Cathode Material For Na-ion Batteries Research Articles

Predominant P3-Type Solid-Solution Phase Transition Enables High-Stability O3-Type Na-Ion Cathodes.

Layered O3-type oxides are one of the most promising cathode materials for Na-ion batteries owing to their high capacity and straightforward synthesis. However, these materials often experience irreversible structure transitions at elevated cutoff voltages, resulting in compromised cycling stability and rate performance. To address such issues, understanding the interplay of the composition, structure, and properties is crucial. Here, we successfully introduced a P-type characteristic into the O3-type layered structure, achieving a P3-dominated solid-solution phase transition upon cycling. This modification facilitated a reversible transformation of the O3-P3-P3' structure with minimal and gradual volume changes. Consequently, the Na0.75Ni0.25Cu0.10Fe0.05Mn0.15Ti0.45O2 cathode exhibited a specific capacity of approximately 113 mAh/g, coupled with exceptional cycling performance (maintaining over 70% capacity retention after 900 cycles). These findings shed light on the composition-structure-property relationships of Na-ion layered oxides, offering valuable insights for the advancement of Na-ion batteries.

Recent Advances in Cathode Materials for Na-Ion Batteries

In the quest for sustainable and cost-effective energy storage solutions, sodium-ion batteries (SIBs) have emerged as a promising alternative to lithium-ion batteries, owing to their similar chemical compositions, mechanisms, and compatibility with existing battery technologies. Despite their potential, SIBs face challenges such as lower capacity and structural instability, which hinder their widespread adoption. This paper provides a comprehensive overview of cathode materials used in SIBs, focusing on their electrochemical properties, limitations, and the ongoing research aimed at overcoming these challenges. We delve into the current state of SIB technology, highlighting the critical role of cathode materials in enhancing the performance, durability, and cost-effectiveness of SIBs. Furthermore, we explore future directions for research and development, including novel materials and innovative approaches to improve the capacity and structural stability of SIBs. By addressing these key issues, this paper aims to contribute to the advancement of SIB technology and its application in next-generation energy storage systems.

Development of High-Performance Iron-Based Phosphate Cathodes toward Practical Na-Ion Batteries.

Iron-based phosphate cathode of Na4Fe3(PO4)2(P2O7) has been regarded as a low-cost and structurally stable cathode material for Na-ion batteries (NIBs). However, their practical application is greatly hindered by the insufficient electrochemical performance and limited energy density. Here, we report a new iron-based phosphate cathode of Na4.5Fe3.5(PO4)2.5(P2O7) with the intergrown heterostructure of the maricite-type NaFePO4 and orthorhombic Na4Fe3(PO4)2(P2O7) phases at a mole ratio of 0.5:1. Benefited from the increased composition ratio and the spontaneous activation of the maricite-type NaFePO4 phase, the as-prepared Na4.5Fe3.5(PO4)2.5(P2O7) composites deliver a reversible capacity over 130 mA h g-1 and energy density close to 400 W h kg-1, which is far beyond that of the single-phase Na4Fe3(PO4)2(P2O7) cathode (∼120 mA h g-1 and ∼350 W h kg-1). Moreover, the kg-level products from the scale-up synthesis demonstrate a stable cycling performance over 2000 times at 3 C in pouch cells. We believe that our findings could show the way forward the practical application of the iron-based phosphate cathodes for NIBs.

Enhancing rate and stability performance of O3-type NiFeMnTi-based layered oxides via Sb/Co dual-doping

