The invention provides a coating or film adapted to be arranged between a separator and at least one electrode of a rechargeable battery. The coating or film comprises a porous layer comprising a layer material having at least a first material and a second material, the first and the second materials being arranged to comprise a plurality of pores for passage of ions therethrough; and the second material is adapted to reduce in size upon drying such that porosity of the porous layer is improved or enhanced at a normal operating temperature; wherein, in response to temperature change, the layer material is adapted to undergo a first phase change during which the pores of said porous layer are adapted to substantially close to thereby substantially reduce or prevent further passage of ions.