An Ultrahigh-Power Mesocarbon Microbeads|Na+ -Diglyme|Na3 V2 (PO4 )3 Sodium-Ion Battery

Anchored VN Quantum Dots Boosting High Capacity and Cycle Durability of Na3V2(PO4)3@NC Cathode for Aqueous Zinc-Ion Battery and Organic Sodium-Ion Battery

Na3V2(PO4)3 is a promising high-voltage cathode for aqueous zinc-ion batteries (ZIBs) and organic sodium-ion batteries (SIBs). However, the poor rate capability, specific capacity, and cycling stability severely hamper it from further development. In this work, Na3V2(PO4)3 (NVP) with vanadium nitride (VN) quantum dots encapsulated by nitrogen-doped carbon (NC) nanoflowers (NVP/VN@NC) are manufactured as cathode using in situ nitridation, carbon coating, and structural adjustment. The outer NC layer increases the higher electronic conductivity of NVP. Furthermore, VN quantum dots with high theoretical capacity not only improve the specific capacity of pristine NVP, but also serve as abundant "pins" between NVP and NC to strengthen the stability of NVP/VN@NC heterostructure. For Zn-ion storage, these essential characteristics allow NVP/VN@NC to attain a high reversible capacity of 135.4 mAh g-1 at 0.1 A g-1, and a capacity retention of 91% after 2000 cycles at 5 A g-1. Meanwhile, NVP/VN@NC also demonstrates to be a stable cathode material for SIBs, which can reach a high reversible capacity of 124.5 mAh g-1 at 0.1 A g-1, and maintain 92% of initial capacity after 11000 cycles at 5 A g-1. This work presents a feasible path to create innovative high-voltage cathodes with excellent reaction kinetics and structural stability.

Simultaneous Modification of Al3+/F- Cosubstitution to Construct a Solid Framework for Na3V2(PO4)3 with High Thermal Stability and Near-Zero Strain Performance

Challenges related to poor electronic conductivity and cycling stability have impeded the development and utilization of Na3V2(PO4)3 (NVP). Therefore, this study focuses on enhancing the performance of NVP by employing a sol-gel method to design various gradients of F/Al-doped and carbon nanotube (CNT)-enwrapped NVP materials. The introduction of F doping replacing PO4 tetrahedra reduces the occupied space, while F monomers can establish stronger bonds with VO6 octahedral pillars closer to O atoms. Additionally, Al doping introduces a new AlO6 octahedral structure at the V site, strengthening the 3D framework. The synergistic substitution of F and Al contributes to improving the stability of the framework, which enhances the Na+ migration channels and overall electrochemical performance. Furthermore, the coating of CNTs plays a crucial role in creating a favorable interface transition layer that facilitates efficient electron transport and enhances electronic conductivity. Comprehensively, the modified FAl-2 exhibits a high capacity of 115.8 mA h g-1 at 0.1C. It reveals 89.3 mA h g-1 at 60C and maintains 83.8 mA h g-1 after 2000 cycles, indicating a capacity retention rate of 93.84%. Electrochemical ex situ X-ray diffraction (XRD) demonstrates that FAl-2 behaves at relatively low values (0.328%-1.075%) of volume shrinkage during the whole charge/discharge process, indicating its near-zero strain property. The postcycled XRD and X-ray photoelectron spectroscopy further verify the significantly enhanced crystal structural stability of FAl-2. Moreover, FAl-2 possesses a higher thermal runaway temperature, indicating a superior thermal stability. The self-releasing heat trend observed in FAl-2 can offer valuable insights into the design of battery management systems.

