Lithium recovery method

Abstract

To provide a method for efficiently recovering lithium from waste lithium batteries, which is simpler and has a faster processing speed than conventional methods, and is also environmentally friendly in terms of the process, by introducing a dry melting smelting method into the recycling of waste lithium batteries. The present invention relates to a method for efficiently recovering valuable metals from used lithium batteries using a dry melting smelting method. More specifically, the present invention relates to a method for recovering lithium by mixing flux and sulfur components with crushed or shredded used lithium battery cells, melting the mixture at a high temperature of 1,400°C or higher, and obtaining the lithium-sulfur compound (Li2S) that is volatilized from the mixture.

Description

[Technical Field]

[0001] The present invention relates to a method for efficiently recovering valuable metals from used lithium batteries using a dry smelting method. More specifically, the present invention relates to a lithium recovery method in which flux and sulfur components are mixed with crushed or shredded used lithium batteries, the mixture is melted at a high temperature of 1400°C or higher, and the resulting volatilized lithium-sulfur compound (LiS: lithium sulfide) is recovered. [Background technology]

[0002] Waste batteries are generated when primary or secondary batteries used as power sources for various electronic devices that people use on a daily basis, such as mobile phones, laptops, cassette toys, and emergency power supplies, reach the end of their lifespan.

[0003] These waste batteries contain hazardous metals such as lead, cadmium, and mercury, and also contain electrolytes such as KOH (potassium hydroxide), NH4Cl (ammonium chloride), lithium salts, H2SO4 (sulfuric acid), and organic solutions, which means that their impact on the environment cannot be ignored. Furthermore, because they contain valuable metals such as silver, cobalt, nickel, zinc, manganese, and lithium, recycling waste batteries is required to protect the environment and use limited resources efficiently.

[0004] In particular, demand for lithium-ion secondary batteries (LiBs) has been increasing since the 1990s along with the portable electronic device market, and in recent years, global demand has further increased sharply with the rapid expansion of the electric vehicle market.

[0005] This will soon exceed the amount of lithium supplied from natural resources, leading to an unstable supply and demand of lithium resources. Furthermore, the continuous accumulation of waste batteries will also pose a major environmental problem.

[0006] To solve these problems, recycling used lithium secondary batteries is very important. That is, if usable materials can be recovered from waste batteries, less raw materials can be extracted from limited underground sources. Furthermore, if waste LiBs are recycled, the serious and negative environmental impacts caused by mining and processing the ore can be avoided.

[0007] There are two methods for recovering valuable metals contained in waste batteries: hydrometallurgy and pyrometallurgy.

[0008] Hydrometallurgy involves pretreatment to recover cathode materials followed by further purification and recovery techniques, such as leaching and selective precipitation, ion exchange, and solvent extraction to extract valuable metals (see Patent Document 2: KR 10-2019-0084081). Some hydrometallurgical processes suffer from relatively long leaching times and low leaching efficiency due to the high valence state of the cathode active material and the strong binding strength of the organic binder. Furthermore, the extensive use of highly concentrated acidic solutions and reducing agents and the complex process produce significant wastewater, which can cause secondary pollution through the emission of wastewater and harmful gases during the leaching process. Lithium, in particular, can become dispersed during these separation and purification processes, leading to low lithium recovery rates.

[0009] To overcome these drawbacks and extract and refine metals, pyrometallurgy can be used (see Patent Documents 1, 3-5: KR 10-2021-0094615, KR 10-2313417, KR 10-0717389, and KR 10-2015-0096849). The pyrometallurgy recycling process offers the advantage of rapid chemical reactions, enabling large-volume processing and reducing processing and process costs. Furthermore, the feedstock is relatively flexible, the process is simple, and the environmental impact of dross is minimal. Because mixed waste batteries are immediately charged into a melting furnace without sorting, this method solves issues such as fire and explosion hazards, particularly when processing lithium batteries. It also eliminates the need to consider the composition of an inert atmosphere during the crushing process in the hydrometallurgy process.

[0010] However, the purity of the recovered metals is low, limiting the recovery of high-value metal powder. Another drawback is the need to treat the exhaust gases generated during the processing. In particular, lithium is absorbed into the slag, requiring an additional process to utilize the lithium.

