A New Anode Material Of Na₂V₆O₁₆ Nanowires For Aqueous Rechargeable Lithium Battery

Nowadays, Li-ion batteries with organic electrolyte have been widely used in portable electronic devices. However, certain drawbacks such as safety issues at abuse conditions, high cost and rigorous operating requirements have greatly limited the further applications, particularly in electric vehicle (EV) and hybrid electric vehicle (HEV). An alternative rechargeable Li-ion battery with an aqueous electrolyte was first reported by Dahn and co-workers in1994. Compared with non-aqueous lithium ion battery, the safety problem is fundamentally settled, and rigorous assembly conditions can be also avoided. Therefore, ARLB and related materials have attracted much attentions in the field of electrochemical energy storage.The development of aqueous rechargeable lithium battery (ARLB) is greatly restricted by the anode material. Herein, Na2V6O16nanowires with high cycling stability in the aqueous solution are firstly proposed as a novel anode material for ARLB. Electrochemical behavior of Na2V6O16electrode in a saturated Li2SO4(2M)with various pH values from7.0to12.0was investigated by cyclic voltammetry. As observed, each electrode demonstrates one large pair of redox peaks between-0.4and-0.7V. The related redox peaks agree well with the lithium-ion insertion/extraction process in an organic electrolyte. The separating of redox peaks in the first cycles can be attributed to the different occupation sites for the lithium ions in the host. However, increasing pH in this paper results in inferior cycling stability. Results above imply that Na2V6O16could be used as lithium reversible intercalated electrode for ARLB and it exhibits the best cycling performance in neutral solution.The ARLB consisting of LiMn2O4, LiFePO4and LiNi1/3Mn1/3Co1/3O2as cathode, Na2V6O16as anode and saturated Li2SO4as electrolyte indicates superior cycling stability. An initial specific discharge capacity of122.7mAhg-1(based on the mass of anode material) can be reached at60mAg-1. The capacity retention is up to80.1%and77%of the initial discharge capacity at300mAg-1after100and200cycles, respectively. No considerable increasing of charge-transfer impedance was discovered from the EIS comparison. There is no doubt that the annealed Na2V6O16nanowires with good structure stability would be significantly beneficial to improvement of the cycling performance for as-studied ARLB.XRD patterns of Na2V6O16at various charged/discharge voltages show the structure of electrolytes can keep stable during the insertion/extraction process. Reasons of capacity fading of LiMn2O4//Na2V6O16lithium ion cell based on structure and dissolution of transition metals were investigated preliminarily. XRD and ICP results showed that the properties of the anode have more impact on the cycle life of the cell. However, the structure Na2V6O16are more stable than other vanadium oxide, which is the main reason of good cycling performance of the cell.