Controlled SnO2 Crystallinity Effectively Dominating Sodium Storage Performance

The exploration of sodium ion batteries (SIBs) is a profound challenge due to the rich sodium abundance and limited supply of lithium on earth. Here, amorphous SnO₂/graphene aerogel (a‐SnO₂/GA) nanocomposites have been successfully synthesized via a hydrothermal method for use as anode materials in SIBs. The designed annealing process produces crystalline SnO₂/graphene aerogel (c‐SnO₂/GA) nanocomposites. For the first time, the significant effects of SnO₂ crystallinity on sodium storage performance are studied in detail. Notably, a‐SnO₂/GA is more effective than c‐SnO₂/GA in overcoming electrode degradation from large volume changes associated with charge–discharge processes. Surprisingly, the amorphous SnO₂ delivers a high specific capacity of 380.2 mAh g^?1 after 100 cycles at a current density of 50 mA g^?1, which is almost three times as much as for crystalline SnO₂ (138.6 mAh g^?1). The impressive electrochemical performance of amorphous SnO₂ can be attributed to the intrinsic isotropic nature, the enhanced Na⁺ diffusion coefficient, and the strong interaction between amorphous SnO₂ and GA. In addition, amorphous SnO₂ particles with the smaller size better function to relieve the volume expansion/shrinkage. This study provides a significant research direction aiming to increase the electrochemical performance of the anode materials used in SIBs.     

Mechanistic Insights of Zn2+ Storage in Sodium Vanadates

Rechargeable aqueous zinc‐ion batteries (ZIBs) with high safety and low‐cost are highly desirable for grid‐scale energy storage, yet the energy storage mechanisms in the current cathode materials are still complicated and unclear. Hence, several sodium vanadates with NaV₃O₈‐type layered structure (e.g., Na₅V₁₂O₃₂ and HNaV₆O₁₆·4H₂O) and β‐Na_0.33V₂O₅‐type tunneled structure (e.g., Na_0.76V₆O₁₅) are constructed and the storage/release behaviors of Zn²⁺ ions are deeply investigated in these two typical structures. It should be mentioned that the 2D layered Na₅V₁₂O₃₂ and HNaV₆O₁₆·4H₂O with more effective path for Zn²⁺ diffusion exhibit higher ion diffusion coefficients than that of tunneled Na_0.76V₆O₁₅. As a result, Na₅V₁₂O₃₂ delivers higher capacity than that of Na_0.76V₆O₁₅, and a long‐term cyclic performance up to 2000 cycles at 4.0 A g^?1 in spite of its capacity fading. This work provides a new perspective of Zn²⁺ storage mechanism in aqueous ZIB systems.     

Heteroatom Doping: An Effective Way to Boost Sodium Ion Storage

In response to the change of energy landscape, sodium‐ion batteries (SIBs) are becoming one of the most promising power sources for the post‐lithium‐ion battery (LIB) era due to the cheap and abundant nature of sodium, and similar electrochemical properties to LIBs. The electrochemical performance of electrode materials for SIBs is closely bound up with their crystal structures and intrinsic electronic/ionic states. Apart from nanoscale design and conductive composite strategies, heteroatom doping is another effective way to enhance the intrinsic transfer characteristics of sodium ions and electrons in crystal structures to accelerate reaction kinetics and thereby achieve high performance. In this review, the recent advancements in heteroatom doping for sodium ion storage of electrode materials are reviewed. Specifically, different doping strategies including nonmetal element doping (e.g., nitrogen, sulfur, phosphorous, boron, fluorine), metal element doping (magnesium, titanium, iron, aluminum, nickel, copper, etc.), and dual/triple doping (such as N–S, N–P, N–S–P) are reviewed and summarized in detail. Furthermore, various doping methods are introduced and their advantages and disadvantages are discussed. The doping effect on crystal structure and intrinsic electronic/ionic state are illustrated and the relationship with capacity and energy/power density is interrogated. Finally, future development trends in doping strategies for advanced SIBs electrodes are analyzed.     

