Effects of cobalt doping on structural, optical, electrical and electrochemical properties of Li4Ti5O12 anode

Cobalt-doped Li4Ti5O12 (LTO) i.e Li4Ti5-xCoxO12 (x = 0, 0.05, 0.1, 0.15, 0.2) powders have been synthesized by solid state reactions and examined for effects of Cobalt (Co) concentration on structural, optical, electrical and electrochemical properties of LTO. X-ray diffraction (XRD), Raman spectroscopy and field-emission scanning electron microscopy (FESEM) evaluate phase composition and morphology of samples. Optical study reveals reduction in bandgap E-g of LTO from 3.4 to 2.7 eV for x = 0.15, with E-g extension into visible region around 515-740 nm due to increased conduction electrons and energy levels from 3d(7) orbitals of Co and induced oxygen vacancies. Electronic conductivity of sample with x = 0.15 increases by 10(4) as compared to LTO due to conversion of Ti4+ to Ti3+ ions and increased Ti4+-V-o-Ti3+ hopping centers. Ionic conductivity and diffusivity increase upto 2.0 x 10(-7) Scm(-1) and 4.6 x 10(-12) cm(-2) s(-1) for x = 0.15, owing to increased lattice spacing by substitution of Ti4+ with Co2+. Frequency dependent conductivity suggests hopping of Li+ ions as dominant conduction in LTO. Thermally activated Li+ ions follow different conduction mechanisms in different temperature regimes. Low activation energies E-a of 0.3-0.5 eV indicate conduction of ions through interstitial pathways i.e 8a-16c-8a. High E-a of 0.7-1.15 eV suggest hopping of ions through vacancy/ defect mediated channels or other long routes. Electrochemical tests demonstrate unexpected degradation in electrochemical performance for dilute dopant concentration; x = 0.05 and 0.1, as compared to LTO, which is attributed to substitution of Co2+ ions at Li+ tetrahedral (8a) sites. However, for x = 0.15 electrochemical activity gets better indicating substitution of more of Co2+ ions at Ti4+ octahedral sites. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

Cobalt-doped Li4Ti5O12 (LTO) powders with varying Cobalt concentrations were synthesized and studied for their structural, optical, electrical, and electrochemical properties. The sample with x = 0.15 showed enhanced electronic and ionic conductivity, reduced bandgap, and increased lattice spacing, leading to improved electrochemical activity. These results highlight the potential of Cobalt-doped LTO as a promising material for energy storage applications.