Hyo-Jun Ahn

Mesoporous LiFePO4/C nanocomposite cathode materials for high power lithium ion batteries with superior performance

Hexagonally ordered mesoporous LiFePO4/C nanocomposites can be synthesized with LiFePO4 nanoparticles embedded in an interconnected carbon framework. Mesoporous LiFePO4/C nanocomposites exhibit superior electrochemical performance and ultra-high specific power density, which makes this architecture suitable for high power applications such as hybrid electric vehicles (HEVs) and stationary energy storage for smart grids.

Effect of Multiwalled Carbon Nanotubes on Electrochemical Properties of Lithium/Sulfur Rechargeable Batteries

In order to bestow high electronic conductivity and prevent dissolution of sulfur into the electrolyte, multiwalled carbon nanotubes (MWNTs) were prepared by thermal chemical vapor deposition as an inactive additive material for elemental sulfur positive electrodes for lithium/sulfur rechargeable batteries. The initial discharge capacity of elemental sulfur positive electrode with MWNT is 485 mAh/g sulfur at 2.0 V vs. The cycle life and rate capability of sulfur cathode is increased with addition of MWNT. The MWNT shows a vital role on polysulfide adsorbtion and is a good electric conductor for a sulfur cathode.

Effects of Nanosized Adsorbing Material on Electrochemical Properties of Sulfur Cathodes for Li/S Secondary Batteries

In order to prevent polysulfide dissolution into liquid electrolytes and to promote the Li/S redox reaction (16Li + S 8 ↔ Li 2 Sn ↔ Li 2 S), nanosized Mg 0.6 Ni 0.4 O, which has the catalytic effect of chemical bond dissociating and is expected to have an adsorbing effect due to the effect of retaining liquid electrolyte of MgO in a Li/iron sulfide secondary battery, 16 was prepared by the sol-gel method as an electrochemically inactive additive for an elemental sulfur cathode for Li/S rechargeable batteries. The Li/S battery using an elemental sulfur cathode with a nanosized Mg 0.6 Ni 0.4 O added showed the improvement of not only the discharge capacity but also cycle durability (maximum discharge capacity: 1185 mAh/g sulfur, C 50 /C 1 = 85%).The rate capability of the sulfur cathode was also increased with the addition of the nanosized Mg 0.6 Ni 0.4 O. From the msults. it is confirmad that the nanosized Mg 0.6 Ni 0.4 O had the polysulfide adsorbing effect and the catalytic elfect of promoting Lt/S redox reaction. Furthermore, it is found that the nanosized Mg 0.6 Ni 0.4 O also increased the porosity of the sulfur cathode.

Solvothermal synthesis of CoS2–graphene nanocomposite material for high-performance supercapacitors

A CoS2–graphene nanocomposite was prepared by a facile solvothermal method. FESEM and TEM analyses have confirmed that CoS2 nanoparticles with sizes of 5–15 nm are densely anchored on graphene nanosheets. The as-prepared nanocomposite was electrochemically tested as an electrode material for supercapacitors. The CoS2–graphene nanocomposite exhibited specific capacitances of 314 F g−1 in the aqueous electrolyte and 141 F g−1 in the organic electrolyte at a current rate of 0.5 A g−1 with excellent cycling stability. The electrochemical performance of the nanocomposite has been significantly improved, compared to bare graphene nanosheets and CoS2 nanoparticles. This could be credited to the 3D nanoarchitecture, in which CoS2 nanoparticles were sandwiched between graphene nanosheets, and the additional electrochemical contribution of the decorated CoS2 nanoparticles.

Electrochemical properties of sulfur electrode containing nano Al2O3 for lithium/sulfur cell

To prevent the dissolution of lithium polysulfides into liquid electrolyte and to promote the lithium/sulfur redox reaction, nano-sized Al2O3 particles having large specific surface area were added into sulfur electrode. The effects of nano-sized Al2O3 particles on the electrochemical properties of sulfur electrode for lithium/sulfur battery were investigated using CV measurements, charge/discharge tests and ionic conductivity measurements of liquid electrolyte. From the results, the sulfur electrode containing nano Al2O3 particles showed good cycle performance and higher discharge capacity of 660 mAh g−1-sulfur than that of the sulfur electrode without nano Al2O3. It is therefore concluded that the addition of nano-sized Al2O3 particles gives the beneficial effects of preventing the dissolution of lithium polysulfides into liquid electrolyte.

