Ion Storage Mechanism Research Articles

Enhanced Electrochemical Performance of Dual-Ion Batteries with T-Nb2O5/Nitrogen-Doped Three-Dimensional Porous Carbon Composites

Niobium pentoxide (T-Nb2O5) is a promising anode material for dual-ion batteries due to its high lithium capacity and fast ion storage and release mechanism. However, T-Nb2O5 suffers from the disadvantages of poor electrical conductivity and fast cycling capacity decay. Herein, a nitrogen-doped three-dimensional porous carbon (RMF) was prepared for loading niobium pentoxide to construct a composite system with excellent electrochemical performance. The obtained T-Nb2O5/RMF composites have a well-developed pore structure and a high specific surface area of 1568.5 m2 g−1, which could effectively increase the contact area between the material and electrolyte, improving the electrode reaction and lithium-ion transfer diffusion. Nitrogen doping increased surface polarity, creating more active sites and accelerating the electrode reaction rate. The introduction of T-Nb2O5 imparted high power density and excellent cycling stability to the battery. The composites exhibited good electrochemical performance when used as dual-ion battery anode, with a stable cycle life of 207.2 mA h g−1 at 1 A g−1 current density after 650 cycles and great rate performance of 181.5 mA h g−1 at 5A g−1 was also obtained. This work provides the possibility for applying T-Nb2O5/RMF as an anode for a high-performance dual-ion battery.

What is the potential of walnut shell-derived carbon in battery applications?

The environmental implications of utilizing walnut shells (WSs) as a material for energy storage are complex, balanced between advancing technologies and improving efficiency. This review aims to address, for the first time, environmental concerns and health effects associated with this material by conducting an in-depth analysis of carbon materials derived from waste management systems. Beginning with a reevaluation of the structural characteristics, cellular morphology, and physicochemical properties of WSs, this study explores their potential for the efficient synthesis of carbon. By examining various methods for the production of WS-derived materials such as hard carbon, we demonstrate the multifaceted nature of WS biomass as a resource. Subsequently, we shift our focus to ion storage mechanisms in the carbon source (C-S), including storage sensitivity, ion intercalation in micropores, and layer intercalation. An electrochemical analysis of the carbon source reveals its potential applications in energy storage systems. Furthermore, life cycle analysis was employed to assess the environmental impact and economic viability of WS utilization. The findings of the analysis suggest that one of the most valuable attributes of WSs is their potential for creating more environmentally sustainable materials, encouraging researchers to promote the use of green components in sodium batteries. This review underscores, for the first time, the significance of WSs in the field of carbon energy storage and their potential to enhance future prospects. The substantial opportunities in this area warrant further research and development, highlighting the relevance of WS-derived materials in advancing sustainable energy storage solutions.

Evaluating Li Ion Storage Mechanism in Carbon Nanotubes (CNT) Anodes for High Energy Density Li-Ion Batteries: An Atomistic Perspective

Current Lithium-ion batteries (LIBs) are limited to energy densities of ~150 Wh/kg and pose safety issues associated with dendrite formation and the use of flammable liquid electrolytes that can result in the common battery failure known as thermal runaway and explosion. Lithium metal is an ideal anode for high energy density LIBs due to its high theoretical capacity (3860 mAh/g) but is dangerous due to its propensity to form dendrites. Carbon nanotubes (CNTs) with superior electronic, mechanical, and structural properties provide an exciting alternative as anode for high energy density LIBs. LIBs with vertically aligned CNTs forest help achieve the capacity retention > 80% and superior efficiency over 1000 charging-discharging cycles. However, a fundamental understanding of Li+ ion storage within CNT anodes is largely unexplored and lacking. Experimental characterization of Li+ ion storage in CNT anodes is expensive and challenging. Previous theoretical studies have evaluated storage mechanism for isolated Li+ ions within small diameter CNTs (< 1.5 nm) forest. In common organic liquid electrolytes, Li+ ions prefer to be solvated and therefore isolated Li+ ions cannot accurately describe the Li+ storage mechanism especially in large diameter CNTs. In the current study, we carefully investigated the de-solvation mechanisms for Li+ ions in EC: EMC (3/7 w/w) 1.2 M LiPF6 liquid electrolytes both inside and outside of pristine CNT. The calculated de-solvation energies for Li+ ion adsorption onto the outside surface (~0.4-0.5 eV) of CNTs show relatively lower energies as compared to inside surface (~ 0.9-1.0 eV) of CNTs. We therefore claim that the Li+ ion storage strongly occurs on the outside surface of pristine defect-free CNTs. We further employ classical molecular dynamics simulations to investigate the Li+ ion storage on the outside of CNTs. The classical molecular dynamics simulations reveal a capacitive-type storage mechanism for pristine CNTs forest. Recent experimental reports suggest a large fraction of storage mechanism in CNT anode to be capacitive type (> 55 %) which supports the findings from atomistic modeling. Introducing structural defects (n-membered C-C rings), functional groups (-OH, =O, -COOH) etc... can lead to intercalation or plating-type Li ion storage in CNT forest which would result in higher capacity as well as energy density. However, for pristine CNTs we report the Li+ ion storage mechanism to be purely capacitive and therefore would serve as potential supercapacitor rather than battery. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Multifactor induction of pseudocapacitive in manganese oxide cathode enabling high-performance aqueous zinc ion batteries

