Effects of fluorinated solvents on electrolyte solvation structures and electrode/electrolyte interphases for lithium metal batteries

Electrolyte is very critical to the performance of the high-voltage lithium (Li) metal battery (LMB), which is one of the most attractive candidates for the next-generation high-density energy-storage systems. Electrolyte formulation and structure determine the physical properties of the electrolytes and their interfacial chemistries on the electrode surfaces. Localized high-concentration electrolytes (LHCEs) outperform state-of-the-art carbonate electrolytes in many aspects in LMBs due to their unique solvation structures. Types of fluorinated cosolvents used in LHCEs are investigated here in searching for the most suitable diluent for high-concentration electrolytes (HCEs). Nonsolvating solvents (including fluorinated ethers, fluorinated borate, and fluorinated orthoformate) added in HCEs enable the formation of LHCEs with high-concentration solvation structures. However, low-solvating fluorinated carbonate will coordinate with Li+ ions and form a second solvation shell or a pseudo-LHCE which diminishes the benefits of LHCE. In addition, it is evident that the diluent has significant influence on the electrode/electrolyte interphases (EEIs) beyond retaining the high-concentration solvation structures. Diluent molecules surrounding the high-concentration clusters could accelerate or decelerate the anion decomposition through coparticipation of diluent decomposition in the EEI formation. The varied interphase features lead to significantly different battery performance. This study points out the importance of diluents and their synergetic effects with the conductive salt and the solvating solvent in designing LHCEs. These systematic comparisons and fundamental insights into LHCEs using different types of fluorinated solvents can guide further development of advanced electrolytes for high-voltage LMBs.

Solvent Control in Electro-Organic Synthesis

Exploiting the solvent control within electro-organic conversions is a far underestimated parameter in prep-scale electrolysis. The beneficial application in several transformations is outlined and in particular discussed for the dehydrogenative coupling of arenes and heteroarenes. This simple electrolytic strategy in fluorinated solvents allows the modulation of the substrate’s nucleophilicity and the stabilization of the intermediates as well as of the final product from over-oxidation.1 Introduction2 Solvent Effects in Kolbe Electrolysis and Anodic Fluorination3 Unique Solvent Effects of 1,1,1,3,3,3-Hexafluoropropan-2-ol (HFIP)4 Anodic Dehydrogenative Coupling Reactions with Use of HFIP as the Solvent5 Conclusion