WO2024078526A1

WO2024078526A1 - A method and apparatus for preparing high-purity metallic lithium based on lithium-ion solid-liquid dual electrolyte

Info

Publication number: WO2024078526A1
Application number: PCT/CN2023/123993
Authority: WO
Inventors: Kai Liu; Di Zhang; Xinzhou LI; Yukang WU; Lemou WU
Original assignee: Beijing Yeeneng New Energy Technology Co., Ltd.
Priority date: 2022-10-11
Filing date: 2023-10-11
Publication date: 2024-04-18
Also published as: CN117904679A

Abstract

A method and apparatus are disclosed for producing high-purity metallic lithium based on a lithium-ion solid-liquid dual electrolyte. The method allows for the direct production of high-purity metallic lithium from low-purity LiCl by using a one-step process. Based on the disclosed techniques, the difficulty of obtaining low-purity LiCl from salt lakes is relatively low, the cost is low, and the environmental impact is minimal.

Description

A METHOD AND APPARATUS FOR PREPARING HIGH-PURITY METALLIC LITHIUM BASED ON LITHIUM-ION SOLID-LIQUID DUAL ELECTROLYTE

CROSS-REFERENCE TO RELATED APPLICATIONS

The present disclosure claims priority to Chinese Patent Application No. 202211241169.7, filed on October 11, 2022. The above application is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present disclosure relates to the technical field of metallic lithium preparation. Specifically, this application relates to a method and apparatus for preparing high-purity metallic lithium based on a lithium-ion solid-liquid dual electrolyte.

BACKGROUND

High-purity metallic lithium is the preferred negative electrode material for the next generation of high-energy density batteries, and it also has important applications in lightweight alloys and chemical synthesis. In 2021, “the dual circulation of domestic and overseas lithium resources” became an important proposition and development opportunity for China's lithium resource industry in the battery supply chain.

The electrolytic refining method is currently the main method for preparing metallic lithium, which requires using high-purity LiCl as a raw material. In addition, the electrolytic voltage is high, the process generates a large amount of chlorine, which is difficult to handle, and the electrolysis temperature is also relatively high (around 400℃ when using KCl as a co-solvent) .

To obtain high-purity LiCl, the current mainstream methods mainly focus on ore smelting and lithium extraction from salt lakes. Among the identified reserves, most of lithium resources are distributed in major salt lakes. Developing mining and metallurgical processes would rely heavily on imported ore resources. Therefore, lithium extraction from salt lake is an important method to China's lithium industry.

The current technologies to extract lithium from salt lakes mainly include chemical precipitation, extraction, and adsorption. However, the high magnesium-lithium ratio in China's salt lakes poses innate challenges for these methods, which require a large amount of reagents to obtain high-purity LiCl, resulting in potential environmental risks.

CN201611162024.2 relates to a method for purifying lithium chloride solution and preparing metallic lithium. The method mainly involves using an adsorption system containing ion exchange resin to adsorb the lithium chloride solution and obtain a purified solution that meets the requirements for impurity detection. The ion exchange resin is used to exchange the cations of sodium, potassium, magnesium, calcium, aluminum, iron, and the anions of borate and sulfate in the original lithium chloride solution, thus purifying it.

CN201910552745.1 provides a method for preparing metallic lithium and its application, which includes the following steps: (1) extracting the purified lithium-containing aqueous phase with an extracted organic phase, and separating the liquid to obtain the lithium-containing organic phase; (2) washing the lithium-containing organic phase obtained in step (1) with a washing solution; and (3) electrolyzing the washed lithium-containing organic phase to obtain metallic lithium.

CN201010111405.4 discloses a method for preparing metallic lithium by molten salt electrolysis, which includes the following steps: (1) drying lithium chloride and potassium chloride separately; (2) mixing the dried lithium chloride and potassium chloride at a weight ratio of 0.8-1.3: 1, and heating the mixture in an electrolytic cell until it is completely melted; (3) when the temperature of the electrolyte is stable at 415℃-450℃, cool the electrolytic cell with cooling water to form a stable crust layer on the cell wall; (4) carry out direct current electrolysis while starting the magnetic pump and fan to circulate the alkali solution in the tail gas recovery system reactor; (5) after the electrolyzing for 0.5-2 hours, collect the liquid metallic lithium produced at the cathode, and cast it into ingots under the protection of an inert gas, and discharge the chlorine generated at the anode, cool it to room temperature and absorb it with an alkali solution to obtain a sodium hypochlorite solution.

CN201110306668.5 discloses a method for preparing the metallic lithium through electrolysis. An aqueous solution containing at least lithium-ions is arranged in an anode cavity of the electrolytic tank, and an organic solvent with lithium-ion conductivity is arranged in the cathode cavity. The diaphragm for separating the anode cavity and the cathode cavity is a lithium-ion conductor ceramic membrane with a lithium-ion conductor property or a composite membrane of a lithium-ion conductor and a polymer. Applying direct-current voltage to the anode current collector and the cathode current collector at room temperature and atmospheric pressure, enabling lithium ions in the water phase in the anode cavity to penetrate through the diaphragm with the lithium-ion conductor characteristic under the voltage driving effect, reducing the lithium ions into metallic lithium elementary substances in the organic solvent of the cathode cavity, and depositing and enriching on the surface of the cathode current collector to obtain a product, wherein the cathode cavity is an inert atmosphere.

CN201980092700.9 discloses an electrolysis method that includes electrolyzing a molten mixture containing lithium salts. In this method, the anode contacts the molten mixture, and the cathode is separated from the molten mixture by a solid electrolyte that can conduct lithium ions. The solid electrolyte allows lithium ions to pass through but not the other atoms.

CN201910377098.5 discloses a method for preparing metallic lithium based on solid-state electrolyte. The method includes using a mixture containing metallic lithium as the anode, and a solid-state electrolyte containing lithium ions as the electrolyte, and carrying out an electrolytic reaction in an electrolysis device to obtain metallic lithium at the cathode.

