Electrode and Electrolyte Co-Energy-Storage Electrochemistry Enables High-Energy Zn-S Decoupled Batteries.

In the search for next-generation green energy storage solutions, Cu-S electrochemistry has recently gained attraction from the battery community owing to its affordability and exceptionally high specific capacity of 3350 mAh gs -1. However, the inferior conductivity and substantial volume expansion of the S cathode hinder its cycling stability, while the low output voltage limits its energy density. Herein, a hollow carbon sphere (HCS) is synthesized as a 3D conductive host to achieve a stable S@HCS cathode, which enables an outstanding cycling performance of 2500 cycles (over 9 months). To address the latter, a Zn//S@HCS alkaline-acid decoupled cell is configured to increase the output voltage from 0.18 to 1.6 V. Moreover, an electrode and electrolyte co-energy storage mechanism is proposed to offset the reduction in energy density resulting from the extra electrolyte required in Zn//S decoupled cells. When combined, the Zn//S@HCS alkaline-acid decoupled cell delivers a record energy density of 334 Wh kg-1 based on the mass of the S cathode and CuSO4 electrolyte. This work tackles the key challenges of Cu-S electrochemistry and brings new insights into the rational design of decoupled batteries.

Organic Molecular Intercalation Enabled Anionic Redox Chemistry with Fast Kinetics for High Performance Magnesium Storage.

Rechargeable magnesium-ion batteries possess desirable characteristics in large-scale energy storage applications. However, severe polarization, sluggish kinetics and structural instability caused by high charge density Mg2+ hinder the development of high-performance cathode materials. Herein, the anionic redox chemistry in VS4 is successfully activated by inducing cations reduction and introducing anionic vacancies via polyacrylonitrile (PAN) intercalation. Increased interlayer spacing and structural vacancies can promote the electrolyte ions migration and accelerate the reaction kinetics. Thanks to this "three birds with one stone" strategy, PAN intercalated VS4 exhibits an outstanding electrochemical performance: high discharge specific capacity of 187.2 mAh g-1 at 200 mA g-1 after stabilization and a long lifespan of 5000 cycles at 2 A g-1 are achieved, outperforming other reported VS4-based materials to date for magnesium storage under the APC electrolyte. Theoretical calculations confirm that the intercalated PAN can indeed induce cations reduction and generate anionic vacancies by promoting electron transfer, which can accelerate the electrochemical reaction kinetics and activate the anionic redox chemistry, thus improving the magnesium storage performance. This approach of organic molecular intercalation represents a promising guideline for electrode material design on the development of advanced multivalent-ion batteries.

Catalyzing Desolvation at Cathode-Electrolyte Interface Enabling High-Performance Magnesium-Ion Batteries.

Magnesium ion batteries (MIBs) are expected to be the promising candidates in the post-lithium-ion era with high safety, low cost and almost dendrite-free nature. However, the sluggish diffusion kinetics and strong solvation capability of the strongly polarized Mg2+ are seriously limiting the specific capacity and lifespan of MIBs. In this work, catalytic desolvation is introduced into MIBs for the first time by modifying vanadium pentoxide (V2 O5 ) with molybdenum disulfide quantum dots (MQDs), and it is demonstrated via density function theory (DFT) calculations that MQDs can effectively lower the desolvation energy barrier of Mg2+ , and therefore catalyze the dissociation of Mg2+ -1,2-Dimethoxyethane (Mg2+ -DME) bonds and release free electrolyte cations, finally contributing to a fast diffusion kinetics within the cathode. Meanwhile, the local interlayer expansion can also increase the layer spacing of V2 O5 and speed up the magnesiation/demagnesiation kinetics. Benefiting from the structural configuration, MIBs exhibit superb reversible capacity (≈300 mAh g-1 at 50 mA g-1 ) and unparalleled cycling stability (15 000 cycles at 2 A g-1 with a capacity of ≈70 mAh g-1 ). This approach based on catalytic reactions to regulate the desolvation behavior of the whole interface provides a new idea and reference for the development of high-performance MIBs.

Theoretical insights into the intercalation mechanism of Li, Na, and Mg ions in a metallic BN/VS2 heterostructure.

