Enhanced Electrochemical Performance of Li4Ti5O12 by Niobium Doping for Pseudocapacitive Applications

Niobium-doped nanocrystalline Li4Ti5O12 (LTO) is synthesized by the solid-state reaction method, and the influence of dopant concentration (x = 2-10 mol%) on microstructural and electrochemical properties is studied. The X-ray diffraction and Raman patterns assessed the cubic spinel structure of Li4Ti5-xNbxO12 phase in all samples. Marginal changes in the lattice parameters, unit cell volume and dislocation density of LTO are observed with Nb substitution. The higher ionic radius of Nb induces a lattice expansion, which may be favorable for more ion intercalation/deintercalation. The SEM and TEM images display uniformly distributed nano-sized cubical particles. The represented (hkl) orientations of the SAED pattern and d-spacing (0.46 nm) between bright fringes confirm the well-crystallized LTO phase. The EDS and elemental mapping results demonstrate that Nb elements are uniformly doped in LTO with a proper stoichiometric ratio. The optimized 8%Nb-doped LTO electrode exhibits pseudocapacitive behavior and delivers a high specific capacitance of 497 F g(-1) at a current density of 1 A g(-1 )with 92.3% of specific capacitance retention even after 5000 cycles.