Study of Interfacial Chemical Reactions on Battery Electrodes Using Operando Imaging Techniques



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For lithium (Li)-ion batteries (LIBs) and Li metal batteries (LMBs), the quality of the solid-electrolyte interphase (SEI) determines the battery's performance. However, the understanding of SEI formation and evolution processes across the electrode interface is still limited due to the lack of in-situ characterization tools. Here, we study and image the local SEI formation and evolution dynamics in conventional LiPF6/carbonate electrolytes with and without 50 ppm water additive, using an operando reflection interference microscope (RIM). The RIM provides high sensitivity to imaging the minimal signals caused by SEI layer and allows us to observe the entire growth and stripping process of SEI in real-time. The results show that the SEI formation and stripping process consists of multiple steps that include an inorganic SEI layer (LiF-rich layer) deposition, an electrical double layer formation, and an organic SEI layer deposition and stripping. The LiF-rich layer forms dominantly in the first cycle and grows slowly during consecutive cycles. On the other hand, the organic SEI layer is deposited and oxidized away in each cycle. 50 ppm of water as an additive in the electrolyte results in a much thicker and higher quality LiF-rich SEI layer, which leads to a thinner organic SEI deposition, less electrolyte consumption, and more uniform Li nucleation on the electrode surface. The mapped LiF-rich and organic SEI layers’ distributions at different potentials indicate that there exist strong reverse correlations between the LiF-rich inner SEI layer and the organic outer SEI layer: a thicker LiF-rich layer leads to a thinner organic SEI layer deposited on the electrode and vice versa. Besides the SEI formation dynamics and spatial characteristics, the Li nucleation also plays a critical role in battery performance. Non-uniform Li growth will cause significant volumetric expansion of the Li metal anode and break the formed SEI, leading to more electrolyte consumption and aggravating the dendrites formation. The concerted operando RIM enables the real-time imaging of the entire Li nucleation process with high spatial and temporal resolutions. The RIM allows us to image and track the individual Li nuclei’s sizes and locations continuously throughout the deposition and stripping processes. Both growth and stripping processes of Li nuclei show two distinct stages. In addition, we find that there are no Li nuclei generated before the overpotential reaches its minimum value. More importantly, the formations of the initial Li nuclei are not at the same time. Different particles start the nucleation at different time points and grow at different speeds, which strongly indicates the localized surface electrochemical environments, including SEI, ion concentration, and surface energy, will determine the Li nucleation and growth. To further illustrate this effect, we extract the localized overpotential map using the particle size dynamics obtained from the RIM and the Barton’s model for the first time. The distribution of overpotentials at different locations reflects the heterogeneous surface environments. The real-time visualization of Li nucleation dynamics and the localized overpotential map achieved for the first time in this work provides a guideline for the battery interphases design to developing high efficiency batteries. In addition to Li-based batteries, uncontrollable dendrite growth also exists in other metal-ion batteries, including magnesium, calcium, aluminum, and zinc batteries, which is tightly related to non-uniform reaction environments. However, there is a lack of understanding and analysis methods to probe the localized electrochemical environment (LEE). Here we investigate the effects of the LEE, including localized ion concentrations, current density, and electric potential, on metal plating/stripping dynamics and dendrite minimization. A novel in-situ 3D microscope was developed to image the morphology dynamics and deposition rate of Zn plating/stripping processes on 3D Zn-Mn anodes. We found that reaction kinetics are highly correlated to LEE and electrode morphology. The digital twin technique was employed to accurately calculate the LEE, which cannot be measured from experiments. It is found that the curvature of the 3D electrode surface will determine the LEE and significantly influence reaction kinetics. This provides us a new strategy to minimize the dendrite formation by designing and optimizing the 3D geometry of the electrode to control the LEE.



Electrode interfacial reactions, Lithium ion batteries, Aqueous Zn ion batteries


Portions of this document appear in: Tian, Huajun, Zhao Li, Guangxia Feng, Zhenzhong Yang, David Fox, Maoyu Wang, Hua Zhou et al. "Stable, high-performance, dendrite-free, seawater-based aqueous batteries." Nature Communications 12, no. 1 (2021): 237; and in: Feng, Guangxia, Jiaming Guo, Huajun Tian, Zhao Li, Yaping Shi, Xiaoliang Li, Xu Yang, David Mayerich, Yang Yang, and Xiaonan Shan. "Probe the localized electrochemical environment effects and electrode reaction dynamics for metal batteries using in situ 3D microscopy." Advanced Energy Materials 12, no. 3 (2022): 2103484.