Enhancing lithium ion diffusion kinetic in hierarchical lithium titanate@erbium oxide from coating to doping via facile one-step co-precipitation

Hierarchical lithium titanate@erbium oxide (Li₄Ti₅O₁₂@Er₂O₃) microspheres from coating to doping were successfully synthesised by a simple and scalable one-step co-precipitation method. Microscopic observations revealed that the Li₄Ti₅O₁₂@Er₂O₃ microspheres present a well-defined hierarchical structure and that Li₄Ti₅O₁₂ is coated by the Er₂O₃ layer. The X-ray photoelectron spectroscopy (XPS) results demonstrate that partial Ti⁴⁺ is reduced to Ti³⁺ and induces oxygen vacancy because partial Er³⁺ dope into octahedral 16d Li⁺/Ti⁴⁺ sites of Li₄Ti₅O₁₂. Owing to the hierarchical microsphere structure, Er₂O₃ coating, and Er³⁺ doping, the material exhibits excess rate capacity (183.7 mAh g⁻¹ at 30C). The hierarchical microsphere structure shortens the diffusion pathways for Li⁺ ions. The Er₂O₃ coating on the surface reduces the adverse interface reaction. Importantly, oxygen vacancy induced by Er³⁺ doping enhances Li⁺ ion diffusion kinetics and offers extra space to store Li⁺ ions, which endows this sample with excess rate capacity.