Tuning fermi level and band gap in Li₄Ti₅O₁₂ by doping and vacancy for ultrafast Li⁺ insertion/extraction

Abstract

Li 4 T i5 O 12 (LTO) attracts great interest due to the "zero strain" during cycles but the poor electronic and ionic conductivity critically impede the practical application.Herein, we report a synergy strategy of tuning localized electrons to shift Fermi level and band gap by Mg/Zr co-doping and oxygen vacancy incorporation, which significantly improves Li + and electronic transport. More importantly, the intrinsic synergistic mechanism has been revealed by neutron diffraction, X-ray absorption spectra, and first-principles calculations. The "elastic effect" of lattice induced by Mg/Zr codoping allows LTO to accommodate more oxygen vacancies to a certain degree without a severe lattice distortion, which largely improves the electronic conductivity. Mg/ Zr co-doping and oxygen vacancy incorporation effectively enhanced the dynamic characteristics of LTO electrode, achieving the excellent rate performance (90 mAh/g at 20C) and cycle stability (96.9% after 500 cycles at 10C). First-principles calculations confirm Fermi level shifts to the conduction band, and the band gap becomes narrowed due to the synergistic modulation, and the intrinsic mechanism of the enhanced electronic and Li-ion conductivity is clarified. This study offers some insights into achieving the fast Li + insertion/extraction by tuning the crystal and electronic structure with lattice doping and oxygen vacancy engineering. K E Y W O R D S anode material, band gap, Fermi level, Li 4 Ti 5 O 12 , synergistic mechanism | 5935 WANG et Al.

Three-Dimensional Network Microstructure Design of the Li4Ti5O12/rGO Nanocomposite as an Anode Material for High-Performance Lithium-Ion Batteries

“…The DOS near the Fermi level was mainly contributed by Ti 3d and O 2p orbital electrons, while Li 2s orbital electrons have almost no contribution, which indicated a strong hybrid coupling between Ti 3d and O 2p states. Similar results were reported that the DOS of LTO was mainly composed of Ti 3d and O 2p states by Wang et al However, the DOS value of the LTO/Gra system was increased at the Fermi level, which was mainly attributed to the contribution of the 2p orbital electrons of the C atom in graphene (see Figure d). This made it easier for electrons to transition from the valence band to the conduction band in the LTO/Gra system, which reduced the electron transport resistance of LTO/Gra.…”

High‐Pressure Induction and Quantitative Regulation of Oxygen Vacancy Defects in Lithium Titanate

“…The structural model of LTO exhibited a bandgap of ≈2 eV (Figure S4a, Supporting Information), illustrating its insulator properties, which is consistent with previous studies. [11,62] However, the Fermi level of LTO 1-x moves in the conduction band (CB), and the bottom of the CB passes through the Fermi level and thus exhibits metallic properties, indicating a qualitative improvement in the intrinsic conductivity of LTO (Figure S4b, Supporting Information). [47,56] Figure 4a displays the total density of states (DOS) of the LTO and LTO 1-x models.…”

Role of Excess Bi on the Properties and Performance of BiFeO3 Thin-Film Photocathodes

“…Shifting of the Fermi level toward the conduction band in BFO-s as compared to BFO-e is also an indication of oxygen vacancies being present in BFO-s. The presence of donor levels due to oxygen vacancies can shift the Fermi level toward the conduction band. , Less vacancies are indirectly also found in the bulk of the materials by means of ToF-SIMS (Figure ), RBS (Supporting Information SI-2), and XRD (Figure ). Both ToF-SIMS and RBS indicated a higher Bi/Fe ratio in BFO-e along with fewer bismuth and oxygen vacancies (Schottky defects) for BFO-e as compared to BFO-s as seen from XPS (from Figure ).…”