A method for preparing electrolyte salt

Abstract

This article discloses a method for preparing electrolyte salt, which belongs to the technical field of lithium extraction from salt lakes. In this article, salt lake brine is first extracted with an organic phase to obtain a lithium-rich organic phase, and the lithium-rich organic phase is used as the cathode electrolyte for electrolysis, which can enrich and recover lithium to the anode chamber while generating lithium hexafluorophosphate. When using lithium-rich electrodes and lithium-poor electrodes for electrolysis, the method has high selectivity for lithium, which can effectively prevent other impurity ions from being extracted into the organic phase. [PF6] in the ionic liquid in the cathode chamber ‑ LiPF6 electrolyte salt is formed in the organic solution that passes through the membrane into the anode compartment.

Description

Technical Field

[0001] This article relates to the technical field of lithium extraction from salt lakes, and specifically to a method for preparing electrolyte salt. Background Art

[0002] Lithium and its compounds are important raw materials used in metallurgy, nuclear reactions and the chemical industry. In particular, with the rapid development of the lithium battery industry in recent years, our demand for lithium has surged. Electrolyte is one of the four main materials of lithium-ion batteries. The main components of lithium battery electrolyte are solvents, solutes and additives. The solute is a provider of lithium ions. Among them, lithium hexafluorophosphate is the most widely used. Currently, lithium hexafluorophosphate is mainly prepared by dissolving lithium halide in anhydrous hydrogen fluoride and then introducing high-purity PF5 gas for reaction.

[0003] Salt lake brine has huge reserves of lithium resources, so lithium extraction from salt lakes has attracted more and more attention. At present, the methods for extracting lithium from salt lake brine mainly include precipitation, adsorption, carbonization, calcination leaching and solvent extraction. Among them, solvent extraction is more widely used. When using solvent extraction, FeCl3 is inevitably used as a co-extractant, which increases the density of the extracted organic phase and reduces the density difference between the two phases. It places high demands on the extraction and separation equipment. Traditional mixing and settling tanks are difficult to meet the process requirements. High-efficiency centrifugal extraction equipment must be used, and the equipment is expensive. In addition, since the organic phase contains the co-extractant FeCl3, the brine must be kept weakly acidic, otherwise it will cause Fe hydrolysis, and the brine entering the extraction section must be acidified.

[0004] In addition, salt lake brine usually contains Na + , K + When the concentration of coexisting cations is too high, it is easy to react with Li + Enter the extract together and give Li + For salt lake brine with high sodium-lithium ratio, it is necessary to pre-treat the salt lake brine with high sodium-lithium ratio to reduce the Na + With Li + The mass ratio of Na+ and K + etc., resulting in a long production cycle. Summary of the Invention

[0005] The purpose of this article is to overcome the shortcomings of the existing technology and provide a method for preparing electrolyte salt, which can prepare LiPF6 electrolyte salt.

[0006] To achieve the above objectives, the technical solutions adopted in this paper are:

[0007] A method for preparing an electrolyte salt comprises the following steps:

[0008] extracting salt lake brine with an organic phase to obtain a lithium-rich organic phase, wherein the organic phase comprises an extractant and a hexafluorophosphate ionic liquid;

[0009] An electrolysis device comprising an anode chamber and a cathode chamber is provided, wherein a lithium-rich electrode is used as an anode, a lithium-poor electrode is used as a cathode, a lithium hexafluorophosphate solution is used as an anolyte, and a lithium-rich organic phase is used as a cathode electrolyte for electrolysis;

[0010] The positions of the lithium-rich electrode and the lithium-poor electrode are interchanged, and electrolysis is performed to form lithium hexafluorophosphate electrolyte salt in the anode chamber.

[0011] In this paper, the salt lake brine is first extracted with an organic phase to obtain a lithium-rich organic phase. The lithium-rich organic phase is used as the cathode electrolyte for electrolysis, which can enrich lithium and recover it to the anode chamber while generating lithium hexafluorophosphate. When using lithium-rich electrodes and lithium-poor electrodes for electrolysis, it has a high selectivity for lithium, which can effectively prevent other impurity ions from being extracted into the organic phase and prevent impurity ions from entering the anode chamber. During electrolysis, the lithium ions in the lithium-rich organic phase are embedded in the lithium-poor electrode, and the lithium ions in the lithium-rich electrode are released into the anode electrolyte. After exchange, the lithium ions embedded in the lithium-poor electrode are released, and the [PF6] in the ionic liquid in the cathode chamber is released. - LiPF6 electrolyte salt is formed in the organic solution that passes through the membrane into the anode compartment.