Layered VS2 has been widely used as a battery anode material owing to its large specific surface area and controllable ion-transport channel. However, its semiconductor properties and poor cycling stability seriously limit its further applications. Herein, a two-dimensional BN/VS2 heterostructure (BVH) was constructed as an anode material for rechargeable metal-ion batteries (RMIBs). Demonstrated using first principles calculations, BVH exhibits a metallic property due to lattice stress between monolayer BN and VS2. BVH displays low ion diffusion energy barriers (0.13, 0.43, and 0.56 eV) and high theoretical capacities (447, 553.5, and 340.7 mA h g-1) for Li+, Na+, and Mg2+ storage. In BVH, the VS2 layer as the main redox center supports charge transfer, while the inactive BN layer enables high structural stability. This synergistic effect is expected to simultaneously achieve a high rate, high capacity, and long life. This design provides an important insight into developing new anode materials for RMIBs.

A two-dimensional VO2/VS2 heterostructure as a promising cathode material for rechargeable Mg batteries: a first principles study.

Rechargeable magnesium batteries (RMBs) are considered as highly promising energy storage systems. However, the lack of cathode materials with fast Mg2+ diffusion kinetics and high energy density severely hinders the development of RMBs. Herein, a two-dimensional (2D) VO2/VS2 heterostructure as a RMB cathode material is proposed by introducing an O-V-O layer in VS2 to improve the discharge voltage and specific capacity while keeping the fast Mg2+ diffusion kinetics. Based on first principle calculations, the geometric structures, electronic characteristics of the VO2/VS2 heterostructure, and the adsorption properties and diffusion behaviors of Mg2+ in VO2/VS2 are systematically studied. The metallic properties of VO2/VS2 and a relatively low diffusion barrier of Mg2+ (0.6 eV) in VO2/VS2 enable a large potential in delivering high rate performance in actual RMBs. Compared with traditional VS2 materials (1.25 V), the average discharge platform of VO2/VS2 could be increased to 1.7 V. The theoretical capacities of the layered VS2 and VO2/VS2 are calculated as 233 and 301 mA h g-1, respectively. Thus, the VO2/VS2 heterostructure exhibits a high theoretical energy density of 511.7 W h kg-1, significantly surpassing that of VS2 (291.3 W h kg-1). This work provides important guidance for designing high-energy and high-rate 2D heterostructure cathode materials for RMBs and other multivalent ion batteries.

Lead exposure disturbs ATP7B-mediated copper export from brain barrier cells by inhibiting XIAP-regulated COMMD1 protein degradation.

The brain barrier is an important structure for metal ion homeostasis. According to studies, lead (Pb) exposure disrupts the transportation of copper (Cu) through the brain barrier, which may cause impairment of the nervous system; however, the specific mechanism is unknown. The previous studies suggested the X-linked inhibitor of apoptosis (XIAP) is a sensor for cellular Cu level which mediate the degradation of the MURR1 domain-containing 1 (COMMD1) protein. XIAP/COMMD1 axis was thought to be an important regulator in Cu metabolism maintenance. In this study, the role of XIAP-regulated COMMD1 protein degradation in Pb-induced Cu disorders in brain barrier cells was investigated. Pb exposure significantly increased Cu levels in both cell types, according to atomic absorption technology testing. Western blotting and reverse transcription PCR (RT-PCR) showed that COMMD1 protein levels were significantly increased, whereas XIAP, ATP7A, and ATP7B protein levels were significantly decreased. However, there were no significant effects at the messenger RNA (mRNA) level (XIAP, ATP7A, and ATP7B). Pb-induced Cu accumulation and ATP7B expression were reduced when COMMD1 was knocked down by transient small interfering RNA (siRNA) transfection. In addition, transient plasmid transfection of XIAP before Pb exposure reduced Pb-induced Cu accumulation, increased COMMD1 protein levels, and decreased ATP7B levels. In conclusion, Pb exposure can reduce XIAP protein expression, increase COMMD1 protein levels, and specifically decrease ATP7B protein levels, resulting in Cu accumulation in brain barrier cells.

Revealing the Interfacial Chemistry of Fluoride Alkyl Magnesium Salts in Magnesium Metal Batteries.

