NiCoS Bi-metal Sulfide Coating on LiNiCoMnO Cathode for High-Performance All-Solid-State Lithium Batteries.

NiCoS nanoparticles (NPs) were dry coated on LiNiCoMnO (NCM622) cathode using a resonant acoustic coating technique to produce all-solid-state lithium batteries. The NiCoS coating improved the electrochemical properties of the NCM622 cathode. In addition, NiCoS 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 NiCoS 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% NiCoS-coated NCM622 had an evenly modified surface with NiCoS NPs. X-ray photoelectron spectroscopy (XPS) revealed that the surface of 0.3 wt% NiCoS-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 NiCoS-coated NCM622 retained a higher specific capacity over multiple cycles than bare NCM622. Especially, 0.3 wt% NiCoS-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% NiCoS-coated NCM622 with minimal side reactions.