Good Lithium-Ion Insertion/Extraction Characteristics of a Novel Double Metal Doped Hexa-Vanadate Compounds Used in an Inorganic Aqueous Solution

Abstract

We report a potassium doped NaV6O15 anode with enhanced electrochemical performance, used for aqueous rechargeable lithium ion battery. Different Na1–xKxV6O15 (x = 0, 0.1, 0.2, 0.3) compounds are prepared and characterized using X-ray diffraction patterns ensuring potassium doping. The electrochemical performances of the various potassium doped anodes NaV6O15, Na0.9K0.1V6O15, Na0.8K0.2V6O15, and Na0.7K0.3V6O15 are evaluated by cyclic voltammetry and galvanostactic charge/discharge methods. The results suggest that potassium-doping has a positive effect on the electrochemical performance of aqueous rechargeable lithium ion batteries. The anode Na0.8K0.2V6O15 is found to be optimized potassium doped anode materials for aqueous rechargeable lithium ion battery. The Na0.8K0.2V6O15 anode displays enhanced cycling and rate performances, an initial specific capacity of 218 mAhg–1, and 133 mAhg–1 is delivered after 50 cycles (61% capacity retention) at the current density of 100 mAg–1. The potassium doping has induced enhanced interlayer spacing in the layered structure of NaV6O15 due to potassium ions having larger ionic radii than sodium. This enhanced interlayer spacing provides wider channels for lithium-ion intercalation/extraction, which in turn increases the lithium-ion diffusion coefficient. The lithium-ion diffusion coefficients for NKVO-2 at 0.09, −0.26, and −0.68 V vs saturated calomel electrode (SCE) were calculated as 1.53 × 10–11, 1.29 × 10–11, and 8.90 × 10–12 cm2s–1, respectively.