Method for recycling waste lithium-ion secondary battery and recycled lithium iron phosphate powder obtained therefrom

Abstract

To provide a method for recovering lithium iron phosphate powder that is a positive electrode material, in an economical and eco-friendly manner from a waste lithium-ion secondary battery using lithium iron phosphate as a positive electrode material, and recycled lithium iron phosphate powder obtainable by the method.SOLUTION: A method for recycling a waste lithium-ion secondary battery includes the steps of: loading an object to be heat-treated into a heat-treatment furnace, the object being at least a part of a waste lithium-ion secondary battery in which lithium iron phosphate powder is a positive electrode material, and including the positive electrode material; increasing the temperature inside the heat-treatment furnace to a range of 200-400°C; maintaining the increased temperature to heat treat the object to be heat-treated; and discharging first powder produced after the completion of the heat treatment. The first powder contains recycled lithium iron phosphate powder.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a recycled lithium iron phosphate powder obtained by recycling used lithium ion batteries whose positive electrode material is lithium iron phosphate, and a recycling method thereof, and more particularly to a lithium iron phosphate powder obtained by heat treating used lithium ion secondary batteries at low temperature, and a recycling method thereof. [Background technology]

[0002] As the automotive industry shifts from internal combustion engine vehicles to electric vehicles, Europe and China, the growth centers of global electric vehicles and secondary batteries, are promoting the expansion of electric vehicles and securing their competitiveness through carbon dioxide regulations and eco-car roadmaps. As a result, rapid growth is expected in the global electric vehicle market.

[0003] Electric vehicle batteries are typically discarded after 5 to 10 years of use, so the waste battery market is expected to take off. The amount of waste electric vehicle batteries generated globally is expected to reach approximately 1.6 million tons by 2030, and many countries, particularly in Europe, are making large-scale investments in developing processes to recover valuable metals from waste batteries.

[0004] Unlike reuse, the waste battery recycling industry recovers valuable metals from waste batteries and recycles them as raw materials, which can solve environmental problems and secure a stable supply of valuable resources at the same time.

[0005] Recycling of waste batteries generally involves discharging, dismantling, and crushing the batteries, followed by extracting valuable metals through hydrometallurgy or pyrometallurgy processes. However, pyrometallurgy, which is suitable for large-volume processing and has a high recovery rate, is attracting attention.

[0006] In dry smelting, the powder obtained by crushing is heated at high temperatures to burn off the organic compounds and polymer components contained in the crushed powder, and then the powder is crushed again and the valuable metals are extracted by wet processing using a strong acid.

[0007] Such a pyrometallurgical process requires a lot of time and equipment for discharge and pulverization, and subsequent complicated processes make it less economical. The resulting product discharged after high temperature heating contains a large amount of impurities, which reduces the extraction rate of valuable components from the whole powder. Furthermore, since the product exists in agglomerated form, further pulverization and the use of strong acids are unavoidable in order to extract valuable components from it, which poses environmental problems.

[0008] In particular, the use of lithium ion secondary batteries in which lithium iron phosphate is used as a positive electrode material has recently increased, making it an important issue to recover lithium iron phosphate powder from waste lithium ion secondary batteries. Summary of the Invention [Problem to be solved by the invention]

[0009] An object of the present invention is to provide a method for economically and environmentally friendly recovery of lithium iron phosphate powder, which is a positive electrode material, from used lithium ion secondary batteries that use lithium iron phosphate as a positive electrode material, and to provide recycled lithium iron phosphate powder obtained thereby. [Means for solving the problem]

[0010] To achieve the above-mentioned object, the method for recycling used lithium ion secondary batteries according to the present invention includes the steps of: (a) loading a heat treatment object, which is at least a part of a cathode material of a used lithium ion secondary battery, in a heat treatment furnace, the cathode material being lithium iron phosphate powder; (b) increasing the internal temperature of the heat treatment furnace to a range of 200 to 400°C; (c) maintaining the increased temperature to heat-treat the heat treatment object; and (d) discharging a first powder produced after the heat treatment is completed, wherein the first powder includes recycled lithium iron phosphate powder.

[0011] In addition, in the method for recycling used lithium ion secondary batteries according to one embodiment of the present invention, the first powder does not contain any organic component and has a fluorine content of 2% by weight or less.

