Lithium metal batteries represent a promising technology in the field of next-generation energy storage, but their cycle life is still short due to the formation of lithium dendrites and the cracking of the cathode. Fluorinated solvents can improve battery life by increasing the LiF content in the solid electrolyte interface, however, the high cost and environmental concerns of fluorinated solvents limit the viability of batteries.
Recently, Professor Wang Chunsheng of the University of Maryland designed a series of fluorine-free solvents through the methylation of 1,2-dimethoxyethane, which can promote the formation of inorganic LiF-rich interfaces through anion reduction and achieve high oxidation stability. Anion-derived LiF interfaces have been shown to inhibit lithium dendrite growth on the lithium anode and minimize cathode cracking at high pressure. In addition, this work investigated the Li+-solvent structure by in-situ techniques and simulations, and derived the correlation between interfacial composition and electrochemical performance. Overall, methylation strategies provide an alternative path to the development of high-pressure electrolytes for electrolyte engineering while reducing reliance on expensive fluorinated solvents.
Key Points of the Article:
1. This work evaluates a range of solvents by selectively methylating DME-α-H atoms to modulate the solvation capacity, ion transport, Li+ desolvation rate, and electrochemical stability of molecules.
2. The authors demonstrated the solvation structure of the 2.0 M LiFSI-DEP electrolyte with a predominantly aggregate structure by in-situ Raman spectroscopy, one-dimensional multinuclear and two-dimensional heteronuclear NMR spectroscopy, and molecular dynamics simulations.
3. A single-salt, single-solvent 2.0 M LiFSI/1,2-diethoxypropane (DEP) electrolyte was found to result in approximately 99.7% CE deposition/stripping of lithium. When paired with a high-pressure NCA cathode, the electrolyte also achieves a high cycle CE of 99.8% and maintains 80% capacity after 600 cycles. In addition, 100 mAh Li||, with 5 g of AhE−1 lean electrolyte (4.0 mAh cm−2, N/P = 1). NCA (4.0 mAh cm−2, N/P = 1) pouch cells retain 95% capacity after 150 cycles.
Finally, the 2.0 M LiFSI/DEP electrolyte makes an anode-free Cu||The NCA (4.0 mAh cm−2, N/P = 0) coin cell achieved a record 250 cycles.
4. The methylation scheme proposed in this work provides a design strategy for lithium metal batteries that stabilizes both the lithium metal anode and NCA cathode without sacrificing ionic conductivity, increasing cost, or causing environmental concerns
Fig.1 Methylation of DME molecules to improve electrochemical performance
Fig.2. Electrochemical performance of 2.0M LiFSI electrolyte using different solvents
Figure 3: Molecular dynamics study
Fig.4 Full battery performance
Original link:
https://doi.org/10.1038/s41557-024-01497-x
Source: Frontiers of Polymer Science