[0012] Exemplarily, the electrolysis device is a conventional electrolysis device in the art, such as an electrolytic cell.

[0013] In one embodiment, the volume ratio of the organic phase to the salt lake brine is (0.5-4):1; controlling the volume ratio of the organic phase to the salt lake brine within this range can effectively enrich the lithium in the salt lake brine.

[0014] In one embodiment, the volume ratio of the organic phase to the salt lake brine is (1-2): 1. Controlling the volume ratio of the organic phase to the salt lake brine within this range can effectively enrich the lithium in the salt lake brine, while improving the phase separation speed and extraction speed.

[0015] In one embodiment, the volume ratio of the extractant to the hexafluorophosphate ionic liquid is (5-30):(60-95).

[0016] In one embodiment, the volume ratio of the extractant to the hexafluorophosphate ionic liquid is (10-30):(60-95).

[0017] In one embodiment, the volume ratio of the extractant to the hexafluorophosphate ionic liquid is (10-20):(80-90).

[0018] In one embodiment, the extractant is tributyl phosphate.

[0019] In one embodiment, the hexafluorophosphate ionic liquid is at least one of 1-butyl-3-methylimidazolium hexafluorophosphate, 1-hexyl-3-methylimidazolium hexafluorophosphate, and 1-octyl-3-methylimidazolium hexafluorophosphate.

[0020] This paper uses tributyl phosphate as the extraction agent, which has high selectivity and high extraction rate for lithium, will not cause emulsification, avoids the use of ferric chloride co-extraction agent, and does not require acidification of the brine. This paper directly electrolyzes after extraction, avoiding the subsequent back-extraction process that uses a large amount of high-concentration acidic liquid to damage the equipment, thereby simplifying the extraction process.

[0021] Among them, the hexafluorophosphate ionic liquid has stable properties and can provide [PF6] - , and then can react with the lithium ions released from the lithium-deficient electrode to form LiPF6 electrolyte salt in the ionic liquid in the cathode chamber.

[0022] In one embodiment, the membrane comprises an anion exchange membrane.

[0023] In one embodiment, the lithium-rich electrode is a LiMn2O4 electrode, a LiFePO4 electrode, a Li2TiO3 electrode, a Li7Ti5O 12 Electrode, LiNi x Co y Mn 1-x-y at least one of the O2 electrodes;

[0024] Among them, 0<x<1, 0<y<1.

[0025] Among them, the representative LiNi x Co y Mn 1-x-y O2 electrode is LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (abbreviated as NCM333) electrode.

[0026] For example, the preparation method of the lithium-rich electrode is illustrated by taking the LiFePO4 electrode as an example: LiFePO4, a conductive agent, and a binder are mixed evenly in a mass ratio of (70-85): (8-15): (8-15), applied to the surface of the current collector, and dried to obtain the LiFePO4 electrode.

[0027] For example, the coating amount is 10 to 30 mg / cm 2 .

[0028] Exemplarily, the conductive agent is at least one of carbon black, acetylene black, carbon nanotubes, and graphene.

[0029] Exemplarily, the binder is PVDF.

[0030] When LiMn2O4 electrode, Li2TiO3 electrode, Li7Ti5O 12 Electrode, LiNi x Co y Mn 1-x-y When using O2 electrode, just replace LiFePO4 with corresponding LiMn2O4, Li2TiO3, Li7Ti5O 12 、LiNi x Co y Mn 1-x-y O2 is enough.

[0031] In one embodiment, the lithium-deficient electrode is Li 1-a MnO4 electrode, Li 1-a FePO4 electrode, Li 2-b TiO3 electrode, Li 7-c Ti5O 12 Electrode, Li 1-a Ni x Co y Mn 1-x-y at least one of the O2 electrodes;

[0032] Among them, 0<a<1, 0<b<2, 0<c<7.

[0033] For example, Li 1-a The preparation method of the lithium-deficient electrode is illustrated as an example of the FePO4 electrode: the LiFePO4 electrode prepared above is used as the positive electrode, the AgCl electrode is used as the negative electrode, and is placed in the electrolyte. Lithium is removed at a constant voltage. When the current is as low as 0.2 mA, the reaction stops and Li 1-a FePO4 electrode.

