A Superior Na3V2(PO4)3-Based Nanocomposite Enhanced by Both N-Doped Coating Carbon and Graphene as the Cathode for Sodium-Ion Batteries

Rate-Dependent Stability and Electrochemical Behavior of Na3NiZr(PO4)3 in Sodium-Ion Batteries

In advancing sodium-ion battery technology, we introduce a novel application of Na3NiZr(PO4)3 with a NASICON structure as an anode material. This research unveils, for the first time, its exceptional ability to maintain high specific capacity and unprecedented cycle stability under extreme current densities up to 1000 mA·g-1, within a low voltage window of 0.01-2.5 V. The core of our findings lies in the material's remarkable capacity retention and stability, which is a leap forward in addressing long-standing challenges in energy storage. Through cutting-edge in situ/operando X-ray diffraction analysis, we provide a perspective on the structural evolution of Na3NiZr(PO4)3 during operation, offering deep insights into the mechanisms that underpin its superior performance.

Constructing a multidimensional porous structure of K/Co co-substituted Na3V2(PO4)3/C attached on the lamellar Ti3C2Tx MXene substrate for superior sodium storage property

Na₃V₂(PO₄)₃ (NVP) materials have emerged as prospective cathodes for sodium-ion batteries (SIBs). However, its weak intrinsic conductivity has limited deeper research. Herein, we adopt the strategy of simultaneous K/Co co-substitution and Ti₃C₂T_x MXene (MX) introduction to optimize NVP. The K/Co co-substitution brings about the synergetic effect of NVP framework stabilization. Doping Co²⁺ generates beneficial holes and accelerating electronic conductivity. The MX plates are stacked at random to form a porous construction, increasing the contact areas to provide more active sites for Na⁺ shuttling and buffering the volume change. Furthermore, the lamellar MX and the carbon layers form efficient conductive networks that increase electron migration. Notably, K_0.1Na_2.95V_1.95Co_0.05(PO₄)₃@MX (KC05@MX) exhibited an initial capacity of 116 mA h g^-1 under 1 C with an extraordinary retention of 86.8% at the 400^th cycle. It realized high performance under 20 C and 50 C, and the outputs were 93.5 and 82.4 mA h g^-1 at the 1^st cycle and 66.6 and 53.4 mA h g^-1 at the 1000^th cycle, respectively, with slight capacity loss at 0.028% and 0.035%. Furthermore, the Bi₂Se₃//KC05@MX asymmetric full cell expressed great electrochemical properties, indicating the superior practical application prospect of KC05@MX.

MoO42--mediated engineering of Na3V2(PO4)3 as advanced cathode materials for sodium-ion batteries

Sodium vanadium phosphate [Na₃V₂(PO₄)₃] with high voltage platform, low cost and environment friendliness has been considered as one of the most promising candidates as cathodes for high-performance sodium-ion batteries. However, the sodium storage property of Na₃V₂(PO₄)₃ is limited because of its low electronic conductivity and poor kinetic performance. Herein, MoO₄^2--doped Na_(3+2x)V₂(PO₄)_(3-x)MoO_4(x) [NVP-MoO₄ (x), x = 0, 0.05, 0.10, 0.15] have been developed and prepared by a feasible solid-state reaction. The optimal NVP-MoO₄ (0.10) delivers a high initial capacity of 108.9 mA h g^-1 and presents an excellent capacity retention of 91.5% at 1 C after 150 cycles. In addition, the NVP-MoO₄ (0.10) shows a good rate capability, delivering a relatively high capacity of 84.2 mA h g^-1 at 50 C. The results of sodium storage measurement and density of states calculation indicate that MoO₄^2- doping can significantly enhance the structural stability, promote the kinetics behavior and boost the electronic conductivity of the materials. In-situ XRD test reveals that the electrochemical reaction of the NVP-MoO₄ (0.10) exhibits a highly reversible phase transition process. This work provides a new insight for the design of advanced cathodes for high-performance sodium-ion batteries by the strategy of unique anion doping.

Facile Preparation of Fe3O4 Nanoparticles/Reduced Graphene Oxide Composite as an Efficient Anode Material for Lithium-Ion Batteries

Iron oxides are considered promising electrode materials owing to their capability of lithium storage, but their poor conductivity and large volume expansion lead to unsatisfactory cycling stability. In this paper, an inexpensive, highly effective, and facile approach to the synthesis of Fe3O4 nanoparticles/reduced graphene oxide composite (Fe3O4/RGO) is designed. The synthesized Fe3O4/RGO composite exhibits high reversible capability and excellent cyclic capacity as an anode material in lithium-ion batteries (LIBs). A reversible capability of 701.8 mAh/g after 50 cycles at a current density of 200 mA·g−1 can be maintained. The synergetic effect of unique structure and high conductivity RGO promises a well soakage of electrolyte, high structure stability, leading to an excellent electrochemical performance. It is believed that the study will provide a feasible strategy to produce transition metal oxide/carbon composite electrodes with excellent electrochemical performance for LIBs.

