Stabilizing Anode-Free Lithium Batteries Via External Thermal Gradients

Abstract

Temperature is known to have a profound impact on battery electrochemistry and performance due to the strong temperature-dependence of kinetics and diffusion. However, the role of temperature on battery behavior has mostly been considered in the case of an isothermal cell. Though active thermal management systems for batteries strive to maintain isothermal control, localized thermal gradients can still develop within individual cells, which can significantly influence local electrochemistry. For this reason, it is important to understand the consequences and also the potential benefits of non-uniform temperature distribution across batteries.Thermal gradients have been applied to lithium symmetric cells to significantly improve performance and stability. The direction of an interelectrode thermal gradient governs lithium plating morphology and dictates whether unstable, one-dimensional Li electroplating or stable, homogeneous electroplating occurs (1). With a warm positive electrode (40°C) and a cold negative electrode (0°C) (negative thermal gradient) we observe unstable cell behavior, extensive side reactions between Li and the electrolyte, and internal shorting. Reversing these temperatures so that the negative electrode is warmer than the positive electrode (a “positive” thermal gradient) decreases overpotentials, minimizes deleterious side reactions between Li and the electrolyte, and encourages long cycle life. Additionally, a positive thermal gradient stabilizes high-rate plating and stripping (1), showing promise for enabling fast-charging in lithium metal batteries.This presentation will discuss the impact of thermal gradients on stabilizing lithium plating and stripping and its application for improving long-term cycle life in anode-free lithium metal batteries. First, we will use symmetric Li metal coin cells to investigate the roles of thermal gradient magnitude and electrode temperatures on lithium plating stability. After identifying optimal thermal conditions for highly reversible Li plating and stripping, we will apply this thermal gradient to an anode-free full cell with LiFePO4 cathode to confirm its benefit on long-term cycling in a practical cell. Operando techniques, such as optical microscopy and internal thermal sensing, as well as post mortem materials characterization, including X-ray diffraction (XRD), scanning electron microscopy (SEM), and Raman spectroscopy, will be used to describe and characterize cell behavior in the presence of an applied thermal gradient.