Lithiumwaschemicallyintercalated from 1-methoxybutane solutionoflithiumand naphthalene intog raphiteand viceversa ,a nd lithiumi sotope fractionationaccompanyingthosei ntercalation and deintercalationp rocessesw asobserved.6 Liwasalways preferentiallyfractionated intothe graphitep hase. The single-stage lithiumi sotope separationf actoru pon intercalationwasabout 1.023 at25 C, nearlyindependentof the structureofthe lithium-graphiteintercalationcompounds formed. Amuchsmallerseparationfactorwasobserved forthe deintercalationprocess,suggesting the existenceo fl ithiumsites(surfaceareas)o thert hanthe sitesbetween graphene layers of the host graphite. Separationf actordatawereconsistentw iththe followingd ecreasingo rderof the 6 Li-to-7 Lireduced partitionf unctionratio (RPFR):R PFR of 1-methoxybutane solution>RPFR of surfaceareas>RPFR of metallithium>RPFR of graphene interlayersites.