[0034] This paper first uses a lithium-rich electrode as the anode and a lithium-poor electrode as the cathode. During the electrolysis process, the lithium ions of the lithium-rich organic phase are embedded in the lithium-poor electrode, and the lithium ions of the lithium-rich electrode are released into the anode electrolyte. After the exchange, the lithium ions embedded in the lithium-poor electrode are released, and the [PF6] in the ionic liquid of the cathode chamber - LiPF6 electrolyte salt is formed in the organic solution that passes through the membrane into the anode compartment.

[0035] In one embodiment, the lithium hexafluorophosphate solution includes lithium hexafluorophosphate and an organic solvent.

[0036] In one embodiment, the concentration of lithium hexafluorophosphate in the lithium hexafluorophosphate solution is 20-100 mmol / L.

[0037] In one embodiment, the concentration of lithium hexafluorophosphate in the lithium hexafluorophosphate solution is 40-60 mmol / L.

[0038] In one embodiment, the organic solvent is at least one of dimethyl carbonate, propylene carbonate, ethylene carbonate, diethyl carbonate, and ethyl methyl carbonate. After electrolysis, the solution in the anode chamber is a mixture of high-purity lithium hexafluorophosphate and the organic solvent. The solution in the anode chamber can be directly used as the electrolyte for a secondary battery.

[0039] In one embodiment, the voltage of the electrolysis is 1-4V.

[0040] The beneficial effects of this paper are as follows: (1) This paper first extracts salt lake brine with an organic phase to obtain a lithium-rich organic phase, and uses the lithium-rich organic phase as the cathode electrolyte for electrolysis, which can enrich lithium and recover it to the anode chamber while generating lithium hexafluorophosphate. When using lithium-rich electrodes and lithium-poor electrodes for electrolysis, it has a high selectivity for lithium, which can effectively prevent other impurity ions from being extracted into the organic phase and prevent impurity ions from entering the anode chamber. During electrolysis, the lithium ions in the lithium-rich organic phase are embedded in the lithium-poor electrode, and the lithium ions in the lithium-rich electrode are released into the anode electrolyte. After exchange, the lithium ions embedded in the lithium-poor electrode are released, and the [PF6] in the ionic liquid in the cathode chamber is released. - LiPF6 electrolyte salt is formed in the organic solution that enters the anode chamber through the membrane; (2) the extractant and hexafluorophosphate ionic liquid in the organic phase of this article have high selectivity and high extraction rate for lithium, and will not cause emulsification, avoid the use of ferric chloride co-extractant, and do not need to acidify the brine. This article directly electrolyzes after extraction, avoiding the subsequent back extraction process using a large amount of high-concentration acidic liquid to damage the equipment, thereby simplifying the extraction process. DETAILED DESCRIPTION

[0041] In order to better illustrate the purpose, technical solutions and advantages of this article, this article will be further described below in conjunction with specific embodiments and comparative examples. The purpose is to understand the content of this article in detail, rather than to limit this article.

[0042] Unless otherwise specified, the experimental reagents and instruments involved in the implementation of this article are commonly used reagents and instruments.

[0043] Example 1

[0044] A method for preparing an electrolyte salt comprises the following steps:

[0045] (1) Preparation of lithium-rich electrode: LiFePO4, carbon black, and PVDF were mixed in a mass ratio of 80:10:10 and heated to 15 mg / cm 2The coating amount is applied on the surface of the carbon cloth and dried to obtain the LiFePO4 lithium-rich electrode.

[0046] (2) Preparation of lithium-poor electrode: The lithium-rich LiFePO4 electrode of step (1) is used as the positive electrode and the AgCl electrode is used as the negative electrode. The electrodes are placed in a 0.5 mol / L NaCl electrolyte and delithiation is performed at a voltage of 1.1 V. When the current is as low as 0.2 mA, the reaction is stopped to obtain Li 1-a FePO4 lithium-poor electrode.

[0047] (3) tributyl phosphate and 1-butyl-3-methylimidazolium hexafluorophosphate were mixed in a volume ratio of 85:15 to obtain an organic phase. The organic phase and the aqueous phase were placed on a constant temperature oscillator in a volume ratio of 1.5:1 for 30 minutes to mix, allowed to stand for 20 minutes, and centrifuged to obtain a lithium-rich organic phase.

