The synergic effects of Na and K co-doping on the crystal structure and electrochemical properties of Li4Ti5O12 as anode material for lithium ion battery

Abstract

The effects of Na and K co-doping on the crystal structure and electrochemical properties of Li4Ti5O12 have been comprehensively investigated by means of X-ray diffraction (XRD), neutron diffraction (ND), scanning electron microscope (SEM) and galvanostatic charge–discharge tests. Rietveld refinements of XRD and ND data indicate that the lattice parameters increase with the doping of Na and K, and Na or K prefers to take 8a site (tetrahedral site) in Li3.98K0.01Na0.01Ti5O12. The lattice parameter and unit cell volume of Li3.98Na0.01K0.01Ti5O12 are even larger than that of Li3.98Na0.02Ti5O12 and Li3.98K0.02Ti5O12 indicating a cooperative effect of Na and K co-doping on the enlargement of lattice parameters and unit cell volume. The electrochemical property results demonstrate that Na and K co-doped Li3.98Na0.01K0.01Ti5O12 has a larger reversible capacity and rate capability as anode material for lithium ion battery compared to un-doped Li4Ti5O12, Na-doped Li3.98Na0.02Ti5O12 or K-doped Li3.98Ka0.02Ti5O12, which indicates the significant synergic effect of Na and K co-doping on the improvement of the electrochemical performances of Li4Ti5O12.