Method for upgrading and regenerating recycled waste lithium iron phosphate material into lithium sulfide

Abstract

The invention relates to a method for recycling a waste lithium iron phosphate material and upgrading and regenerating the waste lithium iron phosphate material into lithium sulfide, and aims to efficiently recycle a lithium resource in a waste lithium iron phosphate battery and produce high-purity lithium sulfide. According to the method, lithium in the waste lithium iron phosphate material is selectively recycled through an ammonium sulfate roasting method, and lithium sulfate is generated. And converting lithium sulfate into lithium sulfide at a high temperature of 800-1000 DEG C by a carbon thermal reduction method. Through reasonable process conditions including proper temperature, reaction time and the ratio of carbon to lithium sulfate, impurities can be effectively removed, and lithium sulfide with the purity greater than or equal to 99% is generated. The technology not only can effectively solve the problem of recovery of the waste lithium iron phosphate battery, but also can provide high-purity lithium sulfide for the fields of battery manufacturing and the like, and has good environmental benefits and economic values.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of recycling and reusing waste lithium iron phosphate materials, and particularly relates to a method for recycling and upgrading waste lithium iron phosphate (LiFePO4) positive electrode materials to lithium sulfide (Li2S). BACKGROUND

[0002] With the increasing demand for electric vehicles, energy storage systems and renewable energy sources worldwide, lithium iron phosphate (LiFePO4) batteries have occupied an important position in the market due to their high safety, long life and cost-effectiveness. However, as the service life of lithium iron phosphate batteries gradually expires, how to efficiently recycle and reuse valuable components in waste batteries has become a problem to be solved. Especially in the context of resource scarcity and increasing environmental pressure, how to achieve efficient recycling of waste lithium iron phosphate batteries through innovative technology has become a key challenge in the field of battery recycling. Lithium in lithium iron phosphate batteries is a very valuable resource, as a key energy metal, its reserves are limited and market demand is increasing. Traditional waste lithium iron phosphate battery recycling technology often has low recovery efficiency, serious resource waste, high processing cost and other problems.

[0003] Lithium sulfide, as a material with high energy density and excellent electrical conductivity, plays a crucial role in solid-state batteries. Solid-state batteries, as a research hotspot of next-generation battery technology, have higher safety, longer service life and higher energy density compared to traditional liquid batteries. Lithium sulfide is considered an important key material in solid-state batteries due to its excellent performance in solid-state electrolytes. Therefore, converting lithium resources in waste lithium iron phosphate batteries into lithium sulfide not only improves the recycling value of waste batteries, but also provides a foundation for the further development of solid-state batteries.

[0004] There are three main methods for the recovery of lithium iron phosphate: pyrometallurgical recovery, hydrometallurgical recovery, and direct repair and regeneration. Pyrometallurgical recovery is a method that uses high-temperature calcination to burn off organic matter in waste batteries, while metals are separated in the form of oxide slag. This method has a simple operation process but high energy consumption and low separation efficiency. However, it is worth noting that some researchers have used the method of sulfate-assisted roasting to efficiently and selectively extract lithium and reduce energy consumption. Hydrometallurgical recovery is a method that uses acid or alkali leaching to extract valuable metals from the positive electrode material. To improve efficiency, excessive amounts of acid or alkali must be used, which generates a large amount of acid or alkali waste liquid, increasing the environmental cost of treating the waste liquid. In hydrometallurgical recovery, selective leaching of lithium is a highly efficient method of recovering lithium, reducing the amount of acid and alkali used. Direct repair and regeneration is a method that restores the activity of the positive electrode material by supplementing lithium, but this method is difficult and not suitable for industrial production. In addition, bioleaching is also considered a promising recovery method, but there is currently no mature research. Regardless of the method, there are drawbacks at this stage. Among the various recovery processes, sulfate-assisted roasting has a significant effect. Ammonium sulfate roasting is suitable for industrial lithium extraction due to its low required roasting temperature and high selectivity, and the process does not require strong acid. During the ammonium sulfate roasting process, ammonium ions are removed as ammonia gas, without introducing new impurities, and the entire process is simple to operate.

