Enhanced Reversible Sodium‐Ion Intercalation by Synergistic Coupling of Few‐Layered MoS2 and S‐Doped Graphene

Sodium‐ion batteries (SIBs) are regarded as the best alternative to lithium‐ion batteries due to their low cost and similar Na⁺ insertion chemistry. It is still challenging but greatly desired to design and develop novel electrode materials with high reversible capacity, long cycling life, and good rate capability toward high‐performance SIBs. This work demonstrates an innovative design strategy and a development of few‐layered molybdenum disulfide/sulfur‐doped graphene nanosheets (MoS₂/SG) composites as the SIB anode material providing a high specific capacity of 587 mA h g^?1 calculated based on the total composite mass and an extremely long cycling stability over 1000 cycles at a current density of 1.0 A g^?1 with a high capacity retention of ≈85%. Systematic characterizations reveal that the outstanding performance is mainly attributed to the unique and robust composite architecture where few‐layered MoS₂ and S‐doped graphene are intimately bridged at the hetero‐interface through a synergistic coupling effect via the covalently doped S atoms. The design strategy and mechanism understanding at the molecular level outlined here can be readily applied to other layered transition metal oxides for SIBs anode and play a key role in contributing to the development of high‐performance SIBs.     

Homogeneous Intercalation Chemistry and Ultralow Strain of 1T’’’ MoS2 for Stable Potassium Storage

Intercalation anodes usually exhibit better cyclability than conversion and alloying anodes for lithium or sodium storage due to the robust layered structure. However, for larger-sized potassium accommodation, these intercalation anodes usually undergo huge layer expansion and structural distortion, triggering severe capacity fading. Herein, the novel 1T’’’ MoS₂ is revealed the intercalation anode for stable K⁺ storage, in which metallic Mo─Mo bonds and puckered S layers accelerate the charge transfer and homogeneous K⁺ insertion. Moreover, the ultralow strain (3.5%) induced by the non-detachable potassium ions pillar sustains the layered structure. Consequently, 1T’’’ MoS₂ achieves a reversible capacity of 125 mA h g⁻¹ at 0.2 C and keeps nearly 100% capacity retention at 1 C over 500 cycles. In situ characterizations and density functional theory simulations reveal the in-depth intercalation reaction accompanied by the MoS₂ phase transformation between 1T’’’ and 1T’ during cycling. Furthermore, a 1T’’’ MoS₂//MCMB K-dual ion battery displays a superior cycling lifespan with 98% capacity retention over 250 cycles. This study provides a new intercalation anode and contribute to the electrode design for stable potassium ion storage.     

General Synthesis of N‐Doped Macroporous Graphene‐Encapsulated Mesoporous Metal Oxides and Their Application as New Anode Materials for Sodium‐Ion Hybrid Supercapacitors

A general method to synthesize mesoporous metal oxide@N‐doped macroporous graphene composite by heat‐treatment of electrostatically co‐assembled amine‐functionalized mesoporous silica/metal oxide composite and graphene oxide, and subsequent silica removal to produce mesoporous metal oxide and N‐doped macroporous graphene simultaneously is reported. Four mesoporous metal oxides (WO_{3? x} , Co₃O₄, Mn₂O₃, and Fe₃O₄) are encapsulated in N‐doped macroporous graphene. Used as an anode material for sodium‐ion hybrid supercapacitors (Na‐HSCs), mesoporous reduced tungsten oxide@N‐doped macroporous graphene (m‐WO_{3? x} @NM‐rGO) gives outstanding rate capability and stable cycle life. Ex situ analyses suggest that the electrochemical reaction mechanism of m‐WO_{3? x} @NM‐rGO is based on Na⁺ intercalation/de‐intercalation. To the best of knowledge, this is the first report on Na⁺ intercalation/de‐intercalation properties of WO_{3? x} and its application to Na‐HSCs.     

