Method for producing lithium salt and system for producing lithium salt

Abstract

This method for producing a lithium salt uses a first liquid L1 and a second liquid L2 which are separated from each other by a cation exchange membrane 4. An adsorbent 1 is immersed in the first liquid L1. Li+ is desorbed from the adsorbent 1 into the first liquid L1. Li+ passes through the cation exchange membrane 4, so that Li+ moves from the first liquid L1 to the second liquid L2. A lithium salt is obtained in the second liquid L2 that contains Li+ which has passed through the cation exchange membrane 4.

Description

Lithium salt manufacturing method and lithium salt manufacturing system

[0001] The present disclosure relates to a method for producing a lithium salt and a system for producing a lithium salt.

[0002] Lithium-ion secondary batteries are used in industrial products such as electric vehicles (EVs), hybrid electric vehicles (HEVs), and portable electronic devices (e.g., smartphones). The raw material for the positive electrode of a lithium-ion secondary battery is Li. ２ CO ３ and lithium compounds (lithium salts) such as LiOH.

[0003] Known conventional methods for producing lithium salts include the flotation method, which uses ore as a raw material, and the brine method, which uses brine as a raw material.

[0004] With the recent rapid increase in demand for electric vehicles, a shortage of lithium salt supply and a rise in the price of lithium salt are expected. However, the conventional method for producing lithium salts based on the brine method requires the cost of a concentration process (e.g., the cost of chemicals). In other words, the conventional production cost of lithium salts is not sufficiently low.

[0005] For example, Patent Document 1 and Patent Document 2 disclose a method for recovering lithium, which includes a step of adsorbing lithium ions in raw water such as brine onto an adsorbent and a step of desorbing the lithium ions from the adsorbent. For example, Non-Patent Document 1 discloses a method for recovering lithium ions in brine onto an adsorbent by ion pumping using an anion exchange membrane. For example, Non-Patent Document 2 discloses a method for recovering lithium ions in brine onto an adsorbent by pumping lithium ions in a lithium chloride aqueous solution onto an anion exchange membrane. ２ A method for adsorption onto an electrode is disclosed.

[0006] Japanese Patent Application Laid-Open No. 6-88277 International Publication No. 2011 / 058841

[0007] Alberto Battistel et al, Electrochemical Methods for LithiumRecovery: A Comprehensive and CriticalReview, Advanced Materials 2020, 32,1905440, published by WILEY-VCH Verlag GmbH& Co. KGaA.H.Kanoh et al, ElectrochemicalRecovery of Lithium Ions in the Aqueous Phase, Separation Science andTechnology Volume 28, 1993, Pages 643-651, published by Taylor & Francis Group.

[0008] An object of one aspect of the present disclosure is to provide a method for the preparation of Li ＋ The present invention provides a method for producing a lithium salt using an adsorbent having a hydroxyl group adsorbed thereon, and a lithium salt production system for carrying out the method.

[0009] For example, one aspect of the present disclosure relates to a method for producing a lithium salt according to any one of the following [1] to [7], and a system for producing a lithium salt according to any one of the following [8] to

[14] .

[0010] [1] A method for absorbing Li from a liquid adsorbent, comprising: a first liquid and a second liquid separated from each other by a cation exchange membrane; an adsorbent immersed in the first liquid; and ＋ is desorbed from the adsorbent into the first liquid, ＋ permeates through the cation exchange membrane, ＋ moves from the first liquid into the second liquid, and the Li ＋ The lithium salt is obtained in the second liquid containing the lithium salt.

[0011] [2] An electrode is immersed in the second liquid, and a voltage is applied between the adsorbent and the electrode, and the potential of the adsorbent is increased above the potential of the electrode, thereby ＋ is desorbed from the adsorbent and permeates the cation exchange membrane, and OH － is generated in the second liquid, and the Li ＋ and the OH － The method for producing a lithium salt according to [1], wherein LiOH is produced from

[0012] [3] The method for producing a lithium salt according to [2], wherein the lithium salt is LiOH.

[0013] [4] The second liquid is ＋ and the cation is adsorbed onto the electrode by applying the voltage between the adsorbent and the electrode.

[0014] [5] The method for producing a lithium salt according to any one of [2] to [4], wherein the electrode contains hexacyanoferrate.

[0015] [6] The Li in the adsorbent ＋ and H in the first liquid ＋ By exchanging with ＋ is desorbed from the adsorbent.

[0016] [7] The method for producing a lithium salt according to any one of [1] to [6], wherein the adsorbent contains an oxide containing manganese.

[0017] [8] A lithium salt production system used in the lithium salt production method according to [1], comprising: the cation exchange membrane, the adsorbent, and a desorption tank; the cation exchange membrane is disposed in the desorption tank; the first liquid, the second liquid, and the adsorbent are placed in the desorption tank; and the first liquid and the second liquid are separated from each other in the desorption tank via the cation exchange membrane.

[0018] [9] The method further includes an electrode and a power source, wherein the electrode is immersed in the second liquid, and the power source applies a voltage between the adsorbent and the electrode, and increases the potential of the adsorbent higher than the potential of the electrode, thereby ＋ is desorbed from the adsorbent and permeates the cation exchange membrane, and OH － is generated in the second liquid, and the Li ＋ and the OH － The lithium salt production system according to [8], wherein LiOH is produced from

[0019]

[10] The lithium salt production system according to [9], wherein the lithium salt is LiOH.

