Effect of annealing atmosphere on LiMn₂O₄ for thin film Li-ion batteries from aqueous chemical solution deposition

Abstract

In this study we demonstrate and explain the direct relationship between precursor chemistry and phase formation of LiMn2O4 powders and thin films from aqueous chemical solution deposition (CSD). The processing conditions applied to transform the precursor into the LiMn2O4 phase are investigated with a focus on the heating atmosphere and temperature. We found that the Mn2+ ions, used as a starting product, already partially oxidize into Mn3+/Mn4+ in the precursor solution. The Mn3+ ions present in the gel or the dried film are extremely sensitive to O-2, leading to fast oxidation towards Mn4+. Here, we suggest that the oxygen, introduced in the precursor solution by the citrate complexing agent, suffices to oxidize the Mn2+ into Mn3+/Mn4+ which is crucial in the formation of phase pure spinet and stoichiometric LiMn2O4. Any additional oxygen, available as O-2 during the final processing, should be avoided as it leads to further oxidation of the remaining Mn3+ into Mn4+ and to the formation of the gamma-Mn2O3 and lambda-MnO2 secondary phases. Based on these insights, the preparation of phase pure, spinet and stoichiometric LiMn2O4 in a N-2 ambient was achieved both in powders and films. Moreover, the study of the precursor chemistry and final annealing leads to the possibility of reducing the final temperature to 450 degrees C, enabling the use of temperature and oxidation sensitive current collectors such as TiN. This inert ambient and low temperature processing of LiMn2O4 provides the opportunity to have large flexibility and compatibility with process conditions for other materials in the thin film battery stack, without undesired oxidations

Synthesis of mesoporous LiMn2O4and LiMn2−xCoxO4thin films using the MASA approach as efficient water oxidation electrocatalysts

“…The water oxidation studies on these LiCoO 2 thin lms also indicate that they exhibit enhanced electrocatalytic performances compared to previous studies. [43][44][45][46][47] Since cobalt is more toxic and less earth-abundant compared to manganese, LiMn 2 O 4 in the form of powder has also been investigated previously. [43][44][45][46][47] Despite the promising electrocatalytic performances of MMLs, little effort has been devoted to investigating their long-term stabilities under real working conditions, e.g.…”

3D LiMn2O4 thin-film electrodes for high rate all solid-state lithium and Li-ion microbatteries

“…In this regard, chemical solution deposition (CSD) of LiMn2O4 thin-films has been explored by the group at University of Hasselt, Belgium. Films of up to ~130nm on planar substrates were fabricated by spin coating from both aqueous and non-aqueous CSD precursor solutions [38][39]. Even though cyclic voltammograms showed electrochemical activity of (at least part of) the films, the capacity of the films nor the rate performance were reported.…”

Economic Manganese-Oxide-Based Anodes for Efficient Water Oxidation: Rapid Synthesis and In Situ Transmission Electron Microscopy Monitoring

“…Annealing of manganese oxides exerts a key effect on all their application options in energy conversion and storage devices. [65][66][67][68][69][70][71] Therefore, insight into the thermal formation and reconstruction pathways of manganese oxides will pave the way to optimize a wide range of their general performance parameters, such as crystallinity, phase purity, true catalyst detection, stability in high-temperature catalysis, etc.…”