Sodium Storage Behavior in Natural Graphite using Ether‐based Electrolyte Systems

This work reports that natural graphite is capable of Na insertion and extraction with a remarkable reversibility using ether‐based electrolytes. Natural graphite (the most well‐known anode material for Li–ion batteries) has been barely studied as a suitable anode for Na rechargeable batteries due to the lack of Na intercalation capability. Herein, graphite is not only capable of Na intercalation but also exhibits outstanding performance as an anode for Na ion batteries. The graphite anode delivers a reversible capacity of ≈150 mAh g^?1 with a cycle stability for 2500 cycles, and more than 75 mAh g^?1 at 10 A g^?1 despite its micrometer‐size (≈100 μm). An Na storage mechanism in graphite, where Na⁺‐solvent co‐intercalation occurs combined with partial pseudocapacitive behaviors, is revealed in detail. It is demonstrated that the electrolyte solvent species significantly affect the electrochemical properties, not only rate capability but also redox potential. The feasibility of graphite in a Na full cell is also confirmed in conjunction with the Na_1.5VPO_4.8F_0.7 cathode, delivering an energy of ≈120 Wh kg^?1 while maintaining ≈70% of the initial capacity after 250 cycles. This exceptional behavior of natural graphite promises new avenues for the development of cost‐effective and reliable Na ion batteries.     

Freestanding Metallic 1T MoS2 with Dual Ion Diffusion Paths as High Rate Anode for Sodium‐Ion Batteries

This work studies for the first time the metallic 1T MoS₂ sandwich grown on graphene tube as a freestanding intercalation anode for promising sodium‐ion batteries (SIBs). Sodium is earth‐abundant and readily accessible. Compared to lithium, the main challenge of sodium‐ion batteries is its sluggish ion diffusion kinetic. The freestanding, porous, hollow structure of the electrode allows maximum electrolyte accessibility to benefit the transportation of Na⁺ ions. Meanwhile, the metallic MoS₂ provides excellent electron conductivity. The obtained 1T MoS₂ electrode exhibits excellent electrochemical performance: a high reversible capacity of 313 mAh g^?1 at a current density of 0.05 A g^?1 after 200 cycles and a high rate capability of 175 mAh g^?1 at 2 A g^?1. The underlying mechanism of high rate performance of 1T MoS₂ for SIBs is the high electrical conductivity and excellent ion accessibility. This study sheds light on using the 1T MoS₂ as a novel anode for SIBs.     

Hierarchical Engineering of Porous P2‐Na2/3Ni1/3Mn2/3O2 Nanofibers Assembled by Nanoparticles Enables Superior Sodium‐Ion Storage Cathodes

Layered transition metal oxides (TMOs) are appealing cathode candidates for sodium‐ion batteries (SIBs) by virtue of their facile 2D Na⁺ diffusion paths and high theoretical capacities but suffer from poor cycling stability. Herein, taking P2‐type Na_2/3Ni_1/3Mn_2/3O₂ as an example, it is demonstrated that the hierarchical engineering of porous nanofibers assembled by nanoparticles can effectively boost the reaction kinetics and stabilize the structure. The P2‐Na_2/3Ni_1/3Mn_2/3O₂ nanofibers exhibit exceptional rate capability (166.7 mA h g^?1 at 0.1 C with 73.4 mA h g^?1 at 20 C) and significantly improved cycle life (≈81% capacity retention after 500 cycles) as cathode materials for SIBs. The highly reversible structure evolution and Ni/Mn valence change during sodium insertion/extraction are verified by in operando X‐ray diffraction and ex situ X‐ray photoelectron spectroscopy, respectively. The facilitated electrode process kinetics are demonstrated by an additional study using the electrochemical measurements and density functional theory computations. More impressively, the prototype Na‐ion full battery built with a Na_2/3Ni_1/3Mn_2/3O₂ nanofibers cathode and hard carbon anode delivers a promising energy density of 212.5 Wh kg^?1. The concept of designing a fibrous framework composed of small nanograins offers a new and generally applicable strategy for enhancing the Na‐storage performance of layered TMO cathode materials.     

