The effect of energetically coated ZrO_x on enhanced electrochemical performances of Li(Ni_1/3Co_1/3Mn_1/3)O₂ cathodes using modified radio frequency (RF) sputtering

To date, most coating layers for electrode materials for Li-ion batteries have been fabricated using the sol-gel method or atomic layer deposition (ALD), which involve complicated processing steps and limited candidates for coating materials. With an emphasis on solving these issues, herein, a new coating methodology based on a sputtering system was developed, and sputtered zirconium oxide was coated on Li(Ni_1/3Co_1/3Mn_1/3)O₂ (L333) cathode powders. The continuous movement of the cathode powders during the coating procedure and the high kinetic energy from the sputtering process resulted in a highly uniform coating layer with multiple structures exhibiting a concentration and valence state gradient of Zr, i.e., surface (mainly Zr⁴⁺) and doped (mainly Zr²⁺) layers. The ZrO_x-coated L333 powders exhibited an outstanding capacity retention (96.3% at the 200th cycle) and superior rate capability compared with the uncoated version in a coin cell with 1 M LiPF₆ in EC : DEC liquid electrolyte. The ZrO_x-coated L333 powders also exhibited an enhanced specific capacity in a solid state battery cell with a sulfide-based inorganic solid-state electrolyte. The improved electrochemical performance of ZrO_x/L333 was attributed to the synergetic effect from the surface and doped layers: physical/chemical protection of the active material surface, enhancement of Li-ion diffusion kinetics, and stabilization of the interfaces.