Method for recycling lithium iron phosphate batteries

Abstract

To provide a method of recycling a lithium iron phosphate battery.SOLUTION: The method comprises the following steps of: i) providing a first powder comprising lithium iron phosphate battery waste; ii) removing copper and aluminum from the first powder to obtain a second powder; iii) dissolving the second powder obtained in the step ii) in nitric acid to obtain a solution; iv) adding carbonic acid in the solution obtained in the step iii) and separating a lithium carbonate precipitate; and v) removing a remaining solution of the step iv) by vacuum distillation to obtain a ferric nitrate crystal.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for recycling lithium iron phosphate batteries, and particularly to a method for recycling valuable metals such as copper, aluminum, lithium, and iron in lithium iron phosphate battery waste.

Background Art

[0002] Lithium iron phosphate (LiFePO 4 , also known as lithium iron phosphate and lithium iron phosphate, and abbreviated as LFP) is a cathode material for lithium-ion batteries. A battery using lithium iron phosphate as the cathode material and carbon as the anode material is called a lithium iron phosphate battery or a lithium-ion battery. The characteristics of such batteries are that they do not contain precious metals such as cobalt. Furthermore, phosphorus and iron are present in large quantities on the earth, their prices are low, and they do not have a shortage problem. Lithium iron phosphate batteries have a working voltage of 3.3V, a battery capacity of 170mAh / g, high discharge power, fast charging characteristics, a long cycle life, and high stability at high temperatures.

[0003] Lithium iron phosphate batteries are widely used in power batteries for electric vehicles because of their advantages of low cost (without cobalt) and high safety. As the usage increases, a large amount of waste is naturally generated. In order to achieve the SDGs (Sustainable Development Goals) and avoid damaging the environment by mining raw ores, international standards for using recycled materials in battery products have begun to be formulated. Currently, common methods for recycling lithium iron phosphate battery waste include the combustion method and the wet method. The combustion method involves burning the waste at a high temperature of 1000°C - 2000°C to melt it into a metal alloy, and then separating and recycling various metals. The combustion method has an overall recycling rate of only 32% - 50%, a complicated process, and consumes energy. In addition, a large amount of carbon dioxide or toxic gases can be generated during the process. The wet method decomposes the cathode material of the lithium iron phosphate battery, dissolves lithium ions and iron ions from the electrode using solvents such as phosphoric acid, hydrochloric acid, and hydrogen peroxide, and then recycles them by precipitation. The wet method has a high recycling rate (<70%), but requires additional steps to decompose the battery waste. The additional steps require additional labor and are very time-consuming. Furthermore, in the wet method, a large amount of solvents such as phosphoric acid, hydrochloric acid, and hydrogen peroxide can be used. During the dissolution process, a large amount of toxic and irritating gases can be generated, which is not environmentally friendly.

[0004] Therefore, there is a need to provide a method for recycling lithium iron phosphate batteries that is easy to operate, safe, environmentally friendly, and has a high recycling rate.

Brief Description of the Drawings

[0005]

Figure 1

Modes for Carrying Out the Invention

[0006] According to an embodiment of the present invention, a method for recycling a lithium iron phosphate battery is provided. The recycling method includes: i) providing a powder containing lithium iron phosphate battery waste; ii) removing copper and aluminum from the powder; iii) dissolving the powder of step ii) in nitric acid to obtain a solution; iv) adding carbonic acid to the solution of step iii) to separate a precipitate of lithium carbonate; and v) removing the remaining solution of step iv) by vacuum distillation to obtain ferric nitrate crystals.

[0007] In one embodiment, the copper is removed from the powder of step ii) by specific gravity separation in step ii). In one embodiment, the aluminum is removed from the powder of step ii) by a Sortinger magnetic separator, and the aluminum is removed after the copper is removed in step ii).

[0008] In one embodiment, the concentration of the nitric acid added in step iii) is between 1M and 10M, the liquid-solid ratio (mL:g) of the nitric acid to the second powder is between 1:1 and 5:1, and in step iii), the dissolution temperature is between 15°C and 90°C.

[0009] In one embodiment, the extraction rates of lithium and iron in the powder of step iii) are greater than 99% by weight. In one embodiment, the recycling method further includes step iv-1) which is a step of reducing the precipitate of lithium carbonate to metallic lithium.

[0010] In one embodiment, step iv) is performed at a temperature between 50°C and 80°C. In one embodiment, the lithium recycling rate of step iv) is 94% by weight or more. In one embodiment, the recycling method further includes step v-1) which is a step of reducing the ferric nitrate crystals to metallic iron.

[0011] In one embodiment, the vacuum distillation in step v) is carried out at a degree of vacuum of about -93.33 kPa to about -99.99 kPa (-700 Torr to -750 Torr) and at a temperature of 50°C to 90°C.

