Li+ ION MIGRATION PATHWAYS IN LITHIUM VANADIUM PHOSPHATE HIGH VOLTAGE CATHODE MATERIALS
Lithium ion secondary batteries have been widely used as high energy density storage devices. From the point of natural resources of transition metal oxides Co-free cathode materials have received much attention to replace the currently predominating LiCoO2 in commercially available lithium ion secondary batteries. Besides the widely investigated olivine-type LiMPO4, several groups explored the insertion properties of the lithium vanadium fluorophosphates, LiVPO4F (space group P-1) and Li5V(PO4)F2 (space group P21/c). LiVPO4F comprises a three-dimensional framework built up from PO4 tetrahedra and VO4F2 octahedral, wherein oxygen atoms are shared between the two environments. The strong inductive effect of PO4 3., combined with the presence of fluorine, moderates the energetics of the transition-metal redox couple such that the reversible lithium insertion reactions for Li1.xVPO4F operate at around 4.2V versus lithium. This unusually high operating potential allows the fluorophosphate phase to be employed as the cathode in high energy density graphite-based lithium-ion cells. The bond valence approach was applied to realize the transport pathways in LiVPO4F and Li5V(PO4)F2.Lowest energy migration pathways in LiVPO4F are found to extend in the x-z plane, whereas Li5V(PO4)F2 showed 3-D migration pathways with lowest migration energy of 0.7 eV. Atomistic molecular dynamics simulations are performed to understand the Li-ion mobility and the conductivity mechanism in these compounds.
R. PRASADA RAO S. ADAMS
Department of Materials Science and Engineering, National University of Singapore,117574, Singapore Department of Materials Science and Engineering, National University of Singapore, 117574, Singapore
国际会议
The 12th Asian Conference on Solid State Ionics(第十二届亚洲固态离子学会议暨第十五届中国固态离子学会议)
武汉
英文
455-462
2010-05-02（万方平台首次上网日期，不代表论文的发表时间）