Although the applicant's previous research has achieved the preparation of metallic lithium through solid-state electrolytes, there are still some shortcomings, such as low spatial utilization, limited lifespan, high production cost, and difficulty in industrial production.

SUMMARY

According to an aspect of the present disclosure, a method for preparing high-purity metallic lithium from low-concentration LiCl by using a lithium-ion solid-liquid dual electrolyte, including: selecting a metal to be inserted into an anodic salt as a sacrificial anode; preparing the anode salt including a mixture obtained by mixing lithium chloride and a chloride of a metal of the sacrificial anode with content of lithium chloride of 1 wt%-98 wt%, wherein the chloride of the metal of the sacrificial anode is selected to provide a melting point of the mixture lower than lithium chloride; providing a lithium-ion solid-liquid dual electrolyte, wherein the lithium-ion solid-liquid dual electrolyte includes an inorganic solid electrolyte with high selectivity for Li ions, and a liquid electrolyte comprising one or more molten salts containing at least one lithium salt, wherein a melting point of the one or more molten salts is lower than an electrolysis temperature of an electrolytic reaction to produce metallic lithium; providing an inert conductor as a cathode; and obtaining metallic lithium by the electrolytic reaction.

In some embodiments, the electrolysis temperature is 100-800℃.

In some embodiments, the electrolysis temperature is 200-700℃.

In some embodiments, the electrolysis temperature is 250-600℃.

In some embodiments, the electrolysis temperature is 300-500℃.

In some embodiments, the electrolytic reaction is conducted with a voltage of 0-3.5V.

In some embodiments, the voltage is 1.0-3.0V.

In some embodiments, the voltage is 1.5-2.5V.

In some embodiments, the liquid electrolyte is positioned between the metallic lithium and the solid electrolyte.

In some embodiments, the electrolytic reaction includes: an overall reaction: Me +nLiCl = MeCl_n + nLi, where Me is the metal of the sacrificial anode, and n = 1, 2, 3, or 4; at the sacrificial anode: Me-ne-=Meⁿ⁺; at the solid electrolyte: Li⁺ (anode) → Li⁺ (liquid electrolyte) ; at the liquid electrolyte: Li⁺ (from solid electrolyte layer) → Li⁺ (at cathode) ; and at the cathode: Li+ + e=Li.

In some embodiments, the liquid electrolyte includes one or more of LiF, KF, NaF, RbF, CsF, BaF₂, LiCl, KCl, NaCl, RbCl, CsCl, BaCl₂, LiBr, KBr, NaBr, RbBr, CsBr, BaBr₂, LiI, KI, NaI, RbI, CsI, BaI₂, LiNO₃, KNO₃, NaNO₃, RbNO₃, CsNO₃, Ba (NO₃) ₂.

In some embodiments, the liquid electrolyte includes LiBr-KBr-CsBr molten salt, wherein LiBr is 30 wt%-50 wt%, KBr is 10 wt%-30 wt%, and CsBr is 30 wt%-50 wt%.

According to another aspect of the present disclosure, a device for preparing high-purity metallic lithium is provided. The device includes a sacrificial anode, anode melt, a lithium-ion solid electrolyte, a lithium-ion liquid electrolyte, a cathode, and a metallic lithium collection structure, wherein: the lithium-ion solid electrolyte includes an inorganic solid-state electrolyte with highly selectivity for Li ions; and the lithium-ion liquid electrolyte includes one or more molten salts containing at least one lithium salt, wherein a melting point of the one or more molten salts is lower than an electrolysis temperature of an electrolytic reaction.

In some embodiments, the lithium-ion liquid electrolyte is placed in a liquid electrolyte storage tank, and the liquid electrolyte storage tank is embedded in the lithium-ion solid electrolyte.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and/or additional aspects and advantages of the present disclosure will become apparent and easily understood from the following description of embodiments in conjunction with the accompanying drawings, in which:

Fig. 1 is a schematic diagram of a device for extracting lithium according to one example embodiment, where 1 represents the metallic lithium product, 2 represents the cathode electrode, 3 represents the liquid electrolyte, 4 represents the solid electrolyte, 5 represents the sacrificial anode electrode, and 6 represents the electrolytic anode.

Fig. 2 is a basic configuration of the device for extracting lithium according to one example embodiment, where 7 represents the cathode electron protection layer, 8 represents the glass seal, 9 represents the metallic lithium product, 10 represents the cathode electrode, 11 represents the liquid electrolyte, 12 represents the solid electrolyte, 13 represents the electrolytic anode, 14 represents the cathode tank support, and 15 represents the sacrificial anode.

Fig. 3 shows a lithium extraction device with an added gas-lifting electrode according to one example embodiment, where 16 represents the gas-lifting electrode, 17 represents the metallic lithium product, 18 represents the glass seal, 19 represents the liquid electrolyte, 20 represents the electrolyte anode, 21 represents the solid electrolyte, and 22 represents the sacrificial anode.

Fig. 4 shows a device for extracting lithium according to one example embodiment, where 23 represents the cathode electrode, 24 represents the glass seal, 25 represents the metallic lithium product, 26 represents the solid electrolyte tube, 27 represents the liquid electrolyte, 28 represents the anode electrode, and 29 represents the sacrificial anode.

Fig. 5 shows the electrochemical curves of the operational process for Example 1.

Figs. 6A and 6B are pictures showing the disassembly of the device of Example 1.

Fig. 7 shows the electrochemical curves of the operational process for Example 2.

Fig. 8 shows the electrochemical curves of the operational process for Example 3.

Fig. 9 is a picture showing the metallic lithium generated at the cathode in Example 3.

