High-Entropy Metal-Organic Frameworks for Highly Reversible Sodium Storage

Enhancing the Reversibility and Kinetics of Heterovalent Ion-Substituted Mn-Based Prussian Blue Analogue Cathodes via Intervalence Charge Transfer

Mn3+ (d4) in manganese-based Prussian blue analogues (MnPBA) exhibits intrinsic orbital degeneracy upon sodiation/desodiation, resulting in severe Jahn-Teller distortion, which usually causes rapid capacity decay and sluggish kinetics. Unfortunately, traditional modification strategies are insufficient for electronic tuning of Mn3+ to mitigate these issues. Herein, Intervalence Charge Transfer (IVCT) of manganese and iron to vanadium ions is unraveled in a series of novel V3+-substituted MnPBA to enhance electrochemical reaction reversibility and kinetics. IVCT drives electron distribution from localized to delocalized, achieves electronic coupling, and mitigates Jahn-Teller by transferring a single-electron of Mn3+ eg orbital. Notably, the reported Na1.2V0.63Mn0.58Fe(CN)6 cathode demonstrates excellent rate capability (136.9 mAh g-1 at 20 mA g-1 and 94.9 mAh g-1 at 20 A g-1), remarkable long-cycle stability (91.6 % capacity retention after 300 cycles at 20 mA g-1 and 90.7 % after 2000 cycles at 2 A g-1), and robust performance across a wide temperature range (98.59 % capacity after 300 cycles at -30 °C and 50 mA g-1), surpassing the majority of reported sodium-ion cathodes. The intrinsic functioning mechanism of IVCT and quasi-zero-strain reaction mechanism were adequately understood through systematic in situ/ex situ characterizations. This study further develops electron-tuning of PBA, opening a new avenue toward advanced sodium-ion battery cathode materials.

Ligand Field-Induced Dual Active Sites Enhance Redox Potential of Nickel Hexacyanoferrate for Ammonium Ion Storage

Enhancing the redox potential of cathode materials is vital for increasing the energy density of aqueous ammonium ion batteries (AIBs). Prussian blue analogues (PBAs), with their inherently high redox potentials and open frameworks, are promising candidates. However, further boosting their redox potential and understanding their NH4 + ion storage mechanisms remain critical challenges. In this work, a novel ligand field-induced dual active sites mechanism is introduced by incorporating Ni into the PBA framework, activating Ni as an additional redox center for NH4 + ion storage. The electron transfer from Ni to Fe within the Ni─N≡C─Fe chain enhances the redox potential and electrochemical performance of nickel hexacyanoferrate (NiHCF). For the first time, the electrochemical activity of Ni is demonstrated in NiHCF during NH4 + ions intercalation and de-intercalation. NiHCF exhibits elevated redox potentials, superior rate performance, and robust cycling stability compared to iron hexacyanoferrate (FeHCF). Advanced characterization techniques and density functional theory calculations confirm the activation of Ni and the enhanced interaction between NH4 + ions and the framework. These findings provide new insights into the NH4 + ion storage mechanism of PBAs and offer a promising strategy for designing high-energy-density cathode materials for AIBs.

A Perspective on the Origin of High-Entropy Solid Electrolytes

As the key material for the all-solid-state batteries (ASSBs), solid electrolytes (SEs) have attracted increasing attention. Recently, a novel design strategy-high-entropy (HE) approach is frequently reported to improve the ionic conductivity and electrochemical performance of SEs. However, the fundamental understandings on the HE working mechanism and applicability evaluation of HE concept are deficient, which would impede the sustainable development of a desirable strategy to enable high-performance SEs. In this contribution, the essence of HE-related approaches and their positive effects on SEs are evaluated. The reported HE strategy stems from complex compositional regulations. The derived structural stability and enhanced property are originally from the modulated system disorder and subtle local-structure evolutions, respectively. While HE ardently describes the increased entropy/disorder during the modification of prevailing SEs, rigorous experimental formulations, and direct correlations between the HE structures and desired properties are necessary to be established. This perspective would be a timely and critical overview for the HE approaches in the context of SEs, aiming to stimulate further discussion and exploration in this emerging research direction.

Recent Progress in Catalysis Using High-Entropy Metal-Organic Frameworks and their Derived Materials

High-entropy metal-organic framework (HE-MOF) and their derived materials are a novel class of multipurpose materials with enormous catalytic potential. By incorporating multiple metal sites into a single MOF structure, HE-MOFs offer tunable electronic structures, diverse active sites, and enhanced stability-key attributes for catalytic applications. This review article presents a complete examination of current progress in HE-MOFs and their derived materials for diverse catalytic reactions, including electrocatalysis, photocatalysis, and thermal catalysis. Various strategies for boosting the catalytic reactivity of HE-MOFs and their derived materials have been discussed, including pore architecture modulation, morphological control, defect engineering, elemental composition tuning, and interface optimization. A thorough investigation has been conducted on various catalytic reactions like water splitting, oxygen reduction, nitrogen reduction, alcohol oxidation, hydrogenation, and cycloaddition. Furthermore, the underlying structure-property correlation governing their activity has been discussed, and key challenges and future directions in this rapidly evolving field have been highlighted. The insights presented in this review aim to guide the rational design of next-generation high-entropy materials for sustainable and efficient catalytic processes.

High-Entropy Prussian Blue Analogs via a Solid-Solution Storage Mechanism for Long Cycle Sodium-Ion Batteries Cathodes

The open-framework characteristics of Prussian blue analogs (PBAs) have been recognized as advantages for cathode application in Sodium-ion batteries (SIBs). Nevertheless, lattice distortions during charge-discharge cycles critically compromise their cyclability. Recent advancements in high-entropy design strategies have significantly improved structural stability and energy storage efficiency within functional materials. In this study, we developed the high-entropy PBAs, K1.68 Mn0.21 Cu0.20 Ni0.20 Co0.19 Fe0.20[Fe(CN)6]0.87□0.13·0.66H2O, via a cost-effective aqueous co-precipitation method. Notably, this approach facilitates the concurrent incorporation of five transition metals (Mn, Cu, Ni, Co, and Fe), thereby establishing a stable crystalline framework. Electrochemical characterization demonstrates that the cathode achieves a specific capacity of 124.9 mAh g-1 at 0.025 A g-1. At various current densities (0.025-1 A g-1), the cathode maintains a particular capacity retention of 62.1% during rate testing. Furthermore, the cathode exhibits exceptional cyclability preserving 78.7% capacity at 1 A g-1 after 3000 cycles. Operando X-ray diffraction (XRD) analysis confirms the formation of a reversible solid-solution intercalation/extraction mechanism process, which prevents phase transitions and enhances cyclability. This high-entropy material holds significant potential as a cathode for SIBs, offering high specific capacity and outstanding long-term cycling stability. These superior properties position it as a competitive candidate for advanced energy storage systems.

High-Entropy V-Based Null Matrix Alloys─Short/Long-Range Structural Features, Chemical Stabilities, and Mechanical Properties

Null matrix alloys are special types of alloys with no peaks in the neutron diffraction patterns. These types of materials have tremendous applications in the neutron scattering community as main components for manufacturing advanced reaction vessels for in situ measurements. In the literature, null matrix alloys are often reported to be composed of two different elements/isotopes. In other words, null matrix alloys with more than two elements/isotopes have never been reported. One main reason was the limited solubility of dopants in the parent phases. As such, their physical/chemical properties could not be easily modified through the conventional doping strategies. For the first time, a new family of high-entropy V-based (HEV) alloys, composed of more than five elements, were developed using a two-step arc-melting method. The six investigated samples included V0.939Nb0.010Ta0.011Al0.020Fe0.008Sn0.012 (HEV1), V0.941Nb0.010Ta0.011Al0.020Fe0.008Mo0.011 (HEV2), V0.937Nb0.010Ta0.011Al0.020Sn0.012Mo0.011 (HEV3), V0.949Nb0.010Ta0.011Fe0.008Sn0.012Mo0.011 (HEV4), V0.939Nb0.010Al0.020Fe0.008Sn0.012Mo0.011 (HEV5), and V0.939Ta0.011Al0.020Fe0.008Sn0.012Mo0.011 (HEV6). All six HEV alloys did not show any diffraction peaks in the neutron diffraction patterns. The dopants were found to be homogeneously distributed over the 2a sites of the Im3̅m structure of V by the Rietveld refinement on high-resolution X-ray diffraction data. X-ray pair distribution function (PDF) analysis and small-angle neutron scattering (SANS) ruled out the possibility of chemical ordering or clustering in the investigated samples. Based on the chemical oxidation analysis of O2 at high temperatures, the HEV alloys are found to be more resistant than that the binary V-based alloys. Among the investigated HEV alloys, HEV4 was found to have the highest engineering yield strength. This work provides an important guideline of designing complex null matrix alloys/materials with novel properties.

