In situ formation of a multicomponent inorganic-rich SEI layer provides a fast charging and high specific energy Li-metal battery

Abstract

The performance of the rechargeable Li metal battery anode is limited by the poor ionic conductivity and poor mechanical properties of its solid-electrolyte interphase (SEI) layer. To overcome this, a 3 : 1 v/v ethyl methyl carbonate (EMC) : fluoroethylene carbonate (FEC) containing 0.8 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and 0.2 M lithium difluoro(oxalate)borate (LiDFOB) dual-salts with 0.05 M lithium hexafluorophosphate (LiPF₆) was tested to promote the formation of a multitude of SEI-beneficial species. The resulting SEI layer was rich in LiF, Li₂CO₃, oligomeric and glass borates, Li₃N, and Li₂S, which enhanced its role as a protective yet Li⁺ conductive film, stabilizing the lithium metal anode and minimizing dead lithium build-up. With a stable SEI, a Li/Li[Ni_0.59Co_0.2Mn_0.2Al_0.01]O₂ Li-metal battery (LMB) retains 75% of its 177 mA h g⁻¹ specific discharge capacity for 500 hours at a coulombic efficiency of greater than 99.3% at the fast charge–discharge rate of 1.8 mA cm⁻².