Atomic Sulfur Covalently Engineered Interlayers of Ti3C2 MXene for Ultra‐Fast Sodium‐Ion Storage by Enhanced Pseudocapacitance

2D MXenes have been widely applied in the field of electrochemical energy storage owning to their high electrical conductivity and large redox‐active surface area. However, electrodes made from multilayered MXene with small interlayer spacing exhibit sluggish kinetics with low capacity for sodium‐ion storage. Herein, Ti₃C₂ MXene with expanded and engineered interlayer spacing for excellent storage capability is demonstrated. After cetyltrimethylammonium bromide pretreatment, S atoms are successfully intercalated into the interlayer of Ti₃C₂ to form a desirable interlayer‐expanded structure via Ti? S bonding, while pristine Ti₃C₂ is hardly to be intercalated. When the annealing temperature is 450 °C, the S atoms intercalated Ti₃C₂ (CT‐S@Ti₃C₂‐450) electrode delivers the improved Na‐ion capacity of 550 mAh g^?1 at 0.1 A g^?1 (≈120 mAh g^?1 at 15 A g^?1, the best MXene‐based Na⁺‐storage rate performance reported so far), and excellent cycling stability over 5000 cycles at 10 A g^?1 by enhanced pseudocapacitance. The enhanced sodium‐ion storage capability has also been verified by theoretical calculations and kinetic analysis. Coupling the CT‐S@Ti₃C₂‐450 anode with commercial AC cathode, the assembled Na⁺ capacitor delivers high energy density (263.2 Wh kg^?1) under high power density (8240 W kg^?1), and outstanding cycling performance.     

Ultrathin MoS2 Nanosheets@Metal Organic Framework‐Derived N‐Doped Carbon Nanowall Arrays as Sodium Ion Battery Anode with Superior Cycling Life and Rate Capability

This study reports the design and fabrication of ultrathin MoS₂ nanosheets@metal organic framework‐derived N‐doped carbon nanowall array hybrids on flexible carbon cloth (CC@CN@MoS₂) as a free‐standing anode for high‐performance sodium ion batteries. When evaluated as an anode for sodium ion battery, the as‐fabricated CC@CN@MoS₂ electrode exhibits a high capacity (653.9 mA h g^?1 of the second cycle and 619.2 mA h g^?1 after 100 cycles at 200 mA g^?1), excellent rate capability, and long cycling life stability (265 mA h g^?1 at 1 A g^?1 after 1000 cycles). The excellent electrochemical performance can be attributed to the unique 2D hybrid structures, in which the ultrathin MoS₂ nanosheets with expanded interlayers can provide shortened ion diffusion paths and favorable Na⁺ insertion/extraction space, and the porous N‐doped carbon nanowall arrays on flexible carbon cloth are able to improve the conductivity and maintain the structural integrity. Moreover, the N‐doping‐induced defects also make them favorable for the effective storage of sodium ions, which enables the enhanced capacity and rate performance of MoS₂.     

Three Electron Reversible Redox Reaction in Sodium Vanadium Chromium Phosphate as a High‐Energy‐Density Cathode for Sodium‐Ion Batteries

A sodium‐ion battery operating at room temperature is of great interest for large‐scale stationary energy storage because of its intrinsic cost advantage. However, the development of a high capacity cathode with high energy density remains a great challenge. In this work, sodium super ionic conductor‐structured Na₃V_2?xCr_x(PO₄)₃ is achieved through the sol–gel method; Na₃V_1.5Cr_0.5(PO₄)₃ is demonstrated to have a capacity of 150 mAh g^?1 with reversible three‐electron redox reactions after insertion of a Na⁺, consistent with the redox couples of V²⁺/³⁺, V³⁺/⁴⁺, and V⁴⁺/⁵⁺. Moreover, a symmetric sodium‐ion full cell utilizing Na₃V_1.5Cr_0.5(PO₄)₃ as both the cathode and anode exhibits an excellent rate capability and cyclability with a capacity of 70 mAh g^?1 at 1 A g^?1. Ex situ X‐ray diffraction analysis and in situ impedance measurements are performed to reveal the sodium storage mechanism and the structural evolution during cycling.     

