Cathode For Sodium-ion Batteries Research Articles

Pore-Free Single-Crystalline Particles for Durable Na-Ion Battery Cathodes.

The O3-type Na[Ni1-x-yCoxMny]O2 cathodes have received significant attention in sodium-ion batteries (SIBs) due to their high energy density. However, challenges such as structural instability and interfacial instability against an electrolyte solution limit their practical use in SIBs. In this study, the single-crystalline O3-type Na[Ni0.6Co0.2Mn0.2]O2 (SC-NCM) cathode has been designed and synthesized to effectively relieve the degradation pathways of the polycrystalline O3-type Na[Ni0.6Co0.2Mn0.2]O2 (PC-NCM) cathode for SIBs. The mechanically robust SC-NCM due to the absence of pores in the particles enhances tolerance to particle cracking, resulting in stable cycling performance with a cycle retention of 73% over 350 cycles. Moreover, the proposed SC-NCM is synthesized using a simple and cost-effective molten-salt synthetic route without the complex quenching process typically associated with PC-NCM synthesis methods, showing good practical applicability. This study will provide an innovative direction for the development of advanced cathode materials for practical SIBs.

Entropy Strategy for Stabilizing O′3-NaMnO2-Layered Cathodes for Sodium-Ion Batteries

Entropy Strategy for Stabilizing O′3-NaMnO₂-Layered Cathodes for Sodium-Ion Batteries

Understanding the Role of Mn Substitution for Boosting High-Voltage Na4Fe3-xMnx(PO4)2P2O7 Cathode in Sodium-Ion Batteries.

Na4Fe3(PO4)2P2O7 is regarded as the most promising polyanionic cathode for sodium-ion batteries (SIBs) due to its superior structural stability, cost-effectiveness, and environmental benignity. However, the low operating voltage inevitably weakens its competitiveness in energy density. Previous works have tried to enhance its operating voltage by Mn doping, which draws on the design idea of LiFexMn1-xPO4 cathode for lithium-ion batteries, but with little success. In this context, uncovering the role of Mn substitution in Na4Fe3-xMnx(PO4)2P2O7 (NFMxPP) cathode is urgently needed. This work discloses the effect of Mn contents on the structure, sodium storage property, and reaction mechanism of NFMxPP cathode for the first time. Introducing a moderate amount of Mn (0.6 ≤ x ≤ 1.2) into NFMxPP can weaken the Fe-O bonding interaction, thus leading to the full utilization of Mn3+/Mn2+ redox couple. As the representative, NFM1.2PP cathode exhibited a high operating voltage of ≈3.3V with a reversible capacity of 109.2 mAh g-1. Note that a Hard carbon||NFM1.2PP full battery manifests considerably high-capacity retention of 92.3% over 1600 cycles. It is believed that an understanding of the role of Mn substitution in this work will promote the practical application of high voltage NFMxPP cathodes for SIBs.

Preparation and application of high-performance sodium-ion batteries cathode material Na3.6Fe2.6(PO4)1.6P2O7 with optimized sodium-iron ratio

Na4Fe3(PO4)2P2O7 (NFPP) has been developed as the most promising polyanion cathode for sodium-ion batteries due to its excellent electrochemical performance, high safety properties, and environmental friendliness. However, the electrochemically inactive impurity (m-NaFePO4) will inevitably generate during synthesis process, which decreases the practical capacity of NFPP significantly. In this paper, a novel Na3.6Fe2.6(PO4)1.6P2O7 cathode material with excellent performance is successfully exploited by optimizing sodium-iron ratio to reduce the formation of impurity phases. In a series of as-prepared materials with sodium-iron ratio between 1.33–1.50, Na3.6Fe2.6(PO4)1.6P2O7 exhibits the highest discharge specific capacity (110.3 mAh g−1 at 0.1C), best rate capability (84.4 mAh g−1 at 30 C) and cycle performance (78.2 % capacity retention after 3000 cycles at 20 C). Furthermore, 20 Kg of the Na3.6Fe2.6(PO4)1.6P2O7 cathode material is prepared by spray drying method, which has been successfully applied in sodium-ion pouch cells (12 Ah) with a commercial hard carbon as the anode materials. The assembled pouch cells display excellent cycle performance (82.4 % capacity retention after 2000 cycles at 1 C), rate capability (88 % capacity retention at 30 C) and low-temperature performance (74 % capacity retention at −40 °C).

