Layered Titanium Niobium Oxides Derived from Solid-Solution Ti- Nb Carbides (MXene) as Anode Materials for Li-Ion Batteries

Mixed-metal oxides (MMOx), oxides with more than one (transition) metal, provide versatile structural and electrochemical properties well exploited in energy conversion and electrochemical energy storage. The preparation of MMOx from single-source precursors benefits from homogeneous composition and uniform metal distribution. Herein, we describe layered mixed-metal carbides (MXenes) as templates to prepare MMOx. Through thermal oxidation of TiNb-based MXenes in CO2, mixtures of Ti and Nb oxides were produced. The Ti-to-Nb ratio in the MXene significantly affects the derived oxide composition but does not show a direct stoichiometric relation between them. At higher Ti ratios, oxide mixtures of TiO2 and titanium niobium oxide are obtained, while with Nb excess, only MMOx are produced. Multilayer MXenes retain carbon upon oxidation and produce TiNbOx/C hybrids, while delaminated MXenes lead to pure TiNbOx. When tested as Li-ion battery electrodes, the multilayer MXene-derived MMOx with Ti/Nb = 1:5 presented 226 mAh.g(-1) at 10 mA.g(-1) and 75% retention after 1000 cycles at 1 A.g(-1).