RESUMEN
Sodium manganese ferrocyanide NaxMn[Fe(CN)6]y is an attractive cathode material for sodium-ion batteries. However, NaxMn[Fe(CN)6]y prepared by simple coprecipitation of Mn2+ and [Fe(CN)6]4- usually shows poor cycling performance, which hinders its practical application. In this work, electrochemical performance of a Na1.6Mn[Fe(CN)6]0.9 (PBM) sample prepared by the simple precipitation method was greatly improved by coating with Na3(VOPO4)2F (NVOPF) via a solution precipitation method. The as-prepared PBM@NVOPF with a coating quantity of 2.0% molar ratio showed enhanced rate capability and superior cyclic stability. The discharge capacities of PBM@NVOPF were 101.5 mA h g-1 (1 C) and 91.4 mA h g-1 (10 C), with a capacity retention of 84.3% after 500 cycles at 1 C, 20 °C. It also exhibited excellent cyclic stability at elevated temperature with an initial capacity of 109.5 mA h g-1 and a capacity retention of 78.8% after 200 cycles at 1 C, 55 °C. In comparison, uncoated PBM showed a discharge capacity of 105.7 mA h g-1 (1 C) and 76.7 mA h g-1 (10 C), with a capacity retention of only 42.0% after 500 cycles at 1 C, 20 °C. The high-temperature performance of bare PBM was very poor, and the capacity retention was only 35.7% after 40 cycles because of serious Mn/Fe dissolution which caused structural deterioration of PBM. NVOPF coating protected the PBM from suffering corrosion in the electrolyte, thus ensured the framework stability of PBM during long-term cycling and contributed to the excellent electrochemical performance.
RESUMEN
The use of lithium-ion batteries (LIBs) is skyrocketing since they are widely applied in portable consumer devices and electric vehicles. However, at the end of their lifetime, large amount of spent LIBs will result in a negative environmental impact and aggravate the problem of resource shortage without proper disposal. Therefore, recycling is an effective solution, which will be enforced in the near future. Herein, the purification, recovery and reuse of transition metals from spent LIBs were thoroughly studied. First, the target impurities in a solution were effectively removed individually. Iron(iii) and aluminum(iii) impurities were removed by adjusting the pH value, whereas copper(ii) was purified using highly selective electrodeposition technology and solvent extraction. Second, Ni0.41Co0.21Mn0.38(OH)2 was co-precipitated by adjusting the pH value of the purified metal solution, containing nickel(ii), cobalt(ii) and manganese(ii) ions to 11 with NaOH and a proper amount of NH3·H2O. The comprehensive loss in nickel(ii), cobalt(ii) and manganese(ii) was only 0.37% in the purification and co-precipitation procedures. Finally, LiNi0.41Co0.21Mn0.38O2 (marked as LNCM-R) synthesized with the recycled materials was tested and compared with LiNi0.41Co0.21Mn0.38O2 (marked as LNCM-N) synthesized with new materials as the control group. The XRD, SEM and TEM results indicate that both samples have the same structure and morphology. Furthermore, the charge-discharge tests, initial dQ/dV curves, EIS and GITT results indicate a similar electrochemical performance of the LNCM-R and LNCM-N samples. The purification and recycling strategies in our research have high efficiency and comparatively low cost, which provide great guidance for the industrial recycling of spent Li-ion batteries.
