Structural and Thermodynamic Properties of Cointercalated Titanium Disulfide
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The structural and electrochemical characteristics of cointercalated titanium disulfide, LixNayTiSz, have been investigated as a function of lithium content, x, for y = 0.0, 0.04, 0.16, 0.34, and 0.50. The open-circuit voltage of LixNayTiSzvs. lithium has been measured as a function of lithium concentration between 30 and 80C. The variation of the EMF as a function of x was the same in LixNayTiS2 for x + y < 1.0 as that in LixTiS2 when x < 1.0. The open-circuit voltage vs. lithium decreased to 1.0V when x 4- y > 1.2 and was nearly constant up to x + y 2.0. Four structures have been observed in the LixNayTiSz materials as the lithium and sodium content is varied: A stage II structure, a stage I(TP) structure, a stage I(TAP) structure, and a IT structure. The structural and open-circuit voltage results have been used to construct a Li-Ti-S isothermal ternary cross section, a Li-Na-TiS2 isothermal pseudoternary cross section and to assess the electrode applications of these novel materials. The Li-Na-TiS2 isothermal pseudoternary cross section indicates that the smaller lithium ion is able to attain higher concentrations within a phase than that of the larger sodium ion. Thus, it appears that ionic size is an important parameter in determining the location of the phase boundaries in intercalated dichalcogenides. 1986, The Electrochemical Society, Inc. All rights reserved.
