TSFZ Growth and Anisotropic Ionic Conductivity of Zr-Doped LiCoO<sub>2</sub> Single Crystals
M. Riju Khandaker, Yuki Maruyama, Masanori Nagao, Satoshi Watauchi, Hirokazu Munakata, Kiyoshi Kanamura, Isao Tanaka
Abstract
To aid the development of cathode materials for use in Li-ion batteries, for the first time, LiCo1–xZrxO2 single crystals were successfully grown via the traveling solvent floating zone (TSFZ) technique. The crystals grown using 0.50 at. % Zr-doped feeds were single crystals with very small (Co, Zr)Ox inclusions (approximately 6 μm in size), whereas large size inclusions segregated in the crystals grown using the feed of 1.00 at. % Zr. The Zr concentrations of the LiCoO2 phase in both crystals were determined to be 0.26 ± 0.01 and 0.26 ± 0.05 at. %, respectively, along the growth direction, which is almost identical to each other but lower than the actual Zr concentration in feeds (0.50 and 1.00 at. % Zr). The ionic conductivities of LiCo0.9974Zr0.0026O2 single crystals along [100] and [001] were 8.3 × 10–6 and 4.0 × 10–8 S·cm–1, respectively, which are approximately twice as large as those of LiCoO2 (σ[100] = 4.0 × 10–6, σ[001] = 2.4 × 10–8 S·cm–1). The anisotropy of ionic conductivity in LiCo0.9974Zr0.0026O2 was found to be 207. The results obtained in this study have the potential to improve the energy density and safety of Li-ion batteries.