High Performance Capacitive Deionization Cathode of Nickel Hexacyanoferrate Doped with Trace Molybdenum: Breaking the Capacity-Stability Trade-Off

Nickel hexacyanoferrate (NiHCF) is considered one of the most promising electrode materials for capacitive deionization (CDI) because of its excellent cycling stability and other advantages. However, the poor desalination ability and low adsorption capacity caused by a single reaction site seriously restrict its practical application. Here, a high-valence transition metal element Mo-doped strategy is proposed to utilize traces of Mo6+ to activate the inert-sites within NiHCF. The Mo-doped NiHCF electrodes (NiMox-HCF) with multiple pairs of redox active sites and long cycling capability were designed, breaking the trade-off between high adsorption capacity and cycling stability. The results show that the preferred NiMo0.3-HCF not only retains the excellent cycling stability (91% after 200 cycles), but also possesses a high adsorption capacity of 90.92 mg g-1 at 1.2 V, which is much better than those of NiHCF under the same conditions. In addition, it has good practical application in simulated brackish water and circulating cooling water. Structural characterization and theoretical calculations indicate that the Mo doping strategy enhanced electronic conductivity while maintaining structural stability. This research proposes a new method to activate inert sites using high-valence elements, thus effectively balancing the adsorption capacity and cycling stability of the electrode.

Thermodynamically-Driven Phase Engineering and Reconstruction Deduction of Medium-Entropy Prussian Blue Analogue Nanocrystals

Prussian blue analogs (PBAs) are exemplary precursors for the synthesis of a diverse array of derivatives.Yet, the intricate mechanisms underlying phase transitions in these multifaceted frameworks remain a formidable challenge. In this study, a machine learning-guided analysis of phase transitions in a medium-entropy PBA system is delineated, utilizing an array of descriptors that encompass crystallographic phases, structural subtleties, and fluctuations in multimetal valence states. By integrating multimodal simulations with experimental validation, a thermodynamics-driven phase transformation model for medium-entropy PBA is established and accurately predicted the critical synthesis parameters. A constellation of advanced techniques-including atomic force microscopy coupled with Kelvin probe force microscopy for individual nanoparticles, X-ray absorption spectroscopy, operando ultraviolet-visible spectroscopy, in situ X-ray diffraction, theoretical calculations, and multiphysics simulations-substantiated that the iron oxide@NiCoZnFe-PBA exhibits both exceptional stability and remarkable electrochemical activity. This investigation provides profound insights into the phase transition dynamics of polymetallic complexes and propels the rational design of other thermally-induced derivatives.

High-Entropy Metal Sulfide Nanocrystal Libraries for Highly Reversible Sodium Storage

Controlled synthesis of high-entropy materials offers a unique platform to explore unprecedented electrochemical properties. High-entropy metal sulfides (HEMSs) have recently emerged as promising electrodes in electrochemical energy storage applications. However, synthesizing HEMSs with a tunable number of components and composition is still challenging. Here, a HEMS library is built by using a general synthetic approach, enabling the synthesis of HEMS with arbitrary combinations of 5 to 12 out of 28 elements in the periodic table. The formation of a solid solution of HEMS is attributed to the two-step method that lowers the energy barrier and facilitates the sulfur diffusion during the synthesis. The hard soft acid base (HSAB) theory is used to precisely describe the conversion rates of the metal precursors during the synthesis. The HEMSs as cathodes in Na-ion batteries (SIBs) is investigated, where 7-component HEMS (7-HEMS) delivers a promising rate capability and an exceptional sodium storage performance with reversible a capacity of 230 mAh g-1 over 3000 cycles. This work paves the way for the multidisciplinary exploration of HEMSs and their potential in electrochemical energy storage.

Tunable Platform Capacity of Metal-Organic Frameworks via High-Entropy Strategy for Ultra-Fast Sodium Storage

Precise regulation of the platform capacity/voltage of electrode materials contributes to the efficient operation of sodium-ion fast-charging devices. However, the design of such electrode materials is still in a blank stage. Herein, based on tunable metal-organic frameworks, we have designed a novel material system-two-dimensional high-entropy metal-organic frameworks (HE-MOFs), which exhibits unique properties in sodium storage and is of vital importance for realizing fast-charging batteries. Furthermore, we have found that the high-entropy effect can regulate the electronic structure, the sodium-ion migration environment, and the sodium-ion storage active sites, thereby meeting the requirements of electrode materials for sodium-ion fast-charging devices. Impressively, the HE-MOFs material still maintains a reversible specific capacity of 89 mAh g-1 at a current density of 20 A g-1. It presents an ideal sodium storage voltage plateau of approximately 0.5 V, and its platform capacity is increased to 122.7 mAh g-1, far superior to that of Mn-MOFs (with no platform capacity). This helps to reduce safety hazards during the fast-charging process and demonstrates its great application value in the fields of fast-charging sodium-ion batteries and capacitors. Our research findings have broken the barriers to the application of non-conductive MOFs as energy storage materials, enhanced the understanding of the regulation of platform capacity and voltage, and paved the way for the realization of high-security sodium-ion fast-charging devices.

Understanding capacity fading from structural degradation in Prussian blue analogues for wide-temperature sodium-ion cylindrical battery

Low-cost Fe-based Prussian blue analogues often suffer from capacity degradation, resulting in continuous energy loss, impeding commercialization for practical sodium-ion batteries. The underlying cause of capacity decrease remains mysterious. Herein, we show that irreversible phase transitions, structural degradation, deactivation of surface redox centres, and dissolution of transition metal ions in Prussian blue analogues accumulate continuously during cycling. These undesirable changes are responsible for massive destruction of their morphology, leading to the capacity decay. A dual regulation strategy is applied to alleviate the above-mentioned problems of Prussian blue analogues. The designed 18650/33140 cylindrical cells using modified Prussian blue analogues and hard carbon display improved cycling stability and wide-temperature working performance (-40 oC-100 oC). The findings resolve the controversy over the origins of Prussian blue analogues cathode degradation, emphasize the necessity of eliminating irreversible crystal/structural changes to guarantee enhanced cycling stability, and demonstrate the potential of Prussian blue analogues cathode for commercial sodium-ion batteries.

High-Entropy Metal-Organic Frameworks and Their Derivatives: Advances in Design, Synthesis, and Applications for Catalysis and Energy Storage

As a nascent class of high-entropy materials (HEMs), high-entropy metal-organic frameworks (HE-MOFs) have garnered significant attention in the fields of catalysis and renewable energy technology owing to their intriguing features, including abundant active sites, stable framework structure, and adjustable chemical properties. This review offers a comprehensive summary of the latest developments in HE-MOFs, focusing on functional design, synthesis strategies, and practical applications. This work begins by presenting the design principles for the synthesis strategies of HE-MOFs, along with a detailed description of commonly employed methods based on existing reports. Subsequently, an elaborate discussion of recent advancements achieved by HE-MOFs in diverse catalytic systems and energy storage technologies is provided. Benefiting from the application of the high-entropy strategy, HE-MOFs, and their derivatives demonstrate exceptional catalytic activity and impressive electrochemical energy storage performance. Finally, this review identifies the prevailing challenges in current HE-MOFs research and proposes corresponding solutions to provide valuable guidance for the future design of advanced HE-MOFs with desired properties.

