Enhanced sodium storage kinetics by volume regulation and surface engineering via rationally designed hierarchical porous FeP@C/rGO

Advanced 3D-Printed Potassium Ammonium Vanadate/rGO Aerogel Cathodes for Durable and High-Capacity Potassium-Ion Batteries

A 3D-printed oxygen-vacancy-rich potassium ammonium vanadate/reduced graphene oxide (KNVOv/rGO) microlattice aerogel is designed for the cathode in high-performance K-ion batteries (KIBs). The 3D-printed KNVOv/rGO electrode with periodic submillimeter microchannels and interconnected printed filaments is composed of highly dispersed KNVOv nanobelts, wrinkled graphene nanoflakes, and abundant micropores. The well-defined 3D porous microlattice structure of the rGO backbone not only provides the interconnected conductive 3D network and the required mechanical robustness but also facilitates the penetration of the liquid electrolyte into inner active sites, consequently ensuring a stable electrochemical environment for K-ion intercalation/deintercalation within the KNVOv nanobelts. The 3D-printed KNVOv/rGO microlattice aerogel electrode has a high discharge capacity of 109.3 mAh g-1 with a capacity retention rate of 92.6% after 200 cycles at 50 mA g-1 and maintains a discharge capacity of 75.8 mAh g-1 after 2000 cycles at 500 mA g-1. The flexible pouch-type KIB battery consisting of the 3D-printed KNVOv/rGO has good mechanical durability and retains a high specific capacity under different forms of deformation such as bending and folding. The results provide valuable insights into the integration of advanced 3D-printed electrode materials into K-ion batteries and the design of flexible and wearable energy storage devices.

Vacancies-Induced Delocalized States Cobalt Phosphide for Binder-Free Anode Toward Stable and High-Rate Sodium-Ion Batteries

Metal phosphides with easy synthesis, controllable morphology, and high capacity are considered as potential anodes for sodium-ion batteries (SIBs). However, the inherent shortcomings of metal phosphating materials, such as conductivity, kinetics, volume strain, etc are not satisfactory, which hinders their large-scale application. Here, a CoP@carbon nanofibers-composite containing rich Co─N─C heterointerface and phosphorus vacancies grown on carbon cloth (CoP1-x@MEC) is synthesized as SIB anode to accomplish extraordinary capacity and ultra-long cycle life. The hybrid composite nanoreactor effectively impregnates defective CoP as active reaction center while offering Co─N─C layer to buffer the volume expansion during charge-discharge process. These vast active interfaces, favored electrolyte infiltration, and a well-structured ion-electron transport network synergistically improve Na+ storage and electrode kinetics. By virtue of these superiorities, CoP1-x@MEC binder-free anode delivers superb SIBs performance including a high areal capacity (2.47 mAh cm-2@0.2 mA cm-2), high rate capability (0.443 mAh cm-2@6 mA cm-2), and long cycling stability (300 cycles without decay), thus holding great promise for inexpensive binder-free anode-based SIBs for practical applications.

Rational Construction of 3D Self-Supported MOF-Derived Cobalt Phosphide-Based Hollow Nanowall Arrays for Efficient Overall Water Splitting At large Current Density

Developing efficient nonprecious bifunctional electrocatalysts for hydrogen and oxygen evolution reactions (HER and OER) in the same electrolyte with a low overpotential and large current density presents an appealing yet challenging goal for large-scale water electrolysis. Herein, a unique 3D self-branched hierarchical nanostructure composed of ultra-small cobalt phosphide (CoP) nanoparticles embedded into N, P-codoped carbon nanotubes knitted hollow nanowall arrays (CoPʘNPCNTs HNWAs) on carbon textiles (CTs) through a carbonization-phosphatization process is presented. Benefiting from the uniform protrusion distributions of CoP nanoparticles, the optimum CoPʘNPCNTs HNWAs composites with high abundant porosity exhibit superior electrocatalytic activity and excellent stability for OER in alkaline conditions, as well as for HER in both acidic and alkaline electrolytes, even under large current densities. Furthermore, the assembled CoPʘNPCNTs/CTs||CoPʘNPCNTs/CTs electrolyzer demonstrates exceptional performance, requiring an ultralow cell voltage of 1.50 V to deliver the current density of 10 mA cm-2 for overall water splitting (OWS) with favorable stability, even achieving a large current density of 200 mA cm-2 at a low cell voltage of 1.78 V. Density functional theory (DFT) calculation further reveals that all the C atoms between N and P atoms in CoPʘNPCNTs/CTs act as the most efficient active sites, significantly enhancing the electrocatalytic properties. This strategy, utilizing 2D MOF arrays as a structural and compositional material to create multifunctional composites/hybrids, opens new avenues for the exploration of highly efficient and robust non-noble-metal catalysts for energy-conversion reactions.

