The Suppression Effect of Functional Gradient Design on Concentration Polarization of Multiple Cations Molten Salt Electrolyte for Thermal Batteries

Abstract

The energy density of traditional Li−Si/FeS2 thermal batteries, which multiple cations are contained in molten salt electrolyte, is limited by the deficiency of Li+ in cathode when a high discharge current is applied. To address this issue, LiCl−KCl is taken as an example to build a functional gradient structure through Li−Si/FeS2 thermal batteries. By levering the Li+ concentration in cathode and preventing the formation of high concentration polarization resistivity as well as molten salt precipitation, the energy density of Li−Si/FeS2 single cell with a discharge current of 500 mA cm−2, increase from 157.0 Wh kg−1 to 218.4 Wh kg−1 at 450 °C (with an increase ratio of 39.1%), compared with the original one. Similarly, a 25.6% raise is observed at 525 °C. Moreover, the effects of LiCl-rich electrolyte and the functional gradient structure on the electrochemical performance of Li−Si/FeS2 single cells are discussed and classified.