Exploring the performance of carbonate and ether-based electrolytes for anode-free lithium metal batteries operating under various conditions

An anode-free lithium metal battery (AFLMB) configuration can be used to develop electrolytes for wide-temperature applications. The charge/discharge performance of an electrolyte consisting of lithium hexafluorophosphate (LiPF6) in a mixture of fluoroethylene carbonate (FEC), 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), and ethyl methyl carbonate (EMC) has been is reported as an electrolyte for lithium metal batteries. It has a good passivating capability and wide electrochemical windows relative to the commercial electrolyte. Conversely, its lower ionic conductivity and high viscosity impede practical application. Hence, an electrolyte of 1 M LiPF6 in EA/FEC/TTE/EMC (2:1:5:2 by vol.) is developed by adding a quaternary solvent of ethyl acetate (EA). The electrolyte exhibits a lower viscosity and higher ionic conductivity than 1 M LiPF6 in FEC/TTE/EMC (3:5:2 by vol.). At 0 °C, 1 M LiPF6 in EA/FEC/TTE/EMC (2:1:5:2 by vol.) provides capacity retention of 30 % and the average Coulombic efficiency (av. CE) of 95 % using the Cu||NMC111 after 40 cycles at a current density of 0.2 mA/cm2. The synergy of higher ionic conductivity and formation of LiF layer in the developed electrolyte extends the service-temperature range of AFLMB. This study opens an avenue in developing low-temperature electrolytes using an AFLMB.