Biomimetic Sn4P3 Anchored on Carbon Nanotubes as an Anode for High-Performance Sodium-Ion Batteries

Template-Assisted Epitaxial Growth of Ordered SnO2 Nanorods Arrays with Different Hollow Structures for High-Performance Sodium Storage

Anode materials for sodium ion batteries (SIBs) are confronted with severe volume expansion and poor electrical conductivity. Construction of assembled structures featuring hollow interior and carbon material modification is considered as an efficient strategy to address the issues. Herein, a novel template-assisted epitaxial growth method, ingeniously exploiting lattice matching nature, is developed to fabricate hollow ordered architectures assembled by SnO2 nanorods. SnO2 nanorods growing along [100] direction can achieve lattice-matched epitaxial growth on (110) plane of α-Fe2O3. Driven by the lattice matching, different α-Fe2O3 templates possessing different crystal plane orientations enable distinct assembly modes of SnO2, and four kinds of hollow ordered SnO2@C nanorods arrays (HONAs) with different morphologies including disc, hexahedron, dodecahedron and tetrakaidecahedron (denoted as Di-, He-, Do-, and Te-SnO2@C) are achieved. Benefiting from the synergy of hollow structure, carbon coating and ordered assembly structure, good structural integrity and stability and enhanced electrical conductivity are realized, resulting in impressive sodium storage performances when utilized as SIB anodes. Specifically, Te-SnO2@C HONAs exhibit excellent rate capability (385.6 mAh·g-1 at 2.0 A·g-1) and remarkable cycling stability (355.4 mAh·g-1 after 2000 cycles at 1.0 A·g-1). This work provides a promising route for constructing advanced SIB anode materials through epitaxial growth for rational structural design.

Engineering sulfur defective Bi2S3@C with remarkably enhanced electrochemical kinetics of lithium-ion batteries

Introducing the appropriate vacancies to augment the active sites and improve the electrochemical kinetics while maintaining high cyclability is a major challenge for its widespread application in electrochemical energy storage. Here, core-shell structured Bi2S3@C with sulfur vacancies was prepared by hydrothermal method and one-step carbonization/sulfuration process, which significantly improves the intrinsic electrical conductivity and ion transport efficiency of Bi2S3. Additionally, the uniform protective carbon layer around surface of composite maintains structural stability and effectively alleviates volume expansion during alloying/dealloying. As a result, the BSC-500 anode exhibits a brilliant reversible capacity of 636 mAh/g at 0.2 A/g and a long-term stable capacity of 524 mAh/g for 500 cycles at a high current density of 3 A/g in lithium-ion batteries. In addition, the assembled Bi2S3@C//LiCoO2 full cell delivered a capacity of 184 mAh/g at 1 A/g and excellent cyclability (125 mAh/g after 1000 cycles). The proposed strategy of combining sulfur vacancies with a core-shell structure to improve the electrochemical kinetics of Bi2S3 in lithium-ion batteries off the prospect for practical applications of transition metal sulfide anodes.

Metal Phosphide Anodes in Sodium-Ion Batteries: Latest Applications and Progress

Sodium-ion batteries (SIBs), as the next-generation high-performance electrochemical energy storage devices, have attracted widespread attention due to their cost-effectiveness and wide geographical distribution of sodium. As a crucial component of the structure of SIBs, the anode material plays a crucial role in determining its electrochemical performance. Significantly, metal phosphide exhibits remarkable application prospects as an anode material for SIBs because of its low redox potential and high theoretical capacity. However, due to volume expansion limitations and other factors, the rate and cycling performance of metal phosphides have gradually declined. To address these challenges, various viable solutions have been explored. In this paper, the recent research progress of metal phosphide materials for SIBs is systematically reviewed, including the synthesis strategy of metal phosphide, the storage mechanism of sodium ions, and the application of metal phosphide in electrochemical aspects. In addition, future challenges and opportunities based on current developments are presented.

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.

