Surface-Confined SnS2 @C@rGO as High-Performance Anode Materials for Sodium- and Potassium-Ion Batteries

Tailoring Stress-Relieved Structure for SnSe Toward High Performance Potassium Ion Batteries

Metal chalcogenides as an ideal family of anode materials demonstrate a high theoretical specific capacity for potassium ion batteries (PIBs), but the huge volume variance and poor cyclic stability hinder their practical applications. In this study, a design of a stress self-adaptive structure with ultrafine SnSe nanoparticles embedded in carbon nanofiber (SnSe@CNF) via the electrospinning technology is presented. Such an architecture delivers a record high specific capacity (272 mAh g-1 at 50 mA g-1) and high-rate performance (125 mAh g-1 at 1 A g-1) as a PIB anode. It is decoded that the fundamental understanding for this great performance is that the ultrafine SnSe particles enhance the full utilization of the active material and achieve stress relief as the stored strain energy from cycling is insufficient to drive crack propagation and thus alleviates the intrinsic chemo-mechanical degradation of metal chalcogenides.

Bi Nanospheres Embedded in N-Doped Carbon Nanowires Facilitate Ultrafast and Ultrastable Sodium Storage

Sodium ion batteries (SIBs) are considered as the ideal candidates for the next generation of electrochemical energy storage devices. The major challenges of anode lie in poor cycling stability and the sluggish kinetics attributed to the inherent large Na+ size. In this work, Bi nanosphere encapsulated in N-doped carbon nanowires (Bi@N-C) is assembled by facile electrospinning and carbonization. N-doped carbon mitigates the structure stress/strain during alloying/dealloying, optimizes the ionic/electronic diffusion, and provides fast electron transfer and structural stability. Due to the excellent structure, Bi@N-C shows excellent Na storage performance in SIBs in terms of good cycling stability and rate capacity in half cells and full cells. The fundamental mechanism of the outstanding electrochemical performance of Bi@N-C has been demonstrated through synchrotron in-situ XRD, atomic force microscopy, ex-situ scanning electron microscopy (SEM) and density functional theory (DFT) calculation. Importantly, a deeper understanding of the underlying reasons of the performance improvement is elucidated, which is vital for providing the theoretical basis for application of SIBs.

Elastic Restraint Induced by Carbon Coating Enhances Potassium-Ion Batteries' Performance via Phase Transition

Potassium-ion batteries (PIBs) possess great potential in the next generation of large-scale energy storage due to their abundant sources and suitable operating voltage. However, the serious volume expansion resulting from the large radius of K+ makes it difficult to insert and extract, which greatly limits the development of PIBs. Herein, tin phosphide coated with carbon (Sn4P3@C) is designed for the PIB anode material by in situ construction of robust physical barriers of carbonaceous materials to accommodate the strain induced by volume expansion. Furthermore, the unique elastic restraint induced by the carbon coating in Sn4P3@C blocks the phase transition of α-Sn to β-Sn during the process of potassiation. Meanwhile, the existence of α-Sn facilitates K+ diffusion dynamics, endowing the Sn4P3@C electrode with high reversible discharge ability, good circularity, and a low discharge plateau. Moreover, the electrode can maintain a capacity of 187 mAh g-1 over repeated 1500 cycles at 1 A g-1. This work not only explores the chemical kinetics of K+ in Sn4P3 but also provides a new idea for basic research of tin-based anode materials.

Structural engineering of SnS quantum dots embedded in N, S Co-Doped carbon fiber network for ultrafast and ultrastable sodium/potassium-ion storage

