Poly (vinylidene fluoride-co-hexafluoropropylene) P(VDF-co-HFP) is an excellent material for polymer electrolytes of lithium ion battery. To enhance the lithium ion transference number, some metal oxides were often embedded into P(VDF-co-HFP). The promising mechanism for the increase in lithium ionic conductivity was Lewis acid-base theory. In this experiment, the Lewis acid-base properties of P(VDF-co-HFP) were measured by inverse gas chromatography (IGC). The Lewis acid constant K-a of P(VDF-co-HFP) is 0.254, and the base constant K-b is 1.199. Compared with other polymers characterized by IGC, P(VDF-co-HFP) is the strongest Lewis basic polymers. Except aluminum ion, lithium ion is the strongest Lewis acidic ion according to their n value of Lewis acids. Therefore, a strong Lewis acid-base interaction will exist between lithium ion and P(VDF-co-HFP). This will restrict the transference of lithium ion in P(VDF-co-HFP). To enhance the lithium ion transference by blending other metal ions into P(VDF-co-HFP), it is suggested that the preferential ions should be Al3+, Mg2+, Na+, and Ca2+ because these metal ions have relative large n values. (c) 2007 Wiley Periodicals, Inc.