Aqueous zinc-ion batteries (AZIBs) have garnered wide attention due to their notable safety, cost-effectiveness, and environmental sustainability. Cathode material is pivotal in dictating the performance of AZIBs, yet the development of high-performing cathode materials is a formidable challenge. Herein, we design and fabricate the Cu-doped MnO2 nanoparticles riveted onto carbon nanofibers (CNFs) as cathode materials. On the one hand, the introduction of CNF and Cu2+ promotes the conductivity and the generation of defect structures, which augments the intrinsic pseudocapacitance. On the other hand, nanoscale MnO2 provides abundant exposed active sites, thereby amplifying the extrinsic pseudocapacitive effect. This unique structure combines both intrinsic and extrinsic pseudocapacitive effects, effectively harnessing the rapid response advantage at the surface layer. Additionally, the introduction of CNF and Cu2+ in MnO2 boosts the ion diffusion capability. In synergy with these effects, the optimized 10C-MO-Cu exhibits a high discharge specific capacity of 442 mAh g−1 at 0.1 A g−1, and a decent capacity retention of 80 % after 750 cycles at 1 A g−1. Furthermore, the zinc ions storage mechanism is elucidated through ex-situ X-ray diffraction and X-ray photoelectron spectroscopy techniques. This work provides a novel perspective to constructing efficient cathode materials for AZIBs with high performance.

Novel Fe-compound incorporating porous carbon substrate promoting electrochemical performance of SiOx anodes for lithium-ion batteries

Silicon oxide (SiOx) shows great potential to be used in grid energy storage as the high-energy density anodes for lithium-ion batteries (LIBs) due to its low cost and high theoretical capacity. While the issues like low conductivity and volume expansion during cycles significantly decay the battery rate capability and cycle stability. To address the overall challenges, we effectively modified SiOx hybrid structure by introducing metal incorporating porous carbon, derived from metal-organic frameworks (MOFs), denoted as Fe-C/SiOx. The core-shell structure, coupled with the unique properties of both Fe-C and SiOx components, offers a synergistic effect that effectively mitigates volume expansion and low conductivity problems, resulting in significant improvements in electrochemical performance. A discharge capacity of 658 mAh g−1 at 100 mA g−1 and an initial coulombic efficiency of 60 % are achieved. Additionally, it exhibits long-term cyclic stability with capacity of 650 mAh g−1 after 300 cycles at 100 mA g−1, and 337 mAh g−1 after 500 cycles at 500 mA g−1. The lithium ion storage mechanism investigation suggests conductive matrix of porous Fe-C primarily facilitates enhanced lithium-ion diffusion dynamics and offers pseudocapacitance to the electrode, which is crucial for practical battery applications where fast charging and discharging are required.