Tin sulfides have received significant attention as potential candidates for sodium-ion batteries (SIBs) and potassium-ion batteries (PIBs) due to their abundance, high theoretical capacity, and favorable working potential. However, the inherent drawbacks such as slow kinetics, low intrinsic electronic conductivity, and significant volume change during cycling, have not been adequately addressed. In this study, we propose a rational and effective approach to simultaneously overcome these challenges by embedding stannous sulfide (SnS) quantum dots (QDs) within a crosslinked nitrogen (N) and sulfur (S) co-doped carbon fiber network (SnS-CFN). The well-dispersed and densely packed SnS QDs, measuring approximately 2 nm, not only minimize the diffusion distance of Na+/K+ ions but also buffer the volume expansion effectively. The N, S co-doped carbon fiber network in SnS-CFN serves as a highly conductive and stable support structure that inhibits SnS QDs aggregation, creates ion/electron transport channels, and alleviates volume variations. Density functional theory (DFT) calculations further confirm that the combination of SnS QDs and the N, S co-doped carbon effectively reduces the adsorbed energies in the interlayer of SnS-CFN. These advantages synergistically contribute to the exceptional sodium/potassium storage performance of the SnS-CFN composite. Consequently, SnS-CFN demonstrates exceptional cyclability, retaining a capacity of 251.5 mAh/g over 10,000 cycles, and exhibits excellent rate capability (299.5 mAh/g at 20 A/g) when employed in SIBs. When used in PIBs, a high capacity of 112.3 mAh/g at 2 A/g after 1000 cycles, a remarkable capacity of 51.4 mAh/g at 5 A/g after 10,000 cycles, and a remarkable rate capability with a specific capacity of 55.5 mAh/g at a high current density of 20 A/g have been achieved.

Metal-Organic Assembly Strategy for the Synthesis of Layered Metal Chalcogenide Anodes for Na+ /K+ -Ion Batteries

Layered transition metal chalcogenides (MX, M=Mo, W, Sn, V; X=S, Se, Te) have large ion transport channels and high specific capacity, making them promising for large-sized Na⁺ /K⁺ energy-storage technologies. Nevertheless, slow reaction kinetics and huge volume expansion will induce an undesirable electrochemical performance. Numerous efforts have been devoted to designing MX anodes and enhancing their electrochemical performance. Based on the metal-organic assembly strategy, nanostructural engineering, combination with carbon materials, and component regulation can be easily realized, which effectively boost the performance of MX anodes. In this Review, we present a comprehensive overview on the synthesis of MX nanostructure using the metal-organic assembly strategy, which can realize the design of MX nanostructures, based on self-sacrificial templates, host@guest tailored templates, post-modified layer and derivative templates. The preparation routes and structure evolution are mainly discussed. Then, Mo-, W-, Sn-, V-based chalcogenides used for Na⁺ /K⁺ energy storage are reviewed, and the relationship between the structure and the electrochemical performance, as well as the energy storage mechanism are emphasized. In addition, existing challenges and future perspectives are also presented.

Investigation of SnS2 -rGO Sandwich Structures as Negative Electrode for Sodium-Ion and Potassium-Ion Batteries

Sodium-ion and potassium-ion batteries (NIBs and KIBs) are considered promising alternatives to replace lithium-ion batteries (LIBs) in energy storage applications due to the natural abundance and low cost of Na and K. Nevertheless, a critical challenge is that the large size of Na⁺ /K⁺ leads to a huge volume change of the hosting material during electrochemical cycling, resulting in rapid capacity decay. Among negative candidates for alkali-metal-ion batteries, SnS₂ is attractive due to the competitively high specific capacity, low redox potential and high abundance. Porous few-layer SnS₂ nanosheets are in situ grown on reduced graphene oxide, forming a SnS₂ -rGO sandwich structure via strong C-O-Sn bonds. This nano-scaled sandwich structure not only shortens Na⁺ /K⁺ and electron transport pathways but also accommodates volume expansion, thereby enabling high and stable electrochemical cycling performance of SnS₂ -rGO. This work explores the influence of different conductive carbons (Super P and C65) on the SnS₂ -rGO electrode. In addition, the effects of the electrolyte additive fluoroethylene carbonate (FEC) on the electrochemical performance in NIBs and KIBs is evaluated. This work provides guidelines for optimized electrode structure design, electrolyte additives and carbon additives for the realization of better NIBs and KIBs.

Multi-heterostructured SnO2/SnSx embedded in carbon framework for high-performance sodium-ion storage

Heterostructure materials, as newborn electrode materials for rechargeable batteries, are attracting increasing attention due to their robust architectures and superior electrochemical performances. It is widely believed that the inner electric field induced at the interface can improve the electric conductivity and ion diffusion kinetics, thus enhancing the long-term stability and high-rate performance of the batteries. Although much progress is made on heterostructure construction, the performance of the batteries is still far from satisfying the commercial applications. In this work, a new type of SnO₂/SnS_x (x = 1, 1.5) heterostructure embedded in carbon framework (C@SnO₂/SnS_x) is constructed via a facile sulfidation process. Compared to a single heterojunction, the multi-heterojunctions generated at SnO₂/SnS_x interface can induce an intensified built-in electric field, which promotes charge transportation and reaction kinetics of the electrode for Na-ions storage. Upon the sodiation process, the induced intensified electric field drives Na ions from Sn₂S₃ or SnO₂ to SnS, while an inverse transportation of Na ions are accelerated upon the desodation process. As a result, C@SnO₂/SnS_x exhibits an outstanding reversible capacity of 510 mA h g^-1 after 300 cycles at 200 mA g^-1.

