Electronic and local structural changes in Li2+xTi3O7 ramsdellite compounds upon electrochemical Li-ion insertion reactions by X-ray absorption spectroscopy

Electronic and local structural changes in ramsdellite-type Li2+xTi3O7 compound were investigated by X-ray absorption spectroscopy (XAS) measurements. Upon electrochemical Li-ion insertions, the host lattice with ramsdellite structure is retained, indicated by X-ray powder diffraction. Ti K-edge extended X-ray absorption fine structure (EXAFS) analysis shows, however, slight local structural distortions around Ti ions. The energy shifts and the changes in the peak intensity of Ti K-edge and Ti L-edge XAS reveal the reducing oxidation states of Ti ions as the amount of electrochemically-inserted Li-ion increases. Equally important, oxide ions have a significant effect on the electronic transfer process, suggested by 0 K-edge XAS. These results on electronic structural changes were interpreted using the Zaanen-Sawatzky-Allen scheme.