Funding: European Regional Development Fund and National Funds, German-Greek Bilateral R&D Cooperation Initiative (2013-2015)
Duration: 1/11/2013-30/11/2015
Partners:

  1. Micro and Nano-Technology Laboratory (MNT Lab) , DUTH
  2. Fraunhofer-Institut für Chemische Technologie (ICT-DE)
  3. Limedion GmbH (LM-DE)
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Technical Objectives of the Project:

Among the energy storage technologies, the lithium ion (Li-ion) system represents one of today’s most operated cell technology. It provides high energy density, long cycle life and high operating voltage (> 3V). At present, these batteries provide commercial battery electric cars with autonomy of around 150km. The performance of the battery strongly depends on the materials used to fabricate the Li-ion cell.

The project aimed to investigate both the anode and cathode materials with a clear objective to manufacture cells with a specific energy density of more than 150Wh/kg with adequate cycling charging/discharging performance, complying with industrial manufacturing practices, safety standards and environmental regulations. DC sputtering is providing high quality thin films with adaptability on large area deposition. Within the scope of our work, lithium iron phosphate (LFP) as cathode has been grown by DC sputtering in order to increase the electrical conductivity of the LFP thin films and to control the texturing of the surface. The project also focused on anode materials and especially on silicon.

It is well known that silicon presents one of the most important anode materials for the improvement of lithium-ion cells in terms of energy density. Indeed, silicon’s high theoretical specific capacity to lithium (more than 3800 mAh/g at room temperature), environmental friendliness, low potential compared to lithium and material abundance turns silicon to a strong candidate for the replacement of carbon-based anodes. However, one of the main drawbacks of silicon’s application to the lithium-ion technology is its poor cycling stability, mainly due to silicon’s huge volume change (around 400%) during lithiation and delithiation that leads to high internal mechanical stress. Therefore, in order to improve silicon’s stability we took into account its adhesion properties to the current collector.

Results of the Project

Half-cells with silicon anodes that have been deposited by DC sputtering technique on various substrates that can be used as current collectors such as copper foil, carbon fibers, special treated copper foils, electro dag coated and CNT coated copper foils and titanium foils were developed by DUTH. From those results, it becomes obvious that the adhesion properties of silicon to the current collector play an immense role to the specific capacity of the anode and most particularly to its stability over cycling. Αnodes with high specific capacity of more than 2000 mAh/g and 2.5 mAh/cm2 were manufactured. Silicon’s capacity was found to be stable for more than 50 galvanostatic cycles.

Concerning the cathode, slurry based LFP was developed and achieved specific capacity of more than 3.5 mAh/cm2 and 180 mAh/g. The electrochemical characterization of these materials and their combinations with various electrolytes was performed in small cells. Based on these results, 820 mAh pouch cells were designed, developed and manufactured (demonstrators). Galvanostatic cycling were performed and an overcharge safety test according to IEC 62660-2. The demonstrator cell with a capacity of nominal 820 mAh was put into a sealed stainless steel can, equipped with an internal camera to observe the cell during the test. Additionally the can was linked to a mass spectroscope, a gas chromatograph and a FTIR device to measure released gas online. Temperature sensors on the demonstrator pouch cell enabled a monitoring of the cell temperature during the test.

The demonstrator was charged with C/2 until the state of charge (SOC) was measured to be 200% and therefore fulfilled the guidelines of IEC 62660-2 successfully. A thermal runaway was enforced when the demonstrator was charged with 4C and had a SOC of 300%. The temperature at thermal runaway was measured to be ~340 °C. This contribution will show a distribution of released gas components during the overcharge safety test and provide information about the harmfulness of these substances. To our knowledge, this is the first time that safety tests were conducted to Si/LFP cells.

Researchers involved (from DUTH)

Filippos Farmakis, Assistant Professor, Electrical Engineering Department @DUTH /Scientific Coordinator
Nikolaos Georgoulas, Professor and Director of MNT Lab, Electrical Engineering Department @DUTH
Ioannis Karafyllides, Professor, Electrical Engineering Department@DUTH
Dimitra Girginoudi, Assistant Professor, Electrical Engineering Department@DUTH
Stavros Matziris, MNT Lab Technician Electrical Engineering Department@DUTH
Petros Selinis, MSc candidate student

Related Publications

Silicon/Lithium Iron Phosphate Safe and High-Energy Density Lithium-Ion Cells: From Material Research to Demonstrator
F. Farmakis, M. Hagen, P. Selinis, P. Fanz, A. Kovacs, S. Schiestel, N. Georgoulas
2016. 18th Intern. Meeting on Lithium Batteries, Chicago,USA, June 2016
Abstract: https://ecs.confex.com/ecs/imlb2016/webprogram/Paper77033.html

High-Energy Micro-grain Silicon Anodes for Lithium-Ion Technology
F.Farmakis, P.Selinis, N.Georgoulas, M.Hagen, P.Fanz, S.Schiestel, A.Kovacs
2015. 227th meeting of the Electrochemical Society (ECS), Chicago, May 2015

High-Energy Micro-grain Silicon Anodes for Lithium-Ion Technology
F.Farmakis, P.Selinis, N.Georgoulas, M.Hagen, P.Fanz, S.Schiestel, A.Kovacs
2015. 4th International Conference on Modern Circuits and Systems Technologies (MOCAST), Thessaloniki, May 2015

Silicon anodes deposited on various current collectors for the development of high-density lithium-ion cells for the automotive applications
F.Farmakis,
M. Hangen, P. Fanz, A. Kovacs, S. Schiestel, P. Selinis, S. Matziris, N., C.Elmasides
2015. 7th German Symposium Advanced Battery Development for Automotive and Utility Applications and their Electric Power Grid, Aachen, April 2015

High energy density amorphous silicon anodes for lithium ion batteries deposited by DC sputtering
F. Farmakis, C.Elmasidis, P. Fanz, M. Hagen and N. Georgoulas
2015. Journal of Power Sources, 293, 301-305. doi: 10.1016/j.jpowsour.2015.05.083


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