[0020]

[11] The second liquid is ＋ and the power supply applies the voltage between the adsorbent and the electrode, thereby causing the cation to be adsorbed onto the electrode.

[0021]

[12] The system for producing a lithium salt according to any one of [9] to

[11] , wherein the electrode contains hexacyanoferrate.

[0022]

[13] The Li in the adsorbent ＋ and H in the first liquid ＋ By exchanging with ＋ The system for producing a lithium salt according to claim 8 , wherein is desorbed from the adsorbent.

[0023]

[14] The system for producing a lithium salt according to any one of [8] to

[13] , wherein the adsorbent contains an oxide containing manganese.

[0024] According to one aspect of the present disclosure, Li ＋ The present invention provides a method for producing a lithium salt using an adsorbent having an adsorbed thereon, and a system for producing a lithium salt for carrying out the method.

[0025] (a) in Fig. 1 is a schematic cross-sectional view of one specific example of a lithium salt production system (desorption tank) according to the present disclosure, and (b) in Fig. 1 is a schematic cross-sectional view of another specific example of a lithium salt production system (desorption tank) according to the present disclosure. Fig. 2 is a schematic cross-sectional view of another specific example of a lithium salt production system according to the present disclosure. Fig. 3 is an X-ray diffraction pattern of the working electrode used in Example 1. Fig. 4 is a graph showing the potential of the working electrode relative to the reference electrode during the desorption step of Example 1 and the potential of the working electrode relative to the reference electrode during the adsorption step of Example 1. Fig. 5 is a graph showing the potential of the working electrode relative to the reference electrode during the desorption step of each of Examples 1 to 4.

[0026] Hereinafter, preferred embodiments of the present disclosure will be described with reference to the drawings. In the drawings, like elements are designated by like reference numerals. The present disclosure is not limited to the following embodiments.

[0027] (Outline of Lithium Salt Manufacturing Method and Lithium Salt Manufacturing System) The lithium salt manufacturing method according to this embodiment includes a desorption step. In the desorption step, a first liquid and a second liquid separated from each other via a cation exchange membrane are used. That is, the first liquid contacts one surface of the cation exchange membrane, and the second liquid contacts the other surface of the cation exchange membrane. Each of the first liquid and the second liquid may contain water. One or both of the first liquid and the second liquid may contain pure water. In the desorption step, one or more adsorbents (Li ＋ The adsorbent (adsorbent having Li adsorbed thereon) is immersed in the first liquid. The adsorbent may be partially or entirely immersed in the first liquid. Immersion of the adsorbent in the first liquid causes the adsorbent to ＋ (lithium ions) are desorbed (desorbed or eluted) from the adsorbent into the first liquid. ＋ By passing through the cation exchange membrane, Li ＋ moves from the first liquid to the second liquid. ＋ After passing through the cation exchange membrane, the Li in the second liquid ＋ and anions to obtain lithium salts. ＋ The second liquid becomes an aqueous solution of lithium salt with reduced impurities or an aqueous solution of concentrated lithium salt by permeating the cation exchange membrane.

[0028] The lithium salts produced by the production method according to this embodiment include LiOH (lithium hydroxide), LiCl (lithium chloride), and Li ２ CO ３ (lithium carbonate), and Li ２ SO ４ (lithium sulfate).

[0029] The lithium salt production system according to this embodiment is used in a lithium salt production method that includes the desorption step. For example, the production system shown in FIG. 1(a) or 1(b) includes a cation exchange membrane 4, an adsorbent 1, and a desorption tank 32. The cation exchange membrane 4 is disposed in the desorption tank 32. The first liquid L1, the second liquid L2, and the adsorbent 1 are contained in the desorption tank 32. The first liquid L1 and the second liquid L2 are separated from each other in the desorption tank 32 via the cation exchange membrane 4.

[0030] Li between the first liquid L1 and the second liquid L2 ＋ Due to the large concentration difference, Li ＋ The first liquid L1 is preferably an aqueous solution of a lithium salt, since the driving force for the movement of the lithium from the first liquid L1 to the second liquid L2 is also large. For example, the first liquid L1 may be an aqueous solution of LiCl, Li ２ CO ３ , and Li ２ SO ４ The first liquid L1 may be an aqueous solution of at least one electrolyte selected from the group consisting of: ＋ , Mg ２＋ , K. ＋ , Ca ２＋ However, it is preferable that these cations are not contained in the first liquid L1. ＋ , Mg ２＋ , K. ＋ , Ca ２＋ When cations such as Li are contained, the cation exchange membrane ＋ The second liquid L2 is preferably a cation exchange membrane 4 that selectively permeates Li. ＋ , Na ＋ , Mg ２＋ , K. ＋ , Ca２＋ The second liquid L2 preferably contains an aqueous solution of an electrolyte having the same anion as the anion of the lithium salt obtained in the second liquid L2, and more preferably, the second liquid L2 contains a lithium salt containing the anion. For example, the second liquid L2 may contain a cation such as OH － , Cl － , CO ３ ２－ , and SO ４ ２－ The second liquid L2 may be an aqueous solution containing at least one anion selected from the group consisting of LiOH, LiCl, Li ２ CO ３ , and Li ２ SO ４ For example, when the lithium salt obtained in the second liquid L2 is LiOH, the second liquid L2 may be an aqueous solution of at least one electrolyte selected from the group consisting of OH － Preferably, the electrolyte in the first liquid is an aqueous solution of an electrolyte having the formula:

