"This is a proof of concept, but the idea of using water or other solvents to 'tune' the transport of ions in a layered material is very exciting," says assistant professor Veronica Augustyn.
"The idea is that this could allow an increased amount of energy to be stored per unit of volume, faster diffusion of ions through the material, and faster charge transfer.
"This line of investigation could ultimately lead to things like thinner batteries, faster storage for renewable-based power grids, or faster acceleration in electric vehicles.”
For this work, the researchers compared two materials: a crystalline tungsten oxide (WO3) and a layered, crystalline tungsten oxide hydrate (WO3∙2H2O) – which consists of crystalline tungsten oxide layers separated by atomically thin layers of water.
When charging the two materials for 10min, the researchers found that the WO3 stored more energy than the hydrate. But when the charging period was only 12s, the hydrate stored more energy than the regular material.
The researchers also claim the hydrate stored energy more efficiently – wasting less energy as heat. Pseudocapacitance in WO3∙2H2O allows for high mass loading electrodes of more than 3mg/cm2 and high areal capacitances of more than 0.25F/cm2 at 200mV/s with simple slurry-cast electrodes.
"The goal for many energy-storage researchers is to create technologies that have the high energy density of batteries and the high power of capacitors," says PhD student James Mitchell. "Pseudocapacitors may allow us to develop technologies that bridge that gap."
