扫描电化学显微镜实时探测钠离子电池正极材料Na3V2(PO4)3/C与电解质界面行为

High performance electrode material is essential to the development of sodium ion batteries (SIB). Na3V2(PO4)3 is a kind of sodium super ion conductor with high stability and its’ standard electropotential (3.4 V vs. Na/Na+) is higher than other available materials, which makes it a good choice as cathode material in SIB. The pure Na3V2(PO4)3 has some limitations to be directly used as electrode material of SIB, because of the poor electrochemical activity, low specific capacity, low round trip energy efficiency. Although, the electrochemical properties of Na3V2(PO4)3 can be improved by carbon coating and 3D microstructure construction, but the problem is how to effectively evaluate these methods. The traditional material analysis and characterization methods cannot provide in-situ study or electrochemical information about electrodes and electrolyte when the battery is functioning. In this project, the renewable carbonfiber microdisc electrodes will be fabricated, and also the graphene modified nanodisc electrochemical sensor will be investigated to be used as the probe of Scanning electrochemical microscopy (SECM). SECM with different working modes will be arranged to study carbonaceous Na3V2(PO4)3 with different microstructures. The substrate generation/tip collection (SG/TC) mode will be implied to investigate the dynamic features of the electrode-electrolyte interface. The probe scan curve (PSC) and linear sweep voltammetry (LSV) techniques will be used to research the transportation mechanisms of all the particles during cycling procedure of batteries. The results are intended to conclude the relationship between the carbon pattern/microstructures and electrochemical properties of Na3V2(PO4)3/C in SIB. According to the electrochemical activities of Na3V2(PO4)3/C in different electrolytes, the optimized combination of electrode/electrolyte can be achieved, and this is the basic element for practical SIB. The properties of Na3V2(PO4)3/C materials under different discharge rates and after different cycles will also be traced, in order to evaluate batteries under different operation conditions. By achieving all this results, we plan to build a new in-situ analysis method for materials of room-temperature energy storage batteries.

高性能电极材料是构建钠离子电池的首要条件，钠离子快导体磷酸矾钠通过碳包覆和材料微观形貌调控改善其导电性和容量之后已成为极具潜力的钠离子电池正极材料。但其倍率性能与稳定性等仍有欠缺，且在不同电解质中的循环效率有较大差别。由于传统材料表征及分析技术不能实现电池关键材料的在线分析，获得电极与电解质体系内发生的电化学过程信息。本项目拟研制可再生碳纤维超微盘电极和石墨烯修饰纳米电极，采用扫描电化学显微镜的电化学现场、微区分析技术探索包覆碳形态、材料微观形貌与Na3V2(PO4)3/C电化学活性间的构效关系，监测电极/电解质界面电化学行为，探索电解质对钠离子传输的影响机制。发展一种室温储能电池关键材料电化学现场微区分析的新方法，为获得高性能电极材料及电解质、构建钠离子电池提供理论基础及实验依据。

聚阴离子型材料Na3V2(PO4)3的电导率低，其直接作为电极材料时往往不能获得令人满意电化学性能。我们首次提出以琼脂糖凝胶构建三维导电网络，制备了三维骨架碳包覆的Na3V2(PO4)3钠离子正极材料，其具有非常优异的电化学性能。在1 C（1 C=117.6 mA/g）的倍率下能释放出113 mA h/g的容量，甚至在50 C时容量仍保持为54.3 mA h/g。当材料在2 C的电流下循环8000圈时，容量保持率为87.5%。随后，采用固进一步提升材料的倍率性能。在20 C的倍率下，材料所能释放的容量仍可达100 mA h/g，循环7000圈后的容量仍有78 mA h/g。与琼脂糖源的硬碳负极材料匹配组装的全电池在200 mA/g的电流密度下循环，其可逆容量为110 mA/g，循环100圈后容量保持率为90%。此外， 制备了3D珊瑚状结构的碳包覆NaVPO4F材料，其特殊的纳米颗粒聚集体结构和较大的比表面积赋予了其优异的电化学性能。同时，开发了一种低成本、高能量密度且环境友好的钠离子电池正极材料Na2.4Fe1.8(SO4)3。在SECM 探针研制方面，以rGO和Nafion为修饰材料，通过滴涂法对碳纤维超微圆盘电极进行了修饰，在不对电极进行蚀刻处理的情况下将有效半径降低了85%，提升了电极在电化学测试中的分辨率，并且有效改善了其稳定性。SECM电池测试方面，以实时在线监测电极/电解质界面电化学行为为目标，构建了新型电解池，以商品化LiCoO2和LiFePO4为样品验证了其进行电化学分析的可行性，并以此为基础探索了电解质成分对电极性能影响，对不同碳含量的Na3V2(PO4)3的界面反应动力学参数进行了定量计算，分析了电极表面电化学活性分布，为开发高性能电极材料提供了实验依据。