DEEP-SENS

The lifetime and reliability of batteries are mainly governed by Electrode-Electrolyte Interfaces (EEI) that are sheltering crucial processes. These interfaces evolve with time and during battery operation, hence a supplementary challenge deals with the monitoring of the EEI’s dynamic nature; a hot topic in the battery community. DEEP-SENS addresses this challenge and aims at a full description of this complex interface by developing operando coupled electrochemical and piezoelectric sensors, in the form of ac-electrogravimetry. With this unique and powerful tool, DEEP-SENS will focus on interfaces pertaining to the promising Na-ion battery (NIB) technology (the closest to maturation “beyond Li-ion battery options”). It will aim to characterize key processes, such as the formation of the SEI (or cathode/electrolyte interface (CEI)), stability of electrodes and characteristics of ion intercalation (including ion (de)solvation). More importantly, our research program will focus on what is unarguably one of the hottest fundamental topics which deals with establishing the local structure of the electrode-electrolyte interface. It enlists the positioning of the partially solvated cations adsorbed within electrochemical double layer, and evaluating/understanding in details the impact of its structure on the rate capability and long-term cyclability of NIBs. We will particularly focus on the Na3V2(PO4)2F3 (NVPF)//Hard carbon (HC) positive/negative electrode couple presently developed by the French battery company TIAMAT. To get a complete picture of the positional cohabitation of ions and solvent molecules within the electrical double layer (EDL), we will probe different penetration depths of the acoustic wave generated by the quartz resonator, allowing spatial resolution analyses of the interface, in order to capture the entire mechanism: all the way from the solvated alkali metal-ion in the electrolyte bulk to its insertion in the host material. To do that, DEEP-SENS consortium, which reunites complementary and talented teams, will develop a new generation advanced ac-electrogravimetry testing unit, working with piezoelectric sensors at different resonant frequencies and under different electrochemical modulation frequencies, hence offering to the battery community a new analytical technique operating with both spatial and temporal resolution, that we call “high-resolution ac-electrogravimetry”. Within DEEP-SENS project, these enhanced temporal and spatial resolution parameters will be implemented in battery research to bring added values in exploring critical interfacial issues with the aim to bring NIBs to their maturation stage. Analyses results from half-cells will be corroborated with those of practical NIB cells configuration with embedded QCM sensors, to take account redox shuttles processes. Operando analyses platform, to be built within the DEEP-SENS, will serve to design better electrode-electrolyte interface (SEI and CEI) and to achieve higher power performance, stability and enhanced cycle-life of NIBs, in view of narrowing the gap with the Li-ion technology. On the technical side, the final aim is to reach a turn-on key device of « high-resolution ac-electrogravimetry » by the end of the project, which will be made in France and that could serve as a whole the battery community worldwide.