Challenges of layer-structured cathodes for sodium-ion batteries

High-Performance Sodium-Ion Batteries with Graphene: An Overview of Recent Developments and Design

Due to their low production cost, sodium-ion batteries (SIBs) are considered attractive alternatives to lithium-ion batteries (LIBs) for next generation sustainable and large-scale energy storage systems. However, during the charge/discharge cycle, a large volume strain is resulted due to the presence of a large radius of sodium ions and high molar compared to lithium ions, which further leads to poor cyclic stability and lower reversible capacity. In the past, researchers have devoted significant efforts to explore various anode materials to achieve SIBs with high energy density. Hence, as a promising anode material for SIBs, the two-dimensional (2D) materials including graphene and its derivatives and metal oxides have attracted remarkable attention due to their layered structure and superior physical and chemical properties. The inclusion of graphene and metal oxides with other nanomaterials in electrodes have led to the significant enhancements in electrical conductivity, reaction kinetics, capacity, rate performance and accommodating the large volume change respectively. Moreover, these 2D materials facilitated large surface areas and shorter paths for sodium ion adsorption and transportation respectively. In this review article, the fabrication techniques, structural configuration, sodium ion storage mechanism and its electrochemical performances will be introduced. Subsequently, an insight into the recent advancements in SIBs associated with 2D anode materials (graphene, graphene oxide (GO), transition metal oxides etc.) and other graphene-like elementary analogues (germanene, stanine etc.) as anode materials respectively will be discussed. Finally, the key challenges and future perspectives of SIBs towards enhancing the sodium storage performance of graphene-based electrode materials are discussed. In summary, we believe that this review will shed light on the path towards achieving long-cycling life, low operation cost and safe SIBs with high energy density using 2D anode materials and to be suitably commercialized for large-scale energy storage applications in the future.

Prilling and Coating Strategy to Synthesize High-Performance Spherical NaNi0.4Fe0.2Mn0.4O2 Cathode Materials for Sodium Ion Batteries

Low-cost sodium ion batteries are of great significance in large-scale energy storage applications. With its high energy density and simple synthesis process, layered transition-metal oxides have become one of the most likely sodium ion battery cathode materials to replace lithium ion batteries in the energy storage market. Here, we report a prilling and MoS2 coating strategy to prepare the spherical cathode material. The spherical micronano particles shorten the diffusion path of Na+, restrain the complexity phase transitions, and enhance the tap density of the materials. In addition, the MoS2 coating improves the electrical conductivity of the material and the structural stability of the cathode material in air. The initial specific discharge capacity is 148.4 mA h g-1 at 0.1 C, which can be maintained at 128.9 mA h g-1 after exposure to air for 10 days. This method dramatically improves the energy density and structural stability of the cathode material, which provides a new scheme for preparing high-performance sodium ion batteries.

Deep insight on Li interlayer migration in O3-type NaLi1/3Mn2/3O2 as a cathode material for Na-ion batteries

Layered manganese transition metal oxides, such as NaMnO2, have attracted great interest due to the low cost and high capacity. However, complex phase transitions in NaMnO2 lead to poor cycling stability. The introduction of Li doping has been confirmed to improve the performance of NaMnO2. O3-type NaLi1/3Mn2/3O2 (NLMO), synthesized in 2021, has demonstrated excellent electrochemical performance. Notably, irreversible Li interlayer migration (Li migrates from the transition metal layer to the alkali metal layer) has been observed during cycling, which is related to the electrochemical performance. Therefore, it is crucial to understand the mechanism underlying Li interlayer migration in O3-NLMO. However, the environment of Li interlayer migration on cycling is complex and involves interlayer spacing, Na-ion concentration, the degree of O-ion oxidation, and phase transition. Here, in this work, we utilized the first-principles method to decouple the coupling factors influencing the Li interlayer migration. Through analyzing the impact of the single-factor on Li interlayer migration, we aim to identify the crucial factors affecting this process. Our results show that a decrease in Na-ion concentration and an increase in O-ion oxidation degree promote the Li interlayer migration, while the O-P phase transition suppresses the Li interlayer migration. Interlayer spacing was found to play a less influential role in Li interlayer migration. Our investigations provide effective strategies for the subsequent regulation of Li interlayer migration.

