A method for recovering lithium carbonate from spent lithium iron phosphate battery cathode materials

Abstract

This invention belongs to the technical field of comprehensive recycling of waste lithium-ion power batteries, specifically relating to a method for recovering battery-grade lithium carbonate from the cathode material of waste lithium iron phosphate batteries. In the recycling process of this invention, lithium iodide is added as a precipitant for impurity metal ions. This not only utilizes the extremely low solubility of Cu, Al, and Mg iodides in anhydrous ethanol, while LiI is highly soluble in ethanol, but also ensures complete precipitation of impurity ions such as Cu, Al, and Mg in the lithium-rich solution, thus achieving impurity removal. Furthermore, in the subsequent lithium precipitation process to prepare lithium carbonate, the added lithium iodide can be converted into lithium carbonate, realizing the secondary utilization of the input material. That is, lithium iodide is used as both an impurity precipitant and a raw material, saving costs and generating revenue.

Description

Technical Field

[0001] This invention belongs to the field of recycling and comprehensive utilization technology of waste lithium-ion power batteries, specifically relating to a method for recovering battery-grade lithium carbonate from the cathode material of waste lithium iron phosphate batteries. Background Technology

[0002] With the rapid development of the global economy, energy demand and consumption are increasing daily. Lithium iron phosphate (LFP) batteries have advantages such as high operating voltage, high energy density, low self-discharge, long cycle life, ease of use, and no memory effect. However, due to the limited lifespan of LFP batteries and the rapid upgrading of electronic products, a large number of waste lithium batteries will be generated. Discarded LFP batteries represent a waste of resources, cause environmental pollution, and further exacerbate the energy crisis. Therefore, recycling waste LFP batteries is a necessary measure to prevent environmental pollution and excessive resource consumption.

[0003] Currently, the recycling processes for spent lithium iron phosphate batteries used both domestically and internationally can be broadly categorized into three types: physical methods, biological methods, and chemical methods. Physical methods primarily utilize high-temperature pyrolysis, where the binder is decomposed through high-temperature incineration, leading to material separation. After metal oxidation, reduction roasting generates precious metals and lithium oxide. High-temperature vapor volatilization is achieved through condensation for separation and collection. The drawbacks of physical methods include a single product, high energy consumption, low recovery rates, and the generation of waste gas, posing a risk of secondary pollution. Biological methods mainly employ bioleaching, utilizing microorganisms to convert useful components into soluble compounds and selectively dissolve them, achieving separation of the target metal from impurities. Biological methods are still in their early stages, with complex microbial cultivation and leaching conditions. Chemical methods can be further divided into chemical precipitation, ion exchange, and solvent extraction. Chemical methods offer high recovery rates and low pollution, but the recovered lithium salts are often of low purity and cannot be directly used in lithium battery production. For impurity removal, existing wet processes typically involve acid leaching followed by neutralization with alkaline reagents, resulting in resource waste and environmental pollution due to the extensive use of alkali.

[0004] In the lithium battery recycling industry, research on the recycling of LiFePO4, a lithium-ion cathode material widely used in high-energy storage, is currently rare. Therefore, it is undoubtedly necessary to develop a LiFePO4 recycling technology, which is also the focus of this invention. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention proposes to develop a new chemical process for recovering the effective components from waste lithium batteries. Compared to current recycling processes, this process can achieve the unified recycling of sintering waste, coating waste, and waste lithium iron phosphate batteries on the same production line, and can obtain battery-grade lithium carbonate with high purity, which is difficult to achieve with existing processes.

[0006] A method for recovering lithium carbonate from spent lithium iron phosphate battery cathode materials includes the following steps:

[0007] (1) First, the waste lithium iron phosphate battery cathode material is roughly washed to remove surface impurities and then dried and sieved to obtain dry lithium iron phosphate powder for later use.

[0008] (2) Prepare an acid solution of 1-10 mol / L and mix it with hydrogen peroxide of 5.5%-30% by mass to prepare a mixed solution. The acid solution is hydrochloric acid or nitric acid solution.

