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The effects of solvents on the preparation of sulfur cathodes were investigated by fabricating binder-free sulfur electrode films using three different solvents: 1-methyl-2-pyrrolidinone (NMP), acetonitrile, and deionized water. These solvents are commonly employed to dissolve binders used to prepare sulfur cathodes for lithium–sulfur batteries. The sulfur electrode fabricated with NMP had a higher discharge capacity and longer cycle life than the ones fabricated with acetonitrile and deionized water. Better adhesion between the current collector and the sulfur electrode accounted for the improved capacity and cycle life of the battery. In addition, the stability of the electrode in the electrolyte was a result of the solubility of sulfur in the solvent. We thus concluded that the solvents used in the fabrication of sulfur electrodes had a positive influence on the electrochemical properties of Li–S batteries.

We prepared sulfur/active carbon composites via a simple solution-based process using the following commercial activated carbon-based materials: coal, coconut shells, and sawdust. Although elemental sulfur was not detected in any of the sulfur/activated carbon composites based on Thermogravimetric analysis, X-ray diffraction, and Raman spectroscopy, Energy-dispersive X-ray spectroscopy results confirmed its presence in the activated carbon. These results indicate that sulfur was successfully impregnated in the activated carbon and that all of the activated carbons acted as sulfur reservoirs. The sulfur/activated carbon composite cathode using coal exhibited the highest discharge capacity and best rate capability. The first discharge capacity at 1 C (1.672 A g−1) was 1240 mAh g−1, and a large reversible capacity of 567 mAh g−1 was observed at 10 C (16.72 A g−1).

Si film electrodes were fabricated on surface-modified Cu current collectors using an oxidation-reduction process. Flower-like nanostructures (FLNSs) with diameters of 2–3 μm and plate-like nanostructures (PLNSs) with lengths of 1 μm were formed on the Cu foil oxidized at 423 K for 0.5 h, but only the PLNSs remained after sonication. Reduction of the preoxidized Cu foil at 673 K resulted in the formation of plate-like and coral-like nanostructures on the Cu foils reduced for 1 and 3 h and a smooth surface without specific structures on the Cu foil reduced for 6 h. The best electrochemical properties in terms of the first columbic efficiency (85.4%) and the cycle performance (67.3% at 50 cycles) were obtained from the Si film electrode fabricated on the Cu foil that had been reduced for 3 h because the coral-like nanostructures on the Cu foil enhanced the adhesion of the Si film and improved the structural stability of the Si film electrode during the electrochemical reactions.

Highlights: • The content of sulfur in activated carbon was controlled by solution process. • The sulfur electrode with low sulfur content shows the best performance. • The Li/S battery has capacity of 1360 mAh/g at 1 C and 702 mAh/g at 10 C. - Abstract: The content of sulfur in sulfur/activated carbon composite is controlled from 32.37 wt.% to 55.33 wt.% by a one-step solution-based process. When the sulfur content is limited to 41.21 wt.%, it can be loaded into the pores of an activated carbon matrix in a highly dispersed state. On the contrary, when the sulfur content is 55.33 wt.%, crystalline sulfur can be detected on the surface of the activated carbon matrix. The best electrochemical performance can be obtained for a sulfur electrode with the lowest sulfur content. The sulfur/activated carbon composite with 32.37 wt.% sulfur afforded the highest first discharge capacity of 1360 mAh g{sup −1} at 1 C rate and a large reversible capacity of 702 mAh g{sup −1} at 10 C (16.75 A/g)

Highlights: • A highly porous carbon (HPC) with regular spherical morphology was synthesized. • Sulfur/HPC composites were prepared by melt–diffusion method. • Sulfur/HPC composites showed improved cyclablity and long-term cycle life. - Abstract: Sulfur composite material with a highly porous carbon sphere as the conducting container was prepared. The highly porous carbon sphere was easily synthesized with resorcinol–formaldehyde precursor as the carbon source. The morphology of the carbon was observed with field emission scanning electron microscope and transmission electron microscope, which showed a well-defined spherical shape. Brunauer–Emmett–Teller analysis indicated that it possesses a high specific surface area of 1563 m{sup 2} g{sup −1} and a total pore volume of 2.66 cm{sup 3} g{sup −1} with a bimodal pore size distribution, which allow high sulfur loading and easy transportation of lithium ions. Sulfur carbon composites with varied sulfur contents were prepared by melt–diffusion method and lithium sulfur cells with the sulfur composites showed improved cyclablity and long-term cycle life.

Sulfur composite was prepared by encapsulating sulfur into CMK-3 mesoporous carbon with different heating times and then used as the cathode material for lithium sulfur batteries. Thermal treatment at 300 °C plays an important role in the sulfur encapsulation process. With 20 h of heating time, a portion of sulfur remained on the surface of carbon, whereas with 60 h of heating time, sulfur is confined deeply in the small pores of carbon that cannot be fully exploited in the redox reaction, thus causing low capacity. The S/CMK-3 composite with thermal treatment for 40 h at 300 °C contained 51.3 wt.% sulfur and delivered a high initial capacity of 1375 mA h g−1 at 0.1 C. Moreover, it showed good capacity retention of 704 mA h g−1 at 0.1 C and 578 mA h g−1 at 2 C even after 100 cycles, which proves its potential as a cathode material for high capability lithium sulfur batteries.

