Constructing Three-Dimensional Macroporous TiO2 Microspheres with Enhanced Pseudocapacitive Lithium Storage under Deep Discharging/Charging Conditions.

Abstract

TiO2 has been intensively investigated as an anode material for lithium-ion batteries (LIBs) in 1.0-3.0 V (vs Li+/Li). However, it is a challenge to realize its theoretical capacity (336 mAh g-1) in this limited potential range. Extending the potential range below 1.0 V would increase its capacity but usually at the expense of its cyclic stability owing to the sluggish ionic diffusion and unsatisfactory structural stability. Here, three-dimensional (3D) macroporous TiO2 microspheres with interconnected pores and nanocrystalline thin walls have been constructed through a scalable template-assisted spray drying method to overcome these obstacles. When applied to LIBs, high and stable discharge capacity (300 mAh g-1 at 0.1 A g-1) as well as superior cyclic stability (242 mAh g-1 after 1000 cycles at 1.0 A g-1) can be achieved under deep discharging/charging conditions (0.01-3.0 V vs Li+/Li). Furthermore, the 3D macroporous structure is well preserved under deep discharging/charging and the in situ X-ray diffraction (XRD) patterns and Raman spectra reveal the dominant pseudocapacitive contribution at low potentials (0.01-1.0 V). This work not only develops a facile method to synthesize macroporous metal oxides but also provides insight into the lithium storage mechanism of TiO2 under deep discharging/charging conditions.