Li-B alloys present higher voltages and better power performances than those of conventional Li-Al and Li-Si anodes for thermal batteries. Herein, the electrochemical characteristics of the Li-B alloy in the LiCl-LiBr-KBr electrolyte, including the discharge mechanism, charge transfer coefficient and exchange current density, were investigated in the temperature range of 623-823 K by open circuit potential (OCP), cyclic voltammetry (CV), chronopotentiometry (CP), linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) techniques. Consequently, the OCP of the Li-B alloy in the LiCl-LiBr-KBr electrolyte is close to that of pure lithium at the investigated temperatures. The discharge of the Li-B alloy electrode includes electrochemical dissolution of free lithium (Li → Li+) and compounded lithium (LiB → Li+ + B). The charge transfer coefficient in the anodic direction (Li → Li+) is about 0.63 at 623 K, which slightly increases as the temperature increases. The exchange current density of the Li (Li-B)/Li+ couple determined by the EIS method increases from 3.84 A cm-2 to 8.40 A cm-2 when the temperature increases from 623 to 823 K, corresponding to an activation energy of 16.4 kJ mol-1. These results suggest that the Li-B anode allows ultrahigh-rate discharge in thermal batteries.