Integral Role of the NiS Electrode/Electrolyte Interface in the Redox Reaction with Lithium

Abstract: Electrochemically synthesized thin-layer NiS electrodes were studied in lithium perchlorate dissolved in 1.3-dioxolane or in a mixture of 1.3-dioxolane and tetrahydrofuran. In the 1.3-dioxolane 1 M LiClO₄ electrolyte, the irreversible capacity was reduced by 20% сompared to the initial capacity. However, the stability of the electrochemical characteristics of NiS electrodes in redox reactions with lithium is unsatisfactory. Much better results of charge–discharge cycling of NiS electrodes were obtained in the electrolyte solutions of 1.3-dioxolane, tetrahydrofuran, and 1 M LiClO₄ demonstrating a stable reversible capacity of 400–450 mAh/g during 50–75 cycles. Using the methods of electron microscopy and IR spectroscopy with Fourier transform, it was established that the reason for the discharge capacity fading of NiS electrodes was associated with the formation of a surface film, which reduces the adhesion and cohesion of NiS particles. This, in turn, leads to a loss in the mechanical strength of NiS electrodes.