Graphene-Roll-Wrapped Prussian Blue Nanospheres as a High-Performance Binder-Free Cathode for Sodium-Ion Batteries

MOF-based nanomaterials for advanced aqueous-ion batteries

Metal-organic frameworks (MOFs)-based nanomaterials have great potential in the field of electrochemical energy storage due to their abundant pore size, high specific surface area, controllable structure and porosity, and homogeneous metal center. MOFs complexes and derivatives not only inherit the original morphology characteristics of MOFs but also provide excellent electrochemical performance. Batteries operating in aqueous electrolytes are cheaper, safer, and have higher ionic conductivity than those operating in conventional organic electrolytes. Therefore, it is useful to summarize the MOFs that should be used for aqueous electrochemical energy storage devices. This manuscript firstly introduces the composition and energy storage mechanism of aqueous Li/Na/Zn ion batteries. In addition, a detailed review of the development of MOFs-based nanomaterials and their commonly used characterization under aqueous conditions is presented. The relationship between the structure and composites of MOFs-based nanomaterials and electrochemical performance is highlighted. The applications of MOFs composites in aqueous batteries in terms of electrode materials and electrolytes are presented and summarized. Finally, research directions and perspectives for MOFs-based nanomaterials in advanced aqueous batteries are presented.

Prussian White/Reduced Graphene Oxide Composite as Cathode Material to Enhance the Electrochemical Performance of Sodium-Ion Battery

Prussian white (PW) is considered a promising cathode material for sodium-ion batteries. However, challenges, such as lattice defects and poor conductivity limit its application. Herein, the composite materials of manganese-iron based Prussian white and reduced graphene oxide (PW/rGO) were synthesized via a one-step in situ synthesis method with sodium citrate, which was employed both as a chelating agent to control the reaction rate during the coprecipitation process of PW synthesis and as a reducing agent for GO. The low precipitation speed helps minimize lattice defects, while rGO enhances electrical conductivity. Furthermore, the one-step in situ synthesis method is simpler and more efficient than the traditional synthesis method. Compared with pure PW, the PW/rGO composites exhibit significantly improved electrochemical properties. Cycling performance tests indicated that the PW/rGO-10 sample exhibited the highest initial discharge capacity and the best cyclic stability. The PW/rGO-10 has an initial discharge capacity of 128 mAh g-1 at 0.1 C (1 C = 170 mA g-1), and retains 49.53% capacity retention after 100 cycles, while the PW only delivers 112 mAh g-1 with a capacity retention of 17.79% after 100 cycles. Moreover, PW/rGO-10 also shows better rate performance and higher sodium ion diffusion coefficient (DNa+) than the PW sample. Therefore, the incorporation of rGO not only enhances the electrical conductivity but also promotes the rapid diffusion of sodium ions, effectively improving the electrochemical performance of the composite as a cathode material for sodium-ion batteries.

Effect of water molecules on the diffusion of alkali metal ions in CuHCF cathodes

Prussian blue analogues have shown promise as cathode materials competing with sodium ion batteries, while the presence of water molecules severely affects their performance in batteries. Based on density functional theory, the effect of water molecules on the diffusion of alkali ions is revealed by employing CuHCF (copper hexacyanoferrate) as a cathode. The diffusions of alkali ions in CuHCF with or without inserted water molecules are investigated. It was found that Li+/Na+ forms hydrated ions with water molecules in the interstitial voids, while K+ cannot form hydrated ions due to spatial constraints. It would lead to a dramatic increase of diffusion barriers when Li+/Na+ ions carrying water molecules diffuse. The number of inserted water molecules significantly impacts the diffusion of Li+/Na+ ions.

Research Progress of Prussian Blue and Its Analogs as High-Performance Cathode Nanomaterials for Sodium-Ion Batteries

Sodium-ion batteries (SIBs) are investigated as promising alternatives to lithium-ion batteries (LIBs) on account of the economical abundance and reliable availability of sodium, as well as its analogous chemical properties compared to lithium. Nevertheless, the performance of SIBs is severely restricted by the availability of satisfactory cathode nanomaterials with stable frameworks to accommodate the transportation of large-sized Na+ ions. These challenges can be effectively resolved when exploiting Prussian blue (PB) and its analogs (PBAs) as SIB cathodes. This is mainly because PB and PBAs have 3D open frameworks with large interstitial space, which are more favorable for fast insertion/extraction of Na+ ions during the charging/discharging process, thus enabling the improvement of integrated performance in SIB systems. This overview offers a comprehensive summarization of recent advancements in the electrochemical performance of PB and PBAs when employing them as cathodes in SIBs. For better understanding, the fabrication strategy, structural characterization, and electrochemical performance exposition are systematically organized and explained according to tuning PB and metal-based PBAs. Additionally, the current trajectories and prospective future directions pertaining to the utilization of PB and PBA cathodes in the SIB system are thoroughly examined and deliberated upon.

