Defect Structure of Li-Doped BPO4: A Nanostructured Ceramic Electrolyte for Li-Ion Batteries

In this paper the defect chemistry of Li-doped BPO4(BPO4–xLi2O, 0>x<0.1) is studied. This nanostructured ceramic electrolyte is used in all-solid-state Li-ion batteries. By changing the Li-doping level the influence on the crystal structure is studied and related to t he properties of the material. X-ray diffraction, Fourier-transformed infra-red spectroscopy (FTIR),31P,11B, and7Li magic-angle-spinning solid state nuclear magnetic resonance, neutron diffraction, and inductively coupled plasma optical-emission spectroscopy measurements are used in order to study the structure. The electrical properties are studied with AC-impedance spectroscopy (AC-IS). The experimental data show that the defect structure of Li-doped BPO4can be described with two defect models, LiʹʹB+2Li·iand VʹʹʹB+3Li·i, suggesting that the ionic conductivity takes place via interstitial Li ions.