[0048] The ion concentrations (g / L) in salt lake brine are: Li + 1.59g / L, Na + 98.56g / L, Mg 2+ 92.47g / L, K + 20.33g / L, B 6.03g / L, Cl - 273.1g / L.

[0049] (4) preparing a lithium hexafluorophosphate solution having a lithium hexafluorophosphate concentration of 50 mmol / L by mixing lithium hexafluorophosphate and dimethyl carbonate;

[0050] (5) The electrolytic cell is divided into an anode chamber and a cathode chamber by an anion exchange membrane, and the LiFePO4 lithium-rich electrode is placed in the anode chamber as the anode. 1-a The FePO4 lithium-poor electrode was placed in the cathode chamber as the cathode, lithium hexafluorophosphate solution was used as the anolyte, and the lithium-rich organic phase was used as the catholyte. A voltage of 2 V was applied to the anode and cathode, and electrolysis was carried out at room temperature for 1.5 h.

[0051] (6) LiFePO4 lithium-rich electrode, Li 1-a The FePO4 lithium-poor electrode was taken out and rinsed, and then the two positions were swapped (i.e. the LiFePO4 lithium-rich electrode was placed in the cathode chamber and the Li 1-a The FePO4 lithium-poor electrode is placed in the anode chamber), a voltage of 2V is applied to the cathode and anode, and electrolysis is carried out at room temperature for 1.5 hours. The anode chamber solution is LiPF6 electrolyte salt.

[0052] Example 2

[0053] A method for preparing an electrolyte salt comprises the following steps:

[0054] (1) Preparation of lithium-rich electrode: LiMn2O4, carbon black and PVDF were mixed in a mass ratio of 80:10:10 and heated to 15 mg / cm 2 The coating amount is applied on the surface of the carbon cloth and dried to obtain the LiMn2O4 lithium-rich electrode.

[0055] (2) Preparation of lithium-poor electrode: The lithium-rich LiMn2O4 electrode of step (1) is used as the positive electrode and the AgCl electrode is used as the negative electrode. The electrodes are placed in a 0.5 mol / L NaCl electrolyte and delithiation is performed at a voltage of 1.1 V. When the current is as low as 0.2 mA, the reaction is stopped to obtain Li 1-a Mn2O4 lithium-poor electrode.

[0056] (3) tributyl phosphate and 1-butyl-3-methylimidazolium hexafluorophosphate were mixed in a volume ratio of 90:10 to obtain an organic phase. Salt lake brine was used as the aqueous phase. The organic phase and the aqueous phase were placed on a constant temperature oscillator in a volume ratio of 1:1 and oscillated for 30 minutes to mix evenly. The mixture was allowed to stand for 20 minutes and centrifuged to obtain a lithium-rich organic phase.

[0057] The ion concentrations (g / L) in salt lake brine are: Li + 1.59g / L, Na + 98.56g / L, Mg 2+ 92.47g / L, K + 20.33g / L, B 6.03g / L, Cl - 273.1g / L.

[0058] (4) preparing a lithium hexafluorophosphate solution having a lithium hexafluorophosphate concentration of 50 mmol / L by mixing lithium hexafluorophosphate, dimethyl carbonate, and ethylene carbonate, wherein the volume ratio of dimethyl carbonate to ethylene carbonate is 2:1;

[0059] (5) The electrolytic cell is divided into an anode chamber and a cathode chamber by an anion exchange membrane, and the LiMn2O4 lithium-rich electrode is placed in the anode chamber as the anode. 1-a The Mn2O4 lithium-poor electrode was placed in the cathode chamber as the cathode, lithium hexafluorophosphate solution was used as the anolyte, and the lithium-rich organic phase was used as the catholyte. A voltage of 2.3 V was applied to the anode and cathode, and electrolysis was carried out at room temperature for 1 hour.

[0060] (6) LiMn2O4 lithium-rich electrode, Li 1-a The Mn2O4 lithium-poor electrode was taken out and rinsed, and then the two positions were swapped (i.e. the LiMn2O4 lithium-rich electrode was placed in the cathode chamber and the Li 1-aThe Mn2O4 lithium-poor electrode is placed in the anode chamber), a voltage of 2.3V is applied to the cathode and anode, and electrolysis is carried out at room temperature for 1 hour. The anode chamber solution is LiPF6 electrolyte salt.

