Revealing the enhancement of Li plating/stripping efficiency in TEGDME-based low-concentration electrolytes for anode-free lithium metal batteries

Abstract

Anode-free lithium metal batteries (AFLMBs) have attracted great attention owing to their higher energy density compared to conventional lithium metal batteries. Unfortunately, AFLMBs still suffer from poor Coulombic efficiency (CE) due to severe dendrite growth and the unstable solid–electrolyte interface (SEI) at the anode. Therefore, we explored the effect of concentration and LiNO₃ additive on the SEI layer and on Li plating/stripping efficiency using a low-concentration tetraethylene glycol dimethyl ether (TEGDME)-based electrolyte in an AFLMB anode half-cell configuration. It was found that the formation of protective Li₂O-based SEI layers when blocking the oxidative subsequent SEI formation (called “OSS”) above 2.2 V vs. Li/Li⁺ improved Li plating/stripping stability, while the LiNO₃ additive suppressed the oxidation of Li₂O into Li₂O₂ and sustained the existence of Li₂O without blocking OSS, therefore improving CE performance. Although increasing the concentration (from 0.4 M to 2.0 M) did not have a major effect, the 2.0 M electrolyte with LiNO₃ additive shifted the dominant SEI species from Li₂O to LiF, further enhancing CE performance.