Studies on linear and cyclic ether co-solvent electrolytes for lithium-metal batteries

Abstract

Li-Metal batteries are emerging as a promising candidate for next-generation batteries due to their much higher anode capacity than conventional Li-ion batteries. However, there are still limitations, such as dendrite formation on the lithium metal surface and low Coulombic efficiency. To address these issues, researchers are focusing on generating inorganic-rich protective layers at the electrode-electrolyte interface. Additionally, developing polymer layers to enhance the surface flexibility and suppress the decomposition of organic electrolytes has recently been recognized as important. In this study, we examined the properties of a polymeric interphase layer during the charge-discharge cycles of lithium-metal batteries using a co-solvent of 1,3-dioxolane (DOL), known for forming polymeric layers on the lithium metal and 1,2-dimethoxyethane (DME), known for its high chemical stability with lithium metal. With $1 M$ lithium bis(fluorosulfonyl)imide (LiFSI) and $4%$ $LiNO_3$ in DME/DOL(1:3, v/v) electrolyte, a longer lithium symmetrical cell cycle life was confirmed compared to using a DOL single solvent. This was attributed to forming a polymeric DOL layer, which thinly coated the lithium metal during charge-discharge cycles. This inhibits the decomposition of DME and the generation of inorganic layers such as LiF, $Li_2O$, and $Li_2CO_3$ from $FSI^-$ and $NO_3^{-}$ anions. Furthermore, improved charge-discharge rate capability was confirmed in the lithium symmetrical cell and the full cell with $LiFePO_4$ cathode, proving that the polymer layer possesses high ion conductivity.