Stabilizing High-Rate Lithium Electroplating Via Inter-Electrode Thermal Gradient at Low Temperature
Authors: Atkinson III Robert , Kingston Todd A. , Klein Emily J , Carter Rachel E. , Love Corey T. 
Published: December 2020

Temperature is known to significantly influence battery electrochemistry and performance due to its strong dependence on kinetics and diffusion. To date, the role of temperature on battery behavior has mostly been considered in an isothermal case. We have shown previously that applying a negative thermal gradient (cathode warmer than anode) in conventional Li+-ion batteries with graphite anodes exacerbates Li plating at the anode, loss of lithium inventory, and rapid loss of cell capacity (1). We have also shown previously that applying inter-electrode thermal gradients in lithium symmetric cells at moderate current densities (1.5 mA cm-2) can significantly improve performance and long-term cycling stability. The direction of an inter-electrode thermal gradient governs lithium plating morphology and dictates whether unstable, one-dimensional Li electroplating or stable, more homogeneous electroplating occurs (2). With a warmer positive electrode (40°C) and a colder negative electrode (0°C) (negative thermal gradient) we previously observed unstable cell behavior, extensive side reactions between Li and the electrolyte, and internal shorting. Reversing these temperatures in the symmetric Li cell so that the negative electrode is warmer than the positive electrode (positive thermal gradient) decreases overpotentials, minimizes deleterious side reactions between Li and the electrolyte, and encourages long cycle life.
This presentation studies the effects of a positive thermal gradient during high-rate electroplating and stripping and shows the promise that this novel thermal control holds for enabling fast-charging in lithium metal batteries. First, we will use symmetric Li metal coin cells to investigate the roles of thermal gradient magnitude and electrode temperatures on high-rate (10 mA cm-2) lithium plating stability. We couple trends in electrochemical impedance spectroscopy (EIS) throughout cycling with post mortem imaging and microscopy to quantify extents of Li deactivation as a function of the applied thermal condition. After identifying optimal thermal conditions for highly reversible Li electroplating and stripping with symmetric Li metal cells, we apply this thermal gradient to an anode-free full cell with a LiFePO4 cathode. Operando video microscopy of Li electrodeposition onto a copper substrate confirms that a positive thermal gradient favorably alters the morphology of electroplated Li compared to isothermal control. Internal thermal sensing and EIS, as well as post mortem materials characterization, including X-ray diffraction (XRD) and scanning electron microscopy (SEM), will be used to discuss and characterize cell behavior in the presence of an applied thermal gradient.
References

R. Carter and C. T. Love, ACS Appl Mater Interfaces, 10, 26328 (2018).

R. W. Atkinson III, R. Carter and C. T. Love, Energy Storage Materials, 22, 18 (2019).

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