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

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.

Recent advances in rational design for high-performance potassium-ion batteries

The growing global energy demand necessitates the development of renewable energy solutions to mitigate greenhouse gas emissions and air pollution. To efficiently utilize renewable yet intermittent energy sources such as solar and wind power, there is a critical need for large-scale energy storage systems (EES) with high electrochemical performance. While lithium-ion batteries (LIBs) have been successfully used for EES, the surging demand and price, coupled with limited supply of crucial metals like lithium and cobalt, raised concerns about future sustainability. In this context, potassium-ion batteries (PIBs) have emerged as promising alternatives to commercial LIBs. Leveraging the low cost of potassium resources, abundant natural reserves, and the similar chemical properties of lithium and potassium, PIBs exhibit excellent potassium ion transport kinetics in electrolytes. This review starts from the fundamental principles and structural regulation of PIBs, offering a comprehensive overview of their current research status. It covers cathode materials, anode materials, electrolytes, binders, and separators, combining insights from full battery performance, degradation mechanisms, in situ/ex situ characterization, and theoretical calculations. We anticipate that this review will inspire greater interest in the development of high-efficiency PIBs and pave the way for their future commercial applications.

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.

Facilitating Layered Oxide Cathodes Based on Orbital Hybridization for Sodium-Ion Batteries: Marvelous Air Stability, Controllable High Voltage, and Anion Redox Chemistry

Layered oxides have become the research focus of cathode materials for sodium-ion batteries (SIBs) due to the low cost, simple synthesis process, and high specific capacity. However, the poor air stability, unstable phase structure under high voltage, and slow anionic redox kinetics hinder their commercial application. In recent years, the concept of manipulating orbital hybridization has been proposed to simultaneously regulate the microelectronic structure and modify the surface chemistry environment intrinsically. In this review, the hybridization modes between atoms in 3d/4d transition metal (TM) orbitals and O 2p orbitals near the region of the Fermi energy level (EF) are summarized based on orbital hybridization theory and first-principles calculations as well as various sophisticated characterizations. Furthermore, the underlying mechanisms are explored from macro-scale to micro-scale, including enhancing air stability, modulating high working voltage, and stabilizing anionic redox chemistry. Meanwhile, the origin, formation conditions, and different types of orbital hybridization, as well as its application in layered oxide cathodes are presented, which provide insights into the design and preparation of cathode materials. Ultimately, the main challenges in the development of orbital hybridization and its potential for the production application are also discussed, pointing out the route for high-performance practical sodium layered oxide cathodes.

Constructing P2/O3 biphasic structure of Fe/Mn-based layered oxide cathode for high-performance sodium-ion batteries

Fe/Mn-based layered oxide cathode is regarded as a competitive candidate for sodium-ion batteries (SIBs) because of its high theoretical capacity, earth abundance and low cost. However, its poor cycling stability still remains a major bottleneck. Herein, P2/O3 biphasic Na0.67Fe0.425Mn0.425Cu0.15O2 layered oxide is successfully synthesized via a sol-gel method. It is observed that Cu substitution can facilitate the conversion of P2 to O3 phase, and the P2/O3 composite structure can be obtained with an appropriate amount of Cu. Meanwhile, in-situ XRD reveals that constructing P2/O3 composite structure can realize the highly reversible phase transition process of P2/O3-P2/P3-OP4/OP2 and decrease the lattice mismatch during Na+ insertion/extraction. Consequently, the biphasic P2/O3-Na0.67Fe0.425Mn0.425Cu0.15O2 electrode exhibits 87.1 % capacity retention after 100 cycles at 1C, while the single phase P2-Na0.67Fe0.5Mn0.5O2 electrode has only 36.4 %. Therefore, the constructing biphasic structure is proved to be an effective strategy for designing high-performance Fe/Mn-based layered oxide cathodes.

Recent Advances on F-Doped Layered Transition Metal Oxides for Sodium Ion Batteries

With the development of social economy, using lithium-ion batteries in energy storage in industries such as large-scale electrochemical energy storage systems will cause lithium resources to no longer meet demand. As such, sodium ion batteries have become one of the effective alternatives to LIBs. Many attempts have been carried out by researchers to achieve this, among which F-doping is widely used to enhance the electrochemical performance of SIBs. In this paper, we reviewed several types of transition metal oxide cathode materials, and found their electrochemical properties were significantly improved by F-doping. Moreover, the modification mechanism of F-doping has also been summed up. Therefore, the application and commercialization of SIBs in the future is summarized in the ending of the review.

