Growth and Characterization of Li-Ion Conducting Oxide Single Crystals for Li-Ion Batteries by Traveling Solvent Floating Zone Method

Single crystals of Li-ion conducting oxide with layered structure were grown by the traveling solvent floating zone (TSFZ) method and ionic conduction properties of these single crystals were investigated. Undoped and cation-doped LiCoO2 single crystals were grown using the TSFZ method with a Li-rich solvent. By cation doping such as Mg or Zr, the ionic conductivity along [100] was 2–18 times higher than undoped LiCoO2 single crystals. In particular, Mg-doped LiCoO2 crystal exhibited significant anisotropic ionic conductivity of σ[100]/σ[001] ≈ 6550. Furthermore, we have successfully grown single crystals of double perovskite-type oxide solid electrolytes such as Li3xLa2/3-xTiO3, LixLa(1-x)/3NbO3 and LixLa(1-x)/3TaO3. Among them, the anisotropy of the ionic conductivity of Li3xLa2/3-xTiO3 (x = 0.059) single crystals is found to be 2.5, with the ionic conductivities along [100] and [001] of 1.75 × 10–3 and 7 × 10–4 S·cm−1, respectively. We elucidated the high ion conductivity properties within the plane.