Printed High-Entropy Prussian Blue Analogs for Advanced Non-Volatile Memristive Devices

Non-volatile memristors dynamically switch between high (HRS) and low resistance states (LRS) in response to electrical stimuli, essential for electronic memories, neuromorphic computing, and artificial intelligence. High-entropy Prussian blue analogs (HE-PBAs) are promising insertion-type battery materials due to their diverse composition, high structural integrity, and favorable ionic conductivity. This work proposes a non-volatile, bipolar memristor based on HE-PBA. The device, featuring an active layer of HE-PBA sandwiched between Ag and ITO electrodes, is fabricated by inkjet printing and microplotting. The conduction mechanism of the Ag/HE-PBA/ITO device is systematically investigated. The results indicate that the transition between HRS and LRS is driven by an insulating-metallic transition, triggered by extraction/insertion of highly mobile Na+ ions upon application of an electric field. The memristor operates through a low-energy process akin to Na+ shuttling in Na-ion batteries rather than depending on formation/rupture of Ag filaments. Notably, it showcases promising characteristics, including non-volatility, self-compliance, and forming-free behavior, and further exhibits low operation voltage (VSET = -0.26 V, VRESET = 0.36 V), low power consumption (PSET = 26 µW, PRESET = 8.0 µW), and a high ROFF/RON ratio of 104. This underscores the potential of high-entropy insertion materials for developing printed memristors with distinct operation mechanisms.

Rational Design of Prussian Blue Analogues for Ultralong and Wide-Temperature-Range Sodium-Ion Batteries

Architecting Prussian blue analogue (PBA) cathodes with optimized synergistic bimetallic reaction centers is a paradigmatic strategy for devising high-energy sodium-ion batteries (SIBs); however, these cathodes usually suffer from fast capacity fading and sluggish reaction kinetics. To alleviate the above problems, herein, a series of early transition metal (ETM)-late transition metal (LTM)-based PBA (Fe-VO, Fe-TiO, Fe-ZrO, Co-VO, and Fe-Co-VO) cathode materials have been conveniently fabricated via an "acid-assisted synthesis" strategy. As a paradigm, the FeVO-PBA (FV) delivers a superb rate capability (148.9 and 56.1 mAh/g under 0.5 and 100 C, respectively), remarkable cycling stability over 30,000 cycles, high energy density (259.7 Wh/kg for the full cell), and a wide operation-temperature range (-60-80 °C). In situ/ex situ techniques and density functional theory calculations reveal the quasi-zero-strain and multielectron redox mechanisms of the FeVO-PBA cathode during cycling, supporting its higher specific capacity and stable cycling. It is considered that the d-d electron compensation effect between Fe and V enhanced the reversibility and kinetics of redox reactions and simultaneously improved the electronic conductivity and structural stability of the FeVO-PBA cathode. This work may pave a new way for the rational design of high-performance cathode materials with bimetallic reaction centers for SIBs.

Metal-Ligand Spin-Lock Strategy for Inhibiting Anion Dimerization in Li-Rich Cathode Materials

Anion dimerization poses a significant challenge for the application of Li-rich cathode materials (LCMs) in high-energy-density Li-ion batteries because of its deleterious effects, including rapid capacity and voltage decay, sluggish reaction kinetics, and large voltage hysteresis. Herein, we propose a metal-ligand spin-lock strategy to inhibit anion dimerization, which involves introducing an Fe-Ni couple having antiferromagnetic superexchange interaction into the LCM to lock the spin orientations of the unpaired electrons in the anions in the same direction. As proof of concept, we applied this strategy to intralayer disordered Li2TiS3 (ID-LTS) to inhibit S-S dimerization. Electrochemical characterization using the galvanostatic charge/discharge and intermittent titration technique demonstrated the considerably enhanced anionic redox activity, reduced voltage hysteresis, and improved kinetics of the Fe-Ni-couple-incorporated ID-LTS. Fe L2,3-edge X-ray absorption spectroscopy and magnetic susceptibility measurements revealed that the metal-ligand spin-lock effect and consequent suppression of anion dimerization involve ligand-to-metal charge transfer between S and Fe. Further electrochemical tests on a Fe-Ni-couple-incorporated Li-rich layered oxide (Li0.7Li0.1Fe0.2Ni0.1Mn0.6O2) indicated the importance of the π backbond in enhancing ligand-to-metal charge transfer from S to Fe. These findings demonstrate the potential application of our metal-ligand spin-lock strategy in the development of high-performance LCMs.

Activating Reversible V4+/V5+ Redox Couple in NASICON-Type Phosphate Cathodes by High Entropy Substitution for Sodium-Ion Batteries

Vanadium-based Na superionic conductor (NASICON) type materials (NaxVM(PO4)3, M = transition metals) have attracted extensive attention when used as sodium-ion batteries (SIBs) cathodes due to their stable structures and large Na+ diffusion channels. However, the materials have poor electrical conductivity and mediocre energy density, which hinder their practical applications. Activating the V4+/V5+ redox couple (V4+/V5+≈4.1 V vs Na+/Na) is an effective way to elevate the energy density of SIBs, whereas the irreversible phase transition of V4+/V5+ and severe structural distortion will inevitably result in fast capacity fading and unsatisfactory rate capability. Herein, a high entropy regulation strategy is proposed to optimize the detailed crystal structure and improve the reversibility of crystalline phase transformation and electrical conductivity of the material. With the activated reversible V4+/V5+ redox couple, stable structure, and fast electrochemical kinetics, the high entropy material Na3.2V1.5Fe0.1Al0.1Cr0.1Mn0.1Cu0.1(PO4)3 (NVMP-HE) exhibits an outstanding electrochemical performance with highly reversible specific capacity of 120.1 mAh g-1 at 0.1 C and excellent cycling stability (92.4% retention after 1000 cycles at 20 C). Besides, the in situ X-ray diffraction (XRD) measurement reveals that a smooth three-phase transition reaction is involved in this high-entropy cathode and the existence of mesophase facilitates a fast phase transition.

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

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

Design Concepts of High-Entropy Materials for Zinc Ion Batteries

Zinc-ion batteries have emerged as strong candidates for replacing Li/Na-ion batteries owing to their high safety and environmental friendliness. However, the large electrostatic repulsion between the cathode and Zn2+, the irreversible growth of zinc dendrites at the anode, and the hydrogen precipitation side reaction in the aqueous electrolyte have hindered the practical application of zinc ion batteries. Fortunately, the emergence of the revolutionary concept of high entropy has provided new opportunities for the development of battery materials. High-entropy materials, with their unique atomic structures and uniform distribution of multiple elements, offer flexible options for material compositions and electronic structures, thus attracting significant attention in battery systems. In this concept article, we summarize the definitions and intrinsic structural characteristics of high-entropy materials and provide a detailed overview of the latest design concepts from the perspectives of cathodes, anodes, and electrolytes. Finally, we outline the challenges faced by high-entropy materials and potential solutions to guide researchers in developing efficient and stable zinc-ion batteries.

Entropy engineering activation of UiO-66 for boosting catalytic transfer hydrogenation

High-entropy metal-organic frameworks (HE-MOFs) hold promise as versatile materials, yet current rare examples are confined to low-valence elements in the fourth period, constraining their design and optimization for diverse applications. Here, a novel high-entropy, defect-rich and small-sized (32 nm) UiO-66 (ZrHfCeSnTi HE-UiO-66) has been synthesized for the first time, leveraging increased configurational entropy to achieve high tolerance to doping with diverse metal ions. The lattice distortion of HE-UiO-66 induces high exposure of metal nodes to create coordination unsaturated metal sites with a concentration of 322.4 μmol/g, which increases the abundance of Lewis acid-base sites, thereby achieving a significant improvement in the performance of the catalytic transfer hydrogenation (CTH) reaction. Systematic investigation manifests that the special electronic structure of HE-UiO-66 enhances the interaction and bonding with substrate molecules and reduces the energy barrier of the hydrogen transfer process. Our approach offers a new strategy for constructing coordination unsaturated metal sites in MOFs.

