Sun-Min Park

Hierarchical porous α-Ni(OH)2 grown from a compact ion layer as an electrode by using one-pot synthesis and its pseudocapacitive behaviour

The advancement of supercapacitor electrodes is predicated using simple and efficient synthesis methods. In this study a simple electrochemical precipitation method is presented for the synthesis of an α-nickel hydroxide (α-Ni(OH)2) electrode directly on a Ti substrate without any templates or surfactants. The α-Ni(OH)2 electrode possessed a hierarchically porous structure with well-developed inner and outer pores and a large specific surface area of 205.6 m2 g−1. A supercapacitor with this electrode exhibited a high specific capacitance of 1582 F g−1 in 1 M potassium hydroxide (KOH) at a scan rate of 2 mV s−1 and a capacitive retention of almost 74% after 1000 cycles at a current density of 5 mA cm−2.

Synthesis of mesoporous spherical TiO2 and its application in negative electrode of hybrid supercapacitor

To fabricate a hybrid supercapacitor comprising activated carbon and TiO2 electrodes, anatase TiO2 was investigated as a candidate negative electrode material. It was synthesized by a combination of the sol-gel and microwave methods using dodecylamine as a structure directing agent. The synthesized TiO2 had uniform size (∼400 nm), a spherical morphology, a mesoporous structure (specific surface area = ∼100 m2g−1, pore size distribution = ∼10 nm), and anatase phase without any impurities. To balance the power and energy densities of positive (activated carbon) and negative electrodes (TiO2), each electrode was confirmed to have the specific capacity of about 190 mAh g−1 and 50 mAh g−1 (at 1 C-rate = 250 mA g−1) through half cell tests. While the specific capacitance (23 F cm−3) of the hybrid supercapacitor achieved about 28% increase compared to an existing supercapacitor (electric double-layer capacitor = 18 F cm−3) at a current density of 0.5 mA cm−2, it had a low retention ratio of 91% during 100 cycles due to the poor electronic conductivity of TiO2. However, it was confirmed that anatase TiO2 is suitable for use as a negative material in hybrid supercapacitors.

Nickel-based layered double hydroxide from guest vanadium oxide anions

The layered double hydroxides (LDHs) are well known for ionic exchange properties to intercalate anionic compound in interlayer region. The Ni/V LDH composite was explored by co-precipitation method. The maximum capacitance of Ni/V LDH composite was 2612 F g−1 at the scan rate 2 mV s−1. As-synthesized Ni/V LDH composite provides a three-dimensional conducting network frame for manifesting electrochemical capacitance. This is because the insertion of vanadium oxide anions (VOx−) into nickel interlayer space between nickel layers is compensated for hydroxyl vacancies during synthesis of lower-pH condition. The network frame makes it possible to promote fast electron transfer for Ni/V LDH composite electrode material and consequently allows the improvement of the electronic conductivity for Ni/V LDH composite electrode material. Thus, the Ni/V LDH composite exhibits high capacitance than β-Ni(OH)2 due to its unique properties, with vanadium oxide anions embedded in the turbostratic structure and shorter diffusion pathway.

Two-dimensional cobalt-based composites grown on Ti plates for application as pseudocapacitor materials

Various cobalt-based composites grown on Ti plates were synthesized using electrochemical precipitation by controlling pH. For all samples, peaks associated with Co3O4, CoOOH, and Co(OH)2 were found in the XRD spectra for the cobalt-based composites. The morphologies of the cobalt oxide/hydroxide exhibited a mixture of 2D hexagonal platelets. The pseudocapacitive properties of cobalt-based composites were investigated using cyclic voltammetry (CV) in a 1M KOH electrolyte solution. Oxidation and reduction peak currents were measured during cycling between −0.2 and 0.4 V (vs. a saturated calomel electrode). The Co3O4/Co(OH)2 electrode synthesized at pH 6.5 exhibited a maximum specific capacitance of 627 F g−1. The results suggest that the use of cobalt-based composites is an effective strategy for producing high energy pseudocapacitors.

Optimization of Capacitance Balance for a Hybrid Supercapacitor Consisted of LiMn 2 O 4 /AC as a Positive and AC Negative Electrode

A hybrid supercapacitor is fabricated using a composite material from (LMO) and activated carbon (AC) as the positive electrode and AC as the negative electrode to form the (LMO + AC)/AC system. Volume ratio (positive : negative) of electrodes is controlled to investigate of the power and energy balance. The (LMO + AC)/AC system shows better performances than the LMO/AC system. Especially, electrochemical impedance spectra, rate charge.discharge and cycle performance testing show that the (LMO + AC)/AC system have an outstanding electrochemical performance at volume ratios of (LMO + AC)/AC

The Synthesis and Electrochemical Performance of Microspherical Porous LiFePO 4 /C with High Tap Density

Over the past few years, has been actively studied as a cathode material for lithium-ion batteries because of its advantageous properties such as high theoretical capacity, good cycle life, and high thermal stability. However, it does not have a very good power capability owing to the low lithium-ion diffusivity and poor electronic conductivity. Reduction in particle size of to the scale of nanometers has been found to dramatically enhance the above properties, according to many earlier reports. However, because of the intrinsically low tap density of nanomaterials, it is difficult to commercialize this method. Many studies are being carried out to improve the volumetric energy density of this material and many methods have been reported so far. This paper provides a brief summary of the synthesis methods and electrochemical performances of micro-spherical having high volumetric energy density.

Synthesis and electrochemical properties of Mn3O4 nanocrystals with controlled morphologies grown from compact ion layers

Different morphologies of Mn3O4 nanocrystals including rod-like, plate-like, and round nanoparticles were successfully prepared by a simple one-step process combining electrodeposition and precipitation, directly growing on Ti substrates without using templates or surfactants. In our system, precursor concentration, alkaline medium (LiOH) as a precipitant and the reaction time play important roles in the microstructure evolution of the Mn3O4 nanocrystal morphologies. The shape-controlled Mn3O4 nanoplates exhibit a maximum specific capacitance of 211 F g−1 at 2 mV s−1 in 1 M Na2SO4 for ultracapacitors.

Size-tunable tavorite LiFe(PO4)(OH) microspheres with a core–shell structure

Core–shell structured tavorite LiFe(PO4)(OH) microspheres were synthesized by means of a simple solvothermal route. These particles have a mesoporous structure consisting of a shell made up of submicro-sized particles and a core of nano-sized particles. The size of the particles can be tuned within a range of 0.7 μm to more than 7 μm, with no hollowing observed despite the longer reaction times needed to create a sufficiently high density for use as a precursor of LiFePO4 in lithium-ion batteries. From the experimental data obtained, mechanisms for particle formation and crystal growth have been proposed based on the low dielectric constant of the reaction medium, the chemical potential difference induced by the adsorption of surfactants into the phosphate group, and the degree of supersaturation. In addition, the dependence of the electrochemical performance on the LiFe(PO4)(OH) particle size is investigated.