Achieving high-capacity and durable sodium storage by constructing a binder-free nanotube array architecture of iron phosphide/carbon

The conversion-type anode material of iron phosphide (FeP) promises enormous prospects for Na-ion battery technology due to its high theoretical capacity and cost-effectiveness. However, the poor reaction kinetics and large volume expansion of FeP significantly degrade the sodium storage, which remains a daunting challenge. Herein, we demonstrate a binder-free nanotube array architecture constructed by FeP@C hybrid on carbon cloth as advanced anodes to achieve fast and stable sodium storage. The nanotubular structure functions in multiple roles of providing short electron/ion transport distances, smooth electrolyte diffusion channels, and abundant active sites. The carbon layer could not only pave high-speed pathways for electron conductance but also cushion the volume change of FeP. Benefiting from these structural virtues, the FeP@C anode receives a high reversible capacity of 881.7 mAh/g at 0.1 A/g, along with a high initial Coulombic efficiency of 90% and excellent rate capability and cyclability in half and full cells. Moreover, the sodium energy reaction kinetics and mechanism of FeP@C are systematically studied. The present work offers a rational design and construction of high-capacity anode materials for high-energy-density Na-ion batteries.

Metal Phosphide Anodes in Sodium-Ion Batteries: Latest Applications and Progress

Sodium-ion batteries (SIBs), as the next-generation high-performance electrochemical energy storage devices, have attracted widespread attention due to their cost-effectiveness and wide geographical distribution of sodium. As a crucial component of the structure of SIBs, the anode material plays a crucial role in determining its electrochemical performance. Significantly, metal phosphide exhibits remarkable application prospects as an anode material for SIBs because of its low redox potential and high theoretical capacity. However, due to volume expansion limitations and other factors, the rate and cycling performance of metal phosphides have gradually declined. To address these challenges, various viable solutions have been explored. In this paper, the recent research progress of metal phosphide materials for SIBs is systematically reviewed, including the synthesis strategy of metal phosphide, the storage mechanism of sodium ions, and the application of metal phosphide in electrochemical aspects. In addition, future challenges and opportunities based on current developments are presented.

Progress and perspectives on iron-based electrode materials for alkali metal-ion batteries: a critical review

Iron-based materials with significant physicochemical properties, including high theoretical capacity, low cost and mechanical and thermal stability, have attracted research attention as electrode materials for alkali metal-ion batteries (AMIBs). However, practical implementation of some iron-based materials is impeded by their poor conductivity, large volume change, and irreversible phase transition during electrochemical reactions. In this review we critically assess advances in the chemical synthesis and structural design, together with modification strategies, of iron-based compounds for AMIBs, to obviate these issues. We assess and categorize structural and compositional regulation and its effects on the working mechanisms and electrochemical performances of AMIBs. We establish insight into their applications and determine practical challenges in their development. We provide perspectives on future directions and likely outcomes. We conclude that for boosted electrochemical performance there is a need for better design of structures and compositions to increase ionic/electronic conductivity and the contact area between active materials and electrolytes and to obviate the large volume change and low conductivity. Findings will be of interest and benefit to researchers and manufacturers for sustainable development of advanced rechargeable ion batteries using iron-based electrode materials.

Metal-Organic Framework-Based Materials for Advanced Sodium Storage: Development and Anticipation

As a pioneering battery technology, even though sodium-ion batteries (SIBs) are safe, non-flammable, and capable of exhibiting better temperature endurance performance than lithium-ion batteries (LIBs), because of lower energy density and larger ionic size, they are not amicable for large-scale applications. Generally, the electrochemical storage performance of a secondary battery can be improved by monitoring the composition and morphology of electrode materials. Because more is the intricacy of a nanostructured composite electrode material, more electrochemical storage applications would be expected. Despite the conventional methods suitable for practical production, the synthesis of metal-organic frameworks (MOFs) would offer enormous opportunities for next-generation battery applications by delicately systematizing the structure and composition at the molecular level to store sodium ions with larger sizes compared with lithium ions. Here, the review comprehensively discusses the progress of nanostructured MOFs and their derivatives applied as negative and positive electrode materials for effective sodium storage in SIBs. The commercialization goal has prompted the development of MOFs and their derivatives as electrode materials, before which the synthesis and mechanism for MOF-based SIB electrodes with improved sodium storage performance are systematically discussed. Finally, the existing challenges, possible perspectives, and future opportunities will be anticipated.

