Electrochemical Properties of DLC/Lzo Double Coated LiNi0.8Co0.15Al0.05O2� cathode Material of All-Solid-State Lithium Ion Battery

The surface of LiNi_0.8Co_0.15Al_0.05O₂  (NCA) cathode material was coated with diamond like carbon (DLC) and LZO (Li₂O-ZrO₂)  by chemical vapor deposition and sol-gel method respectively, in order to prevent the side reaction at the interface and stabilize the surface Ni-O bonds during charge and discharge process for sulfide based all-solid state lithium-ion batteries.  The double coated (DLC/LZO) material showed a higher capacity with significantly improve in surface resistance and high rate performance than the single coating of DLC or LZO and without coating.  The interface resistance between the cathode active material and the solid electrolyte significantly decreases by double coating onto the NCA powder.  The discharge capacity of DLC coated sample at 0.05C was 123 mAhg⁻¹ while that of bared one was about 102 mAhg⁻¹.  The charge and discharge cut off potentials were 4.0 and 2.8 V, respectively.  The thickness of the DLC/LZO coated layer was verified by transmission electron microscope (TEM), and was about 10�-20 nm.  The sp2 bonding ratio of the DLC coated LiNi_0.8Co_0.15Al_0.05O₂  powder was estimated from the C-KELNES spectra to be 50�-55%.  In this work, the diamond like carbon (DLC) and combination with LZO coating were proposed for the first time as buffer coating layers for all-solid state battery.  We demonstrated that the combination of lithium ion conductivity (LZO) and DLC will reduce the interface resistance between cathode material and sulfide based electrolyte.