Isotopic Labeling:\nA Powerful Tool to Investigate\nLithium Transport in a Polymer-Ceramic Composite Electrolyte Designed\nfor Solid-State Batteries

Developing safe and high-energy-density batteries is\na significant\nchallenge, especially for Li-ion configurations. Using Li-metal as\nthe negative electrode could greatly boost energy density but requires\nthe replacement of liquid electrolytes by solid-state electrolytes\n(SSEs) to work properly and safely. Nonvolatile SSEs may prevent dendrite\ngrowth related to inhomogeneous Li electrodeposition leading to low-capacity\nretention and potential short circuit. Challenges persist in ensuring\nclose electrode/SSE contact, enhancing ionic conductivities, electrochemical\nstability at operating temperatures, cycle life, and fast charging\ncapabilities. Here, a composite SSE composed of a dispersion of ionic\nconductive ceramic particles in a polymer electrolyte matrix is studied\nto leverage different SSE types. Li<sup>+</sup> ions migration is\ninvestigated at 60 °C with Li-isotopic tracing\nafter applying an electrical field. High-resolution solid-state NMR\nand orthogonal time-of-flight secondary ion mass spectrometry are\nemployed for characterizing the Li-isotopic relative abundance in\nthe SSE at global and local levels, respectively. By differentiating\nLi in the polymer phase from ceramic particles, both techniques reveal\nthat Li<sup>+</sup>ions preferentially diffuse through ceramic dispersion.\nSurprisingly, electrochemical impedance spectroscopy analyses indicate\nno enhancement in ionic conductivity between the polymer and composite\nelectrolytes, highlighting the impact of other parameters such as\npercolation or polymer/ceramic interface properties.