Structural Engineering of Prussian Blue Analogues Enabling All-Climate and Ultralong Cycling Sodium-Ion Batteries

The development of cost-efficient, long-lifespan, and all-climate sodium-ion batteries is of great importance for advancing large-scale energy storage but is plagued by the lack of suitable cathode materials. Here, we report low-cost Na-rich Mn-based Prussian blue analogues with superior rate capability and ultralong cycling stability over 10,000 cycles via structural optimization with electrochemically inert Ni atoms. Their thermal stability, all-climate properties, and potential in full cells are investigated in detail. Multiple in situ characterizations reveal that the outstanding performances benefit from their highly reversible three-phase transformations and trimetal (Mn-Ni-Fe) synergistic effects. In addition, a high sodium diffusion coefficient and a low volume distortion of 2.3% are observed through in situ transmission electron microscopy and first-principles calculations. Our results provide insights into the structural engineering of Prussian blue analogues for advanced sodium-ion batteries in large-scale energy storage applications.

Promising Cathode Materials for Sodium-Ion Batteries from Lab to Application

Sodium-ion batteries (SIBs) are seen as an emerging force for future large-scale energy storage due to their cost-effective nature and high safety. Compared with lithium-ion batteries (LIBs), the energy density of SIBs is insufficient at present. Thus, the development of high-energy SIBs for realizing large-scale energy storage is extremely vital. The key factor determining the energy density in SIBs is the selection of cathodic materials, and the mainstream cathodic materials nowadays include transition metal oxides, polyanionic compounds, and Prussian blue analogs (PBAs). The cathodic materials would greatly improve after targeted modulations that eliminate their shortcomings and step from the laboratory to practical applications. Before that, some remaining challenges in the application of cathode materials for large-scale energy storage SIBs need to be addressed, which are summarized at the end of this Outlook.

Unraveling Sodium-Ion Dynamics in Honeycomb-Layered Na2MgxZn2-xTeO6 Solid Electrolytes with Solid-State NMR

All-solid-state sodium-ion batteries (SIBs) have the potential to offer large-scale, safe, cost-effective, and sustainable energy storage solutions by supplementing the industry-leading lithium-ion batteries. However, for the enhanced bulk properties of SIB components (e.g., solid electrolytes), a comprehensive understanding of their atomic-scale structure and the dynamic behavior of sodium (Na) ions is essential. Here, we utilize a robust multinuclear (23Na, 125Te, 25Mg, and 67Zn) magnetic resonance approach to explore a novel Mg/Zn homogeneously mixed-cation honeycomb-layered oxide Na2MgxZn2-xTeO6 solid solution series. These new intermediate compounds exhibit tailorable bulk Na-ion conductivity (σ) with the highest σ = 0.14 × 10-4 S cm-1 for Na2MgZnTeO6 at room temperature suitable for SIB solid electrolyte applications as observed by powder electrochemical impedance spectroscopy (EIS). A combination of powder X-ray diffraction (XRD), energy-dispersive X-ray (EDX) spectroscopy, and field emission scanning electron microscopy (FESEM) reveals highly crystalline phase-pure compounds in the P6322 space group. We show that the Mg/Zn disorder is random within the honeycomb layers using 125Te nuclear magnetic resonance (NMR) and resolve multiple Na sites using two-dimensional (triple-quantum magic-angle spinning (3QMAS)) 23Na NMR. The medium-range disorder in the honeycomb layer is revealed through the combination of 25Mg and 67Zn NMR, complemented by electronic structure calculations using density functional theory (DFT). Furthermore, we expose very fast local Na-ion hopping processes (hopping rate, 1/τNMR = 0.83 × 109 Hz) by using a laser to achieve variable high-temperature (∼860 K) 23Na NMR, which are sensitive to different Mg/Zn ratios. The Na2MgZnTeO6 with maximum Mg/Zn disorder displays the highest short-range Na-ion dynamics among all of the solid solution members.

