Auswahl der wissenschaftlichen Literatur zum Thema „Na3V2(PO4)2F3“

Na3V2(PO4)2F3 is an ideal cathode material for sodium-ion batteries with a high theoretical energy density. In this paper, the electronic conductivity of Na3V2(PO4)2F3 was improved by using a simple surface carbon coating method, and excellent electrochemical properties were obtained.

Recently, an interest in NASICON-type materials revived, as they are considered potential cathode materials in sodium–ion batteries used in large-scale energy storage. We applied a facile technique of thermal nanocrystallization of glassy analogs of these compounds to enhance their electrical parameters. Six nanomaterials of the Na3M2(PO4)2F3 (M = V, Ti, Fe) system were studied. Samples with nominal compositions of Na3V2(PO4)2F3, Na3Ti2(PO4)2F3, Na3Fe2(PO4)2F3, Na3TiV(PO4)2F3, Na3FeV(PO4)2F3 and Na3FeTi(PO4)2F3 have been synthesized as glasses using the melt-quenching method. X-ray diffraction measurements were conducted for as-synthesized samples and after heating at elevated temperatures to investigate the structure. Extensive impedance measurements allowed us to optimize the nanocrystallization process to enhance the electrical conductivity of cathode nanomaterials. Such a procedure resulted in samples with the conductivity at room temperature ranging from 1×10−9 up to 8×10−5 S/cm. We carried out in situ impedance spectroscopy measurements (in an ultra-high-frequency range up to 10 GHz) and compared them with thermal events observed in differential thermal analysis studies.

This work provides a reliable view for understanding the phase and composition of as-prepared Na3V2(PO4)2F3, showing that the proper introduction of oxygen substitution for fluorine is beneficial to the electrochemical performance.

The biomass bagasse carbon-coated Na3V2(PO4)2F3/C with nano-scale spherical morphology, prepared by spray drying and high temperature calcination, were proved to have excellent specific capacity and good cycling performance by electrochemical testing.

Renewable electricity products, for example, from wind and photovoltaic energy, need large-scale and economic energy storage systems to guarantee the requirements of our daily lives. Sodium-ion batteries are considered more economical than lithium-ion batteries in this area. Na3V2(PO4)2F3, NaVPO4F, and Na3(VO)2(PO4)2F are one type of material that may be used for Na-ion batteries. In order to better understand the synthesis of these materials, the phase formation in a NaH2PO4–VOSO4–NaF–H2O system under hydrothermal conditions was studied and is reported herein. This research focused on the influences of the sodium fluoride content and hydrothermal crystallization time on phase formation and phase purity. The phase transformation between Na(VO)2(PO4)2(H2O)4 and Na3V2O2x(PO4)2F3-2x was also studied. Na3V2O2x(PO4)2F3-2x with a high degree of crystallinity can be obtained in as short as 2 h via hydrothermal synthesis using a conventional oven at 170 °C without agitation. All compounds obtained in this research were studied mainly using powder X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectrometry, and Fourier-transform infrared spectroscopy.

Investigation of the effects of Al substitution for V on the structural properties and electrochemical performances for two of the most promising positive electrode materials for Na-ion batteries, Na₃V₂(PO₄)₂F₃ and Na₃V₂(PO₄)₂FO₂.