Fig. 10 shows the configuration of the device in Example 4, where 30 represents the cathode electrode, 31 represents the metallic lithium product, 32 represents the heat-resistant cement, 33 represents the glass seal, 34 represents the liquid electrolyte, 35 represents the electrolytic anode, and 36 represents the sacrificial anode.

Figs. 11 and 12 are the electrochemical curves of the operating process of Example 4.

Fig. 13 shows the metallic lithium generated at the cathode in Example 4.

Fig. 14 shows a device photo of Example 5.

Fig. 15 shows the operating data of the device in Example 5.

Fig. 16 shows the metallic lithium generated on the cathode in Example 5.

DETAILED DESCRIPTION OF EMBODIMENTS

The present disclosure provides a method and apparatus for preparing high-purity metallic lithium based on a dual-electrolyte system having solid and liquid lithium-ion electrolytes. The method can use low-purity LiCl as a raw material to directly produce high-purity metallic lithium in one step. The production of low-purity LiCl from salt lakes is relatively easy, low-cost, and environmentally friendly. Therefore, the disclosed technology can help in the development and utilization of salt lake lithium resources.

The present disclosure provides a technique for obtaining high-purity metallic lithium (with a purity of ≥96 wt%) based on a dual solid-liquid electrolyte system. One of the technical advantages of this solution is that it can use low-purity LiCl (with a LiCl content of 1wt%-98wt%) as a raw material. The lithium-ion solid-state electrolyte (including but not limited to inorganic solid-state electrolytes such as Ta-doped Li₇La₃Zr₂O₁₂ (LLZTO) and Li_1+xAlxTi_2-x (PO₄) ₃ (x=0-0.5, abbreviated as LATP) has high selectivity for lithium ions, and the lithium-ion liquid electrolyte (including but not limited to low-melting lithium-containing mixed salts such as LiI-CsI, LiBr-KBr-CsBr) is used to separate the solid-state electrolyte from metallic lithium to reduce the corrosion of the solid-state electrolyte by metallic lithium. High-purity metallic lithium may be obtained in one step under electrolysis. Compared with traditional purification processes, this method is more environmentally friendly, has fewer steps, has lower purification costs, and does not produce chlorine. Additionally, it has a lower electrolysis voltage.

The present disclosure also provides devices and configurations for realizing the above-mentioned techniques.

The present disclosure first provides a technique for preparing high-purity metallic lithium from low-concentration LiCl using a lithium-ion solid-liquid dual electrolyte. The solution can include the following steps.

First, this technique is configured to be conducted at higher temperatures, with the temperature at 100-800℃;

① sacrificial anode: inserting a metal (such as Al, Zn, etc. ) participating in the reaction into the anode salt as a sacrificial anode. For example, aluminum may be used as the sacrificial anode due to its advantages of easy availability of raw materials, low cost, and low reaction potential.

② anode salt: Metal chlorides (such as AlCl₃, ZnCl₂, etc. ) participating in the reaction are mixed with low-purity LiCl raw materials to form a low-melting-point mixture salt as the anode salt. The salt is melted by heating above its melting point during the purification process.

③ lithium-ion solid-liquid dual electrolyte: The solid electrolyte layer uses inorganic solid electrolytes with high lithium-ion selectivity such as LLZTO or LATP. The solid electrolyte can exist in different physical forms with unlimited size, such as plate-like, columnar, bowl-shaped, box-shaped, and tubular. The liquid electrolyte is located between the metallic lithium and the solid electrolyte, and uses one or more of LiF, KF, NaF, RbF, CsF, BaF₂, LiCl, KCl, NaCl, RbCl, CsCl, BaCl₂, LiBr, KBr, NaBr, RbBr, CsBr, BaBr₂, LiI, KI, NaI, RbI, CsI, BaI₂, LiNO₃, KNO₃, NaNO₃, RbNO₃, CsNO₃, Ba (NO₃) ₂ to form a low-melting-point molten salt (containing at least one lithium salt, with a melting point lower than the operating temperature of the device) to protect the solid electrolyte and reduce the corrosion of the solid electrolyte by the metallic lithium while ensuring smooth lithium-ion transport.

④ cathode: An inert conductor is used as the cathode, inserted into the liquid electrolyte and kept as close as possible to the solid electrolyte without touching it.

The reaction including:

an overall reaction: Me + nLiCl = MeCl_n + nLi, where Me is the metal of the sacrificial anode, and n = 1, 2, 3, or 4;

at the sacrificial anode: Me -ne^-= Meⁿ⁺;

at the solid electrolyte: Li⁺ (anode) → Li⁺ (liquid electrolyte) ;

at the liquid electrolyte: Li⁺ (from solid electrolyte layer) → Li⁺ (at cathode) ; and

at the cathode: Li⁺ + e^-= Li.

In some embodiments, the reaction is conducted between a temperature of 100℃-800℃.

The present disclosure provides a method for preparing high-purity metallic lithium from low-concentration LiCl through a lithium-ion solid-liquid dual electrolyte, including:

(1) choosing a metal to be inserted into the anode salt as the sacrificial electrode;

(2) preparing a low-melting-point anode melt, which is a mixture of lithium chloride and other salts;

(3) selecting a lithium-ion solid-liquid dual electrolyte, where the solid electrolyte is an inorganic solid electrolyte with high selectivity for lithium ions and the liquid electrolyte is a low-melting point molten salt consisting of one or more salts, including at least one lithium salt, with a melting point lower than the operating temperature of the electrolysis process;

(4) choosing an inert conductor as the cathode;

(5) preparing metallic lithium through electrolytic reaction.

In some embodiments, the electrolytic reaction may be conducted at a temperature of 100-800℃, 200-700℃, 250-600℃, or 300-500℃.

In some embodiments, the voltage range for the electrolytic reaction may be 0-3.5V, 1.0-3.0V, or 1.5-2.5V

In some embodiments, the liquid electrolyte is positioned between the metallic lithium and the solid electrolyte layer.

