Nanosized Li₄Ti₅O₁₂ (LTO) materials enabling high rate performance suffer from a large specific surface area and low tap density lowering the cycle life and practical energy density. Microsized LTO materials have high density which generally compromises their rate capability. Aiming at combining the favorable nano and micro size properties, a facile method to synthesize LTO microbars with micropores created by ammonium bicarbonate (NH₄HCO₃) as a template is presented. The compact LTO microbars are in situ grown by spinel LTO nanocrystals. The as-prepared LTO microbars have a very small specific surface area (6.11 m² g⁻¹) combined with a high ionic conductivity (5.53 × 10⁻¹² cm⁻² s⁻¹) and large tap densities (1.20 g cm⁻³), responsible for their exceptionally stable long-term cyclic performance and superior rate properties. The specific capacity reaches 141.0 and 129.3 mAh g⁻¹ at the current rate of 10 and 30 C, respectively. The capacity retention is as high as 94.0% and 83.3% after 500 and 1000 cycles at 10 C. This work demonstrates that, in situ creating micropores in microsized LTO using NH₄HCO₃ not only facilitates a high LTO tap density, to enhance the volumetric energy density, but also provides abundant Li-ion transportation channels enabling high rate performance.

Through a facile sodium sulfide (Na₂S)-assisted hydrothermal treatment, clean and nondefective surfaces are constructed on micrometer-sized Li₄Ti₅O₁₂ particles. The remarkable improvement of surface quality shows a higher first cycle Coulombic efficiency (≈95%), a significantly enhanced cycling performance, and a better rate capability in electrochemical measurements. A combined study of Raman spectroscopy and inductive coupled plasma emission spectroscopy reveals that the evolution of Li₄Ti₅O₁₂ surface in a water-based hydrothermal environment is a hydrolysis–recrystallization process, which can introduce a new phase of anatase-TiO₂. While, with a small amount of Na₂S (0.004 mol L⁻¹ at least), the spinel-Li₄Ti₅O₁₂ phase is maintained without a second phase. During this process, the alkaline environment created by Na₂S and the surface adsorption of the sulfur-containing group (HS⁻ or S²⁻) can suppress the recrystallization of anatase-TiO₂ and renew the particle surfaces. This finding gives a better understanding of the surface–property relationship on Li₄Ti₅O₁₂ and guidance on preparation and modification of electrode material other than coating or doping.