A New rGO‐Overcoated Sb2Se3 Nanorods Anode for Na+ Battery: In Situ X‐Ray Diffraction Study on a Live Sodiation/Desodiation Process

Sodium ion batteries (SIBs) are a promising alternative to lithium ion batteries for a broader range of energy storage applications in the future. However, the development of high‐performance anode materials is a bottleneck of SIBs advancement. In this work, Sb₂Se₃ nanorods uniformly wrapped by reduced graphene oxide (rGO) as a promising anode material for SIBs are reported. The results show that such Sb₂Se₃/rGO hybrid anode yields a high reversible mass‐specific energy capacity of 682, 448, and 386 mAh g^?1 at a rate of 0.1, 1.0, and 2.0 A g^?1, respectively, and sustains at least 500 stable cycles at a rate of 1.0 A g^?1 with an average mass‐specific energy capacity of 417 mAh g^?1 and capacity retention of 90.2%. In situ X‐ray diffraction study on a live SIB cell reveals that the observed high performance is a result of the combined Na⁺ intercalation, conversion reaction between Na⁺ and Se, and alloying reaction between Na⁺ and Sb. The presence of rGO also plays a key role in achieving high rate capacity and cycle stability by providing good electrical conductivity, tolerant accommodation to volume change, and strong electron interactions to the base Sb₂Se₃ anode.     

In‐Plane Assembled Orthorhombic Nb2O5 Nanorod Films with High‐Rate Li+ Intercalation for High‐Performance Flexible Li‐Ion Capacitors

Organic hybrid supercapacitors that consist of a battery electrode and a capacitive electrode show greatly improved energy density, but their power density is generally limited by the poor rate capability of battery‐type electrodes. In addition, flexible organic hybrid supercapacitors are rarely reported. To address the above issues, herein an in‐plane assembled orthorhombic Nb₂O₅ nanorod film anode with high‐rate Li⁺ intercalation to develop a flexible Li‐ion hybrid capacitor (LIC) is reported. The binder‐/additive‐free film exhibits excellent rate capability (≈73% capacity retention with the rate increased from 0.5 to 20 C) and good cycling stability (>2500 times). Kinetic analyses reveal that the high rate performance is mainly attributed to the excellent in‐plane assembly of interconnected single‐crystalline Nb₂O₅ nanorods on the current collector, ensuring fast electron transport, facile Li‐ion migration in the porous film, and greatly reduced ion‐diffusion length. Using such a Nb₂O₅ film as anode and commercial activated carbon as cathode, a flexible LIC is designed. It delivers both high gravimetric and high volumetric energy/power densities (≈95.55 Wh kg^?1/5350.9 W kg^?1; 6.7 mW h cm^?3/374.63 mW cm^?3), surpassing previous typical Li‐intercalation electrode‐based LICs. Furthermore, this LIC device still keeps good electrochemical attributes even under serious bending states (30°–180°).     

