preparing lithium iodide. This method can process lithium source materials based on waste battery materials, achieve resource recycling, and reduce cationic impurities, anionic impurities, and water molecules to obtain high-yield, high-purity lithium salts. The main difference between this method and the aforementioned method for reducing anionic impurities and water molecules is the addition of a step in step one to remove cationic impurities (such as Fe, Mn, Co, Ni, etc.). For example, the aforementioned lithium source materials (waste battery materials) include waste lithium iron phosphate cathode materials.

[0071] In some embodiments, the reaction atmosphere further includes an oxidizing gas, which includes one or more of air, oxygen, and ozone. The oxidizing gas in the reaction atmosphere can oxidize cationic impurities to higher valence states, forming insoluble oxide / hydroxide precipitates, thereby facilitating the conversion and separation of cationic impurities, which are then removed by solid-liquid separation after the reaction.

[0072] In some embodiments, the first mixture further includes an organothiol, which includes one or more of alkyl thiols, aromatic thiols, and heteroaryl thiols, wherein the molar ratio of the organothiol to the quaternary ammonium base is (2-5):(0.05-0.5). For example, the molar ratio of the organothiol to the quaternary ammonium base can be 2:0.5, 2.5:0.4, 3:0.3, 3.5:0.2, 4:0.1, 4.5:0.75, 5:0.05, or any value within the range of any two of the above values. Organothiols have strong chelating properties and can complex residual soluble ions, jointly inhibiting their entry into the aqueous phase, thereby helping to further reduce impurities in the aqueous phase. At the same time, controlling the molar ratio of the organothiol to the quaternary ammonium base within the above range helps to balance the removal effect of cationic and anionic impurities, while reducing the introduction of organic impurities when there are more organothiols or quaternary ammonium bases.

[0073] Understandably, when lithium source materials contain cationic impurities, it is difficult to effectively complex the polyvalent transition metal cations dissolved during the leaching process without the addition of organic thiols. These ions may enter the lithium-containing aqueous phase in a soluble form or form colloidal precipitates that are difficult to separate completely, leading to an increase in the content of metal impurities in subsequent intermediates and final products, affecting the purity of lithium iodide. At the same time, some metal ions may also catalyze or participate in unnecessary side reactions, interfering with the selective leaching process of lithium and causing a decrease in lithium yield.

[0074] In some embodiments, organothiols include one or more of alkyl thiols, aromatic thiols, and heteroaryl thiols. The organothiols select for their ability to complex residual soluble ions, collectively inhibiting their entry into the aqueous phase, thereby contributing to further reduction of impurities in the aqueous phase.

[0075] In some embodiments, the oxidizing gas includes one or more of air, oxygen, and ozone. The selection of these gases as oxidizing gases helps to oxidize cationic impurities (such as Fe, Mn, Co, Ni, etc.) to higher valence states, forming insoluble oxide / hydroxide precipitates, thereby facilitating the conversion and separation of cationic impurities, which are then removed by solid-liquid separation after the reaction.

[0076] Therefore, the preparation method of this application has a certain degree of universality, as it can both process complex waste battery materials for resource recycling and deeply purify industrial lithium salts. Through the preparation method of this application, high-yield, high-purity lithium salts can be obtained from the aforementioned raw materials.

[0077] One embodiment of this application also provides a solid-state battery comprising lithium iodide prepared by the above-described preparation method.

[0078] The lithium iodide prepared by the method of this application has high purity. When the lithium iodide is applied to solid-state batteries, its low water content and low impurity characteristics help to reduce the blockage and damage of impurities to lithium-ion transport channels, which is conducive to building a more stable electrode-electrolyte interface with lower impedance, thereby synergistically improving the ionic conductivity, interface compatibility and long-term cycle performance of solid-state batteries.

[0079] The present application will be described below through specific embodiments and comparative examples. Those skilled in the art should understand that the preparation methods described in this application are merely examples, and any other suitable preparation methods are within the scope of this application.