In some embodiments, the sacrificial anode electrode selected for the anode may be a metal, alloy or conductor with higher metallicity than Li, including but not limited to elemental metals such as Al and Zn, and alloys thereof.

In some embodiments, the anode molten salt may be a low-melting mixed salt obtained by mixing chloride of the sacrificial anode metal and salts (including but not limited to AlCl₃, ZnCl₂) that can coordinate with LiCl to lower the melting point of the system with crude LiCl raw materials.

Further, the main material components of the solid-state electrolyte include but are not limited to Li₇La₃Zr₂O₁₂ (LLZO) , Li_1+xAlxTi_2-x (PO₄) ₃ (x=0-0.5) (LATP) and their doped materials, which are applicable to the solid-state electrolyte. Ta-doped Li₇La₃Zr₂O₁₂ (LLZTO) may be used. The solid-state electrolyte is not limited by its physical form, including but not limited to plate, tube, column, bowl, trough, box, and other forms. The plate-shaped structure may be employed.

In some embodiments, one or more of the following low-melting-point salts may be used as the liquid electrolyte: LiF, KF, NaF, RbF, CsF, BaF₂, LiCl, KCl, NaCl, RbCl, CsCl, BaCl₂, LiBr, KBr, NaBr, RbBr, CsBr, BaBr₂, LiI, KI, NaI, RbI, CsI, BaI₂, LiNO₃, KNO₃, NaNO₃, RbNO₃, CsNO₃, Ba (NO₃) ₂, where the low-melting-point salts contains at least one lithium salt and have a melting point lower than the operating temperature of the device. The low-melting-point salt may be LiBr-KBr-CsBr, for example.

In some embodiments, the electrolysis cathode may use an inert conductor as the cathode, which is inserted into the liquid electrolyte and is as close as possible to the solid electrolyte without touching it. The material for the cathode may be nickel, nickel alloys or stainless steel.

In some embodiments, the electrolytic reaction including:

at the sacrificial anode: Me -ne^-= Meⁿ⁺;

at the solid electrolyte: Li⁺ (anode) → Li⁺ (liquid electrolyte)

at the liquid electrolyte: Li⁺ (from solid electrolyte layer) → Li⁺ (at cathode)

at the cathode: Li⁺ + e^-= Li

The present disclosure provides a device for preparing high-purity metallic lithium through a lithium-ion solid-liquid dual electrolyte, which includes an anode sacrificial electrode, an anode molten salt, a lithium-ion solid-state electrolyte, a lithium-ion liquid-state electrolyte, a cathode, and a metallic lithium collection structure. The lithium-ion solid-state electrolyte is an inorganic solid-state electrolyte having high selectivity for Li ions, and the lithium-ion liquid-state electrolyte is one or more low-melting-point molten salts, at least one of which contains a lithium salt, and the melting point of the molten salt is lower than the operating temperature of the electrolysis.

In some embodiments, the lithium-ion liquid electrolyte is placed in a liquid electrolyte storage tank, which is embedded in the solid electrolyte.

In some embodiments, the liquid electrolyte storage tank embedded in the solid electrolyte is positioned inside the anode electrolytic cell, and the outer side of the solid electrolyte is completely immersed in the sacrificial anode.

In some embodiments, the main material of the storage tank is selected to stabilize the metallic lithium, for example, 304, 316 or nickel-based stainless steel. An insulating and stable covering layer can be coated on the outside of the tank. The solid electrolyte and the main body of the tank are to be sealed and embedded, and the transition layer can be selected, which may be, but is not limited to, one or more sealing technologies such as glass sealants and high-temperature resistant inorganic adhesive sealants.

In some embodiments, the anode molten salt is stored in the anode electrolysis cell for storing the anode molten salt and sacrificial anode. The material is selected to be resistant to molten salt corrosion, for example, 304, 316L, or alumina.

In some embodiments, the sacrificial anode used in the present disclosure is a metal, alloy, or conductive material that is more reactive than lithium, including but not limited to elemental metals such as Al and Zn, with a preference for Al and Zn alloys. The sacrificial anode is positioned inside the anode electrolysis cell, immersed in the anode molten salt and as close as possible to the solid-state electrolyte without contacting it. The other end of the sacrificial anode is connected to a dropout wire that passes through the anode electrolysis cell and is connected to the positive electrode.

In some embodiments, the cathode is made of an inert conductor and is positioned inside the liquid electrolyte. The cathode and the solid electrolyte should be as close as possible but not in contact with each other. The other end of the cathode is led out through a wire passing through the metallic lithium collection tank and connected to the negative electrode of the power source. Preferably, the cathode is made of metal Ni and its alloy or stainless steel.

In some embodiments, the electrolytic reaction may be conducted at a temperature of 100℃-800℃, 200℃-700℃, 250℃-600℃, or 300℃-500℃.

In some embodiments, the voltage of the electrolytic reaction may be 0V-3.5V, 1.0V-3.0V, or 1.5V-2.5V.

In some embodiments, the anode sacrificial electrode is made of a metal, alloy or conductor with a stronger affinity for electrons than Li, including but not limited to metal elements such as Al and Zn. Pure Al or an Al alloy may be employed.

In some embodiments, the anode molten salt may be a mixed salt of a low-melting point formed by mixing a chloride of a sacrificial anode metal and a salt (including but not limited to AlCl₃, ZnCl₂, etc. ) that can coordinate with LiCl to lower the melting point of the system. The LiCl content in the anode molten salt may be 1wt%-98wt%, or 10wt%-90wt%, or 20wt%-80wt%, or 30wt%-70wt%, or 40wt%-60wt%.