Improved electrochemical performance of lanthanum-modified Na3V2(PO4)3/C cathode materials for sodium-ion batteries

A series of lanthanum-doped Na₃V_2−xLa_x(PO₄)₃/C (0 ≤ x ≤ 0.03) composites have been fabricated via a simple sol–gel approach.

Sponge-like NaFe2PO4(SO4)2@rGO as a high-performance cathode material for sodium-ion batteries

Sponge-like NaFe₂PO₄(SO₄)₂@reduced graphene oxide composite is prepared as cathode material for sodium-ion batteries. The corresponding full cells matched with hard carbon anode exhibit favorable rate and cyclic performance.

High-Rate and Long-Cycle Cathode for Sodium-Ion Batteries: Enhanced Electrode Stability and Kinetics via Binder Adjustment

Sodium-ion batteries (SIBs) are heralded as promising candidates for grid-scale energy storage systems due to their low cost and abundant sodium resources. Excellent rate capacity and outstanding cycling stability are always the goals for SIBs. Up to now, nearly all attention has been focused on the control of morphology and structure of electrode materials, but the influence of binders on their performance is neglected, especially in cathode materials. Herein, using Na₃V₂(PO₄)₂O₂F (NVPOF) as a cathode material, the influence of four different binders (sodium alginate, SA; carboxymethylcellulose sodium, CMC; poly(vinylidene fluoride), PVDF; and poly(acrylic latex), LA133) on its electrochemical performance is studied. As a result, when using SA as the binder, the electrochemical performance of the NVPOF electrode is improved significantly, which is mainly because of the high water solubility, rich carboxyl and hydroxyl groups, and high adhesive and cohesive properties of the SA binder, leading to the uniform distribution of active materials NVPOF and carbon black in electrodes, good integrity, low polarization, and superior kinetic properties of the NVPOF electrodes, as demonstrated by scanning electron microscopy, cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic intermittent titration technique. More importantly, when coupled with a hard carbon anode, the fabricated sodium-ion full cells also exhibit excellent rate performance, thus providing a preview of their practical application. This work shows that the battery performance can be improved by matching suitable binder systems, which is believed to have great importance for the further optimization of the electrochemical performance of SIBs.

Research Progress on Na3V2(PO4)3 Cathode Material of Sodium Ion Battery

Sodium ion batteries (SIBs) are one of the most potential alternative rechargeable batteries because of their low cost, high energy density, high thermal stability, and good structure stability. The cathode materials play a crucial role in the cycling life and safety of SIBs. Among reported cathode candidates, Na₃V₂(PO₄)₃ (NVP), a representative electrode material for sodium super ion conductor, has good application prospects due to its good structural stability, high ion conductivity and high platform voltage (~3.4 V). However, its practical applications are still restricted by comparatively low electronic conductivity. In this review, recent progresses of Na₃V₂(PO₄)₃ are well summarized and discussed, including preparation and modification methods, electrochemical properties. Meanwhile, the future research and further development of Na₃V₂(PO₄)₃ cathode are also discussed.

Carbon-coating-increased working voltage and energy density towards an advanced Na3V2(PO4)2F3@C cathode in sodium-ion batteries

One main challenge for phosphate cathodes in sodium-ion batteries (SIBs) is to increase the working voltage and energy density to promote its practicability. Herein, an advanced Na₃V₂(PO₄)₂F₃@C cathode is prepared successfully for sodium-ion full cells. It is revealed that, carbon coating can not only enhance the electronic conductivity and electrode kinetics of Na₃V₂(PO₄)₂F₃@C and inhibit the growth of particles (i.e., shorten the Na⁺-migration path), but also unexpectedly for the first time adjust the dis-/charging plateaux at different voltage ranges to increase the mean voltage (from 3.59 to 3.71 V) and energy density (from 336.0 to 428.5 Wh kg^-1) of phosphate cathode material. As a result, when used as cathode for SIBs, the prepared Na₃V₂(PO₄)₂F₃@C delivers much improved electrochemical properties in terms of larger specifc capacity (115.9 vs. 93.5 mAh g^-1), more outstanding high-rate capability (e.g., 87.3 vs. 60.5 mAh g^-1 at 10 C), higher energy density, and better cycling performance, compared to pristine Na₃V₂(PO₄)₂F₃. Reasons for the enhanced electrochemical properties include ionicity enhancement of lattice induced by carbon coating, improved electrode kinetics and electronic conductivity, and high stability of lattice, which is elucidated clearly through the contrastive characterization and electrochemical studies. Moreover, excellent energy-storage performance in sodium-ion full cells further demonstrate the extremely high possibility of Na₃V₂(PO₄)₂F₃@C cathode for practical applications.

