A method for recovering lithium carbonate and phosphate from lithium iron manganese phosphate waste powder

Abstract

The invention discloses a method for recovering lithium carbonate and phosphate from lithium iron manganese phosphate waste powder, comprising the following steps: S1. thermally sintering the lithium iron manganese phosphate waste powder in an air-carbon dioxide-water vapor atmosphere, removing the carbon layer, cooling, and obtaining a mixture powder; S2. washing the mixture powder with hot water, precipitating a gray-green powder after washing, the gray-green powder being phosphate, and collecting the washing liquid; S3. filtering the washing liquid to remove impurities, and obtaining a white powder after rotary evaporation and drying, the white powder being lithium carbonate crystals. The recovery method of the present invention has a simple process, does not require the addition of additional reagents, does not generate wastewater, has low cost, and the recovered lithium carbonate and phosphate are of high purity, and can be reused for the preparation of lithium iron manganese phosphate.

Description

Technical Field

[0001] The invention relates to the field of waste lithium iron manganese phosphate positive electrode material resource recovery, and in particular to a method for recovering lithium carbonate and phosphate from waste lithium iron manganese phosphate powder. Background Art

[0002] Lithium iron manganese phosphate has the advantages of high energy density, good safety performance and low cost. It is considered to be the most promising cathode material for lithium-ion power batteries and is widely used in the field of new energy vehicles. The life cycle of lithium-ion power batteries is generally 5-8 years, and some are even shorter. Therefore, with the widespread application of lithium iron manganese phosphate cathode materials and the passage of time, a large number of waste lithium-ion power batteries will be generated. How to efficiently recycle the lithium iron manganese phosphate materials in these waste lithium-ion power batteries has become an important task.

[0003] In the prior art, Chinese patent CN108736090A discloses a recycling method for positive electrode materials of lithium iron manganese phosphate batteries, wherein ferromanganese and lithium elements are separated by leaching with oxidizing acid, ferromanganese slag is added to sodium hydroxide for roasting, and ferromanganese phosphate and sodium manganate solution are obtained, and a reducing agent is added to the sodium manganate solution to obtain manganese dioxide through redox reaction. This recycling method not only has a complex process flow, including roasting, reduction reaction and other steps, but also has the problems of high pollution and high energy consumption, and the method uses sodium persulfate as an oxidizing acid, and the recycling cost is high, which cannot reflect its economic efficiency. Summary of the invention

[0004] Based on the problems existing in the background technology, the present invention provides a method for recovering lithium carbonate and phosphate from lithium iron manganese phosphate waste powder. The recovery method has a simple process, does not require the addition of additional reagents, does not generate wastewater, has low cost, and the recovered lithium carbonate and phosphate are of high purity and can be reused in the preparation of lithium iron manganese phosphate.

[0005] The present invention is implemented by the following technical solutions:

[0006] A method for recovering lithium carbonate and phosphate from waste lithium iron manganese phosphate powder comprises the following steps:

[0007] S1. The waste lithium iron manganese phosphate powder is sintered in an air-carbon dioxide-water vapor atmosphere to remove the carbon layer and cool to obtain a mixture powder;

[0008] S2. The mixture powder is washed with hot water, and the precipitate after washing is a gray-green powder, which is a phosphate, and the washing liquid is collected;

[0009] S3. Filter the washing liquid to remove impurities, and then dry it by rotary evaporation to obtain a white powder, which is lithium carbonate crystals.

[0010] Furthermore, in step S1, the volume ratio of each component in the air-carbon dioxide-water vapor atmosphere is (60-80):20:(10-20).

[0011] Furthermore, in step S1, the sintering temperature is 300-450° C., and the sintering time is 3-6 hours.

[0012] Furthermore, the temperature of the hot water in step S2 is 50-100°C.

[0013] Furthermore, the phosphate obtained in step S2 has a general structural formula of Mn y Fe (1-y) PO4.

[0014] Beneficial effects of the present invention:

[0015] 1. The present invention first heat-sinters the waste lithium iron manganese phosphate powder in an air-carbon dioxide-water vapor atmosphere, removes the carbon layer by controlling the volume ratio of air-carbon dioxide-water vapor, separates lithium and iron manganese, obtains a mixture of lithium carbonate and phosphate, and then separates the slightly soluble lithium carbonate and phosphate by hot water washing to complete the separation. The recovery method of the present invention has a simple process, does not require the addition of additional acid and alkali reagents, does not generate wastewater, and greatly reduces the recovery cost.

[0016] 2. The lithium carbonate recovered by the present invention has high purity; the general structural formula of the recovered phosphate is Mn y Fe (1-y) PO4 can be used again to prepare lithium manganese iron phosphate positive electrode material.

