Sodium-ion Batteries Research Articles

A Cross-Linked Polymer Coating Strategy to Enhance the Performance of NaNi0.33Fe0.33Mn0.33O2 Cathode for Sodium-Ion Batteries.

O3-type layered oxide materials are regarded as optimal cathode candidates for sodium-ion batteries (SIBs) on account of their exceptional energy density. Nevertheless, the rapid decline in capacity resulting from the instability of the interface structure represents a significant challenge to the practical implementation of these materials. In this study, we propose an innovative method to modify the O3-type NaNi0.33Fe0.33Mn0.33O2 (NFM) cathode material by applying a cross-linked polymer (CLP) coating. X-ray photoelectron spectroscopy (XPS) analysis demonstrates that the CLP coating effectively inhibits the decomposition of the cathode electrolyte interface (CEI) membrane in the course of cycling, leading to a substantial improvement in the stability of the electrode material's interface. Moreover, the oxygen-containing groups within the coating can compete with propylene carbonate (PC) solvent molecules in the electrolyte for Na+ coordination, reducing the coordination between Na+ and PC molecules. This process facilitates more efficient diffusion of Na+, thereby enhancing the rate performance. Consequently, CLP-coated NFM (NFM@CLP) materials exhibit enhanced electrochemical performance. After 300 cycles at 25 °C, NFM@CLP retains 72.36% of its capacity, compared to 62.59% for pristine NFM. Even at elevated temperatures (65 °C), the capacity retention of NFM@CLP remains high at 63.84% after 200 cycles, whereas pristine NFM drops to 3.65%. In full-cell tests (vs hard carbon), the NFM@CLP also exhibits better capacity retention (85.07% after 150 cycles). This study offers an effective and simple approach to enhancing the capacity retention and rate performance of O3-type layered materials in SIBs, providing unique insights into advanced energy storage materials.

Spray-Drying Synthesis of Na4Fe3(PO4)2P2O7@CNT Cathode for Ultra-Stable and High-Rate Sodium-Ion Batteries

Iron-based phosphate is a promising cathode for sodium-ion batteries due to its low cost and abundant resources; however, the practical application is hindered by poor electronic conductivity, sluggish Na+ diffusion, and a lack of low-cost and scalable synthesis methods. To address such issues, herein, we present a low-cost and scalable spray-drying strategy to synthesize Na4Fe3(PO4)2P2O7@CNT (NFPP@CNT) hollow microspheres. The NFPP@CNT composite has the following advantages: highly conductive CNT can significantly improve the electronic conductivity of the cathode, and the flexible CNT-based microsphere architecture facilitates Na+ diffusion and guarantees excellent mechanical properties to mitigate structural degradation during cycling. These merits make the NFPP@CNT cathode display outstanding electrochemical performances: the NFPP@CNT-1% electrode demonstrates a high reversible capacity of 103.9 mAh g−1 at 0.1 C and maintains a very high capacity retention of 99.9% after 1000 cycles even at a high rate of 5 C.

Mn Dopant Na3Zr2Si2PO12 with Enhanced Ionic Conductivity for Quasi-Solid-State Sodium-Metal Battery.

As a promising solid electrolyte, the NASICON-type Na3Zr2Si2PO12 holds excellent application in solid-state sodium-ion batteries, which are an alternative to lithium batteries. However, its insufficient conductivity is one of the key factors impeding its applications. Herein, we report Mn2+-doped Na3Zr2Si2PO12, demonstrating enhanced ionic conductivity and electrochemical properties. We systematically investigate the effect of doping content on the ionic conductivity. The results show that Na3.4Zr1.8Mn0.2Si2PO12 has an extremely high room-temperature ionic conductivity of 3.3 mS cm-1, which is 4 times that of undoped Na3Zr2Si2PO12. According to the Meyer-Nedle rule, it can be known that as the activation energy decreases, the ionic conductivity shows a gradually increasing trend. Additionally, the Na symmetric batteries using Mn2+-doped Na3Zr2Si2PO12 exhibit improved cycling performance. The quasi-solid-state sodium-metal battery using Na3V2(PO4)3 achieves a high discharge specific capacity of 91.3 mAh g-1 at 0.1C, with a high capacity retention of 92.2% after 260 cycles, far surpassing the counterpart based on undoped Na3Zr2Si2PO12. This work provides an effective strategy for enhancing the performance of Na3Zr2Si2PO12 for its application in sodium-metal batteries.

