Simultaneous operando Nuclear Forward Scattering and transmission X-ray diffraction and ⁵⁷Fe Mössbauer spectroscopy measurements were carried out in order to investigate the electrochemical mechanism of NaFeO₂ vs. Na metal using a specifically designed in situ cell. The obtained data were analysed using an alternative and innovative data analysis approach based on chemometric tools such as Principal Component Analysis (PCA) and Multivariate Curve Resolution - Alternating Least Squares (MCR-ALS). This approach, which allows the unbiased extraction of all possible information from the operando data, enabled the stepwise reconstruction of the independent “real” components permitting the description of the desodiation mechanism of NaFeO₂. This wealth of information allows a clear description of the electrochemical reaction at the redox-active iron centres, and thus an improved comprehension of the cycling mechanisms of this material vs. sodium.

Developing multifunctional polymeric binders is key to the design of energy storage technologies with value-added features. We report that a multigram-scale synthesis of perylene diimide polymer (PPDI), from a single batch via polymer analogous reaction route, yields high molecular weight polymers with suitable thermal stability and minimized solubility in electrolytes, potentially leading to improved binding affinity toward electrode particles. Further, it develops strategies for designing copolymers with virtually any desired composition via a subsequent grafting, leading to purpose-built binders. PPDI dye as both binder and electroactive additive in lithium half-cells using lithium iron phosphate exhibits good electrochemical performance.

X-ray absorption and small-angle x-ray scattering spectra were simultaneously acquired under operando conditions in a joined technique approach, for the first time applied in the field of energy storage materials. This approach allows one to closely follow the electronic and local structure evolution, as well as monitor and quantify the morphological and nanostructural changes occurring during electrochemical cycling. Here we demonstrate its potential on the example of doped and non-doped Fe₂O₃ anode material vs. Li. Our results reveal that upon discharge Fe³⁺ is gradually reduced to the metallic state and segregated as nanoparticles. For the relithiation reaction, upon subsequent charge, we observe improved reversibility for the Sr-doped compared to non-doped and Ca-doped Fe₂O₃. We highlight that this combined technique approach is a reliable, facile and powerful tool to investigate electrode materials under realistic cycling condition. It provides an unbiased and holistic picture of the morphological and structural changes occurring during operation, which allows for adequate material tailoring.

The demand for energy storage systems with superior performance has led to the creation of hybrid supercapacitor device. With proper designs, the hybrid supercapacitive materials can achieve high performance while reducing the overall cost. Herein, a novel method is developed for preparing three-dimensional hierarchical graphitic carbon nanocomposites with highly dispersed mixed Co-Ni oxide nanoparticles (Co-Ni-O/3DG) by a facile one-pot process involving carbonization and subsequent oxidation of metal ion doped biopolymer precursors. The mixed metal nanoparticles produced during carbonization enabled a top-down preparation of 3D graphitic carbon nanosheets. The nanocomposites were fully characterized and showed excellent electrochemical performance supported by the DFT calculation. Specific capacitance of 1586 F·g ^-1 was achieved (current density 1.0 A·g ^-1 ), with capacitance retention of 94.5% after 10 000 cycles demonstrating exceptional cycling stability. In an asymmetric full-cell system using a Co-Ni-O/3DG positive electrode, high energy densities of 32.8-54.7 Wh kg ^-1 associated with very high power densities of 11358-748.6 W kg ^-1 were obtained, comparable to the most advanced contemporary supercapacitive materials, while they also possesses an improved cyclability as well as using biosourced staring materials, underlining the electrode's potential application in hybrid supercapacitor devices.

To this day, elucidating the charge transfer process in electrode materials upon electrochemical cycling remains a challenge, primarily due to the complexity of chemical reactions at the electrode surfaces. Here, we present an elegant and reliable method to probe bulk-sensitive soft edges for elucidating anodic and cathodic charge compensation contribution via X-ray Raman scattering spectroscopy. By using a hard X-ray incident beam, this technique circumvents surface limitations and is practically free of self-absorption due to its nonresonant nature. In addition, it does not require complex sample preparation or experimental setups, making it an ideal tool for potential in situ analysis of the electronic structure of electrode materials. In this study, we monitored, for the first time, bulk soft edges of both oxygen and transition metal (iron) of the cathode material Li₂FeSiO₄ during one complete electrochemical cycle concurrently. Our results reveal that the redox mechanism relies primarily on the iron (cathodic) contribution. Nevertheless, a change in electron confinement of the oxygen suggests its active involvement in the charge compensation process (anodic). Moreover, we were able to support the experimentally observed changes in the electronic structure with ab initio-based simulation.

Pyrolysis is an effective way to convert biomass into biofuel while obtaining highly porous active carbon materials. In this study, a facile approach, involving hydrothermal and pyrolysis steps, is described for preparing hybrid metal oxide nanoparticle-embedded porous hard carbon matrices (MnO/C) from the biowaste rice husk and organometallic precursors. It was found that the pyrolysis/calcination temperature had a strong influence over the microstructure, especially over the porosity, but also over the carbon content and crystallinity of the nanocomposites; hence, the electrical properties can be controlled. Galvanostatic measurements showed that the nanocomposite obtained at 600 °C exhibited the highest charge/discharge capacity and best stability, delivering an initial discharge capacity of 1104 mA·h·g^-1 at a current density of 200 mA·g^-1, and retaining a value of 830 mA·h·g^-1 after 200 cycles, suggesting excellent cycle stability. A discharge capacity of 581 mA·h·g^-1 was obtained even at a current density as high as 2400 mA·g^-1, demonstrating superb rate capability. This outstanding electrochemical performance, ascribed to high electrochemical activity of the embedded MnO nanoparticles enhanced by electrical conductivity provided through the high surface area of the active porous carbon support, is discussed in relation to the microstructure of the nanocomposite.

