• Journal of the Semiconductor & Display Technology
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• v.21 no.3
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• pp.114-118
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• 2022

The stabilized all-solid-state battery structure indicate a fundamental alternative to the development of next-generation energy storage devices. Existing liquid electrolyte structures severely limit battery stability, creating safety concerns due to the growth of Li dendrites during rapid charge/discharge cycles. In this study, a low-dimensional graphene quantum dot layer structure was applied to demonstrate stable operating characteristics based on Li+ ion conductivity and excellent electrochemical performance. Transmission electron microscopy analysis was performed to elucidate the microstructure at the interface. The low-dimensional structure of GQD-based solid electrolytes has provided an important strategy for stable scalable solid-state lithium battery applications at room temperature. This study indicates that the low-dimensional carbon structure of Li-GQDs can be an effective approach for the stabilization of solid-state Li matrix architectures.

• Electronics and Telecommunications Trends
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• v.38 no.6
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• pp.128-136
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• 2023

Lithium accounts for only 0.0017% of the earth crust, and it is produced in geographically limited regions such as South America, the United States, and China. Since the first half of 2017, the price of lithium has been continuously increasing, and with the rapid adoption of electric vehicles, lithium resources are expected to be depleted in the near future. In addition, economic blocs worldwide face intensifying scenarios such as competition for technological supremacy and protectionism of domestic industries. Consequently, Korea is deepening its dependence on China for core materials and is vulnerable to the influence of the United States Inflation Reduction Act. We analyze post-lithium secondary battery technologies that rely on more earth-abundant elements to replace lithium, whose production is limited to specific regions. Specifically, we focus on the technological status and issues of sodium-ion, zinc-air, and redox-flow batteries. In addition, research trends in post-lithium secondary batteries are examined. Post-lithium secondary batteries seem promising for large-capacity energy storage systems while reducing the costs of raw materials compared with existing lithium-based technologies.

• Journal of the Korean Society of Industry Convergence
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• v.26 no.6_1
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• pp.1001-1010
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• 2023

To solve the problem that photovoltaic panels can not harvest electrical energy at a cloudy day and night, a floating solar thermoelectric generator (FSTEG, hereafter) is studied. The FSTEG is consisted of a dome shaped Fresnel lens to condense solar energy, a thermoelectric module connected with a heat sink to keep temperature difference, a floating system simulating a wavy ocean and an electrical circuit for energy storage. The dome shaped Fresnel lens was designed to have 29 prisms and its optical performance was evaluated outdoors under natural sunlight. Four thermoelectric modules were electrically connected and its performance was evaluated. The generated energy w as stored in a Li-ion battery by using a DC-DC step-up converter. For the application of ocean environment, the FSTEG was covered by the dome shaped Fresnel lens and sealed to float in a water-filled reservoir. The harvested energy shows a potential and a method that the FSTEG is suitable for the energy generation in the ocean environment.

• Journal of Ceramic Processing Research
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• v.21 no.2
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• pp.278-283
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• 2020

We report the synthesis of citrate stabilized iron oxide (C-Fe3O4) spherical nanoparticles for supercapacitor electrodes. The citrate functional group present in the surface of the Fe3O4 nanoparticles effectively controls the morphology and the surface area of the nanostructures. The C-Fe3O4 electrodes exhibited a battery-like energy storage properties with a maximum specific capacity of 146 Cg-1 (242 Fg-1) which is much higher than the specific capacity of citrate free Fe3O4 electrode (62 Cg-1; 112 Fg-1). Moreover, the C-Fe3O4 electrode showed better cyclic stability (75%) than the citrate free Fe3O4 electrode (~35%) after 1000 charge/discharge cycles.

• Journal of the Korean Electrochemical Society
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• v.15 no.4
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• pp.207-215
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• 2012

Soft carbons are prepared by heat-treatment of cokes with different amounts of phosphoric acid (2, 4.5, and 10 wt% vs. cokes) at $900^{\circ}C$ to be used as anode materials for lithium ion batteries. From electrochemical measurements combined with structural analyses, we confirm that abundant nano-pores are existed in the microstructure of soft carbons prepared with the phosphoric acid, which are responsible for further lithium ion storage. Significant increase in reversible capacity of soft carbon is attained in proportion to added amount of the phosphoric acid. We also demonstrate the effect of structural modification with phosphoric acid on electrochemical performance of soft carbon to elucidate the origin of additional capacity.

