Local Structure and Dynamics in Solvent-Free Molten Salt -Electrolytes

Calcium batteries (CaBs) fundamentally offer a promise of sustainable high energy density storage. However, the development of functional CaB electrolytes remains a key challenge. Here, molecular simulations are used to investigate structural and dynamic properties of solvent-free molten salt electrolytes (MSEs) containing $$ and alkali cations ($$, $$, $$), paired with either FSI or TFSI anions. Two equimolar MSEs, [Li, Na, K, Ca]FSI and [Li, Na, K, Ca] TFSI, are examined across a range of temperatures to better understand cation–anion interactions, coordination and local structure, and ion mobility, in particular with respect to $$. The interplay between cation charge density, anion structure, and thermal effects provides valuable insights into the MSEs’ macroscopic behavior. These insights inform the design of advanced electrolytes that enhance $$ mobility, supporting the development of next-generation CaBs.