Acid-assisted synthesis of core-shell Prussian blue cathode for sodium-ion batteries.

In recent years, core-shell structured Prussian Blue Analogues (PBAs) have been considered as highly promising cathode materials for sodium-ion batteries. Reducing production costs and simplifying the preparation method for core-shell PBAs have also become crucial considerations. This paper presents a novel approach for the first time: by acid-treating the as-synthesized solution from a simple coprecipitation reaction, a high-crystallinity, sodium-rich Mn2+-doped iron hexacyanoferrate (Fe/MnHCF) shell material is self-grown on the surface of manganese hexacyanoferrate (MnHCF). This method significantly improves the electrochemical properties of the MnHCF material. The core-shell structured PBA exhibits excellent cycling performance (with a capacity retention of 95.5 % for 400 cycles at 1 A/g) and high rate performance (134.2mAh/g@10 mA/g, 95.2mAh/g@1 A/g). In this article, we explore the growth mechanism of the high-sodium content, high-crystallinity shell structure and introduce a green chelating agent that is better suited for the crystallization of Mn and Fe-type PBA systems. Our study demonstrates that Mn2+ doping enhances the conductivity of the shell material. Meanwhile, the heterojunction structure of MnHCF@Fe/MnHCF conducive to charge separation and migration. This straightforward synthesis strategy offers a novel approach for fabricating high-performance core-shell structured Prussian Blue Analogue materials.

Engineering (FeSn)/S nanocubes heterojunctions for improved sodium ion battery performance.

Transition metal sulfides have emerged as compelling anode materials for sodium-ion batteries (SIBs), leveraging their abundant elemental reserves and high theoretical capacities. However, the reaction of sulfur with Na ions is usually accompanied by significant volume dilation, which hinders their further development and application. Hence, constructing bimetallic sulfide (FeSn)/S for SIBs anode material greatly alleviates the circulation attenuation caused by volume expansion. Through constructing bimetallic heterojunction materials from nanocube precursors, the (FeSn)/S anode material retains a high specific capacity of 578 mAh/g at an intense current density of 2 A/g after 1000 cycles, and exhibits an great rate capability, delivering 796 mAh/g at 100 mA/g. The excellent electrochemical performance of the heterojunction material presents a promising solution to the enduring quest for enhanced anode material for SIBs.

A novel NASICON-type Na3MnTi0.5Zr0.5(PO4)3 cathode material with multivalent redox reaction for high performance sodium-ion batteries.

Na3MnZr(PO4)3, a typical manganese-based NASICON-type material, has consistently been at the forefront of research on cathode materials for sodium-ion batteries due to the abundant manganese reserve and high operating voltage. However, the severe Jahn-Teller effect, poor electronic conductivity and kinetic limitation of Na3MnZr(PO4)3 impose constraints on its rate capability and cycling performance, thereby hindering its practical application. To address this challenge, a ternary NASICON-type material Na3MnTi0.5Zr0.5(PO4)3/C, with a multi-metal synergistic effect, is proposed in this study. The substitution of Ti at Zr site significantly mitigates the Jahn-Teller effect induced by Mn3+. Furthermore, the stability of the ZrO bond is enhanced, leading to a more robust crystal structure overall. Cyclic voltammetry and constant-current intermittent titration techniques reveal that the appropriate Ti substitution markedly boosts the electronic conductivity and Na+ diffusion coefficient of the electrode material, thereby mitigating polarization effects and expediting electrode reaction rates. Leveraging the multi-effect of Ti substitution, the prepared Na3MnTi0.5Zr0.5(PO4)3/C presents an improved electrochemical performance. Notably, Na3MnTi0.5Zr0.5(PO4)3/C enables a high discharge capacity of 71.0 mAh g-1 at 10C and maintains 78.8 % capacity after 1000 cycles at 2C rate. This investigation establishes a robust theoretical foundation for comprehending the synergistic effects of multimetal systems in NASICON materials and offers insights into the development of cost-effective, high-performance cathode materials.

