Low temperature electrochemical production of silicon

Abstract

A method for the electrochemical production silicon comprises applying an electrical potential across an anode and a cathode to provide electrons at the cathode. The anode and the cathode are in contact with an electrolyte melt at a reaction temperature. The electrolyte melt comprises a molten salt or a mixture of molten salts; a silicon-containing precursor at least partially dissolved in the electrolyte melt to provide soluble silicon-containing ions in the electrolyte melt; and a supporting electrolyte at least partially dissolved in the electrolyte melt to provide O 2− ions in the electrolyte melt. The soluble silicon-containing ions at the cathode undergo reduction reactions with the electrons to release O 2− ions and deposit silicon on the cathode.

What is claimed is: 
     
         1 . A method for the electrochemical production silicon, the method comprising applying an electrical potential across an anode and a cathode to provide electrons at the cathode, the anode and the cathode in contact with an electrolyte melt at a reaction temperature,
 wherein the electrolyte melt comprises
 a molten salt or a mixture of molten salts; 
 a silicon-containing precursor at least partially dissolved in the electrolyte melt to provide soluble silicon-containing ions in the electrolyte melt; and 
 a supporting electrolyte at least partially dissolved in the electrolyte melt to provide O 2−  ions in the electrolyte melt; 
   and further wherein the soluble silicon-containing ions at the cathode undergo reduction reactions with the electrons to release O 2−  ions and deposit silicon on the cathode.   
     
     
         2 . The method of  claim 1 , wherein the reaction temperature is no more than about 900° C. 
     
     
         3 . The method of  claim 1 , wherein the electrolyte melt comprises an eutectic mixture of metal halides. 
     
     
         4 . The method of  claim 1 , wherein the soluble silicon-containing ions comprise SiO 3   2−  ions, SiO 4   4−  ions, or both. 
     
     
         5 . The method of  claim 1 , wherein the silicon-containing precursor is a silicate. 
     
     
         6 . The method of  claim 5 , wherein the silicate is an orthosilicate, an inosilicate, a phyllosilicate, an aluminosilicate or combinations thereof. 
     
     
         7 . The method of  claim 5 , wherein the silicate is selected from MSiO 3 , M 2 SiO 4 , or combinations thereof, wherein M is selected from alkali metals, alkaline earth metals or combinations thereof. 
     
     
         8 . The method of  claim 5 , wherein the silicate is CaSiO 3 . 
     
     
         9 . The method of  claim 1 , wherein the silicon-containing precursor is SiO 2 . 
     
     
         10 . The method of  claim 1 , wherein the supporting electrolyte is selected from alkali metal oxides, alkaline earth metal oxides, and combinations thereof. 
     
     
         11 . The method of  claim 10 , wherein the supporting electrolyte is selected from CaO, Na 2 O, or combinations thereof. 
     
     
         12 . The method of  claim 1 , wherein the amount of supporting electrolyte saturates the electrolyte melt with O 2−  ions. 
     
     
         13 . The method of  claim 10 , wherein the silicon-containing precursor is SiO 2  and the supporting electrolyte is of a type and at an amount to dissolve the SiO 2  to provide the soluble silicon-containing ions in situ via the formation of a silicate. 
     
     
         14 . The method of  claim 13 , wherein the supporting electrolyte is CaO. 
     
     
         15 . The method of  claim 1 , wherein at least a portion of the silicon-containing precursor and at least a portion of the supporting electrolyte are provided as molten glass, molten coal ash, molten cinder ash, or combinations thereof. 
     
     
         16 . The method of  claim 15 , wherein additional SiO 2 , additional CaO, additional Na 2 O, or combinations thereof are added to the electrolyte melt. 
     
     
         17 . The method of  claim 1 , wherein the silicon produced is crystalline. 
     
     
         18 . The method of  claim 17 , wherein the crystalline silicon has a purity of at least about 95 atomic %. 
     
     
         19 . The method of  claim 1 , wherein the silicon produced is in the form of nanowires. 
     
     
         20 . The method of  claim 1 , wherein the method provides a yield of silicon of at least about 20% at the temperature of about 650° C. and a reaction time of about 3 hours.