Crystal and electronic structure of Li15Si4

Silicon is one of the most promising anode materials for future rechargeable batteries because of its high theoretical capacity. New crystalline Li15Si4 was found as the fully electrochemical lithiated phase of crystalline Si or amorphous Si. Density functional theory was used to study the crystal and electronic structure of Li15Si4. Li15Si4 is formed by the unit figure in which six Li atoms surround a Si atom with two different Li-Si bond lengths. The Li atom has negative charge of 0.56-0.63 in Li15Si4. The average intercalation voltage for the lithium intercalation reaction from crystalline Si to Li15Si4 is 0.303 V, which is in good agreement with that predicted by the Coulometric titration experiment result for Li-Si alloys. (C) 2007 American Institute of Physics.