Implications of Na-ion solvation on Na anode–electrolyte interphase

Abstract

The ever-increasing demand for efficient rechargeable batteries requires a solid understanding of both electrodes and electrolytes. The creation of a chemically and mechanically stable electrode–electrolyte interface is crucial to ensure high reversibility of metal anode batteries. Recent findings have shown that the stability of the solid electrolyte interphase (SEI) on a sodium-metal anode can be affected by microscopic processes such as sodium-ion solvation/desolvation dynamics and the magnitude of various interactions between ion–ion and ion–solvent molecules. Careful selection of sodium salts, solvents, and electrolyte additives is pivotal in controlling the dynamics of sodium-ion solvation. Identification of the nature and chemistry of ion-pair formation by combining in situ characterization and theoretical investigation can catalyze the understanding of stable SEI formation. Sodium-metal anode battery technologies have revolutionized energy storage research. In recent years, new insights have been gained regarding the solid electrolyte interphase (SEI) on a sodium-metal anode; however, several questions remain to be answered, in particular the impact of electrolyte structure on the composition and physicochemical stability of the SEI. In addition, the impact of ion-solvation chemistry on the crystallinity of the SEI warrants a more detailed understanding. This review discusses the crucial aspects of sodium-ion solvation chemistry and its impact on the stability of the SEI. The core principles guiding the design of electrolytes through additives, ion–solvent interaction, and ion-pair formation are highlighted. Future research directions necessary to design a stable sodium-metal anode are also discussed. Sodium-metal anode battery technologies have revolutionized energy storage research. In recent years, new insights have been gained regarding the solid electrolyte interphase (SEI) on a sodium-metal anode; however, several questions remain to be answered, in particular the impact of electrolyte structure on the composition and physicochemical stability of the SEI. In addition, the impact of ion-solvation chemistry on the crystallinity of the SEI warrants a more detailed understanding. This review discusses the crucial aspects of sodium-ion solvation chemistry and its impact on the stability of the SEI. The core principles guiding the design of electrolytes through additives, ion–solvent interaction, and ion-pair formation are highlighted. Future research directions necessary to design a stable sodium-metal anode are also discussed. the ratio of the discharge capacity to the charge capacity of a cell. Electrochemical reversibility of a cell can be quantified by the Coulombic efficiency, which is an indication of the stability as well. a sharp, needle-like deposit formed from uncontrolled and nonuniform electrodeposition of metal, mainly due to the unstable SEI layer over a metal anode. Sodium dendrites can grow with prolonged cycling and protrude from the separator, causing premature cell failure by internal short circuits. a thermodynamics concept where the change in Gibbs free energy denotes the spontaneity and nonspontaneity of a chemical reaction. In relation to SMBs, the calculation of Gibbs free energy for the sodium-ion solvation reaction provides insights into the concepts of spontaneity and thermodynamic equilibrium. conductivity due to the migration of mobile charged species, known as ions, through a matrix/medium under an electric field. Ionic conductivity can be quantified by the product of the concentration, the carrier charge, and the mobility of species due to the application of the electric field. a salt that exists in the liquid state at temperatures below 100°C. Unlike molecular liquids, high-magnitude electrostatic interactions make ionic liquids viscous, nonvolatile, nonflammable, and thermally stable. Moreover, ionic liquids possess comparable ionic conduction with a wide electrochemical window, making them suitable for use as electrolytes in SMBs. the highest occupied molecular orbital (HOMO), referred to as the bonding orbital, and the LUMO, referred to as the antibonding orbital, are derived from electronic structure theory in quantum chemistry. These energy levels can easily be influenced by the electrostatic interactions between ions and solvents. Chemical stability and solvent reactivity in the presence of sodium metal can be predicted from HOMO and LUMO values. an insoluble passivation layer formed at the electrode–electrolyte interface due to quasi-reversible electrochemical reactions between electrode and electrolyte molecules. The SEI comprises randomly distributed multicomponents of organic and inorganic compounds. Electrochemical properties such as sodium ion migration and the reversible plating/stripping process, which relates to the stability and cycling performance, strongly depend on the nature and thickness of the SEI. interaction of a solute with the solvent, leading to stabilization of the solute in solution. Sodium ions in the solvated state are surrounded or complexed by a concentric shell of solvent molecules in solution. Solvation involves bond formation, hydrogen bonding, and van der Waals forces, and solvated species are often characterized by their coordination number and stability constant. the maximum possible amount of charge which can be extracted or inserted per unit mass of the active materials in an electrochemical cell. The capacity can be quantified by the product of current and time.