Operando synchrotron techniques provide unique insights into the internal processes of lithium-ion batteries, but radiation-induced effects can alter cell behavior and compromise data interpretation. To better understand these phenomena, we developed an operando cell specifically designed for controlled irradiation studies, replicating synchrotron-like conditions, but at the laboratory scale. The electrolyte was selectively irradiated with an electron beam at doses of 5 and 10 kGy, and the resulting impacts on the electrochemical performance of a silicon-based electrode, gas evolution, and solid electrolyte interphase (SEI) composition were investigated. Irradiation led to immediate and dose-dependent degradation of cycling performance, with the 10 kGy-irradiated cells failing within four cycles. Gas analysis revealed increased formation of H2, CO2, CO, and CH4, the latter two gases being not produced in the nonirradiated cells, as well as the generation of specific compounds such as C2H6 and CH3CHO, absent in nonirradiated cells. While most gases showed dose-dependent production, H2 remained relatively insensitive to irradiation levels, likely due to residual water content. After irradiation followed by cycling of the cell, microscopic and electrochemical impedance spectroscopy analyses indicated significant modifications of the electrode surface and SEI morphology, with the formation of porous or inhomogeneous layers that promote further electrolyte degradation and gas release. These findings underscore the importance of accounting for beam-induced effects in operando studies, with a focus on the effect of the irradiation of the electrolyte, and provide a framework for understanding radiation-accelerated aging mechanisms in lithium-ion batteries.

Aqueous solutions are crucial to most domains in biology and chemistry, including in energy fields such as catalysis and batteries. Water-in-salt electrolytes (WISEs), which extend the stability of aqueous electrolytes in rechargeable batteries, are one example. While the hype for WISEs is huge, commercial WISE-based rechargeable batteries are still far from reality, and there remain several fundamental knowledge gaps such as those related to their long-term reactivity and stability. Here, we propose a comprehensive approach to accelerating the study of WISE reactivity by using radiolysis to exacerbate the degradation mechanisms of concentrated LiTFSI-based aqueous solutions. We find that the nature of the degradation species depends strongly on the molality of the electrolye, with degradation routes driven by the water or the anion at low or high molalities, respectively. The main aging products are consistent with those observed by electrochemical cycling, yet radiolysis also reveals minor degradation species, providing a unique glimpse of the long-term (un)stability of these electrolytes.

This paper reports the benefits of a carbon coated aluminum current collector specifically designed to promote LiNi1.5M1.5O4 (LNMO) as high potential positive electrode material. This underlayer allows efficient protection of the aluminum surface in 1 M LiTFSI/[EC/DMC] electrolyte for more than 100 cycles (C/2 – D/2) in experimental conditions mimicking the electrochemical response of LNMO. The design of such coating appears therefore as a very encouraging strategy to make the use of imide-based electrolytes possible despite their corrosive properties towards aluminum. The as-developed carbon coating also reduces the interfacial impedance of an LNMO-based electrode by a factor of 5 in 1 M LiPF6/[EC/DMC] electrolyte therefore paving the way to accelerate the industrial deployment of safe "5 V" Li-ion batteries.

The protection of current collectors against anodic dissolution at high potential has been identified as crucial for next generation of high energy and safe lithium-ion batteries. Herein, a systematic study of the electrochemical behavior of two grades of aluminum current collectors has been performed in five representative liquid electrolytes. Analysis of electrochemical data and microscopy images have notably shown that aluminum current collectors appear to be stable up to 5 V vs. Li+/Li in the presence of the reactive LiPF6 salt whereas imide salts trigger the aluminum anodic dissolution except in ionic liquid medium. It was also observed that the grade of the tested aluminum current collectors had little impact. To support the robustness of this study dedicated to practical developments of the ?5 V? Li-ion battery technology, a statistical analysis has been performed for the most corrosive electrolyte formulation (1 M LiTFSI/[EC/DMC]). These data show the anodic dissolution systematically occurs in a reproducible way whatever the sampling area of the aluminum foil.

