Search for a space charge layer in thin film battery materials with low-energy muons

In an all solid state Li-ion battery, it is crucial to reduce ionic resistivity at the interface between the electrode and the electrolyte in order to enhance Li+ mobility across the interface. Recent first principles calculations predict the presence of a space-charge layer (SCL) at the interface due to the difference in the Li+ chemical potential at the interface between two different materials, as in the metal-semiconductor junction in electronic devices. However, the presence of SCL has never been experimentally observed. Our first attempt in a fresh multilayer sample, Cu(10 nm)/Li3PO4(50 nm)/LiCoO2(100 nm) on a sapphire substrate, with low-energy mu+SR (LE mu+SR) revealed a gradual change in the nuclear magnetic field distribution width as a function of implantation depth even across the interface between Li3PO4 and LiCoO2. This implies that the change in the field distribution width at SCL of the sample is too small to be detected by LE mu+SR.

Automated summary

In an all solid state Li-ion battery, reducing ionic resistivity at the electrode-electrolyte interface is essential for enhancing Li+ mobility. Recent calculations predict a space-charge layer (SCL) at the interface due to chemical potential differences, similar to electronic devices. However, the presence of SCL has never been experimentally observed. Our first attempt using low-energy mu+SR revealed a small change in field distribution width across the interface, suggesting the change at the SCL is too small to be detected.