[0061] Example 3

[0062] A method for preparing an electrolyte salt comprises the following steps:

[0063] (1) Preparation of lithium-rich electrode: LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, carbon black and PVDF were mixed evenly in a mass ratio of 80:10:10 and the mixture was heated to 15 mg / cm 2 The coating amount is applied on the surface of the carbon cloth and dried to obtain LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 lithium-rich electrode.

[0064] (2) Preparation of lithium-poor electrode: LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 The O2 lithium-rich electrode is used as the positive electrode and the AgCl electrode is used as the negative electrode. It is placed in a 0.5 mol / L NaCl electrolyte and delithiation is carried out at a voltage of 1.1 V. When the current is as low as 0.2 mA, the reaction stops and LiNi is obtained. 1-d Co 1 / 3 Mn 1 / 3 O2 lithium-poor electrode.

[0065] (3) tributyl phosphate and 1-hexyl-3-methylimidazolium hexafluorophosphate were mixed in a volume ratio of 80:20 to obtain an organic phase. Salt lake brine was used as the aqueous phase. The organic phase and the aqueous phase were placed on a constant temperature oscillator in a volume ratio of 2:1 and oscillated for 30 minutes to mix evenly. The mixture was allowed to stand for 20 minutes and centrifuged to obtain a lithium-rich organic phase.

[0066] The ion concentrations (g / L) in salt lake brine are: Li + 1.59g / L, Na + 98.56g / L, Mg 2+ 92.47g / L, K + 20.33g / L, B 6.03g / L, Cl - 273.1g / L.

[0067] (4) preparing a lithium hexafluorophosphate solution having a lithium hexafluorophosphate concentration of 50 mmol / L by mixing lithium hexafluorophosphate, dimethyl carbonate and ethyl methyl carbonate, wherein the volume ratio of dimethyl carbonate to ethyl methyl carbonate is 1:1;

[0068] (5) Use an anion exchange membrane to divide the electrolytic cell into an anode chamber and a cathode chamber, and LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 The O2 lithium-rich electrode is placed in the anode chamber as the anode, and the LiNi 1-d Co 1 / 3 Mn 1 / 3 The O2 lithium-poor electrode was placed in the cathode chamber as the cathode, lithium hexafluorophosphate solution was used as the anolyte, and lithium-rich organic phase was used as the catholyte. A voltage of 1 V was applied to the anode and cathode, and electrolysis was carried out at room temperature for 2 h.

[0069] (6) LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 lithium-rich electrode, LiNi 1-d Co 1 / 3 Mn 1 / 3 The O2 lithium-poor electrode was taken out and rinsed, and then the two positions were swapped (LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 The O2 lithium-rich electrode is placed in the cathode chamber, and the LiNi 1-d Co 1 / 3Mn 1 / 3 The O2 lithium-poor electrode is placed in the anode chamber), a voltage of 1V is applied to the cathode and anode, and electrolysis is carried out at room temperature for 2 hours. The anode chamber solution is LiPF6 electrolyte salt.

[0070] Example 4

[0071] A method for preparing an electrolyte salt comprises the following steps:

[0072] (1) Preparation of lithium-rich electrode: LiFePO4, carbon black, and PVDF were mixed in a mass ratio of 80:10:10 and heated to 15 mg / cm 2 The coating amount is applied on the surface of the carbon cloth and dried to obtain the LiFePO4 lithium-rich electrode.

[0073] (2) Preparation of lithium-poor electrode: The lithium-rich LiFePO4 electrode of step (1) is used as the positive electrode and the AgCl electrode is used as the negative electrode. The electrodes are placed in a 0.5 mol / L NaCl electrolyte and delithiation is performed at a voltage of 1.1 V. When the current is as low as 0.2 mA, the reaction is stopped to obtain Li 1-a FePO4 lithium-poor electrode.

[0074] (3) tributyl phosphate and 1-butyl-3-methylimidazolium hexafluorophosphate were mixed in a volume ratio of 85:15 to obtain an organic phase. The organic phase and the aqueous phase were placed on a constant temperature oscillator in a volume ratio of 1.5:1 for 30 minutes to mix, allowed to stand for 20 minutes, and centrifuged to obtain a lithium-rich organic phase.

[0075] The ion concentrations (g / L) in salt lake brine are: Li + 0.55g / L, Na + 49.39g / L, Mg 2+ 122.42g / L, K + 16.97g / L, B 5.37g / L, Cl - 72.19g / L.

