Deep-Lithiation-Enabled Pseudocapacitive Intercalation in Practical Micro-Sized Li4Ti5O12 Electrodes

Micro-sized Li4Ti5O12 is attractive for fast-charging Li-ion batteries because its dense particles can improve electrode packing and reduce surface reactivity, but the long solid-state transport distance is expected to limit rapid Li+ storage. Here, we demonstrate that micro-sized Li4Ti5O12 retains two voltage-selective storage regimes with distinct kinetic signatures. Within the conventional 2.5–1.0 V window, the two-phase Li4Ti5O12/Li7Ti5O12 transition reaction exhibits a pronounced voltage plateau, peak current scaling close to the square root of the scan rate (v)1/2, and a dominant long-time impedance relaxation, consistent with diffusion- and phase-transformation-controlled storage. Extending the lower cutoff potential to 0.005 V activates a low-voltage pseudocapacitive process from Li7Ti5O12 to Li8Ti5O12, characterized by a linear dependence of peak current on the scan rate (v), power-law exponents of 0.83–0.85, and a substantially reduced slow-relaxation contribution during deep lithiation. When discharged to 0.005 V, micro-sized Li4Ti5O12 delivers reversible capacities of 233 mAh·g−1 at 20 mA·g−1 and 155 mAh·g−1 at 1000 mA·g−1. Post-cycling XRD, Raman spectroscopy, HRTEM, and Ti L2,3-edge EELS further show that the LTO framework remains preserved, with enhanced lithiation and Ti reduction near the particle surface. These results demonstrate that pseudocapacitive Li+ storage can persist in micro-Li4Ti5O12 and be accessed through voltage-window control.