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With the advent of high brilliance 4th generation synchrotron sources, the issue of beam damage on the samples cannot be ignored and deserves a wide attention. It is especially true for operando studies in batteries, since the intense photon fluxes are commonly used to probe ever finer effects. Here we report on a quantitative study on the causes and consequences of synchrotron X-ray beam damage in batteries, based on the case study of operando X-ray diffraction. We show that beam damage is caused by the mingled action of dose and dose rate. The after-effects can lie in a broad range, from mild modifications of the crystalline structure to artificial phase transitions, and can thus impede or bias the understanding of the mechanisms at play. From our results, we estimate the doses at which the different effects appear, and provide recommendations for the design of operando synchrotron experiments.

Promising theoretical capacities and high voltages are offered by Li-rich disordered rocksalt oxyfluoride materials as cathodes in lithium-ion batteries. However, as has been discovered for many other Li-rich materials, the oxyfluorides suffer from extensive surface degradation, leading to severe capacity fading. In the case of Li$_{2}$VO$_{2}$F, we have previously determined this to be a result of detrimental reactions between an unstable surface layer and the organic electrolyte. Herein, we present the protection of Li$_{2}$VO$_{2}$F particles with AlF$_{3}$ surface modification, resulting in a much-enhanced capacity retention over 50 cycles. While the specific capacity for the untreated material drops below 100 mA h g$^{-1}$ after only 50 cycles, the treated materials retain almost 200 mA h g$^{-1}$. Photoelectron spectroscopy depth profiling confirms the stabilization of the active material surface by the surface modification and reveals its suppression of electrolyte decomposition.

Li-rich disordered rock-salt structures have, because of their high theoretical capacity, gained a lot of attention as a promising class of cathode materials for battery applications. However, the ...

We re-examine the charge transfer mechanism in the Chevrel phase Mo6S8 upon Mg intercalation and deintercalation by the mean of X-ray photoemission spectroscopy. We highlighted a two-step reversible charge transfer process involving successively axial sulfurs and Mo6 cluster redox center. In parallel, the Mg 2p and Mg KLL Auger transition evolution evidenced two insertion sites having different polarizations in accordance with previous studies. The nonconventional metal transition redox reaction, involved during Mg intercalation in Chevrel phase, might be at the origin of its excellent reversibility and intercalation kinetics.

Lithium-rich manganese-based layered oxides Li[Li(x)Mn(y)TM(1-x-y)]O2 with TM standing for Ni, Co, or Fe are of great interest as cathode materials for lithium ion batteries. Indeed, among all of the materials, they offer the highest rechargeable capacity and energy density. However, when used, they suffer from complex evolutions that need to be understood before their practical use. Here we report on such evolutions studied using advanced transmission electron microscopy. Structural modifications are directly observed at the atomic scale using Cs corrected STEM HAADF imaging technique, and the chemical modifications are probed by the means of STEM EELS experiments. For the first time, segregation between nickel and manganese close the particle surface is pointed out. Finally, observed evolutions are correlated within a proposed mechanism that leads to the densification of the material. Our results allow understanding the link between the decrease of electrochemical performance and these evolutions occurring into the material upon cycling.

The evolutions of the structure occurring into the lithium rich cobalt free layered cathode material Li1.2Mn0.61Ni0.18Mg0.01O2 upon the first electrochemical cycle were investigated by the means of high angle annular dark field (HAADF) imaging in a scanning transmission electron microscope and electron diffraction in a transmission electron microscope. They are coupled with electron energy loss spectroscopy (EELS) experiments in order to probe the chemical evolutions occurring during the first charge/discharge cycle. In the pristine material, the analysis of the HAADF images and electron diffraction patterns confirmed the ordering between the cations (Li or Ni with Mn) and the existence of disoriented domains stacked along the c axis. Moreover, the partial solid solution of Ni into Li2MnO3 leading to a composite material is evidenced. Upon the first charge, a loss of material is shown to have occurred, and the presence of a defect spinel phase due to the transfer of transition metal cations to the intersl...