Flexible Electrochemical Cell with Fiber-like Geometry and Coaxially Structured Electrodes
The proposed technology is a flexible electrochemical cell with cylindrical, fiber-like geometry. As opposed to the sandwich-like structure of planar cells, the cell has coaxial electrodes with the separator in between such that all components are concentric cylinders.
A flexible electrochemical cell consists of a carbon nanotube yarn as the inner electrode and supportive material. A polymer electrolyte is coated on the yarn followed by the application of an outer carbon nanotube network electrode. Chemical modification of the electrodes is possible to enhance or tailor the electrochemical properties.
The inclusion of these carbon nanotube electrodes enables the integration of an electronic conductor and active material of each electrode in a single component. The features of the flexible electrical devices described herein beneficially enable the device to maintain high volumetric energy and power densities during device deformations. Without being limited to a single theory, a coaxial design of the flexible electrical device permits uniform primary current distribution because of the radial ion transport between electrodes.
The initial prototypes fabricated had diameters - 500 micron and future size reductions are very feasible. Tailoring the materials used in the cell design allows for a number of different applications. Prototype super capacitor fibers and humidity sensing fibers have been developed.
The high aspect ratio fiber geometry also provides a cell design able to undergo flexural deformation with minimal impact on the electrochemical properties, and > 95% of the energy density and > 99% of the power density was retained when wound around an I l cm diameter cylinder.