In-Situ Liquid EC-(S)TEM Study of Li2O2 growth Mechanism and Morphology in Li-O2 Battery
Authors: Mehdi Beata Layla , Nasybulin Eduard , Gu Meng , Abellan Patricia , Wang Chongmin , Xu Wu , Zhang Ji-Guang , Evans James E , Browning Nigel 
Published: February 2020

The high demand for new energy storage materials has created the need for novel experimental techniques that can provide real-time information on the dynamic structural changes and processes that occur locally at the electrode/electrolyte interface during battery operation. The recent development of in-situ liquid electrochemical stages for (scanning) transmission electron microscopes ((S)TEM) enables fabrication of a “nano-battery” to study the details of electrochemical processes under operando conditions. However, high complexity of electrochemical process during the battery cycling requires careful calibration of the system prior to in-situ/operando observations to circumvent i.e. beam damage. Therefore, affecting stability and introducing varies degradation mechanisms in battery electrolytes. Here, we describe the effect of the electron beam in the operando observations and determine the condition to minimize electrolyte damage. In addition, we demonstrate application of an in-situ liquid electrochemical (S)TEM cell paying particular attention to rechargeable Li-O2 battery system as an alternative to Li-ion batteries.
Currently, Li-O2 batteries are being considered for application in the next generation electric vehicles [1-3], due to their high theoretical energy densities, which are comparable to gasoline [4]. The operation of Li-O2 battery is based on the reversible mechanisms of formation/oxidation of lithium peroxide (Li2O2) at the carbon-based cathode, which ultimately determines battery performance. However, the high capacity values are limited to only few full charge-discharge cycles due to the decomposition of both electrolyte and electrode material during oxygen reduction and evolution. These degradation leads to accumulation of insulating side products, which causes high overpotential and fast capacity fading during cycling.
Here, we employed the in-situ liquid electrochemical (S)TEM cell to create rechargeable Li-O2 “nano-battery” cell. By using the “closed-cell” approached both Li metal-anode and carbon-based cathode submersed in high vapor pressure organic electrolyte (1 M LiTf in tetraglyme). These enabled direct observation of Li2O2 nanoparticles formation at the SWNTs/electrolyte interface at both high spatial and temporal resolution during battery operation.

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Acknowledgement

The research described in this presentation is part of the Chemical Imaging Initiative at Pacific Northwest National Laboratory under Contract DE-AC05-76RL01830 operated for DOE by Battelle. This work is supported in part by the United States Department of Energy, Basic Energy Sciences Grant No. DE-FG02-03ER46057. A portion of the research was performed using EMSL, a national scientific user facility sponsored by the Department of Energy's Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory.