METHOD FOR PREPARING LITHIUM METAL BY MOLTEN SALT ELECTROLYSIS

Abstract

A method for preparing lithium metal by molten salt electrolysis is provided. The method is carried out by using an electrolytic cell. The electrolytic cell is divided into an anode chamber and a cathode chamber. The anode chamber is filled with an anode molten salt electrolyte and inserted with an anode, and the cathode chamber is filled with a cathode molten salt electrolyte and inserted with a cathode. The bottom of the electrolytic cell is further filled with a liquid alloy. After the electrolytic cell is powered on, raw materials including 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.

Claims

1. A method for preparing a lithium metal by a molten salt electrolysis, wherein the method is carried out by using an electrolytic cell, the electrolytic cell is divided into an anode chamber and a cathode chamber, the anode chamber is filled with an anode molten salt electrolyte containing lithium ions and inserted with an anode, the cathode chamber is filled with a cathode molten salt electrolyte containing lithium ions and inserted with a cathode, a bottom of the electrolytic cell is further filled with a liquid alloy, and the anode molten salt electrolyte and the cathode molten salt electrolyte are connected via the liquid alloy without contacting each other; after the electrolytic cell is powered on, adding a lithium raw material into the anode chamber for an oxidation reaction occurring on an anode surface, wherein the lithium ions in the anode molten salt electrolyte are reduced to lithium atoms at an 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 an interface between the cathode molten salt electrolyte and the liquid alloy and enter the cathode molten salt electrolyte, the lithium ions in the cathode molten salt electrolyte are reduced to lithium atoms on a surface of the cathode, and a lithium metal product is formed in the cathode chamber; and the lithium raw material comprises at least one of lithium chloride, lithium carbonate, lithium hydroxide, and lithium oxide.

2. The method for preparing the lithium metal by the molten salt electrolysis according to claim 1, wherein the anode molten salt electrolyte is a lithium salt, or contains a lithium salt and an additive; the lithium salt is one or more of LiCl, LiF, and Li.sub.2CO.sub.3; and the additive is one or more of KCl, KF, and BaCl.sub.2.

3. The method for preparing the lithium metal by the molten salt electrolysis according to claim 1, wherein when the lithium raw material is the lithium chloride, the anode molten salt electrolyte consists of LiCl and one or more of KCl, LiF, and KF.

4. The method for preparing the lithium metal by the molten salt electrolysis according to claim 3, wherein a mole percentage of LiCl in the anode molten salt electrolyte is 40-85%.

5. The method for preparing the lithium metal by the molten salt electrolysis 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, and LiI; and the modifier is one or more of KF, KCl, KBr, and KI.

6. The method for preparing the lithium metal by the molten salt electrolysis according to claim 5, wherein when the cathode molten salt electrolyte contains the lithium salt and the modifier, a mole percentage of the lithium salt is not less than 40%.

7. The method for preparing the lithium metal by the molten salt electrolysis according to claim 1, wherein the liquid alloy is a Li-M alloy, M is a metal element denser and less active than the lithium metal; and a density of the liquid alloy is greater than a density of the anode molten salt electrolyte and a density of the cathode molten salt electrolyte.

8. The method for preparing the lithium metal by the molten salt electrolysis according to claim 7, wherein a content of lithium in the liquid alloy is 5-90 at %.

9. The method for preparing the lithium metal by the molten salt electrolysis according to claim 1, wherein the anode is a carbon material; the cathode is a metal material or an alloy material that is-difficult to alloy with lithium.

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

11. The method for preparing the lithium metal by the molten salt electrolysis according to claim 1, wherein when the electrolytic cell works normally, an electrolysis temperature is 380-800? C. and a current density of the cathode is 0.1-5.0 A/cm.sup.2.

12. The method for preparing the lithium metal by the molten salt electrolysis according to claim 1, wherein the lithium raw material is the lithium chloride, and when the electrolytic cell works normally, a current density of the anode is controlled at 0.1-2.0 A/cm.sup.2 and a temperature is 380-650? C.

13. The method for preparing the lithium metal by the molten salt electrolysis according to claim 1, wherein the lithium raw material is the lithium carbonate, and when the electrolytic cell works normally, an electrolysis temperature is 400-800? ? C., and a current density of the cathode is 0.1-5.0 A/cm.sup.2.