[0012] In addition, in the method for recycling used lithium ion secondary batteries according to an embodiment of the present invention, the first powder does not contain organic components and fluorine.

[0013] In addition, in the recycling method for used lithium ion secondary batteries according to an embodiment of the present invention, gas generated from inside the heat treatment furnace is forcibly exhausted in the steps (b) and (c).

[0014] In addition, in the recycling method for used lithium ion secondary batteries according to an embodiment of the present invention, in the steps (b) and (c), the inside of the heat treatment furnace is made into a negative pressure state and the forced evacuation is performed.

[0015] In the method for recycling used lithium ion secondary batteries according to one embodiment of the present invention, the forced exhaust is performed through a fan disposed in the heat treatment furnace in the steps (b) and (c).

[0016] In the method for recycling used lithium ion secondary batteries according to an embodiment of the present invention, the forced exhaust through the fan may be performed intermittently.

[0017] In the method for recycling used lithium ion secondary batteries according to an embodiment of the present invention, the object to be heat-treated in step (a) may be a cathode material recovered by disassembling the used lithium ion batteries.

[0018] In the method for recycling used lithium ion secondary batteries according to an embodiment of the present invention, the recycled lithium iron phosphate powder contained in the first powder may be a powder complexed with a conductive agent.

[0019] The method for recycling used lithium ion secondary batteries according to an embodiment of the present invention may further include a step of mixing the recycled lithium iron phosphate powder with a lithium compound and heat treating the mixture at a temperature ranging from 600 to 800°C.

[0020] Meanwhile, the present invention can provide recycled lithium iron phosphate powder recovered through the above-described method for recycling used lithium ion secondary batteries.

[0021] In addition, the present invention can provide a lithium ion secondary battery using recycled lithium iron phosphate powder recovered through the above-described method for recycling used lithium ion secondary batteries. [Effects of the Invention]

[0022] The recycling method for used lithium ion secondary batteries according to the present invention is economical and environmentally friendly, so that it can increase the recycling rate of used lithium ion secondary batteries and solve environmental problems that may occur during recycling.

[0023] Furthermore, the recycled lithium iron phosphate powder obtained by the present invention can be used to manufacture highly economical lithium ion secondary batteries. [Brief explanation of the drawings]

[0024] [Figure 1] 1 shows an X-ray diffraction pattern of recycled lithium iron phosphate powder according to one embodiment of the present invention.

[0025] [Figure 2] 1 is a transmission electron microscope image of recycled lithium iron phosphate powder according to an embodiment of the present invention.

[0026] [Figure 3] 1 shows the results of Raman spectrum analysis of recycled lithium iron phosphate powder according to an embodiment of the present invention.

[0027] [Figure 4] 1 shows the results of XRF analysis of recycled lithium iron phosphate powder according to one embodiment of the present invention.

[0028] [Figure 5] 1 shows an image of the powder recovered after processing according to a comparative example and the results of XRF analysis.

[0029] [Figure 6] 1 shows a scanning electron microscope image of recycled lithium iron phosphate powder recovered according to an embodiment of the present invention and an EDX (Energy Dispersive X-ray spectroscopy) mapping result obtained through the image.

[0030] [Figure 7] 1 is a graph showing an evaluation of cycle characteristics of recycled lithium iron phosphate powder recovered according to an embodiment of the present invention. BEST MODE FOR CARRYING OUT THE INVENTION

[0031] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] The present invention will now be described in detail with reference to the accompanying drawings, so that those skilled in the art can easily understand the present invention. However, the present invention may be embodied in various different forms and is not limited to the embodiments described herein.

[0032] Throughout this specification, unless specifically stated to the contrary, the term "comprising" a part means that it may further include other elements, rather than excluding other elements.

[0033] As used herein, terms of degree such as "about," "substantially," and the like are used in the sense of a numerical value or close to a numerical value when manufacturing and material tolerances inherent in the referred meaning are given, and are used to facilitate understanding of the present application and to prevent unscrupulous infringers from unfairly exploiting the disclosure in which precise or absolute numerical values ​​are referred to. Furthermore, throughout the present specification, "the step of" or "the step of" does not mean "the step for."