A New Triclinic Phase Na2Ti3O7 Anode for Sodium‐Ion Battery

A new phase Na₂Ti₃O₇ compound is synthesized by solid‐state method for the first time, which is verified to belong to the triclinic structure in P‐1 space group. Compared to the conventional monoclinic Na₂Ti₃O₇ (m‐NTO), in P2₁/m1 space group, the triclinic Na₂Ti₃O₇ (t‐NTO) possesses a shorter O‐O band in the distorted TiO₆ octahedron, which accounts for more smooth Na⁺ transport channels and a more stable layered structure with smaller fluctuation. The experimental results show that the t‐NTO keeps a low charge potential plateau at 0.3 V compared to the m‐NTO, but with much promoted structure resilience. It delivers a capacity retention of 94.7%, far exceeding the 25.7% of the m‐NTO upon decades of cycles. In situ X‐ray diffraction reveals that the conventional m‐NTO experiences an irreversible phase transition during insertion/de‐insertion of Na⁺, while the new t‐NTO can recover its structure reversibly after discharge and charge, which is consistent with its improved cycling performance. The results demonstrate a new t‐NTO anode and provide a new understanding for the phase diversity of sodium‐ion battery materials.     

Vanadium Doping Enhanced Electrochemical Performance of Molybdenum Oxide in Lithium‐Ion Batteries

Molybdenum trioxide (MoO₃) suffers from poor conductivity, a low rate capability, and unsatisfactory cycling stability in lithium‐ion batteries. The aliovalent ion doping may present an effective way to improve the electrochemical performances of MoO₃. Here, it is shown, by first‐principle calculations, that doping MoO₃ with V by 12.5% can modulate significantly electronic structure and provide a small diffusion barrier for enhancing the electrochemical performance of MoO₃. The ultralong Mo_0.88V_0.12O_2.94 nanostructures, which retain the h‐MoO₃ structure and present an exceptionally high conductivity and fast ionic diffusion due to the substitution of V, facilitating lithiation/delithiation behavior, and induce a fine nanosized structure with a reduced volume change are prepared. As a result, the stress and strain are alleviated during the Li‐ion intercalation/deintercalation processes, improving the cycling stability and rate capability. Such a large improvement in the electrochemical properties can be ascribed to the stabilizing effect of V, the small migration energy barrier, and short diffusion path, which arise from the introduction of V into MoO₃. The unique engineering strategy and facile synthesis route open up a new avenue in modifying and developing other species of electrode materials.     

Electrochemical Mechanism Investigation of Cu2MoS4 Hollow Nanospheres for Fast and Stable Sodium Ion Storage

Sodium ion batteries (SIBs) are promising alternatives to lithium ion batteries with advantages of cost effectiveness. Metal sulfides as emerging SIB anodes have relatively high electronic conductivity and high theoretical capacity, however, large volume change during electrochemical testing often leads to unsatisfactory electrochemical performance. Herein bimetallic sulfide Cu₂MoS₄ (CMS) with layered crystal structures are prepared with glucose addition (CMS1), resulting in the formation of hollow nanospheres that endow large interlayer spacing, benefitting the rate performance and cycling stability. The electrochemical mechanisms of CMS1 are investigated using ex situ X‐ray photoelectron spectroscopy and in situ X‐ray absorption spectroscopy, revealing the conversion‐based mechanism in carbonate electrolyte and intercalation‐based mechanism in ether‐electrolyte, thus allowing fast and reversible Na⁺ storage. With further introduction of reduced graphene oxide (rGO), CMS1–rGO composites are obtained, maintaining the hollow structure of CMS1. CMS1–rGO delivers excellent rate performance (258 mAh g^?1 at 50 mA g^?1 and 131.9 mAh g^?1 at 5000 mA g^?1) and notably enhanced cycling stability (95.6% after 2000 cycles). A full cell SIB is assembled by coupling CMS1–rGO with Na₃V₂(PO₄)₃‐based cathode, delivering excellent cycling stability (75.5% after 500 cycles). The excellent rate performance and cycling stability emphasize the advantage of CMS1–rGO toward advanced SIB full cells assembly.     