[0076] (4) preparing a lithium hexafluorophosphate solution having a lithium hexafluorophosphate concentration of 50 mmol / L by mixing lithium hexafluorophosphate and dimethyl carbonate;

[0077] (5) The electrolytic cell is divided into an anode chamber and a cathode chamber by an anion exchange membrane, and the LiFePO4 lithium-rich electrode is placed in the anode chamber as the anode. 1-a The FePO4 lithium-poor electrode was placed in the cathode chamber as the cathode, lithium hexafluorophosphate solution was used as the anolyte, and the lithium-rich organic phase was used as the catholyte. A voltage of 2 V was applied to the anode and cathode, and electrolysis was carried out at room temperature for 1.5 h.

[0078] (6) LiFePO4 lithium-rich electrode, Li 1-a The FePO4 lithium-poor electrode was taken out and rinsed, and then the two positions were swapped (i.e. the LiFePO4 lithium-rich electrode was placed in the cathode chamber and the Li 1-a The FePO4 lithium-poor electrode is placed in the anode chamber), a voltage of 2V is applied to the cathode and anode, and electrolysis is carried out at room temperature for 1.5 hours. The anode chamber solution is LiPF6 electrolyte salt.

[0079] Example 5

[0080] A method for preparing an electrolyte salt comprises the following steps:

[0081] (1) Preparation of lithium-rich electrode: Li2TiO3, carbon black and PVDF were mixed in a mass ratio of 80:10:10 and heated to 15 mg / cm 2 The coating amount is applied on the surface of the carbon cloth and dried to obtain the Li2TiO3 lithium-rich electrode.

[0082] (2) Preparation of lithium-poor electrode: The lithium-rich Li2TiO3 electrode of step (1) is used as the positive electrode and the AgCl electrode is used as the negative electrode. The electrodes are placed in a 0.5 mol / L NaCl electrolyte and delithiation is performed at a voltage of 1.1 V. When the current is as low as 0.2 mA, the reaction is stopped to obtain Li 2-b TiO3 lithium-poor electrode.

[0083] (3) tributyl phosphate and 1-butyl-3-methylimidazolium hexafluorophosphate were mixed in a volume ratio of 85:15 to obtain an organic phase. The organic phase and the aqueous phase were placed on a constant temperature oscillator in a volume ratio of 1.5:1 for 30 minutes to mix, allowed to stand for 20 minutes, and centrifuged to obtain a lithium-rich organic phase.

[0084] The ion concentrations (g / L) in salt lake brine are: Li + 1.59g / L, Na + 98.56g / L, Mg 2+ 92.47g / L, K + 20.33g / L, B 6.03g / L, Cl - 273.1g / L.

[0085] (4) preparing a lithium hexafluorophosphate solution having a lithium hexafluorophosphate concentration of 50 mmol / L by mixing lithium hexafluorophosphate and dimethyl carbonate;

[0086] (5) The electrolytic cell is divided into an anode chamber and a cathode chamber by an anion exchange membrane, and the Li2TiO3 lithium-rich electrode is placed in the anode chamber as the anode. 2-b A TiO3 lithium-poor electrode was placed in the cathode chamber as the cathode, lithium hexafluorophosphate solution was used as the anolyte, and a lithium-rich organic phase was used as the catholyte. A voltage of 2 V was applied to the anode and cathode, and electrolysis was carried out at room temperature for 1.5 h.

[0087] (6) Li2TiO3 lithium-rich electrode, Li 2-b The TiO3 lithium-poor electrode was taken out and rinsed, and then the two positions were swapped (i.e. the Li2TiO3 lithium-rich electrode was placed in the cathode chamber, and the Li 2-b A TiO3 lithium-poor electrode is placed in the anode chamber), a voltage of 2V is applied to the cathode and anode, and electrolysis is carried out at room temperature for 1.5 hours. The anode chamber solution is LiPF6 electrolyte salt.

[0088] Comparative Example 1

[0089] A method for preparing an electrolyte salt comprises the following steps:

[0090] (1) Preparation of lithium-rich electrode: LiFePO4, carbon black, and PVDF were mixed in a mass ratio of 80:10:10 and heated to 15 mg / cm 2 The coating amount is applied on the surface of the carbon cloth and dried to obtain the LiFePO4 lithium-rich electrode.

