High energy density of Li 3−x Na x V 2 (PO 4 ) 3 /C cathode material with high rate cycling performance for lithium-ion batteries

Abstract

Abstract A serials of micro-sized Li 3− x Na x V 2 (PO 4 ) 3 /C composite has been synthesized by sol-gel method, comprised of numerous primary nanocrystals. This structure can efficiently facilitate lithium-ion transport in secondary aggregated individual particles due to the short diffusion distance among primary nanocrystals, along with a high tap density. With the increasing of Na doping content, the structure evolution occurs in Li 3- x Na x V 2 (PO 4 ) 3 from a single-phase structure to a two-phase structure. The appearance of rhombohedral phase can provide a larger free volume of the interstitial space, fastening ionic movement to offer an excellent high rate capability. Furthermore, Na doping can stabilize the rhombohedral structure of the V 2 (PO 4 ) 3 framework, leading to the remarkable cycling stability. Among all the composites, Li 2.6 Na 0.4 V 2 (PO 4 ) 3 /C presents the best electrochemical performance with a high energy density of 478.8 Wh kg −1 , delivering high initial discharge capacities of 121.6, 113.8 and 109.7 mAh g −1 at the rate of 5 C, 10 C and 20 C in a voltage range of 3.0 – 4.3 V, respectively. It also exhibit an excellent high rate cycling performance, with capacity retention of 85.9 %, 81.7 % and 76.5 % after 1000 cycles at the rate of 5 C, 10 C and 20 C in a voltage range of 3.0 – 4.3 V.