Insights into the Li Diffusion Dynamics and Nanostructuring of H2Ti12O25 To Enhance Its Li Storage Performance

Exploring the Effect of Cation Vacancies in TiO2: Lithiation Behavior of n-Type and p-Type TiO2

TiO₂ offers several advantages over graphite as an anode material for Li-ion batteries (LIBs) but suffers from low electrical conductivity and Li-diffusion issues. Control over defect chemistry has proven to be an effective strategy to overcome these issues. However, defect engineering has primarily been focused on oxygen vacancies (V_O). The role of another intrinsic TiO₂ vacancy [i.e., titanium vacancies (V_Ti)] with regard to the Li⁺ storage behavior of TiO₂ has largely evaded attention. Hence, a comparison of V_O- and V_Ti-defective TiO₂ can provide valuable insight into how these two types of defects affect Li⁺ storage behavior. To eliminate other factors that may also affect the Li⁺ storage behavior of TiO₂, we carefully devised synthesis protocols to prepare TiO₂ with either V_O (n-TiO₂) or V_Ti (p-TiO₂). Both TiO₂ materials were verified to have a very similar morphology, surface area, and crystal structure. Although V_O provided additional sites that improved the capacity at low C-rates, the benefit obtained from over-lithiation turned out to be detrimental to cycling stability. Unlike V_O, V_Ti could not serve as an additional lithium reservoir but could significantly improve the rate performance of TiO₂. More importantly, the presence of V_Ti prevented over-lithiation, significantly improving the cycling stability of TiO₂. We believe that these new insights could help guide the development of high-performance TiO₂ for LIB applications.

High Lithium Insertion Voltage Single-Crystal H2 Ti12 O25 Nanorods as a High-Capacity and High-Rate Lithium-Ion Battery Anode Material

H₂ Ti₁₂ O₂₅ holds great promise as a high-voltage anode material for advanced lithium-ion battery applications. To enhance its electrochemical performance, control of the crystal orientation and morphology is an effective way to cope with slow Li⁺ -ion diffusion inside H₂ Ti₁₂ O₂₅ with severe anisotropy. In this report, Na₂ Ti₆ O₁₃ nanorods, prepared from Na₂ CO₃ and anatase TiO₂ in molten NaCl medium, were used as a precursor in the synthesis of long single-crystal H₂ Ti₁₂ O₂₅ nanorods with reactive facets. The as-prepared H₂ Ti₁₂ O₂₅ nanorods with a diameter of 100-200 nm showed higher charge (extraction) specific capacity and better rate performance than previously reported systems. The reversible capacity of H₂ Ti₁₂ O₂₅ was 219.8 mAh g^-1 at 1C after 100 cycles, 172.1 mAh g^-1 at 10C, and 144.4 mAh g^-1 at 20C after 200 cycles; these values are higher than those of H₂ Ti₁₂ O₂₅ prepared by the conventional soft-chemical method. Moreover, the as-prepared H₂ Ti₁₂ O₂₅ nanorods exhibited superior cycle stability with more than 94 % retention of capacity with nearly 100 % coulombic efficiency after 100 cycles at 1C. On the basis of the above results, long single-crystal H₂ Ti₁₂ O₂₅ nanorods synthesized in molten NaCl with outstanding electrochemical characteristics hold a significant amount of promise for hybrid electric vehicles and energy-storage systems.