Unravelling the anionic stability of an ether-based electrolyte with a hard carbon or metallic sodium anode for high-performance sodium-ion batteries.

In hard carbon (HC) anodes, elucidating the relationship between the solid electrolyte interphase formation and the solvated Na+ co-intercalation mechanism is crucial, particularly considering different anionic salts in ether-based electrolytes. Here, we comprehensively explore the impact of different anionic salts on the electrochemical performance of HC/Na half-cell and elucidate the underlying mechanism through experimental studies and theoretical calculations. The surface morphology of the HC anode and its interphasial property are further investigated to evaluate the differences endowed by the presence of various anionic salts in diglyme (2G). The HC/Na half-cells with NaPF6-2G and sodium trifluoromethanesulfonate (NaCF3SO3)-2G display superior electrochemical performance with faster kinetics and lower interfacial resistance than those with NaClO4-2G, sodium bis-(fluorosulfonyl) imide (NaFSI)-2G and sodium bis-(trifluoromethanesulfonyl) imide (NaTFSI)-2G. NaClO4-2G forms a relatively thick interphase layer with high resistance at the electrode/electrolyte interface owing to its insufficient stability. NaFSI-2G and NaTFSI-2G exhibit severe side reactions with Na metal, producing a thick interphase layer on the HC surface with high interfacial resistance from excess electrolyte decomposition, thus deteriorating the electrochemical performance. In summary, the study on the stability of different anionic salts in ether-based electrolyte for the HC anode with the intercalation mechanism provides valuable insights for screening appropriate conductive salts for high-performance sodium-ion batteries, especially when considering Na metal counter/reference electrodes.

Engineering a superionic conductor surface enables fast Na+ transport kinetics for high-stable layered oxide cathode.

Unstable cathode/electrolyte interphase and severe interfacial side reaction have long been identified as the main cause for the failure of layered oxide cathode during fast charging and long-term cycling for rechargeable sodium-ion batteries. Here, we report a superionic conductor (Na3V2(PO4)3, NVP) bonding surface strategy for O3-type layered NaNi1/3Fe1/3Mn1/3O2 (NFM) cathode to suppress electrolyte corrosion and near-surface structure deconstruction, especially at high operating potential. The strong bonding affinity at the NVP/NFM contact interface stabilizes the crystal structure by inhibiting surface parasitic reactions and transition metal dissolution, thus significantly improving the phase change reversibility at high desodiation state and prolonging the lifespan of NFM cathode. Due to the high-electron-conductivity of NFM, the redox activity of NVP is also enhanced to provide additional capacity. Therefore, benefiting from the fast ion transport kinetics and electrochemical Na+-storage activity of NVP, the composite NFM@NVP electrode displays a high initial coulombic efficiency of 95.5 % at 0.1 C and excellent rate capability (100 mAh g-1 at 20 C) within high cutoff voltage of 4.2 V. The optimized cathode also delivers preeminent cyclic stability with ∼80 % capacity retention after 500 cycles at 2 C. This work sheds light on a facile and universal strategy on improving interphase stability to develop fast-charging and sustainable batteries.

Crosslinking modification of starch improves the structural stability of hard carbon anodes for high-capacity sodium storage.

Compared with the complex components of raw biomass, biomass derivatives with defined structures are more conducive to the controllable synthesis of hard carbon (HC) materials. Starch-based HC has garnered significant attention because of its cost-effectiveness; however, its practical applicability is limited by poor thermal stability. Herein, we propose a strategy for improving the stability of starch through self-assembly crosslinking modification, yielding high-performance HC. Starch and citric acid form a dense crosslinked structure through esterification between hydroxyl and carboxyl groups, effectively overcoming the poor thermal stability. The resulting HC exhibits a low specific surface area (SSA) and abundant closed pore structures, thereby enabling substantial sodium-ion storage. The optimized HC exhibits an improved reversible capacity of 378 mAh g-1 and an initial Coulombic efficiency (ICE) of 90.9 %. After 100 cycles at 0.5 C, it retains 98 % initial capacity. The assembled full-cell shows a high energy density of 248 Wh kg-1. Furthermore, the structure-performance relationship analysis reveals that the slope capacity is primarily affected by the defect concentration, while the plateau capacity is mainly determined by the closed pore structure. Galvanostatic intermittent titration technique (GITT) tests and in-situ Raman spectroscopy reveal that the sodium-ion storage mechanism in starch-based HC is "adsorption-intercalation/filling."