Guard Cell-Inspired Ion Channels: Harnessing the Photomechanical Effect via Supramolecular Assembly of Cross-Linked Azobenzene/Polymers

Stimuli-responsive ion nanochannels have attracted considerable attention in various fields because of their remote controllability of ionic transportation. For photoresponsive ion nanochannels, however, achieving precise regulation of ion conductivity is still challenging, primarily due to the difficulty of programmable structural changes in confined environments. Moreover, the relationship between noncontact photo-stimulation in nanoscale and light-induced ion conductivity has not been well understood. In this work, a versatile design for fabricating guard cell-inspired photoswitchable ion channels is presented by infiltrating azobenzene-cross-linked polymer (AAZO-PDAC) into nanoporous anodic aluminum oxide (AAO) membranes. The azobenzene-cross-linked polymer is formed by azobenzene chromophore (AAZO)-cross-linked poly(diallyldimethylammonium chloride) (PDAC) with electrostatic interactions. Under UV irradiation, the trans-AAZO isomerizes to the cis-AAZO, causing the volume compression of the polymer network, whereas, in darkness, the cis-AAZO reverts to the trans-AAZO, leading to the recovery of the structure. Consequently, the resultant nanopore sizes can be manipulated by the photomechanical effect of the AAZO-PDAC polymers. By adding ionic liquids, the ion conductivity of the light-driven ion nanochannels can be controlled with good repeatability and fast responses (within seconds) in multiple cycles. The ion channels have promising potential in the applications of biomimetic materials, sensors, and biomedical sciences.

Engineering Ultrathin Carbon Layer on Porous Hard Carbon Boosts Sodium Storage with High Initial Coulombic Efficiency

Hard carbon (HC) has been widely adopted as the anode material for sodium ion batteries (NIBs). However, it is troubled by a low initial Coulombic efficiency (ICE) due to its porous structure. Herein, a graphitized and ultrathin carbon layer coating on HC is proposed to solve this challenge. The as-prepared porous carbon material coated with an ultrathin carbon layer composite (PCS@V@C) exhibits a cavity structure, which is prepared by using bis(cyclopentadienyl) nickel (CP-Ni) as the carbon source for outer coating, glucose carbon spheres as porous carbon, and introducing a silica layer to facilitate the coating process. When utilized as the anode for NIBs, the material shows an ICE increase from 47.1% to 85.3%, and specific capacity enhancement at 0.1 A g-1 from 155.3 to 216.7 mA h g-1. Moreover, its rate capability and cycling performance are outstanding, demonstrating a capacity of 140.3 mA h g-1 at 10 A g-1, and a retaining capacity of 225.6 mA h g-1 after 300 cycles at 0.1 A g-1 with the Coulombic efficiency of 100% at the second cycle. The excellent electrochemical performance of the PCS@V@C is attributed to the ultrathin carbon layer, which is beneficial for the formation of a stable solid electrolyte interphase (SEI) film. Therefore, this study provides a feasible surface modification method for the preparation of anode materials for NIBs with high specific capacity and ICE.

Nitrogen-Rich WN Clusters with Atomic Disorders and Non-Grain Boundaries Confined in Carbon Nanosheets Boosting Sodium-Ion Storage

Sodium-ion batteries (SIBs) as economic candidates have received considerable attention for large-scale energy storage applications. However, crystalline metal compounds with specific transport routes and rigid structures restrict their practical applications. Herein, the atomically dispersed N-rich amorphous WN clusters confined in the carbon nanosheets (WN/CNSs) are reported. Through advanced tests and calculations, the structural advantages, reaction mechanisms, and kinetic behaviors of the clusters are systematically analyzed. Compared with the crystalline W₂ N with low theoretical capacity (only 209.3 mAh g^-1 ), the amorphous WN clusters have the advantages of atomic disorders and non-grain boundaries and can afford abundant active sites (unsaturated dangling bonds) and isotropic charge transfer channels, which can be further enhanced by the N-rich characteristics and high electronegativity of the clusters. The encapsulation of CNSs has high conductivity and structural stability, which promotes electron transfer and effectively buffers volume expansions. As a SIB anode, the reversible capacity of WN/CNSs reaches 421.2 mAh g^-1 at 0.1 A g^-1 . Even at 20 A g^-1 , the reversible capacity of 170.7 mAh g^-1 is maintained after 8000 cycles. This study focuses on the advantages of amorphous nitrides, which have important guiding significance for the design of atomic clusters for high-performance metal ion batteries.