[0091] (2) Preparation of lithium-poor electrode: The lithium-rich LiFePO4 electrode of step (1) is used as the positive electrode and the AgCl electrode is used as the negative electrode. The electrodes are placed in a 0.5 mol / L NaCl electrolyte and delithiation is performed at a voltage of 2 V. When the current is as low as 0.2 mA, the reaction is stopped to obtain Li 1-a FePO4 lithium-poor electrode.

[0092] (3) tributyl phosphate and 1-butyl-3-methylimidazolium hexafluorophosphate were mixed in a volume ratio of 85:15 to obtain an organic phase. The organic phase and the aqueous phase were placed on a constant temperature oscillator in a volume ratio of 1.5:1 for 30 minutes to mix, allowed to stand for 20 minutes, and centrifuged to obtain a lithium-rich organic phase.

[0093] The ion concentrations (g / L) in salt lake brine are: Li + 1.59g / L, Na + 98.56g / L, Mg 2+ 92.47g / L, K + 20.33g / L, B 6.03g / L, Cl - 273.1g / L.

[0094] (4) preparing a lithium hexafluorophosphate solution having a lithium hexafluorophosphate concentration of 50 mmol / L by mixing lithium hexafluorophosphate and dimethyl carbonate;

[0095] (5) The electrolytic cell is divided into an anode chamber and a cathode chamber by an anion exchange membrane, and the LiFePO4 lithium-rich electrode is placed in the anode chamber as the anode. 1-a The FePO4 lithium-poor electrode is placed in the cathode chamber as the cathode, lithium hexafluorophosphate solution is used as the anode electrolyte, and the lithium-rich organic phase is used as the cathode electrolyte. A voltage of 2V is applied to the anode and cathode, and electrolysis is carried out at room temperature for 1.5 hours. The anode chamber solution is LiPF6 electrolyte salt.

[0096] Comparative Example 2

[0097] Comparative Example 2 was extracted and then back-extracted with hydrochloric acid.

[0098] A method for preparing an electrolyte salt comprises the following steps:

[0099] (1) tributyl phosphate and 1-butyl-3-methylimidazolium hexafluorophosphate were mixed in a volume ratio of 85:15 to obtain an organic phase, and salt lake brine was used as the aqueous phase. The organic phase and the aqueous phase were placed on a constant temperature oscillator in a volume ratio of 1.5:1 and oscillated for 30 minutes to mix evenly, allowed to stand for 20 minutes, and centrifuged to obtain a lithium-rich organic phase;

[0100] The ion concentrations (g / L) in salt lake brine are: Li + 1.59g / L, Na + 98.56g / L, Mg 2+ 92.47g / L, K + 20.33g / L, B 6.03g / L, Cl - 273.1g / L.

[0101] (2) Add 0.5 mol / L hydrochloric acid solution to the lithium-rich organic phase after extraction, with the volume ratio of hydrochloric acid solution to lithium-rich organic phase being 1:1, oscillate on a constant temperature oscillator for 30 minutes, and allow to stand for phase separation to obtain a stripping organic phase.

[0102] Comparative Example 3

[0103] Comparative Example 3 was subjected to back extraction with hydrochloric acid after extraction.

[0104] A method for preparing an electrolyte salt comprises the following steps:

[0105] (1) tributyl phosphate and 1-butyl-3-methylimidazolium hexafluorophosphate were mixed in a volume ratio of 85:15 to obtain an organic phase, and salt lake brine was used as the aqueous phase. The organic phase and the aqueous phase were placed on a constant temperature oscillator in a volume ratio of 1.5:1 and oscillated for 30 minutes to mix evenly, allowed to stand for 20 minutes, and centrifuged to obtain a lithium-rich organic phase;

[0106] The ion concentrations (g / L) in salt lake brine are: Li + 0.55g / L, Na + 98.56g / L, Mg 2+ 92.47g / L, K + 20.33g / L, B 6.03g / L, Cl - 273.1g / L.

[0107] (2) Add 1 mol / L hydrochloric acid solution to the lithium-rich organic phase after extraction, with the volume ratio of hydrochloric acid solution to lithium-rich organic phase being 1:1, oscillate on a constant temperature oscillator for 30 minutes, and allow to stand for phase separation to obtain a stripping organic phase.

