报告题目：

Field-limited migration of Li-ions in Li-ion battery and Analysis of Electrowetting of a Conducting Droplet on a Dielectric Layer

 报告人:               Prof. Fuqian Yang

Department of Chemical and Materials Engineering

University of Kentucky, Lexington, KY 40506

时间：2014年12月31日(周三)  9: 00         

地点：中国科学院力学研究所主楼小礼堂内会议室

报告摘要：

The migration/diffusion of Li-ions in active materials in lithium-ion battery cannot be simply described by Fick’s second law; the interactions among ionic migration, field, and stress need to be taken into account when analyzing the insertion/diffusion of Li-ions. The first part of this talk is focused on the development of the transport equation for analyzing the migration of lithium ions under the action of mechanical stress and electric current. Using the theory of thermal activation process, the flux for ionic migration under the simultaneous action of electric field and mechanical stress is found to be a nonlinear function of the gradient of electric potential and the gradient of stress. Under the action of small electric field and uniform stress, the temporal growth of the lithiation layer follows a parabolic law. Electric field can either accelerate or retard the growth of the lithiation layer, depending on polarity of the field.

Electrowetting has been used to actuate and control the motion of droplets on solid surfaces. An analysis based on the theories of thermodynamics and thermal activation processes is presented for the electrowetting of a conducting droplet on a dielectric layer. The concept of release rate of electric energy is proposed. The release rate of electric energy is proportional to the square of the applied electric voltage and the derivative of electric capacitance with respect to the surface area of the corresponding electric system. The velocity of a contact line under the action of an electric voltage is a hyperbolic sine function of the release rate of electric energy. Using the release rate of electric energy and introducing line tension in the analysis, the contact angle of a droplet at a stationary state under the action of a constant electric voltage is found to be a linear function of the release rate of electric energy and the line tension. The line tension introduces the droplet-size effect on the contact angle. A critical contact angle as a function of the applied electric voltage, the thickness of the dielectric layer, and the radius of the contact area is obtained. There exist stable and unstable zones, depending on the relative value of the contact angle and the critical contact angle. There exists an upper bound of electric voltage with the corresponding contact angle of 65.89° between 60~70° of the saturated contact angle reported for electrowetting of conducting droplets. This result suggests that the saturation of contact angle likely is related to the condition determining the field-induced stability of the contact line.

报告人简介：

Dr. Fuqian Yang received his B.S. in Engineering Physics from Tsinghua University, M.S. in Mechanical Engineering and Ph.D. in Materials Science and Engineering from the University of Rochester. He is a full professor in the Department of Chemical and Materials Engineering at the University of Kentucky. He is a member of editorial board for Materials Science and Engineering A, Materials and Metallurgical Transaction A, Smart Grid and Renewable Energy and Annals of Materials Science & Engineering. Dr. Yang’s research focuses on electrical-chemical-mechanical behavior of advanced materials, including creep behavior of materials, adhesive deformation of materials, electromechanical interaction of materials, stress-diffusion interaction, and fluid flow.

报告联系人：沈楠  (office@lnm.imech.ac.cn 82543935)