Crystal water-capturing and film-forming bifunctional electrolyte additive for stabilizing sodium iron hexacyanoferrate cathode for Na-ion batteries

Due to its affordability, strong structural stability, and high rate capability, rhombohedral sodium ferrous hexacyanoferrate (FeHCF) has been identified as a potential cathode material for sodium ion batteries. Nevertheless, the presence of inherent crystal water and the susceptibility of its interface stability significantly hinder its capacity and cycling performance. In this study, we propose a novel modification approach involving the addition of ZnCl2 to effectively capture crystal water and facilitate the in-situ formation of a ZnO coating on the FeHCF surface. Due to the decreased crystal water content and the presence of stable ZnO interphases, the occurrence of side reactions between the electrode and electrolyte, as well as crystal particle cracks in FeHCF during repeated sodiation/desodiation processes, is effectively reduced. Consequently, the modified FeHCF demonstrates an extended operational lifespan of 1000 cycles, with an initial discharge capacity of 112.0 mAh/g and a capacity retention rate of 77.8 % at a current rate of 1C within the voltage range of 2.0–4.2 V. Our research offers valuable insights into the removal of crystal water and the engineering of incident interfaces to enhance the cycle life of FeHCF cathodes in sodium-ion batteries.

Lithium substitution modulation of P2-type manganese-rich oxide toward high-stable and high-voltage cathode for sodium-ion batteries

P2-type manganese-rich layered oxide have attracted much attention as cathodes of sodium-ion batteries owing to the low cost, high capacity and fast sodium ion diffusion kinetics. However, the Jahn-Teller effect of Mn3+, P2-O2 phase transition and anionic redox on charging to the high-voltage, resulted in a severe capacity delay. Herein, an effective Li substitution strategy is proposed to suppress the Jahn-Teller effect of Mn3+, the harmful phase transition of P2-O2 and the anionic redox. As a result, the as-prepared sample Na0.67(Ni0.25Mn0.75)0.9Li0.1O2 (67L10) displays a discharge specific capacity of 168.6 mA h g−1 at 0.1 C, enhanced average working voltage, and improved cycling stability at 1 C after 200 cycles within 1.5–4.5 V voltage window (capacity retention of 83.3 %, specific capacity of 106.8 mA h g−1) compared with that of pristine Na0.67Ni0.25Mn0.75O2(capacity retention of 34.2 %, specific capacity of 51.3 mA h g−1). This work demonstrates the favorable effect of Li doping in P2-type layered materials to suppress the phase transition and inhibit the redox activity of Mn and O ions, and it provides an effective approach for the development of cathodes for sodium-ion batteries with high specific energy and long life.

Hollow Core-Shelled Na4Fe2.4Ni0.6(PO4)2P2O7 with Tiny-Void Space Capable Fast-Charge and Low-Temperature Sodium Storage.

Iron-based mixed polyanion phosphate Na4Fe3(PO4)2P2O7 (NFPP) is recognized as a promising cathode for Sodium-ion Batteries (SIBs) due to its low cost and environmental friendliness. However, its inherent low conductivity and sluggish Na+ diffusion limit fast charge and low-temperature sodium storage. This study pioneers a scalable synthesis of hollow core-shelled Na4Fe2.4Ni0.6(PO4)2P2O7 with tiny-void space (THoCS-0.6Ni) via a one-step spray-drying combined with calcination process due to the different viscosity, coordination ability, molar ratios, and shrinkage rates between citric acid and polyvinylpyrrolidone. This unique structure with interconnected carbon networks ensures rapid electron transport and fast Na+ diffusion, as well as efficient space utilization for relieving volume expansion. Incorporating regulation of lattice structure by doping Ni heteroatom to effectively improve intrinsic electron conductivity and optimize Na+ diffusion path and energy barrier, which achieves fast charge and low-temperature sodium storage. As a result, THoCS-0.6Ni exhibits superior rate capability (86.4 mAh g-1 at 25 C). Notably, THoCS-0.6Ni demonstrates exceptional cycling stability at -20 °C with a capacity of 43.6 mAh g-1 after 2500 cycles at 5 C. This work provides a universal strategy to design the hollow core-shelled structure with tiny-void space cathode materials for reversible batteries with fast-charge and low-temperature Na-storage features.

