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 the properties of the material. X-ray diffraction, Fourier-transformed infra-red spectroscopy (FT-IR), 31P, 11B, and 7Li 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 BPO4 can be described with two defect models, LiBdouble-prime + 2Lii and VB''' + 3Lii, suggesting that the ionic conductivity takes place via interstitial Li ions