Tailoring ion-accessible pores of robust nitrogen heteroatomic carbon nanoparticles for high-capacity and long-life Zn-ion storage

Designing highly endogenous zincophilic sites and ion-accessible pore architectures is crucial but remains a formidable challenge for carbon cathodes in zinc-ion hybrid capacitors (ZHCs) with superior capacity activity and ultralong cycling life. Herein, nitrogen heteroatomic carbon nanoparticles with hierarchical porous architectures were tailor-made by a well-established and efficient Schiff base reaction. The nucleophilic addition of amine modules and reactive carbonyl groups forms ordered organic nanoparticles with the specific internal ring pore size (1.27 nm) and high-level N heteroatomic doping. The tailored internal ring pore size, the robust macroporous networks formed by aggregated and interwoven nanoparticles and controlled carbonization/activation processes collaborate to obtain hierarchical porous architectures, robust carbon skeletons and high specific surface area (SSA) (2504 m2 g−1). Most notably, the pore architectures of NHPCs-700 (∼1.2 nm) can perfectly match the solvated ion diameter of Zn2+ (0.86 nm) and CF3SO3− (1.16 nm), realizing highly accessibility of zincophilic sites and fast diffusion behaviors. Additionally, ex-situ characterization and DFT calculation reveal the following energy storage mechanism: the ultrahigh zinc-ion capturing ability of pyridine N motifs, and fast diffusion behaviors alternately physical uptake of Zn2+/CF3SO3− charge carriers. The highly endogenous zincophilic sites, ion-accessible pore architectures and dual ion storage mechanism ensure exceptional specific capacity (253 mAh g−1 at 0.2 A g−1), outstanding energy density (157.8 Wh kg−1 at 125.3 W kg−1), and ultralong cycling life (200, 000 cycles at 10 A g−1). This work provides a strategic fabrication method for the advanced carbon cathodes with highly endogenous zincophilic site.

Metal-organic framework on graphene derived hierarchical carbon supported tin dioxide nanocomposite for superior lithium ion storage

Tin dioxide (SnO2) based anode material is investigated as an alternative choice to current graphite counterpart for lithium-ion batteries. Effective dispersing SnO2 nanocrystals in a rationally designed carbon matrix with distinctive microstructures is critical for the enhancement of the electrochemical performances. Herein, 1,3,5-benzenetricarboxylic acid (C9H6O6, H3BTC) based 1D metal–organic framework (MOF) material Sn-BTC and tea polyphenol (TP) modified 2D reduced graphene oxide (RGO) samples are firstly prepared, which are further employed to engineer a Sn-BTC/TP-RGO precursor with unique microstructures in a mild hydrothermal condition. Finally, the Sn-BTC/TP-RGO can be directly converted the hierarchical SnO2/C/RGO sample, in which SnO2 nanocrystals are well dispersed by the 1D pyrolytic carbon and 2D RGO skeleton after a thermal treatment. Critical challenges of MOF degradation, inhomogeneous distribution of SnO2 nanocrystals and over reassembly of the RGO layers are well addressed. The SnO2/C/RGO nanocomposite shows superior lithium ion storage behaviors than the controlled samples in half-cell, which has a high specific capacity of 780.03 mAh·g−1 over 200 cycles at a low-density current of 200 mA·g−1, a stable capacity of about 698.27 mAh·g−1 over 1000 cycles at a high-density current of 1000 mA·g−1. Moreover, the full-cell performance and the lithium ion storage mechanism of the SnO2/C/RGO sample are studied.

Realizing Dual-Mode Zinc-Ion Storage of Generic Vanadium-Based Cathodes via Organic Molecule Intercalation.

Intercalation engineering is a promising strategy to promote zinc-ion storage of layered cathodes; however, is impeded by the complex fabrication routes and inert electrochemical behaviors of intercalators. Herein, an organic imidazole intercalation strategy is proposed, where V2O5 and NH4V3O8 (NVO) model materials are adopted to verify the feasibility of the imidazole intercalator in improving the zinc storage capabilities of vanadium-based cathodes. The intercalated imidazole molecules could not only expand interlayer spacing and strengthen structural stability by serving as extra "pillars" but also provide extra coordination sites for zinc storage via the coordination reaction between Zn2+ and the C═N group. This gives rise to a dual-mode ion storage mechanism and favorable electrochemical performances. As a result, imidazole-intercalated V2O5 delivers a capacity of 179.9 mAh g-1 after 5000 cycles at 20 A g-1, while the imidazole-intercalated NVO harvests a high capacity output of 170.2 mAh g-1 after 700 cycles at 2 A g-1. This work is anticipated to boost the application potentials of vanadium-based cathodes in aqueous zinc-ion batteries.

High-Performance Sodium-Ion Batteries with Graphene: An Overview of Recent Developments and Design.