O3-type layered metal oxides have been consider as a highly suitable cathode materials for Na-ion batteries (SIBs) due to their distinct advantages of high capacity, simple synthesis and affordable price. Nonetheless, the rapid capacity attenuation and the sluggish Na+ diffusion kinetic seriously impede their practical application. Herein, a dual-doping strategy of incorporating Stibium (Sb) and cobalt (Co) elements to a quaternary oxide cathode material (Na(Ni0.3Fe0.2Mn0.5)0.9Ti0.1O2) was proposed to further ameliorate the rate capability and the cycle stability. Because of the enlarged Na and TM interlayer spacing, Sb/Co dual-doping is verified to provide a higher Na+ diffusion rate and a more stable structure. Furthermore, Co doping is found to inhibit the formation of Ni2O3 and Na0.7MnO2 impurities triggered by Sb doping. The modified Na(Ni0.3Fe0.2Mn0.5)0.8Ti0.1Sb0.05Co0.05O2 electrode represents a high discharge specific capacity of 171.6 mAh g-1 at 0.1C within the voltage range from 2.0 V to 4.3 V, and an excellent rate capability of 82.0 mAh g-1 at 5C. More significantly, it shows a splendid capacity retention of 74.69 % over 300 cycles at 1C.

Synergetic impact of dual substitution on anionic–Cationic activity of P2-type sodium manganese oxide

P2-type sodium-deficient cathodes with the local Na–O–A configuration (A=Li, Mg, Zn, and vacancy) have attracted great interest due to their high capacity, stemming from the additional contribution of the oxygen-redox chemistry. However, such materials suffer from irreversible oxygen redox, oxygen release, structural distortion, and capacity fading. Herein, we introduce a dual-doping Li/Cu strategy to improve the properties of P2-NaxMnO2 cathode material. The unique sodium-storage mechanism in P2-Na0.75[Li0.15Cu0.15Mn0.7]O2 is verified using operando X-ray diffraction (o-XRD), X-ray absorption, X-ray photoelectron spectroscopy, and magnetic susceptibility methods. O-XRD and 7Li solid-state nuclear magnetic resonance analysis reveal that the P2 phase is maintained within charge and discharge; however, at high voltage, a small portion of O-type stacking faults are emerged due to the migration of Li to octahedral Na sites. Furthermore, various spectroscopy and magnetometry techniques combined with density functional theory calculation demonstrate the stable activity of cationic Cu2+/Cu3+ and Mn3+/Mn4+ and anionic O2−/(O2)n− redox processes. This work highlights the efficacy of Li and Cu doping in P2-type layered materials and the contribution of oxygen redox to additional capacity at high voltages, suggesting the potential for future development of cathode materials for Na-ion batteries with oxygen redox.

A high entropy O3-Na1.0Li0.1Ni0.3Fe0.1Mn0.25Ti0.25O2 cathode with reversible phase transitions and superior electrochemical performances for sodium-ion batteries

O3-type Ni/Mn/Fe-based layered oxides are very promising cathode materials for Na-ion batteries (SIBs) due to their high redox potential of Ni2+/ Ni4+ and Jahn-Teller inactive centers (Ni2+, Fe3+, and Mn4+)....

MgO coated P2-Na0.67Mn0.75Ni0.25O2 layered oxide cathode for Na-Ion batteries

In this study, we propose an effective strategy to improve the electrochemical performance of a P2-Na0.67Mn0.75Ni0.25O2 (P2-MNO) cathode material for Na-ion batteries based on MgO surface coating. The MgO coating, with a thickness of ∼20–50 nm, is obtained by means of a facile wet-chemistry approach followed by heat treatment carried out at comparatively low temperatures (400–500 °C) in order to avoid possible Mg doping in the bulk of the P2-MNO. Detailed electrochemical investigations demonstrate improved electrochemical performance of the MgO-coated material (M-P2-MNO) in comparison to pristine bare one at both room and elevated (40 °C) temperatures. Operando differential electrochemical mass spectroscopy (DEMS) demonstrate that the MgO coating is effective in suppressing unwanted gas evolution due to side reactions thus stabilizing the cathode/electrolyte interface.