Exploring promising electrolyte-system with high reversible Mg plating/stripping and excellent stability is essential for rechargeable magnesium batteries (RMBs). Fluoride alkyl magnesium salts (Mg(ORF )2 ) not only possess high solubility in ether solvents but also compatible with Mg metal anode, thus holding a vast application prospect. Herein, a series of diverse Mg(ORF )2 were synthesized, among them, perfluoro-tert-butanol magnesium (Mg(PFTB)2 )/AlCl3 /MgCl2 based electrolyte demonstrates highest oxidation stability, and promotes the in situ formation of robust solid electrolyte interface. Consequently, the fabricated symmetric cell sustains a long-term cycling over 2000 h, and the asymmetric cell exhibits a stable Coulombic efficiency of 99.5 % over 3000 cycles. Furthermore, the Mg||Mo6 S8 full cell maintains a stable cycling over 500 cycles. This work presents guidance for understanding structure-property relationships and electrolyte applications of fluoride alkyl magnesium salts.

Mo2 C Nanoparticles Embedded in Carbon Nanowires with Surface Pseudocapacitance Enables High-Energy and High-Power Sodium Ion Capacitors.

Electrochemical sodium-ion storage technologies have become an indispensable part in the field of large-scale energy storage systems owing to the widespread and low-cost sodium resources. Molybdenum carbides with high electron conductivity are regarded as potential sodium storage anode materials, but the comprehensive sodium storage mechanism has not been studied in depth. Herein, Mo2 C nanowires (MC-NWs) in which Mo2 C nanoparticles are embedded in carbon substrate are synthesized. The sodium-ion storage mechanism is further systematically studied by in/ex situ experimental characterizations and diffusion kinetics analysis. Briefly, it is discovered that a faradaic redox reaction occurs in the surface amorphous molybdenum oxides on Mo2 C nanoparticles, while the inner Mo2 C is unreactive. Thus, the as-synthesized MC-NWs with surface pseudocapacitance display excellent rate capability (a high specific capacity of 76.5 mAh g-1 at 20 A g-1 ) and long cycling stability (a high specific capacity of 331.2 mAh g-1 at 1 A g-1 over 1500 cycles). The assembled original sodium ion capacitor displays remarkable power density and energy density. This work provides a comprehensive understanding of the sodium storage mechanism of Mo2 C materials, and constructing pseudocapacitive materials is an effective way to achieve sodium-ion storage devices with high power and energy density.

Two-Dimensional Mesoporous Heterostructure Delivering Superior Pseudocapacitive Sodium Storage via Bottom-Up Monomicelle Assembly.

Two-dimensional (2D) heterostructures endowed with mesoporosities offer exciting opportunities in electrocatalysis, photocatalysis, energy storage, and conversion technologies due to their integrated functionalities, abundant active sites and shortened diffusion distance. However, layered mesostructures have not been combined due to the immense difficulties by conventional chemical, mechanical exfoliation or self-assembly approaches. Herein, we explore a bottom-up strategy, carried out under mild conditions, for the facile synthesis of monolayered mesoporous-titania-mesoporous-carbon vertical heterostructure with uniform mesopore size, which enables ultrahigh rate capability and cycling longevity for pseudocapacitive sodium-ion storage in nonaqueous electrolyte. Such a brand-new type of heterostructure consists of well-ordered monolayered mesoporous titania nanosheets and surrounding two mesoporous carbon monolayers assembled at both sides. Remarkably, the combination of interconnected large mesoporosity and heterointerface leads to highly promoted reversible pseudocapacitance (96.4% of total charge storage at a sweep rate of 1 mV s-1), and it enables the material to retain strong mechanical stability during the rapid sodiation and desodiation processes. This study reveals the importance of incorporating mesopores into heterointerface as a strategy for enhancing charge storage kinetics of electroactive materials.

Strongly Coupled Pyridine-V2 O5 ·nH2 O Nanowires with Intercalation Pseudocapacitance and Stabilized Layer for High Energy Sodium Ion Capacitors.

Developing pseudocapacitive cathodes for sodium ion capacitors (SICs) is very significant for enhancing energy density of SICs. Vanadium oxides cathodes with pseudocapacitive behavior are able to offer high capacity. However, the capacity fading caused by the irreversible collapse of layer structure remains a major issue. Herein, based on the Acid-Base Proton theory, a strongly coupled layered pyridine-V2 O5 ·nH2 O nanowires cathode is reported for highly efficient sodium ion storage. By density functional theory calculations, in situ X-ray diffraction, and ex situ Fourier-transform infrared spectroscopy, a strong interaction between protonated pyridine and VO group is confirmed and stable during cycling. The pyridine-V2 O5 ·nH2 O nanowires deliver long-term cyclability (over 3000 cycles), large pseudocapacitive behavior (78% capacitive contribution at 1 mV s-1 ) and outstanding rate capability. The assembled pyridine-V2 O5 ·nH2 O//graphitic mesocarbon microbead SIC delivers high energy density of ≈96 Wh kg-1 (at 59 W kg-1 ) and power density of 14 kW kg-1 (at 37.5 Wh kg-1 ). The present work highlights the strategy of realizing strong interaction in the interlayer of V2 O5 ·nH2 O to enhance the electrochemical performance of vanadium oxides cathodes. The strategy could be extended for improving the electrochemical performance of other layered materials.

