Full structural and electrochemical characterization of Li2Ti6O13 as anode for Li-ion batteries

Abstract

A detailed structural and electrochemical study of the ion exchanged Li₂Ti₆O₁₃ titanate as a new anode for Li-ion batteries is presented. Subtle structural differences between the parent Na₂Ti₆O₁₃, where Na is in an eightfold coordinated site, and the Li-derivative, where Li is fourfold coordinated, determine important differences in the electrochemical behaviour. While the Li insertion in Na₂Ti₆O₁₃ proceeds reversibly the reaction of lithium with Li₂Ti₆O₁₃ is accompanied by an irreversible phase transformation after the first discharge. Interestingly, this new phase undergoes reversible Li insertion reaction developing a capacity of 170 mAh g⁻¹ at an average voltage of 1.7 V vs. Li⁺/Li. Compared with other titanates this result is promising to develop a new anode material for lithium ion rechargeable batteries. Neutron powder diffraction revealed that Na in Na₂Ti₆O₁₃ and Li in Li₂Ti₆O₁₃ obtained by Na/Li ion exchange at 325 °C occupy different tunnel sites within the basically same (Ti₆O₁₃)²⁻ framework. On the other hand, electrochemical performance of Li₂Ti₆O₁₃ itself and the phase released after the first full discharge is strongly affected by the synthesis temperature. For example, heating Li₂Ti₆O₁₃ at 350 °C produces a drastic decrease of the reversible capacity of the phase obtained after full discharge, from 170 mAh g⁻¹ to ca. 90 mAh g⁻¹. This latter value has been reported for Li₂Ti₆O₁₃ prepared by ion exchange at higher temperature.