Interfacial SbOC bond and structural confinement synergistically boosting the reaction kinetics and reversibility of Sb2Se3/NC nanorods anode for sodium storage.

Antimony selenide (Sb2Se3) has been considered as a prospective material for sodium-ion batteries (SIBs) because of its large theoretical capacity. Whereas, grievous volume expansion caused by the conversion-alloying reaction leads to fast capacity decay and inferior cycle stability. Herein, the confined Sb2Se3 nanorods in nitrogen-doped carbon (Sb2Se3/NC) with interfacial chemical bond is designed to further enhance sodium storage properties of Sb2Se3. The robust enhancing effect of interfacial SbOC bonds can significantly promote electron transfer, Na+ ions diffusion kinetics and alloying reaction reversibility, combining the synergistic effect of the unique confinement structure of N-doped carbon shells can efficiently alleviate the volume change to ensure the structural integrity. Moreover, in-situ X-ray diffraction reveals intercalation/de-intercalation, conversion/reversed conversion reaction and alloying/de-alloying reaction mechanisms, and the kinetics analysis demonstrates the diffusion-controlled to contribute high capacity. As a result, Sb2Se3/NC anode delivers a high reversible capacity of 612.6 mAh/g at 0.1 A/g with a retentive specific capacity of 471.4 mAh/g after 1000 cycles, and long-cycle durability of over 2000 cycle with the reversible capacities of 371.1 and 297.3 mAh/g at 1 and 2 A/g are achieved, respectively, and an good rate capability. This distinctive interfacial chemical bonds and confinement effect design shows potential applications in the improved conversion/alloying-type materials for SIBs.

Confined Mo2C/MoC heterojunction nanocrystals-graphene superstructure anode for enhanced conversion kinetics in sodium-ion batteries.

Heterostructure design and integration with conductive materials play a crucial role in enhancing the conversion kinetics of electrode materials for metal-ion batteries. However, integrating nanocrystal heterojunctions into a conductive layer to form a superstructure is a significant challenge, mainly due to the difficulty in maintaining the structural integrity. Here we report a unique glucose-induced heterogeneous nucleation method that enables the independent manipulation of nucleation and growth of Mo2C/MoC heterojunction nanocrystals within 2D layers. Our investigations reveal that the rGO-Mo2C/MoC-rGO superstructure is formed by a topological transformation induced by subsequent heat treatment of the initial hydrothermally prepared rGO-MoO2-rGO precursor. This novel structure embeds Mo2C/MoC heterojunction nanocrystals within a 2D graphene matrix, providing enhanced mechanical stability, accelerated Na+ transport, and improved electron conduction. Ex situ XRD and Raman spectroscopy analyses reveal that the rGO-Mo2C/MoC-rGO superstructure significantly enhances the stability and reversibility of anodes. Leveraging these unique characteristics, the newly developed superstructural anode exhibits remarkable long-term cycling stability and outstanding rate performance. As a result, superstructure anodes demonstrate superior electrochemical capabilities, delivering a specific capacity of 106 mAh/g after enduring 5000 cycles at 1 A/g. Our study underscores the critical importance of superstructure design in propelling the advancement of battery materials.

Air stable and fast-charging cathode material for all climate sodium-ion batteries.

