One-dimensional (1D) nanostructured β-AgVO3 fibers have been successfully synthesized at 300°C for 3 h via the low-temperature molten salt synthesis (LT-MSS) method where LiNO3 was employed as reaction media. The crystal structure and morphology of the as-obtained β-AgVO3 fibers were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The results revealed that the LT-MSS product displayed a high crystallinity and consisted of fibrous crystals with widths of 150 nm to 1 µm and lengths of several to several tens of micrometers. Electrochemical measurements indicated that the as-synthesized β-AgVO3 fibers exhibited higher discharge capacity and better cycleability compared with the counterparts from the liquid phase synthesis (LPS) and the high temperature solid state synthesis (HT-SSS) methods.
Polyacrylates were applied as binder for the electrode of a particulate mixture of silicon, graphite, and Ketjen black for lithium-ion batteries. We found that poly(alkali acrylate) binder remarkably improved the electrochemical lithiation and delithiation performance of the silicon-graphite electrode compared to that of conventional binders. The polyacrylate coating on Si and graphite particles suppressed the electrode deterioration. When the electrode was prepared with 30 wt% poly(sodium acrylate) binder, the higher specific capacity and initial efficiency were obtained with much improved cycleability.
A cobalt (catalyst) is sputtered at different time levels on graphite foil on which carbon nanotubes are subsequently directly grown by chemical vapor deposition (CVD). Next, carbon nanotubes are modified by RF (radio frequency) oxygen-plasma at different volume flow rates of oxygen and then immersed in nitric acid solution. The longer Co sputtering time led to the thicker Co film thickness. Higher specific capacitance of 140.2 F g−1 is obtained under a certain condition (Co sputtering time=15 min and flow rate of oxygen=30 cm3 min−1). This shows good specific capacitance. Furthermore, the higher flow rate of oxygen caused the higher carbonyl functional group (C=O), thus leading to higher specific capacitance.
We prepared LixMn0.5Ni0.5O2 by solid-state and solution methods, and investigated their thermodynamic stabilities, crystal and electronic structures and cathode performances. The cycle performance of LixMn0.5Ni0.5O2 depended on its synthetic method and Li content; that is, the samples synthesized by a solid-state reaction seemed to show better cycle performance than those prepared by a solution method, and the samples with x=1.03∼1.05 exhibited larger discharge capacity and higher capacity retention regardless of the synthetic process. Crystal structure analyses using a neutron source suggested that an existence of Ni2+ at Li+ site and/or a higher distortion around the transition metals deteriorated the cycle performance. It was also clarified by XAFS measurements that such a distortion was localized in the Mn-O6 octahedron. From reaction enthalpies of the materials evaluated by calorimetries, it was suggested that higher thermodynamic stability was one of the reasons for better cathode performance.
As a simultaneous electrochemical measurement of oxygen reduction reaction (ORR) and surface oxidation/reduction on Pt/C, a shielding measurement using rotating ring disk electrode (RRDE) has been investigated. The ORR current was determined by the decrease of the ring current which was the diffusion limiting current of oxygen with collection efficiency of the RRDE. The difference between the disk current and the oxygen reduction reaction current was corresponded to cyclic voltammogram (CV) in inert atmosphere with correction of transient delay for the response of the ring electrode from the disk electrode. The delay of the ring electrode was 0.31 s for 6 mm in diameter of the disk electrode and 7 mm in the inner diameter of the ring at 900 rpm. To separate ORR current and CV clearly, significant level of the CV component in the disk current was needed. More than 40 µg cm−2 of Pt loading allowed the clear separation. At that time, apparent activity of Pt/C was less than one third of 10 µg cm−2 in Pt loading because of too thick the catalyst layer for the activity measurements. The mentioned above, the shielding measurement using RRDE could be applied for simultaneous separation of ORR and surface oxidation/reduction on Pt/C, and will be a strong tool to measure the relationship between the catalytic activity and the degree of the surface oxidation.