Transmission Electron Microscope Studies of LiNi1/3Mn1/3Co1/3O2 before and after Long-Term Aging at 70°C

LiNi1/3Mn1/3Co1/3O2 is a potential cathode material for high-power applications in lithium-ion batteries. While cation ordering on a sqrt(3)×sqrt(3) R30° in-plane superlattice was proposed for the layered structure, the experimental data do not fully support this model. Here, we present a systematic electron diffraction study of LiNi1/3Mn1/3Co1/3O2 in the pristine state and after aging. Our results show that a mixture of different phases in the starting material transforms to the O3-type phase and the cubic spinel phase after aging, accompanied by an increase in the percentage of polycrystals

Self-organized carbon nanostrips with a new LiC10 structure derived from carbon nanotubes

Single walled carbon nanotubes (SWNTs) were reacted with molten lithium at 220 °C for two weeks. This induced dramatic changes in their structure as shown by x-ray and electron diffractometry and Raman spectroscopy. A significant fraction of the initial SWNTs transformed into flat nanostrips having intercalated lithium in between them. Lithium forms a superlattice commensurate with that of the graphitelike nanostrips with [square root of]7×[square root of]3 in-plane distribution. This new structure corresponds to the LiC10 composition

Hexagonal to Cubic Spinel Transformation in Lithiated Cobalt Oxide

A transmission electron microscopy (TEM) investigation was performed on LiCoO2 before and after it had been subjected to charge/discharge cycling in electrochemical cells, as well as on delithiated Li(1–x)CoO2 before and after thermal aging. Turbostratic disorder involving small rotations of the O-Co-O slabs was found in as-received material, and in material subjected to a few cycles. In LiCoO2 subjected to extensive charge/discharge cycling, it was found that increasing amounts of the trigonal O3 phase had transformed to H1-3 phase and to the cubic spinel phase. The transformation appears to initiate on the surfaces of trigonal crystals. The orientation relationship between the trigonal and spinel phases was determined from diffraction patterns to be {0001}trigonal parallel {111}cubic and trigonal parallel cubic. The difference in unit cell dimensions leads to transformation stresses when spinel crystals are formed, and spallation of surface layers was observed. The formation of a spinel phase could suppress electrochemical performance of LiCoO2 cathodes in heavily cycled cells. Aging in the charged state also can alter particle surfaces and therefore the performance

Mechanism of electrochemical performance decay in LiCoO₂ aged at high voltage

International audienceElectrochemical cells of LiCoO2 were charged to 4.7 V versus lithium, and held at this high voltage for various times. After this high voltage aging, the cells suffered irreversible losses of capacity and suppressed kinetics. Transmission electron microscopy showed the formation of some cubic spinel phase in the LiCoO2 material subjected to high voltage aging, and an increased density of dislocations and internal strains

Carbon Surface Layers on a High-Rate LiFePO4

Transmission electron microscopy (TEM) was used to image particles of a high-rate LiFePO4 sample containing a small amount of in situ carbon. The particle morphology is highly irregular, with a wide size distribution. Nevertheless, coatings, varying from about 5-10 nm in thickness, could readily be detected on surfaces of particles as well as on edges of agglomerates. Elemental mapping using Energy Filtered TEM (EFTEM) indicates that these very thin surface layers are composed of carbon. These observations have important implications for the design of high-rate LiFePO4 materials in which, ideally, a minimal amount of carbon coating is used