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.

What is claimed is: 
     
         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 2 CO 3 ; and   the additive is one or more of KCl, KF, and BaCl 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 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 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 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.