Mechanical energy harvesters are important for powering wearable devices and microelectronics. Most mechanical energy harvesters supply high voltages (10^0^-10^2^ V), low currents (10^-4^-10^-2^ mA/cm^2^), and operate at high frequencies (\~20-100 Hz). The high voltage and low current outputs, however, do not interface well with most microelectronics (which use low voltage and high current) and the high operation frequency does not match the low frequency of most mechanical energy sources in daily life. Here, we report the first mechanical energy harvester that uses the piezoelectrochemical effect in a lithium-ion battery cathode material to deliver ultra-high current from low-frequency mechanical energy input. Our energy harvester consists of a pair of lithium cobalt oxide (LCO) electrodes with identical composition and different thicknesses. When an external load is applied to the device, the corresponding stress is concentrated on the thick electrode. As the thick electrode volume changes, the free energy of LCO bonds is modified and results in a shift in the electrochemical voltage. When the unloaded LCO is electrically connected to the loaded LCO, the potential difference drives a current through an external circuit while lithium ion migration between electrodes modifies the LCO composition until there is 0 V between the electrodes. When the pressure is removed, an opposite potential difference is generated between electrodes. The device can be cycled between low displacements (\<100 μm) loads at a wide range of frequencies (10^-4^-10^-1^ Hz) to convert mechanical energy in into ultra-high currents (0.87 mA/cm^2^) and low voltage (\~10 mV) power.

Molten salt electrodeposition allowed the synthesis of up to 95% dense and 100 μm thick monolithic LCO electrodes with no additives, which improved the performance over slurry cast electrodes with binders found in battery electrodes. By reducing mechanical loses that occur in the polymer binders, the high density and single component electrodes enabled the high voltage output which was close to the theoretical value. Furthermore, the laser-based fabrication process enabled small electrode gaps which contribute to low internal resistance and high output current. The design can be scaled to form array of harvesters connected in series or parallel to generate higher current or voltage to meet the demands of different applications. The usage of aqueous electrolyte in our energy harvester not only can effectively decrease the potential toxic and combustion hazardous but also avoid the high requirements for the device packaging. Our work demonstrates an energy harvester with high current capabilities that will create new opportunities for wearables and microelectronics with increased functionality.


Ultra-High Current Mechanical Energy Harvester Based on Lithium Cobalt Oxide

Division / Sponsors: 
Aerospace Division

Paper Proceedings: https://asmedigitalcollection.asme.org/SMASIS/SMASIS2020/volume/84027

SMASIS2020 - Virtual Conference

Supporting the need among researchers worldwide for additional online and multimedia content, ASME now offers the ASME Conference Video Collection. This platform will collect and provide long-term access to conference presentation videos, encompassing all technology areas within ASME's technical conference and events program. About 30,000-40,000 engineers across all mechanical engineering and related disciplines participate in ASME conferences each year. This includes authors of approximately 6,000 to 8,000 technical papers published by ASME, the majority of whom also submit video presentations for our virtual conferences. The video collection will be available as an add-on to existing product packages or as a separate subscription.