Engineering high-energy-density sodium battery anodes for improved cycling with superconcentrated ionic-liquid electrolytes

Abstract

Non-uniform metal deposition and dendrite formation in high density energy storage devices reduces the efficiency, safety, and life of batteries with metal anodes. Superconcentrated ionic liquid (IL) electrolytes (e.g. 1:1 IL:alkali ion) coupled with anode preconditioning at more negative potentials can completely mitigate these issues, and therefore revolutionize high density energy storage devices. However, the mechanisms by which very high salt concentration and preconditioning potential enable uniform metal deposition and prevent dendrite formation at the metal anode during cycling are poorly understood, and therefore not optimized. Here, we use atomic-force microscopy and molecular dynamics simulations to unravel the influence of these factors on the interface chemistry in a sodium electrolyte, demonstrating how a molten salt like structure at the electrode surface results in dendrite free metal cycling at higher rates. Such a structure will support the formation of a more favorable solid electrolyte interphase (SEI) accepted as being a critical factor in stable battery cycling. This new understanding will enable engineering of efficient anode electrodes by tuning interfacial nanostructure via salt concentration and high voltage preconditioning. File list (2) download file view on ChemRxiv supplementary.pdf (5.03 MiB) download file view on ChemRxiv Manuscript-V1.pdf (2.06 MiB)

Insights into the Nanostructure, Solvation, and Dynamics of Liquid Electrolytes through Small‐Angle X‐Ray Scattering

“…Recently, Rakov et al. [ 59 ] reported that superconcentrated ionic‐liquid electrolytes, such as 1:1 N ‐methyl‐N‐propylpyrrolidinium bis(fluorosulfonyl)imide (C3mpyr‐FSI): sodium bis(fluorosulfonyl) imide (NaFSI), coupled with anode preconditioning at more negative potentials could completely mitigate dendrite formation. Sun et al.…”

“…X-ray scattering revealed that Li + −O(FSI − ) atom−atom correlation has an average distance of about 1.94 Å, which is evidently longer than that of the Li + −O(TFSI − ) (1.86 Å). Recently, Rakov et al [59] reported that superconcentrated ionic-liquid electrolytes, such as 1:1 N-methyl-N-propylpyrrolidinium bis(fluorosulfonyl)imide (C3mpyr-FSI): sodium bis(fluorosulfonyl) imide (NaFSI), coupled with anode preconditioning at more negative potentials could completely mitigate dendrite formation. Sun et al [60] found that 5 m LiFSI in EMim-FSI with 0.1 m NaTFSI as key additive can form hybrid passivation interphases and avoid lithium plating.…”

Solid Electrolyte Interphases on Sodium Metal Anodes

“…Lately, the role of the electrolyte structure at the anode in improving the stability of the SEI layer and Na deposition was revealed. [ 133 ] Figure 7h shows a distinct effect on the interfacial structure from NaFSI concentration through AFM force measurement and molecular dynamics (MD). A highly aggregated Na x (FSI) y structure in the form of molten salt was found in the innermost electrolyte layers, especially on the negatively charged surface.…”

“…h) Interfacial layering nanostructure comparation for C 3 mpyrFSI IL with different NaFSI salt concentrations (h 1 :0 mol%; h 2 :10 mol%; h 3 :50 mol%) by AFM and MD. Reproduced with permission [133]. Copyright 2020, Nature Publishing Group.…”

Structure Code for Advanced Polymer Electrolyte in Lithium‐Ion Batteries

“…Therefore, several methods have been developed and optimized such as the introduction of small molecule plasticizers, e.g., ionic liquids (ILs), [ 5 ] carbonates, [ 6 ] or ethers, [ 7 ] to polymer‐salt developed gel polymer electrolytes (GPEs) in the quasi‐solid‐state. [ 8 ] The solid polymer hosts provide robust mechanical strength and binding to liquid electrolytes, avoiding the safety risks caused by leakage, while the Li + transport proceeds mainly along the liquid track distributed in the polymer matrix.…”