WO2022237513A1 - Method for preparing lithium metal by means of molten salt electrolysis - Google Patents

Abstract

The present invention relates to a method for preparing lithium metal by means of molten salt electrolysis. The method is carried out by using an electrolytic cell. The electrolytic cell is divided into an anode chamber and a cathode chamber, wherein the anode chamber is filled with an anode molten salt electrolyte and has an anode, and the cathode chamber is filled with a cathode molten salt electrolyte and has a cathode. The bottom of the electrolytic cell is further filled with a liquid alloy. After the electrolytic cell is powered on, raw materials comprising lithium chloride, lithium carbonate, lithium hydroxide, lithium oxide etc. are added into the anode chamber so as to obtain a lithium metal product in the cathode chamber. The method of the present invention has advantages such as continuous production, low requirements for a lithium chloride raw material, and high purity of a lithium metal product.

Description

A kind of molten salt electrolysis method for preparing metal lithium technical field

The invention belongs to the field of lithium metallurgy, and in particular relates to a method for preparing metal lithium by a molten salt electrolysis method.

Background technique

Lithium metal is known as "the energy metal of the 21st century". It is widely used in energy storage materials, nuclear industry, light alloys and other fields, especially the rise of lithium metal batteries with high energy density has further stimulated the demand for battery-grade metals. Lithium (Li≥99.90%) demand.

technical problem

The industrial production methods of lithium metal are mainly divided into vacuum reduction method and molten salt electrolysis method. The raw material used in the vacuum reduction method is lithium carbonate, lithium hydroxide or lithium oxide, which reacts with a reducing agent under high temperature and vacuum conditions to obtain lithium vapor, which is then condensed to obtain metallic lithium. This method has the advantages of low cost of raw materials, but also has the disadvantages of low production capacity and efficiency, working temperature as high as 1000°C, and strict requirements for the material of the reduction tank. In contrast, the molten salt electrolysis method has become the mainstream process for the production of lithium metal due to its continuous production, good performance of the electrolytic cell, and mature technology. -Electrolysis is carried out in the electrolytic cell of KCl molten salt electrolyte at 420~460°C, Cl ⁻ on the anode graphite undergoes an oxidation reaction and chlorine gas is precipitated, and Li ⁺ on the cathode steel rod undergoes a reduction reaction to obtain liquid metal lithium. However, the molten salt electrolyte solution has the following two major disadvantages:

1. The cost of raw materials is high. The moisture brought into the raw material will have a side reaction with the metallic lithium floating on the surface of the molten salt, resulting in lithium loss, and the impurity elements such as sodium, calcium, magnesium, iron in the raw material will be preferentially reduced and enter the metallic lithium liquid, resulting in the product The purity of lithium decreases, so the raw material for electrolysis is required to be high-purity anhydrous lithium chloride. Usually Li2CO3 or _LiOH is used as raw material to obtain high _- purity anhydrous lithium chloride through recrystallization, low-sodium hydrochloric acid dissolution, solution purification, evaporation crystallization, drying and dehydration, etc., which is used to prepare battery-grade lithium metal batteries Grade anhydrous lithium chloride (YS/T 744-2010) requires LiCl≥99.5wt%, moisture≤0.3wt%, Na≤0.0015wt%, K≤0.05wt%.

Second, the purity of lithium metal products is not high. Metal lithium products obtained by electrolysis usually do not meet the requirements of battery-grade metal lithium. Na is the main impurity element. In order to obtain battery-grade metal lithium, further distillation and purification of industrial-grade metal lithium is required, which greatly increases the cost of equipment. and production costs.

In order to avoid the use of expensive high-purity anhydrous lithium chloride and avoid the generation of chlorine gas, researchers have proposed many alternative raw materials, such as Li ₂ CO ₃ and LiOH. However, in the existing single-chamber electrolyzer, the Li ₂ CO ₃ or LiOH raw material in the molten salt is very easy to have a side reaction with the metal lithium product, resulting in a very low current efficiency.

In short, the electrolytic preparation of lithium metal using lithium chloride as a raw material is still the mainstream industrial application choice at present, and the electrolytic preparation of metallic lithium from molten salts such as lithium carbonate and lithium hydroxide can achieve chlorine-free production. Now there is an urgent need for a A new molten salt electrolysis method with wide adaptability of raw material types, low raw material purity requirements, and high purity metal lithium products.

technical solution

The object of the present invention is to provide a kind of lithium chloride, lithium carbonate as lithium raw material, the method that adopts molten salt electrolysis to produce metal lithium, described method has lithium raw material requirement low, operation can be continuous, can directly obtain higher purity Lithium metal.

To achieve the above object, the present invention adopts the following technical solutions:

The method is implemented using an electrolytic cell, and the electrolytic cell is divided into an anode chamber and a cathode chamber, the anode chamber contains an anode molten salt electrolyte containing lithium ions and is inserted with an anode, and the cathode chamber contains a cathode molten salt electrolyte containing lithium ions and is inserted with a The cathode, the bottom of the electrolytic cell also contains a liquid alloy; the anode molten salt electrolyte and the cathode molten salt electrolyte are not in contact with each other and are connected by a liquid alloy;

The electrolytic cell is energized and operated, lithium raw materials are added to the anode chamber, an oxidation reaction occurs on the surface of the anode, and the lithium ions in the anode molten salt electrolyte are reduced to lithium atoms at the interface between the anode molten salt electrolyte and the liquid alloy and enter the liquid alloy , the lithium atoms in the liquid alloy are oxidized to lithium ions at the interface between the cathode molten salt electrolyte and the liquid alloy and enter the cathode molten salt electrolyte, and the lithium ions in the cathode molten salt electrolyte are reduced to lithium atoms on the surface of the cathode, forming in the cathode chamber Lithium metal products;

The lithium raw material includes at least one of lithium chloride, lithium carbonate, lithium hydroxide, and lithium oxide.