Focusing on the Subsequent Coulombic Efficiencies of SiOx: Initial High-Temperature Charge after Over-Capacity Prelithiation for High-Efficiency SiOx-Based Full-Cell Battery

SiO_x-based anode materials are considered to be promising and have been gradually commercialized due to their high specific capacity as well as the acceptable volume change during lithiation/delithiation and preferable cycling stability compared to that of Si. Nevertheless, their inherently low Coulombic efficiency hinders the large-scale application. Up to now, researchers have paid much attention to the initial Coulombic efficiency and developed a series of effective prelithiation strategies. However, the subsequent cycles (focusing on the 2nd to 10th), during which the SiO_x anode suffers great lithium consumption as well, have received scarcely any concerns. In this work, a strategy of high-temperature (50 °C) initial charge after an overcapacity prelithiation for a SiO_x-based full-cell battery is proposed. As high temperature can promote the reaction between lithium and the SiO₂ matrix of SiO_x, SiO₂ will experience a one-step thorough reduction rather than gradual conversion in subsequent cycles, improving the subsequent Coulombic efficiencies (SCEs) accordingly. Overcapacity prelithiation can be achieved safely at 50 °C without Li metal depositon, just enough to meet the more initial lithium demand of anode at 50 °C. Furthermore, the initial deeper reduction of SiO₂ will release extra Si, improving the reversible capacity consequently. With the 50 °C initial charge after an overcapacity prelithiation, the full-cell battery exhibits considerable capacity retention as expected. This work raises concerns on SCEs of SiO_x-based anode innovatively, providing a feasible avenue for improving the capacity retention of a SiO_x-based full-cell battery.

Large-scale synthesis of few-layered copper antimony sulfide nanosheets as electrode materials for high-rate potassium-ion storage

Metal chalcogenides (MCs) have received widespread attentions in potassium ion storage, due to their high theoretical specific capacity and low cost. However, practical applications are still a challenge because of the slow diffusion rate and large ionic radius, leading to dramatic volume expansion and slow rate performance. Herein, we introduce a simple and large scale solvothermal method to synthesize high-quality two-dimensional (2D) layered CuSbS₂ nanosheets with a thickness of about 5 nm. The thin 2D layered structure has a weak van der Waals gap and a large exposed surface area to contact the electrolyte and promotes rapid K⁺ diffusion kinetics. In addition, the in-situ copper exsolution during potassiation process enhances the rate capability of K⁺ storage. CuSbS₂ half cells exhibited excellent rate performance, delivering specific capacities of 573, 505, 476, 230, 177 mAh g^-1 at current densities of 0.1, 0.5, 1, 5, 10 A g^-1, respectively. The unique K⁺ electrochemical storage mechanism and resistance change during reaction process was revealed in detail by operando XRD, XPS and TEM. Finally, potassium ion hybrid capacitors (PIHCs) with CuSbS₂ nanosheets as anode and AC as cathode demonstrated excellent performances with the maximum energy density of 127 W h kg^-1 and the power density of 2415 W kg^-1, providing an example of rationally design a high rate battery-type PIHC anode.

Heterostructure engineering of ultrathin SnS2/Ti3C2Tx nanosheets for high-performance potassium-ion batteries