14. The method for preparing the lithium metal by the molten salt electrolysis according to claim 5, wherein when the lithium raw material is lithium chloride, the cathode molten salt electrolyte is the lithium salt, or consists of the lithium salt and the modifier.

15. The method for preparing the lithium metal by the molten salt electrolysis according to claim 2, wherein the liquid alloy is a Li-M alloy, M is a metal element denser and less active than the lithium metal; and a density of the liquid alloy is greater than a density of the anode molten salt electrolyte and a density of the cathode molten salt electrolyte.

16. The method for preparing the lithium metal by the molten salt electrolysis according to claim 3, wherein the liquid alloy is a Li-M alloy, M is a metal element denser and less active than the lithium metal; and a density of the liquid alloy is greater than a density of the anode molten salt electrolyte and a density of the cathode molten salt electrolyte.

17. The method for preparing the lithium metal by the molten salt electrolysis according to claim 4, wherein the liquid alloy is a Li-M alloy, M is a metal element denser and less active than the lithium metal; and a density of the liquid alloy is greater than a density of the anode molten salt electrolyte and a density of the cathode molten salt electrolyte.

18. The method for preparing the lithium metal by the molten salt electrolysis according to claim 5, wherein the liquid alloy is a Li-M alloy, M is a metal element denser and less active than the lithium metal; and a density of the liquid alloy is greater than a density of the anode molten salt electrolyte and a density of the cathode molten salt electrolyte.

19. The method for preparing the lithium metal by the molten salt electrolysis according to claim 6, wherein the liquid alloy is a Li-M alloy, M is a metal element denser and less active than the lithium metal; and a density of the liquid alloy is greater than a density of the anode molten salt electrolyte and a density of the cathode molten salt electrolyte.

20. The method for preparing the lithium metal by the molten salt electrolysis according to claim 7, wherein M is one or more of Sn, Zn, Pb, Ag, In, Ga, Bi, and Sb.

21. The method for preparing the lithium metal by the molten salt electrolysis according to claim 9, wherein the anode is graphite; and the cathode is one of steel, tungsten, and molybdenum.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0046] FIG. 1 is a schematic cross-sectional view of the electrolytic cell of the method carried out in solution 1. In FIG. 1, 1insulating partition; 2cathode; 3lithium metal product; 4cathode molten salt electrolyte; 5liquid alloy; 6electrolytic cell; 7anode molten salt electrolyte; 8anode.

[0047] FIG. 2 is an electrolysis device diagram of the method for preparing lithium metal by molten salt electrolysis in solution 2. In FIG. 2, 1liquid alloy; 2anode chamber; 3cathode chamber; 4anode molten salt electrolyte; 5cathode molten salt electrolyte; 6anode; 7cathode; 8heating resistance wire; 9feed inlet; 10refractory ceramic; 11lithium metal; 12argon gas inlet; 13argon gas outlet; 14sealing flange.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0048] In order to make the object, technical solution, and advantages of the present invention clearer, the technical solution of the present invention will be described in detail below. It is obvious that the described examples are only part of and not all of the examples of the present invention. Based on the examples in the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort fall within the scope of protection of the present invention.

1. Solution for Continuously Preparing Lithium Metal Using Lithium Chloride as the Raw Material (Solution 1):

[0049] A method for preparing lithium metal by electrolysis of lithium chloride in solution 1 is carried out by using an electrolytic cell shown in FIG. 1. The bottom of the electrolytic cell 6 is filled with a liquid alloy 5. An internal region of the electrolytic cell 6 above the liquid alloy 5 is divided into an anode chamber and a cathode chamber by an insulating partition 1. The anode chamber is filled with an anode molten salt electrolyte 7 and inserted with an anode 8. The cathode chamber is filled with a cathode molten salt electrolyte 4 and inserted with cathode 2. The anode molten salt electrolyte 7 and the cathode molten salt electrolyte 4 are connected via the liquid alloy 5 without contacting each other.

