Cation-deficient MoySnxO2 oxides as anodes for lithium ion batteries

Fine powders of tin dioxide doped with Mo were prepared under hydrothermal conditions and tested in lithium cells. X-ray and IR data revealed the form ation of single-phase products with a rutile-like structure that is maintai ned upon calcining at 800 degreesC. Mo6+ ions change the habit growth of cr ystals and are randomly distributed at octahedral positions, thus promoting the formation of cation vacancies. The addition of Mo increases the revers ibility of the lithium insertion/de-insertion process, as reflected in the simplified differential specific capacity plots obtained, which result in a single, rather symmetric peak in the anodic and cathodic waves. Furthermor e, increasing the Mo content improves retention capacity at the expense of reversible capacity because the transition element acts as an inactive comp onent in the electrochemical process. The following arguments account for t he improved performance of these mixed oxides. (i) A diluent effect of Mo a toms that facilitates dispersion of the Sn atoms formed during the reductio n process; (ii) hindered formation of large clusters and decreased interfac ial strains; (iii) restriction of the number of alloying/de-alloying proces ses through a decreased reversible capacity during the first few cycles; an d (iv) an increased chemical diffusion coefficient for lithium, that result s partially from the structural disorder caused by the replacement of tin w ith molybdenum. (C) 2000 Elsevier Science Ltd. All rights reserved.