Tuning oxygen release of sodium-ion layered oxide cathode through synergistic surface coating and doping

Layered transition metal oxides have the greatest potential for commercial application as cathode materials for sodium-ion batteries. However, transition metal oxides inevitably undergo an irreversible oxygen loss process during cycling, which leads to structural changes in the material and ultimately to severe capacity degradation. In this work, using density function theory (DFT) calculations, the Ni-O bond is revealed to be the weakest of the M-O bonds, which may lead to structural failure. Herein, the synergistic surface CeO2 modification and the trace doping of Ce elements stimulate oxygen redox and improve its reversibility, thus improving the structural stability and electrochemical performance of the material. Theoretical calculations prove that Na0.67Mn0.7Ni0.2Co0.1O2 (MNC) obtains electrons from CeO2, avoiding destruction of the Ni-O bond by over-energy released during the charging process and inhibiting oxygen loss. The capacity retention was 77.37% for 200 cycles at 500 mA g-1, compared to 33.84% for the unmodified Na0.67Mn0.7Ni0.2Co0.1O2. Overall, the present work demonstrates that the synergistic effect of surface coating and doping is an effective strategy for realizing tuning oxygen release and high electrochemical performance.

NASICON-Type NaTi2(PO4)3 Surface Modified O3-Type NaNi0.3Fe0.2Mn0.5O2 for High-Performance Cathode Material for Sodium-Ion Batteries

Sodium-ion batteries (SIBs) have shown great potential as energy storage devices due to their low price and abundant sodium content. Among them, O3-type layered oxides are a promising cathode material for sodium-ion batteries; however, most of them suffer from slow kinetics and unfavorable structural stability, which seriously hinder their practical application. O3-NaNi0.3Fe0.2Mn0.5O2 surface modification is performed by a simple wet chemical method of coating NaTi2(PO4)3 on the surface. The NASICON-type NaTi2(PO4)3 coating layer has a special three-dimensional channel, which facilitates the rapid migration of Na+, and the NaTi2(PO4)3 coating layer also prevents direct contact between the electrode and the electrolyte, ensuring the stability of the interface. In addition, the NaTi2(PO4)3 coating layer induces part of the Ti4+ doping into the transition metal layer of NaNi0.3Fe0.2Mn0.5O2, which increases the stability of the transition metal layer and reduces the resistance of Na+ diffusion. More importantly, the NaTi2(PO4)3 coating layer can suppress the O3-P3 phase transition and reduce the volume change of the materials throughout the charge/discharge process. Thus, the NaTi2(PO4)3 coating layer can effectively improve the electrochemical performance of the cathode materials. The NFM@NTP3 has a capacity retention of 86% (2.0-4.0 V vs Na+/Na, 300 cycles) and 85% (2.0-4.2 V vs Na+/Na, 100 cycles) at 1C and a discharge capacity of 107 mAh g-1 (2.0-4.0 V vs Na+/Na) and 125 mAh g-1 (2.0-4.2 V vs Na+/Na) at 10C, respectively. Therefore, this surface modification strategy provides a simple and effective way to design and develop high-performance layered oxide cathode materials for sodium-ion batteries.

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.

Multifunctional Effect of Fe Substitution in Na Layered Cathode Materials for Enhanced Storage Stability

Developing stable cathode materials that are resistant to storage degradation is essential for practical development and industrial processing of Na-ion batteries as many sodium layered oxide materials are susceptible to hygroscopicity and instability upon exposure to ambient air. Among the various layered compounds, Fe-substituted O3-type Na(Ni1/2Mn1/2)1-xFexO2 materials have emerged as a promising option for high-performance and low-cost cathodes. While previous reports have noted the decent air-storage stability of these materials, the role and origin of Fe substitution in improving storage stability remain unclear. In this study, we investigate the air-resistant effect of Fe substitution in O3-Na(Ni1/2Mn1/2)1-xFexO2 cathode materials by performing systematic surface and structural characterizations. We find that the improved storage stability can be attributed to the multifunctional effect of Fe substitution, which forms a surface protective layer containing an Fe-incorporated spinel phase and decreases the thermodynamical driving force for bulk chemical sodium extraction. With these mechanisms, Fe-containing cathodes can suppress the cascades of cathode degradation processes and better retain the electrochemical performance after air storage.

Investigation of W6+-doped in high-nickel LiNi0.83Co0.11Mn0.06O2 cathode materials for high-performance lithium-ion batteries

WO₃ as tungsten dopant is introduced into lithium nickel cobalt manganese (LiNi_0.83Co_0.11Mn_0.06O₂, NCM) layered oxide powders to synthesize W⁶⁺-doped NCM cathode materials during the lithiation process of the hydroxide precursor. Introducing W⁶⁺ into the lattice can lead to the diversities of the crystal structure, surface morphology, and electrochemical performance. The crystal structure confirmed by X-ray diffraction indicates that the W⁶⁺-doped oxide powders present a typical R-3m layered structure with larger interplanar distance and cell volume. Also, scanning electron microscope images reveal that the primary particles shrink forming a tighter surface under the effect of W⁶⁺, while the specific changes gradually aggravate with increase in the content of W⁶⁺ added. The excellent electrochemical stability of W⁶⁺-doped samples is observed, as the stable host structure is reinforced by the strong W-O bond. The stable structure does not only inhibit the anisotropic volume change caused by repetitive H2 ⇔ H3 phase transitions, but also sustains the integrated structure to impede the formation of microcracks and the appearance of more side reactions. This research provides an effective route on investigating the potential association between electrochemical performance and structure change for W⁶⁺-doped strategy.