Lithium secondary battery of improved rate capability

Abstract

Disclosed is a lithium secondary battery with improved rate characteristics. More particularly, disclosed is a lithium secondary battery including a cathode, an anode, a separator disposed between the cathode and the anode, and an electrolyte, wherein the electrolyte includes a mixed solvent of a cyclic carbonate-based material and a propionate-based material, the cathode includes a lithium manganese composite oxide represented by Formula 1 below as a cathode active material, and the anode includes a lithium metal oxide represented by Formula 2 below as an anode active material: Li x M y Mn 2−y O 4−z A z   (1) wherein 0.9≦x≦1.2, 0<y<2, and 0≦z<0.2, M is at least one element selected from the group consisting of Al, Mg, Ni, Co, Fe, Cr, V, Ti, Cu, B, Ca, Zn, Zr, Nb, Mo, Sr, Sb, W, Ti, and Bi; and A is at least one monovalent or divalent anion, Li a M′ b O 4−x A c   (2) wherein M′ is at least one element selected from the group consisting of Ti, Cu, Pb, Sb, Zn, Fe, In, Al, and Zr; 0.1≦a≦4 and 0.2≦b≦4 wherein a and b are determined according to oxidation number of M′; 0≦c<0.2 wherein c is determined according to oxidation number of A; and A is at least one monovalent or divalent anion.

1 . A lithium secondary battery comprising a cathode, an anode, a separator disposed between the cathode and the anode, and an electrolyte,
 wherein the electrolyte comprises a mixed solvent of a cyclic carbonate-based material and a propionate-based material, the cathode comprises a lithium manganese composite oxide represented by Formula I below as a cathode active material, and the anode comprises a lithium metal oxide represented by Formula 2 below as an anode active material:
   Li x M y Mn 2−y O 4−z A z   (1)
 
   wherein 0.9≦x≦1.2, 0<y<2, and 0≦z<0.2; M is at least one element selected from the group consisting of Al, Mg, Ni, Co, Fe, Cr, V, Ti, Cu, B, Ca, Zn, Zr, Nb, Mo, Sr, Sb, W, Ti, and Bi; and A is at least one monovalent or divalent anion,
   Li a M′ b O 4−c A c   (2)
 
   wherein M′ is at least one element selected from the group consisting of Ti, Sn, Cu, Pb, Sb, Zn, Fe, In, Al, and Zr; 0.1≦a≦4 and 0.2≦b≦4 wherein a and b are determined according to oxidation number of M′; 0≦c<0.2 wherein c is determined according to oxidation number of A; and A is at least one monovalent or divalent anion.   
     
     
         2 . The lithium secondary battery according to  claim 1 , wherein the propionate-based material is represented by Formula 3 below:
   R 1 —COO—R 2   (3)
   wherein R 1  is a substituted or unsubstituted ethyl group, and R 2  is a substituted or unsubstituted C 1 -C 4  linear or branched alkyl group.   
     
     
         3 . The lithium secondary battery according to  claim 1 , wherein the Propionate-based material is one selected from the group consisting of methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), butyl propionate (BP), and combinations thereof. 
     
     
         4 . The lithium secondary battery according to  claim 1 , wherein an amount of the cyclic carbonate-based material is in a range of 1 wt % to 30 wt % based on a total weight of the electrolyte. 
     
     
         5 . The lithium secondary battery according to  claim 1 , wherein a mixing weight ratio of the cyclic carbonate-based material to the propionate-based material is in a range of 5 to 15:85 to 95. 
     
     
         6 . The lithium secondary battery according to  claim 5 , wherein the mixing weight ratio of the cyclic carbonate-based material to the propionate-based material is 10:90. 
     
     
         7 . The lithium secondary battery according to  claim 1 , wherein the lithium manganese composite oxide of Formula 1 is a lithium nickel manganese complex oxide (LNMO) represented by Formula 4 below:
   Li x Ni y Mn 2−y O 4   (4)
   wherein 0.9≦x≦1.2 and 0.4≦y≦0.5.   
     
     
         8 . The lithium secondary battery according to  claim 7 , wherein the lithium nickel manganese composite oxide of Formula 4 is LiNi 0.5 Mn 1.5 O 4  or LiNi 0.4 Mn 1.6 O 4 . 
     
     
         9 . The lithium secondary battery according to  claim 1 , wherein the lithium metal oxide of Formula 2 is a lithium titanium oxide (LTO) represented by Formula 5 below:
   Li a Ti b O 4   (5)
   wherein 0.5≦a≦3 and 1≦b≦2.5.   
     
     
         10 . The lithium secondary battery according to  claim 9 , wherein the lithium titanium oxide of Formula 5 is Li 1.33 Ti 1.67 O 4  and LiTi 2 O 4 . 
     
     
         11 . A battery module comprising the lithium secondary battery according to  claim 1  as a unit cell. 
     
     
         12 . A battery pack comprising the battery module according to  claim 11 . 
     
     
         13 . A device comprising the battery pack according to  claim 12 . 
     
     
         14 . The device according to  claim 13 , wherein the device is an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, or a system for storing power.