Atomic Layer Deposition and Lithium-ion Batteries : Studies on new materials and reactions for battery development

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.Litiumioniakkuja käytetään runsaasti niin kulutuselektroniikassa (puhelimet, kannettavat tietokoneet ym.) kuin hybridi- ja sähköautoissakin. Litiumioniakut ovat valikoituneet näihin käyttökohteisiin korkeiden energia- ja tehotiheyksiensä ansiosta. Tulevaisuus tuo kuitenkin mukanaan yhä suurempia haasteita nykyisille akkuteknologioille: litiumioniakkujen nestemäisten elektrolyyttien turvallisuus on puhuttanut viime aikoina, minkä vuoksi uusia, kiinteitä epäorgaanisia elektrolyyttimateriaaleja etsitään aktiivisesti. Toisaalta uudet teknologiat vaativat yhä tehokkaampia akkuja, joten akkujen koko tulee pienenemään ja erilaiset 3D-rakenteet yleistymään. Kiinteät elektrolyyttimateriaalit ovat tärkeä osa näitä tulevaisuuden 3D-akkurakenteita. Atomikerroskasvatus eli ALD on ohutkalvojen kaasufaasikasvatusmenetelmä, jossa kaasumaiset lähdeaineet reagoivat pinnan kanssa yksi kerrallaan. Pulssittamalla pinnalle eri lähdeaineita voidaan valmistaa hyvinkin monimutkaisia kalvomateriaaleja. Atomikerroskasvatukselle on ominaista, että kalvo kasvaa erittäin toistettavasti ja tasaisesti kaikille pinnoille, joten ALD soveltuu erityisen hyvin haastavien 3D-rakenteiden pinnoittamiseen. Tämän vuoksi atomikerroskasvatus on yksi lupaavimmista menetelmistä uusien litiumioniakkumateriaalien valmistamiseen. Litiumia sisältävien materiaalien kasvattamista ALD:llä on tutkittu vasta suhteellisen lyhyen aikaa, sillä ensimmäinen aihetta käsittelevä tutkimusartikkeli julkaistiin vasta 2009. Viimeisen vuosikymmenen aikana on käynyt selväksi, että litiumionit voivat reagoida yllättävillä tavoilla ALD-kasvatusolosuhteissa. Tästä huolimatta useita potentiaalisia litiumioniakkumateriaaleja on jo kyetty valmistamaan atomikerroskasvatusta hyödyntäen. Tämän väitöskirjan kirjallisuusosuudessa on käsitelty litiumia sisältävien ohutkalvomateriaalien kasvatusta ALD-menetelmällä. Erityisenä kiinnostuksen kohteena on ollut litiumin käyttäytyminen kasvatuksen aikana. Työn kokeellisessa osassa kehitettiin uudet ALD-prosessit LiF- ja AlF3-ohutkalvojen valmistamiseksi. Molemmat prosessit tuottavat toistettavasti puhtaita ohutkalvoja. Väitöskirjatyössä tutkittiin myös litiumin vaihtoreaktioita ALD-olosuhteissa, mikä tuotti uudet prosessit LiF- ja Li3AlF6-kalvojen kasvattamiseen. Lisäksi LiTaO3-, LiNbO3- ja Li2TiO3-ohutkalvoja valmistettiin yhdistämällä ALD:tä ja kiinteän tilan reaktioita: kuumentamalla ALD-ohutkalvoja ilmassa voitiin tuottaa puhtaita, kiteisiä kalvoja

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

Lithium-ion batteries are the enabling technology for a variety of modern day devices, including cell phones, laptops and electric vehicles. To answer the energy and voltage demands of future applications, further materials engineering of the battery components is necessary. To that end, metal fluorides could provide interesting new conversion cathode and solid electrolyte materials for future batteries. To be applicable in thin film batteries, metal fluorides should be deposited with a method providing a high level of control over uniformity and conformality on various substrate materials and geometries. Atomic layer deposition (ALD), a method widely used in microelectronics, offers unrivalled film uniformity and conformality, in conjunction with strict control of film composition. In this review, the basics of lithium-ion batteries are shortly introduced, followed by a discussion of metal fluorides as potential lithium-ion battery materials. The basics of ALD are then covered, followed by a review of some conventional lithium-ion battery materials that have been deposited by ALD. Finally, metal fluoride ALD processes reported in the literature are comprehensively reviewed. It is clear that more research on the ALD of fluorides is needed, especially transition metal fluorides, to expand the number of potential battery materials available.Peer reviewe

