Thin Films and Coatings for Fuel Cells & Batteries
Thursday, May 1, 2014 1:30 PM in Room Royal Palm 4-6
F6-1 Surface Modification of Electrode Materials for Lithium-ion Batteries
Christian Julien (Université Paris-6, France); Alain Mauger (UPMC, Paris, France); Karim Zaghib (IREQ, Canada)
While little success has been obtained over the past few years in attempts to increase the capacity of Li-ion batteries, significant improvement in the power density has been achieved, opening the route to new applications, from hybrid electric vehicles to high-power electronics and regulation of the intermittency problem of electric energy supply on smart grids. This success has been achieved not only by decreasing the size of the active particles of the electrodes to few tens of nanometers, but also by surface modification and the synthesis of new multi-composite particles. It is the aim of this talk to review the different approaches that have been successful to obtain Li-ion batteries with improved high-rate performance and to discuss how these results prefigure further improvement in the near future.
Currently, it is recognized that the main limiting elements of a Li-ion battery are the positive electrode materials which can be divided into three different families. One is the family of lamellar compounds obtained by the multi-ion substitution of transition-metal ions. The archetype of this family is LiNi1/3Mn1/3Co1/3O2 (NMC). The second family is the olivine group, the archetype of which is LiFePO4 (LFP) for which coating the particles with conductive carbon has been a remarkably successful surface modification. The third family consists of compounds with spinel structure such as LiMn1.5Ni0.5O4 (LMN), which is of great interest because it provides access to the Ni(IV)–Ni(II) formal valences at about 4.7 V vs. Li+/Li. However, cathode/electrolyte surface reactions lead to degradation in the electrochemical performance.
Recent progress in the reduction in size of the active particles of the electrodes below 100 nm has increased the surface contact with the electrolytes, thus improving the power density of the Li-ion batteries. At the same time, however, the surface-over-volume ratio increases, so that the surface layer, as well as SEI effects, becomes increasingly important. Recent improvements for the positive electrodes have been obtained by well-crystallized surface layer of both lamellar compounds and olivine compounds. The increase of energy density with remarkable thermal stability has been achieved by LiFePO4-coated particles working at higher operating voltage. The coating is protecting the inner core of the particles from contact and reaction with the electrolyte, which not only prevents the formation of a resistive SEI layer, but also increases the safety of the Li-ion batteries. In particular, the multi-composite particles open the route towards the 5 V operating Li-ion batteries will be presented.
F6-3 Experimental and Ab Initio Investigations on Textured Li-Mn-O Spinel Thin Film Cathodes
Julian Fischer (Karlsruhe Institute of Technology (KIT), Germany); Denis Music (RWTH Aachen University, Germany); Thomas Bergfeldt, Carlos Ziebert, Sven Ulrich, HansJürgen Seifert (Karlsruhe Institute of Technology (KIT), Germany)
This paper describes the tailored preparation of nearly identical Lithium-Manganese-Oxide thin film cathodes with different global grain orientations. The thin films were produced by r.f. magnetron sputtering from a LiMn2O4-target in a pure argon plasma. Under appropriate processing conditions, thin films with a cubic spinel structure and a nearly similar density and surface topography but different grain orientation, i.e. (111)- and (440)-textured films, can be achieved. The chemical composition was determined by inductively coupled plasma optical emission spectroscopy and carrier gas hot extraction. The constitution- and microstructure were evaluated by X-ray diffraction and Raman spectroscopy. The surface morphology and roughness were investigated by scanning electron and atomic force microscopy. The differently textured films represent an ideal model system for studying potential effects of grain orientation on the lithium ion diffusion and electrochemical behavior in LiMn2O4-based thin films. They are nearly identical in their chemical composition, atomic bonding behavior, surface-roughness, morphology and thickness. Our initial ab initio molecular dynamics data indicate that Li ion transport is faster in (111)-textured structure than in (440)-textured one.
