Method for recycling and preparing low-hygroscopic lithium dihydrogen phosphate from waste lithium batteries
By leaching, filtering impurities, and controlling crystallization of spent lithium iron phosphate batteries, low-hygroscopic lithium dihydrogen phosphate is prepared, solving the problems of low lithium resource recovery rate and high product hygroscopicity, and realizing efficient and stable lithium resource recovery and utilization.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- JIANGXI LONGKAI CYCLE TECHNOLOGY CO LTD
- Filing Date
- 2026-05-14
- Publication Date
- 2026-06-23
AI Technical Summary
Existing technologies suffer from low lithium resource recycling rates, complex processes, insufficient product conversion and utilization, and the hygroscopic nature of lithium dihydrogen phosphate, leading to large batch-to-batch fluctuations and resulting in resource waste and environmental pollution.
Low-hygroscopic lithium dihydrogen phosphate was prepared by adding acid to lithium iron phosphate black powder to leach lithium, adjusting the pH to filter impurities, adding a precipitant to precipitate lithium ions, and controlling the crystallization conditions and cooling process.
The lithium resource recovery rate is increased to over 98%, the product particle size distribution is stable, and the hygroscopicity is reduced to ≤1.5%, achieving efficient resource utilization and environmentally friendly recycling.
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Figure CN122254451A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of lithium resource recycling and inorganic salt preparation technology, and in particular to a method for recycling and preparing low-hygroscopic lithium dihydrogen phosphate from waste lithium batteries. Background Technology
[0002] With the rapid development of new energy vehicles, energy storage systems, and consumer electronics, the demand for lithium-ion batteries continues to grow. Among them, lithium iron phosphate batteries are widely used in power batteries and energy storage fields due to their high safety, long cycle life, and relatively low cost. As a large number of lithium iron phosphate batteries gradually enter the retirement stage, the recycling and disposal of waste lithium iron phosphate batteries is receiving increasing attention.
[0003] Waste lithium iron phosphate batteries contain a certain amount of lithium and phosphate resources. Direct disposal not only wastes resources but may also have potential environmental impacts. Therefore, recycling waste lithium iron phosphate batteries to extract lithium resources and convert them into lithium salt products with application value has significant economic and environmental importance.
[0004] Lithium dihydrogen phosphate (LiH2PO4) is an important lithium salt compound that can be used as a raw material for preparing lithium iron phosphate cathode materials and other phosphate materials, and has certain application value in the fields of new energy materials and chemicals. Currently, LiH2PO4 is usually prepared by reacting lithium carbonate or lithium hydroxide with phosphoric acid. However, this method mainly relies on mineral lithium resources, which is costly. At the same time, it fails to fully utilize the lithium resources in waste lithium batteries, and LiH2PO4 is prone to moisture absorption and agglomeration, resulting in large batch fluctuations in product quality.
[0005] Existing technologies have proposed some methods for recovering lithium resources from spent lithium iron phosphate batteries, but these methods still suffer from problems such as product hygroscopicity, complex process steps, low lithium recovery rate, unstable product purity, and insufficient subsequent conversion and utilization. Therefore, developing a process that can effectively recover lithium resources from spent lithium iron phosphate batteries and prepare lithium dihydrogen phosphate is of great significance for improving resource utilization, reducing production costs, and promoting the resource utilization of spent lithium batteries. Summary of the Invention
[0006] The purpose of this invention is to provide a method for recovering and preparing low-hygroscopic lithium dihydrogen phosphate from waste lithium batteries, in order to solve the problems of low lithium resource recycling rate, complex process flow, insufficient product conversion and utilization, and large batch fluctuations in the existing technology.