[0011] Furthermore, most research results on the recycling of lithium-based batteries have focused on the separation and recovery of Co and Ni, and currently only a small amount has been done on Li.

[0012] Therefore, it is important to develop innovative recycling processes to more efficiently extract and separate lithium among valuable metals from waste batteries, which contain high proportions of heavy metals and toxic electrolytes. [Prior art documents] [Patent documents]

[0013] [Patent Document 1] Korean Patent Publication No. 10-2015-0096849 [Patent Document 2] Korean Patent Publication No. 10-2019-0084081 [Patent Document 3] Korean Patent Publication No. 10-2021-0094615 [Patent Document 4] Korean Patent No. 10-0717389 [Patent Document 5] Korean Patent No. 10-2313417 Summary of the Invention [Problem to be solved by the invention]

[0014] The present invention has been made in view of the above-mentioned problems of the conventional art, and an object of the present invention is to provide a method for recycling waste lithium batteries by introducing a dry smelting method, which is simpler and faster than conventional methods, while also being environmentally friendly and capable of efficiently recovering lithium in terms of process. [Means for solving the problem]

[0015] In order to solve the above problems, the present invention provides a method for recovering lithium from waste lithium batteries, comprising: a pre-treatment step of crushing or pulverizing waste lithium battery cells; a step of mixing the treated waste lithium battery cells with a flux and a sulfur component; a step of melting the mixture in a heating furnace at a high temperature of 1,400°C or more; and a step of collecting lithium-sulfur compounds volatilized from the molten slag in the form of dust by air-cooling the molten slag.

[0016] The waste lithium battery cells include any one of cells, cell packs, assemblies, or scraps thereof.

[0017] The flux contains at least one of SiO2 (silicon dioxide), CaO (calcium oxide), FeO (iron oxide), MnO (manganese oxide), and Al2O3 (alumina).

[0018] The sulfur component includes any one of sulfur, sulfur ions, sulfur compounds, sulfates, and sulfur mixtures.

[0019] The melting step is carried out at a temperature in the range of 1,400°C to 1,800°C.

[0020] The lithium-sulfur compound can be Li2S.

[0021] The sulfur component may also be added in the process of melting the flux without being mixed with it.

[0022] An apparatus for recovering lithium from waste lithium batteries using the lithium recovery method is provided.

[0023] The lithium-sulfur compound for all-solid-state batteries obtained by the lithium recovery method is provided. [Effects of the Invention]

[0024] As described above, the present invention has the effect of reducing the time and cost required for the pre-treatment process by immediately crushing and pulverizing waste lithium batteries into cells, packs, and modules. In addition, the mixed waste batteries are immediately charged into the melting furnace for treatment without going through a sorting process, which eliminates the risk of fire and explosion during the treatment of lithium batteries.

[0025] Furthermore, since the present invention utilizes a pyrometallurgical recycling process, there is no discharge of wastewater or environmental pollutants, and a rapid chemical reaction allows for large-scale treatment, thereby reducing treatment and process costs.

[0026] Furthermore, the present invention makes it possible to extract 90% or more of lithium, which was difficult to recover using conventional wet methods, by using dust collection equipment or the like. [Brief explanation of the drawings]

[0027] [Figure 1] 1 is a flowchart illustrating steps of a lithium recovery method according to an embodiment of the present invention. [Figure 2] 1 is a flowchart illustrating steps of a lithium recovery method according to another embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0028] The present invention will be described in detail below.

[0029] The terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted as meanings and concepts that are consistent with the technical idea of ​​the present invention, based on the principle that an inventor can appropriately define the concepts of terms in order to best describe his or her own invention.

[0030] The present invention relates to a method for efficiently recovering valuable metals from used lithium batteries that have reached the end of their life by a pyrometallurgical process.

[0031] In this specification, the term "lithium battery" is used to mean any primary battery, secondary battery, or all-solid-state battery containing lithium. Lithium batteries that have reached the end of their life or are discarded after use are collectively referred to as "waste lithium batteries."

[0032] Generally, primary batteries, unlike secondary batteries, are batteries that cannot be electrically recharged after one use and must be discarded. Secondary batteries are energy storage devices that can be repeatedly charged and discharged over 500 times and are capable of converting chemical energy into electrical energy and the reverse process. Representative batteries include lithium-ion, lithium polymer, nickel-cadmium, and nickel-metal hydride batteries. Among these, lithium-ion batteries have far superior energy storage capacity and lifespan compared to other secondary batteries.

