Antioxidant-coated lead acid battery separators having improved electrical and mechanical properties

Abstract

An oxidation resistant, microporous polyolefin web exhibiting high-strength mechanical and low electrical resistance properties is a solid matrix that includes an ultrahigh molecular weight polyolefin component and a friable precipitated silica component. The ultrahigh molecular weight polyolefin component provides high-strength mechanical properties to the web. The friable precipitated silica component is broken down into predominately discrete silica aggregates dispersed throughout the microporous web to maintain a low electrical resistance in the presence of an electrolyte. In an alternative preferred embodiment, a polyethylene web includes an antioxidant coating that is applied to the separator web following extraction of the majority of the process oils and drying of the extraction fluid from the separator pores. The resultant “sheath” of antioxidant protects the mechanical integrity of the polyethylene separator by suppressing polyethylene degradation.

1 . A battery separator, comprising: 
 a polymer web having first and second major surfaces and including an ultrahigh molecular weight polyolefin of a molecular weight that provides sufficient molecular chain entanglement to impart high-strength mechanical properties to the polymer web and a silica component that facilitates separator wettability; and    an antioxidant material present on at least one of the first and second major web surfaces to suppress polyolefin degradation.    
     
     
         2 . The battery separator of  claim 1 , in which the antioxidant material includes (tetrakis[methylene(3,5-di-tert-butyl-4-hydroxyhydrocinnamate] methane).  
     
     
         3 . The battery separator of  claim 1 , in which the antioxidant material is present on both of the first and second major web surfaces.  
     
     
         4 . The battery separator of  claim 1 , in which the polymer web includes an interior portion between the first and second major surfaces, and in which a portion of the antioxidant material is present in the interior portion.  
     
     
         5 . The battery separator of  claim 1 , in which the antioxidant material present on the first major surface of the polymer web is applied by a method selected from the group consisting essentially of brushing, spraying, immersion, and roller-based application.  
     
     
         6 . The battery separator of  claim 1 , in which the first major surface of the polymer web is positioned adjacent an electrode structure to form a battery assembly into which is placed an electrolyte that is at least partly absorbed by the electrode structure.