Synthesis, electrochemistry and transition metal-doping of monoclinic Li4Ti5O12 and Na4Ti5O12

Abstract

A new candidate Li-ion battery anode material, monoclinic M-Li4Ti5O12, has been prepared for the first time by ion-exchange from monoclinic M-Na4Ti5O12, and found to offer a stable electrochemical performance at rates of C/20 and 2C. The structural and electrochemical effects of transition metal M(III) doping of M-Na4Ti5O12 and Li4Ti5O12 have also been investigated. Doping was found to: facilitate the synthesis of the M-Na4Ti5O12 type structure, eliminating the need for strongly reducing conditions; increase the Na-ion content; and improve the stability in atmospheric conditions. Neutron powder diffraction and ex situ X-ray powder diffraction data collected at various points during electrochemical cycling reveal that phase changes in Li4Ti5O12 proceed via a two-phase mechanism, in contrast to M-Na4Ti5O12 which proceeds via a solid-solution mechanism.