[0108] Test Case

[0109] Performance testing: The lithium ion concentration and other impurity concentrations of the lithium-rich organic phase and LiPF6 electrolyte salt of Examples 1 to 5 and Comparative Example 1, as well as the lithium-rich organic phase and stripping organic phase of Comparative Examples 1 and 2 were tested using an inductively coupled plasma spectrometer (ICP) as shown in Table 1.

[0110] Table 1

[0111]

[0112]

[0113] It can be seen from Table 1 that the purity of lithium in the LiPF6 electrolyte salt of the examples in this article is as high as over 98%, indicating that after being treated by the method of this article, the content of impurity ions in the obtained LiPF6 electrolyte salt is extremely low, the purity of the LiPF6 electrolyte salt is high, and compared with the traditional stripping methods of Comparative Examples 2 and 3, the electrolysis effect of this article is significantly better than that of stripping.

Claims

1. A method for preparing an electrolyte salt, characterized in that: The following steps are involved: extracting salt lake brine with an organic phase to obtain a lithium-rich organic phase, wherein the organic phase comprises an extractant and a hexafluorophosphate ionic liquid; An electrolysis device comprising an anode chamber and a cathode chamber is provided, wherein a lithium-rich electrode is used as an anode, a lithium-poor electrode is used as a cathode, a lithium hexafluorophosphate solution is used as an anolyte, and a lithium-rich organic phase is used as a cathode electrolyte for electrolysis; wherein the anode chamber and the cathode chamber are separated by a membrane, and the membrane comprises an anion exchange membrane; The positions of the lithium-rich electrode and the lithium-poor electrode are interchanged, and electrolysis is performed to form lithium hexafluorophosphate electrolyte salt in the anode chamber.

2. The method for preparing an electrolyte salt according to claim 1, wherein The volume ratio of the organic phase to the salt lake brine is (0.5-4):

1.

3. The method for preparing an electrolyte salt according to claim 2, wherein The volume ratio of the organic phase to the salt lake brine is (1-2):

1.

4. The method for preparing an electrolyte salt according to claim 1, wherein The volume ratio of the extractant to the hexafluorophosphate ionic liquid is (5-30):(60-95).

5. The method for preparing an electrolyte salt according to claim 4, wherein The volume ratio of the extractant to the hexafluorophosphate ionic liquid is (10-30): (60-95).

6. The method for preparing an electrolyte salt according to claim 4, wherein The volume ratio of the extractant to the hexafluorophosphate ionic liquid is (10-20): (80-90).

7. The method for preparing an electrolyte salt according to claim 1, wherein The extractant is tributyl phosphate.

8. The method for preparing an electrolyte salt according to claim 1, wherein The hexafluorophosphate ionic liquid is at least one of 1-butyl-3-methylimidazolium hexafluorophosphate, 1-hexyl-3-methylimidazolium hexafluorophosphate, and 1-octyl-3-methylimidazolium hexafluorophosphate.

9. The method for preparing an electrolyte salt according to claim 1, wherein The lithium-rich electrode is a LiMn2O4 electrode, a LiFePO4 electrode, a Li2TiO3 electrode, a Li7Ti5O 12 Electrode, LiNi x Co y Mn 1-x-y at least one of the O2 electrodes; Among them, 0<x<1, 0<y<1.

10. The method for preparing an electrolyte salt according to claim 9, wherein The lithium-poor electrode is Li 1-a MnO4 electrode, Li 1-a FePO4 electrode, Li 2-b TiO3 electrode, Li 7-c Ti5O 12 Electrode, Li 1-a Ni x Co y Mn 1-x-y at least one of the O2 electrodes; Among them, 0<a<1, 0<b<2, 0<c<7.

11. The method for preparing an electrolyte salt according to claim 1, wherein The lithium hexafluorophosphate solution includes lithium hexafluorophosphate and an organic solvent.

12. The method for preparing an electrolyte salt according to claim 11, wherein The concentration of lithium hexafluorophosphate in the lithium hexafluorophosphate solution is 20 to 100 mmol / L.

13. The method for preparing an electrolyte salt according to claim 11, wherein The concentration of lithium hexafluorophosphate in the lithium hexafluorophosphate solution is 40 to 60 mmol / L.

14. The method for preparing an electrolyte salt according to claim 13, wherein The organic solvent is at least one of dimethyl carbonate, propylene carbonate, ethylene carbonate, diethyl carbonate, and ethyl methyl carbonate.

15. The method for preparing an electrolyte salt according to claim 1, wherein The voltage of the electrolysis is 1-4V.

Images