[0031] The cation exchange membrane 4 may contain an organic material. The organic material contains at least one functional group selected from the group consisting of a carboxy group, a sulfo group, a sulfonimide group, a sulfonamide group, and the like, and H in the functional group ＋ Li ＋ , Na ＋ , and K ＋ The cation exchange membrane 4 may be an organic material containing a polymer substituted with at least one cation selected from the group consisting of cations ... ｘ , La ｙ ) TiO ｚ(x=3a-2b, y=2 / 3-a, z=3-b, 0<a≦1 / 6, 0≦b≦0.06, x>0). ＋ The cation exchange membrane 4 may be a membrane that selectively permeates the first liquid L1 and the second liquid L2. The thickness of the cation exchange membrane 4 may be 1 μm or more and 500 mm or less. A plurality of stacked cation exchange membranes 4 may be disposed between the first liquid L1 and the second liquid L2.

[0032] Li in the first liquid L1 ＋ The concentration (unit: mol / L) of Li in the second liquid L2 ＋ The concentration of Li between the first liquid L1 and the second liquid L2 may be higher than the concentration of Li ＋ Due to the concentration difference, Li in the first liquid L1 ＋ is able to permeate the cation exchange membrane 4 and move into the second liquid L2.

[0033] The voltage between the adsorbent 1 in the first liquid L1 and the electrode in the second liquid L2 ＋ It is also possible for Li to permeate the cation exchange membrane 4 and migrate into the second liquid L2. For example, the production system shown in FIG. 1(b) further includes one or more electrodes 3 and a power source 10. The electrode 3 may be partially or entirely immersed in the second liquid L2. The electrode 3 is a counter electrode of the adsorbent 1. The adsorbent 1 and the electrode 3 are electrically connected to the power source 10 and are spaced apart from each other in the desorption tank 32. The adsorbent 1 in the desorption step is an anode (positive electrode), and the electrode 3 in the desorption step is a cathode (negative electrode). The power source 10 applies a voltage between the adsorbent 1 and the electrode 3, and increases the potential of the adsorbent 1 above the potential of the electrode 3, thereby ionizing the Li ＋ is desorbed from the adsorbent 1 and permeates the cation exchange membrane 4.

[0034] When the voltage between the adsorbent 1 and the electrode 3 generates LiOH as a lithium salt in the second liquid L2, the second liquid L2 may be basic, and the pH of the first liquid L1 may be lower than the pH of the second liquid L2. For example, the first liquid L1 may be acidic or neutral. When the adsorbent 1 is immersed in the first liquid L1 having a lower pH than the second liquid L2, and the electrode 3 is immersed in the basic second liquid L2, the potential of the adsorbent 1 required for water electrolysis increases, and the electrolysis of water and the generation of oxygen in the adsorbent 1 are suppressed, resulting in the formation of LiOH. ＋ is easily desorbed from the adsorbent 1. Furthermore, since the first liquid L1 is acidic or neutral, the adsorbent 1 is prevented from eluting into the first liquid L1, and contamination of the second liquid L2 and the electrode 3 by impurities such as manganese derived from the adsorbent 1 is suppressed, making it easier to obtain a high-purity lithium salt.

[0035] During the desorption process, the voltage between the adsorbent 1 and the electrode 3 ＋ The reaction of Li desorbed from the adsorbent 1 (anode) may be represented by the following chemical formula 1. ｘ M represents the adsorbent 1. In the following chemical formula 1, x represents Li ｘ M is a real number representing the molar ratio of Li in M. M in the following chemical formula 1 represents the components of adsorbent 1 excluding lithium and hydrogen. Li ｘ M → M + xLi ＋ +xe － (1) The reaction occurring at the electrode 3 (cathode) due to the voltage between the adsorbent 1 and the electrode 3 during the desorption process may be represented by the following chemical formula 2: xH ２ O+xe － → (x / 2)H ２ + xOH － (2) The reaction in which LiOH is produced in the second liquid L2 may be represented by the following chemical formula 3: Li ＋ +OH － → LiOH (3)

[0036] The voltage (desorption voltage) applied between the adsorbent 1 and the electrode 3 in the desorption step is not particularly limited. For example, the voltage (potential of the adsorbent 1) relative to the standard hydrogen electrode in the desorption step may be 0 V vs. SHE or more and 1.23 V vs. SHE or less.

