Garnet-type Li₇La₃Zr₂O₁₂ solid electrolyte thin films grown by Co₂-laser assisted CVD for all-solid-state batteries

The detailed characterization of garnet-type Li-ion conducting Li₇La₃Zr₂O₁₂ (LLZO) solid electrolyte thin films grown by novel CO2-laser assisted chemical vapor deposition (LA-CVD) is reported. A deposition process parameter study reveals that an optimal combination of deposition temperature and oxygen partial pressure is essential to obtain high quality tetragonal LLZO thin films. The polycrystalline tetragonal LLZO films grown on platinum have a dense and homogeneous microstructure and are free of cracks. A total lithium ion conductivity of 4.2·10−6 S·cm−1 at room temperature, with an activation energy of 0.50 eV, is achieved. This is the highest total lithium ion conductivity value reported for tetragonal LLZO thin films so far, being about one order of magnitude higher than previously reported values for tetragonal LLZO thin films prepared by sputtering and pulsed laser deposition. The results of this study suggest that the tetragonal LLZO thin films grown by LA-CVD are applicable for the use in all-solid-state thin film lithium ion batteries

Introducing a large polar tetragonal distortion into Ba doped BiFeO3 by low temperature fluorination

This article reports on the synthesis and crystallographic and magnetic structure of barium-doped BiFeO3 compounds with approximate composition Bi(1-x)BaxFeO(3-x/2), as well as those of the fluorinated compounds Bi(1-x)BaxFeO(3-x)F(x) (both with x = 0.2, 0.3), prepared by low-temperature fluorination of the oxide precursors using polyvinylidenedifluoride. Whereas the oxide compounds were obtained as cubic (x = 0.2) and slightly tetragonal (x = 0.3, c/a approximate to 1.003) distorted perovskite compounds, a large tetragonal polar distortion was observed for the oxyfluoride compounds (c/a approximate to 1.08 for x = 0.2 and similar to 1.05 for x = 0.3), being isostructural to tetragonal PbTiO3. Although described differently in previous reports on Ba-doped BiFeO3, the observed remanent magnetization is found to agree well with the amount of BaFe12O19 only detectable by neutron diffraction and the well-known magnetic properties of BaFe12O19. The oxyfluoride compounds show G-type antiferromagnetic ordering with magnetic moments lying in the a/b plane

Synthesis, structural characterisation and proton conduction of two new hydrated phases of barium ferrite BaFeO_2.5−x(OH)_2x

Materials exhibiting mixed electronic and proton conductivity are of great interest for applications ranging from electrodes for proton conducting ceramic fuel cells to hydrogen separation membranes. In this work, we report a detailed investigation of the effect of water incorporation in BaFeO2.5 on the structure and conductivity. BaFeO2.5 is shown to be topochemically transformed to two different hydrated modifications, low-water (LW-) and high-water (HW-) BaFeO2.5. A combined analysis of neutron and X-ray diffraction data was used to determine the crystal structure of LW-BaFeO2.5 (BaFeO2.33(OH)0.33), which shows a unique ordering pattern of anion vacancies for perovskite type compounds, with structural relaxations around vacancies being similar to the chemically similar compound BaFeO2.33F0.33. Approximate proton positions were determined using the bond valence method. Conductivity studies of hydrated and pure BaFeO2.5 (with additional comparison to oxidized BaFeO2.5) show a significant enhancement of the conductivity on water incorporation, which can be attributed to proton conductivity. This is the first report of significant grain proton conduction (∼10−6 to 10−7 S cm−1) in an iron based perovskite. Water uptake is further shown to be completely reversible, with reformation of BaFeO2.5 when heating the compound to temperatures above ∼450 K under Ar

Advanced Chemical Vapor Deposition Methods for All-Solid-State, Conversion-Type and 3D Li-Ion Battery Concepts

