Roles of Fast-Ion Conductor LiTaO3 Modifying Ni-rich Cathode Material for Li-Ion Batteries.

Limited cycling stability hampers the commercial application of Ni-rich materials, which are regarded as one of the most promising cathode materials for Li-ion batteries. Ni-rich LiNi0.9 Co0.06 Mn0.04 O2 layered cathode was modified with different amounts of LiTaO3 , and the influences of fast-ion conductor material on cathode materials were explored. Detailed analysis of the materials revealed the formation of a uniformly epitaxial LiTaO3 coating layer and a little Ta5+ doping into the lattice structure of Ni-rich materials. The coating-layer thickness increased with the amount of LiTaO3 added, protecting the electrode from erosion by electrolyte and suppressing undesired parasitic reactions on the cathode-electrolyte interface. Meanwhile, the doped Ta5+ increased the interplanar spacing of materials, accelerating Li+ transfer. Using the positive synergistic effects of LiTaO3 -coating and Ta5+ -doping, improved capacity retentions of the modified materials, especially for 0.25 and 0.5 wt%-coated Ni-rich materials, were obtained after long-term cycling, showing the potential applications of LiTaO3 modification. Further, the relations between one excessively thick coating layer and transfer of Li+ /electron between the cathode and electrolyte was established, proving that very thick coating layers, even layers containing Li ions, have adverse effects on electrochemical performances. This finding may help to understand the roles of the coating layer better.