Tin–carbon composites as anodic material in Li-ion batteries obtained by copyrolysis of petroleum vacuum residue and SnO2

Composite materials with tin nanoparticles surrounded by a “muffling” carbon matrix are formed simultaneously by adding 20% SnO2 to a vacuum residue and following carbonisation between 700 °C and 1000 °C. The primary purpose of the carbonaceous material is the reduction of SnO2, giving rise to SnS and Sn as nanoparticles. The homogenous distribution of both components induces therefore a synergetic effect on the properties of the electrode material, not only from the electrochemical point of view but also from that mechanical. Thus, the carbon matrix hinders the agglomeration of Li–Sn alloys during long term cycling and, simultaneously, tin particles improve the conductivity of the material and increase the overall capacity as compared with the reference carbon. In addition, a CVD treatment increases the performance of the material. 119Sn Mössbauer and 7Li MAS NMR spectroscopies allow a detailed study of partially charged/discharged samples and, therefore, the phases, steps and mechanisms occurring during the electrochemical process.