Octahedral/Tetrahedral Vacancies in Fe3O4 as K-Storage Sites: A Case of Anti-Spinel Structure Material Serving as High-Performance Anodes for PIBs

Potassium-ion batteries (PIBs) have attracted more and more attention as viable alternatives to lithium-ion batteries (LIBs) due to the deficiency and uneven distribution of lithium resources. However, it is shown that potassium storage in some compounds through reaction or intercalation mechanisms cannot effectively improve the capacity and stability of anodes for PIBs. The unique anti-spinel structure of magnetite (Fe₃O₄) is densely packed with thirty-two O atoms to form a face-centered cubic (fcc) unit cell with tetrahedral/octahedral vacancies in the O-closed packing structure, which can serve as K⁺ storage sites according to the density functional theory (DFT) calculation results. In this work, carbon-coated Fe₃O₄@C nanoparticles are prepared as high-performance anodes for PIBs, which exhibit high reversible capacity (638 mAh g⁻¹ at 0.05 A g⁻¹) and hyper stable cycling performance at ultrahigh current density (150 mAh g⁻¹ after 9000 cycles at 10 A g⁻¹). In situ XRD, ex-situ Fe K-edge XAFS, and DFT calculations confirm the storage of K⁺ in tetrahedral/octahedral vacancies.     

Birnessite Nanosheet Arrays with High K Content as a High‐Capacity and Ultrastable Cathode for K‐Ion Batteries

Potassium‐ion batteries (PIBs) are one of the emerging energy‐storage technologies due to the low cost of potassium and theoretically high energy density. However, the development of PIBs is hindered by the poor K⁺ transport kinetics and the structural instability of the cathode materials during K⁺ intercalation/deintercalation. In this work, birnessite nanosheet arrays with high K content (K_0.77MnO₂?0.23H₂O) are prepared by “hydrothermal potassiation” as a potential cathode for PIBs, demonstrating ultrahigh reversible specific capacity of about 134 mAh g^?1 at a current density of 100 mA g^?1, as well as great rate capability (77 mAh g^?1 at 1000 mA g^?1) and superior cycling stability (80.5% capacity retention after 1000 cycles at 1000 mA g^?1). With the introduction of adequate K⁺ ions in the interlayer, the K‐birnessite exhibits highly stabilized layered structure with highly reversible structure variation upon K⁺ intercalation/deintercalation. The practical feasibility of the K‐birnessite cathode in PIBs is further demonstrated by constructing full cells with a hard–soft composite carbon anode. This study highlights effective K⁺‐intercalation for birnessite to achieve superior K‐storage performance for PIBs, making it a general strategy for developing high‐performance cathodes in rechargeable batteries beyond lithium‐ion batteries.     

Amine–Aldehyde Condensation-Derived N-Doped Hard Carbon Microspheres for High-Capacity and Robust Sodium Storage

Hard carbon is generally accepted as the choice of anode material for sodium-ion batteries. However, integrating high capacity, high initial Coulombic efficiency (ICE), and good durability in hard carbon materials remains challenging. Herein, N-doped hard carbon microspheres (NHCMs) with abundant Na⁺ adsorption sites and tunable interlayer distance are constructed based on the amine–aldehyde condensation reaction using m-phenylenediamine and formaldehyde as the precursors. The optimized NHCM-1400 with a considerable N content (4.64%) demonstrates a high ICE (87%), high reversible capacity with ideal durability (399 mAh g⁻¹ at 30 mA g⁻¹ and 98.5% retention over 120 cycles), and decent rate capability (297 mAh g⁻¹ at 2000 mA g⁻¹). In situ characterizations elucidate the adsorption–intercalation-filling sodium storage mechanism of NHCMs. Theoretical calculation reveals that the N-doping decreases the Na⁺ adsorption energy on hard carbon.     

