Na3 V2 Research Articles

Achieving Ultra-Stable All-Solid-State Sodium Metal Batteries with Anion-Trapping 3D Fiber Network Enhanced Polymer Electrolyte.

All-solid-state sodium metal batteries paired with solid polymer electrolytes (SPEs) are considered a promising candidate for high energy-density, low-cost, and high-safety energy storage systems. However, the low ionic conductivity and inferior interfacial stability with Na metal anode of SPEs severely hinder their practical applications. Herein, an anion-trapping 3D fiber network enhanced polymer electrolyte (ATFPE) is developed by infusing poly(ethylene oxide) matrix into an electrostatic spun fiber framework loading with an orderly arranged metal-organic framework (MOF). The 3D continuous channel provides a fast Na+ transport path leading to high ionic conductivity, and simultaneously the rich coordinated unsaturated cation sites exposed on MOF can effectively trap anions, thus regulating Na+ concentration distribution for constructing stable electrolyte/Na anode interface. Based on such advantages, the ATFPE exhibits high ionic conductivity and considerable Na+ transference number, as well as enhanced interfacial stability. Consequently, Na/Na symmetric cells using this ATFPE possess cyclability over 600h at 0.1mA cm-2 without discernable Na dendrites. Cooperated with Na3 V2 (PO4 )3 cathode, the all-solid-state sodium metal batteries (ASSMBs) demonstrate significantly improved rate and cycle performances, delivering a high discharge capacity of 117.5 mAh g-1 under 0.1 C and rendering high capacity retention of 78.2% after 1000 cycles even at 1 C.

Single-Atom Metallophilic Sites for Liquid NaK Alloy Confinement toward Stable Alkali-Metal Anodes.

Room temperature liquid NaK alloy is a promising candidate for high performance metal batteries, due to its dendrite-free property and high energy density. However, its practical application is hindered by the high surface tension of liquid NaK, which causes difficulties in maintaining a stable contact with a current collector. Here, the authors demonstrate the extraordinary stable confinement of NaK alloy at room temperature by constructing a super-wetting substrate, which is based on highly dispersed cobalt-single-atom carbon nanoarrays. The developed liquid anode electrode prevented successfully the leakage of NaK alloy even in harsh stress (>5MPa) or sharp shock conditions. The symmetric cells achieved ultra-long reversible plating/stripping cycling life in both Na-ion (>1010hrs) and K-ion electrolytes (>4000hrs) at 10mA cm-2 /10mAh cm-2 . Upon fitting with Na3 V2 (PO4 )3 , the NaK assembled full battery provided high energy density (332.6kWh kg-1 ) and power density (11.05kW kg-1 ) with excellent stability after >21600cycles, which is the best value reported so far. The prepared pouch cell was able to drive a four-axis aircraft, demonstrating a great prospect in practical application. This work offers a new approach in the preparation of advanced dendrite-free liquid metal anodes with promising applications in electrochemical energy storage.

Polyanion-Type Na3 V2 (PO4 )2 F3 @rGO with High-Voltage and Ultralong-Life for Aqueous Zinc Ion Batteries.

Aqueous zinc ion batteries (AZIBs) have attracted much interest in the next generation of energy storage devices because of their elevated safety and inexpensive price. Polyanionic materials have been considered as underlying cathodes owing to the high voltage, large ionic channels and fast ionic kinetics. However, the low electronic conductivity limits their cycling stability and rate performance. Herein, mesoporous Na3 V2 (PO4 )2 F3 (N3VPF) nanocuboids with the size of 80-220nm cladded by reduced graphene oxide (rGO) have been successfully prepared to form 3D composite (N3VPF@rGO) by a novel and fast microwave hydrothermal with subsequent calcination strategy. The enhanced conductivity, strengthened pseudocapacitive behaviors, enlarged DZn 2+ , and stable structure guarantee N3VPF@rGO with splendid Zn2+ storage performance, such as high capacity of 126.9 mAh g-1 at 0.5 C (1 C = 128mA g-1 ), high redox potentials at 1.48/1.57V, high rate capacity of 93.9 mAh g-1 at 20 C (short charging time of 3 mins) and extreme cycling stability with capacity decay of 0.0074% per cycle after 5000 cycles at 15 C. The soft package batteries also present preeminent performance, demonstrating the practical application values. In situ X-ray diffraction, ex situ transmission electron microscopy and X-ray photoelectron spectroscopy reveal a reversible Zn2+ insertion/extraction mechanism.

