Mesoporous nanoreactor with accelerated ion transport for high-performance SnO₂-based anodes in sodium-ion batteries

Tin dioxide (SnO₂) is a promising anode material for sodium-ion batteries owing to its high theoretical capacity, yet its practical application is severely hindered by drastic volume expansion and intrinsically sluggish Na⁺ diffusion kinetics. Herein, we report a mesoporous yolk-shell SnO₂-based nanoreactor (SnO₂mCNR) constructed via a facile interfacial polymerization assembly and selective etching strategy. The architecture features a SnO₂ nanocube core, an internal void space, and a mesoporous carbon shell permeated with interconnected channels (∼7 nm). This unique design simultaneously accommodates the large volume changes during sodiation/desodiation and provides low-resistance pathways for rapid Na⁺ transport. Compared with its non-porous counterpart (SnO₂ CNR), SnO₂mCNR exhibits a ∼ 3.5-fold higher Na⁺ diffusion coefficient and a transition toward pseudocapacitive-dominated charge storage (b-value of 0.90). Consequently, SnO₂mCNR delivers a high reversible capacity of 650.3 mAh g^-1 at 0.05 A g^-1, excellent rate capability (218.7 mAh g^-1 at 5 A g^-1), and outstanding cycling stability with 95.1% capacity retention over 1800 cycles at 1 A g^-1. A full pouch cell assembled with a Na₃V₂(PO₄)₃-based cathode achieves a high energy density of 292.2 Wh kg^-1, indicating promising application potential at the electrode-material level. This work establishes shell porosity engineering as a generalizable design principle for high-performance conversion/alloying-type anodes in sodium-ion batteries.