Magnesium batteries with Innovative electrolyte and efficient Organic or Sulfur Cathodes – MAIOSC

The emergence of a commercial magnesium battery with high performances is conditioned by the development of new electrolytes and electrode materials beyond the current state of the art. Indeed, the use of divalent cations, Mg2 +, imposes the development of breaking strategies, both in terms of the design of new magnesium salts and positive electrode adapted to the divalent character. of Mg2+. Thus the MAIOSC project aims to address these scientific drawback and proposes new electrolytes, high-performance positive electrodes i.e. organic material or sulfur, coupled to a metallic Mg as negative electrode. This innovative materials aspect of the project is coupled with a fundamental approach to study electrolytes/electrode interfaces and bulk material in order to advance in understanding the effect of Mg2+ complexation in solution on the reactivity at interfaces by in situ and operando measurements.

Various anions obtained by reaction between BH4 - and phenol derivatives (4 compounds evaluated) or thiophenol were synthesized. The use of thiophenol makes it possible to obtain an improvement in the reversibility of the Mg / Mg2 + reaction. Regarding the p-conjugated compounds, more than 10 compounds were evaluated, the most notable results in terms of reversibility of the Mg / Mg2 + reaction are those obtained with anthracene and ter-butyl anthracene at low concentration.
On the positive organic electrode side, the Mg (Li2) -p-DHT and Li4-p-DHT compounds were synthesized and characterized. The electrochemical performances of Mg (Li2) -p-DHT and Li4-p-DHT were evaluated, in 3 Mg electrode cells configuration (and in Li cell for comparison). If the expected behavior has been obtained in Li cells, very low reversibility is obtained in cavity electrode and Mg cells whatever the electrolyte used. The synthesis of polyhydroxybenzoquinonedisulfide (PHBQD) was carried out, its electrochemical properties were evaluated in lithium and magnesium version. In lithium battery, stable capacity has been obtained in sulfolane medium. In the Mg version, reversibility is observed even if a notable loss of capacity is obtained during cycling. This decrease in capacity seems to be linked to a difficult extraction of Mg2 + from the polymeric structure.

Different positive electrode materials will be synthesized at IMN and characterized in a cavity electrode and Mg cell at LEPMI. Targets are derivatives of anthraquinone, quinone (such as thioazoloquinone) and pyrene for organic salts. MOFs will also be evaluated, such as CPO-27 and its sulfur-containing homologue. The characterization of the Mg / electrolyte interfaces will be continued. The electrochemical mechanisms associated with the oxidation / reduction of organic compounds (positive electrode) will be studied by operando studies coupling electrochemistry to spectroscopy (FTIR and Raman)

Oral presentation “Organic cathode based on quinone-sulfide polymer for both Li and Mg batteries”. A. Ngo et al. 237th ECS meeting, 10-14 May 2020. Canceled due to COVID-19

Today, the development of energy technologies is essential for our industrialized societies, and a rapid overview of our modern way of life shows how much we are tributary of them. The environmental concerns over the use of fossils fuels and the limited resources have induced great interest in producing electric energy from renewable sources. However these renewable sources need electrical energy storage to smooth out the intermittency of their energy production. In addition, the development of hybrid and electric vehicles accentuate the demand in efficient and low cost electric energy storage. Since their commercial appearance, Li-ion batteries have flooded the energy storage market. Lithium production has doubled in the last ten years. Even though Li reserves are estimated to be quite large, their concentration in specific geographic areas makes Li a strategic metal. Moreover metallic Li cannot be directly used with liquid electrolytes due to safety issues related to the formation of dendrites during Li plating, which may induce short circuits. Consequently large attention has been paid to develop alternative rechargeable devices using metal electrodes. Rechargeable magnesium batteries are currently considered among the most promising candidates for next generation energy storage system because of the following assets high performances, low cost, safety and less environmental impact. The emergence of marketable magnesium battery more efficient than their Li-ion based counterparts cannot succeed without the development of new electrolytes and positive electrode materials outdoing the state of the art. The effective use of divalent cations must go through ground-breaking strategies into those developed for Li, in terms both of the design of the new magnesium salts and of the positive electrode materials adapted to the divalent character. Large scientific advances are necessary in order to propose i) electrolytes that are non-corrosive, electrochemically stable over a wide potential window, allowing the reversibility of the magnesium electrode and ii) positive electrodes exhibiting high capacity and potential enabling high energy density. Thus, the MAIOSC project, "Magnesium Innovative electrolyte and efficient Organic or Sulfur Cathodes", aims to address these scientific challenges and proposes innovative and efficient electrode, organic material and sulfur for positive electrodes and evaluate their performances in a cell coin with magnesium metal as negative. Unlike inorganic active materials, organic electrode materials and sulfur are very well adapted to the divalent character of Mg2+, and constitute a veritable solution in the development of innovative electrodes with high capacities and high cyclability. In MAIOSC project the development of innovating material are coupled with fundamental studies with the aim to understand the magnesium II complexation and its effect on the reactivity at interfaces. Therefore the Mg in situ and operando measurements will be performed on the metal electrode / electrolyte interfaces.
Moreover, the innovative materials proposed by of MAIOSC are, environmentally friendly, by using a green chemistry, and allow, in the medium term, the development of commercially available magnesium batteries