Self-charging battery both generates and stores energy

Self-charging battery both generates and stores energy:

A cross-sectional scanning electron microscope image of the self-charging power cell (left), and the enlarged TiO2 nanotube anode (right). Image credit: Xue, et al. ©2012 American Chemical Society In order to apply a stress to the separator, the researchers attached the coin-sized battery to the bottom of a shoe, and found that walking could generate enough compressive energy to charge the battery. A compressive force with a frequency of 2.3 Hz could increase the voltage of the device from 327 to 395 mV in 4 minutes. This 65 mV increase is significantly higher than the 10 mV increase it took when the power cell was separated into a PVDF piezoelectric generator and Li-ion battery with the conventional polyethylene separator. The improvement shows that achieving a mechanical-to-chemical energy conversion in one step is much more efficient than the mechanical-to-electric and electric-to-chemical two-step process used for charging a traditional battery. Ads by Google 7-Axis Humanoid Robot Arm - Low-cost dexterous robot arms for home, research, and education. - www.robai.com Once the new equilibrium between electrodes is reached, the self-charging process ceases. The cell can begin supplying power after the applied stress is released, since the piezoelectric field disappears and the Li ions can diffuse back from the anode to the cathode to reach a new equilibrium. As in a conventional Li-ion battery, ion diffusion involves electrochemical reduction-oxidation reactions, which here generate a current of about 1 μA that can be used to power a small electronic device. “The Li ions will not flow back immediately after the applied stress is removed because it forms a new compound with the anode material (LiTiO),” Zhong Lin Wang said. “The charges are preserved as in a conventional battery. They are released at a later time when power is required.” Although these voltages and currents are low, the researchers showed that the power cell can also self-charge with higher voltages of around 1.5 V, which could make it useful for a broader range of applications. The researchers predict they can further improve the power cell’s performance by making several modifications, such as by using flexible casing to allow for greater deformation of the piezoelectric material. More information: Xinyu Xue, et al. “Hybridizing Energy Conversion and Storage in a Mechanical-to-Electrochemical Process for Self-Charging Power Cell.” Nano Letters. DOI: 10.1021/nl302879t Journal reference: Nano Letters Copyright 2012 Phys.org All rights reserved. This material may not be published, broadcast, rewritten or redistributed in whole or part without the express written permission of PhysOrg.com.

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