Cycle life improvement of ZrO2-coated spherical LiNi1/3Co1/3Mn1/3O2 cathode material for lithium ion batteries

A modified synthesis process was developed based on co-precipitation method followed by spray drying process. In this process, a spherical shaped (Co_1/3Ni_1/3Mn_1/3)(OH)₂ precursor was synthesized by co-precipitation and pre-heated at 500 °C to form a high structural stability spinel (CoNiMn)O₄ to maintain its shape for further processing. The spherical LiNi_1/3Co_1/3Mn_1/3O₂ was then prepared by spray drying process using spherical spinel (CoNiMn)O₄. LiNi_1/3Co_1/3Mn_1/3O₂ powders were then modified by coating their surface with a uniform and nano-sized layer of ZrO₂. The ZrO₂-coated LiNi_1/3Co_1/3Mn_1/3O₂ material exhibited an improved rate capability and cycling stability under a high cut-off voltage of 4.5 V. X-ray diffraction (XRD) measurements revealed that the material had a well-ordered layered structure and Zr was not doped into the LiNi_1/3Co_1/3Mn_1/3O₂. Electrochemical impedance spectroscopy measurements showed that the coated material has stable cell resistance regardless of cycle number. The interrupt charging/discharging test indicated that the ZrO₂ coating can suppress the polarization effects during the charging and discharging process. From these results, it is believed that the improved cycling performance of ZrO₂-coated LiNi_1/3Co_1/3Mn_1/3O₂ is attributed to the ability of ZrO₂ layer in preventing direct contact of the active material with the electrolyte resulting in a decrease of electrolyte decomposition reactions.