Isostructural and Multivalent Anion Substitution toward Improved Phosphate Cathode Materials for Sodium-Ion Batteries

Polyanion-type phosphate materials are highly promising cathode candidates for next-generation batteries due to their excellent structural stability during cycling; however, their poor conductivity has impeded their development. Isostructural and multivalent anion substitution combined with carbon coating is proposed to greatly improve the electrochemical properties of phosphate cathode in sodium-ion batteries (SIBs). Specifically, multivalent tetrahedral SiO₄ ^4- substitute for PO₄ ^3- in Na₃ V₂ (PO₄ )₃ (NVP) lattice, preparing the optimal Na_3.1 V₂ (PO₄ )_2.9 (SiO₄ )_0.1 with high-rate capability (delivering a high capacity of 82.5 mAh g^-1 even at 20 C) and outstanding cyclic stability (≈98% capacity retention after 500 cycles at 1 C). Theoretical calculation and experimental analyses reveal that the anion-substituted Na_3.1 V₂ (PO₄ )_2.9 (SiO₄ )_0.1 reduces the bandgap of NVP lattice and enhanced its structural stability, Na⁺ -diffusion kinetics and electronic conductivity. This strategy of multivalent and isostructural anion substitution chemistry provides a new insight to develop advanced phosphate cathodes.

Improved electrochemical performance of 2D accordion-like MnV2O6 nanosheets as anode materials for Li-ion batteries

MnV₂O₆ is a promising anode material for lithium ion batteries with high theoretical specific capacity, abundant reserves and inexpensive constituent elements.

One-Pot Hydrothermal Synthesis of Ternary 1T-MoS2 /Hexa-WO3 /Graphene Composites for High-Performance Supercapacitors

A new ternary composite of 1T-molybdenum disulfide, hexagonal tungsten trioxide, and reduced graphene oxide (M-W-rGO) is synthesized by using a one-pot hydrothermal process. The synergetic effect of 1T-MoS₂ and hexa-WO₃ nanoflowers improves the electrochemical performance for supercapacitors by inducing additional active sites and hexagonal tunnels, respectively, which lead to high storage capacity and easy transfer of electrolyte ions. The ternary M-W-rGO composite has a high specific capacitance of 836 F g^-1 at 1 A g^-1 , which is nearly twice that of binary composites of M-rGO and W-rGO with high capacitance retention of 86.35 % after 3000 cycles at a high current density of 5 A g^-1 . This study provides a new ternary composite that can be used as an electrode material for high-performance supercapacitors.

Amorphous FePO4/Carbon Nanotube Cathode Preparation via in Situ Nanoprecipitation and Coagulation in a Microreactor

In this article, nanostructured amorphous FePO₄ (a-FePO₄)-carbon nanotube (CNT) composites, with high purity of FePO₄ and a controllable FePO₄/C ratio, were directly synthesized by a fast nanoprecipitation process in a microreactor, using Fe(NO₃)₃ and (NH₄)₃PO₄ as precursors. Oxidized CNTs are well dispersed via strong electrostatic repulsion in a high pH solution system. Subsequently, a-FePO₄ nanoparticles are adhered onto CNTs just following the fast nanoprecipitation process; then, the precipitated composites are compacted by ball-milling, forming a compact conductive network with well dispersed and highly loaded active materials. As cathode materials for lithium-ion batteries, the composites exhibit a capacity of 175.8 mAh g^-1 at 0.1 C, close to the theoretical capacity (178 mAh g^-1), and a good cycle performance with a reversible capacity of 137.0 mAh g^-1 after 500 cycles at 5 C. Importantly, the enhanced micromixing enables fast nanoprecipitation in suspension and opens a shortcut for constructing nanostructured composites that have potential in functionalization and are easy to handle.

