An investigation of some lithium insertion compounds

Lithium insertion compounds are of technical interest as storage-battery electrodes; they are also of scientific interest as they offer low-temperature synthetic routes to compounds having unusual atomic ordering and to formal valence states that may not be accessible at higher temperatures normally employed in solid-state reactions. In this study lithium insertion compounds have been investigated to understand structure-property relationships of some V and Ni compounds and also to explore new cathode and anode materials for lithium secondary batteries. An investigation of the systems Li{dollar}sb{lcub}rm 1-x{rcub}{dollar}VO{dollar}sb2{dollar} and LiV{dollar}sb{lcub}rm 1-y{rcub}{dollar}M{dollar}sb{lcub}rm y{rcub}{dollar}O{dollar}sb2{dollar}, where M = Cr or Ti, has been carried out to determine a critical V-V separation R{dollar}sb{lcub}rm c{rcub}{dollar} for the transition from strongly correlated (R {dollar}>{dollar} R{dollar}sb{lcub}rm c{rcub}{dollar}, W {dollar}{dollar} U) electrons in a V-3d band associated with octahedral-site V{dollar}sp{lcub}3+{rcub}{dollar} ions sharing common octahedral-site edges with six like nearest neighbors in an oxide. A first-order transition on passing from the itinerant-electron regime R {dollar}{dollar} R{dollar}sb{lcub}rm c{rcub}{dollar} has been established. The behavior of the phase transition in Li{dollar}sb{lcub}rm 1-x{rcub}{dollar}VO{dollar}sb2{dollar} in the compositional range 0 {dollar}le{dollar} x {dollar}le{dollar} 0.12 has also been studied, and it has been shown that the transition temperature T{dollar}sb{lcub}rm t{rcub}{dollar} is controlled more by the lattice energy change through the distortion than by the enthalpy of the transition. Li{dollar}sb{lcub}rm 1-x{rcub}{dollar}NiO{dollar}sb2{dollar} and the spinel Li (Ni{dollar}sb2{dollar}) O{dollar}sb4{dollar} have been prepared chemically for the first time; the 90{dollar}spcirc{dollar} Ni-O-Ni interactions in these compounds are shown, from electronic and magnetic measurements, to yield properties that are quite different from the 180{dollar}spcirc{dollar} Ni-O-Ni interactions in the perovskite LaNiO{dollar}sb3{dollar}. Li{dollar}sb{lcub}rm 1-x{rcub}{dollar}NiO{dollar}sb2{dollar} and the spinel Li (Ni{dollar}sb2{dollar}) O{dollar}sb4{dollar} are found to be semiconductors, and both exhibit ferromagnetic interatomic-exchange interactions. Lithium insertion into NASICON frameworks Li{dollar}sb{lcub}rm x{rcub}{dollar}M{dollar}sb2{dollar}(PO{dollar}sb4)sb3{dollar} (M = Ti, Nb, Sb, Zr) was investigated with a view to prepare novel electrodes for lithium secondary batteries. The systems Li{dollar}sb{lcub}rm 1+x{rcub}{dollar}Ti{dollar}sb2{dollar}(PO{dollar}sb4)sb3{dollar}, Li{dollar}sb{lcub}rm x{rcub}{dollar}NbTi(PO{dollar}sb4)sb3{dollar} and Li{dollar}sb{lcub}rm x{rcub}{dollar}SbTi(PO{dollar}sb4)sb3{dollar} accept lithium to x = 2, 3, and 4 respectively; the latter two systems are reduced to an unusual valence state at one of the cations.