嵌入型硅/N-掺杂石墨烯纳米复合负极材料的一步固相合成及其性能研究

Silicon is one of the most promising anode materials for next-generation lithium-ion batteries (LIBs) due to its low discharge potential, long potential plateau and highest energy capacity for lithium storage. However, the commercial applications of silicon in LIBs have been limited by the large volume charge, low conductivity and dynamic change of SEI layer during the charge/discharge processes. Development of silicon/carbon nano-composites is an efficient method to solve above-mentioned questions and improve the electrochemical performance of silicon. Among them,embedded-type silicon/graphene nano-composite is a very attractive system with great application potentail. However, some basic problems in the preparation technology and composite structures still need to be solved.For example,nano-Si structures are difficult to be well-dispersed in the graphene matrix and obtain a homogeneous composite and graphene also cannot thoroughly wrap the silicon nano-structures, and therefore leads a low coulombic efficiency, low capacity and poor cycle capability.In this project, we first proposed a novel "bottom-up" synthesis strategy, embedded-type Si/N-doped graphene nano-composties .can be prepared by in-situ solid-state synthesis and one-step microwave synthesis. N-doped graphene is in-situ grown and fully wraps the Si nano-structures by pyrolysis of metal phthalocyanines and their derivatives or metal phthalocyanine derivatives directly synthesized from basic precursors in microwave. All the silicon nano-structures can be uniformly dispersed and thorougly wrapped in the graphene matrix.In addition，more secondary porous architectures can be fabricated within embedded-type Si/N-doped graphene nano-composties via a approach combining chemical deposition-dissolution processes and one-step solid-state synthesis.Such novel silicon/N-doped graphene nano-composites may exhibit high energy capacity, low cost and excellent rate and cycle capability.

硅材料是最具应用潜力的锂离子电池负极材料之一，但显著的体积效应、低导电率和循环过程中SEI膜的动态变化都限制了其商业化应用。制备硅/碳纳米复合材料可有效解决上述问题，提高硅材料的电化学性能。嵌入型硅/石墨烯纳米复合材料是其中很有开发和应用前景的体系,但因合成方法的限制，普遍存在石墨烯包覆不完整，硅纳米材料分散不均匀、易团聚的问题，导致复合材料库伦效率下降，比容量和循环性能难以兼顾。本项目拟采用"自下而上"的合成策略，从金属酞菁及其衍生物，或金属酞菁衍生物的合成初始物出发，通过原位固相和微波固相一步合成的手段，以硅纳米材料为中心，原位生长N-掺杂石墨烯包覆层，可获得石墨烯包覆完整紧密，硅纳米材料高度有序分散的复合材料；结合化学沉积-溶解方法，还可以在复合材料内部进一步制造精细的次级多孔空间结构。上述硅/N-掺杂石墨烯纳米复合材料有望成为具有高容量、低成本、倍率和循环性能优异的新型负极材料。

硅材料是商业化石墨负极最具潜力的替代材料之一，但剧烈的体积效应、低导电率和循环过程中SEI膜的动态变化极大地限制了其实际应用。嵌入型硅/石墨烯纳米复合材料可有效解决上述问题，提高硅材料的电化学性能，但因合成方法的限制，普遍存在石墨烯包覆不完整，硅纳米材料分散不均匀、易团聚的问题，导致复合材料库伦效率下降，比容量和循环性能较差且难以兼顾。.本项目针对上述瓶颈问题，采取“自下而上”的合成策略，通过发展高温固相方法，从酞菁铁出发，以硅纳米材料为中心原位生长N-掺杂石墨烯包覆网络，一步制备出石墨烯包覆完整紧密、硅纳米材料高度有序分散的复合材料。该复合材料表现出优异的循环和倍率性能。在此基础上，我们使用价格更为低廉的葡萄糖和过渡金属无机盐混合物替代酞菁铁，并严格控制前驱物种与活性材料间的物质量比，通过高温固相反应，在LiFePO4纳米颗粒表面首次原位生长超薄石墨化碳完整包覆层（约2.5 nm）和向空间延伸的三维石墨烯导电网络，得到具有优异电化学性能的LiFePO4@graphene正极材料。 结合高分辨透射电镜，我们对石墨烯在纳米界面上的生长机制进行了深入研究，提出了石墨烯在金属“纳米岛”表面催化生长的基元步骤以及石墨烯在不同的碳源和催化剂前驱体比例下的生长模式。.在上述工作基础上，我们采用化学沉积-溶解结合高温原位固相一步制备方法，实现了石墨烯空心球包覆硅纳米颗粒复合材料的可控合成。该复合材料经600次充/放后，可逆容量保持在1410 mAh.g-1，保持率为62.6%；且在30C（126 A g-1）放电制度下依然可表现出1266.9 mAh.g-1的容量。我们还将上述方法成功应用于过渡金属银、铜微/纳颗粒表面的石墨烯紧密包覆层生长，并开展相关增强拉曼光谱的研究。.此外，我们开发出钙离子交联三维网络状高强度粘结剂，可显著增强硅基极片的机械性能，保持其长期循环过程中结构和导电网络的稳定性。硅电极经500次充/放后，可逆容量保持在2522 mAh.g-1，保持率为75.6%。在解决硅基负极价格瓶颈方面，我们将廉价光伏产业硅切割高纯废料引入到锂离子电池负极，可批量制备高纯度电池级硅纳米片，为硅材料的商业化应用提供了可能性。.项目发表SCI论文18篇，其中14篇为通讯作者，1篇论文被选为ESI高被引论文；申请专利3项，授权1项；获2015年度江苏省科学技术二等奖1项。