title: Chemical and electrochemical insertion of Li into the spinel structure of CuCr2Se4: ex situ and in situ observations by X-ray diffraction and scanning electron microscopy.
abstract: The chemical and electrochemical insertion of lithium into the spinel structure of CuCr(2)Se(4) was studied and the chemical reaction pathway was followed by ex situ X-ray diffraction on samples with different Li contents. The electrochemical reaction was investigated by in situ X-ray diffraction and in situ scanning electron microscopy. In the early steps of chemical intercalation, two phases with a different Li content coexist and Cu is extruded from the host material. After 4 days of Li intercalation, a conversion reaction is observed. The overall Li uptake is 8 Li ions per formula unit. The structural behaviour of the two intercalated phases at the early stages of intercalation is totally different. For one phase a strong expansion of the a-axis is observed while for the other phase it is only slightly affected by Li uptake. A three-step mechanism was found consisting of reduction of Se(-) followed by a Cu-Li exchange and finally a complete reduction of Cr(3+) to the metallic state accompanied by the formation of Li(2)Se. The discharge capacity of the first cycle amounts to 530 mAh g(-1) and drops to about 380 mAh g(-1) in the fifth cycle. In in situ SEM images the occurrence of Cu whiskers that partially grow out of the crystallites can be observed.
authors.affiliation: Institute of Inorganic Chemistry, University of Kiel, Kiel, Germany. wbensch@ac.uni-kiel.de
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Bensch
authors.forename: Jannes
authors.initials: J
authors.lastname: Ophey
authors.forename: Holger
authors.initials: H
authors.lastname: Hain
authors.forename: Holger
authors.initials: H
authors.lastname: Gesswein
authors.forename: Di
authors.initials: D
authors.lastname: Chen
authors.forename: Reiner
authors.initials: R
authors.lastname: Mönig
authors.forename: Patric A
authors.initials: PA
authors.lastname: Gruber
authors.forename: Sylvio
authors.initials: S
authors.lastname: Indris