CuSe2 Nanocubes Enabling Efficient Sodium Storage

As the most promising candidate for lithium-ion batteries (LIBs), the electrochemical performance of sodium-ion batteries (SIBs) is highly dependent on the electrode materials. Copper selenides have established themselves as potential anode materials for SIBs due to their high theoretical capacity and good conductivity. However, the poor rate performance and fast capacity fading are the major challenges to their practical application in SIBs. Herein, single-crystalline CuSe₂ nanocubes (CuSe₂ NCs) are successfully synthesized via a solvothermal method. As an anode of SIBs, the CuSe₂ NCs render an almost 100% initial Coulombic efficiency, an outstanding long cycle life, e.g., 380 mA h g^-1 after 1700 cycles at 10 A g^-1, and an unprecedented rate performance of 344 mA h g^-1 at 50 A g^-1. Ex situ X-ray diffraction (XRD) patterns reveal the crystalline transformation of energy-storage materials, and the density functional theory (DFT) conclusion suggests that fast and stable ion diffusion kinetics enhances their electrochemical performance upon sodiation/desodiaton. The investigation into the mechanism provides a theoretical basis for subsequent practical applications.

Highly Sensitive Photoelectrochemical Immunosensor Based on Organic Multielectron Donor Nanocomposite as Signal Probe

Organic photoelectric materials with conjugated electron-rich structures and good biocompatibilities have broad application prospects in biosensors. Herein, we report a promising organic photoelectric multielectron donor nanocomposite for highly sensitive PEC immunoassays. Specifically, the organic multielectron donor nanocomposite (DA-ZnTCPP-g-C₃N₄) was prepared from dopamine (DA, polyphenol hydroxyl structure substance), zinc tetracarboxylate porphyrin (ZnTCPP, large p-π conjugated heterocyclic compound), and two-dimensional graphene-like nitrogen carbide (g-C₃N₄) via an amidation reaction. With a multielectron donor structure and photoelectricity, this nanocomposite can achieve sensitization by self-structure without the addition of an electron donor in the test solution. It was utilized to label the carcinoembryonic detection antibody as a immuno-probe (Ab2-DA-ZnTCPP-g-C₃N₄). Meanwhile, the glassy carbon electrode electrodeposited with gold nanoparticles anchoring the capture antibody was used as a PEC immunomatrix (Ab1/DpAu/GCE). The enhanced PEC current, "signal on", was confirmed by the immunosensor via sandwich immunorecognition of a carcinoembryonic antigen (CEA). Under optimal conditions, the as-prepared sensing platform displayed high sensitivity for CEA with a dynamic linear response range from 10 fg·mL^-1 to 1 mg·mL^-1 and a lower detection limit of 3.6 fg·mL^-1. This organic nanocomposite showed good sensitivity and stability in an immunosensing system with a low background. This strategy affords a promising approach for biological applications of organic photoelectric materials.

Recent Advances on Heterojunction-Type Anode Materials for Lithium-/Sodium-Ion Batteries

Rechargeable batteries are key in the field of electrochemical energy storage, and the development of advanced electrode materials is essential to meet the increasing demand of electrochemical energy storage devices with higher density of energy and power. Anode materials are the key components of batteries. However, the anode materials still suffer from several challenges such as low rate capability and poor cycling stability, limiting the development of high-energy and high-power batteries. In recent years, heterojunctions have received increasing attention from researchers as an emerging material, because the constructed heterostructures can significantly improve the rate capability and cycling stability of the materials. Although many research progress has been made in this field, it still lacks review articles that summarize this field in detail. Herein, this review presents the recent research progress of heterojunction-type anode materials, focusing on the application of various types of heterojunctions in lithium/sodium-ion batteries. Finally, the heterojunctions introduced in this review are summarized, and their future development is anticipated.

