Artificial solid electrolyte interphase for aqueous lithium energy storage systems

Aqueous lithium energy storage systems address environmental sustainability and safety issues. However, significant capacity fading after repeated cycles of charge-discharge and during float charge limit their practical application compared to their nonaqueous counterparts. We introduce an artificial solid electrolyte interphase (SEI) to the aqueous systems and report the use of graphene films as an artificial SEI (G-SEI) that substantially enhance the overall performance of an aqueous lithium battery and a supercapacitor. The thickness (1 to 50 nm) and the surface area (1 cm(2) to 1 m(2)) of the G-SEI are precisely controlled on the LiMn2O4-based cathode using the Langmuir trough-based techniques. The aqueous battery with a 10-nm-thick G-SEI exhibits a discharge capacity as high as 104 mA circle hour g(-1) after 600 cycles and a float charge current density as low as 1.03 mA g-1 after 1 day, 26% higher (74 mA circle hour g(-1)) and 54% lower (1.88 mA g(-1)) than the battery without the G-SEI, respectively. We propose that the G-SEI on the cathode surface simultaneously suppress the structural distortion of the LiMn2O4 (the Jahn-Teller distortion) and the oxidation of conductive carbon through controlled diffusion of Li+ and restricted permeation of gases (O-2 and COx), respectively. The G-SEI on both small (similar to 1 cm(2) in 1.15 mA circle hour cell) and large (similar to 9 cm(2) in 7 mA circle hour cell) cathodes exhibit similar property enhancement, demonstrating excellent potential for scale-up and manufacturing.