In the present invention, the lithium raw material is preferably lithium chloride and/or lithium carbonate.

In the present invention, the anode molten salt electrolyte is lithium salt, or contains lithium salt and additives. The lithium salt is one or more of LiCl, LiF, Li ₂ CO ₃ . The additive is one or more of KCl, KF, BaCl ₂ .

In the preferred scheme of the present invention, when the lithium raw material is lithium chloride, the anode molten salt electrolyte is preferably composed of one or more of LiCl, KCl, LiF, and KF; and the molar percentage of LiCl in the anode molten salt electrolyte Preferably it is 40~85%. At the working temperature, the decomposition voltages of KCl, LiF, and KF are all greater than LiCl, which can ensure the preferential decomposition of LiCl, and the above-mentioned halides have a large solubility for LiCl, and fluoride is beneficial to improve the physical properties of molten salts. Chemical properties such as surface tension and volatility.

In the preferred solution of the present invention, when the lithium raw material is lithium carbonate, the anode molten salt electrolyte is lithium salt, or consists of lithium salt and additives; the lithium salt is one _of LiCl, _LiF , Li2CO3 One or more, the additive is one or more of KCl, KF, BaCl ₂ . The decomposition voltage of LiCl, LiF, KCl, KF, and BaCl ₂ is higher than that of Li ₂ CO ₃ , and Li ₂ CO ₃ in molten salt or raw material will be preferentially electrolyzed in the anode chamber. In addition, Li ₂ CO ₃ has a large solubility in LiCl or LiF molten salt. For example, Li ₂ CO ₃ -LiF molten salt with a molar ratio of 0.5:0.5 can completely melt at 650°C, while a molar ratio of 0.3: 0.7 Li ₂ CO ₃ -LiCl molten salt can also completely melt at 550 ° C, and the addition of KCl, KF, BaCl ₂ and other additives is beneficial to improve the physical and chemical properties of the anode molten salt electrolyte, such as reducing the primary crystal temperature and adjusting the melting temperature. salt density.

In the present invention, the cathode molten salt electrolyte is a lithium salt, or contains a lithium salt and a modifier (also referred to as an additive in the present invention). The lithium salt is preferably one or more of LiF, LiCl, LiBr, LiI. The regulator is preferably one or more of KF, KCl, KBr, and KI. When the cathode molten salt electrolyte contains lithium salt and regulator, the molar percentage of the lithium salt is not less than 40%.

In the present invention, when the lithium raw material is lithium chloride, the cathode molten salt electrolyte is a lithium salt, or consists of a lithium salt and a regulator, wherein the lithium salt is one or more of LiF, LiCl, LiBr, LiI The additive is one or more of KF, KCl, KBr, and KI. When the cathode molten salt electrolyte is composed of lithium salt and regulator, the molar percentage of lithium salt is not less than 40%.

In the cathode chamber, only the Li ⁺ +e ⁻ ↔Li reaction is involved, not the oxidation reaction of halide ions, so the cathode molten salt electrolyte can be selected to be composed of one or more lithium salts (LiF, LiCl, LiBr or LiI) , or add other halide salts (one or more of KF, KCl, KBr, KI) on this basis to adjust the melting point and other physical and chemical properties of the cathode molten salt electrolyte.

According to the molten salt electrolysis method for preparing metal lithium according to a specific embodiment of the present invention, the liquid alloy is a Li-M alloy, wherein M is a metal element with a density greater than that of metal lithium and an activity less than that of metal lithium, preferably, M is Sn, Zn, Pb , Ag, In, Ga, Bi, Sb in one or more liquid alloys. The content of lithium in the liquid alloy is preferably 5-90 at%. The density of the liquid alloy is greater than the density of the anode molten salt electrolyte and the cathode molten salt electrolyte.

According to the alloy phase diagram, Sn, Zn, Pb, Ag and other metals can form liquid alloys with lithium with a melting point of less than 800 °C, further less than 650 °C, and a lithium content greater than 5 at%. Moreover, the densities of these metal elements are much higher than that of metallic lithium, so the ratio of metals can be effectively adjusted to form a liquid alloy with a density higher than that of molten salt electrolytes.

Liquid alloys (Li-M alloys) can be prepared by melting metal lithium and metal or alloy M, or by electrolysis, for example: using tin as the liquid cathode, graphite as the anode, and a molar ratio of 3:2 LiCl-KCl is a molten salt electrolyte, which can be electrolyzed at 420~450°C to obtain a lithium-tin alloy.

As the electrolysis proceeds, the lithium content in the liquid alloy may decrease, so the lithium metal can be supplemented by methods such as the fusion method or the electrolysis method. When the impurities are enriched to a certain extent, the liquid alloy is drawn out for purification.

According to the molten salt electrolysis method for preparing metallic lithium according to a specific embodiment of the present invention, the anode is a carbon material, and the cathode is a metal or alloy material that is difficult to alloy with lithium, such as steel, tungsten, and molybdenum. Preferably, the anode is graphite, and the cathode is cheap steel. Preferably, the steel is stainless steel. The anode and cathode can be made of the above components, for example, the anode is made of carbon material, and the cathode is made of stainless steel, tungsten, molybdenum.

