Lithium metal batteries have the potential to enhance the energy and power density of commercial rechargeable batteries. A lithium metal anode may increase the energy density by 30% relative to current lithium-ion battery technologies. The promise of these improvements hinges on a successful solid electrolyte that is thin (< 30 μm).

Inorganic ceramic electrolytes can offer reasonable ionic conductivities but are typically bottlenecked by intensive processing. Solid polymer electrolytes offer the advantages of flexibility, low-cost processing, and a greater adhesion to the electrodes than a ceramic. The biggest drawback to solid polymer electrolytes is their low ionic conductivity. A composite electrolyte consisting of a hard ceramic phase and a processible polymer phase aims to utilize the advantages of each as a solution for solid-state electrolytes.

Here we introduce an approach to fabricate a solid composite electrolyte film that is thin, highly ionically conductive, and mechanically robust with good manufacturability. Without the use of plasticizers, our composite film has an ionic conductivity of approximately 1.0 × 10^-4 S/cm at 30°C with an activation energy of ca. 0.44 eV. The high conductivity was achieved by creating a 3D, interconnected structure of the ceramic with greatly reduced interparticle resistance. Ion conduction path in the composite electrolyte is investigated by finite element analysis.

Acknowledgements: This research at Oak Ridge National Laboratory, managed by UT Battelle, LLC, for the U.S. Department of Energy (DOE), under contract DE-AC05-00OR22725, was primarily sponsored by the Office of Energy Efficiency and Renewable Energy for the Vehicle Technologies Office’s Advanced Battery Materials Research program and partially sponsored by the Laboratory Directed Research and Development Program (LDRD) of ORNL.