Boosting the operation stability of sodium-rich vanadium manganese-based NASICON phosphate as a cathode material for Na-ion batteries by Zn pinning effect

Recently, NASICON-type Na4VMn(PO4)3, as a promising cathode material for sodium-ion batteries (SIBs), has received widespread attention owing to its high working voltage, high theoretical capacity, and fast Na+ migration kinetics. Unfortunately, serious structural deformation issue, caused by the Jahn-Teller effect of Mn3+, is still inevitable during repetitive charge/discharge processes, resulting in fast capacity fade. Therefore, designing a stable structure is crucial for developing practical vanadium manganese-based NASICON-type electrode materials. Herein, Zn2+-doped NASICON-type Na4VMn1−xZnx(PO4)3 can reduce Jahn-Teller effect of Mn3+ and expand the migration pathways of mobile Na+ ions. When being used as cathode materials for SIBs, Na4VMn0.9Zn0.1(PO4)3/C can provide 77.6% capacity retention at 1100 mA g−1 after the 500th cycle, which is much higher than that (67.6%) of Zn-undoped Na4VMn(PO4)3/C. Moreover, the reversible reactions of Mn3+/Mn2+ and V4+/V3+ redox couples are validated by ex-situ Powder X-ray diffraction (XRD) analyses of electrode materials cycled at different charge and discharge voltages. The fast reaction kinetics of the Na4VMn0.9Zn0.1(PO4)3/C electrode is confirmed via Galvanostatic intermittent titration technique (GITT). This research work offers an effective approach for devising high operation stability NASICON-type cathode materials for SIBs by pinning effect.

Optimizing Dopant for Enhanced Oxygen-Redox Performance in P2-Na Cathode Materials for Sodium-Ion Batteries

Recently, there has been a lot of interest in using oxygen-redox-based cathode materials for sodium-ion batteries (SIBs) due to their potential for providing additional capacity in the high-voltage range. However, they have some matter, including fast capacity fading and poor rate capability. Herein, P2-Na0.7[Li0.1Ni0.1Mg0.1Mn0.7]O2 is introduced, an layered oxide cathode material for Na-ion batteries based on oxygen-redox. The effect of Ni doping is improved electrochemical performance. Mg2+ in transition metal layer delivered relatively higher capacity via oxygen redox in high voltage region by comparison with Mg-free P2-Na0.75[Li0.15Ni0.15Mn0.7]O2, showing a specific discharge capacity of 175mAh g-1 with 83% of capacity retention after 100 cycles. This study show how the co-doping of Li, Ni and Mg can impact P2-type layered materials and proposes a novel approach to utilizing Mn-rich cathode materials through oxygen redox, with a focus on optimizing the dopant for sodium-ion batteries.

Enhancing Structural of P2-Type Layered Cathode Material for Sodium-Ion Batteries through Cu Substitution

Oxygen-redox-based layered cathode materials for Sodium-ion batteries (SIBs) have been recognized as a promising alternative to Lithium-ion batteries (LIBs) due to high energy density and additional capacity in the high voltage. However, their irreversible oxygen-redox activity during cycling leads to structural distortion and capacity fading. Herein, we introduce a layered P2-Na0.75[Li0.15Cu0.15Mn0.7]O2 cathode material, in which Cu substitution improves electro-conductivity and cyclability. Na0.75[Li0.15Cu0.15Mn0.7]O2 delivers a reversible capacity of 170 mAh g-1 at 0.1C in Na cell. Operando-XRD measurement display the material maintain the P2 structure even upon full Na+ extraction and insertion. Furthermore, magnetic susceptibility provide further information Cu2+/Cu3+, Mn3+/Mn4+, and O2-/(O2)n- ion distribution in Na0.75[Li0.15Cu0.15Mn0.7]O2. This research highlight the effect of Li and Cu doping in P2-type layered materials and the contribution of oxygen redox to additional capacity in high voltages, suggesting the potential for future development of cathode materials for Na-ion batteries with oxygen redox.