A Na-Free Surface Enables "Three-In-One" Enhancement of Structural, Interfacial and Air Stability for Sodium-Ion Battery Cathodes.

O3-type layered oxides are regarded as one of the most promising cathode materials for sodium-ion batteries. However, the multistep phase transitions, severe electrode/electrolyte parasitic reactions, and moisture sensitivity are challenging for their practical application because of the highly active Na+. Here, a Na-free layer is built on the surface of NaNi1/3Mn1/3Fe1/3O2 (NMF111) via a leaching treatment and the subsequent surface reconstruction. Accordingly, both the structural degradation from bulk to surface and the overgrowth of the solid electrolyte interface (SEI) are greatly ameliorated, which results in the improved capacity retention of modified NMF111 from 58.3% to 89.6% after 400 cycles at 1 C. Besides, the Na-free surface with rock-salt structure prevents the H+/Na+ exchange and then enables good reversibility and low polarization of the optimal NMF111 when exposed to wet air (50% RH) for 4 days. This work opens a new avenue for the comprehensive cyclability improvement of layered oxides via surface reconstruction.

Functional carbon dots induced defect configuration entropy strengthening polyanion cathode for ultrafast-charging sodium ion batteries in a wide temperature

The development of fast-charging and wide-temperature sodium-ion batteries (SIBs) is of great significance to all-climate energy storage. However, the gigantic challenge lies in achieving super dynamic performance and stability of cathode materials. Herein, the defect configuration entropy (DCE) is conceptualized in Na3V2(PO4)3/carbon composite (NVP/C) cathode by manipulating heteroatoms and vacancies in the surface carbon layer. It is found that the bonding energy between the carbon layer and NVP interface increases with the DCE. Accompanying, the Na+ migration energy barrier is reduced and the electronic conductivity is enhanced, which are pivotal factors underpinning the low-temperature performance. Furthermore, the increase of DCE engenders the formation of a NaF-rich cathode-electrolyte interface, furnishing support for high-temperature stability. As a result, the DCE-strengthened NVP/carbon composite cathode exhibits a high capacity of ∼88 mAh g−1 at an ultrahigh rate of 200 C (13 s per charge process). Moreover, the superior electrochemical performance in the wide temperature range of −30–60 °C is achieved with 0.101 % capacity decay per cycle at −20 ℃, and 0.0047 % capacity decay per cycle at 60 ℃.

Zr-doped O3-type NaNi1/3Fe1/3Mn1/3O2 cathodes with enhanced structure stability for sodium-ion batteries

O3-type NaTMO2 (TM = transition metal) is highly anticipated as a cathode for sodium-ion batteries due to its high theoretical specific capacity and low cost. However, the irreversible phase transition during sodiation/desodiation and the Jahn-Teller effect induced by Mn3+ have hindered its steps towards industrialization. Herein, we propose a doping strategy to enhance the structural stability of O3-type NaNi1/3Fe1/3Mn1/3O2 through Zr doping. On the one hand, the Na+ transport channels are broadened due to the enlarged layer spacing, which accelerates the kinetic processes. On the other hand, Zr doping maintains structural integrity, inhibiting the decay of the layered structure. As a result, the uniquely designed material NNFMZO-6000 exhibited a discharge specific capacity of 113.8 mAh g−1 at 1 C and a capacity retention of 67.54 % after 200 cycles. This work presents an effective modification method to optimize the properties of O3-type NaTMO2 materials.

