A method for preferentially extracting Li from waste LiCoO2 positive electrode and simultaneously recovering Co3O4 by chlorination roasting

Abstract

A method for preferentially extracting Li from waste LiCoO2 positive electrode and recovering Co3O4 by chlorination roasting belongs to the field of lithium battery recycling and reuse. First, weigh the pretreated waste LiCoO2 positive electrode material and calcium chloride; after fully mixing the raw materials, roast them under high temperature conditions of 700-780°C; step S3, the roasted product is impregnated with water and filtered, lithium chloride is obtained in the liquid phase, and Co3O4 is obtained in the filtered solid phase. The present invention adjusts the chlorine-oxygen ratio in the system by controlling the amount of calcium chloride. Under low chlorination conditions, lithium ions can be converted into water-soluble lithium salts, while the relatively stable Co-O octahedral structure is not easily destroyed, and Co3O4 remains in the residue. LiCoO2 is completely decomposed and converted into LiCl and Co3O4 after roasting at 750°C. Under the reaction conditions of reaction temperature of 750°C, reaction time of 30min, and w(LiCoO2) / w(CaCl2) mass ratio of 1:2, the extraction rate of Li is 99.49%, and the residual rate of Co in the liquid phase is only 1.80%. The method of the invention has high efficiency, strong operability and is environmentally friendly, and provides a reliable guarantee for the preferential extraction of lithium from the positive electrode materials of waste lithium-ion batteries by chlorination technology.

Description

Technical Field

[0001] The present invention belongs to the field of lithium battery waste recycling and relates to a method for recycling waste LiCoO 2 Preferentially selectively increasing Li and simultaneously recovering Co in cathode materials 3 O 4 method. Background Art

[0002] Lithium-ion batteries (LIBs), an environmentally friendly high-energy carrier for a wide range of applications, including portable electronic devices, electric vehicles, and electrical energy storage, have developed rapidly over the past few decades, which has accelerated the supply demand for key metals such as lithium, cobalt, nickel, and manganese. At the same time, the amount of spent lithium batteries is increasing dramatically every year. Therefore, recovering valuable metals from spent lithium-ion batteries contributes to resource sustainability.

[0003] The main method for preferential lithium extraction is to convert lithium into water-soluble compounds based on chemical differences, while transition metal elements exist in the form of monomers or oxides that are insoluble in water and can be separated by water leaching. At present, in order to improve the selectivity of metal elements, carbon thermal reduction roasting is widely used to preferentially extract lithium elements. Oxygen-free carbon reduction roasting can obtain water-soluble Li 2 CO 3 and water-soluble transition metal oxides, subsequent water leaching can achieve selective extraction of lithium. 2 CO 3 The water solubility of is low, and its yield needs to be considered. Another phase conversion method, such as sulfation roasting, has been used to study the preferential and selective extraction of lithium from waste lithium battery positive electrode materials. Wang et al. pointed out in his study that the higher the metal abundance of different metals, the higher the tendency to form metal sulfates. Therefore, Li 2 O on SO 2 Lithium sulfate is more easily formed in the atmosphere than in other gases. Lithium can be selectively converted into lithium sulfate by controlling the amount of sulfating agent and the operating temperature. More than 90% of lithium can be selectively leached out by water. Inspired by this, Xu et al. proposed using NH 4 Cl is used as a chlorinating agent to treat the chlorination roasting of LMO cathode materials. In this process, the reduction drive is controlled at a low level, and lithium can be extracted preferentially, while other metal elements remain in the residue. However, even under the optimal conditions, the recovery rate of lithium is only 91.73%. Therefore, the problem of low lithium recovery rate and selectivity needs to be considered. Summary of the invention

[0004] The present invention aims to select calcium chloride (CaCl 2 ) is the only chlorinating agent, and a method for recovering waste LiCoO 2 The strategy of prioritizing lithium extraction in the positive electrode is to use CaCl2 As a chlorinating agent, the waste LiCoO 2 Lithium is first extracted from the positive electrode, and the calcined product is extracted with lithium and Co by water leaching. 3 O 4 By controlling the amount of calcium chloride used to adjust the chlorine-oxygen ratio in the system, the preferential selective extraction of lithium can be achieved.

