F-Doped NaTi2(PO4)3/C Nanocomposite as a High-Performance Anode for Sodium-Ion Batteries

Optimized Porous KTi2(PO4)3@N-Doped Carbon Electrode for Enhanced Sodium/Potassium-Storage and Accelerated Activation Process

Porous KTi2(PO4)3 nanoparticles are synthesized via a solvothermal method and subsequently modified with nitrogen-doped carbon layers by using polydopamine as the carbon source. The resultant KTi2(PO4)3@N-doped carbon composite (KTP@NC) exhibits a preserved porous structure with abundant pores, facilitating ion diffusion and electrolyte infiltration. Various characterizations, including X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and Raman spectroscopy, reveal the successful formation of an interconnected nitrogen-doped carbon network. Theoretical calculations and experimental results demonstrate that the nitrogen-doped carbon layer significantly enhances the electronic conductivity of the material and increases the adsorption energy for the sodium and potassium ions. As an electrode for sodium-ion batteries, the KTP@NC composite shows a reversible capacity of 88.4 mA h g-1 at 30C and retains 97.3% of its capacity after 400 cycles at 5C, with only 10 activation cycles required. Additionally, it displays outstanding cycle stability at 50 °C. For potassium-ion batteries, the KTP@NC electrode provides a specific capacity of 98.9 mA h g-1 at 0.5C and maintains 92.9% capacity retention after 150 cycles at 1C. The enhanced electrochemical performance of the KTP@NC electrode can be attributed to the improved reaction kinetics and electronic conductivity enabled by the nitrogen-doped carbon coating.

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

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

Manipulating amorphous and crystalline hybridization of Na3V2(PO4)3/C for enhancing sodium-ion diffusion kinetics

Na3V2(PO4)3 (NVP) has attracted considerable attention as a promising cathode material for sodium-ion batteries (SIBs). But its insufficient electronic conductivity, limited capacities, and fragile structure hinder its extended application, particularly in scenarios involving rapid charging and prolonged cycling. A hybrid cathode material has been developed to integrate both amorphous and crystalline phases, with the objective of improving the rate performance and Na storage capacity by leveraging bi-phase coordination. Consequently, the combination of amorphous and crystalline phases enhanced the kinetics of Na-ion diffusion, resulting in a 1-2 orders of magnitude enhancement in diffusion dynamics. Furthermore, the existence of amorphous states has been demonstrated to elevate the active Na2 site content, resulting in an increased reversible capacity. This assertion is substantiated by evidence derived from solid-state nuclear magnetic resonance (ss-NMR) and electrochemical characteristics. The innovative bi-phase collaborative material provides a specific capacity of 114 mAh/g at 0.2 C, exceptional rate performance of 82 mAh/g at 10 C, and remarkable long-term cycle stability, retaining 95 mAh/g at 5 C even after 300 cycles. In conclusion, the homogeneous hybridization of amorphous and crystalline phases presents itself as a promising and effective strategy for improving Na-ion storage capacity of cathodes in SIBs.

Electrosprayed hierarchical mesoporous Mn0.5Ti2(PO4)3@C microspheres as promising High-Performance anode for Potassium-Ion batteries

NASICON-structured Ti-based polyanion compounds benefit from a stable structural framework, large ion channels, and fast ion mobility. However, the large radius of potassium and its poor electronic conductivity restrict its use in potassium-ion batteries. Herein, hierarchical mesoporous Mn0.5Ti2(PO4)3@C microspheres have been successfully synthesized using a simple electrospraying method. These microspheres consist of Mn0.5Ti2(PO4)3 nanoparticles evenly embedded in three-dimensional mesoporous carbon microspheres. The hierarchical mesoporous micro/nanostructure facilitates the rapid insertion and extraction of K+, while the three-dimensional carbon microspheres matrix enhances electrical conductivity and prevents active materials from collapsing during cycling. So the hierarchical mesoporous Mn0.5Ti2(PO4)3@C microspheres exhibit a high reversible discharge specific capacity (306 mA h g-1 at 20 mA g-1), a notable rate capability (123 mA h g-1 at 5000 mA g-1), and exceptional cycle performance (148 mA h g-1 at 500 mA g-1 after 1000 cycles). The results show that electrosprayed Mn0.5Ti2(PO4)3@C microspheres are a promising anode for PIBs.

