Emerging Era of Electrolyte Solvation Structure and Interfacial Model in Batteries

Abstract

Over the past two decades, the solid–electrolyte interphase (SEI) layer that forms on an electrode’s surface has been believed to be pivotal for stabilizing the electrode’s performance in lithium-ion batteries (LIBs). However, more and more researchers currently are realizing that the metal-ion solvation structure (e.g., Li+) in electrolytes and the derived interfacial model (i.e., the desolvation process) can affect the electrode’s performance significantly. Thus, herein we summarize recent research focused on how to discover the importance of an electrolyte’s solvation structure, develop a quantitative model to describe the solvation structure, construct an interfacial model to understand the electrode’s performance, and apply these theories to the design of electrolytes. We provide a timely review on the scientific relationship between the molecular interactions of metal ions, anions, and solvents in the interfacial model and the electrode’s performance, of which the viewpoint differs from the SEI interpretations before. These discoveries may herald a new, post-SEI era due to their significance for guiding the design of LIBs and their performance improvement, as well as developing other metal-ion batteries and beyond.

Structural regulation chemistry of lithium ion solvation for lithium batteries

“…Schematic diagram of the de‐solvation process 31 . Reproduced with permission: 2022, American Chemical Society 31 …”

“…Quantum chemistry calculations showed that the binding energies were À5.27 and F I G U R E 7 Schematic diagram of the de-solvation process. 31 Reproduced with permission: 2022, American Chemical Society 31 À1.38 kJ mol À1 when FEC/FEMC and FEC/DEC were at a ratio of 1:3, much lower than EC/DMC (3:1 molar) of À37.86 kJ mol À1 . Their binding energies were further reduced after they were dissolved in high-fluorine solvents.…”

“…The interactions among anions and cations, solvents, co‐solvents, and additives can be changed dynamically in the whole complex electrolyte system, which brings great difficulties for us to analyze the behavior of the electrolytes 26,27 . Fortunately, advanced characterization methods and computational simulations have been developed to analyze the Li + solvation structure for studying the behavior of electrolytes 28–31 …”

“…26,27 Fortunately, advanced characterization methods and computational simulations have been developed to analyze the Li + solvation structure for studying the behavior of electrolytes. [28][29][30][31] As a function of Li salt in solvents with additives, Li + solvation structure could determine many properties of the electrolytes, and especially the structural model Li +…”

Promoting Mechanistic Understanding of Lithium Deposition and Solid‐Electrolyte Interphase (SEI) Formation Using Advanced Characterization and Simulation Methods: Recent Progress, Limitations, and Future Perspectives

“…[ 51 ] However, it remains challenging to elucidate the desolvation process of Li ions (as well as other ions), since the process is abstractive, dynamic, and non‐quantitative. [ 52 ] Moreover, the structure of the Li‐ion solvation and the electric double layer determine this dynamic process but could easily be altered if changing either the electrolyte concentration or composition (salts, solvents, and additives). A lack of feasible operando characterization tools further hinders an in‐depth understanding of the Li‐ions dynamics at the electrochemical interface.…”