Dimensionally-stable microporous webs
Multi-layer structures are disclosed herein containing a microporous polymer web having two major surfaces and an inorganic material including nano- and micro-particles formed as a first porous layer on one or both of the major surfaces of the microporous polymer web. The first porous layer provides high-temperature dimensional stability and preserved multi-layer structure above the melting point of the microporous polymer web even as fluid permeability of the unitary multi-layer structure is decreased at elevated temperature. The first porous layer has improved peel strength as compared to an equivalent layer devoid of nanoparticles.
1 . A battery separator comprising:
a free-standing unitary multi-layer structure comprising a microporous polymer web characterized by a melting point and having two major surfaces and an inorganic material including nano-particles and micro-particles formed as a first porous layer on both of the major surfaces of the microporous polymer web, the nano-particles exhibiting a mean size less than or equal to 100 nm and the micro-particles exhibiting a mean size greater than 100 nm, the nano-particles forming 10% to 90% by weight of the inorganic material, the first porous layer comprising an organic hydrogen bonding component comprising one or more polyacrylic polymers, the inorganic material including sufficient nano-particles such that the first porous layer exhibits an average peel strength of at least 47 N/m, the first porous layer providing high-temperature dimensional stability and preserved multi-layer structure above the melting point of the microporous polymer web even as fluid permeability of the unitary multi-layer structure is decreased at elevated temperature.
2 . The battery separator of claim 1 , in which the inorganic material comprises an inorganic oxide, carbonate, hydroxide, or mixtures thereof.
3 . The battery separator of claim 2 , in which the inorganic material comprises alumina, silica, zirconia, titania, mica, boehmite, magnesium hydroxide, calcium carbonate, or mixtures thereof.
4 . The battery separator of claim 1 , wherein the first porous layer exhibits an average peel strength of 47 N/m to 200 N/m.
5 . The battery separator of claim 1 , in which the inorganic material exhibits a thermogravimetric weight loss of 1120 ppm to 2010 ppm over a 60° C. to 120° C. differential.
6 . The battery separator of claim 1 , in which the structure further comprises a second porous layer comprising a gel-forming polymer material with passageways.
7 . The battery separator of claim 6 , in which the gel-forming polymer material comprises polyvinylidene fluoride, poly(vinylidene fluoride-hexafluoropropylene) copolymers, poly(vinylidene fluoride-acrylic acid) copolymers, polyvinylpyrrolidone, polyacrylamide, or mixtures thereof.
8 . The battery separator of claim 1 , in which the microporous polymer web comprises a polyolefin.
9 . The battery separator of claim 8 , in which the polyolefin comprises polyethylene, polypropylene, or mixtures thereof.
10 . The battery separator of claim 9 , in which the polyolefin comprises ultrahigh molecular weight polyethylene (UHMWPE).
11 . The battery separator of claim 1 , in which the first porous layer has a median pore size of 15 nm to 100 nm.
12 . The battery separator of claim 1 , in which the micro-particles of the first porous layer comprises platelet-like particles.
13 . The battery separator of claim 1 , in which the first porous layer comprises less than 10% by weight of the organic hydrogen bonding component.
14 . The battery separator of claim 13 , in which the first porous layer comprises less than 10% by weight of the one or more polyacrylic polymers.
15 . The battery separator of claim 1 , in which the first porous layer exhibits an average peel strength of 47 N/m to 84 N/m.
16 . The battery separator of claim 1 , wherein the first porous layer consists essentially only of the nano-particles, the micro-particles, and a hydrogen bonding component forming 1% to 6%, by weight, of the first porous layer.