Robust Pitaya-Structured Pyrite as High Energy Density Cathode for High-Rate Lithium Batteries

Fine Structure and Electrochemical Performance Investigations of Spherical LiMn0.6Fe0.4PO4/C Cathode Material Synthesized via a Spray-Drying Route at Various Calcination Temperatures

LiMnxFe1-xPO4/C is characterized by excellent multiplicative performance and high operating voltage, and as a type of cathode material, it has a high electronic conductivity and thus has received much attention. In this paper, carbon-coated LiMn0.6Fe0.4PO4/C was synthesized using glucose + PEG2000 as the carbon source by wet sanding and spray-drying. The experimental results show that the use of sanding and the spray-drying method can make the particle size distribution of LiMn0.6Fe0.4PO4/C powder more uniform. The initial discharge specific capacity of the LiMn0.6Fe0.4PO4/C battery was 144.3 mA h g-1, and after 100 cycles at 1 C current, the discharge specific capacity of the battery remained at 128.2 mA h g-1 with a cycling efficiency of 94.3%. At the same time, the oxidation states and coordination environments of the elements Fe and Mn were elucidated by X-ray absorption fine structure spectroscopy. And the ex-Fe-MS was tested under different charging and discharging conditions. The sample optimized by the orthogonal test has good cycle stability and multiplication performance.

Iron/Molybdenum Sulfide Nanozyme Cocatalytic Fenton Reaction for Photothermal/Chemodynamic Efficient Wound Healing

The issue of bacterial infectious diseases remains a significant concern worldwide, particularly due to the misuse of antibiotics, which has caused the emergence of antibiotic-resistant strains. Fortunately, the rapid development of nanomaterials has propelled significant progress in antimicrobial therapy, offering promising solutions. Among them, the utilization of nanoenzyme-based chemodynamic therapy (CDT) has become a highly hopeful approach to combating bacterial infectious diseases. Nevertheless, the application of CDT appears to be facing certain constraints for its low efficiency in the Fenton reaction at the infected site. In this study, we have successfully synthesized a versatile nanozyme, which was a composite of molybdenum sulfide (MoS2) and iron sulfide (FeS2), through the hydrothermal method. The results showed that iron/molybdenum sulfide nanozymes (Fe/Mo SNZs) with desirable peroxidase (POD) mimic activity can generate cytotoxic reactive oxygen species (ROS) by successfully triggering the Fenton reaction. The presence of MoS2 significantly accelerates the conversion of Fe2+/Fe3+ through a cocatalytic reaction that involves the participation of redox pairs of Mo4+/Mo6+, thereby enhancing the efficiency of CDT. Additionally, based on the excellent photothermal performance of Fe/Mo SNZs, a near-infrared (NIR) laser was used to induce localized temperature elevation for photothermal therapy (PTT) and enhance the POD-like nanoenzymatic activity. Notably, both in vitro and in vivo results demonstrated that Fe/Mo SNZs with good broad-spectrum antibacterial properties can help eradicate Gram-negative bacteria like Escherichia coli and Gram-positive bacteria like Staphylococcus aureus. The most exciting thing is that the synergistic PTT/CDT exhibited astonishing antibacterial ability and can achieve complete elimination of bacteria, which promoted wound healing after infection. Overall, this study presents a synergistic PTT/CDT strategy to address antibiotic resistance, providing avenues and directions for enhancing the efficacy of wound healing treatments and offering promising prospects for further clinical use in the near future.

Tailoring Alkalized and Oxidized V2CTx as Anode Materials for High-Performance Lithium Ion Batteries

V2CTx MXenes have gained considerable attention in lithium ion batteries (LIBs) owing to their special two-dimensional (2D) construction with large lithium storage capability. However, engineering high-capacity V2CTx MXenes is still a great challenge due to the limited interlayer space and poor surface terminations. In view of this, alkalized and oxidized V2CTx MXenes (OA-V2C) are envisaged. SEM characterization confirms the accordion-like layered morphology of OA-V2C. The XPS technique illustrates that undergoing alkalized and oxidized treatment, V2CTX MXene replaces -F and -OH with -O groups, which are more conducive to pseudocapacitive properties as well as Na ion diffusion, providing more active sites for ion storage in OA-V2C. Accordingly, the electrochemical performance of OA-V2C as anode materials for LIBs is evaluated in this work, showing excellent performance with high reversible capacity (601 mAh g-1 at 0.2 A g-1 over 500 cycles), competitive rate performance (222.2 mAh g-1 and 152.8 mAh g-1 at 2 A g-1 and 5 A g-1), as well as durable long-term cycling property (252 mAh g-1 at 5 A g-1 undergoing 5000 cycles). It is noted that the intercalation of Na+ ions and oxidation co-modification greatly reduces F surface termination and concurrently increases interlayer spacing in OA-V2C, significantly expediting ion/electron transportation and providing an efficient way to maximize the performance of MXenes in LIBs. This innovative refinement methodology paves the way for building high-performance V2CTx MXenes anode materials in LIBs.

Degradation and mechanism of PFOA by peroxymonosulfate activated by nitrogen-doped carbon foam-anchored nZVI in aqueous solutions

Perfluorooctanoic acid (PFOA) is an emerging pollutant that is non-biodegradable and presents severe environmental and human health risks. In this study, we present an effective and mild approach for PFOA degradation that involves the use of nitrogen-doped carbon foam anchored with nanoscale zero-valent iron (nZVI@NCF) to activate low concentration peroxymonosulfate (PMS) for the treatment. The nZVI@NCF/PMS system efficiently removed 84.4% of PFOA (2.4 μM). The active sites of nZVI@NCF including Fe0 (110) and graphitic nitrogen played crucial roles in the degradation. Electrochemical analyses and density functional theory calculations revealed that nZVI@NCF acted as an electronic donor, transferring electrons to both PMS and PFOA during the reaction. By further analyzing the electron paramagnetic resonance and byproducts, it was determined that electron transfer and singlet oxygen were responsible for PFOA degradation. Three degradation pathways involving decarboxylation and surface reduction of PFOA in the nZVI@NCF/PMS system were determined. Finding from this study indicate that nZVI@NCF/PMS systems are effective in degrading PFOA and thus present a promising persulfate-advanced oxidation process technology for PFAS treatment.