Stable Cycling of Ultrahigh Mass Loaded MnO2 for Low-Cost Sodium-Ion Batteries

Achieving cost-effective and sustainable solutions for large-scale energy storage is critical for advancing the global clean energy transition. The intermittent nature of green energy underscores the inadequacy of current large scale energy storage technologies like pumped hydroelectricity which is susceptible to geographic and water resource constraints, making batteries a prime candidate for this role. Although lithium-ion batteries (LIBs) with high energy and power density are a viable solution, the high cost and uneven distribution of lithium reserves limits the widespread application of LIBs for grid energy storage. Considering these developments and the challenges posed by limited lithium reserves, sustainable and low-cost sodium-ion batteries (SIBs) emerge as a promising alternative.Among the various battery electrode materials, manganese dioxide (MnO2) stands out as a promising choice for large-scale energy storage applications due to its earth abundance, cost-effectiveness and non-toxic nature. Although MnO2 is known as a pseudocapacitive material with superior cycling stability in aqueous electrolytes, its dissolution in non-aqueous electrolytes has restricted its widespread use in long lifetime batteries. In this study, we demonstrate that an ether-based electrolyte solution (1M NaClO4 in diglyme) is able to achieve stable cycling of electrodeposited ε-MnO2 as a cathode for SIBs, reaching a over 75% capacity retention over 1000 cycles. This response surpasses conventional ester-based electrolytes (58% of 1M NaClO4 in EC/PC). A comparative cycling stability study, coupled with electrochemical quartz crystal microbalance characterization, validates the efficacy of the ether-based electrolyte in mitigating MnO2 dissolution. Furthermore, the integration of 3D printed graphene aerogel (3D GA) as a scaffold for electrodeposited MnO2 leads to enhanced electrochemical performance of the MnO2 electrode (3D MnO2/GA), resulting in a high areal capacity of 4.4 mAh cm-2 at a current density of 10 mA cm-2. The 3D MnO2/GA electrode possesses scalable electrochemical performance with mass loadings from 20 mg cm-2 to 80 mg cm-2. Using this electrode, a high mass loaded sodium-ion battery (SIB) device was fabricated by using utilizing 58 mg cm-2 3D MnO2/GA as the cathode and 16 mg cm-2 dip-coated TiO2@Cu foam as the anode. This MnO2 | TiO2 device delivered a notable areal capacity of 6.2 mWh cm-2 and a high areal power density of 70.7 mW cm-2. Moreover, the SIB device demonstrates 85% capacity retention after 500 cycles, underscoring the stable cycling of this high-energy and power-density SIB device.

One-Pot Aqueous Spray Drying of Hierarchical Na3V2(PO4)3 (NVP) Particles for High-Performance Sodium-Ion Batteries

Sodium-ion batteries (NIBs) have been recognized as a promising alternative to lithium-ion batteries (LIBs), especially for stationary large-scale applications that favor inexpensive storage over high energy density, as their cathode materials don’t require scarce and expensive elements such as Li, Co, and Ni.1,2 Na3V2(PO4)3 (NVP) offers high ionic conductivity and long term stability due to its sodium super ionic conductor (NASICON) structure3. However, it suffers from poor electronic conductivity and requires energy-intensive synthesis routes4. Spray drying has recently become a common energy-effective route but requires organic solvents5 or complex carbon additives6. In this study, a more efficient and sustainable aqueous spray-drying method is presented to synthesize carbon-coated NVP by using L-ascorbic acid as a carbon source. Additionally, the role of conductive additives is explored in low-carbon samples. NVP sodium-ion half cells showed very high reversible capacity (114.7 mAh g-1 at 0.2C), high rate capability (80.8% capacity retention at 30C), and long cycling performance (93.8% capacity retention after 5000 cycles at 10C). The exceptional cycle life makes it a promising candidate for grid level energy storage. Furthermore, if configured without an intercalation anode material, the "host-free" NVP cells hold the promise to substitute the widely used LiFePO4 batteries for EV applications7. References (1) Liu, J. Addressing the Grand Challenges in Energy Storage. Advanced Functional Materials. February 25, 2013, pp 924–928. https://doi.org/10.1002/adfm.201203058.(2) Schneider, S. F.; Bauer, C.; Novák, P.; Berg, E. J. A Modeling Framework to Assess Specific Energy, Costs and Environmental Impacts of Li-Ion and Na-Ion Batteries. Sustain Energy Fuels 2019, 3 (11), 3061–3070. https://doi.org/10.1039/c9se00427k.(3) Zhang, X.; Rui, X.; Chen, D.; Tan, H.; Yang, D.; Huang, S.; Yu, Y. Na 3 V 2 (PO 4 ) 3 : An Advanced Cathode for Sodium-Ion Batteries. Nanoscale. Royal Society of Chemistry February 14, 2019, pp 2556–2576. https://doi.org/10.1039/c8nr09391a.(4) Tang, X.; Ding, H.; Teng, J.; Zhao, H.; Li, J.; Zhang, K. Green and Scalable Synthesis of Na3V2(PO4)3 Cathode and the Study on the Failure Mechanism of Sodium-Ion Batteries. ACS Appl Energy Mater 2023, 6 (16), 8443–8454. https://doi.org/10.1021/acsaem.3c01195.(5) Pi, Y.; Gan, Z.; Li, Z.; Ruan, Y.; Pei, C.; Yu, H.; Han, K.; Ge, Y.; An, Q.; Mai, L. Methanol-Derived High-Performance Na3V2(PO4)3/C: From Kilogram-Scale Synthesis to Pouch Cell Safety Detection. Nanoscale 2020, 12 (41), 21165–21171. https://doi.org/10.1039/d0nr04884d.(6) Zhang, J.; Fang, Y.; Xiao, L.; Qian, J.; Cao, Y.; Ai, X.; Yang, H. Graphene-Scaffolded Na3V2(PO4)3 Microsphere Cathode with High Rate Capability and Cycling Stability for Sodium Ion Batteries. ACS Appl Mater Interfaces 2017, 9 (8), 7177–7184. https://doi.org/10.1021/acsami.6b16000.(7) Ma, B.; Lee, Y.; Bai, P. Dynamic Interfacial Stability Confirmed by Microscopic Optical Operando Experiments Enables High-Retention-Rate Anode-Free Na Metal Full Cells. Advanced Science 2021, 8 (12). https://doi.org/10.1002/advs.202005006. Figure 1

