原位气泡软模板构筑氟磷酸钒钠多壁中空微球及其电化学性能

Sodium-ion batteries (SIBs) have attracted extensive attention because of the identical working principle as the dominant lithium-ion batteries (LIBs) and the highly abundant sodium resources in the Earth's crust. Cathode materials with superior electrochemical properties have been the key for developing the energy-storage batteries. Constructing crystal particles with 3D fine micro-structures is one of the main methods for improving the performance of cathode materials. Three-dimensional hollow multi-shelled microspheres made from the zero-dimensional nanoparticles display the mutual advantages of both low-dimensional nanoparticles and three-dimensional hollow multi-shelled microstructures during the process of Na+ insertion/extraction. Sodium vanadium fluorophosphates (NVPFs) with a high average discharge voltage (of ~ 3.75 V) and a high theoretical specific capacity (of ~130 mA h g-1), as a class of cathode materials, have attracted tremendous attention in recent years. This project would artfully construct in-situ formed bubbles as soft templates through employing high-valence vanadium as vanadium sources and hydroxylamine as a reductive agent. In the presences of fluorine and phosphorus, we would explore the self-assemble behaviors of multiple particles and the key soft-template role of in-situ formed bubbles through investigating the various impact factors on the information of multi-shelled hollow microstructures, then reveal the interfacial properties and the co-precipitation theory in the current gas-liquid-solid multi-phase reaction system, and the nucleation-and-growth mechanism of multi-shelled hollow NVPFs microspheres. This research can effectively enrich the fabrication methods of the 3D multi-shelled hollow microstructures and it is also very significant for developing cathode materials with high performances for the energy-storage batteries.

钠电池由于具有与锂电池相同的工作原理，且地壳中钠元素含量丰富而得到广泛关注。正极材料的性能一直以来是储能电池发展的关键。构筑具有三维精细微结构的晶体颗粒是提升正极材料性能的主要方法之一。由零维纳米颗粒构建的三维中空多壁微球，兼具低维度纳米颗粒以及三维中空多壁微观结构在钠离子嵌入拔出过程中的共同优势。氟磷酸钒钠是近年来研究较多的一类正极材料，具有较高的放电电压(~3.75 V) 和理论比容 (130 mAh/g)。本项目以高价钒作为钒源，盐酸羟胺为特定还原剂，构筑原位气泡软模板，氟、磷存在下，通过系统研究各因素对多壁中空微观结构形成的影响，探讨气液固多相反应体系中多种粒子的自组装以及原位气泡软模板的关键作用，揭示气液固多相反应体系的界面性质、共沉淀机理以及氟磷酸钒钠多壁中空微结构的成核成长机制。本研究将丰富三维多壁空心微结构的制备方法,同时对于开发高性能钠离子储能电池用正极材料具有重要意义。

钠电池由于具有与锂电池相同的工作原理，且地壳中钠元素含量丰富而得到广泛关注。正极材料的性能一直以来是储能电池发展的关键。构筑具有三维精细微结构的晶体颗粒是提升正极材料性能的主要方法之一。由零维纳米颗粒构建的三维中空多壁微球，兼具低维度纳米颗粒以及三维中空多壁微观结构在钠离子嵌入拔出过程中的共同优势。氟磷酸钒钠是近年来研究较多的一类正极材料，具有较高的放电电压(~3.75 V) 和理论比容 (130 mAh/g)。本项目以高价钒作为钒源，盐酸羟胺为特定还原剂，构筑原位气泡软模板，氟、磷存在下，通过系统研究各因素对多壁中空微观结构形成的影响，探讨气液固多相反应体系中多种粒子的自组装以及原位气泡软模板的关键作用，揭示气液固多相反应体系的界面性质、共沉淀机理以及氟磷酸钒钠多壁中空微结构的成核成长机制。基于上述反应，我们进一步开发了无溶剂机械化学法制备原位碳纳米骨架包覆的纳米氟磷酸钒钠，导电性大大增强，并将反应时间从6天缩短到30分钟。进一步，为了提高共沉淀效率，调控颗粒形貌，采用硫酸氧钒作为钒源，基于“自发”室温共沉淀机理，在反应物接触瞬间快速制备氟磷酸钒钠亚微纳米颗粒。以此种方法获得的公斤级产品，与商业硬碳匹配了1.7Ah 26650圆柱电芯，在5C倍率下循环2000周后仍然具有高达95.2%的容量保持率，展示了优越的低温性能。本研究将加速氟磷酸钒钠的工业应用。