Incorporating ionic liquid electrolytes into polymer gels for solid-state ultracapacitors

Electrolytes are an important component in determining the performance and cycle life of ultracapacitors. Good electrolytes should have high ionic conductivity, large electrochemical windows, and excellent thermal and chemical stability. Ionic liquids are possibly ideal electrolytes to satisfy these requirements. In the present work, we developed easy-to-use methods to incorporate ionic liquids into a polymer matrix to synthesize gel polymer electrolytes (GPEs). Combining the advantages of both the ionic liquids and the conventional GPEs, the resultant solid-state ionic liquid-incorporated gel polymer electrolytes (ILGPEs) possess better properties than these two components considered individually. Our synthesized ILGPE films are flexible and mechanically strong and have a wide electrochemical window of 4 V, a high ionic conductivity up to 3.5 mS/cm (at room temperature), and a high thermal stability up to 350 degrees C. These ILGPEs have been used to fabricate solid-state ultracapacitors that demonstrate improved performance and cycle life. (c) 2008 The Electrochemical Society.