Lithium-ion storage properties of a micro/nanosheet-like NaV₆O₁₅ anode in aqueous solution

The micromorphologies of NaV₆O₁₅ materials synthesized using the hydrothermal method and calcination comprise staggered micro/nanosheet-like shapes. These materials can act as anode active materials in aqueous rechargeable lithium-ion batteries (ARLBs). NaV₆O₁₅ has a charge transfer resistance of several ohms in the ARLB, which is an order of magnitude smaller than in traditional lithium-ion batteries. The lithium-ion diffusion coefficients at 0.15, -0.21 and -0.65 V vs. saturated calomel electrode (SCE) were calculated as 7.3 × 10^-9, 3 × 10^-12, 7.6 × 10^-11 cm² s^-1, respectively, from the Warburg spectrum, which were three orders of magnitude larger than in conventional lithium-ion batteries. Furthermore, NaV₆O₁₅ materials used in this ARLB have a high energy density of about 134.9 Wh kg^-1 at a power of 640 W kg^-1. In contrast to traditional LIB behavior, we found that the capacity retention and coulombic efficiency of the as-synthesized materials increased with the increasing ARLB discharge current density, which showed potential for this new ARLB system to be applied in the field of large-scale energy storage and power source devices.