Synthesis Strategies for Highly Stable Sodium and Potassium Manganese Hexacyanoferrates

Sodium- and potassium-ion batteries (NIBs and KIBs) have been recognized as a promising alternative to lithium-ion batteries (LIBs), especially for stationary grid-scale applications that favor inexpensive storage over high energy density.1 NASICON-structured phosphates and alluaudite sulfates offer cheap synthesis routes but demonstrate low energy density2,3. Layered oxides can provide a higher energy density but require complex synthesis routes and degrade quickly4. Prussian Blue Analogues (PBAs) benefit from facile precipitation synthesis, flat voltage plateaus, and specific capacities greater than 150 mAh g-1.5 However, capacity fading due to Jahn-Teller distortion, manganese dissolution, and residual interstitial water limit their cycle life6,7. In this study, synthesis parameters and post-synthesis treatment of Na2Mn[Fe(CN)6] and K2Mn[Fe(CN)6] are discussed. Furthermore, the addition of solubilized conductive carbon additives to synthesis solutions, both to enhance electronic conductivity and provide a flexible framework to reduce strain during cycling, is explored. Na2Mn[Fe(CN)6] electrodes demonstrate a specific capacity of 149.6 mAh g-1 and surpass 250 cycles at 1C before dipping below 80% capacity retention. K2Mn[Fe(CN)6] electrodes demonstrate a specific capacity of 155.1 mAh g-1 with negligible capacity fading over the first 50 cycles at 0.1C. Our results indicate that lowering the temperature during synthesis improves morphology and cycling performance even when a chelating agent is used to control the reaction speed. References (1) Liu, J. Addressing the Grand Challenges in Energy Storage. Advanced Functional Materials. February 25, 2013, pp 924–928. https://doi.org/10.1002/adfm.201203058.(2) Zhang, X.; Rui, X.; Chen, D.; Tan, H.; Yang, D.; Huang, S.; Yu, Y. Na 3 V 2 (PO 4 ) 3 : An Advanced Cathode for Sodium-Ion Batteries. Nanoscale. Royal Society of Chemistry February 14, 2019, pp 2556–2576. https://doi.org/10.1039/c8nr09391a.(3) Niu, Y.; Zhao, Y.; Xu, M. Manganese‐based Polyanionic Cathodes for Sodium‐ion Batteries. Carbon Neutralization 2023, 2 (2), 150–168. https://doi.org/10.1002/cnl2.48.(4) Xiao, J.; Li, X.; Tang, K.; Wang, D.; Long, M.; Gao, H.; Chen, W.; Liu, C.; Liu, H.; Wang, G. Recent Progress of Emerging Cathode Materials for Sodium Ion Batteries. Materials Chemistry Frontiers. Royal Society of Chemistry May 21, 2021, pp 3735–3764. https://doi.org/10.1039/d1qm00179e.(5) Wang, Q.; Li, J.; Jin, H.; Xin, S.; Gao, H. Prussian-Blue Materials: Revealing New Opportunities for Rechargeable Batteries. InfoMat. John Wiley and Sons Inc June 1, 2022. https://doi.org/10.1002/inf2.12311.(6) Shang, Y.; Li, X.; Song, J.; Huang, S.; Yang, Z.; Xu, Z. J.; Yang, H. Y. Unconventional Mn Vacancies in Mn–Fe Prussian Blue Analogs: Suppressing Jahn-Teller Distortion for Ultrastable Sodium Storage. Chem 2020, 6 (7), 1804–1818. https://doi.org/10.1016/j.chempr.2020.05.004.(7) Ge, J.; Fan, L.; Rao, A. M.; Zhou, J.; Lu, B. Surface-Substituted Prussian Blue Analogue Cathode for Sustainable Potassium-Ion Batteries. Nat Sustain 2022, 5 (3), 225–234. https://doi.org/10.1038/s41893-021-00810-7.

