Hezhang Chen

CNT-Decorated Na3V2(PO4)3 Microspheres as a High-Rate and Cycle-Stable Cathode Material for Sodium Ion Batteries

A novel cathode material, carbon nanotube (CNT)-decorated Na3V2(PO4)3 (NVP) microspheres, was designed and synthesized via spray-drying and carbothermal reduction methods. The microspheres were covered and embedded by CNTs, the surfaces of which were also covered by amorphous carbon layers. Thus, a carbon network composed of CNTs and amorphous carbon layers formed in the materials. The polarization of a 10 wt % CNT-decorated NVP (NVP/C10) electrode was much less compared with that of the electrode with pristine NVP without CNTs. The capacity of the NVP/C10 electrode only decreased from 103.2 to 76.2 mAh g-1 when the current rates increased from 0.2 to 60 C. Even when cycled at a rate of 20 C, the initial discharge capacity of the NVP/C10 electrode was as high as 91.2 mAh g-1, and the discharge capacity was 76.9 mAh g-1 after 150 cycles. The charge-transfer resistance and ohmic resistance became smaller because of CNT decorating. Meanwhile, the addition of CNTs can tune the size of the NVP particles and increase the contact area between NVP and the electrolyte. Consequently, the resulted NVP had a larger sodium ion diffusion coefficient than that of the pristine NVP.

Preparation and electrochemical performance of 2LiFe1–xCoxPO4–Li3V2(PO4)3/C cathode material for lithium-ion batteries

Abstract 2LiFe 1– x Co x PO 4 –Li 3 V 2 (PO 4 ) 3 /C was synthesized using Fe 1–2 x Co 2 x VO 4 as precursor which was prepared by a simple co-precipitation method. 2LiFe 1– x Co x PO 4 –Li 3 V 2 (PO 4 ) 3 /C samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical measurements. All 2LiFe 1– x Co x PO 4 –Li 3 V 2 (PO 4 ) 3 /C composites are of the similar crystal structure. The XRD analysis and SEM images show that 2LiFe 0.96 Co 0.04 PO 4 –Li 3 V 2 (PO 4 ) 3 /C sample has the best-ordered structure and the smallest particle size. The charge–discharge tests demonstrate that these powders have the best electrochemical properties with an initial discharge capacity of 144.1 mA·h/g and capacity retention of 95.6% after 100 cycles when cycled at a current density of 0.1 C between 2.5 and 4.5 V.

Reduced Graphene Oxide Decorated Na3V2(PO4)3 Microspheres as Cathode Material With Advanced Sodium Storage Performance

Reduced graphene oxide (rGO) sheet decorated Na3V2(PO4)3 (NVP) microspheres were successfully synthesized by spray-drying method. The NVP microspheres were embedded by rGO sheets, and the surface of the particles were coated by rGO sheets and amorphous carbon. Thus, the carbon conductive network consisted of rGO sheets and amorphous carbon generated in the cathode material. NVP microspheres decorated with different content of rGO (about 0, 4, 8, and 12 wt%) were investigated in this study. The electrochemical performance of NVP exhibited a significant enhancement after rGO introduction. The electrode containing about 8 wt% rGO (NVP/G8) showed the best rate and cycle performance. NVP/G8 electrode exhibited the discharge capacity of 64.0 mAh g−1 at 70°C, and achieved high capacity retention of 95.5% after cycling at 10°C for 100 cycles. The polarization of the electrode was inhibited by the introduction of rGO sheets. Meanwhile, compared with the pristine NVP electrode, NVP/G8 electrode exhibited small resistance and high diffusion coefficient of sodium ions.