Isomeric Li–La–Zr–O Amorphous–Crystalline Composite Thin-Film Electrolytes for All-Solid-State Lithium Batteries

Amorphous Li–La–Zr–O (LLZO) solid-state electrolyte thin films are promising alternatives to the well-established lithium phosphorus oxynitride (LiPON) electrolyte for all-solid-state lithium batteries due to their potentially higher Li-ion conductivity and stability. Herein, the enhancement methodology in the ionic conductivity of amorphous LLZO-based thin films is investigated. By doping with Ta, the conductivity of the amorphous LLZO film at 30 °C (3.9 × 10–7 S cm–1) can be enhanced by up to an order of magnitude (2.6 × 10–6 S cm–1), ascribed to tuning Li conduction in local near-order LLZO nanodomains. On that basis, an isomeric Li–La–Zr–Ta–O (LLZTO) amorphous–crystalline composite thin film is prepared via incorporating cubic LLZTO particles into the amorphous LLZTO matrix. The composite film with 10 wt % cubic LLZTO filler can further achieve an ionic conductivity of 0.8 × 10–5 S cm–1 at 30 °C, which is comparable to the best values obtained for the state-of-art LLZO-based thin films. Li transport through the well-connected cubic LLZTO filler network and along the interfaces between the crystallites and the amorphous matrix in the LLZTO composite thin film may offer fast and long-range Li-conduction pathways, which supplement the ionic conduction in the amorphous matrix with short-range-ordered and long-range-disordered structures.