In some embodiments, the main constituent materials of the solid electrolyte include, but are not limited to, Li₇La₃Zr₂O₁₂ (LLZO) , Li_1+xAl_xTi_2-x (PO₄) ₃ (x=0-0.5) (LATP) , and their dopants, etc., which are applicable materials for solid electrolytes. The dopant may be Ta-doped Li₇La₃Zr₂O₁₂ (LLZTO) . The solid electrolyte is not limited by physical form, including but not limited to plate-shaped, tubular, columnar, bowl-shaped, trough-shaped, box-shaped, and the like. In some embodiments, a plate-like structure may be employed.

In some embodiments, the liquid electrolyte is a low-melting-point molten salt formed by a mixture of one or more of LiF, KF, NaF, RbF, CsF, BaF₂, LiCl, KCl, NaCl, RbCl, CsCl, BaCl₂, LiBr, KBr, NaBr, RbBr, CsBr, BaBr₂, LiI, KI, NaI, RbI, CsI, BaI₂, LiNO₃, KNO₃, NaNO₃, RbNO₃, CsNO₃, Ba (NO₃) ₂ (containing at least one lithium salt with a melting point lower than the operating temperature of the device) . The molten salt may be LiBr-KBr-CsBr, with LiBr ranging from 30wt%-50wt%, or 35wt%, or 40wt%, or 45wt%; KBr ranging from 10wt%-30wt%, or 15wt%, or 20wt%, or 25wt%; and CsBr ranging from 30wt%-50wt%, or 35wt%, or 40wt%, or 45wt%.

In some embodiments, the device includes a cathode gas-inflatable electrode.

In some embodiments, the main material of the storage tank for the metallic lithium collection groove may be a material that can stabilize the metallic lithium, which may be 304, 316 or nickel-based stainless steel. The opening of the tank is placed downwards, immersed in the liquid electrolyte molten salt without contacting the solid electrolyte, and the opening needs to be completely covered by the electrolytic cathode.

In some embodiments, under the electrochemical behavior, the metallic lithium is purified and formed in the metallic lithium collection tank.

The present disclosure also discloses a device and configuration for obtaining high-purity metallic lithium based on lithium-ion solid and liquid electrolyte double electrolysis, as shown in Fig. 1.

Specific technical implementations can refer to the methods described in the examples. In Example 1 and Example 4 (described below) , the lithium extraction devices based on tubular and plate-type configurations, respectively, are provided. Through relevant experimental data and results, the generation of high-purity metallic lithium is observed, with a purity of up to 99.98wt%, or 99-99.98wt%.

In examples 2 and 3 (described below) , the principle and effect of the metallic lithium purification based on the plate-type structure device were presented, which fully demonstrated the feasibility of the plate-type lithium extraction structure.

Example 5 (described below) provides a lithium purification device based on a cathode air-inflated electrode with related data. The device can operate for a long time and the purification purity reaches as high as 99.91wt%or 99-99.98wt%.

The electrolysis process, as shown in Fig. 1, involves the sacrifice of the anode plate at the anode end, which loses electrons to form metal cations that enter the molten salt system. At the same time, lithium ions with the same charge enter the liquid electrolyte through the solid electrolyte and then into the liquid electrolyte molten salt under the applied electric field. These ions are reduced to metallic Li at the inert electrode of the cathode by accepting electrons. Under the action of gravity and buoyancy, the molten metallic lithium separates from the liquid electrolyte molten salt and floats on the surface of the liquid electrolyte to form a product layer, that is, the metallic lithium layer. In FIG. 1, 1 represents the metallic lithium product, 2 represents the cathode electrode, 3 represents the liquid electrolyte, 4 represents the solid electrolyte, 5 represents the sacrificial anode electrode, and 6 represents the electrolytic anode

As shown in Fig. 2, based on the principle described in Fig. 1, a device configuration for implementing the principal scheme is formed. The configuration is an example of an implementation scheme based on the technical principle, and the specific implementation form is not limited to the configuration shown in Fig. 2. In FIG. 2, 7 represents the cathode electron protection layer, 8 represents the glass seal, 9 represents the metallic lithium product, 10 represents the cathode electrode, 11 represents the liquid electrolyte, 12 represents the solid electrolyte, 13 represents the electrolytic anode, 14 represents the cathode tank support, and 15 represents the sacrificial anode.

As shown in Fig. 3, based on the configuration in Fig. 2, the gas-lifting electrode is further optimized to increase the protection of inert gas atmosphere and further reduce the requirement for device sealing. In FIG. 3, 16 represents the gas-lifting electrode, 17 represents the metallic lithium product, 18 represents the glass seal, 19 represents the liquid electrolyte, 20 represents the electrolyte anode, 21 represents the solid electrolyte, and 22 represents the sacrificial anode.

The solid electrolyte is encapsulated in the device with insulating and sealing materials such as glass and ceramics, above the reserved hole of the liquid electrolyte tank. The tank material is selected to be structurally stable and corrosion-resistant to Li, with good impermeability. Stainless steel can be used, and the tank is filled with the liquid electrolyte, thus constructing the core structure of the device with solid and liquid electrolyte.

The device may be added an air-blown electrode to the actual device structure to provide an inert gas atmosphere protection for the metallic lithium product, while preventing self-discharge of the lithium product.

The positive pressure atmosphere provided by the gas-pressurized electrode in the cathode chamber allows the lithium product to be spontaneously squeezed out of the cathode chamber and form metallic lithium product.

In some embodiments, a metallic lithium collection tray is installed inside the liquid electrolyte reservoir. The collection tray is placed with its opening facing downwards and submerged in the molten liquid electrolyte, but not in contact with the solid electrolyte.

In some embodiments, the inert cathode electrode plate may be immersed into the liquid electrolyte, which is positioned inside the metallic lithium collecting groove and slightly higher than the opening position of the collecting groove.

In some embodiments, the device is operated by applying a voltage between 0V-3.5V while being heated to a temperature of 100℃-800℃ during the operation according to the described principle.