Since 2015, ARMOR has been designing and producing coated current collectors for lithium-ion batteries and super-capacitors. The En’Safe® technology (represented in Figure 1) uses a thin conductive coating made of carbon and polymer deposited on a metallic substrate. The presence of this thin layer results in lower contact resistance and improved adhesion between the substrate and the electrode which ultimately allows for improved power performances and better cyclability of these energy storage systems (1). At the industrial scale, the deployment of high-voltage positive material (such as LiNi0,5Mn1,5O4) for new Li-ion battery generation is still facing many issues. Indeed, the different cell components of the positive side can suffer from degradation when polarized at high voltage and high performances are still not achieved. According to our extended investigation, the use of imide-based lithium supporting salts (LiTFSI or LiFSI) is very promising for next generation battery as it is much safer than LiPF6 and enable to stabilize the positive electrode/electrolyte interface, However, traditional aluminium current collector suffers from severe oxidation from 3.7 V vs. Li+/Li in such media. In this contribution, we will present the new challenges facing ARMOR coated current collectors for next generation lithium-ion batteries with special emphasis on aluminium stability when polarized at high voltage in Al3+-complexing electrolyte media. We will show that the ARMOR coating effectively suppresses aluminium oxidation without any additive or change in solvent. In addition, we are also developing novel aluminium coatings stable enough up to 5 V vs. Li+/Li in order to ensure a high electronic conduction and a long time life of the positive current collector. (1) C. Busson et al., Journal of Power Sources 406 (2018) 7. Figure 1

Aqueous batteries, particularly those integrating organic active materials functioning in a neutral pH environment, stand out as highly promising contenders in the stationary electrochemical storage domain, owing to their unparalleled safety, sustainability and low-cost materials. Herein, a novel di-block oligomer (DNVBr), serving as the negative electrode of an all-organic aqueous battery, is shown to offer exceptional output capabilities. The battery's performance is further enhanced by a unique intermixed p/n-type storage mechanism, which is able to simultaneously exchange light and naturally abundant Na+, Mg2+ and Cl-. Reaching up to 105 mAh/g, this system shows remarkable capacity retention for several thousand cycles (6500 cycles, ~40 days) in various neutral electrolytes, including raw ocean water (~3000 cycles, ~75 days). The surprisingly fast kinetics of this di-block oligomer allow to attain an unmatched specific capacity of near to 60mAh/g electrode while entirely devoid of conducting additives, and more than 80mAh/g electrode with 10% carbon additive, as well as displaying an areal capacity as high as 3.4mAh/cm2 at C rate. Full cell validation was demonstrated over 1600 cycles by virtue of a commercial TEMPO molecule, which permitted an energy density of close to 40Wh/kgmaterials at C rate in a self-pH-buffered and inexpensive aqueous electrolyte.

