Preparation conditions of NiS active material in high-boiling solvents for all-solid-state lithium secondary batteries

Abstract

Nickel sulfide particles were synthesized by thermal decomposition of nickel acetylacetonate in a mixed solution of 1-dodecanethiol and high-boiling solvents. Nickel sulfide was formed by thermal decomposition of nickel(II) dodecanethiolate in the high-boiling solvent, and the crystal phases of nickel sulfide were controlled by selection of the solvent. NiS was obtained in 1-octadecene as a noncoordinating solvent. On the other hand, Ni₉S₈ was prepared in oleylamine as a coordinating solvent because oleylamine molecules have a strong capping ability for nickel ions in nickel(II) dodecanethiolate, and thus the oleylamine molecules prevent the diffusion of sulfur derived from nickel(II) dodecanethiolate and free 1-dodecanethiol. All-solid-state cells were fabricated by using composite electrodes prepared by wet milling in hexane. At a current density of 1.3 mA cm⁻², the cell using a composite electrode prepared by wet milling exhibited a discharge capacity of 500 mA h g⁻¹ for 30 cycles and a better cycle performance than the cell using a composite electrode prepared by hand-grinding in a mortar.