Cathode Material For Sodium-ion Batteries Research Articles

Mesoporous hollow Fe4[Fe(CN)6)]3 hierarchical nanocrystal architecture for advanced sodium-ion batteries

Prussian blue (PB) has been broadly recognized as promising cathode materials for sodium-ion batteries (SIBs) due to its large interstitial space and robust frame structure, whereas their applications are impeded by unsatisfied long-term cyclability and poor rate capability due to its inherent lattice defects. Herein, we report to fabricate the mesoporous hollow Fe4(Fe(CN)6)3 (one kind of PB) hierarchical nanocrystal architecture by the hydrothermal crystallization and HCl etching of the mesoporous precursor Fe4[Fe(CN)6]3 cubic particles, leading to high crystallinity and large specific surface area. The resultant Fe4[Fe(CN)6]3 cathode for SIBs exhibits a good reversibility and cycling stability with a capacity retention of 75.6 % at 0.5 C after 200 cycles as well as superb rate capability featuring a stable discharge specific capacity of 30.2 mAh g−1 at as high as 10 C, demonstrating the fast kinetics and low polarization of electrochemical reaction, which might be ascribed to the unique architecture and high crystallinity. This offers a new route to designing PB cathode of for SIBs with high rate capabilities.

A Comprehensive Review on Strategies for Enhancing the Performance of Polyanionic-Based Sodium-Ion Battery Cathodes.

The significant consumption of fossil fuels and the increasing pollution have spurred the development of energy-storage devices like batteries. Due to their high cost and limited resources, widely used lithium-ion batteries have become unsuitable for large-scale energy production. Sodium is considered to be one of the most promising substitutes for lithium due to its wide availability and similar physiochemical properties. Designing a suitable cathode material for sodium-ion batteries is essential, as the overall electrochemical performance and the cost of battery depend on the cathode material. Among different types of cathode materials, polyanionic material has emerged as a great option due to its higher redox potential, stable crystal structure, and open three-dimensional framework. However, the poor electronic and ionic conductivity limits their applicability. This review briefly discusses the strategies to deal with the challenges of transition-metal oxides and Prussian blue analogue, recent developments in polyanionic compounds, and strategies to improve electrochemical performance of polyanionic material by nanostructuring, surface coating, morphology control, and heteroatom doping, which is expected to accelerate the future design of sodium-ion battery cathodes.

Manipulating Local Chemistry and Coherent Structures for High-Rate and Long-Life Sodium-Ion Battery Cathodes.

Layered sodium transition-metal (TM) oxides generally suffer from severe capacity decay and poor rate performance during cycling, especially at a high state of charge (SoC). Herein, an insight into failure mechanisms within high-voltage layered cathodes is unveiled, while a two-in-one tactic of charge localization and coherent structures is devised to improve structural integrity and Na+ transport kinetics, elucidated by density functional theory calculations. Elevated Jahn-Teller [Mn3+O6] concentration on the particle surface during sodiation, coupled with intense interlayer repulsion and adverse oxygen instability, leads to irreversible damage to the near-surface structure, as demonstrated by X-ray absorption spectroscopy and in situ characterization techniques. It is further validated that the structural skeleton is substantially strengthened through the electronic structure modulation surrounding oxygen. Furthermore, optimized Na+ diffusion is effectively attainable via regulating intergrown structures, successfully achieved by the Zn2+ inducer. Greatly, good redox reversibility with an initial Coulombic efficiency of 92.6%, impressive rate capability (86.5 mAh g-1 with 70.4% retention at 10C), and enhanced cycling stability (71.6% retention after 300 cycles at 5C) are exhibited in the P2/O3 biphasic cathode. It is believed that a profound comprehension of layered oxides will herald fresh perspectives to develop high-voltage cathode materials for sodium-ion batteries.

Constructing a Size-Controllable Spherical P2-Type Layered Oxides Cathode That Achieves Practicable Sodium-Ion Batteries.

