Challenge for Detecting the Interface between Electrode and Electrolyte with β-NMR

It is widely believed that a space-charge layer (SCL) exists at the vicinity of a boundary between a solid electrolyte layer and electrode layer in an all solid-state Li-ion battery due to the difference of their chemical potentials, although there are no direct experimental evidences. Here, the Li concentration is predicted to decrease drastically in the SCL. In order to clarify whether SCL exists or not, we have attempted to measure the ⁸Li β-NMR spectrum for a multilayer sample, MgO (50 nm)/Li₃PO₄ (70 nm)/LiCoO₂ (200 nm) as a function of implanted energy of ⁸Li. The resonance spectrum was fitted by a combination of two Lorentzians and one background signal. Furthermore, the line width of the resonance signal from the Li₃PO₄ layer is found to become broad towards the boundary with the LiCoO₂ layer. This is consistent with the presence of an SCL.