Carbon materials are a kind of widely used electrode materials, which have good corrosion resistance to halide molten salts, and are inert (non-consumable) to the anode chlorine evolution reaction; the above-mentioned cathode materials are stable in the working temperature range. It is difficult to form an alloy with lithium metal, which effectively prevents the pollution of lithium metal by cathode materials and ensures the purity of lithium metal products.

According to the molten salt electrolysis method for preparing metallic lithium according to a specific embodiment of the present invention, the content of the main components in the lithium raw material is not less than 80wt%. For example, the content of LiCl in the lithium chloride raw material is not less than 80wt%. The raw material of lithium chloride can be high-purity anhydrous lithium chloride currently used in industry, or common anhydrous lithium chloride, or a mixture containing anhydrous lithium chloride and monohydrate lithium chloride. For another example, the lithium raw material is lithium carbonate raw material, and the purity of lithium carbonate therein is not less than 80%. The beneficial effect of the invention is to relax the quality of raw materials, and can produce metal lithium with high purity without very pure lithium carbonate, and the impurities in the lithium carbonate are trapped in the molten salt electrolyte and liquid alloy in the anode chamber.

In the method of the present invention, lithium raw materials such as lithium carbonate and lithium chloride are added to the anode molten salt electrolyte, and lithium ions are dissolved in the anode molten salt electrolyte. The ions are reduced at the interface between the anode molten salt electrolyte and the lithium-containing liquid alloy, and enter the lithium-containing liquid alloy. At the same time, the lithium-containing liquid alloy and the cathode molten salt electrolyte interface undergo an oxidation reaction of lithium, and lithium ions are generated and enter the cathode molten salt electrolyte. , the lithium ions in the cathode molten salt electrolyte are reduced to metal lithium on the surface of the cathode, floating on the upper layer of the cathode molten salt electrolyte.

During the electrolysis process, the metal ion reduction process occurs at the interface between the anode molten salt electrolyte and the lithium ^- containing liquid alloy. During the metal oxidation process that occurs at the alloy interface, metals that are more difficult to oxidize than lithium remain in the lithium-containing liquid alloy (such as Na, Mg, Fe, etc.). Therefore, only lithium ions enter the cathode molten salt electrolyte, and impurities in lithium orthocarbonate is removed, and the purity of the reduction product metal lithium reaches battery level (purity > 99.9%).

In the present invention, the electrolysis temperature is comprehensively considered according to the melting points of the anode molten salt electrolyte, the cathode molten salt electrolyte and the liquid alloy to ensure that the above three are in a molten state at the selected electrolysis temperature.

Preferably, the electrolysis operation is performed under an inert atmosphere, preferably an argon atmosphere.

In the present invention, when the electrolyzer is working normally, the preferred electrolysis temperature is 380-800°C.

In the present invention, when the electrolytic cell is working normally, the cathode current density is 0.1-5.0A/cm ² .

In the preferred solution of the present invention, when the lithium raw material is lithium chloride and the electrolytic cell is working normally, the anode current density is preferably 0.1-2.0A/cm ² , and the temperature is preferably 380-650°C.

Another preferred solution of the present invention, when the lithium raw material is lithium carbonate, the electrolysis temperature is 400-800°C when the lithium electrolytic cell is working normally; the cathode current density is preferably 0.1-5.0A/cm ² .

Taking the lithium raw material as lithium chloride as an example, the principle is:

In the anode chamber, the added lithium chloride raw material can be dissolved in the anode molten salt electrolyte and dissociated into Cl ⁻ and Li ⁺ , the Cl ⁻ in the anode molten salt electrolyte loses electrons on the surface of the anode and turns into chlorine gas, and Li ⁺ Electrons are obtained at the interface between the anode molten salt electrolyte and the liquid alloy, which are reduced to Li and enter the liquid alloy; at the same time, Li in the liquid alloy undergoes an oxidation reaction at the interface between the cathode molten salt electrolyte and the liquid alloy to generate Li ⁺ and enters the cathode molten salt electrolyte, and Li ⁺ in the cathode molten salt electrolyte obtains electrons at the cathode and is reduced to Li and enters/forms metal lithium products. The overall electrolytic equation is:

LiCl=Li+0.5Cl ₂ ↑

Since the lithium chloride raw material is added to the anode molten salt electrolyte in the anode chamber, and the lithium metal product is produced from the cathode molten salt electrolyte in the cathode chamber, the moisture (crystal water or free water) in the lithium chloride raw material cannot It migrates to the cathode cathode molten salt electrolyte, but dehydration or evaporation reaction occurs at high temperature and enters the gas phase and is discharged with the air flow. The metal lithium product is basically not affected.

Based on the difference in electrode potential of different elements, the impurities in the lithium chloride raw material have different electrochemical behaviors, among which elements that are more active than lithium (such as K, Ba) will be enriched in the molten salt electrolyte, while elements that are more inert than lithium Elements (such as Na, Mg, Fe) will be enriched in the liquid alloy, and they are all difficult to enter among the metal lithium product, so adopting the method of the present invention has not only guaranteed the purity of the metal lithium product that makes, also can Appropriately relax the quality requirements for lithium chloride raw materials.

Taking the lithium raw material as lithium carbonate as an example, the principle is:

Using lithium carbonate as raw material, lithium carbonate is added to the anode molten salt electrolyte, and the carbonate radical is dissolved or partially dissolved in the anode molten salt electrolyte. Based on the difference in redox potential of the metal/metal ion, the lithium ions in the anode molten salt electrolyte The interface between the electrolyte and the liquid alloy is reduced and enters the liquid alloy. At the same time, the oxidation reaction of lithium occurs at the interface between the liquid alloy and the cathode molten salt electrolyte, and lithium ions are generated and enter the cathode molten salt electrolyte. The lithium ions in the cathode molten salt electrolyte are in the cathode The surface is reduced to metallic lithium, which floats on the upper layer of the cathode molten salt electrolyte.