Sodium/Potassium-Ion Batteries: Boosting the Rate Capability and Cycle Life by Combining Morphology,Defect and Structure Engineering

Carbon-based materials have been considered as the most promising anode materials for both sodium-ion batteries (SIBs) and potassium-ion batteries (PIBs), owing to their good chemical stability, high electrical conductivity, and environmental benignity. However, due to the large sizes of sodium and potassium ions, it is a great challenge to realize a carbon anode with high reversible capacity, long cycle life, and high rate capability. Herein, by rational design, N-doped 3D mesoporous carbon nanosheets (N-CNS) are successfully synthesized, which can realize unprecedented electrochemical performance for both SIBs and PIBs. The N-CNS possess an ultrathin nanosheet structure with hierarchical pores, ultrahigh level of pyridinic N/pyrrolic N, and an expanded interlayer distance. The beneficial features that can enhance the Na-/K-ion intercalation/deintercalation kinetic process, shorten the diffusion length for both ions and electrons, and accommodate the volume change are demonstrated. Hence, the N-CNS-based electrode delivers a high capacity of 239 mAh g⁻¹ at 5 A g⁻¹ after 10 000 cycles for SIBs and 321 mAh g⁻¹ at 5 A g⁻¹ after 5000 cycles for PIBs. First-principles calculation shows that the ultrahigh doping level of pyridinic N/pyrrolic N contributes to the enhanced sodium and potassium storage performance by modulating the charge density distribution on the carbon surface.     

Constructing Active B?N Sites in Carbon Nanosheets for High-Capacity and Fast Charging Toward Potassium Ion Storage

Nitrogen doping is an effective strategy to improve potassium ion storage of carbon electrodes via the creation of adsorption sites. However, various undesired defects are often uncontrollably generated during the doping process, limiting doping effect on capacity enhancement and deteriorating the electric conductivity. Herein, boron element is additionally introduced to construct 3D interconnected B, N co-doped carbon nanosheets to remedy these adverse effects. This work demonstrates that boron incorporation preferentially converts pyrrolic N species into B N sites with lower adsorption energy barrier, further enhancing the capacity of B, N co-doped carbon. Meanwhile, the electric conductivity is modulated via the conjugation effect between the electron-rich N and electron-deficient B, accelerating the charge-transfer kinetics of potassium ions. The optimized samples deliver a high specific capacity, high rate capability, and long-term cyclic stability (532.1 mAh g⁻¹ at 0.05 A g⁻¹, 162.6 mAh g⁻¹ at 2 A g⁻¹ over 8000 cycles). Furthermore, hybrid capacitors using the B, N co-doped carbon anode deliver a high energy and power density with excellent cycle life. This study demonstrates a promising approach using B N sites for adsorptive capacity and electric conductivity enhancement in carbon materials for electrochemical energy storage applications.     

Double-Walled NiTeSe–NiSe2 Nanotubes Anode for Stable and High-Rate Sodium-Ion Batteries

Electrodes made of composites with heterogeneous structure hold great potential for boosting ionic and charge transfer and accelerating electrochemical reaction kinetics. Herein, hierarchical and porous double-walled NiTeSe–NiSe₂ nanotubes are synthesized by a hydrothermal process assisted in situ selenization. Impressively, the nanotubes have abundant pores and multiple active sites, which shorten the ion diffusion length, decrease Na⁺ diffusion barriers, and increase the capacitance contribution ratio of the material at a high rate. Consequently, the anode shows a satisfactory initial capacity (582.5 mA h g⁻¹ at 0.5 A g⁻¹), a high-rate capability, and long cycling stability (1400 cycles, 398.6 mAh g⁻¹ at 10 A g⁻¹, 90.5% capacity retention). Moreover, the sodiation process of NiTeSe–NiSe₂ double-walled nanotubes and underlying mechanism of the enhanced performance are revealed by in situ and ex situ transmission electron microscopy and theoretical calculations.     

