An Unprecedented Case: A Low Specific Surface Area Anatase/N-Doped Carbon Nanocomposite Derived from a New Single Source Precursor Affords Fast and Stable Lithium Storage.

Abstract

A nanocomposite of ultrafine anatase nanoparticles (<5 nm) embedded N-doped carbon (TiO2-NPs/NC) with a relatively low specific surface area was successfully synthesized by in situ pyrolysis of a new and cheap single source precursor of (H2en)3[Ti4(O2)4(Hcit)2(cit)2]·12H2O (en = ethylenediamine and H4cit = citric acid) under 550 °C and an inert atmosphere. The precursor in crystalline state was isolated from an aqueous solution containing of titanium butoxide, citric acid, hydrogen peroxide, and ethylenediamine and was characterized. The crystal structure was determined by X-ray single crystal diffraction. To our surprise, the low surface area TiO2-NPs/NC exhibits a high specific capacity, superior rate capability, excellent cycle performance, and good processability as a negative material for rechargeable lithium-ion batteries (LIBs). A large reversible capacity of 360 and 125 mA h g-1 and a high Coulombic efficiency (the average value is ∼99.8%) could be kept even after 1000 cycles under a current density of 0.3 and 6 A g-1, respectively. An analysis of the voltammetric sweep data shows that the pseudocapacitive behavior occurred at the surface of the material and the lithium intercalation processes contribute to the total stored charge, resulting in the high capacity of the TiO2-NPs/NC nanocomposite. The potentiostatic intermittent titration technique used to determine the lithium ion diffusion (DLi+) suggested the TiO2-NPs/NC nanocomposite displays a high DLi+. In addition, the high electric conductivity provided by the NC substrate and the ultrafine anatase particles can mitigate the diffusion path for electrons and ions and tolerate higher strain, and thus effectively decrease pulverization and improve the rate and cycle performance. In particular, the observed superior lithium storage properties, resulting from the low surface area nanocomposite with ultrafine nanoparticles embedded NC substrate, are expected to have fundamental and practical implications for the preparation of high performance electrodes in LIBs or other cells.