Constructing Heterostructured Bimetallic Selenides on an N-Doped Carbon Nanoframework as Anodes for Ultrastable Na-Ion Batteries

Rational Design of Quasi-1D Multicore-Shell MnSe@N-Doped Carbon Nanorods as High-Performance Anode Material for Sodium-Ion Batteries

Sodium-ion batteries (SIBs) are considered one of the promising candidates for energy storage devices due to the low cost and low redox potential of sodium. However, their implementation is hindered by sluggish kinetics and rapid capacity decay caused by inferior conductivity, lattice deterioration, and volume changes of conversion-type anode materials. Herein, we report the design of a multicore-shell anode material based on manganese selenide (MnSe) nanoparticle encapsulated N-doped carbon (MnSe@NC) nanorods. Benefiting from the conductive multicore-shell structure, the MnSe@NC anodes displayed prominent rate capability (152.7 mA h g-1 at 5 A g-1) and long lifespan (132.7 mA h g-1 after 2000 cycles at 5 A g-1), verifying the essence of reasonable anode construction for high-performance SIBs. Systematic in situ microscopic and spectroscopic methods revealed a highly reversible conversion reaction mechanism of MnSe@NC. Our study proposes a promising route toward developing advanced transition metal selenide anodes and comprehending electrochemical reaction mechanisms toward high-performance SIBs.

In-Depth Understanding of Interfacial Na+ Behaviors in Sodium Metal Anode: Migration, Desolvation, and Deposition

Interfacial Na+ behaviors of sodium (Na) anode severely threaten the stability of sodium-metal batteries (SMBs). This review systematically and in-depth discusses the current fundamental understanding of interfacial Na+ behaviors in SMBs including Na+ migration, desolvation, diffusion, nucleation, and deposition. The key influencing factors and optimization strategies of these behaviors are further summarized and discussed. More importantly, the high-energy-density anode-free sodium metal batteries (AFSMBs) are highlighted by addressing key issues in the areas of limited Na sources and irreversible Na loss. Simultaneously, recent advanced characterization techniques for deeper insights into interfacial Na+ deposition behavior and composition information of SEI film are spotlighted to provide guidance for the advancement of SMBs and AFSMBs. Finally, the prominent perspectives are presented to guide and promote the development of SMBs and AFSMBs.

Fabricating a high-performance anode by coating a carbon layer on a yolk-shell bimetallic selenide microsphere for enhanced lithium storage

The rational synthesis of an electrode material with a highly active and stable architecture is very critical to achieving high-performance electrochemical energy storage. Herein, N-doped carbon restricting yolk-shell CoSe2/Ni3Se4 (CoSe2/Ni3Se4@NC) flower-like microspheres were successfully synthesized from solid CoNi-glycerate microspheres using a coating technology as an anode material for lithium-ion batteries (LIBs). The unique yolk-shell CoSe2/Ni3Se4@NC microspheres with hierarchical pores can increase the contact area with the electrolyte and provide enough transfer channels for the diffusion of Li+. The carbon layer on the surface of CoSe2/Ni3Se4@NC can not only improve the conductivity of the electrode but also provide the protective effect of active nanosheets during the process of synthesis, avoiding the overall structure collapse during the charge/discharge process of LIBs. Benefiting from the high conductivity, hollow structure, and elastic NC shell bestowed by the unique architecture, the yolk-shell CoSe2/Ni3Se4@NC anode shows excellent lithium storage performances, such as an excellent reversible specific capacity of 319 mA h g-1 at a current density of 1000 mA g-1 after 500 cycles and excellent cycling stability. This synthesis strategy provides a new way to optimize the lithium storage performance of transition metal compound electrode materials, which is helpful to the design of the next generation of high-performance LIBs.

Fabrication of a Stable and Highly Effective Anode Material for Li-Ion/Na-Ion Batteries Utilizing ZIF-12

Transition metal selenides (TMSs) are receiving considerable interest as improved anode materials for sodium-ion batteries (SIBs) and lithium-ion batteries (LIBs) due to their considerable theoretical capacity and excellent redox reversibility. Herein, ZIF-12 (zeolitic imidazolate framework) structure is used for the synthesis of Cu2Se/Co3Se4@NPC anode material by pyrolysis of ZIF-12/Se mixture. When Cu2Se/Co3Se4@NPC composite is utilized as an anode electrode material in LIB and SIB half cells, the material demonstrates excellent electrochemical performance and remarkable cycle stability with retaining high capacities. In LIB and SIB half cells, the Cu2Se/Co3Se4@NPC anode material shows the ultralong lifespan at 2000 mAg-1, retaining a capacity of 543 mAhg-1 after 750 cycles, and retaining a capacity of 251 mAhg-1 after 200 cycles at 100 mAg-1, respectively. The porous structure of the Cu2Se/Co3Se4@NPC anode material can not only effectively tolerate the volume expansion of the electrode during discharging and charging, but also facilitate the penetration of electrolyte and efficiently prevents the clustering of active particles. In situ X-ray difraction (XRD) analysis results reveal the high potential of Cu2Se/Co3Se4@NPC composite in building efficient LIBs and SIBs due to reversible conversion reactions of Cu2Se/Co3Se4@NPC for lithium-ion and sodium-ion storage.

