Nickel sulfides as a cathode for all-solid-state ceramic lithium batteries

The nickel sulfide, Ni₃S₂, was examined as a potential cathode material of the all-solid-state-lithium-batteries using thio-LISICON, Li₂S–GeS₂–P₂S₅, as the solid-electrolyte. Ni₃S₂and Li₂S–GeS₂–P₂S₅ system, was synthesized with a new sintering system, which proceed under a flowing argon in the reusable quartz tube. The highest ionic conductivity 2.39×10⁻³$2.39\times 10^{-3}$ S cm⁻¹ was observed for a sample prepared at 700 °C with 10% of excess P₂S₅, and bear comparison with the maximum conductivity reported for the thio-LISICON, Li_3.35Ge_0.35P_0.65S₄. An all-solid-state-lithium-battery based on, Ni₃S₂/Li_3.35Ge_0.35P_0.65S₄/Li–Al alloy, showed electrochemical capacities of greater than ∼$\sim$300 mAh g⁻¹ after 30 cycles. The cycling performances of the cells were found to be dependent on the Ni₃S₂/thio-LISICON compositions in the cathode mixture, with a cell containing 60 wt.% of Ni₃S₂ exhibiting the most stable reversible capacities. As the depth of the first discharge capacity also influences the cycling properties, Ni₃S₂ consumed during the discharge reaction may play an important role in the nickel reduction mechanism.