[0080] Example 1:

[0081] A method for preparing lithium iodide, comprising:

[0082] Step 1: Mix 1 kg of waste lithium iron phosphate powder, 1.5 kg of cyclohexyl mercaptan, 120 g of tetrahexylammonium hydroxide, 8 kg of pure water, and 4 kg of dichloromethane. Control the carbon dioxide flow rate at 10 m³ / s. 3 / h, oxygen flow rate 10 m³ 3 The reaction was carried out at 30 °C for 4.0 h, followed by solid-liquid separation to obtain an oil-water mixture and waste residue.

[0083] Step 2: The oil-water mixture was allowed to stand at 40 ℃ for 10 min to separate into layers. The aqueous phase was collected and pyrolyzed at 90 ℃ for 4.5 h. Solid-liquid separation was achieved, and the mixture was dried at 100 ℃ for 3.5 h to obtain a solid phase. The solid phase was mainly composed of lithium carbonate. This solid phase was calcined at 800 ℃ for 2 h to obtain an intermediate, which was mainly composed of lithium oxide.

[0084] Step 3: Mix 45 g of intermediate, 100 g of lithium hydroxide monohydrate, 1000 g of tetramethylammonium iodide and 5000 g of ethylene glycol, and react at 40 °C for 30 min under nitrogen protection. Separate the solid and liquid phases to obtain the liquid phase, which contains lithium iodide.

[0085] Step 4: Mix the liquid phase with 6300 g of diethyl ether and extract at 5 °C for 10 min, with 3 extraction stages, to obtain a lithium-containing organic phase; concentrate the lithium-containing organic phase by vacuum evaporation at 30 °C under argon protection to obtain crystals, and dry the crystals under vacuum at -0.3 MPa and 30 °C for 4.0 h to obtain anhydrous lithium iodide.

[0086] Example 2:

[0087] A method for preparing lithium iodide, comprising:

[0088] Step 1: Mix 0.5 kg lithium carbonate, 300 g tetrahexylammonium hydroxide, 30 kg pure water, and 6 kg dichloromethane. Control the carbon dioxide flow rate at 5 m³ / s. 3 / h, oxygen flow rate 10 m³ 3 The reaction was carried out at 40 °C for 4.0 h, followed by solid-liquid separation to obtain an oil-water mixture and waste residue.

[0089] Step 2: The oil-water mixture was allowed to stand at 30 ℃ for 30 min to separate into layers. The aqueous phase was collected and pyrolyzed at 95 ℃ for 3.5 h. Solid-liquid separation was achieved, and the mixture was dried at 100 ℃ for 3.5 h to obtain a solid phase. Analysis showed that the solid phase was mainly composed of lithium carbonate. This solid phase was calcined at 800 ℃ for 2 h to obtain an intermediate, which was mainly composed of lithium oxide.

[0090] Step 3: Mix 5 g of intermediate, 80 g of lithium hydroxide monohydrate, 1000 g of tetraethylammonium iodide and 10000 g of propylene glycol, and react at 80 °C for 30 min under nitrogen protection. Separate the solid and liquid phases to obtain the liquid phase, which contains lithium iodide.

[0091] Step 4: Mix the liquid phase with 20,000 g of ethyl acetate and extract at 5 °C for 10 min, with 4 extraction stages, to obtain a lithium-containing organic phase; concentrate the lithium-containing organic phase by vacuum evaporation at 30 °C under argon protection to obtain crystals, and dry the crystals under vacuum at -0.3 MPa at 60 °C for 3.0 h to obtain anhydrous lithium iodide.

[0092] Example 3:

[0093] A method for preparing lithium iodide, comprising:

[0094] Step 1: Mix 1 kg lithium hydroxide monohydrate, 300 g tetraoctylammonium hydroxide, 30 kg pure water, and 6 kg chloroform. Control the carbon dioxide flow rate to 5 m³ / s. 3 / h, oxygen flow rate 10 m³ 3 The reaction was carried out at 20 °C for 4.0 h, followed by solid-liquid separation to obtain an oil-water mixture and waste residue.