[0012] In one embodiment, the iron recycling rate in step v) is 99% by weight or more. In one embodiment, the distillate obtained in step v) is an aqueous nitric acid solution. In one embodiment, the powder in step i) is obtained by at least one of discharging, crushing, and pulverizing the lithium iron phosphate battery waste.

[0013] For a clearer and more understandable description of the above and other aspects of the present invention, the following specific embodiments are described in detail in conjunction with the accompanying drawings. Please refer to FIG. 1 showing a flowchart of a method for recycling a lithium iron phosphate battery according to an embodiment of the present invention. The method for recycling a lithium iron phosphate battery of the present invention may include five steps: specific gravity separation (S01), sorting magnetic separator (S02), acid dissolution (S03), metal lithium precipitation (S04), and metal iron crystallization (S05). After the lithium iron phosphate battery waste is treated by the recycling method of the present invention, valuable metals (such as copper, aluminum, lithium, iron, etc.) contained therein can be effectively recovered / recycled. A plurality of examples are described in detail below.

[0014] Lithium iron phosphate battery waste The lithium iron phosphate battery waste of this embodiment is in powder form, and the source of the powder is a private recycling plant. The private recycling plant collects the lithium iron phosphate battery waste, and after preliminary screening and the discharging process, the battery waste can be deformed into powder by physical destruction methods such as crushing, pulverization, and mincing (in some embodiments, the screening process is after the destruction process). There is a possibility of omission in the screening process, and since the recycling plant generally does not disassemble the battery meticulously, the collected waste powder may contain impurities such as electrolytes, anode materials, or other types of batteries.

[0015] Subsequently, in order to facilitate the calculation of the recycling rate of each metal, the composition analysis of the metal (valuable metal) to be recovered / recycled in the powder is first performed. The analysis method is the known aqua regia decomposition method. Such a method treats the sample to be analyzed (i.e., the waste powder) with aqua regia (a 3:1 mixture of hydrochloric acid and nitric acid), heats this sample solution, and decomposes it in a microwave digestion furnace. An inductively coupled plasma mass spectrometer (ICP-MS) is used to measure the measured amounts of elements (valuable metals) in the decomposed sample solution. As long as it is possible to quantify the content of the metal to be recovered / recycled in the powder, other composition analysis methods can also be used. The valuable metal content of the lithium iron phosphate battery waste powder of this embodiment is shown in Table 1 below.

[0016] Table 1 Valuable Metal Content of Lithium Iron Phosphate Battery Waste Powder

[0017]

Table 1

[0018] As can be understood from Table 1, the content of valuable metals (lithium, iron, copper, and aluminum) only accounts for about 32.7% in the lithium iron phosphate battery waste powder of this embodiment. The rest of the waste powder is impurities.

[0019] Copper removal Next, as shown in step S01, the copper in the lithium iron phosphate battery waste powder is removed by specific gravity separation.

[0020] The density of lithium iron phosphate (LiFePO 4 ) is 1.5 g / cm 3 , the density of aluminum is 2.7 g / cm 3 , and the density of copper is 8.9 g / cm 3 . Since the densities of these three metals are very different, it is possible to effectively remove copper with the highest density by specific gravity separation. The remaining solid powder contains lithium iron phosphate and aluminum.

[0021] The specific gravity separation method used in this example is the vibration separation method. The powder can be placed on a table with an inclination angle of 3° - 5°, and separation can be carried out at a vibration frequency of 18 Hz - 22 Hz to obtain the powder after copper removal. The aqua regia decomposition method can be used again to measure the copper content in the remaining powder, and then the copper recycling rate can be calculated. The calculation formula for the copper recycling rate is [1 - ((copper content of the powder after copper removal) / (copper content of the lithium iron phosphate battery waste powder))] × 100%. The operating parameters of specific gravity separation and the copper recycling rate of this embodiment are shown in Table 2 below.

[0022] Table 2 Results of copper removal by specific gravity separation

[0023]

Table 2

[0024] As can be understood from Table 2, by the specific gravity separation method, it is possible to effectively remove copper with the highest density, and the recycling rate is higher than 99%. However, the present invention does not limit the copper removal method. In addition to the specific gravity separation method used in this embodiment, as long as the copper in the lithium iron phosphate battery waste powder can be effectively removed, other copper removal methods can also be used.

[0025] Demetallization of aluminum Next, as shown in step S02, aluminum in the lithium iron phosphate battery waste powder is removed by a Sortinger magnetic separator.

[0026] The conductivity of lithium iron phosphate is very low (about 10 -9 S / cm), while aluminum is a good conductor (with a conductivity of about 37.8×10 4 S / cm). Since conductive substances can move in a magnetic field, it is possible to effectively remove aluminum by a magnetic field, and the remaining solid powder is lithium iron phosphate.