P2-type layered metal oxides are regarded as promising cathode materials for sodium-ion batteries due to their high voltage platform and rapid Na+ diffusion kinetics. However, limited capacity and unfavorable cycling stability resulting from inevitable phase transformation and detrimental structure collapse hinder their future application. Herein, based on P2-type Na0.67Ni0.18Mn0.67Cu0.1Zn0.05O2, we synthesized a series of secondary spherical morphology cathodes with different radii derived from controlling precursors prepared by a coprecipitation method, which can be promoted to large-scale production. Consequently, the synthesized materials possessed a high tap density of 1.52 g cm-3 and a compacted density of 3.2 g cm-3. The half cells exhibited a specific capacity of 111.8 mAh g-1 at a current density of 0.1 C as well as an 82.64% capacity retention with a high initial capacity of 85.80 mAh g-1 after 1000 cycles under a rate of 5 C. Notably, in situ X-ray diffraction revealed a reversible P2-OP4 phase transition and displayed a tiny volume change of 6.96% during the charge/discharge process, indicating an outstanding cycling stability of the modified cathode. Commendably, the cylindrical cell achieved a capacity of 4.7 Ah with almost no change during 1000 cycles at 2 C, suggesting excellent potential for future applications.

Air Corrosion of Layered Cathode Materials for Sodium-Ion Batteries: Cation Mixing and a Practical Suppression Strategy.

Layered oxide cathodes of sodium-ion batteries (SIBs) are considered promising candidates due to their fascinating high capacity, good cyclability, and environmental friendliness. However, the air sensitivity of layered SIB cathodes causes high electrode manufacturing costs and performance deterioration, hampering their practical application. Herein, a commercial O3-type layered Na(Ni1/3Fe1/3Mn1/3)O2 (NNFM) material is adopted to investigate the air corrosive problem and the suppression strategy. We reveal that once the layered material comes in contact with ambient air, cations migrate from transition metal (TM) layers to sodium layers at the near surface, although Na+ and TM ions show quite different ion radii. Experimental results and theoretical calculations show that more Ni/Na disorder occurs in the air-exposed O3-NNFM materials, owing to a lower Ni migration energy barrier. The cation mixing results in detrimental structural distortion, along with the formation of residual alkali species on the surface, leading to high impedance for Na+ diffusion during charge/discharge. To tackle this problem, an ultrathin and uniform hydrophobic molecular layer of perfluorodecyl trimethoxysilane is assembled on the O3-NNFM surface, which significantly suppresses unfavorable chemistry and structure degradation during air storage. The in-depth understanding of the structural degradation mechanism and suppression strategy presented in this work can facilitate high-energy cathode manufacturing from the perspective of future practical implementation and commercialization.

High stability of Cu-doped O3-type NaNi1/3Fe1/3Mn1/3O2 cathode material for sodium-ion battery

High stability of Cu-doped O3-type NaNi1/3Fe1/3Mn1/3O2 cathode material for sodium-ion battery

Interfacial Spinel Local Interlocking Strategy Toward Structural Integrity in P3 Oxide Cathodes.

P3-layered transition oxide cathodes have garnered considerable attention owing to their high initial capacity, rapid Na+ kinetics, and less energy consumption during the synthesis process. Despite these merits, their practical application is hindered by the substantial capacity degradation resulting from unfavorable structural transformations, Mn dissolution and migration. In this study, we systematically investigated the failure mechanisms of P3 cathodes, encompassing Mn dissolution, migration, and the irreversible P3-O3' phase transition, culminating in severe structural collapse. To address these challenges, we proposed an interfacial spinel local interlocking strategy utilizing P3/spinel intergrowth oxide as a proof-of-concept material. As a result, P3/spinel intergrowth oxide cathodes demonstrated enhanced cycling performance. The effectiveness of suppressing Mn migration and maintaining local structure of interfacial spinel local interlocking strategy was validated through depth-etching X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, and in situ synchrotron-based X-ray diffraction. This interfacial spinel local interlocking engineering strategy presents a promising avenue for the development of advanced cathode materials for sodium-ion batteries.