Potassium-Rich Iron Hexacyanoferrate/Carbon Cloth Electrode for Flexible and Wearable Potassium-Ion Batteries

The fast development of flexible and wearable electronics increases the demand for flexible secondary batteries, and the emerging high-performance K-ion batteries (KIBs) have shown immense promise for the flexible electronics due to the abundant and cost-effective potassium resources. However, the implementation of flexible cathodes for KIBs is hampered by the critical issues of low capacity, rapid capacity decay with cycles, and limited initial Coulombic efficiency. To address these pressing issues, a freestanding K-rich iron hexacyanoferrate/carbon cloth (KFeHCF/CC) electrode is designed and fabricated by cathodic deposition. This innovative binder-free and self-supporting KFeHCF/CC electrode not only provides continuous conductive channels for electrons, but also accelerates the diffusion of potassium ions through the active electrode-electrolyte interface. Moreover, the nanosized potassium iron hexacyanoferrate particles limit particle fracture and pulverization to preserve the structure and stability during cycling. As a result, the K-rich KFeHCF/CC electrode shows a reversible discharging capacity of 110.1 mAh g-1 at 50 mA g-1 after 100 cycles in conjunction with capacity retention of 92.3% after 1000 cycles at 500 mA g-1 . To demonstrate the commercial feasibility, a flexible tubular KIB is assembled with the K-rich KFeHCF/CC electrode, and excellent flexibility, capacity, and stability are observed.

Ultrahigh areal capacity and long cycling stability of sodium metal anodes boosted using a 3D-printed sodiophilic MXene/rGO microlattice aerogel

Sodium metal has emerged as a highly promising anode material for sodium-based batteries, owing to its intrinsic advantages, including its high theoretical capacity, low working plateau and low cost. However, the uncontrolled formation of sodium dendrites accompanied by unrestricted volume expansion severely limits its application. To tackle these issues, we propose an approach to address these issues by adopting a three-dimensional (3D) structure of Ti3C2Tx/reduced graphene oxide (Ti3C2Tx/rGO) constructed by a direct-ink writing (DIW) 3D printing technique as the Na metal anode host electrode. The combination of the 3D-printed rGO skeleton offering artificial porous structures and the incorporation of sodiophilic Ti3C2Tx nanosheets provides abundant nucleation sites and promotes uniform sodium metal deposition. This specially designed architecture significantly enhances the Na metal cycling stability by effectively inhibiting dendrite formation. The experimental results show that the designed Ti3C2Tx/rGO electrode can achieve a high coulombic efficiency (CE) of 99.91% after 1800 cycles (3600 h) at 2 mA cm-2 with 2 mA h cm-2. Notably, the adopted electrodes exhibit a long life span of more than 1400 h with a high CE over 99.93% when measured with an ultra-high capacity of 50 mA h cm-2 at 5 mA cm-2. Furthermore, a 3D-printed full cell consisting of a Na@Ti3C2Tx/rGO anode and a 3D-printed Na3V2(PO4)3C-rGO (NVP@C-rGO) cathode was successfully demonstrated. This 3D-printed cell could provide a notable capacity of 85.3 mA h g-1 at 100 mA g-1 after 500 cycles. The exceptional electrochemical performance achieved by the 3D-printed full cell paves the way for the development of practical sodium metal anodes.

In Situ Transmission Electron Microscopy for Sodium-Ion Batteries

Sodium-ion batteries (SIBs) have attracted tremendous attentions in recent years due to the abundance and wide distribution of Na resource on the earth. However, SIBs still face the critical issues of low energy density and unsatisfactory cyclic stability at present. The enhancement of electrochemical performance of SIBs depends on comprehensive and precise understanding of the underlying sodium storage mechanism. Although extensive transmission electron microscopy (TEM) investigations have been performed to reveal the sodium storage property and mechanism of SIBs, a dedicated review on the in situ TEM investigations of SIBs has not been reported. In this review, recent progress in the in situ TEM investigations on the morphological, structural, and chemical evolutions of cathode materials, anode materials, and solid-electrolyte interface during the sodium storage of SIBs is comprehensively summarized. The detailed relationship between structure/composition of electrode materials and electrochemical performance of SIBs has been clarified. This review aims to provide insights into the effective selection and rational design of advanced electrode materials for high-performance SIBs.

