面向高体积能量密度锂离子电池的碳笼结构精确定制

Considering the continuing demand for the miniaturization of electrochemical energy storage devices, volumetric energy density has become a critical parameter for lithium batteries. The replacement of graphitic anodes by silicon anodes is a promising strategy to realize a high volumetric performance of a lithium-ion battery. However, the real application of silicon anode materials is currently limited by their huge volume expansion during cycling. The purpose of the proposed project is to develop the precisely designed carbon cages for silicon particles based on the densification of graphene network for high volumetric lithium storage, and further achieve the construction of dense and thick carbon-caged silicon anodes. This project focused on following several aspects: 1) Developing a strategy leveraging flexible sacrificial agent with controlled utility of void space in carbon cage for silicon materials; 2) Research on the effect of the mechanically strong and flexible carbon cage for buffering the volume fluctuations, and the improvement on the confinement effect for silicon particles, allowing silicon particles expand within the cage in dense carbon-caged silicon electrodes; 3) Optimizing the electronic and ionic pathway to ensure the charge transport to deliver high capacity at a thick electrode with practical mass loading. In general, this project is of great importance not only from the point of fundamental study for high-volumetric materials design but also promoting the high-capacity noncarbon anodes based on nanocarbons into the real electrochemical energy storage devices.

随着用户便携性要求的提高和使用空间的限制，体积能量密度成为锂电池至关重要的性能指标。硅作为新一代负极材料有望取代目前商用石墨，但循环过程中巨大的体积膨胀严重限制了其体积性能优势的发挥。本项目的研究目标是基于三维石墨烯网络致密化过程，精确定制碳笼实现硅/碳复合电极材料的高体积容量设计，进而构建高密度、高负载量硅/碳“厚密”电极。在石墨烯网络致密化过程中，引入可流动、可变形、易去除的“变形金刚”柔性模板，实现碳笼内部预留空间定制；探究碳笼的机械强度对硅体积膨胀的缓冲效果，调控碳笼对硅活性颗粒的限域结合作用，获得高密度、长循环的硅/碳复合电极；进而构建有序、短程离子传输通道，保持电极导电连续性，解决电极厚度增加后的电荷传输问题。本项目的实施不仅为硅/碳复合电极材料高体积容量设计提供新的思路，具有重要的理论研究价值，而且有助于推动基于碳纳米材料的复合电极材料在电化学储能器件中的实用化进程。

随着用户便携性要求的提高和使用空间的限制，体积能量密度成为锂电池至关重要的性能指标。本项目的研究目标是基于三维石墨烯网络致密化过程，精确定制碳笼实现硅碳复合电极材料的高体积容量设计，进而构建高密度、高负载量硅碳“厚密”电极。本项目揭示了石墨烯水凝胶的致密化机制，证明了与表面张力关联的毛细管力是决定组装体材料密度和孔隙的源动力，实现了三维石墨烯网络孔隙率与密度的连续精确调控；基于石墨烯致密化组装提出了“类细胞”结构的力学强化设计微米硅碳负极；提出了液态金属、表面皮肤、纳米弹簧等硅碳负极表界面调控与优化策略，解决了体积变化过程硅负极界面稳定性难题，获得了1000周循环寿命的微米硅碳负极与1000 Wh L-1超高体积能量密度致密型锂离子电池。本项目阐明了石墨烯致密组装的机制，突破了微米硅的实用化瓶颈，为锂离子电池所面临的空间焦虑提出了解决方案，进而将碳界面调控思想拓展至碱金属电池，对高比能碱金属离子电池碳负极材料的结构设计具有重要的理论指导价值。