Crystalline-to-Amorphous Phase Transformations As a Key Ingredient to Enhanced Rate Performance and Cycle Life in Mg- and Na-Ion Battery Anodes: Operando x-Ray Scattering Studies

摘要

The increasing popularity of Li-ion batteries in new applications such as electric vehicles is expected to cause the key resources (Li, Ni and Co) used in these batteries to become scarce. Alternative battery technologies, including Mg-ion, Na-ion, and metal-air batteries are therefore desirable. In this talk, I will discuss the use of operando wide-angle X-ray scattering (WAXS) to study the crystalline to amorphous phase transformations that are key to the outstanding performance of state-of-the-art alloy-type Mg- and Na-ion anodes. The 1st part of the talk will be on the impact of the crystalline-to-amorphous transformation on batteries cycle life. Here I will discuss our novel self-healing Ga/Mg anode, which holds the current record for cycle performance and rate capability in alloy-type Mg-ion battery anodes, owing to a crystalline Mg_2Ga_5 to amorphous liquid Ga phase transformation occurring near room temperature, preventing the well-known pulverization issue in alloy-type anodes. The 2nd part of the talk will detail the impact of the crystalline-to-amorphous transformation on the rate capabilities of batteries. Here, I will present our nanoporous Sb/Na system, which transforms from crystalline Na_3Sb to crystalline Sb, going through an amorphous intermediate. It will be shown using a combination of WAXS, electrochemical characterization, and computational study based on ab initio grand canonical (aiGCMC) simulations that the amorphous intermediate phase favors high rate Na storage in Sb.