Outstanding long cycle stability provide by bismuth doped Na3V2(PO4)3 enwrapped with carbon nanotubes cathode for sodium-ion batteries

Na3V2(PO4)3 cathode materials for advanced sodium-ion batteries: Modification strategies and density functional theory calculations

With the rapid development of electric vehicles and smart grids, the demands for energy supply systems such as secondary batteries are increasing exponentially. Despite the world-renowned achievements in portable devices, lithium-ion batteries (LIBs) have struggled to meet the demands due to the constraints of total lithium resources. As the most promising alternative to LIBs, sodium-ion batteries (SIBs) are generating widespread research enthusiasm around the world. Among all components, the cathode material remains the primary obstacle to the practical application of SIBs due to its inability to match the performance of other components. Na3V2(PO4)3 (NVP) stands out as a promising cathode material for SIBs, given its suitable theoretical specific capacity, appropriate operating voltage, robust structural stability, and excellent ionic conductivity. In this article, we first review recent modification strategies for NVP, including conductive substance coating, ion doping (single-, dual- and multi-site doping) and morphology modulation (from zero-dimensional (0D) to three-dimensional (3D)). Subsequently, we summarize five ways in which density functional theory (DFT) calculations can be applied in guiding NVP modification studies. Furthermore, a series of emerging studies combining DFT calculations are introduced. Finally, the remaining challenges and the prospects for optimization of NVP in SIBs are presented.

Unraveling the Function Mechanism of N-Doped Carbon-Encapsulated Na3V2(PO4)3 Cathode toward High-Performance Sodium-Ion Battery with Ultrahigh Cycling Stability

The NASICON-type Na3V2(PO4)3 (NVP) is recognized as a potential cathode material for Na-ion batteries (SIBs). Nevertheless, its inherent small electronic conductivity induces limited cycling stability and rate performance. Carbon coating, particularly N-doped carbon, has been identified as an effective strategy to address these challenges. Hence, N-doped carbon-coated NVP was successfully produced by a straightforward high-temperature solid-phase method, and the mechanism of N-doped carbon coating in regulating the electrochemical kinetics of NVP was unraveled. The N-doped carbon layer establishes a robust conductive network that interconnects the active particles, facilitating electron transfer within the electrode. SEM images after cycling show that the uniform carbon coating mitigated NVP agglomeration, thereby reducing undesired side reactions between electrode and electrolyte. The discharge capacities of NVP/N-C2 electrodes at 0.1, 0.2, 0.5, 1, 2, 5, and 10C reach 116.0, 114.6, 112.6, 111, 108.7, 104.2, and 99.4 mAh g-1, respectively. Even at 20C, the discharge capacity remains up to 92.2 mAh g-1, which is approximately 80% of the discharge capacity at 0.1C. When the rate returns to 0.1C, the NVP/N-C2 cathode still exhibits a discharge capacity of 115.9 mAh g-1, showing excellent electrochemical reversibility. This study presents a viable approach for fabricating NVP with a N-doped carbon coating, showcasing enhanced sodium storage properties.

Optimization Strategies of Na3V2(PO4)3 Cathode Materials for Sodium-Ion Batteries

Na3V2(PO4)3 (NVP) has garnered great attentions as a prospective cathode material for sodium-ion batteries (SIBs) by virtue of its decent theoretical capacity, superior ion conductivity and high structural stability. However, the inherently poor electronic conductivity and sluggish sodium-ion diffusion kinetics of NVP material give rise to inferior rate performance and unsatisfactory energy density, which strictly confine its further application in SIBs. Thus, it is of significance to boost the sodium storage performance of NVP cathode material. Up to now, many methods have been developed to optimize the electrochemical performance of NVP cathode material. In this review, the latest advances in optimization strategies for improving the electrochemical performance of NVP cathode material are well summarized and discussed, including carbon coating or modification, foreign-ion doping or substitution and nanostructure and morphology design. The foreign-ion doping or substitution is highlighted, involving Na, V, and PO43- sites, which include single-site doping, multiple-site doping, single-ion doping, multiple-ion doping and so on. Furthermore, the challenges and prospects of high-performance NVP cathode material are also put forward. It is believed that this review can provide a useful reference for designing and developing high-performance NVP cathode material toward the large-scale application in SIBs.

Doping Engineering in Electrode Material for Boosting the Performance of Sodium Ion Batteries

In recent years, sodium ion batteries (SIBs) emerged as promising alternative candidates for lithium ion batteries (LIBs) due to the high abundance and low cost of sodium resources. However, their commercialization has been hindered by inherent limitations, such as low energy density and poor cycling stability. To address these issues, doping methodology is one of the most promising approaches to boosting the structural and electrochemical properties of SIB electrodes. This review provides a comprehensive overview of recent advancements in doping strategies, focusing on the improvement of the performance of SIBs. Various dopants including s- and p-block elements, transition metals, oxides, carbonaceous materials, and many more dopants are discussed in terms of their effects on enhancing the electrochemical properties of SIBs. Furthermore, the mechanisms responsible for the improvement in the performance of doped SIBs materials are also discussed. It also highlights the importance of doping sites in the crystal lattice, which also play a crucial role in doping in optimizing electrode structure, enhancing ion diffusion kinetics, and stabilizing electrode/electrolyte interfaces. The review ends by looking at the recent studies in simultaneous multiple heteroatom doping, offering valuable perspectives for a high performance SIB. This study provides valuable insight into the researchers and battery industries striving for advancements in energy storage technologies.

