Hard and soft templating approaches in evaporative sol-gel synthesis of TiNb2O7 nanostructures as active materials for Li-ion batteries

Abstract

As a promising alternative anode material for Li-ion batteries, monoclinic titanium niobate (TiNb₂O₇) offers the inherent safety associated with high lithiation potential combined with gravimetric capacities compared to that of graphite. Herein, evaporative sol-gel method has been employed to obtain TiNb₂O₇ with tailored morphology and crystallite structures. Using F127 co-polymer as structure directing soft template, the otherwise irregular morphology of the ceramic after calcination turns into an intricate assembly of interconnected particles with appropriately sized morphological voids for electrolyte contact and damping of the volumetric changes associated with lithiation process. Using cellulose as hard template will in turn increase the size scale of the interconnected particulates and associated morphological voids and enhances the crystallite characteristics known to enhance lithium diffusion and storage. The samples under study were subjected to high-resolution transmission electron microscopy, field-emission scanning electron microscopy, powder X-ray diffraction, selected area electron diffraction, Fourier transform infrared spectroscopy, diffuse reflectance spectroscopy and electrochemical analysis based on half-cells with lithium metal as counter electrode. Electrochemical characterization of the representative samples under study clearly shows a delicate balance between material characteristics which should simultaneously satisfy strict conditions for optimized performance. The optimized sample shows an initial Columbic efficiently of 99.2% at 0.1 C and cyclable capacity of 155 mAhg⁻¹ with a 76% retention upon 100 cycles of charge-discharge.

Graphical Abstract