Building Robust Manganese Hexacyanoferrate Cathode for Long-Cycle-Life Sodium-Ion Batteries

Manganese Hexacyanoferrate (Mn─HCF) is a preferred cathode material for sodium-ion batteries used in large-scale energy storage. However, the inherent vacancies and the presence of H2O within the imperfect crystal structure of Mn─HCF lead to material failure and interface failure when used as a cathode. Addressing the challenge of constructing a stable cathode is an urgent scientific problem that needs to be solved to enhance the performance and lifespan of these batteries. In this review, the crystal structure of Mn─HCF is first introduced, explaining the formation mechanism of vacancies and exploring the various ways in which H2O molecules can be present within the crystal structure. Then comprehensively summarize the mechanisms of material and interfacial failure in Mn─HCF, highlighting the key factors contributing to these issues. Additionally, eight modification strategies designed to address these failure mechanisms are encapsulated, including vacancy regulation, transition metal substitution, high entropy, the pillar effect, interstitial H2O removal, surface coating, surface vacancy repair, and cathode electrolyte interphase reinforcement. This comprehensive review of the current research advances on Mn─HCF aims to provide valuable guidance and direction for addressing the existing challenges in their application within SIBs.

Zero-Strain Sodium Nickel Ferrocyanide as Cathode Material for Sodium-Ion Batteries with Ultra-Long Lifespan

Prussian blue analogues are recognized as one of the most promising cathode materials for sodium-ion batteries (SIBs) owing to the open 3D framework structure with large interstitial sites and developed Na-ion diffusion channels. However, high content of anion vacancy and poor structural stability have hampered the prospect of their application. In this work, sodium nickel ferrocyanide (Na1.34Ni[Fe(CN)6]0.92, NNHCF) is proposed as cathode material for SIBs. N-coordinated Ni-ion can boost NNHCF to possess less Fe[(CN)6]4- defect, low Na-ion migration barrier, and more negative formation energy compared with Na0.91Cu[Fe(CN)6]0.77 (NCHCF), thus exhibiting more active sites, fast electrochemical kinetics behavior and great structure stability. It is confirmed that NNHCF undergoes a solid solution mechanism without phase evolution for reversible Na-ion intercalation/deintercalation, employing Fe associated with C atom as redox center for charge compensation. Therefore, NNHCF contributes a high initial energy density of 180.94 Wh·g-1 at 10 mA·g-1, excellent rate capability, superior cycling stability with ultra-long lifespan of 13 000 cycles, and low fading rate of 0.0027% per cycle at 500 mA·g-1. This work sheds light on the construction of low-defect PBA cathodes with outstanding dynamics and stability.

Synthesis Strategies for High Entropy Nanoparticles

Nanoparticles (NPs) of high entropy materials (HEMs) have attracted significant attention due to their versatility and wide range of applications. HEM NPs can be synthesized by fragmenting bulk HEMs or disintegrating and recrystallizing them. Alternatively, directly producing HEMs in NP form from atomic/ionic/molecular precursors presents a significant challenge. A widely adopted strategy involves thermodynamically driving HEM NP formation by leveraging the entropic contribution but incorporating strategies to limit NP growth at the elevated temperatures used for maximizing entropy. A second approach is to kinetically drive HEM NP formation by promoting rapid reactions of homogeneous reactant mixtures or using highly diluted precursor dissolutions. Additionally, experimental evidence suggests that enthalpy plays a significant role in driving HEM NP formation processes at moderate temperatures, with the high energy cost of generating additional surfaces and interfaces at the nanoscale stabilizing the HEM phase. This review critically assesses the various synthesis strategies developed for HEM NP preparation, highlighting key illustrative examples and offering insights into the underlying formation mechanisms. Such insights are critical for fine-tuning experimental conditions to achieve specific outcomes, ultimately enabling the effective synthesis of optimized generations of these advanced materials for both current and emerging applications across various scientific and technological fields.

Synthesis-Structure-Property of High-Entropy Layered Oxide Cathode for Li/Na/K-Ion Batteries

Increasing demand for rechargeable batteries necessitates improvements in electrochemical performance. Traditional optimal approaches such as elemental doping and surface modification are insufficient for practical applications of the batteries. High-entropy materials (HEMs) possess stable solid-state phases and unparalleled flexibility in composition and electronic structure, which facilitate rapid advancements in battery materials. This review demonstrates the properties of HEMs both qualitatively and quantitatively, and the mechanisms of their enhancement on battery properties. It also illustrates the progress in high-entropy layered oxide cathode materials (HELOs) for lithium/sodium/potassium ion batteries (LIBs/SIBs/PIBs) in the perspectives of synthesis, characterization and application, and elucidating the synthesis-structure-property relationship. Furthermore, it outlines future directions for high-entropy strategies in battery study: precise synthesis control, understanding of reaction mechanisms through structural characterization, elucidation of structure-performance correlations, and the computational and experimental methods integration for rapid screening and analysis of HEMs. The perspective aims to inspire researchers in the development of high-performance rechargeable batteries.

High-Entropy and Na-Rich-Designed High-Energy-Density Na3V2(PO4)3/C Cathode

The Na3V2(PO4)3 (NVP) cathode holds the merit of a stable 3D NASICON structure for ultrafast Na+ diffusion, yet it is still confronted with poor electronic conductivity (10-9 S cm-1) and insufficient energy density (∼370 W h kg-1). Herein, a series of high-entropy-doped Na3+xV1.76-xZnx(GaCrAlIn)0.06(PO4)3 (x = 0, 0.2, 0.35, and 0.5) cathodes are systematically prepared with an activated V5+⇌V4+ high-voltage plateau (4.0 V) and elevated discharge capacity, which is derived from the charge compensation of divalent Zn substituting for trivalent V accompanied by extra Na+ input to create an Na-rich phase. A range of in situ/ex situ characterization studies and DFT calculations radically verify the charge conservation mechanism, enhanced bulk conductivity, and robust structural stability. Accordingly, in half-cells, the optimized cathode (x = 0.35) is capable of giving a much-improved discharge capacity (126.8 mA h g-1), reliable cycling stability (97.4%@5000 cycles@40 C), and a competitive energy density (426.1 W h kg-1) at 2.0-4.3 V. Upon reducing the discharge cutoff voltage to 1.4 V, the three-electron reaction (V5+⇌V2+) is entirely activated with superior stability, delivering an unparalleled capacity of 193.4 mA h g-1 with higher energy density (544.3 W h kg-1). Besides, it displays high capacity (126.1 mA h g-1) and energy density (417.2 W h kg-1) in NVPZGCAI-35//hard carbon full-cells at 1.6-4.1 V. Hence, this pioneering high-entropy and Na-rich strategy is above rubies for developing high-energy-density and high-stability sodium-ion batteries.

High-Entropy Layered Oxide Cathode Materials with Moderated Interlayer Spacing and Enhanced Kinetics for Sodium-Ion Batteries

Sodium-ion batteries (SIBs) with low cost and environmentally friendly features have recently attracted significant attention for renewable energy storage. Sodium layer oxides stand out as a type of promising cathode material for SIBs owing to their high capacity, good rate performance, and high compatibility for manufacturing. However, the poor cycling stability of layer oxide cathodes due to structure distortion greatly impacts their practical applications. Herein, a high entropy doped Cu, Fe, and Mn-based layered oxide (HE-CFMO), Na0.95Li0.05Mg0.05Cu0.20Fe0.22Mn0.35Ti0.13O2 for high-performance SIBs, is designed. The HE-CFMO cathode possesses high-entropy transition metal (TM) layers with a homogeneous stress distribution, providing a moderated interlayer spacing to maintain the structure stability and enhance Na+ ion diffusion. In addition, Li doping in TM layers increases the Mn valence state, which effectively suppresses John-Teller effect, thus stabilizing the layered structure during cycling. Furthermore, the use of nontoxic and low-cost raw materials benefits future commercialization and reduces the risk of environmental pollution. As a result, the HE-CFMO cathode exhibits a super cycling performance with a 95% capacity retention after 300 cycles. This work provides a promising strategy to improve the structure stability and reaction kinetics of cathode materials for SIBs.