[0005] A chlorination roasting method for waste LiCoO 2 The positive electrode prioritizes Li and simultaneously recycles Co 3 O 4 The method is characterized by comprising:

[0006] Step S1: weigh the pretreated waste LiCoO 2 Positive electrode material and calcium chloride;

[0007] Step S2, after the raw materials are fully mixed, roasting at a high temperature of 700-780°C;

[0008] Step S3: After calcination, the product is soaked in water and filtered to obtain lithium chloride in the liquid phase and Co in the filtered solid phase. 3 O 4 .

[0009] Furthermore, waste LiCoO 2 The mass ratio of the positive electrode material to calcium chloride is 1:1.5-2.5.

[0010] Furthermore, waste LiCoO 2 The preferred mass ratio of the positive electrode material to calcium chloride is 1:2.

[0011] Furthermore, the chlorine-oxygen ratio of the roasting system under the high temperature conditions in step S2 is 1:2 to 1:8.

[0012] Furthermore, the calcination time in step S2 is 20-60 minutes.

[0013] Furthermore, the calcination time in step S2 is preferably 30 minutes.

[0014] Furthermore, in step S2, the reaction raw materials are calcined in a closed reaction vessel. The lithium recovery rate reaches 99.49%, and 98.10% of Co is converted into Co 3 O 4 form of recycling.

[0015] Mechanism of the invention

[0016] In order to study the transformation mechanism of this process, the present invention first uses Gibbs free energy (ΔG) to evaluate the thermodynamic driving force of the relevant substances. The relationship between chemical reaction and ΔG is as follows Figure 3It can be observed that when the temperature is higher than 400 °C, the Gibbs free energy ΔG of the reaction (R1-R4) is less than 0 ( Figure 3 a), which indicates that CaCl 2 It can decompose into HCl and Cl in the air 2 The members of the research team of this invention explored the 2 With LiO 2 and Co 3 O 4 It can be found that in the temperature range of 0-1000℃, the reaction (R6-R8) is always less than 0 ( Figure 3 b). The ΔG of R7 and R8 is more negative than that of R6, indicating that reactions R7 and R8 have higher driving forces. In other words, the more negative the Gibbs free energy (ΔG), the more the chemical reaction tends to occur first.

[0017] To further analyze the strategy of preferential lithium chloride extraction, the inventors plotted the Li / Co-Cl-O system (log(pCl 2 )-T / log(pO 2 )-log(pCl 2 )) to illustrate the existence of metal compounds under different reaction conditions. The results are as follows Figure 3 As shown. Lithium chloride can be used at lower temperatures than cobalt chloride and Cl 2 The partial pressure forms Figure 3 c and 3d). Figure 3 f and Figure 3 g shows that whether the metal oxide is chlorinated is also closely related to the chlorine-oxygen partial pressure (chlorine-oxygen ratio) in the system. 3 O 4 Can be chlorinated to water-soluble CoCl at high chlorine to oxygen ratio 2 Therefore, a certain oxygen atmosphere should be maintained. It can be observed that the dominance map can be divided into three regions ( Figure 3 e and Figure 3 h). Region 2 can form water-soluble LiCl and water-insoluble Co 3 O 4 Therefore, through thermodynamic calculations and verification experiments, the inventors determined a feasible target lithium extraction strategy. In order to determine the appropriate chlorination roasting conditions for this study, three key parameters, namely calcium chloride dosage, roasting temperature, and roasting time, were selected for qualitative analysis, that is, lithium chloride was preferentially generated at the appropriate temperature and chlorine-oxygen ratio.

