Tin alloy-graphite composite anode for lithium-ion batteries

A composite anode material was prepared that contains nanosize (<100 nm) particles of tin alloy Sn65Sb18Cu17 and Sn62Sb21Cu17. The alloys were electroplated at high current densities (above i(L)) from aqueous solutions, directly onto the copper current collector, and were coated by a polyvinylidene fluoride-graphite matrix at a ratio of alloy: graphite matrix 70:30 and 80:20 w/w, respectively. The processes involved in electrode production by this method are inexpensive, simple, and fast. Over 40 (100% depth of discharge) cycles were demonstrated, in half-cell, and over 30 were demonstrated with a LiCoO2 battery containing 1 M LiPF6 ethylene carbonate-diethyl carbonate electrolyte. The faradaic efficiency (Q(De-ins)/Q(Ins)) is less than 100%. Lithium is fully deinserted from the host matrix only when the anode is cycled at low current densities. The kinetics of lithium insertion to and deinsertion from the composite anode material, slow gradually as the cycle number increases. X-ray diffraction patterns of the anode material show that the alloy becomes amorphous during cycling, while the graphite does not. X-ray photoelectron-spectroscopy measurements reveal that the solid electrolyte interphase consists of mainly LiF, small amounts of Li2O, and possibly, polymeric substances. The electrochemical behavior of the alloy changes with cycle number, while that of the graphite does not. The fall of the deinsertion capacity of the graphite from the first cycle to the 34th by more than 50% proves that the active material in the anode suffers from particle-to-particle break off. (C) 2002 The Electrochemical Society.