Synthesis and electrochemical performance of Na3-xLixV2(PO4)3/C as cathode materials for Li-ion batteries

Herein, a series of lithium-sodium hybrid ion Na3-xLixV2(PO4)(3)/C (x = 2.5, 2.0, 1.5, 1.0, 0.5) as cathode materials are prepared by sol-gel method. The lithium storage properties of Na3-xLixV2(PO4)(3)/C reveal that the lithium sodium ratio has a strong influence on material structure and the electrochemical properties. The multiple voltage platforms are observed at charge and discharge curve for the Na0.5Li2.5V2(PO4)(3) material, as it contains rhombohedral and monoclinic Li3V2(PO4)(3) phases, whereas a single voltage platform can be observed when x is less than 2, which are mixtures of Na3V2(PO4)3 with rhombohedral structure and Li3V2(PO4)(3) with rhombohedral structure. Notably, NaLi2V2(PO4)(3)/C prepared by the calcination at 700 degrees C for 8 hours contains a single rhombohedral phase. And when the charging and discharging voltage at the range 2.5 to 4.5 V and current density at 0.5C, NaLi2V2(PO4)(3)/C and Na2.5Li0.5V2(PO4)(3)/C are prepared by the pre-calcination at 400 degrees C for 4 hours and subsequent calcination at 750 degrees C for 8 hours exhibit high first-cycle specific discharge capacities of 124.8 and 130.0 mAh center dot g(-1). The capacities are 118.4 and 115.1 mAh center dot g(-1) after 50 cycles, indicating excellent capacity retention.