An interfacial compatible Ti4P8S29 polysulfide cathode with open channels for high-rate solid-state polymer sodium batteries

An interfacial compatible Ti4P8S29 polysulfide cathode with open channels for high-rate solid-state polymer sodium batteries

Composite Polymer Solid Electrolytes for All-Solid-State Sodium Batteries.

Sodium-ion batteries (SIBs) are emerging as a promising alternative to lithium-ion batteries, primarily due to their plentiful raw materials and cost-effectiveness. However, the use of traditional organic liquid electrolytes in sodium battery applications presents significant safety risks, prompting the investigation of solid electrolytes as a more viable solution. Despite their advantages, single solid electrolytes encounter challenges, including low conductivity of sodium ions at room temperature and incompatibility with electrode materials. To overcome these limitations, the researchers develop composite polymer solid electrolytes (CPSEs), which merge the strengths of high ionic conductivity of inorganic solid electrolytes and the flexibility of polymer solid electrolytes. CPSEs are usually composed of inorganic materials dispersed in the polymer matrix. The final performance of CPSEs can be further improved by optimizing the particle size, relative content, and form of inorganic fillers. CPSEs show great advantages in improving ionic conductivity and interface compatibility, making them an important direction for future solid-state sodium battery research. Therefore, this paper summarizes recent advancements in composite solid electrolytes, discusses the impact of their preparation processes on performance, and outlines potential future developments in sodium-ion solid-state batteries.

The Role of Fluorine in Polyanionic Cathode Materials for Sodium-Ion Batteries.

With the growing global demand for renewable energy and the increasing scarcity of lithium resources, sodium-ion batteries have received extensive attention and research as a potential alternative. Among many cathode materials for sodium-ion batteries, polyanion materials are favored for their high operating voltage, stable cycling performance, and good safety. However, the low electronic conductivity and low energy density of polyanionic materials limit their potential for large-scale commercial applications. To overcome this challenge, various strategies have been explored to improve their electrochemical performance. Among them, fluorine doping has been proven to be an effective means. In this study, we have systematically explored the effects of trace fluorine doping and mass fluorine substitution on the structure, dynamics, and electrochemistry of polyanionic cathode materials for sodium-ion batteries and deeply analyzed their reaction mechanisms. The analysis results show that trace fluorine doping can effectively improve the electronic conductivity of the material, thus enhancing its electrochemical performance. A large amount of fluorine substitution can effectively improve the voltage plateau of the material, thus enhancing its energy density. However, the environmental and safety challenges associated with the introduction of fluorine should also be addressed. Overall, the introduction of fluorine in polyanionic cathode materials can further optimize the electronic structure and electrochemical performance, thus realizing the wide application of high-performance sodium-ion batteries and making them a competitive battery technology.

Anionic-Based Layered Oxide Cathodes with High Electrochemical Performance through Dual-Site Substitutions for Sodium-Ion Batteries.

Mn-rich layered oxide cathodes with anionic redox promise high energy density for sodium-ion batteries (SIBs) due to ultra-high capacity derived from both Mn and O redox couples. Nevertheless, instability of the reactions that lead to poor electrochemical stability hinders the cathodes from practical applications. Here, the Al and Zn dual-site substitution strategy is proposed to enhance electrochemical performance. The designed cathode, Na0.73Zn0.03Li0.25Mn0.76Al0.01O2 (AlZn), delivers a high discharge capacity of 242 mAh g-1 with an impressive rate capability (162 mAh g-1 at 1000 mA g-1) and excellent capacity retention (89.69% over 150 cycles). In addition, full-cell SIB based on AlZn coupled with hard carbon exhibits a high energy density of 317 Wh kg-1 (based on both cathode and anode mass) and a reasonable capacity retention of 80.8% after 250 cycles. Revealed by advanced investigations, the synergy of robust Al-O in TM layers and O-Zn-O pillars in Na layers helps alleviate severe inactive spinel/rock-salt phase transformation and intragranular cracks in the AlZn cathode. This consequently leads to greatly enhanced electrochemical performance over the pristine cathode. This work provides insight into improving electrochemical properties of anionic-redox-based layered oxides by Al/Zn co-substitutions toward high-energy SIBs.

