350-400 Wh/kg Li-S prototyping pouch cells have been demonstrated in literature, although cycle life is still limited to less than 100 cycles. To meet application requirements, improving cell stability and cycle life are imperatively needed.

In such content, LISA project was born with the aim to deliver 20 Ah Li-S pouch cells with high gravimetric energy of 450 Wh/kg and volumetric energy density of 700 Wh/L, safety and stability for at least 1000 cycles. Additionally, the fabrication of proof-of-concept 3 Ah 21700 cylindrical cells was also targeted, to cover the demand of smaller cell formats with similar performances than the larger pouch cells.

To achieve such ambitious targets, a strong multidisciplinary consortium was built, including CIC energiGUNE, with 13 partners from 6 different European countries, such as Fraunhofer IWS, Varta Microbattery, Renault or VDL, and the Spanish institution LEITAT.

12 work packages (WP) were designed, covering all relevant aspects of the Li-S battery. Lithium metal anode stability, high loading cathode development and novel strategies for high performing stand-alone electrolyte systems are core tasks of the project.

CIC energiGUNE’s role in LISA

In this context, CIC energiGUNE plays a pivotal role leading the WP devoted to the development of a stand-alone dielectric as solid-state electrolyte for high performing Li-S cells, a key component of LISA cell concept.

The WP aims at the integration of a thin solid Li-ion conducting film in the final Li-S cells, to limit the amount of liquid electrolyte needed and increasing the energy density of the system. Moreover, this film can also act as protective layer against the growth of lithium dendrites, one of the most important challenges of this technology to achieve long cycling life of Li-S cells.

Together with the French partner Arkema, who provided the raw materials of the solid electrolyte, and thanks to CIC energiGUNE’s Prototyping line with dry room facilities and roll-to-roll comma bar equipment, we were able to fabricate > 100 m of thin electrolyte coating, to be used in the assembly of the final Li-S pouch cells (Figure 1). Indeed, the upscaling of the electrolyte coating production represents one of the most important critical steps accomplished in the project.

Figure 1. (a) Image of the comma bar coating machine used in this project. (b) Images of the thin film coating on a testing substrate.

Besides, CIC energiGUNE also contributes importantly on the WP of lithium anode development. The main target is to obtain thin lithium films as anode for the final Li-S cells, this way optimizing the amount of lithium per cell and, hence, influencing on the final energy density. The tasks not only focus on the deposition of lithium, but also on the integration of solid-state protective layers on top of it.

The most relevant innovation relates to the batch fabrication of these protective layers by a forefront thin film deposition technique such as pulsed laser deposition, carried out by the Finn LISA partner Pulsedeon.

In the workflow, CIC energiGUNE is in charge of the structural and electrochemical characterization of the prepared films, using techniques such as X-ray diffraction analysis (XRD), X-ray photoelectron spectroscopy (XPS), Scanning Electron Microscope (SEM) or Electrochemical Impedance Spectroscopy (EIS) (Figure 2). The advanced platform facilities and experience on surface and thin film characterization of CIC energiGUNE is being fundamental for the achievement of the WP objectives.

Figure 2. Some of the key characterization equipment used at CIC energiGUNE for LISA project: (a) SEM, (b) XPS, (c) XRD.

Developed thin solid Li-ion conducting film as electrolyte and the protected thin Li film as anode, combined with a high loading sulfur cathode being developed within the project by the German partner Fraunhofer IWS, will be eventually merged in the final optimized Li-S cell to meet the targets of high safety, high energy density and long lifespan.

Such cells can be applied in drones, electric trucks and planes, satellite and stationery energy storage facilities etc. LISA partner VDL aims at the integration of the developed cells in electric buses. This would potentially open and further increase the share of Li-S batteries in battery market.

Last but not least, the advances of the project will pave the way towards the consecution of high performing all-solid-state Li-S cells in the future.

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