Hydrothermal synthesis and characterization of novel vanadium oxides and their application as cathodes in lithium secondary batteries

Novel layered or tunneled vanadium oxides are sought as a substitute for the expensive {dollar}rm Lisb{lcub}x{rcub}CoOsb2{dollar} cathode material in lithium rechargeable batteries. The hydrothermal synthesis approach was taken in search of new vanadium oxides in the presence of a structure directing cation, TMA. A systematic study was done on the hydrothermal synthesis of the {dollar}rm Vsb{lcub}2{rcub}Osb{lcub}5{rcub}{dollar}-TMAOH-LiOH system. It was determined from this study that the pH of the reaction mixture was very critical in the formation of many compounds. Acetic acid utilized to adjust the pH of the reaction mixture in the presence of TMA behaved as a buffer and maintained a constant pH during the reaction. Hydrothermal synthesis conducted between pH 10 and 2 resulted in the formation of 7 compounds. At the highest pH, a well known compound {dollar}rm Lisb3VOsb4{dollar}, was formed. Between pH 5.2-9, a layered compound, TMAV{dollar}rmsb3Osb7{dollar} resulted. The thermal treatment of TMAV{dollar}rmsb3Osb7{dollar} under oxygen lead to an oxidized phase, TMAV{dollar}rmsb3Osb8{dollar}, which increased its lithium capacity significantly. Between pH 5-6, a cluster compound, {dollar}rm TMAsb8lbrack Vsb{lcub}22{rcub}Osb{lcub}54{rcub}(CHsb3COO)rbrack{lcub}cdot{rcub}4Hsb2O{dollar} with the acetate ion trapped inside the caged {dollar}rm Vsb{lcub}22{rcub}Osb{lcub}54{rcub}{dollar} cluster, and a layered vanadium oxide, {dollar}rm Lisb{lcub}x{rcub}Vsb{lcub}2-delta{rcub}Osb{lcub}4-delta{rcub}{lcub}cdot{rcub}Hsb2O{dollar} was obtained. The {dollar}rm Lisb{lcub}x{rcub}Vsb{lcub}2-delta{rcub}Osb{lcub}4-delta{rcub}{lcub}cdot{rcub}Hsb2O{dollar} compound was dehydrated to form {dollar}rm Lisb{lcub}x{rcub}Vsb{lcub}2-delta{rcub}Osb{lcub}4-delta{rcub}{dollar} and the lithium was removed electrochemically to form a new type of "VO{dollar}sb2{dollar}". Several alkylamines, DMSO and an additional water molecule were intercalated to swell the layers of {dollar}rm Lisb{lcub}x{rcub}Vsb{lcub}2-delta{rcub}Osb{lcub}4-delta{rcub}{lcub}cdot{rcub}Hsb2O{dollar}. Lowering the pH between 3.0-3.5, resulted in layered compound, TMAV{dollar}rmsb4Osb{lcub}10{rcub}{dollar}, with TMA residing between the layers. Layered compounds, TMAV{dollar}rmsb8Osb{lcub}20{rcub}{dollar} and {dollar}rm TMAsb{lcub}0.17{rcub}Hsp+sb{lcub}0.1{rcub}Vsb2Osb5{dollar}, were obtained at very acidic conditions. The hydrothermally grown {dollar}rm TMAsb{lcub}0.17{rcub}Hsp+sb{lcub}0.1{rcub}Vsb2Osb5{dollar} is similar to the xerogel {dollar}rm Vsb2Osb5{dollar} intercalated with TMA synthesized by the sol-gel process. Several trends were observed as the pH was varied, in this study. The vanadium coordination changed from only tetrahedra at the highest pH in {dollar}rm Lisb3VOsb4{dollar}, to tetrahedra and square pyramids in {dollar}rm TMAVsb3Osb7{dollar}, to only square pyramids in {dollar}rm TMAsb8lbrack Vsb{lcub}22{rcub}Osb{lcub}54{rcub}(CHsb3COO)rbrack{lcub}cdot{rcub}4Hsb2O, Lisb{lcub}x{rcub}Vsb{lcub}2-delta{rcub}Osb{lcub}4-delta{rcub}{lcub}cdot{rcub}Hsb2O{dollar} and {dollar}rm TMAVsb4Osb{lcub}10{rcub}{dollar}, to octahedra in {dollar}rm TMAVsb8Osb{lcub}20{rcub}{dollar} and {dollar}rm TMAsb{lcub}0.17{rcub}Hsp+sb{lcub}0.1{rcub}Vsb2Osb5{dollar}. The TMA content in the compounds decreased as the pH was decreased. Electrochemical studies indicated that the lithium capacity of the TMA containing layered compounds increased as the content of TMA decreased. Preliminary shadies indicated that the acids used to adjust the pH of the reaction mixture can also influence the type of products obtained by the hydrothermal method. The synthesis and the detailed characterization of these vanadium oxides are thoroughly discussed in this dissertation.