The overall electrolytic equation is:

Li ₂ CO ₃ +0.5C=2Li(l)+1.5CO ₂ (g).

Beneficial effect

(1) The production of the electrolysis process is continuous. In principle, the electrolysis process only consumes lithium raw materials such as LiCl and lithium carbonate. Therefore, continuous production can be realized by timely replenishing lithium raw materials into the anode chamber and timely taking out liquid metal lithium products from the cathode chamber, with high production efficiency.

(2) Raw material quality requirements are relaxed. Lithium chloride raw materials with a certain moisture and impurity content can be used to produce metallic lithium by electrolysis, which reduces the raw material production cost brought by the need for high-purity anhydrous lithium chloride raw materials in traditional electrolysis methods. In addition, as a bulk industrial lithium salt, lithium carbonate itself does not contain crystal water and will not deliquesce in the air, so it can be used as a stable and easy-to-obtain raw material for lithium electrolysis; the electrolysis operation is continuous, the production efficiency is high, and the anode chamber can be realized Continuous feeding in the middle and continuous discharge in the cathode chamber; in the electrolysis process, the generation of chlorine gas can be avoided, the control of impurity content can be relaxed, the cost of production raw materials and equipment is reduced, and the purity of the product lithium metal is higher. The traditional molten salt electrolysis method with lithium as raw material has obvious advantages.

(3) Product purity is guaranteed. Impurity ions with different electrochemical behaviors can be effectively controlled in the molten salt electrolyte or liquid alloy, and the purity of lithium metal products can reach more than 99.50%. Under optimized conditions, battery-grade lithium metal products can also be directly obtained, which improves the product quality. value and economic advantages.

Description of drawings

Fig. 1 is the electrolyzer sectional schematic diagram of scheme 1 implementation method; Among Fig. 1, 1-insulating separator; 2-negative electrode; 3-metal lithium product; 4-cathode molten salt electrolyte; 5-liquid alloy; 6-electrolyzer; 7-anode molten salt electrolyte; 8-anode.

Fig. 2 is the electrolytic device diagram of the method for preparing metallic lithium by molten salt electrolysis described in this scheme 2; Among Fig. 2, 1-liquid alloy; 2-anode chamber; 3-cathode chamber; 4-anode molten salt electrolyte; 5-cathode Molten salt electrolyte; 6-anode; 7-cathode; 8-heating resistance wire; 9-feed inlet; 10-refractory ceramics; 11-metal lithium; 12-argon gas inlet; 13-argon gas outlet; 14 -Sealing flange.

Embodiments of the present invention

In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be described in detail below. Apparently, the described embodiments are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other implementations obtained by persons of ordinary skill in the art without making creative efforts fall within the protection scope of the present invention.

1. The preparation scheme of continuous metal lithium using lithium chloride as raw material (scheme 1 ):

The method for producing metallic lithium by the electrolysis of lithium chloride in scheme 1 is implemented by utilizing the electrolytic cell shown in Figure 1, wherein the liquid alloy 5 is filled at the bottom of the electrolytic cell 6, and the inner region of the electrolytic cell 6 above the liquid alloy 5 is separated by an insulating barrier. The plate 1 is divided into an anode chamber and a cathode chamber. The anode chamber contains an anode molten salt electrolyte 7 and is inserted with an anode 8. The cathode chamber contains a cathode molten salt electrolyte 4 and is inserted with a cathode 2. The anode molten salt electrolyte 7 and the cathode molten The salt electrolytes 4 are not in contact with each other but are connected by a liquid alloy 5 .

In scheme 1, described method utilizes Fig. 1 electrolytic cell to implement, and electrolytic cell is divided into anode chamber and cathode chamber, anode chamber is filled with the anode molten salt electrolyte containing lithium ion and is inserted with anode, and cathode chamber is filled with the cathode chamber containing lithium ion The molten salt electrolyte is inserted with a cathode, and the bottom of the electrolytic cell is also filled with liquid alloy; the anode molten salt electrolyte and the cathode molten salt electrolyte are not in contact with each other and are connected through the liquid alloy; Add lithium chloride raw material, oxidation reaction occurs on the surface of the anode, the lithium ions in the anode molten salt electrolyte are reduced to lithium atoms at the interface between the anode molten salt electrolyte and the liquid alloy and enter the liquid alloy, and the lithium atoms in the liquid alloy are in the cathode molten salt The interface between the electrolyte and the liquid alloy is oxidized to lithium ions and enters the cathode molten salt electrolyte, and the lithium ions in the cathode molten salt electrolyte are reduced to lithium atoms, forming lithium metal products in the cathode chamber. The anode molten salt electrolyte is composed of LiCl and one or more of KCl, LiF and KF. In the anode molten salt electrolyte, the molar percentage of LiCl is 40-85%. The cathode molten salt electrolyte is lithium salt, or consists of lithium salt and additives; the lithium salt is one or more of LiF, LiCl, LiBr, LiI, and the additive is KF, KCl, KBr, KI one or more of . When the cathode molten salt electrolyte is composed of lithium salt and additives, the molar percentage of the lithium salt is not less than 40%. The liquid alloy is a Li-M alloy, wherein M is a metal element with a density greater than that of lithium metal and an activity less than lithium metal, preferably, M is one or more of Sn, Zn, Pb, Ag, In, Ga, Bi, Sb kind. The density of the liquid alloy is greater than the density of the anode molten salt electrolyte and the cathode molten salt electrolyte. The content of lithium in the liquid alloy is 5-90 at%. The anode is a carbon material, preferably graphite, and the cathode is a metal or alloy material that is difficult to alloy with lithium, preferably one of steel, tungsten, and molybdenum. The content of LiCl in the lithium chloride raw material is not less than 80wt%. When the electrolyzer is working normally, the anode current density is controlled at 0.1~2.0A/cm ² , and the temperature is 380~650℃.

