https://phys.org/news/2018-05-microscopy-advance-reveals-unexpected-role.html

To address this question, researchers from North Carolina State University, the Oak Ridge National Laboratory (ORNL) and Texas A&M University used a new methodology. The new technique relies on AFM to track the expansion and contraction of the material at the atomic scale and in real time as an electronic instrument called a potentiostat moves charge in and out of the material. This technique allowed the team to detect even minor deformations in the material as charge moved through it.

"We tested both crystalline tungsten oxide dihydrate and crystalline tungsten oxide – which lacks the water layers," says Veronica Augustyn, an assistant professor of materials science and engineering at NC State and corresponding author of a paper on the work. "And we found that the water layers appear to play a significant role in how the material responds mechanically to energy storage."