[0050] In solution 1, the method is carried out by using an electrolytic cell in FIG. 1. The electrolytic cell is divided into an anode chamber and a cathode chamber. The anode chamber is filled with an anode molten salt electrolyte containing lithium ions and inserted with an anode. The cathode chamber is filled with a cathode molten salt electrolyte containing lithium ions and has a cathode. The bottom of the electrolytic cell is further filled with a liquid alloy. The anode molten salt electrolyte and the cathode molten salt electrolyte are connected via the liquid alloy without contacting each other. After the electrolytic cell is powered on, a lithium chloride raw material is added into the anode chamber and oxidized 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. 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. The lithium ions in the cathode molten salt electrolyte are reduced to lithium atoms on the surface of the cathode. A lithium metal product is formed in the cathode chamber. The anode molten salt electrolyte consists of LiCl and one or more of KCl, LiF, and KF. The mole percentage of LiCl in the anode molten salt electrolyte is 40-85%. The cathode molten salt electrolyte is a lithium salt, or consists of a lithium salt and an additive. The lithium salt is one or more of LiF, LiCl, LiBr, and LiI, and the additive is one or more of KF, KCl, KBr, and KI. When the cathode molten salt electrolyte consists of a lithium salt and an additive, the mole percentage of the lithium salt is not less than 40%. The liquid alloy is a Li-M alloy. M is a metal element that is denser and less active than lithium metal. Preferably, M is one or more of Sn, Zn, Pb, Ag, In, Ga, Bi, and Sb. The density of the liquid alloy is greater than that of the anode molten salt electrolyte and that of the cathode molten salt electrolyte. The content of lithium in the liquid alloy is 5-90 at %. The anode is carbon material, preferably graphite. The cathode is metal or alloy material that is difficult to alloy with lithium, and is preferably one of steel, tungsten, and molybdenum. The content of LiCl in the lithium chloride raw material is not less than 80 wt %. When the electrolytic cell works normally, the current density of the anode is controlled at 0.1-2.0 A/cm.sup.2, and the temperature is 380-650? C.

[0051] Typical cases of solution 1 include:

Example 1-1

[0052] The bottom of the electrolytic cell was filled with a pre-alloyed LiPb alloy with Li content of 40 at %. The anode was graphite, and the cathode was stainless steel. The anode molten salt electrolyte was LiClKCl with the mole ratio of 1:1, and the cathode molten salt electrolyte was LiClKCl with the mole ratio of 3:2. The electrolytic cell was placed in an atmosphere filled with dry argon gas, and the temperature was programmed to 500? C. and kept for 2 h. The current density of the anode was controlled at 1.0 A/cm.sup.2 after powering on, and the electrolysis lasts for 10 h. During the electrolysis, a lithium chloride raw material (containing 98.4 wt % LiCl and 0.8 wt % water) was added regularly, and the content of Li in cathode lithium metal product was determined to be 99.92%.

Example 1-2

[0053] The bottom of the electrolytic cell was filled with a pre-alloyed LiIn alloy with Li content of 80 at %. The anode was modified graphite, and the cathode was a tungsten wire. The anode molten salt electrolyte was LiClKClKF with the mole ratio of 6:3.5:0.5, and the cathode molten salt electrolyte was LiFLiCl with the mole ratio of 3:7. The electrolytic cell was placed in an atmosphere filled with dry argon gas, and the temperature was programmed to 550? C. and kept for 2 h. The current density of the anode was controlled at 2.0 A/cm.sup.2 after powering on, and the electrolysis lasts for 10 h. During the electrolysis, a lithium chloride raw material (containing 89.4 wt % LiCl and 6.1 wt % water) was added regularly, and the content of Li in cathode lithium metal product was determined to be 99.83%.

Example 1-3

[0054] The bottom of the electrolytic cell was filled with a pre-alloyed LiAg alloy with Li content of 70 at %. The anode was graphite, and the cathode was a molybdenum wire. The anode molten salt electrolyte was LiClKClLiF with the mole ratio of 6:3.9:0.1, and the cathode molten salt electrolyte was LiClLiI with the mole ratio of 3.5:6.5. The electrolytic cell was placed in an atmosphere filled with dry argon gas, and the temperature was programmed to 450? C. and kept for 2 h. The current density of the anode was controlled at 0.8 A/cm.sup.2 after powering on, and the electrolysis lasts for 10 h. During the electrolysis, a lithium chloride raw material (containing 93.8 wt % LiCl and 3.2 wt % water) was added regularly, and the content of Li in cathode lithium metal product was determined to be 99.90%.

