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The chemical instability of the traditional electrolyte remains a safety issue in widely used energy storage devices such as Li-ion batteries. Li-ion batteries for use in devices operating at elevated temperatures require thermally stable and non-flammable electrolytes. Ionic liquids (ILs), which are non-flammable, non-volatile, thermally stable molten salts, are an ideal replacement for flammable and low boiling point organic solvent electrolytes currently used today. We herein describe the procedures to: 1) synthesize mono- and di-phosphonium ionic liquids paired with chloride or bis(trifluoromethane)sulfonimide (TFSI) anions; 2) measure the thermal properties and stability of these ionic liquids by differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA); 3) measure the electrochemical properties of the ionic liquids by cyclic voltammetry (CV); 4) prepare electrolytes containing lithium bis(trifluoromethane)sulfonamide; 5) measure the conductivity of the electrolytes as a function of temperature; 6) assemble a coin cell battery with two of the electrolytes along with a Li metal anode and LiCoO2 cathode; and 7) evaluate battery performance at 100 °C. We additionally describe the challenges in execution as well as the insights gained from performing these experiments.

The synthesis and physicochemical properties of a series of non-flammable, thermally stable alkyl ether containing piperidinium ionic liquid electrolytes, containing lithium bis(trifluoromethanesulfonyl)imide, are described along with the superior performance of a lithium-ion supercapacitor containing a piperidinium electrolyte compared to a standard carbonate-based electrolyte at 100 °C. [ABSTRACT FROM AUTHOR]

Given the increased use of room temperature ionic liquid electrolytes in Li-ion batteries, due to their non-flammability and negligible volatility, this study evaluates the lithiation kinetics to understand and improve the rate performance of Li-ion batteries. Lithium titanate spinel is used as a model electrode and the electrolyte is composed of LiTFSI and TFSI-coordinated alkoxy-modified phosphonium ionic liquid. Based on the analysis of activation energies for each process, we report that the charge-transfer reaction at the electrode/electrolyte interface is the rate-limiting step for cell operation. This finding is further supported by the observation that a 50-fold decrease in charge-transfer resistance at higher temperatures leads to a significant performance improvement over that of a traditional organic electrolyte at room temperature. Charge-transfer resistance and electrolyte wetting on the electrode surface are critical processes for optimal battery performance, and such processes need to be included when designing new ionic liquids in order to exceed the power density obtained with the use of current carbonate-based electrolytes. [ABSTRACT FROM AUTHOR]

An ionic polymeric network based on a disulfide diphosphonium ionic liquid and a tetraanion was designed and studied in order to explore two self-assembly strategies: weak covalent bonds and ionic interactions. When the disulfide diphosphonium ionic liquid was complexed with a multianion, a crosslinked network structure was obtained. By applying external stimuli such as temperature or inducing a mild redox reaction, the network could be disrupted. The disruption/formation of the network is reversible. The thermal, rheological and electrochemical properties were also studied to further characterize these materials and to better understand the resulting structure–property relationships. [ABSTRACT FROM AUTHOR]