Recent Progress of Layered Transition Metal Oxide Cathodes for Sodium-Ion Batteries

Constructing hierarchical MoS2/WS2 heterostructures in dual carbon layer for enhanced sodium ions batteries performance

The escalating global demand for clean energy has spurred substantial interest in sodium-ion batteries (SIBs) as a promising solution for large-scale energy storage systems. However, the insufficient reaction kinetics and considerable volume changes inherent to anode materials present significant hurdles to enhancing the electrochemical performance of SIBs. In this study, hierarchical MoS2/WS2 heterostructures were constructed into dual carbon layers (HC@MoS2/WS2@NC) and assessed their suitability as anodes for SIBs. The internal hard carbon core (HC) and outer nitrogen-doped carbon shell (NC) effectively anchor MoS2/WS2, thereby significantly improving its structural stability. Moreover, the conductive carbon components expedite electron transport during charge-discharge processes. Critically, the intelligently engineered interface between MoS2 and WS2 modulates the interfacial energy barrier and electric field distribution, promoting faster ion transport rates. Capitalizing on these advantageous features, the HC@MoS2/WS2@NC nanocomposite exhibits outstanding electrochemical performance when utilized as an anode in SIBs. Specifically, it delivers a high capacity of 415 mAh/g at a current density of 0.2 A/g after 100 cycles. At a larger current density of 2 A/g, it maintains a commendable capacity of 333 mAh/g even after 1000 cycles. Additionally, when integrated into a full battery configuration with a Na3V2(PO4)3 cathode, the Na3V2(PO4)3//HC@MoS2/WS2@NC full cell delivers a high capacity of 120 mAh/g after 300 cycles at 1 A/g. This work emphasizes the substantial improvement in battery performance that can be attained through the implementation of dual carbon confinement, offering a constructive approach to guide the design and development of next-generation anode materials for SIBs.

Architecting O3/P2 layered oxides by gradient Mn doping for sodium-ion batteries

O3 phase layered oxides are highly attractive cathode materials for sodium-ion batteries because of their high capacity and decent initial Coulombic efficiency. However, their rate capability and long cycling life are unsatisfactory due to the narrow Na+ transfer channel and irreversible phase transitions of O3 phase during sodiation/desodiation process. Constructing O3/P2 multiphase structures has been proven to be an effective strategy to overcome these challenges. In this study, we synthesized bi-phasic structured O3/P2 Na(Ni2/9Fe1/3Cu1/9Mn1/3)1-xMnxO2 (x = 0.01, 0.02, 0.03, 0.04, 0.05) materials through Mn doping during sodiation process. Benefiting from surface P2 phase layer with the enhanced Na+ transfer dynamics and high structural stability, the Na(Ni2/9Fe1/3Cu1/9Mn1/3)0.98Mn0.02O2 (NFCM-M2) cathode delivers a reversible capacity of 139.1 mA h g-1 at 0.1 C, and retains 71.4 % of its original capacity after 300 cycles at 1 C. Our work provides useful guidance for designing multiphase cathodes and offers new insights into the structure-performance correlation for sodium-ion cathode materials.

Boosting sodium-ion battery performance by anion doping in NASICON Na4MnCr(PO4)3 cathode

Na superionic conductor (NASICON)-structured Na4MnCr(PO4)3 (NMCP) possessing unique three-electron transfer process renders admirable energy density for sodium ion batteries (SIBs). However, the current issues like its sluggish Na+ diffusion kinetics, deficient intrinsic conductivity, and unsatisfactory structural stability, hinder its practical application. Herein, a selective replacement of O elements in PO4 group by Cl anions in the NMCP system was developed to significantly enhance its electrochemical performance. The results affirm that the enhanced performance of Cl doped samples can be attributed to the enlargement of cell size, the creation of Na vacancies and the weakness of Na2O bond after Cl doping. The as-prepared Na3.85□0.15MnCr(PO3.95Cl0.05)3/C (NMCPC - 15/C) cathode delivers a high capacity (128.0 mAh/g at 50 mA g-1) and excellent rate performance (73.0 mAh/g at 1000 mA g-1) in contrast to NMCP/C that merely provides 105.2 mAh/g at 50 mA g-1 and reduces to 47.4 mAh/g at 1000 mA g-1. Meanwhile, NMCPC - 15/C shows a capacity retention of 60.7 % at 1000 mA g-1 after 500 cycles, while only 37.1 % for NMCP/C in the same test conditions. Moreover, the satisfactory performance and energy density of NMCPC - 15/C||hard carbon (HC) full cell confirm the potential practicality of NMCPC - 15. Therefore, chloride ions doping into NMCP has practical application prospects in the preparation of high-performance cathode materials and our work also offers new inspiration to apply anion doping strategies in promoting the performance of the other NASICON-structured cathodes for SIBs.

Fast Na+ Kinetics and Suppressed Voltage Hysteresis Enabled by a High-Entropy Strategy for Sodium Oxide Cathodes

O3-type layered transition metal cathodes are promising energy storage materials due to their sufficient sodium reservoir. However, sluggish sodium ions kinetics and large voltage hysteresis, which are generally associated with Na+ diffusion properties and electrochemical phase transition reversibility, drastically minimize energy density, reduce energy efficiency, and hinder further commercialization of sodium-ion batteries (SIBs). Here, this work proposes a high-entropy tailoring strategy through manipulating the electronic local environment within transition metal slabs to circumvent these issues. Experimental analysis combined with theoretical calculations verify that high-entropy metal ion mixing contributes to the improved reversibility of redox reaction and O3-P3-O3 phase transition behaviors as well as the enhanced Na+ diffusivity. Consequently, the designed O3-Na0.9Ni0.2Fe0.2Co0.2Mn0.2Ti0.15Cu0.05O2 material with high-entropy characteristic could display a negligible voltage hysteresis (<0.09 V), impressive rate capability (98.6 mAh g-1 at 10 C) and long-term cycling stability (79.4% capacity retention over 2000 cycles at 5 C). This work provides insightful guidance in mitigating the voltage hysteresis and facilitating Na+ diffusion of layered oxide cathode materials to realize high-rate and high-energy SIBs.

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.

Routes to high-performance layered oxide cathodes for sodium-ion batteries

Sodium-ion batteries (SIBs) are experiencing a large-scale renaissance to supplement or replace expensive lithium-ion batteries (LIBs) and low energy density lead-acid batteries in electrical energy storage systems and other applications. In this case, layered oxide materials have become one of the most popular cathode candidates for SIBs because of their low cost and comparatively facile synthesis method. However, the intrinsic shortcomings of layered oxide cathodes, which severely limit their commercialization process, urgently need to be addressed. In this review, inherent challenges associated with layered oxide cathodes for SIBs, such as their irreversible multiphase transition, poor air stability, and low energy density, are systematically summarized and discussed, together with strategies to overcome these dilemmas through bulk phase modulation, surface/interface modification, functional structure manipulation, and cationic and anionic redox optimization. Emphasis is placed on investigating variations in the chemical composition and structural configuration of layered oxide cathodes and how they affect the electrochemical behavior of the cathodes to illustrate how these issues can be addressed. The summary of failure mechanisms and corresponding modification strategies of layered oxide cathodes presented herein provides a valuable reference for scientific and practical issues related to the development of SIBs.

