Comparative behavior of a thin-layer Co₉S₈ in redox reactions with lithium in polymer and liquid electrolytes

Thin-layer Ñî₉S₈ electrodes were synthesized via the electrolysis technique onto aluminum foil and tested in redox reactions with lithium in polymer and liquid electrolytes. It was established the difference between the discharge characteristics of the Co₉S₈-electrode in the polymer electrolyte with a gel-like consistency and in solid film electrolyte. The starting discharge capacity of Ñî₉S₈ both in a gel-like electrolyte and in a liquid electrolyte may reach 600 mA․h/g, which exceeds its theoretical value (544 mA․h/g). The reversible capacity of Ñî₉S₈/Li in the polymer electrolyte is about 280-250 mA․h/g at the average discharge voltage of 1.40-1.45 V. During a long cycling, the discharge capacity of Co₉S₈ decreases both in the polymer electrolyte and in the liquid electrolyte. The discharge capacity of a metal-sulfide material/Li system in the polymer electrolyte is mainly reduced due to an increase in the polarization resistance of the lithium electrode caused by the disruption of its contact with the polymer electrolyte and a drying of the electrolyte in the porous space of the polymer gel matrix. The irreversible capacity of Ñî₉S₈/Li can be reduced under the influence of an anionic polyelectrolyte (sodium polyacrylate) that was used as an additive to the electrolyte for the synthesis of Ñî₉S₈. Norit conductive filler added to the electrolyte for the synthesis of Ñî₉S₈ was tested to improve the electrochemical characteristics of Co₉S₈. A positive effect of Norit may be associated with the stabilization of the reversible capacity of Ñî₉S₈ electrodes that reaches 400 mA․h/g.