Phosphorus-Based Materials for High-Performance Alkaline Metal Ion Batteries: Progress and Prospect

Alkaline metal-ion batteries (AIBs) such as lithium-ion batteries (LIBs), sodium-ion batteries (NIBs), and potassium-ion batteries (KIBs) are potential energy storage systems. Currently, although LIBs are widely used in consumer electronics and electric vehicles, the electrochemical performance, safety, and cost of current AIBs are still unable to meet the needs for many future applications, such as large-scale energy storage, due to the low theoretical capacity of cathode/anode materials, flammability of electrolytes and limited Li resources. It is thus imperative to develop new materials to improve the properties of AIBs. Several promising cathodes, anodes, and electrolytes have been developed and among the new battery materials, phosphorus-based (P-based) materials have shown great promise. For example, P and metal phosphide anodes have high theoretical capacity, resource abundance, and environmental friendliness boding well for future high-energy-density AIBs. Besides, phosphate cathode materials have the advantages of low cost, high safety, high voltage, and robust stability, and P-based materials like LiPF₆ and lithium phosphorus oxynitride are widely used electrolytes. In this paper, the latest development of P-based materials in AIBs, challenges, effective solutions, and new directions are discussed.

Ultrathin-Walled Bi2 S3 Nanoroll/MXene Composite toward High Capacity and Fast Lithium Storage

It is extremely important to develop a high energy density power source with rapid charge-discharge rate to meet people's growing needs. Hence, the development of advanced electrode materials is the top priority. Herein, a simple yet elaborate vacuum-assisted room-temperature phase transfer method is reported to transform MXene nanosheets from water into organic solution. Subsequently, an in-situ growth strategy is employed to deposit ultrathin-walled bismuth sulfide (Bi₂ S₃ ) nanorolls on MXene surface to prepare Bi₂ S₃ /MXene composite as an efficient and high-performance anode material for lithium-ion batteries. Attributed to the unique nanoroll-like structure and the strong synergistic effect, the Bi₂ S₃ /MXene-10 composite can deliver the high discharge capacities of 849 and 541 mAh g^-1 at 0.1 and 5 A g^-1 , respectively. The Bi₂ S₃ /MXene-10 electrode can deliver a high specific capacity of 541 mAh g^-1 even after 600 cycles at a large current density of 1 A g^-1 , proving the superb cycling stability of the Bi₂ S₃ /MXene-10 composite. Additionally, the simple vacuum-assisted room-temperature phase transfer strategy can enlighten researchers to expand the potential application of MXene. Furthermore, the formation mechanism of Bi₂ S₃ nanorolls is also proposed, which may open a new avenue to design and fabricate other nanoroll-like structures.

Hierarchical multi-yolk-shell copper oxide@copper-1, 3, 5-benzenetricarboxylate as an ultrastable anode for lithium ion batteries

The capacity attenuation of transition metal oxides (TMOs) and metal-organic frameworks (MOFs) is the obstacle for practical application in lithium ion batteries, due to the extensive volume variation upon charge/discharge cycles. Herein, a hierarchical composite material with copper oxide (CuO) multi-yolks and copper-1, 3, 5-benzenetricarboxylate (Cu-BTC) shell is synthesized by a facile method to study the effect of the hierarchical structure on the electrochemical performance. The porosity and pore volume of CuO@Cu-BTC composites are optimized to buffer the volume change and facilitate the infiltration of electrolytes by altering reaction conditions. The CuO@Cu-BTC (20 h) with the largest surface area and pore volume delivers an excellent reversible capacity of 780.7 mAh g^-1 at 200 mA g^-1 after 100 cycles, and ultrastable long-term performance with a specific capacity of 569 mAh g^-1 at a current density of 1000 mA g^-1 after 900 cycles. The corresponding full battery shows moderate capacity retention from 149.4 to 125.8 mAh g^-1 after 70 cycles, with a specific capacity retention of 84.2%, based on the mass of lithium iron phosphate (LiFePO₄) at 0.2 C (1 C = 170 mA g^-1). This strategy applies copper oxide as the metal source of the coordination compound, as well as the internal yolks, which can be extended to the in-situ construction of other hierarchical composites, providing a new avenue for practical application of TMOs and MOFs as anode materials.

