Electrochemical reaction of lithium with the CoSb3 skutterudite

Abstract

The crystalline solid CoSb ₃ with the skutterudite structure was used as the starting cathodic material in Li|LiClO ₄ (propylene carbonate–ethylene carbonate)|CoSb ₃ cells. The galvanostatic 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 reversible 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 and FTIR spectroscopy. The first discharge involves the irreversible decomposition of the solid to non-crystalline cobalt and Li ₃ Sb alloy. On cycling, the reversible extraction–insertion of lithium in the antimony alloy takes place. Part of the irreversible capacity is ascribable to the formation of a passivating film on the surface of the electrode material, which contains ROCO ₂ ^– and CO ₃ ^2– groups. This material shows superior properties relative to a pure antimony electrode and can be considered as an interesting candidate for the negative electrode of lithium-ion cells.