Monoclinic Bimetallic Prussian Blue Analog Cathode with High Capacity and Long Life for Advanced Sodium Storage

Antimony Telluride as Bifunctional Host Material for Dendrite-Free Sodium Metal Batteries

The development of the sodium metal anode is hampered by uncontrolled Na dendrite growth and unstable solid electrolyte interface (SEI). Herein, Sb2Te3 nanosheets are anchored into the fibers of carbon cloth (CC) to construct Sb2Te3@CC material as Na metal host for sodium metal batteries (SMBs). The alloying product of Na3Sb with strong sodiophilicity serves as a nucleation seed to induce homogeneous Na deposition and boost the formation of a dendrite-free Na metal anode. Meanwhile, the conversion product of Na2Te covers the surface of Na metal to form a robust SEI film. Low current density, uniform Na ionic flux, and suppressed volume expansion can be guaranteed by three-dimensional carbon fibers. Therefore, a Na@Sb2Te3@CC electrode contributes ultrastable cyclic performance for over 1600 h with a low overpotential of 30.5 mV. The assembled Na metal full batteries deliver a high initial energy density of 307.3 Wh kg-1 and superior cycling stability with an ultralong lifespan of over 2000 cycles.

Synthesis of Low-Defect Iron-Based Prussian Blue with Low Water Content for High-Stability Sodium-Ion Batteries

This study proposes an innovative two-step synthesis strategy to significantly enhance the performance of sodium-ion batteries by developing low-defect, low water content iron-based Prussian blue (PB) materials. Addressing the limitations of traditional co-precipitation methods-such as rapid reaction rates leading to excessive crystal defects and interstitial water content-the research team introduced a synergistic approach combining non-aqueous phase precursor synthesis and controlled water-concentration secondary crystallization. The process involves preparing a PB precursor in a glycerol system, followed by secondary crystallization in a water-/ethanol-mixed solvent with a precisely regulated water content, achieving the dual objectives of water content reduction and crystal morphology optimization. Systematic characterization revealed that water concentration during secondary synthesis critically influences the material's crystal structure, morphological features, and water content. The optimized PB50-24 material exhibited a highly regular cubic morphology with a sodium content of 9.2% and a remarkably low interstitial water content of 2.1%. Electrochemical tests demonstrated outstanding performance-an initial charge-discharge capacity of 120 mAh g-1 at a 1C rate, the retention of 105 mAh g-1 after 100 cycles, and a high rate capability of 86 mAh g-1 at 10C, representing significant improvements in cycling stability and rate performance over conventional methods. This work not only establishes a cost-effective, scalable synthesis pathway for Prussian blue materials but also provides theoretical guidance for developing other metal-based Prussian blue analogs, offering substantial value for advancing the industrial application of sodium-ion batteries in next-generation energy storage systems.

Sodium-Rich Prussian Blue Analogs Synthesized with Reducing Sodium Salt for Enhanced Rate and Cycling Stability Sodium-Ion Storage

Prussian blue analogs (PBAs) as cathode material for sodium-ion batteries have attracted widespread attention due to their affordability, simple synthesis, and high theoretical capacity. Nevertheless, the oxidation of Fe2+ and sodium loss lead to poor electrochemical properties which restrict the practical use of PBAs. Herein, a simple coprecipitation approach based on sodium salt-reduction-assisted synthesis was proposed to construct high-sodium PBAs. The sodium bisulfite (NaHSO3) not only effectively inhibits the oxidation of Fe2+ but also increases the mole ratio of Na+ in the resulting products. The optimized sample exhibits excellent specific capacity (131.1 mAh g-1 at 0.1C), high rate performance (103.9 mAh g-1 at 10C), and good cyclic performance (94.8% capacity retention after 200 cycles). Experimental results reveal that the sample synthesized with sodium bisulfite possesses improved sodium-ion diffusion kinetics and stable crystal structure. In this study, a scalable method is introduced for the synthesis of PBAs with excellent electrochemical properties and further applications.

