Bernard Fraisse

Better Cycling Performances of Bulk Sb in Na-Ion Batteries Compared to Li-Ion Systems: An Unexpected Electrochemical Mechanism

Pure micrometric antimony can be successfully used as negative electrode material in Na-ion batteries, sustaining a capacity close to 600 mAh g(-1) at a high rate with a Coulombic efficiency of 99 over 160 cycles, an extremely high capacity compared to any other compound tested against both Li and Na. The reaction mechanism with Na does not simply go through the alloying mechanism observed for Li where the intermediate species are those expected from the phase diagram. In the case of Na, the intermediate phases are mostly amorphous and could not be precisely identified. Surprisingly, we evidenced that a competition takes place at the end of the discharge of the Sb/Na cell between the formation of the hexagonal and the cubic polymorphs of Na(3)Sb, the last being described in the literature as unstable at atmospheric pressure and only synthesized under high pressure (1-9 GPa). In addition, fluoroethylene carbonate added to the electrolyte combined with an appropriate electrode formulation based on carboxymethyl cellulose, carbon black, and vapor ground carbon fibers seems to be determinant in the excellent performances of this material.

Nanoconfined phosphorus in mesoporous carbon as an electrode for Li-ion batteries: performance and mechanism

Phosphorus–mesoporous carbon composites have been prepared by direct vaporization–condensation of phosphorus onto mesoporous carbon. The as-prepared P1–C1 composite showed improved performance in batteries vs. Li compared with classical P mainly due to the electronic modification of the nanoconfined P. By combining the electrochemical analysis with 31P and 7Li NMR, in situ X-ray diffraction and Raman spectroscopy we have characterized the electrochemical mechanism of the P1–C1 composite vs. Li in the battery. Such activated P is able to react reversibly with Li to form Li3P and this reaction takes place at higher potential than that of classical P. This study demonstrates that the effects of nano-confinement of an active material (AM) (here P) on mesoporous carbons paves a way (i) to stabilize different polymorphs of an active element (vs. Li) that present a modified reactivity vs. Li and (ii) to enhance the electrochemical performance of AM vs. Li. Last but not least it is demonstrated that the nature of carbon is determinant for the electrochemical performance.

TiSnSb a new efficient negative electrode for Li-ion batteries: mechanism investigations by operando-XRD and Mössbauer techniques

We report the electrochemical study of TiSnSb towards Li, as a negative electrode for Li-ion batteries. TiSnSb can reversibly take up more than 5 lithiums per formula unit leading to reversible capacities of 540 mA h g−1 and 4070 mA h cm−3 at 2 C rate. From complementary operandoXRD and Mossbauer spectroscopy measurements, it was shown that during the first discharge the TiSnSb undergoes a conversion process leading simultaneously to the formation of Li–Sb and Li–Sn alloys. At the end of the discharge, Li3Sb and Li7Sn2 were identified. Once the first discharge is achieved, both phases were shown to form Ti–Sn or Ti–Sb or Ti–Sn–Sb nanocomposites. The cycling performance of TiSnSb was shown to be excellent with maintaining 90% of the specific capacity during 60 cycles at 2 C rate. The good electrochemical performance of TiSnSb (compared to Sn and Sb) seems to be a consequence of the presence of the non-active metal. The comparative study of Ti/Sn/Sb composite demonstrated that the structural feature of the pristine material clearly impacts both the mechanism involved during the cycling and the corresponding performance.

The Quest for Polysulfides in Lithium–Sulfur Battery Electrolytes: An Operando Confocal Raman Spectroscopy Study

Confocal Raman spectra of a lithium-sulfur battery electrolyte are recorded operando in a depth-of-discharge resolved manner for an electrochemical cell with a realistic electrolyte/sulfur loading ratio. The evolution of various possible polysulfides is unambiguously identified by combining Raman spectroscopy data with DFT simulations.

A combined Mössbauer spectroscopy and x-ray diffraction operando study of Sn-based composite anode materials for Li-ion accumulators

