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Sulfur-Aluminium Battery with Advanced Polymeric Gel Electrolytes

Periodic Reporting for period 2 - SALBAGE (Sulfur-Aluminium Battery with Advanced Polymeric Gel Electrolytes)

Okres sprawozdawczy: 2018-11-01 do 2021-04-30

Batteries are nowadays one of the hottest topics in R&D due to the spread of the electrical vehicles (EV) along with the self-consumption and storage markets. However, most of the batteries used today are based in expensive and relatively scarce resources such as lithium and recent estimations foresee an increase of the Li prices by 25% in the next few years . Lithium has another important issue: safety, as shown in the recent case of commercial products from the company Samsung, for instance.

To reach the goal of cutting down emissions by 2030, a change in the global energy production and consumption is paramount, and storage mechanisms must adapt to such changes. With this all in mind, for the mid and long-term needs of the society, the search of alternative and new energy storage systems and battery technologies are of the most importance, in good alignment with the EU interests for the years to come.

In this sense, the SALBAGE project addresses the problem from a very innovative point of view, with a series of approaches which combination, has never been tried before including:

• The use of inexpensive and rather available materials as ALUMINIUM and SULFUR for anode and cathode of a new concept of SECONDARY BATTERY.
• The introduction of POLYMER GEL ELECTROLYTES (PGEs) based on Ionic Liquids and Deep Eutectic Solvents.
• The novel use of REDOX MEDIATORS to boost performance in the SULFUR CATHODE.

The success in the combination of aluminium, sulfur and a PGE in a battery with that specific energy and voltage will pave the way towards the development of a new technology in the energy storage field, with real impact in the society progress towards more affordable and safer batteries.
The activities carried out in the framework of SALBAGE project during the first year of the project has focused on the development of the POLYMER ELECTROLYTE, ANODE AND CATHODE of the ALUMINIUM-SULFUR BATTERY. All the activities were supported by computational modelling in order to develop electrolyte characterization and screening of materials for anode and cathode .

The development of the electrolyte comprised the formulation of a protocol to synthesize Deep Eutectic Solvents (DES) and Ionic liquids (ILs). Aluminium deposition/dissolution mechanism was studied in the different DES and ILs. Among different electrolytes investigated, a DES based on cheap and sustainable materials as AlCl3 and Urea (Uralumina) showed promising properties towards Al deposition/stripping what allows its use in an Aluminium-Sulfur battery. This electrolyte was selected for further development on the basis of a combination of factors including overall technical performance, thermal stability and cost.

The first attempts to obtain a polymer electrolyte were based on the use of polyethylene oxide (PEO) as structural polymer scaffold. The preliminary results have been outstanding, both regarding its remarkable efficiency of PEO as scaffolding and regarding the electrochemical performance of the polymer-containing electrolytes, as compared to the neat liquid electrolytes.

Regarding the anode, the first task accomplished the design of a versatile and reliable electrode holders which allow a transfer of the Al electrodes from the glovebox into the electron microscope under inert gas for further characterization. The use of this standard procedure generated a baseline for the comparison of the electrochemical behaviour of various Al alloys in different ILs, DES and polymeric gel electrolytes. In combination with computational studies, several Aluminium alloys have been identified as the most prone to facilitate the activation of the anode surface and increase the overall efficiency of the battery.

Similarly to the anode, the first activities on sulfur cathode have been focused on developing a reliable experimental set-up to study rechargeable Aluminium-Sulfur batteries. New cell designs have been developed employing a careful selection of materials resistant towards chemical degradation. Insights into the mechanism of sulfur reactions have been gained by performing a systematic electrochemical study of a number of materials and DFT calculations. A variety of different sulfur-carbon composites have been studied. So far, the best performing combination of different carbon and sulfur materials delivered an energy density value of ca 600 Wh/kgS in the first discharge.
The different research lines followed in the framework of SALBAGE project for obtaining a rechargeable Aluminium-Sulfur battery have already obtained remarkable results during the first year of the project. The main advances beyond the state of the art were the following:

-A new method for the synthesis of the electrolytes has been defined, based on cheap one-pot synthesis instead of using the more expensive Schlenk line.
- A combination of computational modelling and experimental work has established that the use of specific Aluminium alloys in the anode have a beneficial impact preventing dendrite formation and disrupting oxide surface layer increasing overall efficiency of the battery.
- A new Sulfur cathode based on a composite of carbon nanotubes, high sulfur content and optimized mixture of binders has allowed obtaining an Aluminium-Sulfur battery with high energy density and cyclability.

The activities carried out during the first year of the project also brought the successful preparation of polymer electrolytes with rheological and electrochemical properties similar to the neat Deep Eutectic Solvents. These results pave the way towards obtaining a secondary Aluminium-Sulfur battery based on solid-like electrolytes during the second part of the project.

In base of all the results highlighted above, the potential impact of SALBAGE project is completely aligned with European Battery Alliance objectives and the Strategic Action Plan for batteries established by the European Commission during 2018. More specifically, SALBAGE is expected to contribute to the following socio-economic aspects:

- Secure access to raw materials for batteries. SALBAGE project seeds for an emerging battery technology based on Aluminium, Sulfur and polymer electrolytes reducing the dependence on Lithium and Cobalt, since Aluminium and Sulfur are among the most abundant elements on the Earth’s crust.
- Support the sustainability of EU battery cell manufacturing industry: the use of solid-like electrolytes in the form of polymer electrolytes will confer unique advantages in terms of manufacturing processes and safety issues: no leakage, no case needed and higher resistance to air and moisture. Furthermore, the use of Aluminium as anode will promote the replacement of lithium ion batteries avoiding thermal runaway and explosive issues inherent to this technology.
- Strengthen industrial leadership through accelerated research and innovation.
- Develop and strengthen a highly skilled workforce along the whole value chain. SALBAGE project will lay the foundations for the creation of quality jobs for researchers and highly skilled personnel.
Scheme of the Al-S battery
Elastic polymer