In some embodiments, under the electrochemical process, metallic lithium is purified and obtained in the metallic lithium collecting groove.

The present disclosure provides a method for obtaining high-purity metallic lithium based on a double-electrolyte including solid-state and liquid-state electrolytes, which includes several layers: an anode raw material molten salt layer and an anode sacrificial electrode layer, a solid-state electrolyte (e.g., made of LLZTO) , a liquid-state electrolyte, and a cathode electrode layer, and a product (metallic lithium) layer.

The present disclosure provides a device configuration for preparing high-purity metallic lithium from low-concentration LiCl via a lithium-ion solid-liquid dual electrolyte, which includes an anode electrolysis tank, a liquid electrolyte storage tank embedded with a solid electrolyte, a metallic lithium collection tank, an anode raw material molten salt, a liquid electrolyte, a sacrificial anode, a cathode, and a cathode gas-pressurized electrode.

The anode electrolysis tank is an anode molten salt storage tank used to store anode molten salt and sacrificial anodes. Its material is selected to be resistant to molten salt corrosion, for example, 304, 316L, or alumina.

The liquid electrolyte storage tank embedded with solid electrolyte is located inside the anode electrolysis tank, and the solid electrolyte is completely immersed and well wetted on the outside of the anode sacrificial electrode. The main material of the storage tank is selected based on stability to metallic lithium, for example, 304, 316, or nickel-based stainless steel. The tank can be appropriately covered with an insulating and stable molten salt coating. The solid electrolyte and the main body of the storage tank need to be sealed and embedded, and the transition layer can be selected but not limited to one or more sealing technologies such as glass sealants and high-temperature-resistant inorganic adhesive sealants.

The metallic lithium collection tank is made of a material that is stable to metallic Li, which may be 304, 316, or nickel-based stainless steel. The tank is positioned with its opening facing downwards and immersed in the liquid electrolyte melt but not in contact with the solid electrolyte. The opening of the tank must be completely covered by the electrolysis cathode.

The anodic raw material molten salt may be a metal, an alloy, or a conductor with higher metallic properties than Li, including but not limited to elemental metals such as Al, Zn, etc. In some embodiments, elemental metals or alloys of Al and Zn may be used.

The liquid electrolyte used is a low-melting-point molten salt mixture of one or more of LiF, KF, NaF, RbF, CsF, BaF₂, LiCl, KCl, NaCl, RbCl, CsCl, BaCl₂, LiBr, KBr, NaBr, RbBr, CsBr, BaBr₂, LiI, KI, NaI, RbI, CsI, BaI₂, LiNO₃, KNO₃, NaNO₃, RbNO₃, CsNO₃, Ba (NO₃) ₂, and must contain at least one lithium salt, with a melting point lower than the operating temperature of the device. The molten salt may be LiBr-KBr-CsBr.

The sacrificial anode used is a metal, alloy, or conductor whose metallic property is stronger than that of lithium, including but not limited to metal elements such as Al, Zn, or alloys thereof. The sacrificial anode is positioned inside the anode electrolysis cell, immersed in the anode melt. The sacrificial anode and the solid electrolyte may be as close as possible without contacting each other. The other end is connected to a lead wire that passes out of the anode electrolysis cell and is connected to the positive electrode.

The cathode is made of an inert conductor, positioned inside the liquid electrolyte and as close to the solid electrolyte as possible without contacting it. The other end of the cathode is led out through a wire that passes through the metallic lithium collection tank and is connected to the negative pole of the power source. Preferred materials for the cathode include nickel and its alloys or stainless steel.

The operating temperature of the device may be 100℃-800℃ with an applied voltage of 0 V -3.5V.

The present disclosure also provides a use of lithium-ion solid-liquid dual electrolyte in the preparation of high-purity metallic lithium.

Compared with traditional techniques, the techniques disclosed in the present disclosure provide advantages including higher purity, environmental friendliness, lower electrolysis voltage, lower production cost, and higher production efficiency.

The present disclosure uses solid-state electrolyte ceramic sheets as the electrolyte layer, which optimizes the spatial utilization rate of the tubular electrolyte. The sheet-like electrolyte may have the advantages of simple preparation, low manufacturing cost, and low difficulty in mass production.

Compared to the tubular structure, the technology disclosed in the present disclosure is more capable of achieving a protective effect on the electrolyte surface and has a longer lifespan (greater than or equal to 100 hours) when using a sheet-type electrolyte.

In this application, the long lifespan of the electrolyte used in the plate-type structure is due to the design of a solid-liquid dual electrolyte structure, where the liquid electrolyte serves as a protective layer for the solid electrolyte, and the ceramic electrolyte effectively isolates the metallic lithium product.

The superiority of the techniques disclosed is further demonstrated by the addition of a bubbler electrode as a means of introducing inert argon for gas protection, which reduces the sealing requirements of the device. The gas disturbance can block the discharge path between the metallic lithium and the anode, ensuring effective preparation of metallic lithium.

In the design of the production line, the present disclosure also provides a positive pressure atmosphere inside the lithium production tank through the use of the air-lifting electrode. The metallic lithium product can be transferred outside the tank for collection through a positive pressure pipeline.

In the following description, certain specific details are set forth in order to provide a thorough understanding of various embodiments of the disclosure. However, one skilled in the art will understand that the disclosure may be practiced without these details. Moreover, while various embodiments of the disclosure are disclosed herein, many adaptations and modifications may be made within the scope of the disclosure in accordance with the common general knowledge of those skilled in this art. Such modifications include the substitution of known equivalents for any aspect of the disclosure in order to achieve the same result in substantially the same way.