Layered metal sulfides are considered as promising candidates for potassium ion batteries (KIBs) owing to the unique interlayer passages for ion diffusion. However, the insufficient electronic conductivity, inevitable volume expansion, and sulfur loss hinder the promotion of K-ion storage performance. Herein, few-layered Ti₃C₂T_x nanosheets were selected as the multi-functional substrate for cooperating few-layered SnS₂ nanosheets, constructing SnS₂/Ti₃C₂T_x hetero-structural nanosheets (HNs) with the thickness as thin as about 5 nm. In this configuration, the formed Ti-S bonds provide robust interaction between SnS₂ and Ti₃C₂T_x nanosheets, which hinders the agglomeration of SnS₂ and the restack of Ti₃C₂T_x, endowing the hybrid material with robust nanostructure. Thus, the shortcomings of the SnS₂ anode are muchly relieved. In this way, the as-prepared SnS₂/Ti₃C₂T_x HNs electrode delivers reversible capacities of 462.1 mAh g^-1 at 0.1 A g^-1 and 166.1 mAh g^-1 at 2.0 A g^-1, respectively, and a capacity of 85.5 mAh g^-1 is remained even after 460 cycles at 2.0 A g^-1. These results are superior to those of the counterpart electrode, confirming aggressive promotion of K-ion storage performance of SnS₂ anode brought by the cooperation of Ti₃C₂T_x, and presenting a reliable strategy to improve the electrochemical performance of sulfide anodes.

Prospects of Electrode Materials and Electrolytes for Practical Potassium-Based Batteries

Potassium-ion batteries (PIBs) have attracted tremendous attention because of their high energy density and low-cost. As such, much effort has focused on developing electrode materials and electrolytes for PIBs at the material levels. This review begins with an overview of the high-performance electrode materials and electrolytes, and then evaluates their prospects and challenges for practical PIBs to penetrate the market. The current status of PIBs for safe operation, energy density, power density, cyclability, and sustainability is discussed and future studies for electrode materials, electrolytes, and electrode-electrolyte interfaces are identified. It is anticipated that this review will motivate research and development to fill existing gaps for practical potassium-based full batteries so that they may be commercialized in the near future.

Dual Enhancement of Sodium Storage Induced through Both S-Compositing and Co-Doping Strategies

As a promising alternative to lithium-ion batteries (LIBs), rechargeable sodium-ion batteries (SIBs) are attracting enormous attention due to the abundance of sodium. However, the lack of high-performance sodium anode materials limits the commercialization of SIBs. In this work, the dual enhancement of SnS₂/graphene anodes in sodium storage is achieved through S-compositing and Co doping via an innovative one-step hydrothermal reaction at a relatively low temperature of 120 °C. The as-prepared 7% Co-SnS₂/S@r-G composite consisting of 15.4 wt % S and 1.49 atom % Co shows both superior cycling stability (over 1000 cycles) and rate capability, giving high reversible specific capacities of 878, 608, and 470 mAh g^-1 at 0.2, 5, and 10 A g^-1, respectively. More encouragingly, the full-cell also exhibits an outstanding long-term cycling performance under 0.5 A g^-1, which delivers a reversible capacity of 500 mAh g^-1 over 200 cycles and still retains a high reversible capacity of 432 mAh g^-1 over 400 cycles. The enhancement mechanism is attributed to the favorable three-dimensional structure of the composite, Co doping, and S-composition, which can induce a synergistic effect.

Conversion-Alloying Anode Materials for Sodium Ion Batteries

The past decade has witnessed a rapidly growing interest toward sodium ion battery (SIB) for large-scale energy storage in view of the abundance and easy accessibility of sodium resources. Key to addressing the remaining challenges and setbacks and to translate lab science into commercializable products is the development of high-performance anode materials. Anode materials featuring combined conversion and alloying mechanisms are one of the most attractive candidates, due to their high theoretical capacities and relatively low working voltages. The current understanding of sodium-storage mechanisms in conversion-alloying anode materials is presented here. The challenges faced by these materials in SIBs, and the corresponding improvement strategies, are comprehensively discussed in correlation with the resulting electrochemical behavior. Finally, with the guidance and perspectives, a roadmap toward the development of advanced conversion-alloying materials for commercializable SIBs is created.