[0037] When a voltage is applied to the adsorbent 1 and the electrode 3 in the desorption step, the second liquid L2 ＋ For example, Li ＋ Cations other than A ＋ By applying a voltage between the adsorbent 1 and the electrode 3, the cation A ＋ is adsorbed onto the electrode 3 in the second liquid L2. ＋ is adsorbed onto the electrode 3, and the Li in the first liquid L1 ＋ As a result, the electrochemical potential of Li ＋ is easily transmitted through the cation exchange membrane 4, and Li is easily transmitted from the first liquid L1 to the second liquid L2. ＋ The migration of Li in the second liquid L2 is promoted, and the generation of lithium salts in the second liquid L2 is also promoted. ＋ Cation A other than ＋ Is, K ＋ (potassium ion), Na ＋ (sodium ion), Mg ２＋ (Magnesium ion), Ca ２＋ (Calcium ion), Al ３＋ (aluminum ion), and NH ４ ＋ (The second liquid L2 may be at least one cation selected from the group consisting of ammonium ions. In other words, the second liquid L2 may be at least one cation selected from the group consisting of cations A ＋ As electrolytes containing ２ CO ３ , K. ２ SO ４ , NaOH, NaCl, Na ２ CO ３ , Na ２ SO ４ , Mg(OH) ２ , MgCl ２ , MgCO ３ , MgSO ４ , Al(OH) ３ , AlCl ３ , Al ２ (CO ３ ) ２ , Al ２ (SO ４ ) ３ , N.H. ３ , and N.H.４ The electrolyte may contain at least one electrolyte selected from the group consisting of:

[0038] Li ＋ Cation A other than ＋ The electrode 3 may contain hexacyanoferrate because hexacyanoferrate is easily adsorbed onto the electrode 3 in the second liquid L2. The electrode 3 may be composed solely of hexacyanoferrate. For example, the hexacyanoferrate contained in the electrode 3 may be potassium nickel hexacyanoferrate (KNiFe(CN)). ６ ), potassium iron hexacyanoferrate (KFe ２ (CN) ６ ), Potassium Copper Hexacyanoferrate (KCuFe(CN) ６ ), potassium nickel hexacyanoferrate (Potassium Ferricyanide; K ３ NiFe(CN) ６ ), Sodium Nickel Hexacyanoferrate (NaNiFe(CN) ６ ), and calcium nickel hexacyanoferrate (Ca[NiFe(CN) ６ ] ２ For example, Li ＋ Cation A other than ＋ is K ＋ and the electrode 3 is KNiFe(CN) ６ If it contains ＋ The reaction of KNiFe(CN) adsorbed onto the electrode 3 may be represented by the following chemical formula 4: ６ +K ＋ +e － → K ２ NiFe(CN) ６ (4)

[0039] Li in adsorbent 1 ＋ and H in the first liquid L1＋ By exchanging with Li ＋ may be desorbed from the adsorbent 1. For example, Li may be desorbed by treating the adsorbent 1 with an acid. ＋ may be desorbed from the adsorbent 1. ＋ and H in the first liquid L1 ＋ When the first liquid L1 is replaced, the first liquid L1 is HCl, HNO ３ , and H ２ SO ４ For example, when the first liquid L1 contains HCl, the Li ＋ and H in the first liquid L1 ＋ Li from adsorbent 1 by exchange with ＋ The desorption of Li may be represented by the following chemical formula 5: ｘ M + xHCl → H ｘ M+xLiCl (5)

[0040] The adsorbent may comprise an oxide containing manganese. For example, Li ＋ The adsorbent adsorbed Li ｘ Mn ２ O ｙ (Li ｘ Mn ２ O ｙ where x satisfies 0.5≦x≦2.0, and Li ｘ Mn ２ O ｙ In the formula, y satisfies the relationship 3.0≦y≦5.0. ＋ The adsorbent that adsorbed Li ｘ Mn ２ O ｙ When containing Li ＋ The adsorbent before Li is adsorbed, or Li ＋ After desorption, the adsorbent contains Mn ２ O ｙ or H ｘ Mn ２ O ｙ For example, as shown in the following chemical formula 6, Li ＋ Li ｘ Mn ２ O ｙ By desorbing from ２ O ｙFor example, as shown in Chemical Formula 7 below, Li may be formed in the adsorption step. ＋ is Mn ２ O ｙ By adsorbing onto ｘ Mn ２ O ｙ may be formed. ｘ Mn ２ O ｙ → Mn ２ O ｙ +xLi ＋ +xe － (6) Mn ２ O ｙ +xLi ＋ +xe － → Li ｘ Mn ２ O ｙ (7) For example, as shown in the following chemical formula 8, in the desorption step, Li ｘ Mn ２ O ｙ Li inside ＋ H ＋ By replacing with ｘ Mn ２ O ｙ For example, as shown in Chemical Formula 9 below, in the adsorption step, H ｘ Mn ２ O ｙ H inside ＋ Li ＋ By replacing with Li ｘ Mn ２ O ｙ may be formed. ｘ Mn ２ O ｙ + xHCl → H ｘ Mn ２ O ｙ +xLiCl (8) H ｘ Mn ２ O ｙ + xLiCl → Li ｘ Mn ２ O ｙ + xHCl (9)

[0041] For example, Li ＋ The adsorbent is LiMn ２ O４ Li ＋ The adsorbent is LiMn ２ O ４ When containing Li ＋ The adsorbent before Li is adsorbed, or Li ＋ After desorption, the adsorbent is λ-MnO ２ (spinel-type manganese dioxide) or HMn ２ O ４ may include:

[0042] For example, Li ＋ The adsorbent adsorbed Li １．６ Mn １．６ O ４ Li ＋ The adsorbent that adsorbed Li １．６ Mn １．６ O ４ When containing Li ＋ The adsorbent before Li is adsorbed, or Li ＋ After desorption, the adsorbent contains Mn １．６ O ４ or H １．６ Mn １．６ O ４ may include:

[0043] Li ＋ The adsorbent 1 adsorbed Li ０．７８ Mn １．８８ O ４ , Li ０．４ Mn ０．６ O, Li ４ Mn ５ O １２ , and Li １．０５ Mn １．９５ O ３．９９ It may contain at least one component selected from the group consisting of:

[0044] Adsorbent 1 is Li ＋The adsorbent 1 may further contain other components in addition to the above-mentioned components (active material components) that adsorb and desorb Li. For example, the adsorbent 1 may be a mixture further containing at least one component selected from a conductive material (conductive additive) and a binder (adhesive) as other components. For example, the conductive material may be at least one component selected from carbon black and an inert metal. For example, the binder may be a resin (e.g., polyvinylidene fluoride). The adsorbent 1 may further contain other components that adsorb and desorb Li. ＋ The adsorbent 1 may include an active material layer containing an active material component that adsorbs and desorbs the adsorbent, and a current collector on which the active material layer is laminated. Both the front and back surfaces of the current collector may be covered with the active material layer. For example, the active material layer may be the above-mentioned mixture containing the active material component, a conductive material, and a binder. For example, the current collector may be a chemically inert metal. The overall shape of the adsorbent 1 may be a plate or belt. During the desorption step, the adsorbent 1 in the form of a plate or belt may move through the first liquid L1.

[0045] The electrode 3, which is the counter electrode of the adsorbent 1 in the desorption step, is not limited to an electrode containing hexacyanoferrate. The electrode 3 may be made of any material that is not easily corroded by the second liquid L2 in which the electrode 3 is immersed. For example, the electrode 3 may contain at least one conductor selected from the group consisting of platinum, platinum black, gold, glassy carbon, diamond, aluminum, iron, nickel, and stainless steel (SUS). The electrode 3 may consist solely of a conductor. During the desorption step, H ２ The electrode 3 preferably contains platinum because platinum is easily generated at the electrode 3. The electrode 3 may have a plate shape.

[0046] The desorption tank 32 may be made of a chemically inert material.

[0047] The second liquid L2 that has undergone the desorption step is recovered from the desorption tank 32. A lithium salt with a reduced content of impurities is recovered from the second liquid L2 that has undergone the desorption step. For example, the lithium salt may be recovered from the second liquid L2 by drying the second liquid L2 recovered from the desorption tank 32. When the second liquid L2 recovered from the desorption tank 32 contains both LiOH and LiCl, one or both of LiOH and LiCl may be recovered from the second liquid L2 by crystallization utilizing the difference in solubility between LiOH and LiCl.

[0048] (Adsorption Step) The method for producing a lithium salt according to this embodiment may further include an adsorption step described below, and the desorption step may be carried out after the adsorption step. For example, as shown in Fig. 2, a lithium salt production system 100 according to this embodiment may further include one or more electrodes 2 different from the counter electrode (electrode 3) used in the desorption step, and one or more adsorption tanks 31, in order to carry out the adsorption step.

[0049] In the adsorption step, raw water 21 containing LiCl, one or more adsorbents 1 (Li ＋ The adsorbent 1 (before adsorption) and one or more electrodes 2 are placed in one adsorption tank 31. A part or the whole of the adsorbent 1 and a part or the whole of the electrode 2 may be immersed in the raw water 21.

[0050] In the adsorption process, the electrode 2 is the counter electrode of the adsorbent 1. The adsorbent 1 and the electrode 2 are electrically connected to a power source 10 and are spaced apart from each other in the raw water 21. In the adsorption process, the adsorbent 1 is the cathode (negative electrode), and the electrode 2 is the anode (positive electrode). In the adsorption process, the power source 10 applies a voltage between the adsorbent 1 and the electrode 2 in the raw water 21, and reduces the potential of the adsorbent 1 below the potential of the electrode 2. As a result, Li in the raw water 21 ＋ In other words, lithium in the raw water 21 can be concentrated in the adsorbent 1 through the adsorption process without carrying out a conventional concentration process using a chemical. ＋The adsorbent 1 after desorption may be used in the adsorption step. The adsorption step and the desorption step after the adsorption step may be repeated by reusing the adsorbent 1. During the adsorption step, the adsorbent 1, which is a plate or a belt, may move through the raw water 21.

[0051] The voltage (adsorption voltage) applied between the adsorbent 1 and the electrode 2 in the adsorption step is not particularly limited. For example, the adsorption voltage may be equal to or lower than a voltage at which oxygen is not generated in the adsorbent 1. For example, the voltage (potential of the adsorbent 1) based on a standard hydrogen electrode (SHE) in the adsorption step may be equal to or higher than 0 V vs. SHE and equal to or lower than 1.23 V vs. SHE.