Sodium Vanadium Fluorophosphates (NVOPF) Array Cathode Designed for High‐Rate Full Sodium Ion Storage Device

3D batteries continue to be of widespread interest for flexible energy storage where the 3D nanostructured cathode is the key component to achieve both high energy and power densities. While current work on flexible cathodes tends to emphasize the use of flexible scaffolds such as graphene and/or carbon nanotubes, this approach is often limited by poor electrical contact and structural stability. This communication presents a novel synthetic approach to form 3D array cathode for the first time, the single‐crystalline Na₃(VO)₂(PO₄)₂F (NVOPF) by using VO₂ array as a seed layer. The NVOPF cathode exhibits both high‐rate capability (charge/discharge in 60 s) and long‐term durability (10,000 cycles at 50 C) for Na ion storage. Utilizing in situ X‐ray diffraction and first principles calculations, the high‐rate properties are correlated with the small volume change, 2D fast ion transport, and the array morphology. A novel all‐array flexible Na⁺ hybrid energy storage device based on pairing the intercalation‐type NVOPF array cathode with a cogenetic pseudocapacitive VO₂ nanosheet array anode is demonstrated.     

Effect of Intrinsic Defects of Carbon Materials on the Sodium Storage Performance

Due to their high conductivity and low cost, carbon materials have attracted great attention in the field of energy storage, especially as anode material for sodium ion batteries. Current research focuses on introducing external defects through heteroatom engineering to improve the sodium storage performance of carbon materials. However, there is still a lack of systematic investigation of the effects of intrinsic defects prevalent in carbon materials on sodium storage performance. Herein, template‐assisted method was used to design carbon materials with different degrees of intrinsic defects and explore their sodium storage properties. The experimental results show that the intrinsic defects in the carbon materials facilitates the adsorption behavior of Na⁺ during the surface induction capacitance process. Among them, the best carbon anode material exhibits high reversible capacity (221 mAh g^?1 at 1 A g^?1) and excellent rate performance. In addition, the density functional theory calculations also show that the existence of intrinsic defects can optimize the distribution of electron density, thereby increasing the Na‐adsorption capacity. This work makes an important contribution to understanding the role of intrinsic defects in the sodium storage performance of carbon materials.     

Liquid‐Phase Exfoliated Metallic Antimony Nanosheets toward High Volumetric Sodium Storage

Metallic antimony (Sb) with gray allotrope has rarely been considered from the viewpoint of two‐dimension layered system is actually a graphite‐like material, in which Sb layers consist of fused, ruffled, and six‐membered rings. Given that metallic Sb nanosheets can be played like graphene, it would be anticipated to obtain a new anode material with superior electrochemical performances for sodium storage. In this work, we propose an efficient strategy to fabricate free‐standing metallic Sb nanosheets via liquid‐phase exfoliation of gray Sb powder in an ios‐propyle alcohol (IPA) solution with a constant concentration of sodium hydroxide. As a proof of the concept, several hybrid films composed of metallic Sb nanosheets and graphene with tunable densities are achieved, in which the notorious volume change of metallic Sb can be efficiently alleviated with the aid of the good flexible graphene, and the whole density of electrode films can be significantly improved by harnessing the high density of Sb nanosheets. As a consequence, the optimized metallic Sb nanosheets‐graphene (SbNS‐G) film displays a high volumetric capacity of 1226 mAh cm^–3, high‐rate capability and good cycle performance for sodium storage.     

Sodium cotransport proteins.

Significant advances have been made in elucidating the structure of Na+ cotransport proteins. Some fifteen of these low-abundance proteins have been cloned, sequenced and functionally expressed. They are members of the 12 membrane-spanning superfamily and they segregate into two groups, the Na+/glucose (SGLT1) and Na+/Cl-/GABA (GAT-1) families. SGLT1 transporters are expressed in bacteria and animal cells, while GAT-1 transporters are mostly expressed in the brain. None have yet been found in plants.     

