A second nearest-neighbor modified embedded atom method (2NN MEAM) interatomic potential for lithium–silicon (Li–Si) alloys is developed by using the particle swarm optimization (PSO) method in conjunction with ab initio calculations. It is shown that the new interatomic potential is capable of simulating the transition from disordered to ordered states of Li–Si crystalline structures, an indication of the stability and robustness of the interatomic potential at finite temperature. Examples are given to demonstrate that the new interatomic potential is also capable of predicting the material properties of both crystalline and amorphous Li–Si alloys, including the elastic modulus, compositional expansion, diffusivity of Li in Li–Si alloys, plastic yield strength, etc.