含表界面效应的锂离子电池颗粒状电极材料变形理论及微结构设计方法研究

Lithium-ion batteries have a wide application in energy, transportation, aerospace and other fields, due to their excellent performance. The intercalation and deintercalation of lithium-ions are accompanied by complex chemical reaction, deformation and heat dissipation in the charging and discharging process. Especially, non-uniform strain due to diffusion leads to material damage and fracture, the degradation of batteries and even break, so mechanical problems are prominent. But the traditional electrochemical theories neglect some factors including elastic stresses and configuration entropy, and the maturational deformation theory of particulate electrode material hasn’t been established in consideration of surface-interface effect. So this project will (1) propose a deformation theory of electrodes in lithium-ion batteries under the electro-chemo-mechanical coupled effect, and verify the established theory by optical experiments in order to indicate the electro-chemo-mechanical coupled mechanism; (2) develop the mesomechanical model of particulate electrode material in consideration of surface and interface effects, and verify our theory by experimental characterization methods such as nanoindentation, in order to establish the relation between mesoscopic electrode particle and macroscopic electrode film; (3) propose microstructure design methods of electrode material in order to optimize working performance of batteries, based on established deformation theory and mesomechanical model. This project expects to gain original achievements in electro-chemo-mechanical deformation theory and mesomechanics in lithium-ion batteries, which will provide profitable guidance for the design, manufacture and engineering application of lithium-ion batteries.

锂离子电池性能优异，广泛应用于能源、交通、航天等领域。在电池充放电过程中，锂离子的嵌、脱伴随着复杂的电化学反应、变形和热量的耗散。尤其是非均匀扩散应变将引起电极材料损伤、断裂，常导致电池性能衰减甚至破坏，其力学问题突出。而传统电化学理论忽略了弹性应力、形位熵等因素，对于这一过程中含表界面效应的颗粒状电极材料变形理论的关系还不成熟。本项目（1）拟提出电化学力学耦合作用下锂电池电极变形理论，并采用光学实验表征方法进行验证，以期揭示电化学和力学耦合作用机理；（2）发展考虑表、界面效应的锂电池颗粒状电极细观力学，通过纳米压痕等实验表征方法进行验证，以期建立细观电极颗粒和宏观电极薄膜之间的联系；（3）基于建立的变形理论、细观力学模型，提出电极材料的微结构设计方法，优化电池工作性能。本项目期望在锂离子电池电化学力学变形理论、细观力学理论获得原创性成果，将为锂电池电极设计、制备和工程应用方面提供指导。

锂离子电池由于优越的性能已广泛应用于消费电子、交通等领域。在充放电过程中，锂离子在电池正负极之间反复脱嵌，并伴随着复杂的电化学反应、机械变形。非均匀扩散和外部约束往往会在电池内部产生较大的应力，导致电极材料的断裂和各组分界面的脱粘等力学衰减行为，电化-力耦合问题突出。但目前对电极材料电化-力耦合作用机理还不完全清楚，实验表征手段有限以及缺乏有效的解决方案。本项目针对锂离子电池电极材料，从理论模型、实验表征和微结构设计对电化-力耦合行为进行研究。主要研究内容包括电极材料电化-力耦合变形理论的建立、电极材料应力及细微观变形的原位实验表征和电极微结构设计。.本项目首先针对颗粒状电极，建立了考虑各向异性性质和表面应力的电化-力耦合变形理论，很好地解释了各向异性电极的充放电策略以及纳米尺度电极表现出的尺寸效应；基于多光束光学传感器和光学显微镜，开发了可以同时获取电极薄膜应力和变形的原位光学观测系统，并很好地应用于硅电极薄膜的应力和厚度方向变形的实时测量；基于扫描电子显微镜，发展了电极材料微观形貌演化的原位实验表征平台，实现对电极微观形貌实时高精度观测，并结合数字图像相关法，计算了电极表面变形场和应变场；基于光学原位表征平台，首次报道了硅薄膜在充放电过程中的变色现象，并揭示了电化-力耦合变色调控机理；基于实验表征结果和变形理论，提出了硅电极微结构空心非等轴设计方法，极大地缓解了电极断裂行为，提高了硅电极的机械完整性和相应的电化学性能；结合普适性的高粘度墨水和可定制化的PDMS软模板，设计制备了自支撑可变形的剪纸电极，具有电极微结构设计性强、机械稳定性高的优点。这些研究结果为电极材料衰减机理、电化-力耦合行为的实验表征和微结构设计等方面提供了新的思路，并将促进下一代锂离子电池的发展。