Entropy-Tuned Layered Oxide Cathodes for Potassium-Ion Batteries

The manganese-based layered oxides as a promising cathode material for potassium ion batteries (PIBs) have attracted considerable interest owing to their simple synthesis, high specific capacity, and low cost. However, due to the irreversible phase transition and the Jahn-Teller distortion of the Mn3+ , its application in potassium ion batteries is limited, leading to slow potassium ion kinetics and severe capacity attenuation. Here, entropy-tuning by changing the content of cathode material composition is proposed to address the above challenges. Compared to low and high entropy variants of K0.45 Mnx Co(1- x )/4 Mg(1- x )/4 Cu(1- x )/4 Ti(1- x )/4 O2 , where x = 0.8, 0.6, and 0.4, the medium entropy K0.45 Mn0.6 Co0.1 Mg0.1 Cu0.1 Ti0.1 O2 shows more balanced electrochemical properties in the PIBs. Benefiting from entropy-tuned suppression of the Jahn-Teller distortion of the Mn3+ , the K0.45 Mn0.6 Co0.1 Mg0.1 Cu0.1 Ti0.1 O2 can achieve a high K+ ion transport rate and alleviated volume variation while retaining high specific capacity. Accordingly, the medium entropy K0.45 Mn0.6 Co0.1 Mg0.1 Cu0.1 Ti0.1 O2 cathode in the full cell exhibits a high capacity of 100 mAh g-1 at 50 mA g-1 , delivers superior rate capability (65.8 mAh g-1 at 500 mA g-1 ) and cycling stability (67.8 mAh g-1 after 350 cycles at 100 mA g-1 ). The entropy-tuning strategy is expected to open new avenues in designing PIB cathode materials and beyond.

Homogeneous regulation of arranged polymorphic manganese dioxide nanocrystals as cathode materials for high-performance zinc-ion batteries

Rechargeable aqueous zinc-ion batteries have emerged as attractive energy storage devices by virtue of their low cost, high safety and eco-friendliness. However, zinc-ion cathodes are bottlenecked by their vulnerable crystal structures in the process of zinc embedding and significant capacity fading during long-term cycling. Herein, we report the rational and homogeneous regulation of polycrystalline manganese dioxide (MnO₂) nanocrystals as zinc cathodes via a surfactant template-assisted strategy. Benefiting from the homogeneous regulation, MnO₂ nanocrystals with an ordered crystal arrangement, including nanorod-like polyvinylpyrrolidone-manganese dioxide (PVP-MnO₂), nanowire-like sodium dodecyl benzene sulfonate-manganese dioxide and nanodot-like cetyltrimethylammonium bromide-manganese dioxide, are obtained. Among these, the nanorod-like PVP-MnO₂ nanocrystals exhibit stable long-life cycling of 210 mAh g^-1 over 180 cycles at a high rate of 0.3 A g^-1 and with a high capacity retention of 84% over 850 cycles at a high rate of 1 A g^-1. The good performance of this cathode significantly results from the facile charge and mass transfer at the interface between the electrode and electrolyte, featuring the crystal stability and uniform morphology of the arranged MnO₂ nanocrystals. This work provides crucial insights into the development of advanced MnO₂ cathodes for low-cost and high-performance rechargeable aqueous zinc-ion batteries.

Multilevel spatial confinement of transition metal selenides porous microcubes for efficient and stable potassium storage

Recently, potassium-ion batteries (PIBs) have been considered as one of the most promising energy storage systems; however, the slow kinetics and large volume variation induced by the large radius of potassium ions (K⁺) during chemical reactions lead to inferior structural stability and weak electrochemical activity for most potassium storage anodes. Herein, a multilevel space confinement strategy is proposed for developing zinc-cobalt bimetallic selenide (ZnSe/Co_0.85Se@NC@C@rGO) as high-efficient anodes for PIBs by in-situ carbonizing and subsequently selenizing the resorcinol-formaldehyde (RF)-coated zeolitic imidazolate framework-8/zeolitic imidazolate framework-67 (ZIF-8/ZIF-67) encapsulated into 2D graphene. The highly porous carbon microcubes derived from ZIF-8/ZIF-67 and carbon shell arising from RF provide rich channels for ion/electron transfer, present a rigid skeleton to ensure the structural stability, offer space for accommodating the volume change, and minimize the agglomeration of active material during the insertion/extraction of large-radius K⁺. In addition, the three-dimensional (3D) carbon network composed of graphene and RF-derived carbon-coated microcubes accelerates the electron/ion transfer rate and improves the electrochemical reaction kinetics of the material. As a result, the as-synthesized ZnSe/Co_0.85Se@NC@C@rGO as the anode of PIBs possesses the excellent rate capability of 203.9 mA h g^-1 at 5 A g^-1 and brilliant long-term cycling performance of 234 mA h g^-1 after 2,000 cycles at 2 A g^-1. Ex-situ X-ray diffraction (Ex-situ XRD) diffraction reveals that the intercalation/de-intercalation of K⁺ proceeds through the conversion-alloying reaction. The proposed strategy based on the spatial confinement engineering is highly effective to construct high-performance anodes for PIBs.