Crystallinity Tuning of Na3 V2 (PO4 )3 : Unlocking Sodium Storage Capacity and Inducing Pseudocapacitance Behavior.

As a promising cathode material of sodium-ion batteries, Na3 V2 (PO4 )3 (NVP) has attracted extensive attention in recent years due to its high stability and fast Na+ ion diffusion. However, the reversible capacity based on the two-electron reaction mechanism is not satisfactory limited by the inactive M1 lattice sites during the insertion/extraction process. Herein, self-supporting 3D porous NVP materials with different crystallinity are fabricated on carbon foam substrates by a facile electrostatic spray deposition method. The V5+ /V4+ redox couple is effectively activated and the three-electron reactions are realized in NVP for sodium storage by a proper crystallinity tuning. In a disordered NVP sample, an ultra-high specific capacity of 179.6 mAh g-1 at 0.2 C is achieved due to the coexistence of redox reactions of the V4+ /V3+ and V5+ /V4+ couples. Moreover, a pseudocapacitive charge storage mechanism induced by the disordered structure is first observed in the NVP electrode. An innovative model is given to understand the disorder-induced-pseudocapacitance phenomenon in this polyanion cathode material.

Dual-Function Presodiation with Sodium Diphenyl Ketone towards Ultra-stable Hard Carbon Anodes for Sodium-Ion Batteries.

Hard carbon (HC) is a promising anode material for sodium-ion batteries, yet still suffers from low initial Coulombic efficiency (ICE) and unstable solid electrolyte interphase (SEI). Herein, sodium diphenyl ketone (Na-DK) is applied to realize dual-function presodiation for HC anodes. It compensates the irreversible Na uptake at the oxygen-containing functional groups and reacts with carbon defects of five/seven-membered rings for quasi-metallic sodium in HC. The as-formed sodium induces robust NaF-rich SEI on HC in 1.0 M NaPF6 in diglyme, favoring the interfacial reaction kinetics and stable Na+ insertion and extraction. This renders the presodiated HC (pHC) with high ICE of ≈100 % and capacity retention of 82.4 % after 6800 cycles. It is demonstrated to couple with Na3 V2 (PO4 )3 cathodes in full cells to show high capacity retention of ≈100 % after 700 cycles. This work provides in-depth understanding of chemical presodiation and a new strategy for highly stable sodium-ion batteries.

Highly Oxidation-Resistant Electrolyte for 4.7 V Sodium Metal Batteries Enabled by Anion/Cation Solvation Engineering.

Sodium metal batteries (SMBs) are considered as promising battery system due to abundant Na sources. However, poor compatibility between electrolyte and cathode severely impedes its development. Herein, we proposed an anion/cation solvation strategy for realizing 4.7 V resistant SMBs electrolyte with NaClO4 and trimethoxy(pentafluorophenyl)silane (TPFS) as dual additives (DA). The ClO4 - can rapidly transfer to the cathode surface and strongly coordinate with Na+ to form stable polymer-like chains with solvents. Meanwhile, TPFS can preferentially enter into the PF6 - anion solvation sheath for reducing PF6 -solvent interaction and effectively scavenge adverse electrolyte species for protecting electrode electrolyte interphases. Thus, such electrolyte elevates the oxidative stability of carbonate electrolytes from 3.77 to 4.75 V, and enables Na||Na3 V2 (PO4 )2 O2 F (NVPF) battery with a capacity retention of 93 % and an average Coulombic efficiency (CE) of 99.6 % after 500 cycles at 4.7 V.

Highly Stable Sb/C Anode for K+ and Na+ Energy Storage Enabled by Pulsed Laser Ablation and Polydopamine Coating.