[0027] In such an example, the powder after copper removal in step S01 is put into a Sortinger magnetic separator, and the conveying speed is controlled at 20 m / min - 100 m / min, and the rotation speed of the belt is controlled to be less than 2000 rpm. Next, the turbine output is adjusted to remove aluminum from the waste powder. The aluminum content in the remaining powder is measured again by the aqua regia decomposition method, and then the aluminum recycling rate is calculated. The calculation formula for the aluminum recycling rate is [1 - ((aluminum content in the powder after demetallization of aluminum) / (aluminum content in the lithium iron phosphate battery waste powder))] × 100%. The operating parameters of the Sortinger magnetic separator and the aluminum recycling rate in this embodiment are shown in Table 3 below.

[0028] Table 3 Results of demetallization of aluminum by Sortinger magnetic separator

[0029]

Table 3

[0030] As can be understood from Table 3, it is possible to effectively remove high-conductivity aluminum by a sorter magnetic separator, and the recycling rate is higher than 97%. However, the present invention does not limit the method of removing aluminum. In addition to the sorter magnetic separator method used in such embodiments, as long as it is possible to effectively remove aluminum in the lithium iron phosphate battery waste powder, other de-aluminum methods can also be used.

[0031] Also, since copper is a metal having high electrical conductivity, in such embodiments, copper needs to be removed before de-aluminum by a sorter magnetic separator. Acid dissolution Next, as shown in step S03, the lithium iron phosphate battery waste powder (from which copper and aluminum have been removed) is dissolved in nitric acid.

[0032] Using impregnation methods under various operating conditions, it is possible to effectively dissolve lithium iron phosphate in nitric acid to obtain an extract. The operating conditions for acid dissolution are shown in Table 4 below, where the calculation formula for the extraction rate of lithium / iron is ((lithium / iron content in the nitric acid extraction solution) / (lithium / iron content in the lithium iron phosphate waste powder))×100%.

[0033] Table 4 Operating conditions and results of acid dissolution of lithium iron phosphate batteries

[0034] [Table 4]

[0035] As can be understood from Table 4, lithium iron phosphate is easily soluble in nitric acid at different temperatures ranging from 15 °C to 90 °C, different concentrations ranging from 1 M to 10 M, and various liquid-solid ratios (mL:g) from 1:1 to 5:1, and has a high extraction rate (>99%). For example, under condition C, it is shown that high extraction rates of lithium and iron can be obtained even at room temperature, but in that case, it takes a long time. Under condition D, a better balance between the heating temperature and the extraction time is achieved, and high extraction rates of lithium and iron can also be obtained.

[0036] Lithium Recycling Next, as shown in step S04, carbonic acid is added to the extract of the acid dissolution step S03. Since carbonic acid can react with lithium ions to form a precipitate of solid lithium carbonate, ferrous ions can remain in the liquid-phase extract. The reaction formula for the precipitation of lithium carbonate is as follows.

[0037] 2Li + +Fe 3+ +2NO 3 - +H 2 CO 3 →Li 2 CO 3 ↓+Fe 3+ +2HNO 3 The results of the precipitation reaction are shown in Table 5. The calculation formula for the lithium recycling rate is [1 - ((lithium content in the extract after lithium carbonate precipitation) / (lithium content in the lithium iron phosphate battery waste powder))] × 100%.

[0038] Table 5 Results of Lithium Recycling by Precipitation Reaction

[0039]

Table 5

[0040] As shown in Table 5, the higher the temperature of the precipitation reaction, the more the reaction equilibrium shifts to the right, and it is possible to obtain a higher lithium recycling rate. Preferably, the temperature of the precipitation reaction in step S04 is between 50°C and 80°C, and the lithium recycling rate is 94% or more.

[0041] It is possible to filter the extract of step S04 to obtain a precipitate of lithium carbonate. It is possible to recycle the metallic lithium in the lithium carbonate by a reduction reaction. Recycling of Iron Finally, as shown in step S05, the remaining liquid-phase extract of step S04 is distilled under reduced pressure to remove the solvent and recycle ferric nitrate Fe(NO 3 ) 3 crystals are obtained. It is possible to remove the solvent in the extract by vacuum distillation, and it is possible to distill the excess nitrate ions to obtain an aqueous nitric acid solution (distillate), and this aqueous nitric acid solution can be reused. The remaining solid crystals are ferric nitrate. Refer to Table 6 for the operating parameters and results of the iron recycling by vacuum distillation. The formula for calculating the iron recycling rate is [1 - ((iron content in the distillate) / (iron content in the lithium iron phosphate battery waste powder))] × 100%.

