No abstract

Two‐dimensional (2D) layered transition metal carbides/nitrides, called MXenes, are attractive alternative electrode materials for electrochemical energy storage. Owing to their metallic electrical conductivity and low ion diffusion barrier, MXenes are promising anode materials for sodium‐ion batteries (SIBs). Herein, we report on a new 2D carbonitride MXene, viz., Ti2C0.5N0.5Tx (Tx stands for surface terminations), and the only second carbonitride after Ti3CNTx so far. A new type of in situ HF (HCl/KF) etching condition was employed to synthesize multilayer Ti2C0.5N0.5Tx powders from Ti2AlC0.5N0.5. Spontaneous intercalation of tetramethylammonium followed by sonication in water allowed for large‐scale delamination of this new titanium carbonitride into 2D sheets. Multilayer Ti2C0.5N0.5Tx powders showed higher specific capacities and larger electroactive surface area than those of Ti2CTx powders. Multilayer Ti2C0.5N0.5Tx powders show a specific capacity of 182 mAh g−1 at 20 mA g−1, the highest among all reported MXene electrodes as SIBs with excellent cycling stability.

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 CO 2 , 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 TiO 2 and titanium niobium oxide are obtained, while with Nb excess, only MMOx are produced. Multilayer MXenes retain carbon upon oxidation and produce TiNbO x /C hybrids, while delaminated MXenes lead to pure TiNbO x . 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 .