Surpassing the 1 Li/Ti capacity limit in chlorine modified TiO[formula omitted]Cl[formula omitted

Abstract

TiO2 is a Li-ion electrode material based on abundant materials which exhibits high cycle life and requires no stringent high temperature processing. Amorphous TiO2 is known to reach the theoretical capacity of 1280 mAh/cm3. This theoretical limit can only be achieved through nano-scaling of the system or through chlorine modification. In both cases, all the available Ti+IV atoms are reduced to Ti+III, with insertion of Li+ ions upon the reductive step. The energy density of batteries containing a TiO2 anode remains limited by the high oxidation potential (1.8V vs. Li+/Li) and suffer from poor rate performance.Two routes can be followed to improve the performance and applicability of TiO2 as Li-ion battery electrode. The first approach focuses on increasing the reversible insertion capacity of LixTiO2 beyond x = 1, alternatively lowering the insertion potential increases the energy density of the anode.High level chlorine modification of TiO2 is observed to significantly enhance the Li-ion storage capability of Lix TiO2, exceeding x = 1, beyond the current theoretical limit of 1280 mAh/cm3 or 330 mAh/g.This work focuses on elucidating the reaction mechanism which increases the insertion capacity. A combination of electrochemical techniques, RBS and TOF-SIMS is used on thin-film electrodes. The lithium insertion beyond x > 1, is associated to the conversion of TiO2 to metallic Ti, similar to the conversion reactions observed in other binary oxides.Through chlorine modification the energy density of the anode is enhanced, both by increasing the capacity of TiO2 and by introducing a low potential insertion reaction.