Abstrakt
Na insertion into sol-gel made nanocrystalline spinel, Li4Ti5O12 (nano LTS) and reference commercial spinel (Aldrich LTS) is studied by cyclic voltammetry and galvanostatic chronopotentiometry at 1C and 2C charging/discharging rates. Nanocrystalline LTS exhibits the best performance for Na storage, its charge capacities reach 156 mAhg(-1) and are twice as high as those of reference Aldrich LTS.
A capacity drop of nano LTS taking place during galvanostatic cycling is ascribed to irreversible structural changes induced by Na accommodation in the Li4Ti5O12 lattice. Raman spectroscopy of nano LTS after Na insertion reveals a formation of orthorhombic Li0.5TiO2 phase in original nanocrystalline Li4Ti5O12.
The occurrence of this phase, which is commonly formed during Li insertion into anatase, is discussed in terms of induced Li redistribution and its accommodation in very minor anatase impurities detectable by Raman spectroelectrochemistry and HRTEM, but visible neither by X-ray diffractometry nor cyclic voltammetry of Na insertion.