[0005] In summary, further improvement in the direction of recycling and regeneration of waste lithium iron phosphate batteries is mainly focused on efficient extraction of lithium and value-added utilization. Therefore, it is necessary to develop a process based on efficient and selective lithium extraction and value-added preparation of high-value products to achieve short process, high efficiency, and purification of lithium, and to truly achieve value-added utilization in the new energy industry by combining the regeneration process. SUMMARY

[0006] To overcome the shortcomings of the prior art, the present application provides a method for recycling waste lithium iron phosphate materials and upgrading them to lithium sulfide, aiming to efficiently recover lithium resources from waste lithium iron phosphate batteries and produce high-purity lithium sulfide. This method selectively recovers lithium from waste lithium iron phosphate materials through ammonium sulfate roasting, producing lithium sulfate. Then, lithium sulfate is converted to lithium sulfide at a high temperature of 800-1000°C through a carbon thermal reduction method. By optimizing the process conditions, including the appropriate temperature, reaction time, and the ratio of carbon to lithium sulfate, impurities can be effectively removed, and lithium sulfide with a purity of ≥99% can be produced. This technology not only effectively solves the problem of recycling waste lithium iron phosphate batteries, but also provides high-purity lithium sulfide for battery manufacturing and other fields, with good environmental benefits and economic value.

[0007] To achieve the above-mentioned purposes, the technical scheme of the present application includes the following steps: 1) Alkali washing and impurity removal of waste lithium iron phosphate battery materials and drying; 2) the material after washing with alkali is mixed with ammonium sulfate and then calcined to obtain a calcined product; 3) the calcined product is subjected to water immersion, filtration to obtain a lithium sulfate solution and evaporation crystallization; 4) the recovered lithium sulfate is mixed with a carbon source and then subjected to a carbothermal reduction reaction to obtain lithium sulfide; 5) the lithium sulfide is subjected to impurity removal by solvent extraction and vacuum drying to obtain lithium sulfide with a purity of ≥ 99%.

[0008] The impurities such as aluminum contained in the waste lithium iron phosphate material in step 1) are removed by alkali washing.

[0009] In step 2), the lithium-sulfur ratio is 3:1-1:1, the calcination temperature is 200-600℃, and the reaction time is 2-3h.

[0010] In step 3), the water immersion temperature is 40-80℃, the water immersion time is 0.5-3h, and the solid-liquid ratio is 10-50g / L.

[0011] In step 4), the mass ratio of lithium sulfate to carbon is 1:1-1:3, and the carbon source is preferably one or more of glucose, sucrose, monoglycol, and carbon nanotubes.

[0012] In step 4), the carbothermal reduction reaction can be carried out at a calcination temperature of 800-1000℃ for 2-6h.

[0013] The lithium sulfide is treated by solvent extraction to remove impurities such as iron, aluminum, and phosphorus, the extraction temperature is 30-60℃, the time is 3-5h, and the extraction solvent is preferably one or more of dichloromethane, acetone, n-hexane, and tricaprylyl phosphate.

[0014] The vacuum drying temperature of the lithium sulfide is 100-150℃, and the drying time is 3-5h.

[0015] The present application realizes efficient recovery and regeneration of waste lithium iron phosphate positive electrode material, avoids resource waste and environmental pollution. By upgrading the waste to Li2S, not only the recycling problem of waste lithium iron phosphate battery can be effectively solved, but also high-purity lithium sulfide can be provided for battery manufacturing and other fields, which has good environmental benefits and economic value. The method is simple, low in cost, and suitable for large-scale industrial production. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 The process flowchart of the present application is shown. DETAILED DESCRIPTION

[0017] Embodiments of the present application will be described in more detail below. The present application can be implemented in various forms and should not be interpreted as being limited to the embodiments set forth herein, which are provided for a more thorough and complete understanding of the present application. It should be understood that the embodiments of the present application are for exemplary purposes only and are not intended to limit the scope of protection of the present application.