Program 1 Typical examples include:

Example 1-1

The bottom of the electrolytic cell contains a pre-alloyed Li-Pb alloy, in which the Li content is 40 at%, the anode is made of graphite, and the cathode is made of stainless steel. The anode molten salt electrolyte is LiCl-KCl with a molar ratio equal to 1:1, and the cathode molten salt electrolyte is LiCl-KCl with a molar ratio equal to 3:2. Place the electrolytic cell in an atmosphere filled with dry argon and program the temperature up to 500°C and keep it warm for 2 hours, turn on the electricity to control the anode current density at 1.0A/cm ² , and perform electrolysis for 10 hours, during which lithium chloride raw materials (LiCl content is 98.4 wt%, containing 0.8wt% water), the Li content in the cathode product lithium metal was analyzed and determined to be 99.92%.

Example 1-2

The bottom of the electrolytic cell contains a pre-alloyed Li-In alloy, in which the Li content is 80 at%, the anode is made of modified graphite, and the cathode is made of tungsten wire. The anode molten salt electrolyte is LiCl-KCl-KF with a molar ratio of 6:3.5:0.5, and the cathode molten salt electrolyte is LiF-LiCl with a molar ratio of 3:7. Place the electrolytic cell in an atmosphere filled with dry argon and program the temperature up to 550°C and keep it warm for 2 hours, turn on the electricity to control the anode current density at 2.0A/cm ² , and perform electrolysis for 10 hours, during which lithium chloride raw materials (LiCl content is 89.4 wt%, containing 6.1wt% water), the Li content in the cathode product lithium metal was analyzed and determined to be 99.83%.

Example 1-3

The bottom of the electrolytic cell contains a pre-alloyed Li-Ag alloy, in which the Li content is 70 at%, the anode is graphite, and the cathode is molybdenum wire. The anode molten salt electrolyte is LiCl-KCl-LiF with a molar ratio equal to 6:3.9:0.1, and the cathode molten salt electrolyte is LiCl-LiI with a molar ratio equal to 3.5:6.5. Place the electrolytic cell in an atmosphere filled with dry argon and program the temperature up to 450°C and keep it warm for 2 hours, turn on the electricity to control the anode current density at 0.8A/cm ² , and perform electrolysis for 10 hours, during which lithium chloride raw materials (LiCl content is 93.8 wt%, containing 3.2wt% water), the Li content in the cathode product lithium metal was analyzed and determined to be 99.90%.

Example 1-4

The bottom of the electrolytic cell contains a pre-alloyed Li-Sn alloy, in which the Li content is 20 at%, the anode is made of graphite, and the cathode is made of stainless steel. The anode molten salt electrolyte is LiCl-KCl with a molar ratio equal to 3:2, and the cathode molten salt electrolyte is LiI-KI-KF with a molar ratio equal to 6:3.5:0.5. Place the electrolytic cell in an atmosphere filled with dry argon and program the temperature up to 385°C and keep it warm for 2 hours, turn on the electricity to control the anode current density at 0.5A/cm ² , and perform electrolysis for 10 hours, during which lithium chloride raw materials (LiCl content of 99.1 wt%, containing 0.6wt% water), the Li content in the cathode product lithium metal was analyzed and determined to be 99.97%.

Example 1-5

The bottom of the electrolytic cell is filled with pre-alloyed Li-Pb alloy, in which the Li content is 90 at%, the anode is made of graphite, and the cathode is made of carbon steel. The anode molten salt electrolyte is LiCl-KCl with a molar ratio equal to 8.5:1.5, and the cathode molten salt electrolyte is LiF-KF with a molar ratio equal to 1:1. Place the electrolytic cell in an atmosphere filled with dry argon and program the temperature up to 650°C and keep it warm for 2 hours, turn on the electricity to control the anode current density at 0.2A/cm ² , and perform electrolysis for 10 hours, during which lithium chloride raw materials (LiCl content is 95.7 wt%, containing 1.5wt% water), the Li content in the cathode product lithium metal was analyzed and determined to be 99.95%.

Example 1-6

The bottom of the electrolytic cell contains a pre-alloyed Li-Ga alloy, in which the Li content is 5 at%, the anode is made of graphite, and the cathode is made of tungsten wire. The anode molten salt electrolyte is LiCl-KCl with a molar ratio equal to 3:2, and the cathode molten salt electrolyte is LiBr-KBr with a molar ratio equal to 3:2. Place the electrolytic cell in an atmosphere filled with dry argon and program the temperature up to 420°C and keep it warm for 2 hours, turn on the electricity to control the anode current density at 0.1A/cm ² , and perform electrolysis for 10 hours, during which lithium chloride raw materials (with a LiCl content of 90.5 wt%, containing 4.3wt% water), and the Li content in the cathode product lithium metal was analyzed and determined to be 99.89%.