A fast and high-efficiency electrochemical exfoliation strategy towards antimonene/carbon composites for selective lubrication and sodium-ion storage applications

Two-dimensional (2D) layered antimony (Sb) materials are of importance due to their unique physicochemical properties, and they can be easily electrochemically exfoliated from bulk Sb in Na₂SO₄ electrolyte solution. However, the exfoliation yield is quite low and the exfoliated products are easily oxidized to Sb₂O₃, which prohibits their practical engineering applications. Herein, an antimonene/carbon composite is successfully fabricated with a high exfoliation yield through electrochemical exfoliation of bulk antimony chunk in a mixed electrolyte solution consisting of Na₂SO₄ and ethylene glycol. When the as-fabricated antimonene/carbon composite is added into PAO6 oil, the lubrication system exhibits a selective lubrication performance when sliding against GCr15 and YG8 ball, and the antiwear enhancement can be further improved by sliding against a YG8 ball. Besides, the antimonene/carbon composite can provide reliability and enough ion corridors during the charge/discharge processes. When tested as an anodic material for sodium-ion batteries, it exhibits a large capacity of 485.0 mA h g^-1 at a current density of 200 mA g^-1 after 150 cycles and a remarkable rate capability (334.5 mA h g^-1 at 5 A g^-1).

Sandwich-Structured Sn4P3@MXene Hybrid Anodes with High Initial Coulombic Efficiency for High-Rate Lithium-Ion Batteries

The high theoretical capacity makes metal phosphides appropriate anode candidates for Li-ion batteries, but their applications are restricted due to the limited structural instability caused by the huge volume change, as in other high-capacity materials. Here, we design an integrated electrode consisting of Sn₄P₃ nanoparticles sandwiched between transition-metal carbide (MXene) nanosheets. Tetramethylammonium hydroxide (TMAOH) plays an essential role in the formation of such sandwich structures by producing negatively charged MXene sheets with expanded layer spacings. The strong C-O-P oxygen bridge bond enables tight anchoring of Sn₄P₃ nanoparticles on the surface of MXene layers. The obtained Sn₄P₃-based nanocomposites exhibit high reversible capacity with an initial Coulombic efficiency of 82% and outstanding rate performance (1519 mAh cm^-3 at a current density of 5 A g^-1). The conductive and flexible MXene layers on both sides of Sn₄P₃ nanoparticles provide the desired electric conductivity and elastomeric space to accommodate the large volume change of Sn₄P₃ during lithiation. Therefore, the Sn₄P₃@MXene hybrid exhibits an enhanced cyclic performance of 820 mAh g^-1 after 300 cycles at a current density of 1 A g^-1.

Co-Salen Complex-Derived CoP Nanoparticles Confined in N-Doped Carbon Microspheres for Stable Sodium Storage

The poor rate and cycle performance rooting from the inferior electrical conductivity and large volume change are bottlenecks for further application of the potential anode material in sodium-ion batteries. To address this problem, homogeneous CoP nanoparticles enwrapped in the N-doped carbon (CoP/NC) microspheres are synthesized by the simultaneous carbonization and phosphorization of Co-salen complex microspheres for the first time. The N-doped carbon enhances its conductivity and diminishes the volume stress, and the dispersed CoP nanoparticles in carbon provide more reaction sites, resulting in a superior sodium storage performance. CoP/NC microspheres exhibit the capacity of 373 mA h g^-1 at 0.1 A g^-1 after 100 cycles. Even at 2 A g^-1 for 2000 cycles, the capacity of 195 mA h g^-1 is also achieved. This work provides an excellent reference for the design and synthesis of sulfide, selenide, and other transition-metal composites. It is also beneficial to expand the application of salen complexes in the design and synthesis of catalysts and energy storage materials.

New Insight into Desodiation/Sodiation Mechanism of MoS2: Sodium Insertion in Amorphous Mo-S Clusters

Molybdenum disulfide (MoS₂) is a promising anode material for sodium batteries due to its high theoretical capacity. While significantly improved electrochemical performance has been achieved, the reaction mechanism is still equivocal. Herein, we applied electron pair distribution function and X-ray absorption spectroscopy to investigate the desodiation/sodiation mechanism of MoS₂ electrodes. The results reveal that Mo-S bonds are well preserved and dominant in the sodiation product matrix but do not convert to metallic Mo and Na₂S even at deep sodiation. The MoS₂ multilayer sheets break into disordered MoS_x clusters with modified octahedral symmetry during discharging. The long-range order was not rebuilt during subsequent charging but with partial recovery of the Mo-S coordination symmetry. The mechanism of the reaction is independent of the carbon matrix, although it prevents the MoS_x clusters from leaching into the electrolyte and thus contributes to an extended cycle life. This work refreshes the fundamental understanding of the desodiation/sodiation mechanism of MoS₂ materials.