Example 1-4

[0055] The bottom of the electrolytic cell was filled with a pre-alloyed LiSn alloy with Li content of 20 at %. The anode was graphite, and the cathode was stainless steel. The anode molten salt electrolyte was LiClKCl with the mole ratio of 3:2, and the cathode molten salt electrolyte was LiIKIKF with the mole ratio of 6:3.5:0.5. The electrolytic cell was placed in an atmosphere filled with dry argon gas, and the temperature was programmed to 385? C. and kept for 2 h. The current density of the anode was controlled at 0.5 A/cm.sup.2 after powering on, and the electrolysis lasts for 10 h. During the electrolysis, a lithium chloride raw material (containing 99.1 wt % LiCl and 0.6 wt % water) was added regularly, and the content of Li in cathode lithium metal product was determined to be 99.97%.

Example 1-5

[0056] The bottom of the electrolytic cell was filled with a pre-alloyed LiPb alloy with Li content of 90 at %. The anode was graphite, and the cathode was carbon steel. The anode molten salt electrolyte was LiClKCl with the mole ratio of 8.5:1.5, and the cathode molten salt electrolyte was LiFKF with the mole ratio of 1:1. The electrolytic cell was placed in an atmosphere filled with dry argon gas, and the temperature was programmed to 650? C. and kept for 2 h. The current density of the anode was controlled at 0.2 A/cm.sup.2 after powering on, and the electrolysis lasts for 10 h. During the electrolysis, a lithium chloride raw material (containing 95.7 wt % LiCl and 1.5 wt % water) was added regularly, and the content of Li in cathode lithium metal product was determined to be 99.95%.

Example 1-6

[0057] The bottom of the electrolytic cell was filled with a pre-alloyed LiGa alloy with Li content of 5 at %. The anode was graphite, and the cathode was a tungsten wire. The anode molten salt electrolyte was LiClKCl with the mole ratio of 3:2, and the cathode molten salt electrolyte was LiBrKBr with the mole ratio of 3:2. The electrolytic cell was placed in an atmosphere filled with dry argon gas, and the temperature was programmed to 420? ? C. and kept for 2 h. The current density of the anode was controlled at 0.1 A/cm.sup.2 after powering on, and the electrolysis lasts for 10 h. During the electrolysis, a lithium chloride raw material (containing 90.5 wt % LiCl and 4.3 wt % water) was added regularly, and the content of Li in cathode lithium metal product was determined to be 99.89%.

Example 1-7

[0058] The bottom of the electrolytic cell was filled with a pre-alloyed LiBi alloy with Li content of 10 at %. The anode was modified graphite, and the cathode was a tungsten bar. The anode molten salt electrolyte was LiClKCl with the mole ratio of 2:3, and the cathode molten salt electrolyte was LiClKCl with the mole ratio of 2:3. The electrolytic cell was placed in an atmosphere filled with dry argon gas, and the temperature was programmed to 600? C. and kept for 2 h. The current density of the anode was controlled at 0.4 A/cm.sup.2 after powering on, and the electrolysis lasts for 10 h. During the electrolysis, a lithium chloride raw material (containing 85.6 wt % LiCl and 8.9 wt % water) was added regularly, and the content of Li in cathode lithium metal product was determined to be 99.71%.

Example 1-8

[0059] The bottom of the electrolytic cell was filled with a pre-alloyed LiZn alloy with Li content of 60 at %. The anode was graphite, and the cathode was stainless steel. The anode molten salt electrolyte was LiFLiCl with the mole ratio of 3:7, and the cathode molten salt electrolyte was LiFLiI with the mole ratio of 1:4. The electrolytic cell was placed in an atmosphere filled with dry argon gas, and the temperature was programmed to 550? C. and kept for 2 h. The current density of the anode was controlled at 1.5 A/cm.sup.2 after powering on, and the electrolysis lasts for 10 h. During the electrolysis, a lithium chloride raw material (containing 81.2 wt % LiCl and 13.1 wt % water) was added regularly, and the content of Li in cathode lithium metal product was determined to be 99.61%.

Comparative Example 1-1

[0060] The comparative example differs from Examples 1-6 in that the bottom of the electrolytic cell was not filled with the LiAg alloy, and the electrolyte was LiClKCl with the mole ratio of 3:2. Other conditions are the same. After electrolysis, the content of Li in cathode lithium metal product was determined to be 97.23%.

