电流密度对微米硅电极断裂行为的影响  

Effects of current density on fracture behaviors for micron-sized crystalline silicon electrodes

作　　者：张兴玉 Zhang Xing-Yu(State Key Laboratory of Mechanics and Control of Mechanical Structures,Interdisciplinary Research Institute of Aeronautics and Astronautics,College of Aerospace Engineering,Nanjing University of Aeronautics and Astronautics,Nanjing 210016,China)

机构地区：[1]南京航空航天大学航空学院,航空航天交叉研究院,机械结构力学及控制国家重点实验室,南京210016

出　　处：《物理学报》2020年第24期290-298,共9页Acta Physica Sinica

基　　金：国家自然科学基金(批准号:11902149);江苏省自然科学基金(批准号:BK20190380);江苏高校优势学科建设工程资助的课题.

摘　　要：高容量硅电极在脱/嵌锂过程中所发生的大体积变形、断裂行为会引起严重的力学衰减,并导致电极的电化学性能退化.这严重制约着硅电极材料在商业锂离子电池中的应用.目前,硅电极断裂行为的一些细节还未被彻底研究清楚.为了进一步研究微米硅电极的断裂行为,本文利用光学显微镜观测了单晶硅电极的形貌演化,分析了不同电流密度下硅电极的断裂行为,并重点研究了在不同电流密度下裂纹形成时硅电极的相对嵌锂深度.结果表明,电流密度越大,硅电极断裂越严重.但是在三种不同电流密度下,裂纹形成时硅电极相对嵌锂深度差异不大(18%—22%).这可能是由于微米硅电极各向异性变形所引起的局部应力集中在主导着断裂行为.这些实验结果与有限元模型预测结果一致.结合裂纹形成时锂化硅和晶体硅的界面位置以及力学模型,讨论了裂纹形成时锂化硅层内部应力分布状态.这些结果深化了对硅电极断裂行为的认识,并为硅电极的设计和合适的脱/嵌锂速率选择提供一定的指导.The large volume change during lithiation/delithiation leads the silicon electrodes in lithium-ion batteries to severely degrade the mechanical performance and the silicon electrodes in lithium-ion batteries to further deteriorate electrochemical properties,which limits the commercial applications of silicon electrodes.After several year’s studies,the whole process of fracture for crystalline silicon anodes has been almost understood.However,the relationship between fracture behaviors and the lithiation depth has not been sufficiently studied.In this work,the in-situ observations of morphological changes(e.g.,volume expansion,crack initiation,propagation,and debonding of lithiated silicon)during lithiation at the different current densities are reported for silicon micropillars fabricated by standard photolithography and a deep reactive ion etching process.Also,this work focuses on the relative depth of lithiation of silicon electrodes at the moment of crack initiation,which is one of the crucial parameters representing the utilization of active materials with no crack.The results show that the silicon micropillars are broken faster(i.e.,crack initiation and pulverization in a shorter lithiation time)and more seriously at a large current density,exhibiting more prominent symmetry of morphology.However,the relative depths of lithiation at the different current densities have just a slight difference(i.e.,18%–22%),when cracks are initiated.Here in this work,a silicon micropillar fracture is confirmed by the optical observation,while the relative depth of lithiation is calculated according to the capacity data recorded by the charge/discharge battery test system.The small fluctuation of the relative depth of lithiation with the large wave of current density can be ascribed to the dominant role of local stress concentration caused by anisotropic volume change in fracture behavior,which is validated by the results obtained by the finite element model(i.e.,the depth of lithiation predicted by numerical simulations

关 键 词：锂离子电池 硅电极 断裂行为 电流密度 

分 类 号：TN304.12[电子电信—物理电子学] TM912[电气工程—电力电子与电力传动]