Amorphous and crystalline Sn{sub}2P{sub}2O{sub}7 anode materials for lithium batteries

摘要

Amorphous Sn{sub}2P{sub}2O{sub}7 was prepared by melt quenching crystalline Sn{sub}2P{sub}2O{sub}7. Both forms of Sn{sub}2P{sub}2O{sub}7 can be considered as intrinsic P doped glasses, similar to the product from the binary solid state reactionbetween SnO and P{sub}2O{sub}5. In the potential range of 0-1.2V (vs. Li/Li{sup}+, amorphous Sn{sub}2P{sub}2O{sub}7 delivers a reversible capacity of 520mAh/g which is higher than that of crystalline Sn{sub}2P{sub}2O{sub}7 (400mAh/g). However, bothdisplay nearly the same capacity and fade characteristics when the upper cut-off limit is increased to 1.4V. Cyclic voltammetry and differential capacity plots indicate the presence of two energetically different sites for Li in crystallineSn{sub}2P{sub}2O{sub}7. A higher potential is required for the complete release of Li{sup}+ in the crystalline form and this may explain the lower capacity of the latter relative to amorphous Sn{sub}2P{sub}2O{sub}7. An alloying mechanism is proposed toexplain the reversibility in charge and discharge reactions. The large initial capacity loss is explained according to the requisite initial irreversible reaction to form metallic tin.