NSLS-II Seminar

Like most materials, there exist very rich microstructure evolution phenomena in lithium battery electrode compounds during battery operation. Elucidating such phenomena through combined modeling and characterization including synchrotron-based techniques could yield valuable insights on how electrode structure should be designed and tailored at the mesoscale to enable stepwise improvement in battery performance. In this talk, I will first present our recent study on the unique aspects of phase transformation kinetics in Li-ion battery electrodes, using LiFePO4 as a model system. Through combined phase-field modeling and transmission x-ray microscopic observation of Li deintercalation process in LiFePO4 microrods, we discovered that intercalation-induced phase transformations can proceed in several distinct kinetic modes with varied electrochemical conditions and particle geometry. In particular, a hybrid mode, in which phase growth is surface-reaction-limited or bulk-diffusion-limited along different directions, is revealed for the first time. In the surface-reaction-limited transformation regime, we predict a surprising effect of antisite defects on accelerating phase boundary migration velocity by two orders of magnitude over defect-free LiFePO4 due to defect-induced increase in the surface reaction area. This finding suggests defect engineering as a fruitful approach to enhance the rate performance of intercalation compounds. The second part of this talk concerns the fundamental mechanism of dendrite growth on Li metal surface during electroplating, which presents a major challenge to the adoption of Li metal anodes in rechargeable batteries. Combining Li electroplating experiments and modeling, we obtained a key insight that Li dendrite growth is a stress-driven process, which is initiated by the compressive residual stress developed in deposited Li during battery cycling. Accordingly, elimination of the plating stress, e.g. via the use of soft substrate for Li