[0052] Li in raw water 21 ＋ The reaction in which Li is adsorbed onto the adsorbent 1 (cathode) may be represented by the following chemical formula 10 or 11. ｘ M represents the adsorbent 1. In the following chemical formulas 10 and 11, x represents Li ｘ M+xLi is a real number representing the molar ratio of Li in M. In the following chemical formulas 10 and 11, M represents the components of the adsorbent 1 excluding lithium and hydrogen. ＋ +xe － → Li ｘ M (10) H ｘ M+xLiCl → Li ｘ M+xHCl (11)

[0053] The reaction occurring at electrode 2 (anode) during the adsorption process may be represented by the following chemical formula 12: ２ (oxygen) may be produced at electrode 2. (3x / 2)H ２ O → (1x / 4)O ２ +xH ３ O ＋ +xe － (12)

[0054] For example, the raw water 21 containing LiCl may include at least one of brine from a salt lake and seawater. The raw water 21 may consist only of brine from a salt lake. The raw water 21 may consist only of seawater. The raw water 21 may include both brine from a salt lake and seawater. The LiCl content (concentration) in the raw water 21 may be 0.1 mass ppm or more and 10 mass% or less in terms of Li. The pH of the raw water 21 containing LiCl may be 7 or more.

[0055] The electrode 2 (counter electrode for the adsorption process) may be made of any material that is not easily corroded by the raw water 21 in which the electrode 2 is immersed. For example, the electrode 2 may contain at least one conductor selected from the group consisting of platinum, platinum black, gold, glassy carbon, diamond, aluminum, iron, nickel, and stainless steel (SUS). The electrode 2 may consist solely of a conductor. The composition of the electrode 2 for the adsorption process may be the same as the composition of the electrode 3 for the desorption process. The composition of the electrode 2 for the adsorption process may be different from the composition of the electrode 3 for the desorption process. The electrode 2 used in the adsorption process may be used as the electrode 3 in the desorption process. For example, the shape of the electrode 2 may be a plate.

[0056] The adsorption vessel 31 may be made of a chemically inert material.

[0057] (Washing Step) The method for producing a lithium salt according to this embodiment may further include a washing step described below. The washing step may be performed after the adsorption step, and the desorption step may be performed after the washing step. For example, as shown in FIG. 2 , the system 100 for producing a lithium salt according to this embodiment may further include one or more washing tanks 33 for performing the washing step.

[0058] In the washing step, a washing liquid 22 containing water and one or more adsorbents 1 (Li ＋ The adsorbent 1) on which the carbon black is adsorbed is placed in one cleaning tank 33. The adsorbent 1 may be partially or entirely immersed in the cleaning liquid 22. During the cleaning process, the adsorbent 1 in the form of a plate or belt may move through the cleaning liquid 22.

[0059] Impurities in the raw materials for the positive electrode of a lithium ion secondary battery deteriorate the performance of the lithium ion secondary battery, so lithium salts with reduced impurity content are desired. Impurities derived from the raw water 21 can be removed from the adsorbent 1 by the washing step. As a result, high-purity lithium salts can be obtained in the desorption step following the washing step. For example, impurities derived from the raw water 21 include Na ＋ (sodium ion), K ＋ (potassium ion), Ca ２＋ (calcium ions), and Mg ２＋ (magnesium ions). When a lithium salt other than LiCl is produced, Cl derived from the raw water 21 may be used. － (chloride ions) are also removed as impurities from the adsorbent 1 by the washing step. By reusing the adsorbent 1, the adsorption step, the washing step after the adsorption step, and the desorption step after the washing step may be repeated in this order. Note that the "high purity lithium salt" in this embodiment refers to the Li salt that has permeated the cation exchange membrane 4 in the desorption step. ＋ The term "high purity" does not necessarily mean that the absolute value of the purity of the lithium salt is higher than the absolute value of the purity of lithium salts obtained by conventional production methods. For example, the purity of the lithium salt produced by the lithium salt production method according to this embodiment may be 99% by mass or more and 100% by mass or less.

[0060] For example, the cleaning liquid 22 may be pure water. When LiOH is produced as the lithium salt, the cleaning liquid 22 may be an aqueous solution of LiOH. When LiCl is produced as the lithium salt, the cleaning liquid 22 may be an aqueous solution of LiCl. When LiCO is produced as the lithium salt, the cleaning liquid 22 may be an aqueous solution of LiCl. ３ is produced, the cleaning solution 22 is LiCO ３ The cleaning solution 22 may be an aqueous solution of the above. The cleaning solution 22 may be neutral or basic (alkaline). For example, the pH of the cleaning solution 22 may be 7.0 or more and 14.0 or less.

[0061] The cleaning tank 33 may be made of a chemically inert material.

[0062] The power supplied to the manufacturing system by the power source 10 may be generated by thermal power generation using fossil fuels or nuclear power generation. The power source 10 may include a renewable energy power generation device that implements at least one power generation method selected from the group consisting of solar power generation, wind power generation, geothermal power generation, hydroelectric power generation, and tidal power generation.

[0063] The present disclosure is not necessarily limited to the above-described embodiments. Various modifications of the present disclosure are possible without departing from the spirit of the present disclosure, and these modifications are also included in the present disclosure.

[0064] The present disclosure will be described in detail with reference to the following examples and comparative examples, but the present disclosure is not limited to the following examples.