Simultaneous Tailoring of Chemical Composition and Morphology Configuration in Metal Hexacyanoferrate for Ultrafast and Durable Sodium-Ion Storage

Metal hexacyanoferrates (MHCFs) with adjustable composition and open framework structures have been considered as intriguing cathode materials for sodium-ion batteries (SIBs). Exploiting MHCFs with ultrafast and durable sodium storage capability as well as comparable capacity is always a goal that many investigators pursue, but remains challenging. Herein, simultaneous tailoring of chemical composition and morphology configuration is carried out to design a hollow monoclinic high-entropy MHCF (HMHE-HCF) assembled by nanocubes for the first time to realize the objective. The "cocktail effect" of high-entropy construction, rich sodium content of monoclinic phase, and unique hollow structure endow HMHE-HCF cathode with fast reaction kinetics and energetically stable performance during continuous charging/discharging processes. As a result, the HMHE-HCF cathode demonstrates superior rate performance up to an ultra-high rate of 100 C (71.1 % retention to 0.1 C), and remarkable cycling stability with a capacity retention of 77.8 % over 25,000 cycles at 100 C, outperforming most reported sodium-ion cathodes. Further, the HMHE-HCF//hard carbon full-cell delivers capacities of 99.0 and 82.3 mAh g-1 at 0.1 C and 10 C, respectively, and retains 98.1 % of the initial capacity after 1,600 cycles at 5 C, demonstrating its potential application for sodium-ion storage.

From lab to field: Prussian blue frameworks as sustainable cathode materials

Prussian blue and Prussian blue analogues have attracted increasing attention as versatile framework materials with a wide range of applications in catalysis, energy conversion and storage, and biomedical and environmental fields. In terms of energy storage and conversion, Prussian blue-based materials have emerged as suitable candidates of growing interest for the fabrication of batteries and supercapacitors. Their outstanding electrochemical features such as fast charge-discharge rates, high capacity and prolonged cycling life make them favorable for energy storage application. Furthermore, Prussian blue and its analogues as rechargeable battery anodes can advance significantly by the precise control of their structure, morphology, and composition at the nanoscale. Their tunable structural and electronic properties enable the detection of many types of analytes with high sensitivity and specificity, and thus, they are ideal materials for the development of sensors for environmental detection, disease trend monitoring, and industrial safety. Additionally, Prussian blue-based catalysts display excellent photocatalytic performance for the degradation of pollutants and generation of hydrogen. Specifically, their excellent light capturing and charge separation capabilities make them stand out in photocatalytic processes, providing a sustainable option for environmental remediation and renewable energy production. Besides, Prussian blue coatings have been studied particularly for corrosion protection, forming stable and protective layers on metal surfaces, which extend the lifespan of infrastructural materials in harsh environments. Prussian blue and its analogues are highly valuable materials in healthcare fields such as imaging, drug delivery and theranostics because they are biocompatible and their further functionalization is possible. Overall, this review demonstrates that Prussian blue and related framework materials are versatile and capable of addressing many technical challenges in various fields ranging from power generation to healthcare and environmental management.

Progress and perspectives on iron-based electrode materials for alkali metal-ion batteries: a critical review

Iron-based materials with significant physicochemical properties, including high theoretical capacity, low cost and mechanical and thermal stability, have attracted research attention as electrode materials for alkali metal-ion batteries (AMIBs). However, practical implementation of some iron-based materials is impeded by their poor conductivity, large volume change, and irreversible phase transition during electrochemical reactions. In this review we critically assess advances in the chemical synthesis and structural design, together with modification strategies, of iron-based compounds for AMIBs, to obviate these issues. We assess and categorize structural and compositional regulation and its effects on the working mechanisms and electrochemical performances of AMIBs. We establish insight into their applications and determine practical challenges in their development. We provide perspectives on future directions and likely outcomes. We conclude that for boosted electrochemical performance there is a need for better design of structures and compositions to increase ionic/electronic conductivity and the contact area between active materials and electrolytes and to obviate the large volume change and low conductivity. Findings will be of interest and benefit to researchers and manufacturers for sustainable development of advanced rechargeable ion batteries using iron-based electrode materials.

