Finding a viable electrolyte for next-generation 5 V-class lithium-ion batteries is of primary importance. A long-standing obstacle has been metal ion dissolution at high voltages. The LiPF₆ salt in conventional electrolytes is chemically unstable, which accelerates transition metal (TM) dissolution of the electrode material, yet beneficially suppresses oxidative dissolution of the aluminium current collector; replacing LiPF₆ with more stable lithium salts may diminish TM dissolution but unfortunately encounters severe aluminium oxidation. Here we report a new electrolyte design that can solve this dilemma. By mixing a higly stable lithium salt with a solvent at extremely high concentrations, we obtain an unsual liquid showing a three-dimension network of anions and solvent molecules that coordinate strongly to Li⁺ ions. This new class of electrolytes inhibits the dissolution of both aluminium and TM at around 5 V, and realizes a high-voltage LiNi_0.5Mn_1.5O₄/graphite battery that exhibits excellent cycling durability and high rate capability. Additionally, the electrolytes show superior thermal stability and flame retardant ability. Therefore, the superconcentrated electrolytes might offer many new opportunities in building safe and stable high-voltage batteries not limited to the lithium-ion.

Figure 1 Discharge capacity retention of high-voltage LiNi_0.5Mn_1.5O₄/natural graphite batteries using lab-made superconcentrated and commercial dilute electrolytes. The inset shows EDS spectra on the graphite electrode surface after the cycling test. Charge and discharge were conducted at 40 °C with a current rate of 29.4 mA g⁻¹ (C/5) on the weight basis of the LiNi_0.5Mn_1.5O₄ electrode.