Manganese Vanadium Oxide Compounds as Cathodes for Lithium Batteries
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Manganese Vanadium Oxide Compounds As Cathodes For Lithium Batteries J. Katana Ngala, Peter Y. Zavalij and M. Stanley Whittingham* Institute for Materials Research and Department of Chemistry State University of New York at Binghamton, Binghamton, NY13902-6000, USA. ABSTRACT A pure form of the compound [(CH3)4N]0.2Mn0.06V2O5+δ•0.2H2O has been synthesized by the hydrothermal technique. A manganese richer compound, [(CH3)4N]0.18Mn0.1V2O5+δ•0.35H2O, has also been synthesized. By comparison to [(CH3)4N]0.17Fe0.1V2O5+δ•0.17H2O, the structure of these compounds consists of double sheets of vanadium oxide with tetramethyl ammonium ions in the interlayer spaces. Both compounds display reversible lithium intercalation with sharp end points. The lithiation capacity is lowered by the increase in manganese content. INTRODUCTION Transition metal oxides may act as cathodes in lithium secondary batteries partly due to the ability of the metal ions to exhibit variable oxidation states, and their highly negative free energies of reaction with lithium ions, in contrast to other chalcogenides. The commercially available layered LiCoO2 has good cyclability. However, it finds limited use such as in lap tops and cellular phones, due to its high cost. The spinel compound, LiMn2O4, which was found to act as an intercalation host in the early 1980s, has been developed for commercial use as a replacement for LiCoO2 in second-generation Li-ion batteries; the manganese is lower cost than cobalt. Unfortunately, only 0.5 Li per Mn may be inserted and deinserted reversibly [1]. This corresponds to a capacity of about 110 Ah/kg in contrast to 130 Ah/kg for LiCoO2. Vanadium oxides have been extensively investigated as possible cathodes for lithium batteries. A class of compounds of particular interest for potential use in batteries is that consisting of the δ-V2O5 structure. This structure type contains double vanadium oxide sheets with the vanadyl groups on the outside of the sheets; the vanadium is in a distorted octahedral coordination rather than the square pyramid typical of V2O5 itself and the well known bronzes, such as LiV2O5. One of the most studied vanadium oxide cathodes,V6O13, contains these sheets and cycles lithium well [2] in secondary cells. Typical simple members of this class are Ni0.25V2O5 [3], [N(CH3)4]0.3Fe0.1V2O5 and Zn0.4V2O5 [4]. We report here on the preparation of a pure phase of [N(CH3)4]yMnzV2O5+δ•nH2O (compound A) by hydrothermal synthesis. Earlier we reported [5] this phase as one component of a two phase mixture. We also report on an isostructural material (compound B) with a higher manganese content. We compare their electrochemical behavior. Hydrothermal synthesis and other soft chemistry techniques such as sol-gel synthesis, have been widely applied for the low temperature syntheses of metal oxides. These techniques are useful in accessing metastable metal oxides.
GG9.16.1
EXPERIMENTAL Compound A was hydrothermally synthesized by the treatment of V2O5 (Alfa-Aesar) with an aqueous solution of HMnO4, in the presen
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