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CAlcium Rechargeable BAttery Technology

Periodic Reporting for period 2 - CARBAT (CAlcium Rechargeable BAttery Technology)

Reporting period: 2018-10-01 to 2021-03-31

We propose calcium based rechargeable batteries to be a FET helping to solve some of the Grand Challenges our modern society is facing: pollution, oil-dependency, and climate change. Today transportation contributes to >25% of the total CO2-emissions globally and while electrification of the sector is on-going still <1% of cars run on batteries – mainly due to issues of cost and driving ranges feasible (energy density limited). While the cost of the totally dominant Li-ion battery (LIB) technology has been reduced by an impressive 50%(!) the last decade, LIBs are slowly reaching their fundamental limits in terms of energy density. Furthermore, the risk of limited lithium supply and associated cost increases cannot be ignored. Therefore, new sustainable battery chemistries must be developed and Next Generation Batteries was indeed ranked as the #2 game-changing technology by the World Economic Forum in Davos 2016.

Batteries based on Ca have promise of leap-frog increase in energy densities and are especially attractive as Ca is the 5th most abundant element on Earth’s crust and can be used as metallic anode in conventional wide potential window electrolytes, as recently showcased by the coordinating partner. The main objective of CARBAT builds on this breakthrough and is to achieve proof-of-concept for a Ca anode rechargeable battery with > 650 Wh/kg and > 1400 Wh/l. CARBAT will accomplish this by combining scientific efforts and excellence in computational screening, solid-state and coordination chemistry, materials science, electrochemistry, and battery engineering, and apply this to: (i) develop cathode active materials operating at 3-4V and with capacities of 200-300 mAh/g (ii) optimize electrolyte formulations for fast Ca2+ transport (>1 mS/cm), and finally (iii) assembly of 100 mAh full cell demonstrators integrating such materials which will be validated and benchmarked vs. the state-of-the-art Li-ion technology using performance and sustainability indicators.
The objective of WP1 was to ensure efficient project coordination, quality, monitoring of progress and reporting to the EC, as well as to guarantee internal communication between the partners and external communication and dissemination of the project’s results.
The project Data management plan, containing a summary of the datasets expected to be produced and key data management practices in accordance with the FAIR principles was submitted in RP1. Datasets produced within the project duration were uploaded on european repositories. IPR Management & Communication and Dissemination plans have also been delivered. A dedicated website, including an intranet platform for internal communication and sharing, were set from the begining of the project. Networking activities with other FET-Open projects in the field of batteries include a joint Twitter account, in addition to the CARBAT Twitter account, and a joint participation at ICT2018 in Vienna. The consortium participated in events organized by FET-FX and FET Briefing projects. A Key Exploitable Result was identified and published on the Horizon Research Platform.

The objective of WP2 was to develop a suitable cathode active material, to allow to reversibly insert and extract Ca2+ cations, with a specific capacity of 200-300 mAh/g and operating at 3-4 V. The Inorganic Crystal Structure Database (ICSD) and the American Mineralogist Crystal Structure Database (AMCSD) were screened for known compounds with suitable composition and crystal structure that may favour reversible intercalation of Ca ions. A complete list including 66 compounds (from which compounds with large formula weight were excluded) was identified and the expected potential and volume variations were computed. For the compounds exhibiting better features, the calculation of energy barriers for the diffusion of Ca2+ ions was performed. The 5 most promising materials, displaying an energy barrier for Ca mobility below 0.7 eV, were chosen for synthesis, electrochemical testing and characterization. After careful experimental investigation, two compounds were identified as electrochemically active and protected via patent apllications.

The objective of WP3 was to develop a new electrolyte with suitable properties. The computational screening within the project expanded upon this SotA picture and excluded some prospective components as less relevant from a technological perspective. Assessment of the impact of the electrolyte formulation on the transport properties, passivation layers, and Ca electrodeposition was completed. The relationship between the coordination number and ion-pair dissociation and intrinsic properties such as thermal stability, conductivity, and viscosity for Ca-battery electrolytes was explored. The analysis of the solvation shell composition and any possible influence on the cation mobility by IR and Raman spectroscopy was completed. Alternative electrolyte concepts were investigated.

The objective of WP4 was the assembly of a demonstrator cell using Ca metal anode, the cathode material developed in WP2 and the electrolyte optimized in WP3. As contingency plan, TiS2 was selected as cathode material for the demonstrator assembly. The cathode manufacturing process was completed and its compatibility with the Ca electrolyte tested.
The CARBAT project is the seed for the exploration of a new high energy battery technology based on abundant elements that addresses the electrochemical energy storage market. The project focus is to obtain proof of concept a full cell. One starting point is cathodes materials screened through DFT calculations. So far three potential compounds have been identified and their viability were evaluated. Another, is novel electrolyte formulations with low viscosity and high ion conductivity which have resulted from a combined computational and experimental approach. These are now subject to detailed analysis and improvement in terms of Ca electrodeposition for practical usage.

The CARBAT existence, goals and partners have been widely communicated in several events, targeting a wide variety of audiences, from general public (e.g. participation in international battery expositions or national job fairs, science festivals, teaching and training activities) to specialized audiences (e.g. invited talks at scientific meetings). The consortium have produced a 2-minute animated video on the project's objectives and made it available to the general society on YouTube. These have all contributed to enhance the visibility of the European action of FET-Open, targeting radically new emerging technologies in general, and allowed a wide range of stakeholders to, at least begin to, grasp the potential impact of a calcium based battery technology. The project’s consortium is at the same time making an effort to contribute to open and collaborative science by participating in the Open Research Data Pilot and following the FAIR principles of data management. CARBAT has for the moment generated fundamental results in modelling and in materials research - 13 publication were published in peer-reviewed journals and 2 patents filed within the project duration. One of the publications is an invited review on Ca battery chemistries in The Chemical Reviews (IF: 52), with the participation of all CARBAT partners, which should serve to further enhance the visibility of the consortium.
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