Example 1-7

The bottom of the electrolytic cell is filled with a pre-alloyed Li-Bi alloy, in which the Li content is 10 at%, the anode is made of modified graphite, and the cathode is a tungsten rod. The anode molten salt electrolyte is LiCl-KCl with a molar ratio equal to 2:3, and the cathode molten salt electrolyte is LiCl-KCl with a molar ratio equal to 2:3. Place the electrolytic cell in an atmosphere filled with dry argon and program the temperature up to 600°C and keep it warm for 2 hours, turn on the electricity to control the anode current density at 0.4A/cm ² , and perform electrolysis for 10 hours, during which lithium chloride raw materials (LiCl content is 85.6 wt%, containing 8.9wt% water), the Li content in the cathode product lithium metal was analyzed and determined to be 99.71%.

Example 1-8

The bottom of the electrolytic cell contains a pre-alloyed Li-Zn alloy, in which the Li content is 60 at%, the anode is made of graphite, and the cathode is made of stainless steel. The anode molten salt electrolyte is LiF-LiCl with a molar ratio equal to 3:7, and the cathode molten salt electrolyte is LiF-LiI with a molar ratio equal to 1:4. Place the electrolytic cell in an atmosphere filled with dry argon and program the temperature up to 550°C and keep it warm for 2 hours, turn on the electricity to control the anode current density at 1.5A/cm ² , and perform electrolysis for 10 hours, during which lithium chloride raw materials (LiCl content is 81.2 wt%, containing 13.1wt% water), and the Li content in the cathode product lithium metal was analyzed and determined to be 99.61%.

comparative example 1-1

The difference between this comparative example and Examples 1-6 is that there is no Li-Ag alloy at the bottom of the electrolytic tank, the electrolyte is LiCl-KCl with a molar ratio equal to 3:2, and other conditions are the same. After the electrolysis, the Li content in the cathode product lithium metal was analyzed and determined to be 97.23%.

It can be seen that in the absence of a liquid alloy (lost the separation effect based on the electrochemical reaction at the liquid alloy/molten salt electrolyte interface), the purity of lithium metal produced by electrolysis of lithium chloride in an ordinary separator electrolyzer is low, and Na, Mg The content of other impurities is relatively high; the moisture in the lithium chloride raw material may have a side reaction with metallic lithium after entering the molten salt electrolyte, resulting in a decrease in current efficiency.

2. The scheme of using lithium carbonate to realize the preparation of metal lithium (scheme 2 )

Scheme 2 is realized by using the electrolysis device described in FIG. 2 . The electrolysis device described in FIG. 2 includes an electrolytic cell body 10 (refractory ceramic 10 ) and a cover plate with a jacket, and the cover plate and the electrolytic cell body pass through The flange 14 is fixed; the outside of the side wall of the electrolytic cell body is provided with a heating resistance wire 8;

The inner chamber of the electrolytic cell body is divided into an upper chamber and a lower chamber; wherein, the lower chamber is filled with liquid alloy 1; the upper chamber is divided into an anode chamber 2 and a cathode chamber 3 arranged left and right through an insulating plate;

The anode chamber 2 includes an anode molten salt electrolyte 4 arranged at the bottom and floating on the surface of the liquid alloy in the lower chamber, an anode 6 inserted in the anode molten salt electrolyte 4 and the other end extending out of the anode chamber; and the top cover plate of the anode chamber The wall is provided with feed inlet 9, argon gas inlet 12 and argon gas outlet 13;

The cathode chamber 3 includes a cathode molten salt electrolyte 5 arranged at the bottom and floating on the surface of the liquid alloy in the lower chamber, a metal lithium product 11 floating on the surface of the cathode molten salt electrolyte, inserted in the cathode molten salt electrolyte, and the other end extends out The cathode 7 outside the anode chamber 3 and the product extraction tube for extracting lithium metal; and the top cover wall of the cathode chamber 3 is provided with an argon gas inlet 12 and an argon gas outlet 13;

The implementation method of scheme 2 is: implement by using an electrolytic cell, which is divided into an anode chamber and a cathode chamber, the anode chamber contains an anode molten salt electrolyte containing lithium ions and is inserted with an anode, and the cathode chamber contains a cathode molten salt containing lithium ions The electrolyte is inserted with a cathode, and the bottom of the electrolytic cell is also filled with liquid alloy; the anode molten salt electrolyte and the cathode molten salt electrolyte are not in contact with each other and are connected through the liquid alloy; Adding lithium carbonate, the lithium ions in the anode molten salt electrolyte are reduced to lithium atoms at the interface between the anode molten salt electrolyte and the liquid alloy and enter the liquid alloy. At the same time, the lithium atoms in the liquid alloy are at the interface between the liquid alloy and the cathode molten salt electrolyte It is oxidized into lithium ions and enters the cathode molten salt electrolyte, and the lithium ions in the cathode molten salt electrolyte are reduced to metal lithium on the surface of the cathode. The anode is made of carbon material, and the cathode is made of stainless steel, tungsten, molybdenum; preferably, the cathode is made of stainless steel. The anode molten salt electrolyte is lithium salt, or consists of lithium salt and additives; the lithium salt is one or more _of LiCl, LiF, Li2CO3, and the additive is _KCl , KF, _BaCl2 one or more of . The purity of described lithium carbonate is not less than 80%. The cathode molten salt electrolyte contains one or more of LiCl, LiF, LiBr and LiI. The cathode molten salt electrolyte contains a lithium salt and a regulator; the lithium salt is one or more of LiCl, LiF, LiBr, and LiI, and the regulator is one of KCl, KF, KBr, and KI or more. The liquid alloy is an alloy formed by at least one of Zn, Ag, Sn, Pb, Sb, Bi, In, Ga and Li; the density of the liquid alloy is greater than that of the anode molten salt electrolyte or the cathode molten salt density of the electrolyte. When the electrolyzer works normally, the cathode current density is 0.1-5.0A/cm ² . When the electrolyzer works normally, the electrolysis temperature is 400-800°C. The electrolysis operation is carried out under an inert atmosphere, preferably an argon atmosphere

