Composite battery separator film and method of making same
A microporous separator film for electrochemical cells and a method of making such films is disclosed. The microporous separator film includes an intimate mixture of an electrically insulating matrix phase and a self-switching voltage activated conductive phase, wherein the voltage activated conductive phase provides a plurality of conductive paths from a first face of the microporous separator film to a second face of the microporous separator film. The method for making the composite microporous separator film includes the steps of forming an intimate mixture of at least an insulating matrix phase and a self-switching voltage activated phase, forming a film from the mixture, and generating pores within the film.
1. A microporous separator film for electrochemical cells comprising:
an intimate mixture of an electrically insulating matrix phase and a self-switching voltage activated conductive phase, wherein the intimate mixture comprises a melt or solution to effectively contain the self switching voltage activated conductive phase within the insulating matrix phase and the insulating matrix phase and the self-switching voltage activated conductive phase to form a mixture of discrete, isolated phase regions which are formed by phase separated mixtures, and wherein the microporous separator film is unobstructed to promote ionic conductivity in the electrochemical cells; and
wherein the voltage activated conductive phase provides a plurality of conductive paths from a first face of the microporous separator film to a second face of the microporous separator film; and wherein the microporous separator film has a porosity that is physically separate from the voltage activated conductive phase.
2. The microporous separator film of claim 1 , wherein the electrically insulating matrix phase is selected from the group consisting of polyolefins, polysulfones, polyvinylchloride, polyvinylfluoride, polytetrafluoroethylene polypropylene copolymer, polyamide, cellulose and polycarbonate or combinations thereof; and wherein porosity is formed after the voltage activated conductive phase and non-conductive components are intimately mixed such that the voltage activated conductive phase is separate from the porosity of the microporous separator film.
3. The microporous separator film of claim 1 , wherein the electrically insulating matrix phase comprises polyethylene.
4. The microporous separator film of claim 1 , wherein the electrically insulating matrix phase comprises polypropylene.
5. The microporous separator film of claim 1 , wherein the electrically insulating matrix phase comprises a combination of polyethylene and polypropylene.
6. The microporous separator film of claim 1 , wherein the self-switching voltage activated conductive phase is selected from the group consisting of polythiophene, polypyrrole, polyfluorene, polybenzene, Silicon, GaAs, and their derivatives.
7. The microporous separator film of claim 1 , wherein the self-switching voltage activated conductive phase is a voltage activated conductive polymer.
8. The microporous separator film of claim 7 , wherein the intimate mixture comprises between 0.01 and 50 weight percentage voltage activated conductive polymer.
9. The microporous separator film of claim 1 , wherein the self-switching voltage activated conductive phase is an essentially insoluble crosslinked voltage activated conductive polymer.
10. The microporous separator film of claim 1 , wherein the self-switching voltage activated conductive phase comprises a rod shaped morphology in which the average diameter of a particle of the self-switching voltage activated conductive phase is less than one half the average length.