Methods for Producing Silicon-Containing Structures Using Redox Mediators and Chemical Reduction

Abstract

Described herein are methods for producing silicon-containing structures using electrochemically generated solutions and chemical reduction of components in such solutions. For example, a cathode solution and an anode solution may be provided a reactor with the cathode solution comprising a cathode solution solvent, a cathode solution salt, and a redox mediator and with the anode solution comprising an anode solution solvent and an anode solution salt. A voltage is then applied between the cathode and anode thereby converting the redox mediator into a reducing agent forming a charged cathode solution. The method may proceed with adding a silicon-containing precursor to the charged cathode solution such that the reducing agent reacts with the silicon-containing precursor and forms silicon-containing structures and a precursor-mixture salt in the precursor mixture. The redox mediator is released into the precursor mixture during this operation. The method proceeds with separating the silicon-containing structures from the precursor mixture.

1 . A method comprising:
 providing a cathode solution and an anode solution in a reactor comprising a cathode, an anode, and a separator, wherein:
 the cathode solution comprises a cathode solution solvent, a cathode solution salt, and a redox mediator, 
 the anode solution comprises an anode solution solvent and an anode solution salt, and 
 both the cathode solution and anode solution comprise charge-carrying ions; 
   applying a voltage between the cathode and the anode thereby converting the cathode solution into a charged cathode solution comprising a reducing agent formed from the redox mediator by adding electrons received from the cathode;   adding a silicon-containing precursor to the charged cathode solution thereby forming a precursor mixture, wherein the reducing agent reacts with the silicon-containing precursor and forms silicon-containing structures and a precursor-mixture salt in the precursor mixture while releasing the redox mediator into the precursor mixture; and   separating the silicon-containing structures from the precursor mixture.   
     
     
         2 . The method of  claim 1 , wherein the reducing agent comprises one or more solvated electrons, a reduced form of the redox mediator, metal hydrides, or reduced metal ions. 
     
     
         3 . The method of  claim 1 , wherein the precursor-mixture salt is same as the cathode solution salt. 
     
     
         4 . The method of  claim 1 , wherein the charge-carrying ions is one or more cations selected from the group consisting of H + , Li + , Na + , K + , Cs + , tetramethylammonium cation (TMA + ), tetraethylammonium cation (TEA + ), tetrapentylammonium cation (TPA + ), tetrabutylammonium cation (TBA + ), and 1-butyl-1-methylpyrrolidinium cation (PYR 14   + ). 
     
     
         5 . The method of  claim 1 , wherein the charge-carrying ions is one or more anions selected from the group consisting of F − , Cl − , Br, I − , perchlorate anion (ClO 4   − ), nitrate anion (NO 3   − ), hexafluorophosphate anion (PF 6   − ), silicon pentachloride anion (SiCl 5   − ), bis(fluorosulfonyl)imide anion (FSI − ), and bis(trifluoromethylsulfonyl)imide (TFSI − ). 
     
     
         6 . The method of  claim 1 , further comprising heat-treating the silicon-containing structures separated from the precursor mixture. 
     
     
         7 . The method of  claim 1 , further comprising:
 after separating the silicon-containing structures from the precursor mixture, reusing the precursor mixture as the cathode solution or anode solution, and   repeating applying the voltage, adding the silicon-containing precursor, and separating the silicon-containing structures from the precursor mixture.   
     
     
         8 . The method of  claim 7 , wherein separating the silicon-containing structures from the precursor mixture further comprises removing the precursor-mixture salt from the precursor mixture thereby forming the cathode solution. 
     
     
         9 . The method of  claim 8 , wherein separating the silicon-containing structures from the precursor mixture further comprises:
 extracting a solid mixture from the precursor mixture;   adding a salt-dissolving solvent to dissolve the precursor-mixture salt formed in the solid mixture, forming a slurry mixture;   separating the slurry mixture into the silicon-containing structures and a salt solution; and   removing the salt-dissolving solvent from the salt solution, prior to reusing the precursor-mixture salt as the cathode solution salt or anode solution salt.   
     
     
         10 . The method of  claim 9 , wherein:
 the cathode solution solvent is diglyme,   the cathode solution salt is a sodium perchlorate (NaClO 4 ),   the redox mediator is naphthalene (C 10 H 8 ),   the separator is NASCION-type solid electrolyte Na 3 Zr 2 Si 2 PO 12  (NZSP),   the charge-carrying ions are sodium ions (Na + ),   the anode solution solvent is water,   the anode solution salt is sodium chloride,   the voltage is −5V,   the silicon-containing precursor is silicon tetrachloride (SiCl 4 ), and   the salt-dissolving solvent is water.   
     