[0017] 3. The overall recycling process of the present invention has low cost and high efficiency, is easy to industrialize, and greatly improves the utilization value and economic benefits of lithium iron manganese phosphate waste powder. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The accompanying drawings are used to provide further explanation of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0019] Figure 1 is the XRD pattern of lithium carbonate in Example 1 of the present invention;

[0020] Figure 2 is the XRD pattern of the phosphate in Example 1 of the present invention;

[0021] Figure 3 is the XRD spectrum of lithium carbonate in Example 2 of the present invention;

[0022] Figure 4 This is the XRD pattern of the phosphate in Example 2 of the present invention. DETAILED DESCRIPTION

[0023] The technical solution of the present invention is further described in detail below in conjunction with specific embodiments, but the protection scope of the present invention is not limited to the following embodiments.

[0024] Example 1

[0025] The method for recovering lithium carbonate and phosphate from waste lithium iron manganese phosphate powder comprises the following steps:

[0026] S1. Take 100g of the recovered lithium iron manganese phosphate powder material, place it in a rotary kiln, heat it to 350°C, and continue to pass air-gas composed of carbon dioxide and water vapor (volume ratio: 70-20-10), roast for 3 hours, cool, and obtain a mixture powder; after testing, the mixture powder is a composite of lithium carbonate and phosphate;

[0027] S2. The mixture powder is washed with hot water at 60°C, and the precipitate after washing is a gray-green powder, which is phosphate, and the washing liquid is collected;

[0028] S3. Filter the washing liquid to remove impurities, and then dry it by rotary evaporation to obtain a white powder, which is lithium carbonate crystals.

[0029] Example 2

[0030] S1. Take 100g of the recovered lithium manganese iron phosphate powder material, place it in a rotary kiln, heat it to 350°C, and continue to pass air-gas composed of carbon dioxide and water vapor (volume ratio: 60-20-20), roast for 5 hours, cool, and obtain a mixture powder; after testing, the mixture powder is a composite of lithium carbonate and phosphate;

[0031] S2. The powder material is washed with hot water at 80°C, and the precipitate after washing is a gray-green powder, which is a phosphate, and the washing liquid is collected;

[0032] S3. Filter the washing liquid to remove impurities, and then dry it by rotary evaporation to obtain a white powder, which is lithium carbonate crystals.

[0033] Example 3

[0034] S1. Take 100g of the recovered lithium manganese iron phosphate powder material, place it in a rotary kiln, heat it to 400°C, and continue to pass air-gas composed of carbon dioxide and water vapor (volume ratio: 65-20-15), roast for 4 hours, cool, and obtain a mixture powder; after testing, the mixture powder is a composite of lithium carbonate and phosphate;

[0035] S2. The powder material is washed with hot water at 80°C, and the precipitate after washing is a gray-green powder, which is a phosphate, and the washing liquid is collected;

[0036] S3. Filter the washing liquid to remove impurities, and then dry it by rotary evaporation to obtain a white powder, which is lithium carbonate crystals.

[0037] Example 4

[0038] S1. Take 100g of the recovered lithium iron manganese phosphate powder material, place it in a rotary kiln, heat it to 450°C, and continue to pass air-gas composed of carbon dioxide and water vapor (volume ratio: 75-20-10), roast for 3.5 hours, cool, and obtain a mixture powder; after testing, the mixture powder is a composite of lithium carbonate and phosphate;

[0039] S2. The powder material is washed with hot water at 70°C, and the precipitate after washing is a gray-green powder, which is a phosphate, and the washing liquid is collected;

[0040] S3. Filter the washing liquid to remove impurities, and then dry it by rotary evaporation to obtain a white powder, which is lithium carbonate crystals.

[0041] Example 5

[0042] S1. Take 100g of the recovered lithium iron manganese phosphate powder material, place it in a rotary kiln, heat it to 400°C, and continue to pass air-gas composed of carbon dioxide and water vapor (volume ratio: 80-20-10), roast for 4 hours, cool, and obtain a mixture powder; after testing, the mixture powder is a composite of lithium carbonate and phosphate;

[0043] S2. The powder material is washed with hot water at 100°C, and the precipitate after washing is a gray-green powder, which is a phosphate, and the washing liquid is collected;

[0044] S3. Filter the washing liquid to remove impurities, and then dry it by rotary evaporation to obtain a white powder, which is lithium carbonate crystals.