Nitrogen‐Doped Wrinkled Carbon Foils Derived from MOF Nanosheets for Superior Sodium Storage

Preparation of hierarchical carbon nanomaterials from metal?organicframeworks (MOFs) offers immense potential in the improvement of energy density, tunability, and stability of functional materials for energy storage and conversion. How interconnected nitrogen (N)‐doped wrinkled carbon foils derived from MOF nanosheets can serve as high‐performance sodium storage materials due to their multiscale porous structure is shown here. The novel N‐doped carbon nanomaterials are synthesized through the pyrolysis of 2D Mn‐based MOFs, which are produced through the assistance of monodentate ligands to enable the planar growth of MOFs. Subsequent acid etching creates hierarchical pores and channels to allow rapid ion transport. The resulting materials achieve high‐rate capability (165 and 150 mA h g^?1 at current densities of 8 and 10 A g^?1, respectively) and high stability (capacity retention 72.8% after 1000 cycling at 1.0 A g^?1), when they are used as anode in sodium‐ion capacitors.     

Mechanism of Sodium Storage in Hard Carbon: An X‐Ray Scattering Analysis

Hard carbon is a standard anode material for Na‐ion batteries. However, its low crystallinity and diverse microstructures make obtaining a full understanding of the sodium storage mechanism challenging. Here, the results of a systematic ex situ small and wide angle X‐ray scattering study of a series of nanostructured hard carbons, which reveal clear evidence of sodium storage in the graphene–graphene interlayers and nanopores, are presented. Particularly, an emergence of a broad peak around q ≈ 2.0–2.1 Å^?1 in the low voltage region is suggested to be an indicator that sodium is densely confined in the nanopores. Thus, classical X‐ray scattering techniques are demonstrated to be effective in elucidating the overall reaction scheme of Na insertion into hard carbon.     

High Capacity Adsorption—Dominated Potassium and Sodium Ion Storage in Activated Crumpled Graphene

Structurally and chemically defective activated‐crumbled graphene (A‐CG) is employed to achieve unique synergy of large reversible potassium (K) and sodium (Na) ion storage capacity with fast charging and extended cyclability. A‐CG synthesis consists of low temperature spraying of graphene oxide slurry, followed by partial reduction annealing and air activation. For K storage, the reversible capacities are 340 mAh g^?1 at 0.04 A g^?1, 261 mAh g^?1 at 0.5 A g^?1, and 210 mAh g^?1 at 2 A g^?1. For Na storage, the reversible capacities are 280 mAh g^?1 at 0.04 A g^?1, 191 mAh g^?1 at 0.5 A g^?1, and 151 mAh g^?1 at 2 A g^?1. A‐CG shows a stable intermediate rate (0.5 Ag^?1) cycling with both K and Na, with minimal fade after 2800 and 8000 cycles. These are among the most favorable capacity—rate capability—cyclability combinations recorded for potassium‐ion battery and sodium‐ion battery carbons. Electroanalytical studies (cyclic voltammetry, galvanostatic intermittent titration technique, b‐value) and density functional theory (DFT) reveal that enhanced electrochemical performance originates from ion adsorption at various defects, such as Stone–Wales defects. Moreover, DFT highlights enhanced thermodynamic stability of A‐CG with adsorbed K versus with adsorbed Na, explaining the unexpected higher reversible capacity with the former.     

Superior Sodium Storage in Na2Ti3O7 Nanotube Arrays through Surface Engineering

Sodium‐ion batteries have attracted extraordinary attention owing to their low cost and raw materials in abundance. A major challenge of practical implementation is the lack of accessible and affordable anodes that can reversibly store a substantial amount of Na ions in a fast and stable manner. It is reported that surface engineered sodium titanate (Na₂Ti₃O₇) nanotube arrays directly grown on Ti substrates can serve as efficient anodes to meet those stringent requirements. The fabrication of the nanotube arrays involves hydrothermal growing of Na₂Ti₃O₇ nanotubes, surface deposition of a thin layer of TiO₂, and subsequent sulfidation. The resulting nanoarrays exhibit a high electrochemical Na‐storage activity that outperforms other Na₂Ti₃O₇ based materials. They deliver high reversible capacities of 221 mAh g^?1 and exhibit a superior cycling efficiency and rate capability, retaining 78 mAh g^?1 at 10 C (1770 mA g^?1) over 10 000 continuous cycles. In addition, the full cell consisting of Na₂Ti₃O₇ nanotube anode and Na_2/3(Ni_1/3Mn_2/3)O₂ cathode is capable of delivering a specific energy of ≈110 Wh kg^?1 (based on the mass of both electrodes). The surface engineering can provide useful tools in the development of high performance anode materials with robust power and cyclability.     

