Pulsed Laser Deposition and Characterization of Heteroepitaxial LiMn₂O₄/La_0.5Sr_0.5CoO₃ Bilayer Thin Films as Model Lithium Ion Battery Cathodes

Abstract

Epitaxial LiMn 2 O 4 (LMO)/La 0.5 Sr 0.5 CoO 3 (LSCO) bilayer thin films were grown on single crystalline SrTiO 3 (STO) (111) substrates as model lithium ion battery cathodes. The LSCO layer was used as an electrically conducting buffer layer for electrochemical testing. The LMO and LSCO layers were both epitaxial, with sub-nano flat LMO/LSCO interfaces as seen by X-ray diffraction, synchrotron X-ray scattering, and high-resolution transmission electron microscopy (HRTEM), but with a large LMO surface roughness due to the relatively large lattice mismatch with LSCO. Threedimensional islands and depressions were formed on the strain-relaxed LMO layer, and misfit dislocations at the LMO/LSCO interface were discerned through HRTEM imaging, suggesting a Stranski−Krastanov (SK) mode thin-film growth. A crystalline structural change from cubic spinel at the LMO surface and interior to tetragonal oxygen-deficient LMO at the LMO/LSCO interface was examined. Electrochemical tests along with in situ synchrotron X-ray scattering measurements on the epitaxial LMO/LSCO bilayers showed a significant loss of capacity after the first cycle, which was attributed to an electrical conductivity loss of the LSCO buffer layer due to irreversible lattice oxygen loss.

Strain-induced structure and oxygen transport interactions in epitaxial La0.6Sr0.4CoO3−δ thin films

“…From the GPA measurements we calculate the distribution of the projected unit cell area d (100)⊥ × d (001)∥ (Fig. 7e, black curve), which is compared to the expected projected area, calculated on the base of the simple Poisson model (the Poisson coefficient for LSCO film υ is about 0.3 34,35 ). As is seen from the comparison of the black and red curves in Fig.…”

Pulsed Laser Deposited Films for Microbatteries

“…Studies of the structure and electrochemical reactivity of heteroepitaxial LiMn2O4/La0.5Sr0.5CoO3 (LMO/LSCO) bilayer thin films deposited on crystalline SrTiO3 substrates show that LSCO reduced the lattice misfit strain with the substrate and favored a lower LMO surface roughness. However, a decrease of the electrical conductivity occurred during the electrochemical test (after first cycle) due to the lattice oxygen loss at the outermost layer (40 nm) [139]. Tang et al reported a comparative investigation of the structures, morphologies, and properties of Li insertion for LMO films with different crystallizations.…”

“…Epitaxial LiMn 2 O 4 /La 0.5 Sr 0.5 CoO 3 (LMO/LSCO) bilayer thin films with sub-nano flat interfaces were deposited on (111)-oriented STO substrates at T s = 650 • C in P O 2 = 4 Pa. After the first charge-discharge cycle, the decrease of the electrical conductivity of the LSCO buffer layer due to lattice oxygen loss induced capacity fading [139]. The PLD growth of a multilayer LMO thin film electrode demonstrated the compensation of lithium loss during deposition [160].…”

Dynamic impedance spectroscopy of LiMn2O4 thin films made by multi-layer pulsed laser deposition

“…Recently, the interest in thin film batteries for micro devices has pushed researchers to investigate and develop thin film cathode and anode materials with desirable features such as cost effectiveness, environment-friendly, high energy density, high power density and high rate capability [1,2,3,4,5,6]. LiMn 2 O 4 has been reported by several research groups as a promising cathode material for thin film batteries as it possesses most of the above listed properties.…”

“…LiMn 2 O 4 has been reported by several research groups as a promising cathode material for thin film batteries as it possesses most of the above listed properties. In addition to that, LiMn 2 O 4 thin films have other advantages such as the ability of improving the electrochemical performances by controlling the phase and micro-structure of the thin films through the adaptation of deposition parameters, such as temperature, background pressure, target-tosubstrate distance and the substrate itself [5,7,8,9,10,11,12,13,14,15]. LiMn 2 O 4 thin films have also been reported to overcome the challenges associated with powder LiMn 2 O 4 such as instability due to manganese dissolution [1,16,17] making them an attractive candidate as a cathode material.…”