[0095] Step 2: The oil-water mixture was allowed to stand at 30 ℃ for 30 min to separate into layers. The aqueous phase was collected and pyrolyzed at 95 ℃ for 3.5 h. Solid-liquid separation was achieved, and the mixture was dried at 100 ℃ for 3.5 h to obtain a solid phase. Analysis showed that the solid phase was mainly composed of lithium carbonate. This solid phase was calcined at 800 ℃ for 2 h to obtain an intermediate, which was mainly composed of lithium oxide.

[0096] Step 3: Mix 5 g of intermediate, 80 g of lithium hydroxide monohydrate, 1000 g of tetraethylammonium iodide and 10000 g of propylene glycol, and react at 80 °C for 30 min under nitrogen protection. Separate the solid and liquid phases to obtain the liquid phase, which contains lithium iodide.

[0097] Step 4: Mix the liquid phase with 20,000 g of ethyl acetate and extract at 5 °C for 10 min, with 4 extraction stages, to obtain a lithium-containing organic phase; concentrate the lithium-containing organic phase by vacuum evaporation at 30 °C under argon protection to obtain crystals, and dry the crystals under vacuum at -0.3 MPa at 60 °C for 3.0 h to obtain anhydrous lithium iodide.

[0098] Example 4:

[0099] A method for preparing lithium iodide, comprising:

[0100] Step 1: Mix 3 kg of waste lithium iron phosphate powder, 8.5 kg of tert-butyl mercaptan, 300 g of tetraoctylammonium hydroxide, 30 kg of pure water, and 10 kg of chloroform. Control the carbon dioxide flow rate to 5 m³ / s. 3 / h, oxygen flow rate 10 m³ 3 The reaction was carried out at 10 °C for 4.0 h, followed by solid-liquid separation to obtain an oil-water mixture and waste residue.

[0101] Step 2: The oil-water mixture was allowed to stand at 30 ℃ for 30 min to separate into layers. The aqueous phase was collected and pyrolyzed at 95 ℃ for 3.5 h. Solid-liquid separation was achieved, and the mixture was dried at 100 ℃ for 3.5 h to obtain a solid phase. Analysis showed that the solid phase was mainly composed of lithium carbonate. This solid phase was calcined at 800 ℃ for 2 h to obtain an intermediate, which was mainly composed of lithium oxide.

[0102] Step 3: Mix 5 g of intermediate, 80 g of lithium hydroxide monohydrate, 1000 g of tetraethylammonium iodide and 10000 g of propylene glycol, and react at 80 °C for 30 min under nitrogen protection. Separate the solid and liquid phases to obtain the liquid phase, which contains lithium iodide.

[0103] Step 4: Mix the liquid phase with 20,000 g of ethyl acetate and extract at 5 °C for 10 min, with 4 extraction stages, to obtain a lithium-containing organic phase; concentrate the lithium-containing organic phase by vacuum evaporation at 30 °C under argon protection to obtain crystals, and dry the crystals under vacuum at -0.3 MPa at 60 °C for 3.0 h to obtain anhydrous lithium iodide.

[0104] Comparative Example 1:

[0105] The difference from Example 1 is that in the first step, tetramethylammonium hydroxide is used instead of tetrahexylammonium hydroxide.

[0106] Comparative Example 2:

[0107] The difference from Example 1 is that in the first step, acetone is used instead of dichloromethane.

[0108] Comparative Example 3:

[0109] The difference from Example 1 is that cyclohexylthiol is not added in the first step.

[0110] Comparative Example 4:

[0111] The difference from Example 1 is that in the third step, dodecyl ammonium iodide is used instead of tetramethyl ammonium iodide.

[0112] Comparative Example 5:

[0113] The difference from Example 1 is that in the third step, ethanol is used instead of ethylene glycol.

