Cathode For Sodium-ion Batteries Research Articles

Sodium layered oxide cathodes: properties, practicality and prospects.

Rechargeable sodium-ion batteries (SIBs) have emerged as an advanced electrochemical energy storage technology with potential to alleviate the dependence on lithium resources. Similar to Li-ion batteries, the cathode materials play a decisive role in the cost and energy output of SIBs. Among various cathode materials, Na layered transition-metal (TM) oxides have become an appealing choice owing to their facile synthesis, high Na storage capacity/voltage that are suitable for use in high-energy SIBs, and high adaptivity to the large-scale manufacture of Li layered oxide analogues. However, going from the lab to the market, the practical use of Na layered oxide cathodes is limited by the ambiguous understanding of the fundamental structure-performance correlation of cathode materials and lack of customized material design strategies to meet the diverse demands in practical storage applications. In this review, we attempt to clarify the fundamental misunderstandings by elaborating the correlations between the electron configuration of the critical capacity-contributing elements (e.g., TM cations and oxygen anion) in oxides and their influence on the Na (de)intercalation (electro)chemistry and storage properties of the cathode. Subsequently, we discuss the issues that hinder the practical use of layered oxide cathodes, their origins and the corresponding strategies to address their issues and accelerate the target-oriented research and development of cathode materials. Finally, we discuss several new Na layered cathode materials that show prospects for next-generation SIBs, including layered oxides with anion redox and high entropy and highlight the use of layered oxides as cathodes for solid-state SIBs with higher energy and safety. In summary, we aim to offer insights into the rational design of high-performance Na layered oxide cathode materials towards the practical realization of sustainable electrochemical energy storage at a low cost.

Unraveling and suppressing the voltage decay of high-capacity cathode materials for sodium-ion batteries

The steric heterogeneity of Mn redox derived from the oxygen loss is the trigger of voltage decay in high-capacity oxygen-redox sodium-based layered oxides. Moreover, an electron localization strategy is developed to eliminate the voltage decay.

Emerging high voltage V4+/V5+ redox reactions in Na3V2(PO4)3-based cathodes for sodium-ion batteries.

Na3V2(PO4)3 (NVP) cathode materials with the advantages of long cycle life and superior thermal stability have been considered promising cathode candidates for SIBs. However, the unsatisfactory energy density derived from low theoretical capacity and operating voltage (3.35 V vs. Na+/Na, based on the V3+/V4+ redox couple) inevitably limits their practical application. Therefore, the activation of the V4+/V5+ redox couple (∼4.0 V vs. Na+/Na) in NVP-based cathode materials to boost the energy density of SIBs has attracted extensive attention. Herein, we first analyze the challenges of activation of the V4+/V5+ redox couple in NVP-based cathode materials. Subsequently, the recent achievement of NVP-based cathode materials with activated V4+/V5+ redox reactions for SIBs is overviewed. Finally, further research directions of high voltage V4+/V5+ redox reactions in NVP-based cathodes are proposed. This review provides valuable guidance for developing high energy density NVP-based cathode materials for SIBs.

A bipolar polymer cathode for sodium-ion batteries.

A bipolar polymer cathode material, containing redox-active azo benzene and diamine moieties, was synthesized for sodium-ion batteries. The n-type azo group and p-type amine group enable a wide cutoff window with an initial capacity of 93 mA h g-1 at 50 mA g-1 and a high voltage plateau at ∼3.3 V.

Is surface modification effective to stabilize high-voltage cycling for layered P2-Na2/3Ni1/3Mn2/3O2 cathodes?

Layered transition metal oxides (TMOs), like the P2-type Na2/3Ni1/3Mn2/3O2, are promising cathodes for sodium-ion batteries but suffer rapid capacity degradation at high voltages. Surface engineering is a popular strategy to modify the high-voltage stability of cathode materials, yet its efficacy for sodium layered TMOs remains elusive, especially given the deleterious layer-gliding phase transition during high-voltage operation. Here, we examined the effect of surface coatings on the high-voltage cycling stability of Na2/3Ni1/3Mn2/3O2, finding that they suppress high-voltage polarization but do not significantly affect capacity retention, which is mainly impacted by bulk structure degradation. Hence, surface engineering must be complemented with bulk structure modification to stabilize high-voltage cycling.

Realizing long-term cycling stability of O3-type layered oxide cathodes for sodium-ion batteries.