A typical implementation case of Scheme 2 is:

Example 2-1

This embodiment provides a method for preparing metallic lithium by molten salt electrolysis, comprising the following steps:

(1) As shown in Figure 2, under the protection of argon atmosphere, add 800g of Sn-Li alloy (the mass percentage of lithium is 6%) to the bottom of the electrolytic cell, heat it to 550°C to melt and form a liquid alloy and separate the anode chamber, The cathode chamber is completely separated; add 200g of molten salt in the anode chamber with a mass fraction of LiCl 44%, KCl 54%, and LiF 2% to the anode chamber; add 200g of molten salt with a mass fraction of LiCl 45% and KCl 55% to the cathode chamber Molten salt in the cathode chamber; after the molten salt in the anode chamber and the molten salt in the cathode chamber are completely melted, insert the graphite anode and the tungsten rod cathode respectively;

(2) Slowly add the 2nd grade Li ₂ CO ₃ in GB/T 11075-2003 into the anode chamber, and at the same time electrify for electrolysis, the cathode current density is 1.2A/cm ² , under inert conditions, after electrolysis for 10h, metal lithium is obtained The purity is 99.92%.

Example 2-2

This embodiment provides a method for preparing metallic lithium by molten salt electrolysis, comprising the following steps:

(1) As shown in Figure 2, under the protection of argon atmosphere, add 800g of Sn-Li alloy (the mass percentage of lithium is 1%) to the bottom of the electrolytic cell, heat it to 400°C to melt and form a liquid alloy and separate the anode chamber, The cathode chamber is completely separated; add 200g of molten salt in the anode chamber with a mass fraction of LiCl 44%, KCl 54%, and LiF 2% to the anode chamber; add 200g of molten salt with a mass fraction of LiCl 45% and KCl 55% to the cathode chamber Molten salt in the cathode chamber; after the molten salt in the anode chamber and the molten salt in the cathode chamber are completely melted, insert the graphite anode and the tungsten rod cathode respectively;

(2) Slowly add Grade 2 Li ₂ CO ₃ in GB/T 11075-2003 to the anode chamber, and at the same time energize for electrolysis, the cathode current density is 0.1A/cm ² , under inert conditions, after electrolysis for 10 hours, metal lithium is obtained The purity is 99.92%.

Example 2-3

This embodiment provides a method for preparing metallic lithium by molten salt electrolysis, comprising the following steps:

(1) As shown in Figure 2, under the protection of an argon atmosphere, add 800g of Ag-Li alloy (the mass percentage of lithium is 20%) to the bottom of the electrolytic cell, heat it to 400°C to melt and form a liquid alloy and separate the anode chamber, The cathode chamber is completely separated; add 200g of molten salt in the anode chamber with a mass fraction of LiCl 45% and KCl 55% to the anode chamber, and add 200g of molten salt in the cathode chamber with a mass fraction of LiCl 45% and KCl 55% to the cathode chamber ; After the molten salt in the anode chamber and the molten salt in the cathode chamber are completely melted, insert the graphite anode and the tungsten rod cathode respectively;

(2) Slowly add the 2nd grade Li ₂ CO ₃ in GB/T 11075-2003 into the anode chamber, and at the same time electrify for electrolysis, the cathode current density is 1.2A/cm ² , under inert conditions, after electrolysis for 10h, metal lithium is obtained 99.93% pure.

Example 2-4

This embodiment provides a method for preparing metallic lithium by molten salt electrolysis, comprising the following steps:

(1) As shown in Figure 2, under the protection of argon atmosphere, add 800g of lithium-containing liquid alloy Ag-Li alloy (the mass percentage of lithium is 20%) to the bottom of the electrolytic cell, and heat it to 800°C to melt to form a liquid alloy And completely separate the anode chamber and the cathode chamber; add 200g of molten salt in the anode chamber with a mass fraction of LiCl 45% and KCl 55% to the anode chamber, and add 200g to the cathode chamber with a mass fraction of LiCl 45% and KCl 55% The molten salt in the cathode chamber; after the molten salt in the anode chamber and the molten salt in the cathode chamber are completely melted, insert the graphite anode and the tungsten rod cathode respectively;

(2) Slowly add Li ₂ CO ₃ with a purity of 80% to the anode chamber, and at the same time energize for electrolysis. The cathode current density is 0.8A/cm ² . Under inert conditions, after 10 hours of electrolysis, the purity of metal lithium is 99.90%.

Example 2-5

This embodiment provides a method for preparing metallic lithium by molten salt electrolysis, comprising the following steps:

(1) As shown in Figure 2, under the protection of argon atmosphere, add 800g of Ag-Li-Sn alloy (the mass fraction of lithium is 20%, the mass fraction of Sn is 20%) to the bottom of the electrolytic cell, and heat to 800 ℃ to melt to form a liquid alloy and completely separate the anode chamber and the cathode chamber; add 200g of molten salt in the anode chamber with mass fractions of LiCl 40%, KCl 50%, and LiF 10% to the anode chamber, and add 200g to the cathode chamber. Molten salt in the cathodic chamber with a mass fraction of 45% LiCl and 55% KCl; insert graphite anode and tungsten rod cathode respectively after the molten salt in the anode chamber and the molten salt in the cathode chamber are completely melted;

(2) Slowly add Li ₂ CO ₃ with a purity of 80% to the anode molten salt electrolyte, and at the same time energize for electrolysis. The cathode current density is 0.8A/cm2. Under inert conditions, after electrolysis for 10 hours, the purity of metal lithium is 99.90%. .

