氮掺杂碳纤维/NiFe2O4复合气凝胶柔性电极的多尺度构筑及其储能性能研究

In our present proposal, starting from multi-scale preparation of the composite aerogel electrodes, cellulose nanofibers and chitin nanofibers are used as a carbon source and a nitrogen source of the flexible nitrogen-doped carbon fiber aerogel, respectively, we are aiming at enhancing the flexibility performance of the NiFe2O4 with nitrogen-doped carbon fiber aerogel with excellent flexibility performance, and at enhancing the energy density of the carbon electrode with NiFe2O4 with excellent storage Properties. During running this proposal, the optimal parameters and multi-scale conditions for synthesizing the nitrogen-doped carbon fiber/NiFe2O4 composite aerogel flexible electrodes will be set up, the network pore structure, micro/nano morphology and distribution for NiFe2O4 and physicochemical properties of the resulting nitrogen-doped carbon fiber/NiFe2O4 composite aerogel electrodes will be investigated, the relationship among multi-scale synthetic conditions- network pore structure of composite aerogels, micro/nano morphology and distribution for NiFe2O4-physicochemcial properties of the resulting nitrogen-doped carbon fiber/NiFe2O4 composite aerogel electrodes will be determined. At the same time, energy density and mechanical flexibility properties of the resulting nitrogen-doped carbon fiber/NiFe2O4 composite aerogel flexible electrodes will be emphatically investigated, the effect of the multi-scale synthetic conditions and composition ratios on the network pore structure of composite aerogels, micro/nano morphology and distribution for NiFe2O4 and ultimately on the energy density and mechanical flexibility properties of the composite aerogel electrodes will be emphatically clarified.

本项目从复合气凝胶柔性电极多尺度构筑出发，纤维素纳米纤维、甲壳素纳米纤维分别作为柔性氮掺杂碳纤维气凝胶的碳源、氮源，以利用氮掺杂碳纤维气凝胶优异的机械柔韧性能来改善NiFe2O4柔韧性能的不足，同时利用NiFe2O4卓越的储能性能来显著提高碳电极的能量密度为目的。探索获得氮掺杂碳纤维/NiFe2O4复合气凝胶柔性电极的工艺路线和多尺度构筑条件，考察获得的复合气凝胶电极的网络孔洞结构、NiFe2O4微纳形貌及分布与物理化学性能，尝试建立多尺度构筑参数—复合气凝胶网络孔洞结构和NiFe2O4微纳形貌及分布—物理化学性能三角关系；同时着重对氮掺杂碳纤维/NiFe2O4复合气凝胶电极的能量密度、机械柔韧性能进行评价，重点阐述多尺度构筑参数和组成比例对复合气凝胶不同尺度结构形貌及NiFe2O4分布的影响，以及最终对氮掺杂碳纤维/NiFe2O4复合气凝胶电极的能量密度和机械柔韧性能的影响。

碳材料具有优异的机械柔韧性能和良好的导电性能，然而其能量密度较低。NiFe2O4具有较高的能量密度，然而其导电性以及机械柔韧性差。本项目以纤维素纳米纤维、甲壳素纳米纤维分别作为碳材料的碳源、氮源。利用氮掺杂碳材料优异的机械柔韧性能来弥补NiFe2O4柔韧性能的不足，同时利用NiFe2O4卓越的储能性能来显著提高碳材料的能量密度。在酸性条件下，纤维素纳米纤维/甲壳素纳米纤维悬浮液通过氢键转变成均匀的复合水凝胶。其机械强度可以通过改变甲壳素纳米纤维含量来有效调控。六棱柱冰晶在复合水凝胶中的定向结晶过程可以将天然纳米纤维随机堆积在冰晶间隙中，进而形成随机堆积纳米片。其微观形貌受复合水凝胶机械强度调控。随机堆积纳米片中存在着丰富的堆积孔结构。碳化后，随机堆积纳米片转变成堆积多孔氮掺杂碳纳米片。具有丰富微孔和中孔的碳纳米片的厚度在15-20 nm范围内。堆积多孔氮掺杂碳纳米片质量比容量高达199 F g-1（0.25 A g-1）。固载无机纳米材料的天然纳米纤维在水中仍能呈现出均匀稳定的分散状态。水热后，均匀稳定的分散体转化成复合水凝胶而其机械强度可以通过NiFe2O4的含量进行有效调控。通过冰晶的定向冷冻技术使天然纳米纤维和NiFe2O4在冰晶间隙中随机堆积来实现对复合气凝胶微观结构以及孔结构的多尺度协同构筑。碳化温度以及时间对氮掺杂碳纳米片/NiFe2O4复合材料的微观形貌以及NiFe2O4尺寸及分布具有良好的调控效果。最佳碳化温度为700 °C；碳化时间为3 h。氮掺杂碳纳米片/NiFe2O4复合材料质量比容量最高可达457.3 F g-1 (0.5 A g-1)。由其制备出的指叉型柔性超级电容器同样具有良好的电化学性能。上述研究可以为协同构筑多组分、多尺度碳/无机纳米复合功能材料提供有益的参考。