Potassium- and sodium-ion batteries (PIBs and SIBs) have great potential as the next-generation energy application owing to the natural abundance of K and Na. Antimony (Sb) is a suitable alloying-type anode for PIBs and SIBs due to its high theoretical capacity and proper operation voltage; yet, the severe volume variation remains a challenge. Herein, a preparation of N-doped carbon-wrapped Sb nanoparticles (L-Sb/NC) using pulsed laser ablation and polydopamine coating techniques, is reported. As the anode for PIB and SIB, the L-Sb/NC delivers superior rate capabilities and excellent cycle stabilities (442.2 and 390.5mA h g-1 after 250 cycles with the capacity decay of 0.037% and 0.038% per cycle) at the current densities of 0.5 and 1.0 A g-1 , respectively. Operando X-ray diffraction reveals the facilitated and stable potassiation and sodiation mechanisms of L-Sb/NC enabled by its optimal core-shell structure. Furthermore, the SIB full cell fabricated with L-Sb/NC and Na3 V2 (PO4 )2 F3 shows outstanding electrochemical performances, demonstrating its practical energy storage application.

Constructing Stable Anion-Tuned Electrode/Electrolyte Interphase on High-Voltage Na3 V2 (PO4 )2 F3 Cathode for Thermally-Modulated Fast-Charging Batteries.

Constructing stable electrode/electrolyte interphase with fast interfacial kinetics is vital for fast-charging batteries. Herein, we investigate the interphase that forms between a high-voltage Na3 V2 (PO4 )2 F3 cathode and the electrolytes consisting of 3.0, 1.0, or 0.3 M NaClO4 in an organic carbonate solvent (47.5 : 47.5 : 5 mixture of EC: PC: FEC) during charging up to 4.5 V at 55 °C. It is found that a higher anion/solvent ratio in electrolyte solvation structure induces anion-dominated interphase containing more inorganic species and more anion derivatives (Cx ClOy ), which leads to a larger interfacial Na+ transport resistance and more unfavorable gas evolution. In comparison, a low anion/solvent ratio derives stable anion-tuned interphase that enables better interfacial kinetics and cycle ability. Importantly, the performance of a failed cathode is restored by triggering the decomposition of Cx ClOy species. This work elucidates the role of tuning interphase in fast-charging batteries.

Electrochemical Performance of High-Valence Mo6+ and Low-Valence Mn2+ Doped- Na3 V2 (PO4 )3 @C Cathode for Sodium-Ion Batteries.

The sodium superionic conductor (NASICON)-Na3 V2 (PO4 )3 (NVP) is an attractive cathode for sodium-ion batteries, which is still confronted with limited rate performance due to its low electronic conductivity. In this paper, a chemical strategy is adopted to partially replace V3+ of the NVP framework by low-valence Mn2+ and high-valence Mo6+ substitution. The crystal structure, sodium-ion diffusion coefficient and electrochemical performance of Mn-Mo-doped [Na3.94 V0.98 Mo0.02 Mn(PO4 )3 @C] cathode were investigated. X-ray diffraction confirmed the NASICON-type structure and XPS analysis confirmed the oxidation state of Mn and Mo in doped NVP cathode. The Na ion diffusion processes were inferred from Cyclic Voltammetry (CV), Galvanostatic intermittent titration technique (GITT) and Electrochemical Impedance Spectroscopy (EIS) measurement, which clearly show rapid Na-ion diffusion in NASICON-type cathode materials. The Mn-Mo-substituted NVP shows smoother charge-discharge profiles, improved rate performance (64.80 mAh/g at 1 C rate), better energy density (308.61 mWh/g) and superior Na-ion kinetics than that of unsubstituted NVP@C cathode. Their enhanced performance is attributed to large interstitial volume mainly created by high valence Mo6+ and enhanced capacity is attributed to the low valence Mn2+ doping. These results demonstrate that Mn-Mo-doped NVP cathode is strongly promising cathode material for sodium-ion batteries.