[0018] The main elements and contents in the waste lithium iron phosphate battery powder after alkali washing in the following examples are shown in Table 1: Table 1 Main elements and contents in waste lithium iron phosphate battery powder after alkali washing

[0019] Example 1: 1. 30 g of waste lithium iron phosphate positive material powder after alkali washing was mixed with ammonium sulfate at a lithium-sulfur ratio of 2:1, and calcined at 300°C for 3 h to obtain a calcined product; 2. The calcined product was subjected to water immersion at a water immersion temperature of 60°C for 1 h at a solid-liquid ratio of 20 g / L, and lithium sulfate was obtained by evaporation crystallization after filtration; 3. The obtained lithium sulfate was mixed with glucose at a mass ratio of 1:2, and calcined at 900°C for 5 h to obtain lithium sulfide; 4. The lithium sulfide was placed in dichloromethane for extraction to remove impurities, the extraction temperature was 50°C, and the extraction time was 4 h; 5. The extracted lithium sulfide was vacuum dried at a temperature of 120°C for 5 h.

[0020] The lithium leaching rate after water immersion was 99.53%, the purity of the final product lithium sulfide was ≥99.9%, the contents of impurities sodium, magnesium, silicon, sulfur, potassium, calcium, chromium, cobalt, nickel, copper, zinc, molybdenum, cadmium, lead were ≤0.003%, and the content of impurity aluminum was ≤0.005%.

[0021] Example 2: 1. 50 g of waste lithium iron phosphate positive material powder after alkali washing was mixed with ammonium sulfate at a lithium-sulfur ratio of 1.5:1, and calcined at 300°C for 4 h to obtain a calcined product; 2. The calcined product was subjected to water immersion in water at a water immersion temperature of 70°C for 2 h at a solid-liquid ratio of 25 g / L, and lithium sulfate was obtained by evaporation crystallization after filtration; 3. The lithium sulfate was mixed with monomethyl glycol at a mass ratio of 1:1.5, and calcined at 850°C for 6 h to obtain lithium sulfide; 4. The obtained lithium sulfide was placed in acetone for extraction to remove impurities, the extraction temperature was 55°C, and the extraction time was 5 h; 5. The extracted lithium sulfide was vacuum dried at a temperature of 130°C for 6 h.

[0022] The lithium leaching rate after water immersion is 99.32%, and the purity of the final product lithium sulfide is ≥99.9%, and the content of impurities sodium, magnesium, silicon, sulfur, potassium, calcium, chromium, cobalt, nickel, copper, zinc, molybdenum, cadmium, lead is ≤0.003%, and the content of impurity aluminum is ≤0.005%.

[0023] Example 3: 1. Take 40g of waste lithium iron phosphate positive electrode material powder after alkali washing and ammonium sulfate, mix them according to the ratio of lithium to sulfur of 1.5:1, and control the roasting process at 350℃ for 4h to obtain the roasted product; 2. The roasted product is water immersed at a water immersion temperature of 65℃ for 1.5h, and the solid-liquid ratio is 15g / L. After filtration, lithium sulfate is obtained by evaporation crystallization; 3. Mix lithium sulfate with sucrose according to the mass ratio of 1:2, and roast at 900℃ for 4h to obtain lithium sulfide; 4. Put the lithium sulfide into dichloromethane for extraction to remove impurities, and set the extraction temperature to 60℃ and the extraction time to 3h; 5. Vacuum dry the extracted lithium sulfide at a temperature of 110℃ for 5h.

[0024] The lithium leaching rate after water immersion is 99.32%, and the purity of the final product lithium sulfide is ≥99.9%, and the content of impurities sodium, magnesium, silicon, sulfur, potassium, calcium, chromium, cobalt, nickel, copper, zinc, molybdenum, cadmium, lead is ≤0.003%, and the content of impurity aluminum is ≤0.005%.

