The development of a weakly coordinating anion/cation-based electrolyte for high energy density for storage applications is advantageous for investigation of electrode processes in low-polarity organic solvents. The improvement arises from the optimization of both ionic conductivity and solubility of ion-pair formed between a substituted tetraarylphosphonium (TAPR) cation and tetrakis-fluoroarylborate (TFAB), a weakly coordinating anion. The chemical “push-pull” between cation and anion afforded a highly conducting ion-pair in low-polarity solvents such as tetrahydrofuran (THF) and dichloromethane (DCM). The limiting conductivity value of the salt, namely tetra-p-methoxy-phenylphosphonium - tetrakis(pentafluorophenyl)borate or TAPR/TFAB (R = p-OCH3) is in the range of lithium hexafluorophosphate (LiPF6), the electrolyte of choice in lithium-ion batteries (LIBs). This TAPR/TFAB salt can, potentially, improve the efficiency and stability of batteries over the existing and commonly used electrolytes by optimizing conductivity tailored to the redox active molecules. Lithium hexafluorophosphate (LiPF6) is unstable with high voltage electrodes that are needed in order to achieve greater energy density. In contrast, the TAPR/TFAB (R = p-OCH3) salt proposed herein is stable, and has a good solubility profile in low-polarity solvents given its relatively great size. And it constitutes a low-cost supporting electrolyte with improved performance and capable of bringing non-aqueous energy storage devices to compete with existing technologies.

Synthesis, crystal structure, and conductivity of a weakly coordinating anion/cation salt for electrolyte application in next generation batteries

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