Zinc-substituted Fe-based Prussian blue analogues induce a weak Jahn-Teller effect to enhance stability of sodium ion batteries

Prussian blue analogues (PBAs) have attracted wide attention as cathode materials for sodium-ion batteries. Nevertheless, the poor cycle performance caused by the [Fe(CN)6]4− defects and Jahn-Teller (J-T) effect hinders its practical application. Here, Zn-substituted PBAs were synthesized through co-precipitation method and studied as cathodes for Na-ion batteries. The synthesized Na1.14Zn0.39Fe0.61[Fe(CN)₆]·4.14H2O (NZFC) and Na1.18Zn0.42Fe0.58[Fe(CN)₆]·4.96H2O (NZFE) showed outstanding exceptional electrochemical properties, including high capacity (first capacity of 114.56 and 97.76 mAh·g−1 at 10 mA·g−1, respectively), excellent rate property (71.81 and 68.69 mAh·g−1 at 500 mA·g−1, respectively), and cycling stability (64.72 % and 80.27 %, respectively) after 350 cycles at 200 mA g−1, which is attribute to introduction of Zn element induced a weak Jahn-Teller effect and a low-spins and a high-spins FeII/FeIII redox sites coordinated by C and N atoms prompt reversible diffusion of sodium ions and without structural transformation in the Na-ion storage. Using combined experiment and theory via ex situ X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) calculations, it is confirmed that the weak J-T distortion contributes significantly to fast-overall kinetics, structural stability, and high electronic conductivity of the electrode. These findings provide new insights into comprehending for the future development of high-performance and stable sodium ion batteries.

On the structural evolution of pristine P2-type Na0.67Ni0.33Mn0.67O2 for symmetric full cell application

P2 type Na0.67Ni0.33Mn0.67O2 (NNMO) is a widely studied layered oxide cathode material for sodium-ion batteries (SIBs) because of its high capacity (160 mAhg-1 practically achieved) and broad voltage window (2–4.5 V). The redox activity in NNMO is shown by both Ni2+ and Mn4+ ions, making it a prospective symmetric SIB electrode material. The average working potential of the symmetric full cell is less due to the limited average working voltages of both the redoxes in a half cell between 2 V and 4.5 V, resulting in poor energy density. Herein, we report the feasibility of the NNMO symmetric full cell by widening the operational voltage window of NNMO. The electrochemical performance of NNMO half cells between 0.01 V and 4 V and the structural evolution during cycling are mapped by ex-situ XRD. Na0.44MnO2-like tunnel-type structure (Pbam) with high Na+ content (>0.90) exists at potentials close to the Mn3+/4+ redox reaction during cycling. The phase change was relatively reversible, implying that the NNMO anode works at such low voltages without the hazard of severe capacity losses. The symmetric full cell made using NNMO cycled between 0.01 V and 3 V and, at C/10 rate, delivered a capacity of ∼68 mAhg−1.

Ion Dynamics at the Intermediate Charging State of the Sodium Vanadium Fluorophosphate Cathode.

Na super ionic conductor (NASICON)-type polyanionic vanadium fluorophosphate Na3V2O2(PO4)2F (NVOPF) is a promising cathode material for high-energy sodium-ion batteries. The dynamic diffusion and exchange of sodium ions in the lattice of NVOPF are crucial for its electrochemical performance. However, standard characterizations are mostly focused on the as-synthesized material without cycling, which is different from the actual battery operation conditions. In this work, we investigated the hopping processes of sodium in NVOPF at the intermediate charging state with 23Na solid-state nuclear magnetic resonance (ssNMR) and density functional theory (DFT) calculations. Our experimental characterizations revealed six distinct sodium coordination sites in the intermediate structure and determined the exchange rates among these sites at variable temperatures. The theoretical calculations showed that these dynamic processes correspond to different ion transport pathways in the crystalline lattice. Our combined experimental and theoretical study uncovered the underlying mechanisms of the ion transport in cycled NVOPF and these understandings may help the optimization of cathode materials for sodium-ion batteries.