A Disordered Rubik's Cube-Inspired Framework for Sodium-Ion Batteries with Ultralong Cycle Lifespan

Sodium-ion batteries (SIBs) with fast-charge capability and long lifespan could be applied in various sustainable energy storage systems, from personal devices to grid storage. Inspired by the disordered Rubik's cube, here, we report that the high-entropy (HE) concept can lead to a very substantial improvement in the sodium storage properties of hexacyanoferrate (HCF). An example of HE-HCF has been synthesized as a proof of concept, which has achieved impressive cycling stability over 50 000 cycles and an outstanding fast-charging capability up to 75 C. Remarkable air stability and all-climate performance are observed. Its quasi-zero-strain reaction mechanism and high sodium diffusion coefficient have been measured and analyzed by multiple in situ techniques and density functional theory calculations. This strategy provides new insights into the development of advanced electrodes and provides the opportunity to tune electrochemical performance by tailoring the atomic composition.

Na1.51 Fe[Fe(CN)6 ]0.87 ·1.83H2 O Hollow Nanospheres via Non-Aqueous Ball-Milling Route to Achieve High Initial Coulombic Efficiency and High Rate Capability in Sodium-Ion Batteries

Prussian blue analogues (PBAs) have attracted extensive attention as cathode materials in sodium-ion batteries (SIBs) due to their low cost, high theoretical capacity, and facile synthesis process. However, it is of great challenge to control the crystal vacancies and interstitial water formed during the aqueous co-precipitation method, which are also the key factors in determining the electrochemical performance. Herein, an antioxidant and chelating agent co-assisted non-aqueous ball-milling method to generate highly-crystallized Na_{2- x} Fe[Fe(CN)₆ ]_y with hollow structure is proposed by suppressing the speed and space of crystal growth. The as-prepared Na_{2- x} Fe[Fe(CN)₆ ]_y hollow nanospheres show low vacancies and interstitial water content, leading to a high sodium content. As a result, the Na-rich Na_1.51 Fe[Fe(CN)₆ ]_0.87 ·1.83H₂ O hollow nanospheres exhibit a high initial Coulombic efficiency, excellent cycling stability, and rate performance via a highly reversible two-phase transition reaction confirmed by in situ X-ray diffraction. It delivers a specific capacity of 124.2 mAh g^-1 at 17 mA g^-1 , presenting ultra-high rate capability (84.1 mAh g^-1 at 3400 mA g^-1 ) and cycling stability (65.3% capacity retention after 1000 cycles at 170 mA g^-1 ). Furthermore, the as-reported non-aqueous ball-milling method could be regarded as a promising method for the scalable production of PBAs as cathode materials for high-performance SIBs.

Prussian Blue Analogues for Sodium-Ion Batteries: Past, Present, and Future

Prussian blue analogues (PBAs) have attracted wide attention for their application in the energy storage and conversion field due to their low cost, facile synthesis, and appreciable electrochemical performance. At the present stage, most research on PBAs is focused on their material-level optimization, whereas their properties in practical battery systems are seldom considered. This review aims to first provide an overview of the history and parameters of PBA materials and analyze the fundamental principles toward rational design of PBAs, and then evaluate the prospects and challenges for PBAs for practical sodium-ion batteries, hoping to bridge the gap between laboratory research and commercial reality.

Polyvinylpyrrolidone-Bridged Prussian Blue/rGO Composite as a High-Performance Cathode for K-Ion Batteries

Prussian blue (PB) is a very promising cathode for K-ion batteries but its low electronic conductivity and deficiencies in the framework aggravate electrochemical performances. Compositing with conductive reduced graphene oxide (rGO) is an effective solution to address this problem. Nevertheless, little attention was paid to the loss of oxygen-containing functional groups on the rGO substrate during the compositing process, which weakens the interaction between PB and rGO and leads to poor electrochemical performance of PB/rGO. Herein, this interaction effect associated with surface functional groups is first openly debated. Two commonly used carbon substrates, graphene oxide (GO) and rGO, are investigated. A more stable interaction between PB and GO contributes to a higher capacity retention (91.8%) than that of PB/rGO (69.7%) after 300 cycles at a current density of 5 C. Meanwhile, polyvinylpyrrolidone (PVP) is employed to repair the weak interaction between PB and rGO substrates. PB is anchored to the rGO surface through the stable covalent linking of amide groups in PVP. A superior rate capability of 72 mA h g^-1 at 10 C and an improved capacity retention of 96.5% over 800 cycles at 5 C are obtained by as-prepared PB/PVP-rGO. This study provides a deeper understanding of fabricating PB/carbon composites with a robust connection.