Aqueous ionic batteries are a promising technology for environmentally friendly grid storage systems as they reduce cost, risk and environmental impact, although this is at the expense of energy density.[1] Designing such batteries from inexpensive, abundant, recyclable and non-toxic organic active materials provides a way towards improving both the environmental and economic impact of these systems. Herein, the first battery materials that work with simultaneous uptake and release of both cations (Na, Mg) and anions are proposed by designing mixed p-type and n-type “di-block” oligomers[2,3]. It demonstrates optimal potential, extremely fast kinetics and highly competitive capacity and cyclability in both neutral Na and Mg electrolytes, including ocean water. Through a combination of UV-Vis spectroelectrochemistry, EQCM, and operando synchrotron-XRD a simultaneous cation/anion insertion mechanism was proven and rationalized. The surprisingly fast kinetics of this di-block oligomer allow to attain an unmatched specific capacity of near to 60mAh/g per gram of electrode while entirely devoid of conducting additives, and more than 80mAh/g per gram of electrode with 10% carbon additive. Based on these findings, full organic cells with millimeter-thick electrodes were assessed [4]. These findings may well provide a viable option, thereby promoting the design of cutting-edge, low-cost, rocking-chair dual-ion aqueous batteries. [1] Wu Li, J. R. Dahn, D. S. Wainwright, Science. 1994, 264, 1115-1118 [2] S. Perticarari, Y. Sayed-Ahmad-Baraza, C. Ewels, P. Moreau, D. Guyomard, P. Poizot, F. Odobel and J. Gaubicher, Adv. Energy Materials, 2018, 8 (8), 1701988 [3] S. Perticarari, T. Doizy, P. Soudan, C. Ewels, C. Latouche, D. Guyomard,F. Odobel, P. Poizot, J. Gaubicher, Adv. Energy Materials, 2019, in press [4] S. Perticarari, E. Grange, T. Doizy, Y. Pellegrin, A.-J Fernandez-Ropero, D. Guyomard, P. Poizot, F. Odobel and J. Gaubicher, Chem . Mater. 2019, (10.1021/acs.chemmater.8b03282

A selection of recent developments at IMN will be reviewed on several research directions dealing with new electrode and electrolyte materials for batteries. We focus on innovative surface modifications of electrode components, new electrode materials, compositions and architectures, and failure mechanism upon cycling by in-depth characterization through coupled advanced techniques. We cover the topics of silicon electrodes for Li-ion batteries, positive and negatives for Na batteries, renewable organic aqueous batteries, and all-solid-state ionogel Li-metal batteries. Surface derivatization of powder oxide materials by molecular grafting modifies their interfacial chemical reactivity, thus increasing cycle life and decreasing self-discharge. Molecular junctions through double-side grafting between non-carbon-coated LFP and multiwall carbon nanotubes (MWCNT) enables original electrode architecture, leading to higher specific capacity and better capacity retention. Our recently synthesized lithium-doped PANI shows excellent performance both as bulk material and as thin layer coating of bare LFP particles. We are also developing organic materials for bulk application in the new generation of renewable organic batteries. New results in the area of organic aqueous batteries for renewable energy storage will be disclosed. In the Na-FePO4 system, we identified the intermediate phase as a fully ordered Na2/3FePO4 composition showing a vacancy ordering along the channels coupled with a Fe(II)/Fe(III) charge ordering. Ab initio DFT total energy and molecular dynamics calculations lead to the optimized structure of the Li2/3FePO4 phase, and show the Na2/3FePO4 phase is thermodynamically stable while the Li2/3FePO4 phase is metastable. In the domain of negatives for non-aqueous Na-ion batteries, we found GaV4S8 is a new material with high cycled capacity of 500 mAh/g and an atypical reaction mechanism. In the field of silicon negative electrodes, we show some examples of nanoscale STEM-EELS imaging of the reaction mechanism upon cycling, and we describe an electrode maturation process that improves the performance whatever the type of silicon, binder and conductive agent. We also identify the end-of-life mechanism that is different in half cell and in full cell. Ionogels, which are confined ionic liquids within various host networks, are developed in order to fabricate self-standing solid-state membranes, all-solid-state Li metal batteries, and all-solid-state supercapacitors with good performance. We analyze as well what are the needed criteria to obtain good cycling efficiency and durability of the Li metal electrode in contact with these ionogel solid electrolytes.