Heterogeneous engineering and carbon confinement strategy to synergistically boost the sodium storage performance of transition metal selenides

Transition metal selenides (TMSs) stand out as a promising anode material for sodium-ion batteries (SIBs) owing to their natural resources and exceptional sodium storage capacity. Despite these advantages, their practical application faces challenges, such as poor electronic conductivity, sluggish reaction kinetics and severe agglomeration during electrochemical reactions, hindering their effective utilization. Herein, the dual-carbon-confined CoSe2/FeSe2@NC@C nanocubes with heterogeneous structure are synthesized using ZIF-67 as the template by ion exchange, resorcin-formaldehyde (RF) coating, and subsequent in situ carbonization and selenidation. The N-doped porous carbon promotes rapid electrolyte penetration and minimizes the agglomeration of active materials during charging and discharging, while the RF-derived carbon framework reduces the cycling stress and keeps the integrity of the material structure. More importantly, the built-in electric field at the heterogeneous boundary layer drives electron redistribution, optimizing the electronic structure and enhancing the reaction kinetics of the anode material. Based on this, the nanocubes of CoSe2/FeSe2@NC@C exhibits superb sodium storage performance, delivering a high discharge capacity of 512.6 mA h g-1 at 0.5 A g-1 after 150 cycles and giving a discharge capacity of 298.2 mA h g-1 at 10 A g-1 with a CE close to 100.0 % even after 1000 cycles. This study proposes a viable method to synthesize advanced anodes for SIBs by a synergy effect of heterogeneous interfacial engineering and a carbon confinement strategy.

Construction of Sugar-Gourd-Shaped Carbon Nanofibers Embedded with Heterostructured Zinc-Cobalt Selenide Nanocages for Superior Potassium-Ion Storage

Transition metal selenides are considered as promising anode materials for potassium-ion batteries (PIBs) due to their high theoretical capacities. However, their applications are limited by low conductivity and large volume expansion. Herein, sugar-gourd-shaped carbon nanofibers embedded with heterostructured ZnCo-Se nanocages are prepared via a facile template-engaged method combined with electrospinning and selenization process. In this hierarchical ZnCo-Se@NC/CNF, abundant phase boundaries of CoSe2/ZnSe heterostructure can promote interfacial electron transfer and chemical reactivity. The interior porous ZnCo-Se@NC nanocage structure relieves volume expansion and maintains structural integrity during K+ intercalation and deintercalation. The exterior spinning carbon nanofibers connect the granular nanocages in series, which prevents the agglomeration, shortens the electron transport distance and enhances the reaction kinetics. As a self-supporting anode material, ZnCo-Se@NC/CNF delivers a high capacity (362 mA h g-1 at 0.1 A g-1 after 100 cycles) with long-term stability (95.9% capacity retention after 1000 cycles) and shows superior reaction kinetics with high-rate K-storage. Energy level analysis and DFT calculations illustrate heterostructure facilitates the adsorption of K+ and interfacial electron transfer. The K+ storage mechanism is revealed by ex situ XRD and EIS analyses. This work opens a novel avenue in designing high-performance heterostructured anode materials with ingenious structure for PIBs.

Boosting Manganese Selenide Anode for Superior Sodium-Ion Storage via Triggering α → β Phase Transition

Sodium-ion batteries (SIBs) have been extensively studied owing to the abundance and low-price of Na resources. However, the infeasibility of graphite and silicon electrodes in sodium-ion storage makes it urgent to develop high-performance anode materials. Herein, α-MnSe nanorods derived from δ-MnO2 (δ-α-MnSe) are constructed as anodes for SIBs. It is verified that α-MnSe will be transferred into β-MnSe after the initial Na-ion insertion/extraction, and δ-α-MnSe undergoes typical conversion mechanism using a Mn-ion for charge compensation in the subsequent charge-discharge process. First-principles calculations support that Na-ion migration in defect-free α-MnSe can drive the lattice distortion to phase transition (alpha → beta) in thermodynamics and dynamics. The formed β-MnSe with robust lattice structure and small Na-ion diffusion barrier boosts great structure stability and electrochemical kinetics. Hence, the δ-α-MnSe electrode contributes excellent rate capability and superior cyclic stability with long lifespan over 1000 cycles and low decay rate of 0.0267% per cycle. Na-ion full batteries with a high energy density of 281.2 Wh·kg-1 and outstanding cyclability demonstrate the applicability of δ-α-MnSe anode.