Integrated Uniformly Microporous C4N/Multi-Walled Carbon Nanotubes Composite Toward Ultra-Stable and Ultralow-Temperature Proton Batteries

Benefiting from the proton's small size and ultrahigh mobility in water, aqueous proton batteries are regarded as an attractive candidate for high-power and ultralow-temperature energy storage devices. Herein, a new-type C₄N polymer with uniform micropores and a large specific surface area is prepared by sulfuric acid-catalyzed ketone amine condensation reaction and employed as the electrode of proton batteries. Multi-walled carbon nanotubes (MWCNT) are introduced to induce the in situ growth of C₄N, and reaped significantly enhanced porosity and conductivity, and thus better both room- and low-temperature performance. When coupled with MnO₂@Carbon fiber (MnO₂@CF) cathode, MnO₂@CF//C₄N-50% MWCNT full battery shows unprecedented cycle stability with a capacity retention of 98% after 11 000 cycles at 10 A g⁻¹ and even 100% after 70 000 cycles at 20 A g⁻¹. Additionally, a novel anti-freezing electrolyte (5 m H₂SO₄ + 0.5 m MnSO₄) is developed and showed a high ionic conductivity of 123.2 mS cm⁻¹ at -70 °C. The resultant MnO₂@CF//C₄N-50% MWCNT battery delivers a specific capacity of 110.5 mAh g⁻¹ even at -70 °C at 1 A g⁻¹, the highest in all reported proton batteries under the same conditions. This work is expected to offer a package solution for constructing high-performance ultralow-temperature aqueous proton batteries.     

Highly Crystalline Prussian Blue for Kinetics Enhanced Potassium Storage

Prussian blue analogs (PBAs) are promising cathode materials for potassium-ion batteries (KIBs) owing to their large open framework structure. As the K⁺ migration rate and storage sites rely highly on the periodic lattice arrangement, it is rather important to guarantee the high crystallinity of PBAs. Herein, highly crystalline K₂Fe[Fe(CN)₆] (KFeHCF-E) is synthesized by coprecipitation, adopting the ethylenediaminetetraacetic acid dipotassium salt as a chelating agent. As a result, an excellent rate capability and ultra-long lifespan (5000 cycles at 100 mA g⁻¹ with 61.3% capacity maintenance) are achieved when tested in KIBs. The highest K⁺ migration rate of 10⁻⁹ cm² s⁻¹ in the bulk phase is determined by the galvanostatic intermittent titration technique. Remarkably, the robust lattice structure and reversible solid-phase K⁺ storage mechanism of KFeHCF-E are proved by in situ XRD. This work offers a simple crystallinity optimization method for developing high-performance PBAs cathode materials in advanced KIBs.     

Liquid Template Assisted Activation for “Egg Puff”-Like Hard Carbon toward High Sodium Storage Performance

The slow solid diffusion dynamics of sodium ions and the side-reaction of sodium metal plating at low potential in the hard carbon anode of sodium ion batteries (SIBs) pose significant challenges to the safety manipulation of high-rate batteries. Herein, a simple yet powerful fabricating method is reported on for “egg puff”-like hard carbon with few N doping using rosin as a precursor via liquid salt template-assisted and potassium hydroxide dual activation. The as-synthesized hard carbon delivers promising electrochemical properties in the ether-based electrolyte especially at high rates, based on the absorption mechanism of fast charge transfer. The optimized hard carbon exhibits a high specific capacity of 367 mAh g⁻¹ at 0.05 A g⁻¹ and 92.9% initial coulombic efficiency (ICE), 183 mAh g⁻¹ at 10 A g⁻¹, and ultra-long cycle stability of reversible discharge capacity of 151 mAh g⁻¹ after 12,000 cycles at 5 A g⁻¹ with the average coulombic efficiency of ≈99% and the decay of 0.0026% per cycle. These studies will undoubtedly provide an effective and practical strategy for advanced hard carbon anode of SIBs based on adsorption mechanism.     