[0009] (3) Add the mixture from step (2) to the dry lithium iron phosphate powder obtained in step (1) according to the liquid-solid ratio L / S = 5-20 mL / g, and stir to carry out the leaching reaction. The leaching temperature is 30-80℃ and the leaching time is 1-3h.

[0010] (4) After leaching, filter to obtain lithium-rich stock solution, and remove water from the lithium-rich stock solution (preferably by evaporation and concentration at 100°C for 3 hours).

[0011] (5) Under stirring, add 1-5 mol / L of anhydrous ethanol solution of lithium iodide to the dehydrated lithium-rich solution, stir the reaction until Cu, Al and Mg ions precipitate out, add anhydrous sodium sulfate to remove water; after filtering again, add saturated Na2CO3 aqueous solution to the filtrate, stir, filter, wash thoroughly and dry to obtain product Li2CO3.

[0012] Furthermore, in step (3), the immersion temperature is 60-75℃ and the immersion time is 2-3 hours;

[0013] Furthermore, in step (2), the concentration of the acid solution is 2.5 mol / L; and the mass percentage of the hydrogen peroxide is 30%.

[0014] Furthermore, in step (2), the volume ratio of acid to hydrogen peroxide is 5:1;

[0015] Furthermore, in step (3), the liquid-to-solid ratio L / S = 5-10 mL / g;

[0016] Furthermore, the drying in step (5) is: drying at 80°C for 4 hours.

[0017] Furthermore, the waste lithium iron phosphate battery cathode material is waste lithium iron phosphate battery cathode powder, coating waste, or lithium iron phosphate sintering waste.

[0018] Furthermore, the specific operation of step (1) is as follows: the waste lithium iron phosphate battery cathode material is sieved through a 60-mesh sieve, and the sieved powder is added to deionized water or ethanol at a liquid-solid ratio of L / S = 10 mL / g for two coarse washes, each for 30 min. Then the washed wet material is dried in an oven at 80°C for 2 h, and then sieved through a 60-mesh sieve to obtain dry lithium iron phosphate powder.

[0019] Compared with the prior art, the technical solution of this application has the following advantages and beneficial effects:

[0020] 1. The prior art discloses that a large amount of acid is required in the leaching step, and a large amount of alkali is required for neutralization in the subsequent sedimentation process. However, the present invention uses lithium iodide for impurity removal. Lithium iodide acts as both an impurity remover and a part of the product, thereby maximizing resource utilization, avoiding unnecessary waste, saving the acid-base neutralization step, avoiding the use of alkaline reagents, and still obtaining battery-grade lithium carbonate. Therefore, compared with methods that require acid-base neutralization, a large amount of alkali source is saved.

[0021] 2. Adding lithium iodide as a precipitant for impurity metal ions not only utilizes the extremely low solubility of Cu, Al, and Mg ions in anhydrous ethanol, while LiI is highly soluble in ethanol, allowing impurity ions such as Cu, Al, and Mg in the lithium-rich solution to be completely precipitated, thus achieving the effect of impurity removal, but also allows the added lithium iodide to be converted into lithium carbonate in the subsequent lithium precipitation process, realizing the secondary utilization of the input material. That is, using lithium iodide as an impurity precipitant and raw material saves costs and creates profits. Detailed Implementation

[0022] The technical solution of the present invention will be described in detail below through specific embodiments.

[0023] In the following examples, lithium iron phosphate sintering waste refers to lithium iron phosphate waste that, after sintering, fails to meet factory requirements and is not suitable for rework during the preparation of lithium iron phosphate using battery-grade iron phosphate and battery-grade lithium carbonate as raw materials. The term "liquid-to-solid ratio" in this invention refers to the ratio of the volume of liquid added to the mass of the solid.

[0024] In the following examples, the content of each component was detected using ICP-OES.

[0025] Example 1: A method for obtaining battery-grade lithium carbonate from waste lithium iron phosphate battery cathode material, comprising the following steps:

[0026] (1) First, the crushed lithium iron phosphate sintering waste is sieved through a 60-mesh sieve. Each time, deionized water is added to the powder after sieving at a liquid-solid ratio of L / S = 10 mL / g for two coarse washes, each for 30 min. Then, the washed wet material is dried in an oven at 80℃ for 2 h and then sieved through a 60-mesh sieve to obtain dried lithium iron phosphate powder. The content of some components is shown in Table 1.