Unveiling the potential of Na2FePO4F@PEG composite as cathode material for sodium-ion batteries

The economic and environmental advantages of Na2FePO4F fluorophosphate have positioned it as a highly promising cathode material for sodium-ion batteries (SIBs). This recognition stems from its demonstrated potential to address key challenges in energy storage systems, making it a subject of extensive research and studies.In this paper, the preparation of Na2FePO4F powder through a simplified, upscaling, and cost-effective approach that involves the direct use of phosphoric acid is described, aiming to evaluate its electrochemical performance. The obtained orthorhombic structure (S.G. Pbcn) is mixed with varying percentages of polyethylene glycol as a carbon source (15% and 20%) to generate large specific surfaces, improve electronic conductivity, and achieve an optimized carbon content for these materials. The 15% and 20% PEG-coated Na2FePO4F are evaluated at a 2 - 4 V voltage range at C/15 in Na-half cells using two electrolyte formulations: 5% FEC 1 M NaClO4:PC and 1 M NaPF6:PC. The NaPF6/FEC electrolyte exhibits better electrochemical characteristics and high cycling stability, especially in the case of the 15% PEG-coated material. These findings are also supported by the data from differential plots and rate capabilities, highlighting the potential of the coated material for applications in high-performance energy storage applications.

Mechanism and enhanced performance of low-dose low-valence molybdenum-doped Na3V2(PO4)2F2O cathodes for sodium batteries

Sodium vanadium oxyfluorophosphate Na3V2(PO4)2F2O is an attractive cathode material for sodium ion batteries due to its high crystalline stability, high specific capacity and high discharge potential. Currently, the poor electronic conductivity and low diffusion rate of Na+ severely impede its development and application. In this work, low-dose Mo2+ doping is proposed through first-principle computation to enhance the structure and performance of Na3V2(PO4)2F2O. It is found that low-dose of Mo2+ doping can reduce the band gap and energy barrier for Na + diffusion in Na3V2(PO4)2F2O. However, heavy doping leads to serious Jahn-Teller distortion of the crystal structure. Therefore, low-dose Mo2+ doping, ranging from x = 0 to x = 0.06 in Na3V2-xMox(PO4)2F2O, is designed and experimentally carried out. The best performance with 118.5 mA h g−1 at 0.1C and 60.6 mA h g−1 at 20C is obtained in Na3V1.96Mo0.04(PO4)2F2O when x = 0.04 in comparison with other doping amounts. The specific discharge capacity at 0.5C decreases gradually from 105.4 to 77.9 mA h g−1 after 400 cycles, indicating a capacity retention of 73.9 %. These results demonstrate that low-dose Mo2+ doping is an effective strategy to enhance the electrochemical performance of Na3V2(PO4)2F2O, making it a promising cathode material for sodium batteries.

Research Progress on Phase Transition of Layered Cathode Materials for Sodium-ion Batteries

Research Progress on Phase Transition of Layered Cathode Materials for Sodium-ion Batteries

Ti-doped O3-NaNi0.5Mn0.5O2 as high-performance cathode materials for sodium-ion batteries

With favorable electrochemical activity, NaNi0.5Mn0.5O2(NNMO) has been a key cathode material in sodium-ion batteries. However, the phase-transition irreversible and kinetics sluggish issues in NaNi0.5Mn0.5O2 greatly limit its application in sodium-ion batteries. Here, various Ti-doped O3-NaNi0.5Mn0.5-xTixO2 cathode materials were fabricated via solid-phase method. The extra Ti-doping treatment effectively stabilized the transition layer of metal and enlarged the Na layer spacing, as well as suppressed the Na+/vacancy ordering. In particular, the obtained O3-NaNi0.5Mn0.46Ti0.04O2 (NNMOTi-4) exhibits initial reversible capacity of 108.6 mAh g−1 at 0.1C and remarkable 65.2% capacity retention after 100 cycles at 1C. Accordingly, this work provides a facile Ti-doping strategy to regulate the structure and electrochemical performance of layered NaxTMO2 for sodium-ion batteries.