A facile precursor route towards the synthesis of Fe1-xS@NC-rGO composite anode materials for high-performance lithium-ion batteries

Iron-based sulfides are considered promising anode materials for lithium-ion batteries (LIBs) due to their low cost and high theoretical specific capacities. However, low conductivity and dissolution of lithium polysulfides during the reaction hamper their practical applications. Herein, we firstly synthesized N-doped carbon-coated Fe_1-xS (Fe_1-xS@NC) sheets through vacuum pyrolysis of the precursor Fe_1-xS(en)_0.5 (en = ethylenediamine). Then Fe_1-xS@NC-rGO composites (rGO = reduced graphene oxide) were prepared in which the Fe_1-xS@NC sheets were anchored on the rGO. The performance of the composites as an anode material for LIBs has been investigated. It is found that coating N-doped C on Fe_1-xS surfaces can improve the surface conductivity and electrochemical kinetics of Fe_1-xS, which is beneficial for the conversion between lithium polysulfides and Fe_1-xS. In addition, the coated N-doped C on the Fe_1-xS sheets can serve as a barrier to direct contact between the electrolyte and the material, reducing the dissolution of polysulfides and preventing the loss of active ingredients. More importantly, the double protection of the N-doped C layer and the flexible rGO substrate minimizes the structural damage caused by the cyclic expansion of Fe_1-xS@NC-rGO. As expected, Fe_1-xS@NC-rGO exhibits good rate performance with a reversible capacity of 939.5 mA h g^-1 after 1690 cycles at a current density of 1.0 A g^-1, along with outstanding charge and discharge performance and excellent long-term cycling stability. This work shows that the introduction of NC coating and the rGO matrix into Fe_1-xS would synergistically enhance the performance of Fe_1-xS for LIBs and highlights the effectiveness of the synthetic strategy for double carbon-based materials-protected sulfides in developing superior LIB electrodes.

Understanding the Electrochemical Performance of FeS2 Conversion Cathodes

Conversion cathodes represent a viable route to improve rechargeable Li+ battery energy densities, but their poor electrochemical stability and power density have impeded their practical implementation. Here, we explore the impact cell fabrication, electrolyte interaction, and current density have on the electrochemical performance of FeS2/Li cells by deconvoluting the contributions of the various conversion and intercalation reactions to the overall capacity. By varying the slurry composition and applied pressure, we determine that the capacity loss is primarily due to the large volume changes during (de)lithiation, leading to a degradation of the conductive matrix. Through the application of an external pressure, the loss is minimized by maintaining the conductive matrix. We further determine that polysulfide loss can be minimized by increasing the current density (>C/10), thus reducing the sulfur formation period. Analysis of the kinetics determines that the conversion reactions are rate-limiting, specifically the formation of metallic iron at rates above C/8. While focused on FeS2, our findings on the influence of pressure, electrolyte interaction, and kinetics are broadly applicable to other conversion cathode systems.

Revealing the reaction and fading mechanism of FeSe2 cathode for rechargeable magnesium batteries

Rechargeable Mg batteries (RMBs) are advantageous large-scale energy-storage devices because of the high abundance and high safety, but exploring high-performance cathodes remains the largest difficulty for the development. Compared with oxides and sulfides, selenides show better Mg-storage performance because the weaker interaction with the Mg2+ cation favors fast kinetics. Herein, nanorods-like FeSe2 was synthesized and investigated as cathodes for RMBs. Compared with microspheres and microparticles, nanorods exhibits higher capacity and better rate capability with the smaller particle size. The FeSe2 nanorods show a high capacity of 191 mAh g-1 at 50 mA g-1 and a good rate performance of 39 mAh g-1 at 1000 mA g-1. Ex-situ characterizations demonstrate the Mg2+ intercalation mechanism for FeSe2, and slight conversion reaction occurs on the surface of the particles. The capacity fading is mainly because of the dissolution of Fe2+, which is caused by the reaction between Fe2+ and Cl- of the electrolyte during the charge process on the surface of the particles. The surface of FeSe2 is mainly selenium after long cycling, which may also dissolve in the electrolyte during cycling. The present work develops a new type of Mg2+ intercalation cathode for RMBs. More importantly, the fading mechanism revealed herein has considered the specificity of Mg battery electrolyte and would assist a better understanding of selenide cathodes for RMBs.

Self-Sacrifice Template Construction of Uniform Yolk-Shell ZnS@C for Superior Alkali-Ion Storage

Secondary batteries have been widespread in the daily life causing an ever-growing demand for long-cycle lifespan and high-energy alkali-ion batteries. As an essential constituent part, electrode materials with superior electrochemical properties play a vital role in the battery systems. Here, an outstanding electrode of yolk-shell ZnS@C nanorods is developed, introducing considerable void space via a self-sacrificial template method. Such carbon encapsulated nanorods moderate integral electronic conductivity, thus ensuring rapid alkali-ions/electrons transporting. Furthermore, the porous structure of these nanorods endows enough void space to mitigate volume stress caused by the insertion/extraction of alkali-ions. Due to the unique structure, these yolk-shell ZnS@C nanorods achieve superior rate performance and cycling performance (740 mAh g-1 at 1.0 A g-1 after 540 cycles) for lithium-ion batteries. As a potassium-ion batteries anode, they achieve an ultra-long lifespan delivering 211.1 mAh g-1 at 1.0 A g-1 after 5700 cycles. The kinetic analysis reveals that these ZnS@C nanorods with considerable pseudocapacitive contribution benefit the fast lithiation/delithiation. Detailed transmission electron microscopy (TEM) and X-ray diffraction (XRD) analyses indicate that such yolk-shell ZnS@C anode is a typical reversible conversion reaction mechanism accomplished by alloying processes. This rational design strategy opens a window for the development of superior energy storage materials.

An expanded sandwich-like heterostructure with thin FeP nanosheets@graphene via charge-driven self-assembly as high-performance anodes for sodium ion battery

In this work, we simply fabricate a novel expanded sandwich-like heterostructure of iron-phosphide nanosheets in between reduced graphene oxide (expanded FeP NSs@rGO) with a high ratio of FeP/Fe-PO_x and an expanded structure via a charge-driven self-assembly method by exploiting polystyrene beads (PSBs) as a sacrificial template. In such a design, even after the decomposition of PSBs during the annealing process, the PSBs successfully provide ample space between the nanosheets, enabling a structure with long-term stability and high ionic conductivity. Importantly, the PSBs are decomposed and simultaneously reacted with oxidized iron-phosphide (Fe-PO_x) on the surface of the nanosheets to reduce into FeP. As a result, the expanded FeP NSs@rGO results in a high content of FeP (52.3%) and remarkable electrochemical performances when it is used for sodium-ion battery anodes. The expanded FeP NSs@rGO exhibits a high capacity of 916.1 mA h g^-1 at 0.1 A g^-1, a superior rate capability of 440.9 mA h g^-1 at 5 A g^-1, and a long-term cycling stability of 85.4% capacity retention after 1000 cycles at 1 A g^-1. In addition, the full cell also exhibits excellent capacity, rate capability, and cycling stability. This study clearly demonstrates that an increase in FeP proportion is directly related to an increase in capacity. This facile method of synthesizing rationally designed heterostructures is expected to provide a novel strategy to create nanostructures for advanced energy storage applications.