Due to their low production cost, sodium-ion batteries (SIBs) are considered attractive alternatives to lithium-ion batteries (LIBs) for next generation sustainable and large-scale energy storage systems. However, during the charge/discharge cycle, a large volume strain is resulted due to the presence of a large radius of sodium ions and high molar compared to lithium ions, which further leads to poor cyclic stability and lower reversible capacity. In the past, researchers have devoted significant efforts to explore various anode materials to achieve SIBs with high energy density. Hence, as a promising anode material for SIBs, the two-dimensional (2D) materials including graphene and its derivatives and metal oxides have attracted remarkable attention due to their layered structure and superior physical and chemical properties. The inclusion of graphene and metal oxides with other nanomaterials in electrodes have led to the significant enhancements in electrical conductivity, reaction kinetics, capacity, rate performance and accommodating the large volume change respectively. Moreover, these 2D materials facilitated large surface areas and shorter paths for sodium ion adsorption and transportation respectively. In this review article, the fabrication techniques, structural configuration, sodium ion storage mechanism and its electrochemical performances will be introduced. Subsequently, an insight into the recent advancements in SIBs associated with 2D anode materials (graphene, graphene oxide (GO), transition metal oxides etc.) and other graphene-like elementary analogues (germanene, stanine etc.) as anode materials respectively will be discussed. Finally, the key challenges and future perspectives of SIBs towards enhancing the sodium storage performance of graphene-based electrode materials are discussed. In summary, we believe that this review will shed light on the path towards achieving long-cycling life, low operation cost and safe SIBs with high energy density using 2D anode materials and to be suitably commercialized for large-scale energy storage applications in the future.

Unraveling the Ionic Storage Mechanism of Flexible Nitrogen-Doped MXene Films for High-Performance Aqueous Hybrid Supercapacitors.

2D MXene nanomaterials have excellent potential for application in novel electrochemical energy storage technologies such as supercapacitors and batteries, but the existing pure MXene is difficult to meet the practical needs. Although the electrochemical properties of modified MXene have been improved, the unclear ion storage mechanism still hinders the development of MXene-based electrode materials. Herein, the study develops flexible self-supported nitrogen-doped Ti3C2 (Py-Ti3C2) films by the highly mobile, high nitrogen content, oxygen-free pyridine-assisted solvothermal method, and then deeply investigates the energy storage mechanism of hybrid supercapacitors in four aqueous electrolytes (H2SO4, Li2SO4, Na2SO4, and MgSO4). The experimental results suggest that the Py-Ti3C2 film electrode exhibits a pseudocapacitance-dominated energy storage mechanism. Particularly, the specific capacity of the Py-Ti3C2 in 1M H2SO4 (506 F g-1 at 0.1 A g-1) is 4-5 times higher than other electrolytes (≈110 F g-1), which could be attributed to the substantially higher ionic diffusion coefficient of H+ than those of Li+, Na+, Mg2+ with small ionic size, high ionic conductivity, and fast pseudocapacitance response. Theoretical analysis further confirms that Py-Ti3C2 has strengthened conductivity and electrical double-layer capacitance performance. Meanwhile, it has lower free energy for protonation and deprotonation of functional groups, which gives excellent pseudocapacitance performance.

Fluoride Ion Storage and Conduction Mechanism in Fluoride Ion Battery Positive Electrode, Ruddlesden-Popper-Type Layered Perovskite La1.2Sr1.8Mn2O7 Crystal.

Structural characteristics on fluoride ion storage and conduction mechanism in La1.2Sr1.8Mn2O7, and its fluoridated materials, La1.2Sr1.8Mn2O7F and La1.2Sr1.8Mn2O7F2, for an all-solid-state fluoride ion battery positive electrode with a high volumetric capacity surpassing those of lithium-ion ones have been revealed using the Rietveld method and maximum entropy method. In La1.2Sr1.8Mn2O7, once the F- ions are taken into the NaCl slabs in its crystal through the charging process, it forms two stable fluoride compounds, La1.2Sr1.8Mn2O7F and La1.2Sr1.8Mn2O7F2, with the help of the Mn oxidation reaction. In these oxyfluorides, thermal vibrations of the F- ions inserted are much larger, especially in the a-b plane, than along the c axis. When surplus energy, such as an electric field for charging, is applied to these crystals at near room temperature or higher, the anions immediately begin to jump to their neighboring lattice sites, resulting in sufficiently rapid and large ionic conduction. The MEM analyses and density functional theory (DFT) calculations have revealed that the F- ions enable to easily travel along the ⟨110⟩ directions in the NaCl slabs of these crystals. These structural features thus make La1.2Sr1.8Mn2O7 and its fluorides possess both of two features incompatible with each other, ion storage and conduction, indispensable for rechargeable batteries.