The development of intercalation chemistry in the early 70s has particularly enabled the deployment of novel and efficient electrode materials for electrochemical storage. A striking example is the commercialization of the first lithium-ion (rocking-chair) battery in 1991. Recently, a resurgence of new intercalation structures has occurred with the development of sodium-ion batteries, and therefore materials able to reversibly accommodate sodium ions in layered or porous solids (e.g., 3d transition-metal oxides). However, not only metal cations can be incorporated into multi-dimensional structures but also polar molecules and anions especially in 2-D host lattices where they can be accommodated through chemical or electrochemical reactions, respectively. Herein, we specifically report on disodium 2,5-(dianilino)terephthalate as a multifunctional organic intercalation material able to chemically exchange metal cations and accommodate organic polar molecules as well as host anions under electrochemical charging conditions. Powder X-ray diffraction measurements coupled with other analytical techniques were performed for evidencing the Na/Li exchange reaction as well as the solvent intercalation. Moreover, galvanostatic cycling tests and impedance spectroscopy measurements were performed to demonstrate the occurrence of anion intercalation process and the resulting effect on the conductivity of the analogous dilithium 2,5-(dianilino)terephthalate compound.

This work reveals the great potential of in situ dielectric spectroscopy for deciphering the motion of ions and electrons on different scales in lithium‐ion battery electrodes. One of the main bottlenecks limiting composite electrode kinetics and energy density, is a critical lack of fundamental understanding with respect to the electronic and the ionic transport within the electrode architecture. The latter is a granular material made up of clusters of particles, in which the particles are separated by boundaries that limit the electronic transport. The ionic transport is also severely restricted due to its tortuous porosity. Here, in situ dielectric spectroscopy is used to study the lithium‐ion battery LiNi1/3Co1/3Mn1/3O2 composite electrodes. Short‐ and long‐range motions of ions are evident in the low‐frequency region. At higher frequencies, the influence of the adsorbed electrolyte ions on the electronic transfer at the micrometer scale is shown.

A suspension of Li4Ti5O12 and of Ketjen black in a solution of 1M lithium bis(trifluoromethanesulfonyl)imide in propylene carbonate is studied as the anolyte for semisolid redox flow batteries. The rheological behavior and electronic conductivity are studied both at rest and under shear flow. The electrochemical behavior is evaluated at rest as a function of the charge/discharge rates and of the thickness of the suspension in the electrochemical cell. The highly beneficial influence of the addition of a non-ionic surfactant in the composition of the suspension is demonstrated. All practical properties are improved with respect to semisolid redox flow applications. The viscosity decreases, the electronic conductivity increases and is less affected by the shear flow, and the electrochemical performance is improved. Moreover, the suspension shows much better stability, so its performance is preserved over time.

In an attempt to optimize a suspension electrode for redox flow batteries, this work demonstrates the effect of solid content and additive material on the electrical and rheological behavior of an anolyte made up of lithium titanium oxide (Li4Ti5O12 (LTO), as active material), carbon black (Ketjen black (KB), as a conductive material) suspended in organic medium (1 M lithium bis(trifluoromethane)sulfonimide; LiTFSI in propylene carbonate). The rheo-electrical properties of the anolyte are very sensitive to the Li4Ti5O12 content. The 20 wt% LTO is the maximum loading the percolated KB network can sustain without significant loss of the electronic conductivity and flowability of the electrode. Interestingly, this critical concentration increases to 25 wt% by addition of trace amount of conductive carbon nanofibers (CNFs) which electronically wire the conductive pathways and even reduce viscosity of the suspension electrode. Under shear flow, the suspension electrodes show three-regime flow curves with intermediate shear-thickening regions in accordance with minima in the conductivity. These minima are sharper at higher KB content, but nearly disappear in suspension electrodes with CNFs additive implying its role in wiring the ruptured conductive pathways under flow. (C) 2014 Elsevier B.V. All rights reserved.