Prussian Blue Analogues for Sodium-Ion Battery Cathodes: A Review of Mechanistic Insights, Current Challenges, and Future Pathways.

Prussian blue analogues (PBAs) have emerged as highly promising cathode materials for sodium-ion batteries (SIBs) due to their affordability, facile synthesis, porous framework, and high theoretical capacity. Despite their considerable potential, practical applications of PBAs face significant challenges that limit their performance. This review offers a comprehensive retrospective analysis of PBAs' development history as cathode materials, delving into their reaction mechanisms, including charge compensation and ion diffusion mechanisms. Furthermore, to overcome these challenges, a range of improvement strategies are proposed, encompassing modifications in synthesis techniques and enhancements in structural stability. Finally, the commercial viability of PBAs is examined, alongside discussions on advanced synthesis methods and existing concerns regarding cost and safety, aiming to foster ongoing advancements of PBAs for practical SIBs.

Dual-ion regulation of coordination chemistry for high-voltage stabilized P2-type cathode

P2-Na2/3Ni1/3Mn2/3O2 has shown great potential as cathode material for sodium-ion batteries with its high theoretical capacity and energy density. However, severe structural changes are induced by charging P2-Na2/3Ni1/3Mn2/3O2 above 4.2 V, resulting in rapid capacity decay and poor kinetic capability. In this study, we propose a Zn/Ti synergistic modification strategy to stabilize the P2-type cathode under high voltage. It is found that the P2-O2 phase transition with large volume change is replaced by a milder P2-Z phase transition with the noteworthy improvement in structural stability and Na+ diffusion kinetics, due to the disordered Na+/vacancy and the suppressed of the sliding of transition metal layers, as disclosed by density functional theory calculations and in-situ X-ray diffraction. Concurrently, The phenomenon of Ni and O reductive coupling is inhibited by regulating local O coordination owing to the incorporation of a strong Ti−O covalence bond, leading to the more reversible charge compensation mechanism and the inhibited lattice O evolution, as clearly revealed by ex-situ X-ray absorption spectroscopy and Differential Electrochemical Mass Spectrometry. Consequently, we obtained a stable P2-Na0.67Zn0.05Ni0.28Mn0.52Ti0.15O2 cathode, achieving an average discharge voltage of 3.62 V at 0.1 C and a capacity retention of 80% after 500 cycles at 2 C. This research provides valuable insights into the enhancement of sodium-ion battery cathode materials by utilizing different functional ions in synergy.

Continuous Flow Electrochemical Synthesis of Olivine-Structured NaFePO4 Cathode Material for Sodium-Ion Batteries from Recycle LiFePO4.

To mitigate the environmental impact of the improper disposal of spent LiFePO4 batteries and reduce resource waste, the development of LiFePO4 recycling technologies is of paramount importance. Meanwhile, olivine-structured NaFePO4 in sodium-ion batteries has received great attention, due to its high theoretical specific capacity of 154 mAh g-1 and excellent stability. However, olivine NaFePO4 only can be synthesized from olivine LiFePO4. Accordingly, in this proposal, developing the continuous flow electrochemical solid-liquid reactor-based metal ion insertion technology is to utilize the olivine FePO4, recycled from LiFePO4, and to synthesize NaFePO4. Additionally, by employing I- as the reducing agent, NaFePO4 is successfully synthesized with a discharge-specific capacity of 134 mAh g-1 at 0.1C and a remarkable capacity retention rate of 86.5% after 100 cycles at 0.2C. And the reasons for sodium deficiency in the synthesized NFP are elucidated through first-principles calculations. Furthermore, the kinetics of the solid-solution reaction 2 (Na2/3+βPO4→ Na1-αFePO4) mechanism improve with cycling and are sensitive to temperature. Utilizing a minimal amount of reducing agent in the electrochemical reactor, NaFePO4 synthesis is successfully achieved. This innovative approach offers a new, cost-effective, and environmentally friendly strategy for preparing NaFePO4 from recycling LiFePO4.

