Preparation and Characterization of Na3V2(PO4)3 Cathode Materials for Sodium-Ion Batteries

• Main Authors: Yi-Tang Chiu, 邱奕棠
• Other Authors: Wei-Ren Liu
• Format: Others
• Language: en_US
• Published: 2017
• Online Access: http://ndltd.ncl.edu.tw/handle/5e395z

碩士 === 中原大學 === 化學工程研究所 === 105 === Abstract Recent years, the demand of green energy is rapidly increased. In the point of view, Li-ion batteries still stands as one of the most promising choices, particularly for the on-going massive demand for electric and plug-in hybrid vehicles. The main limiting factor of lithium-ion battery is limited resource of Lithium metal availability in the world. Hence, the researchers are focused on alternative device such as sodium-ion batteries and other batteries. Among that, Sodium-ion batteries began to be regarded as one of the alternative energy storage devices for lithium-ion batteries due to their low cost and similarity of electrochemical property. However, there are still many challenges for sodium-ion batteries. Since, the sodium ion radius (1.02 Å) is bigger than lithium ions (0.76 Å), that will affect the transport performance of ions and lead to structural changes, volume changes during the Na-ions extraction and insertion process. Na3V2(PO4)3 as a potential cathode material for sodium-ion batteries due to their peculiar advantages like that high theoretical energy density, more stable covalent network and high thermal stability and so on. In this regard, in the present investigation focused on synthesis and development of Na3V2(PO4)3 as dual electrode material for sodium-ion battery half and full-cell applications. This research provides a step-by-step improvement for NASICON type Na3V2(PO4)3 sodium ion battery cathode material: (1). Modified synthetic formula (2). Dispersed powder agglomeration and stacked situation (3). F-doped NVP. In this research, The NVP and F-doped NVP nano-materials were successfully prepared by the sol-gel method. Subsequent through electrochemical performance test, confirmed that these improved samples have batter electrochemical properties. Therefore, the NVP and F-NVP are potential electrode materials for sodium- ion battery. In the present work, Chapter-1 and Chapter-2 describes the basic idea of sodium-ion batteries, developments of cathode materials and recent research reviews. Chapter-3 explains the used chemicals purity, characterized instruments details with specification, preparation of Na3V2(PO4)3 and fabrication of sodium-ion half and full-cell details. Chapter-4 a brief description of preparation and characterization of Na3V2(PO4)3 as a electrode materials for sodium-ion batteries. Na3V2(PO4)3 was prepared by sol-gel method with optimization of Na content. The results show that after increased the proportion of sodium, the battery cycle life becomes batter. On the other hand, the rapid charge and discharge performance is also significantly improved. The excess sodium sample can delivers a specific discharge capacity of 61.1 mAh/g which is higher than the original sample (46.9 mAh/g) at 1.0 A /g. In this study, the bare NVP sample were observed for uneven aggregation and stacking. After a decentralized process, we successfully reducing the powder agglomerated and stacked situation, and enhance the electrochemical performance. After the modified process, the discharge capacity of first cycle increased from 82.2 mAh/g to 92.3 mAh/g. The modified sample delivers a specific discharge capacity of 76.9mAh/g over 250 cycles at 0.1 A/g. In addition, the development of NVP was carried out by doping of fluorine. The fluorine content was optimized for sodium-ion batteries electrodes. X-ray diffraction and Transmission electron microscopy data unveiled high purity NASICON phosphate phases and amorphous carbon coating that enhances the electron conducting properties of the composite electrode material. The optimal doping concentration of F in Na3V2(PO4)3 is 0.15 mol %. By neutron powder diffraction data, we confirm that the chemical composition that we obtained from the fits is Na2.85V2(PO3.95F0.05)3. Subsequent to SEM, TEM, we found a lot of visible porosity generation. The BET results agree with the SEM & TEM, the increased surface area and the decreased average pore size were observed, confirming that the voids were significantly altered the morphology. The half-cell of Na2.85V2(PO3.95F0.05)3 cathode exhibits a good stable discharge capacity of 98 and 93 % of capacity retention over 250 cycles at 0.1 A/g, which is higher than bare Na3V2(PO4)3 (92 mAh/g & 78%). The high rate capability of Na2.85V2(PO3.95F0.05)3 is also dramatically enhanced via increase the conductivity of host material by F-doping. Moreover, the symmetricalal Na-ion full-cell was fabricated using Na2.85V2(PO3.95F0.05)3 as cathode and anode materials. It was achieved that the good reversibility and superior cycling stability about 98 % of capacity retention with 100 % of coulombic efficiency at 1.0 A/g throughout 1000 cycles. Finally, Chapter-5 elucidates the conclusion of this investigation.