Microporous fibrous polymer electrolytes were prepared by immersing electrospun poly͑acrylonitrile͒ ͑PAN͒-based fibrous membranes into lithium salt-based electrolytes. They showed high ionic conductivities of up to 1.0 ϫ 10 −3 S/cm at 20°C, and sufficient electrochemical stabilities of up to 4.5 V. Their ion conduction depended on the physicochemical properties of the lithium salt-based electrolytes trapped in pores, as well as on the interactions among the Li + ion, the carbonate, and the PAN. From the Fourier transform-Raman data, lithium ion transport was mainly achieved by the lithium salt-based electrolytes in pores via the interaction between the Li + ion and the C=O group of carbonate molecules, and was also affected by the PAN through the interaction between the Li + ion and the CϵN groups of PAN. Their electrochemical stabilities were enhanced by the swelling of the electrospun PAN nanofibers because of the dipolar interaction between the CϵN groups of PAN and the C=O groups of carbonate in the lithium salt-based electrolytes. Prototype cells using electrospun PAN-based fibrous polymer electrolytes thus showed different cyclic performances, according to the composition of the lithium salt-based electrolytes. The prototype cell with 1 M LiPF 6-ethylene carbonate/dimethyl carbonate ͑1/1͒ showed the highest discharge capacity and the most stable cyclic performance among them.

Microporous fibrous membranes were prepared from poly(vinylidenefluoride-co-hexafluoropropylene) P(VdF-HFP) solutions in an acetone/N,N-dimethylacetamide mixture using the electrospinning method. Varying the P(VdF-HFP) polymer concentration in electrospinning can easily control the pore size and the porosity of the electrospun fibrous membranes (ES-FMs). The usefulness of the ES-FMs as a matrix of polymer electrolyte for a lithium-ion polymer battery with high performance was evaluated. Electrospun fibrous polymer electrolyte membranes (ES-FPEMs) showed excellent electrochemical properties of ionic conductivity, higher than 1×10−3 S/cm at room temperature, and the electrochemical stability window, up to 4.5 V vs. Li+/normalLi. At a C/2 rate, the prototype cell using the ES-FPEM showed a good charge/discharge property, with little capacity fade under constant current and constant voltage conditions at 20 and 60°C. © 2004 The Electrochemical Society. All rights reserved.