ICMCTF2011 Session TS2: Coatings and Materials for Fuel Cells and Batteries

Tuesday, May 3, 2011 1:30 PM in Room Sunrise

Tuesday Afternoon

Time Period TuA Sessions | Abstract Timeline | Topic TS2 Sessions | Time Periods | Topics | ICMCTF2011 Schedule

Start Invited? Item
1:30 PM TS2-3 Development of Li-Mn-O Thin Film Cathodes for Lithium-Ion Batteries by Magnetron Sputtering and Laser-Assisted Structuring and Annealing
Carlos Ziebert, Julian Fischer, Nico Thiel, Johannes Proell, Robert Kohler, Monika Rinke, Wilhelm Pfleging, Sven Ulrich (Karlsruhe Institute of Technology, Germany)

Li-Mn-O thin film cathodes for Li-ion batteries have been deposited onto Si and gold coated stainless steel substrates by non-reactive r.f. magnetron sputtering at a constant power of 200 W and various working gas pressures ranging from 0.25 to 25 Pa. The composition, crystal structure and thin film morphology were examined using inductive coupled plasma optical emission spectroscopy (ICP-OES), inert gas fusion analysis (IGFA), X-ray diffraction (XRD), Raman spectroscopy, atomic force microscopy (AFM) and scanning electron microscopy (SEM). Intrinsic stress and film density were determined and battery tests have been performed in Swagelok cells with Li-Mn-O film as cathode, Li metal as anode and standard EC:DMC (1:1) electrolyte containing 1 mol LiPF6.

Using ICP-OES and IGFA a pressure-dependent variation of the stoichiometry from LiMn0.9O1.9 at 0.25 Pa to LiMn2.3O3.3 at 25 Pa was found. As slight Li loss and an increase in the O content upon furnace annealing were expected based on our previous study on LiCoO2, we focused on a gas pressure of 10 Pa, because the related composition LiMn1.9O3.13 offered the best conditions for the formation of the desired LiMn2O4 spinel phase. B y XRD and Raman spectroscopy it was revealed that during furnace annealing at 600 °C for 3 hours in argon/oxygen atmosphere (Ar:O2=4.5:5) of 10 Pa the layered orthorhombic LiMnO2 phase developed. Thus laser annealing using a high power diode laser with a maximum laser output power of 50 W and a wavelength of 940 nm was performed. It was shown that at 600 °C the spinel phase could be adjusted by an appropriate choice of laser annealing time. After 10 s the inactive monoclinic Li2MnO3 rock salt phase formed, which could be transformed into the spinel phase using annealing times up to 100 s.

To investigate the effect of different surface morphologies on the battery performance, selected Li-Mn-O films were patterned by laser ablation with a UV laser of wavelength λ = 248 nm. For the systematic investigation of topography, erosion rate and roughness parameters an ablation array was generated by systematically varying the number of lasers pulses and the laser fluence and were studied by SEM. The formation of flat and smooth ablation profiles was observed at laser fluences above 0.5 J/cm2 independent of the process gas (He, O2). The battery performance of the as grown, the structured and the annealed thin film cathodes was studied and it was revealed that the discharge capacity strongly depends on the crystal structure, the morphology and the surface structure of the thin films, which offers further opportunities for the optimisation of the performance of future 3D thin film batteries.

1:50 PM TS2-5 Influence of a Coating on the Oxidation Resistance and Resistivity of Several Chromia Former Alloys for High Temperature Vapor Electrolysis Application
Sébastien Guillou, Clara Desgranges (CEA, France); Sébastien Chevalier (University of Bourgogne, France)

High Temperature Vapor Electrolysis (HTVE) has been studied since several years as a promising solution for future hydrogen massive production plant. HTVE device is similar to SOFC system and consists in several stacks. Each stack is composed of a pile of ceramics cells working at a temperature range about 700°C to 900°C . Cells are connected together via metallic interconnects that separate anodic and cathodic parts, and permit the current supply of the cells for the electrolysis reaction. To guarantee the HTVE lifetime with a good efficiency, interconnects have to resist to high temperature environment. Chromia former alloys are good candidates for interconnects because it forms at high temperature a compact and dense Cr2O3 scale that protects the alloy from the oxidant atmosphere as a barrier. However, the volatility of chromium oxides and hydroxydes may cause degradation of cells efficiency, particularly in presence of water vapor.

Increase in the performance of the alloys can be achieved using MOCVD (Metal-Organic Chemical Vapor Deposition) coatings. In a previous study performed for SOFC application, La2O3 coating applied by MOCVD improved kinetics oxidation rate in SOFC type atmospheres1,2 and also modified the electronical properties of the oxide layer by increasing its conductivity2,3,4.