In Situ Carbon‐Doped Mo(Se0.85S0.15)2 Hierarchical Nanotubes as Stable Anodes for High‐Performance Sodium‐Ion Batteries

Sodium‐ion batteries (SIBs) are promising energy storage devices, but suffer from poor cycling stability and low rate capability. In this work, carbon doped Mo(Se_0.85S_0.15)₂ (i.e., Mo(Se_0.85S_0.15)₂:C) hierarchical nanotubes have been synthesized for the first time and serve as a robust and high‐performance anode material. The hierarchical nanotubes with diameters of 300 nm and wall thicknesses of 50 nm consist of numerous 2D layered nanosheets, and can act as a robust host for sodiation/desodiation cycling. The Mo(Se_0.85S_0.15)₂:C hierarchical nanotubes deliver a discharge capacity of 360 mAh g⁻¹ at a high current density of 2000 mA g⁻¹ and keep a 81.8% capacity retention compared to that at a current density of 50 mA g⁻¹, showing superior rate capability. Comparing with the second cycle discharge capacities, the nanotube anode can maintain capacities of 102.2%, 101.9%, and 97.8% after 100 cycles at current densities of 200, 500, and 1000 mA g⁻¹, respectively. This work demonstrates the best cycling performance and high‐rate sodium storage capabilities of MoSe₂ for SIBs to date. The hollow interior, hierarchical organization, layered structure, and carbon doping are beneficial for fast Na⁺‐ion and electron kinetics and are responsible for the stable cycling performance and high rate capabilities.     

Design of High-Capacity MoS3 Decorated Nitrogen Doped Carbon Coated Cu2S Electrode Structures with Dual Heterogenous Interfaces for Outstanding Sodium-Ion Storage

The hierarchical Cu₂S@NC@MoS₃ heterostructures have been firstly constructed by the high-capacity MoS₃ and high-conductive N-doped carbon to co-decorate the Cu₂S hollow nanospheres. During the heterostructure, the middle N-doped carbon layer as the linker facilitates the uniform deposition of MoS₃ and enhances the structural stability and electronic conductivity. The popular hollow/porous structures largely restrain the big volume changes of active materials. Due to the cooperative effect of three components, the new Cu₂S@NC@MoS₃ heterostructures with dual heterogenous interfaces and small voltage hysteresis for sodium ion storage display a high charge capacity (545 mAh g⁻¹ for 200 cycles at 0.5 A g⁻¹), excellent rate capability (424 mAh g⁻¹ at 15 A g⁻¹) and ultra-long cyclic life (491 mAh g⁻¹ for 2000 cycles at 3 A g⁻¹). Except for the performance test, the reaction mechanism, kinetics analysis, and theoretical calculation have been performed to explain the reason of excellent electrochemical performance of Cu₂S@NC@MoS₃. The rich active sites and rapid Na⁺ diffusion kinetics of this ternary heterostructure is beneficial to the high efficient sodium storage. The assembled full cell matched with Na₃V₂(PO₄)₃@rGO cathode likewise displays remarkable electrochemical properties. The outstanding sodium storage performances of Cu₂S@NC@MoS₃ heterostructures indicate the potential applications in energy storage fields.     

Confine,Defect, and Interface Manipulation of Fe3Se4/3D Graphene Targeting Fast and Stable Potassium-Ion Storage

