Hydrothermal Synthesis and Characterization of A Series of Novel Zinc Vanadium Oxides as Cathode Materials
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structures like
N(CH 3) 4V 30 7 [14]
and
[N(CH 3) 415VI 80 46
[15].
Vanadium oxides have been extensively investigated as possible cathodes for lithium batteries. In particular, V20 5 and V60 13 have been the most extensively studied. Although showing good redox behavior, their cyclability is not as good as the lithium cobalt oxide cathodes and the discharge curve slopes much more, making electronic control more difficult.
367 Mat. Res. Soc. Symp. Proc. Vol. 496 01998 Materials Research Society
This paper describes the formation of new vanadium oxide cathodes for rechargeable lithium batteries by the hydrothermal reaction of zinc chloride and vanadium pentoxide in the presence of the tetramethyl ammonium cation, N(CH 3)4+. Four new vanadium oxides, Zno.4V2 0 5 0.3H 20, [N(CH 3 )4]0 .5 Zn0 .4V2O5 , Zn 3(OH) 2 (V20 7)oH20, and Zn 2(OH) 3 (VO3 ), with layered structures were found. The tendency of this cation to direct the synthesis toward layered structure has been previously noted [1,3] EXPERIMENTAL The zinc vanadium oxides were synthesized by mixing ZnCI2 and V 20 5 powder from Johnson and Matthey with 25% tetramethyl ammonium hydroxide solution from Alfa in
different molar ratios, as the following 1:1:1, 1:1:2, 1:1:3, 1:1:4. The products, synthesized from the above molar ratios, are Zn 0.4V2 O5o0.3H 2 O, [N(CH 3)4 ]0 .5 Zn0 .4 V 2O5 , Zn 3(OH) 2(V 2 O7)°H 2 O, and Zn2 (OH) 3(VO 3), respectively. When [N(CH 3)4 ]0.5 Zn0 .4 V2O 5 was synthesized, the pH of the solution was adjusted to 3.67-4.00 by acetic acid. No acid was added in the other reactions. The resulting solution was transferred to a 125-ml Teflon-lined autoclave (Parr Bomb), sealed, and reacted hydrothermally for 2.5 days at 165°C. The resulting crystals of each compound were filtered and dried in air. The colors of these four compounds are greenish black, black, white and white, respectively. X-ray powder diffraction was performed using Cu Koc radiation on a Scintag 0-0 diffractometer. The data was collected from 4'20 to 90020 with 0.03'20 steps and 15 sec per step. The FTIR data was obtained on a Perkin-Elmer 1500 series. Chemical analysis was performed using TGA, a JEOL8900 Electron Microprobe, and an ARL Spectrospan-7 DCP Atomic Emission Spectrometer. The degree of reduction of the vanadium oxide by lithium was determined by reaction with n-butyl lithium from Aldrich Chemicals, following standard procedures [16]. Initial electrochemical studies were conducted in lithium cells using 1 molar LiAsF 6 in a 1:1 propylene/dimethyl carbonate mixture as the electrolyte; the vanadium oxide was mixed with 10% carbon black and 10% Teflon powder, and hot pressed for 20 minutes at 440'F. A MacPile potentiostat was used to cycle the cells. RESULTS AND DISCUSSION X-Ray Diffraction Determination The X-ray diffraction data of the four compounds, Zn0 .4V 2 0 5 0.3H 20, [N(CH 3)4]o0 sZno.4 V20 5, Zn 3(OH) 2 (V 2O7)oH2O, and Zn 2(OH) 3(VO 3), are shown in Fig. 1. The pattern of Zn 0 .4V2 0 5 0.3H 2 0 shows a repeat distance of 10.43A. Preliminary analysis of the
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