From Lab to Application: Challenges and Opportunities in Achieving Fast Charging with Polyanionic Cathodes for Sodium-Ion Batteries

Sodium-ion batteries (SIBs), recognized for balanced energy density and cost-effectiveness, are positioned as a promising complement to lithium-ion batteries (LIBs) and a substitute for lead-acid batteries, particularly in low-speed electric vehicles and large-scale energy storage. Despite their extensive potential, concerns about range anxiety due to lower energy density underscore the importance of fast-charging technologies, which drives the exploration of high-rate electrode materials. Polyanionic cathode materials are emerging as promising candidates in this regard. However, their intrinsic limitation in electronic conductivity poses challenges for synchronized electron and ion transport, hindering their suitability for fast-charging applications. This review provides a comprehensive analysis of sodium ion migration during charging/discharging, highlighting it as a critical rate-limiting step for fast charging. By delving into intrinsic dynamics, key factors that constrain fast-charging characteristics are identified and summarized. Innovative modification routes are then introduced, with a focus on shortening migration paths and increasing diffusion coefficients, providing detailed insights into feasible strategies. Moreover, the discussion extends beyond half cells to full cells, addressing challenges and opportunities in transitioning polyanionic materials from the laboratory to practical applications. This review aims to offer valuable insights into the development of high-rate polyanionic cathodes, acknowledging their pivotal role in advancing fast-charging SIBs.

Fast-Charging Anode Materials for Sodium-Ion Batteries

Sodium-ion batteries (SIBs) have undergone rapid development as a complementary technology to lithium-ion batteries due to abundant sodium resources. However, the extended charging time and low energy density pose a significant challenge to the widespread use of SIBs in electric vehicles. To overcome this hurdle, there is considerable focus on developing fast-charging anode materials with rapid Na⁺ diffusion and superior reaction kinetics. Here, the key factors that limit the fast charging of anode materials are examined, which provides a comprehensive overview of the major advances and fast-charging characteristics across various anode materials. Specifically, it systematically dissects considerations to enhance the rate performance of anode materials, encompassing aspects such as porous engineering, electrolyte desolvation strategies, electrode/electrolyte interphase, electronic conductivity/ion diffusivity, and pseudocapacitive ion storage. Finally, the direction and prospects for developing fast-charging anode materials of SIBs are also proposed, aiming to provide a valuable reference for the further advancement of high-power SIBs.

Off-Stoichiometry of Sodium Iron Pyrophosphate as Cathode Materials for Sodium-Ion Batteries with Superior Cycling Stability

As one of the important devices for large-scale electrochemical energy storage, sodium-ion batteries have received much attention due to the abundant resources of raw materials. However, whether it is a base station power source, an energy storage power station, or a start-stop power supply, long energy cycle life (more than 5000 cycles), high stability, and safety performance are application prerequisites. Regrettably, currently, few sodium-ion batteries can meet this requirement, mainly due to shortcomings in positive electrode performance. We report a sufficiently stable sodium-ion battery cathode material, Na2Fe0.95P2O7, that retains 97.5% capacity after 5000 charge/discharge cycles. The use of nonstoichiometry in the lattice enables simultaneous modification of the crystal and electronic structure, promoting Na2Fe0.95P2O7 to be extremely stable while still being able to achieve a capacity of 92 mAh g-1 and stable cycling at high temperatures up to 60 °C. Our results confirm the positive effect of nonstoichiometric ratios on the performance of Na2Fe0.95P2O7 and provide a reliable idea to promote the practical application of sodium-ion batteries.

Solvent-Mediated, Reversible Ternary Graphite Intercalation Compounds for Extreme-Condition Li-Ion Batteries

Traditional Li-ion intercalation chemistry into graphite anodes exclusively utilizes the cointercalation-free or cointercalation mechanism. The latter mechanism is based on ternary graphite intercalation compounds (t-GICs), where glyme solvents were explored and proved to deliver unsatisfactory cyclability in LIBs. Herein, we report a novel intercalation mechanism, that is, in situ synthesis of t-GIC in the tetrahydrofuran (THF) electrolyte via a spontaneous, controllable reaction between binary-GIC (b-GIC) and free THF molecules during initial graphite lithiation. The spontaneous transformation from b-GIC to t-GIC, which is different from conventional cointercalation chemistry, is characterized and quantified via operando synchrotron X-ray and electrochemical analyses. The resulting t-GIC chemistry obviates the necessity for complete Li-ion desolvation, facilitating rapid kinetics and synchronous charge/discharge of graphite particles, even under high current densities. Consequently, the graphite anode demonstrates unprecedented fast charging (1 min), dendrite-free low-temperature performance, and ultralong lifetimes exceeding 10 000 cycles. Full cells coupled with a layered cathode display remarkable cycling stability upon a 15 min charging and excellent rate capability even at -40 °C. Furthermore, our chemical strategies are shown to extend beyond Li-ion batteries to encompass Na-ion and K-ion batteries, underscoring their broad applicability. Our work contributes to the advancement of graphite intercalation chemistry and presents a low-cost, adaptable approach for achieving fast-charging and low-temperature batteries.

