TiNb₂O₇ and Ti₂Nb₁₀O₂₉ were first reported by Roth [1] and Wadsley [2] in the 1950s, however it is only in 1983 that Cava [3] showed the possibility of chemical insertion of Li⁺ in their sheared structures. Han and Goodenough [4,5] followed 28 years later with the first report on the electrochemical activity of sol–gel TiNb₂O₇ showing promising capacities and rate performances along with its full cell performances with a LiNi_0.5Mn_1.5O₄ cathode in the coin cell format. These interesting performances make it a serious contender to the replacement of Li₄Ti₅O₁₂ as anode material. Between 2013 and 2016, a large number of studies were dedicated to optimize TiNb₂O₇ morphology and composition to increase its electrochemical performances [6-9]. On the other hand, the electrochemical performances of Ti₂Nb₁₀O₂₉ have only been reported after the solid state reaction [10]. Amongst those reports, only few have evaluated the electrochemical performances of those two oxides in Li-ion configuration and always at a coin cell level. Evaluation in a larger size pouch cell format is a pre-requisite prior to industrial consideration. The common swelling of Li₄Ti₅O₁₂ based soft shell full cells has been one of the (safety) limitations preventing further industrial development. The first mention of package swelling was reported for Li₄Ti₅O₁₂/LiMn₂O₄ pouch cells by Du Pasquier in 2003 [11]. This issue has only been further investigated more recently by Belharouak et al. [12], Wu et al. [13]. These reports assigned the gassing phenomenon to the electrolysis of water traces, contained in the electrolyte or absorbed on the electrodes, for which Li₄Ti₅O₁₂ can act as a catalyst. The reduction of water contributes to the release of high concentrations of H₂, representing 80 wt% of the generated gases. Further reaction between Ti⁴⁺ and carbonate solvents leads to electrolyte decomposition via the generation of CO, CO₂ and C1–C3 hydrocarbons, and formation of an SEI layer at the surface of Li₄Ti₅O₁₂. While further enhancement of electrochemical performances of TiNb₂O₇ and Ti₂Nb₁₀O₂₉ is still a possibility as will be demonstrated in this presentation, the probability of the gassing phenomenon of these two oxides in full cells should be monitored.

We will present the development of a synthesis route for both TiNb₂O₇ and Ti₂Nb₁₀O₂₉. The combination of a solvothermal treatment to a ball milling step was designed to enhance the electrochemical performances of the two oxides by (1) increasing the accessible capacity at high cycling rates and (2) limiting the effect of capacity fading over time. In the second part, full cell cycling and gassing properties of as-prepared TiNb₂O₇ will be reported and compared to the ones of Li₄Ti₅O₁₂ with LiMn_1.5Ni_0.5O₄ and Li(Ni_1/3Mn_1/3Co_1/3)O₂ cathodes.

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