Stabilizing LiMn2O4 cathode in aqueous electrolyte with optimal concentration and components

Aqueous lithium ion batteries (ALIBs) receive increasing attention due to their intrinsic non-flammable nature. However, their practical application, has been limited by the poor comprehensive properties of aqueous electrolytes, which severely restricts the cycle life and cost of ALIBs. In this study, the concentration and components of aqueous electrolytes were optimized to balance the battery performance and cost of ALIBs. The wide electrochemical stability window of around 2 V is achieved for just 9 ~15 m LiTFSI solutions other than the counterparts of widely used LiNO3 solutions, attributed to most water molecules in crystalline hydrates. A great improvement in the performance of LiMn2O4 electrodes is carried out. The optimal LiTFSI solution of 15 m allows LiMn2O4 to be long cycled at 1C with a discharge capacity of 111mAh∙g−1 and a high capacity retention of 88% after 1400 cycles. At the high C-rate of 5 C, a discharge capacity of 91 mAh∙g−1 and a capacity retention rate of as high as 92% after 3000 cycles are achieved. In highly concentrated LiTFSI solutions beyond 15 m, a decay in the performance of LiMn2O4 electrodes is found, especially the rate capability, attributed to the rather low ion conductivity.