Development of the Ca/FeS₂ chemistry for thermal batteries

Alternative battery chemistries are the focus of growing attention due to their potential advantages over lithium; however, the field of thermal batteries sees much less research into alternative chemistries, as the current lithium alloy–metal sulfide cell is seen as the “gold standard”. In this work, we demonstrate the operation of a thermal battery using a calcium-containing eutectic and calcium metal against the FeS₂ cathode material. An initial assessment of the CaCl₂–NaCl eutectic is presented, showing that it is a good candidate for use as an electrolyte. Cells were assembled and characterized using a range of physical and electrochemical techniques, and their properties were studied. Discharge voltages at low current densities were promising, with cells displaying discharge voltages >2 V and capacities in excess of 100 mAh g^–1. Rate capability was also explored, which can be improved by modification of the cathode. Although the cathode material was not fully utilized during discharge, there was evidence of electrochemical reactions occurring, which were explored in detail using powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), and neutron diffraction. It is hoped that these results will stimulate development and ideas for high-temperature battery chemistries, expanding the horizons of these types of batteries for new applications.