Carbon coated Na3+xV2-xCux(PO4)3@C cathode for high-performance sodium ion batteries

Na3V2(PO4)3 is considered as one of the most promising cathodes for sodium ion batteries owing to its fast Na+ diffusion, good structural stability and high working potential. However, its practical application is limited by its low intrinsic electronic conductivity. Herein, a carbon coated Cu2+-doped Na3V2(PO4)3 cathode was prepared. The carbon coating not only improve its apparent conductivity, but also inhibit crystal growth and prevent agglomeration of particles. Moreover, Cu2+ doping contributes to an enhanced intrinsic conductivity and decreased Na+ diffusion energy barrier, remarkably boosting its charge transfer kinetics. Based on the structure characterizations, electrochemical performances tests, charge transfer kinetics analyses and theoretical calculations, it's proved that such an elaborate design ensures the excellent rate performances (116.9 mA h g-1 at 0.1C; 92.6 mA h g-1 at 10C) and distinguished cycling lifespan (95.8 % retention after 300 cycles at 1C; 84.8 % retention after 3300 cycles at 10C). Besides, a two-phase reaction mechanism is also confirmed via in-situ XRD. This research is expected to promote the development of Na3V2(PO4)3-based sodium ion batteries with high energy/power density and excellent cycling lifespan.

Facile Al2O3 coating suppress dissolution of Mn2+ in Mn-substituted Na3V2(PO4)3 with outstanding electrochemical performance for full sodium ion batteries

Na3V2(PO4)3 (NVP) encounters significant obstacles, including limited intrinsic electronic and ionic conductivities, which hinder its potential for commercial feasibility. Currently, the substitution of V3+ with Mn2+ is proposed to introduce favorable carriers, enhancing the electronic conductivity of the NVP system while providing structural support and stabilizing the NASICON framework. This substitution also widens the Na+ migration pathways, accelerating ion transport. Furthermore, to bolster stability, Al2O3 coating is applied to suppress the dissolution of transition metal Mn in the electrolyte. Notably, the Al2O3 coating serves a triple role in reducing HClO4 concentration in the electrolyte, inhibiting Mn dissolution, and functioning as the ion-conducting phase. Likewise, carbon nanotubes (CNTs) effectively hinder the agglomeration of active particles during high-temperature sintering, thereby optimizing the conductivity of NVP system. In addition, the excellent structural stability is investigated by in situ XRD measurement, effectively improving the volume collapse during Na+ de-embedding. Moreover, the Na3V5.92/3Mn0.04(PO4)3/C@CNTs@1wt.%Al2O3 (NVMP@CNTs@1wt.%Al2O3) possesses unique porous structure, promoting rapid Na+ transport and increasing the interface area between the electrolyte and the cathode material. Comprehensively, the NVMP@CNTs@1wt.%Al2O3 sample demonstrates a remarkable reversible specific capacity of 122.6 mAh/g at 0.1 C. Moreover, it maintains a capacity of 115.9 mAh/g at 1 C with a capacity retention of 90.2 mAh/g after 1000 cycles. Even at 30 C, it achieves a capacity of 87.9 mAh/g, with a capacity retention rate of 84.87 % after 6000 cycles. Moreover, the NVMP@CNTs@1wt.%Al2O3//CHC full cell can deliver a high reversible capacity of 205.5 mAh/g at 0.1 C, further indicating the superior application potential in commercial utilization.

Simultaneous modification of dual-substitution with CeO2 coating boosting high performance sodium ion batteries

Na3V2(PO4)3 (NVP) is highly valued based on the stable construction among the polyanionic compounds. Nevertheless, the drawback of low intrinsic conductivity has been impeded its further application. In this paper, the internal channels of the crystal structure are extended by the introduction of larger radius Ce3+, which increases the transport rate of Na+. The introduction of Mo6+ replacing the V site leads to a beneficial n-type doping effect and facilitates the transportation of electrons. Besides, CeO2 cladding is introduced to further enhance the electronic conductivity of NVP system. Initially, CeO2 serves as an n-type semiconductor and functions as a conductive additive to significantly enhance the electronic conductivity of the electrode, thereby improving the electrochemical characteristics. Moreover, CeO2 functions as an oxygen buffer, aiding in the maintenance of active metal dispersion during operation and enabling efficient electron transfer between CeO2 and [VO6] octahedra in NVP, thus fostering outstanding electrical connectivity between the oxides. CeO2 cladding can be effectively integrated with the carbon layer to stabilize the NVP system. Comprehensively, the modified Na3V1.79Ce0.07Mo0.07(PO4)3/C@8wt.%CeO2 (CeMo0.07@8wt.%CeO2) composite exhibits excellent rate and cycling properties. It delivers a capacity of 113.4 mAh/g at 1C with a capacity retention rate of 80.3 % after 150 cycles. Even at 10C and 40C, it also submits high capacities of 84.7 mAh/g and 76 mAh/g, respectively. Furthermore, the CHC//CeMo0.07@8wt.%CeO2 asymmetric full cell possesses excellent sodium storage property, indicating its prospective application potentials.

Promising Cathode Materials for Sodium-Ion Batteries from Lab to Application

Sodium-ion batteries (SIBs) are seen as an emerging force for future large-scale energy storage due to their cost-effective nature and high safety. Compared with lithium-ion batteries (LIBs), the energy density of SIBs is insufficient at present. Thus, the development of high-energy SIBs for realizing large-scale energy storage is extremely vital. The key factor determining the energy density in SIBs is the selection of cathodic materials, and the mainstream cathodic materials nowadays include transition metal oxides, polyanionic compounds, and Prussian blue analogs (PBAs). The cathodic materials would greatly improve after targeted modulations that eliminate their shortcomings and step from the laboratory to practical applications. Before that, some remaining challenges in the application of cathode materials for large-scale energy storage SIBs need to be addressed, which are summarized at the end of this Outlook.