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SiO x electrodes are promising for high-energy-density lithium-ion batteries (LIBs) due to their ability to mitigate volume expansion-induced degradation. Here, we investigate the surface dynamics of SiO x thin-film electrodes cycled in different carbonate-based electrolytes using a combination of ex situ X-ray photoelectron spectroscopy (XPS) and operando synchrotron X-ray reflectivity analyses. The thin-film geometry allows us to probe the depth-dependent chemical composition and electron density from surface to current collector through the solid electrolyte interphase (SEI), the active material, and the thickness evolution during cycling. Results reveal that SiO x lithiation initiates below 0.4 V vs Li + /Li and indicate a close relationship between SEI formation and SiO x electrode lithiation, likely due to the high resistivity of SiO x . We find similar chemical compositions for the SEI in FEC-containing and FEC-free electrolytes but observe a reduced thickness in the former case. In both cases, the SEI thickness decreases during delithiation due to the removal or dissolution of some carbonate species. These findings give insights into the (de)lithiation of SiO x , in particular, during the formation stage, and the effect of the presence of FEC in the electrolyte on the evolution of the SEI during cycling.

The current sustained demand for "smart" and connected devices has created a need for more miniaturized power sources, hence for microbatteries. Lithium-ion or "lithium-free" all-solid-state thin-film batteries are adapted solutions to this issue. The capability to carry out spatially resolved chemical analysis is fundamental for the understanding of the operation in an all-solid-state microbattery. Classically cumbersome and not straightforward techniques as TEM/STEM/EELS and FIB preparation methods could be used to address this issue. The challenge in this work is to make the characterization of Li-based material possible by coupling ion-milling cross section preparation method and AES techniques to characterize the behavior of a LiCoO 2 positive electrode in an all solid state microbattery. The surface chemistry of LiCoO 2 has been studied before and after LiPON deposition. Modifications of the chemical environments characteristic of the positive electrode have been reported at different steps of the electrochemical process. An original qualitative and a semiquantitative analysis has been used in this work with the peak deconvolution method based on real, certified reference spectra to better understand the lithiation/delithiation process. This original coupling has demonstrated that a full study of the pristine, cycled, and post mortem positive electrode in a microbattery is also possible. The ion-milling preparation method allows access to a large area, and the resolution of Auger analysis is highly resolved in energy to separate the lithium and the cobalt signals in an accurate way.

A dual redox process involving Ti 3+ /Ti 4+ cation species and S 2- /(S 2 ) 2- anion species is highlighted in oxygenated lithium titanium sulfide thin film electrodes during lithium (de)insertion, leading to a high specific capacity. These cathodes for all-solid-state lithium-ion microbatteries are synthesized by sputtering of LiTiS 2 targets prepared by different means. The limited oxygenation of the films that is induced during the sputtering process favors the occurrence of the S 2- /(S 2 ) 2- redox process at the expense of the Ti 3+ /Ti 4+ one during the battery operation, and influences its voltage profile. Finally, a perfect reversibility of both electrochemical processes is observed, whatever the initial film composition. All-solid-state lithium microbatteries using these amorphous lithiated titanium disulfide thin films and operated between 1.5 and 3.0 V/Li + /Li deliver a greater capacity (210-270 mAh g -1 ) than LiCoO 2 , with a perfect capacity retention (-0.0015% cycle -1 ).

CuO thin films were prepared by radio frequency magnetron sputtering using a copper target in a (Ar + O2) reactive mixture. Different sputtering parameters were varied including oxygen flow rate, total pressure, target-substrate distance, substrate temperature and target orientation. As expected, the thin film chemical composition is strongly dependent on the oxygen flow rate. CuO thin films having a good electronic conductivity (9.3 × 10(-1) S·cm(-1)) were obtained with an oxygen concentration of 12%. The texture and the columnar growth are amplified when the target is tilted. Preliminary electrochemical results highlight that CuO thin film performances in lithium systems are tightly related to their morphology and structure.

Thermal treatment of the Tavorite-type material FePO(4)·H(2)O leads to the formation of two crystallized iron phosphates, very similar in structure. Their structural description is proposed taking into account results obtained from complementary characterization tools (thermal analyses, diffraction, and spectroscopy). These structures are similar to that of the pristine material FePO(4)·H(2)O: iron atoms are distributed between the chains of corner-sharing FeO(6) octahedra observed in FePO(4)·H(2)O and the octahedra from the tunnels previously empty, in good agreement with the formation of a Fe(4/3)PO(4)(OH)-type phase. The formation of an extra disordered phase was also proposed. These samples obtained by thermal-treatment of FePO(4)·H(2)O also intercalate lithium ions through the reduction of Fe(3+) to Fe(2+) at an average voltage of ~2.6 V (vs Li(+)/Li), with a good cyclability and a reversible capacity around 120 mA h g(-1) (>160 mA h g(-1) during the first discharge).

Pure tavorite LiFePO4(OH) was synthesized through a hydrothermal route. A fine structural analysis was done by X-ray and neutron diffraction techniques. The structure consists of a three-dimensional network with iron(III) octahedra (FeO6) sharing corners, forming chains that run along the b direction. These chains are interconnected by PO4 tetrahedra, such as the resulting framework encloses tunnels of two different sizes running along the a and c axis. The lithium and hydrogen atoms were precisely localized in these tunnels. Theoretical (GGA + U) calculations performed for LiFePO4X materials (X = OH, F) confirmed our results and revealed that a unique lithium position is expected in LiFePO4(OH), as experimentally observed. For the first time, lithium intercalation was shown to occur in LiFePO4(OH) through the reduction of Fe3+ to Fe2+ at an average voltage of ~2.3 V (vs. Li(+)/Li) with a good cyclability.

A sample having stoichiometry Li[Ti(1.5)Ni(0.5)]O(4) has been synthesized to obtain a spinel structure. The resulting crystalline powder revealed a multiphase nature with spinel as the minor phase. The main phase is a new trigonal phase having a = 5.05910 (1), c = 32.5371 (1) A. The structure has been solved by direct methods working on a three-dimensional set of intensities obtained from a precession electron-diffraction experiment, and refined on synchrotron powder diffraction data in the space group P3c1. The model consists of hexagonal layers of edge-sharing octahedra occupied either by the heavy cations Ti and Ni, or preferentially by Li. On the basis of cation-site occupancies the stoichiometry becomes Li(4)Ti(8)Ni(3)O(21), which is compatible with the microanalysis results.

Lithium iron phosphate is one of the most promising positive-electrode materials for the next generation of lithium-ion batteries that will be used in electric and plug-in hybrid vehicles. Lithium deintercalation (intercalation) proceeds through a two-phase reaction between compositions very close to LiFePO(4) and FePO(4). As both endmember phases are very poor ionic and electronic conductors, it is difficult to understand the intercalation mechanism at the microscopic scale. Here, we report a characterization of electrochemically deintercalated nanomaterials by X-ray diffraction and electron microscopy that shows the coexistence of fully intercalated and fully deintercalated individual particles. This result indicates that the growth reaction is considerably faster than its nucleation. The reaction mechanism is described by a 'domino-cascade model' and is explained by the existence of structural constraints occurring just at the reaction interface: the minimization of the elastic energy enhances the deintercalation (intercalation) process that occurs as a wave moving through the entire crystal. This model opens new perspectives in the search for new electrode materials even with poor ionic and electronic conductivities.