[0007] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for preparing low-hygroscopic lithium dihydrogen phosphate from waste lithium batteries, comprising the following steps: 1) Add acid to lithium iron phosphate black powder to leach out lithium from the black powder and obtain lithium-containing leachate; 2) By adjusting the pH of the lithium-containing leachate, metal impurities are filtered out to obtain a pure lithium-containing solution; 3) Add a precipitant to the lithium-containing solution in step 2) to precipitate lithium ions in the form of lithium carbonate; 4) The precipitated lithium carbonate is reacted with a phosphorus source to obtain lithium dihydrogen phosphate. Low hygroscopic lithium dihydrogen phosphate is obtained by controlling the crystallization conditions and cooling process.
[0008] Furthermore, the acid is sulfuric acid with a volume fraction of 3-8%, and hydrogen peroxide is added during the leaching of black powder to oxidize ferrous iron and prevent iron ions from leaching out.
[0009] Furthermore, in step 2), the pH is adjusted to 6-11, and the filtered metal impurities include calcium, magnesium, aluminum, and iron impurities.
[0010] Furthermore, the precipitant is sodium carbonate.
[0011] Furthermore, the phosphorus source is phosphoric acid, and crystallization is carried out at 70~90℃. After crystallization, the temperature is reduced by 1~2℃ / min to promote crystal growth rather than the generation of new nuclei.
[0012] Furthermore, after the cooling process is complete, continue to cook for another 20-40 minutes.
[0013] The beneficial effects of this invention are: This invention addresses the problems in existing technologies for recycling spent lithium iron phosphate batteries, such as low lithium recovery rates, low product added value, insufficient utilization of phosphorus resources, and the high hygroscopicity and unstable particle size distribution of lithium dihydrogen phosphate products. It proposes a process for recovering lithium from spent lithium iron phosphate batteries and preparing lithium dihydrogen phosphate. By systematically controlling the leaching, purification, conversion, and crystallization processes, efficient resource utilization and optimized product performance are achieved. Specific technical effects are as follows.
[0014] I. Improve lithium resource recovery rate
[0015] This invention optimizes leaching conditions and solution conversion pathways to ensure that lithium elements in spent lithium batteries fully enter the liquid phase system and reduce losses in the residue. In the preferred embodiment, the lithium leaching rate can reach ≥98%; the total lithium recovery rate can reach 90%–95%. Compared with traditional processes, this invention significantly improves the efficiency of lithium resource utilization.
[0016] II. Obtaining lithium dihydrogen phosphate products with controllable particle size
[0017] This invention regulates the nucleation and growth behavior during crystallization by controlling the degree of evaporation and concentration, the cooling rate, and the amount of seed crystals added, thereby obtaining a product with a stable particle size distribution. Under preferred conditions: the product particle size is mainly distributed between 200–800 μm; the maximum particle size is controlled to <1 mm; the particle size distribution is concentrated, and the dispersion is reduced. This effect can meet the requirements of battery materials for uniform particle size of raw materials.
[0018] 3. Significantly reduces product hygroscopicity
[0019] The present invention reduces the hygroscopicity of lithium dihydrogen phosphate by the following measures: controlling the crystal morphology to be dense particles; and using ethanol washing to reduce surface adsorbed water.
[0020] Tests showed that after 24 hours of storage at 25°C and 75% relative humidity, the moisture absorption weight gain rate of the product was ≤1.5%; compared to the 3%-6% moisture absorption weight gain rate of products processed by conventional methods, the moisture absorption is significantly reduced. The product is less prone to clumping during storage, and its flowability is significantly improved.
[0021] IV. Environmental and Social Benefits
[0022] This invention enables the reuse of lithium resources from spent lithium batteries. It avoids the potential environmental pollution caused by spent batteries, reduces dependence on primary lithium resources, and promotes the development of a circular economy in the lithium battery industry.
