Spectroscopic studies of the local structure in positive electrodes for lithium batteries

Abstract

The vibrational properties of manganese dioxides and lithiated transition-metal oxides with either spinel-type or layered-type structure used as positive electrode materials in Li-ion batteries have been studied. Raman spectroscopy yields a reliable description of materials such as the manganese dioxides where crystalline disorder may be expected. The local arrangement in the γ-MnO₂ structure is investigated as a function of the intergrowth rate, Pr, of pyrolusite in the ramsdellite matrix. The phase evolution in four-volt positive electrode materials is recorded as a function of the degree of intercalation or deintercalation in Li_xCoO₂ and Li_xMn₂O₄. Lattice dynamics are studied using either a classical group theoretical analysis or a local environment model. Raman and FTIR bands are identified on the basis of vibrational modes of polyhedral units which are the basis of the oxide structure. Structural and electronic modifications induced by an intercalation–deintercalation process are examined.