Vacancy Control in TiNb₂O₇: Implications for Energy Applications

Rapid global electrification, including for transportation, has dramatically increased demand for long-lasting and faster-charging batteries. Titanium niobium oxide (TiNb2O7) is one of the most promising anode materials for high-power lithium-ion batteries (LIBs). However, the intrinsic low electronic conductivity of TiNb2O7 is a significant drawback. Herein, an almost 10 orders of magnitude increase in conductivity is achieved via reduction of TiNb2O7 in H2 at 900 °C. The observed dramatic increase in electron conductivity upon reduction is unprecedented and opens new possibilities to produce niobium-based conductive materials for next-generation energy storage. Upon extended reduction, TiNb2O7 converts into a distorted rutile TiNb2O6 structure, which can be reoxidized back into the crystallographic shear phase. In addition, TiNb2O7 can be thermally reduced in an inert atmosphere and reoxidized by CO2 with excellent oxygen exchange capacity. Thus, the TiNb2O7 Wadsley–Roth phase demonstrates outstanding potential for solar-driven thermochemical CO2 splitting at 1400 °C. These findings manifest that controlling defect chemistry paves the way for developing advanced materials for LIBs and solar-driven thermochemical fuel production

Probing Capacity Trends in MLi₂Ti₆O₁₄ Lithium-Ion Battery Anodes Using Calorimetric Studies

Due to higher packing density, lower working potential, and area specific impedance, the MLi2Ti6O14 (M = 2Na, Sr, Ba, and Pb) titanate family is a potential alternative to zero-strain Li4Ti5O12 anodes used commercially in Li-ion batteries. However, the exact lithiation mechanism in these compounds remains unclear. Despite its structural similarity, MLi2Ti6O14 behaves differently depending on charge and size of the metal ion, hosting 1.3, 2.7, 2.9, and 4.4 Li per formula unit, giving charge capacity values from 60 to 160 mAh/g in contrast to the theoretical capacity trend. However, high-temperature oxide melt solution calorimetry measurements confirm strong correlation between thermodynamic stability and the observed capacity. The main factors controlling energetics are strong acid–base interactions between basic oxides MO, Li2O and acidic TiO2, size of the cation, and compressive strain. Accordingly, the energetic stability diminishes in the order Na2Li2Ti6O14 > BaLi2Ti6O14 > SrLi2Ti6O14 > PbLi2Ti6O14. This sequence is similar to that in many other oxide systems. This work exhibits that thermodynamic systematics can serve as guidelines for the choice of composition for building better batteries