One-Dimensional Hetero-Nanostructures for Rechargeable Batteries.

Rechargeable batteries are regarded as one of the most practical electrochemical energy storage devices that are able to convert and store the electrical energy generated from renewable resources, and they function as the key power sources for electric vehicles and portable electronics. The ultimate goals for electrochemical energy storage devices are high power and energy density, long lifetime, and high safety. To achieve the above goals, researchers have tried to apply various morphologies of nanomaterials as the electrodes to enhance the electrochemical performance. Among them, one-dimensional (1D) materials show unique superiorities, such as cross-linked structures for external stress buffering and large draw ratios for internal stress dispersion. However, a homogeneous single-component electrode material can hardly have the characteristics of high electronic/ionic conductivity and high stability in the electrochemical environment simultaneously. Therefore, designing well-defined functional 1D hetero-nanostructures that combine the advantages and overcome the limitations of different electrochemically active materials is of great significance. This Account summarizes fabrication strategies for 1D hetero-nanostructures, including nucleation and growth, deposition, and melt-casting and electrospinning. Besides, the chemical principles for each strategy are discussed. The nucleation and growth strategy is suitable for growing and constructing 1D hetero-nanostructures of partial transition metal compounds, and the experimental conditions for this strategy are relatively accessible. Deposition is a reliable strategy to synthesize 1D hetero-nanostructures by decorating functional layers on 1D substrate materials, on the condition that the preobtained substrate materials must be stable in the following deposition process. The melt-casting strategy, in which 1D hetero-nanostructures are synthesizes via a melting and molding process, is also widely used. Additionally, the main functions of 1D hetero-nanostructures are summarized into four aspects and reviewed in detail. Appropriate surface modification can effectively restrain the structure deterioration and the regeneration of the solid-electrolyte interphase layer caused by the volume change. A porous or semihollow external conducting material coating provides advanced electron/ion bicontinuous transmission. Suitable atomic heterogeneity in the crystal structure is beneficial to the expansion and stabilization of the ion diffusion channels. Multiphase-assisted structural design is also an accessible way for the sulfur electrode material restriction. Moreover, some outlooks about the further industrial production, more effective and cheaper fabrication strategies, and new heterostructures with smaller-scale composition are given in the last part. By providing an overview of fabrication methods and performance-enhancing mechanisms of 1D hetero-nanostructured electrode materials, we hope to pave a new way to facile and efficient construction of 1D hetero-nanostructures with practical utility.

Polyol Solvation Effect on Tuning the Universal Growth of Binary Metal Oxide Nanodots@Graphene Oxide Heterostructures for Electrochemical Applications.

Tuning the uniformity and size of binary metal oxide nanodots on graphene oxide (BMO NDs@GO) is significant but full of challenges in wet-chemistry, owing to the difficulties of controlling the complicated cation/anion co-adsorption, heterogeneous nucleation, and overgrowth processes. Herein, the aim is to tune these processes by understanding the functions of various alcohol solvents for NDs growth on GO. It is found that the polyol solvation effect is beneficial for obtaining highly uniform BMO NDs@GO. Polyol shell capped metal ions exhibit stronger hydrogen-bond interactions with the GO surface, leading to a uniform cation/anion co-adsorption and followed heterogeneous nucleation. The polyol-solvated ions with large diffusion energy barrier drastically limit the ion diffusion kinetics in liquids and at the solid/liquid interface, resulting in a slow and controllable growth. Moreover, the synthesis in polyol systems is highly controllable and universal, thus eleven BMO and polynary metal oxide NDs@GO are obtained by this method. The synthetic strategy provides improved prospects for the manufacture of inorganic NDs and their expanding electrochemical applications.

High-Performance Na-O2 Batteries Enabled by Oriented NaO2 Nanowires as Discharge Products.

