Aqueous electrolyte with moderate concentration enables high-energy aqueous rechargeable lithium ion battery for large scale energy storage

The intrinsic safe and environmentally friendly aqueous rechargeable lithium ion battery (ARLIB) is a promising candidate for large scale energy storage system application. However, the low energy density and limited cycle life hamper its practical application. Here, a deep eutectic electrolyte composed of LiClO4·3H2O and urea with a moderate concentration of 5 M is explored, in which the population of free water molecules is depleted leading to the expanded electrochemical stability window to ∼3.2 V. In addition, the diminished population of free water suppresses the anodic Al dissolution. Combining with graphene coating, the Al current collector exhibits strong corrosion resistant. A Li4Ti5O12/LiMn2O4 battery of 2.2 V using such electrolyte and current collector delivers cycle life up to 1000 times and a high energy density of 135 Wh kg−1. The results open a new avenue to advance high-energy ARLIB, contributing to the low cost and grid-scale energy storage applications.