Spinel-Type Lithium Titanium Oxide/Graphene Composite and Method of Preparing the Same

Abstract

A spinel-type lithium titanium oxide/graphene composite and a method of preparing the same are provided. The method can be useful in simplifying a manufacturing process and shortening a manufacturing time using microwave associated solvothermal reaction and post heat treatment, and the spinel-type lithium titanium oxide/graphene composite may have high electrochemical performances due to its excellent capacity and rate capability and long lifespan, and thus be used as an electrode material of the lithium secondary battery.

1 . A method of preparing a transition metal oxide/graphene composite comprising:
 (a) mixing a transition metal (M1) salt, water and a solution of graphite oxide dispersed in a polyol solvent;   (b) preparing a transition metal (M1) oxide/graphene composite by applying microwaves to the mixed solution; and   (c) preparing a transition metal (M1M2) oxide/graphene composite by applying microwaves to a solution obtained by mixing the transition metal (M1) oxide/graphene composite with a transition metal (M2) salt,   wherein M1 and M2 are the same as or different from each other, and represent lithium, ruthenium, nickel, vanadium, cobalt, manganese, iron, or titanium.   
     
     
         2 . The method of  claim 1 , wherein, in step (a), a powder of the graphite oxide is dispersed in the polyol solvent using sonication. 
     
     
         3 . The method of  claim 1 , wherein, in step (a), the water is mixed at a content of 5 to 90 parts by weight, based on 100 parts by weight of the mixed solution. 
     
     
         4 . The method of  claim 1 , wherein, in step (b), the microwaves have an oscillation frequency of 2.45 to 60 GHz. 
     
     
         5 . The method of  claim 1 , wherein, in step (b), the transition metal (M1) salt of step (a) is titanium salt, and a TiO 2 /graphene composite is formed by applying microwaves to a mixed solution containing the titanium salt to form titanium oxide nanoparticles on a surface of the graphene. 
     
     
         6 . The method of  claim 5 , wherein the titanium oxide nanoparticles have particle sizes of 2 to 10 nm. 
     
     
         7 . The method of  claim 1 , further comprising:
 washing and drying the transition metal (M1) oxide/graphene composite prepared in step (b).   
     
     
         89 . The method of  claim 7 , wherein the transition metal (M1) oxide/graphene composite is washed with alcohol or distilled water. 
     
     
         9 . The method of  claim 1 , wherein the reaction in step (c) is performed for 10 to 30 minutes under microwaves having an oscillation frequency of 2.45 to 60 GHz. 
     
     
         10 . The method of  claim 1 , wherein, in step (c), the transition metal (M2) salt is lithium salt, and a Li 4 Ti 5 O 12 /graphene composite is formed by applying microwaves to a mixed solution containing the lithium salt to form lithium titanium oxide nanoparticles on a surface of the graphene. 
     
     
         11 . The method of  claim 10 , wherein the lithium titanium oxide nanoparticles have particle sizes of 5 to 30 nm. 
     
     
         12 . The method of  claim 1 , further comprising:
 subjecting the transition metal (M1M2) oxide/graphene composite to heat treatment under an argon atmosphere containing hydrogen.   
     
     
         13 . The method of  claim 13 , wherein the heat treatment is performed in a temperature range in which the transition metal (M1M2) oxide can be structurally changed into a transition metal (M1M2) oxide having a spinel structure without decomposing a nanostructure of the transition metal (M1M2) oxide. 
     
     
         14 . The method of  claim 13 , wherein the heat treatment is performed at 500 to 900° C. 
     
     
         15 . A lithium titanium oxide (Li 4 Ti 5 O 12 )/graphene composite having a spinel structure, comprising:
 graphene; and   lithium titanium oxide (Li 4 Ti 5 O 12 ) having a nano-sized spinel structure stacked on a surface of the graphene.   
     
     
         16 . The lithium titanium oxide (Li 4 Ti 5 O 12 )/graphene composite of  claim 15 , wherein the lithium titanium oxide having a spinel structure has a particle size of 5 to 30 nm. 
     
     
         17 . An anode material for lithium secondary batteries comprising a lithium titanium oxide (Li 4 Ti 5 O 12 )/graphene composite having a spinel structure defined in  claim 15 . 
     
     
         18 . The anode material of  claim 17 , wherein the anode material has a capacity at a 100 C rate of 101 mAh/g or more. 
     
     
         19 . The anode material of  claim 17 , wherein the anode material has an initial discharging capacity of 98% or more after the 100 discharging cycles at a 1 C rate, and a discharging capacity of 97% or more after the 100 discharging cycles at a 10 C rate. 
     
     
         20 . A lithium secondary battery comprising an electrode formed of an anode material defined in  claim 17 .