Anodic properties of tin oxides with pyrochlore structure for lithium ion batteries

Abstract

Mixed tin oxides, M₂Sn₂O₇ (M = Y, Nd), with cubic pyrochlore structure were synthesized and characterized by X-ray diffraction and SEM. Galvanostatic cycling versus Li metal in the voltage range, 0.005-1.0 V at the current density of 60 mA g⁻¹ showed that the first-discharge capacities are 913 and 722 mA hg⁻¹ whereas the first-charge capacities are 350 and 265 (±3) mA hg⁻¹, for M = Y and Nd, respectively. The corresponding number of moles of recyclable Li are 3.4 and 3.2 for M = Y and Nd. Crystal structure destruction occurs during the first-discharge leading to the formation of nano-particles of Sn-metal and finally Li_4.4Sn in a matrix of Li-M-O. After 50 cycles, both compounds showed a capacity-retention of 89 (±1)% of the 10th cycle reversible capacity. The coulombic efficiency is ~ 98%. The average charge and discharge voltages in both compounds are 0.5 and 0.25 V, respectively. Cyclic voltammograms complement the galvanostatic results and showed that a good operating voltage range is 0.005-1.0 V. The electrodic performances of M₂Sn₂O₇ have been compared with those exhibited by other crystalline ternary tin oxides.