Regulating the microstructure of cross-linked starch-derived hard carbon for highly reversible sodium-ion storage

Optimizing the interlayer spacing and closed porosity of hard carbon (HC) is crucial for enhancing the reversible capacity of sodium-ion batteries (SIBs). Nevertheless, the unclear structure-performance relationship and the sodium storage mechanism significantly hinder the precise tuning of HC structures. Herein, this paper reports an esterified cross-linked starch-derived HC material and investigates its evolution mechanisms of microcrystalline carbon layers and closed porosity at various carbonization temperatures. By adjusting the spacing of the carbon layers and the distribution of closed pores, effective sodium ion storage is achieved. The optimized HC exhibits an initial Coulombic efficiency (ICE) of 90 % and a high reversible capacity of 376 mAh g−1, including a plateau capacity of 246 mAh g−1. After 100 cycles at 0.5 C, it retains a high capacity retention rate of 99.6 %. The sodium ion storage mechanism is investigated in depth using galvanostatic intermittent titration technique (GITT) and in-situ Raman, revealing that the plateau capacity is related to the insertion of sodium ions between carbon layers and the filling in pores, providing new evidence for the “adsorption-intercalation/filling” mechanism. Moreover, the assembled full-cell achieves a high energy density of 212 Wh kg−1.

The morphologic dependence of MnO2 electrodes in capacitive deionization process

Manganese dioxide (MnO2) materials are one of promising cathode candidates for capacitive deionization (CDI) applications, with their morphology significantly impacting the performance of the electrode material itself. Therefore, this study systematically investigates the structure-performance relationships and the micro-interface ion storage mechanisms of four morphologies of MnO2 (1D nanorods (NNMO), nanowires (NWMO), 3D microspheres (MMO), and hollow urchin-like spheres (HUMO)) in relation to their capacitive deionization performance with typical heavy metal ions (Cd2+) through experimental and theoretical calculations. In terms of pore morphology, capacitance significantly increases with increasing surface curvature of materials, demonstrating a clear pore structure-dependent characteristic. NNMO, with the smallest pore size, has much lower surface capacitance (∼0.15 μF cm−2) than other materials (∼0.33 μF cm−2). As pore size increases, the capacitance distribution difference driven by pore structure size gradually disappears. Regarding surface and interface characteristics, high-energy crystal facets facilitate electron transfer ({310}>{200}≈{211}>{100}) and increase the proportion of surface active sites (Osur), thus promoting CDI absorption kinetics. During the capacitive deionization process, the pore structure (∼77 %) and surface-interface characteristics (∼23 %) exhibit highly coupled features and the driving force for interfacial ion storage among the four materials is in the order of HUMO>MMO>NWMO>NNMO. This work elucidates the morphology-dependent capacitive processes of MnO2 nanomaterials, enhancing the understanding of structure- electrochemical process at the nanoscale but also providing effective guidance for the design and development of practical, high-performance CDI electrode materials.

Linking the size of hard carbon particles with electrochemical response in sodium ion storage

Hard carbon is considered to be one of the most promising anodes for sodium-ion batteries (SIBs) owing to its high capacity and abundant resources. However, the role of particle size on sodium ion storage is unclear, which leads to low capacity and initial coulombic efficiency (ICE) in practical application. In this work, a series of hard carbons with different particle sizes were prepared by an “up to down” strategy using simple grinding and ball-milling method to investigate the effect of particle size on electrochemical response of sodium ion storage. The particle size of hard carbon has negligible effect on initial specific capacity. However, it has a strong effect on the ICE and rate capability. The ICE reduces as the particle size decreases, but the rate performance in reverse. Moreover, impedance analysis and electrochemical kinetics show huge differences for different particle sizes. In-situ Raman technique was also adopted to further illustrate the sodium ion storage mechanism of hard carbon, and an “adsorption-intercalation-pore filling” mechanism is proposed. This work could provide a new perspective for the design of hard carbon materials with suitable structure for efficient sodium ion storage, helping to develop high performance SIBs.

