Synthesis and Electrochemical Behaviour of Ramsdellite LiCrTiO 4
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Synthesis and Electrochemical Behaviour of Ramsdellite LiCrTiO4 F. García-Alvarado, M. Martín-Gil and A. Kuhn Departament of Chemistry, Universidad San Pablo CEU, E-28688 Boadilla del Monte, Madrid (Spain); e-mail: [email protected] Abstract A ramsdellite with composition LiCrTiO4 has been obtained by heating the spinel of same composition to high temperature. The new ramsdellite has been investigated in view of its possible use as an electrode material in lithium rechargeable batteries. Lithium can be partially extracted from ramsdellite LiCrTiO4 and further intercalated into, by contrast to the spinel of same composition. The average operating voltage during lithium extraction is 4 Volts vs. lithium, and the process produces a specific capacity of 90 mAh/g at 0.1 mA/cm2. On the other hand, upon reduction from open circuit voltage, lithium can be reversibly intercalated into the ramsdellite polymorph at ca. 1.5 V vs. lithium yielding a rechargeable capacity of 110 mAh/g at 0.1 mA/cm2.
Introduction Among the compounds that intercalate lithium at low voltage, several titanium oxides have been found [1-5]. A common feature in all these materials is partial or complete reduction of Ti4+ to Ti3+ at voltages close to 1.5 Volts. This value can be regarded relatively high when compared to carbonaceous or tin-based compounds. However, the great advantage is that Ti-O framework sustains a good cycle life. For the particular case of Li2Ti3O7 we demonstrated that the titanate suffers a low internal stress upon intercalation, which was directly related to the observed good cycling behaviour [5]. Another example can be found in Li4Ti5O12 [6]. Recently, new titanium-based ramsdellites have been reported: ramsdellite-like LiTi2O4 was obtained by heat treatment of the spinel of same composition [7] and lithium can be either chemically or electrochemically removed [8,9]. Furthermore, ramsdellite-like LiTi2O4 has been investigated in view of its potential use as negative electrode [9-11] in lithium ion batteries. It has been shown that ramsdellite LiTi2O4 shows excellent electrochemical behaviour in both reduction and oxidation, i.e. it can undertake both lithium intercalation (Li1+xTi2O4) and lithium extraction reactions (Li1-xTi2O4) [8,9]. It has been pointed out that only part of the total capacity would be useful for negative electrode use in rechargeable lithium ion batteries [9].This part corresponds to the capacity involved in the process characterised by a low voltage plateau located at 1.5 V vs. Li, which corresponds to the region where LiTi2O4 transforms to Li2Ti2O4 through a biphasic region. Regarding lithium extraction from LiTi2O4, a continuous variation of voltage, from 3 to 1.5 V vs. Li+/Li is observed. This explains why the maximum useful capacity as negative electrode of both ramsdellites Li2Ti3O7 and LiTi2O4 are finally very similar (190 mAh/g). In the same way, a study of the complete solid solution series of ramsdellite phases Li1+xTi2-2xO4 has been recently performed regarding their possible application as
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