Investigation of ramsdellite titanates as possible new negative electrode materials for Li batteries

Transition metal oxides with ramsdellite and spinel structures have been th e subject of considerable investigation as candidate electrode materials fo r lithium-ion batteries. Good ionic conductivity has been reported for the ramsdellite Li2Ti3O7, and the spinel Li4Ti5O12 has been shown to exhibit go od electrochemical properties as a Li-anode material. We have recently demo nstrated that ramsdellite series Li1+xTi2-2xO4 displays a complete range of solubility at high temperatures between compositions LiTi2O4 and Li2Ti3O7 and that these phases can be preserved to room temperature by quenching. In this study we report on the electrochemical properties of members of this series of ramsdellite phases and the ramsdellite form of TiO2. Comparison i s made with the electrochemical properties of the spinel phase Li4Ti5O12 In cyclic voltammetry, spinel Li4Ti5O12 showed a major, reversible peak at ab out 1.55 V vs. Li. The ramsdellite phases showed a similar reversible peak at just less than -1.5 V; however, a number of additional reversible peaks were observed at up to 2.0 V. As the x value in Li1+xTi2-2xO4 increased, th ese extra peaks moved to smaller potentials, and they were observed to merg e with the 1.5 V peak for Li2Ti3O7 The presence of these extra peaks is tho ught to reflect the availability of additional sites in the ramsdellites. O n charging and discharging, the potential was in the range from 1.5 to 2.5 V, although the, behavior was not as flat as for the spinel, sigh capacitie s were observed, typically approaching 200 mAh/g. initial cycling efficienc ies were generally on the order of 80-90%, although no attempt has yet been made to optimize morphology. On cycling TiO2 ramsdellite, capacity general ly faded from an initial value of 300 mAh g(-1) to a stable capacity of 190 mAh g(-1) by cycle ten. (C) 1999 The Electrochemical Society. S0013-4651(9 9)07-058-5. All rights reserved.