Redesign of Li2MP2O7 (M = Fe or Mn) by Tuning the Li Diffusion in Rechargeable Battery Electrodes

Defects in crystals such as antisites generally lead-to the deterioration of the ionic conductivity of solid-state ionic conductors. Herein, using first principles calculations, we demonstrate that the Li diffusion in Li2MP2O7 (M = Fe or Mn), a promising battery material, is sensitively affected by the presence of Li/M antisites; however, unexpectedly, the antisites significantly promote Li diffusion. The calculations reveal that the presence of antisites reduces the barrier of Li hopping and opens new paths for Li diffusion in the Li2MP2O7 crystal. In our experimental verification, we succeeded in synthesizing crystalline Li2MnP2O7 with varying Li/Mn antisite contents and demonstrated that the inclusion of antisites results in improved power capability with faster Li diffusion for Li-ion battery electrodes. We believe that this unexpected finding of increasing the ionic conductivity by introducing antisite defects broadens our understanding of solid-state ionic conductors and provides a new strategy for improving Li diffusion in conventional electrode materials for Li rechargeable batteries.