[0034] Throughout this specification, the term "combinations thereof" contained in a Markush expression means a mixture or combination of one or more elements selected from the group of elements set forth in the Markush expression, and means including one or more elements selected from the group of elements.

[0035] Throughout this specification, the phrase "A and / or B" means "A or B, or A and B."

[0036] According to one aspect of the present invention, there is provided a method for recycling used lithium ion secondary batteries, the method including: (a) loading a heat treatment object, which is at least a portion of a used lithium ion secondary battery, including lithium iron phosphate powder as a cathode material, into a heat treatment furnace; (b) increasing the internal temperature of the heat treatment furnace to a range of 200 to 400°C; (c) maintaining the increased temperature to heat treat the heat treatment object; and (d) discharging a first powder produced after the heat treatment is completed, wherein the first powder includes recycled lithium iron phosphate powder.

[0037] The waste lithium ion secondary batteries to be recycled in the present invention are waste lithium ion secondary batteries that use lithium iron phosphate as a positive electrode material.

[0038] The waste lithium ion secondary batteries fed into the heat treatment furnace may be whole cells of waste lithium ion secondary batteries, or at least a portion containing such lithium iron phosphate. Also, they may be black mass, which is a powder made by disassembling and crushing waste lithium ion secondary batteries, or waste lithium ion secondary batteries that are discarded due to defects during the manufacturing process.

[0039] In addition, in one embodiment of the present invention, in order to effectively recover lithium iron phosphate, the waste lithium ion secondary battery may be disassembled to separate only the positive electrode, which is a composite of the current collector and the positive electrode material, and then the separated positive electrode may be placed inside a heat treatment furnace.

[0040] The conventional recycling process for used lithium-ion secondary batteries involves disassembling the batteries, pyrolyzing them at high temperatures to form agglomerates, and then pulverizing them. As a result, the agglomerates, including not only the cathode and anode materials to be recovered but also the cases and current collectors, contain many impurities, and are pulverized in a state where they are in agglomerated form, resulting in the cathode and anode materials not being maintained in their raw state but undergoing significant deformation.

[0041] In contrast, the recycling method according to the present invention removes the electrolyte through low-temperature heat treatment and decomposes the binder contained in the positive electrode, making it possible to easily separate the lithium iron phosphate powder, which is the positive electrode material, from the current collector.

[0042] The recycled lithium iron phosphate powder, which is the cathode material separated in this manner, can be recycled for the manufacture of lithium ion batteries either directly or after undergoing simple steps such as washing or pickling.

[0043] The heat treatment process carried out to recover recycled lithium iron phosphate powder in the present invention may be carried out in the range of 200 to 400°C, or may be in the range of 200 to 350°C, or 250 to 350°C. By heating the battery at a relatively low temperature, the binder, electrolyte, and other components contained in the battery are thermally decomposed and removed. In particular, the internal binder, electrolyte, and other components may generate heat and undergo thermal decomposition.

[0044] Compared to conventional recycling methods, the heat treatment is performed at a lower temperature, which reduces energy costs. In addition, the low-temperature heat treatment recovers the lithium iron phosphate powder, which is the cathode material, without damaging it, allowing the recovered powder to be recycled as is without additional post-processing, which requires a lot of time and money.

[0045] Meanwhile, in the above-mentioned steps (b) and (c), it is preferable to forcibly exhaust gases generated from inside the heat treatment furnace.

[0046] The key to discharging such gases is that the gases generated by the decomposition of binders, electrolytes, etc. during heat treatment contain fluorine. If such fluorine-containing gases remain in the heat treatment furnace, they will combine with the cathode material, anode material, etc. to form strongly bonded agglomerates. If the heat-treated powders combine to form agglomerates, they will be difficult to pulverize through post-treatment such as powder processing. Therefore, rapid discharge of fluorine-containing gases is an important issue. However, conventional high-temperature heat treatment inevitably produces a rapid generation of fluorine-containing gases, which causes the gases to remain in the heat treatment furnace for a long time, accelerating the agglomeration of the powder.

[0047] In contrast, the method for recycling used lithium ion secondary batteries according to the present invention controls the decomposition rate of binders and the like through low-temperature heat treatment, thereby suppressing the rapid generation of fluorine component gas and keeping the amount of generated gas at an appropriate level. At the same time, by forcibly venting the generated gas quickly, the time that the fluorine component-containing gas remains in the heat treatment furnace can be minimized, and the agglomeration of powder due to fluorine can be prevented.

