Construction of Bimetallic Selenides Encapsulated in Nitrogen/Sulfur Co‐Doped Hollow Carbon Nanospheres for High‐Performance Sodium/Potassium‐Ion Half/Full Batteries

Metallic selenides have been widely investigated as promising electrode materials for metal‐ion batteries based on their relatively high theoretical capacity. However, rapid capacity decay and structural collapse resulting from the larger‐sized Na⁺/K⁺ greatly hamper their application. Herein, a bimetallic selenide (MoSe₂/CoSe₂) encapsulated in nitrogen, sulfur‐codoped hollow carbon nanospheres interconnected reduced graphene oxide nanosheets (rGO@MCSe) are successfully designed as advanced anode materials for Na/K‐ion batteries. As expected, the significant pseudocapacitive charge storage behavior substantially contributes to superior rate capability. Specifically, it achieves a high reversible specific capacity of 311 mAh g^?1 at 10 A g^?1 in NIBs and 310 mAh g^?1 at 5 A g^?1 in KIBs. A combination of ex situ X‐ray diffraction, Raman spectroscopy, and transmission electron microscopy tests reveals the phase transition of rGO@MCSe in NIBs/KIBs. Unexpectedly, they show quite different Na⁺/K⁺ insertion/extraction reaction mechanisms for both cells, maybe due to more sluggish K⁺ diffusion kinetics than that of Na⁺. More significantly, it shows excellent energy storage properties in Na/K‐ion full cells when coupled with Na₃V₂(PO₄)₂O₂F and PTCDA@450 °C cathodes. This work offers an advanced electrode construction guidance for the development of high‐performance energy storage devices.     

Pseudocapacitive Sodium Storage by Ferroelectric Sn2P2S6 with Layered Nanostructure

Sodium ion batteries (SIB) are considered promising alternative candidates for lithium ion batteries (LIB) because of the wide availability and low cost of sodium, therefore the development of alternative sodium storage materials with comparable performance to LIB is urgently desired. The sodium ions with larger sizes resist intercalation or alloying because of slow reaction kinetics. Most pseudocapacitive sodium storage materials are based on subtle nanomaterial engineering, which is difficult for large‐scale production. Here, ferroelectric Sn₂P₂S₆ with layered nanostructure is developed as sodium ion storage material. The ferroelectricity‐enhanced pseudocapacitance of sodium ion in the interlayer spacing makes the electrochemical reaction easier and faster, endowing the Sn₂P₂S₆ electrode with excellent rate capability and cycle stability. Furthermore, the facile solid state reaction synthesis and common electrode fabrication make the Sn₂P₂S₆ that becomes a promising anode material of SIB.     

Multidimensional Synergistic Nanoarchitecture Exhibiting Highly Stable and Ultrafast Sodium‐Ion Storage

Conversion‐type anodes with multielectron reactions are beneficial for achieving a high capacity in sodium‐ion batteries. Enhancing the electron/ion conductivity and structural stability are two key challenges in the development of high‐performance sodium storage. Herein, a novel multidimensionally assembled nanoarchitecture is presented, which consists of V₂O₃ nanoparticles embedded in amorphous carbon nanotubes that are then coassembled within a reduced graphene oxide (rGO) network, this materials is denoted V₂O₃?C‐NTs?rGO. The selective insertion and multiphase conversion mechanism of V₂O₃ in sodium‐ion storage is systematically demonstrated for the first time. Importantly, the naturally integrated advantages of each subunit synergistically provide a robust structure and rapid electron/ion transport, as confirmed by in situ and ex situ transmission electron microscopy experiments and kinetic analysis. Benefiting from the synergistic effects, the V₂O₃?C‐NTs?rGO anode delivers an ultralong cycle life (72.3% at 5 A g^?1 after 15 000 cycles) and an ultrahigh rate capability (165 mAh g^?1 at 20 A g^?1, ≈30 s per charge/discharge). The synergistic design of the multidimensionally assembled nanoarchitecture produces superior advantages in energy storage.     