Interface Engineering of MOF-Derived Co3O4@CNT and CoS2@CNT Anodes with Long Cycle Life and High-Rate Properties in Lithium/Sodium-Ion Batteries

Metal-organic framework materials can be converted into carbon-based nanoporous materials by pyrolysis, which have a wide range of applications in energy storage. Here, we design special interface engineering to combine the carbon skeleton and nitrogen-doped carbon nanotubes (CNTs) with the transition metal compounds (TMCs) well, which mitigates the bulk effect of the TMCs and improves the conductivity of the electrodes. Zeolitic imidazolate framework-67 is used as a precursor to form a carbon skeleton and a large number of nitrogen-doped CNTs by pyrolysis followed by the in situ formation of Co3O4 and CoS2, and finally, Co3O4@CNTs and CoS2@CNTs are synthesized. The obtained anode electrodes exhibit a long cycle life and high-rate properties. In lithium-ion batteries (LIBs), Co3O4@CNTs have a high capacity of 581 mAh g-1 at a high current of 5 A g-1, and their reversible capacity is still 1037.6 mAh g-1 after 200 cycles at 1 A g-1. In sodium-ion batteries (SIBs), CoS2@CNTs have a capacity of 859.9 mAh g-1 at 0.1 A g-1 and can be retained at 801.2 mAh g-1 after 50 cycles. The unique interface engineering and excellent electrochemical properties make them ideal anode materials for high-rate, long-life LIBs and SIBs.

Using Highly Electronegative Zn to Regulate the Superlattice Structure for the Na-Ion Layered Oxide Cathode with Superior Electrochemical Performance

The introduction of a superlattice structure into layered oxide cathode materials is a novel strategy to improve the structural stability of sodium-ion batteries (SIBs). However, the superlattice structure gradually disappears during cycling, which shortens the long life of SIBs. Here, the highly electronegative Zn is introduced into a P2-type layered oxide to regulate the superlattice structure. The obtained P2-Na0.80Li0.13Ni0.20Zn0.03Mn0.64O2 exhibits excellent cycling performance (the capacity retention is 96.7% after 100 cycles at 0.5C) and rate capability (95.8 mAh g-1 at 5C). Zn effectively inhibits the Li migration and the Mn dissolution, which ensures the integrity of the Li/Mn superlattice structure during long cycling, thus achieving an ultralong cycling life of SIBs. The introduction of Zn dramatically increases the length of the c-axis, leading to a faster de-embedding rate of Na+ and a better diffusion kinetics. Meanwhile, the larger pristine volume can withstand more stress/strain due to the sharp increase in the level of O-O repulsion during the desodiation process. In addition, Raman test results show that Zn can inhibit the Na+/vacancy ordering transition and improve the structural stability. This study confirms the feasibility of a Zn-regulated superlattice structure. It provides inspiration for the construction of stable layered oxide cathode materials for SIBs.

Recent Advances and Perspectives on the Promising High-Voltage Cathode Material of Na3 (VO)2 (PO4 )2 F

Na3 (VO)2 (PO4 )2 F (NVOPF) has emerged as one of the most promising cathode materials for sodium-ion batteries (SIBs) attributed to its high specific capacity (130 mAh g-1 ), high operation voltage (>3.9 V vs Na+ /Na), and excellent structural stability (<2% volume change). However, the comparatively low intrinsic electronic conductivity (≈10-7 S cm-1 ) of NVOPF leads to unsatisfactory electrochemical performance, especially at high rates, limiting its practical applications. To improve the conductivity and enhance Na storage performance, many efforts have been devoted to designing NVOPF, including morphology optimization, hybridization with conductive materials, metal-ion doping, Na-site regulation, and F/O ratio adjustment. These attempts have shown some encouraging achievements and shed light on the practical application of NVOPF cathodes. This work aims to provide a general introduction, synthetic methods, and rational design of NVOPF to give a deeper understanding of the recent progress. Additionally, the unique microstructure of NVOPF and its relationship with Na storage properties are also described in detail. The current status, as well as the advances and limitations of such SIB cathode material, are reported. Finally, future perspectives and guidance for advancing high-performance NVOPF cathodes toward practical applications are presented.

Novel Bismuth Nanoflowers Encapsulated in N-Doped Carbon Frameworks as Superb Composite Anodes for High-Performance Sodium-Ion Batteries

Bismuth (Bi) has attracted attention as a promising anode for sodium-ion batteries (SIBs) owing to its suitable potential and high theoretical capacity. However, the large volumetric changes during cycling leads to severe degradation of electrochemical performance and limits its practical application. Herein, Bi nanoflowers are encapsulated in N-doped carbon frameworks to construct a novel Bi@NC composite via a facile solvothermal method and carbonization strategy. The well-designed composite structure endows the Bi@NC with uniformly dispersed Bi nanoflowers to alleviate the attenuation while the N-doped carbon frameworks improve the conductivity and ion transport of the whole electrode. As for sodium-ion half-cell, the electrode exhibits a high specific capacity (384.8 mAh g-1 at 0.1 A g-1 ) and excellent rate performance (341.5 mAh g-1 at 10 A g-1 ), and the capacity retention rate still remains at 94.9% after 5000 cycles at 10 A g-1 . Furthermore, the assembled full-cell with Na3 V2 (PO4 )3 cathode and Bi@NC anode can deliver a high capacity of 251.5 mAh g-1 at 0.1 A g-1 , and its capacity attenuates only 0.009% in each cycle after 2000 times at 5.0 A g-1 . This work offers a convenient, low-cost, and eco-friendliness approach for high-performance electrodes in the field of sodium ion electrochemical storage technology.