[0065] (Example 1) Based on the method described in Non-Patent Document 2, LiMn ２ O ４ A working electrode (WE) was fabricated, which consisted of an adsorbent made of the above and a platinum plate covered with the adsorbent. The details of the fabrication method of the working electrode were as follows.

[0066] The platinum plate had a square shape and dimensions of 20 mm length x 20 mm width.

[0067] LiNO ３ and Mn(NO ３ ) ２ The molar ratio of Li to Mn (Li / Mn) in the mixed solution was adjusted to 0.5. ２ O ４ The final concentration of LiNO in the mixed solution is 2 mol / L. ３ and Mn(NO ３ ) ２ The concentrations of each were adjusted.

[0068] Paper wipers (Kimwipes manufactured by Nippon Paper Crecia Co., Ltd.) ＴＭThe mixed solution was then applied to the entire surface of the platinum plate using the wiper. The platinum plate with the mixed solution applied was dried at room temperature. After drying, the platinum plate was heated at 820°C for several minutes in the air. ２ O ４ The heated platinum plate was cooled to room temperature. The above series of steps, including applying the mixed solution to the platinum plate, drying the platinum plate, heating, and cooling, was repeated 15 times. Finally, the platinum plate was heated in air at 820°C for 5 minutes.

[0069] By the above method, a working electrode was produced.

[0070] Before carrying out chronopotentiometry, which will be described later, the X-ray diffraction (XRD) pattern of the unused working electrode was measured. ＴＭ A type diffractometer was used. The measurement conditions for the XRD pattern were as follows: X-ray source: CuKα radiation; Generation voltage: 40 kV; Generation current: 40 mA; Measurement angle (2θ range): 10° to 50°; Divergence slit: 1°; Divergence vertical limiting slit: 2 mm; Scattering slit: 1°; Receiving slit: 0.3 mm; Monochrome receiving slit: None; Step size: 0.02°; Scan speed: 1° / min; Measurement mode: 2θ / θ mode; Scan type: Continuous scan; Time / step: 1 second; Measurement environment: Atmosphere

[0071] The XRD pattern is shown in Figure 3. The XRD pattern is ２ O ４ The XRD pattern contained peaks derived from the lattice plane of LiMn ２ O ４ It was confirmed that the LiMn alloy had a spinel crystal structure. ２ O ４ The lattice constant of LiMn in Figure 3 was 0.812 nm. The XRD pattern also contained peaks derived from the lattice plane of Pt. ２ O ４The peaks resulting from the lattice plane of Pt are marked with circles. The peaks resulting from the lattice plane of Pt in FIG. 3 are marked with squares.

[0072] Chronopotentiometry was performed in the following manner.

[0073] An aqueous solution of LiCl (first solution) and an aqueous solution of LiOH (second solution) were placed in an electrolysis device (desorption tank). The first and second solutions in the electrolysis device were separated from each other by a cation exchange membrane. That is, the first solution was in contact with one surface of the cation exchange membrane, and the second solution was in contact with the other surface of the cation exchange membrane.

[0074] The concentration of LiCl in the first solution was 100 mM. The concentration of LiOH in the second solution was 100 mM. Note that 1 mM is 1 × 10 －３ Equal to mol / L.

[0075] The cation exchange membrane used was Neocepta CSE manufactured by Astom Corporation. ＴＭ Neocepta CSE was used. ＴＭ The ionic conductivity of －３ S / cm. Neocepta CSE ＴＭ The membrane thickness of Neocepta CSE was 160 μm. ＴＭ The electrical resistance is 1.8 Ω cm ２ It was.

[0076] The working electrode described above was immersed in the first solution (aqueous solution of LiCl). An electrode consisting of only a platinum plate was immersed in the second solution (aqueous solution of LiOH) as a counter electrode (Counter Electrode; CE) to the working electrode. The working electrode and counter electrode were connected to a power supply to apply a voltage between them. A reference electrode (Reference Electrode; RE) was installed in the electrolysis apparatus to measure the potential of the working electrode. A silver / silver chloride electrode (Ag / AgCl electrode) was used as the reference electrode.

[0077] Chronopotentiometry was carried out using the following desorption step followed by the following adsorption step: Both the desorption step and the adsorption step were carried out at room temperature (20-25°C).

[0078] The potential of the working electrode during the desorption process was maintained at a value higher than the potential of the counter electrode. The voltage applied between the working electrode and the counter electrode was continuously adjusted so that the current at the working electrode during the desorption process was maintained at 0.5 mA (constant current). The potential of the working electrode relative to the reference electrode during the desorption process was continuously measured at 2-second intervals for 15,000 seconds. The time-dependent change in the potential E (unit: V) of the working electrode relative to the reference electrode during the desorption process of Example 1 is shown in Figures 4 and 5.

[0079] After the desorption step, the XRD pattern of the working electrode was measured by the above-mentioned method. The XRD pattern of the working electrode after the desorption step is also shown in FIG. 3. From the XRD pattern, it was found that the adsorbent after the desorption step was λ-MnO ２ It was confirmed that the λ-MnO ２ The lattice constant of the adsorbent (LiMn ２ O ４ ) from Li ＋ The lattice constant of the adsorbent decreased with the desorption of . ２ Peaks arising from lattice planes are marked with triangles.