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.

Recent progress and strategic perspectives of inorganic solid electrolytes: fundamentals, modifications, and applications in sodium metal batteries

Solid-state electrolytes (SEs) have attracted overwhelming attention as a promising alternative to traditional organic liquid electrolytes (OLEs) for high-energy-density sodium-metal batteries (SMBs), owing to their intrinsic incombustibility, wider electrochemical stability window (ESW), and better thermal stability. Among various kinds of SEs, inorganic solid-state electrolytes (ISEs) stand out because of their high ionic conductivity, excellent oxidative stability, and good mechanical strength, rendering potential utilization in safe and dendrite-free SMBs at room temperature. However, the development of Na-ion ISEs still remains challenging, that a perfect solution has yet to be achieved. Herein, we provide a comprehensive and in-depth inspection of the state-of-the-art ISEs, aiming at revealing the underlying Na⁺ conduction mechanisms at different length scales, and interpreting their compatibility with the Na metal anode from multiple aspects. A thorough material screening will include nearly all ISEs developed to date, i.e., oxides, chalcogenides, halides, antiperovskites, and borohydrides, followed by an overview of the modification strategies for enhancing their ionic conductivity and interfacial compatibility with Na metal, including synthesis, doping and interfacial engineering. By discussing the remaining challenges in ISE research, we propose rational and strategic perspectives that can serve as guidelines for future development of desirable ISEs and practical implementation of high-performance SMBs.

Synthesis of F-doped materials and applications in catalysis and rechargeable batteries

Elemental doping is one of the most essential techniques for material modification. It is well known that fluorine is considered to be a highly efficient and inexpensive dopant in the field of materials. Fluorine is one of the most reactive elements with the highest electronegativity (χ = 3.98). Compared to cationic doping, anionic doping is another valuable method for improving the properties of materials. Many materials have physicochemical limitations that affect their practical application in the field of catalysis and rechargeable ion batteries. Many researchers have demonstrated that F-doping can significantly improve the performance of materials for practical applications. This paper reviews the applications of various F-doped materials in photocatalysis, electrocatalysis, lithium-ion batteries, and sodium-ion batteries, as well as briefly introducing their preparation methods and mechanisms to provide researchers with more ideas and options for material modification.

Doping Regulation in Polyanionic Compounds for Advanced Sodium-Ion Batteries

It has long been the goal to develop rechargeable batteries with low cost and long cycling life. Polyanionic compounds offer attractive advantages of robust frameworks, long-term stability, and cost-effectiveness, making them ideal candidates as electrode materials for grid-scale energy storage systems. In the past few years, various polyanionic electrodes have been synthesized and developed for sodium storage. Specifically, doping regulation including cation and anion doping has shown a great effect in tailoring the structures of polyanionic electrodes to achieve extraordinary electrochemical performance. In this review, recent progress in doping regulation in polyanionic compounds as electrode materials for sodium-ion batteries (SIBs) is summarized, and their underlying mechanisms in improving electrochemical properties are discussed. Moreover, challenges and prospects for the design of advanced polyanionic compounds for SIBs are put forward. It is anticipated that further versatile strategies in developing high-performance electrode materials for advanced energy storage devices can be inspired.

Engineering a High-Voltage Durable Cathode/Electrolyte Interface for All-Solid-State Lithium Metal Batteries via In Situ Electropolymerization

Poly(ethylene oxide) (PEO)-based polymer electrolytes have been widely studied as a result of their flexibility, excellent interface contact, and high compatibility with a lithium metal anode. Owing to the poor oxidation resistance of ethers, however, the PEO-based electrolytes are only compatible with low-voltage cathodes, which limits their energy density. Here, a high-voltage stable solid-state interface layer based on polyfluoroalkyl acrylate was constructed via in situ solvent-free bulk electropolymerization between the LiNi_0.8Mn_0.1Co_0.1O₂ (NCM811) cathode and the PEO-based solid polymer electrolyte. The electrochemical oxidation window of the as-synthesized electrolyte was therefore expanded from 4.3 V for the PEO-based matrix electrolyte to 5.1 V, and the ionic conductivity was improved to 1.02 × 10^-4 S cm^-1 at ambient temperature and 4.72 × 10^-4 S cm^-1 at 60 °C as a result of the improved Li⁺ migration. This fabrication process for the interface buffer layer by an in situ electrochemical process provides an innovative and universal interface engineering strategy for high-performance and high-energy-density solid-state batteries, which has not been explicitly discussed before, paving the way toward the large-scale production of the next generation of solid-state lithium batteries.

