Hydrate-melt electrolytes for high-energy-density aqueous batteries

Aqueous Li-ion batteries are attracting increasing attention because they are potentially low in cost, safe and environmentally friendly. However, their low energy density ( 130 Wh kg−1) and high voltage (∼2.3–3.1 V) represent significant progress towards performance comparable to that of commercial non-aqueous batteries (with energy densities of ∼150–400 Wh kg−1 and voltages of ∼2.4–3.8 V). Aqueous Li-ion batteries have considerably lower energy density than their non-aqueous counterparts. Here the authors report a room-temperature hydrate metal salt electrolyte that, when coupled with a spinel Li4Ti5O12 electrode, displays an energy density of 130 Wh kg−1.