[0018] When the waste LiCoO 2The leaching rate of lithium increased significantly when the mass ratio of positive electrode material to calcium chloride was 1:1.5-2.5, the calcination temperature was from 650℃ to 750℃, and the reaction time was 20-60min. When the temperature range was 750-800℃, there was a short plateau in the recovery of lithium, which means that the maximum conversion of LiCl occurred at 750℃, while the leaching of water-soluble cobalt was at a lower level. We found that when the temperature was increased to 800℃, more elemental cobalt was converted into soluble cobalt chloride. Figure 2 a shows the XRD analysis of the chlorinated roasted product at different temperatures (700℃-800℃) to study the phase transition and explain the leaching results. A small amount of LCO still exists at 700℃, indicating that LCO is not completely decomposed. As the roasting temperature increases to 750℃, the LCO diffraction peak eventually disappears completely. Some new Co 3 O 4 and LiClH 2 O diffraction peak. When the temperature rises to 800°C, the XRD diffraction peak does not change much. The inventors used atomic absorption spectroscopy to quantitatively analyze the concentrations of Li and Co in the aqueous solution. First, as the temperature rises, calcium chloride decomposes into Cl 2 and HCl; at the same time, the layered structure of LCO is destroyed and converted into Co 3 O 4 and Li 2 O. The chlorine-oxygen ratio (air atmosphere) of the reaction system is controlled by adjusting the amount of calcium chloride, so that the reaction is carried out under low chlorination conditions. As the chlorination partial pressure decreases, the difference between the weak electrovalent bond of Li-O and the strong covalent bond of Co-O is reflected. Therefore, under low chlorination and 750 degrees Celsius, lithium ions are released and react with Cl - The octahedral structure of Co-O is relatively stable and not easily destroyed, so it is combined with water-insoluble Co 3 O 4 exists in the form of.

[0019] The key points of the present invention are:

[0020] Calcium chloride is selected as the only roasting aid, and the recovery rate of lithium element is controlled by controlling the amount of calcium chloride, roasting temperature, roasting time and the chlorine-oxygen ratio in the air atmosphere.

[0021] Comparative Document 1 ENVIRONMENTAL PROTECTION OF CHEMICAL INDUSTRY 2022, Volume 42, Issue 5 published an article involving "The method of alkaline leaching after molten salt roasting was used to preferentially leach lithium from the positive electrode material of waste ternary lithium-ion batteries. The effects of molten salt type and addition amount, roasting temperature, and sodium hydroxide solution pH on the leaching effect were investigated, and the leaching mechanism was analyzed using XRD technology. The experimental results show that the addition of calcium chloride for molten salt roasting and then alkaline leaching, under the optimal recovery conditions of roasting temperature 800°C, calcium chloride addition amount 30% (mass ratio), solid-liquid ratio 1:5, sodium hydroxide solution pH 11, leaching temperature 60°C, and leaching time 120min, the lithium leaching rate can reach 99.5%, and the total leaching rate of nickel, cobalt and manganese is less than 1%, achieving efficient and selective leaching of lithium."

[0022] The present invention has been found through research. Figure 2 a shows the relationship between w(LCO) and w(CaCl 2 The effect of roasting temperature on the water leaching of Li and Co roasting products when the ratio of LiCl to water is 1:2 and the reaction time is 30min. The leaching rate of lithium increases significantly from 650℃ to 750℃. When the temperature range is 750-800℃, there is a short plateau in the recovery of lithium, which means that the maximum conversion of LiCl occurs at 750℃, while the leaching of water-soluble cobalt is at a lower level. We found that when the temperature is increased to 800℃, more elemental cobalt is converted into soluble cobalt chloride. Figure 2 a shows the XRD analysis of the chlorinated roasted product at different temperatures (700℃-800℃) to study the phase transition and explain the leaching results. A small amount of LCO still exists at 700℃, indicating that LCO is not completely decomposed. As the roasting temperature increases to 750℃, the LCO diffraction peak eventually disappears completely. Some new Co 3 O 4 and LiClH 2 O diffraction peak. When the temperature rises to 800℃, the XRD diffraction peak does not change much. Therefore, we choose 750℃ as the optimal temperature.

