Aluminum Anode Characterization of a Novel Aluminum-Sulfur Secondary Battery David Moser1, Sandra Steiner2, Bernhard Gollas2, Gerald Kothleitner1 3 1. Institute of Electron Microscopy and Nanoanalysis, Graz University of Technology, Steyrergasse 17, 8010 Graz, Austria 2. Institute for Chemistry and Technology of Materials, Graz University of Technology, Stremayergasse 9, 8010 Graz, Austria 3. Graz Centre for Electron Microscopy (ZFE), Steyrergasse 17, 8010 Graz, Austria
Introduction Current energy storage devices have significant issues in capacity, safety and availability of raw materials. [1] In this context, new technologies are intensively researched. As a part of the SALBAGE (Sulfur-Aluminum Battery with Advanced Polymeric Gel Electrolyte) consortium (EU FETOPEN project), the aim of this work is to investigate the morphological changes of solid aluminum caused by electrochemical processes during deposition and stripping. Therefore, the electrodes are prepared and tested in electrochemical cells (Swagelok) at the Institute of Chemistry and Technology of Materials (ICTM, TU Graz) and subsequently transferred to the Institute of Electron Microscopy and Nanoanalysis (FELMI-ZFE, TU Graz) where further characterization is done. The combination of multiple analytical techniques applied to the same sample should allow a deeper understanding of this battery anode.
Methods and Instrumentation
Issues • Dendritic growth during electrochemical Al deposition and other changes in morphology can lead to device failure • Rapid oxide layer formation by atmospheric oxygen, which can lead to surface changes during transport
• Glove box with argon atmosphere electrochemical instrumentation (ICTM) • Inert gas transfer sample holder • FEG-SEM with EDX • STEM-EELS
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Results The electrical performance of the cell is highly related to the passivation of the electrodes. Hence, a suitable preparation technique for high purity aluminum (99.999 %) electrodes had to be found in the initial phase of the project. Due to the high ductility of aluminum, mechanical preparation steps led to excessive surface contamination by grinding and polishing particles. According to their size and EDX analysis, the big particles may originated from grinding with SiC (mesh size #4000). The smaller ones likely consisted of SiO2 form the fine polishing step.
used for flattening of the coarse electrode structure. Subsequently, polishing was done 3 µm diamond suspension (Struers DiaPro, 8min). As a last step, pressedin particles were removed by extensive fine polishing (Struers OP-S, colloidal SiO2, 0.04 µm, pH 10, >20 min). The samples were rinsed with deionised water and detergent and finally treated in an ultrasonic bath of Ethanol for 5 minutes. The result is an electrode with a clean surface which only shows grain contrast.
Fig.2: Clean electrode surface, showing only grain contrast Fig.1: Particles from multiple preparation steps are pressed into the surface.
Because this contamination certainly has undesirable effects on the operation of the electrode, a new preparation method was set up. Grinding (Struers SiC paper) was reduced to three steps: #1200 for fast leveling of the electrode holder and the electrode. #2400 and #4000 were there is no secret message, just continue reading
Conclusion A new polishing method is now used to obtain a clean and even Al surface for reproducible electrochemical investigations. In the future, it will be researched, how the electrochemical performance is affected by the thickness of the oxide layer and if dendrite growth can be observed “insitu”.
Contact david.moser@felmi-zfe.at www.felmi-zfe.at
Further, the native oxide layer of Al was investigated by STEM. Its thickness is in the range of 3 to 5 nm.
5 nm
5 nm
Fig.3+4: Native Oxide layer formed on high purity Aluminum at ambient conditions
References/Literature [1] SALBAGE proposal, No. 766581, FETOPEN-01-20162017, (17.01.2017)
Acknowledgements The Institute for Electron Microscopy and Nanoanalysis (FELMI) and the Center for Electron Microscopy Graz (ZFE) as well as the Institute for Chemistry and Technology of Materials (ICTM) are thanked for provision of the infrastructure. This research is funded by the European Commission in the H2020-FETOPEN project “SALBAGE”.