Intrinsic Distortion Against Jahn‐Teller Distortion: A New Paradigm for High‐Stability Na‐Ion Layered Mn‐Rich Oxide Cathodes

Layered manganese‐rich oxides (LMROs) are widely recognized as the leading cathode candidates for grid‐scale sodium‐ion batteries (SIBs) owing to their high specific capacities and cost benefits, but the notorious Jahn‐Teller (J‐T) distortion of Mn3+ always induces severe structural degradation and consequent rapid cathode failure, impeding the practical implementation of such materials. Herein, we unveil the "intrinsic distortion against J‐T distortion" mechanism to effectively stabilize the layered frameworks of LMRO cathodes. The intrinsic distortion simply constructed by introducing bulk oxygen vacancies is systematically confirmed by advanced synchrotron X‐ray techniques, atomic‐scale imaging characterizations, and theoretical computations, which can counteract the J‐T distortion during cycling due to their opposite deformation orientations. This greatly decreases and uniformizes the lattice strain within the ab plane and along the c axis of the material, thereby alleviating the P2‐P'2 phase transition as well as suppressing the edge dislocation and intragranular crack formation upon repeated cycles. As a result, the tailored P2‐Na0.72Mg0.1Mn0.9O2 cathode featuring intrinsic distortion delivers a considerably enhanced cycling durability (91.9% capacity retention after 500 cycles) without sacrificing the Mn3+/Mn4+ redox capacity (186.5 mAh g‐1 at 0.3 C). This intrinsic distortion engineering paves a brand‐new and prospective avenue toward achieving high‐performance LMRO cathodes for SIBs.

Stabilizing Cathode‐Electrolyte Interface by Low‐Cost Ethyl Methylsulfone Co‐Solvent for High‐Voltage Sodium‐ion Batteries

Raising the upper cut‐off voltage of cathode is an effective method to improve the energy density of sodium‐ion batteries (SIBs). However, the high upper cut‐off voltage could cause severe side reactions and injure the cycle life of SIBs as the absence of stable cathode‐electrolyte interface. Some fluorinated co‐solvents have been ever employed and proven effective in stabilizing the cathode‐electrolyte interface to support the normal operation of SIBs under a high upper cut‐off voltage. However, the high‐cost of fluorinated co‐solvents would notably improve battery expenses. In this study, a low‐cost co‐solvent called ethyl methylsulfone (EMS) is introduced into the electrolyte for the Na0.67Mn0.8Cu0.2O2 cathode with a high upper cut‐off voltage of 4.5 V. It is found that a stable and uniform cathode‐electrolyte interface (CEI) forms on the cathode, which mitigates the cathode degradation and enhances the cycling stability of cathode. Consequently, this cathode with the designed electrolyte achieves a high capacity retention of 83.2% after 750 cycles at a current density of 1 C (1 C=110 mAh g‐1). This work provides valuable insights into the development of electrolytes for sodium‐ion batteries working at high‐voltage.

Stable Na+ Ion Storage via Dual Active Sites Utilization in Covalent Organic Framework-Carbon Nanotube Composite.