Synergistic Engineering of Defects and Heterostructures Enhance Lithium/Sodium Storage Properties of F-SnO2-x -SnS2-x Nanocrystals Supported on N,S-Graphene

Phase engineering of the electrode materials in terms of designing heterostructures, introducing heteroatom and defects, improves great prospects in accelerating the charge storage kinetics during the repeated Li⁺ /Na⁺ insertion/deintercalation. Herein, a new design of Li/Na-ion battery anodes through phase regulating is reported consisting of F-doped SnO₂ -SnS₂ heterostructure nanocrystals with oxygen/sulfur vacancies (V_O /V_S ) anchored on a 2D sulfur/nitrogen-doped reduced graphene oxide matrix (F-SnO_2-x -SnS_2-x @N/S-RGO). Consequently, the F-SnO_2-x -SnS_2-x @N/S-RGO anode demonstrates superb high reversible capacity and long-term cycling stability. Moreover, it exhibits excellent great rate capability with 589 mAh g^-1 for Li⁺ and 296 mAh g^-1 at 5 A g^-1 for Na⁺ . The enhanced Li/Na storage properties of the nanocomposites are not only attributed to the increase in conductivity caused by V_O /V_S and F doping (confirmed by DFT calculations) to accelerate their charge-transfer kinetics but also the increased interaction between F-SnO_2-x -SnS_2-x and Li/Na through heterostructure. Meanwhile, the hierarchical F-SnO_2-x -SnS_2-x @N/S-RGO network structure enables fast infiltration of electrolyte and improves electron/ion transportation in the electrode, and the corrosion resistance of F doping contributes to prolonged cycle stability.

Research progress in transition metal chalcogenide based anodes for K-ion hybrid capacitor applications: a mini-review

Metal ion capacitors have gained a lot of interest as a new kind of capacitor-battery hybrid energy storage system because of their high power density while maintaining energy density and a long lifetime. Potassium ion hybrid capacitors (PIHCs) have been suggested as possible alternatives to lithium-ion/sodium-ion capacitors because of the plentiful potassium supplies, and their lower standard electrode potential and low cost. However, due to the large radius of the potassium ion, PIHCs also face unsatisfactory reaction kinetics, low energy density, and short lifespan. Recently, transition metal chalcogenide (TMC)-based materials with distinctive structures and fascinating characteristics have been considered an emerging candidate for PIHCs, owing to their unique physical and chemical properties. This mini-review mainly focuses on the recent research progress on TMC-based materials for the PIHC applications summarized. Finally, the existing challenges and perspectives are given to improve further and construct advanced TMC-based electrode materials.

Metal ion capacitors have gained a lot of interest as a new kind of capacitor-battery hybrid energy storage system because of their high power density while maintaining energy density and a long lifetime.

Dual Confinement of CoSe2 Nanorods with Polyphosphazene-Derived Heteroatom-Doped Carbon and Reduced Graphene Oxide for Potassium-Ion Batteries

High-capacity and highly stable anode materials are some of the keys to the realization of the application of potassium-ion batteries (PIBs). Cobalt diselenide (CoSe₂) has been regarded as a high-potential anode material for PIBs. However, solving the problems of sluggish kinetics and large volumetric expansion during intercalation/deintercalation of K⁺ ions is always very challenging in terms of cobalt diselenide-based anode materials. Herein, reduced graphene oxide-encapsulated polyphosphazene-derived S, P, and N codoped carbon (SPNC)-coated CoSe₂ nanorods (CoSe₂⊂SPNC⊂rGO) were designed as PIB anode materials. CoSe₂⊂SPNC⊂rGO delivers an excellent reversible capacity of 287.2 mAh g^-1 at 100 mA g^-1. Benefiting from the coating of heteroatom-doped carbon and encapsulation of rGO, the CoSe₂⊂SPNC⊂rGO anodes exhibit a remarkable rate capability (100-1500 mA g^-1 current density) and high stability (208.8 mAh g^-1 after 500 cycles at 500 mA g^-1). The results demonstrate that S, P, and N codoping in carbon layers provides active sites for K⁺ ion storage and increases the electrical conductivity. More importantly, the dual confinement of CoSe₂ nanorods with carbon layers and rGO significantly reduced the volume expansion and kept the electrode structural integrity with repeating intercalation/deintercalation of K⁺ ions.

State-of-the-art anodes of potassium-ion batteries: synthesis, chemistry, and applications

The growing demand for green energy has fueled the exploration of sustainable and eco-friendly energy storage systems. To date, the primary focus has been solely on the enhancement of lithium-ion battery (LIB) technologies. Recently, the increasing demand and uneven distribution of lithium resources have prompted extensive attention toward the development of other advanced battery systems. As a promising alternative to LIBs, potassium-ion batteries (KIBs) have attracted considerable interest over the past years owing to their resource abundance, low cost, and high working voltage. Capitalizing on the significant research and technological advancements of LIBs, KIBs have undergone rapid development, especially the anode component, and diverse synthesis techniques, potassiation chemistry, and energy storage applications have been systematically investigated and proposed. In this review, the necessity of exploring superior anode materials is highlighted, and representative KIB anodes as well as various structural construction approaches are summarized. Furthermore, critical issues, challenges, and perspectives of KIB anodes are meticulously organized and presented. With a strengthened understanding of the associated potassiation chemistry, the composition and microstructural modification of KIB anodes could be significantly improved.