Following embodiment 2-6～embodiment 2-12 compares with embodiment 2-1:

comparative example 2-1

Add 1000g of molten salt with a mass fraction of LiCl 45% and KCl 55% to the electrolytic cell, heat to 450°C to melt, use graphite as the anode, and use tungsten rods as the cathode to immerse in the electrolyte respectively;

Under the condition of argon atmosphere, slowly add the second-grade lithium carbonate (purity: 98.5%) in GB/T 11075-2003 to the molten salt electrolyte of the anode, and conduct electrolysis with the current density of the anode at 1.2A/cm2. After 10 hours of electrolysis, The purity of metal lithium obtained from the cathode is 98%.

The above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Anyone skilled in the art can easily think of changes or substitutions within the technical scope disclosed in the present invention. Should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be determined by the protection scope of the claims.

Claims (13)

1. A molten salt electrolysis method for preparing lithium metal, characterized in that,

   The method is implemented using an electrolytic cell, and the electrolytic cell is divided into an anode chamber and a cathode chamber, the anode chamber contains an anode molten salt electrolyte containing lithium ions and is inserted with an anode, and the cathode chamber contains a cathode molten salt electrolyte containing lithium ions and is inserted with a The cathode, the bottom of the electrolytic cell also contains a liquid alloy; the anode molten salt electrolyte and the cathode molten salt electrolyte are not in contact with each other and are connected by a liquid alloy;

   The electrolytic cell is energized and operated, lithium raw materials are added to the anode chamber, an oxidation reaction occurs on the surface of the anode, and the lithium ions in the anode molten salt electrolyte are reduced to lithium atoms at the interface between the anode molten salt electrolyte and the liquid alloy and enter the liquid alloy , the lithium atoms in the liquid alloy are oxidized to lithium ions at the interface between the cathode molten salt electrolyte and the liquid alloy and enter the cathode molten salt electrolyte, and the lithium ions in the cathode molten salt electrolyte are reduced to lithium atoms on the surface of the cathode, forming in the cathode chamber Lithium metal products;

   The lithium raw material includes at least one of lithium chloride, lithium carbonate, lithium hydroxide, and lithium oxide.
2. The molten salt electrolysis method for preparing metallic lithium according to claim 1, wherein the anode molten salt electrolyte is lithium salt, or contains lithium salt and additives;

   The lithium salt is one or more _of LiCl, _LiF , Li2CO3;

   The additive is one or more of KCl, KF, BaCl ₂ .
3. The molten salt electrolysis method for preparing lithium metal according to claim 1, wherein when the lithium raw material is lithium chloride, the anode molten salt electrolyte is composed of one or more of LiCl, KCl, LiF, and KF .
4. The molten salt electrolysis method for preparing lithium metal according to claim 3, characterized in that, in the anode molten salt electrolyte, the molar percentage of LiCl is 40-85%.
5. The molten salt electrolysis method for preparing metallic lithium according to claim 1, wherein the cathode molten salt electrolyte is a lithium salt, or contains a lithium salt and a modifier;

   The lithium salt is one or more of LiF, LiCl, LiBr, LiI;

   The regulator is one or more of KF, KCl, KBr, KI;

   Preferably, when the lithium raw material is lithium chloride, the cathode molten salt electrolyte is lithium salt, or consists of lithium salt and regulator.
6. The molten salt electrolysis method for preparing metallic lithium according to claim 5, wherein when the cathode molten salt electrolyte contains a lithium salt and a regulator, the molar percentage of the lithium salt is not less than 40%.
7. The molten salt electrolysis method for preparing lithium metal according to claims 1 to 6, wherein the liquid alloy is a Li-M alloy;

   Wherein M is a metal element whose density is greater than and activity is less than lithium metal;

   The density of the liquid alloy is greater than the density of the anode molten salt electrolyte and the density of the cathode molten salt electrolyte;

   Preferably, M is one or more of Sn, Zn, Pb, Ag, In, Ga, Bi, Sb.
8. The molten salt electrolysis method for preparing metallic lithium according to claim 7, wherein the content of lithium in the liquid alloy is 5-90 at%.
9. A kind of molten salt electrolysis method for preparing metallic lithium according to claim 1, is characterized in that, described anode is carbonaceous material, is preferably graphite;

   The cathode is a metal or alloy material that is difficult to alloy with lithium, preferably one of steel, tungsten, and molybdenum;

   Preferably, the steel is stainless steel.
10. The molten salt electrolysis method for preparing lithium metal according to claim 1, wherein the lithium raw material is a lithium chloride raw material, and wherein the content of LiCl is not less than 80wt%;

    The lithium raw material is lithium carbonate raw material, and the purity of lithium carbonate wherein is not less than 80%.
11. The molten salt electrolysis method for preparing lithium metal according to claim 1, wherein the electrolysis temperature is 380-800°C when the electrolytic cell is in normal operation; the cathode current density is preferably 0.1-5.0A/cm ² .
12. The method for preparing metallic lithium by molten salt electrolysis according to claim 1, wherein the lithium raw material is lithium chloride, and when the electrolytic cell is in normal operation, the anode current density is controlled at 0.1-2.0A/cm ² , and the temperature It is 380~650°C.
13. The molten salt electrolysis method for preparing metallic lithium according to claim 1 is characterized in that, the lithium raw material is lithium carbonate, and when the lithium electrolyzer is working normally, the electrolysis temperature is 400-800°C; the cathode current density is preferably 0.1- 5.0A/cm ² .