O3-type layered oxide cathodes are promising for practical sodium-ion batteries (SIBs) owing to their high theoretical capacity, facile synthesis, and sufficient Na+ storage. However, they face challenges such as rapid capacity loss and poor cycling stability, mainly attributed to irreversible phase transitions. To address these challenges, a novel cathode material, Li/Sn co-substituted O3-Na0.95Li0.07Sn0.01Ni0.22Fe0.2Mn0.5O2 (LSNFM), has been designed by regulating the electronic structure, in which Li+ activates more redox reactions of Ni2+/3+ and Fe3+/4+ above 2.5 V and suppresses the redox reactivity of Mn3+/4+ below 2.5 V, while Sn4+ can prevent the charge delocalization in the transition metal layer, contributing to structural stability. Due to this synergistic effect, the as-prepared LSNFM electrode with high structural reversibility displays a 27.2% capacity increase contributed by the high-voltage transition metal ion redox activity and exhibits excellent long-term cycling stability, an 84.0% capacity retention after 500 cycles at 1 C and an 84.7% capacity retention after 2000 cycles at 5 C. The fundamental mechanism is fully investigated using systematic in situ/ex situ characterization techniques and density functional theory computations. This work provides a paradigm for designing long-term cycle life cathode materials by synergistically regulating the electronic structure in practical SIBs.

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.

Promoting fast Na-storage and fabricating a stable layered cathode for sodium-ion batteries via site-selective substitution in triple crystallographic sites

An advanced Na0.66Ca0.05[Ni0.25Li0.11Mn0.64]O1.95F0.05 with fast Na storage and long-life was designed via a site-selective substitution of Ca2+, Li+ and F−, and investigated by a series of physical/electrochemical tests and theoretical calculation.

Revealing the effect of conductive carbon materials on the sodium storage performance of sodium iron sulfate.

Na2Fe2(SO4)3 (NFS), as a promising cathode for sodium-ion batteries, is still plagued by its poor intrinsic conductivity. In general, hybridization with carbon materials is an effective strategy to improve the sodium storage performance of NFS. However, the role of carbon materials in the electrochemical performance of NFS cathode materials has not been thoroughly investigated. Herein, the effect of carbon materials was revealed by employing various conductive carbon materials as carbon sources. Among these, the NFS coated with Ketjen Black (NFS@KB) shows the largest specific surface area, which is beneficial for electrolyte penetration and rapid ionic/electronic migration, leading to improved electrochemical performance. Therefore, NFS@KB shows a long cycle life (74.6 mA h g-1 after 1000 cycles), superior rate performance (61.5 mA h g-1 at a 5.0 A g-1), and good temperature tolerance (-10 °C to 60 °C). Besides, the practicality of the NFS@KB cathode was further demonstrated by assembling a NFS@KB//hard carbon full cell. Therefore, this research indicates that a suitable carbon material for the NFS cathode can greatly activate the sodium storage performance.

Recent Progress in Layered Oxide Cathodes for Sodium-ion Batteries: Stability,Phase transition and Solutions

Due to their cost efficiency and the sustainable availability of sodium resources, sodium-ion batteries (SIBs) are regarded as an economical alternative or additional choice to the well-established lithium-ion batteries (LIBs),...

Redox Couple Modulation in NASICON Phosphates toward High-Performance Cathodes for Na-Ion Batteries

Natrium superionic conductor (NASICON)-type phosphates have aroused a great interest as cathode materials for sodium-ion batteries (SIBs) by virtue of their stable 3-dimensional frameworks, flexible molecular formula tunability, and superior ionic conductivity. Nevertheless, the intrinsic low electronic conductivity and relatively low theoretical specific capacity place obstacles in their way toward achieving higher electrochemical performance. In addition, only 2-electron reactions in most NASICON cathodes and poor reversibility of high-voltage redox couples severely limit their energy density. To address the above tough issues, an in-depth understanding of transition metal selection, elements ratio optimization, and Na-storage mechanism is of paramount importance. Here, this mini review summarizes the latest progresses on the NASICON-type phosphate cathodes for SIBs from the perspective of redox couple modulation. NASICON cathodes featuring high operating voltage and multielectron reactions are discussed in detail. Finally, the remaining challenges and personal outlooks based on redox couple regulation are put forward, shedding light on the designing rules for high-energy and long-durability NASICON-type phosphate cathodes for SIBs in the future.

