Nickel(II) chloride materials were synthesized via a novel two-step variable-temperature method for the use as a cathode material in Li-B/NiCl2 cells with the LiCl-LiBrLiF electrolyte. The influence of temperature on its structure, surface morphology, and electrochemical performance was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), and electrochemical measurements of single cells. XRD results showed that after pre-dehydration for 2 h at 270°C followed by sintering for 5 h at 600°C, the crystal water in nickel chloride hexahydrate could be removed effectively. The SEM results showed that particles recombined to form larger coarse particles and presented a layered structure. Discharge tests showed that the 600°C-treated materials demonstrated remarkable specific c apacities of 210.42 and 242.84 mA h g −1 at constant currents of 0.5 and 2.0 A, respectively. Therefore, the Li-B/NiCl2 thermal battery showed excellent discharge performance. The present work demonstrates that NiCl2 is a promising cathode material for thermal batteries and this two-step variable-temperature method is a simple and useful method for the fabrication of NiCl2 materials.