[0027] Table 1

[0028] Component Na K Ca Mg Al Cu Li Fe wt% 0.001 0.001 0.014 0.001 0.026 0.001 4.36 35.45

[0029] (2) Prepare 125 mL of 2.5 mol / L hydrochloric acid and mix it with 25 mL of 30 wt% hydrogen peroxide to make a mixture;

[0030] (3) With a liquid-to-solid ratio of L / S = 5 mL / g, add the mixture prepared in step (2) to 30 g of lithium iron phosphate powder in step (1) and stir to carry out the leaching reaction. The leaching temperature range is 60℃ and the leaching time is 2 h.

[0031] (4) After leaching, filter to obtain lithium-rich stock solution. Further evaporate and concentrate the lithium-rich stock solution at 100℃ for 3 hours until the water in it is basically evaporated to obtain concentrated lithium-rich solution.

[0032] (5) While stirring, add 50 mL of 1 mol / L lithium iodide anhydrous ethanol solution to the concentrated lithium-rich solution, and then react for 30 min until the impurity ions such as Cu, Al, and Mg in the lithium-rich solution are completely precipitated. After filtration, add 3 g of anhydrous sodium sulfate to the filtrate to remove water.

[0033] (6) After filtering again, 40 mL of saturated sodium carbonate aqueous solution was added to the filtrate, stirred for 30 min, filtered and washed thoroughly (in the embodiments of the present invention, each washing step was done with 100 mL of deionized water, for a total of 3 washes, each wash for 10 min), and dried in an oven at 80 °C for 4 h to obtain 8.33 g of battery-grade Li2CO3. The composition detection results are shown in Table 2.

[0034] Table 2

[0035] Component <![CDATA[Li2CO3]]> Na K Ca Mg Fe Al Pb Cu wt% 99.7 0.003 0.003 0.003 0.001 0.002 0.001 0.001 0.001

[0036] Example 2: A method for obtaining battery-grade lithium carbonate from waste lithium iron phosphate battery cathode material, comprising the following steps:

[0037] (1) First, the waste lithium iron phosphate cathode material powder is sieved through a 60-mesh sieve. Each time, anhydrous ethanol is added to the sieved powder at a liquid-solid ratio of L / S = 10 mL / g for two coarse washes, each for 30 min. Then, the washed wet material is dried in an 80℃ oven for 2 h and then sieved through a 60-mesh sieve to obtain dried lithium iron phosphate powder. The content of some components is shown in Table 3.

[0038] Table 3

[0039] Component Na K Ca Mg Al Cu Li Fe wt% 0.001 0.001 0.006 0.012 0.036 0.025 3.01 28.14

[0040] (2) Prepare 125 mL of 2.5 mol / L hydrochloric acid and mix it with 25 mL of 30 wt% hydrogen peroxide to make a mixture;

[0041] (3) With a liquid-to-solid ratio of L / S = 5 mL / g, add the prepared mixture to 30 g of dry lithium iron phosphate powder and stir to carry out the leaching reaction. The leaching temperature range is 60℃ and the leaching time is 2 h.

[0042] (4) After leaching, filter to obtain lithium-rich stock solution. Further evaporate and concentrate the lithium-rich stock solution at 100℃ for 3 hours until the water in it is basically evaporated to obtain concentrated lithium-rich solution.

[0043] (5) While stirring, add 50 mL of 1 mol / L lithium iodide anhydrous ethanol solution to the concentrated lithium-rich solution, and then react for 30 min until the impurity ions such as Cu, Al, and Mg in the lithium-rich solution are completely precipitated. Filter and add 3 g of anhydrous sodium sulfate to the filtrate to remove water.

[0044] (6) After filtering again, 25 mL of saturated sodium carbonate aqueous solution was added to the filtrate, stirred for 30 min, filtered and washed thoroughly, and dried in an oven at 80 °C for 4 h to obtain 6.28 g of battery-grade Li2CO3. The composition detection results are shown in Table 4.

