Electrospun Nanofibers for Energy Storage
Mataz Alcoutlabi, North Carolina State University
Research and development in textiles have gone beyond the conventional applications as clothing and furnishing materials; for example, the convergence of textiles, nanotechnologies, and energy science opens up the opportunity to take on one of the major challenges in the 21st century - energy.
Among the various existing energy storage technologies, rechargeable lithium-ion batteries are considered as effective solution to the increasing need for high-energy density electrochemical power sources.
Rechargeable lithium-ion batteries offer energy densities 2-3 times and power densities 5-6 times higher than conventional Ni-Cd and Ni-MH batteries, and as a result, they weigh less, take less space, and deliver more energy. In addition to high energy and power densities, lithium-ion batteries also have other advantages, such as high coulombic efficiency, low self-discharge, high operating voltage, and no “memory effect”.
Each lithium-ion battery consists of an anode and a cathode separated by an electrolyte containing dissociated lithium salts, which enables transfer of lithium ions between the two electrodes, as illustrated in Figure 1. When the battery is being charged, an external electrical power source injects electrons into the anode.
At the same time, the cathode gives up some of its lithium ions, which move through the
electrolyte to the anode and remain there. During this process, electricity is stored in the battery in the form of chemical energy. When the battery is discharging, the lithium ions move back across the electrolyte to the cathode, enabling the release of electrons to the outer circuit to do the electrical work.
Current lithium-ion batteries were developed mainly for portable applications (such as cell phones and lap-tops) and they depend on using active powder materials (such as graphite powder in the anode and LiCoO2 powder in the cathode) to store energy. However, powder materials have long diffusion path for lithium ions and slow electrode reaction kinetics, and as a result, the performance of current lithium-ion batteries has not reached their potential.
Therefore, new energy-storage materials and electrodes must be developed to obtain advanced lithium-ion batteries that outperform current technologies and can be used in large-scale systems.