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.