[0023] This invention achieves the preparation of lithium dihydrogen phosphate products with high recovery rate, controllable particle size, and low hygroscopicity by efficiently recovering lithium resources from waste lithium iron phosphate batteries and precisely controlling the lithium dihydrogen phosphate crystallization process, which has good prospects for industrial application. Attached Figure Description
[0024] Figure 1 This is a flowchart of the preparation process of the present invention; Figure 2 This is a schematic diagram illustrating the mechanism for producing low-hygroscopic lithium dihydrogen phosphate according to the present invention. Detailed Implementation
[0025] This invention provides a method for preparing low-hygroscopic lithium dihydrogen phosphate from waste lithium batteries, comprising the following steps: 1) Add acid to lithium iron phosphate black powder to leach out lithium from the black powder and obtain lithium-containing leachate; 2) By adjusting the pH of the lithium-containing leachate, metal impurities are filtered out to obtain a pure lithium-containing solution; 3) Add a precipitant to the lithium-containing solution in step 2) to precipitate lithium ions in the form of lithium carbonate; 4) The precipitated lithium carbonate is reacted with a phosphorus source to obtain lithium dihydrogen phosphate. Low hygroscopic lithium dihydrogen phosphate is obtained by controlling the crystallization conditions and cooling process.
[0026] In this invention, the acid is sulfuric acid with a volume fraction of 3-8%. Hydrogen peroxide is added during the leaching of black powder to oxidize ferrous iron and prevent iron ions from leaching out. The volume fraction of sulfuric acid is preferably 4-7%, and more preferably 5%.
[0027] In this invention, in step 2), the pH is adjusted to 6-11, and the filtered metallic impurities include calcium, magnesium, aluminum, and iron impurities. The pH is first adjusted to 6 for filtration, and then adjusted to 11 for a second filtration to remove the calcium, magnesium, aluminum, and iron impurities, resulting in a purified lithium-containing solution.
[0028] In this invention, the precipitant is sodium carbonate.
[0029] In this invention, the phosphorus source is phosphoric acid, and crystallization is carried out at 70~90°C, preferably 75~85°C, and more preferably 80°C; after crystallization, the temperature is reduced at 1~2°C / min, preferably 1°C / min, to promote crystal growth rather than the generation of new nuclei.
[0030] In this invention, after the cooling process is completed, the aging process can continue for 20 to 40 minutes, preferably 30 minutes.
[0031] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.
[0032] Example 1
[0033] 1) Add lithium iron phosphate black powder to the reactor and leach it with 5% sulfuric acid. Add hydrogen peroxide to oxidize ferrous iron to prevent iron ions from leaching out, and obtain lithium-containing leachate with a leaching rate of 99.13%.
[0034] 2) Adjust the pH to 6 and filter, then adjust it to 11 for a second filtration to remove calcium, magnesium, aluminum and iron impurities, and obtain purified lithium-containing liquid.
[0035] 3) Sodium carbonate is added to the solution to precipitate lithium carbonate, which is used as a raw material for the synthesis of lithium dihydrogen phosphate. The purity of lithium carbonate is 99.11%.
[0036] 4) First, add water (solid-liquid ratio 1:2) to lithium carbonate to prepare a slurry. Then, add an excess of 15% (by mass) of 85% phosphoric acid to obtain a lithium dihydrogen phosphate solution. Transfer the lithium dihydrogen phosphate solution to an evaporator crystallizer and concentrate it at 80°C until the solution reaches near-supersaturation. Then, add lithium dihydrogen phosphate seed crystals while maintaining stirring. After evaporation, cool and crystallize at a rate of 1°C / min to a final temperature of 25°C. During the cooling process, control the system to remain in the metastable region to promote crystal growth rather than the formation of new nuclei. After cooling, continue stirring and maturing for 30 minutes. After drying, the low-hygroscopic lithium dihydrogen phosphate product is obtained.
[0037] Performance of low hygroscopic lithium dihydrogen phosphate products: After being placed at 25°C and 75% relative humidity for 24 hours: The moisture absorption weight gain rate of the product in Example 1 was 1.43%.