Hierarchically porous nanosheets-constructed 3D carbon network for ultrahigh-capacity supercapacitor and battery anode

An advanced hierarchically porous nanosheets-constructed three-dimensional (3D) carbon material (HPNSC) is prepared by using low-cost agricultural waste-nelumbium seed-pods as the precursor, and potassium hydroxide (KOH) as the activator. The as-prepared HPNSC material has a hierarchically porous nanosheets-constructed structure with 3D carbon nanosheet network morphology, which can enable fast and efficient transfer of Li⁺/Na⁺/H⁺ during charge-discharge process. The assembled HPNSC//HPNSC symmetric supercapacitors exhibit an improved energy density of 41.3 W h kg^-1 with a power density of 180 W kg^-1 in 1 mol l^-1 Na₂SO₄ electrolyte. The energy density can still be maintained at 16.3 W h kg^-1 even if the power density is increased to 9000 W kg^-1. When acting as the reversible electrode for lithium ion batteries, this HPNSC material can achieve a high specific capacity of 1246 mA h g^-1 at 0.1 A g^-1. Moreover, sodium ion battery with HPNSC electrode exhibits excellent cycling performance of 161.8 mA h g^-1 maintained even after being cycled 3350 times. The electrochemical performances clearly indicate that the HPNSC developed in this work is a very promising energy storage electrode material, and can further provide new insights for designing and developing highly porous materials for energy storage in other fields.

A first-principles investigation of the influence of polyanionic boron doping on the stability and electrochemical behavior of Na3V2(PO4)3

Na₃V₂(PO₄)₃ (NVP) is one of the most promising candidates for use as cathodes in room-temperature sodium ion batteries owing to its high structural stability and rapid Na⁺ transportation kinetics. The cationic doping of foreign ions at Na or V sites in the NVP lattice has proven to be an effective approach for enhancing the electrochemical performance of NVP. In this work, we present a first-principles density functional theory investigation of the impact of polyanionic boron doping at P sites on the structural and electrochemical behavior of NVP. Our simulation results suggest that B doping considerably increases the structural stability of NVP while shrinking its lattice size to some extent. Since B donates far fewer electrons to connected O atoms, the surrounding V atoms become more positive, causing the operating voltage to increase with B content. However, the reduction in lattice size is not beneficial for the Na⁺ transportation kinetics. As demonstrated by a search for the transition state, a concerted ion-exchange mechanism is preferred for Na⁺ transportation, and increased B doping leads to a higher Na⁺ diffusion barrier. Improvements in electrochemical performance due to B doping see (Hu et al. Adv Sci 3(12):1600112, 2016) appear to originate mainly from the resulting increased electrical conductivity.

Na3V2(PO4)3@C as Faradaic Electrodes in Capacitive Deionization for High-Performance Desalination

Among various desalination technologies, capacitive deionization (CDI) has rapidly developed because of its low energy consumption and environmental compatibility, among other factors. Traditional CDI stores ions within the electric double layers (EDLs) in the nanopores of the carbon electrode, but carbon anode oxidation, the co-ion expulsion effect, and a low salt adsorption capacity (SAC) block its further application. Herein, the Faradaic-based electrode is proposed to overcome the above limitations, offering an ultrahigh adsorption capacity and a rapid removal rate. In this paper, the open framework structure Na₃V₂(PO₄)₃@C is applied for the first time as a novel Faradaic electrode in the hybrid capacitive deionization (HCDI) system. During the adsorption and desorption process, sodium ions are intercalated/deintercalated through the crystal structure of Na₃V₂(PO₄)₃@C while chloride ions are physically trapped or released by the AC electrode. Different concentrations of feedwater are investigated, and a high SAC of 137.20 mg NaCl g^-1 NVP@C and low energy consumption of 2.157 kg-NaCl kWh^-1 are observed at a constant voltage of 1.0 V, a concentration of 100 mM, and a flow rate of 15 mL min^-1. The outstanding performance of the Na₃V₂(PO₄)₃@C Faradaic electrode demonstrates that it is a promising material for desalination and that HCDI offers great future potential.