Unless the context requires otherwise, throughout the present specification and claims, the word “comprise” and variations thereof, such as, “comprises” and “comprising” are to be construed in an open, inclusive sense, that is as “including, but not limited to. ” Recitation of numeric ranges of values throughout the specification is intended to serve as a shorthand notation of referring individually to each separate value falling within the range inclusive of the values defining the range, and each separate value is incorporated in the specification as it were individually recited herein. Additionally, the singular forms “a, ” “an” and “the” include plural referents unless the context clearly dictates otherwise.

Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present disclosure. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment, but may be in some instances. In some embodiments, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of the present application. The terminology used is only for describing specific embodiments and is not intended to limit the exemplary embodiments based on the present application.

Example 1

Assemble the device with the configurations as shown in Fig. 4, and perform the purification of metallic lithium using the CT3002K tester produced by Wuhan Blue Electric Company. The electrochemical curves during the purification process is shown in Fig. 5, and the phenomenon observed after the operation is shown in Figs. 6A and 6B.

The apparatus shown in Fig. 4 was assembled for the purification of metallic lithium using the CT3002K tester produced by Wuhan Landian Company. The apparatus may be operated at a temperature of 500℃, which is selected at the critical point between the gas phase and the liquid phase of the molten salt. The anode molten salt was a mixture of LiCl+AlCl₃ (with a LiCl content of 25wt%) . The liquid electrolyte was a mixed molten salt of LiBr+KBr+CsBr (with a LiBr content of 39wt%, a KBr content of 18wt%, and a CsBr content of 43wt%) . The solid electrolyte was an LLZTO ceramic tube, which was bonded to a stainless steel shell in a glass-sealed form. The main material of the electrolytic cell was selected as 304 stainless steel. The anode sacrificial electrode was made of aluminum, and the cathode current collector was a nickel strip. The electrolytic current and cell voltage were shown in Fig. 5.

It can be seen that under the drive of the current, the cell voltage of the electrolytic cell reaches 1.7V, and under the idle program, the cell voltage can be kept stable at 1.7V. Electrochemical data shows that the voltage is maintained, indicating the generation of metallic lithium on the electrolytic cathode. Based on the calculation of the charging capacity, the production of metallic lithium is about 0.11g. The specific observation of the phenomenon is shown in the Fig. above, where the metallic luster of metallic lithium formed on the inside of the electrolyte tube wall is clearly observed at the position marked with a red box.

The purified product was subjected to ICP analysis, and the results are shown in Table 1.

Table 1. Lithium Product ICP Test Results

As shown in the table, the purity of the purified metallic lithium reached 99.98wt%, which is higher than the target purity of 99.9wt%for high-purity metallic lithium. This example demonstrates that the method disclosed in the present disclosure has the advantages of simple process, low cost, high purification purity, and environmental friendliness for the production of purified metallic lithium.

Example 2

Assemble the device with the principal configuration shown in Fig. 2, and carry out the purification operation of metallic lithium under Land testing system. The electrochemical curves during the operation are shown in Fig. 7.

The apparatus is assembled according to the principal configuration shown in Fig. 2, and the purification of metallic lithium is carried out under the Land testing system. The apparatus may be operated at a temperature of 400℃. The anodic molten salt is a mixture of LiCl+AlCl₃. The liquid electrolyte is a mixture of LiBr, KBr, and CsBr. Their contents are similar to those in Example 1. The solid electrolyte is an LLZTO ceramic sheet bonded to the electrolytic cell shell in a glass-sealed form. The main material of the electrolytic cell is 304 stainless steel. The anodic sacrificial electrode is made of Al, and the cathode current collector is a nickel strip. The electrolytic current and cell voltage are shown in Fig. 7.

It can be seen that the electrolysis cell voltage reached 1.8V, and under the idle program, the cell voltage could be maintained at a stable level of 0.7V. Electrochemical data indicates that the voltage stability indicates the generation of metallic lithium at the cathode.

Example 3

Assemble the principal configuration device according to Fig. 2 and carry out the purification of metallic lithium in the Land test system. The electrochemical curves during the operation are shown in Fig. 8, and the purified metallic lithium observed after the operation is shown in Fig. 9.

The device shown in Fig. 2 may be operated under the conditions of 350℃. The anode molten salt is a mixture of LiCl+AlCl₃. The liquid electrolyte adopts a mixed molten salt of LiBr+KBr+CsBr. Their contents are similar to those in Example 1. The solid electrolyte is an LLZTO ceramic sheet bonded to the electrolysis cell shell in a glass sealing form. The main material of the electrolysis cell is 304 stainless steel. The anode sacrificial electrode is made of Al and the cathode current collector is a nickel strip. The electrolysis current and cell voltage are shown in Fig. 8.

From this, the electrolysis cell voltage reached 2.1V, and under static conditions, the cell voltage can remain stable at 2V. Electrochemical data indicates that the voltage holding indicates the generation of metallic lithium on the electrolytic cathode. According to the charging capacity calculation, the production of metallic lithium is about 0.0155g. The disassembled and sampled metallic lithium is shown in Fig. 9.

Example 4

Assemble the principal configuration device shown in Fig. 10 and perform the purification of metallic lithium under Land testing system. The electrochemical curves during the operation are shown in Figs. 11 and 12, and the phenomena observed after the operation are shown in Fig. 13. Fig. 11 shows the current-voltage curves, indicating a low voltage for lithium purification and a low energy consumption. Fig. 12 shows the current-capacity curve, which can determine the lithium purification capacity, which can be further converted into the lithium purification mass.

The apparatus shown in Fig. 10 may be operated under the condition of 350℃. The anode molten salt is LiCl+AlCl₃ mixed molten salt, and the liquid electrolyte is a mixed molten salt of LiBr+KBr+CsBr. Their contents are similar to those in Example 1. The solid electrolyte is an LLZTO ceramic sheet, which is bonded to the electrolytic cell shell in a glass sealing form. The main material of the electrolytic cell body is 304 stainless steel, the sacrificial anode electrode is Al, and the cathode current collector is a nickel strip. The electrolysis current and cell voltage are shown in Figs. 11 and 12, respectively.