[0038] Example 2
[0039] 1) Lithium iron phosphate black powder was added to a reaction vessel and acid-leached with 3% sulfuric acid by volume. Hydrogen peroxide was added to oxidize ferrous iron to prevent iron ions from leaching out. The lithium-containing leachate was obtained by filtration, and the lithium leaching rate was measured to be 99.32%.
[0040] 2) Adjust the pH of the lithium-containing leachate to 7, filter to remove the precipitated iron and aluminum impurities; continue to adjust the pH to 10, filter to remove calcium and magnesium impurities, and obtain a pure lithium-containing solution.
[0041] 3) Add sodium carbonate as a precipitant to a pure lithium-containing solution, control the reaction temperature at 85°C, stir for 2 hours to precipitate lithium ions in the form of lithium carbonate, filter and wash to obtain lithium carbonate intermediate product with a purity of 99.24%.
[0042] 4) The obtained lithium carbonate was mixed with water at a solid-liquid ratio of 1:2.5 to form a slurry. Phosphoric acid (85% by mass, 1.2 times the theoretical amount) was added, and the mixture was reacted at 75°C to generate a lithium dihydrogen phosphate solution. The solution was transferred to an evaporator crystallizer and concentrated at 75°C to a solution density of 1.45 g / cm³. Lithium dihydrogen phosphate seed crystals (0.5% of the theoretical product mass) were added, and the temperature was lowered to 25°C at a rate of 1.5°C / min, with stirring maintained during the cooling process. After cooling, the mixture was allowed to mature for 25 minutes and then dried to obtain a low-hygroscopic lithium dihydrogen phosphate product.
[0043] Performance of low hygroscopic lithium dihydrogen phosphate products: After being placed at 25°C and 75% relative humidity for 24 hours: The moisture absorption weight gain rate of the product in Example 2 was 1.59%.
[0044] Example 3
[0045] 1) Add lithium iron phosphate black powder to the reactor and leach it with sulfuric acid with a volume fraction of 8%. Add hydrogen peroxide (5% of the mass of black powder), control the leaching temperature at 50℃, and the reaction time for 2 hours. After filtration, a lithium-containing leachate is obtained with a lithium leaching rate of 98.95%.
[0046] 2) Adjust the pH of the lithium-containing leachate to 6.5 with sodium hydroxide solution, filter to remove iron and aluminum precipitates; then adjust the pH to 11, filter to remove calcium and magnesium precipitates, and obtain a pure lithium-containing solution.
[0047] 3) Add sodium carbonate to the pure lithium-containing solution. The amount of sodium carbonate used is 1.1 times the theoretical amount. Stir at 90°C for 1.5 hours to precipitate lithium carbonate. Filter, wash with deionized water until neutral, and dry. The purity of lithium carbonate is 99.27%.
[0048] 4) Mix lithium carbonate with water at a solid-liquid ratio of 1:1.8 to form a slurry, add 85% phosphoric acid (10% excess), and react at 90℃ to generate a lithium dihydrogen phosphate solution. Transfer the solution to a crystallizer and evaporate and concentrate it at 90℃ to the critical point where crystals precipitate. Add seed crystals (0.3%), and cool to 20℃ at a cooling rate of 2℃ / min. During cooling, control the stirring speed at 80 rpm to avoid secondary nucleation. After cooling, allow to mature for 40 minutes, and then dry to obtain a low-hygroscopic lithium dihydrogen phosphate product.
[0049] Performance of low hygroscopic lithium dihydrogen phosphate products: After being placed at 25°C and 75% relative humidity for 24 hours: The moisture absorption weight gain rate of the product in Example 3 was 1.81%.
[0050] Comparative Example
[0051] The process steps are the same as in Example 1, except that no seed crystals are added for crystallization control and no programmed cooling is used. The solution is placed in a crystallizer and allowed to cool naturally to 20°C. After cooling, it is allowed to mature for 40 minutes and then dried to obtain the lithium dihydrogen phosphate product.
