Ultra-Thin ReS2 Nanosheets Grown on Carbon Black for Advanced Lithium-Ion Battery Anodes.

ReS2 nanosheets are grown on the surface of carbon black (CB) via an efficient hydrothermal method. We confirmed the ultra-thin ReS2 nanosheets with ≈1-4 layers on the surface of the CB (ReS2@CB) by using analytical techniques of field emission scanning electron microscopy (FESEM) and high-resolution transmission electron microscopy (HRTEM). The ReS2@CB nanocomposite showed high specific capacities of 760, 667, 600, 525, and 473 mAh/g at the current densities of 0.1 (0.23 C), 0.2 (0.46 C), 0.3 (0.7 C), 0.5 (1.15 C) and 1.0 A/g (2.3 C), respectively, in conjunction with its excellent cycling performance (432 mAh/g at 2.3 C; 91.4% capacity retention) after 100 cycles. Such LIB performance is greatly higher than pure CB and ReS2 powder samples. These results could be due to the following reasons: (1) the low-cost CB serves as a supporter enabling the formation of ≈1-4 layered nanosheets of ReS2, thus avoiding its agglomeration; (2) the CB enhances the electrical conductivity of the ReS2@CB nanocomposite; (3) the ultra-thin (1-4 layers) ReS2 nanosheets with imperfect structure can function as increasing the number of active sites for reaction of Li+ ions with electrolytes. The outstanding performance and unique structural characteristics of the ReS2@CB anodes make them promising candidates for the ever-increasing development of advanced LIBs.

Highly Efficient Nanocarbon Coating Layer on the Nanostructured Copper Sulfide-Metal Organic Framework Derived Carbon for Advanced Sodium-Ion Battery Anode.

High theoretical capacity and low-cost copper sulfide (CuxS)-based anodes have gained great attention for advanced sodium-ion batteries (SIBs). However, their practical application may be hindered due to their unstable cycling performance and problems with the dissolution of sodium sulfides (NaxS) into electrolyte. Here, we employed metal organic framework (MOF-199) as a sacrificial template to fabricate nanoporous CuxS with a large surface area embedded in the MOF-derived carbon network (CuxS-C) through a two-step process of sulfurization and carbonization via H2S gas-assisted plasma-enhanced chemical vapor deposition (PECVD) processing. Subsequently, we uniformly coated a nanocarbon layer on the Cu1.8S-C through hydrothermal and subsequent annealing processes. The physico-chemical properties of the nanocarbon layer were revealed by the analytical techniques of high-resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray spectroscopy (EDS), and scanning electron microscopy (SEM). We acquired a higher SIB performance (capacity retention (~93%) with a specific capacity of 372 mAh/g over 110 cycles) of the nanoporous Cu1.8S-C/C core/shell anode materials than that of pure Cu1.8S-C. This encouraging SIB performance is attributed to the key roles of a nanocarbon layer coated on the Cu1.8S-C to accommodate the volume variation of the Cu1.8S-C anode structure during cycling, enhance electrical conductivity and prevent the dissolution of NaxS into the electrolyte. With these physico-chemical and electrochemical properties, we ensure that the Cu1.8S-C/C structure will be a promising anode material for large-scale and advanced SIBs.

Cross-Linked Poly(vinylidene fluoride-co-hexafluoropropene) (PVDF-co-HFP) Gel Polymer Electrolyte for Flexible Li-Ion Battery Integrated with Organic Light Emitting Diode (OLED).

Here, we fabricate poly(vinylidene fluoride-co-hexafluoropropene) (PVDF-co-HFP) by electrospinning for a gel polymer electrolyte (GPE) for use in flexible Li-ion batteries (LIBs). As a solvent, we use N-methyl-2-pyrrolidone (NMP), which helps produce the cross-linked morphology of PVDF-co-HFP separator, owing to its low volatility. The cross-linked PVDF-co-HFP separator shows an uptake rate higher than that of a commercialized polypropylene (PP) separator. Moreover, the PVDF-co-HFP separator shows an ionic conductivity of 2.3 × 10-3 S/cm at room temperature, comparable with previously reported values. An LIB full-cell assembled with the PVDF-co-HFP-based GPE shows capacities higher than its counterpart with the commercialized PP separator, confirming that the cross-linked PVDF-co-HFP separator provides highly efficient ionic conducting pathways. In addition, we integrate a flexible LIB cell using the PVDF-co-HFP GPE with a flexible organic light emitting diode (OLED), demonstrating a fully flexible unit of LIB and OLED.