Metal-Organic Framework-Based Materials for Advanced Sodium Storage: Development and Anticipation

As a pioneering battery technology, even though sodium-ion batteries (SIBs) are safe, non-flammable, and capable of exhibiting better temperature endurance performance than lithium-ion batteries (LIBs), because of lower energy density and larger ionic size, they are not amicable for large-scale applications. Generally, the electrochemical storage performance of a secondary battery can be improved by monitoring the composition and morphology of electrode materials. Because more is the intricacy of a nanostructured composite electrode material, more electrochemical storage applications would be expected. Despite the conventional methods suitable for practical production, the synthesis of metal-organic frameworks (MOFs) would offer enormous opportunities for next-generation battery applications by delicately systematizing the structure and composition at the molecular level to store sodium ions with larger sizes compared with lithium ions. Here, the review comprehensively discusses the progress of nanostructured MOFs and their derivatives applied as negative and positive electrode materials for effective sodium storage in SIBs. The commercialization goal has prompted the development of MOFs and their derivatives as electrode materials, before which the synthesis and mechanism for MOF-based SIB electrodes with improved sodium storage performance are systematically discussed. Finally, the existing challenges, possible perspectives, and future opportunities will be anticipated.

Self-terminating, heterogeneous solid-electrolyte interphase enables reversible Li-ether cointercalation in graphite anodes

Ether solvents are suitable for formulating solid-electrolyte interphase (SEI)-less ion-solvent cointercalation electrolytes in graphite for Na-ion and K-ion batteries. However, ether-based electrolytes have been historically perceived to cause exfoliation of graphite and cell failure in Li-ion batteries. In this study, we develop strategies to achieve reversible Li-solvent cointercalation in graphite through combining appropriate Li salts and ether solvents. Specifically, we design 1M LiBF4 1,2-dimethoxyethane (G1), which enables natural graphite to deliver ~91% initial Coulombic efficiency and >88% capacity retention after 400 cycles. We captured the spatial distribution of LiF at various length scales and quantified its heterogeneity. The electrolyte shows self-terminated reactivity on graphite edge planes and results in a grainy, fluorinated pseudo-SEI. The molecular origin of the pseudo-SEI is elucidated by ab initio molecular dynamics (AIMD) simulations. The operando synchrotron analyses further demonstrate the reversible and monotonous phase transformation of cointercalated graphite. Our findings demonstrate the feasibility of Li cointercalation chemistry in graphite for extreme-condition batteries. The work also paves the foundation for understanding and modulating the interphase generated by ether electrolytes in a broad range of electrodes and batteries.

Interlayer Confined Water Enabled Pseudocapacitive Sodium-Ion Storage in Nonaqueous Electrolyte

Electrochemical capacitors have faced the limitations of low energy density for decades, owing to the low capacity of electric double-layer capacitance (EDLC)-type positive electrodes. In this work, we reveal the functions of interlayer confined water in iron vanadate (FeV3O8.7·nH2O) for sodium-ion storage in nonaqueous electrolyte. Using an electrochemical quartz crystal microbalance, in situ Raman, and ex situ X-ray diffraction and X-ray photoelectron spectroscopy, we demonstrate that both nonfaradaic (surficial EDLC) and faradaic (pseudocapacitance-dominated Na+ intercalation) processes are involved in the charge storages. The interlayer confined water is able to accelerate the fast Na+ intercalations and is highly stable (without the removal of water or co-intercalation of [Na-diglyme]+) in the nonaqueous environment. Furthermore, coupling the pseudocapacitive FeV3O8.7·nH2O with EDLC-type activated carbon (FeVO-AC) as the positive electrode brings comprehensive enhancements, displaying the enlarged compaction density of ∼2 times, specific capacity of ∼1.5 times, and volumetric capacity of ∼3 times compared to the AC electrode. Furthermore, the as-assembled hybrid sodium-ion capacitor, consisting of an FeVO-AC positive electrode and a mesocarbon microbeads negative electrode, shows a high energy density of 108 Wh kg-1 at 108 W kg-1 and 15.3 Wh kg-1 at 8.3 kW kg-1. Our results offer an emerging route for improving both specific and volumetric energy densities of electrochemical capacitors.