Recent Advancement and Structural Engineering in Transition Metal Dichalcogenides for Alkali Metal Ions Batteries

Currently, transition metal dichalcogenides-based alkaline metal ion batteries have been extensively investigated for renewable energy applications to overcome the energy crisis and environmental pollution. The layered morphologys with a large surface area favors high electrochemical properties. Thermal stability, mechanical structural stability, and high conductivity are the primary features of layered transition metal dichalcogenides (L-TMDs). L-TMDs are used as battery materials and as supporters for other active materials. However, these materials still face aggregation, which reduces their applicability in batteries. In this review, a comprehensive study has been undertaken on recent advancements in L-TMDs-based materials, including 0D, 1D, 2D, 3D, and other carbon materials. Types of structural engineering, such as interlayer spacing, surface defects, phase control, heteroatom doping, and alloying, have been summarized. The synthetic strategy of structural engineering and its effects have been deeply discussed. Lithium- and sodium-ion battery applications have been summarized in this study. This is the first review article to summarize different morphology-based TMDs with their intrinsic properties for alkali metal ion batteries (AMIBs), so it is believed that this review article will improve overall knowledge of TMDs for AMIBS applications.

Phosphorus/Phosphide-Based Materials for Alkali Metal-Ion Batteries

Phosphorus- and phosphide-based materials with remarkable physicochemical properties and low costs have attracted significant attention as the anodes of alkali metal (e.g., Li, Na, K, Mg, Ca)-ion batteries (AIBs). However, the low electrical conductivity and large volume expansion of these materials during electrochemical reactions inhibit their practical applications. To solve these problems, various promising solutions have been explored and utilized. In this review, the recent progress in AIBs using phosphorus- and phosphide-based materials is summarized. Thereafter, the in-depth working principles of diverse AIBs are discussed and predicted. Representative works with design concepts, construction approaches, engineering strategies, special functions, and electrochemical results are listed and discussed in detail. Finally, the existing challenges and issues are concluded and analyzed, and future perspectives and research directions are given. This review can provide new guidance for the future design and practical applications of phosphorus- and phosphide-based materials used in AIBs.

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

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

Microscopic Understanding of the Growth and Structural Evolution of Narrow Bandgap III-V Nanostructures

III–V group nanomaterials with a narrow bandgap have been demonstrated to be promising building blocks in future electronic and optoelectronic devices. Thus, revealing the underlying structural evolutions under various external stimuli is quite necessary. To present a clear view about the structure–property relationship of III–V nanowires (NWs), this review mainly focuses on key procedures involved in the synthesis, fabrication, and application of III–V materials-based devices. We summarized the influence of synthesis methods on the nanostructures (NWs, nanodots and nanosheets) and presented the role of catalyst/droplet on their synthesis process through in situ techniques. To provide valuable guidance for device design, we further summarize the influence of structural parameters (phase, defects and orientation) on their electrical, optical, mechanical and electromechanical properties. Moreover, the dissolution and contact formation processes under heat, electric field and ionic water environments are further demonstrated at the atomic level for the evaluation of structural stability of III–V NWs. Finally, the promising applications of III–V materials in the energy-storage field are introduced.

Regulating Na deposition by constructing a Au sodiophilic interphase on CNT modified carbon cloth for flexible sodium metal anode

Na metal anode has attracted increasing attentions as the anode of sodium ion batteries (SIBs) due to its high theoretical capacity, low redox potential and high abundance. However, the formation of uncontrollable Na dendrite during repeated plating/stripping cycles hinders its further development and application. Herein, a sodiophilic Na metal anode host is developed by sputtering gold nanoparticles (Au NPs) into interconnected carbon nanotube modified carbon cloth (CNT/CC) to form a Au-CNT/CC architecture. Sodiophilic Au NPs effectively guide the Na metal uniform deposition and three-dimensional (3D) microporous structure offers a large surface area for nucleation and reducing the current densities. The regulated uniform Na metal deposition mechanism is investigated by the in-situ optical microscopy and simulation analysis. As a result, Au-CNT/CC electrode exhibits a low nucleation overpotential (2.2 mV) and stable cycle performance for 1600 h at 1 mA cm^-2 with 2 mAh cm^-2. Moreover, it even exhibits a long cycle stability for more than 800 h at 5 mA cm^-2 with 2 mAh cm^-2. To explore its application, a full cell coupled with a sodium vanadium phosphate coated with carbon layer (NVP@C) cathode is assembled and delivers an average discharge capacity of 80.6 mAh g^-1 and coulombic efficiency of 99.6% for 400 cycles at 100 mAh g^-1. Furthermore, a flexible pouch cell with Na@Au-CNT/CC as the anode is fabricated and demonstrated good flexibility and future application of wearable electronics.

