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The integration of lithium-ion batteries, featuring ultra-high discharge rates, directly into silicon-based semiconductor devices opens unique paths towards the development of new mobile micro-electronics applications. Nevertheless, the small and mobile lithium ions have to be confined within the battery area of the silicon chip, otherwise the nearby fine microelectronics devices will be irreversibly damaged. Hence, a barrier material that blocks Li+ transport from the active components of the battery into the surrounding crystalline Si is needed. Here we evaluated the capability of magnetron sputtered barrier films of nitrides and alloys of refractory metals to prevent lithium ion diffusion and, thus, the formation of Li–Si phases outside the battery area. In order to determine the Li profiles in the barrier layer and in the silicon substrate, time-of-flight secondary ion mass spectroscopy was applied for profiling the first microns. In combination with electrochemical testing it turned out that titanium nitride as well as tantalum nitride barriers are able to significantly block Li ion migration.

Mobil Nachhaltig TC Plattling MoMo

Zeitschriftenartikel

A. Dunst, Michael Sternad, M. Wilkening

Overall conductivity and NCL-type relaxation behavior in nanocrystalline sodium peroxide Na 2 O 2 —Consequences for Na-oxygen batteries

Materials Science and Engineering: B, vol. 211, no. September, pp. 85-93

2016

DOI: 10.1016/j.mseb.2016.06.002

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Metal air batteries are considered as promising candidates for room-temperature batteries with high-energy densities. On discharge, atmospheric oxygen is reduced at the positive electrode which, in the ideal case, forms the discharge products in a reversible cell reaction. In Na-O2 batteries upon discharge either sodium peroxide (Na2O2) or sodium superoxide (NaO2) is reported to be formed. So far, the charge carrier transport remains relatively unexplored but is expected to crucially determine the efficiency of such energy storage systems. Na2O2 is predicted to be an electrical insulator wherein the transport presumably is determined by very slow hopping processes. Understanding the basic fundamental properties of the overall charge carrier transport, including also nanostructured forms of Na2O2, is key to developing high-energy metal oxygen batteries. The present study answers the question how overall, i.e., total, conductivity changes when going from microcrystalline to nanocrystalline, defect-rich Na2O2. Nanocrystalline Na2O2 was prepared via a top-down approach, viz by high-energy ball milling. Milling does not only shrink the average crystallite diameter but also introduces a large amount of defects which are anticipated to influence total conductivity. It turned out that even after vigorous mechanical treatment the conductivity of the sample is only increased by ca. one order of magnitude. The activation energy remains almost untouched. Thus, the increase seen might be attributed to an enhanced number of charge carriers. Low-temperature data reveals nearly constant loss relaxation behavior which has frequently explained in terms of strictly localized electrical relaxation processes.

Mobil Nachhaltig TC Plattling MoMo

Vortrag

A. Dunst, Michael Sternad, V. Epp, M. Wilkening

Fast Li Self-Diffusion in Amorphous Li-Si Electrochemically Prepared from Semiconductor Grade, Monocrystalline Silicon — Insights from Spin-Locking Nuclear Magnetic Relaxometry

Poster presentation

20th International Conference on Solid State Ionics, Keystone, CO, USA

2015

Mobil Nachhaltig TC Plattling MoMo

Zeitschriftenartikel

A. Dunst, Michael Sternad, V. Epp, M. Wilkening

Fast Li+ Self-Diffusion in Amorphous Li–Si Electrochemically Prepared from Semiconductor Grade, Monocrystalline Silicon: Insights from Spin-Locking Nuclear Magnetic Relaxometry

The Journal of Physical Chemistry C, vol. 119, no. 22, pp. 12183-12192

2015

DOI: 10.1021/acs.jpcc.5b02490

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Silicon is one of the most promising anode materials for lithium-based rechargeable batteries. Provided the volume changes during Li uptake can be brought under control, Li ion diffusivity is expected to crucially determine the performance of such next-generation energy storage systems. Therefore, studying diffusion properties in e.g. amorphous Li–Si underpins applied research that is being directed toward the development of powerful storage devices. So far, only little information is available on Li+ self-diffusion in amorphous Si. Here, we used 7Li NMR spectroscopy to precisely quantify microscopic activation energies and Li jump rates in amorphous Li–Si which is primarily formed if monocrystalline Si is lithiated electrochemically. Surprisingly, our results reveal relatively fast Li ion diffusivity with low activation energies for localized Li+ motions being in agreement with results from theory. The average activation energy for long-range ion transport is as high as ca. 0.65 eV; jump rates turn out to be in the order of 2.5 × 105 s–1 at 246 K. Our results point to complex dynamics that is most likely governed by nonexponential motional correlation functions originating from a distribution of activation energies. The data obtained might help optimizing Li-based silicon batteries whose performance critically depend on fast Li ion transport.

Mobil Nachhaltig TC Plattling MoMo

Vortrag

A. Dunst, Michael Sternad, V. Epp, M. Wilkening

Lithium ion dynamics in amorphous Li-Si electrochemically prepared from semiconductor grade, monocrystalline silicon — An NMR Study

Poster presentation

Materials Day 2015, Graz, Österreich

2015

Mobil Nachhaltig TC Plattling MoMo

Vortrag

A. Dunst, Michael Sternad, V. Epp, M. Wilkening

Fast Li self-diffusion in Li-Si Electrochemically Prepared from Semiconductor Grade, Monocrystalline Silicon

15th European Conference on Solid State Chemistry (ECSSC), Wien, Österreich