[0023] Figure 2 b and 2e show different CaCl 2 The changes of Li and Co leaching efficiency and XRD diffraction peaks under different dosages. When the leaching amount of cobalt is very low, with the increase of LiCoO 2 / CaCl 2 The recovery rate of Li increased significantly when the mass ratio increased from 1:0.5 to 1:1. XRD results show that when the ratio does not exceed 1:1, LCO still has a small amount of diffraction peaks. This indicates that the low mass ratio is not enough to achieve complete conversion of LCO. 2 / CaCl2 When the mass ratio of is further increased from 1.1 to 2.0, the lithium leaching rate is further improved. Figure 2 e shows that the leaching rate of Li is 99.49%, while that of elemental Co is only 1.80%. XRD analysis shows that the LCO phase disappears completely and is converted into the product LiCl and Co 3 O 4 When the mass ratio exceeds 1:2, the leaching rate of Li reaches a stable level. 2 The diffraction peak of the Co leaching peak gradually increases, and the leaching efficiency of Co increases with the increase of CaCl 2 The addition degree of excess calcium chloride and Co 3 O 4 The results also showed that CaCl 2 The dosage is the key operating condition that determines the efficiency and selectivity of lithium leaching, which is consistent with the results of thermodynamic analysis. 2 ) is best at a ratio of 1:2.

[0024] Effects of calcination time on lithium extraction rate and phase transition of calcined products Figure 2 c. The results show that when the leaching time is 30 min, the optimal leaching rate of Li is 99.49%, and the XRD results show that Co has been completely converted into Co 3 O 4 (II, III), indicating that LCO has been completely converted. When the roasting time is extended to 60 min, the leaching rate of Li begins to decrease, indicating that the roasting reaction is fast and the reaction is completed at 30 min. Considering the purity and processing energy of recovered Li, the inventors chose 30 min as the optimal roasting time.

[0025] The inventors also found that the chlorine-oxygen ratio of the roasting system under high temperature conditions also has a very important influence on improving the recovery rate of lithium chloride. If the chloride ion content is too high, the excess calcium chloride and the Co in the residue will react with each other. 3 O 4 Chlorination reaction occurs and dissolves into the leaching solution, increasing the cobalt content in the solution and also reducing the recovery rate of lithium. Therefore, the chlorine-oxygen ratio must be kept in the range of 1:2 to 1:8 to fully ensure the recovery rate of lithium.

[0026] In the reaction process of the present invention, as the temperature rises, calcium chloride decomposes into Cl 2 and HCl; meanwhile, LiCoO 2 The layered structure is destroyed and converted into Co 3 O 4 and Li 2O. The chlorine-oxygen ratio of the reaction system is controlled by adjusting the amount of calcium chloride, so that the reaction is carried out under low chlorination conditions. As the chlorination partial pressure decreases, the difference between the weak electrovalent bond of Li-O and the strong covalent bond of Co-O is reflected. Therefore, under low chlorination and suitable temperature conditions, lithium ions are released and react with Cl - The octahedral structure of Co-O is relatively stable and not easily destroyed, so it is combined with water-insoluble Co 3 O 4 exists in the form of.

[0027] The beneficial effects brought about by the technical solution provided by the present invention include at least:

[0028] The present invention combines chlorination roasting and water leaching to obtain LiCoO from waste water. 2 Lithium is extracted first from the positive electrode, with cheap calcium chloride as the only chlorinating agent. The chlorine-oxygen ratio in the system is adjusted by controlling the amount of calcium chloride and the roasting process conditions. In this process, lithium ions can be extracted and converted into water-soluble lithium chloride under low chlorination conditions, and the relatively stable Co-O octahedral structure is not easily destroyed. 3 O 4 The precipitate remains in the residue in the form of , and no additional chemical reagent is added except calcium chloride. The method provided by the invention has higher efficiency, operability and environmental friendliness. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a schematic diagram of the process flow of the present invention;

[0030] Figure 2 The XRD spectra and lithium recovery rate diagrams of the products under different process conditions of the present invention, wherein (a) is the XRD spectra of the calcined products at different calcination temperatures; (b) is the XRD spectra of the calcined products under different raw material ratios; (c) is the XRD spectra of the calcined products under different calcination times; (d) is the lithium recovery rate diagram at different calcination temperatures; (e) is the lithium recovery rate diagram under different raw material ratios; (f) is the lithium recovery rate diagram under different calcination times;

