Controlling the Changes in Electrolyte Composition in the Cathode to Reduce the Voltage Decay of NiCl2 Thermal Batteries

Because of the high open-circuit voltage and good performance under high current loading, NiCl2 has become a promising cathode material for thermal batteries. Unfortunately, the high resistivity and the occurrence of voltage decay during the discharge process limit the application of NiCl2. In this work, Br-doped NiCl2 is synthesized to reduce this voltage decay. The ion mobility of NiCl2 is improved by bromine doping, and the rise of the melting point of the electrolyte in the positive electrode is delayed by releasing both LiCl and LiBr in the discharge process. Thus, the voltage decay is reduced. The capacity of NiCl1.6Br0.4 at its voltage platform (>2.0 V) is 255 mA h g–1 and that of NiCl2 is only 200 mA h g–1 (under 200 mA cm–2). Moreover, Br doping also improves the conductivity of NiCl2. Therefore, the maximum voltage at the discharge of NiCl1.6Br0.4 (2.02 V) is higher than that of NiCl2 (1.76 V) under 500 mA cm–2 constant current loading.