Synthesis and Characterization of Manganese Vanadium Oxides as Cathodes in Lithium Batteries
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monoclinic structure, a=11.66(2)A, b=3.610(9)A, c= l3.91(4)A, P= 108.8(2)'. It has a disordered V20 5 double layer and the Mn and N(CH 3)4 ions reside between the layers. The y-type MnV 205
is orthorhombic, belongs to the space group Pnma, a=9.7585(2) A, b=3.5825(l)A, c= 11.2653(2) A. These compounds were also characterized by electron microprobe, FTIR and TGA. They reacted readily with lithium, and their electrochemical behavior in lithium cells was determined. INTRODUCTION Lithium is a very attractive material for high energy density batteries because of its low equivalent weight and high electrode potential. There has been much effort recently to find more cost-effective oxide cathodes for advanced lithium batteries, to replace the technically excellent but expensive lithium cobalt oxide. Soft chemistry was shown to be an effective method for the preparation of high surface area transition metal oxides that offer many advantages as cathodes in rechargeable lithium batteries. There has been much interest in the last two decades in layered vanadium oxides and their intercalates because of their potential use as secondary cathode materials for advanced lithium batteries. Therefore, the already rich crystal chemistry of the vanadates with open framework was expanded with many new structures. A significant part of them were done in our group. Earlier we reported the use of the tetramethyl ammonium ion (TMA) as a structure-directing cation [1] and showed that a number of new phases of tungsten, molybdenum, and vanadium could be formed. In the case of vanadium, two new structure types were reported in 1995 [2], the layered N(CH 3)4V 40 1 0 [3] and a hydrated vanadium dioxide [4, 5], also a new structure type formed by iron chloride and vanadium oxide in 1997, the layered [N(CH 3)4],FeyV 2O 59nH 20, where z is 1/6, y= 0.1 and n is 1/6 [6]. Several other layer structure vanadium oxides were formed by various groups [7-9]. To date only the tetramethyl ammonium ion has shown the ability to form a range of different structure with differing organic to vanadium ratios [10]; the present count is six structures including two with a string-like morphology formed at pH values of 3 or less, N(CH 3)4V 30 7 and [N(CH 3 ) 4 15 V] 8 0 46 . A variety of new structures can also be formed when a second 'transition' metal is present, for example with zinc four new compounds, Zno 0 4V 20 5o0.27H 20, Zno. 39V2 0 5o0.5TMA,
497 Mat. Res. Soc. Symp. Proc. Vol. 5'1 0 2000 Materials Research Society
Zn 3(OH) 2(V20 7).H2 0, and Zn 2 (OH) 3(VO 3), have been reported [11, 12]. Nickel forms [NH 2(CH 2 )2NH 2] 2NiV6O 1 4 [13], whose structure is related to N(CH 3)4V 30 7 . We also found that cobalt forms several compounds, including both the 8- and V 30 7-type phases; however, they were contaminated with other phases such as C0 2V20 7 and COV 20 6 [14]. Manganese compounds are of particular interest for use as cathodes in reversible lithium batteries, because of their low cost. We have therefore made a study of the Mn-V-O system, using hydrotherm
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