Highly Strengthened and Toughened Zn-Li-Mn Alloys as Long-Cycling Life and Dendrite-Free Zn Anode for Aqueous Zinc-Ion Batteries

Zn-ion batteries (ZIBs) using aqueous electrolyte, recently, have been a hot topic owing to the high safety, low cost, and high specific energy capacity. However, the formation of dendrite and side reactions on the Zn anode during cycling inhibit the application of ZIBs. An advanced Zn anode by alloying a small amount of Li and Mn with Zn is hereby reported. It is found that Li and Mn can form cationic ions which restrain lateral diffusion of Zn ions and regulate zinc electrodeposition through the electrostatic shield mechanism. As a result, the formation of Zn dendrite is greatly inhibited. This process also mitigates the formation of Zn-based byproduct and Zn passivation. Consequently, the symmetric ZnLiMn/ZnLiMn cell presents a small overpotential of 30 mV at 1 mA cm^-2 , greatly enhanced cycling durability (1000 h at a current density of 1 mA cm^-2 ), and a dendrite-free morphology after cycles. Moreover, the authors find that the ZnLiMn alloy has greatly enhanced mechanical properties. The assembled ZnLiMn/MnO₂ full cell can retain 96% capacity after 400 cycles at 1 C. Thus, the alloying low-cost Li/Mn strategy is very promising for large-scale production of dendrite-free Zn electrode in rechargeable ZIBs.

Pyrite-embedded porous carbon nanocatalysts assembled in polyvinylidene difluoride membrane for organic pollutant oxidation

FeS₂-embedded in porous carbon (FeS₂/C) was prepared by simultaneous sulfidation and carbonization of an iron-based metal-organic framework precursor, and subsequently immobilized in polyvinylidene fluoride membranes (FeS₂/C@PVDF) for organics removal via peroxymonosulfate (PMS) activation. The composition, structure, and morphology of the FeS₂/C@PVDF membrane were extensively characterized. Scanning electron microscopy images manifest that the FeS₂/C nanoparticles with an average diameter of 40 nm are assembled on the external and internal membrane surface. The as-prepared FeS₂/C@PVDF membrane exhibits excellent performances over a wide pH range of 1.53-9.50, exceeding carbon-free syn-FeS₂@PVDF. The effective degradation could be improved by inner pyrite FeS₂ cores and thus enhanced the electron transfer between carbon shell and PMS. Electron paramagnetic resonance and quenching experiments elucidated that radical (HO^∙, SO₄^∙-) and nonradical (¹O₂) species were the predominant reactive oxidants. In addition, FeS₂/C@PVDF exhibited high stability with low Fe leaching (0.377 mg/L) owing to the effective protection of the outer carbon skeleton. Plentiful porosity of PVDF membranes not only affords a controlled size and confined uniform distribution of the immobilized FeS₂/C nanoparticles, but also enables a persistent exposure of active sites and enhanced mass transfer efficiency. Our findings demonstrate a promise for utilizing the novel FeS₂/C@PVDF membrane as an efficient catalyst for the environmental cleanup.

A novel "caterpillar with eggs" mesostructured iron sulfide as an anode for a Li-ion battery displaying stable electrochemical performance

Emerging anodes are important for high energy-density lithium-ion batteries. Here, we present a mesostructured FeS₂ comprising nanoparticles embedded in a nanoneedle-assembled nanotube to form a novel "caterpillar with eggs" (CWE) structure. The voids alleviated the volumetric change upon charge-discharge; the nanoneedles-assembled shell provided rapid transport pathways for ions and electrons. The FeS₂ anode exhibited a high capacity of 805.1 mA h g^-1 after 500 cycles at 2 A g^-1. When cycling at -10 °C and 45 °C, the anode provided capacities of 754.5 and 744.4 mA h g^-1 after 100 cycles at 1 A g^-1, respectively. This good electrochemical performance will enable our special design to find broad applications for developing high-performance energy-storage systems.

3D Nano-heterostructure of ZnMn2O4@Graphene-Carbon Microtubes for High-Performance Li-Ion Capacitors

Heterostructures show great potential in energy storage due to their multipurpose structures and function. Recently, two-dimensional (2D) graphene has been widely regarded as an excellent substrate for active materials due to its large specific surface area and superior electrical conductivity. However, it is prone to self-aggregation during charging and discharging, which limits its electrochemical performance. To address the graphene agglomeration problem, we interspersed polypyrrole carbon nanotubes between the graphene cavities and designed three-dimensional (3D)-heterostructures of ZnMn2O4@rGO-polypyrrole carbon nanotubes (ZMO@G-PNTs), which demonstrated a high rate and cyclic stability in lithium-ion capacitors (LICs). Furthermore, the 3D porous structure provided more surface capacity contribution than 2D graphene, ultimately resulting in a better stability (333 mAh g-1 after 1000 cycles at 1 A g-1) and high rate capacity (208 mAh g-1 at 5 A g-1). Also, the mechanism of performance difference between ZMO@G-PNTs and ZMO@G was investigated in detail. Moreover, LICs built from ZMO@G-PNTs as an anode and activated carbon as a cathode showed an energy density of 149.3 Wh kg-1 and a power density of 15 kW kg-1 and cycling stability with a capacity retention of 61.5% after 9000 cycles.