Tailoring the Boron Configurations in B‐doped Na3V2(PO4)3@Carbon for Fast and Durable Sodium Storage

Na3 V2 (PO4 )3 (NVP) is a widely studied cathode material for sodium-ion batteries because of its high ionic conductivity and attractive charge/discharge plateau (3.4 V vs. Na/Na+ ). However, its poor electronic conductivity and severe volume expansion during sodium storage need to be addressed before its intensive application could be realized. Herein, boron-doped NVP was synthesized through a facile electrospinning method. By adding boric acid into the reaction mixture during electrospinning followed by carbonization, boron could be directly inserted into the carbon matrix, giving rise to B-doped carbon nanofiber wrapped NVP. By tuning the doping amount, the boron-containing configurations could be facilely manipulated, playing different roles in promoting the sodium storage properties of the composite. Based on the calculation results, BC2 O enhanced sodium diffusion by lowering the energy barrier, while BCO2 improved the structural stability. Due to these specific functionalities of the configurations, the as-prepared composite with a balanced amount of BC2 O and BCO2 demonstrated superior sodium storage capacity of 113 mAh g-1 at 1 C, outstanding long cycling performance of 103 mAh g-1 at 10 C, and retained 91 mAh g-1 after 1500 cycles. This gave rise to a capacity loss of only 0.08‰ per cycle, much better than the undoped counterpart.

Formation of NaF-Rich Solid Electrolyte Interphase on Na Anode through Additive-Induced Anion-Enriched Structure of Na+ Solvation.

High-capacity sodium (Na) anodes suffer from dendrite growth due to the high reactivity, which can be overcome through inducing a stable NaF-rich solid electrolyte interphase (SEI). Herein, we propose an additive strategy for realizing the anion-enriched structure of Na+ solvation to obtain a NaF-rich SEI. The electron-withdrawing acetyl group in 4-acetylpyridine (4-APD) increases the coordination number of PF6 - in the Na+ solvation sheath to facilitate PF6 - to decompose into NaF. Thus, the NaF-rich SEI with high mechanical stability and interfacial energy is formed to repress the growth of Na dendrites. With the 4-APD-contained electrolyte, the symmetric Na||Na cells show excellent cycling performance over 360 h at 1.0 mA cm-2 . Meanwhile, excellent stability is also achieved for Na||Na3 V2 (PO4 )2 O2 F full cells with high Coulombic efficiency (97 %) and capacity retention (91 %) after 200 cycles.

Unravelling Li+ Intercalation Mechanism and Cathode Electrolyte Interphase of Na3 V2 (PO4 )3 and Na3 (VOPO4 )2 F Cathode as Robust Framework Towards High-Performance Lithium-Ion Batteries.

Although lithium-ion batteries (LIBs) are promising towards high energy density and superior safety energy storage systems (ESS), severe depletion of Li reserve cannot meet the ever-growing demand for LIBs due to the uneven distribution and limited amount of Li resource. Li-free polyanionic cathodes, such as Na3 V2 (PO4 )3 (NVP) and Na3 (VOPO4 )2 F (NVOPF), show intriguing electrochemical performances with prospective future for LIBs due to their appropriate crystallographic sites, robust host structure, and abundant Na resource. In this work, NVP and NVOPF were systematically investigated as cathodes for LIBs using different voltage windows of 2.5-4.3, 2.0-4.3, and 1.5-4.8 V, along with their electrochemical mechanisms, cathode electrolyte interphase properties, and electrode morphologies for comparison. Ex-situ X-ray diffraction, ex-situ X-ray photoelectron spectroscopy, and post-mortem scanning electron microscopy revealed that their mechanisms shifted from a predominant Na+ intercalation/deintercalation in the first charging/discharging to a mixed Li+ /Na+ intercalation/deintercalation at the subsequent cycling. Due to the residual Na+ acting as pillar in the structure, NVP and NVPF could serve as robust host framework, providing appropriate crystallographic sites for repeated Li+ /Na+ intercalation/deintercalation. NVP electrode delivered a higher discharge capacity of 107.6 mAh g-1 with superior capacity retention of 84.3 % after 1000 cycles (2.5-4.3 V, 100 mA g-1 ) than NVOPF electrode (97.3 mAh g-1 , 68.8 %). Electrode polarization and kinetic analysis manifested one energetically similar and two energetically nonequivalent crystallographic Na sites within the R c and I4/mmm polyanionic structure of NVP and NVOPF. This work comprehensively demonstrates the feasibility and prospect of sodium-based NVP and NVOPF polyanions serving as advanced Li-free cathodes for LIBs, which provides novel insights into seeking Li-free candidates as prospective cathodes for LIBs towards a more sustainable society and a cost-effective battery manufacturing system.

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.