Exploration of PVP-Combustion Synthesis and Electrochemical Performance of O3-type NaxNi0.33Fe0.33Mn0.33O2 Layered Material for Sodium-Ion Batteries

The performance of sodium-ion batteries critically depends on the cathode materials used, making it essential to explore and optimize suitable candidates. Among them, O3-structured NaNi0.33Fe0.33Mn0.33O2 has emerged as one of the most promising cathode materials due to its outstanding electrochemical properties. However, there still exists a knowledge gap regarding the detailed synthesis conditions and the comprehensive performance of the full cell using this material. In this study, we investigated the influence of synthesis temperature, time, and sodium content on the electrochemical performance and charge-discharge kinetics of O3-structured NaNi0.33Fe0.33Mn0.33O2, prepared via the PVP-gel combustion method. Through systematic analysis, we elucidated the impact of these synthesis parameters on the material’s properties and battery performance. The results revealed that the optimized conditions led to a cathode material with superior electrochemical performance, exhibiting enhanced capacity with 139 mAh g−1 at 0.1 C and 96 mAh g−1 at 10 C. Additionally, a full cell using the optimized cathode material was studied, showing promising performance. This research sheds light on the significance of synthesis parameters in tailoring the electrochemical properties of O3-structured NaNi0.33Fe0.33Mn0.33O2 for sodium-ion batteries. The insights gained from this study hold valuable implications for the further development of practical sodium-ion battery cathode materials.

A NASICON-type Na3.67Cu0.17Fe0.5V1.33(PO4)3 cathode with multi-electron reaction for high-energy sodium-ion battery

A NASICON structured Na3.67Cu0.17Fe0.5V1.33(PO4)3 (NCFVP) sodium-ion battery cathode material with multi-electron redox reaction has been designed. The obtained NCFVP demonstrates a high capacity, high energy density, and ideal cyclability.

Na3V2(PO4)3-decorated Na3V2(PO4)2F3 as a high-rate and cycle-stable cathode material for sodium ion batteries.

Since Na3V2(PO4)3 (NVP) possesses modest volume deformation and three-dimensional ion diffusion channels, it is a potential sodium-ion battery cathode material that has been extensively researched. Nonetheless, NVP still endures the consequences of poor electronic conductivity and low voltage platforms, which need to be further improved. On this basis, a high voltage platform Na3V2(PO4)2F3 was introduced to form a composite with NVP to increase the energy density. In this study, the sol-gel technique was successfully used to synthesize a Na3V2(PO4)2.75F0.75/C (NVPF·3NVP/C) composite cathode material. The citric acid-derived carbon layer was utilized to construct three-dimensional conducting networks to effectively promote ion and electron diffusion. Furthermore, the composites' synergistic effect accelerates the quick ionic migration and improves the kinetic reaction. In particular, NVP as the dominant phase enhanced the structural stability and significantly increased the capacitive contribution. Therefore, at 0.1C, the discharge capacity of the modified NVPF·3NVP/C composite is 120.7 mA h g-1, which is greater than the theoretical discharge capacity of pure NVP (118 mA h g-1). It discharged 110.9 mA h g-1 of reversible capacity even at an elevated multiplicity of 10C, and after 200 cycles, it retained 64.1% of its capacity. Thus, the effort produced an optimized NVPF·3NVP/C composite cathode material that may be used in the sodium ion cathode.

Weberite Na2MM′F7 (M, M′ = redox-active metal) as promising fluoride-based sodium-ion battery cathodes

Systematic evaluation of viable fluoride-based materials as promising cathodes for Na-ion batteries with improved performance that can surpass LIBs.

Prospective hazard and toxicity screening of sodium-ion battery cathode materials

Sodium-ion batteries (SIBs) are a promising alternative to LIBs, but selecting low hazard cathode materials is challenging. Our screening covers three hazard perspectives in early TRLs of SIBs and supports the sustainable by design discourse.

Developing an abnormal high-Na-content P2-type layered oxide cathode with near-zero-strain for high-performance sodium-ion batteries.

Layered transition metal oxides (NaxTMO2) possess attractive features such as large specific capacity, high ionic conductivity, and a scalable synthesis process, making them a promising cathode candidate for sodium-ion batteries (SIBs). However, NaxTMO2 suffer from multiple phase transitions and Na+/vacancy ordering upon Na+ insertion/extraction, which is detrimental to their electrochemical performance. Herein, we developed a novel cathode material that exhibits an abnormal P2-type structure at a stoichiometric content of Na up to 1. The cathode material delivers a reversible capacity of 108 mA h g-1 at 0.2C and 97 mA h g-1 at 2C, retaining a capacity retention of 76.15% after 200 cycles within 2.0-4.3 V. In situ diffraction studies demonstrated that this material exhibits an absolute solid-solution reaction with a low volume change of 0.8% during cycling. This near-zero-strain characteristic enables a highly stabilized crystal structure for Na+ storage, contributing to a significant improvement in battery performance. Overall, this work presents a simple yet effective approach to realizing high Na content in P2-type layered oxides, offering new opportunities for high-performance SIB cathode materials.