Stress Distortion Restraint to Boost the Sodium Ion Storage Performance of a Novel Binary Hexacyanoferrate

Mn‐based hexacyanoferrate Na_xMnFe(CN)₆ (NMHFC) has been attracting more attention as a promising cathode material for sodium ion storage owing to its low cost, environmental friendliness, and its high voltage plateau of 3.6 V, which comes from the Mn²⁺/Mn³⁺ redox couple. In particular, the Na‐rich NMHFC (x > 1.40) with trigonal phase is considered an attractive candidate due to its large capacity of ≈130 mAh g^?1, delivering high energy density. Its unstable cycle life, however, is holding back its practical application due to the dissolution of Mn²⁺ and the trigonal‐cubic phase transition during the charge–discharge process. Here, a novel hexacyanoferrate (Na_1.60Mn_0.833Fe_0.167[Fe(CN)₆], NMFHFC‐1) with Na‐rich cubic structure and dual‐metal active redox couples is developed for the first time. Through multiple structural modulation, the stress distortion is minimized by restraining Mn²⁺ dissolution and the trigonal‐cubic phase transition, which are common issues in manganese‐based hexacyanoferrate. Moreover, NMFHFC‐1 simultaneously retains an abundance of Na ions in the framework. As a result, Na_1.60Mn_0.833Fe_0.167[Fe(CN)₆] electrode delivers high energy density (436 Wh kg^?1) and excellent cycle life (80.2% capacity retention over 300 cycles), paving the way for the development of novel commercial cathode materials for sodium ion storage.     

A Robust Approach for Efficient Sodium Storage of GeS2 Hybrid Anode by Electrochemically Driven Amorphization

Sodium ion batteries (NIBs) have become attractive promising alternatives to lithium ion batteries in a broad field of future energy storage applications. The development of high‐performance anode materials has become an essential factor and a great challenge toward satisfying the requirements for NIBs, advancement. This work is the first report on GeS₂ nanocomposites uniformly distributed on reduced graphene oxide (rGO) as promising anode materials for NIBs prepared via a facile hydrothermal synthesis and a unique carbo‐thermal annealing. The results show that the GeS₂/rGO hybrid anode yields a high reversible specific capacity of 805 mA h g^?1 beyond the theoretical capacity, an excellent rate capability of 616 mA h g^?1 at 5 A g^?1, and a cycle retention of 89.4% after 100 cycles. A combined ex situ characterization study reveals that the electrochemically driven amorphization plays a key role in achieving efficient sodium storage by accommodating excess sodium ions in the electrode materials. Understanding the sequential conversion‐alloying reaction mechanism for GeS₂/rGO hybrid anodes provides a new approach for developing high‐performance energy storage applications.     

3D Nanowire Arrayed Cu Current Collector toward Homogeneous Alloying Anode Deposition for Enhanced Sodium Storage

Alloying electrodes are regarded as promising anodes for lithium/sodium storage thanks to their multielectron reaction capacity, moderate voltage plateau, and high electrical conductivity. However, huge volume change upon cycling, especially for sodium storage, usually causes the loss of electrical connection between active components and their delaminations from traditional current collectors, thus leading to rapid capacity decay. Herein, a unique 3D current collector is assembled from 1D nanowire arrays anchored on 3D porous Cu foams for constructing core‐shelled Cu@Sb nanowires as advanced sodium‐ion battery (SIB) anodes. The so‐formed hierarchical 3D anode with interconnected 3D micrometer sized pores and abundant voids between nanowires not only effectively accommodates the structural strains during repeated cycling but also ensures the structural integrity and contributes to a uniform ion/electron scattered distribution throughout the whole surface. When employed as anodes for SIBs, the obtained electrode shows a high capacity of 605.3 mAh g^?1 at 330 mA g^?1, and demonstrates a high capacity retention of 84.8% even at a high current density of 3300 mA g^?1. The 3D nanowire arrayed Cu current collector in this work can offer a promising strategy for designing and building advanced alloy anodes for lithium/sodium storage.     