Highly ordered mesoporous cobalt oxide nanostructures: synthesis, characterisation, magnetic properties, and applications for electrochemical energy devices

Highly ordered mesoporous Co(3)O(4) nanostructures were prepared using KIT-6 and SBA-15 silica as hard templates. The structures were confirmed by small angle X-ray diffraction, high resolution transmission electron microscopy, and N(2) adsorption-desorption isotherm analysis. Both KIT-6 cubic and SBA-15 hexagonal mesoporous Co(3)O(4) samples exhibited a low Néel temperature and bulk antiferromagnetic coupling due to geometric confinement of antiferromagnetic order within the nanoparticles. Mesoporous Co(3)O(4) electrode materials have demonstrated the high lithium storage capacity of more than 1200 mAh g(-1) with an excellent cycle life. They also exhibited a high specific capacitance of 370 F g(-1) as electrodes in supercapacitors.

Single Crystalline Na0.7MnO2 Nanoplates as Cathode Materials for Sodium‐Ion Batteries with Enhanced Performance

Single crystalline rhombus-shaped Na(0.7)MnO2 nanoplates have been synthesized by a hydrothermal method. TEM and HRTEM analyses revealed that the Na(0.7)MnO2 single crystals predominantly exposed their (100) crystal plane, which is active for Na(+)-ion insertion and extraction. When applied as cathode materials for sodium-ion batteries, Na(0.7)MnO2 nanoplates exhibited a high reversible capacity of 163 mA h g(-1), a satisfactory cyclability, and a high rate performance. The enhanced electrochemical performance could be ascribed to the predominantly exposed active (100) facet, which could facilitate fast Na(+)-ion insertion/extraction during the discharge and charge process.

First-principles study on the enhancement of lithium storage capacity in boron doped graphene

The adsorption of Li ions on boron doped graphene was investigated using a first-principles method. Our results show that, as boron doping turns graphene into an electron-deficient system, more Li ions can be captured around boron doped centers than in pristine graphene. One boron atom doped into graphene (6C ring unit) can adsorb six Li ions, which indicates that boron doped graphene is an efficient Li-ion storage material for lithium batteries. Further investigations show that, under limited conditions, boron doped graphene (BC5) can form Li6BC5 compound after Li-ion adsorption, corresponding to a lithium storage capacity of 2271 mAh/g which is six times that of graphite.

A Microwave Synthesis of Mesoporous NiCo2O4 Nanosheets as Electrode Materials for Lithium-Ion Batteries and Supercapacitors

A facile microwave method was employed to synthesize NiCo2 O4 nanosheets as electrode materials for lithium-ion batteries and supercapacitors. The structure and morphology of the materials were characterized by X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy and Brunauer-Emmett-Teller methods. Owing to the porous nanosheet structure, the NiCo2 O4 electrodes exhibited a high reversible capacity of 891 mA h g(-1) at a current density of 100 mA g(-1) , good rate capability and stable cycling performance. When used as electrode materials for supercapacitors, NiCo2 O4 nanosheets demonstrated a specific capacitance of 400 F g(-1) at a current density of 20 A g(-1) and superior cycling stability over 5000 cycles. The excellent electrochemical performance could be ascribed to the thin porous structure of the nanosheets, which provides a high specific surface area to increase the electrode-electrolyte contact area and facilitate rapid ion transport.

Hydrothermal synthesis of α-MnO2 and β-MnO2 nanorods as high capacity cathode materials for sodium ion batteries

Two types of MnO2 polymorphs, α-MnO2 and β-MnO2 nanorods, have been synthesized by a hydrothermal method. Their crystallographic phases, morphologies, and crystal structures were characterized by XRD, FESEM and TEM analysis. Different exposed crystal planes have been identified by TEM. The electrochemical properties of α-MnO2 and β-MnO2 nanorods as cathode materials in Na-ion batteries were evaluated by galvanostatic charge/discharge testing. Both α-MnO2 and β-MnO2 nanorods achieved high initial sodium ion storage capacities of 278 mA h g−1 and 298 mA h g−1, respectively. β-MnO2 nanorods exhibited a better electrochemical performance such as good rate capability and cyclability than that of α-MnO2 nanorods, which could be ascribed to a more compact tunnel structure of β-MnO2 nanorods. Furthermore, the one-dimensional architecture of nanorods could also contribute to facile sodium ion diffusion in the charge and discharge process.