Insight into engineering the LMNO/LLTO/LTO thin-film solid-state micro batteries: structural understandings and electrochemical evaluation

The advancement of all-solid-state thin-film batteries (TFBs) is pivotal for achieving safe, long-lasting, and miniaturized energy storage systems. This study presents the fabrication and characterization of a full thin-film micro battery using LiMn 1.5 Ni 0.5 O 4 (LMNO) as the cathode, Li 0.33 La 0.557 TiO 3 (LLTO) as the solid electrolyte and Li 4 Ti 5 O 12 (LTO) as the anode. All the layers are deposited via RF magnetron sputtering into sandwich type - half cell studies of these followed by a full cell approach. Comprehensive structural and morphological characterizations using X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM) and scanning transmission electron microscopy (STEM) confirmed the phase purity, crystallinity and uniform layer morphology inclusive of thickness of each layer. Half-cell studies carried out on cathode and anode thin film layers indicate their excellent electrochemical properties. LMNO cathode film exhibit stable charge discharge capacity over 500 cycles, demonstrating good capacity retention. Discharge capacity stabilizes at around 2.5 µAh/cm 2 after an initial drop in the first few cycles. The specific capacity of LTO anode layer remains at 6 μAh/cm 2 after 100 cycles, demonstrating high cycling stability which purely depends on the mass loading. At increasing current densities from 10 μA/cm 2 to 50 μA/cm 2 , the specific capacity decreases gradually, reflecting good rate performance and is regained back upon running for 10 μA/cm 2 . LLTO thin film exhibit room temperature conductivity in the order of 1.903 × 10 -3 S/cm. Present study even involves the electrochemical feasibility and performance expectations of the LMNO/LLTO/LTO configuration based on literature reports and experimental observations. This work emphasizes the potential of this full-cell architecture for future integration into micro-scale solid-state battery systems, while also identifying critical challenges related to interface compatibility and electrochemical activation.