[0025] Example 4: 1. Take 60g of waste lithium iron phosphate positive electrode material powder after alkali washing and ammonium sulfate, mix them according to the ratio of lithium to sulfur of 2.5:1, and control the roasting process at 280℃ for 5h to obtain the roasted product; 2. The roasted product is water immersed at a water immersion temperature of 80℃ for 2h, and the solid-liquid ratio is 30g / L. After filtration, lithium sulfate is obtained by evaporation crystallization; 3. Mix lithium sulfate with carbon nanotubes according to the mass ratio of 1:1.8, and roast at 950℃ for 7h to obtain lithium sulfide; 4. Put the obtained lithium sulfide into dichloromethane for extraction to remove impurities, and set the extraction temperature to 45℃ and the extraction time to 6h; 5. Vacuum dry the extracted lithium sulfide at a temperature of 125℃ for 4h.

[0026] The lithium leaching rate after water immersion is 99.32%, and the purity of the final product lithium sulfide is ≥99.9%, and the content of impurities sodium, magnesium, silicon, sulfur, potassium, calcium, chromium, cobalt, nickel, copper, zinc, molybdenum, cadmium, lead is ≤0.003%, and the content of impurity aluminum is ≤0.005%.

[0027] The preparation method of the present application is to selectively recover lithium in waste lithium iron phosphate material by ammonium sulfate roasting method to generate lithium sulfate. Then the lithium sulfate is converted into lithium sulfide at a high temperature of 800-1000 DEG C by carbon thermal reduction method. Through reasonable process conditions, including appropriate temperature, reaction time and the ratio of carbon to lithium sulfate, impurities can be effectively removed to generate lithium sulfide with purity of 99%. The technology not only effectively solves the recycling problem of waste lithium iron phosphate battery, but also provides high-purity lithium sulfide for battery manufacturing and other fields, which has good environmental benefits and economic value.

[0028] The above is only a specific embodiment of the present application, but the protection scope of the present application is not limited thereto, any person skilled in the art can easily think of changes or replacements within the technical range disclosed in the present application, which should be covered within the protection scope of the present application, therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A method for recycling waste lithium iron phosphate material and generating lithium sulfide, characterized in that, The method comprises the following steps: 1) Alkaline cleaning and impurity removal of waste lithium iron phosphate battery materials and drying; 2) Mixing the alkali cleaned material with ammonium sulfate and then roasting to obtain a roasted product; 3) Water immersion of the roasted product, filtration to obtain a lithium sulfate solution and evaporation crystallization; 4) Carbon thermal reduction reaction of the recovered lithium sulfate and carbon source to obtain lithium sulfide; 5) Impurity removal of lithium sulfide by solvent extraction and vacuum drying to obtain lithium sulfide with a purity of ≥99%.

2. The method of claim 1, wherein the aluminum and other impurities contained in the waste lithium iron phosphate battery material in step 1) are removed by alkaline cleaning.

3. The method of claim 1, wherein the lithium-sulfur ratio in step 2) is 3:1 to 1:1, the roasting temperature is 200-600℃, and the reaction time is 2-3h.

4. The method of claim 1, wherein the water immersion temperature in step 3) is 40-80℃, the water immersion time is 0.5-3h, and the solid-liquid ratio is 10-50g / L.

5. The method of claim 1, wherein the mass ratio of lithium sulfate to carbon in step 4) is 1:1 to 1:3, and the carbon source is preferably one or more of glucose, sucrose, monomethyl glycol, and carbon nanotubes.

6. The method of claim 1, wherein the carbon thermal reduction reaction in step 4) is carried out at a roasting temperature of 800-1000℃ for 2-6h.

7. The method of claim 1, wherein the lithium sulfide is treated by solvent extraction to remove iron, aluminum, phosphorus and other impurities, and the extraction solvent is preferably one or more of dichloromethane, acetone, n-hexane, and tricresyl phosphate.

8. The method of claim 1, wherein the vacuum drying temperature of lithium sulfide is 100-150℃, and the drying time is 3-5h.

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