Structural Investigations of LiFePO4 Electrodes by Fe X-ray Absorption Spectroscopy

The influence of the Li+ addition rate during the hydrothermal synthesis of LiFePO4 on the average and local structure

In hydrothermal synthesis of LiFePO4 a slower addition of Li+ to a mixture of Fe2+ + PO43- increased Fe2+ oxidation, defects within the LiFePO4 structure and iron impurities in the product. No link was seen between Li3PO4 formation and addition rate.

Cobalt-Phthalocyanine-Derived Molecular Isolation Layer for Highly Stable Lithium Anode

The uneven consumption of anions during the lithium (Li) deposition process triggers a space charge effect that generates Li dendrites, seriously hindering the practical application of Li-metal batteries. We report on a cobalt phthalocyanine electrolyte additive with a planar molecular structure, which can be tightly adsorbed on the Li anode surface to form a dense molecular layer. Such a planar molecular layer cannot only complex with Li ions to reduce the space charge effect, but also suppress side reactions between the anode and the electrolyte, producing a stable solid electrolyte interphase composed of amorphous lithium fluoride (LiF) and lithium carbonate (LiCO₃ ), as verified by X-ray absorption near-edge spectroscopy. As a result, the Li|Li symmetric cell exhibits excellent cycling stability above 700 h under a high plating capacity of 3 mAh cm^-2 . Moreover, the assembled Li|lithium iron phosphate (LiFePO₄ , LFP) full-cell can also deliver excellent cycling over 200 cycles under lean electrolyte conditions (3 μL mg^-1 ).

A laboratory-based hard x-ray monochromator for high-resolution x-ray emission spectroscopy and x-ray absorption near edge structure measurements

We report the development of a laboratory-based Rowland-circle monochromator that incorporates a low power x-ray (bremsstrahlung) tube source, a spherically bent crystal analyzer, and an energy-resolving solid-state detector. This relatively inexpensive, introductory level instrument achieves 1-eV energy resolution for photon energies of ∼5 keV to ∼10 keV while also demonstrating a net efficiency previously seen only in laboratory monochromators having much coarser energy resolution. Despite the use of only a compact, air-cooled 10 W x-ray tube, we find count rates for nonresonant x-ray emission spectroscopy comparable to those achieved at monochromatized spectroscopy beamlines at synchrotron light sources. For x-ray absorption near edge structure, the monochromatized flux is small (due to the use of a low-powered x-ray generator) but still useful for routine transmission-mode studies of concentrated samples. These results indicate that upgrading to a standard commercial high-power line-focused x-ray tube or rotating anode x-ray generator would result in monochromatized fluxes of order 10(6)-10(7) photons/s with no loss in energy resolution. This work establishes core technical capabilities for a rejuvenation of laboratory-based hard x-ray spectroscopies that could have special relevance for contemporary research on catalytic or electrical energy storage systems using transition-metal, lanthanide, or noble-metal active species.

Improved high-temperature capacity retention of the LiMn2O4 cathode lithium-ion battery by ion exchange polymer coating

An ion exchange polymer coating on the LiMn₂O₄ cathode to overcome capacity fading of a lithium-ion battery at high temperatures is first demonstrated, and it shows very good capacity retention compared with the pristine LiMn₂O₄ cathode without coating.

Characterization of Sol−Gel-Synthesized LiFePO4 by Multiple Scattering XAFS

X-ray absorption spectroscopy (XAS) was used to investigate the local structure arrangements of submicrocrystalline lithium iron phosphate and its precursors. The former material, proven to be very promising as active cathode material in lithium metal and lithium-ion batteries, was synthesized through a new procedure that combines a simple sol-gel precipitation with a moderate temperature (e.g., low cost) heat treatment. X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectra taken at the Fe K-edge pointed out the modification of the Fe site during the synthesis steps that allow one to produce the submicrometer size crystalline LiFePO4 (active material) useful for batteries applications. The XAS investigation has shown that such a material is different from the conventional crystalline LiFePO4 on the short-range order. The difference is attributed to the synthesis procedure.