Oak Ridge National Laboratory researchers have developed a thin-film, highly conductive solid-state electrolyte made of a polymer and ceramic-based composite for lithium metal batteries.

Solid electrolytes are promising in enabling lithium metal to replace the conventional graphite anode to significantly increase the capacity and energy density of lithium-ion batteries. There are two classes of solid electrolytes, inorganic oxide- or sulfide-based electrolytes and polymer-based electrolytes.

Inorganic electrolytes offer superb ionic conductivities (10^-4 – 10^-2 S/cm) but they suffer from brittleness and lack of processability. Solid polymer electrolytes offer the advantages of flexibility, low-cost processing, and good adhesion to the electrodes, but they typically have low room-temperature ionic conductivity and not sufficient mechanical modulus to stop dendrite growth.

A composite combining inorganic and polymer electrolytes may boast the advantages of each to create a highly conductive, mechanically robust and easily manufacturable solid electrolyte.

—Palmer et al.

The researchers started with a doped-lithium aluminum titanium phosphate ceramic thin film with thickness of ~25 μm formed by aqueous spray coating. The film is partially sintered to form a three-dimensionally interconnected structure with a dense backbone. It is then backfilled with a crosslinkable poly(ethylene oxide) (PEO)-based polymer electrolyte.

A thin film solid-state electrolyte with a three-dimensionally interconnected structure was fabricated by ORNL researchers. The structure increased conductivity through the ceramic base. Credit: Xi Chen/Oak Ridge National Laboratory, US Dept. of Energy

The resulting electrolyte’s novel design, detailed in a paper in the journal Energy Storage Materials, is a three-dimensional interconnected structure that can provide mechanical robustness and high lithium ionic conductivity at room temperature.

The composite has very high ceramic loading of 77 wt% (61 vol%) and an ionic conductivity of 3.5 × 10^-5 S/cm at 20 °C with an activation energy of 0.43 eV. The main ion transport pathway is through the ceramic network, predicted by modelling and verified by experiments. Owing to the interconnected structure of the ceramic, the composite electrolyte exhibits much improved mechanical strength.

We combined the advantages of both materials to form a thin composite film. The film was formed by partially sintering a three-dimensionally interconnected ceramic structure and the polymer filled the pores to make a robust membrane.

—Xi Chen, corresponding author

Resources

• Max J. Palmer, Sergiy Kalnaus, Marm B. Dixit, Andrew S. Westover, Kelsey B. Hatzell, Nancy J. Dudney, X. Chelsea Chen (2020) “A three-dimensional interconnected polymer/ceramic composite as a thin film solid electrolyte,” Energy Storage Materials, Volume 26, Pages 242-249 doi: 10.1016/j.ensm.2019.12.031