Lithium secondary battery and method for producing the same

A lithium secondary battery comprising an electrode group obtained by winding a positive electrode, a negative electrode and a separator disposed between said positive electrode and said negative electrode,

• said positive electrode including a positive electrode current collector and a positive electrode active material layer carried on said positive electrode current collector,
• said negative electrode including a negative electrode current collector and a negative electrode active material layers carried on said negative electrode current collector,
• an exposed portion on which said positive electrode active material layer is not carried being provided on said positive electrode current collector at at least one of an initial winding end and a final winding end of said positive electrode,
• an exposed portion on which said negative electrode active material layer is not carried being provided on said negative electrode current collector at at least one of an initial winding end and a final winding end of said negative electrode,
• wherein a heat-resistant layer including a filler and a binder is formed on at least a part of said exposed portion of said negative electrode current collector, and at least a part of a surface of said negative electrode active material layer that includes said end of said negative electrode active material layer,
• at least one of said initial winding end and said final winding end of said negative electrode active material layer is opposite to said exposed portion of said positive electrode current collector, and
• said positive electrode comprises an insulating tape attached onto at least a part of said exposed portion of said positive electrode current collector that is opposite to said end of said negative electrode active material layer.

A method for producing a lithium secondary battery comprising an electrode group in which a positive electrode including a positive electrode current collector and a positive electrode active material layer carried on said positive electrode current collector, and a negative electrode including a negative electrode current collector and a negative electrode active material layer carried on said negative electrode current collector are wound, said method comprising the steps of:

• (A) producing a positive electrode in which an exposed portion is provided on said positive electrode current collector at at least one of an initial winding end and a final winding end of said positive electrode;
• (B) producing a negative electrode in which an exposed portion is provided on said negative electrode current collector at at least one of an initial winding end and a final winding end of said negative electrode;
• (C) mixing a filler, a binder and a dispersion medium to prepare a paste for forming a heat-resistant layer;
• (D) applying said paste onto at least a part of said exposed portion of said negative electrode current collector, and the entire surface of said negative electrode active material layer, followed by drying, thereby forming a heat-resistant layer;
• (E) attaching an insulating tape onto a part of said exposed portion of said positive electrode current collector that is opposite to said end of said negative electrode active material layer;
• and
• (F) winding said positive electrode including said insulating tape attached thereon, and said negative electrode including said heat-resistant layer formed thereon to obtain an electrode group.

A method for producing a lithium secondary battery comprising an electrode group in which a positive electrode including a positive electrode current collector and a positive electrode active material layer carried on said positive electrode current collector, a negative electrode including a negative electrode current collector and a negative electrode active material layer carried on said negative electrode current collector, and a separator disposed between said positive electrode and said negative electrode are wound, said method comprising the steps of:

• (a) producing a positive electrode in which an exposed portion is provided on said positive electrode current collector at at least one of an initial winding end and a final winding end of said positive electrode;
• (b) producing a negative electrode in which an exposed portion is provided on said negative electrode current collector at at least one of an initial winding end and a final winding end of said negative electrode;
• (c) mixing a filler, a binder and a dispersion medium to prepare a paste for forming a heat-resistant layer;
• (d) applying said paste onto at least a part of said exposed portion of said negative electrode current collector, and at least a part of a surface of said negative electrode active material layer that includes said end of said negative electrode active material layer, followed by drying, thereby forming a heat-resistant layer;
• (e) attaching an insulating tape onto a part of said exposed portion of said positive electrode current collector that is opposite to said end of said negative electrode active material layer;
• and
• (f) winding said positive electrode including said insulating tape attached thereon, and said negative electrode including said heat-resistant layer formed thereon, with a separator interposed between said positive electrode and said negative electrode to obtain an electrode group.