In-situ constructing porous N-doped carbon skeleton with rich defects from modified polyamide acid to boost the high performance of Na3V2(PO4)3 cathode for full sodium-ion batteries

Generally, the transport of electrons and Na+ is seriously constrained in Na3V2(PO4)3 (NVP) due to intense interactions of V-O and PO bonds. Besides, polyamide acid (PAA) is hardly used in the sol-gel route due to insolubility. This work develops a facile liquid synthesis strategy based on modified PAA, achieving in-situ construction of a porous N-doped carbon framework with rich defects to improve the kinetics of NVP. The addition of triethylamine (TEA) reacts with carboxyls in PAA to achieve acid-base neutralization, turning PAA into polyamide salts with good solubility. The special morphology construction mechanism of this unique system was observed by ex-situ scanning electron microscopy (SEM) and Transmission electron microscopy (TEM). Specifically, PAA undergoes in-situ conversion into chain-like polyimide (PI) through a thermal polymerization mechanism during the pre-sintering process. Meanwhile, NVP precursors are evenly dispersed in the PI fibers, efficiently reducing the particle size. After the final treatment, the favorable porous carbon skeleton could be generated derived from the partial decomposition of PI, on which small active grains are in situ grown. The resulting N-doped carbon substrate contains rich defects, benefiting from the migration of Na+. Furthermore, the porous construction is conducive to alleviating the stress and strain generated by the high current impact, increasing the contact area between electrodes/electrolytes to improve the utilization efficiency of active substances. Comprehensively, the optimized samples exhibit a capacity of 82.1 mAh g-1 at 15C with a retention rate of 95.45 % after 350 cycles. It submits a capacity of 67.6 mAh g-1 at 90C and remains 52.2 mAh g-1 after 1500 cycles. Even in full cells, it reveals a value of 110.6 mAh g-1. This work guides the application of in-situ multiple modifications of polymers in electrode materials.

Promising Cathode Materials for Sodium-Ion Batteries from Lab to Application

Sodium-ion batteries (SIBs) are seen as an emerging force for future large-scale energy storage due to their cost-effective nature and high safety. Compared with lithium-ion batteries (LIBs), the energy density of SIBs is insufficient at present. Thus, the development of high-energy SIBs for realizing large-scale energy storage is extremely vital. The key factor determining the energy density in SIBs is the selection of cathodic materials, and the mainstream cathodic materials nowadays include transition metal oxides, polyanionic compounds, and Prussian blue analogs (PBAs). The cathodic materials would greatly improve after targeted modulations that eliminate their shortcomings and step from the laboratory to practical applications. Before that, some remaining challenges in the application of cathode materials for large-scale energy storage SIBs need to be addressed, which are summarized at the end of this Outlook.

Boosted Redox Kinetics Enabling Na3V2(PO4)3 with Excellent Performance at Low Temperature through Cation Substitution and Multiwalled Carbon Nanotube Cross-Linking