It can be seen that the voltage in the electrolysis cell reaches 2.3V and can be maintained steadily above 2V during the idle program, and the reason for the subsequent increase in voltage during the electrolysis process is due to the depletion of raw materials. Electrochemical data shows that the voltage is maintained, indicating that metallic lithium is generated in the electrolytic cathode. According to the calculation of the charging capacity, the yield of metallic lithium is about 0.18g. Specific observations of the phenomenon, as shown in Fig. 13, can be used to refine metallic lithium with metallic luster.

Example 5

An inflation electrode device was added, and the principal configuration device was assembled as shown in Fig. 3. The physical device is shown in Fig. 14. The metallic lithium purification operation was performed using the Land testing system, and the electrochemical curves during the operation are shown in Fig. 15. The sampling and test results after the operation are shown in Fig. 16.

The device shown in Fig. 14 may be operated under 250℃. The anode molten salt used is a coarse mixture of LiCl + AlCl₃, and the liquid electrolyte is a mixture of LiBr, KBr, and CsBr. Their contents are similar to those in Example 1. The solid electrolyte is an LLZTO ceramic piece, which is bonded to the electrolytic cell shell in a glass-sealed form. The main material of the electrolytic cell is 304 stainless steel. The anode sacrificial electrode is made of Al, and the cathode current collector is a nickel strip. The electrolysis current and cell voltage are shown in Fig. 15.

As shown in Fig. 15, as the purification time increases, the lithium extraction capacity gradually increases, and the lithium extraction capacity and energy consumption exhibit a similar linear increasing trend. During the purification period of up to 5 days, the purification voltage operated stably with only minor fluctuations. Under conditions of high current up to 100mA and current density of 32mA/cm², the voltage remained within the range of 1.9V-2V, with only a slight overpotential of 0.1V-0.2V. This fully verifies the feasibility of the device principle.

The purity of metallic lithium obtained from the sample is as high as 99.91wt%. The test results of impurity content show that the content of Mg is 0.43ppm, the content of K is 867ppm, and the content of Al is 2.96ppm. The test results indicate the production of high purity metallic lithium.

Claims

A method for preparing high-purity metallic lithium from low-concentration LiCl by using a lithium-ion solid-liquid dual electrolyte, comprising:

selecting a metal to be inserted into an anodic salt as a sacrificial anode;

preparing the anode salt including a mixture obtained by mixing lithium chloride and a chloride of a metal of the sacrificial anode with content of lithium chloride of 1 wt%-98 wt%, wherein the chloride of the metal of the sacrificial anode is selected to provide a melting point of the mixture lower than lithium chloride;

providing a lithium-ion solid-liquid dual electrolyte, wherein the lithium-ion solid-liquid dual electrolyte comprises an inorganic solid electrolyte with high selectivity for Li ions, and a liquid electrolyte comprising one or more molten salts containing at least one lithium salt, wherein a melting point of the one or more molten salts is lower than an electrolysis temperature of an electrolytic reaction to produce metallic lithium;

providing an inert conductor as a cathode; and

obtaining metallic lithium by the electrolytic reaction.
The method according to claim 1, wherein the electrolysis temperature is 100-800℃.
The method according to claim 2, wherein the electrolysis temperature is 200-700℃.
The method according to claim 3, wherein the electrolysis temperature is 250-600℃.
The method according to claim 4, wherein the electrolysis temperature is 300-500℃.
The method according to claim 1, wherein the the electrolytic reaction is conducted with a voltage of 0-3.5V.
The method according to claim 6, wherein the voltage is 1.0-3.0V.
The method according to claim 7, wherein the voltage is 1.5-2.5V.
The method according to claim 1, wherein the liquid electrolyte is positioned between the metallic lithium and the solid electrolyte.
The method according to claim 1, wherein the electrolytic reaction comprises:

an overall reaction: Me + nLiCl = MeCl_n + nLi, where Me is the metal of the sacrificial anode, and n = 1, 2, 3, or 4;

at the sacrificial anode: Me-ne-=Meⁿ⁺;

at the solid electrolyte: Li⁺ (anode) → Li⁺ (liquid electrolyte) ;

at the liquid electrolyte: Li⁺ (from solid electrolyte layer) → Li⁺ (at cathode) ; and

at the cathode: Li+ + e=Li.
The method according to claim 1, wherein the liquid electrolyte comprises one or more of LiF, KF, NaF, RbF, CsF, BaF₂, LiCl, KCl, NaCl, RbCl, CsCl, BaCl₂, LiBr, KBr, NaBr, RbBr, CsBr, BaBr₂, LiI, KI, NaI, RbI, CsI, BaI₂, LiNO₃, KNO₃, NaNO₃, RbNO₃, CsNO₃, Ba (NO₃) ₂.
The method according to claim 11, wherein the liquid electrolyte comprises LiBr-KBr-CsBr molten salt, wherein LiBr is 30 wt%-50 wt%, KBr is 10 wt%-30 wt%, and CsBr is 30 wt%-50 wt%.
A device for preparing high-purity metallic lithium, the device comprising a sacrificial anode, anode melt, a lithium-ion solid electrolyte, a lithium-ion liquid electrolyte, a cathode, and a metallic lithium collection structure, wherein:

the lithium-ion solid electrolyte comprises an inorganic solid-state electrolyte with highly selectivityfor Li ions; and

the lithium-ion liquid electrolyte comprises one or more molten salts containing at least one lithium salt, wherein a melting point of the one or more molten salts is lower than an electrolysis temperature of an electrolytic reaction.
The device according to claim 13, wherein the lithium-ion liquid electrolyte is placed in a liquid electrolyte storage tank, and the liquid electrolyte storage tank is embedded in the lithium-ion solid electrolyte.