Abstract

Advanced liquid electrolytes can achieve dense Li deposition with a Coulombic efficiency (CE) of approximately 99%. New characterization tools, including cryogenic electron microscopies and quantitative chemical analytical tools, have enhanced the current understanding of Li failure mechanisms. Quantification of inactive Li reveals that the underlying cause of low CE in Li-metal anodes is the large amount of unreacted metallic Li. The sluggish progress of battery technologies has drastically hindered the rapid development of electric vehicles and next-generation portable electronics. The lithium (Li) metal anode is critical to break the energy-density bottleneck of current Li-ion chemistry. After being intensively studied in recent years, the Li-metal field has developed new understanding and made unprecedented progress in preventing Li-dendrite growth and improving Coulombic efficiency, especially through development of advanced electrolytes and novel analytical tools. In this Opinion, we revisit the controversial issues surrounding Li metal as an anode based upon recent advances, revealing the underlying cause of Li-metal failure and the true role of ‘solid electrolyte interphase’ in Li-metal anodes. Finally, we propose future directions that must be taken in order for Li-metal batteries to become commercially viable. The sluggish progress of battery technologies has drastically hindered the rapid development of electric vehicles and next-generation portable electronics. The lithium (Li) metal anode is critical to break the energy-density bottleneck of current Li-ion chemistry. After being intensively studied in recent years, the Li-metal field has developed new understanding and made unprecedented progress in preventing Li-dendrite growth and improving Coulombic efficiency, especially through development of advanced electrolytes and novel analytical tools. In this Opinion, we revisit the controversial issues surrounding Li metal as an anode based upon recent advances, revealing the underlying cause of Li-metal failure and the true role of ‘solid electrolyte interphase’ in Li-metal anodes. Finally, we propose future directions that must be taken in order for Li-metal batteries to become commercially viable. also known as Faraday efficiency; it describes the efficiency with which charge is transferred in a system facilitating an electrochemical reaction. In a closed secondary battery system, the CE directly reflects the battery cyclability. an electron microscopy technique applied on samples cooled down to cryogenic temperatures. This technique significantly reduces the electron beam damage on fragile samples and has been widely adopted in structure biology field to obtain atomic-resolution images. Recently, this technique has been introduced to the battery field and serves as a powerful tool to investigate the nature of extremely beam–sensitive lithium metal and SEI. compounds with layered structures that can host the reversible insertion of molecules or ions into the material. Common intercalation electrode compounds include graphite (anode), TiS2 (cathode), layered oxides (cathode; e.g., LiCoO2 and LiNi0.8Mn0.1Co0.1O2). the interface between the electrode and electrolyte. It forms from the (electro)chemical reaction between the electrode and electrolyte, and the electrochemical decomposition of electrolyte, ensuring the kinetic stabilization of electrode–electrolyte interfaces. It remains conductive to ions but insulates electrons. a new analytical method used to quantify trace amount of metals. It is a combination of protic solvent titration and quantification of H2 amount by gas chromatography. The amount of metals can be calculated from the H2 amount.