Composition for forming lithium reduction resistant layer, method for forming lithium reduction resistant layer, and lithium secondary battery

Abstract

A composition for forming a lithium reduction resistant layer includes a solvent, and a lithium compound, a lanthanum compound, a zirconium compound, and a compound containing a metal M, each of which shows solubility in the solvent, and in which with respect to the stoichiometric composition of a compound represented by the general formula (I), the lithium compound is contained in an amount 1.05 times or more and 2.50 times or less, the lanthanum compound and the zirconium compound are contained in an amount 0.70 times or more and 1.00 times or less, and the compound containing a metal M is contained in an equal amount. Li 7−x La 3 (Zr 2−x , M x )O 12   (I)

What is claimed is: 
     
         1 . A composition for forming a lithium reduction resistant layer, comprising:
 a solvent;   a lithium compound; a lanthanum compound; a zirconium compound; and a compound containing a metal M, wherein   the lithium compound, the lanthanum compound, the zirconium compound, and the compound containing a metal M each show solubility in the solvent,   the lithium compound is contained in an amount 1.05 times or more and 2.50 times or less with respect to the stoichiometric composition of a compound represented by the general formula (I),   the lanthanum compound is contained in an amount 0.70 times or more and 1.00 times or less with respect to the stoichiometric composition of the compound represented by the general formula (I),   the zirconium compound is contained in an amount 0.70 times or more and 1.00 times or less with respect to the stoichiometric composition of the compound represented by the general formula (I), and   the compound containing a metal M is contained in an equal amount with respect to the stoichiometric composition of the compound represented by the general formula (I):
   Li 7−x La 3  (Zr 2−x , M x )O 12    (I)
 
   (wherein the metal M represents at least one metal selected from Nb, Sc, Ti, V, Y, Hf, Ta, Al, Si, Ga, Ge, Sn, and Sb, and X represents 0 to 2).   
     
     
         2 . The composition for forming a lithium reduction resistant layer according to  claim 1 , wherein
 the lithium compound is at least one compound selected from a lithium metal salt compound and a lithium alkoxide compound,   the lanthanum compound is at least one compound selected from a lanthanum metal salt compound and a lanthanum alkoxide compound,   the zirconium compound is at least one compound selected from a zirconium metal salt compound and a zirconium alkoxide compound, and   the compound containing a metal M is at least one compound selected from a metal salt compound of the metal M and a metal alkoxide compound of the metal M.   
     
     
         3 . The composition for forming a lithium reduction resistant layer according to  claim 1 , wherein the solvent is any of water, a single organic solvent, a mixed solvent containing water and at least one organic solvent, and a mixed solvent containing at least two or more organic solvents. 
     
     
         4 . A method for forming a lithium reduction resistant layer, comprising:
 forming a liquid coating film using the composition for forming a lithium reduction resistant layer according to  claim 1 ; and   heating the liquid coating film, wherein   a lithium reduction resistant layer containing the compound represented by the general formula (I) is obtained.   
     
     
         5 . The method for forming a lithium reduction resistant layer according to  claim 4 , wherein the liquid coating film is formed by using a coating method. 
     
     
         6 . The method for forming a lithium reduction resistant layer according to  claim 4 , wherein the heating of the liquid coating film includes a first heating treatment for drying the liquid coating film, a second heating treatment for producing metal oxides of lithium, lanthanum, zirconium, and the metal M, and a third heating treatment for producing and sintering the compound represented by the general formula (I). 
     
     
         7 . The method for forming a lithium reduction resistant layer according to  claim 6 , wherein the heating temperature in the first heating treatment is 50° C. or higher and 250° C. or lower. 
     
     
         8 . The method for forming a lithium reduction resistant layer according to  claim 6 , wherein the heating temperature in the second heating treatment is 400° C. or higher and 550° C. or lower. 
     
     
         9 . The method for forming a lithium reduction resistant layer according to  claim 6 , wherein the heating temperature in the third heating treatment is 600° C. or higher and 900° C. or lower. 
     
     
         10 . A lithium secondary battery, comprising:
 a solid electrolyte layer; and   a lithium reduction resistant layer disposed in contact with the solid electrolyte layer, wherein   the lithium reduction resistant layer contains a compound represented by the general formula (I), and   an interface between the lithium reduction resistant layer and the solid electrolyte layer is a continuous layer of the lithium reduction resistant layer and the solid electrolyte layer:
   Li 7−x La 3  (Zr 2−x , M x )O 12    (I)
 
   
       (wherein the metal M represents at least one metal selected from Nb, Sc, Ti, V, Y, Hf, Ta, Al, Si, Ga, Ge, Sn, and Sb, and X represents 0 to 2). 
     
     
         11 . The lithium secondary battery according to  claim 10 , wherein
 the lithium secondary battery further comprises an active material molded body, and   the active material molded body is provided such that a first surface which is a part of the surface thereof is in contact with the lithium reduction resistant layer, and a second surface which is a surface other than the first surface is in contact with the solid electrolyte layer, and   in the first surface, at an interface between the lithium reduction resistant layer and the active material molded body, a continuous layer of the lithium reduction resistant layer and the active material molded body is formed.