[0045] Comparative Example 1

[0046] The method for recovering lithium carbonate and phosphate from waste lithium iron manganese phosphate powder comprises the following steps:

[0047] S1. Take 100g of the recovered lithium manganese iron phosphate powder material, place it in a rotary kiln, heat it to 350°C, and continue to pass air-gas composed of carbon dioxide and water vapor (volume ratio: 80-10-10), roast for 3 hours, cool, and obtain a mixture powder; after testing, the mixture powder is a composite of lithium carbonate and phosphate;

[0048] S2. The mixture powder is washed with hot water at 60°C, and the precipitate after washing is a gray-green powder, which is phosphate, and the washing liquid is collected;

[0049] S3. Filter the washing liquid to remove impurities, and then dry it by rotary evaporation to obtain a white powder, which is lithium carbonate crystals.

[0050] Test example

[0051] The lithium carbonate and phosphate recovered in Examples 1 and 2 and Comparative Example 1 were tested, and the specific results are shown in Table 1.

[0052] Table 1

[0053]

[0054] Note: The content of lithium carbonate is determined by potentiometric titration and ICP; the element content of phosphate is determined by ICP-OES.

[0055] From the results in Table 1, it can be seen that the purity of the lithium carbonate and phosphate recovered in Examples 1-5 reached more than 99.3%, and the percentage of Li element reached more than 18.64%, which is close to the percentage of Li element in lithium carbonate, and the recovered lithium carbonate only contains trace amounts of Fe, Mn and P elements. In Comparative Example 1, the volume ratio of air-carbon dioxide and water vapor was adjusted, the percentage of Li element was 18.21%, and the content of Fe, Mn and P elements increased significantly. It can be seen that the purity of the recovered lithium carbonate was significantly reduced, only 96.9%. The purity of the phosphate recovered in Examples 1-5 reached more than 99.3%, and the Li element content was low; the Li element content of the phosphate recovered in Comparative Example 1 increased, resulting in a decrease in the purity of the phosphate, but the percentage of Fe, Mn and P elements in the phosphate did not change significantly. It can be seen from the data in Table 1 that the volume ratio of air-carbon dioxide and water vapor has a significant effect on the separation of lithium and manganese iron phosphorus elements.

[0056] Take 112.6g of lithium carbonate recovered from Examples 1, 2 and Comparative Example 1, mix with 500g of phosphate and 50g of glucose, add 5L of water, wet grind, spray into powder, sinter at 700°C for 8 hours in a nitrogen atmosphere to obtain a positive electrode material, and test the positive electrode material. The positive electrode material of each group is used as a positive electrode active material, and the positive electrode active material: SP (superconducting carbon black): PVDF (polyvinylidene fluoride) is homogenized at a mass ratio of 90:5:5, and coated on a 20μm thick aluminum foil to make a positive electrode sheet with a surface density of 8mg / cm 2 , and then through drying, rolling, die cutting, punching into positive electrode sheet B; positive electrode sheet B, separator and lithium sheet were assembled into button battery for testing in the glove box. The button battery was charged and discharged in the voltage range of 2.0 to 4.3V, and the test results are shown in Table 2.

[0057] Table 2

[0058] Group 0.1C gram capacity mAh / g First effect% Example 1 149.3 95.3 Example 2 150.1 94.9 Comparative Example 1 143.2 92.1

[0059] From the results in Table 2, it can be seen that the positive electrode material prepared by using the lithium carbonate and phosphate recovered in Examples 1 and 2 of the present invention has excellent battery performance. The electrode has a gram capacity of more than 149.3 mAh / g at 0.1C, and the first efficiency reaches more than 94.9%. The lithium carbonate and phosphate recovered in Comparative Example 1 have lower purity than those in Examples 1 and 2, so the battery performance of the prepared positive electrode material is significantly lower than that of Examples 1 and 2.

[0060] Finally, it should be noted that the above-mentioned embodiments only express several implementation methods of the present invention and are not intended to limit the invention. For those skilled in the art, any modification, equivalent replacement, improvement, etc. made without departing from the concept of the present invention should be included in the protection scope of the invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for recovering lithium carbonate and phosphate from waste lithium iron manganese phosphate powder, characterized in that: The following steps are involved: S1. The waste lithium iron manganese phosphate powder is sintered in an air-carbon dioxide-water vapor atmosphere to remove the carbon layer and cool to obtain a mixture powder; S2. The mixture powder is washed with hot water, and the precipitate after washing is a gray-green powder, which is a phosphate, and the washing liquid is collected; S3. The washing liquid was filtered to remove impurities, and dried by rotary evaporation to obtain a white powder, which was lithium carbonate crystals; Wherein, the volume ratio of each component in the air-carbon dioxide-water vapor atmosphere in step S1 is (60-80):20:(10-20); In step S1, the sintering temperature is 300-450°C and the sintering time is 3-6 hours; The temperature of the hot water in step S2 is 50-100°C.

2. The method for recovering lithium carbonate and phosphate according to claim 1, characterized in that: The phosphate structure obtained in step S2 is generally Mn y Fe (1-y) PO4.

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