Recent Progress on Intercalation-Based Anode Materials for Low-Cost Sodium-Ion Batteries

Intercalation-based anode materials can be considered as the most promising anode candidates for large-scale sodium-ion batteries (SIBs), owing to their long-term cycling stability and environmental friendliness, as well as their natural abundance. Nevertheless, their low energy density, low initial coulombic efficiency, and poor cycling lifespan, as well as sluggish sodium diffusion dynamics are still the main issues for the application of intercalation-based anode materials in SIBs in terms of meeting the benchmark requirements for commercialization. Over the past few years, tremendous efforts have been devoted to improving the performance of SIBs. In this Review, recent progress in the development of intercalation-based anode materials, including TiO₂ , Li₄ Ti₅ O₁₂ , Na₂ Ti₃ O₇ , and NaTi₂ (PO₄ )₃ , is summarized in terms of their sodium storage performance, critical issues, sodiation/desodiation behavior, and effective strategies to enhance their electrochemical performance. Additionally, challenges and perspectives are provided to further understand these intercalation-based anode materials.

Triggering the Reversible Reaction of V3+/V4+/V5+ in Na3V2(PO4)3 by Cr3+ Substitution

Sodium-ion batteries (SIBs) have grabbed worldwide attention as an alternative to lithium-ion batteries on account of the abundance and accessibility of the sodium element in nature. For the sake of meeting the requirements for various applications containing grid-scale energy storage system, electric vehicles, and so forth, a stable and high-voltage cathode is decisive to enhance the energy and power density of SIBs. In this research, sodium super ionic conductor structured Na₃V_1.5-xCr_0.5+x(PO₄)₃ with different V/Cr ratios to balance the V³⁺/V⁴⁺ and V⁴⁺/V⁵⁺ redox couples was investigated as the potential cathode for SIBs. Among these candidates, Na₃V_1.3Cr_0.7(PO₄)₃ manifested high energy density together with good cycling performance and rate capability. Combining the structural analysis and density functional theory calculation, the underlying mechanism of V³⁺ substitution by Cr³⁺ was uncovered, accounting for the improvement of electrochemical performance.

Co-Modification of commercial TiO2 anode by combining a solid electrolyte with pitch-derived carbon to boost cyclability and rate capabilities

The bad electrochemical performance circumscribes the application of commercial TiO₂ (c-TiO₂) anodes in Li-ion batteries. Carbon coating could ameliorate the electronic conductivity of TiO₂, but the ionic conductivity is still inferior. Herein, a co-modification method was proposed by combining the solid electrolyte of lithium magnesium silicate (LMS) with pitch-derived carbon to concurrently meliorate the electronic and ionic conductivities of c-TiO₂. The homogeneous mixtures were heated at 750 °C, and the co-modified product with suitable amounts of LMS and carbon demonstrates cycling capacities of 256.8, 220.4, 195.9, 176.4, and 152.0 mA h g^-1 with multiplying current density from 100 to 1600 mA g^-1. Even after 1000 cycles at 500 mA g^-1, the maintained reversible capacity was 244.8 mA h g^-1. The superior rate performance and cyclability correlate closely with the uniform thin N-doped carbon layers on the surface of c-TiO₂ particles to favor the electrical conduction, and with the ion channels in LMS as well as the cation exchangeability of LMS to facilitate the Li⁺ transfer between the electrolyte, carbon layers, and TiO₂ particles. The marginal amount of fluoride in LMS also contributes to the excellent cycling stability of the co-modified c-TiO₂.

Enhancing Na-ion storage in Na3V2(PO4)3/C cathodes for sodium ion batteries through Br and N co-doping

Br and N co-doping can enhance the electronic/ionic conductivities of carbon-coating layers and lower the activation energy of V⁴⁺/V⁵⁺ redox reactions.