Synthesis of new two‐dimensional titanium carbonitride Ti₂C_0.5N_0.5T_xMXene and its performance as an electrode material for sodium‐ion battery

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.

Surface potential-determined performance of Ti3C2T2 (T = O, F, OH) and Zr3C2T2 (T = O, F, OH, S) MXenes as anode materials of sodium ion batteries

“…30 The introduction of nitrogen generally increases the sodium capacity on these Ti-containing MXenes. 31,32 A high specific capacity of 182 mA h g −1 was realized for Ti 2 C 0.5 N 0.5 T x , which is the highest capacity of all reported multilayer MXenes. 31 The introduction of sulphur also enhances the storage capacity.…”

“…31,32 A high specific capacity of 182 mA h g −1 was realized for Ti 2 C 0.5 N 0.5 T x , which is the highest capacity of all reported multilayer MXenes. 31 The introduction of sulphur also enhances the storage capacity. 33,34 In particular, a high capacity of 550 mA h g −1 at 0.1 A g −1 was reported in sulphur intercalated Ti 3 C 2 T x .…”

2D non-carbide MXenes: an emerging material class for energy storage and conversion

“…1b). 17,25,37–40 The difficulty in synthesizing non-carbide MXenes could be attributed to two significant factors. Firstly, Ti n +1 N n has less cohesive energy than Ti n +1 C n ; thus, the nitride MXene structures have lower stability and dissolve easily in the hydrofluoric acid (HF) solution, the etchant widely used to produce carbide MXenes from their MAX phases.…”

“…Liang and co-workers reported the synthesis of Ti 2 C 0.5 N 0.5 T x MXene from its MAX phase Ti 2 AlC 0.5 N 0.5 using the KF-HCl ( in situ HF) etching approach similar to that of the LiF–HCl mild etching method. 17 Until now, Ti 2 C 0.5 N 0.5 T x and Ti 3 CNT x are the only synthesized carbonitride MXenes. An absence in the MXene peaks and increased weight loss in the material indicated that HF etching is not the optimum method to synthesize Ti 2 C 0.5 N 0.5 T x MXene.…”

“…14 Furthermore, DFT calculations predicted that non-carbide MXenes have higher Young's modulus, active surface area, magnetic moments, and stability in the aqueous medium than carbide MXenes with the same stoichiometry. 15–17 Most of the reviews reported on MXenes are limited only to the general synthesis, properties, and applications of carbide MXenes. 3,4,6,18–21 Although Johnson and his group recently published a review on the underlying energy storage mechanisms of nitride MXenes, there is no detailed review focusing on the synthesis and properties of non-carbide MXenes.…”