Porous Carbon Interlayer Derived from Traditional Korean Paper for Li-S Batteries.

A carbonized interlayer effectively helps to improve the electrochemical performance of lithium-sulfur (Li-S) batteries. In this study, a simple and inexpensive carbon intermediate layer was fabricated using a traditional Korean paper called "hanji". This carbon interlayer has a fibrous porous structure, with a specific surface area of 91.82 m2 g-1 and a BJH adsorption average pore diameter of 26.63 nm. The prepared carbon interlayer was utilized as an intermediary layer in Li-S batteries to decrease the charge-transfer resistance and capture dissolved lithium polysulfides. The porous fiber-shaped carbon interlayer suppressed the migration of polysulfides produced during the electrochemical process. The carbon interlayer facilitates the adsorption of soluble lithium polysulfides, allowing for their re-utilization in subsequent cycles. Additionally, the carbon interlayer significantly reduces the polarization of the cell. This simple strategy results in a significant improvement in cycle performance. Consequently, the discharge capacity at 0.5 C after 150 cycles was confirmed to have improved by more than twofold, reaching 230 mAh g-1 for cells without the interlayer and 583 mAh g-1 for cells with the interlayer. This study demonstrates a simple method for improving the capacity of Li-S batteries by integrating a functional carbon interlayer.

Electrochemical Generation of Mesopores and Residual Oxygen for the Enhanced Activity of Silver Electrocatalysts.

The development of stable and efficient electrocatalysts is of key importance for the establishment of a sustainable society. The activity of a metal electrocatalyst is determined by its electrochemically active surface area and intrinsic activity, which can be increased using highly porous structures and heteroatomic doping, respectively. Herein, we propose a general strategy of generating mesopores and residual oxygen in metal electrocatalysts by reduction of metastable metal oxides using Ag2O3 electrodeposited onto carbon paper as a model system and demonstrating that the obtained multipurpose porous Ag electrocatalyst has high activity for the electroreduction of O2 and CO2. The presence of mesopores and residual oxygen is confirmed by electrochemical and spectroscopic techniques, and quantum mechanical simulations prove the importance of residual oxygen for electrocatalytic activity enhancement. Thus, the adopted strategy is concluded to allow the synthesis of highly active metal catalysts with controlled mesoporosity and residual oxygen content.

Effect of Applied Current Density on Anodic Oxidation Behavior of AZ31 Mg Alloy in NaOH Solution.

This paper reports three different anodic oxidation behaviors of AZ31 Mg alloy in NaOH solutions, depending on the applied current density and concentration of NaOH between 0.1 M and 0.6 M. When applied current density is lower than about 30 mA/cm², dark anodic film was formed with a very low film formation voltage of less than 6 V and it was found to grow with anodizing time. If applied current density is higher than a critical value about 30 mA/cm², bright metallic surface appearance with small number of pits and/or trenches was obtained. The formation of the pits or trenches was attributed to the result of repeated formation and detachment of plasma electrolytic oxidation (PEO) films at the same site or neighboring places, as strongly supported by repeated micro-arc generations at the same surface site of the specimen during the anodic oxidation process. When applied current density exceeds about 80 mA/cm² in 0.6 M NaOH solution, micro-arcs were generated uniformly over the entire surface, resulting in grey surface appearance and the formation of PEO films with cracks and pores. Based on the experimental results obtained in this work, it is concluded that dark anodic films and grey colored PEO films can be formed on the AZ31 Mg alloy surface in NaOH solution if the applied current density is controlled to be lower than a critical value and if the applied current density and NaOH concentration are controlled to exceed critical values of about 80 mA/cm² and 0.6 M, respectively.

LiI-Doped Sulfide Solid Electrolyte: Enabling a High-Capacity Slurry-Cast Electrode by Low-Temperature Post-Sintering for Practical All-Solid-State Lithium Batteries.

All-solid-state lithium batteries (ASSLBs) based on sulfide solid electrolytes (SEs) have received great attention because of the high ionic conductivity of the SEs, intrinsic thermal safety, and higher energy density achievable with a Li metal anode. However, studies on practical slurry-cast composite electrodes show an extremely limited battery performance than the binder-free pelletized electrodes because of the poor interfacial robustness between the active materials and SEs by the presence of a polymeric binder. Here, we employ a low-temperature post-sintering process for the slurry-cast composite electrodes in order to overcome the binder-induced detrimental effects on the electrochemical performance. The LiI-doped Li3PS4 SEs are chosen because the addition of iodine not only improves the Li-ion conductivity and Li metal compatibility but also lowers the glass-transition and crystallization temperatures. Low-temperature post-sintering of composite cathodes consisting of a LiNi0.6Co0.2Mn0.2O2-active material, LiI-doped Li3PS4 SE, polymeric binder, and conducting agent shows a significantly improved electrochemical performance as compared to a conventional slurry-cast electrode containing pre-annealed SEs. Detailed analyses by electrochemical impedance spectroscopy and galvanostatic intermittent titration technique confirm that post-sintering effectively reduces the interfacial resistance and enhances the chemomechanical robustness at solid-solid interfaces, which enables the development of practical slurry-cast ASSLBs with sulfide SEs.