Correlation of Electrochemical Characteristics with Structural, Optical, and Electrical Properties in Tungsten-Doped Li₄Ti₅O₁₂ Anodes

Abstract

Tungsten (W) doping boosts electrochemical performance of the lithium titanate (LTO) anode accredited to varied fundamental features, i.e, crystalline and electronic structures and electronic/ionic conductivities. W6+ induces partial reduction of Ti4+ ions to Ti3+ owing to increased conduction electrons/energy levels, causing a reduced band gap of LTO and increased room-temperature electronic conductivity to a maximum of 1.3 × 10–6 S cm–1 for an optimal W concentration of x ∼0.15. An improved room-temperature Li-ion conductivity/diffusivity of 6.5 × 10–8 S cm–1/1.6 × 10–12 cm2s–1 for x ∼0.15 is owed to increased lattice spacing on the substitution of W6+ at Ti4+ octahedral sites. Temperature-dependent impedance over 25–300 °C depicts increases in ionic and electronic conductivities from 10–8 to 10–4 S cm–1 and 10–8 to 10–6 S cm–1, respectively. Activation energies E a of 0.48–0.50 eV for both undoped and doped LTOs illustrate the same conduction mechanism of Li ions through 8a-16c-8a pathways. Electrochemical characteristics improve in correlation to the type of dopant, doping concentration, substitutional site of dopant, resulting structural variations, and varying electronic/ionic conductivities and conduction mechanisms.