Patent ID: 8027147

Claim:
An ultracapacitor comprising: a negative porous electrode in contact with a negative conducting plate; a positive porous electrode in contact with a positive conducting plate an ultracapacitor separator separating said negative porous electrode from said positive porous electrode; and an electrolytic solution impregnating said positive and negative porous electrodes and said ultracapacitor separator; where said ultracapacitor separator having a change in thickness of less than 8% when heated to a temperature of at least 200° C.; and said ultracapacitor separator including a microporous material comprising: an ultrahigh molecular weight polyethylene (UHMWPE) and a particulate filler distributed throughout said microporous material; where said filler constitutes from about 5 percent to 95 percent by weight of said microporous material; where said microporous material has a network of interconnecting pores communicating throughout said microporous material, said pores constituting at least 25 percent by volume of said microporous material, where said pores create a pore distribution; where said microporous material has no pores greater in size than 1.0 micrometers; and where change in volume divided by log d for the pores of said microporous material is less than 2 cc/g for the entire pore distribution.