The fast electrochemical kinetics behavior and long cycling life have been the goals in developing anode materials for potassium ion batteries (PIBs). On account of high electron conductivity and theoretical capacity, transition metal selenides have been deemed as one of the promising anode materials for PIBs. Herein, a systematic structural manipulation strategy, pertaining to the confine of Fe₃Se₄ particles by 3D graphene and the dual phosphorus (P) doping to the Fe₃Se₄/3DG (DP-Fe₃Se₄/3DG), has been proposed to fulfill the efficient potassium-ion (K-ion) evolution kinetics and thus boost the K-ion storage performance. The theoretical calculation results demonstrate that the well-designed dual P doping interface can effectively promote K-ion adsorption behavior and provide a low energy barrier for K-ion diffusion. The insertion-conversion and adsorption mechanism for multi potassium storage behavior in DP-Fe₃Se₄/3DG composite has been also deciphered by combining the in situ/ex situ X-ray diffraction and operando Raman spectra evidences. As expected, the DP-Fe₃Se₄/3DG anode exhibits superior rate capability (120.2 mA h g⁻¹ at 10 A g⁻¹) and outstanding cycling performance (157.9 mA h g⁻¹ after 1000 cycles at 5 A g⁻¹).     

Edge Graphitized Oxygen-Rich Carbon Based on Stainless Steel-Assisted High-energy Ball Milling for High-Capacity and Ultrafast Sodium Storage

Oxygen doping is an effective strategy for constructing high-performance carbon anodes in Na ion batteries; however, current oxygen-doped carbons always exhibit low doping levels and high-defect surfaces, resulting in limited capacity improvement and low initial Coulombic efficiency (ICE). Herein, a stainless steel-assisted high-energy ball milling is exploited to achieve high-level oxygen doping (19.33%) in the carbon framework. The doped oxygen atoms exist dominantly in the form of carbon-oxygen double bonds, supplying sufficient Na storage sites through an addition reaction. More importantly, it is unexpected that the random carbon layers on the surface are reconstructed into a quasi-ordered arrangement by robust mechanical force, which is low-defect and favorable for suppressing the formation of thick solid electrolyte interfaces. As such, the obtained carbon presents a large reversible capacity of 363 mAh g⁻¹ with a high ICE up to 83.1%. In addition, owing to the surface-dominated capacity contribution, an ultrafast Na storage is achieved that the capacity remains 139 mAh g⁻¹ under a large current density of 100 A g⁻¹. Such good Na storage performance, especially outstanding rate capability, has rarely been achieved before.     

Confined Assembly of Hydrated Vanadium Oxide into Hollow Mesoporous Carbon Nanospheres for Fast and Stable K+ Storage Capability

The rational structural design of the electrode materials is significant to enhance the electrochemical performance for potassium ion storage, benefiting from the shortened ion diffusion distance, increased conductivity, and pseudo-capacitance promotion. Herein, hydrated vanadium oxide (HVO) nanosheets with enriched oxygen defects are well confined into hollow mesoporous carbon spheres (HMCS), producing O_d-VOH@C nanospheres through one-step hydrothermal reaction. Attributed to the restricted growth in the HMCS, the HVO nanosheets are loosely packed, generating abundant interfacial boundaries and large specific areas. As a result, O_d-VOH@C nanospheres show increased reaction kinetics and well buffer the volume effects for the K⁺ storage. O_d-VOH@C delivers stable capacities of 138 mAh g⁻¹ at 2.0 A g⁻¹ over 10 000 cycles in half-cells attributed to the high pseudo-capacitance contribution. The K⁺ storage mechanism of insertion and conversion reaction is confirmed by ex situ X-ray diffraction, Raman, and X-ray photoelectron spectroscopy analyses. Moreover, the symmetric potassium-ion capacitors of O_d-VOH@C//O_d-VOH@C deliver a high energy density of 139.6 Wh kg⁻¹ at the power density of 948.3 W kg⁻¹.     