[0033] In addition, while lithium-ion batteries are composed of a positive electrode, a negative electrode, a separator, and an electrolyte, solid-state batteries have a solid electrolyte rather than a liquid. Therefore, solid-state batteries do not require safety devices or separators to protect against temperature changes and external impacts, which allows for cost reduction and high capacity implementation in the same size, and has the advantage of eliminating the risk of fire.

[0034] The core material used in the positive electrode of lithium-ion batteries is LCO (LiCoO) depending on the metal salt components. 2、 Examples of materials that can be used include lithium cobalt oxide (NCM), NCM (Li[Ni (nickel), Co (cobalt), Mn (manganese)]O), NCA (Li[Ni, Co, Al (aluminum)]O), LMO (LiMn2O4, lithium manganese oxide), and LFP (LiFePO4, lithium iron phosphate), and the negative electrode material may be carbonaceous material such as graphite or copper.

[0035] The present invention utilizes a dry melting method, which is a high-temperature heat treatment method, to efficiently recover valuable metals such as cobalt, copper, aluminum, iron, and lithium contained in large amounts among the constituent materials into economically valuable waste resources.

[0036] Generally, the term smelting refers to a process in which ore is broken down using heat and chemical reducing agents, driving off other elements into gases or slag, leaving only the metal. The reducing agent is typically a carbon source such as coke or initial charcoal. The carbon removes oxygen from the ore, leaving only the metal element. Thus, carbon (C) is oxidized to produce carbon dioxide. Because most ores are impure, accompanying rock must be removed as slag using fluxes such as limestone.

[0037] Figure 1 is a flow chart showing the steps of a lithium recovery method according to one embodiment of the present invention. The method includes a pretreatment step of crushing or pulverizing used lithium battery cells to recover lithium from the batteries; a step of mixing a flux and a sulfur component (S) with the treated used lithium battery cells; a step of melting the mixture in a heating furnace at a high temperature of 1,400°C or higher; and a step of air-cooling the lithium-sulfur compound volatilized from the molten slag to collect it as dust. In summary, the method involves recovering lithium from used lithium battery cells into a lithium-sulfur compound. The lithium-sulfur compound may be LiS.

[0038] That is, most of the lithium is produced from the molten slag by adding sulfur components in the mixing process, and LiS is generated according to the following chemical reaction formula. This gas is then released and collected in the form of dust after air cooling.

[0039] <Chemical reaction formula> Li2O+S+CO(g) →Li2S+CO2(g)

[0040] In the above reaction equation, the Gibbs free energy, ΔG, is < 0, so it is a spontaneous reaction, and as the temperature rises, it reacts with S to produce volatile Li2S. The boiling point of Li2S is 1,372°C, and its vapor pressure is approximately 1 atm at 1,400°C, and it volatilizes below 1,400°C.

[0041] If the melting temperature is too high, the ability to remove impurities such as aluminum will decrease, so the melting temperature is preferably in the range of 1,400°C to 1,800°C, and the melting time is preferably maintained at the melting temperature for one hour or more.

[0042] Here, it is necessary to prevent oxidation of the sulfur component (S) by blocking oxygen or introducing an inert gas such as N2 or Ar during the temperature rise.

[0043] In another embodiment of the present invention, in the mixing step after the pretreatment step, the sulfur component may not be added together with the flux, but may be added separately to the liquid slag during or after melting (see FIG. 2).

[0044] The amount of sulfur component added may be based on the stoichiometry of the lithium in the slag, i.e., 0.5 to 10 times the lithium equivalent may be mixed, and 2 to 4 times the lithium equivalent is preferred, but not limited thereto.

[0045] The sulfur components mentioned above may include not only sulfur, sulfur ions, sulfur compounds, sulfates, and sulfur mixtures, but also all sulfur compounds and sulfur mixtures containing sulfur. Examples of sulfur compounds include hydrogen sulfide, sulfur dioxide, carbon disulfide, sodium sulfide, copper sulfide, and nickel sulfide. Examples of sulfates include, but are not limited to, copper sulfate, manganese sulfate, nickel sulfate, cobalt sulfate, magnesium sulfate, and calcium sulfate.

