Isotopic Labeling: A Powerful Tool to Investigate Lithium Transport in a Polymer-Ceramic Composite Electrolyte Designed for Solid-State Batteries

Developing safe and high-energy-density batteries is a significant challenge, especially for Li-ion configurations. Using Li-metal as the negative electrode could greatly boost energy density but requires the replacement of liquid electrolytes by solid-state electrolytes (SSEs) to work properly and safely. Nonvolatile SSEs may prevent dendrite growth related to inhomogeneous Li electrodeposition leading to low-capacity retention and potential short circuit. Challenges persist in ensuring close electrode/SSE contact, enhancing ionic conductivities, electrochemical stability at operating temperatures, cycle life, and fast charging capabilities. Here, a composite SSE composed of a dispersion of ionic conductive ceramic particles in a polymer electrolyte matrix is studied to leverage different SSE types. Li + ions migration is investigated at 60 °C with Li-isotopic tracing after applying an electrical field. High-resolution solid-state NMR and orthogonal time-of-flight secondary ion mass spectrometry are employed for characterizing the Li-isotopic relative abundance in the SSE at global and local levels, respectively. By differentiating Li in the polymer phase from ceramic particles, both techniques reveal that Li + ions preferentially diffuse through ceramic dispersion. Surprisingly, electrochemical impedance spectroscopy analyses indicate no enhancement in ionic conductivity between the polymer and composite electrolytes, highlighting the impact of other parameters such as percolation or polymer/ceramic interface properties.