[0080] Following the desorption step, an adsorption step was carried out. Before the start of the adsorption step, the second liquid in which the counter electrode was immersed was replaced with an aqueous solution of LiCl. The concentration of LiCl in the second liquid used in the adsorption step was 100 mM. In the adsorption step, the working electrode, counter electrode, first liquid, and cation exchange membrane that had undergone the desorption step were used as they were. The potential of the working electrode during the desorption step was maintained at a value lower than the potential of the counter electrode. The potential of the working electrode relative to the reference electrode during the adsorption step was continuously measured in the same manner as in the desorption step, except that the potential of the working electrode was lower than the potential of the counter electrode. The change over time in the potential E (unit: V) of the working electrode relative to the reference electrode during the adsorption step of Example 1 is shown in Figure 4.

[0081] (Examples 2 to 4) The concentration of LiCl in the first liquid of Example 2 before the desorption step was started was 100 mM. The concentration of LiOH in the second liquid of Example 2 before the desorption step was started was 800 mM.

[0082] The concentration of LiCl in the first liquid of Example 3 before the desorption step was started was 4000 mM. The concentration of LiOH in the second liquid of Example 3 before the desorption step was started was 4000 mM.

[0083] The concentration of LiCl in the first liquid of Example 4 before the desorption step was 4000 mM. The concentration of LiOH in the second liquid of Example 4 before the desorption step was 100 mM.

[0084] Except for the above-mentioned points, the desorption step of each of Examples 2 to 4 was carried out in the same manner as in Example 1. The change over time in the potential E (unit: V) of the working electrode with respect to the reference electrode during the desorption step of each of Examples 2 to 4 is shown in FIG.

[0085] For example, the method for producing a lithium salt according to one aspect of the present disclosure may be implemented as a method for producing a raw material for the positive electrode of a lithium ion secondary battery.

[0086] 1...adsorbent, 2...electrode for adsorption process, 3...electrode for desorption process, 4...cation exchange membrane, 10...power source, 21...raw material water containing LiCl, 22...cleaning liquid, L1...first liquid, L2...second liquid, 31...adsorption tank, 32...desorption tank, 33...cleaning tank, 100...lithium salt production system

Claims

1. A method for detecting Li+ in a cation exchange membrane, comprising: a first liquid and a second liquid separated from each other by a cation exchange membrane; an adsorbent immersed in the first liquid; ＋ is desorbed from the adsorbent into the first liquid, ＋ is passed through the cation exchange membrane, ＋ moves from the first liquid into the second liquid, and the Li ＋ The lithium salt is obtained in the second liquid containing the lithium salt.

2. An electrode is immersed in the second liquid, and a voltage is applied between the adsorbent and the electrode, and the potential of the adsorbent is increased above the potential of the electrode, thereby ＋ is desorbed from the adsorbent and permeates the cation exchange membrane, and OH － is generated in the second liquid, and the Li ＋ and the OH － The method for producing a lithium salt according to claim 1 , wherein LiOH is produced from 3. The method for producing a lithium salt according to claim 2, wherein the lithium salt is LiOH.

4. The second liquid is ＋ The method for producing a lithium salt according to claim 2 , wherein the adsorbent contains a cation other than 5. The method for producing a lithium salt according to claim 4, wherein the electrode contains hexacyanoferrate.

6. The Li in the adsorbent ＋ and H in the first liquid ＋ By exchanging with ＋ The method for producing a lithium salt according to claim 1 , wherein is desorbed from the adsorbent.

7. The method for producing a lithium salt according to claim 1 or 2, wherein the adsorbent contains an oxide containing manganese.

8. A lithium salt production system used in the lithium salt production method described in claim 1, comprising the cation exchange membrane, the adsorbent, and a desorption tank, wherein the cation exchange membrane is disposed in the desorption tank, the first liquid, the second liquid, and the adsorbent are contained in the desorption tank, and the first liquid and the second liquid are separated from each other within the desorption tank via the cation exchange membrane.

9. The method further comprises providing an electrode and a power source, wherein the electrode is immersed in the second liquid, and the power source applies a voltage between the adsorbent and the electrode, and increases the potential of the adsorbent higher than the potential of the electrode, thereby converting the Li ＋ is desorbed from the adsorbent and permeates the cation exchange membrane, and OH － is generated in the second liquid, and the Li ＋ and the OH － The system for producing a lithium salt according to claim 8 , wherein LiOH is produced from 10. The lithium salt production system according to claim 9, wherein the lithium salt is LiOH.

11. The second liquid is ＋ 10. The system for producing a lithium salt according to claim 9, wherein the lithium salt contains cations other than the above, and the power source applies the voltage between the adsorbent and the electrode, thereby causing the cations to be adsorbed onto the electrode.

12. The system for producing a lithium salt according to claim 11, wherein the electrode comprises hexacyanoferrate.

13. The Li in the adsorbent ＋ and H in the first liquid ＋ By exchanging with ＋ The system for producing a lithium salt according to claim 8 , wherein is desorbed from the adsorbent.

14. The system for producing a lithium salt according to claim 8 or 9, wherein the adsorbent comprises an oxide containing manganese.

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