The newly established CO2-laser assisted chemical vapor deposition (LA-CVD) is applied to research multicomponent Li-ion battery materials, which are very difficult to prepare with conventional CVD precursor delivery systems. The capabilities of LA-CVD to grow functional thin films for application in next generation Li-ion batteries, i.e., all-solid-state, conversion-type, and 3D architecture concepts, are assessed in comparison with aerosol assisted chemical vapor deposition (AA-CVD), which is another advanced precursor delivery method. The growth of high quality, well-performing battery materials is successfully achieved with both CVD techniques. AA-CVD allows for a more precise control over the stoichiometry of the films, exemplified by depositions of LiCoO2, LiCo1-xNixO2, and Li(Ni1/3Mn1/3Co1/3)O2 (NMC) cathodes. But with LA-CVD the microstructure of the films can be tailored between highly dense and porous providing more flexibility towards application. Both CVD processes make conformal coatings of 3D architectures possible with structure sizes down to several 10 μm (AA-CVD) and 1.5 μm (LA-CVD), thus have high potential for coatings in 3D battery concepts. Efforts are made to develop thin films of garnet-type oxide solid electrolytes due to their high Li-ion conductivity paired with a wide electrochemical stability window qualifying them for the use in all-solid-state batteries (ASSBs). It is found that AA-CVD is unsuited for the growth of garnet-type solid electrolytes, whereas LA-CVD is capable of growing garnet-type thin films of composition Li5La3Ta2O12 (LLTaO) and Li7La3Zr2O12 (LLZrO). The result that cubic LLTaO can be stabilized easier than cubic LLZrO via LA-CVD is exploited to study the influence of grain boundaries in fine-grained and coarse-grained LLTaO thin films. Furthermore, the chemical stability between LLTaO and Li on the atomic level is proven experimentally for the first time resolving a recent debate on their interfacial stability. Both CVD methods are well suited for the growth of conversion-type transition metal (TM) oxide anodes. By investigating the kinetics and degradation mechanisms of TM-oxide films (TM = Co, Ni, Mn) a clear correlation between microstructure and performance is found. Higher porosity and smaller structure size lead to increased rate capability and higher specific capacity. Therefore, TM-oxide thin film anodes with nanoparticulate microstructure grown by AA-CVD and LA-CVD bear great potential for application in conversion-type battery concepts. Having accomplished every battery component individually, model experiments on different garnet based ASSBs are pursued. Cycling a thin film battery based on LiCoO2 | LLTaO grown consecutively by LA-CVD failed, however, a hybrid cell with additional liquid electrolyte could be cycled successfully. Moreover, ASSBs combining pelletized LLZrO with a LiCoO2 thin film grown by LA-CVD, with and without interface modification by Nb, can be reversibly cycled at 25 °C with superior performance to the majority of literature reports on garnet based ASSBs. Several of the investigated Li-ion battery materials are grown for the first time via CVD such as thin films of LiNiO2, LiCo1-xNixO2 and NMC cathodes, LLTaO and LLZrO solid electrolytes as well as Ni- and Mn-oxide anodes. Besides, garnet-type LLTaO and LLZrO grown by LA-CVD and NiO grown by AA-CVD show best-in-class performances indicating the high quality of thin films grown by either method. Consequently, this dissertation demonstrates that the use of advanced CVD precursor delivery methods opens up a powerful playground for Li-ion battery applications in terms of material development, fundamental research, and realization of next generation Li-ion battery concepts

Advanced Chemical Vapor Deposition Methods for All-Solid-State, Conversion-Type and 3D Li-Ion Battery Concepts

The newly established CO2-laser assisted chemical vapor deposition (LA-CVD) is applied to research multicomponent Li-ion battery materials, which are very difficult to prepare with conventional CVD precursor delivery systems. The capabilities of LA-CVD to grow functional thin films for application in next generation Li-ion batteries, i.e., all-solid-state, conversion-type, and 3D architecture concepts, are assessed in comparison with aerosol assisted chemical vapor deposition (AA-CVD), which is another advanced precursor delivery method. The growth of high quality, well-performing battery materials is successfully achieved with both CVD techniques. AA-CVD allows for a more precise control over the stoichiometry of the films, exemplified by depositions of LiCoO2, LiCo1-xNixO2, and Li(Ni1/3Mn1/3Co1/3)O2 (NMC) cathodes. But with LA-CVD the microstructure of the films can be tailored between highly dense and porous providing more flexibility towards application. Both CVD processes make conformal coatings of 3D architectures possible with structure sizes down to several 10 μm (AA-CVD) and 1.5 μm (LA-CVD), thus have high potential for coatings in 3D battery concepts. Efforts are made to develop thin films of garnet-type oxide solid electrolytes due to their high Li-ion conductivity paired with a wide electrochemical stability window qualifying them for the use in all-solid-state batteries (ASSBs). It is found that AA-CVD is unsuited for the growth of garnet-type solid electrolytes, whereas LA-CVD is capable of growing garnet-type thin films of composition Li5La3Ta2O12 (LLTaO) and Li7La3Zr2O12 (LLZrO). The result that cubic LLTaO can be stabilized easier than cubic LLZrO via LA-CVD is exploited to study the influence of grain boundaries in fine-grained and coarse-grained LLTaO thin films. Furthermore, the chemical stability between LLTaO and Li on the atomic level is proven experimentally for the first time resolving a recent debate on their interfacial stability. Both CVD methods are well suited for the growth of conversion-type transition metal (TM) oxide anodes. By investigating the kinetics and degradation mechanisms of TM-oxide films (TM = Co, Ni, Mn) a clear correlation between microstructure and performance is found. Higher porosity and smaller structure size lead to increased rate capability and higher specific capacity. Therefore, TM-oxide thin film anodes with nanoparticulate microstructure grown by AA-CVD and LA-CVD bear great potential for application in conversion-type battery concepts. Having accomplished every battery component individually, model experiments on different garnet based ASSBs are pursued. Cycling a thin film battery based on LiCoO2 | LLTaO grown consecutively by LA-CVD failed, however, a hybrid cell with additional liquid electrolyte could be cycled successfully. Moreover, ASSBs combining pelletized LLZrO with a LiCoO2 thin film grown by LA-CVD, with and without interface modification by Nb, can be reversibly cycled at 25 °C with superior performance to the majority of literature reports on garnet based ASSBs. Several of the investigated Li-ion battery materials are grown for the first time via CVD such as thin films of LiNiO2, LiCo1-xNixO2 and NMC cathodes, LLTaO and LLZrO solid electrolytes as well as Ni- and Mn-oxide anodes. Besides, garnet-type LLTaO and LLZrO grown by LA-CVD and NiO grown by AA-CVD show best-in-class performances indicating the high quality of thin films grown by either method. Consequently, this dissertation demonstrates that the use of advanced CVD precursor delivery methods opens up a powerful playground for Li-ion battery applications in terms of material development, fundamental research, and realization of next generation Li-ion battery concepts

