CONICET | Buscador de Institutos y Recursos Humanos

Since its invention in 1991, lithium-ion batteries have depended on graphite as anodic material, since this material has a good cycling stability, while it solves the security problems presented by the metallic lithium anode. However, graphite?s specific capacity (372 mAh/g) [1] is relatively low compared to other materials. A great effort has been invested in trying to replace it with alloy-type anode materials such as, Sn (998 mAh/g) [2] and Si (3579 mAh/g) [3], but these suffer from a significant capacity loss during cycling due to huge volume changes upon lithiation when forming the Li-alloys. Therefore, a good strategy to overcome this problem is to combine graphite with these kind of materials, trying to preserve the advantages of both.In this work, we synthesized several Si-Sn-graphite composites by simple and inexpensive ball-milling of its precursors. The goal is to study the effect of the composition in the specific capacity of the synthesized composite materials and its cyclability. The anodes were made using polyacrylic acid as binder and Super P, in a pH 3.0 buffered aqueous solution. Electrochemical cells were assembled using 1.0 M LiPF6 in ethylene carbonate/ethyl methyl carbonate (1:1 v:v) with 10.0 wt.% fluoroethylene carbonate as electrolyte. The different composites were characterized by XRD and SEM-EDS. For the electrochemical characterization, the cells were galvanostatically cycled for > 100 cycles. This was complemented with morphology analysis of the electrodes through SEM before and after heavy cycling. After characterization, no evidence of alloy formation were observed, implying that there are no changes in the nature of the used materials. Tri-phase ?heat maps? were constructed with specific capacity, capacity retention and dependency with mass composition of Si-Sn-graphite composites. The intersection shows the optimal composition for the preparation of electrodes with outstanding capacities and high capacity retention. A clear synergic behavior is observed between the different materials, but the resultant electrochemical performance is dependent on the amount of each component. After a comparative analysis of the studied compositions, we found that the mixture formed with 33 wt.% of each component, presents a specific capacity of 989 mAh/g after 120 cycles at 1.5 A/g, and the best capacity retention. On the other hand, the study of morphological changes for the different compositions before and after cycling, gives us insight about the interaction between each component and how it changes when the composition varies. Hence, we expect that this work can help in the design of new electroactive materials made from combinations of Sn, Si and graphite.References [1]. M. Klett et al. Journal of The Electrochemical Society, 164 (2017) (1) A6095-A6102 [2] Z. Li, J. Ding, D. Mitlin Acc. Chem Res. 48 (2015) 1657 - 1665[3] S.D. Beattie et al. Journal of Power Sources 302 (2016) 426 - 430