X-ray absorption spectroscopy (XAS) is a synchrotron-based, element-specific, short-range structural method largely used in the study of materials, already widely employed for the study of the electrochemical processes in battery systems. The high penetration of the X-rays makes XAS particularly suited for the study of battery materials under operando conditions using specifically developed in situ electrochemical cells. In this paper, the application of XAS to the study of battery materials carried out at Institut Charles Gerhardt Montpellier (France) will be outlined, illustrating the type of information provided by XAS. The challenging study of the sodiation of Bi_0.50Sb_0.50 followed individually and simultaneously at both metals will be also presented in order to highlight the typical advantages of this technique even when it is pushed at its technical limits.

In the last decade, a rapidly growing number of operando spectroscopy analyses have helped unravelling the electrochemical mechanism of lithium and post-lithium battery materials. The corresponding experiments usually produce large datasets containing many tens or hundreds of spectra. This considerable amount of data is calling for a suitable strategy for their treatment in a reliable way and within reasonable time frame. To this end, an alternative and innovating approach allowing one to extract all meaningful information from such data is the use of chemometric tools such as Principal Component Analysis (PCA) and multivariate curve resolution (MCR). PCA is generally used to discover the minimal particular structures in multivariate spectral data sets. In the case of operando spectroscopy data, it can be used to determine the number of independent components contributing to a complete series of collected spectra during electrochemical cycling. The number of principal components determined by PCA can then be used as the basis for MCR analysis, which allows the stepwise reconstruction of the “real” spectral components without needing any pre-existing model or any presumptive information about the system. In this paper, we will show how such approach can be effectively applied to different techniques, such as Mössbauer spectroscopy, X-ray absorption spectroscopy or transmission soft X-ray microscopy, for the comprehension of the electrochemical mechanisms in battery studies.

As it has been recently shown in the literature, SnSb exhibits better performance in Na-ion than in Li-ion batteries in spite of its even larger volume expansion. Where is this special behaviour coming from? In this work, the reversible sodiation-desodiation reaction of SnSb was investigated by simultaneous operando Sn and Sb K-edge X-ray absorption spectroscopy along with operando¹¹⁹Sn Mössbauer spectroscopy. Chemometric tools such as principal component analysis and multivariate curve resolution-alternating least squares were used to analyse the whole data sets to gain information on the nature and sequence of formation of different species during electrochemical cycling vs. Na. The obtained results indicate that the sodiation reaction is a two-step process clearly distinct from the reaction of SnSb vs. Li. Firstly Sb is sodiated to form Na₃Sb and an intermediate phase of nanosized metallic Sn, which we were able to identify as α-Sn, commonly unstable at ambient conditions. During the second step, this tin phase is fully sodiated to form Na₁₅Sn₄, as rarely observed for pure Sn-based electrodes. Finally, EXAFS analysis proves that the amorphous SnSb phase formed after one complete cycle is clearly distinct from the pristine material. These new insights on the mechanism of SnSb vs. Na provide a basis for understanding the exceptional electrochemical performance, which is superior not only to SnSb vs. Li but also to Sn vs. Na. The key to the enhanced cycle life and capacity retention lies in the gradual formation of amorphous, nano-confined intermediate phases and correlated elastic softening of highly sodiated tin and antimony phases which have enhanced ability to absorb and mitigate the strong volume changes occurring upon sodiation and desodiation.

In this study, we want to highlight the assets and restrictions of X-ray absorption spectroscopy (XAS) and Mössbauer spectroscopy for investigating the mechanism of the electrochemical reaction of antimony electrode materials vs. Na. For this, operando XAS was carried out during the first one and a half cycles, and the whole set of measured data was analysed using a statistical-chemometric approach, while low temperature Mössbauer spectroscopy measurements were carried out ex situ on selected samples stopped at different points of the electrochemical reaction. Complementary ab initio calculations were performed to support the experimental findings. Both techniques show that, upon the first sodiation, most Sb reacts with Na to form disordered Na ₃ Sb. This step is accompanied by the formation of amorphous Sb as an intermediate. Upon inversion of the current Na ₃ Sb is desodiated and an amorphous Sb phase, distinct from the pristine bulk Sb state, is gradually formed. However, both XAS and Mössbauer spectroscopy were unable to spot the formation of intermediate Na _x Sb phases, which were evinced in previous works by operando Pair Distribution Function analyses. The results shown here clearly assign such failure to the intrinsic inability of both techniques to identify these intermediates.

The electrochemical cycling mechanism of the ternary intermetallic TiSnSb, a promising conversion-type negative electrode material for lithium batteries, was thoroughly studied by operando X-ray absorption spectroscopy (XAS) at three different absorption edges, i.e., Ti, Sn, and Sb K-edge. Chemometric tools such as principal component analysis and multivariate curve resolution-alternating least squares were applied on the extensive data set to extract the maximum contained information in the whole set of operando data. The evolution of the near-edge (XANES) fingerprint and of the extended fine-structure (EXAFS) of the XAS spectra confirms the reversibility of the conversion mechanism, revealing that Ti forms metallic nanoparticles upon lithiation and binds back to both Sn and Sb upon the following delithiation. The formation of both Li₇Sn₂ and Li₃Sb upon lithiation was also clearly confirmed. The application of chemometric tools allowed the identification of a time shift between the reaction processes of Sn and Sb lithiation, indicating that the two metals do not react at the same time, in spite of a certain overlap between their respective reaction. Furthermore, XANES and EXAFS fingerprint show that the Ti-Sn-Sb species formed after one complete lithiation/delithiation cycle is distinct from the starting material TiSnSb.