Confined Growth of Nano-Na3V2(PO4)3 in Porous Carbon Framework for High-Rate Na-Ion Storage

Nanoscale Na₃V₂(PO₄)₃ particles are grown in the interconnected conductive framework via a simple sol-gel method with the assistance of a hierarchical porous carbon. The porous carbon with strong adsorption ability absorbs the Na₃V₂(PO₄)₃ reactants from the aqueous solution during the sol-gel process. After crystallization, the Na₃V₂(PO₄)₃ particles are grown in the carbon pores with a spatially confined effect. Due to the pore size confinement, the Na₃V₂(PO₄)₃ particles are limited to nanoscale size and prevented from aggregation. Furthermore, the carbon matrix provides the electric conductive framework and the unfilled pores offer interconnected ion transport channels as well as capacitive contribution, which are beneficial for tolerating high current attack. As a result, the pore-confined nano-Na₃V₂(PO₄)₃ in the carbon framework exhibits high Na-ion storage capacity (116.2 mAh g^-1 at 0.2 C), excellent long-term cycling stability (capacity retention of 82.1% after 10 000 cycles), and especially, outstanding high-rate performance (80.1, 60.6, and 45.7 mAh g^-1 at 50, 75, and 100 C). The pore-confined nano-Na₃V₂(PO₄)₃ with superior rate performance is believed to be a promising candidate for Na-ion batteries, and the preparation method based on confined growth in porous carbon framework provides a simple and effective strategy for high-rate electrode material design.

An FeP@C nanoarray vertically grown on graphene nanosheets: an ultrastable Li-ion battery anode with pseudocapacitance-boosted electrochemical kinetics

In order to develop promising anode materials for lithium-ion batteries (LIBs), a unique nanocomposite abbreviated as G⊥FP@C-NA, in which a carbon-coated FeP nanorod array (FP@C-NA) is vertically grown on a conductive reduced graphene oxide (G) network, has been successfully prepared via a scalable strategy. Benefiting from the distinctive structure, G⊥FP@C-NA exhibits much improved conductivity, structural stability and pseudocapacitance-boosted ultrafast electrochemical kinetics for Li storage. As a result, the G⊥FP@C-NA delivers a high Li-storage capacity (1106 mA h g-1 at 50 mA g-1), outstanding rate capability (565 mA h g-1 at 5000 mA g-1) and long-term cycling stability (1009 mA h g-1 at 500 mA g-1 after 500 cycles and 310 mA h g-1 at 2000 mA g-1 after 2000 cycles) when used as an anode material for LIBs. As expected, this kind of nanoarray structure is attractive and can also be extended to other electrode materials for various energy storage systems.

In Situ Synthesis and Unprecedented Electrochemical Performance of Double Carbon Coated Cross-Linked Co3O4

Improving the structural stability and the electron/ion diffusion rate across whole electrode particles is crucial for transition metal oxides as next-generation anodic materials in lithium-ion batteries. Herein, we report a novel structure of double carbon-coated Co₃O₄ cross-linked composite, where the Co₃O₄ nanoparticle is in situ covered by nitrogen-doped carbon and further connected by carbon nanotubes (Co₃O₄ NP@NC@CNTs). This double carbon-coated Co₃O₄ NP@NC@CNTs framework not only endows a porous structure that can effectively accommodate the volume changes of Co₃O_4, but also provides multidimensional pathways for electronic/ionic diffusion in and among the Co₃O₄ NPs. Electrochemical kinetics investigation reveals a decreased energy barrier for electron/ion transport in the Co₃O₄ NP@NC@CNTs, compared with the single carbon-coated Co₃O₄ NP@NC. As expected, the Co₃O₄ NP@NC@CNT electrode exhibits unprecedented lithium storage performance, with a high reversible capacity of 1017 mA h g^-1 after 500 cycles at 1 A g^-1, and a very good capacity retention of 75%, even after 5000 cycles at 15 A g^-1. The lithiation/delithiation process of Co₃O₄ NP@NC@CNTs is dominated by the pseudocapacitive behavior, resulting in excellent rate performance and durable cycle stability.

Advanced P2-Na2/3Ni1/3Mn7/12Fe1/12O2 Cathode Material with Suppressed P2-O2 Phase Transition toward High-Performance Sodium-Ion Battery