Structural Evolution of Air-Exposed Layered Oxide Cathodes for Sodium-Ion Batteries: An Example of Ni-doped NaxMnO2

Sodium-ion batteries have recently aroused the interest of industries as possible replacements for lithium-ion batteries in some areas. With their high theoretical capacities and competitive prices, P2-type layered oxides (NaxTMO2) are among the obvious choices in terms of cathode materials. On the other hand, many of these materials are unstable in air due to their reactivity toward water and carbon dioxide. Here, Na0.67Mn0.9Ni0.1O2 (NMNO), one of such materials, has been synthesized by a classic sol-gel method and then exposed to air for several weeks as a way to allow a simple and reproducible transition toward a Na-rich birnessite phase. The transition between the anhydrous P2 to the hydrated birnessite structure has been followed via periodic XRD analyses, as well as neutron diffraction ones. Extensive electrochemical characterizations of both pristine NMNO and the air-exposed one vs sodium in organic medium showed comparable performances, with capacities fading from 140 to 60 mAh g-1 in around 100 cycles. Structural evolution of the air-exposed NMNO has been investigated both with ex situ synchrotron XRD and Raman. Finally, DFT analyses showed similar charge compensation mechanisms between P2 and birnessite phases, providing a reason for the similarities between the electrochemical properties of both materials.

A NaCrO2@C free-standing cathode via electrospinning for sodium-ion batteries

A flexible free-standing cathode is innovatively constructed with NaCrO2 as the electrochemical active substance via an electrospinning technique. The as constructed NaCrO2@C flexible free-standing cathode exhibits exceptional rate performance (106 mA h g-1 at 10C) and cyclability (retention rate of 87.5% after 300 cycles at 0.2C). This work provides a brand-new perspective to the development of flexible free-standing cathodes.

Structural and electrochemical progress of O3-type layered oxide cathodes for Na-ion batteries

Sodium-ion batteries (SIBs) have attracted great attention being the most promising sustainable energy technology owing to their competitive energy density, great safety and considerable low-cost merits. Nevertheless, the commercialization process of SIBs is still sluggish because of the difficulty in developing high-performance battery materials, especially the cathode materials. The discovery of layered transition metal oxides as the cathode materials of SIBs brings infinite possibilities for practical battery production. Thereinto, the O3-type layered transition metal oxides exhibit attractive advantages in terms of energy density benefiting from their higher sodium content compared to other kinds of layered transition metal oxides. Enormous research studies have largely put forward their progress and explored a wide range of performance improvement approaches from the morphology, coating, doping, phase structure and redox aspects. However, the progress is scattered and has not logically evolved, which is not beneficial for the further development of more advanced cathode materials. Therefore, our work aims to comprehensively review, classify and highlight the most recent advances in O3-type layered transition metal oxides for SIBs, so as to scientifically cognize their progress and remaining challenges and provide reasonable improvement ideas and routes for next-generation high-performance cathode materials.

Optimization of Sodium Storage Performance by Structure Engineering in Nickel-Cobalt-Sulfide

The development of high-performance electrode materials is crucial for the advancement of sodium ion batteries (SIBs), and NiCo2 S4 has been identified as a promising anode material due to its high theoretical capacity and abundant redox centers. However, its practical application in SIBs is hampered by issues such as severe volume variations and poor cycle stability. Herein, the Mn-doped NiCo2 S4 @graphene nanosheets (GNs) composite electrodes with hollow nanocages were designed using a structure engineering method to relieve the volume expansion and improve the transport kinetics and conductivity of the NiCo2 S4 electrode during cycling. Physical characterization and electrochemical tests, combined with density functional theory (DFT) calculations indicate that the resulting 3 % Mn-NCS@GNs electrode demonstrates excellent electrochemical performance (352.9 mAh g-1 at 200 mA g-1 after 200 cycles, and 315.3 mAh g-1 at 5000 mA g-1 ). This work provides a promising strategy for enhancing the sodium storage performance of metal sulfide electrodes.

Mitigating Jahn-Teller Effect in Layered Cathode Material Via Interstitial Doping for High-Performance Sodium-Ion Batteries

Layered transition metal oxides are promising cathode materials for sodium-ion batteries due to their high energy density and appropriate operating potential. However, the poor structural stability is a major drawback to their widespread application. To address this issue, B3+ is successfully introduced into the tetrahedral site of Na0.67 Fe0.5 Mn0.5 O2 , demonstrating the effectiveness of small-radius ion doping in improving electrochemical performance. The obtained Na0.67 Fe0.5 Mn0.5 B0.04 O2 exhibits excellent cycling performance with 88.8% capacity retention after 100 cycles at 1 C and prominent rate performance. The structure-property relationship is constructed subsequently by neutron powder diffraction, in situ X-ray diffraction and X-ray absorption spectroscopy, which reveal that the Jahn-Teller distortion and the consequent P2-P2' phase transformation are effectively mitigated because of the occupancy of B3+ at the interstitial site. Furthermore, it is found that the transition metal layers are stabilized and the transition metal dissolution are suppressed, resulting in excellent cycling performance. Besides, the prominent rate performance is attributed to the enhanced diffusion kinetics associated with the rearrangement of Na+ . This work provides novel insight into the action mechanism of interstitial site doping and demonstrates a universal approach to improve the electrochemical properties of P2-type manganese-based sodium cathode materials.

Stabilizing Lattice Oxygen in a P2-Na0.67Mn0.5Fe0.5O2 Cathode via an Integrated Strategy for High-Performance Na-Ion Batteries

P2-type Na_0.67Mn_0.5Fe_0.5O₂ (MF) has attracted great interest as a promising cathode material for sodium-ion batteries (SIBs) due to its high specific capacity and low cost. However, its poor cyclic stability and rate performance hinder its practical applications, which is largely related to lattice oxygen instability. Here, we propose to coat the cathode of SIBs with Li₂ZrO₃, which realizes the "three-in-one" modification of Li₂ZrO₃ coating and Li⁺, Zr⁴⁺ co-doping. The synergy of Li₂ZrO₃ coating and Li⁺/Zr⁴⁺ doping improves both the cycle stability and rate performance, and the underlying modification mechanism is revealed by a series of characterization methods. The doping of Zr⁴⁺ increases the interlayer spacing of MF, reduces the diffusion barrier of Na⁺, and reduces the ratio of Mn³⁺/Mn⁴⁺, thus inhibiting the Jahn-Teller effect. The Li₂ZrO₃ coating layer inhibits the side reaction between the cathode and the electrolyte. The synergy of Li₂ZrO₃ coating and Li⁺, Zr⁴⁺ co-doping enhances the stability of lattice oxygen and the reversibility of anionic redox, which improves the cycle stability and rate performance. This study provides some insights into stabilizing the lattice oxygen in layered oxide cathodes for high-performance SIBs.

