Enhanced Sodium Metal/Electrolyte Interface by a Localized High-Concentration Electrolyte for Sodium Metal Batteries: First-Principles Calculations and Experimental Studies

Abstract

The applications of Na metal batteries (SMBs) are restricted owing to the capacity attenuation and safety hazards during the cycling process, while a rational design of the electrolyte is critical on solving this problem. In this work, an electrolyte is designed by adding 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropylether (TTE) into a 3.8 M sodium bis­(fluorosulfonyl)­imide/1,2-dimethoxyethane (NaFSI/DME) electrolyte, forming the localized high-concentration electrolyte (LHCE) for constructing a stable solid electrolyte interface (SEI) for SMBs. Ab initio molecular dynamics (AIMD) results indicate that the solvation degree of Na+ ions with DME molecules in LHCE is lower than that in HCE, which leads to more FSI– anions but less DME molecules to decompose on the Na metal anode. And the TTE could also decompose on the Na metal anode, which synergistically builds a NaF-rich compact SEI with low surface resistance and good mechanical property so that it is favorable for the transportation of Na+ ions and suppression of the Na dendrite growth. Therefore, the optimized LHCE electrolyte in SMBs exhibits an outstanding electrochemical performance. This study provides an updated perspective on the understanding and design of localized high-concentration electrolytes for SMBs.

Applying Classical, Ab Initio, and Machine-Learning Molecular Dynamics Simulations to the Liquid Electrolyte for Rechargeable Batteries

“…MD results from Piao et al suggest four and five FSI – -coordinated Li + ions accounted for a larger percentage in the diluent-added electrolyte (T3) compared to the original HCEs (D1, D4, and D7) (Figure e) . A lower degree of Na + solvation by DME solvents in the LCE than the HCE was also reported by Wang et al, which leads to more FSI – anions but fewer DME molecules decomposing on Na metal anodes . The above examples demonstrate the wide applicability of LHCEs in various rechargeable batteries.…”

Emerging Era of Electrolyte Solvation Structure and Interfacial Model in Batteries

“…179 Additionally, Xiang et al reported that a NaF-rich SEI was formed on the Na anode surface when TTE was added into 3.8 M NaFSI/DME electrolyte to form an LHCE, as the formed Na + -1DME-2FSI − solvation structure led to the decomposition of more FSI − with less DME decomposition, enabling a high capacity retention of 98.4% after 1046 cycles at 2C in a Na||Na 3 V 2 (PO 4 ) 3 (NVP) cell (Figure 11i). 180 Moreover, Guo et al found that a robust and flexible organic−inorganic SEI layer can be formed in the electrolyte with the low LUMO energy (i.e., 1.0 M KFSI/EC + DEC), where the EC/DEC mixed solvents and FSI are more easily decomposed, enabling fast K + ion diffusion/desolvation for better potassium metal protection and cycling stability (Figure 11j). 166 However, these studies partially emphasize that the good stability of the solvation-structure-derived SEI contributes to the high metal anode performance but fail to take the interfacial behavior of the solvation structure into consideration, which can rationally illustrate the different performances observed in different electrolytes, as interpreted by Ming et al earlier in this section.…”

“…Copyright 2020 Wiley-VCH. Reprinted with permission from ref . Copyright 2021 American Chemical Society.…”

Exploring the Sodium‐Storage Mechanism of Nanosized Disodium Rhodizonate as the Anode Active Material

“…After 90s of Ar + sputtering, the F 1s peak of electrolyte salt/NaPF y /Na x PF y O z completely disappears, but the F 1s peak of NaF can still be observed (Figure b, Supporting Information), further proving that NaF accumulates gradually inside the SEI layer and contributes to its stability and Na + permeability. [ 36 ] The above results clearly show that the practical capacity of nanosized Na 2 C 6 O 6 is close to its theoretical capacity, which means that ≈2 extra Na + are being accommodated into the Na 2 C 6 O 6 in the range of 0.5–1.5 V. The exploration of its energy storage mechanism has not been performed between 0.5 and 1.5 V, so the related ex‐situ XRD patterns were shown in Figures a,b during the first cycle at various potentials versus Na/Na + . The open‐circuit voltage of the pristine nanosized Na 2 C 6 O 6 electrode is ≈2.5 V (stage i).…”