As a promising cathode material of sodium-ion battery, P2-type Na_2/3Ni_1/3Mn_2/3O₂ (NNMO) possesses a theoretically high capacity and working voltage to realize high energy storage density. However, it still suffers from poor cycling stability mainly incurred by the undesirable P2-O2 phase transition. Herein, the electrochemically active Fe³⁺ ions are introduced into the lattice of NNMO, forming Na_2/3Ni_1/3Mn_{2/3- x}Fe _xO₂ ( x = 0, 1/24, 1/12, 1/8, 1/6) to effectively stabilize the P2-type crystalline structure. In such Fe-substituted materials, both Ni²⁺/Ni⁴⁺ and Fe³⁺/Fe⁴⁺ couples take part in the redox reactions, and the P2-O2 phase transition is well restrained during cycling, as verified by ex situ X-ray diffraction. As a result, the optimized Na_2/3Ni_1/3Mn_7/12Fe_1/12O₂ (1/12-NNMF) has a long-term cycling stability with the fading rate of 0.05% per cycle over 300 cycles at 5 C. Furthermore, the 1/12-NNMF delivers excellent rate capabilities (65 mA h g^-1 at 25 C) and superior low-temperature performance (the capacity retention of 94% at -25 °C after 80 cycles) owing to the enhanced Na diffusion upon Fe doping, which is deduced by the studies of electrode kinetics. More significantly, the 1/12-NNMF also displays remarkable sodium-ion full-cell properties when merged with an LS-Sb@G anode, thus implying the possibility of their practical application.

Pseudocapacitance-boosted ultrafast Na storage in a pie-like FeS@C nanohybrid as an advanced anode material for sodium-ion full batteries

In order to develop promising anode materials for sodium-ion batteries (SIBs), a novel pie-like FeS@C (P-FeS@C) nanohybrid, in which all ultrasmall FeS nanocrystals (NCs) are completely embedded into the carbon network and sealed by a protective carbon shell, has been prepared. The unique pie-like structure can effectively speed up the kinetics of electrode reactions, while the carbon shell stabilizes the FeS NCs inside. Studies show that the electrochemical reaction processes of P-FeS@C electrodes are dominated by the pseudocapacitive behavior, leading to an ultrafast Na+-insertion/extraction reaction. Hence, the prepared P-FeS@C nanohybrid exhibits superior Na-storage properties especially high rate capability in half cells. For example, it can deliver reversible capacities of 555.1 mA h g-1 at 0.2 A g-1 over 150 cycles and about 60.4 mA h g-1 at 80 A g-1 (an ultrahigh current density even higher than that of the capacitor test). Furthermore, an advanced P-FeS@C//Na3V2(PO4)2O2F full cell has been assembled out, which delivers a stable specific capacity of 441.2 mA h g-1 after 80 cycles at 0.5 A g-1 with a capacity retention of 91.8%.

N-Doped Dual Carbon-Confined 3D Architecture rGO/Fe3O4/AC Nanocomposite for High-Performance Lithium-Ion Batteries

To address the issues of low electrical conductivity, sluggish lithiation kinetics and dramatic volume variation in Fe₃O₄ anodes of lithium ion battery, herein, a double carbon-confined three-dimensional (3D) nanocomposite architecture was synthesized by an electrostatically assisted self-assembly strategy. In the constructed architecture, the ultrafine Fe₃O₄ subunits (∼10 nm) self-organize to form nanospheres (NSs) that are fully coated by amorphous carbon (AC), formatting core-shell structural Fe₃O₄/AC NSs. By further encapsulation by reduced graphene oxide (rGO) layers, a constructed 3D architecture was built as dual carbon-confined rGO/Fe₃O₄/AC. Such structure restrains the adverse reaction of the electrolyte, improves the electronic conductivity and buffers the mechanical stress of the entire electrode, thus performing excellent long-term cycling stability (99.4% capacity retention after 465 cycles relevant to the second cycle at 5 A g^-1). Kinetic analysis reveals that a dual lithium storage mechanism including a diffusion reaction mechanism and a surface capacitive behavior mechanism coexists in the composites. Consequently, the resulting rGO/Fe₃O₄/AC nanocomposite delivers a high reversible capacity (835.8 mA h g^-1 for 300 cycles at 1 A g^-1), as well as remarkable rate capability (436.7 mA h g^-1 at 10 A g^-1).

High performance of porous silicon/carbon/RGO network derived from rice husks as anodes for lithium-ion batteries

Rice husk-derived porous Si/C synthesized via activation and magnesiothermic reduction reaction possesses excellent electrochemistry performance as a lithium-ion battery anode.

Hard Carbon Wrapped Na3V2(PO4)3@C Porous Composite Extending Cycling Lifespan for Sodium-Ion Batteries

Although the NASICON-type of Na₃V₂(PO₄)₃ is regarded as a potential cathode candidate for advanced sodium-ion batteries (SIBs), it has an undesirable rate performance and low cyclability, which are a result of its poor electronic conductivity. Here, we utilized conductive polyaniline (PANI) grown in situ to obtain the hard carbon-coated porous Na₃V₂(PO₄)₃@C composite (NVP@C@HC) with a typically simple and effective sol-gel process. Based on the restriction of double carbon layers, the NVP size decreases distinctly, which can curtail the sodium-ion diffusion distance and enhance the electronic conductivity. As expected, the product displays good discharge capacity (111.6 mA h g^-1 at 1 C), outstanding rate capacity (60.4 mA h g^-1 at 50 C), and remarkable cycling stability (63.3 mA h g^-1 with a retention of 83.3% at 40 C over 3000 cycles). Also, it performs a long-term cycling capacity of 58.5 mA h g^-1 exceeding 15 000 cycles at 20 C (with a capacity loss of 0.24% per cycle).

