TORONTO – The onus of improving power efficiency in smartphones has often been placed on other components such as the memory or flash storage, but within the next decade they may have self-charging batteries, thanks to researchers at a Canadian university.
In collaboration with provincial power utility Hydro-Québec's research institute, IREQ, Montreal's McGill University may eliminate the frustrating experience of being without use of a phone after forgetting to recharge it. In an interview with EE Times, professor George Demopoulos, the university's chair of mining and materials engineering, said that while lithium-ion batteries have enabled the proliferation of all kinds of mobile devices, they still require frequent recharging because of their limited energy density.
This limitation has led to the development of portable solar chargers, but these hybrid devices are difficult to miniaturize due to their complex circuitry and packaging issues, he said. Scientists at McGill have hit a first milestone in developing single device capable of harvesting and storing energy using light, he added.
Schematic representation of the FTO/LFP NPs/DYE electrode.
Demopoulos has been collaborating with Hydro Quebec since 2010 on lithium batteries and solar cell fabrication. In 2014, he took a sabbatical from the university to spend time at the utility's research facility where, together with post doc researcher Andrea Paolella, he experimented with the idea that light, as done in dye-sensitized solar cells, could be harnessed to create a self-charging battery. Demopoulos has been working with dye-sensitized solar cells since 2007, which is what brought him to working with batteries.
in the early stages, the research focused on a single photoelectrode -- a half cell to set up with a lamp as a demonstration to see if the cell could absorb light and store electricity. “We had these two devices in front of us, can it become one? After a few weeks of illumination of the photoelectrode, we started see to current," said Demopoulos, who credits the patience of Paolella, as nothing happened for the first two weeks.
The research team is already working on phase two of this project, thanks to a grant from the Natural Sciences and Engineering Research Council of Canada (NSERC). The process of how a dye-synthesized solar cell technology was combined with lithium-ion materials to investigate light-assisted battery charging has been thoroughly described by the researchers in the April 2017 issue of Nature Communications.
Essentially, lithium iron phosphate acts effectively as a reversible redox agent for the regeneration of the dye, and the researchers' findings outline possibilities in advancing the design principles for photo-rechargeable lithium ion batteries.
The first phase of the experiment didn't have an actual device, and was conducted in a dry room without humidity. In addition, the various physical components were never packaged together in a single container. “Oxygen in the experiment played a key role, not just light," said Demopoulos. “In a battery we can't have oxygen, so the next phase is to see about replacing oxygen, then go further and package it."
The research is expected to be a five- to 10-year project, he said. “We will need to redesign a mobile device for light absorption." The screen could be light absorbing, for example.
Open circuit voltage (OCV) under Neon light exposure (red line): the voltage after a plateau at 3.40 V increased to 3.75 V and in the dark using a black box (blue line), the voltage, as expected, slightly decreases from 3.44 to 3.41 V in 500 h. The inset shows the change in OCV upon illumination with a solar simulator (green line).
Dr. Karim Zaghib, IREQ's director of energy storage and conservation, said now that an electrode that absorbs light has been designed, the NSERC grant will give them the opportunity to bridge the gap and demonstrate that a light-chargeable battery is possible. The utility's work with lithium batteries goes back 50 years; he personally has been there for 22 years. Coming up with new ways of charging batteries is a key challenge that Zaghib and other researchers are focused on solving. "We need a fast charge and we need to find another source," he said.
Having one device that can both harvest energy and store it has been a recurring theme, he said. Size of the battery is not the issue because the researchers are using ion phosphate batteries rather than lithium. “The issue is not energy density, we have the solution for that," said Zaghib. “The issue here is how to make charging fast." Another challenge is to get enough cycles in the battery; the target over the next five years is to get 500 cycles.
A self-charging battery could also have applications in the home, getting charged during the day by light and used at night, he said, as the trend over the next 10 years is that smart homes will be increasingly solar-powered. And while the current research is around small-scale batteries, Zaghib said there is potential for larger, 10 -20 kilowatt hour batteries in energy storage applications. "Today if you need to have sources for your home, you need to have the solar cells on your roof and the batteries are in your basement or garage," he said.
The self-charging battery concept would mean that the solar power system in a home would only be on a roof, he said, and the concept could even be put into cars, but it requires more thinking, said Zaghib, as car batteries are usually in chassis. “We are thinking about some new designs," Zaghib said.
—Gary Hilson is a general contributing editor with a focus on memory and flash technologies for EE Times.