Redox-active covalent organic frameworks (COFs) with metal binding sites are increasingly recognized for developing cost-effective, eco-friendly organic electrodes in rechargeable energy storage devices. Here, we report a microwave-assisted synthesis and characterization of a triazine-based polyimide COF that features dual redox-active sites (-C=O from pyromellitic and -C=N- from triazine) and COF@CNT nanocomposites (COF@CNT-X, where X=10, 30, and 50 wt % of NH2-MWCNT) formed through covalent linking with amino-functionalized multiwalled carbon nanotubes. These composites are evaluated as cathode materials for the sodium-ion batteries (SIBs). The amine functionalization renders the covalent bond between COF and CNT, improving electronic conductivity, structural rigidity, and long-term stability. The interfacial growth of COF layers on CNTs increases accessible redox-active sites, enhancing sodium diffusion kinetics during sodiation/desodiation. The COF@CNT-50 composite exhibits outstanding Na+ ion storage performance (reversible capacity of 164.3 mAh g-1 at 25 mA g-1) and excellent stability over 1000 cycles at ambient temperature. At elevated temperature (65 °C), it also maintains good capacity and cycle stability. Ex situ XPS analysis confirms the importance of dual active sites in the Na+ diffusion mechanism. Density functional theory (DFT) calculations reveal insights into Na+ binding sites and corresponding binding energies into COF structure, elucidating the experimental storage capacity and voltage profile.

Intrinsic Distortion Against Jahn-Teller Distortion: A New Paradigm for High-Stability Na-Ion Layered Mn-Rich Oxide Cathodes.

Layered manganese-rich oxides (LMROs) are widely recognized as the leading cathode candidates for grid-scale sodium-ion batteries (SIBs) owing to their high specific capacities and cost benefits, but the notorious Jahn-Teller (J-T) distortion of Mn3+ always induces severe structural degradation and consequent rapid cathode failure, impeding the practical implementation of such materials. Herein, we unveil the"intrinsic distortion against J-T distortion"mechanism to effectively stabilize the layered frameworks of LMRO cathodes. The intrinsic distortion simply constructed by introducing bulk oxygen vacancies is systematically confirmed by advanced synchrotron X-ray techniques, atomic-scale imaging characterizations, and theoretical computations, which can counteract the J-T distortion during cycling due to their opposite deformation orientations. This greatly decreases and uniformizes the lattice strain within the ab plane and along the c axis of the material, thereby alleviating the P2-P'2 phase transition as well as suppressing the edge dislocation and intragranular crack formation upon repeated cycles. As a result, the tailored P2-Na0.72Mg0.1Mn0.9O2 cathode featuring intrinsic distortion delivers a considerably enhanced cycling durability (91.9% capacity retention after 500 cycles) without sacrificing the Mn3+/Mn4+ redox capacity (186.5 mAh g-1 at 0.3 C). This intrinsic distortion engineering paves a brand-new and prospective avenue toward achieving high-performance LMRO cathodes for SIBs.

High-Energy, High-Power Sodium-Ion Batteries from a Layered Organic Cathode.

Sodium-ion batteries (SIBs) attract significant attention due to their potential as an alternative energy storage solution, yet challenges persist due to the limited energy density of existing cathode materials. In principle, redox-active organic materials can tackle this challenge because of their high theoretical energy densities. However, electrode-level energy densities of organic electrodes are compromised due to their poor electron/ion transport and severe dissolution. Here, we report the use of a low-bandgap, conductive, and highly insoluble layered metal-free cathode material for SIBs. It exhibits a high theoretical capacity of 355 mAh g-1 per formula unit, enabled by a four-electron redox process, and achieves an electrode-level energy density of 606 Wh kg-1electrode (90 wt % active material) along with excellent cycling stability. It allows for facile two-dimensional Na+ diffusion, which enables a high intrinsic rate capability. Growth of the active cathode material in the presence of as little as 2 wt % carboxyl-functionalized carbon nanotubes improves charge transport and charge transfer kinetics and further enhances the power performance. Altogether, these allow the construction of SIB cells built from an affordable, sustainable organic small molecule, which provide a cathode energy density of 472 Wh kg-1electrode when charging/discharging in 90 s and a top specific power of 31.6 kW kg-1electrode.

