To provide a separator for constituting a lithium secondary battery having high reliability, and to provide a porous membrane for constituting the separator, and a lithium secondary battery having the separator.

The porous membrane is composed of at least insulating fine particles stable to an organic electrolyte and a binder, and a binder (A) having at least a tensile strength of 10 MPa or more and a modulus of elasticity in tension of 100 MPa or more, or a binder (B) having a breaking elongation of 300% or more is used as the binder. The separator for the battery has the porous membrane, and the lithium secondary battery has the separator for the battery.

COPYRIGHT: (C)2008,JPO&INPIT