Enhanced Potassium Storage Capability of Two-Dimensional Transition-Metal Chalcogenides Enabled by a Collective Strategy

Potassium-ion batteries (PIBs) have been considered as a promising alternative to lithium-ion batteries due to their merits of high safety and low cost. Two-dimensional transition-metal chalcogenides (2D TMCs) with high theoretical specific capacities and unique layered structures have been proven to be amenable materials for PIB anodes. However, some intrinsic properties including severe stacking and unsatisfactory conductivity restrict their electrochemical performance, especially rate capability. Herein, we prepared a heterostructure of high-crystallized ultrathin MoSe₂ nanosheet-coated multiwall carbon nanotubes and investigated its electrochemical properties with a view to demonstrating the enhancement of a collective strategy for K storage of 2D TMCs. In such a heterostructure, the constructive contribution of CNTs not only suppresses the restacking of MoSe₂ nanosheets but also accelerates electron transport. Meanwhile, the MoSe₂ nanosheets loaded on CNTs exhibit an ultrathin feature, which can expose abundant active sites for the electrochemical reaction and shorten K⁺ diffusion length. Therefore, the synergistic effect between ultrathin MoSe₂ and CNTs endows the resulting nanocomposite with superior structural and electrochemical properties. Additionally, the high crystallinity of the MoSe₂ nanosheets further leads to the improvement of electrochemical performance. The composite electrode delivers high-rate capacities of 209.7 and 186.1 mAh g^-1 at high current densities of 5.0 and 10.0 A g^-1, respectively.

SnS2 Nanosheets Anchored on Nitrogen and Sulfur Co-Doped MXene Sheets for High-Performance Potassium-Ion Batteries

Potassium-ion batteries (KIBs) are emerging as the prospective alternatives to lithium-ion batteries in energy storage systems owing to the sufficient resources and relatively low cost of K-related materials. However, serious volume expansion and low specific capacity are found in most materials systems resulting from the large intrinsic radius of K⁺. Herein, SnS₂ nanosheets anchored on nitrogen and sulfur co-doped MXene (SnS₂ NSs/MXene) are creatively designed as advanced anode materials for KIBs. SnS₂ NSs/MXene with a unique hierarchical structure can not only provide fast transmission channels for K⁺ but also avoid the accumulation of K⁺ and volume expansion. These novel features make SnS₂ NSs/MXene electrodes exhibit a superior reversible specific capacity of 342.4 mA h g^-1 under 50 mA g^-1. Also, they maintain 206.1 mA h g^-1 at an even higher current density of 0.5 A g^-1 over 800 cycles almost without capacity decay. Moreover, the multistep alloying reaction mechanism of SnS₂ NSs/MXene composites and K⁺ is revealed by the ex situ X-ray diffraction measurement. In addition, the density functional theory calculations confirm the existence of Ti-S bonds between SnS₂ nanosheets and MXene, which significantly enhance the structural stability and cycling electrochemical performance of SnS₂ NSs/MXene composites.

Iron Selenide Microcapsules as Universal Conversion-Typed Anodes for Alkali Metal-Ion Batteries

Rechargeable alkali metal-ion batteries (AMIBs) are receiving significant attention owing to their high energy density and low weight. The performance of AMIBs is highly dependent on the electrode materials. It is, therefore, quite crucial to explore suitable electrode materials that can fulfil the future requirements of AMIBs. Herein, a hierarchical hybrid yolk-shell structure of carbon-coated iron selenide microcapsules (FeSe₂ @C-3 MCs) is prepared via facile hydrothermal reaction, carbon-coating, HCl solution etching, and then selenization treatment. When used as the conversion-typed anode materials (CTAMs) for AMIBs, the yolk-shell FeSe₂ @C-3 MCs show advantages. First, the interconnected external carbon shell improves the mechanical strength of electrodes and accelerates ionic migration and electron transmission. Second, the internal electroactive FeSe₂ nanoparticles effectively decrease the extent of volume expansion and avoid pulverization when compared with micro-sized solid FeSe₂ . Third, the yolk-shell structure provides sufficient inner void to ensure electrolyte infiltration and mobilize the surface and near-surface reactions of electroactive FeSe₂ with alkali metal ions. Consequently, the designed yolk-shell FeSe₂ @C-3 MCs demonstrate enhanced electrochemical performance in lithium-ion batteries, sodium-ion batteries, and potassium-ion batteries with high specific capacities, long cyclic stability, and outstanding rate capability, presenting potential application as universal anodes for AMIBs.

