Performances and Gassing Behavior of Mixed Ti/Nb Oxides As High Potential Li-Ion Anodes
Authors: Colin Jean-Francois , Buannic Lucienne , Chapuis Marlène , Chakir Mohamed 
Published: February 2020

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 LiNi0.5Mn1.5O4 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 LiMn1.5Ni0.5O4 and Li(Ni1/3Mn1/3Co1/3)O2 cathodes.

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Figure 1