The efficient production, storage and use of clean energy at large scale is arguably one of the major challenges that society will have to face in the next decades. The dependence of the current energy sector on dwindling fossil fuel resources makes this a timely concern for the next generation of scientists. The deployment of renewable energy carriers is largely hampered by inefficient energy storage and conversion devices. Technologies with high energy density such as water splitting/fuel cells suffer from poor efficiencies because the involved processes at solid/liquid and solid/solid interfaces are far from being understood and optimized. In particular, sluggish kinetics associated with the oxygen evolution reaction (OER) is one of the major roadblocks preventing the development of electrolyzers. Numerous studies were devoted to the development of cost-effective and efficient transition metal oxides as OER catalsysts as well as to the understanding of the complex reaction taking place on their surfaces. Even though major findings were made, no OER catalyst satisfies for the moment industrial targets in terms of activity and durability. Nevertheless, very recent findings pointed out that the OER activity can be sensibly enhanced by activating surface oxygen as active site for the reaction to proceed. Doing so, the reaction proceed through a newly uncovered mechanism for which the O-O bond formation is no more the rate limiting step, but rather the proton transfer becomes kinetically limiting. Unfortunately, we also understand that enhancing the OER activity of transition metal oxides by triggering the participation of surface oxygen to the reaction is at the expense of the stability of these catalysts. Hence, the competition is fierce among researchers to provide the adequate solution to this equation. Indeed, this correlation defines a hard line for the development of new OER catalysts and we can already foresee that it will not be overcome by using a classical approach based on controlling the surface binding energy of intermediates to the reaction. Instead, researchers have to look for extrinsic properties so to independently control the activity and the stability of the catalysts. For that, we must look at the catalyst at a different scale and consider the interfaces involved into the reaction, i.e. the solid/liquid and the solid/solid interface. In MIDWAY, a dual materials science/chemistry approach will be pursued to combat the limitations pertaining to the development of OER catalysts. For that, we propose to use to our own advantage the oxidation reaction occurring when triggering the redox activity of surface oxygen. The main goal is to prepare perovskite catalysts and activate their surface through a selective oxidation process. Doing so, we aim at understanding better the charge compensation mechanism occurring at the bulk/surface interface and the limitations related associated to the proton exchange and diffusion from the surface to the electrolyte to circumvent them. To study these complex phenomena and interfaces, the development of unique tools will be needed. Hence, online electrochemical mass spectroscopy (OLEMS) cell, in situ cells for X-ray absorption spectroscopy (XAS) and electrochemical setup for the in situ determination of the nature of the catalyst/substrate junction by Mott Schottky measurements will be developed hand to hand with the acquisition of fundamental understanding to the science underpinning the OER reaction.

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.

Since the revival of the Li-Air technology by K.M. Abraham in 1996 using non-aqueous electrolyte, this technology has been foreseen as the savior by the automobile industry, generating a worldwide competition at an academic level supported by private funding (Toyota or IBM for instance) and public agencies such as the Department of Energy as well as with the creation of startups such as Liox Power or PolyPlus Battery for instance. Even though considerable progresses have been made in the last years, the battery community realizes that Li-O2 cells have a long way to go before to be commercialized: a better understanding of the fundamental mechanisms at play during the cycling is necessary. Hence, international groups at the forefront of this field such as Bruce’s, Nazar’s, McCloskey’s, Shao-Horn’s, Gasteiger’s, Janek’s groups and others are currently placing a lot of efforts on understanding the effect of solvent properties on the discharge product formation as well as the use of redox mediators in solution as a way to overcome the large overpotential encountered during the charge. Our approach in ECCENTRIC project is in line with this worldwide push for knowledge creation regarding the physico-chemical processes upon cycling. Nevertheless, while other groups are largely focusing on the understanding of the solvent influence on the cycling properties, only few has been done concerning the understanding of the electroactive material functioning and this project aim to fill this gap with an in depth study of the electrode impact on the charge/discharge mechanism. Thus, the ECCENTRIC project starts with fundamental researches on air electrodes, further used to develop new materials electrodes for positive electrode for Li-Air batteries. The aim of ECCENTRIC is to demonstrate that viable metal-air battery can be developed following an innovation-through-science approach, involving the acquisition of new knowledges and understandings of the science underpinning the lithium-air batteries. The ECCENTRIC consortium involves three well-recognized fundamental research groups that will put together their complementary skills in Surface science and Nanosciences (CEA LICSEN partner), Material science and Processing (LCMCP) and batteries testing and characterization as well as chemistry (Collège de France UMR UMR 8260) to develop new materials and study their catalytic and electronic properties from single building block to their assembly into complex 2D and 3D network. The building blocks will be assembled in interpenetrated networks or through core/shell structures thanks to electrospinning, a simple and upscalable technique. Li-Air batteries tests made in real cycling conditions will guide the finding of the most suitable parameters for the discharge/charge processes. The project opens new avenues to other fields, such as Na-Air systems, electrode nanostructuration, as well as multiphase transport and reactivity.