Stable Interfaces in a Sodium Metal-Free, Solid-State Sodium-Ion Battery with Gradient Composite Electrolyte

Composite electrolytes (CE) combining a ceramic filler and a polymer matrix is an effective way to enhance battery safety. But the increased ceramic filler mass fraction decreases the flexibility, which increases the interfacial resistance. To alleviate interfacial resistance further, a gradient composite electrolyte (GCE) using a Sc, Ge-doped Na₃Zr₂Si₂PO₁₂ (NZSP) as the ceramic filler and poly(ethylene oxide) (PEO) as the polymer matrix is proposed. The outer layer contains a low concentration of ceramic filler to improve interfacial contact, and the central layer contains a high concentration of ceramic filler to inhibit dendrite penetration. This GCE possesses an enhanced conductivity (4.0 × 10^-5 S cm^-1 at 30 °C) and a reduced interfacial resistance. Furthermore, the safety was boosted using Sn₄P₃@CNT/C as the high-capacity anode active material and Na₃V₂(PO₄)₃ (NVP) as the cathode active material. This ultrasafe sodium metal-free, solid-state sodium-ion battery (SSSIB) displays an impressive cycling performance.

Bimetallic Sulfide SnS2/FeS2 Nanosheets as High-Performance Anode Materials for Sodium-Ion Batteries

Transition-metal sulfide SnS₂ has aroused wide concern due to its high capacity and nanosheet structure, making it an attractive choice as the anode material in sodium-ion batteries. However, the large volume expansion and poor conductivity of SnS₂ lead to inferior cycle stability as well as rate performance. In this work, FeS₂ was in situ introduced to synchronously grow with SnS₂ on rGO to prepare a heterojunction bimetallic sulfide nanosheet SnS₂/FeS₂/rGO composite. The composition and distinctive structure facilitate the rapid diffusion of Na⁺ and improve the charge transfer at the heterogeneous interface, providing sufficient space for volume expansion and improving anode materials' structural stability. SnS₂/FeS₂/rGO bimetallic sulfide electrode boasts a capacity of 768.3 mA h g^-1 at the current density of 0.1 A g^-1, and 541.2 mA h g^-1 at the current density of 1 A g^-1 in sodium-ion batteries, which is superior to that of either single metal sulfide SnS₂ or FeS₂. TDOS calculation further confirms that the binding of FeS₂/SnS₂-Na is more stable than FeS₂ and SnS₂ alone. The superior electrochemical performance of the SnS₂/FeS₂/rGO composite material makes it a promising candidate for sodium storage.

In Situ Monitoring the Potassium-Ion Storage Enhancement in Iron Selenide with Ether-Based Electrolyte

As one of the promising anode materials, iron selenide has received much attention for potassium-ion batteries (KIBs). Nevertheless, volume expansion and sluggish kinetics of iron selenide result in the poor reversibility and stability during potassiation-depotassiation process. In this work, we develop iron selenide composite matching ether-based electrolyte for KIBs, which presents a reversible specific capacity of 356 mAh g^-1 at 200 mA g^-1 after 75 cycles. According to the measurement of mechanical properties, it is found that iron selenide composite also exhibits robust and elastic solid electrolyte interphase layer in ether-based electrolyte, contributing to the improvement in reversibility and stability for KIBs. To further investigate the electrochemical enhancement mechanism of ether-based electrolyte in KIBs, we also utilize in situ visualization technique to monitor the potassiation-depotassiation process. For comparison, iron selenide composite matching carbonate-based electrolyte presents vast morphology change during potassiation-depotassiation process. When changing to ether-based electrolyte, a few minor morphology changes can be observed. This phenomenon indicates an occurrence of homogeneous electrochemical reaction in ether-based electrolyte, which results in a stable performance for potassium-ion (K-ion) storage. We believe that our work will provide a new perspective to visually monitor the potassium-ion storage process and guide the improvement in electrode material performance.

