相分离结构硬炭负极材料的可控制备及石墨烯原位诱导机理研究

As anode material for lithium-ion batteries, hard carbon suffers from three inherent disadvantages including large voltage hysteresis between charge and discharge, low initial coulombic efficiency and low compacting density, which strongly limit its application. Herein, we propose a novel idea and technical route to fabricate hard carbon using resin as precursor, which include adding functionalized graphene into resin precursor, decreasing the precursor particle size and precisely regulating the heat-treatment temperature and heating rate during the micropore structure formation and evolution stage. Hard carbon with high-degree graphitization local areas and large amount of three-dimensional connected open-micropores can be obtained due to the in-situ induced graphitization and oriented pyrolytic gas escape from graphene. That is why hard carbon fabricated by this method is phase-separated, including graphite crystallite phase, disordered amorphous carbon phase and open-micropore phase. Highly dispersed graphite crystallite phase can provide both good electronic conductivity and a certain degree of plasticity. The large interlayer spacing of disordered amorphous carbon phase can enhance lithium ion diffusion ability and cycle performance. Abundant and connected open-micropores with small pore size can ensure high reversible capacity and initial coulombic efficiency. This project provides a new promising technical method to fabricate hard carbon anode materials with excellent electrochemical performance for lithium ion battery. The idea and research achievement in this project may provide technical guidance for structure design and controllable preparation of hard carbon anodes for sodium ion battery, and provide important theoretical foundation for the performance improvement of engineering carbon material.conductivity and a certain degree of plasticity. The large interlayer spacing of disordered amorphous carbon phase can enhance lithium ion diffusion ability and cycle performance. Abundant and connected open-micropores with small pore size can ensure high reversible capacity and initial coulombic efficiency. This project provides a new promising technical method to fabricate hard carbon anode materials with excellent electrochemical performance for lithium ion battery. The idea and research achievement in this project may provide technical guidance for structure design and controllable preparation of hard carbon anodes for sodium ion battery, and provide important theoretical foundation for the performance improvement of engineering carbon material.

针对锂离子电池硬炭负极材料电压滞后大、首次效率和压实密度偏低的固有问题，申请者提出在硬炭前驱体树脂中添加功能化石墨烯，再通过减小前驱体颗粒尺寸并在孔隙形成和演变阶段控制热处理温度及升温速率，利用石墨烯的原位诱导石墨化和原位诱导热解气体定向逸出作用，在硬炭中同时形成局部石墨度较高的区域和三维连通开口微孔的新思路和技术路线。按照这种设计思路制备的硬炭，呈相分离结构，包括石墨微晶相、无定型炭相和开口微孔相。因形成高度分散的石墨微晶相而具有较高的电子导电性和一定的塑性形变特性；因无定型炭相具有较大的层间距而具有良好的离子扩散性能和循环性能；因存在丰富且连通的小孔径开口微孔而具有高的可逆容量和首次效率。研究工作有望发展成为一种制备综合电化学性能优异的硬炭负极材料的新方法；相关研究思路和成果还可用于指导钠离子电池硬炭负极材料的结构设计和可控制备；对于改善基础炭材料的综合性能也有重要的理论指导作用。

针对碱金属离子电池用硬炭负极材料电压滞后大、首次效率和压实密度偏低的固有问题，在筛选酚醛树脂种类，优化固化、炭化等热处理工艺，阐明酚醛树脂基硬炭负极材料构效关系的基础上，重点研究了在硬炭前驱体树脂中添加微晶石墨或功能化氧化石墨烯，再通过减小前驱体颗粒尺寸并在孔隙形成和演变阶段控制热处理温度及升温速率，在硬炭中同时形成局部石墨度较高的区域和三维连通开口孔，制备出具有多相（石墨微晶相、无定型炭相和开口微孔相）分离结构和优异电化学性能的酚醛树脂基硬炭负极材料。研究发现酚醛树脂基硬炭结构中表征石墨微晶层间距的d002和表征缺陷数量的激光拉曼强度比ID/IG对硬炭的电化学性能有较大影响，硬炭的d002和结构缺陷随酚醛树脂交联程度提高而增大，当d002为3.71 Å左右时具有最优的电化学性能；添加天然微晶石墨或功能化氧化石墨烯的硬炭中形成了大量微孔或中孔，同时在硬炭中形成沿石墨或石墨烯平面方向生长的类石墨微晶，有利于提高硬炭的容量和倍率性能，证实微晶石墨或石墨烯对相邻酚醛树脂碳的原位诱导石墨化和原位诱导热解气体定向逸出作用机理。研究还发现，在添加量较低时，添加天然微晶石墨的硬炭中以微孔为主，而添加氧化石墨烯的硬炭中同时存在微孔和中孔，中孔的形成源于氧化石墨烯中的含氧官能团在热处理过程中的大量逸出，大量中孔的存在导致添加氧化石墨烯的硬炭首次库伦效率较低。.相关研究思路和方法还用于指导钠、钾离子电池用生物质硬炭负极材料、微晶石墨/纳米Si/硬炭复合负极材料的结构设计和可控制备，有效提高了材料的容量、首次库伦效率和倍率性能。.研究工作有望发展成为一种制备综合电化学性能优异的硬炭负极材料的新方法，研究成果不仅对碱金属离子电池用硬炭负极材料的可控制备，而且对于改善基础炭材料的综合性能也有重要的理论指导作用。