[0048] Due to the forced exhaust during the heat treatment process, a negative pressure state may be maintained inside the heat treatment furnace, and gases generated when the binder, electrolyte, separator, etc. are decomposed as the waste lithium ion secondary batteries are heated in the heat treatment furnace can be discharged to the outside by maintaining the negative pressure state. To maintain the negative pressure state, the heat treatment furnace may have a gas exhaust port and a pump for maintaining the negative pressure may be connected to the exhaust port.

[0049] In addition, exhausting the atmosphere inside the heat treatment furnace can be performed through a fan disposed in the heat treatment furnace. The decomposition gas generated inside the heat treatment furnace can be continuously or intermittently exhausted through the fan. If the exhaust rate is too high, it may be difficult to increase and maintain the temperature inside the heat treatment furnace, so exhausting may be performed intermittently in conjunction with the internal temperature.

[0050] Therefore, maintaining a negative pressure inside the heat treatment furnace or exhausting the internal atmosphere through a fan can be controlled in conjunction with the temperature inside the heat treatment furnace.

[0051] Finally, by removing the internal organic matter and fluorine components, the lithium iron phosphate, which is the cathode material, can be recovered in powder form, eliminating the need for additional crushing processes, and the recovered lithium iron phosphate powder can be recycled directly into the production of new batteries.

[0052] The first powder recovered after heat treatment in this recycling method for used lithium-ion secondary batteries may contain recycled lithium iron phosphate powder but may be free of organic components and fluorine. Because impurities such as binders are completely removed through low-temperature heat treatment and forced evacuation, the recycled lithium iron phosphate powder is free of organic components and fluorine, making it easy to recover in powder form and immediately usable for manufacturing lithium-ion secondary batteries without any special reprocessing. Here, "free of fluorine" means that it cannot be detected by X-ray fluorescence analysis.

[0053] On the other hand, the first powder described above does not contain any organic components and may contain fluorine at a concentration of 2% by weight or less. Even if a small amount of fluorine is contained, once it is below a certain level, it can be recovered in powder form without the powder agglomerating.

[0054] In addition, the recycled lithium iron phosphate powder contained in the first powder discharged after the heat treatment process may be a powder complexed with the conductive agent contained in the positive electrode. Alternatively, the first powder may be pickled with an acid such as hydrochloric acid to remove the complexed conductive agent, thereby recovering a pure lithium iron phosphate powder.

[0055] However, the performance of recovered recycled lithium iron phosphate powder may deteriorate due to repeated recycling, such as a lack of lithium ions or partial structural instability. To restore the deteriorated performance to the original level, a post-heat treatment process may be added, in which the powder is mixed with a lithium compound. This post-heat treatment may be performed by mixing the recycled lithium iron phosphate powder recovered by a conventional solid-state process with a lithium compound such as lithium carbonate or lithium hydroxide, and then heat-treating the mixture at a high temperature (600-800°C).

[0056] <Example>

[0057] A used lithium ion secondary battery using a lithium iron phosphate positive electrode material was treated by the recycling method according to the present invention, and the first powder was collected.

[0058] Waste lithium-ion secondary batteries that had not been discharged were placed in a heat treatment furnace, and the internal temperature of the heat treatment furnace was adjusted to 250°C, where the batteries were heat treated. The temperature was increased for 6 hours and then maintained at the increased temperature for 12 hours. During the reaction, the internal atmosphere was exhausted using a fan, and the internal temperature was maintained within the range of 250±15°C in conjunction with a temperature sensor.

[0059] After the reaction was completed, the powdered material was collected to obtain the first powder, which was then added to water, ultrasonicated, and filtered to separate and collect the lithium iron phosphate powder.

[0060] Figure 1 shows the results of X-ray diffraction analysis of the recovered lithium iron phosphate powder. It can be seen that the diffraction peaks of lithium iron phosphate are strong, and at the same time, the diffraction peaks of crystalline carbon appear.

[0061] Figure 2 shows a transmission electron microscope image of the recovered lithium iron phosphate powder. It shows that the conductive carbon nanotubes and black smoke are in a composite state.