Half‐Cell and Full‐Cell Applications of Highly Stable and Binder‐Free Sodium Ion Batteries Based on Cu3P Nanowire Anodes

Sodium‐ion battery (SIB) is especially attractive in cost‐effective energy storage device as an alternative to lithium‐ion battery. Particularly, metal phosphides as potential anodes for SIBs have recently been demonstrated owing to their higher specific capacities compared with those of carbonaceous materials. Unfortunately, most reported metal phosphides consist of irregular particles ranged from several hundreds nanometers to tens of micrometers, thus delivering limited cyclic stability. This paper reports the sodium storage properties of additive‐free Cu₃P nanowire (CPNW) anode directly grown on copper current collector via an in situ growth followed by phosphidation method. Therefore, as a result of its structure features, CPNW anode demonstrates highly stable cycling ability with an ≈70% retention in capacity at the 260th cycle, whereas most reported metal phosphides have limited cycle numbers ranged between 30 and 150. Besides, the reaction mechanism between Cu₃P and Na is investigated by examining the intermediate products at different charge/discharge stages using ex situ X‐ray diffraction measurements. Furthermore, to explore the practical application of CPNW anode, a pouch‐type Na⁺ full cell consisting of CPNW anode and Na₃V₂(PO₄)₃ cathode is assembled and characterized. As a demonstration, a 10 cm × 10 cm light‐emmiting diode (LED) screen is successfully powered by the Na⁺ full cell.     

Fabrication and Shell Optimization of Synergistic TiO2‐MoO3 Core–Shell Nanowire Array Anode for High Energy and Power Density Lithium‐Ion Batteries

A novel synergistic TiO₂‐MoO₃ (TO‐MO) core–shell nanowire array anode has been fabricated via a facile hydrothermal method followed by a subsequent controllable electrodeposition process. The nano‐MoO₃ shell provides large specific capacity as well as good electrical conductivity for fast charge transfer, while the highly electrochemically stable TiO₂ nanowire core (negligible volume change during Li insertion/desertion) remedies the cycling instability of MoO₃ shell and its array further provides a 3D scaffold for large amount electrodeposition of MoO₃. In combination of the unique electrochemical attributes of nanostructure arrays, the optimized TO‐MO hybrid anode (mass ratio: ca. 1:1) simultaneously exhibits high gravimetric capacity (ca. 670 mAh g^?1; approaching the hybrid's theoretical value), excellent cyclability (>200 cycles) and good rate capability (up to 2000 mA g^?1). The areal capacity is also as high as 3.986 mAh cm^?2, comparable to that of typical commercial LIBs. Furthermore, the hybrid anode was assembled for the first time with commercial LiCoO₂ cathode into a Li ion full cell, which shows outstanding performance with maximum power density of 1086 W kg_total ^?1 (based on the total mass of the TO‐MO and LiCoO₂) and excellent energy density (285 Wh kg_total ^?1) that is higher than many previously reported metal oxide anode‐based Li full cells.     

Layered P2‐Type K0.65Fe0.5Mn0.5O2 Microspheres as Superior Cathode for High‐Energy Potassium‐Ion Batteries

Potassium‐ion batteries have been regarded as the potential alternatives to lithium‐ion batteries (LIBs) due to the low cost, earth abundance, and low potential of K (?2.936 vs standard hydrogen electrode (SHE)). However, the lack of low‐cost cathodes with high energy density and long cycle life always limits its application. In this work, high‐energy layered P2‐type hierarchical K_0.65Fe_0.5Mn_0.5O₂ (P2‐KFMO) microspheres, assembled by the primary nanoparticles, are fabricated via a modified solvent‐thermal method. Benefiting from the unique microspheres with primary nanoparticles, the K⁺ intercalation/deintercalation kinetics of P2‐KFMO is greatly enhanced with a stabilized cathodic electrolyte interphase on the cathode. The P2‐KFMO microsphere presents a highly reversible potassium storage capacity of 151 mAh g^?1 at 20 mA g^?1, fast rate capability of 103 mAh g^?1 at 100 mA g^?1, and long cycling stability with 78% capacity retention after 350 cycles. A full cell with P2‐KFMO microspheres as cathode and hard carbon as anode is constructed, which exhibits long‐term cycling stability (>80% of retention after 100 cycles). The present high‐performance P2‐KFMO microsphere cathode synthesized using earth‐abundant elements provides a new cost‐effective alternative to LIBs for large‐scale energy storage.     

