Vanadium Oxide Frameworks Modified with Transition Metals
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Vanadium Oxide Frameworks Modified with Transition Metals Peter Y. Zavalij and M. Stanley Whittingham Institute for Materials Research and Chemistry Department, State University of New York at Binghamton, Binghamton, NY, 13902-6016, USA ABSTRACT It is well known that vanadium oxides readily form open structures that defines the potential use of vanadium compounds as cathode materials for lithium batteries. In order to stabilize open frameworks during electrochemical cycling and improve their performance, vanadium oxide can be modified with other transition metals. This work presents the structural analysis of vanadium oxide frameworks modified with Mn and Zn as well as reporting on several interesting new structures, such as TMA4[Zn4V21O58] and NaMn(VO3)4·2H2O. INTRODUCTION The great interest in vanadium compounds is due to their potential use both as cathode materials for advanced lithium batteries and as catalysts. The special characteristics of vanadium that distinguishes it from other transition metals consists in wide range of oxidation states (from 5+ to 3+ and even 2+), the often present vanadyl group, its red-ox properties and whole spectra of coordination polyhedra (tetrahedra (T), trigonal bipyramid (TB), distorted (OD) and regular (O) octahedra). Naturally, such great variety of oxidation states and coordination polyhedra results in even greater variety of vanadium oxide frameworks: from chains and tunnel structures through single and double sheets layers to 3D nets. Some of our earlier work on the pure vanadium oxide frameworks has been published as a review [1]. The vanadium oxide framework can be modified with such transition metals as Mn, Fe, Co, Ni, Cu, Zn and others. Interacting with the vanadium oxide framework transition metals modify the electronic configuration and therefore the compound stability and properties that provides an additional variable in the search for new materials. This work presents the structural analysis of vanadium oxide frameworks modified with manganese and zinc as well as reporting on several interesting new structures, such as TMA4[Zn4V21O58] and NaMn(VO3)4·2H2O. EXPERIMENTAL In the last decade hydrothermal synthesis at mild conditions was successfully used to obtain various often-metastable structures with open framework. A review on vanadium oxide synthesis using hydrothermal method has been published in [2]. pH also plays an important role in the framework formation [3] – lower pH increases coordination number of vanadium and therefore increases dimensions and connectivity of the framework. Our results of vanadium oxides prepared hydrothermally in presence of Mn and Zn are summarized in Table I and II respectively, where initial pH is given along with the polyhedra present and their connectivity in framework.
GG10.7.1
Table I. Mn compounds prepared hydrothermally Mn compound
Initial pH
Mn7(OH)3(VO4)4 γ-MnV2O5 NaMn(VO3)4·2H2O β-MnV2O6 δ-TMAxMnyV4O10·nH2O
11 6 5 4-5 3-4
Polyhedra Mn O O O O O
V T SP/O SP/O OD OD
Connectivity 3D; 3D; 3D; 3D; 3D;
Mn-3D V-2D V,Mn-
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