(146b) Transport and Dynamics of Ionic Species in Block Copolymer Electrolytes for Solid-State Lithium Batteries

Solvent-free block copolymer electrolytes are promising materials for solid-state lithium batteries, as their tunable compositions and nanoscale morphologies enable simultaneous control of their ionic conductivities and mechanical properties. However, quantifying and distinguishing the transport and dynamics of the different ionic species can be challenging, which are linked to the complex hierarchy of motional processes of the polymer chains. We measured ion transport properties and dynamics with solid-state nuclear magnetic resonance (NMR) spectroscopy in different poly(ethylene oxide) (PEO)-based polymer electrolytes containing lithium bis(trifluoromethane)sulfonomide (LiTFSI), including neutral and anionic triblock copolymers and their homopolymer analogue. The diffusion coefficients of the Li⁺ and TFSI^- ions, apparent diffusional activation energies, ion transport numbers, and tortuosity factors were established quantitatively by ⁷Li and ¹⁹F pulsed-field-gradient (PFG) NMR measurements, which are compared with results from electrical conductivity measurements. Characteristic correlation times of motion were extracted from ⁷Li and ¹⁹F NMR relaxometry, yielding insights into ion dynamics over nanosecond timescales. In situ ⁷Li NMR imaging measurements of symmetric lithium metal-polymer electrolyte cells yield insight into the growth and inhibition of lithium dendritic structures through the different polymer electrolytes. The results are expected to aid the rational design of new block copolymer electrolytes with controllable ion transport and mechanical properties.