[0062] Figure 3 shows the results of Raman analysis of the lithium iron phosphate powder recovered after water washing. The powder shows no other organic peaks other than those of lithium iron phosphate and carbon, indicating that the organic matter has been completely removed.

[0063] FIG. 4 shows the results of XRF (X-ray fluorescence) analysis of the lithium iron phosphate powder recovered after the water washing process, and it was found that no hydrofluoric acid was detected.

[0064] On the other hand, Figure 5 shows the powder recovered after heat treatment of commercial black mass at low temperature, but without evacuation. The powder recovered in this way was hard and agglomerated, making it difficult to pulverize, and a large amount of fluorine was detected.

[0065] Figure 6 shows the scanning electron microscope image of the recovered lithium iron phosphate powder and the EDX (Energy Dispersive X-ray spectroscopy) mapping results. It was found that the binder was completely removed from the recovered lithium iron phosphate, leaving the lithium iron phosphate positive electrode powder intact.

[0066] Figure 7 shows the results of a cell test using a coin cell made from the recovered lithium iron phosphate powder. The initial capacity was confirmed at a charge / discharge rate of 0.1C, and the cycle test was conducted at 0.5C. The initial capacity was confirmed to be at the same level as the discharge capacity of typical unrecycled lithium iron phosphate, and the cycle characteristics were also confirmed to be stable.

[0067] As described above, the recycled lithium iron phosphate powder recovered through the method for recycling used lithium ion batteries according to the present invention can be directly used to manufacture lithium ion batteries without any additional post-treatment, enabling highly economical manufacturing of lithium ion batteries. Furthermore, since the method is performed through low-temperature heat treatment, it is economical and environmentally friendly, increasing the recycling rate of used lithium ion secondary batteries and solving environmental problems that may arise during recycling.

Claims

1. (a) charging a heat treatment object, which is at least a part of a cathode material of a waste lithium ion secondary battery, in a heat treatment furnace, the cathode material being lithium iron phosphate powder; (b) increasing the internal temperature of the heat treatment furnace to a range of 200 to 400°C; (c) maintaining the elevated temperature to heat-treat the object; and (d) discharging the first powder produced after the heat treatment is completed; 10. The method for recycling used lithium ion secondary batteries, wherein the first powder comprises recycled lithium iron phosphate powder.

2. 2. The method for recycling used lithium ion secondary batteries according to claim 1, wherein the first powder does not contain any organic component and has a fluorine content of 2% by weight or less.

3. The method for recycling used lithium ion secondary batteries according to claim 1 , wherein the first powder does not contain organic components and fluorine.

4. 2. The method of claim 1, wherein gas generated from the heat treatment furnace is forcibly exhausted in steps (b) and (c).

5. 5. The method for recycling used lithium ion secondary batteries according to claim 4, wherein in steps (b) and (c), the inside of the heat treatment furnace is made into a negative pressure state to forcibly exhaust the gas.

6. 5. The method of claim 4, wherein in steps (b) and (c), the gas is forcibly exhausted through a fan disposed in the heat treatment furnace.

7. 7. The method for recycling used lithium ion secondary batteries according to claim 6, wherein the forced exhaust through the fan is performed intermittently.

8. 2. The method of claim 1, wherein in step (a), the object to be heat-treated is a positive electrode recovered by disassembling the used lithium ion battery.

9. 2. The method of claim 1, wherein after step (d), the first powder is washed with water, and the washing is performed using water at a temperature of 30° C. or less.

10. 2. The method of claim 1, further comprising the step of pickling the first powder after step (d).

11. 2. The method for recycling used lithium ion secondary batteries according to claim 1, wherein the recycled lithium iron phosphate powder contained in the first powder is a powder composited with a conductive agent.

12. 2. The method for recycling used lithium ion secondary batteries according to claim 1, further comprising the step of mixing the recycled lithium iron phosphate powder with a lithium compound and heat treating the mixture at a temperature ranging from 600 to 800°C.

13. A recycled lithium iron phosphate powder, which is recovered through the recycling method for used lithium ion secondary batteries according to any one of claims 1 to 12.

14. A lithium ion secondary battery, characterized in that it is manufactured using recycled lithium iron phosphate powder recovered through the recycling method for used lithium ion secondary batteries according to any one of claims 1 to 12.

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