Laser-Engineered Hollow Na ₃ V ₂ (PO ₄ ) ₃ with In Situ Carbon Quantum Dots for Enhanced Interfacial Stability and Phase-Transition Kinetics in Sodium-Ion batteries

Na 3 V 2 (PO 4 ) 3 (NVP) cathodes suffer from intrinsically low electronic conductivity and sluggish, nonuniform two-phase conversion, which together limit their rate capability, cycle life, and low-temperature performance. A pulsed-laser strategy is developed to simultaneously generate hollow NVP spheres and achieve in situ anchors 3–4 nm carbon quantum dots (CQDs) onto NVP, yielding a hollow/CQD architecture (NVP-L). The hollow morphology shortens Na + diffusion paths and buffers transformation-induced strain, while uniformly distributed CQDs form an internal conductive network that enhances local electronic transport and homogenizes interfacial reaction environments. Temperature-dependent GITT and Arrhenius analyses reveal a pronounced reduction of the effective activation energy from 0.51 eV for pristine NVP to 0.07 eV for NVP-L, accompanied by a several-fold increase in the Na + chemical diffusion coefficient. Consequently, NVP-L delivers a high specific discharge capacity of 105.1 mAh g –1 at 20 C and retains 87.1% of its capacity after 3000 cycles and maintains 89.7 mAh g –1 after 500 cycles at −20 °C and 1 C. A full cell paired with a Na 3 Ti 2 (PO 4 ) 3 anode achieves an energy density of 148.5 Wh kg –1 and retains 91.6% and 88.7% of its capacity after 200 cycles at 1 and 5 C, respectively. This low-energy, scalable pulsed-laser approach provides a practical route to concurrently tailor morphology and interfaces, lower phase-conversion barriers, and realize fast, durable NASICON-type sodium-ion cathodes.