• Applied Chemistry for Engineering
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• v.4 no.2
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• pp.393-402
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• 1993

Redox flow secondary battery have been studied actively as one of the most promising electrochemical energy storage devices for a wide range of applications, such as electric vehicles, photovoltaic arrays, and excess power generated by electric power plants. In all-vanadium redox flow battery using solution of vanadium-sulfuric acid as a active material, the difficulty in developing an efficient ion selective membrane can still be identified. The asymmetric cation exchange membrane(M-30) as a separator of all-vanadium redox flow battery which were obtained by the reaction of chlorosulfonation for 30 minutes under the irradiation of UV, showed its superiority in the transport number of 0.94 and electrical resistivity of $0.5{\Omega}{\cdot}cm^2$. The base membrane were prepared by lamination a low density polyethlene film of $10{\mu}m$ thickness on polyolefin membrane(HIPORE 120). The electrical resistivity of M-30 membrane in real solution of vanadium-sulfuric acid was $3.79{\Omega}{\cdot}cm^2$ and it was similar to that of Nafion 117 membrane. Also the cell resistivity was $6.6{\Omega}{\cdot}cm^2$and lower than that of Nafion 117. In considertion of electrochemical properties and costs of membranes, M-30 membrane was better than that of Nafion 117 and CMV of Asahi glass Co. as a separator of all-vanadium redox flow battery.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.6
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• pp.80-85
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• 2019

Vanadium dioxide is a well-known metal-insulator phase transition material. Lots of researches of vanadium redox flow batteries have been researched as large scale energy storage system. In this study, vanadium oxide($VO_x$) thin films were applied to cathode for lithium ion battery. The $VO_x$ thin films were deposited on Si substrate($SiO_2$ layer of 300 nm thickness was formed on Si wafer via thermal oxidation process), quartz substrate by RF magnetron sputter system for 60 minutes at $500^{\circ}C$ with different RF powers. The surface morphology of as-deposited $VO_x$ thin films was characterized by field-emission scanning electron microscopy. The crystallographic property was confirmed by Raman spectroscopy. The optical properties were characterized by UV-visible spectrophotometer. The coin cell lithium-ion battery of CR2032 was fabricated with cathode material of $VO_x$ thin films on Cu foil. Electrochemical property of the coin cell was investigated by electrochemical analyzer. As the results, as increased of RF power, grain size of as-deposited $VO_x$ thin films was increased. As-deposited thin films exhibit $VO_2$ phase with RF power of 200 W above. The transmittance of as-deposited $VO_x$ films exhibits different values for different crystalline phase. The cyclic performance of $VO_x$ films exhibits higher values for large surface area and mixed crystalline phase.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.12
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• pp.339-345
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• 2020

In the field of defense, one-shot devices such as missiles are stored for a long period of time after they are manufactured, so it is essential to predict their storage life. A study was conducted to find the shelf life of a Li-ion battery used in one-shot devices. To do this, a Li-ion battery that has been used in weapon systems for more than 5 years was secured. A non-functional test was performed on the battery to check for external changes or failures. After the non-functional test, a discharge test was performed to measure the performance after storing it. Through the test, the performance was checked, including the initial charging voltage, discharge time, and battery temperature, and the trend of the change was identified. An F-test, One-way ANOVA, and regression analysis were performed to verify the aging, and the shelf life of the battery was estimated by an approximation formula that was derived through a regression analysis. As a result of the ANOVA, the p-value was less than the reference value of 0.05, and the performance of the battery decreased by more than 15% after a certain period of time. This change is assumed to result from the change in physical properties of the lithium polymer cell.

• Applied Chemistry for Engineering
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• v.33 no.1
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• pp.58-63
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• 2022

Graphite has been used as an anode material for lithium-ion batteries for the past 30 years due to its low de-/lithiation voltage, high theoretical capacity of 372 mAh/g, low price, and long life properties. Recently, all-solid-state lithium-ion batteries (ASSLB), which are composed of inorganic solid materials with high stability, have received great attention as electric vehicles and next-generation energy storage devices, but research works on graphite that works well for ASSLB systems are insufficient. Therefore, we induced the performance improvement of ASSLB anode electrode graphite material by removing the amorphous carbon present in the carbon material surface, acting as a resistive layer from the graphite. As a result of X-ray diffraction (XRD) analysis using heat treated graphite in air at 400, 500, and 600 ℃, the full width at half maximum (FWHM) at (002) peak was reduced compared to that of bare graphite, indicating that the crystallinity of graphite was improved after heat treatment. In addition, the discharge capacity, initial coulombic efficiency (ICE) and cycle stability increased as the crystallinity of graphite increased after heat treatment. In the case of graphite annealed in air at 500 ℃, the high capacity retention rate of 331.1 mAh/g and ICE of 86.2% and capacity retention of 92.7% after 10-cycle measurement were shown.

• Korean Journal of Materials Research
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• v.11 no.4
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• pp.294-299
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• 2001

Effects of the surface fluorination on the electrochemical charge-discharge properties of $Mg_2$Ni electrode in Ni-MH batteries fabricated by mechanical alloying were investigated. After 20h ball milling, Mg and Ni powder formed nanocrystalline $Mg_2$Ni. Discharge capacity of this alloy increased greatly at first one cycle, but due to the formation of Mg(OH)$_2$ passive layer, it showed a rapid degradation in alkaline solution within 10cyc1es. In case of 6N KOH +xN KF electrolyte (x = 0.5, 1, 2), a continuous and stable fluorinated layer formed by adding excess F$^{[-10]}$ ion, increased durability of $Mg_2$Ni electrode greatly and high rate discharge capability(90-100mAh/g). 2N KF addition led to the highest durability of all tested here. The reason of the improvement is due to thin MgF$_2$, which can prevent the $Mg_2$Ni electrode from forming Mg(OH)$_2$layer that is the main cause of degradation.