Ionothermal Synthesis of High-Voltage Alluaudite Na2+2xFe2-x(SO4)3 Sodium Insertion Compound: Structural, Electronic, and Magnetic Insights

Accelerating the Phase Formation Kinetics of Alluaudite Sodium Iron Sulfate Cathodes via Ultrafast Thermal Shock

Alluaudite sodium iron sulfate (NFS) exhibits great potential for use in sodium-ion battery cathodes due to its elevated operating potential and abundant element reserves. However, conventional solid-state methods demonstrate a low heating/cooling rate and sluggish reaction kinetics, requiring a long thermal treatment to effectively fabricate NFS cathodes. Herein, we propose a thermal shock (TS) strategy to synthesize alluaudite sodium iron sulfate cathodes using either hydrous or anhydrous raw materials. The analysis of the phase formation process reveals that TS treatment can significantly facilitate the removal of crystal water and decomposition of the intermediate phase Na2Fe(SO4)2 in the hydrous precursor. In the case of the anhydrous precursor, the kinetics of the combination reaction between Na2SO4 and FeSO4 can be also accelerated by TS treatment. Consequently, pure NFS phase formation can be completed after a substantially shorter time of post-sintering, thereby saving significant time and energy. The TS-treated NFS cathode derived from hydrous precursor exhibits higher retention after 200 cycles at 1C and better rate capability than the counterpart prepared by conventional long-term tube furnace sintering, demonstrating the great potential of this novel strategy.

Spherical Shell with CNTs Network Structuring Fe-Based Alluaudite Na2+2 δ Fe2- δ (SO4 )3 Cathode and Novel Phase Transition Mechanism for Sodium-Ion Battery

Iron-based sulfate cathodes of alluaudite Na2+2 δ Fe2- δ (SO4 )3 (NFS) in sodium-ion batteries with low cost, steady cycling performance, and high voltage are promising for grid-scale energy storage systems. However, the poor electronic conductivity and the limited understanding of the phase-evolution of precursors hinder obtaining high-rate capacity and the pure phase. Distinctive NFS@C@n%CNTs (n = 1, 2, 5, 10) sphere-shell conductive networks composite cathode materials are constructed creatively, which exhibit superior reversible capacity and rate performance. In detail, the designed NFS@C@2%CNTs cathode delivers an initial discharge capacity of 95.9 mAh g-1 at 0.05 C and up to 60 mAh g-1 at a high rate of 10 C. The full NFS@C@2%CNTs//HC cell delivers a practical operating voltage of 3.5 V and mass-energy density of 140 Wh kg-1 at 0.1 C, and it can also retain 67.37 mAh g-1 with a capacity retention rate of 96.4% after 200 cycles at 2 C. On the other hand, a novel combination reaction mechanism is first revealed for forming NFS from the mixtures of Na2 Fe(SO4 )2 ·nH2 O (n = 2, 4) and FeSO4 ·H2 O during the sintering process. The inspiring results would provide a novel perspective to synthesize high-performance alluaudite sulfate and analogs by aqueous methods.

How Effective are Metal Nanotherapeutic Platforms Against Bacterial Infections? A Comprehensive Review of Literature

The emergence of multidrug-resistant bacteria has been deemed a global crisis that affects humans worldwide. Novel anti-infection strategies are desperately needed because of the limitations of conventional antibiotics. However, the increasing gap between clinical demand and antimicrobial treatment innovation, as well as the membrane permeability obstacle especially in gram-negative bacteria fearfully restrict the reformation of antibacterial strategy. Metal-organic frameworks (MOFs) have the advantages of adjustable apertures, high drug-loading rates, tailorable structures, and superior biocompatibilities, enabling their utilization as drug delivery carriers in biotherapy applications. Additionally, the metal elements in MOFs are usually bactericidal. This article provides a review of the state-of-The-art design, the underlying antibacterial mechanisms and antibacterial applications of MOF- and MOF-based drug-loading materials. In addition, the existing problems and future perspectives of MOF- and MOF-based drug-loading materials are also discussed.

Progress on Fe-Based Polyanionic Oxide Cathodes Materials toward Grid-Scale Energy Storage for Sodium-Ion Batteries

The development of large-scale energy storage systems (EESs) is pivotal for applying intermittent renewable energy sources such as solar energy and wind energy. Lithium-ion batteries with LiFePO₄ cathode have been explored in the integrated wind and solar power EESs, due to their long cycle life, safety, and low cost of Fe. Considering the penurious reserve and regional distribution of lithium resources, the Fe-based sodium-ion battery cathodes with earth-abundant elements, environmental friendliness, and safety appear to be the better substitutes in impending grid-scale energy storage. Compared to the transition metal oxide and Prussian blue analogs, the Fe-based polyanionic oxide cathodes possess high thermal stability, ultra-long cycle life, and adjustable voltage, which is more commercially viable in the future. This review summarizes the research progress of single Fe-based polyanionic and mixed polyanionic oxide cathodes for the potential sodium-ion batteries EESs candidates. In detail, the synthesized method, crystal structure, electrochemical properties, bottlenecks, and optimization method of Fe-based polyanionic oxide cathodes are discussed systematically. The insights presented in this review may serve as a guideline for designing and optimizing Fe-based polyanionic oxide cathodes for coming commercial sodium-ion batteries EESs.