Challenges and Strategies toward Cathode Materials for Rechargeable Potassium-Ion Batteries

With increasing demand for grid-scale energy storage, potassium-ion batteries (PIBs) have emerged as promising complements or alternatives to commercial lithium-ion batteries owing to the low cost, natural abundance of potassium resources, the low standard reduction potential of potassium, and fascinating K⁺ transport kinetics in the electrolyte. However, the low energy density and unstable cycle life of cathode materials hamper their practical application. Therefore, cathode materials with high capacities, high redox potentials, and good structural stability are required with the advancement toward next-generation PIBs. To this end, understanding the structure-dependent intercalation electrochemistry and recognizing the existing issues relating to cathode materials are indispensable prerequisites. This review summarizes the recent advances of PIB cathode materials, including metal hexacyanometalates, layered metal oxides, polyanionic frameworks, and organic compounds, with an emphasis on the structural advantages of the K⁺ intercalation reaction. Moreover, major current challenges with corresponding strategies for each category of cathode materials are highlighted. Finally, future research directions and perspectives are presented to accelerate the development of PIBs and facilitate commercial applications. It is believed that this review will provide practical guidance for researchers engaged in developing next-generation advanced PIB cathode materials.

A Pyrite Iron Disulfide Cathode with a Copper Current Collector for High-Energy Reversible Magnesium-Ion Storage

Owing to its low cost, high theoretical capacity, and environmentally friendly characteristics, pyrite FeS₂ demonstrates promise as a cathode material for high-energy metal-anode-based rechargeable batteries. When it is used in a rechargeable magnesium battery (RMB), the electrode couple exhibits an extremely low theoretical volume change upon full discharge. However, its electrochemical Mg-ion storage is considerably hindered by slow reaction kinetics. In this study, a high-performance FeS₂ cathode for RMBs using a copper current collector is reported, which is involved in cathode reactions via a reversible redox process between copper and cuprous sulfide. This phase transformation with the formation of copper nanowires during discharge activates the redox reactions of FeS₂ via a two-step and four-electron Mg-ion transfer that dominates the cathode reactions. As a result, the as-prepared FeS₂ nanomaterial cathode delivers a significantly enhanced reversible capacity of 679 mAh g^-1 at 50 mA g^-1 . The corresponding energy density of 714 Wh kg^-1 is superior to those of all previously reported metal chalcogenide cathodes in RMBs or hybrid batteries using a Mg metal anode. Notably, the as-assembled FeS₂ -Mg battery can operate over 1000 cycles with a good capacity retention at 400 mA g^-1 .

A Polymorphic FeS2 Cathode Enabled by Copper Current Collector Induced Displacement Redox Mechanism

In this contribution, we fabricated a composite consisting of two polymorphs of FeS₂, pyrite (P-FeS₂) and marcasite (M-FeS₂), for high-performance Li-FeS₂ battery. A series of electrochemical, microscopic, and spectroscopic characterizations indicate that the introduction of metastable M-FeS₂ into P-FeS₂ enables the four-electron reduction between FeS₂ and lithium to generate Fe and Li₂S, providing a high specific capacity of 894 mAh/g with specific energy over 1300 Wh/kg. Moreover, it is verified that the electrochemical irreversibility of this composite toward lithium storage is mainly rooted in the shuttle effect, caused by the elemental sulfur which is inevitably produced during the oxidation process of Li₂S and Fe. To tackle this issue, copper (Cu) current collector is adopted to chemically immobilize the soluble lithium polysulfides and fundamentally alter the reaction pathway. It is shown that compared with Fe, Li₂S prefers to react with Cu current collector to generate Cu₂S through the thermodynamically facile displacement reaction mechanism benefiting from the similar lattice framework between Cu₂S and Li₂S. Such displacement reaction without lattice reconstruction renders the composite superior rate capability (∼730 mAh/g@2 A/g) and long lifespan (89.7% capacity retention after 3200 cycles). Present work allows for the fabrication of high-performance electrodes based on metal chalcogenides.

Multifunctional Metal Phosphides as Superior Host Materials for Advanced Lithium-Sulfur Batteries

For the past few years, a new generation of energy storage systems with large theoretical specific capacity has been urgently needed because of the rapid development of society. Lithium-sulfur (Li-S) batteries are regarded as one of the most promising candidates for novel battery systems, since their resurgence at the end of the 20th century Li-S batteries have attracted ever more attention, attributed to their notably high theoretical energy density of 2600 W h kg^-1 , which is almost five times larger than that of commercial lithium-ion batteries (LIBs). One of the determining factors in Li-S batteries is how to design/prepare the sulfur cathode. For the sulfur host, the major technical challenge is avoiding the shuttling effect that is caused by soluble polysulfides during the reaction. In past decades, though the sulfur cathode has developed greatly, there are still some enormous challenges to be conquered, such as low utilization of S, rapid decay of capacity, and poor cycle life. This article spotlights the recent progress and foremost findings in improving the performance of Li-S batteries by employing multifunctional metal phosphides as host materials. The current state of development of the sulfur electrode of Li-S batteries is summarized by emphasizing the relationship between the essential properties of metal phosphide-based hybrid nanomaterials, the chemical reaction with lithium polysulfides and the latter's influence on electrochemical performance. Finally, trends in the development and practical application of Li-S batteries are also pointed out.

Long-Life Dendrite-Free Lithium Metal Electrode Achieved by Constructing a Single Metal Atom Anchored in a Diffusion Modulator Layer

Lithium metal electrodes have shown great promise for high capacity and the lowest potential. However, wide application is restricted by uncontrollable plating/stripping lithium behaviors, an uneven solid electrolyte interphase, and a lithium dendrite. Herein, the highly active single metal atom anchored in vacant catalyst is synthesized on the hierarchical porous nanocarbon (SACo/ADFS@HPSC). Acting as an artificial protective modulation layer on the lithium surface, the numerous atomic sites show the superiority in modulating lithium ion behaviors and smoothing the lithium surface without dendrite growth. As a consequence, the SACo/ADFS@HPSC-modified Li electrode lowers nucleation barrier (15 mV), extends the smooth plating lifespan (1600 h), and improves Coulombic efficiency, significantly accelerating the horizonal deposition of plated lithium. Coupled with a sulfur cathode, the fabricated pouch cell with 5.4 mg cm^-2 delivers a high capacity of 3.78 mA h cm^-2 corresponding to 1505 Wh kg^-1, showing the promising practical application.