Challenges and Perspectives for NASICON-Type Electrode Materials for Advanced Sodium-Ion Batteries

Sodium-ion batteries (SIBs) have attracted increasing attention in the past decades, because of high overall abundance of precursors, their even geographical distribution, and low cost. Apart from inherent thermodynamic disadvantages, SIBs have to overcome multiple kinetic problems, such as fast capacity decay, low rate capacities and low Coulombic efficiencies. A special case is sodium super ion conductor (NASICON)-based electrode materials as they exhibit - besides pronounced structural stability - exceptionally high ion conductivity, rendering them most promising for sodium storage. Owing to the limiting, comparatively low electronic conductivity, nano-structuring is a prerequisite for achieving satisfactory rate-capability. In this review, we analyze advantages and disadvantages of NASICON-type electrode materials and highlight electrode structure design principles for obtaining the desired electrochemical performance. Moreover, we give an overview of recent approaches to enhance electrical conductivity and structural stability of cathode and anode materials based on NASICON structure. We believe that this review provides a pertinent insight into relevant design principles and inspires further research in this respect.

Iso-Oriented NaTi2(PO4)3 Mesocrystals as Anode Material for High-Energy and Long-Durability Sodium-Ion Capacitor

Sodium-ion capacitors (SIC) combine the merits of both high-energy batteries and high-power electrochemical capacitors as well as the low cost and high safety. However, they are also known to suffer from the severe deficiency of suitable electrode materials with high initial Coulombic efficiency (ICE) and kinetic balance between both electrodes. Herein, we report a facile solvothermal synthesis of NaTi₂(PO₄)₃ nanocages constructed by iso-oriented tiny nanocrystals with a mesoporous architecture. It is notable that the NaTi₂(PO₄)₃ mesocrystals exhibit a large ICE of 94%, outstanding rate capability (98 mA h g^-1 at 10 C), and long cycling life (over 77% capacity retention after 10 000 cycles) in half cells, all of which are in favor to be utilized into a full cell. When assembled with commercial activated carbon to an SIC, the system delivers an energy density of 56 Wh kg^-1 at a power density of 39 W kg^-1. Even at a high current rate of 5 A g^-1 (corresponds to finish a full charge/discharge process in 2 min), the SIC still works well after 20 000 cycles without obvious capacity degradation. With the merits of impressive energy/power densities and longevity, the obtained hybrid capacitor should be a promising device for highly efficient energy storage systems.

High-Energy/Power and Low-Temperature Cathode for Sodium-Ion Batteries: In Situ XRD Study and Superior Full-Cell Performance

Sodium-ion batteries (SIBs) are still confronted with several major challenges, including low energy and power densities, short-term cycle life, and poor low-temperature performance, which severely hinder their practical applications. Here, a high-voltage cathode composed of Na₃ V₂ (PO₄ )₂ O₂ F nano-tetraprisms (NVPF-NTP) is proposed to enhance the energy density of SIBs. The prepared NVPF-NTP exhibits two high working plateaux at about 4.01 and 3.60 V versus the Na⁺ /Na with a specific capacity of 127.8 mA h g^-1 . The energy density of NVPF-NTP reaches up to 486 W h kg^-1 , which is higher than the majority of other cathode materials previously reported for SIBs. Moreover, due to the low strain (≈2.56% volumetric variation) and superior Na transport kinetics in Na intercalation/extraction processes, as demonstrated by in situ X-ray diffraction, galvanostatic intermittent titration technique, and cyclic voltammetry at varied scan rates, the NVPF-NTP shows long-term cycle life, superior low-temperature performance, and outstanding high-rate capabilities. The comparison of Ragone plots further discloses that NVPF-NTP presents the best power performance among the state-of-the-art cathode materials for SIBs. More importantly, when coupled with an Sb-based anode, the fabricated sodium-ion full-cells also exhibit excellent rate and cycling performances, thus providing a preview of their practical application.

