Recent Advances in Layered Metal-Oxide Cathodes for Application in Potassium-Ion Batteries.

To meet future energy demands, currently, dominant lithium-ion batteries (LIBs) must be supported by abundant and cost-effective alternative battery materials. Potassium-ion batteries (KIBs) are promising alternatives to LIBs because KIB materials are abundant and because KIBs exhibit intercalation chemistry like LIBs and comparable energy densities. In pursuit of superior batteries, designing and developing highly efficient electrode materials are indispensable for meeting the requirements of large-scale energy storage applications. Despite using graphite anodes in KIBs instead of in sodium-ion batteries (NIBs), developing suitable KIB cathodes is extremely challenging and has attracted considerable research attention. Among the various cathode materials, layered metal oxides have attracted considerable interest owing to their tunable stoichiometry, high specific capacity, and structural stability. Therefore, the recent progress in layered metal-oxide cathodes is comprehensively reviewed for application to KIBs and the fundamental material design, classification, phase transitions, preparation techniques, and corresponding electrochemical performance of KIBs are presented. Furthermore, the challenges and opportunities associated with developing layered oxide cathode materials are presented for practical application to KIBs.

Growth Temperature Influence on Atomic-Layer-Deposited In2O3 Thin Films and Their Application in Inorganic Perovskite Solar Cells.

Recently, indium oxide (In2O3) thin films have emerged as a promising electron transport layer (ETL) for perovskite solar cells; however, solution-processed In2O3 ETL suffered from poor morphology, pinholes, and required annealing at high temperatures. This research aims to carry out and prepare pinhole-free, transparent, and highly conductive In2O3 thin films via atomic layer deposition (ALD) seizing efficiently as an ETL. In order to explore the growth-temperature-dependent properties of In2O3 thin film, it was fabricated by ALD using the triethyl indium (Et3In) precursor. The detail of the ALD process at 115-250 °C was studied through the film growth rate, crystal structure, morphology, composition, and optical and electrical properties. The film growth rate increased from 0.009 nm/cycle to 0.088 nm/cycle as the growth temperature rose from 115 °C to 250 °C. The film thickness was highly uniform, and the surface roughness was below 1.6 nm. Our results confirmed that film's structural, optical and electrical properties directly depend on film growth temperature. Film grown at ≥200 °C exhibited a polycrystalline cubic structure with almost negligible carbon impurities. Finally, the device ALD-In2O3 film deposited at 250 °C exhibited a power conversion efficiency of 10.97% superior to other conditions and general SnO2 ETL.

Defect-Induced Gas-Sensing Properties of a Flexible SnS Sensor under UV Illumination at Room Temperature.

Tin sulfide (SnS) is known for its effective gas-detecting ability at low temperatures. However, the development of a portable and flexible SnS sensor is hindered by its high resistance, low response, and long recovery time. Like other chalcogenides, the electronic and gas-sensing properties of SnS strongly depend on its surface defects. Therefore, understanding the effects of its surface defects on its electronic and gas-sensing properties is a key factor in developing low-temperature SnS gas sensors. Herein, using thin SnS films annealed at different temperatures, we demonstrate that SnS exhibits n-type semiconducting behavior upon the appearance of S vacancies. Furthermore, the presence of S vacancies imparts the n-type SnS sensor with better sensing performance under UV illumination at room temperature (25 °C) than that of a p-type SnS sensor. These results are thoroughly investigated using various experimental analysis techniques and theoretical calculations using density functional theory. In addition, n-type SnS deposited on a polyimide substrate can be used to fabricate high-stability flexible sensors, which can be further developed for real applications.

An Electrospun Core-Shell Nanofiber Web as a High-Performance Cathode for Iron Disulfide-Based Rechargeable Lithium Batteries.

FeS2 /C core-shell nanofiber webs were synthesized for the first time by a unique synthesis strategy that couples electrospinning and carbon coating of the nanofibers with sucrose. The design of the one-dimensional core-shell morphology was found to be greatly beneficial for accommodating the volume changes encountered during cycling, to induce shorter lithium ion diffusion pathways in the electrode, and to prevent sulfur dissolution during cycling. A high discharge capacity of 545 mAh g-1 was retained after 500 cycles at 1 C, exhibiting excellent stable cycling performance with 98.8 % capacity retention at the last cycle. High specific capacities of 854 mAh g-1 , 518 mAh g-1 , and 208 mAh g-1 were obtained at 0.1 C, 1 C, and 10 C rates, respectively, demonstrating the exceptional rate capability of this nanofiber web cathode.

Growth and Structural Characteristics of CuGaSe2 Films Fabricated from Metallic Precursors Followed by an Elemental Se Reaction Process.

We investigated the growth, structural and optical characteristics of CuGaSe2 thin films prepared with the selenium reaction. Metallic precursor layers from Cu0:5Ga0.5 and Cu0.8Ga0.2 alloy targets were prepared on a sodalime glass substrate by using DC magnetron sputtering, and then annealed to form CuGaSe2 in a rapid thermal process (RTP) with selenium radicals generated by a thermal cracker. The base and sputtering pressures were < 5 x 10(-7) Torr and 30 mTorr, respectively. At ambient temperature, the precursors from the Cu0.5Ga0.5 and Cu0.8Ga0.2 targets were deposited at the rates of 42 nm/min. and 45 nm/min., respectively. The film thicknesses were about 300 nm. Selenization was carried out at different annealing temperatures of T(a) = 450 degrees C, 500 degrees C, 550 degrees C, and 600 degrees C for time periods of 15 min., 30 min., and 60 min. We found that high quality CuGaSe2 films of crystal grains (-1 µm in dia.) fabricated with a reaction using elemental Se at temperatures as low as 450 degrees C for 30 min. When T(a) ≤ 350 degrees C, the Se reaction was insufficient to form CuGaSe2. However, the annealing time had little effect on the formation of CuGaSe2 at T(a) ≥ 450 degrees C. For all the samples, the photoluminescence (PL) emission was only from the donor-acceptor interband transition D1A1 for all the composition ratios of the films [Ga]/[Cu] -1.