The power of light for internet of underwater things
by King Abdullah University of Science and Technology
Rational design of the multi-functional electrolyte solvent. The important functions of high-voltage tolerance (oxidation stability and SEI formation) and non-flammability are allocated to each part of the molecular structure. Credit: Zheng et al.
In light of the ongoing shift toward renewable energy technologies and the growing number of Internet of Things (IoT) devices, researchers worldwide have been trying to develop batteries that can operate more efficiently and for longer periods of time. Lithium-ion batteries (LIBs) are currently the preferred energy-storage technology for portable electronics, as they contain organic electrolytes, which typically enable high operating voltages and energy densities.
Despite their widespread use, further increasing the performance of existing LIBs could have a significant impact on their safety. In fact, these batteries contain highly volatile and flammable organic carbonates, which, if ignited, can cause considerable damage.
In recent years, researchers have made significant efforts toward overcoming these safety issues, for instance, by using additional substances or by optimizing the materials separating battery components. While some of these strategies successfully reduced the risk of the battery catching fire, as long as LIBs are made with highly flammable electrolytes, accidents may still occur.
In hope of paving the way for safer and better-performing LIBs, researchers at the University of Tokyo have recently designed and synthesized an alternative cyclic phosphate-based electrolyte that is non-flammable. Their electrolyte, presented in a paper published in Nature Energy, enables safe, highly stable operation and high voltage, outperforming solvents contained in most existing LIBs.
"The electrolyte solvent for lithium-ion batteries (LIBs) has been unchanged for nearly 30 years," Prof. Atsuo Yamada, one of the researchers who developed the new electrolyte, told TechXplore. "We thus think that there should be large room for developing advanced LIBs, if we find an alternative solvent. With this in mind, under the guidance of Prof. Makoto Gonokami, president of the University of Tokyo, we set out a collaboration with Prof. Eiichi Nakamura, who is a highly established researcher in the field of organic synthesis, to design a new electrolyte solvent with the goal of increasing battery performance and safety."
Yamada, Nakamura and their colleagues designed their cyclic phosphate-based electrolyte by fusing the chemical structures of the conventional electrolyte solvent EC and a fire retardant. This gives the phosphate properties of both molecules, including the high-voltage tolerance of the solvent and the non-flammability of the fire retardant, minimizing the risk of LIBs catching fire.
When synthesizing the electrolyte, the researchers found that the most effective formula contained 0.95 M LiN (SO2F)2 in TFEP/2,2,2-trifluoroethyl methyl carbonate. This specific composition enabled the synthesis of an electrolyte with remarkable non-flammability and a self-extinguishing time of zero, as well as stable operation of graphite anodes and high-voltage LiNi0.5Mn1.5O4 cathodes.
"Unexpectedly, the new electrolyte solvent can increase the battery voltage from current 3.8 V to 4.6 V and also improve the battery life," Prof. Yamada said. "We were surprised to see that the designed solvent indeed showed both high-voltage tolerance and fire-retarding ability, as we expected from its chemical structure. Importantly, this is the first case that such a rational design of chemical structures succeeded in battery electrolytes."
Yamada, Nakamura, and their colleagues are among the first to identify an alternative electrolyte solvent that could increase the safety of LIBs while also enhancing their performance. In the future, their cyclic phosphate-based electrolyte could be used to create safe and highly efficient batteries for a wide range of electronic devices.
"We hope that our work will stimulate many researchers to design and develop a variety of new materials for better batteries," Prof. Yamada said. "We now plan to continue working on this new electrolyte solvent for commercial battery applications and develop new multifunctional battery materials based on our design strategy."
A 1.5-meter-long experimental setup was used to test the effectiveness of a submerged temperature sensor to charge and transmit instructions to a solar panel. Credit: 2020 Filho et al.
A system that can concurrently transmit light and energy to underwater energy devices is under development at KAUST. Self-powered internet of underwater things (IoUT) that harvest energy and decode information transferred by light beams can enhance sensing and communication in the seas and oceans. KAUST researchers are now solving some of the many challenges to this technology being employed in such harsh and dynamic environments.
"Underwater acoustic and radio wave communications are already in use, but both have huge drawbacks. Acoustic communication can be used over large distances but lacks stealth (making it detectable by a third party) and can only access a small bandwidth," explains master's student Jose Filho. "Furthermore, radio waves lose their energy in seawater, which limits their use in shallow depths. They also require bulky equipment and lots of energy to run," he explains.
"Underwater optical communication provides an enormous bandwidth and is useful for reliably transmitting information over several meters," says co-first author Abderrahmen Trichili. "KAUST has conducted some of the first tests of high-bit-rate underwater communication, setting records on the distance and capacity of underwater transmission in 2015."
Led by Khaled Salama, Filho, Trichili and team are investigating the use of simultaneous lightwave information and power transfer (SLIPT) configurations for transmitting energy and data to underwater electronic devices.
"SLIPT can help charge devices in inaccessible locations where continuous powering is costly or not possible," explains Filho.
Self-powered internet of underwater things devices in an underwater environment using lasers to communicate and get powered by an unmanned aerial vehicle, a stationary buoy, a boat and a remotely operated underwater vehicle. Credit: © 2020 Jose Filho
In one experiment, the KAUST team was able to charge and transmit instructions across a 1.5-meter-long water tank to a solar panel on a submerged temperature sensor. The sensor recorded temperature data and saved it on a memory card, later transmitting it to a receiver when information in the light beam instructed it to do so.
In another experiment, the battery of a camera submerged at the bottom of a tank supplied with Red Sea water was charged via its solar panel within an hour and a half by a partially submerged, externally powered laser source. The fully charged camera was able to stream one-minute-long videos back to the laser transmitter.
"These demonstrations were the first stand-alone devices to harvest energy, decode information and perform a particular function—in this case temperature sensing and video streaming," says Salama.
The KAUST team is now working on the deployment of underwater SLIP configurations. They are finding ways to overcome the effects of turbulence on underwater reception and looking into the use of ultraviolet light for transmissions that face underwater obstructions. They are also developing smart underwater optical positioning algorithms that could help locate relay devices set up to extend the communication ranges of IoUT devices.
Their and others' research in the field could ultimately lead to the deployment of self-powered underwater sensors for tracking climate change effects on coral reefs, detecting seismic activity and monitoring oil pipelines. It could also lead to the development of small autonomous robots for more accurate and extensive underwater search and rescue operations.