“It gives us fundamental insights into how batteries work,” said Jongwoo Lim, post-doctoral researcher at the Stanford Institute for Materials and Energy Sciences at SLAC. “Previously, most studies investigated the average behaviour of the whole battery. Now, we can see and understand how individual battery particles charge and discharge.”
The basic processes – known as lithiation (discharge) and delithiation (charge) – are hampered by the ions not inserting themselves uniformly across the surface of the electrodes. Instead, certain areas take on more ions, and others fewer. These inconsistencies eventually lead to mechanical stress as areas of the crystal lattice become overburdened with ions and develop tiny fractures, sapping battery performance and shortening battery life.
The team fashioned a transparent battery consisting of two thin, transparent silicon nitride ‘windows’. The battery electrode, made of a single layer of lithium iron phosphate nanoparticles, sits on the membrane inside the gap between the two windows. An electrolyte flows in the gap, delivering the lithium ions to the nanoparticles.
In their study, the researchers discovered that delithiation is significantly less uniform than the lithiation. The researchers also found that faster charging improves uniformity, which could lead to better battery designs and power management strategies.
“The improved uniformity lowers the damaging mechanical stress on the electrodes and improves battery cyclability,” said William Chueh, assistant professor of materials science and engineering at Stanford. “Beyond batteries, this work could have far-reaching impact on many other electrochemical materials.”