原位孪生聚合法设计构筑石墨烯复合电极材料及其锂离子电容器

In response to the limited fossil resources and ever-increasing energy consumption, the development of energy devices with high energy and power densities has become more important than ever. Supercapacitors have high power density but suffer from low energy density because of non-Faradaic capacitive materials used. Lithium ion batteries (LIBs) can deliver high energy density while low power density by using Faradaic redox reactions throughout active materials. To combine their respective advantages of LIBs and supercapacitors in a single device, lithium ion capacitors (LICs) are emerging that couple a battery anode and a capacitor cathode. LICs are promising in achieving high energy density of LIBs without significantly sacrificing high power density of supercapacitors. However, the kinetics imbalance in the power capability between two electrodes often leads to poor rate capability and low cycling stability. Herein we attempt to develop new electrode materials by in-situ twin polymerization of organic-inorganic hybrid monomers in the presence of sulfonated-graphene oxide and subsequent high-temperature carbonization under an inert atmosphere. The high-capacity battery-type materials, graphene/GeO2/doped-carbon hybrids, can be produced by using Ge-containing twin monomers. The capacitor-type materials of graphene/porous doped-carbon hybrids can be prepared by using twin polymerization of Si-containing monomer precursors followed by thermal carbonization and HF etching to remove ultra-small nanosized-silica phase. LICs will be constructed by employing such graphene-enabled highly-conductive electrodes, and their electrochemical performances will be systematically examined by cyclic voltammetry, galvanostatic charge/discharge, and electrochemical impedance spectroscopy. Special attentions are paid to the relationship of electrochemical performance with material components, chemical doping states, and micro-/nano-structures. It aims at finding efficient strategies to fabricate graphene-based electrode materials with tunable nanostructures and hence large capacity, high electronic conduction, and fast lithium-ion diffusion. Electrode kinetics and charge storage/transport mechanisms will be clearly addressed to understand the kinetics balance between the Faradaic anode and the non-Faradaic capacitive cathode. This should be the first report on utilizing a new twin-polymerization methodology to guide the rational design of active materials with large specific capacity, high electrical conductivity, and fast lithium-ion diffusion. The present proposal may open up a novel avenue for the fabrication of hierarchically-porous, chemically-doped, and microstructure-tailored electrodes, enabling the rapid development of LICs with high power and energy densities, long cycling life, and excellent rate capability.

针对超级电容器和锂离子电池面临高能量大功率应用的限制，本项目设计合成含有N、S有机基元和Ge、Si无机基元的孪生杂化单体，继而与磺化氧化石墨烯发生原位孪生聚合反应，对电极材料同步进行化学掺杂、结构调控和纳米复合，再经高温炭化或化学刻蚀，制备出石墨烯/GeO2/掺杂碳、石墨烯/层次孔掺杂碳复合材料，并以前者为电池活性负极材料、后者为电容活性正极材料构建锂离子电容器。研究材料组成、化学掺杂、微纳结构与器件性能之间的相互关系，揭示电极过程动力学、界面反应机理和电荷传输/存储机制，进而指导锂离子电容器正负极的优化设计与合理匹配，协同调控正极表面双电层电荷吸脱附与负极体相中锂离子扩散的动力学平衡，实现两种储能体系的性能优势互补。建立孪生聚合新方法设计构筑复合材料的调控策略，发展比容量大、电导率高和离子扩散快的电极材料，为构建能量高、功率大、寿命长和倍率性能优异的新型储能器件提供实践指导和理论依据。

在本项目执行期内，完成工作主要包括：（1）基于分子设计原理和功能导向策略，成功地合成了系列有机-无机单元偶联的含Si、Ti、Sn、Ge单体，建立了孪生（同步）聚合法衍生构筑多孔碳、碳基负载金属氧化物纳米晶的新方法；利用空间限域效应，在单分子水平上同时进行原位化学掺杂、层次孔结构调控或纳米晶均匀负载，揭示了单体分子结构、限域聚合机理、形貌演变过程与材料微观结构的内在关系，开启了聚合导向机制设计合成电极材料的新思路。（2）通过聚合物衍生制备了系列碳质电容材料，揭示了材料组成、微观结构与储能特性之间的相互关系，厘清了电极过程、表/界面反应和电荷输运存储机制，提高超级电容器的比电容和能量密度。（3）基于水热、溶剂热、超声化学、机械化学等方法发展了系列石墨烯基复合材料（MnO2、Co3O4、VS2、Ni(OH)2）；通过纳米复合、结构调控构建三维混杂网络，抑制石墨烯和金属化合物纳米粒子的团聚，增加电化学活性位点，促进电子传输和离子扩散，并抑制、缓冲金属化合物在充放电过程中的体积波动，维持电极结构完整性和循环稳定性，继而协同提高器件的能量密度、循环寿命和倍率性能。（4）基于电极材料匹配构建了锂离子电容器、非对称超级电容器，结合电容器、电池储能特性优势，解决非对称电极的动力学不平衡和比容量不匹配问题，为构建高能量、大功率、长循环的新型高效储能器件提供了重要的实践基础和理论指导。受本项目资助，以通讯作者发表了影响因子大于10的论文10篇，影响因子大于5的论文19篇；取得了具有自主知识产权的创新成果，授权中国发明专利3项；毕业博士生1名、硕士生5名。