The open NASICON framework and high reversible capacity enable Na3V2(PO4)3 (NVP) to be a highly promising cathode candidate for sodium-ion batteries (SIBs). Nevertheless, the unsatisfied cyclic stability and degraded rate capability at low temperatures due to sluggish ionic migration and poor conductivity become the main challenges. Herein, excellent sodium storage performance for the NVP cathode can be received by partial potassium (K) substitution and multiwalled carbon nanotube (MWCNT) cross-linking to modify the ionic diffusion and electronic conductivity. Consequently, the as-fabricated Na3-xKxV2(PO4)3@C/MWCNT can maintain a capacity retention of 79.4% after 2000 cycles at 20 C. Moreover, the electrochemical tests at -20 °C manifest that the designed electrode can deliver 89.7, 73.5, and 64.8% charge of states, respectively, at 1, 2, and 3 C, accompanied with a capacity retention of 84.3% after 500 cycles at 20 C. Generally, the improved electronic conductivity and modified ionic diffusion kinetics resulting from K doping and MWCNT interconnecting endows the resultant Na3-xKxV2(PO4)3@C/MWCNT with modified electrochemical polarization and improved redox reversibility, contributing to superior performance at low temperatures. Generally, this study highlights the potential of alien substitution and carbon hybridization to improve the NASICON-type cathodes toward high-performance SIBs, especially at low temperatures.

Single-Crystal Growth of P2-Type Layered Oxides with Increased Exposure of {010} Planes for High-Performance Sodium-Ion Batteries

An increase in the size of single-crystal particles can effectively reduce the interfacial side reactions of layered oxides for sodium-ion batteries at high voltages but may result in sluggish Na+ transport. Herein, single-crystal Na0.66Ni0.26Zn0.07Mn0.67O2 with increased proportions of {010} planes is synthesized by adding low-cost NaCl as the molten salt. With the assistance of a NaCl molten salt, the median diameter (D50) of single-crystal Na0.66Ni0.26Zn0.07Mn0.67O2 increases to 10.46 μm relative to that of the comparison sample without NaCl (6.57 μm). Electrolyte decomposition on the surface of single-crystal Na0.66Ni0.26Zn0.07Mn0.67O2 is considerably suppressed, owing to a decrease in the specific surface area. Moreover, the increased exposure of {010} planes is favorable for improving the Na+ transport kinetics of single-crystal particles. Therefore, at 100 mA g-1, single-crystal Na0.66Ni0.26Zn0.07Mn0.67O2 exhibits a high-capacity retention of 96.6% after 100 cycles, which is considerably greater than that of the comparison sample (86.8%). Moreover, the rate performance of single-crystal Na0.66Ni0.26Zn0.07Mn0.67O2 (average discharge capacity of 81.2 mAh g-1) is superior to that of the comparison sample (average discharge capacity of 61.2 mAh g-1) at 2000 mA g-1. This work provides a new approach for promoting the single-crystal growth of layered oxides for highly stable interfaces at high voltages without compromising Na+ transport kinetics.

Investigating the Superior Performance of Hard Carbon Anodes in Sodium-Ion Compared With Lithium- and Potassium-Ion Batteries

Emerging sodium-ion batteries (NIBs) and potassium-ion batteries (KIBs) show promise in complementing lithium-ion battery (LIB) technology and diversifying the battery market. Hard carbon is a potential anode candidate for LIBs, NIBs, and KIBs due to its high capacity, sustainability, wide availability, and stable physicochemical properties. Herein, a series of hard carbons is synthesized by hydrothermal carbonization and subsequent pyrolysis at different temperatures to finely tune their structural properties. When tested as anodes, the hard carbons exhibit differing ion-storage trends for Li, Na, and K, with NIBs achieving the highest reversible capacity. Extensive materials and electrochemical characterizations are carried out to study the correlation of structural features with electrochemical performance and to explain the specific mechanisms of alkali-ion storage in hard carbons. In addition, the best-performing hard carbon is tested against a sodium cathode Na3 V2 (PO4 )3 in a Na-ion pouch cell, displaying a high power density of 2172 W kg-1 at an energy density of 181.5 Wh kg-1 (based on the total weight of active materials in both anode and cathode). The Na-ion pouch cell also shows stable ultralong-term cycling (9000 h or 5142 cycles) and demonstrates the promising potential of such materials as sustainable, scalable anodes for beyond Li-batteries.