Rational Design of MOF-Based Materials for Next-Generation Rechargeable Batteries

This review summarizes recent progresses in pristine metal–organic frameworks (MOFs), MOF composites, and their derivatives for next-generation rechargeable batteries including lithium–sulfur batteries, lithium–oxygen batteries, sodium-ion batteries, potassium-ion batteries, Zn-ion batteries, and Zn–air batteries.

The design strategies for MOF-based materials as the electrode, separator, and electrolyte are outlined and discussed.

The challenges and development strategies and of MOF-related materials for battery applications are highlighted.

Metal–organic framework (MOF)-based materials with high porosity, tunable compositions, diverse structures, and versatile functionalities provide great scope for next-generation rechargeable battery applications. Herein, this review summarizes recent advances in pristine MOFs, MOF composites, MOF derivatives, and MOF composite derivatives for high-performance sodium-ion batteries, potassium-ion batteries, Zn-ion batteries, lithium–sulfur batteries, lithium–oxygen batteries, and Zn–air batteries in which the unique roles of MOFs as electrodes, separators, and even electrolyte are highlighted. Furthermore, through the discussion of MOF-based materials in each battery system, the key principles for controllable synthesis of diverse MOF-based materials and electrochemical performance improvement mechanisms are discussed in detail. Finally, the major challenges and perspectives of MOFs are also proposed for next-generation battery applications.

Zn-Ion Batteries: Boosting the Rate Capability and Low-temperature Performance by Combining Structure and Morphology Engineering

Prussian blue analogues (PBAs) have been considered as one kind of the most promising cathode materials for Zn-ion batteries (ZIBs) due to their low cost, high performance, high safety, and high abundance. However, owing to the low conductivity and single electron reaction, it is a great challenge to obtain a PBA cathode material with high reversible capacity, high rate capability, and good temperature adaptability. Here, a cathode material, K_1.14(VO)_3.33[Fe(CN)₆]₂·6.8H₂O (KVHCF), with a multielectron reaction and double conductive carbon framework (DCCF) is designed and synthesized by combining structure and morphology engineering. With the multielectron reaction and high electronic conductivity simultaneously, the KVHCF@DCCF cathode material delivers a high specific capacity (180 mAh·g^-1 @ 400 mA·g^-1) and the best rate performance (116 mAh·g^-1 @ 8000 mA·g^-1) of the reported PBAs. Moreover, KVHCF@DCCF presents a high specific capacity of 132 mAh·g^-1 @ 400 mA·g^-1 at 0 °C. Even at -10 °C, it still delivers specific capacities of 127 mAh·g^-1 @ 40 mA·g^-1 and 80 mAh·g^-1 @ 400 mA·g^-1 with a retention of 86% after 700 cycles. In situ X-ray diffraction (XRD) and ex situ X-ray photoelectron spectroscopy (XPS) are carried out to investigate the charge-discharge electrochemical reaction mechanism.

CNT-modified two-phase manganese hexacyanoferrate as a superior cathode for sodium-ion batteries

The two-phase KNa-MnFe(CN)₆@CNT material was synthesized via a facile concentration-gradient coprecipitation method. The outstanding electrochemical performance was achieved for KNa-MnFe(CN)₆@CNT material with the addition of CNT.

Binder-Free Electrodes for Advanced Sodium-Ion Batteries

Sodium-ion batteries (SIBs) have recently emerged as one of the favored contenders for use in medium and large-scale stationary energy storage owing to the abundance of the resources required to fabricate them, their low cost, and the fact that have properties similar to equivalent Li batteries. However, their development also faces challenges such as poor cycling stability and unsatisfying rate performance. In traditional electrodes, binders are commonly used to integrate individual active materials with conductive additives. Unfortunately, binders are generally electrochemically inactive and insulating, which reduces the overall energy density and leads to poor cycling stability. Therefore, binder-free electrodes provide great opportunity for high-performance SIBs in terms of both improved electronic conductivity and electrochemical reaction reversibility. This Progress Report provides an overview of the recent progress in binder-free electrodes for SIBs. It focuses on the current challenges of binder-free electrodes and provides an outlook for their future in energy conversion and storage.

