NASICON-type Na3V2(PO4)3 is a promising cathode material for sodium-ion batteries (SIBs). However, large-scale synthesis of Na3V2(PO4)3 with a robust microstructure favoring enhanced sodium-ion storage, which is crucial for commercial usage as an electrode for SIBs, is still illusive. In this work, in situ carbon-coated Na3V2(PO4)3 (C-NVP) nanoparticles embedded in a three-dimensional mesoporous carbon matrix has been prepared by the scalable microwave-assisted sol–gel route. It delivers stable specific capacities of ∼112 and ∼102 mA h g–1 at 0.1 and 1 C-rates (1 C = 118 mA g–1), respectively, in the potential window of 2.3–3.9 V versus Na/Na+. In a wider potential window of 1.2–3.9 V, C-NVP shows reversible insertion/extraction of ∼2.4 moles of Na+ ions corresponding to a specific capacity of ∼143 mA h g–1, with 75% capacity retention after 500 cycles at 1.0 C-rate. We attribute such unusual stability at higher moles of Na+-ion insertion to the ability of nanocrystallites to freely expand against mesoporous carbon as Na3V2(PO4)3 converts to Na4V2(PO4)3. Moreover, a symmetric full cell using C-NVP as both cathode and anode shows excellent cyclability and rate performance, with a high specific capacity of 50 mA h g–1 at 2 A g–1 stable for >10,000 cycles, corresponding to specific energy and power density of 88 W h kg–1 and 3504 W kg–1, respectively. A proto-type pouch cell (symmetric full cell) delivers 7 mA h capacity at 0.1 A g–1. The scalable microwave-assisted sol–gel route provides a robust solution for the large-scale synthesis of C-NVP with superior sodium-ion storage performance.

The objectives of this study were to produce ultrafine-grained (UFG) AA2024 aluminum alloy by cryorolling followed by aging and to evaluate its corrosion behavior. Solutionized samples were cryorolled to ~85% reduction in thickness. Subsequent aging resulted in a UFG structure with finer precipitates of Al 2 CuMg in the cryorolled alloy. The (1) solutionized and (2) solutionized and cryorolled samples were uniformly aged at 160°C/24 h and were designated as CGPA and CRPA, respectively; these samples were subsequently subjected to corrosion studies. Potentiodynamic polarization studies in 3.5wt% NaCl solution indicated an increase in corrosion potential and a decrease in corrosion current density for CRPA compared to CGPA. In the case of CRPA, electrochemical impedance spectroscopic studies indicated the presence of two complex passive oxide layers with a higher charge transfer resistance and lower mass loss during intergranular corrosion tests. The improved corrosion resistance of CRPA was mainly attributed to its UFG structure, uniform distribution of fine precipitates, and absence of coarse grain-boundary precipitation and associated precipitate-free zones as compared with the CGPA alloy.

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