Iron Phosphide Confined in Carbon Nanofibers as a Free-Standing Flexible Anode for High-Performance Lithium-Ion Batteries

Iron phosphide with high specific capacity has emerged as an appealing candidate for next-generation lithium-ion battery anodes. However, iron phosphide could undergo conversion reactions and generally suffer from a rapid capacity degradation upon cycling due to its structure pulverization. Chemomechanical breakdown of iron phosphide due to its rigidity has been a challenge to fully realizing its electrochemical performance. To address this challenge, we report here on an enticing opportunity: a flexible, free-standing iron phosphide anode with Fe₂P nanoparticles confined in carbon nanofibers may overcome existing challenges. For the synthesis, we introduce a facile electrospinning strategy that enables in situ formation of Fe₂P within a carbon matrix. Such a carbon matrix can effectively minimize the structure change of Fe₂P particles and protect them from pulverization, allowing the electrodes to retain a free-standing structure after long-term cycling. The produced electrodes showed excellent electrochemical performance in lithium-ion half and full cells, as well as in flexible pouch cells. These results demonstrate the successful development of iron phosphide materials toward high capacity, light weight, and flexible energy storage.

Construction of MoS2/Mxene heterostructure on stress-modulated kapok fiber for high-rate sodium-ion batteries

Molybdenum disulfide (MoS₂) has possession of a layered structure and high theoretical capacity, which is a candidate anode material for sodium ion batteries. However, unmodified MoS₂ are inflicted with a poor cycling stability and an inferior rate capability upon charge/discharge processes. Considering that the shape and size of anode materials play a key role in the performance of anode materials, this paper proposes a multi-level composite structure formed by the micro-nano materials based on self-assembled molybdenum disulfide (MoS₂) nanoflowers, Mxene and hollow carbonized kapok fiber (CKF). The micro-nano materials can be connected to form heterojunction and agglomeration can be avoided. The load bearing of heterostructure and stress release of CKF are coordinated to form a double protection mechanism, which improves the conductivity and structural stability of hybrid materials. Based on the above advantages, it has higher specific capacity than pure MoS₂, and has better rate performance (639.3, 409.5, 386.2, 372, 338, 422.8 and 434.7 mAh g^-1 at the current density of 0.05, 0.1, 0.2, 0.5, 1 ,0.1 and 0.05 A·g^-1, respectively). The stress-modulated strategies can provide new insights for the design and construction of transition metal sulfides heterostructures to achieve high performance sodium ion batteries.

Bimetallic Antimony-Vanadium Oxide Nanoparticles Embedded in Graphene for Stable Lithium and Sodium Storage

Bimetallic oxides have received considerable attention as anodes for lithium/sodium-ion batteries (LIBs/SIBs) due to their high electrochemical activity and theoretical specific capacity. However, their cycling performance is limited by large volume variation, severe aggregation, and pulverization of bimetallic oxide nanoparticles during repeated metal ion insertion/extraction processes. Herein, bimetallic antimony-vanadium oxide nanoparticles embedded in graphene (SbVO₄/G) composites are prepared by a one-step hydrothermal method. Bimetallic SbVO₄ with abundant redox reaction sites can provide high specific capacity by a multi-electron reaction. A robust graphene substrate can not only alleviate volume expansion but also prevent aggregation and collapse of highly active bimetallic SbVO₄. Due to the excellent synergy between the two building components, SbVO₄/G hybrids exhibit excellent electrochemical activity, structural stability, and electrochemical performance. When employed as anodes for LIBs and SIBs, SbVO₄/G composites display excellent cycling performance (1079.5 mAh g^-1 at 0.1 A g^-1 after 150 cycles for LIBs and 401.6 mAh g^-1 at 0.1 A g^-1 after 450 cycles for SIBs) and impressive rate capability. This work demonstrates that SbVO₄/G composites are promising anodes for both LIBs and SIBs.

Voltage-Modulated Structure Stress for Enhanced Electrochemcial Performances: The Case of μ-Sn in Sodium-Ion Batteries

Alloy-type anodes in alkaline ion batteries have to face the challenges of huge volume change and giant structure strain/stress upon cycling. Here, reducing the structure stress for advanced performances by voltage regulation is demonstrated by using microsized Sn (μ-Sn) for sodium ion batteries as a model. Density functional theory and finite element analysis indicate that Sn/NaSn₃ is the crucial phase transition highly responsible for inducing surface cracks, particle aggregations, and cell failures. Eliminating this phase transition by the control of cutoff voltages successfully extends the cycle life of μ-Sn to 2500 cycles at 2 A g^-1, much longer than ∼40 cycles in a regular voltage window. The specific capacity is still retained at ∼455 mAh g^-1, leading to a capacity decay of only ∼0.0088% per cycle. The results provide a simple way to achieve the outstanding performances without complicated preparation, expensive reagents, and laborious processing.

