Using aqueous electrolytes in lithium-ion batteries (LIB) has been difficult due to the narrow electrochemical stability window (1.23 V) of water. Super-concentrated aqueous electrolytes provide a way to overcome this challenge, expanding the stable voltage window to 4 V. Thus, the high concentration of salts in aqueous electrolytes, also called ‘water-in-salt’ systems, opened an avenue to replace flammable organic electrolytes without compromising the energy density of LIB. However, the cathodic stability limit of this super-concentrated aqueous electrolyte (1.9 V versus Li) is still too high to provide a sufficiently large difference of electrochemical potential between cathode and anode pairs to achieve a high theoretical energy density. Here we report synthesis methods to introduce artificial solid-electrolyte interphase (SEI) layer that prevents access of water molecules on anodes while passing lithium-ions to sustain battery reactions in an aqueous environment. We investigated the ideal composition of artificial SEI layer to enhance the transport of lithium-ions in super-concentrated aqueous electrolytes by evaluating the cycle life of batteries.