Enhancing the Performance of Zero-Excess Lithium Metal Batteries: A Contribution to a Practical Guide

Abstract Zero-excess Li metal batteries (ZELMB), also called “anode-free” LMBs, promise high energy, low cost, and reduced complexity by abandoning traditional negative electrode materials. They combine a plain current collector with a conventional positive composite electrode. However, charge/discharge cycling results in poor capacity retention due to inhomogeneous and dendritic Li deposition, “dead” Li formation, and parasitic side reactions between Li metal and the electrolyte. To address these challenges, many cell components or formation and operation conditions of ZELMB were varied. Yet, a systematic, integrated understanding about the fundamentals of constructing well-functioning ZELMBs is lacking. Therefore, this study aims to comparatively evaluate the influence of key factors on the electrochemical performance of ZELMBs within a common framework regarding the design of cells and experiments. Starting from a baseline configuration, modifications to electrodes, electrolyte, operating conditions, and cycling protocol were successively implemented, leading up to a robust configuration. The influence of each optimization step is monitored in terms of resulting capacity retention and cumulative discharge capacity, correlating these values to underlying physical, chemical, and electrochemical mechanisms. This provides a facile and practical guide to accelerate the development of high-performance ZELMBs with maximized capacity retention that contributes a big step towards commercialization.