K2Ti2O5@C Microspheres with Enhanced K+ Intercalation Pseudocapacitance Ensuring Fast Potassium Storage and Long‐Term Cycling Stability

Benefiting from the natural abundance and low standard redox potential of potassium, potassium‐ion batteries (PIBs) are regarded as one of the most promising alternatives to lithium‐ion batteries for low‐cost energy storage. However, most PIB electrode materials suffer from sluggish thermodynamic kinetics and dramatic volume expansion during K⁺ (de)intercalation. Herein, it is reported on carbon‐coated K₂Ti₂O₅ microspheres (S‐KTO@C) synthesized through a facile spray drying method. Taking advantage of both the porous microstructure and carbon coating, S‐KTO@C shows excellent rate capability and cycling stability as an anode material for PIBs. Furthermore, the intimate integration of carbon coating through chemical vapor deposition technology significantly enhances the K⁺ intercalation pseudocapacitive behavior. As a proof of concept, a potassium‐ion hybrid capacitor is constructed with the S‐KTO@C (battery‐type anode material) and the activated carbon (capacitor‐type cathode material). The assembled device shows a high energy density, high power density, and excellent capacity retention. This work can pave the way for the development of high‐performance potassium‐based energy storage devices.     

Construction of the Fast Potassiation Path in SbxBi1-x@NC Anode with Ultrahigh Cycling Stability for Potassium-Ion Batteries

Due to the scarce of lithium resources, potassium-ion batteries (PIBs) have attracted extensive attention due to their similar electrochemical properties to lithium-ion batteries (LIBs) and more abundant potassium resources. Even though there is considerable progress in SbBi alloy anode for LIBs and PIBs, most studies are focused on the morphology/structure tuning, while the inherent physical features of alloy composition's effect on the electrochemical performance are rarely investigated. Herein, combined the nanonization, carbon compounding, and alloying with composition regulation, the anode of nitrogen-doped carbon-coated Sb_xBi_1-x (Sb_xBi_1-x@NC) with a series of tuned chemical compositions is designed as an ideal model. The density functional theory (DFT) calculation and experimental investigation results show that the K⁺ diffusion barrier is lower and the path is easier to carry out when element Bi dominates the potassiation reaction, which is also the reason for better circulation. The optimized Sb_0.25Bi_0.75@NC shows an excellent cycling performance with a reversible specific capacity of 301.9 mA h g⁻¹ after 500 cycles at 0.1 A g⁻¹. Meanwhile, the charge–discharge mechanism is intuitively invetigated and analyzed by in situ X-ray diffraction (XRD) and transmission electron microscopy (TEM) in detail. Such an alloy-type anode synthesis approach and in situ observation method provide an adjustable strategy for the designing and investigating of PIB anodes.     

Highly Flexible K-Intercalated MnO2/Carbon Membrane for High-Performance Aqueous Zinc-Ion Battery Cathode

The layered MnO₂ is intensively investigated as one of the most promising cathode materials for aqueous zinc-ion batteries (AZIBs), but its commercialization is severely impeded by the challenging issues of the inferior intrinsic electronic conductivity and undesirable structural stability during the charge–discharge cycles. Herein, the lab-prepared flexible carbon membrane with highly electrical conductivity is first used as the matrix to generate ultrathin δ-MnO₂ with an enlarged interlayer spacing induced by the K⁺-intercalation to potentially alleviate the structural damage caused by H⁺/Zn²⁺ co-intercalation, resulting in a high reversible capacity of 190 mAh g⁻¹ at 3 A g⁻¹ over 1000 cycles. The in situ/ex-situ characterizations and electrochemical analysis confirm that the enlarged interlayer spacing can provide free space for the reversible deintercalation/intercalation of H⁺/Zn²⁺ in the structure of δ-MnO₂, and H⁺/Zn²⁺ co-intercalation mechanism contributes to the enhanced charge storage in the layered K⁺-intercalated δ-MnO₂. This work provides a plausible way to construct a flexible carbon membrane-based cathode for high-performance AZIBs.     