[0114] This application describes the atomic emission spectrometry (ICP) and chemical analysis of lithium iodide prepared using the methods described in Examples 1-4 and Comparative Examples 1-5. The yields and purity of lithium carbonate and lithium oxide (process products) obtained in the second step, and the yield and purity of lithium iodide (final product) obtained in the fourth step, are shown in Table 1. The impurity content of the process products and the final product are shown in Table 2. In Table 2, the cationic impurities of the process products include sodium, potassium, calcium, barium, copper, manganese, cobalt, and nickel, and the anionic impurities include SO42-. 2- PO4 3- The cationic impurities in the final product include sodium, potassium, calcium, iron, copper, manganese, cobalt, and nickel.

[0115] Table 1. Yield and purity analysis results of process products and final products in Examples 1-4 and Comparative Examples 1-5 of this application.

[0116]

[0117] Table 2. Impurity content analysis results of process products and final products in Examples 1-4 and Comparative Examples 1-5 of this application.

[0118]

[0119] Examples 1-4 of this application selectively enhance the carbonization leaching of Li in lithium source materials based on the CO2 capture characteristics, phase transfer characteristics of specific quaternary ammonium bases, and ion exchange characteristics of specific iodide quaternary ammonium salts, while simultaneously reducing SO4 content in the lithium source materials. 2- PO4 3- The method achieves the goal of deep anion removal; furthermore, it enables anion exchange of lithium-containing intermediates in an organic phase to prepare high-purity anhydrous lithium iodide, avoiding the problems of difficult removal of lithium iodide crystal water and easy hydrolysis caused by aqueous systems. Tests show that the lithium salt yield according to the method of this invention is higher than 96%, and the purity of the lithium salt is higher than 99.9%. In addition, this invention has the advantages of simple operation process, environmental friendliness, controllable quality, and ease of industrialization, which can generate good economic and social benefits and has broad application prospects.

[0120] Examples 2 and 3 obtained high-yield, high-purity lithium salts by processing lithium source materials based on lithium compounds. Examples 1 and 4 achieved resource recovery by processing lithium source materials based on waste battery materials, obtaining high-yield, high-purity lithium salts. In these examples, oxidizing gases were used to oxidize cationic impurities to higher valence states, forming insoluble oxide / hydroxide precipitates, which facilitated the conversion and separation of cationic impurities. These impurities were then removed by solid-liquid separation after the reaction. Furthermore, the strong chelating properties of organothiols were utilized to complex residual soluble ions, jointly inhibiting their entry into the aqueous phase, thereby further reducing impurities in the aqueous phase.

[0121] Compared with Examples 1-4, Comparative Example 1 uses tetramethylammonium hydroxide instead of tetrahexylammonium hydroxide. The main difference is that the long carbon chain substituent (hexyl) in the quaternary ammonium base is replaced with a shorter carbon chain substituent (methyl). This reduces the partition coefficient and solubility stability of the quaternary ammonium base in the first solvent (hydrophobic organic phase), weakens its ability to effectively cycle between the oil and water phases as a phase transfer catalyst, and leads to a decrease in CO2 capture efficiency and lithium leaching rate. At the same time, the short carbon chain structure has insufficient affinity and extraction selectivity for anionic impurities, making it difficult to achieve deep removal. This makes it easier for impurities to enter the lithium-containing aqueous phase, ultimately affecting the purity of the intermediate.

[0122] Compared with Examples 1-4, Comparative Example 2 uses acetone instead of dichloromethane. Since acetone is highly miscible with water, it will disrupt the clear separation of the oil and water phases, resulting in the quaternary ammonium base and chelated metal impurities not being effectively confined in an independent organic phase. At the same time, acetone has poor solubility for the above-mentioned quaternary ammonium salt, which will reduce the effective concentration of the quaternary ammonium salt in the system and weaken the impurity removal effect based on phase distribution.