     
         11 . The method of  claim 1 , wherein separating the silicon-containing structures from the precursor mixture further comprises extracting and recycling the precursor-mixture salt from the precursor mixture thereby forming the cathode solution salt or anode solution salt. 
     
     
         12 . The method of  claim 1 , wherein applying a voltage between the cathode and the anode comprises:
 determining an equivalent charge of the charged cathode solution, and   determining an amount of the silicon-containing precursor added to the charged cathode solution based on the equivalent charge of the charged cathode solution.   
     
     
         13 . The method of  claim 1 , wherein:
 the cathode solution solvent is tetrahydrofuran (THF),   the cathode solution salt is a lithium hexafluorophosphate (LiPF 6 ),   the redox mediator is biphenyl (C 12 H 10 ),   the voltage is −3V, and   the silicon-containing precursor is silicon tetrachloride (SiCl 4 ).   
     
     
         14 . The method of  claim 1 , wherein separating the silicon-containing structures from the precursor mixture is performed using a centrifuge or filtration. 
     
     
         15 . The method of  claim 1 , wherein at least one of the cathode and the anode comprises a metal, a carbon, a conductive polymer, a conductive ceramic, or a conductive silicon. 
     
     
         16 . The method of  claim 1 , wherein the cathode solution solvent is one of:
 an ether selected from the group consisting of tetrahydrofuran (THF), monoglyme, diglyme, triglyme, and tetraglyme,   an organic carbonate selected from the group consisting of propylene carbonate (PC), and dimethyl carbonate (DMC), and   an ionic liquid selected from the group consisting of 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR14TFSI), N-propyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR13TFSI), 1-Ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM]TFSI), 1-butyl-3-methylimidazolium tetrachloroaluminate ([BMIM]AlCl 4 ), and acetonitrile (C 2 H 3 N).   
     
     
         17 . The method of  claim 1 , wherein the cathode solution salt is selected from the group consisting of lithium chloride (LiCl), sodium chloride (NaCl), potassium chloride (KCl), magnesium chloride (MgCl 2 ), aluminum chloride (AlCl 3 ), tetramethylammonium chloride (TMACl), tetraethylammonium chloride (TEACl), tetrapentylammonium chloride (TPACl), tetrabutylammonium chloride (TBACl), tetrabutylammonium bromide (TBABr), N-butyl-N-methylpyrrolidinium chloride (PYR 14 Cl), N-methyl-N-propylpyrrolidinium chloride (PYR13Cl), lithium hexafluorophosphate (LiPF 6 ), sodium hexafluorophosphate (NaPF 6 ), lithium perchlorate (LiClO 4 ), sodium perchlorate (NaClO 4 ), lithium bis(trifluoromethane)sulfonimide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), sodium bis(trifluoromethane)sulfonimide (NaTFSI), and NaFSI. 
     
     
         18 . The method of  claim 1 , wherein the redox mediator is selected from the group consisting of biphenyl (C 12 H 10 ), naphthalene (C 10 H 8 ), methylamine (CH 3 NH 2 ), a crown ether, metallocene, cobaltocene (Co(η 5 C 5 H 5 ) 2 ]), decamethylcobaltocene (C 20 H 30 Co), ferrocene, decamethylferrocene, chromocene, nickelocene, metal carbonyl, nickel tetracarbonyl, iron pentacarbonyl, chromium hexacarbonyl, and dimanganese decacarbonyl. 
     
     
         19 . The method of  claim 1 , wherein the separator comprises one or more materials selected from the group consisting of a dense solid electrolyte, dense or porous ion-selective membrane, porous polymer, porous glass, and porous ceramic. 
     
     
         20 . The method of  claim 1 , wherein the separator is one of:
 an ion-selective membrane selected from the group consisting of NASCION-structured Na 3 Zr 2 Si 2 PO 12 , lithium aluminum titanium phosphate (LATP), Garnet-type lithium lanthanum zirconium oxide (LLZO), and ABO3-type Lithium niobate (LiNbO 3 ),   a cation exchange polymer electrolyte selected from the group consisting of NAFION™, polyether ether ketone (PEEK), and polyethylene oxide (PEO), and   anion exchange polymer electrolyte selected from the group consisting of polymeric quaternary ammonium chloride and bromide.