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.

Li-ion batteries used in portable electronic devices and electric vehicles require high safety standards, necessitating the use of high-performance structural materials for battery casings. Super duplex stainless steel (SDSS) is a structural material suitable for portable electronic products owing to its excellent strength and corrosion resistance. SDSS AISI2507 was used to construct a Li-ion battery casing, a Ag coating was applied via physical vapor deposition (PVD) after the heat treatment of AISI2507 with or without a secondary phase, and the coating thickness was controlled by varying the PVD time. The thickness of the Ag coating layer increased proportionally with time, thereby enhancing the electrical conductivity. The structure and coating behavior were confirmed using FE-SEM, XRD, and GDS. The secondary phase was crystallized by the segregation of the alloy and formed a BCC structure. The FCC lattice structure exhibited excellent coating behavior on the austenite (FCC structure) of AISI2507. Conversely, the secondary phase exhibited low adhesion owing to differences in composition and crystal structure. However, the Ag coating layer on AISI2507 exhibited excellent electrical conductivity, outperforming conventional Ni-plated Li-ion battery casings comprising AISI304. However, the precipitation of the secondary phase must be controlled, as the formation of the secondary phase acts as a factor that decreases electrical conductivity from 58.8 to 53.6 (ICAS) %. The excellent performance of Ag-coated AISI2507 makes it suitable for the fabrication of enhanced Li-ion battery casings.

Hanji-derived porous carbon has been developed and utilized as a cathode material for Li-S batteries, demonstrating exceptional electrochemical performance and stability. The unique porous structure and high surface area of Hanji-based carbon enhanced S utilization and significantly improved the overall efficiency of the battery. The material exhibited excellent electrical conductivity and structural stability, effectively addressing the major challenges of Li-S batteries, such as the polysulfide shuttle effect and active material loss. In addition, flake carbon-coated separators (FCCSs) were integrated into Li-S cells to further enhance their performance, achieving a high initial specific capacity of approximately 1200 mAh/g and maintaining a capacity of 620 mAh/g after 100 cycles. In contrast, cells with conventional polypropylene separators exhibited lower initial capacities (946 mAh/g), which decreased to 366 mAh/g after 100 cycles. FCCSs also demonstrated superior capacity retention and stability under varying charge–discharge rates, maintaining a capacity of 200 mAh/g at 3 C and recovering to 730 mAh/g when the rate was 0.1 C. This study provides valuable insights into the development of sustainable and efficient Li-S battery systems, with Hanji-based carbon and FCCSs emerging as promising components for commercial applications.