Zn3V3O8/NC hybrid microspheres self-assembled by layered porous nanosheets as a superior anode material for lithium/sodium-ion batteries

Zinc-vanadium oxides have been attracting increasing consideration as anode materials for lithium/sodium-ion batteries (LIBs and SIBs) recently. Present applications are hampered by issues, including their inferior electric conductivity and enormous volume variation. Herein, nitrogen-doped carbon wrapped Zn₃V₃O₈ (Zn₃V₃O₈/NC) microspheres composed of abundant nanosheets were developed as an anode material by a self-assembly strategy and subsequent surface decoration. The resulting Zn₃V₃O₈/NC porous hybrid exhibited a high specific capacity, impressive rate capability, and long-term cycling stability for both LIBs and SIBs. Notably, the superior electrochemical properties could be assigned to novel meso/microporous features, hybrid nitrogen-doped carbon, and mixed storage mechanisms.

MXene-encapsulated hollow Fe3O4 nanochains embedded in N-doped carbon nanofibers with dual electronic pathways as flexible anodes for high-performance Li-ion batteries

Fe3O4 is one of the promising anode materials in Li-ion batteries and a potential alternative to graphite due to the high specific capacity, natural abundance, environmental benignity, non-flammability, and better safety. Nevertheless, the sluggish intrinsic reaction kinetics and huge volume variation severely limit the reversible capacity and cycling life. In order to overcome these hurdles and enhance the cycling life of Fe3O4, a one-dimensional (1D) nanochain structure composed of 2D Ti3C2-encapsulated hollow Fe3O4 nanospheres homogeneously embedded in N-doped carbon nanofibers (Fe3O4@MXene/CNFs) is designed and demonstrated as a high-performance anode in Li-ion batteries. The distinctive 1D nanochain structure not only inherits the high electrochemical activity of Fe3O4, but also exhibits excellent electron and ion conductivity. The Ti3C2 layer on the Fe3O4 hollow nanospheres forms the primary electron transport pathway and the N-doped carbon nanofiber network provides the secondary transport pathway. At the same time, Ti3C2 flakes partially accommodate the large volume change of Fe3O4 during Li+ insertion/extraction. Density functional theory (DFT) calculations demonstrate that the Fe3O4@MXene/CNFs electrode can efficiently enhance the adsorption of Li+ to promote Li+ storage. As a result of the electrospinning process, self-restacking of Ti3C2 flakes and aggregation of Fe3O4 nanospheres can be prevented resulting in a larger surface area and more accessible active sites on the flexible anode. The Fe3O4@MXene/CNFs anode has remarkable electrochemical properties at high current densities. For example, a reversible capacity of 806 mA h g-1 can be achieved at 2 A g-1 even after 500 cycles, corresponding to an area specific capacity of 1.612 mA h cm-2 at 4 mA cm-2 and a capacity as high as 613 mA h g-1 is retained at 5 A g-1, corresponding to an area capacity of 1.226 mA h cm-2 at 10 mA cm-2. The results indicate that the Fe3O4@MXene/CNFs anode has excellent properties for Li-ion storage.

Ni-Rich Layered Oxide with Preferred Orientation (110) Plane as a Stable Cathode Material for High-Energy Lithium-Ion Batteries

The cathode, a crucial constituent part of Li-ion batteries, determines the output voltage and integral energy density of batteries to a great extent. Among them, Ni-rich LiNi_xCo_yMn_zO₂ (x + y + z = 1, x ≥ 0.6) layered transition metal oxides possess a higher capacity and lower cost as compared to LiCoO₂, which have stimulated widespread interests. However, the wide application of Ni-rich cathodes is seriously hampered by their poor diffusion dynamics and severe voltage drops. To moderate these problems, a nanobrick Ni-rich layered LiNi_0.6Co_0.2Mn_0.2O₂ cathode with a preferred orientation (110) facet was designed and successfully synthesized via a modified co-precipitation route. The galvanostatic intermittent titration technique (GITT) and electrochemical impedance spectroscopy (EIS) analysis of LiNi_0.6Co_0.2Mn_0.2O₂ reveal its superior kinetic performance endowing outstanding rate performance and long-term cycle stability, especially the voltage drop being as small as 67.7 mV at a current density of 0.5 C for 200 cycles. Due to its unique architecture, dramatically shortened ion/electron diffusion distance, and more unimpeded Li-ion transmission pathways, the current nanostructured LiNi_0.6Co_0.2Mn_0.2O₂ cathode enhances the Li-ion diffusion dynamics and suppresses the voltage drop, thus resulting in superior electrochemical performance.

Selective Pseudocapacitive Deionization of Calcium Ions in Copper Hexacyanoferrate

In recent years, the capacitive deionization (CDI) technology has gradually become a promising technology for hard water treatment. Up to now, most of the work for water softening in CDI was severely limited by the inferior selectivity and electrosorption performances of carbon-based electrodes in spite of combining Ca²⁺-selective ion-exchange resin or membranes. Pseudocapacitive electrode materials that selectively interact with specific ions by Faradic redox reactions or ion (de)intercalation offer an alternative strategy for highly selective electrosorption of Ca²⁺ from water because of brilliant ion adsorption capacity. Here, we first used copper hexacyanoferrate (CuHCF) as a pseudocapacitive electrode to methodically study the selective pseudocapacitive deionization of Ca²⁺ over Na⁺ and Mg²⁺. Using the hybrid CDI cell consisting of a CuHCF cathode and an activated carbon anode without any ion-exchange membrane, the outstanding Ca²⁺ electrosorption capacity of 42.8 mg·g^-1 and superior selectivity &(Ca²⁺/Na⁺) of 3.05 at a molar ratio of 10:1 were obtained at 1.4 V, surpassing those of the reported carbon-based electrodes. Finally, electrochemical measurements and molecular dynamics (MD) simulations provided an in-depth understanding of the selective pseudocapacitive deionization of Ca²⁺ ions in a CuHCF electrode. Our study would be helpful for developing high-efficiency selective electrosorption of target charged ions by intrinsic properties of pseudocapacitive materials.

