Ordered Large-Pore Mesoporous Li₄Ti₅O₁₂ Spinel Thin Film Electrodes with Nanocrystalline Framework for High Rate Rechargeable Lithium Batteries: Relationships among Charge Storage, Electrical Conductivity, and Nanoscale Structure

Abstract

Herein is reported the soft-templating synthesis and characterization of mesoporous lithium titanate (Li4Ti5O12) thin film electrodes with a nanocrystalline framework. Various state-of-the-art techniques, including electron microscopy, grazing incidence small-angle X-ray scattering, impedance spectroscopy, time-of-flight secondary ion mass spectrometry, and X-ray photoelectron spectroscopy verify that the sol–gel derived Li4Ti5O12 materials employed in this work are well-defined at both the nanoscale and the microscale. In addition, the data show that the thin films are highly crystalline after annealing in air at 650 °C and adopt the spinel structure in phase-pure form. The data also show that the conversion of the initially amorphous framework comes at little cost to the ordering of the distorted cubic network of pores averaging 18 nm in diameter. Apart from the structural characterization, we also examine the electrical conductivity and the charging/discharging behavior and show the benefits of producing a high quality material with mesoporous morphology. Mesoporous Li4Ti5O12 thin film electrodes not only exhibit enhanced lithium ion storage capabilities at short charging times but also are able to maintain stable cycling performance at rates as high as 64C. We contend that the unique combination of open nanoscale porosity with electrical conductivity of the same order as that of ordinary bulk nanocrystalline Li4Ti5O12 is responsible for the facile lithium intercalation observed in these thin film materials.