NiCo(2)S(4) Bi-metal Sulfide Coating on LiNi(0.6)Co(0.2)Mn(0.2)O(2) Cathode for High-Performance All-Solid-State Lithium Batteries

[Image: see text] NiCo(2)S(4) nanoparticles (NPs) were dry coated on LiNi(0.6)Co(0.2)Mn(0.2)O(2) (NCM622) cathode using a resonant acoustic coating technique to produce all-solid-state lithium batteries. The NiCo(2)S(4) coating improved the electrochemical properties of the NCM622 cathode. In addition, NiCo(2)S(4) eliminated the space-charge layer and the cathode showed an excellent affinity with the interface with a sulfide-based solid electrolyte as an inert material. X-ray diffraction patterns of NCM622 coated with NiCo(2)S(4) showed the same peak separations and lattice parameters as those of bare NCM622. Field-emission scanning electron microscopy and electron dispersive spectroscopy mapping analyses showed that 0.3 wt% NiCo(2)S(4)-coated NCM622 had an evenly modified surface with NiCo(2)S(4) NPs. X-ray photoelectron spectroscopy (XPS) revealed that the surface of 0.3 wt% NiCo(2)S(4)-coated NCM622 had two different S 2p peaks, a Co–S peak, and Ni and Co peaks, compared to those of bare NCM622. Electrochemical studies with electrochemical impedance spectroscopy and galvanostatic charge–discharge cycle performances showed that NiCo(2)S(4)-coated NCM622 retained a higher specific capacity over multiple cycles than bare NCM622. Especially, 0.3 wt% NiCo(2)S(4)-coated NCM622 exhibited a capacity retention of 60.6% at a current density of 15 mA/g for 20 cycles, compared to only 37.3% for bare NCM622. Finally, interfacial XPS and transmission electron microscopy-electron energy loss spectroscopy analyses confirmed the stable state of 0.3 wt% NiCo(2)S(4)-coated NCM622 with minimal side reactions.