Spinel Li₄Ti₅O₁₂ is known as a “zero-strain” anode material for rechargeable Li-ion batteries due to the minute structural changes upon Li insertion/extraction. Li₄Ti₅O₁₂ possesses a flat potential of about 1.55 V (vs Li⁺/Li) with a theoretical capacity of 175 mAh/g. Compared with the currently most used anode material, graphite, Li₄Ti₅O₁₂ has lower energy density, but it is safer has longer cycle life  and an excellent power density resulting from its 3D Li-ion mobility in the spinel structure. This implies that Li₄Ti₅O₁₂ has huge potential  as anode material in high power density and long cycle life applications, such as electric vehicles (EV) and stationary power plants. Spinel Li₄Ti₅O₁₂can be synthesized by many different techniques: solid-state reaction sol−gel methods microwave-assisted synthesis and spray pyrolysis and in hydrothermal batch reactors .

For practical applications, the solid-state method is the most widely used method since it is easy to scale-up, and the precursors are cheap and abundant. Anatase TiO₂ and Li₂CO₃ are the most commonly used starting material for the solid state synthesis of Li₄Ti₅O₁₂ . However, it has proven difficult to achieve pure phase Li₄Ti₅O₁₂, and rutile TiO₂ and Li₂TiO₃ are usually observed as impurity phases in the synthesis product . The lithium rich Li2TiO3 phase is known to be located on the Li₄Ti₅O₁₂ surface . There are few reports considering the impact of Li₂TiO₃ on the electrochemical performance of Li₄Ti₅O₁₂ LTO.

In this work, first of all, we have been interested in preparing monoclinic Li₂TiO₃ by solid-state method (binary Li₂O-TiO₂).  When used as cathode in primary lithium battery, the performances appear as low (theoretical capacity for 1e- process of 244 mAh/g) but at the same potential than the one of a LTO.

By accurate phase determination of a commercial LTO containing as impurities Li₂TiO₃  we have calculated the true efficiency of the LTO phase. As for most of commercial products, the 150 mAh/g discharge capacity registered appears as due to the proportion of low electrochemically active Li₂TiO₃ phase. Then in order to come over this Li₂TiO₃phase, we have chosen to make surface fluorination on this commercial LTO.

Indeed, surface fluorination has already been successfully performed on for example LiMn2O4 by using NF₃ gas . Recently, a thin and homogeneous Li₂TiF₆ coating has been introduced onto an over-lithiated layered oxide (OLO, namely Li_1.17Ni_0.17Co_0.1Mn_0.56O₂) surface via simple co-precipitation at ambient temperature by using Li₂CO₃ and H₂TiF₆ aqueous solutions . The cycle performance and rate capability of the coated samples were superior to that of pristine OLO by reducing polarizations owing to the surface lithium conductive phase. Furthermore, the Li₂TiF₆coating, which had strong fluoride bonding, hindered thermal side reactions at elevated temperature and the associated drawbacks by passivating the OLO surface.

So we have decided to manage fluorination in order to try to convert Li₂TiO₃ into Li₂TiF₆. Two fluorination ways were made: flash fluorination by a quick exposure of LTO with pure fluorine gas flow at 100°C and fluorination by XeF₂ decomposition at 120°C. In the first case, the fluorinating agent is F₂ whereas in the second, it is mainly F°. Both fluorination ways succeeded in disappearing LiTi₂O₃.Only flash fluorination allows to get Li₂TiF₆ onto LTO whereas after fluorination by XeF₂, Li₂TiF₆ is generated together with LiF and TiOF₂ as shown by XRD  and XPS.

The electrochemical performances of commercial LTO fluorinated either by flash fluorination or XeF₂ decomposition have been used as cathode in secondary lithium battery. For both fluorinations, the charge-discharge capacities at the first cycle are clearly enhanced by comparison with those of commercial LTO. Fluorinated parts give an oxidation potential at around 3.0V for LTO fluorinated by  XeF₂ and this oxidation phenomenon remains upon cycle. It can be attributed to redox properties of TiOF₂ . For LTO-F₂, no clear new redox potential is visible, Li₂TiF₆ seems to act only on the SEI formation and as a consequence on the first cycle. The own electrochemical properties of Li₂TiF₆ could be interesting to perform latter.