Advanced Anode Materials for Rechargeable Sodium-Ion Batteries

Rechargeable sodium-ion batteries (SIBs) have been considered as promising energy storage devices owing to the similar "rocking chair" working mechanism as lithium-ion batteries and abundant and low-cost sodium resource. However, the large ionic radius of the Na-ion (1.07 Å) brings a key scientific challenge, restricting the development of electrode materials for SIBs, and the infeasibility of graphite and silicon in reversible Na-ion storage further promotes the investigation of advanced anode materials. Currently, the key issues facing anode materials include sluggish electrochemical kinetics and a large volume expansion. Despite these challenges, substantial conceptual and experimental progress has been made in the past. Herein, we present a brief review of the recent development of intercalation, conversion, alloying, conversion-alloying, and organic anode materials for SIBs. Starting from the historical research progress of anode electrodes, the detailed Na-ion storage mechanism is analyzed. Various optimization strategies to improve the electrochemical properties of anodes are summarized, including phase state adjustment, defect introduction, molecular engineering, nanostructure design, composite construction, heterostructure synthesis, and heteroatom doping. Furthermore, the associated merits and drawbacks of each class of material are outlined, and the challenges and possible future directions for high-performance anode materials are discussed.

ZIF-67-derived Co/CoSe ultrafine nanocrystal Schottky heterojunction decorated hollow carbon nanospheres as new-type anodes for potassium-ion batteries

Metal-organic frameworks (MOFs) have the advantages of controllable chemical properties, rich pore structures and reaction sites and are expected to be high-performance anode materials for the next generation of potassium-ion batteries (PIBs). However, due to the large radius of potassium ions, the pure MOF crystal structure is prone to collapse during ion insertion and processing, so its electrochemical performance is quite limited. In this work, a hollow carbon sphere-supported MOF-derived Co/CoSe heterojunction anode material for potassium-ion batteries was developed by a hydrothermal method. The anode has high potassium storage capacity (461.9 mA h/g after 200 cycles at 1 A/g), excellent cycling stability and superior rate performance. It is worth noting that the potassium ion storage capacity of the anode material shows a gradual upward trend with the charge-discharge cycle, which is 145.9 mA h/g after 3000 cycles at a current density of 10 A/g. This work demonstrates that MOF-derived CoSe anodes with high capacity and low cost may be promising candidates for the introduction of potassium ion storage.

Self-assembled nanoflower-like FeSe2/MoSe2 heterojunction anode with enhanced kinetics for superior-performance Na-ion half/full batteries

Transition metal selenides are a research hotspot in sodium-ion batteries (SIBs). However, slow kinetics and rapid capacity decay due to volume changes during cycling limit their commercial applications. Heterostructures have the ability to accelerate charge transport and are widely used in energy storage devices due to their abundant active sites and lattice interfaces. A rational design of heterojunction electrode materials with excellent electrochemical performance is essential for SIBs. Herein, a novel anode material heterostructured FeSe₂/MoSe₂ (FMSe) nanoflower for SIBs was successfully prepared through a facile co-precipitation and hydrothermal route. The as-prepared FMSe heterojunction exhibits excellent electrochemical performance, including a high invertible capacity (493.7 mA h g^-1 after 150 cycles at 0.2 A g^-1), long-term cycling stability (352.2 mA h g^-1 even after 4200 cycles at 5.0 A g^-1) and competitive rate capability (361.2 mA h g^-1 at 20 A g^-1). By matching with a Na₃V₂(PO₄)₃ cathode, it can even exhibit ideal cycling stability (123.5 mA h g^-1 at 0.5 A g^-1 after 200 cycles). Furthermore, the sodium storage mechanism of the FMSe electrodes was systematically determined by ex situ electrochemical techniques. Theoretical calculation also reveals that the heterostructure on the FMSe interface enhances charge transport and promotes reaction kinetics.