[0045] Table 4

[0046] Component <![CDATA[Li2CO3]]> Na K Ca Mg Fe Al Pb Cu wt% 99.6 0.001 0.001 0.002 0.001 0.001 0.001 0.001 0.001

[0047] Example 3: A method for obtaining battery-grade lithium carbonate from waste lithium iron phosphate battery cathode material, comprising the following steps:

[0048] (1) First, the unqualified positive electrode coating of lithium iron phosphate battery (materials that can only be discarded due to unqualified indicators during the positive electrode coating preparation process) is sieved through a 60-mesh sieve. Each time, anhydrous ethanol is added to the powder after sieving at a liquid-solid ratio of L / S = 10 mL / g for two rough washes, each for 30 min. Then, the washed wet material is dried in an 80℃ oven for 2 h, and then sieved through a 60-mesh sieve to obtain dried lithium iron phosphate powder. The content of some components is shown in Table 5.

[0049] Table 5

[0050] Component Na K Ca Mg Al Cu Li Fe wt% 0.001 0.005 0.014 0.013 3.65 2.74 2.81 29.14

[0051] (2) Prepare 125 mL of 2.5 mol / L hydrochloric acid and mix it with 25 mL of 30 wt% hydrogen peroxide to prepare a mixed solution;

[0052] (3) With a liquid-to-solid ratio of L / S = 10 mL / g, the prepared mixture was added to 15 g of dry lithium iron phosphate powder and stirred to carry out the leaching reaction. The leaching temperature was 75 °C and the leaching time was 3 h.

[0053] (4) After leaching, filter to obtain lithium-rich stock solution. Further evaporate and concentrate the lithium-rich stock solution at 100℃ for 3 hours until the water in it is basically evaporated to obtain concentrated lithium-rich solution.

[0054] (5) While stirring, add 50 mL of 5 mol / L lithium iodide anhydrous ethanol solution to the concentrated lithium-rich solution, and then react for 30 min until the impurity ions such as Cu, Al, and Mg in the lithium-rich solution are completely precipitated. After filtration, add 3 g of anhydrous sodium sulfate to the filtrate to remove water.

[0055] (6) After filtering again, 25 mL of saturated sodium carbonate aqueous solution was added to the filtrate, stirred for 30 min, filtered and washed thoroughly, and dried in an oven at 80 °C for 4 h to obtain 10.89 g of battery-grade Li2CO3. The composition detection results are shown in Table 6.

[0056] Table 6

[0057] Component <![CDATA[Li2CO3]]> Na K Ca Mg Fe Al Pb Cu wt% 99.5 0.003 0.002 0.003 0.001 0.001 0.001 0.001 0.001

[0058] Example 4:

[0059] The method of Example 2 was followed, using the same batch of waste materials. The difference was that the hydrochloric acid in step (2) of Example 2 was replaced with nitric acid solution of the same molar concentration and volume. The other steps were exactly the same as in Example 2. The composition detection results of the obtained product 6.25g Li2CO3 are shown in Table 7.

[0060] Table 7

[0061] Component <![CDATA[Li2CO3]]> Na K Ca Mg Fe Al Pb Cu wt% 99.7 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001

[0062] Example 5:

[0063] The method of Example 2 was followed, using the same batch of waste materials. The difference was that the anhydrous ethanol solution of lithium iodide in step (5) of Example 2 was replaced with anhydrous ethanol solution of sodium iodide with the same molar concentration and volume. The other steps were exactly the same as in Example 2. The composition detection results of the obtained product 4.43g Li2CO3 are shown in Table 8.

[0064] Table 8

[0065] Component <![CDATA[Li2CO3]]> Na K Ca Mg Fe Al Pb Cu wt% 99.5 0.001 0.001 0.001 0.001 0.001 0.002 0.001 0.001

[0066] Comparative Example 1:

[0067] The method of Example 1 was followed, using the same batch of waste materials. The difference was that step (5) was performed as follows: 500 mL of 1 mol / L lithium iodide aqueous solution was added to the concentrated lithium-rich solution under stirring, and the reaction was stirred for 30 min. Other steps were exactly the same as in Example 1. The composition detection results of the obtained product 7.14 g Li2CO3 are shown in Table 9.

