树枝状碳纤维-氧化石墨烯三维框架构建调控高能量密度锂硫电池研究

In this proposal, a high energy lithium-sulfur battery with dendritic carbon fiber frameworks is designed to solve capacity decay problems and to improve energy density. The porous structure of dendritic carbon fiber is employed as cathode, increasing the electronic conductivity and load of active sulfur. The sulfur is locked within the cathode, simultaneously. A quasi-solid electrolyte that consists of functional graphene oxide frameworks absorbing liquid electrolyte will be used for the battery to simultaneously achieve high lithium ionic conductivity and inhibition ability of polysulfide dissolution and diffusion. This research will focus on investigation of synthesis mechanisms and effects of critical process parameters on physical-chemical properties of the branched porous cathode material frameworks as well as influence of the frameworks on electrochemical performance of the batteries. Relationships among molecular structures, surface charges and construction of the frameworks and electrolyte properties will be explored to obtain optimization strategies of the quasi-solid electrolyte. In addition, ion and electronmobility at the electrolyte/cathode interface will be characterized and a model of electrochemical reaction process will be built to reveal the key factors of electrode reaction rates. This project will provide theoretical basis for designs of high energy density, high power density and long cycling lithium-sulfur batteries.

针对锂硫电池循环过程容量衰减快、高能量密度难以发挥的问题，设计了基于枝状碳纤维框架的高能锂硫电池新体系。该体系正极拟采用具有多孔结构的枝状碳纤维，不仅能极大地提高正极电子导电性和活性物质硫的负载量，还能有效地控制硫的流失；其电解质是氧化石墨烯框架吸附电解液构筑的类固体电解质，通过框架表面分子改性可提高锂离子传输性能，阻止多硫化物的溶解和扩散。本项目通过研究枝状多空正极材料的合成反应机理、关键制备工艺参数对其理化性质的影响以及对电池电化学性能的作用规律，也将探索电解质分子结构、框架结构、框架表面电性、电解质性能之间的内在联系，确立类固体电解质性能调控策略；同时，研究离子-电子在电解质/正极界面的传输特性，建立起电池电极反应过程模型，找到影响电极反应速度的控制步骤。项目的研究可为高体积能量密度、高功率密度与长循环寿命锂硫电池设计提供理论依据。

针对锂硫电池存在的硫及其放电产物固有的电子/离子绝缘性、多硫化物溶解穿梭、缓慢的硫氧化还原反应动力学及充放电体积膨胀等关键问题，设计构建了基于多孔碳纤维框架-硫复合正极和WS2/CNTs框架类固体电解质的高比能长寿命锂硫电池储能新体系。该体系正极采用集流体和硫载体一体化设计，以调控制备的多孔结构碳纤维为导电载体，不仅极大地提高了正极电子导电性和活性硫负载量，而且综合发挥限域-吸附-催化多重机制抑制穿梭效应，构建获得了高载硫高比容长寿命硫正极材料（硫载量4-6mg/cm2下，可逆容量不小于800mAh/g，循环300次的容量保持率不低于70%）；其电解质是以设计的WS2/CNTs框架吸附电解液构筑的高离子电导率类固体电解质，通过框架表面分子改性促进锂离子传输，抑制多硫化物溶解和扩散。研究获得了多孔碳纤维-硫正极材料制备技术及理论、关键制备工艺对电极电化学性能的作用规律和优化策略；确立了电解质框架结构、表面性质与电解质性能之间关联关系及调控方法；掌握了多孔碳纤维框架-硫电极与类固体电解质匹配规律，阐明了电极/电解质界面离子/电子传输特性以及表界面反应原理和控制机制；完成了软包电池器件组装、性能优化与示范应用，实现了软包单体300Wh/kg能量密度。此外，还设计获得了新型轻质的锂硫电池复合功能隔膜和基于三维多孔集流体的稳定锂金属负极。项目研究为高能量密度、高功率密度与长循环寿命锂硫电池设计提供理论依据和技术支撑。