Guest Ion-Dependent Reaction Mechanisms of New Pseudocapacitive Mg3 V4 (PO4 )6 /Carbon Composite as Negative Electrode for Monovalent-Ion Batteries

Polyanion-type phosphate materials, such as M₃ V₂ (PO₄ )₃ (M = Li/Na/K), are promising as insertion-type negative electrodes for monovalent-ion batteries including Li/Na/K-ion batteries (lithium-ion batteries (LIBs), sodium-ion batteries (SIBs), and potassium-ion batteries (PIBs)) with fast charging/discharging and distinct redox peaks. However, it remains a great challenge to understand the reaction mechanism of materials upon monovalent-ion insertion. Here, triclinic Mg₃ V₄ (PO₄ )₆ /carbon composite (MgVP/C) with high thermal stability is synthesized via ball-milling and carbon-thermal reduction method and applied as a pseudocapacitive negative electrode in LIBs, SIBs, and PIBs. In operando and ex situ studies demonstrate the guest ion-dependent reaction mechanisms of MgVP/C upon monovalent-ion storage due to different sizes. MgVP/C undergoes an indirect conversion reaction to form Mg⁰ , V⁰ , and Li₃ PO₄ in LIBs, while in SIBs/PIBs the material only experiences a solid solution with the reduction of V³⁺ to V²⁺ . Moreover, in LIBs, MgVP/C delivers initial lithiation/delithiation capacities of 961/607 mAh g^-1 (30/19 Li⁺ ions) for the first cycle, despite its low initial Coulombic efficiency, fast capacity decay for the first 200 cycles, and limited reversible insertion/deinsertion of 2 Na⁺ /K⁺ ions in SIBs/PIBs. This work reveals a new pseudocapacitive material and provides an advanced understanding of polyanion phosphate negative material for monovalent-ion batteries with guest ion-dependent energy storage mechanisms.

Suppressing the Dynamic Oxygen Evolution of Sodium Layered Cathodes through Synergistic Surface Dielectric Polarization and Bulk Site-Selective Co-Doping

Utilizing anionic redox activity within layered oxide cathode materials represents a transformational avenue for enabling high-energy-density rechargeable batteries. However, the anionic oxygen redox reaction is often accompanied with irreversible dynamic oxygen evolution, leading to unfavorable structural distortion and thus severe voltage decay and rapid capacity fading. Herein, it is proposed and validated that the dynamic oxygen evolution can be effectively suppressed through the synergistic surface CaTiO₃ dielectric coating and bulk site-selective Ca/Ti co-doping for layered Na_2/3 Ni_1/3 Mn_2/3 O₂ . The surface dielectric coating layer not only suppresses the surface oxygen release but more importantly inhibits the bulk oxygen migration by creating a reverse electric field through dielectric polarization. Meanwhile, the site-selective doping of oxygen-affinity Ca into Na layers and Ti into transition metal layers effectively stabilizes the bulk oxygen through modulating the O 2p band center and the oxygen migration barrier. Such a strategy also leads to a reversible structural evolution with a low volume change because of the enhanced structural integrality and improved oxygen rigidity. Because of these synergistic advantages, the designed electrode exhibits greatly suppressed voltage decay and capacity fading upon long-term cycling. This study affords a promising strategy for regulating the dynamic oxygen evolution to achieve high-capacity layered cathode materials.

Rational design of intergrowth P2/O3 biphasic layered structure with reversible anionic redox chemistry and structural evolution for Na-ions batteries

Layered oxides have attracted unprecedented attention for their outstanding performance in sodium-ion battery cathodes. Among them, the two typical candidates P2 and O3 type materials generally demonstrate large diversities in specific capacity and cycling endurance with their advantages. Thus, composite materials that contain both P2 and O3 have been widely designed and constructed. Nevertheless, the anionic/cationic ions' behavior and structural evolution in such complex structures remain unclear. In this study, a deep analysis of an advanced Na_0.732Ni_0.273Mg_0.096Mn_0.63O₂ material that contains 78.39 wt% P2 phase and 21.61 wt% O3 phase is performed based on two typical cathodes P2 Na_0.67Ni_0.33Mn_0.67O2 and O3 NaNi_0.5Mn_0.5O₂ that have the same elemental constitution but different crystal structures. Structural analysis and density functional theory (DFT) calculations suggest that the composite is preferred to form a symbiotic structure at the atomic level, and the complex lattice texture of the biphase structure can block unfavorable ion and oxygen migration in the electrode process. Consequently, the biphase structure has significantly improved the electrochemical performance and kept preferable anionic oxygen redox reversibility. Furthermore, the hetero-epitaxy-like structure of the intergrowth of P2 and O3 structures share multi-phase boundaries, where the inconsistency in electrochemical behavior between P2 and O3 phases leads to an interlocking effect to prevent severe structural collapse and relieves the lattice strain from Na⁺ de/intercalation. Hence, the symbiotic P2/O3 composite materials exhibited a preferable capacity and cyclability (∼130 mAh g^-1 at 0.1 C, 73.1% capacity retention after 200 cycles at 1 C), as well as reversible structural evolution. These findings confirmed the advantages of using the bi/multi-phase cathode for high-energy Na-ion batteries.

Recent Progress in Rechargeable Sodium Metal Batteries: A Review

Sodium metal batteries (SMBs) have been widely studied owing to their relatively high energy density and abundant resources. However, they still need systematic improvement to fulfill the harsh operating conditions for their commercialization. In this review, we summarize the recent progress in SMBs in terms of sodium anode modification, electrolyte exploration, and cathode design. Firstly, we give an overview of the current challenges facing Na metal anodes and the corresponding solutions. Then, the traditional liquid electrolytes and the prospective solid electrolytes for SMBs are summarized. In addition, insertion- and conversion-type cathode materials are introduced. Finally, an outlook for the future of practical SMBs is provided.

Opportunities and Challenges in the Development of Layered Positive Electrode Materials for High-Energy Sodium Ion Batteries: A Computational Perspective

In recent years, high-energy-density sodium ion batteries (SIBs) have attracted enormous attention as a potential replacement for LIBs due to the chemical similarity between Li and Na, high natural abundance, and low cost of Na. Despite the promise of high energy, SIBs with layered cathode materials face several challenges including irreversible capacity loss, voltage hysteresis, voltage decay, irreversible TM migrations that lead to fast capacity fading, and structural degradation. However, their electrochemical performance can be improved by introducing reversible anionic redox along with conventional cationic redox. This Perspective systematically summarizes different factors that trigger the irreversible anionic redox in Na-based cathode materials. Additionally, this Perspective highlights the mechanistic understanding and key challenges for reversible anionic redox and proposes plausible solutions to overcome these limitations. The overview of various existing experimental and theoretical approaches presented here could provide a futuristic pathway to design Na-based cathode materials for high-energy-density SIBs.