Hence, in the present work, the same La2O3 coating has been applied to several alloys, such as Haynes®230, Haynes®242 and K41X (AISI441). The alloys were oxidized at 800°C in the both atmospheres representative of the HTVE operating conditions: ie Ar-1%H2-9%H2O (on cathodic side) and air (on anodic side). Oxidation kinetics were measured with a thermobalance and the Area Specific Resistance (ASR) was evaluated via contact resistance measurements. XRD, SEM coupled with EDS analyses were used to characterize the thermally grown oxide scale. Results are discussed through the comparison of the behaviors in HTVE type atmospheres of uncoated and La2O3 coated samples.

Beyond the possible coating beneficial influence, several additional experiments was carried out to understand the mechanism involved in presence of the coating or/and the oxide scale. 18O tracer experiments and PhotoElectroChemistry characterizations were used in order to identify the diffusion mechanism. The possible role played by the protons on the conductivity and the oxidation kinetics was investigated using atmospheres enriched in deuterium.

[1]S. Fontana and al, J. Power Sources 193 Issue 1 (2009) 136-145.

[2]S. Fontana and al, J. Power Sources 171 (2007) 652-662.

[3]W.Z. Zhu, S.C. Deevi, Mater. Res. Bull. 38 (2003) 957-972.

[4]Chandra-Amborn, PhD report, Grenoble Institute of Technology, (2006)

2:10 PM TS2-6 Deposition and Post-Annealing of Ceria Films Deposited by Pulsed Unbalanced Mangetron Sputtering
In-Wook Park, John Moore, Jianliang Lin (Colorado School of Mines); Michele Manuel (University of Florida); Anter El-Azab (Florida State University); Todd Allen, Peng Xu (University of Wisconsin); David Hurley, Marat Khafizov (Idaho National Laboratory)
Ceria films were deposited on silicon wafer substrates in argon-oxygen atmosphere using pulsed unbalanced magnetron sputtering (P-UBMS) from a pure Ce target (99.99%) with a substrate heating capability system. Ceria films were also annealed using a rapid thermal annealing (RTA) with much higher temperatures in a range from room temperature to 1100°C. The crystallinity of the annealed samples was characterized by x-ray diffraction (XRD, PHILIPS, X’pert-MPD) using CuKα radiation. X-ray photoelectron spectroscopy (XPS, PHI XPS System, 5600LS) using a monochromatic Al source was also performed to determine the contents of Ce and O and to observe the bonding status of the annealed ceria samples. A MTS nano-indenter equipped with Berkovich diamond indenter was used to perform depth sensing nanoindentation testing on the annealed CeO2 films and to obtain mechanical values of nanohardness and Young’s modulus with a Poisson’s ratio of 0.25. In the present work, microstructural changes and properties of the films were investigated and correlated with deposition parameters.
2:30 PM TS2-7 Sputtered Lanthanum Silicate Electrolytes for SOFCs
Joao Oliveira (University of Coimbra, Portugal); Milena Vieira (Polytechnic Institute of Leiria, Portugal); Aliaksandr Shaula, Alabano Cavaleiro (University of Coimbra, Portugal)

The development of IT-SOFCs will also require electrolyte materials with ionic conductivity higher than the conventional yttria-stabilised zirconia (YSZ) at moderate temperatures. Recently, lanthanum silicates materials (La9.33Si6O26) with an apatite-like structure have attracted considerable interest as potential low cost electrolyte materials. Some of these materials show conductivities comparable to, or better than, YSZ at 875 K, and are thus potential electrolytes for economic feasible fuel cells. Their high level of oxide ion mobility is related to the presence of oxygen channels along the c axis which facilitate the diffusion of anionic species (O2- for SOFC applications).

Magnetron sputtering has already been used to synthesize thin film electrolytes for SOFCs owing to its versatility as well as the ability to control composition and morphology. Most of the reported work focuses on the deposition of thin dense yttria-stabilised zirconia (YSZ) gadolinium doped ceria (GDC) and lanthanum gallate electrolyte layers. The main objective of this work is the production of apatite-like lanthanum silicates thin films by magnetron sputtering. La-Si-O films with the appropriate La/Si atomic ratios were deposited by reactive magnetron sputtering from La-Si and Si targets and subsequently annealed in controlled atmosphere to obtain the targeted lanthanum silicate oxide.

The chemical composition of the coatings was determined by electron probe microanalysis (EPMA). The structure of the coatings was studied by X-ray diffraction (XRD) using a Phillips diffractometer operated in Bragg-Brentano configuration with Co(Kα) radiation. The cross section and surface topography of the La-Si films were examined on a JEOL scanning electron microscope (SEM) equipped with an EDAX energy dispersive spectrometer (EDS). The electrical properties of the films were measured by AC impedance spectroscopy (HP4284A precision LCR meter, 20 Hz – 1 MHz).

