Electrochemical Behavior of the Amorphous Tin–Cobalt Anode

Abstract

study of the kinetics of its reaction with lithium, its thermal stability, and structural changes as a function of annealing temperature. The last gives insight into the synthesis methods that must be used for such nanoamorphous-materials. Experimental The amorphous tin anode was obtained as in our earlier study 13 from a commercial SONY hybrid lithium-ion battery NP-FP71. Disks with an area of 1.2 cm 2 were punched from the negative electrode and used as the working electrode in 2325 coin cells. Since in the commercial battery, the SnCo active material is coated on both side of the Cu current collector, the material on one side of the disk was scratched off to fit the electrochemical test in the coin system. The electrodes were not washed before use. For the comparative studies, tin in the form of foil was used Aldrich, 99.999, 0.025 mm thick. For the heat-treatment test, about 0.2 g of the amorphous tin material was heated to the chosen temperature, in the range from 100 to 450°C in an 8.5% H2/He atmosphere. All samples were heated to the chosen temperature at 5°C/min and held there for 4 h; they were cooled to room temperature naturally. For the electrochemical test, the electrode was prepared by mixing the heated sample with 10 wt % carbon black and 10 wt % polytetrafluoroethylene powder; this mixture was hot pressed into a stainless steel Exmet grid for 30 min at 100°C. The electrochemical properties were determined in 2325 coin cells using pure lithium foil as both the counter and reference electrodes, 1 M LiPF6 in 1:1 ethylene carbonate/dimethyl carbonate as electrolyte, and a Celgard 2400 separator. The cycling was performed between certain voltage ranges as described in the discussion section. The X-ray studies were done on a Scintag XDS 2000 diffractometer using Cu K radiation.