Field Of Li-ion Batteries Research Articles

The Spin-Polarized Electronic Structure of LiFePO4 and FePO4 Evidenced by in-Lab XPS

LiFePO4 has an interesting spin-polarized electronic structure showing a (3d↑)5(3d↓)1 electron configuration of the Fe2+ ion. In this work, we have experimentally evidenced the valence electronic structure of LiFePO4 and of its delithiated compound FePO4 by X-ray photoelectron spectroscopy (XPS), which allows a visualization of the occupied densities of states (DOS) in the valence band. XPS valence spectra were compared with the DOS obtained from DFT calculations by considering GGA and GGA + U approaches. Thanks to electrochemical extraction/insertion of Li+ ions in LiFePO4/FePO4, it was possible to display the Fe 3d spin-down electron of LiFePO4, which is not present in the valence spectrum of FePO4. We show that the study of XPS valence spectra is an efficient way to access the lithium insertion rate in LixFePO4 positive electrode materials for lithium-ion batteries. Besides the contribution to the Li-ion battery field, this paper is also a rare example of experimental evidence of a spin-resolved electr...

In situ X-ray absorption spectroscopy of germanium evaporated thin film electrodes

The understanding of germanium Li-ion insertion/extraction reaction mechanism is drawing more and more attention in the field of Li-ion batteries. When a germanium thin film electrode is inserted with Li ions, the material remains amorphous until it crystallizes into Li 15Ge 4 as evidenced by X-ray diffraction. The local coordination environment of the Ge atoms of the intermediate amorphous phases was investigated by in situ X-ray absorption spectroscopy. Li-ion insertion and extraction were electrochemically controlled by continuous and intermittent galvanostatic methods. The evolution of the coordination number and interatomic distance of Ge–Ge and Ge–Li shells was determined as a function of Li composition. From a short range ordering perspective, it was observed that the first Ge–Ge interatomic distance increases and the Ge–Ge coordination number decreases with increasing Li content. The opposite is observed for the first Li–Ge interaction. Moreover, it was found that electrochemical lithiation is reversible at the atomic scale.

Ionothermal Synthesis of Li-Based Fluorophosphates Electrodes

Fluoride-based materials have regained interest within the field of Li-ion batteries largely due to the advent of nanosizing which has transformed the insulating insertion compounds into attractive electrode materials. Herein we demonstrate the effectiveness of ionothermal synthesis in the preparation of nanometric LiFePO4F and LiTiPO4F phases with structures isotopic to tavorite LiFePO4(OH) at temperatures of only 260 °C, while temperatures of 600−700 °C are required to obtain coarse powders via the ceramic method. However, the redox-active phases, which are obtained in a high state of division, have lower redox voltages than LiFePO4 despite the presence of fluorine. Additionally, LiTiPO4F shows staircase charge/discharge profiles with Ti2/3+ and Ti3/4+ couples. Though quite unusual in lithium intercalation oxides, a hint of a Li-driven Fe3/4+ transition has been detected in LiFePO4F.

Characterization of Sn–Co Nanowires Grown into Alumina Template

Nanowires of Sn-Co alloys were grown inside the channels of anodic alumina membrane by potentiostatic deposition. The scanning electron microscope images showed the formation of cylindrical nanowires whose height was increasing with deposition time. The X-ray patterns did not show significant diffraction peaks, suggesting the formation of amorphous phases. The higher content of Co in the nanowires, in comparison to the initial composition of the electrolytic bath, was attributed to a higher rate of Co electrodeposition. These nanowires seem to possess specific features suitable for innovative application in the field of Li-ion batteries due to their dimensional stability and high specific surface.

Lithium containing silazanes as precursors for SiCN:Li ceramics—A potential material for electrochemical applications

Lithium containing silicon carbonitride ceramics (SiCN:Li) were synthesized via precursor-to-ceramic-transformation of Li-containing (poly)silazanes. The precursors were obtained by lithiation of the model compound 2,4,6-trimethyl-2,4,6-trivinylcyclotrisilazane and of a commercial poly(organosilazane) VL20 ® with n-butyllithium in different molar ratios. According to Raman spectroscopic measurements, lithiation takes place at the NH groups of the molecular organosilazane structure. If the amount of n-BuLi exceeds the stoichiometric amount of NH groups, addition of n-BuLi at the vinyl groups (attached as substituents at the Si atoms of the silazane) occurs. Thermal analysis coupled with in situ mass spectrometry evidenced the loss of methane and hydrogen as the main gaseous by-products formed during the precursor-to-ceramic-transformation. The ceramization process is completed at 1100 °C in argon and yielded Li-containing silicon carbonitride, SiCN:Li. X-ray powder diffraction revealed that the resulting SiCN:Li ceramics were basically amorphous and contained LiSi 2N 3 as a crystalline phase with increasing amount of Li. Possible applications of the new SiCN:Li ceramics are seen in the field of Li-ion batteries as alternative anode or solid electrolyte material.