P2-type layered oxide cathode with honeycomb-ordered superstructure for sodium-ion batteries

Sodium-ion batteries (SIBs) have been proved as one of the most alternative to Lithium-ion batteries (LIBs) by the virtue of the abundant resources of Na. Among the cathodes, layered oxides stand out owing to their high energy density. The Jahn–Teller distortion, structural phase transition and oxygen release are main drawbacks of Mn/Ni based layered oxides. Hence, Li-Ni-Cu co-substituted Na0.67Li0.1(Mn0.7Ni0.2Cu0.1)0.9O2 (NLMNC) sample was prepared. The NLMNC sample exhibits the honeycomb-ordered superstructure at about 22° which is ascribed to cation ordering. By virtue of the Li-Ni-Cu co-substitute, the Jahn–Teller distortion of Mn is suppressed. Attributed to Li+ migrating from the metal oxide layer to the interlayer and the Li+ can play the part of pillar in the interlayer, NLMNC cathode displays the capacity retention rate of 82.5 % at 200 mA g−1 after 100 cycles. The anionic redox reaction of NLMNC is related to the addition of Li ions and O 2p non-bonding which is different from the anionic redox reaction of electrons removing from O 2p in the eg* (Ni–O) states of Na2/3Ni1/3Mn2/3O2. During charge process, peroxo O− emerges with the oxidation of lattice oxygen. During discharge process, the intensity of peroxo O− gradually decreases. DFT calculations were also carried out to reveal the reaction mechanism of NLMNC. The DFT results showed that the anionic redox reaction occurs near Mn ions, while the Ni ions are stable which is corresponding with our results. It is proven that such Li-Ni-Cu co-substituted NLMNC presents a promising cathode material for SIBs.

Preparation of N-doped carbon-modified Na3V2(PO4)2F3 based on ZIF-8 as a template and its electrochemical properties

N-doped porous carbon material (N-PC) was generated through high-temperature cracking, using ZIF-8 as a template, and preparation of Na3V2(PO4)2F3/N-PC composites were designed and prepared as cathode materials for sodium-ion batteries, and the electrochemical sodium storage performance was systematically investigated. The physical characterization results showed that the addition of N-PC played a role in increasing the electrical conductivity of Na3V2(PO4)2F3 material and improving the specific surface area. The electrochemical test results showed that the discharge specific capacity of Na3V2(PO4)2F3/N-PC composite was 109.56 mAh/g at 0.1C, and the capacity retention rate was 85.10 % after 100 cycles, and the RSEI of Na3V2(PO4)2F3/N-PC composite (81.55 Ω) is better than that of Na3V2(PO4)2F3 pure-phase material (142.5 Ω), which indicates that the ion transfer impedance of the modified material has been effectively reduced, and the ion de-embedding is more fluent.

Compositing pine pollen derived carbon matrix with Na4FeV(PO4)3 nanoparticle for cost-effective sodium-ion batteries cathode

Na super-ion conductor type material Na3V2(PO4)3 has been widely researched as the cathode of sodium-ion batteries (SIBs) in recent years, but the unsatisfying cost of Na3V2(PO4)3 impedes its wide application in SIBs. In this study, iron element is used to replace part of vanadium in Na3V2(PO4)3 to reduce its expense, and pine pollen is applied for the first time as a very effective carbon source to improve the performance of Na4FeV(PO4)3. The fabricated composite material achieves a capacity of 105 mA h g−1 under 0.2 C and fascinating cycling stability over 94 % under 2 C for 500 cycles and 98 % under 10 C for 1000 cycles. The excellent cycle performance is caused by the involvement of pine pollen that acts as a carbon matrix to enhance the electron conductivity and block the agglomeration of active material effectively, thus the well-dispersed nano sized Na4FeV(PO4)3 shortens the diffusion path of sodium ion and gains a remarkable rate capability. Moreover, the distinguished reversibility during the charge and discharge procedures is ascribed also to the robust structure of Na4FeV(PO4)3. This work provides an efficient route to realize the economic cathode material of SIBs with good performance.