Recent Progress on Graphene-Based Nanocomposites for Electrochemical Sodium-Ion Storage

In advancing battery technologies, primary attention is paid to developing and optimizing low-cost electrode materials capable of fast reversible ion insertion and extraction with good cycling ability. Sodium-ion batteries stand out due to their inexpensive price and comparable operating principle to lithium-ion batteries. To achieve this target, various graphene-based nanocomposites fabricate strategies have been proposed to help realize the nanostructured electrode for high electrochemical performance sodium-ion batteries. In this review, the graphene-based nanocomposites were introduced according to the following main categories: graphene surface modification and doping, three-dimensional structured graphene, graphene coated on the surface of active materials, and the intercalation layer stacked graphene. Through one or more of the above strategies, graphene is compounded with active substances to prepare the nanocomposite electrode, which is applied as the anode or cathode to sodium-ion batteries. The recent research progress of graphene-based nanocomposites for SIBs is also summarized in this study based on the above categories, especially for nanocomposite fabricate methods, the structural characteristics of electrodes as well as the influence of graphene on the performance of the SIBs. In addition, the relevant mechanism is also within the scope of this discussion, such as synergistic effect of graphene with active substances, the insertion/deintercalation process of sodium ions in different kinds of nanocomposites, and electrochemical reaction mechanism in the energy storage. At the end of this study, a series of strategies are summarized to address the challenges of graphene-based nanocomposites and several critical research prospects of SIBs that provide insights for future investigations.

Aqueous spray-drying synthesis of alluaudite Na2+2xFe2−x(SO4)3 sodium insertion material: studies of electrochemical activity, thermodynamic stability, and humidity-induced phase transition

In pursuit of high-energy density sodium insertion materials, polyanionic frameworks can be designed with tuneable high-voltage operation stemming from inductive effect. Alluaudite Na2Fe2(SO4)3 polysulfate forms one such earth-abundant compound registering the highest Fe3+/Fe2+ redox potential (ca. 3.8 V vs. Na/Na+). While this SO4-based system exhibits high voltage operation, it is prone to thermal decomposition and moisture attack leading to hydrated derivatives, making its synthesis cumbersome. Also, the Na–Fe–S–O quaternary system is rich with (anhydrous to hydrated) phase transitions. Herein, we demonstrate scalable aqueous-based spray drying synthesis of alluaudite Na2+2xFe2−x(SO4)3 sodium insertion material involving the formation of bloedite Na2Fe(SO4)2·4H2O as an intermediate phase. Moreover, a reversible phase transition from alluaudite to bloedite under controlled conditions of temperature and relative humidity is reported for the first time. Thermochemistry measurements revealed the enthalpies of formation (ΔH°f) of alluaudite and bloedite are exothermic. Hydrated bloedite (ΔH°f =  −117.16 ± 1.10 kJ/mol) was found to be significantly more energetically stable than anhydrous alluaudite (ΔH°f =  −11.76 ± 1.25 kJ/mol). The calorimetric data support the observed synthesis and transformation (hydration-dehydration) pathways. Spray drying route led to spherical morphology delivering capacity ~80 mAh/g. Spray drying can be extended for rapid economic synthesis of sulfate class of battery materials.

Defect Thermodynamics in Nonstoichiometric Alluaudite-Based Polyanionic Materials for Na-Ion Batteries

Sodium iron sulfate in the form of alluaudite Na_2+2xFe_2-x(SO₄)₃ (or NFSx) has emerged as one of the most promising cathodes for Na-ion batteries due to its highest Fe^2+/3+ redox potential, low cost, sustainability, and high rate capability. Unlike most of the other cathodes, NFSx generally crystalizes in its nonstoichiometric form with partial Na substitution for Fe sites and contains a small amount of impurities. However, profound explanations behind this inherent behavior including others, like phase stability, configurational structure, and defect formation are still ambiguous. We therefore performed first-principles calculations combined with a random swapping method to determine the minimum energy configurations of NFSx (with x = 0, 0.25, and 0.5) and find a correlation between the Na distribution pattern and energetics in which the site preference for Na⁺ ion is in a sequence of Na4 > Na1 > Na2 > Na3. Our result points out that the nonstoichiometry cannot be properly described under the framework of primitive structures. Moreover, we investigated phase stability diagrams and defect formations based on thermodynamic criteria. Our predicted phase diagrams can explain the inevitable impurity precipitation, which can be reduced as x diminishes. Defect formation analysis indicates an unlikely formation of channel blockage and identifies the dominant formation of Fe_Na + V_Na and Na_i + Na_Fe complexes. While the former can become spontaneous in a Na-deficient environment, the latter occurs mainly in NFS0 and accommodates the presence of nonstoichiometry.

