Harnessing the energy generated from small movements provides a supply of energy, but it can be limited. Researchers from the Massachusetts Institute of Technology (MIT) created a new way of reaping energy from natural human motions such as walking, running and other daily activities that would be enough to power up devices.
The new system uses electrochemical principles. MIT materials science and engineering professor Ju Li and a team of graduate students used sandwiched, bendable sheets of polymer and metal for the research.
Past efforts in harnessing small motion energy used devices based on the triboelectric effect and piezoelectrics. The triboelectric effect is basically friction, which is what happens when a balloon is rubbed on wool clothing. Piezoelectrics uses crystals that can create small amounts of voltage when compressed or bent.
These two systems work well for high-frequency motions such as those that come from machinery vibrations. However, they are limiting for small-scale human motions such as running or walking. Li added that apart from mismatches with the timescales of human activities, the older devices have a high bending rigidity and electrical impedance. They can also be expensive to produce.
The newly developed system is flexible and simple. By using an electrochemical process similar to that of lithium-ion batteries, the new system is definitely more inexpensive to produce even at a large scale. The new system's high flexibility transforms it into a wearable technology with less chances of breakage due to mechanical stress.
The new system has two thin layers of lithium alloys which act as electrodes. Between the two lithium alloy layers is a sheet of porous polymer saturated with liquid electrolyte. The porous polymer sheet is an efficient transporter of lithium ions from one metal plate to another.
A standard rechargeable battery absorbs, stores and releases electricity while the new system absorbs mechanical energy and then releases electricity. When bent, the sandwiched layers create pressure that compresses the lithium ions through the polymer. Along with an electrical current between the two electrodes, a counteracting voltage is created that can power devices.
The system also requires very little bending to create a voltage, and it can be attached to a leg or an arm while doing daily activities. The device's output comes as an alternating current, with the flow moving first in one way and then toward the other direction as the device bends and unbends.
Li said the system "is not limited by the second law of thermodynamics ... so in principle, it could be 100 percent [efficient]."
After 1,500 cycle bends, the test devices showed consistent performance ratings. The technology is currently in its early stage of development but the researchers envision a wide range of use across major industries.
The technology can also be manufactured in various sizes and could be transformed into a wearable technology that can power devices as people go for a walk.
The research was published in Nature Communications on Jan. 6.
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