Improved Electrochemical Performance of NASICON Type Na3V2-xCox(PO4)3/C (x = 0-0.15) Cathode for High Rate and Stable Sodium-Ion Batteries.

In recent years, the Na-ion SuperIonic CONductor (NASICON) based polyanionics are considered pertinent cathode materials in sodium-ion batteries due to their 3D open framework, which can accommodate a wide range of Na content and can offer high ionic conductivity with great structural stability. However, owing to the inferior electronic conductivity, these materials suffer from unappealing rate capability and cyclic stability for practical applications. Therefore, in this work we investigate the effect of Co substitution at the V site on the electrochemical performance and diffusion kinetics of Na3V2-xCox(PO4)3/C (x = 0-0.15) cathodes. All the samples are characterized through Rietveld refinement of the X-ray diffraction patterns, Raman spectroscopy, transmission electron microscopy, etc. We demonstrate improved electrochemical performance for the x = 0.05 electrode with a reversible capacity of 105 mAh g-1 at 0.1 C. Interestingly, the specific capacity of 80 mAh g-1 is achieved at 10 C with retention of about 92% after 500 cycles and 79.5% after 1500 cycles and having nearly 100% Coulombic efficiency. The extracted diffusion coefficient values through the galvanostatic intermittent titration technique and cyclic voltammetry are found to be in the range of 10-9 to 10-11 cm2 s-1. The post-mortem studies show excellent structural and morphological stability after testing for 500 cycles at 10 C. Our study reveals the role of optimal dopant of Co3+ ions at the V site in improving the cyclic stability at a high current rate.

Unraveling the Role of Li and Mg Substitution in Layered Sodium Oxide Cathodes for Sodium-Ion Batteries.

Substituting electrochemically active elements such as Li and Mg in P2-type layered sodium oxide is an effective strategy for developing competitive cathode materials for sodium-ion batteries. However, the lack of atomic-level understanding regarding the distribution of substitution positions complicates the comprehension of the roles of substituting atoms and the mechanism of sodium-ion intercalation. In this study, we identified the stable configurations of Na in Na0.75Ni0.3Mn0.7O2 and Na0.75Li0.15Mg0.05Ni0.1Mn0.7O2 materials using the site exclusion method. Through simulating the complete charging process for both materials, the structure evolution of the cathodes during the cycling and the impact of the partial substitution of Ni elements by Li and Mg atoms were comprehensively elucidated. Our findings revealed that Mg atoms effectively regulate the distribution of forces within the materials, essentially serving as supportive pillars within the cathode. Meanwhile, Li atoms efficiently mitigated electron localization, consequently diminishing volume fluctuations during the charging process. More importantly, the substitution with Li and Mg atoms could synergistically reduce the interaction between transition metals and sodium ions, thereby reducing the diffusion energy barrier of Na ions. This study not only enhances the comprehension of substituted metal atoms in P2 layered oxides but also offers new insights for the development of sodium-ion cathode materials.

Dehydration Achieving the Iron Spin State Regulation of Prussian Blue for Boosted Sodium-Ion Storage Performance.

