Electroreduction of Nickel(II) Chloride and Nickel(II) Fluoride Mixtures in a Heat Activated Battery

Abstract—The discharge characteristics of heat activated batteries (HABs) containing NiCl₂–NiF₂ mixtures as a positive electrode are studied. For the current density range from 0.25 to 1.5 A cm^–2, this cathodic material is characterized by stable electrical characteristics in a temperature range of 480–600°C. The optimum composition of the cathodic mixture for the discharge conditions of HAB cells under study is determined. The reduction products of the NiCl₂–NiF₂ cathodic mixtures are studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), and simultaneous thermal analysis (STA). The components of the cathodic mixture are reduced via the two-electron electrochemical reaction. The reduction products are metallic nickel and lithium halides. Lithium salts form solid solutions based on lithium chloride. Nickel forms the dendrite sponge that grows during HAB cell discharge and shifts deep inside the positive electrode. Pores of the dendrite sponge are filled with the salt fraction with a melting point of 470–490°C. The melting point of the salt fraction predetermines the lower boundary of the working temperature range of the HAB cell under study.