Electrochemical Performance of Layer-Structured Ni0.8Co0.1Mn0.1O2 Cathode Active Materials Synthesized by Carbonate Co-Precipitation

The layered Ni-rich NiCoMn (NCM)-based cathode active material Li[Ni_xCo_(1-x)/2Mn_(1-x)/2]O₂ (x ≥ 0.6) has the advantages of high energy density and price competitiveness over an LiCoO₂-based material. Additionally, NCM is beneficial in terms of its increasing reversible discharge capacity with the increase in Ni content; however, stable electrochemical performance has not been readily achieved because of the cation mixing that occurs during its synthesis. In this study, various layer-structured Li_1.0[Ni_0.8Co_0.1Mn_0.1]O₂ materials were synthesized, and their electrochemical performances were investigated. A NiCoMnCO₃ precursor, prepared using carbonate co-precipitation with Li₂CO₃ as the lithium source and having a sintering temperature of 850 °C, sintering time of 25 h, and metal to Li molar ratio of 1.00-1.05 were found to be the optimal parameters/conditions for the preparation of Li_1.0[Ni_0.8Co_0.1Mn_0.1]O₂. The material exhibited a discharge capacity of 160 mAhg^-1 and capacity recovery rate of 95.56% (from a 5.0-0.1 C-rate).

Ti-substituted O3-type layered oxide cathode material with high-voltage stability for sodium-ion batteries

O3-type layered transition metal oxides (Na_xTMO₂) have attracted extensive attention as a promising cathode material for sodium-ion batteries because of their high capacity. However, the irreversible phase transition especially cycled under high voltage remains a concerning challenge for Na_xTMO₂. Herein, a Ti-substituted NaNi_0.5Co_0.2Mn_0.3O₂ cathode with strongly suppressed phase transition and enhanced storage stability is investigated. The Ti substitution effectively inhibits the irreversible phase transition and alleviates the structural change even charged to 4.3 V during the repeated Na⁺ deintercalation process. After storing in air or water, the original O3 phase structure of the material is integrally maintained without the generation of impurity phase. As a result, the as-prepared material shows excellent long-term cycle stability and rate performance when charged to a high voltage of 4.3 V.

Promoting Fast Na Ion Transport at Low Temperatures for Sodium Metal Batteries

Cost concerns have promoted the rise of Na-based batteries as an alternative to Li-based batteries, and the energy density pursuits have brought attention to Na metal anodes. Numerous studies have been conducted on the failure mechanisms and improvement methods of Na metal batteries (NMBs) at room temperature; however, the low-temperature applications are still faced with more complex challenges. On the basis of the concentration effect of the electrolytes, we propose a dilute electrolyte for the low-temperature operation of NMBs. With the low salt concentration and tetrahydrofuran cosolvent, the affinity between Na ions and the solvent molecules is weakened to achieve fast reaction kinetics at low temperatures. The designed electrolyte enables an effectively decreased cell impedance, which improves the cycling stability of Na symmetric cells. As a result, the full cell paired with the Na₃V₂(PO₄)₃ cathode maintains a capacity of 80 mAh/g over 250 cycles at -20 °C. This work provides an electrolyte design strategy toward low-temperature NMBs.

Progress on Fe-Based Polyanionic Oxide Cathodes Materials toward Grid-Scale Energy Storage for Sodium-Ion Batteries

The development of large-scale energy storage systems (EESs) is pivotal for applying intermittent renewable energy sources such as solar energy and wind energy. Lithium-ion batteries with LiFePO₄ cathode have been explored in the integrated wind and solar power EESs, due to their long cycle life, safety, and low cost of Fe. Considering the penurious reserve and regional distribution of lithium resources, the Fe-based sodium-ion battery cathodes with earth-abundant elements, environmental friendliness, and safety appear to be the better substitutes in impending grid-scale energy storage. Compared to the transition metal oxide and Prussian blue analogs, the Fe-based polyanionic oxide cathodes possess high thermal stability, ultra-long cycle life, and adjustable voltage, which is more commercially viable in the future. This review summarizes the research progress of single Fe-based polyanionic and mixed polyanionic oxide cathodes for the potential sodium-ion batteries EESs candidates. In detail, the synthesized method, crystal structure, electrochemical properties, bottlenecks, and optimization method of Fe-based polyanionic oxide cathodes are discussed systematically. The insights presented in this review may serve as a guideline for designing and optimizing Fe-based polyanionic oxide cathodes for coming commercial sodium-ion batteries EESs.

Transition metal oxides as a cathode for indispensable Na-ion batteries

The essential requirement to harness well-known renewable energy sources like wind energy, solar energy, etc. as a component of an overall plan to guarantee global power sustainability will require highly efficient, high power and energy density batteries to collect the derived electrical power and balance out variations in both supply and demand. Owing to the continuous exhaustion of fossil fuels, and ever increasing ecological problems associated with global warming, there is a critical requirement for searching for an alternative energy storage technology for a better and sustainable future. Electrochemical energy storage technology could be a solution for a sustainable source of clean energy. Sodium-ion battery (SIB) technology having a complementary energy storage mechanism to the lithium-ion battery (LIB) has been attracting significant attention from the scientific community due to its abundant resources, low cost, and high energy densities. Layered transition metal oxide (TMO) based materials for SIBs could be a potential candidate for SIBs among all other cathode materials. In this paper, we discussed the latest improvement in the various structures of the layered oxide materials for SIBs. Moreover, their synthesis, overall electrochemical performance, and several challenges associated with SIBs are comprehensively discussed with a stance on future possibilities. Many articles discussed the improvement of cathode materials for SIBs, and most of them have pondered the use of Na x MO2 (a class of TMOs) as a possible positive electrode material for SIBs. The different phases of layered TMOs (Na x MO2; TM = Co, Mn, Ti, Ni, Fe, Cr, Al, V, and a combination of multiple elements) show good cycling capacity, structural stability, and Na+ ion conductivity, which make them promising cathode material for SIBs. This review discusses and summarizes the electrochemical redox reaction, structural transformations, significant challenges, and future prospects to improve for Na x MO2. Moreover, this review highlights the recent advancement of several layered TMO cathode materials for SIBs. It is expected that this review will encourage further development of layered TMOs for SIBs.

Simply Prepared Magnesium Vanadium Oxides as Cathode Materials for Rechargeable Aqueous Magnesium Ion Batteries

Vanadium-oxide-based materials exist with various vanadium oxidation states having rich chemistry and ability to form layered structures. These properties make them suitable for different applications, including energy conversion and storage. Magnesium vanadium oxide materials obtained using simple preparation route were studied as potential cathodes for rechargeable aqueous magnesium ion batteries. Structural characterization of the synthesized materials was performed using XRD and vibrational spectroscopy techniques (FTIR and Raman spectroscopy). Electrochemical behavior of the materials, observed by cyclic voltammetry, was further explained by BVS calculations. Sluggish Mg²⁺ ion kinetics in MgV₂O₆ was shown as a result of poor electronic and ionic wiring. Complex redox behavior of the studied materials is dependent on phase composition and metal ion inserted/deinserted into/from the material. Among the studied magnesium vanadium oxides, the multiphase oxide systems exhibited better Mg²⁺ insertion/deinsertion performances than the single-phase ones. Carbon addition was found to be an effective dual strategy for enhancing the charge storage behavior of MgV₂O₆.