High Performance Lithium-Ion Hybrid Capacitors Employing Fe3O4-Graphene Composite Anode and Activated Carbon Cathode

Lithium-ion capacitors (LICs) are considered as promising energy storage devices to realize excellent electrochemical performance, with high energy-power output. In this work, we employed a simple method to synthesize a composite electrode material consisting of Fe₃O₄ nanocrystallites mechanically anchored among the layers of three-dimensional arrays of graphene (Fe₃O₄-G), which exhibits several advantages compared with other traditional electrode materials, such as high Li storage capacity (820 mAh g^-1 at 0.1 A g^-1), high electrical conductivity, and improved electrochemical stability. Furthermore, on the basis of the appropriated charge balance between cathode and anode, we successfully fabricated Fe₃O₄-G//activated carbon (AC) soft-packaging LICs with a high energy density of 120.0 Wh kg^-1, an outstanding power density of 45.4 kW kg^-1 (achieved at 60.5 Wh kg^-1), and an excellent capacity retention of up to 94.1% after 1000 cycles and 81.4% after 10 000 cycles. The energy density of the Fe₃O₄-G//AC hybrid device is comparable with Ni-metal hydride batteries, and its capacitive power capability and cycle life is on par with supercapacitors (SCs). Therefore, this lithium-ion hybrid capacitor is expected to bridge the gap between Li-ion battery and SCs and gain bright prospects in next-generation energy storage fields.

NASICON-Structured Materials for Energy Storage

The demand for electrical energy storage (EES) is ever increasing, which calls for better batteries. NASICON-structured materials represent a family of important electrodes due to its superior ionic conductivity and stable structures. A wide range of materials have been considered, where both vanadium-based and titanium-based materials are recommended as being of great interest. NASICON-structured materials are suitable for both the cathode and the anode, where the operation potential can be easily tuned by the choice of transition metal and/or polyanion group in the structure. NASICON-structured materials also represent a class of solid electrolytes, which are widely employed in all-solid-state ion batteries, all-solid-state air batteries, and hybrid batteries. NASICON-structured materials are reviewed with a focus on both electrode materials and solid-state electrolytes.

Phosphate Framework Electrode Materials for Sodium Ion Batteries

Sodium ion batteries (SIBs) have been considered as a promising alternative for the next generation of electric storage systems due to their similar electrochemistry to Li-ion batteries and the low cost of sodium resources. Exploring appropriate electrode materials with decent electrochemical performance is the key issue for development of sodium ion batteries. Due to the high structural stability, facile reaction mechanism and rich structural diversity, phosphate framework materials have attracted increasing attention as promising electrode materials for sodium ion batteries. Herein, we review the latest advances and progresses in the exploration of phosphate framework materials especially related to single-phosphates, pyrophosphates and mixed-phosphates. We provide the detailed and comprehensive understanding of structure-composition-performance relationship of materials and try to show the advantages and disadvantages of the materials for use in SIBs. In addition, some new perspectives about phosphate framework materials for SIBs are also discussed. Phosphate framework materials will be a competitive and attractive choice for use as electrodes in the next-generation of energy storage devices.

Surface Modification of Na3V2(PO4)3 by Nitrogen and Sulfur Dual-Doped Carbon Layer with Advanced Sodium Storage Property

Nitrogen and sulfur dual-doped carbon layer wrapped Na₃V₂(PO₄)₃ nanoparticles (NVP@NSC) have been successfully fabricated by the facile solid-state method. In this hierarchical structure, the Na₃V₂(PO₄)₃ nanoparticles are well dispersed and closely coated by nitrogen and sulfur dual-doped carbon layer, constructing an effective and interconnected conducting network to reduce the internal resistance. Furthermore, the uniform coating layers alleviate the agglomeration of Na₃V₂(PO₄)₃ as well as mitigate the side reaction between electrode and electrolyte. Because of the excellent electron transfer mutually enhancing sodium diffusion for this extraordinary structure, the NVP@NSC composite delivers an impressive discharge capacity of 113.0 mAh g^-1 at 1 C and shows a capacity retention of 82.1% after 5000 cycles at an ultrahigh rate of 50 C, suggesting the remarkable rate capability and long cyclicity. Surprisingly, a reversible capacity of 91.1 mAh g^-1 is maintained after 1000 cycles at 5 C under the elevated temperature of 55 °C. The approach of nitrogen and sulfur dual-doped carbon-coated Na₃V₂(PO₄)₃ provides an effective and promising strategy to enhance the ultrahigh rate and ultralong life property of cathode, which can be used for large-scale commercial production in sodium ion batteries.