MXene-Induced Pseudocapacitive Transformation in Battery-Type Metal Sulfide: A Paradigm for High-Rate Sodium Storage

High-rate sodium-ion storage is hindered by the sluggish kinetics of battery-type materials. Here, we present a universal MXene-enabled capacitive enhancement strategy, exemplified by interlayer-confined SnS₂ quantum dots (QDs) within Ti₃C₂T_x MXene to form a porous 0D/2D heterostructure. Strong interfacial electronic coupling generates built-in electric fields, while quantum confinement shifts Na⁺ storage from diffusion-dominated to pseudocapacitive behavior (94% contribution at 2 mV s^-1). MXene nanoconfinement buffers volume changes and ensures uniform QD dispersion, enabling ultrafast Na⁺/electron transport. The electrode delivers 348 mAh g^-1 at 0.05 A g^-1, retains 88.8% capacity after 3000 cycles, and achieves Na⁺ diffusion coefficients of 10^-10-10^-11 cm² s^-1. This work elucidates interfacial modulation as a powerful design principle for transforming battery-type materials into pseudocapacitive electrodes, providing a general pathway toward high-rate, durable sodium-ion energy storage.