The new method is based on electrochemical principles, which can harvest energy from a broader range of natural motions.
It is also based on the slight bending of a sandwich of metal and polymer sheets.
Previous devices have been based on the triboelectric effect or piezoelectrics and work well for high-frequency sources of motion such as those that are produced by machinery vibrations.
These systems have limits for typical human-scale motions such as walking or exercising.
MIT Nuclear Science and Engineering and professor of materials science and engineering Battelle Energy Alliance Professor Li said: "When you put in an impulse" to such traditional materials, "they respond very well, in microseconds. But this doesn’t match the timescale of most human activities.
"Also, these devices have high electrical impedance and bending rigidity and can be quite expensive."
The new flexible device uses technology similar to that in lithium ion batteries and can produce inexpensively at large scale. It is also compatible with wearable technology.
The system is electrochemical and uses two thin sheets of lithium alloys as electrodes that are separated by a layer of porous polymer soaked with liquid electrolyte.
Output from the new system, which needs only a small amount of bending to produce a voltage, comes in the form of alternating current (AC).
"This device converts mechanical to electrical energy; therefore, "it is not limited by the second law of thermodynamics," Li added.
The researchers suggest that the system can also be used as an actuator with biomedical applications, or used for embedded stress sensors in settings such as roads, bridges, keyboards, or other structures.
Image: The new device uses technology similar to that in lithium ion batteries. Photo: courtesy of the researchers/MIT