The wide goal of SPICS project is to provide enhanced electrode materials for supercapacitor application. SPICS aims at developing innovative 2D carbon layered materials with enhanced storage capability thanks to the use of redox active pillars. We aim to reach volumetric capacitance of about 400 F/cm3. The original idea of SPICS is to go beyond the use of simple mechanical pillars and to introduce redox functionality to enhance specific interactions with the electrolyte leading to improved charge storage capability. To achieve this goal, an important part of the project will be devoted to an in-depth analysis of the charge compensation mechanisms through the use and development of cutting-edge characterization techniques. Indeed, these fundamental investigations based on ss-NMR and DNP, SECM (Scanning Electrochemical Microscope) and QCM derived techniques (conventional EQCM, QCM coupled with EIS and QCM coupled to electroacoustic impedance) will be undertaken to understand the impact of these active pillars on the dynamics of ion transfer at the electrode/electrolyte interface, on kinetic rate transfer constants and on faradic reactions occurrences, and will also allow to evaluate the electromechanical and structural stress experienced by the material during cycling. For the electrochemical evaluations, different electrolytes will be tested (from ammoniums salt in CH3CN to ionic liquids-based electrolytes). This tight relation between material development, advanced characterization and electrochemical evaluation will lead to the establishment of a virtuous circle resulting in a major breakthrough in correlating electroadsorption/charge transfer phenomena to smart 2D carbon materials properties, enabling the design of refined material and the selection of the most promising ones. The best material will also be tested with a solid-state electrolyte based on the use of ionogel. Supercapacitors with performances at the state of the art are expected to be achieved with these innovative 2D smart carbon materials, capacitances as high as 300 F/g and 400 F/cm3 with 90% charge retention over 10 000 cycles. Hence SPICS bridges fundamental mechanisms understandings efforts to preliminary tests responding to an important societal demand. The development and optimization of these next generation active pillared graphene materials will be enabled a close partnership between CEA, CIRIMAT and LISE. The expertise and complementarity of the 3 partners - in graphene–based materials developments, ss-NMR analysis of modified samples, electrochemical material characterization, advanced and SECM techniques - are fundamental to the success of the project. Indeed, the skills and know-how of each partners are highly relevant and necessary to address the project WPs inter-connexion, to allow an efficient project progression, to finally achieve the objectives stated above.

Li-ion batteries offer the highest energy density among current rechargeable devices and have thus become essantial for a wide range of applications. Aqueous electrolytes could in principle be an alternative to the current organic ones, provided that one can increase their cost/performance ratio. For that, their operating electrochemical window must be enlarged. Within this context, recent reports pointed toward the use of superconcentrated aqueous electrolytes, poised as water-in-salt electrolytes (WiSEs), to enlarge the operating voltage from 1.23 V to 3 V. Nevertheless, as for any new finding, rationale must be provided to understand the real practability of this approach. More specifically, questions regarding the real figures of merits in terms of capacity retention, energy and coulombic efficiencies, rate capabilities at both low and high temperature, degradation mechanisms, self-discharge and degassing must be answered. Within this context, the objective of the BALWISE project is to answer these questions through a combination of fundamental science and prototype construction and testing. More specifically, we aim at understanding the kinetic protection of the electrode by the growth of a F-based solid electrolyte interphase that passivates the negative electrode after an initial step. Furthermore, by using new derivative of the TFSI anions we aim at controlling the formation of this F-based SEI to better tune the ion transport/charge transfer at the materials interface. We will then explore a grafting strategy enlisting electrochemically assisted self-assembly of mesoporous hydrophobic thin film. Eventually, the gained knowledge about SEI formation and solvation properties of the newly studied WiSEs will be used to assemble aqueous Li-ion cells in either coin cell or pouch cells configurations and determine their performances metrics to judge on the practical viability of this approach.