Phase-Dependent Energy Storage Performance of the NixSey Polymorphs for Supercapacitor-Battery Hybrid Devices

Transition-metal chalcogenides have emerged as a promising class of materials for energy storage applications due to their earth abundance, high theoretical capacity, and high electrical conductivity. Herein, we introduce a facile and one-pot electrodeposition method to prepare high-performance nickel selenide Ni_xSe_y (0.5 ≤ x/y ≤ 1.5) nanostructures (specific capacity = 180.3 mA h g^-1 at 1 A g^-1). The as-synthesized nickel selenide (NS) nanostructure is however converted to other polymorphs of nickel selenide including orthorhombic NiSe₂, trigonal Ni₃Se₂, hexagonal NiSe, and orthorhombic Ni₆Se₅ over cycling. Interestingly, NiSe₂ and Ni₃Se₂ polymorphs that display a more metallic character and superior energy storage performance are the predominant phases after a few hundred cycles. We fabricated a hybrid device using activated carbon (AC) as a supercapacitor-type negative electrode and NS as a high-rate battery-type positive electrode (AC||NS). This hybrid device provides a high specific energy of 71 W h kg^-1, an excellent specific power of up to 31 400 W kg^-1, and exceptional cycling stability (80% retention of the initial capacity after 20 000 cycles). The higher energy storage performance of the device is a result of the development of high-performance NiSe₂ and Ni₃Se₂ polymorphs. Moreover, the reduction of the critical dimension of the NS particles to the nanoscale partially induces an extrinsic pseudocapacitive behavior that improves the rate capability and durability of the device. We also explored the origin of the superior energy storage performance of the NS polymorphs using density functional theory calculations in terms of the computed density of states around the Fermi level, electrical conductivity, and quantum capacitance that follows the trend NiSe₂ > Ni₃Se₂ > NiSe > Ni₆Se₅. The present study thus provides an appealing approach for tailoring the phase composition of NS as an alternative to the commonly used templated synthesis methods.

N4-Vacancy-Functionalized Carbon for High-Rate Li-Ion Storage

Although heteroatom doping and pore management separately influence the Li⁺ adsorption and Li⁺ diffusion properties, respectively, merging their functions into a single unit is intriguing and has not been fully investigated. Herein, we have successfully incorporated both heteroatom doping and pore management within the same functional unit of N₄-vacancy motifs, which is realized via acid etching of formamide-derived Zn-N₄-functionalized carbon materials (Zn₁NC). The N₄-vacancy-rich porous carbon (V-NC) renders multiple merits: (1) a high N content of 13.94 atom % for large Li-storage capacity, (2) edged unsaturated N sites favoring highly efficient Li⁺ adsorption and desolvation, and (3) a shortening of the Li⁺ diffusion length through N₄ vacancy, thereby enhancing the Li-storage kinetics and high-rate performance. This work serves as an inspiration for the creation of heteroatom-edged porous structures with controllable pore sizes for high-rate alkali-ion battery applications.

Amylopectin-Assisted Fabrication of In Situ Carbon-Coated Na3V2(PO4)2F3 Nanosheets for Ultra-Fast Sodium Storage

Na₃V₂(PO₄)₂F₃ is one of the most studied polyanion type cathode materials for sodium-ion batteries (SIBs) and offers great promises. However, the inferior rate capability induced by its sluggish diffusion of electrons and ions greatly limits the practical application of electrode materials in SIBs. Herein, we develop an efficient method to fabricate in situ carbon-coated Na₃V₂(PO₄)₂F₃ nanosheets by using cost-effective amylopectin. The amylopectin not only could induce the nucleation of Na₃V₂(PO₄)₂F₃ along its backbone to form a 2D nanostructure, but also act as a source of amorphous carbon for in situ coating on the active material surface. The composite exhibits extraordinary rate capability (104 mA h g^-1 at 40 C, 51 mA h g^-1 at 150 C) and desirable cycling stability. Such satisfactory achievements, especially the superior rate performance, should be ascribed to its unique 2D nanostructure which shortens the Na⁺ diffusion length, and the in situ carbon coating endows the composites with effective electron transport. Even applied to full cells, the obtained devices still display an exceptionally high energy density (94.8 W h kg^-1), high power density (7295 W kg^-1), and excellent cyclic stability.

Research progress on ZnSe and ZnTe anodes for rechargeable batteries

Transition-metal chalcogenides (TMCs) with tunable direct bandgaps and interlayer spacing are attractive for energy-related applications. Semiconducting zinc chalcogenides, especially their selenides (ZnSe) and tellurides (ZnTe), with enhanced conductivity, high theoretical capacity, low operation voltage and abundance, have appeared on the horizon and receive increasing interest in terms of electrochemical energy storage and conversion. Despite the existing typical obstruction owing to the large volume change, relatively low electrical conductivity and sluggish ion diffusion kinetics into the bulk phase, several effective strategies such as compositing, doping, nanostructuring, and electrode/cell design have exhibited promising applications. We herein provide a timely and systematic overview of recent research and significant advances regarding ZnSe, ZnTe and their hybrids/composites, covering synthesis to electrode design and to applications, especially in advanced Li/Na/K-ion batteries, as well as the reaction mechanisms thereof. It is hoped that the overview will shed new light on the development of ZnSe and ZnTe for next-generation rechargeable batteries.