Lithium ion recovery method

Abstract

To provide a lithium ion recovery method capable of recovering lithium from an electrolyte without chemically modifying the electrolyte.SOLUTION: A lithium ion recovery method includes placing an organic electrolyte solution containing lithium ions in a container in which a pair of electrodes are disposed via a semipermeable membrane, creating a potential difference between the pair of electrodes, and migrating the lithium ions into the space on one of the electrodes in the container via the semipermeable membrane, thereby recovering the lithium ions.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a method for recovering lithium ions. [Background technology]

[0002] In recent years, non-aqueous electrolyte secondary batteries such as lithium ion batteries have been proposed and put to practical use as batteries that are expected to be smaller, lighter, and have higher capacity. Lithium ion batteries are composed of a positive electrode and a negative electrode that have the property of reversibly inserting and removing lithium ions, and a non-aqueous electrolyte.

[0003] The negative electrode active material of the lithium ion battery is generally a carbon-based material, or a metal material such as Si or Sn that has the property of being able to reversibly insert and remove lithium ions, or a Li-containing metal oxide. Examples of such Li-containing metal oxides include lithium titanate (Li4Ti5O 12 ) are mentioned.

[0004] The positive electrode of a lithium-ion battery is made of a positive electrode material mixture containing a positive electrode material and a binder, etc. The positive electrode active material is, for example, a Li-containing metal oxide such as lithium hexafluorophosphate (LiPF6) that has the property of being able to reversibly insert and remove lithium ions.

[0005] A non-aqueous solvent is used as the electrolyte of a lithium-ion battery. A positive electrode active material that oxidizes and reduces at a high potential and a negative electrode active material that oxidizes and reduces at a low potential can be applied to the non-aqueous solvent. This makes it possible to realize a lithium-ion battery with a high voltage.

[0006] The demand for lithium-ion batteries will continue to grow in the future, and there is a need for a stable method of supplying and extracting lithium (Li). One method of supplying and extracting lithium is to recycle lithium and to extract lithium from seawater.

[0007] As a method for recovering lithium, for example, there is known a method having a pH conversion step of producing a treatment liquid, which is an alkaline aqueous solution containing lithium, from a raw material liquid, which is a non-alkaline aqueous solution containing lithium, and a recovery step of recovering lithium in a recovery liquid using the treatment liquid after the pH conversion step as a raw liquid (for example, see Patent Document 1).

[0008] As a method for recovering lithium, for example, a method is known in which a lithium ion selectively permeable membrane impregnated with an ionic liquid having lithium ion selectivity between an anode electrode and a cathode electrode is used for fractionation to form a lithium solution cell on the anode electrode side and a lithium ion separation and recovery cell on the cathode electrode side, a solution is supplied to the lithium solution cell, and lithium ions that permeate the lithium ion selectively permeable membrane by electrodialysis and are dialyzed into the lithium ion separation and recovery cell are recovered (for example, see Patent Document 2).

[0009] As a method for recovering lithium, for example, in a treatment tank partitioned into a first tank and a second tank by a lithium ion conductive electrolyte membrane, 6 Li and 7 Li and lithium ions in the form of an aqueous solution, 6 A method for enriching lithium isotopes is known in which an aqueous solution containing lithium ions with a high Li isotope ratio is recovered in a second tank, in which a positive voltage is intermittently applied to the first tank side of porous electrodes provided in contact with both sides of a lithium ion conductive electrolyte membrane, relative to the second tank side (see, for example, Patent Document 3). [Prior art documents] [Patent documents]

[0010] [Patent Document 1] JP 2017-131863 A [Patent Document 2] JP 2012-055881 A [Patent Document 3] JP 2019-141808 A Summary of the Invention [Problem to be solved by the invention]

[0011] In typical recycling processes for recovering lithium from the electrolyte of lithium-ion batteries, such as roasting or melting, the electrolyte is decomposed by heat, etc., making it difficult to recover some or all of the lithium contained in the electrolyte.

[0012] The present invention has been made in consideration of the above circumstances, and has an object to provide a method for recovering lithium ions that can recover lithium from an electrolyte solution without chemically denaturing the electrolyte solution. [Means for solving the problem]

[0013] The present invention has the following aspects. [1] A method for recovering lithium ions, comprising: placing an organic electrolyte solution containing lithium ions in a container in which a pair of electrodes are disposed with a semipermeable membrane interposed therebetween; creating a potential difference between the pair of electrodes; and causing the lithium ions to migrate to a space on one electrode side in the container with the semipermeable membrane interposed therebetween, thereby recovering the lithium ions. [2] The method for recovering lithium ions according to [1], wherein the organic electrolyte solution is recovered from a used battery so as not to be chemically altered. [3] The method for recovering lithium ions according to [1], wherein the semipermeable membrane is made of a material resistant to an organic electrolyte solution. [4] The method for recovering lithium ions according to [1], wherein the potential difference is 0 V or more and 50 V or less. Effect of the Invention

[0014] According to the present invention, it is possible to provide a method for recovering lithium ions, which is capable of recovering lithium from an electrolytic solution without chemically denaturing the electrolytic solution. [Brief description of the drawings]

[0015] [Figure 1]FIG. 1 is a schematic diagram showing an electrodialysis device used in a lithium ion recovery method according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] An embodiment of the method for recovering lithium ions according to the present invention will be described. It should be noted that the present embodiment is specifically described to allow a better understanding of the gist of the invention, and does not limit the present invention unless otherwise specified.

[0017] [How to recover lithium ions] A method for recovering lithium ions according to one embodiment of the present invention includes storing an organic electrolyte solution containing lithium ions in a container in which a pair of electrodes are disposed via a semipermeable membrane, creating a potential difference between the pair of electrodes, and causing the lithium ions to migrate to a space on one electrode side in the container via the semipermeable membrane, thereby recovering the lithium ions.