The off-stoichiometric compound Na3.12Fe2.44(P2O7)2 (NFPO) is a highly promising, cost-effective, and structurally robust cathode material for sodium-ion batteries (SIBs). However, the slowing Na-ion migration kinetics and poor interface stability have seriously limited its rate capability and air stability. In this work, we successfully synthesis a sodium titanium pyrophosphate (NaTiP2O7 donated as NTPO) coating NFPO (denoted as NFPO-NTPO) cathode material via a liquid phase coating method for SIBs. After optimizing NTPO content, at 0.1C, NFPO-NTPO-4 % cathode achieves a reversible specific capacity of 108.4 mAh g-1. Remarkably, it maintains 88.39 % capacity at 10C comparing to 0.1C and stabilizes over 3000 cycles with 92.66 % retention rate. Moreover, it retains 88.89 % capacity after 5000 cycles at 20C, even after 28 days of air exposure. The NFPO-Ti cathode, alongside the complete battery system, exhibits remarkable electrochemical performance across a broad temperature range spanning from -40 to 60 ℃.

High-throughput arousing interconnected interfaces for excellent sodium storage chemistry.

Heterostructures endow electrochemical hybrids with promising energy storage properties owing to synergistic effects and interfacial interaction. However, developing a facile but effective approach to maximize interface effects is crucial but challenging. Herein, a bimetallic sulfide/carbon heterostructure is realized in a confined carbon network via a high-throughput template-assisted strategy to induce highly active and stable electrode architecture. The designed heterostructures not only yield abundant interconnected Co9S8/MoS2/N-doped carbon (Co9S8/MoS2/NC) heterojunctions with continuous channels for ion/electron transfer but maintain excellent conversion reversibility. Serving as anode for sodium storage, the Co9S8/MoS2/NC framework displayed excellent sodium storage properties (reversible capacity of 480 mAh/g after 100 cycles at 0.2 A/g and 286.2 mAh/g after 500 cycles at 2 A/g). Given this, this study can guide future design protocols for interface engineering by forming dynamic channels of conversion reaction kinetics for potential applications in high-performance electrodes.

In-situ synthesis of heteroatom-doped hard carbon for sodium-ion batteries: Dual benefits for green energy and environment.

Heteroatom-doped carbon has been widely investigated as anode materials for sodium-ion batteries (SIBs). However, simplifying the preparation process and precisely controlling their microstructure to achieve excellent Na+ storage performance remain significant challenges. Therefore, in this study, high-performance N, P co-doped Na+ storage carbon anode electrode materials were prepared by one-step carbonization using N, P-rich Eichhornia crassipes (EC) as raw materials and systematically tested for their Na+ storage performance. The doping levels of N and P atoms as well as the spatial structure of the carbon material were adjusted by changing the carbonization temperature during the pyrolysis process. Among them, the anode material corresponding to 1300 °C (EC-PN1300) showed an excellent Na+ storage capacity of 336 ± 4 mAh g-1 (50 mA g-1) and excellent cycling stability (99.8 % retention after 2000 cycles). In addition, the Na+ storage mechanism of EC-PN1300 was systematically analyzed using galvanostatic intermittent titration (GITT), ex-situ XPS and in-situ Raman spectroscopy, providing accurate research directions for developing carbon anode electrode materials with superior electrochemical performance. This study not only provides some insights into the preparation of carbon anode materials in alkali metal batteries and the development of carbon materials in other fields, but also realizes the interaction between environmental protection and new energy development.

Confining WS2 hierarchical structures into carbon core-shells for enhanced sodium storage.

The growing demand for clean energy has heightened interest in sodium-ion batteries (SIBs) as promising candidates for large-scale energy storage. However, the sluggish reaction kinetics and significant volumetric changes in anode materials present challenges to the electrochemical performance of SIBs. This work introduces a hierarchical structure where WS2 is confined between an inner hard carbon core and an outer nitrogen-doped carbon shell, forming HC@WS2@NCs core-shell structures as anodes for SIBs. The inner hard carbon core and outer nitrogen-doped carbon shell anchor WS2, enhancing its structural integrity. The highly conductive carbon materials accelerate electron transport during charge/discharge, while the rationally constructed interfaces between carbon and WS2 regulate the interfacial energy barrier and electric field distribution, improving ion transport. This synergistic interaction results in superior electrochemical performance: the HC@WS2@NCs anode delivers a high capacity of 370 mAh g-1 at 0.2 A/g after 200 cycles and retains261 mAh g-1 at 2 A/g after 2000 cycles. In a full battery with a Na3V2(PO4)3 cathode, the Na3V2(PO4)3//HC@WS2@NC full-cell achieves an impressive initial capacity of 220 mAh g-1 at 1 A/g. This work provides a strategic approach for the systematic development of WS2-based anode materials for SIBs.