[0042] Table 6 Results of Iron Recycling by Vacuum Distillation

[0043]

Table 6

[0044] The degree of vacuum represents the difference between the actual air pressure and 1 atmosphere (about 101.3 kPa (760 Torr)). As shown in Table 6, the lower the degree of vacuum (the lower the actual air pressure), the lower the required heating temperature. On the other hand, the higher the degree of vacuum, the closer the air pressure is to 1 atmosphere, and a higher heating temperature is required. Preferably, the degree of vacuum in the vacuum distillation step is between about -93.33 kPa and about -99.99 kPa (-700 Torr to -750 Torr), and the heating temperature is between 50°C and 90°C.

[0045] In order to achieve the purpose of recycling, it is possible to further subject the ferric nitrate crystals obtained in step S05 to a reduction reaction to obtain metallic iron. In the method for recycling a lithium iron phosphate battery according to an embodiment of the present invention, two recycling methods, a dry method and a wet method, are combined. The dry method is as shown in steps S01 (specific gravity separation) and S02 (Sortinger magnetic separator) in FIG. 1, by which copper and aluminum are physically removed. The wet method is as shown in step S03 in FIG. 1, in which the lithium iron phosphate battery waste is immersed in an acidic solution and then lithium iron phosphate is dissolved. Table 7 shows a comparison between the acid dissolution step of the present invention and a conventional recycling method.

[0046] Table 7 Comparison between the recycling method according to an embodiment of the present invention and the conventional wet method

[0047]

Table 7

[0048] As shown in Table 7, compared with the conventional wet method, in the acid dissolution step S03 of the present invention, impurities such as copper and aluminum are removed earlier, so it can be carried out at a lower temperature. Furthermore, this step has a shorter recycling time, a higher extraction rate, does not generate waste water and irritating / toxic gases, and is more environmentally friendly.

[0049] The method for recycling a lithium iron phosphate battery according to an embodiment of the present invention can effectively recover lithium iron phosphate battery waste. Since it is not necessary to disassemble the positive electrode of the battery, the process is more suitable for mass production. Such a method has a high recycling rate for valuable metals (copper, aluminum, lithium, and iron), and the average recycling rate is over 94%. This recycling rate is better than that of the conventional wet method. In addition, in such a recycling method, a physical method can be used to first remove copper and aluminum, and it is possible to greatly reduce the amount of acid used in the impregnation method. The method is a recycling method with relatively low toxicity, low energy consumption, and low carbon emissions, and is suitable for the current environmental protection requirements and the trend of carbon reduction. Moreover, the nitric acid used in the impregnation method can be recycled in a subsequent vacuum distillation process, thereby reducing wastewater and achieving sustainable production.

[0050] The present invention is disclosed above using embodiments, but they are not intended to limit the present invention. After referring to the above teachings, those skilled in the art can appropriately modify the content of the above embodiments and still be able to achieve the effects claimed in this application. Therefore, the protection scope of the present invention is determined according to the appended claims.

Claims

1. A method for recycling a lithium iron phosphate battery, comprising: i) providing a first powder containing lithium iron phosphate battery waste; ii) removing copper and aluminum from the first powder to obtain a second powder, wherein the aluminum is removed from the first powder by a sorting magnetic separator, and the aluminum is removed after the copper is removed; iii) dissolving the second powder in nitric acid to obtain a solution; iv) adding carbonic acid to the solution in step iii) to separate a precipitate of lithium carbonate; v) removing the remaining solution in step iv) by vacuum distillation to obtain ferric nitrate crystals.

2. The recycling method according to claim 1, wherein the copper is removed from the first powder by specific gravity separation in step ii).

3. In step iii), the concentration of the nitric acid is between 1 M and 10 M, the liquid-solid ratio (mL:g) of the nitric acid to the second powder is between 1:1 and 5:1, and in step iii), the dissolution temperature is between 15°C and 90°C. The recycling method according to claim 1.

4. The extraction rate of lithium and iron from the second powder in step iii) is greater than 99% by weight. The recycling method according to claim 3.

5. The recycling method according to claim 1, further comprising step iv-1): reducing the precipitate of lithium carbonate to metallic lithium.

6. Step iv) is performed at a temperature between 50°C and 80°C. The recycling method according to claim 1.

7. The recycling rate of lithium in step iv) is 94% by weight or more. The recycling method according to claim 6.

8. The recycling method according to claim 1, further comprising step v-1): reducing the ferric nitrate crystals to metallic iron.

9. The vacuum distillation in step v) is performed at a vacuum degree of about -93.33 kPa to about -99.99 kPa (-700 Torr to -750 Torr) and a temperature of 50°C to 90°C. The recycling method according to claim 1.

10. The iron recycling rate in step v) is 99% by weight or more. The recycling method according to claim 9.

11. The distillate obtained in step v) is an aqueous nitric acid solution. The recycling method according to claim 1.

12. The recycling method according to claim 1, wherein the first powder is obtained by at least one of discharging, crushing, and pulverizing the lithium iron phosphate battery waste.

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