[0123] Compared with Examples 1-4, Comparative Example 3 did not add cyclohexylthiol, making it more difficult to effectively complex the polyvalent transition metal cations dissolved during the leaching process. These ions may enter the lithium-containing aqueous phase in a soluble form or form colloidal precipitates that are difficult to separate completely, leading to an increase in the content of metal impurities in subsequent intermediates and final products, affecting the purity of lithium iodide. At the same time, some metal ions may also catalyze or participate in unnecessary side reactions, interfering with the selective leaching process of lithium and causing a decrease in lithium yield.

[0124] Compared with Examples 1-4, Comparative Example 4 uses dodecyl ammonium iodide instead of tetramethyl ammonium iodide. The main difference is that the short carbon chain substituent (methyl) in the quaternary ammonium iodide salt is replaced with a longer carbon chain substituent (dodecyl). Its larger molecular volume and hydrophobicity will increase its dissolution resistance and system viscosity in the second solvent (polyol), thereby inhibiting the mass transfer rate and reaction completeness of the ion exchange reaction, resulting in a decrease in lithium conversion efficiency. At the same time, the long carbon chain structure is more likely to remain in the lithium-containing organic phase in the subsequent extraction steps, which is difficult to completely remove through phase separation. As a result, it is introduced into the final product as an organic impurity, which damages the crystal purity and chemical stability of lithium iodide.

[0125] Compared with Examples 1-4, Comparative Example 5 uses ethanol instead of ethylene glycol. Due to the low boiling point and weak polarity of ethanol, it is difficult to maintain a stable reaction environment at high temperatures, which may lead to incomplete reaction. At the same time, ethanol has limited solubility for intermediate lithium oxide and reaction product lithium iodide, and cannot provide an effective homogeneous reaction system. This will reduce the rate and conversion efficiency of ion exchange reaction, resulting in a decrease in lithium recovery rate. It will also lead to the introduction of some organic impurities into the final product, which will damage the crystal purity and chemical stability of lithium iodide.

[0126] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0127] The embodiments described above are merely illustrative of several implementations of the technical solution of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the technical solution of this application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the inventive concept of this application, and these modifications and improvements all fall within the protection scope of this application. Therefore, the protection scope of this application should be determined by the appended claims.

Claims

1. A method for producing lithium iodide, characterized by, The preparation method comprises the following steps: mixing a lithium source material, water, a first solvent, an organic thiol, and a quaternary amine base having a chemical formula of [(C n1 H 2n1+1 ) n2 N(CH3) n3 ] + OH - wherein n1≥6, n2>0, n3≥0, n2+n3=4, the solubility of the quaternary amine base in the first solvent is greater than or equal to 10 g / L at 20 ℃ to 25 ℃, the organic thiol comprises one or more of an alkyl thiol, an arene thiol, and a heteroaryl thiol, to obtain a first mixture, reacting the quaternary amine base in the first mixture with carbon dioxide in a reaction atmosphere comprising carbon dioxide to generate HCO3 - , and reacting HCO3 - with lithium ions in the lithium source material to generate lithium bicarbonate, and collecting an aqueous phase after the reaction; decomposing lithium bicarbonate in the aqueous phase to generate lithium carbonate, and collecting a solid phase; decomposing the lithium carbonate in the solid phase to generate lithium oxide, to obtain an intermediate; dissolving a quaternary ammonium iodide salt in a second solvent, adding the intermediate to obtain a second mixture, converting the lithium oxide in the second mixture to lithium hydroxide, and ion exchanging the lithium hydroxide with the quaternary ammonium iodide salt to form lithium iodide, and collecting the liquid phase; the second solvent comprises a polyol, and the chemical formula of the quaternary ammonium iodide salt is [(C n H 2n+1 )4N] + I - wherein n≤4; collecting lithium iodide in the liquid phase.