Insights into the Redox Chemistry and Structural Evolution of a P2-Type Cathode Material in Sodium-Ion Batteries

Insights into the Redox Chemistry and Structural Evolution of a P2-Type Cathode Material in Sodium-Ion Batteries

Role of metal-organic frameworks (MOFs) in electrochemical energy storage devices including batteries and supercapacitors

Abstract Better energy storage systems are becoming more and more in demand as electric cars, portable electronics, and renewable energy sources become more prevalent. Supercapacitors and batteries, such as lithium-ion batteries (LIBs), sodium-ion batteries (NIBs), lithium sulfur/air batteries, and lithium selenium batteries, are major components of these technologies; yet, stability, cycle life, and energy density are some of the challenges they face. MOFs have emerged as a new material that can solve the problems with unique structural properties. Large surface area and porosity are properties of MOFs which improve the energy density, life cycle and stability of energy storage devices when MOF are used as alectrode material in these devices.This paper analyzes and focuses on the application of MOFs in supercapacitors, LIBs, and SIBs, in which it emphasizes improvement in terms of stability and performance. This review article ends with an overview of the important challenges and the prospects for future research to fully meet the promise of Metal organic frameworks in energy storage applications.

In Situ TEM Characterization of Battery Materials.

Transmission electron microscopy (TEM) is an indispensable analytical technique in materials research as it probes material information down to the atomic level and can be utilized to examine dynamic phenomena during material transformations. In situ TEM resolves transient metastable states via direct observation of material dynamics under external stimuli. With innovative sample designs developed over the past decades, advanced in situ TEM has enabled emulation of battery operation conditions to unveil nanoscale changes within electrodes, at interfaces, and in electrolytes, rendering it a unique tool to offer unequivocal insights of battery materials that are beam-sensitive, air-sensitive, or that contain light elements, etc. In this review, we first briefly outline the history of advanced electron microscopy along with battery research, followed by an introduction to various in situ TEM sample cell configurations. We provide a comprehensive review on in situ TEM studies of battery materials for lithium batteries and beyond (e.g., sodium batteries and other battery chemistries) via open-cell and closed-cell in situ TEM approaches. At the end, we raise several unresolved points regarding sample preparation protocol, imaging conditions, etc., for in situ TEM experiments. We also provide an outlook on the next-stage development of in situ TEM for battery material study, aiming to foster closer collaboration between in situ TEM and battery research communities for mutual progress.

Designing Crystalline/Amorphous NVNPF/NCK Cathode Toward High-Performance Fully-Printed Flexible Aqueous Rechargeable Sodium-Ion Batteries (ARSIBs).

The flexible ARSIBs have great potential in portable and wearable electronics due to their high cost-effectiveness, safety, and amazing flexibility. Nevertheless, achieving both outstanding flexibility and high energy density remains a challenge. Herein, a battery-supercapacitor composite material Na3V1.95Ni0.05(PO4)2F3/10%NC-KOH (NVNPF/NCK) with coexistence of crystalline and amorphous phases is fabricated by loading nitrogenous carbon (NC) onto Na3V1.95Ni0.05(PO4)2F3 (NVNPF) and etching with KOH. It demonstrates high specific capacity (187.26 mAh g-1), ultrahigh energy density (262.16Wh kg-1), and excellent cycle performance (the capacity retention is 81% at 1 C after 500 cycles). The high performance is achieved by doping Ni2⁺loading NC and etching with KOH, which generates vacancy defects, enhances structural stability, and accelerates ion-diffusion kinetics. Furthermore, the fully-printed ARSIBs (F-NTP//NVNPF/NCK) with high specific capacity (60.37 mAh g-1), amazing energy density (72.44Wh kg-1), and excellent cycle performance, are fabricated using screen-printing technique based on the NVNPF/NCK cathode and NaTi1.7Fe0.3(PO4)3 (F-NTP) anode. To the best of the authors' knowledge, F-NTP//NVNPF/NCK is the highest-performing fully-printed flexible ARSIB to date. In particular, these batteries can achieve tunability in shape and size, integration, and high-throughput manufacturing. Thus, this work can offer greater possibilities for the development of high-performance flexible ARSIBs.