NASICON-type air-stable and all-climate cathode for sodium-ion batteries with low cost and high-power density

The development of low-cost and long-lasting all-climate cathode materials for the sodium ion battery has been one of the key issues for the success of large-scale energy storage. One option is the utilization of earth-abundant elements such as iron. Here, we synthesize a NASICON-type tuneable Na₄Fe₃(PO₄)₂(P₂O₇)/C nanocomposite which shows both excellent rate performance and outstanding cycling stability over more than 4400 cycles. Its air stability and all-climate properties are investigated, and its potential as the sodium host in full cells has been studied. A remarkably low volume change of 4.0% is observed. Its high sodium diffusion coefficient has been measured and analysed via first-principles calculations, and its three-dimensional sodium ion diffusion pathways are identified. Our results indicate that this low-cost and environmentally friendly Na₄Fe₃(PO₄)₂(P₂O₇)/C nanocomposite could be a competitive candidate material for sodium ion batteries.

Here Chou and co-authors demonstrate a NASICON-type low-cost Fe-based cathode material for sodium ion batteries. Na₄Fe₃(PO₄)₂(P₂O₇) allows for long-term cycling and high-power density and is featured by its air stability and all-climate property with 3D diffusion pathways for Na⁺ ions.

Sulfate-Based Cathode Materials for Li- and Na-Ion Batteries

Electrochemical energy storage via Li-ion batteries has changed modern life drastically and has enabled technologies such as portable electronic devices, electric vehicles and stationary grid storage. However, with the steadfast technological evolution and increasing energy demands, batteries need to be constantly improved to meet the needs of our society. Furthermore, increasing concerns are raised regarding sustainability, availability of raw materials and cost. Therefore, extensive research efforts have been focused on the development of new battery types leading to the emergence of the Na-ion technology and the discovery of a myriad of new materials. In this context, polyanions became a prominent alternative to layered oxides. A large variety of polyanionic frameworks has been studied in the past years including phosphates, silicates and borates, but it was especially sulfates, which attracted a lot of attention due to their elevated operating voltages. The here presented article gives an overview of the exhaustive research on sulfate-based cathode materials for Li- and Na-ion batteries discussing recent findings and future perspectives.

Current computational trends in polyanionic cathode materials for Li and Na batteries

A long-standing effort has been devoted for the development of high energy density cathodes both for Li- and Na-ion batteries (LIBs and SIBs). The scientific communities in battery research primarily divide the Li- and Na-ion cathode materials into two categories: layered oxides and polyanionic compounds. Researchers are trying to improve the energy density of such materials through materials screening by mixing the transition metals or changing the concentration of Li or Na in the polyanionic compounds. Due to the fact that there is more stability in the polyanionic frameworks, batteries based on these materials mostly provide a prolonged cycling life as compared to the layered oxide materials. Nevertheless, the bottleneck for such compounds is the weight penalty from polyanionic groups that results into the lower capacity. The anion engineering could be considered as an essential way out to design such polyanionic compounds to resolve this issue and to fetch improved cathode performance. In this topical review we present a systematic overview of the polyanionic cathode materials used for LIBs and SIBs. We will also present the computational methodologies that have become significantly relevant for battery research. We will make an attempt to provide the theoretical insight with a current development in sulfate (SO₄), silicate (SiO₄) and phosphate (PO₄) based cathode materials for LIBs and SIBs. We will end this topical review with the future outlook, that will consist of the next generation organic electrode materials, mainly based on conjugated carbonyl compounds.

Nitrogen/sulfur co-doped hollow carbon nanofiber anode obtained from polypyrrole with enhanced electrochemical performance for Na-ion batteries

Polypyrrole and sulfur derived hollow carbon nanofibers co-doped with nitrogen/sulfur are synthesized and applied as the anode for Na-ion batteries (NIBs). Successful doping of hollow carbon nanofiber with nitrogen and sulfur is confirmed by X-ray photoelectron spectroscopy, scanning and tunneling electron microscopy. Further analysis certifies that sulfur doping has a significant impact in improving the elecctrochemical performance of the carbon-based anodes for NIBs. The obtained N-doped hollow carbon nanofiber and N/S co-doped hollow carbon nanofiber exhibit similar morphologies but different electrochemical behavior. As expected, the N/S co-doped hollow carbon nanofiber anode exhibits enhanced electrochemical performance, including high specific capacity, outstanding long-term stability, and good rate stability.