Hierarchical Porous Nanosheets Constructed by Graphene‐Coated,Interconnected TiO2 Nanoparticles for Ultrafast Sodium Storage

Sodium‐ion batteries (SIBs) are considered promising next‐generation energy storage devices. However, a lack of appropriate high‐performance anode materials has prevented further improvements. Here, a hierarchical porous hybrid nanosheet composed of interconnected uniform TiO₂ nanoparticles and nitrogen‐doped graphene layer networks (TiO₂@NFG HPHNSs) that are synthesized using dual‐functional C₃N₄ nanosheets as both the self‐sacrificing template and hybrid carbon source is reported. These HPHNSs deliver high reversible capacities of 146 mA h g^?1 at 5 C for 8000 cycles, 129 mA h g^?1 at 10 C for 20 000 cycles, and 116 mA h g^?1 at 20 C for 10 000 cycles, as well as an ultrahigh rate capability up to 60 C with a capacity of 101 mA h g^?1. These results demonstrate the longest cyclabilities and best rate capability ever reported for TiO₂‐based anode materials for SIBs. The unprecedented sodium storage performance of the TiO₂@NFG HPHNSs is due to their unique composition and hierarchical porous 2D structure.     

Controllable Design of MoS2 Nanosheets Grown on Nitrogen‐Doped Branched TiO2/C Nanofibers: Toward Enhanced Sodium Storage Performance Induced by Pseudocapacitance Behavior

In this work, expanded MoS₂ nanosheets grown on nitrogen‐doped branched TiO₂/C nanofibers (NBT/C@MoS₂ NFs) are prepared through electrospinning and hydrothermal treatment method as anode materials for sodium‐ion batteries (SIBs). The continuous 1D branched TiO₂/C nanofibers provide a large surface area to grow expanded MoS₂ nanosheets and enhance the electronic conductivity and cycling stability of the electrode. The large surface area and doping of nitrogen can facilitate the transfer of both Na⁺ ions and electrons. With the merits of these unique design and extrinsic pseudocapacitance behavior, the NBT/C@MoS₂ NFs can deliver ultralong cycle stability of 448.2 mA h g^?1 at 200 mA g^?1 after 600 cycles. Even at a high rate of 2000 mA g^?1, a reversible capacity of 258.3 mA h g^?1 can still be achieved. The kinetic analysis demonstrates that pseudocapacitive contribution is the major factor to achieve excellent rate performance. The rational design and excellent electrochemical performance endow the NBT/C@MoS₂ NFs with potentials as promising anode materials for SIBs.     

Efficient Sodium Storage in Rolled‐Up Amorphous Si Nanomembranes

Alloying‐type materials are promising anodes for high‐performance sodium‐ion batteries (SIBs) because of their high capacities and low Na‐ion insertion potentials. However, the typical candidates, such as P, Sn, Sb, and Pb, suffer from severe volume changes (≈293–487%) during the electrochemical reactions, leading to inferior cycling performances. Here, a high‐rate and ultrastable alloying‐type anode based on the rolled‐up amorphous Si nanomembranes is demonstrated. The rolled‐up amorphous Si nanomembranes show a very small volume change during the sodiation/desodiation processes and deliver an excellent rate capability and ultralong cycle life up to 2000 cycles with 85% capacity retention. The structural evolution and pseudocapacitance contribution are investigated by using the ex situ characterization techniques combined with kinetics analysis. Furthermore, the mechanism of efficient sodium‐ion storage in amorphous Si is kinetically analyzed through an illustrative atomic structure with dangling bonds, offering a new perspective on understanding the sodium storage behavior. These results suggest that nanostructured amorphous Si is a promising anode material for high‐performance SIBs.     

A Liquid‐Metal‐Enabled Versatile Organic Alkali‐Ion Battery

Despite the high specific capacity and low redox potential of alkali metals, their practical application as anodes is still limited by the inherent dendrite‐growth problem. The fusible sodium–potassium (Na–K) liquid metal alloy is an alternative that detours this drawback, but the fundamental understanding of charge transport in this binary electroactive alloy anode remains elusive. Here, comprehensive characterization, accompanied with density function theory (DFT) calculations, jointly expound the Na–K anode‐based battery working mechanism. With the organic cathode sodium rhodizonate dibasic (SR) that has negligible selectivity toward cations, the charge carrier is screened by electrolytes due to the selective ionic pathways in the solid electrolyte interphase (SEI). Stable cycling for this Na–K/SR battery is achieved with capacity retention per cycle to be 99.88% as a sodium‐ion battery (SIB) and 99.70% as a potassium‐ion battery (PIB) for over 100 cycles. Benefitting from the flexibility of the liquid metal and the specially designed carbon nanofiber (CNF)/SR layer‐by‐layer cathode, a flexible dendrite‐free alkali‐ion battery is achieved with an ultrahigh areal capacity of 2.1 mAh cm^?2. Computation‐guided materials selection, characterization‐supported mechanistic understanding, and self‐validating battery performance collectively promise the prospect of a high‐performance, dendrite‐free, and versatile organic‐based liquid metal battery.     