Solid and flexible ionogel-based membranes are obtained by a simple one-step process. Tuning the composition of the silica–polymer hybrid membranes allows the attainment of highly specific properties. The high ionic conductivities of the solid membranes are in the range of those of the ionic liquid electrolytes on which they are based. Good mechanical properties and high transparency from 250 to 1000 nm are also observed. The membranes are successfully applied within entirely solid lithium batteries. As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re-organized for online delivery, but are not copy-edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Sodium-ion batteries (SIB) are considered as an attractive alternative to lithium-ion batteries (LIB) as they could potentially be much less expensive, safer, and environmentally friendlier[1]. Clearly, one of the major concerns that we are currently faced with consists in determining to what extent the results gathered over the past twenty years in the Li battery field, can be transferred to the Na one. Our research directly addresses this issue by highlighting two facts: 1-The Na intercalation process in FePO4 is significantly different from the Li one with the existence of a stable intermediate composition Na2/3FePO4.[2],[3],[4],[5] By combining electronic and X-Ray synchrotron radiation diffractions as well as Mössbauer and NMR spectroscopies, we identified the intermediate phase as a fully ordered Na2/3FePO4 composition showing a vacancy ordering along the channels coupled with a FeII/FeIII charge ordering. Thanks to ab initio DFT calculations a very good agreement between all analytical methods was found and definitely confirms the good assignment of the superstructure.[6] 2-Contrary to what has hitherto been observed for Li batteries, the thermodynamic phase diagram of FePO4[3] needs thorough reassessment as far as the dynamic intercalation/deintercalation of Na ions within a cycling battery is concerned. Indeed, based on operando synchrotron X-Ray diffraction, we show that structural phase transformation does not proceed at constant composition. Instead, we witnessed the occurrence of vastly extended limits of solubility, which are characterized by continuous variations in the lattice metric mirroring that of the Na occupancy. This striking result[7], hitherto unseen in material science, to our knowledge, results in Na batteries having an enormous advantage over Li ones, since the lattice volume mismatch during phase transformation is reduced by a factor of 30% and 10% on charge and discharge, respectively when compared to what is predicted based on the thermodynamic phase diagram. Kinetically controlled structural behavior such as this could clearly compensate for the less efficient Na-related SEI, as well as the larger size of Na ions compared to Li ones. We anticipate the elucidation of further noteworthy examples pertaining to the influence of dynamics on the structural behavior of positive and especially negative electrode materials of Na batteries in the near future. In light of these findings the Na intercalation process in FePO4 will be discussed. [1] Ellis, B. L. & Nazar, L. F. Current Opinion in Solid State & Materials Science, 2012, 16, 168-177 [2] Moreau, P.; Guyomard, D.; Gaubicher, J.; Boucher, F. Chem Mater 2010, 22, 4126–4128. [3] Casas-Cabanas, M.; Roddatis, V. V.; Saurel, D.; Kubiak, P.; Carretero-Gonzalez, J.; Palomares, V.; Serras, P.; Rojo, T. J Mater Chem 2012, 22, 17421–17423. [4] Lu, J.; Chung, S. C.; Nishimura, S.; Oyama, G.; Yamada, A. Chemistry of Materials 2013, 25, 4557–4565. [5] Zaghib, K.; Trottier, J.; Hovington, P.; Brochu, F.; Guerfi, A.; Mauger, A.; Julien, C. M. J Power Sources, 2011, 196, 9612-9617 [6] Boucher, F. ; Gaubicher J.; Guyomard D. ; Moreau, P., Chem. Mat., submitted [7] Gaubicher, J.; Boucher, F.; Moreau, P.; Cuisinier, M.; Soudan, P.; Elkaim, E.; Guyomard, D. Electrochem Commun, 2014, 38, 104-106