Heterostructured Nanocube‐Shaped Binary Sulfide (SnCo)S2 Interlaced with S‐Doped Graphene as a High‐Performance Anode for Advanced Na+ Batteries

Heterostructuring electrodes with multiple electroactive and inactive supporting components to simultaneously satisfy electrochemical and structural requirements has recently been identified as a viable pathway to achieve high‐capacity and durable sodium‐ion batteries (SIBs). Here, a new design of heterostructured SIB anode is reported consisting of double metal‐sulfide (SnCo)S₂ nanocubes interlaced with 2D sulfur‐doped graphene (SG) nanosheets. The heterostructured (SnCo)S₂/SG nanocubes exhibit an excellent rate capability (469 mAh g^?1 at 10.0 A g^?1) and durability (5000 cycles, 487 mAh g^?1 at 5.0 A g^?1, 92.6% capacity retention). In situ X‐ray diffraction reveals that the (SnCo)S₂/SG anode undergoes a six‐stage Na⁺ storage mechanism of combined intercalation, conversion, and alloying reactions. The first‐principle density functional theory calculations suggest high concentration of p–n heterojunctions at SnS₂/CoS₂ interfaces responsible for the high rate performance, while in situ transmission electron microscopy unveils that the interlacing and elastic SG nanosheets play a key role in extending the cycle life.     

Surface Oxygen Coordination of Hydrogen Bond Chemistry for Aqueous Ammonium Ion Hybrid Supercapacitor

Aqueous ammonium ion hybrid supercapacitor (A-HSC) combines the charge storage mechanisms of surface adsorption and bulk intercalation, making it a low-cost, safe, and sustainable energy storage candidate. However, its development is hindered by the low capacity and unclear charge storage fundamentals. Here, the strategy of phosphate ion-assisted surface functionalization is used to increase the ammonium ion storage capacity of an α-MoO₃ electrode. Moreover, the understanding of charge storage mechanisms via structural characterization, electrochemical analysis, and theoretical calculation is advanced. It is shown that NH₄⁺ intercalation into layered α-MoO₃ is not dominant in the A-HSC system; rather, the charge storage mainly depends on the adsorption energy of surface “O” to NH₄⁺. It is further revealed that the hydrogen bond chemistry of the coordination between “O” of surface phosphate ion and NH₄⁺ is the reason for the capacity increase of MoO₃. This study not only advances the basic understanding of rechargeable aqueous A-HSC but also demonstrates the promising future of surface engineering strategies for energy storage devices.     

Prussian White Hierarchical Nanotubes with Surface‐Controlled Charge Storage for Sodium‐Ion Batteries

Coordination compounds such as Prussian blue and its analogues are acknowledged as promising candidates for electrochemical sodium storage owing to their tailorable and open frameworks. However, a key challenge for these electrode materials is the trade‐off between energy and power. Here, it is demonstrate that Prussian white (Na_3.1Fe₄[Fe(CN)₆]₃) hierarchical nanotubes with fully open configurations render extrinsic Na⁺ intercalation pseudocapacitance. The cathode exhibits a capacity up to 83 mA h g^?1 at an ultrahigh rate of 50 C and an unprecedented cycle life over 10 000 times for sodium storage. In situ Raman spectroscopy together with in situ X‐ray diffraction analysis reveal that intercalation pseudocapacitance enables full reaction of N‐Fe^III/Fe^II sites in Prussian white with a negligible volume expansion (<2.1%). The discovery of surface‐controlled charge storage occurring inside the entire bulk of intercalation cathodes paves a new way for developing high power, high energy, and long life‐span sodium‐ion batteries.