Sukeun Yoon

Facile microwave synthesis of CoFe2O4 spheres and their application as an anode for lithium-ion batteries

CoFe2O4 spheres were synthesized using a microwave-hydrothermal reaction and characterized by X-ray diffraction, electron microscopy, and electrochemical analysis. This simple synthesis method led to a uniform dispersion of nanosized building blocks in the spheres, which exhibit significantly improved cycling performance and rate capability in lithium cells. The excellent electrochemical performances of CoFe2O4 sphere are attributed to an increased lithium wetting property at the electrode–electrolyte interface, facile lithium-ion diffusion, and better alleviation of the structure pulverization during charge–discharge process.

Effect of nitridation on LiMn1.5Ni0.5O4 and its application as cathode material in lithium-ion batteries

Nitridated LiMn1.5Ni0.5O4 was prepared by a solid-state reaction followed by nitridation to investigate the effect of nitrogen on the structural and electrochemical performance of LiMn1.5Ni0.5O4 cathode material for lithium-ion batteries. The structural and morphological features of the synthesized samples were characterized by various techniques. X-ray photoelectron spectrometer analysis revealed the existence of a trace amount of nitrogen on the surface and slight changes in Mn and Ni valence states. Electrochemical studies on the nitridated LiMn1.5Ni0.5O4 was conducted using the galvanostatic charge–discharge process and electrochemical impedance spectroscopy. The nitridated LiMn1.5Ni0.5O4 exhibited enhanced cyclability and rate capability compared with LiMn1.5Ni0.5O4, which originated from the improved electrical conductivity caused by increased proximity between active Ni redox centers as well as the increased number of Mn3+ hopping carriers.Graphical abstract

A conductive thin layer on prepared positive electrodes by vapour reaction printing for high-performance lithium-ion batteries

Surface modification, especially by thin-layer coating, has provided a major breakthrough in high-performance lithium-ion batteries (LIBs). Surface coating with conductive materials at the level of single active particles has been used to overcome poor conductivity in electrodes. Nevertheless, the resulting decrease in the volumetric capacity and the complexity of the required manufacturing conditions are problematic for particle-scale coating techniques. Here, we report a facile alternative route to coating conformal thin-layer conducting poly(3,4-ethylenedioxythiophene) (PEDOT) through vapour reaction printing (VRP) on prepared electrodes. A positive electrode based on micron-sized LiFePO4 (LFP) was used to highlight the possible improvements in the intrinsic limitations of poor electrical and ionic conductivity. The effective conformal surface coating of the thin PEDOT layer was confirmed by scanning electron microscopy and X-ray photoelectron spectroscopy. The PEDOT coated LFP electrodes exhibited outstanding improvements not only in cycling stability, showing 96.6% retention of the initial capacity after 100 cycles, but also in their rate capability, achieving 0.668 mA h at a rate of 1C. The uncoated pristine LFP electrode showed only 23.5% of the initial capacity after 100 cycles and 0.181 mA h at a rate of 1C. These remarkable results were attributed to the conformal PEDOT layer, which offers improved conduction pathways and ion diffusion. Therefore, this new method of coating prepared electrodes with a conductive conformal thin layer is promising for the design of electrodes for high-performance lithium-ion batteries.

Improved electrochromic device performance from silver grid on flexible transparent conducting electrode prepared by electrohydrodynamic jet printing

Flexible transparent conducting electrodes (TCEs) are promising for use in electrochromic devices (ECDs), owing to their flexibility to operate in nonplanar configuration. The successful introduction of indium tin oxide (ITO)-coated glass into rigid and planar display devices made ITO on a transparent polymer film an attractive option for flexible devices. However, the flexible characteristic of the ITO film is compromised by its higher surface resistance compared to that of ITO glass. Here, we report printing silver grid on ITO film using an electrohydrodynamic (EHD) jet method, varying the grid pitch. This mask-free method to introduce silver grids onto ITO was used for ECD fabrication. The results showed improvements in colour quality and response time that are attributed to the enhanced conductivity of the silver grid ITO film under low-voltage (1.0 V) operation. Our approach can be used to improve soft ECDs by improving the performance of flexible TCEs.

Li1+xMn2−xO4 (0 ≤ x ≤ 0.2) spinel mesorod cathode materials for rechargeable lithium batteries

AbstractLi1+xMn2−xO4 (0 ≤ x ≤ 0.2) mesorods have been synthesized by using β-MnO2 mesorods as a self-template, and obtained by a hydrothermal reaction of K2Mn4O8. Various techniques were used to characterize the structural and morphological features of the synthesized samples. Among the Li1+xMn2−xO4 (0 ≤ x ≤ 0.2) compositions investigated, the Li1.05Mn1.95O4 mesorods exhibit the best electrochemical performance, with a reversible capacity of 108 and 102 mAh g−1 at 3 C and 5 C rates, respectively, with a capacity retention of 89% over 100 cycles. The enhanced electrochemical performance is attributed to a facile lithium-ion and electron transport, facilitated by the mesorod morphology.