RESUMO
Na2Ti3/2Mn1/2(PO4)3 nanodots uniformly planted in a carbon matrix are reported for the first time as a promising low-cost anode for aqueous sodium-ion batteries, showing ultrafast Na-intercalation chemistry with stable capacities of 78.8 mA h g-1 at 0.5C and 65.1 mA h g-1 at 10C, and a capacity retention of 93% after 200 cycles.
RESUMO
Sodium vanadium fluorophosphate (Na3(VO)2(PO4)2F, denoted as NVPF) has attracted particular interests as cathode for high-energy sodium-ion batteries (SIBs) owing to the high working potential, high specific capacity, and robust structural framework. However, it is challenged by the low electron conductivity and lack of available facile synthesis method. Herein, an environmentally benign, cost-effective synthesis route is reported to produce NVPF nanoparticles encapsulated in conductive graphene network (NVPF/C), involving low-temperature synthesis of NVPF nanoparticles in absolute aqueous solvents and subsequent construction of conductive network through thermally induced transformation of graphene-oxide nanosheets. The resultant product is structurally and electrochemically investigated by combining X-ray diffraction, fourier transform infrared spectroscopy, scanning electron microscope, transition electron microscope, and electrochemical analysis. Experimental results show that the optimized NVPF/C product possesses a three-dimensional graphene-encapsulation nanostructure composed of â¼100â¯nm NVPF nanoparticles and â¼4â¯nm carbon-coating layer. The unique hierarchical structure enables it cycling with excellent electrochemical performance in terms of a high reversible capacity (116.4â¯mAâ¯hâ¯g-1 at 0.2â¯C), excellent high-rate capability (87.4â¯mAâ¯hâ¯g-1 at 10â¯C) and long-term lifetime (82.1% capacity retention after 1200 cycles). It is indicated that the facile synthesis route can achieve high-performance NVPF/C material for SIBs.