Reaction of Li with grain-boundary atoms in nanostructured compounds

Intermetallic compounds react with Li to produce high capacity negative electrodes for lithium-ion batteries. Because of the violent reactions occurring during the alloying process between lithium atoms and the active alloy, the cycle life of these materials is generally poor. In this paper we show that nanostructured SnMn3C, which has a low affinity for lithium, behaves differently from any intermetallic system reported to date. Using in situ X-ray diffraction, in situ Sn-119 Mossbauer spectroscopy, and electrochemical experiments on mechanically alloyed samples of nanostructured SnMn3C, we show that the grain boundaries apparently act as channels to allow Li to enter the particles. The lithium atoms then reversibly react with Sn atoms at and within the grain boundaries to deliver a working capacity of approximately 150 mAh/g with no capacity loss with cycle number. (C) 2000 The Electrochemical Society. S0013-4651(00)03-043-3. All rights reserved.