In Situ Experimental Measurement Technology And Mechanical Analysis Of Graphite Electrode In Electrochemistry

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.