Laser-driven structural modification of bulk MnO₂ for enhanced aqueous sodium-ion energy storage

Aqueous sodium-ion batteries (ASIBs) have attracted increasing attention as safe, low-cost, and environmentally benign energy storage systems for large-scale applications. Commercial β-MnO₂ suffers from substantial limitations, including its intrinsically poor electronic conductivity, narrow one-dimensional (1 × 1) tunnel structure, and limited interstitial space, which severely restricts Na⁺ insertion/extraction. Furthermore, its dense bulk morphology and structural rigidity lead to sluggish ion diffusion kinetics and significant polarization during cycling, resulting in poor capacity and rate performance. Herein, we report a laser-driven structural modification strategy to convert commercially available bulk β-MnO₂ into a highly active electrode material. Upon laser irradiation, the initially irregular and densely packed β-MnO₂ particles undergo rapid localized heating, fragmentation, and reorganization, forming uniformly distributed nanosized quasi-spherical particles. This transformation effectively reduces particle size, increases active surface area, and shortens Na⁺ diffusion pathways. As a result, the laser-processed β-MnO₂ electrode delivers a high reversible capacity of 70.6 mAh g⁻¹ at 0.1 A g⁻¹, superior rate capability, and stable cycling performance with 99.8% capacity retention over 1000 cycles at a high current density 5 Ag⁻¹, significantly outperforming pristine β-MnO₂. Kinetic analysis reveals increased pseudocapacitive contribution and reduced charge-transfer resistance, confirming accelerated electrochemical reactions. This work demonstrates a simple, scalable approach to transform structurally constrained β-MnO₂ into an efficient sodium-ion storage material, offering new insights into laser-induced engineered nanostructure for next-generation energy storage systems.