Effects of Aluminum Doping on The Phase Stability and Electrochemical Properties of LiCoO 2 and LiMnO 2
- PDF / 1,327,133 Bytes
- 6 Pages / 414.72 x 648 pts Page_size
- 79 Downloads / 182 Views
ABSTRACT Aluminum is of interest as a constituent for Li battery electrodes due to its low cost and low mass, and because ab initio calculations indicate that solid solution of LiAIO 2 with LiMO 2 (M = transition metal) in the a-NaFeO 2 structure can increase intercalation voltage [1]. In this study, we investigated the effect of Al doping on LiCoO 2 and LiMnO 2. Single phase LiAlyCoi1yO 2 has been synthesized up to y = 0.5 by firing homogenous hydroxide precursors. A systematic increase in the open circuit voltage is observed with Al content. In LiAlyMnjiyO 2, the addition of LiAIO 2 stabilizes LiMnO 2 in the at-NaFeO 2 structure under conditions where neither endmember is stable in the structure. High reversible capacity was obtained over both a 4 V and 3 V plateau, indicating that the compound transforms to a spinel-related structure during cycling, but that the cooperative Jahn-Teller distortion is suppressed. INTRODUCTION Compounds of the type LiMO 2 (M = Co [2], Ni [3]) with the (x-NaFeO 2 structure (space group R 3 m) have been extensively studied as cathodes for Li-ion batteries. The effects of doping with other transition metal elements have also been studied [4-6]. Recently, a related polymorph of LiMnO 2 (space group C2/m) has been obtained by the ion-exchange reaction of lithium salts with (x-NaMnO 2 [7,8]. Compared with the transition metals, Al has not received wide attention
as a dopant, with only a few reports on LiAlyM 1 yO2 (M=Co, Ni) systems to date [9-11]. However, doping with Al is of significant interest for several reasons. Ab initio calculations by Aydinol et al. [1] have shown that LiAIO 2 has a theoretical intercalation voltage of -5 V vs. Li/Li , which is higher than that of any other lithium transition-metal oxide. While pure LiAIO 2 is electrochemically inactive, the solid solution of LiAIO 2 with lithiated transition-metal oxides can potentially increase the intercalation voltage and energy density. Secondly, the fact that LiAIO 2 is stable in the at-NaFeO 2 structure at temperatures below -600'C [12] suggests that it could have a stabilizing effect on other compounds. Finally, its low cost and low density make LiAIO 2 attractive as an intercalation compound constituent. In this paper, we report effects of Al doping on the phase stability and electrochemical properties of LiCoO 2 and LiMnO 2 . EXPERIMENT SYNTHESIS LiAlyCo1 .yO2 (y = 0, 0.25, 0.5) and LiAlyMnj.yO 2 (y = 0, 0.25) samples were synthesized by firing homogenous precursor powders obtained by a co-precipitation and freeze-drying technique [13]. Mixed aluminum-cobalt or aluminum-manganese hydroxides were co-precipitated from mixed aqueous solutions of AI(NO 3)3 "9H20 and Co(NO 3)2"6H20 or Mn(N0 3)3"6H 20, respectively. A more 403 Mat. Res. Soc. Symp. Proc. Vol. 496 © 1998 Materials Research Society
detailed description of precursor preparation can be found elsewhere [13]. Precursors thus obtained for LiAlyCo0.yO 2 were fired for 2 h at 800'C in air. In the case of LiAlyMnj-yO 2, the valence of Mn ions, firing atmosphere was
Data Loading...
