Cyclic Carbonate-Based, Single-Ion Conducting Polymer Electrolytes for Li-Ion Batteries: Electrolyte Design

Abstract

Solid polymer electrolytes (SPEs) have been the focus of study to address Li-ion battery issues including thermal runaway by mitigating the danger from volatile solvents. A single ion conductor has a high transference number which eliminates uncontrolled mass transport by immobilizing the anion to the polymer matrix. Problems with undesired side reactions and lithium dendrite growth can also be improved by providing a mechanical barrier. Unfortunately, single-ion conducting SPEs suffer from poor lithium-ion mobility and conductivity due to the immobilized nature of the anions, poor ion-pair dissociation, and the slower time scale diffusion in a polymer matrix compared to liquid electrolytes.In this study, cyclic carbonate-based polymer electrolytes were synthesized to mimic the beneficial properties of conventional carbonate-based liquid electrolytes, such as high level of ion dissociation and solid electrolyte interphase (SEI) formation. A series of copolymers were synthesized varying the structure and composition of the anionic monomer and polar cyclic carbonate containing monomer. The tertiary hydrogen on these carbonate monomers can act as a crosslinking point in free radical polymerizations or UV curing processes to provide robust mechanical properties to the SPEs at elevated temperatures. Although the inherent conductivities of the single-ion SPEs are on the order of 10-7 mS/cm, the addition of plasticizers can improve these conductivities to 0.1 mS/cm.