[0061] It can be seen that in the absence of the liquid alloy (the separation effect based on electrochemical reactions at the interface between the liquid alloy and the molten salt electrolyte are lost), the purity of lithium metal produced by electrolyzing lithium chloride with an ordinary partition electrolytic cell was low, and the content of impurities such as Na and Mg was high. Water in the lithium chloride raw material may react with lithium metal after entering the molten salt electrolyte, thus reducing the current efficiency.

2. Solution for Preparing Lithium Metal Using Lithium Carbonate (Solution 2):

[0062] Solution 2 is realized by an electrolysis device in FIG. 2. The electrolysis device in FIG. 2 includes an electrolytic cell 10 (refractory ceramic 10) with a jacket and a cover plate. The cover plate and the electrolytic cell are fixed by a flange 14. A heating resistance wire 8 is arranged outside a side wall of the electrolytic cell.

[0063] An inner chamber of the electrolytic cell is divided into an upper chamber and a lower chamber. The lower chamber is filled with a liquid alloy 1. The upper chamber is divided into an anode chamber 2 and a cathode chamber 3 arranged left and right by an insulating plate.

[0064] 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, and an anode 6 inserted in the anode molten salt electrolyte 4 and having the other end extending out of the anode chamber. And a top cover plate wall of the anode chamber is provided with a feed inlet 9, an argon gas inlet 12, and an argon gas outlet 13.

[0065] 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 lithium metal product 11 floating on the surface of the cathode molten salt electrolyte, a cathode 7 inserted in the cathode molten salt electrolyte and having the other end extending out of the anode chamber 3, and a product extraction tube for extracting lithium metal. And a top cover plate wall of the cathode chamber 3 is provided with an argon gas inlet 12 and an argon gas outlet 13.

[0066] The method of solution 2 is carried out by using an electrolytic cell. The electrolytic cell is divided into an anode chamber and a cathode chamber. The anode chamber is filled with an anode molten salt electrolyte containing lithium ions and inserted with an anode. The cathode chamber is filled with a cathode molten salt electrolyte containing lithium ions and inserted with a cathode. The bottom of the electrolytic cell is further filled with a liquid alloy. The anode molten salt electrolyte and the cathode molten salt electrolyte are connected via the liquid alloy without contacting each other. After the electrolytic cell is powered on, lithium carbonate is added into the anode molten salt electrolyte. 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. Meanwhile, the lithium atoms in the liquid alloy are oxidized to lithium ions at the interface between the liquid alloy and the cathode molten salt electrolyte and enter the cathode molten salt electrolyte. The lithium ions in the cathode molten salt electrolyte are reduced to lithium metal on the surface of the cathode. The anode is made of a carbon material, and the cathode is made of stainless steel, tungsten or molybdenum. Preferably, the cathode is made of stainless steel. The anode molten salt electrolyte is a lithium salt, or consists of a lithium salt and an additive. The lithium salt is one or more of LiCl, LiF, and Li.sub.2CO.sub.3, and the additive is one or more of KCl, KF, and BaCl.sub.2. The purity of 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 modifier. The lithium salt is one or more of LiCl, LiF, LiBr, and LiI, and the modifier is one or more of KCl, KF, KBr, and KI. The liquid alloy is an alloy formed by at least one of Zn, Ag, Sn, Pb, Sb, Bi, In, and Ga, and Li. The density of the liquid alloy is greater than that of the anode molten salt electrolyte or that of the cathode molten salt electrolyte. When the electrolytic cell works normally, the current density of the cathode is 0.1-5.0 A/cm.sup.2. When the electrolytic cell works normally, the electrolysis temperature is 400-800? C. An electrolysis operation is performed in an inert atmosphere. The inert atmosphere is preferably an argon atmosphere.

[0067] Typical implementation cases of solution 2 are:

Example 2-1

[0068] This example provides a method for preparing lithium metal by molten salt electrolysis, including the following steps:

[0069] (1) As shown in FIG. 2, under the protection of an argon atmosphere, 800 g SnLi alloy (the mass percentage of lithium was 6%) was added to the bottom of the electrolytic cell, the alloy was heated to 550? C. and in a molten state to completely separate the anode chamber and the cathode chamber. 200 g anode chamber molten salt with the mass fraction of LiCl 44%, KCl 54%, and LiF 2% was added into the anode chamber, and 200 g cathode chamber molten salt with the mass fraction of LiCl 45% and KCl 55% was added into the cathode chamber. After the anode chamber molten salt and the cathode chamber molten salt were completely molten, a graphite anode and a tungsten bar cathode were inserted respectively.

