Ostwald Ripening Tailoring Hierarchically Porous Na₃V₂(PO₄)₂O₂F Hollow Nanospheres for Superior High‐Rate and Ultrastable Sodium Ion Storage

Abstract

Low cost sodium-ion batteries (SIBs), have been widely recognized as one of the competitive next-generation electrical energy-storage technologies, owing to the widespread distribution and huge abundance of sodium resources. [2,3] From the perspective of the overall energy-and costeffectiveness of SIBs, cathode material is the key component that determines the energy density, electrochemical performance, and cost. [4-6] Thus, extensive efforts have been devoted to the investigations on cathode materials to boost the commercial availability of SIBs. Compared to its lithium counterpart, the large ionic radius and heavy atomic mass of Na + leads to sluggish electrode reaction kinetics and undesirable structure degradation during repeated Na + insertion/extraction, severely limiting the electrochemical performance of SIBs. Therefore, exploiting promising cathode materials with not only high energy density but also the capabilities of fast Na + diffusion and stable cyclability is of great importance to meet the urgent requirements for practical applications. Among various cathode materials for SIBs, Na +-superionic conductor (NASICON) type compounds are intensively investigated as favorable candidates owing to their high Na + mobility, rich structural diversity, and pronounced structural Sodium-ion batteries (SIBs) are receiving considerable attention as economic candidates for large-scale energy storage applications. Na 3 V 2 (PO 4) 2 O 2 F (NVPF) is intensively regarded as one of the most promising cathode materials for SIBs, due to its high energy density, fast ionic conduction, and robust Na +-super-ionic conductor (NASICON) framework. However, poor rate capability ascribed to the intrinsically low electronic conductivity severely hinders their practical applications. Here, high-rate and highly reversible Na + storage in NVPF is realized by optimizing nanostructure and rational porosity construction. Hierarchical porous NVPF hollow nanospheres are designed to modify the issues of inconvenient electrolyte transportation and unfavorable charge transfer behavior faced by solid-structured electrode materials. The individual unique nanosphere is assembled from numerous nanoparticles, which shortens the length of Na + transport in solid state and thus facilites the Na + migration. Hollow nanostructure hierarchically porous configuration enables adequate electrolyte penetration, continuous electrolyte supplementation, and facile electrolyte transportation, leading to barrier-free Na + /e − diffusion and high-rate cycling. In addition, the large electrolyte accessible surface area boosts the charge transfer in the whole electrode. Therefore, the present NVPF demonstrates unprecedented rate capability (85.4 mAh g −1 at 50 C) and long-term cyclability (62.2% capacity retention after 2000 cycles at 20 C).

Plasmonic Superstructure Arrays Fabricated by Laser Near-Field Reduction for Wide-Range SERS Analysis of Fluorescent Materials

“…The reduction time for complete wrapping is dependent on the laser intensity; therefore, control of the laser intensity and reduction time can create bowl nanostructures (see Supplementary Material, Figure S5b ) or hollow nanoclusters (see Supplementary Material, Figure S5c ) after elimination of the silica spheres using hydrofluoric acid. Such bowl and hollow nanoclusters have gained attention in recent years due to physical properties such as high specific surface area, and structural properties that benefit the applications for plasmonic devices and energy storage [ 13 , 14 , 15 ]. Although the hollow nanoclusters are generally synthesized by wet-chemical methods, the laser near-field reduction can create pure metal nanostructures because it does not require additional agents such as photoinitiators and surfactants.…”

Mainstream Optimization Strategies for Cathode Materials of Sodium‐Ion Batteries

“…Reproduced with permission. [ 86 ] Copyright 2020, Wiley‐VCH. c) Schematic illustration of the architecture of the coral‐like Na 3.12 Fe 2.44 (P 2 O 7 ) 2 /C composite.…”

“…[ 90 ] These structures were combined to produce composite structures and synergistic effects. For example, Hou's group [ 86 ] synthesized hierarchical porous NVPF hollow nanospheres through the Ostwald ripening mechanism. As shown in Figure 9b, the hollow structure enables adequate electrolyte penetration and continuous electrolyte supplementation.…”

“…has been reported widely. Some special structures, such as 1D carbon nanotubes [ 83 ] having rapid ion and electron migration, 2D graphene nanosheets, [ 84 ] 3D graphene frame structures, [ 85 ] core–shell structures, [ 86,87 ] coral structures, [ 88 ] flower‐like structures, [ 89 ] and so forth, have also been reported. [ 90 ] These structures were combined to produce composite structures and synergistic effects.…”

“…b) The schematic illustration of the structural engineering of hollow nanosphere NVPF material. Reproduced with permission [86]. Copyright 2020, Wiley-VCH.…”