Water‐Pillared Sodium Vanadium Bronze Nanowires for Enhanced Rechargeable Magnesium Ion Storage

Owing to the advantages of high safety, low cost, high theoretical volumetric capacities, and environmental friendliness, magnesium‐ion batteries (MIBs) have more feasibility for large‐scale energy storage compared to lithium‐ion batteries. However, lack of suitable cathode materials due to sluggish kinetics of magnesium ion is one of the biggest challenges. Herein, water‐pillared sodium vanadium bronze nanowires (Na₂V₆O₁₆·1.63H₂O) are reported as cathode material for MIBs, which display high performance in magnesium storage. The hydrated sodium ions provide excellent structural stability. The charge shielding effect of lattice water enables fast Mg²⁺ diffusion. It exhibits high specific capacity of 175 mAh g^?1, long cycle life (450 cycles), and high coulombic efficiency (≈100%). At high current density of 200 mA g^?1, the capacity retention is up to 71% even after 450 cycles (compared to the highest capacity), demonstrating excellent long‐term cycling performance. The nature of charge storage kinetics is explored. Furthermore, a highly reversible structure change during the electrochemical process is proved by comprehensive electrochemical analysis. The remarkable electrochemical performance makes Na₂V₆O₁₆·1.63H₂O a promising cathode material for low‐cost and safe MIBs.     

Highly Efficient Sodium Storage in Iron Oxide Nanotube Arrays Enabled by Built‐In Electric Field

High‐power sodium–ion batteries capable of charging and discharging rapidly and durably are eagerly demanded to replace current lithium–ion batteries. However, poor activity and instable cycling of common sodium anode materials represent a huge barrier for practical deployment. A smart design of ordered nanotube arrays of iron oxide (Fe₂O₃) is presented as efficient sodium anode, simply enabled by surface sulfurization. The resulted heterostructure of oxide and sulfide spontaneously develops a built‐in electric field, which reduces the activation energy and accelerates charge transport significantly. Benefiting from the synergy of ordered architecture and built‐in electric field, such arrays exhibit a large reversible capacity, a superior rate capability, and a high retention of 91% up to 200 cycles at a high rate of 5 A g^?1, outperforming most reported iron oxide electrodes. Furthermore, full cells based on the Fe₂O₃ array anode and the Na_0.67(Mn_0.67Ni_0.23Mg_0.1)O₂ cathode deliver a specific energy of 142 Wh kg^?1 at a power density of 330 W kg^?1 (based on both active electrodes), demonstrating a great potential in practical application. This material design may open a new door in engineering efficient anode based on earth‐abundant materials.     

Ti‐Based Oxide Anode Materials for Advanced Electrochemical Energy Storage: Lithium/Sodium Ion Batteries and Hybrid Pseudocapacitors

Titanium‐based oxides including TiO₂ and M‐Ti‐O compounds (M = Li, Nb, Na, etc.) family, exhibit advantageous structural dynamics (2D ion diffusion path, open and stable structure for ion accommodations) for practical applications in energy storage systems, such as lithium‐ion batteries, sodium‐ion batteries, and hybrid pseudocapacitors. Further, Ti‐based oxides show high operating voltage relative to the deposition of alkali metal, ensuring full safety by avoiding the formation of lithium and sodium dendrites. On the other hand, high working potential prevents the decomposition of electrolyte, delivering excellent rate capability through the unique pseudocapacitive kinetics. Nevertheless, the intrinsic poor electrical conductivity and reaction dynamics limit further applications in energy storage devices. Recently, various work and in‐depth understanding on the morphologies control, surface engineering, bulk‐phase doping of Ti‐based oxides, have been promoted to overcome these issues. Inspired by that, in this review, the authors summarize the fundamental issues, challenges and advances of Ti‐based oxides in the applications of advanced electrochemical energy storage. Particularly, the authors focus on the progresses on the working mechanism and device applications from lithium‐ion batteries to sodium‐ion batteries, and then the hybrid pseudocapacitors. In addition, future perspectives for fundamental research and practical applications are discussed.     

