(594a) Evaluating Performance of PYR13FSI As an Electrolyte with Lifsi Salt

One of the principal components of battery systems is the electrolyte. The electrolyte passes current through ions between the two electrodes. Important characteristics of the electrolyte include its conductivity and stability. The conductivity of the electrolyte determines the ohmic loss of a cell where higher conductivity leads to lower losses. The cathodic stability of the electrolyte determines the composition and thickness of a layer that forms on the negative electrode surface because of side reactions between the active material and the electrolyte. This layer is called the solid electrolyte interphase or SEI. The formation of an SEI layer leads to capacity fade in the cell because of the loss of active material. However, the formation of a stable SEI layer is essential to preventing continuous capacity fade in a cell. The SEI layer, when formed, reduces the rate of further side reactions while ideally still allowing ions to pass.

Recently, ionic liquids have been explored as a possible new electrolyte. Ionic liquids have shown promise in increasing stability of conventional battery systems. Ionic liquids are considered a safer, more environmentally friendly solution than current conventional electrolytes. N-Propyl-N-Methylpyrrolidinium bis(fluorosulfonyl)imide (PYR13FSI) has been identified among ionic liquids as showing promise for performing well as an electrolyte. LiFePO₄cells using LiTFSI and LiFSI salts in PYR13FSI have been cycled. The cycling behaviors along with postmortem SEM images of electrode surfaces are compared. Mixtures of this ionic liquid electrolyte with a conventional electrolyte (EC:DEC) have also been examined.