A Nuclear Magnetic Resonance Study of Cation and Anion Dynamics in Polymer-Ceramic Composite Solid Electrolytes

Polymer-ceramic composite electrolytes are promising for the application of all-solid-state lithium-ion batteries with high energy density and improved safety. In this work, we employ temperature-dependent 7Li and 19F NMR to examine the chemical environment and the dynamics of Li+ cation and triflate anion in poly(ethylene oxide) (PEO)-lithium triflate (LiTf) polymer electrolyte and a composite electrolyte containing 55 vol % doped lithium aluminum titanium phosphate (LICGC). The line shape analysis and spin-lattice relaxation (T1) measurements suggest both the Li+ cations and the Tf- anions reside in two distinct environment: a mobile environment and an immobile environment. In the semicrystalline state, a large ratio (>70%) of immobile Li+ and Tf- is observed. In the melt state, the ratio of mobile cations and anions significantly increases. With the presence of LICGC ceramic, an increased ratio of immobile Li+ and Tf- and reduced mobility of the mobile components are observed, indicating that the ceramic negatively impacts the transport of both the cations and the anions. NMR characterizations are corroborated by conductivity results, which reveal that the intrinsic ionic conductivity of the polymer phase of the composite electrolyte was only 0.15 of the ceramic-free polymer electrolyte at room temperature. These results shed light on the challenges inherent to composite electrolytes with the goal of achieving both enhanced Li+ transference number and ionic conductivity.