A 1D Honeycomb‐Like Amorphous Zincic Vanadate for Stable and Fast Sodium‐Ion Storage

Developing nanomaterials with synergistic effects of various structural merits is considered to be an effective strategy to improve the sluggish ion kinetics and severe structural degradation of sodium‐ion battery (SIB) anodes. Herein, honeycomb‐like amorphous Zn₂V₂O₇ (ZVO‐AH) nanofibers as SIBs anode material with plentiful defective sites, complex cavities, and good mechanical flexibility are reported. The fabrication strategy relies on the expansive and volatile nature of the organic vanadium source, based on a simple electrospinning with subsequent calcination. Originating from the synergies of amorphous nature and honeycomb‐like cavities, ZVO‐AH shows increased electrochemical activity, accelerated Na‐ion diffusion, and robust structure. Impressively, the ZVO‐AH anode delivers superior cycle stability (112% retention at 5 A g^?1 after 5000 cycles) and high rate capability (150 mAh g^?1 at 10 A g^?1). The synthetic versatility is able to synergistically promote the practical application of more potential materials in sodium‐ion storage.     

Rational Design and General Synthesis of S‐Doped Hard Carbon with Tunable Doping Sites toward Excellent Na‐Ion Storage Performance

Heteroatom‐doping is a promising strategy to tuning the microstructure of carbon material toward improved electrochemical storage performance. However, it is a big challenge to control the doping sites for heteroatom‐doping and the rational design of doping is urgently needed. Herein, S doping sites and the influence of interlayer spacing for two kinds of hard carbon, perfect structure and vacancy defect structure, are explored by the first‐principles method. S prefers doping in the interlayer for the former with interlayer distance of 3.997 Å, while S is doped on the carbon layer for the latter with interlayer distance of 3.695 Å. More importantly, one step molten salts method is developed as a universal synthetic strategy to fabricate hard carbon with tunable microstructure. It is demonstrated by the experimental results that S‐doping hard carbon with fewer pores exhibits a larger interlayer spacing than that of porous carbon, agreeing well with the theoretical prediction. Furthermore, the S‐doping carbon with larger interlayer distance and fewer pores exhibits remarkably large reversible capacity, excellent rate performance, and long‐term cycling stability for Na‐ion storage. A stable and reversible capacity of ≈200 mAh g^?1 is steadily kept even after 4000 cycles at 1 A g^?1.     

Hierarchical Octahedra Constructed by Cu2S/MoS2⊂Carbon Framework with Enhanced Sodium Storage

Metal sulfides have aroused considerable attention for efficient sodium storage because of their high capacity and decent redox reversibility. However, the poor rate capability and fast capacity decay greatly hinder their practical application in sodium‐ion batteries. Herein, a self‐template‐based strategy is designed to controllably synthesize hierarchical microoctahedra assembled with Cu₂S/MoS₂ heterojunction nanosheets in the porous carbon framework (Cu₂S/MoS₂?PCF) via a facile coprecipitation method coupled with vulcanization treatment. The Cu₂S/MoS₂?PCF microoctahedra with 2D hybrid nanosubunits reasonably integrate several merits including facilitating the diffusion of electrons and Na⁺ ions, enhancing the electric conductivity, accelerating the ion and charge transfer, and buffering the volume variation. Therefore, the Cu₂S/MoS₂?PCF composite manifests efficient sodium storage performance with high capacity, long cycling life, and excellent rate capability.     

A Functionalized Carbon Surface for High‐Performance Sodium‐Ion Storage

Sodium‐ion batteries (SIBs) are promising for large‐scale energy storage systems and carbon materials are the most likely candidates for their electrodes. The existence of defects in carbon materials is crucial for increasing the sodium storage ability. However, both the reversible capacity and efficiency need to be further improved. Functionalization is a direct and feasible approach to address this issue. Based on the structural changes in carbon materials produced by surface functionalization, three basic categories are defined: heteroatom doping, grafting of functional groups, and the shielding of defects. Heteroatom doping can improve the electrochemical reactivity, and the grafting of functional groups can promote both the diffusion‐controlled bulk process and surface‐confined capacitive process. The shielding of defects can further increase the efficiency and cyclic stability without sacrificing reversible capacity. In this Review, recent progresses in the ways to produce surface functionalization are presented and the related impact on the physical and chemical properties of carbon materials is discussed. Moreover, the critical issues, challenges, and possibilities for future research are summarized.     