Atomic layer deposition of GdF3 thin films

doi: 10.1116/6.0001629Gadolinium fluoride is an attractive optical material with applications in, e.g., deep-UV lithography, solar cells, and medical imaging. Despite the interest toward this material, no atomic layer deposition (ALD) process has been published. In this article, an ALD process for GdF3 using Gd(thd)(3) and NH4F as precursors is presented. The deposition was studied at temperatures 275-375 & DEG;C, but 285-375 & DEG;C produce the purest films. The saturation of the growth per cycle (GPC) with respect to precursor pulses and purges was proved at 300 & DEG;C. The GPC value at this temperature is & SIM;0.26 & ANGS;, and the deposition temperature has very little effect on the GPC. According to x-ray diffraction, all the films consist of orthorhombic GdF3. The impurity contents, evaluated by time-of-flight elastic recoil detection analysis, is low, and the films are close to stoichiometric. The nitrogen content is less than < 0.04 at. %. The antireflection properties were qualitatively evaluated by UV-vis spectrometry in a transmission mode at a 190-1100 nm range: on sapphire substrates, GdF3 serves as an antireflective coating. Dielectric properties of the films were studied, and for example, a permittivity value of 9.3 was measured for a & SIM;64 nm film deposited at 300 & DEG;C.Peer reviewe

Studies on Li3AlF6 thin film deposition utilizing conversion reactions of thin films

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Studies on solid state reactions of atomic layer deposited thin films of lithium carbonate with hafnia and zirconia

In this paper, results on the solid state reactions of atomic layer deposited Li2CO3 with HfO2 and ZrO2 are reported. An Li2CO3 film was deposited on top of hafnia and zirconia, and the stacks were annealed at various temperatures in air to remove the carbonate and facilitate lithium diffusion into the oxides. It was found that Li+ ions are mobile in hafnia and zirconia at high temperatures, diffusing to the film-substrate interface and forming silicates with the Si substrate during heating. Based on grazing incidence x-ray diffraction experiments, no changes in the oxide phases take place during this process. Field emission scanning electron microscopy images reveal that some surface defects are formed on the transition metal oxide surfaces during lithium diffusion. The authors also show that lithium can diffuse through hafnia and react with a potential lithiumion battery electrode material TiO2 residing below the HfO2 layer, forming Li2TiO3. Published by the AVS.Peer reviewe

Understanding the Stabilizing Effects of Nanoscale Metal Oxide and Li–Metal Oxide Coatings on Lithium-Ion Battery Positive Electrode Materials

Nickel-rich layered oxides, such as LiNi0.6Co0.2Mn0.2O2 (NMC622), are high-capacity electrode materials for lithium-ion batteries. However, this material faces issues, such as poor durability at high cut-off voltages (>4.4 V vs Li/Li+), which mainly originate from an unstable electrode-electrolyte interface. To reduce the side reactions at the interfacial zone and increase the structural stability of the NMC622 materials, nanoscale (Peer reviewe

Atomic layer deposition of CoF2, NiF2 and HoF3 thin films

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Atomic Layer Deposition of ScF3 and ScxAl yFz Thin Films

In this paper, we present an ALD process for ScF3 using Sc(thd)(3) and NH4F as precursors. This is the first material made by ALD that has a negative thermal expansion over a wide-temperature range. Crystalline films were obtained at the deposition temperatures of 250-375 degrees C, with a growth per cycle (GPC) increasing along the deposition temperature from 0.16 to 0.23 & Aring;. Saturation of the GPC with respect to precursor pulses and purges was studied at 300 degrees C. Saturation was achieved with Sc(thd)(3), whereas soft saturation was achieved with NH4F. The thickness of the films grows linearly with the number of applied ALD cycles. The F/Sc ratio is 2.9:3.1 as measured by ToF-ERDA. The main impurity is hydrogen with a maximum content of 3.0 at %. Also carbon and oxygen impurities were found in the films with maximum contents of 0.5 and 1.6 at %. The ScF3 process was also combined with an ALD AlF3 process to deposit ScxAlyFz films. In the AlF3 process, AlCl3 and NH4F were used as precursors. It was possible to modify the thermal expansion properties of ScF3 by Al3+ addition. The ScF3 films shrink upon annealing, whereas the ScxAlyFz films show thermal expansion, as measured with HTXRD. The thermal expansion becomes more pronounced as the Al content in the film is increased.Peer reviewe