The chemical evolution of solid electrolyte interface in sodium metal batteries

Abstract

The solid electrolyte interface (SEI) formed on the anode is one of the key factors that determine the life span of sodium metal batteries (SMBs). However, the continuous evolution of SEI during charging/discharging processes complicates the fundamental understanding of its chemistry and structure. In this work, we studied the underlying mechanisms of the protection effect offered by the SEI derived from sodium difluoro(oxalato)borate (NaDFOB). In situ nuclear magnetic resonance (NMR) shows that the prior reduction of DFOB anion contributes to the SEI formation, and it suppresses the decomposition of carbonate solvents. Depth-profiling x-ray photoelectron spectroscopy and high-resolution solid-state NMR reveal that the DFOB anion is gradually turned into borate and fluoride-rich SEI with cycling. The protection effect of SEI reaches the optimum at 50 cycles, which triples the life span of SMB. The detailed investigations provide valuable guidelines for the SEI engineering.

Rational design and regulation of tremella-like selenium-doped MoS2 for highly reversible sodium storage

“…MoS 1.5 Se 0.5 @C delivers initial discharge and charge capacities of 780.7 and 603.5 mA h g −1 with 77.3% initial coulombic efficiency (ICE), which is the best among MoS 2 @C (598.8/316.1 mA h g −1 , 52.8%), MoS 1.8 Se 0.2 (670.0/402.6 mA h g −1 , 60.1%), MoS 1.5 Se 0.5 (662.3/438.5 mA h g −1 , 66.2%), MoSSe (677.2/423.2 mA h g −1 , 62.5%), MoS 1.8 Se 0.2 @C (776.4/537.2 mA h g −1 , 69.2%) and MoSSe@C (689.9/487.1 mA h g −1 , 70.6%). The irreversible capacity loss for the rst cycle is due to the formation of a solidliquid interface SEI layer, 34,35 while the enhanced ICE of 77.3% for MoS 1.5 Se 0.5 @C is due to improved stability resulting from carbon coating and an appropriate amount of Se doping. In order to investigate the inuence of different amounts of Se doping and carbon coating on electrochemical performance, the sodium storage performance of all samples was evaluated from their rate performance (Fig.…”

High-Ionicity Electrolytes Based on Bulky Fluoroborate Anions for Stable Na-Metal Cycling

“…Alternatives include borates, of which sodium difluoro(oxalato)borate (NaDFOB) has demonstrated stable and prolonged cycling owing to the borate-and fluoride-rich SEI formation on the Na-metal electrode. 24 Monitoring Na symmetric cells containing NaDFOB/EC:DMC via in situ nuclear magnetic resonance (NMR) spectroscopy demonstrated a decline in 11 B and 19 F NMR signals, indicating that [DFOB] − is preferentially consumed to form a B-and F-rich SEI, enabling stable Na cycling over 150 cycles. In contrast, cell cycling with conventional NaPF 6 /EC:DMC measured declining signals for both 19 F and 1 H NMR, indicating concurrent anion and solvent decomposition, resulting in a cell shortcircuit after 100 cycles.…”

“…Thus, NaPF 6 and NaFSI provide valid electrochemical benchmarks; however, the search for alternative salts with improved safety, stability, performance, and cost is still ongoing. Alternatives include borates, of which sodium difluoro­(oxalato)­borate (NaDFOB) has demonstrated stable and prolonged cycling owing to the borate- and fluoride-rich SEI formation on the Na-metal electrode . Monitoring Na symmetric cells containing NaDFOB/EC:DMC via in situ nuclear magnetic resonance (NMR) spectroscopy demonstrated a decline in 11 B and 19 F NMR signals, indicating that [DFOB] − is preferentially consumed to form a B- and F-rich SEI, enabling stable Na cycling over 150 cycles.…”

Exploring ionic liquid-laden metal-organic framework composite materials as hybrid electrolytes in metal (ion) batteries

“…In addition to complying with thermal stability in a wide range of operating temperatures (it should not be forgotten that the battery in its natural operation emits heat) ( Xu and He, 2014 ) and a high level of ion transport, it must be mechanically robust enough to prevent the growth of dendrites, but also flexible enough not to crack during handling processes ( Takada, 2018 ). Furthermore, two of the main challenges related to the implementation of SSEs are their low ionic conductivity ( Yang and Wu, 2022 ) and the formation of an inefficient electrode-electrolyte interface ( Chen et al, 2020 ; Gao et al, 2022 ). The function of the electrolyte is to build a channel that enables the movement of metallic ions between the anode and cathode during charge and discharge cycles.…”