Unraveling the Beneficial Microstructure Evolution in Pyrite for Boosted Lithium Storage Performance

Pyrite FeS₂ as a high-capacity electrode material for lithium-ion batteries (LIBs) is hindered by its unstable cycling performance owing to the large volume change and irreversible phase segregation from coarsening of Fe. Here, the beneficial microstructure evolution in MoS₂ -modified FeS₂ is unraveled during the cycling process; the microstructure evolution is responsible for its significantly boosted lithium storage performance, making it suitable for use as an anode for LIBs. Specifically, the FeS₂ /MoS₂ displays a long cycle life with a capacity retention of 116 % after 600 cycles at 0.5 A g^-1 , which is the best among the reported FeS₂ -based materials so far. A series of electrochemical tests and structural characterizations substantially revealed that the introduced MoS₂ in FeS₂ experiences an irreversible electrochemical reaction and thus the in situ formed metallic Mo could act as the conductive buffer layer to accelerate the dynamics of Li⁺ diffusion and electron transport. More importantly, it can guarantee the highly reversible conversion in lithiated FeS₂ by preventing Fe coarsening. This work provides a fundamental understanding and an effective strategy towards the microstructure evolution for boosting lithium storage performances for other metal sulfide-based materials.

Superfine MnO2 Nanowires with Rich Defects Toward Boosted Zinc Ion Storage Performance

The core challenge of MnO₂ as the cathode material of zinc-ion batteries remains to be their poor electrochemical kinetics and stability. Herein, MnO₂ superfine nanowires (∼10 nm) with rich crystal defects (oxygen vacancies and cavities) are demonstrated to possess high efficient zinc-ion storage capability. Experimental and theoretical studies demonstrate that the defects facilitate the adsorption and diffusion of hydrogen/zinc for fast ion transportation and the build of a local electric field for improved electron migration. In addition, the superfine nanostructure could provide sufficient active sites and short diffusion pathways for further promotion of capacity and reaction kinetics of MnO₂. Remarkably, the defect-enriched MnO₂ nanowires manifest an energy density as high as 406 W h kg^-1 and an excellent durability over 1000 cycles without noticeable capacity degradation. Mechanistic analysis substantiates a reversible coinsertion/extraction process of H⁺ and Zn²⁺ with a simultaneous deposition/dissolution of zinc sulfate hydroxide hydrate nanoflakes. This work could enrich the fundamental understanding of defect engineering and nanostructuring on the development of advanced MnO₂ materials toward high-performance zinc-ion batteries.

Functional Localized High-Concentration Ether-Based Electrolyte for Stabilizing High-Voltage Lithium-Metal Battery

Localized high-concentration electrolytes have attracted much attention of researchers due to their low viscosity, low cost, and relatively higher electrochemical performance than their low-concentration counterparts. In our work, 1.5 M (mol L^-1) locally concentrated ether-based electrolyte has been obtained by adding 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (HFE) into a 4 M LiFSI concentrated dimethoxyethane (DME)-based electrolyte. The optimal ratio is determined by density functional theory (DFT) calculation and experimental combination, and finally, DH(3/5)-1.5M-LiFSI (DME/HFE = 3:5 by volume) is obtained. The electrolyte not only has relatively good physical properties such as low viscosity and high conductivity but also shows decent electrochemical performance. Li∥Cu half-cells can maintain a coulombic efficiency of no less than 99% after circulating for 250 cycles under the condition of 1 mA cm^-2 current density and 1 mAh cm^-2 lithium deposition for each cycle, and the stable battery polarization voltage was about 50 mV. Furthermore, 0.15 M lithium trifluoromethyl acetate (LiCO₂CF₃) has been added as an additive to enhance the oxidation stability. The new electrolyte DH(3/5)-1.65M-LiFC (LiFC/LiFSI + LiCO₂CF₃) makes Li||NCM523 batteries maintain about 83% capacity after cycling for 250 times with a 0.5 C charge current density and a 1 C discharge current density of 160 mAh g^-1 when charged to 4.3 V. Furthermore, this new additive has a little negative effect on the Li||Cu half-cell performance under the same condition as before, indicating this new type of localized high-concentration DME-based electrolyte benefits both high-voltage cathode and lithium-metal anode.

Bio-Inspired Passion Fruit-like Fe3O4@C Nanospheres Enabling High-Stability Magnetorheological Performances

Magnetorheological (MR) fluids have been successfully utilized in versatile fields but are still limited by their relatively inferior long-term dispersion stability. Herein, bio-inspired passion fruit-like Fe₃O₄@C nanospheres were fabricated via a simple hydrothermal and calcination approach to tackle the settling challenge. The unique structures provide sufficient active interfaces for the penetration of carrier mediums, leading to preferable wettability between particles and medium oils. Compared with the bare Fe₃O₄ nanoparticle suspension, the resulting Fe₃O₄@C nanosphere-based MR fluid exhibits desirable stability and relatively low field-off viscosity even at a high particle concentration up to 35 vol %.

Boosting the lithium-ion and sodium-ion storage performances of pyrite by regulating the energy barrier of ion transport

Pyrite (FeS2) is a functional material of great importance for lithium/sodium ion batteries (LIBs/SIBs), but its sluggish dynamics greatly hinder its high performance. Here, we demonstrate an effective strategy of regulating the energy barrier of ion transport to significantly enhance the sluggish dynamics of FeS2 by Co doping. Compared to pristine FeS2, a series of Co-doped FeS2 shows enhanced alkali metal ion storage performance and most typically, the optimized Fe0.7Co0.3S2 sample displays high reversible capacities, of 1170 mA h g-1 for LIBs and 650 mA h g-1 for SIBs at a current density of 0.1 A g-1 as well as super long-life cycling stability for SIBs (1200 cycles at 5 A g-1). The evidently enhanced performances of Fe0.7Co0.3S2 for LIBs/SIBs can be attributed to its significantly decreased activation energy of ion transport, thus leading to greatly accelerated ion transport dynamics. Furthermore, galvanostatic intermittent titration technique (GITT) experiments also support this important regulation effect of Co doping on the ion transport dynamics of FeS2. The excellent ion transport dynamics induce a strong pseudo-capacitance behavior in both SIBs and LIBs, and their pseudo-capacitance contributions are more than 90% at 1.0 mV s-1. This work provides a new perspective to improve the alkali metal ion storage performance by optimizing the ion transport dynamics.

