Aqueous lithium-ion batteries with niobium tungsten oxide anodes for superior volumetric and rate capability

Lithium-ion batteries with aqueous electrolytes have substantial safety and cost benefits over the flammable, expensive and moisture sensitive organic electrolytes used in current batteries. However aqueous batteries suffer in terms of a reduced electrochemical stability window and offer much lower energy and power densities relative to batteries with organic electrolytes. Here we report that the use of niobium tungsten oxide anodes in conjunction with lithium manganese oxide cathodes and water-in-salt electrolytes, enables aqueous lithium-ion batteries with outstanding volumetric capacity and rate capability. Our battery could be cycled stably with high coulombic efficiency and a volumetric capacity of similar to 200 Ah l(-1) was observed at 1C rate, which is much higher than state-of-art graphite (50-110 Ah l(-1)). Moreover, the battery could be cycled at high rates - increasing the charge/discharge rate by an order of magnitude (0.5C-5C) resulted in only about 25% reduction in capacity. The volumetric energy and power density of our full-cell device is far superior to what was been reported for "aqueous" lithium-ion batteries and is attributed to the dense-packing of micron size niobium tungsten oxide particles in the anode, as well as the abundance of tunnels within the particles that allow fast diffusion of lithium ions. The facile synthesis, ease of handling, safety (non-flammable nature) and high-performance, makes aqueous lithium-ion batteries with niobium tungsten oxide anodes an attractive alternative to traditional batteries, especially in applications where high volumetric energy and power density are desired.