The synthesis of Na x K y Fe[Fe(CN) 6 ] through a simple co-precipitation method and the application of these nanoparticles in sodium-ion batteries are presented. K 1.90 Fe[Fe(CN) 6 ] with a cubic structure shows low volumetric change during electrochemical cycling. It is clarified by ex-situ X-ray diffraction and cyclic voltammetry curves that K + influences the intercalation sites of the neighboring Na +. More significantly, this hexacyanoferrate delivers a high capacity of 137.0 mAh g − 1 at a current density of 14 mA g − 1 and superior cyclability with 94% capacity retention after 120 cycles, showing great promise for sodium-ion battery applications.
A complete and ordered layered structure on the surface of LiNiCoAlO (NCA) has been achieved via a facile surface-oxidation method with NaSO. The field-emission transmission electron microscopy images clearly show that preoxidation of the hydroxide precursor can eliminate the crystal defects and convert Ni(OH) into layered β-NiOOH, which leads to a highly ordered crystalline NCA, with its (006) planes perpendicular to the surface in the sintering process. X-ray photoelectron spectroscopy and Raman shift results demonstrate that the contents of Ni and Co ions are reduced with preoxidization on the surface of the hydroxide precursor. The level of Li/Ni disordering in the modified NCA determined by the peak intensity ratio I/I in X-ray diffraction patterns decreases. Thanks to the complete and ordered layered structure on the surface of secondary particles, lithium ions can easily intercalate/extract in the discharging-charging process, leading to greatly improved electrochemical properties.
Ascorbic acid acts as both an antioxidant and a surfactant to form organic groups (first carbon source) on the surface of as-solvothermal products, in which the-OH (or H 2 O) groups of glucose (second carbon source) are closely bonded to the surface to form a uniform adsorption layer. Uniform mixed-carbon-coated LiMn 0.4 Fe 0.6 PO 4 nanopowders are formed after calcination, which demonstrate excellent electrochemical performances.
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