In situ fabrication of a graphene-coated three-dimensional nickel oxide anode for high-capacity lithium-ion batteries.

The high theoretical specific capacity of nickel oxide (NiO) makes it attractive as a high-efficiency electrode material for electrochemical energy storage. However, its application is limited due to its inferior electrochemical performance and complicated electrode fabrication process. Here, we developed an in situ fabrication of a graphene-coated, three-dimensional (3D) NiO-Ni structure by simple chemical vapor deposition (CVD). We synthesized NiO layers on Ni foam through a thermal oxidation process; subsequently, we grew graphene layers directly on the surface of NiO after a hydrogen-assisted reduction process. The uniform graphene coating renders high electrical conductivity, structural flexibility and high elastic modulus at atomic thickness. The graphene-coated 3D NiO-Ni structure delivered a high areal density of ∼23 mg cm-2. It also exhibits a high areal capacity of 1.2 mA h cm-2 at 0.1 mA cm-2 for its Li-ion battery performance. The high capacity is attributed to the high surface area of the 3D structure and the unique properties of the graphene layers on the NiO anode. Since the entire process is carried out in one CVD system, the fabrication of such a graphene-coated 3D NiO-Ni anode is simple and scalable for practical applications.

The role of thermal annealing on the microstructures of (Ti, Fe)-alloyed Si thin-film anodes for high-performance Li-ion batteries.

Here, we studied the effect of thermal annealing on the microstructure and cyclic stability of a (Ti, Fe)-alloyed Si thin-film fabricated by a simple sputtering deposition method for Li-ion battery (LIB) anodes. The anode samples annealed at different temperatures (300-600 °C) were subjected to microstructure analysis and LIB performance test. The (Ti, Fe)-alloyed Si thin-film anode delivered a high capacity of 1563 mA h g-1 for 100 cycles at 0.1 A g-1 with nearly 100% capacity retention. Post-mortem analysis using field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) disclosed the microstructural changes of the cycled anodes, revealing that (Ti, Fe) silicides served as a structural buffer against the large volume change of active Si during cycling for enhanced LIB performance.

Correction: The role of thermal annealing on the microstructures of (Ti, Fe)-alloyed Si thin-film anodes for high-performance Li-ion batteries.

[This corrects the article DOI: 10.1039/C7RA13172K.].

Vertically oriented MoS2 nanoflakes coated on 3D carbon nanotubes for next generation Li-ion batteries.

The advent of advanced electrode materials has led to performance enhancement of traditional lithium ion batteries (LIBs). We present novel binder-free MoS2 coated three-dimensional carbon nanotubes (3D CNTs) as an anode in LIBs. Scanning transmission electron microscopy analysis shows that vertically oriented MoS2 nanoflakes are strongly bonded to CNTs, which provide a high surface area and active electrochemical sites, and enhanced ion conductivity at the interface. The electrochemical performance shows a very high areal capacity of ~1.65 mAh cm-2 with an areal density of ~0.35 mg cm-2 at 0.5 C rate and coulombic efficiency of ~99% up to 50 cycles. The unique architecture of 3D CNTs-MoS2 is indicative to be a promising anode for next generation Li-ion batteries with high capacity and long cycle life.

Three-dimensional free-standing carbon nanotubes for a flexible lithium-ion battery anode.

Flexible lithium-ion batteries (LIBs) have received considerable attention as energy sources for wearable electronics. In recent years, much effort has been devoted to study light-weight, robust, and flexible electrodes. However, high areal and volumetric capacities need to be achieved for practical power and energy densities. In this paper, we report the use of three-dimensional (3D) free-standing carbon nanotubes (CNTs) as a current collector-free anode to demonstrate flexible LIBs with enhanced areal and volumetric capacities. High density CNTs grown on copper (Cu) mesh are transferred to a flexible graphene/polyethylene terephthalate  film and integrated into a flexible LIB. A fully flexible LIB cell integrated with the 3D CNT anode delivers a high areal capacity of 0.25 mAh cm(-2) at 0.1C and shows fairly consistent open circuit voltage under bending. These findings may provide significant advances in the application of flexible LIB based electronic devices.