Portable Power - Rechargeable Batteries

The main issues with current rechargeable batteries are: lack of power output, rate at which batteries can be recharged and discharged, loss of charge over time (even when not in use), and lifespan (number of times a battery can be recharged). Nanotechnology can offer solutions to each of these. For example, the latest line of Sony camcorder batteries uses nanotechnology to increase lifespan and also decrease charge-time.

The most efficient rechargeable batteries use lithium. The total energy that a battery can hold is proportional to the amount of lithium that it contains. Lithium, in the form of positively charged ions, migrates between the two electrodes, moving to the anode (negative electrode) during the course of charging a battery, and the cathode (positive electrode) when the battery is in use (i.e. discharging). Higher energy batteries can be achieved by incorporating more lithium, however this puts strain on the electrodes which have to cope with large increases in volume due to the migration of lithium during the charging and discharging cycles (this can lead to fracturing of electrodes). Higher power is achieved by increasing the speed at which the lithium ions can migrate between electrodes.

The use of nanomaterials has allowed both high energy and high power batteries to be achieved. Nanocomposites of lithium and electrode materials keep the bulk lithium in small particles which are easily broken up during the discharge process, and the porosity of the electrodes let the ions exit and enter much more rapidly. Such nanocomposites also help reduce self-discharge (i.e. loss of power during storage). Advances in electrolytes (that allow the passage of the lithium ions between electrodes) also enhance these effects.

Image source: NEC/TOKIN