Synergistic Catalytic Sites in High-Entropy Metal Hydroxide Organic Framework for Oxygen Evolution Reaction

The integration of multiple elements in a high-entropy state is crucial in the design of high-performance, durable electrocatalysts. High-entropy metal hydroxide organic frameworks (HE-MHOFs) are synthesized under mild solvothermal conditions. This novel crystalline metal-organic framework (MOF) features a random, homogeneous distribution of cations within high-entropy hydroxide layers. HE-MHOF exhibits excellent electrocatalytic performance for the oxygen evolution reaction (OER), reaching a current density of 100 mA cm-2 at ≈1.64 VRHE, and demonstrates remarkable durability, maintaining a current density of 10 mA cm-2 for over 100 h. Notably, HE-MHOF outperforms precious metal-based electrocatalysts despite containing only ≈60% OER active metals. Ab initio calculations and operando X-ray absorption spectroscopy (XAS) demonstrate that the high-entropy catalyst contains active sites that facilitate a multifaceted OER mechanism. This study highlights the benefits of high-entropy MOFs in developing noble metal-free electrocatalysts, reducing reliance on precious metals, lowering metal loading (especially for Ni, Co, and Mn), and ultimately reducing costs for sustainable water electrolysis technologies.

Full Exploitation of Charge Compensation of O3-type Cathode Toward High Energy Sodium-Ion Batteries by High Entropy Strategy

O3-type cathodes with sufficient Na content are considered as promising candidates for sodium-ion batteries (SIBs). However, these cathodes suffer from insufficient utilization of the active elements, restraining the delivered capacity. In this work, a high entropy strategy is applied to a typical O3 cathode NaLi0.1Ni0.35Mn0.55O2 (NLNM), forming a high entropy oxide NaLi0.1Ni0.15Cu0.1Mg0.1Ti0.2Mn0.35O2 (Na-HE). Results show that the active elements are fully exploited in Na-HE, with a two-electron reaction by Ni2+/4+ (further extended to Cu redox and even oxygen redox), vastly different from a one-electron reaction of Ni2+/3+ in NLNM. The full utilization of the active elements dramatically improves the output capacity of the cathode (122.6 mAh g-1 of Na-HE versus 81 mAh g-1 of NLNM). Moreover, the detrimental phase transition is well suppressed in Na-HE. The cathode exhibits high capacity retention of 88.7% after 100 cycles at 130 mA g-1, compared to only 36.4% for NLNM. These findings provide new insight for the design of new cathode materials for SIBs with high energy density and robust stability.

Near-zero-waste processing of jarosite waste to achieve sustainability: A state-of-the-art review

Jarosite waste is a by-product generated from iron removal process in the jarosite process, which typically contains valuable metals including zinc, nickel, cobalt, silver, indium, and lead. Due to the large amount of jarosite and the less efficient and costly methods of recovering residual metals, it is mainly disposed by landfills. However, leachate generated from the landfills can release high concentrations of heavy metals, which contaminate nearby water resources and pose environmental and health risks. In this review, the environmental and resource properties of jarosite waste were briefly summarized. Then those pyrometallurgical, hydrometallurgical and biological methods were discussed. In this review, considering the polymetallic properties and the low content of valuable metal elements of the jarosite waste, it is indicated that these processes had their own benefits and drawbacks such as overall yield, economic and technical constraints, and the necessity for combined processes to recycle multiple metal ions from jarosite wastes. Finally, this paper provided a critical and systematic review of studies on the novel green recycling technology for metals and material preparation based on the jarosite waste. This review can lay a guidance for the near-zero-waste processing of jarosite waste, with a particular focus on the combination of chemical and biological processes and waste-to-materials.

High-Entropy Metal-Organic Frameworks (HEMOFs): A New Frontier in Materials Design for CO2 Utilization

High-entropy materials (HEMs) emerged as promising candidates for a diverse array of chemical transformations, including CO2 utilization. However, traditional HEMs catalysts are nonporous, limiting their activity to surface sites. Designing HEMs with intrinsic porosity can open the door toward enhanced reactivity while maintaining the many benefits of high configurational entropy. Here, a synergistic experimental, analytical, and theoretical approach to design the first high-entropy metal-organic frameworks (HEMOFs) derived from polynuclear metal clusters is implemented, a novel class of porous HEMs that is highly active for CO2 fixation under mild conditions and short reaction times, outperforming existing heterogeneous catalysts. HEMOFs with up to 15 distinct metals are synthesized (the highest number of metals ever incorporated into a single MOF) and, for the first time, homogenous metal mixing within individual clusters is directly observed via high-resolution scanning transmission electron microscopy. Importantly, density functional theory studies provide unprecedented insight into the electronic structures of HEMOFs, demonstrating that the density of states in heterometallic clusters is highly sensitive to metal composition. This work dramatically advances HEMOF materials design, paving the way for further exploration of HEMs and offers new avenues for the development of multifunctional materials with tailored properties for a wide range of applications.

Highly Crystalline Multivariate Prussian Blue Analogs via Equilibrium Chelation Strategy for Stable and Fast Charging Sodium-Ion Batteries

Prussian blue analogs (PBAs) have been widely recognized as superior cathode materials for sodium-ion batteries (SIBs) owing to numerous merits. However, originating from the rapid crystal growth, PBAs still suffer from considerable vacancy defects and interstitial water, making the preparation of long-cycle-life PBAs the greatest challenge for its practical application. Herein, a novel equilibrium chelation strategy is first proposed to synthesize a high crystallinity (94.7%) PBAs, which is realized by modulating the chelating potency of strong chelating agents via "acid effect" to achieve a moderate chelating effect, forcefully breaking through the bottleneck of poor cyclic stability for PBAs cathodes. Impressively, the as-prepared highly crystalline PBAs represent an unprecedented level of electrochemical performance including ultra-long lifespan (10000 cycles with 86.32% capacity maintenance at 6 A g-1), excellent rate capability (82.0 mAh g-1 at 6 A g-1). Meanwhile, by pairing with commercial hard carbon, the as-prepared PBAs-based SIBs exhibit high energy density (350 Wh kg-1) and excellent capacity retention (82.4% after 1500 cycles), highlighting its promising potential for large-scale energy storage applications.

Stabilizing Layered Cathodes by High-Entropy Doping

Layered Ni-rich oxide cathodes in lithium-ion batteries (LIBs) often struggle with poor thermal safety and capacity fade. Xin and colleagues' studies in Nature and Nature Energy demonstrate a novel high-entropy (compositionally complex) doping strategy, introducing "cocktail effects" from multiple constituents. This approach substantially improves cycling performance and stability, reduces material cost, and may pave the way toward the development of advanced electrodes for next-generation LIBs.

