氧空位过渡金属氧化物-石墨烯泡沫复合电极材料的结构调控与储能机理研究

Aqueous asymmetric supercapacitior is a high effective energy-storage devicethat integrate electric double layer and surface redox charge storage modes, which have many advantages including potentially large operational voltage window, high energy density and low cost. Transition metal oxides have significant application value for asymmetric supercapacitor owing to its high redox property. However, similar to many psedocapacitance materials, the poor electrical conductivity of Transition metal oxide -based layered double hydroxid seriously affects its energy storage properties and application. Therefore, we expect to combine the advantages of the good redox property and high sepicific capacitance of Transition metal oxides and the large area and high conductivity of grapheme foam, to synthesize the three-dimensional structure of Transition metal oxides - graphene foam composites using graphene foam as conductive network, graphene oxide as pore controlled agent and nuclear, and Transition metal oxides with oxygen vacancy as the raw materials. On this basis, asymmetric supercipacitors were constructed with the as-prepared electrode materials as the positive electrode and active carbon material as negative electrode to enhance energy density. The project will systematically study the structure-activity relationship between the morphology and microstructure of the electrode and its electrochemical properties, and try to clarify the energy storage mechanism of the electrode material, providing theoretical guidance and practical basis for the development and wide application of electrode materials of asymmetric supercapacitiors.

水系非对称超级电容器是集物理和化学储能于一体的高效储能器件，具有电压窗口宽、能量密度大和成本低等特点。过渡金属氧化物具有较高的理论比容量和电化学活性，在非对称超级电容器中具重要的应用价值。然而与多数赝电容材料类似，导电性差的缺点严重影响了过渡金属氧化物的储能性能与应用。本课题拟以同时具有高比表面积和高导电率的石墨烯泡沫为层次孔结构的导电骨架网络，高活性的多孔氧化石墨烯作为过渡金属氧化物的载体及石墨烯泡沫的孔结构调节剂，结合导电性提高的表面氧空位金属氧化物，合成出氧空位金属氧化物-石墨烯泡沫复合电极材料。将所制材料与活性炭进一步组装非对称电容器，增大电容器的工作电压，进而有效提升其储能密度。本项目将系统研究复合电极材料形貌、微观结构、表面化学与电化学特性之间构效关系，阐明储能机制，为超级电容器电极材料的开发与应用提供理论和实践基础。

非对称超级电容器，与对称超级电容器相比，具有更高的能量密度和更广阔的应用领域而备受关注，获得高性能电极材料是研究热点。本项目在具有较高理论比容量的过渡金属氧化物中引入氧空位，与电导率高的石墨烯复合，发挥二者的协同效用，制备出系列正极材料和空心炭微球负极材料，并组装成非对称超级电容器，表征分析各阶段材料的结构和测试电化学性能，探讨氧空位在电化学反应过程中的储能机理。主要研究内容如下：.（1）采用泡沫镍为生长基底，通过水热法、固-气相磷化还原法、空气/氮气退火等多步骤，制备了系列一元金属氧化物MnO2、NiO和二元金属氧化物Ni2MnO4，及其对应的磷掺杂氧空位金属氧化物P-MnO2-x、P-NiO1-x、P-Ni2MnO4-x，并进行多种微观结构表征分析和电化学性能测试。结果表明，P-MnO2-x、P-NiO1-x、P-Ni2MnO4-x的比电容和倍率性能均高于对应的无氧空位样品，二元氧空位金属氧化物P-Ni2MnO4-x电化学性能高于一元氧空位金属氧化物P-MnO2-x、P-NiO1-x。.（2）一元氧空位过渡金属氧化物P-MnO2-x、P-NiO1-x、F-NiO1-x和二元氧空位过渡金属氧化物P-Ni2MnO4-x分别与石墨烯(G)复合后电容性能进一步大幅提高。P-Ni2MnO4-x@G的电化学综合性能最佳，在电流密度为1 A g−1时，比电容达到1202.0 F g−1。 .（3）采用淀粉为原料和钾铁复合盐为催化剂，经一步炭化法制备出高比表面积（1595.2 m2 g-1）的空心炭微球（CMS）作负极材料，与所制系列正极材料组装成非对称超级电容器。其中，P-Ni2MnO4-x@G//CMS非对称超级电容器的比电容、倍率性能及能量密度最佳。 .（4）采用密度泛函理论（DFT）进行理论模拟计算，正极材料中引入氧空位后，表面原子重排为具有较大间距的不规则结构，自旋态密度变得更加对称。这表明引入氧空位后出现了更多暴露的活性位点和更稳定的结构，利于提高电化学综合性能，验证了氧空位提升电容性能的实验结果。