New Insights on the Reversible Lithiation Mechanism of $TiO_{2}$(B) by Operando X-ray Absorption Spectroscopy and X-ray Diffraction Assisted by First-Principles Calculations

Operando X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD) measurements provide new insights on the mechanism of lithium insertion into TiO$_2$(B). The investigation of the evolution of electronic, long-range, and local structure during electrochemical cycling indicates a purely monophasic insertion mechanism upon lithium insertion, while global and local structure are only slightly modified. While XRD reflects an anisotropic lattice expansion, EXAFS reveals a wide distribution of Ti–O bond length, in line with the presence of two distinct distorted octahedral Ti environments, in agreement with previous DFT calculations. Upon lithium insertion, these Ti–O coordination shells undergo significant modifications which are enhanced once the insertion of 0.4 Li is exceeded, connoting a two regime process that is in good agreement with the electrochemical signature of this material. DFT calculations and local chemical bond analyses were coupled with experimental results, thus providing additional insights into the structural response of TiO$_2$(B) upon lithiation