Unraveling the Synthesis of Positive Electrodes for Na-Ion Batteries by in Situ XRD

In situ diffraction studies can capture transient crystalline phases forming during chemical reactions. Whether the reaction is a chemical solid-state synthesis, or an electrochemical intercalation process within typical active compounds used as battery electrodes, proper sample environments allow nowadays to perform in situ diffraction experiments with high temporal and angular resolution even when using laboratory diffractometers. In both cases, the time-resolved nature of the experiments allows to obtain a greatly increased amount of information. For example, in the synthesis of inorganic materials, reactions often yield non-equilibrium kinetic byproducts instead of the thermodynamic equilibrium phase [1]. On the other hand, often stable compounds cannot be synthesized. To rationalize that, the competition between thermodynamics and kinetics occurring during the process need to be investigated in real time. Fully determining the reaction pathway is a key requirement to achieve the rational synthesis of target materials [2, 3]. In this presentation, recent unpublished examples will be reported from our work applying in situ XRD to understand the synthesis of cathode materials for Na-ion batteries. We focus on layered materials and on the relationship between P2 and P3 polymorphs in series of samples of the same composition NaxDyNizMn1-y-zO2 (where D is a substitutional element and Ni and Mn are in divalent and tetravalent oxidation state, respectively) and highlight the transformation of a phase into the other during calcination. Moreover, we provide electrochemical and morphologic characterizations of the target compounds, aiming to answer the question: does one or the other polymorph offer better performances? The charge compensation mechanism, involving Ni redox but also O redox, will be reported. Finally, the presentation will also briefly cover the investigation of novel solid-state synthesis routes for cathodes of the fluorophosphate Na3V2(PO4)2F3-xOx family.

Disclosing the Interfacial Electrolyte Structure of Na-Insertion Electrode Materials: Origins of the Desolvation Phenomenon.

Among a variety of promising cathode materials for Na-ion batteries, polyanionic Na-insertion compounds are among the preferred choices due to known fast sodium transfer through the ion channels along their framework structures. The most interesting representatives are Na3V2(PO4)3 (NVP) and Na3V2(PO4)2F3 (NVPF), which display large Na+ diffusion coefficients (up to 10-9 m2 s-1 in NVP) and high voltage plateaux (up to 4.2 V for NVPF). While the diffusion in the solid material is well-known to be the rate-limiting step during charging, already being thoroughly discussed in the literature, interfacial transport of sodium ions from the liquid electrolyte toward the electrode was recently shown to be important due to complex ion desolvation effects at the surface. In order to fill the blanks in the description of the electrode/electrolyte interface in Na-ion batteries, we performed a molecular dynamics study of the local nanostructure of a series of carbonate-based sodium electrolytes at the NVP and the NVPF interfaces along with careful examination of the desolvation phenomenon. We show that the tightness of solvent packing at the electrode surface is a major factor determining the height of the free energy barrier associated with desolvation, which explains the differences between the NVP and the NVPF structures. To rationalize and emphasize the remarkable properties of this family of cathode materials, a complementary comparative analysis of the same electrolyte system at the carbon electrode interface was also performed.

Superstructure and Correlated Na+ Hopping in a Layered Mg-Substituted Sodium Manganate Battery Cathode are Driven by Local Electroneutrality.

In this work, we present a variable-temperature 23Na NMR and variable-temperature and variable-frequency electron paramagnetic resonance (EPR) analysis of the local structure of a layered P2 Na-ion battery cathode material, Na0.67[Mg0.28Mn0.72]O2 (NMMO). For the first time, we elucidate the superstructure in this material by using synchrotron X-ray diffraction and total neutron scattering and show that this superstructure is consistent with NMR and EPR spectra. To complement our experimental data, we carry out ab initio calculations of the quadrupolar and hyperfine 23Na NMR shifts, the Na+ ion hopping energy barriers, and the EPR g-tensors. We also describe an in-house simulation script for modeling the effects of ionic mobility on variable-temperature NMR spectra and use our simulations to interpret the experimental spectra, available upon request. We find long-zigzag-type Na ordering with two different types of Na sites, one with high mobility and the other with low mobility, and reconcile the tendency toward Na+/vacancy ordering to the preservation of local electroneutrality. The combined magnetic resonance methodology for studying local paramagnetic environments from the perspective of electron and nuclear spins will be useful for examining the local structures of materials for devices.