Emerging Potassium-ion Hybrid Capacitors

As a new type of capacitor-battery hybrid energy storage device, metal-ion capacitors have attracted widespread attention because of their high-power density while ensuring energy density and long lifespan. Potassium-ion capacitors (KICs) featuring the merits of abundant potassium resources, lower standard electrode potential, and low cost have been considered as potential alternatives to lithium-/sodium-ion capacitors. However, KICs still face issues including unsatisfactory reaction kinetics, low energy density, and poor lifetime owing to the large radius of the potassium ion. In this Review, the importance of emerging potassium-ion capacitor is addressed. The Review offers a brief discussion of the fundamental working principle of KICs, along with an overview of recent advances and achievements of a variety of electrode materials for dual carbon and non-dual carbon KICs. Furthermore, electrolyte chemistry, binders as well as electrode/electrolyte interface, are summarized. Finally, existing challenges and perspectives on further development of KICs are also presented.

Structural Engineering of SnS2 Encapsulated in Carbon Nanoboxes for High-Performance Sodium/Potassium-Ion Batteries Anodes

Conversion-alloying type anode materials like metal sulfides draw great attention due to their considerable theoretical capacity for sodium-ion batteries (SIBs) and potassium-ion batteries (PIBs). However, poor conductivity, severe volume change, and harmful aggregation of the material during charge/discharge lead to unsatisfying electrochemical performance. Herein, a facile and green strategy for yolk-shell structure based on the principle of metal evaporation is proposed. SnS₂ nanoparticle is encapsulated in nitrogen-doped hollow carbon nanobox (SnS₂ @C). The carbon nanoboxes accommodate the volume change and aggregation of SnS₂ during cycling, and form 3D continuous conductive carbon matrix by close contact. The well-designed structure benefits greatly in conductivity and structural stability of the material. As expected, SnS₂ @C exhibits considerable capacity, superior cycling stability, and excellent rate capability in both SIBs and PIBs. Additionally, in situ Raman technology is unprecedentedly conducted to investigate the phase evolution of polysulfides. This work provides an avenue for facilely constructing stable and high-capacity metal dichalcogenide based anodes materials with optimized structure engineering. The proposed in-depth electrochemical measurements coupled with in situ and ex situ characterizations will provide fundamental understandings for the storage mechanism of metal dichalcogenides.

Advanced Anode Materials of Potassium Ion Batteries: from Zero Dimension to Three Dimensions

Potassium ion batteries (PIBs) with the prominent advantages of sufficient reserves and economical cost are attractive candidates of new rechargeable batteries for large-grid electrochemical energy storage systems (EESs). However, there are still some obstacles like large size of K⁺ to commercial PIBs applications. Therefore, rational structural design based on appropriate materials is essential to obtain practical PIBs anode with K⁺ accommodated and fast diffused. Nanostructural design has been considered as one of the effective strategies to solve these issues owing to unique physicochemical properties. Accordingly, quite a few recent anode materials with different dimensions in PIBs have been reported, mainly involving in carbon materials, metal-based chalcogenides (MCs), metal-based oxides (MOs), and alloying materials. Among these anodes, nanostructural carbon materials with shorter ionic transfer path are beneficial for decreasing the resistances of transportation. Besides, MCs, MOs, and alloying materials with nanostructures can effectively alleviate their stress changes. Herein, these materials are classified into 0D, 1D, 2D, and 3D. Particularly, the relationship between different dimensional structures and the corresponding electrochemical performances has been outlined. Meanwhile, some strategies are proposed to deal with the current disadvantages. Hope that the readers are enlightened from this review to carry out further experiments better.

