Synthesis and electrochemical properties of layered Li0.9Ni0.45Ti0.55O2

Abstract

New Li0.9Ni0.45Ti0.55O2 positive electrode materials were synthesized by means of ion exchange from Na0.9Ni0.45Ti0.55O2. Powder X-ray diffraction (XRD) patterns for these materials indicate that they are isostructural with alpha-NaFeO2. The degree of cation disordering in the material depends critically on the synthesis conditions. Higher temperatures and longer ion-exchange times induce more cation disordering. Surprisingly, the partially disordered phase shows better capacity retention than the least disordered phase. First-principles calculations indicated the poor capacity retention in the least disordered phase could be attributed to the migration of Ti4+ into the Li layer during the electrochemical testing. The Ti4+ migration seems to depend sensitively on the Ni2+-Ti4+ configuration in the transition metal layer. Density of states (DOS) obtained from first-principles calculations indicate that only Ni participates in the electronic conductivity and that the poor conductivity of this material could be another reason for its low specific capacity.