Sulfur-Embedded FeS2 as a High-Performance Cathode for Room Temperature All-Solid-State Lithium-Sulfur Batteries

All-solid-state lithium-sulfur batteries employing sulfur electrodes and a solid electrolyte at room temperature are still a great challenge owing to the low conductivities of sulfur cathodes. In this work, we report room temperature all-solid-state lithium-sulfur batteries using thin sulfur layer-embedded FeS₂ (FeS₂@S) microsphere composites as active materials in the FeS₂@S-Li₁₀GeP₂S₁₂-Super P cathode electrode. Setting the cut-off voltage between 1.5 and 2.8 V, only lithiation-delithiation reactions between L₂FeS₂ and FeS_y and direct reaction between Li₂S and S will occur, which avoids large volume change of FeS₂ caused by the conversion reaction, leading to the structure integrity of FeS₂@S. The resultant batteries exhibit excellent rate and cyclic performances, delivering specific capacities of 1120.9, 937.2, 639.7, 517.2, 361.5, and 307.0 mA h g^-1 for the FeS₂@S composite cathode, corresponding to the normalized capacities of 1645.5, 1252.9, 782.5, 700.2, 478.4, and 363.6 mA h g^-1 for sulfur at 30, 50, 100, 500, 1000, and 5000 mA g^-1, respectively. Besides, they can retain the normalized capacity of 430.7 mA h g^-1 for sulfur at 1000 mA g^-1 after 200 cycles at room temperature.

Bimetallic Sulfide Sb2S3@FeS2 Hollow Nanorods as High-Performance Anode Materials for Sodium-Ion Batteries

Constructing a heterojunction and introducing an interfacial interaction by designing ideal structures have the inherent advantages of optimizing electronic structures and macroscopic mechanical properties. An exquisite hierarchical heterogeneous structure of bimetal sulfide Sb₂S₃@FeS₂ hollow nanorods embedded into a nitrogen-doped carbon matrix is fabricated by a concise two-step solvothermal method. The FeS₂ interlayer expands in situ grow on the interface of hollow Sb₂S₃ nanorods within the nitrogen-doped graphene matrix, forming a delicate heterostructure. Such a well-designed architecture affords rapid Na⁺ diffusion and improves charge transfer at the heterointerfaces. Meanwhile, the strongly synergistic coupling interaction among the interior Sb₂S₃, interlayer FeS₂, and external nitrogen-doped carbon matrix creates a stable nanostructure, which extremely accelerates the electronic/ion transport and effectively alleviates the volume expansion upon long cyclic performance. As a result, the composite, as an anode material for sodium-ion batteries, exhibits a superior rate capability of 537.9 mAh g^-1 at 10 A g^-1 and excellent cyclic stability with 85.7% capacity retention after 1000 cycles at 5 A g^-1. Based on the DFT calculation, the existing constructing heterojunction in this composite can not only optimize the electronic structure to enhance the conductivity but also favor the Na₂S adsorption energy to accelerate the reaction kinetics. The outstanding electrochemical performance sheds light on the strategy by the rational design of hierarchical heterogeneous nanostructures for energy storage applications.

Effect of Continuous Capacity Rising Performed by FeS/Fe3 C/C Composite Electrodes for Lithium-Ion Batteries

FeS-based composites are sustainable conversion electrode materials for lithium-ion batteries, combining features like low cost, environmental friendliness, and high capacities. However, they suffer from fast capacity decay and low electron conductivity. Herein, novel insights into a surprising phenomenon of this material are provided. A FeS/Fe₃ C/C nanocomposite synthesized by a facile hydrothermal method is compared with pure FeS. When applied as anode materials for lithium-ion batteries, these two types of materials show different capacity evolution upon cycling. Surprisingly, the composite delivers a continuous increase in capacity instead of the expected capacity fading. This unique behavior is triggered by a catalyzing effect of Fe₃ C nanoparticles. The Fe₃ C phase is a beneficial byproduct of the synthesis and was not intentionally obtained. To further understand the effect of interconnected carbon balls on FeS-based electrodes, complementary analytic techniques are used. Ex situ X-ray radiation diffraction and ex situ scanning electron microscopy are employed to track phase fraction and morphology structure. In addition, the electrochemical kinetics and resistance are evaluated by cyclic voltammetry and electrochemical impedance spectroscopy. These results reveal that the interconnected carbon balls have a profound influence on the properties of FeS-based electrodes resulting in an increased electrode conductivity, reduced particle size, and maintenance of the structure integrity.

Hollow Porous Carbon Coated FeS2-Based Nanocatalysts for Multimodal Imaging-Guided Photothermal, Starvation, and Triple-Enhanced Chemodynamic Therapy of Cancer

Specific chemical reactions only happen in the tumor region and produce abundant special chemicals to in situ trigger a train of biological and pathological effects that may enable tumor-specific curative effects to treat cancer without causing serious side effects on normal cells or organs. Chemodynamic therapy (CDT) is a rising tactic for cancer therapy, which induces cancer cell death via a localized Fenton reaction. However, the tumor therapeutic effect is limited by the efficiency of the chemical reaction and relies heavily on the catalyst. Here, we constructed hollow porous carbon coated FeS₂ (HPFeS₂@C)-based nanocatalysts for triple-enhanced CDT. Tannic acid was encapsulated in HPFeS₂@C for reducing Fe³⁺ to Fe²⁺, which had a better catalytic activity to accelerate the Fenton reaction. Afterward, glucose oxidase (GOx) in nanocatalysts could consume glucose in the tumor microenvironment and in situ synchronously produce H₂O₂, which could improve Fenton reaction efficiency. Meanwhile, the consumption of glucose could lead to the starvation effect for cancer starvation therapy. The photothermal effects of HPFeS₂@C could generate heat, which further sped up the Fenton process and implemented synergetic photothermal therapy/starvation therapy/CDT. The biodistribution of nanoparticles was investigated by multimodal magnetic resonance, ultrasound, and photoacoustic imaging. These nanocatalysts could trigger the catalytic Fenton reaction at a high degree, which might provide a good paradigm for nanocatalytic tumor therapy.