Anion-Reinforced Solvation for a Gradient Inorganic-Rich Interphase Enables High-Rate and Stable Sodium Batteries.

Metallic Na is a promising anode for rechargeable batteries, however, it is plagued by an unstable solid electrolyte interphase (SEI) and Na dendrites. Herein, a robust anion-derived SEI is constructed on Na anode in a high-concentration 1,2-dimethoxyethane (DME) based electrolyte with a cosolvent hydrofluoroether, which effectively restrains Na dendrite growth. The hydrofluoroether can tune the solvation configuration of the electrolyte from three-dimensional network aggregates to solvent-cation-anion clusters, enabling more anions to enter and reinforce the inner solvation sheath and their stepwise decomposition. The gradient inorganic-rich SEI leads to a reduced energy barrier of Na+ migration and enhanced interfacial kinetics. These render the Na||Na3 V2 (PO4 )3 battery with an excellent rate capability of 79.9 mAh g-1 at 24 C and a high capacity retention of 94.2 % after 6000 cycles at 2 C. This highlights the modulation of the electrode-electrolyte interphase chemistry for advanced batteries.

High-Efficiency and Stable Zn-Na3 V2 (PO4 )3 Aqueous Battery Enabled by Electrolyte-Induced Interphasial Engineering.

Aqueous zinc batteries have been regarded as a promising energy storage technology due to their high energy, high material abundance, low toxicity, and intrinsic safety. NASICON-type materials have been proposed as efficient cathodes for rechargeable batteries, yet they suffer from fast degradation and low Coulombic efficiency in aqueous batteries. Here we demonstrate that a rationally designed aqueous electrolyte containing a supporting Na salt and polymer additive can efficiently suppress the water activity through hydrogen bonding and facilitate the anion involvement in interfacial reactions, thus enabling the stable operation of sodium superionic conductor (NASICON) cathodes in aqueous zinc batteries. As exemplified by a Na3 V2 (PO4 )3 cathode, the cell with zinc metal anode exhibits high cycling Coulombic efficiencies (around 99.9 % in average) with a steady output voltage and capacity retention for 300 cycles. This work addresses the potential issues with NASICON-type cathodes in aqueous zinc batteries and proposes an effective solution via fundamental interphasial chemistry to design efficient and sustainable aqueous electrolytes.

Synergistic Effect, Structural and Morphology Evolution, and Doping Mechanism of Spherical Br-Doped Na3 V2 (PO4 )2 F3 /C toward Enhanced Sodium Storage.

Na3 V2 (PO4 )2 F3 has attracted wide attention due to its high voltage platform, and stable crystal structure. However, its application is limited by the low electronic conductivity and the ease formation of impurity. In this paper, the spherical Br-doped Na3 V2 (PO4 )2 F3 /C is successfully obtained by a one-step spray drying technology. The hard template polytetrafluoroethylene (PTFE) supplements the loss of fluorine, forming porous structure that accelerates the infiltration of electrolyte. The soft template cetyltrimethylammonium bromide (CTAB) enables doping of bromine and can also control the fluorine content, meanwhile, the self-assembly effect strengthens the structure and refines the size of spherical particles. The loss, compensation, and regulation mechanism of fluorine are investigated. The Br-doped Na3 V2 (PO4 )2 F3 /C sphere exhibits superior rate capability with the capacities of 116.1, 105.1, and 95.2mAhg-1 at 1, 10, and 30 C, and excellent cyclic performance with 98.3% capacity retention after 1000 cycles at 10 C. The density functional theory (DFT) calculation shows weakened charge localization and enhanced conductivity, meanwhile the diffusion energy barrier of sodium ions is reduced with Br doping. This paper proposes a strategy to construct fluorine-containing polyanions cathode, which enables the precise regulation of structure and morphology, thus leading to superior electrochemical performance.

Fabrication of Na-Ion Full-Cells using Carbon-Coated Na3 V2 (PO4 )2 O2 F Cathode with Conversion Type CuO Nanoparticles from Spent Li-Ion Batteries.

