Method for recycling positive plate of lithium-ion battery

Abstract

A method for recycling a lithium iron phosphate positive plate with low energy consumption and low Al content, including: crushing a lithium iron phosphate positive plate to be recycled into a granular material with a particle size of 1-15 mm by using a crusher; heating the granular material obtained in step (1) to 350-500° C. in an atmosphere furnace in an inert atmosphere; and keeping the granular material at 350-500° C. for 0.5-2 h followed by cooling to a preset temperature to obtain a calcined product; grinding the calcined product obtained in step (2) by using a grinder to obtain a ground product with D50 larger than or equal to 50 μm; and classifying the ground product obtained in step (3) by using an air classifier to remove Al simple substance to obtain a recovered positive material with an Al content below 200 ppm.

Claims

1. A method for recycling a lithium iron phosphate positive plate, comprising; (1) crushing a lithium iron phosphate positive plate to be recycled into a granular material with a particle size of 1-15 mm by using a crusher; (2) heating the granular material obtained in step (1) to 350-500° C. in an atmosphere furnace in an inert atmosphere; and keeping the granular material at 350-500° C. for 0.5-2 h followed by cooling to a preset temperature to obtain a calcined product; (3) grinding the calcined product obtained in step (2) by using a grinder to obtain a ground product with D50 larger than or equal to 50 μm; and (4) classifying the ground product obtained in step (3) by using an air classifier to remove Al simple substance to obtain a recovered positive material; wherein in step (1), a part of an interior of the crusher contacting with the lithium iron phosphate positive plate to be recycled is coated with tungsten carbide; and in step (4), an interior of the air classifier is coated with tungsten carbide or ceramic lining.

2. The method of claim 1, wherein in step (4), an Al content of the recovered positive material is less than 200 ppm.

3. The method of claim 1, wherein in step (1), the particle size of the granular material is 5-10 mm.

4. The method of claim 1, wherein in step (3), the D50 of the ground product is 50-80 μm.

5. The method of claim 1, wherein in step (2), an oxygen content in the atmosphere furnace is less than 1 ppm.

6. The method of claim 1, wherein in step (2), the preset temperature is less than or equal to 100° C.

7. The method of claim 5, wherein the inert atmosphere is nitrogen, argon, helium or a combination thereof.

8. The method of claim 5, wherein the atmosphere furnace is a roller furnace, a rotary furnace or a push-type slab furnace.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a flow chart of a method of recycling positive plates according to an embodiment of the present disclosure;

(2) FIGS. 2A-2B are physical pictures of the lithium iron phosphate positive plates, where 2A: before the recycling process; and 2B: after the recycling process;

(3) FIG. 3 shows effect of calcination temperature and time on Al content;

(4) FIG. 4 shows effect of secondary grinding on Al content under different calcination temperatures and times; and

(5) FIG. 5 illustrates comparison of positive materials with different Al impurity contents in terms of cell cycle performance.

DETAILED DESCRIPTION OF EMBODIMENTS

(6) To make the object, technical solutions, and beneficial effects clearer, the disclosure will be described in detail below with reference to accompanying drawings and embodiments.

(7) It should be noted that the drawings only depict the structure and/or processing steps closely related to the solutions of the present disclosure, and do not show the irrelevant details to avoid obscuring the present disclosure.

(8) Furthermore, it should also be noted that the terms “compromise”, “include” or any other variants are intended to indicate non-exclusive inclusion so that the processes, methods, items, or equipment comprising a series of elements not only include the listed elements but also include other elements that are not displayed specifically, or include the inherent elements for the above-mentioned processes, methods, items or equipment.

(9) Referring to FIG. 1, this disclosure provides a method for recycling a lithium iron phosphate positive plate, which is specifically described as follows.

(10) (1) Primary Crushing

(11) A lithium iron phosphate positive plate to be recycled is crushed into a granular material with a particle size of 1-15 mm, preferably 5-10 mm, by using a crusher. In this case, the calcination can be accelerated, and the granular material has a greater permeability, which facilitates rendering the calcining process more thorough, resulting in a reduced calcination temperature and shortened calcination time. In the traditional pyrometallurgical process, it is less likely to crush the electrode plate into small particle size before the calcination considering that the Al foil will also be crushed at the same time, and the separation will become more difficult.

(12) In an embodiment, the above-mentioned positive plate to be recycled is a positive plate of a lithium iron phosphate battery.

