double bonds are created in cellulose wherein u2014 ch 2 oh groups of cellulose are subjected to dehydration creating c u2550 c bonds for example the creation of c u2550 c bonds in cellulose can be confirmed by ir spectrum for example wherein carbon carbon double bond introduced cellulose shows a peak spectrum at about 1522 cm u2212 1 which indicates stretching vibration of c u2550 c and a peak spectrum at about 1423 cm u2212 1 which indicates bending vibration of c u2014 c u2014 c in some embodiments carbon carbon double bond introduced cellulose shows a peak spectrum at 1522 cm u2212 1 whose absorbance is as intense as about a half of the absorbance of the peak spectrum at 1423 cm u2212 1 the separator for the lithium ion capacitor proposed by the present invention contains cellulose that has been given a treatment to create carbon carbon double bonds the treatment method to create carbon carbon double bonds in cellulose is not specifically limited and any method can be used as long as it can create carbon carbon double bonds in cellulose treatment methods to create carbon carbon double bonds in cellulose include for example alkali treatment involving soaking and heat treating of cellulose in alkali solution and heat treatment alkali treatment of cellulose is performed by for example soaking in a 1 0 m aqueous sodium hydroxide solution a known structure constituted by a known material that.