Spent lithium-ion batteries (LIBs) offer immense potential in the form of resources such as Li, transition metals (Co, Ni, and Mn), graphite, and Cu, which can be recovered through suitable recycling procedures. The Cu-current collector is recovered from spent LIBs and converted as a copper oxide (CuO) anode for Na-ion batteries. The performance of CuO is evaluated with carboxymethyl cellulose (CMC) (CuO-C), and polyvinylidene fluoride (PVdF) (CuO-P) binders in CuO half-cell and CuO/carbon-coated Na3 V2 (PO4 )2 O2 F (CuO/NVPOF) full-cell assemblies. The CuO-C half-cell displays superior electrochemical performance than CuO-P in terms of cycling and rate performance showing 88% more capacity. To study the stabilization and solid electrolyte interphase growth in CuO-C, an in situ impedance study is conducted. However, the full-cell, CuO-P/NVPOF displays better capacity retention during cycling with Coulombic efficiency >95%from the second cycle, whereas CuO-C/NVPOF could hardly maintain only >90%.For conversion type CuO, it is apparent that, though the CMC binder supports half-cell performance, the PVdF binder is suitable for the practical cell/full-cell configuration.

Regulating Sodium Deposition through Gradiently-Graphitized Framework for Dendrite-Free Na Metal Anode.

Na metal anode (NMA) is one of the most promising candidate materials for next-generation low-cost sodium metal batteries. However, the preferred deposition of Na metal at the anode/separator interface increases the risk of dendrite penetration of the separator, consequently, reduces safety and life of batteries with NMA. In this study, a Na deposition-regulating strategy is shown by designing a gradiently graphitized 3D carbon fiber (CF) framework as host (grad-CF), whereby Na is guided to deposit preferentially at the bottom of the anode, safely away from the separator. The obtained Na anode significantly reduces the probability of dendrite-induced short circuits. The grad-CF host enables NMA stable cycling at a high current density of 6mAcm-2 . When the Na@grad-CF is applied as anode in full cells pared with Na3 V2 (PO4 )3 (NVP) cathode, it exhibits a reversible capacity of 73mA hg-1 after 500 cycles with a low decay rate of 0.13%.

Introducing the Solvent Co-Intercalation Mechanism for Hard Carbon with Ultrafast Sodium Storage.

As the most successful anode material for sodium-ion batteries, hard carbon has attracted extensive attention from researchers. However, its storage mechanism is still controversial. In this paper, a solvent co-intercalation mechanism into hard carbon is proposed and is proved by in situ XRD and ex situ TEM XPS results successfully. Thanks to the co-intercalation of solvent, the platform capacity of hard carbon maintains well at very high current densities. It can even exhibit 245 mAh g-1 at 5 A g-1 , which is the best rate performance obtained for hard carbon anode as far as it is known. The full battery assembled with Na3 V2 (PO4 )3 has a high energy density of 157Wh kg-1 at 3800 W kg-1 (relative to the electrode). This finding brings new insights with regard to the design of hard carbon materials and sodium storage mechanisms.

A 3D Hierarchical Host with Enhanced Sodiophilicity Enabling Anode-Free Sodium-Metal Batteries.

Sodium-metal batteries (SMBs) are considered as a compliment to lithium-metal batteries for next-generation high-energy batteries because of their low cost and the abundance of sodium (Na). Herein, a 3D nanostructured porous carbon particle containing carbon-shell-coated Fe nanoparticles (PC-CFe) is employed as a highly reversible Na-metal host. PC-CFe has a unique 3D hierarchy based on sub-micrometer-sized carbon particles, ordered open channels, and evenly distributed carbon-coated Fe nanoparticles (CFe) on the surface. PC-CFe achieves high reversibility of Na plating/stripping processes over 500 cycles with a Coulombic efficiency of 99.6% at 10 mA cm-2 with 10 mAh cm-2 in Na//Cu asymmetric cells, as well as over 14400 cycles at 60mA cm-2 in Na//Na symmetric cells. Density functional theory calculations reveal that the superior cycling performance of PC-CFe stems from the stronger adsorption of Na on the surface of the CFe, providing initial nucleation sites more favorable to Na deposition. Moreover, the full cell with a PC-CFe host without Na metal and a high-loading Na3 V2 (PO4 )3 cathode (10mg cm-2 ) maintains a high capacity of 103 mAh g-1 at 1mA cm-2 even after 100 cycles, demonstrating the operation of anode-free SMBs.