Manipulating Molecular Structure and Morphology to Invoke High‐Performance Sodium Storage of Copper Phosphide

Copper is used as current collector in rechargeable ion batteries due to its outstanding electronic conductivity and low cost. The intrinsic inactivity of copper, however, makes it a poor candidate for an electrode material without further structural modification. To fully utilize its high electronic conductivity, herein, the incorporation of heterogeneous phosphorus combined with building a unique 3D hollow structure is proposed. The as‐prepared copper phosphide hollow nanocubes deliver a stable capacity of 325 mAh·g^?1 at 50 mA·g^?1 and fast charging and discharging via pseudocapacitance behavior. The outstanding electrochemical performance is attributed to the synergetic effects of high electronic conductivity of copper and the high sodium storage capability of phosphorus. In addition, this facile synthesis method is also easily scaled up for practical applications. Thus, copper phosphide is a promising anode material for sodium ion batteries.     

Encapsulating Trogtalite CoSe2 Nanobuds into BCN Nanotubes as High Storage Capacity Sodium Ion Battery Anodes

Trogtalite CoSe₂ nanobuds encapsulated into boron and nitrogen codoped graphene (BCN) nanotubes (CoSe₂@BCN‐750) are synthesized via a concurrent thermal decomposition and selenization processes. The CoSe₂@BCN‐750 nanotubes deliver an excellent storage capacity of 580 mA h g^?1 at current density of 100 mA g^?1 at 100th cycle, as the anode of a sodium ion battery. The CoSe₂@BCN‐750 nanotubes exhibit a significant rate capability (100–2000 mA g^?1 current density) and high stability (almost 98% storage retention after 4000 cycles at large current density of 8000 mA g^?1). The reasons for these excellent storage properties are illuminated by theoretical calculations of the relevant models, and various possible Na⁺ ion storage sites are identified through first‐principles calculations. These results demonstrate that the insertion of heteroatoms, B–C, N–C as well as CoSe₂, into BCN tubes, enables the observed excellent adsorption energy of Na⁺ ions in high energy storage devices, which supports the experimental results.     

Promoting Highly Reversible Sodium Storage of Iron Sulfide Hollow Polyhedrons via Cobalt Incorporation and Graphene Wrapping

Sodium ion batteries (SIBs) have drawn significant attention owing to their low cost and inherent safety. However, the absence of suitable anode materials with high rate capability and long cycling stability is the major challenge for the practical application of SIBs. Herein, an efficient anode material consisting of uniform hollow iron sulfide polyhedrons with cobalt doping and graphene wrapping (named as CoFeS@rGO) is developed for high‐rate and long‐life SIBs. The graphene‐encapsulated hollow composite assures fast and continuous electron transportation, high Na⁺ ion accessibility, and strong structural integrity, showing an extremely small volume expansion of only 14.9% upon sodiation and negligible volume contraction during the desodiation. The CoFeS@rGO electrode exhibits high specific capacity (661.9 mAh g^?1 at 100 mA g^?1), excellent rate capability (449.4 mAh g^?1 at 5000 mA g^?1), and long cycle life (84.8% capacity retention after 1500 cycles at 1000 mA g^?1). In situ X‐ray diffraction and selected‐area electron diffraction patterns show that this novel CoFeS@rGO electrode is based on a reversible conversion reaction. More importantly, when coupled with a Na₃V₂(PO₄)₃/C cathode, the sodium ion full battery delivers a superexcellent rate capability (496.8 mAh g^?1 at 2000 mA g^?1) and ≈96.5% capacity retention over 200 cycles at 500 mA g^?1 in the 1.0–3.5 V window. This work indicates that the rationally designed anode material is highly applicable for the next generation SIBs with high‐rate capability and long‐term cyclability.