Electrochemical reaction of lithium with the CoSb3 skutterudite

The crystalline solid CoSb3 with the skutterudite structure was used as the starting cathodic material in Lithylene carbonate)ic discharge takes place in two successive plateaux around 0.5 V, leading to a maximum capacity of ca. 800 mA h g(-1). Further cycling leads to higher voltages and a reversib le capacity in the range 350-200 mA h g(-1) during the first 10 cycles. The mechanism of the reaction with lithium was studied by X-ray diffraction an d FTIR spectroscopy. The first discharge involves the irreversible decompos ition of the solid to non-crystalline cobalt and Li3Sb alloy. On cycling, t he reversible extraction-insertion of lithium in the antimony alloy takes p lace. Part of the irreversible capacity is ascribable to the formation of a passivating film on the surface of the electrode material, which contains ROCO2- and CO32- groups. This material shows superior properties relative t o a pure antimony electrode and can be considered as an interesting candida te for the negative electrode of lithium-ion cells.