Na-O2 batteries are emerging rechargeable batteries due to their high theoretical energy density and abundant resources, but they suffer from sluggish kinetics due to the formation of large-size discharge products with cubic or irregular particle shapes. Here, we report the unique growth of discharge products of NaO2 nanowires inside Na-O2 batteries that significantly boosts the performance of Na-O2 batteries. For this purpose, a high-spin Co3O4 electrocatalyst was synthesized via the high-temperature oxidation of pure cobalt nanoparticles in an external magnetic field. The discharge products of NaO2 nanowires are 10-20 nm in diameter and ∼10 µm in length, characteristics that provide facile pathways for electron and ion transfer. With these nanowires, Na-O2 batteries have surpassed 400 cycles with a fixed capacity of 1000 mA h g-1, an ultra-low over-potential of ∼60 mV during charging, and near-zero over-potential during discharging. This strategy not only provides a unique way to control the morphology of discharge products to achieve high-performance Na-O2 batteries but also opens up the opportunity to explore growing nanowires in novel conditions.

Binary Mg-1†at%Gd alloy anode for high-performance rechargeable magnesium batteries.

Rechargeable magnesium batteries (RMBs) become a highly promising candidate for the large-scale energy storage system by right of the high volumetric capacity, intrinsic safety and abundant resources of Mg anode. However, the uneven Mg stripping and large overpotential will cause a severe pitting perforation and the followed failure of Mg anode. Herein, we proposed a high-performance binary Mg-1 at% Gd alloy anode prepared by the melting and hot extrusion. The introduction of 1 at% Gd element can effectively reduce the Mg2+ diffusion energy barrier (0.34 eV) on alloy surface and induces the formation of a robust and low-resistance electrolyte/anode interphase, thus enabling a uniform and fast Mg plating/stripping. As a result, the Mg-1 at.% Gd anode displays a largely enhanced life of 220 h and a low overpotential of 213 mV at a high current density of 5.0 mA cm-2 with 2.5 mAh cm-2 . Moreover, the assembled Mg-1 at.% Gd//Mo6 S8 full cell delivers a high rate performance (73.5 mAh g-1 at 5 C) and ultralong cycling stability of 8000 cycles at 5 C. This work brings new insights to design the new-type and practical Mg alloy anodes for commercial RMBs.

Enhancing Proton Co-Intercalation in Iron Ion Batteries Cathodes for Increased Capacity.

Recently, aqueous iron ion batteries (AIIBs) using iron metal anodes have gained traction in the battery community as low-cost and sustainable solutions for green energy storage. However, the development of AIIBs is significantly hindered by the limited capacity of existing cathode materials and the poor intercalation kinetic of Fe2+. Herein, we propose a H+ and Fe2+ co-intercalation electrochemistry in AIIBs to boost the capacity and rate capability of cathode materials such as iron hexacyanoferrate (FeHCF) and Na4Fe3(PO4)2(P2O7) (NFPP). This is achieved through an electrochemical activation step during which a FeOOH nanowire layer is formed in situ on the cathode. This layer facilitates H+ co-intercalation in AIIBs, resulting in a high specific capacity of 151 mAh g-1 and 93% capacity retention over 500 cycles for activated FeHCF cathodes. We found that this activation process can also be applied to other cathode chemistries, such as NFPP, where we found that the cathode capacity is doubled as a result of this process. Overall, the proposed H+/Fe2+ co-insertion electrochemistry expands the range of applications for AIBBs, in particular as a sustainable solution for storing renewable energy.

Redesigning Solvation Structure toward Passivation-Free Magnesium Metal Batteries.

Simple magnesium (Mg) salt solutions are widely considered as promising electrolytes for next-generation rechargeable Mg metal batteries (RMBs) owing to the direct Mg2+ storage mechanism. However, the passivation layer formed on Mg metal anodes in these electrolytes is considered the key challenge that limits its applicability. Numerous complex halogenide additives have been introduced to etch away the passivation layer, nevertheless, at the expense of the electrolyte's anodic stability and cathodes' cyclability. To overcome this dilemma, here, we design an electrolyte with a weakly coordinated solvation structure which enables passivation-free Mg deposition while maintaining a high anodic stability and cathodic compatibility. In detail, we successfully introduce a hexa-fluoroisopropyloxy (HFIP-) anion into the solvation structure of Mg2+, the weakly [Mg-HFIP]+ contact ion pair facilitates Mg2+ transportation across interfaces. As a consequence, our electrolyte shows outstanding compatibility with the RMBs. The Mg||PDI-EDA and Mg||Mo6S8 full cells use this electrolyte demonstrating a decent capacity retention of ∼80% over 400 cycles and 500 cycles, respectively. This represents a leap in cyclability over simple electrolytes in RMBs while the rest can barely cycle. This work offers an electrolyte system compatible with RMBs and brings deeper understanding of modifying the solvation structure toward practical electrolytes.

