Concerns over scarcity, high prices and safety regarding the long-term use of lithium-ion batteries has prompted a team of researchers from Rensselaer Polytechnic Institute to propose a greener, more efficient and less expensive energy storage alternative.
In a paper in the Proceedings of the National Academy of Sciences, corresponding author Nikhil Koratkar, a professor of engineering at Rensselaer, and his team suggest that calcium ions could be used as an alternative to lithium ions in batteries because of calcium’s abundance and low cost.
“The vast majority of rechargeable battery products are based on lithium-ion technology, which is the gold standard in terms of performance,” said Koratkar. “However, the Achilles’ heel for lithium-ion technology is cost. Lithium is a limited resource on the planet, and its price has increased drastically in recent years. We are working on an inexpensive, abundant, safe and sustainable battery chemistry that uses calcium ions in an aqueous, water-based electrolyte.”
The problem with this approach, however, is that the larger size and higher charge density of calcium ions relative to lithium ions can impair their diffusion kinetics and cyclic stability. Koratkar and his team have now come up with a solution to this problem, in the form of oxide structures containing big open spaces (heptagonal and hexagonal channels). In this latest study, they demonstrated an aqueous calcium-ion battery containing orthorhombic and trigonal polymorphs of molybdenum vanadium oxide (MoVO) as a host for calcium ions.
“The calcium ion is divalent, and hence one ion insertion will deliver two electrons per ion during battery operation,” explained Koratkar. “This allows for a highly efficient battery with reduced mass and volume of calcium ions. However, the higher ionic charge and the larger size of calcium ions relative to lithium makes it very challenging to insert calcium ions into the battery electrodes. We overcome this problem by developing a special class of materials called molybdenum vanadium oxides that contain large hexagonal- and heptagonal-shaped channels or tunnels that run through the material.”
The team demonstrated that calcium ions can be rapidly inserted into and extracted from this material, with the tunnels acting as ‘conduits’ for reversible and fast ion transport. Their findings indicate that MoVO provides one of the best performances reported to date for the storage of calcium ions.
“Calcium-ion batteries might one day, in the not-so-distant future, replace lithium-ion technology as the battery chemistry of choice that powers our society,” said Koratkar. “This work can lead to a new class of high-performing calcium-based batteries that use Earth-abundant and safe materials, and are therefore affordable and sustainable. Such batteries could find widespread use in portable and consumer electronics, electric vehicles, as well as grid and renewable energy storage.”
This story is adapted from material from Rensselaer Polytechnic Institute, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.