2:50 PM TS2-8 Nanostructured Titania Materials for PEM Fuel Cell Water Management
Mahmoud Elhamid, Gayatri Dadheech (General Motors)
Transition-metal oxide surfaces play an important role in a wide range of applications such as heterogeneous catalysis, photo catalysis, photo-electrolysis of water, biocompatibility, functional materials and green energy applications. More recently, transition metal oxide films are being considered as important materials for the removal of water in fuel cell applications. Defects such as oxygen vacancies present in such oxide film structure often dominate the electronic and chemical properties of transition-metal oxide surfaces. In this study, we explore the use of nanocrystalline titanium oxide material structures to improve water management on bipolar plates inside PEM fuel cells. Titanium oxide nanotubes structures and nanoparticles structures are more stable than other forms of hydrophilic surface treatments. Furthermore, these materials are also found to be contamination robust.
3:10 PM TS2-9 Electrolytic Co-Deposition for Synthesis of (Mn,Co)3O4 Spinel Coatings to Protect SOFC Interconnect Alloys
Jiahong Zhu, Matthew Lewis (Tennessee Technological University)

A novel process to synthesize the (Mn,Co)3O4 spinel coating for protecting ferritic interconnect alloys has been developed, which is based on thermal conversion of an electrolytically co-deposited composite layer. Simultaneous electrolytic deposition of Co and Mn3O4 onto a Crofer 22 APU substrate resulted in a composite coating layer consisting of a Co matrix embedded with the Mn3O4 particles. Thermal conversion of the as-deposited layer in air at 850ºC led to the formation of a dense and adherent (Mn,Co)3O4 spinel coating on the substrate. The spinel coating was effective in blocking Cr migration and improving the electrical performance of the interconnect alloy.

3:30 PM TS2-10 Development of Low Cost Protection Coatings for SOFC Interconnect Applications
Guanguang (Gordon) Xia, Xiaohong (Shari) Li, Joshua Templeton, Ryan Scott, Jeffry Stevenson (Pacific Northwest National Laboratory)
Due to their low cost, high temperature oxidation resistance, and comparable thermal expansion coefficient to adjacent components of anode-supported planer SOFC stacks, chromia-forming ferritic stainless steels, such as AISI 441, are among the most promising candidate materials for interconnect applications. However, bare alloys cannot be directly used for interconnects because the rapid growth of chromia scale will lead to high internal electrical resistance and the migration of chromium species via this scale can cause cathode poisoning and cell performance degradation. To mitigate these issues for long term SOFC operation, protection coatings on ferritic stainless steel interconnects have been developed at PNNL. Manganese-cobalt spinels, particularly, Mn1.5Co1.5O4, are proven to be highly effective protection coating materials. Currently, considerable efforts have been devoted to the cost reduction for materials and processing via investigating alternative precursors and compositions for interconnect coatings while maintain their protection effectiveness. Recent progress in this area will be summarized in this paper.
3:50 PM TS2-4 Lithium Insertion into Vertically-Aligned Carbon Nanotubes During Growth
Kuldeep Rana, Gokce Kucukayan, Erman Bengu (Bilkent University, Turkey)
The possibility of growing vertically-aligned carbon nanotubes using Li-containing catalysts was investigated, and insertation of lithium into carbon nanotubes (CNTs) during the growth process was examined in this work. CNTs were synthesized by chemical vapor deposition technique. The catalyst layers were prepared by the calcination of Li, Co and Al nitrate containing ethanol-based solutions. Two different solutions were studied in the present work containing (i) Co and Al nitrate and (ii) Li, Co and Al nitrates. These solutions were applied on oxidized Si (100) wafers using a dropper and left to dry at room temperature. Then, subsequent calcination, reduction and reaction for CNT growth were run in a vacuum-capable atmosphere-controlled tube furnace. Final products at the end of CNT growth were analyzed to understand the effect of lithium on CNT chemistry and structure. Scanning electron microscopy analysis confirmed the growth of CNTs with the use of both Li-containing and non Li-containing catalyst. Raman spectral analysis of these CNT arrays indicated a shift in the G-band for those grown with lithium-based catalyst. This observation is related to charge transfer between CNTs and lithium, which is a result of insertion of lithium into CNT structure. Furthermore, we have analyzed these materials using x-ray photoelectron spectroscopy (XPS). We have observed shifts in binding energy of Li1s and C1s peaks confirming the presence of lithium in CNTs grown with lithium-based catalyst. In this study, we have shown that it is possible to grow vertically aligned CNTs using Li-containing metallic catalysts. Under proper synthesis conditions, we demonstrated that Li can be inserted into CNT structures during growth without the need for further post-processing. We believe that this material can be potentially used as an anode material for lithium ion batteries to improve the performance.
Time Period TuA Sessions | Abstract Timeline | Topic TS2 Sessions | Time Periods | Topics | ICMCTF2011 Schedule