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.

A document-level information extraction pipeline for layered cathode materials for sodium-ion batteries

Natural language processing techniques enable extraction of valuable information from large amounts of published literature for the application of data science and technology, i.e. machine learning in the field of materials science. Nevertheless, the automated extraction of data from full-text documents remains a complex task. We propose a document-level natural language processing pipeline for literature extraction of comprehensive information on layered cathode materials for sodium-ion batteries. The pipeline enhances entity recognition with contextual supplementary information while capturing the article structure. Finally, a heuristic multi-level relationship extraction algorithm is employed in relation extraction to extract experimental parameters and complex performance relationships respectively. We successfully extracted a comprehensive dataset containing 5265 records from 1747 documents, encompassing essential information such as chemical composition, synthesis parameters, and electrochemical properties. By implementing our pipeline, we have made significant progress in overcoming the challenges associated with data scarcity in battery informatics. The extracted datasets provide a valuable resource for further research and development in the field of layered cathode materials.

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.

Synergetic impact of high-entropy microdoping modification in Na3V2(PO4)3

High entropy polyanionic Na3V1.9(Ca,Mg,Cr,Ti,Mn)0.1(PO4)3 was synthesized, which activated a reversible redox reaction of V4+/V5+ and reached a remarkable capacity of 116 mA h g-1 at 1C and maintained 90% capacity retention after 1000 cycles at 10C. Structure evolution and sodium storage mechanisms were revealed by an in situ XRD method, which disclosed the high-entropy effect of material design. Together with the full battery tests, these findings promote the wide applications of high-entropy polyanionic cathodes in SIBs.

Sustainable, low Ni-containing Mg-doped layered oxides as cathodes for sodium-ion batteries

The supply of battery-grade nickel to produce positive electrodes of sodium-ion batteries may soon become insufficient. For this reason, it is crucial to find new electrode materials that minimize its use or even fully remove this element from synthesis. We have prepared a Na0.67Mg0.05FexNiyMnzO2 (0 ≤ x ≤ 0.2; y = 0.05, 0.15; 0.6 ≤ z ≤ 0.9) series with low Ni and Fe contents by a single and easily scalable sol-gel method. This procedure yields high-purity and crystalline samples as evidenced by structural, morphological, and spectroscopic studies, including X-ray diffraction, electron microscopy, and X-ray photoelectron spectroscopy. The electrochemical tests showed an exceptional performance for the F0N05 sample with the lowest (Ni + Fe) contents, at 5 C (ca. 100 mA h g-1), and good capacity retention after 100 cycles. This excellent behaviour was also evidenced when cycling at -15 °C. These results were confirmed by electrochemical techniques, such as cyclic voltammetry and impedance spectroscopy, that evidenced a fast exchange of sodium ions due to a significant capacitive contribution and high apparent diffusion coefficients. Post-mortem analysis of the F0N05 electrodes by XRD showed the reversible insertion and the absence of detrimental P2-O2 and P2-P2' transitions, while XPS spectra demonstrated the reversible redox activity of both transition metals and oxygen.

Recent Progress on Honeycomb Layered Oxides as a Durable Cathode Material for Sodium-Ion Batteries

Sodium-ion batteries (SIBs) are becoming promising candidates for energy storage devices due to the low cost, abundant reserves, and excellent electrochemical performance. As the most important unit, layered cathodes attract much attention, where honeycomb-layered-oxides (HLOs) manifest outstanding structural stability, high redox potential, and long-life electrochemistry. Here, recent progress on HLOs as well as Na₃ Ni₂ SbO₆ and Na₃ Ni₂ BiO₆ as two representative materials are introduced, and the crystal and electronic structure, electrochemical performance, and modification strategies are summarized. The advanced high nickel HLOs are highlighted toward development of state-of-the-art sodium-ion batteries. This review would deepen the understanding of superstructure in layered oxides, as well as structure-property relationship, and inspire more interest in high output voltage, long lifespan sodium-ion batteries.