F6-4 Production of Core–shell Copper/Tin/MWCNT Composite Electrodes for Li-ion Batteries
Mehmet Uysal (Sakarya University, Engineering Faculty, Turkey); Tugrul Cetinkaya (Sakarya University, Turkey); Muhammet Kartal (Sakarya University, Engineering Faculty, Turkey); Mehmet Guler, Ahmet Alp, Hatem Akbulut (Sakarya University, Turkey)
In this work, firstly core Sn/Cu composite powders were produced using an electroless process. Then, Sn/Cu/MWCNTs composite electrodes were prepared with dispersing different amount of MWCNT (10 wt. %, 20 wt.%, 40 wt.%) by high energy mechanical milling method. The surface morphology of the produced Sn/Cu/MWCNTs composite powders was characterized using scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) was used to determine the elemental surface composition of the composites. X-ray diffraction (XRD) analysis was performed to investigate the structure of the Sn/Cu/MWCNTs composite powders. The electrochemical performance of Sn/Cu/MWCNTs nanocomposites studied by charge/discharge tests and cyclic voltammetry experiments. Cyclic voltammetry (CV) tests were performed for revealing the reversible reactions of tin with lithium. Galvanostatic charge/discharge (GC) measurements were carried out in the assembled CR2016 cells by using anode Sn/Cu/MWCNTs produced by electroless method
F6-5 Influences of Feedstocks on the Processes and Microstructures of the Flame-sprayed SOFC Anode
Han-Cheng Tseng, Yung-Chin Yang (National Taipei University of Technology, Taiwan)
This study is to fabricate a porous anode coating of solid oxide fuel cell by flame spraying technique. Flame spraying method, with a reduced thermal stresses and the advantages of easy process, is relatively low temperature in the manufacturing process. Since the low-temperature flame spray coating process, the initial selection of the feedstocks will affect the coating preparation. The anode of SOFC is a porous cermet material, therefore, choose Ni-based materials with yttria stabilized zirconia (8YSZ) as the raw materials. In this study, two groups of feedstocks were employed. One is prepared using spraying dried powder, NiO/8YSZ, Ni/8YSZ, NiO/8YSZ/Na2CO3 were included. Second is the commercial thermal spray powder, nickel coated graphite powder (Ni-coated graphite, NiGr) and 8YSZ powder. With different powder mix and spraying parameters used for anode coating preparation were studied. The results showed that NiO/YSZ powder can be obtained uniform, flat, small pores and good adhesion coating. Using Ni/YSZ powder can be obtained non-flat and multi-pores coating, which has bad adhesion with substrate. Using NiO/YSZ/Na2CO3 powders can be obtained uniform, non-flat, good adhesion coating, which can be increased porosity by removing pore former. Using commercial thermal powder of Ni-coated graphite can be obtained non-uniform, multi-pores and good adhesion coating, which can be created continues pore by oxidation treatment. Using ceramic YSZ powder can be obtained non-flat and bad adhesion coating. The above results show that use of NiO / YSZ / NiGr (1 : 1: 1 wt. %)powder, experimental parameters for the working distance 150mm, neutral flame parameters of preparation, can be obtained relatively smooth, uniform, and porous structure coating(30 - 40% )
F6-6 Li Ion Technology for Vehicle Electrification
Gayatri Dadheech, Mark Verbrugge (General Motors Research and Development Center, US); Suresh Sriramulu (TIAX, Inc., US)
Electric vehicles with high energy density Li ion batteries show great promise that can revolutionize the automotive industry in coming years. The success of lithium ion batteries would largely depend on its component material properties in order to achieve high energy, power, cycle life, abuse tolerance and cost. In this talk, we would discuss the developments and challenges of high capacity electrodes materials and the potential surface engineering approaches to overcome them.
F6-8 Improvement on the Corrosion Behaviour and Surface Conductivity of Coblast Coatings by Pack Cementation
Atinuke Oladoye, James Carton (Dublin City University, Ireland); Abdul Olabi (University of the West of Scotland, UK)
Stainless steel alloys offer many advantages over traditional graphite bipolar plates in proton exchange membrane fuel cells (PEMFC). However, low corrosion resistance and the resultant loss of surface conductivity of these alloys in the warm and humid environment of the PEMFC are major concerns. In this work, pack cementation was employed to enhance the functionality of graphite/alumina coatings deposited on AISI316 stainless steel alloy via a microblasting process named CoBlast™. The coatings were characterised and electrochemically polarised in 0.5M H2SO4 +2ppm HF at 700C while contact resistance was measured at room temperature. The results showed that the hybrid coatings formed at 900oC showed about three order of magnitude reductions in the corrosion current and about fourfold decease in the contact resistance of the initial coatings at typical PEMFC compaction pressure. The chromized coatings also exhibited better stability under PEMFC working conditions. These results are discussed in relation to the targets for bipolar plates.