Hollow Layered Iron-Based Prussian Blue Cathode with Reduced Defects for High-Performance Sodium-Ion Batteries

Fe-based Prussian blue (Fe-PB) analogues have emerged as promising cathode materials for sodium-ion batteries, owing to their cost-effectiveness, high theoretical capacity, and environmental friendliness. However, their practical application is hindered by [Fe(CN)6] defects, negatively impacting capacity and cycle stability. This work reports a hollow layered Fe-PB composite material using 1,3,5-benzenetricarboxylic acid (BTA) as a chelating and etching agent by the hydrothermal method. Compared to benzoic acid, our approach significantly reduces defects and enhances the yield of Fe-PB. Notably, the hollow layered structure shortens the diffusion path of sodium ions, enhances the activity of low-spin Fe in the Fe-PB lattice, and mitigates volume changes during Na-ion insertion/extraction into/from Fe-PB. As a sodium-ion battery cathode, this hollow layered Fe-PB exhibits an impressive initial capacity of 95.9 mAh g-1 at a high current density of 1 A g-1. Even after 500 cycles, it still maintains a considerable discharge capacity of 73.1 mAh g-1, showing a significantly lower capacity decay rate (0.048%) compared to the control sample (0.089%). Moreover, the full cell with BTA-PB-1.6 as the cathode and HC as the anode provides a considerable energy density of 312.2 Wh kg-1 at a power density of 291.0 W kg-1. This research not only enhances the Na storage performance of Fe-PB but also increases the yield of products obtained by hydrothermal methods, providing some technical reference for the production of PB materials using the low-yield hydrothermal method.

Isostructural Synthesis of Iron-Based Prussian Blue Analogs for Sodium-Ion Batteries

Rechargeable sodium ion batteries (SIBs) have promising applications in large-scale energy storage systems. Iron-based Prussian blue analogs (PBAs) are considered as potential cathodes owing to their rigid open framework, low-cost, and simple synthesis. However, it is still a challenge to increase the sodium content in the structure of PBAs and thus suppress the generation of defects in the structure. Herein, a series of isostructural PBAs samples are synthesized and the isostructural evolution of PBAs from cubic to monoclinic after modifying the conditions is witnessed. Accompanied by, the increased sodium content and crystallinity are discovered in PBAs structure. The as-obtained sodium iron hexacyanoferrate (Na1.75 Fe[Fe(CN)6 ]0.9743 ·2.76H2 O) exhibits high charge capacity of 150 mAh g-1 at 0.1 C (17 mA g-1 ) and excellent rate performance (74 mAh g-1 at 50 C (8500 mA g-1 )). Moreover, their highly reversible Na+ ions intercalation/de-intercalation mechanism is verified by in situ Raman and Powder X-ray diffraction (PXRD) techniques. More importantly, the Na1.75 Fe[Fe(CN)6 ]0.9743 ·2.76H2 O sample can be directly assembled in a full cell with hard carbon (HC) anode and shows excellent electrochemical performances. Finally, the relationship between PBAs structure and electrochemical performance is summarized and prospected.

Iron-Vanadium Incorporated Ferrocyanides as Potential Cathode Materials for Application in Sodium-Ion Batteries

Sodium-ion batteries (SIBs) are potential replacements for lithium-ion batteries owing to their comparable energy density and the abundance of sodium. However, the low potential and low stability of their cathode materials have prevented their commercialization. Prussian blue analogs are ideal cathode materials for SIBs owing to the numerous diffusion channels in their 3D structure and their high potential vs. Na/Na⁺. In this study, we fabricated various Fe-V-incorporated hexacyanoferrates, which are Prussian blue analogs, via a one-step synthesis. These compounds changed their colors from blue to green to yellow with increasing amounts of incorporated V ions. The X-ray photoelectron spectroscopy spectrum revealed that V³⁺ was oxidized to V⁴⁺ in the cubic Prussian blue structure, which enhanced the electrochemical stability and increased the voltage platform. The vanadium ferrocyanide Prussian blue (VFPB1) electrode, which contains V⁴⁺ and Fe²⁺ in the Prussian blue structure, showed Na insertion/extraction potential of 3.26/3.65 V vs. Na/Na⁺. The cycling test revealed a stable capacity of ~70 mAh g^-1 at a rate of 50 mA g^-1 and a capacity retention of 82.5% after 100 cycles. We believe that this Fe-V-incorporated Prussian green cathode material is a promising candidate for stable and high-voltage cathodes for SIBs.