Lithium secondary battery and method of fabricating the same

1. A lithium secondary battery comprising:

an electrode assembly;

a battery case configured to accommodate the electrode assembly;

a surface layer comprising an engineering plastic located on the outer side of the battery case; and

lead terminals connected with the electrode assembly and drawn out of the battery case,

wherein the battery case comprises a sealing part, and

wherein the surface layer is located on an entire surface of the outer side of the battery case including the sealing part,

wherein the surface layer has a thickness of 1 μm to 10 μm,

wherein the engineering plastic includes at least one or two selected from the group consisting of polyamide (PA), polyacetal (POM), polycarbonate (PC), modified polyphenylene ether (PPE), polybutylene terephthalate (PBT), GF-reinforced-polyethylene terephthalate (GF-PET), ultra-high-molecular-weight polyethylene (UHPE), polysulfone (PSF), polyethersulfone (PES), polyphenylenesulfide (PPS), polyarylate (PAR), polyamideimide (PAI), polyetherimide (PEI), polyetheretherketone (PEEK), polyimide (PI), liquid crystal polyester (LCP), polytetrafluoroethylene (PTFE), polyaminobismaleimide (PABM), and polybisamidetriazole (PBT), and

wherein the battery case is a pouch-type battery case having a multiple layer structure comprising an aluminum layer, an outer layer located on one surface of the aluminum layer and an inner layer located on the other surface of the aluminum layer,

wherein the battery case is not thermal bonded and the surface layer is formed by dip coating.

2. The lithium secondary battery according to claim 1 , wherein the materials for the outer layer and the inner layer are insulating materials.

3. The lithium secondary battery according to claim 2 , wherein the insulating materials are polypropylene (PP), biaxially oriented nylon (ONY), polyethylene terephthalate (PET), polybutylene terephthalate, a copolymer ester or polycarbonate.

4. The lithium secondary battery according to claim 1 , wherein the lithium secondary battery includes a polymer electrolyte.

5. A method of fabricating a lithium secondary battery of claim 1 , comprising forming a surface layer comprising an engineering plastic on the outer side of a battery case accommodating an electrode assembly so as to draw lead terminals connected with the electrode assembly out of the battery case,

wherein the battery case comprises a sealing part, and

wherein the surface layer is located on an entire surface of the outer side of the battery case including the sealing part.

6. The method according to claim 5 , wherein the forming of the surface layer comprises:

a first step of dip-coating the battery case in a solution comprising an engineering plastic; and

a second step of drying the dip-coated battery case at 170 to 190° C. for 2 to 4 hours to form the surface layer.