【作者】 杨伟；

【导师】 亢一澜；

【作者基本信息】 天津大学 ， 固体力学， 2019， 硕士

【摘要】 锂离子扩散是锂离子电池内部重要的电化学过程,当锂离子在电极材料中嵌入与脱出时,会引起材料结构变形、浓度变化等力-电化学耦合问题,进而造成对电极的变形破坏、容量衰减等性能退化问题,其中力学作用影响尤为显著。本文针对电化学中电极材料的力-电化学参数展开实验测量,重点关注实验中应变与锂浓度的实时原位测量技术,以及基于实验测量结果对嵌脱锂过程中的变形场分布与锂浓度演化规律分析,进一步推导实现电化学中电极材料的应力可视化表征,并分析力学因素对电化学行为之间的耦合过程。主要工作包括以下几个方面:首先研制了高稳定性的荧光散斑颗粒,并进行了电化学过程中电极试件表面散斑的制备。以数字图像相关方法为基础,基于主动光学测量原理,扩展改进数字图像相关技术,通过单色激光光源与滤光片的结合使用,完善电极变形测量系统,实现电极变形在电化学领域中的高精度实验测量,解决了电极材料在电化学充放电过程中由于颜色背景光场变化引起的散斑退化无法识别的难题,为电极材料在电化学复杂环境中应变场测量提供了可能。采用了电极材料应变场与浓度场原位协同实验测量技术,设计搭建了灰度图像与颜色图像同时采集的双光路实验采集系统,研制了可视化电池装置与边对边电极结构设计,实现了石墨电极在嵌锂与脱锂过程中应变场与浓度场的实时采集,并同时给出了其时空分布结果的演化信息。基于实验结果,对比分析了嵌锂与脱锂过程中应变与浓度之间的相互耦合关系。分析结果表明,应变与浓度在实验过程中都表现出明显的非均匀性,且两者之间的演化规律存在相似之处。开展电极材料在电化学实验中的原位测量技术以及应变、浓度等参数的实验测量对于深入探究力-电化耦合问题具有重要的科学的意义。实现了圆环形电极电化学应力场的表征。设计电极边对边的排布方式,采用无边缘约束作用的圆环形电极结构设计,利用实验技术手段原位获得的应变与浓度数值,通过推导计算得到电极在充放电过程中的应力演化,实现了石墨电极可视化应力场的时序测量表征。综合浓度、应变与应力因素,分析三者之间在电化学作用下的耦合过程与相互影响机制。更多还原

【Abstract】 Lithium ion diffusion is an important electrochemical process inside lithium ion batteries.When lithium ions are embedded and desorbed in the electrode material,it will cause force-electrochemical coupling problems such as material structure deformation and concentration change,which will cause deformation damage and performance degradation to the electrode.Among that,the mechanical effect is particularly significant.This article focuses on the experimental measurement of the force-electrochemical parameters of electrode materials in electrochemistry,importantly focusing on the real-time in-situ measurement of strain and lithium concentration in the experiment,and the deformation field distribution and lithium concentration evolution during the insertion and removal of lithium based on the experimental measurement results.We further realize the visual characterization of the stress of electrode materials in electrochemistry,and analyze the coupling process between mechanical factors and electrochemical behavior.The main works include the following aspects:First,high-stability fluorescent speckle particles were developed,and speckles on the the electrode specimen surface were prepared during the electrochemical process.Based on the digital image correlation method and the principle of active optical measurement,the digital image correlation technology was extended and improved.Through the combination of a monochromatic laser light source and a filter,the electrode deformation measurement system was improved to achieve high-precision experimental measurement of electrode deformation in the electrochemistry field.This technology solves the problem that the speckle degradation caused by the change of color background light field during the electrochemical charging and discharging,and provides a possibility for measuring the strain field of the electrode material in the electrochemical complex environment.The in-situ synchronous experimental measurement technology of the strain field and concentration field of the electrode material was adopted,and a dual-optical path experimental acquisition system for simultaneous acquisition of grayscale images and color images was designed.We developed a visual battery device and edge-to-edge electrode structure design,realizing the real-time collection of the strain field and concentration field of the graphite electrode during lithium intercalation and delithiation,and also provided the evolution information of its space-time distribution results.Based on the experimental results,the mutual coupling relationship between strain and concentration during lithiation and delithiation was compared and analyzed.The analysis results showed that both strain and concentration present obvious nonuniformity during the experiment,and there were similarities in the evolution laws between the two.It is of great scientific significance to carry out in-situ experimental techniques of electrode materials and experimental measurements of the parameters such as strain and concentration for the in-depth exploration of the forceelectrochemical coupling problem.The mechanical characterization of the electrochemical stress field of the circular electrode was realized.We designed the electrode edge-to-edge arrangement,and adopted the circular electrode structure design without edge restraint.Through the strain and concentration values obtained in situ by experimental technical means,we derived the stress evolution of the electrode during the charge and discharge process,implementing the measurement and characterization of visual stress field of graphite electrode.Considering the concentration,strain and stress factors,we analyzed the coupling process and interaction mechanism among them during electrochemical processes.更多还原