(13) In an embodiment, a part of an interior of the crusher contacting with the above-mentioned positive plate to be recycled is coated with tungsten carbide.

(14) (S2) Calcination

(15) The granular material obtained in step (1) is heated to 350-500° C. in an atmosphere furnace under an inert atmosphere, kept at 350-500° C. for 0.5-2 h and then cooled to a preset temperature to obtain a calcined product.

(16) In an embodiment, an oxygen content in the above-mentioned atmosphere furnace is less than 1 ppm. The oxygen content should be controlled strictly to prevent aluminum from oxidizing, avoiding an increase in Al content in the recovered material.

(17) In an embodiment, the preset temperature is less than or equal to 100° C. If the preset temperature is too high, the crystal structure of the positive active material may be damaged due to the rapid cooling, and the positive active material may be also prone to oxidation after exposure to oxygen.

(18) In an embodiment, the inert atmosphere is nitrogen, argon, helium or a combination thereof. The above-mentioned atmosphere furnace is a roller furnace, a rotary furnace, or a push-type slab furnace.

(19) During the calcination process at 350-500° C., the polymer in the positive plate, such as binders, are oxidized and decomposed, so that the positive active substance can be separated from an aluminum foil. The particle size of the granular material is moderate, which facilitates lowering the calcination temperature and shortening the calcination time, allowing for lower energy consumption.

(20) (3) Secondary Grinding

(21) The calcined material obtained in step (2) is ground by using a grinder to obtain a ground material with D50 more than or equal to 50 μm.

(22) In an embodiment, the D50 of the ground material is 50-80 μm. It has been found that the active substance may coat the aluminum foil during the calcination process. In view of this, the calcined material is further ground to mechanically separate the active materials from the Al foil. By contrast, in order to facilitate the separation of aluminum foil and active materials, it is less likely to subject the calcined product to another grinding treatment in the prior art.

(23) (4) Removal of Al by Classification

(24) The ground material obtained in step (3) is subjected to classification by using an air classifier to remove the Al simple substance to obtain a recycled positive material. With the help of the air classifier, the active material can be efficiently separated from the Al foil according to their differences in particle size and density.

(25) In an embodiment, an interior of the air classifier is coated with tungsten carbide or ceramic lining.

(26) Based on the above-mentioned processes, the method provided herein can control the Al content of the recovered positive material to be less than 200 ppm, so as to meet the related requirements of the positive material. In addition, this application has low energy consumption and green and efficient process, and is thus suitable for industrial application.

Example 1

(27) Provided herein was a method for recycling a lithium iron phosphate positive plate with low energy consumption and low Al content, which was specifically described as follows.

(28) (S1) A lithium iron phosphate positive plate to be recycled was crushed into a granular material with a particle size of about 5-10 mm by using a grinder.

(29) (S2) The granular material was heated to 450° C. under N.sub.2 atmosphere in a roller furnace, kept at 450° C. for 1 h and cooled to 95° C. to obtain a calcined material, where the temperature-rising process lasted for 2 h.

(30) (S3) The calcined material was ground to obtain a ground product with D50 more than or equal to 50 μm by using a grinder.

(31) (S4) The ground product was classified by using an air classifier to remove the Al simple substance to obtain a desired lithium iron phosphate positive material, which was detected by inductively coupled plasma (ICP) to have an Al content of 176 ppm.

(32) Referring to FIGS. 2A-2B, it can be seen that the lithium iron phosphate positive material was successfully separated from the Al foil.

Examples 2-6 and Comparative Examples 1-7

(33) The methods provided in Examples 2-6 and Comparative Examples 1-7 were different from the method in Example 1 in the calcination temperature and time (listed in Table 1), and further with respect to the Comparative Examples 1˜4 and 6, the step (S3) was absent.

