Thermodynamic and Kinetic Origins of Lithiation-Induced Amorphous-to-Crystalline Phase Transition of Phosphorus

Abstract

Despite its fundamental.. importance, real-time observation of atomic motions during phase transition is challenging because the transition processes usually occur on ultrafast time scales. Herein, we directly monitored a fleeting and,spontaneous crystallization of Li3P from amorphous LixP phases with x similar to 3 at room temperature via first-principles molecular dynamics simulations. The crystallization is a collective atomic ordering process continued for 0.4 ps and it is driven by the following key impetuses: (1) the crystalline Li3P phase is more Stable than its amorphous counterpart, (2) the amorphous LixP phase corresponds thermodynamically to the local minimum energy state at x similar to 3, which enables its crystallization under an electrochemical equilibrium condition without net flux of lithium ions in the host material, (3) the crystalline and amorphous structures of Li3P are so similar that the average displacement of the mobile Li atoms during crystallization is only 0.56 angstrom, and (4) highly lithiated materials with all-isolated host elements, such as the amorphous Li3P phase, are advantageous for crystallization because the isolation induces a kinetically favorable low-barrier transition without complicated multistep P-P bond breaking/forming processes.