3D Sulfur and Nitrogen Codoped Carbon Nanofiber Aerogels with Optimized Electronic Structure and Enlarged Interlayer Spacing Boost Potassium‐Ion Storage

Carbonaceous materials are promising anodes for potassium‐ion batteries (PIBs). However, it is hard for large K ions (1.38 Å) to achieve long‐distance diffusion in pristine carbonaceous materials. In this work, the following are synthesized: S/N codoped carbon nanofiber aerogels (S/N‐CNFAs) with optimized electronic structure by S/N codoping, enhanced interlayer spacing by S doping, and a 3D interconnected porous structure of aerogel, through a pyrolysis sustainable seaweed (Fe‐alginate) aerogel strategy. Specifically, the S/N‐CNFAs electrode delivers high reversible capacities of 356 and 112 mA h g^?1 at 100 and 5000 mA g^?1, respectively. The capacity reaches 168 mA h g^?1 at 2000 mA g^?1 after 1000 cycles. A full cell with a S/N‐CNFAs anode and potassium prussian blue cathode displays a specific capacity of 198 mA h g^?1 at 200 mA g^?1. Density functional theory calculations indicate that S/N codoping is beneficial to synergistically improve K ions storage of S/N‐CNFAs by enhancing the adsorption of K ions and reducing the diffusion barrier of K ions. This work offers a facile heteroatom doping paradigm for designing new carbonaceous anodes for high‐performance PIBs.     

Manipulating Molecular Structure to Trigger Ultrafast and Long-Life Potassium Storage of Fe0.4Ni0.6S Solid Solution

Currently, the main obstacle to the widespread utilization of metal chalcogenides (MS_x) as anode for potassium-ion batteries (PIBs) is their poor rate capability and inferior cycling stability as a result of the undesirable electrical conductivity and severe pulverization of the nanostructure during large K-ions intercalation-extraction processes. Herein, an ultrafast and long-life potassium storage of metal chalcogenide is rationally demonstrated by employing Fe_0.4Ni_0.6S solid-solution (FNS/C) through molecular structure engineering. Benefiting from improved electroactivity and intense interactions within the unique solid solution phase, the electrical conductivity and structure durability of Fe_0.4Ni_0.6S are vastly improved. As anticipated, the FNS/C electrode delivers superior rate properties (538.7 and 210.5 mAh g⁻¹ at 0.1 and 10 A g⁻¹, respectively) and long-term cycle stability (180.8 mAh g⁻¹ at 5 A g⁻¹ after 2000 cycles with a capacity decay of 0.011% per cycle). Moreover, the potassium storage mechanisms of Fe_0.4Ni_0.6S solid solution are comprehensively revealed by several in situ characterizations and theoretical calculations. This innovative molecular structure engineering strategy opens avenues to achieve high-quality metal chalcogenides for future advanced PIBs.     

Low-temperature synthesis of CeB6 nanowires and nanoparticles as feasible lithium-ion anode materials

Metallic CeB₆ nanomaterials were prepared via the low-temperature solution combustion method (nanoparticles) and high-pressure solid state reaction (nanowires). X-ray diffraction patterns and High-resolution transmission electron microscopy images reveal that CeB₆ nanoparticles are highly crystalline and CeB₆ nanowires are single crystals. The X-ray photoelectron spectroscopy analysis indicates that the cerium is present in the +3 and +4 mixed-valence state in CeB₆. As lithium-ion anodes, CeB₆ nanowires (nanoparticles) electrode achieves a capacity of ~531 (338) mA h g⁻¹ in the initial cycle and keeps a reversible capacity of ~225 (185) mA h g⁻¹ after 60 cycles. CeB₆ nanowires are tested for 6000 cycles at 1000 mA g⁻¹, which shows a specific capacity approaching to the capacity at 100 mA g⁻¹ in spite of fluctuation within a narrow range, and keep ~168 mA h g⁻¹ after 6000 cycles, indicating a stable cycling performance owing to the excellent metal-like conductivity of (~5.67 × 10³ S m⁻¹). The reason of capacity rising is that the reduction and oxidation levels of CeB₆ electrodes are improved after the 2nd cycle with Li⁺ insertion/extraction. Meanwhile, kinetic analysis reveals that the Li⁺ storage mechanism is mainly controlled by a surface capacitive behavior.