Porosity Engineering of MXene Membrane towards Polysulfide Inhibition and Fast Lithium Ion Transportation for Lithium-Sulfur Batteries

Detrimental lithium polysulfide (LiPS) shuttle effects and sluggish electrochemical conversion kinetics in lithium-sulfur (Li-S) batteries severely hinder their practical application. Separator modification has been extensively investigated as an effective strategy to address above issues. Nevertheless, in the case of functional separators, how to effectively block the LiPSs from diffusion while enabling the rapid Li ion transport remains a challenge. Herein, by using an "oxidation-etching" method, MXene membranes are presented with controllable in-plane pores as interlayer to regulate Li ion transportation and LiPS immobilization. Porous MXene membranes with optimized pore density and size can simultaneously anchor LiPS and ensure fast Li ion diffusion. Consequently, even with pure sulfur cathode, the improved Li-S batteries deliver excellent rate performance up to 2 C with a reversible capacity of 677.6 mAh g^-1 and long-term cyclability over 500 cycles at 1 C with a low capacity decay of 0.07% per cycle. This work sheds new insights into the design of high-performance interlayers with manipulated nanochannels and tailored surface chemistry to regulate LiPSs trapping and Li ion diffusion in Li-S batteries.

Robust VS4@rGO nanocomposite as a high-capacity and long-life cathode material for aqueous zinc-ion batteries

Although vanadium (V)-based sulfides have been investigated as cathodes for aqueous zinc-ion batteries (ZIBs), the performance improvement and the intrinsic zinc-ion (Zn²⁺) storage mechanism revelation is still challenging. Here, VS₄@rGO composite with optimized morphology is designed and exhibits ultrahigh specific capacity (450 mA h g^-1 at 0.5 A g^-1) and high-rate capability (313.8 mA h g^-1 at 10 A g^-1) when applied as cathode material for aqueous ZIBs. Furthermore, the VS₄@rGO cathode presents long-life cycling stability with capacity retention of ∼82% after 3500 cycles at 10 A g^-1. The structural evolution, redox, and degradation mechanisms of VS₄ during (dis)charge processes are further probed by in situ XRD/Raman techniques and TEM analysis. Our results indicate that the main energy storage mechanism is derived from the intercalation/deintercalation reactions in the open channels of VS₄. Notably, an irreversible phase transition of VS₄ into Zn₃(OH)₂V₂O₇·2H₂O (ZVO) during the charging process and the further transition from ZVO to ZnV₃O₈ during long-term cycles are also observed, which might be the main reason leading to the capacity degradation of VS₄@rGO. Our study further improves the electrochemical performance of VS₄ in aqueous ZIBs through morphology design and provides new insights into the energy storage and performance degradation mechanisms of Zn²⁺ storage in VS₄, and thus may endow the large-scale application of V-based sulfides for energy storage systems.

Nanostructured metal phosphides: from controllable synthesis to sustainable catalysis

Metal phosphides (MPs) with unique and desirable physicochemical properties provide promising potential in practical applications, such as the catalysis, gas/humidity sensor, environmental remediation, and energy storage fields, especially for transition metal phosphides (TMPs) and MPs consisting of group IIIA and IVA metal elements. Most studies, however, on the synthesis of MP nanomaterials still face intractable challenges, encompassing the need for a more thorough understanding of the growth mechanism, strategies for large-scale synthesis of targeted high-quality MPs, and practical achievement of functional applications. This review aims at providing a comprehensive update on the controllable synthetic strategies for MPs from various metal sources. Additionally, different passivation strategies for engineering the structural and electronic properties of MP nanostructures are scrutinized. Then, we showcase the implementable applications of MP-based materials in emerging sustainable catalytic fields including electrocatalysis, photocatalysis, mild thermocatalysis, and related hybrid systems. Finally, we offer a rational perspective on future opportunities and remaining challenges for the development of MPs in the materials science and sustainable catalysis fields.