Ultrastable Potassium Storage Performance Realized by Highly Effective Solid Electrolyte Interphase Layer

Potassium ion‐batteries (PIBs) have attracted tremendous attention recently due to the abundance of potassium resources and the low standard electrode potential of potassium. Particularly, the solid‐electrolyte interphase (SEI) in the anode of PIBs plays a vital role in battery security and battery cycling performance due to the highly reactive potassium. However, the SEI in the anode for PIBs with traditional electrolytes is mainly composed of organic compositions, which are highly reactive with air and water, resulting in inferior cycle performance and safety hazards. Herein, a highly stable and effective inorganic SEI layer in the anode is formed with optimized electrolyte. As expected, the PIBs exhibit an ultralong cycle performance over 14 000 cycles at 2000 mA g^?1 and an ultrahigh average coulombic efficiency over 99.9%.     

Formation of Hierarchical Cu‐Doped CoSe2 Microboxes via Sequential Ion Exchange for High‐Performance Sodium‐Ion Batteries

Electrode materials based on electrochemical conversion reactions have received considerable interest for high capacity anodes of sodium‐ion batteries. However, their practical application is greatly hindered by the poor rate capability and rapid capacity fading. Tuning the structure at nanoscale and increasing the conductivity of these anode materials are two effective strategies to address these issues. Herein, a two‐step ion‐exchange method is developed to synthesize hierarchical Cu‐doped CoSe₂ microboxes assembled by ultrathin nanosheets using Co–Co Prussian blue analogue microcubes as the starting material. Benefitting from the structural and compositional advantages, these Cu‐doped CoSe₂ microboxes with improved conductivity exhibit enhanced sodium storage properties in terms of good rate capability and excellent cycling performance.     

Fe2VO4 Hierarchical Porous Microparticles Prepared via a Facile Surface Solvation Treatment for High‐Performance Lithium and Sodium Storage

Preventing the aggregation of nanosized electrode materials is a key point to fully utilize the advantage of the high capacity. In this work, a facile and low‐cost surface solvation treatment is developed to synthesize Fe₂VO₄ hierarchical porous microparticles, which efficiently prevents the aggregation of the Fe₂VO₄ primary nanoparticles. The reaction between alcohol molecules and surface hydroxy groups is confirmed by density functional theory calculations and Fourier transform infrared spectroscopy. The electrochemical mechanism of Fe₂VO₄ as lithium‐ion battery anode is characterized by in situ X‐ray diffraction for the first time. This electrode material is capable of delivering a high reversible discharge capacity of 799 mA h g^?1 at 0.5 A g^?1 with a high initial coulombic efficiency of 79%, and the capacity retention is 78% after 500 cycles. Moreover, a remarkable reversible discharge capacity of 679 mA h g^?1 is achieved at 5 A g^?1. Furthermore, when tested as sodium‐ion battery anode, a high reversible capacity of 382 mA h g^?1 can be delivered at the current density of 1 A g^?1, which still retains at 229 mA h g^?1 after 1000 cycles. The superior electrochemical performance makes it a potential anode material for high‐rate and long‐life lithium/sodium‐ion batteries.     

Conversion Reaction Mechanism of Ultrafine Bimetallic Co‐Fe Selenides Embedded in Hollow Mesoporous Carbon Nanospheres and Their Excellent K‐Ion Storage Performance

Potassium‐ion batteries (KIBs) are considered as promising alternatives to lithium‐ion batteries owing to the abundance and affordability of potassium. However, the development of suitable electrode materials that can stably store large‐sized K ions remains a challenge. This study proposes a facile impregnation method for synthesizing ultrafine cobalt–iron bimetallic selenides embedded in hollow mesoporous carbon nanospheres (HMCSs) as superior anodes for KIBs. This involves loading metal precursors into HMCS templates using a repeated “drop and drying” process followed by selenization at various temperatures, facilitating not only the preparation of bimetallic selenide/carbon composites but also controlling their structures. HMCSs serve as structural skeletons, conductive templates, and vehicles to restrain the overgrowth of bimetallic selenide particles during thermal treatment. Various analysis strategies are employed to investigate the charge–discharge mechanism of the new bimetallic selenide anodes. This unique‐structured composite exhibits a high discharge capacity (485 mA h g^?1 at 0.1 A g^?1 after 200 cycles) and enhanced rate capability (272 mA h g^?1 at 2.0 A g^?1) as a promising anode material for KIBs. Furthermore, the electrochemical properties of various nanostructures, from hollow to frog egg‐like structures, obtained by adjusting the selenization temperature, are compared.