The reaction mechanisms of Li with Sn/BPO4 composites to be used as negative electrode materials for Li-ion batteries were studied during electrochemical cycling by operando Mössbauer spectroscopy and X-ray diffraction using a specifically conceived in situ electrochemical cell. The starting composites consist of three main components: β-Sn particles as the electrochemically active species, an inactive matrix of BPO4 and an amorphous SnII-borophosphate interfacial phase linking the two former components and improving the cohesion of the composite. During the first discharge, the latter Sn(II) species are first reduced to zerovalent tin forming Li-poor Li–Sn alloys. After its complete reduction, the reaction of Li continues with β-Sn leading to Li–Sn alloys increasingly rich in Li, with a final composition between those of Li7Sn2 and Li13Sn5. X-ray diffraction shows a progressive loss of long range order of the composites with the suppression of the diffraction peaks of the initial β-Sn and the formation of an ill-defined mixture of Li–Sn alloys. The evolution of this mechanism is investigated on going from a reference Sn/BPO4 composite prepared by conventional ceramic methods with common micrometric BPO4 to a new improved material prepared by carbothermal synthesis starting from nanometric BPO4. With the new composite prepared by carbothermal synthesis, a significant improvement of the reversible capacity at the first cycle is obtained together with a slight improvement of the cycling behaviour. An additional improvement can be obtained by increasing the rate of the first discharge, and thus hampering the formation of the thermodynamically stable LiSn intermetallic.

Experimental Electron Density Study of Tetrakis-μ-(acetylsalicylate)dicopper(II): a Polymeric Structure with Cu···Cu Short Contacts

The electron density, its topological features, and the electrostatic potential of tetrakis-mu-(acetylsalicylate)dicopper(II), Cu[C(9)H(7)O(4)](2), have been derived from an accurate high-resolution diffraction experiment at 100 K. This complex exhibits a polymeric structure involving one acetyl oxygen atom as a bridge in the solid state. Only van der Waals interactions between the polymeric chains are observed. The copper cation is octahedrally coordinated with five oxygen atoms of the aspirinate ligands and one adjacent Cu with short Cu...Cu contact distances in the range of 2.6054(1) A. The Cu-O bond lengths are equal to 1.96 A except the apical one which is 2.2183(7) A. The multipole refinements were carried out using the Hansen-Coppens model coded in the MOPRO computer program. Starting from the 3d(10)4s(1) copper electron configuration, the electron density analysis and Cu d-orbital populations reveal that the observed configuration is close to being [Ar]3d(9)4s(1). As expected from the ligand field theory, the most depopulated 3d-orbital is the d(x(2)-y(2)) (1.17 e) one with lobes pointing toward the carboxylic oxygen atoms. Conversely, the d(z(2)) is the most populated orbital for a z-axis directed along the Cu...Cu bond. The atomic charges were derived from a kappa-refinement and yielded a metal net charge of +1.20(3) e. Deficits of +0.72(6) and +0.59(7) e are obtained for the acetyl carbon atoms of the aspirinate ligands, those involved in the drug activity of aspirin. Comparisons are made to the results of our previous work on the zinc-aspirinate complex.

SnSb electrodes for Li-ion batteries: the electrochemical mechanism and capacity fading origins elucidated by using operando techniques

SnSb was synthesized by ultra-fast microwave solid-state synthesis. The lithiation/delithiation mechanism of SnSb was fully revisited through operando X-ray diffraction (XRD) and 119Sn Mossbauer spectroscopy. While many studies have underlined the attractive electrochemical performance of SnSb as the electrode material for Li-ion batteries, only a few of them have focused on the complex electrochemical mechanism. In this work, the complementary results of operando XRD and Mossbauer spectroscopy were used to fully investigate this complex electrochemical system. The alloying mechanism with the reversible formation of Li3Sb and LiySn lithiated phases was confirmed and complemented with additional information on the nature of the LiySn phases, namely Li2Sn5, LiSn, Li5Sn2 and Li7Sn2. Moreover, we demonstrated that the improved performance of SnSb compared to a physical mixture of Sn and Sb lies in the nature of the interfaces between the lithiated phases at the end of discharge. The progressive decrease of the availability/accessibility of Sn for the regeneration of SnSb at the end of the charge was also identified as a major failure mechanism for the long-term cycling stability of SnSb electrodes.

Tetraaqua-bis(3-hydroxy-4-nitrobenzoato) Co(II) and Ni(II) complexes and diaqua-bis(2-hydroxy-4-methoxybenzoato) Zn(II) complex: crystal structure and thorough metal-coordination investigation

Reactions of Co(II) and Ni(II) salts with the monosodium salt of 3-hydroxy-4-nitrobenzoic acid (3) in aqueous solution resulted in isomorphous covalent complexes 3C and 3D, of centrosymmetric geometries. In similar conditions, 2-hydroxy-4-methoxybenzoic acid (5) led to the covalent Zn(II) complex 5A, exhibiting a marked dissymmetric geometry. The present crystallographic data with structural data for a series of closely related metal complexes previously reported allow a tentative rationalization of the solid-state architecture of such complexes. The dissymmetry in 5A was interpreted on the basis of a mixed (monodentate and bidentate) metal-ligation mode and a pyramidal coordination at the metal.