(34) TABLE-US-00001 TABLE 1 Preparation conditions and Al content of Examples 1-6 and Comparative examples 1-7 Samples Temperature (° C.) Time (h) Al content/ppm Example 1 450 1 176 Comparative 450 1 248.7 Example 1 Example 2 350 1 195.93 Comparative 350 1 226.3 Example 2 Example 3 400 1 183 Comparative 400 1 208.4 Example 3 Example 4 400 0.5 160.8 Example 5 500 1 190.77 Comparative 500 1 283.2 Example 4 Example 6 500 2 186.49 Comparative 500 4 217.7 Example 5 Comparative 550 1 346.7 Example 6 Comparative 650 2 489.2 Example 7

(35) TABLE-US-00002 TABLE 2 Comparison of internal resistance of cells with different Al contents Before formation After capacity grading Internal Internal Capac- Voltage/ resistance/ Voltage/ resistance/ ity/ Groups V mΩ V mΩ Ah Commercially- 0.1320 26.17 3.3310 29.27 1.15 available positive material Positive material 0.0851 26.24 3.3302 35.23 1.15 containing 400 ppm of Al Positive material 0.0779 28.00 3.3346 41.26 1.15 containing 1000 ppm of Al

(36) As shown in Table 1 and FIGS. 3-4, when the calcination temperature in step (S2) was higher than 500° C., or the holding time in step (S2) was more than 2 h, the Al content in the recovered product exceeded 200 ppm, and the Al content increased with the rise of the calcination temperature. In addition, with regard to the comparative examples without the secondary grinding process, the Al content was increased significantly (more than 200 ppm). These results can be explained by that the calcined material was ground into a particle size of 50-80 μm, which can mechanically separate the active materials from the Al-containing impurities coated therein at a certain extent, and then with the help of an air classifier, the active materials were further separated from the Al foil according to their differences in particle size and density. Through the steps of primary crushing, calcination, secondary grinding and air classification, the method provided herein was capable of separating the positive active material from the aluminum foil by heating merely at 350-500° C. for 0.5-2 h, which can significantly reduce the energy consumption.

(37) It can be seen from Table 2 and FIG. 5 that with the increase of Al content in the positive materials, the voltage dropped and the internal resistance increased before the cell formation, while the internal resistance after the capacity grading increased significantly. As a consequence, the Al content in the positive material recovered by the method provided herein was below 200 ppm, which can improve the electrochemical performance of the positive materials.

Examples 7˜9 and Comparative Example 8

(38) The methods provided in Examples 7-9 and Comparative Example 8 were different from the method in Example 1 merely in the particle size of the crushed material and the D50 of the ground material (as shown in Table 3).

(39) TABLE-US-00003 TABLE 3 Preparation conditions and Al content of Examples 7~9 and Comparative Examples 8 Particle size of D50 of the the crushed ground material Samples material (mm) (μm) Al content/ppm Example 7 1-5 50-80 196 Example 8 10-15 50-80 174 Example 9  5-10  80-100 207 Comparative  5-10 30-50 234 example 8

(40) As shown in Table 3, when the particle size of the crushed material obtained in step (S1) was in a range of 1-15 mm, if the D50 was more than 80 μm or less than 50 μm, the Al content of the obtained product would exceed 200 ppm. Only when the particle size of the crushed material in step (S1) was 1-15 mm and the D50 was 50-80 μm, could the Al content of the recovered products be controlled below 200 ppm. Therefore, in the primary crushing process, the positive plate was crushed into a particle size of 1-15 mm, which is conducive to accelerating the calcination process and rendering the calcining process more thorough, leading to a reduced calcining temperature and shortened calcining time. Then the calcined material was ground into a particle size of 50-80 μm, such that the active materials can be efficiently separated from the Al foil by using an air classifier according to their differences in particle size and density.

(41) The positive plates are first broken into a granular material with a particle size of 1-15 mm, which facilitates accelerating the calcination and make the calcination process more thorough, enabling the calcination to be carried out under a reduced temperature for a shortened period of time. The calcination is performed at 350-500° C. for 0.5-2 h, during which the organic materials such as binders in the positive plates are oxidized and decomposed, so that the positive active substances can be separated from the Al foil. The particle sizes of the crushed material are moderate so that the calcining temperature and time can be reduced significantly compared with the prior art, which can efficiently decrease the energy consumption. The subsequent grinding process of the calcined material can mechanically separate the active materials from the Al-containing impurities therein at a certain extent to obtain the ground material with a D50 of 50-80 μm. Then with the help of an air classifier, the active materials can be efficiently separated from the Al foil according to their differences in particle size and density. Based on the above-mentioned processes, the method provided herein can control the Al content of the recovered positive material to be less than 200 ppm, so as to meet the related requirements of the positive material. In addition, this application has low energy consumption and green and efficient process, and is thus suitable for industrial application.

(42) Described above are merely preferred embodiments of this application, which are not intended to limit the application. It should be understood that modifications and replacements made by those skilled in the art without departing from the spirit of the application should fall within the scope of the application.