Inhibition of Crystallization of Poly(ethylene oxide) by Ionic Liquid: Insight into Plasticizing Mechanism and Application for Solid-State Sodium Ion Batteries

All-solid-state sodium ion batteries (ASIBs) possess enhanced safety and desired cycling life compared with conventional liquid sodium batteries, showing great potential in large-scale energy storage systems. Polymer electrolytes based on poly(ethylene oxide) (PEO) have been extensively studied for ASIBs due to superior flexibility and processability. However, PEO-based electrolyte without any modification can hardly meet the requirements of ASIBs at room temperature. In the past decade, unremitting efforts have been attached to inhibiting crystallization of PEO, especially via ionic liquid plasticizing. However, the plasticizing mechanism is not clear. Here we incorporated Pyr₁₃FSI into PEO-NaClO₄ electrolyte to investigate the plasticizing effect by infrared spectrum characterizations and DFT calculations. The results indicate that FSI^- anions tend to adhere to the PEO backbone, generating enhanced coordination ability and more coordination sites. Solid-state sodium ion batteries using PEO-NaClO₄-40 wt % Pyr₁₃FSI as polymer electrolyte exhibit good cycling and rate performance. Insights into the plasticizing mechanism contribute to fabricating polymer electrolyte with high performance for ASIBs.

Chemical Properties, Structural Properties, and Energy Storage Applications of Prussian Blue Analogues

Prussian blue analogues (PBAs, A₂ T[M(CN)₆ ], A = Li, K, Na; T = Fe, Co, Ni, Mn, Cu, etc.; M = Fe, Mn, Co, etc.) are a large family of materials with an open framework structure. In recent years, they have been intensively investigated as active materials in the field of energy conversion and storage, such as for alkaline-ion batteries (lithium-ion, LIBs; sodium-ion, NIB; and potassium-ion, KIBs), and as electrochemical catalysts. Nevertheless, few review papers have focused on the intrinsic chemical and structural properties of Prussian blue (PB) and its analogues. In this Review, a comprehensive insight into the PBAs in terms of their structural and chemical properties, and the effects of these properties on their materials synthesis and corresponding performance is provided.

Na+-Conductive Na2Ti3O7-Modified P2-type Na2/3Ni1/3Mn2/3O2 via a Smart in Situ Coating Approach: Suppressing Na+/Vacancy Ordering and P2-O2 Phase Transition

Sodium-ion batteries (SIBs) have shown great superiority for grid-scale storage applications because of their low cost and the abundance of sodium. P2-type Na_2/3Ni_1/3Mn_2/3O₂ cathode materials have attracted much attention for their high capacities and operating voltages as well as their simple synthesis processes. However, Na⁺/vacancy ordering and the P2-O2 phase transition are unavoidable during Na⁺ insertion/extraction, leading to undesired voltage plateaus and deficient battery performances. We show that this defect can be effectually eliminated by coating a moderate Na⁺ conductor Na₂Ti₃O₇ with a smart in situ coating approach and a concomitant doping of Ti⁴⁺ into the bulk structure. Based on the combined analysis of ex situ X-ray diffraction, scanning electron microscopy, electrochemical performance tests, and electrochemical kinetic analyses, Na₂Ti₃O₇ coating and Ti⁴⁺ doping effectively refrain Na⁺/vacancy ordering and P2-O2 phase transition during cycling. Additionally, the Na₂Ti₃O₇ coating layer suppresses particle exfoliation and accelerates Na⁺ diffusion at the cathode and electrolyte interface. Hence, Na₂Ti₃O₇-coated Na_2/3Ni_1/3Mn_2/3O₂ exhibits excellent cycling stability (almost no capacity decay after 200 cycles at 5 C) and outstanding rate capability (31.1% of the initial capacity at a high rate of 5 C compared to only 10.4% for the pristine electrode). This coating strategy can provide a new guide for the design of prominent cathode materials for SIBs that are suitable for practical applications.