Monolithic nickel sulfide electrodes were prepared using a facile synthesis method, sulfuration and annealing. As-prepared Ni3S2 electrodes were characterized by X-ray diffractometry and field emission scanning electron microscopy. Thermal stability was determined by thermal gravimetric analysis and differential scanning calorimetry. Electrochemical properties were measured by galvanostatic charge and discharge cycling for Na-ion batteries. Three kinds of Ni3S2 electrodes were prepared by varying the sulfuration time (5, 15 and 25 min). The electrochemical results indicated that the capacities increased with an increase in sulfuration time and the cycle performance was stable as a result of monolithic integration of nanostructured Ni3S2 on Ni plates, leading to low interfacial resistance.

Tin dioxide was investigated as an anode material for sodium-ion batteries. The Na/SnO2 cell delivered a first discharge capacity of 747 mAh/g, but the first charge capacity was 150 mAh/g. The irreversible capacity in the first cycle was examined through characterization by X-ray diffraction and scanning electron microscopy. X-ray diffraction analysis revealed that the SnO2 active material was not reduced fully to metallic Sn. Furrows and wrinkles were formed on the electrode surface owing to the volumetric expansion upon first discharge, which led to a deterioration of the electrode structure and a loss of electrical contact between the active materials. The analysis is summarized in the schematic drawing.

Pure α-NaMnO 2 cathode materials were prepared by solid-state reaction with Mn 2 O 3 and Na 2 CO 3 at 750 °C. Electrochemical properties of Na/α-NaMnO 2 battery was investigated with electrolytes as 1 M NaClO 4 EC/DEC and 1 M NaBF 4 TEGDME. First discharge capacity of Na/α-NaMnO 2 cell using 1 M NaClO 4 EC/DEC electrolyte and 1 M NaBF 4 TEGDME electrolyte was 146 mAh g −1 and 136 mAh g −1 discharge capacity for the first cycle at 0.2 C rate and 104 mAh g −1 97 mAh g −1 after 20 cycles, respectively. Na/α-NaMnO 2 battery with 1 M NaClO 4 EC/DEC electrolyte shows higher initial charge/discharge capacity than that using 1 M NaBF 4 TEGDME because of high ionic conductivity of electrolyte and low interfacial resistance between the electrolyte and electrode. However, Na/α-NaMnO 2 battery with 1 M NaBF 4 TEGDME electrolyte has better stability for the 20th cycle from coulombic efficiency result because of stability of interfacial resistance.

LiCoO2 single-layer and LiCoO2/LiNiO2 multi-layer thin film electrodes were successfully fabricated by magnetron sputtering. Their microstructure and electrochemical properties were investigated. Once annealed, both films had the (0 0 3) preferred orientation to minimize the surface energy. The initial discharge capacity of the multi-layer thin film was approximately 53.1 μAh/cm2 μm, which was higher than that of the LiCoO2 single-layer thin film having similar thickness. The capacity retention of the multi-layer thin film was superior to that of the single-layer thin film. These findings indicate that the multi-layer thin film is a promising cathode material for the fabrication of high-performance thin film batteries.

Magnesium doped Li1−2xMgxFePO4/C (x = 0.00, 0.01, 0.03, 0.05) cathode materials were synthesized by sol–gel method, and the effect of magnesium doping as well as its content on the electrochemical properties for lithium batteries was also investigated. Their morphology was studied with field emission scanning electron microscope and Li1−2xMgxFePO4 materials showed the olivine phase without impurities. The thin carbon layer of Li1−2xMgxFePO4/C was confirmed by high resolution transmission electron microscopy. The magnesium doped Li1−2xMgxFePO4/C particles were smaller than those undoped. The Li1−2xMgxFePO4/C materials showed better cycling behavior than undoped LiFePO4, especially at high C-rate in which Li0.94Mg0.03FePO4/C composition exhibited the best electrochemical properties.

LiCoO 2 thin films were fabricated on Al substrate by direct current magnetron sputtering method. The effects of Ar/O 2 gas rates and annealing temperatures were investigated. Crystal structures and surface morphologies of the deposited films were investigated by X-ray diffraction, Raman scattering spectroscopy and field emission scanning electron microscopy. The as-deposited LiCoO 2 thin films exhibited amorphous structure. The crystallization starts at the annealing temperature over 400 °C. However, the annealed films have the partially disordered structure without completely ordered crystalline structure even at 600 °C annealing. The electrochemical properties of the LiCoO 2 films were investigated by the charge–discharge and cycle measurements. The 500 °C annealing film has the highest capacity retention rate of 78.2% at 100th cycles.

All-solid-state lithium/sulfur (Li/S) battery is prepared using siloxane cross-linked network solid electrolyte at room temperature. The solid electrolytes show high ionic conductivity and good electrochemical stability with lithium and sulfur. In the first discharge curve, all-solid-state Li/S battery shows three plateau potential regions of 2.4 V, 2.12 V and 2.00 V, respectively. The battery shows the first discharge capacity of 1044 mAh g −1 -sulfur at room temperature. This first discharge capacity rapidly decreases in 4th cycle and remains at 512 mAh g −1 -sulfur after 10 cycles.