MRI Studies of Plastic Crystals

Abstract

Over three decades ago, plastic crystals were proposed as a solid-state alternative to conventional liquid electrolytes. Particular attention has been later drawn to organic ionic plastic crystals (OIPCs) and OIPC-based electrolytes. These ionic solids exhibit crucial characteristics of a safe electrolyte material such as nonflammability, nonvolatility, electrochemical stability, and plasticity. Versatility of ionic pairs available to date and ongoing research on molecular design will provide OIPCs for specific operating conditions within a broad range of electrochemical applications. Single-point ramped imaging with T1 enhancement (SPRITE), an MRI method known for its capability to visualize solids, has played a key role in the discovery of several novel phenomena inherent in OIPCs. This chapter is an overview of these solid-state MRI studies. SPRITE imaging of polycrystalline morphology revealed a striking T2* contrast anisotropy and shed light on molecular dynamics in solid phases of plastic crystals. These observations suggest the possibility of macroscopically anisotropic ion conduction supported by impedance spectroscopy and in situ MRI experiments. MRI studies of operating electrochemical cells have led to a breakthrough in understanding the function of doped plastic crystals. The discovered hybrid solid–liquid property of OIPC electrolytes is the key for their successful commercialization.