[0031] Figure 3 (a)-(b) Relationship between ΔG of chlorination reaction and temperature, (c)-(h) advantage diagram of Li / Co-Cl-O. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical solution and advantages of the present invention more clear, the technical solution of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0033] Example 1

[0034] First, the waste lithium cobalt oxide batteries are pretreated to obtain LiCoO 2 The positive electrode material is LiCoO 2 The mixture was weighed and mixed evenly with calcium chloride in a ratio of 1:2, and then transferred into a corundum crucible and covered with a lid. The mixture was transferred into a tube furnace and heated to 750°C at a heating rate of 10°C / min and kept warm for 30 minutes. After the reaction was completed, the calcined product was dissolved in deionized water for water immersion, and then filtered to obtain LiCl filtrate and Co 3 O 4 The filtrate was evaporated to obtain LiCl. The recovery rate of Li was 99.49%.

[0035] Example 2

[0036] First, the waste lithium cobalt oxide batteries are pretreated to obtain LiCoO 2 The positive electrode material is LiCoO 2 The mixture was weighed and mixed with calcium chloride at a ratio of 1:1.5, and then placed in a corundum crucible without a lid, and placed in a tube furnace and heated to 700°C at a heating rate of 10°C / min, and kept warm for 50 minutes. After the reaction was completed, the calcined product was dissolved in deionized water for water immersion, and then filtered to obtain LiCl filtrate and Co 3 O 4 The filtrate was evaporated to obtain LiCl. The recovery rate of Li at this time was 87.98%. Under the same reaction conditions, the recovery rate of Li was 93.26% when the calcination was carried out under the condition of covering the lid. This shows that the reaction in a closed reaction vessel can effectively improve the recovery rate of lithium.

[0037] Example 3 First, waste lithium cobalt oxide batteries are pretreated to obtain LiCoO 2 The positive electrode material is LiCoO 2 The mixture was weighed and mixed with calcium chloride at a ratio of 1:2.5, and then placed in a corundum crucible without a lid, and placed in a tube furnace and heated to 780°C at a heating rate of 10°C / min, and kept warm for 20 minutes. After the reaction was completed, the calcined product was dissolved in deionized water for immersion, and then filtered to obtain LiCl filtrate and Co 3 O 4 The filtrate was evaporated to obtain LiCl. The recovery rate of Li at this time was 89.73%. Under the same reaction conditions, the recovery rate of Li was 96.56% when the calcination was carried out under the condition of covering the lid. This shows that the reaction in a closed reaction vessel can effectively improve the recovery rate of lithium.

[0038] The experiment found that when LiCoO 2The best effect is achieved when the mass ratio of LiCoO to calcium chloride is 1:2 and the calcination is carried out at 750℃ for 30min. This is because the calcination reaction occurs faster and when the temperature is lower (e.g. 700℃), LiCoO 2 It cannot be completely decomposed, and when the temperature reaches 800℃, cobalt begins to gradually transform into cobalt chloride; and excessive calcium chloride will also cause cobalt to transform into cobalt chloride. Under the optimal conditions, the leaching rate of Li is 99.49%, and 98.10% of Co is converted into Co 3 O 4 form of recycling.

[0039] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art who is familiar with the technical field can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A method for preferentially extracting Li from waste LiCoO2 positive electrode and simultaneously recovering Co3O4 by chlorination roasting, characterized in that: include: Step S1, weighing the pretreated waste LiCoO2 positive electrode material and calcium chloride, the mass ratio of LiCoO2 to calcium chloride is 1:2; Step S2, after the raw materials are fully mixed, the reaction raw materials are roasted in a closed reaction container at 750° C. for 30 min; the chlorine-oxygen ratio of the roasting system in step S2 is 1:2 to 1:8; Step S3, the calcined product is immersed in water and filtered, lithium chloride is obtained in the liquid phase, and Co3O4 is obtained in the filtered solid phase.

2. The method of claim 1 wherein the chlorination roasting method preferentially extracts Li from waste LiCoO2 positive electrode and simultaneously recovers Co3O4, characterized in that: The lithium recovery rate reached 99.49%, and 98.10% of Co was recovered in the form of Co3O4.

Images