First principles calculations have been used to explore the Li-Bi-F ternary phase diagram. Our results confirm the thermodynamic stability of previously observed phases and find no new phases in this system. Electrochemical voltage profiles for the reaction of Li and BiF3 are in reasonable agreement with experiment. The driving force to form ternary Li-Bi-F intermediates is small. We also investigated the effect of particle size on the reaction voltage and find a potential decrease when nanoscale vs bulk Bi forms upon reacting BiF3 with Li.