Enhancing the sodium storage performance of hard carbon by constructing thin carbon coatings via esterification reactions.

Hard carbons derived from pitch are considered a competitive low-cost anode for sodium-ion batteries. However, the preparation of pitch-based hard carbon (PHC) requires the aid of a pre-oxidation strategy, which introduces unnecessary defects and oxygen elements, which leads to low initial Coulombic efficiency (ICE) and poor cycling stability. Herein, we demonstrate a new surface engineering strategy by grafting chemically active glucose molecules on the PHC surface via esterification reactions, which can achieve low-cost nano-scaled carbon coating. Thin glucose coating can be carbonized at a lower temperature, which results in a more closed pore structure and fewer functional groups. The as prepared PHC exhibits a high reversible capacity of 328.5 mAh/g with a high ICE of 92.08 % at 0.02 A/g. It is noteworthy that the PHC can be adapted to a variety of cathode materials for full-cell assembling without pre-sodiation, which maintains the characteristics of high capacity and excellent cycling stability. The performance of resin-based hard carbon coated with a similar method was also improved, demonstrating the universality of the technique.

An improved N-N dimethylacetamide-based non-flammable molecular crowding electrolyte using NaOTf for cobalt-based prussian blue//hard carbon aqueous solution battery.

Aqueous sodium-ion batteries (ASIBs) are promising for large-scale electrical energy storage (LSEES) applications due to their cost and safety advantages. However, the low voltage stabilization window of water (∼1.23 V) and the lack of cathode with high specific capacity and long cycle life have limited their development. Cobalt-based Prussian blue analogues (NaCoPBAs) have the advantage of high theoretical specific capacity but short cycle life. Recently, the molecular crowding electrolyte (MCE) strategy has been proposed to improve the electrolyte voltage stability window (ESW) of electrolytes, in this work, we report an improved xMC (x: ratio, MC: molecular crowding agent) electrolyte that uses N-N dimethylacetamide (DMAC) as the molecular crowding agent and NaOTf as the advanced salt with an ESW of 2.65 V and excellent nonflammability. The side reactions of the NaCoPBA//Hard Carbon (HC) full-cell active material are improved with the aid of the electrolyte. Capacity retention of 75 % after 600 cycles with excellent cycling stability. These results demonstrate that this advanced MCE strategy can be utilized for practical applications designed for safety, high specific capacity and long cycle (ASIB).

Natural Pitch-Derived Carbon Networks Induced Lattice Strain Engineering in Nickel-Based Heterostructures Enables Efficient Anodes for Sodium-Ion Batteries.

The development of high-performance sodium-ion batteries (SIBs) relies on enhancing the electrochemical properties of the electrodes, particularly the transition metal compounds (TMCs) through effective carbon coatings. Herein, a straightforward approach using polymerized natural pitch-derived carbon (PNPC) via step-growth polymerization regulates the lattice strain in Ni3S2-NiO heterostructures (NSNO) on nickel foam (NF). This method replaces the complex multistep carbon coatings with a cost-effective liquid-phase application of PNPC, followed by pyrolysis to create PNPC@NSNO/NF. Comparative analysis shows that PNPC effectively modulates lattice strain, achieving 3.50% tensile strain compared to 5.60% for non-polymerized carbon. The optimized PNPC@NSNO/NF electrode exhibits exceptional high areal capacity of 2.72 mAh cm-2@1 mA cm-2, impressive rate capability, and 97.28% capacity retention after 200 cycles. The enhanced contact area and electrical conductivity provided by the PNPC improve charge transfer kinetics and overall performance. Theoretical analyses confirm that the PNPC@NSNO/NF electrode with 3.50% lattice strain lowers the Na⁺ diffusion barrier, enhances charge transfer, and improves charge distribution, boosting the electrode performance. This work establishes a straightforward method for synthesizing lattice-strained SIB anodes, highlighting its potential for advancing SIB technology.