Formulating High-Rate and Long-Cycle Heterostructured Layered Oxide Cathodes by Local Chemistry and Orbital Hybridization Modulation for Sodium-Ion Batteries

It is still very urgent and challenging to simultaneously develop high-rate and long-cycle oxide cathodes for sodium-ion batteries (SIBs) because of the sluggish kinetics and complex multiphase evolution during cycling. Here, the concept of accurately manipulating structural evolution and formulating high-performance heterostructured biphasic layered oxide cathodes by local chemistry and orbital hybridization modulation is reported. The P2-structure stoichiometric composition of the cathode material shows a layered P2- and O3-type heterostructure that is explicitly evidenced by various macroscale and atomic-scale techniques. Surprisingly, the heterostructured cathode displays excellent rate performance, remarkable cycling stability (capacity retention of 82.16% after 600 cycles at 2 C), and outstanding compatibility with hard carbon anode because of the integrated advantages of intergrowth structure and local environment regulation. Meanwhile, the formation process from precursors during calcination and the highly reversible dynamic structural evolution during the Na⁺ intercalation/deintercalation process are clearly articulated by a series of in situ characterization techniques. Also, the intrinsic structural properties and corresponding electrochemical behavior are further elucidated by the density of states and electron localization function of density functional theory calculations. Overall, this strategy, which finely tunes the local chemistry and orbitals hybridization for high-performance SIBs, will open up a new field for other materials.

Ion Substitution Strategy of Manganese-Based Layered Oxide Cathodes for Advanced and Low-Cost Sodium Ion Batteries

Sodium ion batteries (SIBs) have recently been promising in the large-scale electric energy storage system, due to the low cost, abundant sodium resources. Mn-based layered oxide cathode materials have been widely investigated, because of the high theoretical specific capacity, low cost, and abundant reserves. However, their development is limited by the problems of Jahn-Teller distortion, Na⁺ /vacancy ordering, complex phase transitions, and irreversible anionic redox during cycling. Ion substitution strategy is one simple and effective way to regulate the crystal structure and boost sodium-storage performances of Mn-based cathode materials. In this review, we summarize the progress and mechanism of ion-substituted Mn-based oxides, establish a composition-crystal structure-electrochemical performance relationship, and also offer perspectives for guiding the design of high-performance Mn-based oxides for SIBs.

Unravelling the Nature of the Intrinsic Complex Structure of Binary-Phase Na-Layered Oxides

The layered sodium transition metal oxide, NaTMO₂ (TM = transition metal), with a binary or ternary phases has displayed outstanding electrochemical performance as a new class of strategy cathode materials for sodium-ion batteries (SIBs). Herein, an in-depth phase analysis of developed Na_1-x TMO₂ cathode materials, Na_0.76 Ni_0.20 Fe_0.40 Mn_0.40 O₂ with P2- and O3-type phases (NFMO-P2/O3) is offered. Structural visualization on an atomic scale is also provided and the following findings are unveiled: i) the existence of a mixed-phase intergrowth layer distribution and unequal distribution of P2 and O3 phases along two different crystal plane indices and ii) a complete reversible charge/discharge process for the initial two cycles that displays a simple phase transformation, which is unprecedented. Moreover, first-principles calculations support the evidence of the formation of a binary NFMO-P2/O3 compound, over the proposed hypothetical monophasic structures (O3, P3, O'3, and P2 phases). As a result, the synergetic effect of the simultaneous existence of P- and O-type phases with their unique structures allows an extraordinary level of capacity retention in a wide range of voltage (1.5-4.5 V). It is believed that the insightful understanding of the proposed materials can introduce new perspectives for the development of high-voltage cathode materials for SIBs.

Tailoring Anionic Redox Activity in a P2-Type Sodium Layered Oxide Cathode via Cu Substitution

Na-ion cathode materials cycling at high voltages with long cycling life and high capacity are of imminent need for developing future high-energy Na-ion batteries. However, the irreversible anionic redox activity of Na-ion layered cathode materials results in structural distortion and poor capacity retention upon cycling. Herein, we develop a facile doping strategy by incorporating copper into the layered cathode material lattice to relieve the irreversible oxygen oxidation at high voltages. On the basis of a comprehensive comparison with the Cu-free material, both the over-oxidation of O^2- to trapped molecular O₂ and Mn-related Jahn-Teller distortion have been effectively inhibited by restraining both the oxygen activity and participation of Mn⁴⁺/Mn³⁺ redox activity. Not limited to discovering stable cycling behavior at high voltages after Cu substitution, our findings also highlight an effective strategy to stabilize the anionic redox activity and elucidate the stabilization mechanism of Cu substitution, thus paving the way for further improvement of layered oxide cathode materials for high-energy Na-ion batteries.

Structural Degradation of O3-NaMnO2 Positive Electrodes in Sodium-Ion Batteries

In this manuscript, we report an extensive study of the physico-chemical properties of different samples of O3-NaMnO2, synthesized by sol–gel and solid state methods. In order to successfully synthesize the materials by sol–gel methods a rigorous control of the synthesis condition has been optimized. The electrochemical performances of the materials as positive electrodes in aprotic sodium-ion batteries have been demonstrated. The effects of different synthesis methods on both structural and electrochemical features of O3-NaMnO2 have been studied to shed light on the interplay between structure and performance. Noticeably, we obtained a material capable of attaining a reversible capacity exceeding 180 mAhg−1 at 10 mAg−1 with a capacity retention >70% after 20 cycles. The capacity fading mechanism and the structural evolution of O3-NaMnO2 upon cycling have been extensively studied by performing post-mortem analysis using XRD and Raman spectroscopy. Apparently, the loss of reversible capacity upon cycling originates from irreversible structural degradations.

Recent Advances in Layered Metal-Oxide Cathodes for Application in Potassium-Ion Batteries

To meet future energy demands, currently, dominant lithium-ion batteries (LIBs) must be supported by abundant and cost-effective alternative battery materials. Potassium-ion batteries (KIBs) are promising alternatives to LIBs because KIB materials are abundant and because KIBs exhibit intercalation chemistry like LIBs and comparable energy densities. In pursuit of superior batteries, designing and developing highly efficient electrode materials are indispensable for meeting the requirements of large-scale energy storage applications. Despite using graphite anodes in KIBs instead of in sodium-ion batteries (NIBs), developing suitable KIB cathodes is extremely challenging and has attracted considerable research attention. Among the various cathode materials, layered metal oxides have attracted considerable interest owing to their tunable stoichiometry, high specific capacity, and structural stability. Therefore, the recent progress in layered metal-oxide cathodes is comprehensively reviewed for application to KIBs and the fundamental material design, classification, phase transitions, preparation techniques, and corresponding electrochemical performance of KIBs are presented. Furthermore, the challenges and opportunities associated with developing layered oxide cathode materials are presented for practical application to KIBs.