Comparative insight into crystal evolutions of monodisperse MNb2O6 (M = Ni, Cu, Zn) spheres during electrochemical cycling in Li/Al-ion batteries

Niobates have emerged as advanced anode materials for lithium-ion batteries, owing to their inherently higher voltage and the occurrence of multiple one-electron redox reactions. However, there is a lack of comprehensive comparative analysis regarding their performance in lithium-ion and aluminum-ion battery applications. In this study, a facile solvothermal process is developed to synthesize uniform submicrospheres of three niobates: NiNb2O6, CuNb2O6, and ZnNb2O6 with large specific surface area and narrow size distribution. Their superior textural properties consisting of interconnected nanograins offer numerous active sites, delivering enhanced capacity and rate performance for the constructed half and full cells. Our in-situ XRD analysis reveals that all three niobates exhibit ultralow crystal volume expansion (< 6 %). But they exhibit distinct ion storage mechanisms: CuNb2O6 undergoes a phase transition to LiNb3O8 and NbO2 upon cyclic insertion of Li+ ions; NiNb2O6 mainly involves a classic hybrid-controlled process, facilitating easy ion insertion/extraction into/from the crystal lattices, especially at low sweep rates; while ZnNb2O6 stores charges via a pseudocapacitive-controlled process. Density functional theory (DFT) calculation and ex-situ XRD analysis confirm that CuNb2O6 outperforms the others, displaying the best electrochemical performance and holding promise as a high-energy electrode material thanks to favorable phase conversion, enhanced transport channels, porous structure and spherical morphology.

Evolutionary Zn ion storage mechanism of hierarchical nanotubular spinel FeV2O4 for Zinc–Metal full cells

A fundamental understanding about the evolution of energy storage mechanism by the structure reconstruction during initial cycling is crucial in establishing their correlation with the unprecedented electrochemical performance of electrodes. Herein, we demonstrate evolutionary zinc (Zn) ion storage mechanism and kinetics of the hierarchical nanotubular FeV2O4 (FeV2O4@NT) coated by turbostratic carbon layers through the anodic hydration-induced crystal reconstruction, where the smaller nanocrystalline FeV2O4 spinel phase was embedded into the newly-formed amorphous V-O-Fe phase at the heterointerface. These FeV2O4@NT cathodes achieved the synergistically combined energy storage mechanism of intercalation and pseudocapacitance for the greatly improved electrochemical performance of pouch full cells, which was not achieved by existing spinel oxides. With the polyoxometalate modified Zn metal anode at the optimized condition of 3.0 M Zn(OTf)2/(ACN/H2O-0.15) in the voltage range of [0.3–1.6 V (vs. Zn/Zn2+)], the POM-Zn||FeV2O4@NT full cells achieved a high capacity of 456.8 mAh g–1 at 200 mA g–1, high rate capacity of 222.0 mAh g−1 even at 10,000 mA g–1, and a large energy density of 337.5 Wh kg–1. Furthermore, the chemical pillar and Fe vacancies in the amorphous V-O-Fe phase allowed FeV2O4@NT electrode to achieve a low capacity decay rate of 0.0152 % per each cycle over 1,000 cycles.

Dual Strategy of Morphology Optimization and Interlayer Expansion in VS2 Cathode Toward High-Performance Mg-Li Hybrid Ion Batteries.

Combining the merits of the dendrite-free formation of a Mg anode and the fast kinetics of Li ions, the Mg-Li hybrid ion batteries (MLIBs) are considered an ideal energy storage system. However, the lack of advanced cathode materials limits their further practical application. Herein, we report a dual strategy of morphology optimization and interlayer expansion for the construction of hierarchical flower-like VS2 architecture coated by N-doped amorphous carbon layers. This tailored hierarchical flower-like structure coupled with homogeneous N-doped amorphous carbon layers cooperatively provide more active sites and buffer volume changes, thus realizing the enhancement of capacity and structural stability. Moreover, the enlarged interlayer spacing caused by the cointercalation of polyvinylpyrrolidone and ammonium ions can effectively promote the charge transfer rate and facilitate the rapid ion diffusion, as further demonstrated by electrochemical results and theoretical calculations. These features endow the hierarchical flower-like VS2 cathode with superior specific energy density (644.4 Wh kg-1, average voltage of 1.2 V vs Mg2+/Mg) and excellent rate capability (181.1 mAh g-1 at 2000 mA g-1). Systematic ex situ characterization measurements are employed to reveal the ion storage mechanism, which confirms that Li+ storage plays a leading role in the capacity contribution of MLIBs. Our strategy is in favor of providing useful insights to design and construct MLIBs with high energy density and excellent rate performance.