[0070] (2) Grade-2 Li.sub.2CO.sub.3 in GB/T 11075-2003 was slowly added into the anode chamber, and electrolysis was performed after powering on. The current density of the cathode was 1.2 A/cm.sup.2. The purity of lithium metal was 99.92% after 10 h of electrolysis under the inert condition.

Example 2-2

[0071] This example provides a method for preparing lithium metal by molten salt electrolysis, including the following steps:

[0072] (1) As shown in FIG. 2, under the protection of an argon atmosphere, 800 g SnLi alloy (the mass percentage of lithium was 1%) was added to the bottom of the electrolytic cell, heated to 400? ? C., and molten into a liquid alloy to completely separate the anode chamber and the cathode chamber. 200 g anode chamber molten salt with the mass fraction of LiCl 44%, KCl 54%, and LiF 2% was added into the anode chamber, and 200 g cathode chamber molten salt with the mass fraction of LiCl 45% and KCl 55% was added into the cathode chamber. After the anode chamber molten salt and the cathode chamber molten salt were completely molten, a graphite anode and a tungsten bar cathode were inserted respectively.

[0073] (2) Grade-2 Li.sub.2CO.sub.3 in GB/T 11075-2003 was slowly added into the anode chamber, and electrolysis was performed after powering on. The current density of the cathode was 0.1 A/cm.sup.2. The purity of lithium metal was 99.92% after 10 h of electrolysis under the inert condition.

Example 2-3

[0074] This example provides a method for preparing lithium metal by molten salt electrolysis, including the following steps:

[0075] (1) As shown in FIG. 2, under the protection of an argon atmosphere, 800 g AgLi alloy (the mass percentage of lithium was 20%) was added to the bottom of the electrolytic cell, heated to 400? C., and molten into a liquid alloy to completely separate the anode chamber and the cathode chamber. 200 g anode chamber molten salt with the mass fraction of LiCl 45% and KCl 55% was added into the anode chamber, and 200 g cathode chamber molten salt with the mass fraction of LiCl 45% and KCl 55% was added into the cathode chamber. After the anode chamber molten salt and the cathode chamber molten salt were completely molten, a graphite anode and a tungsten rod cathode were inserted respectively.

[0076] (2) Grade-2 Li.sub.2CO.sub.3 in GB/T 11075-2003 was slowly added into the anode chamber, and electrolysis was performed after powering on. The current density of the cathode was 1.2 A/cm.sup.2. The purity of lithium metal was 99.93% after 10 h of electrolysis under the inert condition.

Example 2-4

[0077] This example provides a method for preparing lithium metal by molten salt electrolysis, including the following steps:

[0078] (1) As shown in FIG. 2, under the protection of an argon atmosphere, 800 g lithium-containing liquid alloy, namely AgLi alloy (the mass percentage of lithium was 20%) was added to the bottom of the electrolytic cell, heated to 800? C., and molten into a liquid alloy to completely separate the anode chamber and the cathode chamber. 200 g anode chamber molten salt with the mass fraction of LiCl 45% and KCl 55% was added into the anode chamber, and 200 g cathode chamber molten salt with the mass fraction of LiCl 45% and KCl 55% was added into the cathode chamber. After the anode chamber molten salt and the cathode chamber molten salt were completely molten, a graphite anode and a tungsten rod cathode were inserted respectively.

[0079] (2) Li.sub.2CO.sub.3 with a purity of 80% was slowly added into the anode chamber, and electrolysis was performed after powering on. The current density of the cathode was 0.8 A/cm.sup.2. The purity of lithium metal was 99.90% after 10 h of electrolysis under the inert condition.

