Abstract
Lithium metal is a very promising anode material for achieving high energy density for next generation battery systems due to its low redox potential and high theoretical specific capacity of 3860 mA h g−1. However, dendrite formation and low coulombic efficiency during cycling greatly hindered its practical applications. The formation of a stable solid electrolyte interphase (SEI) on the lithium metal anode (LMA) holds the key to resolving these problems. A lot of techniques such as electrolyte modification, electrolyte additive introduction, and artificial SEI layer coating have been developed to form a stable SEI with capability to facilitate fast Li+ transportation and to suppress Li dendrite formation and undesired side reactions. It is well accepted that the chemical and physical properties of the SEI on the LMA are closely related to the kinetics of Li+ transport across the electrolyte–electrode interface and Li deposition behavior, which in turn affect the overall performance of the cell. Unfortunately, the chemical and structural complexity of the SEI makes it the least understood component of the battery cell. Recently various advanced in situ and ex situ characterization techniques have been developed to study the SEI and the results are quite interesting. Therefore, an overview about these new findings and development of SEI engineering and characterization is quite valuable to the battery research community. In this perspective, different strategies of SEI engineering are summarized, including electrolyte modification, electrolyte additive application, and artificial SEI construction. In addition, various advanced characterization techniques for investigating the SEI formation mechanism are discussed, including in situ visualization of the lithium deposition behavior, the quantification of inactive lithium, and using X-rays, neutrons and electrons as probing beams for both imaging and spectroscopy techniques with typical examples.
Highlights
The lithium metal anode (LMA) has been considered as the most promising anode for generation devices owing to its high theoretical capacity (3860 mA h gÀ1), low density (0.534 g cmÀ3), and low electrochemical potential (À3.040 V vs. standard hydrogen electrode).[1]
If the as-formed solid electrolyte interphase (SEI) is unstable during lithium plating/stripping, fresh Li will be exposed to the electrolyte and undesired side reactions will occur continuously, resulting in low coulombic efficiency (CE), short cycling life and lithium dendrite formation of lithium metal batteries (LMBs) and severely limited practical applications of LMBs
Quantitative analysis revealed that SEI-LiF is in high abundance in SEI samples collected from high concentration electrolytes, in which uorine-containing anions in the solvation sheath provide a uorine source to form SEI-LiF and result in a high coulombic efficiency compared with low concentration electrolytes
Summary
The lithium metal anode (LMA) has been considered as the most promising anode for generation devices owing to its high theoretical capacity (3860 mA h gÀ1), low density (0.534 g cmÀ3), and low electrochemical potential (À3.040 V vs. standard hydrogen electrode).[1]. She obtained her PhD degree in Physical Chemistry from the MEET Battery Research Center at University of Munster (Westfalische Wilhelms-Universitat), Germany She has been exploring the battery electrolyte area for more than 10 years, and her major research focuses on the development of electrolytes and fundamental understanding of electrode/electrolyte interphases to enable stable and safe cycling of high-energy-density rechargeable lithium batteries. Dr Xiao-Qing Yang is the group leader of the electrochemical energy storage group in the Chemistry Division of Brookhaven National Laboratory (BNL) He is the Principal Investigator (PI) for several Battery Material Research (BMR) programs including the Batter[500] consortium at BNL funded by the Office of Vehicle Technologies, EE&RE, U.S Department of Energy (USDOE). We hope that this perspective could provide in-depth insights to the battery community and inspirations for future LMB development
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