Unveiling the Microscopic Origin of Ultrahigh Initial Coulombic Efficiency of High-Entropy Metal-Organic Frameworks for Sodium Storage

The initial irreversible capacity loss during the first charging process largely reduces the affordable energy and power density of sodium storage devices, and developing advanced materials is the efficient way to solve this problem, which is fraught with challenges. Herein, inspired by theoretical calculations and the high-entropy concept, a series of fewer layers of high-entropy metal-organic frameworks (FLHE-MOFs) are successfully fabricated, delivering an ultrahigh initial Coulombic efficiency (ICE) of 86.1% and excellent cycling performance, which is far more than that of the other electrode materials (generally <70%). Greatly, the storage behavior of high-, medium-, and low-entropy MOFs is clarified by theoretical calculations and in-/ex-situ characterization, revealing that Co and Fe species can provide substantial sodium storage sites and largely enhance the charge transfer rate, whereas high-entropy effect can enable structural reversibility. Sodium ion capacitors constructed with FLHE-MOFs as the anode can provide an ultrahigh energy density of 121.8 W h kg-1 (200 W kg-1) and an extremely long-term cycle lifespan. This work not only breaks the limitation of MOF materials with poor performance for sodium storage but also provides an effective strategy for the fabrication and application of high-performance MOF-based anode materials with high ICE, in which this idea may also be applied in other fields.

Confined Element Distribution with Structure-Driven Energy Coupling for Enhanced Prussian Blue Analogue Cathode

The structural failure of Na2Mn[Fe(CN)6] could not be alleviated with traditional modification strategies through the adjustable composition property of Prussian blue analogues (PBAs), considering that the accumulation and release of stress derived from the MnN6 octahedrons are unilaterally restrained. Herein, a novel application of adjustable composition property, through constructing a coordination competition relationship between chelators and [Fe(CN)6]4- to directionally tune the enrichment of elements, is proposed to restrain structural degradation and induce unconventional energy coupling phenomenon. The non-uniform distribution of elements at the M1 site of PBAs (NFM-PB) is manipulated by the sequentially precipitated Ni, Fe, and Mn according to the Irving-William order. Electrochemically active Fe is operated to accompany Mn, and zero-strain Ni is modulated to enrich at the surface, synergistically mitigating with the enrichment and release of stress and then significantly improving the structural stability. Furthermore, unconventional energy coupling effect, a fusion of the electrochemical behavior between FeLS and MnHS, is triggered by the confined element distribution, leading to the enhanced electrochemical stability and anti-polarization ability. Consequently, the NFM-PB demonstrates superior rate performance and cycling stability. These findings further exploit potentialities of the adjustable composition property and provide new insights into the component design engineering for advanced PBAs.

High-Entropy Electrode Materials: Synthesis, Properties and Outlook

High-entropy materials represent a new category of high-performance materials, first proposed in 2004 and extensively investigated by researchers over the past two decades. The definition of high-entropy materials has continuously evolved. In the last ten years, the discovery of an increasing number of high-entropy materials has led to significant advancements in their utilization in energy storage, electrocatalysis, and related domains, accompanied by a rise in techniques for fabricating high-entropy electrode materials. Recently, the research emphasis has shifted from solely improving the performance of high-entropy materials toward exploring their reaction mechanisms and adopting cleaner preparation approaches. However, the current definition of high-entropy materials remains relatively vague, and the preparation method of high-entropy materials is based on the preparation method of single metal/low- or medium-entropy materials. It should be noted that not all methods applicable to single metal/low- or medium-entropy materials can be directly applied to high-entropy materials. In this review, the definition and development of high-entropy materials are briefly reviewed. Subsequently, the classification of high-entropy electrode materials is presented, followed by a discussion of their applications in energy storage and catalysis from the perspective of synthesis methods. Finally, an evaluation of the advantages and disadvantages of various synthesis methods in the production process of different high-entropy materials is provided, along with a proposal for potential future development directions for high-entropy materials.

High-Entropy and Component Stoichiometry Tuning Strategies Boost the Sodium-Ion Storage Performance of Cobalt-Free Prussian Blue Analogues Cathode Materials

Prussian blue analogs (PBAs) are appealing cathode materials for sodium-ion batteries because of their low material cost, facile synthesis methods, rigid open framework, and high theoretical capacity. However, the poor electrical conductivity, unavoidable presence of [Fe(CN)6] vacancies and crystalline water within the framework, and phase transition during charge-discharge result in inferior electrochemical performance, particularly in terms of rate capability and cycling stability. Here, cobalt-free PBAs are synthesized using a facile and economic co-precipitation method at room temperature, and their sodium-ion storage performance is boosted due to the reduced crystalline water content and improved electrical conductivity via the high-entropy and component stoichiometry tuning strategies, leading to enhanced initial Coulombic efficiency (ICE), specific capacity, cycling stability, and rate capability. The optimized HE-HCF of Fe0.60Mn0.10-hexacyanoferrate (referred to as Fe0.60Mn0.10-HCF), with the chemical formula Na1.156Fe0.599Mn0.095Ni0.092Cu0.109Zn0.105 [Fe(CN)6]0.724·3.11H2O, displays the most appealing electrochemical performance of an ICE of 100%, a specific capacity of around 115 and 90 mAh·g-1 at 0.1 and 1.0 A·g-1, with 66.7% capacity retention observed after 1000 cycles and around 61.4% capacity retention with a 40-fold increase in specific current. We expect that our findings could provide reference strategies for the design of SIB cathode materials with superior electrochemical performance.

Leveraging Entropy and Crystal Structure Engineering in Prussian Blue Analogue Cathodes for Advancing Sodium-Ion Batteries

The synergistic engineering of chemical complexity and crystal structures has been applied to Prussian blue analogue (PBA) cathodes in this work. More precisely, the high-entropy concept has been successfully introduced into two structure types of identical composition, namely, cubic and monoclinic. Through the utilization of a variety of complementary characterization techniques, a comprehensive investigation into the electrochemical behavior of the cubic and monoclinic PBAs has been conducted, providing nuanced insights. The implementation of the high-entropy concept exhibits crucial selectivity toward the intrinsic crystal structure. Specifically, while the overall cycling stability of both cathode systems is significantly improved, the synergistic interplay of crystal structure engineering and entropy proves particularly significant. After optimization, the cubic PBA demonstrates structural advantages, showcasing good reversibility, minimal capacity loss, high thermal stability, and unparalleled endurance even under harsh conditions (high specific current and temperature).

General synthesis of high-entropy single-atom nanocages for electrosynthesis of ammonia from nitrate

Given the growing emphasis on energy efficiency, environmental sustainability, and agricultural demand, there's a pressing need for decentralized and scalable ammonia production. Converting nitrate ions electrochemically, which are commonly found in industrial wastewater and polluted groundwater, into ammonia offers a viable approach for both wastewater treatment and ammonia production yet limited by low producibility and scalability. Here we report a versatile and scalable solution-phase synthesis of high-entropy single-atom nanocages (HESA NCs) in which Fe and other five metals-Co, Cu, Zn, Cd, and In-are isolated via cyano-bridges and coordinated with C and N, respectively. Incorporating and isolating the five metals into the matrix of Fe resulted in Fe-C5 active sites with a minimized symmetry of lattice as well as facilitated water dissociation and thus hydrogenation process. As a result, the Fe-HESA NCs exhibited a high selectivity toward NH3 from the electrocatalytic reduction of nitrate with a Faradaic efficiency of 93.4% while maintaining a high yield rate of 81.4 mg h-1 mg-1.

Element Screening of High-Entropy Silicon Anodes for Superior Li-Storage Performance of Li-Ion Batteries

The high-entropy silicon anodes are attractive for enhancing electronic and Li-ionic conductivity while mitigating volume effects for advanced Li-ion batteries (LIBs), but are plagued by the complicated elements screening process. Inspired by the resemblances in the structure between sphalerite and diamond, we have selected sphalerite-structured SiP with metallic conductivity as the parent phase for exploring the element screening of high-entropy silicon-based anodes. The inclusion of the Zn in the sphalerite structure is crucial for improving the structural stability and Li-storage capacity. Within the same group, Li-storage performance is significantly improved with increasing atomic number in the order of BZnSiP3 < AlZnSiP3 < GaZnSiP3 < InZnSiP3. Thus, InZnSiP3-based electrodes achieved a high capacity of 719 mA h g-1 even after 1,500 cycles at 2,000 mA g-1, and a high-rate capacity of 725 mA h g-1 at 10,000 mA g-1, owing to its superior lithium-ion affinity, faster electronic conduction and lithium-ion diffusion, higher Li-storage capacity and reversibility, and mechanical integrity than others. Additionally, the incorporation of elements with larger atomic sizes leads to greater lattice distortion and more defects, further facilitating mass and charge transport. Following these screening rules, high-entropy disordered-cation silicon-based compounds such as GaCuSnInZnSiP6, GaCu(or Sn)InZnSiP5, and CuSnInZnSiP5, as well as high-entropy compounds with mixed-cation and -anion compositions, such as InZnSiPSeTe and InZnSiP2Se(or Te), are synthesized, demonstrating improved Li-storage performance with metallic conductivity. The phase formation mechanism of these compounds is attributed to the negative formation energies arising from elevated entropy.

