Search for Li-electrochemical activity and Li-ion conductivity among lithium bismuth oxides

Previously reported lithium bismuth oxides, LiBiO2, LiBiO3, Li3BiO3, Li3BiO4, Li5BiO5, and Li7BiO6 were prepared either via ceramic or hydrothermal synthesis methods, and their feasibility as lithium battery cathode materials was tested. None of the oxides showed any desirable electrochemical activity at higher potentials, except for the limited capacity observed during the first discharge in LiBiO3. In contrast, these phases uptake large amounts of Li+ via conversion reactions when cycled down to zero volt, but the reversibility is poor. The transformation of LiBiO3 to LiBiO2 and Li3BiO3 to Li3BiO4 observed via X-ray diffraction showed absence of intermediate phases with mixed Bi3+/Bi5+ oxidation states. Among the materials studied, the highest ionic conductivity of 3.8×10−8 S/cm at 25°C was measured for LiBiO2. The Li+ conduction pathways deduced from bond valence energy landscape approach suggest the best Li diffusion characteristics in Li7BiO6 among the Li-Bi-O phases studied.