锂离子电池用低平台、高倍率硬炭基负极材料的形成机制及其电化学性能研究

Aiming at the problem of high potential platform of hard carbon anode, the purpose of researches in this project is to prepare the hard carbon anode with low platform and excellent rate performances for lithium ion batteries. The initial selection of precursor will be conducted by taking the content of benzene ring and H/C ratio as indexes. The pyrolysis mechanisms of precursors will be discussed according to their pre-decomposition and pyrolysis progresses. The microstructures of hard carbon will be regulated and the hard carbon anodes with low potential platform will be synthesized. The formation mechanisms of pore will be investigated on the basis of thermal analysis and characteristics of micropore. The influences of the kinds of pore-making agent and use level on the microstructure, characteristics of micropore and tap density of hard carbon anode will be studied. The relations between the pore structures and electrochemical performances of hard carbon will be investigated. Hard carbon sources, such as poly(vinyl alcohol), poly p-phenylene and carboxymethyl cellulose, will be used as the coating precursors to prepare the hard carbon composite with high conductive carbon layers. The effects of coating steps, coating thickness, mixing conditions and heat treatment technology on the microstructure of composite will be systematically investigated after the thermal analysis of coating precursor. Pitches with different hydrogen and oxygen contents will be utilized to prepare the soft carbon coated hard carbon composite. The influence mechanisms of the coating conditions of pitch, accelerator of graphitization and heat treatment system on the development of microcrystal of composite will be researched. The internal relations between the potential platform, rate performances and the microstructures of hard carbon composite anodes will be discussed thoroughly.

针对硬炭负极材料倍率性能好但电位平台较高的问题，旨在制备兼有低电位平台和良好倍率性能的锂离子电池用硬炭基负极材料。以苯环含量和H/C比为考核指标对前驱体进行初步筛选，考察前驱体的预分解和热解历程，探讨其热解机制；对硬炭的微观结构进行调控，制备具有低电位平台的硬炭负极材料。通过热分析和微孔特性测试，探讨造孔剂的造孔机理；系统考察造孔剂的种类和用量对硬炭微观结构、微孔特性和振实密度的影响，分析孔结构与电化学性能的联系。选择聚乙烯醇、聚对苯和羧甲基纤维素等硬炭作包覆前驱体，制备表面为高导电率硬炭层包覆的硬炭复合材料。考察包覆前驱体的热解行为，探讨包覆步骤、包覆厚度、混合条件和包覆后的热处理工艺等对复合材料微观结构的影响。选择不同氢氧含量的沥青来制备软炭包覆的硬炭复合材料。研究包覆条件、石墨化促进剂和热处理条件等对材料中微晶生长的影响机制。深入分析复合材料的电位平台、倍率性能与微观结构的内在联系

本项目针对硬炭负极电位平台高的问题，以苯环含量和H/C为指标，选择酚醛环氧树脂为前驱体，以获得兼有低电位平台和良好倍率性能的锂离子电池负极。制备了性能优良的硬炭负极，查明了相关的形成机制，提出改善首次库伦效率的技术，这些成果将为锂离子电池的进步做出贡献。.在热解前增加了预分解过程，探讨了酚醛环氧树脂的热解机制，查明了预分解对硬炭结构和电化学性能的影响；发现增加预分解过程的硬炭具有更小的ID/IG，更大的比表面积、微孔体积和比容量。500度预分解1h制备的硬炭具有最大的充电容量390mAh/g、远高于未预分解的210mAh/g，而且还有较低的电位平台。.发现造孔剂与前驱体形成的微相分离结构是形成孔隙的主要原因，聚乙二醇造孔所得硬炭的孔径位于2-10nm之间，其质量比为50%时硬炭的可逆容量最高可达432.6mAh/g。KOH造孔的硬炭以小于2nm的微孔为主，随着KOH用量增加，硬炭的总孔容和比表面积不断增大，首次充放电容量和循环性能明显改善。.氧化石墨烯高温热还原后不仅能构建优良的导电网络，还使硬炭颗粒接触更充分，加快锂离子的传输。其含量为20%、1000度热还原的硬炭在20、2000mA/g时的充电容量为最高的480、200mAh/g，电流减小后能恢复原来的容量。提出的预嵌锂技术能提高硬炭的首次库伦效率、弥补电池的容量损失、改善电池的能量密度。.硼酸作催化剂能提高硬炭的有序化程度、减小层间距，从而改善硬炭的倍率性能。当硼酸占比10%时，硬炭的可逆容量为最高的461.1mAh/g。煤沥青软炭包覆硬炭能显著改善硬炭的高低温电化学性能，其含量为20%时硬炭的电化学性能最佳，在50、25、-10度具有优异的容量568、413、298mAh/g。碳酸亚乙烯酯添加剂能促进SEI膜的稳定形成、抑制电解质的分解、改善高温性能，其浓度为1%时硬炭的可逆容量为最高的486mAh/g。