Dans le système de batterie à ions sodium (SIB), l'électrode positive joue un rôle important. Bien que plus faibles que les matériaux d'oxyde lamellaire sous certains aspects, comme la conductivité électrique, les matériaux polyanioniques sont devenus l'une des deux principales catégories de matériaux d'électrode positive grâce à leur excellente stabilité électrochimique et leur tension de fonctionnement élevée. La famille Na3V2(PO4)2F3-yOy (0 ≤ y ≤ 2) est notamment la plus remarquable en termes de performances électrochimiques. Cependant, les performances électrochimiques sont limitées en raison de la conductivité électronique plutôt faible induite par les unités de vanadium bi-octaèdre isolées au sein de la structure. De nombreuses études ont été menées pour améliorer les propriétés électrochimiques du Na3V2(PO4)2F3-yOy au moyen d'un revêtement de carbone et d'une morphologie spéciale, etc. Cependant, des améliorations inconscientes dans de multiples aspects peuvent conduire à négliger la compréhension d'un élément spécifique modifié, en raison de l'amélioration finale des performances électrochimiques. Par conséquent, cette thèse de doctorat consiste à bien contrôler toutes les variétés et à comparer l'impact de la morphologie et de la composition de Na3V2(PO4)2F3-yOy afin d'améliorer ses performances électrochimiques finales dans une perspective plus fondamentale. Ainsi, ce travail est composé des parties suivantes sous forme d'articles déposés. Dans le premier chapitre, qui constitue un état de l'art, le contexte du développement des batteries et en particulier des SIBs sera brièvement présenté. Les matériaux communs pour chaque partie différente de SIBs seront décrits plus en détail. Ensuite, l'attention sera portée sur le Na3V2(PO4)2F3-yOy et l'état actuel de ses recherches sera présenté en détail en termes de structure cristalline et de synthèse, etc. Ensuite, dans le deuxième chapitre, une série de synthèses légèrement ajustées avec les mêmes précurseurs a été réalisée pour obtenir des particules de Na3V2(PO4)2F3-yOy de différentes morphologies et de composition similaire, puis pour étudier l'effet des morphologies sur les performances de stockage d'énergie. Dans le chapitre III, à partir de la morphologie la plus performante trouvée dans le deuxième chapitre, l'effet de la teneur en oxygène sur les propriétés de transport et la performance électrochimique dans Na3V2(PO4)2F3-yOy (différents pourcentages de substitution de O2-) a été étudié, tout en gardant les morphologies inchangées. Dans le chapitre IV, les Na3V2(PO4)2FO2 trouvés dans le chapitre III ont été comparés avec ceux synthétisés par différentes méthodes avec la même composition de particules mais des morphologies et une fonctionnalisation de surface totalement différentes afin de mieux comprendre l'impact de la morphologie et du revêtement de surface sur la capacité de stockage d'énergie.Enfin, le solvant eutectique profond, un type de liquide ionique, a été utilisé comme nouveau moyen de synthèse pour atteindre une morphologie totalement nouvelle et spéciale qui n'avait pas été signalée auparavant et une nouvelle approche pour fabriquer un revêtement de carbone. En général, les différentes morphologies et compositions de Na3V2(PO4)2F3-yOy sont obtenues séparément en contrôlant et en affinant une série de méthodes de synthèse. Leurs influences sur l'électrochimie finale du matériau ont également été étudiées séparément. Ces études contribuent à la compréhension de ce matériau d'un point de vue fondamental, facilitant ainsi son optimisation ultérieure
In the sodium ion battery system, the positive electrode plays an important role. Although weaker than layered oxide materials in some aspects, such as electrical conductivity, polyanionic materials have become one of the two main categories of positive electrode materials with their excellent electrochemical stability and high operating voltage. Na3V2(PO4)2F3-yOy (0≤y≤2) family is especially the most outstanding in terms of electrochemical performance. However, the electrochemical performance is limited because of the rather poor electronic conductivity induced by the isolated vanadium bi-octahedra units within the structure. There have been many studies to improve the electrochemical properties of Na3V2(PO4)2F3-yOy by means of carbon coating and special morphology etc. However, unconscious improvements in multiple aspects can lead to neglected further understanding of one specific changed element, due to the ultimately electrochemical performance enhancements. Therefore, this PhD thesis is consistent of well controlling all the varieties and comparing the morphology and composition impact of Na3V2(PO4)2F3-yOy without any carbon coating in order to improve its final electrochemical performance through a more fundamental perspective. Thus, this work is composed of the next parts under the form of deposited articles. In the first chapter, which is a state of the art, the background of the development of batteries and especially the sodium ion batteries will be briefly introduced. The common materials for each different part of the sodium ion battery will be further described. Next, attention will be focused on Na3V2(PO4)2F3-yOy and show the current status of its research in detail in terms of crystal structure and synthesis, etc. Then in the second chapter, a series of slightly tuned synthesis with the same precursors were carried out to obtain the Na3V2(PO4)2F3-yOy particles with different morphologies and similar composition and then investigate the effect of morphologies on energy storage performance. In the subsequent chapter III, from one most performant morphology found in the second chapter, the effect of the oxygen content on transport properties and electrochemical performance within Na3V2(PO4)2F3-yOy (different O2- substitution percent) were investigated, while keeping the morphologies unchanged. In the next chapter IV, the Na3V2(PO4)2FO2 found in chapter III with those synthesized through different methods with the same particle composition but totally different morphologies and surface functionalization were compared to further understand the morphology and surface coating impact on the energy storage capacity. At last, deep eutectic solvent, one kind of ionic liquid, was used as a new synthesis medium to reach a totally new and special morphology does not reported before and a new approach to make a carbon coating. In general, the different morphologies and compositions of Na3V2(PO4)2F3-yOy are obtained separately by controlling and refining a series of synthesis methods. Their influences on the final electrochemistry of the material have also been investigated separately. These studies contribute to the understanding of this material from a fundamental point of view, thus facilitating further optimization

