4.0 V Aqueous Li-Ion Batteries

Summary Although recent efforts have expanded the stability window of aqueous electrolytes from 1.23 V to >3 V, intrinsically safe aqueous batteries still deliver lower energy densities (200 Wh/kg) compared with state-of-the-art Li-ion batteries (∼400 Wh/kg). The essential origin for this gap comes from their cathodic stability limit, excluding the use of the most ideal anode materials (graphite, Li metal). Here, we resolved this "cathodic challenge" by adopting an "inhomogeneous additive" approach, in which a fluorinated additive immiscible with aqueous electrolyte can be applied on anode surfaces as an interphase precursor coating. The strong hydrophobicity of the precursor minimizes the competitive water reduction during interphase formation, while its own reductive decomposition forms a unique composite interphase consisting of both organic and inorganic fluorides. Such effective protection allows these high-capacity/low-potential anode materials to couple with different cathode materials, leading to 4.0 V aqueous Li-ion batteries with high efficiency and reversibility.