Prussian Blue Analogues for Sodium-Ion Battery Cathodes: A Review of Mechanistic Insights, Current Challenges, and Future Pathways

Prussian blue analogues (PBAs) have emerged as highly promising cathode materials for sodium-ion batteries (SIBs) due to their affordability, facile synthesis, porous framework, and high theoretical capacity. Despite their considerable potential, practical applications of PBAs face significant challenges that limit their performance. This review offers a comprehensive retrospective analysis of PBAs' development history as cathode materials, delving into their reaction mechanisms, including charge compensation and ion diffusion mechanisms. Furthermore, to overcome these challenges, a range of improvement strategies are proposed, encompassing modifications in synthesis techniques and enhancements in structural stability. Finally, the commercial viability of PBAs is examined, alongside discussions on advanced synthesis methods and existing concerns regarding cost and safety, aiming to foster ongoing advancements of PBAs for practical SIBs.

Inhibiting the Jahn-Teller Effect of Manganese Hexacyanoferrate via Ni and Cu Codoping for Advanced Sodium-Ion Batteries

Manganese (Mn)-based Prussian blue analogs (PBAs) are of great interest as a prospective cathode material for sodium-ion batteries (SIBs) due to their high redox potential, easy synthesis, and low cost. However, the Jahn-Teller effect and low electrical conductivity of Mn-based PBA cause poor structure stability and unsatisfactory performance during the cycling. Herein, a novel nickel- and copper-codoped K2Mn[Fe(CN)6] cathode is developed via a simple coprecipitation strategy. The doping elements improve the electrical conductivity of Mn-based PBA by reducing the bandgap, as well as suppress the Jahn-Teller effect by stabilizing the framework, as verified by the density functional theory calculations. Simultaneously, the substitution of sodium with potassium in the lattice is beneficial for filling vacancies in the PBA framework, leading to higher average operating voltages and superior structural stability. As a result, the as-prepared Mn-based cathode exhibits excellent reversible capacity (116.0 mAh g-1 at 0.01 A g-1) and superior cycling stability (81.8% capacity retention over 500 cycles at 0.1 A g-1). This work provides a profitable doping strategy to inhibit the Jahn-Teller structural deformation for designing stable cathode material of SIBs.

Interlayer Entropy Engineering Inducing the Symmetry-Broken Layered Oxide Cathodes to Activate Reversible High-Voltage Redox Reaction

The as-reported doping entropy engineering of electrode materials that are usually realized by the sharing of multiple metal elements with the metal element from the lattice body, potentially has three shortages of stringent synthesis conditions, large active element loss, and serious lattice distortion. Herein, an interlayer entropy engineering of layered oxide cathodes is proposed, where the multiple metal ions are simultaneously intercalated into the same interlayer sites, thus avoiding the three shortages. Concretely, a novel interlayer medium-entropy V2O5 ((MnCoNiMgZn)0.26V2O5∙0.84H2O) is successfully constructed by a one-step hydrothermal method. The interlayer medium-entropy effect is revealed to be that five metal ions pre-intercalation induces the local symmetry-broken [VO6] octahedra in bilayer V2O5, thus activating the reversible high-voltage redox reaction, inhibiting the layer slip and following phase transformation by its pinning effect, and enhancing the charge transfer kinetics. As a result, the medium-entropy cathode realizes the trade-off between specific capacity and structural stability with a discharge capacity of 152 mAh g-1 at 0.1 A g-1 after 100 cycles, and a capacity retention rate of 98.7% at 0.5 A g-1 after 150 cycles for Li+ storage. This engineering provides a new guideline for the rational design of high-performance layered oxide cathodes.

High-Entropy Lanthanide-Organic Framework as an Efficient Heterogeneous Catalyst for Cycloaddition of CO2 with Epoxides and Knoevenagel Condensation

Multimetallic synergistic effects have the potential to improve CO2 cycloesterification and Knoevenagel reaction processes, outperforming monometallic MOFs. The results demonstrate superior performance in these processes. To investigate this, we created and characterized a selection of single-component Ln(III)-MOFs (Ln=Eu, Tb, Gd, Dy, Ho) and high-entropy lanthanide-organic framework (HE-LnMOF) using solvent-thermal conditions. The experiments revealed that HE-LnMOF exhibited heightened catalytic efficiency in CO2 cycloesterification and Knoevenagel reactions compared to single-component Ln(III) MOFs. Moreover, the HE-LnMOF displayed significant stability, maintaining their structural integrity after five cycles while sustaining elevated conversion and selectivity rates. The feasible mechanisms of catalytic reactions were also discussed. HE-LnMOF possess multiple unsaturated metal centers, acting as Lewis acid sites, with oxygen atoms connecting the metal, and hydroxyl groups on the ligand serving as base sites. This study introduces a novel method for synthesizing HE-LnMOF and presents a fresh application of HE-LnMOF for converting CO2.

High-Entropy Prussian Blue Analogues Enable Lattice Respiration for Ultrastable Aqueous Aluminum-Ion Batteries

Aqueous aluminum ion batteries (AAIBs) hold significant potential for grid-scale energy storage owing to their intrinsic safety, high theoretical capacity, and abundance of aluminum. However, the strong electrostatic interactions and delayed charge compensation between high-charge-density aluminum ions and the fixed lattice in conventional cathodes impede the development of high-performance AAIBs. To address this issue, this work introduces, for the first time, high-entropy Prussian blue analogs (HEPBAs) as cathodes in AAIBs with unique lattice tolerance and efficient multipath electron transfer. Benefiting from the intrinsic long-range disorder and robust lattice strain field, HEPBAs enable the manifestation of the lattice respiration effect and minimize lattice volume changes, thereby achieving one of the best long-term stabilities (91.2% capacity retention after 10 000 cycles at 5.0 A g-1) in AAIBs. Additionally, the interaction between the diverse metal atoms generates a broadened d-band and reduced degeneracy compared with conventional Prussian blue and its analogs (PBAs), which enhances the electron transfer efficiency with one of the best rate performance (79.2 mAh g-1 at 5.0 A g-1) in AAIBs. Furthermore, exceptional element selectivity in HEPBAs with unique cocktail effect can facile tune electrochemical behavior. Overall, the newly developed HEPBAs with a high-entropy effect exhibit promising solutions for advancing AAIBs and multivalent-ion batteries.

Entropy Engineering Constrain Phase Transitions Enable Ultralong-life Prussian Blue Analogs Cathodes

Prussian blue analogs (PBAs) are considered as one of the most potential electrode materials in capacitive deionization (CDI) due to their unique 3D framework structure. However, their practical applications suffer from low desalination capacity and poor cyclic stability. Here, an entropy engineering strategy is proposed that incorporates high-entropy (HE) concept into PBAs to address the unfavorable multistage phase transitions during CDI desalination. By introducing five or more metals, which share N coordination site, high-entropy hexacyanoferrate (HE-HCF) is constructed, thereby increasing the configurational entropy of the system to above 1.5R and placing it into the high-entropy category. As a result, the developed HE-HCF demonstrates remarkable cycling performance, with a capacity retention rate of over 97% after undergoing 350 ultralong-life cycles of adsorption/desorption. Additionally, it exhibits a high desalination capacity of 77.24 mg g-1 at 1.2 V. Structural characterization and theoretical calculation reveal that high configurational entropy not only helps to restrain phase transition and strengthen structural stability, but also optimizes Na+ ions diffusion path and energy barrier, accelerates reaction kinetics and thus improves performance. This research introduces a new approach for designing electrodes with high performance, low cost, and long-lasting durability for capacitive deionization applications.

