Krystan Marquardt

An Overview and Future Perspectives of Aluminum Batteries.

A critical overview of the latest developments in the aluminum battery technologies is reported. The substitution of lithium with alternative metal anodes characterized by lower cost and higher abundance is nowadays one of the most widely explored paths to reduce the cost of electrochemical storage systems and enable long-term sustainability. Aluminum based secondary batteries could be a viable alternative to the present Li-ion technology because of their high volumetric capacity (8040 mAh cm(-3) for Al vs 2046 mAh cm(-3) for Li). Additionally, the low cost aluminum makes these batteries appealing for large-scale electrical energy storage. Here, we describe the evolution of the various aluminum systems, starting from those based on aqueous electrolytes to, in more details, those based on non-aqueous electrolytes. Particular attention has been dedicated to the latest development of electrolytic media characterized by low reactivity towards other cell components. The attention is then focused on electrode materials enabling the reversible aluminum intercalation-deintercalation process. Finally, we touch on the topic of high-capacity aluminum-sulfur batteries, attempting to forecast their chances to reach the status of practical energy storage systems.

Insights into the reversibility of aluminum graphite batteries

Herein we report a novel study on the reaction mechanism of non-aqueous aluminum/graphite cell chemistry employing 1-ethyl-3-methylimidazolium chloride:aluminum trichloride (EMIMCl:AlCl3) as the electrolyte. This work highlights new insights into the reversibility of the anion intercalation chemistry besides confirming its outstanding cycle life exceeding 2000 cycles, corresponding to more than 5 months of cycling test. The reaction mechanism, involving the intercalation of AlCl4− in graphite, has been fully characterized by means of ex situ X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), X-ray absorption near edge structure spectroscopy (XANES) and small-angle X-ray scattering (SAXS), evidencing the accumulation of anionic species into the cathode as the main factor responsible for the slight initial irreversibility of the electrochemical process.

Assembly and Hermetic Encapsulation of Wafer Level Secondary Batteries

A new technology was developed for the construction and hermetic encapsulation of chip-size secondary lithium-ion batteries on a wafer-level plane. To reduce the size of the package and improve the handling and assembly of miniature batteries, we established a wafer-level process that combines foil processing of Li batteries and wafer technologies for battery contacts and encapsulation. Parylene and thin-film metal deposition was used for hermetic encapsulation of the batteries. With this technology, battery sizes between 1 mm2and 1 cm2, and as thin as 250 µ m, can be fabricated. A discharge capacity of 860 Ah/cm2was achieved with secondary lithium wafer-level batteries. The proportion of active material is thus increased to over 70%, despite the system’s very flat structure. The impact of the formation procedure on the battery performance was investigated. Electrical charge and discharge cycling tests have been carried out. The presented technology allows the transformation of the high energy density of cylindrical or prismatic cells to integrated micro batteries.

Development of micro batteries based on micro fluidic MEMS packaging

A cost effective and reliable technology allowing extreme miniaturization of batteries into silicon, glass chips and electronic packages has been developed, employing a dispense-print process for battery electrodes and liquid electrolyte. Lithium-ion micro batteries (active area 6×8 mm2, 0.2–0.4 mAh) with interdigitated electrodes and glass housing were fabricated, tested and finally compared with the traditional battery architecture of stacked electrodes. All processes for micro battery fabrication were established; in particular a micro fluidic electrolyte filling process that allows simultaneous electrolyte supply of all cells on a planar substrate. Electrode mass reproducibility was sufficient for adequate electrode balancing. Current capability similar to the conventional face-to-face electrode configuration was achieved with interdigital electrodes. The cells were successfully cycled; several 100 cycles can be achieved.

Polyacrylonitrile Separator for High-Performance Aluminum Batteries with Improved Interface Stability

Herein we report, for the first time, an overall evaluation of commercially available battery separators to be used for aluminum batteries, revealing that most of them are not stable in the highly reactive 1-ethyl-3-methylimidazolium chloride:aluminum trichloride (EMIMCl:AlCl3) electrolyte conventionally employed in rechargeable aluminum batteries. Subsequently, a novel highly stable polyacrylonitrile (PAN) separator obtained by the electrospinning technique for application in high-performance aluminum batteries has been prepared. The developed PAN separator has been fully characterized in terms of morphology, thermal stability, and air permeability, revealing its suitability as a separator for battery applications. Furthermore, extremely good compatibility and improved aluminum interface stability in the highly reactive EMIMCl:AlCl3 electrolyte were discovered. The use of the PAN separator strongly affects the aluminum dissolution/deposition process, leading to a quite homogeneous deposition compared to that of a glass fiber separator. Finally, the applicability of the PAN separator has been demonstrated in aluminum/graphite cells. The electrochemical tests evidence the full compatibility of the PAN separator in aluminum cells. Furthermore, the aluminum/graphite cells employing the PAN separator are characterized by a slightly higher delivered capacity compared to those employing glass fiber separators, confirming the superior characteristics of the PAN separator as a more reliable separator for the emerging aluminum battery technology.

Thin Film Encapsulation for Secondary Batteries on Wafer Level

This paper presents results concerning the realization and characterization of thin film encapsulated wafer-level batteries. Initially, the technology concept for the construction and hermetic encapsulation of chip-size lithium-ion secondary batteries on wafer level is introduced. Parylene and thin-film metal deposition was used for hermetic encapsulation of the batteries. With this technology, battery sizes between 1 mm2 and 1 cm2, and as thin as 225 mum, can be fabricated. The chemical compatibility of the EC/DEC electrolyte with the encapsulation material was proven. To characterize the encapsulation layer, optical light microscopy and transmitting light microscopy have been used. Li(1-x)(Ni)CoO 2 and LixC6 were used as active intercalation materials for cathode and anode electrode respectively. Using a small fraction of PVdF binder is essential for achieving a high energy density. In this work, the focus was set on increasing the energy density of active battery laminates. To obtain a high discharge capacity, the preparation of battery materials was revised and the lamination process was optimized. Electric measurement on laminated battery foils with an area of 0.96 cm2 and a thickness of less than 220 mum has been carried out. As a result a capacity density of 1.33 mAh/cm2 was reached while cycling a battery sample under laboratory conditions. The presented technology allows the transformation of the high energy density of cylindrical or prismatic cells to integrated micro batteries

Micro patterned test cell arrays for high-throughput battery materials research

A cost effective and reliable technology for the fabrication of electrochemical test cell arrays for battery materials investigation, based on batch fabricated glass micro packages was developed and tested. Semi-automatic micro dispensing was investigated as a process for the standardized application of different electrode materials and SiO2-based separator. The process shows sufficient reproducibility over the whole range of investigated materials, especially for the cells with interdigital (side-by-side) electrodes. Such setup gives rise to an improved reliability and reproducibility of electrochemical experiments. The economic fabrication of our test chips by batch processing allows for their single-use in electrochemical experiments, herby preventing contamination issues due to repeated use as in conventional laboratory test cells. In addition, the integration of micro pseudo reference electrodes was demonstrated. Thus, the presented test cell array together with the developed electrode/electrolyte deposition technology represents a highly efficient tool for combinatorial and high throughput testing of battery materials on system level (full cell tests). The method will speed up electrochemical materials research significantly.