Rechargeable Batteries – Looking Forward

In 2007, assistant professor Yi Cui and colleagues at Stanford University’s Department of Materials Science and Engineering discovered that using silicon nanowires as the anode in rechargeable batteries increases the volumetric charge density of the anode by up to a factor of 10. This is significant because it offers an opportunity to use new types of active components for the batteries.

The active components in a secondary cell are the chemicals that make up the positive and negative active materials, and the electrolyte. The positive and negative are made up of different materials, with the positive exhibiting a reduction potential and the negative having an oxidation potential. The sum of these potentials is the standard cell potential or voltage.

In primary cells the positive and negative electrodes are known as the cathode and anode, respectively. In rechargeable cells the positive electrode is the cathode on discharge and the anode on charge, and vice versa for the negative electrode.

Already, several alternatives to rechargeable batteries exist or are under development. For transportation, uninterruptible power supply systems and laboratories, flywheel energy storage systems store energy in a spinning rotor for reconversion to electric power when needed; such systems may be used to provide large pulses of power that would otherwise be objectionable on a common electrical grid. For uses like portable radios and flashlights, rechargeable batteries may be replaced by clockwork mechanisms or dynamos which are cranked by the user to provide power.

A future development could be ultracapacitors for transportation, using a large capacitor to store energy instead of the rechargeable battery banks used in hybrid vehicles. One drawback to capacitors compared with batteries is that the terminal voltage drops rapidly; a capacitor that has 25% of its initial energy left in it will have one-half of its initial voltage. However, there are potential benefits in cycle efficiency, lifetime, and weight compared with the rechargeable batteries system.