Organic solid-electrolyte interface layers for Zn metal anodes.

Zinc ion batteries (ZIBs) have emerged as promising candidates for renewable energy storage owing to their affordability, safety, and sustainability. However, issues with Zn metal anodes, such as dendrite growth, hydrogen evolution reaction (HER), and corrosion, significantly hinder the practical application of ZIBs. To address these issues, organic solid electrolyte interface (SEI) layers have gained traction in the ZIB community as they can, for instance, help achieve uniform Zn plating/stripping and suppress side reactions. This article summarizes recent advances in organic artificial SEI layers for ZIB anodes, including their fabrication methods, electrochemical performance, and degradation suppression mechanisms.

Percolating Network of Anionic Vacancies in Prussian Blue: Origin of Superior Ammonium-Ion Storage Performance.

Emerging aqueous ammonium-ion batteries (AIBs) are considered inexpensive, highly safe, ecofriendly, and sustainable energy storage systems. Although some high-performance electrode materials have been reported for AIBs, a comprehensive understanding of the origin of the high ammonium-ion storage performance is still lacking. Herein, the percolating network of anionic vacancies is determined to be the origin of the superior ammonium-ion storage properties of the Prussian blue analogues based on ab initio molecular dynamics simulation and electrochemical kinetic analyses. Fe[Fe(CN)6] with a percolating anionic vacancy network delivers an outstanding rate of 64.7 mAh g-1 at 2000 mA g-1 in addition to a capacity retention of 94.5% after 10 000 cycles. The low-strain intercalation ammonium-ion storage mechanism of highly deficient Fe Prussian blue with Fe as the redox center is revealed by in situ X-ray diffraction and ex situ X-ray absorption fine structure analysis. The results provide insights into the mechanism of ammonium-ion storage in Prussian blue analogues and guidance in the development of aqueous AIBs.

Large-Scale Integration of the Ion-Reinforced Phytic Acid Layer Stabilizing Magnesium Metal Anode.

Rechargeable magnesium batteries (RMBs) have garnered significant attention for their potential in large-scale energy storage applications. However, the commercial development of RMBs has been severely hampered by the rapid failure of large-sized Mg metal anodes, especially under fast and deep cycling conditions. Herein, a concept proof involving a large-scale ion-reinforced phytic acid (PA) layer (100 cm × 7.5 cm) with an excellent water-oxygen tolerance, high Mg2+ conductivity, and favorable electrochemical stability is proposed to enable rapid and uniform plating/stripping of Mg metal anode. Guided by even distributions of Mg2+ flux and electric field, the as-prepared large-sized PA-Al@Mg electrode (5.8 cm × 4.5 cm) exhibits no perforation and uniform Mg plating/stripping after cycling. Consequently, an ultralong lifespan (2400 h at 3 mA cm-2 with 1 mAh cm-2) and high current tolerance (300 h at 9 mA cm-2 with 1 mAh cm-2) of the symmetric cell using the PA-Al@Mg anode could be achieved. Notably, the PA-Al@Mg//Mo6S8 full cell demonstrates exceptional stability, operating for 8000 cycles at 5 C with a capacity retention of 99.8%, surpassing that of bare Mg (3000 cycles, 74.7%). Moreover, a large-sized PA-Al@Mg anode successfully contributes to the stable pouch cell (200 and 750 cycles at 0.1 and 1 C), further confirming its significant potential for practical utilization. This work provides valuable theoretical insights and technological support for the practical implementation of RMBs.

Mg-substituted Prussian blue as a low-strain cathode material for aqueous Fe-ion batteries.

Aqueous Fe-ion batteries (FIBs) have gradually emerged in recent years due to their inherent merits. Herein, we constructed a Mg-substituted Prussian blue analogue (MgFeHCF) as cathode for FIBs, achieving higher capacity (96 mA h g-1) and better stability (70.9% capacity retention over 500 cycles). The Fe-ion storage mechanism was revealed using the in situ XRD technique and DFT calculations were employed to analyse the battery performance.