Lithium has been inserted into the spinel Li 4 Ti 5 O 12 by both chemical and electrochemical methods. The cation distribution in the lithiated phases has been analyzed by 6,7 Li NMR, Raman spectroscopy, and X-ray diffraction, and the distribution in the chemically inserted compound has been analyzed additionally by neutron diffraction. A refinement of structural parameters has been carried out by applying the Rietveld method to the neutron diffraction pattern. It is shown that the two insertion methods are based on different mechanisms. Chemically inserted lithium ions are trapped in the (48f) sites of the spinel structure from which they cannot be extracted by electrochemical means. In contrast to the electrochemical Li-insertion, which is accompanied by a spinel to rocksalt phase transition, no such structural change is found for chemical insertion. The consequences of the two different mechanisms for the reversibility of the insertion process are discussed.

Crystalline CoSn2 powders prepared by a ceramic route under an Ar/H2 controlled atmosphere are examined as a negative electrode for lithium-ion batteries. Ex situ X-ray diffraction measurements show that an electrochemically driven solid-state transformation of CoSn2 occurs during the first reaction period. The complete reaction mechanism of CoSn2 is investigated by in situ 119Sn Mössbauer spectroscopy using a Li-ion plastic cell. The conversion reaction proceeds through a biphasic system, with CoSn2 direct transformation into both a lithium-rich Li y Sn (where y ≈ 3.5) compound and metallic Co nanoparticles. On charge, the electrochemical process is more complex and it includes the conversion of the Li y Sn compound into a modified CoSn2 nanocompound with a variable composition, i.e., a Li y Co z Sn2 matrix, which is the active species for the following cycles.