The increasing interest in both portable electronic devices and electric vehicles has given rise to a new wave of research into lithium-ion batteries. Lithium-ion batteries are the technology of choice for these applications, as they offer both high power and high energy densities. However, much research on this subject is still needed to answer the technology demands of future applications. For example, the safety concerns related to liquid electrolytes in the batteries of electric vehicles could be resolved by moving to all-solid-state batteries, which would not combust in the case of an accident. In addition, all-solid-state batteries could be manufactured into 3D structures, which would decrease the footprint area of the battery without sacrificing the amount of material. Thus, these structures would make even higher energy densities possible, which is important for example for laptops and cellphones. In addition, by combining smaller batteries with energy harvesters, such as solar cells, integrated autonomous devices could be realized. Atomic layer deposition, or ALD, is a thin film deposition method based on sequential, saturative reactions of gaseous precursors with a substrate surface. ALD generally produces highly pure films with very good thickness uniformity also in difficult, 3D substrates. Therefore, ALD should be well-suited for the deposition of Li-ion battery materials for future applications. The deposition of lithium containing materials is a fairly new avenue for ALD, the first paper being published only in 2009. It has been found that the Li-ion often bends the basic rules of ALD with its high reactivity and mobility during film growth, resulting in both unexpected reactions and film stoichiometries. This thesis provides a comprehensive review on the atomic layer deposition of lithium containing materials with a focus on the behavior of lithium in the growth process. In the experimental part, new ALD processes were developed for potential Li-ion battery materials LiF and AlF3. Both processes show reasonable ALD characteristics and produce pure films in proper deposition temperatures. In addition, conversion reactions taking place in ALD conditions were studied, and both LiF and Li3AlF6 were deposited using these reactions. The conversions were very clean, illustrated by the low impurity contents of the converted films. Lastly, the deposition of lithium containing ternary oxides was studied by heating atomic layer deposited film stacks in air. This ALD-solid state reaction -procedure resulted in pure, crystalline films of LiTaO3, LiNbO3 and Li2TiO3.
|Publication status||Published - 2017|
|MoE publication type||G5 Doctoral dissertation (article)|
- atomic layer deposition
- lithium-ion batteries
- battery development