2. The production method according to claim 1, wherein The preparation method further satisfies at least one of the following conditions: (1) the mass ratio of the lithium source material, the water and the first solvent is 1:(8-50):(4-25); (2) the mass ratio of the second solvent and the quaternary ammonium iodide is (5-30):1; (3) the flow rate of the reaction atmosphere is 1 m 3 / h to 30 m 3 / h; (4) the second mixture further comprises lithium hydroxide, and the molar ratio of the lithium oxide, the lithium hydroxide and the quaternary ammonium iodide is (0.05-0.3):(0.4-0.5):1; (5) the first solvent comprises one or more of dichloromethane, chloroform and toluene.

3. The production method according to claim 1, wherein The liquid phase is extracted by an organic solvent to obtain a lithium-containing organic phase, and the lithium-containing organic phase is subjected to concentration and crystallization treatment to collect the lithium iodide in the liquid phase.

4. The production method according to claim 3, wherein The preparation method further satisfies at least one of the following conditions: (1) the organic solvent comprises an ether organic solvent and a chain carbonate organic solvent; (2) the volume ratio of the liquid phase and the organic solvent is 1:(2-5); (3) the extraction comprises multi-stage extraction, and the extraction stage number of the multi-stage extraction is greater than or equal to 3; (4) the extraction temperature is 5-40 ℃, and the extraction time is 10-60 min; (5) the concentration and crystallization treatment temperature is 30-100 ℃.

5. The production method according to claim 1, wherein The preparation method further satisfies at least one of the following conditions: (1) the reaction temperature for generating the lithium bicarbonate is 10-50 ℃, and the reaction time is 4-24 h; (2) the reaction temperature for the ion exchange is 5-40 ℃, and the reaction time is 30-180 min; (3) the aqueous phase is heated to decompose the lithium bicarbonate in the aqueous phase to generate the lithium carbonate, and the heating temperature is 85-100 ℃, and the heating time is 1.5-4 h; (4) the solid phase is subjected to heat treatment to decompose the lithium carbonate in the solid phase to generate the lithium oxide, and the heat treatment temperature is 600-1000 ℃, and the heat treatment time is 1-6 h.

6. The production method according to claim 1, wherein The preparation method further satisfies at least one of the following conditions: (1) the aqueous phase is collected, comprising the following steps: solid-liquid separation of a reaction liquid, collection of an oil-water mixture, static stratification of the oil-water mixture, and collection of the aqueous phase, wherein the static stratification temperature is 5-40 ℃, and the static stratification time is 10-60 min; (2) before the lithium carbonate is decomposed to generate the lithium oxide, the preparation method further comprises: drying treatment of the solid phase, wherein the drying treatment temperature is 85-150 ℃, and the drying treatment time is 1.5-4 h; (3) after the lithium iodide in the liquid phase is collected, the preparation method further comprises: vacuum drying of the lithium iodide, wherein the vacuum drying temperature is 30-80 ℃, the vacuum drying time is 1-4 h, and the air pressure is less than or equal to-0.3 Mpa. (4) the ion exchange is performed in a protective gas atmosphere; (5) the collecting of the lithium iodide in the liquid phase is performed in a protective gas atmosphere.

7. The production method according to any one of claims 1 to 6, wherein The lithium source material includes lithium hydroxide, and a ratio of a substance amount of the lithium hydroxide in the lithium source material to the quaternary ammonium base is 1:(0.05-0.5).

8. The production method according to any one of claims 1 to 6, wherein The lithium source material includes lithium carbonate, and a ratio of a substance amount of the lithium carbonate in the lithium source material to the quaternary ammonium base is 1:(0.05-0.5).

9. The production method according to any one of claims 1 to 6, wherein The lithium source material includes waste lithium iron phosphate positive electrode material, and the preparation method further satisfies at least one of the following conditions: (1) a ratio of a substance amount of the organic mercaptan to the quaternary ammonium base is (2-5):(0.05-0.5); (2) the reaction atmosphere further includes an oxidizing gas, and the oxidizing gas includes one or more of air, oxygen, and ozone.

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