FePS₃-Ti₃C₂T<i> _x </i> (2D–2D) heterostructure anode for high interfacial and pseudocapacitive Na-ion storage

Abstract The development of sodium-ion batteries (NIBs) offers a promising solution to energy storage challenges, offering lower material costs and greater resource availability compared to lithium-ion batteries (LIBs). Nevertheless, NIBs lack a suitable anode comparable to the role graphite has played in LIBs. Existing anode materials are constrained by their inherent limitations in terms of capacity, rate capability and cycling stability. Herein, we have synthesized a 2D–2D heterostructure (FePS 3 -Ti 3 C 2 T x ) by mixing both constituents, followed by a freeze-drying process. The synergistic combination of FePS 3 , a two-dimensional transition metal thiophosphite with a high theoretical capacity, and Ti 3 C 2 T x MXene, known for its structural flexibility, results in an improvement in the overall electrochemical performance. FePS 3 , FePS 3 -Ti 3 C 2 T x , and Ti 3 C 2 T x were tested for their rate performance and cycling stability. Even though the capacity of FePS 3 was higher at 1.0 A g −1 , when it was cycled at 10.0 A g −1 the heterostructure outperformed FePS 3 . Additionally, the cycling of FePS 3 -Ti 3 C 2 T x at 10 A g −1 was conducted, which showed a capacity of 205 mAh g −1 at the end of 100 cycles and 195.8 mAh g −1 at the end of 500 cycles, with a capacity retention of about 95% at the end. These results establish that the heterostructure exhibits high rate capability with minimal capacity fading over extended cycles, indicating its potential as an anode for long-term use in high-power sodium ion battery applications. Furthermore, its enhanced electrochemical kinetics can be attributed to efficient interfacial and pseudocapacitive storage, along with the structural integrity maintained throughout the galvanostatic charge–discharge cycles. MXene provides a conductive network to accelerate electrochemical performance by buffering the volume change. The 2D–2D heterostructure facilitates Na + ion diffusion and promotes pseudocapacitive behavior, as confirmed by cyclic voltammetry and electrochemical impedance spectroscopy. In addition, ex situ transmission electron microscopy analysis showed the good mechanical integration of the heterostructure after repeated cycling. These findings demonstrate the potential of FePS 3 -Ti 3 C 2 T x as an anode for next-generation sodium ion batteries.