(266i) Effect of Lithium Salt Dissociation on the Ion Transport Properties in Block Copolymer Electrolytes

Salt-doped polymers are attractive candidates as components of solid electrolytes necessary for development of novel battery designs that are powerful, efficient and cost-effective. The mechanical and electrochemical properties of poly(ethylene oxide) (PEO)-based electrolytes highly depend on the salt concentration. Salt concentration impacts block copolymer and crystallite morphology, as well as PEO chain dynamics and in turn ion transport. Due to the functional dependences of these properties being more complicated at high salt concentration, it is important to understand the relationship between ion dissociation and transport at a fundamental level in order to have accurate estimation and practical design of battery performance. In this study, the effect of salt concentration on the electrochemical and transport properties in block copolymer electrolytes was investigated in terms of dissociation states of the ions. The dissociation of lithium salt was studied by Fourier transform infrared spectroscopy and Raman spectroscopy. Quantitative analysis showed increasing ion pairs with increasing salt concentration. The transport properties were measured by electrochemical and spectroscopic measurements. The ionic conductivity, diffusion coefficient and transference number showed non-monotonic behavior with increasing salt concentration due to increasing non-ideality of concentrated system. The discussion of this study focuses on revealing the relationship between salt dissociation, ionic transport and electrochemical performance of PEO-based block copolymer electrolytes. The observations from this work strongly support the inferences of the correlation of the state and transport of the ions in the polymer electrolytes proposed in numerous previous electrochemical studies.