Operando Raman Gradient Analysis for Temperature-Dependent Electrolyte Characterization

Transport and thermodynamic properties are integral parameters to understand, model, and optimize state-of-the-art and next-generation battery electrolytes. The accurate measurement of these properties is experimentally challenging as well as time- and resource-intensive, and consequently, reports are scarce. Their dependence on temperature is explored even less and is commonly limited to a few temperature points. Recently, we introduced an operando Raman gradient analysis (ORGA) tool to extract transport and thermodynamic properties. Here, we expand the capabilities of ORGA by incorporating a temperature-sensitive external reference into the design. With this enhancement, we are able to visualize the local concentration of any Raman-active species in the electrolyte and detect lithium filament nucleation. We demonstrate and validate this new functionality of ORGA via an examination of lithium bis­(fluorosulfonyl)­imide (LiFSI) in tetraethylene glycol dimethyl ether (G4) as a function of temperature. All transport properties and activation energies are reported, and the effect of temperature is discussed.