Challenges in computational evaluation of redox and magnetic properties of Fe-based sulfate cathode materials of Li- and Na-ion batteries

Several Fe-based sulfates have been proposed recently as cathode materials characterized by a high average operating voltage (i.e. Li2Fe(SO4)2 and Na2Fe2(SO4)3) or low fabrication temperature (e.g. Na2Fe(SO4)2·2H2O)). In this work, we apply three methods to evaluate the redox potentials and magnetic properties of these materials: (1) local density functional theory (DFT) in Perdew-Burke-Ernzerhof parametrization; (2) rotationally invariant DFT  +  U; and (3) DFT  +  U with magnetic exchange, suggested herein. The U parameters used for DFT  +  U calculations have been evaluated by using a linear response method (this applies to DFT  +  U as well as DFT  +  U calculations with a magnetic exchange term). Moreover, we have performed adjustments of U and, for the case of magnetic exchange, J parameters, to find better agreement with experimental measurements of redox and magnetic properties. We find that a self-consistent DFT  +  U/linear response approach yields quite overestimated redox potentials as compared to experiment. On the other hand, we also show that DFT  +  U calculations are not capable of providing a reasonably accurate description of both redox and magnetic properties for the case of Li2Fe(SO4)2, even when adjusted U parameters are employed. As a solution, we demonstrate that a DFT  +  U methodology augmented by a magnetic exchange term potentially provides more precise values for both the redox potentials and the magnetic moments of the Fe ions in the studied materials. Thus our work shows that for a more accurate description of redox and magnetic properties, further extensions of the DFT  +  U method, such as inclusion of the contribution of magnetic exchange, should be considered.

Mechanical properties, electronic structure and alkali-ion diffusion of Eldfellite-type AFe(SO4)2 (A = Li, Na, K) as potential cathode materials comparing with LiFePO4

To elucidate the structure-performance relationship of the new potential cathode materials AFe(SO4)2 ([Formula: see text], Na, K) compared with LiFePO4, first-principles calculations are performed to investigate the structure, mechanical stabilities and electronic properties of them. The calculated results show that AFe(SO[Formula: see text] ([Formula: see text], Na, K) compounds are mechanically stable and exhibit strong anisotropy. LiFe(SO[Formula: see text], NaFe(SO[Formula: see text] and KFe(SO[Formula: see text] are more brittle and have higher elastic modulus than LiFePO4, which is attributed to the strong chemical bonding of them. Electronic structure are predicted by HSE06 functional and the band gaps are 5.006, 4.996, 5.146 and 3.711[Formula: see text]eV for LiFe(SO[Formula: see text], NaFe(SO[Formula: see text], KFe(SO[Formula: see text] and LiFePO4, respectively. Full ab initio molecular dynamics simulations are performed to calculate the mean square displacements and diffusion coefficients of the alkali-ion. NaFe(SO[Formula: see text] has large diffusion coefficient as [Formula: see text][Formula: see text]m2/s at 1273[Formula: see text]K, as well as larger activation energy as 0.167[Formula: see text]eV. All the results contribute to understand the microscopic origin of the different behaviors of intercalation cathode used in rechargeable battery.

Na2.32Co1.84(SO4)3 as a new member of the alluaudite family of high-voltage sodium battery cathodes

A novel alluaudite, Na_2+2xCo_2−x(SO₄)₃, has been unveiled as a potential high-voltage (ca. 4.8–5.8 V) sodium battery cathode demonstrating antiferromagnetic ordering.

The alluaudite-type crystal structures of Na2(Fe/Co)2Co(VO4)3 and Ag2(Fe/Co)2Co(VO4)3

Single crystals of the title compounds, disodium di(cobalt/iron) cobalt tris-(orthovanadate), Na2(Fe/Co)2Co(VO4)3, and disilver di(cobalt/iron) cobalt tris-(orthovanadate), Ag2(Fe/Co)2Co(VO4)3, were grown from a melt consisting of stoichiometric mixtures of three metallic cation precursors and vanadium pentoxide. The difficulty to distinguish between cobalt and iron by using X-ray diffraction alone forced us to explore several models, assuming an oxidation state of +II for Co and +III for Fe and a partial cationic disorder in the Wyckoff site 8f containing a mixture of Co and Fe with a statistical distribution for the Na compound and an occupancy ratio of 0.4875:0.5125 (Co:Fe) for the Ag compound. The alluaudite-type structure is made up from [10-1] chains of [(Co,Fe)2O10] double octa-hedra linked by highly distorted [CoO6] octa-hedra via a common edge. The chains are linked through VO4 tetra-hedra, forming polyhedral sheets perpendicular to [010]. The stacking of the sheets defines two types of channels parallel to [001] where the Na(+) cations (both with full occupancy) or Ag(+) cations (one with occupancy 0.97) are located.