Pouch-type lithium secondary battery

1. A pouch-type lithium secondary battery, comprising:

an electrode assembly having an anode, a cathode, and a separator interposed between the cathode and the anode for electrical insulation therebetween;

a pouch-type case made of a sheet to provide a space in which the electrode assembly is housed; and

a non-aqueous electrolyte injected into the electrode assembly,

wherein the non-aqueous electrolyte is a non-linear carbonate-based non-aqueous electrolyte including a lithium salt, (a) a cyclic carbonate compound, and (b) a linear ester compound selected from the group consisting of propionate-based compound, methyl butyrate, propyl acetate, and mixtures thereof, and does not contain a linear carbonate compound, and

wherein, during LiPF 6 1M dissolution, the non-aqueous electrolyte has an ionic conductivity of 9 mS/cm or above at about 23° C., wherein a volume ratio (a:b) of the (a) component and (b) component is about 2:8 to about 4:6.

2. The pouch-type lithium secondary battery according to claim 1 , wherein the cyclic carbonate compound includes any one material or a mixture of at least two materials selected from the group consisting of ethylene carbonate, propylene carbonate, fluoroethylene carbonate, and butylene carbonate.

3. The pouch-type lithium secondary battery according to claim 1 , wherein the propionate-based compound may be propionate-based ester compound expressed by the following Chemical Formula 1:

where R 1 and R 2 are independently a linear or branched C 1-6 alkyl group, and R 1 and R 2 may be unsubstituted or substituted with at least one halogen, respectively.

4. The pouch-type lithium secondary battery according to claim 3 , wherein the propionate-based ester compound expressed by the Chemical Formula 1 includes at least one compound selected from the group consisting of methyl propionate-based compound, ethyl propionate-based compound, propyl propionate-based compound, and butyl propionate-based compound.

5. The pouch-type lithium secondary battery according to claim 4 , wherein the ethyl propionate-based compound is any one material or a mixture of at least two materials selected from the group consisting of ethyl propionate, ethyl 3-fluoropropanoate, ethyl 3,3-difluoropropanoate, ethyl 3,3,3-trifluoropropanoate, 2-fluoroethyl propionate, 2,2-difluoroethyl propionate, 2,2,2-trifluoroethyl propionate, 2,2,2-trifluoroethyl 3-fluoropropanoate, 2,2,2-trifluoroethyl 3,3-difluoropropanoate, and 2,2,2-trifluoroethyl 3,3,3-trifluoropropanoate.

6. The pouch-type lithium secondary battery according to claim 1 , wherein the lithium salt includes any one material or a mixture of at least two materials selected from the group consisting of LiPF 6 , LiBF 4 , LiSbF 6 , LiAsF 6 , LiClO 4 , LiN(C 2 F 5 SO 2 ) 2 , LiN(CF 3 SO 2 ) 2 , CF 3 SO 3 Li and LiC(CF 3 SO 2 ) 3 .

7. The pouch-type lithium secondary battery according to claim 1 , wherein the anode is made of carbon material capable of occluding or emitting lithium ions.

8. The pouch-type lithium secondary battery according to claim 7 , wherein the carbon material capable of occluding or emitting lithium ions is a low-crystalline carbon or high-crystalline carbon.

9. The pouch-type lithium secondary battery according to claim 1 , wherein the cathode is made of lithium-containing oxide.

10. The pouch-type lithium secondary battery according to claim 9 , wherein the lithium-containing oxide is a lithium-containing transition metal oxide.

11. The pouch-type lithium secondary battery according to claim 10 , wherein the lithium-containing transition metal oxide is any one material or a mixture of at least two materials selected from the group consisting of LiCoO 2 , LiNiO 2 , LiMnO 2 , LiMn 2 O 4 , Li(Ni a Co b Mn c )O 2 (0≦a≦1, 0≦b≦1, 0≦c≦1, a+b+c=1), LiNi 1-y Co y O 2 , LiCo 1-y Mn y O 2 , LiNi 1-y Mn y O 2 (0≦y<1), Li(Ni a Co b Mn c )O 4 (0<a<2, 0<b<2, 0<c<2, a+b+c=2), LiMn 2 —, Ni 3 O 4 , LiMn 2 —, CO 3 O 4 (0<z<2). LiCoPO 4 and LiFePO 4 .

12. The pouch-type lithium secondary battery according to claim 1 , wherein a ratio of discharge capacity of the battery at 2 C rate to discharge capacity of the battery at 0.2 C rate ranges from 81.3% to 83.5%, and

wherein a thickness increase during storage of the battery at 90° C. ranges from 0.14 millimeters (mm) to 0.25 mm.

13. A pouch-type lithium secondary battery, comprising:

an electrode assembly having an anode, a cathode, and a separator interposed between the cathode and the anode for electrical insulation therebetween;

a pouch-type case made of a sheet to provide a space in which the electrode assembly is housed; and

a non-aqueous electrolyte injected into the electrode assembly,

wherein the non-aqueous electrolyte is a non-linear carbonate-based non-aqueous electrolyte including a lithium salt, (a) a cyclic carbonate compound, and (b) a linear ester compound selected from the group consisting of propionate-based compound, methyl butyrate, propyl acetate, and mixtures thereof, and does not contain a linear carbonate compound,

wherein a ratio of discharge capacity of the battery at 2 C rate to discharge capacity of the battery at 0.2 C rate ranges from 81.3% to 83.5%, and

wherein a thickness increase during storage of the battery at 90° C. ranges from 0.14 millimeters (mm) to 0.25 mm.