Synergistic Heterointerface Engineering of Ti₃C₂T_x/g–C₃N₄ Bilayers for Robust Sn-Based Alloying-Type Negatrodes for Sodium-ion Pouch Batteries

Futuristic sodium-ion negatrode technologies with higher energy capabilities is critical for overcoming the bottlenecks in large-scale commercialization of beyond-coin-cell battery formats. Therefore, this study reports a Ti₃C₂T_x/g–C₃N₄ bilayer hybrid strategy for supporting tin (Sn) nanostructures for pouch-sized sodium-ion battery negatrodes. Our results indicate that this bilayer hybrid approach solves the inherent issues of alloying-type Sn-based system. Initially, Ti₃C₂T_x/g–C₃N₄ bilayers with varying Ti₃C₂T_x and g–C₃N₄ ratios are optimized to obtain a stable, porous matrix, which is subsequently used to support Sn nanostructures. As a result, a homogeneous Sn distribution within a conductive Ti₃C₂T_x scaffold and nitrogen-rich g–C₃N₄ framework is achieved. Structural and surface analyses confirm the formation of the robust Sn–Ti₃C₂T_x/g–C₃N₄ bilayer hybrid heterostructure with DFT simulations predicting strong interfacial interactions that enhance (de)sodiation processes. The final optimized Sn–Ti₃C₂T_x/g–C₃N₄[1:2] bilayer hybrid nanocomposite negatrode delivers a reversible capacity of 511 mAh∙g⁻¹ (0.5 C) with 89.12% retention (1500 cycles) in a 4.5 × 3 cm half-pouch cells. Combined with a Na_2−xNi[Fe(CN)₆]_1-y positrode, the resulting full-pouch cells deliver a reversible discharge capacity of 49.9 mAh∙g⁻¹ (total mass, 1.0 C), translating to an energy density of 124.25 Wh∙kg⁻¹ with 88.2% retention (1000 cycles).