Development of a high-rate-capable O3-structured 'layered' Na transition metal oxide by tuning the cation-oxygen bond covalency

By developing a high-rate-capable O3-structured Na(Li_0.05Ni_0.3Si_0.05Ti_0.45Cu_0.1Mg_0.05)O₂-based cathode material for Na-ion batteries, wherein partial substitution of more electronegative Si⁴⁺ for Ti⁴⁺ in the transition metal layer has weakened-cum-lengthened the Na-O bond, enlarged the 'inter-slab' spacing and, thus, enhanced the Na-transport kinetics, a design criterion has been laid-out in the above context.

Unprecedented Cyclability and Moisture Durability of NaCrO2 Sodium-Ion Battery Cathode via Simultaneous Al Doping and Cr2O3 Coating

Although there are many cathode candidates for sodium-ion batteries (NIBs), NaCrO₂ remains one of the most attractive materials due to its reasonable level of capacity, nearly flat reversible voltages, and high thermal stability. However, the cyclic stability of NaCrO₂ needs to be further improved in order to compete with other state-of-the-art NIB cathodes. In this study, we show that Cr₂O₃-coated and Al-doped NaCrO₂, which is synthesized through a simple one-pot synthesis, can achieve unprecedented cyclic stability. We confirm the preferential formation of a Cr₂O₃ shell and a Na(Cr_1-2xAl_2x)O₂ core, rather than xAl₂O₃/NaCrO₂ or Na_1/1+2x(Cr_1/1+2xAl_2x/1+2x)O₂, through spectroscopic and microscopic methods. The core/shell compounds exhibit superior electrochemical properties compared to either Cr₂O₃-coated NaCrO₂ without Al dopants or Al-doped NaCrO₂ without shells because of their synergistic contributions. As a result, Na(Cr_0.98Al_0.02)O₂ with a thin Cr₂O₃ layer (5 nm) shows no capacity fading during 1000 charge/discharge cycles while maintaining the rate capability of pristine NaCrO₂. In addition, the compound is inert against humid air and water. We also discuss the reasons for the excellent performance of Cr₂O₃-coated Na(Cr_1-2xAl_2x)O₂.

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.

Metal Substitution versus Oxygen-Storage Modifier to Regulate the Oxygen Redox Reactions in Sodium-Deficient Three-Layered Oxides

Sodium-deficient nickel-manganese oxides with three-layered stacking exhibit the unique property of dual nickel-oxygen redox activity, which allows them to achieve enormous specific capacity. The challenge is how to stabilize the oxygen redox activity during cycling. This study demonstrates that oxygen redox activity of P3-Na2/3Ni1/2Mn1/2O2 during both Na+ and Li+ intercalation can be regulated by the design of oxide architecture that includes target metal substituents (such as Mg2+ and Ti4+) and oxygen storage modifiers (such as CeO2). Although the substitution for nickel with Ti4+ amplifies the oxygen redox activity and intensifies the interaction of oxides with NaPF6- and LiPF6-based electrolytes, the Mg2+ substituents influence mainly the nickel redox activity and suppress the deposition of electrolyte decomposed products (such as MnF2). The CeO2-modifier has a much stronger effect on the oxygen redox activity than that of metal substituents; thus, the highest specific capacity is attained. In addition, the CeO2-modifier tunes the electrode–electrode interaction by eliminating the deposition of MnF2. As a result, the Mg-substituted oxide modified with CeO2 displays high capacity, excellent cycling stability and exceptional rate capability when used as cathode in Na-ion cell, while in Li-ion cell, the best performance is achieved for Ti-substituted oxide modified by CeO2.

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.