Revealing the Nature of Binary-Phase on Structural Stability of Sodium Layered Oxide Cathodes

The emergence of layered sodium transition metal oxides featuring a multiphase structure presents a promising approach for cathode materials in sodium-ion batteries, showcasing notably improved energy storage capacity. However, the advancement of cathodes with multiphase structures faces obstacles due to the limited understanding of the integrated structural effects. Herein, the integrated structural effects by an in-depth structure-chemistry analysis in the developed layered cathode system NaxCu0.1Co0.1Ni0.25Mn0.4Ti0.15O2 with purposely designed P2/O3 phase integration, are comprehended. The results affirm that integrated phase ratio plays a pivotal role in electrochemical/structural stability, particularly at high voltage and with the incorporation of anionic redox. In contrast to previous reports advocating solely for the enhanced electrochemical performance in biphasic structures, it is demonstrated that an inappropriate composite structure is more destructive than a single-phase design. The in situ X-ray diffraction results, coupled with density functional theory computations further confirm that the biphasic structure with P2:O3 = 4:6 shows suppressed irreversible phase transition at high desodiated states and thus exhibits optimized electrochemical performance. These fundamental discoveries provide clues to the design of high-performance layered oxide cathodes for next-generation SIBs.

Emerging high voltage V4+/V5+ redox reactions in Na3V2(PO4)3-based cathodes for sodium-ion batteries

Na3V2(PO4)3 (NVP) cathode materials with the advantages of long cycle life and superior thermal stability have been considered promising cathode candidates for SIBs. However, the unsatisfactory energy density derived from low theoretical capacity and operating voltage (3.35 V vs. Na+/Na, based on the V3+/V4+ redox couple) inevitably limits their practical application. Therefore, the activation of the V4+/V5+ redox couple (∼4.0 V vs. Na+/Na) in NVP-based cathode materials to boost the energy density of SIBs has attracted extensive attention. Herein, we first analyze the challenges of activation of the V4+/V5+ redox couple in NVP-based cathode materials. Subsequently, the recent achievement of NVP-based cathode materials with activated V4+/V5+ redox reactions for SIBs is overviewed. Finally, further research directions of high voltage V4+/V5+ redox reactions in NVP-based cathodes are proposed. This review provides valuable guidance for developing high energy density NVP-based cathode materials for SIBs.

Toward Ultrahigh Rate and Cycling Performance of Cathode Materials of Sodium Ion Battery by Introducing a Bicontinuous Porous Structure

The emerging sodium-ion batteries (SIBs) are one of the most promising candidates expected to complement lithium-ion batteries and diversify the battery market. However, the exploitation of cathode materials with high-rate performance and long-cycle stability for SIBs has remained one of the major challenges. To this end, an efficient approach to enhance rate and cycling performance by introducing an ordered bicontinuous porous structure into cathode materials of SIBs is demonstrated. Prussian blue analogues (PBAs) are selected because they are recognized as a type of most promising SIB cathode materials. Thanks to the presence of 3D continuous channels enabling fast Na+ ions diffusion as well as the intrinsic mechanical stability of bicontinuous architecture, the resultant PBAs exhibit excellent rate capability (80 mAh g-1 at 2.5 A g-1) and ultralong cycling life (>3000 circulations at 0.5 A g-1), reaching the top performance of the reported PBA-based cathode materials. This study opens a new avenue for boosting sluggish ion diffusion kinetics in electrodes of rechargeable batteries and also provides a new paradigm for solving the dilemma that electrodes' failure due to high-stress concentration upon ion storage.

Achieving Fast and Stable Sodium Storage in Na4Fe3(PO4)2(P2O7) via Entropy Engineering

Na4Fe3(PO4)2(P2O7) (NFPP) has been considered a promising cathode material for sodium-ion batteries (SIBs) owing to its environmental friendliness and economic viability. However, its electrochemical performance is constrained by connatural low electronic conductivity and inadequate sodium ion diffusion. Herein, a high-entropy substitution strategy is employed in NFPP to address these limitations. Ex situ X-ray diffraction analysis reveals a single-phase electrochemical reaction during the sodiation/desodiation processes and the increased configurational entropy in HE-NFPP endows an enhanced structure, which results in a minimal volume variation of only 1.83%. Kinetic analysis and density functional theory calculation further confirm that the orbital hybrid synergy of high-entropy transition metals offers a favorable electronic structure, which efficaciously boosts the charge transfer kinetics and optimizes the sodium ion diffusion channel. Based on this versatile strategy, the as-prepared high-entropy Na4Fe2.5Mn0.1Mg0.1Co0.1Ni0.1Cu0.1(PO4)2(P2O7) (HE-NFPP) cathode can deliver a prominent rate performance of 55 mAh g-1 at 10 A g-1 and an ultra-long cycling lifespan of over 18 000 cycles at 5 A g-1. When paired with a hard carbon (HC) anode, HE-NFPP//HC full cell exhibits a favorable cycling durability of 1000 cycles. This high-entropy engineering offers a feasible route to improve the electrochemical performance of NFPP and provides a blueprint for exploring high-performance SIBs.

A High-Entropy Prussian Blue Analog for Aqueous Potassium-Ion Batteries

Aqueous potassium-ion batteries (AKIBs) are considered promising electrochemical energy storage systems owing to their high safety and cost-effectiveness. However, the structural degradation resulting from the repeated accommodation of large K-ions and the dissolution of active electrode materials in highly dielectric aqueous electrolytes often lead to unsatisfactory electrochemical performance. This study introduces a high-entropy Prussian blue analog (HEPBA) cathode material for AKIBs, demonstrating significantly enhanced structural stability and reduced dissolution. The HEPBA exhibits a highly reversible specific capacity of 102.4 mAh g-1, with 84.4% capacity retention after undergoing 3448 cycles over a duration of 270 days. Mechanistic insights derived from comprehensive experimental investigations, supported by theoretical calculations, reveal that the HEPBA features a robust structure resistant to dissolution, a solid-solution reaction pathway with negligible volume variation during charge-discharge, and efficient ion transport kinetics characterized by a reduced band gap and a low energy barrier. This study represents a measurable step forward in the development of long-lasting electrode materials for aqueous AKIBs.

Hollow Stair-Stepping Spherical High-Entropy Prussian Blue Analogue for High-Rate Sodium Ion Batteries

Prussian blue analogues (PBAs) are considered to be one of the most suitable sodium storage materials, especially with the introduction of the high-entropy (HE) concept into their structure to further improve their various abilities. However, severe agglomeration of the HEPBA particles still limits the fast charging capabilities. Here, an HEPBA (Nax(FeMnCoNiCu)[Fe(CN)6]y□1-y·nH2O) with a hollow stair-stepping spherical structure has been prepared through the chemical etching process of the traditional cubic structure of HEPBA. Electrochemical characterization (sodium ion battery), kinetic analysis, and COMSOL Multiphysics simulations reveal that the nature of the high-entropy and the hollow stair-stepping spherical structure can greatly improve the diffusion behavior of Na+ ions. Moreover, the hollow structure effectively mitigates the volume change of HEPBA during SIBs operation, ultimately extending the lifespan. Consequently, the as-prepared HEPBA cathode exhibits excellent rate performance (126.5 and 76.4 mAh g-1 at 0.1 and 4.0 A g-1, respectively) and stable long-term capability (maintaining its 75.6% capacity after 1000 cycles) due to its unique structure. Furthermore, the waste of the etching process can easily be recycled to prepare more HEPBA product. This processing method holds great promise for designing nanostructures of advanced high-entropy Prussian blue analogues for sodium ion batteries.