Reduced Graphene Oxide-Anchored Manganese Hexacyanoferrate with Low Interstitial H2O for Superior Sodium-Ion Batteries

Low-cost manganese hexacyanoferrate (NMHCF) possesses many favorable advantages including high theoretical capacity, ease of preparation, and robust open channels that enable faster Na⁺ diffusion kinetics. However, high lattice water and low electronic conductivity are the main bottlenecks to their pragmatic realization. Here, we present a strategy by anchoring NMHCF on reduced graphene oxide (RGO) to alleviate these problems, featuring a specific discharge capacity of 161/121 mA h g^-1 at a current density of 20/200 mA g^-1. Moreover, the sodiation process is well revealed by ex situ X-ray diffraction, EIS and Car-Parrinello molecular dynamics simulations. At a rate of 20 mA g^-1, the hard carbon//NMHCF/RGO full cell affords a stable discharge capacity of 84 mA h g^-1 (based on the weights of cathode mass) over 50 cycles, thus highlighting NMHCF/RGO an alternative cathode for sodium-ion batteries.

A 3D graphene current collector boosts ultrahigh specific capacity in a highly uniform Prussian blue@graphene composite as a freestanding cathode for sodium ion batteries

For the first time, a uniform graphene aerogel (GA) supported Prussian blue (PB) nanocube structure was synthesized by fitting the nanocube into the GA with a specific pore size and employing it in a freestanding sodium ion battery cathodic electrode. In this electrode, the graphene framework not only offers mechanical support, but also plays the role of a binder-free current collector. The theoretical specific capacity of Prussian blue was exceeded with an ultrahigh specific capacity of 214 mA h g-1 at 0.5 C. With the help of the electronic double layer capacitance of the graphene framework, this ultrahigh value can be achieved. We studied the influence of the mass loading of the PB nanocube on the specific capacity, finding that the GA-induced freestanding electrode has the potential to load a maximum of 72 wt% of the PB nanocube. Furthermore, we separated the capacitance and the capacity of the electrode through kinetic analysis, and discovered that the GA-induced carbon collector contributed to a surface-controlled capacitance, which accounted for 55% of the total capacity.

Prussian Blue Analogs for Rechargeable Batteries

Non-lithium energy storage devices, especially sodium ion batteries, are drawing attention due to insufficient and uneven distribution of lithium resources. Prussian blue and its analogs (Prussian blue analogs [PBAs]), or hexacyanoferrates, are well-known since the 18th century and have been used for hydrogen storage, cancer therapy, biosensing, seawater desalination, and sewage treatment. Owing to their unique features, PBAs are receiving increasing interest in the field of energy storage, such as their high theoretical specific capacity, ease of synthesis, as well as low cost. In this review, a general summary and evaluation of the applications of PBAs for rechargeable batteries are given. After a brief review of the history of PBAs, their crystal structure, nomenclature, synthesis, and working principle in rechargeable batteries are discussed. Then, previous works classified based on the combination of insertion cations and transition metals are analyzed comprehensively. The review includes an outlook toward the further development of PBAs in electrochemical energy storage.

New P2-Type Honeycomb-Layered Sodium-Ion Conductor: Na2Mg2TeO6

A novel solid sodium-ion conductor, Na₂Mg₂TeO₆ (NMTO) with a P2-type honeycomb-layered structure, has been synthesized for the first time by a simple solid-state synthetic route. The conductor of NMTO exhibits high conductivity of 2.3 × 10^-4 S cm^-1 at room temperature (RT) and a large electrochemical window of ∼4.2 V (versus Na⁺/Na). The conductor is remarkably stable, both in the ambient environment and within its metallic Na anode. This facile sodium-ion conductor displays potential for use in all-solid-state sodium-ion batteries (SS-SIBs).

Recent Progress in Iron-Based Electrode Materials for Grid-Scale Sodium-Ion Batteries

Grid-scale energy storage batteries with electrode materials made from low-cost, earth-abundant elements are needed to meet the requirements of sustainable energy systems. Sodium-ion batteries (SIBs) with iron-based electrodes offer an attractive combination of low cost, plentiful structural diversity and high stability, making them ideal candidates for grid-scale energy storage systems. Although various iron-based cathode and anode materials have been synthesized and evaluated for sodium storage, further improvements are still required in terms of energy/power density and long cyclic stability for commercialization. In this Review, progress in iron-based electrode materials for SIBs, including oxides, polyanions, ferrocyanides, and sulfides, is briefly summarized. In addition, the reaction mechanisms, electrochemical performance enhancements, structure-composition-performance relationships, merits and drawbacks of iron-based electrode materials for SIBs are discussed. Such iron-based electrode materials will be competitive and attractive electrodes for next-generation energy storage devices.