碩士
國立臺灣科技大學
機械工程系
106
This study was focused on the synthesis and characterization of NVP and NVPF, and found the differences between them. In this study, ascorbic acid and citric acid were used as the mesoporous carbon-coated precursors of NVP and NVPF, respectively. The samples were synthesized by sol-gel method. X-ray diffraction with Topas software for crystal structure refinement, the lattice constant of NVP which a-axis was 8.7336 Å, c-axis was 21.8370 Å; the lattice constant of NVPF which a-axis was 9.0396 Å, c-axis was 10.7544 Å. SEM, TEM help us observe the NVP particle size which was 100-200nm; NVPF was 1-2μm. With the test of BET, the specific surface area of the NVP was 27 m2/g, the diameter of the pores was 4nm, the specific surface area of the NVPF was 18 m2/g, and the diameter of the pores was 4nm, respectively. The Asp3 / Asp2 values were measured with Raman spectroscopy, NVP was 0.26, and NVPF was 0.35. TGA showed that the carbon coating amounts of NVP and NVPF were 6.5 wt% and 6.8 wt%, respectively. In this experiment, NVP has a single charge / discharge plateau at 3.4V with a specific capacity of 94 mAh/g (theoretical capacity of 117.6 mAh/g). And NVPF had three charge discharge plateaus, (A) 3.35V / 3.41V, (B) 3.67V / 3.71V, (C) 4.22V / 4.15V, the capacity was up to 127.68mAh/g (theoretical capacity of 128 mAh/g). Finally, confirmed that the NVPF have better electrochemical performance.

碩士
中原大學
化學工程研究所
107
The demand of green energy has rapidly increased in these years, particularly for the on-going massive demand for electric and plug-in hybrid vehicles. The main limiting factor of lithium-ion battery arises from the limited resource of lithium metal availability in the world. During recent decades, sodium-ion batteries (SIBs) have been regarded as a promising alternative to lithium-ion batteries as a result of their advantages, such as abundancy, low cost, safety and high-power energy storage. In this regard, present investigation focused on the synthesis and development of Na3V2(PO4)2F3 as a cathode material for sodium-ion battery application. Na3V2(PO4)3 (NVP) and Na3V2(PO4)2F3 (NVPF) are known as two appealing NASICON-type materials capable of motivating intercalation chemistry for sodium ions. This research provides a step-by-step improvement for NASICON-type Na3V2(PO4)2F3 sodium-ion battery cathode materials. It involves finding the optimal concentration suitable for the sol-gel method and evaluating the best dopant for NVPF. The electrochemical tests revealed that C-rate performance was enhanced when an excess of sodium fluoride (NaF) was used. The batteries obtained capacities of 72.8 and 98.7 mAh/g for standard and excess NaF content, respectively when cycled back to 0.1C. In addition, ionic conductivity and diffusion of NVPF was improved by doing it with chromium and aluminum. X-ray diffraction and transmission electron microscopy confirm that high purity doped NVPF samples were obtained. Furthermore, electronic conductivity was augmented through amorphous carbon coating. The results indicate that NVCrPF-0.03 and NVAlPF-0.07 provided.

Ce chapitre présente le potentiel des matériaux polyanoniques Na3V2(PO4)3 et Na3V2(PO4)2F3, de structures différentes, à l'électrode positive de batteries Na-ion. Sont notamment discutés les voies de synthèse les plus adaptées pour les obtenir, le contrôle de la relation composition - structure – propriétés, mais aussi le défi que représente leur stabilisation lors de l’extraction du troisième sodium de la structure, celle-ci se faisant aujourd’hui au détriment des performances électrochimiques.