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Batteries based on Calcium: from electrolyte development to full cell proof-of-concept

Periodic Reporting for period 1 - BATCA (Batteries based on Calcium: from electrolyte development to full cell proof-of-concept)

Okres sprawozdawczy: 2017-05-16 do 2019-05-15

The development of rechargeable batteries based on multivalent cations as charge carriers holds promise of enhanced energy density when compared to single valent ions such as lithium or sodium. Proof-of-concept has been achieved for magnesium batteries with complex electrolyte compositions but an analogous technology based on calcium ion would hold promise for faster reaction kinetics due to its lower polarizing character and enhanced energy density due to its lower reduction potential.

The recently demonstrated feasibility of calcium electrodeposition at moderate temperatures using conventional organic electrolytes constitutes the first step towards proof of concept. The main goal of the present proposal is to achieve proof-ofconcept of a full Ca-ion battery with high energy density through i) optimizing the electrolyte formulation enabling operation at room temperature by minimizing ion pairing and ii) developing a suitable high capacity cathode material.

The proposed research contributed to the study of new classes of electrolyte for calcium cation based batteries with high resilience upon oxidation and low tendency to ion pair formation while at the same time attempting the design of suitable cathode materials enabling calcium ion diffusion and based on suitable redox couples operating at high potential.

The approach behind the scientific project relies on the synergy between the respective expertises of the applicant and the host institution in electrolytes and crystal chemistry of battery materials. This fellowship represents also an excellent opportunity to the researcher for personal and professional development providing him with novel and advanced skills to achieve a status of professional maturity and independent thinking.
In the project, the molecular interactions within the electrolytes were studied and gave a better understanding of the complexation and ionicity. It is clear that ion-pairing and solvation hinder the kinetic of charges and this effect is larger when going from Na to Ca. It affects a large number of properties of interest such as conductivity, charge transfer and desolvation energies.

Secondly, new cathode materials were synthesized via different routes and the most promising was found to be Ca3MO6. Indeed, it was possible to extract Ca from the structure at room temperature at high potential in laboratory cell prototypes, which will be further investigated.

Finally, a study carried with an energy-cost model developed buy Berg are even more encouraging as the parameters needed (voltage and electrode capacity) to supersede Li-ion are realistically achievable.
The aim of the research program developed in BATCA was to go beyond the state-of-the-art of Li-ion technology by designing a Ca metal battery. Even if the final objective of optimizing efficient electrolytes and cathodes for full Ca battery cells, this work paved the way to further improvement.

First, a solid explanation of molecular interaction with electrolytes using sodium has been provided and will be publish in the current of the year. Secondly, now cathode materials have been synthesized using different route and have shown electrochemical activity as Ca2+ could be partially extracted from Ca3MO6 at room temperature. Until now it is the only cathode material which has shown an electrochemical activity at RT.

The electrolyte being the limiting factor, the development of a new stable electrolyte for Ca battery should allow improving performance. Moreover, both the low cost and toxicity of Ca together with an advantageous worldwide repartition makes this potential technology appealing on an industrial viewpoint.