High-Entropy Doping Boosts Ion/Electronic Transport of Na4 Fe3 (PO4 )2 (P2 O7 )/C Cathode for Superior Performance Sodium-Ion Batteries

Fe-based mixed phosphate cathodes for Na-ion batteries usually possess weak rate capacity and cycle stability challenges resulting from sluggish diffusion kinetics and poor conductivity under the relatively low preparation temperature. Here, the excellent sodium storage capability of this system is obtained by introducing the high-entropy doping to enhance the electronic and ionic conductivity. As designed high-entropy doping Na4 Fe2.85 (Ni,Co,Mn,Cu,Mg)0.03 (PO4 )2 P2 O7 (NFPP-HE) cathode can release 122 mAh g-1 at 0.1 C, even 85 mAh g-1 at ultrahigh rate of 50 C, and keep a high retention of 82.3% after 1500 cycles at 10 C. Besides, the cathode also exhibits outstanding fast charge capacity in terms of the cyclability and capacity with 105 mAh g-1 at 5 C/1 C, corresponding 94.3% retention after 500 cycles. The combination of in situ X-ray diffraction, density functional theory, conductive-atomic force microscopy, and galvanostatic intermittent titration technique tests reveal that the reversible structure evolution with optimized Na+ migration path and energy barrier boost the Na+ kinetics and improve the interfacial electronic transfer, thus improving performance.

Boron-Doping Induced Electron Delocalization in Fluorophosphate Cathode: Enhanced Na-Ion Diffusivity and Sodium-Ion Full Cell Performance

Na3 V2 (PO4 )2 O2 F (NVPOF) is widely accepted as advanced cathode material for sodium-ion batteries with high application prospects ascribing to its considerable specific capacity and high working voltage. However, challenges in the full realization of its theoretical potential lie in the novel structural design to accelerate its Na+ diffusivity. Herein, considering the important role of polyanion groups in constituting Na+ diffusion tunnels, boron (B) is doped at the P-site to obtain Na3 V2 (P2- x Bx O8 )O2 F (NVP2- x Bx OF). As evidenced by density functional theory modeling, B-doping induces a dramatic decrease in the bandgap. Delocalization of electrons on the O anions in BO4 tetrahedra is observed in NVP2- x Bx OF, which dramatically lowers the electrostatic resistance experienced by Na+ . As a result, the Na+ diffusivity in the NVP2- x Bx OF cathode has accelerated up to 11 times higher, which secures a high rate property (67.2 mAh g-1 at 60 C) and long cycle stability (95.9% capacity retention at 108.6 mAh g-1 at 10 C after 1000 cycles). The assembled NVP1.90 B0.10 OF//Se-C full cell demonstrates exceptional power/energy density (213.3 W kg-1 @ 426.4 Wh kg-1 and 17970 W kg-1 @ 119.8 Wh kg-1 ) and outstanding capability to withstand long cycles (90.1% capacity retention after 1000 cycles at 105.3 mAh g-1 at 10 C).

Highly Stable MWCNT@NVP Composite as a Cathode Material for Na-Ion Batteries

A 3D framework with Nasicon structured polyanionic Na₃V₂(PO₄)₃ (NVP) has been emphasized as a leading cathode material for sodium-ion batteries (SIBs) due to its high working voltage plateau, structural stability, and good rate performance. Herein, pristine NVP and MWCNT@NVP composite synthesized via a facile solid-state method are examined and compared as cathode materials for Na-ion batteries. The morphological study confirms the uniform distribution of MWCNTs in the pristine NVP structure. Impedance spectroscopy clearly confirms more diffusion of Na ions for the MWCNT@NVP composite as compared to pristine NVP, considering its diffusion coefficient which directly implies on an increase in specific capacity. MWCNT@NVP (FNV-2) showed specific discharge capacity 110 mAhg-1 at 0.1C current rate which is almost stable at higher current rates with marginal fading. However, the pristine NVP shows capacity loss at a higher current rate. It is noteworthy that the MWCNT@NVP composite shows stable performance with marginal specific capacity fading (1%) compared to pristine (15%). This is because of the mechanical integrity and stability afforded to the composite by the intertwined MWCNT framework in the MWCNT@NVP composite matrix against electrode degradation during the electrochemical reaction. More significantly, even at a higher current rate, that is, at 10 C, the composite recorded a very stable and excellent Columbic efficiency of 97% with a reversible specific capacity of 94 mAhg^-1 after 2000 cycles. An enhanced electrochemical performance, that is, rate capability and cycling stability, demonstrates the high potential of the MWCNT@NVP composite for Na-ion storage. Moreover, a sodium-ion full cell with hard carbon demonstrated a reversible capacity of 103 mAhg^-1 at C/20 current rate, which clearly demonstrates that MWCNT@NVP is a promising cathode material for sodium-ion batteries.