Enhancing the electrochemical properties of Na2Mn2P3O9N by partial substitution at Mn site: A first-principles study

Nitridophosphate materials have recently emerged as promising cathode materials for Na-ion batteries due to their excellent ionic conductivity, but their low electronic conductivity has limited their practical applications. In this study, the electrochemical properties of Na2Mn2P3O9N, a nitridophosphate material containing manganese was examined for the first time and the prevalent issue of low electronic conductivity in nitridophosphate-based materials was addressed through partial substitution of transition metal (TM) at the Mn site. The present work aims at improving the electronic conductivity of this material while maintaining desirable properties such as ionic conductivity, voltage, and structural stability. The study employed density functional theory (DFT) calculations to explore the role of TM substitutions in electronic conductivity and electrochemical properties. From the partial substitution of different electrochemical active and inactive elements at the Mn site, we found that the Cu/Ag substitutions improve the electronic conductivity while retaining other desirable electrochemical properties. The electronic and electrochemical properties of these materials were further studied in detail to reveal the redox mechanisms. Our DFT-assisted studies prove that the parent and Ag-substituted materials exhibit a stable O network even under a high state of charge. Furthermore, our nudged elastic band calculations revealed that Na2Mn2P3O9N, along with the Cu/Ag substituted variants, exhibit favourable Na-ion diffusion. The parent and Ag-substituted materials demonstrate exceptional ionic conductivities comparable to existing commercial cathodes used in Li-ion batteries. These findings suggest that partial substitution of copper/silver at the manganese site could be a promising strategy for improving the electronic conductivity of nitridophosphate materials without compromising their beneficial properties to use in higher energy density Na-ion batteries.

High Na-content P2 and P2-O3 layered oxide cathodes for high performance Na-ion batteries

P2-NaxTMO2, (x ≤0.67, TM-transition metal) oxides are promising cathode materials for Na-ion batteries, however they suffer from Na+-vacancy ordering and huge structural transformations (P2→O2→OP4). In contrast, high Na content in P2-type cathodes enables high structural stability and promotes active elements to their lower oxidation state and thereby achieving high capacity and cycling stability. Herein, light-weight elements boron and lithium doped in P2-type Na0.67Ni0.33Mn0.67O2 using cationic potential approach, aiming to improve the Na content. Li-B doped Na0.8Ni0.3Mn0.6Li0.05B0.05O2 delivers a capacity of 85 mAh/g and excellent capacity retention (88 % after 500 cycles). The effects of Li-B doping in P2-type Na0.67Ni0.33Mn0.67O2 are systematically investigated.

Electrochemical performance of different high-entropy cathode materials for Na-ion batteries

Li-ion batteries have become the most popular electrochemical energy storage solution, finding widespread applications in electronic devices, tools, electric vehicles, and large-scale energy systems. However, due to the increasing demand, we soon may encounter shortages in lithium resources and a rise in the cost of Li-ion batteries. Therefore, it is imperative to explore alternative options, one of which is Na-ion technology. Herein, we present and compare three sodium-based cathode materials from the high-entropy layered oxides group: NaMn0.2Fe0.2Co0.2Ni0.2Ti0.2O2 (HEO-T), NaMn1/6Fe1/6Co1/6Ni1/6Ti1/6Cu1/6O2 (HEO-TC), and NaMn0.2Fe0.2Co0.2Ni0.2Sn0.1Al0.05Mg0.05O2 (HEO-SAM), all of which exhibit intriguing structural and electrochemical properties. To analyse the crystal structure and microstructure, we conducted X-ray diffraction (XRD) measurements and captured scanning electron microscopy (SEM) images. The core of our research focuses on the electrochemical performance of these materials. We assembled CR2032 test cells and subjected them to testing at various current rates, ranging from C/10–5 C. Furthermore, to gain insights into the mechanisms governing HEO-based cells during operation, we conducted operando-XRD measurements. These experiments revealed the O3-P3 phase transition in each material, occurring at different sodium contents within each compound, which significantly impacts their electrochemical performance. Additionally, we present the electrochemical properties of full-cells with the general formula: Sb|Na+|HEO-SAM, tested under various current rates and subjected to long-term cycling under C/2 and 1 C current loads.