High-Voltage Stabilization of O3-Type Layered Oxide for Sodium-Ion Batteries by Simultaneous Tin Dual Modification

O3-type layered oxide materials are considered to be a highly suitable cathode for sodium-ion batteries (NIBs) due to their appreciable specific capacity and energy density. However, rapid capacity fading caused by serious structural changes and interfacial degradation hampers their use. A novel Sn-modified O3-type layered NaNi_1/3Fe_1/3Mn_1/3O₂ cathode is presented, with improved high-voltage stability through simultaneous bulk Sn doping and surface coating in a scalable one-step process. The bulk substitution of Sn⁴⁺ stabilizes the crystal structure by alleviating the irreversible phase transition and lattice structure degradation and increases the observed average voltage. In the meantime, the nanolayer Sn/Na/O composite on the surface effectively inhibits surface parasitic reactions and improves the interfacial stability during cycling. A series of Sn-modified materials are reported. An 8%-Sn-modified NaNi_1/3Fe_1/3Mn_1/3O₂ cathode exhibits a doubling in capacity retention increase after 150 cycles in the wide voltage range of 2.0-4.1 V vs Na/Na⁺ compared to none, and 81% capacity retention is observed after 200 cycles in a full cell vs hard carbon. This work offers a facile process to simultaneously stabilize the bulk structure and interface for the O3-type layered cathodes for sodium-ion batteries and raises the possibility of similar effective strategies to be employed for other energy storage materials.

Cationic vacancies as defects in honeycomb lattices with modular symmetries

Layered materials tend to exhibit intriguing crystalline symmetries and topological characteristics based on their two dimensional (2D) geometries and defects. We consider the diffusion dynamics of positively charged ions (cations) localized in honeycomb lattices within layered materials when an external electric field, non-trivial topologies, curvatures and cationic vacancies are present. The unit (primitive) cell of the honeycomb lattice is characterized by two generators, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$J_1, J_2 \in \mathrm{SL}_2({\mathbb {Z}})$$\end{document}J1,J2∈SL2(Z) of modular symmetries in the special linear group with integer entries, corresponding to discrete re-scaling and rotations respectively. Moreover, applying a 2D conformal metric in an idealized model, we can consistently treat cationic vacancies as topological defects in an emergent manifold. The framework can be utilized to elucidate the molecular dynamics of the cations in exemplar honeycomb layered frameworks and the role of quantum geometry and topological defects not only in the diffusion process such as prediction of conductance peaks during cationic (de-)intercalation process, but also pseudo-spin and pseudo-magnetic field degrees of freedom on the cationic honeycomb lattice responsible for bilayers.

Challenges of layer-structured cathodes for sodium-ion batteries

As the most promising alternative to lithium-ion batteries (LIBs), sodium-ion batteries (SIBs) still face many issues that hinder their large-scale commercialization. Layered transition metal oxide cathodes have attracted widespread attention owing to their large specific capacity, high ionic conductivity, and feasible preparation conditions. However, their electrochemical properties are usually limited by the irreversible phase transition and harsh storage conditions caused by humidity sensitivity. Recently, tremendous efforts have been devoted to solving these issues toward advanced high-performance layered oxide cathodes. Herein, we summarize these remaining challenges of layered oxide cathodes and the corresponding modification strategies such as the variations in chemical compositions, the architecture of (nano)micro-structures, surface engineering, and the regulation of phase compositions. We hope that the understanding presented in this review can provide useful guidance to developing high-performance layer-structured cathode materials for advanced SIBs.

Lithium-rich sulfide/selenide cathodes for next-generation lithium-ion batteries: challenges and perspectives

The extraordinarily high capacity exhibited by lithium-rich oxides has motivated intensive investigations towards both the cationic and anionic redox processes. With recent main focus on the anionic redox behavior, the anionic redox chemistry has emerged as a new orientation to pursue higher-energy cathodes for lithium-ion batteries. However, the key practical issues such as voltage decay, voltage hysteresis, and irreversible oxygen loss of lithium-rich oxides have triggered researchers to act on the ligand by designing novel lithium-rich sulfides/selenides. In light of this, we herein provide a timely and in-depth perspective on the development of these lithium-rich sulfides/selenides with various structures and coordinations. We highlighted both the variations of phases and structures, lithium storage mechanism, detailed change of sulfur/selenide through anionic redox, and potentials for higher energy densities. We also outlined the main academic and commercial obstacles or challenges for these Li-rich sulfides/selenides for next-generation lithium-ion batteries.

Fast Ionic Storage in Aqueous Rechargeable Batteries: From Fundamentals to Applications

The highly dynamic nature of grid-scale energy systems necessitates fast kinetics in energy storage and conversion systems. Rechargeable aqueous batteries are a promising energy-storage solution for renewable-energy grids as the ionic diffusivity in aqueous electrolytes can be up to 1-2 orders of magnitude higher than in organic systems, in addition to being highly safe and low cost. Recent research in this regard has focussed on developing suitable electrode materials for fast ionic storage in aqueous electrolytes. In this review, breakthroughs in the field of fast ionic storage in aqueous battery materials, and 1D/2D/3D and over-3D-tunnel materials are summarized, and tunnels in over-3D materials are not oriented in any direction in particular. Various materials with different tunnel sizes are developed to be suitable for the different ionic radii of Li⁺ , Na⁺ , K⁺ , H⁺ , NH₄ ⁺ , and Zn²⁺ , which show significant differences in the reaction kinetics of ionic storage. New topochemical paths for ion insertion/extraction, which provide superfast ionic storage, are also discussed.

Toward Highly Stable Anode for Secondary Batteries: Employing TiO2 Shell as Elastic Buffering Marix for FeOx Nanoparticles

Transition metal oxides are considered promising anode materials for next-generation lithium-ion and sodium-ion batteries (LIBs and SIBs) because of their high theoretical capacities; however, their practical application is limited by the detrimental large volume expansion that occurs upon cycling. In this work, a rationally designed TiO₂ @Fe@FeO_x nanocomposite encapsulated by a TiO₂ shell with unique core-shell structure is synthesized and exhibits outstanding electrochemical performance as an anode in LIBs and SIBs. The nanocomposite exhibits a reversible capacity of 619.2 mAh g^-1 at 1 A g^-1 with a coulombic efficiency over 99.5% after 1000 cycles when used as a LIB anode. The nanocomposite also exhibits superior sodium storage performance (267 mAh g^-1 at 50 mA g^-1 , capacity retention of 65.4% after 1000 cycles at 200 mA g^-1 ). The TiO₂ shell serves as a strong conformal layer and soft matrix that can tolerate the volume expansion and maintain the structural integrity of the anode during discharging and charging. Moreover, the open active diffusion channels of the shell contribute to high ion diffusivity and improved ionic, and electronic diffusion. These findings indicate that adoption of TiO₂ coating is an effective strategy to optimize the electrochemical performance of transition metal oxide anode materials.

