(135f) Defect Engineering in Strained Low-Dimensional ABO3 Perovskite Nanoparticles for Next-Generation Energy Storage Devices

Owing to their charge/discharge stability and high Li-ion conductivity, Olivine-type structures (LiMPO₄, M = Fe, Mn, Co, etc.) have been industrially commercialized as cathode materials for Li-ion batteries. Although these materials possess relatively high specific capacity (~170 mAh/g), their low room-temperature electronic conductivity has been identified as a limitation for high performance batteries. To overcome this issue, metallic-like ABO₃ (B = Nb, Ta, Mo, etc.) nanoparticles (NPs) can be utilized to improve the electronic conductivity of olivine LiFePO₄ cathodes. Therefore, this work takes advantage of the core-shell nanoarchitecture to synergistically couple the metallic conduction of the SrBO₃ (SBO) perovskite core with the high Li-ion conductivity of the LiMPO₄ shell layer to obtain enhanced electrochemical performance.

As a representative structure, SrNbO₃ NPs (SNO, ~20 nm) were fabricated using a two-step co-precipitation/pressure-controlled molten salt technique. This synthetic route limits available oxygen during the crystallization process allowing for systematic control of defects (i.e. oxygen vacancies and dopant incorporation) and thereby stabilizing the Nb oxidation state. Next, the synthesized NPs were annealed in H₂/Ar atmospheres to remove excess oxygen and modify their electronic structure by inducing an insulator to metal transition. XRD, HRTEM, TGA-DSC, XPS, and UV-Vis results show that increasing the annealing time results in a systematic change in the powder color from white (insulator) to dark blue (metal). Similar optoelectronic behaviors are observed with the synthesis of other metastable ABO₃ perovskites (B = Ta/Mo), further affirming the ability to induce metallic responses in these materials. Finally, a LiFePO₄ shell layer is deposited around the conductive SNO core NPs. EIS spectroscopy was performed to study the changes in the Li-ion/electron intercalation and migration as a result of incorporating the conductive SNO core NPs. Additionally, the presence of this core-shell nanoarchitecture is correlated to improvements in the electrochemical performance using charge-discharge measurements. Overall, these structural, optoelectronic, and electrochemical characterization results demonstrate that these low-dimensional ABO₃ perovskites have the potential to improve the electrochemical performance of olivine materials, which is critical for the design of next-generation Li-ion batteries.