Example 2-5

[0080] This example provides a method for preparing lithium metal by molten salt electrolysis, including the following steps:

[0081] (1) As shown in FIG. 2, under the protection of an argon atmosphere, 800 g AgLiSn alloy (the mass fraction of lithium was 20% and the mass fraction of Sn was 20%) was added to the bottom of the electrolytic cell, heated to 800? C., and molten into a liquid alloy to completely separate the anode chamber and the cathode chamber. 200 g anode chamber molten salt with the mass fraction of LiCl 40%, KCl 50%, and LiF 10% was added into the anode chamber, and 200 g cathode chamber molten salt with the mass fraction of LiCl 45% and KCl 55% was added into the cathode chamber. After the anode chamber molten salt and the cathode chamber molten salt were completely molten, a graphite anode and a tungsten rod cathode were inserted respectively.

[0082] (2) Li.sub.2CO.sub.3 with a purity of 80% was slowly added into the anode molten salt electrolyte, and electrolysis was performed after powering on. The current density of the cathode was 0.8 A/cm.sup.2. The purity of lithium metal was 99.90% after 10 h of electrolysis under the inert condition.

[0083] Examples 2-6 to examples 2-12 below were compared with Example 2-1:

TABLE-US-00001 Purity Anode Cathode Current of molten molten density of lithium Alloy Temperature/ salt salt cathode/ Raw metal/ Example component ? C. electrolyte electrolyte Anode Cathode A .Math. cm.sup.?2 material % 2-1 Sn-6 500 LiCl LiCl Graphite Tungsten 1.2 Grade-2 99.92 wt. % Li 44 wt. % 45 wt. % bar Li.sub.2CO.sub.3 KCl KCl in GB/T 54 wt. % 55 wt. % 11075-2003 LIF 2 wt. % 2-6 Sn-6 500 LiCl LiCl Graphite Stainless 1.2 Grade-2 99.92 wt. % Li 44 wt. % 45 wt. % steel Li.sub.2CO.sub.3 KCl KCl in GB/T 54 wt. % 55 wt. % 11075-2003 LIF 2 wt. % 2-7 Sn-10 500 LiCl LiCl Graphite Tungsten 1.2 Grade-2 99.92 wt. % Li 44 wt. % 45 wt. % bar Li.sub.2CO.sub.3 KC1 KCl in GB/T 54 wt. % 55 wt. % 11075-2003 LiF 2 wt. % 2-8 Sn-6 600 LiCl LiCl Graphite Stainless 1.2 Grade-2 99.92 wt. % Li 44 wt. % 45 wt. % steel Li.sub.2CO.sub.3 KCl KCl in GB/T 54 wt. % 55 wt. % 11075-2003 LiF 2 wt % 2-9 Ag-10 800 LiCl LiCl Graphite Stainless 0.1 Grade-2 99.92 wt. % Li 50 wt. % 50 wt. % steel Li.sub.2CO.sub.3 LiF LIF in GB/T 50 wt. % 50 wt. % 11075-2003 2-10 Ag-20 400 LiCl LiCl Graphite Stainless 0.1 Grade-2 99.93 wt. % Li 45 wt. % 45 wt. % steel Li.sub.2CO.sub.3 KCl KCl in GB/T 55 wt. % 55 wt. % 11075-2003 2-11 Pb-5 800 LIF LIF Graphite Tungsten 0.1 Grade-2 99.94 wt. % Li 80 wt. % 60 wt. % bar Li.sub.2CO.sub.3 Li.sub.2CO.sub.3 LiCl in GB/T 20 wt. % 40 wt. % 11075-2003 2-12 Ag-20 400 LiCl LiCl Graphite Tungsten 0.1 Li.sub.2CO.sub.3 99.90 wt. % Li 45 wt. % 45 wt. % bar with KCl KCl purity of 55 wt. % 55 wt. % 85%

Comparative Example 2-1

[0084] 1000 g molten salt with the mass fraction of 45% LiCl and 55% KCl was added into the electrolytic cell, heated to 450? C., and molten, and graphite as anode and a tungsten rod as cathode were immersed in the electrolyte respectively.

[0085] Grade-2 lithium carbonate (with a purity of 98.5%) in GB/T 11075-2003 was slowly added into the anode molten salt electrolyte in the argon atmosphere, and electrolysis was performed after powering on. The current density of the anode was 1.2 A/cm.sup.2. The purity of lithium metal was 98% at the cathode after 10 h of electrolysis.

[0086] The above descriptions are only specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions which may be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be covered by the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be subject to the scope of protection of the claims.