碳纤维增强复合材料结构电极的嵌锂机制及其化学-力学耦合模型

Multi-functionalization is an important trend in upgrading the structures in aviation, aerospace and transportation, etc. Carbon fiber reinforced composites have low densities, high strengths and excellent designable characteristics, and have been more and more extensively used. Carbon fibers are composed of many graphite crystallines, enable lithium ion insertion and extraction, which can be applied in structural electrodes. The lithiation/delithiation in carbon fibers have a significant influence on the mechanical properties of the structure electrodes. However, lithium insertion mechanism in carbon fiber is not well illustrated at the micro scale and no models are established accordingly. This work aims at lithium intercalation mechanism in carbon fiber structural electrodes. Lithium ion distribution during lithium insertion in carbon fibers is in-situ observed. The expansion and the tensile properties of carbon fibers after lithiation are measured. Based on the experimental mechanisms, the chemical-mechanical coupling model is established to calculate the strain and stress distribution in carbon fibers after lithium insertion. Furthermore, the composite structural electrode is prepared with carbon fiber and polymer electrolyte and its mechanical properties are measured during charging and discharging. Based on the calculation results of the chemical-mechanical coupling model of carbon fiber lithiation, a representative volume element model is established to predict the mechanical properties of the structure electrode after lithium intercalation, and the validity of the model is verified by comparison with the experimental results. This research can provide an basic theoretical basis for the study and application of carbon fiber structural batteries.

多功能化是航空、航天、交通运输等领域装备结构升级的重要趋势。碳纤维增强复合材料具有轻质、高强、可设计的优点，应用越来越广泛。碳纤维中含有大量的石墨微晶，适合锂离子的嵌入和脱出，是一种良好的结构电极材料。碳纤维嵌/脱锂会对结构电极的力学性能产生重要影响，而国内外对碳纤维结构电极嵌锂的微观机制研究尚不完善，模型研究尚属空缺。本项目基于此，原位观察测量碳纤维嵌锂过程中锂离子扩散分布情况，表征嵌锂碳纤维的膨胀形变以及拉伸性能；基于微观机制，建立锂离子在碳纤维中扩散的化学-力学耦合模型，模拟嵌锂碳纤维的应变以及应力分布；制备由碳纤维和固态聚合物电解质组成的复合材料结构电极，测量其充放电过程中的力学性能，并基于碳纤维嵌锂化学-力耦合模型计算结果，建立代表性体积元模型，预报结构电极嵌锂后的力学性能，并与实验结果对比验证模型的有效性。最终为碳纤维结构电池研究和应用提供的重要理论基础和方法支撑。

碳纤维结构储能复合材料兼具优异的力学承载和电化学储能多功能特性，根据电化学工作原理不同，可分为复合材料结构电池和复合材料结构超级电容器。碳纤维结构电极电化学作用过程会对复合材料结构电极的力学性能的影响机理，反过来，力学承载过程对电化学储能特性也有重要影响。本项目建立碳纤维结构电极及复合材料多功能器件的制备、表征、机理分析和优化方法，通过复合材料工艺优化\、有限元模拟及机器学习算法，建立了碳纤维储能复合材料的相关实验表征方法以及模型，完成了碳纤维结构电极设计制备以及机理表征、碳纤维结构电极的制备以及模型机理分析、碳纤维层合结构电池的设计与实现、碳纤维结构电极在结构超级电容器上的应用等研究内容，为碳纤维结构储能复合材料的电极力-电作用机理和性能设计提供示范性研究，也为航空航天飞行器等装备复合材料升级提供的重要理论基础和方法支撑。