Redox-flow batteries (RFBs) store electrochemical energy in two fluids contained in external tanks, so called anolyte and catholyte which are pumped and flow through an electrochemical reactor in which electro-active species are oxidized and reduced. This feature provides to RFBs a unique ability in decoupling the energy and the power, therefore providing a significant design freedom for stationary applications. An interesting concept to deal with the energy density of RFBs, proposed by Chiang et al. [1], consists to use solid electro-active particles suspended in a Li+ containing electrolyte. The interest of such Semi-Solid Flow Cell (SSFC) system has recently been demonstrated with energy density ten times higher compared to classical RFBs [2,3]. Subsequently, Gogotsi et al. proposed an analogous to supercapacitors, the so called electrochemical flow capacitor (EFC) in which the energy is stored in the electric double layer of charged carbon particles [4]. A flowable carbon-electrolyte mixture is employed as the active material for capacitive energy storage, and is handled in a similar fashion to flow as for semi-solid batteries. Performance of SSFC (and EFC) system strongly depends on the flow ability of the anolyte and catholyte suspensions combined with their electronic conductivity which is governed by the extent of the carbon black percolation. In this regards, we have recently investigated the rheological and electrical behaviours of two carbon blacks [5], namely, Ketjen black EC-300 (KB) and C-NERGY Super C45, which differ by their primary particle size, and blends of Li4Ti5O12 (LTO) and KB, suspended in an organic electrolyte, a solution of 1M of Lithium bis(trifluoromethanesulphonyl)imide (LiTFSI) in propylene carbonate (PC). The electrochemical performance of the LTO/KB/PC-LiTFSI suspension was investigated vs. lithium metal electrode as function of the cycling rate in static mode (i.e. no flow) and using a home-made cell that allows studying the influence of the thickness of the suspension [6]. Recently, we demonstrated the very beneficial influence of the addition of a nonionic surfactant in the composition of the LTO/KB/PC-LiTFSI anolyte suspension. All practical properties are improved with respect to semi-solid redox flow application. As a matter of fact, the viscosity is decreased, the electronic conductivity is increased and is less affected by the shear flow, and the electrochemical performance is increased. Moreover, a much better stability with time of the suspension is obtained, which means the preservation of its performance with time. References [1] Y.-M. Chiang, W. C. Carter, B. Ho, and M. Duduta, WO2009151639A1, 2009. [2] M. Duduta, B. Ho, V. C. Wood, P. Limthongkul, V. E. Brunini, W. C. Carter, Y.-M. Chiang, Adv. Mater., 1, 511 (2011). [3] S. Hamelet, T. Tzedakis, J.-B. Leriche, S. Sailler, D. Larcher, P.-L. Taberna, P. Simon and J.-M. Tarascon, J. Electrochem. Soc., 159, A1360 (2012). [4] V. Presser, C. R. Dennison, J. Campos, K. W. Knehr, E. C. Kumbur, and Y. Gogotsi, Adv. Energy Mater., 2, 895 (2012). [5] M. Youssry, L. Madec, P. Soudan, M. Cerbelaud, D. Guyomard and B. Lestriez, Phys. Chem. Chem. Phys., 15, 14476 (2013). [6] L. Madec, M. Youssry, M. Cerbelaud, P. Soudan, D. Guyomard and B. Lestriez, J. Electrochem. Soc.,161, A693 (2014) Figure 1. (a) Variation of the (a) conductivity Σ and of the (b) viscosity η with the shear rate for 20LTO3KB composite suspensions at 0 and 5 wt% TX (at 25 °C). (c) Comparison of the typical galvanostatic discharge/charge profiles of 20LTO3KB anolyte suspensions without and with 5 wt% of the non-ionic surfactant (TX) obtained in static mode (no flow) at C/25 rate for 0.75 mm thickness. The arrows denote the signature of an heterogeneous electronic wiring of the LTO particles in the 0TX anolyte.

