A lithium powder electrode is applied as an anode in a lithium-sulfur battery system to examine the effects of changes in the anode surface area on electrochemical behavior. Besides preventing dendrite growth, as in other lithium-ion batteries, the lithium powder anode achieves an elevation in lithium-ion transfer, which can be attributed to an increase in the exchange current density caused by expansion of the surface area of the anode. This promotion of lithium-ion diffusion also leads to an increase in lithium-ion transfer near the cathode site and contributes to the reversible reaction between the lithium ion and sulfur. As a result, the reversibility in cathodic reactions is enhanced, thereby improving its specific capacity and retention. Scanning electron microscopy and X-ray photoelectron spectroscopy reveal that the morphology of the cathode is maintained throughout the process, and a solid electrolyte interphase (SEI) with lower electrolyte decomposition can be constructed. Impedance analysis also confirms that a stable electrochemical reaction is achieved with low resistance values.
Composite materials can be successfully applied to the manufacturing process in the consumer electronics field and can drastically reduce the weight of the several parts. For this reason, it is important to predict the shape change after carrying out compression molding of composite material and to determine the key parameters of the manufacturing process. In this paper, the compression molding process of a notebook computer cover using composite materials was analyzed by the finite element method. In addition, the signal-to-noise ratio has been calculated for the warpage deformations that occurred on the surface of the notebook computer cover. The design of experiment method was applied to determine the optimal parameters in the process. Levels of the optimal process factors were selected for minimum warpage deformation and to verify the proposed method; a physical notebook computer cover was manufactured using these optimal conditions. Experimental results, including those on warpage deformations, show that the proposed method can be useful in the manufacturing of lightweight notebook computer covers using a compression molding machine.
New hollow shell structured lithium trivanadate (LiV 3 O 8 ) microspheres were synthesized by a spray drying method, and the effect of a vapor-phase-polypyrrole coating on the surface of this active material was studied. A thin and uniform coating layer could form by a simple vapor-phase-polymerization (VPP) method. The polypyrrole coating layer not only compensates for the low conductivity of the active material but also prevents its direct contact with the electrolyte and reduces vanadium dissolution. The LiV 3 O 8 morphology and presence of the coating layer were confirmed using Fourier-transform infrared spectroscopy, field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, and transmission electron microscopy. The electrochemical performance was analyzed using a battery testing system and impedance spectroscopy. The cycle performance of the Li-powder/polypyrrole-VPPcoated hollow shell LiV 3 O 8 cell showed a higher capacity and greater capacity retention (LiV 3 O 8 : 160.80 mA h g −1 , 62.31%; coated LiV 3 O 8 : 206.55 mA h g −1 , 82.02%) in the range of 1.8-4.0 V at a 0.2 C-rate, even after 200 cycles. The rate capability at various current densities was also high. Further, it had a low charge transfer resistance, which remained low even after many cycles. Thus, the combined effect of hollow-shell-structure and polypyrrole-VPP coating, led LiV 3 O 8 to its improved electrochemical performance.
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