The effect of energetically coated ZrOx on enhanced electrochemical performances of Li(Ni1/3Co1/3Mn1/3)O2 cathodes using modified radio frequency (RF) sputtering

Abstract

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.