The fruitful contribution of Broadband Dielectric Spectroscopy (BDS) to study hierarchical materials applied to batteries electrodes has been previously shown [1-5]. The results demonstrate that the broadband dielectric spectroscopy technique is very sensitive to the different scales of the electrode architecture involved in the electronic transport, from interatomic distances to macroscopic sizes, as well as to the morphology at these scales, coarse or fine distribution of the constituents. When the frequency increases, different kinds of polarizations appear from interatomic distances to macroscopic sizes (Fig. 1) and give rise to dielectric relaxations in the following order: (a) space-charge polarization (low-frequency range) due to the interface sample/current collector; (b) polarization of clusters of particles (micronic scale) and (c) polarization of particles due to the existence of resistive junctions between them; d) electron transfers (nanometric or interatomic scale). The BDS measurement was up to now ex situ measurement, on dry electrode. They provide a fundamental insight into the conduction properties at all scales of the materials before being integrated in a real battery. An innovative device (measurement cell) has been developed to make synchronized BDS measurements and electrochemical cycling. The frequency range is about 103 - 1010 Hz. In this work, data acquisitions were made on dry electrode (LiNi1/3Co1/3Mn1/3O2 / Carbon black / PVdF) and then on the same electrode wetted with an electrolyte. Short- and long-range motions of ions are evidenced in the low-frequency region. At higher frequencies, the study shows for the first time the influence of the ions of the electrolyte on the transfer of the electronic charges (holes) in LiNi1/3Co1/3Mn1/3O2at the micronic scale. Acknowledgements Financial funding from CNRS, Université de Nantes, UMICORE, and the ANR program n° ANR-09-STOCK-E-02-01 is acknowledged. References 1. J.C. Badot, E. Ligneel, O. Dubrunfaut, D. Guyomard, and B. Lestriez, Adv. Funct. Mater. 2009, 19, 2749. 2. J.C. Badot, E. Ligneel, O. Dubrunfaut, J. Gaubicher, D. Guyomard, B. Lestriez, Phys. Chem. Chem. Phys. 2012, 14, 9500. 3. K. Seid, J.C. Badot, O. Dubrunfaut, S. Levasseur, D. Guyomard, B. Lestriez, J. Mater. Chem. 2012, 22, 2641. 4. K. Seid, J.C. Badot, O. Dubrunfaut, S. Levasseur, D. Guyomard, B. Lestriez, J. Mater. Chem. 2012, 22, 24057. 5. K. Seid, J.-C. Badot, O. Dubrunfaut, M.T. Caldes, N. Stephant, L. Gautier, D. Guyomard B. Lestriez. Phys. Chem. Chem. Phys. 2013, 15, 19790. Figure 1. Schematic description of a hierarchical architecture at different scales of a powdered material: different sources of polarizations vs. frequency and size.

We report on the rheological and electrical properties of non-aqueous carbon black (CB) suspensions at equilibrium and under steady shear flow. The smaller the primary particle size of carbon black is, the higher the magnitude of rheological parameters and the conductivity are. The electrical percolation threshold ranges seem to coincide with the strong gel rather than the weak gel rheological threshold ones. The simultaneous measurements of electrical properties under shear flow reveal the well-known breaking-and-reforming mechanism that characterises such complex fluids. The small shear rate breaks up the network into smaller agglomerates, which in turn transform into anisometric eroded ones at very high shear rates, recovering the network conductivity. The type of carbon black, its concentration range and the flow rate range are now precisely identified for optimizing the performance of a redox flow battery. A preliminary electrochemical study for a composite anolyte (CB/Li4Ti5O12) at different charge-discharge rates and thicknesses is shown.

To improve the performance of the positive electrode in batteries, it is important to thoroughly characterize these materials during battery cycling, beyond just electrochemical characterization. Among the very few techniques available for operando studies, X-ray Absorption Spectroscopy (XAS) appears very powerful, with high spatial and time resolutions provided by synchrotron radiation. Moreover XAS is well known for its capabilities in charge transfer and structure determinations, both being the major changes induced by electrochemical cycling of electrode materials. By an appropriate combination of three XAS beamlines using a specially designed electrochemical cell, we have studied composite positive electrodes made with LiFePO4 as the active material. We directly observed the heterogeneity of the electrode during operation, some parts being delayed and others advanced, compared to the mean charge state of the electrode. A mapping of this heterogeneity was made at different length scales.