Atomic Layer Deposition of Spinel Lithium Manganese Oxide by Film-Body-Controlled Lithium Incorporation for Thin-Film Lithium-Ion Batteries

Abstract

Lithium manganese oxide spinels are promising candidate materials for thin-film lithium-ion batteries owing to their high voltage, high specific capacity for storage of electrochemical energy, and minimal structural changes during battery operation. Atomic layer deposition (ALD) offers many benefits for preparing all-solidstate thin-film batteries, including excellent conformity and thickness control of the films. Yet, the number of available lithium-containing electrode materials obtained by ALD is limited. In this article, we demonstrate the ALD of lithium manganese oxide, Li x Mn 2 O 4 , from Mn(thd) 3 , Li(thd), and ozone. Films were polycrystalline in their asdeposited state and contained less than 0.5 at. % impurities. The chemical reactions between the lithium precursor and the film were found not to be purely surface-limited but to include a bulk component as well, contrary to what is usually found for ALD processes. In addition, we show a process for using Li(thd)/ozone and LiO t Bu/water treatments to transform ALD-MnO 2 and ALD-V 2 O 5 into Li x Mn 2 O 4 and Li x V 2 O 5 , respectively. The formed Li x Mn 2 O 4 films were characterized electrochemically and found to show high electrochemical capacities and high cycling stabilities.

Metal Fluorides as Lithium-Ion Battery Materials: An Atomic Layer Deposition Perspective

“…The capacity retention was very good up to 550 cycles at 200 µA. Similar to LiMn 2 O 4 , vanadium oxide V 2 O 5 could also be lithiated by pulsing either LiO t Bu and water or Lithd and ozone on top of the oxide film [90]. Using the Lithd and ozone precursors, lithium contents as high as 15 at% were obtained with only 100 cycles of the Li 2 CO 3 process applied on the 200 nm oxide film.…”

“…The lithium manganese spinel process is unique in that while the growth rate of the films stays rather constant at below 0.3 Å/cycle, the lithium content increases very rapidly and reaches a high value with very small Li-subcycle numbers [90]. This indicates that the mechanism of this process differs significantly from conventional ternary ALD processes.…”

“…Lithium manganese spinel Li x Mn 2 O 4 is an interesting cathode material for lithium-ion batteries due to its low volume change during (de)lithiation, high voltage and environmentally benign elements. The material has been deposited by ALD by Miikkulainen et al using various methods [90]. Firstly, Mn(thd) 3 and ozone were used as precursors for manganese oxide and this process was combined with the Lithd + O 3 process for lithium incorporation.…”

“…Therefore, the bulk must be playing a role in the deposition process. Miikkulainen et al postulated that the reduction needed for manganese to change from +IV in MnO 2 to +III/+IV in LiMn 2 O 4 takes place during the Lithd pulse, which affects not only the surface but also deeper parts of the film [90]. The following ozone pulse removes organic residues from the surface and re-oxidizes the topmost manganese ions on the surface.…”

“…Miikkulainen et al continued their studies on LiMn 2 O 4 , using both LiO t Bu and water and Lithd and ozone exposures on MnO 2 at 225 • C [90]. Interestingly, 110 nm of manganese oxide could be converted to the spinel phase with only 100 cycles of the lithium carbonate process applied on top of the film.…”