Garnet-Type Li 7 La 3 Zr 2 O 12 Solid Electrolyte Thin Films Grown by CO 2 -Laser Assisted CVD for All-Solid-State Batteries

The detailed characterization of garnet-type Li-ion conducting Li7La3Zr2O12 (LLZO) solid electrolyte thin films grown by novel CO2-laser assisted chemical vapor deposition (LA-CVD) is reported. A deposition process parameter study reveals that an optimal combination of deposition temperature and oxygen partial pressure is essential to obtain high quality tetragonal LLZO thin films. The polycrystalline tetragonal LLZO films grown on platinum have a dense and homogeneous microstructure and are free of cracks. A total lithium ion conductivity of 4.2·10−6 S·cm−1 at room temperature, with an activation energy of 0.50 eV, is achieved. This is the highest total lithium ion conductivity value reported for tetragonal LLZO thin films so far, being about one order of magnitude higher than previously reported values for tetragonal LLZO thin films prepared by sputtering and pulsed laser deposition. The results of this study suggest that the tetragonal LLZO thin films grown by LA-CVD are applicable for the use in all-solid-state thin film lithium ion batteries

Evidence of the chemical stability of the garnet-type solid electrolyte Li 5 La 3 Ta 2 O 12 towards lithium by a surface science approach

The chemical stability between Li metal and garnet-type solid electrolytes is currently under debate, mainly catalyzed by theoretical studies. Here, we investigate the stability of Li5La3Ta2O12 (LLTaO) towards lithium experimentally. Using a surface science approach, lithium is stepwise evaporated on an LLTaO thin film grown by CO2-laser assisted chemical vapor deposition. By annealing of the LLTaO thin film, the Li2CO3 surface layer can be removed, leaving only small traces of Li2CO3, Li2O2 and Li2O behind. The interface formation of LLTaO towards lithium is then monitored by means of X-ray and ultraviolet photoelectron spectroscopy. Neither reaction products related to decomposition nor structural changes in the matrix of the Ta-based garnet-type solid-electrolyte can be detected, indicating that LLTaO exhibits chemical stability under equilibrium conditions. Furthermore, a model for the energy level alignment at the LLTaO/Li interface is discussed

On processing-structure-property relations and high ionic conductivity in garnet-type Li 5 La 3 Ta 2 O 12 solid electrolyte thin films grown by CO 2 -laser assisted CVD

This study reports on the optimization of garnet-type Li-ion conducting Li5La3Ta2O12 (LLTaO) solid electrolyte thin film growth by CO2-laser assisted chemical vapor deposition (LA-CVD) and the films' detailed structural as well as electrochemical characterization. By adapting the LA-CVD process parameters, high quality LLTaO films with tailored microstructures are successfully grown, which allows to correlate the films' microstructure and phase composition with their electrochemical performance. Explicitly, the influence of grain boundaries on the ionic conductivity is studied, and possible strategies to lower the grain boundary resistance are given. As deposited LLTaO films show a total ionic conductivity of 7.8·10− 6 S·cm− 1 at 298 K (activation energy of 0.66 eV). By applying a post-annealing treatment the total ionic conductivity is improved up to 3.8·10− 5 S·cm− 1 at 298 K (activation energy of 0.52 eV). This is among the highest ionic conductivities reported for Li-ion conducting garnet-type thin films so far. A better suitability of garnet-type Li5La3Ta2O12 films for fundamental research as well as for application in all-solid-state thin film lithium ion batteries compared to commonly investigated Li7La3Zr2O12 films is proposed and discussed

CO2-Laser Flash Evaporation as Novel CVD Precursor Delivery System for Functional Thin Film Growth

A novel approach for functional thin film deposition using laser flash evaporation as the precursor delivery system is reported. In this newly established CO2-laser-assisted (LA)CVD, solid precursors with low volatility are non-selectively sublimated by absorption of infrared laser radiation. Thus, the method allows for the highly controlled growth of multicomponent thin films with desired composition and stoichiometry over the entire growth period. Thin film microstructural features, such as the morphology, density, and thickness of the films can be adjusted by tuning the process parameters. These features, characterized by means of scanning electron microscopy (SEM), X-ray diffraction (XRD), and Raman spectroscopy (RS), are discussed for LiCoO2 thin films. Additional analyses include X-ray photoelectron spectroscopy (XPS), inductively coupled plasma optical emission spectrometry (ICP-OES), cyclic voltammetry (CV), and galvanostatic cycling