Graphene aerogel-supported Na3V2(PO4)3/C cathodes for sodium-ion batteries

Na3V2(PO4)3 (NVP) is a preferred cathode material for Na-ion batteries due to its good thermal stability and long cycle life, but its low electrical conductivity limits its use. The carbon coating method is widely available in the literature but can solve the problem to a limited extent. Graphene aerogel-based composite materials with lightweight, high surface area and 3-dimensional (3D) porous structure are prepared, and the properties are tried to be improved further. In this study, carbon-coated Na3V2(PO4)3 (NVP/C) and graphene aerogel-carbon-coated Na3V2(PO4)3 (GA-NVP/C) composite have been synthesized. The produced samples have been analyzed using Field emission scanning electron microscopy, X-ray diffraction, Raman spectrum, Thermal Gravity Analysis, X-ray photoelectron spectroscopy, Brunauer-Emmett-Teller and Transmission electron microscopy. Then, the effect of graphene aerogel additive on electrochemical performances as cathode materials has been investigated. Even though GA-NVP/C and NVP/C have similar discharge capacities in the first cycle, GA-NVP/C shows high cycle stability when compared to NVP/C after 250 cycles. The GA-NVP/C cathode also has a higher discharge capacity than the NVP/C cathode at different current rates. The diffusion coefficient calculated using the cyclic voltammetry curve of GA-NVP/C is also high, supporting the graphene aerogel's positive results. In conclusion, we show that adding GA with a 3-dimensional porous structure greatly improves the electrochemical properties of the cathode in Na-ion batteries.

Advantages of a Solid Solution over Biphasic Intercalation for Vanadium-Based Polyanion Cathodes in Na-Ion Batteries.

The efficient operation of metal-ion batteries in harsh environments, such as at temperatures below -20 °C or at high charge/discharge rates required for EV applications, calls for a careful selection of electrode materials. In this study, we report advantages associated with the solid solution (de)intercalation over the two-phase (de)intercalation pathway and identify the main sources of performance limitations originating from the two mechanisms. To isolate the (de)intercalation pathway as the main variable, we focused on two cathode materials for Na-ion batteries: a recently developed KTiOPO4-type NaVPO4F and a well-studied Na3V2(PO4)2F3. These materials have the same elemental composition, operate within the same potential range, and demonstrate very close ionic diffusivities, yet follow different (de)intercalation routes. To avoid any interpretation uncertainties, we obtained these materials in the form of particles with merely identical morphology and size. A detailed electrochemical study revealed a much lower capacity and energy density retention for phase-transforming Na3V2(PO4)2F3 compared to NaVPO4F, which exhibits a single-phase behavior over a wide range of Na concentrations. The reasons for the inferior rate capability and temperature tolerance for the phase-separating Na3V2(PO4)2F3 material should be affiliated with slow phase boundary propagation. We hope that the comprehensive information on limiting factors provided for both mechanisms is useful for the further optimization of electrode materials toward a new generation of high-power and low-temperature metal-ion batteries.

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.

Titanium doping induced the suppression of irreversible phase transformation at high voltage for V-based Phosphate Cathodes of Na-ion Batteries.

Polyanionic material, specifically the NASICON-type material, is considered a promising cathode material for Na-ion batteries (SIBs) because of its stable structure and high operating voltage. Further, it improves the energy density correlated with the well utilization of all Na in the compound. For Na3V2(PO4)2F3(NVPF), the extraction of the third Na, reported as the electrochemical inactivated, can be realized at a high voltage region while forming an irreversible tetragonal phase. In this study, we introduce Ti doping to the Na2VTi(PO4)2F3(NVTPF) material; we reveal that the Ti-doped NVTPF could effectively suppress the irreversible phase transformation, thus successfully harnessing Na in a wide voltage range. Experimental study discloses that the Ti-substituted Na2VTi(PO4)2F3 could take up the Na+ from Amam phase to Cmc21 phase between 1.0 V and 4.8 V reversibly accounting for the 2 Na+ transportation that shows favorable Na+ kinetics and structural stability. Our research provides the strategy to stabilize the polyanion structure upon charging at a high voltage range and inspires the utilization of full sodium in the polyanionic materials, which could be considered as a material design for future conventional applications.