Highly Reversible and Rapid Sodium Storage in GeP3 with Synergistic Effect from Outside-In Optimization

The composite GeP₃/C@rGO as a sodium ion battery anode material was fabricated by introducing a carbon matrix into GeP₃ through high-energy ball milling, followed by encapsulating the resultant composite with graphene via a solution-based ultrasonic method. To delineate the individual role of carbon matrix and graphene, material characterization and electrochemical analyses were performed for GeP₃/C@rGO and three other samples: bare GeP₃, GeP₃ with graphene coating (GeP₃@rGO), and GeP₃ with carbon matrix (GeP₃/C). GeP₃/C@rGO exhibits the highest electric conductivity (5.89 × 10^-1 S cm^-1) and the largest surface area (167.85 m² g^-1) among the four samples. The as-prepared GeP₃/C@rGO delivered a reversible high capacity of 1084 mA h g^-1 at 50 mA g^-1, excellent rate capacity (435.4 mA h g^-1 at a high rate of 5 A g^-1), and long-term cycling stability (400 cycles with a reversible capacity of 823.3 mA h g^-1 at 0.2 A g^-1), all of which outperform the other three samples. The kinetics investigation reveals a "pseudocapacitive behavior" in GeP₃/C and GeP₃/C@rGO, where solely faradic reactions took place in bare GeP₃ and GeP₃@rGO with a typical "battery behavior". Based on ex-situ X-ray photoelectron spectroscopy and ex-situ electrochemical impedance spectroscopy, the carbon matrix serves to activate and stabilize the interior of the composite, while the graphene protects and restrains the exterior surface. Benefiting from the synergistic combination of these two components, GeP₃/C@rGO achieved extremely stable cycling stability as well as outstanding rate performance.

Recent Advances of Two-Dimensional (2 D) MXenes and Phosphorene for High-Performance Rechargeable Batteries

The design and development of advanced electrode materials for high-performance rechargeable batteries have been subjected to extensive studies. Very recently, two-dimensional (2 D) nanomaterials have become promising candidates for batteries, owing to their unique physicochemical properties. In particular, MXenes and phosphorene, which exhibit tailored electrical conductivity and ion storage capability, have attracted increasing attention. This Review presents a comprehensive summary of recent advances in the development of 2 D MXenes and phosphorene as electrode materials for high-performance batteries. Their physicochemical properties, including structural configurations and electronic properties of MXenes and direct band gap and anisotropic properties of phosphorene, are firstly discussed. Then, synthesis methods of the two materials are introduced. Thereafter, their applications as electrode materials in batteries, including lithium-ion batteries (LIBs), sodium-ion batteries (SIBs), potassium-ion batteries (PIBs), lithium-sulfur (Li-S) batteries, and metal-air batteries, are summarized and discussed in detail. An emphasis is placed on analyzing performance enhancement mechanisms to elucidate fundamental understanding. Finally, future challenges and opportunities for MXenes and phosphorene as electrode materials for batteries are considered.

Amorphous Sb2S3 Nanospheres In-Situ Grown on Carbon Nanotubes: Anodes for NIBs and KIBs

Antimony sulfide (Sb2S3) with a high theoretical capacity is considered as a promising candidate for Na-ion batteries (NIBs) and K-ion batteries (KIBs). However, its poor electrochemical activity and structural stability are the main issues to be solved. Herein, amorphous Sb2S3 nanospheres/carbon nanotube (Sb2S3/CNT) nanocomposites are successfully synthesized via one step self-assembly method. In-situ growth of amorphous Sb2S3 nanospheres on the CNTs is confirmed by X-ray diffraction, field-emission scanning electron microscopy, and transmission electron microscopy. The amorphous Sb2S3/CNT nanocomposites as an anode for NIBs exhibit excellent electrochemical performance, delivering a high charge capacity of 870 mA h g-1 at 100 mA g-1, with an initial coulomb efficiency of 77.8%. Even at 3000 mA g-1, a charge capacity of 474 mA h g-1 can be achieved. As an anode for KIBs, the amorphous Sb2S3/CNT nanocomposites also demonstrate a high charge capacity of 451 mA h g-1 at 25 mA g-1. The remarkable performance of the amorphous Sb2S3/CNT nanocomposites is attributed to the synergic effects of the amorphous Sb2S3 nanospheres and 3D porous conductive network constructed by the CNTs.