025_EETE

EETE SEPTEMBER 2012

Self-charging piezo-power cell converts and frequency of 2.3 Hertz, the researchers increased the voltage stores energy chemically in a single unit in the power cell from 327 to 395 millivolts in just four minutes. The device was then discharged back to its original voltage with Researchers from the Georgia Institute of Technology have a current of one milliamp for about two minutes. The research- developed a self-charging power cell that directly converts me- ers estimated the stored electric capacity of the power cell to chanical energy to chemical energy, storing the power until it is be approximately 0.036 milliamp-hours. So far, Wang and his released as electrical current. By eliminating the need to convert research team – which included Xinyu Xue, Sihong Wang, Wenxi mechanical energy to electrical energy for charging a battery, the Guo and Yan Zhang – have built and tested more than 500 of the new hybrid generator-storage cell uses mechanical energy more power cells. Wang estimates that the generator-storage cell will efficiently than systems using separate generators and batteries. be as much as five times more efficient at converting mechanical he power cell consists of a cathode made from lithium-cobalt energy to chemical energy for as a two-cell generator-storage oxide (LiCoO2) and an anode consisting of titanium dioxide (TiO2) system. nanotubes grown atop a titanium film. We have always known what we wanted to do... Mission-critical, high reliability resistive products. The two electrodes are separated by a they’re our specialty. For over forty years we membrane made from poly(vinylidene have applied painstaking research, rigid quality fluoride) (PVDF) film, which generates a programs, piezoelectric charge when placed under strain. When the power cell is mechani- and hard work cally compressed, the PVDF film gener- to produce the ates a piezoelectric potential that serves world’s most as a charge pump to drive the lithium reliable resistors! ions from the cathode side to the anode side. The energy is then stored in the anode as lithium-titanium oxide. By harnessing a compressive force, such as a shoe heel hitting the pavement from a person walking, the power cell gener- ates enough current to power a small Let us worry calculator. Charging occurs in cycles about quality, with the compression of the power cell creating a piezopotential that drives the reliability migration of lithium ions until a point at which the chemical equilibrium of the two and delivery. electrodes are re-established and the dis- That is what we do. tribution 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 State of the Art, Inc. that oxidizes a small amount of lithium- cobalt oxide at the cathode to Li1-xCoO2 Resistive PRoducts and reduces a small amount of titanium Made dioxide to LixTiO2 at the anode. Com- in the USA. pressing the power cell again repeats the cycle. When an electrical load is con- nected 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 www.electronics-eetimes.com Electronic Engineering Times Europe September 2012 25


EETE SEPTEMBER 2012
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