[0018] In the method for recovering lithium ions according to the present embodiment, for example, as shown in FIG. 1, an electrodialysis device 1 is used. The electrodialysis device 1 includes an electrodialysis cell 10, a semipermeable membrane 20, and electrodes 31 and 32.

[0019] The electrodialysis cell 10 is a container that contains an organic electrolyte solution containing lithium ions and performs electrodialysis of the organic electrolyte solution. The electrodialysis cell 10 is divided into two spaces via a semipermeable membrane 20. An electrode 31 (anode) is disposed in one space 11 of the electrodialysis cell 10, and an electrode 32 (cathode) is disposed in the other space 12 of the electrodialysis cell 10.

[0020] The electrodialysis cell 10 is not particularly limited, but is preferably made of a material that is durable against an organic electrolyte (resistance to an organic electrolyte). Resistance to an organic solvent means a property that does not deteriorate even when in contact with an organic electrolyte. Examples of materials that are resistant to an organic electrolyte include glass and ceramics.

[0021] The semipermeable membrane 20 is not particularly limited, but is preferably made of a material that is resistant to an organic electrolyte solution.

[0022] The electrode 31 (anode) and the electrode 32 (cathode) are not particularly limited, but examples thereof include platinum, nickel, stainless steel, and carbon.

[0023] The organic electrolyte contains an organic solvent and an electrolyte containing lithium. The organic electrolyte is not particularly limited as long as it contains lithium ions, but it is preferable that the organic electrolyte is recovered from a used battery so as not to be chemically altered, since this can further increase the recovery rate of lithium ions.

[0024] The method for recovering the organic electrolyte from a used battery without chemically denaturing the battery is not particularly limited, but examples thereof include a method of sucking the organic electrolyte from the battery case, and a method of destroying the battery case by cutting or the like to extract the organic electrolyte.

[0025] Examples of the organic solvent include ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and mixtures of these.

[0026] Examples of the electrolyte include lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium tetrafluoroborate (LiBF4), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSA).

[0027] In the lithium ion recovery method of this embodiment, a potential difference is provided between electrode 31 (anode) and electrode 32 (cathode) to move lithium ions contained in the organic electrolyte from one space 11 to the other space 12.

[0028] The potential difference between the electrodes 31 and 32 is preferably 0 V to 50 V, more preferably 0 V to 30 V, even more preferably 0 V to 10 V, and particularly preferably 0 V to 5 V. If the potential difference is equal to or greater than the lower limit, the movement of lithium ions through the semipermeable membrane occurs beyond the natural diffusion caused by the concentration difference. If the potential difference is equal to or less than the upper limit, the oxidation-reduction reaction of the dissolved chemical species on the electrodes is suppressed to a level that does not interfere with the recovery of lithium.

[0029] The time for which the potential difference is provided is not particularly limited and may be continuous or intermittent, and is appropriately adjusted depending on the amount of organic electrolyte solution to be treated and the amount (concentration) of lithium ions contained in the organic electrolyte solution.

[0030] The temperature of the organic electrolyte when the potential difference is provided is not particularly limited, but is preferably 10°C to 150°C, more preferably 40°C to 100°C. When the temperature of the organic electrolyte is equal to or higher than the lower limit, the organic electrolyte maintains a high fluidity, and lithium ions are efficiently supplied to the semipermeable membrane. When the temperature of the organic electrolyte is equal to or lower than the upper limit, hydrogen fluoride and the like are not generated due to chemical decomposition of the organic electrolyte, and the dialysis reaction can be continued stably.

[0031] As described above, by providing a potential difference between the electrodes 31 and 32, the lithium ion concentration in the other space 12 increases. That is, lithium ions are concentrated in the organic electrolyte in the other space 12. When it is confirmed that there is no change in the increase in the lithium ion concentration in the space 12, it is determined that the movement of lithium from one space 11 to the other space 12 is completed. The change in the increase in the lithium ion concentration is indicated, for example, by the average lithium ion concentration in the space 11 per hour becoming 1% or less compared to the initial level.

[0032] Possible methods for recovering lithium ions from an organic electrolyte, in other words, for separating the organic solvent from the lithium ions, include liquid-liquid extraction using an extractant solution, solid-phase extraction using a carrier, heating to remove the organic solvent and converting it into a lithium salt, and combinations of these methods.

[0033] According to the method for recovering lithium ions of the present embodiment, there is no need to heat the organic electrolyte solution, and therefore the electrolyte solution is not chemically altered, and lithium can be recovered at a high concentration from the electrolyte solution. [Explanation of symbols]

[0034] 1 Electrodialysis equipment 10 Electrodialysis cell 20 Semi-permeable membrane 31 Electrode (Anode) 32 Electrode (cathode)

Claims

1. A method for recovering lithium ions, comprising: placing an organic electrolyte solution containing lithium ions in a container in which a pair of electrodes are disposed with a semipermeable membrane interposed therebetween; creating a potential difference between the pair of electrodes; and causing the lithium ions to migrate to a space on one electrode side in the container with the semipermeable membrane interposed therebetween, thereby recovering the lithium ions.

2. 2. The method for recovering lithium ions according to claim 1, wherein the organic electrolyte is recovered from a used battery so as not to be chemically altered.

3. The method for recovering lithium ions according to claim 1 , wherein the semipermeable membrane is made of a material having resistance to an organic electrolyte solution.

4. The method for recovering lithium ions according to claim 1 , wherein the potential difference is 0 V or more and 50 V or less.

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