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Chem. Mater. 2004, 16, 2840
Reply to Comment on A New La2/3LixTi1-xAlxO3 Solid Solution: Structure, Microstructure, and Li+ Conductivity and A New La2/3-xSrxLixTiO3 Solid Solution: Structure, Microstructure, and Li+ Conductivity The aim of the electrochemical experiments shown in the two already published papers mentioned by Dr. Bohnke was to study the electrochemical window of the materials for their use as solid electrolytes in lithium secondary batteries. It is well-demonstrated that reduction of Ti4+ to Ti3+ occurs at 1.75 V due to the electrochemical Li+ intercalation into the material. Therefore, the statement “the materials can be used as solid electrolytes down to 1.75 V” is perfectly correct. It is obvious that Li metal cannot be used as an anode in such kinds of cells, unless a separator is situated to prevent contact between both components, as is the usual method, and we are perfectly aware of this scientific point. In fact, we do not propose to put into contact both materials (the word “contact” does not appear in any sentence of the papers). Therefore, it is allowed that Li metal be used as an anode in secondary batteries with our materials as electrolytes, as long as prevention of short-circuiting is taken into account, as we indeed knew Kobayashi et al. have done and also many other authors. We admit that it would perhaps have been better to conclude, “The materials are stable above 1.75 V vs Li, which means that they can be used as electrolytes in secondary batteries down to 1.75 V”. However, to completely test the performance of these titanates as solid electrolytes, appropriate electrode materials, which operate above 1.75 V giving a good capacity and cyclability of the cell, should be used. This subject is out of the scope of our two papers. In this sense, the reading of some of the works by Birke et al.,1,2 (1) Birke, P.; Scharner, S.; Huggins, R. A.; Wepper, W. J. Electrochem. Soc. 1997, 144 (6), L67.
for instance, is interesting. They study the electrochemical window of Li0.29La0.57TiO3 and Li1.3Al0.3Ti1.7(PO4)3. They find that in the case of Li0.29La0.57TiO3 “the electrolytic stability range of the material does not extend below 1.7 V vs Li” (first sentence of the second paragraph of the conclusions in ref 1). This means that the titanate can be used as an electrolyte above 1.7 V. In the case of Li1.3Al0.3Ti1.7(PO4)3, Ti4+ begins to reduce to Ti3+ at 2.4 V vs Li, although the slow kinetics of this reduction reaction and the addition of a sintering compound to block the electronic conductivity allows the use of Li1.3Al0.3Ti1.7(PO4)3 as an electrolyte to be extended until potentials slightly lower than 2.4 V, as is shown in the performance of the cell Li4Ti5O12/ Li1.3Al0.3Ti1.7(PO4)3/LiMn2O4 (Figure 8 in ref 2). Besides, we would like to remark that those two papers, subject of the comments of Dr. Bohnke, report not only the synthesis of new Ti4+-containing oxides, but also a rigorous study on the stoichiometry range, crystal microstructure (indeed essential to propose a model for the crystal structure of this kind of titanate (see ref 3), and electrical properties of the system. Moreover, our “electrochemical results have not been misinterpreted, leading to totally wrong conclusions”; we properly establish the electrochemical stability of our materials vs Li from the galvanostatic and potentiostatic electrochemical experiments described in these documents.
Susana Garcı´a-Martı´n* and Miguel A Ä . Alario-Franco Departamento de Quı´mica Inorga´ nica, Facultad de Ciencias Quı´micas, Universidad Complutense de Madrid, 28040 Madrid, Spain Received May 23, 2003 CM031085G (2) Birke, P.; Salam, F.; Do¨ring, S.; Wepper, W. Solid State Ionics 1999, 118, 149. (3) Garcı´a-Martı´n, S.; Alario-Franco, M. A Ä .; Ehrenberg, H.; Rodrı´guez-Carvajal, J.; Amador, U. J. Am. Chem. Soc. 2004, 126, 3587.
10.1021/cm031085g CCC: $27.50 © 2004 American Chemical Society Published on Web 06/11/2004
