Following the steady stream of wearable power research brings up on a fairly regular basis new developments in this field. The latest, highly interesting wearable power concept is based on the piezoelectric effect and the mechanical energy generated by walking.
But there is a unique twist in this particular power-walk research carried out by researcher Xinyu Xue, Sihong Wang, Wenxi Guo, Yan Zhang, and Zhong Lin Wang at the Georgia Institute of Technology in Atlanta.
The technological twist is the conversion of mechanical energy directly into chemical energy, omitting the usual step of converting mechanical energy such as wind, coal, or solar into electrical energy and use the electrical energy to store it as chemical energy in a battery.
It is essentially a self-charging battery cell what the researcher have created by replacing the polyethylene separator that normally separates the two electrodes in a battery with their PVDF film.
PVDF film is a piezoelectric material that generates a charge when pressure is applied. When this PVDF film is placed between the two electrodes in a battery, positive Li ions migrate from the cathode to the anode. The ion migration charges the battery directly without the need for the additional energy conversion step of conventional energy transfer during the battery charge process.
First experiments with a modified coin-type Li-ion battery demonstrated the potential of energy efficiency. The energy conversion cycle improved by about 20% compared with current energy conversion from mechanical to electrical to chemical.
The first small scale prototype generates only a few mV and micro Amps but tuning the system and scaling it up can lead to a power walk battery of 1.5V, not enough to let us use a shoe to make phone calls but capable to run a range of sensors in future, connected shoes.