[0052] The process and product performance of Example 1 of this application are compared with those of the comparative example, as shown in Table 1 below: Table 1 Comparison of Process and Product Performance
[0053] As shown in the above embodiments, this invention provides a method for preparing low-hygroscopic lithium dihydrogen phosphate from waste lithium batteries. Tests showed that after 24 hours of storage at 25°C and 75% relative humidity, the moisture absorption weight gain rate of the product from this invention was ≤1.5%; compared to the 3%-6% moisture absorption weight gain rate of products from conventional processes, the hygroscopicity is significantly reduced. The product is less prone to clumping during storage, and its flowability is significantly improved.
[0054] Figure 2This diagram illustrates the mechanism for producing low-hygroscopic lithium dihydrogen phosphate according to the present invention. The vertical axis represents the supersaturation of the solution, and the horizontal axis represents the crystallization process. The diagram includes unstable, metastable, and stable regions, with the metastable region located between the nucleation curve and the solubility curve. The present invention controls the system to operate within the metastable region and adds seed crystals at appropriate times, causing the system to crystallize along path b. This suppresses spontaneous nucleation and promotes crystal growth, while simultaneously improving crystal density through a ripening process. In contrast, the conventional process operates along path a, easily entering the stable region, leading to extensive nucleation and the formation of plate-like or fine crystals.
[0055] This invention involves leaching waste lithium iron phosphate cathode materials to dissolve lithium elements in the residue. Through subsequent separation, conversion, and crystallization processes, the lithium ions in the solution are converted into lithium dihydrogen phosphate, thereby achieving lithium resource recycling. This method effectively improves the utilization efficiency of lithium resources in waste lithium iron phosphate materials and converts the recovered lithium resources into valuable lithium dihydrogen phosphate products. Compared with existing technologies, the method provided by this invention features a relatively simple process flow, high lithium resource recovery rate, wide availability of raw materials, and a high degree of resource utilization, offering a new technical approach for the resource utilization of waste lithium batteries.
[0056] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.
Claims
1. A method for recovering and preparing low-hygroscopic lithium dihydrogen phosphate from waste lithium batteries, characterized in that, Includes the following steps: 1) Add acid to lithium iron phosphate black powder to leach out lithium from the black powder and obtain lithium-containing leachate; 2) By adjusting the pH of the lithium-containing leachate, metal impurities are filtered out to obtain a pure lithium-containing solution; 3) Add a precipitant to the lithium-containing solution in step 2) to precipitate lithium ions in the form of lithium carbonate; 4) The precipitated lithium carbonate is reacted with a phosphorus source to obtain lithium dihydrogen phosphate. Low hygroscopic lithium dihydrogen phosphate is obtained by controlling the crystallization conditions and cooling process.
2. The method for preparing low-hygroscopic lithium dihydrogen phosphate from waste lithium batteries according to claim 1, characterized in that, The acid is sulfuric acid with a volume fraction of 3-8%. Hydrogen peroxide is added during the leaching of black powder to oxidize ferrous iron and prevent iron ions from leaching out.
3. The method for preparing low-hygroscopic lithium dihydrogen phosphate from waste lithium batteries according to claim 1 or 2, characterized in that, In step 2), the pH is adjusted to 6-11, and the filtered metal impurities include calcium, magnesium, aluminum, and iron impurities.
4. The method for preparing low-hygroscopic lithium dihydrogen phosphate from waste lithium batteries according to claim 1, characterized in that, The precipitant is sodium carbonate.
5. The method for preparing low-hygroscopic lithium dihydrogen phosphate from waste lithium batteries according to claim 1, 2, or 4, characterized in that, The phosphorus source is phosphoric acid. Crystallization is carried out at 70~90℃. After crystallization, the temperature is reduced by 1~2℃ / min to promote crystal growth rather than the generation of new nuclei.
6. The method for preparing low-hygroscopic lithium dihydrogen phosphate from waste lithium batteries according to claim 5, characterized in that, After the cooling process is complete, continue to cook for another 20-40 minutes.