Solid electrolyte for all solid-state lithium-ion battery and manufacturing method therefor

Abstract

The method for manufacturing a solid electrolyte using an LLZ material for a lithium-ion battery comprises the steps of: providing a starting material in which lanthanum nitrate [La(NO 3 ) 3 .6H 2 O] and zirconium nitrate [ZrO(NO 3 ) 2 .6H 2 O] are mixed at a mole ratio of 3:2; forming an aqueous solution by dissolving the starting material; forming a precipitate by putting ammonia, which is a complex agent, and sodium hydroxide, which adjusts the pH of a reactor, into the aqueous solution, mixing the same, and then co-precipitating the mixture; forming a primary precursor powder by cleaning, drying and pulverizing the precipitate; forming a secondary precursor powder by mixing lithium powder [LiOH.H2O] with the primary precursor powder and ball-milling the mixture so as to solidify the lithium; and forming a solid electrolyte powder by heat-treating the secondary precursor powder.

What is claimed is: 
     
         1 . A method of manufacturing a solid electrolyte for a lithium-ion battery, the method comprising:
 providing a starting material in which lanthanum nitrate [La(NO 3 ) 3 .6H 2 O] and zirconium nitrate [ZrO(NO 3 ) 2 .6H 2 O] are mixed at a molar ratio of 3:2;   forming an aqueous solution by dissolving the starting material;   forming a precipitate by adding a complex agent (NH4OH) and a solution (NaOH) for pH of a reactor to the aqueous solution in a reactor, followed by mixing and co-precipitation;   forming primary precursor powder by washing, drying and pulverizing the precipitate;   forming secondary precursor powder by mixing and ball-milling the primary precursor powder with lithium powder [LiOH.H2O] to solidify lithium; and   wherein the solid electrolyte powder has a composition of Li x La y Zr z O 12 , where x is 6 to 9 moles, y is 2 to 4 moles, and z is 1 to 3 moles.   
     
     
         2 . The method of  claim 1 , further comprising:
 forming the heat-treated solid electrolyte powder into a pellet sheet; and   additionally heat-treating the pellet sheet to change to a crystal structure in which a cubic structure predominates.   
     
     
         3 . The method of  claim 1 , wherein the solid electrolyte powder is changed to a crystal structure in which one of a cubic structure and a tetragonal structure predominates depending on heat treatment temperature. 
     
     
         4 . The method of  claim 1 , wherein heat treatment temperature is 600 to 1200° C., and the solid electrolyte powder has a structure in which a cubic structure and a tetragonal structure coexist or a particular structure predominates. 
     
     
         5 . The method of  claim 3  or  4 , wherein the treatment temperature is 600 to 1200° C., and physical properties are improved using a characteristic that the cubic structure or the tetragonal structure is changed at a calcination temperature the same as or higher than the heat treatment temperature. 
     
     
         6 . The method of  claim 1 , wherein heat treatment temperature is 700 to 800° C., and the solid electrolyte powder is changed into a material in which a complete cubic structure or tetragonal structure predominates by calcination at 1200° C. for 2 to 8 hours. 
     
     
         7 . The method of  claim 6 , wherein the solid electrolyte powder is changed into a material having a predominating cubic structure and a fine structure with a high density of 90% or higher by calcination at 1200° C. for 5 hours. 
     
     
         8 . The method of  claim 1 , wherein heat treatment temperature is approximately 900° C., and the solid electrolyte powder is manufactured by calcination at approximately 900° C. for 10 hours or longer. 
     
     
         9 . The method of  claim 1 , wherein heat treatment temperature is approximately 900° C., and the solid electrolyte powder is manufactured by calcination at approximately 900° C. for 2 to 10 hours. 
     
     
         10 . The method of  claim 9 , wherein the solid electrolyte powder has a predominating tetragonal structure and a high-density fine structure with a relative density of 60% or higher by calcination at approximately 900° C. for 5 hours. 
     
     
         11 . The method of  claim 1 , wherein the complex agent is 5 N ammonia solution, and the complex agent and sodium hydroxide are added such that the aqueous solution has a pH of 10 to 11. 
     
     
         12 . The method of  claim 11 , wherein the mixing of the complex agent is performed by titration with the starting material at 4 ml/min simultaneously with titration with the complex agent at 4 ml/min. 
     
     
         13 . The method of  claim 11 , wherein a sodium hydroxide (NaOH) solution is added for pH adjustment in the forming of the precipitate, and the NaOH solution is 1 M and automatically titrated based on a pH change in a co-precipitation reactor with co-precipitation proceeding. 
     
     
         14 . The method of  claim 1 , further comprising:
 putting the solid electrolyte powder into a uniaxial compression molding mold and molding the solid electrolyte powder;   compressing the mold; and   heat-treating a pellet formed in the compressed mold at the same temperature as heat treatment temperature of the secondary precursor powder to form a high-density fine structure.   
     
     
         15 . A solid electrolyte for a lithium-ion battery manufactured by forming powder of the solid electrolyte by heat treatment to have a composition of Li x La y Zr z O 12 , where x is 6 to 9 moles, y is 2 to 4 moles, and z is 1 to 3 moles, and by using a characteristic that a predominating crystal structure is changed to a cubic structure and a tetragonal structure depending on heat treatment temperature. 
     
     
         16 . The solid electrolyte of  claim 15 , wherein heat treatment temperature of the powder of the solid electrolyte is 600 to 1200° C., and the powder of the solid electrolyte has a structure in which a cubic structure and a tetragonal structure coexist. 
     
     
         17 . The solid electrolyte of  claim 15 , wherein the powder of the solid electrolyte is heat-treated at 600 to 1200° C. to have a changed crystal structure. 
     
     
         18 . The solid electrolyte of  claim 15 , wherein heat treatment temperature of the powder of the solid electrolyte is 700 to 800° C., and the powder of the solid electrolyte is manufactured into pellets and calcinated at 1200° C. for 5 hours or longer to change to a complete cubic structure. 
     
     
         19 . The solid electrolyte of  claim 15 , wherein heat treatment temperature of the powder of the solid electrolyte is approximately 900° C., and the powder of the solid electrolyte is manufactured into pellets and calcinated at approximately 900° C. for 5 hours or longer.