Unraveling Anionic Redox for Sodium Layered Oxide Cathodes: Breakthroughs and Perspectives

Sodium-ion batteries (SIBs) as the next generation of sustainable energy technologies have received widespread investigations for large-scale energy storage systems (EESs) and smart grids due to the huge natural abundance and low cost of sodium. Although the great efforts are made in exploring layered transition metal oxide cathode for SIBs, their performances have reached the bottleneck for further practical application. Nowadays, anionic redox in layered transition metal oxides has emerged as a new paradigm to increase the energy density of rechargeable batteries. Based on this point, in this review, the development history of anionic redox reaction is attempted to systematically summarize and provide an in-depth discussion on the anionic redox mechanism. Particularly, the major challenges of anionic redox and the corresponding available strategies toward triggering and stabilizing anionic redox are proposed. Subsequently, several types of sodium layered oxide cathodes are classified and comparatively discussed according to Na-rich or Na-deficient materials. A large amount of progressive characterization techniques of anionic oxygen redox is also summarized. Finally, an overview of the existing prospective and the future development directions of sodium layered transition oxide with anionic redox reaction are analyzed and suggested.

Emerging Theranostic Nanomaterials in Diabetes and Its Complications

Diabetes mellitus (DM) refers to a group of metabolic disorders that are characterized by hyperglycemia. Oral subcutaneously administered antidiabetic drugs such as insulin, glipalamide, and metformin can temporarily balance blood sugar levels, however, long-term administration of these therapies is associated with undesirable side effects on the kidney and liver. In addition, due to overproduction of reactive oxygen species and hyperglycemia-induced macrovascular system damage, diabetics have an increased risk of complications. Fortunately, recent advances in nanomaterials have provided new opportunities for diabetes therapy and diagnosis. This review provides a panoramic overview of the current nanomaterials for the detection of diabetic biomarkers and diabetes treatment. Apart from diabetic sensing mechanisms and antidiabetic activities, the applications of these bioengineered nanoparticles for preventing several diabetic complications are elucidated. This review provides an overall perspective in this field, including current challenges and future trends, which may be helpful in informing the development of novel nanomaterials with new functions and properties for diabetes diagnosis and therapy.

Structural, optical, electric and dielectric characterization of a NaCu0.2Fe0.3Mn0.5O2 compound

The compound NaCu0.2Fe0.3Mn0.5O2 was synthesized using a solid-state method and it crystallized in a hexagonal system with a R3̄m space group in an O3-type phase.

Suppressing the P2 - O2 phase transformation and Na+/vacancy ordering of high-voltage manganese-based P2-type cathode by cationic codoping

High-voltage and low-cost manganese-based P2-type oxides show real promise as promising cathode for sodium-ion batteries (SIBs). But the P2 - O2 phase transformation and Na⁺/vacancy ordering results in the inferior structural stability and Na⁺ diffusion coefficient, which further leads to rapid decay of capacity and poor rate capability. Herein, in consideration of the synergetic effects of dual cationic doping, electrochemically inactive Li⁺ and active Co³⁺ codoping are proposed to solve the above issues. The novel two-step doping strategy, Co doping during synthesis of precursors via coprecipitation reaction followed by Li doping during solid-state reaction, are rationally developed. As anticipated, the Li/Co codoped P2-type oxide exhibits the absence of P2 - O2 phase transformation and Na⁺/vacancy disordering, which gives rise to an outstanding cycling stability (86.7% capacity retention within 100 cycles at 0.1C) and high-rate capability (reversible capacity of 109 mAh g^-1 even at 10C). In addition, the full-cells composed of the codoped P2-type positive and hard carbon negative show high energy-density, good lifespan and high-rate property. This proposed cationic codoping provides an effective and scalable tactics for modulating the structural properties of high-voltage P2-type cathodes for advanced SIBs.

Activating a Multielectron Reaction of NASICON-Structured Cathodes toward High Energy Density for Sodium-Ion Batteries

The increasing demand to efficiently store and utilize the electricity from renewable energy resources in a sustainable way has boosted the request for sodium-ion battery technology due to the high abundance of sodium sources worldwide. Na superionic conductor (NASICON) structured cathodes with a robust polyanionic framework have been intriguing because of their open 3D structure and superior thermal stability. The ever-increasing demand for higher energy densities with NASICON-structured cathodes motivates us to activate multielectron reactions, thus utilizing the third sodium ion toward higher voltage and larger capacity, both of which have been the bottlenecks for commercializing sodium-ion batteries. A doping strategy with Cr inspired by first-principles calculations enables the activation of multielectron redox reactions of the redox couples V²⁺/V³⁺, V³⁺/V⁴⁺, and V⁴⁺/V⁵⁺, resulting in remarkably improved energy density even in comparison to the layer structured oxides and Prussian blue analogues. This work also comprehensively clarifies the role of the Cr dopant during sodium storage and the valence electron transition process of both V and Cr. Our findings highlight the importance of a broadly applicable doping strategy for achieving multielectron reactions of NASICON-type cathodes with higher energy densities in sodium-ion batteries.

Degradation of Layered Oxide Cathode in a Sodium Battery: A Detailed Investigation by X-Ray Tomography at the Nanoscale

The degradation mechanism in a sodium cell of a layered Na_0.48 Al_0.03 Co_0.18 Ni_0.18 Mn_0.47 O₂ (NCAM) cathode with P3/P2 structure is investigated by revealing the changes in microstructure and composition upon cycling. The work aims to rationalize the gradual performance decay and the alteration of the electrochemical response in terms of polarization, voltage signature, and capacity loss. Spatial reconstructions of the electrode by X-ray computed tomography at the nanoscale supported by quantitative and qualitative analyses show fractures and deformations in the cycled layered metal-oxide particles, as well as inorganic side compounds deposited on the material. These irreversible morphological modifications reflect structural heterogeneities across the cathode particles due to formation of various domains with different Na⁺ intercalation degrees. Besides, X-ray photoelectron spectroscopy data suggest that the latter inorganic species in the cycled electrode are mainly composed of NaF, Na₂ O, and NaCO₃ formed by parasitic electrolyte decomposition. The precipitation of these insulating compounds at the electrode/electrolyte interphase and the related structural stresses induced in the material lead to a decrease in cathode particle size and partial loss of electrochemical activity. The retention of the NCAM phase after cycling suggests that electrolyte upgrade may improve the performance of the cathode to achieve practical application for sustainable energy storage.