Crystal Modulation of Mn-Based Layered Oxide toward Long-Enduring Anionic Redox with Fast Kinetics for Sodium-Ion Batteries.

Mn-based layered oxide cathodes for sodium-ion batteries with anionic redox reactions hold great potential for energy storage applications due to their ultra-high capacity and cost effectiveness. However, achieving high capacity requires overcoming challenges such as oxygen-redox failure, sluggish kinetics, and structural degradation. Herein, we employ an innovative crystal modulation strategy, using Mn-based Na0.72Li0.24Mn0.76O2 as a representative cathode material, which shows that the highly exposed {010} active facets enable an enhanced rate capability (119.6 mAh g-1 at 10C) with fast kinetics. Meanwhile, the reinforced Mn-O bond inhibits excessive oxidation of lattice oxygen and O-O cohesion loss, stabilizing and maintaining a long-enduring reversible oxygen-redox activity (100% high capacity retention after 100 cycles at 0.5C and 84.28% retention after 300 cycles at 5C). Time-resolved operando two-dimensional X-ray diffraction reveals the robust structural stability, zero-strain behavior, and suppressed phase transition with ultra-low volume variation during cycling at different rates (0.1C: 1.75%, 1C: 0.31%, 5C: 0.04%). Additionally, the full cell coupled with hard carbon achieves a high energy density of approximately 211 Wh kg-1 with superior performance. This work highlights the significance of crystal modulation and presents a universal approach in developing Mn-based oxide cathodes with stable anionic redox for high-performance sodium-ion batteries.

Revealing the fast reaction kinetics and interfacial behaviors of CuFeS2 hollow nanorods for durable and high-rate sodium storage.

The synergistic effect of two metallic elements in metal sulfides is regarded as a promising route for constructing advanced anodes for sodium-ion batteries (SIBs). However, the explorations of intricate interactions and structural evolution in host material are often overlooked, which are crucial for the performance optimization. Herein, a bimetallic sulfide CuFeS2 and FeS2/CuS heterostructure with similar hollow nanorods morphology is obtained by regulating sulfuration conditions. Compared to the FeS2/CuS heterostructure, the interaction between CuSFe in CuFeS2 weakens the strength of iron-sulfur bonds, thereby facilitating the kinetics of the sodiation reaction and enabling fast-charging capability. Moreover, the higher adsorption of NaF enables CuFeS2 to form a thinner solid electrolyte interface film with richer content of inorganic components. Coupled with the presence of stable intermediate phase, CuFeS2 delivers the excellent electrochemical performances, including a high capacity of 611 mAh/g after 200 cycles at 1 A/g, and 408 mAh/g after 1000 cycles at 30 A/g. Furthermore, CuFeS2 also demonstrates a remarkable capacity retention of 88 % after 200 cycles at 1 A/g in full-cells. This work highlights the potential of CuFeS2 in SIBs while elucidating the underlying factors contributing to the exceptional performance of bimetallic sulfides.

Cation/Anion Doping Strategy for Na4MnV(PO4)3 with High Energy Density and Long Cycling Life through Construction by Aspergillus niger.