Engineering Crystal Growth and Surface Modification of Na3 V2 (PO4 )2 F3 Cathode for High-Energy-Density Sodium-Ion Batteries

Na₃ V₂ (PO₄ )₂ F₃ (NVPF) is a suitable cathode for sodium-ion batteries owing to its stable structure. However, the large radius of Na⁺ restricts diffusion kinetics during charging and discharging. Thus, in this study, a phosphomolybdic acid (PMA)-assisted hydrothermal method is proposed. In the hydrothermal process, the NVPF morphologies vary from bulk to cuboid with varying PMA contents. The optimal channel for accelerated Na⁺ transmission is obtained by cuboid NVPF. With nitrogen-doping of carbon, the conductivity of NVPF is further enhanced. Combined with crystal growth engineering and surface modification, the optimal nitrogen-doped carbon-covered NVPF cuboid (c-NVPF@NC) exhibits a high initial discharge capacity of 121 mAh g^-1 at 0.2 C. Coupled with a commercial hard carbon (CHC) anode, the c-NVPF@NC||CHC full battery delivers 118 mAh g^-1 at 0.2 C, thereby achieving a high energy density of 450 Wh kg^-1 . Therefore, this work provides a novel strategy for boosting electrochemical performance by crystal growth engineering and surface modification.

A High-Energy NASICON-Type Na3.2 MnTi0.8 V0.2 (PO4 )3 Cathode Material with Reversible 3.2-Electron Redox Reaction for Sodium-Ion Batteries

Na superionic conductor (NASICON) structured cathode materials with robust structural stability and large Na⁺ diffusion channels have aroused great interest in sodium-ion batteries (SIBs). However, most of NASICON-type cathode materials exhibit redox reaction of no more than three electrons per formula, which strictly limits capacity and energy density. Herein, a series of NASICON-type Na_3+x MnTi_1-x V_x (PO₄ )₃ cathode materials are designed, which demonstrate not only a multi-electron reaction but also high voltage platform. With five redox couples from V^5+/4+ (≈4.1 V), Mn^4+/3+ (≈4.0 V), Mn^3+/2+ (≈3.6 V), V^4+/3+ (≈3.4 V), and Ti^4+/3+ (≈2.1 V), the optimized material, Na_3.2 MnTi_0.8 V_0.2 (PO₄ )₃ , realizes a reversible 3.2-electron redox reaction, enabling a high discharge capacity (172.5 mAh g^-1 ) and an ultrahigh energy density (527.2 Wh kg^-1 ). This work sheds light on the rational construction of NASICON-type cathode materials with multi-electron redox reaction for high-energy SIBs.

Pore-forming mechanisms and sodium-ion-storage performances in a porous Na3V2(PO4)3/C composite cathode

Na₃V₂(PO₄)₃ (NVP) is regarded as one of the most promising cathode materials for sodium-ion batteries (SIBs). However, it suffers from a dense bulk structure and low intrinsic electronic conductivity, which lead to limited electrochemical performances. Herein, we propose a surfactant-assisted molding strategy to regulate the pore-forming process in NVP/C composite cathode materials. More precisely, the forming process of the pores in NVP could be easily controlled by utilizing the huge difference in critical micelle concentration of a surfactant (cetyltrimethylammonium bromide, CTAB) in water and ethanol. By reasonably modulating the ratio of water and ethanol in the solution, the as-synthesized NVP/C sample exhibited a three-dimensional interconnected structure with hierarchical micro/meso/macro-pores. Benefiting from these hierarchical porous structures in NVP/C, the structural stability, contact surface with the electrolyte, and electronic/ionic conductivity were improved simultaneously; whereby the optimized porous NVP/C sample exhibited an excellent high-rate performance (61.3 mA h g^-1 at 10 C) and superior cycling stability (90.2% capacity retention after 500 cycles at 10 C).