One-Step Solvothermal Route to Sn4P3-Reduced Graphene Oxide Nanohybrids as Cycle-Stable Anode Materials for Sodium-Ion Batteries

Sn₄P₃, owing to its high theoretical volumetric capacity, good electrical conductivity, and relatively appropriate potential plateau, has been recognized as an ideal anode for sodium-ion batteries (NIBs). However, the current synthetic routes for Sn₄P₃-based nanohybrids typically involve foreign-template-based multistep procedures, limiting their large-scale production and applications in NIBs. Using commercial red phosphorus as the phosphorus source and nontoxic ethanolamine as the solvent, we herein report a facile and scalable solvothermal protocol for the one-step preparation of Sn₄P₃-reduced oxide graphene (denoted as Sn₄P₃-rGO) hybrid materials. Benefiting from the novel strategy and elaborate design, ultrasmall Sn₄P₃ nanoparticles (2.7 nm on average) are homogeneously anchored onto rGO. The high conductivity of the rGO network and the short electron/ion diffusion path of ultrasmall Sn₄P₃ nanoparticles give the Sn₄P₃-rGO hybrid high capacities and stable long-term cyclability. Specifically, the optimized Sn₄P₃-rGO hybrid displays a remarkable reversible capacity of 663.5 mA h g^-1 at a current density of 200 mA g^-1, ultralong-term cycle life (301 mA h g^-1 after 2500 cycles at a high current density of 2000 mA g^-1), and excellent rate capability, presenting itself as a highly promising anode material for NIBs.

The Carbon-Coated ZnCo2O4 Nanowire Arrays Pyrolyzed from PVA for Enhancing Lithium Storage Capacity

In this paper, ZnCo2O4 nanowire arrays with a uniform carbon coating were introduced when polyvinyl alcohol (PVA) served as the carbon source. The coating process was completed by a facile bath method in PVA aqueous solution and subsequent pyrolyzation. The PVA-derived carbon-coated ZnCo2O4 nanowire array composites can be used directly as the binder-free and self-supported anode materials for lithium-ion batteries. In the carbon-coated ZnCo2O4 composites, the carbon layer carbonized from PVA can accelerate the electron transfer and accommodate the volume swing during the cycling process. The lithium storage properties of the carbon-coated ZnCo2O4 composites are investigated. It is believed that the novel carbon-coating method is universal and can be applied to other nanoarray materials.

Willow-Leaf-Like ZnSe@N-Doped Carbon Nanoarchitecture as a Stable and High-Performance Anode Material for Sodium-Ion and Potassium-Ion Batteries

ZnSe is regarded as a promising anode material for energy storage due to its high theoretical capacity and environment friendliness. Nevertheless, it is still a significant challenge to obtain superior electrode materials with stable performance owing to the serious volume change and aggregation upon cycling. Herein, a willow-leaf-like nitrogen-doped carbon-coated ZnSe (ZnSe@NC) composite synthesized through facile solvothermal and subsequent selenization process is beneficial to expose more active sites and facilitate the fast electron/ion transmission. These merits significantly enhance the electrochemical performances of ZnSe@NC for sodium-ion batteries (SIBs) and potassium-ion batteries (PIBs). The obtained ZnSe@NC exhibits outstanding rate performance (440.3 mAh g^-1 at 0.1 A g^-1 and 144.4 mAh g^-1 at 10 A g^-1 ) and ultralong cycle stability (242.2 mAh g^-1 at 8.0 A g^-1 even after 3200 cycles) for SIBs. It is noted that 106.5 mAh g^-1 can be retained after 550 cycles and 71.4 mAh g^-1 is still remained after 1500 cycles at 200 mA g^-1 when applied as anode for PIBs, indicating good cycle stability of the electrode. The possible electrochemical mechanism and the ionic diffusion kinetics of the ZnSe@NC are investigated using ex situ X-ray diffraction, high-resolution transmission electron microscopy, and a series of electrochemical analyses.