[0068] Table 9

[0069] Component <![CDATA[Li2CO3]]> Na K Ca Mg Fe Al Pb Cu wt% 99.4 0.008 0.010 0.015 0.009 0.001 0.006 0.001 0.005

[0070] Comparative Example 2: Referring to Example 1 of Chinese Patent CN 108155432 A, the specific steps are as follows:

[0071] 1) Directly use the pre-treated waste material from Example 2;

[0072] 2) Leaching: Prepare an acidic solution by mixing pure water and sulfuric acid in a certain proportion. Add the lithium iron phosphate powder from step 1) to the acidic solution in a certain proportion and stir to react. The liquid-to-solid ratio is 1.5. According to the stoichiometry of ferrous ions in lithium iron phosphate powder, the sulfuric acid is in excess by 20 wt%. The reaction temperature is controlled at 25℃ and the reaction time is 2.5 h.

[0073] 3) Filtration and separation: Filter the reaction product from step 2), and the filtrate is a low-concentration lithium-containing solution;

[0074] 4) Repeat step 2): Replace the pure water in step 2) with the above low-concentration lithium-containing solution and repeat the reaction of step 2) once to obtain a high-concentration lithium-containing solution; that is, the lithium-containing solution before impurity removal.

[0075] 5) First-stage impurity removal: Add sodium hydroxide to the above high-concentration lithium-containing solution, adjust the pH of the solution to 6.5, react for 1 hour, filter, and collect the filtrate;

[0076] 6) Secondary impurity removal: Heat the filtrate from step 5) to 80°C, add sodium hydroxide, adjust the pH of the system to 10, react for 3 hours, filter, and a high-purity, high-concentration lithium-containing solution is obtained.

[0077] 7) Add Na2CO3 to a high-concentration lithium-containing solution, stir for 30 min, filter and wash thoroughly, and dry in an 80℃ oven for 4 h to obtain battery-grade Li2CO3. The composition detection results are shown in Table 10. It can be seen that although the obtained product can reach battery grade, its preparation steps are significantly more complicated than those in the example, and the use of alkali source is also increased.

[0078] Table 10

[0079] Component <![CDATA[Li2CO3]]> Na K Ca Mg Fe Al Pb Cu wt% 99.5 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001

Claims

1. A method for recovering lithium carbonate from waste lithium iron phosphate battery cathode materials, comprising the following steps: (1) First, the waste lithium iron phosphate battery cathode material is roughly washed to remove surface impurities and then dried and sieved to obtain dry lithium iron phosphate powder for later use. (2) Prepare an acid solution of 1-10 mol / L and mix it with hydrogen peroxide of 5.5%-30% by mass to prepare a mixed solution. The acid solution is hydrochloric acid or nitric acid solution. (3) Add the mixture from step (2) to dry lithium iron phosphate powder according to the liquid-solid ratio L / S=5-10 mL / g, stir to carry out the leaching reaction, the leaching temperature is 60-75℃, and the leaching time is 2-3h. (4) After leaching, filter to obtain lithium-rich stock solution and remove water from the lithium-rich stock solution; (5) Under stirring, add 1-5 mol / L of anhydrous ethanol solution of lithium iodide to the dehydrated lithium-rich solution, stir the reaction until Cu, Al and Mg ions precipitate out, add anhydrous sodium sulfate to remove water; after filtering again, add saturated Na2CO3 solution to the filtrate, stir, filter and wash thoroughly, and dry to obtain product Li2CO3.

2. The method according to claim 1, characterized in that, In step (2), the concentration of the acid solution is 2.5 mol / L; the mass percentage of the hydrogen peroxide is 30%.

3. The method according to claim 2, characterized in that, In step (2), the volume ratio of acid to hydrogen peroxide is 5:

1.

4. The method according to claim 1, characterized in that, In step (5), the drying process involves drying at 80°C for 4 hours.

5. The method according to claim 1, characterized in that, The method for removing water from the lithium-rich stock solution in step (4) is to evaporate and concentrate it at 100 °C for 3 hours.

6. The method according to claim 1, characterized in that, The cathode material of the waste lithium iron phosphate battery is cathode material powder, coating waste, or lithium iron phosphate sintering waste from waste lithium iron phosphate batteries.