Marrying Fe nanoclusters with 3D carbon nanofiber aerogels: Triggering fast and robust faradic capacitive deionization

Faradic-capacitive deionization (FDI) has emerged promising research branch of capacitive deionization (CDI) to address the crisis in freshwater supply due to its high desalination capacity and unique ion storage mechanism over traditional CDI. However, the ion-storage mechanism of FDI imposes notable limitations on its desalination kinetics, while issues such as volumetric expansion (as well as the damage caused to the composite material’s structure) contribute to poor cycling stability. Herein, we developed a rational material design of Fe nanocluster-impregnated CNFAs (Fe NCs@CNFAs) and further used it as chloride-capturing electrode for FDI. This unique nanostructure not only provides fast surface-driven pseudo capacitance but also establishes a flexible scaffold that effectively protects the Fe NCs from severe morphology changes. As a result, our Fe NCs@CNFAs-based FDI exhibited both ultrahigh desalination capacity (120.38 mg g−1) and fast desalination rate (0.42 mg g−1 s−1), with robust cycling stability (showing only a 15.25 % decrease in desalination capacity after 100 cycles). This study underscores the significance of the problem-driven approach by leveraging soft scaffold-protected ultrasmall nanocluster to induce fast and durable desalination performance.

Unlocking plateau capacity with versatile precursor crosslinking for carbon anodes in Na-ion batteries

As the precursor material inherently determines the fundamental structure of hard carbons, a direct manipulation of precursors at the molecular level promises enhanced flexibility in designing hard carbon architectures, which plays a pivotal role in dictating the final microstructural properties and, ultimately, the overall sodium storage performance. In this study, we present a novel generalized strategy utilizing P and O double cross-linking to convert pitch into a thermosetting precursor, creating copious micropores within pitch-based carbon. These micropores serve as essential pathways and active binding sites for sodium ion transport and storage, leading to pitch-derived hard carbons with a remarkable specific capacity of 416.1 mAh/g and an impressive initial Coulombic efficiency of 89.7%. Extensive study revealed a strong correlation between the increased plateau capacity and the closed pore volume, validating the micropore-driven sodium ion storage mechanism. Our findings underscores the groundbreaking significance of cross-linking in precursor modification, paving the way for the design and synthesis of high-performance hard carbon anodes for next-generation Na-ion batteries.

Heterostructured MnSe/FeSe nanorods encapsulated by carbon with enhanced Na+ diffusion as anode materials for sodium-ion batteries

The natural abundance of sodium has fostered the development of sodium-ion batteries for large-scale energy storage. However, the low capacity of the anodes hinders their future application. Herein, carbon-encapsulated MnSe-FeSe nanorods (MnSe-FeSe@C) have been fabricated by the in-situ transformation from polydopamine-coated MnO(OH)-Fe2O3. The heterostructure constructed by MnSe and FeSe nanocrystals induces the formation of built-in electric fields, accelerating electron transfer and ion diffusion, thereby improving reaction kinetics. In addition, carbon enclosure can buffer the volumetric stress and enhance the electrical conductivity. These aspects cooperatively endow the anode with superior cycling stability and distinguished rate performance. Specifically, the discharge capacity of MnSe-FeSe@C reaches 414.3 mA h g−1 at 0.1 A g−1 and 388.8 mA h g−1 even at a high current density of 5.0 A g−1. In addition, it still retains a high reversible capacity of 449.2 mA h g−1 after 700 long cycles at 1.0 A g−1. Further, the ab initio calculation has been employed to authenticate the existence of the built-in electric field by Bader charge, indicating that 0.24 electrons in MnSe were transferred to FeSe. The in-situ XRD has been used to evaluate the phase transition during the charging/discharging process, revealing the sodium ion storage mechanism. The construction of heterostructure material paves a new way to design performance-enhanced anode materials for sodium-ion batteries.