Memory Effect in Lithium Titanate Driven by Interfacial Oxygen Vacancies

Abstract

Memory effect is undesirable abnormal voltage behavior in batteries that appears as a result of certain usage history. Al-doped Li4Ti5O12 (LTO), LiFePO4, and TiO2 that undergo phase transformations during lithiation/delithiation are known to possess a memory effect. Memory effect in these materials typically arises because of delayed onset of potential overshoot at the beginning of the delithiation voltage profile. In general, memory effect is associated with the sluggish electrochemical kinetics of phase transformation. Herein, we reveal a new source of memory effect in undoped LTO, which originates from an unstable LTO/electrolyte interface that can be produced by a distorted and defect-ridden particle surface. Electrochemical impedance spectroscopy shows that deep lithiation leads to variable resistance toward charge transfer, which produces a memory effect in the proceeding cycles. This work indicates the importance of controlling the particle/electrolyte interface to prevent an unprecedented memory effect in LTO.