Doping Regulation in Polyanionic Compounds for Advanced Sodium-Ion Batteries

It has long been the goal to develop rechargeable batteries with low cost and long cycling life. Polyanionic compounds offer attractive advantages of robust frameworks, long-term stability, and cost-effectiveness, making them ideal candidates as electrode materials for grid-scale energy storage systems. In the past few years, various polyanionic electrodes have been synthesized and developed for sodium storage. Specifically, doping regulation including cation and anion doping has shown a great effect in tailoring the structures of polyanionic electrodes to achieve extraordinary electrochemical performance. In this review, recent progress in doping regulation in polyanionic compounds as electrode materials for sodium-ion batteries (SIBs) is summarized, and their underlying mechanisms in improving electrochemical properties are discussed. Moreover, challenges and prospects for the design of advanced polyanionic compounds for SIBs are put forward. It is anticipated that further versatile strategies in developing high-performance electrode materials for advanced energy storage devices can be inspired.

Halogenated Carboxylates as Organic Anodes for Stable and Sustainable Sodium-Ion Batteries

Organic materials are competitive as anodes for Na-ion batteries (NIBs) due to the low cost, abundance, environmental benignity, and high sustainability. Herein, we synthesized three halogenated carboxylate-based organic anode materials to exploit the impact of halogen atoms (F, Cl, and Br) on the electrochemical performance of carboxylate anodes in NIBs. The fluorinated carboxylate anode, disodium 2, 5-difluoroterephthalate (DFTP-Na), outperforms the other carboxylate anodes with H, Cl, and Br, in terms of high specific capacity (212 mA h g^-1), long cycle life (300 cycles), and high rate capability (up to 5 A g^-1). As evidenced by the experimental and computational results, the two F atoms in DFTP reduce the solubility, enhance the cyclic stability, and interact with Na⁺ during the redox reaction, resulting in a high-capacity and stable organic anode material in NIBs. Therefore, this work proves that fluorinating carboxylate compounds is an effective approach to developing high-performance organic anodes for stable and sustainable NIBs.

Robust Artificial Interphases Constructed by a Versatile Protein-Based Binder for High-Voltage Na-Ion Battery Cathodes

The multiple issues of unstable electrode/electrolyte interphases, sluggish reaction kinetics, and transition-metal (TM) dissolution have long greatly affected the rate and cycling performance of cathode materials for Na-ion batteries. Herein, a multifunctional protein-based binder, sericin protein/poly(acrylic acid) (SP/PAA), is developed, which shows intriguing physiochemical properties to address these issues. The highly hydrophilic nature and strong H-bond interaction between crosslinking SP and PAA leads to a uniform coating of the binder layer, which serves as an artificial interphase on the high-voltage Na₄ Mn₂ Fe(PO₄ )₂ P₂ O₇ cathode material (NMFPP). Through systematic experiments and theoretical calculations, it is shown that the SP/PAA binder is electrochemically stable at high voltages and possesses increased ionic conductivity due to the interaction between sericin and electrolyte anion ClO₄ ^- , which can provide additional sodium-migration paths with greatly reduced energy barriers. Besides, the strong interaction force between the binder and the NMFPP can effectively protect the cathode from electrolyte corrosion, suppress Mn-dissolution, stabilize crystal structure, and ensure electrode integrity during cycling. Benefiting from these merits, the SP/PAA-based NMFPP electrode displays enhanced rate and cycling performance. Of note, the universality of the SP/PAA binder is further confirmed on Na₃ V₂ (PO₄ )₂ F₃ . It is believed that the versatile protein-based binder is enlightening for the development of high-performance batteries.