By eliminating the need to convert mechanical energy to electrical energy for charging a battery, the new hybrid generator-storage cell utilizes mechanical energy more efficiently than systems using separate generators and batteries.
At the heart of the self-charging power cell is a piezoelectric membrane that drives lithium ions from one side of the cell to the other when the membrane is deformed by mechanical stress. The lithium ions driven through the polarized membrane by the piezoelectric potential are directly stored as chemical energy using an electrochemical process.
By harnessing a compressive force, such as a shoe heel hitting the pavement from a person walking, the power cell generates enough current to power a small calculator. A hybrid power cell the size of a conventional coin battery can power small electronic devices – and could have military applications for soldiers who might one day recharge battery-powered equipment as they walked.
"People are accustomed to considering electrical generation and storage as two separate operations done in two separate units," said Zhong Lin Wang, a Regents professor in the School of Materials Science and Engineering at the Georgia Institute of Technology. "We have put them together in a single hybrid unit to create a self-charging power cell, demonstrating a new technique for charge conversion and storage in one integrated unit."
The research was reported Aug. 9, 2012 in the journal Nano Letters. The research was supported by the Defense Advanced Research Projects Agency (DARPA), the U.S. Air Force, the U.S. Department of Energy, the National Science Foundation, and the Knowledge Innovation Program of the Chinese Academy of Sciences.
The power cell consists of a cathode made from lithium-cobalt oxide (LiCoO2) and an anode consisting of titanium dioxide (TiO2) nanotubes grown atop a titanium film. The two electrodes are separated by a membrane made from poly(vinylidene fluoride) (PVDF) film, which generates a piezoelectric charge when placed under strain. When the power cell is mechanically compressed, the PVDF film generates a piezoelectric potential that serves as a charge pump to drive the lithium ions from the cathode side to the anode side. The energy is then stored in the anode as lithium-titanium oxide.
Charging occurs in cycles with the compression of the power cell creating a piezopotential that drives the migration of lithium ions until a point at which the chemical equilibriums of the two electrodes are re-established and the distribution of lithium ions can balance the piezoelectric fields in the PVDF film. When the force applied to the power cell is released, the piezoelectric field in the PVDF disappears, and the lithium ions are kept at the anode through a chemical process.
The charging cycle is completed through an electrochemical process that oxidizes a small amount of lithium-cobalt oxide at the cathode to Li1-xCoO2 and reduces a small amount of titanium dioxide to LixTiO2 at the anode. Compressing the power cell again repeats the cycle.
When an electrical load is connected between the anode and cathode, electrons flow to the load, and the lithium ions within the cell flow back from the anode side to the cathode side.
Using a mechanical compressive force with a frequency of 2.3 Hertz, the researchers increased the voltage in the power cell from 327 to 395 millivolts in just four minutes. The device was then discharged back to its original voltage with a current of one milliamp for about two minutes. The researchers estimated the stored electric capacity of the power cell to be approximately 0.036 milliamp-hours.
So far, Wang and his research team – which included Xinyu Xue, Sihong Wang, Wenxi Guo and Yan Zhang – have built and tested more than 500 of the power cells. Wang estimates that the generator-storage cell will be as much as five times more efficient at converting mechanical energy to chemical energy for as a two-cell generator-storage system.
Much of the mechanical energy applied to the cells is now consumed in deforming the stainless steel case the researchers are using to house their power cell. Wang believes the power storage could be boosted by using an improved case.
"When we improve the packaging materials, we anticipate improving the overall efficiency," he said. "The amount of energy actually going into the cell is relatively small at this stage because so much of it is consumed by the shell."
Beyond the efficiencies that come from directly converting mechanical energy to chemical energy, the power cell could also reduce weight and space required by separate generators and batteries. The mechanical energy could come from walking, the tires of a vehicle hitting the pavement, or by harnessing ocean waves or mechanical vibrations.
"One day we could have a power package ready to use that takes advantage of this hybrid approach," Wang said. "Almost anything that involves mechanical action could provide the strain needed for charging. People walking could be generating electricity as they move."
This research was supported by DARPA (HR0011-09-C-0142); the U.S. Air Force, the U.S. Department of Energy, Office of Basic Energy Sciences (DE-FG02-07ER46394), the National Science Foundation (CMMI-0403671), and the Knowledge Innovation Program of the Chinese Academy of Sciences (KJCX2-YW-M13). The content is solely the responsibility of the authors and does not necessarily represent the official views of DARPA, the U.S. Air Force, the Department of Energy or the National Science Foundation.
Citation: Xinyu Xue, Sihong Wang, Wenxi Guo, Yan Zhang and Zhong Lin Wang, Hybridizing Energy Conversion and Storage in a Mechanical-to-Electrochemical Process for Self-Charging Power Cell, Nano Letters. DOI: 10.1021/nl302879t
John Toon | EurekAlert!
Further reports about: > battery > Ambient Air > Chinese herbs > DARPA > Energy Science > Gates Foundation > PVDF > Science TV > Self-charging > chemical energy > chemical process > cobalt oxide > electric field > lithium ions > mechanical energy > mechanical vibration > packaging material > titanium dioxide
Organic-inorganic heterostructures with programmable electronic properties
29.03.2017 | Technische Universität Dresden
Researchers use light to remotely control curvature of plastics
23.03.2017 | North Carolina State University
The Institute of Semiconductor Technology and the Institute of Physical and Theoretical Chemistry, both members of the Laboratory for Emerging Nanometrology (LENA), at Technische Universität Braunschweig are partners in a new European research project entitled ChipScope, which aims to develop a completely new and extremely small optical microscope capable of observing the interior of living cells in real time. A consortium of 7 partners from 5 countries will tackle this issue with very ambitious objectives during a four-year research program.
To demonstrate the usefulness of this new scientific tool, at the end of the project the developed chip-sized microscope will be used to observe in real-time...
Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.
The results will be published on March 22 in the journal „Astronomy & Astrophysics“.
Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...
Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.
Ubiquitin is a small protein that can be linked to other cellular proteins, thereby controlling and modulating their functions. The attachment occurs in many...
In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...
20.03.2017 | Event News
14.03.2017 | Event News
07.03.2017 | Event News
29.03.2017 | Materials Sciences
29.03.2017 | Physics and Astronomy
29.03.2017 | Earth Sciences