Na4MnV(PO4)3 (NMVP) has gained attention for its high redox potential, good cycling stability, and competitive price but suffers from poor intrinsic electronic conductivity and Jahn-Teller effect from Mn3+. In this work, cation/anion doping strategy was used for Aspergillus niger-bioderived carbon-coated NMVP (NMVP/AN) to improve the structural stability and electrochemical performance, where Al3+ doping inhibited the dissolution of Mn and enhanced the Mn3+/Mn2+ redox pair activity; besides, F- doping not only weakens the Na2-O bond but also endows the hierarchical and porous structure of NMVP/AN, which led to a more rapid and fluid transfer of Na+. The elaborately designed Na3.9Mn0.9Al0.1V(PO4)3/AN (NMAVP/AN) exhibits 105.9 mA h g-1 at 0.5 C, and the as-prepared Na3.1MnV(PO3.7F0.3)3/AN (NMVPF/AN) delivers 104.1 mA h g-1 at 5 C. Further demonstration of the hard carbon//NMAVP/AN full cell manifests the good potential of Al3+-doped NMVP/AN for practical applications (100.6 mA h g-1 at 1 C). These findings open up the possibility of unlocking the high-performance Na superionic conductor (NASICON).

Electronic Confinement-Restrained Mn Na · ${\mathrm{Mn}}_{{\mathrm{Na}}}

Sodium (Na) super-ionic conductor structured Na3MnTi(PO4)3 (NMTP) cathodes have garnered interest owing to their cost-effectiveness and high operating voltages. However, the voltage hysteresis phenomenon triggered by Mn Na · ${\mathrm{Mn}}_{{\mathrm{Na}}}^{\mathrm{\cdot}}$ anti-site defects ( Mn Na · ${\mathrm{Mn}}_{{\mathrm{Na}}}^{\mathrm{\cdot}}$ -ASD), namely, the occupation of Mn2+ in the Na2 vacancies in NMTP, leads to sluggish diffusion kinetics and low energy efficiency. This study employs an innovative electronic confinement-restrained strategy to achieve the regulation of Mn Na · ${\mathrm{Mn}}_{{\mathrm{Na}}}^{\mathrm{\cdot}}$ -ASD. Partial replacement of titanium (Ti) with electron-rich vanadium (V) favors strong electronic interactions with Mn2+, restraining Mn2+ migration. The results suggest that this strategy can significantly increase the vacancy formation energy and migration energy barrier of manganese (Mn), thus inhibiting Mn Na · ${\mathrm{Mn}}_{{\mathrm{Na}}}^{\mathrm{\cdot}}$ -ASD formation. As proof of this concept, an Na-rich Na3.5MnTi0.5V0.5(PO4)3 (NMTVP) material is designed, wherein the electronic interaction enhanced the redox activity and achieved more Na+ storage under high-voltage. The NMTVP cathode delivered a reversible specific capacity of up to 182.7 mAh g-1 and output an excellent specific energy of 513.8 Wh kg-1, corresponding to ≈3.2 electron transfer processes, wherein the energy efficiency increased by 35.5% at 30 C. Through the confinement effect of electron interactions, this strategy provides novel perspectives for the exploitation and breakthrough of high-energy-density cathode materials in Na-ion batteries.

Three-Dimensional Flexible SnO2@Hard Carbon@MoS2@Soft Carbon Fiber Film Anode toward Ultrafast and Stable Sodium Storage.

Developing flexible electrodes for the application in sodium-ion batteries (SIBs) has received great attention and has been still challenging due to their merits of additive-free, lightweight, and high energy density. In this work, a free-standing 3D flexible SIB anode with the composition of SnO2@hard carbon@MoS2@soft carbon is designed and successfully synthesized. This electrode combines the energy storage advantages and hybrid sodium storage mechanisms of each material, manifested in the enhanced flexibility, specific capacity, conductivity, rate, cycling performances, etc. Based on the synergistic effects, it exhibits much higher specific capacity than SnO2 carbon nanofibers, as well as more excellent cycling performance (250 mA h g-1 after 500 cycles at 1 A g-1) than MoS2 nanospheres (32 mA h g-1). In addition, relevant kinetic mechanisms are also expounded with the aid of theoretical calculation. This work provides a feasible and advantageous strategy for constructing high-performance and flexible energy storage electrodes based on hybrid mechanisms and synergistic effects.