The ongoing electrification of the transportation sector has sparked the search for high energy dense batteries in recent years, which led to a revived interest in lithium metal as an anode material. The lithium-metal battery (LMB), introduced nearly half a century ago, was replaced quickly after its initial discovery due to rapid capacity fading and safety hazards. The main concern of LMB relates to the formation of dendritic lithium deposits emerging on the anode, which leads to premature cell failure and poses a major safety risk, as the lithium dendrites can puncture the separator, causing an internal shorting of the cell. In addition, these dendrites are a catalyst for several other failure mechanisms of LMBs, including the formation of so-called “dead” lithium, which consists of electrochemically inactive metallic lithium detached from the lithium anode, as well as the consumption of liquid electrolyte.
Our study showed that the used electrolyte volume is closely related to the capacity decay observed with lithium anodes and simply using more electrolyte could significantly improve the lifetime of the corresponding cell. This capacity loss could not be fully regained by just adding new electrolyte to the cell. In situ electrochemical impedance spectroscopy (EIS) measurements revealed that in addition to the increase in electrolyte resistance, the interfacial resistance grew disproportionately with less electrolyte present during galvanostatic cycling. Subsequent post-mortem analysis revealed that the origin of the interfacial resistance growth and the eventual loss of capacity could be attributed to the lithium metal anode, which quickly deteriorates by forming a resistive interphase layer with small amounts of electrolyte present during cycling.