Understanding the lithium transport mechanism in Li9Cr3P8O29cathode material by molecular dynamics modeling

Abstract

In this work, the atomistic simulation method based on Pedone model is applied to observe the concerted motion of lithium-ions in the perfect lattice of possible Li9Cr3(P2O7)3(PO4)2 cathode material. The simulation is carried out at a series of increasingly elevated temperatures in a super cell containing 27 unit cells. The superimposed Li+ trajectory at all timeframes offers an intuitive, reliable image of the Li+ migration in the crystal lattice. It reveals that lithium-ion propagates in a–b plane in an isotropic way and the propagation along the c axis is negligible. A typical lithium-ion migration path along the a or b axis can be described as migrating consecutively in the repeated sequence of Li1, Li3, Li1, and Li2. The energy barrier of Li9Cr3(P2O7)3(PO4)2 cathode material is about 0.345 eV and the estimated lithium-ion diffusion coefficients at room temperature are estimated at ca. 1.96 × 10−9 cm2 s−1. Compared with those intensively investigated cathode materials for lithium-ion batteries, which are normally considered to be highly potential or already in practical use, the lithium-ion conduction in the crystal grain for Li9Cr3(P2O7)3(PO4)2 cathode material is comparable or even superior. Therefore, the Li+ mobility is sufficiently high to exhibit good performances as a cathode material for lithium-ion batteries. More researches concerning the preparation, phase transformation, doping, surface modification, and the characterization of electro-chemical performance are urgently needed.