Continuous-Flow Synthesis of High-Entropy Sodium Vanadium Fluorophosphate for High Rate Capacity in Sodium-Ion Batteries

Continuous-Flow Synthesis of High-Entropy Sodium Vanadium Fluorophosphate for High Rate Capacity in Sodium-Ion Batteries

Regulation of Coordination Chemistry To Accelerate Na+ Transfer Kinetics of Polyanionic Cathodes for Ultrastable Sodium-Ion Batteries.

Alluaudite-type iron-based sulfate structure (Na2+2xFe2-x(SO4)3) has attracted wide attention due to its high working voltage and low cost. However, their practical application is hindered by challenges such as limited reversible capacity and sluggish transfer kinetics. Herein, we proposed an anion substitution strategy to optimize iron-based sulfate cathode materials. The electrochemical characterization and theoretical calculations confirmed a reduction in the migration barrier of Na+ ions in various pathways. Besides, fluorine weakened the electron density of the crystal plane, thereby impeding the continuous side reaction of the electrolyte. As expected, the NFSF cathode can exhibit a capacity of 121.5 mAh g-1 at 12 mA g-1 and keep a high retention of 78.8% after 1000 cycles at 600 mA g-1. In addition, the NFSF-based cathode and hard carbon (HC)-based anode were assembled into a laboratory-scale pouch cell to demonstrate the electrochemical performance and practical applications.

Entropy-Tailored Fast-Charging Sodium Layered Cathodes.

O3-type layered transition metal (TM) oxides are widely used as cathode materials for Na-ion batteries due to their high energy density potential, enabled by the state of charge (SoC)-dependent transition from octahedral (O-type) to prismatic (P-type) structures during Na-ion (de)sodiation. However, the O-P transition is often criticized for compromising the Na-ion mobility and limiting the cycle life. Herein, we reveal the intrinsic correlation between O-P transitions, oxygen behaviors, and Na-ion kinetics. We demonstrate that a compositionally versatile, entropy-tailored approach can promote preferred transitions (characterized by large lattice parameter deviations in the O-type region and rapid O-P biphasic reactions), enhancing Na-ion migration, as revealed by in situ high-energy synchrotron X-ray diffraction (HEXRD). Additionally, irreversible oxygen loss at high SoC is effectively mitigated, while TM migration and surface reconstruction are greatly suppressed, further accelerating Na-ion transport and stabilizing the structure, as confirmed by X-ray absorption spectroscopy (XAS) and theoretical analyses. The result is an exceptionally high rate capability of 88.7 mAh g-1 at 20 C (2.4 A g-1) with a superior normalized retention of 72.6%, accompanied by a prolonged lifetime with 74.3% retention after 1000 cycles. This work advances the understanding of the chemistry-property relationships in O3-type layered cathodes and broadens the prospects for fabricating high-power-density electrodes.

Structural Optimization of NVP/C Composites by an Advanced Two-Step Spray Technique for High Energy Density and Long-Life Symmetric Sodium-Ion Batteries.

Sodium superionic conductor (NASICON)-type Na3V2(PO4)3 (NVP) has emerged as a pivotal cathode material for the development of high-durability sodium-ion batteries, owing to its distinctive 3D open framework and exceptional chemical stability. Enhancing the electrochemical performance of NVP through the incorporation of conductive materials and precise control of the pore structure requires refining and optimizing the synthesis methodologies. In this study, robust NVP composites combined with dextrin-derived carbon (D-NVP/Dex) and carbon nanotubes (D-NVP/CNT) are developed with stable cycling characteristics and high energy densities, exhibiting high capacities of 99.0 and 93.0mA h g-1, respectively, at 1.0 C after the 300 cycles, via a two-step synthesis approach utilizing spray techniques. These structural features, including the conformal carbon layer encapsulating the NVP particles and the connections formed through CNT networks, are validated to enhance their electrical and ionic conductivities, as demonstrated by evaluations of both half-cell and symmetric full-cell configurations. Specifically, symmetric D-NVP/Dex||D-NVP/Dex and D-NVP/Dex||P-NVP sodium-ion batteries exhibit excellent cyclability, achieving capacities of 46.5 and 49.0mA h g-1, respectively, after 150 cycles at 0.5 C.