Comparative analysis of thermal stability and electrochemical performance of NaNi1/3Fe1/3Mn1/3O2 cathode in different electrolytes for sodium ion batteries

The electrochemical compatibility and thermal stability of cathode and electrolyte guarantee the intrinsic safety of batteries. The NaNi1/3Fe1/3Mn1/3O2 (NaNFM) cathode for sodium ion batteries (SIBs) has not received, sufficient attention concerning its thermal safety compared to its electrochemical properties. Herein, we investigated the thermal stability of NaNFM, exothermic reaction and electrochemical performance of NaNFM with various electrolytes. The comprehensive electrochemical performance of NaNFM in different electrolytes followed this sequence: sodium hexafluorophosphate (NaPF6) > sodium bis(trifluoromethyl-sulfonyl)imide (NaTFSI) > sodium perchlorate (NaClO4)- based electrolytes. Additionally, ethylene carbonate (EC): propylene carbonate (PC)- type electrolytes displayed superior cycling stability compared to ethylene carbonate (EC): diethyl carbonate (DEC)- type electrolytes. Moreover, the heat flow profiles demonstrated that the thermal stability between NaNFM and various electrolytes could be ordered according to the total heat release as: NaClO4 < NaPF6 < NaTFSI-based electrolyte. X-ray diffractometer (XRD), scanning electron microscope (SEM) and x-ray photoelectron spectrometer (XPS) analyses were carried out to investigate the changes in crystal structure, morphology and valence state of thermal reaction products after microcalorimetric analysis experiments. These findings provide valuable insights for the safe application of the NaNFM cathode in SIBs.

Promoting threshold voltage of P2-Na0.67Ni0.33Mn0.67O2 with Cu2+ cation doping toward high-stability cathode for sodium-ion battery

P2-type Na0.67Ni0.33Mn0.67O2 has attracted considerable attraction as a cathode material for sodium-ion batteries owing to its high operating voltage and theoretical specific capacity. However, when the charging voltage is higher than 4.2 V, the Na0.67Ni0.33Mn0.67O2 cathode undergoes a detrimental irreversible phase transition of P2-O2, leading to a drastic decrease in specific capacity. To address this challenge, we implemented a Cu-doping strategy (Na0.67Ni0.23Cu0.1Mn0.67O2) in this work to stabilize the structure of the transition metal layer. The stabilization strategy involved reinforcing the transition metal–oxygen (TMO) bonds, particularly the MnO bond and inhibiting interlayer slip during deep desodiation. As a result, the irreversible phase transition voltage is delayed, with the threshold voltage increasing from 4.2 to 4.4 V. Ex-situ X-ray diffraction measurements revealed that the Na0.67Ni0.23Cu0.1Mn0.67O2 cathode maintains the P2 phase within the voltage window of 2.5–4.3 V, whereas the P2-Na0.67Ni0.33Mn0.67O2 cathode transforms entirely into O2-type Na0.67Ni0.33Mn0.67O2 when the voltage exceeds 4.3 V. Furthermore, absolute P2-O2 phase transition of the Na0.67Ni0.23Cu0.1Mn0.67O2 cathode occurred at 4.6 V, indicating that Cu2+ doping enhances the stability of the layer structure and increases the threshold voltage. The resulting Na0.67Ni0.23Cu0.1Mn0.67O2 cathode exhibited superior electrochemical properties, demonstrating an initial reversible specific capacity of 89.1 mAh/g at a rate of 2C (360 mA g−1) and retaining more than 78 % of its capacity after 500 cycles.

From Rotten to Magical: Transition Metal Migration in Layered Sodium‐Ion Battery Cathodes

AbstractLayered oxides, the most commercially promising cathode materials for sodium‐ion batteries (SIBs), are extensively investigated due to their low cost, abundant raw materials, flexible structure, and high capacity. However, although the “rotten” transition metal (TM) migration phenomenon in layered oxide cathode materials leads to unfavorable structure reconstruction, sluggish Na+ diffusion and subsequent performance degradation, TM migration has not been systematically summarized and intensively discussed. Herein, a comprehensive insight into the recent advances of TM migration in layered SIB cathodes is provided, aiming to realize the “magical” utilization of TM migration. First, the negative effects of TM migration on crystal structure and electrochemical properties are discussed. Then, the origin of TM migration is intensively analyzed, and three main mechanisms of the migration are presented, including Cr4+–Cr4+–Cr4+ triplets, Jahn–Teller Fe4+ and Na‐free layers. Additionally, the latest research findings on exploring the origin are fully discussed. Finally, the suppression and utilization of TM migration are discussed, and the further exploration of TM migration and the future directions of suppressing/utilizing TM migration are outlooked. It is believed that this perspective will provide guidelines for the design of high‐performance layered oxide cathodes involving TM migration by turning the “rotten” into the “magical.”