基于萃取分离制备一体化策略合成氟磷酸钒钠及其储钠性能研究

With the rapid development of renewable energy sources, such as solar energy, wind energy, etc., it is urgent for the demand of long-life and low-cost storage batteries. Developing high-performance cathode materials and reducing their production costs are still the key for the energy-storage batteries. With a relatively low-temperature solution method to replace the traditional high-temperature solid-phase method, and the employment of inexpensive precursors are the primary means to reduce costs of cathode materials. Based on a strategy of integrating extraction, separation and preparation, this work would firstly use now-available extraction technologies to realize the extraction and separation of vanadium from vanadium slag, and then use the resulting metavanadate as vanadium source, under the action of reducing agent, fluorine source and phosphorus source, to synthesize nano/micro- sodium vanadium fluorophosphates through a green and low energy-consumption route based on a hypothesis 'It is easy for metal ions to nucleate and grow, finally form fluorine-phosphorus compounds crystals in the aqueous solutions in the presence of fluorine and phosphates.' Thus, the impact of various factors on the material synthesis would be systematically investigated. The nucleation-and-growth mechanism of crystal particles in the presence of multi anions and cations would be explored, and the correlation among the electrochemical properties, the degree of crystallinity, morphology and structures, will be clearly elaborated. The research is important to develop and design new cathode materials for sodium ion energy-storage batteries. In addition, it would conform a complete research strategy and technique pathway about the integration of extraction, separation and preparation of nano-/micro- functional materials. All of these also have great significance for enhancing the added value of the metal-separation products, transformating and upgrading the current separation industries.

随着可再生能源如太阳能、风能等的快速发展，迫切需要长寿命、低成本的储能电池。开发高性能的正极材料并降低其制备成本依然是储能电池发展的关键。用相对低温的溶液法来代替传统的高温固相法，并采用价格低廉的前驱体是降低正极材料成本的主要手段。基于萃取分离制备一体化思路，本课题将利用现有萃取分离技术实现钒渣中钒的提取分离，并将得到的偏钒酸盐作为钒源，在还原剂、氟源和磷源的作用下，以水溶液中氟和磷酸根存在时金属离子易于成核生长的假设为前提，拟实现纳微氟磷酸钒钠的绿色低能耗合成。课题将系统研究各因素对材料合成的影响，探讨多种阴阳离子共存时晶体颗粒成核成长机制，掌握储钠性能与颗粒的结晶度、形貌结构之间的相关性。课题的研究不仅对开发钠离子储能电池用正极材料具有重要意义，并将形成一套完整的萃取分离-纳微功能材料制备一体化的研究思路和技术路线，同时对提升金属分离产品的附加值以及分离产业的转型升级意义重大。

钠离子电池具有资源丰富、成本低廉、清洁高效的特点，适用于大规模储能、用户侧储能、通讯基站及军用等多个领域，是规模储能的优选技术之一。然而，钠离子电池在能量密度、倍率性能以及长循环方面需要进一步提升，而开发高性能的正极材料是其性能提升的主要突破点之一。此外，据报道正极材料的制造成本是一个电化学储能系统成本的主要决定性因素之一。课题以聚阴离子化合物氟磷酸钒钠为研究对象，开发了系列低成本低能耗的共沉淀制备方法，以期取代现有的高温固相法，并通过界面调控来强化材料的电化学性能。研究表明，以硫酸氧钒和磷酸二氢钠分别为钒源和磷源，水热共沉淀过程中通过调控反应温度和pH，可以形成不同活性的中空微球；基于萃取分离制备一体化思路，发现室温共沉淀可以获得多壳层的氟磷酸钒钠微球，这大大降低了原料钒的成本并缩短了制备流程；开发的氟磷酸钒钠颗粒的原位包碳和纳米一体化的机械球磨制备方法，本质上是高盐浓度条件下的共沉淀反应，获得了公斤级粉体Na3(VOPO4)2F@KB，所制得的粉体在充放电过程中具有超理论容量的电化学行为特点，且在20C下循环10,000周后依然具有98%的循环保持率。以此为正极材料，进一步与商业化硬碳负极匹配，研制了Ah级钠离子26650电池，电池的能量密度接近90 Wh/KG，全电池的性能有望通过匹配性能更好的硬碳负极和电解液进一步提升。具有良好性能的氟磷酸钒钠材料的公斤级制备以及Ah级工业电池雏形的研制，对于推动这一材料的工业化应用具有重要意义。在进一步的研究工作中，可以通过降低聚阴离子化合物钒的磷酸盐中钒的用量，来降低其原材料的成本，进一步推动聚阴离子化合物磷酸钒钠盐的工业化应用。