The electrochemical lithium reactions of monoclinic ZnP2 material

Abstract

Monoclinic ZnP₂ particles were synthesized by vacuum annealing of a mixture consisting of P and Zn powders at 1000 °C. In contrast to a tetragonal Zn₃P₂ phase, a very large plateau corresponding to 1000 mAh g⁻¹ at ∼0.45 V was developed, and out to 545 mAh g⁻¹, only topotactic lithium ion intercalation into the molecule pores was observed. The excess Li ion uptake beyond simple Li intercalation (>545 mAh g⁻¹) into molecular pores can break a chemical bond between Zn and the phosphorus atoms. During discharge, the formation of the Li_nP clusters (LiP₅ and LiP) and Zn, LiZnP phases were dominant as a result of the local structural distortion around the ZnP₄ tetrahedral site. During charge, Zn and LiP₅ phases transformed into ZnP₂ and LiP phases. However, decomposition reactions of the LiP and ZnP₂ phases with the electrolyte led to the capacity fade of the cell.