[0046] In particular, the sulfur component is preferably a sulfur compound, which can be decomposed into sulfur during the melting process.

[0047] The waste lithium battery cells may be cells, cell packs, assemblies, or scraps thereof.

[0048] The flux of the present invention may contain at least one of SiO2, CaO, FeO, MnO, and Al2O3, and is charged into a refining furnace in the form of granules or powder. The composition ratio of the above components may be varied in consideration of the melting point, and additional components may be used as needed.

[0049] Preferably, a CaO-based flux containing SiO2, MnO, Al2O3, etc., which has a high removal efficiency for aluminum, an impurity contained in large amounts in waste lithium batteries, and also has sufficient viscosity at the melting temperature, is used.

[0050] The amount of the flux may vary depending on the type of waste battery cells, but may be 0.5 to 10 times the weight of the waste lithium battery cells, and preferably 2 to 5 times the weight.

[0051] In the end, if the amount of sulfur component and flux as well as the ratio of carbon, which is a reducing agent, are adjusted in the chemical reaction formula, the lithium-sulfur compound (LiS) required for waste lithium recovery can be obtained.

[0052] Li2S, which is volatilized into a gas after production, can be separated or collected using a scrubber, a backhouse filter, an electrostatic precipitator, a cyclone, or the like.

[0053] <Embodiment 1> 1 kg of discarded lithium battery cells that had reached the end of their lifespan were crushed into pieces that could be easily put into the furnace. The crushed lithium battery cells were then placed in a heating furnace along with 2 kg of CaO-based flux containing SiO2, MnO, and Al2O3. The sulfur component was immediately added and mixed together, and the mixture was heated to 1,500°C in an Ar atmosphere at a heating rate of 5°C / min or more. Oxygen was then added in small amounts to melt the material in a low oxygen partial pressure region, and the mixture was then left in an Ar atmosphere for 1 to 3 hours to volatilize the resulting Li2S. The resulting material was then air-cooled and collected in the form of dust.

[0054] <Embodiment 2> The sulfur was not added immediately in the mixing step, but was added separately after melting and then heated and melted. The rest of the procedure was the same as in Example 1.

[0055] <Embodiment 3> Sodium sulfide was used instead of sulfur, and the other steps were the same as in Example 1.

[0056] It has been confirmed that this method is highly suitable for recovering lithium from waste lithium batteries with a high recovery rate of over 90%.

[0057] All-solid-state batteries, which have improved energy density and stability compared to lithium-ion batteries, are characterized by the use of solid electrolytes. Since Li2S is a core material of solid electrolytes, the Li2S obtained by the present invention can be recycled as a raw material for all-solid-state batteries.

Claims

1. A method for recovering lithium from waste lithium batteries, comprising: A pre-treatment step of crushing or shredding the waste lithium battery cells; mixing the treated waste lithium battery cells with a flux and a sulfur component; A step of charging the mixture into a heating furnace and melting it at a high temperature of 1,400°C or higher; and collecting the lithium-sulfur compound volatilized from the molten slag in the form of dust by air-cooling the compound. A method characterized by:

2. The waste lithium battery cells include any one of cells, cell packs, assemblies, or scraps thereof. The method of claim 1.

3. The flux is SiO ２ , CaO, FeO, MnO and Al ２ O ３ Contains at least one of the following: The method of claim 1.

4. The sulfur component includes any one of sulfur, sulfur ions, sulfur compounds, sulfates, and sulfur mixtures. The method of claim 1.

5. The temperature of the melting step is in the range of 1,400°C to 1,800°C. The method of claim 1.

6. The lithium-sulfur compound is Li ２ It is S The method of claim 1.

7. A method for recovering lithium from waste lithium batteries, comprising: A pre-treatment step of crushing or shredding the waste lithium battery cells; mixing a flux with the treated waste lithium battery cells; charging the mixture into a heating furnace and melting it at a high temperature of 1,400°C or higher while adding a sulfur component; and collecting the lithium-sulfur compound volatilized from the molten slag in the form of dust by air-cooling the compound. A method characterized by:

8. The lithium recovery method according to any one of claims 1 to 7 is used to recover lithium from waste lithium batteries. An apparatus characterized in that

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