Prussian blue analogs (PBAs) show promise as cathodes for sodium-ion batteries due to their notable cycle stability, cost-effectiveness, and eco-friendly nature, yet the presence of interstitial water limits the specific capacity and obstructs Na+ mobility within the material. Although considerable experimental efforts are focused on dehydrating water for capacity enhancement, there is still a deficiency of a comprehensive understanding of the low capacity of low-spin Fe resulting from interstitial water, which holds significance in Na+ storage. This study introduces a novel gas-assisted heat treatment method to efficiently remove interstitial water from Fe-based PBA (NaFeHCF) electrodes and combines experiments and theoretical calculations to reveal the iron spin state regulation that is related to the capacity enhancement mechanism. This dehydration strategy significantly enhances battery capacity, especially the portion at higher voltages (3.4-4.0V). The increase in capacity is attributed to the following factors: an enhanced proportion of Fe2+, reduced water content which facilitates faster charge transfer, and the activation of low spin Fe2+. The optimized NaFeHCF demonstrated impressive half-cell performance of retaining 87.3% capacity after 2000 cycles at a 5C rate and achieving 100mAhg-1 capacity over 200 cycles when being paired with hard carbon, exhibiting its practical potential.

A scalable approach to Na4Fe3(PO4)2P2O7@carbon/expanded graphite as cathode for ultralong-lifespan and low-temperature sodium-ion batteries

A scalable approach to Na4Fe3(PO4)2P2O7@carbon/expanded graphite as cathode for ultralong-lifespan and low-temperature sodium-ion batteries

Ribbon-Ordered Superlattice Enables Reversible Anion Redox and Stable High-Voltage Na-Ion Battery Cathodes.

High-voltage layered oxide cathodes attract great attention for sodium-ion batteries (SIBs) due to the potential high energy density, but high voltage usually leads to rapid capacity decay. Herein, a stable high-voltage NaLi0.1Ni0.35Mn0.3Ti0.25O2 cathode with a ribbon-ordered superlattice is reported, and the intrinsic coupling mechanism between structure evolution and the anion redox reaction (ARR) is revealed. Li introduction constructs a special Li-O-Na configuration activating reversible nonbonded O 2p (|O2p)-type ARR and regulates the structure evolution way, enabling the reversible Li ions out-of-layer migration instead of the irreversible transition metal ions out-of-layer migration. The reversible structure evolution enhances the reversibility of the bonded O 2p (O2p)-type ARR and inhibits the generation of oxygen dimers, thus suppressing the irreversible molecular oxygen (O2)-type ARR. After the structure regulation, the structure evolution becomes reversible, |O2p-type ARR is activated, O2p-type ARR becomes stable, and O2-type ARR is inhibited, which largely suppresses the capacity degradation and voltage decay. The discharge capacity is increased from 154 to 168 mA h g-1, the capacity retention after 200 cycles significantly increases from 35 to 84%, and the voltage retention increases from 78 to 93%. This study presents some guidance for the design of high-voltage, O3-type oxide cathodes for high-performance SIBs.

Conjugated layered and tunnel structure enables long-lifespan and high-rate sodium-ion battery cathodes

A cathode material Na0.42Mn0.96Ti0.04O2 with conjugated layered and tunnel structures was synthesized via a convenient solid-state method. The designed conjugated structure enables superior electrochemical properties such as 93.9% capacity retention after 200 cycles at 1 C and excellent rate capability with a reversible capacity of 83.9 mAh g−1 at 20 C.

La-doped O3-type layered oxide cathode with enhanced cycle stability for sodium-ion batteries

Despite the considerable potential of O3-type layered oxide cathodes in sodium-ion batteries due to their high theoretical capacities, the rapid capacity degradation caused by high Na+ diffusion barriers and irreversible phase transitions seriously hampers their practical application. Herein, we propose the La-doping strategy in O3-type layered oxide to decrease diffusion barriers and strengthen transition metal–oxygen (TM-O) bonds, thereby significantly improving the electrochemical performance. The strong La-O bonding facilitates highly reversible O3-P3 phase transitions during (de)sodiation and enhances the stability of lattice oxygen at high voltages. Specifically, the La-doped O3-type oxide exhibits impressive cycling stability, with the capacity retention increasing from 63 % to 80 % after 500 cycles at 1C. The full cell assembly with La-doped oxide as cathode and hard carbon as anode demonstrates a high energy density of 323.7 Wh kg−1 at 0.1C, with a capacity retention of 74.6 % after 300 cycles at 1C. This work provides new insights in La-doping to promote the commercial application of O3-type cathodes for sodium ion batteries.